Intranuclear inclusions in oculopharyngeal muscular dystrophy contain poly(A) binding protein 2.

Intranuclear inclusions are one of the ultrastructural hallmarks of oculopharyngeal muscular dystrophy (OPMD), a disorder caused by small polyalanine (GCG) expansions in the gene that codes for a ubiquitous nuclear protein called poly(A) binding protein 2 (PABP2). We studied OPMD skeletal muscle and found that 1.0 to 10.0% of myocyte nuclei contained discreet PABP2 immunoreactive intranuclear inclusions, providing the first direct evidence of the relation between the proposed gene for OPMD and the pathology of OPMD.

Intranuclear inclusions and neuritic aggregates in transgenic mice expressing a mutant N-terminal fragment of huntingtin.

Huntington's disease (HD) is an inherited, neurodegenerative disorder caused by the expansion of a glutamine repeat in the N-terminus of the huntingtin protein. To gain insight into the pathogenesis of HD, we generated transgenic mice that express a cDNA encoding an N-terminal fragment (171 amino acids) of huntingtin with 82, 44 or 18 glutamines. Mice expressing relatively low steady-state levels of N171 huntingtin with 82 glutamine repeats (N171-82Q) develop behavioral abnormalities, including loss of coordination, tremors, hypokinesis and abnormal gait, before dying prematurely. In mice exhibiting these abnormalities, diffuse nuclear labeling, intranuclear inclusions and neuritic aggregates, all immunoreactive with an antibody to the N-terminus (amino acids 1-17) of huntingtin (AP194), were found in multiple populations of neurons. None of these behavioral or pathological phenotypes were seen in mice expressing N171-18Q. These findings are consistent with the idea that N-terminal fragments of huntingtin with a repeat expansion are toxic to neurons, and that N-terminal fragments are prone to form both intranuclear inclusions and neuritic aggregates.

Intranuclear neuronal inclusions in Huntington's disease and dentatorubral and pallidoluysian atrophy: correlation between the density of inclusions and IT15 CAG triplet repeat length.

Huntington's disease (HD) is caused by CAG triplet repeat expansion in IT15 which leads to polyglutamine stretches in the HD protein product, huntingtin. The pathological hallmark of HD is the degeneration of subsets of neurons, primarily those in the striatum and neocortex. Specific morphological markers of affected cells have not been identified in patients with HD, although a unique itranuclear inclusion was recently reported in neurons of transgenic animals expressing a construct encoding the N-terminal part (including the glutamine repeat) of huntingtin (Davies et al., 1997). In order to understand the importance of this finding, we sought for comparable nuclear abnormalities in autopsy material from patients with HD. In all 20 HD cases examined, anti-ubiquitin and N-terminal huntingtin antibodies identified itranuclear inclusions in neurons and the frequency of these lesions correlated with the length of the CAG repeat in IT15. In addition, examination of material from the related HD-like triplet repeat disorder, dentatorubral and pallidoluysian atrophy, also revealed intranuclear neuronal inclusions. These findings suggest that intranuclear inclusions containing protein aggregates may be common feature of the pathogenesis of glutamine repeat neurodegenerative disorders.

Widespread expression of Huntington's disease gene (IT15) protein product.

Huntington's Disease (HD) is caused by expansion of a CAG repeat within a putative open reading frame of a recently identified gene, IT15. We have examined the expression of the gene's protein product using antibodies developed against the N-terminus and an internal epitope. Both antisera recognize a 350 kDa protein, the predicted size, indicating that the CAG repeat is translated into polyglutamine. The HD protein product is widely expressed, most highly in neurons in the brain. There is no enrichment in the striatum, the site of greatest pathology in HD. Within neurons, the protein is diminished in nuclei and mitochondria and is present in the soluble cytoplasmic compartment, as well as loosely associated with membranes or cytoskeleton, in cell bodies, dendrites, and axons. It is concentrated in nerve terminals, including terminals within the caudate and putamen. Thus, the normal HD gene product may be involved in common intracellular functions, and possibly in regulation of nerve terminal function. The product of the expanded allele is expressed, consistent with a gain of function mechanism for HD at the protein level.

Guinea pig striatum as a model of human dopamine deamination: the role of monoamine oxidase isozyme ratio, localization, and affinity for substrate in synaptic dopamine metabolism.

The kinetic properties of type A and type B monoamine oxidase (MAO) were examined in guinea pig striatum, rat striatum, and autopsied human caudate nucleus using 3,4-dihydroxyphenylethylamine (dopamine, DA) as the substrate. MAO isozyme ratio in guinea pig striatum (28% type A/72% type B) was similar to that in human caudate nucleus (25% type A/75% type B) but different from that in rat striatum (76% type A/24% type B). Additional similarities between guinea pig striatum and human caudate nucleus were demonstrated for the affinity constants (Km) of each MAO) isozyme toward DA. Endogenous concentrations of DA, 3-methoxytyramine, 3,4-dihydroxyphenylacetic acid, and homovanillic acid were also measured in guinea pig and rat striatum following selective type A (clorgyline-treated) and type B (deprenyl-treated) MAO inhibition. In guinea pig, DA metabolism was equally but only partially affected by clorgyline or deprenyl alone. Combined treatment with clorgyline and deprenyl was required for maximal alterations in DA metabolism. By contrast, DA metabolism in rat striatum was extensively altered by clorgyline but unaffected by deprenyl alone. Finally, the deamination of DA in synaptosomes from guinea pig striatum was examined following selective MAO isozyme inhibition. Neither clorgyline nor deprenyl alone reduced synaptosomal DA deamination. However, clorgyline and deprenyl together reduced DA deamination by 94%. These results suggest that the isozyme localization and/or isozyme affinity for DA, rather than the absolute isozyme content, determines the relative importance of type A and type B MAO in synaptic DA deamination. Moreover, based on the enzyme kinetic properties of each MAO isozyme, guinea pig striatum may serve as a suitable model of human DA deamination.