Publications by authors named "C Florian Bentzinger"

37 Publications

Best supporting actors.

Science 2019 Mar;363(6431):1051

Département de Pharmacologie-Physiologie, Université de Sherbrooke, Sherbrooke, Quebec J1H 5N4, Canada.

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http://dx.doi.org/10.1126/science.aaw3613DOI Listing
March 2019

Aging Disrupts Muscle Stem Cell Function by Impairing Matricellular WISP1 Secretion from Fibro-Adipogenic Progenitors.

Cell Stem Cell 2019 03 24;24(3):433-446.e7. Epub 2019 Jan 24.

Nestlé Research, EPFL Innovation Park, 1015 Lausanne, Switzerland; School of Life Sciences, Ecole Polytechnique Federale de Lausanne (EPFL), 1015 Lausanne, Switzerland. Electronic address:

Research on age-related regenerative failure of skeletal muscle has extensively focused on the phenotypes of muscle stem cells (MuSCs). In contrast, the impact of aging on regulatory cells in the MuSC niche remains largely unexplored. Here, we demonstrate that aging impairs the function of mouse fibro-adipogenic progenitors (FAPs) and thereby indirectly affects the myogenic potential of MuSCs. Using transcriptomic profiling, we identify WNT1 Inducible Signaling Pathway Protein 1 (WISP1) as a FAP-derived matricellular signal that is lost during aging. WISP1 is required for efficient muscle regeneration and controls the expansion and asymmetric commitment of MuSCs through Akt signaling. Transplantation of young FAPs or systemic treatment with WISP1 restores the myogenic capacity of MuSCs in aged mice and rescues skeletal muscle regeneration. Our work establishes that loss of WISP1 from FAPs contributes to MuSC dysfunction in aged skeletal muscles and demonstrates that this mechanism can be targeted to rejuvenate myogenesis.
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http://dx.doi.org/10.1016/j.stem.2018.12.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6408230PMC
March 2019

The Muscle Stem Cell Niche in Health and Disease.

Curr Top Dev Biol 2018 24;126:23-65. Epub 2017 Nov 24.

Faculté de médecine et des sciences de la santé, Université de Sherbrooke, Sherbrooke, QC, Canada. Electronic address:

The regulation of stem cells that maintain and regenerate postnatal tissues depends on extrinsic signals originating from their microenvironment, commonly referred to as the stem cell niche. Complex higher-order regulatory interrelationships with the tissue and factors in the systemic circulation are integrated and propagated to the stem cells through the niche. The stem cell niche in skeletal muscle tissue is both a paradigm for a structurally and functionally relatively static niche that maintains stem cell quiescence during tissue homeostasis, and a highly dynamic regenerative niche that is subject to extensive structural remodeling and a flux of different support cell populations. Conditions ranging from aging to chronically degenerative skeletal muscle diseases affect the composition of the niche and thereby impair the regenerative potential of muscle stem cells. A holistic and integrative understanding of the extrinsic mechanisms regulating muscle stem cells in health and disease in a broad systemic context will be imperative for the identification of regulatory hubs in the niche interactome that can be targeted to maintain, restore, or enhance the regenerative capacity of muscle tissue. Here, we review the microenvironmental regulation of muscle stem cells, summarize how niche dysfunction can contribute to disease, and discuss emerging therapeutic implications.
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http://dx.doi.org/10.1016/bs.ctdb.2017.08.003DOI Listing
February 2019

R-spondin1 Controls Muscle Cell Fusion through Dual Regulation of Antagonistic Wnt Signaling Pathways.

Cell Rep 2017 03;18(10):2320-2330

Sorbonne Universités, UPMC Univ Paris 06, INSERM UMRS974, CNRS FRE3617, Center for Research in Myology, 75013 Paris, France. Electronic address:

Wnt-mediated signals are involved in many important steps in mammalian regeneration. In multiple cell types, the R-spondin (Rspo) family of secreted proteins potently activates the canonical Wnt/β-catenin pathway. Here, we identify Rspo1 as a mediator of skeletal muscle tissue repair. First, we show that deletion of Rspo1 results in global alteration of muscle regeneration kinetics following acute injury. We find that muscle progenitor cells lacking Rspo1 show delayed differentiation due to reduced activation of Wnt/β-catenin target genes. Furthermore, muscle cells lacking Rspo1 have a fusion phenotype leading to larger myotubes containing supernumerary nuclei both in vitro and in vivo. The increase in muscle fusion was dependent on downregulation of Wnt/β-catenin and upregulation of non-canonical Wnt7a/Fzd7/Rac1 signaling. We conclude that reciprocal control of antagonistic Wnt signaling pathways by Rspo1 in muscle stem cell progeny is a key step ensuring normal tissue architecture restoration following acute damage.
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http://dx.doi.org/10.1016/j.celrep.2017.02.036DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5357729PMC
March 2017

Loss of fibronectin from the aged stem cell niche affects the regenerative capacity of skeletal muscle in mice.

Nat Med 2016 08 4;22(8):897-905. Epub 2016 Jul 4.

Nestlé Institute of Health Sciences (NIHS), Campus École Polytechnique Fédérale de Lausanne, École Polytechnique Fédérale de Lausanne Innovation Park, Lausanne, Switzerland.

Age-related changes in the niche have long been postulated to impair the function of somatic stem cells. Here we demonstrate that the aged stem cell niche in skeletal muscle contains substantially reduced levels of fibronectin (FN), leading to detrimental consequences for the function and maintenance of muscle stem cells (MuSCs). Deletion of the gene encoding FN from young regenerating muscles replicates the aging phenotype and leads to a loss of MuSC numbers. By using an extracellular matrix (ECM) library screen and pathway profiling, we characterize FN as a preferred adhesion substrate for MuSCs and demonstrate that integrin-mediated signaling through focal adhesion kinase and the p38 mitogen-activated protein kinase pathway is strongly de-regulated in MuSCs from aged mice because of insufficient attachment to the niche. Reconstitution of FN levels in the aged niche remobilizes stem cells and restores youth-like muscle regeneration. Taken together, we identify the loss of stem cell adhesion to FN in the niche ECM as a previously unknown aging mechanism.
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http://dx.doi.org/10.1038/nm.4126DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5467443PMC
August 2016

PAX7 is required for patterning the esophageal musculature.

Skelet Muscle 2015 3;5:39. Epub 2015 Dec 3.

Department of Developmental and Regenerative Biology, Mount Sinai School of Medicine, New York, NY 10029 USA ; Graduate School of Biological Sciences, One Gustave L. Levy Place, Icahn School of Medicine at Mount Sinai, New York, NY 10029 USA.

Background: The mammalian esophageal musculature is unique in that it makes a transition from smooth to skeletal muscle, with most of this process occurring after birth. In order to better understand the mechanisms that control esophageal musculature development, we investigated the roles in this process of the paired box transcription factor, PAX7, a principal regulator of skeletal myogenic progenitor cells. Previous studies showed that Pax7 is important for determining the esophageal muscle composition.

Results: We characterized the postnatal development of the esophageal musculature in Pax7 (-/-) mice by analyzing morphology, muscle composition, and the expression of markers of myogenesis, cell proliferation, and apoptosis. Pax7 (-/-) mice displayed megaesophagus with a severe defect in the postnatal developmental process whereby esophageal smooth muscle is replaced by skeletal muscle. Pax7 (-/-) esophagi have substantially reduced skeletal muscle, most likely due to diminished proliferation and premature differentiation of skeletal muscle precursor cells. This impaired the proximal-to-distal progression of skeletal myogenesis and indirectly affected the patterning of the smooth muscle-containing portion of the esophageal musculature.

Conclusions: Postnatal patterning of the esophageal musculature appears to require robust, PAX7-dependent cell proliferation to drive the proximal-to-distal progression of skeletal myogenesis. This process in turn influences distal smooth muscle morphogenesis and development of the mature pattern of the esophageal musculature.
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http://dx.doi.org/10.1186/s13395-015-0068-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4668666PMC
December 2015

Dystrophin expression in muscle stem cells regulates their polarity and asymmetric division.

Nat Med 2015 Dec 16;21(12):1455-63. Epub 2015 Nov 16.

Sprott Center for Stem Cell Research, Ottawa Hospital Research Institute, Regenerative Medicine Program, Ottawa, Ontario, Canada.

Dystrophin is expressed in differentiated myofibers, in which it is required for sarcolemmal integrity, and loss-of-function mutations in the gene that encodes it result in Duchenne muscular dystrophy (DMD), a disease characterized by progressive and severe skeletal muscle degeneration. Here we found that dystrophin is also highly expressed in activated muscle stem cells (also known as satellite cells), in which it associates with the serine-threonine kinase Mark2 (also known as Par1b), an important regulator of cell polarity. In the absence of dystrophin, expression of Mark2 protein is downregulated, resulting in the inability to localize the cell polarity regulator Pard3 to the opposite side of the cell. Consequently, the number of asymmetric divisions is strikingly reduced in dystrophin-deficient satellite cells, which also display a loss of polarity, abnormal division patterns (including centrosome amplification), impaired mitotic spindle orientation and prolonged cell divisions. Altogether, these intrinsic defects strongly reduce the generation of myogenic progenitors that are needed for proper muscle regeneration. Therefore, we conclude that dystrophin has an essential role in the regulation of satellite cell polarity and asymmetric division. Our findings indicate that muscle wasting in DMD not only is caused by myofiber fragility, but also is exacerbated by impaired regeneration owing to intrinsic satellite cell dysfunction.
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http://dx.doi.org/10.1038/nm.3990DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4839960PMC
December 2015

Satellite Cells and Skeletal Muscle Regeneration.

Compr Physiol 2015 Jul;5(3):1027-59

Sprott Centre for Stem Cell Research, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada.

Skeletal muscles are essential for vital functions such as movement, postural support, breathing, and thermogenesis. Muscle tissue is largely composed of long, postmitotic multinucleated fibers. The life-long maintenance of muscle tissue is mediated by satellite cells, lying in close proximity to the muscle fibers. Muscle satellite cells are a heterogeneous population with a small subset of muscle stem cells, termed satellite stem cells. Under homeostatic conditions all satellite cells are poised for activation by stimuli such as physical trauma or growth signals. After activation, satellite stem cells undergo symmetric divisions to expand their number or asymmetric divisions to give rise to cohorts of committed satellite cells and thus progenitors. Myogenic progenitors proliferate, and eventually differentiate through fusion with each other or to damaged fibers to reconstitute fiber integrity and function. In the recent years, research has begun to unravel the intrinsic and extrinsic mechanisms controlling satellite cell behavior. Nonetheless, an understanding of the complex cellular and molecular interactions of satellite cells with their dynamic microenvironment remains a major challenge, especially in pathological conditions. The goal of this review is to comprehensively summarize the current knowledge on satellite cell characteristics, functions, and behavior in muscle regeneration and in pathological conditions.
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http://dx.doi.org/10.1002/cphy.c140068DOI Listing
July 2015

Raptor ablation in skeletal muscle decreases Cav1.1 expression and affects the function of the excitation-contraction coupling supramolecular complex.

Biochem J 2015 Feb;466(1):123-35

*Departments of Anesthesia and of Biomedicine, Basel University Hospital, Hebelstrasse 20, 4031 Basel, Switzerland.

The protein mammalian target of rapamycin (mTOR) is a serine/threonine kinase regulating a number of biochemical pathways controlling cell growth. mTOR exists in two complexes termed mTORC1 and mTORC2. Regulatory associated protein of mTOR (raptor) is associated with mTORC1 and is essential for its function. Ablation of raptor in skeletal muscle results in several phenotypic changes including decreased life expectancy, increased glycogen deposits and alterations of the twitch kinetics of slow fibres. In the present paper, we show that in muscle-specific raptor knockout (RamKO), the bulk of glycogen phosphorylase (GP) is mainly associated in its cAMP-non-stimulated form with sarcoplasmic reticulum (SR) membranes. In addition, 3[H]-ryanodine and 3[H]-PN200-110 equilibrium binding show a ryanodine to dihydropyridine receptors (DHPRs) ratio of 0.79 and 1.35 for wild-type (WT) and raptor KO skeletal muscle membranes respectively. Peak amplitude and time to peak of the global calcium transients evoked by supramaximal field stimulation were not different between WT and raptor KO. However, the increase in the voltage sensor-uncoupled RyRs leads to an increase of both frequency and mass of elementary calcium release events (ECRE) induced by hyper-osmotic shock in flexor digitorum brevis (FDB) fibres from raptor KO. The present study shows that the protein composition and function of the molecular machinery involved in skeletal muscle excitation-contraction (E-C) coupling is affected by mTORC1 signalling.
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http://dx.doi.org/10.1042/BJ20140935DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4843809PMC
February 2015

Inhibition of JAK-STAT signaling stimulates adult satellite cell function.

Nat Med 2014 Oct 7;20(10):1174-81. Epub 2014 Sep 7.

1] Sprott Center For Stem Cell Research, Ottawa Hospital Research Institute, Regenerative Medicine Program, Ottawa, Ontario, Canada. [2] Department of Cellular and Molecular Medicine, University of Ottawa, Faculty of Medicine, Ottawa, Ontario, Canada.

Diminished regenerative capacity of skeletal muscle occurs during adulthood. We identified a reduction in the intrinsic capacity of mouse adult satellite cells to contribute to muscle regeneration and repopulation of the niche. Gene expression analysis identified higher expression of JAK-STAT signaling targets in 3-week [corrected] 18-month-old mice [corrected]. Knockdown of Jak2 or Stat3 significantly stimulated symmetric satellite stem cell divisions on cultured myofibers. Genetic knockdown of Jak2 or Stat3 expression in prospectively isolated satellite cells markedly enhanced their ability to repopulate the satellite cell niche after transplantation into regenerating tibialis anterior muscle. Pharmacological inhibition of Jak2 and Stat3 activity similarly stimulated symmetric expansion of satellite cells in vitro and their engraftment in vivo. Intramuscular injection of these drugs resulted in a marked enhancement of muscle repair and force generation after cardiotoxin injury. Together these results reveal age-related intrinsic properties that functionally distinguish satellite cells and suggest a promising therapeutic avenue for the treatment of muscle-wasting diseases.
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http://dx.doi.org/10.1038/nm.3655DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4191983PMC
October 2014

Wnt7a stimulates myogenic stem cell motility and engraftment resulting in improved muscle strength.

J Cell Biol 2014 Apr 7;205(1):97-111. Epub 2014 Apr 7.

Regenerative Medicine Program, Ottawa Hospital Research Institute, Ottawa, ON K1H 8L6, Canada.

Wnt7a/Fzd7 signaling stimulates skeletal muscle growth and repair by inducing the symmetric expansion of satellite stem cells through the planar cell polarity pathway and by activating the Akt/mTOR growth pathway in muscle fibers. Here we describe a third level of activity where Wnt7a/Fzd7 increases the polarity and directional migration of mouse satellite cells and human myogenic progenitors through activation of Dvl2 and the small GTPase Rac1. Importantly, these effects can be exploited to potentiate the outcome of myogenic cell transplantation into dystrophic muscles. We observed that a short Wnt7a treatment markedly stimulated tissue dispersal and engraftment, leading to significantly improved muscle function. Moreover, myofibers at distal sites that fused with Wnt7a-treated cells were hypertrophic, suggesting that the transplanted cells deliver activated Wnt7a/Fzd7 signaling complexes to recipient myofibers. Taken together, we describe a viable and effective ex vivo cell modulation process that profoundly enhances the efficacy of stem cell therapy for skeletal muscle.
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http://dx.doi.org/10.1083/jcb.201310035DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3987134PMC
April 2014

Rejuvenating aged muscle stem cells.

Nat Med 2014 Mar;20(3):234-5

1] Regenerative Medicine Program, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada, and in the Faculty of Medicine, Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada. [2] Sprott Center for Stem Cell Research, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada.

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http://dx.doi.org/10.1038/nm.3499DOI Listing
March 2014

A truncated Wnt7a retains full biological activity in skeletal muscle.

Nat Commun 2013 ;4:2869

1] Sprott Center for Stem Cell Research, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada K1H8L6 [2] Leibniz Institute for Age Research, Fritz Lipmann Institute (FLI), Beutenbergstrasse 11, 07445 Jena, Germany.

Wnt signaling has essential roles during embryonic development and tissue homoeostasis. Wnt proteins are post-translationally modified and the attachment of a palmitate moiety at two conserved residues is believed to be a prerequisite for the secretion and function of Wnt proteins. Here we demonstrate that a mammalian Wnt protein can be fully functional without palmitoylation. We generate a truncated Wnt7a variant, consisting of the C-terminal 137 amino acids lacking the conserved palmitoylation sites and show that it retains full biological activity in skeletal muscle. This includes binding to and signaling through its receptor Fzd7 to stimulate symmetric expansion of satellite stem cells by activating the planar-cell polarity pathway and inducing myofibre hypertrophy by signaling through the AKT/mTOR pathway. Furthermore, this truncated Wnt7a shows enhanced secretion and dispersion compared with the full-length protein. Together, these findings open important new avenues for the development of Wnt7a as a treatment for muscle-wasting diseases and have broad implications for the therapeutic use of Wnts as biologics.
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http://dx.doi.org/10.1038/ncomms3869DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3868162PMC
October 2014

Cellular dynamics in the muscle satellite cell niche.

EMBO Rep 2013 Dec 15;14(12):1062-72. Epub 2013 Nov 15.

Sprott Center for Stem Cell Research, Ottawa Hospital Research Institute, 501 Smyth Road, Ottawa, Ontario K1H 8L6, Canada.

Satellite cells, the quintessential skeletal muscle stem cells, reside in a specialized local environment whose anatomy changes dynamically during tissue regeneration. The plasticity of this niche is attributable to regulation by the stem cells themselves and to a multitude of functionally diverse cell types. In particular, immune cells, fibrogenic cells, vessel-associated cells and committed and differentiated cells of the myogenic lineage have emerged as important constituents of the satellite cell niche. Here, we discuss the cellular dynamics during muscle regeneration and how disease can lead to perturbation of these mechanisms. To define the role of cellular components in the muscle stem cell niche is imperative for the development of cell-based therapies, as well as to better understand the pathobiology of degenerative conditions of the skeletal musculature.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3849491PMC
http://dx.doi.org/10.1038/embor.2013.182DOI Listing
December 2013

Treating muscular dystrophy by stimulating intrinsic repair.

Regen Med 2013 May;8(3):237-40

Sprott Centre for Stem Cell Research, Ottawa Hospital Research Institute, Ottawa, ON K1H 8L6, Canada.

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http://dx.doi.org/10.2217/rme.13.27DOI Listing
May 2013

Differential response of skeletal muscles to mTORC1 signaling during atrophy and hypertrophy.

Skelet Muscle 2013 Mar 6;3(1). Epub 2013 Mar 6.

Biozentrum, University of Basel, Basel, CH-4056, Switzerland.

Background: Skeletal muscle mass is determined by the balance between protein synthesis and degradation. Mammalian target of rapamycin complex 1 (mTORC1) is a master regulator of protein translation and has been implicated in the control of muscle mass. Inactivation of mTORC1 by skeletal muscle-specific deletion of its obligatory component raptor results in smaller muscles and a lethal dystrophy. Moreover, raptor-deficient muscles are less oxidative through changes in the expression PGC-1α, a critical determinant of mitochondrial biogenesis. These results suggest that activation of mTORC1 might be beneficial to skeletal muscle by providing resistance to muscle atrophy and increasing oxidative function. Here, we tested this hypothesis by deletion of the mTORC1 inhibitor tuberous sclerosis complex (TSC) in muscle fibers.

Method: Skeletal muscles of mice with an acute or a permanent deletion of raptor or TSC1 were examined using histological, biochemical and molecular biological methods. Response of the muscles to changes in mechanical load and nerve input was investigated by ablation of synergistic muscles or by denervation .

Results: Genetic deletion or knockdown of raptor, causing inactivation of mTORC1, was sufficient to prevent muscle growth and enhance muscle atrophy. Conversely, short-term activation of mTORC1 by knockdown of TSC induced muscle fiber hypertrophy and atrophy-resistance upon denervation, in both fast tibialis anterior (TA) and slow soleus muscles. Surprisingly, however, sustained activation of mTORC1 by genetic deletion of Tsc1 caused muscle atrophy in all but soleus muscles. In contrast, oxidative capacity was increased in all muscles examined. Consistently, TSC1-deficient soleus muscle was atrophy-resistant whereas TA underwent normal atrophy upon denervation. Moreover, upon overloading, plantaris muscle did not display enhanced hypertrophy compared to controls. Biochemical analysis indicated that the atrophy response of muscles was based on the suppressed phosphorylation of PKB/Akt via feedback inhibition by mTORC1 and subsequent increased expression of the E3 ubiquitin ligases MuRF1 and atrogin-1/MAFbx. In contrast, expression of both E3 ligases was not increased in soleus muscle suggesting the presence of compensatory mechanisms in this muscle.

Conclusions: Our study shows that the mTORC1- and the PKB/Akt-FoxO pathways are tightly interconnected and differentially regulated depending on the muscle type. These results indicate that long-term activation of the mTORC1 signaling axis is not a therapeutic option to promote muscle growth because of its strong feedback induction of the E3 ubiquitin ligases involved in protein degradation.
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http://dx.doi.org/10.1186/2044-5040-3-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3622636PMC
March 2013

MicroRNA-133 controls brown adipose determination in skeletal muscle satellite cells by targeting Prdm16.

Cell Metab 2013 Feb;17(2):210-24

Regenerative Medicine Program, Ottawa Hospital Research Institute, Ottawa, ON K1H 8L6, Canada.

Brown adipose tissue (BAT) is an energy-dispensing thermogenic tissue that plays an important role in balancing energy metabolism. Lineage-tracing experiments indicate that brown adipocytes are derived from myogenic progenitors during embryonic development. However, adult skeletal muscle stem cells (satellite cells) have long been considered uniformly determined toward the myogenic lineage. Here, we report that adult satellite cells give rise to brown adipocytes and that microRNA-133 regulates the choice between myogenic and brown adipose determination by targeting the 3'UTR of Prdm16. Antagonism of microRNA-133 during muscle regeneration increases uncoupled respiration, glucose uptake, and thermogenesis in local treated muscle and augments whole-body energy expenditure, improves glucose tolerance, and impedes the development of diet-induced obesity. Finally, we demonstrate that miR-133 levels are downregulated in mice exposed to cold, resulting in de novo generation of satellite cell-derived brown adipocytes. Therefore, microRNA-133 represents an important therapeutic target for the treatment of obesity.
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http://dx.doi.org/10.1016/j.cmet.2013.01.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3641657PMC
February 2013

Fibronectin regulates Wnt7a signaling and satellite cell expansion.

Cell Stem Cell 2013 Jan;12(1):75-87

Regenerative Medicine Program, Ottawa Hospital Research Institute, Ottawa, ON, Canada.

The influence of the extracellular matrix (ECM) within the stem cell niche remains poorly understood. We found that Syndecan-4 (Sdc4) and Frizzled-7 (Fzd7) form a coreceptor complex in satellite cells and that binding of the ECM glycoprotein Fibronectin (FN) to Sdc4 stimulates the ability of Wnt7a to induce the symmetric expansion of satellite stem cells. Newly activated satellite cells dynamically remodel their niche via transient high-level expression of FN. Knockdown of FN in prospectively isolated satellite cells severely impaired their ability to repopulate the satellite cell niche. Conversely, in vivo overexpression of FN with Wnt7a dramatically stimulated the expansion of satellite stem cells in regenerating muscle. Therefore, activating satellite cells remodel their niche through autologous expression of FN that provides feedback to stimulate Wnt7a signaling through the Fzd7/Sdc4 coreceptor complex. Thus, FN and Wnt7a together regulate the homeostatic levels of satellite stem cells and satellite myogenic cells during regenerative myogenesis.
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http://dx.doi.org/10.1016/j.stem.2012.09.015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3539137PMC
January 2013

Wnt signaling in myogenesis.

Trends Cell Biol 2012 Nov 31;22(11):602-9. Epub 2012 Aug 31.

Sprott Center for Stem Cell Research, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada.

The formation of skeletal muscle is a tightly regulated process that is critically modulated by Wnt signaling. Myogenesis is dependent on the precise and dynamic integration of multiple Wnt signals allowing self-renewal and progression of muscle precursors in the myogenic lineage. Dysregulation of Wnt signaling can lead to severe developmental defects and perturbation of muscle homeostasis. Recent work has revealed novel roles for the non-canonical planar cell polarity (PCP) and AKT/mTOR pathways in mediating the effects of Wnt on skeletal muscle. In this review, we discuss the role of Wnt signaling in myogenesis and in regulating the homeostasis of adult muscle.
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http://dx.doi.org/10.1016/j.tcb.2012.07.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3479319PMC
November 2012

The emerging biology of muscle stem cells: implications for cell-based therapies.

Bioessays 2013 Mar 6;35(3):231-41. Epub 2012 Aug 6.

The Sprott Centre for Stem Cell Research, Regenerative Medicine Program, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada.

Cell-based therapies for degenerative diseases of the musculature remain on the verge of feasibility. Myogenic cells are relatively abundant, accessible, and typically harbor significant proliferative potential ex vivo. However, their use for therapeutic intervention is limited due to several critical aspects of their complex biology. Recent insights based on mouse models have advanced our understanding of the molecular mechanisms controlling the function of myogenic progenitors significantly. Moreover, the discovery of atypical myogenic cell types with the ability to cross the blood-muscle barrier has opened exciting new therapeutic avenues. In this paper, we outline the major problems that are currently associated with the manipulation of myogenic cells and discuss promising strategies to overcome these obstacles.
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http://dx.doi.org/10.1002/bies.201200063DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3594813PMC
March 2013

Building muscle: molecular regulation of myogenesis.

Cold Spring Harb Perspect Biol 2012 Feb 1;4(2). Epub 2012 Feb 1.

The Sprott Centre for Stem Cell Research, Regenerative Medicine Program, Ottawa Health Research Institute, Ottawa, Ontario, Canada.

The genesis of skeletal muscle during embryonic development and postnatal life serves as a paradigm for stem and progenitor cell maintenance, lineage specification, and terminal differentiation. An elaborate interplay of extrinsic and intrinsic regulatory mechanisms controls myogenesis at all stages of development. Many aspects of adult myogenesis resemble or reiterate embryonic morphogenetic episodes, and related signaling mechanisms control the genetic networks that determine cell fate during these processes. An integrative view of all aspects of myogenesis is imperative for a comprehensive understanding of muscle formation. This article provides a holistic overview of the different stages and modes of myogenesis with an emphasis on the underlying signals, molecular switches, and genetic networks.
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http://dx.doi.org/10.1101/cshperspect.a008342DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3281568PMC
February 2012

Wnt7a-Fzd7 signalling directly activates the Akt/mTOR anabolic growth pathway in skeletal muscle.

Nat Cell Biol 2011 Dec 18;14(2):186-91. Epub 2011 Dec 18.

Sprott Center for Stem Cell Research, Ottawa Hospital Research Institute, Ottawa, Ontario K1H 8L6, Canada.

Wnt7a signals through its receptor Fzd7 to activate the planar-cell-polarity pathway and drive the symmetric expansion of satellite stem cells resulting in enhanced repair of skeletal muscle. In differentiated myofibres, we observed that Wnt7a binding to Fzd7 directly activates the Akt/mTOR growth pathway, thereby inducing myofibre hypertrophy. Notably, the Fzd7 receptor complex was associated with Gα(s) and PI(3)K and these components were required for Wnt7a to activate the Akt/mTOR growth pathway in myotubes. Wnt7a-Fzd7 activation of this pathway was completely independent of IGF-receptor activation. Together, these experiments demonstrate that Wnt7a-Fzd7 activates distinct pathways at different developmental stages during myogenic lineage progression, and identify a non-canonical anabolic signalling pathway for Wnt7a and its receptor Fzd7 in skeletal muscle.
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http://dx.doi.org/10.1038/ncb2404DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3271181PMC
December 2011

Myopathy caused by mammalian target of rapamycin complex 1 (mTORC1) inactivation is not reversed by restoring mitochondrial function.

Proc Natl Acad Sci U S A 2011 Dec 5;108(51):20808-13. Epub 2011 Dec 5.

Biozentrum, University of Basel, 4056 Basel, Switzerland.

Mammalian target of rapamycin complex 1 (mTORC1) is central to the control of cell, organ, and body size. Skeletal muscle-specific inactivation of mTORC1 in mice results in smaller muscle fibers, fewer mitochondria, increased glycogen stores, and a progressive myopathy that causes premature death. In mTORC1-deficient muscles, peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α), which regulates mitochondrial biogenesis and glucose homeostasis, is strongly down-regulated. Here we tested whether induction of mitochondrial biogenesis pharmacologically or by the overexpression of PGC-1α is sufficient to reverse the phenotype of mice deficient for mTORC1. We show that both approaches normalize mitochondrial function, such as oxidative capacity and expression of mitochondrial genes. However, they do not prevent or delay the progressive myopathy. In addition, we find that mTORC1 has a much stronger effect than PGC-1α on the glycogen content in muscle. This effect is based on the strong activation of PKB/Akt in mTORC1-deficient mice. We also show that activation of PKB/Akt not only affects glycogen synthesis but also diminishes glycogen degradation. Thus, our work provides strong functional evidence that mitochondrial dysfunction in mice with inactivated mTORC1 signaling is caused by the down-regulation of PGC-1α. However, our data also show that the impairment of mitochondria does not lead directly to the lethal myopathy.
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http://dx.doi.org/10.1073/pnas.1111448109DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3251091PMC
December 2011

Extrinsic regulation of satellite cell specification.

Stem Cell Res Ther 2010 Aug 26;1(3):27. Epub 2010 Aug 26.

The Sprott Centre for Stem Cell Research, Regenerative Medicine Program, Ottawa Health Research Institute, Ottawa, Ontario K1 H 8L6, Canada.

Cellular commitment during vertebrate embryogenesis is controlled by an interplay of intrinsic regulators and morphogenetic signals. These mechanisms recruit a subset of cells in the developing organism to become the ancestors of skeletal muscle. Signals that control progression through the myogenic lineage converge on a battery of hierarchically organized transcription factors which modulate the cells to either remain in a primitive state or allow their commitment and differentiation into skeletal muscle fibers. A small population of cells will retain a largely unspecified state throughout development. Such stem cells, in conjunction with more committed myogenic progenitors, form a heterogeneous population that colonizes adult skeletal muscle as satellite cells. The satellite cell pool is responsible for the remarkable regenerative capacity of skeletal muscle. Similar to their counterparts during embryonic development, satellite cells are capable of self-renewal and can give rise to myogenic progeny. Impaired satellite cell homeostasis has been associated with numerous muscular disorders. Due to intense research efforts in the past two decades, the complex biology of muscle stem cells has now revealed some of its secrets and new avenues for the development of therapeutic molecules have emerged. In the present review we focus on the extrinsic mechanisms that control self-renewal, specification and differentiation of satellite cells and their significance for the development of biologic drugs.
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http://dx.doi.org/10.1186/scrt27DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2941119PMC
August 2010

Oxidative status of muscle is determined by p107 regulation of PGC-1alpha.

J Cell Biol 2010 Aug 16;190(4):651-62. Epub 2010 Aug 16.

Regenerative Medicine Program, Ottawa Health Research Institute, Ottawa, Ontario, Canada.

Mice lacking p107 exhibit a white adipose deficiency yet do not manifest the metabolic changes typical for lipodystrophy, and instead exhibit low levels of serum triglycerides and a normal liver phenotype. When fed a high fat diet, p107-null mice still did not accumulate fat in the liver, and display markedly elevated energy expenditures together with an increased energy preference for lipids. Skeletal muscle was therefore examined, as this is normally the major tissue involved in whole body lipid metabolism. Notably, p107-deficient muscle express increased levels of peroxisome proliferator-activated receptor gamma co-activator-1alpha (PGC-1alpha) and contained increased numbers of the pro-oxidative type I and type IIa myofibers. Chromatin immunoprecipitation revealed binding of p107 and E2F4 to the PGC-1alpha proximal promoter, and this binding repressed promoter activity in transient transcription assays. Ectopic expression of p107 in muscle tissue in vivo results in a pronounced 20% decrease in the numbers of oxidative type IIa myofibers. Lastly, isolated p107-deficient muscle tissue display a threefold increase in lipid metabolism. Therefore, p107 determines the oxidative state of multiple tissues involved in whole body fat metabolism, including skeletal muscle.
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http://dx.doi.org/10.1083/jcb.201005076DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2928004PMC
August 2010

Skeletal muscle-specific ablation of raptor, but not of rictor, causes metabolic changes and results in muscle dystrophy.

Cell Metab 2008 Nov;8(5):411-24

Biozentrum, University of Basel, CH-4056 Basel, Switzerland.

Mammalian target of rapamycin (mTOR) is a central controller of cell growth. mTOR assembles into two distinct multiprotein complexes called mTOR complex 1 (mTORC1) and mTORC2. Here we show that the mTORC1 component raptor is critical for muscle function and prolonged survival. In contrast, muscles lacking the mTORC2 component rictor are indistinguishable from wild-type controls. Raptor-deficient muscles become progressively dystrophic, are impaired in their oxidative capacity, and contain increased glycogen stores, but they express structural components indicative of oxidative muscle fibers. Biochemical analysis indicates that these changes are probably due to loss of activation of direct downstream targets of mTORC1, downregulation of genes involved in mitochondrial biogenesis, including PGC1alpha, and hyperactivation of PKB/Akt. Finally, we show that activation of PKB/Akt does not require mTORC2. Together, these results demonstrate that muscle mTORC1 has an unexpected role in the regulation of the metabolic properties and that its function is essential for life.
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http://dx.doi.org/10.1016/j.cmet.2008.10.002DOI Listing
November 2008

Overexpression of mini-agrin in skeletal muscle increases muscle integrity and regenerative capacity in laminin-alpha2-deficient mice.

FASEB J 2005 Jun;19(8):934-42

Biozentrum, University of Basel, Basel, Switzerland.

Mutations in the gene encoding the alpha2 subunit of laminins cause the severe "merosin-deficient congenital muscular dystrophy" (MDC1A). We have recently shown that overexpression of a miniaturized form of the molecule agrin (mini-agrin) counteracts the disease in dy(W)/dy(W) mice, a model for MDC1A. However, these mice express some residual truncated laminin-alpha2, suggesting that the observed amelioration might be due to mini-agrin's presenting the residual laminin-alpha2 to its receptors. Here we show that the mini-agrin counteracts the disease in dy(3K)/dy(3K) mice, which are null for laminin-alpha2. As in dy(W)/dy(W) mice, mini-agrin improves both the function and structure of muscle. We show that muscle regeneration after injury is severely impaired in dy(3K)/dy(3K) mice but is restored in the mini-agrin-expressing littermates. In summary, our results 1) show that the direct linkage of muscle basal lamina with the sarcolemma is the basis of mini-agrin-mediated amelioration and 2) provide unprecedented evidence that this linkage is important for proper regeneration of muscle fibers after injury. Our findings thus suggest that treatment with mini-agrin might be beneficial over the entire spectrum of the MDC1A disease, whose severity inversely correlates with expression levels and the size of the truncation in laminin-alpha2.
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http://dx.doi.org/10.1096/fj.04-3376comDOI Listing
June 2005

Flumazenil in benzodiazepine antagonism. Actions and clinical use in intoxications and anaesthesiology.

Med Toxicol Adverse Drug Exp 1987 Nov-Dec;2(6):411-29

Department of Clinical Research, F. Hoffmann-La Roche & Co. Ltd, Basel.

In anaesthesia and in the intensive care unit, benzodiazepines have proven safe and effective agents for the induction and maintenance of sedation for a variety of therapeutic goals. However, in these contexts, or in benzodiazepine overdose, it is often desirable to be able to terminate or interrupt sedation without waiting for the effect of the benzodiazepine to become dissipated by normal metabolism and excretion. Flumazenil, a 1,4-imidazobenzodiazepine, is a highly effective, specific benzodiazepine antagonist which is indicated for use when the effect of a benzodiazepine must be attenuated or terminated at short notice. It acts by displacing other benzodiazepines from the receptor site by competitive inhibition. The onset of effect after intravenous administration occurs within 1 to 3 minutes. The optimal dosage is determined for each patient by a dose titration procedure and lies in the range 0.2 to 1.0mg in anaesthesiology, and 0.1 to 2.0mg in intensive care use. Despite its short elimination half-life of around 1 hour, after general anaesthesia or conscious to moderate sedation for short procedures, a single dose of flumazenil is usually sufficient to attain and maintain the desired level of consciousness. After intoxication with high benzodiazepine doses, the duration of effect of a single dose of flumazenil is not expected to exceed 1 hour. In such cases, the period of wakefulness can be prolonged as necessary by repeated low intravenous doses of flumazenil or by infusion (0.1 mg/hour). Flumazenil is well tolerated both systemically and locally. The only adverse events seen with greater frequency after flumazenil compared with placebo were nausea and/or vomiting after general anaesthesia, although the incidence of actual vomiting was not significantly different between the 2 groups. Since these effects were virtually absent in studies of intensive care patients and after sedation for short procedures, and were not seen in tolerability studies in healthy volunteers receiving intravenous bolus doses of up to 100mg, there may be a link between these symptoms and the other agents used in general anaesthesia, some of which have well-known emetic properties. Thus, flumazenil provides a safe and effective means of attenuating or reversing the CNS-depressant effects of benzodiazepines whenever indicated, e.g. following benzodiazepine-induced general anaesthesia, conscious sedation, or after benzodiazepine overdose, either alone or in combination with other agents.(ABSTRACT TRUNCATED AT 400 WORDS)
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http://dx.doi.org/10.1007/BF03259876DOI Listing
February 1988