神経科学：繰り返される頭部外傷は若年アスリートの脳細胞を変化させる

Repeated head impacts in young athletes can cause neuron loss and inflammation long before signs of neurodegenerative diseases appear, according to a study published in Nature. The findings may help explain early symptoms in individuals exposed to contact sports and could guide future efforts to detect and treat brain damage earlier.

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with repetitive head impacts, often sustained in contact sports such as American football. Currently, it can only be diagnosed after death by identifying abnormal tau protein accumulation in specific brain regions. However, many young athletes show symptoms before this protein appears, highlighting the need to understand early brain changes.

Jonathan Cherry and colleagues analysed post-mortem brain tissue from 28 individuals under the age of 51, including 8 people with no history of head trauma, 9 contact sport athletes with no signs of tau protein accumulation and 11 contact sport athletes diagnosed with early-stage CTE. All but one athlete played American football. The researchers found that all contact sport athletes, regardless of CTE status, showed increased neuroinflammation, blood vessel damage and neuron loss compared with non-athlete controls. Notably, they observed a 56% reduction of neurons in the superficial cortical layer, a key region for thinking and mood, in contact sport athletes compared with age-matched individuals without head trauma. This neuron loss was not associated with tau protein accumulation, suggesting it occurs earlier and independently of CTE’s defining pathology. The authors also found that the amount of inflammatory microglia, immune cells in the brain, increased with increasing years of football play. Additionally, they identified a potential signalling pathway between microglia and blood vessels that may help explain how repeated head trauma leads to lasting brain changes and could inform future treatments.

The findings suggest that repetitive head trauma alone can induce long-term cellular changes in the brain, potentially contributing to early symptoms before the accumulation of tau protein. Although further research is needed in larger and more diverse cohorts, the study highlights the importance of protecting young athletes and provides new directions for potential diagnostic and therapeutic targets of brain changes caused by repetitive head impact.