1,721,054 research outputs found
Strenuous exercise triggers a life-threatening response in mice susceptible to malignant hyperthermia
No full textIn humans, hyperthermic episodes can be triggered by halogenated anesthetics [malignant hyperthermia (MH) susceptibility] and by high temperature [environmental heat stroke (HS)]. Correlation between MH susceptibility and HS is supported by extensive work in mouse models that carry a mutation in ryanodine receptor type-1 (RYR1Y522S/WT) and calsequestrin-1 knockout (CASQ1-null), 2 proteins that control Ca2+ release in skeletal muscle. As overheating episodes in humans have also been described during exertion, here we subjected RYR1Y522S/WT and CASQ1-null mice to an exertional-stress protocol (incremental running on a treadmill at 34°C and 40% humidity). The mortality rate was 80 and 78.6% in RYR1Y522S/WT and CASQ1-null mice, respectively, vs. 0% in wild-type mice. Lethal crises were characterized by hyperthermia and rhabdomyolysis, classic features of MH episodes. Of importance, pretreatment with azumolene, an analog of the drug used in humans to treat MH crises, reduced mortality to 0 and 12.5% in RYR1Y522S/WT and CASQ1-null mice, respectively, thanks to a striking reduction of hyperthermia and rhabdomyolysis. At the molecular level, azumolene strongly prevented Ca2+dependent activation of calpains and NF-kB by lowering myoplasmic Ca2+ concentration and nitro-oxidative stress, parameters that were elevated in RYR1Y522S/WT and CASQ1-null mice. These results suggest that common molecular mechanisms underlie MH crises and exertional HS in mice.—Michelucci, A., Paolini, C., Boncompagni, S., Canato, M., Reggiani, C., Protasi, F. Strenuous exercise triggers a life-threatening response in mice susceptible to malignant hyperthermia
Structural differentiation of skeletal muscle fibers in the absence of innervation in humans.
Full text linkProc Natl Acad Sci U S A. 2007 Dec 4;104(49):19339-44. Epub 2007 Nov 27.
Structural differentiation of skeletal muscle fibers in the absence of innervation in humans.
Boncompagni S, Kern H, Rossini K, Hofer C, Mayr W, Carraro U, Protasi F.
Source
Interuniversitary Institute of Miology, Centro Scienze dell'Invecchiamento, Università degli Studi G. d'Annunzio, I-66013 Chieti, Italy.
Abstract
The relative importance of muscle activity versus neurotrophic factors in the maintenance of muscle differentiation has been greatly debated. Muscle biopsies from spinal cord injury patients, who were trained with an innovative protocol of functional electrical stimulation (FES) for prolonged periods (2.4-9.3 years), offered the unique opportunity of studying the structural recovery of denervated fibers from severe atrophy under the sole influence of muscle activity. FES stimulation induced surprising recovery of muscle structure, mass, and force even in patients whose muscles had been denervated for prolonged periods before the beginning of FES training (up to 2 years) and had almost completely lost muscle-specific internal organization. Ninety percent (or more) of the fibers analyzed by electron microscopy showed a striking recovery of the ultrastructural organization of myofibrils and Ca(2+)-handling membrane systems. This functional/structural restoration follows a pattern that mimics some aspects of normal muscle differentiation. Most importantly, the recovery occurs in the complete absence of motor and sensory innervation and of nerve-derived trophic factors, that is, solely under the influence of muscle activity induced by electrical stimulation.
PMID:
18042706
[PubMed - indexed for MEDLINE]
PMCID: PMC2148291
Free PMC Articl
Atrophy-resistant fibers in permanent peripheral denervation of human skeletal muscle
No full textNeurol Res. 2008 Mar;30(2):137-44.
Atrophy-resistant fibers in permanent peripheral denervation of human skeletal muscle.
Biral D, Kern H, Adami N, Boncompagni S, Protasi F, Carraro U.
Source
Italian C.N.R. Institute of Neuroscience, and Laboratory of Translational Myology, Interdepartmental Research Center of Myology, c/o Department of Biomedical Sciences, University of Padova, I-35121 Padova, Italy.
Abstract
OBJECTIVE:
Human muscle fibers usually undergo severe atrophy/degeneration as a result of long-term peripheral denervation. However, some biopsies from paraplegic patients suffering complete conus cauda syndrome display the presence of a small percentage of muscle fibers with a very large diameter (big fibers). The objective of the present study is to determine if these big fibers are the result of residual innervation/reinnervation, or if instead they are fibers resistant to atrophy.
METHODS:
Human muscle biopsies were harvested from the vastus lateralis of spinal cord injury (SCI) patients affected by complete lower motor neuron lesion (LML). The specimens were either processed for light microscopy or embedded for electron microscopy (EM).
RESULTS:
Our results indicate that the big fibers are neither the results of residual innervation or sparse reinnervation. In spite of the fact that the extrasynaptic NCAM immunostaining disappear a few months after SCI, the big fibers are characterized by positive molecular markers of denervation, that is, the differential labeling of their dystrophin molecule by anti-C and anti-N terminals antibodies. Furthermore, the EM analysis shows that these cells present the peculiar ultrastructural disarrangements of the contractile apparatus and of the internal membrane systems characteristic of 'peripheral denervation'. No fibers presenting large areas of cross-striation were found. The EM analysis provides the final evidence that these big fibers are muscle fibers which are indeed denervated, very different from normal and/or disused (e.g. upper motor neuron lesion) muscle fibers.
DISCUSSION:
Although these large muscle fibers are surprisingly more frequent in human muscle biopsies after 3 years from SCI than earlier, it remains to be determined whether their presence in some biopsies but not in others is caused by sampling, or is related to other factors such as to subjects' background genetics, or the extent of passive stretching induced by different rehabilitation strategies.
PMID:
18397604
[PubMed - indexed for MEDLINE
Improper Remodeling of Organelles Deputed to Ca 2+ Handling and Aerobic ATP Production Underlies Muscle Dysfunction in Ageing
Full text linkProper skeletal muscle function is controlled by intracellular Ca2+ concentration and by efficient production of energy (ATP), which, in turn, depend on: (a) the release and re-uptake of Ca2+ from sarcoplasmic-reticulum (SR) during excitation–contraction (EC) coupling, which controls the contraction and relaxation of sarcomeres; (b) the uptake of Ca2+ into the mitochondrial matrix, which stimulates aerobic ATP production; and finally (c) the entry of Ca2+ from the extracellular space via store-operated Ca2+ entry (SOCE), a mechanism that is important to limit/delay muscle fatigue. Abnormalities in Ca2+ handling underlie many physio-pathological conditions, including dysfunction in ageing. The specific focus of this review is to discuss the importance of the proper architecture of organelles and membrane systems involved in the mechanisms introduced above for the correct skeletal muscle function. We reviewed the existing literature about EC coupling, mitochondrial Ca2+ uptake, SOCE and about the structural membranes and organelles deputed to those functions and Finally, we summarized the data collected in different, but complementary, projects studying changes caused by denervation and ageing to the structure and positioning of those organelles: a. denervation of muscle fibers—an event that contributes, to some degree, to muscle loss in ageing (known as sarcopenia)—causes misplacement and damage: (i) of membrane structures involved in EC coupling (calcium release units, CRUs) and (ii) of the mitochondrial network; b. sedentary ageing causes partial disarray/damage of CRUs and of calcium entry units (CEUs, structures involved in SOCE) and loss/misplacement of mitochondria; c. functional electrical stimulation (FES) and regular exercise promote the rescue/maintenance of the proper architecture of CRUs, CEUs, and of mitochondria in both denervation and ageing. All these structural changes were accompanied by related functional changes, i.e., loss/decay in function caused by denervation and ageing, and improved function following FES or exercise. These data suggest that the integrity and proper disposition of intracellular organelles deputed to Ca2+ handling and aerobic generation of ATP is challenged by inactivity (or reduced activity); modifications in the architecture of these intracellular membrane systems may contribute to muscle dysfunction in ageing and sarcopenia
Stable muscle atrophy in long-term paraplegics with complete upper motor neuron lesion from 3- to 20-year SCI.
No full textSpinal Cord. 2008 Apr;46(4):293-304. Epub 2007 Oct 23.
Stable muscle atrophy in long-term paraplegics with complete upper motor neuron lesion from 3- to 20-year SCI.
Kern H, Hofer C, Mödlin M, Mayr W, Vindigni V, Zampieri S, Boncompagni S, Protasi F, Carraro U.
Source
Department of Physical Medicine, Ludwig Boltzmann Institute of Electrostimulation and Physical Rehabilitation, Wilhelminenspital, Vienna, Austria.
Abstract
STUDY DESIGN:
Unrandomized trial.
OBJECTIVES:
To investigate the structural and functional relationships and the progression of muscle atrophy up to 20 years of spastic paraplegia.
SETTING:
Clinical follow-up in Vienna, Austria; muscle biopsies analyzed by light microscopy in Padova and by electron microscopy (EM) in Chieti, Italy.
METHODS:
Force was measured as knee extension torque; trophism by computer tomography scan; tissue composition and fiber morphology by histopathology and EM.
RESULTS:
In the long-term group of patients (17.0+/-2.6 years), force and size of thigh muscles were only slightly different from those of mid-term subjects (2.2+/-0.5 years). Histology and ultrastructure confirm that the difference in average size of muscle fibers between long-term and mid-term paralyzed leg muscles is actually very small. In addition, muscle fibers maintain the striated appearance characteristic of normal skeletal fibers even after 14-20 years of paralysis. Ultrastructural alterations of the activating and metabolic machineries, and the presence of fibers with lower motor neuron denervation features, may explain the low-force output and the reduced endurance of paretic muscles.
CONCLUSION:
The stable muscle atrophy that characterizes long-lasting spastic paraplegia suggests that there are no upper-time limits to begin a training program based on functional electrical stimulation.
PMID:
17955034
[PubMed - indexed for MEDLINE
Long-Term Exercise Reduces Formation of Tubular Aggregates and Promotes Maintenance of Ca2+ Entry Units in Aged Muscle
No full textTubular aggregates (TAs) in skeletal muscle fibers are unusual accumulation of sarcoplasmic reticulum (SR) tubes that are found in different disorders including TA myopathy (TAM). TAM is a muscular disease characterized by muscle pain, cramping, and weakness that has been recently linked to mutations in STIM1 and ORAI1. STIM1 and ORAI1 are the two main proteins mediating store-operated Ca2+ entry (SOCE), a mechanism activated by depletion of intracellular Ca2+ stores (e.g., SR) that allows recovery of Ca2+ from the extracellular space during repetitive muscle activity. We have recently shown that exercise triggers the formation of unique intracellular junctions between SR and transverse tubules named Ca2+ entry units (CEUs). CEUs promote colocalization of STIM1 with ORAI1 and improve muscle function in presence of external Ca2+. TAs virtually identical to those of TAM patients are also found in fast-twitch fibers of aging male mice. Here, we used a combination of electron and confocal microscopy, Western blotting, and ex vivo stimulation protocols (in presence or absence of external Ca2+) to evaluate the presence of TAs, STIM1-ORAI1 localization and expression and fatigue resistance of intact extensor digitorum longus (EDL) muscles in wild-type male adult (4-month-old) and aged (24-month-old) mice and in mice trained in wheel cages for 15 months (from 9 to 24 months of age). The results collected indicate that (i) aging causes STIM1 and ORAI1 to accumulate in TAs and (ii) long-term exercise significantly reduced formation of TAs. In addition, (iii) EDL muscles from aged mice exhibited a faster decay of contractile force than adult muscles, likely caused by their inability to refill intracellular Ca2+ stores, and (iv) exercise in wheel cages restored the capability of aged EDL muscles to use external Ca2+ by promoting maintenance of CEUs. In conclusion, exercise prevented improper accumulation of STIM1 and ORAI1 in TAs during aging, maintaining the capability of aged muscle to refill intracellular Ca2+ stores via SOCE
Store-operated calcium entry: From physiology to tubular aggregate myopathy
No full textStore-Operated Ca2+ entry (SOCE) is recognized as a key mechanism in muscle physiology necessary to refill intracellular Ca2+ stores during sustained muscle activity. For many years the cell structures expected to mediate SOCE in skeletal muscle fibres remained unknown. Recently, the identification of Ca2+ Entry Units (CEUs) in exercised muscle fibres opened new insights into the role of extracellular Ca2+ in muscle contraction and, more generally, in intracellular Ca2+ homeostasis. Accordingly, intracellular Ca2+ unbalance due to alterations in SOCE strictly correlates with muscle disfunction and disease. Mutations in proteins involved in SOCE (STIM1, ORAI1, and CASQ1) have been linked to tubular aggregate myopathy (TAM), a disease that causes muscle weakness and myalgia and is characterized by a typical accumulation of highly ordered and packed membrane tubules originated from the sarcoplasmic reticulum (SR). Achieving a full understanding of the molecular pathways activated by alterations in Ca2+ entry mechanisms is a necessary step to design effective therapies for human SOCE-related disorders
Altered Ca2+ handling and oxidative stress underlie mitochondrial damage and skeletal muscle dysfunction in aging and disease
No full textSkeletal muscle contraction relies on both high-fidelity calcium (Ca2+) signals and robust capacity for adenosine triphosphate (ATP) generation. Ca2+ release units (CRUs) are highly organized junctions between the terminal cisternae of the sarcoplasmic reticulum (SR) and the transverse tubule (T-tubule). CRUs provide the structural framework for rapid elevations in myoplasmic Ca2+ during excitation–contraction (EC) coupling, the process whereby depolarization of the T-tubule membrane triggers SR Ca2+ release through ryanodine receptor-1 (RyR1) channels. Under conditions of local or global depletion of SR Ca2+ stores, store-operated Ca2+ entry (SOCE) provides an additional source of Ca2+ that originates from the extracellular space. In addition to Ca2+, skeletal muscle also requires ATP to both produce force and to replenish SR Ca2+ stores. Mitochondria are the principal intracellular organelles responsible for ATP production via aerobic respiration. This review provides a broad overview of the literature supporting a role for impaired Ca2+ handling, dysfunctional Ca2+-dependent production of reactive oxygen/nitrogen species (ROS/RNS), and structural/functional alterations in CRUs and mitochondria in the loss of muscle mass, reduction in muscle contractility, and increase in muscle damage in sarcopenia and a wide range of muscle disorders including muscular dystrophy, rhabdomyolysis, central core disease, and disuse atrophy. Understanding the impact of these processes on normal muscle function will provide important insights into potential therapeutic targets designed to prevent or reverse muscle dysfunction during aging and disease
Estrogens Protect Calsequestrin-1 Knockout Mice from Lethal Hyperthermic Episodes by Reducing Oxidative Stress in Muscle
No full textOxidative stress has been proposed to play a key role in malignant hyperthermia (MH), a syndrome caused by excessive Ca2+ release in skeletal muscle. Incidence of mortality in male calsequestrin-1 knockout (CASQ1-null) mice during exposure to halothane and heat (a syndrome closely resembling human MH) is far greater than that in females. To investigate the possible role of sex hormones in this still unexplained gender difference, we treated male and female CASQ1-null mice for 1 month, respectively, with Premarin (conjugated estrogens) and leuprolide (GnRH analog) and discovered that during exposure to halothane and heat Premarin reduced the mortality rate in males (79-27% and 86-20%), while leuprolide increased the incidence of mortality in females (18-73% and 24-82%). We then evaluated the (a) responsiveness of isolated muscles to temperature and caffeine, (b) sarcoplasmic reticulum (SR) Ca2+ release in single fibers, and (c) oxidative stress and the expression levels of main enzymes involved in the regulation of the redox balance in muscle. Premarin treatment reduced the temperature and caffeine sensitivity of EDL muscles, normalized SR Ca2+ release, and reduced oxidative stress in males, suggesting that female sex hormones may protect mice from lethal hyperthermic episodes by reducing both the SR Ca2+ leak and oxidative stress
Long-term denervation in humans causes degeneration of both contractile and excitation-contraction coupling apparatus, which is reversible by functional electrical stimulation (FES): a role for myofiber regeneration?
No full textJ Neuropathol Exp Neurol. 2004 Sep;63(9):919-31.
Long-term denervation in humans causes degeneration of both contractile and excitation-contraction coupling apparatus, which is reversible by functional electrical stimulation (FES): a role for myofiber regeneration?
Kern H, Boncompagni S, Rossini K, Mayr W, Fanò G, Zanin ME, Podhorska-Okolow M, Protasi F, Carraro U.
Source
From Ludwig Boltzmann Institute of Electrostimulation and Physical Rehabilitation, Department of Physical Medicine, Wilhelminenspital, Vienna, Austria.
Abstract
Over the last 30 years there has been considerable interest in the use of functional electrical stimulation (FES) to restore movement to the limbs of paralyzed patients. Spinal cord injury causes a rapid loss in both muscle mass and contractile force. The atrophy is especially severe when the injury involves lower motoneurons because many months after spinal cord injury, atrophy is complicated by fibrosis and fat substitution. In this study we describe the effects of long-term lower motoneuron denervation of human muscle and present the structural results of muscle trained using FES. By means of an antibody for embryonic myosin, we demonstrate that many regenerative events continue to spontaneously occur in human long-term denervated and degenerated muscle (DDM). In addition, using electron microscopy, we describe i) the overall structure of fibers and myofibrils in long-term denervated and degenerated muscle, including the effects of FES, and ii) the structure and localization of calcium release units, or triads; the structures reputed to activate muscle contraction during excitation-contraction coupling (ECC). Both apparatus undergo disarrangement and re-organization following long-term denervation and FES, respectively. The poor excitability of human long-term DDM fibers, which extends to the first periods of FES training, may be explained in terms of the spatial disorder of the ECC apparatus. Its disorganization and re-organization following long-term denervation and FES, respectively, may play a key role in the parallel disarrangement and re-organization of the myofibrils that characterize denervation and FES training. The present structural studies demonstrate that the protocol used during FES training is effective in reverting long-term denervation atrophy and dystrophy. The mean fiber diameter in FES biopsies is 42.2 +/- 14.8 SD (p < 0.0001 vs DDM 14.9 +/- 6.0 SD); the mean percentile of myofiber area of the biopsy is 94.3 +/- 5.7 SD (p < 0.0001 vs DDM 25.7 +/- 23.7 SD); the mean percentile fat area is 2.1 +/- 2.4 SD (p < 0.001 vs DDM 12.8 +/- 12.1 SD); and the mean percentile connective tissue area is 3.6 +/- 4.6 SD (p < 0.001 vs DDM 61.6 +/- 20.1 SD). In DDM biopsies more than 50% of myofibers have diameter smaller than 10 microm, while the FES-trained subjects have more that 50% of myofibers larger than 30 microm. The recovery of muscle mass seems to be the result of both a size increase of the surviving fibers and the regeneration of new myofibers.
PMID:
15453091
[PubMed - indexed for MEDLINE
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