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theses

There is little information regarding the molecular events that govern the beneficial adaptations of equine skeletal muscle in response to acute exercise and training. This work addressed this subject in two manners. First, based on the comparative mammalian literature, signaling and gene expression markers related to S-ER stress and proteostasis were analyzed in equine gluteus medius biopsies before and after acute high-intensity exercise in the untrained and trained states. Protein expression analysis revealed that S-ER stress signaling was apparent, however, many downstream mRNA expression markers were not significantly impacted by acute high-intensity fatiguing exercise in the untrained state. Twelve wks of training, however, altered S-ER stress signaling as well as the expression of genes related to apoptosis and protein degradation. Additionally, mRNA expression markers of protein degradation were not impacted by acute fatiguing exercise in the untrained state; however, training status did alter the exercise-induced gene expression of the E3-ubiquitin ligase, Fbxo32. Lastly, training also compressed the mRNA expression variability in most S-ER stress-related genes, both basally and post-exercise.
Second, based on the gene expression data, a non-targeted metabolomics approach was employed in order to assess the phenotypic variability in skeletal muscle at the level of metabolites. Metabolic differences in the early (3 h) and late (24 h) recovery periods were also assessed. In agreement with the gene expression findings, PCA and hierarchical clustering analysis of muscle biopsies revealed that training dominated the skeletal muscle phenotype and produced a homogeneous basal and exercise-induced metabolic signature among the horses. Early metabolic alterations largely centered on the branched-chain amino acids, microbial-derived xenobiotics, and a variety of lipid and nucleotide-derived compounds, especially in the trained state. Further, training increased the abundances of almost every identified long-chain free-fatty acid and complex lipid species in the pre-exercise condition. These elevations declined over 24 h following acute fatiguing exercise and were associated with increased gene expression related to lipid uptake and utilization.
Finally, in an extension of the first two studies, the final objective of this work was to identify the impacts of prolonged training and detraining on body composition and aerobic and athletic capacities, as very little information exists regarding these training periods in the horse. Twelve wks of training caused a robust increase in VO2max and athletic capacity, with geldings outperforming mares. There was, however, no concomitant improvement in body composition during this period. An additional 60 wks of training was accompanied by a worsening of body composition in both sexes whereas aerobic capacity and athletic capabilities were maintained. Interestingly, 20 wks of detraining resulted in a maintenance of VO2max and performance despite a statistically significant reduction in FFM.
In summary, this work revealed novel exercise and training-induced alterations in gene expression and metabolic signatures in equine skeletal muscle that are associated with cellular homeostasis and energy production and utilization. Further, to the best of the author’s knowledge, this is the first report in horses regarding changes in physiologic performance measures during periods of extended training and detraining. These findings characterize some of the putative cellular governors of exercise and training adaptations in equine skeletal muscle and may be used to improve the health, longevity, and management of the performance horse during periods of vigorous training and inactivity.

ETD_9328

Ph.D.

Includes bibliographical references

by Dylan Joseph Klein

doi:10.7282/t3-yckf-z920

ETD doctoral

The author owns the copyright to this work.