CHIP(-/-)-Mouse Liver: Adiponectin-AMPK-FOXO-Activation Overrides CYP2E1-Elicited JNK1-Activation, Delaying Onset of NASH: Therapeutic Implications.

Sung-Mi Kim,James P Grenert,Cam Patterson,Maria Almira Correia

doi:10.1038/srep29423

Abstract

Genetic ablation of C-terminus of Hsc70-interacting protein (CHIP) E3 ubiquitin-ligase impairs hepatic cytochrome P450 CYP2E1 degradation. Consequent CYP2E1 gain of function accelerates reactive O2 species (ROS) production, triggering oxidative/proteotoxic stress associated with sustained activation of c-Jun NH2-terminal kinase (JNK)-signaling cascades, pro-inflammatory effectors/cytokines, insulin resistance, progressive hepatocellular ballooning and microvesicular steatosis. Despite this, little evidence of nonalcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH) was found in CHIP−/−-mice over the first 8–9-months of life. We herein document that this lack of tissue injury is largely due to the concurrent up-regulation and/or activation of the adiponectin-5′-AMP-activated protein kinase (AMPK)-forkhead box O (FOXO)-signaling axis stemming from at the least three synergistic features: Up-regulated expression of adipose tissue adiponectin and its hepatic adipoR1/adipoR2 receptors, stabilization of hepatic AMPKα1-isoform, identified herein for the first time as a CHIP-ubiquitination substrate (unlike its AMPKα2-isoform), as well as nuclear stabilization of FOXOs, well-known CHIP-ubiquitination targets. Such beneficial predominance of the adiponectin-AMPK-FOXO-signaling axis over the sustained JNK-elevation and injurious insulin resistance in CHIP−/−-livers apparently counteracts/delays rapid progression of the hepatic microvesicular steatosis to the characteristic macrovesicular steatosis observed in clinical NASH and/or rodent NASH-models.

Highlights

Genetic ablation of C-terminus of Hsc70-interacting protein (CHIP) E3 ubiquitin-ligase impairs hepatic cytochrome P450 CYP2E1 degradation
Using relatively selective P450 functional probes we document that CYP2E1 largely, and CYP3A to a lesser extent, contribute to the age-dependent oxidative damage and proteotoxic stress in CHIP−/−-livers. We document that such chronic CYP2E1-elicited oxidative stress in CHIP−/−-hepatocytes is associated with the sustained activation of stress-activated protein kinase (SAPK)/c-Jun NH2-terminal kinase (JNK)-signaling cascades, nuclear factor κB (NF-κB) and inflammatory cytokines and chemokines and the Nod-like receptor P3 (NLRP3)-inflammasome, which may significantly contribute to the age-dependent cellular ballooning and microvesicular steatosis observed in CHIP−/−-livers
Upon Western-immunoblotting (IB) analyses, appreciably higher CYP3A and CYP2E1 protein stabilization was observed in cultured CHIP−/−-hepatocyte lysates than in CHIP+/+-hepatocyte lysates, irrespective of mouse age (Fig. S2B), thereby verifying that CHIP-knockout stabilized both hepatic CYP3A and CYP2E1 content

Summary

Introduction

Genetic ablation of C-terminus of Hsc70-interacting protein (CHIP) E3 ubiquitin-ligase impairs hepatic cytochrome P450 CYP2E1 degradation. We document that this lack of tissue injury is largely due to the concurrent up-regulation and/or activation of the adiponectin-5′-AMP-activated protein kinase (AMPK)-forkhead box O (FOXO)-signaling axis stemming from at the least three synergistic features: Up-regulated expression of adipose tissue adiponectin and its hepatic adipoR1/ adipoR2 receptors, stabilization of hepatic AMPKα1-isoform, identified for the first time as a CHIP-ubiquitination substrate (unlike its AMPKα2-isoform), as well as nuclear stabilization of FOXOs, well-known CHIP-ubiquitination targets Such beneficial predominance of the adiponectin-AMPKFOXO-signaling axis over the sustained JNK-elevation and injurious insulin resistance in CHIP−/−livers apparently counteracts/delays rapid progression of the hepatic microvesicular steatosis to the characteristic macrovesicular steatosis observed in clinical NASH and/or rodent NASH-models. Our findings reinforce the growing awareness of the beneficial role of adiponectin-AMPK-FOXO-signaling pathway in the pathogenesis of NAFLD/NASH24,25, suggesting that its therapeutic targeting could be exploited as a management strategy

Methods

Results

Conclusion