Fiber Atrophy Research Articles

Muscle Disuse Atrophy Caused by Discord of Intracellular Signaling.

Significance: Regular contractile activity plays a critical role in maintaining skeletal muscle morphological integrity and physiological function. If the muscle is forced to stop contraction, such as during limb immobilization (IM), the IGF/Akt/mTOR signaling pathway that normally stimulates protein synthesis and inhibits proteolysis will be suppressed, whereas the FoxO-controlled catabolic pathways such as ubiquitin-proteolysis and autophagy/mitophagy will be activated and dominate, resulting in muscle fiber atrophy. Recent Advances: Mitochondria occupy a central position in the regulation of both protein synthesis and degradation through several redox-sensitive pathways, including peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), mitochondrial fusion and fission proteins, mitophagy, and sirtuins. Prolonged IM downregulates PGC-1α due to AMPK (5'-AMP-activated protein kinase) and FoxO activation, thus decreasing mitochondrial biogenesis and causing oxidative damage. Decrease of mitochondrial inner membrane potential and increase of mitochondrial fission can trigger cascades of mitophagy leading to loss of mitochondrial homeostasis (mitostasis), inflammation, and apoptosis. The phenotypic outcomes of these disorders are compromised muscle function and fiber atrophy. Critical Issues: Given the molecular mechanism of the pathogenesis, it is imperative that the integrity of intracellular signaling be restored to prevent the deterioration. So far, overexpression of PGC-1α via transgene and in vivo DNA transfection has been found to be effective in ameliorating mitostasis and reduces IM-induced muscle atrophy. Nutritional supplementation of select amino acids and phytochemicals also provides mechanistic and practical insights into the prevention of muscle disuse atrophy. Future Directions: In light of the importance of mitochondria in regulating the various critical signaling pathways, future work should focus on exploring new epigenetic strategies to restore mitostasis and redox balance.

Familial dropped head syndrome with extremity muscle weakness

AbstractWe report a new case of familial dropped head syndrome (DHS) due to myopathy. The proband is a 63‐year‐old woman, and her younger sister and son also showed DHS. She was not good at sport since elementary school and showed unique muscle weakness in her paraspine and four limbs. A blood test showed a slight increase in creatine kinase (237 IU/mL) and myoglobin (95 ng/mL). An electromyogram showed myogenic change, and computed tomography revealed a normal muscle volume of the neck but paraspinal muscle atrophy. Muscle biopsy of the right femoral muscle found type 2 fiber atrophy. Based on these unique clinical features, this is the first report of familial DHS which probably due to congenital myopathy.

The concept of skeletal muscle memory: Evidence from animal and human studies.

Within the current paradigm of the myonuclear domain theory, it is postulated that a linear relationship exists between muscle fibre size and myonuclear content. The myonuclear domain is kept (relatively) constant by adding additional nuclei (supplied by muscle satellite cells) during muscle fibre hypertrophy and nuclear loss (by apoptosis) during muscle fibre atrophy. However, data from recent animal studies suggest that myonuclei that are added to support muscle fibre hypertrophy are not lost within various muscle atrophy models. Such myonuclear permanence has been suggested to constitute a mechanism allowing the muscle fibre to (re)grow more efficiently during retraining, a phenomenon referred to as “muscle memory.” The concept of “muscle memory by myonuclear permanence” has mainly been based on data attained from rodent experimental models. Whether the postulated mechanism also holds true in humans remains largely ambiguous. Nevertheless, there are several studies in humans that provide evidence to potentially support or contradict (parts of) the muscle memory hypothesis. The goal of the present review was to discuss the evidence for the existence of “muscle memory” in both animal and human models of muscle fibre hypertrophy as well as atrophy. Furthermore, to provide additional insight in the potential presence of muscle memory by myonuclear permanence in humans, we present new data on previously performed exercise training studies. Finally, suggestions for future research are provided to establish whether muscle memory really exists in humans.

Intraoperative Hemidiaphragm Stimulation Offsets Slow‐Twitch Muscle Fiber Atrophy and Contractile Dysfunction

Prolonged mechanical ventilation induces considerable atrophy of slow‐ and fast‐twitch fibers in the human diaphragm. In pilot work, we detected early atrophy and specific force decrement in fast‐twitch fibers of patients following an average 4.6‐hour thoracic operations. We now present interim data from a larger controlled trial of diaphragm stimulation as a means to reduce slow‐ and fast‐twitch‐ fiber atrophy and metabolic derangements that occur with mechanical ventilation. We hypothesized that intraoperative hemidiaphragm would mitigate both slow‐ and fast‐twitch fiber contractile dysfunction in the human diaphragm. Twelve adults (6F, age 62 ±12 years) consented to participate in this IRB‐approved study. During cardiothoracic surgical procedures, one hemidiaphragm underwent 1 minute of electrical phrenic nerve stimulation every 30 minutes (30 twitches/minute, 1.5 milliseconds pulse duration, amplitude variable to produce a strong twitch contraction, up to 25 mA), while the contralateral hemidiaphragm remained inactive. Thirty minutes following the last stimulation bout, biopsies were obtained from both hemidiaphragms. Muscle fibers were buffered, permeabilized, and separated for evaluation of cross‐sectional area and force‐generating properties. A mixed effects model with random intercept for each subject was used to evaluate the fixed effects of stimulation and fiber type on single‐fiber force mechanics, and significance was p<0.05. Subjects underwent an average 7 ±2 hemidiaphragm stimulations at 17 ±2 mA, and biopsies were collected after 4.75 ±1.03 hours of mechanical ventilation. Cross‐sectional area of unstimulated slow‐twitch fibers was significantly smaller than stimulated slow‐twitch fibers (5632 ±349 vs 4619 ±247 μM2), with no effect on fast‐twitch fibers (5631 ±350 vs 5768 ±351 μM2), [p<0.005]. Likewise, stimulation resulted in significantly higher specific force of slow‐twitch (106 ±6 vs 97 ±6 kN/m2), but not fast‐twitch diaphragm single fibers (126 ±6 vs 130 ±6 kN/m2), [p<0.001]. Stimulation did not appreciably alter fiber calcium‐sensitivity properties of either fiber type. Our data suggest that stimulation attenuates diaphragm slow‐twitch fiber atrophy and contractile dysfunction induced by mechanical ventilation. Fiber type‐specific changes with short periods of mechanical ventilation may be attributed to predominant slow fiber recruitment during tidal breathing.Support or Funding InformationThis work was supported by National Institute of Arthritis and Musculoskeletal and Skin Diseases, award R01 AR072328

Ca2+ Sensitivity of Limb Muscle Fibers in Young and Older Adults

Age‐induced declines in skeletal muscle contractile function have been attributed to multiple cellular factors, including a loss of peak force (PO), decreased Ca2+ sensitivity, and reduced shortening velocity (VO). However, changes in these cellular properties with aging remain unresolved, especially in older women, and the effect of submaximal Ca2+ on contractile function is unknown. Thus, we compared contractile properties of muscle fibers from 19 young (24±3 years; 11 women) and 21 older adults (77±7 years; 7 women) under maximal and submaximal Ca2+ and assessed the abundance of three proteins thought to influence Ca2+ sensitivity. Fast fibers showed marked atrophy with aging in both men (young=8,599 μm2; old=5,404 μm2) and women (young=4,909 μm2; old=3,174 μm2) that corresponded with a decreased absolute PO in men (young=1.48 mN; old=0.92 mN) and women (young=0.85 mN; old=0.60 mN). There were no differences in fast fiber size‐specific PO, indicating the age‐related decline in force was explained by differences in fiber size. Except for fiber size and absolute PO, no age or sex differences were observed in Ca2+ sensitivity, rate of force development (ktr), or VO. Submaximal Ca2+ depressed ktr and VO, but the effects were not altered by age in either sex. Contrary to rodent studies, regulatory light chain (RLC) and myosin binding protein‐C abundance and RLC phosphorylation were unaltered by age or sex. These data suggest the age‐induced decline in whole‐muscle contractile function is primarily due to the atrophy of fast fibers and that caution is warranted when extending results from rodent studies to humans.Support or Funding InformationNational Institute on Aging grant (R01AG048262) to Robert Fitts and Sandra Hunter and an American Heart Association postdoctoral fellowship (19POST34380411) to Christopher Sundberg

Tracheobronchomegaly, cough and recurrent chest infection: Mounier-Kuhn syndrome.

Mounier-Kuhn Syndrome (MKS) is a rare disease characterised by recurrent chest infections, and dilation of the trachea and main bronchi, most likely to due to atrophy of elastic fibres https://bit.ly/3azhDjr

Age‐Related Loss of Phrenic Motor Neurons: Reduced Myogenic Influence?

There is an age‐associated loss of phrenic motor neurons (PhMNs) and withdrawal of pre‐synaptic terminals at neuromuscular junctions (NMJs) in 24‐month old Fischer 344 (F344) rats. Previously, we showed that age‐related PhMN loss is concomitant with neuromuscular transmission failure and diaphragm muscle (DIAm) sarcopenia (an age‐related atrophy of muscle fibers and a decrease in specific force). It is unknown if pre‐synaptic terminal withdrawal precedes PhMN loss, which would implicate a reduction in a trophic influence emanating from muscle fibers (myogenic). We hypothesized that age‐related PhMN loss results from pre‐synaptic terminal withdrawal and reduced myogenic influence, which occurs predominantly at type IIx and/or IIb DIAm fibers (innervated by larger PhMNs). F344 rats were obtained from the National Institutes of Aging. Experimental ages were chosen to represent 100% and 50% survival at 6 months and 24 months‐old, respectively. PhMNs were first retrogradely labeled by intrapleural injection of cholera toxin‐subunit B (CTB), which is dependent on binding to pre‐synaptic terminal gangliosides. Thus, with pre‐synaptic terminal withdrawal, PhMNs would not be labeled. Subsequently (3 days after CTB), PhMNs were retrogradely labeled by sectioning the phrenic nerve and dipping the proximal end into a Rhodamine dextran (Rho) solution – this labeling is not dependent on pre‐synaptic terminals. CTB and Rho labeled PhMNs were visualized by confocal microscopy. Only optical slices containing the nucleus of Rho‐ and/or CTB‐labeled PhMNs were counted. We analyzed the differences in labeling of PhMNs by CTB and Rho in both age groups. In labeled PhMNs, short and long axis measurements were used to determine somal surface areas by assuming a prolate spheroid shape. In 6‐month old rats, there was no significant difference in the number of PhMNs labeled by CTB or Rho. In 24‐month old rats, the total number of labeled PhMNs was reduced compared to the 6‐month old rats, which primarily affected larger PhMNs. Furthermore, at 24‐months, fewer PhMNs were labeled with CTB compared to Rho and those labeled with Rho had larger somal surface areas. These results support our hypothesis that the age‐related loss of larger PhMNs results from pre‐synaptic terminal withdrawal and reduced myogenic influence.Support or Funding InformationSupport: NIH R01‐AG044615American Physiological Society

Early Biomarkers of Muscle Atrophy and of Neuromuscular Alterations During 10‐Day Bed Rest

IntroductionDisuse atrophy may not only arise from a reduction in mechanical loading but also from muscle denervation and neuromuscular junction damage, triggered by inactivity [1, 2]. The identification of biomarkers of muscle atrophy and of neuromuscular degeneration is therefore needed for an early detection of neuromuscular alterations induced by inactivity. The aim of this study was to investigate the onset of muscle atrophy and of neuromuscular alterations during a short‐term inactivity period.MethodsTen healthy males (aged 23±5 years) participated to a 10‐day bed rest (BR) study, after Ethical approval and informed consent. Blood samples were collected every two days for the assessment of NMJ damage from serum levels of c‐terminal agrin fragment (CAF). Muscle fibre denervation was determined from the expression of neural cell adhesive molecule (N‐CAM) in myofibres obtained from vastus lateralis (VL) muscle biopsies at baseline, 5 and 10 days of BR. Myofibre atrophy was assessed from mean fibre cross‐sectional area (CSA). Whole muscle atrophy was assessed from measurements of muscle architecture (pennation angle and muscle CSA) every two days of BR using ultrasonography. Significance of differences was tested with repeated‐measures Anova, level of significance was set at p<0.05.ResultsAtrophy of whole muscle and of myofibers, represented by decreases of 5.8% in muscle CSA (P<0.0001), 7.3% in pennation angle (P<0.0001), and by a 21% reduction in mean fibre CSA (P<0.01) were detected after 10 days of BR. A 19% increase (p<0.01) in CAF levels was found on BR day 10, together with a 18‐fold increase in N‐CAM positive myofibres. The analysis of myofiber CSA and N‐CAM expression at BR 5 day is in progress.ConclusionsThese findings show a very early onset (within 10 days) of whole muscle and fiber atrophy accompanied by NMJ damage and myofiber denervation in response to chronic inactivity. We suggest that countermeasures against neuromuscular maladaptation to chronic inactivity ought to be implemented as early as possible.Support or Funding InformationFunding by ASI, MARS‐PRE Project, n. DC‐VUM‐2017‐006, is acknowledged.

A comparative study of "constant volume" animal model and "constant pressure" animal model of intra-abdominal hypertension

To select the animal model more consistent with the pathophysiology of abdominal compartment syndrome (ACS) through the comparative study of the methods of multiple water sacs superimposed compression and gas perfusion. Ten experimental pigs were randomly divided into two groups (n = 5): the "constant volume model" (constant volume model group) and the "constant pressure model" (constant pressure model group) of intra-abdominal hypertension. The models were prepared by the method of water sac superposition and pressurization, and artificial pneumoperitoneum respectively. The abdominal pressures of both groups were 25 mmHg (1 mmHg = 0.133 kPa) and observed for 4 hours. The pressure was measured once an hour for 4 hours and the pressure-time curves of the two groups were drawn respectively. The experimental animals were sacrificed 4 hours after modeling. The heart and lung were harvested, and the histopathological changes were observed by hematoxylin-eosin (HE) staining. Two groups of experimental pigs were successfully modeled. The abdominal pressure gradually increased at 0, 1, 2, 3, 4 hours after operation in the constant volume model group (mmHg: 25.0±0, 27.1±0.2, 29.4±0.1, 30.9±0.2, 33.1±0.1), and there was a positive correlation between the abdominal pressure and time (functional equation: Y1 = 25.102 0+1.996 0X1; R2 = 0.996 2, P = 0.000 1). The abdominal pressure value in the constant pressure model group at 0, 1, 2, 3, 4 hours were maintained 25 mmHg, and there was no linear correlation between the abdominal pressure and time (functional equation: Y2 = 25). HE staining showed that in the constant volume model group, the myocardial fibers were accompanied with hyaline degeneration, significantly reduced transverse lines, part of myocardial fiber atrophy, and visible nuclear aggregation; hemorrhage, chronic inflammatory cell infiltration and inflammatory exudation were found in the lung tissues. In the constant pressure model group, partial atrophy of myocardial fiber, partial hypertrophy, focal hyaline degeneration, disappearance of local striae, hyaline degeneration of myocardial fiber, dilation and congestion of intermyocardial artery were observed. Slight hyperplasia of alveolar epithelium in some areas, heart failure cells, dilation and congestion of bronchi and trachea artery, a large number of red blood cells and uniform light staining substances in lumen were found. After the model was made by the method of multiple water sacs, the pressure of the abdominal cavity continued to increase with the development of the disease, which was in line with the clinical pathological changes of ACS, and was more suitable for making the animal model of the intra-abdominal hypertension.

Muscle Fiber Atrophy With Single‐Limb Immobilization is Associated With a Significant Decrease in Muscle‐Derived α‐Klotho of Male Mice

Loss of muscle mass associated with aging, known as sarcopenia, is attributed to an increased risk of fractures and falls among the elderly population. The mechanisms underlying the development and progression of sarcopenia are, however, not well‐understood. Recent studies suggest that the anti‐aging factor α‐Klotho (α‐KL) plays a role in muscle regeneration, though its relevance for muscle disuse atrophy and atrophy has not been examined. This study aimed to investigate the response of α‐KL and inflammatory factors after immobilization. Twelve‐month C57/Bl6 mice were subjected to two weeks of hindlimb immobilization, consisting of wrapping surgical tape from the pad of the foot, connecting to cast padding and winding several times around the hindlimb. A layer of vetwrap was put on top followed by multiple layers of tape for protection with a drop of super glue applied on the top of the foot. This immobilization technique induced muscle atrophy through significant reduction of relative quadriceps weight (p<0.005) and a significant reduction in fiber size (p<0.005) in the immobilized legs of wild type mice. A significant increase in body weight was seen in the male mice (N=9, p=0.006), while no difference was seen in the females. PCR investigation showed that immobilized muscles had significantly increased TNF‐alpha expression (p<0.05) by a mean change of 67.37%. α‐KL ELISA analysis of muscle lysate revealed that muscle α‐KL was significantly decreased by a mean change of 44.23% in immobilized male muscles compared to controls (p<0.05), while female muscles showed the same trend but was not significant (p=0.2). RT2 profiling of myogenesis and myopathy in mouse skeletal muscles revealed that ten genes were upregulated (Dysf, Dmpk, Prkag3, Akt1, Musk, Myf6, Acvr2b, Prkab2, Hdac5, Myh1) and six were downregulated (Igfbp3, Tnnt1, Myat, Crayb, Trim63, Mb). Transcription factor Sp1, which regulates α‐KL expression, is also involved in regulating three of these genes (Tnnt1, Dmpk, Acvr2b, Cryab). Our data reveal that immobilization simulated disuse atrophy resulting in increased TNF‐α expression which lead to decreased α‐KL in muscle cells in male mice. This indicates that perhaps treatment with α‐KL could alleviate atrophy seen with acute muscle injury.Support or Funding InformationThis research was funded by the National Institutes of Aging (NIA P01 AG036675).

Endurance Exercise Training Does Not Alter Key Receptors Within the Renin‐Angiotensin System in Skeletal Muscle

Prolonged skeletal muscle inactivity results in muscle fiber atrophy and weakness. Interestingly, endurance exercise training promotes a protective phenotype in skeletal muscle fibers that resists inactivity‐induced muscle wasting. The mechanism(s) responsible for this exercise‐induced preconditioning of muscle remain unknown and are explored in these experiments. In this regard, evidence reveals that activation of the classical arm of the renin‐angiotensin system (RAS) contributes to inactivity‐induced muscle wasting. Specifically, activation of the classical RAS pathway via the angiotensin II type I receptor (AT1R) is associated with activation of proteases and muscle fiber atrophy. Additionally, a non‐classical RAS axis exists that acts antagonistically to the classical RAS axis. Therefore, activation of the non‐classical RAS pathway via the Mas receptor (MasR) inhibits signaling through the classical RAS pathway. Indeed, pharmacological studies reveal that blockade of the AT1R and/or activation of the non‐classical RAS axis protects skeletal muscle against inactivity‐induced muscle atrophy. Studies also reveal that endurance exercise training decreases the abundance of AT1R and increases the quantity of MasR in blood vessels. If similar changes occur in skeletal muscles, these changes in receptor abundance could shift the RAS signaling to favor the non‐classical RAS axis and reduce activation of classical RAS signaling in muscle fibers during prolonged inactivity. These experiments test the hypothesis that endurance exercise training decreases the abundance of AT1R and increases the abundance of MasR in skeletal muscle fibers. To test this postulate, adult rats performed 10 days of endurance exercise training (60 min/day @ ~70% VO2Max). At the completion of the training protocol, the abundance of both AT1R and MasR were determined in isolated single muscle fibers. Moreover, a sensitive angiotensin II (Ang‐II) binding assay was employed to confirm exercise‐induced changes in AT1R abundance in muscle. The results reveal that endurance exercise training does not alter the protein abundance of either the AT1R or MasR in the soleus, plantaris, or diaphragm muscle fibers. Moreover, exercise training did not change the Ang II‐binding affinity within skeletal muscles. Collectively, these results do not support the hypothesis that endurance exercise training results in a decrease in the abundance of AT1R and an increase in MasR in skeletal muscle fibers. It follows that exercise‐induced changes in the abundance of RAS receptors does not appear to be the mechanism responsible for exercise‐induced protection of muscle fibers against inactivity‐induced muscle atrophy.Support or Funding InformationNIH AR064189 (SKP).

Evaluation of Periarticular Pathology Surrounding Knee Joint Tissues in an Osteoarthritis Rat Model

Osteoarthritis (OA) is a multifactorial disease associated with pathological changes in a wide variety of musculoskeletal tissues, including articular cartilage degeneration, synovitis, ligament tears as well as muscle wasting. Cartilage is known as a predominant pathology, however the association between the pathogenesis of OA around the knee joint tissues and pain is limited. Infrapatellar fat pad (IFP) fibrosis and muscle atrophy are the main features of chronic OA phenomenon that cause joint pain, stiffness and impairment of skeletal muscle, which contributing to locomotor restriction in OA patients. Despite a high prevalence of knee OA, there is still a lack of comprehensive information explaining the interplaying mechanisms among these OA features. Although various animal models of OA have been characterized, none of them can truly represent all aspects of the OA features. Monoiodoacetate (MIA)‐induced OA is one of the most common animal model used in the OA research, in which intra‐articular injection of MIA can lead to articular cartilage destruction and development of pain‐like behaviour. This study aimed to characterize and determine the suitable time point, at which MIA could significantly induce the development of IFP fibrosis and hind limb muscle atrophy in this OA rat model. IFP and soleus muscle were collected for histological analysis at 4 and 8 weeks post‐OA induction. In addition, pain‐related behavior was also evaluated using hind limb weight distribution test. Semi‐quantitative analysis of Masson’s trichrome staining revealed that the percentage of IFP fibrosis area was not significantly different at 4 weeks compared to 8 weeks post‐OA induction. In addition, there was a significant (p<0.05) reduction of soleus muscle fiber cross‐sectional area at 4 and 8 weeks of OA‐induced groups compared to their relative controls; however, the muscle fiber atrophy was more pronounced at 4 weeks compared to 8 weeks. Moreover, there was a significant reduction in the mean values of percent weight borne on the injured hind limb for the OA‐induced group compared to the saline group throughout the study period (p<0.05). Interestingly, pain response significantly reversed at 8 weeks compared to 4 weeks (p<0.001), suggesting that this reversal in pain response could be the contributing factor on alleviation of soleus muscle atrophy under chronic OA pain. These results suggested that at 4 weeks post‐MIA injection is sufficient and suitable period to investigate OA‐related pain, IFP fibrosis and muscle atrophy. Taken together, a MIA‐induced OA rat can be used as a representative model in translational research to understand IFP fibrosis and hind limb muscle atrophy in OA as an integrated musculoskeletal disease.

Resistance exercise training promotes fiber type-specific myonuclear adaptations in older adults.

Aging induces physiological decline in human skeletal muscle function and morphology, including type II fiber atrophy and an increase in type I fiber frequency. Resistance exercise training (RET) is an effective strategy to overcome muscle mass loss and improve strength, with a stronger effect on type II fibers. In the present study, we sought to determine the effect of a 12-wk progressive RET program on the fiber type-specific skeletal muscle hypertrophic response in older adults. Nineteen subjects [10 men and 9 women (71.1 ± 4.3 yr)] were studied before and after the 12-wk program. Immunohistochemical analysis was used to quantify myosin heavy chain (MyHC) isoform expression, cross-sectional area (CSA), satellite cell abundance, myonuclear content, and lipid droplet density. RET induced an increase in MyHC type II fiber frequency and a concomitant decrease in MyHC type I fiber frequency. Mean CSA increased significantly only in MyHC type II fibers (+23.3%, P < 0.05), but myonuclear content increased only in MyHC type I fibers (P < 0.05), with no change in MyHC type II fibers. Satellite cell content increased ~40% in both fiber types (P > 0.05). RET induced adaptations to the capillary supply to satellite cells, with the distance between satellite cells and the nearest capillary increasing in type I fibers and decreasing in type II fibers. Both fiber types showed similar decrements in intramuscular lipid density with training (P < 0.05). Our data provide intriguing evidence for a fiber type-specific response to RET in older adults and suggest flexibility in the myonuclear domain of type II fibers during a hypertrophic stimulus.NEW & NOTEWORTHY In older adults, progressive resistance exercise training (RET) increased skeletal muscle fiber volume and cross-sectional area independently of myonuclear accretion, leading to an expansion of the myonuclear domain. Fiber type-specific analyses illuminated differential adaptation; type II fibers underwent hypertrophy and exhibited myonuclear domain plasticity, whereas myonuclear accretion occurred in type I fibers in the absence of a robust hypertrophic response. RET also augmented satellite cell-capillary interaction and reduced intramyocellular lipid density to improve muscle quality.

Sarcopenia is attenuated by TRB3 knockout in aging mice via the alleviation of atrophy and fibrosis of skeletal muscles

BackgroundSarcopenia causes several adverse events in elderly people. Muscle fibre atrophy and interstitial fibrosis are the main histopathological changes in sarcopenia and account for decreased muscle function. Tribbles homologue 3 (TRB3) was previously reported to exhibit age‐related expression and play a vital role in cell proliferation, differentiation, and fibrosis. We aimed to investigate how TRB3 affects sarcopenia.MethodsWild‐type and TRB3 knockout C57/BL6J mice were randomly divided into young and old groups. Exercise capacity was evaluated, and single‐muscle function was detected by electrophysiological techniques, after which the mice were sacrificed to collect their gastrocnemius muscles for assessment of atrophy and fibrosis by histopathological and molecular biological methods. TRB3 expression, autophagy level, and MAPK signalling pathway activity were evaluated through western blotting. The interaction of TRB3 with P62 and the association between TRB3 and the MAPK signalling pathway were detected by co‐immunoprecipitation.ResultsIn aged mice, exercise capacity and cross‐sectional area of skeletal muscle fibres were decreased significantly, whereas TRB3, atrophy‐related markers atrogin 1 and MuRF 1, and interstitial fibrosis, including collagen volume fraction, contents of collagens I and III, and ratio of collagens I to III, were increased significantly (P < 0.05 for all). Following TRB3 knockout, the cross‐sectional area of muscle fibres, mainly fast fibres, was elevated (P < 0.05 for both), the atrogin 1 expression was decreased (P = 0.0163), and the corresponding tetanic force of fast muscles was increased (P = 0.0398). Conversely, interstitial fibrosis was substantially decreased and exercise capacity was significantly increased in the knockout mice. In terms of the underlying mechanisms, the autophagy receptor p62 was markedly increased and the MAPK signalling pathway was activated in aged skeletal muscles, which might be attributed to the interaction of TRB3 with p62 and MAPKKs, including MEK1/MEK2, MEK3/MEK6, and MEK4/MKK4. Notably, TRB3 knockout reduced the accumulation of p62 and LC3 (P < 0.05 for both), decreased the phosphorylation of JNK (P = 0.0015), and increased p38 phosphorylation (P = 0.0021).ConclusionsTRB3 knockout in mice attenuated muscle fibre atrophy and reduced skeletal muscle fibrosis by increasing autophagy and inhibiting the MAPK signalling pathway. Correspondingly, in aged knockout mice, exercise capacity was improved. Interfering with TRB3 expression in aged skeletal muscles may serve as a target for the prevention and treatment of age‐related sarcopenia.

Sympathetic hyperinnervation in myofascial trigger points

ObjectiveTo evaluate the local distribution and activity of sympathetic nerves in myofascial trigger points (MTrPs) and explore the pathological mechanism of myofascial pain syndrome (MPS) using a rat model of disease. MethodsMPS was modeled in the model group (MG) by a combination of blunt trauma and eccentric exercise in Sprague-Dawley rats (n = 8). Eight rats were randomly assigned to the control group (CG). Histopathology was applied to detect the local conditions of the MTrPs. Tyrosine hydroxylase (TH), nerve growth factor (NGF), and norepinephrine (NE) were detected in the MTrPs to evaluate sympathetic remodeling. ResultsMuscle fiber rupture, atrophy and shape irregularity were universally observed in the MTrPs. TH expression was significantly increased in the MG, as detected by immunofluorescence, and NGF and TH expression was also higher in MTrPs in the MG than in MTrPs in the CG, as determined by immunohistochemistry. Furthermore, the expression of NE was significantly increased in MTrPs, as determined by ELISA. ConclusionThere was sympathetic hyperinnervation in MTrPs, which could partially explain the symptoms of MTrPs and is an interesting and useful new perspective regarding the diagnosis and treatment of MPS. PerspectiveThe sympathetic nerves in MTrPs are remodeled, leading to sympathetic hyperinnervation. Sympathetic hyperinnervation can partially explain the symptoms of MPS. The pathological mechanism of sympathetic hyperinnervation may be a new perspective for the diagnosis and treatment of MPS.

Evaluation of an Antioxidant and Anti-inflammatory Cocktail Against Human Hypoactivity-Induced Skeletal Muscle Deconditioning.

Understanding the molecular pathways involved in the loss of skeletal muscle mass and function induced by muscle disuse is a crucial issue in the context of spaceflight as well as in the clinical field, and development of efficient countermeasures is needed. Recent studies have reported the importance of redox balance dysregulation as a major mechanism leading to muscle wasting. Our study aimed to evaluate the effects of an antioxidant/anti-inflammatory cocktail (741 mg of polyphenols, 138 mg of vitamin E, 80 μg of selenium, and 2.1 g of omega-3) in the prevention of muscle deconditioning induced by long-term inactivity. The study consisted of 60 days of hypoactivity using the head-down bed rest (HDBR) model. Twenty healthy men were recruited; half of them received a daily antioxidant/anti-inflammatory supplementation, whereas the other half received a placebo. Muscle biopsies were collected from the vastus lateralis muscles before and after bedrest and 10 days after remobilization. After 2 months of HDBR, all subjects presented muscle deconditioning characterized by a loss of muscle strength and an atrophy of muscle fibers, which was not prevented by cocktail supplementation. Our results regarding muscle oxidative damage, mitochondrial content, and protein balance actors refuted the potential protection of the cocktail during long-term inactivity and showed a disturbance of essential signaling pathways (protein balance and mitochondriogenesis) during the remobilization period. This study demonstrated the ineffectiveness of our cocktail supplementation and underlines the complexity of redox balance mechanisms. It raises interrogations regarding the appropriate nutritional intervention to fight against muscle deconditioning.

Diaphragm weakness and proteomics (global and redox) modifications in heart failure with reduced ejection fraction in rats

Inspiratory dysfunction occurs in patients with heart failure with reduced ejection fraction (HFrEF) in a manner that depends on disease severity and by mechanisms that are not fully understood. In the current study, we tested whether HFrEF effects on diaphragm (inspiratory muscle) depend on disease severity and examined putative mechanisms for diaphragm abnormalities via global and redox proteomics. We allocated male rats into Sham, moderate (mHFrEF), or severe HFrEF (sHFrEF) induced by myocardial infarction and examined the diaphragm muscle. Both mHFrEF and sHFrEF caused atrophy in type IIa and IIb/x fibers. Maximal and twitch specific forces (N/cm2) were decreased by 19 ± 10% and 28 ± 13%, respectively, in sHFrEF (p < .05), but not in mHFrEF. Global proteomics revealed upregulation of sarcomeric proteins and downregulation of ribosomal and glucose metabolism proteins in sHFrEF. Redox proteomics showed that sHFrEF increased reversibly oxidized cysteine in cytoskeletal and thin filament proteins and methionine in skeletal muscle α-actin (range 0.5 to 3.3-fold; p < .05). In conclusion, fiber atrophy plus contractile dysfunction caused diaphragm weakness in HFrEF. Decreased ribosomal proteins and heighted reversible oxidation of protein thiols are candidate mechanisms for atrophy or anabolic resistance as well as loss of specific force in sHFrEF.

Oesophageal sarcocystosis in an Indian female buffalo (Bubalus bubalis) - A case study

An adult female Murrah water buffalo (Bubalus bubalis) carcass from Cattle and Buffalo Farm, ICAR-Indian Veterinary Research Institute (ICAR-IVRI), Izatnagar, Bareilly, Uttar Pradesh, India (28°10'N and 78°58'E) was sent to Postmortem Examination Facility of Division of Pathology, ICAR-IVRI and necropsy was carried out. On systematic examination, large, opaque white, boiled rice-like cysts and typical fusiform shape with wide middle and tapered ends, and embedded in the muscularis externa, underneath the serosa and visible through the serosal surface of the oesophagus. They were easily separated from oesophagus. Sarcocysts were noticed in entire oesophagus from pharyngeal part to abdominal oesophagus. The cysts were of different size (ranges from 7-20 mm length and 2-5 mm width) with uniform shape. The contents of cyst showed crescent shaped bradyzoites and few metrocytes. On histopathological examination, cyst wall was thin and smooth with 1-3 pm thickness. Ground substance beneath the cyst wall contained metrocytes. Inner compartmentalization contained various intensities of bradyzoites. Hyaline degeneration and atrophy of oesophageal muscle fibers were noticed. In the present study, based on the distinctive shape (fusiform shaped with wide middle and tapered ends) and size (7-20 mm in length and 2-5 mm in width) of cysts and microscopic cyst wall thickness (thin and smooth cyst wall with 1-3 pm width), the sarcocyst was confirmed as macrosarcocyst of S. fusiformis.

Jitter evaluation in denervation and reinnervation in 32 cases of chronic radiculopathy

ObjectiveTo measure the jitter parameters in muscles with denervation/reinnervation in 32 chronic radiculopathy cases. MethodsMeasurements were done in chronic denervated muscles by voluntary and electrical activation using a concentric needle electrode. ResultsMean jitter was abnormal in 87.5% (mean 49.2 µs) and 81.25% (mean 36.8 µs), for voluntary and electrical activation. In muscles with fibrillation potentials (FPs), the mean jitter was abnormal in all cases, and impulse blocking was frequent (53.4–92.3%). In muscles without FPs, the mean jitter was abnormal in 78.9% for voluntary activation and 68.4% for electrical activation. No correlation was found between jitter and motor unit action potential amplitude. ConclusionThe muscles with FPs were associated with the immature spread of acetylcholine receptors (AChRs) throughout the muscle membrane. Conversely, the neuromuscular junctions (NMJs) assemble may be repressed by the already reinnervated muscles. For those, higher jitter may be due to the persistence of atrophic fibers expressing neonatal myosin heavy chain (MHC) and immaturity of NMJ composting instead of the overspread of immature AChRs. SignificanceJitter measurement must be avoided in chronic denervated muscles, regardless of FPs’ presence. The activity of reinnervated muscle could maintain neonatal MHC and repress new NMJs development.

Vitamin D and Muscle Sarcopenia in Aging.

Sarcopenia, the age-dependent decline of muscle mass and performance, is a common condition among elderly population and is related to numerous adverse health outcomes. Due to the effect of sarcopenia on quality of life, disability, and mortality, a greater awareness is important in order to correctly recognize the condition both in community and geriatric settings. Research on sarcopenia prevention and treatment is growing quickly, but many questions are still unanswered. The core of the sarcopenia state includes quantitative and qualitative declines of skeletal muscle. These two aspects should therefore be considered when designing and examining preventive and therapeutic interventions. The role of vitamin D in skeletal muscle metabolism has been highlighted in recent years. The interest arises from the important findings of studies indicating multiple impacts of vitamin D on this tissue, which can be divided into genomic (direct impacts) and non-genomic impacts (indirect impacts). Another important dimension to be considered in the study of vitamin D and muscle fiber metabolism is associated with different expressions of the vitamin D receptor, which differs in muscle tissue, depending on age, gender, and pathology. Vitamin D inadequacy or deficiency is related to muscle fiber atrophy, elevated risk of chronic musculoskeletal pain, sarcopenia, and falls. This review describes the effect of vitamin D in skeletal muscle tissue function and metabolism and includes discussion of possible mechanisms in skeletal muscle.