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Thürkauf M, Lin S, Oliveri F, Grimm D, Platt RJ, Rüegg MA. Fast, multiplexable and efficient somatic gene deletions in adult mouse skeletal muscle fibers using AAV-CRISPR/Cas9. Nat Commun 2023; 14:6116. [PMID: 37777530 PMCID: PMC10542775 DOI: 10.1038/s41467-023-41769-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2023] [Accepted: 09/19/2023] [Indexed: 10/02/2023] Open
Abstract
Molecular screens comparing different disease states to identify candidate genes rely on the availability of fast, reliable and multiplexable systems to interrogate genes of interest. CRISPR/Cas9-based reverse genetics is a promising method to eventually achieve this. However, such methods are sorely lacking for multi-nucleated muscle fibers, since highly efficient nuclei editing is a requisite to robustly inactive candidate genes. Here, we couple Cre-mediated skeletal muscle fiber-specific Cas9 expression with myotropic adeno-associated virus-mediated sgRNA delivery to establish a system for highly effective somatic gene deletions in mice. Using well-characterized genes, we show that local or systemic inactivation of these genes copy the phenotype of traditional gene-knockout mouse models. Thus, this proof-of-principle study establishes a method to unravel the function of individual genes or entire signaling pathways in adult skeletal muscle fibers without the cumbersome requirement of generating knockout mice.
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Affiliation(s)
| | - Shuo Lin
- Biozentrum, University of Basel, Basel, Switzerland
| | | | - Dirk Grimm
- Department of Infectious Diseases/Virology, Section Viral Vector Technologies, Medical Faculty, Heidelberg University, Heidelberg, Germany
- BioQuant, University of Heidelberg, Heidelberg, Germany
- German Center for Infection Research (DZIF) and German Center for Cardiovascular Research (DZHK), Heidelberg, Germany
| | - Randall J Platt
- Department of Biosystems Science and Engineering (D-BSSE), ETH Zurich, Basel, Switzerland
- Department of Chemistry, University of Basel, Basel, Switzerland
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2
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Blandino-Rosano M, Louzada RA, Werneck-De-Castro JP, Lubaczeuski C, Almaça J, Rüegg MA, Hall MN, Leibowitz G, Bernal-Mizrachi E. Raptor levels are critical for β-cell adaptation to a high-fat diet in male mice. Mol Metab 2023; 75:101769. [PMID: 37423392 PMCID: PMC10391668 DOI: 10.1016/j.molmet.2023.101769] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/20/2023] [Revised: 06/19/2023] [Accepted: 06/29/2023] [Indexed: 07/11/2023] Open
Abstract
OBJECTIVE The essential role of raptor/mTORC1 signaling in β-cell survival and insulin processing has been recently demonstrated using raptor knock-out models. Our aim was to evaluate the role of mTORC1 function in adaptation of β-cells to insulin resistant state. METHOD Here, we use mice with heterozygous deletion of raptor in β-cells (βraHet) to assess whether reduced mTORC1 function is critical for β-cell function in normal conditions or during β-cell adaptation to high-fat diet (HFD). RESULTS Deletion of a raptor allele in β-cells showed no differences at the metabolic level, islets morphology, or β-cell function in mice fed regular chow. Surprisingly, deletion of only one allele of raptor increases apoptosis without altering proliferation rate and is sufficient to impair insulin secretion when fed a HFD. This is accompanied by reduced levels of critical β-cell genes like Ins1, MafA, Ucn3, Glut2, Glp1r, and specially PDX1 suggesting an improper β-cell adaptation to HFD. CONCLUSION This study identifies that raptor levels play a key role in maintaining PDX1 levels and β-cell function during the adaptation of β-cell to HFD. Finally, we identified that Raptor levels regulate PDX1 levels and β-cell function during β-cell adaptation to HFD by reduction of the mTORC1-mediated negative feedback and activation of the AKT/FOXA2/PDX1 axis. We suggest that Raptor levels are critical to maintaining PDX1 levels and β-cell function in conditions of insulin resistance in male mice.
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Affiliation(s)
- Manuel Blandino-Rosano
- Department of Internal Medicine, Division of Endocrinology, Diabetes and Metabolism, Miller School of Medicine, University of Miami, Miami, FL, USA; Miami VA Health Care System, Miami, FL, USA.
| | - Ruy Andrade Louzada
- Department of Internal Medicine, Division of Endocrinology, Diabetes and Metabolism, Miller School of Medicine, University of Miami, Miami, FL, USA
| | - Joao Pedro Werneck-De-Castro
- Department of Internal Medicine, Division of Endocrinology, Diabetes and Metabolism, Miller School of Medicine, University of Miami, Miami, FL, USA; Miami VA Health Care System, Miami, FL, USA
| | - Camila Lubaczeuski
- Department of Internal Medicine, Division of Endocrinology, Diabetes and Metabolism, Miller School of Medicine, University of Miami, Miami, FL, USA
| | - Joana Almaça
- Department of Internal Medicine, Division of Endocrinology, Diabetes and Metabolism, Miller School of Medicine, University of Miami, Miami, FL, USA
| | - Markus A Rüegg
- Biozentrum, University of Basel, CH-4056, Basel, Switzerland
| | - Michael N Hall
- Biozentrum, University of Basel, CH-4056, Basel, Switzerland
| | - Gil Leibowitz
- Diabetes Unit and Endocrine Service, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
| | - Ernesto Bernal-Mizrachi
- Department of Internal Medicine, Division of Endocrinology, Diabetes and Metabolism, Miller School of Medicine, University of Miami, Miami, FL, USA; Miami VA Health Care System, Miami, FL, USA.
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3
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Reinhard JR, Porrello E, Lin S, Pelczar P, Previtali SC, Rüegg MA. Nerve pathology is prevented by linker proteins in mouse models for LAMA2-related muscular dystrophy. PNAS Nexus 2023; 2:pgad083. [PMID: 37038437 PMCID: PMC10082391 DOI: 10.1093/pnasnexus/pgad083] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2022] [Accepted: 03/06/2023] [Indexed: 03/17/2023]
Abstract
Abstract
LAMA2-related muscular dystrophy (LAMA2 MD or MDC1A) is a devastating congenital muscular dystrophy that is caused by mutations in the LAMA2 gene encoding laminin-α2, the long chain of several heterotrimeric laminins. Laminins are essential components of the extracellular matrix that interface with underlying cells. The pathology of LAMA2 MD patients is dominated by an early-onset, severe muscular dystrophy that ultimately leads to death by respiratory insufficiency. However, pathology in non-muscle tissues has been described. Prior work in the dyW/dyW mouse model for LAMA2 MD has shown that two linker proteins, mini-agrin and αLNNd, when expressed in skeletal muscle fibers, greatly increase survival from a few months up to more than 2 years. However, the restoration of skeletal muscle function accentuates the pathology in non-muscle tissue in dyW/dyW mice, first and foremost in the peripheral nerve resulting in paralysis of the hindlimbs. We now show that expression of the two linker proteins in all tissues ameliorates the muscular dystrophy and prevents the appearance of the hindlimb paralysis. Importantly, the same ameliorating effect of the linker proteins was seen in dy3K/dy3K mice, which represent the most severe mouse model of LAMA2 MD. In summary, these data show that the two linker proteins can compensate the loss of laminin-α2 in muscle and peripheral nerve, which are the two organs most affected in LAMA2 MD. These results are of key importance for designing appropriate expression constructs for mini-agrin and αLNNd to develop a gene therapy for LAMA2 MD patients.
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Affiliation(s)
| | - Emanuela Porrello
- Neuromuscular Repair Unit, InSpe and Division of Neuroscience, IRCCS Ospedale San Raffaele , Milano , Italy
| | - Shuo Lin
- Biozentrum, University of Basel , Basel , Switzerland
| | - Pawel Pelczar
- Center for Transgenic Models, University of Basel , Basel , Switzerland
| | - Stefano C Previtali
- Neuromuscular Repair Unit, InSpe and Division of Neuroscience, IRCCS Ospedale San Raffaele , Milano , Italy
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4
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Kaiser MS, Milan G, Ham DJ, Lin S, Oliveri F, Chojnowska K, Tintignac LA, Mittal N, Zimmerli CE, Glass DJ, Zavolan M, Rüegg MA. Dual roles of mTORC1-dependent activation of the ubiquitin-proteasome system in muscle proteostasis. Commun Biol 2022; 5:1141. [PMID: 36302954 PMCID: PMC9613904 DOI: 10.1038/s42003-022-04097-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Accepted: 10/11/2022] [Indexed: 12/02/2022] Open
Abstract
Muscle size is controlled by the PI3K-PKB/Akt-mTORC1-FoxO pathway, which integrates signals from growth factors, energy and amino acids to activate protein synthesis and inhibit protein breakdown. While mTORC1 activity is necessary for PKB/Akt-induced muscle hypertrophy, its constant activation alone induces muscle atrophy. Here we show that this paradox is based on mTORC1 activity promoting protein breakdown through the ubiquitin-proteasome system (UPS) by simultaneously inducing ubiquitin E3 ligase expression via feedback inhibition of PKB/Akt and proteasome biogenesis via Nuclear Factor Erythroid 2-Like 1 (Nrf1). Muscle growth was restored by reactivation of PKB/Akt, but not by Nrf1 knockdown, implicating ubiquitination as the limiting step. However, both PKB/Akt activation and proteasome depletion by Nrf1 knockdown led to an immediate disruption of proteome integrity with rapid accumulation of damaged material. These data highlight the physiological importance of mTORC1-mediated PKB/Akt inhibition and point to juxtaposed roles of the UPS in atrophy and proteome integrity. Exploring the relationship between mTORC1 and the ubiquitin-proteasome system, light is shed on the paradox between mTORC1-mediated muscle hypertrophy induced by PKB/Akt and the muscle atrophy induced by mTORC1 alone.
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Affiliation(s)
- Marco S Kaiser
- Biozentrum, University of Basel, Basel, Switzerland.,BIOREBA AG, Christoph Merian-Ring 7, 4153, Reinach, Switzerland
| | - Giulia Milan
- Biozentrum, University of Basel, Basel, Switzerland. .,Department of Biomedicine, University of Basel, Hebelstrasse 20, 4031, Basel, Switzerland.
| | - Daniel J Ham
- Biozentrum, University of Basel, Basel, Switzerland.
| | - Shuo Lin
- Biozentrum, University of Basel, Basel, Switzerland
| | | | - Kathrin Chojnowska
- Biozentrum, University of Basel, Basel, Switzerland.,AstraZeneca AG, Neuhofstrasse 34, 6340, Baar, Switzerland
| | - Lionel A Tintignac
- Biozentrum, University of Basel, Basel, Switzerland.,Neuromuscular Research Group, Departments of Neurology and Biomedicine, University of Basel, University Hospital Basel, Basel, Switzerland
| | | | - Christian E Zimmerli
- Biozentrum, University of Basel, Basel, Switzerland.,Department of Molecular Sociology, Max Planck Institute of Biophysics, Max-von-Laue-Straße 3, 60438, Frankfurt am Main, Germany
| | - David J Glass
- Novartis Institutes for Biomedical Research, Cambridge, MA, USA.,Regeneron Pharmaceuticals, Tarrytown, NY, USA
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5
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Blandino-Rosano M, Scheys JO, Werneck-de-Castro JP, Louzada RA, Almaça J, Leibowitz G, Rüegg MA, Hall MN, Bernal-Mizrachi E. Novel roles of mTORC2 in regulation of insulin secretion by actin filament remodeling. Am J Physiol Endocrinol Metab 2022; 323:E133-E144. [PMID: 35723227 PMCID: PMC9291412 DOI: 10.1152/ajpendo.00076.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Mammalian target of rapamycin (mTOR) kinase is an essential hub where nutrients and growth factors converge to control cellular metabolism. mTOR interacts with different accessory proteins to form complexes 1 and 2 (mTORC), and each complex has different intracellular targets. Although mTORC1's role in β-cells has been extensively studied, less is known about mTORC2's function in β-cells. Here, we show that mice with constitutive and inducible β-cell-specific deletion of RICTOR (βRicKO and iβRicKO mice, respectively) are glucose intolerant due to impaired insulin secretion when glucose is injected intraperitoneally. Decreased insulin secretion in βRicKO islets was caused by abnormal actin polymerization. Interestingly, when glucose was administered orally, no difference in glucose homeostasis and insulin secretion were observed, suggesting that incretins are counteracting the mTORC2 deficiency. Mechanistically, glucagon-like peptide-1 (GLP-1), but not gastric inhibitory polypeptide (GIP), rescued insulin secretion in vivo and in vitro by improving actin polymerization in βRicKO islets. In conclusion, mTORC2 regulates glucose-stimulated insulin secretion by promoting actin filament remodeling.NEW & NOTEWORTHY The current studies uncover a novel mechanism linking mTORC2 signaling to glucose-stimulated insulin secretion by modulation of the actin filaments. This work also underscores the important role of GLP-1 in rescuing defects in insulin secretion by modulating actin polymerization and suggests that this effect is independent of mTORC2 signaling.
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Affiliation(s)
- Manuel Blandino-Rosano
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida
| | - Joshua O Scheys
- Medical School, Division of Metabolism, Endocrinology, and Diabetes and Brehm Center for Diabetes Research, Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan
| | - Joao Pedro Werneck-de-Castro
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida
| | - Ruy A Louzada
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida
| | - Joana Almaça
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida
| | - Gil Leibowitz
- Diabetes Unit and Endocrine Service, Hadassah-Hebrew University Medical Center, Jerusalem, Israel
| | | | | | - Ernesto Bernal-Mizrachi
- Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine, University of Miami Miller School of Medicine, Miami, Florida
- Miami VA Healthcare System, Miami, Florida
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6
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Pereira JA, Gerber J, Ghidinelli M, Gerber D, Tortola L, Ommer A, Bachofner S, Santarella F, Tinelli E, Lin S, Rüegg MA, Kopf M, Toyka KV, Suter U. Mice carrying an analogous heterozygous dynamin 2 K562E mutation that causes neuropathy in humans develop predominant characteristics of a primary myopathy. Hum Mol Genet 2021; 29:1253-1273. [PMID: 32129442 PMCID: PMC7254847 DOI: 10.1093/hmg/ddaa034] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Revised: 02/21/2020] [Accepted: 02/25/2020] [Indexed: 12/13/2022] Open
Abstract
Some mutations affecting dynamin 2 (DNM2) can cause dominantly inherited Charcot–Marie–Tooth (CMT) neuropathy. Here, we describe the analysis of mice carrying the DNM2 K562E mutation which has been associated with dominant-intermediate CMT type B (CMTDIB). Contrary to our expectations, heterozygous DNM2 K562E mutant mice did not develop definitive signs of an axonal or demyelinating neuropathy. Rather, we found a primary myopathy-like phenotype in these mice. A likely interpretation of these results is that the lack of a neuropathy in this mouse model has allowed the unmasking of a primary myopathy due to the DNM2 K562E mutation which might be overshadowed by the neuropathy in humans. Consequently, we hypothesize that a primary myopathy may also contribute to the disease mechanism in some CMTDIB patients. We propose that these findings should be considered in the evaluation of patients, the determination of the underlying disease processes and the development of tailored potential treatment strategies.
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Affiliation(s)
- Jorge A Pereira
- Department of Biology, Institute of Molecular Health Sciences, Swiss Federal Institute of Technology, ETH Zurich, 8093 Zurich, Switzerland
| | - Joanne Gerber
- Department of Biology, Institute of Molecular Health Sciences, Swiss Federal Institute of Technology, ETH Zurich, 8093 Zurich, Switzerland
| | - Monica Ghidinelli
- Department of Biology, Institute of Molecular Health Sciences, Swiss Federal Institute of Technology, ETH Zurich, 8093 Zurich, Switzerland
| | - Daniel Gerber
- Department of Biology, Institute of Molecular Health Sciences, Swiss Federal Institute of Technology, ETH Zurich, 8093 Zurich, Switzerland
| | - Luigi Tortola
- Department of Biology, Institute of Molecular Health Sciences, Swiss Federal Institute of Technology, ETH Zurich, 8093 Zurich, Switzerland
| | - Andrea Ommer
- Department of Biology, Institute of Molecular Health Sciences, Swiss Federal Institute of Technology, ETH Zurich, 8093 Zurich, Switzerland
| | - Sven Bachofner
- Department of Biology, Institute of Molecular Health Sciences, Swiss Federal Institute of Technology, ETH Zurich, 8093 Zurich, Switzerland
| | - Francesco Santarella
- Department of Biology, Institute of Molecular Health Sciences, Swiss Federal Institute of Technology, ETH Zurich, 8093 Zurich, Switzerland
| | - Elisa Tinelli
- Department of Biology, Institute of Molecular Health Sciences, Swiss Federal Institute of Technology, ETH Zurich, 8093 Zurich, Switzerland
| | - Shuo Lin
- Biozentrum, University of Basel, Klingelbergstrasse 50/70, CH-4056 Basel, Switzerland
| | - Markus A Rüegg
- Biozentrum, University of Basel, Klingelbergstrasse 50/70, CH-4056 Basel, Switzerland
| | - Manfred Kopf
- Department of Biology, Institute of Molecular Health Sciences, Swiss Federal Institute of Technology, ETH Zurich, 8093 Zurich, Switzerland
| | - Klaus V Toyka
- Department of Neurology, University Hospital of Würzburg, University of Würzburg, 97080 Würzburg, Germany
| | - Ueli Suter
- Department of Biology, Institute of Molecular Health Sciences, Swiss Federal Institute of Technology, ETH Zurich, 8093 Zurich, Switzerland
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7
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Börsch A, Ham DJ, Mittal N, Tintignac LA, Migliavacca E, Feige JN, Rüegg MA, Zavolan M. Molecular and phenotypic analysis of rodent models reveals conserved and species-specific modulators of human sarcopenia. Commun Biol 2021; 4:194. [PMID: 33580198 PMCID: PMC7881157 DOI: 10.1038/s42003-021-01723-z] [Citation(s) in RCA: 37] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2020] [Accepted: 01/19/2021] [Indexed: 02/07/2023] Open
Abstract
Sarcopenia, the age-related loss of skeletal muscle mass and function, affects 5-13% of individuals aged over 60 years. While rodents are widely-used model organisms, which aspects of sarcopenia are recapitulated in different animal models is unknown. Here we generated a time series of phenotypic measurements and RNA sequencing data in mouse gastrocnemius muscle and analyzed them alongside analogous data from rats and humans. We found that rodents recapitulate mitochondrial changes observed in human sarcopenia, while inflammatory responses are conserved at pathway but not gene level. Perturbations in the extracellular matrix are shared by rats, while mice recapitulate changes in RNA processing and autophagy. We inferred transcription regulators of early and late transcriptome changes, which could be targeted therapeutically. Our study demonstrates that phenotypic measurements, such as muscle mass, are better indicators of muscle health than chronological age and should be considered when analyzing aging-related molecular data.
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Affiliation(s)
- Anastasiya Börsch
- Biozentrum, University of Basel and Swiss Institute of Bioinformatics, Basel, Switzerland
| | - Daniel J Ham
- Biozentrum, University of Basel, Basel, Switzerland
| | - Nitish Mittal
- Biozentrum, University of Basel and Swiss Institute of Bioinformatics, Basel, Switzerland
| | - Lionel A Tintignac
- Department of Biomedicine, Pharmazentrum, University of Basel, Basel, Switzerland
| | | | - Jérôme N Feige
- Nestlé Research, EPFL Innovation Park, Lausanne, Switzerland
| | | | - Mihaela Zavolan
- Biozentrum, University of Basel and Swiss Institute of Bioinformatics, Basel, Switzerland.
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8
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Castets P, Ham DJ, Rüegg MA. The TOR Pathway at the Neuromuscular Junction: More Than a Metabolic Player? Front Mol Neurosci 2020; 13:162. [PMID: 32982690 PMCID: PMC7485269 DOI: 10.3389/fnmol.2020.00162] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2020] [Accepted: 08/05/2020] [Indexed: 12/18/2022] Open
Abstract
The neuromuscular junction (NMJ) is the chemical synapse connecting motor neurons and skeletal muscle fibers. NMJs allow all voluntary movements, and ensure vital functions like breathing. Changes in the structure and function of NMJs are hallmarks of numerous pathological conditions that affect muscle function including sarcopenia, the age-related loss of muscle mass and function. However, the molecular mechanisms leading to the morphological and functional perturbations in the pre- and post-synaptic compartments of the NMJ remain poorly understood. Here, we discuss the role of the metabolic pathway associated to the kinase TOR (Target of Rapamycin) in the development, maintenance and alterations of the NMJ. This is of particular interest as the TOR pathway has been implicated in aging, but its role at the NMJ is still ill-defined. We highlight the respective functions of the two TOR-associated complexes, TORC1 and TORC2, and discuss the role of localized protein synthesis and autophagy regulation in motor neuron terminals and sub-synaptic regions of muscle fibers and their possible effects on NMJ maintenance.
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Affiliation(s)
- Perrine Castets
- Department of Cell Physiology and Metabolism, Faculty of Medicine, University of Geneva, Geneva, Switzerland
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9
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Ham AS, Chojnowska K, Tintignac LA, Lin S, Schmidt A, Ham DJ, Sinnreich M, Rüegg MA. mTORC1 signalling is not essential for the maintenance of muscle mass and function in adult sedentary mice. J Cachexia Sarcopenia Muscle 2020; 11:259-273. [PMID: 31697050 PMCID: PMC7015237 DOI: 10.1002/jcsm.12505] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/09/2019] [Accepted: 09/09/2019] [Indexed: 12/14/2022] Open
Abstract
BACKGROUND The balance between protein synthesis and degradation (proteostasis) is a determining factor for muscle size and function. Signalling via the mammalian target of rapamycin complex 1 (mTORC1) regulates proteostasis in skeletal muscle by affecting protein synthesis and autophagosomal protein degradation. Indeed, genetic inactivation of mTORC1 in developing and growing muscle causes atrophy resulting in a lethal myopathy. However, systemic dampening of mTORC1 signalling by its allosteric inhibitor rapamycin is beneficial at the organismal level and increases lifespan. Whether the beneficial effect of rapamycin comes at the expense of muscle mass and function is yet to be established. METHODS We conditionally ablated the gene coding for the mTORC1-essential component raptor in muscle fibres of adult mice [inducible raptor muscle-specific knockout (iRAmKO)]. We performed detailed phenotypic and biochemical analyses of iRAmKO mice and compared them with muscle-specific raptor knockout (RAmKO) mice, which lack raptor in developing muscle fibres. We also used polysome profiling and proteomics to assess protein translation and associated signalling in skeletal muscle of iRAmKO mice. RESULTS Analysis at different time points reveal that, as in RAmKO mice, the proportion of oxidative fibres decreases, but slow-type fibres increase in iRAmKO mice. Nevertheless, no significant decrease in body and muscle mass or muscle fibre area was detected up to 5 months post-raptor depletion. Similarly, ex vivo muscle force was not significantly reduced in iRAmKO mice. Despite stable muscle size and function, inducible raptor depletion significantly reduced the expression of key components of the translation machinery and overall translation rates. CONCLUSIONS Raptor depletion and hence complete inhibition of mTORC1 signalling in fully grown muscle leads to metabolic and morphological changes without inducing muscle atrophy even after 5 months. Together, our data indicate that maintenance of muscle size does not require mTORC1 signalling, suggesting that rapamycin treatment is unlikely to negatively affect muscle mass and function.
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Affiliation(s)
| | | | - Lionel A Tintignac
- Department of Biomedicine, Pharmazentrum, University of Basel, Basel, Switzerland
| | - Shuo Lin
- Biozentrum, University of Basel, Basel, Switzerland
| | - Alexander Schmidt
- Proteomics Core Facility, Biozentrum, University of Basel, Basel, Switzerland
| | - Daniel J Ham
- Biozentrum, University of Basel, Basel, Switzerland
| | - Michael Sinnreich
- Department of Biomedicine, Pharmazentrum, University of Basel, Basel, Switzerland
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10
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Donadon I, Bussani E, Riccardi F, Licastro D, Romano G, Pianigiani G, Pinotti M, Konstantinova P, Evers M, Lin S, Rüegg MA, Pagani F. Rescue of spinal muscular atrophy mouse models with AAV9-Exon-specific U1 snRNA. Nucleic Acids Res 2019; 47:7618-7632. [PMID: 31127278 PMCID: PMC6698663 DOI: 10.1093/nar/gkz469] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Revised: 05/10/2019] [Accepted: 05/16/2019] [Indexed: 12/12/2022] Open
Abstract
Spinal Muscular Atrophy results from loss-of-function mutations in SMN1 but correcting aberrant splicing of SMN2 offers hope of a cure. However, current splice therapy requires repeated infusions and is expensive. We previously rescued SMA mice by promoting the inclusion of a defective exon in SMN2 with germline expression of Exon-Specific U1 snRNAs (ExspeU1). Here we tested viral delivery of SMN2 ExspeU1s encoded by adeno-associated virus AAV9. Strikingly the virus increased SMN2 exon 7 inclusion and SMN protein levels and rescued the phenotype of mild and severe SMA mice. In the severe mouse, the treatment improved the neuromuscular function and increased the life span from 10 to 219 days. ExspeU1 expression persisted for 1 month and was effective at around one five-hundredth of the concentration of the endogenous U1snRNA. RNA-seq analysis revealed our potential drug rescues aberrant SMA expression and splicing profiles, which are mostly related to DNA damage, cell-cycle control and acute phase response. Vastly overexpressing ExspeU1 more than 100-fold above the therapeutic level in human cells did not significantly alter global gene expression or splicing. These results indicate that AAV-mediated delivery of a modified U1snRNP particle may be a novel therapeutic option against SMA.
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Affiliation(s)
- Irving Donadon
- Human Molecular Genetics, International Centre for Genetic Engineering and Biotechnology, Padriciano 99, 34149 Trieste, Italy
| | - Erica Bussani
- Human Molecular Genetics, International Centre for Genetic Engineering and Biotechnology, Padriciano 99, 34149 Trieste, Italy
| | - Federico Riccardi
- Human Molecular Genetics, International Centre for Genetic Engineering and Biotechnology, Padriciano 99, 34149 Trieste, Italy
| | - Danilo Licastro
- CBM S.c.r.l., Area Science Park, 34149 Basovizza, Trieste, Italy
| | - Giulia Romano
- Human Molecular Genetics, International Centre for Genetic Engineering and Biotechnology, Padriciano 99, 34149 Trieste, Italy
| | - Giulia Pianigiani
- Human Molecular Genetics, International Centre for Genetic Engineering and Biotechnology, Padriciano 99, 34149 Trieste, Italy
| | - Mirko Pinotti
- Department of Life Sciences and Biotechnology, University of Ferrara, 44121 Ferrara, Italy
| | - Pavlina Konstantinova
- Department of Research & Development, uniQure biopharma B.V., Amsterdam, The Netherlands
| | - Melvin Evers
- Department of Research & Development, uniQure biopharma B.V., Amsterdam, The Netherlands
| | - Shuo Lin
- Biozentrum, University of Basel, Klingelbergstrasse 70, 4056 Basel, Switzerland
| | - Markus A Rüegg
- Biozentrum, University of Basel, Klingelbergstrasse 70, 4056 Basel, Switzerland
| | - Franco Pagani
- Human Molecular Genetics, International Centre for Genetic Engineering and Biotechnology, Padriciano 99, 34149 Trieste, Italy
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11
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Rion N, Castets P, Lin S, Enderle L, Reinhard JR, Rüegg MA. mTORC2 affects the maintenance of the muscle stem cell pool. Skelet Muscle 2019; 9:30. [PMID: 31791403 PMCID: PMC6886171 DOI: 10.1186/s13395-019-0217-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2019] [Accepted: 10/23/2019] [Indexed: 01/15/2023] Open
Abstract
Background The mammalian target of rapamycin complex 2 (mTORC2), containing the essential protein rictor, regulates cellular metabolism and cytoskeletal organization by phosphorylating protein kinases, such as PKB/Akt, PKC, and SGK. Inactivation of mTORC2 signaling in adult skeletal muscle affects its metabolism, but not muscle morphology and function. However, the role of mTORC2 in adult muscle stem cells (MuSCs) has not been investigated. Method Using histological, biochemical, and molecular biological methods, we characterized the muscle phenotype of mice depleted for rictor in the Myf5-lineage (RImyfKO) and of mice depleted for rictor in skeletal muscle fibers (RImKO). The proliferative and myogenic potential of MuSCs was analyzed upon cardiotoxin-induced injury in vivo and in isolated myofibers in vitro. Results Skeletal muscle of young and 14-month-old RImyfKO mice appeared normal in composition and function. MuSCs from young RImyfKO mice exhibited a similar capacity to proliferate, differentiate, and fuse as controls. In contrast, the number of MuSCs was lower in young RImyfKO mice than in controls after two consecutive rounds of cardiotoxin-induced muscle regeneration. Similarly, the number of MuSCs in RImyfKO mice decreased with age, which correlated with a decline in the regenerative capacity of mutant muscle. Interestingly, reduction in the number of MuSCs was also observed in 14-month-old RImKO muscle. Conclusions Our study shows that mTORC2 signaling is dispensable for myofiber formation, but contributes to the homeostasis of MuSCs. Loss of mTORC2 does not affect their myogenic function, but impairs the replenishment of MuSCs after repeated injuries and their maintenance during aging. These results point to an important role of mTORC2 signaling in MuSC for muscle homeostasis.
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Affiliation(s)
- Nathalie Rion
- Biozentrum, University of Basel, CH-4056, Basel, Switzerland
| | - Perrine Castets
- Biozentrum, University of Basel, CH-4056, Basel, Switzerland.,Department PHYM, Centre Médical Universitaire de Genève, Geneva, Switzerland
| | - Shuo Lin
- Biozentrum, University of Basel, CH-4056, Basel, Switzerland
| | - Leonie Enderle
- Biozentrum, University of Basel, CH-4056, Basel, Switzerland.,Toronto Recombinant Antibody Centre/The Donnelly Centre, University of Toronto, M5G 1 L6, Toronto, ON, Canada
| | | | - Markus A Rüegg
- Biozentrum, University of Basel, CH-4056, Basel, Switzerland.
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12
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Ding X, Willenborg S, Bloch W, Wickström SA, Wagle P, Brodesser S, Roers A, Jais A, Brüning JC, Hall MN, Rüegg MA, Eming SA. Epidermal mammalian target of rapamycin complex 2 controls lipid synthesis and filaggrin processing in epidermal barrier formation. J Allergy Clin Immunol 2019; 145:283-300.e8. [PMID: 31401286 DOI: 10.1016/j.jaci.2019.07.033] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2019] [Revised: 06/21/2019] [Accepted: 07/08/2019] [Indexed: 12/31/2022]
Abstract
BACKGROUND Perturbation of epidermal barrier formation will profoundly compromise overall skin function, leading to a dry and scaly, ichthyosis-like skin phenotype that is the hallmark of a broad range of skin diseases, including ichthyosis, atopic dermatitis, and a multitude of clinical eczema variants. An overarching molecular mechanism that orchestrates the multitude of factors controlling epidermal barrier formation and homeostasis remains to be elucidated. OBJECTIVE Here we highlight a specific role of mammalian target of rapamycin complex 2 (mTORC2) signaling in epidermal barrier formation. METHODS Epidermal mTORC2 signaling was specifically disrupted by deleting rapamycin-insensitive companion of target of rapamycin (Rictor), encoding an essential subunit of mTORC2 in mouse epidermis (epidermis-specific homozygous Rictor deletion [RicEKO] mice). Epidermal structure and barrier function were investigated through a combination of gene expression, biochemical, morphological and functional analysis in RicEKO and control mice. RESULTS RicEKO newborns displayed an ichthyosis-like phenotype characterized by dysregulated epidermal de novo lipid synthesis, altered lipid lamellae structure, and aberrant filaggrin (FLG) processing. Despite a compensatory transcriptional epidermal repair response, the protective epidermal function was impaired in RicEKO mice, as revealed by increased transepidermal water loss, enhanced corneocyte fragility, decreased dendritic epidermal T cells, and an exaggerated percutaneous immune response. Restoration of Akt-Ser473 phosphorylation in mTORC2-deficient keratinocytes through expression of constitutive Akt rescued FLG processing. CONCLUSION Our findings reveal a critical metabolic signaling relay of barrier formation in which epidermal mTORC2 activity controls FLG processing and de novo epidermal lipid synthesis during cornification. Our findings provide novel mechanistic insights into epidermal barrier formation and could open up new therapeutic opportunities to restore defective epidermal barrier conditions.
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Affiliation(s)
- Xiaolei Ding
- Department of Dermatology, University of Cologne, Cologne, Germany; Center for Molecular Medicine Cologne (CMMC), University of Cologne, Cologne, Germany
| | | | - Wilhelm Bloch
- Department of Molecular and Cellular Sport Medicine, German Sport University Cologne, Cologne, Germany
| | - Sara A Wickström
- Paul Gerson Unna Group "Skin Homeostasis and Ageing", Max Planck Institute for Biology of Ageing, Cologne, Germany; Helsinki Institute of Life Science, Biomedicum Helsinki, University of Helsinki, Helsinki, Finland; Wihuri Research Institute, Biomedicum Helsinki, University of Helsinki, Helsinki, Finland; Cluster of Excellence Cellular Stress Responses in Aging-associated Diseases (CECAD), University of Cologne, Cologne, Germany
| | - Prerana Wagle
- Cluster of Excellence Cellular Stress Responses in Aging-associated Diseases (CECAD), University of Cologne, Cologne, Germany
| | - Susanne Brodesser
- Cluster of Excellence Cellular Stress Responses in Aging-associated Diseases (CECAD), University of Cologne, Cologne, Germany
| | - Axel Roers
- Institute for Immunology, Medical Faculty Carl Gustav Carus, TU Dresden, Dresden, Germany
| | - Alexander Jais
- Max Planck Institute for Metabolism Research, Cologne, Germany
| | - Jens C Brüning
- Center for Molecular Medicine Cologne (CMMC), University of Cologne, Cologne, Germany; Cluster of Excellence Cellular Stress Responses in Aging-associated Diseases (CECAD), University of Cologne, Cologne, Germany; Max Planck Institute for Metabolism Research, Cologne, Germany
| | | | | | - Sabine A Eming
- Department of Dermatology, University of Cologne, Cologne, Germany; Center for Molecular Medicine Cologne (CMMC), University of Cologne, Cologne, Germany; Cluster of Excellence Cellular Stress Responses in Aging-associated Diseases (CECAD), University of Cologne, Cologne, Germany.
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13
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Willmann R, Gordish-Dressman H, Meinen S, Rüegg MA, Yu Q, Nagaraju K, Kumar A, Girgenrath M, Coffey CBM, Cruz V, Van Ry PM, Bogdanik L, Lutz C, Rutkowski A, Burkin DJ. Improving Reproducibility of Phenotypic Assessments in the DyW Mouse Model of Laminin-α2 Related Congenital Muscular Dystrophy. J Neuromuscul Dis 2019; 4:115-126. [PMID: 28550268 PMCID: PMC5467719 DOI: 10.3233/jnd-170217] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Laminin-α2 related Congenital Muscular Dystrophy (LAMA2-CMD) is a progressive muscle disease caused by partial or complete deficiency of laminin-211, a skeletal muscle extracellular matrix protein. In the last decade, basic science research has queried underlying disease mechanisms in existing LAMA2-CMD murine models and identified possible clinical targets and pharmacological interventions. Experimental rigor in preclinical studies is critical to efficiently and accurately quantify both negative and positive results, degree of efficiency of potential therapeutics and determine whether to move a compound forward for additional preclinical testing. In this review, we compare published available data measured to assess three common parameters in the widely used mouse model DyW, that mimics LAMA2-CMD, we quantify variability and analyse its possible sources. Finally, on the basis of this analysis, we suggest standard set of assessments and the use of available standardized protocols, to reduce variability of outcomes in the future and to improve the value of preclinical research.
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Affiliation(s)
- Raffaella Willmann
- Swiss Foundation for Research on Muscle Diseases, Cortaillod, Switzerland.,Biozentrum, University of Basel, Basel, Switzerland
| | | | | | | | - Qing Yu
- Center for Genetic Medicine Research, Children's National Medical Center, Washington, DC, USA
| | - Kanneboyina Nagaraju
- Center for Genetic Medicine Research, Children's National Medical Center, Washington, DC, USA
| | - Ayar Kumar
- Department of Health Sciences, Boston University, Boston, MA, USA
| | | | - Caroline B M Coffey
- Department of Pharmacology, University of Nevada School of Medicine, Reno, NV, USA
| | - Vivian Cruz
- Department of Pharmacology, University of Nevada School of Medicine, Reno, NV, USA
| | - Pam M Van Ry
- Department of Pharmacology, University of Nevada School of Medicine, Reno, NV, USA
| | | | | | - Anne Rutkowski
- Cure Congenital Muscular Dystrophy and Kaiser SCPMG, Los Angeles, CA, USA
| | - Dean J Burkin
- Department of Pharmacology, University of Nevada School of Medicine, Reno, NV, USA
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14
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Rion N, Castets P, Lin S, Enderle L, Reinhard JR, Eickhorst C, Rüegg MA. mTOR controls embryonic and adult myogenesis via mTORC1. Development 2019; 146:dev.172460. [PMID: 30872276 DOI: 10.1242/dev.172460] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2018] [Accepted: 03/04/2019] [Indexed: 12/11/2022]
Abstract
The formation of multi-nucleated muscle fibers from progenitors requires the fine-tuned and coordinated regulation of proliferation, differentiation and fusion, both during development and after injury in the adult. Although some of the key factors that are involved in the different steps are well known, how intracellular signals are coordinated and integrated is largely unknown. Here, we investigated the role of the cell-growth regulator mTOR by eliminating essential components of the mTOR complexes 1 (mTORC1) and 2 (mTORC2) in mouse muscle progenitors. We show that inactivation of mTORC1, but not mTORC2, in developing muscle causes perinatal death. In the adult, mTORC1 deficiency in muscle stem cells greatly impinges on injury-induced muscle regeneration. These phenotypes are because of defects in the proliferation and fusion capacity of the targeted muscle progenitors. However, mTORC1-deficient muscle progenitors partially retain their myogenic function. Hence, our results show that mTORC1 and not mTORC2 is an important regulator of embryonic and adult myogenesis, and they point to alternative pathways that partially compensate for the loss of mTORC1.This article has an associated 'The people behind the papers' interview.
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Affiliation(s)
- Nathalie Rion
- Biozentrum, University of Basel, CH-4056 Basel, Switzerland
| | | | - Shuo Lin
- Biozentrum, University of Basel, CH-4056 Basel, Switzerland
| | - Leonie Enderle
- Biozentrum, University of Basel, CH-4056 Basel, Switzerland
| | | | | | - Markus A Rüegg
- Biozentrum, University of Basel, CH-4056 Basel, Switzerland
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15
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van Putten M, Aartsma-Rus A, Grounds MD, Kornegay JN, Mayhew A, Gillingwater TH, Takeda S, Rüegg MA, De Luca A, Nagaraju K, Willmann R. Update on Standard Operating Procedures in Preclinical Research for DMD and SMA Report of TREAT-NMD Alliance Workshop, Schiphol Airport, 26 April 2015, The Netherlands. J Neuromuscul Dis 2018; 5:29-34. [PMID: 29480217 PMCID: PMC5836406 DOI: 10.3233/jnd-170288] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
A workshop took place in 2015 to follow up TREAT-NMD activities dedicated to improving quality in the preclinical phase of drug development for neuromuscular diseases. In particular, this workshop adressed necessary future steps regarding common standard experimental protocols and the issue of improving the translatability of preclinical efficacy studies.
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Affiliation(s)
- Maaike van Putten
- Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands
| | - Annemieke Aartsma-Rus
- Department of Human Genetics, Leiden University Medical Center, Leiden, The Netherlands
| | - Miranda D Grounds
- School of Anatomy, Physiology and Human Biology, The University of Western Australia, Perth, WA, Australia
| | - Joe N Kornegay
- College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, TX, USA
| | - Anna Mayhew
- John Walton Muscular Dystrophy Research Centre, Newcastle University, Newcastle, UK
| | - Thomas H Gillingwater
- Edinburgh Medical School, Biomedical Sciences, University of Edinburgh, Edinburgh, UK
| | - Shin'ichi Takeda
- National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo, Japan
| | | | - Annamaria De Luca
- Department of Pharmacy and Drug Sciences, Unit of Pharmacology, University of Bari, Bari, Italy
| | | | - Raffaella Willmann
- Biozentrum, University of Basel, Basel, Switzerland.,Swiss Foundation for Research on Muscle Diseases, Cortaillod, Switzerland
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16
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Reinhard JR, Lin S, McKee KK, Meinen S, Crosson SC, Sury M, Hobbs S, Maier G, Yurchenco PD, Rüegg MA. Linker proteins restore basement membrane and correct LAMA2-related muscular dystrophy in mice. Sci Transl Med 2018; 9:9/396/eaal4649. [PMID: 28659438 DOI: 10.1126/scitranslmed.aal4649] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2016] [Revised: 03/03/2017] [Accepted: 05/04/2017] [Indexed: 12/12/2022]
Abstract
LAMA2-related muscular dystrophy (LAMA2 MD or MDC1A) is the most frequent form of early-onset, fatal congenital muscular dystrophies. It is caused by mutations in LAMA2, the gene encoding laminin-α2, the long arm of the heterotrimeric (α2, β1, and γ1) basement membrane protein laminin-211 (Lm-211). We establish that despite compensatory expression of laminin-α4, giving rise to Lm-411 (α4, β1, and γ1), muscle basement membrane is labile in LAMA2 MD biopsies. Consistent with this deficit, recombinant Lm-411 polymerized and bound to cultured myotubes only weakly. Polymerization and cell binding of Lm-411 were enhanced by addition of two specifically designed linker proteins. One, called αLNNd, consists of the N-terminal part of laminin-α1 and the laminin-binding site of nidogen-1. The second, called mini-agrin (mag), contains binding sites for laminins and α-dystroglycan. Transgenic expression of mag and αLNNd in a mouse model for LAMA2 MD fully restored basement membrane stability, recovered muscle force and size, increased overall body weight, and extended life span more than five times to a maximum survival beyond 2 years. These findings provide a mechanistic understanding of LAMA2 MD and establish a strong basis for a potential treatment.
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Affiliation(s)
| | - Shuo Lin
- Biozentrum, University of Basel, 4056 Basel, Switzerland
| | - Karen K McKee
- Robert Wood Johnson Medical School, Rutgers University, Piscataway, NJ 08854, USA
| | - Sarina Meinen
- Biozentrum, University of Basel, 4056 Basel, Switzerland
| | - Stephanie C Crosson
- Robert Wood Johnson Medical School, Rutgers University, Piscataway, NJ 08854, USA
| | - Maurizio Sury
- Biozentrum, University of Basel, 4056 Basel, Switzerland
| | - Samantha Hobbs
- Robert Wood Johnson Medical School, Rutgers University, Piscataway, NJ 08854, USA
| | | | - Peter D Yurchenco
- Robert Wood Johnson Medical School, Rutgers University, Piscataway, NJ 08854, USA
| | - Markus A Rüegg
- Biozentrum, University of Basel, 4056 Basel, Switzerland.
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17
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Abstract
Recent research has revealed that autophagy, a major catabolic process in cells, is dysregulated in several neuromuscular diseases and contributes to the muscle wasting caused by non-muscle disorders (e.g. cancer cachexia) or during aging (i.e. sarcopenia). From there, the idea arose to interfere with autophagy or manipulate its regulatory signalling to help restore muscle homeostasis and attenuate disease progression. The major difficulty for the development of therapeutic strategies is to restore a balanced autophagic flux, due to the dynamic nature of autophagy. Thus, it is essential to better understand the mechanisms and identify the signalling pathways at play in the control of autophagy in skeletal muscle. A comprehensive analysis of the autophagic flux and of the causes of its dysregulation is required to assess the pathogenic role of autophagy in diseased muscle. Furthermore, it is essential that experiments distinguish between primary dysregulation of autophagy (prior to disease onset) and impairments as a consequence of the pathology. Of note, in most muscle disorders, autophagy perturbation is not caused by genetic modification of an autophagy-related protein, but rather through indirect alteration of regulatory signalling or lysosomal function. In this review, we will present the mechanisms involved in autophagy, and those ensuring its tight regulation in skeletal muscle. We will then discuss as to how autophagy dysregulation contributes to the pathogenesis of neuromuscular disorders and possible ways to interfere with this process to limit disease progression.
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Affiliation(s)
| | - Stephan Frank
- Institute of Pathology, Division of Neuropathology Basel University Hospital, Basel, Switzerland
| | - Michael Sinnreich
- Neuromuscular Research Center, Departments of Neurology and Biomedicine, Pharmazentrum, Basel, Switzerland
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18
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Yurchenco PD, McKee KK, Reinhard JR, Rüegg MA. Laminin-deficient muscular dystrophy: Molecular pathogenesis and structural repair strategies. Matrix Biol 2017; 71-72:174-187. [PMID: 29191403 DOI: 10.1016/j.matbio.2017.11.009] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2017] [Revised: 11/15/2017] [Accepted: 11/16/2017] [Indexed: 12/19/2022]
Abstract
Laminins are large heterotrimers composed of the α, β and γ subunits with distinct tissue-specific and developmentally regulated expression patterns. The laminin-α2 subunit, encoded by the LAMA2 gene, is expressed in skeletal muscle, Schwann cells of the peripheral nerve and astrocytes and pericytes of the capillaries in the brain. Mutations in LAMA2 cause the most common type of congenital muscular dystrophies, called LAMA2 MD or MDC1A. The disorder manifests mostly as a muscular dystrophy but slowing of nerve conduction contributes to the disease. There are severe, non-ambulatory or milder, ambulatory variants, the latter resulting from reduced laminin-α2 expression and/or deficient laminin-α2 function. Lm-211 (α2β1γ1) is responsible for initiating basement membrane assembly. This is primarily accomplished by anchorage of Lm-211 to dystroglycan and α7β1 integrin receptors, polymerization, and binding to nidogen and other structural components. In LAMA2 MD, Lm-411 replaces Lm-211; however, Lm-411 lacks the ability to polymerize and bind to receptors. This results in a weakened basement membrane leading to the disease. The possibility of introducing structural repair proteins that correct the underlying abnormality is an attractive therapeutic goal. Recent studies in mouse models for LAMA2 MD reveal that introduction of laminin-binding linker proteins that restore lost functional activities can substantially ameliorate the disease. This review discusses the underlying mechanism of this repair and compares this approach to other developing therapies employing pharmacological treatments.
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Affiliation(s)
- Peter D Yurchenco
- Dept. Pathology & Laboratory Medicine, Rutgers University, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA.
| | - Karen K McKee
- Dept. Pathology & Laboratory Medicine, Rutgers University, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
| | | | - Markus A Rüegg
- Biozentrum, University of Basel, 4056 Basel, Switzerland.
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19
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Bozadjieva N, Blandino-Rosano M, Chase J, Dai XQ, Cummings K, Gimeno J, Dean D, Powers AC, Gittes GK, Rüegg MA, Hall MN, MacDonald PE, Bernal-Mizrachi E. Loss of mTORC1 signaling alters pancreatic α cell mass and impairs glucagon secretion. J Clin Invest 2017; 127:4379-4393. [PMID: 29106387 DOI: 10.1172/jci90004] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Accepted: 09/26/2017] [Indexed: 01/19/2023] Open
Abstract
Glucagon plays a major role in the regulation of glucose homeostasis during fed and fasting states. However, the mechanisms responsible for the regulation of pancreatic α cell mass and function are not completely understood. In the current study, we identified mTOR complex 1 (mTORC1) as a major regulator of α cell mass and glucagon secretion. Using mice with tissue-specific deletion of the mTORC1 regulator Raptor in α cells (αRaptorKO), we showed that mTORC1 signaling is dispensable for α cell development, but essential for α cell maturation during the transition from a milk-based diet to a chow-based diet after weaning. Moreover, inhibition of mTORC1 signaling in αRaptorKO mice and in WT animals exposed to chronic rapamycin administration decreased glucagon content and glucagon secretion. In αRaptorKO mice, impaired glucagon secretion occurred in response to different secretagogues and was mediated by alterations in KATP channel subunit expression and activity. Additionally, our data identify the mTORC1/FoxA2 axis as a link between mTORC1 and transcriptional regulation of key genes responsible for α cell function. Thus, our results reveal a potential function of mTORC1 in nutrient-dependent regulation of glucagon secretion and identify a role for mTORC1 in controlling α cell-mass maintenance.
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Affiliation(s)
- Nadejda Bozadjieva
- Department of Internal Medicine, Division of Metabolism, Endocrinology and Diabetes, and.,Graduate Program in Cellular and Molecular Biology, University of Michigan, Ann Arbor, Michigan, USA
| | - Manuel Blandino-Rosano
- Department of Internal Medicine, Division of Metabolism, Endocrinology and Diabetes, and.,Department of Internal Medicine, Division Endocrinology, Metabolism and Diabetes, Miller School of Medicine, University of Miami, Miami, Florida, USA
| | - Jennifer Chase
- Graduate Program in Cellular and Molecular Biology, University of Michigan, Ann Arbor, Michigan, USA
| | - Xiao-Qing Dai
- Alberta Diabetes Institute and Department of Pharmacology, Edmonton, Alberta, Canada
| | - Kelsey Cummings
- Department of Internal Medicine, Division of Metabolism, Endocrinology and Diabetes, and
| | - Jennifer Gimeno
- Department of Internal Medicine, Division Endocrinology, Metabolism and Diabetes, Miller School of Medicine, University of Miami, Miami, Florida, USA
| | - Danielle Dean
- Department of Medicine, Division of Diabetes, Endocrinology, and Metabolism, and
| | - Alvin C Powers
- Department of Medicine, Division of Diabetes, Endocrinology, and Metabolism, and.,Department of Molecular Physiology & Biophysics, Vanderbilt University, Nashville, Tennessee, USA.,VA Tennessee Valley Healthcare, Nashville, Tennessee, USA
| | - George K Gittes
- Children's Hospital, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | | | | | - Patrick E MacDonald
- Alberta Diabetes Institute and Department of Pharmacology, Edmonton, Alberta, Canada
| | - Ernesto Bernal-Mizrachi
- Department of Internal Medicine, Division of Metabolism, Endocrinology and Diabetes, and.,Graduate Program in Cellular and Molecular Biology, University of Michigan, Ann Arbor, Michigan, USA.,Department of Internal Medicine, Division Endocrinology, Metabolism and Diabetes, Miller School of Medicine, University of Miami, Miami, Florida, USA.,Veterans Affairs Medical Center, Miami, Florida, USA
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20
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Karakatsani A, Marichal N, Urban S, Kalamakis G, Ghanem A, Schick A, Zhang Y, Conzelmann KK, Rüegg MA, Berninger B, Ruiz de Almodovar C, Gascón S, Kröger S. Neuronal LRP4 regulates synapse formation in the developing CNS. Development 2017; 144:4604-4615. [PMID: 29061639 DOI: 10.1242/dev.150110] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2017] [Accepted: 10/11/2017] [Indexed: 01/19/2023]
Abstract
The low-density lipoprotein receptor-related protein 4 (LRP4) is essential in muscle fibers for the establishment of the neuromuscular junction. Here, we show that LRP4 is also expressed by embryonic cortical and hippocampal neurons, and that downregulation of LRP4 in these neurons causes a reduction in density of synapses and number of primary dendrites. Accordingly, overexpression of LRP4 in cultured neurons had the opposite effect inducing more but shorter primary dendrites with an increased number of spines. Transsynaptic tracing mediated by rabies virus revealed a reduced number of neurons presynaptic to the cortical neurons in which LRP4 was knocked down. Moreover, neuron-specific knockdown of LRP4 by in utero electroporation of LRP4 miRNA in vivo also resulted in neurons with fewer primary dendrites and a lower density of spines in the developing cortex and hippocampus. Collectively, our results demonstrate an essential and novel role of neuronal LRP4 in dendritic development and synaptogenesis in the CNS.
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Affiliation(s)
- Andromachi Karakatsani
- Department of Physiological Genomics, Ludwig-Maximilians-University, Grosshaderner Str. 9, D-82152 Planegg-Martinsried, Germany.,Biochemistry Center (BZH), Heidelberg University, 69120 Heidelberg, Germany.,Interdisciplinary Center for Neurosciences, Heidelberg University, 69120 Heidelberg, Germany
| | - Nicolás Marichal
- Institute of Physiological Chemistry, University Medical Center of the Johannes Gutenberg University Mainz, Hanns-Dieter-Hüsch Weg 19, D-55128 Mainz, Germany.,Focus Program Translational Neurosciences Mainz, Johannes Gutenberg University Mainz, Langenbeckstrasse 1, D-55131 Mainz, Germany
| | - Severino Urban
- Biochemistry Center (BZH), Heidelberg University, 69120 Heidelberg, Germany.,Interdisciplinary Center for Neurosciences, Heidelberg University, 69120 Heidelberg, Germany
| | - Georgios Kalamakis
- Division of Molecular Neurobiology, German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany
| | - Alexander Ghanem
- Max von Pettenkofer Institute and Gene Center, Ludwig-Maximilians-University, D-81377, Munich, Germany
| | - Anna Schick
- Department of Physiological Genomics, Ludwig-Maximilians-University, Grosshaderner Str. 9, D-82152 Planegg-Martinsried, Germany
| | - Yina Zhang
- Department of Physiological Genomics, Ludwig-Maximilians-University, Grosshaderner Str. 9, D-82152 Planegg-Martinsried, Germany
| | - Karl-Klaus Conzelmann
- Max von Pettenkofer Institute and Gene Center, Ludwig-Maximilians-University, D-81377, Munich, Germany
| | - Markus A Rüegg
- Biozentrum, University of Basel, 4056 Basel, Switzerland
| | - Benedikt Berninger
- Institute of Physiological Chemistry, University Medical Center of the Johannes Gutenberg University Mainz, Hanns-Dieter-Hüsch Weg 19, D-55128 Mainz, Germany.,Focus Program Translational Neurosciences Mainz, Johannes Gutenberg University Mainz, Langenbeckstrasse 1, D-55131 Mainz, Germany
| | - Carmen Ruiz de Almodovar
- Biochemistry Center (BZH), Heidelberg University, 69120 Heidelberg, Germany.,Interdisciplinary Center for Neurosciences, Heidelberg University, 69120 Heidelberg, Germany
| | - Sergio Gascón
- Department of Physiological Genomics, Ludwig-Maximilians-University, Grosshaderner Str. 9, D-82152 Planegg-Martinsried, Germany .,Institute for Stem Cell Research, Helmholtz Center Munich at the Biomedical Center (BMC), Grosshaderner Strasse 9, D-82152 Planegg-Martinsried, Germany.,Toxicology and Pharmacology Department, Faculty of Veterinary Medicine, Complutense University, Ave. Puerta de Hierro s/n, 28040 Madrid, Spain
| | - Stephan Kröger
- Department of Physiological Genomics, Ludwig-Maximilians-University, Grosshaderner Str. 9, D-82152 Planegg-Martinsried, Germany
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21
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Hodson N, McGlory C, Oikawa SY, Jeromson S, Song Z, Rüegg MA, Hamilton DL, Phillips SM, Philp A. Differential localization and anabolic responsiveness of mTOR complexes in human skeletal muscle in response to feeding and exercise. Am J Physiol Cell Physiol 2017; 313:C604-C611. [PMID: 28971834 DOI: 10.1152/ajpcell.00176.2017] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Revised: 09/22/2017] [Accepted: 09/23/2017] [Indexed: 12/31/2022]
Abstract
Mechanistic target of rapamycin (mTOR) resides as two complexes within skeletal muscle. mTOR complex 1 [mTORC1-regulatory associated protein of mTOR (Raptor) positive] regulates skeletal muscle growth, whereas mTORC2 [rapamycin-insensitive companion of mTOR (Rictor) positive] regulates insulin sensitivity. To examine the regulation of these complexes in human skeletal muscle, we utilized immunohistochemical analysis to study the localization of mTOR complexes before and following protein-carbohydrate feeding (FED) and resistance exercise plus protein-carbohydrate feeding (EXFED) in a unilateral exercise model. In basal samples, mTOR and the lysosomal marker lysosomal associated membrane protein 2 (LAMP2) were highly colocalized and remained so throughout. In the FED and EXFED states, mTOR/LAMP2 complexes were redistributed to the cell periphery [wheat germ agglutinin (WGA)-positive staining] (time effect; P = 0.025), with 39% (FED) and 26% (EXFED) increases in mTOR/WGA association observed 1 h post-feeding/exercise. mTOR/WGA colocalization continued to increase in EXFED at 3 h (48% above baseline) whereas colocalization decreased in FED (21% above baseline). A significant effect of condition (P = 0.05) was noted suggesting mTOR/WGA colocalization was greater during EXFED. This pattern was replicated in Raptor/WGA association, where a significant difference between EXFED and FED was noted at 3 h post-exercise/feeding (P = 0.014). Rictor/WGA colocalization remained unaltered throughout the trial. Alterations in mTORC1 cellular location coincided with elevated S6K1 kinase activity, which rose to a greater extent in EXFED compared with FED at 1 h post-exercise/feeding (P < 0.001), and only remained elevated in EXFED at the 3 h time point (P = 0.037). Collectively these data suggest that mTORC1 redistribution within the cell is a fundamental response to resistance exercise and feeding, whereas mTORC2 is predominantly situated at the sarcolemma and does not alter localization.
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Affiliation(s)
- Nathan Hodson
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Chris McGlory
- Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada
| | - Sara Y Oikawa
- Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada
| | - Stewart Jeromson
- Faculty of Health Sciences and Sport, University of Stirling, Stirling, United Kingdom; and
| | - Zhe Song
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom
| | | | - D Lee Hamilton
- Faculty of Health Sciences and Sport, University of Stirling, Stirling, United Kingdom; and
| | - Stuart M Phillips
- Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada
| | - Andrew Philp
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom;
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22
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Abstract
Long non-coding RNAs (lncRNAs) belong to the ever-increasing number of transcripts that are thought not to encode proteins. A recent study has now identified a small polypeptide encoded by the lncRNA LINC00961 that inhibits amino acid-induced mTORC1 activation in skeletal muscle.
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McKee KK, Crosson SC, Meinen S, Reinhard JR, Rüegg MA, Yurchenco PD. Chimeric protein repair of laminin polymerization ameliorates muscular dystrophy phenotype. J Clin Invest 2017; 127:1075-1089. [PMID: 28218617 DOI: 10.1172/jci90854] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2016] [Accepted: 12/30/2016] [Indexed: 12/28/2022] Open
Abstract
Mutations in laminin α2-subunit (Lmα2, encoded by LAMA2) are linked to approximately 30% of congenital muscular dystrophy cases. Mice with a homozygous mutation in Lama2 (dy2J mice) express a nonpolymerizing form of laminin-211 (Lm211) and are a model for ambulatory-type Lmα2-deficient muscular dystrophy. Here, we developed transgenic dy2J mice with muscle-specific expression of αLNNd, a laminin/nidogen chimeric protein that provides a missing polymerization domain. Muscle-specific expression of αLNNd in dy2J mice resulted in strong amelioration of the dystrophic phenotype, manifested by the prevention of fibrosis and restoration of forelimb grip strength. αLNNd also restored myofiber shape, size, and numbers to control levels in dy2J mice. Laminin immunostaining and quantitation of tissue extractions revealed increased Lm211 expression in αLNNd-transgenic dy2J mice. In cultured myotubes, we determined that αLNNd expression increased myotube surface accumulation of polymerization-deficient recombinant laminins, with retention of collagen IV, reiterating the basement membrane (BM) changes observed in vivo. Laminin LN domain mutations linked to several of the Lmα2-deficient muscular dystrophies are predicted to compromise polymerization. The data herein support the hypothesis that engineered expression of αLNNd can overcome polymerization deficits to increase laminin, stabilize BM structure, and substantially ameliorate muscular dystrophy.
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Brockhoff M, Rion N, Chojnowska K, Wiktorowicz T, Eickhorst C, Erne B, Frank S, Angelini C, Furling D, Rüegg MA, Sinnreich M, Castets P. Targeting deregulated AMPK/mTORC1 pathways improves muscle function in myotonic dystrophy type I. J Clin Invest 2017; 127:549-563. [PMID: 28067669 DOI: 10.1172/jci89616] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Accepted: 11/17/2016] [Indexed: 12/13/2022] Open
Abstract
Myotonic dystrophy type I (DM1) is a disabling multisystemic disease that predominantly affects skeletal muscle. It is caused by expanded CTG repeats in the 3'-UTR of the dystrophia myotonica protein kinase (DMPK) gene. RNA hairpins formed by elongated DMPK transcripts sequester RNA-binding proteins, leading to mis-splicing of numerous pre-mRNAs. Here, we have investigated whether DM1-associated muscle pathology is related to deregulation of central metabolic pathways, which may identify potential therapeutic targets for the disease. In a well-characterized mouse model for DM1 (HSALR mice), activation of AMPK signaling in muscle was impaired under starved conditions, while mTORC1 signaling remained active. In parallel, autophagic flux was perturbed in HSALR muscle and in cultured human DM1 myotubes. Pharmacological approaches targeting AMPK/mTORC1 signaling greatly ameliorated muscle function in HSALR mice. AICAR, an AMPK activator, led to a strong reduction of myotonia, which was accompanied by partial correction of misregulated alternative splicing. Rapamycin, an mTORC1 inhibitor, improved muscle relaxation and increased muscle force in HSALR mice without affecting splicing. These findings highlight the involvement of AMPK/mTORC1 deregulation in DM1 muscle pathophysiology and may open potential avenues for the treatment of this disease.
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25
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Ruegsegger C, Stucki DM, Steiner S, Angliker N, Radecke J, Keller E, Zuber B, Rüegg MA, Saxena S. Impaired mTORC1-Dependent Expression of Homer-3 Influences SCA1 Pathophysiology. Neuron 2016; 89:129-46. [PMID: 26748090 DOI: 10.1016/j.neuron.2015.11.033] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2015] [Revised: 10/06/2015] [Accepted: 11/17/2015] [Indexed: 11/25/2022]
Abstract
Spinocerebellar ataxia type 1 (SCA1), due to the expansion of a polyglutamine repeat within the ubiquitously expressed Ataxin-1 protein, leads to the premature degeneration of Purkinje cells (PCs), the cause of which is poorly understood. Here, we identified the unique proteomic signature of Sca1(154Q/2Q) PCs at an early stage of disease, highlighting extensive alterations in proteins associated with synaptic functioning, maintenance, and transmission. Focusing on Homer-3, a PC-enriched scaffold protein regulating neuronal activity, revealed an early decline in its expression. Impaired climbing fiber-mediated synaptic transmission diminished mTORC1 signaling, paralleling Homer-3 reduction in Sca1(154Q/2Q) PCs. Ablating mTORC1 within PCs or pharmacological inhibition of mTORC1 identified Homer-3 as its downstream target. mTORC1 knockout in Sca1(154Q/2Q) PCs exacerbated and accelerated pathology. Reinstating Homer-3 expression in Sca1(154Q/2Q) PCs attenuated cellular dysfunctions and improved motor deficits. Our work reveals that impaired mTORC1-Homer-3 activity underlies PC susceptibility in SCA1 and presents a promising therapeutic target.
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Affiliation(s)
- Céline Ruegsegger
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, CH-3012 Bern, Switzerland; Graduate School for Cellular and Biomedical Sciences, University of Bern, CH-3012 Bern, Switzerland
| | - David M Stucki
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, CH-3012 Bern, Switzerland; Graduate School for Cellular and Biomedical Sciences, University of Bern, CH-3012 Bern, Switzerland
| | - Silvio Steiner
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, CH-3012 Bern, Switzerland
| | - Nico Angliker
- Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland
| | - Julika Radecke
- Institute of Anatomy, University of Bern, Baltzerstrasse 2, CH-3012 Bern, Switzerland; Graduate School for Cellular and Biomedical Sciences, University of Bern, CH-3012 Bern, Switzerland
| | - Eva Keller
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, CH-3012 Bern, Switzerland
| | - Benoît Zuber
- Institute of Anatomy, University of Bern, Baltzerstrasse 2, CH-3012 Bern, Switzerland
| | - Markus A Rüegg
- Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland
| | - Smita Saxena
- Institute of Cell Biology, University of Bern, Baltzerstrasse 4, CH-3012 Bern, Switzerland.
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26
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Guridi M, Kupr B, Romanino K, Lin S, Falcetta D, Tintignac L, Rüegg MA. Alterations to mTORC1 signaling in the skeletal muscle differentially affect whole-body metabolism. Skelet Muscle 2016; 6:13. [PMID: 27004103 PMCID: PMC4800774 DOI: 10.1186/s13395-016-0084-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Accepted: 02/23/2016] [Indexed: 12/22/2022] Open
Abstract
Background The mammalian target of rapamycin complex 1 (mTORC1) is a central node in a network of signaling pathways controlling cell growth and survival. This multiprotein complex integrates external signals and affects different nutrient pathways in various organs. However, it is not clear how alterations of mTORC1 signaling in skeletal muscle affect whole-body metabolism. Results We characterized the metabolic phenotype of young and old raptor muscle knock-out (RAmKO) and TSC1 muscle knock-out (TSCmKO) mice, where mTORC1 activity in skeletal muscle is inhibited or constitutively activated, respectively. Ten-week-old RAmKO mice are lean and insulin resistant with increased energy expenditure, and they are resistant to a high-fat diet (HFD). This correlates with an increased expression of histone deacetylases (HDACs) and a downregulation of genes involved in glucose and fatty acid metabolism. Ten-week-old TSCmKO mice are also lean, glucose intolerant with a decreased activation of protein kinase B (Akt/PKB) targets that regulate glucose transporters in the muscle. The mice are resistant to a HFD and show reduced accumulation of glycogen and lipids in the liver. Both mouse models suffer from a myopathy with age, with reduced fat and lean mass, and both RAmKO and TSCmKO mice develop insulin resistance and increased intramyocellular lipid content. Conclusions Our study shows that alterations of mTORC1 signaling in the skeletal muscle differentially affect whole-body metabolism. While both inhibition and constitutive activation of mTORC1 induce leanness and resistance to obesity, changes in the metabolism of muscle and peripheral organs are distinct. These results indicate that a balanced mTORC1 signaling in the muscle is required for proper metabolic homeostasis. Electronic supplementary material The online version of this article (doi:10.1186/s13395-016-0084-8) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Maitea Guridi
- Biozentrum, University of Basel, 4056 Basel, Switzerland
| | - Barbara Kupr
- Biozentrum, University of Basel, 4056 Basel, Switzerland
| | - Klaas Romanino
- Biozentrum, University of Basel, 4056 Basel, Switzerland
| | - Shuo Lin
- Biozentrum, University of Basel, 4056 Basel, Switzerland
| | - Denis Falcetta
- Biozentrum, University of Basel, 4056 Basel, Switzerland
| | - Lionel Tintignac
- Biozentrum, University of Basel, 4056 Basel, Switzerland ; Present address: Neuromuscular Research Center, Departments of Neurology and Biomedicine, Pharmazentrum, University of Basel, 4056 Basel, Switzerland
| | - Markus A Rüegg
- Biozentrum, University of Basel, 4056 Basel, Switzerland
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27
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Zhang L, Tschumi BO, Lopez-Mejia IC, Oberle SG, Meyer M, Samson G, Rüegg MA, Hall MN, Fajas L, Zehn D, Mach JP, Donda A, Romero P. Mammalian Target of Rapamycin Complex 2 Controls CD8 T Cell Memory Differentiation in a Foxo1-Dependent Manner. Cell Rep 2016; 14:1206-1217. [PMID: 26804903 DOI: 10.1016/j.celrep.2015.12.095] [Citation(s) in RCA: 87] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Revised: 11/23/2015] [Accepted: 12/18/2015] [Indexed: 11/18/2022] Open
Abstract
Upon infection, antigen-specific naive CD8 T cells are activated and differentiate into short-lived effector cells (SLECs) and memory precursor cells (MPECs). The underlying signaling pathways remain largely unresolved. We show that Rictor, the core component of mammalian target of rapamycin complex 2 (mTORC2), regulates SLEC and MPEC commitment. Rictor deficiency favors memory formation and increases IL-2 secretion capacity without dampening effector functions. Moreover, mTORC2-deficient memory T cells mount more potent recall responses. Enhanced memory formation in the absence of mTORC2 was associated with Eomes and Tcf-1 upregulation, repression of T-bet, enhanced mitochondrial spare respiratory capacity, and fatty acid oxidation. This transcriptional and metabolic reprogramming is mainly driven by nuclear stabilization of Foxo1. Silencing of Foxo1 reversed the increased MPEC differentiation and IL-2 production and led to an impaired recall response of Rictor KO memory T cells. Therefore, mTORC2 is a critical regulator of CD8 T cell differentiation and may be an important target for immunotherapy interventions.
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Affiliation(s)
- Lianjun Zhang
- Ludwig Center for Cancer Research, University of Lausanne, 1066 Epalinges, Switzerland.
| | - Benjamin O Tschumi
- Ludwig Center for Cancer Research, University of Lausanne, 1066 Epalinges, Switzerland
| | | | | | - Marten Meyer
- German Cancer Research Center, 69120 Heidelberg, Germany
| | - Guerric Samson
- Ludwig Center for Cancer Research, University of Lausanne, 1066 Epalinges, Switzerland
| | - Markus A Rüegg
- Biozentrum, University of Basel, 4056 Basel, Switzerland
| | - Michael N Hall
- Biozentrum, University of Basel, 4056 Basel, Switzerland
| | - Lluis Fajas
- Department of Physiology, University of Lausanne, 1011 Lausanne, Switzerland
| | - Dietmar Zehn
- Swiss Vaccine Research Institute, 1066 Epalinges, Switzerland
| | - Jean-Pierre Mach
- Department of Biochemistry, University of Lausanne, 1066 Epalinges, Switzerland
| | - Alena Donda
- Ludwig Center for Cancer Research, University of Lausanne, 1066 Epalinges, Switzerland
| | - Pedro Romero
- Ludwig Center for Cancer Research, University of Lausanne, 1066 Epalinges, Switzerland.
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28
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Schell C, Kretz O, Liang W, Kiefer B, Schneider S, Sellung D, Bork T, Leiber C, Rüegg MA, Mallidis C, Schlatt S, Mayerhofer A, Huber TB, Grahammer F. The Rapamycin-Sensitive Complex of Mammalian Target of Rapamycin Is Essential to Maintain Male Fertility. Am J Pathol 2015; 186:324-36. [PMID: 26683665 DOI: 10.1016/j.ajpath.2015.10.012] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2015] [Revised: 10/15/2015] [Accepted: 10/21/2015] [Indexed: 10/22/2022]
Abstract
The mammalian target of rapamycin complex 1 (mTORC1) inhibitor rapamycin and its analogs are being increasingly used in solid-organ transplantation. A commonly reported side effect is male subfertility to infertility, yet the precise mechanisms of mTOR interference with male fertility remain obscure. With the use of a conditional mouse genetic approach we demonstrate that deficiency of mTORC1 in the epithelial derivatives of the Wolffian duct is sufficient to cause male infertility. Analysis of spermatozoa from Raptor fl/fl*KspCre mice revealed an overall decreased motility pattern. Both epididymis and seminal vesicles displayed extensive organ regression with increasing age. Histologic and ultrastructural analyses demonstrated increased amounts of destroyed and absorbed spermatozoa in different segments of the epididymis. Mechanistically, genetic and pharmacologic mTORC1 inhibition was associated with an impaired cellular metabolism and a disturbed protein secretion of epididymal epithelial cells. Collectively, our data highlight the role of mTORC1 to preserve the function of the epididymis, ductus deferens, and the seminal vesicles. We thus reveal unexpected new insights into the frequently observed mTORC1 inhibitor side effect of male infertility in transplant recipients.
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Affiliation(s)
- Christoph Schell
- Renal Division, University Medical Center Freiburg, Freiburg, Germany; Spemann Graduate School of Biology and Medicine (SGBM), Albert-Ludwigs University Freiburg, Freiburg, Germany; Faculty of Biology, Albert-Ludwigs University Freiburg, Freiburg, Germany
| | - Oliver Kretz
- Renal Division, University Medical Center Freiburg, Freiburg, Germany; Faculty of Neuroanatomy, Albert-Ludwigs University Freiburg, Freiburg, Germany
| | - Wei Liang
- Renal Division, University Medical Center Freiburg, Freiburg, Germany; Division of Nephrology, Renmin Hospital of Wuhan University, Wuhan, China
| | - Betina Kiefer
- Renal Division, University Medical Center Freiburg, Freiburg, Germany
| | - Simon Schneider
- Renal Division, University Medical Center Freiburg, Freiburg, Germany
| | - Dominik Sellung
- Renal Division, University Medical Center Freiburg, Freiburg, Germany
| | - Tillmann Bork
- Renal Division, University Medical Center Freiburg, Freiburg, Germany
| | - Christian Leiber
- Division of Urology, University Medical Center Freiburg, Freiburg, Germany
| | - Markus A Rüegg
- Biozentrum Basel, University of Basel, Basel, Switzerland
| | - Con Mallidis
- Center for Reproductive Medicine and Andrology, University Hospital Münster, Münster, Germany
| | - Stefan Schlatt
- Center for Reproductive Medicine and Andrology, University Hospital Münster, Münster, Germany
| | - Artur Mayerhofer
- Anatomy III, Cell Biology, Ludwig-Maximillians University Munich, Munich, Germany
| | - Tobias B Huber
- Renal Division, University Medical Center Freiburg, Freiburg, Germany; Spemann Graduate School of Biology and Medicine (SGBM), Albert-Ludwigs University Freiburg, Freiburg, Germany; BIOSS Center for Biological Signalling Studies, Albert-Ludwigs University Freiburg, Freiburg, Germany; Center for Systems Biology (ZBSA), Albert-Ludwigs University Freiburg, Freiburg, Germany.
| | - Florian Grahammer
- Renal Division, University Medical Center Freiburg, Freiburg, Germany
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29
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Shende P, Xu L, Morandi C, Pentassuglia L, Heim P, Lebboukh S, Berthonneche C, Pedrazzini T, Kaufmann BA, Hall MN, Rüegg MA, Brink M. Cardiac mTOR complex 2 preserves ventricular function in pressure-overload hypertrophy. Cardiovasc Res 2015; 109:103-14. [DOI: 10.1093/cvr/cvv252] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/08/2015] [Accepted: 11/06/2015] [Indexed: 11/12/2022] Open
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30
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Guridi M, Tintignac LA, Lin S, Kupr B, Castets P, Rüegg MA. Activation of mTORC1 in skeletal muscle regulates whole-body metabolism through FGF21. Sci Signal 2015; 8:ra113. [DOI: 10.1126/scisignal.aab3715] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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31
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Angliker N, Burri M, Zaichuk M, Fritschy JM, Rüegg MA. mTORC1 and mTORC2 have largely distinct functions in Purkinje cells. Eur J Neurosci 2015; 42:2595-612. [DOI: 10.1111/ejn.13051] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2015] [Revised: 08/13/2015] [Accepted: 08/14/2015] [Indexed: 12/17/2022]
Affiliation(s)
- Nico Angliker
- Biozentrum; University of Basel; Klingelbergstrasse 70 CH-4056 Basel Switzerland
| | - Michael Burri
- Biozentrum; University of Basel; Klingelbergstrasse 70 CH-4056 Basel Switzerland
| | - Mariana Zaichuk
- Institute of Pharmacology and Toxicology; University of Zürich; Zürich Switzerland
| | - Jean-Marc Fritschy
- Institute of Pharmacology and Toxicology; University of Zürich; Zürich Switzerland
| | - Markus A. Rüegg
- Biozentrum; University of Basel; Klingelbergstrasse 70 CH-4056 Basel Switzerland
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32
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Abstract
The neuromuscular junction is the chemical synapse between motor neurons and skeletal muscle fibers. It is designed to reliably convert the action potential from the presynaptic motor neuron into the contraction of the postsynaptic muscle fiber. Diseases that affect the neuromuscular junction may cause failure of this conversion and result in loss of ambulation and respiration. The loss of motor input also causes muscle wasting as muscle mass is constantly adapted to contractile needs by the balancing of protein synthesis and protein degradation. Finally, neuromuscular activity and muscle mass have a major impact on metabolic properties of the organisms. This review discusses the mechanisms involved in the development and maintenance of the neuromuscular junction, the consequences of and the mechanisms involved in its dysfunction, and its role in maintaining muscle mass during aging. As life expectancy is increasing, loss of muscle mass during aging, called sarcopenia, has emerged as a field of high medical need. Interestingly, aging is also accompanied by structural changes at the neuromuscular junction, suggesting that the mechanisms involved in neuromuscular junction maintenance might be disturbed during aging. In addition, there is now evidence that behavioral paradigms and signaling pathways that are involved in longevity also affect neuromuscular junction stability and sarcopenia.
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Affiliation(s)
- Lionel A. Tintignac
- Biozentrum, University of Basel, Basel, Switzerland; Department of Biomedicine, University of Basel, Basel, Switzerland; and INRA, UMR866 Dynamique Musculaire et Métabolisme, Montpellier, France
| | - Hans-Rudolf Brenner
- Biozentrum, University of Basel, Basel, Switzerland; Department of Biomedicine, University of Basel, Basel, Switzerland; and INRA, UMR866 Dynamique Musculaire et Métabolisme, Montpellier, France
| | - Markus A. Rüegg
- Biozentrum, University of Basel, Basel, Switzerland; Department of Biomedicine, University of Basel, Basel, Switzerland; and INRA, UMR866 Dynamique Musculaire et Métabolisme, Montpellier, France
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33
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Willmann R, Luca AD, Nagaraju K, Rüegg MA. Best Practices and Standard Protocols as a Tool to Enhance Translation for Neuromuscular Disorders. J Neuromuscul Dis 2015; 2:113-117. [PMID: 27858730 DOI: 10.3233/jnd-140067] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Recent years witnessed an exciting increase in the number of clinical trials for neuromuscular disorders, in particular for Duchenne Muscular Dystrophy and Spinal Muscle Atrophy. Given the high emotional impact of such developments for devastating diseases with an urgent medical need, it is particularly important to justify human trials on the basis of robust preclinical studies and to avoid a waste of hopes and of funds.This review focuses the discussion on the quality in the conduct clinically-oriented preclinical assessments in rare neuromuscular disease models and on the importance in reporting of preclinical confirmatory studies. Accordingly, it invites scientists, journal publishers and funding agencies to require quality standards to improve translatability of preclinical findings.
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Affiliation(s)
- Raffaella Willmann
- Swiss Foundation for Research on Muscle Diseases, Cortaillod, Switzerland
| | - Annamaria De Luca
- Unit of Pharmacology, Department of Pharmacy and Drug Sciences, University of Bari "A. Moro," Bari, Italy
| | - Kanneboyina Nagaraju
- Center for Genetic Medicine Research, Children's National Medical Center, Washington, D.C., United States of America
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34
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Ma S, Venkatesh A, Langellotto F, Le YZ, Hall MN, Rüegg MA, Punzo C. Loss of mTOR signaling affects cone function, cone structure and expression of cone specific proteins without affecting cone survival. Exp Eye Res 2015; 135:1-13. [PMID: 25887293 DOI: 10.1016/j.exer.2015.04.006] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2015] [Revised: 04/01/2015] [Accepted: 04/09/2015] [Indexed: 10/23/2022]
Abstract
Cones are the primary photoreceptor (PR) cells responsible for vision in humans. They are metabolically highly active requiring phosphoinositide 3-kinase (PI3K) activity for long-term survival. One of the downstream targets of PI3K is the kinase mammalian target of rapamycin (mTOR), which is a key regulator of cell metabolism and growth, integrating nutrient availability and growth factor signals. Both PI3K and mTOR are part of the insulin/mTOR signaling pathway, however if mTOR is required for long-term PR survival remains unknown. This is of particular interest since deregulation of this pathway in diabetes results in reduced PR function before the onset of any clinical signs of diabetic retinopathy. mTOR is found in two distinct complexes (mTORC1 & mTORC2) that are characterized by their unique accessory proteins RAPTOR and RICTOR respectively. mTORC1 regulates mainly cell metabolism in response to nutrient availability and growth factor signals, while mTORC2 regulates pro-survival mechanisms in response to growth factors. Here we analyze the effect on cones of loss of mTORC1, mTORC2 and simultaneous loss of mTORC1 & mTORC2. Interestingly, neither loss of mTORC1 nor mTORC2 affects cone function or survival at one year of age. However, outer and inner segment morphology is affected upon loss of either complex. In contrast, concurrent loss of mTORC1 and mTORC2 leads to a reduction in cone function without affecting cone viability. The data indicates that PI3K mediated pro-survival signals diverge upstream of both mTOR complexes in cones, suggesting that they are independent of mTOR activity. Furthermore, the data may help explain why PR function is reduced in diabetes, which can lead to deregulation of both mTOR complexes simultaneously. Finally, although mTOR is a key regulator of cell metabolism, and PRs are metabolically highly active, the data suggests that the role of mTOR in regulating the metabolic transcriptome in healthy cones is minimal.
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Affiliation(s)
- Shan Ma
- Tianjin Medical University Eye Hospital, No. 251 Fu Kang Road, Nankai District, Tianjin 300384, PR China; Department of Ophthalmology, University of Massachusetts Medical School, 368 Plantation Street, Worcester, MA 01605, USA.
| | - Aditya Venkatesh
- Department of Ophthalmology, University of Massachusetts Medical School, 368 Plantation Street, Worcester, MA 01605, USA.
| | - Fernanda Langellotto
- Department of Ophthalmology, University of Massachusetts Medical School, 368 Plantation Street, Worcester, MA 01605, USA.
| | - Yun Z Le
- Department of Medicine Endocrinology, University of Oklahoma Health Sciences Center, BSEB 302G, 941 S L Young Blvd., Oklahoma City 73104, USA.
| | - Michael N Hall
- Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland.
| | - Markus A Rüegg
- Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland.
| | - Claudio Punzo
- Department of Ophthalmology, University of Massachusetts Medical School, 368 Plantation Street, Worcester, MA 01605, USA.
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Venkatesh A, Ma S, Le YZ, Hall MN, Rüegg MA, Punzo C. Activated mTORC1 promotes long-term cone survival in retinitis pigmentosa mice. J Clin Invest 2015; 125:1446-58. [PMID: 25798619 DOI: 10.1172/jci79766] [Citation(s) in RCA: 105] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Accepted: 02/05/2015] [Indexed: 02/06/2023] Open
Abstract
Retinitis pigmentosa (RP) is an inherited photoreceptor degenerative disorder that results in blindness. The disease is often caused by mutations in genes that are specific to rod photoreceptors; however, blindness results from the secondary loss of cones by a still unknown mechanism. Here, we demonstrated that the mammalian target of rapamycin complex 1 (mTORC1) is required to slow the progression of cone death during disease and that constitutive activation of mTORC1 in cones is sufficient to maintain cone function and promote long-term cone survival. Activation of mTORC1 in cones enhanced glucose uptake, retention, and utilization, leading to increased levels of the key metabolite NADPH. Moreover, cone death was delayed in the absence of the NADPH-sensitive cell death protease caspase 2, supporting the contribution of reduced NADPH in promoting cone death. Constitutive activation of mTORC1 preserved cones in 2 mouse models of RP, suggesting that the secondary loss of cones is caused mainly by metabolic deficits and is independent of a specific rod-associated mutation. Together, the results of this study address a longstanding question in the field and suggest that activating mTORC1 in cones has therapeutic potential to prolong vision in RP.
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36
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Carr TD, Feehan RP, Hall MN, Rüegg MA, Shantz LM. Conditional disruption of rictor demonstrates a direct requirement for mTORC2 in skin tumor development and continued growth of established tumors. Carcinogenesis 2015; 36:487-97. [PMID: 25740823 DOI: 10.1093/carcin/bgv012] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2014] [Accepted: 02/15/2015] [Indexed: 12/31/2022] Open
Abstract
Activation of signaling dependent on the mammalian target of rapamycin (mTOR) has been demonstrated in a variety of human malignancies, and our previous work suggests that mTOR complex (mTORC) 1 and mTORC2 may play unique roles in skin tumorigenesis. The purpose of these studies was to investigate the function of mTORC2-dependent pathways in skin tumor development and the maintenance of established tumors. Using mice that allow spatial and temporal control of mTORC2 in epidermis by conditional knockout of its essential component Rictor, we studied the effect of mTORC2 loss on both epidermal proliferation and chemical carcinogenesis. The results demonstrate that mTORC2 is dispensable for both normal epidermal proliferation and the hyperproliferative response to treatment with tetradecanoyl phorbol acetate (TPA). In contrast, deletion of epidermal Rictor prior to initiation in DMBA/TPA chemical carcinogenesis was sufficient to dramatically delay tumor development and resulted in reduced tumor number and size compared with control groups. Silencing of Rictor expression in tumor-bearing animals triggered regression of established tumors and increased caspase-3 cleavage without changes in proliferation. In vitro experiments demonstrate an increased sensitivity to caspase-dependent apoptosis in the absence of rictor, which is dependent on mTORC2 signaling. These studies demonstrate that mTORC2 activation is essential for keratinocyte survival, and suggest that inhibition of mTORC2 has value in chemoprevention by eliminating carcinogen-damaged cells during the early stages of tumorigenesis, and in therapy of existing tumors by restricting critical pro-survival pathways.
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Affiliation(s)
- Theresa D Carr
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA and
| | - Robert P Feehan
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA and
| | - Michael N Hall
- Biozentrum, University of Basel, CH-4056 Basel, Switzerland
| | - Markus A Rüegg
- Biozentrum, University of Basel, CH-4056 Basel, Switzerland
| | - Lisa M Shantz
- Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, PA 17033, USA and
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Abstract
The mammalian target of rapamycin (mTOR) assembles into two distinct multi-protein complexes called mTORC1 and mTORC2. While mTORC1 controls the signaling pathways important for cell growth, the physiological function of mTORC2 is only partially known. Here we comment on recent work on gene-targeted mice lacking mTORC2 in the cerebellum or the hippocampus that provided strong evidence that mTORC2 plays an important role in neuron morphology and synapse function. We discuss that this phenotype might be based on the perturbed regulation of the actin cytoskeleton and the lack of activation of several PKC isoforms. The fact that PKC isoforms and their targets have been implicated in neurological disease including spinocerebellar ataxia and that they have been shown to affect learning and memory, suggests that aberration of mTORC2 signaling might be involved in diseases of the brain.
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38
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Zhang Y, Lin S, Karakatsani A, Rüegg MA, Kröger S. Differential regulation of AChR clustering in the polar and equatorial region of murine muscle spindles. Eur J Neurosci 2014; 41:69-78. [PMID: 25377642 DOI: 10.1111/ejn.12768] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2014] [Revised: 09/29/2014] [Accepted: 10/02/2014] [Indexed: 12/16/2022]
Abstract
Intrafusal fibers of muscle spindles are innervated in the central region by afferent sensory axons and at both polar regions by efferent γ-motoneurons. We previously demonstrated that both neuron-muscle contact sites contain cholinergic synapse-like specialisation, including aggregates of the nicotinic acetylcholine receptor (AChR). In this study we tested the hypothesis that agrin and its receptor complex (consisting of LRP4 and the tyrosine kinase MuSK) are involved in the aggregation of AChRs in muscle spindles, similar to their role at the neuromuscular junction. We show that agrin, MuSK and LRP4 are concentrated at the contact site between the intrafusal fibers and the sensory- and γ-motoneuron, respectively, and that they are expressed in the cell bodies of proprioceptive neurons in dorsal root ganglia. Moreover, agrin and LRP4, but not MuSK, are expressed in γ-motoneuron cell bodies in the ventral horn of the spinal cord. In agrin- and in MuSK-deficient mice, AChR aggregates are absent from the polar regions. In contrast, the subcellular concentration of AChRs in the central region where the sensory neuron contacts the intrafusal muscle fiber is apparently unaffected. Skeletal muscle-specific expression of miniagrin in agrin(-/-) mice in vivo is sufficient to restore the formation of γ-motoneuron endplates. These results show that agrin and MuSK are major determinants during the formation of γ-motoneuron endplates but appear dispensable for the aggregation of AChRs at the central region. Our results therefore suggest different molecular mechanisms for AChR clustering within two domains of intrafusal fibers.
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Affiliation(s)
- Yina Zhang
- Department of Physiological Genomics, Ludwig-Maximilians-University, Pettenkoferstrasse 12, D-80336, Munich, Germany; Helmholtz Center Munich, Neuherberg, Germany
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Norrmén C, Figlia G, Lebrun-Julien F, Pereira JA, Trötzmüller M, Köfeler HC, Rantanen V, Wessig C, van Deijk ALF, Smit AB, Verheijen MHG, Rüegg MA, Hall MN, Suter U. mTORC1 controls PNS myelination along the mTORC1-RXRγ-SREBP-lipid biosynthesis axis in Schwann cells. Cell Rep 2014; 9:646-60. [PMID: 25310982 DOI: 10.1016/j.celrep.2014.09.001] [Citation(s) in RCA: 91] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2014] [Revised: 04/05/2014] [Accepted: 08/28/2014] [Indexed: 11/26/2022] Open
Abstract
Myelin formation during peripheral nervous system (PNS) development, and reformation after injury and in disease, requires multiple intrinsic and extrinsic signals. Akt/mTOR signaling has emerged as a major player involved, but the molecular mechanisms and downstream effectors are virtually unknown. Here, we have used Schwann-cell-specific conditional gene ablation of raptor and rictor, which encode essential components of the mTOR complexes 1 (mTORC1) and 2 (mTORC2), respectively, to demonstrate that mTORC1 controls PNS myelination during development. In this process, mTORC1 regulates lipid biosynthesis via sterol regulatory element-binding proteins (SREBPs). This course of action is mediated by the nuclear receptor RXRγ, which transcriptionally regulates SREBP1c downstream of mTORC1. Absence of mTORC1 causes delayed myelination initiation as well as hypomyelination, together with abnormal lipid composition and decreased nerve conduction velocity. Thus, we have identified the mTORC1-RXRγ-SREBP axis controlling lipid biosynthesis as a major contributor to proper peripheral nerve function.
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Affiliation(s)
- Camilla Norrmén
- Institute of Molecular Health Sciences, Department of Biology, Swiss Federal Institute of Technology Zurich, ETH Zürich, CH-8093 Zurich, Switzerland.
| | - Gianluca Figlia
- Institute of Molecular Health Sciences, Department of Biology, Swiss Federal Institute of Technology Zurich, ETH Zürich, CH-8093 Zurich, Switzerland
| | - Frédéric Lebrun-Julien
- Institute of Molecular Health Sciences, Department of Biology, Swiss Federal Institute of Technology Zurich, ETH Zürich, CH-8093 Zurich, Switzerland
| | - Jorge A Pereira
- Institute of Molecular Health Sciences, Department of Biology, Swiss Federal Institute of Technology Zurich, ETH Zürich, CH-8093 Zurich, Switzerland
| | - Martin Trötzmüller
- Core Facility for Mass Spectrometry, Center for Medical Research, Medical University of Graz, 8010 Graz, Austria
| | - Harald C Köfeler
- Core Facility for Mass Spectrometry, Center for Medical Research, Medical University of Graz, 8010 Graz, Austria
| | - Ville Rantanen
- Research Programs Unit, Genome-Scale Biology, and Institute of Biomedicine, Biochemistry and Developmental Biology, University of Helsinki, 00014 Helsinki, Finland
| | - Carsten Wessig
- Department of Neurology, University of Würzburg, 97080 Würzburg, Germany
| | - Anne-Lieke F van Deijk
- Department of Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University, 1081HV Amsterdam, the Netherlands
| | - August B Smit
- Department of Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University, 1081HV Amsterdam, the Netherlands
| | - Mark H G Verheijen
- Department of Molecular and Cellular Neurobiology, Center for Neurogenomics and Cognitive Research, Neuroscience Campus Amsterdam, VU University, 1081HV Amsterdam, the Netherlands
| | - Markus A Rüegg
- Biozentrum, University of Basel, 4056 Basel, Switzerland
| | - Michael N Hall
- Biozentrum, University of Basel, 4056 Basel, Switzerland
| | - Ueli Suter
- Institute of Molecular Health Sciences, Department of Biology, Swiss Federal Institute of Technology Zurich, ETH Zürich, CH-8093 Zurich, Switzerland.
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Steiner E, Enzmann GU, Lyck R, Lin S, Rüegg MA, Kröger S, Engelhardt B. The heparan sulfate proteoglycan agrin contributes to barrier properties of mouse brain endothelial cells by stabilizing adherens junctions. Cell Tissue Res 2014; 358:465-79. [PMID: 25107608 PMCID: PMC4210653 DOI: 10.1007/s00441-014-1969-7] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2014] [Accepted: 07/17/2014] [Indexed: 01/13/2023]
Abstract
Barrier characteristics of brain endothelial cells forming the blood–brain barrier (BBB) are tightly regulated by cellular and acellular components of the neurovascular unit. During embryogenesis, the accumulation of the heparan sulfate proteoglycan agrin in the basement membranes ensheathing brain vessels correlates with BBB maturation. In contrast, loss of agrin deposition in the vasculature of brain tumors is accompanied by the loss of endothelial junctional proteins. We therefore wondered whether agrin had a direct effect on the barrier characteristics of brain endothelial cells. Agrin increased junctional localization of vascular endothelial (VE)-cadherin, β-catenin, and zonula occludens-1 (ZO-1) but not of claudin-5 and occludin in the brain endothelioma cell line bEnd5 without affecting the expression levels of these proteins. This was accompanied by an agrin-induced reduction of the paracellular permeability of bEnd5 monolayers. In vivo, the lack of agrin also led to reduced junctional localization of VE-cadherin in brain microvascular endothelial cells. Taken together, our data support the notion that agrin contributes to barrier characteristics of brain endothelium by stabilizing the adherens junction proteins VE-cadherin and β-catenin and the junctional protein ZO-1 to brain endothelial junctions.
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Affiliation(s)
- Esther Steiner
- Theodor Kocher Institute, University of Bern, Freiestrasse 1, 3012, Bern, Switzerland
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41
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Zhang L, Tschumi BO, Corgnac S, Rüegg MA, Hall MN, Mach JP, Romero P, Donda A. Mammalian target of rapamycin complex 1 orchestrates invariant NKT cell differentiation and effector function. J Immunol 2014; 193:1759-65. [PMID: 25015820 DOI: 10.4049/jimmunol.1400769] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Invariant NKT (iNKT) cells play critical roles in bridging innate and adaptive immunity. The Raptor containing mTOR complex 1 (mTORC1) has been well documented to control peripheral CD4 or CD8 T cell effector or memory differentiation. However, the role of mTORC1 in iNKT cell development and function remains largely unknown. By using mice with T cell-restricted deletion of Raptor, we show that mTORC1 is selectively required for iNKT but not for conventional T cell development. Indeed, Raptor-deficient iNKT cells are mostly blocked at thymic stage 1-2, resulting in a dramatic decrease of terminal differentiation into stage 3 and severe reduction of peripheral iNKT cells. Moreover, residual iNKT cells in Raptor knockout mice are impaired in their rapid cytokine production upon αGalcer challenge. Bone marrow chimera studies demonstrate that mTORC1 controls iNKT differentiation in a cell-intrinsic manner. Collectively, our data provide the genetic evidence that iNKT cell development and effector functions are under the control of mTORC1 signaling.
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Affiliation(s)
- Lianjun Zhang
- Translational Tumor Immunology Group, Ludwig Center for Cancer Research, University of Lausanne, 1066 Epalinges, Switzerland
| | - Benjamin O Tschumi
- Translational Tumor Immunology Group, Ludwig Center for Cancer Research, University of Lausanne, 1066 Epalinges, Switzerland
| | - Stéphanie Corgnac
- Translational Tumor Immunology Group, Ludwig Center for Cancer Research, University of Lausanne, 1066 Epalinges, Switzerland
| | - Markus A Rüegg
- Biozentrum, University of Basel, 4003 Basel, Switzerland; and
| | - Michael N Hall
- Biozentrum, University of Basel, 4003 Basel, Switzerland; and
| | - Jean-Pierre Mach
- Department of Biochemistry, University of Lausanne, 1066 Epalinges, Switzerland
| | - Pedro Romero
- Translational Tumor Immunology Group, Ludwig Center for Cancer Research, University of Lausanne, 1066 Epalinges, Switzerland
| | - Alena Donda
- Translational Tumor Immunology Group, Ludwig Center for Cancer Research, University of Lausanne, 1066 Epalinges, Switzerland;
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Chou PC, Oh WJ, Wu CC, Moloughney J, Rüegg MA, Hall MN, Jacinto E, Werlen G. Mammalian target of rapamycin complex 2 modulates αβTCR processing and surface expression during thymocyte development. J Immunol 2014; 193:1162-70. [PMID: 24981454 DOI: 10.4049/jimmunol.1303162] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
An efficient immune response relies on the presence of T cells expressing a functional TCR. Whereas the mechanisms generating TCR diversity for antigenic recognition are well defined, what controls its surface expression is less known. In this study, we found that deletion of the mammalian target of rapamycin complex (mTORC) 2 component rictor at early stages of T cell development led to aberrant maturation and increased proteasomal degradation of nascent TCRs. Although CD127 expression became elevated, the levels of TCRs as well as CD4, CD8, CD69, Notch, and CD147 were significantly attenuated on the surface of rictor-deficient thymocytes. Diminished expression of these receptors led to suboptimal signaling, partial CD4(-)CD8(-) double-negative 4 (CD25(-)CD44(-)) proliferation, and CD4(+)CD8(+) double-positive activation as well as developmental blocks at the CD4(-)CD8(-) double-negative 3 (CD25(+)CD44(-)) and CD8-immature CD8(+) single-positive stages. Because CD147 glycosylation was also defective in SIN1-deficient fibroblasts, our findings suggest that mTORC2 is involved in the co/posttranslational processing of membrane receptors. Thus, mTORC2 impacts development via regulation of the quantity and quality of receptors important for cell differentiation.
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Affiliation(s)
- Po-Chien Chou
- Department of Biochemistry and Molecular Biology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ 08854
| | - Won Jun Oh
- Department of Biochemistry and Molecular Biology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ 08854
| | - Chang-Chih Wu
- Department of Biochemistry and Molecular Biology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ 08854
| | - Joseph Moloughney
- Department of Biochemistry and Molecular Biology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ 08854
| | - Markus A Rüegg
- Biozentrum, University of Basel, CH 4056 Basel, Switzerland; and
| | - Michael N Hall
- Biozentrum, University of Basel, CH 4056 Basel, Switzerland; and
| | - Estela Jacinto
- Department of Biochemistry and Molecular Biology, Rutgers-Robert Wood Johnson Medical School, Piscataway, NJ 08854;
| | - Guy Werlen
- Department of Cell Biology and Neuroscience, Rutgers, The State University of New Jersey, Piscataway, NJ 08854
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Miloslavski R, Cohen E, Avraham A, Iluz Y, Hayouka Z, Kasir J, Mudhasani R, Jones SN, Cybulski N, Rüegg MA, Larsson O, Gandin V, Rajakumar A, Topisirovic I, Meyuhas O. Oxygen sufficiency controls TOP mRNA translation via the TSC-Rheb-mTOR pathway in a 4E-BP-independent manner. J Mol Cell Biol 2014; 6:255-66. [PMID: 24627160 DOI: 10.1093/jmcb/mju008] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Cells encountering hypoxic stress conserve resources and energy by downregulating the protein synthesis. Here we demonstrate that one mechanism in this response is the translational repression of TOP mRNAs that encode components of the translational apparatus. This mode of regulation involves TSC and Rheb, as knockout of TSC1 or TSC2 or overexpression of Rheb rescued TOP mRNA translation in oxygen-deprived cells. Stress-induced translational repression of these mRNAs closely correlates with the hypophosphorylated state of 4E-BP, a translational repressor. However, a series of 4E-BP loss- and gain-of-function experiments disprove a cause-and-effect relationship between the phosphorylation status of 4E-BP and the translational repression of TOP mRNAs under oxygen or growth factor deprivation. Furthermore, the repressive effect of anoxia is similar to that attained by the very efficient inhibition of mTOR activity by Torin 1, but much more pronounced than raptor or rictor knockout. Likewise, deficiency of raptor or rictor, even though it mildly downregulated basal translation efficiency of TOP mRNAs, failed to suppress the oxygen-mediated translational activation of TOP mRNAs. Finally, co-knockdown of TIA-1 and TIAR, two RNA-binding proteins previously implicated in translational repression of TOP mRNAs in amino acid-starved cells, failed to relieve TOP mRNA translation under other stress conditions. Thus, the nature of the proximal translational regulator of TOP mRNAs remains elusive.
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Affiliation(s)
- Rachel Miloslavski
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research - Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel
| | - Elad Cohen
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research - Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel Present address: Migal-Galilee Research Institute, Kiryat Shmona 11016, Israel
| | - Adam Avraham
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research - Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel
| | - Yifat Iluz
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research - Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel
| | - Zvi Hayouka
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research - Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel
| | - Judith Kasir
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research - Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel
| | - Rajini Mudhasani
- Department of Cell Biology, University of Massachusetts Medical School, North Worcester, MA 01655, USA Present address: United States Army Medical Research Institute of Infectious Diseases, Frederick, MD 21702-5011, USA
| | - Stephen N Jones
- Department of Cell Biology, University of Massachusetts Medical School, North Worcester, MA 01655, USA
| | - Nadine Cybulski
- Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland Present address: ADAM, Montreal, QC H3N 2C7, Canada
| | - Markus A Rüegg
- Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland
| | - Ola Larsson
- Department of Oncology-Pathology, Karolinska Institute, Stockholm SE-171 76, Sweden
| | - Valentina Gandin
- Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, and Department of Oncology, McGill University, Montréal, QC H3T 1E2, Canada
| | - Arjuna Rajakumar
- Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, and Department of Oncology, McGill University, Montréal, QC H3T 1E2, Canada
| | - Ivan Topisirovic
- Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, and Department of Oncology, McGill University, Montréal, QC H3T 1E2, Canada
| | - Oded Meyuhas
- Department of Biochemistry and Molecular Biology, The Institute for Medical Research - Israel-Canada, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel
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Chen J, Tu X, Esen E, Joeng KS, Lin C, Arbeit JM, Rüegg MA, Hall MN, Ma L, Long F. WNT7B promotes bone formation in part through mTORC1. PLoS Genet 2014; 10:e1004145. [PMID: 24497849 PMCID: PMC3907335 DOI: 10.1371/journal.pgen.1004145] [Citation(s) in RCA: 108] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2013] [Accepted: 12/12/2013] [Indexed: 11/30/2022] Open
Abstract
WNT signaling has been implicated in both embryonic and postnatal bone formation. However, the pertinent WNT ligands and their downstream signaling mechanisms are not well understood. To investigate the osteogenic capacity of WNT7B and WNT5A, both normally expressed in the developing bone, we engineered mouse strains to express either protein in a Cre-dependent manner. Targeted induction of WNT7B, but not WNT5A, in the osteoblast lineage dramatically enhanced bone mass due to increased osteoblast number and activity; this phenotype began in the late-stage embryo and intensified postnatally. Similarly, postnatal induction of WNT7B in Runx2-lineage cells greatly stimulated bone formation. WNT7B activated mTORC1 through PI3K-AKT signaling. Genetic disruption of mTORC1 signaling by deleting Raptor in the osteoblast lineage alleviated the WNT7B-induced high-bone-mass phenotype. Thus, WNT7B promotes bone formation in part through mTORC1 activation. The human bone tissue is of considerable regenerative capacity as reflected in bone remodeling and in fracture healing. However, bone tissue regeneration deteriorates with age, and tremendous unmet medical needs exist for safe and effective strategies to stimulate bone formation in older individuals commonly inflicted with osteoporosis or osteopenia. WNT signaling has emerged as a promising target pathway for developing novel bone anabolic therapeutics. Identifying bone-promoting WNT ligands and elucidating the underlying mechanisms may lead to useful therapeutic targets. The present study reports that WNT7B potently enhances bone formation through activation of mTORC1 in the mouse.
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Affiliation(s)
- Jianquan Chen
- Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Xiaolin Tu
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Emel Esen
- Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, Missouri, United States of America
- Division of Biology and Biomedical Sciences, Washington University in St. Louis, St. Louis, Missouri, United States of America
| | - Kyu Sang Joeng
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, United States of America
- Division of Biology and Biomedical Sciences, Washington University in St. Louis, St. Louis, Missouri, United States of America
| | - Congxin Lin
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Jeffrey M. Arbeit
- Department of Surgery, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | | | | | - Liang Ma
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, United States of America
- Division of Biology and Biomedical Sciences, Washington University in St. Louis, St. Louis, Missouri, United States of America
- Department of Developmental Biology, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Fanxin Long
- Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, Missouri, United States of America
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, United States of America
- Division of Biology and Biomedical Sciences, Washington University in St. Louis, St. Louis, Missouri, United States of America
- Department of Developmental Biology, Washington University School of Medicine, St. Louis, Missouri, United States of America
- * E-mail:
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Abstract
Autophagy impairment has been implicated in several muscle disorders and in age-related dysfunction. Although previous reports pointed to FOXO as a positive regulator of autophagy in skeletal muscle, it remained unclear what is triggering autophagy. We found that TSC muscle knockout (TSCmKO) mice, characterized by specific depletion of TSC1 in skeletal muscle, and thus constant activation of MTORC1, develop a late-onset myopathy marked by the accumulation of autophagic substrates. In those mice, autophagy induction is blocked despite FOXO activation because of constant MTORC1-dependent inhibition of ULK1. Treatment of TSCmKO mice with rapamycin is sufficient to restore autophagy and to alleviate, at least in part, the myopathy. Inversely, inactivation of the MTORC1 pathway in RPTOR-depleted muscles triggers LC3B lipidation in spite of FOXO inhibition. In conclusion, MTORC1 constitutes the master regulator of autophagy induction in skeletal muscle and its deregulation leads to pathologic alterations of muscle homeostasis.
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Affiliation(s)
- Perrine Castets
- Biozentrum; University of Basel; Basel, Switzerland; Neuromuscular Research Center; Departments of Neurology and Biomedicine; Pharmazentrum; Basel University Hospital; Basel, Switzerland
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46
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Castets P, Lin S, Rion N, Di Fulvio S, Romanino K, Guridi M, Frank S, Tintignac LA, Sinnreich M, Rüegg MA. Sustained activation of mTORC1 in skeletal muscle inhibits constitutive and starvation-induced autophagy and causes a severe, late-onset myopathy. Cell Metab 2013; 17:731-44. [PMID: 23602450 DOI: 10.1016/j.cmet.2013.03.015] [Citation(s) in RCA: 186] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/31/2012] [Revised: 11/22/2012] [Accepted: 03/21/2013] [Indexed: 10/26/2022]
Abstract
Autophagy is a catabolic process that ensures homeostatic cell clearance and is deregulated in a growing number of myopathological conditions. Although FoxO3 was shown to promote the expression of autophagy-related genes in skeletal muscle, the mechanisms triggering autophagy are unclear. We show that TSC1-deficient mice (TSCmKO), characterized by sustained activation of mTORC1, develop a late-onset myopathy related to impaired autophagy. In young TSCmKO mice, constitutive and starvation-induced autophagy is blocked at the induction steps via mTORC1-mediated inhibition of Ulk1, despite FoxO3 activation. Rapamycin is sufficient to restore autophagy in TSCmKO mice and improves the muscle phenotype of old mutant mice. Inversely, abrogation of mTORC1 signaling by depletion of raptor induces autophagy regardless of FoxO inhibition. Thus, mTORC1 is the dominant regulator of autophagy induction in skeletal muscle and ensures a tight coordination of metabolic pathways. These findings may open interesting avenues for therapeutic strategies directed toward autophagy-related muscle diseases.
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Thomanetz V, Angliker N, Cloëtta D, Lustenberger RM, Schweighauser M, Oliveri F, Suzuki N, Rüegg MA. Ablation of the mTORC2 component rictor in brain or Purkinje cells affects size and neuron morphology. ACTA ACUST UNITED AC 2013; 201:293-308. [PMID: 23569215 PMCID: PMC3628512 DOI: 10.1083/jcb.201205030] [Citation(s) in RCA: 172] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
The mTOR complex 2 (mTORC2) is essential in the central nervous system for normal neuronal structure and function, potentially through effects on PKC signaling and independent of the related mTOR complex 1 (mTORC1). The mammalian target of rapamycin (mTOR) assembles into two distinct multi-protein complexes called mTORC1 and mTORC2. Whereas mTORC1 is known to regulate cell and organismal growth, the role of mTORC2 is less understood. We describe two mouse lines that are devoid of the mTORC2 component rictor in the entire central nervous system or in Purkinje cells. In both lines neurons were smaller and their morphology and function were strongly affected. The phenotypes were accompanied by loss of activation of Akt, PKC, and SGK1 without effects on mTORC1 activity. The striking decrease in the activation and expression of several PKC isoforms, the subsequent loss of activation of GAP-43 and MARCKS, and the established role of PKCs in spinocerebellar ataxia and in shaping the actin cytoskeleton strongly suggest that the morphological deficits observed in rictor-deficient neurons are mediated by PKCs. Together our experiments show that mTORC2 has a particularly important role in the brain and that it affects size, morphology, and function of neurons.
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Bentzinger CF, Lin S, Romanino K, Castets P, Guridi M, Summermatter S, Handschin C, Tintignac LA, Hall MN, Rüegg MA. Differential response of skeletal muscles to mTORC1 signaling during atrophy and hypertrophy. Skelet Muscle 2013; 3:6. [PMID: 23497627 PMCID: PMC3622636 DOI: 10.1186/2044-5040-3-6] [Citation(s) in RCA: 106] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2012] [Accepted: 02/15/2013] [Indexed: 02/06/2023] Open
Abstract
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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Affiliation(s)
| | - Shuo Lin
- Biozentrum, University of Basel, Basel, CH-4056, Switzerland
| | - Klaas Romanino
- Biozentrum, University of Basel, Basel, CH-4056, Switzerland
| | - Perrine Castets
- Biozentrum, University of Basel, Basel, CH-4056, Switzerland.,Neuromuscular Research Center, Department of Biomedicine, University of Basel, Basel, CH-4056, Switzerland
| | - Maitea Guridi
- Biozentrum, University of Basel, Basel, CH-4056, Switzerland
| | | | | | - Lionel A Tintignac
- Biozentrum, University of Basel, Basel, CH-4056, Switzerland.,INRA, UMR866, Université Montpellier 1, Université Montpellier 2, Montpellier, France
| | - Michael N Hall
- Biozentrum, University of Basel, Basel, CH-4056, Switzerland
| | - Markus A Rüegg
- Biozentrum, University of Basel, Basel, CH-4056, Switzerland
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Meinen S, Lin S, Rüegg MA, Punga AR. Fatigue and muscle atrophy in a mouse model of myasthenia gravis is paralleled by loss of sarcolemmal nNOS. PLoS One 2012; 7:e44148. [PMID: 22952904 PMCID: PMC3429452 DOI: 10.1371/journal.pone.0044148] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2012] [Accepted: 07/30/2012] [Indexed: 02/01/2023] Open
Abstract
Myasthenia Gravis (MG) patients suffer from chronic fatigue of skeletal muscles, even after initiation of proper immunosuppressive medication. Since the localization of neuronal nitric oxide synthase (nNOS) at the muscle membrane is important for sustained muscle contraction, we here study the localization of nNOS in muscles from mice with acetylcholine receptor antibody seropositive (AChR+) experimental autoimmune MG (EAMG). EAMG was induced in 8 week-old male mice by immunization with AChRs purified from torpedo californica. Sham-injected wild type mice and mdx mice, a model for Duchenne muscular dystrophy, were used for comparison. At EAMG disease grade 3 (severe myasthenic weakness), the triceps, sternomastoid and masseter muscles were collected for analysis. Unlike in mdx muscles, total nNOS expression as well as the presence of its binding partner syntrophin α-1, were not altered in EAMG. Immunohistological and biochemical analysis showed that nNOS was lost from the muscle membrane and accumulated in the cytosol, which is likely the consequence of blocked neuromuscular transmission. Atrophy of all examined EAMG muscles were supported by up-regulated transcript levels of the atrogenes atrogin-1 and MuRF1, as well as MuRF1 protein, in combination with reduced muscle fiber diameters. We propose that loss of sarcolemmal nNOS provides an additional mechanism for the chronic muscle fatigue and secondary muscle atrophy in EAMG and MG.
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MESH Headings
- Animals
- Autoantibodies/immunology
- Cytosol/enzymology
- Disease Models, Animal
- Immunization
- Male
- Mice
- Mice, Inbred C57BL
- Models, Biological
- Muscle Denervation
- Muscle Fatigue
- Muscle, Skeletal/enzymology
- Muscle, Skeletal/immunology
- Muscle, Skeletal/pathology
- Muscle, Skeletal/physiopathology
- Muscular Atrophy/complications
- Muscular Atrophy/immunology
- Muscular Atrophy/pathology
- Muscular Atrophy/physiopathology
- Myasthenia Gravis, Autoimmune, Experimental/complications
- Myasthenia Gravis, Autoimmune, Experimental/immunology
- Myasthenia Gravis, Autoimmune, Experimental/pathology
- Myasthenia Gravis, Autoimmune, Experimental/physiopathology
- Nitric Oxide Synthase Type I/deficiency
- Nitric Oxide Synthase Type I/genetics
- Nitric Oxide Synthase Type I/metabolism
- Phenotype
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Receptors, Cholinergic/metabolism
- Sarcolemma/enzymology
- Sarcolemma/pathology
- Weight Loss
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Affiliation(s)
- Sarina Meinen
- Department of Neurobiology/Pharmacology, Biozentrum, University of Basel, Basel, Switzerland
| | - Shuo Lin
- Department of Neurobiology/Pharmacology, Biozentrum, University of Basel, Basel, Switzerland
| | - Markus A. Rüegg
- Department of Neurobiology/Pharmacology, Biozentrum, University of Basel, Basel, Switzerland
| | - Anna Rostedt Punga
- Department of Neurobiology/Pharmacology, Biozentrum, University of Basel, Basel, Switzerland
- * E-mail:
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Steiner E, Enzmann GU, Lin S, Ghavampour S, Hannocks MJ, Zuber B, Rüegg MA, Sorokin L, Engelhardt B. Loss of astrocyte polarization upon transient focal brain ischemia as a possible mechanism to counteract early edema formation. Glia 2012; 60:1646-59. [DOI: 10.1002/glia.22383] [Citation(s) in RCA: 77] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2012] [Accepted: 06/07/2012] [Indexed: 11/10/2022]
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