Effects of Tumor Necrosis Factor-alpha on Podocyte Expression of Monocyte Chemoattractant Protein-1 and in Diabetic Nephropathy

Abstract

Background/Aims: Tumor necrosis factor (TNF)-alpha is believed to play a role in diabetic kidney disease. This study explores the specific effects of TNF-alpha with regard to nephropathy-relevant parameters in the podocyte. Methods: Cultured mouse podocytes were treated with recombinant TNF-alpha and assayed for production of monocyte chemoattractant protein-1 (MCP-1) by enzyme-linked immunosorbent assay (ELISA). TNF-alpha signaling of MCP-1 was elucidated by antibodies against TNF receptor (TNFR) 1 or TNFR2 or inhibitors of nuclear factor-kappaB (NF kappa B), phosphatidylinositol 3-kinase (PI3K) or Akt. In vivo studies were done on male db/m and type 2 diabetic db/db mice. Levels of TNF-alpha and MCP-1 were measured by RT-qPCR and ELISA in the urine, kidney and plasma of the two cohorts and correlated with albuminuria. Results: Podocytes treated with TNF-alpha showed a robust increase (similar to 900%) in the secretion of MCP-1, induced in a dose-and time-dependent manner. Signaling of MCP-1 expression occurred through TNFR2, which was inducible by TNF-alpha ligand, but did not depend on TNFR1. TNF-alpha then proceeded via the NF-kappa B and the PI3K/Akt systems, based on the effectiveness of the inhibitors of those pathways. For in vivo relevance to diabetic kidney disease, TNF-alpha and MCP-1 levels were found to be elevated in the urine of db/db mice but not in the plasma. Conclusion: TNF-alpha potently stimulates podocytes to produce MCP-1, utilizing the TNFR2 receptor and the NF-kappa B and PI3K/Akt pathways. Both TNF-alpha and MCP-1 levels were increased in the urine of diabetic db/db mice, correlating with the severity of diabetic albuminuria. (C) 2015 S. Karger AG, Basel