Serum-free cultures of C2C12 cells show different muscle phenotypes which can be estimated by metabolic profiling

Inhibitory effects of high extracellular L-glutamate concentrations on skeletal myogenesis

L-glutamate (Glu) is accumulated abundantly in skeletal muscle cells and plays a central role in energy production, amino acid metabolism, and protein synthesis. If intracellular Glu leaks due to plasma membrane fragility or injury, it may adversely affect the surrounding myocytes. In the present study, we examined the effects of high extracellular Glu concentration on skeletal myogenesis. Five mM Glu stimulation decreased the expression of fast-twitch myosin heavy chain isoforms and myogenin, an indicator of C2C12 cell differentiation into myocytes, and inhibited the cell fusion. This stimulation reduced the expression of metabotropic glutamate receptor 5 (mGluR5) and N-methyl-D-aspartate receptor 1 (NMDAR), which are glutamate receptors on the C2C12 plasma membrane. Furthermore, phosphorylation of p38 mitogen-activated protein kinase, myocyte enhancer factor 2A, and cAMP response element binding protein, which are downstream of these Glu receptors, was reduced, and the expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) decreased. Moreover, reduced mGluR5 and NMDAR expression and muscle weight were observed in the tibialis anterior muscle of mice with increased aging markers. These findings provide insights into the molecular mechanisms contributing to age-related muscle fragility and highlight the potential detrimental effects of elevated Glu on muscle health.

Enhancing Viability in Static and Perfused 3D Tissue Constructs Using Sacrificial Gelatin Microparticles

Current limitations in engineered tissues arise from the inability to provide sufficient nutrients to cells deep within constructs, restricting their viability. This study focuses on enhancing diffusion by creating a microporous microenvironment using gelatin microparticles within collagen scaffolds. By leveraging the FRESH (Freeform Reversible Embedding of Suspended Hydrogels) 3D bioprinting technique, gelatin microparticles are utilized both as a support material and as a thermoresponsive porogen to establish interconnected pores. The results indicate that scaffolds with 75% porosity significantly increase diffusion rates and cell viability, extending beyond the conventional ∼200 μm limit. Additionally, integrating vascular-like channels with porous scaffolds and applying perfusion improved nutrient transport, leading to enhanced cell survival in larger constructs. This combination of microporosity and perfusion represents a promising approach to create thicker tissues without necrotic regions, potentially paving the way for scalable tissue engineering applications. The findings suggest that optimizing pore sizes and scaffold perfusion can bridge the gap between rapid tissue formation and slower vascularization processes, enabling the future development of functional tissue constructs at clinically relevant scales.

Lycium barbarum polysaccharide mitigates high-fat-diet-induced skeletal muscle atrophy by promoting AMPK/PINK1/Parkin-mediated mitophagy

Sarcopenic obesity (SO) defined as the coexistence of obesity and sarcopenia. While the anti-obesity effects of Lycium barbarum polysaccharide (LBP), the main component of L. barbarum extract, are known, its efficacy against SO remains unexplored. Consequently, we aimed to investigate the therapeutic effects of LBP on SO and the elucidate the underlying mechanisms. Our results revealed that LBP administration decreased obesity-related factors, and increased muscle-related factors in mice fed a high-fat diet (HFD). LBP administration ameliorated PA- and HFD-induced hyperglycaemia by modulating IRS-1 and GLUT-4 levels while also mitigating the ectopic fat deposition. Furthermore, our results demonstrated that LBP can mitigate mitochondrial structural abnormalities and dysfunction-characterized by increased mitochondrial membrane potential and ATP levels, reduced reactive oxygen species levels-through the activation of mitophagy. However, these beneficial effects of LBP on skeletal muscle were negated by AMPK inhibitor and siRNA knockdown of Parkin expression. Taken together, our findings indicate that LBP may effectively modulate glucose and lipid metabolism while ameliorating skeletal muscle atrophy via the activation of the AMPK/PINK1/Parkin-mediated mitophagy pathway, thereby repairing the mitochondrial structure and function. Consequently, LBP emerges as a promising therapeutic candidate for addressing obesity-related impacts on skeletal muscle.

Myokines as potential mediators of changes in glucose homeostasis and muscle mass after bariatric surgery

Myokines are bioactive peptides released by skeletal muscle. Myokines exert auto-, para-, or endocrine effects, enabling them to regulate many aspects of metabolism in various tissues. However, the contribution of myokines to the dramatic changes in glucose homeostasis and muscle mass induced by bariatric surgery has not been established. Our review highlights that myokines such as brain-derived neurotrophic factor (BDNF), meteorin-like protein (Metrnl), secreted protein acidic and rich in cysteine (SPARC), apelin (APLN) and myostatin (MSTN) may mediate changes in glucose homeostasis and muscle mass after bariatric surgery. Our review also identifies myonectin as an interesting candidate for future studies, as this myokine may regulate lipid metabolism and muscle mass after bariatric surgery. These myokines may provide novel therapeutic targets and biomarkers for obesity, type 2 diabetes and sarcopenia.

Hyaluronic Acid-Coated Melt Electrowritten Scaffolds Promote Myoblast Attachment, Alignment, and Differentiation

Purpose

In muscle tissues, anisotropic cell alignment is essential for optimal muscle fiber development and function. Biomaterials for muscle tissue engineering must guide cellular alignment while supporting cell proliferation and myogenic differentiation.

Methods

Here, we describe the fabrication of a tissue-engineered construct consisting of a scaffold of aligned poly(ε-caprolactone) (PCL) microfibers coated in a dynamic covalent hydrazone crosslinked hyaluronic acid (HA) hydrogel to support myoblast attachment, alignment, and differentiation. Norbornene modification of HA further enabled functionalization with fibronectin-derived arginine-glycine-aspartic acid (RGD) peptide. Scaffolds were fabricated using melt electrowriting (MEW), a three-dimensional (3D)-printing technique that uses stabilization of fluid columns to produce precisely aligned polymeric microfibers. We evaluated scaffolds with fiber diameters of 10 μm, 20 μm, and 30 μm of non-coated, HA-coated, and HA-RGD-coated MEW scaffolds through immunocytochemistry and creatine kinase activity assays.

Results

HA-coated and HA-RGD-coated scaffolds showed increased cellular attachment of C2C12 mouse skeletal myoblasts on all fiber diameters compared to non-coated scaffolds, with HA-RGD-coated scaffolds demonstrating the highest cell attachment. All scaffolds supported cellular alignment along the fibers. Cells differentiated on scaffolds showed anisotropic alignment with increased myotube formation on HA-RGD-coated scaffolds as seen by myosin heavy chain (MHC) staining. Highest creatine kinase (CK) activity on day 5 signified the successful differentiation of C2C12 cells into mature myotubes.

Conclusion

This unique combination of tunable biophysical and biochemical cues enables the creation of a biomimetic tissue engineered scaffold, providing a platform for new therapeutic approaches for muscle regeneration.

The role of primary cilia in myoblast proliferation and cell cycle regulation during myogenesis

The process of mammalian myogenesis is fundamental to understanding muscle development and holds broad relevance across multiple fields, from developmental biology to regenerative medicine. This review highlights two key aspects: myoblast proliferation and the role of cilia in this process. Myoblasts, as muscle precursor cells, must undergo tightly regulated cycles of proliferation and differentiation to ensure proper muscle growth and function. Recent research has uncovered an essential role for primary cilia, hair-like sensory organelles on the cell surface, in modulating signaling pathways crucial to myogenesis. Cilium-mediated signaling appears to regulate various stages of myogenesis, including the control of myoblast differentiation. Furthermore, primary cilia undergo multiple cycles of formation and disassembly during myogenesis, presumably enabling detailed, context-dependent regulation of their functions. In particular, the regulation of myoblast proliferation through cell cycle control by primary cilia is an important topic that requires further investigation. By examining the interactions between primary cilia and myoblasts, this review aims to provide new insights into the molecular and cellular mechanisms driving muscle development, with potential applications for understanding muscle-related diseases and advancing therapeutic strategies. Additionally, advancements in imaging and image analysis technologies have become indispensable for studying these processes at the cellular level. This review also addresses these technological advancements and current challenges.Key words: myogenesis, myoblast, proliferation, cilia, imaging.

Cutting-Edge Technologies of Meat Analogs: A Review

This study was conducted to investigate the recent research trends of alternative protein foods being developed to replace traditional livestock foods and thus determine the current state of the technology and the potential for industrialization. The results of this study showed that the technology related to cultured meat has not yet reached industrialization. However, serum-free media development, technologies to improve culture efficiency, and technologies to improve taste and flavor are being researched. In addition, the research on improving the production efficiency of cultured meat is increasingly expanding from using muscle satellite cells obtained from animal muscles to research on cell lines or immortalized cell lines. Edible insect-derived proteins have a wide range of food applications, and researchers are actively working on utilizing their functional properties. Plant-derived protein materials are also being studied to improve the flavor and texture of plant-based meat products to make them more similar to traditional livestock foods, as well as to remove allergens. In conclusion, despite ongoing technological development, the industrialization of cultured meat is expected to take some time. There is a growing body of research on the types, functionalities, extraction, and texturizing technologies of plant-derived, mycoprotein, or insect-derived ingredients for formulating meat alternative products, and it is expected that improved products will continue to enter the market. Although animal product substitutes are not expected to significantly replace traditional livestock products, continuous improvement research will contribute to the expansion of the alternative protein food market.

Establishment and characterization of the Cuvier's beaked whale (Ziphius cavirostris) myogenic cell line

In this study we present the first in vitro model based on a muscle-derived cell line from a male Cuvier's Beaked whale stranded along the Italian coastline. In the myogenic cell line at T0 stage we performed the growth rate assay, the karyotyping, the CBA chromosome banding, G banding, nucleolar organizer regions and telomere analysis and immunocytochemical analysis. The cell characterization at the T2 and T4 stage included: assessment of fusion index, the ultrastructural analysis and immunocytochemical analysis. The population doubling time was determined to be ∼54 h. The cell fusion index at the T2 stage was 8.2 +/- 5 %, at the T4 stage increased at index 28 +/- 10 %. The karyotype analysis revealed a 2n = 42, XY, two pairs of nucleolus organizer regions (NORs), characteristic CBA-banding and PNA-telomeric regions by FISH-mapping. The immunocytochemical results revealed that we generated a heterogeneous population of myogenic cells. A cell population express β-actin, myosin and vimentin and a sub-population of cells was desmin-positive. In details, at the T0 stage, both cell populations were undifferentiated mononucleated myoblast. At the T2 and T4 stage, the cells were capable of fusion in elongated multinucleated myotubes, probably resulting from the fusion of the myoblasts. This Cuvier's Beaked whale cell line, represents a new opportunity to better understand the physiological features of the cetacean Ziphius cavirostris myogenic cells. The possibility of setting up culture conditions that mimic the in vivo microenvironment, strengthen the importance of in vitro models for toxicological studies investigating water pollutants effects on cells.

Exploring cost reduction strategies for serum free media development

Cultivated meat production offers solutions in addressing global food security and sustainability challenges. However, serum-free media (SFM) used in cultivating the cells are expensive, contributing to at least 50% of variable operating costs. This review explores technologies for cost-effective SFM, focusing on reducing cost from using growth factors and recombinant proteins, using affordable raw materials for basal media, and implementing cost-saving measures like media recycling and reducing waste build-up.

Exchange of free and capsule conjugated cyanine dyes between cells

Fluorescent dyes (especially photoconvertible cyanine dyes) are traditionally used as labels to study single-cell or cell-group interactions and migration. Nevertheless, their application has some disadvantages, such as cytotoxicity and dye transfer between cells during co-cultivation. The latter can lead to serious distortions in research results. At the same time, the lack of a worthy alternative explains the reasons for hushing up this serious problem. Here, we propose low-cytotoxicity encapsulated forms of cyanine 3.5 and cyanine 5.5, enabling intracellular uptake and facilitating single-cell labeling and tracking as an efficient alternative to existing staining. Only 16.9% of myoblasts (C2C12) exchanged encapsulated dyes compared with 99.7% of cells that exchanged the free form of the same dyes. Simultaneous application of several encapsulated cyanine dyes, combined with the possibility of photoconversion, provides multi-color coding of individual cells. Encapsulation of cyanine dyes allows reliable labeling and reduces the transfer of the dyes between cells.

An efficient serum-free medium for ex vivo expansion of myoblasts from Larimichthys crocea for cultured meat production

The large-scale production of cultured meat has been restricted by high cost of serum, batch difference and unclear composition, thus it is important to develop serum-free media for cell growth. Here we obtained a serum-free medium (SFM), which was suitable for ex vivo culturing of myoblasts from larimichthys crocea. It offered simple composition and high effectiveness that supporting myoblast attachment, expansion and differentiation. Our findings revealed that the optimal SFM consisted of DMEM/F12 base medium, 5 mg/mL bovine serum albumin (BSA), 20 mmol HEPES, 1 % penicillin/streptomycin mixture (PS) and the exogenous additive hydrocortisone. The living cells of SFM could occupy about 65 % of the serum-containing medium (SM). Additionally, differentiation assays showed that myoblasts cultured without serum still differentiated into more muscle tubes, with a higher fusion index than those cultured with serum. Finally, transcriptome sequencing was conducted to demonstrate that hydrocortisone might act as a ligand binding to G protein-coupled receptors, triggering the downstream PI3K/AKT signaling pathway and leading to cell proliferation. Our findings will provide a basis for large-scale cell expansion and cell culture meat production in the future.

The important role of cellular mechanical microenvironment in engineering structured cultivated meat: Recent advances

Cultivated meat (CM) provides a potential solution to meet the rising demand for eco-friendly meat supply systems. Recent efforts focus on producing CM that replicates the architecture and textural toughness of natural skeletal muscle. Significance of the regulated role of cellular microenvironment in myogenesis has been reinforced by the substantial influence of mechanical cues in mediating the muscle tissue organization. However, the formation of structured CM has not been adequately described in context of the mechanical microenvironment. In this review, we provide an updated understanding of the myogenesis process within mechanically dynamic three-dimensional microenvironments, discuss the effects of environmental mechanical factors on muscle tissue regeneration and how cell mechanics respond to the mechanical condition, and further highlight the role of mechanical cues as important references in constructing a sustainable Hydrocolloids-based biomaterials for CM engineering. These findings help to overcome current limitations in improving the textural properties of CM.

Kaempferol-Enhanced Migration and Differentiation of C2C12 Myoblasts via ITG1B/FAK/Paxillin and IGF1R/AKT/mTOR Signaling Pathways

SCOPE

Kaempferol (KMP), a bioactive flavonoid compound found in fruits and vegetables, contributes to human health in many ways but little is known about its relationship with muscle mass. The effect of KMP on C2C12 myoblast differentiation and the mechanisms that might underlie that effect are studied.

METHODS AND RESULTS

This study finds that KMP (1, 10 µM) increases the migration and differentiation of C2C12 myoblasts in vitro. Studying the possible mechanism underlying its effect on migration, the study finds that KMP activates Integrin Subunit Beta 1 (ITGB1) in C2C12 myoblasts, increasing p-FAK (Tyr398) and its downstream cell division cycle 42 (CDC42), a protein previously associated with cell migration. Regarding differentiation, KMP upregulates the expression of myosin heavy chain (MHC) and activates IGF1/AKT/mTOR/P70S6K. Interestingly, pretreatment with an AKT inhibitor (LY294002) and siRNA knockdown of IGF1R leads to a decrease in cell differentiation, suggesting that IGF1/AKT activation is required for KMP to induce C2C12 myoblast differentiation.

CONCLUSION

Together, the findings suggest that KMP enhances the migration and differentiation of C2C12 myoblasts through the ITG1B/FAK/paxillin and IGF1R/AKT/mTOR pathways. Thus, KMP supplementation might potentially be used to prevent or delay age-related loss of muscle mass and help maintain muscle health.

Decellularised plant scaffolds facilitate porcine skeletal muscle tissue engineering for cultivated meat biomanufacturing

Cultivated meat (CM) offers a sustainable and ethical alternative to conventional animal agriculture, involving cell maturation in a controlled environment. To emulate the structural complexity of traditional meat, the development of animal-free and edible scaffolds is crucial, providing vital physical and biological support during tissue development. The aligned vascular bundles of the decellularised asparagus scaffold were selected to facilitate the attachment and alignment of murine myoblasts (C2C12) and porcine adipose-derived mesenchymal stem cells (pADMSCs). Muscle differentiation was assessed through immunofluorescence staining with muscle markers, including Myosin heavy chain (MHC), Myogenin (MYOG), and Desmin. The metabolic activity of Creatine Kinase in C2C12 differentiated cells significantly increased compared to proliferated cells. Quantitative PCR analysis revealed a significant increase in Myosin Heavy Polypeptide 1 (MYH1) and MYOG expression compared to Day 0. These results highlight the application of decellularised plant scaffold (DPS) as a promising, edible material conducive to cell attachment, proliferation, and differentiation into muscle tissue. To create a CM prototype with biological mimicry, pADMSC-derived muscle and fat cells were also co-cultured on the same scaffold. The co-culture was confirmed through immunofluorescence staining of muscle markers and LipidTOX staining, revealing distinct muscle fibres and adipocytes containing lipid droplets respectively. Texture profile analysis conducted on uncooked CM prototypes and pork loin showed no significant differences in textural values. However, the pan-fried CM prototype differed significantly in hardness and chewiness compared to pork loin. Understanding the scaffolds' textural profile enhances our insight into the potential sensory attributes of CM products. DPS shows potential for advancing CM biomanufacturing.

Nuclear Phospholipids and Signaling: An Update of the Story

In the last three decades, the presence of phospholipids in the nucleus has been shown and thoroughly investigated. A considerable amount of interest has been raised about nuclear inositol lipids, mainly because of their role in signaling acting. Here, we review the main issues of nuclear phospholipid localization and the role of nuclear inositol lipids and their related enzymes in cellular signaling, both in physiological and pathological conditions.

Gromwell (Lithospermum erythrorhizon) Attenuates High-Fat-Induced Skeletal Muscle Wasting by Increasing Protein Synthesis and Mitochondrial Biogenesis

Gromwell (Lithospermum erythrorhizon, LE) can mitigate obesity-induced skeletal muscle atrophy in C2C12 myotubes and high-fat diet (HFD)-induced obese mice. The purpose of this study was to investigate the anti-skeletal muscle atrophy effects of LE and the underlying molecular mechanism. C2C12 myotubes were pretreated with LE or shikonin, and active component of LE, for 24 h and then treated with 500 μM palmitic acid (PA) for an additional 24 h. Additionally, mice were fed a HFD for 8 weeks to induced obesity, and then fed either the same diet or a version containing 0.25% LE for 10 weeks. LE attenuated PA-induced myotubes atrophy in differentiated C2C12 myotubes. The supplementation of LE to obese mice significantly increased skeletal muscle weight, lean body mass, muscle strength, and exercise performance compared with those in the HFD group. LE supplementation not only suppressed obesity-induced skeletal muscle lipid accumulation, but also downregulated TNF-α and atrophic genes. LE increased protein synthesis in the skeletal muscle via the mTOR pathway. We observed LE induced increase of mitochondrial biogenesis and upregulation of oxidative phosphorylation related genes in the skeletal muscles. Furthermore, LE increased the expression of peroxisome proliferator-activated receptor-gamma coactivator-1 alpha and the phosphorylation of adenosine monophosphate-activated protein kinase. Collectively, LE may be useful in ameliorating the detrimental effects of obesity-induced skeletal muscle atrophy through the increase of protein synthesis and mitochondrial biogenesis of skeletal muscle.

FoxP1 Represses MEF2A in Striated Muscle

Myocyte enhancer factor 2 (MEF2) proteins are involved in multiple developmental, physiological, and pathological processes in vertebrates. Protein-protein interactions underlie the plethora of biological processes impacted by MEF2A, necessitating a detailed characterization of the MEF2A interactome. A nanobody based affinity-purification/mass spectrometry strategy was employed to achieve this goal. Specifically, the MEF2A protein complexes were captured from myogenic lysates using a GFP-tagged MEF2A protein immobilized with a GBP-nanobody followed by LC-MS/MS proteomic analysis to identify MEF2A interactors. After bioinformatic analysis, we further characterized the interaction of MEF2A with a transcriptional repressor, FOXP1. FOXP1 coprecipitated with MEF2A in proliferating myogenic cells which diminished upon differentiation (myotube formation). Ectopic expression of FOXP1 inhibited MEF2A driven myogenic reporter genes (derived from the creatine kinase muscle and myogenin genes) and delayed induction of endogenous myogenin during differentiation. Conversely, FOXP1 depletion enhanced MEF2A transactivation properties and myogenin expression. The FoxP1:MEF2A interaction is also preserved in cardiomyocytes and FoxP1 depletion enhanced cardiomyocyte hypertrophy. FOXP1 prevented MEF2A phosphorylation and activation by the p38MAPK pathway. Overall, these data implicate FOXP1 in restricting MEF2A function in order to avoid premature differentiation in myogenic progenitors and also to possibly prevent re-activation of embryonic gene expression in cardiomyocyte hypertrophy.

Generation of Mature Toxoplasma gondii Bradyzoites in Human Immortalized Myogenic KD3 Cells

Toxoplasma gondii is a zoonotic protozoan parasite and one of the most successful foodborne pathogens. Upon infection and dissemination, the parasites convert into the persisting, chronic form called bradyzoites, which reside within cysts in muscle and brain tissue. Despite their importance, bradyzoites remain difficult to investigate directly, owing to limited in vitro models. In addition, the need for new drugs targeting the chronic stage, which is underlined by the lack of eradicating treatment options, remains difficult to address since in vitro access to drug-tolerant bradyzoites remains limited. We recently published the use of a human myotube-based bradyzoite cell culture system and demonstrated its applicability to investigate the biology of T. gondii bradyzoites. Encysted parasites can be functionally matured during long-term cultivation in these immortalized cells and possess many in vivo-like features, including pepsin resistance, oral infectivity, and antifolate resistance. In addition, the system is scalable, enabling experimental approaches that rely on large numbers, such as metabolomics. In short, we detail the cultivation of terminally differentiated human myotubes and their subsequent infection with tachyzoites, which then mature to encysted bradyzoites within four weeks at ambient CO2 levels. We also discuss critical aspects of the procedure and suggest improvements. Key features • This protocol describes a scalable human myotube-based in vitro system capable of generating encysted bradyzoites featuring in vivo hallmarks. • Bradyzoite differentiation is facilitated through CO2 depletion but without additional artificial stress factors like alkaline pH. • Functional maturation occurs over four weeks.

Role of Dgat2 in Glucose Uptake and Fatty Acid Metabolism in C2C12 Skeletal Myotubes

Acyl-coenzyme A (CoA):diacylglycerol acyltransferase 2 (DGAT2) catalyzes the last stage of triacylglycerol (TAG) synthesis, a process that forms ester bonds with diacylglycerols (DAG) and fatty acyl-CoA substrates. The enzymatic role of Dgat2 has been studied in various biological species. Still, the full description of how Dgat2 channels fatty acids in skeletal myocytes and the consequence thereof in glucose uptake have yet to be well established. Therefore, this study explored the mediating role of Dgat2 in glucose uptake and fatty acid partitioning under short interfering ribonucleic acid (siRNA)-mediated Dgat2 knockdown conditions. Cells transfected with Dgat2 siRNA downregulated glucose transporter type 4 (Glut4) messenger RNA (mRNA) expression and decreased the cellular uptake of [1-14C]-labeled 2-deoxyglucose up to 24.3% (p < 0.05). Suppression of Dgat2 deteriorated insulininduced Akt phosphorylation. Dgat2 siRNA reduced [1-14C]-labeled oleic acid incorporation into TAG, but increased the level of [1-14C]-labeled free fatty acids at 3 h after initial fatty acid loading. In an experiment of chasing radioisotope-labeled fatty acids, Dgat2 suppression augmented the level of cellular free fatty acids. It decreased the level of re-esterification of free fatty acids to TAG by 67.6% during the chase period, and the remaining pulses of phospholipids and cholesteryl esters were decreased by 34.5% and 61%, respectively. Incorporating labeled fatty acids into beta-oxidation products increased in Dgat2 siRNA transfected cells without gene expression involving fatty acid oxidation. These results indicate that Dgat2 has regulatory function in glucose uptake, possibly through the reaction of TAG with endogenously released or recycled fatty acids.

Current technologies, regulation, and future perspective of animal product analogs - A review

The purpose of this study was to investigate the recent development of meat analog, industrialization, and the related legal changes worldwide. Summarizing the current status of the industrialization of meat analog, studies on plant-based meat, mycoprotein, and edible insects were mainly conducted to investigate their sensory properties (texture, taste, flavor, and color resembling meat), nutritional and safety evaluations, acquisition method of meat alternatives, and commercialization. Cultured meat is mainly studied for developing muscle satellite cell acquisition and support techniques or materials for the formation of structures. However, these technologies have not reached the level for active industrialization. Even though there are differences in the food categories and labeling between countries, it is common to cause confusion or to relay false information to consumers; therefore, it is important to provide accurate information. In this study, there were some differences in the food classification and food definition (labeling) contents for each country and state depending on the product shape or form, raw materials, and ingredients. Therefore, this study can provide information about the current research available on meat alternatives, improve regulation, and clarify laws related to the meat analog industry, which can potentially grow alongside the livestock industry.

Indian Ornamental Tarantula (Poecilotheria regalis) Venom Affects Myoblast Function and Causes Skeletal Muscle Damage

Envenomation by the Indian ornamental tarantula (Poecilotheria regalis) is medically relevant to humans, both in its native India and worldwide, where they are kept as pets. Muscle-related symptoms such as cramps and pain are commonly reported in humans following envenomation by this species. There is no specific treatment, including antivenom, for its envenomation. Moreover, the scientific knowledge of the impact of this venom on skeletal muscle function is highly limited. Therefore, we carried out this study to better understand the myotoxic properties of Poecilotheria regalis venom by determining its effects in cultured myoblasts and in the tibialis anterior muscle in mice. While there was no effect found on undifferentiated myoblasts, the venom affected differentiated multinucleated myotubes resulting in the reduction of fusion and atrophy of myotubes. Similarly, intramuscular administration of this venom in the tibialis anterior muscle in mice resulted in extensive muscle damage on day 5. However, by day 10, the regeneration was evident, and the regeneration process continued until day 20. Nevertheless, some tissue abnormalities including reduced dystrophin expression and microthrombi presence were observed on day 20. Overall, this study demonstrates the ability of this venom to induce significant muscle damage and affect its regeneration in the early stages. These data provide novel mechanistic insights into this venom-induced muscle damage and guide future studies to isolate and characterise individual toxic component(s) that induce muscle damage and their significance in developing better therapeutics.

Repurposing biomedical muscle tissue engineering for cellular agriculture: challenges and opportunities

Cellular agriculture is an emerging field rooted in engineering meat-mimicking cell-laden structures using tissue engineering practices that have been developed for biomedical applications, including regenerative medicine. Research and industrial efforts are focused on reducing the cost and improving the throughput of cultivated meat (CM) production using these conventional practices. Due to key differences in the goals of muscle tissue engineering for biomedical versus food applications, conventional strategies may not be economically and technologically viable or socially acceptable. In this review, these two fields are critically compared, and the limitations of biomedical tissue engineering practices in achieving the important requirements of food production are discussed. Additionally, the possible solutions and the most promising biomanufacturing strategies for cellular agriculture are highlighted.

The ensured proliferative capacity of myoblast in serum-reduced conditions with Methyl-β-cyclodextrin

To produce muscle fibers for cultured meat on a large scale, it is important to expand myoblasts in a serum-reduced or serum-free medium to avoid cost, ethical, and environmental issues. Myoblasts such as C2C12 cells differentiate quickly into myotubes and lose their ability to proliferate when the serum-rich medium is replaced with a serum-reduced medium. This study demonstrates that Methyl-β-cyclodextrin (MβCD), a starch-derived agent that depletes cholesterol, can inhibit further differentiation of myoblasts at the MyoD-positive stage by reducing plasma membrane cholesterol on C2C12 cells and primary cultured chick muscle cells. Furthermore, MβCD efficiently blocks cholesterol-dependent apoptotic cell death of myoblasts, which is one of the mechanisms by which it inhibits the differentiation of C2C12 myoblast cells, as dead cells of myoblast are necessary for the fusion of adjacent myoblasts during the differentiation process into myotubes. Importantly, MβCD maintains the proliferative capacity of myoblasts only under differentiation conditions with a serum-reduced medium, suggesting that its mitogenic effect is due to its inhibitory effect on myoblast differentiation into myotube. In conclusion, this study provides significant insights into ensuring the proliferative capacity of myoblasts in a future serum-free condition for cultured meat production.

Serum-free alginate-C2C12 cells microcapsule as a model of alternative animal protein source

Due to the climate change crisis, and environmental impacts of the traditional meat sector, the production of artificial animal protein based on in vitro cell culture technology is proposed as an alternative. Furthermore, since traditional animal serum-supplemented cultures pose scientific challenges such as batch variation and contamination risks, artificial animal protein cultures are currently in urgent need of not only serum-free cultures, but also microcarrier culture systems for scalability. However, serum-free microcarrier-based culture system for the differentiation of muscle cells is not available to date. Therefore, we established an edible alginate microcapsules culture system for the differentiation of C2C12 cells in serum-free conditions. Furthermore, metabolites related to central carbon metabolism were profiled based on targeted metabolomics using mass spectrometry. The C2C12 cells cultured in alginate microcapsules displayed high viability throughout 7 days and successfully differentiated within 4 days in serum and serum-free cultures except for AIM-V cultures, which was confirmed by CK activity and MHC immunostaining. Lastly, to the best of our knowledge, this is the first report to compare metabolite profiles between monolayer and alginate microcapsule culture systems. Alginate microcapsule culture showed higher levels of intracellular glycolysis and TCA cycle intermediates, lactate, and the contribution of essential amino acids compared to the monolayer culture. We believe our serum-free alginate microcapsule culture system is adaptable to different species of muscle cells and contributes to future food technology as a proof of concept for the scalability of alternative animal protein source production.

Polygonatum cyrtonema Hua Polysaccharide Alleviates Fatigue by Modulating Osteocalcin-Mediated Crosstalk between Bones and Muscles

Osteocalcin was reported to regulate muscle energy metabolism, thus fighting fatigue during exercise. The current work aimed to investigate the anti-fatigue effect and the underlying mechanism of a homogeneous polysaccharide (PCPY-1) from Polgonatum cyrtonema after structure characterization. In the exhaustive swimming mouse model and the co-culture system of BMSCs/C2C12 cells, PCPY-1 significantly stimulated BMSC differentiation into osteoblasts as determined by ALP activity, matrix mineralization, and the protein expressions of osteogenic markers BMP-2, phosphor-Smad1, RUNX2, and osteocalcin. Meanwhile, PCPY-1 remarkably enhanced myoblast energy metabolism by upregulating osteocalcin release and GPRC6A protein expression; the phosphorylation levels of CREB and HSL; the mRNA levels of GLUT4, CD36, FATP1, and CPT1B; and ATP production in vitro and in vivo. Accordingly, PCPY-1 exhibited good anti-fatigue capacity in mice as confirmed by fatigue-related indicators. Our findings indicated PCPY-1 could enhance osteocalcin-mediated communication between bones and muscles, which was conducive to muscle energy metabolism and ATP generation, thus alleviating fatigue in exhausted swimming mice.

Zebrafish Models for Skeletal Muscle Senescence: Lessons from Cell Cultures and Rodent Models

Human life expectancy has markedly increased over the past hundred years. Consequently, the percentage of elderly people is increasing. Aging and sarcopenic changes in skeletal muscles not only reduce locomotor activities in elderly people but also increase the chance of trauma, such as bone fractures, and the incidence of other diseases, such as metabolic syndrome, due to reduced physical activity. Exercise therapy is currently the only treatment and prevention approach for skeletal muscle aging. In this review, we aimed to summarize the strategies for modeling skeletal muscle senescence in cell cultures and rodents and provide future perspectives based on zebrafish models. In cell cultures, in addition to myoblast proliferation and myotube differentiation, senescence induction into differentiated myotubes is also promising. In rodents, several models have been reported that reflect the skeletal muscle aging phenotype or parts of it, including the accelerated aging models. Although there are fewer models of skeletal muscle aging in zebrafish than in mice, various models have been reported in recent years with the development of CRISPR/Cas9 technology, and further advancements in the field using zebrafish models are expected in the future.

H3K18 lactylation marks tissue-specific active enhancers

Background

Histone lactylation has been recently described as a novel histone post-translational modification linking cellular metabolism to epigenetic regulation.

Results

Given the expected relevance of this modification and current limited knowledge of its function, we generate genome-wide datasets of H3K18la distribution in various in vitro and in vivo samples, including mouse embryonic stem cells, macrophages, adipocytes, and mouse and human skeletal muscle. We compare them to profiles of well-established histone modifications and gene expression patterns. Supervised and unsupervised bioinformatics analysis shows that global H3K18la distribution resembles H3K27ac, although we also find notable differences. H3K18la marks active CpG island-containing promoters of highly expressed genes across most tissues assessed, including many housekeeping genes, and positively correlates with H3K27ac and H3K4me3 as well as with gene expression. In addition, H3K18la is enriched at active enhancers that lie in proximity to genes that are functionally important for the respective tissue.

Conclusions

Overall, our data suggests that H3K18la is not only a marker for active promoters, but also a mark of tissue specific active enhancers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13059-022-02775-y.

Spent media analysis suggests cultivated meat media will require species and cell type optimization

Cell culture media design is perhaps the most significant hurdle currently facing the commercialization of cultivated meat as an alternative source of dietary protein. Since media optimization for a specific culture system requires a significant amount of effort and investment, a major question remaining is whether media formulations can be easily shared across multiple production schemes for cells of different species and lineages. Here, we perform spent medium analysis to compare the specific nutrient utilization of primary embryonic chicken muscle precursor cells and fibroblasts to the murine C2C12 myoblast cell line. We demonstrate that these related cell types have significantly different nutrient utilization patterns collectively and on a per-cell basis, and that many components of conventional media do not appear to be depleted by the cells. Namely, glucose was not consumed as rapidly nor as completely by the chicken muscle precursors compared to other cells overall, and there were significant differences in specific consumption rates for several other key nutrients over the first day of culture. Ultimately, our results indicate that no one medium is likely ideal and cost effective to culture multiple cell types and that novel methods to streamline media optimization efforts will be important for the industry to develop.

The impact of serum-free culture on HEK293 cells: From the establishment of suspension and adherent serum-free adaptation cultures to the investigation of growth and metabolic profiles

Serum-free cultures are preferred for application in clinical cell therapy and facilitate the purification processes of bioproducts, such as vaccines and recombinant proteins. It can replace traditional cell culture - eliminating potential issues posed by animal-derived serum supplementation, such as lot to lot variation and risks of pathogen infection from the host animal. However, adapting cells to serum-free conditions can be challenging and time-consuming, and is cell line and medium dependent. In addition, the knowledge of the impact of serum-free culture on cellular metabolism is limited. Herein, we successfully established serum-free suspension and adherent cultures through two adaptation procedures for HEK293 cells in serum-free Freestyle 293 medium. Furthermore, growth kinetics and intracellular metabolic profiles related to central carbon metabolism were investigated. The entire adaptation procedure took 1 month, and high cell viability (>90%) was maintained throughout. The serum-free adherent culture showed the best growth performance, measured as the highest cell density and growth rate. The largest differences in metabolic profiles were observed between culture modes (adherent vs. suspension), followed by culture medium condition (control growth medium vs. serum-free medium). Metabolic differences related to the adaptation procedures were only seen in suspension cultures. Interestingly, the intracellular itaconate concentration was significantly higher in suspension cells compared to adherent cells. Furthermore, when the cells back-adapted from serum-free to serum-supplemented control medium, their metabolic profiles were immediately reversed, highlighting the effect of extracellular components on metabolic phenotype. This study provides strategies for efficient serum-free cultivation and deeper insights into the cellular responses related to growth and metabolism responses to diverse culture conditions.

PDIA4, a new endoplasmic reticulum stress protein, modulates insulin resistance and inflammation in skeletal muscle

INTRODUCTION

Endoplasmic reticulum (ER) stress has emerged as a key player in insulin resistance (IR) progression in skeletal muscle. Recent reports revealed that ER stress-induced the expression of protein disulfide isomerase family a member 4 (PDIA4), which may be involved in IR-related diseases. A previous study showed that metformin modulated ER stress-induced IR. However, it remained unclear whether metformin alleviated IR by regulating PDIA4 expression in skeletal muscle.

METHODS

Herein, we used palmitate-induced IR in C2C12 cells and a high-fat diet-induced IR mouse model to document the relations between metformin, IR, and PDIA4.

RESULTS

In C2C12 cells, palmitate-induced IR increased inflammatory cytokines and PDIA4 expression. Besides, knocking down PDIA4 decreased palmitate-induced IR and inflammation in C2C12 cells. Furthermore, metformin modulated PDIA4 expression and alleviated IR both in vitro and in vivo. In addition, serum PDIA4 concentrations are associated with IR and inflammatory cytokines levels in human subjects.

DISCUSSION

Thus, this study is the first to demonstrate that PDIA4 participates in the metformin-induced effects on skeletal muscle IR and indicates that PDIA4 is a potential novel therapeutic target for directly alleviating IR.