View Abstract

A2935 - Anti-Inflammatory Glucocorticoids Paradoxically Increase Airway Smooth Muscle Stiffness and Contraction Through CD151
Author Block: S. Tan1, H. Lam2, T. Saw3, M. Nai3, C. Lim3, S. S. An2, T. Tran1; 1Physiology, National University of Singapore, Singapore, Singapore, 2Environmental Health Sciences, Johns Hopkins University, Baltimore, MD, United States, 3Mechanobiology Institute, National University of Singapore, Singapore, Singapore.
Background: Asthma is characterized by airway inflammation and bronchial obstruction due to airway smooth muscle (ASM) contraction. However, the link between the immunologic phenotype and the resulting mechanical phenotype, including airway hyperresponsiveness (AHR), associated with disease presentation remains poorly understood. We previously identified an increased expression of CD151 in bronchial biopsy specimens from asthmatic patients and localized predominantly to ASM cells. In isolated human ASM cells, we also showed that glucocorticoids (GCs) increase CD151 expression. Here we tested the hypothesis that GC-induced CD151 expression is directly associated with enhanced ASM contraction in vitro and ex vivo. Method: We used a constellation of experimental methods, including collagen gel contraction assay, traction force microscopy (TFM), atomic force microscopy (AFM), magnetic twisting cytometry (MTC), and isometric force myography. Results: Dexamethasone-induced increase in CD151 expression was a class-effect of GCs, as fluticasone propionate, budesonide and prednisolone all concentration-dependently (0.1nM - 1uM) increased CD151 protein abundance, and was reduced by GC-receptor antagonist RU486 (1uM). Dexamethasone- and fluticasone propionate-induced CD151 expression was not specific to ASM cells as similar responses were observed in bronchial epithelial cells. In isolated human ASM cells, Dexamethasone significantly increased the stiffness and contraction in a concentration dependent manner. The mechanical response to Dexamethasone was similar in magnitude to histamine response, albeit at a slower rate. More importantly, siRNA-mediated knockdown of CD151 prevented and reversed Dexamethasone-induced mechanical phenotype of asthma in ASM cells. Conclusion: We showed anti-inflammatory GCs directly elevate CD151 expression and increased ASM stiffness and contraction. These results provide a novel mechanistic basis for explaining the lack of efficacy of GCs, which are used as first-line therapy in the prophylactic treatment of asthma, in reducing bronchoconstriction in asthmatic patients. The data are also suggestive of an uncoupling of airway inflammation and AHR in patients whose asthma is not controlled with GC therapy. Taken together, our findings now bring to light a paradoxical effect of anti-inflammatory agents on mechanical phenotype of asthma in ASM cells.