Tubular GM-CSF promotes late MCP-1/CCR2-mediated fibrosis and inflammation after ischemia/reperfusion injury

Abstract

Background After bilateral kidney ischemia/reperfusion injury (IRI), monocytes infiltrate the kidney and differentiate into proinflammatory macrophages in response to the initial kidney damage, and then transition to a form that promotes kidney repair. In the setting of unilateral IRI (U-IRI), however, we have previously shown that macrophages persist beyond the time of repair and may promote fibrosis. Methods Macrophage homing/survival signals were determined at 14 days after injury in mice subjected to U-IRI and in vitro using coculture ofmacrophages and tubular cells.Mice genetically engineered to lack Ccr2 and wild-type mice were treated 6CCR2 antagonist RS102895 and subjected to U-IRI to quantify macrophage accumulation, kidney fibrosis, and inflammation 14 and 30 days after the injury. Results Failure to resolve tubular injury after U-IRI results in sustained expression of granulocyte-macrophage colony-stimulating factor by renal tubular cells, which directly stimulates expression of monocyte chemoattractant protein-1 (Mcp-1) bymacrophages. AnalysisofCD45+ immune cells isolated fromwild-type kidneys 14 days after U-IRI reveals high-level expression of the MCP-1 receptor Ccr2. In mice lacking Ccr2 and wild-type mice treated with RS102895, the numbers of macrophages, dendritic cells, and T cell decreased followingU-IRI, as did the expression of profibrotic growth factors and proimflammatory cytokines. This results in a reduction in extracellular matrix and kidney injury markers. Conclusions GM-CSF-induced MCP-1/CCR2 signaling plays an important role in the cross-talk between injured tubular cells and infiltrating immune cells and myofibroblasts, and promotes sustained inflammation and tubular injury with progressive interstitial fibrosis in the late stages of U-IRI.