Role of SQSTM1/p62 in regulating Mallory-Denk body in alcohol-associated liver disease.

Background: Alcohol-associated liver disease (ALD) is a global health problem without an effective treatment. Mallory-Denk body (MDB) is a protein aggregate commonly found in alcohol-associated hepatitis (AH). MDB primarily contains ubiquitinated proteins, cytokeratin 8 and sequestosome 1 (SQSTM1)/p62. Stress granule (SG) is a cytosolic, membrane-less aggregate composed of various RNA-binding proteins and untranslated mRNA. However, the role and mechanisms of MDB and SG induced by alcohol and their implications in the pathogenesis of ALD remain largely unknown. Methods: SQSTM1/p62 whole body knockout and matched wild-type mice were subjected to the Gao-binge alcohol model or fed a 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet alongside Gao-binge alcohol model. ALD mouse liver tissues and human AH liver tissues underwent immunohistochemistry (IHC) staining and western blot analysis for SG and MDB markers. Results: We found that the livers of patients with AH had higher levels of SQSTM1/p62 (MDB marker) and Ras-GTPase-activating protein-binding protein 1 (an SG marker) using IHC staining, and these increased protein levels were enriched in detergent-insoluble fractions compared with healthy individuals. We further discovered that Gao-binge alcohol feeding increased insoluble SG markers, such as phosphorylated eukaryotic initiation factor 2 in mouse livers. Mice fed a DDC diet with Gao-binge alcohol had greater hepatic MDB formation and liver injury than those fed either diet alone. Loss of SQSTM1/p62 led to reduced protein aggregation involved in SGs and MDBs but increased liver injury in DDC plus Gao-binge alcohol-fed mice, indicating that SQSTM1/p62 is required for MDB formation and protects against alcohol-induced liver injury. Conclusion: Chronic plus binge alcohol exposure increases hepatic MDBs and moderate levels of SGs. p62/SQSTM1 is critical for the formation but is not essential for the clearance of MDBs, a process that may act as an adaptive protective mechanism against ALD.