TY - JOUR
T1 - Protective and Detrimental Roles of p38α Mitogen-Activated Protein Kinase in Different Stages of Nonalcoholic Fatty Liver Disease
AU - Hwang, Seonghwan
AU - Wang, Xiaolin
AU - Rodrigues, Robim M.
AU - Ma, Jing
AU - He, Yong
AU - Seo, Wonhyo
AU - Park, Seol Hee
AU - Kim, Seung Jin
AU - Feng, Dechun
AU - Gao, Bin
N1 - Funding Information:
C57BL/6J and albumin-Cre mice were obtained from the Jackson Laboratory (Bar Harbor, ME). p38a-floxed mice were kindly provided by Dr. Yibin Wang (University of California, Los Angeles) and were crossed with albumin-Cre mice through several steps to generate hepatocyte-specific p38a knockout (p38aHep-/-) mice. All animal experiments were approved by the National Institute on Alcohol Abuse and Alcoholism Institutional Animal Care and Use Committee. C57BL/6J and albumin-Cre mice were obtained from the Jackson Laboratory (Bar Harbor, ME). p38a-floxed mice were kindly provided by Dr. Yibin Wang (University of California, Los Angeles) and were crossed with albumin-Cre mice through several steps to generate hepatocyte-specific p38a knockout (p38aHep-/-) mice. All animal experiments were approved by the National Institute on Alcohol Abuse and Alcoholism Institutional Animal Care and Use Committee. To induce steatosis in mice, p38aHep-/- mice and p38a-floxed littermate control mice (defined as WT mice) (male, 6-7 weeks of age) were fed an HFD (60 kcal% fat; D12492, Research Diets, New Brunswick, NJ) for 3 months and sacrificed for analyses. To induce NASH, C57BL/6J, p38aHep-/-, and p38a-floxed littermate WT control mice (male, 6-7 weeks of age) were fed an HFD for 3 months followed by a tail vein injection with adenovirus-expressing (Ad) mouse CXCL1 (Ad-Cxcl1) or green fluorescent protein (Ad-Gfp) as a control. In some experiments, mice were also injected with Ad-Cxcl1 concomitantly with human Ad-IL-8. Adenoviruses were purchased from Applied Biological Materials (Richmond, Canada). Mice were continued on an HFD for 2 or 4 weeks after the adenovirus infection before sacrifice for analyses. To test the efficacy of p38α/β inhibitors (LY-2228820 and PH-797804; Selleckchem, Houston, TX), mice were injected intraperitoneally with LY-2228820 (3 mg/kg) and PH-797804 (10 mg/kg) on days 7, 9, 11, and 13 after adenoviral infection. Data are expressed as mean ± SEM and were analyzed using GraphPad Prism (v. 7.0a; GraphPad Software, La Jolla, CA). To compare values obtained from two groups, the Student t test was performed. Data from multiple groups were compared with one-way ANOVA followed by Tukey’s post hoc test. P values of <0.05 were considered significant.
Publisher Copyright:
Published 2020. This article is a U.S. Government work and is in the public domain in the USA.
PY - 2020/9/1
Y1 - 2020/9/1
N2 - Background and Aims: Neutrophil infiltration is a hallmark of nonalcoholic steatohepatitis (NASH), but how this occurs during the progression from steatosis to NASH remains obscure. Human NASH features hepatic neutrophil infiltration and up-regulation of major neutrophil-recruiting chemokines (e.g., chemokine [C-X-C motif] ligand 1 [CXCL1] and interleukin [IL]-8). However, mice fed a high-fat diet (HFD) only develop fatty liver without significant neutrophil infiltration or elevation of chemokines. The aim of this study was to determine why mice are resistant to NASH development and the involvement of p38 mitogen-activated protein kinase (p38) activated by neutrophil-derived oxidative stress in the pathogenesis of NASH. Approach and Results: Inflamed human hepatocytes attracted neutrophils more effectively than inflamed mouse hepatocytes because of the greater induction of CXCL1 and IL-8 in human hepatocytes. Hepatic overexpression of Cxcl1 and/or IL-8 promoted steatosis-to-NASH progression in HFD-fed mice by inducing liver inflammation, injury, and p38 activation. Pharmacological inhibition of p38α/β or hepatocyte-specific deletion of p38a (a predominant form in the liver) attenuated liver injury and fibrosis in the HFD+Cxcl1-induced NASH model that is associated with strong hepatic p38α activation. In contrast, hepatocyte-specific deletion of p38a in HFD-induced fatty liver where p38α activation is relatively weak exacerbated steatosis and liver injury. Mechanistically, weak p38α activation in fatty liver up-regulated the genes involved in fatty acid β-oxidation through peroxisome proliferator-activated receptor alpha phosphorylation, thereby reducing steatosis. Conversely, strong p38α activation in NASH promoted caspase-3 cleavage, CCAAT-enhancer-binding proteins homologous protein expression, and B cell lymphoma 2 phosphorylation, thereby exacerbating hepatocyte death. Conclusions: Genetic ablation of hepatic p38a increases simple steatosis but ameliorates oxidative stress-driven NASH, indicating that p38α plays distinct roles depending on the disease stages, which may set the stage for investigating p38α as a therapeutic target for the treatment of NASH.
AB - Background and Aims: Neutrophil infiltration is a hallmark of nonalcoholic steatohepatitis (NASH), but how this occurs during the progression from steatosis to NASH remains obscure. Human NASH features hepatic neutrophil infiltration and up-regulation of major neutrophil-recruiting chemokines (e.g., chemokine [C-X-C motif] ligand 1 [CXCL1] and interleukin [IL]-8). However, mice fed a high-fat diet (HFD) only develop fatty liver without significant neutrophil infiltration or elevation of chemokines. The aim of this study was to determine why mice are resistant to NASH development and the involvement of p38 mitogen-activated protein kinase (p38) activated by neutrophil-derived oxidative stress in the pathogenesis of NASH. Approach and Results: Inflamed human hepatocytes attracted neutrophils more effectively than inflamed mouse hepatocytes because of the greater induction of CXCL1 and IL-8 in human hepatocytes. Hepatic overexpression of Cxcl1 and/or IL-8 promoted steatosis-to-NASH progression in HFD-fed mice by inducing liver inflammation, injury, and p38 activation. Pharmacological inhibition of p38α/β or hepatocyte-specific deletion of p38a (a predominant form in the liver) attenuated liver injury and fibrosis in the HFD+Cxcl1-induced NASH model that is associated with strong hepatic p38α activation. In contrast, hepatocyte-specific deletion of p38a in HFD-induced fatty liver where p38α activation is relatively weak exacerbated steatosis and liver injury. Mechanistically, weak p38α activation in fatty liver up-regulated the genes involved in fatty acid β-oxidation through peroxisome proliferator-activated receptor alpha phosphorylation, thereby reducing steatosis. Conversely, strong p38α activation in NASH promoted caspase-3 cleavage, CCAAT-enhancer-binding proteins homologous protein expression, and B cell lymphoma 2 phosphorylation, thereby exacerbating hepatocyte death. Conclusions: Genetic ablation of hepatic p38a increases simple steatosis but ameliorates oxidative stress-driven NASH, indicating that p38α plays distinct roles depending on the disease stages, which may set the stage for investigating p38α as a therapeutic target for the treatment of NASH.
UR - http://www.scopus.com/inward/record.url?scp=85088024898&partnerID=8YFLogxK
U2 - 10.1002/hep.31390
DO - 10.1002/hep.31390
M3 - Article
C2 - 32463484
AN - SCOPUS:85088024898
SN - 0270-9139
VL - 72
SP - 873
EP - 891
JO - Hepatology
JF - Hepatology
IS - 3
ER -