Effects Of VEGI On The Activation And Polarization Of Microglia In Traumatic Brain Injury Mice

Objective: The latest research suggests that the brain inflammation resulted by traumatic brain injury can exacerbate the pathophysiological process of secondary brain injury, leading to the aggravate of brain edema symptoms, increase of intracranial pressure, neuronal apoptosis and the loss of neurological function, which greatly increased the harm caused by primary brain damage. Vascular endothelial cell growth inhibitory factor(VEGI) is a member of the tumor necrosis factor superfamily, the role of VEGI has been reported in a variety of diseases and received lots of attention. VEGI not only can inhibit the angiogenesis of tumor, but also can regulate the inflammation and inhibit the edema formation. In this study, the model of closed traumatic brain injury was made by Fluid Percussion Injury method. Then we explored whether the activation of microglia after traumatic brain injury, the change of polarization time and the application of VEGI had any impact on activation and polarization of microglia. The mice were administrated with VEGI after treated with traumatic brain injury application. Finally, the brain edema, blood brain barrier permeability, and the recovery of cognitive function were observed.Methods: 180 clean grade healthy adult male mice C57BL/6 were selected, and the closed brain injury model of mice were prepared by the method of Fluid Percussion Injury(FPI). Mice were randomly divided into sham operation group(Sham group), traumatic brain injury group(TBI group) and brain trauma treated with VEGI group(TBI+VEGI group). According to the different killed time after injury, the brain injury group(TBI group) were divided into 1 h, 6 h, 1 D, 3 D, 7 d, 14 d and 21 d group, each group had 5 mice. The animals were sacrificed at different time points after the injury, the brain tissues were taken for immunohistochemical staining, and the changes of the small glial cells in the wound were observed. According to the different killed time after injury, brain trauma treated with VEGI group(TBI+VEGI group) were divided into 1 h, 6 h, 1 D, 3 D, 7 d, 14 d and 21 d group, each group had 5 mice. The animals were sacrificed at different time points after the injury, and the brain tissues of the wounded area were taken for immunohistochemical staining, and the changes of the small glial cells in the wound were observed. The mice in TBI group and TBI+VEGI group were sacrificed at the first days and the third day after injury, take wet and dry weight method to detect the water content of brain tissue after injury in each group of mice. The blood brain barrier permeability was measured by Evans blue method on the third day after injury. Finally, evaluation of neurological behavioral function in mice were detected by modified neurological function score(m NSS).Results: The severe craniocerebral injury mice model can be establish by application of Fluid Percussion Injury method, the typical pathological changes were observed by HE staining as TBI. Immunohistochemical staining showed that after brain injury, the microglia were activated in a different subtype(M1 and M2). And generalized microglia reached the peak in the 7th day after injury, then decreased. Whereas M1 and M2 microglia reached a peak at 5th day; the M1 remained at high values, followed by a slow decline, but M2 had a rapid decrease after peak. Compared with TBI group, the number of infiltrating microglia around the mouse traumatic lesions were significantly reduced in TBI+VEGI group on the 3rd day, 5th day and 7th day(P<0.05). Further study found that VEGI can affect the polarization of microglia after brain injury in mice, compared with the TBI group, the number of M1(CD11C+) microglia in TBI+VEGI group was significantly decreased after trauma, while the number of M2(Arg-1+) microglia was significantly higher than that of TBI group, and each group had statistical significance(P<0.05). The dry and wet weight method explained that TBI group and TBI+VEGI group showed a significant increase in brain water content compared with the blank control group. On the 3rd day, 5th day and 7th day after injury, the water content of brain tissue in TBI+VEGI group was significantly lower than that of TBI group, and the differences were statistically significant(P<0.05). The Evans blue permeability experiment found that the permeability of blood brain barrier in group TBI+VEGI was lower than that in TBI group on the 3rd day after traumatic brain injury(P < 0.05).Conclusions:1. After brain injury, microglia can be activated and reach the peak at the 7th day after injury; M1 microglia reached a peak at the 5th day, followed by a slight decrease; M2 microglial cells reached the peak at the 5th day, then decreased. 2. Brain edema after traumatic brain injury in mice increased dramatically, reached the peak at the 3rd day.3. VEGI can reduce the activation of microglia after TBI, inhibit the activation of M1 microglia, as well as increase the activation of M2 microglia cells. Therefore, VEGI can affect the inflammatory response after traumatic brain injury by adjusting the polarization of microglia.4. VEGI can effectively reduce brain edema and promote the recovery of neurological function by regulating the inflammatory response in the brain of TBI.