M2 macrophage-derived exosomes induce angiogenesis and increase skin flap survival through HIF1AN/HIF-1/VEGFA control

Background: Skin flap transplantation is a routine strategy in plastic and reconstructive surgery for skin-soft tissue defects. Recent research has shown that M2 macrophages have the potential for pro-angiogenesis during tissue healing.Methods: In our research, we extracted the exosomes from M2 macrophages(M2-exo) and applied the exosomes in the model of skin flap transplantation. The flap survival area was measured, and the choke vessels were assessed by morphological observation. Hematoxylin and eosin (H&E) staining and Immunohistochemistry were applied to assess the neovascularization. The effect of M2-exo on the function of Human umbilical vein endothelial cells (HUVECs) was also investigated. We also administrated 2-methoxyestradiol (2-ME2, an inhibitor of HIF-1 alpha) to explore the underlying mechanism. We tested the effects of M2-Exo on the proliferation of HUVECs through CCK8 assay and EdU staining assay.Results: The survival area and number of micro-vessels in the skin flaps were increased in the M2-exo group. Besides, the dilation rate of choke vessels was also enhanced in the M2-exo group. Additionally, compared with the control group, M2-exo could accelerate the proliferation, migration and tube formation of HUVECs in vitro. Furthermore, the expression of the pro-angiogenesis factors, HIF-1 alpha and VEGFA, were overexpressed with the treatment of the M2-exo. The expression of HIF1AN protein level was decreased in the M2-exo group. Finally, treatment with HIF-1 alpha inhibitor reverses the pro-survival effect of M2-exo on skin flaps by interfering with the HIF1AN/HIF-1 alpha/VEGFA signaling pathway.Conclusion: This study showed that M2-exosomes promote skin flap survival by enhancing angiogenesis, with HIF1AN/HIF-1 alpha/VEGFA playing a crucial role in this process.