Adipose Tissue Transcriptomics Reveals Differential Expression in Equine Subcutaneous and Internal Fat Depots

Equine metabolic syndrome is characterized by obesity, regional adiposity, insulin resistance, predisposition to laminitis, and systemic inflammation.  Unlike humans, horses are typically able to indefinitely produce insulin, resulting in compensated insulin resistance without development of diabetes mellitus.  Currently, the underlying pathophysiology of equine metabolic syndrome is not well understood.  It has been shown in humans and mice that visceral fat is associated with insulin resistance and development of diabetes, and is more metabolically active and pro-inflammatory than other fat depots.  Regional adiposity in horses is characterized by subcutaneous fat deposits at the crest of the neck, behind the shoulder, and at the tail head, and increased neck circumference is associated with insulin resistance.  Subcutaneous neck crest fat in horses has previously been found to be more metabolically active than visceral fat.  We have collected samples from six adipose tissue depots: neck, shoulder, tailhead, visceral, omental, and retroperitoneal from 6 individuals to describe differences in gene expression between these depots in normal horses.  An average of 19,085,946 100bp paired-end reads per tissue were sequenced on an Illumina HiSeq platform. Reads were mapped with the STAR aligner and mapping rates ranged from 82% to 94%.  Preliminary analysis with GOexpress indicates that the three subcutaneous fat depots have similar metabolic profiles, as do the three internal fat depots.  In contrast to other species subcutaneous fat in horses appears more pro-inflammatory than internal fat, with increased expression of leptin, natural killer cell stimulatory factor 1, lymphocyte antigen 96, and tumor necrosis factor.