KDM4E is a histone demethylase that catalyzes the removal of methyl groups from histone H3, primarily converting trimethylated lysine-9 (H3K9me3) to monomethylated forms and also demethylating trimethylated lysine-56 (H3K56me3). As a member of the 2-oxoglutarate-dependent oxygenase family, KDM4E activity is regulated by oxygen availability, showing graded responses across physiologically relevant oxygen concentrations 1. Beyond core histone substrates, KDM4E can demethylate linker histone H1 isoforms, demonstrating substrate flexibility 2. KDM4E is transcriptionally activated during early mammalian development, specifically at the cleavage stage, and is necessary for converting embryonic stem cells to 2-cell-embryo-like states 3. In cancer contexts, KDM4E expression is frequently reduced in triple-negative breast cancer, where it functions as a tumor suppressor by demethylating the H3K9me3 mark in the BICD1 promoter, enabling PAR1 signaling inhibition 4. Small-molecule KDM4E inhibitors, including DA-24905 and fluorinated 2,4-PDCA derivatives, have been developed as potential anti-cancer agents 5 6. Additionally, KDM4E participates in metabolic regulation during cellular stress: in mesenchymal stem cells exposed to excess branched-chain amino acids—a hallmark of post-ischemic hearts—a mTORC1/DUX4/KDM4E axis mediates pathological H3K9me3 loss and cellular dysfunction 7.