Skeletal Muscle Architecture Research Articles

Diabetic Conditions Confer Metabolic and Structural Modifications to Tissue-Engineered Skeletal Muscle.

Skeletal muscle is a tissue that is directly involved in the progression and persistence of type 2 diabetes (T2D), a disease that is becoming increasingly common. Gaining better insight into the mechanisms that are affecting skeletal muscle dysfunction in the context of T2D has the potential to lead to novel treatments for a large number of patients. Through its ability to emulate skeletal muscle architecture while also incorporating aspects of disease, tissue-engineered skeletal muscle (TE-SkM) has the potential to provide a means for rapid high-throughput discovery of therapies to treat skeletal muscle dysfunction, to include that which occurs with T2D. Muscle precursor cells isolated from lean or obese male Zucker diabetic fatty rats were used to generate TE-SkM constructs. Some constructs were treated with adipogenic induction media to accentuate the presence of adipocytes that is a characteristic feature of T2D skeletal muscle. The maturity (compaction and creatine kinase activity), mechanical integrity (Young's modulus), organization (myotube orientation), and metabolic capacity (insulin-stimulated glucose uptake) were all reduced by diabetes. Treating constructs with adipogenic induction media increased the quantity of lipid within the diabetic TE-SkM constructs, and caused changes in construct compaction, cell orientation, and insulin-stimulated glucose uptake in both lean and diabetic samples. Collectively, the findings herein suggest that the recapitulation of structural and metabolic aspects of T2D can be accomplished by engineering skeletal muscle in vitro.

Dysregulation of ghrelin in diabetes impairs the vascular reparative response to hindlimb ischemia in a mouse model; clinical relevance to peripheral artery disease

Type 2 diabetes is a prominent risk factor for peripheral artery disease (PAD). Yet, the mechanistic link between diabetes and PAD remains unclear. This study proposes that dysregulation of the endogenous hormone ghrelin, a potent modulator of vascular function, underpins the causal link between diabetes and PAD. Moreover, this study aimed to demonstrate the therapeutic potential of exogenous ghrelin in a diabetic mouse model of PAD. Standard ELISA analysis was used to quantify and compare circulating levels of ghrelin between (i) human diabetic patients with or without PAD (clinic) and (ii) db/db diabetic and non-diabetic mice (lab). Db/db mice underwent unilateral hindlimb ischaemia (HLI) for 14 days and treated with or without exogenous ghrelin (150 µg/kg/day.) Subsequently vascular reparation, angiogenesis, hindlimb perfusion, structure and function were assessed using laser Doppler imaging, micro-CT, microangiography, and protein and micro-RNA (miRNA) analysis. We further examined hindlimb perfusion recovery of ghrelin KO mice to determine whether an impaired vascular response to HLI is linked to ghrelin dysregulation in diabetes. Patients with PAD, with or without diabetes, had significantly lower circulating levels of endogenous ghrelin, compared to healthy individuals. Diabetic db/db mice had ghrelin levels that were only 7% of non-diabetic mice. The vascular reparative capacity of diabetic db/db mice in response to HLI was impaired compared to non-diabetic mice and, importantly, comparable to ghrelin KO mice. Daily therapeutic treatment of db/db mice with ghrelin for 14 days post HLI, stimulated angiogenesis, and improved skeletal muscle architecture and cell survival, which was associated with an increase in pro-angiogenic miRNAs-126 and -132. These findings unmask an important role for endogenous ghrelin in vascular repair following limb ischemia, which appears to be downregulated in diabetic patients. Moreover, these results implicate exogenous ghrelin as a potential novel therapy to enhance perfusion in patients with lower limb PAD, especially in diabetics.

Volumetric muscle loss disrupts length-dependent architectural and functional characteristics of skeletal muscle

ABSTRACT Purpose/Aim: Skeletal muscle architecture is a primary determinant of function. Volumetric muscle loss (VML) injury is destructive; however, the impact on muscle architecture is uncharacterized. Methods: Architectural and functional effects of VML were assessed in rat tibialis anterior (TA) muscle model 4 weeks post-injury. Results: VML caused a 31% and 33% reduction in muscle weight (p < 0.001) and fiber length (p = 0.002), respectively, culminating a 34% reduction of fiber to muscle length ratio (FL:ML; p < 0.001). Fiber pennation angle (+14%; p = 0.150) and physiological cross-sectional area (PCSA; −12%; p = 0.220) were unchanged. VML injury reduced peak isometric force (Po) by 36% (p < 0.001), specific force (sPo = Po/PCSA) by 41% (vs. Po, p > 0.999), and force per gram muscle weight (Po/mw) by 18% (vs. Po, p < 0.001). VML injury increased the length at which Po was produced (Lo) by 8% (p = 0.009), and reduced functional excursion by 35% (p = 0.035). Conclusion: The architectural changes after VML injury preserved PCSA, and therefore preserved “potential” maximal force-producing capacity. At most, only half the Po deficit was due directly to the cumulative effect of horizontal and longitudinal tissue loss. Highlighting the impact of longitudinal muscle loss, VML injury reduced fiber length, and FL:ML and grossly disrupted length-dependent functional properties. These findings raise the importance of augmenting length-dependent muscle properties to optimize functional recovery after VML injury.

Ultrasound imaging to assess skeletal muscle architecture during movements: a systematic review of methods, reliability, and challenges.

B-mode ultrasound is often used to quantify muscle architecture during movements. Our objectives were to 1) systematically review the reliability of fascicle length (FL) and pennation angles (PA) measured using ultrasound during movements involving voluntary contractions; 2) systematically review the methods used in studies reporting reliability, discuss associated challenges, and provide recommendations to improve the reliability and validity of dynamic ultrasound measurements; and 3) provide an overview of computational approaches for quantifying fascicle architecture, their validity, agreement with manual quantification of fascicle architecture, and advantages and drawbacks. Three databases were searched until June 2019. Studies among healthy human individuals aged 17-85 yr that investigated the reliability of FL or PA in lower-extremity muscles during isoinertial movements and that were written in English were included. Thirty studies (n = 340 participants) were included for reliability analyses. Between-session reliability as measured by coefficient of multiple correlations (CMC), and coefficient of variation (CV) was FL CMC: 0.89-0.96; CV: 8.3% and PA CMC: 0.87-0.90; CV: 4.5-9.6%. Within-session reliability was FL CMC: 0.82-0.99; CV: 0.0-6.7% and PA CMC: 0.91; CV: 0.0-15.0%. Manual analysis reliability was FL CMC: 0.89-0.96; CV: 0.0-15.9%; PA CMC: 0.84-0.90; and CV: 2.0-9.8%. Computational analysis FL CMC was 0.82-0.99, and PA CV was 14.0-15.0%. Eighteen computational approaches were identified, and these generally showed high agreement with manual analysis and high validity compared with phantoms or synthetic images. B-mode ultrasound is a reliable method to quantify fascicle architecture during movement. Additionally, computational approaches can provide a reliable and valid estimation of fascicle architecture.

What makes long-term resistance-trained individuals so strong? A comparison of skeletal muscle morphology, architecture, and joint mechanics.

The greater muscular strength of long-term resistance-trained (LTT) individuals is often attributed to hypertrophy, but the role of other factors, notably maximum voluntary specific tension (ST), muscle architecture, and any differences in joint mechanics (moment arm), have not been documented. The aim of the present study was to examine the musculoskeletal factors that might explain the greater quadriceps strength and size of LTT vs. untrained (UT) individuals. LTT (n = 16, age 21.6 ± 2.0 yr) had 4.0 ± 0.8 yr of systematic knee extensor heavy-resistance training experience, whereas UT (n = 52; age 25.1 ± 2.3 yr) had no lower-body resistance training experience for >18 mo. Knee extension dynamometry, T1-weighted magnetic resonance images of the thigh and knee, and ultrasonography of the quadriceps muscle group at 10 locations were used to determine quadriceps: isometric maximal voluntary torque (MVT), muscle volume (QVOL), patella tendon moment arm (PTMA), pennation angle (QΘP) and fascicle length (QFL), physiological cross-sectional area (QPCSA), and ST. LTT had substantially greater MVT (+60% vs. UT, P < 0.001) and QVOL (+56%, P < 0.001) and QPCSA (+41%, P < 0.001) but smaller differences in ST (+9%, P < 0.05) and moment arm (+4%, P < 0.05), and thus muscle size was the primary explanation for the greater strength of LTT. The greater muscle size (volume) of LTT was primarily attributable to the greater QPCSA (+41%; indicating more sarcomeres in parallel) rather than the more modest difference in FL (+11%; indicating more sarcomeres in series). There was no evidence in the present study for regional hypertrophy after LTT.NEW & NOTEWORTHY Here we demonstrate that the larger muscle strength (+60%) of a long-term (4+ yr) resistance-trained group compared with untrained controls was due to their similarly larger muscle volume (+56%), primarily due to a larger physiological cross-sectional area and modest differences in fascicle length, as well as modest differences in maximum voluntary specific tension and patella tendon moment arm. In addition, the present study refutes the possibility of regional hypertrophy, despite large differences in muscle volume.

Changes in human skeletal muscle architecture and function induced by extended spaceflight

The aim of this study was to quantitatively describe the relationships between joint angles and muscle architecture (lengths (Lf) and angles (Θf) of fascicles) of human triceps surae [medial (MG) and lateral (LG) gastrocnemius and soleus (SOL) muscles] invivo for three men-cosmonaut after long-duration spaceflight. Sagittal sonographs of MG, LG, SOL were taken at ankle was positioned at 15° (dorsiflexion), 0° (neutral position), +15°, and +30° (plantarflexion), with the knee at 90° at rest and after a long-duration spaceflight. At each position, longitudinal ultrasonic images of the MG and LG and SOL were obtained while the cosmonauts was relaxed from which fascicle lengths and angles with respect to the aponeuroses were determined. After space flight plantarflexor force declined significantly (26%; p < 0.001). The internal architecture of the GM, and LG, and SOL muscle was significantly altered. In the passive condition, Lf changed from 45, 53, and 39 mm (knee, 0°, ankle, −15°) to 26, 33, and 28 mm (knee, 90° ankle, 30°) for MG, LG, and SOL, respectively. Different lengths and angles of fascicles, and their changes by contraction, might be related to differences in force-producing capabilities of the muscles and elastic characteristics of tendons and aponeuroses. The three heads of the triceps surae muscle substantially differ in architecture, which probably reflects their functional roles. Differences in fiber length and pennation angle that were observed among the muscles and could be associated with differences in force production and in elastic properties of musculo-tendinous complex and aponeuroses.

Systemic AAV8-mediated delivery of a functional copy of muscle glycogen phosphorylase (Pygm) ameliorates disease in a murine model of McArdle disease.

McArdle disease is a disorder of carbohydrate metabolism that causes painful skeletal muscle cramps and skeletal muscle damage leading to transient myoglobinuria and increased risk of kidney failure. McArdle disease is caused by recessive mutations in the muscle glycogen phosphorylase (PYGM) gene leading to absence of PYGM enzyme in skeletal muscle and preventing access to energy from muscle glycogen stores. There is currently no cure for McArdle disease. Using a preclinical animal model, we aimed to identify a clinically translatable and relevant therapy for McArdle disease. We evaluated the safety and efficacy of recombinant adeno-associated virus serotype 8 (rAAV8) to treat a murine model of McArdle disease via delivery of a functional copy of the disease-causing gene, Pygm. Intraperitoneal injection of rAAV8-Pygm at post-natal day 1-3 resulted in Pygm expression at 8weeks of age, accompanied by improved skeletal muscle architecture, reduced accumulation of glycogen and restoration of voluntary running wheel activity to wild-type levels. We did not observe any adverse reaction to the treatment at 8weeks post-injection. Thus, we have investigated a highly promising gene therapy for McArdle disease with a clear path to the ovine large animal model endemic to Western Australia and subsequently to patients.

In vivo muscle morphology comparison in post-stroke survivors using ultrasonography and diffusion tensor imaging

Skeletal muscle architecture significantly influences the performance capacity of a muscle. A DTI-based method has been recently considered as a new reference standard to validate measurement of muscle structure in vivo. This study sought to quantify muscle architecture parameters such as fascicle length (FL), pennation angle (PA) and muscle thickness (tm) in post-stroke patients using diffusion tensor imaging (DTI) and to quantitatively compare the differences with 2D ultrasonography (US) and DTI. Muscle fascicles were reconstructed to examine the anatomy of the medial gastrocnemius, posterior soleus and tibialis anterior in seven stroke survivors using US- and DTI-based techniques, respectively. By aligning the US and DTI coordinate system, DTI reconstructed muscle fascicles at the same scanning plane of the US data can be identified. The architecture parameters estimated based on two imaging modalities were further compared. Significant differences were observed for PA and tm between two methods. Although mean FL was not significantly different, there were considerable intra-individual differences in FL and PA. On the individual level, parameters measured by US agreed poorly with those from DTI in both deep and superficial muscles. The significant differences in muscle parameters we observed suggested that the DTI-based method seems to be a better method to quantify muscle architecture parameters which can provide important information for treatment planning and to personalize a computational muscle model.

Sex Differences in Correlations Between Muscle Architecture and Impulse in a Heterogenous Group of Athletes

BACKGROUND: Previous investigations have identified moderate to strong relationships between skeletal muscle architecture (SMA) and performance measures in athletes, however differences between males and females in this regard are not well known. A better understanding of relationships between task-specific impulse windows and SMA in males and females may allow coaches to direct training stimuli toward improving specific morphological underpinnings of sport performance for the athletes under their care. PURPOSE: The purpose of this analysis was to determine relationships between components of SMA and isometric impulse in male and female athletes. METHODS: Pennation angle (PA), fascicle length (FL), and anatomical cross-sectional area (ACSA) were determined for the vastus lateralis muscle via β-mode ultrasonography in a group of male (n = 94) and female (n = 61) collegiate, club, and international athletes. Net isometric impulse at 50, 90, 200, and 250 ms was measured during an isometric mid-thigh pull (IMTP) test administered pre-season as part of an ongoing athlete monitoring program. RESULTS: Pearson product-moment correlation revealed weak correlations between FL and impulse in males (r = 0.33 to 0.36, p < 0.05) but not in females, weak correlations between CSA and impulse in males (r = 0.39 to 0.48, p < 0.05), and weak to moderate correlations between CSA and impulse in females (r = 0.55 to 0.62, p < 0.05). CONCLUSIONS: These results indicate that there may be sex-based differences in the physiological underpinnings of impulse generation in trained athletes, particularly in relation to both muscle size and fascicle length of the vastus lateralis. Further research should investigate changes in these relationships over time and consider contributions from neuromuscular components.

Dietary Linoleic Acid Targets Skeletal Muscle to Impact Energy Metabolism (P08-124-19)

ObjectivesInvestigate the impact of dietary linoleic acid (LA) on whole-body energy metabolism, fatty acid uptake, oxylipin metabolites, and energy production machinery in skeletal muscle. MethodsMice were fed modified AIN-93 M diets containing 6% wt of LA or palmitic acid (PA) for 5 weeks. To address energy balance, grip strength, blood glucose, and body composition were measured weekly and indirect calorimetry was performed after 4.5 weeks of diet. To address skeletal muscle architecture, cross-sectional area was quantified in quadriceps. To determine the effect of LA diet on skeletal muscle lipids, fatty acid composition was measured in quadriceps using GC. Targeted lipidomics using LC-MS/MS was utilized to measure LA-derived oxylipins in mitochondria isolated from gastrocnemius. ResultsNo difference in food intake, body weight, blood glucose, or body composition were observed between diet groups. Mice fed the LA diet exhibited higher heat production and lower respiratory exchange ratio, independent of ambulatory activity compared to mice fed the PA diet. Cross sectional area analysis in quadriceps muscle revealed that mice fed the LA diet had smaller muscle fibers compared to mice fed the PA diet. The LA diet increased LA level in quadriceps. Using hierarchal cluster analysis, we identified several unique patterns of oxylipins that impact insulin sensitivity and may be associated with increased mitochondrial capacity. Mice fed the LA diet exhibited a three-fold increase of oxylipin metabolites 9- and 13-HODE, and 12,13-diHOME. ConclusionsMice fed a diet fortified in LA have increased LA in skeletal muscle, changes to skeletal muscle architecture, favorable changes to whole body energy metabolism, and increases in LA-derived oxylipins in skeletal muscle mitochondria. Our discovery that LA generates 9-HODE and 13-HODE in muscle mitochondria suggests that downstream pathways, including PPARg transactivation, may be linked with effects on muscle energy metabolism. Funding SourcesFunding was provided by the National Institutes of Health (NIH) R21CA185140, Ohio Agriculture Research and Development Center and the Carol S. Kennedy Professorship. DBS is supported by the Center for Muscle Health and Neuromuscular Disorders Predoctoral Research Fellowship.

CAP2 deficiency delays myofibril actin cytoskeleton differentiation and disturbs skeletal muscle architecture and function

Actin filaments (F-actin) are key components of sarcomeres, the basic contractile units of skeletal muscle myofibrils. A crucial step during myofibril differentiation is the sequential exchange of α-actin isoforms from smooth muscle (α-SMA) and cardiac (α-CAA) to skeletal muscle α-actin (α-SKA) that, in mice, occurs during early postnatal life. This "α-actin switch" requires the coordinated activity of actin regulators because it is vital that sarcomere structure and function are maintained during differentiation. The molecular machinery that controls the α-actin switch, however, remains enigmatic. Cyclase-associated proteins (CAP) are a family of actin regulators with largely unknown physiological functions. We here report a function for CAP2 in regulating the α-actin exchange during myofibril differentiation. This α-actin switch was delayed in systemic CAP2 mutant mice, and myofibrils remained in an undifferentiated stage at the onset of the often excessive voluntary movements in postnatal mice. The delay in the α-actin switch coincided with the onset of motor function deficits and histopathological changes including a high frequency of type IIB ring fibers. Our data suggest that subtle disturbances of postnatal F-actin remodeling are sufficient for predisposing muscle fibers to form ring fibers. Cofilin2, a putative CAP2 interaction partner, has been recently implicated in myofibril actin cytoskeleton differentiation, and the myopathies in cofilin2 and CAP2 mutant mice showed striking similarities. We therefore propose a model in which CAP2 and cofilin2 cooperate in actin regulation during myofibril differentiation.

Abstract 17273: Long Non-Coding RNA Ppp1r1b Regulates Myogenic Differentiation Through Modulating Histone 3 Methylation

Introduction: Long noncoding RNAs (lncRNAs), emerged as critical epigenetic regulators of transcriptome, play important roles in cardiac development and might be targeted to treat human cardiomyocyte dysfunction. In our work, we identified a novel lncRNA that regulates myogenesis. Hypothesis: LncRNA Ppp1r1b regulates myogenesis by modulating Histone 3 methylation Methods: After treated with antisense oligonucleotides (GapmeR) or siRNA against Ppp1r1b-LncRNA, real time PCR and Western blot analyses were performed to examine the expression of myogenic and sarcomere genes. Chromatin immunoprecipitation (CHIP) was used to comparatively analyze gene specific histone modification level. RNA pull-down was employed to identify the protein molecules that interact with Ppp1r1b-LncRNA. Results: By silencing Ppp1r1b-LncRNA with GapmeR, C2C12, a skeletal myoblast cell line, did not develop fully differentiated myotubes, but tend to remain in a quiescent mono-nucleated status. In vivo analysis of GapmeR injected neonatal mouse heart and in vitro siRNA silenced human skeletal myoblasts further confirmed the important role of Ppp1r1b-LncRNA on myogenesis. Members of the MyoD family of muscle-specific transcription factors (MyoD and myogenin) failed to be up-regulated during myogenic differentiation when treated with Ppp1r1b-LncRNA specific GapmeR or siRNA. Key proteins essential for establishing and maintaining normal skeletal muscle architecture, including Tcap and Dystropnin, are also suppressed in Ppp1r1b LncRNA- deficient heart. Analysis of histone modification levels at Myogenin, MyoD1 and Tcap in C2C12 cells revealed more histone tri-methylation at these myogenic and sarcomere structural genes compared to untreated cells. Additional lncRNA- protein complex isolation has further revealed insight into the biological roles of Ppp1r1b-LncRNA. Conclusions: Our results support the role of Ppp1r1b-LncRNA in promoting myogenic differentiation. Ppp1r1b-lncRNA function is mediated by inhibiting histone methylation on promoters of multiple myogenic and sarcomere genes. In particular, the identification of EZH2 in pulled Pp1r1b LncRNA: protein complex implies that Polycomb repressive complex 2 (PRC2) is involved in Ppp1r1b-LncRNA modulated myoblast differentiation.

Modular and programmable material systems drawing from the architecture of skeletal muscle

A specially designed modular material can adopt many force-generating and energy-storing postures, which could be useful for soft robotics.

Diffusion Tensor Imaging of the Calf Muscles in Subjects With and Without Diabetes Mellitus.

Diffusion tensor imaging (DTI) has been used to characterize calf skeletal muscle architecture. To assess the diffusional properties of the calf muscles of subjects with and without diabetes, at rest and during isometric plantarflexion exercise. Prospective. Twenty-six subjects in two groups: 13 healthy and 13 subjects with type 2 diabetes (DM); each group consisted of seven females and six males. 3T/2D single-shot spin echo planar imaging. Fractional anisotropy (FA), mean diffusivity (MD), diffusion eigenvalues, and fiber tracking indices were obtained from the medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus (SOL) muscles of the calf at rest and during isometric plantarflexion exercise. We used a combination of nonparametric (Wilcoxon) and parametric (t-test) statistical assessments. The medial gastrocnemius muscle had more indices with significant differences between the two groups (six indices with P < 0.05) than did the lateral gastrocnemius (three indices with P < 0.05) and soleus muscles (only one index with P < 0.05). While the healthy group showed elevated MD values from rest to exercise (MG = 5.83%, LG = 13.45%, and SOL = 11.68%), the diabetic MD showed higher increases (MG = 19.74%, LG = 29.31%, and SOL = 20.84%) that were different between groups (MG: P = 0.009, LG: P = 0.037, and SOL: P = 0.049). Our results indicate considerable diffusional changes between healthy subjects and subjects with diabetes at rest and during isometric plantarflexion exercise in the calf muscles. The medial gastrocnemius muscle displayed the most diffusion sensitivity to diabetes-related microstructural changes. 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:1285-1295.

Functional deficits may be explained by plantarflexor remodeling following Achilles tendon rupture repair: Preliminary findings

Achilles tendon ruptures are common injuries that often lead to long-term functional deficits. Despite the prevalence of these injuries, the mechanism responsible for limited function has not yet been established. Therefore, the purpose of this study was to present preliminary findings that support a hypothesis that skeletal muscle remodeling is the driving factor of poor outcomes in some patients. Biomechanical and ultrasonography assessments were performed on a patient that presented with poor functional outcomes 2.5 years after a surgically-repaired acute Achilles tendon rupture. Single-leg heel raise height was decreased by 75% in the affected limb (3.0 cm compared to 11.9 cm) while walking mechanics showed no deficits. Ultrasonography revealed that the affected medial gastrocnemius muscle was less thick and had shorter, more pennate fascicles compared to the unaffected limb. A simple computational model of a maximal-effort plantarflexion contraction was employed to test the implications of changes in muscle architecture on single-leg heel raise function. Subject-specific measurements of fascicle length and pennation were input into the model, which supported these architectural parameters as being drivers of heel raise function. These preliminary findings support the hypothesis that an Achilles tendon rupture elicits changes in skeletal muscle architecture, which reduces the amount of work and power the joint can generate. This multidisciplinary framework of biomechanical, imaging, and computational modeling provides a unique platform for studying the complex interactions between structure and function in patients recovering from Achilles tendon injuries.

Human Amniotic Membrane Improves Healing in a Chronic, Massive Rotator Cuff Repair Model

Objectives:Rotator cuff tendon heals by fibrovascular scar that is weaker than native tissue leading to repairs that are prone to failure. Our objective was to investigate the ability of an amniotic membrane-derived human allograft to improve rotator cuff tendon-bone healing and skeletal muscle architecture in a chronic massive rotator cuff injury and repair model in rats. We hypothesized that application of human amniotic membrane to the tendon-bone interface at the time of repair will result in increased attachment strength and rotator cuff muscle fiber force secondary to improved bone formation and nthesis histomorphometry, less plasminogen activator inhibitor-1 (PAI-1) expression, and induced muscle repair gene expression.Methods:Eighty-five male Sprague-Dawley rats were allocated to one of four groups: (1) uninjured (U), (2) injury only (IO), (3) chronic injury and repair (CR), or (4) chronic injury and augmented repair (ER). The IO, CR, and ER groups underwent unilateral detachment of the supraspinatus and infraspinatus tendons with injection of the corresponding muscle with 3 u/kg Onabotulinum toxin A. Four weeks following injury, a surgical repair was performed in the CR and ER groups using transosseous suture fixation with human amniotic membrane applied to the tendon-bone repair site in the ER group. Animals were euthanized at four weeks following the repair. Biomechanical testing of the supraspinatus and infraspinatus tendon-bone complex and single fiber contractility testing of the supraspinatus muscle were performed. Microcomputed tomography was utilized to quantitate bone microstructure at the repair site. The healing tendon-bone interface was evaluated with histomorphometric quantification of fibrocartilage formation and collagen organization, and immunostaining with PAI-1. The rotator cuff muscle was evaluated with immunohistochemical localization for lipid deposition and total cross-sectional area. Real-time polymerase chain reaction evaluated relative expression of genes relevant to muscle repair. Statistical analysis was performed using a nonparametric Kruskal-Wallis test with significance set at p<0.05.Results:Augmentation with amniotic membrane did not lead to increased load-to-failure or stiffness compared to CR. The cross-sectional area, maximum isometric force, and specific force of individual supraspinatus muscle fibers were significantly greater with ER compared to CR (Figure 1). Microcomputed tomography revealed a larger volume of newly formed bone present at the bony footprint with ER compared to CR. Histomorphometric analysis demonstrated significantly greater fibrocartilage area and collagen organization at the healing tendon-bone insertion site with ER compared to CR at 4 week. Qualitatively, there was less PAI-1 immunostaining noted at the tendon-bone interface in the ER group. There was less lipid deposition and greater cross-sectional area of the rotator cuff muscle fibers in the ER group. Rotator cuff muscle gene expression with ER demonstrated a downregulation of apoptosis regulatory genes BCL2 and Caspase-3, adipogenesis regulatory genes FITM1 and FITM2, TNF-alpha and TGF-beta 3 compared to CR.Conclusion:Augmentation with human amniotic membrane in a chronic, massive rotator cuff injury and repair model led to greater bone formation, more organized tendon enthesis, induced muscle repair gene expression, and greater rotator cuff muscle fiber force secondary to less PAI-1 expression.

Attenuation of autophagy impacts on muscle fibre development, starvation induced stress and fibre regeneration following acute injury

Autophagy has been implicated as a major factor in the development of a number of diseases of skeletal muscle. However, its role in skeletal muscle homeostasis is still evolving. We examined skeletal muscle architecture in a mouse model, Atg16L1, where autophagy is attenuated but importantly still present. We show that muscle fibres from Atg16L1 mice were smaller than wild-type counterparts, proving a role for this process in the growth of these cells. We show that mild attenuation of autophagy results in accelerated muscle loss during the initial phase of acute starvation. Furthermore, we show that regeneration of skeletal muscle following cardiotoxin (CTX) mediated injury is slower in the Atg16L1 mouse compared to wild-type. Lastly, we show that autophagy controls the integrity of the sarcolemma. Attenuated autophagy makes muscle fibres more susceptible to infiltration by circulating immunoglobulins following muscle injury with CTX. These fibres internalise dystrophin and nNOS. Importantly these fibres are able to restore dystrophin and nNOS localisation and do not die. In conclusion, these studies shed new light into the ability of skeletal muscle fibres to cope with injury and establish a link between the fine-tuning of autophagy and skeletal muscle regeneration.

Effects of Instrument Assisted Soft Tissue Mobilization on Biceps Femoris Muscle Architecture

Instrument assisted soft tissue mobilization (IASTM) is a popular therapeutic modality that is often used to treat skeletal muscle restriction and injury. The efficacy and mechanism by which IASTM elicits a therapeutic effect is not fully understood. This study was designed to explore if any reported benefits of IASTM stem from changes in skeletal muscle architecture. PURPOSE: Examine the effects of IASTM on biceps femoris (BF) ultrasonography (US) baseline measurements of cross sectional area (CSA) and echo intensity (EI) as well as pennation angle (PA) at three different joint positions. Joint positions included 90°, mid- (MidROM), and end-range of motion (ROM) (EndROM). METHODS: Seventeen female participants (mean±SD: age=21.12±0.78 years) participated in this study. Participants were placed in a prone position for the IASTM treatment and for CSA and EI measures of the BF. Participants were also placed in a supine position, with the right hip and knee joints at 90° of flexion against a horizontal support for PA measurements. PA measurements were recorded at 90°, MidROM, and the EndROM joint positions. US settings were enhanced to improve image quality, including gain (50dB), depth (8cm), and frequency (12MHz). For the IASTM protocol, the BF received 3 sets of 7 strokes in both proximal and distal directions at a treatment angle of 45°. Paired samples t-tests [Time (Pre vs Post)] were used to analyze CSA and EI US data. A two-way repeated measures ANOVA [Joint position (90° vs MidROM vs EndROM) × Time (Pre vs Post)] was used to analyze PA data. An alpha value of P ≤ 0.05 was considered statistically significant for all comparisons. RESULTS: No significant difference was observed across time for CSA (p=0.220) or EI (p=0.515). Additionally, there was no significant joint position × time interaction (p=0.851) for PA. However, a significant main effect (p=0.001) for joint position was observed. Pairwise comparison revealed significant decreases in PA between 90° and MidROM (p=0.038), 90° and EndROM (p=0.001) and MidROM and EndROM (p=0.001). CONCLUSION: Although PA was altered with the corresponding changes in joint position, this was not a result of IASTM. These results indicate that a single bout of IASTM may not evoke architectural change in the hamstrings as measured by ultrasonography.

Nonvolitional assessment of tibialis anterior force and architecture during critical illness.

Contemporaneous measures of muscle architecture and force have not previously been conducted during critical illness to examine their relationship with intensive care unit (ICU)-acquired weakness. Ankle dorsiflexor muscle force (ADMF) with high-frequency electrical peroneal nerve stimulation and skeletal muscle architecture via ultrasound were measured in 21 adult, critically ill patients, 16 at ICU admission. Thirteen patients were measured on 2 occasions. Among these, 10 who were measured at ICU admission demonstrated muscle weakness. Despite significant reductions in tibialis anterior (Δ = -88.5 ± 78.8 mm2 , P = 0.002) and rectus femoris (Δ = -126.1 ± 129.1 mm2 , P = 0.006) cross-sectional areas between occasions, ADMF did not change (100-HZ ankle dorsiflexor force 9.8 [IQR, 8.0-14.4] kg vs. 8.6 (IQR, 6.7-19.2) kg, P = 0.9). Muscle weakness was evident at ICU admission. No additional decrements were observed 7 days later despite significant reductions in muscle size. These data suggest that not all ICU weakness is truly "acquired" and questions our understanding of muscle function during critical illness. Muscle Nerve 57: 964-972, 2018.

Non-Destructive Determination of Muscle Architectural Variables Through the Use of DiceCT.

The fascicular architecture of skeletal muscle dictates functional parameters such as force production and contractile velocity. Muscle microarchitecture is typically determined by means of manual dissection, a technique that is inherently destructive to specimens. Furthermore, fascicle lengths and pennation angles are commonly assessed at only a limited number of sampling sites per muscle. We present the results of a digital technique to non-destructively assess muscle architectural variables for three jaw-adductor muscles within a specimen of the cercopithecine primate Macaca fascicularis (crab-eating macaque). The specimen is first subjected to a contrast-enhanced staining protocol to increase the density of internal soft tissues. High-resolution µCT scans are then collected and segmented to isolate individual muscles. A textural orientation algorithm is then applied to each muscle volume to reconstruct constituent muscle fascicles in three dimensions. Using this technique, we report muscle volume, fascicle length, angle of pennation, and physiological cross-sectional area (PCSA) for each muscle. These data are compared to results collected using traditional dissection of the contralateral muscles. Reconstructions of muscle volume and pennation angle closely correspond to the dissection results. The degree of similarity between measurements of fascicle length and PCSA varies between muscles, with temporalis demonstrating the greatest disparity between techniques; likely reflecting the complex geometry and fascicular arrangement of this muscle. The described technique samples a much larger number of fascicles than had previously been possible and non-destructively investigates the internal architecture of preserved specimens. We conclude that this approach demonstrates great potential for quantifying muscle internal architecture. Anat Rec, 301:363-377, 2018. © 2018 Wiley Periodicals, Inc.