Expression of TGF-β-induced matrix protein βig-h3 is up-regulated in the diabetic rat kidney and human proximal tubular epithelial cells treated with high glucose

Abstract

Backgrounds. βig-h3 is an extracellular matrix protein whose expression in several cell types is greatly increased by transforming growth factor-β (TGF-β). TGF-β is believed to be involved in the development of diabetic nephropathy and thus we have assessed the possibility that βig-h3 may be a down-stream molecule in this pathogenic process. Methods. Immunoblotting and immunohistochemistry were done using an antibody against mouse βig-h3 protein. βig-h3 and TGF-β concentrations were measured by enzyme-linked immunosorbent assay (ELISA). Cell adhesion and migration were assessed by measuring activity of N-acetyl-β-D-glucosaminidase and using a transwell plate, respectively. Results. Immunohistochemistry revealed that βig-h3 occurs mainly in the basement membrane of proximal tubules, particularly the S3 segment but also to lesser extents in the basement membranes of the cortical thick ascending limb cells and the parietal glomerular epithelial cells in Bowman's capsule. Immunoblotting revealed that ∼68 kD bands were seen only in the cortex + the outer stripe of the outer medulla. Rats with streptozotocin (STZ)-induced diabetes exhibited a marked and sustained increase in renal βig-h3 abundance. This was mirrored by urinary βig-h3 levels. In vitro experiments with human primary renal proximal tubular epithelial cells revealed that their expression of βig-h3 was greatly increased by either TGF-β or glucose. High glucose levels also stimulated TGF-β production by renal proximal tubular epithelial cells and the high glucose-induced βig-h3 expression was almost completely blocked by anti-TGF-β antibody. βig-h3 mediated renal proximal tubular epithelial cells adhesion and migration. Conclusion. βig-h3 may be important in the development of diabetic nephropathy. Furthermore, the level of urinary βig-h3 may be useful as an early marker reflecting disease onset and progression.