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Metformin attenuates renal tubulointerstitial fibrosis via upgrading autophagy in the early stage of diabetic nephropathy.

ABSTRACT: This study aimed at comparing the effects of metformin on tubulointerstitial fibrosis (TIF) in different stages of diabetic nephropathy (DN) in vivo and evaluating the mechanism in high glucose (HG)-treated renal tubular epithelial cells (RTECs) in vitro. Sprague-Dawley (SD) rats were used to establish a model of DN, and the changes of biochemical indicators and body weight were measured. The degree of renal fibrosis was quantified using histological analysis, immunohistochemistry, and immunoblot. The underlying relationship between autophagy and DN, and the cellular regulatory mechanism of metformin on epithelial-to-mesenchymal transition (EMT) were investigated. Metformin markedly improved renal function and histological restoration of renal tissues, especially in the early stages of DN, with a significant increase in autophagy and a decrease in the expression of fibrotic biomarkers (fibronectin and collagen I) in renal tissue. Under hyperglycemic conditions, renal tubular epithelial cells inactivated p-AMPK and activated partial EMT. Metformin-induced AMPK significantly ameliorated renal autophagic function, inhibited the partial EMT of RTECs, and attenuated TIF, all of which effectively prevented or delayed the onset of DN. This evidence provides theoretical and experimental basis for the following research on the potential clinical application of metformin in the treatment of diabetic TIF.

SUBMITTER: Wang F

PROVIDER: S-EPMC8357942 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundRenal tubulointerstitial fibrosis is the hallmark of various chronic kidney diseases. Symmetric dimethylarginine (SDMA) is an independent cardiovascular risk factor in patients with chronic kidney diseases, which is mostly excreted through renal tubules. However, the effect of SDMA on kidneys in a pathological condition is currently unknown. In this study, we investigated the role of SDMA in renal tubulointerstitial fibrosis and explored its underlying mechanisms.MethodsMouse unilateral ureteral obstruction (UUO) and unilateral ischemia-reperfusion injury (UIRI) models were established to study renal tubulointerstitial fibrosis. SDMA was injected into kidneys through ureter retrogradely. TGF-β stimulated human renal epithelial (HK2) cells were used as an in vitro model and treated with SDMA. Signal transducer and activator of transcription-4 (STAT4) was inhibited by berbamine dihydrochloride or siRNA or overexpressed by plasmids in vitro. Masson staining and Western blotting were performed to evaluate renal fibrosis. Quantitative PCR was performed to validate findings derived from RNA sequencing analysis.ResultsWe observed that SDMA (from 0.01 to 10 µM) dose-dependently inhibited the expression of pro-fibrotic markers in TGF-β stimulated HK2 cells. Intrarenal administration of SDMA (2.5 µmol/kg or 25 µmol/kg) dose-dependently attenuated renal fibrosis in UUO kidneys. A significant increase in SDMA concentration (from 19.5 to 117.7 nmol/g, p < 0.001) in mouse kidneys was observed after renal injection which was assessed by LC-MS/MS. We further showed that intrarenal administration of SDMA attenuated renal fibrosis in UIRI induced mouse fibrotic kidneys. Through RNA sequencing analysis, we found that the expression of STAT4 was reduced by SDMA in UUO kidneys, which was further confirmed by quantitative PCR and Western blotting analysis in mouse fibrotic kidneys and renal cells. Inhibition of STAT4 by berbamine dihydrochloride (0.3 mg/ml or 3.3 mg/ml) or siRNA reduced the expression of pro-fibrotic markers in TGF-β stimulated HK2 cells. Furthermore, blockage of STAT4 attenuated the anti-fibrotic effect of SDMA in TGF-β stimulated HK2 cells. Conversely, overexpression of STAT4 reversed the anti-fibrotic effect of SDMA in TGF-β stimulated HK2 cells.ConclusionTaken together, our study indicates that renal SDMA ameliorates renal tubulointerstitial fibrosis through inhibition of STAT4.

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Metformin attenuates renal tubulointerstitial fibrosis via upgrading autophagy in the early stage of diabetic nephropathy.

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