Traumatic Brain Injury Modulates Synuclein-Associated Transcription, Amyloid Plaque Morphology and Cognitive Performance in APPswe/PS1dE9/Blg Mice

Background/Goals: Traumatic brain injury (TBI) is increasingly recognised as an important risk factor for delayed neurodegeneration and has been implicated in the modulation of Alzheimer’s disease (AD)-related amyloid pathology. However, experimental evidence remains equivocal, suggesting that the effects of TBI on amyloidogenesis are context-dependent and influenced by factors including disease stage, injury severity, and the pre-existing neurodegenerative background. This study aimed to comprehensively assess the effects of TBI on cognitive function, synuclein-family gene expression, neuroinflammatory gene expression and amyloid plaque morphology in APPswe/PS1dE9/Blg mice. Methods: Wild-type and APP/PS1 mice were assigned to four experimental groups: WT, WT-TBI, APP/PS1 and APP/PS1-TBI. TBI was induced at 6 months of age using a controlled cortical impact device (precision impactor). Behavioural assessments were conducted at two post-injury time points to evaluate locomotor activity, object recognition memory, short-term spatial memory and spatial learning. Cortex and hippocampus samples were analysed by qRT-PCR to evaluate synuclein-family gene expression and neuroinflammation-related markers. Amyloid plaque pathology was evaluated in Congo red-stained brain sections using QuPath-based image analysis. Results: TBI did not induce a consistent increase in amyloid plaque burden in APP/PS1 mice. Instead, TBI was associated with changes in plaque-size distribution, particularly at the later post-injury time point. Behavioural assessments revealed early trauma-associated cognitive impairmen; whereas, impairments observed at later stages appeared to be driven predominantly by progression of the APP/PS1 phenotype. Gene expression analysis revealed region- and genotype-dependent alterations in synuclein-family transcripts and inflammatory markers with the most pronounced changes observed in the cortex. Conclusions: These findings indicate that TBI does not uniformly accelerate β-amyloid deposition in APP/PS1 mice with established amyloid pathology. Rather, TBI appears to modify the temporal progression and morphological characteristics of amyloid pathology while interacting with genotype-dependent transcriptional responses involving synuclein-family genes and neuroinflammatory pathways. These results highlight the complex interplay between traumatic injury and pre-existing neurodegenerative processes and warrant further studies at the protein-level and over extended follow-up periods to elucidate the underlying mechanisms.