Inhibition of connexin hemichannels alleviates non-alcoholic steatohepatitis in mice

Background and aims: Connexins are the molecular constituents of gap junctions and hemichannels. In liver, connexin32 is the predominant connexin species expressed by hepatocytes, whereas non-parenchymal cells typically harbor connexin43. While gap junctions mediate intercellular communication and support liver homeostasis, hemichannels provide a circuit for paracrine signaling and are preferentially opened by pathological stimuli, including inflammation and oxidative stress. The latter are essential features of non-alcoholic steatohepatitis, being the most prevalent chronic liver disease in the Western world. In the present study, it was investigated whether hemichannels composed of connexin32 and connexin43 play a role in non-alcoholic steatohepatitis. Methods: Mice were fed a choline-deficient high-fat diet for 8 weeks to induce non-alcoholic steatohepatitis. TAT-Gap24 or TAT-Gap19, specific inhibitors of hemichannels composed of connexin32 and connexin43, respectively, were administered for 2 weeks via an abdominal osmotic pump, followed by the testing of a number of clinically and mechanistically relevant read-outs, including markers of histopathological examination as well as various indicators of inflammation, liver damage, oxidative stress and lipid metabolism. Results: Diet-fed animals treated with TAT-Gap24 or TAT-Gap19 displayed decreased amounts of liver triglycerides and cholesterol, reduced quantities of inflammatory markers, as well as augmented levels of superoxide dismutase in comparison with saline-treated counterparts. Furthermore, TAT-Gap19-treated diseased mice exhibited less fat weight and lower serum alanine aminotransferase quantities, while TAT-Gap24 decreased malondialdehyde levels in the liver of fatty mice. Channel specificity of TAT-Gap24 and TAT-Gap19 was confirmed in vitro by performing fluorescence recovery after photobleach analysis and measurement of extracellular release of adenosine triphosphate. Conclusion: These findings show for the first time the involvement of connexin32 and connexin43 hemichannels in non-alcoholic steatohepatitis as well as their potential as drug targets in this highly prevalent type of chronic liver disease