MLL1 is required for PAX7 expression and satellite cell self-renewal in mice

Abstract PAX7 is a paired-homeobox transcription factor that specifies the myogenic identity of muscle stem cells and acts as a nodal factor by stimulating proliferation while inhibiting differentiation. We previously found that PAX7 recruits the H3K4 methyltransferases MLL1/2 to epigenetically activate target genes. Here we report that in the absence of Mll1, myoblasts exhibit reduced H3K4me3 at both Pax7 and Myf5 promoters and reduced Pax7 and Myf5 expression. Mll1-deficient myoblasts fail to proliferate but retain their differentiation potential, while deletion of Mll2 had no discernable effect. Re-expression of PAX7 in committed Mll1 cKO myoblasts restored H3K4me3 enrichment at the Myf5 promoter and Myf5 expression. Deletion of Mll1 in satellite cells reduced satellite cell proliferation and self-renewal, and significantly impaired skeletal muscle regeneration. Pax7 expression was unaffected in quiescent satellite cells but was markedly downregulated following satellite cell activation. Therefore, MLL1 is required for PAX7 expression and satellite cell function in vivo. Furthermore, PAX7, but not MLL1, is required for Myf5 transcriptional activation in committed myoblasts.

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Myostatin negatively regulates satellite cell activation and self-renewal

The Journal of Cell Biology ◽

10.1083/jcb.200207056 ◽

2003 ◽

Vol 162 (6) ◽

pp. 1135-1147 ◽

Cited By ~ 483

Author(s):

Seumas McCroskery ◽

Mark Thomas ◽

Linda Maxwell ◽

Mridula Sharma ◽

Ravi Kambadur

Keyword(s):

Satellite Cell ◽

Satellite Cells ◽

Cell Activation ◽

Unit Length ◽

Immunohistochemical Analysis ◽

Cell Number ◽

Negative Regulator ◽

Self Renewal ◽

Satellite Cell Activation

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.

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Metformin Delays Satellite Cell Activation and Maintains Quiescence

Stem Cells International ◽

10.1155/2019/5980465 ◽

2019 ◽

Vol 2019 ◽

pp. 1-19 ◽

Cited By ~ 11

Author(s):

Theodora Pavlidou ◽

Milica Marinkovic ◽

Marco Rosina ◽

Claudia Fuoco ◽

Simone Vumbaca ◽

...

Keyword(s):

Satellite Cell ◽

Muscle Tissue ◽

Satellite Cells ◽

Cell Activation ◽

Myogenic Differentiation ◽

Metabolic State ◽

Cell Pool ◽

Age Related ◽

Satellite Cell Activation

The regeneration of the muscle tissue relies on the capacity of the satellite stem cell (SC) population to exit quiescence, divide asymmetrically, proliferate, and differentiate. In age-related muscle atrophy (sarcopenia) and several dystrophies, regeneration cannot compensate for the loss of muscle tissue. These disorders are associated with the depletion of the satellite cell pool or with the loss of satellite cell functionality. Recently, the establishment and maintenance of quiescence in satellite cells have been linked to their metabolic state. In this work, we aimed to modulate metabolism in order to preserve the satellite cell pool. We made use of metformin, a calorie restriction mimicking drug, to ask whether metformin has an effect on quiescence, proliferation, and differentiation of satellite cells. We report that satellite cells, when treated with metformin in vitro, ex vivo, or in vivo, delay activation, Pax7 downregulation, and terminal myogenic differentiation. We correlate the metformin-induced delay in satellite cell activation with the inhibition of the ribosome protein RPS6, one of the downstream effectors of the mTOR pathway. Moreover, in vivo administration of metformin induces a belated regeneration of cardiotoxin- (CTX-) damaged skeletal muscle. Interestingly, satellite cells treated with metformin immediately after isolation are smaller in size and exhibit reduced pyronin Y levels, which suggests that metformin-treated satellite cells are transcriptionally less active. Thus, our study suggests that metformin delays satellite cell activation and differentiation by favoring a quiescent, low metabolic state.

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A Role for Nitric Oxide in Muscle Repair: Nitric Oxide–mediated Activation of Muscle Satellite Cells

Molecular Biology of the Cell ◽

10.1091/mbc.11.5.1859 ◽

2000 ◽

Vol 11 (5) ◽

pp. 1859-1874 ◽

Cited By ~ 275

Author(s):

Judy E. Anderson

Keyword(s):

Nitric Oxide ◽

Satellite Cell ◽

Satellite Cells ◽

Knockout Mice ◽

Cell Activation ◽

Mdx Mice ◽

Muscle Repair ◽

Muscle Satellite Cells ◽

Satellite Cell Activation

Muscle satellite cells are quiescent precursors interposed between myofibers and a sheath of external lamina. Although their activation and recruitment to cycle enable muscle repair and adaptation, the activation signal is not known. Evidence is presented that nitric oxide (NO) mediates satellite cell activation, including morphological hypertrophy and decreased adhesion in the fiber-lamina complex. Activation in vivo occurred within 1 min after injury. Cell isolation and histology showed that pharmacological inhibition of nitric oxide synthase (NOS) activity prevented the immediate injury-induced myogenic cell release and delayed the hypertrophy of satellite cells in that muscle. Transient activation of satellite cells in contralateral muscles 10 min later suggested that a circulating factor may interact with NO-mediated signaling. Interestingly, satellite cell activation in muscles of mdx dystrophic mice and NOS-I knockout mice quantitatively resembled NOS-inhibited release of normal cells, in agreement with reports of displaced and reduced NOS expression in dystrophin-deficient mdx muscle and the complete loss of NOS-I expression in knockout mice. Brief NOS inhibition in normal and mdx mice during injury produced subtle alterations in subsequent repair, including apoptosis in myotube nuclei and myotube formation inside laminar sheaths. Longer NOS inhibition delayed and restricted the extent of repair and resulted in fiber branching. A model proposes the hypothesis that NO release mediates satellite cell activation, possibly via shear-induced rapid increases in NOS activity that produce “NO transients.”

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Brain-derived Neurotrophic Factor Regulates Satellite Cell Differentiation and Skeltal Muscle Regeneration

Molecular Biology of the Cell ◽

10.1091/mbc.e10-02-0154 ◽

2010 ◽

Vol 21 (13) ◽

pp. 2182-2190 ◽

Cited By ~ 73

Author(s):

Charlene Clow ◽

Bernard J. Jasmin

Keyword(s):

Skeletal Muscle ◽

Satellite Cell ◽

Satellite Cells ◽

Neurotrophic Factor ◽

Cell Function ◽

Brain Derived Neurotrophic Factor ◽

Postnatal Growth ◽

Adult Skeletal Muscle

In adult skeletal muscle, brain-derived neurotrophic factor (BDNF) is expressed in myogenic progenitors known as satellite cells. To functionally address the role of BDNF in muscle satellite cells and regeneration in vivo, we generated a mouse in which BDNF is specifically depleted from skeletal muscle cells. For comparative purposes, and to determine the specific role of muscle-derived BDNF, we also examined muscles of the complete BDNF−/− mouse. In both models, expression of the satellite cell marker Pax7 was significantly decreased. Furthermore, proliferation and differentiation of primary myoblasts was abnormal, exhibiting delayed induction of several markers of differentiation as well as decreased myotube size. Treatment with exogenous BDNF protein was sufficient to rescue normal gene expression and myotube size. Because satellite cells are responsible for postnatal growth and repair of skeletal muscle, we next examined whether regenerative capacity was compromised. After injury, BDNF-depleted muscle showed delayed expression of several molecular markers of regeneration, as well as delayed appearance of newly regenerated fibers. Recovery of wild-type BDNF levels was sufficient to restore normal regeneration. Together, these findings suggest that BDNF plays an important role in regulating satellite cell function and regeneration in vivo, particularly during early stages.

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Canonical NF-κB signaling regulates satellite stem cell homeostasis and function during regenerative myogenesis

Journal of Molecular Cell Biology ◽

10.1093/jmcb/mjy053 ◽

2018 ◽

Vol 11 (1) ◽

pp. 53-66 ◽

Cited By ~ 3

Author(s):

Alex R Straughn ◽

Sajedah M Hindi ◽

Guangyan Xiong ◽

Ashok Kumar

Keyword(s):

Skeletal Muscle ◽

Satellite Cell ◽

Satellite Cells ◽

Muscle Regeneration ◽

Cell Function ◽

Skeletal Muscle Regeneration ◽

Cell Homeostasis ◽

Adult Skeletal Muscle ◽

Adult Mice ◽

And Function

Abstract Skeletal muscle regeneration in adults is attributed to the presence of satellite stem cells that proliferate, differentiate, and eventually fuse with injured myofibers. However, the signaling mechanisms that regulate satellite cell homeostasis and function remain less understood. While IKKβ-mediated canonical NF-κB signaling has been implicated in the regulation of myogenesis and skeletal muscle mass, its role in the regulation of satellite cell function during muscle regeneration has not been fully elucidated. Here, we report that canonical NF-κB signaling is induced in skeletal muscle upon injury. Satellite cell-specific inducible ablation of IKKβ attenuates skeletal muscle regeneration in adult mice. Targeted ablation of IKKβ also reduces the number of satellite cells in injured skeletal muscle of adult mice, potentially through inhibiting their proliferation and survival. We also demonstrate that the inhibition of specific components of the canonical NF-κB pathway causes precocious differentiation of cultured satellite cells both ex vivo and in vitro. Finally, our results highlight that the constitutive activation of canonical NF-κB signaling in satellite cells also attenuates skeletal muscle regeneration following injury in adult mice. Collectively, our study demonstrates that the proper regulation of canonical NF-κB signaling is important for the regeneration of adult skeletal muscle.

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Heterogeneity of satellite cells implicates DELTA1/NOTCH2 signaling in self-renewal

10.1101/824359 ◽

2019 ◽

Author(s):

Valeria Yartseva ◽

Leonard D. Goldstein ◽

Julia Rodman ◽

Lance Kates ◽

Mark Z. Chen ◽

...

Keyword(s):

Cell Fate ◽

Satellite Cell ◽

Satellite Cells ◽

Receptor Expression ◽

Self Renewal ◽

Cell Fate Decisions ◽

Muscle Homeostasis ◽

Early Regeneration ◽

Time Point

SUMMARYHow satellite cells and their progenitors balance differentiation and self-renewal to achieve sustainable tissue regeneration is not well understood. A major roadblock to understanding satellite cell fate decisions has been the difficulty to study this process in vivo. By visualizing expression dynamics of myogenic transcription factors during early regeneration in vivo, we identified the time point at which cells undergo decisions to differentiate or self-renew. Single-cell RNA sequencing revealed heterogeneity of satellite cells during both muscle homeostasis and regeneration, including a subpopulation enriched in Notch2 receptor expression. Furthermore, we reveal that differentiating cells express the Dll1 ligand. Using antagonistic antibodies we demonstrate that the DLL1 and NOTCH2 signaling pair is required for satellite cell self-renewal. Thus, differentiating cells provide the self-renewing signal during regeneration, enabling proportional regeneration in response to injury while maintaining the satellite cell pool. These findings have implications for therapeutic control of muscle regeneration.

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Targeting PKCθ Promotes Satellite Cell Self-Renewal

International Journal of Molecular Sciences ◽

10.3390/ijms21072419 ◽

2020 ◽

Vol 21 (7) ◽

pp. 2419

Author(s):

Anna Benedetti ◽

Piera Filomena Fiore ◽

Luca Madaro ◽

Biliana Lozanoska-Ochser ◽

Marina Bouché

Keyword(s):

Satellite Cell ◽

Protein Localization ◽

Active Form ◽

Skeletal Muscle Regeneration ◽

Acute Injury ◽

Self Renewal ◽

Genetic Ablation ◽

Promising Target ◽

Inflammatory Milieu

Skeletal muscle regeneration following injury depends on the ability of satellite cells (SCs) to proliferate, self-renew, and eventually differentiate. The factors that regulate the process of self-renewal are poorly understood. In this study we examined the role of PKCθ in SC self-renewal and differentiation. We show that PKCθ is expressed in SCs, and its active form is localized to the chromosomes, centrosomes, and midbody during mitosis. Lack of PKCθ promotes SC symmetric self-renewal division by regulating Pard3 polarity protein localization, without affecting the overall proliferation rate. Genetic ablation of PKCθ or its pharmacological inhibition in vivo did not affect SC number in healthy muscle. By contrast, after induction of muscle injury, lack or inhibition of PKCθ resulted in a significant expansion of the quiescent SC pool. Finally, we show that lack of PKCθ does not alter the inflammatory milieu after acute injury in muscle, suggesting that the enhanced self-renewal ability of SCs in PKCθ-/- mice is not due to an alteration in the inflammatory milieu. Together, these results suggest that PKCθ plays an important role in SC self-renewal by stimulating their expansion through symmetric division, and it may represent a promising target to manipulate satellite cell self-renewal in pathological conditions.

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Caspase 3 cleavage of Pax7 inhibits self-renewal of satellite cells

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1512869112 ◽

2015 ◽

Vol 112 (38) ◽

pp. E5246-E5252 ◽

Cited By ~ 36

Author(s):

Sarah A. Dick ◽

Natasha C. Chang ◽

Nicolas A. Dumont ◽

Ryan A. V. Bell ◽

Charis Putinski ◽

...

Keyword(s):

Skeletal Muscle ◽

Satellite Cells ◽

Posttranslational Modifications ◽

Caspase 3 ◽

Myogenic Differentiation ◽

Skeletal Muscle Regeneration ◽

Stem Cell Population ◽

Myoblast Differentiation ◽

Self Renewal

Compensatory growth and regeneration of skeletal muscle is dependent on the resident stem cell population, satellite cells (SCs). Self-renewal and maintenance of the SC niche is coordinated by the paired-box transcription factor Pax7, and yet continued expression of this protein inhibits the myoblast differentiation program. As such, the reduction or removal of Pax7 may denote a key prerequisite for SCs to abandon self-renewal and acquire differentiation competence. Here, we identify caspase 3 cleavage inactivation of Pax7 as a crucial step for terminating the self-renewal process. Inhibition of caspase 3 results in elevated Pax7 protein and SC self-renewal, whereas caspase activation leads to Pax7 cleavage and initiation of the myogenic differentiation program. Moreover, in vivo inhibition of caspase 3 activity leads to a profound disruption in skeletal muscle regeneration with an accumulation of SCs within the niche. We have also noted that casein kinase 2 (CK2)-directed phosphorylation of Pax7 attenuates caspase-directed cleavage. Together, these results demonstrate that SC fate is dependent on opposing posttranslational modifications of the Pax7 protein.

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Androgen regulation of satellite cell function

Journal of Endocrinology ◽

10.1677/joe.1.05976 ◽

2005 ◽

Vol 186 (1) ◽

pp. 21-31 ◽

Cited By ~ 72

Author(s):

Yue Chen ◽

Jeffrey D Zajac ◽

Helen E MacLean

Keyword(s):

Satellite Cell ◽

Satellite Cells ◽

Cell Activation ◽

Cell Function ◽

Dependent Manner ◽

Androgen Treatment ◽

Androgen Action ◽

Androgen Regulation ◽

And Function

Androgen treatment can enhance the size and strength of muscle. However, the mechanisms of androgen action in skeletal muscle are poorly understood. This review discusses potential mechanisms by which androgens regulate satellite cell activation and function. Studies have demonstrated that androgen administration increases satellite cell numbers in animals and humans in a dose–dependent manner. Moreover, androgens increase androgen receptor levels in satellite cells. In vitro, the results are contradictory as to whether androgens regulate satellite cell proliferation or differentiation. IGF-I is one major target of androgen action in satellite cells. In addition, the possibility of non-genomic actions of androgens on satellite cells is discussed. In summary, this review focuses on exploring potential mechanisms through which androgens regulate satellite cells, by analyzing developments from research in this area.

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Loss of the adipokine lipocalin-2 impairs satellite cell activation and skeletal muscle regeneration

AJP Cell Physiology ◽

10.1152/ajpcell.00195.2017 ◽

2018 ◽

Vol 315 (5) ◽

pp. C714-C721 ◽

Cited By ~ 10

Author(s):

Irena A. Rebalka ◽

Cynthia M. F. Monaco ◽

Nina E. Varah ◽

Thorsten Berger ◽

Donna M. D’souza ◽

...

Keyword(s):

Skeletal Muscle ◽

Satellite Cell ◽

Satellite Cells ◽

Muscle Regeneration ◽

Cell Activation ◽

Skeletal Muscle Regeneration ◽

Matrix Remodeling ◽

Muscle Repair ◽

Lipocalin 2 ◽

The Impact

Lipocalin-2 (LCN2) is an adipokine previously described for its contribution to numerous processes, including innate immunity and energy metabolism. LCN2 has also been demonstrated to be an extracellular matrix (ECM) regulator through its association with the ECM protease matrix metalloproteinase-9 (MMP-9). With the global rise in obesity and the associated comorbidities related to increasing adiposity, it is imperative to gain an understanding of the cross talk between adipose tissue and other metabolic tissues, such as skeletal muscle. Given the function of LCN2 on the ECM in other tissues and the importance of matrix remodeling in skeletal muscle regeneration, we examined the localization and expression of LCN2 in uninjured and regenerating wild-type skeletal muscle and assessed the impact of LCN2 deletion (LCN2−/−) on skeletal muscle repair following cardiotoxin injury. Though LCN2 was minimally present in uninjured skeletal muscle, its expression was increased significantly at 1 and 2 days postinjury, with expression present in Pax7-positive satellite cells. Although satellite cell content was unchanged, the ability of quiescent satellite cells to become activated was significantly impaired in LCN2−/− skeletal muscles. Skeletal muscle regeneration was also significantly compromised as evidenced by decreased embryonic myosin heavy chain expression and smaller regenerating myofiber areas. Consistent with a role for LCN2 in MMP-9 regulation, regenerating muscle also displayed a significant increase in fibrosis and lower ( P = 0.07) MMP-9 activity in LCN2−/− mice at 2 days postinjury. These data highlight a novel role for LCN2 in muscle regeneration and suggest that changes in adipokine expression can significantly impact skeletal muscle repair.

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