Angiotensin II Regulates the Clonogenicity, Self-Renewal and Gene Expression of Murine Adventitial Macrophage Progenitor Cells (AMPCs)

Background: Angiotensin II (ATII) mediates diverse haematopoietic, inflammatory and vascular disease processes, through different cellular targets including macrophages. Here we investigated its effects on adventitial macrophage progenitor cells (AMPCs), a newly identified cell population that acts as a local source of self-renewing macrophages in murine arteries. Methods and Results: Single-cell digests of C57BL/6 J mouse aortas were cultured in methylcellulose-based assays and the number of haematopoietic colony forming units (CFUs) counted. Aortas displayed a marked (>95%) predilection to form macrophage CFUs (CFU-M), reflecting their content of clonogenic AMPCs. Secondary cultures of CFU-M resulted in a 5-10-fold enrichment in CFU-M yield (p < 0.005), confirming the self-renewal property of AMPCs. In primary and secondary CFU-M cultures, we observed enrichment of a distinct population of AMPCs that was Lin-CD45+CD11b-F4/80-Sca-1+c-kit+CX3CR1+ and expressed angiotensin converting enzyme (ACE) at high levels (86.8 ± 4.6%, n = 4). Treatment of aortic cells with ATII resulted in a dose-dependent 3-fold increase in primary CFU-M (p < 0.05), while Enalapril (ACE inhibitor), Losartan and PD 123,319 (ATII receptor antagonists) had the opposite effect. Despite marginal effects on phenotypic surface marker expression, ATII resulted in striking changes in mRNA transcript levels in AMPCs, greatly upregulating pluripotent, macrophage progenitor, M2 macrophage and endothelial genes, as well as angiotensin receptors, Agtr1 and Agtr2. Conclusion: ATII regulates the clonogenicity, self-renewal and gene expression signature of murine AMPCs providing new insights into adventitial biology. These effects may contribute to the well-known ability of ATII to drive proliferation of adventitial macrophages and their differentiation towards M2-like cells in atherosclerosis, aneurysm and vascular fibrosis.