Expression and localization of MT1-MMP and furin in the glomerular wall of short- and long-term diabetic rats

Diabetic glomerulopathy has been linked to shifts in balance between the synthetic and degradative pathways of the glomerular basement membrane (GBM), a key player in the permselectivity properties of the glomerular wall. The goal of this study was to trace the expression and localization of membrane type-1 metalloprotease (MT1-MMP) and its activating enzyme furin, key proteins involved in basement membrane turnover, in short- and long-term diabetic rat renal tissues. Quantitative immunogold was carried out for MT1-MMP and furin and their expression was evaluated in renal tissues of young and old, control and diabetic rats. To corroborate immunocytochemical findings, Western blots were performed on glomerular lysates. Electron microscopy revealed that the overall expression of MT1-MMP and furin is reduced in plasma membranes of all glomerular cell types of old normoglycemic animals, a phenomenon that is exacerbated in long-term diabetic animals. This observation supports the prevailing theory that diabetes fosters acceleration in the aging process. Interestingly, while biochemical results confirmed a decrease in MT1-MMP expression, an increase in furin was observed. Immunocytochemical studies resolved this discrepancy by tracing the increased furin expression in endoplasmic reticulum and Golgi membranes of podocytes, indicating that furin is retained in the secretory pathway in a diabetic environment. Disturbances at the molecular level of the otherwise tightly regulated MT1-MMP/furin interactions found at the cell surface must account for a lack in extracellular matrix remodeling, increased deposition of GBM material, and loss of glomerular filtration integrity.