Contractile Properties of Intrapulmonary Airway Smooth Muscle in Cystic Fibrosis

CFTR dysfunction in smooth muscle drives TGFβ dependent airway hyperreactivity

BACKGROUND

The primary underlying defect in cystic fibrosis (CF) is disrupted ion transport in epithelia throughout the body. It is unclear if symptoms such as airway hyperreactivity (AHR) and increased airway smooth muscle (ASM) volume in people with CF are due to inherent abnormalities in smooth muscle or are secondary to epithelial dysfunction. Transforming Growth Factor beta 1 (TGFβ) is an established genetic modifier of CF lung disease and a known driver of abnormal ASM function. Prior studies have demonstrated that CF mice develop greater AHR, goblet cell hyperplasia, and ASM hypertrophy after pulmonary TGFβ exposure. However, the mechanism driving these abnormalities in CF lung disease, specifically the contribution of CFTR loss in ASM, was unknown.

METHODS

In this study, mice with smooth muscle-specific loss of CFTR function (Cftrfl/fl; SM-Cre mice) were exposed to pulmonary TGFβ. The impact on lung pathology and physiology was investigated through examination of lung mechanics, Western blot analysis, and pulmonary histology.

RESULTS

Cftrfl/fl; SM-Cre mice treated with TGFβ demonstrated greater methacholine-induced AHR than control mice. However, Cftrfl/fl; SM-Cre mice did not develop increased inflammation, ASM area, or goblet cell hyperplasia relative to controls following TGFβ exposure.

CONCLUSIONS

These results demonstrate a direct smooth muscle contribution to CF airway obstruction mediated by TGFβ. Dysfunction in non-epithelial tissues should be considered in the development of CF therapeutics, including potential genetic therapies.

Automated, high temporal resolution mechanics measurements during incubation of contractile tissues

Muscle tissue mechanics and contractility measurements have a great advantage over cultured cell level experiments as their mechanical and contractile properties are much closer to in vivo tissue properties. However, tissue level experiments cannot be combined with incubation with the same time resolution and consistency as cell culture studies. Here we present a system in which contractile tissues can be incubated for days while intermittently being tested for their mechanical and contractile properties. A two-chamber system was developed with control of temperature in the outer chamber and CO₂ and humidity control in the inner, sterile chamber. Incubation medium, to which biologically active components may be added, is reused after each mechanics test to preserve both added and released components. Mechanics and contractility are measured in a different medium to which, through a high accuracy syringe pump, up to 6 different agonists in a 100-fold dose range can be added. The whole system can be operated through fully automated protocols from a personal computer. Testing data shows accurate maintenance of temperature, CO₂ and relative humidity at pre-set levels. Equine trachealis smooth muscle tissues tested in the system showed no signs of infection after 72 h with incubation medium replacement every 24 h. Methacholine dosing and electrical field stimulation every 4 h showed consistent responses. In conclusion, the developed system is a great improvement on the manual incubation techniques being used thus far, improving on time resolution, repeatability and robustness, while reducing contamination risk and tissue damage from repeated handling.

Ureteral Obstruction Promotes Ureteral Inflammation and Fibrosis

BACKGROUND

Hydronephrosis and renal impairment may persist even after relieving an obstruction, particularly in cases of chronic obstruction. Obstruction can cause fibrotic changes of the ureter, potentially contributing to long-term kidney damage.

OBJECTIVE

To characterise pathophysiological changes of obstructed ureters with focus on inflammatory responses triggering fibrosis and potential impairment of ureteral function.

DESIGN, SETTING, AND PARTICIPANTS

Eighty-eight mice were randomly assigned to unilateral ureteral obstruction (UUO) for 2 d, UUO for 7 d, and UUO for 7 d followed by 8 d of recovery, or a control group (no prior surgical intervention).

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Peristaltic rate was determined over 2 min by direct visualisation with a microscope, while hydronephrosis was assessed by ultrasound. Obstructed and contralateral ureters were harvested, and underwent histopathological evaluation. We quantified 44 cytokines/chemokines, and five matrix metalloproteases using Luminex technology. Cell composition was characterised via immunofluorescence. Statistical significance was assessed using Welch analysis of variance, Kruskal-Wallis test, and Dunnett's T3 multiple comparison test.

RESULTS AND LIMITATIONS

Obstruction resulted in hydronephrosis and significantly impaired peristalsis. Marked fibrosis was observed in lamina propria, muscle layer, and adventitia. Connective tissue in obstructed ureters showed hyperaemia and leucocyte infiltration. Unsupervised hierarchical clustering demonstrated different cytokine/chemokine patterns between groups. Ureters obstructed for 7 d followed by recovery were notably different from other groups. Inflammatory cytokines, chemoattractants, and matrix metalloproteases increased significantly in obstructed ureters. Contralateral unobstructed ureters showed significantly increased levels of chemokines and matrix metalloproteases. Immunofluorescence confirmed activation of T cells, Th1 and Th2 cells, and M1 macrophages in obstructed and contralateral ureters, and a shift to M2 macrophages following prolonged obstruction.

CONCLUSIONS

Ureteral obstruction triggers severe inflammation and fibrosis, which may irreversibly impair ureteral functionality. Function of the unobstructed contralateral ureter may be regulated by a systemic immune response as a result of the obstruction.

PATIENT SUMMARY

Here, we studied in more detail the way the ureter responds to being blocked. We conclude that a strong immune response is activated by the blockage, leading to changes in the structure of the ureter possibly impacting function, which may not be reversible. This immune response also spreads to the opposite ureter, possibly allowing it to change its function to compensate for the reduced functionality of the blocked ureter.

Mucus Release and Airway Constriction by TMEM16A May Worsen Pathology in Inflammatory Lung Disease

Activation of the Ca²⁺ activated Cl⁻ channel TMEM16A is proposed as a treatment in inflammatory airway disease. It is assumed that activation of TMEM16A will induce electrolyte secretion, and thus reduce airway mucus plugging and improve mucociliary clearance. A benefit of activation of TMEM16A was shown in vitro and in studies in sheep, but others reported an increase in mucus production and airway contraction by activation of TMEM16A. We analyzed expression of TMEM16A in healthy and inflamed human and mouse airways and examined the consequences of activation or inhibition of TMEM16A in asthmatic mice. TMEM16A was found to be upregulated in the lungs of patients with asthma or cystic fibrosis, as well as in the airways of asthmatic mice. Activation or potentiation of TMEM16A by the compounds Eact or brevenal, respectively, induced acute mucus release from airway goblet cells and induced bronchoconstriction in mice in vivo. In contrast, niclosamide, an inhibitor of TMEM16A, blocked mucus production and mucus secretion in vivo and in vitro. Treatment of airway epithelial cells with niclosamide strongly inhibited expression of the essential transcription factor of Th2-dependent inflammation and goblet cell differentiation, SAM pointed domain-containing ETS-like factor (SPDEF). Activation of TMEM16A in people with inflammatory airway diseases is likely to induce mucus secretion along with airway constriction. In contrast, inhibitors of TMEM16A may suppress pulmonary Th2 inflammation, goblet cell metaplasia, mucus production, and bronchoconstriction, partially by inhibiting expression of SPDEF.

Bronchodilator responsiveness in cystic fibrosis children treated for pulmonary exacerbations

BACKGROUND

Cystic fibrosis (CF) pulmonary exacerbations (PEx) are associated with a significant drop in pulmonary function. The clinical value of measuring bronchodilator (BD) responsiveness during treatment for PEx to monitor or predict recovery of lung function is unclear.

METHODS

A retrospective analysis of spirometry with BD response testing obtained during hospital admissions for PEx in pediatric CF patients. Repeated events were included for patients with BD testing during multiple admissions.

RESULTS

Two hundred forty-nine spirometries with BD testing in 102 patients were completed around Day 7 (Days 4-10) of hospital admission for treatment of CF PEx. Median (IQR) forced expiratory volume in 1 s (FEV₁ ) was 70.6% predicted (58.1, 84.6) before the PEx event (best FEV₁ in 6 months before admission), 54.4% (41.5, 66.9) at admission, 62.3% (48.4, 74.7) around Day 7 of admission and 67.1% predicted (53.8, 78.2) at the end of treatment. BD response around Day 7 correlated poorly with FEV₁ before PEx (r = -.16, p = .02) and did not correlate with recovery to baseline FEV₁ at end of treatment (r = .08, p = .22). Only 23/249 (9%) individual tests had a BD response in FEV₁ of ≥12% and 200 ml. BD response was not related to age or severity of lung disease and led to an immediate change in clinical management in only four cases.

CONCLUSIONS

Significant BD response in CF patients treated for PEx is rare, shows poor correlation with baseline pulmonary function and does not correlate with the recovery of FEV₁ with treatment. These data suggest that routine testing for BD response is not indicated during PEx.

Asthma in Cystic Fibrosis: Definitions and Implications of This Overlap Syndrome

PURPOSE OF REVIEW

Cystic fibrosis (CF) is a multisystem, autosomal recessive disease that leads to progressive loss of lung function. Respiratory symptoms for both CF and asthma include cough, wheezing, and dyspnea. There is debate within the CF community on how to best define and distinguish CF-asthma overlap syndrome (CFAOS) from asthma-like features, though CFAOS is well-recognized. We aim to review the epidemiology, diagnosis, and treatment of asthma in CF and explore areas where further research is needed.

RECENT FINDINGS

There has been considerable improvement in the understanding and treatment of asthma over the past two decades leading to novel therapies such as biologic agents that target the airway inflammation in asthmatics based on their asthma phenotype. These therapies are being studied in CFAOS and are promising treatments. This review provides a comprehensive overview of the definition, epidemiology, diagnosis, and current treatment of CFAOS.

Attenuation of relaxing response induced by pituitary adenylate cyclase-activating polypeptide in bronchial smooth muscle of experimental asthma

Bronchomotor tone is regulated by contraction and relaxation of airway smooth muscle (ASM). A weakened ASM relaxation might be a cause of airway hyperresponsiveness (AHR), a characteristic feature of bronchial asthma. Pituitary adenylyl cyclase-activating polypeptide (PACAP) is known as a mediator that causes ASM relaxation. To date, whether or not the PACAP responsiveness is changed in asthmatic ASM is unknown. The current study examined the hypothesis that relaxation induced by PACAP is reduced in bronchial smooth muscle (BSM) of allergic asthma. The ovalbumin (OA)-sensitized mice were repeatedly challenged with aerosolized OA to induce asthmatic reaction. Twenty-four hours after the last antigen challenge, the main bronchial smooth muscle (BSM) tissues were isolated. Tension study showed a BSM hyperresponsiveness to acetylcholine in the OA-challenged mice. Both quantitative RT-PCR and immunoblot analyses revealed a significant decrease in PAC₁ receptor expression in BSMs of the diseased mice. Accordingly, in the antigen-challenged group, the PACAP-induced PAC₁ receptor-mediated BSM relaxation was significantly attenuated, whereas the relaxation induced by vasoactive intestinal polypeptide was not changed. These findings suggest that the relaxation induced by PACAP is impaired in BSMs of experimental asthma due to a downregulation of its binding partner PAC₁ receptor. Impaired BSM responsiveness to PACAP might contribute to the AHR in asthma.

Subacute TGFβ Exposure Drives Airway Hyperresponsiveness in Cystic Fibrosis Mice through the PI3K Pathway

Cystic fibrosis (CF) is a lethal genetic disease characterized by progressive lung damage and airway obstruction. The majority of patients demonstrate airway hyperresponsiveness (AHR), which is associated with more rapid lung function decline. Recent studies in the neonatal CF pig demonstrated airway smooth muscle (ASM) dysfunction. These findings, combined with observed CF transmembrane conductance regulator (CFTR) expression in ASM, suggest that a fundamental defect in ASM function contributes to lung function decline in CF. One established driver of AHR and ASM dysfunction is transforming growth factor (TGF) β1, a genetic modifier of CF lung disease. Prior studies demonstrated that TGFβ exposure in CF mice drives features of CF lung disease, including goblet cell hyperplasia and abnormal lung mechanics. CF mice displayed aberrant responses to pulmonary TGFβ, with elevated PI3K signaling and greater increases in lung resistance compared with controls. Here, we show that TGFβ drives abnormalities in CF ASM structure and function through PI3K signaling that is enhanced in CFTR-deficient lungs. CF and non-CF mice were exposed intratracheally to an adenoviral vector containing the TGFβ1 cDNA, empty vector, or PBS only. We assessed methacholine-induced AHR, bronchodilator response, and ASM area in control and CF mice. Notably, CF mice demonstrated enhanced AHR and bronchodilator response with greater ASM area increases compared with non-CF mice. Furthermore, therapeutic inhibition of PI3K signaling mitigated the TGFβ-induced AHR and goblet cell hyperplasia in CF mice. These results highlight a latent AHR phenotype in CFTR deficiency that is enhanced through TGFβ-induced PI3K signaling.

Characterization of cystic fibrosis airway smooth muscle cell proliferative and contractile activities

Cystic fibrosis (CF) is a genetic disease that causes multiple airway abnormalities. Two major respiratory consequences of CF are airway hyperresponsiveness (AHR) and airway remodeling. Airway smooth muscle (ASM) is hypothesized to be responsible for the airway dysfunction, since their thickening is involved in remodeling, and excessive contraction by the ASM may cause AHR. It is unclear whether the ASM is intrinsically altered to favor increased contractility or proliferation or if microenvironmental influences induce pathological behavior in vivo. In this study, we examined the contractile and proliferative properties of ASM cells isolated from healthy donor and CF transplant lungs. Assays of proliferation showed that CF ASM proliferates at a higher rate than healthy cells. Through calcium analysis, no differences in contractile activation in response to histamine were found. However, CF ASM cells lagged in their reuptake of calcium in the sarcoplasmic reticulum. The combination CFTR corrector and potentiator, VX-809/770, used to restore CFTR function in CF ASM, resulted in a reduction in proliferation and in a normalization of calcium reuptake kinetics. These results show that impaired CFTR function in ASM cells causes intrinsic changes in their proliferative and contractile properties.

Niclosamide repurposed for the treatment of inflammatory airway disease

Inflammatory airway diseases, such as asthma, cystic fibrosis (CF), and chronic obstructive pulmonary disease (COPD), are characterized by mucus hypersecretion and airway plugging. In both CF and asthma, enhanced expression of the Ca2+-activated Cl- channel TMEM16A is detected in mucus-producing club/goblet cells and airway smooth muscle. TMEM16A contributes to mucus hypersecretion and bronchoconstriction, which are both inhibited by blockers of TMEM16A, such as niflumic acid. Here we demonstrate that the FDA-approved drug niclosamide, a potent inhibitor of TMEM16A identified by high-throughput screening, is an inhibitor of both TMEM16A and TMEM16F. In asthmatic mice, niclosamide reduced mucus production and secretion, as well as bronchoconstriction, and showed additional antiinflammatory effects. Using transgenic asthmatic mice, we found evidence that TMEM16A and TMEM16F are required for normal mucus production/secretion, which may be due to their effects on intracellular Ca2+ signaling. TMEM16A and TMEM16F support exocytic release of mucus and inflammatory mediators, both of which are blocked by niclosamide. Thus, inhibition of mucus and cytokine release, bronchorelaxation, and reported antibacterial effects make niclosamide a potentially suitable drug for the treatment of inflammatory airway diseases, such as CF, asthma, and COPD.