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

Abstract

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.

Pathophysiologic Implications of Reduced Podocyte Number in a Rat Model of Progressive Glomerular Injury

“…7,36 In the latter case, podocytes may be found in the urine. [37][38][39] Here, we observed a positive correlation in MWF rats between the capillary tuft volume per podocyte and both urinary protein excretion and incidence of glomerulosclerosis. The intercepts of these plots were 6.1 or 8.6 ϫ 10 3 m 3 , respectively, and might represent the threshold values of glomerular volume, above which proteinuria or glomerulosclerosis would be expected to occur.…”

Regulation of Renal Fatty Acid and Cholesterol Metabolism, Inflammation, and Fibrosis in Akita and OVE26 Mice With Type 1 Diabetes

“…Well-known changes in diabetes-related renal function and structure include mesangial expansion and podocyte injury and loss, which result in glomerulosclerosis, proteinuria, and a decline in glomerular filtration rate (21)(22)(23)(24)(25)(26)(27)(28)(29).…”

α-Actinin-4 Is Required for Normal Podocyte Adhesion

“…1A shows a representative Western blot performed using mouse urinary protein. To detect WT1 expression by Western blot, we used a mouse monoclonal antibody previously shown to be specific for podocytes of mature kidneys (21,27). We have detected urinary podocytes from Actn4 Ϫ/Ϫ mice as early as 8 days of age.…”

“…There have been numerous reports detailing methods to estimate podocyte number and podocyte loss (5,21,27,41). It is difficult to determine an exact number of podocytes per glomerulus given the complex capillary loop structure on which the podocytes reside.…”