Alzheimer's disease (AD) is a devastating and progressive neurodegenerative disease and is characterized pathologically by the accumulation of amyloid beta (Aβ) and the hyperphosphorylation of tau proteins in the brain. The deposition of Aβ aggregates triggers synaptic dysfunction, hyperphosphorylation of tau, and neurodegeneration, which lead to cognitive disorders. Here, we investigated the neuroprotective effect of fisetin in the Aβ1-42 mouse model of AD. Single intracerebroventricular injections of Aβ1-42 (3 μl/5 min/mouse) markedly induced memory/synaptic deficits, neuroinflammation, and neurodegeneration. Intraperitoneal injections of fisetin at a dose of 20 mg/kg/day for 2 weeks starting 24 h after Aβ1-42 injection significantly decreased the Aβ1-42-induced accumulation of Aβ, BACE-1 expression, and hyperphosphorylation of tau protein at serine 413. Fisetin treatment also markedly reversed Aβ1-42-induced synaptic dysfunction by increasing the levels of both presynaptic (SYN and SNAP-25) and postsynaptic proteins (PSD-95, SNAP-23, p-GluR1 (Ser 845), p-CREB (Ser 133) and p-CAMKII (Thr 286) and ultimately improved mouse memory, as observed in the Morris water maze test. Fisetin significantly activated p-PI3K, p-Akt (Ser 473), and p-GSK3β (Ser 9) expression in Aβ1-42-treated mice. Moreover, fisetin prevented neuroinflammation by suppressing various activated neuroinflammatory mediators and gliosis; it also suppressed the apoptotic neurodegeneration triggered by Aβ1-42 injections in the mouse hippocampus. Fluorojade-B and immunohistochemical staining for caspase-3 revealed that fisetin prevented neurodegeneration in Aβ1-42-treated mice. Our results suggest that fisetin has a potent neuroprotective effect against Aβ1-42-induced neurotoxicity. These results demonstrate that polyphenolic flavonoids such as fisetin could be a beneficial, effective and safe neuroprotective agent for preventing neurological disorders such as AD.
Keywords: Alzheimer’s disease; Beta-amyloid (Aβ1–42); Fisetin; Neurodegeneration; Neuroinflammation; Synaptic dysfunctions.