Mus musculus strain:C57BL/6J Transcriptome or Gene expression. Mus musculus strain:C57BL/6J

Background: Paracrine activation of hepatic cannabinoid receptor 1 by hepatic stellate cell (HSC)-derived 2-arachidnoylglycerol (2-AG) is one of the critical mechanisms mediating alcoholic steatosis by stimulating de novo lipogenesis in hepatocytes. However, the precise mechanism of 2-AG production in HSCs is unknown.Methods: To examine alcohol-induced glutamate excretion, endocannabinoid production and consequent steatosis, C57BL/6 wild type, global metabotropic glutamate receptor 5 (mGluR5) knockout and hepatocyte-specific xCT knockout mice were fed liquid ethanol diet for 8 weeks. RNA sequencing, histology, immunoblots, quantitative polymerase chain reaction, and metabolite measurements were performed.Results: We found that chronic ethanol consumption significantly increased glutamate levels in blood and liver of ethanol-fed mice and blood of patients with alcoholic liver disease compared to controls. To find out the mechanism, RNA sequencing analysis exhibited the upregulation of xCT (a cystine-glutamate antiporter) through the antioxidant transcription factor Nrf2 in the liver of ethanol-fed mice. Mechanistically, cysteine deficiency and subsequent glutathione depletion was induced by impaired transsulfuration pathway in ethanol-fed mice, which leads to the glutamate excretion for cystine uptake (immediately reduced to cysteine) via upregulation of xCT in hepatocytes. Intriguingly, comparing with other hepatic cells, the mGluR5 was highly expressed in HSCs and 2-AG production in HSCs was remarkably increased by mGluR5 activation. Consistently, genetic or pharmacologic inhibition of mGluR5 or xCT significantly attenuated alcoholic steatosis in ethanol-fed mice, followed by suppression of 2-AG production and de novo lipogenesis.Conclusion: Taken together, our findings demonstrate that increased excretion of hepatic glutamate by xCT as a lipogenic mediator promotes alcoholic steatosis through mGluR5-mediated 2-AG production in HSCs, which could be a potential therapeutic target for alcoholic liver disease.