NeuroD1 gene therapy converts reactive astrocytes to functional new neurons in a mouse model of Alzheimer’s disease

Alzheimer's disease is characterized by the presence of amyloid-beta plaques, neurofibrillary tangles, and chronic neuroinflammation. Effective therapies capable of restoring neuronal loss, a key pathological feature of Alzheimer's disease are lacking. Our previous studies have demonstrated that overexpression of neuronal differentiation 1 (NeuroD1) in astrocytes can convert astrocytes into neurons in Alzheimer's disease models and this astrocyte-to-neuron conversion technology can rescue pathological features in models of stroke and epilepsy. This study investigated whether NeuroD1-mediated in vivo reprogramming of reactive astrocytes into functional neurons could rescue neurodegeneration and cognitive decline in amyloid precursor protein/presenilin 1 transgenic Alzheimer's disease model mice. Using retro-orbital delivery of AAV-PHP.eB-GFAP-NeuroD1-GFP, we achieved broad astrocyte-to-neuron conversion throughout the brain of 7-month-old Alzheimer's disease mice. Three months post-treatment, immunostaining revealed significant neuronal regeneration in the cortex and hippocampus, accompanied by a marked reduction in neuroinflammatory markers. The converted neurons exhibited mature electrophysiological properties, including action potentials and synaptic activity, which correlated with increased neuronal density in the hippocampus. Morris water maze test demonstrated that NeuroD1-treated mice exhibited restored spatial learning and memory compared with control animals. These findings demonstrate that NeuroD1-driven neuroregeneration via gene therapy not only replenishes neuronal populations but also reduces key pathological features related to Alzheimer's disease, including neuroinflammation and amyloid plaque burden, ultimately reducing cognitive impairment. Our findings highlight in vivo astrocyte-to-neuron reprogramming through systemic astrocyte-to-neuron delivery as a promising and transformative strategy for treating Alzheimer's disease and related neurodegenerative disorders.