Moderate alcohol induces stress proteins HSF1 and hsp70 and inhibits pro-inflammatory cytokines resulting in endotoxin tolerance1, 2

Binge or moderate alcohol exposure impairs host defense and increases susceptibility to infection due to compromised innate immune responses. However there is a lack of consensus on the molecular mechanism by which alcohol mediates this immunosuppression. Here, we show that cellular stress proteins HSF1 and hsp70 play a mechanistic role in alcohol-mediated inhibition of the TLR4/MyD88 pathway. Alcohol exposure induced transcription factor HSF1 mRNA expression and DNA binding activity in primary human monocytes and murine macrophages. Furthermore HSF1 target gene hsp70 mRNA and protein are upregulated by alcohol in monocytes. In vitro pre-exposure of moderate alcohol reduced subsequent LPS-induced NF-κB promoter activity and downstream TNFα, IL-6 and IL-1β production, exhibiting endotoxin tolerance. Mechanistic analysis demonstrates that alcohol induced HSF1 binds to the TNFα promoter in macrophages at early timepoints exerting transrepression and decreased TNFα expression. Furthermore, association of hsp70 with NF-κB subunit p50 in alcoholtreated macrophages correlates with reduced NF-κB activation at later timepoints. Hsp70 overexpression in macrophages was sufficient to block LPS-induced NF-κB promoter activity suggesting alcoholmediated immunosuppression by hsp70. The direct crosstalk of hsp70 and HSF1 was further confirmed by the loss of alcohol-mediated endotoxin tolerance in hsp70 and HSF1 silenced macrophages. Altogether, our data suggest that alcohol-mediated activation of HSF1 and induction of hsp70 inhibits TLR4-MyD88 signaling and are required for alcohol-induced endotoxin tolerance. Using stress proteins as direct drug targets would be clinically relevant in alcohol abuse patients and may serve to provide a better understanding of alcohol-mediated immunosuppression.