The Role of Shear-Induced Transforming Growth Factor-? Signaling in the EndotheliumSignificance

Abstract

Objective Vascular endothelial cells (ECs) are continuously exposed to blood flow that contributes to the maintenance of vessel structure and function; however, the effect of hemodynamic forces on transforming growth factor-β (TGF-β) signaling in the endothelium is poorly described. We examined the potential role of TGF-β signaling in mediating the protective effects of shear stress on ECs. Approach and Results Human umbilical vein endothelial cells (HUVECs) exposed to shear stress were compared to cells grown under static conditions. Signaling through the TGF-β receptor ALK5 was inhibited with SB525334. Cells were examined for morphological changes and harvested for real-time PCR, western blot analysis, apoptosis, proliferation and immunocytochemistry. Shear stress resulted in ALK5-dependent alignment of HUVECs as well as attenuation of apoptosis and proliferation compared to static controls. Shear stress lead to an ALK5-dependent increase in TGF-β3 and Krüppel-like factor 2 (KLF2), phosphorylation of endothelial nitric oxide synthase (eNOS) and NO release. Addition of the NO donor S-nitroso-N-acetylpenicillamine (SNAP) rescued the cells from apoptosis due to ALK5 inhibition under shear stress. Knockdown of TGF-β3, but not TGF-β1, disrupted the HUVEC monolayer and prevented the induction of KLF2 by shear. Conclusions Shear stress of HUVECs induces TGF-β3 signaling and subsequent activation of KLF2 and NO, and represents a novel role for TGF-β3 in the maintenance of HUVEC homeostasis in a hemodynamic environment.