Quercetin alleviates diabetic nephropathy by inhibiting M1 macrophage polarization via targeting NLRC5/NLRP3 pathway

The activation imbalance of M1/M2 macrophage phenotypes is crucial in diabetic nephropathy (DN). This study aimed to explore the molecular mechanisms underlying quercetin's action against DN.

In vitro, RAW 264.7 macrophages were incubated with high glucose (HG) with or without quercetin. Overexpression of NLRC5 was investigated to elucidate the mechanism. M1/M2 macrophage differentiation was assessed by flow cytometry using cell surface markers CD86 and CD206. In vivo, a DN mouse model was created using a high-fat diet and streptozotocin (STZ). Quercetin was administered intragastrically to DN mice at 50 mg/kg and 100 mg/kg. After euthanasia, mouse kidneys were analyzed by hematoxylin and eosin (H&E), Masson's trichrome, and immunohistochemistry (IHC) staining. ELISA assay and western blot analysis were performed to determine related molecular levels.

In vitro, quercetin significantly reduced HG-induced expressions of CD86, iNOS, NLRC5, NLRP3, and pro-inflammatory cytokines (TNF-α, IL-6, IL-1β), while increasing HG-induced CD206, Arg-1, and IL-10 in RAW 264.7 macrophages. However, these effects of quercetin were abolished when NLRC5 was overexpressed. In DN mice, quercetin administration ameliorated renal histopathological injury and fibrosis. Notably, there was a significant reduction in expressions of NLRC5, NLRP3, Col1a1, and α-SMA, along with decreased expressions of pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β).

This study showed that quercetin improves DN by inhibiting M1-type macrophages through targeting the NLRC5/NLRP3 pathway.