Circulating monocytes expressing CD31: implications for acute and chronic angiogenesis

Area of Science:

• Cell Biology
• Immunology
• Oncology

Background:

• Angiogenesis, the formation of new blood vessels, is crucial for tissue repair and tumor growth.
• The specific roles of circulating cells, such as endothelial cells, stem cells, and progenitor cells, in angiogenesis remain incompletely understood.
• Understanding these cellular contributions is vital for developing targeted therapies, particularly in cancer treatment.

Purpose of the Study:

• To elucidate the contributions of various circulating cells to the process of angiogenesis.
• To identify specific cell types involved in neovascularization during different phases of tissue repair and tumor development.
• To explore potential therapeutic targets for anticancer treatments based on cellular mechanisms of angiogenesis.

Main Methods:

• Parabiosis was established between wild-type and green fluorescent protein (GFP)-transgenic syngeneic mice to enable cell tracking.
• Angiogenesis was studied in acute, subacute, and chronic phases using wound healing, implanted gel foam, and subcutaneous tumor models, respectively.
• Immunofluorescence and in vitro analyses were performed to characterize cell markers (F4/80, CD31, VEGFR2, CD133, von Willebrand factor, desmin) on circulating and newly formed vascular cells.

Main Results:

• Circulating monocytes expressed F4/80, CD31, and VEGFR2, distinguishing them from endothelial cells which expressed CD31, VEGFR2, and von Willebrand factor.
• GFP-positive cells within newly formed vessels in all angiogenesis models were identified as macrophages (expressing F4/80 and CD31).
• Pericytes (CD31 and desmin positive) were observed in tumor-associated vessels and within tumors.

Conclusions:

• Monocytes expressing CD31 and F4/80 are recruited to sites of tissue injury and directly contribute to angiogenesis.
• These findings reinforce the interconnectedness of the reticuloendothelial system and vascular development.
• The direct role of monocytes in angiogenesis presents promising targets for novel anticancer therapies.