Apolipoprotein A-I improves hepatic autophagy through the AMPK pathway.

ABSTRACT

Dysfunction in lipid metabolism may result in a decrease in hepatic autophagy, which contributes to the pathogenesis of non-alcoholic steatohepatitis. ATP-binding cassette transporter A1 transports free cholesterol and phospholipids to apolipoprotein A-I (apoA-I) to form nascent high-density lipoprotein particles. Results from previous studies showed that the overexpression of apoA-I significantly reduced levels of hepatic lipids and endoplasmic reticulum stress by modifying lipid transport. Here, we investigated the effects of apoA-I overexpression on hepatic autophagy in cultured hepatocytes and mice. The overexpression of apoA-I in HepG2 cells resulted in an increase in the levels of autophagy as well as the phosphorylation of AMP-activated protein kinase α (AMPKα) and ULK1 and a decrease in the phosphorylation of mammalian target of rapamycin (mTOR). An AMPK inhibitor and siRNA eliminated this apoA-I effect. Consistently, apoA-I transgenic mice showed increased autophagy and AMPKα phosphorylation. These results suggest that apoA-I overexpression alleviates steatohepatitis by increasing hepatic autophagy through the AMPK-mTOR-ULK1 pathway.