Abstract
Background and Objective: Humanized models of Alzheimer's disease (AD) provide valuable tools for investigating the mechanisms of this neurodegenerative disorder, the leading cause of dementia. These models enable the study of AD progression and the potential disease-modifying properties of drugs or dietary nutrients delivered through nutrition. Here, we examine molecular markers of metabolic and synaptic dysfunction in the hippocampus of 6-month-old 3×Tg-AD mice and assess whether a dietary insulin sensitizer can delay synaptic decline. Methods: First we characterized the molecular phenotype of 3×Tg-AD at 12 months using shotgun proteomics and phosphoproteomics to assess metabolic and synaptic changes in the hippocampus. Then, we characterized the effects of early daily oral D-chiro-inositol (DCI, Gyneos(®)) for three months, starting at 3 months of age, to test restoration of insulin signaling and glutamatergic synaptic markers. To this end we evaluated a) insulin signaling pathway components (insulin receptor, IRS1, PI3K, AKT, GSK3β) at mRNA, protein, and phosphorylation levels, and b) the expression of glutamate receptors (mGluR5, GluR1, GluR2, NMDAR1, NMDAR2A, NMDAR2B). Sex effects were explored. Results: 12-month 3×Tg-AD mice exhibit metabolic and synaptic dysfunction in the hippocampus, with phosphoproteomic changes suggesting altered glutamatergic synapses. At 6 months, disruptions in insulin signaling were evident, including altered expression and phosphorylation of insulin pathway components, and changes in glutamate receptor subunits. Early DCI treatment largely reversed these alterations. Several effects showed sex dependency. Conclusions: Early insulin-sensitizing intervention via DCI can restore insulin signaling and counteract hippocampal synaptic impairments in this AD model, supporting the potential for nutrient-based strategies to delay synaptic decline. Sex differences underscore the need to tailor therapeutic approaches in modifying AD progression.