Mechanical stretch induces TGF-beta synthesis in hepatic stellate cells

It is known that mechanical stress induces extracellular matrix via transforming growth factor-beta (TGF-beta) synthesis in vascular smooth muscle cells. Activated hepatic stellate cells (HSCs) are an important source of TGF-beta in the liver. However, it remains unclear whether mechanical stress induces TGF-beta in HSCs. The Rho small GTP-binding protein (Rho) has recently emerged as an important regulator of actin and cytoskeleton. We examined whether TGF-beta is expressed in stretched HSCs and whether Rho is involved in stretch-induced TGF-beta synthesis.

A cultured human HSC cell line, LI90, was used for this study. Hepatic stellate cells were cyclically stretched using the Flexercell(R) strain unit. Concentration of TGF-beta in the conditioned medium was estimated by a bioassay using mink lung epithelial cells transfected with a plasminogen activator inhibitor-1 promoter-luciferase construct. Transforming growth factor-beta mRNA expression of HSCs was estimated by a reverse-transcription polymerase chain reaction. Replication-defective adenoviral vectors expressing a dominant negative type of Rho was utilized to suppress its effect on HSCs.

Transforming growth factor-beta concentration of the conditioned media of stretched HSCs showed time-dependent increases as compared to nonstretched HSCs from 2 h to 24 h. Transforming growth factor-beta mRNA expression in stretched HSCs was increased compared with that in nonstretched HSCs. Transfection of dominant negative Rho inhibited the stretch-induced TGF-beta synthesis.

Mechanical stretch enhanced TGF-beta expression on mRNA and protein level in HSCs. Rho was closely related to stretch-induced TGF-beta synthesis in HSCs.