Role of M2 Macrophages in Sepsis-Induced Acute Kidney Injury.

BACKGROUND: Sepsis is a major cause of acute kidney injury (AKI), with high rates of morbidity and mortality. M2 macrophages have been shown to play important roles in the secretion of anti-inflammatory and tissue repair mediators. In this study, we investigate the role of M2 macrophages in sepsis-induced AKI by depleting these cells in vivo through the systemic administration of liposomal clodronate (LC).

METHODS: Male Sprague-Dawley rats were subjected to cecal ligation and puncture (CLP) or sham surgery. Biochemical and histological renal damage was assessed. Macrophage infiltration and M2 macrophage depletion were assessed by immunohistochemistry. RT-PCR was used to investigate the expression of the inducible nitric oxide synthase (iNOS), arginase 1 (Arg-1), and found in inflammatory zone 1 (FIZZ1) mRNAs. Western blots were performed to assay the tissue levels of interleukin-10 (IL-10) and tumor necrosis factor alpha (TNF-α).

RESULTS: M2 macrophages were obviously detected 72 h after sepsis-induced AKI. Kidney injury was more severe, renal function was decreased, and blood creatinine and blood urea nitrogen (BUN) levels were higher after M2 macrophage depletion. M2 macrophage depletion significantly inhibited the proliferation of tubular cells. M2 macrophage depletion also downregulated IL-10 expression and increased TNF-α secretion during sepsis-induced AKI.

CONCLUSIONS: M2 macrophages attenuate sepsis-induced AKI, presumably by upregulating IL-10 expression and suppressing TNF-α secretion.