RESUMEN
Laminar shear stress (LSS), induced by flowing blood, plays a key role in determining vascular health by modulating endothelial behaviour and vascular tone. In systemic endothelium many of the beneficial effects of chronic LSS are mediated through the transcription factor Kruppel-like factor 2 (KLF2), but little is known regarding the role of chronic LSS in the renal glomerulus. We demonstrate that exposure of glomerular endothelial cells to chronic (>24h) LSS of 10 dyn/cm(2) increases phosphorylation of extra-cellular signal-related kinase 5 (ERK5) and increases expression of KLF2, leading to increased expression of the downstream molecules endothelial nitric oxide synthase (eNOS), thrombomodulin, endothelin-1 and nitric oxide. However, the proportion of eNOS which was phosphorylated at serine 1117 and threonine 495 residues was decreased. We demonstrated dependence of these effects on the ERK5 pathway by using the inhibitor UO126. We found high levels of KLF2 expression in human glomeruli confirming the relevance of our in vitro observations and, as KLF2 is specifically induced by chronic LSS, suggesting the physiological importance of shear stress in the glomerulus. Conditioned medium from glomerular endothelial cells under chronic LSS decreased podocyte monolayer resistance and increased phosphorylation of vasodilator-stimulated phosphoprotein. The latter effect was more pronounced using a novel insert-based direct co-culture system in which endothelial cells were exposed to chronic LSS. These data provide the first direct evidence of glomerular endothelial cell to podocyte cross-talk.
