Draxin Induces Cognitive Impairment in Mice via Wnt/β-Catenin-Mediated Tau Phosphorylation

Background: Dorsal repellent axon guidance protein (draxin) is a secreted protein that plays an establishment role in the formation of proper connections between neurons. Although draxin is known to regulate the elongation of axons from various types of neurons in vitro, its specific role in mature neurons remains unclear. Draxin expression in the hippocampal region of patients with Alzheimer’s disease (AD) has been reported to be higher than in normal subjects. The present study investigated the effect of draxin on the expression of microtubule-associated protein 2 (MAP2) and neuronal nuclear antigen (NeuN), and on tau protein phosphorylation in mouse hippocampal neurons (HT22 cells) and AD cellular models. In addition, stereotactic techniques were used to inject neuronal-targeted adeno-associated virus (AAV) into the hippocampus of C57BL/6 mice to assess the effects of draxin overexpression on hippocampal neurons, as well as on behavioral and pathological features. Methods: In vitro experiments were conducted using mouse hippocampal neuronal cells (HT22 cells) and established AD cellular models, focusing on evaluating draxin’s effects on the expression of neuronal markers (MAP2 and NeuN) and the phosphorylation status of tau protein. For in vivo validation, neuron-targeted AAV was delivered into the hippocampus of C57BL/6 mice via brain stereotactic injection to achieve draxin overexpression. Subsequent assessments included analyses of hippocampal neuronal integrity, behavioral tests (Y-maze and Morris water maze, to evaluate spatial learning and memory), and detection of AD-related pathological markers. Results: In vitro experiments revealed that draxin overexpression decreased the cell survival rate, increased the apoptosis rate, decreased the expression of MAP2 and NeuN, and showed a trend for increased phosphorylation of tau protein compared with the control group. Notably, the spatial learning memory ability of mice with draxin overexpression in the brain, as determined by the Y-maze and Morris water maze tests, was significantly diminished compared with the control group. These mice also showed elevated tau protein phosphorylation and altered expression of wingless-related integration site (Wnt)/β-catenin/glycogen Synthase Kinase 3 beta (GSK-3β) pathway components. Conclusions: Our results suggest for the first time that neuronal overexpression of draxin may induce neuronal damage via the Wnt/β-catenin/GSK-3β signaling pathway, leading to AD-like neuropathological damage and cognitive dysfunction.