Genome-wide epigenetic modifications in sports horses during training as an adaptation phenomenon

With his bicentennial breeding history based on athletic performance, the Thoroughbred horse can be considered the equine sport breed. Although genomic and transcriptomic tools and knowledge are at the state of the art in equine species, the epigenome and its modifications in response to environmental stimuli, such as training, are less studied. One of the major epigenetic modifications is cytosine methylation at 5' of DNA molecules. This crucial biochemical modification directly mediates biological processes and, to some extent, determines the organisms' phenotypic plasticity. Exercise indeed affects the epigenomic state, both in humans and in horses. In this study, we highlight, with a genome-wide analysis of methylation, how the adaptation to training in the Thoroughbred can modify the methylation pattern throughout the genome. Twenty untrained horses, kept under the same environmental conditions and sprint training regimen, were recruited, collecting peripheral blood at the start of the training and after 30 and 90 days. Extracted leukocyte DNA was analyzed with the methylation content sensitive enzyme ddRAD (MCSeEd) technique for the first time applied to animal cells. Approximately one thousand differently methylated genomic regions (DMRs) and nearby genes were called, revealing that methylation changes can be found in a large part of the genome and, therefore, referable to the physiological adaptation to training. Functional analysis via GO enrichment was also performed. We observed significant differences in methylation patterns throughout the training stages: we hypothesize that the methylation profile of some genes can be affected early by training, while others require a more persistent stimulus.