TLR4 signaling and the inhibition of liver hepcidin expression by alcohol

AIM: To understand the role of toll-like receptor 4 (TLR4) signaling in the regulation of iron-regulatory hormone, hepcidin by chronic alcohol consumption. METHODS: For chronic alcohol intake studies, TLR4 mutant mice on C3H/HeJ background and wildtype counterpart on C3H/HeOuJ background were pair-fed with regular (control) and ethanol-containing Lieber De Carli liquids diets. Gene expression was determined by real-time quantitative PCR. Protein-protein interactions and protein expression were determined by co-immunoprecipitation and western blotting. The occupancy of hepcidin gene promoter was determined by chromatin immunoprecipitation assays. RESULTS: Chronic alcohol intake suppressed hepcidin mRNA expression in the livers of wildtype, but not TLR4 mutant, mice. The phosphorylation and nuclear translocation of nuclear factor (NF)-κB p65 subunit protein was observed in alcohol-fed wildtype, but not in alcohol-fed TLR4 mutant, mice. Similarly, alcohol induced the binding of NF-κB p50 subunit protein to hepcidin gene promoter in wildtype, but not in TLR4 mutant, mice. In contrast, the phosphorylation of Stat3 in the liver was stronger in alcohol-treated TLR4 mutant mice compared to alcohol-treated wildtype mice. The occupancy of hepcidin gene promoter by Stat3 was observed in alcohol-fed mutant, but not in wildtype, mice. An interaction between NF-κB p65 subunit protein and small heterodimer partner protein (SHP) was observed in the livers of both wildtype and TLR4 mutant mice fed with the control diet, as shown by co-immunoprecipitation studies. Alcohol intake elevated cytosolic SHP expression but attenuated its interaction with NF-κB in the liver, which was more prominent in the livers of wildtype compared to TLR4 mutant mice. CONCLUSION: Activation of TLR4 signaling and NF-κB are involved in the suppression of hepcidin gene transcription by alcohol in the presence of inflammation in the liver.