Zinc transporter proteins in the retina as potential biomarkers for staging early Alzheimer's disease: Comparative analysis in human and mouse models.

Zinc plays a critical role in memory, learning, and neuronal function, with dysregulation increasingly implicated in neurodegenerative diseases such as Alzheimer's disease (AD). This study aimed to investigate whether changes in the expression of zinc transporter proteins, ZnT3 and ZIP3, in the retina mirror those in the brain, and to explore their potential as non-invasive biomarkers for early AD detection. Immunofluorescence and Western blotting were used to assess ZnT3 and ZIP3 expression in the retina and hippocampus of APP/PS1 and WT mice (9 and 18 months), as well as in human post-mortem tissues (9 AD and 6 control cases). To further investigate the regulatory role of ZnT3 in zinc homeostasis and its influence on tissue zinc concentrations, we quantified zinc levels in retinal and hippocampal tissues from WT and ZnT3 knockout mice using inductively coupled plasma-mass spectrometry (ICP-MS). ZnT3 and ZIP3 levels were significantly higher in the retina and hippocampus of healthy controls compared to AD cases across both mouse and human samples. ICP-MS analysis confirmed significantly lower zinc concentrations in ZnT3 knockout mice compared to WT controls in both the These findings demonstrate that retinal ZnT3 and ZIP3 expression changes mirror those observed in the hippocampus during AD progression. This suggests their potential as retinal biomarkers for Alzheimer's disease. Notably, ZnT3 shows strong promise for early, non-invasive detection of AD. Further validation in larger cohorts is warranted.