Human Gastrocnemius Research Articles

Abstract 3018: Expression Of The Aim2 Inflammasome In Skeletal Is Modulated By Surgical Bypass And Is A Target To Reduce Ischemic Myopathy In Pad

Introduction: Peripheral arterial disease (PAD) causes skeletal muscle myopathy and impairment, yet relevant pathways are understudied. We reported a new role for the absent in melanoma 2 (AIM2) inflammasome in PAD myocyte function. We hypothesize that AIM2 is an important mediator of cell death pathways in PAD muscle and is reduced by revascularization. Methods: Myocytes were obtained commercially or from ischemic and perfused PAD muscle using cell sorting. mRNA libraries underwent next generation sequencing (NGS) and differential gene expression (DGE) mapped to the GRCh368 human genome. Ingenuity Pathway Analysis (IPA) identified relevant biological pathways filtered by both fold change (fc) >2 and false discovery rate of p< 0.05. Sections were procured from human gastrocnemius before and after vascular bypass and analyzed for AIM2 with immunofluorescence (IF) and western blot (WB). Inflammatory caspase-1 activity was measured +/- siRNA against AIM2. Statistical analysis included t- test and ANOVA + post-hoc analysis. P<0.05 was considered significant. Results: DGE and IPA on isolated myocytes highlighted Neutrophil Degranulation and Pathogen Induced Cytokine Storm Signaling Pathways to be significantly altered in ischemic muscle cells (Fig1, p < 1xE-30 each, N=4) emphasizing AIM2 inflammasome activation (CASP1, fc 30.73; NLRP3/ASC/CASP1, fc 27.23; PYCARD fc 40.63; IL1B fc 63.49). AIM2 protein was high in PAD by IF and WB. Caspase-1 activity was attenuated in the presence of AIM2 inhibition (N=3; ****p<0.0001 in PAD). AIM2 expression was significantly reduced after surgery for PAD (p<0.05, N=6/group, t-test). Conclusion: AIM2 inflammasome expression in PAD induces pyroptotic caspase activity and is attenuated by surgical bypass, directly demonstrating a unique biologic benefit of muscle revascularization in PAD. Targeting AIM2 pathways either pharmacologically or by surgery may help to reduce myopathic damage in ischemic muscle from PAD.

Correlation between skeletal muscle acetylcarnitine and phosphocreatine metabolism during submaximal exercise and recovery: interleaved 1H/31P MRS 7 T study

Acetylcarnitine is an essential metabolite for maintaining metabolic flexibility and glucose homeostasis. The in vivo behavior of muscle acetylcarnitine content during exercise has not been shown with magnetic resonance spectroscopy. Therefore, this study aimed to explore the behavior of skeletal muscle acetylcarnitine during rest, plantar flexion exercise, and recovery in the human gastrocnemius muscle under aerobic conditions. Ten lean volunteers and nine overweight volunteers participated in the study. A 7 T whole-body MR system with a double-tuned surface coil was used to acquire spectra from the gastrocnemius medialis. An MR-compatible ergometer was used for the plantar flexion exercise. Semi-LASER-localized 1H MR spectra and slab-localized 31P MR spectra were acquired simultaneously in one interleaved exercise/recovery session. The time-resolved interleaved 1H/31P MRS acquisition yielded excellent data quality. A between-group difference in acetylcarnitine metabolism over time was detected. Significantly slower τPCr recovery, τPCr on-kinetics, and lower Qmax in the overweight group, compared to the lean group was found. Linear relations between τPCr on-kinetics, τPCr recovery, VO2max and acetylcarnitine content were identified. In conclusion, we are the first to show in vivo changes of skeletal muscle acetylcarnitine during acute exercise and immediate exercise recovery with a submaximal aerobic workload using interleaved 1H/31P MRS at 7 T.

Role of toll-like receptor 4 in skeletal muscle damage in chronic limb-threatening ischemia

ObjectiveToll-like receptors (TLRs) are key pattern recognition receptors in the innate immune system. In particular, the TLR4-mediated immune response has been implicated in ischemia-induced tissue injury. Mounting evidence supports a detrimental role of the innate immune system in the pathophysiology of skeletal muscle damage in patients with chronic limb-threatening ischemia (CLTI), in whom patient-oriented functional outcomes are poor. The overall aim of this study was to investigate the potential role of TLR4 in skeletal muscle dysfunction and damage in CLTI. MethodsThe role of TLR4 in ischemic muscle was investigated by (1) studying TLR4 expression and distribution in human gastrocnemius muscle biopsies, (2) evaluating the functional consequences of TLR4 inhibition in myotubes derived from human muscle biopsies, and (3) assessing the therapeutic potential of modulating TLR4 signaling in ischemic muscle in a mouse hindlimb ischemia model. ResultsTLR4 was found to be expressed in human muscle biopsies, with significant upregulation in samples from patients with CLTI. In vitro studies using cultured human myotubes demonstrated upregulation of TLR4 in ischemia, with activation of the downstream signaling pathway. Inhibition of TLR4 before ischemia was associated with reduced ischemia-induced apoptosis. Upregulation of TLR4 also occurred in ischemia in vivo and TLR4 inhibition was associated with decreased inflammatory cell infiltration and diminished apoptosis in the ischemic limb. ConclusionsTLR4 is upregulated and activated in ischemic skeletal muscle in patients with CLTI. Modulating TLR4 signaling in vitro and in vivo was associated with attenuation of ischemia-induced skeletal muscle damage. This strategy could be explored further for potential clinical application.

Myonuclei Are Retained In Human Gastrocnemius Muscle After Achilles Tendon Rupture

Myonuclei Are Retained In Human Gastrocnemius Muscle After Achilles Tendon Rupture

Sex-specific alteration in human muscle transcriptome with age.

Sarcopenia is a medical condition that progressively develops with age and results in reduced skeletal muscle mass, alteration in muscle composition, and decreased muscle strength. Several clinical studies suggested that sarcopenia disproportionally affects males and females with age. Despite this knowledge, the molecular mechanism governing the pathophysiology is not well understood in a sex-specific manner. In this study, we utilized human gastrocnemius muscles from males and females to identify differentially regulated genes with age. We found 269 genes with at least a twofold expression difference in the aged muscle transcriptome. Among the female muscle samples, there were 239 differentially regulated genes, and the novel protein-coding genes include KIF20A, PIMREG, MTRNR2L6, TRPV6, EFNA2, RNF24, and SFN. In aged male skeletal muscle, there were 166 differentially regulated genes, and the novel-protein coding genes are CENPK, CDKN2A, BHLHA15, and EPHA. Gene Ontology (GO) enrichment revealed glucose catabolism, NAD metabolic processes, and muscle fiber transition pathways that are involved in aged female skeletal muscle, whereas replicative senescence, cytochrome C release, and muscle composition pathways are disrupted in aged male skeletal muscle. Targeting these novels, differentially regulated genes, and signaling pathways could serve as sex-specific therapeutic targets to combat the age-related onset of sarcopenia and promote healthy aging.

Transcription factor motif activity as a biomarker of muscle aging

In prior work, we analyzed gene expression profiles of mouse, rat and human gastrocnemius muscles to identify conserved regulators of muscle aging processes. By further comparing data obtained from different muscles we found stronger conservation of aging-related factors at the level of molecular pathways than at the level of individual genes. Here we compared the predictive power of models based on gene expression levels and those based on transcription factor motif activities for an individual's age. Although somewhat less accurate than models based on gene expression, models based on motif activities achieve good prediction of muscle age, further providing insights into aging-related molecular pathways.

3D localized lactate detection in muscle tissue using double-quantum filtered 1 H MRS with adiabatic refocusing pulses at 7T.

Lactate is a key metabolite in skeletal muscle and whole-body physiology. Its MR visibility in muscle is affected by overlapping lipid signals and fiber orientation. Double-quantum filtered (DQF) 1 H MRS selectively detects lactate at 1.3ppm, but at ultra-high field the efficiency of slice-selective 3D-localization with conventional RF pulses is limited by bandwidth. This novel 3D-localized 1 H DQF MRS sequence uses adiabatic refocusing pulses to unambiguously detect lactate in skeletal muscle at 7T. Lactate double-quantum coherences were 3D-localized using slice-selective Shinnar-Le Roux optimized excitation and adiabatic refocusing pulses (similar to semi-LASER). DQF MR spectra were acquired at 7T from lactate phantoms, meat specimens with injected lactate (exploring multiple TEs and fiber orientations), and human gastrocnemius in vivo during and after exercise (without cuff ischemia). Lactate was readily detected, achieving the full potential of 50% signal with a DQF, in solution. The effects of fiber orientation and TE on the lactate doublet (peak splitting, amplitude, and phase) were in good agreement with theory and literature. Exercise-induced lactate accumulation was detected with 30s time resolution. This novel 3D-localized 1 H DQF MRS sequence can dynamically detect glycolytically generated lactate in muscle during exercise and recovery at 7T.

Retinoic acid exerts sexually dimorphic effects on muscle energy metabolism and function

The retinol dehydrogenase Rdh10 catalyzes the rate-limiting reaction that converts retinol into retinoic acid (RA), an autacoid that regulates energy balance and reduces adiposity. Skeletal muscle contributes to preventing adiposity, by consuming nearly half the energy of a typical human. We report sexually dimorphic differences in energy metabolism and muscle function in Rdh10+/− mice. Relative to wild-type (WT) controls, Rdh10+/− males fed a high-fat diet decrease reliance on fatty-acid oxidation and experience glucose intolerance and insulin resistance. Running endurance decreases 40%. Rdh10+/− females fed this diet increase fatty acid oxidation and experience neither glucose intolerance nor insulin resistance. Running endurance increases 220%. We therefore assessed RA function in the mixed-fiber type gastrocnemius muscles (GM), which contribute to running, rather than standing, and are similar to human GM. RA levels in Rdh10+/− male GM decrease 38% relative to WT. Rdh10+/− male GM increase expression of Myog and reduce Eif6 mRNAs, which reduce and enhance running endurance, respectively. Cox5A, complex IV activity, and ATP decrease. Increased centralized nuclei reveal existence of muscle malady and/or repair in GM fibers. Comparatively, RA in Rdh10+/− female GM decreases by less than half the male decrease, from a more modest decrease in Rdh10 and an increase in the estrogen-induced retinol dehydrogenase Dhrs9. Myog mRNA decreases. Cox5A, complex IV activity, and ATP increase. Centralized GM nuclei do not increase. We conclude that Rdh10/RA affects whole body energy use and insulin resistance partially through sexual dimorphic effects on skeletal muscle gene expression, structure, and mitochondria activity.

Quantitative Estimation of Passive Elastic Properties of Individual Skeletal Muscle in Vivo Using Normalized Elastic Modulus-Length Curve.

Precise characterization of the passive elastic properties of human skeletal muscle could provide valuable information for functional assessment and medical diagnosis. Using normalized elastic modulus-length curve based on a piecewise exponential model, a non-invasive ultrasonography (US) method was developed for estimating three physiologically meaningful parameters, termed as passive-elastic coefficient k, slack length l0 and slack elastic modulus G0, to quantify the passive elastic properties of human gastrocnemius (GM) muscle, and correlate different findings with healthy and atrophic subjects. Dynamic B-mode US and shear wave elastography (SWE) videos of right GM muscles were performed in 32 healthy subjects and 18 atrophic patients with their ankle angles from 40° plantarflexion to 30° dorsiflexion by an isokinetic dynamometer. During muscle passive stretching induced by ankle rotation, consecutive muscle lengths were measured by automatically tracking the distal muscle-tendon junction positions in B-mode imaging frames using Hough transform and an active contour method. The corresponding elastic moduli were obtained using SWE imaging frames. The Gauss-Newton algorithm was used to estimate the parameters k, l0 and G0 from normalized elastic modulus-length curve. In-vivo experimental results showed that the measured muscle elastic modulus-length data fitted well to the proposed model with three estimated parameters for all subjects (0.942 < R2 < 0.997). The passive-elastic coefficient k was significantly higher for atrophic subjects compared with normal subjects (105.5 ± 45.3 versus 48.4 ± 16.0, p < 0.001). The proposed parameters allow further characterization of muscle essential mechanical properties and have a potential to become effective indexes for muscular disease diagnosis.

In Vivo Human Gastrocnemius Architecture With Changing Joint Angle at Rest and During Graded Isometric Contraction of Normal and Weak Muscle

Architectural properties of the triceps surae muscles complex were determined In Vivo for thirty subjects. These subjects were assigned to two groups. The first group of subjects consisted of 8 healthy men and the second group of subjects was composed of 22 patients with motor disorders. The ankle was positioned at -15 ° (dorsiflexion), and 0 ° (neutral anatomical position), and 15 °, and 30 ° (plantarflexion), with the knee set at 120 °and with an angle in the ankle joint of 90 °. At each position, longitudinal ultrasonic images of the Medial (MG) and Lateral (LG) Gastrocnemius and Soleus (SOL) muscles were obtained while the subject was relaxed (passive) and performed 50 % maximal voluntary isometric plantar flexion (active), from which fascicle Lengths (L) and angles (Θ) with respect to the aponeuroses were determined. From the ultrasonic image, it was observed that and Θ changed during an isometric contraction of the triceps surae muscle. Changes in L and were expressed as a function of relative torque. The Θ change was not identical for the three muscles. The fascicle Θ of MG demonstrated the greatest variation in three muscles. The effects of activation and relaxation positions were significant in all three muscles. The differences in MG fascicle Θ because of changes in ankle positions were significant among control and patients both in the passive and active conditions. Fascicle Θ of LG and SOL not differed among control and patient in the relaxation condition but not in the activation condition. For LG, and SOL ol fascicle Θ were changes were larger in control with the patients. The mean values fascicle Θ of MG, LG, and SOL an isometric contraction (50 % MVC) in the control groups increased by 60 %, 41 %, and 41 %, respectively; in the patient groups were a smaller increase, by 28 %, 26 %, and 36 %, respectively. Different lengths and angles of fascicles, and their changes bу contraction by patients and normal subjects, might bе related to differences in force-producing capabilities of the muscles and elastic characteristics of tendons and aponeuroses.

In vitro compressive properties of skeletal muscles and inverse finite element analysis: Comparison of human versus animals

Virtual finite element human body models have been widely used in biomedical engineering, traffic safety injury analysis, etc. Soft tissue modeling like skeletal muscle accounts for a large portion of a human body model establishment, and its modeling method is not enough explored. The present study aims to investigate the compressive properties of skeletal muscles due to different species, loading rates and fiber orientations, in order to obtain available parameters of specific material laws as references for building or improving the human body model concerning both modeling accuracy and computational cost. A series of compressive experiments of skeletal muscles were implemented for human gastrocnemius muscle, bovine and porcine hind leg muscle. To avoid long-time preservation effects, all experimental tests were carried out in 24 h after that the samples were harvested. Considering computational cost and generally used in the previous human body models, one-order hyperelastic Ogden model and three-term simplified viscoelastic quasi-linear viscoelastic (QLV) were selected for numerical analysis. Inverse finite element analysis was employed to obtain corresponding material parameters. With good fitting records, the simulation results presented available material parameters for human body model establishment, and also indicated significant differences of muscle compressive properties due to species, loading rates and fiber orientations. When considering one-order Ogden law, it is worthy of noting that the inversed material parameters of the porcine muscles are similar to those of the human gastrocnemius regardless of fiber orientations. In conclusion, the obtained material parameters in the present study can be references for global human body and body segment modeling.

Control of a Transtibial Prosthesis with Monoarticular and Biarticular Actuators

Common active ankle joint prostheses comprise monoarticular actuators mimicking the function of the human soleus and tibialis anterior muscles, but lack the function of the biarticular human gastrocnemius muscle. Although these devices can mimic human ankle biomechanics in the sagittal plane, persons with transtibial amputation still show compensatory movements and asymmetric gait patterns. The goal of our research is to investigate the benefits of a biarticular transtibial prosthesis comprising mono- and biarticular actuators. This contribution presents the hardware configuration, control design and bypass testing of a biarticular prosthesis prototype with two actuators. A control structure consisting of a model-based feedforward control and a feedback controller to control the actuator torque is introduced. Modeling of the actuators and identification of all relevant system parameters is demonstrated. A reference trajectory based on healthy human ankle biomechanics and a control allocation are introduced. The system’s capability to track desired torques is demonstrated in a walking experiment. It is able to generate human ankle torques and ankle angles with a variable distribution of torque between the mono- and biarticular actuator. Based on these results, further investigations on the torque allocation to improve the gait patterns of persons with transtibial amputation can be conducted.

Recurrent TTN metatranscript‐only c.39974–11T&gt;G splice variant associated with autosomal recessive arthrogryposis multiplex congenita and myopathy

We present eight families with arthrogryposis multiplex congenita and myopathy bearing a TTN intron 213 extended splice-site variant (NM_001267550.1:c.39974-11T>G), inherited in trans with a second pathogenic TTN variant. Muscle-derived RNA studies of three individuals confirmed mis-splicing induced by the c.39974-11T>G variant; in-frame exon 214 skipping or use of a cryptic 3' splice-site effecting a frameshift. Confounding interpretation of pathogenicity is the absence of exons 213-217 within the described skeletal muscle TTN N2A isoform. However, RNA-sequencing from 365 adult human gastrocnemius samples revealed that 56% specimens predominantly include exons 213-217 in TTN transcripts (inclusion rate ≥66%). Further, RNA-sequencing of five fetal muscle samples confirmed that 4/5 specimens predominantly include exons 213-217 (fifth sample inclusion rate 57%). Contractures improved significantly with age for four individuals, which may be linked to decreased expression of pathogenic fetal transcripts. Our study extends emerging evidence supporting a vital developmental role for TTN isoforms containing metatranscript-only exons.

Vibration settling time of the gastrocnemius remains constant during an exhaustive run in rear foot strike runners

In this study, vibrations of human gastrocnemius during an exhaustive run protocol are considered for analysis. Previous studies have shown increased vibration intensity and damping coefficient within the soft tissue with fatigue. The question of this study was to investigate if the vibration settling time remains constant during a prolonged running. Eleven semi-professional middle/long distance runners ran to exhaustion on a treadmill with their preferred constant speed (4.29 ± 0.33 m/s) for 3873 ± 1147 m. Vibration of the gastrocnemius lateralis, electrical activity of the tibialis anterior and the gastrocnemius medialis along with ground reaction force (GRF) were recorded. The results demonstrated significant increase in impact peak and loading rate, and the frequency content of the impact, with no significant change in active peak of the vertical GRF. Fatigue resulted in increased vibration intensity, damping coefficient, and energy dissipation of vibration with no change in vibration settling time. Furthermore, peak acceleration significantly linearly (R = 0.59) increased as a function of running time. The mean frequency of muscle activity of the gastrocnemius medialis and the intensity of muscle activity in TA significantly decreased. The results suggest that constant vibration settling time might either be an objective for muscle tuning which is more pronounced in fatigued state or a passive by-product of muscle function in running. Further studies are needed to address this point.

Muscle-tendon behaviour during sprint in road cyclists: effect of the force-velocity condition

Muscle-tendon behaviour during sprint in road cyclists: effect of the force-velocity condition

Managing the power grid: how myoglobin can regulate PO2 and energy distribution in skeletal muscle.

Managing the power grid: how myoglobin can regulate PO2 and energy distribution in skeletal muscle.

Towards rapid prediction of personalised muscle mechanics: integration with diffusion tensor imaging

ABSTRACT Diffusion tensor imaging (DTI) has been widely used to characterise the 3D fascicle architecture in muscle mechanics. However, the computational expense associated with continuum models make their use in graphics and medical visualisation intractable. This study presents an integration of continuum muscle mechanics with partial least-squares regression to create a fast mechanostatistical model. We use the human gastrocnemius muscle (medial and lateral heads) as an example informed though DTI. Our statistical models predicted muscle shape (within 0.063 mm root-mean-square (RMS) error), musculotendon force (within 1% error), and tissue strain (within 8% max error during muscle contraction), compared to a finite-element model simulation. The technique presented here is a step towards integrating expensive continuum mechanics with fast rigid body solutions in biomechanics. While muscle force is a primary objective in rigid body solvers the additional information including 3D muscle shape and stress/strain fields may now be integrated. One of the key benefits is that muscle interaction with other soft tissues is accounted for, muscle moment arms are not estimated, and the detailed rich 3D continuum fascicle architecture is no longer simplified but plays a full role in biomechanics simulation. This has implications for musculoskeletal biomechanics, orthopaedics and medical visualisation.

A finite element muscle building block derived from 3D ultrasound: application to the human gastrocnemius

Muscle fascicle structure characterises muscle function, which in turn plays a key role in computer simulation of muscle shape. In this study, we use 3D ultrasound from the human medial gastrocnemius muscle to identify and map the muscle fascicle orientation and deformation during passive motion in four subjects. This muscle fascicle description is integrated into a representative muscle volume element using a free-form deformation technique to create a muscle primitive building block that deforms according to the embedded muscle fascicles within. For each subject computed passive tensile force was used to optimise the constitutive behaviour so that the known deformation matched this load. Each subject was fit to match deformation at 25, 50, 75 and 100% of muscle stretch. The subjects that exhibited a larger muscle fascicle pennation angle change during passive stretch were characterised best by a less stiff constitutive law. In contrast, subjects that had a more parallel muscle fascicle deformation, showed stiffer behaviour. The medial gastrocnemius muscle built from these muscle primitives exhibited a contractile shape that is consistent to that observed in human gastrocnemius contraction. This shape was evaluated against the same muscle embedded with muscle fascicles derived from diffusion tensor magnetic resonance imaging and was in good qualitative agreement. Muscle principal strain was shown to align with muscle fascicle direction and was spatially non-uniform. Muscle primitives may be used as building blocks to build large muscle volumes for mechanics simulation, visualisation and medical education.

Development and Evaluation of a Powered Artificial Gastrocnemius for Transtibial Amputee Gait

Existing robotic transtibial prostheses provide only ankle joint actuation and do not restore biarticular function of the gastrocnemius muscle. This paper presents the first powered biarticular transtibial prosthesis, which is a combination of a commercial powered ankle-foot prosthesis and a motorized robotic knee orthosis. The orthosis is controlled to emulate the human gastrocnemius based on neuromuscular models of matched nonamputees. Together with the ankle-foot prosthesis, the devices provide biarticular actuation. We evaluate differences between this biarticular condition and a monoarticular condition with the orthosis behaving as a free-joint. Six participants with transtibial amputation walk with the prosthesis on a treadmill while motion, force, and metabolic data are collected and analyzed for differences between conditions. The biarticular prosthesis reduces affected-side biological knee flexion moment impulse and hip positive work during late-stance knee flexion, compared to the monoarticular condition. The data do not support our hypothesis that metabolism decreases for all participants, but some participants demonstrate large metabolic reductions with the biarticular condition. These preliminary results suggest that a powered artificial gastrocnemius may be capable of providing large metabolic reductions compared to a monoarticular prosthesis, but further study is warranted to determine an appropriate controller for achieving more consistent metabolic benefits.

Acute effect of static stretching on passive stiffness of the human gastrocnemius fascicle measured by ultrasound shear wave elastography.

Passive muscle stiffness and muscle architecture at a given joint angle, as well as slack angle of the muscle have been shown to change after an acute bout of stretching. However, it remains unclear whether passive muscle stiffness at a given fascicle length is reduced after stretching. We aimed to elucidate the acute effect of static stretching on the passive fascicle stiffness using ultrasound shear wave elastography. Shear modulus, fascicle length, and slack angle of the medial gastrocnemius (MG) as well as passive plantar flexion torque during passive dorsiflexion were measured before and after a 5-min static stretching in 14 healthy males. After stretching, passive torques were significantly reduced at >50% of range of motion (ROM). Shear modulus at a given fascicle length was significantly reduced at >80% of the change in fascicle length during passive dorsiflexion. Slack angle of MG was observed at the middle part of ROM and significantly shifted toward more dorsiflexed position after stretching. The present study showed the significant effectiveness of static stretching on the passive fascicle stiffness. Furthermore, the present results suggest that both the shift in slack angle and the reduction in passive fascicle stiffness contribute to produce the change in passive torque-joint angle relationship during passive dorsiflexion. Notably, the contribution of the reduced passive fascicle stiffness to the decrease in passive torque is substantial over the latter part of ROM.