Single‐cell <scp>RNA</scp> sequencing reveals the protective role of renal Cx3cr1 ⁺ macrophages in cisplatin‐induced acute kidney injury

Acute kidney injury (AKI) is a common and often fatal condition characterized by tubular epithelial cell necrosis and immune cell infiltration. The macrophage (MФ) plays multiple roles in kidney injury and repair after AKI. However, the classification and function of MФ subsets involved in AKI remain poorly understood. In this study, kidney bulk-sequencing showed the injury pattern (day 0 to day 3) to repair pattern (day 4 to day 7) after cisplatin-induced AKI (Cis-AKI). Single-cell RNA sequencing of Cis-AKI mouse kidneys dissected the transcriptome heterogeneity of renal MФs, and depletion and adoptive transfer experiments were used to explore the functional distinction of MФ subsets. The single-cell atlas identified four MФ subsets with distinct transcriptomic profiles (Mo-MФ, Mki67⁺MФ, Cd74⁺MФ, Cx3cr1⁺MФ). The dynamic proportion change of MФ subsets from progression to regression analyses revealed that Mo-MФ, defined as recruit-MФ in this study, was primarily distributed in the progression stage, whereas the other MФ subsets, defined as resident-MФ, were dominant in the non-pathological condition and regression stage. By depletion and adoptive transfer experiments, our results confirmed that the Cx3cr1⁺MФ subset plays a crucial role in the protection against Cis-AKI. Further cell coculture experiments revealed that the tyrosine-protein kinase receptor UFO (AXL)-growth arrest-specific protein 6 (GAS6) ligand-receptor pair is involved in regulating the efferocytosis of apoptotic renal tubular epithelial cells by Cx3cr1⁺MФs, representing one of the molecular mechanisms in promoting kidney repair. In conclusion, our study dissected the heterogeneity of renal macrophage subsets during Cis-AKI, and the discovery of the protective Cx3cr1⁺MФ subset may provide new therapeutic targets for AKI intervention.