Inhibition of endothelial cell migration by shear stress

Angiogenesis is a multistep process involving endothelial cell (EC) migration and proliferation, tightly regulated by a complex system of promoting and inhibiting factors [1]. Stimulation of angiogenesis by increased shear stress in vivo is associated with an increase in production of vascular endothelial growth factor (VEGF) and nitric oxide (NO) in skeletal muscle [2,3]. The shear sensor that tranduces the increased shear into an angiogenic signal is poorly understood. Evidence suggests that CD31 expressed on ECs may act as part of a mechanosensory complex [4]. Thus, we aimed to investigate the hypothesis that shear stress and VEGF interact to modulate migration of ECs, and hence control angiogenesis. In addition, we investigated the roles of CD31 as a potential sensor and NO as potential effector of shear-induced changes in this model. Using real time PCR, changes in expression of genes known to play a role in angiogenesis; VEGF, VEGF receptor (R) 1 & 2, endothelial NO synthase(eNOS), angiopoietin (ANG) 1 & 2, neuropilin (NP) 1 & 2, were investigated in human umbilical vein EC (HUVEC) cultured under stasis or shear stress (1.5 Pa) for 24h, ±VEGF in the final 4h. To assess migration, confluent HUVEC were wounded and then exposed to stasis or shear stress (0.3 Pa or 1.5 Pa) ±VEGF; wound recovery was measured at 0 and 16h. In similar experiments, the effect of NO or CD31 was investigated using the NOS inhibitor L-NAME or siRNA for CD31, respectively. Gene expression analysis showed that shear alone increased eNOS, VEGFR2 and NP2 expression, but decreased expression of ANG 1 & 2 and NP1. These shear-induced changes were all maintained in the presence of VEGF. Shear decreased EC wound recovery (higher the shear = lower migration; P<0.001 1.5 Pa vs. Static). Nevertheless, EC preferentially migrated in the direction of flow (P<0.01). VEGF enhanced wound recovery to the same extent under static and shear (P<0.05). Neither NOS inhibition nor reduced expression of CD31 modified the shearinduced inhibition in wound recovery. Shear stress leads to differential regulation of a number of genes involved in the control of angiogenesis. Interestingly, shear appears to be regulating molecules that modify VEGF effects, rather than VEGF per se. VEGF appears to have little effect on any of these key angiogenic genes. Whereas in vivo results show that shear stimulates angiogenesis [2], our results show that shear decreases migration of ECs, suggesting that in vivo additional cellular responses are being modulated. CD31 does not appear to be the sensor involved in shear-induced inhibition of migration, and NO does not appear to be the effector of this response in this model. Egginton (2008) Pflugers Arch –Eur J Physiol.