Skeletal Muscle Tissue Research Articles (Page 1)

Cellular alignment is essential for the function of anisotropic tissues such as skeletal muscle, tendon, cardiac, or neuronal tissues, where cell polarization governs mechanical integrity and signal transduction. However, engineering 3D tissue constructs with anisotropic extracellular microenvironments remains challenging, especially in larger constructs, which are commonly fabricated using extrusion-based bioprinting of cell-laden hydrogels, also known as bioinks. Here, a new class of bioprintable fibrous filler materials, fibrillar bundles, is presented that can be incorporated into bioinks and harness shear forces during extrusion bioprinting to achieve in situ alignment without the need for additional processing steps. These fibril bundles consist of multiple submicrometer fibrils fused into a larger bundle. They support robust cell adhesion and effectively promote polarization and alignment across multiple cell types. When incorporated into bioinks and printed with muscle cells, the fibrillar bundles enhance cellular alignment, and quantitative analysis confirms the directional growth of multinuclear myotubes and their morphological maturation. This approach offers a scalable and integrative solution for inducing anisotropy within 3D biofabricated tissues, holding promise for applications in muscle tissue engineering and beyond.

Abstract The prevalence of both osteoporosis and sarcopenia increases with age, and 60% of elderly sarcopenia patients also develop osteoporosis. However, the co-occurrence of osteoporosis and sarcopenia remains unclear. We performed single-cell 5’RNA-seq on human skeletal muscle tissues and investigated the enrichment of heritability for musculoskeletal traits in cell type specific cis-regulatory regions. We found the fibroblast-specific cis-regulatory regions are highly enriched in the heritability of bone mineral density (BMD). Using GWAS, we identified estrogen receptor α (ESR1) as a common transcription factor that correlated with both BMD and lean mass. We hypothesized that deficiency of estrogen signaling in fibroblast may attenuate musculoskeletal homeostasis. Therefore, we generated mice lacking Esr1 in PDGFRα (a fibroblast marker) + cells (Esr1ΔPα). Although muscle mass and grip strength were not different between groups, distal femoral BMD and cortical thickness were significantly lower in Esr1ΔPα compared to control. Bone histomorphometry showed that cortical bone in Esr1ΔPα exhibited a high turnover bone phenotype. Bulk RNA-seq using PDGFRα+ cells revealed that Igfbp5 expression was significantly higher in Esr1ΔPα compared to control. Furthermore, serum IGFBP5 level was significantly higher in Esr1ΔPα. IGFBP5 treatment in vitro significantly suppressed osteoblast differentiation and facilitated osteoclast differentiation. These results suggest that estrogen signaling in PDGFRα+ cells suppresses Igfbp5 expression, then maintains bone mass, indicating that estrogen signaling in PDGFRα+ cells plays a significant role in bone metabolism.


Conductive materials play a crucial role in enhancing functional performance in muscle tissue engi-neering. This study investigates the impact of the conductive polymer polyaniline (PANi) in Polycapro-lactone-Collagen Type I (PCL-collagen I) nanofiber scaffolds designed to support the coculture of hu-man adipose-derived stem cells (ADSCs) and myoblasts. 
Objectives:
The effect of varying PANi concentrations (0%, 2%, 4%, 6%) in PCL-collagen I nanofiber scaffolds was evaluated concerning the cell alignment, differentiation and gene expression of cocultured my-oblasts and ADSC.
Methods:
Nanofiber scaffolds with different PANi concentrations were analyzed. Acetatic acid was used as a non-toxic and biocompatible solvent for electrospinning the nanofibers. In vitro experiments involved a 1:1 coculture of myoblasts and ADSCs for up to 28 days on the scaffolds. The cell viability, differentia-tion and myotube morphology were assessed using live-dead-assay, CCK-8-assay, immunofluores-cence staining and gene expression analysis.
Results:
Scaffolds with 2% and 4% PANi showed a higher percentage of live cells compared to the control at both 7 and 28 days. The nanofibers with 2%, 4% and 6% PANi concentration showed promising re-sults in terms of cell differentiation and myotube morphology. After 14 days, the scaffolds with 4% PANi showed superior cell differentiation with strong myotube alignment along the nanofibers. At high-er PANi concentrations (6%), only the myotube width increased significantly, whereas 4% PANi re-sulted in a markedly higher myotube number.
Conclusion:
PCL-collagen I nanofibers incorporating PANi enhance myoblast alignment and differentiation com-pared to the control group, showing promise for muscle tissue engineering applications. The non-toxic solvent makes the nanofibers suitable for translational purposes. Further in vivo studies are needed to explore the full impact on cellular function and regeneration.
&#xD.

Precise remote control of skeletal muscle contraction could be beneficial to the study and treatment of muscular dysfunction. Recently, we reported a method regulating intracellular calcium signaling using molecular motors (MMs), molecules that rotate submolecular components unidirectionally upon absorption of light. Here, we explore the application of this methodology to skeletal muscle tissue. Our results demonstrate that MMs induce intracellular calcium release in C2C12 myoblasts and differentiated myotubes via IP3-mediated signaling in a fashion that depends on their fast unidirectional rotation. Inhibition of proteins involved in the cAMP pathway such as adenylyl cyclase and protein kinase A also reduced the magnitude of the elicited calcium responses. We further show that, in differentiated C2C12 myotubes, the calcium signaling events driven by MM activation cause localized myotube contraction. This work demonstrates the use of a molecular mechanical technique to directly control skeletal muscle contraction, expanding the scope of available tools to study muscle contraction in a single-cell regime and treat a range of myopathies.

X-linked myotubular myopathy (XLMTM) due to MTM1 mutations is a rare and often lethal congenital myopathy. Its downstream molecular and cellular mechanisms are currently incompletely understood. The most abundant protein in muscle, myosin, has been implicated in the pathophysiology of other congenital myopathies. Hence, in the present study, we aimed to define whether myosin is also dysfunctional in XLMTM and whether it thus may constitute a potential drug target. To this end, we used skeletal muscle tissue from human patients and canine/mouse models; we performed Mant-ATP chase experiments coupled with X-ray diffraction analyses and LC/MS-based proteomics studies. In XLMTM humans, we found that myosin molecules are structurally disordered and preferably adopt their ATP-consuming biochemical state. This phosphorylation-related (mal)adaptation was mirrored by a striking remodelling of the myofibre energetic proteome in XLMTM dogs. In line with these, we confirmed an accrued myosin ATP consumption in mice lacking MTM1. Hence, we treated these, with a myosin ATPase inhibitor, mavacamten. After a four-week treatment period, we observed a partial restoration of the myofibre proteome, especially proteins involved in cytoskeletal, sarcomeric and energetic pathways. Altogether, our study highlights myosin inhibition as a new potential drug mechanism for the complex XLMTM muscle phenotype.

Background: Loss of dysferlin results in the rare, currently untreatable muscular dystrophy known as Limb Girdle Muscular Dystrophy 2B (LGMD2B). In LGMD2B mice, skeletal muscle undergoes progressive myopathy, whereas cardiac deficits only arise with advanced age, stress, or injury – suggesting the heart may harbor protective mechanisms that could guide future therapy developments. While dysferlin’s roles in membrane repair, Ca 2+ handling, and metabolism are well characterized in skeletal muscle, its function in the heart is poorly defined. We therefore engineered 3D LGMD2B cardiac and skeletal muscle tissues (“cardio- and myobundles”) to compare dysferlin’s differential roles in cardiac vs. skeletal muscle. Methods: Three healthy (HLT) and three LGMD2B human induced pluripotent stem cell (hiPSC) lines were differentiated into cardiomyocytes (hCMs) and muscle progenitor cells to generate cardio- and myobundles. After 2 weeks of culture, we performed isometric force tests, Ca 2+ transient imaging, and optical mapping of action potential propagation. To probe membrane repair capacity, osmotic shock injury (OSI) was induced with ~30 mOsm medium for 5 min followed by 15 min recovery, with contractile force recorded every minute. Tissues were also immunostained for sarcomere structure and dysferlin localization. Results: Both HLT and LGMD2B cardio- and myobundles exhibited aligned, cross-striated sarcomeric structure with dysferlin predominantly localized at the plasma membrane. Dysferlin-deficiency in myobundles resulted in a ~2-fold decrease in specific force generation and Ca 2+ transient amplitude. In contrast, loss of dysferlin did not affect cardiobundle specific force generation, Ca 2+ transient amplitude, conduction velocity, or action potential duration. Following OSI, cardiobundles lost >60 % of peak force independent of phenotype, while LGMD2B myobundles exhibited significantly greater force loss than HLT controls. Conclusions: We present the first in vitro tissue-engineered model of human LGMD2B cardiac muscle and show that, unlike engineered skeletal muscle and similar to in vivo findings, dysferlin deficiency does not compromise engineered cardiac tissue structure or function. Ongoing transcriptional analysis of HLT and LGMD2B cardiobundles vs. myobundles will probe putative cardioprotective pathways, with subsequent loss- and gain-of-function studies planned to validate novel therapeutic targets transferable to skeletal muscle.

Introduction: Impairments in cardiac diastolic reserve during physiological stress characterize HFpEF and may antecede resting state abnormalities. Biomarkers associated with cardiac diastolic reserve may assist in early identification of diastolic impairment. Methods: Among community-based participants in the multi-ethnic Dallas Heart Study who participated in the third study phase (2020-2024) and underwent protocol echocardiography at rest and during pedaling on a supine bicycle at a fixed workload of 30W, we measured aptamer-based plasma proteomics (SomaLogic; 7172 aptamers corresponding to 6490 unique proteins) in 189 participants. We assessed associations with change in E/e’ ratio from rest to 30W stress using multivariable linear regression, adjusting for age, sex, stroke volume (SV) at rest and stress, heart rate (HR) at rest and stress, cardiac reserve (SV*HR) at rest and stress, and systolic blood pressure at rest and stress. An FDR p<0.05 was used to define statistical significance. Results: Mean age was 60±11 years, 51% were female, the average E/e’ ratio at rest was 9.9±3.9, the average E/e’ at 30W was 9.8±3.0, and the change in E/e’ was -0.1±2.7. At FDR significance, 16 proteins were associated with the change in E/e’ from rest to 30W: 15 with a decrease and 1 with an increase in E/e’ (Figure 1). Of these, the majority were associated with changes in E wave as opposed to e’ from rest to 30W (9 vs 0 respectively). Several of these proteins are enriched in skeletal muscle (SELENOW, MAPT, TMP1) and cardiac muscle (TMP1) tissue, and are involved in PKR-mediated signaling (MAPT, NPM1) and BAG2 signaling (MAPT, PSMB4) pathways which play roles in response to cellular stress. Conclusion: We uncovered a set of proteins significantly associated with exercise-provoked changes in E/e’ among community-based older adults. The extent to which these proteins predict development of resting diastolic dysfunction or HFpEF requires further study.

Rhabdomyosarcoma (RMS) is an aggressive soft tissue sarcoma with myogenic features affecting children and adolescents. The high-risk fusion-positive RMS subtype (FP-RMS), driven by the oncogenic chimeric transcription factor PAX3–FOXO1, shows 5-year overall survival not exceeding 30%. Here, we examine the impact of neddylation inhibition, a post-translational modification in which the NEDD8 peptide is conjugated to proteins, on the tumorigenic properties of FP-RMS. Here, we report that the NAE1 and UBA3 genes encoding the two subunits of the NEDD8-activating enzyme (NAE) heterodimer are upregulated in FP-RMS patients compared to healthy skeletal muscle tissues and highly expressed in RMS among several tumor types. Furthermore, DepMap analyses showed that FP-RMS cell lines are among the most sensitive to both NAE1 and UBA3 CRISPR-mediated knockout as well as to NAE pharmacological inhibition with MLN4924 compared to other cancer cell lines. In agreement, FP-RMS cells treated in vitro with MLN4924 (Pevonedistat) exhibited cell proliferation decrease, G2/M cell cycle arrest, senescence, and caspase- and PARP1-dependent apoptosis. These phenotypes were associated with increased γH2AX nuclear foci and protein levels, DNA double-strand breaks (DSB), and reduced RAD51 levels. NAE1 and UBA3 individual silencing mirrors the major effects of MLN4924. In addition, MLN4924 also prevented FP-RMS tumor growth in vivo. Combining MLN4924 with irradiation enhanced apoptosis and the inhibition of colony formation, cell cycle progression, and anchorage-independent and tumor spheroids growth compared to single treatments. Molecularly, MLN4924 amplified the irradiation-induced DNA damage by increasing γH2AX and DSBs, while reducing RAD51 expression and DNA-PKcs activation, both of which are involved in DNA repair. Collectively, our results suggest that the neddylation pathway is deregulated in FP-RMS, representing a potential therapeutic target. Therefore, MLN4924 could be considered as an anti-tumorigenic compound and a novel radiosensitizer in FP-RMS.

Regulation of energy homeostasis by the small guanosine triphosphatase Rac1 in skeletal muscle and adipose tissue.

Protein-in-polysaccharide bioink for 3D bioprinting of muscle mimetic tissue constructs to treat volumetric muscle loss.

TRPV1 signaling in skeletal muscle: A mini review of physiological and pathological roles.

Maternal obesogenic diet causes insulin resistance by modulating insulin signaling pathways in peripheral tissues of offspring: a systematic review.

Overtraining, which results in central nervous system (CNS)‐fatigue‐related symptoms, leads to a long‐term decline in performance. This study investigated CNS‐derived EV protein content under overtraining conditions to identify potential biomarkers. Eight‐week‐old C57BL/6J mice were randomly divided into three groups: sedentary (SED, n = 7), exercise control (EX, n = 8), and overtraining (OT, n = 9) groups. The OT group underwent an 8‐week downhill treadmill‐based overtraining induction protocol. Exercise capacity was assessed using the incremental load, exhaustion, grip strength, and rotarod tests, while motor deficits, depression and anxiety were assessed using the nest building test. Proinflammatory cytokines were measured in blood plasma, skeletal muscle, and brain tissue. CNS‐derived EVs were isolated using a two‐step EV isolation protocol. Isolated EVs underwent proteomic analyses. Mice exhibited a significant decrease in aerobic exercise capacity, high‐intensity exercise tolerance, and muscular strength. OT increased quadriceps IL‐6 and hypothalamic IL‐1β/TNFα compared to EX. Plasma IL‐2 levels tended to be higher in OT than in EX. Proteomic analysis of CNS‐derived EVs revealed a decrease in lipid metabolism‐related proteins and an increase in stress‐related proteins. Valosin‐containing proteins and catalase, which are upregulated in organs under oxidative stress, were increased. Therefore, CNS‐derived EV protein contents indicated CNS fatigue under overtraining conditions.

Dynamic changes of systemic and local myokines in burn patients undergoing physiotherapy: A pilot prospective study.

Lysosomes are membrane-bound organelles responsible for the degradation of damaged or dysfunctional cellular components, including mitochondria. Their acidic internal environment and the presence of an array of hydrolytic enzymes facilitate the efficient breakdown of macromolecules such as proteins, lipids, and nucleic acids. Mitochondria play a critical role in maintaining skeletal muscle homeostasis to meet the energy demands under physiological and pathological conditions. Mitochondrial quality control within skeletal muscle during processes such as exercise, disuse, and injury is regulated by mitophagy, where dysfunctional mitochondria are targeted for lysosomal degradation. The limited understanding of quality control mechanisms in skeletal muscle necessitates the need for isolating intact lysosomes to assess organelle integrity and the degradative functions of hydrolytic enzymes. Although several methods exist for lysosome isolation, the complex structure of skeletal muscle makes it challenging to obtain relatively pure and functional lysosomes due to the high abundance of contractile proteins. Here, we describe a method to isolate functional lysosomes from small amounts of mouse skeletal muscle tissue, preserving membrane integrity. We also describe functional assays that allow direct evaluation of lysosomal enzymatic activity, and we provide data indicating reduced lysosomal degradative activity in lysosomes from aging muscle. We hope that this protocol provides a valuable tool to advance our understanding of lysosomal biology in skeletal muscle, supporting investigations into lysosome-related dysfunction in aging, disease, and exercise adaptations.NEW & NOTEWORTHY Lysosomes within skeletal muscle function to degrade dysfunctional debris and initiate retrograde signaling pathways. We developed a method to isolate purified lysosomal fractions using small portion of skeletal muscle, eliminating the need for density gradients or lysosome-modifying agents, ensuring high lysosomal purity without compromising structure or function. By enabling functional analysis via acid phosphatase, cathepsin-B activity, and calcium release, this approach offers a powerful tool to study lysosomal roles in muscle physiology, disease, and exercise.

Background The muscle-adipose index (MAI), a novel nutritional parameter for assessing body composition, has emerged as a potential prognostic indicator. This study aimed to research MAI and its longitudinal changes before and after chemoradiotherapy (CRT) and to evaluate the prognostic implications of these changes in patients with inoperable esophageal squamous cell carcinoma (ESCC). Methods This retrospective cohort included 180 ESCC patients treated with CRT (2020-2024). MAI was derived from CT-based quantification of skeletal muscle and subcutaneous adipose tissue at the third lumbar vertebra(L3). Baseline (preMAI), post-treatment (postMAI), and their longitudinal changes (ΔMAI) were analyzed. Optimal cutoff values for MAI imbalance were determined using X-tile software. Overall survival (OS) and progression-free survival (PFS) were assessed using Kaplan-Meier and Cox regression analyses. Results Among 180 enrolled patients, 111 (61.7%) patients died during follow-up (median OS:23.0 months; median PFS:16.0 months).PreMAI and postMAI demonstrated statistically significant associations with OS (preMAI: HR = 5.934,95%CI=3.943-8.929, P<0.001; postMAI: HR = 9.123,95%CI=5.769-14.426, P<0.001) and PFS (preMAI: HR = 5.316, 95%CI=3.583-7.889, P<0.001; postMAI: HR = 8.008, 95%CI=5.213-12.303, P<0.001). The 0 group ( pre balance- post balance) demonstrated significantly better survival outcomes than the remaining groups, both in terms of OS (HR = 9.454, 95%CI=5.830-15.331, P<0.001) and PFS (HR = 8.444, 95%CI=5.360-13.303, P< 0.001). Multivariate analysis confirmed ΔMAI as an independent prognostic factor for OS (HR = 2.953, 95%CI=1.070-8.151, P = 0.037) and PFS (HR = 3.204, 95%CI=1.166-8.806, P = 0.024). Conclusion CT-derived MAI was a robust prognostic biomarker in ESCC. These findings highlighted the clinical utility of MAI for risk stratification and personalized therapeutic strategies in inoperable ESCC patients.

Discovery of placental microRNAs associated with maternal insulin sensitivity during pregnancy.

ABSTRACTAlthough photobiomodulation (PBM) therapy (i.e., the application of light with a 600–1100 nm wavelength using laser or light‐emitting diode devices, a power density of less than 100 mW/cm2, and an energy density of less than 10 J/cm2 at the target) is emerging as a significant noninvasive strategy of promoting regeneration of damaged skeletal muscle tissue, its actual benefits remain debated. In particular, operating parameters exhibiting positive effects on regenerative muscle satellite stem cells need to be clearly identified. Hence, we investigated the effects of red PBM carried out by a laser diode (635 ± 10 nm; 0.4, 4, and 8 J/cm2; 4 mW/cm2; non‐contact mode; continuous wave; single exposure) on murine myoblasts undergoing differentiation and on mature myotubes by combining morphological, biochemical, and functional analyses. Red PBM, especially with a 4 J/cm2 energy density, did not alter cell viability but successfully promoted the expression of myogenic transcription factors as myoblast determination protein 1 (MyoD) and myogenin, as well as myotube formation, mitochondrial metabolism, and biogenesis. Consistently, electrophysiological analyses of cell membrane passive properties and inward ion currents indicated the acquisition of a more differentiated phenotype in PBM‐treated cells. Moreover, we found that PBM was able to enhance the release of extracellular vesicles (EVs) during cell differentiation according to a promyogenic phenotype. Red PBM treatment did not alter mature myotube viability and dimension while increasing their secretion of promyogenic EVs. Overall, this study provides experimental evidence supporting promyogenic effects of red PBM and the essential groundwork for further preclinical and clinical studies in the field of skeletal muscle regenerative medicine.

Targeting Cellular Senescence in Dystrophin-/-/Utrophin-/-Double Knockout Mice Improves Musculoskeletal Health and Increases Lifespan.

BackgroundRhabdomyolysis (RML) is a complex disorder caused by muscle cell injury and the subsequent release of intracellular components into circulation. Statins are widely used and generally well tolerated; however, some patients report muscle weakness, particularly in the lower extremities. The concomitant use of statins with other substances, including herbal products such as khat (Catha edulis), may increase the risk of adverse events. Khat chewing is known to cause multiple health problems and has been associated with musculoskeletal weakness.AimThis study aimed to evaluate the effects of khat extract on atorvastatin-induced rhabdomyolysis in rats.MethodsMethanolic extraction of khat leaves was performed, and phytochemical analysis confirmed the presence of alkaloids, tannins, flavonoids, and other bioactive compounds. Twenty-four healthy rats were randomly divided into four groups: control, khat extract (500 mg/kg), atorvastatin (40 mg/kg), and khat extract plus atorvastatin. Treatments were administered orally for 28 days. On day 28, blood samples were collected for biochemical assays of myoglobin, creatine kinase (CK-MM), lactate dehydrogenase (LDH, LDH5), alkaline phosphatase (ALP), troponin fast skeletal (fsTnI), creatinine, albumin, and total protein. Histopathological analysis of skeletal muscle and kidney tissues was also conducted. Data were analyzed using the Kruskal–Wallis, expression by median(IQR), CI(95%) with significance set at p < 0.05.ResultsThe khat–atorvastatin group showed significant weight reduction and marked increases in biochemical markers compared with controls. The khat-only and atorvastatin-only groups also demonstrated elevated biomarkers but at lower levels. Histopathology confirmed severe muscle necrosis and kidney tubular injury in the khat–atorvastatin group, while mild myopathy was evident in the khat-only and atorvastatin-only groups.ConclusionKhat extract contributes to biochemical and histopathological changes indicative of muscle injury. When combined with atorvastatin, these effects are exacerbated, leading to pronounced myopathy and kidney damage. These findings suggest that khat use may potentiate statin-induced rhabdomyolysis and increase the risk of musculoskeletal and renal complications.