Mechanical stretch modulates TGF-beta 1 and alpha 1(I) collagen expressionin fetal human intestinal smooth muscle cells

Intestinal muscle undergoes stretch intermittently during peristalsis and p ersistently proximal to obstruction. The influence of this pervasive biomec hanical force on developing smooth muscle cell function remains unknown. We adapted a novel in vitro system to study whether stretch modulates transfo rming growth factor-beta 1 (TGF-beta 1) and type I collagen protein and com ponent alpha 1 chain [alpha 1(I) collagen] expression in fetal human intest inal smooth muscle cells. Primary confluent cells at 20-wk gestation, cultu red on flexible silicone membranes, were subjected to two brief stretches o r 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 determ ined by Northern blot analysis, quantitated by phosphorimaging, and normali zed 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, stret ch upregulates transcription for TGF-beta 1, which stimulates alpha 1(I) co llagen gene expression in smooth muscle from developing gut.