The effect of strenuous exercise on mRNA concentrations of interleukin-12, interferon-gamma and interleukin-4 in equine pulmonary and peripheral blood mononuclear cells

Epigenetic control of exercise adaptations in the equine athlete: Current evidence and future directions

Horses (Equus ferus caballus) have evolved over the past 300 years in response to man-made selection for particular athletic traits. Some of the selected traits were selected based on the size and horses' muscular power (eg Clydesdales), whereas other breeds were bred for peak running performance (eg Thoroughbred and Arabian). Although the physiological changes and some of the cellular adaptations responsible for athletic potential of horses have been identified, the molecular mechanisms are only just beginning to be comprehensively investigated. The purpose of this review was to outline and discuss the current understanding of the molecular mechanisms underpinning the athletic performance and cardiorespiratory fitness in athletic breeds of horses. A brief review of the biology of epigenetics is provided, including discussion on DNA methylation, histone modifications and small RNAs, followed by a summary and critical review of the current work on the exercise-induced epigenetic and transcriptional changes in horses. Important unanswered questions and currently unexplored areas that deserve attention are highlighted. Finally, a rationale for the analysis of epigenetic modifications in the context with exercise-related traits and ailments associated with athletic breeds of horses is outlined in order to help guide future research.

Comparison of pre-race inflammatory marker mRNA expression with race-related parameters in Thoroughbreds

Research in Thoroughbred racehorses has demonstrated continual training leads to a decrease in pro-inflammatory gene expression as horses become race fit, although not all horses experience this predicted decrease. Here, the goal was to determine whether pre-race inflammatory marker mRNA expression correlates with race performance and other horse-specific parameters. Single blood samples in Tempus RNA stabilisation tubes were collected during pre-race total CO2 testing at a Thoroughbred racetrack in Kentucky. mRNA was isolated and quantitative PCR performed on the samples for the pro-inflammatory markers interleukin (IL)-1β, IL-6, IL-8, IL-17, and tumour necrosis factor (TNF)-α. Expression data was analysed using one-way ANOVA on Ranks. There was no predictive value of inflammatory marker expression for race performance other than decreased IL-6 in race favourites that finished in the top three positions. Horses entered into graded stakes races had significantly lower expression of pro-inflammatory cytokines IL-1β and TNF-α, as well as a lower average of all 5 markers combined, when compared to allowance and claiming horses. Additionally, some claiming horses had evidence of increased pro-inflammatory marker expression. Lower inflammatory marker expression in graded stakes horses likely arose from both the fitness level and management practices of these horses, as these horses had a lower number of and greater interval between starts when compared to claiming and allowance horses. Evidence of increased inflammatory marker expression in some horses would suggest that they are not sufficiently conditioned or recovered fully between races or bouts of high-speed training. While there were other significant differences detected, their biological importance remains unclear.

The Effect of Race Training on the Basal Gene Expression of Alveolar Macrophages Derived From Standardbred Racehorses

Mild-to-moderate equine asthma is prevalent in young racehorses, particularly early in their training period. Although the precise etiopathogenesis remains undetermined, it is possible that the susceptibility of this population might partly reflect an exercise-associated immune derangement at the level of the airway. We performed a genome-wide basal gene expression scan on alveolar macrophages (AMs) isolated from Standardbred racehorses before and after commencement of competition race training with a view to identifying any exercise-associated gene expression modulation consistent with functional alterations, which might reflect training-associated immunological derangement. Microarray technology was used to analyze the basal gene expression profiles of bronchoalveolar fluid-derived AMs, harvested from six systemically healthy Standardbred racehorses before (T0) and after (T1) entry into training. In addition, AM lipopolysaccharide (LPS)-induced TNF-α and IL-10 release at T0 and T1 was assessed. Although the data revealed significant interhorse heterogeneity in relation to the magnitude of individual gene expression at each timepoint, within each horse, several inflammatory-related genes [e.g., chemokine ligands, interferons, and nuclear factor kappa-light-chain-enhancer of activated B cells (NFKB)] declined in expression from T0 to T1. Entry into training did not significantly alter AM LPS-induced TNF-α or IL-10 release. The data support a direct effect of training on AM basal gene expression, particularly with respect to immune-related genes. The pattern of training-associated differential gene expression may indicate relative downregulation of inflammatory-related genes, consistent with an immunosuppressive effect of training and an increased susceptibility to opportunistic pathogens.

Influences of age and sex on leukocytes of healthy horses and their ex vivo cytokine release

Leukocytes and their functional capacities are used extensively as biomarkers in immunological research. Commonly employed indicators concerning leukocytes are as follows: number, composition in blood, response to discrete stimuli, cytokine release, and morphometric characteristics. In order to employ leukocytes as biomarkers for disease and therapeutic monitoring, physiological variations and influencing factors on the parameters measured have to be considered. The aim of this report was to describe the ranges of selected leukocyte parameters in a sample of healthy horses and to analyse whether age, sex, breed, and sampling time point (time of day) influence peripheral blood leukocyte composition, cell morphology and release of cytokines ex vivo. Flow cytometric comparative characterisation of cell size and complexity in 24 healthy horses revealed significant variance. Similarly, basal release of selected cytokines by blood mononuclear cells also showed high variability [TNFα (65-16,624pg/ml), IFNγ (4-80U/ml), IL-4 (0-5069pg/ml), IL-10 (49-1862pg/ml), and IL-17 (4-1244U/ml)]. Each animal's age influenced leukocyte composition, cell morphology and cytokine release (TNFα, IL-4, IL-10) ex vivo. Geldings showed smaller monocytes and higher spontaneous production of IL-10 when compared to the mares included. The stimulation to spontaneous release ratios of TNFα, IL-4 and IL-17 differed in Warmblood and Thoroughbred types. Sampling time influenced leukocyte composition and cell morphology. In summary, many animal factors - age being the dominant one - should be considered for studies involving the analysis of equine leukocytes. In addition, high inter-individual variances argue for individual baseline measurements.

Evaluation of the reactivity of commercially available monoclonal antibodies with equine cytokines

Research on equine cytokines is often performed by analyses of mRNA. For many equine cytokines an analysis on the actual protein level is limited by the availability of antibodies against the targeted cytokines. Generation of new antibodies is ongoing but time consuming. Thus, testing the reactivity of commercially available antibodies for cross-reactivity with equine cytokines is of particular interest. Fifteen monoclonal antibodies against IL-1β, IL-6, IL-8, IL-12, IL-18 and Granulocyte Macrophage Colony stimulating factor (GM-CSF) of different species were evaluated for reactivity with their corresponding equine cytokines. Dot Blot (DB) and Western Blot (WB) analyses were performed using recombinant equine cytokines as positive controls. Immunohistochemistry (IHC) was carried out on equine tissue and flow cytometry on equine PBMC as positive controls. As expected, three equine IL-1β antibodies detected equine IL-1β in DB, WB and IHC. For these, reactivity in IHC has not been described before. One of them was also found to be suitable for intracellular staining of equine PBMC and flow cytometric analysis. Two antibodies raised against ovine GM-CSF cross-reacted with equine GM-CSF in DB, WB and IHC. For these anti-GM-CSF mAbs this is the first experimental description of cross-reactivity with equine GM-CSF (one mAb was predicted to be cross-reactive in WB in the respective data sheet). The other clone additionally proved to be appropriate in flow cytometric analysis. Two mAbs targeting porcine IL-18 cross-reacted in IHC, but did not show specificity in the other applications. No reactivity was shown for the remaining five antibodies in DB, although cross-reactivity of two of the antibodies was described previously. The results obtained in this study can provide beneficial information for choosing of antibodies for immunological tests on equine cytokines.

Biomarkers of antioxidant status, inflammation, and cartilage metabolism are affected by acute intense exercise but not superoxide dismutase supplementation in horses

Objectives were to evaluate effects of (1) repetitive arthrocentesis on biomarkers of inflammation (prostaglandin E(2), PGE(2)) and aggrecan synthesis (chondroitin sulfate-846; CS) in synovial fluid (SF); (2) exercise and superoxide dismutase (SOD) supplementation on biomarkers of inflammation, antioxidant status, and aggrecan synthesis, in horses. Preliminary trial. Standardbreds underwent four arthrocentesis procedures within 48 h and exhibited elevated CS and no changes in PGE(2). Exercise trial. this randomized crossover design used twelve Standardbred mares which received either treatment (3000 IU d(-1) oral SOD powder) or placebo (cellulose powder) for 6 wks which culminated with them running a repeated sprint exercise test (RSET). Samples were collected before (PRE), during (PEAK), and following exercise (POST). Exercise resulted in increased (P < 0.05) antioxidant defenses including erythrocyte SOD, total glutathione, glutathione peroxidase, gene transcripts for interferon-gamma, interleukin-10, and interleukin-1β in blood, and decreased plasma nitric oxide. Exercise increased (P < 0.05) SF CS and adjusted-PGE(2), and higher (P < 0.05) CS and PGE(2) were found in hock versus carpus joints. No treatment effects were detected. Results suggest normal adaptive responses likely due to exercise-induced tissue microdamage and oxidative stress. Additional research is needed to identify benefit(s) of SOD supplementation in horses.

Effect of strenuous exercise and ex vivo TLR3 and TLR4 stimulation on inflammatory gene expression in equine pulmonary leukocytes

The effects of strenuous exercise and ex vivo stimulation of TLR3 and TLR4 pathways on the expression of six inflammatory genes in equine pulmonary leukocytes were investigated. The genes tested were interferon-beta (IFN-β), interleukin-1-beta (IL-1β), interleukin-6 (IL-6), interferon gamma-induced protein 10 (IP-10), chemokine (c-c motif) ligand 5 (RANTES) and tumor necrosis factor-alpha (TNF-α). We hypothesized that strenuous exercise would modulate basal gene expression on one hand and modulate the response to bacterial lipopolysaccharide (LPS) and to polyinosinic:polycytidylic acid (Poly IC) on the other hand. Eight young Thoroughbred mares were selected for the experiment. Bronchoalveolar lavages were performed on horses 48 h before and 24h after the completion of treadmill exercise until fatigue. Differential counts were performed on the bronchoalveolar lavage cells. Real-time PCR was used to quantify cytokine expression in pulmonary leukocytes. Target gene expression was normalized to the expression of three housekeeping genes (HKG). There were no significant differences in the mRNA expression of the six cytokines between pre-exercise and post-exercise cells. LPS and Poly IC induced respectively significant increases of TNF-α, IFN-β, IL-6, IL-1β, and TNF-α, IFN-β, IP-10 and RANTES, both before and after exercise. However, exercise induced a significant decrease of the genes response to LPS and Poly IC. These findings may suggest that strenuous treadmill exercise exerts a deleterious effect on part of the pulmonary immune response in horses 24h following an intense physical activity.

Exercise-induced increases in inflammatory cytokines in muscle and blood of horses

REASONS FOR PERFORMING STUDY

Studies have demonstrated increases in mRNA expression for inflammatory cytokines following exercise in horses and have suggested those markers of inflammation may play a role in delayed onset muscle soreness. However, measurement of mRNA expression in white blood cells is an indirect method. No studies to date have documented the cytokine response to exercise directly in muscle in horses.

HYPOTHESIS

This study tested the hypothesis that exercise increases cytokine markers of inflammation in blood and muscle.

METHODS

Blood and muscle biopsies were obtained from 4 healthy, unfit Standardbred mares (∼ 500 kg). The randomised crossover experiment was performed with the investigators performing the analysis blind to the treatment. Each horse underwent either incremental exercise test (GXT) or standing parallel control with the trials performed one month apart. During the GXT horses ran on a treadmill (1 m/s increases each min until fatigue, 6% grade). Blood and muscle biopsies were obtained 30 min before exercise, immediately after exercise and at 0.5, 1, 2, 6 and 24 h post GXT or at matched time points during the parallel control trials. Samples were analysed using real time-PCR for measurement of mRNA expression of interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) and interleukin-1 (IL-1). Data were analysed using t tests with the null hypothesis rejected when P < 0.10.

RESULTS

There were no changes (P > 0.10) in IL-1, IL-6, IFN-gamma or TNF-alpha during control. Exercise induced significant increases in IFN-gamma, IL1 and TNF-alpha in blood and significant increases in IFN-gamma, IL-6 and TNF-alpha in muscle. There were no significant changes in mRNA expression of IL-1 in muscle or IL-6 in blood following the GXT. These cytokine markers of inflammation all returned to preGXT levels by 24 h post GXT.

CONCLUSION

High intensity exercise results in a transient increase in the expression of inflammatory cytokines in muscle and blood.

Peripheral blood leukocytes

Assessment of peripheral blood leukocytes is the most common clinical pathology test in equine practice. It is always a part of complete body function assessment and frequently is used alone, or in conjunction with, fibrinogen to monitor response to treatment.

Effect of orange peel and black tea extracts on markers of performance and cytokine markers of inflammation in horses

This study tested the hypothesis that orange peel (O) and decaffeinated black tea (T) extracts would alter markers of exercise performance as well as exercise-induced mRNA expression for the inflammatory cytokines IL-6, TNF-alpha and IFN-gamma. Nine healthy, unfit Standardbred mares (age: 10±4years, ∼450kg) were assigned to three treatment groups in a randomized crossover design where each horse was administered one of the following; placebo (O; 21 water), black tea extract in water (T; 21) or orange peel extract in water (W; 21), via a nasogastric tube. One hour later the horses completed an incremental graded exercise test (GXT) on a treadmill at a fixed 6% grade with measurements and blood samples obtained at rest, at the end of each 1min step of the GXT and at 2 and 5min post-GXT. An additional set of blood samples for Polymerase Chain Reaction (PCR) measurements of mRNA was obtained before exercise and at 5 and 30min and 1, 2, 4 and 24h post-GXT. The GXTs were conducted between 0700 and 1200h not less than 7days apart. There were no differences (P>0.05) in VO2max, respiratory exchange ratio, run time, velocity at VO2max, core body temperature, haematocrit, creatine kinase (CK), plasma lactate concentrations, HR, right ventricular pressure (RVP) or pulmonary artery pressure (PAP) across treatments. A major finding was that orange peel extract significantly reduced post-exercise VO2 recovery time (W = 112±7, O = 86±6, and T = 120±11s). There was a significant difference in plasma total protein concentration (TP) in the O runs compared with water and T. TNF-alpha mRNA expression was lower in the T runs compared with water and O trials. IFN-gamma mRNA expression levels appeared to be lower in both the T and O extract runs compared with the water trials. The mRNA expression of IL-6 was unaltered across treatment groups. These data suggest that orange peel and black tea extracts may modulate the cytokine responses to intense exercise. Orange peel extract reduced post-exercise recovery time and may potentially enhance the ability of horses to perform subsequent bouts of high-intensity exercise.

Selection of a set of reliable reference genes for quantitative real-time PCR in normal equine skin and in equine sarcoids

BACKGROUND

Real-time quantitative PCR can be a very powerful and accurate technique to examine gene transcription patterns in different biological conditions. One of the critical steps in comparing transcription profiles is accurate normalisation. In most of the studies published on real-time PCR in horses, normalisation occurred against only one reference gene, usually GAPDH or ACTB, without validation of its expression stability. This might result in unreliable conclusions, because it has been demonstrated that the expression levels of so called "housekeeping genes" may vary considerably in different tissues, cell types or disease stages, particularly in clinical samples associated with malignant disease. The goal of this study was to establish a reliable set of reference genes for studies concerning normal equine skin and equine sarcoids, which are the most common skin tumour in horses.

RESULTS

In the present study the gene transcription levels of 6 commonly used reference genes (ACTB, B2M, HPRT1, UBB, TUBA1 and RPL32) were determined in normal equine skin and in equine sarcoids. After applying the geNorm applet to this set of genes, TUBA1, ACTB and UBB were found to be most stable in normal skin and B2M, ACTB and UBB in equine sarcoids.

CONCLUSION

Based on these results, TUBA1, ACTB and UBB, respectively B2M, ACTB and UBB can be proposed as reference gene panels for accurate normalisation of quantitative data for normal equine skin, respectively equine sarcoids. When normal skin and equine sarcoids are compared, the use of the geometric mean of UBB, ACTB and B2M can be recommended as a reliable and accurate normalisation factor.

Cytokine gene expression in response to SnSAG1 in horses with equine protozoal myeloencephalitis

Equine protozoal myeloencephalitis (EPM) is a neurologic syndrome seen in horses from the Americas and is mainly caused by Sarcocystis neurona. Recently, a 29-kDa surface antigen from S. neurona merozoites was identified as being highly immunodominant on a Western blot. This antigen has been sequenced and cloned, and the expressed protein has been named SnSAG1. In a previous study, cell-mediated immune responses to SnSAG1 were shown to be statistically significantly reduced in horses with EPM in comparison to EPM-negative control horses. It therefore appears as though the parasite is able to induce immunosuppression towards parasite-derived antigens as parasite-specific responses are decreased. Isolated peripheral blood lymphocytes from 21 EPM (cerebrospinal fluid [CSF] Western blot)-negative horses with no clinical signs and 21 horses with clinical signs of EPM (CSF Western blot positive) were cocultured with SnSAG1 for 48 and 72 h, and the effect on cytokine production was investigated by means of reverse transcriptase PCR. Cytokines assayed include gamma interferon (IFN-gamma), tumor necrosis factor alpha, interleukin (IL)-2, IL-4, and IL-6. beta-Actin was used as the housekeeping gene. A Wilcoxon signed-rank test of the findings indicated that there was a statistically significant decrease in IFN-gamma production after 48 h in culture for samples from horses with clinical disease. There was also a statistically significant increase in IL-4 production after 72 h in culture for samples from horses with EPM. These results further support the notion that this parasite is able to subvert the immune system in horses with clinical disease.

Immunostimulatory DNA activates production of type I interferons and interleukin-6 in equine peripheral blood mononuclear cells in vitro

This study aimed to evaluate different nucleic acid preparations as cytokine inducers in equine cells. To induce cytokine production, bacterial plasmid DNA or short synthetic oligodeoxyribonucleotides (ODN), with or without the transfection reagent lipofectin, were added to cultures of purified equine peripheral blood mononuclear cells (PBMC). Cytokine activity was detected with bioassays in cell culture supernatants after 24h of induction and cytokine mRNA expression was detected using RT-PCR at 6h post induction. For IFN-alpha/beta it was found that both plasmid DNA and phosphodiester ODN, containing an unmethylated CpG-motif, were able to induce IFN production in the presence of lipofectin but not without. The levels of IFN varied with individuals and were often quite low. Moreover, methylation or removal of the CpG sequence completely abolished IFN induction. CpG-containing ODN with poly-guanine (G) sequences in the 5' and 3' ends induced considerably higher levels of IFN, especially when the poly-G sequences had a phosphorothioate backbone. ODN with poly-G sequences also had the ability to induce IFN in the absence of lipofectin but the levels of IFN induced were radically reduced compared to those induced with lipofectin. In contrast to IFN, which was only detected upon induction, low spontaneous IL-6 production was observed in unstimulated control cultures. Nevertheless, plasmid DNA and CpG-containing ODN were able to increase the IL-6 production threefold. All the IFN inducing ODN also induced IL-6 production and the levels of IL-6 induced seemed influenced by addition of lipofectin and presence of poly-G sequences in the same way as was observed for the IFN-production. However, a complete phosphorothioate ODN with a central CpG-motif and poly-C sequences, that did not induce IFN, readily induced IL-6 both in the presence and absence of lipofectin. In addition, there was also evidence that some ODN induced increased expression of IL-12p40 mRNA. To conclude, equine PBMC were able to recognize CpG-DNA and respond with both IFN-alpha/beta and/or IL-6 production. The levels of cytokine induced, and sometimes which cytokine induced, varied with, e.g., CpG-motifs used, the presence of poly-G sequences, ODN backbone chemistry and presence of lipofectin.

Inhibition of lymphocyte proliferation and activation: a mechanism used by equine invasive trophoblast to escape the maternal immune response

At days 36-38 of gestation, the equine invasive trophoblast cells migrate into the endometrium of the pregnant mare to form the endometrial cups. During their migration, they become surrounded by maternal CD4+ and CD8+ T lymphocytes, and stimulate a cytotoxic antibody response to the paternal major histocompatibility complex class I antigens that they express. Nevertheless, endometrial cup cells remain viable at the site of uterine invasion up to days 80-100 of gestation, suggesting the participation of immunomodulatory mechanisms to the maternal cellular immune response. To determine the effects of the invasive trophoblast cells on lymphocyte proliferation, an in vitro co-culture system was developed using isolated equine invasive trophoblast cells and peripheral blood lymphocytes. Fetal fibroblast cells from the same conceptuses were used as controls. The presence of invasive trophoblast cells or their pre-conditioned medium inhibited 50% or more of lymphocyte proliferation, while fetal fibroblasts had no effect. The invasive trophoblast cell inhibitory factor needed to be present constantly to affect lymphocyte proliferation, and it was ineffective if lymphocytes had been previously stimulated to proliferate. The lymphoproliferative inhibitory mechanism affected lymphocyte subpopulations similarly. In addition, lymphocyte expression of cytokine mRNA including IFNgamma, IL-2, IL-4, and IL-10 was affected compared to controls. The implication of these observations in vivo may explain, in part, the apparent equine maternal immune acceptance of the presence and development of endometrial cup cells.

Cold weather exercise and airway cytokine expression

Athletes who perform repeated exercise while breathing cold air have a high prevalence of asthmalike chronic airway disease, but the mechanism linking such activity to airway inflammation is unknown. We used a novel animal model (exercising horses) to test the hypothesis that exercise-induced chronic airway disease is caused by exposure of intrapulmonary airways to unconditioned air, resulting in the upregulation of cytokine expression. Bronchoalveolar lavage fluid (BALF) was obtained from eight horses 5 h after submaximal exercise while they breathed room temperature or subfreezing air in a random crossover design. BALF total and differential nucleated cell counts were determined, and relative cytokine mRNA expression in BALF nucleated cells was quantified by real-time RT-PCR using primer and probe sequences specific for equine targets. There were no significant changes in total or differential cell concentrations between BALF recovered after warm and cold air exercise, although there was a strong trend toward increased concentrations of airway epithelial cells after cold air exercise (P = 0.0625). T(H)2 cytokines IL-4, IL-5, and IL-10 were preferentially upregulated after cold air exercise 12-, 9-, and 10-fold, respectively, compared with warm air exercise. Other cytokines (IL-2 and IL-6) were upregulated to a lesser extent (6- and 3-fold, respectively) or not at all (IL-1, IL-8, IFN-gamma, and TNF-alpha). These results suggest that cold weather exercise can lead to asthmalike airway disease through the local induction of cytokines typical of the T(H)2 phenotype.

Recurrent airway obstruction (RAO) in horses is characterized by IFN-gamma and IL-8 production in bronchoalveolar lavage cells

In horses prone to developing recurrent airway obstruction (RAO), we tested the hypotheses that the cytokine profile in the bronchoalveolar lavage (BAL) cells of affected horses would reflect a polarized Th-2 response; that cytokine and chemokine alterations would occur within 24 h of allergen exposure; and that allergen exposure would induce alterations in the expression of the transcription factor t-bet (t-box-expressed in T-cells). The expression levels of interleukin-4 (IL-4), IL-13, Interferon-gamma (IFN-gamma), t-bet, IL-8 and granulocyte-macrophage colony stimulating factor (GM-CSF) were measured in BAL cells obtained from control and RAO-susceptible horses during an asymptomatic phase and at 24 h and 5 weeks post-stabling and hay exposure. At each sampling time, BAL neutrophil percentages in the RAO-group exceeded controls. In the RAO-group, only IL-13 expression was decreased 2-fold during the asymptomatic phase. No differences in cytokine or chemokine expression were detected during the acute exposure phase. During the chronic phase, IFN-gamma and IL-8 expression levels were 2.5- and 3-fold greater, respectively, in the RAO-group. No other differences in gene expression were detected. We conclude that the cytokine profile of the airway cells does not reflect a polarized Th-2 response; that increases in IFN-gamma result from a t-bet independent pathway and that chemokines from epithelial or interstitial cells may contribute to early neutrophil influx.