Exercise-induced up-regulation of MMP-1 and IL-8 genes in endurance horses

Dietary supplementation of a Saccharomyces cerevisiae fermentation product attenuates exercise-induced stress markers in young horses

Mitigation of exercise-induced stress is of key interest in determining ways to optimize performance horse health. To test the hypothesis that dietary supplementation of a Saccharomyces cerevisiae fermentation product would decrease markers of exercise-induced stress and inflammation in young horses, Quarter Horse yearlings (mean ± SD; 9 ± 1 mo) were randomly assigned to receive either no supplementation (CON; n = 8) or 21 g/d S. cerevisiae fermentation product (10.5 g/feeding twice daily; SCFP; n = 10) top-dressed on a basal diet of custom-formulated grain as well as ad libitum Coastal bermudagrass hay. After 8 wk of dietary treatments, horses underwent a 2-h submaximal exercise test (SET) on a free-stall mechanical exerciser. Serum was collected before dietary treatment supplementation (week 0), at week 8 pre-SET, and 0, 1, and 6 h post-SET and analyzed for concentrations of cortisol and serum amyloid A (SAA) by commercial enzyme-linked immunosorbent assay (ELISA) and for cytokine concentrations by commercial bead-based ELISA. Data were analyzed using linear models with repeated measures in SAS v9.4. From week 0 to 8 (pre-SET), serum cortisol decreased (P = 0.01) and SAA did not change, but neither were affected by diet. Serum concentrations of all cytokines decreased from week 0 to 8 (P ≤ 0.008), but granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor, and interleukin-8 (IL-8) decreased to a greater extent in CON than in SCFP horses (P ≤0.003). In response to the week 8 SET, serum cortisol increased in all horses (P < 0.0001) but returned to pre-SET levels by 1 h post-SET in horses receiving SCFP. At 6 h post-SET, cortisol concentrations in CON horses returned to pre-SET concentrations, whereas cortisol declined further in SCFP horses to below pre-SET levels (P = 0.0002) and lower than CON (P = 0.003) at that time point. SAA increased at 6 h post-SET in CON (P < 0.0001) but was unchanged through 6 h in SCFP horses. All cytokines except G-CSF increased in response to the SET (P < 0.0001) but showed differing response patterns. Concentrations of IL-1β, IL-6, and tumor necrosis factor-alpha were lesser (P ≤ 0.05), and concentrations of G-CSF and IL-18 tended to be lesser (P ≤ 0.09) in SCFP compared with CON horses throughout recovery from the SET. In summary, 8 wk of dietary supplementation with 21 g/d of SCFP may mitigate cellular stress following a single, prolonged submaximal exercise bout in young horses.

The effect of lower airway inflammation on inflammatory cytokine gene expression in bronchoalveolar lavage fluid and whole blood in racing Thoroughbreds

BACKGROUND

Immunological mechanisms involved in the pathogenesis of mild to moderate equine asthma (MEA) are not completely understood. There are limited data on bronchoalveolar lavage fluid (BALF) and blood inflammatory cytokine profiles in racehorses with MEA, and the effect of racing on inflammatory cytokines is unknown.

HYPOTHESIS/OBJECTIVES

We hypothesized that inflammatory cytokine gene expression in BALF and resting blood would be higher in racehorses with lower airway inflammation compared to healthy controls, and that gene expression in blood collected immediately post-race would be increased compared to resting blood in racehorses with lower airway inflammation.

ANIMALS

38 racing Thoroughbreds (samples: 30 resting blood, 22 post-race BALF, 41 post-race blood).

METHODS

Prospective observational study. Inflammatory cytokine gene expression was determined in resting blood, post-race BALF and post-race blood from racehorses with lower airway inflammation and controls.

RESULTS

Lower airway inflammation was diagnosed in 79 % of racehorses (23 % neutrophilic, 67 % mastocytic, and 10 % mixed). There was no difference in gene expression in BALF or resting blood between racehorses with lower airway inflammation and controls. IL-8 gene expression was higher in post-race blood compared to resting peripheral blood, regardless of disease (p = 0052). BALF neutrophil proportions increased with increasing IL-1β gene expression in all sample types (p = 0.0025). BALF mast cell proportions increased with increasing TNF-α gene expression in post-race blood (p = 0.015).

CONCLUSIONS AND CLINICAL IMPORTANCE

Lower airway inflammation was common in a population of racehorses without respiratory signs or exercise intolerance. Exercise alone increased peripheral blood IL-8 gene expression. Inflammatory cytokine gene expression was not increased in BALF or resting blood in horses with subclinical lower airway inflammation, precluding its diagnostic utility in clinical practice.

Expression of select mRNA in Thoroughbreds with catastrophic racing injuries

BACKGROUND

The ability to identify horses at risk for catastrophic injuries continues to be a pressing issue for the racing industry, especially given recent events in North America.

OBJECTIVES

Since most catastrophic injuries occur in areas of existing pathology and this pathology is likely to elicit an inflammatory response, it was hypothesised that analysis of messenger RNA (mRNA) expression would detect significant changes in select genes in horses at risk for a catastrophic injury.

STUDY DESIGN

Prospective cohort study.

METHODS

Five racing jurisdictions across the United States participated in this study. A total of 686 Tempus^® RNA Blood Tube samples were collected for mRNA analysis from 107 catastrophically injured horses, as well as from noninjured horses sampled either prerace (n = 374) or postrace (n = 205). A subset of horses (n = 37) were sampled both prerace and postrace for analysis of expression changes during the postrace period.

RESULTS

Of 21 genes analysed via RT-qPCR, the expression of 12 genes (ALOX5AP, CD14, IL-10, IL-1β, IL-6, IL-8, MMP1, PTGS2, TLR4, TNFα, TNFSF13B and VEGFA) changed significantly within 45 minutes after a race and were excluded. Of the remaining nine genes (BMP-2, IGF-1, IL1RN, MMP2, MMP9, Osteoprotegrin, RANKL, SAA1 and TGFβ), three genes (IGF-1, IL1RN and MMP2) were found to be significantly different between catastrophically injured and noninjured horses using multiple logistic regression modelling. Receiver operating characteristic analysis of models, which included mRNA expression, demonstrated sensitivities from 76%-82% (95% CI: 67%-93%) and specificities from 84%-88% (95% CI: 71%-94%) at the Youden Index.

MAIN LIMITATIONS

Samples were collected as soon as possible postinjury (within 30 minutes).

CONCLUSIONS

Analysis of mRNA expression of specific genes in the future may be considered as an economical, accessible and noninvasive means by which horses at risk for catastrophic injury can be identified.

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

Physical exercise is universally recognized as stressful. Among the "sport species", the horse is probably the most appropriate model for investigating the genomic response to stress due to the homogeneity of its genetic background. The aim of this work is to dissect the whole transcription modulation in Peripheral Blood Mononuclear Cells (PBMCs) after exercise with a time course framework focusing on unexplored regions related to introns and intergenic portions. PBMCs NGS from five 3 year old Sardinian Anglo-Arab racehorses collected at rest and after a 2000 m race was performed. Apart from differential gene expression ascertainment between the two time points the complexity of transcription for alternative transcripts was identified. Interestingly, we noted a transcription shift from the coding to the non-coding regions. We further investigated the possible causes of this phenomenon focusing on genomic repeats, using a differential expression approach and finding a strong general up-regulation of repetitive elements such as LINE. Since their modulation is also associated with the "exonization", the recruitment of repeats that act with regulatory functions, suggesting that there might be an active regulation of this transcriptional shift. Thanks to an innovative bioinformatic approach, our study could represent a model for the transcriptomic investigation of stress.

Guanylin, Uroguanylin and Guanylate Cyclase-C Are Expressed in the Gastrointestinal Tract of Horses

Guanylate cyclase-C (GC-C) is a multifunctional receptor encoded by the GUCY2C gene, representing an attractive target for therapy in several gastrointestinal diseases in humans. Little is known about this system in horses. We investigated for the first time the gene expression of guanylin, uroguanylin and GC-C receptors in different horse’s gastrointestinal tracts. Tissue samples from stomach, duodenum, jejunum, ileum, head and body of cecum, left and right dorsal colon, left and right ventral colon, pelvic flexure, transverse colon, descending colon and rectum were collected from adult horses within 1 h post mortem. For each sample, total RNA was extracted from 100 mg of ground tissue, and qRT-PCR performed on GUCA2a, GUCA2b and GUCY2 transcripts on a CFX96 Touch instrument. Data analysis was carried out with Bio-Rad CFX Manager software, and genes of interest normalized relative to the abundance of the two reference genes (SDHA, HPRT). Additionally, the protein expression levels of GC-C receptor were analyzed through western blotting. A common pattern of expression throughout the gastrointestinal lumen for all three investigated transcripts was found. The expression of GUCA2a, GUCA2b and GUCY2 genes was higher in jejunum, ileum, descending colon and rectum. The levels of expression of GC-C protein confirmed these data. The findings of this study might open new scenarios for the therapeutic approach to enteric diseases of horse using selective agonists of GC-C.

Profiling of exercise-induced transcripts in the peripheral blood cells of Thoroughbred horses

Transcriptome analyses based on DNA microarray technology have been used to investigate gene expression profiles in horses. In this study, we aimed to identify exercise-induced changes in the expression profiles of genes in the peripheral blood of Thoroughbred horses using DNA microarray technology (15,429 genes on 43,603 probes). Blood samples from the jugular vein were collected from six horses before and 1 min, 4 hr, and 24 hr after all-out running on a treadmill. After the normalization of microarray data, a total of 26,830 probes were clustered into four groups and 11 subgroups showing similar expression changes based on k-mean clustering. The expression level of inflammation-related genes, including interleukin-1 receptor type II (IL-1R2), matrix metallopeptidase 8 (MMP8), protein S100-A8 (S100-A8), and serum amyloid A (SAA), increased at 4 hr after exercise, whereas that of c-Fos (FOS) increased at 1 min after exercise. These results indicated that the inflammatory response increased in the peripheral blood cells after exercise. Our study also revealed the presence of genes that may not be affected by all-out exercise. In conclusion, transcriptome analysis of peripheral blood cells could be used to monitor physiological changes induced by various external stress factors, including exercise, in Thoroughbred racehorses.

RNA sequencing of the exercise transcriptome in equine athletes

The horse is an optimal model organism for studying the genomic response to exercise-induced stress, due to its natural aptitude for athletic performance and the relative homogeneity of its genetic and environmental backgrounds. Here, we applied RNA-sequencing analysis through the use of SOLiD technology in an experimental framework centered on exercise-induced stress during endurance races in equine athletes. We monitored the transcriptional landscape by comparing gene expression levels between animals at rest and after competition. Overall, we observed a shift from coding to non-coding regions, suggesting that the stress response involves the differential expression of not annotated regions. Notably, we observed significant post-race increases of reads that correspond to repeats, especially the intergenic and intronic L1 and L2 transposable elements. We also observed increased expression of the antisense strands compared to the sense strands in intronic and regulatory regions (1 kb up- and downstream) of the genes, suggesting that antisense transcription could be one of the main mechanisms for transposon regulation in the horse under stress conditions. We identified a large number of transcripts corresponding to intergenic and intronic regions putatively associated with new transcriptional elements. Gene expression and pathway analysis allowed us to identify several biological processes and molecular functions that may be involved with exercise-induced stress. Ontology clustering reflected mechanisms that are already known to be stress activated (e.g., chemokine-type cytokines, Toll-like receptors, and kinases), as well as "nucleic acid binding" and "signal transduction activity" functions. There was also a general and transient decrease in the global rates of protein synthesis, which would be expected after strenuous global stress. In sum, our network analysis points toward the involvement of specific gene clusters in equine exercise-induced stress, including those involved in inflammation, cell signaling, and immune interactions.

Effect of training status on immune defence related gene expression in Thoroughbred: are genes ready for the sprint?

Athletic performance is both a stress factor and an adaptive response to exercise that may be modulated by training, reduce inflammation and help prevent disease. Studies on the endocrinology of exercise and training have demonstrated the existence of an integrated metabolic network of hormone and cytokine regulation. Subsequent molecular studies have shown that repeated bouts of exercise may establish new basal levels of gene expression at rest. The Thoroughbred horse may be a useful 'exercise model' for inter-individual comparisons between subjects with homogeneous genetic and environmental backgrounds and similar exercise management practices. In this study, the effects of training and acute effort on gene expression were evaluated with a real time PCR approach in athletic (n=10) and sedentary horses (n=9), using a previously characterised panel of genes known to be highly modulated during effort (CXCL2, TLR4, IL1β, IL8, IL1RII, IL18, IL6 and CEBPβ). A 'rest comparison' was performed to evaluate a training effect in both groups while a 'race comparison' was performed in athletic horses only (before, immediately after, and 12h after racing) to determine the effect of acute effort. The results indicated that many of the investigated genes (TLR4, IL1β, IL1RII, IL18, IL6 and CEBPβ) were expressed to a greater extent in athletic horses compared to sedentary animals when both were at rest. However, a time-course comparison in the athletic horses revealed that genes exhibiting the highest levels of expression at rest did not show significant changes after the race. The findings suggested that training may exert a conditioning on gene expression at rest leading to a more prompt response to exercise-induced stress in Thoroughbreds.

Athletic humans and horses: comparative analysis of interleukin-6 (IL-6) and IL-6 receptor (IL-6R) expression in peripheral blood mononuclear cells in trained and untrained subjects at rest

BACKGROUND

Horses and humans share a natural proclivity for athletic performance. In this respect, horses can be considered a reference species in studies designed to optimize physical training and disease prevention. In both species, interleukin-6 (IL-6) plays a major role in regulating the inflammatory process induced during exercise as part of an integrated metabolic regulatory network. The aim of this study was to compare IL-6 and IL-6 receptor (IL-6R) mRNA expression in peripheral blood mononuclear cells (PBMCs) in trained and untrained humans and horses.

RESULTS

Nine highly trained male swimmers (training volume: 21.6 ± 1.7 h/wk in 10-12 sessions) were compared with two age-matched control groups represented by eight lightly trained runners (training volume: 6.4 ± 2.6 h/wk in 3-5 sessions) and nine untrained subjects. In addition, eight trained horses (training volume: 8.0 ± 2.1 h/wk in 3-4 sessions) were compared with eight age-matched sedentary mares. In humans, IL-6 mRNA levels in PBMCs determined by quantitative reverse transcription-polymerase chain reaction were significantly higher in highly trained subjects, whereas IL-6R expression did not differ among groups. In horses, transcripts of both IL-6 and IL-6R were significantly up-regulated in the trained group.

CONCLUSIONS

Up-regulation of IL-6R expression in PBMCs in horses could reflect a mechanism that maintains an adequate anti-inflammatory environment at rest through ubiquitous production of anti-inflammatory cytokines throughout the body. These findings suggest that the system that controls the inflammatory response in horses is better adapted to respond to exercise than that in humans.