Roles of CCR2 and CCR5 for Hepatic Macrophage Polarization in Mice With Liver Parenchymal Cell-Specific NEMO Deletion

Macrophages are key regulators of inflammation and cancer promotion in the liver, and their recruitment and activation is linked to chemokine receptor signaling. However, the exact roles of the chemokine receptors CCR2 and CCR5 for macrophage functions in the liver is obscure.

To study CCR2 and CCR5 in inflammatory liver injury, we used mice with a hepatocyte-specific knock-out of the nuclear factor κB (NF-κB) essential modulator (NEMO), termed NEMO^LPC-KO mice, and generated NEMO^LPC-KOCcr2^-/- and NEMO^LPC-KOCcr5^-/- mice. NEMO^LPC-KO mice develop hepatitis and fibrosis after two and liver tumors after six months.

We found that both CCR2 and CCR5 deficiency led to reduced fibrosis, while CCR5 deficiency increased steatosis and tumor burden in NEMO^LPC-KO mice. CCR2 was required for recruitment of hepatic macrophages, whereas CCR5 promoted stellate cell activation. The reduction of monocytes and macrophages by either anti-Gr1 antibody or clodronate-loaded liposomes (CLL), but not of CD8⁺ T cells or NK cells, significantly aggravated liver injury in NEMO^LPC-KO mice and was further increased in NEMO^LPC-KOCcr5^-/- mice. CLL-induced liver injury was dampened by the adoptive transfer of ex vivo generated macrophages, whereas the adoptive transfer of control CD115⁺ immature monocytes or B cells did not reduce liver injury.

Although CCR2 and CCR5 principally promote liver fibrosis, they exert differential functions on hepatic macrophages during liver disease progression in NEMO^LPC-KO mice. While CCR2 controls the recruitment of monocytes to injured livers, CCR5-dependent functions of liver macrophages limit hepatic injury, thereby reducing steatosis and hepatocarcinogenesis.