MANF improves cognitive function and attenuates neuroinflammation in APP/PS1 transgenic mice through the TLR4/MYD88/NF-κB signaling pathway.

Background: Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder, characterized by progressive cognitive decline, as well as pathological features such as β-amyloid (Aβ) plaque deposition, tau hyperphosphorylation, synaptic dysfunction, and neuronal loss. Growing evidence suggests that neuroinflammation, oxidative stress, and apoptosis play critical roles in the pathogenesis of AD, thereby contributing to neuronal damage and cognitive decline. Mesencephalic astrocyte-derived neurotrophic factor (MANF), an endoplasmic reticulum stress-inducible protein, has been shown to exert neuroprotective effects by modulating immune responses, alleviating oxidative stress, and suppressing apoptosis in various neurological disease models. These properties suggest that MANF could serve as a promising therapeutic candidate treating AD. This study investigated the therapeutic potential of MANF in improving cognitive function and ameliorating pathological changes in APP/PS1 transgenic (Tg) mice by modulating neuroinflammation and enhancing neural plasticity. Methods: Beginning at 10 months of age, male APP/PS1 transgenic mice received daily intraperitoneal injections of recombinant human MANF (rhMANF) at a dose of 1 μg/g for a duration of one month. Behavioral assessments, including the Morris water maze, open field, and fear conditioning tests, were conducted to evaluate cognitive function. Brain tissue was analyzed for β-amyloid (Aβ) deposition, neuroinflammation, oxidative stress, and neuronal apoptosis using immunofluorescence, immunohistochemistry, western blotting, and enzyme-linked immunosorbent assay. RNA sequencing (RNA-seq) and a BV2 microglial/HT22 neuronal co-culture system were used to further elucidate the mechanisms underlying MANF's effects. Results: rhMANF treatment significantly improved cognitive function in APP/PS1 Tg mice by reducing Aβ deposition, inhibiting microglial activation, and suppressing inflammatory cytokines (TNF-α, IL-1β, and IL-6). MANF also mitigated oxidative stress, reduced neuronal apoptosis, and restored synaptic protein levels, including those of Postsynaptic density protein-95(PSD95) and synaptophysin (SYN). In vitro studies confirmed that MANF effectively counteracts Aβ1-42-induced toxicity in the BV2/HT22 co-culture system. Transcriptomic analysis identified that MANF exerts its protective effects by regulating the TLR4/MYD88/NF-κB signaling pathway, thereby reducing inflammation and promoting synaptic plasticity. Conclusions: This study demonstrates the protective role of MANF in AD and establishes MANF as a promising therapeutic candidate for AD and aging-related neurodegenerative disorders.