Synapsin III promotes neuronal-like transdifferentiation of glioblastoma stem cells by disrupting JAG1-Notch1 interaction.

Abstract

Background: Glioblastoma (GBM), a formidable and highly aggressive form of brain cancer, is predominantly driven by GBM stem cells (GSCs), which are characterized by their ability for self-renewal and aberrant differentiation. Targeting the terminal differentiation of GSCs represents a promising therapeutic strategy. This study aimed to elucidate the role of synapsin III (SYN3) in driving the differentiation of GSCs into neuron-like cells and its effect on the tumor-suppressive pathways in GBM.

Methods: Proliferation assays, limited dilution assays, immunocytochemistry, western blot, RT-qPCR, and GSC tumor models were used to determine gene function and assess the role of γ-secretase inhibitors. Co-immunoprecipitation and microscale thermophoresis were conducted to explore the underlying regulatory mechanisms. Intracranial orthotopic injection of adeno-associated virus (AAV) was performed to evaluate therapeutic potential.

Results: We demonstrate that SYN3, uniquely within the synapsin family, acts as a tumor suppressor by steering GSCs toward neuronal-like transdifferentiation. Mechanistically, SYN3 enhances the expression of Neuregulin 3 (NRG3), which serves as a non-canonical antagonist of Notch signaling by competitively binding to specific epitopes within the EGF-like domain of JAG1, a critical site for the canonical engagement of Notch receptors. This critical interaction disrupts the JAG1-Notch1 signaling pathway, a key mechanism driving GSCs toward neuronal-like transdifferentiation, thereby reducing their stemness. Furthermore, SYN3 demonstrated significant antineoplastic activity in a mouse model harboring GSCs. AAV-mediated overexpression of SYN3 markedly impeded GBM progression.

Conclusions: Our research reveals the therapeutic potential of SYN3 in regulating GSC fate and offers a novel differentiation-based approach for GBM therapy.