[Berberine regulates glucose and lipid metabolism via clock-controlled genes to ameliorate insulin resistance of hepatocytes].

Abstract

This study aims to investigate the mechanism of berberine in regulating the metabolism network via clock-controlled genes represented by brain and muscle arnt-like 1(BMAL1) to ameliorate insulin resistance(IR) of hepatocytes in vitro. The HepG2 cell model of dexamethasone-induced IR(IR-HepG2) was established and treated with 5, 10, and 20 μmol·L~(-1) berberine, respectively, for 24 h. The glucose oxidase method and cell counting kit-8(CCK-8) assay were employed to measure extracellular glucose concentration and cell viability, respectively. Periodic acid-Schiff(PAS) staining and lipid fluorescence method were used to detect glycogen and lipids. The immunofluorescence(IF) assay was employed to detect the nuclear localization of BMAL1 and circadian locomotor output cycles kaput(CLOCK) in IR-HepG2 cells. Western blot was employed to determine the protein levels of BMAL1, CLOCK, period circadian clock 2(PER2), cryptochrome circadian regulator 1(CRY1), Rev-Erbα, carbohydrate response element-binding protein(ChREBP), peroxisome proliferator-activated receptors alpha and gamma(PPARα/γ), sterol regulatory element-binding protein 1C(SREBP-1C), mammalian target of rapamycin(mTOR), protein kinase B(Akt), glycogen synthase kinase-3β(GSK3β), acetyl coenzyme A carboxylase 1(ACC1), fatty acid synthase(FASN), carnitine palmitoyltransferase 1α(CPT1α), nicotinamide phosphoribosyltransferase(NAMPT), silent information regulator 1(SIRT1), adiponectin(ADPN), insulin receptor substrate 2(IRS2), and phosphatidylinositol 3-kinase regulatory subunit p85(PI3Kp85). In addition, the levels of phosphorylated adenosine monophosphate-activated protein kinase alpha(AMPKα), Akt, GSK3β, BMAL1, and mTOR were determined. Furthermore, 20 μmol·L~(-1) CLK8 was added to measure the glucose consumption as well as the protein levels of ChREBP, PPARα, and mTOR in IR-HepG2 cells. The results showed that berberine increased the glucose consumption, lowered the lipid levels, increased the expression and nuclear localization of BMAL1 and CLOCK, and up-regulated the level of BMAL1 in IR-HepG2 cells. Furthermore, berberine up-regulated the levels of ADPN, IRS2, PI3Kp85, p-Akt(Ser473)/Akt, p-mTOR(Ser2448)/mTOR, PPARα, and CPT1α, and down-regulated the levels of p-GSK3β(Ser9)/GSK3β, ChREBP, SREBP-1C, ACC1, and FASN. The addition of CLK8 reduced glucose consumption in IR-HepG2 cells, up-regulated the ChREBP level, and down-regulated PPARα and mTOR levels by inhibiting the BMAL1 and CLOCK interaction. In summary, berberine regulated glucose and lipid metabolism via clock-controlled genes with BMAL1 at the core to ameliorate IR of hepatocytes.