Insulin increases the expression of contractile phenotypic markers in airway smooth muscle

Unraveling the Link between Ιnsulin Resistance and Bronchial Asthma

Evidence from large epidemiological studies has shown that obesity may predispose to increased Th2 inflammation and increase the odds of developing asthma. On the other hand, there is growing evidence suggesting that metabolic dysregulation that occurs with obesity, and more specifically hyperglycemia and insulin resistance, may modify immune cell function and in some degree systemic inflammation. Insulin resistance seldom occurs on its own, and in most cases constitutes a clinical component of metabolic syndrome, along with central obesity and dyslipidemia. Despite that, in some cases, hyperinsulinemia associated with insulin resistance has proven to be a stronger risk factor than body mass in developing asthma. This finding has been supported by recent experimental studies showing that insulin resistance may contribute to airway remodeling, promotion of airway smooth muscle (ASM) contractility and proliferation, increase of airway hyper-responsiveness and release of pro-inflammatory mediators from adipose tissue. All these effects indicate the potential impact of hyperinsulinemia on airway structure and function, suggesting the presence of a specific asthma phenotype with insulin resistance. Epidemiologic studies have found that individuals with severe and uncontrolled asthma have a higher prevalence of glycemic dysfunction, whereas longitudinal studies have linked glycemic dysfunction to an increased risk of asthma exacerbations. Since the components of metabolic syndrome interact with one another so much, it is challenging to identify each one's specific role in asthma. This is why, over the last decade, additional studies have been conducted to determine whether treatment of type 2 diabetes mellitus affects comorbid asthma as shown by the incidence of asthma, asthma control and asthma-related exacerbations. The purpose of this review is to present the mechanism of action, and existing preclinical and clinical data, regarding the effect of insulin resistance in asthma.

Hyperglycaemia and Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) may coexist with type 2 diabetes mellitus (T2DM). Patients with COPD have an increased risk of developing T2DM compared with a control but, on the other side, hyperglycaemia and DM have been associated with reduced predicted levels of lung function. The mechanistic relationships between these two diseases are complicated, multifaceted, and little understood, yet they can impact treatment strategy. The potential risks and benefits for patients with T2DM treated with pulmonary drugs and the potential pulmonary risks and benefits for patients with COPD when taking antidiabetic drugs should always be considered. The interaction between the presence and/or treatment of COPD, risk of infection, presence and/or treatment of T2DM and risk of acute exacerbations of COPD (AECOPDs) can be represented as a vicious circle; however, several strategies may help to break this circle. The most effective approach to simultaneously treating T2DM and COPD is to interfere with the shared inflammatory substrate, thus targeting both lung inflammation (COPD) and vascular inflammation (DM). In any case, it is always crucial to establish glycaemic management since the reduction in lung function found in people with diabetes might decrease the threshold for clinical manifestations of COPD. In this article, we examine possible connections between COPD and T2DM as well as pharmacological strategies that could focus on these connections.

Cardiovascular diseases or type 2 diabetes mellitus and chronic airway diseases: mutual pharmacological interferences

Chronic airway diseases (CAD), mainly asthma and chronic obstructive pulmonary disease (COPD), are frequently associated with different comorbidities. Among them, cardiovascular disease (CVD) and type 2 diabetes mellitus (T2DM) pose problems for the simultaneous treatment of CAD and comorbidity. Indeed, there is evidence that some drugs used to treat CAD negatively affect comorbidity, and, conversely, some drugs used to treat comorbidity may aggravate CAD. However, there is also growing evidence of some beneficial effects of CAD drugs on comorbidities and, conversely, of the ability of some of those used to treat comorbidity to reduce the severity of lung disease. In this narrative review, we first describe the potential cardiovascular risks and benefits for patients using drugs to treat CAD and the potential lung risks and benefits for patients using drugs to treat CVD. Then, we illustrate the possible negative and positive effects on T2DM of drugs used to treat CAD and the potential negative and positive impact on CAD of drugs used to treat T2DM. The frequency with which CAD and CVD or T2DM are associated requires not only considering the effect that drugs used for one disease condition may have on the other but also providing an opportunity to develop therapies that simultaneously favorably impact both diseases.

Mechanistic Links Between Obesity and Airway Pathobiology Inform Therapies for Obesity-Related Asthma

Obesity-related asthma is associated with a high disease burden and a poor response to existent asthma therapies, suggesting that it is a distinct asthma phenotype. The proposed mechanisms that contribute to obesity-related asthma include the effects of the mechanical load of obesity, adipokine perturbations, and immune dysregulation. Each of these influences airway smooth muscle function. Mechanical fat load alters airway smooth muscle stretch affecting airway wall geometry, airway smooth muscle contractility, and agonist delivery; weight loss strategies, including medically induced weight loss, counter these effects. Among the metabolic disturbances, insulin resistance and free fatty acid receptor activation influence distinct signaling pathways in the airway smooth muscle downstream of both the M2 muscarinic receptor and the β2 adrenergic receptor, such as phospholipase C and the extracellular signal-regulated kinase signaling cascade. Medications that decrease insulin resistance and dyslipidemia are associated with a lower asthma disease burden. Leptin resistance is best understood to modulate muscarinic receptors via the neural pathways but there are no specific therapies for leptin resistance. From the immune perspective, monocytes and T helper cells are involved in systemic pro-inflammatory profiles driven by obesity, notably associated with elevated levels of interleukin-6. Clinical trials on tocilizumab, an anti-interleukin antibody, are ongoing for obesity-related asthma. This armamentarium of therapies is distinct from standard asthma medications, and once investigated for its efficacy and safety among children, will serve as a novel therapeutic intervention for pediatric obesity-related asthma. Irrespective of the directionality of the association between asthma and obesity, airway-specific mechanistic studies are needed to identify additional novel therapeutic targets for obesity-related asthma.

The Association Between Insulin Use and Asthma: An Epidemiological Observational Analysis and Mendelian Randomization Study

BACKGROUND

Asthma is a common respiratory disease caused by genetic and environmental factors, but the contribution of insulin use to the risk of asthma remains unclear. This study aimed to investigate the association between insulin use and asthma in a large population-based cohort, and further explore their causal relationship by Mendelian randomization (MR) analysis.

METHODS

An epidemiological study including 85,887 participants from the National Health and Nutrition Examination Survey (NHANES) 2001-2018 was performed to evaluate the association between insulin use and asthma. Based on the inverse-variance weighted approach, MR analysis were conducted to estimate the causal effect of insulin use on asthma from the UKB and FinnGen datasets, respectively.

RESULTS

In the NHANES cohort, we found that insulin use was associated with an increased risk of asthma [odd ratio (OR) 1.38; 95% CI 1.16-1.64; p < 0.001]. For the MR analysis, we found a causal relationship between insulin use and a higher risk of asthma in both Finn (OR 1.10; p < 0.001) and UK Biobank cohorts (OR 1.18; p < 0.001). Meanwhile, there was no causal association between diabetes and asthma. After multivariable adjustment for diabetes in UKB cohort, the insulin use remained significantly associated with an increased risk of asthma (OR 1.17, p < 0.001).

CONCLUSIONS

An association between insulin use and an increased risk of asthma was found via the real-world data from the NHANES. In addition, the current study identified a causal effect and provided a genetic evidence of insulin use and asthma. More studies are needed to elucidate the mechanisms underlying the association between insulin use and asthma.

Metabolic Contributions to Pathobiology of Asthma

Asthma is a heterogenous disorder driven by inflammatory mechanisms that result in multiple phenotypes. Given the complex nature of this condition, metabolomics is being used to delineate the pathobiology of asthma. Metabolomics is the study of metabolites in biology, which includes biofluids, cells, and tissues. These metabolites have a vital role in a disease as they contribute to the pathogenesis of said condition. This review describes how macrometabolic and micrometabolic studies pertaining to these metabolites have contributed to our current understanding of asthma, as well as its many phenotypes. One of the main phenotypes this review will discuss in further detail is obesity as well as diabetes. Distinct roles of metabolites in endotyping asthma and their translation to potential therapy development for asthma is also discussed in this review.

Obesity-related asthma in children and adolescents

There is substantial epidemiological and experimental evidence of an obesity-related asthma phenotype. Compared to children of healthy weight, children with obesity are at higher risk of asthma. Children with obesity who have asthma have greater severity and poorer control of their asthma symptoms, more frequent asthma exacerbations, and overall lower asthma-related quality of life than children with asthma who have a healthy weight. In this Review, we examine some of the latest evidence on the characteristics of this phenotype and its main underlying mechanisms, including genetics and genomics, changes in airway mechanics and lung function, sex hormone differences, alterations in immune responses, systemic and airway inflammation, metabolic dysregulation, and modifications in the microbiome. We also review current recommendations for the treatment of these children, including in the management of their asthma, and current evidence for weight loss interventions. We then discuss initial evidence for potential novel therapeutic approaches, such as dietary modifications and supplements, antidiabetic medications, and statins. Finally, we identify knowledge gaps and future directions to improve our understanding of asthma in children with obesity, and to improve outcomes in these susceptible children. We highlight important needs, such as designing paediatric-specific studies, implementing large multicentric trials with standardised interventions and outcomes, and including racial and ethnic groups along with other under-represented populations that are particularly affected by obesity and asthma.

Pediatric Obesity-Related Asthma: The Role of Nutrition and Nutrients in Prevention and Treatment

Childhood obesity rates have dramatically risen in numerous countries worldwide. Obesity is likely a factor in increased asthma risk, which is already one of the most widespread chronic respiratory pathologies. The pathogenic mechanism of asthma risk has still not yet been fully elucidated. Moreover, the role of obesity-related inflammation and pulmonary overreaction to environmental triggers, which ultimately result in asthma-like symptoms, and the importance of dietary characteristics is well recognized. Diet is an important adjustable element in the asthma development. Food-specific composition of the diet, in particular fat, sugar, and low-quality nutrients, is likely to promote the chronic inflammatory state seen in asthmatic patients with obesity. An unbalanced diet or supplementation as a way to control asthma more efficiently has been described. A personalized dietary intervention may improve respiratory symptoms and signs and therapeutic response. In this narrative review, we presented and discussed more recent literature on asthma associated with obesity among children, focusing on the risk of asthma among children with obesity, asthma as a result of obesity focusing on the role of adipose tissue as a mediator of systemic and local airway inflammation implicated in asthma regulation, and the impact of nutrition and nutrients in the development and treatment of asthma. Appropriate early nutritional intervention could possibly be critical in preventing and managing asthma associated with obesity among children.

Diabetes, insulin resistance, and asthma: a review of potential links

PURPOSE OF REVIEW

Disorders of glucose metabolism, including insulin resistance, prediabetes, and diabetes, have been identified as risk factors for worsened asthma. This review summarizes emerging evidence for their role as modifiable risk factors in asthma, including the potential benefit of diabetes medications on asthma outcomes.

RECENT FINDINGS

Experimental studies show that hyperinsulinemia associated with insulin resistance is associated with airway smooth muscle proliferation and promotes contractility. Epidemiologic studies have identified a higher prevalence of glycemic dysfunction among those with severe and uncontrolled asthma, and longitudinal studies have associated prediabetes and diabetes with higher risk of asthma exacerbations. The potential benefits of thiazolidinediones (TZDs), glucagon-like peptide-1 agonists, and metformin being investigated in asthma, but thus far interventional studies of TZDs have reported null results. On the contrary, observational studies have inconsistently controlled for relevant confounders which leaves conclusions vulnerable to misattribution of relationships due to corelated metabolic disorders, including dyslipidemia.

SUMMARY

Developing evidence suggests that disorders of glucose metabolism may be associated with worsening asthma. However, these conditions arise within a network of obesity-related metabolic diseases that may themselves worsen asthma. Few interventional trials have not identified a benefit, but data have been limited. Additional research is needed to define the potential independent impact of disorders of glucose metabolism in asthma.

Perinatal Nutritional and Metabolic Pathways: Early Origins of Chronic Lung Diseases

Lung development is not completed at birth, but expands beyond infancy, rendering the lung highly susceptible to injury. Exposure to various influences during a critical window of organ growth can interfere with the finely-tuned process of development and induce pathological processes with aberrant alveolarization and long-term structural and functional sequelae. This concept of developmental origins of chronic disease has been coined as perinatal programming. Some adverse perinatal factors, including prematurity along with respiratory support, are well-recognized to induce bronchopulmonary dysplasia (BPD), a neonatal chronic lung disease that is characterized by arrest of alveolar and microvascular formation as well as lung matrix remodeling. While the pathogenesis of various experimental models focus on oxygen toxicity, mechanical ventilation and inflammation, the role of nutrition before and after birth remain poorly investigated. There is accumulating clinical and experimental evidence that intrauterine growth restriction (IUGR) as a consequence of limited nutritive supply due to placental insufficiency or maternal malnutrition is a major risk factor for BPD and impaired lung function later in life. In contrast, a surplus of nutrition with perinatal maternal obesity, accelerated postnatal weight gain and early childhood obesity is associated with wheezing and adverse clinical course of chronic lung diseases, such as asthma. While the link between perinatal nutrition and lung health has been described, the underlying mechanisms remain poorly understood. There are initial data showing that inflammatory and nutrient sensing processes are involved in programming of alveolarization, pulmonary angiogenesis, and composition of extracellular matrix. Here, we provide a comprehensive overview of the current knowledge regarding the impact of perinatal metabolism and nutrition on the lung and beyond the cardiopulmonary system as well as possible mechanisms determining the individual susceptibility to CLD early in life. We aim to emphasize the importance of unraveling the mechanisms of perinatal metabolic programming to develop novel preventive and therapeutic avenues.

Asthmatic Eosinophils Promote Contractility and Migration of Airway Smooth Muscle Cells and Pulmonary Fibroblasts In Vitro

Enhanced contractility and migration of airway smooth muscle cells (ASMC) and pulmonary fibroblasts (PF) are part of airway remodeling in asthma. Eosinophils are the central inflammatory cells that participate in airway inflammation. However, the role of asthmatic eosinophils in ASMC and PF contractility, migration, and differentiation to contractile phenotype has not yet been precisely described. A total of 38 individuals were included in this study: 13 steroid-free non-severe allergic asthma (AA) patients, 11 severe non-allergic eosinophilic asthma (SNEA) patients, and 14 healthy subjects (HS). For AA patients and HS groups, a bronchial allergen challenge with D. pteronyssinus was performed. Individual combined cell cultures were prepared from isolated peripheral blood eosinophils and immortalized ASMC or commercial PF cell lines separately. The migration of ASMC and PF was evaluated using wound healing assay and contractility using collagen gel assay. Gene expression of contractile apparatus proteins, COL1A1, COL5A1, and FN, in ASMC and PF was evaluated using qRT-PCR. We found that contractility and migration of ASMC and PF significantly increased after incubation with asthmatic eosinophils compared to HS eosinophils, p < 0.05, and SNEA eosinophils demonstrated the highest effect on contractility of ASMC and migration of both cell lines, p < 0.05. AA and SNEA eosinophils significantly increased gene expression of contractile apparatus proteins, COL1A1 and FN, in both cell lines, p < 0.05. Furthermore, the allergen-activated AA eosinophils significantly increased the contractility of ASMC, and migration and gene expression in ASMC and PF, p < 0.05. Thus, asthmatic eosinophils change ASMC and PF behavior by increasing their contractility and migration, contributing to airway remodeling.

Role of Airway Smooth Muscle in Inflammation Related to Asthma and COPD

Airway smooth muscle contributes to both contractility and inflammation in the pathophysiology of asthma and COPD. Airway smooth muscle cells can change the degree of a variety of functions, including contraction, proliferation, migration, and the secretion of inflammatory mediators (phenotype plasticity). Airflow limitation, airway hyperresponsiveness, β₂-adrenergic desensitization, and airway remodeling, which are fundamental characteristic features of these diseases, are caused by phenotype changes in airway smooth muscle cells. Alterations between contractile and hyper-contractile, synthetic/proliferative phenotypes result from Ca²⁺ dynamics and Ca²⁺ sensitization. Modulation of Ca²⁺ dynamics through the large-conductance Ca²⁺-activated K⁺ channel/L-type voltage-dependent Ca²⁺ channel linkage and of Ca²⁺ sensitization through the RhoA/Rho-kinase pathway contributes not only to alterations in the contractile phenotype involved in airflow limitation, airway hyperresponsiveness, and β₂-adrenergic desensitization but also to alteration of the synthetic/proliferative phenotype involved in airway remodeling. These Ca²⁺ signal pathways are also associated with synergistic effects due to allosteric modulation between β₂-adrenergic agonists and muscarinic antagonists. Therefore, airway smooth muscle may be a target tissue in the therapy for these diseases. Moreover, the phenotype changing in airway smooth muscle cells with focuses on Ca²⁺ signaling may provide novel strategies for research and development of effective remedies against both bronchoconstriction and inflammation.

Asthma and Obesity in Children

Asthma and obesity are two major chronic diseases in children and adolescents. Recent scientific evidence points out a causative role of obesity in asthma predisposition. However, studies assessing the real impact of excessive weight gain on lung function in children have shown heterogeneous results. In this review, the pathological mechanisms linking obesity and development of asthma in children are summarized and factors influencing this relationship are evaluated. Common disease modifying factors including age, sex, ethnicity, development of atopic conditions, and metabolic alterations significantly affect the onset and phenotypic characteristics of asthma. Given this, the impact of these several factors on the obesity–asthma link were considered, and from revision of the literature we suggest the possibility to define three main clinical subtypes on the basis of epidemiological data and physiological–molecular pathways: obese-asthmatic and atopy, obese-asthmatic and insulin-resistance, and obese-asthmatic and dyslipidemia. The hypothesis of the different clinical subtypes characterizing a unique phenotype might have an important impact for both future clinical management and research priorities. This might imply the necessity to study the obese asthmatic child with a “multidisciplinary approach”, evaluating the endocrinological and pneumological aspects simultaneously. This different approach might also make it possible to intervene earlier in a specific manner, possibly with a personalized and tailored treatment. Surely this hypothesis needs longitudinal and well-conducted future studies to be validated.

Preserving Airway Smooth Muscle Contraction in Precision-Cut Lung Slices

Precision-cut lung slices (PCLS) are ideal for measuring small airway contraction. However, these measurements are currently limited to acute exposure scenarios that typically last a few minutes to a few hours. Using an insulin-supplemented culture medium, we prolong the small airway contractility in mouse PCLS for up to two weeks. Compared to conventional culture medium, insulin-supplemented culture medium provides no additional benefit in preserving cellular viability or airway structure. However, it protects the airway smooth muscle (ASM) against a loss of smooth muscle myosin heavy chain (SMMHC) expression. We elucidate the significance of this new culture medium for chronic disease modeling of IL-13-induced airway hyper-responsiveness.

Disruption of AKAP-PKA Interaction Induces Hypercontractility With Concomitant Increase in Proliferation Markers in Human Airway Smooth Muscle

With the ability to switch between proliferative and contractile phenotype, airway smooth muscle (ASM) cells can contribute to the progression of airway diseases such as asthma and chronic obstructive pulmonary disease (COPD), in which airway obstruction is associated with ASM hypertrophy and hypercontractility. A-kinase anchoring proteins (AKAPs) have emerged as important regulatory molecules in various tissues, including ASM cells. AKAPs can anchor the regulatory subunits of protein kinase A (PKA), and guide cellular localization via various targeting domains. Here we investigated whether disruption of the AKAP-PKA interaction, by the cell permeable peptide stearated (st)-Ht31, alters human ASM proliferation and contractility. Treatment of human ASM with st-Ht31 enhanced the expression of protein markers associated with cell proliferation in both cultured cells and intact tissue, although this was not accompanied by an increase in cell viability or cell-cycle progression, suggesting that disruption of AKAP-PKA interaction on its own is not sufficient to drive ASM cell proliferation. Strikingly, st-Ht31 enhanced contractile force generation in human ASM tissue with concomitant upregulation of the contractile protein α-sm-actin. This upregulation of α-sm-actin was independent of mRNA stability, transcription or translation, but was dependent on proteasome function, as the proteasome inhibitor MG-132 prevented the st-Ht31 effect. Collectively, the AKAP-PKA interaction appears to regulate markers of the multi-functional capabilities of ASM, and this alter the physiological function, such as contractility, suggesting potential to contribute to the pathophysiology of airway diseases.

Pediatric obesity-related asthma: A prototype of pediatric severe non-T2 asthma

Childhood obesity contributes to many diseases, including asthma. There is literature to suggest that asthma developing as a consequence of obesity has a nonallergic or non-T2 phenotype. In this review, obesity-related asthma is utilized as a prototype of non-T2 asthma in children to discuss several nonallergic mechanisms that underlie childhood asthma. Obesity-related asthma is associated with systemic T helper (Th)1 polarization occurring with monocyte activation. These immune responses are mediated by insulin resistance and dyslipidemia, metabolic abnormalities associated with obesity, that are themselves associated with pulmonary function deficits in obese asthmatics. As in other multifactorial diseases, there is both a genetic and an environmental contribution to pediatric obesity-related asthma. In addition to genetic susceptibility, differential DNA methylation is associated with non-T2 immune responses in pediatric obesity-related asthma. Initial investigations into the biology of non-T2 immune responses have identified the upregulation of genes in the CDC42 pathway. CDC42 is a RhoGTPase that plays a key role in Th cell physiology, including preferential naïve Th cell differentiation to Th1 cells, and cytokine production and exocytosis. Although these novel pathways are promising findings to direct targeted therapy development for obesity-related asthma to address the disease burden, there is evidence to suggest that dietary interventions, including diet modification, rather than caloric restriction alone, decrease disease burden. Adoption of a diet rich in micronutrients, including carotenoids and 25-OH cholecalciferol, a vitamin D metabolite, may be beneficial since these are positively correlated with pulmonary function indices, while being protective against metabolic abnormalities associated with the obese asthma phenotype.

Association of pediatric obesity and asthma, pulmonary physiology, metabolic dysregulation, and atopy; and the role of weight management

Introduction: Obesity affects about 40% of US adults and 18% of children. Its impact on the pulmonary system is best described for asthma. Areas covered: We reviewed the literature on PubMed and Google Scholar databases and summarize the effect of obesity, its associated metabolic dysregulation and altered systemic immune responses, and that of weight gain and loss on pulmonary mechanics, asthma inception, and disease burden. We include a distinct approach for diagnosing and managing the disease, including pulmonary function deficits inherent to obesity-related asthma, in light of its poor response to current asthma medications. Expert opinion: Given the projected increase in obesity, obesity-related asthma needs to be addressed now. Research on the contribution of metabolic abnormalities and systemic immune responses, intricately linked with truncal adiposity, and that of lack of atopy, to asthma disease burden, and pulmonary function deficits among obese children is fairly consistent. Since current asthma medications are more effective for atopic asthma, investigation for atopy will guide management by distinguishing asthma responsive to current medications from the non-responsive disease. Future research is needed to elucidate mechanisms by which obesity-mediated metabolic abnormalities and immune responses cause medication non-responsive asthma, which will inform repurposing of medications and drug discovery.

Short-term high-fat diet feeding protects from the development of experimental allergic asthma in mice

BACKGROUND

A close association between obesity and asthma has been described. The nature of this association remains elusive, especially with respect to allergic asthma. Controversial findings exist regarding the impact of short-term high-fat diet (HFD) feeding on the development of allergic asthma.

OBJECTIVE

To delineate the impact of short-term HFD feeding on the development of experimental allergic asthma.

METHODS

Female C57BL/6JRJ mice were fed with a short-term HFD or chow diet (CD) for 12 weeks. Allergic asthma was induced by intraperitoneal OVA/alum sensitization followed by repeated OVA airway challenges. We determined airway hyperresponsiveness (AHR) and pulmonary inflammation by histologic and flow cytometric analysis of immune cells. Furthermore, we assessed the impact of HFD on dendritic cell (DC)-mediated activation of T cells.

RESULTS

Female mice showed a mild increase in body weight accompanied by mild metabolic alterations. Upon OVA challenge, CD-fed mice developed strong AHR and airway inflammation, which were markedly reduced in HFD-fed mice. Mucus production was similar in both treatment groups. OVA-induced increases in DC and CD4⁺ T-cell recruitment to the lungs were significantly attenuated in HFD-fed mice. MHC-II expression and CD40 expression in pulmonary CD11b⁺ DCs were markedly lower in HFD-fed compared to CD-fed mice, which was associated in vivo with a decreased T helper (Th) 1/17 differentiation and Treg formation without impacting Th2 differentiation.

CONCLUSIONS/CLINICAL RELEVANCE

These findings suggest that short-term HFD feeding attenuates the development of AHR, airway inflammation, pulmonary DC recruitment and MHC-II/CD40 expression leading to diminished Th1/17 but unchanged Th2 differentiation. Thus, short-term HFD feeding and associated metabolic alterations may have protective effects in allergic asthma development.

Long-term observational study on the impact of GLP-1R agonists on lung function in diabetic patients

INTRODUCTION

Preclinical research suggests a role of Glucagon Like Peptide-1 Receptors (GLP-1R) on the regulation of human bronchial tone. We investigated the effect of GLP-1R agonists on lung function of Type 2 Diabetes Mellitus (T2DM) population without co-existing chronic obstructive respiratory disorders.

METHODS

This was a prospective cohort study that examined change in lung function measurements over two years of T2DM patients (n = 32) treated with metformin monotherapy (control cohort), metformin plus GLP-1R agonists (GLP-1R agonists cohort), or metformin plus insulin (insulin cohort).

RESULTS

After 24 months of treatment, the forced expiratory volume in 1 s (FEV₁) significantly (p < 0.05) increased from baseline in the GLP-1R agonists cohort (218 ml [95%CI 88-246]), but not in the control and insulin cohorts (94 ml [95%CI -28 - 216] and 26 ml [95%CI -174 - 226], respectively; p > 0.05 vs. baseline). The average increase in FEV₁ in the GLP-1R agonists cohort was significantly greater than that in the control and insulin cohorts (delta: 110 ml [95%CI 18-202] and 177 ml [95%CI 85-270], respectively, p < 0.05). The forced vital capacity (FVC) also increased significantly more in the GLP-1R agonists cohort than in the control and insulin cohorts (overall delta FVC: 183 ml [95%CI 72-295], p < 0.05). The maximal expiratory flow at 50-75% significantly (p < 0.05) improved from baseline in the GLP-1R agonists cohort, but not in the control and insulin cohorts (p > 0.05).

CONCLUSION

Our preliminary results suggest a potential new therapeutic perspective to treat airway disorders with GLP-1R agonists.

Obesity increases airway smooth muscle responses to contractile agonists

The asthma-obesity syndrome represents a major public health concern that disproportionately contributes to asthma severity and induces insensitivity to therapy. To date, no study has shown an intrinsic difference between human airway smooth muscle (HASM) cells derived from nonobese subjects and those derived from obese subjects. The objective of this study was to address whether there is a greater response to agonist-induced calcium mobilization, phosphorylation of myosin light chain (MLC), and greater shortening in HASM cells derived from obese subjects. HASM cells derived from nonobese and obese subjects were age and sex matched. Phosphorylation of MLC was measured after having been stimulated by carbachol. Carbachol- or histamine-induced mobilization of calcium and cell shortening were assessed in HASM cells derived from nonobese and obese donors. Agonist-induced MLC phosphorylation, mobilization of calcium, and cell shortening were greater in obese compared with non-obese-derived HASM cells. The MLC response was comparable in HASM cells derived from obese nonasthma and nonobese fatal asthma subjects. HASM cells derived from obese female subjects were more responsive to carbachol than HASM cells derived from obese male subjects. Insulin pretreatment had little effect on these responses. Our results show an increase in agonist-induced calcium mobilization associated with an increase in MLC phosphorylation and an increase in ASM cell shortening in favor of agonist-induced hyperresponsiveness in HASM cells derived from obese subjects. Our studies suggest that obesity induces a retained phenotype of hyperresponsiveness in cultured human airway smooth muscle cells.

Metabolic Dysregulation, Systemic Inflammation, and Pediatric Obesity-related Asthma

Obesity-related asthma is a distinct pediatric asthma phenotype. It is associated with higher disease burden, lower pulmonary function, and suboptimal response to current asthma medications. Recent studies have made inroads into elucidating its pathophysiology. Systemic immune responses in obese children with asthma are skewed to a nonatopic T-helper cell type 1 (Th1) pattern that correlates with pulmonary function deficits. The prevalence of metabolic dysregulation is also higher among obese children with asthma than among normal-weight children with asthma. Insulin resistance and dyslipidemia, particularly low levels of high-density lipoprotein (HDL), are associated with lower airway obstruction and low expiratory reserve volume. These associations are independent of truncal and general adiposity and thereby suggest a direct association between metabolic abnormalities and pulmonary function. Furthermore, insulin resistance is associated with Th1 polarization, whereas low HDL is associated with monocyte activation. Although insulin resistance mediates the association of Th1 polarization with pulmonary function, HDL does not have a similar influence on the association of monocyte activation with pulmonary function. Together, these recent studies have paved the way to the understanding of obesity-related asthma as a distinct asthma phenotype and have begun to identify the complex relationships between metabolic dysregulation, systemic inflammation, and pulmonary function deficits in obese children with asthma. Studies are now needed to elucidate the mechanisms that link metabolic dysregulation and systemic immune responses to pulmonary function.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Is impaired glucose metabolism the missing piece in the obesity-asthma puzzle?

Obesity is a major risk factor for several conditions including atherosclerotic disease, metabolic syndrome, and upper airway dysfunction. However, the purported link between obesity and asthma has remained more difficult to define, in part due to limitations in past epidemiologic studies and the inherent challenge in accurately defining asthma in children. It is possible that obesity leads to asthma only in the presence of a mediating variable such as an obesity-related conditions such as esophageal reflux or insulin resistance. The article by Karampatakis and colleagues in this week's edition of the journal is important because it addresses the hypothesis that altered glucose metabolism/insulin resistance associates with bronchial hyperresponsiveness (BHR), a central and objectively measured marker of asthma. They studied pre-pubertal children with and without asthma with a range of body mass indices and found for the first time in pre-pubertal asthmatic children that both insulin resistance and impaired glucose tolerance were more closely related to BHR than was obesity. Their work opens the way for directed mechanistic study of the effects of impaired glucose metabolism on airway development during childhood and airway responsiveness, and for the study of insulin sensitizing therapies in children to prevent lower airway disease. Pediatr Pulmonol. 2017;52:147-150. © 2016 Wiley Periodicals, Inc.

Cooperative signaling by TGF-β1 and WNT-11 drives sm-α-actin expression in smooth muscle via Rho kinase-actin-MRTF-A signaling

Airway smooth muscle (ASM) remodeling is a key feature in asthma and includes changes in smooth muscle-specific gene and protein expression. Despite this being a major contributor to asthma pathobiology, our understanding of the mechanisms governing ASM remodeling remains poor. Here, we studied the functional interaction between WNT-11 and TGF-β1 in ASM cells. We demonstrate that WNT-11 is preferentially expressed in contractile myocytes and is strongly upregulated following TGF-β1-induced myocyte maturation. Knock-down of WNT-11 attenuated TGF-β1-induced smooth muscle (sm)-α-actin expression in ASM cells. We demonstrate that TGF-β1-induced sm-α-actin expression is mediated by WNT-11 via RhoA activation and subsequent actin cytoskeletal remodeling, as pharmacological inhibition of either Rho kinase by Y27632 or actin remodeling by latrunculin A attenuated sm-α-actin induction. Moreover, we show that TGF-β1 regulates the nuclear expression of myocardin-related transcription factor-A (MRTF-A) in a Rho kinase-dependent fashion, which in turn mediates sm-α-actin expression. Finally, we demonstrate that TGF-β1-induced MRTF-A nuclear translocation is dependent on endogenous WNT-11. The present study thus demonstrates a WNT-11-dependent Rho kinase-actin-MRTF-A signaling axis that regulates the expression of sm-α-actin in ASM cells.

Early-onset obesity dysregulates pulmonary adipocytokine/insulin signaling and induces asthma-like disease in mice

Childhood obesity is a risk factor for asthma, but the molecular mechanisms linking both remain elusive. Since obesity leads to chronic low-grade inflammation and affects metabolic signaling we hypothesized that postnatal hyperalimentation (pHA) induced by maternal high-fat-diet during lactation leads to early-onset obesity and dysregulates pulmonary adipocytokine/insulin signaling, resulting in metabolic programming of asthma-like disease in adult mice. Offspring with pHA showed at postnatal day 21 (P21): (1) early-onset obesity, greater fat-mass, increased expression of IL-1β, IL-23, and Tnf-α, greater serum leptin and reduced glucose tolerance than Control (Ctrl); (2) less STAT3/AMPKα-activation, greater SOCS3 expression and reduced AKT/GSK3β-activation in the lung, indicative of leptin resistance and insulin signaling, respectively; (3) increased lung mRNA of IL-6, IL-13, IL-17A and Tnf-α. At P70 body weight, fat-mass, and cytokine mRNA expression were similar in the pHA and Ctrl, but serum leptin and IL-6 were greater, and insulin signaling and glucose tolerance impaired. Peribronchial elastic fiber content, bronchial smooth muscle layer, and deposition of connective tissue were not different after pHA. Despite unaltered bronchial structure mice after pHA exhibited significantly increased airway reactivity. Our study does not only demonstrate that early-onset obesity transiently activates pulmonary adipocytokine/insulin signaling and induces airway hyperreactivity in mice, but also provides new insights into metabolic programming of childhood obesity-related asthma.

Hyperinsulinemia adversely affects lung structure and function

There is limited knowledge regarding the consequences of hyperinsulinemia on the lung. Given the increasing prevalence of obesity, insulin resistance, and epidemiological associations with asthma, this is a critical lacuna, more so with inhaled insulin on the horizon. Here, we demonstrate that insulin can adversely affect respiratory health. Insulin treatment (1 μg/ml) significantly (P < 0.05) increased the proliferation of primary human airway smooth muscle (ASM) cells and induced collagen release. Additionally, ASM cells showed a significant increase in calcium response and mitochondrial respiration upon insulin exposure. Mice administered intranasal insulin showed increased collagen deposition in the lungs as well as a significant increase in airway hyperresponsiveness. PI3K/Akt mediated activation of β-catenin, a positive regulator of epithelial-mesenchymal transition and fibrosis, was observed in the lungs of insulin-treated mice and lung cells. Our data suggests that hyperinsulinemia may have adverse effects on airway structure and function. Insulin-induced activation of β-catenin in lung tissue and the contractile effects on ASM cells may be causally related to the development of asthma-like phenotype.

TGF-β-induced profibrotic signaling is regulated in part by the WNT receptor Frizzled-8

TGF-β is important in lung injury and remodeling processes. TGF-β and Wingless/integrase-1 (WNT) signaling are interconnected; however, the WNT ligand-receptor complexes involved are unknown. Thus, we aimed to identify Frizzled (FZD) receptors that mediate TGF-β-induced profibrotic signaling. MRC-5 and primary human lung fibroblasts were stimulated with TGF-β1, WNT-5A, or WNT-5B in the presence and absence of specific pathway inhibitors. Specific small interfering RNA was used to knock down FZD8. In vivo studies using bleomycin-induced lung fibrosis were performed in wild-type and FZD8-deficient mice. TGF-β1 induced FZD8 specifically via Smad3-dependent signaling in MRC-5 and primary human lung fibroblasts. It is noteworthy that FZD8 knockdown reduced TGF-β1-induced collagen Iα1, fibronectin, versican, α-smooth muscle (sm)-actin, and connective tissue growth factor. Moreover, bleomycin-induced lung fibrosis was attenuated in FZD8-deficient mice in vivo Although inhibition of canonical WNT signaling did not affect TGF-β1-induced gene expression in vitro, noncanonical WNT-5B mimicked TGF-β1-induced fibroblast activation. FZD8 knockdown reduced both WNT-5B-induced gene expression of fibronectin and α-sm-actin, as well as WNT-5B-induced changes in cellular impedance. Collectively, our findings demonstrate a role for FZD8 in TGF-β-induced profibrotic signaling and imply that WNT-5B may be the ligand for FZD8 in these responses.-Spanjer, A. I. R., Baarsma, H. A., Oostenbrink, L. M., Jansen, S. R., Kuipers, C. C., Lindner, M., Postma, D. S., Meurs, H., Heijink, I. H., Gosens, R., Königshoff, M. TGF-β-induced profibrotic signaling is regulated in part by the WNT receptor Frizzled-8.

γ-Tocotrienol reduces human airway smooth muscle cell proliferation and migration

AIMS

Vitamin E is an antioxidant that occurs in 8 different forms (α, β, γ, and δ tocopherol and tocotrienol). Clinical trials of tocopherol supplementation to assess the impact of antioxidant activity in asthma have yielded equivocal results. Tocotrienol exhibits greater antioxidant activity than tocopherol in several biological phenomena in vivo and in vitro. We tested the effect of tocotrienol on human airway smooth muscle (ASM) cell growth and migration, both of which mediate airway remodeling in asthma.

MAIN METHODS

We measured platelet-derived growth factor-BB (PDGF-BB)-induced ASM cell proliferation and migration by colorimetric and Transwell migration assays in the presence and absence of γ-tocotrienol (an isoform of tocotrienol).

KEY FINDINGS

PDGF-BB-induced ASM cell proliferation and migration were inhibited by γ-tocotrienol. This effect was associated with inhibition of RhoA activation, but it had no effect on p42/p44 mitogen-activated protein kinase (MAPK) or Akt1 activation. We confirmed that pharmacological inhibition of Rho kinase activity was sufficient to inhibit PDGF-BB-induced ASM cell proliferation and migration.

SIGNIFICANCE

γ-Tocotrienol could impart therapeutic benefits for airway remodeling in asthma by inhibiting human ASM cell proliferation and migration.

[Asthma and metabolic syndrome: Clinical and pathogenetic relationships]

Asthma and metabolic syndrome (MS) are common and social diseases. External and internal factors influencing the development and manifestations of asthma are identified; among which there is obesity that is a major risk factor for MS. Accordingly, the concurrence of asthma and MS and to study their clinical and pathogenetic relationships are a topical problem. There is a tendency to identify a particular asthma phenotype that is characterized by later-onset disease in the presence of obesity; the low prevalence of atopy, low serum level of IgE, and a poorly-controlled course with a trend of standard therapy resistance. It is necessary to understand the essence of asthma cause-effect relationships in the presence of obesity for defining management tactics for this group of patients.

Integrins: therapeutic targets in airway hyperresponsiveness and remodelling?

Integrins are a group of transmembrane heterodimeric proteins that mediate cell-cell and cell-extracellular matrix (ECM) interactions. Integrins have been under intense investigation for their role in inflammation in asthma. Clinical trials investigating integrin antagonists, however, have shown that these compounds are relatively ineffective. Airway remodelling is another pathological feature of asthma that is thought to make an important contribution to airway hyperresponsiveness (AHR) and lung function decline. Recent studies have identified integrins as important players in this process, with a particular role for β1 and αv integrins. Here we review the role of these integrins in airway remodelling and hyperresponsiveness in obstructive airway disease and their potential as pharmacological targets for future treatment.

Lipid-based carriers for pulmonary products: preclinical development and case studies in humans

A number of lipid-based technologies have been applied to pharmaceuticals to modify their drug release characteristics, and additionally, to improve the drug loading for poorly soluble drugs. These technologies, including solid-state lipid microparticles, many of which are porous in nature, liposomes, solid lipid nanoparticles and nanostructured lipid carriers, are increasingly being developed for inhalation applications. This article provides a review of the rationale for the use of these technologies in the pulmonary delivery of drugs, and summarizes the manufacturing processes and their limitations, the in vitro and in vivo performance of these systems, the safety of these lipid-based systems in the lung, and their promise for commercialization.

Insulin and the lung: connecting asthma and metabolic syndrome

Obesity, metabolic syndrome, and asthma are all rapidly increasing globally. Substantial emerging evidence suggests that these three conditions are epidemiologically and mechanistically linked. Since the link between obesity and asthma appears to extend beyond mechanical pulmonary disadvantage, molecular understanding is necessary. Insulin resistance is a strong, independent risk factor for asthma development, but it is unknown whether a direct effect of insulin on the lung is involved. This review summarizes current knowledge regarding the effect of insulin on cellular components of the lung and highlights the molecular consequences of insulin-related metabolic signaling cascades that could adversely affect lung structure and function. Examples include airway smooth muscle proliferation and contractility and regulatory signaling networks that are associated with asthma. These aspects of insulin signaling provide mechanistic insight into the clinical evidence for the links between obesity, metabolic syndrome, and airway diseases, setting the stage for novel therapeutic avenues targeting these conditions.

Focal adhesion kinase regulates collagen I-induced airway smooth muscle phenotype switching

Increased extracellular matrix (ECM) deposition and airway smooth muscle (ASM) mass are major contributors to airway remodeling in asthma. Recently, we demonstrated that the ECM protein collagen I, which is increased surrounding asthmatic ASM, induces a proliferative, hypocontractile ASM phenotype. Little is known, however, about the signaling pathways involved. Using bovine tracheal smooth muscle, we investigated the role of focal adhesion kinase (FAK) and downstream signaling pathways in collagen I-induced ASM phenotype modulation. Phosphorylation of FAK was increased during adhesion to both uncoated and collagen I-coated culture dishes, without differences between these matrices. Nor were any differences found in cellular adhesion. Inhibition of FAK activity by overexpression of the FAK deletion mutants FAT (focal adhesion targeting domain) and FRNK (FAK-related nonkinase) attenuated adhesion. After attachment, FAK phosphorylation increased in a time-dependent manner in cells cultured on collagen I, whereas no activation was found on an uncoated plastic matrix. In addition, collagen I increased in a time- and concentration-dependent manner the cell proliferation, which was fully inhibited by FAT and FRNK. Similarly, the specific pharmacologic FAK inhibitor PF-573228 [6-((4-((3-(methanesulfonyl)benzyl)amino)-5-trifluoromethylpyrimidin-2-yl) amino)-3,4-dihydro-1H-quinolin-2-one] as well as specific inhibitors of p38 mitogen-activated protein kinase (MAPK) and Src also fully inhibited collagen I-induced proliferation, whereas partial inhibition was observed by inhibition of phosphatidylinositol-3-kinase (PI3-kinase) and mitogen-activated protein kinase kinase (MEK). The inhibition of cell proliferation by these inhibitors was associated with attenuation of the collagen I-induced hypocontractility. Collectively, the results indicate that induction of a proliferative, hypocontractile ASM phenotype by collagen I is mediated by FAK and downstream signaling pathways.

Distinct PKA and Epac compartmentalization in airway function and plasticity

Asthma and chronic obstructive pulmonary disease (COPD) are obstructive lung diseases characterized by airway obstruction, airway inflammation and airway remodelling. Next to inflammatory cells and airway epithelial cells, airway mesenchymal cells, including airway smooth muscle cells and (myo)fibroblasts, substantially contribute to disease features by the release of inflammatory mediators, smooth muscle contraction, extracellular matrix deposition and structural changes in the airways. Current pharmacological treatment of both diseases intends to target the dynamic features of the endogenous intracellular suppressor cyclic AMP (cAMP). This review will summarize our current knowledge on cAMP and will emphasize on key discoveries and paradigm shifts reflecting the complex spatio-temporal nature of compartmentalized cAMP signalling networks in health and disease. As airway fibroblasts and airway smooth muscle cells are recognized as central players in the development and progression of asthma and COPD, we will focus on the role of cAMP signalling in their function in relation to airway function and plasticity. We will recapture on the recent identification of cAMP-sensing multi-protein complexes maintained by cAMP effectors, including A-kinase anchoring proteins (AKAPs), proteins kinase A (PKA), exchange protein directly activated by cAMP (Epac), cAMP-elevating seven-transmembrane (7TM) receptors and phosphodiesterases (PDEs) and we will report on findings indicating that the pertubation of compartmentalized cAMP signalling correlates with the pathopysiology of obstructive lung diseases. Future challenges include studies on cAMP dynamics and compartmentalization in the lung and the development of novel drugs targeting these systems for therapeutic interventions in chronic obstructive inflammatory diseases.

Muscarinic receptor stimulation augments TGF-β1-induced contractile protein expression by airway smooth muscle cells

Acetylcholine (ACh) is the primary parasympathetic neurotransmitter in the airways. Recently, it was established that ACh, via muscarinic receptors, regulates airway remodeling in animal models of asthma and chronic obstructive pulmonary disease (COPD). The mechanisms involved are not well understood. Here, we investigated the functional interaction between muscarinic receptor stimulation and transforming growth factor (TGF)-β(1) on the expression of contractile proteins in human airway smooth muscle (ASM) cells. ASM cells expressing functional muscarinic M(2) and M(3) receptors were stimulated with methacholine (MCh), TGF-β(1), or their combination for up to 7 days. Western blot analysis revealed a strong induction of sm-α-actin and calponin by TGF-β(1), which was increased by MCh in ASM cells. Immunocytochemistry confirmed these results and revealed that the presence of MCh augmented the formation of sm-α-actin stress fibers by TGF-β(1). MCh did not augment TGF-β(1)-induced gene transcription of contractile phenotype markers. Rather, translational processes were involved in the augmentation of TGF-β(1)-induced contractile protein expression by muscarinic receptor stimulation, including phosphorylation of glycogen synthase kinase-3β and 4E-binding protein 1, which was enhanced by MCh. In conclusion, muscarinic receptor stimulation augments functional effects of TGF-β(1) in human ASM cells on cellular processes that underpin ASM remodeling in asthma and COPD.

Functional consequences of human airway smooth muscle phenotype plasticity

BACKGROUND AND PURPOSE

Airway smooth muscle (ASM) phenotype plasticity, characterized by reversible switching between contractile and proliferative phenotypes, is considered to contribute to increased ASM mass and airway hyper-responsiveness in asthma. Further, increased expression of collagen I has been observed within the ASM bundle of asthmatics. Previously, we showed that exposure of intact bovine tracheal smooth muscle (BTSM) to collagen I induces a switch from a contractile to a hypocontractile, proliferative phenotype. However, the functional relevance of this finding for intact human ASM has not been established.

EXPERIMENTAL APPROACH

We investigated the effects of exposure of human tracheal smooth muscle (HTSM) strips to monomeric collagen I and PDGF on contractile responses to methacholine and KCl. Expression of contractile proteins sm-α-actin and sm-MHC was assessed by Western blot analysis. The proliferation of HTSM cells was assessed by cell counting, measuring mitochondrial activity (Alamarblue conversion) and [(3) H]-thymidine incorporation. Proliferation of intact tissue slices was assessed by [(3) H]-thymidine incorporation.

KEY RESULTS

Culturing HTSM strips in the presence of collagen I or PDGF for 4 days reduced maximal contractile responses to methacholine or KCl and the expression of contractile proteins. Conversely, collagen I and PDGF increased proliferation of HTSM cells and proliferative responses in tissue slices. PDGF additively increased the proliferation of HTSM cells cultured on collagen I; this additive effect was not observed on contractility, contractile protein expression or proliferation of intact tissue.

CONCLUSION AND IMPLICATIONS

These findings indicate that collagen I and PDGF induce a functionally hypocontractile, proliferative phenotype of human ASM, which may contribute to airway remodelling in asthma.

Novel non-canonical TGF-β signaling networks: emerging roles in airway smooth muscle phenotype and function

The airway smooth muscle (ASM) plays an important role in the pathophysiology of asthma and chronic obstructive pulmonary disease (COPD). ASM cells express a wide range of receptors involved in contraction, growth, matrix protein production and the secretion of cytokines and chemokines. Transforming growth factor beta (TGF-β) is one of the major players in determining the structural and functional abnormalities of the ASM in asthma and COPD. It is increasingly evident that TGF-β functions as a master switch, controlling a network of intracellular and autocrine signaling loops that effect ASM phenotype and function. In this review, the various elements that participate in non-canonical TGF-β signaling, including MAPK, PI3K, WNT/β-catenin, and Ca(2+), are discussed, focusing on their effect on ASM phenotype and function. In addition, new aspects of ASM biology and their possible association with non-canonical TGF-β signaling will be discussed.

Muscarinic receptors on airway mesenchymal cells: novel findings for an ancient target

Since ancient times, anticholinergics have been used as a bronchodilator therapy for obstructive lung diseases. Targets of these drugs are G-protein-coupled muscarinic M(1), M(2) and M(3) receptors in the airways, which have long been recognized to regulate vagally-induced airway smooth muscle contraction and mucus secretion. However, recent studies have revealed that acetylcholine also exerts pro-inflammatory, pro-proliferative and pro-fibrotic actions in the airways, which may involve muscarinic receptor stimulation on mesenchymal, epithelial and inflammatory cells. Moreover, acetylcholine in the airways may not only be derived from vagal nerves, but also from non-neuronal cells, including epithelial and inflammatory cells. Airway smooth muscle cells seem to play a major role in the effects of acetylcholine on airway function. It has become apparent that these cells are multipotent cells that may reversibly adopt (hyper)contractile, proliferative and synthetic phenotypes, which are all under control of muscarinic receptors and differentially involved in bronchoconstriction, airway remodeling and inflammation. Cholinergic contractile tone is increased by airway inflammation associated with asthma and COPD, resulting from exaggerated acetylcholine release as well as increased expression of contraction related proteins in airway smooth muscle. Moreover, muscarinic receptor stimulation promotes proliferation of airway smooth muscle cells as well as fibroblasts, and regulates cytokine, chemokine and extracellular matrix production by these cells, which may contribute to airway smooth muscle growth, airway fibrosis and inflammation. In line, animal models of chronic allergic asthma and COPD have recently demonstrated that tiotropium may potently inhibit airway inflammation and remodeling. These observations indicate that muscarinic receptors have a much larger role in the pathophysiology of obstructive airway diseases than previously thought, which may have important therapeutic implications.

Glucocorticosteroids and β₂-adrenoceptor agonists synergize to inhibit airway smooth muscle remodeling

Airway remodeling, including increased airway smooth muscle (ASM) mass and contractility, contributes to increased airway narrowing in asthma. Increased ASM mass may be caused by exposure to mitogens, including platelet-derived growth factor (PDGF) and collagen type I, which induce a proliferative, hypocontractile ASM phenotype. In contrast, prolonged exposure to insulin induces a hypercontractile phenotype. Glucocorticosteroids and β₂-adrenoceptor agonists synergize to increase glucocorticosteroid receptor translocation in ASM cells; however, the impact of this synergism on phenotype modulation is unknown. Using bovine tracheal smooth muscle, we investigated the effects of the glucocorticosteroids fluticasone (10 nM), budesonide (30 nM), and dexamethasone (0.1-1 μM) and the combination of low concentrations of fluticasone (3-100 pM) and fenoterol (10 nM) on ASM phenotype switching in response to PDGF (10 ng/ml), collagen type I (50 μg/ml), and insulin (1 μM). All glucocorticosteroids inhibited PDGF- and collagen I-induced proliferation and hypocontractility, with the effects of collagen I being less susceptible to glucocorticosteroid action. At 100-fold lower concentrations, fluticasone (100 pM) synergized with fenoterol to prevent PDGF- and collagen I-induced phenotype switching. This inhibition of ASM phenotype switching was associated with a normalization of the PDGF-induced decrease in the cell cycle inhibitors p21(WAF1/CIP1) and p57(KIP2). At this concentration, fluticasone also prevented the insulin-induced hypercontractile phenotype. At even lower concentrations, fluticasone (3 pM) synergized with fenoterol to inhibit this phenotype switch. Collectively, these findings indicate that glucocorticosteroids and β₂-agonists synergistically inhibit ASM phenotype switching, which may contribute to the increased effectiveness of combined treatment with glucocorticosteroids and β₂-agonists in asthma.

High glucose enhances responsiveness of human airways smooth muscle via the Rho/ROCK pathway

Glucose moves into airway secretions after a glucose load. Therefore people with diabetes or hyperglycemia spend a significant proportion of each day with glucose in their airways secretions. This study investigated the effects of glucose on isolated human airways and on cultured airway smooth muscle (ASM) cells. Human isolated bronchi were stimulated with acetylcholine, histamine, and transmural stimulation and treated with the selective ROCK inhibitors Y27632 and SB772077B under high-glucose conditions. The effect of high glucose concentrations on intracellular calcium flux and the phosphorylation of MYPT1 in ASM cells was also investigated. High (44 mM for 6 h) glucose, but not mannitol, concentrations led to an enhanced responsiveness of ASM to contractile agents. Y27632 and SB772077B completely abolished (P < 0.05) the enhanced contractile effects with a high-concentration glucose solution, compared with control tissues. In cultured ASM cells, incubation with high glucose concentrations significantly (P < 0.05) enhanced bradykinin-induced intracellular calcium flux and the levels of pMYPT1, which were inhibited by Y27632 (P < 0.05). Our study has demonstrated that high glucose concentrations leads to hyperresponsiveness of human isolated bronchi and enhances intracellular calcium release in cultured ASM cells via a Rho/ROCK- and pMYPT1-dependent pathway, suggesting that this crucial pathway may contribute to the reduced lung function observed in patients with diabetes. These data propose novel targets for the treatment of patients with respiratory diseases that also suffer from diabetes mellitus.

Caveolins and lung function

The primary function of the mammalian lung is to facilitate diffusion of oxygen to venous blood and to ventilate carbon dioxide produced by catabolic reactions within cells. However, it is also responsible for a variety of other important functions, including host defense and production of vasoactive agents to regulate not only systemic blood pressure, but also water, electrolyte and acid-base balance. Caveolin-1 is highly expressed in the majority of cell types in the lung, including epithelial, endothelial, smooth muscle, connective tissue cells, and alveolar macrophages. Deletion of caveolin-1 in these cells results in major functional aberrations, suggesting that caveolin-1 may be crucial to lung homeostasis and development. Furthermore, generation of mutant mice that under-express caveolin-1 results in severe functional distortion with phenotypes covering practically the entire spectrum of known lung diseases, including pulmonary hypertension, fibrosis, increased endothelial permeability, and immune defects. In this Chapter, we outline the current state of knowledge regarding caveolin-1-dependent regulation of pulmonary cell functions and discuss recent research findings on the role of caveolin-1 in various pulmonary disease states, including obstructive and fibrotic pulmonary vascular and inflammatory diseases.