Immunohistochemical Analysis of <scp>Tom</scp> 20 in Choroid Plexus Epithelial Cells From Elderly Brains With Neurodegenerative Diseases

The choroid plexus (CP) contributes to cerebrospinal fluid (CSF) production and regulation of circadian rhythm. Recently, many neuroimaging studies have reported enlarged CP volumes in patients with neurodegenerative diseases, including Alzheimer's disease (AD). While previous morphometric analysis revealed age-related enlargement of CP epithelial cells, the metabolic significance of such morphological changes including eosinophilic enlarged changes remains unclear. In this study, we investigated mitochondrial alterations in CP epithelial cells using immunohistochemistry for Tom20, a marker of the mitochondrial outer membrane. Temporal lobes, including CP, in patients with AD, vascular dementia, Parkinson's disease, and multiple system atrophy, and neuropathologically unremarkable controls were examined. Quantitative image analysis was performed using AI-assisted segmentation (cellpose) and Python-based processing (OpenCV, NumPy, and Pandas). Cell area and the proportion of Tom20-positive pixels (brown ratio) were measured in 13 090 epithelial cells from 20 cases, and data were analyzed using Spearman's rank correlation. The brown ratio was positively correlated with cell area. Enlarged epithelial cells frequently exhibited strong Tom20 immunoreactivity. These findings suggest that cellular enlargement in the CP epithelium is accompanied by increased mitochondrial content, highlighting a potential metabolic response in neurodegenerative brains.