The effect of pulsatile flow on co-cultured retinal endothelial & pericyte cells

Abstract

Microvascular cell fate decisions are hallmarks of the microvascular cell response to injury and play a crucial role in the pathogenesis of retinal disease. Abnormalities in retinal blood flow play a critical role in remodeling of the retinal vasculature by altering microvascular endothelial and pericyte cell fate (proliferation, apoptosis and migration). Retinal blood flow is controlled locally by vasodilators such as nitric oxide, prostacyclin and the vasoconstrictor endothelin-1 , with considerable evidence linking retinal pathologies such as Normal Tension Glaucoma and Diabetic Retinopathy to altered retinal blood flow Shear stress has previously been shown to modulate EC production of these vasoactive agents in macrovascular cells. Therefore, using a perfused transcapillary coculture of bovine microvascular retinal endothelial cells (BRECs) and bovine retinal pericytes (BRPs), we examined the acute and chronic effect of pulsatile flow on the release of these vasoactive mediators and their subsequent role in modulating retinal vascular cell fate. Acute exposure to pulsatile flow increased BREC NO, PGI2 & ET-1 formation and release Similarly, chronic exposure to pulsatile flow enhanced NO and PGI2 release while concomitantly inhibiting ET-1 in these cells In parallel studies, there was an increase in BRP apoptosis following exposure to high pulsatile flow, whereas BREC apoptosis decreased. Furthermore, the pulsatile flow-induced increases in BRP apoptosis is dependent on increased PGI2 , whereas both ET-1 and NO mediate the protective effect of increased flow on BRECs survival. Notch receptor-hgand interactions and the Hedgehog signalling pathway have been strongly implicated in vascular morphogenesis and remodelling of the embryonic vasculature, with Hedgehog acting upstream of Notch signalling during development. We therefore tested the hypothesis that Hedgehog (Hh) and Notch pathway interact to promote changes in vascular cell fate in BRECs and BRPs in vitro in response to changes in pulsatile flow