Muscle Mechanics Research Articles

Shear wave elastography reveals passive and active mechanics of triceps surae muscles in vivo: From shear modulus-ankle angle to stress-strain characteristics.

Characterizing individual muscle behavior is crucial for understanding joint function and adaptations to exercise, diseases, or aging. Shear wave elastography (SWE) is a promising tool for measuring the intrinsic material properties of muscle. This study assessed the passive and active shear modulus of the triceps surae muscle group in 14 volunteers (7 females, 25.9±2.5 years) using SWE. Ankle moment, surface electromyography, and SWE of the gastrocnemius medialis (GM), gastrocnemius lateralis (GL), and soleus (SOL) muscles were measured from 30° plantar flexion (PF) to 15° dorsiflexion (DF) ankle angles during passive and isometric contractions at 25%, 50%, and 75% of maximum voluntary contraction (MVC). Muscle length, passive and active ankle moment, and passive shear modulus increased from PF to DF (p<0.001 for all). At 15° DF, the passive shear modulus of the SOL was 76% lower than that of the GM (p<0.001), suggesting that the SOL operates within a lower strain range. The active shear modulus decreased from PF to DF (e.g., by 36.8% at 75% MVC, p=0.009) and was lowest in SOL. The decreasing active shear modulus suggests the muscles operate at shorter-than-optimal to optimal lengths. Contraction intensity also affected the shear modulus (p<0.001), indicating distinct force-sharing strategies, with GL possibly playing a crucial role at higher-intensity contractions and longer lengths. This study demonstrated SWE's potential to characterize muscle mechanics in vivo. If validated, predictions from SWE could facilitate studying muscle behavior and force-sharing strategies, serving as a diagnostic or monitoring tool for muscle function and performance.

The Overaction of the Inferior Oblique Muscle and Associated Vertical Strabismus: Prevalence, Etiology and Diagnosis

Introduction: Vertical strabismus, commonly caused by the overaction of the inferior oblique (IO) muscle, is a frequent oculomotor disorder. It affects one-third of all patients with strabismus, with 70% of these cases coexisting with esotropia. Currently, there is no universally accepted method for quantifying the magnitude of IO overaction (IOOA), as existing classifications are subjective and may not be entirely appropriate. Standardization of IOOA classification is crucial to better understand its severity, develop effective treatment strategies, and predict surgical outcomes. The mechanism of action of the IO muscle is complex and varies with the globe's position during contraction. Beyond horizontal and vertical movements, the IO muscle also contributes to torsional eye movements, impacting the diagnosis and treatment of vertical strabismus and cyclotropia. Materials and Methods: The biomechanical properties of the IO muscle and its triple-action characteristics (horizontal, vertical and torsional movements) were analyzed. A review of current diagnostic practices was conducted, emphasizing the need for comprehensive clinical examinations to identify the signs and symptoms of IOOA and determine its severity. Results: Disorders of the IO muscle often result in vertical strabismus and cyclotropia, complicating strabismus treatment. The variability of the IO muscle's mechanism of action highlights the inadequacy of subjective classification systems. Incorporating the triple-action characteristics of the IO muscle into diagnostic evaluations enables a more accurate understanding of IOOA and its clinical manifestations. Conclusion: Standardizing the classification of IOOA is essential for accurately assessing its severity, guiding treatment strategies, and predicting surgical outcomes. Comprehensive diagnostic examinations that consider the triple-action nature of the IO muscle are necessary to improve the management and treatment of patients with IOOA.

Muscle mechanics and energetics in chronic ankle instability and copers during landing: Strategies for adaptive adjustments in locomotion pattern

Muscle mechanics and energetics in chronic ankle instability and copers during landing: Strategies for adaptive adjustments in locomotion pattern

Examination of Sex-Related Differences in Fatigability and Frequency Components of Mechanomyographic Signals During Sustained Exercise

Background: Surface mechanomyographic (sMMG) signals have been used to examine sex-specific differences in the mechanical behavior of muscle during fatiguing exercise. However, studies often utilize simple amplitude- and frequency-based analyses, which only reveal the static components of the sMMG signal. Methods: Thus, a wavelet-based analysis was used to examine changes in the spectral intensity of the non-dominant limb’s vastus lateralis during a fatiguing, maximal, unilateral isometric leg extension in recreationally active men (n = 11) and women (n = 10). Relative changes in spectral intensities and instantaneous mean frequency (IMF) were examined using linear mixed-effect models. Time-to-task failure was compared using an independent sample t-test. Results: The neuromuscular responses demonstrated parallel decreases in IMF (p &lt; 0.001). Further, there were parallel, nonlinear, decreases in spectral intensity across wavelets (p &lt; 0.001) and there were no sex differences in time-to-task failure (p = 0.15). Conclusions: These data showed no sex-specific differences in exercise fatigability or muscle mechanics during fatiguing exercise of the leg extensors. However, when collapsed across sex, wavelet-specific changes in spectral intensity over time reveal novel insights into the interplay between low- and high-frequency components during fatigue.

Stochastic force generation in an isometric binary mechanical system.

Accurate models of muscle contraction are necessary for understanding muscle performance and the molecular modifications that enhance it (e.g., therapeutics, posttranslational modifications, etc.). As a thermal system containing millions of randomly fluctuating atoms that on the thermal scale of a muscle fiber generate unidirectional force and power output, muscle mechanics are constrained by the laws of thermodynamics. According to a thermodynamic muscle model, muscle's power stroke occurs with the shortening of an entropic spring consisting of an ensemble of force-generating myosin motor switches, each induced by actin binding and gated by inorganic phosphate release. This model differs fundamentally from conventional molecular power stroke models that assign springs to myosin motors in that it is physically impossible to describe an entropic spring in terms of the springs of its molecular constituents. A simple two-state thermodynamic model (a binary mechanical system) accurately accounts for muscle force-velocity relationships, force transients following rapid mechanical and chemical perturbations, and a thermodynamic work loop. Because this model transforms our understanding of muscle contraction, it must continue to be tested. Here, we show that a simple stochastic kinetic simulation of isometric muscle force predicts four phases of a force-generating loop that bifurcates between periodic and stochastic beating through mechanisms framed by two thermodynamic equations. We compare these model predictions with experimental data including observations of spontaneous oscillatory contractions (SPOCs) in muscles and periodic force generation in small myosin ensembles.

Potential compensatory mechanisms preserving cardiac function in myotubular myopathy

X-Linked myotubular myopathy (XLMTM) is characterized by severe skeletal muscle weakness and reduced life expectancy. The pathomechanism and the impact of non-muscular defects affecting survival, such as liver dysfunction, are poorly understood. Here, we investigated organ-specific effects of XLMTM using the Mtm1−/y mouse model. We performed RNA-sequencing to identify a common mechanism in different skeletal muscles, and to explore potential phenotypes and compensatory mechanisms in the heart and the liver. The cardiac and hepatic function and structural integrity were assessed both in vivo and in vitro. Our findings revealed no defects in liver function or morphology. A disease signature common to several skeletal muscles highlighted dysregulation of muscle development, inflammation, cell adhesion and oxidative phosphorylation as key pathomechanisms. The heart displayed only mild functional alterations without obvious structural defects. Transcriptomic analyses revealed an opposite dysregulation of mitochondrial function, cell adhesion and beta integrin trafficking pathways in cardiac muscle compared to skeletal muscles. Despite this dysregulation, biochemical and cellular experiments demonstrated that these pathways were strongly affected in skeletal muscle and normal in cardiac muscle. Moreover, biomarkers reflecting the molecular activity of MTM1, such as PtdIns3P and dynamin 2 levels, were increased in the skeletal muscles but not in cardiac muscle. Overall, these data suggest a compensatory mechanism preserving cardiac function, pointing to potential therapeutic targets to cure the severe skeletal muscle defects in XLMTM.

Active and passive material response of urinary bladder smooth muscle tissue in uniaxial and biaxial tensile testing.

The urinary bladder is a hollow organ that undergoes significant deformation as it receives, stores, and releases urine. To understand the organ mechanics, it is necessary to obtain information about the material properties of the tissues involved. In displacement-controlled tensile tests, tissue samples are mounted on a device that applies stretches to the tissue in one or more directions, resulting in a specific stress response. For this study, we performed uniaxial and biaxial stretch experiments on tissue samples (n = 36) from the body region of the porcine urinary bladder. We analyzed the stress-relaxation, activation dynamics, and passive and active stretch-stress response. Main findings of our experiments are: (1) For uniaxial and biaxial stretching, the time constants for stress-relaxation depend on the stretch amplitude, (2) biaxially stretched samples experienced slower activation with τact increasing by 163% compared to uniaxial stretching, (3) biaxial tests are characterized by reduced optimum stretches λopt by -18%, and (4) biaxial and uniaxial tests showed no significant difference in maximum active stresses σopt. To interpret the results, we present a continuum mechanical model based on a viscoelastic, isotropic solid extended by a set of active muscle fibers. Model predictions show that results (3) and (4) can be explained by a uniform distribution of fiber orientations and a specific shape of the active fiber stress-stretch relationship. This study highlights how deformation modes during tensile testing affects smooth muscle mechanics, proving insights for interpreting experimental data and improving organ modeling. STATEMENT OF SIGNIFICANCE: In this study, we examined the mechanical properties of porcine bladder smooth muscle using uniaxial and equibiaxial tensile tests. To our knowledge, this is the first instance where the active stress-stretch relationships of smooth muscle tissue have been analysed under equibiaxial stretch. The data collected offer a detailed understanding of the connection between deformation and active stress production, surpassing the insights provided by existing uniaxial tests in the literature. These findings are crucial for comprehending the physiology of smooth muscle tissue and for developing constitutive muscle models that can make more accurate predictions about the functionality of hollow organs in both health and disease. Additionally, our findings on smooth muscle active stress could aid in the creation of biomaterials that interact with or even replace natural muscle.

Adenosine relaxes vagina smooth muscle through the cyclic guanosine monophosphate- and cyclic guanosine monophosphate-dependent pathways.

In males, adenosine (ADO) is known to relax penile smooth muscles, although its role in the vagina is not yet fully elucidated. This study investigated the effect of ADO on vagina smooth muscle activity, using a validated female Sprague-Dawley rat model. Contractility studies, using noradrenaline-precontracted vaginal strips, tested the effects of ADORA1/3 antagonists and ADORA2A/2B antagonists and agonists. Increasing doses of ADO were tested after in vivo or in vitro treatment with Nω-nitro-L-arginine-methyl-ester hydrochloride (L-NAME) or with guanylate or adenylate cyclase inhibitors. Immunopositivity for ADORA2A and ADORA2B was assessed, and messenger RNA (mRNA) analysis was performed. Cyclic ADO monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) were quantified both in rat vagina smooth muscle cells (rvSMCs) and in vaginal tissues with increasing doses of ADO. Demonstrating ADO's role in the relaxing/contractile mechanism in distal vagina smooth muscle. All ADO receptors mRNAs were expressed in vaginal tissue, with a prevalent content of ADORA2B. A high expression of genes regulating ADO catabolism (ADK) and de novo synthesis (NT5E) was found. In vaginal strips, ADO induced relaxation with IC50 = 144.7μM and a flat pseudo-Hill coefficient value = -0.42, indicating an activity on heterogeneous receptors. Blocking ADORA1/3 shifted ADO response to the left and with a steeper slope. ADORA2A/2B agonists showed a higher potency than ADO in inducing relaxation. Immunolocalization confirmed the presence of ADORA2A/2B in vaginal musculature, in the blood vessels endothelium, and in the epithelium. ADO stimulation of vagina tissues induced a significant increase in cAMP and cGMP contents. Experiments on rvSMCs confirmed that ADO time- and dose-dependently stimulated cAMP production in these cells. However, ADORA2A/2B antagonists, although reducing the ADO-induced relaxation, did not completely block it. A similar inhibition was obtained by blocking adenylate cyclase. Overall, these findings suggest that ADO relaxation involves other pathways, eg, nitric oxide (NO)/cGMP. Accordingly, blocking NO formation through L-NAME substantially blunted ADO responsiveness, as it does the block of cGMP formation through 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one. Simultaneous incubation with cGMP and cAMP blockers completely inhibited ADO responsiveness. The study highlights ADO's role in regulating vaginal smooth muscle activity, suggesting its potential effect on the vagina. This is the first study on ADO in the vagina, although the results are preliminary and limited to the rat model. These results show that ADO acts as a vaginal relaxing modulator through selective activation of receptors involving not only cAMP but also cGMP.

Acute resistance exercise and training reduce desmin phosphorylation at serine 31 in human skeletal muscle, making the protein less prone to cleavage

Desmin intermediate filaments play a crucial role in stress transmission and mechano-protection. The loss of its integrity triggers myofibril breakdown and muscle atrophy for which desmin phosphorylation (pDes) is a priming factor. We investigated whether eccentric accentuated resistance exercise (RE) influences the regulation of pDes, effecting its susceptibility to cleavage. Ten healthy persons performed 14 RE-sessions (2 per week). Muscle biopsies were collected in both untrained and trained conditions at rest (pre 1, pre 14) and one hour after RE (post 1, post 14). Western blotting and immunohistochemistry were utilized to assess desmin content, phosphorylation at several sites and susceptibility to cleavage. In untrained condition (pre 1, post 1), RE induced dephosphorylation of serin 31 and 60. Trained muscle exhibited more pronounced dephosphorylation at Serin 31 post-RE. Dephosphorylation was accompanied by reduced susceptibility of desmin to cleavage. Additionally, training increased total desmin content, upregulated baseline serine 31 phosphorylation and attenuated pDes at serine 60 and threonine 17. Our findings suggest that acute and repeated RE changes the phosphorylation pattern of desmin and its susceptibility to cleavage, highlighting pDes as an adaptive mechanism in skeletal muscle, contributing to the proteostatic regulation in response to recurring stress.

Investigating in vivo force and work production of rat medial gastrocnemius at varying locomotor speeds using a muscle avatar.

Traditional work loop studies, that use sinusoidal length trajectories with constant frequencies, lack the complexities of in vivo muscle mechanics observed in modern studies. This study refines methodology of the 'avatar' method (a modified work loop) to infer in vivo muscle mechanics using ex vivo experiments with mouse extensor digitorum longus (EDL) muscles. The 'avatar' method involves using EDL muscles to replicate in vivo time-varying force, as demonstrated by previous studies focusing on guinea fowl lateral gastrocnemius (LG). The present study extends this method by using in vivo length trajectories and electromyographic activity from rat medial gastrocnemius (MG) during various gaits on a treadmill. Methodological enhancements from previous work, including adjusted stimulation protocols and systematic variation of starting length, improved predictions of in vivo time-varying force production (R2=0.80-0.96). The study confirms there is a significant influence of length, stimulation and their interaction on work loop variables (peak force, length at peak force, highest and average shortening velocity, and maximum and minimum active velocity), highlighting the importance of these interactions when muscles produce in vivo forces. We also investigated the limitations of traditional work loops in capturing muscle dynamics in legged locomotion (R2=0.01-0.71). While in vivo length trajectories enhanced force prediction, accurately predicting work per cycle remained challenging. Overall, the study emphasizes the utility of the 'avatar' method in elucidating dynamic muscle mechanics and highlights areas for further investigation to refine its application in understanding in vivo muscle function.

Bayesian Estimation of Muscle Mechanisms and Therapeutic Targets Using Variational Autoencoders.

Cardiomyopathies, often caused by mutations in genes encoding muscle proteins, are traditionally treated by phenotyping hearts and addressing symptoms post irreversible damage. With advancements in genotyping, early diagnosis is now possible, potentially introducing earlier treatment. However, the intricate structure of muscle and its myriad proteins make treatment predictions challenging. Here we approach the problem of estimating therapeutic targets for a mutation in mouse muscle using a spatially explicit half sarcomere muscle model. We selected 9 rate parameters in our model linked to both small molecules and cardiomyopathy-causing mutations. We then randomly varied these rate parameters and simulated an isometric twitch for each combination to generate a large training dataset. We used this dataset to train a Conditional Variational Autoencoder (CVAE), a technique used in Bayesian parameter estimation. Given simulated or experimental isometric twitches, this machine learning model is able to then predict the set of rate parameters which are most likely to yield that result. We then predict the set of rate parameters associated with twitches from control mice with the cardiac Troponin C (cTnC) I61Q variant and control twitches treated with the myosin activator Danicamtiv, as well as model parameters that recover the abnormal I61Q cTnC twitches.

Bayesian estimation of muscle mechanisms and therapeutic targets using variational autoencoders

Cardiomyopathies, often caused by mutations in genes encoding muscle proteins, are traditionally treated by phenotyping hearts and addressing symptoms post irreversible damage. With advancements in genotyping, early diagnosis is now possible, potentially introducing earlier treatment. However, the intricate structure of muscle and its myriad proteins make treatment predictions challenging. Here, we approach the problem of estimating therapeutic targets for a mutation in mouse muscle using a spatially explicit half sarcomere muscle model. We selected nine rate parameters in our model linked to both small molecules and cardiomyopathy-causing mutations. We then randomly varied these rate parameters and simulated an isometric twitch for each combination to generate a large training data set. We used this data set to train a conditional variational autoencoder, a technique used in Bayesian parameter estimation. Given simulated or experimental isometric twitches, this machine learning model is able to then predict the set of rate parameters that are most likely to yield that result. We then predict the set of rate parameters associated with twitches from control mice with the cardiac troponin C (cTnC) I61Q variant and control twitches treated with the myosin activator Danicamtiv, as well as model parameters that recover the abnormal I61Q cTnC twitches.

How to effectively prevent hamstring injury and acute treatment measures

Hamstring injury (HSI) is one of the most common injuries in competitive sports, the recurrence of this injury is high, which has a huge impact on the athlete's return to the game. Muscle strength, flexibility, muscle fatigue and age may contribute to damage to the hamstring. Current studies have shown that some static stretching, proprioceptive neuromuscular facilitation (PNF), warm-up and rest before and after the game, and the use of equipment such as foam shaft can effectively improve flexibility and prevent injuries, and hamstring strength training can also prevent injuries. The acute phase after injury can be managed by P.R.I.C.E principle to avoid aggravation of injury. This paper describes the dissolving structure, injury mechanism, risk factors, preventive measures and treatment of the hamstring muscle by citing literature and has a more comprehensive understanding of the prevention and treatment methods of hamstring muscle injury and provides some suggestions for athletes and rehabilitation therapists.

Modeling the mechanism of Ca2+ release in skeletal muscle by DHPRs easing inhibition at RyR I1-sites.

Ca2+ release from the sarcoplasmic reticulum (SR) plays a central role in excitation-contraction coupling (ECC) in skeletal muscles. However, the mechanism by which activation of the voltage-sensors/dihydropyridine receptors (DHPRs) in the membrane of the transverse tubular system leads to activation of the Ca2+-release channels/ryanodine receptors (RyRs) in the SR is not fully understood. Recent observations showing that a very small Ca2+ leak through RyR1s in mammalian skeletal muscle can markedly raise the background [Ca2+] in the junctional space (JS) above the Ca2+ level in the bulk of the cytosol indicate that there is a diffusional barrier between the JS and the cytosol at large. Here, I use a mathematical model to explore the hypothesis that a sudden rise in Ca2+ leak through DHPR-coupled RyR1s, caused by reduced inhibition at the RyR1 Ca2+/Mg2+ inhibitory I1-sites when the associated DHPRs are activated, is sufficient to enable synchronized responses that trigger a regenerative rise of Ca2+ release that remains under voltage control. In this way, the characteristic response to Ca2+ of RyR channels is key not only for the Ca2+ release mechanism in cardiac muscle and other tissues, but also for the DHPR-dependent Ca2+ release in skeletal muscle.

Abstract B008: Twist1 drives pancreatic ductal adenocarcinoma-mediated muscle cachexia

Abstract Cancer cachexia is a debilitating syndrome that affects the survival and quality of life of cancer patients. Up to 95% of pancreatic ductal adenocarcinoma (PDAC) patients experience muscle cachexia, yet the underlying mechanisms remain poorly understood. The transcription factor Twist1 plays essential roles in mesenchymal stem cell fate determination, and its deregulation contributes to cancer progression and metastasis. In this study, we report on the serendipitous finding that Twist1 functions in PDAC to drive muscle cachexia. We found that conditional overexpression of Twist1 in the pancreatic epithelium (pTwist1) during early development resulted in severe growth retardation, which was mainly characterized by muscle hypotrophy. This intriguing observation prompted us to inquire whether pTwist1 could function in the pancreatic epithelium to regulate muscle mass, and if so, whether this has any implication as it relates to PDAC-mediated muscle cachexia. We found that enforced expression of pTwist1 in healthy adult animals was sufficient to elicit the cardinal features of muscle cachexia, including progressive decline in body weight, physical activity, muscle force, and muscle mass. In the context of PDAC, enforced expression of pTwist1 in a KrasG12D background led to a dramatic acceleration of tumor progression, and this was associated with severe muscle cachexia. To the best of our knowledge, these findings provide the first evidence that the pro-malignant transcription factor Twist1 functions in PDAC to drive muscle cachexia, thus revealing new insights into the underlying mechanisms of muscle that could be harnessed to curb this debilitating syndrome. Citation Format: Parash Parajuli, Azeddine Atfi. Twist1 drives pancreatic ductal adenocarcinoma-mediated muscle cachexia [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B008.

Characterizing Mechanical Changes in the Biceps Brachii Muscle in Mild Facioscapulohumeral Muscular Dystrophy Using Shear Wave Elastography.

There is no general consensus on evaluating disease progression in facioscapulohumeral muscular dystrophy (FSHD). Recently, shear wave elastography (SWE) has been proposed as a noninvasive diagnostic tool to assess muscle stiffness in vivo. Therefore, this study aimed to characterize biceps brachii (BB) muscle mechanics in mild-FSHD patients using SWE. Eight patients with mild FSHD, the BB were assessed using SWE, surface electromyography (sEMG), elbow moment measurements during rest, maximum voluntary contraction (MVC), and isometric ramp contractions at 25%, 50%, and 75% MVC across five elbow positions (60°, 90°, 120°, 150°, and 180° flexion). The mean absolute percentage deviation (MAPD) was analyzed as a measure of force control during ramp contractions. The shear elastic modulus of the BB in FSHD patients increased from flexed to extended elbow positions (e.g., p < 0.001 at 25% MVC) and with increasing contraction intensity (e.g., p < 0.001 at 60°). MAPD was highly variable, indicating significant deviation from target values during ramp contractions. SWE in mild FSHD is influenced by contraction level and joint angle, similar to findings of previous studies in healthy subjects. Moreover, altered force control could relate to the subjective muscle weakness reported by patients with dystrophies.

Bibliometric analysis of skeletal muscle ischemia/reperfusion (I/R) research from 1986 to 2022

IntroductionTissue damage due to ischemia and reperfusion is a critical medical problem worldwide. Studies in this field have made remarkable advances in understanding the pathogenesis of ischemia/reperfusion (I/R) injury and its treatment with new and known drugs. However, no bibliometric analysis exists in this area of research. MethodsResearch articles and reviews related to skeletal muscle I/R from 1986 to 2022 were retrieved from the Web of Science Core Collection. Bibliometric analysis was performed using Microsoft Excel 2019, VOSviewer (version 1.6.19), Bibliometrix (R-Tool for R-Studio), and CiteSpace (version 6.1.R5). ResultsA total of 3682 research articles and reviews from 2846 institutions in 83 countries were considered in this study. Most studies were conducted in the USA. Hobson RW (UMDNJ-New Jersey Medical School) had the highest publication, and Korthuis RJ (Louisiana State University) had the highest co-citations. Our analysis showed that, though the Journal of Surgical Research was most favored, the Journal of Biological Chemistry had the highest number of co-citations. The pathophysiology, interventions, and molecular mechanisms of skeletal muscle I/R injury emerged as the primary research areas, with “apoptosis,” “signaling pathway,” and “oxidative stress” as the main keywords of research hotspots. ConclusionsThis study provides a thorough overview of research trends and focal points in skeletal muscle I/R injury by applying bibliometric and visualization techniques. The insights gained from our findings offer a profound understanding of the evolving landscape of skeletal muscle I/R injury research, thereby functioning as a valuable reference and roadmap for future investigations.

Strain-dependent dynamic re-alignment of collagen fibers in skeletal muscle extracellular matrix

Collagen fiber architecture within the skeletal muscle extracellular matrix (ECM) is significant to passive muscle mechanics. While it is thought that collagen fibers re-orient themselves in response to changes in muscle length, this has not been dynamically visualized and quantified within a muscle. The goal of this study was to measure changes in collagen alignment across a range of muscle lengths and compare the corresponding alignment to muscle mechanics. We hypothesized that collagen fibers dynamically increase alignment in response to muscle stretching, and this change in alignment is related to passive muscle stiffness. Further, we hypothesized that digesting collagen fibers with collagenase would reduce the re-alignment response to muscle stretching. Using DBA/2J and D2.mdx mice, we isolated extensor digitorum longus (EDL), soleus, and diaphragm muscles for collagenase or sham treatment and decellularization to isolate intact or collagenase-digested decellularized muscles (DCMs). These DCMs were mechanically tested and imaged using second harmonic generation microscopy to measure collagen alignment across a range of strains. We found that collagen alignment increased in a strain-dependent fashion, but collagenase did not significantly affect the strain-dependent change in alignment. We also saw that the collagen fibers in the diaphragm epimysium (surface ECM) and perimysium (deep ECM) started at different angles, but still re-oriented in the same direction in response to stretching. These robust changes in collagen alignment were weakly related to passive DCM stiffness. Overall, we demonstrated that the architecture of muscle ECM is dynamic in response to strain and is related to passive muscle mechanics. Statement of significanceOur study presents a unique visualization and quantification of strain-induced changes in muscle collagen fiber alignment as they relate to passive mechanics. Using dynamic imaging of collagen in skeletal muscle we demonstrate that as skeletal muscle is stretched, collagen fibers re-orient themselves along the axis of stretch and increase their alignment. The degree of alignment and the increase in alignment are each weakly related to passive muscle stiffness. Collagenase treatments further demonstrate that the basis for muscle Extracellular matrix stiffness is dependent on factors beyond collagen crosslinking and alignment. Together the study contributes to the knowledge of the structure-function relationships of muscle extracellular matrix to tissue stiffness relevant to conditions of fibrosis and aberrant stiffness.

Exploration of Synergistic Regulation Mechanisms of Cerebral Ganglion and Muscle in Eriocheir sinensis Activated in Response to Alkalinity Stress.

The cerebral ganglion and muscle are important regulatory tissues in Eriocheir sinensis. Therefore, it is of great significance to explore their synergistic roles in this organism's anti-stress response. In this study, proteomics, metabolomics, and combination analyses of the cerebral ganglion and muscle of E. sinensis under alkalinity stress were performed. The cerebral ganglion and muscle played a significant synergistic regulatory role in alkalinity adaptation. The key regulatory pathways involved were amino acid metabolism, energy metabolism, signal transduction, and the organismal system. They also played a modulatory role in the TCA cycle, nerve signal transduction, immune response, homeostasis maintenance, and ion channel function. In conclusion, the present study provides a theoretical reference for further research on the mechanisms regulating the growth and development of E. sinensis in saline-alkaline environments. In addition, it provides theoretical guidelines for promoting the vigorous development of the E. sinensis breeding industry in saline-alkaline environments in the future.

Citrulline activates adenosine receptors: New insight into metabolic pathways interaction

Citrulline is a non-proteinogenic amino acid that forms as by-product in nitric oxide (NO) synthesis from arginine and may act in concert with NO as an independent signaling molecule that involves in the mechanism of vascular smooth muscle vasodilation.In this study we examined the effects of citrulline on pulmonary artery smooth muscles. Experimental design comprised outward potassium currents measurements in enzymatically isolated rat pulmonary artery smooth muscle (PASMc) cells using whole-cell patch clamp technique, isometric contractile force recordings on rat pulmonary artery rings and method of molecular docking simulation.Citrulline in a concentration 10−9-10−5 M relaxed phenylephrine (PHE)-preactivated SM of rat pulmonary artery in a dose-dependent manner (EC50 0,67 μM). This citrulline-induced relaxation was dependent on an intact endothelium. Bath application of citrulline (10-8-10-5 M) on isolated PASMc induced a significant increase in the amplitude of outward potassium current (Ik). The adenosine antagonist caffeine (10-6 M) effectively blocked both the citrulline-induced relaxation response and Ik increment. Molecular docking modeling suggests that caffeine blocking the potent activity of citrulline results from competitive interactions at the A2 adenosine receptor binding site.In summary, our data suggest that citrulline, released with NO at low concentrations, can effectively interact with adenosine receptors in smooth muscle cells, causing their relaxation, indicating surprising interaction between NO and adenosine pathways.