Saikosaponin D attenuates metabolic associated fatty liver disease by coordinately tuning PPARα and INSIG/SREBP1c pathway

BACKGROUND

Metabolic associated fatty liver disease (MAFLD) is a progressive chronic liver disease, yet there is still a lack of effective pharmacological therapies at present. Saikosaponin D (SSd) has been reported to exhibit hepatoprotective and anti-steatosis activities in our previous research.

PURPOSE

The current study aims to further investigate the underlying mechanisms of SSd on MAFLD from the perspectives of the crosstalk between fatty acid (FA) biosynthesis and catabolism to provide strong support for further clinical management of MAFLD.

METHODS

A MAFLD mouse model induced by a high-fat diet and glucose-fructose water (HFSW) was used for in vivo study. HepG2 cells, primary mouse hepatocytes and adipocytes were further employed for in vitro studies.

RESULTS

SSd improved intracellular lipid accumulation both in the liver and adipose tissues in HFSW-fed mice. Mechanistically, SSd may serve as a potent PPARα agonist, and the activation of PPARα by SSd in both hepatocytes and adipocytes not only promoted FA oxidation but also concurrently induced INSIG1/2 expression, which subsequently inhibited SREBP1c maturation and ultimately FA synthesis. Moreover, the regulative effect of SSd on lipid metabolism was abolished by the PPARα inhibitor, GW6471.

CONCLUSION

This study demonstrated that SSd improved lipid homeostasis by coordinately regulating PPARα activation-mediated both inhibition of SREBP1c-dependent FA biosynthesis and induction of FA degradation, and thus shed novel light on the discovery of SSd-based therapeutic strategies for MAFLD.

Policosanol attenuates Pi-induced calcification via AMPK-mediated INSIGs expression in rat VSMCs

Policosanol is a hypocholesterolemic derived from sugar cane and corn that downregulates blood cholesterol levels. It can further lower blood pressure and reduce liver inflammation. Policosanol can also affect vascular calcification, however, its molecular mechanisms are not well understood. This study investigated the effect of policosanol on vascular calcification and its molecular mechanism. Policosanol decreased the expression of inorganic phosphate (Pi)-induced osteogenic genes such as distal-less homeobox 5 (Dlx5) and runt-related transcription factor 2 (Runx2). In addition, following policosanol treatment, adenosine monophosphate-activated protein kinase (AMPK) phosphorylation increased in a time-dependent manner. The constitutively active form of AMPK (CA-AMPK) dramatically suppressed Pi-induced Dlx5 and Runx2 protein levels. Inactivation of AMPK using compound C (Com. C; AMPK inhibitor) recovered policosanol-suppressed Alizarin Red S staining levels. Insulin-induced genes (INSIGs) were induced by CA-AMPK, their overexpression suppressed Pi-induced Dlx5 and Runx2 expression. Taken together, the results demonstrate that policosanol inhibits Pi-induced vascular calcification by regulating AMPK-induced INSIG expression in vascular smooth muscle cells.