59,888 research outputs found

    Macrophage-released ADAMTS1 promotes muscle stem cell activation.

    Get PDF
    Coordinated activation of muscle stem cells (known as satellite cells) is critical for postnatal muscle growth and regeneration. The muscle stem cell niche is central for regulating the activation state of satellite cells, but the specific extracellular signals that coordinate this regulation are poorly understood. Here we show that macrophages at sites of muscle injury induce activation of satellite cells via expression of Adamts1. Overexpression of Adamts1 in macrophages in vivo is sufficient to increase satellite cell activation and improve muscle regeneration in young mice. We demonstrate that NOTCH1 is a target of ADAMTS1 metalloproteinase activity, which reduces Notch signaling, leading to increased satellite cell activation. These results identify Adamts1 as a potent extracellular regulator of satellite cell activation and have significant implications for understanding the regulation of satellite cell activity and regeneration after muscle injury.Satellite cells are crucial for growth and regeneration of skeletal muscle. Here the authors show that in response to muscle injury, macrophages secrete Adamts1, which induces satellite cell activation by modulating Notch1 signaling

    Post-transcriptional regulation of satellite cell quiescence by TTP-mediated mRNA decay.

    Get PDF
    Skeletal muscle satellite cells in their niche are quiescent and upon muscle injury, exit quiescence, proliferate to repair muscle tissue, and self-renew to replenish the satellite cell population. To understand the mechanisms involved in maintaining satellite cell quiescence, we identified gene transcripts that were differentially expressed during satellite cell activation following muscle injury. Transcripts encoding RNA binding proteins were among the most significantly changed and included the mRNA decay factor Tristetraprolin. Tristetraprolin promotes the decay of MyoD mRNA, which encodes a transcriptional regulator of myogenic commitment, via binding to the MyoD mRNA 3' untranslated region. Upon satellite cell activation, p38α/β MAPK phosphorylates MAPKAP2 and inactivates Tristetraprolin, stabilizing MyoD mRNA. Satellite cell specific knockdown of Tristetraprolin precociously activates satellite cells in vivo, enabling MyoD accumulation, differentiation and cell fusion into myofibers. Regulation of mRNAs by Tristetraprolin appears to function as one of several critical post-transcriptional regulatory mechanisms controlling satellite cell homeostasis

    Culture conditions influence satellite cell activation and survival of single myofibers

    Get PDF
    Single myofiber isolation protocols allow to obtain an in vitro system in which the physical association between the myofiber and its stem cells, the satellite cells, is adequately preserved. This technique is an indispensable tool by which the muscle regeneration process can be recapitulated and studied in each specific phase, from satellite cell activation to proliferation, from differentiation to fusion. This study aims to clarify the effect of different culture conditions on single myofibers, their associated satellite cells, and the physiological behavior of the satellite cells upon long term culture. By direct observations of the cultures, we compared different experimental conditions and their effect on both satellite cell behavior and myofiber viability

    Functionally heterogeneous human satellite cells identified by single cell RNA sequencing.

    Get PDF
    Although heterogeneity is recognized within the murine satellite cell pool, a comprehensive understanding of distinct subpopulations and their functional relevance in human satellite cells is lacking. We used a combination of single cell RNA sequencing and flow cytometry to identify, distinguish, and physically separate novel subpopulations of human PAX7+ satellite cells (Hu-MuSCs) from normal muscles. We found that, although relatively homogeneous compared to activated satellite cells and committed progenitors, the Hu-MuSC pool contains clusters of transcriptionally distinct cells with consistency across human individuals. New surface marker combinations were enriched in transcriptional subclusters, including a subpopulation of Hu-MuSCs marked by CXCR4/CD29/CD56/CAV1 (CAV1+). In vitro, CAV1+ Hu-MuSCs are morphologically distinct, and characterized by resistance to activation compared to CAV1- Hu-MuSCs. In vivo, CAV1+ Hu-MuSCs demonstrated increased engraftment after transplantation. Our findings provide a comprehensive transcriptional view of normal Hu-MuSCs and describe new heterogeneity, enabling separation of functionally distinct human satellite cell subpopulations

    Skeletal muscle stem cells express anti-apoptotic ErbB receptors during activation from quiescence

    Get PDF
    To be effective for tissue repair, satellite cells (the stem cells of adult muscle) must survive the initial activation from quiescence. Using an in vitro model of satellite cell activation, we show that erbB1, erbB2 and erbB3, members of the EGF receptor tyrosine kinase family, appear on satellite cells within 6 h of activation. We show that signalling via erbB2 provides an anti-apoptotic survival mechanism for satellite cells during the first 24 h, as they progress to a proliferative state. Inhibition of erbB2 signalling with AG825 reduced satellite cell numbers, concomitant with elevated caspase-8 activation and TUNEL labelling of apoptotic satellite cells. In serum-free conditions, satellite cell apoptosis could be largely prevented by a mixture of erbB1, erbB3 and erbB4 ligand growth factors, but not by neuregulin alone (erbB3/erbB4 ligand). Furthermore, using inhibitors specific to discrete intracellular signalling pathways, we identify MEK as a pro-apoptotic mediator, and the erbB-regulated factor STAT3 as an anti-apoptotic mediator during satellite cell activation. These results implicate erbB2 signalling in the preservation of a full compliment of satellite cells as they activate in the context of a damaged muscle

    The role of HIF1alpha and HIF2alpha in muscle development and satellite cell function

    Get PDF
    Hypoxia inducible factors (HIFs) are central mediators of cellular responses to fluctuations of oxygen, an environmental regulator of stem cell activity. Muscle satellite cells are myogenic stem cells whose quiescence, activation, self-renewal and differentiation are influenced by microenvironment oxygen levels. However, the in vivo roles of HIFs in quiescent satellite cells and activated satellite cells (myoblasts) are poorly understood. Expression analyses indicate that HIF1α and HIF2α are preferentially expressed in pre- and post-differentiation myoblasts, respectively. Interestingly, double knockout of HIF1α and HIF2α (HIF1α/2α dKO) in embryonic myoblasts results in apparently normal muscle development and growth. However, HIF1α/2α dKO in postnatal satellite cells impairs injury-induced muscle repair, accompanied by a reduced number of myoblasts during regeneration. Analysis of satellite cell dynamics on myofibers confirms that HIF1α/2α dKO myoblasts exhibit reduced self-renewal but more pronounced myogenic differentiation under hypoxia conditions. Mechanistically, HIF1α/2α dKO blocks hypoxia-induced activation of Notch signaling, a key determinant of satellite cell self-renewal. Constitutive activation of Notch signaling can rescue HIF1α/2α dKO induced inhibition of satellite cell self-renewal. Together, HIF1α and HIF2α are dispensable for muscle stem cell function under normoxia, but are required for maintaining satellite cell self-renewal under hypoxic environment

    Mobilisation of satellite cells following ischaemia and reperfusion in primate skeletal muscle

    Get PDF
    Objective. To describe the morphological and morphometric features of activated skeletal muscle satellite cells in primates, using an ischaemic reperfusion model. Setting. The study was undertaken at the Biomedical Resource Centre and the Electron Microscopy Unit of the University of KwaZulu-Natal. Interventions. Eight vervet monkeys were anaesthetised and subjected to 3 hours of tourniquet-induced lower limb ischaemia. Open muscle biopsies were taken from tibialis anterior muscle immediately after tourniquet release and 12, 24, 36 and 48 hours after tourniquet release. Control biopsies were taken from the opposite limb. Main outcome measures. Description of the morphological and morphometric changes in satellite cells after activation, as seen on transmission electron microscopy. Results. Two distinct patterns of satellite cell activation are described. In group 1, the cytoplasm of the satellite cell expands around the myocyte and the gap between the satellite cell and the myocyte appears to break down, or in group 2, the novel observation of the satellite cell breaking away from the myofibre and becoming a myocyte totally encased in its own basal lamina. The satellite cells of group 1 were significantly longer than the group 2 cells (p = 0.018) and this was associated with a significant reduction in the percentage of nuclear to cell area (p = 0.011). Conclusions. Tourniquet-induced ischaemic reperfusion injury is shown to result in two distinct patterns of satellite cell activation which may represent different functions or subsets of satellite cells. South African Journal of Sports Medicine Vol.16(1) 2004: 17-2

    Myostatin negatively regulates satellite cell activation and self-renewal

    Get PDF
    Satellite cells are quiescent muscle stem cells that promote postnatal muscle growth and repair. Here we show that myostatin, a TGF-β member, signals satellite cell quiescence and also negatively regulates satellite cell self-renewal. BrdU labeling in vivo revealed that, among the Myostatin-deficient satellite cells, higher numbers of satellite cells are activated as compared with wild type. In contrast, addition of Myostatin to myofiber explant cultures inhibits satellite cell activation. Cell cycle analysis confirms that Myostatin up-regulated p21, a Cdk inhibitor, and decreased the levels and activity of Cdk2 protein in satellite cells. Hence, Myostatin negatively regulates the G1 to S progression and thus maintains the quiescent status of satellite cells. Immunohistochemical analysis with CD34 antibodies indicates that there is an increased number of satellite cells per unit length of freshly isolated Mstn−/− muscle fibers. Determination of proliferation rate suggests that this elevation in satellite cell number could be due to increased self-renewal and delayed expression of the differentiation gene (myogenin) in Mstn−/− adult myoblasts. Taken together, these results suggest that Myostatin is a potent negative regulator of satellite cell activation and thus signals the quiescence of satellite cells

    Canonical nuclear factor-κB signaling in satellite stem cell homeostasis and function.

    Get PDF
    Satellite cells are adult stem cells that are required for the regeneration of skeletal muscle following injury. However, the signaling mechanisms that regulate satellite stem cell homeostasis and function in adult animals remain less understood. Nuclear factor-kappa B (NF-kB) is a major nuclear transcription factor that regulates the gene expression of a plethora of molecules involved in cellular proliferation, differentiation, survival, and the inflammatory immune response. NF-kB can be activated through a canonical or non-canonical pathway. However, the role of canonical NF-kB signaling in the regulation of satellite stem cell function during skeletal muscle regeneration has not been yet investigated using genetic mouse models. In the present work, we demonstrate that physiological levels of activation of the canonical NF-κB pathway promotes satellite cell proliferation, survival, and differentiation. Satellite cell-specific inducible deletion of Inhibitor of Kappa B Kinase β (IKKβ), a critical kinase of the canonical NF-kB pathway, attenuates muscle regeneration in adult mice. Targeted ablation of IKKβ also reduces the number of satellite cells and their fusion to injured skeletal muscle of adult mice. Inhibition of canonical NF-κB pathway causes precocious differentiation of satellite cells both ex vivo and in vitro. We also found that siRNA-mediated knockdown of components of the canonical NF-kB pathway reduces the survival of cultured satellite cells. Intriguingly, our results also demonstrate that supra-physiological activation of canonical NF-kB inhibits satellite stem cell function during skeletal muscle regeneration. Overexpression of a constitutively active mutant of IKKβ (IKKβca) in satellite cells attenuates initial stages of myofiber regeneration following injury. While not affecting their self-renewal, overexpression of IKKβ causes precocious differentiation of satellite cells. Furthermore, our results suggest that constitutive activation of canonical NF-kB pathway inhibits proliferation and reduces survival of satellite cells. Lastly, we found that inducible expression of IKKβca in satellite cells was insufficient to rescue the regenerative deficits observed in satellite cell-specific TAK1-knockout mice. Altogether, our study suggests that a tight regulation of canonical NF-kB pathway is important for maintaining satellite cell pool and skeletal muscle regeneration

    Absence of CD34 on Murine Skeletal Muscle Satellite Cells Marks a Reversible State of Activation during Acute Injury

    Get PDF
    Background: Skeletal muscle satellite cells are myogenic progenitors that reside on myofiber surface beneath the basal lamina. In recent years satellite cells have been identified and isolated based on their expression of CD34, a sialomucin surface receptor traditionally used as a marker of hematopoietic stem cells. Interestingly, a minority of satellite cells lacking CD34 has been described. Methodology/Principal Findings: In order to elucidate the relationship between CD34+ and CD34- satellite cells we utilized fluorescence-activated cell sorting (FACS) to isolate each population for molecular analysis, culture and transplantation studies. Here we show that unless used in combination with a7 integrin, CD34 alone is inadequate for purifying satellite cells. Furthermore, the absence of CD34 marks a reversible state of activation dependent on muscle injury. Conclusions/Significance: Following acute injury CD34- cells become the major myogenic population whereas the percentage of CD34+ cells remains constant. In turn activated CD34- cells can reverse their activation to maintain the pool of CD34+ reserve cells. Such activation switching and maintenance of reserve pool suggests the satellite cell compartment is tightly regulated during muscle regeneration
    corecore