BMP-7 Treatment Increases M2 Macrophage Differentiation and Reduces Inflammation and Plaque Formation in Apo E-/- Mice

Inflammation plays a fundamental role in the inception and development of atherosclerosis (ATH). Mechanisms of inflammation include the infiltration of monocytes into the injured area and subsequent differentiation into either pro-inflammatory M1 macrophages or anti-inflammatory M2 macrophages. We have previously published data suggesting bone morphogenetic protein-7 (BMP-7) enhances M2 macrophage differentiation and anti-inflammatory cytokine secretion in vitro. In this regard, we hypothesized BMP-7 would inhibit plaque formation in an animal model of ATH through monocytic plasticity mediation. ATH was generated in male and female Apo E^-/- mice via partial left carotid artery (PLCA) ligation and mice were divided into 3 groups: Sham, PLCA, and PLCA+BMP-7 (200ug/kg; i.v.). Our data suggest that BMP-7 inhibits plaque formation and increases arterial systolic velocity. Furthermore, we report inhibition of monocyte infiltration and a decrease in associated pro-inflammatory cytokines (MCP-1, TNF-α, and IL-6) in the PLCA+BMP-7 mice. In contrast, our data suggest a significant (p<0.05) increase in M2 macrophage populations with consequential enhanced anti-inflammatory cytokine (IL-1RA, IL-10, and Arginase 1) expression following BMP-7 treatment. We have also observed that mechanisms promoting monocyte into M2 macrophage differentiation by BMP-7 involve the upregulation and activation of the BMP-7 receptor (BMP-7RII). In conclusion, we report that BMP-7 has the potential to mediate cellular plasticity and mitigate the inflammatory immune response, which results in decreased plaque formation and improved blood velocity.