ECSS Paris 2023: CP-PN27
INTRODUCTION: Renalase is a secreted cytokine that mediates intercellular communication and contributes to systemic physiological regulation. Although its cardiovascular and metabolic functions have been widely studied, emerging evidence indicates that renalase is responsive to exercise and may participate in skeletal muscle adaptation. Circulating renalase levels increase after exercise training, and previous studies have also reported that skeletal muscle renalase expression is elevated following training, supporting a role for muscle-derived renalase in exercise-induced physiological remodeling. However, whether renalase is required for normal training adaptations in skeletal muscle and whole-body performance remains unclear. Therefore, this study examined the functional significance of renalase during exercise training using renalase knockout mice. METHODS: Male Rnls-deficient (KO) and wild-type (WT) mice were assigned to sedentary or treadmill-trained conditions for two months. Training consisted of treadmill running at 25 m/min for 30 min/day, five days per week. Exercise performance, blood lactate, body weight, and transcriptomic profiles of the soleus muscle assessed by RNA sequencing were evaluated to determine physiological and molecular adaptations. RESULTS: Exercise training improved performance-related parameters overall; however, renalase deficiency attenuated these training-induced phenotypic adaptations. KO mice showed reduced post-training exercise capacity compared with WT mice despite similar baseline characteristics. Transcriptomic analysis revealed minimal genotype-dependent differences under sedentary conditions, whereas marked differential gene expression appeared after exercise training, indicating that renalase specifically contributes to molecular responses to training rather than basal muscle homeostasis. Differential expression and volcano plot analyses further demonstrated pronounced divergence in transcriptional regulation between WT and KO muscles following training, consistent with impaired adaptive remodeling in the absence of renalase. CONCLUSION: These findings indicate that renalase is a key mediator of exercise-induced physiological and transcriptional adaptations in skeletal muscle. The reduced training responsiveness observed in renalase-deficient mice suggests that renalase functions as an exercise-responsive cytokine required for optimal performance improvement and muscle remodeling, highlighting its potential as a molecular target for enhancing training adaptation and metabolic health.
Read CV Katsuyuki TokinoyaECSS Paris 2023: CP-PN27
INTRODUCTION: Recent findings suggest that, in older adults, resistance exercise performed in the morning may promote greater skeletal muscle hypertrophy than equivalent training conducted later in the day. This temporal pattern appears to differ from that reported in younger populations. The purpose of this study was to examine time-of-day–dependent adaptations to resistance training in older individuals, with particular emphasis on skeletal muscle and plasma lipidomic profiling. METHODS: Twenty-eight previously untrained older adults (20 women and 8 men; 65–75 years of age) were allocated to either a morning training group (MT, n = 14) or an afternoon training group (AT, n = 14). Both groups completed the same 12-week resistance training protocol, performed at two distinct times of day: 8:00–9:00 AM for MT and 4:00–5:00 PM for AT. Assessments conducted before and after the intervention included physical performance testing, body composition analysis, bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA). Targeted shotgun lipidomics were performed on fasting morning blood plasma and skeletal muscle samples from the vastus lateralis. A non-exercising control group was also part of the broader study but is not described for the lipidomic profile in the present report. RESULTS: Isometric knee extension muscle strength increased significantly in both training groups, however, the AT improved significantly more compared to MT. Resistance training did not elicit notable changes in total lean mass or bone mineral density. In skeletal muscle tissue, 1014 lipids were found. Training increased several types of lipids. Profound changes were found if cardiolipin. Time-dependent changes in lipid turnover (Triglyceride-Free Fatty Acid cycle) were found in plasma lipid classes. CONCLUSION: These preliminary findings suggest that time-of-day-specific resistance training induces distinct changes in plasma and skeletal muscle lipids and muscle strength. The study was supported by the Slovak Research and Development Agency (grant no. APVV-21-0164).
Read CV Milan SedliakECSS Paris 2023: CP-PN27
INTRODUCTION: It is known that repeated exposure to heat leads to acclimation, which improves whole-body thermoregulatory mechanisms and enhances exercise performance in hot conditions. However, the impact of heat stress on equine skeletal muscle is not yet fully understood. In this study, we examined the direct effects of heat stress treatment on mitochondrial respiratory function and transcriptomic responses using primary equine skeletal muscle culture cells. METHODS: Ten Thoroughbred horses performed incremental exercise tests (IET) under hot conditions (wet bulb globe temperature: 30°C). Biopsies from the gluteus medius muscle were taken before IET, and cultured myoblasts were incubated at 37°C (control) or 43°C (heat) for 1 h. Oxygen consumption rate was measured using a Seahorse XF96 Extracellular Flux Analyzer. At 3 h after the heat treatment, differential gene expression was identified using DESeq2 (false discovery rate cutoff: 0.05, minimal fold change: 1.5). RESULTS: There was a trend of correlation between exercise duration during IET and maximal respiration of cultured myoblasts from each horse (r=0.59, p=0.07). Immediately following heat treatment, both basal and maximal respiration decreased significantly while proton leak remained unchanged. Heat exposure upregulated 331 genes and downregulated 414 genes in equine myoblasts compared with control cells. Pathway analysis revealed heat-induced upregulation of outer mitochondrial membrane organization and downregulation of mitophagy. CONCLUSION: Our results suggest that hyperthermia transiently decreases the efficiency of cellular respiration and triggers mitochondrial remodeling in equine skeletal muscle. These observations may provide insights for improving exercise performance in hot conditions.
Read CV Yu KitaokaECSS Paris 2023: CP-PN27