Depot-Specific Transcriptomic Analysis of Equine Adipose Tissue

Adipose tissue is an important and dynamic endocrine organ critical for regulating metabolism in both health and disease. Depot-specific gene expression and brown fat-like adipose tissue is poorly understood in horses. In adult humans, brown fat is found in suprascapular and retroperitoneal depots which have unique gene signatures. These depots are analogous to nuchal and retroperitoneal depots in the horse, To evaluate metabolic differences between equine adipose tissue depots, and to determine if adult horses have brown-fat like adipose tissue, we collected nuchal, shoulder, tail head, visceral, omental, and retroperitoneal adipose samples from six horses of varying age, breed, and sex. To quantify the differences in gene expression in the depots, an average of ~19 million paired-end RNA sequencing reads per sample were generated on an Illumina HiSeq sequencer. Limma-voom identified 4,588 differentially expressed (DE) genes between nuchal fat and the other depots, 2,917 DE genes between retroperitoneal fat and the other depots, and 4,142 DE genes between nuchal and retroperitoneal. Growth and differentiation pathways predominated in all comparisons, but in opposite directions, with upregulation in retroperitoneal relative to the other tissues. Nuchal fat directly compared to retroperitoneal tissue revealed primarily differentiation and brown fat upstream regulators. ZIC1, a specific marker for brown fat, has a 275x fold change in nuchal tissue relative to other tissues. Several HOX genes, responsible for cranial-caudal patterning during development, are downregulated up to 150x in nuchal vs other tissues. These data show clear functional stratification of the equine adipose tissue transcriptome.