From Traumatic Brain Injury to Alzheimer’s Disease: Multilevel Biomechanical, Neurovascular, and Molecular Mechanisms with Emerging Therapeutic Directions

Traumatic brain injury (TBI) is being increasingly recognized as a major risk factor for chronic neurodegenerative disease, including chronic traumatic encephalopathy (CTE) and Alzheimer’s disease (AD). Biomechanical forces during head trauma, particularly rotational acceleration and angular deformation, produce diffuse axonal injury (DAI) and widespread white matter damage that trigger persistent neurobiological cascades. These include axonal transport failure, blood–brain barrier (BBB) disruption, neuroinflammation, neurovascular and mitochondrial dysfunction, and pathological protein aggregation, closely paralleling core AD features. Epidemiological data support a dose–response relationship between TBI severity or repetition and subsequent dementia risk, moderated by genetic factors such as apolipoprotein E4 (ApoE4). Converging experimental and early clinical studies have begun to target shared injury and neurodegenerative pathways through acute neuroprotection, stem cell-based strategies for BBB restoration and neural repair, transcriptional and hormonal modulation, mitochondrial stabilization, and immunomodulation of chronic inflammation. This review synthesizes evidence linking biomechanical injury to molecular and neurovascular pathways of neurodegeneration and summarizes emerging temporally targeted interventions. By integrating mechanistic and therapeutic perspectives, we aim to narrow the translational gap between TBI and AD, refine identification of at-risk populations, and inform priorities for prevention and development of disease-modifying therapies.