Bone marrow-independent adventitial macrophage progenitor cells contribute to angiogenesis

Florian Kleefeldt,Georg Eckner,Heike Bömmel,Jan Allmanritter,Uwe Rueckschloss,Jochen Bauer,Süleyman Ergün,Barbara Braunger,Berin Upcin,Christian Schulz

doi:10.1038/s41419-022-04605-2

Abstract

Pathological angiogenesis promotes tumor growth, metastasis, and atherosclerotic plaque rupture. Macrophages are key players in these processes. However, whether these macrophages differentiate from bone marrow-derived monocytes or from local vascular wall-resident stem and progenitor cells (VW-SCs) is an unresolved issue of angiogenesis. To answer this question, we analyzed vascular sprouting and alterations in aortic cell populations in mouse aortic ring assays (ARA). ARA culture leads to the generation of large numbers of macrophages, especially within the aortic adventitia. Using immunohistochemical fate-mapping and genetic in vivo-labeling approaches we show that 60% of these macrophages differentiate from bone marrow-independent Ly6c+/Sca-1+ adventitial progenitor cells. Analysis of the NCX−/− mouse model that genetically lacks embryonic circulation and yolk sac perfusion indicates that at least some of those progenitor cells arise yolk sac-independent. Macrophages represent the main source of VEGF in ARA that vice versa promotes the generation of additional macrophages thereby creating a pro-angiogenetic feedforward loop. Additionally, macrophage-derived VEGF activates CD34+ progenitor cells within the adventitial vasculogenic zone to differentiate into CD31+ endothelial cells. Consequently, depletion of macrophages and VEGFR2 antagonism drastically reduce vascular sprouting activity in ARA. In summary, we show that angiogenic activation induces differentiation of macrophages from bone marrow-derived as well as from bone marrow-independent VW-SCs. The latter ones are at least partially yolk sac-independent, too. Those VW-SC-derived macrophages critically contribute to angiogenesis, making them an attractive target to interfere with pathological angiogenesis in cancer and atherosclerosis as well as with regenerative angiogenesis in ischemic cardiovascular disorders.

Highlights

Angiogenesis, the formation of new blood vessels based on preexisting vasculature, is involved in physiological and pathological processes like wound healing, organ growth, and maintenance as well as retinopathy, cardiovascular diseases, and tumor progression [1–4]
In order to elucidate the origin of tumor-associated macrophages (TAMs), Fujimoto et al showed augmented infiltration of circulating macrophages into the tumor due to stromal expression of macrophage chemoattractant protein-1 (MCP-1) that resulted in increased angiogenesis as well as tumor growth in a murine tumor model [21]
Generation of macrophages during aortic ring assays (ARA) affects vascular sprouting The presence of mature macrophages in cross-sections of FIA and after 11 days of ARA was analyzed by immunostaining for F4/80 [50, 51]

Summary

Introduction

Angiogenesis, the formation of new blood vessels based on preexisting vasculature, is involved in physiological and pathological processes like wound healing, organ growth, and maintenance as well as retinopathy, cardiovascular diseases, and tumor progression [1–4]. The formation of new blood vessels is a complex process involving different cell types and endogenous factors that either promote or inhibit it. During the last decades increasing attention has been paid to the impact of nonvascular cell types like macrophages [11, 12], especially in the context of tumor angiogenesis [13]. These macrophages that are abundant in tumors are called tumor-associated macrophages (TAMs) [14, 15]. In clinical studies, tumor treatment via inhibition of monocyte recruitment was very inefficient [22–28]

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