Lineage-Dependent Regulation of Glutathione Homeostasis by EAAC1 and GTRAP3-18 During Differentiation of Mesenchymal Stem Cells into Neuron-like Cells

Adult bone marrow-derived mesenchymal stem cells (BMSCs) are multipotent progenitors capable of differentiating into diverse cell lineages, including osteogenic, chondrogenic, adipogenic, and neuronal lineages. In BMSCs, intracellular glutathione (GSH) is a critical determinant of stemness maintenance and differentiation outcomes. However, how intracellular GSH homeostasis is regulated during BMSC-to-neuron differentiation remains unclear. In neurons, GSH synthesis critically depends on cysteine uptake mediated by the excitatory amino acid carrier 1 (EAAC1). Here, we investigated the expression, subcellular localization, and functional contribution of EAAC1 and its regulatory protein, glutamate transporter-associated protein 3-18 (GTRAP3-18) in mouse BMSCs and neuron-like BMSCs generated by Notch intracellular domain-based induction (NICD-3F BMSCs). BMSCs exhibited higher intracellular GSH levels than NICD-3F BMSCs, despite comparable levels of EAAC1 protein. In contrast, EAAC1-dependent cysteine uptake and plasma membrane localization of EAAC1 were markedly reduced in BMSCs, indicating differentiation-dependent regulation of EAAC1 trafficking. Treatment with the xCT inhibitor erastin reduced intracellular GSH levels in both BMSCs and NICD-3F BMSCs. GTRAP3-18 expression was high in BMSCs and significantly reduced in NICD-3F BMSCs. Notably, GTRAP3-18 knockout decreased intracellular GSH levels in BMSCs without altering total EAAC1 protein or intracellular cysteine levels, whereas in NICD-3F BMSCs, both GSH and EAAC1 protein levels were increased. These findings demonstrate lineage-dependent divergence in GSH regulatory mechanisms and reveal previously unrecognized functions of GTRAP3-18 in redox control during stem–to–neuron differentiation.