Can non-invasive motor unit analysis reveal distinct neural strategies of force production in young with uncomplicated type 1 diabetes?

PURPOSE: to investigate the early consequences of type 1 diabetes (T1D) on the neural strategies of muscle force production. METHODS: motor unit (MU) activity was recorded from the vastus lateralis muscle with High-Density surface Electromyography during isometric knee extension at 20 and 40% of maximum voluntary contraction (MVC) in 8 T1D (4 males, 4 females, 30.5 ± 3.6 years) and 8 matched control (4 males, 4 females, 27.3 ± 5.9 years) participants. Muscle biopsies were also collected from vastus lateralis for fiber type analysis, including myosin heavy chain (MyHC) isoform content via protein and mRNA expression. RESULTS: MVC was comparable between groups as well as MU conduction velocity, action potentials' amplitude and proportions of MyHC protein isoforms. Nonetheless, MU discharge rate, relative derecruitment thresholds and mRNA expression of MyHC isoform I were lower in T1D. CONCLUSIONS: young people with uncomplicated T1D present a different neural control of muscle force production. Furthermore, differences are detectable non-invasively in absence of any functional manifestation (i.e., force production and fiber type distribution). These novel findings suggest that T1D has early consequences on the neuromuscular system and highlights the necessity of a better characterization of neural control in this population.

Resveratrol, a Multitasking Molecule That Improves Skeletal Muscle Health.

Resveratrol is a natural polyphenol utilized in Chinese traditional medicine and thought to be one of the determinants of the "French Paradox". More recently, some groups evidenced its properties as a calorie-restriction mimetic, suggesting that its action passes through the modulation of skeletal muscle metabolism. Accordingly, the number of studies reporting the beneficial effects of resveratrol on skeletal muscle form and function, in both experimental models and humans, is steadily increasing. Although studies on animal models confer to resveratrol a good potential to ameliorate skeletal muscle structure, function and performance, clinical trials still do not provide clear-cut information. Here, we first summarize the effects of resveratrol on the distinct components of the skeletal muscle, such as myofibers, the neuromuscular junction, tendons, connective sheaths and the capillary bed. Second, we review clinical trials focused on the analysis of skeletal muscle parameters. We suggest that the heterogeneity in the response to resveratrol in humans could depend on sample characteristics, treatment modalities and parameters analyzed; as well, this heterogeneity could possibly reside in the complexity of skeletal muscle physiology. A systematic programming of treatment protocols and analyses could be helpful to obtain consistent results in clinical trials involving resveratrol administration.

Experimental models for ageing research.

Ageing is a biological process caused by the malfunctioning of multiple cellular mechanisms, ascribable to nine hallmarks: genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication. These ageing pillars have three common traits: (i) they appear during normal ageing; (ii) their experimental intensification accelerates ageing; and (iii) their experimental reduction delays ageing. The evidence that the elderly are more prone to develop pathologies such as cancer, diabetes and degenerative diseases, together with data showing that the elderly population is steadily increasing, has stimulated an important effort to find specific countermeasures to physiological ageing. Unfortunately, the investigation of ageing processes and the search for countermeasures in humans is very difficult. Therefore, researchers must rely on a wide range of experimental models that span from unicellular to more complex organisms. Unfortunately, experimental models are not devoid of pitfalls, flaws or obstacles that can have an impact in ageing research. In the present review we describe the most exploited experimental models in the field, such as in vitro, animal and human models, highlighting the characteristics that justify their application in the laboratory routine, and translation to human research.

The Potential of Calorie Restriction and Calorie Restriction Mimetics in Delaying Aging: Focus on Experimental Models.

Aging is a biological process determined by multiple cellular mechanisms, such as genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, and altered intercellular communication, that ultimately concur in the functional decline of the individual. The evidence that the old population is steadily increasing and will triplicate in the next 50 years, together with the fact the elderlies are more prone to develop pathologies such as cancer, diabetes, and degenerative disorders, stimulates an important effort in finding specific countermeasures. Calorie restriction (CR) has been demonstrated to modulate nutrient sensing mechanisms, inducing a better metabolic profile, enhanced stress resistance, reduced oxidative stress, and improved inflammatory response. Therefore, CR and CR-mimetics have been suggested as powerful means to slow aging and extend healthy life-span in experimental models and humans. Taking into consideration the difficulties and ethical issues in performing aging research and testing anti-aging interventions in humans, researchers initially need to work with experimental models. The present review reports the major experimental models utilized in the study of CR and CR-mimetics, highlighting their application in the laboratory routine, and their translation to human research.

Are muscle fibres of body builders intrinsically weaker? A comparison with single fibres of aged-matched controls.

AIM: Skeletal muscles of Body Builders (BB) represent an interesting model to study muscle mass gains in response to high volume resistance training. It is debated whether muscle contractile performance improves in proportion to mass. Here, we aim to assess whether muscle hypertrophy does not occur at the expense of performance. METHODS: Six BB and Six untrained controls (CTRL) were recruited. Cross-sectional area (CSA) and maximum voluntary contraction (MVC) of quadriceps femoris muscle (QF) and CSA and architecture of vastus lateralis (VL) were determined. Moreover, a biopsy was taken from VL mid-portion and single fibres were analysed. RESULTS: QF CSA and MVC were 32% (n.s., P = .052) and 58% (P = .009) higher in BB than in CTRL, respectively. VL CSA was 37% higher in BB (P = .030). Fast 2A fibres CSA was 24% (P = .048) greater in BB than in CTRL, when determined in immunostained sections of biopsy samples. Single permeabilized fast fibres CSA was 37% (n.s., P = .052) higher in BB than in CTRL, and their force was slightly higher in BB (n.s.), while specific tension (P0 ) was 19% (P = .024) lower. The lower P0 was not explained either by lower myosin content or by impaired calcium diffusion. Conversely, the swelling caused by skinning-induced permeabilization was different and, when used to correct P0 , differences between populations disappeared. CONCLUSIONS: The results show that high degree of muscle hypertrophy is not detrimental for force generation capacity, as increases in fibre size and force are strictly proportional once the differential swelling response is accounted for.

Musculoskeletal adaptations to strength training in frail elderly: a matter of quantity or quality?

BACKGROUND: The improvement in muscle strength generally exceeds the increase in muscle size following strength training in frail elderly, highlighting the complex aetiology of strength deficit in aging. The aim of this study was to investigate the effect of heavy-load strength training on a broad number of factors related to specific strength in frail elderly. METHODS: Thirty-four frail elderly men (n = 18) and women (n = 16) aged 67 to 98 (86 ± 7 years) were randomized to either a group performing strength training twice a week for 10 weeks (ST) or a non-exercising control group (CON). Knee extensor muscle strength was tested as one-repetition maximum (1RM) and isometric maximal voluntary contraction (MVC) torque. Muscle activation was assessed by the interpolated twitch technique, and muscle density [mean Hounsfield units (HU)] and intermuscular adipose tissue (IMAT) by computed tomography scans of the quadriceps femoris. Muscle biopsies from the vastus lateralis were obtained to investigate changes in intramyocellular lipids and single-fibre specific tension. RESULTS: In ST, knee extension 1RM and MVC improved by 17 and 7%, respectively. Muscle cross-sectional area of the quadriceps femoris increased by 7%, accompanied by a 4% increase of muscle density. No changes in IMAT, voluntary activation level, single-fibre specific tension, or lipid content were observed. CONCLUSIONS: In contrast to several previous reports, the improvements in isometric muscle strength and muscle area were in good agreement in the present study. The training-induced increase in muscle density was not due to changes in skeletal muscle lipid content. Instead, the increase in muscle density may reflect increased packing of contractile material or simply an increased ratio of muscle tissue relative to IMAT.

Skeletal Muscle Fiber Size and Gene Expression in the Oldest-Old With Differing Degrees of Mobility.

The oldest-old, in the ninth and tenth decades of their life, represent a population characterized by neuromuscular impairment, which often implies a loss of mobility and independence. As recently documented by us and others, muscle atrophy and weakness are accompanied by an unexpected preservation of the size and contractile function of skeletal muscle fibers. This suggests that, while most fibers are likely lost with their respective motoneurons, the surviving fibers are well preserved. Here, we investigated the mechanisms behind this fiber preservation and the relevance of physical activity, by comparing a group of 6 young healthy controls (YG: 22-28 years) with two groups of oldest-old (81-96 years), one able to walk (OW: n = 6, average 86 years) and one confined to a wheelchair (ONW n = 9, average 88 years). We confirmed previous results of fiber preservation and, additionally, observed a shift in fiber type, toward slow predominance in OW and fast predominance in ONW. Myonuclear density was increased in muscles of ONW, compared to YG and OW, potentially indicative of an ongoing atrophy process. We analyzed, by RT-qPCR, the expression of genes relevant for fiber size and type regulation in a biopsy sample from the vastus lateralis. In all oldest-old both myostatin and IGF-1 expression were attenuated compared to YG, however, in ONW two specific IGF-1 isoforms, IGF-1EA and MGF, demonstrated a further significant decrease compared to OW. Surprisingly, atrogenes (MURF1 and atrogin) expression was also significantly reduced compared to YG and this was accompanied by a close to statistically significantly attenuated marker of autophagy, LC3. Among the determinants of the metabolic fiber type, PGC1α was significantly reduced in both OW and ONW compared to YG, while AMPK was down-regulated only in ONW. We conclude that, in contrast to the shift of the balance in favor of pro-atrophy factors found by other studies in older adults (decreased IGF-1, increase of myostatin, increase of atrogenes), in the oldest-old the pro-atrophy factors also appear to be down-regulated, allowing a partial recovery of the proteostasis balance. Furthermore, the impact of muscle activity, as a consequence of lost or preserved walking ability, is limited.

Age-dependent variations in the expression of myosin isoforms and myogenic factors during the involution of the proximal sesamoidean ligament of sheep.

In ungulates the stability of the fetlock joint is dependent on several muscles, which are exposed to high stress and strain. Among those muscles, the proximal sesamoidean ligament or PSL (also known as the suspensory ligament or Ruini's elasto-tendinous organ) is organized at birth in layers of muscle fibres alternated with abundant tendinous tissue that, during the postnatal development, becomes the predominant tissue. In this study we analysed the PSL of the sheep at the age of 1, 30 and 180 days and determined the expression of several genes which either (a) are markers of muscle fibre growth and maturation, or (b) play a role as signal molecules. We observed an accelerated maturation, as indicated by the transition of MyHC isoform expression towards the slow isoforms and a reduced regenerative potential indicated by the low Pax7 expression and the altered Wnt signalling. We also found a specific myogenic expression pattern of MyoD, Myf5 and Myogenin in the developing PSL and high mRNA levels of specific fibrogenic factors, as TGF-ß1, that, undoubtedly, stimulate the growth of connective tissue. Our observations confirmed, at molecular level, the peculiarity of the fast involution observed in PSL a muscle that undergoes a very specific active differentiation process during early development, which implies myofibres involution and their replacement with connective tissue.

Resveratrol treatment reduces the appearance of tubular aggregates and improves the resistance to fatigue in aging mice skeletal muscles.

Resveratrol (RES) is a polyphenolic compound found in grapes, peanuts, and in some berries. RES has been reported to exhibit antioxidant, anti-inflammatory, anti-proliferative properties, and to target mitochondrial-related pathways in mammalian cells and animal models. Therefore, RES is currently advised as supplement in the diet of elderly individuals. Although it is hypothesized that some of RES beneficial actions likely arise from its action on the skeletal muscle, the investigation of RES effects on this tissue remains still elusive. This study reports the effects of a 0,04% RES-supplemented diet for six months, on the skeletal muscle properties of C57/BL6 aging mice. The analysis of the morphology, protein expression, and functional-mechanical properties of selected skeletal muscles in treated compared to control mice, revealed that treated animals presented less tubular aggregates and a better resistance to fatigue in an ex-vivo contraction test, suggesting RES as a good candidate to reduce age-related alterations in muscle.

Loss of maximal explosive power of lower limbs after 2 weeks of disuse and incomplete recovery after retraining in older adults.

KEY POINTS: Disuse in older adults can critically decrease lower limb muscle power, leading to compromised mobility and overall quality of life. We studied how muscle power and its determinants (muscle mass, single muscle fibre properties and motor control) adapted to 2 weeks of disuse and subsequent 2 weeks of physical training in young and older people. Disuse decreased lower limb muscle power in both groups; however, different adaptations in single muscle fibre properties and co-contraction of leg muscles were observed between young and older individuals. Six physical training sessions performed after disuse promoted the recovery of muscle mass and power. However, they were not sufficient to restore muscle power to pre-disuse values in older individuals, suggesting that further countermeasures are required to counteract the disuse-induced loss of muscle power in older adults. ABSTRACT: Disuse-induced loss of muscle power can be detrimental in older individuals, seriously impairing functional capacity. In this study, we examined the changes in maximal explosive power (MEP) of lower limbs induced by a 14-day disuse (bed-rest, BR) and a subsequent 14-day retraining, to assess whether the impact of disuse was greater in older than in young men, and to analyse the causes of such adaptations. Sixteen older adults (Old: 55-65 years) and seven Young (18-30 years) individuals participated in this study. In a subgroup of eight Old subjects, countermeasures based on cognitive training and protein supplementation were applied. MEP was measured with an explosive ergometer, muscle mass was determined by magnetic resonance, motor control was studied by EMG, and single muscle fibres were analysed in vastus lateralis biopsy samples. MEP was ∼33% lower in Old than in Young individuals, and remained significantly lower (-19%) when normalized by muscle volume. BR significantly affected MEP in Old (-15%) but not in Young. Retraining tended to increase MEP; however, this intervention was not sufficient to restore pre-BR values in Old. Ankle co-contraction increased after BR in Old only, and remained elevated after retraining (+30%). Significant atrophy occurred in slow fibres in Old, and in fast fibres in Young. After retraining, the recovery of muscle fibre thickness was partial. The proposed countermeasures were not sufficient to affect muscle mass and power. The greater impact of disuse and smaller retraining-induced recovery observed in Old highlight the importance of designing suitable rehabilitation protocols for older individuals.

Identification and characterization of three novel mutations in the CASQ1 gene in four patients with tubular aggregate myopathy.

Here, we report the identification of three novel missense mutations in the calsequestrin-1 (CASQ1) gene in four patients with tubular aggregate myopathy. These CASQ1 mutations affect conserved amino acids in position 44 (p.(Asp44Asn)), 103 (p.(Gly103Asp)), and 385 (p.(Ile385Thr)). Functional studies, based on turbidity and dynamic light scattering measurements at increasing Ca2+ concentrations, showed a reduced Ca2+ -dependent aggregation for the CASQ1 protein containing p.Asp44Asn and p.Gly103Asp mutations and a slight increase in Ca2+ -dependent aggregation for the p.Ile385Thr. Accordingly, limited trypsin proteolysis assay showed that p.Asp44Asn and p.Gly103Asp were more susceptible to trypsin cleavage in the presence of Ca2+ in comparison with WT and p.Ile385Thr. Analysis of single muscle fibers of a patient carrying the p.Gly103Asp mutation showed a significant reduction in response to caffeine stimulation, compared with normal control fibers. Expression of CASQ1 mutations in eukaryotic cells revealed a reduced ability of all these CASQ1 mutants to store Ca2+ and a reduced inhibitory effect of p.Ile385Thr and p.Asp44Asn on store operated Ca2+ entry. These results widen the spectrum of skeletal muscle diseases associated with CASQ1 and indicate that these mutations affect properties critical for correct Ca2+ handling in skeletal muscle fibers.

Role of p66shc in skeletal muscle function.

p66shc is a growth factor adaptor protein that contributes to mitochondrial ROS production. p66shc is involved in insulin signaling and its deletion exerts a protective effect against diet-induced obesity. In light of the role of skeletal muscle activity in the control of systemic metabolism and obesity, we investigated which is the contribution of p66shc in regulating muscle structure and function. Here, we show that p66shc-/- muscles are undistinguishable from controls in terms of size, resistance to denervation-induced atrophy, and force. However, p66shc-/- mice perform slightly better than wild type animals during repetitive downhill running. Analysis of the effects after placing mice on a high fat diet (HFD) regimen demonstrated that running distance is greatly reduced in obese wild type animals, but not in overweight-resistant p66shc-/- mice. In addition, muscle force measured after exercise decreases upon HFD in wild type mice while p66shc-/- animals are protected. Our data indicate that p66shc affect the response to damage of adult muscle in chow diet, and it determines the maintenance of muscle force and exercise performance upon a HFD regimen.

Age-dependent neuromuscular impairment in prion protein knockout mice.

INTRODUCTION: The cellular prion protein (PrP(C) ) is commonly recognized as the precursor of prions, the infectious agents of the fatal transmissible spongiform encephalopathies, or prion diseases. Despite extensive effort, the physiological role of PrP(C) is still ambiguous. Evidence has suggested that PrP(C) is involved in different cellular functions, including peripheral nerve integrity and skeletal muscle physiology. METHODS: We analyzed the age-dependent influence of PrP(C) on treadmill test-based aerobic exercise capacity and on a series of morphological and metabolic parameters using wild-type and genetically modified mice of different ages expressing, or knockout (KO) for, PrP(C) . RESULTS: We found that aged PrP-KO mice displayed a reduction in treadmill performance compared with PrP-expressing animals, which was associated with peripheral nerve demyelination and alterations of skeletal muscle fiber type. CONCLUSION: PrP-KO mice have an age-dependent impairment of aerobic performance as a consequence of specific peripheral nerve and muscle alterations.

Protein supplementation increases postexercise plasma myostatin concentration after 8 weeks of resistance training in young physically active subjects.

Myostatin (MSTN) is a negative regulator of muscle growth even if some studies have shown a counterintuitive positive correlation between MSTN and muscle mass (MM). Our aim was to investigate the influence of 2 months of resistance training (RT) and diets with different protein contents on plasma MSTN, interleukin 1 beta (IL-1ß), interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-α), and insulin-like growth factor 1 (IGF-1). Eighteen healthy volunteers were randomly divided in two groups: high protein (HP) and normal protein (NP) groups. Different protein diet contents were 1.8 and 0.85 g of protein·kg bw(-1)·day(-1) for HP and NP, respectively. Subjects underwent 8 weeks of standardized progressive RT. MSTN, IGF-1, IL-1ß, IL-6, and TNF-α were analyzed before and after the first and the last training sessions. Lean body mass, MM, upper-limb muscle area, and strength were measured. Plasma MSTN showed a significant increase (P<.001) after the last training in the HP group compared with NP group and with starting value. IGF-1 plasma concentration showed a positive correlation with MSTN in HP after the last training (r(2)=0.6456; P=.0295). No significant differences were found between NP and HP for IL-1ß, IL-6, TNF-α, and strength and MM or area. These findings suggest a "paradoxical" postexercise increase of plasma MSTN after 8 weeks of RT and HP diets. This MSTN elevation correlates positively with IGF-1 plasma level. This double increase of opposite (catabolic/anabolic) mediators could explain the substantial overlapping of MM increases in the two groups.

Effect of hyperbaric oxygenation and gemcitabine on apoptosis of pancreatic ductal tumor cells in vitro.

BACKGROUND: Gemcitabine is first-line therapy for advanced pancreatic ductal adenocarcinoma (PDAC) with a poor survival and response rate. Hyperbaric oxygenation (HBO) enhances delivery of oxygen to hypoxic tumor cells and increases their susceptibility to cytotoxic effects of chemotherapy. We hypothesized that the anticancer activity of gemcitabine (GEM) may be enhanced if tumor cells are placed in an oxygen-rich environment. The present study evaluated the effects of gemcitabine, HBO and their combination on apoptosis of tumor cells. MATERIALS AND METHODS: PANC-1 and AsPc-1 PDAC tumor cell lines were used. Cultured tumor cells were treated with GEM at its growth-inhibitory concentration (IC50) and HBO at 2.5 ATA for 90 min or a combination of both (HBO then GEM and GEM then HBO). Twenty-four hours later, apoptotic cells in each group were analyzed and the apoptotic index (AI) was calculated. RESULTS: PANC-1 cell line: HBO alone had no effect on AI: 6.5 ± 0.1 vs. 5.9 ± 0.1. HBO before and after gemcitabine did not further increase AI: 8.2 ± 0.1 (HBO-GEM), 8.5 ± 0.1 (GEM-HBO) vs. 8.1 ± 0.1 (GEM). The combination of HBO and gemcitabine significantly increased AI: 10.7 ± 0.02 (p<0.001 vs. all groups). AsPc-1 cell line: HBO-alone had no effect on AI: 5.9 ± 0.1 vs. 5.9 ± 0.1. HBO before and after gemcitabine did not further increase AI: 8.2 ± 0.1 (HBO-GEM), 8.4 ± 0.1 (GEM-HBO) vs. 8.0 ± 0.1 (GEM). The combination of HBO and gemcitabine significantly increased AI: 9.7 ± 0.1 (p<0.001 vs. all groups). CONCLUSION: HBO-alone, whether administered before and after gemcitabine has no effect on apoptosis of PDAC cells in vitro. HBO significantly enhanced gemcitabine-induced apoptosis when administered during gemcitabine. Our findings suggest that the time window would be critical for using HBO as adjuvant to chemotherapy.

Mitochondrial Ca2+-handling in fast skeletal muscle fibers from wild type and calsequestrin-null mice.

Mitochondrial calcium handling and its relation with calcium released from sarcoplasmic reticulum (SR) in muscle tissue are subject of lively debate. In this study we aimed to clarify how the SR determines mitochondrial calcium handling using dCASQ-null mice which lack both isoforms of the major Ca(2+)-binding protein inside SR, calsequestrin. Mitochondrial free Ca(2+)-concentration ([Ca(2+)]mito) was determined by means of a genetically targeted ratiometric FRET-based probe. Electron microscopy revealed a highly significant increase in intermyofibrillar mitochondria (+55%) and augmented coupling (+12%) between Ca(2+) release units of the SR and mitochondria in dCASQ-null vs. WT fibers. Significant differences in the baseline [Ca(2+)]mito were observed between quiescent WT and dCASQ-null fibers, but not in the resting cytosolic Ca(2+) concentration. The rise in [Ca(2+)]mito during electrical stimulation occurred in 20-30 ms, while the decline during and after stimulation was governed by 4 rate constants of approximately 40, 1.6, 0.2 and 0.03 s(-1). Accordingly, frequency-dependent increase in [Ca(2+)]mito occurred during sustained contractions. In dCASQ-null fibers the increases in [Ca(2+)]mito were less pronounced than in WT fibers and even lower when extracellular calcium was removed. The amplitude and duration of [Ca(2+)]mito transients were increased by inhibition of mitochondrial Na(+)/Ca(2+) exchanger (mNCX). These results provide direct evidence for fast Ca(2+) accumulation inside the mitochondria, involvement of the mNCX in mitochondrial Ca(2+)-handling and a dependence of mitochondrial Ca(2+)-handling on intracellular (SR) and external Ca(2+) stores in fast skeletal muscle fibers. dCASQ-null mice represent a model for malignant hyperthermia. The differences in structure and in mitochondrial function observed relative to WT may represent compensatory mechanisms for the disease-related reduction of calcium storage capacity of the SR and/or SR Ca(2+)-leakage.

Myosin isoforms and contractile properties of single fibers of human Latissimus Dorsi muscle.

The aim of our study was to investigate fiber type distribution and contractile characteristics of Latissimus Dorsi muscle (LDM). Samples were collected from 18 young healthy subjects (9 males and 9 females) through percutaneous fine needle muscle biopsy. The results showed a predominance of fast myosin heavy chain isoforms (MyHC) with 42% of MyHC 2A and 25% of MyHC 2X, while MyHC 1 represented only 33%. The unbalance toward fast isoforms was even greater in males (71%) than in females (64%). Fiber type distribution partially reflected MyHC isoform distribution with 28% type 1/slow fibers and 5% hybrid 1/2A fibers, while fast fibers were divided into 30% type 2A, 31% type A/X, 4% type X, and 2% type 1/2X. Type 1/slow fibers were not only less abundant but also smaller in cross-sectional area than fast fibers. During maximal isometric contraction, type 1/slow fibers developed force and tension significantly lower than the two major groups of fast fibers. In conclusion, the predominance of fast fibers and their greater size and strength compared to slow fibers reveal that LDM is a muscle specialized mainly in phasic and powerful activity. Importantly, such specialization is more pronounced in males than in females.

Latissimus dorsi fine needle muscle biopsy: a novel and efficient approach to study proximal muscles of upper limbs.

BACKGROUND: The muscle biopsy based on the Bergström needle has been widely used for more than 40 y for diagnosis and experimental studies on muscle. More recently, thinner needles and tru-cut needles have also been introduced. Such techniques have been largely tested on various muscles, including the quadriceps, with few studies on upper limb muscles like deltoid, and no studies on latissimus dorsi muscle (LDM). In this study, we implemented and validated a protocol to collect samples of LDM for experimental purposes, causing minimal discomfort to volunteers. Two main problems were considered: the anatomical localization of the biopsy site and the selection of an appropriate needle. MATERIAL AND METHODS: A strict protocol of palpatory anatomy was adopted and validated with ultrasonography to localize the biopsy site in LDM in subjects with various degrees of muscle development. A 14 gauge tru-cut needle was selected as the smallest and still effective device for sampling. Biopsy sampling was performed in 18 subjects without any complications, or complains of pain or functional limitations. RESULTS: Approximately 4 mg of tissue were recovered from each introduction of the inner notched cannula of the needle. With three consecutive samplings, an amount of tissue sufficient to prepare proteins for gel electrophoresis and Western blot and to dissect single fiber segment for functional experiments, was obtained. CONCLUSIONS: Taken together, the results suggest that this biopsy technique opens to experimental studies muscles until now never considered accessible.

Effects of local vibrations on skeletal muscle trophism in elderly people: mechanical, cellular, and molecular events.

Several studies have examined the effects of vibrations on muscle mass and performance in young healthy people. We studied the effects of vibrations on muscles of elderly male and female volunteers (65-85 years of age) diagnosed with sarcopenia. We applied mechanical vibrations locally (local vibrational training) to the thigh muscles at 300 Hz for a period of 12 weeks, starting with a session of 15 min stimulation once a week and increasing to three sessions of 15 min per week. Treated muscles displayed enhanced maximal isometric strength and increased content of fast MyHC-2X myosin. Single muscle fiber analysis did not show any change in cross-sectional area or in specific tension. Analysis of transcriptional profiles by microarray revealed changes in gene expression after 12 weeks of local vibrational training. In particular, pathways related with energy metabolism, sarcomeric protein balance and oxidative stress response were affected. We conclude that vibration treatment is effective in counteracting the loss of muscular strength associated with sarcopenia and the mode of action of vibration is based on cellular and molecular changes which do not include increase in fiber or muscle size.

Inducible activation of Akt increases skeletal muscle mass and force without satellite cell activation.

A better understanding of the signaling pathways that control muscle growth is required to identify appropriate countermeasures to prevent or reverse the loss of muscle mass and force induced by aging, disuse, or neuromuscular diseases. However, two major issues in this field have not yet been fully addressed. The first concerns the pathways involved in leading to physiological changes in muscle size. Muscle hypertrophy based on perturbations of specific signaling pathways is either characterized by impaired force generation, e.g., myostatin knockout, or incompletely studied from the physiological point of view, e.g., IGF-1 overexpression. A second issue is whether satellite cell proliferation and incorporation into growing muscle fibers is required for a functional hypertrophy. To address these issues, we used an inducible transgenic model of muscle hypertrophy by short-term Akt activation in adult skeletal muscle. In this model, Akt activation for 3 wk was followed by marked hypertrophy ( approximately 50% of muscle mass) and by increased force generation, as determined in vivo by ankle plantar flexor stimulation, ex vivo in intact isolated diaphragm strips, and in single-skinned muscle fibers. No changes in fiber-type distribution and resistance to fatigue were detectable. Bromodeoxyuridine incorporation experiments showed that Akt-dependent muscle hypertrophy was accompanied by proliferation of interstitial cells but not by satellite cell activation and new myonuclei incorporation, pointing to an increase in myonuclear domain size. We can conclude that during a fast hypertrophic growth myonuclear domain can increase without compromising muscle performance.