Tubular GM-CSF Promotes Late MCP-1/CCR2-Mediated Fibrosis and Inflammation after Ischemia/Reperfusion Injury

Significance Statement Clinical evidence suggests that monocyte chemoattractant protein-1 (MCP-1) may be a useful biomarker to identify patients at risk for kidney fibrosis and CKD progression. Using a mouse model of unilateral ischemia/reperfusion injury (U-IRI), the authors show that sustained GM-CSF expression by renal tubular cells markedly increases Mcp-1 expression in macrophages during the transition from normal kidney repair to maladaptive fibrosis. Eliminating CCR2, the receptor of MCP-1, by using genetic engineering or a drug that blocks CCR2 decreases the accumulation and persistence of macrophages, dendritic cells, and T cells in the kidney, and reduces fibrosis and inflammation after a U-IRI. The results highlight the role of GM-CSF/MCP-1 signaling during the transition from AKI to CKD and suggest that therapeutic inhibition of MCP-1/CCR2 signaling may suppress kidney fibrosis. 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 of macrophages and tubular cells. Mice genetically engineered to lack Ccr2 and wild-type mice were treated ±CCR2 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 ) by macrophages. Analysis of CD45 + immune cells isolated from wild-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 following U-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.