The Yin-Yang functions of macrophages in metabolic disorders

Macrophages are widely distributed in various metabolic tissues/organs and play an essential role in the immune regulation of metabolic homeostasis. Macrophages have two major functions: adaptive defenses against invading pathogens by triggering inflammatory cytokine release and eliminating damaged/dead cells via phagocytosis to constrain inflammation. The pro-inflammatory role of macrophages in insulin resistance and related metabolic diseases is well established, but much less is known about the phagocytotic function of macrophages in metabolism. In this review, we review our current understanding of the ontogeny, tissue distribution, and polarization of macrophages in the context of metabolism. We also discuss the Yin-Yang functions of macrophages in the regulation of energy homeostasis. Third, we summarize the crosstalk between macrophages and gut microbiota. Lastly, we raise several important but remain to be addressed questions with respect to the mechanisms by which macrophages are involved in immune regulation of metabolism.