Role of dystrophin in airway smooth muscle phenotype, contraction and lung function

Re-examination of therapeutic management of muscular dystrophies using a vascular smooth muscle-centered approach

In contrast to the long-standing focus on the pathophysiology of skeletal muscles in the hunt for a cure for Duchenne muscular dystrophy (DMD), we opine that the malfunctioning of dystrophin produced by vascular smooth muscle is a major contributor to the pathology of the illness. We believe that a biological response modifier glucan (BRMG), which has been shown in clinical studies of DMD to boost the expression of vascular smooth muscle dystrophin and provide anti-fibrotic and anti-inflammatory effects, may play a key role in reducing the pathogenesis of DMD. According to the evaluation of biomarkers, this BRMG, which is safe and side-effect-free, reduces the pathogenesis of DMD. We describe the possible mechanisms of action by which this BRMG helps in alleviating the symptoms of DMD by targeting smooth muscle dystrophin, in addition to its advantages over other therapeutic modalities, as well as how it can serve as a valuable adjunct to existing therapies. We suggest that using BRMG adjuncts that target smooth muscle dystrophin would be a potential therapeutic approach that prolongs the lifespan and extends the duration of ambulation from the onset of DMD. Further studies are needed to validate this hypothesis.

Dystrophin in the Neonatal and Adult Rat Intestine

Background: Gastrointestinal (GI) complaints are frequently noted in aging dystrophinopathy patients, yet their underlying molecular mechanisms are largely unknown. As dystrophin protein isoform 71 (Dp71) is particularly implicated in the development of smooth muscle cells, we evaluated its distribution in the neonatal and adult rat intestine in this study. Methods: Dp71 expression levels were assessed in the proximal (duodenum, jejunum and ileum) and distal (caecum, colon and rectum) intestine by Western blotting and qPCR. In addition, the cellular distribution of total Dp was evaluated in the duodenum and colon by immunohistochemical colocalization studies with alpha-smooth muscle actin (aSMA), Hu RNA binding proteins C and D (HuC/HuD) for neurons and vimentin (VIM) for interstitial cells. Results: In neonatal and adult rats, the distal intestine expressed 2.5 times more Dp71 protein than the proximal part (p < 0.01). This regional difference was not observed in Dp71 mRNA. During both stages, Dp-immunoreactivity was predominant in the muscularis propria, where it co-localized with aSMA and HuC/HuD. Conclusions: In neonatal and adult rats, Dp71 was expressed highest in the distal intestine. Together with the observation that Dp may be expressed by myenteric neurons, this warrants a paradigm shift in the treatment of GI comorbidities.

Targeting Airway Smooth Muscle Hypertrophy in Asthma: An Approach Whose Time Has Come

Airway smooth muscle (ASM) cell dysfunction is an important component of several obstructive pulmonary diseases, particularly asthma. External stimuli such as allergens, dust, air pollutants, and change in environmental temperatures provoke ASM cell hypertrophy, proliferation, and migration without adequate mechanistic controls. ASM cells can switch between quiescent, migratory, and proliferative phenotypes in response to extracellular matrix proteins, growth factors, and other soluble mediators. While some aspects of airway hypertrophy and remodeling could have beneficial effects, in many cases these contribute to a clinical phenotype of difficult to control asthma. In this review, we discuss the factors responsible for ASM hypertrophy and proliferation in asthma, focusing on cytokines, growth factors, and ion transporters, and discuss existing and potential approaches that specifically target ASM hypertrophy to reduce the ASM mass and improve asthma symptoms. The goal of this review is to highlight strategies that appear ready for translational investigations to improve asthma therapy.

Prevalence of smooth muscle dysfunction among children with Duchenne muscular dystrophy

Smooth muscle dysfunction in Duchenne muscular dystrophy (DMD) has been rarely studied. A cross-sectional study was conducted to estimate the prevalence of smooth muscle dysfunction (vascular, upper gastrointestinal, and bladder smooth muscle) in children with DMD using questionnaires (Pediatric Bleeding Questionnaire, Pediatric Gastroesophageal Symptom Questionnaire, and Dysfunctional Voiding Symptom Score). Investigations included bleeding time estimation, nuclear scintigraphy for gastroesophageal reflux, and uroflowmetry for urodynamic abnormalities. Ninety-nine subjects were included in the study. The prevalence of vascular, upper gastrointestinal, and bladder smooth muscle dysfunction was 27.2%. Mean bleeding time was prolonged by 117.5 seconds. The prevalence of gastroesophageal reflux was 21%. Voided volume/estimated bladder capacity over 15% and abnormal flow curves on uroflowmetry were seen in 18.2% and 9.7% of the subjects, respectively. Our study highlights the need for addressing issues related to smooth muscle dysfunction in the routine clinical care of patients with DMD.

Nutraceutical and pharmaceutical cocktails did not preserve diaphragm muscle function or reduce muscle damage in D2-mdx mice

NEW FINDINGS

What is the central question of this study? We previously demonstrated that quercetin transiently preserved respiratory function in dystrophin-deficient mice. To gain lasting therapeutic benefits, we tested quercetin in combination with nicotinamide riboside, lisinopril and prednisolone in the D2-mdx model. What is the main finding and its importance? We demonstrated that these quercetin-based cocktails did not preserve respiratory or diaphragmatic function or reduce histological damage after 7 months of treatment starting at 4 months of age.

ABSTRACT

Duchenne muscular dystrophy is characterized by the absence of dystrophin protein and causes muscle weakness and muscle injury, culminating in respiratory failure and cardiomyopathy. Quercetin transiently improved respiratory function but failed to maintain long-term therapeutic benefits in mdx mice. In this study, we combined quercetin with nicotinamide riboside (NR), lisinopril and prednisolone to assess the efficacy of quercetin-based cocktails. We hypothesized that quercetin, NR and lisinopril independently would improve respiratory function and decrease diaphragmatic injury and when combined would have additive effects. To address this hypothesis, in vivo respiratory function, in vitro diaphragmatic function and histological injury were assessed in DBA (healthy), D2-mdx (dystrophic) and D2-mdx mice treated with combinations of quercetin, NR and lisinopril from 4 to 11 months of age. Respiratory function, assessed using whole-body plethysmography, was largely similar between healthy and dystrophin-deficient mice. Diaphragm specific tension was decreased by ∼50% in dystrophic mice compared with healthy mice (P < 0.05), but fatigue resistance was similar between groups. Contractile area was decreased by ∼10% (P < 0.05) and fibrotic area increased from 3.5% in healthy diaphragms to 27% (P < 0.05) in dystrophic diaphragms. Contrary to expectations, these functional and histological parameters of disease were not offset by any intervention. These data suggest that quercetin, NR and lisinopril, independently and in combination, did not prevent diaphragmatic injury or preserve respiratory function.

The Involvement of Type 2 Innate Lymphoid Cells in Airway Inflammation of Asthma

The airway inflammatory response is closely associated with asthma. The purpose of this article was to study the roles of innate lymphoid cells (ILCs) in the process of airway inflammatory response in asthma. We established the asthmatic mice model with intraperitoneal injected ovalbumin medium, then with the flow cytometry analysis, we detected the ILCs and their surface proteins in the mice blood samples, besides, we analyzed the amounts of inflammatory cytokines and secreted proteins in the mice bronchoalveolar lavage fluid and blood serum. Moreover, Western blot analyzed the proteins in the mice bronchial epithelial tissues. The ILC2 amounts were obviously increased in young asthmatic mice model. And, the proteins CD25 and CCR10 were highly expressed in the sorted ILC2s. Besides, the cytokines interleukin (IL)-5, IL-13, IL-33, CCL22, and CCL27 were abundant in the bronchoalveolar lavage fluid of asthmatic mice model. And, the secretion of IL-5, IL-13, IL-33, TSLP, and CCL22 in blood serum was much more in asthmatic mice model than in the normal control mice, whereas the secretion of PGD2 was suppressed in asthmatic mice bronchoalveolar lavage fluid and blood serum. Additionally, the guanine nucleotide-binding proteins Gα12 and Gα13 were upregulated in asthmatic mice bronchial tissues, and the protein SERCA2 was downregulated; moreover, the proteins NFAT, IRF4, and its downstream signal STAT6 were all upregulated in the asthmatic mice bronchial tissues. ILC2s were involved in the response of airway inflammation through secretion of proinflammatory cytokines and chemokines to dysregulate the Ca²⁺ homeostasis in airway in the process of asthma. [Figure: see text].

Latent process model of the 6-minute walk test in Duchenne muscular dystrophy : A Bayesian approach to quantifying rare disease progression

Duchenne muscular dystrophy (DMD) is a rare X-linked genetic pediatric disease characterized by a lack of functional dystrophin production in the body, resulting in muscle deterioration. Lower body muscle weakness progresses to non-ambulation typically by early teenage years, followed by upper body muscle deterioration and ultimately death by the late twenties. The objective of this study was to enhance the quantitative understanding of DMD disease progression through nonlinear mixed effects modeling of the population mean and variability of the 6-min walk test (6MWT) clinical endpoint. An indirect response model with a latent process was fit to digitized literature data using full Bayesian estimation. The modeling data set consisted of 22 healthy controls and 218 DMD patients from one interventional and four observational trials. The model reasonably described the central tendency and population variability of the 6MWT in healthy subjects and DMD patients. An exploratory categorical covariate analysis indicated that there was no apparent effect of corticosteroid administration on DMD disease progression. The population predicted 6MWT began to rise at 1.32 years of age, plateauing at 654 meters (m) at 17.2 years of age for the healthy population. The DMD trajectory reached a maximum of 411 m at 8.90 years before declining and falling below 1 m at age 18.0. The model has potential to be used as a Bayesian estimation and posterior simulation tool to make informed model-based drug development decisions that incorporate prior knowledge with new data.

Autophagy Activation in Asthma Airways Remodeling

Current asthma therapies fail to target airway remodeling that correlates with asthma severity driving disease progression that ultimately leads to loss of lung function. Macroautophagy (hereinafter "autophagy") is a fundamental cell-recycling mechanism in all eukaryotic cells; emerging evidence suggests that it is dysregulated in asthma. We investigated the interrelationship between autophagy and airway remodeling and assessed preclinical efficacy of a known autophagy inhibitor in murine models of asthma. Human asthmatic and nonasthmatic lung tissues were histologically evaluated and were immunostained for key autophagy markers. The percentage area of positive staining was quantified in the epithelium and airway smooth muscle bundles using ImageJ software. Furthermore, the autophagy inhibitor chloroquine was tested intranasally in prophylactic (3 wk) and treatment (5 wk) models of allergic asthma in mice. Human asthmatic tissues showed greater tissue inflammation and demonstrated hallmark features of airway remodeling, displaying thickened epithelium (P < 0.001) and reticular basement membrane (P < 0.0001), greater lamina propria depth (P < 0.005), and increased airway smooth muscle bundles (P < 0.001) with higher expression of Beclin-1 (P < 0.01) and ATG5 (autophagy-related gene 5) (P < 0.05) together with reduced p62 (P < 0.05) compared with nonasthmatic control tissues. Beclin-1 expression was significantly higher in asthmatic epithelium and ciliated cells (P < 0.05), suggesting a potential role of ciliophagy in asthma. Murine asthma models demonstrated effective preclinical efficacy (reduced key features of allergic asthma: airway inflammation, airway hyperresponsiveness, and airway remodeling) of the autophagy inhibitor chloroquine. Our data demonstrate cell context-dependent and selective activation of autophagy in structural cells in asthma. Furthermore, this pathway can be effectively targeted to ameliorate airway remodeling in asthma.

[Pathogenesis of cognitive disorders in patients with Duchenne muscular dystrophy]

AIM

Clarification of the pathogenesis of cognitive disorders in patients with Duchenne muscular dystrophy in the clinical laboratory and molecular genetic study.

MATERIAL AND METHODS

Thirty-six male patients with Duchenne muscular dystrophy (DMD), aged from 5 to 22 years (mean age 13.7 years), were examined. The control group consisted of 30 healthy people (7-22 years old, mean age 13.8). The clinical, molecular-genetic and laboratory study was conducted. The search for mutations in the dystrophin gene was carried out using multiplex PCR and multiplex ligation-dependent probe amplification. The laboratory study included determination of neurotrophins: brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF) and ciliary neurotrophic factor (CNTF) using immunoenzyme method in serum.

RESULTS AND CONCLUSION

Severe cognitive impairment was found in 33% of patients with DMD. The distribution of mutations in the DMD gene was not uniform, most often the mutations were found in the region from exon 43 to exon 50. Serum concentration of NGF in patients with DMD was higher than in the control group (2391 pg/ml [1587; 4136] and 553 pg / ml [314; 864], respectively (p<0.001)). In the group of patients with cognitive disorders, there was a decreased concentration of BGF (23 670 [21 700; 30 720] pg/ml (p<0.001)). In patients with BGF concentration less than 31 000 pg/ml, the chances of cognitive disorders were more than 10 times higher (p<0.001, odds ratio OR=12.0, 95% CI [1.9-76.4]). Thus, biochemical mechanisms, such as NGF overexpression and BGF deficiency, are involved in the development of cognitive disorders in patients with DMD.

Phenotype and Functional Features of Human Telomerase Reverse Transcriptase Immortalized Human Airway Smooth Muscle Cells from Asthmatic and Non-Asthmatic Donors

Asthma is an obstructive respiratory disease characterised by chronic inflammation with airway hyperresponsiveness. In asthmatic airways, there is an increase in airway smooth muscle (ASM) cell bulk, which differs from non-asthmatic ASM in characteristics. This study aimed to assess the usefulness of hTERT immortalisation of human ASM cells as a research tool. Specifically we compared proliferative capacity, inflammatory mediator release and extracellular matrix (ECM) production in hTERT immortalised and parent primary ASM cells from asthmatic and non-asthmatic donors. Our studies revealed no significant differences in proliferation, IL-6 and eotaxin-1 production, or CTGF synthesis between donor-matched parent and hTERT immortalised ASM cell lines. However, deposition of ECM proteins fibronectin and fibulin-1 was significantly lower in immortalised ASM cells compared to corresponding primary cells. Notably, previously reported differences in proliferation and inflammatory mediator release between asthmatic and non-asthmatic ASM cells were retained, but excessive ECM protein deposition in asthmatic ASM cells was lost in hTERT ASM cells. This study shows that hTERT immortalised ASM cells mirror primary ASM cells in proliferation and inflammatory profile characteristics. Moreover, we demonstrate both strengths and weaknesses of this immortalised cell model as a representation of primary ASM cells for future asthma pathophysiological research.

Caveolin-1: Functional Insights into Its Role in Muscarine- and Serotonin-Induced Smooth Muscle Constriction in Murine Airways

An increased bronchoconstrictor response is a hallmark in the progression of obstructive airway diseases. Acetylcholine and 5-hydroxytryptamine (5-HT, serotonin) are the major bronchoconstrictors. There is evidence that both cholinergic and serotonergic signaling in airway smooth muscle (ASM) involve caveolae. We hypothesized that caveolin-1 (cav-1), a structural protein of caveolae, plays an important regulatory role in ASM contraction. We analyzed airway contraction in different tracheal segments and extra- and intrapulmonary bronchi in cav-1 deficient (cav-1−/−) and wild-type mice using organ bath recordings and videomorphometry of methyl-beta-cyclodextrin (MCD) treated and non-treated precision-cut lung slices (PCLS). The presence of caveolae was investigated by electron microscopy. Receptor subtypes driving 5-HT-responses were studied by RT-PCR and videomorphometry after pharmacological inhibition with ketanserin. Cav-1 was present in tracheal epithelium and ASM. Muscarine induced a dose dependent contraction in all airway segments. A significantly higher Emax was observed in the caudal trachea. Although, caveolae abundancy was largely reduced in cav-1−/− mice, muscarine-induced airway contraction was maintained, albeit at diminished potency in the middle trachea, in the caudal trachea and in the bronchus without changes in the maximum efficacy. MCD-treatment of PLCS from cav-1−/− mice reduced cholinergic constriction by about 50%, indicating that cholesterol-rich plasma domains account for a substantial portion of the muscarine-induced bronchoconstriction. Notably, cav-1-deficiency fully abrogated 5-HT-induced contraction of extrapulmonary airways. In contrast, 5-HT-induced bronchoconstriction was fully maintained in cav-1-deficient intrapulmonary bronchi, but desensitization upon repetitive stimulation was enhanced. RT-PCR analysis revealed 5-HT1B, 5-HT2A, 5-HT6, and 5-HT7 receptors as the most prevalent subtypes in the airways. The 5-HT-induced-constriction in PCLS could be antagonized by ketanserin, a 5-HT2A receptor inhibitor. In conclusion, the role of cav-1, caveolae, and cholesterol-rich plasma domains in regulation of airway tone are highly agonist-specific and dependent on airway level. Cav-1 is indispensable for serotonergic contraction of extrapulmonary airways and modulates cholinergic constriction of the trachea and main bronchus. Thus, cav-1/caveolae shall be considered in settings such as bronchial hyperreactivity in common airway diseases and might provide an opportunity for modulation of the constrictor response.

Bitter Taste Receptor Agonists Mitigate Features of Allergic Asthma in Mice

Asthma is characterized by airway inflammation, mucus secretion, remodeling and hyperresponsiveness (AHR). Recent research has established the bronchodilatory effect of bitter taste receptor (TAS2R) agonists in various models. Comprehensive pre-clinical studies aimed at establishing effectiveness of TAS2R agonists in disease models are lacking. Here we aimed to determine the effect of TAS2R agonists on features of asthma. Further, we elucidated a mechanism by which TAS2R agonists mitigate features of asthma. Asthma was induced in mice using intranasal house dust mite or aerosol ova-albumin challenge, and chloroquine or quinine were tested in both prophylactic and treatment models. Allergen challenge resulted in airway inflammation as evidenced by increased immune cells infiltration and release of cytokines and chemokines in the lungs, which were significantly attenuated in TAS2R agonists treated mice. TAS2R agonists attenuated features of airway remodeling including smooth muscle mass, extracellular matrix deposition and pro-fibrotic signaling, and also prevented mucus accumulation and development of AHR in mice. Mechanistic studies using human neutrophils demonstrated that inhibition of immune cell chemotaxis is a key mechanism by which TAS2R agonists blocked allergic airway inflammation and exerted anti-asthma effects. Our comprehensive studies establish the effectiveness of TAS2R agonists in mitigating multiple features of allergic asthma.

NGF-dependent axon growth and regeneration are altered in sympathetic neurons of dystrophic mdx mice

Duchenne muscular dystrophy (DMD) is a lethal disease, determined by lack of dystrophin (Dp427), a muscular cytoskeletal protein also expressed by selected neuronal populations. Consequently, besides muscular wasting, both human patients and DMD animal models suffer several neural disorders. In previous studies on the superior cervical ganglion (SCG) of wild type and dystrophic mdx mice (Lombardi et al. 2008), we hypothesized that Dp427 could play some role in NGF-dependent axonal growth, both during development and adulthood. To address this issue, we first analyzed axon regeneration potentials of SCG neurons of both genotypes after axotomy in vivo. While noradrenergic innervation of mdx mouse submandibular gland, main source of nerve growth factor (NGF), recovered similarly to wild type, iris innervation (muscular target) never did. We, therefore, evaluated whether dystrophic SCG neurons were poorly responsive to NGF, especially at low concentration. Following in vitro axotomy in the presence of either 10 or 50ng/ml NGF, the number of regenerated axons in mdx mouse neuron cultures was indeed reduced, compared to wild type, at the lower concentration. Neurite growth parameters (i.e. number, length), growth cone dynamics and NGF/TrkA receptor signaling in differentiating neurons (not injured) were also significantly reduced when cultured with 10ng/ml NGF, but also with higher NGF concentrations. In conclusion, we propose a role for Dp427 in NGF-dependent cytoskeletal dynamics associated to growth cone advancement, possibly through indirect stabilization of TrkA receptors. Considering NGF activity in nervous system development/remodeling, this aspect could concur in some of the described DMD-associated neural dysfunctions.

Respiratory impedance in patients with Duchenne muscular dystrophy

Impulse oscillometry (IOS) evaluates non-effort-dependent respiratory mechanics, and thus it may be useful to evaluate patients with Duchenne muscular dystrophy (DMD).

OBJECTIVES

We aimed (1) to describe the behavior of IOS parameters in patients with DMD, and compare it to those from a control group; (2) to determine whether resistances and reactances differ in relation to the severity of DMD; and (3) to compare IOS parameters with spirometry and maximal inspiratory (MIP) and expiratory (MEP) pressures.

METHODS

Children and adolescents (<20 years old) with biopsy-confirmed DMD and age-paired subjects were cross-sectionally evaluated. All results were transformed to z scores with respect to the healthy subjects (reference population).

RESULTS

Anthropometric characteristics did not differ between the 31 patients and 69 controls included in the study. Compared with controls, patients with DMD had higher IOS resistances and lower reactances. As expected, FEV₁ and FVC were lower in patients and always declined as age increased. By contrast, MIP and MEP were lower-than-normal in youngest patients, tended to improve around puberty initiation, and declined thereafter. In general, there was a poor correlation between IOS parameters and spirometric variables or respiratory pressures, excepting for X20 Hz, which had an inverse correlation with FEV₁ . Interestingly, IOS resistances were higher in patients with less disability (lower Vignos score; better FVC), but tended to be normalized in advanced stages of the disease.

CONCLUSION

This study showed that IOS is feasible in children and adolescents with DMD and yields information about respiratory function not achievable with the usual forced techniques. Pediatr Pulmonol. 2016;51:1072-1079. © 2016 Wiley Periodicals, Inc.

Biosignature for airway inflammation in a house dust mite-challenged murine model of allergic asthma

House dust mite (HDM) challenge is commonly used in murine models of allergic asthma for preclinical pathophysiological studies. However, few studies define objective readouts or biomarkers in this model. In this study we characterized immune responses and defined molecular markers that are specifically altered after HDM challenge. In this murine model, we used repeated HDM challenge for two weeks which induced hallmarks of allergic asthma seen in humans, including airway hyper-responsiveness (AHR) and elevated levels of circulating total and HDM-specific IgE and IgG1. Kinetic studies showed that at least 24 h after last HDM challenge results in significant AHR along with eosinophil infiltration in the lungs. Histologic assessment of lung revealed increased epithelial thickness and goblet cell hyperplasia, in the absence of airway wall collagen deposition, suggesting ongoing tissue repair concomitant with acute allergic lung inflammation. Thus, this model may be suitable to delineate airway inflammation processes that precede airway remodeling and development of fixed airway obstruction. We observed that a panel of cytokines e.g. IFN-γ, IL-1β, IL-4, IL-5, IL-6, KC, TNF-α, IL-13, IL-33, MDC and TARC were elevated in lung tissue and bronchoalveolar fluid, indicating local lung inflammation. However, levels of these cytokines remained unchanged in serum, reflecting lack of systemic inflammation in this model. Based on these findings, we further monitored the expression of 84 selected genes in lung tissues by quantitative real-time PCR array, and identified 31 mRNAs that were significantly up-regulated in lung tissue from HDM-challenged mice. These included genes associated with human asthma (e.g. clca3, ear11, il-13, il-13ra2, il-10, il-21, arg1 and chia1) and leukocyte recruitment in the lungs (e.g. ccl11, ccl12 and ccl24). This study describes a biosignature to enable broad and systematic interrogation of molecular mechanisms and intervention strategies for airway inflammation pertinent to allergic asthma that precedes and possibly potentiates airway remodeling and fibrosis.

Summary: This study describes a systematic analysis of molecular end points in an murine model of allergic asthma. The biosignature described can be used to interrogate molecular mechanisms and intervention strategies for airway inflammation pertinent to allergic asthma that precedes and possibly potentiates airway remodeling and fibrosis.

Characterization of the dystrophin-glycoprotein complex in airway smooth muscle: role of δ-sarcoglycan in airway responsiveness

The dystrophin-glycoprotein complex (DGC) is an integral part of caveolae microdomains, and its interaction with caveolin-1 is essential for the phenotype and functional properties of airway smooth muscle (ASM). The sarcoglycan complex provides stability to the dystroglycan complex, but its role in ASM contraction and lung physiology in not understood. We tested whether δ-sarcoglycan (δ-SG), through its interaction with the DGC, is a determinant of ASM contraction ex vivo and airway mechanics in vivo. We measured methacholine (MCh)-induced isometric contraction and airway mechanics in δ-SG KO and wild-type mice. Last, we performed immunoblotting and transmission electron microscopy to assess DGC protein expression and the ultrastructural features of tracheal smooth muscle. Our results reveal an age-dependent reduction in the MCh-induced tracheal isometric force and significant reduction in airway resistance at high concentrations of MCh (50.0 mg/mL) in δ-SG KO mice. The changes in contraction and lung function correlated with decreased caveolin-1 and β-dystroglycan abundance, as well as an age-dependent loss of caveolae in the cell membrane of tracheal smooth muscle in δ-SG KO mice. Collectively, these results confirm and extend understanding of a functional role for the DGC in the contractile properties of ASM and demonstrate that this results in altered lung function in vivo.