Probiotic‐generated product protects against alcoholic liver disease through increasing intestinal AhR‐IL22‐Reg3 and Nrf2 signaling

Background Probiotics are known to modulate intestinal barrier integrity against alcohol‐induced endotoxin leakiness and bacterial translocation. Our previous studies showed that Lactobacillus rhamnosus GG (LGG) and its culture supernatant protected against alcoholic liver disease (ALD) through increasing intestinal mucus and epithelial tight junction protein expression resulting in a reduction of circulation LPS level. The precise mechanisms underlying this protective effect are still not clear. Recent studies demonstrated the critical role of intestinal aryl hydrocarbon receptor (AhR) in the regulation of RORγt + innate lymphoid cell (ILC3) function to produce IL22, which modulates intestinal microbiota homeostasis and barrier function through increasing the expression of epithelial antimicrobial peptide regenerating islet‐derived protein 3γ (Reg3γ) and Reg3β. Methods We isolated a product (LGGp) from LGG and examined its role in the modulation of ALD. C57B6 mice were subjected the Lieber DeCarli liquid diet containing 5% alcohol for 10 days, and one bolus of alcohol (5 g/kg) was gavaged on the last day 9 hours before tissue collecting. Control mice were fed isocaloric maltose dextrin. LGGp was supplemented on day 7 once a day for three days. Results This three‐day administration of LGGp reversed alcohol‐induced hepatic steatosis and injury, demonstrated by reduced Oil red O staining of liver section, decreased serum ALT and AST levels and reduced hepatic apoptosis. The protective effects were associated with decreased circulating LPS concentration and hepatic bacterial load, indicating an increased gut barrier function. Further analysis showed that LGGp activated AhR luciferase activity and increased Cyp1a1 (AhR target) enzymatic activity. LGGp treatment increased intestinal mRNA expression of IL22, Cyp1a1, Reg3g and Reg3b, which play a critical role in modulating intestinal immune response to bacteria invasion and translocation. In addition, LGGp treatment significantly increased intestinal epithelial nuclear factor erythroid 2‐related factor 2 (Nrf2) protein expression, which were associated with increased protein expression of epithelial tight junctions ZO‐1, occludin, claudin‐1. Furthermore, LGGp inhibited LPS‐induced pro‐inflammatory factors TNFα and IL1β in mRNA and protein levels in Raw264.7 macrophage cells. Conclusions Our results demonstrate that LGGp treatment protects against ALD through activation of intestinal AhR‐mediated upregulation of IL22 and Reg3 and through Nrf2‐mediated upregulation of intestinal tight junction proteins that lead to the decreased LPS release and bacterial translocation and reversal of ALD. Support or Funding Information Supported by grants from NIH.