We know that traumatic brain injury increases the risk of later developing neurodegenerative disorders such as Alzheimer's disease, but we haven't known why. New mouse studies suggest a reason.
In the research, mice who had a toxic form of tau protein (taken from mice who had suffered TBI) injected into their hippocampus, showed impaired memory and cognition. Moreover, levels of the aggregated tau protein not only increased in the hippocampus, but also in the cerebellum (which is quite some distance away from the hippocampus). This is consistent with other research showing that tau tangles spread from the initial injection site, using mice modeling Alzheimer's disease.
The study followed on from previous research showing that this form of tau protein increases after a traumatic brain injury and may contribute to development of chronic traumatic encephalopathy (a condition experienced by many professional athletes and military personnel).
The findings support the hypothesis that many of the symptoms of TBI may be down to an increase in these tau tangles, and that this may also be responsible for the increased risk for neurodegenerative disease. As an obvious corollary, it also suggests that the tau tangles are an important therapeutic target.
 . Tau oligomers derived from Traumatic Brain Injury cause cognitive impairment and accelerate onset of pathology in Htau mice. Journal of Neurotrauma [Internet]. 2016 . Available from: http://online.liebertpub.com/doi/abs/10.1089/neu.2015.4262