Combined Preventive and Preconditioning Treatments for the Comorbidity of Alzheimer’s Disease and Ischemic Stroke in a GluN3A Knockout Mouse and a 5xFAD Mouse

Alzheimer’s disease (AD) and stroke have been identified as risk factors for each other. More than half of AD patients suffer stroke attacks and worse ischemic injuries. There has been a lack of research focus and clinical treatment for the comorbidity of these neurological disorders. AD and ischemic stroke share characteristic pathophysiology, including hyperactivities of excitatory neurons and NMDA receptors (NMDARs), excitotoxicity, and synapse/neurovascular destruction. Our recent investigations identified the deficiency of the NMDAR regulatory GluN3A (NR3A) subunit as a novel pathogenesis of sporadic AD. The present investigation tested a preemptive treatment to prevent AD development in two AD models and, in the meantime, to prime the susceptible brain against upcoming ischemic attacks. In the preclinical stage of 3-month-old GluN3A KO mice, an NMDAR-mediated sporadic AD model, and 5xFAD mice, an amyloid-based familial AD model, treatments with memantine (MEM), an NMDAR antagonist (10 mg/kg/day in drinking water) and a drug-free control were started when cognition of these mice was generally normal. Three months later, the mice were subjected to focal cerebral ischemic surgery, followed by continued 1.5–2.0 months of MEM or vehicle control. Morphological, pathological, and functional assessments were performed and compared at different time points. In both AD models, the early MEM treatment confined AD progression before and after stroke, reduced ischemia-induced brain injury, suppressed neuroinflammation, and improved locomotion, sensorimotor, psychological, and cognitive functions. This is the first report endorsing a shared mechanism of NMDAR hyperactivity in AD and stroke in AD models with distinctive risk factors. The dual therapeutic effects of the preemptive MEM treatment provide a disease-modifying possibility for individuals who are susceptible to sporadic or familial AD as well as ischemic stroke.