Traumatic brain injury or head impacts from contact sports are associated with tau astrogliopathy

Exposure to traumatic brain injury (TBI) and/or repetitive head impacts (RHI) increase the risk of a range of neurodegenerative pathologies, including chronic traumatic encephalopathy neuropathologic change (CTE-NC). Astrocytic tau pathology reminiscent of ageing-related tau astrogliopathy is a component feature of CTE-NC in many cases. Yet the relationship between TBI/RHI exposure and wider tau astrogliopathy, beyond that of CTE-NC, remains poorly characterized. Autopsy-derived material from 556 individuals was selected to include cases with a history of moderate or severe traumatic brain injury (survival >6 months, n = 77) or a history of participation in contact sports (n = 45), for comparison with uninjured controls with (n = 397) or without (n = 37) neuropathologically confirmed neurodegenerative disease. Representative tissue sections from multiple brain regions were then immunostained for hyperphosphorylated tau (p-tau; PHF-1) and assessed in accordance with the harmonized evaluation criteria for ageing-related tau astrogliopathy. PHF-1-immunoreactive thorn-shaped astrocytes were observed more frequently in contact sports participants (75.6%) versus controls with (32.5%; P < 0.001) and without (8.1%; P < 0.001) neurodegenerative disease. In addition, although the prevalence of thorn-shaped astrocytes following moderate/severe TBI (32.5%) was similar to neurodegenerative disease controls, regression analyses demonstrated increased odds of thorn-shaped astrocytes, when adjusting for age and sex (odds ratio 2.42, 95% confidence interval 1.29-4.54). These findings were observed regardless of whether the pathognomonic lesion of CTE-NC was present in the regions examined. Intriguingly, although subpial thorn-shaped astrocytes at sulcal depths were occasionally observed in aged controls with (3.6%) and without (2.8%) neurodegenerative disease, this pathology was considerably more common following RHI/TBI (42.2%; P < 0.001). These findings support a history of RHI or TBI as an independent risk factor for the development of thorn-shaped tau astrogliopathy, over and above ageing-related tau astrogliopathy observed in ageing and wider neurodegenerative disease. Moreover, trauma might be associated with thorn-shaped astrocytes within specific distributions, including the subpial region of the cortical sulcal depths. The clinical significance of these observations will be important to determine.