Comparative Morphological and Proteomic Characterization of Adipose Tissues from Different Anatomical Sites in Yili Horses

Adipose tissue functions not only as a primary energy reservoir but also as a metabolically active endocrine organ. However, the morphological and molecular differences among adipose depots from different anatomical sites in Yili horses remain unclear. This study aimed to compare the morphological characteristics and proteomic profiles of subcutaneous adipose tissue (SAT) and pericardial adipose tissue (PCAT). To this end, adipose tissue samples from 18 Yili horses were analyzed using hematoxylin and eosin (H&E) staining, while a subset of samples from 6 horses was subjected to proteomic analysis. The results demonstrated that adipocytes in PCAT showed significantly larger areas and diameters but a lower number per field than those in SAT (p < 0.01). Proteomic profiling identified 451 differentially expressed proteins (DEPs) between SAT and PCAT. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses indicated that these DEPs were primarily involved in fatty acid catabolism, glycolysis, ECM–receptor interaction, thermogenesis, Wnt signaling, and other related pathways. Notably, enrichment analyses further revealed that SAT exhibited more active substrate utilization, energy metabolism, and lipid turnover, whereas PCAT was more associated with structural regulation and cardiovascular-related signaling pathways. Furthermore, correlation analysis between adipocyte morphological metrics and proteomic data identified ACAA2, ENO1, TPI1, PLIN1, COL6A3, and ITGB1 as candidate proteins regulating the site-specific differences in morphology and metabolic function between SAT and PCAT. These findings reveal distinct morphological and proteomic features of different adipose depots in Yili horses, providing a foundation for understanding depot-specific adipose function and its underlying regulatory mechanisms.