Impaired autophagic flux in the human brain after traumatic brain injury

Abstract

Emerging evidence indicates that dysfunctional autophagic flux significantly contributes to the pathology of experimental traumatic brain injury (TBI). The current study aims to clarify its role post-TBI using brain tissues from TBI patients. Histological examinations, including hematoxylin and eosin, Nissl staining, and brain water content analysis, were employed to monitor brain damage progression. Electron microscopy was used to visualize autophagic vesicles. Western blotting and immunohistochemistry were performed to analyze the levels of important autophagic flux-related proteins such as Beclin1, autophagy-related protein 5, lipidated microtubule-associated protein light-chain 3 (LC3-II), autophagic substrate sequestosome 1 (SQSTM1/p62), and cathepsin D (CTSD), a lysosomal enzyme. Immunofluorescence assays evaluated LC3 colocalization with NeuN, P62, or CTSD, and correlation analysis linked autophagy-related protein levels with brain water content and Nissl bodies. Early-stage TBI results showed increased autophagic vesicles and LC3-positive neurons, suggesting autophagosome accumulation due to enhanced initiation and reduced clearance. As TBI progressed, LC3-II and P62 levels increased, while CTSD levels decreased. This indicates autophagosome overload from impaired degradation rather than increased initiation. The study reveals a potential association between worsening brain damage and impaired autophagic flux post-TBI, positioning improved autophagic flux as a viable therapeutic target for TBI.