Bisphenol A or BPA in Pregnancy and Asthma Study

The Barcelona Institute for Global Health supported study concludes suggests that in utero BPA exposure may be associated with higher odds of asthma and wheeze among school-age girls.

Study Background

In utero, (before birth) exposure to bisphenols, widely used in consumer products, may alter lung development and increase the risk of respiratory morbidity in the offspring. However, evidence is scarce and mostly focused on bisphenol A (BPA) only.

Study Objectives

There is growing concern over the role of chemical pollutants on early life origins of respiratory diseases (Gascon et al., 2013, Vrijheid et al., 2016, Casas and Gascon, 2020, Abellan and Casas, 2021), specifically on bisphenols due to their large production worldwide (CHEMTrust, 2018) and its widespread exposure to human populations (Calafat et al., 2008, Haug et al., 2018). Bisphenol A (BPA) is the most commonly used bisphenol. It is present in polycarbonate plastics and epoxy resins, used in many consumer products, and diet is the main source of exposure (Liao and Kannan, 2013). In 2017, the European Chemical Agency considered BPA as a “substance of very high concern” (Calafat et al., 2008, Agency and Bisfenol, 2017). Consequently, BPA production is restricted in some countries, which has resulted in the emergence of substitutes such as bisphenol F (BPF) and bisphenol S (BPS), with suspected similar toxicity (Lehmler et al., 2018, Rochester and Bolden, 2015). Bisphenols can cross the placenta and are also found in breastmilk, which results in exposure to foetuses and newborns (Lee et al., 2018). To examine the associations of in utero exposure to BPA, bisphenol F (BPF), and bisphenol S (BPS) with asthma, wheeze, and lung function in school-age children, and whether these associations differ by sex.

Methods

We included 3,007 mother–child pairs from eight European birth cohorts. Bisphenol concentrations were determined in maternal urine samples collected during pregnancy (1999–2010). Between 7 and 11 years of age, current asthma and wheeze were assessed from questionnaires and lung function by spirometry. Wheezing patterns were constructed from questionnaires from early to mid-childhood. We performed adjusted random-effects meta-analysis on individual participant data.

In utero exposure to bisphenols, widely used in consumer products, may alter lung development and increase the risk of respiratory morbidity in the offspring. However, evidence is scarce and mostly focused on bisphenol A (BPA) only.

Study Objective

To examine the associations of in utero exposure to BPA, bisphenol F (BPF), and bisphenol S (BPS) with asthma, wheeze, and lung function in school-age children, and whether these associations differ by sex.

Results

Exposure to BPA was prevalent with 90% of maternal samples containing concentrations above detection limits. BPF and BPS were found in 27% and 49% of samples. In utero exposure to BPA was associated with higher odds of current asthma (OR = 1.13, 95% CI = 1.01, 1.27) and wheeze (OR = 1.14, 95% CI = 1.01, 1.30) (p-interaction sex = 0.01) among girls, but not with wheezing patterns nor lung function neither in overall nor among boys. We observed inconsistent associations of BPF and BPS with the respiratory outcomes assessed in overall and sex-stratified analyses.

Conclusion

This study suggests that in utero BPA exposure may be associated with higher odds of asthma and wheeze among school-age girl

According the U.S. National Institute of Health, Bisphenol A (BPA) is a chemical produced in large quantities for use primarily in the production of polycarbonate plastics. It is found in various products including shatterproof windows, eyewear, water bottles, and epoxy resins that coat some metal food cans, bottle tops, and water supply pipes.

How does BPA get into the body?

The primary source of exposure to BPA for most people is through the diet. While air, dust, and water are other possible sources of exposure, BPA in food and beverages accounts for the majority of daily human exposure.

Bisphenol A can leach into food from the protective internal epoxy resin coatings of canned foods and from consumer products such as polycarbonate tableware, food storage containers, water bottles, and baby bottles. The degree to which BPA leaches from polycarbonate bottles into liquid may depend more on the temperature of the liquid or bottle, than the age of the container. BPA can also be found in breast milk.

Why are people concerned about BPA?
One reason people may be concerned about BPA is because human exposure to BPA is widespread. The 2003-2004 National Health and Nutrition Examination Survey (NHANES III) conducted by the Centers for Disease Control and Prevention (CDC) found detectable levels of BPA in 93% of 2517 urine samples from people six years and older. The CDC NHANES data are considered representative of exposures in the United States. Another reason for concern, especially for parents, may be because some animal studies report effects in fetuses and newborns exposed to BPA.

If I am concerned, what can I do to prevent exposure to BPA?

Some animal studies suggest that infants and children may be the most vulnerable to the effects of BPA. Parents and caregivers can make the personal choice to reduce exposures of their infants and children to BPA:

  • Don’t microwave polycarbonate plastic food containers. Polycarbonate is strong and durable, but over time it may break down from over use at high temperatures.
    Plastic containers have recycle codes on the bottom. Some, but not all, plastics that are marked with recycle codes 3 or 7 may be made with BPA.
  • Reduce your use of canned foods.
    When possible, opt for glass, porcelain or stainless steel containers, particularly for hot food or liquids.
  • Use baby bottles that are BPA free.

There is growing concern over the role of chemical pollutants on early life origins of respiratory diseases (Gascon et al., 2013, Vrijheid et al., 2016, Casas and Gascon, 2020, Abellan and Casas, 2021), specifically on bisphenols due to their large production worldwide (CHEMTrust, 2018) and its widespread exposure to human populations (Calafat et al., 2008, Haug et al., 2018). Bisphenol A (BPA) is the most commonly used bisphenol. It is present in polycarbonate plastics and epoxy resins, used in many consumer products, and diet is the main source of exposure (Liao and Kannan, 2013). In 2017, the European Chemical Agency considered BPA as a “substance of very high concern” (Calafat et al., 2008, Agency and Bisfenol, 2017). Consequently, BPA production is restricted in some countries, which has resulted in the emergence of substitutes such as bisphenol F (BPF) and bisphenol S (BPS), with suspected similar toxicity (Lehmler et al., 2018, Rochester and Bolden, 2015). Bisphenols can cross the placenta and are also found in breastmilk, which results in exposure to foetuses and newborns (Lee et al., 2018).

Asthma and Environmental Fungi – interview with Marie-Claire Arrieta Ph.D.

World Asthma FoundationDefeating Asthma Series uncovers New Hope for Asthma Managementant

Our understanding of Asthma and the way we treat it may soon be radically different from what currently exists, due to new research on the human microbiome and how the microbiome affects asthma.

In this interview with Marie-Claire Arrieta Ph.D, Assistant Professor Depts. of Physiology and Pharmacology & Pediatrics Cumming School of Medicine University of Calgary Health Research Innovation Centre, Calgary, Alberta, Canada we learn that:

  • A significant proportion of asthmatics have severe asthma that also cannot be controlled easily with the current treatments
  • The microbiome is not only bacteria just like other ecosystems. Not only bacteria but they’re mix including environmental fungi
  • The microbiome is full of viruses as well

Interview

World Asthma Foundation: Dr. Arrieta, what prompted your research in this area?

Dr. Arrieta: As you know, asthma has no known cures. A significant proportion of asthmatics have severe asthma that also cannot be controlled easily with the current treatments, so we’re trying to figure out ways of improving both the prevention and the potential therapies for asthma. We also know that asthma has become an epidemic disease in Canada. At least it’s quadrupled in incidence over only 30 years, and we know that it’s mainly environmental factors that are explaining or possibly explaining this really great increase in incidence for asthma.

We’ve come to learn in the past 10 years that the microbiome is implicated. The gut microbiome is this very large community of microbes that we all harbor in our inner guts. However, The vast majority of these studies of the microbiome and asthma have only included bacteria, including studies that I have participated in before. This only provides a part of the view of this vast variety of microbes that we know inhabit this microbial ecosystem.

The microbiome is not only bacteria just like other ecosystems. Not only bacteria but they’re mixed, and they definitely include fungi. We thought that studying the role of fungi would be important because molds and environmental fungi are quite common triggers of asthma attacks in asthmatics, also for people with allergies. This, we thought, may suggest that the fungi in the microbiome, that no one has been studying much before, may be involved in some of the immune education that happens early in life that may later in childhood lead to this uncontrolled inflammation in the airways towards environmental fungi, along with other environmental triggers of asthma. That’s why we wanted to look at fungi.

World Asthma Foundation: Excellent. Great study. I’m most impressed. What are some of the key findings?

Dr. Arrieta: We found by giving specific species or types of fungi and/or bacteria to mice, and we used a specific type of mouse known as the germ-free mouse. These are mice that are kept completely devoid of microbes, so they’re like a blank state that you can associate with microbes in a way that would allow you to then make good conclusions from the experiment.

We found that fungi have a very important role in the way the microbiome establishes early in life. When I say microbiome, now I mean a combination of both bacteria and fungi. We also found that fungi are sensed by the immune system differently than bacteria in a way that they seem to amplify the immune response. For example, we found that mice that were colonized only with fungi were more susceptible to asthma.

World Asthma Foundation: Interesting. Along with that, what were some of the other key findings?

Dr. Arrieta: The story’s definitely developing. This study was certainly a proof of concept, but based on this work as well as others that are starting to look at fungi too, we think that when fungi in the intestine of babies bloom, for example, during an antibiotic treatment, this may change the way the immune system responds to this microbiome that is now higher in proportion with certain fungi. This may also increase the susceptibility to those immune alterations that can later lead to asthma in certain people.

World Asthma Foundation: Interesting. I noticed that you mentioned several references to Candida albicans. How does that fit into the mix?

Dr. Arrieta: We don’t know yet. We chose Candida because it’s a very common yeast in our guts. Virtually everyone would have some candida in their bodies, not just in their guts, but it’s a very common inhabitant. Because of that, we wanted to use a species that was common. We found that Candida certainly can outgrow during antibiotic treatments. It may be one of the species implicated, but we’re not there yet. We’re now trying more species of fungi. In fact, we started a new set of experiments based on an infant clinical study that we just completed that showed us exactly which are the yeast and fungal species that bloom when babies are given antibiotics.

This was an interesting clinical study. We ran it at the emergency department of one of our children’s hospitals where we enrolled babies under six months of age, that for one reason or another had to take an antibiotic. This is a very common occurrence for infants. Then what we did was that we followed the microbiome during this antibiotic treatment, and we were able to identify the most common yeasts that seem to outgrow during the antibiotic treatment. We’re focusing on those, and surprisingly, Candida is not one of those all the time. It seems that, of course, Candida is there, but there’s other fungi that are able to outcompete other ones including Candida. Those are the ones that we’re focusing on now.

World Asthma Foundation: Thank you for that. By outcompete, the suggestion or the inference would be that the imbalance of fungi and bacteria are what’s causing the inflammation process?

Dr. Arrieta: That could be that case. That will be the next step, but as I said, the story is very much developing. I think we’re one of the first ones, but we’re not the only ones interested in studying the fungal component of the microbiome and how it relates to allergies and asthma. I think that in the next couple of years we’re going to learn a lot more.

World Asthma Foundation: Fair enough. What implications are there for asthma? Asthma rates are on the rise. What would you like asthmatics to know about your study?

Dr. Arrieta: For now, because the study is developing, I think what we know for sure is that the gut microbiome during early life is extremely important when it comes to, in general, immune development. Because asthma, of course, is an immune disease, these changes in the gut microbiome can certainly determine a baby’s risk to develop this disease, especially as we now understand in families that have a familial history of asthma as well.

What is important to asthmatics to know? There are certain lifestyle, changes, or behaviors that are now being recommended, including natural birth if, of course, is safe and possible, the use of breast milk over formula if it is possible. One of the things that we’re learning more about is that one of the ways to foster a healthy microbiome early in life is when babies start eating solid foods to make the diet as healthy as possible, the way nutritionists have been asking as to do so for decades now because this will foster a varied microbiome.

World Asthma Foundation: Good point. A fair amount of adult asthmatics suffer from fungal issues relative to lung inflammation and infection. Any thoughts on that?

Dr. Arrieta: There’s a couple of clinical studies, and I wish I remember from the top of my head the name of the drug exactly, that is being tested right now. I’m by no means, involved in this. I have just been reading it with great interest because it is an immune modulator. It’s a biological drug that targets some of the immune mechanisms that we now know recognize fungi. It’ll be really interesting to see now from the point of view of these patients, both children, and adults, that have fungal asthma, if this is really going to change their treatment options because as you know, those asthma tend to be more severe and harder to treat as well.

World Asthma Foundation: What would you like the scientific community to know about your research?

Dr. Arrieta: That within this revolution of studying that microbiome, I think we’re missing out by only focusing on bacteria. There’s a great deal that I have learned from my colleagues in microbial ecology. I am not an ecologist, but I started to partner up with them because of the methods and the concepts, and scientific frameworks that they used to study the microbiome. The microbiome is an ecosystem, and we have experts that have been studying ecosystems for decades before biomedical researchers started to study ecosystems. The inclusion of fungi, I think, will get us more answers. Also, the inclusion of other microorganisms that very few people, if any, are considering right now in the context of asthma research, which are viruses, very popular of course now because we’re under a pandemic. The microbiome is full of viruses and children experience many viral infections during the first year of life or the first two years of life. How does the immune system react to that? How does it get educated? I think that using a broader, more ecologically informed approach to study the microbiome is a lesson that I have learned over the years and I hope that others follow suit too.

Gut and Lung Connection to Asthma – Rodney Dietert, PhD

In this fifth in a series of interviews with Rodney Dietert PhD, he talks about communication between the gut and lung. Dr. Dietert is Cornell University Professor Emeritus, Health Scientist Head of Translational Science + Education for SEED and the Author of the Human Super-Organism How the Microbiome is Revolutionizing the Pursuit of a Healthy Life we learn about:

* The Gut and lung communication and its relationship to Asthma

World Asthma FoundationDefeating Asthma Series uncovers New Hope for Asthma Managementant

Asthmatics: Our understanding of Asthma and the way we treat it may soon be radically different from what currently exists, due to new research on the human microbiome and how the microbiome affects asthma.

Interview

World Asthma Foundation: Research into the Microbiome and its relationship to health has improved significantly in the last few years. For example, we now know about the relationship between the gut and health. We’ve also learned about communication between the gut and the lung and the impact on Asthma. Dr. Dietert, so there’s some crosstalk, right?

Video interview: Asthma Connection to Gut and Lung Cross Talk – Rodney Dietert, PhD

Dr. Dietert: Tremendous crosstalk, absolutely tremendous. You’re correct that if you’re looking at endpoints, something like risk of asthma or management of asthma, then you really, at a minimum, are going to focus both on the respiratory system microbiome and the gut microbiome. That’s not necessarily the exclusion of others but those two are really important. Just like the gut microbiome can affect the brain, it can affect behavior, mood. You don’t need lots of hardcore meds as an antidepressant when you’ve got the solution sitting right in your gut in terms of the microbiome.

With the respiratory system, you’ve got both the local microbes being extremely important but you have crosstalk, you have chemical interactions that are originating in the gut that are affecting the respiratory system as well.

World Asthma Foundation: Dr. Dietert, we certainly thank you for your time, all that you do for the microbiome and the community. Good afternoon, and thanks again.

Dr. Dietert: Well, and thank you for all you do with the World Asthma foundation, Bill. Pleasure.

To learn more about Dr. Dietert, go here.

Gut and Lung crosstalk interview with Rodney Dietert.

Asthma and the Microbiome – Rodney Dietert PhD Interview

Defeating Asthma Series uncovers New Hope for Asthma Management

In this interview with Rodney Dietert, PhD Cornell University Professor Emeritus, Health Scientist Head of Translational Science + Education for SEED and the Author of the Human Super-Organism How the Microbiome is Revolutionizing the Pursuit of a Healthy Life we learn that we’re a superorganism and we are, by several measures, primarily microbial, living on a microbial planet.

Our understanding of Asthma and the way we treat it may soon be radically different from what currently exists, due to new research on the human microbiome and how the microbiome affects asthma.

Interview

World Asthma Foundation: What prompted your interest in this area?

Dr. Dietert: It was literally the result of a dream. Woke up in the middle of the night, I had been struggling to write a new paper. The paper was supposed to identify the single, most important thing that you could measure in a newborn baby that would be the best predictor of whether that baby’s life was filled with health or filled with disease. That’s a challenging but a worthwhile idea. What could you measure in a newborn baby? I was pretty sure I had the answer because I’d been working for decades on the developing immune system and it was something surrounding that.

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Dr. Dietert: I started to write the paper and it was a very frustrating, terrible effort. Got a couple of paragraphs down and very unconvincing and uninspired and so I went to bed and woke up in the middle of the night and had a magnificent dream, which I don’t really remember the details of but it’s like, “Wow, have I been dreaming? Wow, do I have this idea?” The idea was the best measurement you could have at that point in time with a newborn is the extent to which the baby has self-completed. By self-completed, I mean acquired a full microbiome from mom, dad, and the environment and that is critical. That’s what we’re supposed to be.

We’re a superorganism and we are, by several measures, primarily microbial, living on a microbial planet. The major life form on the planet are bacteria. Really anything that disrupts that completion, in my mind, is viewed as a type of birth defect. It’s a correctable birth defect but nevertheless, it’s like missing a limb or missing a different organ. To miss the seeding events, to miss the microbiome the baby is intended to have is an incredibly serious biological effect that has really serious health ramifications.

My wife helped me put together the scrambled ideas coming off a dream. We wrote the paper and that wound up really turning my career in a whole different direction because it was seen by some filmmakers who were making a wonderful documentary called Microbirth, and it won the Life Science Film Festival Award for 2014. In that documentary, I was able to explain this concept and why it was so critical for preventing essentially diseases like asthma or really reducing the risk dramatically.

That we had control of these risks, the risk for diabetes, for asthma, for psoriasis, for inflammatory bowel, for a whole host of diseases that were to some extent under more control to a greater degree than we had ever envisioned. The reason we had that opportunity was because there was a new biology that we as humans were not what we had been taught or at least what I was taught decades ago in school and what I taught at Cornell for a number of years. That we were quite different.

Once we’ve recognize that difference, then it changes everything. It changes how you approach diet, how you approach what a healthy life looks like, how you approach medicine, therapeutics, drug development, environmental chemicals. Everything changes. Really that’s been my path, to try and help chart and provide useful information on how we, as a superorganism, can lead a healthier life.

World Asthma Foundation: With that, Dr. Dietert, we certainly thank you for your time, all that you do for the microbiome, and the patient population in the community. With that, good afternoon, and thanks again.

Dr. Dietert: Well, and thank you for all you do with the World Asthma foundation, Bill. Pleasure.

World Asthma Foundation: Thank you so much.

 

Asthma and the Microbiome – Justin L. Sonnenburg PhD Interview

Defeating Asthma Series uncovers New Hope for Asthma Management

In this interview with Justin L. Sonnenburg PhD, Associate Professor of Microbiology and Immunology at Stanford University, we learn diseases largely driven by inflammation and an altered immune system may benefit from taking our microbiome into account.

Our understanding of Asthma and the way we treat it may soon be radically different from what currently exists, due to new research on the human microbiome and how the microbiome affects asthma.

“Diseases largely driven by inflammation and an altered immune system. If we start to take our gut microbiota into account, as we live our life, as we make medical decisions, eat different foods and potentially even eventually reintroduce some of these lost microbes, how profound can the impact be on our health?” Justin L. Sonnenburg Ph.D

Interview

World Asthma Foundation: Dr. Justin L. Sonnenburg Associate Professor of Microbiology and Immunology at Stanford University, well known author, sought after speaker and an infectious disease investigator.

Dr. Sonnenburg’s interest includes the basic principles that govern interactions within the intestinal microbiota and between the microbiota and the host. To pursue these aims, they colonize germ-free (gnotobiotic) mice with simplified, model microbial communities, apply systems approaches (e.g. functional genomics), and use genetic tools for the host and microbes to gain mechanistic insight into emergent properties of the host-microbial super-organism.

World Asthma Foundation: Good afternoon, Dr. Sonnenburg, and thanks for agreeing to the interview.

Dr. Justin L. Sonnenburg: Great to be with you.

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World Asthma Foundation: Super. Asthmatics want to know some things you’ve written about the gut. We know for example that we need more fiber. We also know that we need to eat healthier, but for some of us, unfortunately, the gut for a variety of reasons is out of whack or disrupted. Some suggested the potential of Missing Microbes. The gut is a delicate ecosystem. The question that I have for you today is can we get some of those microbes back?

Dr. Justin L. Sonnenburg: I think that’s a key question. It’s very clear that we’ve done things during the process of industrialization and things that are associated with our modernized lifestyle now, antibiotics, highly processed food, C-sections, baby formula. There are a lot of things that have been associated with microbiome deterioration.

The question is when we lose microbes or change this malleable component of our biology, our gut microbiota, how meaningful is that for our biology? I think what’s really interesting and notable is that at the same time that our microbiome has been changing, we’ve seen this incredible rise in what we call Western diseases or non-communicable chronic diseases.

Diseases largely driven by inflammation and an altered immune system. I think that a big question is if we start to take our gut microbiota into account, as we live our life, as we make medical decisions, eat different foods and potentially even eventually reintroduce some of these lost microbes, how profound can the impact be on our health?

Can we greatly improve the status of our immune system? Potentially both preventing the onset of chronic diseases and maybe even helping to treat or reduce the severity of some of these diseases.

Asthma and Indoor Air Pollution:

Key insights for Asthmatics:

  • Makes Asthma Worse
  • Significant Association with Exacerbations
  • Among this panel of relatively moderate to severe asthmatics, the respiratory irritants produced by several domestic combustion sources were associated with increased morbidity.
  • Although there is abundant clinical evidence of asthmatic responses to indoor aeroallergens, the symptomatic impacts of other common indoor air pollutants from gas stoves, fireplaces, and environmental tobacco smoke have been less well characterized. These combustion sources produce a complex mixture of pollutants, many of which are respiratory irritants.
  • Results of an analysis of associations between indoor pollution and several outcomes of respiratory morbidity in a population of adult asthmatics residing in the U.S. Denver, Colorado, metropolitan area. A panel of 164 asthmatics recorded in a daily diary the occurrence of several respiratory symptoms, nocturnal asthma, medication use, and restrictions in activity, as well as the use of gas stoves, wood stoves, or fireplaces, and exposure to environmental tobacco smoke.
  • Multiple logistic regression analysis suggests that the indoor sources of combustion have a statistically significant association with exacerbations of asthma. For example, after correcting for repeated measures and autocorrelation, the reported use of a gas stove was associated with moderate or worse shortness of breath (OR, 1.60; 95% CI, 1.11-2.32), moderate or worse cough (OR, 1.71; 95% CI, 0.97-3.01), nocturnal asthma (OR, 1.01; 95% CI, 0.91-1.13), and restrictions in activity (OR, 1.47; 95% CI, 1.0-2.16
  • The WAF Editorial Board wishes to thank and acknowledge B D Ostro 1 , M J Lipsett, J K Mann, M B Wiener, J Selner
    California Environmental Protection Agency, Berkeley for their contribution to Asthma education and research.

Asthma and COVID-19 Update Study on Risk

Asthma does not appear to increase the risk or influence its severity, according to University study

Whats new

Rutgers researchers say further study is needed but those with the chronic respiratory disease don’t appear to be at a higher risk of getting extremely ill or dying from coronavirus.“Older age and conditions such as heart disease, high blood pressure, chronic obstructive pulmonary disease, diabetes and obesity are reported risk factors for the development and progression of COVID-19,” said Reynold A. Panettieri Jr., a pulmonary critical care physician and director of the Rutgers Institute for Translational Medicine and Science and co-author of a paper published in the Journal of Allergy and Clinical Immunology.

“However, people with asthma — even those with diminished lung function who are being treated to manage asthmatic inflammation — seem to be no worse affected by SARS-CoV-2 than a non-asthmatic person. There is limited data as to why this is the case — if it is physiological or a result of the treatment to manage the inflammation.”

Children and young adults with asthma suffer mainly from allergic inflammation, while older adults who experience the same type of airway inflammation can also suffer from eosinophilic asthma — a more severe form. In these cases, people experience abnormally high levels of a type of white blood cell that helps the body fight infection, which can cause inflammation in the airways, sinuses, nasal passages and lower respiratory tract, potentially making them more at risk for a serious case of COVID-19.

Further Study Needed

Panettieri discusses what we know about asthma and inflammation and the important questions that still need to be answered.

How might awareness of SARS-CoV-2 affect the health of people with asthma?
Since the news has focused our attention on the effects of COVID-19 on people in vulnerable populations, those with asthma may become hyper-vigilant about personal hygiene and social distancing. Social distancing could improve asthma control since people who are self-quarantined are also not as exposed to seasonal triggers that include allergens or respiratory viruses. There is also evidence that people are being more attentive to taking their asthma medication during the pandemic, which can contribute to overall health.

What effect might inhaled steroids have on COVID-19 outcomes?
Inhaled corticosteroids, which are commonly used to protect against asthma attacks, also may reduce the virus’s ability to establish an infection. However, studies have shown that steroids may decrease the body’s immune response and worsen the inflammatory response. Steroids also have been shown to delay the clearing of the SARS and MERS virus — similar to SARS-CoV-2 — from the respiratory tract and thus may worsen COVID-19 outcomes. Future studies should address whether inhaled steroids in patients with asthma or allergies increase or decrease the risks of SARS-CoV-2 infection, and whether these effects are different depending on the steroid type.

In what way does age play a role in how asthma patients react to exposure to the virus?
A person’s susceptibility to and severity of COVID-19 infection increases with age. However, since asthma sufferers tend to be younger than those with reported high-risk conditions, age-adjusted studies could help us better understand if age is a factor in explaining why asthma patients may not be at greater risk for infection.

Children and young adults with asthma suffer mainly from allergic inflammation, while older adults who experience the same type of airway inflammation can also suffer from eosinophilic asthma — a more severe form. In these cases, people experience abnormally high levels of a type of white blood cell that helps the body fight infection, which can cause inflammation in the airways, sinuses, nasal passages and lower respiratory tract, potentially making them more at risk for a serious case of COVID-19.

In addition, an enzyme attached to the cell membranes in the lungs, arteries, heart, kidney and intestines that has been shown to be an entry point for SARS-CoV-2 into cells is increased in response to the virus. This enzyme is also thought to be beneficial in clearing other respiratory viruses, especially in children. How this enzyme affects the ability of SARS-CoV-2 to infect people with asthma is still unclear.

How might conditions in addition to asthma affect a person’s risk of infection?
Asthma tends to be associated with far fewer other conditions than chronic obstructive pulmonary disease or cardiovascular disease. If SARS-CoV-2 is a disease that causes dysfunction in the cells that line blood vessels throughout the body, then diabetes, heart disease, obesity and other diseases associated with this condition may make people more susceptible to the virus than those who are asthmatic.

Important to know

However, older people with asthma who also have high blood pressure, diabetes or heart disease may have similar instances of COVID-19 as non-asthmatics with those conditions.

Why Cell Biology of Asthma Matters

Cell types responsible for the major pathology in asthma:
1. Epithelial cells – initiate airway inflammation mucus, and
2. Smooth muscle cells – contract excessively to cause airway narrowing.

The clinical manifestations of asthma are caused by obstruction of the conducting airways of the lung. Two airway cell types are critical for asthma pathogenesis: epithelial cells and smooth muscle cells. Airway epithelial cells, which are the first line of defense against inhaled pathogens and particles, initiate airway inflammation and produce mucus, an important contributor to airway obstruction. The other main cause of airway obstruction is contraction of airway smooth muscle. Complementary experimental approaches involving cultured cells, animal models, and human clinical studies have provided many insights into diverse mechanisms that contribute to airway epithelial and smooth muscle cell pathology in this complex disease. Continued attention to the study of the cell biology of asthma will be crucial for generating new ideas for asthma prevention and treatment based on normalizing epithelial and smooth muscle function.

Note from the WAF editorial board: We wish to acknowledge and thank David J. Erle and Dean Sheppard, Lung Biology Center and Department of Medicine, University of California, San Francisco for their support for Asthma research and education.

Asthma is a common disease that affects up to 8% of children in the United States (Moorman et al., 2007) and is a major cause of morbidity worldwide. The principal clinical manifestations of asthma are repeated episodes of shortness of breath and wheezing that are at least partially reversible, recurrent cough, and excess airway mucus production. Because asthma involves an integrated response in the conducting airways of the lung to known or unknown triggers, it is a multicellular disease, involving abnormal responses of many different cell types in the lung (Locksley, 2010). Here we focus on the two cell types that are ultimately responsible for the major symptomatic pathology in asthma—epithelial cells that initiate airway inflammation in asthma and are the source of excess airway mucus, and smooth muscle cells that contract excessively to cause symptomatic airway narrowing. The current thinking about cell–cell communications that drive asthma (Fig. 1) is that known and unknown inhaled stimuli (i.e., proteases and other constituents of inhaled allergens, respiratory viruses, and air pollutants) stimulate airway epithelial cells to secrete the cytokines TSLP, interleukin (IL)-25, and IL-33, which act on subepithelial dendritic cells, mast cells, and innate lymphoid cells (iLCs) to recruit both innate and adaptive hematopoietic cells and initiate the release of T helper 2 (Th2) cytokines (principally IL-5 and IL-13; Locksley, 2010; Scanlon and McKenzie, 2012; Bando et al., 2013; Barlow et al., 2013; Nussbaum et al., 2013). Environmental stimuli also activate afferent nerves in the airway epithelium that can themselves release biologically active peptide mediators and also trigger reflex release of acetylcholine from efferent fibers in the vagus nerve. This initial response is amplified by the recruitment and differentiation of subsets of T cells that sustain secretion of these cytokines and in some cases secrete another cytokine, IL-17, at specific strategic sites in the airway wall. The released cytokines act on epithelial cells and smooth muscle cells and drive the pathological responses of these cells that contribute to symptomatic disease. The cell biology underlying the responses of the relevant hematopoietic lineages is not specific to asthma and has been discussed elsewhere (Locksley, 2010; Scanlon and McKenzie, 2012). We focus our discussion on the contributions of epithelial cells and airway smooth muscle cells.
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Figure 1.

Cell–cell communication in the airway wall in asthma. Environmental triggers concurrently act on airway afferent nerves (which both release their own peptide mediators and stimulate reflex release of the bronchoconstrictor acetylcholine) and airway epithelial cells to initiate responses in multiple cell types that contribute to the mucous metaplasia and airway smooth muscle contraction that characterize asthma. Epithelial cells release TSLP and IL-33, which act on airway dendritic cells, and IL-25, which together with IL-33 acts on mast cells, basophils, and innate type 2 lymphocytes (iLC2). These secreted products stimulate dendritic cell maturation that facilitates the generation of effector T cells and triggers the release of both direct bronchoconstrictors and Th2 cytokines from innate immune cells, which feed back on both the epithelium and airway smooth muscle and further facilitate amplification of airway inflammation through subsequent adaptive T cell responses.

Cell biology of airway epithelium

The airway is covered with a continuous sheet of epithelial cells (Crystal et al., 2008; Ganesan et al., 2013). Two major airway cell types, ciliated and secretory cells, establish and maintain the mucociliary apparatus, which is critical for preserving airway patency and defending against inhaled pathogens and allergens. The apparatus consists of a mucus gel layer and an underlying periciliary layer. Ciliated cells each project ?300 motile cilia into the periciliary layer that are critical for propelling the mucus layer up the airway. In addition, cilia are coated with membrane-spanning mucins and tethered mucopolysaccharides that exclude mucus from the periciliary space and promote formation of a distinct mucus layer (Button et al., 2012). Secretory cells produce a different class of mucins, the polymeric gel-forming mucins. The two major airway gel-forming mucins are MUC5AC and MUC5B. Some secretory cells, known as mucous or goblet cells, produce mucins and store them within easily visualized collections of mucin granules, whereas other cells produce and secrete mucins (especially MUC5B) but lack prominent granules. Gel-forming mucins are secreted into the airway lumen and are responsible for the characteristic viscoelastic properties of the mucus gel layer.
Airway epithelial injury and remodeling in asthma

A variety of structural changes in the epithelium and other portions of the airway, termed “airway remodeling,” is frequently seen in individuals with asthma (Elias et al., 1999). These changes include airway wall thickening, epithelial hypertrophy and mucous metaplasia, subepithelial fibrosis, myofibroblast hyperplasia, and smooth muscle cell hyperplasia and hypertrophy. Airway remodeling is thought to represent a response to ongoing tissue injury caused by infectious agents, allergens, or inhaled particulates and by the host responses to these stimuli. Signs of frank epithelial injury, including loss of epithelial integrity, disruption of tight junctions, impairment of barrier function, and cell death, have been identified in some studies and may correlate with asthma severity (Laitinen et al., 1985; Jeffery et al., 1989; Barbato et al., 2006; Holgate, 2007). However, in many individuals asthma symptoms and features of airway remodeling, including mucous metaplasia and subepithelial fibrosis, are seen in the absence of signs of active airway infection or overt tissue injury (Ordoñez et al., 2000), suggesting that other processes account for the persistence of asthma in these individuals. Substantial evidence suggests that the persistence of asthma is driven by ongoing host immune responses that generate mediators driving airway remodeling and airway dysfunction. The epithelium is both a site of production of these mediators and a source of cells that respond to mediators produced by immune cells and other cells within the airway. How airway epithelial cells recognize and respond to viruses, allergens, and other stimuli has been comprehensively reviewed elsewhere (Lambrecht and Hammad, 2012). Here we will focus on the contribution of the epithelium to production of and responses to Th2 cytokines.
Airway epithelial contributions to Th2 responses.

Th2 cytokines, especially IL-13, play critical roles in asthma. Multiple cytokines, including TSLP, GM-CSF, IL-1, IL-25, and IL-33, are produced by the epithelium and promote production of Th2 cytokines by immune cells (Cates et al., 2004; Hammad et al., 2009; Locksley, 2010; Nagarkar et al., 2012). Genome-wide association studies implicate multiple Th2-related genes, including IL13, IL33, and TSLP, in asthma (Moffatt et al., 2010; Torgerson et al., 2011). IL-13 is produced by innate lymphoid cells (Neill et al., 2010; Price et al., 2010; Saenz et al., 2010; Hasnain et al., 2011) and Th2 cells (Grünig et al., 1998; Wills-Karp et al., 1998) during allergic inflammation and by macrophages in a mouse model of virus-induced airway disease (Kim et al., 2008). IL-13 induces characteristic changes in airway epithelial mRNA (Kuperman et al., 2005b; Woodruff et al., 2007; Zhen et al., 2007) and miRNA (Solberg et al., 2012) expression patterns in airway epithelial cells. The IL-13 transcriptional “signature” can be used to identify individuals with “Th2 high” and “Th2 low” asthma (Woodruff et al., 2009). The IL-13–induced protein periostin is secreted basally from airway epithelial cells and can be used as a biomarker for Th2 high asthma (Jia et al., 2012; Parulekar et al., 2014). Roughly half of individuals with asthma are Th2 high, and these individuals have better responses to treatment with inhaled corticosteroids (Woodruff et al., 2009) or anti–IL-13 antibody (Corren et al., 2011). The key drivers of Th2 low asthma remain poorly understood, although Th17 family cytokines may be important (Newcomb and Peebles, 2013).

Mucous metaplasia.

Although mucus is critical for host defense, pathological mucus production is an important contributor to asthma morbidity and mortality. In fatal asthma, airways are often plugged with tenacious mucus plugs that obstruct movement of gas (Kuyper et al., 2003). This catastrophic phenomenon likely reflects increased mucin production and secretion as well as changes in mucin cross-linking, mucus gel hydration, and mucus clearance. Abnormalities in mucus are not limited to severe asthma exacerbations because an increase in intracellular mucin stores (mucous metaplasia) is seen even in individuals with stable, mild to moderate asthma (Ordoñez et al., 2001). In mouse allergic airway disease models of asthma, mucous metaplasia results from increased production and storage of mucins (especially MUC5AC) in preexisting secretory cells, including club cells (Evans et al., 2004), rather than transdifferentiation of ciliated cells (Pardo-Saganta et al., 2013). However, in virus-driven models of asthma mucous cells might arise from transdifferentiation of ciliated cells (Tyner et al., 2006). A variety of stimuli and signaling pathways have been shown to regulate mucin production and secretion in airway epithelial cells.
IL-13 stimulates mucin production in Th2 high asthma.

Direct effects of IL-13 on airway epithelial cells induce mucous metaplasia in human airway epithelial cells in culture (Laoukili et al., 2001; Zhen et al., 2007) and in mouse airway epithelial cells in vivo (Kuperman et al., 2002). IL-13 is necessary for mucous metaplasia in many mouse asthma models (Grünig et al., 1998; Wills-Karp et al., 1998; Tyner et al., 2006). Individuals with Th2 high asthma have elevated levels of bronchial epithelial cell MUC5AC mRNA compared with healthy controls or individuals with Th2 low asthma (Woodruff et al., 2009). Recent transgenic mouse studies demonstrate roles for MUC5AC in clearance of enteric nematode infections (Hasnain et al., 2011) and protection against influenza infection (Ehre et al., 2012). Increased MUC5AC expression is therefore part of an integrated immune response that contributes to host defense against pathogens or inhaled particulates. A less well-recognized feature of Th2-high asthma is the substantial decrease in expression of MUC5B (Woodruff et al., 2009). The recent discovery that MUC5B is required for normal mucociliary clearance and defense against airway infection (Roy et al., 2014) suggests further attention should be directed to the possibility that a reduction in MUC5B may be an important contributor to airway dysfunction in asthma.

IL-13 is recognized by cell surface receptors expressed on almost all cell types, including airway epithelial cells (Fig. 2). The airway epithelial cell IL-13 receptor that is critical for mucous metaplasia is a heterodimer composed of IL-13R?1 and IL-4R?. Removal of this receptor in airway epithelial secretory cells (driven by the CCSP promoter) prevented mucous metaplasia in an allergic asthma model (Kuperman et al., 2005a). IL-13 binding leads to activation of Jak kinases associated with the receptor cytoplasmic domain and subsequent phosphorylation of signal transducer and activator of transcription 6 (STAT6). STAT6 activation is required for IL-13–induced mucous metaplasia (Kuperman et al., 2002).
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Figure 2.

Mechanisms of IL-13–induced mucous metaplasia. IL-13 binds to its receptor on the surface of mucous cell progenitors (e.g., club cells) leading to phosphorylation of STAT6 and translocation of STAT6 heterodimers to the nucleus, where they bind to promoters of STAT6-responsive genes. STAT6-dependent processes that contribute to mucous metaplasia include a CLCA1-dependent pathway, a Serpin-dependent pathway, and a 15-lipoxygenase-1–dependent pathway. The transcription factor SPDEF is a master regulator of mucous cell differentiation. It inhibits FOXA2, which represses mucous cell differentiation, and activates transcription of other genes that are expressed in mucous cells.

The series of events that link STAT6 activation to mucous metaplasia are only partly understood. STAT6 does not appear to directly regulate MUC5AC transcription (Young et al., 2007) and the critical direct targets of STAT6 have not been determined. One pathway that depends upon STAT6 activation involves the protein calcium-activated chloride channel 1 (CLCA1). CLCA1 is among the most highly induced genes in airway epithelial cells from individuals with asthma (Hoshino et al., 2002; Toda et al., 2002). Despite its name, CLCA1 does not appear to function as an ion channel but instead undergoes extracellular secretion and cleavage. Extracellular CLCA1 can induce MUC5AC expression via activation of the MAP kinase MAPK13 (p38?-MAPK; Alevy et al., 2012), although the presumed CLCA1 receptor and the relevant MAPK13 targets have not yet been identified. A second pathway involves the protease inhibitor Serpin3a, the mouse orthologue of human SERPINB3 and SERPINB4. These serpins are induced by IL-13 in a STAT6-dependent fashion (Ray et al., 2005). After allergen challenge, Serpin3a?/? mice had less mucous metaplasia than wild-type mice (Sivaprasad et al., 2011), despite an intact inflammatory response. These results suggest that serpins inhibit proteases that normally degrade one or more proteins required for mucous metaplasia, although the relevant proteases and their protein substrates are not yet known. Another IL-13–induced pathway involves the enzyme 15-lipoxygenase-1 (15-LO-1; Zhao et al., 2009). 15-LO-1 converts arachidonic acid to 15-hydroxyeicosatetraenoic acid, which was shown to enhance MUC5AC expression in human airway epithelial cells.

IL-13– and STAT6-mediated mucous metaplasia depends upon changes in the activity of a network of transcription factors. Allergen-induced IL-13–mediated STAT6 activation leads to increased expression of the SAM-pointed domain–containing Ets-like factor (SPDEF; Park et al., 2007; Chen et al., 2009). The induction of SPDEF depends at least in part on FOXM1, a member of the Forkhead box (FOX) family of transcription factors (Ren et al., 2013). The SPDEF program is also important for mucous metaplasia triggered by other stimuli, including rhinoviruses (Korfhagen et al., 2012). Although SPDEF does not appear to directly regulate mucin gene transcription, SPDEF initiates a transcriptional program that is necessary and sufficient to induce mucous metaplasia. One of the effects of SPDEF is inhibition of the expression of another FOX family gene, FOXA2. In mice, deletion of Foxa2 in mucous cell precursors is sufficient to induce mucous metaplasia, and overexpression of FOXA2 inhibits allergen-induced mucous metaplasia (Zhen et al., 2007; G. Chen et al., 2010). The relationship between IL-13 and FOXA2 is complex. IL-13 inhibits expression of FOXA2, which contributes to mucous metaplasia. However, deletion of Foxa2 in airway epithelial cells during fetal development resulted in Th2 inflammation and production of IL-13 in the airway (G. Chen et al., 2010). The direct targets that are responsible for these effects of FOXA2 are not yet known.
The EGFR pathway induces mucin gene expression and mucous metaplasia.

Epidermal growth factor receptor (EGFR) binds multiple ligands including EGF, TGF-?, heparin-binding EGF, amphiregulin, ?-cellulin, and epiregulin. Ligand binding activates the EGFR kinase domain, initiating signaling cascades that are central to many fundamental biological processes, including cell proliferation, differentiation, survival, and migration. EGFR ligands induce expression of MUC5AC in human airway epithelial cell lines and a tyrosine kinase inhibitor that inhibits EGFR kinase prevents mucous metaplasia induced either by an EGFR ligand or by allergen challenge (Takeyama et al., 1999). Subsequent studies showed that bronchial epithelial EGFR levels are increased in asthma and correlate with disease severity (Takeyama et al., 2001a), and that epithelial EGFR signaling contributes to mucous metaplasia in a chronic asthma model (Le Cras et al., 2011).

Various stimuli, including bacterial products (Kohri et al., 2002; Lemjabbar and Basbaum, 2002;Koff et al., 2008), viruses (Tyner et al., 2006; Zhu et al., 2009; Barbier et al., 2012), cigarette smoke (Takeyama et al., 2001b; Basbaum et al., 2002), and inflammatory cell products (Burgel et al., 2001) can activate the EGFR pathway in airway epithelial cells. Some stimuli have been shown to initiate the EGFR signaling cascade by activating the PKC isoforms PKC ? and PKC ?, leading to recruitment of the NADPH oxidase subunits p47phox and p67phox to membrane-associated dual oxidase-1 and the generation of reactive oxygen species (ROS) at the cell surface (Shao and Nadel, 2005). ROS in turn activate latent TGF-?–converting enzyme resulting in cleavage of surface EGFR pro-ligands (Shao et al., 2003). EGFR ligand binding leads to activation of the Ras–Raf–MEK1/2–ERK1/2 pathway and MUC5AC transcriptional induction, which depends upon the Sp1 transcription factor and Sp1-binding sites within the MUC5AC promoter (Takeyama et al., 2000; Perrais et al., 2002). The IL-13 and EGFR pathways make critical but distinct contributions to gene regulation in airway epithelial cells (Zhen et al., 2007). Both pathways inhibit expression of FOXA2, suggesting that this transcription factor may represent a final common pathway for IL-13– and EGFR-induced mucous metaplasia.

Notch signaling regulates mucous cell differentiation.

Notch signaling is also important for mucous metaplasia (Tsao et al., 2011). Notch is a transmembrane receptor that binds to cell-surface ligands in the Delta-like and Jagged families. Ligand binding activates ?-secretase–mediated proteolytic cleavage and liberates the Notch intracellular domain, which enters the nucleus, associates with transcription factors, and drives expression of downstream Notch genes. Genetic manipulation of Notch signaling in mice has different effects depending on the developmental stage. In explanted embryonic lungs, addition of Notch ligand or expression of a constitutively active form of Notch increased MUC5AC-containing mucous cells, whereas a ?-secretase inhibitor reduced mucous cells (Guseh et al., 2009). Notch-induced mucous metaplasia did not require STAT6 activation, suggesting that the Notch and STAT6 pathways may operate in parallel. In contrast, in postnatal mouse lung, disruptions of Notch signaling induced mucous metaplasia (Tsao et al., 2011), a process that principally depends on the Notch ligand Jagged1 (Zhang et al., 2013). The Notch target Hes1 appears to be critical for inhibition of mucous metaplasia and MUC5AC transcription, although inactivation of Hes1 was not sufficient to induce mucous metaplasia (Ou-Yang et al., 2013). The observation that a ?-secretase inhibitor reduced IL-13–induced mucous metaplasia in cultured human airway epithelial cells (Guseh et al., 2009) suggests that further attention to the role of epithelial Notch signaling in asthma is warranted.

The secretory pathway in mucous cells

Mucin monomers are large (?5,000 amino acid residue) proteins that require extensive processing in the ER and Golgi. Each mucin monomer contains ?200 cysteine residues that can potentially participate in intra- and intermolecular disulfide bonds. The ER of mucous cells contains specialized molecules that are not widely expressed in other cell types and are required for efficient processing of mucins. One of these is anterior gradient 2 (AGR2) homologue, a member of the protein disulfide isomerase family. An active site cysteine residue in AGR2 forms mixed disulfide bonds with mucins in the ER and mice deficient in AGR2 have profound defects in intestinal mucin production (Park et al., 2009). In a mouse model of allergic asthma, AGR2-deficient mice had reduced mucus production compared with allergen-challenged wild-type mice (Schroeder et al., 2012). The reduction in mucus production was associated with activation of the unfolded protein response, a characteristic response to ER stress (Walter and Ron, 2011). AGR2 may therefore either have a direct role in mucin folding or another function necessary for maintaining normal function of the mucous cell ER. Another molecule found in the mucous cell ER is inositol-requiring enzyme 1? (IRE1?), a transmembrane ER stress sensor. IRE1? is found in mucus-producing cells in the intestine and the airways, but not in other cells. IRE1? regulates AGR2 transcription, and mice deficient in IRE1? had reduced AGR2 expression and impaired airway mucin production in an allergic asthma model (Martino et al., 2013). AGR2 and IRE1? have apparently evolved to meet the unusual demands posed by the need to produce large amounts of mucins.

ORMDL3, a member of the Orm family of transmembrane ER proteins, has also been implicated in asthma. Genetic polymorphisms at loci close to ORMDL3 were strongly associated with asthma in multiple genome-wide association studies (Moffatt et al., 2007; Galanter et al., 2008). Allergen challenge induced ORMDL3 expression in airway epithelial cells in a STAT6-dependent fashion, although ORMDL3 does not appear to be a direct target of STAT6 (Miller et al., 2012). Studies involving overexpression or knockdown of ORDML3 in HEK293 cells indicate that ORMDL3 is involved in regulating ER stress responses and ER-mediated calcium signaling (Cantero-Recasens et al., 2010). In addition, Orm proteins form complexes with serine palmitoyl-CoA transferase (SPT), the first and rate-limiting enzyme in sphingolipid production, and may thereby help coordinate lipid metabolism in the secretory pathway (Breslow et al., 2010). Genetic and pharmacologic reductions in SPT activity induced airway hyperresponsiveness in the absence of inflammation or mucous metaplasia (Worgall et al., 2013). Further studies are required to determine whether ORMDL3’s role in modulating sphingolipid production, ER stress, calcium signaling, or other ER functions in airway epithelial cells or other cells is important in asthma.

Mucins travel from the ER to the Golgi and then are packaged into large granules for secretion. In the Golgi, mucins are extensively O-glycosylated and undergo further multimerization before being released from the cell by regulated exocytosis. Throughout the airways of normal mice and in distal (smaller) airways of humans, basal secretion accounts for most mucin release, and mucin-producing cells retain too little mucin to detect using histological stains. However, mucous cells found in larger airways of humans and allergen-challenged mice contain readily detectable accumulations of mucin-containing granules that can be released by various stimuli, including the P2Y2 receptor ligands ATP and UTP and proteases that cleave protease-activated receptors. Mice lacking the exocytic priming protein Munc13-2 accumulate mucin in secretory cells that normally have minimal intracellular mucin (club cells) but can secrete mucin in response to stimulation (Zhu et al., 2008). In contrast, allergen-challenged mice lacking the low affinity calcium sensor synaptotagmin-2 have a severe defect in acute agonist-stimulated airway mucin secretion, but have preserved basal secretion and do not accumulate mucins in club cells (Tuvim et al., 2009). Agonist-stimulated secretion also depends upon the IL-13–inducible calcium-activated chloride channel TMEM16A, which is increased in mucous cells from individuals with asthma (Huang et al., 2012). Because increased production of MUC5AC via transgenic overexpression was not in itself sufficient to cause airway obstruction (Ehre et al., 2012), it seems likely that qualitative defects in mucin processing, secretion, or hydration that affect the physicochemical properties of mucus contribute to airway obstruction in asthma. Epithelial transport of water and ions, including H+ and bicarbonate, is important in maintaining the normal properties of mucus (E. Chen et al., 2010; Paisley et al., 2010; Garland et al., 2013). Rapid secretion of stored mucin, which is not fully hydrated, may result in the formation of concentrated, rubbery mucus that cannot be cleared normally by cilia or by coughing (Fahy and Dickey, 2010). Hence, IL-13 (Danahay et al., 2002; Nakagami et al., 2008) and other asthma mediators that affect airway epithelial cell water and ion transport could contribute to airway obstruction by altering the physicochemical properties of mucus.
Ciliated cell structure and function in asthma

In comparison with the extensive asthma literature regarding mucous cells, relatively few reports have focused on ciliated cells. One study of epithelial cell strips obtained by endobronchial brushing found decreased ciliary beat frequency and increases in abnormal ciliary beating patterns and ciliary ultrastructural defects in individuals with asthma compared with healthy controls (Thomas et al., 2010). These abnormalities were more pronounced in severe asthma. Ciliary abnormalities were accompanied by increases in the numbers of dead cells and evidence of loss of epithelial structural integrity, which suggests that ciliary dysfunction may be a consequence of a generalized epithelial injury. In any case, these results suggest that ciliary dysfunction might be an important contributor to impaired mucociliary clearance in asthma.
Cell biology of airway smooth muscle in asthma

The excessive airway narrowing that can lead to severe shortness of breath, respiratory failure, and death from asthma is largely due to contraction of the bands of smooth muscle present in the walls of large- and medium-sized conducting airways in the lung. In the large central airways of humans, these bands of muscle are present in the posterior portion of the airways and attach to the anterior airway cartilage rings, but in more peripheral airways smooth muscle is present circumferentially around the airways. In both locations, contraction of smooth muscle, which can be physiologically induced by release of acetylcholine from efferent parasympathetic nerves or by release of histamine and cysteinyl leukotrienes from mast cells and basophils, causes airway narrowing, with the most extensive narrowing in medium-sized airways. In healthy mammals, including humans, physiological responses to release of acetylcholine from efferent nerves or release of histamine and leukotrienes from mast cells and basophils causes only mild and generally asymptomatic airway narrowing. Normal mammals are also generally resistant to marked airway narrowing in response to pharmacologic administration of high concentrations of these contractile agonists directly into the airways. However, people with asthma have a marked increase in sensitivity to all of these agonists that can readily be demonstrated by dramatic increases in airway resistance and associated drops in maximal expiratory airflow rates during forced expiratory maneuvers (Boushey et al., 1980). Recent comparisons between responses to inhaled allergens in allergic asthmatic subjects and other subjects with similarly severe cutaneous immune responses to allergens makes it clear that all allergic humans release largely similar amounts of bronchoconstrictors into the airways (i.e., histamine and leukotrienes), but only asthmatics develop exaggerated airway narrowing in response to these mediators (Becky Kelly et al., 2003).
Mechanisms regulating generation of force by airway smooth muscle actin–myosin coupling

Force generation by airway smooth muscle is mediated by interactions between actin and myosin that depend on phosphorylation of the myosin light chain by the serine–threonine kinase, myosin light chain kinase (Fig. 3). This process is negatively regulated by myosin phosphatase. Increases in intracellular calcium concentration in smooth muscle cells induce contraction by two parallel pathways. When bound to calcium, the serine–threonine kinase calmodulin directly phosphorylates, and thereby activates, myosin light chain kinase. Increased calcium also increases GTP loading of the GTPase, RhoA, which increases the activity of its downstream effector kinases Rho-associated coiled-coil–containing protein kinases 1 and 2 (ROCK 1 and 2). ROCKs directly phosphorylate myosin light chain phosphatase, an effect that inactivates the phosphatase, further enhancing myosin phosphorylation. RhoA can also be activated independently of increases in intracellular calcium.

Core signaling pathways responsible for airway smooth muscle contraction. Airway smooth muscle contractile force is generated by cyclic cross-bridging of actin and smooth muscle myosin, which depends on myosin phosphorylation. Myosin phosphorylation is regulated by cyclic increases in cytosolic calcium (Ca2+) that activate calmodulin (CaM) to phosphorylate myosin light chain kinase (MLCK), which directly phosphorylates myosin. In parallel, the small GTPase, RhoA, is activated by both calcium-dependent and -independent pathways. Rho directly activates Rho-associated coiled-coil protein kinase (ROCK) which, in turn, phosphorylates and thereby inactivates myosin light chain phosphatase (MLCP), which normally dephosphorylates myosin. The most important physiological pathway for increasing cytosolic calcium in airway smooth muscle involves activation of G?q by G protein–coupled receptors that respond to extracellular contractile agonists, such as methacholine (Mch), serotonin (5-HT), and histamine. G?q activates phospholipase C ? (PLC?), which generates IP3 to bind to IP3 receptors on the sarcoplasmic reticulum and release sequestered Ca2+.

There are multiple upstream paths to increased i[Ca] in airway smooth muscle. Acetylcholine, released from post-ganglionic parasympathetic efferent nerves that innervate the muscle, activates G protein–coupled M2 muscarinic receptors, which are coupled to G?q. GTP-loaded G?q activates its downstream effector, PLC?, which phosphorylates PIP2 to generate IP3. IP3, in turn, binds to IP3 receptors on the sarcoplasmic reticulum to trigger translocation of calcium into the cytosol. Other contractile agonists, including histamine, bradykinin, and serotonin (5-HT; the specific agonists and receptors vary across mammalian species) bind to different G protein–coupled receptors to trigger the same pathway. Agonist-induced airway smooth muscle contraction is usually associated with cyclic oscillations in i[Ca], thought to be induced by local changes in cytosolic calcium triggering reuptake of calcium by the sarcoplasmic reticulum, and the magnitude of contractile force induced is most closely associated with the frequency of these calcium oscillations rather than their amplitude (Bergner and Sanderson, 2002).

Increases in cytosolic calcium concentration can also be induced by an influx of calcium from the extracellular space, generally due to the opening of voltage-gated calcium channels in the plasma membrane. These channels can be opened experimentally by increasing the extracellular concentration of potassium ions, which also induces airway smooth muscle contraction. Increased extracellular potassium concentrations also increase release of acetylcholine from post-ganglionic efferent nerves, so proper interpretation of the effects of KCl requires simultaneous addition of a muscarinic antagonist such as atropine.
Regulation of airway smooth muscle force generation by integrin-containing adhesion complexes

For smooth muscle cell contraction to be translated into the force required for airway narrowing, the contracting smooth muscle cell must be firmly tethered to the underlying ECM. Linkage to the ECM is accomplished through the organization of multi-protein complexes nucleated by integrins. The short cytoplasmic domains of integrins can organize surprisingly large multi-protein machines that modulate multiple signaling pathways and link integrins (and thus their ECM ligands) to the actin–myosin cytoskeleton (Yamada and Geiger, 1997; Zaidel-Bar et al., 2007). Many of the contractile agonists that stimulate myosin phosphorylation and actin–myosin interaction simultaneously enhance the formation of integrin signaling complexes, induce actin polymerization at sites of adhesion, and strengthen coupling between the actin–myosin cytoskeleton and the ECM (Mehta and Gunst, 1999; Tang et al., 1999, 2003; Gunst and Fredberg, 2003; Gunst et al., 2003; Opazo Saez et al., 2004). These events appear to also be quite important for generation of maximal contractile force because interventions that inhibit the formation or activity of adhesion complexes can inhibit the strength of contraction without affecting myosin phosphorylation (Mehta and Gunst, 1999; Tang et al., 2003; Opazo Saez et al., 2004).
Lessons from abnormal behavior of airway smooth muscle in animal models
Mice lacking ?9?1 integrin in airway smooth muscle.

Although there are large differences between the organization of airways in mice and humans, in vivo abnormalities in airway narrowing seen in mouse models do provide some insight into pathways that potentially contribute to abnormal airway smooth muscle contraction in asthma. For the purposes of this review, we will cite three illustrative examples. The integrin ?9?1 is highly expressed in airway smooth muscle (Palmer et al., 1993). Conditional knockout of the integrin ?9 subunit (uniquely found in the ?9?1 integrin) results in a spontaneous increase in in vivo airway responsiveness (as measured by increases in pulmonary resistance in response to intravenous acetylcholine), and to increased contractile responses to cholinergic agonists of both airways in lung slices and tracheal rings studied in an organ bath (Chen et al., 2012). Interestingly, although tracheal rings from these mice also have increased contractile responses to other G protein–coupled receptor agonists (e.g., serotonin), they have normal contractile responses to depolarization with KCl. These findings suggest that loss of ?9?1 increases airway responsiveness at some step upstream of calcium release from the sarcoplasmic reticulum (Fig. 4 A). In this case, increased airway responsiveness appears to be due to loss of co-localization of the polyamine-catabolizing enzyme spermidine/spermine N1-acetyltransferase (SSAT), which binds directly to the ?9 cytoplasmic domain (Chen et al., 2004), and the lipid kinase, PIP5K1?, which binds directly to talin, an integrin ?1 subunit binding partner. Spermine and spermidine are critical cofactors for PIP5K1?, so its juxtaposition with SSAT effectively reduces enzymatic activity. PIP5K1? converts PI4P to PIP2 and is responsible for most of the PIP2 produced in airway smooth muscle cells (Chen et al., 1998). PIP2 is the substrate for IP3 generation by PLC?, so when ?9?1 is present and ligated, contractile agonists that activate receptors coupled to G?q induce less IP3 generation (Chen et al., 2012) and thus less Ca2+ release through IP3 receptors in the sarcoplasmic reticulum. The importance of this pathway was confirmed by the observations that the frequency of Ca2+ oscillations induced by cholinergic agonists was reduced in lung slices from mice lacking ?9?1, and that all of the abnormalities in smooth muscle from these animals could be rescued by addition of a cell-permeable form of PIP2 (Chen et al., 2012).

Pathways that negatively regulate airway smooth muscle contraction. (A) The integrin ?9?1 negatively regulates airway smooth muscle contraction by colocalizing the polyamine-catabolizing enzyme, spermine spermidine acetyltransferase (SSAT), which directly binds to the ?9 subunit with the lipid kinase, PIP5K1?, the major source of PIP2 in airway smooth muscle, which binds to talin, a direct interactor with the ?1 subunit. PIP5K1? depends on spermine and spermidine for maximal activity, so the local breakdown of spermine and spermidine reduces PIP5K1? activity, thereby decreasing PIP2 concentrations and the amount of IP3 that is generated by activation of contractile G protein–coupled receptors (such as those activated by acetylcholine or serotonin [5-HT]). (B) The secreted scaffold protein, milk fat globule-EGF factor 8 (MFGE8), inhibits the smooth muscle hypercontractility induced by IL-13, IL-17, and tumor necrosis factor ? (TNF) by inhibiting the induction and activation of the small GTPase, RhoA. Active RhoA contributes to smooth muscle contraction by directly activating Rho-associated coiled-coil protein kinase (ROCK) which, in turn, phosphorylates and thereby inactivates myosin light chain phosphatase (MLCP), which normally dephosphorylates myosin.
Effects of T cell cytokines on airway smooth muscle contractility.

Several studies conducted over the past 15 years have suggested that cytokines released from T cells can contribute to airway hyperresponsiveness in allergic asthma (Locksley, 2010). The Th2 cytokine IL-13 has been most extensively studied, and can induce both mucous metaplasia and airway hyperresponsiveness when administered directly into the airways of mice (Grünig et al., 1998; Wills-Karp et al., 1998). In vitro, incubation of tracheal rings or lung slices increases narrowing of airways in lung slices and increases force generation by mouse tracheal rings, at least in part by inducing a dramatic increase in expression of the small GTPase, RhoA (Chiba et al., 2009), which is a critical effector of airway smooth muscle contraction (Fig. 4 B). Chronic allergen challenge or direct administration of IL-13 into the airways of mice also increased RhoA expression, in association with induction of airway hyperresponsiveness. A recent study suggested that IL-17 can also increase airway smooth muscle contractility and airway narrowing by induction of RhoA in airway smooth muscle cells (Kudo et al., 2012). In that study, mice lacking the ?v?8 integrin specifically on antigen-presenting dendritic cells were protected from allergen-induced airway hyperresponsiveness. These mice had the same degree of general airway inflammation and mucous metaplasia in response to allergen as wild-type control mice, but had a very specific defect in the generation of antigen-specific Th17 cells, an important source of IL-17 in lungs (Kudo et al., 2012). In vitro, IL-17 was shown to directly increase the contractility of mouse tracheal rings and to increase the levels of RhoA protein and its downstream effector, ROCK2, and to increase phosphorylation of the direct ROCK target, myosin phosphatase. Phosphorylation of myosin phosphatase inhibits its function, and IL-17 was also shown to consequently increase phosphorylation of myosin light chain kinase. Importantly, all of these biochemical effects were dramatically induced in vivo in airway smooth muscle of control mice in response to allergen sensitization and challenge, but all were markedly reduced in mice lacking ?v?8 on dendritic cells. Furthermore, tracheal rings removed from these knockout mice after allergen challenge had decreased in vitro contractility compared with rings from allergen challenged control mice, but this difference in contractility was eliminated by exogenous addition of IL-17. These findings strongly suggest that both IL-13 and IL-17 can contribute to airway hyperresponsiveness by directly inducing RhoA expression in airway smooth muscle (Fig. 4 B). Tumor necrosis factor ?, also implicated in asthma pathogenesis, has been shown to increase airway smooth muscle contractility by a similar mechanism (Goto et al., 2009).
Enhanced cytokine-mediated airway smooth muscle contraction in MFGE8-deficient mice.

Milk fat globule EGF factor 8 (MFGE8) is a secreted protein composed of two EGF repeats and two discoidin domains. MFGE8 was originally described to facilitate uptake of apoptotic cells by phagocytes (Hanayama et al., 2004). Mice lacking MFGE8 have normal baseline lung morphology and function, but have exaggerated airway responsiveness after allergen sensitization and challenge (Kudo et al., 2013). However, this abnormality did not appear to be related to any effects on reuptake of apoptotic cells. Immunostaining demonstrated that secreted MFGE8 was concentrated adjacent to airway smooth muscle. Tracheal rings removed from MFGE8 knockout mice had normal contractile responses at baseline, but had markedly enhanced contractile responses after overnight incubation with IL-13, and this increase in contractility could be rescued by addition of recombinant MFGE8 to the muscle bath. Importantly, rescue required the presence of at least one of the discoidin domains and of the integrin-binding RGD motif of the second EGF repeat. In mouse tracheal rings and cultured airway smooth muscle, loss of MFGE8 greatly enhanced the IL-13–induced increase in RhoA protein. These findings suggest that ligation of one or more RGD-binding integrins on airway smooth muscle by extracellular MFGE8 normally serves as a brake on cytokine-mediated RhoA induction and thereby limits maximal cytokine-induced airway hyperresponsiveness (Fig. 4 B). The specific integrin(s) involved in this response, the molecular mechanisms linking integrin ligation to inhibition of RhoA, and the role and binding partner(s) of the MFGE8 discoidin domains that are required for RhoA inhibition all remain to be determined.

Conclusions

Rapid progress has been made toward identifying epithelial and smooth muscle cell molecules and pathways that can produce many of the abnormalities found in individuals with asthma. Because these discoveries were made in diverse experimental systems, we still face major challenges in understanding how these molecules and pathways interact in vivo and in identifying the pathways that are most relevant in people with asthma. Asthma is a heterogeneous disease, and recent progress toward identifying subtypes with distinct pathophysiologic mechanisms promises to focus attention on certain pathways in epithelial and smooth muscle cells (Lötvall et al., 2011). It will be especially important to understand mechanisms underlying severe asthma. Approximately 5–10% of individuals with asthma have severe disease, with symptoms that persist despite standard therapy with bronchodilators and inhaled corticosteroids (Brightling et al., 2012). These individuals have high rates of asthma exacerbations leading to hospitalization and are at relatively high risk for fatal asthma attacks. Continued attention to the study of the cell biology of asthma will be crucial for generating new ideas for asthma prevention and treatment based on normalizing epithelial and smooth muscle function.

Asthma Symptoms Impairs Sleep

Asthma symptoms impair sleep quality and school performance in children

#ATS2013, PHILADELPHIA ? The negative effects of poorly controlled asthma symptoms on sleep quality and academic performance in urban schoolchildren has been confirmed in a new study.

“While it has been recognized that missed sleep and school absences are important indicators of asthma morbidity in children, our study is the first to explore the associations between asthma, sleep quality, and academic performance in real time, prospectively, using both objective and subjective measures,” said principal investigator Daphne Koinis-Mitchell, PhD, Associate Professor of Psychiatry & Human Behavior (Research) and Associate Professor of Pediatrics (Research) at Brown University’s Alpert Medical School in Providence, Rhode Island. “In our sample of urban schoolchildren (aged 7 to 9), we found that compromised lung function corresponded with both poor sleep efficiency and impaired academic performance.”

The results of the study will be presented at the American Thoracic Society’s 2013 International Conference.

The study included data on 170 parent-child dyads from urban and African-American, Latino, and non-Latino white backgrounds who reside in Greater Providence, RI. These data are part of a larger 5-year study of asthma and allergic rhinitis symptoms, sleep quality and academic performance (which will include 450 urban children with persistent asthma and healthy controls) funded by The Eunice Kennedy Shriver National Institute of Child Health and Human Development. Project NAPS (Nocturnal Asthma and Performance in School) is administered through Rhode Island Hospital at The Bradley Hasbro Research Center.

Asthma symptoms were assessed over three 30-day monitoring periods across the school year by spirometry, which measures the amount and speed of exhaled air, and with diaries maintained by children and their caregivers. Sleep quality was assessed with actigraphy, which measures motor activity that can be used to estimate sleep parameters. Asthma control was assessed with the Asthma Control Test (ACT), a brief questionnaire used to measure asthma control in children. Academic functioning was assessed by teacher report during the same monitoring periods.

Compared with children with well-controlled asthma, those with poorly controlled asthma had lower quality school work and were more careless with their school work, according to teacher reports. Higher self-reported and objectively measured asthma symptom levels were associated with lower quality school work. Poorer sleep quality was also associated with careless school work. Increased sleep onset latency (the amount of time children take to fall asleep) was associated with more difficulty in remaining awake in class.

“Our findings demonstrate the detrimental effects that poorly controlled asthma may have on two crucial behaviors that can enhance overall health and development for elementary school children; sleep and school performance,” said Dr. Koinis-Mitchell. “Urban and ethnic minority children are at an increased risk for high levels of asthma morbidity and frequent health care utilization due to asthma. Given the high level of asthma burden in these groups, and the effects that urban poverty can have on the home environments and the neighborhoods of urban families, it is important to identify modifiable targets for intervention.”

“Family-level interventions aimed at asthma control and improving sleep quality may help to improve academic performance in this vulnerable population,” Dr. Konis-Mitchell continued. “In addition, school-level interventions can involve identifying children with asthma who miss school often, appear sleepy and inattentive during class, or who have difficulty with school work. Working collaboratively with the school system as well as the child and family may ultimately enhance the child’s asthma control.”

* Please note that numbers in this release may differ slightly from those in the abstract. Many of these investigations are ongoing; the release represents the most up-to-date data available at press time.

Abstract 42716

Asthma, Sleep, And School Functioning In Urban Children
Type: Scientific Abstract
Category: 02.03 – Disparities in Lung Disease and Treatment (BSHSR)
Authors: D. Koinis Mitchell; Brown Medical School/Rhode Island Hospital – Providence, RI/US; and the Project NAPS Study Group

Abstract Body

Rationale: Urban children are at an increased risk for asthma morbidity. Poor quality sleep is an indicator that asthma is in poor control. Asthma and poor sleep can affect children’s academic performance. No studies have examined asthma, sleep quality, and academic functioning in urban children with asthma using objective and subjective methods. This study investigates associations among asthma symptoms (FEV1 and symptom reports), asthma control, sleep efficiency (through actigraphy) and academic functioning in a sample of urban children.

Methods: Data are from a larger study of asthma and allergic rhinitis symptoms, sleep quality and academic performance in urban children (aged 7-9).To date, data are collected from 170 parent-child dyads from African-American, Latino, and non-Latino white backgrounds. Asthma symptoms were assessed by FEV1 percent predicted via the AM2 (electronic hand-held spirometer) over three, 30 day monitoring periods across the academic year. Children and caregivers also recorded days when asthma symptoms were present via a standard diary. Sleep quality was assessed through actigraphy for 3, 30 day periods across the academic year. Asthma diagnosis and persistent asthma status were confirmed through clinician assessment using standardized procedures (NHLBI, 2007). Asthma control was assessed using the ACT. Teachers reported on children’s academic functioning during the same time periods when asthma and sleep data were collected.

Results: Results to date show that children with poorly controlled asthma had lower quality school work by teacher report (MN=2.2) relative to their counterparts with well controlled asthma (MN=2.8; F(1,73)=4.9, p=.03). Similarly, on average, children with poor asthma control were reported to be more careless with their school-work (MN=3.1) relative to children with good asthma control (MN=2.5; F(1,73)=4.5, p=.04).

Higher levels of asthma symptoms (by diary report) were related to lower quality of school work (r= – .24, p=.03) by teacher report. Careless and hasty schoolwork was negatively associated with objectively measured asthma symptoms (FEV1), (r= -.25, p=.05).

Careless school work was associated with poorer sleep quality (r= -.25, p=.03). Teacher report of children’s struggle to stay awake in class was negatively associated with sleep onset latency (r=-.29, p=.01), suggesting that children who are more alert in class have less difficulty falling asleep.

Conclusions: Results to date indicate that children’s asthma symptoms correspond with sleep efficiency indicators using objective and subjective methods, and children’s academic performance by teacher report. Results can inform family and school-based interventions designed to improve asthma control, sleep quality and academic performance in urban children.

Nutrition and Asthma

The Role of Nutrition and Nutritional Supplements in Asthma

Nutrition and Nutritional Supplements in Asthma Interview with Nicholas Kenyon, M.D. Associate Professor of Medicine Division of Pulmonary and Critical Care Medicine University of California, Davis.

We learn about:

* Increased consumption of vegetables and fruit led to fewer respiratory symptoms and improved lung function
* Is obesity an independent risk factor for asthma in adults?
* Mouse model to adult trials in asthma. These options are cheap, readily available, and there is decent biological rationale to study them in severe asthma
* Effect of oral magnesium supplementation on measures of airway resistance and subjective assessment of asthma control
* Nitric oxide may be protective against the development of allergic airway inflammation and airways hyper-responsiveness
* Fish oils and Asthma
* Essential Vitamins, Elements, and Amino Acids—potential treatments such as
-Magnesium
-Vitamin A
-L-arginine
* EPA-enriched omega3 fatty acids as asthma supplements
* Diet’s impact on the immune system will be focus of increasing research
* Recommendations such as
– Olive oil !!!
– Walnut !!!
– Omega 3 fatty acids !!
– L- arginine !!
– Vitamins A, D !
– DASH diet – Fruit/Veg !!