MOLECULAR SIGNATURE OF IN UTERO HYPERTHERMIA ON THE MAMMARY FAT PAD OF NEWBORN HEIFERS
This study investigated the effects of in utero heat stress on the microstructure and transcriptomic profile of the mammary fat pad in Holstein heifers at birth. Calves were gestated under either heat stress (iuHS; n = 6) or cooling conditions (iuCL; n = 6) during the last 54 ±5 days of gestation in a subtropical summer. At birth, mFP samples were collected for histologic and transcriptomic analysis. Compared to iuCL heifers, iuHS calves exhibited a higher number of small adipocytes and fewer large adipocytes in their mammary fat pads. Transcriptomic analysis revealed 122 differentially expressed genes (FDR < 0.01, |Log2FC| = 1.5) in iuHS mFP, including 40 upregulated and 82 downregulated. Downregulated genes were involved in fatty acid synthesis, adipocyte hypertrophy, metabolic regulation, and adipogenesis suppression (ACACA, ALMS1, PPARGC1A, SMAD2); while upregulated genes were associated with thermogenesis and cAMP/PKA signaling (GNB1, AKAP14, PRKACA), lipogenesis (PLD2), extracellular matrix remodeling (THBS4), and insulin resistance/adipocyte remodeling (FOXO6, ARVCF, LIMK2). Functional enrichment predicted activation of pathways related to cell death, inflammation, and oxidative stress, and inhibition of prolactin and gap junction signaling, and several key intracellular cascades (e.g., PI3K/AKT, MAPK, STAT3, ILK, ERK5). Nuclear receptors (ESR1), transcription factors (FOXO1, ATF4, HMG), and growth factors (EGF, BMP4) were predicted to be inactivated in iuHS mFP, indicating a coordinated suppression of cell differentiation, lipid metabolism, hormone/nutrient sensing, and stress adaptation. Overall design: RNA sequencing of uterus under heat stress on the  transcriptomic profile of the mammary fat pad Holstein heifers at birth. Calves were gestated under either heat stress (iuHS; n = 6) or cooling conditions (iuCL; n = 6) during the last 54 ± 5 days of gestation in a subtropical summer.