Regulation of c-fos expression by static stretch in rat myometrial smooth muscle cells

OBJECTIVE: We investigated whether mechanical stretch stimulates expression of the immediate early gene c-fos messenger RNA in rat myometrial smooth muscle cells. STUDY DESIGN: Freshly isolated myometrial smooth muscle cells (from virgin rats) were plated on flexible culture plates that were coated with either collagen I, laminin, elastin, or pronectin and were subjected to a static stretch with a computerized strain unit. Immunocytochemistry was used to define smooth muscle cell phenotype, and c-fos expression levels were assessed by Northern blotting. RESULTS: Myometrial smooth muscle cells maintained their phenotype for at least 7 days in culture. Stretch induced a dramatic increase in levels of c-fos messenger RNA, which peaked after 30 minutes. Stimulation of c-fos gene expression was dependent on the degree of stretch (maximum induction at 25% elongation). Interestingly, as little as 1 minute of stretch was sufficient to induce maximal c-fos expression at 30 minutes. The most dramatic induction of c-fos was observed in smooth muscle cells that were stretched on collagen I-coated plates. CONCLUSION: Myometrial smooth muscle cells can directly respond to mechanical stretch with a strength- and matrix component-dependent increase in c-fos messenger RNA. The time delay between the initial stimulus and the cumulative elevation of c-fos messenger RNA suggests a complex regulation from mechanoreception to c-fos gene expression.