HRD1 promotes chronic alcoholic liver disease by mediating ACSL3 ubiquitination and degradation

Alcohol-associated liver disease (ALD), one of the most frequent chronic liver diseases globally, is characterized by steatosis. HMG-CoA reductase-degrading protein 1 (HRD1) participates in the endoplasmic reticulum-associated protein degradation pathway through the recognition, translocation, and ubiquitination of substrate proteins. HRD1 is implicated in endoplasmic reticulum stress, oxidative stress and cell metabolism; however, the function of HRD1 in ALD remains unclear.

We aimed to explore the contribution and underlying molecular mechanism of HRD1 in alcoholic liver disease.

Mice were administered adeno-associated virus 9 encoding HRD1- or ACSL3-specific shRNA via intravenous injection, followed by feeding with a Lieber-DeCarli liquid diet containing 5 % ethanol. HepG2 cells were transfected with either HRD1 siRNA or HRD1 overexpression plasmids prior to ethanol exposure.

Hepatic HRD1 expression was significantly increased under alcohol conditions. Hepatocyte-specific HRD1 knockdown markedly attenuated alcohol-induced hepatic injury, inflammation, oxidative stress and lipid metabolism disorders in vivo. Additionally, similar results were shown in vitro. Mechanistically, acyl-CoA synthetase long chain family member 3 (ACSL3), a key regulator known to ameliorate hepatic steatosis, was identified as a novel substrate of HRD1. HRD1 facilitates the ubiquitination and degradation of ACSL3. Interestingly, HRD1 knockdown significantly suppressed fatty acid synthesis and promoted fatty acid oxidation, which was reversed by ACSL3 silencing both in vivo and in vitro.

In summary, HRD1 functions as a key mediator of ALD by ubiquitinating ACSL3, thereby promoting lipid dyshomeostasis, and aggravating ALD. Our findings reveal novel mechanistic insights into HRD1 and identify ACSL3 as a new downstream target of HRD1 to facilitate ALD treatment.