Suppression by glutamate of proliferative activity through glutathione depletion mediated by the Cystine/Glutamate antiporter in mesenchymal C3H10T1/2 stem cells

Although previous studies including ours have demonstrated the functional expression of different glutamate (Glu) signaling machineries such as Glu receptors (GluRs) and transporters in osteoblasts and chondrocytes, little attention has been paid to the role of Glu in their ancestral mesenchymal stem cells to date. In the present study, we have evaluated the possible functionality of Glu in cultured mouse mesenchymal stem cell line C3H10T1/2 cells endowed to proliferate for the self-renewal and to differentiate toward osteoblast, chondrocyte, adipocyte, and myocyte lineages. Expression of mRNA was for the first time shown with the cystine/Glu antiporter composed of xCT and 4F2hc subunits, in addition to particular excitatory amino acid transporter (EAAT) isoforms and ionotropic GluRs, in undifferentiated C3H10T1/2 cells. Glu significantly suppressed the proliferation activity at a concentration over 500 mu M without inducing cell death or differentiation, while the suppression occurred in a manner sensitive to the prevention by cystine and reduced glutathione (GSH), but not by EAAT inhibitors. A significant decrease was seen in intracellular GSH levels in C3H10T1/2 cells cultured with Glu, whereas the cellular proliferation activity was drastically decreased by the addition of the GSH depleter cyclohexene-l-one and the GSH biosynthesis inhibitor L-buthionine-[S,R]-sulfoximine, respectively. Transient overexpression of both xCT and 4F2hc subunits led to an increased basal proliferative activity in C3H10T1/2 cells. These results suggest that Glu could suppress the cellular proliferation toward self-renewal through a mechanism associated with the depletion of intracellular GSH after promoting the retrograde operation of the cystine/Glu antiporter in C3H10T1/2 cells.