Heterogeneity of water-soluble amyloid beta-peptide in Alzheimer's disease and Down's syndrome brains

Water-soluble amyloid beta-peptides (sA beta), ending at residue 42, precede amyloid plaques in Down's syndrome (DS). Here we report that sA beta consists of the full-length A beta(1-42) and peptides truncated and modified by cyclization of the N-terminal glutamates, A beta[3(pE)-42] and A beta[11(pE)-42]. The A beta[3(pE)-42] peptide is the most abundant form of sA beta in Alzheimer's disease (AD) brains. In DS, sA beta[3(pE)-42] concentration increases with age and the peptide becomes a dominant species in the presence of plaques. Both pyroglutamate-modified peptides and the full-length A beta form a stable aggregate that is water soluble. The findings point to a crucial role of the aggregated and modified sA beta in the plaque formation and pathogenesis of AD.

Biopsy diagnosis of Creutzfeldt-Jakob disease by western blot: a case report

Creutzfeldt-Jakob disease is a clinically and pathologically heterogeneous disorder that often requires brain biopsy for definitive diagnosis. We report the case of a 62-year-old man who underwent brain biopsy for progressive neurological deterioration. Histopathologically, there was minimal spongiform change that could not be unequivocally attributed to Creutzfeldt-Jakob disease. A 16 mg portion of gray matter saved frozen was subsequently analyzed by Western blot and showed definitive protease-resistant prion protein. This case illustrates applicability, ease in interpretation, and accuracy of Western blot analysis for protease-resistant prion protein in small brain biopsy specimens. Given the importance of accurate diagnosis in suspected prion disease, we recommend that a small portion of tissue from any brain biopsy performed in this setting be kept frozen for possible biochemical studies.

Transthyretin amyloidosis: a new mutation associated with dementia

Familial transthyretin (TTR) amyloidosis commonly presents with peripheral neuropathy and involvement of visceral organs. In contrast, signs of central nervous system (CNS) involvement are exceptional. We report that members of a kindred affected by a slowly progressive dementia, seizures, ataxia, hemiparesis, and decreased vision without neuropathy have TTR amyloid deposits in the leptomeninges, the brain parenchyma, and the eye. This condition, previously labeled oculoleptomeningeal amyloidosis, is linked to a mutation at codon 30 of TTR gene, resulting in the substitution of valine with glycine in this family, TTR amyloid deposits were present in the leptomeninges, especially the leptomeningeal vessels, and in the subependymal regions of the ventricular system where they disrupted the ependymal lining and resulted in amyloid-glial formations protruding into and narrowing the ventricular system. Hydrocephalus and atrophy and infarction of cerebral and cerebellar cortexes were also present. Review of the literature shows that amyloid deposition in the leptomeninges is not uncommon in TTR amyloidoses clinically characterized by peripheral neuropathy and lack of CNS signs. The present kindred, which presented exclusively with signs of CNS involvement, expands the phenotype of TTR amyloidosis and raises questions concerning the mechanisms determining phenotypic expression in TTR familial amyloidosis.

Evidence for the conformation of the pathologic isoform of the prion protein enciphering and propagating prion diversity

The fundamental event in prion diseases seems to be a conformational change in cellular prion protein (PrPC) whereby it is converted into the pathologic isoform PrPSc. In fatal familial insomnia (FFI), the protease-resistant fragment of PrPSc after deglycosylation has a size of 19 kilodaltons, whereas that from other inherited and sporadic prion diseases is 21 kilodaltons. Extracts from the brains of FFI patients transmitted disease to transgenic mice expressing a chimeric human-mouse PrP gene about 200 days after inoculation and induced formation of the 19-kilodalton PrPSc fragment, whereas extracts from the brains of familial and sporadic Creutzfeldt-Jakob disease patients produced the 21-kilodalton PrPSc fragment in these mice. The results presented indicate that the conformation of PrPSc functions as a template in directing the formation of nascent PrPSc and suggest a mechanism to explain strains of prions where diversity is encrypted in the conformation of PrPSc.

Early pathologic and biochemical changes in Creutzfeldt-Jakob disease: study of brain biopsies

We examined brain biopsy tissue from five patients with a neurologic syndrome consistent with Creutzfeldt-Jakob disease using Western blot analysis and immunohistochemistry for the detection of protease-resistant prion protein, in addition to histopathologic examination. Our results indicate that the formation of protease-resistant prion protein is an early event in disease pathogenesis and Western blot analysis can detect protease-resistant prion protein in the absence of structural lesions using a small amount of brain biopsy tissue.

Molecular basis of phenotypic variability in sporadic Creutzfeldt-Jakob disease

We sequenced the prion protein gene and studied the biochemical characteristics and the intracerebral distribution of protease-resistant prion protein with Western blot and immunohistochemistry in 19 cases of sporadic Creutzfeldt-Jakob disease. We identified four groups of subjects defined by the genotype at codon 129 of the prion protein gene, the site of a common methionine/valine polymorphism, and two types of protease-resistant prion proteins that differed in size and glycosylation. The four Creutzfeldt-Jakob disease groups showed distinct clinicopathological features that corresponded to previously described variants. The typical Creutzfeldt-Jakob disease phenotype or myoclonic variant and the Heidenhain variant were linked to methionine homozygosity at codon 129 and to "type 1" protease-resistant prion protein. The atypical and rarer variants such as that with dementia of long duration, the ataxic variant, and the variant with kuru plaques were linked to different genotypes at codon 129 and shared the "type 2" protease-resistant prion protein. Our data indicate that the sporadic form of Creutzfeldt-Jakob disease comprises a limited number of variants. The methionine/valine polymorphism at codon 129 of the prion protein gene and two types of protease-resistant prion proteins are the major determinants of these variants. These findings suggest the existence of prion strains in humans and provide the molecular basis for a novel classification of sporadic Creutzfeldt-Jakob disease.

Amyloid precursor protein metabolism in primary cell cultures of neurons, astrocytes, and microglia

Amyloid precursor protein (APP) gives rise by proteolytic processing to the amyloid beta peptide (A beta) found abundantly in cerebral senile plaques of individuals with Alzheimer's disease. APP is highly expressed in the brain. To assess the source of cerebral A beta, the metabolism of APP was investigated in the major cell types of the newborn rat cerebral cortex by pulse/chase labeling and immunoprecipitation of the APP and APP metabolic fragments. We describe a novel C-terminally truncated APP isoform that appears to be made only in neurons. The synthesis, degradation, and metabolism of APP were quantified by phosphorimaging in neurons, astrocytes, and microglia. The results show that although little APP is metabolized through the amyloidogenic pathways in each of the three cultures, neurons appear to generate more A beta than astrocytes or microglia.

The neuropathology of chromosome 17-linked dementia

We recently described a family with chromosome 17-linked dementia, characterized clinically by disinhibition-dementia-parkinsonism-amyotrophy complex. We report now the neuropathology of 6 affected family members. This included semiquantitative scoring of neuronal loss, gliosis, and spongiosis and immunocytochemical and ultrastructural characterization of neuronal and glial inclusions. The changes consisted of circumscribed neuronal loss, gliosis, and spongiosis of limbic neocortical areas and frontal, temporal, and occipital association areas. Similar changes were present in subcortical nuclei, most severe in the substantia nigra, but also involved the ventral striatum and amygdala. The hippocampus was spared except for degeneration of the afferent perforant tract, secondary to entorhinal nerve cell loss. Argyrophilic neuronal inclusions, with a characteristic immunocytochemical profile, were found in brainstem nuclei, hypothalamus and basal ganglia. Ultrastructurally, in 3 patients these inclusions showed hitherto undescribed abnormally assembled filaments. Glial cytoplasmic inclusions were widespread in white matter structures. Immunocytochemistry failed to demonstrate the protease-resistant prion protein. The pathology appears to be unique, involving various cortical and subcortical structures, and is consistent with the clinical findings of Kluver-Bucy-like syndrome, parkinsonism, and frontal lobe dementia. For this entity we suggest the term "chromosome 17-linked dementia."

Effect of the D178N mutation and the codon 129 polymorphism on the metabolism of the prion protein

Prion diseases are thought to be caused by the conversion of the normal, or cellular, prion protein (PrPC)(PrPres). There are three familial forms of human prion disease, Creutzfeldt-Jakob disease (CJD), Gerstmann-Straussler-Scheinker syndrome, and fatal familial insomnia (FFI) which are all expressed at advanced age despite the congenital presence of the mutant prion protein (PrPM). The cellular mechanisms that result in the age-dependent conversion of PrPM into PrPres and the unique phenotypes associated with each PrPM are unknown. FFI and a familial type of Creutzfeldt-Jakob disease (CJD178), share the D178N mutation in the PrP gene but have distinct phenotypes linked to codon 129, the site of a methionine/valine polymorphism (129M/V). We analyzed PrP processing in cells transfected with constructs reproducing the FFI and CJD178 genotypes. The D178N mutation results in instability of the mutant PrP which is partially corrected by N-glycosylation. Hence, only the glycosylated forms of PrPM reach the cell surface whereas the unglycosylated PrPM is also under-represented in the brain of FFI patients validating the cell model. These results offer new insight into the effect of the D178N mutation on the metabolism of the prion protein.

Fatal familial insomnia: behavioral and cognitive features

Fatal familial insomnia (FFI) is a familial prion disease linked to a mutation of the prion protein gene. Neuropsychological investigations in seven patients with FFI belonging to two different families showed that the main behavioral and neuropsychological features are (1) early impairment of attention and vigilance, (2) memory deficits, mainly of the working memory, (3) impairment of temporal ordering of events, and (4) a progressive dream-like state with neuropsychological and behavioral features of a confusional state. Neuropathologic examination of six patients showed prominent neuronal loss and gliosis involving the anterior ventral and mediodorsal thalamic nuclei, with additional cerebral cortical involvement in two cases. Clinicopathologic correlations indicate that FFI is associated with a neuropsychological and behavioral syndrome that is distinct from the cortical and subcortical dementias, and Wernicke-Korsakoff syndrome. These findings offer insights into the function of the thalamic nuclei and challenge the notion of thalamic dementia.

Presence of soluble amyloid beta-peptide precedes amyloid plaque formation in Down's syndrome

Abnormal and excessive accumulation of the amyloid beta-peptide (A beta) in the brain is a major and common characteristic of all Alzheimer's disease (AD) forms irrespective of their genetic background. Insoluble aggregates of A beta are identified as amyloid plaques. These deposits are thought to form when the amount of A beta is increased in the brain parenchyma as a result of either overexpression or altered processing of the amyloid precursor protein (APP). Soluble A beta ending at carboxyl-terminal residue 40 (A beta 40) and, in lesser amount, the form ending at residue 42 (A beta 42), are normal products of the APP metabolism in cell cultures. Increased secretion of soluble A beta 42 has been observed in cells transfected with constructs modeling APP gene mutations of familial forms of AD (refs 4, 5). On the basis of these in vitro data it has been hypothesized that the presence of soluble A beta 42 plays a role in the formation of amyloid plaques. Subjects affected by Down's syndrome (DS) have an increased APP gene dosage and overexpress APP. Apparently because of this overexpression, they almost invariably develop amyloid deposits after the age of 30 years, although they are free of them at earlier ages. Moreover, it has been observed that A beta 42 precedes A beta 40 in the course of amyloid deposition in DS brain. Thus, DS subjects provide the opportunity to investigate in the human brain the metabolic conditions that precede the formation of the amyloid deposits. Here we report that soluble A beta 42 is present in the brains of DS-affected subjects aged from 21 gestational weeks to 61 years but it is undetectable in age-matched controls. It is argued that overexpression of APP leads specifically to A beta 42 increase and that the presence of the soluble A beta 42 is causally related to plaque formation in DS and, likely, in AD brains.

Evidence for oxidative stress in Pick disease and corticobasal degeneration

Oxidative stress is increasingly implicated in a number of neurodegenerative disorders characterized by abnormal filament accumulation in affected neurons, including Alzheimer disease, Parkinson disease, and amyotrophic lateral sclerosis. To further evaluate the role of oxidative stress in the neurodegenerative process and the accumulation of abnormal filaments, we examined the pathologic lesions in Pick disease and of corticobasal degeneration with immunocytochemistry by using antisera to heme oxygenase-1 (HO-1) - a putative marker of oxidative injury. Immunoreactivity to HO-1 was demonstrated in ballooned neurons, Pick bodies, neuropil threads, and glial inclusions (the latter two in a case of corticobasal degeneration). By immunoelectron microscopy, HO-1 immunolabelling of Pick bodies was closely associated with the abnormal filaments comprising the inclusion. Apparently unaffected neurons in all cases showed only background levels of HO-1 immunoreactivity. These data suggest that oxidative stress is important in the formation of the lesions characteristic of Pick disease and corticobasal degeneration. Moreover, taken together with our previous demonstration that HO-1 immunoreactivity is associated with the neurofibrillary pathology of Alzheimer disease, progressive supranuclear palsy, and subacute sclerosing panencephalitis, it appears that oxidative stress specifically targets the cytoskeleton in a variety of neurodegenerative disorders characterized by abnormal filament accumulation.

Truncated forms of the human prion protein in normal brain and in prion diseases

The cellular form of the prion protein (PrPc) is a glycoprotein anchored to the cell membrane by a glycosylphosphatidylinositol moiety. An aberrant form of PrPc that is partially resistant to proteases, PrPres, is a hallmark of prion diseases, which in humans include Cruetzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker syndrome, and fatal familial insomnia. We have characterized the major forms of PrP in normal and pathological human brains. A COOH-terminal fragment of PrPc, designated C1, is abundant in normal and CJD brains as well as in human neuroblastoma cells. Sequence analysis revealed that C1 contains alternative NH2 termini starting at His-111 or Met-112. Like PrPc, C1 is glycosylated, anchored to the cell membrane, and is heat-stable. Consistent with the lack of the NH2-terminal region of PrPc, C1 is more acidic than PrPc and does not bind heparin. An additional fragment longer than C1, designated C2, is present in substantial amounts in CJD brains. Like PrPres, C2 is resistant to proteases and is detergent-insoluble. Our data indicate that C1 is a major product of normal PrPc metabolism, generated by a cleavage that disrupts the neurotoxic and amyloidogenic region of PrP comprising residues 106-126. This region remains intact in C2, suggesting a role for C2 in prion diseases.

Creutzfeldt-Jakob disease after liver transplantation

We report a 57-year-old woman who died from Creutzfeldt-Jakob disease 2 years after a liver transplantation. The liver donor had no history of neurological disease. In one albumin donor, possible Creutzfeldt-Jakob disease developed 3 years later. The patient initially had cerebellar symptoms. Neuropathology included "Kuru-type" plaques and prion protein (PrP) deposits involving the cerebellum predominantly. The patient was homozygote valine at codon 129 of the PrP gene while the liver was homozygote methionine. This observation raises the possibility of transmission of Creutzfeldt-Jakob disease by the graft itself or the associated albumin transfusions and, on a wider extent, by nonneural tissue.

Human prion diseases

Major advances have been made in prion diseases. Recent data indicate that the prion protein is likely to be a synaptic protein with a functional role in synaptic transmission. An impressive body of evidence suggests that (1) the normal prion protein plays a central role in prion replication; (2) the replication process implies an interaction between the normal prion protein and the pathogenic prion protein; and (3) the pathogenic prion protein is the infectious agent, the infectivity of which is dependent on its abnormal conformation. Genetic and protein analyses have expanded the spectrum of prion diseases and have underlined the complexity of genotype-phenotype interactions.

Sleep-wake cycle abnormalities in fatal familial insomnia. Evidence of the role of the thalamus in sleep regulation

Alterations in sleep organization were longitudinally studied in 6 new cases of fatal familial insomnia (FFI) by 24 h polygraphic recording. All patients showed an early reduction in sleep spindles and K complexes, and a drastic reduction in total sleep time and disruption of the cyclic sleep organization. Complete abolition of NREM sleep and persistence of only brief residual periods of REM sleep without atonia were features characteristic of the 3 patients with a short (less than 1 year) clinical course, and lacking in the 3 cases with a longer (more than 2 years) disease course. In the latter, sudden transitions from waking to NREM or REM sleep occurred, sometimes recurring periodically. Our findings confirm that impairment of sleep-wake regulation is a consistent distinctive feature of FFI.

Fatal familial insomnia: sleep, neuroendocrine and vegetative alterations

Fatal Familial Insomnia (FFI) is an autosomal dominant prion disease, characterized by prominent degeneration of the thalamus and involving impaired control of the sleep-wake cycle and of autonomic and endocrine functions. Profound alterations in the sleep-wake cycle consist of progressive decrease or complete absence of sleep activity and loss of any intrinsic cyclic organization of residual sleep. Unbalanced sympathergic activation with preserved parasympathetic drive, associated with chronic secondary hypertension and loss of the physiological nocturnal decrease in blood pressure constitute the characteristic autonomic changes. Neuroendocrine studies document hypercortisolism with abnormal feed-back suppression of adrenocorticotrophic hormone, constantly elevated catecholamine levels and abnormal secretory patterns of growth hormone, prolactin and melatonin. Advanced stages of the disease are invariably characterized by the disappearance of any circadian autonomic and neuroendocrine rhythmicity. FFI represents a model disease emphasizing the correlations among the different sleep, autonomic and neuroendocrine functions. Clinico-pathological correlations demonstrate the role of the thalamus as an integrative neural structure placed between the limbic system and the hypothalamus and controlling the homeostatic balance of the organism.

In memory of Amico Bignami (1930-1994)

Amico Bignami, neuropathologist and neuroscientist, professor of Neuropathology at Harvard Medical School, died on August 5, 1994. He is best known for his pioneering work on spongiform encephalopathies and intermediate filaments, in particular glial fibrillary acidic protein (GFAP).

Fatal familial insomnia and familial Creutzfeldt-Jakob disease: clinical, pathological and molecular features

Fatal familial insomnia (FFI) and a subtype of familial Creutzfeldt-Jakob disease (CJD178) are two prion diseases that have different clinical and pathological features, the same aspartic acid to asparagine mutation (D178N) at codon 178 of the prion protein (PrP) gene, but distinct genotypes generated by the methionine-valine polymorphism at codon 129 (129M or 129V) in the mutant allele of the PrP gene. The D178N, 129M allele segregates with FFI while the D178N, 129V allele segregates with CJD178. The proteinase K resistant PrP (PrPres) isoforms present in FFI and CJD178 differ in degree of glycosylation and size. Thus, the amino acid, methionine or valine, at position 129 of the mutant allele, in conjunction with D178N mutation results in significant alterations of PrPres in FFI and CJD178. The 129 polymorphic site also exerts influence through the normal allele: the course of the disease is shorter in the patients homozygous at codon 129 and other minor but consistent phenotypic differences occur between homozygous and heterozygous FFI patients. The comparative study of PrPres distribution in FFI homozygotes and heterozygotes at codon 129 has lead to the conclusion that the phenotypic differences observed between these two FFI patient populations may be the result of different rates of conversion of normal PrP into PrPres, at least in some brain regions.