Network visualization of genes involved in skeletal muscle myogenesis in livestock animals.

BACKGROUND: Muscle growth post-birth relies on muscle fiber number and size. Myofibre number, metabolic and contractile capacities are established pre-birth during prenatal myogenesis. The aim of this study was to identify genes involved in skeletal muscle development in cattle, sheep, and pigs - livestock. RESULTS: The cattle analysis showed significant differences in 5043 genes during the 135-280 dpc period. In sheep, 444 genes differed significantly during the 70-120 dpc period. Pigs had 905 significantly different genes for the 63-91 dpc period.The biological processes and KEGG pathway enrichment results in each species individually indicated that DEGs in cattle were significantly enriched in regulation of cell proliferation, cell division, focal adhesion, ECM-receptor interaction, and signaling pathways (PI3K-Akt, PPAR, MAPK, AMPK, Ras, Rap1); in sheep - positive regulation of fibroblast proliferation, negative regulation of endothelial cell proliferation, focal adhesion, ECM-receptor interaction, insulin resistance, and signaling pathways (PI3K-Akt, HIF-1, prolactin, Rap1, PPAR); in pigs - regulation of striated muscle tissue development, collagen fibril organization, positive regulation of insulin secretion, focal adhesion, ECM-receptor interaction, and signaling pathways (PPAR, FoxO, HIF-1, AMPK). Among the DEGs common for studied animal species, 45 common genes were identified. Based on these, a protein-protein interaction network was created and three significant modules critical for skeletal muscle myogenesis were found, with the most significant module A containing four recognized hub genes - EGFR, VEGFA, CDH1, and CAV1. Using the miRWALK and TF2DNA databases, miRNAs (bta-miR-2374 and bta-miR-744) and transcription factors (CEBPB, KLF15, RELA, ZNF143, ZBTB48, and REST) associated with hub genes were detected. Analysis of GO term and KEGG pathways showed that such processes are related to myogenesis and associated with module A: positive regulation of MAP kinase activity, vascular endothelial growth factor receptor, insulin-like growth factor binding, focal adhesion, and signaling pathways (PI3K-Akt, HIF-1, Rap1, Ras, MAPK). CONCLUSIONS: The identified genes, common to the prenatal developmental period of skeletal muscle in livestock, are critical for later muscle development, including its growth by hypertrophy. They regulate valuable economic characteristics. Enhancing and breeding animals according to the recognized genes seems essential for breeders to achieve superior gains in high-quality muscle mass.

Identification of Hub Genes and Target miRNAs Crucial for Milk Production in Holstein Friesian Dairy Cattle.

Dairy milk production is a quantitative trait that is controlled by many biological and environmental factors. This study employs a network-driven systems approach and clustering algorithm to uncover deeper insights into its genetic associations. We analyzed the GSE33680 dataset from the GEO database to understand the biological importance of milk production through gene expression and modules. In this study, we employed CytoNCA and ClusterONE plugins within Cytoscape for network analysis. Moreover, miRWalk software was utilized to detect miRNAs, and DAVID was employed to identify gene ontology and pathways. The results revealed 140 up-regulated genes and 312 down-regulated genes. In addition, we have identified 91 influential genes and 47 miRNAs that are closely associated with milk production. Through our examination of the network connecting these genes, we have found significant involvement in important biological processes such as calcium ion transit across cell membranes, the BMP signaling pathway, and the regulation of MAPK cascade. The conclusive network analysis further reveals that GAPDH, KDR, CSF1, PYGM, RET, PPP2CA, GUSB, and PRKCA are closely linked to key pathways essential for governing milk production. Various mechanisms can control these genes, making them valuable for breeding programs aiming to enhance selection indexes.

Does ß-Hydroxy-ß-Methylbutyrate Have Any Potential to Support the Treatment of Duchenne Muscular Dystrophy in Humans and Animals?

Skeletal muscle is the protein reservoir of our body and an important regulator of glucose and lipid homeostasis. The dystrophin gene is the largest gene and has a key role in skeletal muscle construction and function. Mutations in the dystrophin gene cause Duchenne and Becker muscular dystrophy in humans, mice, dogs, and cats. Duchenne muscular dystrophy (DMD) is an X-linked neuromuscular condition causing progressive muscle weakness and premature death. ß-hydroxy ß-methylbutyrate (HMB) prevents deleterious muscle responses under pathological conditions, including tumor and chronic steroid therapy-related muscle losses. The use of HMB as a dietary supplement allows for increasing lean weight gain; has a positive immunostimulatory effect; is associated with decreased mortality; and attenuates sarcopenia in elderly animals and individuals. This study aimed to identify some genes, metabolic pathways, and biological processes which are common for DMD and HMB based on existing literature and then discuss the consequences of that interaction.

Identification of Key Genes and Biological Pathways Associated with Skeletal Muscle Maturation and Hypertrophy in Bos taurus, Ovis aries, and Sus scrofa.

The aim of the current study was to identify the major genes and pathways involved in the process of hypertrophy and skeletal muscle maturation that is common for Bos taurus, Ovis aries, and Sus scrofa species. Gene expression profiles related to Bos taurus, Ovis aries, and Sus scrofa muscle, with accession numbers GSE44030, GSE23563, and GSE38518, respectively, were downloaded from the GEO database. Differentially expressed genes (DEGs) were screened out using the Limma package of R software. Genes with Fold Change > 2 and an adjusted p-value < 0.05 were identified as significantly different between two treatments in each species. Subsequently, gene ontology and pathway enrichment analyses were performed. Moreover, hub genes were detected by creating a protein−protein interaction network (PPI). The results of the analysis in Bos taurus showed that in the period of 280 dpc−3-months old, a total of 1839 genes showed a significant difference. In Ovis aries, however, during the period of 135dpc−2-months old, a total of 486 genes were significantly different. Additionally, in the 91 dpc−adult period, a total of 2949 genes were significantly different in Sus scrofa. The results of the KEGG pathway enrichment analysis and GO function annotation in each species separately revealed that in Bos taurus, DEGs were mainly enriched through skeletal muscle fiber development and skeletal muscle contraction, and the positive regulation of fibroblast proliferation, positive regulation of skeletal muscle fiber development, PPAR signaling pathway, and HIF-1 signaling pathway. In Ovis aries, DEGs were mainly enriched through regulating cell growth, skeletal muscle fiber development, the positive regulation of fibroblast proliferation, skeletal muscle cell differentiation, and the PI3K-Akt signaling, HIF-1 signaling, and Rap1 signaling pathways. In Sus scrofa, DEGs were mainly enriched through regulating striated muscle tissue development, the negative regulation of fibroblast proliferation and myoblast differentiation, and the HIF-1 signaling, AMPK signaling, and PI3K-Akt signaling pathways. Using a Venn diagram, 36 common DEGs were identified between Bos taurus, Ovis aries, and Sus scrofa. A biological pathways analysis of 36 common DEGs in Bos taurus, Ovis aries, and Sus scrofa allowed for the identification of common pathways/biological processes, such as myoblast differentiation, the regulation of muscle cell differentiation, and positive regulation of skeletal muscle fiber development, that orchestrated the development and maturation of skeletal muscle. As a result, hub genes were identified, including PPARGC1A, MYOD1, EPAS1, IGF2, CXCR4, and APOA1, in all examined species. This study provided a better understanding of the relationships between genes and their biological pathways in the skeletal muscle maturation process.

The Intersection of Human and Veterinary Medicine-A Possible Direction towards the Improvement of Cell Therapy Protocols in the Treatment of Perianal Fistulas.

The effective treatment of perianal fistulizing Crohn's disease is still a challenge. Local administration of mesenchymal stromal cells (MSCs) is becoming a part of accepted treatment options. However, as a fledgling technique, it still can be optimized. A new trend in translational research, which is in line with "One Health" approach, bases on exploiting parallels between naturally occurring diseases affecting humans and companion animals. Canine anal furunculosis (AF) has been indicated as condition analogous to human perianal Crohn's disease (pCD). This narrative review provides the first comprehensive comparative analysis of these two diseases based on the published data. The paper also outlines the molecular mechanisms of action of MSCs which are likely to have a role in modulating the perianal fistula niche in humans, and refers them to the current knowledge on the immunomodulatory properties of canine MSCs. Generally, the pathogenesis of both diseases shares main determinants such as the presence of genetic predispositions, dysregulation of immune response and the relation to intestine microbiota. However, we also identified many aspects which should be further specified, such as determining the frequency of true fistulas formation in AF patients, elucidating the role of TNF and Th17 pathway in the pathogenesis of AF, or clarifying the role of epithelial-to-mesenchymal transition phenomenon in the formation of canine fistulae. Nevertheless, the available data support the hypothesis that the results from testing cell therapies in dogs with anal furunculosis have a significant translational value in optimizing MSC transplants procedures in pCD patients.

Transcriptomic profile of semitendinosus muscle of bulls of different breed and performance.

The aim of the study was to compare the transcriptomic profiles of fully differentiated skeletal muscle derived from bulls belonging to different breeds of varying performance. Microarray analyses were performed to determine the differences in the expression profiles of genes between semitendinosus muscles of 15-month-old beef-breed bulls (Limousin-LIM and Hereford-HER) and dairy-breed bulls (Holstein Friesian-HF). These analyses allowed for the identification of those genes the expression of which is similar and characteristic of fully differentiated muscle in beef breeds, but differs in skeletal muscle of a typical dairy breed. The analysis revealed 463 transcripts showing similar expression in the semitendinosus muscle of beef breeds (LIM/HER), in comparison with the dairy breed (HF). Among the identified genes, 227 were upregulated and 236 were downregulated in beef breeds. The ontological analyses revealed that the largest group of genes similarly expressed in LIM and HER was involved in the processes of protein metabolism and development of muscle organ. In beef breeds, some genes involved in protein synthesis and proteolysis showed an upregulation, including ctsd, ctsf, fhl2, fhl3, fst, sirt1, and trim63, whereas some were downregulated, including bmpr1a, bmpr2, mstn, smad2, hspa8, gsk3ß, and tgfß2. The expression of the chosen genes was confirmed by RT-qPCR technique. Thus, it can be assumed that the identified genes involved in the regulation of growth and development of muscle tissue and the processes of protein metabolism in the examined cattle breeds may be responsible for the greater gain of muscle mass in beef-breed bulls.

Transcriptomic Profile of Primary Culture of Skeletal Muscle Cells Isolated from Semitendinosus Muscle of Beef and Dairy Bulls.

The aim of the study was to identify differences in the transcriptomic profiles of primary muscle cell cultures derived from the semitendinosus muscle of bulls of beef breeds (Limousin (LIM) and Hereford (HER)) and a dairy breed (Holstein-Friesian (HF)) (n = 4 for each breed). Finding a common expression pattern for proliferating cells may point to such an early orientation of the cattle beef phenotype at the transcriptome level of unfused myogenic cells. To check this hypothesis, microarray analyses were performed. The analysis revealed 825 upregulated and 1300 downregulated transcripts similar in both beef breeds (LIM and HER) and significantly different when compared with the dairy breed (HF) used as a reference. Ontological analyses showed that the largest group of genes were involved in muscle organ development. Muscle cells of beef breeds showed higher expression of genes involved in myogenesis (including erbb-3, myf5, myog, des, igf-1, tgfb2) and those encoding proteins comprising the contractile apparatus (acta1, actc1, myh3, myh11, myl1, myl2, myl4, tpm1, tnnt2, tnnc1). The obtained results confirmed our hypothesis that the expression profile of several groups of genes is common in beef breeds at the level of proliferating satellite cells but differs from that observed in typical dairy breeds.

Transcriptomic analysis on the promoter regions discover gene networks involving mastitis in cattle.

Mastitis is one of the costliest diseases in dairy farms caused by infection of different microorganisms such as Escherichia coli, Streptococcus uberis and Staphylococcus aureus. Promoters are significantly involved in regulating gene expression and shedding light on the mechanisms of transcriptional regulation in physiological and immunological processes of the infections. Exploiting regulatory elements such as transcription factor binding sites (TFBSs modules) on the promoter region could reveal co-regulated genes, which allow screating regulatory models and executing a cross-sectional analysis on several databases. In this study, the promoter regions of 11 genes associated with contagious mastitis including CCL4, CXCL8, STAT3, IKBKB, MAPK14, NFKBIA, NFKB1, TNF, IL18, IL6, and HCK were investigated to predict the activating regulatory modules on promoters and to discover the key related transcription factors. By exploring the promoter regions, 228 genes were discovered comprising the same transcription factors modules. Out of 228 genes, 36 were validated using five microarray datasets. The promoter research of these genes revealed that as many as 7 down-regulated and 12 up-regulated genes are predictable in the network. The genes whose functions were associated with the initial gene list (11 genes), were identified by DAVID queries with TFBSs models implying that the approach provides a clear image of the underlying regulatory mechanism of gene expression profile and offers a novel approach in designing gene networks in cattle.

Identification of Biological Pathways Contributing to Marbling in Skeletal Muscle to Improve Beef Cattle Breeding.

Red meat is an important dietary source that provides part of the nutritional requirements. Intramuscular fat, known as marbling, is located throughout skeletal muscle. Marbling is a trait of major economic relevance that positively influences sensory quality aspects. The aim of the present study was to identify and better understand biological pathways defining marbling in beef cattle. Pathway analysis was performed in PathVisio with publicly available transcriptomic data from semitendinosus muscle of well-marbled and lean-marbled beef. Moreover, for Bos taurus we created a gene identifier mapping database with bridgeDb and a pathway collection in WikiPathways. The regulation of marbling is possibly the result of the interplay between signaling pathways in muscle, fat, and intramuscular connective tissue. Pathway analysis revealed 17 pathways that were significantly different between well-marbled and lean-marbled beef. The MAPK signaling pathway was enriched, and the signaling pathways that play a role in tissue development were also affected. Interestingly, pathways related to immune response and insulin signaling were enriched.

Nutraceutical functions of beta-glucans in human nutrition

Recent studies have shown that naturally occurring substances found in the food of the daily human diet are important for preventing chronic non-communicable diseases. One of them is beta-glucan, which is a natural polysaccharide, occurring in plant cell walls, mainly oats, barley and wheat. It is also present in baker's yeast cells, fungal cell walls, and some microorganisms. Beta-glucan belongs to one of the dietary fiber fractions, which are attributed a number of beneficial health properties, including the prevention and treatment of certain digestive diseases and supporting the immune system. This compound has biological activity that depends on the size, molecular weight, conformation, frequency of bonds, solubility and changes in structure. Beta-glucan reduces cholesterol and glucose concentrations in the blood, which reduces the risk of cardiovascular disease and diabetes. In addition to its effects on lipid levels and glucose metabolism, beta-glucan also exhibits antioxidant properties by scavenging reactive oxygen species, thereby reducing the risk of diseases, including atherosclerosis, cardiovascular diseases, neurodegenerative diseases, diabetes, and cancer. Immunostimulatory and antitumor effects have also been reported. The immunostimulatory activity of beta-glucan occurs as a result of its attachment to specific receptors present on the immune cell surface. Beta-glucan belongs to the group of prebiotics which stimulate the growth and activity of the desired natural intestinal microbiota, while inhibiting the growth of pathogens. It plays an important role in the proper functioning of the gastrointestinal tract and preventing inflammation as well as colon cancer. Such a number of health benefits resulting from the properties of beta-glucan may play a key role in improving health and preventing chronic non-communicable diseases, such as diabetes, hypercholesterolemia, obesity, cardiovascular diseases, and cancer.

Simultaneous miRNA and mRNA Transcriptome Profiling of Differentiating Equine Satellite Cells Treated with Gamma-Oryzanol and Exposed to Hydrogen Peroxide.

Gamma-oryzanol (GO) is a popular supplement for performance horses, dogs, and humans. Previous studies indicated that GO supplementation decreases creatine kinase activity and lactate level after exercise and may affect oxidative stress in Thoroughbred horses. GO may change genes expression in equine satellite cells (ESC). The purpose of this study was to evaluate the effect of GO on miRNA, gene expression, oxidative stress, and cell damage and viability in differentiating ESC pretreated with hydrogen peroxide (H2O2). ESCs were obtained from a young horse's skeletal muscle. ESCs were pre-incubated with GO (24 h) and then exposed to H2O2 for one hour. For the microRNA and gene expression assessment, the microarray technique was used. Identified miRNAs and genes were validated using real time-quantitative polymerase chain reaction. Several tests related to cell viability, cell damage, and oxidative stress were performed. The microarray analysis revealed differences in 17 miRNAs and 202 genes between GO-treated and control ESC. The tests related to apoptosis, cell viability, and oxidative stress showed that GO affects these processes to varying degrees. Our results suggest that GO can change miRNA and gene expression and may impact the processes involved in tissue repairing after an injury.

Effect of ß-hydroxy-ß-methylbutyrate on miRNA expression in differentiating equine satellite cells exposed to hydrogen peroxide.

BACKGROUND: Skeletal muscle injury activates satellite cells to initiate processes of proliferation, differentiation, and hypertrophy in order to regenerate muscle fibers. The number of microRNAs and their target genes are engaged in satellite cell activation. ß-Hydroxy-ß-methylbutyrate (HMB) is known to prevent exercise-induced muscle damage. The purpose of this study was to evaluate the effect of HMB on miRNA and relevant target gene expression in differentiating equine satellite cells exposed to H2O2. We hypothesized that HMB may regulate satellite cell activity, proliferation, and differentiation, hence attenuate the pathological processes induced during an in vitro model of H2O2-related injury by changing the expression of miRNAs. METHODS: Equine satellite cells (ESC) were isolated from the samples of skeletal muscle collected from young horses. ESC were treated with HMB (24 h) and then exposed to H2O2 (1 h). For the microRNA and gene expression assessment microarrays, technique was used. Identified miRNAs and genes were validated using real-time qPCR. Cell viability, oxidative stress, and cell damage were measured using colorimetric method and flow cytometry. RESULTS: Analysis of miRNA and gene profile in differentiating ESC pre-incubated with HMB and then exposed to H2O2 revealed difference in the expression of 27 miRNAs and 4740 genes, of which 344 were potential target genes for identified miRNAs. Special attention was focused on differentially expressed miRNAs and their target genes involved in processes related to skeletal muscle injury. Western blot analysis showed protein protection in HMB-pre-treated group compared to control. The viability test confirmed that HMB enhanced cell survival after the hydrogen peroxide exposition. CONCLUSIONS: Our results suggest that ESC pre-incubated with HMB and exposed to H2O2 could affect expression on miRNA levels responsible for skeletal muscle development, cell proliferation and differentiation, and activation of tissue repair after injury. Enrichment analyses for targeted genes revealed that a large group of genes was associated with the regulation of signaling pathways crucial for muscle tissue development, protein metabolism, muscle injury, and regeneration, as well as with oxidative stress response.

Breed-dependent microRNA expression in the primary culture of skeletal muscle cells subjected to myogenic differentiation.

BACKGROUND: Skeletal muscle in livestock develops into meat, an important source of protein and other nutrients for human consumption. The muscle is largely composed of a fixed number of multinucleated myofibers determined during late gestation and remains constant postnatally. A population of postnatal muscle stem cells, called satellite cells, gives rise to myoblast cells that can fuse with the existing myofibers, thus increasing their size. This requires a delicate balance of transcription and growth factors and specific microRNA (miRNA) expressed by satellite cells and their supporting cells from the muscle stem cell niche. The role of transcription and growth factors in bovine myogenesis is well-characterized; however, very little is known about the miRNA activity during this process. We have hypothesized that the expression of miRNA can vary between primary cultures of skeletal muscle cells isolated from the semitendinosus muscles of different cattle breeds and subjected to myogenic differentiation. RESULTS: After a 6-day myogenic differentiation of cells isolated from the muscles of the examined cattle breeds, we found statistically significant differences in the number of myotubes between Hereford (HER)/Limousine (LIM) beef breeds and the Holstein-Friesian (HF) dairy breed (p ≤ 0.001). The microarray analysis revealed differences in the expression of 23 miRNA among the aforementioned primary cultures. On the basis of a functional analysis, we assigned 9 miRNA as molecules responsible for differentiation progression (miR-1, -128a, -133a, -133b, -139, -206, -222, -486, and -503). The target gene prediction and functional analysis revealed 59 miRNA-related genes belonging to the muscle organ development process. CONCLUSION: The number of myotubes and the miRNA expression in the primary cultures of skeletal muscle cells derived from the semitendinosus muscles of the HER/LIM beef cattle breeds and the HF dairy breed vary when cells are subjected to myogenic differentiation. The net effect of the identified miRNA and their target gene action should be considered the result of the breed-dependent activity of satellite cells and muscle stem cell niche cells and their mutual interactions, which putatively can be engaged in the formation of a larger number of myotubes in beef cattle-related cells (HER/LIM) during in vitro myogenesis.

Characterisation of equine satellite cell transcriptomic profile response to ß-hydroxy-ß-methylbutyrate (HMB).

ß-Hydroxy-ß-methylbutyrate (HMB) is a popular ergogenic aid used by human athletes and as a supplement to sport horses, because of its ability to aid muscle recovery, improve performance and body composition. Recent findings suggest that HMB may stimulate satellite cells and affect expressions of genes regulating skeletal muscle cell growth. Despite the scientific data showing benefits of HMB supplementation in horses, no previous study has explained the mechanism of action of HMB in this species. The aim of this study was to reveal the molecular background of HMB action on equine skeletal muscle by investigating the transcriptomic profile changes induced by HMB in equine satellite cells in vitro. Upon isolation from the semitendinosus muscle, equine satellite cells were cultured until the 2nd day of differentiation. Differentiating cells were incubated with HMB for 24 h. Total cellular RNA was isolated, amplified, labelled and hybridised to microarray slides. Microarray data validation was performed with real-time quantitative PCR. HMB induced differential expressions of 361 genes. Functional analysis revealed that the main biological processes influenced by HMB in equine satellite cells were related to muscle organ development, protein metabolism, energy homoeostasis and lipid metabolism. In conclusion, this study demonstrated for the first time that HMB has the potential to influence equine satellite cells by controlling global gene expression. Genes and biological processes targeted by HMB in equine satellite cells may support HMB utility in improving growth and regeneration of equine skeletal muscle; however, the overall role of HMB in horses remains equivocal and requires further proteomic, biochemical and pharmacokinetic studies.

Gene expression profiling in skeletal muscle of Holstein-Friesian bulls with single-nucleotide polymorphism in the myostatin gene 5'-flanking region.

Myostatin (GDF-8) is a key protein responsible for skeletal muscle growth and development, thus mutations in the mstn gene can have major economic and breeding consequences. The aim of the present study was to investigate myostatin gene expression and transcriptional profile in skeletal muscle of Holstein-Friesian (Black-and-White) bulls carrying a polymorphism in the 5'-flanking region of the mstn gene (G/C transversion at position -7828). Real-time qRT-PCR and cDNA microarray revealed significantly lower mstn expression in muscle of bulls with the CC genotype, as compared to GG and GC genotypes. The direct comparison of skeletal muscle transcriptional profiles between the CC genotype and GG and GC genotypes resulted in identification of genes, of which at least some can be putative targets for myostatin. Using cDNA microarray, we identified 43 common genes (including mstn) with significantly different expression in skeletal muscle of bulls with the CC genotype, as compared to GG and GC genotypes, 15 of which were upregulated and 28 were downregulated in the CC genotype. Classification of molecular function of differentially expressed genes revealed the highest number of genes involved in the expression of cytoskeleton proteins (9), extracellular matrix proteins (4), nucleic acid-binding proteins (4), calcium-binding proteins (4), and transcription factors (4). The biological functions of the largest number of genes involved: protein metabolism and modification (10), signal transduction (10), cell structure (8), and developmental processes (8). The main identified signaling pathways were: Wnt (4), chemokines and cytokines (4), integrin (4), nicotine receptor for acetylocholine (3), TGF-beta (2), and cytoskeleton regulation by Rho GTPase (2). We identified previously unrecognized putatively myostatin-dependent genes, encoding transcription factors (EGR1, Nf1b, ILF1), components of the proteasomal complex (PSMB7, PSMD13) and proteins with some other molecular function in skeletal muscle (ITGB1BP3, Pla2g1b, ISYNA1, TNFAIP6, MST1, TNNT1, CALB3, CACYBP, and CTNNA1).

Delineation of signalling pathway leading to antioxidant-dependent inhibition of dexamethasone-mediated muscle cell death.

The molecular mechanism of the cell death-promoting effect of dexamethasone (Dex) was studied during myogenesis (10 days) in L6 muscle cells by making use of several indices such as cell viability (protein synthesis, mitochondrial respiration), mortality (DNA fragmentation, chromatin condensation, structural modifications) and immunocytochemical studies [hydrogen peroxide, m-calpain (calpain 2)]. Dex initially (2 nM) stimulated protein synthesis (P < 0.001), but a further increase (20 nM) did not stimulate, whereas a higher dose (200 nM) inhibited formation of cellular proteins (P < 0.001). The latter, apparently, resulted from impaired cell viability (P < 0.001). From the day 4, structural changes featuring cell death were observed. Antioxidants [sodium ascorbate (ASC), catalase (CAT) or N-acetyl-L-cysteine (NAC)] as well as the inhibition of transcription and translation by actinomycin D abrogated Dex-induced cell death (P < 0.001). Using a fluorescent probe (DCFH-DA) we directly corroborated the working hypothesis of the mediating role of H2O2 in the reduction of cell viability by the excess of glucocorticoids. We also found that tPKC, PLCgamma, PLA2 were required to induce Dex-dependent cell death since inactivation of tPKC by H7 completely abolished the cytotoxic effect of Dex, while the blockade of PLCgamma and PLA2 by U 73122 partially abolished the effect. Cell death was triggered by Ca2+ influx necessary to activate m-calpain since it was reversed by the calcium chelator EGTA or m-calpain inhibitor ALLN but not EDTA nor ALLM. However, cell viability impaired by Ca2+ ionophore A 23187 (P < 0.001) was neither reversed by EGTA, nor EDTA, nor caspase-3 blocker--Ac DEVD CHO, nor ALLN, nor antioxidants--ASC, NAC, CAT. Specific caspase-3 inhibitor Ac DEVD CHO also did not rescue cells from Dex-induced cell death (P < 0.001), in contrast to m-calpain inhibitor--ALLN. Taken together, these findings suggest that reactive oxygen species inhibit protein synthesis and amplify m-calpain-dependent proteolysis. The events that led to the death of L6 muscle cells most likely resulted from Dex-mediated repression of antioxidative defences on the genomic level.

A novel antioxidant-inhibited dexamethasone-mediated and caspase-3-independent muscle cell death.

Dexamethasone (Dex)-mediated cell death is associated with repression of survival factors (AP-1, c-myc, NF-kappaB). Dex suppressed the activity of genes encoding antioxidant enzymes leading to impaired viability and apoptotic cell death. These findings suggest that reactive oxygen species inhibit protein synthesis and amplify m-calpain-dependent proteolysis. The events that led to death of L6 muscle cells were most likely triggered by Dex-mediated repression of antioxidative defenses on the genomic level.