Idh2-α-KG axis dysregulation disrupts epigenetic landscape and imprinted genes, inducing placental hypertrophy in SCNT cattle

Placental hypertrophy is a major cause of pregnancy failure in somatic cell nuclear transfer (SCNT) animals, with metabolic-epigenetic crosstalk proposed as a key regulatory node, yet its molecular mechanism remains elusive. Isocitrate dehydrogenase 2 (Idh2) is a critical mitochondrial metabolic enzyme that controls the production of α-Ketoglutarate (α-KG), a central regulator of epigenetic modifications. In SCNT bovine placentomes and derived placental mesenchymal cells, this study found abnormally elevated α-KG levels. Further functional experiments in these cells suggested that elevated α-KG levels were associated with significant increases in 5-hydroxymethylcytosine (5hmC) and the active histone marker H3K4me3, as well as decreases in the repressive markers H3K9me3 and H3K27me3, accompanied by altered expression of ten-eleven translocation (TET) dioxygenases and lysine demethylase (KDMs). This ultimately led to the dysregulation of key imprinted genes associated with placental development, including upregulation of Igf2r and Znf597, and downregulation of Phlda2, Peg10, and Magel2. Further analysis revealed that Idh2, a key enzyme for α-KG synthesis, was significantly upregulated in SCNT bovine placentas, with tis promoter region exhibiting hypomethylation, increased H3K4me3 modification, and enhanced chromatin accessibility. Targeted knockdown of Idh2 via CRISPR-Cas9 or inhibition of α-KG production using specific inhibitors effectively reversed these epigenetic abnormalities and improved the placental hypertrophy phenotype. In mouse validation experiments, maternal α-KG supplementation during pregnancy induced placental hypertrophy, whereas inhibiting Idh2 activity completely rescued this phenotype. This study is the first to elucidate the molecular mechanism by which Idh2-α-KG axis regulates placental development through a "metabolism-epigenetics" axis, providing novel strategies to improve cloning efficiency and potential intervention targets for treating placenta-related diseases (e.g., placental macrosomia).