MCP-1/CCR2 system is involved in podocyte apoptosis under diabetic conditions

Abstract

Previous studies have demonstrated the importance of monocyte chemoattractant protein-1 (MCP-1) in the pathogenesis of diabetic nephropathy in terms of inflammation, but the direct role of MCP-1 and its receptor (CCR2) on podocyte apoptosis under diabetic conditions has never been explored. In vitro, mouse podocytes were exposed to a medium containing 5.6 mM glucose or 30 mM glucose (HG) with or without mutant MCP-1 (mMCP-1), CCR2 small interfering RNA (siRNA), or CCR2 inhibitor (RS102895). To examine the relationship between MCP-1 and transforming growth factor-β1 (TGF-β1), podocytes were also treated with MCP-1 (20 ng/ml) or TGF-β1 (2 ng/ml) with or without anti-TGF-β1 antibody, mutant MCP-1 (mMCP-1), CCR2 siRNA, or CCR2 inhibitor. In vivo, 32 rats were intraperitoneally injected with a diluent (C, n=16) or streptozotocin (DM, n=16). Eight rats from each group were treated with empty lentivirus vector (LV-empty) or lentivirus vector containing mMCP-1 (LV-mMCP-1). Western blot for active fragments of caspase-3 was performed with cell lysates and isolated glomeruli. Apoptosis was also identified by Hoechst 33342 and TUNEL staining. HG-induced apoptosis and TGF-β1 levels were significantly abrogated by the administration of mMCP-1, CCR2 siRNA, and RS102895. Treatment with MCP-1 directly increased active fragments of caspase-3 protein expression and apoptotic cells, and these increases were ameliorated by anti-TGF-β1 antibody. TGF- β1-induced apoptosis was also significantly attenuated by the inhibition of the MCP-1/CCR2 system. In addition, glomerular expression of active fragments of casapse-3 and apoptotic cells within glomeruli were significantly decreased in the DM-LV-mMCP-1 group compared to the DM-LV-empty group. These results suggest that interactions between the MCP-1/CCR2 system and TGF-β1 may contribute to podocyte apoptosis under diabetic conditions.