Exosome Derived From Traumatic Brain Injury Patients Accelerates Fracture Healing via SMAD7 Signaling Regulation

Abstract: Background: Extremity injuries, especially for bone fracture, predominate in warfare, and around one-third of military personnel sustain at least one kind of traumatic brain injury (TBI). The beneficial role of TBI in osteogenic differentiation and fracture healing was found in clinic, however, the underlying mechanism of this interesting finding is elusive. Exosome (Exos) is nanosized extracellular vesicles, and their regulatory role in bone remodeling have attracted accumulative attention.MethodsUltra-high speed gradient centrifugation was used to extract exosomes (Exos) both from fracture patients combined with TBI (TBI-Exos), and from isolated fracture patients (Ctr-Exos). Human mesenchymal stem cells (hMSCs) proliferation was checked by qRT-PCR, western blotting, ALP staining, alizarin red staining, and EdU (5-ethynyl-2’-deoxyuridine) assays. In addition, C57BL/6J mice were randomly divided into different groups according to the treatments, and the radiographic and histopathological results were analyzed to evaluate the effect of TBI-Exos on fracture healing. Results: In vitro, suppression of SMAD7 promoted osteogenic differentiation, whereas knock down of miR-21-5p in TBI-Exos deprived this bone-beneficial effect at a great extent. Similarly, our results confirmed that pre-injection of TBI-Exos leads to enhanced bone formation, whereas knock down of exosomal miR-21-5p was capable to markedly impair this bone-beneficial effect in vivo. Conclusion: Our findings provide a potential mechanism of the beneficial role of TBI in fracture healing with a particular focus on the TBI-Exos, and suggest that the use of nanosized materials combined with miR-21-5p-mimics may be a promising therapeutic approach to enhance fracture healing in the future.