A Novel Repetitive Mild Traumatic Brain Injury Mouse Model For Chronic Traumatic Encephalopathy Research

Objective Athletes,military personnel and mobility-declined elderly people are prone to repetitive mild traumatic brain injury(rm TBI).The injury does not cause acute pathological changes,but leads to chronic neurodegeneration,long-term cognitive dysfunction and even chronic traumatic encephalopathy(CTE).CTE is a progressive neurodegenerative disease associated with repeated mild traumatic brain injury,often accompanied by symptoms of emotional and behavioral changes,such as irritability,impulsivity,aggression,depression and long-term cognitive dysfunction.At present,the pathogenesis of CTE,biomarkers with diagnostic value,and effective treatment methods are still unclear.A suitable animal model is the basis for studying its pathogenesis,biomarkers,and treatments.Many existing rm TBI animal models reported uncontrollable adverse effects and long experiment period.Therefore,an improved model needs to be designed,and we hope to provide a convenient and effective animal model for CTE research.Methods Healthy male adult C57BL/6 mice were provided by the Chinese Academy of Military Sciences(Beijing China)and randomly divided into 3 groups: control group,single mild traumatic brain injury group(sm TBI)and repeated mild traumatic brain injury group(rm TBI).Our rm TBI mouse model is a modification of the closed head injury method using electronic controlled cortical impact system.For the rm TBI mice,repetitive injury was induced for totally 4 times with a 48-h interval.The sm TBI mice were sham-operated for the first 3 times,and were only impacted at the last time.The sham mice underwent the same operating procedures except for the impact for all the 4 times.The Rotarod test was conducted at 1 h before each impact and 24 h post each impact to assess the transient motor deficits in rm TBI mice during the impacting procedure.The gross pathology was examined at 1 day post last-injury(1DPI).Brain tissue water content was measured on 1 and 3DPI.RT-PCR was performed on 1,3,7,14,35 DPI to evaluate the level of inflammatory factors.H&E staining was performed on brain sections of 1,3,7,14 and 35 DPI to examine pathological changes.Western blotting and ELISA were conducted on 35 DPI to detect pathological protein.Immunofluorescence staining was also used to assess the number of neurons and axonal damage.Cognitive function was evaluated by new object recognition test.The MWM test was conducted to evaluate spatial learning and memory ability of rm TBI mice on 36–40 DPI.All data are based on at least 3 independent experiments.Results 1.rm TBI did not induce acute macroscopic brain damage and brain edema.2.rm TBI led to sustained inflammatory response in injured brain.3.rm TBI led to chronic neurodegeneration in injured brain.4.rm TBI could result in cognitive dysfunctionConclusion Our rm TBI model didn't induce acute macroscopic contusion,brain edema.But it could lead to sustained neuroinflammtion and chronic neurodegeneration in injured brain,and resulted in cognitive dysfunction within 5 weeks post injury.It could serve as a platform for research on the pathogenesis,diagnosis and potential therapeutics for rm TBI and CTE.