Fiber Type Profile Research Articles

Comparative Muscle Physiology of Ringed (Pusa hispida), Bearded (Erignathus barbatus), and Spotted (Phoca largha) Seals from the Bering and Chukchi Seas

The physiological properties of marine mammal skeletal muscle are foundational in defining diving and foraging capacities. Further, these parameters can be useful when assessing the behavioral flexibility of species faced with environmental change or disturbance. Herein, we define species- and age-specific muscle physiology for three ice-associated seal species experiencing Arctic warming. Specifically, we evaluated myoglobin content ([Mb]), nonbicarbonate buffering capacity (β), and fiber type profiles of a major locomotor muscle, the longissimus dorsi. Muscle samples were obtained from subsistence harvested ringed (Pusa hispida; n = 11), bearded (Erignathus barbatus; n = 41), and spotted (Phoca largha; n = 12) seals of all ages in the Bering and Chukchi Seas. Adult ringed seals had the highest [Mb] (6.67 ± 0.20 g 100 g wet tissue-1), followed by spotted (5.38 ± 0.29 g 100 g wet tissue-1) and bearded (4.55 ± 0.07 g 100 g wet tissue-1) seals. [Mb] increased with age for all species, but rates of increase differed by species. In contrast, β was similar for all species and age classes. We documented higher proportions of fast-twitch relative to slow-twitch fibers in these species, and fiber type proportions did not differ significantly with age. Adult bearded seals exhibited the greatest proportion of fast-twitch fibers (68.7 ± 1.5%), followed by ringed (59.0 ± 4.8%) and spotted (55.1 ± 2.1%) seals. Overall, our data suggest a strong link between muscle physiology, diving behavior, and life history strategies, and provide insight into the physiological capacities of these potentially vulnerable species.

Intact Short, Intermediate, and Long Skeletal Muscle Fibers Obtained by Enzymatic Dissociation of Six Hindlimb Muscles of Mice: Beyond Flexor Digitorum Brevis.

Skeletal muscle fibers obtained by enzymatic dissociation of mouse muscles are a useful model for physiological experiments. However, most papers deal with the short fibers of the flexor digitorum brevis (FDB), which restrains the scope of results dealing with fiber types, limits the amount of biological material available, and impedes a clear connection between cellular physiological phenomena and previous biochemical and dynamical knowledge obtained in other muscles. This paper describes how to obtain intact fibers from six muscles with different fiber type profiles and lengths. Using C57BL/6 adult mice, we show the muscle dissection and fiber isolation protocol and demonstrate the suitability of the fibers for Ca2+ transient studies and their morphometric characterization. The fiber type composition of the muscles is also presented. When dissociated, all muscles rendered intact, living fibers that contract briskly for more than 24 h. FDB gave short (<1 mm), peroneus digiti quarti (PDQA) and peroneus longus (PL) gave intermediate (1-3 mm), while extensor digitorum longus (EDL), extensor hallucis longus (EHL), and soleus muscles released long (3-6 mm) fibers. When recorded with the fast dye Mag-Fluo-4, Ca2+ transients of PDQA, PL, and EHL fibers showed the fast, narrow kinetics reminiscent of the morphology type II (MT-II), known to correspond to type IIX and IIB fibers. This is consistent with the fact that these muscles have over 90% of type II fibers compared with FDB (~80%) and soleus (~65%). Moving beyond FDB, we demonstrate for the first time the dissociation of several muscles, which render fibers spanning a range of lengths between 1 and 6 mm. These fibers are viable and give fast Ca2+ transients, indicating that the MT-II can be generalized to IIX and IIB fast fibers, regardless of their muscle source. These results increase the availability of models for mature skeletal muscle studies.

The impact of sarcolipin ablation on calcineurin signalling and muscle phenotype with aging

Sarcolipin (SLN), a small protein inhibitor of the sarco(endo)plasmic reticulum Ca 2+ -ATPase (SERCA), is dynamically upregulated in atrophic unloading and disease states where it promotes muscle health by activating calcineurin (Cn) and the dephosphorylation and subsequent nuclear translocation of nuclear factor of activated T-cells (NFAT). This study sought to examine how the ablation of SLN impacted Cn signalling, fibre type profile and muscle mass in both male and female mice with aging. Male and female, wild type (WT) and SLN knockout (SLNKO) mice were assessed at two age groups (young adult (4-6M) and older adult (18+M)) for muscle mass (soleus:body weight ratio, fibre type specific cross-sectional area), fibre type profile and protein expression (SLN, Cn, and NFAT). SLN content was significantly greater in WT females (p &lt;00.1) and older animals (5&lt;0.05) and absent from SLNKO. As SLN has been linked to Cn signalling previously, we hypothesized that the increased SLN content in female and aged animals may promote Cn signalling. While there was a trend for lower Cn expression with aging (p=0.10), neither sex nor genotype significantly impacted Cn expression. To examine activation of Cn, the ratio of inactive phosphorylated NFAT to total NFAT was assessed via Western Blotting. We found that aging significantly increased the activation of Cn (p&lt;0.01) and there was a trend (p=0.10) towards greater NFATp/NFAT with SLN ablation signifying a reduction in Cn signalling. As Cn is a known regulator of muscle fibre type, we examined fibre type profile using immunofluorescence and found aging increased the percentage of type I fibres (p&lt;0.001), which was witnessed more predominately in female mice regardless of genotype. Furthermore, when examining type II fibres, we found a significant sex by age interaction (p&lt;0.05) in which both WT and SLNKO females displayed reduced type II fibres with aging while males did not display this apparent shift. With respect to muscle mass, aging, regardless of sex or genotype, was shown to significantly reduce relative muscle mass (p&lt;0.001), however no significant reductions were found in total fibre count, or cross-sectional area of Type I or Type II fibres. In summary, this study found that WT female and aged animals display increased SLN content. Aligning with our hypothesis, there was a trend towards lower Cn signalling with SLN ablation, regardless of age or sex. However, this does not seem to be linked to changes in muscle fibre type or muscle mass, as SLNKO animals did not display significant differences from their WT counterparts. Further studies should seek to examine the role of SLN in both sex and aging further, with special focus on metabolic energy expenditure and SERCA protection. NSERC This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Distinct myofibre domains of the human myotendinous junction revealed by single nucleus RNA-seq.

The myotendinous junction (MTJ) is a specialized domain of the multinucleated myofibre, faced with the challenge of maintaining robust cell-matrix contact with the tendon under high mechanical stress and strain. Here, we profiled 24,161 nuclei in semitendinosus muscle-tendon samples from 3 healthy males by single nucleus RNA-sequencing (snRNA-seq), alongside spatial transcriptomics, to gain insight into the genes characterizing this specialization in humans. We identified a cluster of MTJ myonuclei, represented by 47 enriched transcripts, of which the presence of ABI3BP, ABLIM1, ADAMTSL1, BICD1, CPM, FHOD3, FRAS1 and FREM2 was confirmed at the MTJ at the protein level by immunofluorescence. Four distinct subclusters of MTJ myonuclei were apparent and segregated into two COL22A1-expressing subclusters and two lacking COL22A1 but with a clear fibre type profile expressing MYH7 or MYH1/2. Our findings reveal distinct myonuclei profiles of the human MTJ, a weak link in the musculoskeletal system, which is selectively affected in pathological conditions, from muscle strains to muscular dystrophies.

Muscle fiber type and metabolic profiles of four muscles from the African black ostrich

Muscle fiber type, fiber cross-sectional area (CSA), enzyme activities (citrate synthase (CS), 3-hydroxyacetyl Co A dehydrogenase (3HAD), lactate dehydrogenase (LDH) and phosphofructokinase (PFK)) and glycogen content were analyzed in the M. iliotibialis cranialis (ITC), M. iliotibialis lateralis, M. gastrocnemius (G) and M. fibularis longus (FL) muscles from 24 ostriches. Type I and II fiber proportions were similar across the 4 muscles, but the ITC had overall the smallest fibers. CS activity was the highest in the ITC, but similar between the remainder of the muscles. 3HAD activities were very low in all muscles, ranging between 1.9 and 2.7 μmol/min/g protein, indicating poor β-oxidation. The ITC also had the lowest PFK activity. Glycogen content averaged ∼85 mmol/kg dry weight across the muscles with large intramuscular variations. The 4 ostrich muscles present with low fat oxidation capacity and low glycogen content, which could have significant implications on meat quality attributes.

Early Postmortem Metabolism and Protease Activation in Fast Glycolytic and Slow Oxidative Bovine Muscles

Muscle properties and metabolism influence muscle to meat conversion. Fiber type profile impacts glycolytic capacity as well as protein turnover rate in vivo. Our objective was to investigate protease content and activation during the early postmortem period using muscles with known divergent metabolism. Samples from longissimus lumborum (LL) and diaphragm (Dia) were taken from predominantly Angus steer carcasses (n = 6) at 1, 3, and 24 h postmortem and frozen. Myosin heavy chain (MyHC) isoforms, ATP, glycogen, glucose, glucose-6-phosphate (G6P), and lactate concentrations were determined. Procaspase-3, calpain-1, calpastatin, desmin, and troponin-T were assessed by immunodetection. Muscles showed contrasting MyHC profiles, with LL represented primarily by IIx and IIa isoforms (∼88%) whereas Dia contained mostly (80%) type I isoform. Glycogen degradation was more pronounced in LL and coincided with more rapid accumulation of glucose and lactate (P &amp;lt; 0.01). Procaspase-3 content was influenced by muscle (m: P &amp;lt; 0.01), being greater in Dia. Fragments indicating activation of procaspase-3 postmortem were not detected. Calpain-1 autolysis and intact calpastatin (135 kDa) content were influenced by muscle and time (m × t: P &amp;lt; 0.01 and P &amp;lt; 0.01, respectively). Calpastatin fragmentation postmortem was not associated with greater procaspase-3 content. In conclusion, fast glycolytic LL displayed faster protease activation and greater proteolysis during the first 24 h postmortem.

Aerobic exercise training prevents skeletal myopathy by myomiRs regulation in heart failure

Abstract Introduction Heart failure (HF) is the endpoint of systemic arterial hypertension. Exercise intolerance is a common symptom, partly due, to changes in the skeletal muscle mass (SM) and fiber type profile. Otherwise, aerobic exercise training (ET) has been used as an important non-pharmacological therapy in HF. MyomiRs are a muscle-specific class of miRNAs, which regulate genes that inhibiting the expression of proteins in pathological and physiological conditions controlling phenotypic changes in the SM, however little is known about these changes in ET-induced HF Purpose To elucidate the molecular mechanisms of ET involved in the metabolic alterations of SM in HF rats of hypertensive etiology. Methods The study was approved by the animal ethics committee (USP-No. 2020/01). 20 male rats, spontaneously hypertensive (SHR), and 10 Wistar Kyoto rats (WKY), SHR controls, nine-months-old, were divided into three groups: sedentary WKY (WKY-S), sedentary SHR (SHR-S), and trained (SHR-T). The ET consisted of swimming sessions with 60 minutes, 1x/day, 5x/week, for 10 weeks, with 5% of body overload. After ET protocol, blood pressure (BP), cardiac morphology and function (Echocardiography), exercise tolerance test, maximal oxygen uptake (VO2 peak), mitochondrial oxygen consumption (Oroboros), immunohistochemistry of the SM, expression of miRNAs (RT-qPCR) were evaluated. Statistical analyzes were performed by one-way ANOVA followed by the Tukey test. The results were expressed as mean ± standard error. Results ET reduced blood pressure levels and cardiac dysfunction in SHR-T compared to SHR-S. The SHR-S group covered smaller distance in the exercise tolerance test (255±22 meters) compared to the WKY-S (419±19 meters, p&amp;lt;0.0001), however ET reestablished the exercise tolerance (SHR-T: 365±20 meters; SHR-S: p&amp;lt;0.001 and WKY-S: p&amp;gt;0.05). The HF induced changes in type I and II fibers composition (I: 73±0.6% and II: 24±0.9%), VO2 peak (50±1.5 mL kg–1 min–1), mitochondrial oxygen consumption (State 3: 3.0±0.2 nmol O2 min–1 mg protein–1) and myomiRs expression (miRNA-208b: 65±4%, -499: 73±5%, -1: 153±10%) in the soleus muscle of SHR-S compared to WKY-S (I: 94±0.6%, II: 6±0.6%, p&amp;lt;0.001; VO2 peak: 59±2.3 mL kg–1 min–1, p&amp;lt;0.01; State 3: 4.0±0.2 nmol O2 min–1 mg protein–1, p&amp;lt;0.05; miRNAs: p&amp;lt;0.01). ET minimized changes in metabolic profile by counteract the muscle fiber type switching, and the oxygen consumption impairment, and myomiRs expression dysregulation (I: 90±0.5%, II: 9±0.6%, SHR-S p&amp;lt;0.01; VO2 peak: 79±2.4 mL kg–1 min–1, SHR-S: p&amp;lt;0.0001; State 3: 5.45±0.32 nmol O2 min–1 mg protein–1, SHR-S: p&amp;lt;0.0001; miRNA-208b: 91±5%, -499: 106±8%, -1: 100±9%; SHR-S: p&amp;lt;0.01). Conclusions ET reestablished structural and metabolic changes in SM, resulting from the progression of HF, through the regulation of myomiRs, improving exercise tolerance. Funding Acknowledgement Type of funding sources: Public Institution(s). Main funding source(s): The Coordination for the Improvement of Higher Education Personnel (CAPES): Academic Excellence Program (Proex).

Myosin Heavy Chain Composition, Creatine Analogues, and the Relationship of Muscle Creatine Content and Fast-Twitch Proportion to Wilks Coefficient in Powerlifters.

Machek, SB, Hwang, PS, Cardaci, TD, Wilburn, DT, Bagley, JR, Blake, DT, Galpin, AJ, and Willoughby, DS. Myosin heavy chain composition, creatine analogues, and the relationship of muscle creatine content and fast-twitch proportion to Wilks coefficient in powerlifters. J Strength Cond Res 34(11): 3022-3030, 2020-Little data exist on powerlifting-specific skeletal muscle adaptations, and none elucidate sex differences in powerlifters. Powerlifters tend to display higher fast-twitch fiber content and phosphagen system dependence. Nevertheless, it is unknown whether fast-twitch fiber or muscle creatine content are predictive of competitive powerlifting performance (via Wilks coefficient). Twelve actively competing powerlifters (PL; n = 6M/6F; age = 21.3 ± 1.0; 3.0 ± 1.8 year competing; 7.3 ± 6.6 meets attended) and 10 sedentary controls (CON; n = 5M/5F; age = 19.4 ± 2.0 year) underwent vastus lateralis muscle biopsies and venipuncture to compare the myosin heavy chain (MHC) fiber type and creatine analogue profiles between groups of both sexes, and determine whether MHC IIa and muscle total creatine (MTC) composition predict powerlifting performance. Samples were analyzed for specific MHC isoform (I, IIa, and IIx) content via mixed homogenate SDS-PAGE, and creatine analogues (MTC, muscle creatine transporter [SLC6A8], serum total creatine [STC], and serum creatinine [CRT]). Furthermore, MHC IIa and MTC content were compared with Wilks coefficient using Pearson correlation coefficients. Male PL MHC content was 50 ± 6% I, 45 ± 6% IIa, and 5 ± 11% IIx, versus 46 ± 6% I, 53 ± 6 IIa, and 0% IIx in female PL. Conversely, male CON MHC content was 33 ± 5% I, 38 ± 7% IIa, and 30 ± 8% IIx, vs. 35 ± 9% I, 44 ± 8% IIa, and 21 ± 17% IIx in female CON. Muscle total creatine, SLC6A8, STC, and CRT did not significantly differ between groups nor sexes. Finally, neither MHC IIa content (r = -0.288; p = 0.364) nor MTC (r = 0.488; p = 0.108) significantly predicted Wilks coefficient, suggesting these characteristics alone do not determine powerlifting skill variation.

The Impact Of Age On The Transcriptional And Morphological Profile Of Skeletal Muscle

Aging is associated with many physiological changes that impact physical function. Most notably, older adults experience a progressive loss of skeletal muscle mass and function, termed sarcopenia. A better understanding of the molecular and phenotypical changes associated with advancing age may provide therapeutic targets for interventions to slow the progression of sarcopenia. PURPOSE: To characterize the transcriptional and morphological profile of aging skeletal muscle. METHODS: Resting vastus lateralis muscle biopsies were collected from 9 young (Y; 27±3yr, 179±7cm, 82±10kg, 26±3BMI) and 9 older adults (O; 68±5yr, 172±8cm, 77±19kg, 26±5BMI) following an overnight fast. Whole transcriptome next-generation RNA sequencing was performed on cDNA synthesized from skeletal muscle RNA. Differentially expressed genes (FDR-adjusted P-value ≤ 0.05) were identified through DESeq2 and subjected to bioinformatic analyses using DAVID (v6.8). Skeletal muscle morphology including fiber type, satellite cell (SC) content, and capillarization was assessed through immunofluorescent microscopy RESULTS: In total, 900 differentially expressed genes were identified in the skeletal muscle of O versus Y (+1.5 fold change = 213; -1.5 fold change = 127). DAVID functional analyses indicated that aging was associated with functions related to glycogen metabolism, amino acid metabolism, ubiquitination, and transition between fast and slow fibers. Consistent with the latter, a significant difference (P=0.048) in myosin heavy chain (MyHC) fiber type profile was identified (Y = MyHCI: 29±4%, MyHCII: 71±4%; O = MyHCI: 46±7%, MyHCII: 54±7%). Moreover, aging was associated with a numerical reduction in SC specific to MyHCI (Y = 0.13±0.02, O = 0.07±0.02 SC/MyHCI fiber, P=0.07) but not MyHCII fibers (Y=0.12±0.03, O=0.08±0.02 P=0.373). Independent of fiber type, capillaries per fiber was significantly lower (P=0.015) in O (1.53±0.34) vs. Y (4.59±0.85). CONCLUSION: Advancing age is associated with changes in the transcriptional and morphological profile of skeletal muscle. These findings highlight potential therapeutic targets for the preservation of skeletal muscle mass and function with advancing age. Supported by a JumpStart Grant, CHS, ASU.

Skeletal Muscle Antioxidant Antioxidant Capacity Correlates With Both Oxidative And Glycolytic Profile In Trained Women Athletes

Muscle antioxidant enzymes may be upregulated in parallel with increased exercise training status and capacity for reactive oxygen species (ROS) formation. PURPOSE: To examine associations between antioxidant protein expression and different physiological markers of endurance exercise in trained women athletes. METHODS: Seventeen competitive women soccer players (age; 23±4 yrs; height; 166±5 cm, weight; 60.2±7.5 kg; VO2max; 50.5±5.1 ml·min-1·kg-1) participated. Participants had a muscle biopsy taken from m. vastus lateralis, which was analyzed for protein expression of superoxide dismutase 1 and 2 (SOD1 and 2), several metabolic enzymes and muscle fiber type profile. Participants also performed a VO2max test, a repeated sprint test (RST), as well as the Yo-Yo Intermittent Endurance, level 1 (YYIE1) and Recovery test, level 1 (YYIR1). Inter-individual relationships between selected variables were analysed using Pearson’s product–moment correlation coefficients. RESULTS: VO2max and SOD2 correlated (P<0.05) with VO2max explaining 24% of the variance in SOD2 protein expression. Myosin Heavy Chain I (MHCI) and IIa (MHCIIa) explained 26 and 25%, respectively, of the variance in SOD2 protein. Oxidative enzymes such as citrate synthase, isocitrate dehydrogenase and cytocrome c oxidase correlated (P<0.05) with SOD2 explaining 24, 31 and 17% of the variance, respectively. Finally, SOD2 protein expression correlated (P<0.05) to monocarboxylate transporter 4 (MCT4; r=0.67) and phosphofructokinase (PFK; r=0.62). No statistical relationship was observed between SOD2 protein and neither Na+-K+ATPase subunits, Na+/H+ exchanger, Acetyl-CoA carboxylase, PECAM-1, nor YYIE1, YYIR1 and RST performance. SOD1 protein expression displayed an inverse correlation with MHCIIa (r=0.61; P<0.05), but did not correlate with any other variable assessed in muscle or physical capacity. CONCLUSIONS: Skeletal muscle antioxidant capacity associates with markers of endurance exercise such as maximal aerobic power, type I and IIa muscle fibers, and mitochondrial function. However, strong relationships were additionally observed between antioxidant profile and lactate production as well as transport capacity, supporting a link between lactate and ROS generation.

Skeletal Muscle Fiber Type in Hypoxia: Adaptation to High-Altitude Exposure and Under Conditions of Pathological Hypoxia.

Skeletal muscle is able to modify its size, and its metabolic/contractile properties in response to a variety of stimuli, such as mechanical stress, neuronal activity, metabolic and hormonal influences, and environmental factors. A reduced oxygen availability, called hypoxia, has been proposed to induce metabolic adaptations and loss of mass in skeletal muscle. In addition, several evidences indicate that muscle fiber-type composition could be affected by hypoxia. The main purpose of this review is to explore the adaptation of skeletal muscle fiber-type composition to exposure to high altitude (ambient hypoxia) and under conditions of pathological hypoxia, including chronic obstructive pulmonary disease (COPD), chronic heart failure (CHF) and obstructive sleep apnea syndrome (OSAS). The muscle fiber-type composition of both adult animals and humans is not markedly altered during chronic exposure to high altitude. However, the fast-to-slow fiber-type transition observed in hind limb muscles during post-natal development is impaired in growing rats exposed to severe altitude. A slow-to-fast transition in fiber type is commonly found in lower limb muscles from patients with COPD and CHF, whereas a transition toward a slower fiber-type profile is often found in the diaphragm muscle in these two pathologies. A slow-to-fast transformation in fiber type is generally observed in the upper airway muscles in rodent models of OSAS. The factors potentially responsible for the adaptation of fiber type under these hypoxic conditions are also discussed in this review. The impaired locomotor activity most likely explains the changes in fiber type composition in growing rats exposed to severe altitude. Furthermore, chronic inactivity and muscle deconditioning could result in the slow-to-fast fiber-type conversion in lower limb muscles during COPD and CHF, while the factors responsible for the adaptation of muscle fiber type during OSAS remain hypothetical. Finally, the role played by cellular hypoxia, hypoxia-inducible factor-1 alpha (HIF-1α), and other molecular regulators in the adaptation of muscle fiber-type composition is described in response to high altitude exposure and conditions of pathological hypoxia.

Partial involvement of Nrf2 in skeletal muscle mitohormesis as an adaptive response to mitochondrial uncoupling

Mitochondrial dysfunction is usually associated with various metabolic disorders and ageing. However, salutary effects in response to mild mitochondrial perturbations have been reported in multiple organisms, whereas molecular regulators of cell-autonomous stress responses remain elusive. We addressed this question by asking whether the nuclear factor erythroid-derived-like 2 (Nrf2), a transcription factor and master regulator of cellular redox status is involved in adaptive physiological responses including muscle mitohormesis. Using a transgenic mouse model with skeletal muscle-specific mitochondrial uncoupling and oxidative phosphorylation (OXPHOS) inefficiency (UCP1-transgenic, TG) we show that additional genetic ablation of Nrf2 abolishes an adaptive muscle NAD(P)H quinone dehydrogenase 1 (NQO1) and catalase induction. Deficiency of Nrf2 also leads to decreased mitochondrial respiratory performance although muscle functional integrity, fiber-type profile and mitochondrial biogenesis were not significantly altered. Importantly, Nrf2 ablation did not abolish the induction of key genes and proteins of muscle integrated stress response including the serine, one-carbon cycle, and glycine synthesis (SOG) pathway in TG mice while further increasing glutathione peroxidase (GPX) activity linked to increased GPX1 protein levels. Conclusively, our results tune down the functions controlled by Nrf2 in muscle mitohormesis and oxidative stress defense during mitochondrial OXPHOS inefficiency.

Dietary supplementation with bovine-derived milk fat globule membrane lipids promotes neuromuscular development in growing rats

BackgroundThe milk fat globule membrane (MFGM) is primarily composed of polar phospho- and sphingolipids, which have established biological effects on neuroplasticity. The present study aimed to investigate the effect of dietary MFGM supplementation on the neuromuscular system during post-natal development.MethodsGrowing rats received dietary supplementation with bovine-derived MFGM mixtures consisting of complex milk lipids (CML), beta serum concentrate (BSC) or a complex milk lipid concentrate (CMLc) (which lacks MFGM proteins) from post-natal day 10 to day 70.ResultsSupplementation with MFGM mixtures enriched in polar lipids (BSC and CMLc, but not CML) increased the plasma phosphatidylcholine (PC) concentration, with no effect on plasma phosphatidylinositol (PI), phosphatidylethanolamine (PE), phosphatidylserine (PS) or sphingomyelin (SM). In contrast, muscle PC was reduced in rats receiving supplementation with both BSC and CMLc, whereas muscle PI, PE, PS and SM remained unchanged. Rats receiving BSC and CMLc (but not CML) displayed a slow-to-fast muscle fibre type profile shift (MyHCI → MyHCIIa) that was associated with elevated expression of genes involved in myogenic differentiation (myogenic regulatory factors) and relatively fast fibre type specialisation (Myh2 and Nfatc4). Expression of neuromuscular development genes, including nerve cell markers, components of the synaptogenic agrin–LRP4 pathway and acetylcholine receptor subunits, was also increased in muscle of rats supplemented with BSC and CMLc (but not CML).ConclusionsThese findings demonstrate that dietary supplementation with bovine-derived MFGM mixtures enriched in polar lipids can promote neuromuscular development during post-natal growth in rats, leading to shifts in adult muscle phenotype.

Beef palatability and its relationship with protein degradation and muscle fibre type profile in longissimus thoracis in Alentejana breed from divergent growth pathways

The traditional beef production in the South of Portugal is based on a discontinuous growth (DG) system that requires lower external inputs and could enhance meat quality and financial returns to cattle producers. This system allows farmers to take advantage of the bull’s compensatory growth when the pasture is abundant and finishes the cattle on concentrates for 2 to 3 months before slaughter. The fast gain rate before slaughter could be a valuable strategy to improve tenderness and to reduce its inconsistency in beef production. Therefore, the aim of this study was to evaluate the effects of production system (continuous growth (CG) v. DG) on longissimus thoracis muscle properties from Alentejana bulls. In total, 40 Alentejana male calves were allocated to two distinct feeding regimes: in the CG system, animals were fed concentrate plus hay and slaughtered at 18 months of age, whereas in the DG system, animals were fed on hay until 15 months of age and then fed the same diet provided to the CG group until 24 months of age. The DG system had a positive impact on meat tenderness (P<0.001) and global acceptability (P<0.001). DG bulls had greater fibre cross-sectional area (CSA) of glycolytic fibres (P<0.05) and relative area of the muscle (RA) occupied by type IIX fibres (P<0.01) and greater levels of α-actinin (P<0.05) and myosin light chain 2 (P<0.01) proteins, and pH24h (P<0.01) than CG bulls. The latter had greater CSA of type I (P<0.05) and type IIA (P<0.01) and greater RA of type IIA (P<0.05) and oxidative (P<0.05) than CG bulls. The compensatory growth production system had a positive impact on meat tenderness and global acceptability, overcoming the negative effects of slaughter of the bulls at a later age. The DG beef system could be a worthwhile strategy of beef production in Mediterranean areas due to the low-quality pasture in summer.

The effect of obesity on the contractile performance of isolated mouse soleus, EDL, and diaphragm muscles.

The effect of obesity on isolated muscle function is surprisingly underresearched. The present study is the first to examine the effects of obesity on isolated muscle performance using a method that more closely represents real-world muscle function. This work uniquely establishes a muscle-specific profile of mechanical changes in relation to underpinning mechanisms. These findings may be important to understanding the negative cycle of obesity and in designing interventions for improving weight status.

Ultrasonography detects early laryngeal muscle atrophy in an equine neurectomy model.

A unilateral neurectomy model was used to study the relationship between histologic and ultrasonographic tissue characteristics during muscle atrophy over time. This investigation was an in vivo experimental study in an equine model (n = 28). Mean pixel intensity of ultrasonographic images was measured, a muscle appearance grade was assigned weekly, and muscles were harvested from 4 to 32 weeks. Minimum fiber diameter, fiber density per unit area, percent collagen, percent fat, and fiber type profile were measured from muscle cryosections and correlated with the ultrasonographic parameters. A significant relationship was identified between collagen content, minimum fiber diameter, and ultrasonographic muscle appearance by as early as 8 weeks. There was no apparent association between fat content of muscle and the ultrasonographic appearance of atrophy before 28 weeks. Early muscle atrophy before fatty infiltration is detectable with ultrasound. The effect of muscle collagen content on echointensity may be mediated by reduced fiber diameter.

Blunted angiogenesis and hypertrophy are associated with increased fatigue resistance and unchanged aerobic capacity in old overloaded mouse muscle.

We hypothesize that the attenuated hypertrophic response in old mouse muscle is (1) partly due to a reduced capillarization and angiogenesis, which is (2) accompanied by a reduced oxidative capacity and fatigue resistance in old control and overloaded muscles, that (3) can be rescued by the antioxidant resveratrol. To investigate this, the hypertrophic response, capillarization, oxidative capacity, and fatigue resistance of m. plantaris were compared in 9- and 25-month-old non-treated and 25-month-old resveratrol-treated mice. Overload increased the local capillary-to-fiber ratio less in old (15 %) than in adult (59 %) muscle (P < 0.05). Although muscles of old mice had a higher succinate dehydrogenase (SDH) activity (P < 0.05) and a slower fiber type profile (P < 0.05), the isometric fatigue resistance was similar in 9- and 25-month-old mice. In both age groups, the fatigue resistance was increased to the same extent after overload (P < 0.01), without a significant change in SDH activity, but an increased capillary density (P < 0.05). Attenuated angiogenesis during overload may contribute to the attenuated hypertrophic response in old age. Neither was rescued by resveratrol supplementation. Changes in fatigue resistance with overload and aging were dissociated from changes in SDH activity, but paralleled those in capillarization. This suggests that capillarization plays a more important role in fatigue resistance than oxidative capacity.

Contractile and metabolic properties of engineered skeletal muscle derived from slow and fast phenotype mouse muscle.

Satellite cells derived from fast and slow muscles have been shown to adopt contractile and metabolic properties of their parent muscle. Mouse muscle shows less distinctive fiber-type profiles than rat or rabbit muscle. Therefore, in this study we sought to determine whether three-dimensional muscle constructs engineered from slow soleus (SOL) and fast tibialis anterior (TA) from mice would adopt the contractile and metabolic properties of their parent muscle. Time-to-peak tension (TPT) and half-relaxation time (1/2RT) was significantly slower in SOL constructs. In agreement with TPT, TA constructs contained significantly higher levels of fast myosin heavy chain (MHC) and fast troponin C, I, and T isoforms. Fast SERCA protein, both slow and fast calsequestrin isoforms and parvalbumin were found at higher levels in TA constructs. SOL constructs were more fatigue resistant and contained higher levels of the mitochondrial proteins SDH and ATP synthase and the fatty acid transporter CPT-1. SOL constructs contained lower levels of the glycolytic enzyme phosphofructokinase but higher levels of the β-oxidation enzymes LCAD and VLCAD suggesting greater fat oxidation. Despite no changes in PGC-1α protein, SOL constructs contained higher levels of SIRT1 and PRC. TA constructs contained higher levels of the slow-fiber program repressor SOX6 and the six transcriptional complex (STC) proteins Eya1 and Six4 which may underlie the higher in fast-fiber and lower slow-fiber program proteins. Overall, we have found that muscles engineered from predominantly slow and fast mouse muscle retain contractile and metabolic properties of their native muscle.

Insights into the skeletal muscle characteristics of three southern African antelope species.

ABSTRACTSkeletal muscle fibre type, cross-sectional area (CSA), maximum enzyme capacities and fibre oxidative capacities were investigated in three southern African antelope species. Muscle samples from blesbok (Damaliscus pygargus phillipsi), mountain reedbuck (Redunca fulvorufula) and greater kudu (Tragelaphus strepsiceros) were collected post mortem from the Vastus lateralis and analysed for myosin heavy chain (MHC) isoform content, citrate synthase (CS), 3-hydroxyacyl Co A dehydrogenase (3-HAD), phosphofructokinase (PFK), lactate dehydrogenase (LDH) and creatine kinase (CK) activities. Histochemistry and immunohistochemistry were performed to determine relative fibre oxidative capacity, fibre type and cross-sectional area (CSA). Type IIX fibres were the most abundant fibre type in all three species, ranging from 43 to 57%. Kudu had less type IIX fibres than mountain reedbuck and blesbok (P<0.05), values confirmed by their respective MHC isoform content. Blesbok had the smallest fibres, followed by mountain reedbuck and finally kudu (P<0.001). Overall, all three species had high oxidative and glycolytic capacities, but species differences were found. Kudu had the lowest CS activity, followed by blesbok and mountain reedbuck, but the highest PFK, LDH and CK activities. This study confirmed large variation in oxidative capacities within a single fibre type, as well as overlap between the fibre types with no distinct differences between the three species. The fibre type profile of each species is discussed and confirms some of their physical attributes and capabilities.

Effects of chronic administration of clenbuterol on contractile properties and calcium homeostasis in rat extensor digitorum longus muscle.

Clenbuterol, a β2-agonist, induces skeletal muscle hypertrophy and a shift from slow-oxidative to fast-glycolytic muscle fiber type profile. However, the cellular mechanisms of the effects of chronic clenbuterol administration on skeletal muscle are not completely understood. As the intracellular Ca2+ concentration must be finely regulated in many cellular processes, the aim of this study was to investigate the effects of chronic clenbuterol treatment on force, fatigue, intracellular calcium (Ca2+) homeostasis and Ca2+-dependent proteolysis in fast-twitch skeletal muscles (the extensor digitorum longus, EDL, muscle), as they are more sensitive to clenbuterol-induced hypertrophy. Male Wistar rats were chronically treated with 4 mg.kg−1 clenbuterol or saline vehicle (controls) for 21 days. Confocal microscopy was used to evaluate sarcoplasmic reticulum Ca2+ load, Ca2+ -transient amplitude and Ca2+ spark properties. EDL muscles from clenbuterol-treated animals displayed hypertrophy, a shift from slow to fast fiber type profile and increased absolute force, while the relative force remained unchanged and resistance to fatigue decreased compared to control muscles from rats treated with saline vehicle. Compared to control animals, clenbuterol treatment decreased Ca2+-transient amplitude, Ca2+ spark amplitude and frequency and the sarcoplasmic reticulum Ca2+ load was markedly reduced. Conversely, calpain activity was increased by clenbuterol chronic treatment. These results indicate that chronic treatment with clenbuterol impairs Ca2+ homeostasis and this could contribute to the remodeling and functional impairment of fast-twitch skeletal muscle.