Zhenqing recipe attenuates non-alcoholic fatty liver disease by regulating the SIK1/CRTC2 signaling in experimental diabetic rats

Abstract Background As a compound Chinese medicine, Zhenqing Recipe (ZQR) has been shown to ameliorate hyperglycemia, hyperlipidemia, fatty liver and insulin resistance in patients with diabetes and diabetic rats. In this paper, we further examined the effect of ZQR on diabetes complicated by non-alcoholic fatty liver disease (NAFLD) and the underlying molecular mechanisms. Methods Diabetic rats with NAFLD were developed by a high-fat diet (HFD) with low-dose streptozotocin (STZ) injection for 4 weeks. These rats were randomly separated into the diabetic model (DM), ZQR, metformin (Met), adenovirus expressing-salt-induced kinase 1 (Ad-SIK1) and adenovirus labeled with green fluorescent protein (Ad-GFP) groups. The effects on hepatic expression of gluconeogenic genes, glycolipid metabolism and pathological changes were subsequently detected. Results Serum glucose, triglycerides (TG), total cholesterol (TC) and hepatic TG were reduced in the ZQR group. The histopathological and immunohistochemical changes in the liver and pancreas in the ZQR group were significantly alleviated. The decrease of SIK1 expression was observed in the liver of diabetic rats induced by HFD and STZ. SIK1 overexpression in the liver relieved hyperglycemia, hyperlipidemia and fatty liver. Both the mRNA and protein levels of CREB-regulated transcription co-activator 2 (CRTC2), phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) in the liver were drastically reduced, whereas those of SIK1 were markedly increased in the ZQR group compared to levels in the DM group. Compared with the DM group, Ser577 phosphorylation of SIK1 was obviously reduced in the liver, while T182 phosphorylation of SIK1 and S171 phosphorylation of CRTC2 were evidently increased in the Ad-SIK1, Met and ZQR groups. Conclusions ZQR ameliorates hepatic gluconeogenesis and lipid storage in diabetic rats induced by HFD and STZ by activating the SIK1/CRTC2 signaling pathway. Upregulating hepatic SIK1 by ZQR may represent an efficient strategy for treating diabetes with NAFLD.