While exogenous administration of recombinant CXCL12 was proposed to activate brown adipocytes in vitro and the CXCL12/CXCR4 axis may modulate BAT function in obesity [22,23], a recent study showed that CXCL12 could be produced by smooth muscle cells in BAT to recruit macrophages and support sympathetic input [24]. Here, CXCL12 is linked to obesity due to melanocortin 4 receptor deficiency.