Alcohol-induced adipose tissue macrophage phenotypic switching is independent of myeloid Toll-like receptor 4 expression

Abstract

Alcoholic liver disease results from a combination of immune and metabolic pathogenic events. In addition to liver injury, chronic alcohol consumption also causes adipose tissue inflammation. The specific immune mechanisms that drive this process are unknown. Here, we sought to determine the role of the innate immune receptor Toll-like receptor 4 (TLR4) in alcohol-induced adipose tissue inflammation. Using a model of chronic, multiple-binge alcohol exposure, we showed that alcohol-mediated accumulation of proinflammatory adipose tissue macrophages was absent in global TLR4 knockout mice. Proinflammatory macrophage accumulation did not depend on macrophage TLR4 expression; LysMCre-driven deletion of Tlr4 from myeloid cells did not affect circulating endotoxin or the accumulation of M1 macrophages in adipose tissue following alcohol exposure. Proinflammatory cytokine/chemokine production in the adipose stromal vascular fraction also occurred independently of TLR4. Finally, the levels of other adipose immune cells, such as dendritic cells, neutrophils, B cells, and T cells, were modulated by chronic, multiple-binge alcohol and the presence of TLR4. Together, these data indicate that TLR4 expression on cells, other than myeloid cells, is important for the alcohol-induced increase in proinflammatory adipose tissue macrophages.