Neuronal expression of E2F4DN restores adult neurogenesis in homozygous 5xFAD mice via TrkB signaling

Abstract

Background: Alzheimer's disease (AD) is increasingly recognized as a disorder that disrupts brain plasticity long before extensive neuronal loss occurs, including early impairment of adult neurogenesis. However, the molecular mechanisms underlying these alterations remain poorly understood. Methods: Neuronal expression of E2F4 carrying the Thr249Ala/Thr251Ala mutation (E2F4DN) was achieved using an AAV.PHP.eB vector in the 5xFAD mouse model of AD. Neurogenic potential was assessed by immunohistochemistry and quantitative PCR (qPCR) targeting neurogenesis-associated markers. For in vitro experiments, neural stem cells (NSCs) isolated from the subventricular zone (SVZ) were exposed to conditioned media from primary cortical neurons expressing E2F4DN, with or without pharmacological inhibitors. NSC proliferation and differentiation were evaluated by immunocytochemistry and qPCR. Results: Neuronal expression of E2F4DN restored the proliferative and differentiation capacity of NSCs in 5xFAD mice both in vivo and in vitro. Pharmacological inhibition of TrkB signaling abolished the pro-neurogenic effects of E2F4DN-conditioned medium, whereas direct activation of TrkB in NSCs recapitulated these effects. Conclusions: These findings identify a mechanism by which neuronal dysfunction in AD compromises neurogenesis through impaired TrkB-mediated signaling. The results uncover a previously underappreciated paracrine communication between neurons and NSCs and highlight neuronal E2F4DN expression and TrkB modulation as promising therapeutic strategies to counteract early neurogenic deficits in AD.