Piezo1 mechanosensitive ion channels convert mechanical stimuli into biochemical signals across diverse tissues, yet their role in the contractile function of adult skeletal muscle remains unclear. Here, we demonstrate that Piezo1 regulates skeletal muscle mechanics through a channel-independent mechanism that tunes the length-tension relationship. We examined the effects of pharmacological modulation using the Piezo1 agonist Yoda1 and antagonist Dooku1 in individual muscle fibers from wild-type mice and from muscles with reduced Piezo1 expression (anti-Piezo1 shRNA) using calcium influx and electrophysiological assays. Ex vivo force measurements were performed on these muscles and compared with the dystrophic mdx model. Piezo1 activation had no effect on force at resting length, whereas its inhibition significantly reduced contractile force at stretched lengths, indicating a selective role in length-dependent force regulation. This effect was independent of extracellular calcium and diminished by Piezo1 knockdown. This reduction was absent in mdx muscle, demonstrating dependence on an intact dystrophin-associated cytoskeleton. These findings identify Piezo1 as a previously unrecognized regulator of muscle mechanical performance that operates independently of ion conduction. Our results uncover a mechanobiological interface between Piezo1 and cytoskeletal integrity, expanding current concepts of muscle mechanoregulation and highlighting Piezo1 as a potential therapeutic target for improving muscle function.

Introduction:Extended exposure to microgravity, such as experienced during spaceflight, significantly alters the mechanical environment of skeletal tissues, impacting cartilage development and function. Mechanical unloading disrupts the balance of cellular signaling and extracellular matrix synthesis in cartilage precursor cells, but the molecular consequences and temporal dynamics of these alterations remain incompletely understood. Methods:We employed simulated microgravity via a random positioning machine (RPM) to investigate stage-specific transcriptomic and phenotypic responses in chondrogenic micromass cultures derived from embryonic chicken (Gallus gallus) limb bud cells. RNA sequencing, bioinformatic pathway analysis, and protein interaction network construction were performed on cultures exposed to microgravity for early (days 0-3), late (days 3-6), and continuous (days 0-6) periods. Results:Continuous microgravity exposure resulted in robust differential expression of 648 genes (adjusted p-value <0.05, |log2 fold change| > 1), including suppression of canonical chondrogenic markers (SOX9, COL2A1) and upregulation of catabolic enzymes (MMP13, ADAMTS family). The affected key signaling pathways included disrupted TGF-β/BMP balance, Wnt/β-catenin activation, and cytoskeletal remodeling. Early and late exposures showed consistent gene expression trends but fewer statistically significant changes. Notably, adrenergic beta receptor 1 (ADRB1) was consistently upregulated across all time points. Discussion:These findings demonstrate that simulated microgravity rapidly induces reversible molecular and cellular adaptations related to cartilage homeostasis and mechanotransduction in this chondrogenic model system. The RPM platform offers a powerful tool to dissect chondrogenesis, cartilage biology, and lineage plasticity under mechanical unloading, providing insights with broad relevance to skeletal tissue mechanobiology.

Synthetic insecticides are recognized as a major factor contributing to the global decline in insect abundance and diversity. Within this context, anthranilic diamides have gained increasing market share in Europe since 2018. We investigated the second-generation diamide cyantraniliprole, which induces aberrant cytoplasmic calcium release in honeybee skeletal muscle cells. In vivo assays demonstrated that acute contact toxicity varied with exposure site, being more severe when applied to the abdomen, antennae, or ventral thorax compared with the dorsal thorax. Following thoracic exposure to sublethal doses, continuous 21-h monitoring revealed a dose-dependent alteration of behavior, with a reduction in locomotor activity, including maximal velocity and total distance traveled. Notably, at the lowest concentration, antennal exposure elicited stronger behavioral impairments, indicating potential disruption of sensory processing and environmental cue perception. Importantly, cyantraniliprole and its parent compound, chlorantraniliprole, also triggered anarchic calcium mobilization in mammalian skeletal muscle fibers, highlighting potential cross-taxa effects. These results strengthen previous evidence of diamides toxicity in bee cardiomyocytes and neurons and emphasize significant gaps in current risk assessment frameworks. Collectively, our findings indicate that anthranilic diamides represent not only an ecological threat to pollinators but also raise concerns for mammalian health, warranting more stringent evaluation of this insecticide class.

Skeletal muscle dysfunction during spaceflight arises from combined mechanical and non-gravitational stressors. Here, we modeled solar particle event-like proton irradiation in C2C12 myogenic cells to examine radiation-induced membrane and mechanosensitive channel alterations. Proton exposure increased membrane rigidity in a dose-dependent manner and significantly reduced the pharmacological activatability of Piezo1 channels, identifying membrane-mediated mechanotransduction as a potential contributor to radiation-induced muscle dysfunction.

Calcium sparks can arise as both voltage-dependent and voltage-independent ligand-activated release events in amphibian skeletal muscle. To assess their gating behavior, calcium sparks were recorded from intact frog skeletal muscle fibers using high-temporal-resolution confocal microscopy (line scans: 15 and 50 µs/line). Sparks were triggered by 1 mmol/L caffeine to open ryanodine receptors (RyRs) or by subthreshold depolarization to a -65 mV membrane potential to activate dihydropyridine receptors (DHPRs). Both treatments increased the frequency of sparks and altered their morphology. The sparks were significantly greater after caffeine treatment than in depolarized cells. The signal mass of sparks (i.e., the amount of calcium released) resembled the amplitude in shape. Additionally, the calcium release flux followed a staggered function during the activation of sparks. The detailed analysis of the sparks' time profile revealed that the events were activated in a stepwise manner. The average step size (in F/F0; 0.071 ± 0.003) remained constant regardless of the scanning speed. The number of steps during the activation of sparks followed a linear function based on the spark's amplitude. Our results suggest that the activation of neighboring release units may occur sequentially, and the amplitude of the sparks depends linearly on the number of activated RyR channels.

Mitochondria are dynamic organelles that undergo fusion and fission. Key proteins are needed to create mitochondrial networks, as well as facilitate biogenesis, fragmentation or movement within the cell. Septins are considered as the fourth component of the cytoskeleton, providing attachment sites for proteins. Besides that, they have important roles in different cellular processes, including mitochondrial fission and fusion (remodelling). Septins form oligomeric complexes comprising various septin subgroups, which can create higher-order structures. Septin7 is the sole member of its subgroup. We aimed to examine how mitochondrial dynamics and oxidative phosphorylation (OXPHOS) are affected in Septin7 downregulated C2C12 (S7-KD) myoblasts and terminally differentiated myotubes compared to scrambled short hairpin RNA-transfected control cells. We detected altered expression of genes related to mitochondrial biogenesis (PGC1α), dynamics (DRP1, OPA1 and MFN2) and autophagy (PINK1 and BNIP3); furthermore, a significant decrease in differentiation-dependent mRNA expression of OXPHOS markers (ATP synthase, COX1 and SDH). Septin7 downregulation also affected the expression of post-translational modifications of MFN2 and DRP1. Functional measurements of OXPHOS revealed decreased O2 consumption (flux) and higher O2 concentration in Septin7 KD cultures following selective inhibition of electron transport complexes. We observed significant alterations in basal respiration and OXPHOS pathways in Septin7 KD cultures. Our results suggest that Septin7, as a cytoskeletal protein, could be a significant regulator of mitochondrial dynamics and oxidative metabolism. Therefore, these molecules, as mitochondrial dynamics modulators, can serve as potential therapeutic targets in diseases related to changes in mitochondrial function. KEY POINTS: Knockdown of Septin7 results in altered gene and protein expression of markers controlling mitochondrial dynamics. Diminished level of Septin7 causes decreased gene expression of members of oxidative phosphorylation. Knockdown of Septin7 has an impact on microRNAs involved in the regulation of mitochondrial markers. Septin7 has an impact on mitochondrial respiration.

Objective To highlight the key translational advances and interdisciplinary discussions from the 2025 University of Debrecen Musculoskeletal Symposium (UD-MUSK), focusing on osteoarthritis (OA) and related musculoskeletal (MSK) diseases. Method The UD-MUSK Symposium convened international and local experts for keynote presentations and scientific dialogue spanning OA and MSK disease mechanisms, translational therapies, and tissue regeneration. Core topics included extracellular matrix (ECM) remodelling, cell/gene therapies, animal disease models, chronic stress, autoimmunity, immunotherapies, and muscle and stem cell biology, reflecting the Symposium’s broad interdisciplinary spectrum. Results ECM proteomics revealed degradation fragments that act as drivers and potential modulators of OA, offering new biomarkers and therapeutic targets. Advances in cell- and gene-based therapies were presented, including the use of growth differentiation factor 6 (GDF6) and CRISPR approaches for cartilage and intervertebral disc repair. Large animal models simulating spatio-temporal changes in human OA, and studies demonstrating chronic stress-accelerated OA via neuroendocrine mechanisms, were highlighted. Novel strategies in immune modulation, such as chimeric antigen receptor (CAR) T cell therapy for autoimmune myopathies, alongside research on muscle regeneration and circadian regulation by mechanical loading, further exemplified the translational breadth of the meeting. Conclusion The symposium underscored the value and need of integrating molecular research and disease modeling. Interdisciplinary collaboration continues to enhance understanding of MSK disease mechanisms and supports development of targeted, regenerative therapies with translational potential for OA and related disorders.

Envenomation by viperid snakes causes acute muscle tissue injury (myonecrosis). An important group of myotoxic components comprises catalytically-inactive Lys49 phospholipase A2 homologs, which disrupt the integrity of the plasma membrane of skeletal muscle fibers through a mechanism that does not involve phospholipid hydrolysis. However, it remains unknown whether other mechanisms are involved in the cytotoxic action of these myotoxins. In this work, isolated calcium release channels (ryanodine receptor, RyR1) incorporated into an artificial lipid bilayer were used to study the action of the Lys49 phospholipase A2 homolog myotoxin II (Mt-II) from the venom of Bothrops asper. Mt-II induced a dose-dependent activation of the RyR1. The open probability of the channel increased with the dose of the toxin. The maximal conductance of the channel remained unchanged during the toxin treatment. Furthermore, the analysis of the open and closed states showed a slight toxin dependency of the latter. These findings suggest that, in addition to the calcium influx from the extracellular space through the disrupted plasma membrane, Ca2+ release from the internal stores may also occur. However, incubation of C2C12 myotubes in culture with the RyR1 antagonist dantrolene did not reduce the extent of cytotoxicity induced by Mt-II, suggesting that the RyR1-mediated increase in cytosolic Ca2+ does not contribute to the overall myotoxicity of this toxin.

Context Increased orbital tissue volume due to matrix expansion, orbital fibroblast (OF) proliferation, and adipocyte differentiation are the hallmarks of thyroid eye disease (TED). Their combination with the presence of hyaluronan-bound excess water in the constrains of the bony orbit results in increased intraorbital pressure. High intraorbital pressure, along with changes in the mechanical properties of orbital tissues, may lead to the activation of mechanosensitive receptors. The expression and role of the Piezo1 mechanoreceptor has not been investigated in TED.Objective We aimed to verify the expression of Piezo1 in OFs, and to study the effect of in vitro Piezo1 activation by its synthetic agonist Yoda1 on adipocyte differentiation.Methods OF cultures established using orbital connective tissues from patients with TED and controls were studied in the presence or absence of adipogenic stimuli. Piezo1 expression was confirmed by Western Blot and immunofluorescent imaging, and its function was verified by intracellular Ca2+ measurement. Adipogenic differentiation was characterized using Oil Red O staining for lipid accumulation, real-time polymerase chain reaction for gene and Western blot for protein expressions indicative in adipogenesis.Results OFs express functional Piezo1 channels. Differentiation into adipocytes is inherent to TED OFs. Piezo1 activation by Yoda1 inhibits the expressions of early (CEBP beta, CEBP delta) and main (PPAR gamma, CEBP alpha) transcription factors, and the terminal marker FABP4 during adipogenesis, resulting in markedly lower intracytoplasmic lipid accumulation.Conclusion Piezo1 channels are expressed and functional in OFs. Modeling orbital pressure by in vitro Piezo1 activation reduces de novo adipogenesis of OFs derived from TED orbits.

Skeletal muscle, constituting 40–50% of total body mass, is vital for mobility, posture, and systemic homeostasis. Muscle contraction heavily relies on ATP, primarily generated by mitochondrial oxidative phosphorylation. Mitochondria play a key role in decoding intracellular calcium signals. The endocannabinoid system (ECS), including CB1 receptors (CB1Rs), broadly influences physiological processes and, in muscles, regulates functions like energy metabolism, development, and repair. While plasma membrane CB1Rs (pCB1Rs) are well-established, a distinct mitochondrial CB1R (mtCB1R) population also exists in muscles, influencing mitochondrial oxidative activity and quality control. We investigated the role of mtCB1Rs in skeletal muscle physiology using a novel systemic mitochondrial CB1 deletion murine model. Our in vivo studies showed no changes in motor function, coordination, or grip strength in mtCB1 knockout mice. However, in vitro force measurements revealed significantly reduced specific force in both fast-twitch (EDL) and slow-twitch (SOL) muscles following mtCB1R ablation. Interestingly, knockout EDL muscles exhibited hypertrophy, suggesting a compensatory response to reduced force quality. Electron microscopy revealed significant mitochondrial morphological abnormalities, including enlargement and irregular shapes, correlating with these functional deficits. High-resolution respirometry further demonstrated impaired mitochondrial respiration, with reduced oxidative phosphorylation and electron transport system capacities in knockout mitochondria. Crucially, mitochondrial membrane potential dissipated faster in mtCB1 knockout muscle fibers, whilst mitochondrial calcium levels were higher at rest. These findings collectively establish that mtCB1Rs are critical for maintaining mitochondrial health and function, directly impacting muscle energy production and contractile performance. Our results provide new insights into ECS-mediated regulation of skeletal muscle function and open therapeutic opportunities for muscle disorders and aging.

The endocannabinoid system (ECS) is known to regulate crucial bodily functions, including healthy muscle activity. However, its precise roles in normal skeletal muscle function and the development of muscle disorders remain unclear. Previously, we developed a tamoxifen-inducible, skeletal muscle-specific CB1 receptor knockdown (skmCB1-KD) mouse model using the Cre/LoxP system. In this study, we aimed to clarify the mechanisms behind the observed reduction in muscle force generation in these mice. To investigate this, we analyzed calcium dynamics following electrical stimulation-induced muscle fatigue, assessed store-operated calcium entry (SOCE), and performed functional analysis of mitochondrial respiration. Our findings suggest that the reduced muscle performance observed in vivo likely arises from interconnected alterations in ATP production by mitochondria. Moreover, in skmCB1-KD mice, we detected a significant decrease in a component of the respiratory chain (complex IV) and a slowed dissipation of mitochondrial membrane potential upon the addition of an un-coupler (FCCP).

Physical activity is an especially important part of everyday life for children with chronic diseases. The aim of the study was to show whether asthma is a barrier to physical activity in our society. The correlations between the severity of the disease, body mass index, and physical activity were analyzed, and parents’ opinions on whether children should participate in active sports were assessed. Physical activity of children with asthma was analyzed by questionnaires; 93 parents and their 93 children were involved in the survey. The age of children was 12.6 ± 3.5 years (mean ± SD), 69.9% were boys, 30.1% were girls. A total of 93.4% of the respondents participated in a physical education program and 56.5% also attended sporting activities on a regular basis. In terms of disease severity, 61.2% of the children had mild asthma, 37.6% moderate, and 1.2% severe, and 6.5% of the respondents also stated that their children’s illness had been consistently or frequently limiting their performance concerning their school or home duties over the past four weeks. Of the parents surveyed, 12% felt that physical activity was not appropriate in the context of this disease. We concluded that fear of the consequences of physical activity depends largely on education, which should involve parents, teachers, and coaches.

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

While expression profile of muscle-specific miRNAs following endurance training is well-characterized, information about exercise-induced changes of metabolism-regulating miRNAs is limited, especially in female and junior athletes. Major aim of this study was to examine a set of miRNAs related to mitochondrial function and metabolism in highly professional junior female athletes. The Hungarian National Junior Triathlon Team (n = 4), completed standardized running and cycling sessions. Expression levels of miR-133a, miR-210, miR-494 and miR-127-3p were determined by RT-qPCR in whole blood and serum samples, withdrawn directly before, and after the exercise, and 24 and 48 h later. The expression of miR-494, miR-127-3p and miR-210 showed strong correlation with each other. In serum, nearly significant increment of miR-127-3p levels was detected, that may be a novel biomarker of exercise adaptation. Its expression was significantly higher than that of miR-210. In whole blood, significantly higher miR-210 than miR-494 and miR-127-3p levels were observed. MiRNA expression profile of the youngest athlete was markedly different compared to others. Our results suggest that miRNAs related to mitochondrial function and metabolism are involved in exercise adaptation. The present study may facilitate further research with larger potential participant pools, contributing to improved prevention and treatment of chronic diseases of civilization.

Here, we investigated the mechanisms by which aging-related reductions of the levels of Numb in skeletal muscle fibers contribute to loss of muscle strength and power, two critical features of sarcopenia. Numb is an adaptor protein best known for its critical roles in development, including asymmetric cell division, cell-type specification, and termination of intracellular signaling. Numb expression is reduced in old humans and mice. We previously showed that, in mouse skeletal muscle fibers, Numb is localized to sarcomeres where it is concentrated near triads; conditional inactivation of Numb and a closely related protein Numb -like ( Numbl ) in mouse myofibers caused weakness, disorganization of sarcomeres, and smaller mitochondria with impaired function. Here, we found that a single knockout of Numb in myofibers causes reduction in tetanic force comparable to a double Numb , Numbl knockout. We found by proteomics analysis of protein complexes isolated from C2C12 myotubes by immunoprecipitation using antibodies against Numb that Septin 7 is a potential Numb-binding partner. Septin 7 is a member of the family of GTP-binding proteins that organize into filaments, sheets, and rings, and is considered part of the cytoskeleton. Immunofluorescence evaluation revealed a partial overlap of staining for Numb and Septin 7 in myofibers. Conditional, inducible knockouts of Numb led to disorganization of Septin 7 staining in myofibers. These findings indicate that Septin 7 is a Numb-binding partner and suggest that interactions between Numb and Septin 7 are critical for structural organization of the sarcomere and muscle contractile function.

Piezo1 mechanosensitive cation channels detect mechanical stimuli and convert it into physiological signals. The role of mechanosensitive channels may be especially important in skeletal muscle compared to non-contractile cell types. There is some proof on its role in muscle regeneration and in muscle satellite cell function, but there is still very little known on the effect of the channel on muscle performance and adult muscle calcium homeostasis. Here we analyzed the role of Piezo1 in skeletal muscle by studying the effect of pharmacological activator and inhibitor in mice.

Although hearing impaired people represent a significant group of handicapped people, only a few studies examine their physical activities. This study was performed in the Spring of 2019 in Debrecen, Hungary by recruiting 86 hearing impaired people. Here the frequency and type of their physical activity as well as their motivation was examined. Average age of the subjects was 42.0±16.9 years, 41.9% of them performs regular physical activity. Out of them 54.1% excercises twice a week, the rest even more often. Soccer, jogging, and cycling were the most preferred sports. Percentage of hearing impaired people performing regular physical activity was about the same as it was for people with normal hearing. Reason for motivation – it makes them happy and they feel better due to the physical activity – or staying at home – their health condition limits them and they have little free time – was also similar in both groups. However, 80% of the people with impaired hearing preferred to do physicial activity together other hearing impaired.

Basic leucine zipper (bZIP) transcription factors are crucial components of differentiation, cellular homeostasis and the environmental stress defense of eukaryotes. In this work, we further studied the consequence of gene deletion and overexpression of two bZIP transcription factors, NapA and RsmA, on superoxide production, mitochondrial morphology and hyphal diameter of Aspergillus nidulans . We have found that reactive oxygen species production was influenced by both gene deletion and overexpression of napA under tert -butylhydroperoxide ( t BOOH) elicited oxidative stress. Furthermore, gene expression of napA negatively correlated with mitochondrial volumetric ratio as well as sterigmatocystin production of A. nidulans . High rsmA expression was accompanied with elevated relative superoxide ratio in the second hyphal compartment. A negative correlation between the expression of rsmA and catalase enzyme activity or mitochondrial volumetric ratio was also confirmed by statistical analysis. Hyphal diameter was independent on either rsmA and napA expression as well as 0.2 mM t BOOH treatment.