Protection of a Ceramide Synthase 2 Null Mouse from Drug-induced Liver Injury: ROLE OF GAP JUNCTION DYSFUNCTION AND CONNEXIN 32 MISLOCALIZATION

Woo-Jae Park,Joo-Won Park,Racheli Erez-Roman,Aviram Kogot-Levin,Jessica R Bame,Boaz Tirosh,Ann Saada,Alfred H Merrill,Yael Pewzner-Jung,Anthony H Futerman

doi:10.1074/jbc.m112.448852

Abstract

Very long chain (C22-C24) ceramides are synthesized by ceramide synthase 2 (CerS2). A CerS2 null mouse displays hepatopathy because of depletion of C22-C24 ceramides, elevation of C16-ceramide, and/or elevation of sphinganine. Unexpectedly, CerS2 null mice were resistant to acetaminophen-induced hepatotoxicity. Although there were a number of biochemical changes in the liver, such as increased levels of glutathione and multiple drug-resistant protein 4, these effects are unlikely to account for the lack of acetaminophen toxicity. A number of other hepatotoxic agents, such as d-galactosamine, CCl4, and thioacetamide, were also ineffective in inducing liver damage. All of these drugs and chemicals require connexin (Cx) 32, a key gap junction protein, to induce hepatotoxicity. Cx32 was mislocalized to an intracellular location in hepatocytes from CerS2 null mice, which resulted in accelerated rates of its lysosomal degradation. This mislocalization resulted from the altered membrane properties of the CerS2 null mice, which was exemplified by the disruption of detergent-resistant membranes. The lack of acetaminophen toxicity and Cx32 mislocalization were reversed upon infection with recombinant adeno-associated virus expressing CerS2. We establish that Gap junction function is compromised upon altering the sphingolipid acyl chain length composition, which is of relevance for understanding the regulation of drug-induced liver injury.

Highlights

Ceramide synthase 2 null mice cannot synthesize very long acyl chain ceramides and display severe hepatopathy
We establish that Gap junction function is compromised upon altering the sphingolipid acyl chain length composition, which is of relevance for understanding the regulation of drug-induced liver injury
In this study we demonstrate that, despite the severe hepatopathy observed in ceramide synthase 2 (CerS2) null mice, these mice are resistant to drug- and chemical-induced liver injury

Summary

Background

Ceramide synthase 2 null mice cannot synthesize very long acyl chain ceramides and display severe hepatopathy. CerS2 null mice display increased rates of hepatocyte death and proliferation, which results in the formation of multiple hepatic nodules and hepatocellular carcinoma [10] They have chronic oxidative stress because of disruption of the mitochondrial respiratory chain [11] and display hepatic insulin resistance because of altered detergent-resistant membranes (DRMs) [12], which appears to be related to changes in membrane biophysical properties [13, 14]. Because of these various liver pathologies, we have examined hepatotoxicity induced by a number of drugs and chemicals. We suggest that the SL pathway might be a novel drug target for alleviating drug-induced liver damage and possibly other forms of acute liver failure

EXPERIMENTAL PROCEDURES

DISCUSSION