New insights into retinal physiology and cerebral microcirculation in the 5xFAD murine model of Alzheimer’s disease

This PhD thesis comprises two complementary research projects concerning early pathological mechanisms and potential intervention strategies in Alzheimer’s disease (AD), employing the 5xFamilial AD (FAD) murine model. The first project investigates the retina as a non-invasive window into early AD-related pathological changes. A detailed morpho-functional and molecular characterization reveals significant alterations in retinal function and structure starting from 6 months of age, including retinal ganglion cell loss, visual acuity deficits, and widespread deposition of amyloid beta (Aβ) and hyperphosphorylated Tau. These changes are accompanied by pronounced microglial activation, neuroinflammation, oxidative stress, and apoptosis. Notably, the downregulation of miR-3968 and miR-124-5p in the retina is strongly associated with enhanced neuroinflammatory and apoptotic signaling, underscoring the role of miRNAs in AD-related retinal pathology. These findings place the retina as a promising biomarker for early AD diagnosis and molecular monitoring. The second project focuses on cerebral microcirculation, highlighting early vascular impairments in 5xFAD mice as early as two months of age. Observed abnormalities include reduced arteriolar density, capillary rarefaction, increased permeability, and early downregulation of claudin-5, indicating disruption of the blood-brain barrier. These cerebrovascular abnormalities are also associated with hypoxic conditions, reduced expression of Aβ-degrading enzymes, increased Aβ burden, and activation of neuroinflammatory pathways. Importantly, dietary administration of Acebuche olive oil demonstrated protective effects by preserving vascular integrity, reducing hypoxia and inflammation, and improving cognitive performance. However, its long-term efficacy was lost at 6 months, likely due to systemic metabolic disturbances, including hepatic steatosis, highlighting the importance of dosing strategies for sustained benefits. Together, these studies emphasize the retina and cerebral vasculature as early and vulnerable targets in AD, driven by shared mechanisms of Aβ accumulation, glial reactivity, and inflammation. Furthermore, these studies advance the investigation of minimally invasive diagnostic tools and dietary interventions with translational applicability. Taken together, the findings provide new perspectives on the systemic pathophysiology of AD and inform the design of integrated, multi-modal strategies for early diagnosis, longitudinal monitoring, and preventive intervention.