Demethylase-independent roles of LSD1 in regulating enhancers and cell fate transition [scRNA-seq]
Metazoan enhancers are decorated by mono-methylation (me1) of the lysine 4 residue on histone H3 (H3K4), a mark deposited by methyltransferases MLL3/MLL4 and removed by the lysine-specific histone demethylase 1A (LSD1 or KDM1A) via its flavin adenine dinucleotide (FAD)-dependent amine oxidase activity. As a component of histone deacetylases HDAC1/2-containing complex CoREST, LSD1 is required for animal development, and is implicated in Kabuki Syndrome-like congenital diseases and multiple types of cancer. Although prior research has investigated the demethylase function of LSD1 extensively, the mechanisms underlying LSD1's role in development and diseases remain enigmatic. Here, we have utilized genetic, epigenetic, genomic, and cell biology approaches to dissect the role of LSD1 and its demethylase activity in gene regulation and cell fate transition. Surprisingly, the catalytic inactivation of LSD1 only has a mild impact on gene expression whereas the loss of LSD1 protein de-represses enhancers globally. Moreover, LSD1 deletion, rather than its catalytic inactivation, causes defects in spontaneous differentiation, the transition from naive to primed pluripotency, embryoid body formation, and cardiomyocyte differentiation. Interestingly, deletion of LSD1 increases H3K27ac levels and binding of P300 to LSD1-targeted enhancers. We further show that the gain in the level of H3K27ac catalyzed by P300/CBP, not the loss of CoREST complex components from chromatin, contributes to the transcription de-repression of LSD1 targets and differentiation defects caused by LSD1 loss. Taken together, our study demonstrates a demethylase-independent role of LSD1 in regulating enhancers and cell fate transition, providing insight into the treatment of diseases driven by LSD1 mutations and misregulation. Overall design: WT and LSD1KO  day 6 EBs were dissociated with TrpLE and cells wer analyzed using scRNA-seq