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Rutherford, N. J. et al. Novel mutations in TARDBP (TDP-43) in patients with familial amyotrophic lateral sclerosis. PLoS Genet. 4, e1000193

Department of Neuroscience, Mayo Clinic, Jacksonville, Florida, United States of America.
PLoS Genetics (Impact Factor: 7.53). 10/2008; 4(9):e1000193. DOI: 10.1371/journal.pgen.1000193
Source: PubMed

ABSTRACT

The TAR DNA-binding protein 43 (TDP-43) has been identified as the major disease protein in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with ubiquitin inclusions (FTLD-U), defining a novel class of neurodegenerative conditions: the TDP-43 proteinopathies. The first pathogenic mutations in the gene encoding TDP-43 (TARDBP) were recently reported in familial and sporadic ALS patients, supporting a direct role for TDP-43 in neurodegeneration. In this study, we report the identification and functional analyses of two novel and one known mutation in TARDBP that we identified as a result of extensive mutation analyses in a cohort of 296 patients with variable neurodegenerative diseases associated with TDP-43 histopathology. Three different heterozygous missense mutations in exon 6 of TARDBP (p.M337V, p.N345K, and p.I383V) were identified in the analysis of 92 familial ALS patients (3.3%), while no mutations were detected in 24 patients with sporadic ALS or 180 patients with other TDP-43-positive neurodegenerative diseases. The presence of p.M337V, p.N345K, and p.I383V was excluded in 825 controls and 652 additional sporadic ALS patients. All three mutations affect highly conserved amino acid residues in the C-terminal part of TDP-43 known to be involved in protein-protein interactions. Biochemical analysis of TDP-43 in ALS patient cell lines revealed a substantial increase in caspase cleaved fragments, including the approximately 25 kDa fragment, compared to control cell lines. Our findings support TARDBP mutations as a cause of ALS. Based on the specific C-terminal location of the mutations and the accumulation of a smaller C-terminal fragment, we speculate that TARDBP mutations may cause a toxic gain of function through novel protein interactions or intracellular accumulation of TDP-43 fragments leading to apoptosis.

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    • "A hexanucleotide repeat expansion in the noncoding region of the gene C9ORF72 and mutations in the progranulin gene (GRN) are the most common known genetic causes of FTLD- TDP. Although TARDBP mutations account for less than 5% of familial ALS (FALS) and some sporadic ALS cases910111213141516, previous studies failed to find evidence for a significant genetic role of TARDBP mutations in FTLD17181920. Most of the few FTD cases in which TARDBP mutations have been identified manifest a heterogeneous phenotype, but always with a significant MND component: MND-FTD [21] , MND-FTD with extrapyramidal symptoms222324 , MND with supranuclear palsy [22] and FTD-MND [25]. "
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    ABSTRACT: INTRODUCTION: Although TDP-43 is the main constituent of the ubiquitinated cytoplasmic inclusions in the most common forms of frontotemporal lobar degeneration, TARDBP mutations are not a common cause of familial frontotemporal dementia, especially in the absence of motor neuron disease. RESULTS: We describe a pedigree presenting with a complex autosomal dominant disease, with a heterogeneous clinical phenotype, comprising unspecified dementia, parkinsonism, frontotemporal dementia and motor neuron disease. Genetic analyses identified a novel P112H TARDBP double variation located in exon 3 coding for the first RNA recognition motif of the protein (RRM1). This double mutation is probably pathogenic based on neuropathological findings, in silico prediction analysis and exome sequencing. The two autopsied siblings described here presented with frontotemporal dementia involving multiple cognitive domains and behavior but lacking symptoms of motor neuron disease throughout the disease course. The siblings presented with strikingly similar, although atypical, neuropathological features, including an unclassifiable TDP-43 inclusion pattern, a high burden of tau-negative β-amyloid neuritic plaques with an AD-like biochemical profile, and an unclassifiable 4-repeat tauopathy. The co-occurrence of multiple protein inclusions points to a pathogenic mechanism that facilitates misfolded protein interaction and aggregation or a loss of TDP-43 function that somehow impairs protein clearance. CONCLUSIONS: TARDBP mutation screening should be considered in familial frontotemporal dementia cases, even without signs or symptoms of motor neuron disease, especially when other more frequent causes of genetic frontotemporal dementia (i.e. GRN, C9ORF72, MAPT) have been excluded and when family history is complex and includes parkinsonism, motor neuron disease and frontotemporal dementia. Further investigations in this family may provide insight into the physiological functions of TARDBP.
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    • "09 ; Wang et al . , 2010 ) . In addition , either UPS inhibition or overexpression of the truncated TDP - 43 fragments could result in increased level of active caspase 3 ( Suzuki et al . , 2011 ; Zhang et al . , 2009 ) , thus leading to increased proteolytic cleavage of the full - length TDP - 43 to generate more TDP - 35 and TDP - 25 fragments ( Rutherford et al . , 2008 ) . In order to exclude the above mentioned side - effects due to overexpression of the truncated TDP - 25 fragment or MG132 induction , we have carried out cyclohexamide - chase experiments and found that degradation of the endogenous full - length TDP - 43 becomes slower in the presence of the caspase 3 inhibitor Z - VAD ( Fig . 3A ) "
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    ABSTRACT: TDP-43 is a pathological signature protein of neurodegenerative diseases with TDP-43 proteinopathies including FTLD-TDP and ALS-TDP. These TDP-43 proteinopathies are characterized with cytoplasmic insoluble TDP-43(+) aggregates in the diseased cells, the formation of which requires the seeding of TDP-25 fragment generated by caspase cleavage of TDP-43. We have investigated the metabolism and mis-metabolism of TDP-43 in cultured cells and found that the endogenous and exogenously over-expressed TDP-43 are degraded not only by ubiquitin proteasome system (UPS) and macroautophagy (MA), but also by the chaperone-mediated autophagy (CMA) mediated through interaction between Hsc70 and ubiquitinated TDP-43. Furthermore, proteolytic cleavage of TDP-43 by caspase(s) is a necessary intermediate step for degradation of a majority of the TDP-43 protein, with the TDP-25/TDP-35 fragments being the main substrates. Finally, we have determined the threshold level of the TDP-25 fragment that is necessary for formation of the cytosolic TDP-43(+) aggregates in cells containing the full-length TDP-43 at an elevated level close to that found in patients with TDP-43 proteinopathies. A comprehensive model of the metabolism and mis-metabolism of TDP-43 in relation to these findings is presented.
    Full-text · Article · May 2014 · Journal of Cell Science
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    • "Mutations in TDP-43 have been identified in familial and sporadic cases of ALS and FTLD-TDP, mainly in the C-terminal glycine-rich region, including the M337V mutation caused by an alteration of an adenine (A) to guanine (G) at position 1009 of TARDBP cDNA [3], [11], [12], [13], [14], [15], [16]. In a recent study using isogenic lines, mutant forms of TDP-43 were reported to be more stable than wild-type which was degraded two to four times faster than mutant TDP-43 [17]. "
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    ABSTRACT: TDP-43 is found in cytoplasmic inclusions in 95% of amyotrophic lateral sclerosis (ALS) and 60% of frontotemporal lobar degeneration (FTLD). Approximately 4% of familial ALS is caused by mutations in TDP-43. The majority of these mutations are found in the glycine-rich domain, including the variant M337V, which is one of the most common mutations in TDP-43. In order to investigate the use of allele-specific RNA interference (RNAi) as a potential therapeutic tool, we designed and screened a set of siRNAs that specifically target TDP-43M337V mutation. Two siRNA specifically silenced the M337V mutation in HEK293T cells transfected with GFP-TDP-43wt or GFP-TDP-43M337V or TDP-43 C-terminal fragments counterparts. C-terminal TDP-43 transfected cells show an increase of cytosolic inclusions, which are decreased after allele-specific siRNA in M337V cells. We then investigated the effects of one of these allele-specific siRNAs in induced pluripotent stem cells (iPSCs) derived from an ALS patient carrying the M337V mutation. These lines showed a two-fold increase in cytosolic TDP-43 compared to the control. Following transfection with the allele-specific siRNA, cytosolic TDP-43 was reduced by 30% compared to cells transfected with a scrambled siRNA. We conclude that RNA interference can be used to selectively target the TDP-43M337V allele in mammalian and patient cells, thus demonstrating the potential for using RNA interference as a therapeutic tool for ALS.
    Full-text · Article · Mar 2014 · PLoS ONE
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