HOXA5 induces M2 macrophage polarization to attenuate carotid atherosclerosis by activating MED1

Macrophage polarization is of great importance in the formation of atherosclerotic plaque. Homeobox A5 (HOXA5), one of the homeobox transcription factors, has been revealed to be closely associated with macrophage phenotype switching. This study aims to investigate the role of HOXA5 in carotid atherosclerosis (CAS). Herein, the role of HOXA5 was explored in polarized RAW264.7 macrophages in vitro and ApoE^-/- mice in vivo. Interestingly, compared with that in M0 macrophages, both the mRNA and protein expression levels of HOXA5 were decreased in lipopolysaccharide (LPS)/interferon (IFN)-γ-induced M1 macrophages, while increased in IL-4-induced M2 macrophages. In addition, in the presence of IL-4, HOXA5-overexpressing RAW264.7 cells preferred to polarizing toward M2 phenotypes. Furthermore, we found that HOXA5 bound to the promoter region and activated the expression of mediator subunit 1 (MED1), a gene known to regulate macrophage differentiation. Knocking MED1 down inhibited HOXA5-enhanced M2 macrophage polarization. In vivo, the CAS model was induced in ApoE^-/- mouse fed with a Western-type diet and placed a perivascular carotid collar. Decreased mRNA and protein expressions of HOXA5 were observed in carotid arteries of CAS mice. Forced overexpression of HOXA5 reduced intimal hyperplasia and lipid accumulation in carotid vessels, and it also promoted the polarization of macrophages to M2 subtypes. The expression of MED1 was decreased in atherosclerotic carotid vessels, while HOXA5 overexpression restored its change. Collectively, HOXA5 in carotid arteries is involved in the macrophage M1/M2 switching in atherosclerotic plaque, which may be associated with its transcriptional regulation of MED1.