Effects Of The Activation Of TGR5 Receptor On The Permeability Of Blood-brain Barrier And Its Mechanismin In Mice With Traumatic Brain Injury

Background and Objective: Traumatic brain injury（TBI）,as one of the most threatening causes of disability and death in the world,has become an urgent social medical problem.Recent studies have shown that the destruction of the blood-brain barrier and traumatic brain edema after TBI promote the formation of intracranial hypertension and cerebral hernia,which are the key factors leading to the poor prognosis of patients with TBI.TGR5 is a plasma membrane-bound G-protein-coupled bile acid receptor,which exists widely in many tissues,including brain tissue,and can induce a variety of signal cascade reactions after activation.As a semisynthetic TGR5 agonist,INT-777 has been found to play a neuroprotective role by activating TGR5 in a variety of central nervous system（CNS）disease models,such as Alzheimer’s disease model,sepsis model,middle cerebral artery occlusion model,subarachnoid hemorrhage model and so on.However,the role of TGR5 receptor activation in TBI-induced blood-brain barrier disruption is unclear.In this study,a mouse TBI model was established to explore the effect of activating the TGR5 receptor on blood-brain barrier permeability after TBI in mice and its related mechanism,to provide a new intervention strategy for clinical treatment of TBI.Methods: 1.Model establishment: C57BL/6J mice were randomly divided into sham operation group（Sham group）,craniocerebral trauma group（TBI group）,solvent control group（TBI+Vehicle group）,and drug intervention group（TBI+INT-777 group）.After anesthesia,the model of traumatic brain injury（TBI）was established by a hydraulic brain percussion instrument.2.Determination of brain water content: the water content of brain tissue was measured by the dry-wet weight method after injury（1 day,2 days,3 days,5 days,7 days）to explore the peak period of brain edema.Then explore the effect of activating the TGR5 receptor on the degree of brain edema in mice.3.Evans blue penetration test: the changes in blood-brain barrier permeability of mice in each group were detected by Evans blue（EB）permeability test.4.HE staining: the brain tissue sections of mice were stained with HE to observe the effect of activating the TGR5 receptor on the degree of brain injury after TBI.5.Western blot: Western blot technique was used to evaluate the expression of tight junction proteins and matrix metalloproteinases in brain tissue.6.Behavioral experiment: the effect of activating TGR5 receptor on neurological dysfunction in mice after TBI was detected by modified neurological deficit score（m NSS）and bar turning test（Rotor-Rod）.Results: 1.The results of the dry-wet specific gravity method showed that the brain water content of mice after TBI was significantly higher than that of the sham group,and the brain water content reached the peak on the 2nd day after TBI.In the follow-up experiment,2 days after TBI can be used as observation time.2.Compared with the Sham group,brain water content and Evans blue（EB）extravasation in the other three groups increased significantly,while brain water content and Evans blue extravasation in the TBI+INT-777 group decreased significantly compared with the TBI group and TBI+Vehicle group（P < 0.05）.3.The results of HE staining showed that the structure of brain tissue in the Sham group was clear,uniform,and dense under the light microscope.The brain structure of mice in the TBI group and TBI+Vehicle group was disordered,local hemorrhage and edema,and neuronal vacuolation with a large number of inflammatory cell infiltration could be seen in the traumatic area.Although the brain tissue of the TBI+INT-777 group showed tissue disorder,compared with the TBI group and TBI+Vehicle group,the swelling of brain tissue was alleviated,and the aggregation of red blood cells was decreased and the degeneration of neurons was less.4.Western blot results showed that activation of the TGR5 receptor could reduce the loss of tight connexin expression（ZO-1,claudin-5,and occludin）and inhibit the high expression of matrix metalloproteinases（MMP-2,MMP-9）in brain tissue of mice after TBI.5.The results of m NSS score and rotated bar test confirmed that activation of the TGR5 receptor could significantly promote the recovery of exercise-related neurological function in the early stage of TBI in mice.Conclusions: 1.The peak of brain edema occurred 48 hours after TBI.Activation of the TGR5 receptor could reduce the degree of brain edema after TBI and stabilize the blood-brain barrier in the early stage of brain injury.2.Activation of the TGR5 receptor can reduce the degree of brain injury induced by TBI in mice.3.The brain protective effect of activating the TGR5 receptor may be related to the reduction of the expression of MMP-2 and MMP-9 and the loss of ZO-1,claudin-5,and occludin in brain tissue after TBI.4.Activation of the TGR5 receptor can alleviate TBI-induced neurological dysfunction in mice and promote the recovery of exercise-related neurological function in the early stage of injury.