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Acta Neuropathol. 2015 Dec;130(6):845-61. doi: 10.1007/s00401-015-1476-2. Epub 2015 Sep 15.

Quantitative analysis and clinico-pathological correlations of different dipeptide repeat protein pathologies in C9ORF72 mutation carriers.

Author information

1
Department of Pathology, University of British Columbia and Vancouver General Hospital, Vancouver, Canada.
2
German Center for Neurodegenerative Diseases (DZNE), Otfried-Müllerstr. 23, 72076, Tübingen, Germany.
3
Institute of Virology, Saarland University Medical School, Homburg, Germany.
4
Department of Neuroscience, Mayo Clinic Florida, Jacksonville, USA.
5
Department of Medicine (Neurology), Brain Research Centre, University of British Columbia, Vancouver, Canada.
6
German Center for Neurodegenerative Diseases (DZNE), Munich, Germany.
7
Munich Cluster of Systems Neurology (SyNergy), Munich, Germany.
8
Institute for Metabolic Biochemistry, Ludwig-Maximilians University Munich, Munich, Germany.
9
Institute of Molecular Immunology, Helmholtz Zentrum München, Munich, Germany.
10
German Center for Neurodegenerative Diseases (DZNE), Rostock, Germany.
11
Department of Neurology, University of Rostock, Rostock, Germany.
12
Department of Neuropathology, Academic Medical Centre, University of Amsterdam, Amsterdam, The Netherlands.
13
German Center for Neurodegenerative Diseases (DZNE), Otfried-Müllerstr. 23, 72076, Tübingen, Germany. manuela.neumann@med.uni-tuebingen.de.
14
Department of Neuropathology, University of Tübingen, Tübingen, Germany. manuela.neumann@med.uni-tuebingen.de.

Abstract

Hexanucleotide repeat expansion in C9ORF72 is the most common genetic cause of frontotemporal dementia and motor neuron disease. One consequence of the mutation is the formation of different potentially toxic polypeptides composed of dipeptide repeats (DPR) (poly-GA, -GP, -GR, -PA, -PR) generated by repeat-associated non-ATG (RAN) translation. While previous studies focusing on poly-GA pathology have failed to detect any clinico-pathological correlations in C9ORF72 mutation cases, recent data from animal and cell culture models suggested that it may be only specific DPR species that are toxic and only when accumulated in certain intracellular compartments. Therefore, we performed a systematic clinico-pathological correlative analysis with counting of actual numbers of distinct types of inclusion (neuronal cytoplasmic and intranuclear inclusions, dystrophic neurites) for each DPR protein in relevant brain regions (premotor cortex, lower motor neurons) in a cohort of 35 C9ORF72 mutation cases covering the clinical spectrum from those with pure MND, mixed FTD/MND and pure FTD. While each DPR protein pathology had a similar pattern of anatomical distribution, the total amount of inclusions for each DPR protein varied remarkably (poly-GA > GP > GR > PR/PA), indicating that RAN translation seems to be more effective from sense than from antisense transcripts. Importantly, with the exception of moderate associations for the amount of poly-GA-positive dystrophic neurites with degeneration in the frontal cortex and total burden of poly-GA pathology with disease onset, no relationship was identified for any other DPR protein pathology with degeneration or phenotype. Biochemical analysis revealed a close correlation between insoluble DPR protein species and numbers of visible inclusions, while we did not find any evidence for the presence of soluble DPR protein species. Thus, overall our findings strongly argue against a role of DPR protein aggregation as major and exclusive pathomechanism in C9ORF72 pathogenesis. However, this does not exclude that DPR protein formation might be essential in C9ORF72 pathogenesis in interplay with other consequences associated with the C9ORF72 repeat expansion.

PMID:
26374446
DOI:
10.1007/s00401-015-1476-2
[Indexed for MEDLINE]
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