Hepatocyte-specific DGAT1 knockout (DGAT1) mice and lysosome-associated membrane protein 2 (LAMP2) overexpression mice were generated and subjected to chronic alcohol feeding. Cell studies were conducted to define the causal role and underlying mechanism of FFA-induced hepatocellular injury.
Hepatocyte-specific DGAT1 deletion exacerbated alcohol-induced liver injury by increasing lipid accumulation and ER stress, reducing LAMP2 protein levels, and impairing autophagy function. Cell studies revealed that FFAs, rather than TG, induced ER stress via ATF4 activation, which, in turn, downregulated LAMP2, thereby impairing autophagy flux. LAMP2 overexpression in the liver restored autophagy function and ameliorated alcohol-induced liver injury in mice. Reducing hepatic FFAs by PPARα activation attenuated ER stress, restored LAMP2 protein levels, and improved autophagy flux. In addition, suppression of LAMP2 and autophagy function was also detected in the liver of patients with severe alcoholic hepatitis.
This study demonstrates that accumulation of hepatic FFAs, rather than TG, plays a crucial role in the pathogenesis of ALD by suppressing LAMP2-autophagy flux pathway through ER stress signaling, which represents an important mechanism of FFA-induced hepatocellular injury in ALD.
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