CX(3)CR1 differentiates F4/80(low) monocytes into pro-inflammatory F4/80(high) macrophages in the liver

The expression of chemokine receptor CX(3)CR1 is related to migration and signaling in cells of the monocyte-macrophage lineage. The precise roles of CX(3)CR1 in the liver have been investigated but not clearly elucidated. Here, we investigated the roles of CX(3)CR1 in hepatic macrophages and liver injury. Hepatic and splenic CX(3)CR1(low)F4/80(low) monocytes and CX(3)CR1(low)CD16(−) monocytes were differentiated into CX(3)CR1(high)F4/80(high) or CX(3)CR1(high)CD16(+) macrophages by co-culture with endothelial cells. Moreover, CX(3)CL1 deficiency in human umbilical vein endothelial cells (HUVECs) attenuated the expression of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), whereas recombinant CX(3)CL1 treatment reversed this expression in co-cultured monocytes. Upon treatment with clodronate liposome, hepatic F4/80(high) macrophages were successfully depleted at day 2 and recovered similarly in CX(3)CR1(+/GFP) and CX(3)CR1(GFP/GFP) mice at week 4, suggesting a CX(3)CR1-independent replacement. However, F4/80(high) macrophages of CX(3)CR1(+/GFP) showed a stronger pro-inflammatory phenotype than CX(3)CR1(GFP/GFP) mice. In clodronate-treated chimeric CX(3)CR1(+/GFP) and CX(3)CR1(GFP/GFP) mice, CX(3)CR1(+)F4/80(high) macrophages showed higher expression of IL-1β and TNF-α than CX(3)CR1(−)F4/80(high) macrophages. In alcoholic liver injury, despite the similar frequency of hepatic F4/80(high) macrophages, CX(3)CR1(GFP/GFP) mice showed reduced liver injury, hepatic fat accumulation, and inflammatory responses than CX(3)CR1(+/GFP) mice. Thus, CX(3)CR1 could be a novel therapeutic target for pro-inflammatory macrophage-mediated liver injury.