ZΟ-1 Expression and Phosphorylation in Diabetic Nephropathy

Abstract

Cellular mechanisms responsible for the loss of capillary wall permselectivity in diabetic nephropathy are not well characterized. ZO-1 is a junctional protein involved in the assembly and proper function of a number of tight junctions and is also expressed at the junction of podocytes with the slit diaphragm. We investigated the effect of diabetes and high glucose concentration on the expression of ZO-1 in animal models of both type 1 and 2 diabetes and in rat glomerular epithelial cells. In diabetic animals, immunohistochemistry and Western blotting showed decreased expression of ZO-1 in glomeruli. Immunogold electron microscopy revealed redistribution of ZO-1 from the podocyte membrane to the cytoplasm in the diabetic animals. Exposure of rat glomerular epithelial cells to high glucose resulted in a decrease in the intensity of ZO-1 staining and redistribution of ZO-1 from the membrane to the cytoplasm, changes that are attenuated by blockade of the angiotensin II type 1 receptor. ZO-1 protein expression and serine and tyrosine phosphorylation of ZO-1 were also decreased in cells exposed to high glucose. These findings suggest that alterations in the content and localization of ZO-1 may be relevant to the pathogenesis of proteinuria in diabetes. Diabetes 55:894 -900, 2006 D iabetic nephropathy is characterized by proteinuria and progressive fibrosis, resulting in a decline in kidney function in humans and experimental models of diabetes. Proteinuria is one of the most important prognostic risk factors for kidney disease progression (1). Cellular and molecular mechanisms underlying the loss of glomerular permselectivity in diabetic nephropathy and other proteinuric states are under intense investigation. Recent studies have identified mutations in the genes encoding podocyte structural proteins nephrin, podocin, CD2AP, neph-1, and ␣-actinin 4, which result in changes in glomerular permeability (2). ZO-1 ␣Ϫ, an 80 -amino acid truncated isoform of the 225-kD tight junction protein ZO-1, is highly expressed within the podocyte in the cytoplasmic aspect of the foot process membrane, adjacent to the insertion of the slit diaphragm (3-5). It links some of the slit diaphragm proteins through its PDZ (PSD-95/discs-large/ZO-1) domains to the actin cytoskeleton. Thus, changes in the expression or properties of ZO-1 may accompany renal diseases associated with proteinuria, including diabetic nephropathy. Studies in humans and experimental animals highlighted the importance of poor glycemic control in the development of the functional and structural changes in the kidney during the evolution of diabetic nephropathy (1,6 -10). Hyperglycemia and exposure of cultured cells to high glucose induce phenotypic modifications of cells that result in tissue injury (11)(12)(13)(14)(15). This study explored the expression of ZO-1 in two models of diabetes and the effect of glucose on ZO-1 expression and phosphorylation in cultured rat glomerular epithelial cells (GECs). RESEARCH DESIGN AND METHODSAnimals were used in accordance with ...

Telmisartan Increases the Permeability of Endothelial Cells through Zonula Occludens-1

“…In a study of diabetic nephropathy, it was found that the decrease in the intensity of ZO-1 staining and redistribution of ZO-1 from the membrane to the cytoplasm which were induced by exposure of rat glomerular epithelial cells to high glucose levels were attenuated by blockage of the angiotensin II type 1 receptor. 21) However, there was no previous study showing that ARB can downregulate the expression and disrupt the localization of tight junctions. In our present study, no obvious effect of valsartan on ZO-1 expression and localization was found, and thus we hypothesize that angiotensin II-independent mechanisms may be involved in the regulation of ZO-1 by telmisartan.…”

The role of cytoskeleton in the regulation of vascular endothelial barrier function

“…Phosphorylation of occludin by PKC in retinal endothelial cells seems to have similar effect [Harhaj et al, 2006]. Earlier, ZO-1 tyrosine phosphorylation was linked to enhanced vascular permeability [Antonetti et al, 1999]; more evidence emerging that Ser/Thr phosphorylation of ZO-1 can also play a role in endothelial barrier regulation [Rincon-Choles et al, 2006]. Adherence junctions are formed by clusters of transmembrane cadherin molecules associated with intracellular α-, β-and γ-catenins and anchored to actin.…”

Formation of tight junctions between neighboring podocytes is an early ultrastructural feature in experimental crescentic glomerulonephritis

“…Similar changes in ZO-1 expression and delocalization in rats with diabetic nephropathy were shown to associate with proteinuria and loss of glomerular function. 22,23 Therefore, glomerular injury disturbing the ZO-1 distribution likely diminishes slit diaphragm and podocyte ultrastructure, mediating glomerular crescent formation.…”