MUSCLE INJURIES AND REPAIR

The Effects of Oleic Acid and Palmitic Acid on Porcine Muscle Satellite Cells

We aimed to determine the effects of oleic acid (OA) and palmitic acid (PA), alone or in combination, on proliferation, differentiation, triacylglycerol (TAG) content, and gene expression in porcine muscle satellite cells (PMSCs). Results revealed that OA-alone- and PA + OA-treated PMSCs showed significantly increased viability than those in the control or PA-alone-treated groups. No significant effects on apoptosis were observed in all three treatments, whereas necrosis was significantly lower in OA-alone- and PA + OA-treated groups than in the control and PA-alone-treated groups. Myotube formation significantly increased in OA-alone and PA + OA-treated PMSCs than in the control and PA-alone-treated PMSCs. mRNA expression of the myogenesis-related genes MyoD1 and MyoG and of the adipogenesis-related genes PPARα, C/EBPα, PLIN1, FABP4, and FAS was significantly upregulated in OA-alone- and PA + OA-treated cells compared to control and PA-alone-treated cells, consistent with immunoblotting results for MyoD1 and MyoG. Supplementation of unsaturated fatty acid (OA) with/without saturated fatty acid (PA) significantly stimulated TAG accumulation in treated cells compared to the control and PA-alone-treated PMSCs. These results indicate that OA (alone and with PA) promotes proliferation by inhibiting necrosis and promoting myotube formation and TAG accumulation, likely upregulating myogenesis- and adipogenesis-related gene expression by modulating the effects of PA in PMSCs.

Triceps brachii insertional footprint: Under-estimated complexity

Background

The detailed complexity of triceps brachii insertional footprint continues to challenge surgeons as evidenced by continued reports of triceps-associated complications following elbow procedures. The purpose of this study is to describe the three-dimensional footprint of the triceps brachii at its olecranon insertion at the elbow.

Methods

22 cadaveric elbows were dissected leaving only the distal insertion of the triceps intact. The insertion was defined and probed with a three-dimensional digitizer to create a digital three-dimensional footprint allowing width, height, and surface area of the footprint to be recorded relative to the bare area. The insertional soft tissues of tendon versus muscle along with the shape of the footprints were qualitatively described.

Results

The mean width and surface area of the lateral segment was greater in males than in females (30.07 mm vs. 24.37 mm, p  =  0.0339 and 282.1 mm vs. 211. 56 mm, p  =  0.0181, respectively). No other statistically significant differences between the sexes were noted. The triceps insertional footprint was "crescent-shaped" and consisted of three regions: central tendon, medial muscular extension, and lateral muscular extension.

Discussion

These findings can help explain the importance of avoiding these muscular structures during triceps-off approaches and provides the framework for future clinical studies. Clinical Relevance: Basic Science, anatomy study, cadaver dissection.

MiR-21 regulates skeletal muscle atrophy and fibrosis by targeting TGF-beta/SMAD7-SMAD2/3 signaling pathway

Long-term denervation-induced atrophy and fibrosis of skeletal muscle due to denervation leads to poor recovery of muscle function. Studies have shown that the transforming growth factor-β1 (TGF-β1)-Smad signaling pathway plays a central role in muscle atrophy and fibrosis. Recent studies demonstrate the role of microRNAs (miRs) in various pathological conditions, including muscle regeneration. miR-21 has been shown to play a dynamic role in inflammatory responses and in accelerating injury responses to fibrosis. We used both RNA sequencing and quantitative RT-PCR strategies to examine the alternations of miRNAs during denervation-induced gastrocnemius muscle atrophy and fibrosis. Our data showed that MiR-21 was upregulated in denervated gastrocnemius muscle tissue, and TGF-β1treatment increased miR-21 expression. Inhibition of miR-21 reduced gastrocnemius muscle fibrosis and significantly downregulated the expression of p-SMAD2/3 and the fibrosis-associated markers TGF-β1, connective tissue growth factor, alpha smooth muscle actin. Masson's trichrome staining revealed that atrophy and fibrosis in gastrocnemius muscle tissue were reduced in the miR-21 inhibition group compared to the control group. We confirmed that SMAD7 is a direct target of miR-21 using a dual luciferase assay. Furthermore, Immunofluorescence and Western blot analyses revealed that miR-21 inhibition reduced SMAD2/3 phosphorylation and nuclear translocation. While SMAD7-siRNA abolished the effect. Consequently, the discovery that miR-21 regulates the atrophy and fibrosis of the gastrocnemius muscle offers a possible therapeutic approach for their management.

Mustn1 in Skeletal Muscle: A Novel Regulator?

Skeletal muscle is a complex organ essential for locomotion, posture, and metabolic health. This review explores our current knowledge of Mustn1, particularly in the development and function of skeletal muscle. Mustn1 expression originates from Pax7-positive satellite cells in skeletal muscle, peaks during around the third postnatal month, and is crucial for muscle fiber differentiation, fusion, growth, and regeneration. Clinically, Mustn1 expression is potentially linked to muscle-wasting conditions such as muscular dystrophies. Studies have illustrated that Mustn1 responds dynamically to injury and exercise. Notably, ablation of Mustn1 in skeletal muscle affects a broad spectrum of physiological aspects, including glucose metabolism, grip strength, gait, peak contractile strength, and myofiber composition. This review summarizes our current knowledge of Mustn1's role in skeletal muscle and proposes future research directions, with a goal of elucidating the molecular function of this regulatory gene.

Agent-based model demonstrates the impact of nonlinear, complex interactions between cytokinces on muscle regeneration

Muscle regeneration is a complex process due to dynamic and multiscale biochemical and cellular interactions, making it difficult to identify microenvironmental conditions that are beneficial to muscle recovery from injury using experimental approaches alone. To understand the degree to which individual cellular behaviors impact endogenous mechanisms of muscle recovery, we developed an agent-based model (ABM) using the Cellular-Potts framework to simulate the dynamic microenvironment of a cross-section of murine skeletal muscle tissue. We referenced more than 100 published studies to define over 100 parameters and rules that dictate the behavior of muscle fibers, satellite stem cells (SSCs), fibroblasts, neutrophils, macrophages, microvessels, and lymphatic vessels, as well as their interactions with each other and the microenvironment. We utilized parameter density estimation to calibrate the model to temporal biological datasets describing cross-sectional area (CSA) recovery, SSC, and fibroblast cell counts at multiple timepoints following injury. The calibrated model was validated by comparison of other model outputs (macrophage, neutrophil, and capillaries counts) to experimental observations. Predictions for eight model perturbations that varied cell or cytokine input conditions were compared to published experimental studies to validate model predictive capabilities. We used Latin hypercube sampling and partial rank correlation coefficient to identify in silico perturbations of cytokine diffusion coefficients and decay rates to enhance CSA recovery. This analysis suggests that combined alterations of specific cytokine decay and diffusion parameters result in greater fibroblast and SSC proliferation compared to individual perturbations with a 13% increase in CSA recovery compared to unaltered regeneration at 28 days. These results enable guided development of therapeutic strategies that similarly alter muscle physiology (i.e. converting extracellular matrix [ECM]-bound cytokines into freely diffusible forms as studied in cancer therapeutics or delivery of exogenous cytokines) during regeneration to enhance muscle recovery after injury.

A Novel Minimally Invasive Surgically Induced Skeletal Muscle Injury Model in Sheep

Sports-related muscle injuries account for 10-55% of all injuries, which is a growing concern, especially given the aging world population. To evaluate the process of skeletal muscle injury and compare it with muscle lesions observed in humans, we developed a novel in vivo model in sheep. In this model, muscle injury was induced by an ultrasound-guided transverse biopsy at the myotendinous junction of the medial gastrocnemius muscle. Twelve male sheep were examined at 3, 7, 14, and 28 days post-injury. Histological, immunofluorescence, and MRI analyses indicate that our sheep model could resemble key human clinicopathological features. Statistically significant differences (p < 0.05) were observed in collagen I, dMHC, α-SMA, and CD68 immunohistochemical detection when comparing injured and healthy muscles. The injured gastrocnemius muscle exhibited elevated levels of type I collagen, infiltration of CD68(+) macrophages, angiogenesis, and the emergence of newly regenerated dMHC(+) myofibers, which persisted for up to 4 weeks post-injury. Similarly, the progression of muscle injury in the sheep model was assessed using advanced clinical 3 T MRI and compared with MRI scans from human patients. The data indicate that the sheep muscle injury model presents features similar to those observed in human skeletal muscle injuries. This makes it a valuable large animal model for studying muscle injuries and developing novel therapeutic strategies.

Agent-based model demonstrates the impact of nonlinear, complex interactions between cytokines on muscle regeneration

Muscle regeneration is a complex process due to dynamic and multiscale biochemical and cellular interactions, making it difficult to identify microenvironmental conditions that are beneficial to muscle recovery from injury using experimental approaches alone. To understand the degree to which individual cellular behaviors impact endogenous mechanisms of muscle recovery, we developed an agent-based model (ABM) using the Cellular Potts framework to simulate the dynamic microenvironment of a cross-section of murine skeletal muscle tissue. We referenced more than 100 published studies to define over 100 parameters and rules that dictate the behavior of muscle fibers, satellite stem cells (SSC), fibroblasts, neutrophils, macrophages, microvessels, and lymphatic vessels, as well as their interactions with each other and the microenvironment. We utilized parameter density estimation to calibrate the model to temporal biological datasets describing cross-sectional area (CSA) recovery, SSC, and fibroblast cell counts at multiple time points following injury. The calibrated model was validated by comparison of other model outputs (macrophage, neutrophil, and capillaries counts) to experimental observations. Predictions for eight model perturbations that varied cell or cytokine input conditions were compared to published experimental studies to validate model predictive capabilities. We used Latin hypercube sampling and partial rank correlation coefficient to identify in silico perturbations of cytokine diffusion coefficients and decay rates to enhance CSA recovery. This analysis suggests that combined alterations of specific cytokine decay and diffusion parameters result in greater fibroblast and SSC proliferation compared to individual perturbations with a 13% increase in CSA recovery compared to unaltered regeneration at 28 days. These results enable guided development of therapeutic strategies that similarly alter muscle physiology (i.e. converting ECM-bound cytokines into freely diffusible forms as studied in cancer therapeutics or delivery of exogenous cytokines) during regeneration to enhance muscle recovery after injury.

Regulation of myo-miR-24-3p on the Myogenesis and Fiber Type Transformation of Skeletal Muscle

Skeletal muscle plays critical roles in providing a protein source and contributing to meat production. It is well known that microRNAs (miRNAs) exert important effects on various biological processes in muscle, including cell fate determination, muscle fiber morphology, and structure development. However, the role of miRNA in skeletal muscle development remains incompletely understood. In this study, we observed a critical miRNA, miR-24-3p, which exhibited higher expression levels in Tongcheng (obese-type) pigs compared to Landrace (lean-type) pigs. Furthermore, we found that miR-24-3p was highly expressed in the dorsal muscle of pigs and the quadriceps muscle of mice. Functionally, miR-24-3p was found to inhibit proliferation and promote differentiation in muscle cells. Additionally, miR-24-3p was shown to facilitate the conversion of slow muscle fibers to fast muscle fibers and influence the expression of GLUT4, a glucose transporter. Moreover, in a mouse model of skeletal muscle injury, we demonstrated that overexpression of miR-24-3p promoted rapid myogenesis and contributed to skeletal muscle regeneration. Furthermore, miR-24-3p was found to regulate the expression of target genes, including Nek4, Pim1, Nlk, Pskh1, and Mapk14. Collectively, our findings provide evidence that miR-24-3p plays a regulatory role in myogenesis and fiber type conversion. These findings contribute to our understanding of human muscle health and have implications for improving meat production traits in livestock.

Therapeutic TNF Inhibitors Exhibit Differential Levels of Efficacy in Accelerating Cutaneous Wound Healing

Adalimumab but neither etanercept nor certolizumab-pegol has been reported to induce a wound-healing profile in vitro by regulating macrophage differentiation and matrix metalloproteinase expression, which may underlie the differences in efficacy between various TNF-α inhibitors in impaired wound healing in patients with hidradenitis suppurativa, a chronic inflammatory skin disease. To examine and compare the efficacy of various TNF inhibitors in cutaneous wound healing in vivo, a human TNF knock-in Leprdb/db mouse model was established to model the impaired cutaneous wound healing as seen in hidradenitis suppurativa. The vehicle group exhibited severe impairments in cutaneous wound healing. In contrast, adalimumab significantly accelerated healing, confirmed by both histologic assessment and a unique healing transcriptional profile. Moreover, adalimumab and infliximab showed similar levels of efficacy, but golimumab was less effective, along with etanercept and certolizumab-pegol. In line with histologic assessments, proteomics analyses from healing wounds exposed to various TNF inhibitors revealed distinct and differential wound-healing signatures that may underlie the differential efficacy of these inhibitors in accelerating cutaneous wound healing. Taken together, these data revealed that TNF inhibitors exhibited differential levels of efficacy in accelerating cutaneous wound healing in the impaired wound-healing model in vivo.

Angiotensin-(1-7) improves skeletal muscle regeneration

Skeletal muscle possesses regenerative potential via satellite cells, compromised in muscular dystrophies leading to fibrosis and fat infiltration. Angiotensin II (Ang-II) is commonly associated with pathological states. In contrast, Angiotensin (1-7) [Ang-(1-7)] counters Ang-II, acting via the Mas receptor. While Ang-II affects skeletal muscle regeneration, the influence of Ang-(1-7) remains to be elucidated. Therefore, this study aims to investigate the role of Ang-(1-7) in skeletal muscle regeneration. C2C12 cells were differentiated in the absence or presence of 10 nM of Ang-(1-7). The diameter of myotubes and protein levels of myogenin and myosin heavy chain (MHC) were determined. C57BL/6 WT male mice 16-18 weeks old) were randomly assigned to injury-vehicle, injury-Ang-(1-7), and control groups. Ang-(1-7) was administered via osmotic pumps, and muscle injury was induced by injecting barium chloride to assess muscle regeneration through histological analyses. Moreover, embryonic myosin (eMHC) and myogenin protein levels were evaluated. C2C12 myotubes incubated with Ang-(1-7) showed larger diameters than the untreated group and increased myogenin and MHC protein levels during differentiation. Ang-(1-7) administration enhances regeneration by promoting a larger diameter of new muscle fibers. Furthermore, higher numbers of eMHC (+) fibers were observed in the injured-Ang-(1-7), which also had a larger diameter. Moreover, eMHC and myogenin protein levels were elevated, supporting enhanced regeneration due to Ang-(1-7) administration. Ang-(1-7) effectively promotes differentiation in vitroand improves muscle regeneration in the context of injuries, with potential implications for treating muscle-related disorders.

Mustn1 ablation in skeletal muscle results in functional alterations

Mustn1, a gene expressed exclusively in the musculoskeletal system, was shown in previous in vitro studies to be a key regulator of myogenic differentiation and myofusion. Other studies also showed Mustn1 expression associated with skeletal muscle development and hypertrophy. However, its specific role in skeletal muscle function remains unclear. This study sought to investigate the effects of Mustn1 in a conditional knockout (KO) mouse model in Pax7 positive skeletal muscle satellite cells. Specifically, we investigated the potential effects of Mustn1 on myogenic gene expression, grip strength, alterations in gait, ex vivo investigations of isolated skeletal muscle isometric contractions, and potential changes in the composition of muscle fiber types. Results indicate that Mustn1 KO mice did not present any substantial phenotypic changes or significant variations in genes related to myogenic differentiation and fusion. However, an approximately 10% decrease in overall grip strength was observed in the 2-month-old KO mice in comparison to the control wild type (WT), but this decrease was not significant when normalized by weight. KO mice also generated approximately 8% higher vertical force than WT at 4 months in the hindlimb. Ex vivo experiments revealed decreases in about 20 to 50% in skeletal muscle contractions and about 10%-20% fatigue in soleus of both 2- and 4-month-old KO mice, respectively. Lastly, immunofluorescent analyses showed a persistent increase of Type IIb fibers up to 15-fold in the KO mice while Type I fibers decreased about 20% and 30% at both 2 and 4 months, respectively. These findings suggest a potential adaptive or compensatory mechanism following Mustn1 loss, as well as hinting at an association between Mustn1 and muscle fiber typing. Collectively, Mustn1's complex roles in skeletal muscle physiology requires further research, particularly in terms of understanding the potential role of Mustn1 in muscle repair and regeneration, as well as with influence of exercise. Collectively, these will offer valuable insights into Mustn1's key biological functions and regulatory pathways.

Symptom burden, fatigue, sleep quality and perceived social support in hemodialysis patients with musculoskeletal discomfort: a single center experience from Egypt

BACKGROUND AND AIMS

Musculoskeletal disorders (MSDs) are commonly encountered in hemodialysis (HD) patients. However, the causes linked to these disorders are still partially defined. The aim of this study was to determine the frequency of MSDs and their relationship to a variety of clinico-social characteristics such as sleep quality, mood disorders, fatigue, and social support, in addition to the patients' clinical and therapeutic profile.

METHOD

The study included 94 patients on maintenance HD. Clinical and Sociodemographic data was gathered. To investigate the prevalence and trends of MSDs, the Nordic Musculoskeletal Questionnaire (NMQ-E) was employed. Patients completed the modified Edmonton Symptom Assessment System, Pittsburgh Sleep Quality Index (PSQI), multidimensional Fatigue Inventory (MFI-20), and Perceived Social Support from Family Scales. Univariate and multivariate regression analysis were used to assess the determinants of MSDs.

RESULTS

The patients' mean age was 49.73 and 59.6% were males. Seventy-two percent of patients were afflicted by MSDs. Knee pain (48.9%), low back pain (43.6%), shoulder pain (41.6%), hip/thigh pain (35.1%), and neck pains (35.1%) were the most reported MSD domains. Pain (p = 0.001), fatigue (p = 0.01), depression (p = 0.015), and anxiety (p = 0.003) scores were substantially higher in patients with MSDs. Furthermore, patients with MSDs engaged in less physical activity (p = 0.02) and perceived less social support (p = 0.029). Patients with MSDs had lower subjective sleep quality, daytime dysfunction domains, and global PSQI scores (p = 0.02, 0.031, 0.036, respectively). Female gender (p = 0.013), fatigue (p = 0.012), depression (p = 0.014), anxiety (p = 0.004), lower activity (p = 0.029), and PSQI score (0.027), use of erythropoiesis-stimulating agents (ESAs), antihypertensive drugs, calcium and Iron supplementation were all significantly associated with MSDs. At the multivariable regression model, administration of ESAs (p = 0.017) and pain score (p = 0.040) were the only independent variables associated with the outcome.

CONCLUSION

MSDs are quite common among HD patients. Female gender, pain, fatigue, depression, anxiety, reduced activity, poor sleep quality, and use of ESAs are all significantly associated with MSDs in HD patients. Patients with MSD perceived less social support compared to the other group. Patients treated with antihypertensive drugs, calcium and iron supplements were more likely to suffer MSDs.

Muscle Belly Repair: Biomechanical Assessment of the Anchor Suture and the Modified Kessler Techniques

Background: Treatment of muscle belly lacerations remains a problem for surgeons. Inadequate repair of lacerations can cause functional disability. To date, there is no consensus on the method of repair for these injuries. We have previously described a technique of repairing mid-substance muscle belly lacerations. The aim of this study was to determine the ultimate strength of an intact muscle belly and to compare the anchor suture (AS) technique with the modified Kessler (MK) technique. Methods: Fifteen fresh frozen hind-legs from adolescent pigs were divided into three groups and used for the testing. Each group consisted of five specimens. Group one was the intact control group, group two was repaired with the MK technique and group three was repaired with the AS technique. Following repair, the muscles were secured in a custom-made fixation apparatus and underwent linear tensioning at a rate of 25 mm/min, generating a load-displacement curve for each specimen. The data regarding ultimate strength, modes of failure and number of intact suture/anchor constructs (for groups 2 and 3) was calculated. Results: The ultimate strength of the intact muscle group of was found to be 608.1 ± 107.9  N. This was significantly (p < 0.05) higher than the pull-out strength of the MK and AS groups. The pull-out strength of the AS group was 143.1 ± 36.7 N, nearly twice that of the MK group 69.8 ± 16.4 N (p = 0.11). Suture pull-out was the most common mode of failure. Conclusions: The AS technique was found to have both higher strain and nearly twice the ultimate pull-out strength compared to the MK repair group. We suggest the AS technique as a viable technique for mid-substance muscle belly repairs.

ALM Therapy Promotes Functional and Histologic Regeneration of Traumatized Peripheral Skeletal Muscle

Skeletal muscle trauma is a common injury with a range of severity. Adenosine, lidocaine and Mg²⁺ (ALM) is a protective solution and improves tissue perfusion and coagulopathy. Male Wistar rats were anesthetized and subjected to standardized skeletal muscle trauma of the left soleus muscle with the protection of the neurovascular structures. Seventy animals were randomly assigned to saline control or ALM. Immediately after trauma, a bolus of ALM solution was applied intravenously, followed by a one-hour infusion. After 1, 4, 7, 14 and 42 days, the biomechanical regenerative capacity was examined using incomplete tetanic force and tetany, and immunohistochemistry was used to examine for proliferation and apoptosis characteristics. Biomechanical force development showed a significant increase following ALM therapy for incomplete tetanic force and tetany on days 4 and 7. In addition, the histological evaluation showed a significant increase in proliferative BrdU-positive cells with ALM therapy on days 1 and 14. Ki67 histology also detected significantly more proliferative cells on days 1, 4, 7, 14 and 42 in ALM-treated animals. Furthermore, a simultaneous decrease in the number of apoptotic cells was observed using the TUNEL method. ALM solution showed significant superiority in biomechanical force development and also a significant positive effect on cell proliferation in traumatized skeletal muscle tissue and reduced apoptosis.

Effects of heat stress exposure on porcine muscle satellite cells

Heat stress (HS) affects cell culture as well as animal production. Although there have been many reports on the disparate effects of heat stress, its effects on mammalian muscle stem cells are still unclear. In this study, we isolated porcine muscle satellite cells (PMSCs) from the femurs of 1-day-old piglets, and cultured them under three temperature conditions: 37 °C, 39 °C, and 41 °C. Exposure to HS not only decreased the viability and proliferation rates of PMSCs, but also regulated the cell cycle and induced apoptosis. High-temperature culture conditions decreased both protein and gene expression of Pax7, a proliferation and maintenance marker of muscle satellite cells, whereas it increased both protein and gene expression of MyoG, a differentiation marker, and promoted myotube formation in the early stage of differentiation induction. In addition, the protein and gene expression of several heat shock proteins (HSPs) in PMSCs increased due to heat treatment. In conclusion, HS induced the cell cycle arrest of PMSCs, thereby reducing the proliferation rate. In addition, high-temperature culture conditions promoted the formation of myotubes at the early stage of differentiation of PMSCs without additives.

Local application of a transcutaneous carbon dioxide paste prevents excessive scarring and promotes muscle regeneration in a bupivacaine-induced rat model of muscle injury

In postoperative patients with head and neck cancer, scar tissue formation may interfere with the healing process, resulting in incomplete functional recovery and a reduced quality of life. Percutaneous application of carbon dioxide (CO₂ ) has been reported to improve hypoxia, stimulate angiogenesis, and promote fracture repair and muscle damage. However, gaseous CO₂ cannot be applied to the head and neck regions. Previously, we developed a paste that holds non-gaseous CO₂ in a carrier and can be administered transdermally. Here, we investigated whether this paste could prevent excessive scarring and promote muscle regeneration using a bupivacaine-induced rat model of muscle injury. Forty-eight Sprague Dawley rats were randomly assigned to either a control group or a CO₂ group. Both groups underwent surgery to induce muscle injury, but the control group received no treatment, whereas the CO₂ group received the CO₂ paste daily after surgery. Then, samples of the experimental sites were taken on days 3, 7, 14, and 21 post-surgery to examine the following: (1) inflammatory (interleukin [IL]-1β, IL-6), and transforming growth factor (TGF)-β and myogenic (MyoD and myogenin) gene expression by polymerase chain reaction, (2) muscle regeneration with haematoxylin and eosin staining, and (3) MyoD and myogenin protein expression using immunohistochemical staining. Rats in the CO₂ group showed higher MyoD and myogenin expression and lower IL-1β, IL-6, and TGF-β expression than the control rats. In addition, treated rats showed evidence of accelerated muscle regeneration. Our study demonstrated that the CO₂ paste prevents excessive scarring and accelerates muscle regeneration. This action may be exerted through the induction of an artificial Bohr effect, which leads to the upregulation of MyoD and myogenin, and the downregulation of IL-1β, IL-6, and TGF-β. The paste is inexpensive and non-invasive. Thus, it may be the treatment of choice for patients with muscle damage.

Icing after skeletal muscle injury decreases M1 macrophage accumulation and TNF-α expression during the early phase of muscle regeneration in rats

Following skeletal muscle injury, both myogenic and immune cells interact closely during the regenerative process. Although icing is still a common acute treatment for sports-related skeletal muscle injuries, icing after muscle injury has been shown to disrupt macrophage accumulation and impair muscle regeneration in animal models. However, it remains unknown whether icing shortly after injury affects macrophage-related phenomena during the early stages of muscle regeneration. Therefore, we focused on the distribution of M1/M2 macrophages and cytokines expressed predominantly by macrophages during the early stages of muscle regeneration after muscle crush injury. Icing resulted in a decrease, not retardation, in the accumulation of M1 macrophages, but not M2 macrophages, in injured muscles. Consistent with the decrease in M1 macrophage accumulation, icing led to a reduction, instead of delay, in the level of tumor necrosis factor-α (TNF-α) expression. Additionally, at subsequent timepoints, icing decreased the number of myogenic precursor cells in the regenerating area and the size of centrally nucleated regenerating myofibers. Together, our findings suggest that icing after acute muscle damage by crushing disturbs muscle regeneration through hindering tM1 macrophage-related phenomena.

[Acute compartment syndrome of the extremities]

Acute compartment syndrome of the extremities is a surgical emergency and a rapid diagnosis and immediate surgical treatment are essential for the outcome. The cause is an increase in the tissue pressure inside a muscle compartment enclosed by fasciae and the resulting disruption of microperfusion. This can have potentially disastrous consequences, such as loss of the extremity due to extensive tissue necrosis or a threat to life due to infectious complications. Although mostly triggered by trauma, a multitude of other causes can lead to the formation of a compartment syndrome, so that a basic knowledge of this condition is of great importance not only for trauma surgeons. This is particularly true because a timely treatment necessitates rapid diagnosis and evaluation of the indications. This article provides an overview of the underlying pathophysiology, the causes, the symptoms and the treatment of acute compartment syndrome.

Sulforaphane regulates Nrf2-mediated antioxidant activity and downregulates TGF-β1/Smad pathways to prevent radiation-induced muscle fibrosis

AIMS

This study aimed to examine the efficacy of sulforaphane (SFN) in preventing radiation-induced muscle fibrosis (RIMF) and the potential role in nuclear factor erythroid 2-related factor 2 (Nrf2)-mediated antioxidant stress.

MAIN METHODS

The RIMF model was established by a single irradiation of the left thigh of C57BL/6 J mice, and the mice were then randomly divided into control, SFN, irradiation (IR), and IR + SFN (IR/SFN) groups. The serum and skeletal muscle were collected eight weeks after irradiation, and changes in oxidative stress and muscle fibrosis were detected.

KEY FINDINGS

The IR group showed a more obvious skeletal muscle fiber atrophy, significantly higher number of collagen fibers, and higher inflammatory cell infiltration compared to control group. Compared to the IR group, the IR/SFN group had orderly arranged muscle fibers, decreased collagen fibers, and infiltration of inflammatory cells. In addition, compared with the control group, the expression of oxidative stress-related indexes was significantly increased, accompanied by activation of the transforming growth factor (TGF-β)/Smad pathway and its downstream fibrogenic molecules in the skeletal muscle of the IR group. After SFN intervention, the above indices were significantly restored. Furthermore, SFN induced the upregulation of Nrf2, activation of AKT, and inhibition of GSK-3β and Fyn accumulation.

SIGNIFICANCE

These results revealed that Nrf2 plays a central role in protecting against RIMF. Furthermore, SFN prevents RIMF by activating Nrf2 via the AKT/GSK-3β/Fyn pathway.

In vitro analysis of genome-engineered muscle-derived stem cells for autoregulated anti-inflammatory and antifibrotic activity

Traumatic muscle injury leads to chronic and pathologic fibrosis in skeletal muscles, primarily driven through upregulation of transforming growth factor-β1 (TGF-β1). Cell-based therapies, such as injection of muscle-derived stem cells (MDSCs), have shown promise in muscle repair. However, injected MDSCs in injured skeletal muscle can differentiate into myofibroblasts under the influence of TGF-β1, and contribute to the development of fibrosis, limiting their regenerative potential. In this study, we created a "smart" cell-based drug delivery system using CRISPR-Cas9 to genetically engineer MDSCs capable of sensing TGF-β1 and producing an antifibrotic biologic, decorin. These gene-edited smart cells, capable of inhibiting fibrosis in a dose-dependent and autoregulating manner, show anti-inflammatory and antifibrotic properties in vitro, without changing the expression of myogenic and stem cell markers as well as their cell proliferation and myogenic differentiation. Additionally, differentiation down a fibrotic lineage is reduced or eliminated in response to TGF-β1. Our results show that gene editing can be used to successfully create smart stem cells capable of producing biologic drugs with antifibrotic capabilities in a controlled and localized manner. This system provides a tool for cell-based drug delivery as the basis for a novel therapeutic approach for a variety of diseases.

Adenosine monophosphate activated protein kinase contributes to skeletal muscle health through the control of mitochondrial function

Skeletal muscle is one of the largest organs in the body and the largest protein repository. Mitochondria are the main energy-producing organelles in cells and play an important role in skeletal muscle health and function. They participate in several biological processes related to skeletal muscle metabolism, growth, and regeneration. Adenosine monophosphate-activated protein kinase (AMPK) is a metabolic sensor and regulator of systemic energy balance. AMPK is involved in the control of energy metabolism by regulating many downstream targets. In this review, we propose that AMPK directly controls several facets of mitochondrial function, which in turn controls skeletal muscle metabolism and health. This review is divided into four parts. First, we summarize the properties of AMPK signal transduction and its upstream activators. Second, we discuss the role of mitochondria in myogenesis, muscle atrophy, regeneration post-injury of skeletal muscle cells. Third, we elaborate the effects of AMPK on mitochondrial biogenesis, fusion, fission and mitochondrial autophagy, and discuss how AMPK regulates the metabolism of skeletal muscle by regulating mitochondrial function. Finally, we discuss the effects of AMPK activators on muscle disease status. This review thus represents a foundation for understanding this biological process of mitochondrial dynamics regulated by AMPK in the metabolism of skeletal muscle. A better understanding of the role of AMPK on mitochondrial dynamic is essential to improve mitochondrial function, and hence promote skeletal muscle health and function.

Quantitative assessment of changes in skeletal muscle injury by computer-aided analysis based on two-dimensional ultrasonography combined with contrast-enhanced ultrasonography and estimated by a modified semi-quantitative scoring system: An experimental study in a contusion model

The aim of this study was to investigate the potential application of computer-aided analysis in the quantitative assessment of changes in skeletal muscle injury in the rabbit contusion model. Forty healthy rabbits were randomly divided into control (n = 5) and contusion (n = 35) groups. Rabbits in the contusion group were used to construct a muscle contusion model induced by a hammer hitting the right gastrocnemius, while the muscles of rabbits in the control group were non-injured. Two-dimensional ultrasound (2D US) and contrast-enhanced ultrasonography (CEUS) were performed on the rabbits that had received skeletal muscle contusion injury at 1 h, and 1, 3, 7, 14, 21 and 28 days after injury. Afterwards, a multiscale blob feature (MBF) method was used to extract the textural features from the 2D US, and the muscle injuries were quantitatively evaluated. The eight textural parameters of skeletal muscle analysed by MBF at 1 h, and 1, 3 and 7 days post-injury were found to be significantly higher in the contusion group than in the control group (p < .05). On Day 14, the textural parameters (e.g., greyscale mean [Mean], greyscale standard deviation [SDev], number of blobs, average size of blobs, homogeneity of distribution, periodicity of distribution [POD] and irregularity) were also evidently higher in the contusion group than in the control group (p < .05). On Day 28, Mean, SDev and POD in the contusion group were markedly higher (p < .05). After that, the microcirculation in the injured areas increased from Day 7 to Day 21 after injury, but decreased on Day 28 after injury. Thus the quantitative assessment of changes in skeletal muscle injury (SMI) using computer-aided analysis allowed us to describe the geometric features of injured muscle fibres and the microperfusion changes estimated by the modified semi-quantitative scoring system. This provides a scientific basis for the development of a novel approach for the evaluation of SMI and rehabilitation process.

Viscoelasticity assessment for in vivo quantification of muscle contusion injury in rats using shear wave elastography

The aim of the study described here was to investigate the role of viscoelasticity in assessing muscle fibrosis and inflammation in a rat model of contusion using quantitative shear wave elastography (SWE). Unilateral gastrocnemius muscle contusion was induced in 32 male rats using an impactor apparatus. The contralateral muscles served as the control group. SWE was applied to the control group and rats 1, 3, 14 and 21 d after successful modeling (each time point group, n = 8). Histologic features were used as reference standards. The degree of fibrosis was moderately correlated with shear wave speed (r = 0.53), whereas the degree of inflammation was well correlated with shear wave dispersion (SWD) slope (r = 0.74). The area under the receiver operating characteristic curve (AUC) for the dispersion slope for muscle inflammation and fibrosis assessment was 0.87 (95% confidence interval: 0.705-0.963), which exceeded that of the shear wave speed (0.68, 95% confidence interval: 0.494-0.834). The larger decline in dispersion slope in the fibrotic stage than in the inflammation stage (1-d group vs. 14-d group or 21-d group, p &lt; 0.05) indicated better predictive performance than the shear wave speed.

A Review of free fatty acid-induced cell signaling, angiopoietin-like protein 4, and skeletal muscle differentiation

Postnatal skeletal muscle differentiation from quiescent satellite cells is a highly regulated process, although our understanding of the contribution of nutritional factors in myogenesis is limited. Free fatty acids (FFAs) are known to cause detrimental effects to differentiated skeletal muscle cells by increasing oxidative stress which leads to muscle wasting and insulin resistance in skeletal muscle. In addition, FFAs are thought to act as inhibitors of skeletal muscle differentiation. However, the precise molecular mechanisms underlying the effects of FFAs on skeletal muscle differentiation remains to be elucidated. There is a clear relationship between dietary FFAs and their ability to suppress myogenesis and we propose the hypothesis that the FFA-mediated increase in angiopoietin-like protein 4 (ANGPTL4) may play a role in the inhibition of differentiation. This review discusses the role of FFAs in skeletal muscle differentiation to-date and proposes potential mechanisms of FFA-induced ANGPTL4 mediated inhibition of skeletal muscle differentiation.

Repair of Subacute Intrasubstance Rupture of the Biceps Brachii in a 16-Year-Old Patient

A 16-year-old boy sustained a complete, closed, intrasubstance rupture of both heads of the biceps brachii after a rope swing accident. The patient was managed with open direct repair of the muscle belly. After the surgery, he underwent an extensive physical therapy regimen and regained full range of motion and strength. To our knowledge, this is the youngest reported case of a subacute intrasubstance rupture of the biceps brachii muscle treated surgically in the literature. There is no consensus in the literature regarding the optimal management of these injuries. Given the satisfactory outcome, we suggest that open direct repair of the muscle belly is a reasonable option for the pediatric population.

The Use of Instrument-Assisted Soft-Tissue Mobilization for Manual Medicine: Aiding Hand Health in Clinical Practice

Instrument-assisted soft-tissue mobilization (IASTM) represents a treatment strategy for soft tissue (skin) and musculoskeletal tissue (myofascia). There are different morphologies of these tools that are used by clinicians and manual therapists for the management of scars, fibrotic formations, muscle-joint pain, and movement limitations. The literature demonstrates the effectiveness of IASTMs in different clinical areas. However, the literature does not consider the use of these tools for the protection of the clinician’s hands. The main objective of this article is to draw attention to the fact that IASTM can protect clinicians from professional joint injuries of the hands and can likely become a preventive tool for the operator. Further research is needed to fully determine the positive adaptations in operators who use IASTMs compared to those who do not use them.

Silk sericin patches delivering miRNA-29-enriched extracellular vesicles-decorated myoblasts (SPEED) enhances regeneration and functional repair after severe skeletal muscle injury

Severe skeletal muscle injuries usually lead to a series of poor recovery issues, such as massive myofibers loss, scar tissue formation, significant muscle function impairment, etc. Here, a silk sericin patch delivering miRNA-29-enriched extracellular vesicles-decorated myoblasts (SPEED) is designed for the rapid regeneration and functional repair after severe skeletal muscle injury. Specifically, miR29-enriched extracellular vesicles (miR29-EVs) are prepared and used to deliver miR29 into primary myoblasts, which promote the myotube formation of myoblasts and increase the expression of myogenic genes while inhibiting the expression of fibrotic genes. Our results indicate that miR29-EVs promote the integration of primary myoblasts and host muscle in a severe mouse tibialis anterior (TA) muscle injury model. Moreover, implantation of SPEED drastically stimulates skeletal muscle regeneration, inhibits fibrosis of injured muscles, and leads to significant improvement of muscle contraction forces and motor ability of mice about 3 weeks after treatment. Subsequently, we further evaluate the transcriptomes of TA muscles and find that SPEED can significantly ameliorate energy metabolism and muscular microenvironment of TA muscles on day 9 after implantation. Additionally, bioinformatic analysis and comprehensive molecular biology studies also reveal that the down-regulation of CDC20-MEF2C signaling axis may participate in the muscle repair process. Together, SPEED may serve as an effective alternative for the rapid repair of severe skeletal muscle injuries in the future.

Stretch-Induced Healing of Injured Muscles Is Associated With Myogenesis and Decreased Fibrosis

BACKGROUND

Alghouth therapeutic stretching exercise has been applied to accelerate the healing of injured skeletal muscles, mechanisms behind the mechanical stretch-induced muscle recovery remain unclear.

PURPOSE

To examine stretch-associated antifibrotic and myogenic responses in injured muscles and to evaluate the feasibility of the ultrasonic Nakagami parametric index (NPI) in assessing muscle morphology during recovery.

STUDY DESIGN

Controlled laboratory study.

METHODS

Skeletal muscle fibrosis was induced in the right hind legs of 48 rats by making a posterior transverse incision in the gastrocnemius muscle; the left hind legs remained intact as a comparative normal reference. After surgery, the 48 rats were randomly divided into the stretch (S) and control (C) groups. The S group received stretching interventions on the injured hind leg from week 3 to week 7 after surgery, while the C group did not receive stretching throughout the study period. The muscle fibrosis percentage and the ultrasonic NPI were examined sequentially after surgery. Relative expressions of myogenesis-related proteins, including myoblast determination protein 1 (MyoD), myogenin, and embryonic myosin heavy chain (MHCemb), were also evaluated during the follow-up.

RESULTS

Mean fibrosis percentages in the injured hind leg were approximately 25% at week 3 in both groups, but they were significantly decreased by approximately 20% from week 4 to the end of the follow-up in the S group only (all, P < .05). Upon injury, the NPI values of injured hind legs in both groups dramatically dropped. Within the S group, stretching increased the NPI values of injured hind legs, which approached those of control hind legs at weeks 6 and 7. The highest MyoD, myogenin, and MHCemb levels were observed at week 6 in both groups. The NPI values corresponded to the MyoD expression in the S group during the follow-up.

CONCLUSION

Stretching induced a decrease in muscle fibrosis and an increase in myogenesis in injured muscles. The NPI values correspond to the myogenesis process.

CLINICAL RELEVANCE

The NPI may be capable of continuously monitoring the injured skeletal muscle morphology during the healing process in clinical settings.

Histomorphological and functional contralateral symmetry in the gastrocnemius muscles of the laboratory rat

It is usual in anatomical and physiological research to assess the effects of some intervention on extremities (e.g., training programmes or injury recovery protocols) using one muscle for the intervention and its contralateral as control. However, the existence of laterality (left‐handedness or right‐handedness) in athletes of different specialities is widely recognized. In rats, gastrocnemius is one of the muscles most widely used because of its importance in locomotion and high relative limb mass. Since we have not found studies reporting laterality assessment on the morphology and function in rat gastrocnemius, our study aimed to evaluate the fibre histochemical, morphometrical and muscle force contractile properties between right and left gastrocnemius of the laboratory rat. Fibre‐type proportion, fibre morphometrical measurements, muscle capillarization and muscle force properties were analysed in the right and left gastrocnemius of six male rats. No statistically significant differences (p = 0.265) were found in gastrocnemius to body weight ratio (‰) between right (6.55 ± 0.40) and left (6.49 ± 0.40) muscles. The muscles analysed showed a great degree of heterogeneity in fibre type distribution, having three clearly distinguished regions named red, mixed and white. In the three regions, there were no statistical differences in fibre type proportions between right and left gastrocnemius, as is indicated by the p‐values (from 0.203 to 0.941) obtained after running t‐Student paired tests for each fibre type. When analysing fibre cross‐sectional area, individual fibre capillarization and fibre circularity, no significant differences between right and left gastrocnemius in any of these morphometrical parameters were found in any muscle region or fibre type. Most of the p‐values (70%) resulting from running t‐Student paired tests were higher than 0.400, and the lowest p‐value was 0.115. Seemingly, global capillary and fibre densities were not statistically different between right and left sides in all muscle regions with p‐values ranging from 0.337 to 0.812. Force parameters normalized to gastrocnemius mass (mN g⁻¹) did not show any significant difference between right (PF = 74.0 ± 13.4, TF = 219.4 ± 13.0) and left (PF = 70.9 ± 10.7, TF = 213.0 ± 18.0) muscles with p = 0.623 (PF) and p = 0.514 (TF). Twitch time parameters (ms) also lacked significant differences between the two sides (CT: 43.4 ± 8.6 vs. 45.0 ± 14.3, p = 0.639; HRT: 77.6 ± 15.0 vs. 82.3 ± 25.3, p = 0.475). Finally, both muscles also showed similar (p = 0.718) fatigue properties. We did find an absence of laterality at the morphological and functional levels, which raises the possibility of using right and left gastrocnemius muscles interchangeably for experimental designs where one muscle is used to analyse data after a physiological intervention and its contralateral muscle plays the control role, thus allowing unbiased paired comparisons to derive accurate conclusions.

An Investigation of the Mechanisms of Radiation-Induced Muscle Injury in a Tree Shrew (Tupaia belangeri) Model

Background

Animal models suitable for investigating mechanisms behind radiation-induced muscle injury are lacking. We developed a tree shrew model of such injury and investigated pathological changes and mechanisms.

Methods

Animals were divided into control (n = 5), radiation-induced acute injury (n = 5), and radiation-induced chronic injury (n = 5) groups. Tensor veli palatini (TVP) muscles of acute injury and chronic injury groups were dissected under a microscope at 1 and 24 weeks after radiation therapy, respectively. TVP muscles were stained with HE and Masson to visualize pathological changes. ELISA was performed to measure oxidative injury. RT-qPCR and immunohistochemical staining was performed to measure expression levels of miR-206 and histone deacetylase 4 (HDAC4).

Results

Compared to the control group, acute injury group showed a significant decrease in miR-206 expression (.061 ± .38, P < .05) and a significant increase in HDAC4 expression (37.05 ± 20.68, P < .05). Chronic injury group showed a significant decrease in miR-206 expression (.23 ± .19, P < .05) and a significant increase in HDAC4 expression (9.66 ± 6.12, P < .05).

Discussion

A tree shrew model of radiation-induced muscle injury was established by exposing TVP muscle region to radiation of 20-Gy. Experimental results indicated that injury caused by radiation persisted despite gradual healing of the TVP muscle and miR-206 regulatory pathway plays a key role in regulating radiation-induced muscle injury.

Plasmonic fusion between fibroblasts and skeletal muscle cells for skeletal muscle regeneration

Normal regeneration of skeletal muscle takes place by the differentiation of muscle-specific stem cells into myoblasts that fuse with existing myofibers for muscle repair. This natural repair mechanism could be ineffective in some cases, for example in patients with genetic muscular dystrophies or massive musculoskeletal injuries that lead to volumetric muscle loss. In this study we utilize the effect of plasmonic cell fusion, i.e. the fusion between cells conjugated by gold nanospheres and irradiated by resonant femtosecond laser pulses, for generating human heterokaryon cells of myoblastic and fibroblastic origin, which further develop into viable striated myotubes. The heterokaryon cells were found to express the myogenic transcription factors MyoD and Myogenin, as well as the Desmin protein that is essential in the formation of sarcomeres, and could be utilized in various therapeutic approaches that involve transplantation of cells or engineered tissue into the damaged muscle.

Inflammation, Fibrosis and Cancer: Mechanisms, Therapeutic Options and Challenges

Uncontrolled inflammation is a salient factor in multiple chronic inflammatory diseases and cancers. In this review, we provided an in-depth analysis of the relationships and distinctions between uncontrolled inflammation, fibrosis and cancers, while emphasizing the challenges and opportunities of developing novel therapies for the treatment and/or management of these diseases. We described how drug delivery systems, combination therapy and the integration of tissue-targeted and/or pathways selective strategies could overcome the challenges of current agents for managing and/or treating chronic inflammatory diseases and cancers. We also recognized the value of the re-evaluation of the disease-specific roles of multiple pathways implicated in the pathophysiology of chronic inflammatory diseases and cancers-as well as the application of data from single-cell RNA sequencing in the success of future drug discovery endeavors.

[CME-Sonography 105: Ultrasound in Sports Injuries]

CME-Sonography 105: Ultrasound in Sports Injuries Abstract. Muscle injuries are frequent in athletes and in the general population. For therapy and prognosis, it is important to understand the total extent of the injury and to be aware of possible complications. In most cases ultrasound is a useful tool for diagnostics of muscle injuries. However, muscle ultrasound is not as common as joint ultrasound; this article discusses the possibilities of high-resolution dynamic ultrasound in diagnostics and its limitations.

Histological and impedance changes of skeletal muscle by whole-body critical irradiation in a rat model

In this study, the electrical resistance of the whole body and histological changes of skeletal muscle were investigated in rats according to the increase in radiation dose. A total of 15 male Sprague-Dawley rats (5-weeks-old) were randomly divided into 5 groups (each, n = 3). Each group received 1 Gy, 5 Gy, 10 Gy and 20 Gy systemic exposure, and the non-irradiated group was used as a control for morphological comparison. After attaching an electrode clip to the forelimb of the rat, an AC frequency was applied before and 4 days after irradiation using an impedance/gain-phase analyzer, and the measurement system was automatically controlled with LabVIEW. Comparing to before irradiation after 4 days, the difference in the average impedance values at 1 Gy, 5 Gy, 10 Gy, and 20 Gy was 1188±989 ohm, 3076±2251 ohm, 7650±6836 ohm, and 10478±6250 ohm, respectively. By comparing the normal group and the experimental group, muscle fiber atrophy and collagen fibers around blood vessels were observed (p < 0.05, control group vs 5 Gy or more high-dose group). These results confirmed the previously reported morphological changes of skeletal muscle and our hypothesis that whole-body impedance measurement enables to reflect tissue changes after irradiation.

The Biological Use of Platelet-Rich Plasma in Skeletal Muscle Injury and Repair

Platelet-rich plasma (PRP) is a blood product that contains several growth factors and active proteins. PRP is thought to be used autologously to assist in the repair of injured tissues as well as to treat pain at the site of injury. The mechanism behind PRP in regenerative medicine has been well investigated and includes the identification and concentration of released growth factors and exosomes. The benefits of PRP have been highly recommended and are used widely in orthopaedics and sports medicine, including repair of injured skeletal muscle. This current report summarizes some of the more recent studies in the use of PRP as it relates to muscle healing, in both the in vitro and clinical arenas.

Feasibility study for inducing the skeletal muscle fibrosis via irradiation using two mouse strains

PURPOSE

Although the mechanism of onset and progression of radiation-induced fibrosis (RIF) has been studied, most studies to date have focused on pulmonary fibrosis. There are few studies on murine RIF in the skeletal muscle, and the pathogenic mechanism remains unclear. This pilot study aimed to evaluate the feasibility to create a murine model of RIF in the skeletal muscle and analyze strain differences in fibrosis sensitivity.

MATERIALS AND METHODS

Two mouse strains, C57BL/6 and C3H/He, were used. Their right hind limbs were irradiated at a dose of 25 Gy once a week for three fractions. Gastrocnemius muscles were collected at day 4, and weeks 2, 4, 8, 12, and 24 after the third irradiation and subjected to histopathological examination and immunoblotting.

RESULTS

In C57BL/6 mice, chronic inflammation and an increased expression of transforming growth factor-β (TGF-β) and fibronectin were observed 2 weeks after irradiation. A significant increase in fibrosis was detected after 8 weeks. However, in C3H/He mice, the expression of TGF-β and fibronectin increased 8 weeks after irradiation, and fibrosis significantly increased after 12 weeks. Moreover, the degrees of inflammation and fibrosis were more remarkable in C57BL/6 mice than in C3H/He mice.

CONCLUSION

The onset and degree of fibrosis may be associated with the expression of TGF-β and fibronectin, and inflammation, in a strain-specific manner. Therefore, a murine model of RIF in the skeletal muscle could be created using the indicated method, suggesting that the C57BL/6 strain is more sensitive to fibrosis in the skeletal muscle, as well as the lung, than the C3H/He strain. Radiation-induced fibrosis in the skeletal muscle could be detected in C57BL/6 and C3H/He mice, with C57BL/6 mice being more sensitive to fibrosis in the skeletal muscle than C3H/He mice.

Electroacupuncture regulates inflammation, collagen deposition and macrophage function in skeletal muscle through the TGF-β1/Smad3/p38/ERK1/2 pathway

Skeletal muscle injury is one of the most common sports injury, which accounts for ~40% of all sports-related injuries among the elderly. In addition, cases of full recovery from treatment are rare. Although electroacupuncture (EA) is an integral aspect of traditional Chinese medicine, the effects of EA on skeletal muscle fibrosis and the possible underlying mechanism remain unclear. To investigate the effect and potential mechanism of EA on skeletal inflammation, collagen deposition and macrophage function, a skeletal muscle injury model was established by injecting 100 µl cardiotoxin into the anterior tibial muscle of Sprague Dawley rats. The animals were randomly divided into the following three groups: Control, model and EA. The expression of inflammation-related factors (IL-6, IL-4, IL-33, IL-10 and TNF-α) were measured using ELISA. H&E staining, Masson's staining and immunohistochemistry (collagen II, Axin2 and β-catenin) were performed to assess collagen deposition and fibrosis in the muscle tissues. Additionally, immunofluorescence was performed to measure the ratio of M₁ to M₂ macrophages. Western blotting was performed to examine the activity of the TGF-β1/Smad3/p38/ERK1/2 pathway. Compared with that in the control rats, the mental state, such as the degree of activity and excitement, of the model rats deteriorated, with clear activity limitations. Compared with those in the model rats, EA-treated rats exhibited improved mental status and activity, reduced levels of IL-6, IL-4 and TNF-α, reduced collagen deposition and fibrosis, in addition to increased expression of IL-33 and IL-10. This improvement became increasingly evident with prolonged intervention time. EA also promoted the transformation of macrophages from the M₁ into the M₂ sub-type, where the M₁/M₂ ratio on day 7 was lower compared with that on day 14. Western blotting results showed that compared with that in the model rats, the expression of TGF-β1, MMP-2, MMP-7 and the activation of Smad3 and p38 was decreased in EA-treated rats, whilst the activation of ERK1/2 was significantly elevated. In conclusion, EA can inhibit inflammation and collagen deposition whilst promoting the transformation of macrophages from the M₁ into the M₂ sub-type. The underlying mechanism was found to be associated with TGF-β1/Smad3/p38/ERK1/2 signaling.

Ultrasound Imaging in Sport-Related Muscle Injuries: Pitfalls and Opportunities

Muscle injuries occur frequently in athletes, accounting for more than one-third of sport-related trauma. Athletes most affected by these injuries are those practicing football and track and field, with hamstrings and gastrocnemius-soleus as the mainly involved sites. Muscle injuries lead to loss of competitions, long recovery times and risk of re-injury with a consequent increase of the management costs. It is therefore advisable to make an accurate and timely diagnosis to establish appropriate interventions for proper healing in the shortest time. In this context, ultrasound imaging is widely used for diagnosis of musculoskeletal disorders because of several advantages including absence of radiation, portability, good spatial resolution, and the ability to perform dynamic tests. The aim of this review is to address the role of US in the evaluation of athletes with muscle injuries. US may play a pivotal role for the management of sport-related muscle injuries because it is fast and relatively cheap, allowing dynamic muscle assessment and time series evaluation of the healing process.

Use of Platelet-Rich Plasma Plus Suramin, an Antifibrotic Agent, to Improve Muscle Healing After Injuries

BACKGROUND

The increasing use of platelet-rich plasma (PRP) to treat muscle injuries raises concerns because transforming growth factor-beta (TGF-β) in PRP may promote fibrosis in the injured muscle and thus impair muscle regeneration.

PURPOSE

To investigate whether suramin (a TGF-β inhibitor) can reduce muscle fibrosis to improve healing of the injured muscle after PRP treatment and identify the underlying molecular mechanism.

STUDY DESIGN

Controlled laboratory study.

METHODS

Myoblasts isolated from the gastrocnemius muscle of Sprague Dawley rats were treated with PRP or PRP plus suramin. MTT assays were performed to evaluate cell viability. The expression of fibrosis-associated proteins (such as type I collagen and fibronectin), Smad2, and phosphorylated Smad2 was determined using Western blot analysis and immunofluorescent staining. An anti-TGF-β antibody was employed to verify the role of TGF-β in fibronectin expression. Gastrocnemius muscles were injured through a partial transverse incision and then treated using PRP or PRP plus suramin. Hematoxylin and eosin staining was conducted to evaluate the healing process 7 days after the injury. Immunofluorescent staining was performed to evaluate fibronectin expression. Muscle contractile properties-fast-twitch and tetanic strength-were evaluated through electric stimulation.

RESULTS

PRP plus 25 μg/mL of suramin promoted myoblast proliferation. PRP induced fibronectin expression in myoblasts, but suramin reduced this upregulation. The anti-TGF-β antibody also reduced the upregulation of fibronectin expression in the presence of PRP. The upregulation of phosphorylated Smad2 by PRP was reduced by either the anti-TGF-β antibody or suramin. In the animal study, no significant difference was discovered in muscle healing between the PRP versus PRP plus suramin groups. However, the PRP plus suramin group had reduced fibronectin expression at the injury site. Fast-twitch strength and tetanic strength were significantly higher in the injured muscle treated using PRP or PRP plus suramin.

CONCLUSION

Simultaneous PRP and suramin use reduced fibrosis in the injured muscle and promoted healing without negatively affecting the muscle's contractile properties. The underlying molecular mechanism may be associated with the phosphorylated Smad2 pathway.

CLINICAL RELEVANCE

Simultaneous PRP and suramin use may reduce muscle fibrosis without compromising muscle contractile properties and thus improve muscle healing.

An Environmental Friendly Tapioca Starch-Alginate Cultured Scaffold as Biomimetic Muscle Tissue

Natural porous scaffolds have been studied and developed for decades in biomedical science in order to support cells with a simulated extracellular matrix in natural tissue as an ideal environment. Such three-dimensional scaffolds provide many degrees of freedom to modulate cell activity, such as porosity, pore size, mechanical strength, biodegradability, and biocompatibility. In this study, a porous, three-dimensional material of alginate incorporating tapioca starch was fabricated. A particular freeze-gelation method was applied to homogenously mix starch in the alginate, and the concentration was controllable. This pure natural composite porous scaffold was characterized physically and biologically. The synergistic functions, including biocompatibility, biodegradability, cell adhesion, and cell proliferation, were also investigated. A myogenic differentiation model further verified that the composite porous scaffold provided a suitable environment, supporting the differentiation effect in the myogenic process. The positive results demonstrated that this novel material has the potential to serve as a biomedical or clean meat appliance.

Enhancement of myogenic potential of muscle progenitor cells and muscle healing during pregnancy

The decline of muscle regenerative potential with age has been attributed to a diminished responsiveness of muscle progenitor cells (MPCs). Heterochronic parabiosis has been used as a model to study the effects of aging on stem cells and their niches. These studies have demonstrated that, by exposing old mice to a young systemic environment, aged progenitor cells can be rejuvenated. One interesting idea is that pregnancy represents a unique biological model of a naturally shared circulatory system between developing and mature organisms. To test this hypothesis, we evaluated the muscle regeneration potential of pregnant mice using a cardiotoxin (CTX) injury mouse model. Our results indicate that the pregnant mice demonstrate accelerated muscle healing compared to nonpregnant control mice following muscle injury based on improved muscle histology, superior muscle regeneration, and a reduction in inflammation and necrosis. Additionally, we found that MPCs isolated from pregnant mice display a significant improvement of myogenic differentiation capacity in vitro and muscle regeneration in vivo when compared to the MPCs from nonpregnant mice. Furthermore, MPCs from nonpregnant mice display enhanced myogenic capacity when cultured in the presence of serum obtained from pregnant mice. Our proteomics data from these studies provides potential therapeutic targets to enhance the myogenic potential of progenitor cells and muscle repair.

Return to Play After a Hamstring Strain Injury: It is Time to Consider Natural Healing

Return to play (RTP) criteria after hamstring strain injuries (HSIs) help clinicians in deciding whether an athlete is ready to safely resume previous sport activities. Today, functional and sport-specific training tests are the gold standard in the decision-making process. These criteria lead to an average RTP time between 11 and 25 days after a grade 1 or 2 HSI. However, the high re-injury rates indicate a possible inadequacy of the current RTP criteria. A possible explanation for this could be the neglect of biological healing time. The present review shows that studies indicating time as a possible factor within the RTP-decision are very scarce. However, studies on biological muscle healing showed immature scar tissue and incomplete muscle healing at the average moment of RTP. Twenty-five percent of the re-injuries occur in the first week after RTP and at the exact same location as the index injury. This review supports the statement that functional recovery precedes the biological healing of the muscle. Based on basic science studies on biological muscle healing, we recommend a minimum period of 4 weeks before RTP after a grade 1 or 2 HSI. In conclusion, we advise a comprehensive RTP functional test battery with respect for the natural healing process. Before deciding RTP readiness, clinicians should reflect whether or not it is biologically possible for the injured tissue to have regained enough strength to withstand the sport-specific forces. In an attempt to reduce the detrimental injury-reinjury cycle, it is time to start considering (biological healing) time.

Investigating Transcriptional Dynamics Changes and Time-Dependent Marker Gene Expression in the Early Period After Skeletal Muscle Injury in Rats

Following skeletal muscle injury (SMI), from post-injury reaction to repair consists of a complex series of dynamic changes. However, there is a paucity of research on detailed transcriptional dynamics and time-dependent marker gene expression in the early stages after SMI. In this study, skeletal muscle tissue in rats was taken at 4 to 48 h after injury for next-generation sequencing. We examined the transcriptional kinetics characteristics during above time periods after injury. STEM and maSigPro were used to screen time-correlated genes. Integrating 188 time-correlated genes with 161 genes in each time-related gene module by WGCNA, we finally identified 18 network-node regulatory genes after SMI. Histological staining analyses confirmed the mechanisms underlying changes in the tissue damage to repair process. Our research linked a variety of dynamic biological processes with specific time periods and provided insight into the characteristics of transcriptional dynamics, as well as screened time-related biological indicators with biological significance in the early stages after SMI.

Muscle Cryoinjury and Quantification of Regenerating Myofibers in Mice

Cryoinjury, or injury due to freezing, is a method of creating reproducible, local injuries in skeletal muscle. This method allows studying the regenerative response following muscle injuries in vivo, thus enabling the evaluation of local and systemic factors that influence the processes of myofiber regeneration. Cryoinjuries are applicable to the study of various modalities of muscle injury, particularly non-traumatic and traumatic injuries, without a loss of substantial volume of muscle mass. Cryoinjury requires only simple instruments and has the advantage over other methods that the extent of the lesion can be easily adjusted and standardized according to the duration of contact with the freezing instrument. The regenerative response can be evaluated histologically by the average maturity of regenerating myofibers as indicated by the cross-sectional areas of myofibers with centrally located nuclei. Accordingly, cryoinjury is regarded as one of the most reliable and easily accessible methods for simulating muscle injuries in studies of muscle regeneration.

Transferrin receptor 1 ablation in satellite cells impedes skeletal muscle regeneration through activation of ferroptosis

BACKGROUND

Satellite cells (SCs) are critical to skeletal muscle regeneration. Inactivation of SCs is linked to skeletal muscle loss. Transferrin receptor 1 (Tfr1) is associated with muscular dysfunction as muscle-specific deletion of Tfr1 results in growth retardation, metabolic disorder, and lethality, shedding light on the importance of Tfr1 in muscle physiology. However, its physiological function regarding skeletal muscle ageing and regeneration remains unexplored.

METHODS

RNA sequencing is applied to skeletal muscles of different ages to identify Tfr1 associated to skeletal muscle ageing. Mice with conditional SC ablation of Tfr1 were generated. Between Tfr1SC/WT and Tfr1SC/KO (n = 6-8 mice per group), cardiotoxin was intramuscularly injected, and transverse abdominal muscle was dissected, weighted, and cryosectioned, followed by immunostaining, haematoxylin and eosin staining, and Masson staining. These phenotypical analyses were followed with functional analysis such as flow cytometry, tread mill, Prussian blue staining, and transmission electron microscopy to identify pathological pathways that contribute to regeneration defects.

RESULTS

By comparing gene expression between young (2 weeks old, n = 3) and aged (80 weeks old, n = 3) mice among four types of muscles, we identified that Tfr1 expression is declined in muscles of aged mice (~80% reduction, P < 0.005), so as to its protein level in SCs of aged mice. From in vivo and ex vivo experiments, Tfr1 deletion in SCs results in an irreversible depletion of SCs (~60% reduction, P < 0.005) and cell-autonomous defect in SC proliferation and differentiation, leading to skeletal muscle regeneration impairment, followed by labile iron accumulation, lipogenesis, and decreased Gpx4 and Nrf2 protein levels leading to reactive oxygen species scavenger defects. These abnormal phenomena including iron accumulation, activation of unsaturated fatty acid biosynthesis, and lipid peroxidation are orchestrated with the occurrence of ferroptosis in skeletal muscle. Ferroptosis further exacerbates SC proliferation and skeletal muscle regeneration. Ferrostatin-1, a ferroptosis inhibitor, could not rescue ferroptosis. However, intramuscular administration of lentivirus-expressing Tfr1 could partially reduce labile iron accumulation, decrease lipogenesis, and promote skeletal muscle regeneration. Most importantly, declined Tfr1 but increased Slc39a14 protein level on cellular membrane contributes to labile iron accumulation in skeletal muscle of aged rodents (~80 weeks old), leading to activation of ferroptosis in aged skeletal muscle. This is inhibited by ferrostatin-1 to improve running time (P = 0.0257) and distance (P = 0.0248).

CONCLUSIONS

Satellite cell-specific deletion of Tfr1 impairs skeletal muscle regeneration with activation of ferroptosis. This phenomenon is recapitulated in skeletal muscle of aged rodents and human sarcopenia. Our study provides mechanistic information for developing novel therapeutic strategies against muscular ageing and diseases.

Maintenance of Skeletal Muscle to Counteract Sarcopenia in Patients with Advanced Chronic Kidney Disease and Especially Those Undergoing Hemodialysis

Life extension in modern society has introduced new concepts regarding such disorders as frailty and sarcopenia, which has been recognized in various studies. At the same time, cutting-edge technology methods, e.g., renal replacement therapy for conditions such as hemodialysis (HD), have made it possible to protect patients from advanced lethal chronic kidney disease (CKD). Loss of muscle and fat mass, termed protein energy wasting (PEW), has been recognized as prognostic factor and, along with the increasing rate of HD introduction in elderly individuals in Japan, appropriate countermeasures are necessary. Although their origins differ, frailty, sarcopenia, and PEW share common components, among which skeletal muscle plays a central role in their etiologies. The nearest concept may be sarcopenia, for which diagnosis techniques have recently been reported. The focus of this review is on maintenance of skeletal muscle against aging and CKD/HD, based on muscle physiology and pathology. Clinically relevant and topical factors related to muscle wasting including sarcopenia, such as vitamin D, myostatin, insulin (related to diabetes), insulin-like growth factor I, mitochondria, and physical inactivity, are discussed. Findings presented thus far indicate that in addition to modulation of the aforementioned factors, exercise combined with nutritional supplementation may be a useful approach to overcome muscle wasting and sarcopenia in elderly patients undergoing HD treatments.

The cold truth: the role of cryotherapy in the treatment of injury and recovery from exercise

Cryotherapy is utilized as a physical intervention in the treatment of injury and exercise recovery. Traditionally, ice is used in the treatment of musculoskeletal injury while cold water immersion or whole-body cryotherapy is used for recovery from exercise. In humans, the primary benefit of traditional cryotherapy is reduced pain following injury or soreness following exercise. Cryotherapy-induced reductions in metabolism, inflammation, and tissue damage have been demonstrated in animal models of muscle injury; however, comparable evidence in humans is lacking. This absence is likely due to the inadequate duration of application of traditional cryotherapy modalities. Traditional cryotherapy application must be repeated to overcome this limitation. Recently, the novel application of cooling with 15 °C phase change material (PCM), has been administered for 3-6 h with success following exercise. Although evidence suggests that chronic use of cryotherapy during resistance training blunts the anabolic training effect, recovery using PCM does not compromise acute adaptation. Therefore, following exercise, cryotherapy is indicated when rapid recovery is required between exercise bouts, as opposed to after routine training. Ultimately, the effectiveness of cryotherapy as a recovery modality is dependent upon its ability to maintain a reduction in muscle temperature and on the timing of treatment with respect to when the injury occurred, or the exercise ceased. Therefore, to limit the proliferation of secondary tissue damage that occurs in the hours after an injury or a strenuous exercise bout, it is imperative that cryotherapy be applied in abundance within the first few hours of structural damage.

Shearwave elastography of the Sartorius muscle

The aim of the study was to study sonoelastographic features of thesartorius muscle, and its relation to the demographic factors.The study included 70 muscles in 35 healthy subjects. High-resolution ultrasound and shearwave elastography were used to evaluate the sartorius muscle. Stiffness values were measured.The mean shear elastic modulus of the sartorius muscle was 21.96 ± 5.1 kPa. Demographic factors showed no relation to the elastic modulus of the left sartorius muscle. Positive statistical correlation was noted between the elastic modulus of the right sartorius muscle, weight, and body mass index.Our results could be a reference point for evaluating sartorius muscle stiffness in future research considering different pathologies.