Induced regulatory T cells (iTregs) are essential to maintain immunological tolerance, immune homeostasis, and prevention of autoimmunity. Some studies suggest that glycogen synthase kinase 3β (GSK3β) is involved in the mouse iTreg differentiation; however, whether GSK3β inhibits or enhances iTreg differentiation is still a matter of controversy. To address this issue, we have utilized human naïve CD4+ T cells and investigated whether GSK3 activity changes during iTreg differentiation and whether altering GSK3 activity influences the development of iTregs and its suppressive function. As a constitutively activated kinase, during iTreg differentiation GSK3β became quickly deactivated (phosphorylated at serine 9), which is dependent on MAPK pathway rather than PI3-kinase/Akt pathway. Our results indicated that inhibition of GSK3β by specific inhibitors, SB216763 or TDZD-8, promoted the differentiation of iTreg and increased their suppressive activity. In contrast, overexpression of GSK3β significantly inhibited iTreg differentiation, whereas transfection of GSK3β S9A did not. Furthermore, GSK3β inhibition enhanced iTreg differentiation through the TGF-β/Smad3 pathway. Taken together, this study demonstrates that inhibition of GSK3β enhances human iTreg differentiation and its suppressive activity, and provides a rationale to target GSK3β as a novel immunotherapeutic strategy.

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