SKELETAL MUSCLE SENSITIVITY TO WASTING INDUCED BY UROTHELIAL CARCINOMA.

BACKGROUND: Skeletal muscle wasting is a common phenotypic feature of several types of cancer, and it is associated with functional impairment, respiratory complications, and fatigue. However, equivocal evidence remains regarding the impact of cancer-induced muscle wasting on the different fiber types. AIM: The aim of this study was to investigate the impact of urothelial carcinoma induced in mice on the histomorphometric features and collagen deposition in different skeletal muscles. MATERIALS AND METHODS: Thirteen ICR (CD1) male mice were randomly assigned into two groups: exposed to 0.05% N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) in drinking water for 12 weeks, plus 8 weeks of tap water (BBN, n = 8) or with access to tap water for 20 weeks (CONT, n = 5). Tibialis anterior, soleus, and diaphragm muscles were collected from all animals. For cross-sectional area and myonuclear domain analysis, muscle sections were stained with hematoxylin and eosin, and for collagen deposition assessment, muscle sections were stained with picrosirius red. RESULTS: All animals from the BBN group developed urothelial preneoplastic and neoplastic lesions, and the tibialis anterior from these animals presented a reduced cross-sectional area (p < 0.001), with a decreased proportion of fibers with a higher cross-sectional area, increased collagen deposition (p = 0.017), and higher myonuclear domain (p = 0.031). BBN mice also showed a higher myonuclear domain in the diaphragm (p = 0.015). CONCLUSION: Urothelial carcinoma induced muscle wasting of the tibialis anterior, expressed by a decreased cross-sectional area, higher infiltration of fibrotic tissue, and increased myonuclear domain, which also increased in the diaphragm, suggesting that fast glycolytic muscle fibers are more susceptible to be affected by cancer development.

Muscle fiber type grouping does not change in response to prolonged resistance exercise training in healthy older men.

BACKGROUND: Ageing of skeletal muscle is characterized in some by muscle fiber type grouping due to denervation-reinnervation cycles, but the severity of fiber type grouping varies widely across individuals of the same chronological age. It remains unknown whether fiber type grouping is associated with lower muscle mass and/or reduced physical function in elderly. Therefore, we assessed the relationship between fiber type grouping and indices of muscle mass and physical function in older adults. In addition, we assessed whether fiber type grouping is affected by prolonged resistance training in older adults. METHODS: Twenty young (21 ± 2 y) and twenty older (70 ± 4 y) healthy men participated in the present study. Body composition (DXA-scan), quadriceps cross-sectional area (CT-scan) and muscle strength (1RM) were assessed at baseline (young and old) and following 12 weeks of resistance training (old only). Percutaneous skeletal muscle biopsies from the vastus lateralis were collected at baseline (young and old) and following exercise training (old only). Immunohistochemical analyses were performed to evaluate type I and type II muscle fiber distribution, size, myonuclear content and grouping. RESULTS: At baseline, type II fibers were significantly (P < 0.05) smaller in older compared with young adults (5366 ± 1288 vs 6705 ± 1168 µm2). Whereas no differences were observed in type I, type II fiber grouping was significantly (P < 0.05) lower in older (18 ± 18 %) compared with young (32 ± 25 %) men. No significant correlations were observed between fiber type grouping and muscle mass or physical function. Prolonged resistance training in old men resulted in a significant increase (P < 0.05) in type II fiber size (from 5366 ± 1288 to 6165 ± 1484 µm2) with no significant changes in the proportion of type I muscle fibers found grouped. CONCLUSION: Muscle fiber type grouping is not associated with lower body strength or muscle mass in healthy, older men. In addition, twelve weeks of resistance exercise training results in type II muscle fiber specific hypertrophy but does not affect fiber type grouping.

Ryanodine receptors mediate high intracellular Ca2+ and some myocyte damage following eccentric contractions in rat fast-twitch skeletal muscle.

Eccentric contractions (ECC) facilitate cytosolic calcium ion (Ca2+) release from the sarcoplasmic reticulum (SR) and Ca2+ influx from the extracellular space. Ca2+ is a vital signaling messenger that regulates multiple cellular processes via its spatial and temporal concentration ([Ca2+]i) dynamics. We hypothesized that 1) a specific pattern of spatial/temporal intramyocyte Ca2+ dynamics portends muscle damage following ECC and 2) these dynamics would be regulated by the ryanodine receptor (RyR). [Ca2+]i in the tibialis anterior muscles of anesthetized adult Wistar rats was measured by ratiometric (i.e., ratio, R, 340/380 nm excitation) in vivo bioimaging with Fura-2 pre-ECC and at 5 and 24 h post-ECC (5 × 40 contractions). Separate groups of rats received RyR inhibitor dantrolene (DAN; 10 mg/kg ip) immediately post-ECC (+DAN). Muscle damage was evaluated by histological analysis on hematoxylin-eosin stained muscle sections. Compared with control (CONT, no ECC), [Ca2+]i distribution was heterogeneous with increased percent total area of high [Ca2+]i sites (operationally defined as R ≥ 1.39, i.e., ≥1 SD of mean control) 5 h post-ECC (CONT, 14.0 ± 8.0; ECC5h: 52.0 ± 7.4%, P < 0.01). DAN substantially reduced the high [Ca2+]i area 5 h post-ECC (ECC5h + DAN: 6.4 ± 3.1%, P < 0.01) and myocyte damage (ECC24h, 63.2 ± 1.0%; ECC24h + DAN: 29.1 ± 2.2%, P < 0.01). Temporal and spatially amplified [Ca2+]i fluctuations occurred regardless of DAN (ECC vs. ECC + DAN, P > 0.05). These results suggest that the RyR-mediated local high [Ca2+]i itself is related to the magnitude of muscle damage, whereas the [Ca2+]i fluctuation is an RyR-independent phenomenon.

Dystrophin-negative slow-twitch soleus muscles are not susceptible to eccentric contraction induced injury over the lifespan of the mdx mouse.

Duchenne muscular dystrophy (DMD) is the second most common fatal genetic disease in humans and is characterized by the absence of a functional copy of the protein dystrophin from skeletal muscle. In dystrophin-negative humans and rodents, regenerated skeletal muscle fibers show abnormal branching. The number of fibers with branches and the complexity of branching increases with each cycle of degeneration/regeneration. Previously, using the mdx mouse model of DMD, we have proposed that once the number and complexity of branched fibers present in dystrophic fast-twitch EDL muscle surpasses a stable level, we term the "tipping point," the branches, in and of themselves, mechanically weaken the muscle by rupturing when subjected to high forces during eccentric contractions. Here, we use the slow-twitch soleus muscle from the dystrophic mdx mouse to study prediseased "periambulatory" dystrophy at 2-3 wk, the peak regenerative "adult" phase at 6-9 wk, and "old" at 58-112 wk. Using isolated mdx soleus muscles, we examined contractile function and response to eccentric contraction correlated with the amount and complexity of regenerated branched fibers. The intact muscle was enzymatically dispersed into individual fibers in order to count fiber branching and some muscles were optically cleared to allow laser scanning confocal microscopy. We demonstrate throughout the lifespan of the mdx mouse that dystrophic slow-twitch soleus muscle is no more susceptible to eccentric contraction-induced injury than age-matched littermate controls and that this is correlated with a reduction in the number and complexity of branched fibers compared with fast-twitch dystrophic EDL muscles.

Pathophysiological Effects of Overactive STIM1 on Murine Muscle Function and Structure.

Store-operated Ca2+ entry (SOCE) is a ubiquitous mechanism regulating extracellular Ca2+ entry to control a multitude of Ca2+-dependent signaling pathways and cellular processes. SOCE relies on the concerted activity of the reticular Ca2+ sensor STIM1 and the plasma membrane Ca2+ channel ORAI1, and dysfunctions of these key factors result in human pathologies. STIM1 and ORAI1 gain-of-function (GoF) mutations induce excessive Ca2+ influx through SOCE over-activation, and cause tubular aggregate myopathy (TAM) and Stormorken syndrome (STRMK), two overlapping disorders characterized by muscle weakness and additional multi-systemic signs affecting growth, platelets, spleen, skin, and intellectual abilities. In order to investigate the pathophysiological effect of overactive SOCE on muscle function and structure, we combined transcriptomics with morphological and functional studies on a TAM/STRMK mouse model. Muscles from Stim1R304W/+ mice displayed aberrant expression profiles of genes implicated in Ca2+ handling and excitation-contraction coupling (ECC), and in vivo investigations evidenced delayed muscle contraction and relaxation kinetics. We also identified signs of reticular stress and abnormal mitochondrial activity, and histological and respirometric analyses on muscle samples revealed enhanced myofiber degeneration associated with reduced mitochondrial respiration. Taken together, we uncovered a molecular disease signature and deciphered the pathomechanism underlying the functional and structural muscle anomalies characterizing TAM/STRMK.

foxm1 Modulates Cell Non-Autonomous Response in Zebrafish Skeletal Muscle Homeostasis.

foxm1 is a master regulator of the cell cycle, contributing to cell proliferation. Recent data have shown that this transcription factor also modulates gene networks associated with other cellular mechanisms, suggesting non-proliferative functions that remain largely unexplored. In this study, we used CRISPR/Cas9 to disrupt foxm1 in the zebrafish terminally differentiated fast-twitching muscle cells. foxm1 genomic disruption increased myofiber death and clearance. Interestingly, this contributed to non-autonomous satellite cell activation and proliferation. Moreover, we observed that Cas9 expression alone was strongly deleterious to muscle cells. Our report shows that foxm1 modulates a muscle non-autonomous response to myofiber death and highlights underreported toxicity to high expression of Cas9 in vivo.

Cancer-induced muscle atrophy is determined by intrinsic muscle oxidative capacity.

We tested the hypothesis that cancer cachexia progression would induce oxidative post-translational modifications (Ox-PTMs) associated with skeletal muscle wasting, with different responses in muscles with the prevalence of glycolytic and oxidative fibers. We used cysteine-specific isotopic coded affinity tags (OxICAT) and gel-free mass spectrometry analysis to investigate the cysteine Ox-PTMs profile in the proteome of both plantaris (glycolytic) and soleus (oxidative) muscles in tumor-bearing and control rats. Histological analysis revealed muscle atrophy in type II fibers in plantaris muscle, with no changes in plantaris type I fibers and no differences in both soleus type I and II fibers in tumor-bearing rats when compared to healthy controls. Tumor progression altered the Ox-PTMs profile in both plantaris and soleus. However, pathway analysis including the differentially oxidized proteins revealed tricarboxylic acid cycle and oxidative phosphorylation as main affected pathways in plantaris muscle from tumor-bearing rats, while the same analysis did not show main metabolic pathways affected in the soleus muscle. In addition, cancer progression affected several metabolic parameters such as ATP levels and markers of oxidative stress associated with muscle atrophy in plantaris muscle, but not in soleus. However, isolated soleus from tumor-bearing rats had a reduced force production capacity when compared to controls. These novel findings demonstrate that tumor-bearing rats have severe muscle atrophy exclusively in glycolytic fibers. Cancer progression is associated with cysteine Ox-PTMs in the skeletal muscle, but these modifications affect different pathways in a glycolytic muscle compared to an oxidative muscle, indicating that intrinsic muscle oxidative capacity determines the response to cancer cachectic effects.

Histopathological changes and oxidative damage in type I and type II muscle fibers in rats undergoing paradoxical sleep deprivation.

BACKGROUND: previous studies have shown that muscle atrophy is observed after sleep deprivation (SD) protocols; however, the mechanisms responsible are not fully understood. Muscle trophism can be modulated by several factors, including energy balance (positive or negative), nutritional status, oxidative stress, the level of physical activity, and disuse. The metabolic differences that exist in different types of muscle fiber may also be the result of different adaptive responses. To better understand these mechanisms, we evaluated markers of oxidative damage and histopathological changes in different types of muscle fibers in sleep-deprived rats. METHODS: Twenty male Wistar EPM-1 rats were randomly allocated in two groups: a control group (CTL group; n = 10) and a sleep deprived group (SD group; n = 10). The SD group was submitted to continuous paradoxical SD for 96  h; the soleus (type I fibers) and plantar (type II fiber) muscles were analyzed for histopathological changes, trophism, lysosomal activity, and oxidative damage. Oxidative damage was assessed by lipid peroxidation and nuclear labeling of 8-OHdG. RESULTS: The data demonstrated that SD increased the nuclear labeling of 8-OHdG and induced histopathological changes in both muscles, being more evident in the soleus muscle. In the type I fibers there was signs of tissue degeneration, inflammatory infiltrate and tissue edema. Muscle atrophy was observed in both muscles. The concentration of malondialdehyde, and cathepsin L activity only increased in type I fibers after SD. CONCLUSION: These data indicate that the histopathological changes observed after 96 h of SD in the skeletal muscle occur by different processes, according to the type of muscle fiber, with muscles predominantly composed of type I fibers undergoing greater oxidative damage and catabolic activity, as evidenced by a larger increase in 8-OHdG labeling, lipid peroxidation, and lysosomal activity.

Puerarin ameliorates skeletal muscle wasting and fiber type transformation in STZ-induced type 1 diabetic rats.

Puerarin is an isoflavonoid extracted from Pueraria lobate with extensive pharmacological effects in traditional Chinese medicine. The evidence implicates that puerarin mitigates hyperglycemia and various relevant complications. Here, the effect of puerarin on skeletal muscle wasting induced by type 1 diabetes (T1D) was explored. Streptozotocin (STZ)-induced T1D male Sprague Dawley (SD) rats were used in this study. Muscle strength, weight and size were measured. L6 rat skeletal muscle cells were applied for in vitro study. Our results showed that eight-week oral puerarin administration (100 mg/kg) increased muscle strengths and weights accompanied by enhanced skeletal muscle cross-sectional areas in diabetic rats. Simultaneously, puerarin also reduced expressions of several muscle wasting marker genes including F-box only protein 32 (Atrogin-1) and muscle-specific RING-finger 1 (Murf-1) in diabetic group both in vitro and in vivo. Transformation from type I fibers (slow muscle) to type II fibers (fast muscle) were also observed under puerarin administration in diabetic rats. Puerarin promoted Akt/mTOR while inhibited LC3/p62 signaling pathway in skeletal muscle cells. In conclusion, our study showed that puerarin mitigated skeletal muscle wasting in T1D rats and closely related with Akt/mTOR activation and autophagy inhibition. Whether this effect in murine applies to humans remains to be determined.

Muscle fiber size in healthy children and adults in relation to sex and fiber types.

BACKGROUND: In adult males, cross-sectional area (CSA) for type II muscle fibers is generally larger than for type I fibers. In this cross-sectional study the aim was to compare sex-related CSAs of various muscle fiber types during childhood-to-adulthood transition. METHODS: Percutaneous biopsy samples were obtained from vastus lateralis in 10-y-old children (10 males and 5 females) and in young adults (9 males and 7 females). Fiber types were classified by myofibrillar ATPase and CSAs from NADH-dehydrogenase staining. RESULTS: Type IIA were larger than type I fibers in adult males, but not in adult females or children (age x sex x fiber type, P < .002). When including all participants, body weight and sex explained 78% of the variation in type IIA CSA but only body weight contributed for type I. CONCLUSIONS: Sex-specific patterns in CSA of the muscle fiber types appears to develop during the transition from childhood to adulthood.

Extraocular Muscle Reveals Selective Vulnerability of Type IIB Fibers to Respiratory Chain Defects Induced by Mitochondrial DNA Alterations.

Purpose: The purpose of this study was to gain insights on the pathogenesis of chronic progressive external ophthalmoplegia, thus we investigated the vulnerability of five extra ocular muscles (EOMs) fiber types to pathogenic mitochondrial DNA deletions in a mouse model expressing a mutated mitochondrial helicase TWINKLE. Methods: Consecutive pairs of EOM sections were analyzed by cytochrome C oxidase (COX)/succinate dehydrogenase (SDH) assay and fiber type specific immunohistochemistry (type I, IIA, IIB, embryonic, and EOM-specific staining). Results: The mean average of COX deficient fibers (COX-) in the recti muscles of mutant mice was 1.04 ± 0.52% at 12 months and increased with age (7.01 ± 1.53% at 24 months). A significant proportion of these COX- fibers were of the fast-twitch, glycolytic type IIB (> 50% and > 35% total COX- fibers at 12 and 24 months, respectively), whereas embryonic myosin heavy chain-expressing fibers were almost completely spared. Furthermore, the proportion of COX- fibers in the type IIB-rich retractor bulbi muscle was > 2-fold higher compared to the M. recti at both 12 (2.6 ± 0.78%) and 24 months (20.85 ± 2.69%). Collectively, these results demonstrate a selective vulnerability of type IIB fibers to mitochondrial DNA (mtDNA) deletions in EOMs and retractor bulbi muscle. We also show that EOMs of mutant mice display histopathological abnormalities, including altered fiber type composition, increased fibrosis, ragged red fibers, and infiltration of mononucleated nonmuscle cells. Conclusions: Our results point to the existence of fiber type IIB-intrinsic factors and/or molecular mechanisms that predispose them to increased generation, clonal expansion, and detrimental effects of mtDNA deletions.

PKM2 Determines Myofiber Hypertrophy In Vitro and Increases in Response to Resistance Exercise in Human Skeletal Muscle.

Nearly 100 years ago, Otto Warburg investigated the metabolism of growing tissues and discovered that tumors reprogram their metabolism. It is poorly understood whether and how hypertrophying muscle, another growing tissue, reprograms its metabolism too. Here, we studied pyruvate kinase muscle (PKM), which can be spliced into two isoforms (PKM1, PKM2). This is of interest, because PKM2 redirects glycolytic flux towards biosynthetic pathways, which might contribute to muscle hypertrophy too. We first investigated whether resistance exercise changes PKM isoform expression in growing human skeletal muscle and found that PKM2 abundance increases after six weeks of resistance training, whereas PKM1 decreases. Second, we determined that Pkm2 expression is higher in fast compared to slow fiber types in rat skeletal muscle. Third, by inducing hypertrophy in differentiated C2C12 cells and by selectively silencing Pkm1 and/or Pkm2 with siRNA, we found that PKM2 limits myotube growth. We conclude that PKM2 contributes to hypertrophy in C2C12 myotubes and indicates a changed metabolic environment within hypertrophying human skeletal muscle fibers. PKM2 is preferentially expressed in fast muscle fibers and may partly contribute to the increased potential for hypertrophy in fast fibers.

Disease mechanism, biomarker and therapeutics for spinal and bulbar muscular atrophy (SBMA).

Spinal and bulbar muscular atrophy (SBMA) is a hereditary neuromuscular disorder caused by CAG trinucleotide expansion in the gene encoding the androgen receptor (AR). In the central nervous system, lower motor neurons are selectively affected, whereas pathology of patients and animal models also indicates involvement of skeletal muscle including loss of fast-twitch type 2 fibres and increased slow-twitch type 1 fibres, together with a glycolytic-to-oxidative metabolic switch. Evaluation of muscle and fat using MRI, in addition to biochemical indices such as serum creatinine level, are promising biomarkers to track the disease progression. The serum level of creatinine starts to decrease before the onset of muscle weakness, followed by the emergence of hand tremor, a prodromal sign of the disease. Androgen-dependent nuclear accumulation of the polyglutamine-expanded AR is an essential step in the pathogenesis, providing therapeutic opportunities via hormonal manipulation and gene silencing with antisense oligonucleotides. Animal studies also suggest that hyperactivation of Src, alteration of autophagy and a mitochondrial deficit underlie the neuromuscular degeneration in SBMA and provide alternative therapeutic targets.

Muscle fiber-type specific terminal Schwann cell pathology leads to sprouting deficits following partial denervation in SOD1G93A mice.

Amyotrophic lateral sclerosis (ALS) is an adult-onset disease characterized by the progressive death of motoneurons and denervation of muscle fibers. To restore motor function, surviving motoneurons in partially denervated muscles typically sprout axons to reinnervate denervated endplates. However, studies on the SOD1G93A rodent models of ALS indicate that sprouting is significantly limited in fast, but not slow, twitch muscles after disease onset. This limitation hastens the rate of muscle weakness and loss of motor function. The causes of this limitation are currently unknown. Sprouting could be limited because the SOD1G93A mutation weakens motoneurons making them incapable of expanding their field of innervation. Alternatively, motoneurons may be capable of sprouting, but unable to do so due to the loss of a permissive sprouting environment. To distinguish between the two possibilities, we compared the sprouting capacity of motoneuron subtypes by partially denervating the fast twitch plantaris (composed of type IIa/IIb muscle fibers) and slow twitch soleus muscles (type I/IIa fibers) prior to disease onset and weakening in SOD1G93A and WT mice. We found that only motoneurons innervating the SOD1G93A plantaris had a limited sprouting capacity. This was correlated with the selective loss of terminal Schwann cells (TSCs) at IIb fibers and an increase in macrophage infiltration. Treating SOD1G93A mice with the tyrosine kinase inhibitor, masitinib, significantly reduced infiltration, prevented TSC loss, and increased the sprouting capacity to near normal. These results suggest that TSCs at denervated type IIb muscle fibers are aberrantly targeted by infiltrating macrophages in SOD1G93A mice, and their loss accounts, at least in part, for the compromised sprouting capacity of the largest motoneurons during early stages of ALS.

Differential protective effects of Radix astragali, herbal medicine, on immobilization-induced atrophy of slow-twitch and fast-twitch muscles.

Radix astragali is a popular traditional herbal medicine that provides significant protection against tissue injury in various models of oxidative stress-related diseases. In this study, we aimed to investigate whether administration of Radix astragali prevented atrophy in both slow- and fast-twitch muscles following cast immobilization. Twenty-seven 12-week-old male F344 rats were divided into three experimental groups: control (CON), immobilized (IM), and immobilized with Radix astragali administration (IM+AR). Rats in the IM and IM+AR groups were subjected to immobilization of both lower extremities using casting-tape for 14 days. Rats in the IM+AR group were orally administered a decoction of Radix astragali daily for 21 days beginning 7 days before cast immobilization. As expected, rats in the IM group showed significant decreases (P < 0.05) in soleus and plantaris muscle-to-body weight ratios by 74.3% and 70.5%, respectively, compared with those in the CON group. Administration of Radix astragali significantly reversed (+35.5%) the weight reduction observed in soleus muscle, but not in the plantaris muscle, compared with that in the IM group. Furthermore, administration of Radix astragali inhibited MuRF1 mRNA expression only in the soleus muscle during cast immobilization. Our results demonstrated that administration of Radix astragali suppressed the immobilization-induced reductions in skeletal muscle mass and expression of MuRF1 mRNA in slow-twitch soleus muscles, but not in fast-twitch plantaris muscles.

An exploratory study of contractile force production in muscle fibers from patients with inflammatory myopathies.

INTRODUCTION: The mechanism by which weakness develops in idiopathic inflammatory myopathies (IIMs) is still unclear. In this study we investigated the maximum force of single muscle fibers from patients with IIMs. METHODS: Permeabilized single muscle fibers from patients with IIMs and healthy controls were subjected to contractility measurements. Maximum force and specific force production (maximum force normalized to fiber size) and fiber type were determined for each isolated fiber. RESULTS: A total of 178 fibers were studied from five patients with IIMs and 95 fibers from four controls. Specific force production was significantly lower in the IIM group for all fiber types. DISCUSSION: The findings from this exploratory study suggest that weakness in IIMs may, in part, be caused by dysfunction of the contractile apparatus. These findings provide a basis for further studies into the mechanisms underlying weakness in IIMs.

Impaired exercise performance is independent of inflammation and cellular stress following genetic reduction or deletion of selenoprotein S.

Selenoprotein S (Seps1) can be protective against oxidative, endoplasmic reticulum (ER), and inflammatory stress. Seps1 global knockout mice are less active, possess compromised fast muscle ex vivo strength, and, depending on context, heightened inflammation. Oxidative, ER, and inflammatory stress modulates contractile function; hence, our aim was to investigate the effects of Seps1 gene dose on exercise performance. Seps1-/- knockout, Seps1-/+ heterozygous, and wild-type mice were randomized to 3 days of incremental, high-intensity treadmill running or a sedentary control group. On day 4, the in situ contractile function of fast tibialis anterior (TA) muscles was determined. Seps1 reduction or deletion compromised exercise capacity, decreasing distance run. TA strength was also reduced. In sedentary Seps1-/- knockout mice, TA fatigability was greater than wild-type mice, and this was ameliorated with exercise. Whereas, in Seps1+/- heterozygous mice, exercise compromised TA endurance. These impairments in exercise capacity and TA contractile function were not associated with increased inflammation or a dysregulated redox state. Seps1 is highly expressed in muscle fibers and blood vessels. Interestingly, Nos1 and Vegfa mRNA transcripts were decreased in TA muscles from Seps1-/- knockout and Seps1-/+ heterozygous mice. Impaired exercise performance with Seps1 reduction or deletion cannot be attributed to heightened cellular stress, but it may potentially be mediated, in part, by the effects of Seps1 on the microvasculature.

Treatment of Dystrophic mdx Mice with an ADAMTS-5 Specific Monoclonal Antibody Increases the Ex Vivo Strength of Isolated Fast Twitch Hindlimb Muscles.

Aberrant extracellular matrix synthesis and remodeling contributes to muscle degeneration and weakness in Duchenne muscular dystrophy (DMD). ADAMTS-5, a secreted metalloproteinase with catalytic activity against versican, is implicated in myogenesis and inflammation. Here, using the mdx mouse model of DMD, we report increased ADAMTS-5 expression in dystrophic hindlimb muscles, localized to regions of regeneration and inflammation. To investigate the pathophysiological significance of this, 4-week-old mdx mice were treated with an ADAMTS-5 monoclonal antibody (mAb) or IgG2c (IgG) isotype control for 3 weeks. ADAMTS-5 mAb treatment did not reduce versican processing, as protein levels of the cleaved versikine fragment did not differ between hindlimb muscles from ADAMTS-5 mAb or IgG treated mdx mice. Nonetheless, ADAMTS-5 blockade improved ex vivo strength of isolated fast extensordigitorumlongus, but not slow soleus, muscles. The underpinning mechanism may include modulation of regenerative myogenesis, as ADAMTS-5 blockade reduced the number of recently repaired desmin positive myofibers without affecting the number of desmin positive muscle progenitor cells. Treatment with the ADAMTS-5 mAb did not significantly affect makers of muscle damage, inflammation, nor fiber size. Altogether, the positive effects of ADAMTS-5 blockade in dystrophic muscles are fiber-type-specific and independent of versican processing.

Diaphragm muscle sarcopenia into very old age in mice.

Sarcopenia is the age-related decline of skeletal muscle mass and function. Diaphragm muscle (DIAm) sarcopenia may contribute to respiratory complications, a common cause of morbidity and mortality in the elderly. From 6 to 24 months (mo) of age, representing ~100% and ~80% survival in C57BL/6 × 129 male and female mice, there is a significant reduction in DIAm force generation (~30%) and cross-sectional area (CSA) of type IIx and/or IIb muscle fibers (~30%), impacting the ability to perform high force, non-ventilatory behaviors. To date, there is little information available regarding DIAm sarcopenia in very old age groups. The present study examined DIAm sarcopenia in C57BL/6 × 129 male and female mice at 24, 27, and 30 mo, representing ~80%, ~60%, and ~30% survival, respectively. We hypothesized that survival into older ages will show no further worsening of DIAm sarcopenia and functional impairment in 30 mo mice compared to 24 or 27 mo C57BL/6 × 129 mice. Measurements included resting ventilation, transdiaphragmatic pressure (Pdi) generation across a range of motor behaviors, muscle fiber CSA, and proportion of type-identified DIAm fibers. Maximum Pdi and resting ventilation did not change into very old age (from 24 to 30 mo). Type IIx and/or IIb fiber CSA and proportions did not change into very old age. The results of the study support a critical threshold for the reduction in DIAm force and Pdi such that survival into very old age is not associated with evidence of progression of DIAm sarcopenia or impairment in ventilation.

Differential structural features in soleus and gastrocnemius of carnitine-treated cancer cachectic rats.

Muscle wasting is associated with chronic diseases and cancer. Elucidation of the biological mechanism involved in the process of muscle mass loss and cachexia may help identify therapeutic targets. We hypothesized that l-carnitine treatment may differentially revert muscle fiber atrophy and other structural alterations in slow- and fast-twitch limb muscles of rats bearing the Yoshida ascites hepatoma. In soleus and gastrocnemius of tumor-bearing rats (108 AH-130 Yoshida ascites hepatoma cells inoculated intraperitoneally) with and without treatment with l-carnitine (1 g/kg body weight for 7 days, intragastric), food intake, body and muscle weights, fiber typing and morphometry, morphological features, redox balance, autophagy and proteolytic, and signaling markers were explored. Levels of carnitine palmitoyl transferase were also measured in all the study muscles. l-Carnitine treatment ameliorated the atrophy of both slow- and fast-twitch fibers (gastrocnemius particularly), muscle structural alterations (both muscles), and attenuated oxidative stress, proteolytic and signaling markers (gastrocnemius). Despite that carnitine palmitoyl transferase-1 levels increased in both muscle types in a similar fashion, l-carnitine ameliorated muscle atrophy and proteolysis in a muscle-specific manner in cancer-induced cachexia. These data reveal the need to study muscles of different fiber type composition and function to better understand whereby l-carnitine exerts its beneficial effects on the myofibers in muscle wasting processes. These findings also have potential clinical implications, since combinations of various exercise and muscle training modalities with l-carnitine should be specifically targeted for the muscle groups to be trained.