Matrix synthesis by bladder smooth muscle cells is modulated by stretch frequency

Summary

The bladder is a physically active organ that undergoes periodic stretching as a part of its normal function. To determine the role that stretching or mechanical deformation may play in altering the synthetic phenotype of bladder wall cells, a series of experiments were carried out to quantify several extracellular matrix (ECM) messenger ribonucleic acids (mRNAs) and their corresponding protein levels after mechanical challenge. Bladder smooth muscle cells were grown on distensible membranes in an apparatus that can reliably and reproducibly subject cells to well-characterized periods of mechanical stretching. For this study, cultured bovine bladder cells were subjected to cyclic mechanical deformation of varying frequencies to determine if this variable altered ECM expression. Using this experimental system, we demonstrated that smooth muscle cells were acutely sensitive to mechanical deformation and showed alteration in the synthesis of the major fibrillar collagens, types I and III. Concomitant analyses of mRNA in these cells show that levels of type I collagen correlate with mRNA levels at all frequencies except at 60 cycles/min, and, thus, type I production appears to be transcriptionally regulated. Interestingly, type III protein levels do not correlate with mRNA measurements except at 20 cycles/min, and, therefore, a different regulatory mechanism likely governs type III production. These studies demonstrate that smooth muscle cell ECM secretory phenotype can be altered by the frequency of mechanical deformation experienced by the cells. These data support the concept that stretching of the bladder wall affects the secretory phenotype of smooth muscle cells and can result in an altered ECM composition.