Figure 3. SAB expression in male mice determines the susceptibility to APAP-induced liver injury in a JNK-dependent fashion. WT C57BL/6N male mice received Ad-lacZ or Ad-SAB. (A) Fourteen days later, SAB expression was analyzed by immunoblotting, and (B) APAP (150 mg/kg) was given i.p., and H&E staining was performed and serum ALT levels were determined after 24 hours. Original magnification, ×10. Scale bars: 100 μm. n = 3/group. ALT: *P < 0.05 versus Ad-lacZ-injected Sab iΔHep mice, by unpaired, 2-tailed Student's t test. Data are presented as the mean ± SD. (C) Sab fl/fl or Sab iΔHep mice received 0.05 5 × 10 9 to approximately 5 × 10 9 IU Ad-lacZ or Ad-SAB. Fourteen days later, SAB expression was determined by immunoblotting. Immunoblot is representative of 3 separate experiments. n = 3/group. *P < 0.05 versus Sab iΔHep + Ad-lacZ, by 1-way ANOVA with Bonferroni's correction. Data are presented as the mean ± SEM. (D) Mice received APAP (300 mg/kg, i.p.), and 24 hours later, liver sections were stained with H&E, and the necrotic area (percentage) was measured. Serum ALT (± SEM) (U/L) was measured. Scale bars: 100 μm. n = 3 mice/group. ALT: *P < 0.05, versus Ad-lacZ-injected Sab fl/fl mice; **P < 0.05, versus Ad-lacZ-injected Sab iΔHep mice, by unpaired, 2-tailed Student's t test. Data are presented as the mean ± SD. (E and F) Jnk1/2 fl/fl mice received AAV8-TBG-GFP (n = 3), AAV8-TBG-Cre (n = 5), or AAV8-TBG-Cre plus Ad-SAB (n = 3). Fourteen days later, JNK and SAB expression levels were determined by immunoblotting, or mice were treated with APAP to analyze liver injury and serum ALT levels. Scale bars: 100 μm. ALT: *P < 0.05, versus AAV8-TBG-GFP, by unpaired, 2-tailed Student's t test. Data are presented as the mean ± SD.

Background and Aims The hepatic mitogen‐activated protein kinase (MAPK) cascade leading to c‐Jun N‐terminal kinase (JNK) activation has been implicated in the pathogenesis of nonalcoholic fatty liver (NAFL)/NASH. In acute hepatotoxicity, we previously identified a pivotal role for mitochondrial SH3BP5 (SAB; SH3 homology associated BTK binding protein) as a target of JNK, which sustains its activation through promotion of reactive oxygen species production. Therefore, we assessed the role of hepatic SAB in experimental NASH and metabolic syndrome. Approach and Results In mice fed high‐fat, high‐calorie, high‐fructose (HFHC) diet, SAB expression progressively increased through a sustained JNK/activating transcription factor 2 (ATF2) activation loop. Inducible deletion of hepatic SAB markedly decreased sustained JNK activation and improved systemic energy expenditure at 8 weeks followed by decreased body fat at 16 weeks of HFHC diet. After 30 weeks, mice treated with control–antisense oligonucleotide (control‐ASO) developed steatohepatitis and fibrosis, which was prevented by Sab‐ASO treatment. Phosphorylated JNK (p‐JNK) and phosphorylated ATF2 (p‐ATF2) were markedly attenuated by Sab‐ASO treatment. After 52 weeks of HFHC feeding, control N‐acetylgalactosamine antisense oligonucleotide (GalNAc‐Ctl‐ASO) treated mice fed the HFHC diet exhibited progression of steatohepatitis and fibrosis, but GalNAc‐Sab‐ASO treatment from weeks 40 to 52 reversed these findings while decreasing hepatic SAB, p‐ATF2, and p‐JNK to chow‐fed levels. Conclusions Hepatic SAB expression increases in HFHC diet–fed mice. Deletion or knockdown of SAB inhibited sustained JNK activation and steatohepatitis, fibrosis, and systemic metabolic effects, suggesting that induction of hepatocyte Sab is an important driver of the interplay between the liver and the systemic metabolic consequences of overfeeding. In established NASH, hepatocyte‐targeted GalNAc‐Sab‐ASO treatment reversed steatohepatitis and fibrosis.

Non-alcoholic fatty liver (NAFL) is the most common chronic liver disease. Activation of mitogen-activated kinases (MAPK) cascade, which leads to c-Jun N-terminal kinase (JNK) activation occurs in the liver in response to the nutritional and metabolic stress. The aberrant activation of MAPKs, especially c-Jun-N-terminal kinases (JNKs), leads to unwanted genetic and epi-genetic modifications in addition to the metabolic stress adaptation in hepatocytes. A mechanism of sustained P-JNK activation was identified in acute and chronic liver diseases, suggesting an important role of aberrant JNK activation in NASH. Therefore, modulation of JNK activation, rather than targeting JNK protein levels, is a plausible therapeutic application for the treatment of chronic liver disease.