Fraxetin Ameliorates Cognitive Impairment in STZ-Induced Mice: Involvement of Suppressed Microglial Hyperactivation and Improved Mitochondrial Dysfunction.

Therapeutic for Alzheimer's disease (AD) remains a pressing medical challenge in the field of neuroscience. Natural compounds with structural diversity and multi-target regulatory properties have attracted increasing attention for the treatment of complex neurodegenerative disorders. ‌Fraxetin, previously identified through computer-aided virtual screening, C. elegans assays, and in vitro cellular models as a potential anti-AD natural compound, was further investigated in this study using established in vivo and in vitro systems to evaluate its efficacy in ameliorating cognitive function and elucidate underlying mechanisms. A sporadic AD mouse model was established by intracerebroventricular injection of STZ (3 mg/kg). Fraxetin (3, 10, and 30 mg/kg/day, po.) was administered until the mouse sacrifices. Cognitive performance was evaluated using the novel object recognition, passive avoidance, and Morris water maze tests. STZ induced cerebral energy metabolism disturbances accompanied by mitochondrial dysfunction, neuroinflammation, oxidative stress, neuronal and synaptic loss, and cholinergic system impairment. ‌Behavioral tests confirmed that fraxetin ameliorated cognitive deficits in STZ-induced mice. Further studies revealed that fraxetin preserved mitochondrial structural integrity and enhanced mitochondrial biogenesis, accompanied by upregulation of the Sirt1/PGC-1α/Nrf1/TFAM pathway. In parallel, fraxetin attenuated microglial overactivation and neuroinflammatory responses. Consistently, in LPS-stimulated BV2 microglial cells, fraxetin inhibited nitric oxide and inflammatory mediator release, which was associated with modulation of the TLR2/MYD88/NF-κB signaling pathway, while restoring cellular bioenergetic status, indicating coordinated regulation of inflammation-associated metabolic dysfunction. Importantly, fraxetin attenuated neurodegenerative alterations in STZ-treated mice, as evidenced by reduced neuronal loss and synaptic degeneration. These effects were associated with activation of the BDNF/TrkB/ERK/CREB neurotrophic pathway and inhibition of acetylcholinesterase activity, supporting preservation of synaptic and cholinergic function. This study provides experimental evidence supporting fraxetin as a promising natural multi-target candidate for the intervention of AD.