101
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Sumner CJ, Kolb SJ, Harmison GG, Jeffries NO, Schadt K, Finkel RS, Dreyfuss G, Fischbeck KH. SMN mRNA and protein levels in peripheral blood: biomarkers for SMA clinical trials. Neurology 2006; 66:1067-73. [PMID: 16481599 DOI: 10.1212/01.wnl.0000201929.56928.13] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
BACKGROUND Clinical trials of drugs that increase SMN protein levels in vitro are currently under way in patients with spinal muscular atrophy. OBJECTIVE To develop and validate measures of SMN mRNA and protein in peripheral blood and to establish baseline SMN levels in a cohort of controls, carriers, and patients of known genotype, which could be used to follow response to treatment. METHODS SMN1 and SMN2 gene copy numbers were determined in blood samples collected from 86 subjects. Quantitative reverse transcription PCR was used to measure blood levels of SMN mRNA with and without exon 7. A cell immunoassay was used to measure blood levels of SMN protein. RESULTS Blood levels of SMN mRNA and protein were measured with high reliability. There was little variation in SMN levels in individual subjects over a 5-week period. Levels of exon 7-containing SMN mRNA and SMN protein correlated with SMN1 and SMN2 gene copy number. With the exception of type I SMA, there was no correlation between SMN levels and disease severity. CONCLUSION SMN mRNA and protein levels can be reliably measured in the peripheral blood and used during clinical trials in spinal muscular atrophy, but these levels do not necessarily predict disease severity.
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102
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Kolb SJ, Gubitz AK, Olszewski RF, Ottinger E, Sumner CJ, Fischbeck KH, Dreyfuss G. A novel cell immunoassay to measure survival of motor neurons protein in blood cells. BMC Neurol 2006; 6:6. [PMID: 16451734 PMCID: PMC1413553 DOI: 10.1186/1471-2377-6-6] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2005] [Accepted: 02/01/2006] [Indexed: 12/03/2022] Open
Abstract
Background The motor neuron degenerative disease spinal muscular atrophy (SMA) is the leading genetic cause of infant mortality and is caused by mutations in the survival of motor neurons (SMN) gene that reduce the expression levels of the SMN protein. A major goal of current therapeutic approaches is to increase SMN levels in SMA patients. The purpose of this study was to develop a reliable assay to measure SMN protein levels from peripheral blood samples. Methods We developed a novel cell immunoassay to quantitatively measure SMN levels from peripheral blood mononuclear cells (PBMCs) using a single anti-SMN antibody. Results SMN levels determined by the cell immunoassay are comparable to levels determined by Western blot, but in contrast, the immunoassay does not involve cell lysis, requires a small amount of patient material, and can be done on a large number of samples simultaneously. SMN levels from PBMCs are not influenced by cell type heterogeneity. Conclusion SMN levels measured from total PBMCs provide an important snapshot of SMN protein expression, which should be a useful aid in SMA diagnosis, and a surrogate marker of efficacy of treatment in SMA clinical trials.
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103
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Di Prospero NA, Fischbeck KH. Therapeutics development for triplet repeat expansion diseases. Nat Rev Genet 2005; 6:756-65. [PMID: 16205715 DOI: 10.1038/nrg1690] [Citation(s) in RCA: 113] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The underlying genetic mutations for many inherited neurodegenerative disorders have been identified in recent years. One frequent type of mutation is trinucleotide repeat expansion. Depending on the location of the repeat expansion, the mutation might result in a loss of function of the disease gene, a toxic gain of function or both. Disease gene identification has led to the development of model systems for investigating disease mechanisms and evaluating treatments. Examination of experimental findings reveals similarities in disease mechanisms as well as possibilities for treatment.
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104
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Sivakumar K, Kyriakides T, Puls I, Nicholson GA, Funalot B, Antonellis A, Sambuughin N, Christodoulou K, Beggs JL, Zamba-Papanicolaou E, Ionasescu V, Dalakas MC, Green ED, Fischbeck KH, Goldfarb LG. Phenotypic spectrum of disorders associated with glycyl-tRNA synthetase mutations. ACTA ACUST UNITED AC 2005; 128:2304-14. [PMID: 16014653 DOI: 10.1093/brain/awh590] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We describe clinical, electrophysiological, histopathological and molecular features of a unique disease caused by mutations in the glycyl-tRNA synthetase (GARS) gene. Sixty patients from five multigenerational families have been evaluated. The disease is characterized by adolescent onset of weakness, and atrophy of thenar and first dorsal interosseus muscles progressing to involve foot and peroneal muscles in most but not all cases. Mild to moderate sensory deficits develop in a minority of patients. Neurophysiologically confirmed chronic denervation in distal muscles with reduced compound motor action potentials were features consistent with both motor neuronal and axonal pathology. Sural nerve biopsy showed mild to moderate selective loss of small- and medium-sized myelinated and small unmyelinated axons, although sensory nerve action potentials were not significantly decreased. Based on the presence or absence of sensory changes, the disease phenotype was initially defined as distal spinal muscular atrophy type V (dSMA-V) in three families, Charcot-Marie-Tooth disease type 2D (CMT2D) in a single family, and as either dSMA-V or CMT2D in patients of another large family. Linkage to chromosome 7p15 and the presence of disease-associated heterozygous GARS mutations have been identified in patients from each of the five studied families. We conclude that patients with GARS mutations present a clinical continuum of predominantly motor distal neuronopathy/axonopathy with mild to moderate sensory involvement that varies between the families and between members of the same family. Awareness of these overlapping clinical phenotypes associated with mutations in GARS will facilitate identification of this disorder in additional families and direct future research toward better understanding of its pathogenesis.
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105
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Puls I, Oh SJ, Sumner CJ, Wallace KE, Floeter MK, Mann EA, Kennedy WR, Wendelschafer-Crabb G, Vortmeyer A, Powers R, Finnegan K, Holzbaur ELF, Fischbeck KH, Ludlow CL. Distal spinal and bulbar muscular atrophy caused by dynactin mutation. Ann Neurol 2005; 57:687-94. [PMID: 15852399 PMCID: PMC1351270 DOI: 10.1002/ana.20468] [Citation(s) in RCA: 151] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Impaired axonal transport has been postulated to play a role in the pathophysiology of multiple neurodegenerative disorders. In this report, we describe the results of clinical and neuropathological studies in a family with an inherited form of motor neuron disease caused by mutation in the p150Glued subunit of dynactin, a microtubule motor protein essential for retrograde axonal transport. Affected family members had a distinct clinical phenotype characterized by early bilateral vocal fold paralysis affecting the adductor and abductor laryngeal muscles. They later experienced weakness and atrophy in the face, hands, and distal legs. The extremity involvement was greater in the hands than in the legs, and it had a particular predilection for the thenar muscles. No clinical or electrophysiological sensory abnormality existed; however, skin biopsy results showed morphological abnormalities of epidermal nerve fibers. An autopsy study of one patient showed motor neuron degeneration and axonal loss in the ventral horn of the spinal cord and hypoglossal nucleus of the medulla. Immunohistochemistry showed abnormal inclusions of dynactin and dynein in motor neurons. This mutation of dynactin, a ubiquitously expressed protein, causes a unique pattern of motor neuron degeneration that is associated with the accumulation of dynein and dynactin in neuronal inclusions.
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106
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Liang GSL, de Miguel M, Gómez-Hernández JM, Glass JD, Scherer SS, Mintz M, Barrio LC, Fischbeck KH. Severe neuropathy with leaky connexin32 hemichannels. Ann Neurol 2005; 57:749-54. [PMID: 15852376 DOI: 10.1002/ana.20459] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
X-linked Charcot-Marie-Tooth disease is one of a set of diseases caused by mutations in gap junction proteins called connexins. We identified a connexin32 missense mutation (F235C) in a girl with unusually severe neuropathy. The localization and trafficking of the mutant protein in cell culture was normal, but electrophysiological studies showed that the mutation caused abnormal hemichannel opening, with excessive permeability of the plasma membrane and decreased cell survival. Abnormal leakiness of connexin hemichannels is likely a mechanism of cellular toxicity in this and perhaps other diseases caused by connexin mutations.
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107
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Kernochan LE, Russo ML, Woodling NS, Huynh TN, Avila AM, Fischbeck KH, Sumner CJ. The role of histone acetylation in SMN gene expression. Hum Mol Genet 2005; 14:1171-82. [PMID: 15772088 DOI: 10.1093/hmg/ddi130] [Citation(s) in RCA: 123] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Increasing survival motor neuron 2 (SMN2) gene expression may be an effective strategy for the treatment of spinal muscular atrophy (SMA). Histone deacetylase (HDAC) inhibitors have been shown to increase SMN transcript and protein levels, but the specific role of histone acetylation in regulating SMN gene expression has not been explored. Using chromatin immunopreciptation, we investigated the levels of acetylated H3 and H4 histones and HDACs associated with different regions of the human and mouse SMN genes in both cultured cells and tissues. We show that the SMN gene has a reproducible pattern of histone acetylation that is largely conserved among different tissues and species. A limited region of the promoter surrounding the transcriptional start site has relatively high levels of histone acetylation, whereas regions further upstream or downstream have lower levels. After HDAC inhibitor treatment, acetylated histone levels increased, particularly at upstream regions, correlating with a 2-fold increase in promoter activity. During development in mouse tissues, histone acetylation levels decreased and associated HDAC2 levels increased at the region closest to the transcriptional start site, correlating with a 40-60% decrease in SMN transcript and protein levels. These data indicate that histone acetylation modulates SMN gene expression and that pharmacological manipulation of this epigenetic determinant is feasible. HDAC2, in particular, may be a future therapeutic target for SMA.
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108
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Scherer SS, Xu YT, Messing A, Willecke K, Fischbeck KH, Jeng LJB. Transgenic expression of human connexin32 in myelinating Schwann cells prevents demyelination in connexin32-null mice. J Neurosci 2005; 25:1550-9. [PMID: 15703409 PMCID: PMC6725992 DOI: 10.1523/jneurosci.3082-04.2005] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2004] [Revised: 01/03/2005] [Accepted: 01/03/2005] [Indexed: 11/21/2022] Open
Abstract
Mutations in Gap Junction beta1 (GJB1), the gene encoding the gap junction protein connexin32 (Cx32), cause the X-linked form of Charcot-Marie-Tooth disease (CMT1X), an inherited demyelinating neuropathy. We investigated the possibility that the expression of mutant Cx32 in other cells besides myelinating Schwann cells contributes to the development of demyelination. Human Cx32 was expressed in transgenic mice using a rat myelin protein zero (Mpz) promoter, which is exclusively expressed by myelinating Schwann cells. Male mice expressing the human transgene were crossed with female Gjb1/cx32-null mice; the resulting male offspring were all cx32-null (on the X chromosome), and one-half were transgene positive. In these transgenic mice, all of the Cx32 was derived from the expression of the transgene and was found in the sciatic nerve but not in the spinal cord or the liver. Furthermore, the Cx32 protein was properly localized (within incisures and paranodes) in myelinating Schwann cells. Finally, the expression of human Cx32 protein "rescued" the phenotype of cx32-null mice, because the transgenic mice have significantly fewer demyelinated or remyelinated axons than their nontransgenic littermates. These results indicate that the loss of Schwann-cell-autonomous expression of Cx32 is sufficient to account for demyelination in CMT1X.
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109
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Verbeek DS, Knight MA, Harmison GG, Fischbeck KH, Howell BW. Protein kinase C gamma mutations in spinocerebellar ataxia 14 increase kinase activity and alter membrane targeting. ACTA ACUST UNITED AC 2004; 128:436-42. [PMID: 15618281 DOI: 10.1093/brain/awh378] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The protein kinase C gamma (PKCgamma) gene is mutated in spinocerebellar ataxia type 14 (SCA14). In this study, we investigated the effects of two SCA14 missense mutations, G118D and C150F, on PKCgamma function. We found that these mutations increase the intrinsic activity of PKCgamma. Direct visualization of labelled PKCgamma in living cells demonstrates that the mutant protein translocates more rapidly to selected regions of the plasma membrane in response to Ca2+ influx. These results point to specific alterations in mutant PKCgamma function that could lead to the selective neuronal degeneration of SCA14.
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110
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Chen YZ, Bennett CL, Huynh HM, Blair IP, Puls I, Irobi J, Dierick I, Abel A, Kennerson ML, Rabin BA, Nicholson GA, Auer-Grumbach M, Wagner K, De Jonghe P, Griffin JW, Fischbeck KH, Timmerman V, Cornblath DR, Chance PF. DNA/RNA helicase gene mutations in a form of juvenile amyotrophic lateral sclerosis (ALS4). Am J Hum Genet 2004; 74:1128-35. [PMID: 15106121 PMCID: PMC1182077 DOI: 10.1086/421054] [Citation(s) in RCA: 551] [Impact Index Per Article: 27.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2004] [Accepted: 03/10/2004] [Indexed: 12/11/2022] Open
Abstract
Juvenile amyotrophic lateral sclerosis (ALS4) is a rare autosomal dominant form of juvenile amyotrophic lateral sclerosis (ALS) characterized by distal muscle weakness and atrophy, normal sensation, and pyramidal signs. Individuals affected with ALS4 usually have an onset of symptoms at age <25 years, a slow rate of progression, and a normal life span. The ALS4 locus maps to a 1.7-Mb interval on chromosome 9q34 flanked by D9S64 and D9S1198. To identify the molecular basis of ALS4, we tested 19 genes within the ALS4 interval and detected missense mutations (T3I, L389S, and R2136H) in the Senataxin gene (SETX). The SETX gene encodes a novel 302.8-kD protein. Although its function remains unknown, SETX contains a DNA/RNA helicase domain with strong homology to human RENT1 and IGHMBP2, two genes encoding proteins known to have roles in RNA processing. These observations of ALS4 suggest that mutations in SETX may cause neuronal degeneration through dysfunction of the helicase activity or other steps in RNA processing.
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111
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Markowitz JA, Tinkle MB, Fischbeck KH. Spinal Muscular Atrophy in the Neonate. J Obstet Gynecol Neonatal Nurs 2004; 33:12-20. [PMID: 14971549 DOI: 10.1177/0884217503261125] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Spinal muscular atrophy (SMA) type I is an autosomal recessive disorder characterized by loss of lower motor neurons in the spinal cord. This severe hereditary neurodegenerative disorder is an important cause of morbidity in the neonate and the leading hereditary cause of infant mortality. The characteristic degeneration of anterior horn cells in the spinal cord leads to progressive muscular weakness and atrophy of the skeletal muscles. In SMA type I, the most severe form of SMA, death usually ensues by 2 years of age from respiratory failure or infection. Accurate diagnosis is now available through genetic testing, and progress is being made toward the development of therapy based on understanding of the disease mechanism. The neonatal nurse plays a pivotal role in identifying and caring for these medically fragile infants and in providing support and education for parents and families.
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112
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Piccioni F, Roman BR, Fischbeck KH, Taylor JP. A screen for drugs that protect against the cytotoxicity of polyglutamine-expanded androgen receptor. Hum Mol Genet 2003; 13:437-46. [PMID: 14709594 DOI: 10.1093/hmg/ddh045] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Spinobulbar muscular atrophy is a neurodegenerative disorder caused by expansion of a CAG triplet repeat sequence encoding a polyglutamine tract in the androgen receptor. It has been shown that the mutant protein is toxic in cell culture and triggers an apoptotic cascade resulting in activation of caspase-3. We developed an assay of caspase-3 activation in cells expressing the mutant androgen receptor. This assay was used to screen 1040 drugs, most of which are approved for clinical use. Drugs that inhibit polyglutamine-dependent activation of caspase-3 were subjected to follow-up screens to identify compounds that reproducibly prevent polyglutamine-induced cytotoxicity. Four drugs satisfied these criteria. Three of these (digitoxin, nerifolin and peruvoside) are structurally and functionally related compounds of the cardiac glycoside class and known inhibitors of Na(+)K(+)-ATPase. The fourth compound, suloctidil, is a calcium channel blocker.
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113
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Sumner CJ, Huynh TN, Markowitz JA, Perhac JS, Hill B, Coovert DD, Schussler K, Chen X, Jarecki J, Burghes AHM, Taylor JP, Fischbeck KH. Valproic acid increases SMN levels in spinal muscular atrophy patient cells. Ann Neurol 2003; 54:647-54. [PMID: 14595654 DOI: 10.1002/ana.10743] [Citation(s) in RCA: 230] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Spinal muscular atrophy (SMA) is an inherited motor neuron disease caused by mutation of the telomeric copy of the survival motor neuron gene (SMN1). Although a centromeric copy of the survival motor neuron gene (SMN2) is retained in all patients with SMA, it differs from SMN1 at a critical nucleotide such that the majority of SMN2 transcripts lack exon 7 and encode an unstable, truncated protein. Here, we show that valproic acid increases levels of exon 7-containing SMN transcript and SMN protein in type I SMA patient-derived fibroblast cell lines. Valproic acid may increase SMN levels both by activating the SMN promoter and by preventing exon 7 skipping in SMN transcripts. Valproic acid and related compounds warrant further investigation as potential treatment for SMA.
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114
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Taylor JP, Taye AA, Campbell C, Kazemi-Esfarjani P, Fischbeck KH, Min KT. Aberrant histone acetylation, altered transcription, and retinal degeneration in a Drosophila model of polyglutamine disease are rescued by CREB-binding protein. Genes Dev 2003; 17:1463-8. [PMID: 12815067 PMCID: PMC196076 DOI: 10.1101/gad.1087503] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Sequestration of the transcriptional coactivator CREB-binding protein (CBP), a histone acetyltransferase, has been implicated in the pathogenesis of polyglutamine expansion neurodegenerative disease. We used a Drosophila model to demonstrate that polyglutamine-induced neurodegeneration is accompanied by a defect in histone acetylation and a substantial alteration in the transcription profile. Furthermore, we demonstrate complete functional and morphological rescue by up-regulation of endogenous Drosophila CBP (dCBP). Rescue of the degenerative phenotype is associated with eradication of polyglutamine aggregates, recovery of histone acetylation, and normalization of the transcription profile. These findings suggest that histone acetylation is an early target of polyglutamine toxicity and indicate that transcriptional dysregulation is an important part of the pathogenesis of polyglutamine-induced neurodegeneration.
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115
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Antonellis A, Ellsworth RE, Sambuughin N, Puls I, Abel A, Lee-Lin SQ, Jordanova A, Kremensky I, Christodoulou K, Middleton LT, Sivakumar K, Ionasescu V, Funalot B, Vance JM, Goldfarb LG, Fischbeck KH, Green ED. Glycyl tRNA synthetase mutations in Charcot-Marie-Tooth disease type 2D and distal spinal muscular atrophy type V. Am J Hum Genet 2003; 72:1293-9. [PMID: 12690580 PMCID: PMC1180282 DOI: 10.1086/375039] [Citation(s) in RCA: 408] [Impact Index Per Article: 19.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2003] [Accepted: 02/20/2003] [Indexed: 11/03/2022] Open
Abstract
Charcot-Marie-Tooth disease type 2D (CMT2D) and distal spinal muscular atrophy type V (dSMA-V) are axonal peripheral neuropathies inherited in an autosomal dominant fashion. Our previous genetic and physical mapping efforts localized the responsible gene(s) to a well-defined region on human chromosome 7p. Here, we report the identification of four disease-associated missense mutations in the glycyl tRNA synthetase gene in families with CMT2D and dSMA-V. This is the first example of an aminoacyl tRNA synthetase being implicated in a human genetic disease, which makes genes that encode these enzymes relevant candidates for other inherited neuropathies and motor neuron diseases.
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116
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Antonellis A, Ellsworth RE, Sambuughin N, Puls I, Abel A, Lee-Lin SQ, Jordanova A, Kremensky I, Christodoulou K, Middleton LT, Sivakumar K, Ionasescu V, Funalot B, Vance JM, Goldfarb LG, Fischbeck KH, Green ED. Glycyl tRNA synthetase mutations in Charcot-Marie-Tooth disease type 2D and distal spinal muscular atrophy type V. Am J Hum Genet 2003. [PMID: 12690580 DOI: 10.1086/375039/s0002-9297(07)60657-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Charcot-Marie-Tooth disease type 2D (CMT2D) and distal spinal muscular atrophy type V (dSMA-V) are axonal peripheral neuropathies inherited in an autosomal dominant fashion. Our previous genetic and physical mapping efforts localized the responsible gene(s) to a well-defined region on human chromosome 7p. Here, we report the identification of four disease-associated missense mutations in the glycyl tRNA synthetase gene in families with CMT2D and dSMA-V. This is the first example of an aminoacyl tRNA synthetase being implicated in a human genetic disease, which makes genes that encode these enzymes relevant candidates for other inherited neuropathies and motor neuron diseases.
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117
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Taylor JP, Tanaka F, Robitschek J, Sandoval CM, Taye A, Markovic-Plese S, Fischbeck KH. Aggresomes protect cells by enhancing the degradation of toxic polyglutamine-containing protein. Hum Mol Genet 2003; 12:749-57. [PMID: 12651870 DOI: 10.1093/hmg/ddg074] [Citation(s) in RCA: 336] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Expression of misfolded protein in cultured cells frequently leads to the formation of juxtanuclear inclusions that have been termed 'aggresomes'. Aggresome formation is an active cellular response that involves trafficking of the offending protein along microtubules, reorganization of intermediate filaments and recruitment of components of the ubiquitin proteasome system. Whether aggresomes are benevolent or noxious is unknown, but they are of particular interest because of the appearance of similar inclusions in protein deposition diseases. Here we present evidence that aggresomes serve a cytoprotective function and are associated with accelerated turnover of mutant proteins. We show that mutant androgen receptor (AR), the protein responsible for X-linked spinobulbar muscular atrophy, forms insoluble aggregates and is toxic to cultured cells. Mutant AR was also found to form aggresomes in a process distinct from aggregation. Molecular and pharmacological interventions were used to disrupt aggresome formation, revealing their cytoprotective function. Aggresome-forming proteins were found to have an accelerated rate of turnover, and this turnover was slowed by inhibition of aggresome formation. Finally, we show that aggresome-forming proteins become membrane-bound and associate with lysosomal structures. Together, these findings suggest that aggresomes are cytoprotective, serving as cytoplasmic recruitment centers to facilitate degradation of toxic proteins.
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118
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Puls I, Jonnakuty C, LaMonte BH, Holzbaur ELF, Tokito M, Mann E, Floeter MK, Bidus K, Drayna D, Oh SJ, Brown RH, Ludlow CL, Fischbeck KH. Mutant dynactin in motor neuron disease. Nat Genet 2003; 33:455-6. [PMID: 12627231 DOI: 10.1038/ng1123] [Citation(s) in RCA: 686] [Impact Index Per Article: 32.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2002] [Accepted: 02/10/2003] [Indexed: 11/09/2022]
Abstract
Impaired axonal transport in motor neurons has been proposed as a mechanism for neuronal degeneration in motor neuron disease. Here we show linkage of a lower motor neuron disease to a region of 4 Mb at chromosome 2p13. Mutation analysis of a gene in this interval that encodes the largest subunit of the axonal transport protein dynactin showed a single base-pair change resulting in an amino-acid substitution that is predicted to distort the folding of dynactin's microtubule-binding domain. Binding assays show decreased binding of the mutant protein to microtubules. Our results show that dysfunction of dynactin-mediated transport can lead to human motor neuron disease.
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119
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120
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Paulson HL, Garbern JY, Hoban TF, Krajewski KM, Lewis RA, Fischbeck KH, Grossman RI, Lenkinski R, Kamholz JA, Shy ME. Transient central nervous system white matter abnormality in X-linked Charcot-Marie-Tooth disease. Ann Neurol 2002; 52:429-34. [PMID: 12325071 DOI: 10.1002/ana.10305] [Citation(s) in RCA: 115] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
X-linked Charcot-Marie-Tooth disease (CMTX) is a hereditary demyelinating neuropathy caused by mutations in the connexin 32 (Cx32) gene. Cx32 is widely expressed in brain and peripheral nerve, yet clinical manifestations of CMTX mainly arise from peripheral neuropathy. We have evaluated two male patients with CMTX who on separate occasions developed transient ataxia, dysarthria, and weakness within 3 days of returning from ski trips at altitudes above 8,000 feet. Magnetic resonance imaging studies in both patients showed nonenhancing, confluent, and symmetrical white matter abnormalities that were more pronounced posteriorly and that resolved over several months. Magnetic transfer images in one patient demonstrated increased magnetization transfer ratios distinct from that seen in demyelination or edema. Both patients returned to their normal baseline within 2 to 3 weeks. These cases suggest that CMTX patients are at risk for developing an acute, transient, neurological syndrome when they travel to places at high altitudes and return to sea level. Cx32 mutations may cause central nervous system dysfunction by reducing the number of functioning gap junctions between oligodendrocytes and astrocytes, making both cells more susceptible to abnormalities of intercellular exchange of ions and small molecules in situations of metabolic stress.
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121
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Lieberman AP, Harmison G, Strand AD, Olson JM, Fischbeck KH. Altered transcriptional regulation in cells expressing the expanded polyglutamine androgen receptor. Hum Mol Genet 2002; 11:1967-76. [PMID: 12165558 DOI: 10.1093/hmg/11.17.1967] [Citation(s) in RCA: 108] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Kennedy's disease is a degenerative disease of motor neurons in which the causative mutation is expansion of a CAG/polyglutamine tract near the 5' end of the androgen receptor gene. The mutant protein misfolds, aggregates, and interacts abnormally with other proteins, leading to a novel, toxic gain of function and an alteration of normal function. We used a cell culture model to explore the mechanisms underlying the alterations in androgen receptor function conferred by the mutation. Here we show that cells expressing the wild-type androgen receptor with 24 CAG repeats respond to ligand by showing trophic effects including prolonged survival in low serum, whereas cells expressing the mutant receptor with 65 CAG repeats do not show a robust trophic response. This partial loss of function correlates with decreased levels of the mutant protein due to its preferential degradation by the ubiquitin-proteasome pathway. Expression analysis using oligonucleotide arrays confirms that the mutant receptor has undergone a partial loss of function, and fails to regulate a subset of genes whose expression is normally affected by ligand activation of the wild-type receptor. The mutant receptor has also undergone several functionally important post-translational modifications in the absence of ligand that the wild-type receptor undergoes in the presence of ligand, including acetylation and phosphorylation. These modifications correlate with a ligand-independent gain of function exhibited by the mutant receptor in expression analysis. Our findings suggest that polyglutamine expansion alters androgen receptor function by promoting its degradation and by modifying its activity as a transcription factor.
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Abstract
A broad range of neurodegenerative disorders is characterized by neuronal damage that may be caused by toxic, aggregation-prone proteins. As genes are identified for these disorders and cell culture and animal models are developed, it has become clear that a major effect of mutations in these genes is the abnormal processing and accumulation of misfolded protein in neuronal inclusions and plaques. Increased understanding of the cellular mechanisms for disposal of abnormal proteins and of the effects of toxic protein accumulation on neuronal survival may allow the development of rational, effective treatment for these disorders.
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Taylor JP, Fischbeck KH. Altered acetylation in polyglutamine disease: an opportunity for therapeutic intervention? Trends Mol Med 2002; 8:195-7. [PMID: 12067622 DOI: 10.1016/s1471-4914(02)02332-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Recent investigations into polyglutamine diseases suggest that aberrant transcriptional regulation might be central to the molecular pathogenesis, perhaps because of inappropriate interaction between mutant proteins and important nuclear factors. Several groups have reported an interaction of mutant polyglutamine with histone acetylases, implicating defective acetylation as a cause of abnormal transcription. An important recent observation is that reversal of the acetylation defect with histone deacetylase inhibitors ameliorates polyglutamine toxicity in yeast, mammalian cell culture, and animal models. These encouraging findings suggest that a novel strategy--pharmacological restoration of histone acetylation-- could prove effective in treating this group of devastating illnesses.
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Hara H, Nolan PM, Scott MO, Bucan M, Wakayama Y, Fischbeck KH. Running endurance abnormality in mdx mice. Muscle Nerve 2002; 25:207-11. [PMID: 11870688 DOI: 10.1002/mus.10023] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The mdx mouse lacks dystrophin and has histological features of Duchenne muscular dystrophy but little weakness in the first year of life. We report here an early deficit in voluntary wheel running, as assayed with a computerized wheel. All mdx mice showed an intermittent running pattern, in contrast to the continuous running seen in controls. The average continuous running time differed significantly between mdx and control mice at all ages tested (5-21 weeks). This assay is noninvasive, has the advantage of unbiased automatic data collection, and should be useful for quantifying the mdx deficit in therapeutic studies.
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125
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McCampbell A, Taye AA, Whitty L, Penney E, Steffan JS, Fischbeck KH. Histone deacetylase inhibitors reduce polyglutamine toxicity. Proc Natl Acad Sci U S A 2001; 98:15179-84. [PMID: 11742087 PMCID: PMC65003 DOI: 10.1073/pnas.261400698] [Citation(s) in RCA: 189] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Polyglutamine diseases include at least nine neurodegenerative disorders, each caused by a CAG repeat expansion in a different gene. Accumulation of mutant polyglutamine-containing proteins occurs in patients, and evidence from cell culture and animal experiments suggests the nucleus as a site of pathogenesis. To understand the consequences of nuclear accumulation, we created a cell culture system with nuclear-targeted polyglutamine. In our system, cell death can be mitigated by overexpression of full-length cAMP response element binding protein (CREB)-binding protein (CBP) or its amino-terminal portion alone. CBP is one of several histone acetyltransferases sequestered by polyglutamine inclusions. We found histone acetylation to be reduced in cells expressing mutant polyglutamine. Reversal of this hypoacetylation, which can be achieved either by overexpression of CBP or its amino terminus or by treatment with deacetylase inhibitors, reduced cell loss. These findings suggest that nuclear accumulation of polyglutamine can lead to altered protein acetylation in neurons and indicate a novel therapeutic strategy for polyglutamine disease.
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