Abstract 549: An Up-regulation Of Matrix Metalloproteinase-9 In Parietal Epithelial Cells Is Associated With A Progressive Podocyte Loss In Diabetic Glomerulopathy

Abstract

As a subfamily of matrix metalloproteinases (MMPs), gelatinases including MMP-2 and MMP-9 play an important role in the remodeling and homeostasis of the extracellular matrix. However, conflicting results have been reported regarding their expression level and activity in the diabetic kidney. This study investigated whether MMP-9 expression and activity were changed in glomerular epithelial cells upon albumin overload. Immunostaining, in situ zymography and Western blot for renal protein expression and MMP activity were evaluated in Zucker lean (Fa/+) and Zucker diabetic fatty (Fa/Fa) rats. Confocal microscopy revealed a focal increase in gelatinase activity and MMP-9 protein in the glomeruli of Fa/Fa rats. Increased glomerular MMP-9 staining was mainly observed in hyperplastic parietal epithelial cells expressing claudin-1 in the diabetic kidneys. Interestingly, an increase in parietal MMP-9 was often accompanied by decreased staining for podocyte markers (nephrin and podocalyxin) in the adjacent area. Additionally, urinary excretion of nephrin and podocalyxin was progressively increased in association with the levels of MMP-9 and total protein in the urine of diabetic animals. To evaluate the direct effect of albumin on expression and activity of MMP-2 and MMP-9, primary cultured rat glomerular parietal epithelial cells were incubated with exogenous albumin. MMP-9 mRNA levels were significantly increased by 306%, 565%, and 829% (n=4-6), respectively, when the cells were exposed to rat serum albumin (0.25, 0.5 and 1 mg/ml) for 24 hour. Meanwhile, albumin administration resulted in a dose-dependent increase in MMP-9 protein (7.4-, 14.1-, and 21.1-fold, respectively) and activity (3.2-, 4.5-, and 6.7-fold, respectively) in the culture supernatants of parietal epithelial cells. In contrast, albumin treatment did not significantly alter the expression level and enzymatic activity of MMP-2 in cultured parietal epithelial cells. Taken together, we have demonstrated that an up-regulation of MMP-9 in activated parietal epithelium is associated with a progressive loss of adjacent podocytes during the development of diabetic glomerulopathy. Albumin overload also induces MMP-9 production in primary cultured glomerular epithelial cells.