Gallop Racing Shifts Mature mRNA towards Introns: Does Exercise-Induced Stress Enhance Genome Plasticity?

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.

Transcriptomic signature related to poor welfare of sport horses

The improvement of horse welfare through housing conditions has become a real issue in recent years and have highlighted the detrimental effect of individual housing of horses on their health and behaviour. In this new study, we analysed the blood transcriptome of 45 sport horses housed individually that were previously examined for their behaviour and gut microbiota. We performed differential and regression analyses of gene expression, followed by downstream bioinformatic analyses, to unveil the molecular pathways related to the behavioural changes associated with welfare impairment in these sport horses. We found that aggressiveness towards humans was the behavioural indicator the most correlated to blood gene expression and that the pathways involved belonged mainly to systemic inflammation. In contrast, the correlations between genes, alert postures and unresponsiveness towards the environment were weak. When blood gene expression profiling was combined with faecal microbiota of a sub-population of horses, stereotypies came out as the most correlated to blood gene expression. This study shows that aggressiveness towards humans and stereotypies are behavioural indicators that covary with physiological alterations. Further studies are needed regarding the biological correlates of unresponsiveness to the environment and alert postures.

Basal Reactivity Evaluated by Infrared Thermography in the "Caballo de Deporte Español" Horse Breed According to Its Coat Color

Horses have been valued for their diversity of coat color since prehistoric times. In particular, the pleiotropic effect that coat color genes have on behavior determines the way the horse perceives and reacts to its environment. The primary aim of this study was to evaluate the influence of coat color on basal reactivity assessed with infrared thermography as eye temperature at rest (ETR), determine their relation with the results obtained by these horses in Show Jumping competitions and to estimate the genetic parameters for this variable to test its suitability for genetic selection. A General Linear Model (GLM) and Duncan post-hoc analysis indicated differences in ETR due to coat color, sex, age, location, and breed-group factors. A Spearman’s rank correlation of 0.11 (p < 0.05) was found with ranking, indicating that less reactive horses were more likely to achieve better rankings. Heritability values ranged from 0.17 to 0.22 and were computed with a model with genetic groups and a model with residual variance heterogeneity. Breeding values were higher with the last genetic model, thus demonstrating the pleiotropic effect of coat color. These results indicate that ETR has a suitable genetic basis to be used in the breeding program to select for basal reactivity due to coat color.

Training associated alterations in equine respiratory immunity using a multiomics comparative approach

Neutrophilic airway inflammation is highly prevalent in racehorses in training, with the term mild to moderate equine asthma (MMEA) being applied to the majority of such cases. Our proposed study is largely derived from the strong association between MMEA in racehorses and their entry into a race training program. The objectives of this study are to characterise the effect of training on the local pulmonary immune system by defining the gene and protein expression of tracheal wash (TW) derived samples from Thoroughbred racehorses prior to and following commencement of race training. Multiomics analysis detected 2138 differentially expressed genes and 260 proteins during the training period. Gene and protein sets were enriched for biological processes related to acute phase response, oxidative stress, haemopoietic processes, as well as to immune response and inflammation. This study demonstrated TW samples to represent a rich source of airway cells, protein and RNA to study airway immunity in the horse and highlighted the benefits of a multiomics methodological approach to studying the dynamics of equine airway immunity. Findings likely reflect the known associations between race-training and both airway inflammation and bleeding, offering further insight into the potential mechanisms which underpin training associated airway inflammation.

Circulating Transcriptional Profile Modulation in Response to Metabolic Unbalance Due to Long-Term Exercise in Equine Athletes: A Pilot Study

Physical exercise has been associated with the modulation of micro RNAs (miRNAs), actively released in body fluids and recognized as accurate biomarkers. The aim of this study was to measure serum miRNA profiles in 18 horses taking part in endurance competitions, which represents a good model to test metabolic responses to moderate intensity prolonged efforts. Serum levels of miRNAs of eight horses that were eliminated due to metabolic unbalance (Non Performer-NP) were compared to those of 10 horses that finished an endurance competition in excellent metabolic condition (Performer-P). Circulating miRNA (ci-miRNA) profiles in serum were analyzed through sequencing, and differential gene expression analysis was assessed comparing NP versus P groups. Target and pathway analysis revealed the up regulation of a set of miRNAs (of mir-211 mir-451, mir-106b, mir-15b, mir-101-1, mir-18a, mir-20a) involved in the modulation of myogenesis, cardiac and skeletal muscle remodeling, angiogenesis, ventricular contractility, and in the regulation of gene expression. Our preliminary data open new scenarios in the definition of metabolic adaptations to the establishment of efficient training programs and the validation of athletes’ elimination from competitions.

Genetic Parameters of Effort and Recovery in Sport Horses Assessed with Infrared Thermography

Simple Summary

The way a horse activates (effort phase-EP) and recovers (recovery phase-RP) during a sport event can affect its sport performance. The aim of this manuscript was to test horses’ adaptation to sport performance and its genetic basis, using eye temperature assessed with infrared thermography. EP and RP were measured in 495 Spanish Sport Horses, during a performance test, considering sex (2) and genetic lines (5) as fixed effects. The ranking position obtained on the official sport competition celebrated the day after the performance test was also collected. Differences in variables due to genetic line and sex effects were found, showing that, regardless of the genetic line, stallions tended to recover better than mares after the sport test developed. High positive correlations were found between EP and RP for both fixed effects, so that, the higher the EP, the higher the RP. However, for the ranking position, a low negative correlation was found, so that the higher the eye temperature increase, the better the position. Heritabilities showed medium–high values with a medium positive genetic correlation between them. Thus, breed origins and sex influence horses’ effort and recovery during sport performance, showing a genetic basis adequate for selection.

Abstract

The way a horse activates (effort phase-EP) and recovers (recovery phase-RP) during a sport event can affect its sport performance. The aim of this manuscript was to test horses’ adaptation to sport performance and its genetic basis, using eye temperature assessed with infrared thermography. EP and RP were measured in 495 Spanish Sport Horses, during a performance test, considering sex (2) and genetic lines (5) as fixed effects. The ranking position obtained on an official sport competition was also collected. Differences in variables due to genetic line and sex effects were found, showing that, regardless of the genetic line, stallions tended to recover better than mares after the sport test developed. High positive intra-class correlations (p < 0.001) were found between EP and RP for both fixed effects, so that the higher the EP, the higher the RP. However, for the ranking position, a low negative correlation (p < 0.01) was found, so that the higher the eye temperature increase, the better the position. Heritabilities showed medium–high values with a medium positive genetic correlation between them. Thus, breed origins and sex influence horses’ effort and recovery during sport performance, showing a genetic basis adequate for selection.

Immune Response in Young Thoroughbred Racehorses under Training

Simple Summary

Stressful stimuli, both infectious and non-infectious, can modify and trigger an innate immune response and inflammation, via an attempt to restore a homeostatic state. Coping with stressors can be measured by different procedures, including the evaluation of immunological parameters. These are also modulated by exercise, which can be considered stress prototypic in the Thoroughbred racehorse. To evaluate the complex of physiological regulations during the training period, twenty-nine clinically healthy, two-year-old Thoroughbred racehorses were followed during their first 3 months of sprint training. Blood collection was performed at rest, three times until 90 days of training, for testing immunological parameters during incremental sprint training to evaluate its effect on the immunological status of the animals. During the training period, we observed the following: (A) an increase in red blood cell parameters that are crucial for exercise performance adaptation, improving O₂ transport and muscle cell respiration; (B) variations of blood granulocytes; and (C) changes in inflammatory cytokine gene expression. On the basis of clinical and laboratory findings, training exercise probably played a major role in the modulation of the above parameters. These latter changes could be seen as a preparation of the innate immune system to respond quickly and adequately to environmental conditions.

Abstract

Training has a great impact on the physiology of an athlete and, like all stressful stimuli, can trigger an innate immune response and inflammation, which is part of a wider coping strategy of the host to restore homeostasis. The Thoroughbred racehorse is a valid animal model to investigate these changes thanks to its homogeneous training and highly selected genetic background. The aim of this study was to investigate modifications of the innate immune response and inflammation in young untrained Thoroughbred racehorses during the first training season through haematological and molecular investigations. Twenty-nine Thoroughbred racehorses were followed during their incremental 3-month sprint exercise schedule. Blood collection was performed at time 0 (T0; before starting the intense training period), 30 days after T0 (T30), and 90 days after T0 (T90). Haematological parameters (red and white blood cells, haemoglobin, and platelets) were evaluated and haematocrit (HCT), mean corpuscular haemoglobin concentration (MCHC), and red cells width distribution + standard deviation (RDW-SD) were calculated. Moreover, via RT-qPCR, we investigated the expression of, Interleukin 1β (IL-1β), Interleukin 4 (IL-4) Interleukin 6 (IL-6), Interleukin 2 (IL-2), Interleukin 3 (IL-3), Interleukin 5 (IL-5) Interleukin 8 (IL-8), Trasformig Growth Factor β and α (TGF-β), Tumor necrosis factor α (TNF-α), and Interferon γ (IFN-γ)genes. Main corpuscular volume (MCV) showed a significant (p = 0.008) increase at T90. Main corpuscular haemoglobin (MCH) and haemoglobin concentration (MCHC) values were significantly augmented at both T30 (p < 0.001) and T90 (p < 0.001). Basophils were significant increased at T30 (p = 0.02) and eosinophils were significantly increased at T90 (p = 0.03). Significant differences in gene expression were found for all the genes under study, with the exception of IFN-γ and TNF-α. In particular, IL-2 (T30, p = 0.011; T90, p = 0.015), IL-4 (T30, p = 0.009; T90, p < 0.001), and IL-8 (T30, p < 0.001; T90, p < 0.001) genes were significantly upregulated at both T30 and T90 with respect to T0, TGF-β was intensely downregulated at T30 (p < 0.001), IL-5 gene expression was significantly decreased at T90 (p = 0.001), while IL-1β (p = 0.005) and IL-3 (p = 0.001) expression was strongly augmented at the same time. This study highlighted long-term adjustments of O₂ transport capability that can be reasonably traced back to exercise adaptation. Moreover, the observed changes of granulocyte numbers and functions and inflammatory cytokine gene expression confirm a major role of the innate immune system in the response to the complex of stressful stimuli experienced during the training period.