METTL3 governs thymocyte development and thymic involution by regulating ferroptosis

Given its central role in immune aging, identifying regulators of thymic involution is important. While conventional programmed cell death plays a fundamental role in thymocyte development, how cell death pathways contribute to thymic involution remains unclear. In this study, we found that CD4+CD8+ double positive (DP) thymocytes acquired characteristics of senescence in aged mice undergoing thymic involution, while expression of the m6A methyltransferase METTL3 (enriched in DP cells from young mice) decreased with aging. By conditionally deleting METTL3 in T cells, we revealed a critical role for METTL3 in DP cell survival, and in restraining features of aging in DP thymocytes by preventing ferroptosis signaling, through glutathione peroxidase 4 (GPX4). Mechanistically, GPX4 was maintained by METTL3 at the translational level, independent of its methyltransferase activity. Furthermore, we found that pharmacological inhibition of ferroptosis promoted DP cell survival, and attenuate d features of aging in DP thymocytes. These findings uncover a role for METTL3-regulated ferroptosis in thymic involution, and identify strategies to restore thymic function.