Skeletal Muscle Injury Research Articles

CXCL12 as a Potential Hub Gene for N-Acetylcysteine Treatment of T1DM Liver Disease

The etiology of type 1 diabetes mellitus (T1DM) is intricate, leading to its classification as an autoimmune metabolic disorder. T1DM often coexists with various visceral diseases. N-acetylcysteine (NAC) is widely acknowledged for its potent antioxidant properties. Studies have demonstrated that the combination of NAC and insulin can effectively alleviate iron-induced nephropathy in T1DM and mitigate oxidative stress injury in skeletal muscle associated with the condition. However, the potential impact of NAC alone on liver disease in individuals with T1DM remains uncertain. In this study, a beagle model was established to simulate T1DM, enabling investigation into the role of NAC in liver disease using RNA-seq biogenic analysis and subsequent validation through molecular biological methods. The findings revealed suppressed expression of CXCL12 chemokine in the livers of individuals with T1DM, while treatment with NAC induced specific activation of CXCL12 within the liver affected by T1DM. These results suggest that CXCL12 may serve as a regulatory factor involved in the therapeutic effects of NAC on liver disease associated with TIDM. This discovery holds significant implications for utilizing NAC as an adjunctive therapy for managing complicated liver diseases accompanying type 1 diabetes mellitus.

Basic research for ultrasound-guided injection into skeletal muscle lesions in an experimental animal model.

Ultrasound-guided injection techniques are expected to enhance therapeutic efficacy for skeletal muscle injuries and disorders, but basic knowledge is lacking. The purpose of this study was to examine the diagnostic accuracy of ultrasound for abnormal skeletal muscle lesions, and to examine the distribution patterns of solution and cells injected into abnormal muscle lesions under ultrasound guidance. A cardiotoxin (CTX)-induced muscle injury model was used. Briefly, CTX was injected into tibialis anterior muscle in rats under ultrasound observation. First, the diagnostic accuracy of abnormal muscle lesions on ultrasound was examined by comparing ultrasound findings and histology. Next, Fast Green solution and green fluorescent protein (GFP)-labelled cells were simultaneously injected into the abnormal muscle lesions under ultrasound guidance, and their distribution was evaluated. Evaluation of short-axis ultrasound images and cross-sectional histological staining showed a strong correlation (r = 0.927; p < 0.001) between the maximum muscle damage area in ultrasound and haematoxylin and eosin (H&E) staining evaluations. Histological analysis showed that ultrasound-guided injection could successfully deliver Fast Green solution around the myofibres at the site of injury. In contrast, the distribution of injected cells was very localized compared to the area stained with Fast Green. This experimental animal study demonstrated the potential of ultrasound to quantitatively visualize abnormalities of skeletal muscle. It also showed that ultrasound-guided injections allowed for highly accurate distribution of solution and cells in abnormal muscle tissue, but the patterns of solution and cell distribution were markedly different. Although future studies using a more clinically relevant model are necessary, these results are important findings when considering biological therapies for skeletal muscle injuries and disorders.

Extrusion-Based Printing of Myoblast-Loaded Fibrin Microthreads to Induce Myogenesis.

Large skeletal muscle injuries such as volumetric muscle loss (VML) disrupt native tissue structures, including biophysical and biochemical signaling cues that promote the regeneration of functional skeletal muscle. Various biofabrication strategies have been developed to create engineered skeletal muscle constructs that mimic native matrix and cellular microenvironments to enhance muscle regeneration; however, there remains a need to create scalable engineered tissues that provide mechanical stability as well as structural and spatiotemporal signaling cues to promote cell-mediated regeneration of contractile skeletal muscle. We describe a novel strategy for bioprinting multifunctional myoblast-loaded fibrin microthreads (myothreads) that recapitulate the cellular microniches to drive myogenesis and aligned myotube formation. We characterized myoblast alignment, myotube formation, and tensile properties of myothreads as a function of cell-loading density and culture time. We showed that increasing myoblast loading densities enhances myotube formation. Additionally, alignment analyses indicate that the bioprinting process confers myoblast alignment in the constructs. Finally, tensile characterizations suggest that myothreads possess the structural stability to serve as a potential platform for developing scalable muscle scaffolds. We anticipate that our myothread biofabrication approach will enable us to strategically investigate biophysical and biochemical signaling cues and cellular mechanisms that enhance functional skeletal muscle regeneration for the treatment of VML.

ProBDNF as a Myokine in Skeletal Muscle Injury: Role in Inflammation and Potential for Therapeutic Modulation of p75NTR.

Brain-derived neurotropic factor (BDNF) is expressed by skeletal muscle as a myokine. Our previous work showed that the active precursor, proBDNF, is the predominant form of BDNF expressed in skeletal muscle, and that following skeletal muscle injury, proBDNF levels are significantly increased. However, the function of the muscle-derived proBDNF in injury-induced inflammation has yet to be fully understood. Using a model of tourniquet-induced ischemia-reperfusion (IR) injury of the hindlimb, this study presents, for the first time, strong and novel evidence that following IR injury, proBDNF is released from skeletal muscle into circulation as an endocrine signaling molecule. Further, this study shows that 1 day post-IR injury, the proBDNF receptor, p75NTR, is upregulated 12-fold in splenic monocytes, which are known to be quickly mobilized to the injury site. We demonstrate that p75NTR plays a role in the activation of splenic monocytes, and that treatment with a p75NTR small-molecule modulator, LM11A-31, significantly reduced monocyte inflammatory responses upon lipopolysaccharide stimulation. Overall, the present study establishes proBDNF as a myokine that plays a significant role in skeletal muscle injury-induced inflammation through its receptor, p75NTR, which may be modulated using LM11A-31 as potential translational therapeutic against injury and inflammation.

Profiling paracrine interactions between hypoxic and normoxic skeletal muscle tissue in a microphysiological system fabricated from 3D printed components.

Disrupted blood flow in conditions such as peripheral artery disease and critical limb ischemia leads to variations in oxygen supply within skeletal muscle tissue, creating regions of poorly perfused, hypoxic skeletal muscle surrounded by regions of adequately perfused, normoxic muscle tissue. These oxygen gradients may have significant implications for muscle injury or disease, as mediated by the exchange of paracrine factors between differentially oxygenated tissue. However, creating and maintaining heterogeneous oxygen landscapes within a controlled experimental setup to ensure continuous paracrine signaling is a technological challenge. Here, we engineer oxygen-controlled microphysiological systems to investigate paracrine interactions between differentially oxygenated engineered muscle tissue. We fabricated microphysiological systems with dual oxygen landscapes that also had engineered control over paracrine interactions between hypoxic and normoxic skeletal muscle tissues, which were differentiated from C2C12 myoblasts cultured on micromolded gelatin hydrogels. The microphysiological systems interfaced with a new 3D-printed oxygen control well plate insert, which we designed to distribute flow to multiple microphysiological systems and minimize evaporation for longer timepoints. With our system, we demonstrated that amphiregulin, a myokine associated with skeletal muscle injury, exhibits unique upregulation in both gene expression and secretion after 24 hours due to paracrine interactions between hypoxic and normoxic skeletal muscle tissue. Our platform can be extended to investigate other impacts of paracrine interactions between hypoxic and normoxic skeletal muscle and can more broadly be used to elucidate many forms of oxygen-dependent crosstalk in other organ systems.

The role of the cyclooxygenase-2 pathway in tissue ischemia and revascularization following skeletal muscle injury induced by bothropic snake venom

Bothrops asper venom (Bav) contains metalloproteinases that disrupt the microvascular system, impairing muscle tissue regeneration after injury. This study investigated the impact of the cyclooxygenase-2 (COX-2) pathway on vascular injury and revascularization in muscle injuries induced by Bav. Mice were injected with Bav into the gastrocnemius muscle and treated with lumiracoxib, a selective COX-2 inhibitor, 30 min, 2 days, and 6 days post-Bav injection. Muscle tissue was analyzed at 24 h, 7 days, and 21 days post-injection. A decrease in COX-2 expression at 24 h post-Bav injection indicated significant necrosis and tissue loss. Both Bav injection and lumiracoxib treatment influenced the decrease of prostaglandin (PG)D2 and PGE2 production. Seven and 21 days post-Bav injections, COX-2 expression increased, along with PGDs levels unaffected by lumiracoxib, indicating that the other isoform COX-1 pathway could contribute to the release of PGs. Bav/lumiracoxib treated animals presented exacerbated limb ischemia, implying that COX-2-derived prostaglandins preserve vessel integrity. CD31, an angiogenesis marker, initially (24 h) decreased post-Bav injection but increased at 7 and 21 days in Bav/lumiracoxib mice, suggesting a down-modulatory role for COX-2-derived prostaglandins in early angiogenesis and tissue regeneration. Vascular endothelial growth factor (VEGF) production rose 7 days post-Bav injection, supporting its role in angiogenesis. Previous treatment with lumiracoxib promoted release of VEGF levels 21 days post-Bav injury showing that the inhibition of COX-2 pathway in the early stage of revascularization stimulates the neovascularization regulated by elevated release of VEGF. Similarly, metalloproteinases (MMPs), such as MMP-9, MMP-10, and MMP-13, crucial for vascular remodeling, were elevated 21 days after Bav/lumiracoxib treatment. In conclusion, the COX-2 pathway is essential to decrease the high grade of ischemia caused by acute injury induced by Bav. However, the decrease of activity in the COX-2 pathway in the first stages of revascularization contributes to the elevated production of key pro-angiogenic mediators that up-regulate the restoration of microvasculature and blood flow in muscle tissue injured by botropic venoms.

Altered sphingolipid profile in response to skeletal muscle injury in a mouse model of type 1 diabetes mellitus.

A complication of type 1 diabetes mellitus (T1DM) is diabetic myopathy that includes reduced regenerative capacity of skeletal muscle. Sphingolipids are a diverse family of lipids with roles in skeletal muscle regeneration. Some studies have found changes in sphingolipid species levels in T1DM, however, the effect of T1DM on a sphingolipid panel in regenerating skeletal muscle has not been examined. Wild-type (WT) and diabetic Ins2Akita+/- (Akita) mice received cardiotoxin-induced muscle injury in their left quadriceps, gastrocnemius-plantaris-soleus, and tibialis anterior muscles with the contralateral muscles serving as uninjured controls. Muscles were collected at 1, 3, 5, or 7 days postinjury. In regenerating muscle from Akita mice, lipid staining with BODIPY 493/503 revealed increased intramyocellular and total lipids and perilipin-1-positive cell numbers as compared with WT. Liquid chromatography-mass spectrometry of quadriceps was used to identify sphingolipid levels in skeletal muscle. The C22:0 and C24:0 ceramides were significantly elevated in uninjured Akita, whereas ceramide C24:1 was decreased in injured Akita compared with WT. Ceramide-1-phosphate was increased in Akita compared with WT regardless of injury, whereas sphingosine-1-phosphate (S1P) was elevated with injury in WT but this response was muted in Akita mice. Western blotting of key enzymes involved in sphingolipid metabolism revealed S1P lyase, the enzyme that degrades S1P irreversibly, was significantly elevated in the injured muscle in Akita mice during regeneration, in accordance with lower S1P levels. This mouse model of T1DM demonstrates sphingolipidomic changes that may contribute to delayed muscle regeneration.NEW & NOTEWORTHY Muscle lipids become elevated, and the sphingolipid profile is altered by T1DM in skeletal muscle regeneration. A loss of S1P is accompanied by greater expression of sphingosine-1-phosphate lyase (SPL) in response to injury in Akita mice, suggesting a role for sphingolipids in the attenuated repair of skeletal muscle in T1DM rodent models. Although ceramide-1-phosphate (C1P) is increased with T1DM, there was no increase in ceramide kinase (CerK) suggesting an alternative route of ceramide phosphorylation in skeletal muscle.

Genetic characterization of diagnostic epitopes of cardiac troponin I in African rhinoceros.

African rhinoceros undergo chemical immobilization and prolonged transport during translocations for conservation purposes and, hence, experience several pathophysiologic changes, including skeletal muscle injury. Potential concurrent myocardial injury has not been investigated due to a lack of validated immunoassays. We aimed to use inferred cardiac troponin I (cTnI) amino acid sequences of southern white (Ceratotherium simum simum) and southern-central black (Diceros bicornis minor) rhinoceros to assess the potential usefulness of several commercial cTnI immunoassays for detecting cTnI in African rhinoceros. We extracted RNA from the myocardium of deceased rhinoceros (2 white, 1 black rhinoceros) followed by primer design, cDNA synthesis via RT-PCR, and Sanger sequencing. The inferred cTnI amino acid sequences were obtained from the mRNA transcript sequences. The homology of epitope binding sites recognized by capture and detection antibodies in 6 human immunoassays was visually evaluated using aligned inferred rhinoceros cTnI amino acid sequences. Percentage identity between white and black rhinoceros cDNA nucleotide sequences was 99%; inferred amino acid sequences were identical. There were 5 amino acid differences between humans and rhinoceros in the epitope binding sites of immunoassay antibodies; 5 assays contained antibodies against epitopes that were not conserved. For one assay, the single capture antibody targeted a short heterologous epitope (residue 87-91), and cross-reactivity with rhinoceros cTnI was deemed unlikely. For the other 5 assays, complete antibody-epitope homology, or the inclusion of multiple detection or capture antibodies, or targeting of long epitopes, indicated that these assays could be suitable for further investigation of cTnI measurement in African rhinoceros.

Fish collagen peptides supplementation ameliorates skeletal muscle injury in high-fat diet mice associated with thyroid function recovery

This study aims to explore the effects of fish collagen peptides (FCP) supplementation on skeletal muscle injury in high-fat (HF) diet mice and their possible mechanisms. Experimental mice were fed a normal diet (4 % fat), HF diet (20 % fat), or FCP diet (20 % fat and 1 % FCPs) for 22 consecutive weeks. Results show that FCP supplementation improves skeletal muscle motor function and histomorphology, and lipid levels; promotes protein synthesis, and inhibits protein degradation in skeletal muscle. Moreover, FCP supplementation also improves mitochondrial biogenesis, promotes energy metabolism and ATP production. Furthermore, FCP supplementation increases antioxidant defenses in the thyroid and skeletal muscle, improves thyroid morphological structure, promotes the synthesis and secretion of thyroid hormones, and enhances the actions of thyroid hormones on its receptor organ skeletal muscle. Cumulatively, these findings indicate that FCP supplementation can alleviate skeletal muscle injury induced by an HF diet associated with thyroid function recovery.

N-butylphthalide (NBP) ameliorated ischemia/reperfusion-induced skeletal muscle injury in male mice via activating Sirt1/Nrf2 signaling pathway.

N-butylphthalide (NBP) has been reported to have potential protective effects in ischemic stroke via its antioxidative properties. The present study was aimed to investigate the protective effects of NBP on ischemia/reperfusion (I/R)-induced skeletal muscle injury. Mouse model of I/R-induced skeletal muscle injury and hypoxia/reoxygenation (H/R)-induced C2C12 myotube injury model were constructed to test the protective effects of NBP both invivo and invitro. Our results showed that I/R resulted in skeletal muscle injury, as evidenced by elevated levels of LDH, CK, ROS, 3-NT, MDA, and 4-HNE as well as decreased activities of SOD, GSH-Px, and decreased expression of Myog and MyoD in gastrocnemius muscle, which was ameliorated by NBP treatment. Mechanistically, NBP treatment increased the expression of Sirt1 and Nrf2 in the injured skeletal muscle. Notably, the protective effects of NBP on I/R-induced skeletal muscle injury was diminished by the treatment of Sirt1 inhibitor. Further studies in H/R-induced C2C12 myotubes injury model also showed that NBP activated the Sirt1/Nrf2 pathway. NBP treatment upregulated the expression of myog and MyoD in H/R-stimulated C2C12 myotubes, which was eliminated by silencing of Sirt1. Taken together, our results suggest that NBP may alleviated I/R-induced skeletal muscle injury by activating Sirt1/Nrf2 signaling pathway.

Diacylglycerol kinase δ is required for skeletal muscle development and regeneration.

Diacylglycerol kinase δ (DGKδ) phosphorylates diacylglycerol to produce phosphatidic acid. Previously, we demonstrated that down-regulation of DGKδ suppresses the myogenic differentiation of C2C12 myoblasts. However, the myogenic roles of DGKδ invivo remain unclear. In the present study, we generated DGKδ-conditional knockout mice under the control of the myogenic factor 5 (Myf5) gene promoter, which regulates myogenesis and brown adipogenesis. The knockout mice showed a significant body weight reduction and apparent mass decrease in skeletal muscle, including the tibialis anterior (TA) muscle. Moreover, the thickness of a portion of the myofibers was reduced in DGKδ-deficient TA muscles. However, DGKδ deficiency did not substantially affect brown adipogenesis, suggesting that Myf5-driven DGKδ deficiency mainly affects muscle development. Notably, skeletal muscle injury induced by a cardiotoxin highly up-regulated DGKδ protein expression, and the DGKδ deficiency significantly reduced the thickness of myofibers, the expression levels of myogenic differentiation markers such as embryonic myosin heavy chain and myogenin, and the number of newly formed myofibers containing multiple central nuclei during muscle regeneration. DGKδ was strongly expressed in myogenin-positive satellite cells around the injured myofibers and centronucleated myofibers. These results indicate that DGKδ has important roles in muscle regeneration in activated satellite cells. Moreover, the conditional knockout mice fed with a high-fat diet showed increased fat mass and glucose intolerance. Taken together, these results demonstrate that DGKδ plays crucial roles in skeletal muscle development, regeneration, and function.

Reactive oxygen species in skeletal muscle injury, fatigue, regeneration and ageing: In memory of John Faulkner

One of the most critical factors impacting healthspan in the elderly is the loss of muscle mass and function, clinically referred to as sarcopenia. Muscle atrophy and weakness lead to loss of mobility, increased risk of injury, metabolic changes and loss of independence. Thus, defining the underlying mechanisms of sarcopenia is imperative to enable the development of effective interventions to preserve muscle function and quality in the elderly and improve healthspan. Over the past few decades, understanding the roles of mitochondrial dysfunction and oxidative stress has been a major focus of studies seeking to reveal critical molecular pathways impacted during aging. In this review, we will highlight how oxidative stress might contribute to sarcopenia by discussing the impact of oxidative stress on the loss of innervation and alteration in the neuromuscular junction (NMJ), on muscle mitochondrial function and atrophy pathways, and finally on muscle contractile function.

Deletion of RBM20 exon 9 impairs skeletal muscle growth and satellite cell function in pigs

Maintaining healthy skeletal tissue is essential for overall well-being and quality of life. Skeletal muscle plays a key role in this process, yet models for studying its detailed function are limited. While RNA-binding motif protein 20 (RBM20) is primarily associated with dilated cardiomyopathy (DCM), its role in skeletal muscle remains largely unexplored. This study investigates RBM20 function in skeletal muscle using an RBM20 exon 9 deletion pig model (RBM20E9D). The deletion of exon 9 resulted in loosely arranged muscle fibers, large inter-fiber gaps, and irregular organization, leading to impaired muscle growth and development. Analysis of skeletal muscle satellite cells revealed significantly reduced proliferation, diminished myotube formation in vitro, and disrupted sarcomere structure due to exon 9 deletion. Given the critical role of satellite cell proliferation and differentiation in muscle repair, RBM20E9D pigs offer a novel model for studying the mechanisms underlying skeletal muscle injury, repair, and growth.

E2 signaling in myofibers promots macrophage efferocytosis in mouse skeletal muscles with cardiotoxin-induced acute injury

To investigate the effect of E2 signaling in myofibers on muscular macrophage efferocytosis in mice with cardiotoxin-induced acute skeletal muscle injury. Female wild-type C57BL/6 mice with and without ovariectomy and male C57BL/6 mice were given a CTX injection into the anterior tibial muscle to induce acute muscle injury, followed by intramuscular injection of β-estradiol (E2) or 4-hydroxytamoxifen (4-OHT). The changes in serum E2 of the mice were detected using ELISA, and the number, phenotypes, and efferocytosis of the macrophages in the inflammatory exudates and myofiber regeneration and repair were evaluated using immunofluorescence staining and flow cytometry. C2C12 cells were induced to differentiate into mature myotubes, which were treated with IFN- γ for 24 before treatment with β -Estradiol or 4-OHT. The treated myotubes were co-cultured with mouse peritoneal macrophages in a 1:2 ratio, followed by addition of PKH67-labeled apoptotic mouse mononuclear spleen cells induced by UV irradiation, and macrophage efferocytosis was observed using immunofluorescence staining and flow cytometry. Compared with the control mice, the female mice with ovariectomy showed significantly increased mononuclear macrophages in the inflammatory exudates, with increased M1 cell percentage, reduced M2 cell percentage and macrophage efferocytosis in the injured muscle, and obviously delayed myofiber regeneration and repair. In the cell co-culture systems, treatment of the myotubes with β-estradiol significantly increased the number and proportion of M2 macrophages and macrophage efferocytosis, while 4-OHT treatment resulted in the opposite changes. In injured mouse skeletal muscles, myofiber E2 signaling promotes M1 to M2 transition to increase macrophage efferocytosis, thereby relieving inflammation and promoting muscle regeneration and repair.

The effect of silymarin on ischemia-reperfusion injury in skeletal muscles of rats silymarin and ischemia-reperfusion injury

Aim: Although the precise process is not entirely elucidated, it is well-known that oxidative stress mediators contribute to ischemia-reperfusion (I/R) injury. The impact of silymarin on I/R injury in many different tissues has been examined. For this purpose, we planned to see the effect of silymarin on muscle tissue in rats subjected to lower extremity I/R injury. Material and Methods: We used 18 male Wistar albino rats weighing 225-275 g. Each of the three groups of rats [Control (C), Ischemia-Reperfusion (I/R), and Silymarin-Ischemia/Reperfusion (S-I/R)] consisted of six rats. Silymarin was administered intraperitoneally 30 minutes before the procedure. (100 mg/kg-1) In Group I/R, the infrarenal abdominal aorta was clamped with a microvascular clamp. The clamp was removed after 120 minutes, and reperfusion was achieved for the next 120 minutes. At the end of the reperfusion period, muscle tissue samples were collected, and Malondialdehyde (MDA), catalase (CAT) enzyme activity levels and histopathological parameters were compared. Results: In the histopathological examination, no degeneration was observed in the muscle fibers in the Group C, while findings of striated muscle damage such as muscle atrophy/hypertrophy, muscle degeneration/congestion, internalization of the muscle nucleus/oval/central nucleus, fragmentation/hyalinization and leukocyte cell infiltration were seen in the Group I/R. In Group S-I/R, muscle atrophy /hypertrophy, internalization of the muscle nucleus/oval/central nucleus, fragmentation/hyalinization, and leukocyte cell infiltration were observed to improve these damaged areas compared to Group I/R. MDA levels in the Group I/R were significantly higher compared to Group C and S-I/R. The activity of the CAT enzyme was much higher in Group I/R compared to Group C. Conclusion: Our study revealed that 100 mg/kg-1 silymarin administered by intraperitoneal injection 30 minutes before ischemia effectively decreased lipid peroxidation, oxidative stress, and the injury caused by I/R in muscle histology in rats.

Mechanistic Studies of Cyclooxygenase-2 (COX-2) in Skeletal Muscle Cells During Rotator Cuff Injury: An In Vitro Study.

The mechanism of rotator cuff injury remains to be elucidated. And COX-2 plays a dual role in skeletal muscle injury and regeneration, would be associated with the development of rotator cuff injury. Therefore, we chose human skeletal muscle cells (HSKMC) as an in vitro muscle tissue model and transfected lentivirus with overexpressed COX-2 to simulate the in vitro environment of rotator cuff injury. To investigate the specific molecular biological mechanism of COX-2, transcriptome sequencing (RNA-Seq) was used to analyze the differentially expressed mRNAs in HSKMC overexpressing COX-2. Enrichment analysis was performed to analyze these differentially expressed genes and real-time quantitative PCR (RT-qPCR) was used to examine the mRNA levels of genes induced by overexpression. Subsequently, the role of COX-2 in cell proliferation was confirmed by cell counting kit-8 (CCK-8), and focal adhesion kinase (FAK) and signal transducer and activator of transcription 3 (STAT3) phosphorylation induced by COX-2 was utilized by western blotting (WB). The results showed that total of 30,759 differentially expressed genes were obtained, and the expression of CYP4F3 and GPR87 was significantly increased. COX-2 could bind CYP4F3 and GPR87 and co-localize with them in the cytoplasm. Finally, COX-2 promoted the proliferation of human skeletal muscle cells by activating the FAK and STAT3 pathways.

In Vivo Functional Assessment of Rat Masseter Muscle Following Surgical Creation of a Volumetric Muscle Loss (VML) Injury.

Volumetric Muscle Loss (VML) is prevalent in civilian and military populations and represents a debilitating skeletal muscle injury surpassing the body's natural regenerative capacity. These injuries disrupt not only muscle fibers but also nerves, blood vessels, and the extracellular matrix, overwhelming the regenerative capacity of skeletal muscle and leading to severe fibrosis and permanent deficiencies in muscle structure and function. Current clinical management has many limitations, and thus, research is ongoing to develop more effective therapeutic approaches. Notably, however, much of the preclinical emphasis on VML injuries has focused on limb and trunk muscles, with limited investigation into craniofacial muscles. Differences in developmental biology and regenerative capacity between craniofacial and limb/trunk muscles may provide crucial insights that drive more injury-specific VML treatment options. Moreover, evaluation of functional recovery is critical to establishing therapeutic efficacy. In this regard, in vivo testing of muscle contraction with percutaneous nerve stimulation is a minimally invasive method that allows for repeated functional assessment over the course of a study - in the same animal. In light of these considerations, this paper describes a method for the in vivo assessment of muscle function in the rat masseter muscle before and after a VML injury. This protocol is the first published instance to detail the creation and functional evaluation of a biologically relevant craniofacial VML injury in the rat.

C60 Fullerene Reduces the Development of Post-Traumatic Dysfunction in Rat Soleus Muscle.

Traumatic skeletal muscle injury is a complex pathology caused by high-energy trauma to muscle tissue. Previously, a positive effect was established when C60 fullerene was administered against the background of muscle ischemia, mechanical muscle injury, and other muscle dysfunctions, which probably protected the muscle tissue from damage caused by oxidative stress. Using tensiometry and biochemical analysis, the biomechanical parameters of skeletal muscle contraction and biochemical indices of the blood of rats 15 days after traumatic injury of the soleus muscle caused by myocyte destruction by compression were studied. The intraperitoneal administration of C60 fullerene aqueous solution (C60FAS) in a daily dose of 1 mg/kg improved its contractile function by 28-40 ± 2% and the values of the investigated biochemical indices of the animals' blood by 15-34 ± 2% relative to the trauma group. The obtained results indicate the potential ability of C60 fullerenes, as powerful antioxidants, to reduce the development of post-traumatic dysfunction of the soleus muscle.

Effect of Porphyromonas gingivalis Infection on Healing of Skeletal Muscle Injury: An In Vivo Study.

Background/Objectives:Porphyromonas gingivalis infection has been associated with various systemic diseases and may cause delayed healing of muscle injury. However, the relationship between muscle injury healing and P. gingivalis infection remains unclear. Our hypothesis was that P. gingivalis infection delays the healing of muscle injuries. Methods: Fifty-six 8-week-old male Wistar rats were randomly divided into two groups: sonicated P. gingivalis was intraperitoneally administered in one group (PG group), whereas saline was administered in the other group (CO group). Skeletal muscle injury was induced via cardiotoxin injections in all animals. The cross-sectional area of regenerating muscle cells was evaluated by haematoxylin-eosin staining, and the degree of muscle fibrosis was evaluated by Masson's trichrome staining. The expression of paired box protein (Pax7) and myoblast determination protein (MyoD) and the identified stages of myocyte regeneration were analysed by immunohistochemical staining. Motion analysis was performed during walking. Results: The cross-sectional area of muscle cells was significantly smaller in the PG group on days 7 and 14 post-injury than in the CO group. The Pax7+/MyoD- ratio was significantly lower in the PG group on day 1 post-injury than in the CO group. Motion analysis of treadmill walking showed that the PG group had a lower minimum calcaneal height on days 3 and 7 post-injury than the CO group. Conclusions: This study suggests that administration of sonicated P. gingivalis in rats can delay the healing process of muscle injury. Further research is needed to understand this mechanism of delay of P. gingivalis.

Comparison of rapid test for high-sensitivity troponin I with laboratory high-sensitivity troponin T in patients with acute chest pain - a prospective monocentric study

Abstract Background and purpose High-sensitivity troponin (hs-Tn) assays are recommended for routine clinical use for diagnosis of acute coronary syndrome (ACS). However, laboratory hs-TnT can be elevated due to non-cardiac conditions, such as pulmonary embolism, skeletal muscle injury or chronic kidney disease. The aim of our study was to compare the diagnostic accuracy of the bed-side rapid hs-troponin I (hs-TnI) assay with hs-TnT measured by routine laboratory. Methods This prospective monocentric study was conducted at a tertiary hospital outpatient cardiac unit with an emergency clinic for patients with acute symptoms. A total of 129 patients were included between May 2021 and August 2022. Hs-TnI was measured via a bed-side test from whole blood directly in the emergency room, while hs-TnT was measured from plasma through the routine laboratory. Definite ACS was confirmed by coronary angiography. Patients were compared by grouping them into definitive diagnosis of ACS or no ACS. Hs-TnI as well as hs-TnT values were compared for accuracy and predictive values. Routine clinical parameters and comorbidities were documented and compared as well. Agreement between hs-TnI and hs-TnT was assessed by likelihood ratios and Bland Altman plot. Results Overall, 129 patients (65.1% male, 61.8 ± 15.6 years) with acute chest pain were analysed. Median hs-TnI was 7.0 ng/L (IQR: 2.7-15.8), while median hs-TnT was 14 ng/L (IQR: 7.0-31.0). Results for TnI were available faster (average: 1:14 h ± 0:54) compared to TnT. Coronary angiography confirmed ACS in 17 patients (13.2%) displaying significant coronary stenoses requiring intervention. The relative risk of ACS patients to have an elevated hs-TnI result was 6.59 compared to that of 2.29 for the hs-TnT test, meaning that a positive hs-TnI test was a better classifier for validated ACS than that of hs-TnT. Hs-TnI exhibited equivalent negative predictive value to hs-TnT (99%) for definite ACS diagnosis, but had comparatively higher positive predictive value (50.0 vs. 25.8%). Bland Altman plot of hs-TnI versus hs-TnT showed an average difference of -4.6 ng/L (95% CI: -12.4 to 3.2) between the tests. In 39 patients with chronic kidney disease (minimum stage 3a CKD) median hs-TnT (27.0 ng/L, IQR: 16.0-55.0) values were higher than hs-TnI (11.2 ng/L, IQR: 7.5-30.7). Conclusion Bed-side hs-TnI is comparable to hs-TnT with a high degree of agreement. Measurement of troponin I using the rapid bed-side hs-TnI assay possesses a shorter blood-draw-to-result-time than routine troponin T measurement.