Differential regulation of macrophage activation by the MIF cytokine superfamily members MIF and MIF-2 in adipose tissue during endotoxemia

Sepsis is a leading cause of death worldwide and recent studies have shown white adipose tissue (WAT) to be an important regulator in septic conditions. In the present study, the role of the inflammatory cytokine macrophage migration inhibitory factor (MIF) and its structural homolog D-dopachrome tautomerase (D-DT/MIF-2) were investigated in WAT in a murine endotoxemia model. Both MIF and MIF-2 levels were increased in the peritoneal fluid of LPS-challenged wildtype mice, yet in visceral WAT, the proteins were differentially regulated, with elevated MIF but down-regulated MIF-2 expression in adipocytes. Mif gene deletion polarized adipose tissue macrophages (ATM) towards an anti-inflammatory phenotype while Mif-2 gene knockout drove ATMs towards a pro-inflammatory phenotype and Mif-deficiency was found to increase fibroblast viability. Additionally, we observed the same differential regulation of these two MIF family proteins in human adipose tissue in septic vs healthy patients. Taken together, these data suggest an inverse relationship between adipocyte MIF and MIF-2 expression during systemic inflammation, with the downregulation of MIF-2 in fat tissue potentially increasing pro-inflammatory macrophage polarization to further drive adipose inflammation.