Characterizing the role of macrophages in cisplatin-induced kidney injury and progression to chronic kidney disease.

Abstract

Cisplatin is a commonly used chemotherapeutic for treatment of many solid-organ cancers. Unfortunately, 30% 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). While traditional rodent toxicity studies have utilized a single, lethal dose of cisplatin, new models of cisplatin-induced kidney injury have 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. C57BL/6 mice are one of the most used mouse strains in research; however, they are resistant to chronic kidney disease-associated pathologies. While repeated 7 mg/kg cisplatin doses induce kidney fibrosis in FVB/n mice, we found that treating C57BL/6 mice with this same dosing regimen does not result in kidney fibrosis. Here, we demonstrate that increasing the dose of cisplatin to 9 mg/kg is sufficient to consistently induce fibrosis in C57BL/6 mice. In addition, we present that cohorts of C57BL/6 mice purchased from Jackson one year apart and mice bred in house display variability in renal outcomes following repeated low dose cisplatin treatment. This variability revealed CCL2 as a marker of cisplatin-induced kidney injury through correlation studies. In addition, significant myeloid cell infiltration was observed in the kidney after four doses of 9 mg/kg cisplatin, indicating macrophages are present during the AKI-to-CKD transition. To further evaluate the role of macrophages in cisplatin-induced fibrosis, we used either C57BL/6 mice with Ccr2 genetic knockout or liposome encapsulated clodronate (Clodrosome) to deplete macrophage populations during repeated, 9 mg/kg cisplatin treatments. We found that Ccr2-/- mice had decreased levels of infiltrating macrophages in the kidney following cisplatin treatments. In contrast, Clodrosome treatment depleted resident and M2 macrophages in the kidney following cisplatin treatment. Furthermore, Clodrosome treatment decreased collagen deposition, myofibroblast accumulation, and inflammatory cytokine production, while Ccr2 genetic knockout had no effect on these markers following cisplatin treatment. These data suggest that Clodrosome depletion of resident and M2 macrophages in the kidney attenuates development of renal fibrosis following repeated, low doses of cisplatin.