Glomerular endothelial cells
Glomerular endothelial cells (GEnC)characterised by non-diaphragmed fenestrations (60-80nm transcellular holes) in their peripheral cytoplasm. The fenestrations occupy a large proportion of the capillary surface allowing the easy movement of water and small molecules across the glomerular filtration barrier. Loss or reduction in these fenestrations results in a reduction in GFR and renal failure as seen experimentally and in human diseases, including diabetic nephropathy (link). Despite the functional and clinical importance of GEnC fenestrations, little is known regarding their regulation and structure. GEnC, including the fenestrations, are coated with a glycocalyx, which is a hydrated poly-anionic gel comprised of proteoglycans, sialoproteins and adsorbed plasma proteins and is found on the luminal surface of all endothelial cells. Amongst other important roles in vascular physiology, the endothelial glycocalyx is increasingly recognised as a key determinant of endothelial permeability both in systemic and glomerular circulations. There is evidence that loss of endothelial glycocalyx is an early feature of diabetic vasculopathy, including diabetic nephropathy. We are currently examining the role of GEnC fenestrations and glycocalyx in glomerular barrier function in health and disease to determine potential theraputic targets.
Throughout the vasculature, laminar shear stress (LSS), induced by flowing blood, is a key determinant of vascular health by modulating endothelial behaviour and its contribution to the vascular wall. However, despite the vital contribution of the glomerular endothelium to the glomerular filtration barrier (GFB), and hence to fundamental filtration function, the study of LSS in the glomerulus has been neglected. Prolonged LSS induces a quiescent, anti-apoptotic, anti-thrombotic and anti-inflammatory endothelial phenotype. Shear stress also regulates production of vasoactive mediators including nitric oxide (NO) and endothelin-1 (ET-1) and so regulates mural cell function and vascular tone. Disturbances in LSS to induce turbulent flow around arterial branch points are heavily implicated in the pathogenesis of atherosclerosis in these atheroprone regions.
Although little studied in the glomerulus, the importance of LSS is clearly demonstrated not only by vital effects on behaviour of other endothelia but also by the dependence of glomerular health on the balance of shear-regulated NO and ET-1. We are currently examining the critical role of LSS to the GEnC contribution to the GFB and hence to normal kidney function.
Interferon (IFN)β is a pleiotropic cytokine used clinically in multiple sclerosis. We have shown that IFNβ treatment dramatically reduces proteinuria in 3 distinct animal models of glomerulonephritis. Contrary to expectations there was no histological evidence that IFNβ reduced inflammation. In vitro, IFNβ caused a marked increase in electrical resistance across GEnC and podocyte monolayers and a corresponding decrease in passage of labelled albumin. This suggests that the reduction in proteinuria in vivo could be explained by these direct cellular effects, opening a new field of investigation – pathways & potential applications of effects of IFNβ in regulating barrier properties of cell layers. We are currently investigating the protective effect of INFβ in animal models of diabetic nephropathy and downstream signalling pathways within our GEnC lines.