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Hypoxia promotes proliferation and inhibits myogenesis in broiler satellite cells

ABSTRACT: Breast muscle myopathies in broilers compromise meat quality and continue to plague the poultry industry. Broiler breast muscle myopathies are characterized by impaired satellite cells (SC)-mediated repair, and localized tissue hypoxia and dysregulation of oxygen homeostasis have been implicated as contributing factors. The present study was designed to test the hypothesis that hypoxia disrupts the behavior of SC essential for multinucleated myotube formation in vitro, and to determine the extent to which effects are reversed by restoration of oxygen tension. Primary SC was isolated from pectoralis major of young (5 d) Cobb 700 chicks and maintained in growth conditions or induced to differentiate under normoxic (20% O2) or hypoxic (1% O2) conditions for up to 48 h. Hypoxia enhanced SC proliferation while inhibiting myogenic potential, with decreased fusion index and suppressed myotube formation. Reoxygenation after hypoxia partially reversed effects on both proliferation and myogenesis. Western blotting showed that hypoxia diminished myogenin expression, activated AMPK, upregulated proliferation markers, and increased molecular signaling of cellular stress. Hypoxia also promoted accumulation of lipid droplets in myotubes. Targeted RNAseq identified numerous differentially expressed genes across differentiation under hypoxia, including several genes that have been associated with myopathies in vivo. Altogether, these data demonstrate localized hypoxia may influence SC behavior in ways that disrupt muscle repair and promote the formation of myopathies in broilers.

ORGANISM(S): Gallus gallus

PROVIDER: GSE241619 | GEO | 2023/10/24

REPOSITORIES: GEO

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Project description:Background Quiescent (non-dividing) muscle satellite cells (SCs) transition into proliferating progenitor cells that differentiate to repair skeletal muscle after injury. Recently, the AP-1 family member, FOS, was found to be rapidly and transiently induced in SCs in response to muscle damage, and its activity is required for effective SC activation and muscle repair. However, why FOS is rapidly down-regulated before SCs enter the cell cycle as progenitor cells remains unclear. In addition, whether boosting FOS expression in primary cycling muscle progenitor cells can enhance their myogenic properties needs to be evaluated. Methods In this study, we established a lentiviral, doxycycline-inducible system to explore the molecular and functional consequences of continued FOS expression in SC-derived, cycling muscle progenitor cells ex vivo. Specifically, we performed cell growth and EdU incorporation assays to measure cellular proliferation; myotube formation assays to evaluate terminal differentiation potential; and RNA-Sequencing (RNA-Seq) in conjunction with high-throughput chromosome conformation capture (Hi-C) to uncover changes in gene expression and long-range chromatin interactions. Results Persistent FOS activity in cycling muscle progenitor cells modestly enhances progenitor cell proliferation, but severely antagonizes their ability to differentiate and form myotubes. Genome-wide RNA-Seq analysis revealed that ectopic FOS activity in cycling muscle progenitor cells suppresses a global pro-myogenic gene expression program, while activating a stress-induced Mitogen-Activated Protein Kinase (MAPK) transcriptional signature. Importantly, we found various chromosomal re-organization events in A/B compartments, TADs, and long-range genomic loops near FOS-regulated differentially expressed genes in cycling muscle progenitor cells ectopically expressing FOS. Conclusions Altogether, our results suggest that elevated FOS activity in proliferating muscle progenitor cells perturbs cellular differentiation by altering the 3-dimensional (3D) chromosome organization near critical pro-myogenic genes. This work highlights the crucial importance of tightly controlling FOS expression in the muscle lineage, and raises the possibility that in states of chronic stress or disease, persistent FOS activity in muscle stem and/or progenitor cells may actually disrupt the muscle forming process.

Project description:Skeletal muscle atrophy is dictated by the balance between protein synthesis and protein breakdown, known as proteostasis. With advanced age, muscle atrophy contributes to development of co-morbidities, loss of strength and independence, and all-cause mortality. Aging also coincides with the accumulation of senescent cells within skeletal muscle that produce inflammatory products, known as the senescence associated secretory phenotype. Previously, we found that a metformin + leucine (MET+LEU) combination treatment had synergistic effects in aged mice to improve skeletal muscle structure and function during disuse atrophy. Therefore, the objective of this study was to determine the mechanisms by which MET+LEU exhibits muscle atrophy protection in vitro and if this occurs through cellular senescence. C2C12 myoblasts differentiated into myotubes were used to determine MET+LEU mechanisms during serum-deprivation (SD) atrophy. Single myofibers were isolated from aged (22-23 mo) C57Bl6/J mice, and human primary myoblasts were extracted from a healthy older adult donor. 25 + 125 µM MET+LEU treatment increased differentiation of myotubes and prevented SD induced atrophy. Low concentration (0.1 + 0.5 µM) MET+LEU had unique effects to prevent myotube atrophy and cause transcriptional reprogramming compared to individual therapies. SD increased inflammatory and cellular senescence pathways that was reversed with MET+LEU treatment. SD resulted in dysregulated proteostasis that was rescued with MET+LEU, and proteasome inhibition with MG-132 also rescued myotube atrophy. Cellular senescence transcriptional pathways and markers increased by SD were reversed with MET+LEU treatment, and dasatinib + quercetin (D+Q) senolytic treatment prevented myotube atrophy similar to MET+LEU. In aged myofibers, MET+LEU prevented SD atrophy, and in human primary myotubes MET+LEU prevented reductions in myonuclei fusion. These data provide evidence that MET+LEU has muscle cell intrinsic properties to prevent atrophy by reversing senescence and improving proteostasis

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Hypoxia promotes proliferation and inhibits myogenesis in broiler satellite cells

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