Mechanical loading stimulates bone angiogenesis through enhancing type H vessel formation and downregulating exosomal miR‐214‐3p from bone marrow‐derived mesenchymal stem cells

Abstract

Exosomes are important transporters of miRNAs, which play varying roles in the healing of the bone fracture. Angiogenesis is one of such critical events in bone healing, and we previously reported the stimulatory effect of mechanical loading in vessel remodeling. Focusing on type H vessels and exosomal miR-214-3p, this study examined the mechanism of loading-driven angiogenesis. MiRNA sequencing and qRT-PCR revealed that miR-214-3p was increased in the exosomes of the bone-losing ovariectomized (OVX) mice, while it was significantly decreased by knee loading. Furthermore, compared to the OVX group, exosomes, derived from the loading group, promoted the angiogenesis of endothelial cells. In contrast, exosomes, which were transfected with miR-214-3p, decreased the angiogenic potential. Notably, knee loading significantly improved the microvascular volume, type H vessel formation, and bone mineral density and contents, as well as BV/TV, Tb.Th, Tb.N, and Tb.Sp. In cell cultures, the overexpression of miR-214-3p in endothelial cells reduced the tube formation and cell migration. Collectively, this study demonstrates that knee loading promotes angiogenesis by enhancing the formation of type H vessels and downregulating exosomal miR-214-3p. K E Y W O R D S knee loading, MiRNA, osteoporosis, type H vessels, vessel remodeling 2 | WANG et Al. F I G U R E 1 Experimental setup, and the characterization of exosomes. A, Timeline (left) and loading site for knee loading (right, Bar = 1 cm). B, Morphology of exosomes with transmission electron microscopy, red arrows pointed to exosomes, Bar = 200 nm. C, The particle distribution was measured via nanoparticle tracking analysis. D, Protein markers of exosomes were detected by Western blot analysis. E, Representative images of HUVECs (red) incubated with PKH67-labelled exosomes (green) for 4 h. Bar = 50 µm

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