Qige Decoction attenuated non-alcoholic fatty liver disease through regulating SIRT6-PPARα-mediated fatty acid oxidation

Background: Sirtuin 6 (SIRT6), a potential therapeutic target for non-alcoholic fatty liver disease (NAFLD), has been shown to regulate fatty acid oxidation (FAO) by interacting with Peroxisome Proliferator-activated Receptor α (PPARα). However, the impact of SIRT6-PPARα pathway on NAFLD phenotype has not yet been reported. Qige decoction (QG), a traditional Chinese medicine (TCM) formula, is widely applied to treat disorders of glycolipid metabolism. Our previous experiments showed that QG reduced hepatic steatosis and provided preliminary evidence that QG may promote FAO. However, a thorough understanding of molecular mechanisms by which QG regulates FAO requires further investigation.

Purpose: To investigate the role of SIRT6-PPARα signalling pathway on NAFLD phenotype and explore the mechanism by which QG improves NAFLD and its relationship with FAO regulated by SIRT6-PPARα signalling pathway.

Methods: In vivo study, NAFLD mice induced by high fat diet (HFD) were divided into two parts. The first part involved four groups: control (CON), model (MOD), PPARα Agonist (WY-14,643, WY), and SIRT6 Inhibitor (OSS-128,167, OS) groups. The second part involved five groups: CON group, MOD group, positive drug (POS) group, low dose QG (QGL) group, and high dose QG (QGH) group. Widely-targeted lipidomic were performed by UHPLC-QTOF/MS to analyse differential lipids (DELs) in the liver, while differentially expressed genes (DEGs) were analysed by transcriptome analysis on the Illumina Sequencing platform. In vitro study, co-immunoprecipitation and dual luciferase assay were employed to further identify the molecular mechanisms of SIRT6-PPARα interaction. The lentiviral vector, TG assay, and acetyl-CoA assay were used to clarify the indispensable role of the SIRT6-PPARα signalling pathway on QG amelioration of lipid accumulation in vitro.

Results: Down-regulation of SIRT6 inhibited PPARα-mediated FAO and aggravated lipid accumulation in hepatocytes both in vivo and in vitro. SIRT6 bound to PPARα in HepG2 cells; however, SIRT6 activation of the PPARα promoter was not detected. Along with QG reduced hepatocyte lipid accumulation, SIRT6-PPARα signalling pathway was upregulated in vivo and in vitro. However, the alleviating effect of QG on lipid accumulation was blocked by SIRT6 silencing in vitro.

Conclusion: This study verified that SIRT6-PPARα signalling pathway inhibition exacerbated NAFLD dyslipidaemia and hepatic steatosis. In addition, this study provided the first in-depth analysis of the molecular mechanisms by which QG ameliorates NFALD, involving promotion of FAO through activation of the SIRT6-PPARα signalling pathway. Our study offers significant insights for the clinical application of QG.

Fatty acid oxidation; Non-alcoholic fatty liver disease; Qi ge decoction; Sirt6-pparα signalling pathway; lipidomics; transcriptomics.