METTL3 safeguards cell identity and epigenome of human trophoblast stem cells.

N6-methyladenosine (m6A) is the most prevalent RNA modification and plays diverse roles in mammalian cells. However, its significance in human trophoblast lineage commitment and placenta development remains poorly understood. Here we show that METTL3, the primary enzyme responsible for m6A depositions, specifically marks cytotrophoblasts in human placenta, and exhibits defective expression in cytotrophoblasts from preeclampsia patients. Through in-depth in vitro investigation, we identify critical roles of METTL3 in generating human trophoblast stem cells (hTSCs) from human expanded potential stem cells, and in maintaining hTSCs' self-renewal and identity. In hTSCs, METTL3 loss induces pro-inflammatory responses and promotes premature senescence, leading to preeclampsia-associated transcriptomic signature. Mechanistically, METTL3-dependent m6A methylation directly regulates histone modifiers such as EP300 and EZH2 to maintain epigenetic homeostasis, as well as various transcription factors, including JUND. Targeted inhibition of EP300 in hTSCs successfully ameliorate preeclampsia signature caused by METTL3 deficiency. These findings reveal METTL3-dependent m6A methylation as a critical regulator of human trophoblast development and its potential involvement in pregnancy-related diseases.