Mild traumatic brain injury (mTBI) or concussion is a very common occurrence in contact sports, and can cause brain damage with long-term symptoms, including depression, aggression, memory loss, and an increased risk of neurodegeneration later in life. Recently, there has been increased attention towards concussion in sport both in research and media, however the nature and pathophysiology of mTBI-induced neurodegeneration remain unknown. The objective of this study is to identify early pathophysiological markers of TBI. This study used a collection of donated postmortem brains with a history of repetitive mTBI in contact sports and non-TBI control brains. Nanostring ncounter’s immune panel was used to evaluate gene expression, and results showed that brains with a history of TBI tended to group with significantly older brains with no history of TBI in regards to their immune profile. Further analysis of this expression panel revealed that genes associated with senescence and secretory phenotype were upregulated in brains with a history of mTBI. Additionally, immunohistochemistry for γ-H2AX (a marker for double stranded DNA breaks) showed that brains with a history of repetitive TBI accumulated a spectrum of DNA damages not present in controls. This damage was widespread and involved mainly glial cells including oligodendrocytes, and astrocytes. The latter showed morphological changes reminiscent of senescence, including soma swelling and beading of processes. Further, these changes were accompanied by translocation of structural nuclear proteins. These changes preceded the appearance of abnormal protein deposition in the brain. Overall, these results suggest that DNA damage and cellular senescence are upstream events in the manifestation of post-mTBI symptoms and pathology, and represent promising opportunities for discovery of biomarkers for early TBI detection and follow-up of progression.
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