Effect of shear stress on the hydraulic conductivity of cultured bovine retinal microvascular endothelial cell monolayers

Abstract

The shear stress of flowing blood on endothelial cells increases water transport (hydraulic conductivity, Lp) in several vascular beds in vivo and has been hypothesized to play a role in elevating vascular transport in ocular diseases such as diabetic retinopathy. The purpose of this study is to determine the response of Lp to varying levels of shear stress using an in vitro model of the blood-retinal barrier: bovine retinal endothelial cells (BRECs) grown on polycarbonate filters. The study also addresses the role of nitric oxide (NO) and other downstream effectors in mediating shear-induced changes in water transport. A step change in shear stress of 10 dyn/cm 2 did not produce a significant change in Lp over 3 hours, whereas a 20 dyn/cm 2 step change elevated Lp by 14.6-fold relative to stationary controls at the end of 3h of shear exposure. 20 dyn/cm 2 of shear stress stimulated the endothelial monolayers to release nitric oxide in a biphasic manner and incubation of the BRECs with a nitric oxide synthase (NOS) inhibitor, L-NMMA, significantly attenuated the shear-induced Lp response. These experiments demonstrate that NO is a key signaling molecule in the pathway linking shear stress and Lp in BRECs. A widely studied pathway downstream of NO involves the activation of guanylate cyclase (GC), guanosine 3', 5'-cyclic monophosphate (cGMP) and protein kinase G (PKG). It was observed that incubation of BRECs with the GC inhibitor, LY83583 (10 µM) or the PKG inhibitor, KT5823 (1 µM) did not significantly alter the shear-induced Lp response. Also the cGMP analogue, 8-br-cGMP (1mM), did not affect the baseline Lp over 4h. These results demonstrate that shear stress elevates hydraulic conductivity in BRECs through a signaling mechanism that involves NO but not the GC/cGMP/PKG pathway.