Human serum‐derived exosomes modulate macrophage inflammation to promote VCAM1‐mediated angiogenesis and bone regeneration

During exogenous bone‐graft‐mediated bone defect repair, macrophage inflammation dictates angiogenesis and bone regeneration. Exosomes from different human cells have shown macrophage immunomodulation‐mediated bone regeneration potential. However, the effect of human serum‐derived exosomes (serum‐Exo) on macrophage immunomodulation‐mediated angiogenesis during bone defect repair has not been investigated yet. In this study, we explored the effects of serum‐Exo on macrophage inflammation regulation‐mediated angiogenesis during bone defect repair and preliminarily elucidated the mechanism. Healthy serum‐Exo was isolated by ultracentrifugation. The effect of serum‐Exo on LPS‐induced M1 macrophage inflammation was analysed in vitro. The conditioned medium of serum‐Exo‐treated LPS‐induced M1 macrophage (serum‐Exo‐treated M1 macrophage‐CM) was used to culture human umbilical vein endothelial cells (HUVEC), and the effect on angiogenesis was analysed by western blot, qRT‐PCR, etc. mRNA‐sequencing of HUVECs was performed to identify deferentially expressed genes. Finally, the rat mandibular defect model was established and treated with Bio‐Oss and Bio‐Oss + Exo. The effect of the Bio‐Oss + Exo combination on mandibular bone regeneration was observed by micro‐computed tomography (micro‐CT), haematoxylin and eosin (HE) staining, Masson staining, and immunohistochemical staining. Serum‐Exo promoted the proliferation of RAW264.7 macrophages and reduced the expression of M1‐related genes such as IL‐6, IL‐1β, iNOS, and CD86. Serum‐Exo‐treated M1 macrophage‐CM induced the proliferation, migration, and angiogenic differentiation of HUVEC, as well as the expression of H‐type blood vessel markers CD31 and endomucin (EMCN), compared with M1 macrophage‐CM. Moreover, higher expression of vascular endothelial adhesion factor 1 (VCAM1) in HUVEC cultured with serum‐Exo‐treated M1 macrophage‐CM compared with M1 macrophages‐CM. Inhibition of VCAM1 signalling abrogated the pro‐angiogenic effect of serum‐Exo‐treated M1 macrophage‐CM on HUVEC. Local administration of serum‐Exo during mandibular bone defect repair reduced the number of M1 macrophages and promoted angiogenesis and osteogenesis. Collectively, our results demonstrate the macrophage inflammation regulation‐mediated pro‐angiogenic potential of serum‐Exo during bone defect repair possibly via upregulation of VCAM1 signalling in HUVEC.