Background: Glucagon-like peptide-1 receptor (GLP1R) agonists, particularly semaglutide, show neuroprotective effects in genetic models of Alzheimer’s disease (AD). However, their delayed and long-term effects in sporadic AD, such as the intracerebroventricular streptozotocin (STZ) injection, remain insufficient. It is unclear how long the effects of GLP1R agonists persist after discontinuation and whether a single course can suppress progressive neurodegeneration. This study aimed to evaluate the delayed effects of semaglutide administration on morphological changes in neurons and glial cells in the hippocampus associated with cognitive impairment in an STZ-induced rat model of AD. Methods: Rats received bilateral intracerebroventricular STZ injections (3 mg/kg) followed by a 5-week course of intraperitoneal administration of semaglutide (0.1 mg/kg, every other day), and were euthanized 60 days after discontinuation of semaglutide administration. Immunomorphological methods were used to detect neuronal, astrocytic and microglial alterations. A novel object recognition test was performed to assess behavioral effects. Results: STZ-treated animals demonstrated cognitive impairments, ventriculomegaly, a significant increase in p-tau protein fluorescence intensity (p = 0.02), a decrease in CA1–CA3 field area (by 23%, p = 0.008), and reduced hippocampal neuronal density. Decreases in TOMM20 (mitochondrial marker) and synaptophysin levels were accompanied by significant glial activation in the hippocampal CA3 field. Semaglutide administration significantly reduced the enlarged ventricular lumen (by 43.5%), decreased p-tau fluorescence intensity, reduced vimentin-positive reactive astrocytes (by 68.4%), and increased synaptophysin fluorescence intensity. Furthermore, it reduced microglial activation (decreasing IBA1 cell density and elongation) and alleviated the disrupted AQP4 distribution. However, semaglutide did not completely halt the neurodegenerative process and showed no effect on the number of doublecortin-positive cells in the dentate gyrus. Conclusions: Hippocampal changes assessment revealed that course administration of semaglutide exerts prolonged effects, attenuating the severity of pathomorphological alterations and behavioral changes in a sporadic AD model after drug discontinuation.

Expanding research indicates that oxidative stress, particularly mitochondrial oxidative stress, is one of the key components in the pathogenesis of Alzheimer’s disease (AD). Mitochondrial oxidative stress is largely driven by impaired function of electron transport chain (ETC) complexes and their regulators. This study conducted an immunohistochemical analysis of ETC proteins (α-subunit of complex V, subunits MTCO1 and MTCO2 of complex IV) and mitochondrial complex V inhibitor IF-1 in the neurons of the caudate nucleus head, hippocampus, anterior cingulate gyrus, middle frontal gyrus, and inferior parietal lobule using autopsy material from patients with sporadic AD. Comparisons were made with similar brain regions in autopsy material from age-matched elderly patients and young patients. The results revealed a pattern of ETC impairment in AD fundamentally distinct from that observed in physiological aging. Specifically, a hippocampus-specific failure of the adaptive response was identified: unlike other brain regions, compensatory upregulation of ATP synthase does not occur here despite critical reduction in the protective protein IF-1, directly explaining the heightened vulnerability of hippocampal neurons to damage. Our data deepen the understanding of AD pathogenesis by highlighting region-specific mitochondrial defects as promising targets for tailored therapeutic intervention.