Selective impairment of gene expression and assembly of nephrin in human diabetic nephropathy

Benigni, Ariela; Gagliardini, Elena; Tomasoni, Susanna; Abbate, Mauro; Ruggenenti, Piero; Kalluri, Raghu; Remuzzi, Giuseppe

doi:10.1111/j.1523-1755.2004.00636.x

Cited by 118 publications

(103 citation statements)

References 34 publications

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“…These authors suggested a geometric model of the organization of the filtration slit based on a "zipper-like" structure, in which the slit diaphragm is composed by regularly spaced rod-like units extending from the lateral membrane of two adjacent podocyte foot processes to a linear central bar, running longitudinally and parallel to the cell membranes. The distance between the adjacent foot processes membrane was calculated to be 39 nm, in line with more recent reports, [12][13][14][15] and the central filament width was calculated to be 11 nm in diameter. The slit diaphragm was suggested to contain rectangular apertures of 4 ϫ 14 nm, originating from filaments perpendicular to the cell membrane.…”

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confidence: 66%

Imaging of the Porous Ultrastructure of the Glomerular Epithelial Filtration Slit

Gagliardini

Conti

Benigni

et al. 2010

Journal of the American Society of Nephrology

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The ultrastructure of the glomerular filtration slit is still controversial. In the last 30 years, observations from transmission electron microscopy (TEM) and theoretical analysis of solute clearance produced conflicting results. Here, we used scanning EM with a high-sensitivity detector to image the deepest regions of the filtration slits and report a previously undescribed organization of the slits' ultrastructure. In contrast to previous TEM imaging, we observed circular and ellipsoidal pores in the podocyte junctions mainly located in the central region of the slit diaphragm. The normal mean pore radius estimated by digital morphometric analysis had a log-normal distribution, with an average value of 12.1 nm. In proteinuric pathologic conditions, the mean pore radius values were also log-normally distributed with the presence of some very large pores, exceeding the sizes observed in normal conditions. Our morphologic analysis suggests that the filtration slit is a heteroporous structure instead of the previously proposed zipper-like structure. Selective changes in the ultrastructural organization of the pores may be responsible for the increased filtration of plasma proteins in glomerular disease. The permeability properties of the glomerular capillary wall allow the filtration of high water flow and small solutes but efficient retention of plasma proteins the size of albumin or larger. 1 It has been indicated that most of the restriction of macromolecule ultrafiltration is caused by the epithelial filtration slits, because plasma proteins can cross endothelial cells and glomerular basement membrane (GBM) more easily. 2 Changes in glomerular permselective function resulting in increased glomerular filtration of plasma proteins and incomplete tubular reabsorption are responsible for loss of proteins in the urine. These events have been linked to the progression of renal diseases. 3 With the aim to characterize the mechanisms behind proteinuria, in the last 30 years, solute clearance techniques have been used to estimate the selective properties of the glomerular barrier in experimental models of nephropathy and in patients. In particular, glomerular size-selective function has been studied using renal clearance of neutral test macromolecules (i.e., neutral dextran and Ficoll) that are not secreted or reabsorbed at the tubular level. Theoretical models of glomerular size selectivity have been conventionally used to derive intrinsic membrane selective properties from fractional clearance of test macromolecules in terms of density and size of hypothetical pores perforating the glomerular capillary wall. 2,4,5 Thus, according to the two-pore

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supporting

confidence: 66%

Imaging of the Porous Ultrastructure of the Glomerular Epithelial Filtration Slit

Gagliardini

Conti

Benigni

et al. 2010

Journal of the American Society of Nephrology

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“…These findings may be relevant to the pathogenesis of proteinuria in diabetic states. Diabetic nephropathy is associated with structural alterations that contribute to the increased permeability of the glomerular capillary wall to macromolecules (21)(22)(23)(24)(25). The cellular mechanisms leading to loss of permselectivity during progression of diabetic nephropathy are not well characterized.…”

Section: Discussionmentioning

confidence: 99%

“…Changes in the nephrin gene and protein expression are associated with podocyte ultrastructural abnormalities, including reduced presence of electron-dense filamentous structures within the slit diaphragm (25).…”

Section: Zo-1 and Diabetic Nephropathymentioning

confidence: 99%

ZΟ-1 Expression and Phosphorylation in Diabetic Nephropathy

et al. 2006

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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 ...

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“…47 Microalbuminuria in individuals with diabetic nephropathy is considered to arise from increased protein losses in the glomerular filtrate caused by defects in the filtration barrier, which separates the blood circulation from the urinary space. 48 In human and animal diabetic nephropathy, glomerular expression of nephrin is downregulated, 49 and a similar change occurred when Ang-2 overexpression was induced in transgenic (nondiabetic) mice. 43 Experimental models of type 1 diabetes are associated with altered renal expression of angiopoietins.…”

Section: Angiopoietin Expression In Acquired Glomerular Diseasementioning

confidence: 99%