Zinc Alleviates Diabetic Muscle Atrophy via Modulation of the SIRT1/FoxO1 Autophagy Pathway Through GPR39
Xing Yu, Xiaojun Chen, Weibin Wu, Huibin Tang, Yunyun Su, Guili Lian, Yujie Zhang, Liangdi Xie
Abstract
BACKGROUND: Muscle atrophy is a severe complication of diabetes, with autophagy playing a critical role in its progression. Zinc has been shown to alleviate hyperglycaemia and several diabetes-related complications, but its direct role in mediating diabetic muscle atrophy remains unclear. This study explores the potential role of zinc in the pathogenesis of diabetic muscle atrophy. METHODS: In vivo, C57BL/6J mice were induced with diabetes by streptozotocin (STZ) and treated with ZnSO₄ (25 mg/kg/day) for six weeks. Gastrocnemius muscles were collected for histological analysis, including transmission electron microscopy (TEM). Serum zinc levels were measured by ICP-MS. Protein expression was evaluated using immunofluorescence (IF), immunohistochemistry (IHC) and Western blotting (WB). Bioinformatics analysis was used to identify key genes associated with muscle atrophy. In vitro, a high-glucose-induced diabetic C2C12 cell model was established and received ZnSO₄, rapamycin, SRT1720, TC-G-1008, or GPR39-CRISPR Cas9 intervention. Autophagy was observed by TEM, and protein expression was assessed by IF and WB. Intracellular zinc concentrations were measured using fluorescence resonance energy transfer (FRET). RESULTS: ), and serum zinc levels (0.2335 ± 0.0227 vs. 0.1561 ± 0.0123 mg/L). ZnSO₄ down-regulated the expression of Atrogin-1 and MuRF1, and decreased the formation of autophagosomes in the gastrocnemius muscle of T1D mice (all p < 0.0001). RNA-seq analysis indicated activation of the SIRT1/FoxO1 signalling pathway in diabetic mice. ZnSO₄ down-regulated LC3B, SIRT1 and FoxO1, while upregulating P62 and GPR39 (all p < 0.05). In vitro, muscle atrophy, autophagy activation, and down-regulation of GPR39 were confirmed in the diabetic cell model (all p < 0.05). Both ZnSO₄ and TC-G-1008 down-regulated Atrogin-1, LC3B, SIRT1, and FoxO1, and up-regulated P62 and GPR39, inhibiting autophagy and improving muscle atrophy (all p < 0.05). The beneficial anti-atrophic effects of ZnSO₄ are diminished following treatment with SRT1720 or RAPA. Upon GPR39 knockout, SIRT1, FoxO1, and Atrogin-1 were upregulated, while P62 was downregulated. Intracellular zinc concentrations in ZnSO₄-treated group remained unchanged (p > 0.05), indicating that zinc supplementation did not affect zinc ion entry but acted through the cell surface receptor GPR39. CONCLUSION: inhibits excessive autophagy in skeletal muscle and alleviates muscle atrophy in diabetic mice via the GPR39-SIRT1/FoxO1 axis. These findings suggest that zinc supplementation may offer a potential therapeutic strategy for managing diabetic muscle atrophy.