Mettl14-dependent m6A modification controls iNKT cells development and function by regulating p53-dependent apoptosis pathway and TCR signaling

N6-methyladenosine (m6A) is the most common modification to mRNA in mammalian cells linked to development and disease. m6A controls CD4+ T cell homeostasis by targeting the IL-7/STAT5/SOCS family pathway and sustains Treg suppressive function. However, the role of m6A modification in non-conventional T cell development and function remains unknown. Here we showed that m6A modification was indispensable for NKT cell homeostasis using mice with T cell-specific deletion of RNA methylation writer METTL14 (T-Mettl14-/-). Loss of METTL14-dependent m6A modification led to the upregulation of p53-mediated apoptosis in double-positive (DP) thymocytes. The decreased lifespan of DP thymocytes reduced the efficiency of distal Va-Ja rearrangement, including the invariant Va14-Ja18 TCR, and therefore led to a profound decrease in the iNKT cell population. The residual iNKT cells in T-Mettl14-/- mice exhibited increased apoptosis and impaired maturation. In addition, loss of METTL14 upregulated Cish expression, which contributed to decreased proliferative response to IL-2 and IL-15 and impaired cytokine production upon TCR stimulation in METTL14-deficient iNKT cells. Furthermore, knocking down METTL14 in mature iNKT cells diminished their cytokine production, correlated with increased Cish expression and decreased TCR signaling. Collectively, our data reveals a critical role for METTL14- dependent-m6A modification in iNKT cell development and function, highlighting the need to take this effect into consideration for targeting m6A pathway in therapeutic settings. DP thymocytes from Mettl14fl/fl/CD4-Cre+ (n=3) and littermate controls (n=3)