Differential Ly6C Expression after Renal Ischemia-Reperfusion Identifies Unique Macrophage Populations

Abstract

Macrophages are a heterogeneous cell type implicated in injury, repair, and fibrosis after AKI, but the macrophage population associated with each phase is unclear. In this study, we used a renal bilateral ischemiareperfusion injury mouse model to identify unique monocyte/macrophage populations by differential expression of Ly6C inCD11b+ cells and todefine the functionof these cells in the pathophysiologyofdiseaseon the basis of microarray gene signatures and reduction strategies. Macrophage populations were isolated from kidney homogenates by fluorescence-activated cell sorting for whole genome microarray analysis. The CD11b+/Ly6Chigh population associated with the onset of renal injury and increase in proinflammatory cytokines, whereas the CD11b+/Ly6Cintermediate population peaked during kidney repair. The CD11b+/Ly6Clow population emerged with developing renal fibrosis. Principal component and hierarchical cluster analyses identified gene signatures unique to each population. The CD11b+/Ly6Cintermediate population had a distinct phenotype of wound healing, confirmed by results of studies inhibiting the macrophage colony-stimulating factor 1 receptor,whereas the CD11b+/Ly6Clow population had a profibrotic phenotype. All populations, including the CD11b+/Ly6Chigh population, carried differential inflammatory signatures. The expression of M2-specific markers was detected in both the CD11b+/Ly6Cintermediate and CD11b+/Ly6Clow populations, suggesting these in vivo populations do not fit into the traditional classifications defined by in vitro systems. Results of this study in a renal ischemia-reperfusion injury model allow phenotype and function to be assigned to CD11b+/Ly6C+ monocyte/macrophage populations in the pathophysiology of disease after AKI.