Neuroanatomic Profile of Polyglutamine Immunoreactivity inHuntington Disease Brains

Division of Neuropathology, Department of Pathology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9073, USA.
Journal of Neuropathology and Experimental Neurology (Impact Factor: 3.8). 04/2009; 68(3):250-61. DOI: 10.1097/NEN.0b013e318198d320
Source: PubMed


A pathologic hallmark of Huntington disease (HD) is the presence of intraneuronal aggregates of polyglutamine-containing huntingtin protein fragments. Monoclonal antibody 1C2 is a commercial antibody to normal human TATA-binding protein that detects long stretches of glutamine residues. Using 1C2 as a surrogate marker formutant huntingtin protein, we immunostained 19 HD cases, 10 normal controls, and 10 cases of frontotemporal degeneration with ubiquitinated inclusions as diseased controls. In the HD cases, there was consistent 1C2 immunoreactivity in the neocortex, striatum, hippocampus, lateral geniculate body, basis pontis, medullary reticular formation, and cerebellar dentate nucleus. The normal and diseased controls demonstrated 1C2 immunoreactivity only in the substantia nigra, locus coeruleus, and pituitary gland. Staining of 5 HD cases and 5 normal controls revealed a less consistent and less diagnostically useful morphologic immunoreactivity profile. These results indicate that widespread 1C2 immunoreactivity is present in diverse central nervous system areas in HD, and that in the appropriate setting, 1C2 staining can be a useful tool in the postmortem diagnosis of HD when neuromelanin-containing neuronal populations are avoided.

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    • "Disease invariably occurs when the CAG repeat in the first exon, which codes for glutamine (Q), expands to ≥39 consecutive CAG repeats. Patients carrying the polyQ expansion exhibit general brain atrophy, prominent cortical- and striatal-neuron loss, and harbor inclusion bodies composed of mutant htt throughout their central nervous system [2]–[4]. These inclusion bodies are found in the nucleus and cytoplasm, and react to antibodies recognizing N-terminal epitopes of htt [5], [6]. "
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    ABSTRACT: N-terminal fragments of mutant huntingtin (htt) that terminate between residues 90-115, termed cleavage product A or 1 (cp-A/1), form intracellular and intranuclear inclusion bodies in the brains of patients with Huntington's disease (HD). These fragments appear to be proteolytic products of the full-length protein. Here, we use an HEK293 cell culture model to investigate huntingtin proteolytic processing; previous studies of these cells have demonstrated cleavage of htt to cp-A/1 like htt fragments. Recombinant N-terminal htt fragments, terminating at residue 171 (also referred to as cp-B/2 like), were efficiently cleaved to produce cp-A/1 whereas fragments representing endogenous caspase, calpain, and metalloproteinase cleavage products, terminating between residues 400-600, were inefficiently cleaved. Using cysteine-labeling techniques and antibody binding mapping, we localized the C-terminus of the cp-A/1 fragments produced by HEK293 cells to sequences minimally limited by cysteine 105 and an antibody epitope composed of residues 115-124. A combination of genetic and pharmacologic approaches to inhibit potential proteases, including γ-secretase and calpain, proved ineffective in preventing production of cp-A/1. Our findings indicate that HEK293 cells express a protease that is capable of efficiently cleaving cp-B/2 like fragments of htt with normal or expanded glutamine repeats. For reasons that remain unclear, this protease cleaves longer htt fragments, with normal or expanded glutamine expansions, much less efficiently. The protease in HEK293 cells that is capable of generating a cp-A/1 like htt fragment may be a novel protease with a high preference for a cp-B/2-like htt fragment as substrate.
    Full-text · Article · Dec 2012 · PLoS ONE
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    • "Despite the debate about their role, there is no doubt that inclusions are a clear histopathological marker of the disease [26]. Inclusions are not found in neurologically normal subjects, but are found throughout the HD brain, particularly in striatum (STR) and cortex (CTX), the brain regions most affected in HD [3], [4], [16], [27], [28]. NIIs are defined as abnormal ubiquitinated aggregates of proteins, predominantly huntingtin and/or fragments of huntingtin and ubiquitin, although a number of other proteins have been found associated with inclusions in transgenic mouse and cell models [29], [30] and human brains [31]. "
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    ABSTRACT: Abnormal insoluble ubiqitinated protein aggregates are found in the brains of Huntington's disease (HD) patients and in mice transgenic for the HTT mutation. Here, we describe the earliest stages of visible NII formation in brains of R6/2 mice killed between 2 and 6 weeks of age. We found that huntingtin-positive aggregates formed rapidly (within 24-48 hours) in a spatiotemporal manner similar to that we described previously for ubiquitinated inclusions. However, in most neurons, aggregates are not ubiquitinated when they first form. It has always been assumed that mutant huntingtin is recognised as 'foreign' and consequently ubiquitinated and targeted for degradation by the ubiquitin-proteasome system pathway. Our data, however, suggest that aggregation and ubiquitination are separate processes, and that mutant huntingtin fragment is not recognized as 'abnormal' by the ubiquitin-proteasome system before aggregation. Rather, mutant Htt appears to aggregate before it is ubiquitinated, and then either aggregated huntingtin is ubiquitinated or ubiquitinated proteins are recruited into aggregates. Our findings have significant implications for the role of the ubiquitin-proteasome system in the formation of aggregates, as they suggest that this system is not involved until after the first aggregates form.
    Full-text · Article · Jul 2012 · PLoS ONE
    • "The inclusions are present prior to symptomatic development of the disease in the human brain and found throughout the cortex, but less frequently in the striatum [92] [93] [94] [95] [96]. Within the cortex, the cells tend to display combinations of nuclear and cytoplasmic as well as neuropil aggregations [95] with the highest levels of intranuclear inclusions found in juvenile cases which tend to have relatively very high CAG repeat Fig. 2. Photomicrographs illustrating the pyramidal neurons in layer III in the primary motor cortex (A–C) and anterior cingulate cortex (D–F) of normal (A, D) and Huntington's disease cases (B, C; E, F). The images illustrate cases with " mainly motor " (B, E), and " mainly mood " (C, F) symptom profiles. "
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    ABSTRACT: We review recent investigations regarding the relationship between selective neurodegeneration in the human brain and the variability in symptom profiles in Huntington's disease. Huntington's disease is a genetic neurodegenerative disorder caused by an expanded CAG repeat in exon 1 of the Huntingtin gene on chromosome 4, encoding a protein called huntingtin. The huntingtin protein is expressed ubiquitously in somatic tissue, however, the major pathology affects the brain with profound degeneration in the striatum and the cerebral cortex. Despite the disease being caused by a single gene, there is a major variability in the neuropathology, as well as major heterogeneity in the symptom profiles observed in Huntington's disease patients. The symptoms may vary throughout the disease course and present as varying degrees of movement disorder, cognitive decline, and mood and behavioral changes. To determine whether there is an anatomical basis underlying symptom variation, recent studies on the post-mortem human brain have shown a relationship between the variable degeneration in the forebrain and the variable symptom profile. In this review, we will summarize the progress relating cell loss in the striatum and cerebral cortex to symptom profile in Huntington's disease.
    No preview · Article · Jan 2012 · Journal of Huntington's disease
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