31 results on '"Jo C. Bruusgaard"'
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2. Computational Assessment of Transport Distances in Living Skeletal Muscle Fibers Studied In Situ
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Jo C. Bruusgaard, Kristian Gundersen, Andreas Våvang Solbrå, and Kenth-Arne Hansson
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In situ ,Multiple nuclei model ,Muscle Fibers, Skeletal ,Biophysics ,Mice ,03 medical and health sciences ,chemistry.chemical_compound ,0302 clinical medicine ,medicine ,Animals ,Equidistant ,Fiber ,Muscle, Skeletal ,030304 developmental biology ,Cell Nucleus ,Soleus muscle ,0303 health sciences ,Articles ,medicine.anatomical_structure ,Myoglobin ,chemistry ,Cytoplasm ,Muscle Fibers, Fast-Twitch ,Nucleus ,030217 neurology & neurosurgery ,Nuclear density - Abstract
Transport distances in skeletal muscle fibers are mitigated by these cells having multiple nuclei. We have studied mouse living slow (soleus) and fast (extensor digitorum longus) muscle fibers in situ and determined cellular dimensions and the positions of all the nuclei within fiber segments. We modeled the effect of placing nuclei optimally and randomly using the nuclei as the origin of a transportation network. It appeared that an equidistant positioning of nuclei minimizes transport distances along the surface for both muscles. In the soleus muscle, however, which were richer in nuclei, positioning of nuclei to reduce transport distances to the cytoplasm were of less importance, and these fibers exhibit a pattern not statistically different from a random positioning of nuclei. We also simulated transport times for myoglobin and found that they were remarkably similar between the two muscles despite differences in nuclear patterning and distances. Together, these results highlight the importance of spatially distributed nuclei to minimize transport distances to the surface when nuclear density is low, whereas it appears that the distribution are of less importance at higher nuclear densities.
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- 2020
3. Enhanced exercise and regenerative capacity in a mouse model that violates size constraints of oxidative muscle fibres
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Saleh Omairi, Antonios Matsakas, Hans Degens, Oliver Kretz, Kenth-Arne Hansson, Andreas Våvang Solbrå, Jo C Bruusgaard, Barbara Joch, Roberta Sartori, Natasa Giallourou, Robert Mitchell, Henry Collins-Hooper, Keith Foster, Arja Pasternack, Olli Ritvos, Marco Sandri, Vihang Narkar, Jonathan R Swann, Tobias B Huber, and Ketan Patel
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muscle ,metabolism ,stem cell ,regeneration ,Medicine ,Science ,Biology (General) ,QH301-705.5 - Abstract
A central tenet of skeletal muscle biology is the existence of an inverse relationship between the oxidative fibre capacity and its size. However, robustness of this relationship is unknown. We show that superimposition of Estrogen-related receptor gamma (Errγ) on the myostatin (Mtn) mouse null background (Mtn-/-/ErrγTg/+) results in hypertrophic muscle with a high oxidative capacity thus violating the inverse relationship between fibre size and oxidative capacity. We also examined the canonical view that oxidative muscle phenotype positively correlate with Satellite cell number, the resident stem cells of skeletal muscle. Surprisingly, hypertrophic fibres from Mtn-/-/ErrγTg/+ mouse showed satellite cell deficit which unexpectedly did not affect muscle regeneration. These observations 1) challenge the concept of a constraint between fibre size and oxidative capacity and 2) indicate the important role of the microcirculation in the regenerative capacity of a muscle even when satellite cell numbers are reduced.
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- 2016
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4. Long-lasting cellular imprinting: Performance hacking towards the Olympics?
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Einar Eftestøl and Jo C. Bruusgaard
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Long lasting ,Psychology ,Neuroscience ,Imprinting (organizational theory) - Published
- 2021
5. Myonuclear content regulates cell size with similar scaling properties in mice and humans
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Einar Eftestøl, Alyssa W. Cramer, Douglas P. Millay, Inga Juvkam, Anders Malthe-Sørenssen, Kristian Gundersen, Jo C. Bruusgaard, and Kenth-Arne Hansson
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0301 basic medicine ,Adult ,Male ,Cytoplasm ,Intravital Microscopy ,Multiple nuclei model ,Science ,Biopsy ,Cell ,Muscle Fibers, Skeletal ,General Physics and Astronomy ,Skeletal muscle ,General Biochemistry, Genetics and Molecular Biology ,Article ,Cell size ,03 medical and health sciences ,chemistry.chemical_compound ,Mice ,Young Adult ,0302 clinical medicine ,Developmental biology ,medicine ,Myocyte ,Animals ,Humans ,Muscle, Skeletal ,Scaling ,Cell Size ,Cell Nucleus ,Syncytium ,Multidisciplinary ,Microscopy, Confocal ,Chemistry ,General Chemistry ,DNA ,Healthy Volunteers ,Cell biology ,030104 developmental biology ,medicine.anatomical_structure ,Female ,Single-Cell Analysis ,030217 neurology & neurosurgery - Abstract
Muscle fibers are the largest cells in the body, and one of its few syncytia. Individual cell sizes are variable and adaptable, but what governs cell size has been unclear. We find that muscle fibers are DNA scarce compared to other cells, and that the nuclear number (N) adheres to the relationship N = aVb where V is the cytoplasmic volume. N invariably scales sublinearly to V (b, Muscle fibers are the largest cells in the body and contain less DNA per unit volume than other cells even if they have multiple nuclei. Here, the authors show that the number of nuclei regulates the cell size with similar scaling properties in mice and humans.
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- 2020
6. Muscle memory: are myonuclei ever lost?
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Truls Raastad, Kerstin Sunding, Hans-Christer Holmberg, Maria Ekblom, Mathias Wernbom, Einar Eftestøl, Kristian Gundersen, Inga Juvkam, Jo C. Bruusgaard, Kristoffer Toldnes Cumming, Niklas Psilander, and Björn Ekblom
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Physiology ,business.industry ,Physiology (medical) ,Health Sciences ,Muscle Fibers, Skeletal ,Humans ,Medicine ,Hälsovetenskaper ,business ,Neuroscience ,Biomedical sciences ,Muscle memory (strength training) - Published
- 2020
7. Effects of training, detraining, and retraining on strength, hypertrophy, and myonuclear number in human skeletal muscle
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Kerstin Sunding, Inga Juvkam, Jo C. Bruusgaard, Hans-Christer Holmberg, Niklas Psilander, Kristian Gundersen, Truls Raastad, Björn Ekblom, Kristoffer Toldnes Cumming, Einar Eftestøl, Maria Ekblom, and Mathias Wernbom
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0301 basic medicine ,medicine.medical_specialty ,Motor learning ,Physiology ,CSA ,Affect (psychology) ,Muscle hypertrophy ,Myonuclei ,03 medical and health sciences ,0302 clinical medicine ,Physical medicine and rehabilitation ,Physiology (medical) ,Health Sciences ,medicine ,Exercise ,biology ,business.industry ,Athletes ,Retraining ,Skeletal muscle ,Hälsovetenskaper ,biology.organism_classification ,Muscle memory (strength training) ,030104 developmental biology ,medicine.anatomical_structure ,business ,Muscle memory ,030217 neurology & neurosurgery ,Biomedical sciences - Abstract
Previously trained mouse muscles acquire strength and volume faster than naïve muscles; it has been suggested that this is related to increased myonuclear density. The present study aimed to determine whether a previously strength-trained leg (mem-leg) would respond better to a period of strength training than a previously untrained leg (con-leg). Nine men and 10 women performed unilateral strength training (T1) for 10 wk, followed by 20 wk of detraining (DT) and a 5-wk bilateral retraining period (T2). Muscle biopsies were taken before and after each training period and analyzed for myonuclear number, fiber volume, and cross-sectional area (CSA). Ultrasound and one repetition of maximum leg extension were performed to determine muscle thickness (MT) and strength. CSA (~17%), MT (~10%), and strength (~20%) increased during T1 in the mem-leg. However, the myonuclear number and fiber volume did not change. MT and CSA returned to baseline values during DT, but strength remained elevated (~60%), supporting previous findings of a long-lasting motor learning effect. MT and strength increased similarly in the mem-leg and con-leg during T2, whereas CSA, fiber volume, and myonuclear number remained unaffected. In conclusion, training response during T2 did not differ between the mem-leg and con-leg. However, this does not discount the existence of human muscle memory, since no increase in the number of myonuclei was detected during T1 and no clear detraining effect was observed for cell size during DT; thus, the present data did not allow for a rigorous test of the muscle memory hypothesis. NEW & NOTEWORTHY If a long-lasting intramuscular memory exists in humans, this will affect strength-training advice for both athletes and the public. Based on animal experiments, we hypothesized that such a memory exists and that it is related to the myonuclear number. However, a period of unilateral strength training, followed by detraining, did not increase the myonuclear number. The training response, during a subsequent bilateral retraining period, was not enhanced in the previously trained leg.
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- 2019
8. Cachexia does not induce loss of myonuclei or muscle fibres during xenografted prostate cancer in mice
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Simen Tennøe, Andreas Våvang Solbrå, Xia Sheng, Ivan Myhre Winje, Kristian Gundersen, Fahri Saatcioglu, Kenth-Arne Hansson, and Jo C. Bruusgaard
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Male ,0301 basic medicine ,medicine.medical_specialty ,Cachexia ,Physiology ,Muscle Fibers, Skeletal ,Transplantation, Heterologous ,Mice, Nude ,030204 cardiovascular system & hematology ,Extensor digitorum longus muscle ,03 medical and health sciences ,0302 clinical medicine ,Atrophy ,Internal medicine ,Myosin ,medicine ,Animals ,Muscle, Skeletal ,Mice, Inbred BALB C ,Syncytium ,business.industry ,Prostatic Neoplasms ,Skeletal muscle ,musculoskeletal system ,medicine.disease ,Disease Models, Animal ,Muscular Atrophy ,Muscle Fibers, Slow-Twitch ,030104 developmental biology ,medicine.anatomical_structure ,Endocrinology ,Muscle Fibers, Fast-Twitch ,Stem cell ,business ,Ex vivo - Abstract
Aim Cachexia is a severe wasting disorder involving loss of body- and muscle mass reducing survival and quality of life in cancer patients. We aim at determining if cachexia is a mere perturbation of the protein balance or if the condition also involves a degenerative loss of myonuclei within the fibre syncytia or loss of whole muscle fibres. Methods We induced cachexia by xenografting PC3 prostate cancer cells in nu/nu mice. Six weeks later, we counted myonuclei by in vivo microscopic imaging of single live fibres in the extensor digitorum longus muscle (EDL), and the EDL, soleus and tibialis anterior muscles were also harvested for ex vivo histology. Results The mice lost on average 15% of the whole-body wt. The muscle wet weight of the glycolytic, fast EDL was reduced by 14%, the tibialis anterior by 17%, and the slow, oxidative soleus by 6%. The fibre cross-sectional area in the EDL was reduced by 21% with no loss of myonuclei or any significant reduction in the number of muscle fibres. TUNEL-positive nuclei or fibres with embryonic myosin were rare both in cachectic and control muscles, and haematoxylin-eosin staining revealed no clear signs of muscle pathology. Conclusion The data suggest that the cachexia induced by xenografted prostate tumours induces a pronounced atrophy not accompanied by a loss of myonuclei or a loss of muscle fibres. Thus, stem cell related treatment might be redundant, and the quest for treatment options should rather focus on intervening with intracellular pathways regulating muscle fibre size.
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- 2018
9. Muscle memory: virtues of your youth?
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Kristian Gundersen, Mads Bengtsen, Einar Eftestøl, Ingrid M. Egner, and Jo C. Bruusgaard
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0301 basic medicine ,medicine.medical_specialty ,Skeletal muscle fibre ,Satellite Cells, Skeletal Muscle ,Physiology ,Muscle Fibers, Skeletal ,Corrections ,DNA, Mitochondrial ,Muscle hypertrophy ,Rats, Sprague-Dawley ,03 medical and health sciences ,Internal medicine ,Physical Conditioning, Animal ,Virtues ,Medicine ,Humans ,Animals ,Muscle Strength ,Cell Nucleus ,Organelle Biogenesis ,business.industry ,Skeletal muscle ,Resistance Training ,Muscle memory (strength training) ,Mitochondria, Muscle ,Rats ,030104 developmental biology ,medicine.anatomical_structure ,Endocrinology ,Female ,business ,Perspectives - Abstract
Referring to the muscle memory theory, previously trained muscles acquire strength and volume much faster than naive muscles. Using extreme experimental models such as synergist ablation or steroid administration, previous studies have demonstrated that the number of nuclei increases when a muscle becomes enlarged, which serves as a cellular muscle memory mechanism for the muscle. In the present study, we found that, when rats were subjected to physiologically relevant resistance training, the number of myonuclei increased and was retained during a long-term detraining period. The acquired myonuclei were related to a greater degree of muscle hypertrophic and mitochondrial biogenesis processes following subsequent hypertrophic conditions. Our data suggest a cellular mechanism supporting the notion that exposing young muscles to resistance training would help to restore age-related muscle loss coupled with mitochondrial dysfunction in later life.Muscle hypertrophy induced by resistance training is accompanied by an increase in the number of myonuclei. The acquired myonuclei are viewed as a cellular component of muscle memory by which muscle enlargement is promoted during a re-training period. In the present study, we investigated the effect of exercise preconditioning on mitochondrial remodelling induced by resistance training. Sprague-Dawley rats were divided into four groups: untrained control, training, pre-training or re-training. The training groups were subjected to weight loaded-ladder climbing exercise training. Myonuclear numbers were significantly greater (up to 20%) in all trained muscles compared to untrained controls. Muscle mass was significantly higher in the re-training group compared to the training group (∼2-fold increase). Mitochondrial content, mitochondrial biogenesis gene expression levels and mitochondrial DNA copy numbers were significantly higher in re-trained muscles compared to the others. Oxidative myofibres (type I) were significantly increased only in the re-trained muscles. Furthermore, in vitro studies using insulin-like growth factor-1-treated L6 rat myotubes demonstrated that myotubes with a higher myonuclear number confer greater expression levels of both mitochondrial and nuclear genes encoding for constitutive and regulatory mitochondrial proteins, which also showed a greater mitochondrial respiratory function. These data suggest that myonuclei acquired from previous training facilitate mitochondrial biogenesis in response to subsequent retraining by (at least in part) enhancing cross-talk between mitochondria and myonuclei in the pre-conditioned myofibres.
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- 2018
10. Deltamethrin resistance in the salmon louse, Lepeophtheirus salmonis (Krøyer): Maternal inheritance and reduced apoptosis
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Marit Jørgensen Bakke, Jo C. Bruusgaard, Arvind Y. M. Sundaram, Tor Einar Horsberg, and Celia Agusti
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0301 basic medicine ,Male ,Non-Mendelian inheritance ,Insecticides ,Drug Resistance ,lcsh:Medicine ,Single-nucleotide polymorphism ,Polymorphism, Single Nucleotide ,Article ,Arthropod Proteins ,Copepoda ,Electron Transport Complex IV ,03 medical and health sciences ,Fish Diseases ,Salmon louse ,Nitriles ,Pyrethrins ,Cytochrome c oxidase ,Animals ,lcsh:Science ,Gene ,Genetics ,Principal Component Analysis ,Multidisciplinary ,biology ,lcsh:R ,NADH dehydrogenase ,biology.organism_classification ,Mitochondria ,Protein Subunits ,030104 developmental biology ,Lepeophtheirus ,biology.protein ,DNA fragmentation ,lcsh:Q ,Female ,Maternal Inheritance ,Transcriptome - Abstract
Resistance towards deltamethrin (DMT) in the crustacean ectoparasite Lepeophtheirus salmonis (Caligidae) is a problem on fish farms lining the North Atlantic Ocean. Two Norwegian strains with different susceptibility towards DMT were crossed in the parental generation (P0), females from a sensitive strain were crossed with males from a resistant strain and vice versa. Individual susceptibility towards DMT was assessed in the second filial generation (F2). DMT resistance was only found in F2 descendants when the P0 females were from the resistant strain, pointing to maternal inheritance. Since maternal inheritance might be linked to the mitochondrial (mt) genome, the nucleotide sequences and the gene expressions of mt-genes were analysed. Twenty non-synonymous single nucleotide polymorphisms (SNPs) were identified in mt-transcripts from resistant F2 parasites, including SNPs in two cytochrome C oxidase subunits (COX1 and COX3) and two subunits of the NADH dehydrogenase complex (ND1 and ND5) previously linked to DMT resistance in the salmon louse. Differential expression analysis between the sensitive and resistant strain revealed strain effect in seven out of twelve mt-genes. The current study also show that DNA fragmentation (indicating apoptosis) was affected by DMT exposure in skeletal muscle tissue and that resistant parasites undergo less apoptosis than sensitive parasites.
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- 2018
11. A cellular memory mechanism aids overload hypertrophy in muscle long after an episodic exposure to anabolic steroids
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Jo C. Bruusgaard, Kristian Gundersen, Ingrid M. Egner, and Einar Eftestøl
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Senescence ,Testosterone propionate ,medicine.medical_specialty ,Anabolism ,Physiology ,Strength training ,Biology ,Muscle hypertrophy ,chemistry.chemical_compound ,Endocrinology ,chemistry ,Internal medicine ,medicine ,Myocyte ,Ex vivo ,Testosterone - Abstract
Previous strength training with or without the use of anabolic steroids facilitates subsequent re-acquisition of muscle mass even after long intervening periods of inactivity. Based on in vivo and ex vivo microscopy we here propose a cellular memory mechanism residing in the muscle cells. Female mice were treated with testosterone propionate for 14 days, inducing a 66% increase in the number of myonuclei and a 77% increase in fibre cross-sectional area. Three weeks after removing the drug, fibre size was decreased to the same level as in sham treated animals, but the number of nuclei remained elevated for at least 3 months (>10% of the mouse lifespan). At this time, when the myonuclei-rich muscles were exposed to overload-exercise for 6 days, the fibre cross-sectional area increased by 31% while control muscles did not grow significantly. We suggest that the lasting, elevated number of myonuclei constitutes a cellular memory facilitating subsequent muscle overload hypertrophy. Our findings might have consequences for the exclusion time of doping offenders. Since the ability to generate new myonuclei is impaired in the elderly our data also invites speculation that it might be beneficial to perform strength training when young in order to benefit in senescence.
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- 2013
12. Author response: Enhanced exercise and regenerative capacity in a mouse model that violates size constraints of oxidative muscle fibres
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Kenth-Arne Hansson, Andreas Våvang Solbrå, Hans Degens, Vihang A. Narkar, Jonathan R. Swann, Antonios Matsakas, Oliver Kretz, Olli Ritvos, Jo C. Bruusgaard, Tobias B. Huber, Ketan Patel, Arja Pasternack, Roberta Sartori, Natasa Giallourou, Keith Foster, Henry Collins-Hooper, Saleh Omairi, Robert Mitchell, Barbara Joch, and Marco Sandri
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Chemistry ,Oxidative phosphorylation ,Cell biology - Published
- 2016
13. Increased hypertrophic response with increased mechanical load in skeletal muscles receiving identical activity patterns
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Ingrid M. Egner, Cecilie Sjåland, Kristian Gundersen, Tom Andersen, Stian Ellefsen, Jo C. Bruusgaard, Ida G. Lunde, and Einar Eftestøl
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0301 basic medicine ,medicine.medical_specialty ,Physiology ,Strength training ,Biology ,Muscle hypertrophy ,Rats, Sprague-Dawley ,03 medical and health sciences ,0302 clinical medicine ,Physical medicine and rehabilitation ,Internal medicine ,Isometric Contraction ,medicine ,Animals ,Mechanotransduction ,Muscle, Skeletal ,Mechanical load ,Fiber type ,Ribosomal Protein S6 Kinases ,TOR Serine-Threonine Kinases ,Cell Biology ,Hypertrophy ,Rats ,030104 developmental biology ,Endocrinology ,Myogenin ,Proto-Oncogene Proteins c-akt ,030217 neurology & neurosurgery ,Signal Transduction - Abstract
It is often assumed that mechanical factors are important for effects of exercise on muscle, but during voluntary training and most experimental conditions the effects could solely be attributed to differences in electrical activity, and direct evidence for a mechanosensory pathway has been scarce. We here show that, in rat muscles stimulated in vivo under deep anesthesia with identical electrical activity patterns, isometric contractions induced twofold more hypertrophy than contractions with 50–60% of the isometric force. The number of myonuclei and the RNA levels of myogenin and myogenic regulatory factor 4 were increased with high load, suggesting that activation of satellite cells is mechano dependent. On the other hand, training induced a major shift in fiber type distribution from type 2b to 2x that was load independent, indicating that the electrical signaling rather than mechanosignaling controls fiber type. RAC-α serine/threonine-protein kinase (Akt) and ribosomal protein S6 kinase β-1 (S6K1) were not significantly differentially activated by load, suggesting that the differences in mechanical factors were not important for activating the Akt/mammalian target of rapamycin/S6K1 pathway. The transmembrane molecule syndecan-4 implied in overload hypertrophy in cardiac muscle was not load dependent, suggesting that mechanosignaling in skeletal muscle is different.
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- 2016
14. Satellite cell depletion prevents fiber hypertrophy in skeletal muscle
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Kristian Gundersen, Jo C. Bruusgaard, and Ingrid M. Egner
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0301 basic medicine ,Genetically modified mouse ,Satellite Cells, Skeletal Muscle ,Muscle Fibers, Skeletal ,Mice, Transgenic ,Biology ,Muscle hypertrophy ,03 medical and health sciences ,Mice ,0302 clinical medicine ,In vivo ,medicine ,Animals ,Muscle, Skeletal ,Molecular Biology ,Cell Nucleus ,Syncytium ,Skeletal muscle ,Anatomy ,Hypertrophy ,musculoskeletal system ,Immunohistochemistry ,Cell biology ,030104 developmental biology ,medicine.anatomical_structure ,Female ,Plantaris muscle ,Stem cell ,030217 neurology & neurosurgery ,Ex vivo ,Developmental Biology - Abstract
The largest mammalian cells are the muscle fibers, and they have multiple nuclei to support their large cytoplasmic volumes. During hypertrophic growth, new myonuclei are recruited from satellite stem cells into the fiber syncytia, but it was recently suggested that such recruitment is not obligatory: overload hypertrophy after synergist ablation of the plantaris muscle appeared normal in transgenic mice in which most of the satellite cells were abolished. When we essentially repeated these experiments analyzing the muscles by immunohistochemistry and in vivo and ex vivo imaging, we found that overload hypertrophy was prevented in the satellite cell-deficient mice, in both the plantaris and the extensor digitorum longus muscles. We attribute the previous findings to a reliance on muscle mass as a proxy for fiber hypertrophy, and to the inclusion of a significant number of regenerating fibers in the analysis. We discuss that there is currently no model in which functional, sustainable hypertrophy has been unequivocally demonstrated in the absence of satellite cells; an exception is re-growth, which can occur using previously recruited myonuclei without addition of new myonuclei.
- Published
- 2015
15. Hypoxia inducible factor 1α links fast-patterned muscle activity and fast muscle phenotype in rats
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Zaheer A. Rana, Ida G. Lunde, Jo C. Bruusgaard, Stian Ellefsen, Siobhan L. Anton, and Kristian Gundersen
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Soleus muscle ,Regulation of gene expression ,medicine.medical_specialty ,Physiology ,Myogenesis ,Biology ,Endocrinology ,Hypoxia-inducible factors ,Internal medicine ,Myosin ,medicine ,Nuclear protein ,Transcription factor ,C2C12 - Abstract
Non-technical summary Muscle fibres change when they are used differently, such as by exercise. Genetic studies have shown that a hyperactive form of the gene regulatory protein hypoxia inducible factor 1α (HIF-1α) occurs twice as often among strength-trained athletes as in the normal population. HIF-1α is ‘sensing’ the oxygen levels in cells, and the oxygen levels change by an order of magnitude in working muscle. We show that an ‘endurance’ type of activity reduces the level of HIF-1α, while short intense bursts of activity increases it. When HIF-1α was produced in higher quantities by introducing artificial genes in the muscle fibres they became larger and faster, and with a less oxidative metabolism. Thus, oxygen itself could be a trigger for changes in muscle. The composition of muscle fibres is strongly correlated to major lifestyle conditions such as diabetes and chronic obstructive pulmonary disease, and HIF-1α might provide a new molecular link. Abstract Exercise influences muscle phenotype by the specific pattern of action potentials delivered to the muscle, triggering intracellular signalling pathways. can be reduced by an order of magnitude in working muscle. In humans, carriers of a hyperactive polymorphism of the transcription factor hypoxia inducible factor 1α (HIF-1α) have 50% more fast fibres, and this polymorphism is prevalent among strength athletes. We have investigated the putative role of HIF-1α in mediating activity changes in muscle. When rat muscles were stimulated with short high frequency bursts of action potentials known to induce a fast muscle phenotype, HIF-1α increased by about 80%. In contrast, a pattern consisting of long low frequency trains known to make fast muscles slow reduced the HIF-1α level of the fast extensor digitorum longus (EDL) muscle by 44%. Nuclear protein extracts from normal EDL contained 2.3-fold more HIF-1α and 4-fold more HIF-1β than the slow soleus muscle, while von-Hippel-Lindau protein was 4.8-fold higher in slow muscles. mRNA displayed a reciprocal pattern; thus FIH-1 mRNA was almost 2-fold higher in fast muscle, while the HIF-1α level was half, and consequently protein/mRNA ratio for HIF-1α was more than 4-fold higher in the fast muscle, suggesting that HIF-1α is strongly suppressed post-transcriptionally in slow muscles. When HIF-1α was overexpressed for 14 days after somatic gene transfer in adult rats, a slow-to-fast transformation was observed, encompassing an increase in fibre cross sectional area, oxidative enzyme activity and myosin heavy chain. The latter was shown to be regulated at the mRNA level in C2C12 myotubes.
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- 2011
16. Myonuclei acquired by overload exercise precede hypertrophy and are not lost on detraining
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Kristian Gundersen, Jo C. Bruusgaard, Ida Beitnes Johansen, Ingrid M. Egner, and Zaheer A. Rana
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Male ,Muscle tissue ,medicine.medical_specialty ,Anabolism ,Strength training ,Muscle Fibers, Skeletal ,Apoptosis ,Biology ,Models, Biological ,Muscle hypertrophy ,Mice ,Atrophy ,Physical Conditioning, Animal ,Internal medicine ,medicine ,Animals ,Humans ,Rats, Wistar ,Cell Nucleus ,Denervation ,Muscle Denervation ,Multidisciplinary ,Resistance Training ,Hypertrophy ,musculoskeletal system ,medicine.disease ,Rats ,Muscle memory (strength training) ,Muscular Atrophy ,medicine.anatomical_structure ,Endocrinology ,Models, Animal ,Female - Abstract
Effects of previous strength training can be long-lived, even after prolonged subsequent inactivity, and retraining is facilitated by a previous training episode. Traditionally, such “muscle memory” has been attributed to neural factors in the absence of any identified local memory mechanism in the muscle tissue. We have used in vivo imaging techniques to study live myonuclei belonging to distinct muscle fibers and observe that new myonuclei are added before any major increase in size during overload. The old and newly acquired nuclei are retained during severe atrophy caused by subsequent denervation lasting for a considerable period of the animal’s lifespan. The myonuclei seem to be protected from the high apoptotic activity found in inactive muscle tissue. A hypertrophy episode leading to a lasting elevated number of myonuclei retarded disuse atrophy, and the nuclei could serve as a cell biological substrate for such memory. Because the ability to create myonuclei is impaired in the elderly, individuals may benefit from strength training at an early age, and because anabolic steroids facilitate more myonuclei, nuclear permanency may also have implications for exclusion periods after a doping offense.
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- 2010
17. Less than recommended training of aerobic fitness and muscle strength: What to expect?
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Haakon B. Benestad, Jo C. Bruusgaard, and Kristin L. Sand
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medicine.medical_specialty ,Time Factors ,Physiology ,Health Status ,Physical fitness ,High-Intensity Interval Training ,030204 cardiovascular system & hematology ,Running ,03 medical and health sciences ,0302 clinical medicine ,Physical medicine and rehabilitation ,Humans ,Medicine ,Aerobic exercise ,Muscle Strength ,Muscle, Skeletal ,Exercise ,business.industry ,030229 sport sciences ,Bicycling ,Physical Fitness ,Muscle strength ,medicine.symptom ,business ,Muscle Contraction ,Muscle contraction - Published
- 2018
18. Specific labelling of myonuclei by an antibody against pericentriolar material 1 on skeletal muscle tissue sections
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Mads Bengtsen, Kristian Gundersen, Jo C. Bruusgaard, Inga Juvkam, Ivan Myhre Winje, and Einar Eftestøl
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Male ,0301 basic medicine ,Cell type ,Physiology ,Cell ,Cell Cycle Proteins ,Autoantigens ,Antibodies ,Muscle hypertrophy ,Rats, Sprague-Dawley ,Mice ,03 medical and health sciences ,0302 clinical medicine ,PCM1 ,Muscular Diseases ,Antibody Specificity ,medicine ,Animals ,Humans ,Muscle, Skeletal ,Pericentriolar material ,Cell Nucleus ,biology ,Skeletal muscle ,Hypertrophy ,musculoskeletal system ,Immunohistochemistry ,Actins ,Cell biology ,Disease Models, Animal ,Luminescent Proteins ,030104 developmental biology ,medicine.anatomical_structure ,biology.protein ,Female ,mCherry ,Dystrophin ,Biomarkers ,030217 neurology & neurosurgery - Abstract
Aim Skeletal muscle is a heterogeneous tissue containing several different cell types, and only about 40%-50% of the cell nuclei within the tissue belong to myofibres. Existing technology, attempting to distinguish myonuclei from other nuclei at the light microscopy level, has led to controversies in our understanding of the basic cell biology of muscle plasticity. This study aims at demonstrating that an antibody against the protein pericentriolar material 1 (PCM1) can be used to reliably identify myonuclei on histological cross sections from humans, mice and rats. Methods Cryosections were labelled with a polyclonal antibody against PCM1. The specificity of the labelling for myonuclei was verified using 3D reconstructions of confocal z-stacks triple-labelled for DNA, dystrophin and PCM1, and by co-localization with nuclear mCherry driven by the muscle-specific Alpha-Actin-1 promoter after viral transduction. Results The PCM1 antibody specifically labelled all myonuclei, and myonuclei only, in cryosections of muscles from rats, mice and men. Nuclei in other cell types including satellite cells were not labelled. Both normal muscles and hypertrophic muscles after synergist ablation were investigated. Conclusion Pericentriolar material 1 can be used as a specific histological marker for myonuclei in skeletal muscle tissue without relying on counterstaining of other structures or cumbersome and subjective analysis of nuclear positioning.
- Published
- 2018
19. Nuclear domains during muscle atrophy: nuclei lost or paradigm lost?
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Jo C. Bruusgaard and Kristian Gundersen
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Muscle tissue ,Pathology ,medicine.medical_specialty ,Stromal cell ,Physiology ,Regeneration (biology) ,Biology ,medicine.disease ,Muscle atrophy ,Muscle hypertrophy ,medicine.anatomical_structure ,Atrophy ,Apoptosis ,medicine ,medicine.symptom ,Stem cell - Abstract
According to the current paradigm, muscle nuclei serve a certain cytoplasmic domain. To preserve the domain size, it is believed that nuclei are injected from satellite cells fusing to fibres undergoing hypertrophy, and lost by apoptosis during atrophy. Based on single fibre observations in and ex vivo we suggest that nuclear domains are not as constant as is often indicated. Moreover, recent time lapse in vivo imaging of single fibres suggests that at least for the first few weeks, atrophy is not accompanied by any loss of nuclei. Apoptosis is abundant in muscle tissue during atrophy conditions, but in our opinion it has not been unequivocally demonstrated that such nuclei are myonuclei. As we see it, the preponderance of current evidence suggests that disuse atrophy is not accompanied by loss of nuclei, at least not for the first 2 months. Moreover, it has not been proven that myonuclear apoptosis does occur in permanent fibres undergoing atrophy; it seems more likely that it is confined to stromal cells and satellite cells. If muscle atrophy is not related to loss of nuclei, design of intervention therapies should focus on protein metabolism rather than regeneration from stem cells.
- Published
- 2008
20. In vivo time-lapse microscopy reveals no loss of murine myonuclei during weeks of muscle atrophy
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Kristian Gundersen and Jo C. Bruusgaard
- Subjects
Pathology ,medicine.medical_specialty ,Time Factors ,Satellite Cells, Skeletal Muscle ,Apoptosis ,Mice ,Atrophy ,medicine ,Animals ,Cell Nucleus ,Denervation ,Microscopy ,Syncytium ,TUNEL assay ,biology ,General Medicine ,musculoskeletal system ,medicine.disease ,Muscle atrophy ,Muscular Atrophy ,Cell nucleus ,medicine.anatomical_structure ,biology.protein ,Female ,Stromal Cells ,medicine.symptom ,Dystrophin ,Muscle Contraction ,Research Article ,Muscle contraction - Abstract
Numerous studies have suggested that muscle atrophy is accompanied by apoptotic loss of myonuclei and therefore recovery would require replenishment by muscle stem cells. We used in vivo time-lapse microscopy to observe the loss and replenishment of myonuclei in murine muscle fibers following induced muscle atrophy. To our surprise, imaging of single fibers for up to 28 days did not support the concept of nuclear loss during atrophy. Muscles were inactivated by denervation, nerve impulse block, or mechanical unloading. Nuclei were stained in vivo either acutely by intracellular injection of fluorescent oligonucleotides or in time-lapse studies after transfection with a plasmid encoding GFP with a nuclear localization signal. We observed no loss of myonuclei in fast- or slow-twitch muscle fibers despite a greater than 50% reduction in fiber cross-sectional area. TUNEL labeling of fragmented DNA on histological sections revealed high levels of apoptotic nuclei in inactive muscles. However, when costained for laminin and dystrophin, virtually none of the TUNEL-positive nuclei could be classified as myonuclei; apoptosis was confined to stromal and satellite cells. We conclude that disuse atrophy is not a degenerative process, but is rather a change in the balance between protein synthesis and proteolysis in a permanent cell syncytium.
- Published
- 2008
21. Muscle hypertrophy induced by the Ski protein: cyto-architecture and ultrastructure
- Author
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Simon M. Hughes, Andrew S. Brack, Kristian Gundersen, and Jo C. Bruusgaard
- Subjects
Pathology ,medicine.medical_specialty ,Physiology ,Muscle Fibers, Skeletal ,Mice, Transgenic ,Hindlimb ,Desmin ,Muscle hypertrophy ,Extensor digitorum longus muscle ,Mice ,Proto-Oncogene Proteins ,medicine ,Animals ,Muscle, Skeletal ,Cell Nucleus ,Specific force ,biology ,SKI protein ,Hypertrophy ,musculoskeletal system ,Mitochondria ,Cell biology ,DNA-Binding Proteins ,Mice, Inbred C57BL ,Microscopy, Electron ,Models, Animal ,Mice, Inbred CBA ,biology.protein ,Ultrastructure ,medicine.symptom ,Muscle Contraction ,Muscle contraction - Abstract
Aim: Transgenic mice overexpressing the c-ski proto-oncogene driven by the MSV promoter undergo muscle hypertrophy, most notably fast fibres of the lower limb. This hypertrophy is not accompanied by a correspondingly large increase in force, and individual skinned muscle fibres exhibit a 30% reduction in force per cross-sectional area. In this respect, the MSV ski model is different from most other hypertrophy models and we here aim at describing the mechanisms for the reduced specific force. Methods: Cyoarchitecture and ultrastructure of muscle fibres from the fast extensor digitorum longus muscle of 2‐3 months old MSV ski mice was studied. In addition to electron microscopy, we used in vivo intracellular injections of myonuclear dye to investigate nuclear number. Results: The number of nuclei did not increase in proportion to size, and consequently nuclear domains were increased compared with wild type. The fraction of the cytoplasm occupied by contractile material was reduced by 18%. In addition we observed poor intracellular alignment of Z-discs. Such staggering has been reported to reduce force in desmin deficient mice, but the amount and distribution of desmin in the MSV ski mice seemed normal. The mitochondria of MSV ski mice showed irregularly spaced cristae that were frequently disrupted. Conclusion: The reduction in specific force observed in MSV ski mice could be explained by a reduced fraction of contractile material and reduced transversal mechanical coupling. The ultrastructural abnormalities could be related to an increase in nuclear domains.
- Published
- 2005
22. Number and spatial distribution of nuclei in the muscle fibres of normal mice studiedin vivo
- Author
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Jo C. Bruusgaard, Kristian Gundersen, Merete Ekmark, K. Kollstad, and Knut Liestøl
- Subjects
Microinjections ,Satellite Cells, Skeletal Muscle ,Physiology ,Muscle Fibers, Skeletal ,Spatial distribution ,Motor Endplate ,Cell size ,Tendons ,Mice ,In vivo ,Image Processing, Computer-Assisted ,Animals ,Statistical analysis ,Cell Size ,Cell Nucleus ,Long axis ,Sarcolemma ,Chemistry ,musculoskeletal, neural, and ocular physiology ,DNA ,Original Articles ,Anatomy ,musculoskeletal system ,Microscopy, Fluorescence ,Cytoplasm ,Isotope Labeling ,Biophysics ,Female - Abstract
We present here a new technique with which to visualize nuclei in living muscle fibres in the intact animal, involving injection of labelled DNA into single cells. This approach allowed us to determine the position of all of nuclei within a sarcolemma without labelling satellite cells. In contrast to what has been reported in tissue culture, we found that the nuclei were immobile, even when observed over several days. Nucleic density was uniform along the fibre except for the endplate and some myotendinous junctions, where the density was higher. The perijunctional region had the same number of nuclei as the rest of the fibre. In the extensor digitorum longus (EDL) muscle, the extrajunctional nuclei were elongated and precisely aligned to the long axis of the fibre. In the soleus, the nuclei were rounder and not well aligned. When comparing small and large fibres in the soleus, the number of nuclei varied approximately in proportion to cytoplasmic volume, while in the EDL the number was proportional to surface area. Statistical analysis revealed that the nuclei were not randomly distributed in either the EDL or the soleus. For each fibre, actual distributions were compared with computer simulations in which nuclei were assumed to repel each other, which optimizes the distribution of nuclei with respect to minimizing transport distances. The simulated patterns were regular, with clear row-like structures when the density of nuclei was low. The non-random and often row-like distribution of nuclei observed in muscle fibres may thus reflect regulatory mechanisms whereby nuclei repel each other in order to minimize transport distances.
- Published
- 2003
23. Overexpression of SMPX in adult skeletal muscle does not change skeletal muscle fiber type or size
- Author
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Einar Eftestøl, Tine Norman Alver, Kristian Gundersen, and Jo C Bruusgaard
- Subjects
Male ,Sarcomeres ,Cell Physiology ,Histology ,Physiology ,lcsh:Medicine ,Muscle Proteins ,Muscle Fibers ,Cell Growth ,Myoblasts ,Mice ,Molecular Cell Biology ,Animals ,Humans ,Rats, Wistar ,lcsh:Science ,Muscle, Skeletal ,Musculoskeletal System ,Cytoskeleton ,Cell Nucleus ,Muscles ,lcsh:R ,Biology and Life Sciences ,Cell Biology ,Protein Transport ,HEK293 Cells ,Cell Processes ,lcsh:Q ,Anatomy ,Cellular Structures and Organelles ,Cellular Types ,Physiological Processes ,Research Article - Abstract
Mechanical factors such as stretch are thought to be important in the regulation of muscle phenotype. Small muscle protein X-linked (SMPX) is upregulated by stretch in skeletal muscle and has been suggested to serve both as a transcription factor and a mechanosensor, possibly giving rise to changes in both fiber size and fiber type. We have used in vivo confocal imaging to study the subcellular localization of SMPX in skeletal muscle fibers of adult rats using a SMPX-EGFP fusion protein. The fusion protein was localized predominantly in repetitive double stripes flanking the Z-disc, and was excluded from all nuclei. This localization would be consistent with SMPX being a mechanoreceptor, but not with SMPX playing a role as a transcription factor. In vivo overexpression of ectopic SMPX in skeletal muscle of adult mice gave no significant changes in fiber type distribution or cross sectional area, thus a role of SMPX in regulating muscle phenotype remains unclear.
- Published
- 2014
24. DNA vaccines: MHC II-targeted vaccine protein produced by transfected muscle fibres induces a local inflammatory cell infiltrate in mice
- Author
-
Inger Øynebråten, Tom-Ole Løvås, Kristian Gundersen, Bjarne Bogen, and Jo C. Bruusgaard
- Subjects
Muscle Fibers, Skeletal ,lcsh:Medicine ,Biochemistry ,Mice ,Animal Cells ,Medicine and Health Sciences ,Vaccines, DNA ,Public and Occupational Health ,lcsh:Science ,Immune Response ,Mice, Inbred BALB C ,Multidisciplinary ,Immune System Proteins ,CD11b Antigen ,biology ,Vaccination ,Vaccination and Immunization ,Naked DNA ,Cytokines ,Cellular Types ,Research Article ,Immune Cells ,Immunology ,Antigen-Presenting Cells ,Major histocompatibility complex ,Transfection ,Antibodies ,DNA vaccination ,Immune Activation ,Antigen ,MHC class I ,Animals ,Antigen-presenting cell ,Antibody-Producing Cells ,Inflammation ,MHC class II ,lcsh:R ,Immunity ,Histocompatibility Antigens Class II ,Biology and Life Sciences ,Proteins ,Cell Biology ,Molecular Development ,Molecular biology ,Eosinophils ,Immune System ,biology.protein ,Leukocyte Common Antigens ,Clinical Immunology ,Immunization ,lcsh:Q ,mCherry ,Developmental Biology - Abstract
Vaccination with naked DNA holds great promise but immunogenicity needs to be improved. DNA constructs encoding bivalent proteins that bind antigen-presenting cells (APC) for delivery of antigen have been shown to enhance T and B cell responses and protection in tumour challenge experiments. However, the mechanism for the increased potency remains to be determined. Here we have constructed DNA vaccines that express the fluorescent protein mCherry, a strategy which allowed tracking of vaccine proteins. Transfected muscle fibres in mice were visualized, and their relationship to infiltrating mononuclear cells could be determined. Interestingly, muscle fibers that produced MHC class II-specific dimeric vaccine proteins with mCherry were for weeks surrounded by a localized intense cellular infiltrate composed of CD45+, MHC class II+ and CD11b+ cells. Increasing numbers of eosinophils were observed among the infiltrating cells from day 7 after immunization. The local infiltrate surrounding mCherry+ muscle fibers was dependent on the MHC II-specificity of the vaccine proteins since the control, a non-targeted vaccine protein, failed to induce similar infiltrates. Chemokines measured on day 3 in immunized muscle indicate both a DNA effect and an electroporation effect. No influence of targeting was observed. These results contribute to our understanding for why targeted DNA vaccines have an improved immunogenicity.
- Published
- 2014
25. A cellular memory mechanism aids overload hypertrophy in muscle long after an episodic exposure to anabolic steroids
- Author
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Ingrid M, Egner, Jo C, Bruusgaard, Einar, Eftestøl, and Kristian, Gundersen
- Subjects
Cell Nucleus ,Mice ,Muscle Fibers, Skeletal ,Physical Exertion ,Animals ,Female ,Testosterone ,Hypertrophy ,Perspectives - Abstract
Previous strength training with or without the use of anabolic steroids facilitates subsequent re-acquisition of muscle mass even after long intervening periods of inactivity. Based on in vivo and ex vivo microscopy we here propose a cellular memory mechanism residing in the muscle cells. Female mice were treated with testosterone propionate for 14 days, inducing a 66% increase in the number of myonuclei and a 77% increase in fibre cross-sectional area. Three weeks after removing the drug, fibre size was decreased to the same level as in sham treated animals, but the number of nuclei remained elevated for at least 3 months (10% of the mouse lifespan). At this time, when the myonuclei-rich muscles were exposed to overload-exercise for 6 days, the fibre cross-sectional area increased by 31% while control muscles did not grow significantly. We suggest that the lasting, elevated number of myonuclei constitutes a cellular memory facilitating subsequent muscle overload hypertrophy. Our findings might have consequences for the exclusion time of doping offenders. Since the ability to generate new myonuclei is impaired in the elderly our data also invites speculation that it might be beneficial to perform strength training when young in order to benefit in senescence.
- Published
- 2013
26. No change in myonuclear number during muscle unloading and reloading
- Author
-
Kristian Gundersen, Sylvie Dupré-Aucouturier, Dominique Desplanches, Tove Klungervik Larsen, Ingrid M. Egner, and Jo C. Bruusgaard
- Subjects
Denervation ,Muscle tissue ,Cell Nucleus ,Physiology ,Multiple nuclei model ,Chemistry ,Muscle Fibers, Skeletal ,Skeletal muscle ,Fiber size ,Anatomy ,Hindlimb Suspension ,musculoskeletal system ,medicine.disease ,Cell biology ,Muscle hypertrophy ,Rats ,Weight-Bearing ,medicine.anatomical_structure ,Atrophy ,Physiology (medical) ,medicine ,Animals ,Female ,Rats, Wistar - Abstract
Muscle fibers are the cells in the body with the largest volume, and they have multiple nuclei serving different domains of cytoplasm. A large body of previous literature has suggested that atrophy induced by hindlimb suspension leads to a loss of “excessive” myonuclei by apoptosis. We demonstrate here that atrophy induced by hindlimb suspension does not lead to loss of myonuclei despite a strong increase in apoptotic activity of other types of nuclei within the muscle tissue. Thus hindlimb suspension turns out to be similar to other atrophy models such as denervation, nerve impulse block, and antagonist ablation. We discuss how the different outcome of various studies can be attributed to difficulties in separating myonuclei from other nuclei, and to systematic differences in passive properties between normal and unloaded muscles. During reload, after hindlimb suspension, a radial regrowth is observed, which has been believed to be accompanied by recruitment of new myonuclei from satellite cells. The lack of nuclear loss during unloading, however, puts these findings into question. We observed that reload led to an increase in cross sectional area of 59%, and fiber size was completely restored to the presuspension levels. Despite this notable growth there was no increase in the number of myonuclei. Thus radial regrowth seems to differ from de novo hypertrophy in that nuclei are only added during the latter. We speculate that the number of myonuclei might reflect the largest size the muscle fibers have had in its previous history.
- Published
- 2012
27. Hypoxia inducible factor 1 links fast-patterned muscle activity and fast muscle phenotype in rats
- Author
-
Ida G, Lunde, Siobhan L, Anton, Jo C, Bruusgaard, Zaheer A, Rana, Stian, Ellefsen, and Kristian, Gundersen
- Subjects
Male ,HEK293 Cells ,Phenotype ,Muscle Fibers, Fast-Twitch ,Animals ,Humans ,RNA, Messenger ,Rats, Wistar ,Hypoxia ,Hypoxia-Inducible Factor 1, alpha Subunit ,Cells, Cultured ,Skeletal Muscle and Exercise ,Rats - Abstract
Exercise influences muscle phenotype by the specific pattern of action potentials delivered to the muscle, triggering intracellular signalling pathways. PO2 can be reduced by an order of magnitude in working muscle. In humans, carriers of a hyperactive polymorphism of the transcription factor hypoxia inducible factor 1α (HIF-1α) have 50% more fast fibres, and this polymorphism is prevalent among strength athletes. We have investigated the putative role of HIF-1α in mediating activity changes in muscle.When rat muscles were stimulated with short high frequency bursts of action potentials known to induce a fast muscle phenotype, HIF-1α increased by about 80%. In contrast, a pattern consisting of long low frequency trains known to make fast muscles slow reduced the HIF-1α level of the fast extensor digitorum longus (EDL) muscle by 44%. Nuclear protein extracts from normal EDL contained 2.3-fold more HIF-1α and 4-fold more HIF-1β than the slow soleus muscle, while von-Hippel-Lindau protein was 4.8-fold higher in slow muscles. mRNA displayed a reciprocal pattern; thus FIH-1 mRNA was almost 2-fold higher in fast muscle, while the HIF-1α level was half, and consequently protein/mRNA ratio for HIF-1α was more than 4-fold higher in the fast muscle, suggesting that HIF-1α is strongly suppressed post-transcriptionally in slow muscles.When HIF-1α was overexpressed for 14 days after somatic gene transfer in adult rats, a slow-to-fast transformation was observed, encompassing an increase in fibre cross sectional area, oxidative enzyme activity and myosin heavy chain. The latter was shown to be regulated at the mRNA level in C2C12 myotubes.
- Published
- 2011
28. Nuclear domains during muscle atrophy: nuclei lost or paradigm lost?
- Author
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Kristian, Gundersen and Jo C, Bruusgaard
- Subjects
Cell Nucleus ,Muscular Atrophy ,Muscle Fibers, Skeletal ,Animals ,Humans ,Topical Review ,Muscle Contraction - Abstract
According to the current paradigm, muscle nuclei serve a certain cytoplasmic domain. To preserve the domain size, it is believed that nuclei are injected from satellite cells fusing to fibres undergoing hypertrophy, and lost by apoptosis during atrophy. Based on single fibre observations in and ex vivo we suggest that nuclear domains are not as constant as is often indicated. Moreover, recent time lapse in vivo imaging of single fibres suggests that at least for the first few weeks, atrophy is not accompanied by any loss of nuclei. Apoptosis is abundant in muscle tissue during atrophy conditions, but in our opinion it has not been unequivocally demonstrated that such nuclei are myonuclei. As we see it, the preponderance of current evidence suggests that disuse atrophy is not accompanied by loss of nuclei, at least not for the first 2 months. Moreover, it has not been proven that myonuclear apoptosis does occur in permanent fibres undergoing atrophy; it seems more likely that it is confined to stromal cells and satellite cells. If muscle atrophy is not related to loss of nuclei, design of intervention therapies should focus on protein metabolism rather than regeneration from stem cells.
- Published
- 2008
29. Regulation of gephyrin assembly and glycine receptor synaptic stability
- Author
-
Cécile Bedet, Line Groth-Pedersen, Jo C. Bruusgaard, Stefan Eimer, Antoine Triller, Christian Vannier, and Sandra Vergo
- Subjects
Cell ,Biochemistry ,Rats, Sprague-Dawley ,Receptors, Glycine ,Chlorocebus aethiops ,medicine ,Animals ,splice ,Molecular Biology ,Glycine receptor ,Cells, Cultured ,Neurons ,Gephyrin ,biology ,Membrane Proteins ,Cell Biology ,Transfection ,Rats ,Postsynaptic membrane ,medicine.anatomical_structure ,Cytoplasm ,G-domain ,COS Cells ,Synapses ,biology.protein ,Biophysics ,Carrier Proteins - Abstract
Gephyrin is required for the formation of clusters of the glycine receptor (GlyR) in the neuronal postsynaptic membrane. It can make trimers and dimers through its N- and C-terminal G and E domains, respectively. Gephyrin oligomerization could thus create a submembrane lattice providing GlyR-binding sites. We investigated the relationships between the stability of cell surface GlyR and the ability of gephyrin splice variants to form oligomers. Using truncated and full-length gephyrins we found that the 13-amino acid sequence (cassette 5) prevents G domain trimerization. Moreover, E domain dimerization is inhibited by the gephyrin central L domain. All of the gephyrin variants bind GlyR beta subunit cytoplasmic loop with high affinity regardless of their cassette composition. Coexpression experiments in COS-7 cells demonstrated that GlyR bound to gephyrin harboring cassette 5 cannot be stabilized at the cell surface. This gephyrin variant was found to deplete synapses from both GlyR and gephyrin in transfected neurons. These data suggest that the relative expression level of cellular variants influence the overall oligomerization pattern of gephyrin and thus the turnover of synaptic GlyR.
- Published
- 2006
30. Distribution of myonuclei and microtubules in live muscle fibers of young, middle-aged, and old mice
- Author
-
Kristian Gundersen, Jo C. Bruusgaard, and Knut Liestøl
- Subjects
Pathology ,medicine.medical_specialty ,Aging ,Physiology ,Muscle Fibers, Skeletal ,Mice, Inbred Strains ,Biology ,Microtubules ,Mice ,Atrophy ,Skeletal pathology ,Microtubule ,Physiology (medical) ,medicine ,Animals ,Cytoskeleton ,Muscle, Skeletal ,Microinjection ,Cell Nucleus ,Anatomy ,musculoskeletal system ,medicine.disease ,Muscular Atrophy ,Sarcopenia ,Muscle Fibers, Fast-Twitch ,Female - Abstract
We have recently published a new technique for visualizing nuclei in living muscle fibers of intact animals, based on microinjection of labeled DNA into single myofibers, excluding satellite cells (Bruusgaard JC, Liestol K, Ekmark M, Kollstad K, and Gundersen K. J Physiol 551: 467–478, 2003). In the present study, we use this technique to study fiber segments of soleus and extensor digitorum longus (EDL) muscles from mice aged 2, 14, and 23 mo. As the animals maturing from 2 to 14 mo, they displayed an increase in size and number of nuclei. Soleus showed little change in nuclear domain size, whereas this increased by 88% in the EDL. For 14-mo-old animals, no significant correlation between fiber size and nuclear number was observed ( R2 = 0.18, P = 0.51) despite a fourfold variation in cytoplasmic volume. This suggests that size and nuclear number is uncoupled in middle-aged mice. When animals aged from 14 to 23 mo, EDL IIb, but not soleus, fibers atrophied by 41%. Both EDL and soleus displayed a reduction in number of nuclei: 20 and 16%, respectively. A positive correlation between number of nuclei and size was observed at 2 mo, and this reappeared in old mice. The atrophy in IIb fibers at old age was accompanied by a disturbance in the orderly positioning of nuclei that is so prominent in glycolytic fibers at younger age. In old animals, changes in nuclear shape and in the peri- and internuclear microtubule network were also observed. Thus changes in myonuclear number and distribution, perhaps related to alterations in the microtubular network, may underlie some of the adverse consequences of aging on skeletal muscle size and function.
- Published
- 2006
31. DNA vaccines: MHC II-targeted vaccine protein produced by transfected muscle fibres induces a local inflammatory cell infiltrate in mice.
- Author
-
Tom-Ole Løvås, Jo C Bruusgaard, Inger Øynebråten, Kristian Gundersen, and Bjarne Bogen
- Subjects
Medicine ,Science - Abstract
Vaccination with naked DNA holds great promise but immunogenicity needs to be improved. DNA constructs encoding bivalent proteins that bind antigen-presenting cells (APC) for delivery of antigen have been shown to enhance T and B cell responses and protection in tumour challenge experiments. However, the mechanism for the increased potency remains to be determined. Here we have constructed DNA vaccines that express the fluorescent protein mCherry, a strategy which allowed tracking of vaccine proteins. Transfected muscle fibres in mice were visualized, and their relationship to infiltrating mononuclear cells could be determined. Interestingly, muscle fibers that produced MHC class II-specific dimeric vaccine proteins with mCherry were for weeks surrounded by a localized intense cellular infiltrate composed of CD45+, MHC class II+ and CD11b+ cells. Increasing numbers of eosinophils were observed among the infiltrating cells from day 7 after immunization. The local infiltrate surrounding mCherry+ muscle fibers was dependent on the MHC II-specificity of the vaccine proteins since the control, a non-targeted vaccine protein, failed to induce similar infiltrates. Chemokines measured on day 3 in immunized muscle indicate both a DNA effect and an electroporation effect. No influence of targeting was observed. These results contribute to our understanding for why targeted DNA vaccines have an improved immunogenicity.
- Published
- 2014
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