Thyroid hormone promotes lipid droplet remodeling and lipophagy through KAT2B/PCAF-dependent histone acetylation in preimplantation embryos.

Thyroid hormones are central regulators of metabolic homeostasis and developmental programming. The active hormone triiodothyronine (T3) modulates transcription through nuclear receptors that recruit epigenetic cofactors to remodel chromatin and regulate metabolic gene networks. Although thyroid hormone signaling is known to influence lipid metabolism, whether it coordinates lipid droplet turnover with autophagy-related pathways during early embryonic development remains largely unknown. Here, transcriptomic profiling revealed distinct metabolic signatures between in vivo and in vitro embryos, with marked differences in fatty acid metabolism. Supplementation with 50 nM T3 enhanced blastocyst formation, particularly when applied from the 4-cell to blastocyst stages, coinciding with elevated thyroid hormone receptor expression. T3 induced robust lipid droplet remodeling, characterized by reduced droplet size, together with increased lipid-mitochondria colocalization and activation of lysosomal and mitochondrial pathways, consistent with enhanced lipid catabolism and organelle coupling. Mechanistically, inhibition of the histone acetyltransferase KAT2B/PCAF abolished T3-mediated developmental gains, reduced H3K9ac and H3K27ac, and resulted in nonselective autophagic stress rather than lipophagy. By contrast, T3 required KAT2B to stimulate cytosolic lipolysis, channel fatty acids into mitochondria, and enhance mitochondrial membrane potential. T3 also upregulated prostaglandin biosynthesis genes and improved outgrowth performance. These findings identify a thyroid hormone-KAT2B epigenetic axis that coordinates lipid droplet remodeling through lipolytic and lipophagic pathways, linking endocrine signaling to organelle crosstalk and mitochondrial activation during early embryogenesis.Abbreviations: ART: assisted reproductive technology; ATG5: autophagy related 5; BSA: bovine serum albumin; BSCL2/SEIPIN: BSCL2 lipid droplet biogenesis associated, seipin; CARM1: coactivator associated arginine methyltransferase 1; COCs: cumulus-oocyte complexes; CPT1A: carnitine palmitoyltransferase 1A; CPT2: carnitine palmitoyltransferase 2; CREBBP/CBP: CREB binding protein; DEGs: differentially expressed genes; DGAT1: diacylglycerol O-acyltransferase 1; EP300: E1A binding protein p300; ER: endoplasmic reticulum; H3K9ac: histone H3 acetyl-Lys9; H3K27ac: histone H3 acetyl-Lys27; HCS: high-content screening; HDACs: histone deacetylases; IVC: in vitro culture; IVF: in vitro-fertilized embryos; IVM: in vitro maturation; IVO: in vivo embryos; KAT2A/GCN5: K(lysine) acetyltransferase 2A; KAT2B/PCAF: K(lysine) acetyltransferase 2B; KAT2Bi (Ki): KAT2B inhibition; KD: knockdown; LC3: microtubule associated protein 1 light chain 3; LDs: lipid droplets; LIPE/HSL: lipase E, hormone sensitive type; MGLL: monoglyceride lipase; MMP: mitochondrial membrane potential; mtDNA: mitochondrial DNA; MT-ND1: mitochondrially encoded NADH:ubiquinone oxidoreductase core subunit 1; PA: parthenogenetically activated; PG: prostaglandin; PLA2G4A: phospholipase A2 group IVA; PLIN2: perilipin 2; PLIN3: perilipin 3; PLIN5: perilipin 5; PNPLA2/ATGL: patatin like phospholipase domain containing 2; PPARD/PPARδ: peroxisome proliferator activated receptor delta; PPARs: peroxisome proliferator activated receptors; PRMT1: protein arginine methyltransferase 1; PTGS1: prostaglandin-endoperoxide synthase 1; PTGS2: prostaglandin-endoperoxide synthase 2; PVA: polyvinyl alcohol; RT: room temperature; RT-qPCR: reverse transcription-quantitative polymerase chain reaction; RXR: retinoid X receptor; SIRT1: sirtuin 1; SLC25A20/CACT: solute carrier family 25 member 20; SLC27A4/FATP4: solute carrier family 27 member 4; SUV39H1: SUV39H1 histone lysine methyltransferase; T3: triiodothyronine; T4: thyroxine; TAGs: triacylglycerols; TEM: transmission electron microscopy; THR: thyroid hormone receptor; THRA: thyroid hormone receptor alpha; THRA-i: thyroid hormone receptor antagonist; THRB: thyroid hormone receptor beta; THs: thyroid hormones; ZGA: zygotic genome activation.