The MCP-1/CCR2 axis in podocytes is involved in apoptosis induced by diabetic conditions

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 the MCP-1/CCR2 system on podocyte apoptosis under diabetic conditions has never been explored. In vitro, mouse podocytes were exposed to a medium containing 30 mM glucose (HG) with or without CCR2 siRNA or CCR2 inhibitor (RS102895). Podocytes were also treated with MCP-1 or TGF-beta 1 with or without anti-TGF-beta 1 antibody, CCR2 siRNA, or CCR2 inhibitor. In vivo, 20 db/m and 20 db/db mice were divided into two groups, and ten mice from each group were treated with RS102895. Western blot and Hoechst 33342 or TUNEL staining were performed to identify apoptosis. HG-induced apoptosis and TGF-beta 1 levels were significantly abrogated by CCR2 inhibition. In addition, treatment with MCP-1 directly induced apoptosis via CCR2. Moreover, TGF-beta 1- and MCP-1-induced apoptosis were significantly ameliorated by the inhibition of CCR2 and anti-TGF-beta 1 antibody, respectively. Glomerular expression of cleaved caspase-3 and apoptotic cells within glomeruli were also significantly increased in db/db mice compared to db/m mice, and these increases were significantly attenuated in db/db + RS102895 mice. These results suggest that interactions between the MCP-1/CCR2 system and TGF-beta 1 may contribute to podocyte apoptosis under diabetic conditions.