Inhibition of p53-MDM2 binding reduces senescent cell abundance and improves the adaptive responses of skeletal muscle from aged mice

Skeletal muscle adaptation to external stimuli, such as regeneration following injury and hypertrophy in response to resistance exercise, are blunted with advanced age. The accumulation of senescent cells, along with defects in myogenic progenitor cell (MPC) proliferation, have been strongly linked as contributing factors to age-associated impairment in muscle adaptation. p53 plays an integral role in all these processes, as upregulation of p53 causes apoptosis in senescent cells and prevents mitotic catastrophe in MPCs from old mice. The goal of this study was to determine if a novel pharmaceutical agent (BI01), which functions by upregulating p53 through inhibition of binding to MDM2, the primary p53 regulatory protein, improves muscle regeneration and hypertrophy in old mice. BI01 effectively reduced the number of senescent cells in vitro but had no effect on MPC survival or proliferation at a comparable dose. Following repeated oral gavage with 2 mg/kg of BI01 (OS) or vehicle (OV), old mice (24 months) underwent unilateral BaCl2 injury in the tibialis anterior (TA) muscle, with PBS injections serving as controls. After 7 days, satellite cell number was higher in the TA of OS compared to OV mice, as was the expression of genes involved in ATP production. By 35 days, old mice treated with BI01 displayed reduced senescent cell burden, enhanced regeneration (higher muscle mass and fiber cross-sectional area) and restoration of muscle function relative to OV mice. To examine the impact of 2 mg/kg BI01 on muscle hypertrophy, the plantaris muscle was subjected to 28 days of mechanical overload (MOV) in OS and OV mice. In response to MOV, OS mice had larger plantaris muscles and muscle fibers than OV mice, particularly type 2b + x fibers, associated with reduced senescent cells. Together our data show that BI01 is an effective senolytic agent that may also augment muscle metabolism to enhance muscle regeneration and hypertrophy in old mice.

The need for speed - Does the force-velocity property significantly alter strain distributions within skeletal muscle?

Skeletal muscles are complex structures with nonlinear constitutive properties. This complexity often requires finite element (FE) modeling to better understand muscle behavior and response to activation, especially the fiber strain distributions that can be difficult to measure in vivo. However, many FE muscle models designed to study fiber strain do not include force-velocity behavior. To investigate force-velocity property impact on strain distributions within skeletal muscle, we modified a muscle constitutive model with active and passive force-length properties to include force-velocity properties. We implemented the new constitutive model as a plugin for the FE software FEBio and applied it to four geometries: 1) a single element, 2) a multiple-element model representing a single fiber, 3) a model of tapering fibers, and 4) a model representing the bicep femoris long head (BFLH) morphology. Maximum fiber velocity and boundary conditions of the finite element models were varied to test their influence on fiber strain distribution. We found that force-velocity properties in the constitutive model behaved as expected for the single element and multi-element conditions. In the tapered fiber models, fiber strain distributions were impacted by changes in maximum fiber velocity; the range of strains increased with maximum fiber velocity, which was most noted in isometric contraction simulations. In the BFLH model, maximum fiber velocity had minimal impact on strain distributions, even in the context of sprinting. Taken together, the combination of muscle model geometry, activation, and displacement parameters play a critical part in determining the magnitude of impact of force-velocity on strain distribution.

Microbiota derived D-malate inhibits skeletal muscle growth and angiogenesis during aging via acetylation of Cyclin A

Metabolites derived from the intestinal microbiota play an important role in maintaining skeletal muscle growth, function, and metabolism. Here, we found that D-malate (DMA) is produced by mouse intestinal microorganisms and its levels increase during aging. Moreover, we observed that dietary supplementation of 2% DMA inhibits metabolism in mice, resulting in reduced muscle mass, strength, and the number of blood vessels, as well as the skeletal muscle fiber type I/IIb ratio. In vitro assays demonstrate that DMA decreases the proliferation of vascular endothelial cells and suppresses the formation of blood vessels. In vivo, we further demonstrated that boosting angiogenesis by muscular VEGFB injection rescues the inhibitory effects of D-malate on muscle mass and fiber area. By transcriptomics analysis, we identified that the mechanism underlying the effects of DMA depends on the elevated intracellular acetyl-CoA content and increased Cyclin A acetylation rather than redox balance. This study reveals a novel mechanism by which gut microbes impair muscle angiogenesis and may provide a therapeutic target for skeletal muscle dysfunction in cancer or aging.

Association of quantitative diffusion tensor imaging measures with time to return to sport and reinjury incidence following acute hamstring strain injury

Hamstring strain injuries (HSI) are a common occurrence in athletics and complicated by limited prognostic indicators and high rates of reinjury. Assessment of injury characteristics at the time of injury (TOI) may be used to manage athlete expectations for time to return to sport (RTS) and mitigate reinjury risk. Magnetic resonance imaging (MRI) is routinely used in soft tissue injury management, but its prognostic value for HSI is widely debated. Recent advancements in musculoskeletal MRI, such as diffusion tensor imaging (DTI), have allowed for quantitative measures of muscle microstructure assessment. The purpose of this study was to determine the association of TOI MRI-based measures, including the British Athletic Muscle Injury Classification (BAMIC) system, edema volume, and DTI metrics, with time to RTS and reinjury incidence. Negative binomial regressions and generalized estimating equations were used to determine relationships between imaging measures and time to RTS and reinjury, respectively. Twenty-six index injuries were observed, with five recorded reinjuries. A significant association was not detected between BAMIC score and edema volume at TOI with days to RTS (p-values ≥ 0.15) or reinjury (p-values ≥ 0.13). Similarly, a significant association between DTI metrics and days to RTS was not detected (p-values ≥ 0.11). Although diffusivity metrics are expected to increase following injury, decreased values were observed in those who reinjured (mean diffusivity, p = 0.016; radial diffusivity, p = 0.02; principal effective diffusivity eigenvalues, p-values = 0.007-0.057). Additional work to further understand the directional relationship observed between DTI metrics and reinjury status and the influence of external factors is warranted.

Differences in Skeletal Muscle Fiber Characteristics Between Affected and Nonaffected Limbs in Individuals With Stroke: A Scoping Review

OBJECTIVE

The objective of this scoping review was to characterize and identify knowledge gaps about the changes in skeletal muscle fiber type proportion and cross-sectional area (CSA) after stroke.

METHODS

This scoping review followed previously proposed frameworks. A systematic search was conducted for articles examining muscle fiber type proportion and CSA in individuals with stroke in EMBASE, MEDLINE, PsycINFO, CINAHL, SPORTDiscus, and Web of Science databases from inception to December 20, 2022. Two independent authors screened and extracted the data. Results were discussed using theories proposed by the authors of the included studies.

RESULTS

Of 13 studies (115 participants), 6 (46%) were case studies or case series, 6 (46%) were cross-sectional studies, and 1 (8%) was an experimental study. Studies had small sample sizes (1-23 participants) and various muscle sampling sites (6 different muscles). All 13 studies examined muscle fiber type distributions, and 6 (46%) examined CSA. Ten (77%) studies examined differences between paretic and nonparetic muscles, and 5 (38%) compared people with stroke to people without stroke. Results from 9 of 13 studies (69%) supported a greater proportion of type II muscle fibers in the paretic limb. Of those, 4 studies (42 participants), 3 studies (17 participants), and 1 study (1 participant) saw no differences, preferential type II and type I CSA loss between limbs, respectively.

CONCLUSION

Of the limited available evidence, stroke appears to result in a shift to a higher proportion of type II muscle fibers in the paretic muscles. There are mixed results for effects on muscle fiber CSA, but there is some evidence of specific atrophy of type II muscle fibers.

IMPACT

Changes in paretic skeletal muscle fibers of individuals with stroke may explain, in part, the substantial losses in strength and power in this population. Interventions to restore type II muscle fiber size may benefit people with stroke.

SIX1+PAX3+ identify a progenitor for myogenic lineage commitment from hPSCs

The earliest skeletal muscle progenitor cells (SMPCs) derived from human pluripotent stem cells (hPSCs) are often identified by factors expressed by a diverse number of progenitors. An early transcriptional checkpoint that defines myogenic commitment could improve hPSC differentiation to skeletal muscle. Analysis of several myogenic factors in human embryos and early hPSC differentiations found SIX1+PAX3+ co-expression was most indictive of myogenesis. Using dCas9-KRAB hPSCs, we demonstrate early inhibition of SIX1 alone significantly decreased PAX3 expression, reduced PAX7+ SMPCs, and myotubes later in differentiation. Emergence of SIX1+PAX3+ precursors can be improved by manipulating seeding density, monitoring metabolic secretion, and altering the concentration of CHIR99021. These modifications resulted in the co-emergence of hPSC-derived sclerotome, cardiac, and neural crest that we hypothesized enhanced hPSC myogenic differentiation. Inhibition of non-myogenic lineages modulated PAX3 independent of SIX1. To better understand SIX1 expression, we compared directed differentiations to fetal progenitors and adult satellite cells by RNA-seq. While SIX1 continued to be expressed across human development, SIX1 co-factor expression was dependent on developmental timing. We provide a resource to enable efficient derivation of skeletal muscle from hPSCs.

Local and systemic administration of AAV vectors with alphaherpesvirus latency-associated promoter 2 drives potent transgene expression in mouse liver, kidney, and skeletal muscle

Adeno-associated virus (AAV) has great potential as a source of treatments for conditions that might respond to potent and ubiquitous transgene expression. However, among its drawbacks, the genetic "payload" of AAV vectors is limited to <4.9 kb and some commonly used gene promoters are sizeable and susceptible to transcriptional silencing. We recently described a short (404 bp), potent, and persistent promoter obtained from the genome of pseudorabies virus (PrV) called alphaherpesvirus latency-associated promoter 2 (LAP2). Here, we evaluated the biodistribution and potency of transgene expression in mouse peripheral tissues in response to local and systemic administration of AAV8-LAP2 and AAV9-LAP2. We found that administration of these vectors resulted in levels of transgene expression that were similar to the larger EF1α promoter. LAP2 drives potent transgene expression in mouse liver and kidney when administered systemically and in skeletal muscle in response to intramuscular delivery. Notably, in skeletal muscle, administration of vectors with LAP2 and EF1α promoters resulted in preferential transduction of myofibers type 2. A direct side-by-side comparison between LAP2 and the EF1α promoter revealed that, despite its smaller size, LAP2 was equally potent to the EF1α promoter and resulted in widespread gene expression after IV and IM administration of AAV8 or AAV9 vectors. Collectively, these findings suggest that constructs that include LAP2 may have the capacity to deliver large therapeutically effective payloads in support of future gene therapy protocols.

Defective Muscle Ketone Body Oxidation Disrupts BCAA Catabolism by Altering Mitochondrial Branched-Chain Aminotransferase

Ketone bodies are an endogenous fuel source generated primarily by the liver to provide alternative energy for extrahepatic tissues during prolonged fasting and exercise. Skeletal muscle is an important site of ketone body oxidation which occurs through a series of reactions requiring the enzyme succinyl-CoA:3-ketoacid-CoA transferase (SCOT/Oxct1). We have previously shown that deleting SCOT in the skeletal muscle protects against obesity-induced insulin resistance by increasing pyruvate dehydrogenase (PDH) activity, the rate-limiting enzyme of glucose oxidation. However, it remains unclear whether inhibiting muscle ketone body oxidation causes hypoglycemia and affects fuel metabolism in the absence of obesity. Here, we show that lean mice lacking skeletal muscle SCOT (SCOT^SkM-/-) exhibited no overt phenotypic differences in glucose and fat metabolism from their human α-skeletal actin-Cre (HSA^Cre) littermates. Of interest, we found that plasma and muscle branched-chain amino acid (BCAA) levels are elevated in SCOT^SkM-/- lean mice compared to their HSA^Cre littermates. Interestingly, this alteration in BCAA catabolism was only seen in SCOT^SkM-/- mice under low-fat feeding and associated with decreased expression of mitochondrial branched-chain aminotransferases (BCATm/Bcat2), the first enzyme in BCAA catabolic pathway. Loss- and gain-of-function studies in C2C12 myotubes demonstrated that suppressing SCOT markedly diminished BCATm expression, whereas overexpressing SCOT resulted in an opposite effect without influencing BCAA oxidation enzymes. Further, SCOT overexpression in C2C12 myotubes significantly increased luciferase activity driven by a Bcat2 promoter construct. Together, our findings indicate that SCOT regulates the expression of the Bcat2 gene, which, through the abundance of its product BCATm, may influence circulating BCAA concentrations.

Lowered muscle glycogen reduces body mass with no effect on short-term exercise performance in men

Performance in short-duration sports is highly dependent on muscle glycogen, but the total degradation is only moderate and considering the water-binding property of glycogen, unnecessary storing of glycogen may cause an unfavorable increase in body mass. To investigate this, we determined the effect of manipulating dietary carbohydrates (CHO) on muscle glycogen content, body mass and short-term exercise performance. In a cross-over design twenty-two men completed two maximal cycle tests of either 1-min (n = 10) or 15-min (n = 12) duration with different pre-exercise muscle glycogen levels. Glycogen manipulation was initiated three days prior to the tests by exercise-induced glycogen-depletion followed by ingestion of a moderate (M-CHO) or high (H-CHO) CHO-diet. Subjects were weighed before each test, and muscle glycogen content was determined in biopsies from m. vastus lateralis before and after each test. Pre-exercise muscle glycogen content was lower following M-CHO than H-CHO (367 mmol · kg^-1 DW vs. 525 mmol · kg^-1 DW, P < 0.00001), accompanied by a 0.7 kg lower body mass (P < 0.00001). No differences were observed in performance between diets in neither the 1-min (P = 0.33) nor the 15-min (P = 0.99) test. In conclusion, pre-exercise muscle glycogen content and body mass was lower after ingesting moderate compared with high amounts of CHO, while short-term exercise performance was unaffected. This demonstrates that adjusting pre-exercise glycogen levels to the requirements of competition may provide an attractive weight management strategy in weight-bearing sports, particularly in athletes with high resting glycogen levels.

Comparing the Fracture Profile of Osteosarcopenic Older Adults with Osteopenia/Osteoporosis Alone

PURPOSE

To determine whether osteosarcopenia is associated with a greater likelihood of recurrent fractures, as well as type of fracture, than osteopenia/osteoporosis or sarcopenia alone.

METHODS

Anthropometry (height/weight; scales and stadiometer), body composition (bone mineral density [BMD] and appendicular lean mass; dual-energy x-ray absorptiometry), grip strength (hydraulic dynamometer), and gait speed (4 m) were measured in an outpatient clinic. WHO definition for osteopenia/osteoporosis (BMD T-score below -1 SDs) while sarcopenia was defined by SDOC or EWGSOP2. Number and location of fractures within the past 5 years were self-reported and verified by medical records (unverified fractures excluded). Univariable and multivariable regressions were used to examine the association between the exposure and outcome while adjusting for confounders.

RESULTS

481 community-dwelling older adults (median age: 78, IQR: 72, 83; 75.9% women) were included. Prevalence of osteosarcopenia depended on the definition (SDOC: 179 (37.2%); EWGSOP2: 123 (25.6%)). In multivariable analysis adjusting for age, sex, alcohol, smoking, BMI, lowest BMD T-score, physical activity, and comorbidities, the likelihood of recurrent fractures (≥ 2 vs 0-1) was significantly higher in those with osteosarcopenia versus osteopenia/osteoporosis irrespective of the definition (SDOC: odds ratio [OR]: 1.63, 95% CI: 1.03, 2.59, p = 0.037; EWGSOP2: OR: 1.83, 95% CI: 1.12, 3.01, p = 0.016]. Associations with sarcopenia alone (SDOC: 10; EWGSOP2: 7) were not possible due to the extremely low prevalence of this condition in those with normal BMD.

CONCLUSION

Our data suggest osteosarcopenia is associated with a greater likelihood of recurrent fractures versus osteopenia/osteoporosis alone. Further studies are needed to evaluate the relationship with sarcopenia alone.

Increased Adiposity is Associated with Altered Skeletal Muscle Energetics

The objective of this pilot study was to characterize relationships between skeletal muscle energy metabolism and body composition in healthy adults with varied amounts and distribution of adipose tissue. In vivo muscle energetics were quantified using dynamic ³¹P magnetic resonance spectroscopy with knee extension exercise standardized to subject lean body mass. Spearman correlation analysis examined relationships between muscle metabolism indices and measures of adiposity including body mass index (BMI), total body fat, and quadriceps intermuscular adipose tissue (IMAT). Post-hoc partial correlations were examined controlling for additional body composition measures. Kruskal-Wallis tests with Dunn-Sidak post-hoc comparisons evaluated group differences in energy metabolism based on body composition profiles (i.e. lean, normal-weight obese, and overweight-obese) and IMAT tertiles. BMI negatively correlated with end-exercise muscle pH after correcting for IMAT and total body fat (r=-0.46, p=.034). Total adiposity negatively correlated with maximum oxidative capacity after correcting for IMAT (r=-0.54, p=.013). IMAT positively correlated with muscle proton buffering capacity after correcting for total body fat (r=0.53, p=.023). Body composition groups showed differences in end-exercise fall in [PCr] with normalized workload (p=.036; post-hoc: overweight-obese < lean, p=.029) and maximum oxidative capacity (p=.021; post-hoc: normal-weight obese < lean, p=.016). IMAT tertiles showed differences in end-exercise fall in [PCr] with normalized workload (p=.035; post-hoc: 3^rd < 1^st, p=.047). Taken together, these results support increased adiposity is associated with reduced muscle energetic efficiency with more reliance on glycolysis, and when accompanied with reduced lean mass, is associated with reduced maximum oxidative capacity.

Bacillus coagulans T4 and Lactobacillus paracasei TD3 Ameliorate Skeletal Muscle Oxidative Stress and Inflammation in High-Fat Diet-Fed C57BL/6J Mice

Background

This study aims to investigate the effects of Bacillus coagulans T4 and Lactobacillus paracasei TD3 probiotics on skeletal muscle inflammation and oxidative stress in C57BL/6J mice fed a high-fat diet (HFD).

Methods

Probiotics B. coagulans T4, and L. paracasei TD3 were administered to male C57BL/6J mice fed with HFD. The gene expression of macrophage infiltration markers, inflammatory cytokines, and oxidative stress indicators in the muscle tissue was investigated.

Results

Treatment with B. coagulans T4 and L. paracasei TD3 reduced macrophage infiltration, accompanied by a decrease in the expression of monocyte chemoattractant protein-1 (MCP-1) and an increase in the expression of interleukin (IL)-10. On the other hand, L. paracasei TD3 decreased malondialdehyde (MDA) while B. coagulans T4 decreased carbonyl and increased catalase activity.

Conclusions

Treatment with probiotics B. coagulans T4 and L. paracasei TD3 partially ameliorated obesity-induced skeletal muscle inflammation in HFD-fed mice.

Demographic and Genome Wide Association Analyses According to Muscle Mass Using Data of the Korean Genome and Epidemiology Study

BACKGROUND

Sarcopenia is commonly found in the elderly due to a decline in muscle mass. Many researchers have performed genome-wide association studies (GWAS) to find genetic risk factors of sarcopenia. Although many studies have discovered sarcopenia associated single nucleotide polymorphisms (SNPs), most of them are studies targeting Caucasians. The purpose of this study was to evaluate genetic correlation according to muscle mass in middle aged Koreans using data of the Korean Genome and Epidemiology Study (KOGES), a large population-based genomic cohort study.

METHODS

Baseline participants were 10,030 subjects aged 40 to 69 years who were from Ansan or Anseong in Gyeonggi-do, South Korea. Among them, 9,351 subjects with laboratory data available were included in this study. To identify sarcopenia associated variants, those in the top 30% and bottom 30% of muscle mass index (MMI) were compared. A total of 7,452 people with an MMI of 30-70% were excluded. A total of 1,004 people were also excluded due to missing data. Finally, 895 people were selected for this study. The Korea Biobank Array generated 500,568 SNPs for this dataset.

RESULTS

When subjects were divided into top 30% and bottom 30% of MMI, the top 30% had 169 men and 308 women and the bottom 30% had 220 men and 198 women. In men, age, body mass index (BMI), waist and hip were significantly (P < 0.005) different between top 30% and bottom 30% MMI groups. In women, age, BMI, waist, hip, and hypertension history were significantly different between the two MMI groups. There were 13 significant SNPs in men and 14 significant SNPs in women. Genes associated with variants in men based on the single-nucleotide polymorphism database (dbSNP) were LRP1B containing rs11679458 and RGS6 containing rs11848300. A gene associated with variants in women was Pi4K2A, which contained rs1189312 as a variant. In addition, rs11189312 was associated with expression quantitative trait loci (eQTL) of ZFYVE27 in skeletal muscles and other SNPs of ZFYVE27 (rs10882883, rs17108378, rs35077384) known to be associated with spastic paraplegia. The eQTL analysis revealed that rs11189312 was a variant associated with SNPs of ZFYVE27.

CONCLUSIONS

In the demographic study, significant results were found in BMI, waist, hip, history of hyperlipidemia, and sedentary life status in male group, and significant results were found in BMI, waist, hip, and hypertension history in female group. Variant rs11189312 was found to be a novel variant affecting ZFYVE27 expressed in skeletal muscles, suggesting that rs11189312 might be related to sarcopenia as a novel discovery of this study. Further study is needed to determine the association between sarcopenia and ZFYVE27 known to be associated with spastic paraplegia.

Methodical approaches to determine the rate of radial muscle displacement using tensiomyography: A scoping review and new reporting guideline

Tensiomyography is a non-invasive method to assess skeletal muscle contractile properties from the stimulated radial displacement. Many studies have used the rate of displacement (Vc) as an indirect measure of muscle contraction velocity. However, no standardised methodical approach exists to measure displacement and determine Vc. This review aimed to provide an overview of concepts to determine Vc and measurement protocols to foster the development of a standardised methodical approach. This review followed the Preferred Reporting Items for Systematic Reviews and meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guideline. Systematic searches were performed within five electronic databases and additional sources. The included 62 studies reported 10 different concepts to determine Vc, which we summarised in three groups. The determination concepts differed mainly regarding time intervals during the contraction phase considered and criteria used to define these intervals. Essential information on the equipment and raters, measurement setup, electrical stimulation procedure, and data analysis were frequently not reported. In conclusion, no consensus on how to determine Vc existed. Incomplete reporting of measurement protocols hindered study comparison, which obstructs developing a standardised approach. Therefore, we propose a new guideline for reporting measurement protocols, which covers the 1) equipment and rater, 2) measurement setup, including positioning of the subject, sensor and electrodes, 3) electrical stimulation, including initial stimulation amplitude, increment, and endpoint, and 4) data analysis, including selection criteria and number of analysed signals and a definition of derived parameters.

Human skeletal muscle nitrate and nitrite in individuals with peripheral arterial disease: Effect of inorganic nitrate supplementation and exercise

Skeletal muscle may act as a reservoir for N-oxides following inorganic nitrate supplementation. This idea is most intriguing in individuals with peripheral artery disease (PAD) who are unable to endogenously upregulate nitric oxide. This study analyzed plasma and skeletal muscle nitrate and nitrite concentrations along with exercise performance, prior to and following 12-weeks of exercise training combined with oral inorganic nitrate supplementation (EX+BR) or placebo (EX+PL) in participants with PAD. Non-supplemented, at baseline, there were no differences in plasma and muscle nitrate. For nitrite, muscle concentration was higher than plasma (+0.10 nmol.g^-1 ). After 12 -weeks, acute oral nitrate increased both plasma and muscle nitrate (455.04 and 121.14 nmol.g^-1 , p < 0.01), which were correlated (r = 0.63, p < 0.01), plasma nitrate increase was greater than in muscle (p < 0.01). Nitrite increased in the plasma (1.01 nmol.g^-1 , p < 0.05) but not in the muscle (0.22 nmol.g^-1 ) (p < 0.05 between compartments). Peak walk time (PWT) increased in both groups (PL + 257.6 s;BR + 315.0 s). Six-minute walk (6 MW) distance increased only in the (EX+BR) group (BR + 75.4 m). We report no substantial gradient of nitrate (or nitrite) from skeletal muscle to plasma, suggesting a lack of reservoir-like function in participants with PAD. Oral nitrate supplementation produced increases in skeletal muscle nitrate, but not skeletal muscle nitrite. The related changes in nitrate concentration between plasma and muscle suggests a potential for inter-compartmental nitrate "communication". Skeletal muscle did not appear to play a role in within compartment nitrate reduction. Muscle nitrate and nitrite concentrations did not appear to contribute to exercise performance in patients with PAD.

Quantification of the forearm muscles mechanical properties using Myotonometer: Intra- and Inter-Examiner reliability and its relation with hand grip strength

The primary objective of this study was to investigate the reliability of the myotonometer in the mechanical properties of the forearm muscles [m. extensor carpi radialis brevis (ECRB), and m. flexor carpi ulnaris (FCU)] in healthy individuals. The secondary objective was to investigate the relationship between the handgrip strength and mechanical properties of these forearm muscles. The mechanical properties (muscle tone, stiffness, and elasticity) of the ECRB and FCU were measured using the MyotonPRO device. Examiner 1 performed two sets of measurements with a time interval of 30 min to determine intra-examiner reliability. Examiner 2 performed measurements during the interval between the two sets of examiner 1. The intra- and inter-examiner reliabilities were excellent (ICC˃0.82) for muscle tone, stiffness, and elasticity of the FCU. Both intra- and inter-examiner reliability in the evaluation of ECRB muscle tone, elasticity, and stiffness was moderate to excellent (ICCs = 0.56-0.98). The muscle tone and stiffness properties of the FCU were positively correlated with the handgrip strength (p <.05). The study findings indicate that the MyotonPRO device is a reliable tool to quantify ECRB, and FCU muscles mechanical properties in healthy individuals.

Exogenous Oncostatin M induces Cardiac Dysfunction, Musculoskeletal Atrophy, and Fibrosis

Musculoskeletal diseases such as muscular dystrophy, cachexia, osteoarthritis, and rheumatoid arthritis impair overall physical health and reduce survival. Patients suffer from pain, dysfunction, and dysmobility due to inflammation and fibrosis in bones, muscles, and joints, both locally and systemically. The Interleukin-6 (IL-6) family of cytokines, most notably IL-6, is implicated in musculoskeletal disorders and cachexia. Here we show elevated circulating levels of OSM in murine pancreatic cancer cachexia and evaluate the effects of the IL-6 family member, Oncostatin M (OSM), on muscle and bone using adeno-associated virus (AAV) mediated over-expression of murine OSM in wildtype and IL-6 deficient mice. Initial studies with high titer AAV-OSM injection yielded high circulating OSM and IL-6, thrombocytosis, inflammation, and 60% mortality without muscle loss within 4 days. Subsequently, to mimic OSM levels in cachexia, a lower titer of AAV-OSM was used in wildtype and Il6 null mice, observing effects out to 4 weeks and 12 weeks. AAV-OSM caused muscle atrophy and fibrosis in the gastrocnemius, tibialis anterior, and quadriceps of the injected limb, but these effects were not observed on the non-injected side. In contrast, OSM induced both local and distant trabecular bone loss as shown by reduced bone volume, trabecular number, and thickness, and increased trabecular separation. OSM caused cardiac dysfunction including reduced ejection fraction and reduced fractional shortening. RNA-sequencing of cardiac muscle revealed upregulation of genes related to inflammation and fibrosis. None of these effects were different in IL-6 knockout mice. Thus, OSM induces local muscle atrophy, systemic bone loss, tissue fibrosis, and cardiac dysfunction independently of IL-6, suggesting a role for OSM in musculoskeletal conditions with these characteristics, including cancer cachexia.

The skeletal muscle phenotype of the DE50-MD dog model of Duchenne muscular dystrophy

Background: Animal models of Duchenne muscular dystrophy (DMD) are essential to study disease progression and assess efficacy of therapeutic intervention, however dystrophic mice fail to display a clinically relevant phenotype, limiting translational utility. Dystrophin-deficient dogs exhibit disease similar to humans, making them increasingly important for late-stage preclinical evaluation of candidate therapeutics. The DE50-MD canine model of DMD carries a mutation within a human 'hotspot' region of the dystrophin gene, amenable to exon-skipping and gene editing strategies. As part of a large natural history study of disease progression, we have characterised the DE50-MD skeletal muscle phenotype to identify parameters that could serve as efficacy biomarkers in future preclinical trials. Methods: Vastus lateralis muscles were biopsied from a large cohort of DE50-MD dogs and healthy male littermates at 3-monthly intervals (3-18 months) for longitudinal analysis, with multiple muscles collected post-mortem to evaluate body-wide changes. Pathology was characterised quantitatively using histology and measurement of gene expression to determine statistical power and sample sizes appropriate for future work. Results: DE50-MD skeletal muscle exhibits widespread degeneration/regeneration, fibrosis, atrophy and inflammation. Degenerative/inflammatory changes peak during the first year of life, while fibrotic remodelling appears more gradual. Pathology is similar in most skeletal muscles, but in the diaphragm, fibrosis is more prominent, associated with fibre splitting and pathological hypertrophy. Picrosirius red and acid phosphatase staining represent useful quantitative histological biomarkers for fibrosis and inflammation respectively, while qPCR can be used to measure regeneration ( MYH3, MYH8), fibrosis ( COL1A1), inflammation ( SPP1), and stability of DE50-MD dp427 transcripts. Conclusion: The DE50-MD dog is a valuable model of DMD, with pathological features similar to young, ambulant human patients. Sample size and power calculations show that our panel of muscle biomarkers are of strong pre-clinical value, able to detect therapeutic improvements of even 25%, using trials with only six animals per group.

The Heat Shock Connection: Skeletal Muscle Hypertrophy and Atrophy

Skeletal muscle is an integral tissue system that plays a crucial role in the physical function of all vertebrates and is a key target for maintaining or improving health and performance across the lifespan. Based largely on cellular and animal models, there is some evidence that various forms of heat stress with or without resistance exercise may enhance skeletal muscle growth or reduce its loss. It is not clear whether these stimuli are similarly effective in humans or meaningful in comparison to exercise alone across various heating methodologies. Furthermore, the magnitude by which heat stress may influence whole body thermoregulatory responses and the connection to skeletal muscle adaptation remains ambiguous. Finally, the underlying mechanisms, which may include interaction between relevant heat shock proteins and intracellular hypertrophy and atrophy related factors, remain unclear. In this narrative mini-review we examine the relevant literature regarding heat stress alone or in combination with resistance exercise emphasizing skeletal muscle hypertrophy and atrophy across cellular and animal models, as well as human investigations. Additionally, we present working mechanistic theories for heat shock protein mediated signaling effects regarding hypertrophy and atrophy related signaling processes. Importantly, continued research is necessary to determine the practical effects and mechanisms of heat stress with and without resistance exercise on skeletal muscle function via growth and maintenance.

A simple and scalable 3D printing methodology for generating aligned and extended human and murine skeletal muscle tissues

Preclinical biomedical and pharmaceutical research on disease causes, drug targets, and side effects increasingly relies on in vitro models of human tissue. 3D printing offers unique opportunities for generating models of superior physiological accuracy, as well as for automating their fabrication. Towards these goals, we here describe a simple and scalable methodology for generating physiologically relevant models of skeletal muscle. Our approach relies on dual-material micro-extrusion of two types of gelatin hydrogel into patterned soft substrates with locally alternating stiffness. We identify minimally complex patterns capable of guiding the large-scale self-assembly of aligned, extended, and contractile human and murine skeletal myotubes. Interestingly, we find high-resolution patterning is not required, as even patterns with feature sizes of several hundred micrometers is sufficient. Consequently, the procedure is rapid and compatible with any low-cost extrusion-based 3D printer. The generated myotubes easily span several millimeters, and various myotube patterns can be generated in a predictable and reproducible manner. The compliant nature and adjustable thickness of the hydrogel substrates, serves to enable extended culture of contractile myotubes. The method is further readily compatible with standard cell-culturing platforms as well as commercially available electrodes for electrically induced exercise and monitoring of the myotubes.

Effect of stimulation frequency on force, power, and fatigue of isolated mouse extensor digitorum longus muscle

This study examined the effect of stimulation frequency (140, 200, 230 and 260 Hz) on isometric force, work loop (WL) power, and the fatigue resistance of extensor digitorum longus (EDL) muscle (n=32), isolated from 8-10-week-old CD-1 female mice. Stimulation frequency had significant effects on isometric properties of isolated mouse EDL, whereby increasing stimulation frequency evoked increased isometric force, quicker activation, and prolonged relaxation (P <0.047), until 230 Hz and above, thereafter force and activation did not differ (P >0.137). Increasing stimulation frequency increased maximal WL power output (P <0.001; 140 Hz, 71.3±3.5; 200 Hz, 105.4±4.1; 230 Hz, 115.5±4.1; 260 Hz, 121.1±4.1 W.kg-1), but resulted in significantly quicker rates of fatigue during consecutive WL's (P <0.004). WL shapes indicate impaired muscle relaxation at the end of shortening and subsequent increased negative work appeared to contribute to fatigue at 230 and 260 Hz, but not at lower stimulation frequencies. Cumulative work was unaffected by stimulation frequency, except at the start of fatigue protocol where 230 and 260 Hz produced more work than 140 Hz (P <0.039). We demonstrate that stimulation frequency affects force, power, and fatigue, but effects are not uniform between different assessments of contractile performance. Therefore, future work examining contractile properties of isolated skeletal muscle should consider increasing stimulation frequency beyond that needed for maximal force when examining maximal power but utilise a sub-maximal stimulation frequency for fatigue assessments to avoid high degree of negative work atypical of in vivo function.

Motoric Cognitive Risk Syndrome: Prevalence and Cognitive Performance. A cross-sectional study

BACKGROUND

Motoric Cognitive Risk Syndrome (MCR) is a predementia stage where slow gait speed and subjective memory complaints are present. The purpose of this study was to estimate the prevalence of MCR and assess its relationship with sociodemographic factors and chronic conditions.

METHODS

This is a secondary analysis of the SABE Colombia study conducted in 2015. The analytic sample consisted of 17·577 participants. After determining MCR prevalence, logistic regression was performed to examine the correlates of MCR.

FINDINGS

The prevalence of MCR was 10·71 %. The median age was 71 years and women composed 74·63 % of the MCR group. After adjusting for confounding variables MCR was associated with increasing age (OR 1·69, CI 1·43 - 1·92), no or low education (OR 1·99, CI 1·67- 2·37), MMSE (OR 0·93, CI 0·91 - 0·95) and chronic conditions such as mental disorders (OR 1·36, CI 1·11-1·67), history of myocardial infarction (OR 1·24, CI 1·04 - 1·47), hypertension (OR 1·23, CI 1·08 - 1·40) and diabetes (OR 1.18, CI 1.01 - 1.37).

INTERPRETATION

This study found a prevalence of 10·71 % of MCR in Colombian older adults. Additionally, MCR was associated with chronic conditions and sociodemographic factors identified in prior studies. These results increase the awareness of a novel predementia stage whose identification can be performed by clinicians in the outpatient clinic, minimizing the cost of a full neuropsychologic evaluation performed in a memory clinic.

FUNDING

Funded by the Administrative Department of Science, Technology and Innovation (Colciencias) and the Ministry of Health and Social Protection of Colombia.

A Fully Automated Deep Learning Pipeline for Multi-Vertebral Level Quantification and Characterization of Muscle and Adipose Tissue on Chest CT Scans

Body composition on chest CT scans encompasses a set of important imaging biomarkers. This study developed and validated a fully automated analysis pipeline for multi-vertebral level assessment of muscle and adipose tissue on routine chest CT scans. This study retrospectively trained two convolutional neural networks on 629 chest CT scans from 629 patients (55% women; mean age, 67 years ± 10 [standard deviation]) obtained between 2014 and 2017 prior to lobectomy for primary lung cancer at three institutions. A slice-selection network was developed to identify an axial image at the level of the fifth, eighth, and 10th thoracic vertebral bodies. A segmentation network (U-Net) was trained to segment muscle and adipose tissue on an axial image. Radiologist-guided manual-level selection and segmentation generated ground truth. The authors then assessed the predictive performance of their approach for cross-sectional area (CSA) (in centimeters squared) and attenuation (in Hounsfield units) on an independent test set. For the pipeline, median absolute error and intraclass correlation coefficients for both tissues were 3.6% (interquartile range, 1.3%-7.0%) and 0.959-0.998 for the CSA and 1.0 HU (interquartile range, 0.0-2.0 HU) and 0.95-0.99 for median attenuation. This study demonstrates accurate and reliable fully automated multi-vertebral level quantification and characterization of muscle and adipose tissue on routine chest CT scans. Keywords: Skeletal Muscle, Adipose Tissue, CT, Chest, Body Composition Analysis, Convolutional Neural Network (CNN), Supervised Learning Supplemental material is available for this article. © RSNA, 2022.

KLB dysregulation mediates disrupted muscle development in intrauterine growth restriction

Abstract

Intrauterine growth restriction (IUGR) is a leading cause of neonatal morbidity and mortality in humans and domestic animals. Developmental adaptations of skeletal muscle in IUGR lead to increased risk of premature muscle loss and metabolic disease in later life. Here, we identified β‐Klotho (KLB), a fibroblast growth factor 21 (FGF21) co‐receptor, as a novel regulator of muscle development in IUGR. Using the pig as a naturally‐occurring disease model, we performed transcriptome‐wide profiling of fetal muscle (day 90 of pregnancy) from IUGR and normal‐weight (NW) littermates. We found that, alongside large‐scale transcriptional changes comprising multiple developmental, tissue injury and metabolic gene pathways, KLB was increased in IUGR muscle. Moreover, FGF21 concentrations were increased in plasma in IUGR fetuses. Using cultures of fetal muscle progenitor cells (MPCs), we showed reduced myogenic capacity of IUGR compared to NW muscle in vitro, as evidenced by differences in fusion indices and myogenic transcript levels, as well as mechanistic target of rapamycin (mTOR) activity. Moreover, transfection of MPCs with KLB small interfering RNA promoted myogenesis and mTOR activation, whereas treatment with FGF21 had opposite and dose‐dependent effects in porcine and also in human fetal MPCs. In conclusion, our results identify KLB as a novel and potentially critical mediator of impaired muscle development in IUGR, through conserved mechanisms in pigs and humans. Our data shed new light onto the pathogenesis of IUGR, a significant cause of lifelong ill‐health in humans and animals.

Key points

Intrauterine growth restriction (IUGR) is associated with large‐scale transcriptional changes in developmental, tissue injury and metabolic gene pathways in fetal skeletal muscle.

Levels of the fibroblast growth factor 21 (FGF21) co‐receptor, β‐Klotho (KLB) are increased in IUGR fetal muscle, and FGF21 concentrations are increased in IUGR fetal plasma.

KLB mediates a reduction in muscle development through inhibition of mechanistic target of rapamycin signalling.

These effects of KLB on muscle cells are conserved in pig and human, suggesting a vital role of this protein in the regulation of muscle development and function in mammals.

Automated cross-sectional analysis of trained, severely atrophied and recovering rat skeletal muscles using MyoVision 2.0

The number of myonuclei within a muscle fiber is an important factor in muscle growth, but its regulation during muscle adaptation is not well understood. We aimed to elucidate the timecourse of myonuclear dynamics during endurance training, loaded and concentric resistance training, and nerve silencing-induced disuse atrophy with subsequent recovery. We modified tibialis anterior muscle activity in free-living rats with electrical stimulation from implantable pulse generators, or with implantable osmotic pumps delivering tetrodotoxin (TTX) to silence the motor nerve without transection. We used the updated, automated software MyoVision to measure fiber type-specific responses in whole tibialis anterior cross-sections (~8000 fibers each). Seven days of continuous low frequency stimulation (CLFS) reduced muscle mass (-12%), increased slower myosin isoforms and reduced IIX/IIB fibers (-32%) and substantially increased myonuclei especially in IIX/IIB fibers (55.5%). High load resistance training (Spillover), produced greater hypertrophy (~16%) in muscle mass and fiber cross-sectional area (CSA) than low load resistance training (concentric, ~6%) and was associated with myonuclear addition in all fiber types (35-46%). TTX-induced nerve silencing resulted in progressive loss in muscle mass, fiber CSA, and myonuclei per fiber cross-section (-50.7%, -53.7%, -40.7%, respectively at 14 days). Myonuclear loss occurred in a fiber type-independent manner, but subsequent recovery during voluntary habitual activity suggested that type IIX/IIB fibers contained more new myonuclei during recovery from severe atrophy. This study demonstrates the power and accuracy provided by the updated MyoVision software and introduces new models for studying myonuclear dynamics in training, detraining, retraining, repeated disuse, and recovery.

Decomposition of tensiomyogram and comparison with torque twitch responses after post-activation potentiation

OBJECTIVES

This study evaluates the effect of post-activation potentiation (PAP) after 5x5s maximal voluntary isometric contractions (activation stimulus, AS) on tensiomyography (TMG) and torque twitch contractile parameters of vastus lateralis (VL) and medialis (VM), respectively. Further, we validated the decomposition of TMG response to separate responses of three fiber types.

METHODS

15 healthy individuals participated in this study (40% women; age 19±2.3 years). A decomposition of VL TMG response was done after optimal fitting of three exponential curves.

RESULTS

We found main effects in contraction time (Tc) for muscle, method and time. Furthermore, we found interactions between muscle*method, method*time and muscle*method*time. Compared to PRE AS, we found shorter TMG Tc in VL and VM during the first two minutes after AS. Torque Tc remained unchanged in VL, while it increased in VM within 30 seconds after AS. A decomposition of VL TMG response confirmed PAP effects being present only in decomposed type IIb muscle fibers.

CONCLUSION

The TMG is a sensitive method to detect PAP effects with a sensor mounted directly above the muscle belly. After the decomposition of the TMG signal to three separate muscle fiber phenotypes, we provided a non-invasive insight in the contribution of each muscle fiber phenotype to the PAP of the whole muscle.

The muscle contractile properties in female soccer players: inter-limb comparison using tensiomyography

OBJECTIVE

The present study aimed to: i) determine the contractile properties of the major lower limb muscles in female soccer players using tensiomyography; ii) investigate inter-limb differences; and iii) compare inter-limb differences between different selections and playing positions.

METHODS

A total of 52 female soccer players (A team; U19 and U17) were recruited. The vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF), biceps femoris (BF), gastrocnemius medialis (GM), lateralis (GL) and tibialis anterior (TA) of both lower limbs were evaluated.

RESULTS

When the entire sample was assessed regardless of selection or playing position, there were significant inter-limb differences in all measured muscles except BF. Compared to the non-dominant limb, the dominant limb had higher delay time in VL (p=0.008), while showing lower values in VM (p=0.023), GL (p=0.043) and GM (p=0.006). Contraction time was lower in the RF of the dominant limb (p=0.005) and VM (p=0.047), while showing higher values in VL (p=0.036) and TA (p<0.001) as compared to the non-dominant limb.

CONCLUSION

Given the differences found between the limbs in the whole sample studied, it is necessary to examine both limbs to gather a more in-depth understanding of underlying mechanisms related to neuromuscular functions in female soccer players.

LEVEL OF EVIDENCE

Prognostic study, Level II.

Aligned Poly(ε-caprolactone) Nanofibers Superimposed on Decellularized Human Amniotic Membrane Promoted Myogenic Differentiation of Adipose Derived Stem Cells

Objective

This study was designed to fabricate a suitable permanent scaffold for the normal aligned myotube formation and improve the process of myogenic differentiation of selected stem cells.

Materials and Methods

In this experimental study, an engineered scaffold composed of decellularized human amniotic membrane (DHAM) and electrospun fibers of poly(ε-caprolactone) (PCL) was fabricated and characterized. PCL nanofibers were superimposed on DHAM (PCL-DHAM) in two different patterns, including randomized fibers (Random) and aligned fibers (Aligned). Adipose derived stem cells (ADSCs) were isolated from adult Wistar rats and cultured on designed scaffold and induced to myotube differentiation. Using an MTT assay, the vitality of cells was determined. Then, myogenic cell differentiation was assessed using scan electron microscopy (SEM), immunofluorescence assay, and reverse transcription-polymerase chain reaction (RT-PCR).

Results

The mechanical properties of engineered PCL-DHAM composite improved significantly compared to DHAM as a control. The engineered PCL-DHAM promoted cell growth and high expression of myosin, Mhc2 and myogenin and thus enhanced the myotube formation.

Conclusion

These findings revealed that bio-composite membrane prepared from PCL nanofibers and DHAM, may represent a promising biomaterial as a desirable scaffold for applying in the bioengineered muscle repair.

Quantification of the Elastic Property of Normal Thigh Muscles Using MR Elastography: Our Initial Experience

Purpose

This study aimed to apply MR elastography (MRE) to achieve in vivo evaluation of the elastic properties of thigh muscles and validate the feasibility of quantifying the elasticity of normal thigh muscles using MRE.

Materials and Methods

This prospective study included 10 volunteer subjects [mean age, 32.5 years, (range, 23-45 years)] who reported normal activities of daily living and underwent both T2-weighted axial images and MRE of thigh muscles on the same day. A sequence with a motion-encoding gradient was used in the MRE to map the propagating shear waves in the muscle. Elastic properties were quantified as the shear modulus of the following four thigh muscles at rest; the vastus medialis, vastus lateralis, adductor magnus, and biceps femoris.

Results

The mean shear modulus was 0.98 ± 0.32 kPa and 1.00 ± 0.33 kPa for the vastus medialis, 1.10 ± 0.46 kPa and 1.07 ± 0.43 kPa for the vastus lateralis, 0.91 ± 0.41 kPa and 0.93 ± 0.47 kPa for the adductor magnus, and 0.99 ± 0.37 kPa and 0.94 ± 0.32 kPa for the biceps femoris, with reader 1 and 2, respectively. No significant difference was observed in the shear modulus based on sex (p < 0.05). Aging consistently showed a statistically significant negative correlation (p < 0.05) with the shear modulus of the thigh muscles, except for the vastus medialis (p = 0.194 for reader 1 and p = 0.355 for reader 2).

Conclusion

MRE is a quantitative technique used to measure the elastic properties of individual muscles with excellent inter-observer agreement. Age was consistently significantly negatively correlated with the shear stiffness of muscles, except for the vastus medialis.

miR-19b-3p is associated with a diametric response to resistance exercise in older adults and regulates skeletal muscle anabolism via PTEN inhibition

Understanding paradoxical responses to anabolic stimulation and identifying the mechanisms for this inconsistency in mobility-limited older adults may provide new targets for the treatment of sarcopenia. Our laboratory has discovered that dysregulation in microRNA (miRNA) that target anabolic pathways is a potential mechanism resulting in age-associated decreases in skeletal muscle mass and function (sarcopenia). The objective of the current study was to assess circulating miRNA expression profiles in diametric response of leg lean mass in mobility-limited older individuals after a 6-mo progressive resistance exercise training intervention (PRET) and determine the influence of differentially expressing miRNA on regulation of skeletal muscle mass. Participants were dichotomized by gain (Gainers; mean +561.4 g, n = 33) or loss (Losers; mean −589.8 g, n = 40) of leg lean mass after PRET. Gainers significantly increased fat-free mass 2.4% vs. −0.4% for Losers. Six miRNA (miR-1-3p, miR-19b-3p, miR-92a, miR-126, miR-133a-3p, and miR-133b) were significantly identified to be differentially expressed between Gainers and Losers, with miR-19b-3p being the miRNA most highly associated with increases in fat-free mass. Using an aging mouse model, we then assessed if miR-19b-3p expression was different in young mice with larger muscle mass compared with older mice. Circulating and skeletal muscle miR-19b-3p expression was higher in young compared with old mice and was positively associated with muscle mass and grip strength. We then used a novel integrative approach to determine if differences in circulating miR-19b-3p potentially translate to augmented anabolic response in human skeletal muscle cells in vitro. Results from this analysis identified that overexpression of miR-19b-3p targeted and downregulated PTEN by 64% to facilitate significant ∼50% increase in muscle protein synthetic rate as measured with SUnSET. The combine results of these three models identify miR-19b-3p as a potent regulator of muscle anabolism that may contribute to an inter-individual response to PRET in mobility-limited older adults.

Activity Levels in Survivors of the Intensive Care Unit

OBJECTIVE

Limited data exist on the quantification of activity levels and functional status in critically ill patients as they transition from the intensive care unit (ICU) to the wards and, subsequently, back into the community. The physical activity of critically ill patients from their ICU stay until 7 days after hospital discharge was characterized, as well as correlate physical activity levels with an objective measure of physical function.

METHODS

This prospective observational study of previously independent adults aged 55 or older, undergoing mechanical ventilation for up to 7 days, recruited participants at the time of spontaneous breathing trials or less than 24 hours after extubation. Participants received an accelerometer at enrollment to wear until 1 week after discharge.

RESULTS

Twenty-two participants received accelerometers; 15 were suitable for analysis. Participants had a mean (SD) age of 68 (9.6) years; 47% were female. Mean step counts were 95 (95% CI = 15-173) in the 3 days before ICU discharge, 257 (95% CI = 114-400) before hospital discharge, 1223 (95% CI = 376-2070) in the first 3 days at home, and 1278 (95% CI = 349-2207) between day 4 and 6 post-hospital discharge. Physical activity was significantly higher post- compared with pre-hospital discharge. Short Physical Performance Battery scores were poor at ICU and hospital discharge; however, they correlated moderately with physical activity levels immediately upon return home.

CONCLUSIONS

Physical activity remained low as survivors of critical illness transitioned from ICU to hospital wards, but significantly increased upon return to the community. Despite poor Short Physical Performance Battery scores at both ICU and hospital discharge, participants were significantly more active immediately after discharge than in their last 3 days of hospitalization. This may represent rapid functional improvement or, conversely, constrained physical activity in hospital.

IMPACT

This study highlights the need for further evaluation of physical activity constraints in hospital and ways to augment physical activity and function upon discharge.

LAY SUMMARY

Physical activity (step counts) increased modestly as survivors of critical illness transitioned from ICU to hospital wards, but significantly increased upon return to the community. This study highlights the need for further evaluation of physical activity constraints in the hospital setting and ways to augment physical activity and function postdischarge.

X-linked myopathy with excessive autophagy: First report of an Israeli family presenting with late onset lower limb girdle weakness

X-linked myopathy with excessive autophagy (XMEA) is a rare disorder characterized by slow progressive muscle weakness and distinctive pathology of excessive autophagic vacuoles on muscle biopsy. Here we report on five patients, in a single family, with proximal lower limb weakness. The proband, a 25-year-old man, presented with 5 years of progressive lower limbs proximal muscle weakness. His maternal grandfather and three of his maternal male cousins had similar clinical findings and were initially suspected to have Becker muscular dystrophy. Muscle biopsy in two affected family members demonstrated autophagic myopathy, and guided the genetic investigations to the identification of a pathogenic mutation, c.272G > C in the VMA21 gene, known to cause XMEA [1]. To the best of our knowledge this is the first identified Israeli Jewish family afflicted by XMEA.

Towards bioengineered skeletal muscle: recent developments in vitro and in vivo

Skeletal muscle is a functional tissue that accounts for approximately 40% of the human body mass. It has remarkable regenerative potential, however, trauma and volumetric muscle loss, progressive disease and aging can lead to significant muscle loss that the body cannot recover from. Clinical approaches to address this range from free-flap transfer for traumatic events involving volumetric muscle loss, to myoblast transplantation and gene therapy to replace muscle loss due to sarcopenia and hereditary neuromuscular disorders, however, these interventions are often inadequate. The adoption of engineering paradigms, in particular materials engineering and materials/tissue interfacing in biology and medicine, has given rise to the rapidly growing, multidisciplinary field of bioengineering. These methods have facilitated the development of new biomaterials that sustain cell growth and differentiation based on bionic biomimicry in naturally occurring and synthetic hydrogels and polymers, as well as additive fabrication methods to generate scaffolds that go some way to replicate the structural features of skeletal muscle. Recent advances in biofabrication techniques have resulted in significant improvements to some of these techniques and have also offered promising alternatives for the engineering of living muscle constructs ex vivo to address the loss of significant areas of muscle. This review highlights current research in this area and discusses the next steps required towards making muscle biofabrication a clinical reality.

The Assessment of Skeletal Muscle and Cortical Bone by Second-generation HR-pQCT at the Tibial Midshaft

BACKGROUND

Peripheral quantitative computed tomography (pQCT) is the current densitometric gold-standard for assessing skeletal muscle at the 66% proximal tibia site. High resolution peripheral quantitative computed tomography (HR-pQCT) is a leading technology for quantifying bone microarchitecture at the distal extremities, and with the second-generation HR-pQCT it is possible to measure proximal limb sites. Therefore, the objectives of this study were to: (1) assess the feasibility of using HR-pQCT to assess skeletal muscle parameters at the 66% proximal tibia site, and (2) test HR-pQCT skeletal muscle measurement reproducibility at this site.

METHODS

Adult participants (9 males; 7 females; ages 31-75) received 1 pQCT scan and 2 HR-pQCT scans at the 66% proximal site of the nondominant tibia. Participants were repositioned between HR-pQCT scans to test reproducibility. HR-pQCT and pQCT scans were analyzed to quantify muscle cross-sectional area (CSA) and muscle density. Coefficients of determination and Bland-Altman plots compared muscle parameters between pQCT and HR-pQCT. For short-term reproducibility, root-mean-square of coefficient of variance and least significant change were calculated.

RESULTS

HR-pQCT and pQCT measured muscle density and muscle CSA were positively correlated (R² = 0.66, R² = 0.95, p < 0.001, respectively). Muscle density was equivalent between HR-pQCT and pQCT; however, there was systematic and directional bias for muscle CSA, such that muscle CSA was 11% lower with HR-pQCT and bias increased with larger muscle CSA. Root-mean-square of coefficient of variance was 0.67% and 0.92% for HR-pQCT measured muscle density and muscle CSA, respectively, while least significant change was 1.4 mg/cm³ and 174.0 mm² for muscle density and muscle CSA, respectively.

CONCLUSION

HR-pQCT is capable of assessing skeletal muscle at the 66% site of the tibia with good precision. Measures of muscle density are comparable between HR-pQCT and pQCT.

2-D08 treatment regulates C2C12 myoblast proliferation and differentiation via the Erk1/2 and proteasome signaling pathways

SUMOylation is one of the post-translational modifications that involves the covalent attachment of the small ubiquitin-like modifier (SUMO) to the substrate. SUMOylation regulates multiple biological processes, including myoblast proliferation, differentiation, and apoptosis. 2-D08 is a synthetically available flavone, which acts as a potent cell-permeable SUMOylation inhibitor. Its mechanism of action involves preventing the transfer of SUMO from the E2 thioester to the substrate without influencing SUMO-activating enzyme E1 (SAE-1/2) or E2 Ubc9-SUMO thioester formation. However, both the effects and mechanisms of 2-D08 on C2C12 myoblast cells remain unclear. In the present study, we found that treatment with 2-D08 inhibits C2C12 cell proliferation and differentiation. We confirmed that 2-D08 significantly hampers the viability of C2C12 cells. Additionally, it inhibited myogenic differentiation, decreasing myosin heavy chain (MHC), MyoD, and myogenin expression. Furthermore, we confirmed that 2-D08-mediated anti-myogenic effects impair myoblast differentiation and myotube formation, reducing the number of MHC-positive C2C12 cells. In addition, we found that 2-D08 induces the activation of ErK1/2 and the degradation of MyoD and myogenin in C2C12 cells. Taken together, these results indicated that 2-D08 treatment results in the deregulated proliferation and differentiation of myoblasts. However, further research is needed to investigate the long-term effects of 2-D08 on skeletal muscles.

Effects of Quercetin and Coenzyme Q10 on Biochemical, Molecular, and Morphological Parameters of Skeletal Muscle in Trained Diabetic Rats

BACKGROUND

Diabetes mellitus (DM) affects the musculoskeletal system through its metabolic perturbations. Exercise modulates blood sugar levels and increases the body's sensitivity to insulin in patients with DM.

OBJECTIVE

This study aimed to investigate the potential effects of combined quercetin and coenzyme Q10 (CoQ10) supplements with or without exercise on the histological, biochemical and molecular structures of diabetic rat's skeletal muscle.

METHOD

A total of 64 adult male albino rats were divided into six groups: control, trained nondiabetic, non-trained diabetic, diabetic rats treated with combined CoQ10 and quercetin, diabetic rats with treadmill training, and diabetic rats treated with treadmill training and CoQ10 and quercetin. Blood and skeletal muscle samples were obtained from all groups for routine histological examination and biochemical determination of cytokine levels and protein activities. Quantitative real-time polymerase chain reaction (qRT-PCR) and morphometric analysis of PAS and Bax expressions were also performed.

RESULTS

Biochemical analysis revealed improvement in all studied parameters with combined CoQ10 and quercetin than exercise training alone. Combined treatment and exercise showed significant improvement in all parameters especially interleukin 6 and malondialdehyde. Fibronectin type III domain-containing protein 5 (FNDC5) expression and irisin levels increased in all trained groups but combined treatment with exercise significantly increased their levels than exercise alone. Histological analysis revealed improvement after exercise or combined treatment; however, when exercise was combined with CoQ10 and quercetin, marked improvement was observed.

CONCLUSION

the combination of CoQ10 and quercetin could be promising in preserving musculoskeletal function in patients with DM concomitantly with physical exercise.

Muscle-bone properties after prolonged voluntary wheel running in a mouse model of dominant severe osteogenesis imperfecta

OBJECTIVE

The objective of the current study is to assess the effect of a seven-week voluntary wheel running intervention on muscles and bones properties in a mouse model mimicking dominant severe osteogenesis imperfecta (OI).

METHODS

Female wild-type (WT) and OI (Col1a1^Jrt/+) mice either performed voluntarily wheel-running exercise for 7-weeks or remained sedentary. Running distance and speed, forelimb grip strength, isolated muscle force and fatigability as well as bone morphology and mechanical properties were assessed.

RESULTS

We demonstrate that female WT and OI mice voluntarily performed exercise, although OI mice exercised less than WT littermates. The exercise regimen increased soleus muscle masses in WT and OI but increased relative grip strength in WT mice only. Specific muscle force and fatigability were similar between WT and OI mice and did not improve with exercise. Furthermore, the exercise regimen did not improve the femoral architectural and biomechanical properties in OI mice.

CONCLUSION

Our study suggests that voluntary wheel running is not appropriate to assess the effects of exercise in a mouse model of OI. Findings from exercising OI mice model studies may not necessarily be transferable to humans.

Mitochondrial misreading in skeletal muscle accelerates metabolic aging and confers lipid accumulation and increased inflammation

We have recently reported on an experimental model of mitochondrial mistranslation conferred by amino acid exchange V338Y in the mitochondrial ribosomal protein MrpS5. Here we used a combination of RNA-Seq and metabolic profiling of homozygous transgenic MrpS5V338Y/V338Y mice to analyze the changes associated with the V338Y mutation in post-mitotic skeletal muscle. Metabolic profiling demonstrated age-dependent metabolic changes in the mutant V338Y animals, which included enhanced levels of age-associated metabolites and which were accompanied by increased glycolysis, lipid desaturation and eicosanoid biosynthesis, and alterations of the pentose phosphate pathway. In addition, transcriptome signatures of aged V338Y mutant muscle pointed to elevated inflammation, likely reflecting the increased levels of bioactive lipids. Our findings indicate that mistranslation-mediated chronic impairment of mitochondrial function affects specific bioenergetic processes in muscle in an age-dependent manner.

The myonuclear DNA methylome in response to an acute hypertrophic stimulus

In addition to multi-nucleated muscle fibres, numerous resident and infiltrating mononuclear cells populate the muscle compartment. As most epigenetic assays in skeletal muscle are conducted on whole tissue homogenates, essentially nothing is known about regulatory processes exclusively within muscle fibres in vivo. Utilizing a novel genetically modified mouse model developed by our laboratory, we (1) outline a simple and rapid workflow for isolating pure myonuclei from small tissue samples via fluorescent activated cell sorting and extracting high-quality large-fragment DNA for downstream analyses, and (2) provide information on myonuclear and interstitial cell nuclear CpG DNA methylation via reduced representation bisulphite sequencing (RRBS) using mice that were subjected to an acute mechanical overload of the plantaris muscle. In 3-month-old mice, myonuclei are ~50% of total nuclei in sham and ~30% in 3-d overloaded muscle, the difference being attributable to mononuclear cell infiltration and proliferation with overload. In purified myonuclei, pathway analysis of hypomethylated promoter regions following overload was distinct from interstitial nuclei and revealed marked regulation of factors that converge on the master regulator of muscle growth mTOR, and on autophagy. Specifically, acute hypomethylation of Rheb, Rictor, Hdac1, and Hdac2, in addition to a major driver of ribosome biogenesis Myc, reveals the epigenetic regulation of hypertrophic signalling within muscle fibres that may underpin the long-term growth response to loading. This study provides foundational information on global myonuclear epigenetics in vivo using RRBS, and demonstrates the importance of isolating specific nuclear populations to study the epigenetic regulation of skeletal muscle fibre adaptation.

Ethanol-Impaired Myogenic Differentiation is Associated With Decreased Myoblast Glycolytic Function

BACKGROUND

Myopathy affects nearly half of individuals with alcohol use disorder (AUD), and impaired skeletal muscle regenerative potential is a probable contributing factor. Previous findings from our laboratory indicate that chronic in vivo and in vitro ethanol (EtOH) treatment decreases myogenic potential of skeletal muscle myoblasts. Myogenesis, a highly coordinated process, requires shifts in cellular metabolic state allowing for myoblasts to proliferate and differentiate into mature myotubes. The objective of this study was to determine whether alcohol interferes with myoblast mitochondrial and glycolytic metabolism and impairs myogenic differentiation.

METHODS

Myoblasts were isolated from vastus lateralis muscle excised from alcohol-naïve adult male (n = 5) and female (n = 5) rhesus macaques. Myoblasts were proliferated for 3 days (day 0 differentiation; D0) and differentiated for 5 days (D5) with or without 50 mM EtOH. Metabolism was assessed using a mitochondrial stress test to measure oxygen consumption (OCR) and extracellular acidification (ECAR) rates at D0. Differentiation was examined at D5. Expression of mitochondrial and glycolytic genes and mitochondrial DNA (mtDNA) was measured at D0 and D5.

RESULTS

Ethanol significantly (p < 0.05) increased myoblast maximal OCR and decreased ECAR at D0, and decreased fusion index, myotubes per field, and total nuclei at D5. The EtOH-induced decrease in ECAR was associated with the EtOH-mediated decreases in fusion index and myotubes per field. EtOH did not alter the decrease in glycolytic gene expression and increase in mtDNA from D0 to D5.

CONCLUSION

During myoblast proliferation, EtOH decreased glycolytic metabolism and increased maximal OCR, suggesting that myoblast metabolic phenotype was dysregulated with EtOH. The EtOH-induced decrease in ECAR was associated with decreased differentiation. These findings suggest that EtOH-mediated shifts in metabolic phenotype may underlie impaired differentiation, which has important clinical implications for myogenesis in those affected by alcoholic myopathy.

Perioperative physical and nutritional therapy for tongue cancer-induced malnutrition and muscle atrophy: A case report

Malnutrition is a common complication in patients with tongue cancer who experience dysphagia and can steadily lead to skeletal muscle atrophy. Additionally, skeletal muscle loss commonly occurs in patients after invasive surgery. Therefore, patients with tongue cancer are at high risk of skeletal muscle atrophy during the perioperative phase of treatment. Over time, physical and nutritional therapy are expected to increase skeletal muscle mass and improve nutritional status. However, immediate benefits for patients in the perioperative phase of treatment are largely unknown. This case report aimed to evaluate the combined effects of physical and nutritional therapy for a patient in the perioperative phase of treatment for tongue cancer. We describe a 48-year-old woman diagnosed with tongue cancer. Her increasing difficulty with eating and swallowing led to malnutrition. After hospital admission for oral surgery, physical and nutritional therapy were initiated. Skeletal muscle mass measured by body composition analyzer and ultrasound apparatus showed increases, whereas blood tests to indicate nutritional status showed no improvement. This case suggests that physical and nutritional therapy are effective for increasing skeletal muscle during perioperative phase treatment in malnourished patients with tongue cancer and assessment of skeletal muscle mass is a reliable method for clinical evaluation.

Ketone Bodies Attenuate Wasting in Models of Atrophy

BACKGROUND

Cancer Anorexia Cachexia Syndrome (CACS) is a distinct atrophy disease negatively influencing multiple aspects of clinical care and patient quality of life. Although it directly causes 20% of all cancer-related deaths, there are currently no model systems that encompass the entire multifaceted syndrome, nor are there any effective therapeutic treatments.

METHODS

A novel model of systemic metastasis was evaluated for the comprehensive CACS (metastasis, skeletal muscle and adipose tissue wasting, inflammation, anorexia, anemia, elevated protein breakdown, hypoalbuminemia, and metabolic derangement) in both males and females. Ex vivo skeletal muscle analysis was utilized to determine ubiquitin proteasome degradation pathway activation. A novel ketone diester (R/S 1,3-Butanediol Acetoacetate Diester) was assessed in multifaceted catabolic environments to determine anti-atrophy efficacy.

RESULTS

Here, we show that the VM-M3 mouse model of systemic metastasis demonstrates a novel, immunocompetent, logistically feasible, repeatable phenotype with progressive tumor growth, spontaneous metastatic spread, and the full multifaceted CACS with sex dimorphisms across tissue wasting. We also demonstrate that the ubiquitin proteasome degradation pathway was significantly upregulated in association with reduced insulin-like growth factor-1/insulin and increased FOXO3a activation, but not tumor necrosis factor-α-induced nuclear factor-kappa B activation, driving skeletal muscle atrophy. Additionally, we show that R/S 1,3-Butanediol Acetoacetate Diester administration shifted systemic metabolism, attenuated tumor burden indices, reduced atrophy/catabolism and mitigated comorbid symptoms in both CACS and cancer-independent atrophy environments.

CONCLUSIONS

Our findings suggest the ketone diester attenuates multifactorial CACS skeletal muscle atrophy and inflammation-induced catabolism, demonstrating anti-catabolic effects of ketone bodies in multifactorial atrophy.

Isolation, Culture, and Differentiation of Primary Myoblasts Derived from Muscle Satellite Cells

The skeletal muscle is key for body mobility and motor performance, but aging and diseases often lead to progressive loss of muscle mass due to wasting or degeneration of muscle cells. Muscle satellite cells (MuSCs) represent a population of tissue stem cells residing in the skeletal muscles and are responsible for homeostatic maintenance and regeneration of skeletal muscles. Growth, injury, and degenerative signals activate MuSCs, which then proliferate (proliferating MuSCs are called myoblasts), differentiate and fuse with existing multinuclear muscle cells (myofibers) to mediate muscle growth and repair. Here, we describe a protocol for isolating MuSCs from skeletal muscles of mice for in vitro analysis. In addition, we provide a detailed protocol on how to culture and differentiate primary myoblasts into myotubes and an immunofluorescent staining procedure to characterize the cells. These methods are essential for modeling regenerative myogenesis in vitro to understand the dynamics, function and molecular regulation of MuSCs.

Efficiency of skeletal muscle decellularization methods and their effects on the extracellular matrix

Extracellular matrix (ECM) is widely considered to be integral to the function of skeletal muscle, providing mechanical support, transmitting force, and contributing to passive stiffness. Many functions and dysfunctions attributed to ECM are thought to stem from its mechanical properties, yet there are few data describing the mechanics of intact ECM. Such measurements require isolating intact ECM from the muscle cells it surrounds. The objectives of this study were to quantify the efficiency of three techniques for this purpose: Triton, Triton with sodium dodecyl sulfate, and latrunculin B; and to determine their impact on properties of the remaining ECM. Efficiency was quantified by DNA content and evaluation of western blot intensities for myosin and actin. The properties of ECM were quantified by collagen content and uniaxial tensile testing. We found that latrunculin B was the most efficient method for removing skeletal muscle cells, reducing DNA content to less than 10% of that seen in control muscles, and substantially reducing the myosin and actin to 15% and 23%, respectively; these changes were larger than for the competing methods. Collagen content after decellularization was not significantly different from control muscles for all methods. Only the stiffness of the muscles decellularized with latrunculin B differed significantly from control, having a Young's modulus reduced by 47% compared to the other methods at matched stresses. Our results suggest that latrunculin B is the most efficient method for decellularizing skeletal muscle and that the remaining ECM accounts for approximately half of the stiffness in passive muscle.

Caveolin-3 deficiency associated with the dystrophy P104L mutation impairs skeletal muscle mitochondrial form and function

BACKGROUND

Caveolin-3 (Cav3) is the principal structural component of caveolae in skeletal muscle. Dominant pathogenic mutations in the Cav3 gene, such as the Limb Girdle Muscular Dystrophy-1C (LGMD1C) P104L mutation, result in substantial loss of Cav3 and myopathic changes characterized by muscle weakness and wasting. We hypothesize such myopathy may also be associated with disturbances in mitochondrial biology. Herein, we report studies assessing the effects of Cav3 deficiency on mitochondrial form and function in skeletal muscle cells.

METHODS

L6 myoblasts were stably transfected with Cav3^P104L or expression of native Cav3 repressed by shRNA or CRISPR/Cas9 genome editing prior to performing fixed/live cell imaging of mitochondrial morphology, subcellular fractionation and immunoblotting, or analysis of real time mitochondrial respiration. Skeletal muscle from wild-type and Cav3^-/- mice was processed for analysis of mitochondrial proteins by immunoblotting.

RESULTS

Caveolin-3 was detected in mitochondrial-enriched membranes isolated from mouse gastrocnemius muscle and L6 myoblasts. Expression of Cav3^P104L in L6 myoblasts led to its targeting to the Golgi and loss of native Cav3 (>95%), including that associated with mitochondrial membranes. Cav3^P104L reduced mitochondrial mass and induced fragmentation of the mitochondrial network that was associated with significant loss of proteins involved in mitochondrial biogenesis, respiration, morphology, and redox function [i.e. PGC1α, succinate dehyrdogenase (SDHA), ANT1, MFN2, OPA1, and MnSOD). Furthermore, Cav3^P104L myoblasts exhibited increased mitochondrial cholesterol and loss of cardiolipin. Consistent with these changes, Cav3^P104L expression reduced mitochondrial respiratory capacity and increased myocellular superoxide production. These morphological, biochemical, and functional mitochondrial changes were phenocopied in myoblasts in which Cav3 had been silenced/knocked-out using shRNA or CRISPR. Reduced mitochondrial mass, PGC1α, SDHA, ANT1, and MnSOD were also demonstrable in Cav3^-/- mouse gastrocnemius. Strikingly, Cav3 re-expression in Cav3KO myoblasts restored its mitochondrial association and facilitated reformation of a tubular mitochondrial network. Significantly, re-expression also mitigated changes in mitochondrial superoxide, cholesterol, and cardiolipin content and recovered cellular respiratory capacity.

CONCLUSIONS

Our results identify Cav3 as an important regulator of mitochondrial homeostasis and reveal that Cav3 deficiency in muscle cells associated with the Cav3^P104L mutation invokes major disturbances in mitochondrial respiration and energy status that may contribute to the pathology of LGMD1C.

Immobilization Leads to Alterations in Intracellular Phosphagen and Creatine Transporter Content in Human Skeletal Muscle

The role of dysregulated intracellular creatine metabolism in disuse atrophy is unknown. In this study, skeletal muscle biopsy samples were obtained after 7-days of unilateral leg immobilization (IMMOB) and the non-immobilized control limb (CTRL) of 15 healthy males (23.1 ± 3.5 yrs). Samples were analyzed for fibre-type cross-sectional area (CSA) and creatine transporter (CreaT) at the cell membrane periphery (MEM) or intracellular (INT) areas, via immunoflouresence microscopy. Creatine kinase (CK) and AMP-activated protein kinase (AMPK) were determined via immunoblot. PCr, Cr and ATP were measured via enzymatic analysis. Body composition and maximal isometric knee extensor strength were assessed before and after disuse. Leg strength and fat-free mass were reduced in IMMOB (~32% and 4%, respectively; P<0.01 for both). Type II fibre CSA was smaller (~12%; P=0.028) and intramuscular PCr lower (~13%; P=0.015) in IMMOB vs. CTRL. CreaT protein was greater in Type I fibres in both limbs (P<0.01). CreaT was greater in IMMOB vs. CTRL (P < 0.01) and inversely associated with PCr concentration in both limbs (P < 0.05). MEM CreaT was greater than the INT CreaT in Type I and II fibres of both limbs (~14% for both; P<0.01 for both). Type I fibre CreaT tended to be greater in IMMOB vs. CTRL (P=0.074). CK was greater, and phospho-to-total AMPKThr172 tended to be greater, in IMMOB vs. CTRL (P=0.013 and 0.051, respectively). These findings suggest that modulation of intracellular creatine metabolism is an adaptive response to immobilisation in young healthy skeletal muscle.

Muscle-specific changes of lower extremities in the early period after total knee arthroplasty: Insight from tensiomyography

OBJECTIVE

This study aimed to evaluate changes in i) muscle contractile properties of both lower extremities by using tensiomyography (TMG); ii) patients' physical function, and iii) electromechanical efficiency (EME) of the gastrocnemius medialis muscle in total knee arthroplasty (TKA) patients from before to one-month after TKA.

METHODS

Twenty-six patients scheduled for TKA were included.

RESULTS

The significant muscle*time interaction was found for sustain time and maximal radial displacement (Dm) (η²≥0.219) only, whereas time*leg interaction was found for time delay and Dm (η²≥0.254) only. Post hoc analysis showed a significant decrease of Dm of vastus medialis and increase in contraction time (Tc) of both the vastus lateralis and rectus femoris muscles of the involved leg, respectively. Furthermore, reduction of knee extensors (-55.4%) and flexors (-22.2%) strength, timed up and go (-26.9%), 30s chair stand (-28.9%) and EME (-38.2%) was observed.

CONCLUSION

TKA treatment altered physical function as well as contractile properties of the main skeletal muscles surrounding the involved joint in the early period after surgery; however, alterations showed to be both limb and muscle-specific. This might provide clinicians and physiotherapist with additional information on how to adapt rehabilitation to the needs of an individual patient.

Chronic Alcohol Consumption Enhances Skeletal Muscle Wasting in Mice Bearing Cachectic Cancers: The Role of TNFα/Myostatin Axis

BACKGROUND

Chronic alcohol consumption enhances cancer-associated cachexia, which is one of the major causes of decreased survival. The precise molecular mechanism of how alcohol consumption enhances cancer-associated cachexia, especially skeletal muscle loss, remains to be elucidated.

METHODS

We used a mouse model of chronic alcohol consumption, in which 20% (w/v) alcohol was provided as sole drinking fluid, and Lewis lung carcinoma to study the underlying mechanisms.

RESULTS

We found that alcohol consumption up-regulated the expression of MAFbx, MuRF-1, and LC3 in skeletal muscle, suggesting that alcohol enhanced ubiquitin-mediated proteolysis and LC3-mediated autophagy. Alcohol consumption enhanced phosphorylation of Smad2/3, p38, and ERK and decreased the phosphorylation of FOXO1. These are the signaling molecules governing protein degradation pathways. Moreover, alcohol consumption slightly up-regulated the expression of insulin receptor substrate-1, did not affect phosphatidylinositol-3 kinase, but decreased the phosphorylation of Akt and mammalian target of rapamycin (mTOR), and down-regulated the expression of Raptor and p70 ribosomal kinase S6 kinase, suggesting that alcohol impaired protein synthesis signaling pathway in skeletal muscle of tumor-bearing mice. Alcohol consumption enhanced the expression of myostatin in skeletal muscle, plasma, and tumor, but did not affect the expression of myostatin in non-tumor-bearing mice. In TNFα knockout mice, the effects of alcohol-enhanced expression of myostatin and protein degradation-related signaling molecules, and decreased protein synthesis signaling in skeletal muscle were abolished. Consequently, alcohol consumption neither affected cancer-associated cachexia nor decreased the survival of TNFα KO mice bearing cachectic cancer.

CONCLUSIONS

Chronic alcohol consumption enhances cancer-associated skeletal muscle loss through suppressing Akt/mTOR-mediated protein synthesis pathway and enhancing protein degradation pathways. This process is initiated by TNFα and mediated by myostatin.

The Basic Study of the Mechanism of Propofol-Related Infusion Syndrome Using a Murine Skeletal Muscle Injury Model

Background

The pathophysiological mechanism of propofol-related infusion syndrome (PRIS) is believed to be due to the injury to the mitochondrial electron transport chain and the resultant metabolic disorders that are caused by both propofol agents and the lipid solvent. However, the mechanisms and causative factors of PRIS have not been fully elucidated.

Objectives

The aim of this study was to evaluate the possibility of a research model using the culture of differentiated C2C12 cells for fundamental research of PRIS.

Methods

First, differentiated C2C12 cells were cultured accompanied by several concentrations of chemical reagents of 2,6-diisopropylphenol (2,6 DIP) or dimethyl sulfoxide (DMSO) for 60 hours and the cell death rate was examined by trypan blue staining. Second, The cells were incubated with a commercially available propofol reagent or lipid reagent for 48 hours. The supernatant fluid of the cell culture medium was gathered and the numbers of floating cells were measured by cell counter. To investigate the mitochondrial disorder by the propofol preparation, JC-1, an experiment using fluorescent reagent, was performed for the 48 hours with 100 µg/mL propofol incubation.

Results

The rate of cell death was increased with elevating concentrations both of chemical reagents of 2,6 DIP group and dimethyl sulfoxide group. The rates of cell death were significantly higher in the 2,6 DIP group than DMSO group. The numbers of floating cells were increased with elevating concentrations both commercially available propofol reagent and lipid reagent groups. The decreased red/green fluorescence ratio by JC-1 staining in the propofol 100µg/mL group proved an attenuated mitochondrial membrane potential.

Conclusions

The dose-dependent cell damage induced by the propofol reagents and a lipid solvent may provide a proposed model as a basic experimental model for further investigations into PRIS.