Neurotropin alleviates Alzheimer's disease pathology by inhibiting FUS-mediated Calhm2 transcription, blocking the Calhm2/EFhd2 interaction, to improve mitochondrial dysfunction-associated microglia polarization

Neurotropin, a non-protein extract widely used for the treatment of neuropathic pain, has recently been reported to protect against ischemic brain injury, enhance remyelination in demyelinating diseases, and ameliorate neuroinflammation and memory deficits. However, its role in microglial polarization and mitochondrial dysfunction in Alzheimer's disease (AD) remains poorly understood. In this study, we investigated the therapeutic potential of Neurotropin in the 5xFAD mouse model of AD. Neurotropin administration alleviated cognitive decline, reduced amyloid-β (Aβ) deposition, suppressed neuroinflammation, and preserved neuronal density. Mechanistically, Neurotropin improved mitochondrial morphology, restored ATP production, increased mitochondrial DNA copy number, and reduced oxidative stress while promoting a shift in microglial polarization from the pro-inflammatory M1 phenotype toward the anti-inflammatory M2 phenotype. Transcriptomic and molecular analyses revealed that calcium homeostasis modulator family member 2 (Calhm2) was markedly upregulated in 5xFAD mice, colocalized with microglia, and transcriptionally regulated by fused in sarcoma (FUS), while Calhm2 interacted with EF-hand domain containing protein D2 (EFhd2). Neurotropin suppressed FUS-mediated Calhm2 transcription and attenuated Calhm2-EFhd2 interaction. Importantly, overexpression of Calhm2 in both microglial cells and 5xFAD mice abolished the beneficial effects of Neurotropin, leading to exacerbated mitochondrial dysfunction, oxidative stress, and inflammatory cytokine release. Together, these findings identify Calhm2 as a critical mediator of Neurotropin's neuroprotective effects and demonstrate that Neurotropin alleviates AD pathology by suppressing FUS-dependent Calhm2 transcription and blocking the Calhm2/EFhd2 interaction. This study provides new insights into the mechanism of Neurotropin action and highlights its therapeutic potential for AD.