Integrin αv Mediates Contractility Whereas Integrin α4 Regulates Proliferation of Human Bladder Smooth Muscle Cells via FAK Pathway under Physiological Stretch

Purpose: The requirement of integrins for mechanotransduction has been recognized for some time. We investigated the role of integrin subunits and their pathway in the physiological stretch induced contractility and proliferation of human bladder smooth muscle cells. Materials and Methods: Human bladder smooth muscle cells were seeded on silicone membrane and subjected to stretch, simulating bladder cycles of various stretches and times, as controlled by customized software on a modified BioDynamic (R) bioreactor. Cell proliferation, viability and cycle were determined by BrdU incorporation assay, the Cell Counting Kit-8 (Beyotime Institute of Biotechnology, Haimen, People's Republic of China) and flow cytometry, respectively. Cell contractility was determined using a collagen gel contraction assay. Results: Physiological stretch increased cell contractility, proliferation and viability. Knockdown of integrin alpha v but not alpha 4 in the cells disrupted the enhanced contractility induced by stretch. Under physiological stretch conditions, the integrin alpha v level and phospho-FAK/FAK ratio correlated positively with cell stretch induced enhanced contractility. Further examination revealed that contractile marker expression was associated with integrin alpha v activation through the FAK pathway. At the same time integrin alpha 4 but not integrin alpha v mediated stretch induced cell proliferation and viability. Conclusions: These data revealed that different integrins have different roles in the contractility and proliferation of human bladder smooth muscle cells under physiological stretch. This suggests that different integrins may become specific therapeutic targets in patients with voiding dysfunction. They may also be used to design a specific microenvironment for optimal bladder tissue regeneration.