Jean-Paul Vonsattel

Neuropathological classification of Huntington's disease.

In postmortem brain specimens from 163 clinically diagnosed cases of Huntingtons disease (HD) the striatum exhibited marked variation in the severity of neuropathological involvement. A system for grading this severity was established by macroscopic and microscopic criteria, resulting in five grades (0–4) designated in ascending order of severity. The grade correlates closely with the extent of clinical disability as assessed by a rating scale. In five cases of clinically diagnosed HD there were no discernible neuropathological abnormalities (grade 0), suggesting that the anatomical changes lag behind the development of clinical abnormalities. In eight cases, neuropathological changes could only be recognized microscopically (grade 1). The earliest changes were seen in the medial paraventricular portions of the caudate nucleus (CN), in the tail of the CN, and in the dorsal part of the putamen. Counts of neurons in the CN reveal that 50% are lost in grade 1 and that 95% are lost in grade 4; astrocytes are greatly increased in grades 2–4. These studies indicate that analyses of the CN in grade 4 would reflect mainly its astrocytic composition with a component of remote neurons projecting to the striatum. Because of the relative preservation of the lateral half of the head of the CN in grades 1–2, these regions would reflect early cellular and biochemical changes in HD.

Minocycline inhibits caspase-1 and caspase-3 expression and delays mortality in a transgenic mouse model of Huntington disease

Huntington disease is an autosomal dominant neurodegenerative disease with no effective treatment. Minocycline is a tetracycline derivative with proven safety. After ischemia, minocycline inhibits caspase-1 and inducible nitric oxide synthetase upregulation, and reduces infarction. As caspase-1 and nitric oxide seem to play a role in Huntington disease, we evaluated the therapeutic efficacy of minocycline in the R6/2 mouse model of Huntington disease. We report that minocycline delays disease progression, inhibits caspase-1 and caspase-3 mRNA upregulation, and decreases inducible nitric oxide synthetase activity. In addition, effective pharmacotherapy in R6/2 mice requires caspase-1 and caspase-3 inhibition. This is the first demonstration of caspase-1 and caspase-3 transcriptional regulation in a Huntington disease model.

Huntingtin is a cytoplasmic protein associated with vesicles in human and rat brain neurons.

The gene defective in Huntingtons disease encodes a protein, huntingtin, with unknown function. Antisera generated against three separate regions of huntingtin identified a single high molecular weight protein of approximately 320 kDa on immunoblots of human neuroblastoma extracts. The same protein species was detected in human and rat cortex synaptosomes and in sucrose density gradients of vesicle-enriched fractions, where huntingtin immunoreactivity overlapped with the distribution of vesicle membrane proteins (SV2, transferrin receptor, and synaptophysin). Immunohistochemistry in human and rat brain revealed widespread cytoplasmic labeling of huntingtin within neurons, particularly cell bodies and dendrites, rather than the more selective pattern of axon terminal labeling characteristic of many vesicle-associated proteins. At the ultrastructural level, immunoreactivity in cortical neurons was detected in the matrix of the cytoplasm and around the membranes of the vesicles. The ubiquitous cytoplasmic distribution of huntingtin in neurons and its association with vesicles suggest that huntingtin may have a role in vesicle trafficking.

Inhibition of caspase-1 slows disease progression in a mouse model of Huntington's disease.

Huntingtons disease is an autosomal-dominant progressive neurodegenerative disorder resulting in specific neuronal loss and dysfunction in the striatum and cortex. The disease is universally fatal, with a mean survival following onset of 15–20 years and, at present, there is no effective treatment. The mutation in patients with Huntingtons disease is an expanded CAG/polyglutamine repeat in huntingtin, a protein of unknown function with a relative molecular mass of 350,000 (M r 350K). The length of the CAG/polyglutamine repeat is inversely correlated with the age of disease onset. The molecular pathways mediating the neuropathology of Huntingtons disease are poorly understood. Transgenic mice expressing exon 1 of the human huntingtin gene with an expanded CAG/polyglutamine repeat develop a progressive syndrome with many of the characteristics of human Huntingtons disease. Here we demonstrate evidence of caspase-1 activation in the brains of mice and humans with the disease. In this transgenic mouse model of Huntingtons disease, expression of a dominant-negative caspase-1 mutant extends survival and delays the appearance of neuronal inclusions, neurotransmitter receptor alterations and onset of symptoms, indicating that caspase-1 is important in the pathogenesis of the disease. In addition, we demonstrate that intracerebroventricular administration of a caspase inhibitor delays disease progression and mortality in the mouse model of Huntingtons disease.

Novel amyloid precursor protein mutation in an Iowa family with dementia and severe cerebral amyloid angiopathy

Several mutations in the amyloid precursor protein (APP) gene have been found to associate with pathologic deposition of the β‐amyloid peptide (Aβ) in neuritic plaques or in the walls of cerebral vessels. We report a mutation at a novel site in APP in a three‐generation Iowa family with autosomal dominant dementia beginning in the sixth or seventh decade of life. The proband and an affected brother had progressive aphasic dementia, leukoencephalopathy, and occipital calcifications. Neuropathological examination of the proband revealed severe cerebral amyloid angiopathy, widespread neurofibrillary tangles, and unusually extensive distribution of Aβ40 in plaques. The affected brothers shared a missense mutation in APP, resulting in substitution of asparagine for aspartic acid at position 694. This site corresponds to residue 23 of Aβ, thus differing from familial Alzheimers disease mutations, which occur outside the Aβ sequence. Restriction enzyme analysis of DNA from 94 unrelated patients with sporadic cerebral amyloid angiopathy‐related hemorrhage found no other instances of this mutation. These results suggest a novel site within Aβ that may promote its deposition and toxicity.

Morphometric Demonstration of Atrophic Changes in the Cerebral Cortex, White Matter, and Neostriatum in Huntington's Disease

We performed morphometric analysis of five standardized coronal brain slices at anterior frontal (AF), caudate-putamen-accumbens (CAP), globus pallidus (GP), lateral geniculate nucleus (LGN), and parieto-occipital fissure (OCP) levels in 30 patients with Huntingtons disease (HD) and 13 controls. Associated with the 30% mean reduction in brain weight in HDpatients (p<0.001) were significantly smaller overall cross-sectional areas of brain at all five levels studied, with striking losses in cerebral cortex (21-29%), white matter (29-34%), caudate (57%), putamen (64%), and thalamus (28%) (all p<0.005). In addition, the ventricular system was dilated up to 2.5 times normal at CAP, GP, and LGN levels, 9.5 times normal at the OCP level, and 13 times normal at the AFlevel. Higher grades of severity of HDhad greater reductions in the cross-sectional area of the caudate, putamen, thalamus, and cerebral cortex (p<0.005-0.001), and larger ventricles (p=0.08) compared to lower (less severe) grades of HD. The findings confirm and quantitate the severe atrophy of the neostriatum, in addition to demonstrating a severe loss of cerebral cortex and subcortical white matter in HD. The global atrophy of cerebral cortex and white matter observed in all degrees of HD may account for the cognitive and neuropsychiatric impairments which often precede the onset of chorea.

Zinc-induced Alzheimer’s Aβ1–40 Aggregation Is Mediated by Conformational Factors

The heterogeneous precipitates of Aβ that accumulate in the brain cortex in Alzheimer’s disease possess varying degrees of resistance to resolubilization. We previously found that Aβ1–40 is rapidly precipitated in vitro by physiological concentrations of zinc, a neurochemical that is highly abundant in brain compartments where Aβ is most likely to precipitate. We now present evidence that the zinc-induced precipitation of Aβ is mediated by a peptide dimer and favored by conditions that promote α-helical and diminish β-sheet conformations. The manner in which the synthetic peptide is solubilized was critical to its behaviorin vitro. Zinc-induced Aβ aggregation was dependent upon the presence of NaCl, was enhanced by α-helical-promoting solvents, but was abolished when the peptide stock solution was stored frozen. The Aβ aggregates induced by zinc were reversible by chelation, but could then be reprecipitated by zinc for several cycles, indicating that the peptide’s conformation is probably preserved in the zinc-mediated assembly. In contrast, Aβ aggregates induced by low pH (5.5) were not resolubilized by returning the pH milieu to 7.4. The zinc-Aβ interaction exhibits features resembling the gelation process of zinc-mediated fibrin assembly, suggesting that, in events such as clot formation or injury, reversible Aβ assembly could be physiologically purposive. Such a mechanism is contemplated in the early evolution of diffuse plaques in Alzheimer’s disease and suggests a possible therapeutic strategy for the resolubilization of some forms of Aβ deposit in the disease.

Strain-Related Differences in Susceptibility to Transient Forebrain Ischemia in SV-129 and C57Black/6 Mice

BACKGROUND AND PURPOSE We explored susceptibility to injury after global ischemia in SV-129 and C57Black/6 mice, two commonly used-background strains in genetically engineered mice. METHODS Mice (n = 84) were subjected to 15, 30, or 75 minutes of bilateral common carotid artery (BCCA) occlusion followed by reperfusion for 72 hours. BCCA occlusion was performed under halothane or chloral hydrate anesthesia, in one experiment, mean arterial blood pressure and regional cerebral blood flow (laser Doppler flowmetry) were matched by controlled exsanguination. Baseline absolute blood flow measurements were obtained in both strains using a tracer, N-isopropyl-[methyl 1,3-14C]-p-iodoamphetamine, indicator fractionation technique (n = 5 per group). Vascular anatomy of the circle of Willis was visualized by intravascular perfusion of carbon black ink (n = 10 per group). Cerebrovascular reactivity was assessed by measuring the diameter of pial vessels (intravital microscopy) to acetylcholine (ACh) superfusion (0.1 to 10 mmol/L) in a closed cranial window preparation (n = 29). RESULTS Resting blood flow values did not differ between groups in striatum, cerebellum, and brain-stem regions. SV-129 mice were less susceptible than C57Black/6 mice to ischemic injury (0.0 +/- 0.0 versus 1.3 +/- 0.3 damage in hippocampal CA1 region after 30 minutes of ischemia in SV-129 and C57Black/6, respectively; P < .01). Cellular damage (grade 1 to 3 injury) comparable to 30-minute BCCA occlusion was achieved only after 75 minutes of ischemia in SV-129 mice (1.1 +/- 0.3). Ischemic damage was also significantly less in SV-129 mice after blood pressure and flow were matched during ischemia in halothane-anesthetized SV-129 mice (0.5 +/- 0.3 versus 1.4 +/- 0.2, P < .05), or after chloral hydrate anesthesia (0.4 +/- 0.2 versus 1.5 +/- 0.4, P < .05). Hypoplastic posterior communicating arteries were found in all 10 C57Black/6 mice and may explain the greater susceptibility of these mice to injury after BCCA occlusion. More robust vasodilation to ACh in C57Black/6 mice could also indicate genetic differences in responses to vasoactive substances. CONCLUSIONS C57Black/6 mice exhibit enhanced susceptibility to global cerebral ischemic injury, an incompletely formed circle of Willis, and augmented pial vessel dilation to ACh compared with SV-129 mice. Our findings suggest that strain differences may confound results when genetically engineered mice generated from more than a single background strain are used.

Gilles de la Tourette's syndrome. A postmortem neuropathological and immunohistochemical study.

Immunocytochemical studies of the human forebrain have shown that enkephalin-like, dynorphin-like and substance-P-like immunoreactivity (respectively ELI, DLI, and SPI) normally present in unique pattern (now termed woolly fibers) in the globus pallidus and substantia nigra, in which their concentration is at its densest. Quantitative determinations moreover indicate that the levels of all 3 peptides are higher in the globus pallidus and substantia nigra than in any other region of the brain. We report here the distribution of immunoreactivity of these 3 peptides in the brain of a patient showing the typical clinical manifestations of Gilles de la Tourettes syndrome (TS); a disease for which no characteristic or consistent neuropathological features have been discerned. In the case described here neuropathological examination by means of the usual histopathological methods showed no abnormalities to which the patients illness could be ascribed. ELI- and SPLI-positive woolly fibers were densely stained and of normal distribution. DLI-staining was, however, considerably less dense throughout the brain than normal. The most striking finding was the total absence of DLI-positive woolly fibers in the dorsal part of the external segment of the globus pallidus; the ventral pallidum showed very faint staining. These observations, which indicate a decrease of dynorphin in striatal fibers projecting to the globus pallidus, are, to our knowledge, the first evidence of a distinct pathological change in the brain in TS.

Clinical and neuropathologic assessment of severity in Huntington's disease

Clinical records were evaluated for 163 Huntingtons disease patients in whom postmortem brain specimens had been graded for degree of neuropathologic involvement in the striatum. Juvenile/adolescent onset (4 to 19 years of age) was associated with very severe neuropathologic involvement produced by an apparent rapid degenerative process. Cases of early (20 to 34 years) and midlife (35 to 49 years) onset had respectively less severe striatal involvement, suggesting a slower degenerative progression. High correlations among the grade of neuropathologic involvement, cell counts of neurons, and a rating of physical disability suggest that each represents a common underlying degenerative process of the disease. The relationship between the age at onset and the extent of neuropathologic involvement suggests that a single mechanism may determine both onset and rate of degenerative disease progression.