Increased hepatic receptor interacting protein kinase 3 expression due to impaired proteasomal functions contributes to alcohol-induced steatosis and liver injury

Abstract

// Shaogui Wang 1, 2 , Hong-Min Ni 2 , Kenneth Dorko 2 , Sean C. Kumer 3 , Timothy M. Schmitt 3 , Atta Nawabi 3 , Masaaki Komatsu 4 , Heqing Huang 1 , Wen-Xing Ding 2 1 Laboratory of Pharmacology and Toxicology, School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, China 2 Department of Pharmacology, Toxicology and Therapeutics, University of Kansas Medical Center, Kansas City, KS 66160, USA 3 Department of General Surgery, University of Kansas Medical Center, Kansas City, KS 66160, USA 4 Department of Biochemistry, School of Medicine Niigata University, Chuo-ku Niigata 951-8510, Japan Correspondence to: Heqing Huang, e-mail: huangheq@mail.sysu.edu.cn Wen-Xing Ding, e-mail: wxding@kumc.edu Keywords: alcohol, RIP3, steatosis, necroptosis, liver injury Received: July 28, 2015     Accepted: December 23, 2015     Published: January 12, 2016 ABSTRACT Chronic alcohol exposure increased hepatic receptor-interacting protein kinase (RIP) 3 expression and necroptosis in the liver but its mechanisms are unclear. In the present study, we demonstrated that chronic alcohol feeding plus binge (Gao-binge) increased RIP3 but not RIP1 protein levels in mouse livers. RIP3 knockout mice had decreased serum alanine amino transferase activity and hepatic steatosis but had no effect on hepatic neutrophil infiltration compared with wild type mice after Gao-binge alcohol treatment. The hepatic mRNA levels of RIP3 did not change between Gao-binge and control mice, suggesting that alcohol-induced hepatic RIP3 proteins are regulated at the posttranslational level. We found that Gao-binge treatment decreased the levels of proteasome subunit alpha type-2 (PSMA2) and proteasome 26S subunit, ATPase 1 (PSMC1) and impaired hepatic proteasome function. Pharmacological or genetic inhibition of proteasome resulted in the accumulation of RIP3 in mouse livers. More importantly, human alcoholics had decreased expression of PSMA2 and PSMC1 but increased protein levels of RIP3 compared with healthy human livers. Moreover, pharmacological inhibition of RIP1 decreased Gao-binge-induced hepatic inflammation, neutrophil infiltration and NF-κB subunit (p65) nuclear translocation but failed to protect against steatosis and liver injury induced by Gao-binge alcohol. In conclusion, results from this study suggest that impaired hepatic proteasome function by alcohol exposure may contribute to hepatic accumulation of RIP3 resulting in necroptosis and steatosis while RIP1 kinase activity is important for alcohol-induced inflammation.