Stretch-induced Up-regulation of Caveolae Formation and SOC Activities in HUVEC

Abstract

We have studied about molecular identities of stretch-activated (SA) channels and the mechanism of Ca2+ influx evoked by mechanical stretch in human umbilical vein endothelial cells (HUVECs). Previously, we showed that a targeting suppression of transient receptor potential 2 (TRPV2) protein expression in HUVEC using a TRPV2-specific morphorino-oligo completely blocked a transient increase of intracellular Ca2+ in response to stretch through the activation of SA channels. Furthermore, after these morphant HUVECs were subjected to 20% uni-axial cyclic stretch at 1 Hz for 1 h, neither a stretch-enhanced stress fiber formation nor a shift in the cell orientation transverse to the strain direction could not be observed. From these results, we concluded that TRPV2 would be a key component of SA channel complex and stretch-induced reorganization of cytoskeletons in HUVEC. Here, we examined the remodeling of Ca2+ responses evoked by uni-axial cyclic stretch in HUVEC. Before and after the cyclic stretch, a magnitude of single stretch-evoked Ca2+ transient did not change. However, the Ca2+ influx through the store-operated Ca2+ channels (SOCs) was significantly increased after stretch stimulation. Recent studies have demonstrated that caveolae are microdomains in the plasma membrane and contain functionally organized signaling molecules, including Ca2+ signaling. Immunohistochemistry revealed accumulation of caveolin-1 and TRPCs, some of which serve as SOCs, in caveolae after the cyclic stretch to HUVEC. Electron microscopy confirmed that the incidence of caveolae in HUVEC was increased after the stretch. On the other hands, TRPV2-knocked down HUVECs suppressed the increased SOC activities and caveolae formation after cyclic stretch. Such the up-regulation of SOC activities through stretch-dependent TRPV2 activation might contribute to sustained intracellular Ca2+ increase, which is thought to be a primary etiology of the vascular remodeling, and a potent risk factor of pressure-dependent hypertrophic diseases.