Arginase-1 Is Required for Macrophage-Mediated Renal Tubule Regeneration

After kidney injury, macrophages transition from initial proinflammatory activation to a proreparative phenotype characterized by expression of arginase-1 ( ), mannose receptor 1 ( ), and macrophage scavenger receptor 1 ( ). The mechanism by which these alternatively activated macrophages promote repair is unknown. We characterized the macrophage and renal responses after ischemia-reperfusion injury with contralateral nephrectomy in mice and littermate controls and used coculture of macrophages and tubular cells to determine how macrophage-expressed arginase-1 promotes kidney repair. After ischemia-reperfusion injury with contralateral nephrectomy, -expressing macrophages were almost exclusively located in the outer stripe of the medulla adjacent to injured S3 tubule segments containing luminal debris or casts. Macrophage expression was reduced by more than 90% in injured mice, resulting in decreased mouse survival, decreased renal tubular cell proliferation and decreased renal repair compared with littermate controls. studies demonstrate that tubular cells exposed apically to dead cell debris secrete high levels of GM-CSF and induce reparative macrophage activation, with those macrophages in turn secreting -dependent factor(s) that directly stimulate tubular cell proliferation. GM-CSF-induced, proreparative macrophages express arginase-1, which is required for the S3 tubular cell proliferative response that promotes renal repair after ischemia-reperfusion injury.