Protein composition of the intranuclear inclusions of FXTAS

• Published in: Brain (London, England : 1878) Vol. 129; no. 1; pp. 256 - 271
• Main Authors: Iwahashi, C. K., Yasui, D. H., An, H.-J., Greco, C. M., Tassone, F., Nannen, K., Babineau, B., Lebrilla, C. B., Hagerman, R. J., Hagerman, P. J.
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press 01-01-2006; Oxford Publishing Limited (England)
• Subjects: Aged; Ataxia - genetics; Ataxia - metabolism; Base Sequence; Biological and medical sciences; Blotting, Western - methods; Brain - ultrastructure; Brain Chemistry; Chromatography, Liquid; Crystallins - analysis; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; dementia; Diseases of striated muscles. Neuromuscular diseases; Electrophoresis, Gel, Two-Dimensional; Flow Cytometry; Fluorescent Antibody Technique; FMR1 = fragile X mental retardation 1 gene; FMRP = FMR1 protein; Fragile X Syndrome - metabolism; FT-ICR = Fourier transform ion cyclotron resonance; FXTAS = fragile X-associated tremor/ataxia syndrome; Heterogeneous-Nuclear Ribonucleoprotein Group A-B - analysis; Heterogeneous-Nuclear Ribonucleoprotein Group A-B - genetics; hnRNP A2 = heterogeneous nuclear ribonucleoprotein A2; HSP = heat shock protein; Humans; Intranuclear Inclusion Bodies - chemistry; lamin; Laminin - analysis; LC = liquid chromatography; Male; MBNL1 = muscle blind-like protein 1; MBP = myelin basic protein; Medical sciences; Molecular Sequence Data; MS = mass spectrometry; Myelin Basic Protein - analysis; Myelin Basic Protein - genetics; neurodegeneration; Neurology; Nuclear Proteins - analysis; Nuclear Proteins - genetics; Parkinson; Peptide Mapping; RNA toxicity; RNA-Binding Proteins - analysis; Spectrum Analysis; Tremor - genetics; Tremor - metabolism; trinucleotide repeat; Ubiquitin - analysis; XCorr = minimum cross-correlation value; Nervous system diseases; RNA toxicity; lamin; Inclusion; Toxicity; Trinucleotide; neurodegeneration; trinucleotide repeat; Protein; Parkinson; Dementia
• ISSN: 0006-8950; 1460-2156
• DOI: 10.1093/brain/awh650

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder caused by premutation expansions (55–200 CGG repeats) in the fragile X mental retardation 1 (FMR1) gene. The pathologic hallmark of FXTAS is the ubiquitin-positive intranuclear inclusion found in neurons and astrocytes in broad distribution throughout the brain. The pathogenesis of FXTAS is likely to involve an RNA toxic gain-of-function mechanism, and the FMR1 mRNA has recently been identified within the inclusions. However, little is known about the proteins that mediate the abnormal cellular response to the expanded CGG repeat allele. As one approach to identify the protein mediators, we have endeavoured to define the protein complement of the inclusion itself. Fluorescence-activated flow-based methods have been developed for the efficient purification of inclusions from the post-mortem brain tissue of FXTAS patients. Mass spectrometric analysis of the entire protein complement of the isolated inclusions, combined with immunohistochemical analysis of both isolated nuclei and tissue sections, has been used to identify inclusion-associated proteins. More than 20 inclusion-associated proteins have been identified on the basis of combined immunohistochemical and mass spectrometric analysis, including a number of neurofilaments and lamin A/C. There is no dominant protein species in the inclusions, and ubiquitinated proteins represent only a minor component; thus, inclusion formation is not likely to reflect a breakdown in proteasomal degradation of nuclear proteins. The list of proteins includes at least two RNA binding proteins, heterogeneous nuclear ribonucleoprotein A2 and muscle blind-like protein 1, which are possible mediators of the RNA gain-of-function in FXTAS.