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      Viable Podocytes Detach in Experimental Diabetic Nephropathy: Potential Mechanism Underlying Glomerulosclerosis

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          Background: A decrease in podocyte number contributes to the development of glomerulosclerosis in diabetic nephropathy. Although podocytes have been detected in the urine in certain glomerular diseases, their viability is poorly understood. Methods: Diabetes was induced in rats with streptozotocin. Urine was collected from control rats (given citrate), and rats with diabetic nephropathy, and cells obtained by centrifugation were resuspended in tissue culture media, and seeded onto collagen-coated tissue culture plates. Cells were grown under standard cell culture conditions ex vivo. Cell number was measured, the cell type in the urine was identified by immunostaining with specific antibodies, and morphology was assessed by light and electron microscopy. Results: Within 24 h, cells obtained from the urine of diabetic rats attached to tissue culture plates ex vivo. Cells were not detected in the urine from control rats. All cells from diabetic rats stained positive for the podocyte-specific proteins synaptopodin, nephrin, podocin and Glepp-1 and negative for mesangial (OX-7), tubular (Tamm-Horsfall protein) and endothelial (RECA) cell antigens. The cell number increased daily, which is consistent with cell growth ex vivo. Conclusions: Rats with diabetic nephropathy shed podocytes into the urine that attach and grow ex vivo. These results are consistent with the detachment of viable podocytes in diabetes and add new perspectives into our understanding of development of glomerulosclerosis in diabetes mellitus.

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          Most cited references 22

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          Podocyte depletion and glomerulosclerosis have a direct relationship in the PAN-treated rat.

          Podocytes are highly differentiated glomerular epithelial cells with limited potential to divide. They are responsible for maintaining and supporting the glomerular basement membrane so as to facilitate efficient filtration. The hypothesis tested was whether the development of glomerulosclerosis in the puromycin aminonucleoside (PAN)-treated rat could be attributed to podocyte depletion. PAN was injected in Sprague-Dawley rats once, twice, or three times at 30-day intervals. Podocytes were counted in glomeruli using immunoperoxidase histochemistry and antibodies to both GLEPP1 (PTPRO) and WT-1. Podocytes were assayed in urine using reverse transcription-quantitative polymerase chain reaction (RT-QPCR). Glomerular areas were measured by computerized morphometry. In a preliminary experiment, a single injection of PAN caused a reduction in the glomerular podocyte count by 25%. Additional independent confirmation that podocytes were lost from glomeruli after PAN injection was obtained identifying detached podocytes in Bowman's space, measurement of nephrin and GLEPP1 mRNAs in urine, ultrastructural analysis of glomeruli, and identification of TUNEL-positive apoptotic podocytes in glomeruli. In a second experiment, sequential podocyte depletion by 15, 31, and 53% was achieved by the administration of one, two, or three injections of PAN at 30-day intervals. The region of the glomerulus devoid of podocytes developed glomerulosclerosis, and this area progressively increased as podocytes were progressively depleted. The correlation coefficient (r(2)) value for the relationship between percent podocyte depletion and glomerulosclerotic area was 0.99. The Y intercept of this plot showed that glomerulosclerosis was initiated when only 10 to 20% of podocytes were lost. This report supports the growing body of data linking glomerulosclerosis directly to a reduction in relative podocyte number [increased glomerular area per podocyte (GAPP)]. It raises important questions related to the mechanisms of podocyte loss, strategies for prevention of podocyte depletion, and the prevention of progression of glomerular diseases.
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            Apoptosis in podocytes induced by TGF-β and Smad7

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              Urinary excretion of podocytes in patients with diabetic nephropathy.

              Detection of podocytes in the urinary sediments of children with glomerulonephritis has been shown to indicate severe injury to the podocytes. The aim of the present study was to determine whether podocytes are present in the urine sediments of adult patients with diabetes with and without nephropathy and whether trandolapril is effective for podocyte injury. Fifty diabetic patients (10 with normoalbuminuria, 15 with microalbuminuria, 15 with macroalbuminuria and 10 with chronic renal failure) and 10 healthy controls were studied. Urinary podocytes were examined by immunofluorescence using monoclonal antibodies against podocalyxin, which is present on the surface of podocytes. In addition, we studied plasma metalloproteinase (MMP)-9 concentrations in all patients. Urinary podocytes were absent in healthy controls, diabetic patients with normoalbuminuria and diabetic patients with chronic renal failure. Podocytes were detected in the urine of eight diabetic patients with microalbuminuria (53%) and of 12 patients with macroalbuminuria (80%). The number of podocytes in the urine of patients with macroalbuminuria was significantly greater than in patients with microalbuminuria (P:<0.01). However, there was no relationship between urinary albumin excretion and urinary podocytes. In addition, plasma MMP-9 concentrations were significantly correlated with the number of urinary podocytes (P:<0.01). Twelve diabetic patients with macroalbuminuria and eight patients with microalbuminuria who had urinary podocytes were treated with the angiotensin-converting enzyme inhibitor trandolapril. Urinary albumin excretion, the number of podocytes and plasma MMP-9 concentrations were reduced by the trandolapril treatment. Podocytes in the urine may be a useful marker of disease activity in diabetic nephropathy. Trandolapril may be effective for podocyte injury.

                Author and article information

                Nephron Exp Nephrol
                Cardiorenal Medicine
                S. Karger AG
                December 2004
                22 December 2004
                : 98
                : 4
                : e114-e123
                aDepartment of Medicine, Division of Nephrology, University of Washington School of Medicine, Seattle, Wash., USA; bDepartment of Medicine, Division of Nephrology, University of Aachen, Aachen, Germany
                81555 Nephron Exp Nephrol 2004;98:e114–e123
                © 2004 S. Karger AG, Basel

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                Figures: 7, Tables: 1, References: 30, Pages: 1
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