Diabetic nephropathy (DN) is the leading cause of end-stage renal disease, partly because of the lack of effective treatments for DN. Curcumin has been shown to exert strong antifibrotic effects in DN, but the underlying mechanisms are not well characterized. In this study, we sought to determine the effects of curcumin on diabetic renal disease in db/db mice and characterize the underlying mechanism of action. We administered curcumin to db/db mice for 16 weeks. In comparison to mock-treated db/db mice, curcumin-treated mice showed diminished renal hypertrophy, reduced mesangial matrix expansion, and a lower level of albuminuria. Furthermore, the upregulated protein and mRNA expressions of collagen IV and fibronectin in the renal cortices of the db/db mice were inhibited by curcumin treatment. Additionally, curcumin treatment was associated with significant reductions in mature interleukin-1β, cleaved caspase-1, and NLRP3 protein levels in the renal cortices of db/db mice as well as in HK-2 cells exposed to high glucose concentration. In summary, curcumin, a potent antifibrotic agent, is a promising treatment for DN, and its renoprotective effects appear to be mediated by the inhibition of NLRP3 inflammasome activity.
We investigated whether microRNA-150 (miR-150)-based RNA interference (RNAi) ameliorates tubular injury and tubulointerstitial fibrosis. Mice injected with folic acid developed tubulointerstitial fibrosis at day 30. miR-150 levels were increased at day 7 and peaked at day 30. At day 30, protein levels of α-smooth muscle actin, fibronectin (FN), and collagen 1 (COL-1) were increased, while suppressor of cytokine signal 1 (SOCS1) was decreased. Kidneys manifested increased macrophage numbers and increased expression of potential mediators: interferon-γ, interleukin-6, and tumor necrosis factor-α. Locked nucleic acid-anti-miR-150, started prior to or after tubular injury and administered twice weekly for 4 weeks, reversed renal inflammation and fibrosis. In HK-2 cells, co-culture with macrophages increased miR-150 expression and decreased SOCS1. Janus kinase (JAK) and signal transducer and activators of transcription (STAT) pathway-related proteins p-JAK1, p-JAK2, p-STAT1, p-STAT3, and pro-fibrotic genes encoding α-smooth muscle actin, FN, and COL-1 were all upregulated. The miR-150 antagonist reversed these transcriptional changes. Lastly, in renal biopsies from patients with chronic interstitial fibrosis, renal miR-150, and pro-fibrotic gene expression and macrophage numbers were increased, while SOCS1 expression was decreased. In conclusion, miR-150-based RNAi is as a potential novel therapeutic agent for tubulointerstitial fibrosis, suppressing the SOCS1/JAK/STAT pathway and reducing macrophage influx.
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