Xiaojuan Chao1, Shaogui Wang1, Sam Fulte1, Xiaowen Ma1, Forkan Ahamed1, Wei Cui2, Zhipeng Liu3, Thomas Rülicke4, Kurt Zatloukal5, Wei-Xing Zong6, Wanqing Liu7, Hong-Min Ni8, Wen-Xing Ding9. 1. Department of Pharmacology, Toxicology and Therapeutics, The University of Kansas Medical Center, Kansas City, KS 66160, USA. 2. Department of Pathology, The University of Kansas Medical Center, Kansas City, KS 66160, USA. 3. Department of Medicinal Chemistry and Molecular Pharmacology, College of Pharmacy, Purdue University, West Lafayette, IN 47907, USA. 4. Department of Biomedical Sciences, University of Veterinary Medicine Vienna Veterinärplatz, Vienna, Austria. 5. The Institute of Pathology, Medical University of Graz, A-8036 Graz, Austria. 6. Department of Chemical Biology, Ernest Mario School of Pharmacy, Rutgers University, Piscataway, NJ 08854, USA. 7. Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Sciences and Department of Pharmacology, School of Medicine, Wayne State University, Detroit, MI 48201, USA. 8. Department of Pharmacology, Toxicology and Therapeutics, The University of Kansas Medical Center, Kansas City, KS 66160, USA. Electronic address: hni@kumc.edu. 9. Department of Pharmacology, Toxicology and Therapeutics, The University of Kansas Medical Center, Kansas City, KS 66160, USA. Electronic address: wxding@kumc.edu.
Abstract
BACKGROUND & AIMS: Either activation of mTORC1 due to loss of Tsc1 (tuberous sclerosis complex 1) or defective hepatic autophagy due to loss of Atg5 leads to spontaneous liver tumorigenesis in mice. The purpose of this study was to investigate the mechanisms by which autophagy contributes to the hepatic metabolic changes and tumorigenesis mediated by mTORC1 activation. METHODS: Atg5 Flox/Flox (Atg5F/F) and Tsc1F/F mice were crossed with albumin-Cre mice to generate liver-specific Atg5 knockout (L-Atg5 KO), L-Tsc1 KO and L-Atg5/Tsc1 double KO (DKO) mice. These mice were crossed with p62/Sqstm1F/F (p62) and whole body Nrf2 KO mice to generate L-Atg5/Tsc1/p62 and L-Atg5/Tsc1-Nrf2 triple KO mice. These mice were housed for various periods up to 12 months, and blood and liver tissues were harvested for biochemical and histological analysis RESULTS: Deletion of Atg5 in L-Tsc1 KO mice inhibited liver tumorigenesis but increased mortality and was accompanied by drastically enhanced hepatic ductular reaction (DR), hepatocyte degeneration and metabolic reprogramming. Deletion of p62 reversed DR, hepatocyte degeneration and metabolic reprogramming as well as the mortality of L-Atg5/Tsc1 DKO mice, but unexpectedly promoted liver tumorigenesis via activation of a group of oncogenic signaling pathways. Nrf2 ablation markedly improved DR with increased hepatocyte population and improved metabolic reprogramming and survival of the L-Atg5/Tsc1 DKO mice without tumor formation. Decreased p62 and increased mTOR activity were also observed in a subset of human hepatocellular carcinomas. CONCLUSIONS: These results reveal previously undescribed functions of hepatic p62 in suppressing tumorigenesis and regulating liver cell repopulation and metabolic reprogramming resulting from persistent mTORC1 activation and defective autophagy. LAY SUMMARY: Metabolic liver disease and viral hepatitis are common chronic liver diseases and risk factors of hepatocellular carcinoma, which are often associated with impaired hepatic autophagy and increased mTOR activation. Using multiple genetically engineered mouse models of defective hepatic autophagy and persistent mTOR activation, we dissected the complex mechanisms behind this observation. Our results uncovered an unexpected novel tumor suppressor function of p62/Sqstm1, which regulated liver cell repopulation, ductular reaction and metabolic reprogramming in liver tumorigenesis.
BACKGROUND & AIMS: Either activation of mTORC1 due to loss of Tsc1 (tuberous sclerosis complex 1) or defective hepatic autophagy due to loss of Atg5 leads to spontaneous liver tumorigenesis in mice. The purpose of this study was to investigate the mechanisms by which autophagy contributes to the hepatic metabolic changes and tumorigenesis mediated by mTORC1 activation. METHODS: Atg5 Flox/Flox (Atg5F/F) and Tsc1F/F mice were crossed with albumin-Cre mice to generate liver-specific Atg5 knockout (L-Atg5 KO), L-Tsc1 KO and L-Atg5/Tsc1 double KO (DKO) mice. These mice were crossed with p62/Sqstm1F/F (p62) and whole body Nrf2 KO mice to generate L-Atg5/Tsc1/p62 and L-Atg5/Tsc1-Nrf2 triple KO mice. These mice were housed for various periods up to 12 months, and blood and liver tissues were harvested for biochemical and histological analysis RESULTS: Deletion of Atg5 in L-Tsc1 KO mice inhibited liver tumorigenesis but increased mortality and was accompanied by drastically enhanced hepatic ductular reaction (DR), hepatocyte degeneration and metabolic reprogramming. Deletion of p62 reversed DR, hepatocyte degeneration and metabolic reprogramming as well as the mortality of L-Atg5/Tsc1 DKO mice, but unexpectedly promoted liver tumorigenesis via activation of a group of oncogenic signaling pathways. Nrf2 ablation markedly improved DR with increased hepatocyte population and improved metabolic reprogramming and survival of the L-Atg5/Tsc1 DKO mice without tumor formation. Decreased p62 and increased mTOR activity were also observed in a subset of human hepatocellular carcinomas. CONCLUSIONS: These results reveal previously undescribed functions of hepatic p62 in suppressing tumorigenesis and regulating liver cell repopulation and metabolic reprogramming resulting from persistent mTORC1 activation and defective autophagy. LAY SUMMARY: Metabolic liver disease and viral hepatitis are common chronic liver diseases and risk factors of hepatocellular carcinoma, which are often associated with impaired hepatic autophagy and increased mTOR activation. Using multiple genetically engineered mouse models of defective hepatic autophagy and persistent mTOR activation, we dissected the complex mechanisms behind this observation. Our results uncovered an unexpected novel tumor suppressor function of p62/Sqstm1, which regulated liver cell repopulation, ductular reaction and metabolic reprogramming in liver tumorigenesis.
Authors: Youngmin A Lee; Luke A Noon; Kemal M Akat; Maria D Ybanez; Ting-Fang Lee; Marie-Luise Berres; Naoto Fujiwara; Nicolas Goossens; Hsin-I Chou; Fatemeh P Parvin-Nejad; Bilon Khambu; Elisabeth G M Kramer; Ronald Gordon; Cathie Pfleger; Doris Germain; Gareth R John; Kirk N Campbell; Zhenyu Yue; Xiao-Ming Yin; Ana Maria Cuervo; Mark J Czaja; M Isabel Fiel; Yujin Hoshida; Scott L Friedman Journal: Nat Commun Date: 2018-11-23 Impact factor: 17.694