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Blatnik AJ, McGovern VL, Burghes AHM. What Genetics Has Told Us and How It Can Inform Future Experiments for Spinal Muscular Atrophy, a Perspective. Int J Mol Sci 2021; 22:8494. [PMID: 34445199 PMCID: PMC8395208 DOI: 10.3390/ijms22168494] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2021] [Revised: 07/28/2021] [Accepted: 08/04/2021] [Indexed: 02/06/2023] Open
Abstract
Proximal spinal muscular atrophy (SMA) is an autosomal recessive neurodegenerative disorder characterized by motor neuron loss and subsequent atrophy of skeletal muscle. SMA is caused by deficiency of the essential survival motor neuron (SMN) protein, canonically responsible for the assembly of the spliceosomal small nuclear ribonucleoproteins (snRNPs). Therapeutics aimed at increasing SMN protein levels are efficacious in treating SMA. However, it remains unknown how deficiency of SMN results in motor neuron loss, resulting in many reported cellular functions of SMN and pathways affected in SMA. Herein is a perspective detailing what genetics and biochemistry have told us about SMA and SMN, from identifying the SMA determinant region of the genome, to the development of therapeutics. Furthermore, we will discuss how genetics and biochemistry have been used to understand SMN function and how we can determine which of these are critical to SMA moving forward.
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Affiliation(s)
| | | | - Arthur H. M. Burghes
- Department of Biological Chemistry & Pharmacology, The Ohio State University Wexner Medical Center, Rightmire Hall, Room 168, 1060 Carmack Road, Columbus, OH 43210, USA; (A.J.B.III); (V.L.M.)
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2
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Blatnik AJ, McGovern VL, Le TT, Iyer CC, Kaspar BK, Burghes AHM. Conditional deletion of SMN in cell culture identifies functional SMN alleles. Hum Mol Genet 2020; 29:3477-3492. [PMID: 33075805 DOI: 10.1093/hmg/ddaa229] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2020] [Revised: 10/01/2020] [Accepted: 10/12/2020] [Indexed: 12/31/2022] Open
Abstract
Spinal muscular atrophy (SMA) is caused by mutation or deletion of survival motor neuron 1 (SMN1) and retention of SMN2 leading to SMN protein deficiency. We developed an immortalized mouse embryonic fibroblast (iMEF) line in which full-length wild-type Smn (flwt-Smn) can be conditionally deleted using Cre recombinase. iMEFs lacking flwt-Smn are not viable. We tested the SMA patient SMN1 missense mutation alleles A2G, D44V, A111G, E134K and T274I in these cells to determine which human SMN (huSMN) mutant alleles can function in the absence of flwt-Smn. All missense mutant alleles failed to rescue survival in the conditionally deleted iMEFs. Thus, the function lost by these mutations is essential to cell survival. However, co-expression of two different huSMN missense mutants can rescue iMEF survival and small nuclear ribonucleoprotein (snRNP) assembly, demonstrating intragenic complementation of SMN alleles. In addition, we show that a Smn protein lacking exon 2B can rescue iMEF survival and snRNP assembly in the absence of flwt-Smn, indicating exon 2B is not required for the essential function of Smn. For the first time, using this novel cell line, we can assay the function of SMN alleles in the complete absence of flwt-Smn.
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Affiliation(s)
- Anton J Blatnik
- Ohio State Biochemistry Program.,Biological Chemistry & Pharmacology
| | | | | | | | - Brian K Kaspar
- Center for Gene Therapy, Nationwide Children's Hospital; Department of Pediatrics, College of Medicine and Public Health, The Ohio State University; and Department of Neuroscience, The Ohio State University, Columbus, OH 43210, USA
| | - Arthur H M Burghes
- Ohio State Biochemistry Program.,Biological Chemistry & Pharmacology.,Molecular Genetics.,Department of Neurology, The Ohio State University Wexner Medical Center, Columbus OH 43210 USA
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Lin CY, Yoshida M, Li LT, Ikenaka A, Oshima S, Nakagawa K, Sakurai H, Matsui E, Nakahata T, Saito MK. iPSC-derived functional human neuromuscular junctions model the pathophysiology of neuromuscular diseases. JCI Insight 2019; 4:124299. [PMID: 31534050 DOI: 10.1172/jci.insight.124299] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2018] [Accepted: 08/08/2019] [Indexed: 01/05/2023] Open
Abstract
The control of voluntary skeletal muscle contraction relies on action potentials, which send signals from the motor neuron through the neuromuscular junction (NMJ). Although dysfunction of the NMJ causes various neuromuscular diseases, a reliable in vitro system for disease modeling is currently unavailable. Here, we present a potentially novel 2-step, self-organizing approach for generating in vitro human NMJs from human induced pluripotent stem cells. Our simple and robust approach results in a complex NMJ structure that includes functional connectivity, recapitulating in vivo synapse formation. We used these in vitro NMJs to model the pathological features of spinal muscular atrophy, revealing the developmental and functional defects of NMJ formation and NMJ-dependent muscular contraction. Our differentiation system is therefore useful for investigating and understanding the physiology and pathology of human NMJs.
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Affiliation(s)
- Chuang-Yu Lin
- Department of Clinical Application, Center for iPS Cell Research and Application (CiRA), Kyoto University, Kyoto, Japan
| | - Michiko Yoshida
- Department of Clinical Application, Center for iPS Cell Research and Application (CiRA), Kyoto University, Kyoto, Japan.,Department of Pediatrics, Kyoto Prefectural University of Medicine, Kyoto, Japan
| | - Li-Tzu Li
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
| | - Akihiro Ikenaka
- Department of Clinical Application, Center for iPS Cell Research and Application (CiRA), Kyoto University, Kyoto, Japan
| | - Shiori Oshima
- Sony Imaging Products & Solutions Inc., Tokyo, Japan
| | | | - Hidetoshi Sakurai
- Department of Clinical Application, Center for iPS Cell Research and Application (CiRA), Kyoto University, Kyoto, Japan
| | - Eriko Matsui
- Sony Imaging Products & Solutions Inc., Tokyo, Japan
| | - Tatsutoshi Nakahata
- Department of Clinical Application, Center for iPS Cell Research and Application (CiRA), Kyoto University, Kyoto, Japan
| | - Megumu K Saito
- Department of Clinical Application, Center for iPS Cell Research and Application (CiRA), Kyoto University, Kyoto, Japan
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Sheng L, Wan B, Feng P, Sun J, Rigo F, Bennett CF, Akerman M, Krainer AR, Hua Y. Downregulation of Survivin contributes to cell-cycle arrest during postnatal cardiac development in a severe spinal muscular atrophy mouse model. Hum Mol Genet 2019; 27:486-498. [PMID: 29220503 DOI: 10.1093/hmg/ddx418] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Accepted: 11/28/2017] [Indexed: 11/13/2022] Open
Abstract
Spinal muscular atrophy (SMA) is the leading genetic cause of infant mortality, characterized by progressive degeneration of spinal-cord motor neurons, leading to atrophy of skeletal muscles. However, accumulating evidence indicates that it is a multi-system disorder, particularly in its severe forms. Several studies delineated structural and functional cardiac abnormalities in SMA patients and mouse models, yet the abnormalities have been primarily attributed to autonomic dysfunction. Here, we show in a severe mouse model that its cardiomyocytes undergo G0/G1 cell-cycle arrest and enhanced apoptosis during postnatal development. Microarray and real-time RT-PCR analyses revealed that a set of genes associated with cell cycle and apoptosis were dysregulated in newborn pups. Of particular interest, the Birc5 gene, which encodes Survivin, an essential protein for heart development, was down-regulated even on pre-symptomatic postnatal day 0. Interestingly, cultured cardiomyocytes depleted of SMN recapitulated the gene expression changes including downregulation of Survivin and abnormal cell-cycle progression; and overexpression of Survivin rescued the cell-cycle defect. Finally, increasing SMN in SMA mice with a therapeutic antisense oligonucleotide improved heart pathology and recovered expression of deregulated genes. Collectively, our data demonstrate that the cardiac malfunction of the severe SMA mouse model is mainly a cell-autonomous defect, caused by widespread gene deregulation in heart tissue, particularly of Birc5, resulting in developmental abnormalities through cell-cycle arrest and apoptosis.
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Affiliation(s)
- Lei Sheng
- Jiangsu Key Laboratory of Neuropsychiatric Diseases, The Second Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215004, China.,Institute of Neuroscience, Soochow University, Suzhou, Jiangsu 215123, China
| | - Bo Wan
- Jiangsu Key Laboratory of Neuropsychiatric Diseases, The Second Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215004, China.,Institute of Neuroscience, Soochow University, Suzhou, Jiangsu 215123, China
| | - Pengchao Feng
- Jiangsu Key Laboratory of Neuropsychiatric Diseases, The Second Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215004, China.,Institute of Neuroscience, Soochow University, Suzhou, Jiangsu 215123, China
| | - Junjie Sun
- Jiangsu Key Laboratory of Neuropsychiatric Diseases, The Second Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215004, China.,Institute of Neuroscience, Soochow University, Suzhou, Jiangsu 215123, China
| | - Frank Rigo
- Ionis Pharmaceuticals, Carlsbad, CA 92010, USA
| | | | - Martin Akerman
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, NY 11724, USA.,Envisagenics, Inc., New York, NY 10017, USA
| | - Adrian R Krainer
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York, NY 11724, USA
| | - Yimin Hua
- Jiangsu Key Laboratory of Neuropsychiatric Diseases, The Second Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215004, China.,Institute of Neuroscience, Soochow University, Suzhou, Jiangsu 215123, China
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Zhao X, Feng Z, Ling KKY, Mollin A, Sheedy J, Yeh S, Petruska J, Narasimhan J, Dakka A, Welch EM, Karp G, Chen KS, Metzger F, Ratni H, Lotti F, Tisdale S, Naryshkin NA, Pellizzoni L, Paushkin S, Ko CP, Weetall M. Pharmacokinetics, pharmacodynamics, and efficacy of a small-molecule SMN2 splicing modifier in mouse models of spinal muscular atrophy. Hum Mol Genet 2016; 25:1885-1899. [PMID: 26931466 PMCID: PMC5062580 DOI: 10.1093/hmg/ddw062] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2015] [Accepted: 02/22/2016] [Indexed: 12/26/2022] Open
Abstract
Spinal muscular atrophy (SMA) is caused by the loss or mutation of both copies of the survival motor neuron 1 (SMN1) gene. The related SMN2 gene is retained, but due to alternative splicing of exon 7, produces insufficient levels of the SMN protein. Here, we systematically characterize the pharmacokinetic and pharmacodynamics properties of the SMN splicing modifier SMN-C1. SMN-C1 is a low-molecular weight compound that promotes the inclusion of exon 7 and increases production of SMN protein in human cells and in two transgenic mouse models of SMA. Furthermore, increases in SMN protein levels in peripheral blood mononuclear cells and skin correlate with those in the central nervous system (CNS), indicating that a change of these levels in blood or skin can be used as a non-invasive surrogate to monitor increases of SMN protein levels in the CNS. Consistent with restored SMN function, SMN-C1 treatment increases the levels of spliceosomal and U7 small-nuclear RNAs and corrects RNA processing defects induced by SMN deficiency in the spinal cord of SMNΔ7 SMA mice. A 100% or greater increase in SMN protein in the CNS of SMNΔ7 SMA mice robustly improves the phenotype. Importantly, a ∼50% increase in SMN leads to long-term survival, but the SMA phenotype is only partially corrected, indicating that certain SMA disease manifestations may respond to treatment at lower doses. Overall, we provide important insights for the translation of pre-clinical data to the clinic and further therapeutic development of this series of molecules for SMA treatment.
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Affiliation(s)
- Xin Zhao
- PTC Therapeutics, Inc., South Plainfield, NJ 07080, USA
| | - Zhihua Feng
- Department of Biological Sciences, Section of Neurobiology, University of Southern California, Los Angeles, CA 90089, USA
| | - Karen K Y Ling
- Department of Biological Sciences, Section of Neurobiology, University of Southern California, Los Angeles, CA 90089, USA
| | - Anna Mollin
- PTC Therapeutics, Inc., South Plainfield, NJ 07080, USA
| | | | - Shirley Yeh
- PTC Therapeutics, Inc., South Plainfield, NJ 07080, USA
| | | | | | - Amal Dakka
- PTC Therapeutics, Inc., South Plainfield, NJ 07080, USA
| | - Ellen M Welch
- PTC Therapeutics, Inc., South Plainfield, NJ 07080, USA
| | - Gary Karp
- PTC Therapeutics, Inc., South Plainfield, NJ 07080, USA
| | - Karen S Chen
- SMA Foundation, 888 Seventh Avenue, Suite 400, New York, NY 10019, USA
| | - Friedrich Metzger
- F. Hoffmann-La Roche, Pharmaceutical Research and Early Development, Roche Innovation Center Basel, Grenzacherstrasse 124, Basel 4070, Switzerland
| | - Hasane Ratni
- F. Hoffmann-La Roche, Pharmaceutical Research and Early Development, Roche Innovation Center Basel, Grenzacherstrasse 124, Basel 4070, Switzerland
| | - Francesco Lotti
- Department of Pathology and Cell Biology, Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA and
| | - Sarah Tisdale
- Department of Pathology and Cell Biology, Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA and
| | | | - Livio Pellizzoni
- Department of Pathology and Cell Biology, Center for Motor Neuron Biology and Disease, Columbia University, New York, NY 10032, USA and
| | - Sergey Paushkin
- SMA Foundation, 888 Seventh Avenue, Suite 400, New York, NY 10019, USA
| | - Chien-Ping Ko
- Department of Biological Sciences, Section of Neurobiology, University of Southern California, Los Angeles, CA 90089, USA,
| | - Marla Weetall
- PTC Therapeutics, Inc., South Plainfield, NJ 07080, USA,
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Giacomotto J, Rinkwitz S, Becker TS. Effective heritable gene knockdown in zebrafish using synthetic microRNAs. Nat Commun 2015; 6:7378. [PMID: 26051838 PMCID: PMC4468906 DOI: 10.1038/ncomms8378] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2015] [Accepted: 05/01/2015] [Indexed: 12/22/2022] Open
Abstract
Although zebrafish is used to model human diseases through mutational and morpholino-based knockdown approaches, there are currently no robust transgenic knockdown tools. Here we investigate the knockdown efficiency of three synthetic miRNA-expressing backbones and show that these constructs can downregulate a sensor transgene with different degrees of potency. Using this approach, we reproduce spinal muscular atrophy (SMA) in zebrafish by targeting the smn1 gene. We also generate different transgenic lines, with severity and age of onset correlated to the level of smn1 inhibition, recapitulating for the first time the different forms of SMA in zebrafish. These lines are proof-of-concept that miRNA-based approaches can be used to generate potent heritable gene knockdown in zebrafish. Zebrafish is a model system for which for no reliable heritable gene silencing method is available. Here the authors provide a system for heritable miRNA-mediated knockdown and demonstrate tunable silencing of the smn1 gene that recapitulate different forms of spinal muscular atrophy.
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Affiliation(s)
- Jean Giacomotto
- Brain and Mind Research Institute, Sydney Medical School, University of Sydney, Camperdown, New South Wales 2050, Australia
| | - Silke Rinkwitz
- Brain and Mind Research Institute, Sydney Medical School, University of Sydney, Camperdown, New South Wales 2050, Australia.,Department of Physiology, Sydney Medical School, University of Sydney, Camperdown, New South Wales 2050, Australia
| | - Thomas S Becker
- Brain and Mind Research Institute, Sydney Medical School, University of Sydney, Camperdown, New South Wales 2050, Australia.,Department of Physiology, Sydney Medical School, University of Sydney, Camperdown, New South Wales 2050, Australia
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Cherry JJ, Kobayashi DT, Lynes MM, Naryshkin NN, Tiziano FD, Zaworski PG, Rubin LL, Jarecki J. Assays for the identification and prioritization of drug candidates for spinal muscular atrophy. Assay Drug Dev Technol 2015; 12:315-41. [PMID: 25147906 DOI: 10.1089/adt.2014.587] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Spinal muscular atrophy (SMA) is an autosomal recessive genetic disorder resulting in degeneration of α-motor neurons of the anterior horn and proximal muscle weakness. It is the leading cause of genetic mortality in children younger than 2 years. It affects ∼1 in 11,000 live births. In 95% of cases, SMA is caused by homozygous deletion of the SMN1 gene. In addition, all patients possess at least one copy of an almost identical gene called SMN2. A single point mutation in exon 7 of the SMN2 gene results in the production of low levels of full-length survival of motor neuron (SMN) protein at amounts insufficient to compensate for the loss of the SMN1 gene. Although no drug treatments are available for SMA, a number of drug discovery and development programs are ongoing, with several currently in clinical trials. This review describes the assays used to identify candidate drugs for SMA that modulate SMN2 gene expression by various means. Specifically, it discusses the use of high-throughput screening to identify candidate molecules from primary screens, as well as the technical aspects of a number of widely used secondary assays to assess SMN messenger ribonucleic acid (mRNA) and protein expression, localization, and function. Finally, it describes the process of iterative drug optimization utilized during preclinical SMA drug development to identify clinical candidates for testing in human clinical trials.
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SMN is essential for the biogenesis of U7 small nuclear ribonucleoprotein and 3'-end formation of histone mRNAs. Cell Rep 2014; 5:1187-95. [PMID: 24332368 DOI: 10.1016/j.celrep.2013.11.012] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Revised: 10/14/2013] [Accepted: 11/07/2013] [Indexed: 02/06/2023] Open
Abstract
Spinal muscular atrophy (SMA) is a neurodegenerative disease caused by a deficiency in the survival motor neuron (SMN) protein. SMN mediates the assembly of spliceosomal small nuclear ribonucleoproteins (snRNPs) and possibly other RNPs. Here, we investigated SMN requirement for the biogenesis and function of U7--an snRNP specialized in the 3'-end formation of replication-dependent histone mRNAs that normally are not polyadenylated. We show that SMN deficiency impairs U7 snRNP assembly and decreases U7 levels in mammalian cells. The SMN-dependent U7 reduction affects endonucleolytic cleavage of histone mRNAs leading to abnormal accumulation of 3'-extended and polyadenylated transcripts followed by downstream changes in histone gene expression. Importantly, SMN deficiency induces defects of histone mRNA 3'-end formation in both SMA mice and human patients. These findings demonstrate that SMN is essential for U7 biogenesis and histone mRNA processing in vivo and identify an additional RNA pathway disrupted in SMA.
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Abstract
Neuromuscular diseases, which encompass disorders that affect muscle and its innervation, are highly heritable. Genetic diagnosis now frequently pinpoints the primary mutation responsible for a given neuromuscular disease. However, the results from genetic testing indicate that neuromuscular disease phenotypes may vary widely, even in individuals with the same primary disease-causing mutation. Clinical variability arises from both genetic and environmental factors. Genetic modifiers can now be identified using candidate gene as well as genomic approaches. The presence of genetic modifiers for neuromuscular disease helps define the clinical outcome and also highlights pathways of potential therapeutic utility. Herein, we will focus on single gene neuromuscular disorders, including muscular dystrophy, spinal muscular atrophy, and amyotrophic lateral sclerosis, and the methods that have been used to identify modifier genes. Animal models have been an invaluable resource for modifier gene discovery and subsequent mechanistic studies. Some modifiers, identified using animal models, have successfully translated to the human counterpart. Furthermore, in a few instances, modifier gene discovery has repetitively uncovered the same pathway, such as TGFβ signaling in muscular dystrophy, further emphasizing the relevance of that pathway. Knowledge of genetic factors that influence disease can have direct clinical applications for prognosis and predicted outcome.
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Affiliation(s)
- Kay-Marie Lamar
- Department of Human Genetics, Department of Medicine, Section of Cardiology, The University of Chicago, Chicago, IL, USA
| | - Elizabeth M McNally
- Department of Human Genetics, Department of Medicine, Section of Cardiology, The University of Chicago, Chicago, IL, USA
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Auld D, Davis MI, Lea W, Parker C, Simeonov A. Literature Search and Review. Assay Drug Dev Technol 2013. [DOI: 10.1089/adt.2013.1109.lr] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- Doug Auld
- Novartis Institutes for BioMedical Research, Cambridge, Massachusetts
| | | | | | - Christian Parker
- Novartis Institutes for BioMedical Research, Novartis Pharma AG, Basel, Switzerland
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