Abstract
Binge/moderate alcohol suppresses TLR4-MyD88 proinflammatory cytokines; however, alcohol's effects on TLR-TRIF signaling, especially after in vivo exposure in humans, are unclear. We performed a comparative analysis of the TLR4-MyD88, TLR4-TRIF, and TLR3-TRIF pathways in human monocytes following binge alcohol exposure. Mechanistic regulation of TLR-TRIF signaling by binge alcohol was evaluated by analyzing IRF3 and TBK1, upstream regulator protein phosphatase 1 (PP1), and immunoregulatory stress proteins HspA1A and XBP-1 in alcohol-treated human and mouse monocytes/macrophages. Two approaches for alcohol exposure were used: in vivo exposure of primary monocytes in binge alcohol-consuming human volunteers or in vitro exposure of human monocytes/murine macrophages to physiological alcohol concentrations (25-50 mM ethanol), followed by LPS (TLR4) or polyinosinic-polycytidylic acid (TLR3) stimulation ex vivo. In vivo and in vitro binge alcohol exposure significantly inhibited the TLR4-MyD88 cytokines TNF-α and IL-6, as well as the TLR4-TRIF cytokines/chemokines IFN-β, IP-10, and RANTES, in human monocytes, but not TLR3-TRIF-induced cytokines/chemokines, as detected by quantitative PCR and ELISA. Mechanistic analyses revealed TBK-1-independent inhibition of the TLR4-TRIF effector IRF3 in alcohol-treated macrophages. Although stress protein XBP-1, which is known to regulate IRF3-mediated IFN-β induction, was not affected by alcohol, HspA1A was induced by in vivo alcohol in human monocytes. Alcohol-induced HspA1A was required for inhibition of TLR4-MyD88 signaling but not TLR4-TRIF cytokines in macrophages. In contrast, inhibition of PP1 prevented alcohol-mediated TLR4-TRIF tolerance in macrophages. Collectively, our results demonstrate that in vivo and in vitro binge alcohol exposure in humans suppresses TLR4-MyD88 and TLR4-TRIF, but not TLR3-TRIF, responses. Whereas alcohol-mediated effects on the PP1-IRF3 axis inhibit the TLR4-TRIF pathway, HspA1A selectively suppresses the TLR4-MyD88 pathway in monocytes/macrophages.