Fluid shear stress increases transforming growth factor beta 1 expression in human osteoblast-like cells: Modulation by cation channel blockades

Mechanical stress is an important regulator of bone metabolism. Fluid shear stress caused by mechanical load in bone tissue has been shown to be important to both the bone structure and function through its effects on osteocytes and osteoblasts. We explored the effects of the fluid shear stress on the expression of growth factors and cytokines in human osteoblast-like SaOS-2 cells with a purpose-built cone-plate viscometer. We showed that the physiological level (1.7-2.0 Pascal) of fluid shear stress increased the mRNA expression of TGF-beta 1 about threefold after 3 hours and also increased TGF-beta 1 protein about threefold after 24 hours in the SaOS-2 cells. However, no mRNA expression of PDGF-A, IGF-I, IGF-II, or IL-6 was detected. To explore the mechanism of up-regulation of TGF-beta 1 expression, we examined the effects of a stretch activated cation nonselective (SA-cat) channel blockade with gadolinium and a voltage-dependent L-type Ca2+ channel blockade with verapamil on the TGF-beta 1 expression at the mRNA levels. The fluid shear stress-induced increase in the TGF-beta 1 mRNA levels was significantly inhibited by both gadolinium and verapamil. These findings suggest that the physiological level of fluid shear stress induces the production of TGF-beta 1 by the SaOS-2 cells via the cation channel function and, as a result, may therefore promote bone formation.