Mechanical stretch modulates TGF-β1 and α1(I) collagen expression in fetal human intestinal smooth muscle cells

Intestinal muscle undergoes stretch intermittently during peristalsis and persistently proximal to obstruction. The influence of this pervasive biomechanical force on developing smooth muscle cell function remains unknown. We adapted a novel in vitro system to study whether stretch modulates transforming growth factor-beta 1 (TGF-beta 1) and type I collagen protein and component alpha 1 chain [alpha 1(I) collagen] expression in fetal human intestinal smooth muscle cells. Primary confluent cells at 20-wk gestation, cultured on flexible silicone membranes, were subjected to two brief stretches or to 18 h tonic stretch. Nonstretched cultures served as controls. TGF-beta 1 protein was measured by ELISA and type I collagen protein was assayed by Western blot. TGF-beta 1 and alpha 1(I) collagen mRNA abundance was determined by Northern blot analysis, quantitated by phosphorimaging, and normalized to 18S rRNA. Transcription was examined by nuclear run-on assay. Tonic stretch increased TGF-beta 1 protein 40%, type I collagen protein 100%, TGF-beta 1 mRNA content 2.16-fold, and alpha 1(I) collagen mRNA 3.80-fold and enhanced transcription of TGF-beta 1 and alpha 1(I) collagen by 3.1- and 4.25-fold, respectively. Brief stretch stimulated a 50% increase in TGF-beta 1 mRNA content but no change in al(I) collagen. Neutralizing anti-TGF-beta 1 ablated stretch-mediated effects on alpha 1(I) collagen. Therefore, stretch upregulates transcription for TGF-beta 1, which stimulates alpha 1(I) collagen gene expression in smooth muscle from developing gut.