Monocyte chemoattractant protein-1 promotes macrophage-mediated tubular injury, but not glomerular injury, in nephrotoxic serum nephritis

Monocyte chemoattractant protein-1 (MCP-1) is upregulated in renal parenchymal cells during kidney disease. To investigate whether MCP-1 promotes tubular and/or glomerular injury, we induced nephrotoxic serum nephritis (NSN) in MCP-1 genetically deficient mice. Mice were analyzed when tubules and glomeruli were severely damaged in the MCP-1-intact strain (day 7). MCP-1 transcripts increased five-fold in MCP-1-intact mice. MCP-1 was predominantly localized within cortical tubules (90%), and most cortical tubules were damaged, whereas few glomerular cells expressed MCP-1 (10%). By comparison, there was a marked reduction (>40%) in tubular injury in MCP-1- deficient mice (histopathology, apoptosis). MCP-1-deficient mice were not protected from glomerular injury (histopathology, proteinuria, macrophage influx). Macrophage accumulation increased adjacent to tubules in MCP-1- intact mice compared with MCP-1-deficient mice (70% P < 0.005), indicating that macrophages recruited by MCP-1 induce tubular epithelial cell (TEC) damage. Lipopolysaccharide-activated bone marrow macrophages released molecules that induced TEC death that was not dependent on MCP-1 expression by macrophages or TEC. In conclusion, MCP- 1 is predominantly expressed by TEC and not glomeruli, promotes TEC and not glomerular damage, and increases activated macrophages adjacent to TEC that damage TEC during NSN. Therefore, we suggest that blockage of TEC MCP-1 expression is a therapeutic strategy for some forms of kidney disease.