Inhibition of connexin hemichannels alleviates non-alcoholic steatohepatitis in mice

Background and aims: Connexins (Cx) are the molecular constituents of gap junctions and hemichannels. In liver, Cx32 is the predominant connexin species expressed by hepatocytes, whereas non-parenchymal cells typically harbor Cx43. 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 (NASH), being the most prevalent chronic liver disease in the Western world, associated with obesity, insulin resistance and metabolic syndrome. In this study, the role of Cx32 and Cx43 hemichannel signaling in NASH was studied. Methods: Mice were fed a choline-deficient high-fat diet. After 8 weeks, TAT-Gap24 or TAT-Gap19, specific inhibitors of Cx32 and Cx43 hemichannels, respectively, were administered intraperitoneally via a surgically implanted osmotic pump. After another 2 weeks, animals were sampled and tested for a battery of clinically and mechanistically relevant read-outs, including markers of histopathological examination as well as various indicators of inflammation, liver damage and lipid metabolism. Whole transcriptome microarray analysis was performed on extracted RNA of liver fragments of saline-, TAT-Gap24- and TAT-Gap19-treated mice. Results: NASH animals treated with TAT-Gap24 and TAT-Gap19 displayed decreased amounts of liver triglycerides and cholesterol, reduced amounts of inflammatory markers, such as interleukin-1β, interleukin-6 and interferon-γ, as well as augmented levels of superoxide dismutase in comparison with saline-treated counterparts. TAT-Gap19-treated mice also exhibited less fat weight and lower alanine aminotransferase quantities in serum, while TAT-Gap24 decreased malondialdehyde levels in the liver of fatty mice. In compliance with these results, liver RNA from TAT-Gap19-treated animals exhibited 25 upregulated and 27 downregulated genes, mostly associated with lipid metabolism, inflammation and oxidative stress. TAT-Gap24-treated animals showed 16 upregulated and 6 downregulated genes with more obscure functions in comparison with saline-treated mice. Conclusion: These findings suggest that connexin hemichannels are involved in the pathogenesis of NASH. Accordingly, inhibition of these hemichannels could represent a novel therapeutic approach in the treatment of NASH.