Berberine Attenuates Development of the Hepatic Gluconeogenesis and Lipid Metabolism Disorder in Type 2 Diabetic Mice and in Palmitate-Incubated HepG2 Cells through Suppression of the HNF-4α miR122 Pathway

Berberine (BBR) has been shown to exhibit protective effects against diabetes and dyslipidemia. Previous studies have indicated that BBR modulates lipid metabolism and inhibits hepatic gluconeogensis by decreasing expression of Hepatocyte Nuclear Factor-4α (HNF-4α). However, the mechanism involved in this process was unknown. In the current study, we examined the mechanism of how BBR attenuates hepatic gluconeogenesis and the lipid metabolism alterations observed in type 2 diabetic (T2D) mice and in palmitate (PA)-incubated HepG2 cells. Treatment with BBR for 4 weeks improve all biochemical parameters compared to T2D mice. Treatment of T2D mice for 4 weeks or treatment of PA-incubated HepG2 cells for 24 h with BBR decreased expression of HNF-4α and the microRNA miR122, the key gluconeogenesis enzymes Phosphoenolpyruvate carboxykinase (PEPCK) and Glucose-6-phosphatase (G6Pase) and the key lipid metabolism proteins Sterol response element binding protein-1 (SREBP-1), Fatty acid synthase-1 (FAS-1) and Acetyl-Coenzyme A carboxylase (ACCα) and increased Carnitine palmitoyltransferase-1(CPT-1) compared to T2D mice or PA-incubated HepG2 cells. Expression of HNF-4α in HepG2 cells increased expression of gluconeogenic and lipid metabolism enzymes and BBR treatment or knock down of miR122 attenuated the effect of HNF-4α expression. In contrast, BBR treatment did not alter expression of gluconeogenic and lipid metabolism enzymes in HepG2 cells with knockdown of HNF-4α. In addition, miR122 mimic increased expression of gluconeogenic and lipid metabolism enzymes in HepG2 cells with knockdown of HNF-4α. These data indicate that miR122 is a critical regulator in the downstream pathway of HNF-4α in the regulation of hepatic gluconeogenesis and lipid metabolism in HepG2 cells. The effect of BBR on hepatic gluconeogenesis and lipid metabolism is mediated through HNF-4α and is regulated downstream of miR122. Our data provide new evidence to support HNF-4α and miR122 regulated hepatic gluconeogenesis and lipid metabolism as promising therapeutic targets for the treatment of T2D.小檗碱（Berberine, BBR）已被证实可对糖尿病与血脂异常发挥保护作用。既往研究表明，小檗碱可通过下调肝细胞核因子4α（Hepatocyte Nuclear Factor-4α, HNF-4α）的表达来调节脂质代谢并抑制肝脏糖异生，然而该过程的具体分子机制尚未明确。本研究旨在探究小檗碱缓解2型糖尿病（T2D）小鼠及棕榈酸（PA）孵育的HepG2细胞中肝脏糖异生及脂质代谢紊乱的具体机制。与T2D模型小鼠相比，经小檗碱干预4周后，所有生化指标均得到改善。分别对T2D小鼠进行4周小檗碱干预，或对PA孵育的HepG2细胞施以24小时小檗碱处理，结果显示，相较于未处理组，二者的HNF-4α及微小RNA miR122的表达均被下调，糖异生关键酶磷酸烯醇式丙酮酸羧激酶（PEPCK）、葡萄糖-6-磷酸酶（G6Pase），以及脂质代谢关键蛋白固醇调节元件结合蛋白1（SREBP-1）、脂肪酸合酶1（FAS-1）和乙酰辅酶A羧化酶α（ACCα）的表达也随之降低；而肉碱棕榈酰转移酶1（CPT-1）的表达则显著升高。在HepG2细胞中，过表达HNF-4α可上调糖异生及脂质代谢相关酶的表达，而小檗碱干预或敲低miR122则可削弱HNF-4α的上述调控作用。与之相反，在HNF-4α敲低的HepG2细胞中，小檗碱处理并未改变糖异生及脂质代谢相关酶的表达水平。此外，向HNF-4α敲低的HepG2细胞中转入miR122模拟物，可上调糖异生及脂质代谢相关酶的表达。上述结果表明，在HepG2细胞中，miR122是HNF-4α下游通路中调控肝脏糖异生及脂质代谢的关键调节因子。小檗碱对肝脏糖异生及脂质代谢的调控作用，是通过HNF-4α介导，并受miR122的下游调控。本研究为HNF-4α与miR122调控的肝脏糖异生及脂质代谢通路作为2型糖尿病治疗的潜在靶点提供了新的实验依据。