Exosome MiR‐21‐5p Upregulated by HIF‐1α Induces Adipose Stem Cell Differentiation to Promote Ectopic Bone Formation

Abstract Heterotopic bone occurs after burns, trauma and major orthopedic surgery, which cannot be completely cured by current treatments. The development of new treatments requires more in‐depth research into the mechanism of HO. Available evidence suggests that miR‐21‐5p plays an important role in bone formation. However, its mechanism in traumatic HO is still unclear. First, we identified exosomes extracted from L6 cells using TEM observation of the structure and western blotting detection of the surface marker CD63. Regulation effect of HIF‐1α to miR‐21‐5p was confirmed by q‐PCR assay. Then we co‐cultured L6 cells with ASCs and performed alizarin red staining and ALP detection. Overexpression of miR‐21‐5p upregulated BMP4, p‐smad1/5/8, OCN and OPN, which suggests the BMP4‐smad signaling pathway may be involved in miR‐21‐5p regulation of osteogenic differentiation of ASCs. Finally in vivo experiments showed that miR‐21‐5p exosomes promoted ectopic formation in traumatized mice. This study confirms that HIF‐1α could modulate miR‐21‐5p exosomes to promote post‐traumatic ectopic bone formation by inducing ASCs cell differentiation. Our study reveals the mechanisms of miR‐21‐5p in ectopic ossification formation after trauma.