Biology subjects

Gejl, K. D.

Publications and source records attributed to Gejl, K. D..

3 recordsLinked to original sources

bioRxiv2025

Increased contact between lipid droplets and mitochondria in skeletal muscles of male elite endurance athletes

Endurance athletes exhibit higher skeletal muscle mitochondrial and lipid droplet (LD) content compared to recreationally active individuals, along with greater whole-body oxygen uptake and maximal fat oxidation rates. In this study, we investigated if these differences manifest in a greater LD-mitochondria contact and how this may relate to the organelles size, shape, and numerical densities. We obtained skeletal muscle biopsies from 17 male elite triathletes and road cyclists and 7 recreationally active men. Using quantitative transmission electron microscopy, we found that the endurance athletes had 2-3-fold greater LD-mitochondria contact length than the recreationally active individuals. This was related to higher numerical densities of both mitochondria and LDs in the intermyofibrillar space. Adding data from untrained individuals with equally high intermyofibrillar LD density as the endurance athletes revealed a 24% greater LD-mitochondria contact length in the endurance athletes. We observed small trivial differences in the shape of both organelles between populations. However, large mitochondrial profiles were more elongated and irregular in shape compared to small mitochondrial profiles, while large LD profiles were more circular and less irregular than small LD profiles. Within the group of athletes, large intermyofibrillar LD profiles correlated with a high fraction of PLIN5-positive LDs and their maximal fat oxidation rate was positively associated with an interaction between the profile size of both intermyofibrillar LDs and mitochondria. In conclusion, male endurance athletes have a greater LD-mitochondria contact than recreationally active and untrained individuals. This muscular phenotype is restricted to the intermyofibrillar space and to fibres rich in mitochondria.

physiology↗

bioRxiv2023

Differential utilisation of subcellular skeletal muscle glycogen pools: A comparative analysis between 1 and 15 minutes of maximal exercise

Distinct subcellular pools of glycogen particles exist within skeletal muscle fibres, distributed both within and between myofibrils and can be found in proximity to, or at a distance from mitochondria. Their precise localisation may influence their degradation rate and role in muscle function. Here, we investigated how exercise at different intensities (1- and 15-min maximal exercise) with known variations in glycogenolytic rate and relative contribution from anaerobic metabolism affects the utilisation of the distinct pools. Further, we investigated how lowered carbohydrate and energy intake affected glycogen volume densities and the storage of glycogen particles (i.e., localisation, size, and number) and their subsequent utilisation during the exercises. Using a randomized, counterbalanced, cross-over design, participants performed two maximal cycle tests of either 1 (n=10) or 15 min (n=10), conducted following consumption of two distinct diets with either high or lowered carbohydrate and energy contents. Muscle biopsies from m. vastus lateralis were obtained before and after the exercises. Intermyofibrillar glycogen was preferentially utilised during the 1-min exercise, whereas intramyofibrillar glycogen was preferentially utilised during the 15-min exercise. The lowered carbohydrate and energy intake decreased the particle size across all subcellular pools and reduced the numerical density in the intramyofibrillar and subsarcolemmal pools, with no effects on the glycogen utilisation during the subsequent exercise. In conclusion, the distinct subcellular glycogen pools were differentially utilised during 1-min and 15-min maximal exercise. Additionally, lowered carbohydrate and energy consumption reduces particle size and numerical density, depending on subcellular localisation.

physiology↗

bioRxiv2020

Pharmacological but not physiological GDF15 suppresses feeding and the motivation to exercise

Growing evidence supports that pharmacological application of growth differentiation factor 15 (GDF15) suppresses appetite but also promotes sickness-like behaviors in rodents via GDNF family receptor -like (GFRAL)-dependent mechanisms1,2. Conversely, the endogenous regulation and secretion of GDF15 and its physiological effects on energy homeostasis and behavior remain elusive. Here we show, in four independent studies that prolonged, moderate- to high-intensity endurance exercise substantially increases circulating GDF15, in a time-dependent and reversible fashion, to peak levels otherwise only observed in pathophysiological conditions. This exercise-induced increase can be recapitulated in mice following forced treadmill running and is accompanied by increased Gdf15 expression in the liver, skeletal muscle, and heart muscle. Compared to other metabolic stressors, like fasting, acute high-fat diet feeding, severe caloric excess and temperature changes, exercise has a greater impact on circulating GDF15 levels. However, whereas pharmacological GDF15 inhibits appetite and suppresses wheel running activity via GFRAL, in response to exercise, the physiological induction of GDF15 does not. In summary, exercise-induced circulating GDF15 correlates with the duration of endurance exercise. However, higher GDF15 levels after exercise are not sufficient to evoke canonical pharmacological GDF15 effects on appetite or responsible for exercise aversion/fatigue. Thus, the physiological effects of GDF15 as an exerkine remain elusive.

physiology↗