SIRT6 Mediates Sterol-Dependent Feedback Regulation of Cholesterol Biosynthetic Genes in Hepatocytes

Metabolic dysfunction-associated steatohepatitis (MASH) is characterized by lipotoxic hepatocellular injury, inflammation, and fibrosis, with excess hepatic cholesterol contributing to disease pathogenesis. While the SCAP-INSIG-SREBP2 pathway classically regulates cholesterol biosynthetic gene expression via sterol sensing at the endoplasmic reticulum, the epigenetic mechanisms coupling cellular sterol status to gene expression remain unclear. Here, we investigated the role of sirtuin 6 (SIRT6), a nuclear histone deacetylase, in sterol-induced feedback regulation of cholesterol biosynthetic genes in hepatocytes. In HepG2 and AML12 cells, 25-hydroxycholesterol (25-HC) reduced the expression of SREBP2 and downstream cholesterol biosynthetic genes, including HMGCR and HMGCS1. This repression was associated with SIRT6 activation, as evidenced by reduced acetylation of histone H3 lysine 9 and lysine 56. Pharmacological SIRT6 inhibition reversed the repression of cholesterol biosynthetic genes, whereas SIRT6 activators phenocopied the inhibitory effects of 25-HC on the SREBP2 pathway. Conversely, sterol depletion via lovastatin inhibited SIRT6 activity, leading to the compensatory upregulation of cholesterol biosynthetic genes. Notably, SIRT6 overexpression or pharmacological activation reversed lovastatin-induced upregulation of SREBP2 and its target genes. These findings establish SIRT6 as a sterol-responsive nuclear regulator that converts intracellular cholesterol status into epigenetic repression of the cholesterol biosynthetic program. This SIRT6-dependent pathway complements endoplasmic reticulum-based sterol sensing and provides a mechanistic insight into hepatic cholesterol dysregulation in MASH.