Effect of sustained tension on bladder smooth muscle cells in three-dimensional culture

Previous studies demonstrated that bladder cells respond to changes in their mechanical environments by exhibiting alterations in cellular functions, such as hypertrophy or fibrosis. In the present study, we hypothesize that changes in smooth muscle cell (SMC) behavior triggered by mechanical stimuli may represent a phenotypic shift between contractile and synthetic phenotypes. Using a custom-made device, rat bladder SMCs were cultured in three-dimensional (3-D) collagen gels and exposed to sustained tension. When compared to no-tension controls, SMCs exposed to tension exhibited significantly (p < 0.05) higher expression of alpha-smooth muscle actin (alpha-SMA), while cell population density was similar in both groups. In addition, both mean and median aspect ratios of SMCs in 3-D collagen constructs exposed to tension were significantly (p < 0.05) greater than those of cells cultured under no externally applied tension, indicating that there are more elongated, spindle-shaped cells in the tension group. These SMCs in 3-D cultures exposed to tension also exhibited cellular alignment along the direction of applied tension. Since contractile SMCs are known to exhibit greater expression of phenotypic marker proteins as well as a more elongated morphology, we concluded that sustained tension on cells is an important mechanical stimulus for maintenance of the contractile phenotype of bladder SMCs in vitro.