F4/80^hi Resident Macrophages Contribute to Cisplatin-Induced Renal Fibrosis

Cisplatin-induced kidney injury remains a major obstacle in utilizing cisplatin as a chemotherapeutic for solid-organ cancers. Thirty percent of patients treated with cisplatin develop acute kidney injury (AKI), and even patients who do not develop AKI are at risk for long-term declines in kidney function and development of chronic kidney disease (CKD). Modeling cisplatin-induced kidney injury in mice has revealed that repeated low doses of cisplatin lead to development of kidney fibrosis. This model can be used to examine AKI-to-CKD transition processes. Macrophages play a role in some of these processes, including immune response, wound healing, and tissue remodeling. Depleting macrophage populations in the kidney reduced fibrosis development in other models of renal fibrosis.

We used either C57BL/6 mice with a Ccr2 genetic knockout or liposome encapsulated clodronate (Clodrosome) to deplete macrophage populations during repeated 9 mg/kg cisplatin treatments. We assessed how immune cell populations were altered in the blood and kidney of these mice and how these alterations affected development of renal fibrosis and kidney injury.

We found that Clodrosome treatment decreased collagen deposition, myofibroblast accumulation, and inflammatory cytokine production, whereas Ccr2 genetic knockout had no effect on these markers after cisplatin treatment. Additionally, Ccr2^-/- mice had decreased levels of F4/80^lo infiltrating macrophages in the kidney after cisplatin treatments, but Clodrosome treatment depleted F4/80^hi resident and CD206⁺ M2 macrophages.

These data suggest that Clodrosome depletion of F4/80^hi and M2 macrophages in the kidney attenuates development of renal fibrosis after repeated low doses of cisplatin.