Recruitment Of Satellite Cells Research Articles

Vibration acceleration enhances proliferation, migration, and maturation of C2C12 cells and promotes regeneration of muscle injury in male rats.

Vibration acceleration (VA) using a whole-body vibration device is beneficial for skeletal muscles. However, its effect at the cellular level remains unclear. We aimed to investigate the effects of VA on muscles invitro and invivo using the C2C12 mouse myoblast cell line and cardiotoxin-induced injury in male rat soleus muscles. Cell proliferation was evaluated using the WST/CCK-8 assay and proportion of Ki-67 positive cells. Cell migration was assessed using wound-healing assay. Cell differentiation was examined by the maturation index in immunostained cultured myotubes and real-time polymerase chain reaction. Regeneration of soleus muscle in rats was assessed by recruitment of satellite cells, cross-sectional area of regenerated muscle fibers, number of centrally nucleated fibers, and conversion of regenerated muscle from fast- to slow-twitch. VA at 30 Hz with low amplitude for 10 min promoted C2C12 cell proliferation, migration, and myotube maturation, without promoting expression of genes related to differentiation. VA significantly increased Pax7-stained satellite cells and centrally nucleated fibers in injured soleus muscles on Day 7 and promoted conversion of fast- to slow-twitch muscle fibers with an increase in the mean cross-sectional area of regenerated muscle fibers on Day 14. VA enhanced the proliferation, migration, and maturation of C2C12 myoblasts and regeneration of injured rat muscles.

White-throated Sparrow (Zonotrichia albicollis) liver and pectoralis flight muscle transcriptomic changes in preparation for migration.

Migratory songbirds undertake challenging journeys to reach their breeding grounds each spring. They accomplish these non-stop flapping feats of endurance through a suite of physiological changes, including the development of substantial fat stores and flight muscle hypertrophy and an increased capacity for fat catabolism. Additionally, migratory birds may show large reductions in organ masses during flight, including the flight muscle and liver, which they must rapidly rebuild during their migratory stopover prior to replenishing their fat stores. However, the molecular basis of this capacity for rapid tissue remodeling and energetic output has not been thoroughly investigated. We performed RNA-seq analysis of the liver and pectoralis flight muscle of captive White-throated Sparrows in the migratory and non-migratory condition to explore the mechanisms of seasonal change to metabolism and tissue mass regulation that may facilitate these migratory journeys. We identified transcriptional alterations to glucose and fatty acid metabolism as well as the production and metabolism of ketone bodies. Based on transcriptional changes, we propose that tissue-specific adjustments in preparation for migration may alleviate the damaging effects of long-duration activity, including a potential increase to the inflammatory response in the muscle. Furthermore, based on transcriptional changes, we hypothesize that seasonal hypertrophy balances satellite cell recruitment and apoptosis, while little evidence appeared in the transcriptome to support MSTN, IGF1, and mTOR-mediated pathways for muscle growth. These findings can encourage more targeted molecular studies on the unique integration of pathways that we find in the development of the migratory endurance phenotype in songbirds.

Muscle regeneration in gilthead sea bream: Implications of endocrine and local regulatory factors and the crosstalk with bone.

Fish muscle regeneration is still a poorly known process. In the present study, an injury was done into the left anterior epaxial skeletal muscle of seventy 15g gilthead sea bream (Sparus aurata) juveniles to evaluate at days 0, 1, 2, 4, 8, 16 and 30 post-wound, the expression of several muscle genes. Moreover, transcripts' expression in the bone (uninjured tissue) was also analyzed. Histology of the muscle showed the presence of dead tissue the first day after injury and how the damaged fibers were removed and replaced by new muscle fibers by day 16 that kept growing up to day 30. Gene expression results showed in muscle an early upregulation of igf-2 and a downregulation of ghr-1 and igf-1. Proteolytic systems expression increased with capn2 and ctsl peaking at 1 and 2 days post-injury, respectively and mafbx at day 8.A pattern of expression that fitted well with active myogenesis progression 16 days after the injury was then observed, with the recovery of igf-1, pax7, cmet, and cav1 expression; and later on, that of cav3 as well. Furthermore, the first days post-injury, the cytokines il-6 and il-15 were also upregulated confirming the tissue inflammation, while tnfα was only upregulated at days 16 and 30 to induce satellite cells recruitment; overall suggesting a possible role for these molecules as myokines. The results of the bone transcripts showed an upregulation first, of bmp2 and ctsk at days 1 and 2, respectively; then, ogn1 and ocn peaked at day 4 in parallel to mstn2 downregulation, and runx2 and ogn2 increased after 8 days of muscle injury, suggesting a possible tissue crosstalk during the regenerative process. Overall, the present model allows studying the sequential involvement of different regulatory molecules during muscle regeneration, as well as the potential relationship between muscle and other tissues such as bone to control musculoskeletal development and growth, pointing out an interesting new line of research in this group of vertebrates.

Omega-3 supplementation during unilateral resistance exercise training in older women: A within subject and double-blind placebo-controlled trial.

SummaryBackground & aimsThe skeletal muscle anabolic effects of n-3 polyunsaturated fatty acids (n-3 PUFA) appear favoured towards women; a property that could be exploited in older women who typically exhibit poor muscle growth responses to resistance exercise training (RET). Here we sought to generate novel insights into the efficacy and mechanisms of n-3 PUFA alongside short-term RET in older women.MethodsWe recruited 16 healthy older women (Placebo n = 8 (PLA): 67±1y, n-3 PUFA n = 8: 64±1y) to a randomised double-blind placebo-controlled trial (n-3 PUFA; 3680 mg/day versus PLA) of 6 weeks fully-supervised progressive unilateral RET (i.e. 6 × 8 reps, 75% 1-RM, 3/wk−1). Strength was assessed by knee extensor 1-RM and isokinetic dynamometry ∼ every 10 d. Thigh fat free mass (TFFM) was measured by DXA at 0/3/6 weeks. Bilateral vastus lateralis (VL) biopsies at 0/2/4/6 weeks with deuterium oxide (D2O) dosing were used to determine MPS responses for 0–2 and 4–6 weeks. Further, fibre cross sectional area (CSA), myonuclei number and satellite cell (SC) number were assessed, alongside muscle anabolic/catabolic signalling via immunoblotting.ResultsRET increased 1-RM equally in the trained leg of both groups (+23 ± 5% n-3 PUFA vs. +25 ± 5% PLA (both P < 0.01)) with no significant increase in maximum voluntary contraction (MVC) (+10 ± 6% n-3 PUFA vs. +13 ± 5% PLA). Only the n-3 PUFA group increased TFFM (3774 ± 158 g to 3961 ± 151 g n-3 PUFA (P < 0.05) vs. 3406 ± 201 g to 3561 ± 170 PLA) and type II fibre CSA (3097 ± 339 μm2 to 4329 ± 264 μm2 n-3 PUFA (P < 0.05) vs. 2520 ± 316 μm2 to 3467 ± 303 μm2 in PL) with RET. Myonuclei number increased equally in n-3 PUFA and PLA in both type I and type II fibres, with no change in SC number. N-3 PUFA had no added benefit on muscle protein synthesis (MPS), however, during weeks 4–6 of RET, absolute synthesis rates (ASR) displayed a trend to increase with n-3 PUFA only (5.6 ± 0.3 g d−1 to 7.1 ± 0.5 g d−1 n-3 PUFA (P = 0.09) vs. 5.5 ± 0.5 g d−1 to 6.5 ± 0.5 g d−1 PLA). Further, the n-3 PUFA group displayed greater 4EBP1 activation after acute RE at 6 weeks.Conclusionn3-PUFA enhanced RET gains in muscle mass through type II fibre hypertrophy, with data suggesting a role for MPS rather than via SC recruitment. As such, the present study adds to a literature base illustrating the apparent enhancement of muscle hypertrophy with RET in older women fed adjuvant n3-PUFA.

Skeletal Muscle Injury by Electroporation: A Model to Study Degeneration/Regeneration Pathways in Muscle.

Skeletal muscle has a remarkable capacity to regenerate after injuries mainly due to a reservoir of precursor cells named satellite cells (SCs), which are responsible for after-birth growth and response to lesions, either by exercise or disease. Upon injury, the regenerative response includes SCs exit of quiescence, activation, proliferation, and fusion to repair or form new myofibers. This process is accompanied by inflammation, with infiltration of immune cells, primarily macrophages. Every phase of regeneration is highly regulated and orchestrated by many molecules and signaling pathways. The elucidation of players and mechanisms involved in muscle degeneration and regeneration is of extreme importance, especially for therapeutic strategies for muscle diseases.Here we are proposing a model of muscle injury induced by electroporation, which is an efficient method to induce muscle damage in order to follow the steps involved in degeneration and regeneration. Three days after electroporation, the muscle shows prominent signals of degeneration, like areas of necrosis and infiltration of macrophages, followed by regeneration, observed by the presence of centrally nucleated myofibers. After 5days the regeneration is very active, with small dMyHC positive fibers. Fifteen days later, we observe a general regeneration of the muscle, with fibers with increased diameter after 60 days. This methodology is an easy and simple alternative to induce muscle lesion. It can be employed to study alterations in gene expression and the process of satellite cell recruitment, both in healthy and dystrophic/myopathic animal models for muscular dystrophy.

The redox-dependent regulation of satellite cells following aseptic muscle trauma (SpEED): study protocol for a randomized controlled trial

BackgroundMuscle satellite cells (SCs) are crucial for muscle regeneration following muscle trauma. Acute skeletal muscle damage results in inflammation and the production of reactive oxygen species (ROS) which may be implicated in SCs activation. Protection of these cells from oxidative damage is essential to ensure sufficient muscle regeneration. The aim of this study is to determine whether SCs activity under conditions of aseptic skeletal muscle trauma induced by exercise is redox-dependent.Methods/designBased on the SCs content in their vastus lateralis skeletal muscle, participants will be classified as either high or low respondents. In a randomized, double-blind, crossover, repeated-measures design, participants will then receive either placebo or N-acetylcysteine (alters redox potential in muscle) during a preliminary 7-day loading phase, and for eight consecutive days following a single bout of intense muscle-damaging exercise. In both trials, blood samples and muscle biopsies will be collected, and muscle performance and soreness will be measured at baseline, pre-exercise, 2 and 8 days post exercise. Biological samples will be analyzed for redox status and SCs activity. Between trials, a 4-week washout period will be implemented.DiscussionThis study is designed to investigate the impact of redox status on SCs mobilization and thus skeletal muscle potential for regeneration under conditions of aseptic inflammation induced by exercise. Findings of this trial should provide insight into (1) molecular pathways involved in SCs recruitment and muscle healing under conditions of aseptic skeletal muscle trauma present in numerous catabolic conditions and (2) whether skeletal muscle’s potential for regeneration depends on its basal SCs content.Trial registrationClinicalTrials.gov, ID: NCT03711838. Registered on 19 Oct 2018.

Extracorporeal Shock Wave Therapy Accelerates Regeneration After Acute Skeletal Muscle Injury

Background: Muscle injuries are among the most common sports-related lesions in athletes; however, optimal treatment remains obscure. Extracorporeal shock wave therapy (ESWT) may be a promising approach in this context, because it has gained increasing importance in tissue regeneration in various medical fields. Hypothesis: ESWT stimulates and accelerates regenerative processes of acute muscle injuries. Study Design: Controlled laboratory study. Methods: Adult Sprague-Dawley rats were divided into 4 experimental groups (2 ESWT+ groups and 2 ESWT– groups) as well as an uninjured control group (n ≥ 6 in each group). An acute cardiotoxin-induced injury was set into the quadriceps femoris muscle of rats in the experimental groups. A single ESWT session was administered to injured muscles of the ESWT+ groups 1 day after injury, whereas ESWT– groups received no further treatment. At 4 and 7 days after injury, 1 each of the ESWT+ and ESWT– groups was euthanized. Regenerating lesions were excised and analyzed by histomorphometry and immunohistochemistry to assess fiber size, myonuclear content, and recruitment of satellite cells. Results: The size and myonuclear content of regenerating fibers in ESWT+ muscle was significantly increased compared with ESWT– muscle fibers at both 4 and 7 days after injury. Similarly, at both time points, ESWT+ muscles exhibited significantly higher contents of pax7-positive satellite cells, mitotically active H3P+ cells, and, of cells expressing the myogenic regulatory factors, myoD and myogenin, indicating enhanced proliferation and differentiation rates of satellite cells after ESWT. Mitotic activity at 4 days after injury was doubled in ESWT+ compared with ESWT– muscles. Conclusion: ESWT stimulates regeneration of skeletal muscle tissue and accelerates repair processes. Clinical Relevance: We provide evidence for accelerated regeneration of damaged skeletal muscle after ESWT. Although further studies are necessary, our findings support the view that ESWT is an effective method to improve muscle healing, with special relevance to sports injuries.

Fibromodulin: a master regulator of myostatin controlling progression of satellite cells through a myogenic program.

Differentiation of muscle satellite cells (MSCs) involves interaction of the proteins present in the extracellular matrix (ECM) with MSCs to regulate their activity, and therefore phenotype. Herein, we report fibromodulin (FMOD), a member of the proteoglycan family participating in the assembly of ECM, as a novel regulator of myostatin (MSTN) during myoblast differentiation. In addition to having a pronounced effect on the expression of myogenic marker genes [myogenin (MYOG) and myosin light chain 2 (MYL2)], FMOD was found to maintain the transcriptional activity of MSTN Moreover, coimmunoprecipitation and in silico studies performed to investigate the interaction of FMOD helped confirm that it antagonizes MSTN function by distorting its folding and preventing its binding to activin receptor type IIB. Furthermore, in vivo studies revealed that FMOD plays an active role in healing by increasing satellite cell recruitment to sites of injury. Together, these findings disclose a hitherto unrecognized regulatory role for FMOD in MSCs and highlight new mechanisms whereby FMOD circumvents the inhibitory effects of MSTN and triggers myoblast differentiation. These findings offer a basis for the design of novel MSTN inhibitors that promote muscle regeneration after injury or for the development of pharmaceutical agents for the treatment of different muscle atrophies.-Lee, E. J., Jan, A. T., Baig, M. H., Ashraf, J. M., Nahm, S.-S., Kim, Y.-W., Park, S.-Y., Choi, I. Fibromodulin: a master regulator of myostatin controlling progression of satellite cells through a myogenic program.

Sphingosine phosphate lyase regulates myogenic differentiation via S1P receptor‐mediated effects on myogenic microRNA expression

S1P lyase (SPL) catalyzes the irreversible degradation of sphingosine-1-phosphate (S1P), a bioactive lipid whose signaling activities regulate muscle differentiation, homeostasis, and satellite cell (SC) activation. By regulating S1P levels, SPL also controls SC recruitment and muscle regeneration, representing a potential therapeutic target for muscular dystrophy. We found that SPL is induced during myoblast differentiation. To investigate SPL's role in myogenesis at the cellular level, we generated and characterized a murine myoblast SPL-knockdown (SPL-KD) cell line lacking SPL. SPL-KD cells accumulated intracellular and extracellular S1P and failed to form myotubes under conditions that normally stimulate myogenic differentiation. Under differentiation conditions, SPL-KD cells also demonstrated delayed induction of 3 myogenic microRNAs (miRNAs), miR-1, miR-206, and miR-486. SPL-KD cells successfully differentiated when treated with an S1P1 agonist, S1P2 antagonist, and combination treatments, which also increased myogenic miRNA levels. SPL-KD cells transfected with mimics for miR-1 or miR-206 also overcame the differentiation block. Thus, we show for the first time that the S1P/SPL/S1P-receptor axis regulates the expression of a number of miRNAs, thereby contributing to myogenic differentiation.

Impaired Macrophage and Satellite Cell Infiltration Occurs in a Muscle-Specific Fashion Following Injury in Diabetic Skeletal Muscle

BackgroundSystemic elevations in PAI-1 suppress the fibrinolytic pathway leading to poor collagen remodelling and delayed regeneration of tibialis anterior (TA) muscles in type-1 diabetic Akita mice. However, how impaired collagen remodelling was specifically attenuating regeneration in Akita mice remained unknown. Furthermore, given intrinsic differences between muscle groups, it was unclear if the reparative responses between muscle groups were different.Principal FindingsHere we reveal that diabetic Akita muscles display differential regenerative responses with the TA and gastrocnemius muscles exhibiting reduced regenerating myofiber area compared to wild-type mice, while soleus muscles displayed no difference between animal groups following injury. Collagen levels in TA and gastrocnemius, but not soleus, were significantly increased post-injury versus controls. At 5 days post-injury, when degenerating/necrotic regions were present in both animal groups, Akita TA and gastrocnemius muscles displayed reduced macrophage and satellite cell infiltration and poor myofiber formation. By 10 days post-injury, necrotic regions were absent in wild-type TA but persisted in Akita TA. In contrast, Akita soleus exhibited no impairment in any of these measures compared to wild-type soleus. In an effort to define how impaired collagen turnover was attenuating regeneration in Akita TA, a PAI-1 inhibitor (PAI-039) was orally administered to Akita mice following cardiotoxin injury. PAI-039 administration promoted macrophage and satellite cell infiltration into necrotic areas of the TA and gastrocnemius. Importantly, soleus muscles exhibit the highest inducible expression of MMP-9 following injury, providing a mechanism for normative collagen degradation and injury recovery in this muscle despite systemically elevated PAI-1.ConclusionsOur findings suggest the mechanism underlying how impaired collagen remodelling in type-1 diabetes results in delayed regeneration is an impairment in macrophage infiltration and satellite cell recruitment to degenerating areas; a phenomena that occurs differentially between muscle groups.

Srf

Adult skeletal muscles adapt their fiber size to workload. We show that serum response factor (Srf) is required for satellite cell-mediated hypertrophic muscle growth. Deletion of Srf from myofibers, and not satellite cells, blunts overload-induced hypertrophy, and impairs satellite cell proliferation and recruitment to pre-existing fibers. We reveal a gene network in which Srf within myofibers modulates interleukin-6 and cyclooxygenase-2/interleukin-4 expressions and therefore exerts a paracrine control of satellite cell functions. In Srf-deleted muscles, in vivo overexpression of interleukin-6 is sufficient to restore satellite cell proliferation, but not satellite cell fusion and overall growth. In contrast, cyclooxygenase-2/interleukin-4 overexpression rescues satellite cell recruitment and muscle growth without affecting satellite cell proliferation, identifying altered fusion as the limiting cellular event. These findings unravel a role for Srf in the translation of mechanical cues applied to myofibers into paracrine signals, which in turn will modulate satellite cell functions and support muscle growth.

Srf-Dependent Paracrine Signals Produced by Myofibers Control Satellite Cell-Mediated Skeletal Muscle Hypertrophy

Adult skeletal muscles adapt their fiber size to workload. We show that serum response factor (Srf) is required for satellite cell-mediated hypertrophic muscle growth. Deletion of Srf from myofibers and not satellite cells blunts overload-induced hypertrophy, and impairs satellite cell proliferation and recruitment to pre-existing fibers. We reveal a gene network in which Srf within myofibers modulates interleukin-6 and cyclooxygenase-2/interleukin-4 expressions and therefore exerts a paracrine control of satellite cell functions. In Srf-deleted muscles, in vivo overexpression of interleukin-6 is sufficient to restore satellite cell proliferation but not satellite cell fusion and overall growth. In contrast cyclooxygenase-2/interleukin-4 overexpression rescue satellite cell recruitment and muscle growth without affecting satellite cell proliferation, identifying altered fusion as the limiting cellular event. These findings unravel a role for Srf in the translation of mechanical cues applied to myofibers into paracrine signals, which in turn will modulate satellite cell functions and support muscle growth.

Calcium influx determines the muscular response to electrotransfer

Cell membrane permeabilization by electric pulses (electropermeabilization), results in free exchange of ions across the cell membrane. The role of electrotransfer-mediated Ca(2+)-influx on muscle signaling pathways involved in degeneration (β-actin and MurF), inflammation (IL-6 and TNF-α), and regeneration (MyoD1, myogenin, and Myf5) was investigated, using pulse parameters of both electrochemotherapy (8 HV) and DNA delivery (HVLV). Three pulsing conditions were used: 8 high-voltage pulses (8 HV), resulting in large permeabilization and ion flux, and a combination of one high-voltage pulse and one low-voltage pulse (HVLV), either alone or in combination with injection of DNA. Mice and rats were anesthetized before pulsing. At the times given, animals were killed, and intact tibialis cranialis muscles were excised for analysis. Uptake of Ca(2+) was assessed using (45)Ca as a tracer. Using gene expression analyses and histology, we showed a clear association between Ca(2+) influx and muscular response. Moderate Ca(2+) influx induced by HVLV pulses results in activation of pathways involved in immediate repair and hypertrophy. This response could be attenuated by intramuscular injection of EGTA reducing Ca(2+) influx. Larger Ca(2+) influx as induced by 8-HV pulses leads to muscle damage and muscle fiber regeneration through recruitment of satellite cells. The extent of Ca(2+) influx determines the muscular response to electrotransfer and, thus, the success of a given application. In the case of electrochemotherapy, in which the objective is cell death, a large influx of Ca(2+) may be beneficial, whereas for DNA electrotransfer, muscle recovery should occur without myofiber loss to ensure preservation of plasmid DNA.

In situ real-time imaging of the satellite cells in rat intact and injured soleus muscles using quantum dots

The recruitment of satellite cells, which are located between the basement membrane and the plasma membrane in myofibers, is required for myofiber repair after muscle injury or disease. In particular, satellite cell migration has been focused on as a satellite cell response to muscle injury because satellite cell motility has been revealed in cell culture. On the other hand, in situ, it is poorly understood how satellite cell migration is involved in muscle regeneration after injury because in situ it has been technically very difficult to visualize living satellite cells localized within skeletal muscle. In the present study, using quantum dots conjugated to anti-M-cadherin antibody, we attempted the visualization of satellite cells in both intact and injured skeletal muscle of rat in situ. As a result, the present study is the first to demonstrate in situ real-time imaging of satellite cells localized within the skeletal muscle. Moreover, it was indicated that satellite cell migration toward an injured site was induced in injured muscle while spatiotemporal change in satellite cells did not occur in intact muscle. Thus, it was suggested that the satellite cell migration may play important roles in the regulation of muscle regeneration after injury. Moreover, the new method used in the present study will be a useful tool to develop satellite cell-based therapies for muscle injury or disease.

POINT: IGF IS THE MAJOR PHYSIOLOGICAL REGULATOR OF MUSCLE MASS

The insulin-like growth factors (IGFs)-I and -II are homologous peptides that are structurally related to insulin. However, IGFs retain the C-peptide, enabling binding to their main signaling receptor, the IGF type 1 receptor (IGF1R). IGF-II, however, can also bind to and signal via the A isoform of

Acute molecular response of mouse hindlimb muscles to chronic stimulation

Stimulation of the mouse hindlimb via the sciatic nerve was performed for a 4-h period to investigate acute muscle gene activation in a model of muscle phenotype conversion. Initial force production (1.6 +/- 0.1 g/g body wt) declined 45% within 10 min and was maintained for the remainder of the experiment. Force returned to initial levels upon study completion. An immediate-early growth response was present in the extensor digitorum longus (EDL) muscle (FOS, JUN, activating transcription factor 3, and musculoaponeurotic fibrosarcoma oncogene) with a similar but attenuated pattern in the soleus muscle. Transcript profiles showed decreased fast fiber-specific mRNA (myosin heavy chains 2A and 2B, fast troponins T(3) and I, alpha-tropomyosin, muscle creatine kinase, and parvalbumin) and increased slow transcripts (myosin heavy chain-1beta/slow, troponin C slow, and tropomyosin 3y) in the EDL versus soleus muscles. Histological analysis of the EDL revealed glycogen depletion without inflammatory cell infiltration in stimulated versus control muscles, whereas ultrastructural analysis showed no evidence of myofiber damage after stimulation. Multiple fiber type-specific transcription factors (tea domain family member 1, nuclear factor of activated T cells 1, peroxisome proliferator-activated receptor-gamma coactivator-1alpha and -beta, circadian locomotor output cycles kaput, and hypoxia-inducible factor-1alpha) increased in the EDL along with transcription factors characteristic of embryogenesis (Kruppel-like factor 4; SRY box containing 17; transcription factor 15; PBX/knotted 1 homeobox 1; and embryonic lethal, abnormal vision). No established in vivo satellite cell markers or genes activated in our parallel experiments of satellite cell proliferation in vitro (cyclins A(2), B(2), C, and E(1) and MyoD) were differentially increased in the stimulated muscles. These results indicated that the molecular onset of fast to slow phenotype conversion occurred in the EDL within 4 h of stimulation without injury or satellite cell recruitment. This conversion was associated with the expression of phenotype-specific transcription factors from resident fiber myonuclei, including the activation of nascent developmental transcriptional programs.

Mitochondrial DNA rejuvenescence: Why Resist?

We previously reported that satellite cells from older adults do not accumulate aging‐associated mitochondrial DNA (mtDNA) deletions (Safdar et al, 2007). Resistance (RES) training induces satellite cell activation and skeletal muscle hypertrophy, and is recommended as an effective countermeasure to sarcopenia in the elderly. We aimed to delineate the protective mechanism underlying this effect. Muscle biopsies were taken from the vastus lateralis of 16 older subjects (70 ± 5 y; 8 women) before and after 6 months of RES training and analyzed for protein content of electron transport chain (complex I ND6, complex III core protein 2, complex IV COX subunits –II and –IV, and complex V alpha subunit), antioxidant enzymes (Mn‐SOD, Cu/Zn‐SOD, and catalase), markers of mitochondrial abundance (citrate synthase CS) and oxidative damage (protein carbonyl PC, 4‐hydroxynonenal 4HNE, and total DNA 8‐hydroxy‐2‐deoxyguanosine 8‐OHdG), mtDNA deletions, as well as CS, COX, and catalase enzyme activity. RES training increased protein content of ND6, core protein 2, COX‐II, COX‐IV, complex V alpha subunit and catalase by 25%, 41%, 62%, 69%, 31%, and 95% respectively (P &lt; 0.042), and COX and catalase enzyme activity by 79% and 89%, respectively (P &lt; 0.028). RES training decreased mtDNA deletions (63%), PC (45%), 4‐HNE (29%), and total DNA 8‐OHdG (45%) content (P &lt; 0.01). We conclude that the improvements in mitochondrial function occurred through RES training‐induced recruitment of satellite cells resulting in mitochondrial gene shifting and rejuvenescence in the skeletal muscle of older adults. We propose that RES training is a viable therapy to attenuate and/or “reverse” mitochondrial abnormalities associated with sarcopenia. (Funded by CIHR Institute of Aging, and Warren Lammert and Kathy Corkins).

The potential benefits of creatine and conjugated linoleic acid as adjuncts to resistance training in older adults

Human aging is associated with a significant reduction in muscle mass (sarcopenia) resulting in muscle weakness and functional limitations in the elderly. Sarcopenia has been associated with mitochondrial dysfunction and the accumulation of mtDNA deletions. Resistance training increases muscle strength and size and can increase mitochondrial capacity and decrease oxidative stress in older adults. Creatine monohydrate (CrM) and conjugated linoleic acid (CLA) have biological effects that could enhance some of the beneficial effects of resistance training in older adults (i.e., up arrow fat-free mass, down arrow total body fat). We have completed two resistance-training studies with CrM alone and CrM+CLA supplementation in older adults to evaluate the independent effects of exercise and dietary supplements, as well as their interactive effects. Our studies, and several others, have found that CrM enhanced the resistance exercise mediated gains in fat-free mass and strength. More recently, we found that the addition of CLA also lead to a significant reduction of body fat after six months of resistance training in older adults. Older adults have fewer wild-type mtDNA copies and higher amounts of mtDNA deletions as compared with younger adults in mature skeletal muscle; however, these deletions are not seen in the satellite cell-derived myoblast cultures. These findings, and the fact that mtDNA deletions are lower and wild-type mtDNA copy number is higher after resistance training in older adults, suggests that activation of satellite cells secondary to resistance exercise-induced muscle damage can dilute or "shift" the proportion of mtDNA genotype towards that of a younger adult. Recent evidence suggests that CrM supplementation in combination with strength training can enhance satellite cell activation and total myonuclei number per muscle fiber in young men. Future studies are required to determine whether the mitochondrial adaptations to resistance exercise in older adults are further enhanced with CrM supplementation and whether this is due to increased recruitment of satellite cells. It will also be important to determine whether these changes are maintained over a longer time period.

Take two NSAIDs and call on your satellite cells in the morning

it is generally agreed that successful skeletal muscle regeneration following intense exercise or injury is facilitated by the protein synthesis machinery and the recruitment of myogenic stem (satellite) cells. Upstream activation of these processes, however, is poorly understood. A growing body of

Changes in skeletal muscle gene expression following clenbuterol administration

BackgroundBeta-adrenergic receptor agonists (BA) induce skeletal muscle hypertrophy, yet specific mechanisms that lead to this effect are not well understood. The objective of this research was to identify novel genes and physiological pathways that potentially facilitate BA induced skeletal muscle growth. The Affymetrix platform was utilized to identify gene expression changes in mouse skeletal muscle 24 hours and 10 days after administration of the BA clenbuterol.ResultsAdministration of clenbuterol stimulated anabolic activity, as indicated by decreased blood urea nitrogen (BUN; P < 0.01) and increased body weight gain (P < 0.05) 24 hours or 10 days, respectively, after initiation of clenbuterol treatment. A total of 22,605 probesets were evaluated with 52 probesets defined as differentially expressed based on a false discovery rate of 10%. Differential mRNA abundance of four of these genes was validated in an independent experiment by quantitative PCR. Functional characterization of differentially expressed genes revealed several categories that participate in biological processes important to skeletal muscle growth, including regulators of transcription and translation, mediators of cell-signalling pathways, and genes involved in polyamine metabolism.ConclusionGlobal evaluation of gene expression after administration of clenbuterol identified changes in gene expression and overrepresented functional categories of genes that may regulate BA-induced muscle hypertrophy. Changes in mRNA abundance of multiple genes associated with myogenic differentiation may indicate an important effect of BA on proliferation, differentiation, and/or recruitment of satellite cells into muscle fibers to promote muscle hypertrophy. Increased mRNA abundance of genes involved in the initiation of translation suggests that increased levels of protein synthesis often associated with BA administration may result from a general up-regulation of translational initiators. Additionally, numerous other genes and physiological pathways were identified that will be important targets for further investigations of the hypertrophic effect of BA on skeletal muscle.