A study on the establishment of a traumatic brain injury model of tree shrews and the observation of neuroinflammatory responses.

Background and objective: The tree shrew (Tupaia belangeri) has become an ideal model for studying various neurological diseases. However, there is no stable tree shrew model of traumatic brain injury (TBI) at present. This study aimed to establish a tree shrew TBI model and clarify the expression characteristics of inflammatory factors after brain injury, as well as the polarization characteristics of glial cells. Methods: Twelve adult female tree shrews were randomly divided into the Sham group and the TBI group, the Marmarou weight-drop impact method was used to establish a TBI model. Open field experiments were conducted after modeling to evaluate the motor ability of tree shrews on the 1st and 7th day. Moreover, magnetic resonance imaging (MRI), HE staining were performed to detect the imaging and morphology changes caused by trauma. The expression levels of inflammatory factors were detected by ELISA 7th days after TBI. Finally, immunofluorescence and Western Blot were used to detect the polarization characteristics of microglia and astrocytes. Results: Open field experiments showed that the total motor distance of tree shrews in TBI group on the 1st and 7th days were significantly reduced. MRI showed high-density shadow in the parietal brain parenchyma, surrounded by low-density edema bands. HE staining showed in the TBI group, some neurons in the hippocampal region showed morphological abnormalities and nuclear condensation, glial cell proliferation, the arrangement of neurons in the cortical area is disordered, and the hierarchical structure is damaged. ELISA assays showed that the levels of pro-inflammatory factors in TBI group were significantly increased, while the anti-inflammatory factors' expressions decreased. Finally, Immunofluorescence staining showed that, compared with Sham group, fluorescence signals of M1 phenotype macroglia marker CD86 and M2 phenotype marker CD206 in different regions of hippocampus in TBI group were significantly enhanced at 7 days after TBI. Western Blotting showed that compared with sham group, the expression of A1 phenotype marker Serping1and A2 phenotype marker Ptx3 protein of astrocytes in TBI group was significantly up-regulated. ELISA results showed that the expression levels of C3 and S100a10 in brain tissue of tree shrews in TBI group were significantly higher than those in Sham group. Conclusions: This study successfully constructed a TBI tree shrew model and confirmed that the polarization imbalance of microglia and astrocytes may form a neurotoxic microenvironment, ultimately causing brain tissue damage.