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Introduction: Skeletal muscle satellite cells (MuSCs or stem cells) play a crucial role in muscle development, maintenance, and regeneration, supporting both hypertrophy and regenerative myogenesis. Syndecans (SDCs) act as communication bridges within the muscle microenvironment, regulating interactions with extracellular matrix components and contributing significantly to tissue repair and inflammation. Specifically, syndecan-4 (SDC4) is involved in muscle regeneration at multiple stages. Methods: This study delves into the emerging challenge of wooden breast (WB) myopathy and its connection with SDC4. Our hypothesis proposes that disruptions in MuSC dynamics through SDC4 contribute to the increased incidence of breast myopathies observed in growing broilers. To test our hypothesis, non-affected and affected broilers were systematically selected, and the characteristics of WB myopathy were studied both in vitro and in vivo. SDC4 overexpression in MuSCs and blocking peptides (BPs) corresponding to the SDC4 ectodomain were used for investigating the role of SDC4 in muscle development and its shedding levels. Results and discussion: In vivo examination of affected muscles revealed smaller fibers and changes in metabolic pathways. In vitro studies unveiled disrupted proliferation of MuSCs in WB myopathy, accompanied by the downregulation of several muscle markers. Investigation of the potential role of SDC4 in the pathogenesis of WB myopathy revealed a decreased tendency in SDC4 gene expression and increased shedding of its ectodomain. Moreover, we showed that SDC4 overexpression is linked to reduced proliferation in MuSCs and affected myogenesis. We detected an impaired proliferation of WB-affected MuSCs, revealing critical insights into the dysfunctional state of these cells in myopathy. Additionally, by treating MuSCs with blocking peptides derived from the SDC4 ectodomain, we identified altered proliferation. Taken together, this work contributes with valuable knowledge on the molecular mechanisms underlying WB myopathy and the role of SDC4 in this chicken myopathy. [ABSTRACT FROM AUTHOR]

Introduction: The skeletal muscle deformity of commercial chickens (Gallus gallus), known as the wooden breast (WB), is associated with fibrotic myopathy of unknown etiology. For future breeding strategies and genetic improvements, it is essential to identify the molecular mechanisms underlying the phenotype. The pathophysiological hallmarks of WB include severe skeletal muscle fibrosis, inflammation, myofiber necrosis, and multifocal degeneration of muscle tissue. The transmembrane proteoglycans syndecans have a wide spectrum of biological functions and are master regulators of tissue homeostasis. They are upregulated and shed (cleaved) as a regulatory mechanism during tissue repair and regeneration. During the last decades, it has become clear that the syndecan family also has critical functions in skeletal muscle growth, however, their potential involvement in WB pathogenesis is unknown. Methods: In this study, we have categorized four groups of WB myopathy in broiler chickens and performed a comprehensive characterization of the molecular and histological profiles of two of them, with a special focus on the role of the syndecans and remodeling of the extracellular matrix (ECM). Results and discussion: Our findings reveal differential expression and shedding of the four syndecan family members and increased matrix metalloproteinase activity. Additionally, we identified alterations in key signaling pathways such as MAPK, AKT, and Wnt. Our work provides novel insights into a deeper understanding of WB pathogenesis and suggests potential therapeutic targets for this condition. [ABSTRACT FROM AUTHOR]

Skeletal muscle function is highly dependent on the ability to regenerate, however, during ageing or disease, the proliferative capacity is reduced, leading to loss of muscle function. We have previously demonstrated the presence of vitamin K2 in bovine skeletal muscles, but whether vitamin K has a role in muscle regulation and function is unknown. In this study, we used primary bovine skeletal muscle cells, cultured in monolayers in vitro, to assess a potential effect of vitamin K2 (MK-4) during myogenesis of muscle cells. Cell viability experiments demonstrate that the amount of ATP produced by the cells was unchanged when MK-4 was added, indicating viable cells. Cytotoxicity analysis show that MK-4 reduced the lactate dehydrogenase (LDH) released into the media, suggesting that MK-4 was beneficial to the muscle cells. Cell migration, proliferation and differentiation was characterised after MK-4 incubation using wound scratch analysis, immunocytochemistry and real-time PCR analysis. Adding MK-4 to the cells led to an increased muscle proliferation, increased gene expression of the myogenic transcription factor myod as well as increased cell migration. In addition, we observed a reduction in the fusion index and relative gene expression of muscle differentiation markers, with fewer complex myotubes formed in MK-4 stimulated cells compared to control cells, indicating that the MK-4 plays a significant role during the early phases of muscle proliferation. Likewise, we see the same pattern for the relative gene expression of collagen 1A, showing increased gene expression in proliferating cells, and reduced expression in differentiating cells. Our results also suggest that MK-4 incubation affect low density lipoprotein receptor-related protein 1 (LRP1) and the low-density lipoprotein receptor (LDLR) with a peak in gene expression after 45 min of MK-4 incubation. Altogether, our experiments show that MK-4 has a positive effect on muscle cell migration and proliferation, which are two important steps during early myogenesis. [ABSTRACT FROM AUTHOR]

Muscle cells undergo changes post-mortem during the process of converting muscle into meat, and this complex process is far from revealed. Recent reports have suggested programmed cell death (apoptosis) to be important in the very early period of converting muscle into meat. The dynamic balance that occurs between anti-apoptotic members, such as Bcl-2, and pro-apoptotic members (Bid, Bim) helps determine whether the cell initiates apoptosis. In this study, we used primary bovine skeletal muscle cells, cultured in monolayers in vitro, to investigate if apoptosis is induced when oxygen is removed from the growth medium. Primary bovine muscle cells were differentiated to form myotubes, and anoxia was induced for 6h. The anoxic conditions significantly increased (P<0.05) the relative gene expression of anti- and pro-apoptotic markers (Aif, Bcl-2, Bid and Bim), and the PARK7 (P<0.05) and Grp75 (Hsp70) protein expressions were transiently increased. The anoxic conditions also led to a loss of mitochondrial membrane potential, which is an early apoptotic event, as well as cytochrome c release from the mitochondria. Finally, reorganization and degradation of cytoskeletal filaments occurred. These results suggest that muscle cells enters apoptosis via the intrinsic pathway rapidly when available oxygen in the muscle diminishes post-mortem. [ABSTRACT FROM AUTHOR]

Recently, two chicken breast fillet abnormalities, termed Wooden Breast (WB) and Spaghetti Meat (SM), have become a challenge for the chicken meat industry. The two abnormalities share some overlapping morphological features, including myofiber necrosis, intramuscular fat deposition, and collagen fibrosis, but display very different textural properties. WB has a hard, rigid surface, while the SM has a soft and stringy surface. Connective tissue is affected in both WB and SM, and accordingly, this study's objective was to investigate the major component of connective tissue, collagen. The collagen structure was compared with normal (NO) fillets using histological methods and Fourier transform infrared (FTIR) microspectroscopy and imaging. The histology analysis demonstrated an increase in the amount of connective tissue in the chicken abnormalities, particularly in the perimysium. The WB displayed a mixture of thin and thick collagen fibers, whereas the collagen fibers in SM were thinner, fewer, and shorter. For both, the collagen fibers were oriented in multiple directions. The FTIR data showed that WB contained more β-sheets than the NO and the SM fillets, whereas SM fillets expressed the lowest mature collagen fibers. This insight into the molecular changes can help to explain the underlying causes of the abnormalities. [ABSTRACT FROM AUTHOR]

Introduction: Skeletal muscle satellite cells (MuSCs or stem cells) play a crucial role in muscle development, maintenance, and regeneration, supporting both hypertrophy and regenerative myogenesis. Syndecans (SDCs) act as communication bridges within the muscle microenvironment, regulating interactions with extracellular matrix components and contributing significantly to tissue repair and inflammation. Specifically, syndecan-4 (SDC4) is involved in muscle regeneration at multiple stages., Methods: This study delves into the emerging challenge of wooden breast (WB) myopathy and its connection with SDC4. Our hypothesis proposes that disruptions in MuSC dynamics through SDC4 contribute to the increased incidence of breast myopathies observed in growing broilers. To test our hypothesis, non-affected and affected broilers were systematically selected, and the characteristics of WB myopathy were studied both in vitro and in vivo . SDC4 overexpression in MuSCs and blocking peptides (BPs) corresponding to the SDC4 ectodomain were used for investigating the role of SDC4 in muscle development and its shedding levels., Results and Discussion: In vivo examination of affected muscles revealed smaller fibers and changes in metabolic pathways. In vitro studies unveiled disrupted proliferation of MuSCs in WB myopathy, accompanied by the downregulation of several muscle markers. Investigation of the potential role of SDC4 in the pathogenesis of WB myopathy revealed a decreased tendency in SDC4 gene expression and increased shedding of its ectodomain. Moreover, we showed that SDC4 overexpression is linked to reduced proliferation in MuSCs and affected myogenesis. We detected an impaired proliferation of WB-affected MuSCs, revealing critical insights into the dysfunctional state of these cells in myopathy. Additionally, by treating MuSCs with blocking peptides derived from the SDC4 ectodomain, we identified altered proliferation. Taken together, this work contributes with valuable knowledge on the molecular mechanisms underlying WB myopathy and the role of SDC4 in this chicken myopathy., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Pejšková, Pisconti, Lunde, Ho, Solberg, Koga, Tengstrand, Carlson, Pedersen and Rønning.)

Introduction: Successful long-term expansion of skeletal muscle satellite cells (MuSCs) on a large scale is fundamental for cultivating animal cells for protein production. Prerequisites for efficient cell expansion include maintaining essential native cell activities such as cell adhesion, migration, proliferation, and differentiation while ensuring consistent reproducibility., Method: This study investigated the growth of bovine MuSC culture using low-volume spinner flasks and a benchtop stirred-tank bioreactor (STR)., Results and Discussion: Our results showed for the first time the expansion of primary MuSCs for 38 days in a bench-top STR run with low initial seeding density and FBS reduction, supported by increased expression of the satellite cell marker PAX7 and reduced expression of differentiation-inducing genes like MYOG, even without adding p38-MAPK inhibitors. Moreover, the cells retained their ability to proliferate, migrate, and differentiate after enzymatic dissociation from the microcarriers. We also showed reproducible results in a separate biological benchtop STR run., Competing Interests: PM and VB were employed by Mosa Meat, BV. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Tzimorotas, Solberg, Andreassen, Moutsatsou, Bodiou, Pedersen and Rønning.)

Background: Extracellular matrix (ECM) remodeling is essential for skeletal muscle development and adaption in response to environmental cues such as exercise and injury. The cell surface proteoglycan syndecan-4 has been reported to be essential for muscle differentiation, but few molecular mechanisms are known. Syndecan-4 -/- mice are unable to regenerate damaged muscle, and display deficient satellite cell activation, proliferation, and differentiation. A reduced myofiber basal lamina has also been reported in syndecan-4 -/- muscle, indicating possible defects in ECM production. To get a better understanding of the underlying molecular mechanisms, we have here investigated the effects of syndecan-4 genetic ablation on molecules involved in ECM remodeling and muscle growth, both under steady state conditions and in response to exercise., Methods: Tibialis anterior (TA) muscles from sedentary and exercised syndecan-4 -/- and WT mice were analyzed by immunohistochemistry, real-time PCR and western blotting., Results: Compared to WT, we found that syndecan-4 -/- mice had reduced body weight, reduced muscle weight, muscle fibers with a smaller cross-sectional area, and reduced expression of myogenic regulatory transcription factors. Sedentary syndecan-4 -/- had also increased mRNA levels of syndecan-2, decorin, collagens, fibromodulin, biglycan, and LOX. Some of these latter ECM components were reduced at protein level, suggesting them to be more susceptible to degradation or less efficiently translated when syndecan-4 is absent. At the protein level, TRPC7 was reduced, whereas activation of the Akt/mTOR/S6K1 and Notch/HES-1 pathways were increased. Finally, although exercise induced upregulation of several of these components in WT, a further upregulation of these molecules was not observed in exercised syndecan-4 -/- mice., Conclusion: Altogether our data suggest an important role of syndecan-4 in muscle development., (Copyright © 2020 Rønning, Carlson, Aronsen, Pisconti, Høst, Lunde, Liland, Sjaastad, Kolset, Christensen and Pedersen.)