Role Of Brain Tissue-derived Exosomes In Bone Healing In Patients With Fracture Combined With Traumatic Brain Injury

Clinical studies have found that in patients with traumatic brain injury and fractures,fracture healing is faster than in patients with a single fracture,manifesting as more bone callus growth at the fracture site,and even heterotopic ossification in other parts of the body.Previous studies have pointed out that its possible mechanism is that brain injury increases the expression of osteoblast-associated cytokines and promotes fracture healing through the action of humoral regulation.Exosomes are a kind of nanoscale membrane vesicles secreted by cells.It contains cell-specific proteins,mi RNAs,and m RNAs that can be passed on to other cells as signaling molecules to influence their function.Different exosomes secreted by different cells contain different components,resulting in different functions.Studies have found that exosomes also play a key role in the process of bone metabolism.It has also been found that the expression of mi RNAs related to osteogenic growth is significantly up-regulated in exosomes secreted by brain tissue after trauma.Therefore,we use the exosome as an entry point to explore the mechanism of brain injury induced fracture healing.In the first part,we established a model of tibial fracture with brain injury in mice and observed the effect of brain injury on the amount of callus in the tibial fracture in mice by imaging examination.Through the histopathological examination of the tibia specimens,the expression of osteoblast related markers was detected.The results suggest that traumatic brain injury can promote the excessive growth of osteophytes in the fracture site and overexpression of osteogenic related factors.In the second part,we first established a model of tibial fracture with brain injury in mice.After collection of blood samples,exosomes in plasma were extracted by ultracentrifugation and the exosomes were identified.CCK-8 was used to examine the effect of exosomes on osteoblast proliferation.The effects of exosomes on osteoblast differentiation were studied at the cellular,protein,and gene levels by ALP staining and activity assays,Western Blot,and Q-PCR,respectively.Through mi RNA sequencing of exosomes in order to find the key role of mi RNA,to explore the possible mechanism of brain trauma to promote fracture healing.The results suggest that exosomes secreted by brain tissue after brain trauma have the ability to promote the proliferation and differentiation of osteoblasts.Sequencing results showed differential expression of osteogenic related mi RNAs,suggesting that the mechanism of brain injury promoting fracture healing may be the increased expression of osteogenesis-related mi RNAs in exosomes secreted by brain tissue after brain trauma,which is transmitted to the osteoblasts in the fracture through exosomes,thereby promoting osteogenic differentiation.