Marcella Catania

A Recessive Mutation in the APP Gene with Dominant-Negative Effect on Amyloidogenesis

β-Amyloid precursor protein (APP) mutations cause familial Alzheimers disease with nearly complete penetrance. We found an APP mutation [alanine-673→valine-673 (A673V)] that causes disease only in the homozygous state, whereas heterozygous carriers were unaffected, consistent with a recessive Mendelian trait of inheritance. The A673V mutation affected APP processing, resulting in enhanced β-amyloid (Aβ) production and formation of amyloid fibrils in vitro. Co-incubation of mutated and wild-type peptides conferred instability on Aβ aggregates and inhibited amyloidogenesis and neurotoxicity. The highly amyloidogenic effect of the A673V mutation in the homozygous state and its anti-amyloidogenic effect in the heterozygous state account for the autosomal recessive pattern of inheritance and have implications for genetic screening and the potential treatment of Alzheimers disease.

Conversion of the BASE prion strain into the BSE strain: the origin of BSE?

Atypical neuropathological and molecular phenotypes of bovine spongiform encephalopathy (BSE) have recently been identified in different countries. One of these phenotypes, named bovine “amyloidotic” spongiform encephalopathy (BASE), differs from classical BSE for the occurrence of a distinct type of the disease-associated prion protein (PrP), termed PrPSc, and the presence of PrP amyloid plaques. Here, we show that the agents responsible for BSE and BASE possess different biological properties upon transmission to transgenic mice expressing bovine PrP and inbred lines of nontransgenic mice. Strikingly, serial passages of the BASE strain to nontransgenic mice induced a neuropathological and molecular disease phenotype indistinguishable from that of BSE-infected mice. The existence of more than one agent associated with prion disease in cattle and the ability of the BASE strain to convert into the BSE strain may have important implications with respect to the origin of BSE and spongiform encephalopathies in other species, including humans.

Prions in the Urine of Patients with Variant Creutzfeldt–Jakob Disease

BACKGROUND Prions, the infectious agents responsible for transmissible spongiform encephalopathies, consist mainly of the misfolded prion protein (PrP(Sc)). The unique mechanism of transmission and the appearance of a variant form of Creutzfeldt-Jakob disease, which has been linked to consumption of prion-contaminated cattle meat, have raised concerns about public health. Evidence suggests that variant Creutzfeldt-Jakob disease prions circulate in body fluids from people in whom the disease is silently incubating. METHODS To investigate whether PrP(Sc) can be detected in the urine of patients with variant Creutzfeldt-Jakob disease, we used the protein misfolding cyclic amplification (PMCA) technique to amplify minute quantities of PrP(Sc), enabling highly sensitive detection of the protein. We analyzed urine samples from several patients with various transmissible spongiform encephalopathies (variant and sporadic Creutzfeldt-Jakob disease and genetic forms of prion disease), patients with other degenerative or nondegenerative neurologic disorders, and healthy persons. RESULTS PrP(Sc) was detectable only in the urine of patients with variant Creutzfeldt-Jakob disease and had the typical electrophoretic profile associated with this disease. PrP(Sc) was detected in 13 of 14 urine samples obtained from patients with variant Creutzfeldt-Jakob disease and in none of the 224 urine samples obtained from patients with other neurologic diseases and from healthy controls, resulting in an estimated sensitivity of 92.9% (95% confidence interval [CI], 66.1 to 99.8) and a specificity of 100.0% (95% CI, 98.4 to 100.0). The PrP(Sc) concentration in urine calculated by means of quantitative PMCA was estimated at 1×10(-16) g per milliliter, or 3×10(-21) mol per milliliter, which extrapolates to approximately 40 to 100 oligomeric particles of PrP(Sc) per milliliter of urine. CONCLUSIONS Urine samples obtained from patients with variant Creutzfeldt-Jakob disease contained minute quantities of PrP(Sc). (Funded by the National Institutes of Health and others.).

Neuropathology of the recessive A673V APP mutation: Alzheimer disease with distinctive features

Mutations of three different genes, encoding β-amyloid precursor protein (APP), presenilin 1 and presenilin 2 are associated with familial Alzheimer’s disease (AD). Recently, the APP mutation A673V has been identified that stands out from all the genetic defects previously reported in these three genes, since it causes the disease only in the homozygous state (Di Fede et al. in Science 323:1473–1477, 2009). We here provide the detailed neuropathological picture of the proband of this family, who was homozygous for the APP A673V mutation and recently came to death. The brain has been studied by histological and immunohistochemical techniques, at the optical and ultrastructural levels. Cerebral Aβ accumulation and tau pathology were severe and extensive. Peculiar features were the configuration of the Aβ deposits that were of large size, mostly perivascular and exhibited a close correspondence between the pattern elicited by amyloid stainings and the labeling obtained with immunoreagents specific for Aβ40 or Aβ42. Moreover, Aβ deposition spared the neostriatum while deeply affecting the cerebellum, and therefore was not in compliance with the hierarchical topographical sequence of involvement documented in sporadic AD. Therefore, the neuropathological picture of familial AD caused by the APP recessive mutation A673V presents distinctive characteristics compared to sporadic AD or familial AD inherited as a dominant trait. Main peculiar features are the morphology, structural properties and composition of the Aβ deposits as well as their topographic distribution in the brain.

Good gene, bad gene: New APP variant may be both

APP mutations cause Alzheimer disease (AD) with virtually complete penetrance. We found a novel APP mutation (A673V) in the homozygous state in a patient with early-onset AD-type dementia and in his younger sister showing initial signs of cognitive decline. It is noteworthy that the heterozygous relatives were not affected, suggesting that this mutation is inherited as an autosomal recessive trait. Studies on molecular events for the recessive mutation in causing disease revealed a double synergistic effect: the A673V APP variant shifts APP processing towards the amyloidogenic pathway with increased production of Aβ peptides and it markedly enhances the aggregation and fibrillogenic properties of both Aβ1-40 and Aβ1-42. However, co-incubation of mutated and wild-type (wt) Aβ species resulted in inhibition of amyloidogenesis, consistent with the observation that heterozygous carriers do not develop the disease. The opposite effects of the A673V mutation in the homozygous and heterozygous state on amyloidogenesis account for the autosomal recessive pattern of inheritance, revealing a new scenario in AD genetics and pathogenesis. The anti-amyloidogenic properties of this novel human Aβ variant may offer grounds for the development of therapeutic strategies for AD based on modified Aβ peptides. Indeed, the interaction between mutated Aβ1-6 and wt full-length Aβ prevents amyloid fibril formation. The anti-amyloidogenic effect is further amplified by the use of a mutated six-mer peptide, constructed entirely from D-amino acids to increase the its stability in vivo. Here we reviewed the studies on pathogenic mechanisms associated with the A673V mutation and the first experimental steps toward the development of a novel disease-modifying therapy for AD.

APP mutations in the Aβ coding region are associated with abundant cerebral deposition of Aβ38

Aβ is the main component of amyloid deposits in Alzheimer disease (AD) and its aggregation into oligomers, protofibrils and fibrils is considered a seminal event in the pathogenesis of AD. Aβ with C-terminus at residue 42 is the most abundant species in parenchymal deposits, whereas Aβ with C-terminus at residue 40 predominates in the amyloid of the walls of large vessels. Aβ peptides with other C-termini have not yet been thoroughly investigated. We analysed Aβ38 in the brains of patients with Aβ deposition linked to sporadic and familial AD, hereditary cerebral haemorrhage with amyloidosis, or Down syndrome. Immunohistochemistry, confocal microscopy, immunoelectron microscopy, immunoprecipitation and the electrophoresis separation of low molecular weight aggregates revealed that Aβ38 accumulates consistently in the brains of patients carrying APP mutations in the Aβ coding region, but was not detected in the patients with APP mutations outside the Aβ domain, in the patients with presenilin mutations or in subjects with Down syndrome. In the patients with sporadic AD, Aβ38 was absent in the senile plaques, but it was detected only in the vessel walls of a small subset of patients with severe cerebral amyloid angiopathy. Our results suggest that APP mutations in the Aβ coding region favour Aβ38 accumulation in the brain and that the molecular mechanisms of Aβ deposition in these patients may be different from those active in patients with familial AD associated with other genetic defects and sporadic AD.

Expression of A2V-mutated Aβ in Caenorhabditis elegans results in oligomer formation and toxicity.

Although Alzheimers disease (AD) is usually sporadic, in a small proportion of cases it is familial and can be linked to mutations in β-amyloid precursor protein (APP). Unlike the other genetic defects, the mutation [alanine-673→valine-673] (A673V) causes the disease only in the homozygous condition with enhanced amyloid β (Aβ) production and aggregation; heterozygous carriers remain unaffected. It is not clear how misfolding and aggregation of Aβ is affected in vivo by this mutation and whether this correlates with its toxic effects. No animal models over-expressing the A673V–APP gene or alanine-2-valine (A2V) mutated human Aβ protein are currently available. Using the invertebrate Caenorhabditis elegans, we generated the first transgenic animal model to express the human Aβ1–40 wild-type (WT) in neurons or possess the A2V mutation (Aβ1–40A2V). Insertion of an Aβ-mutated gene into this nematode reproduced the homozygous state of the human pathology. Functional and biochemical characteristics found in the A2V strain were compared to those of transgenic C. elegans expressing Aβ1–40WT. The expression of both WT and A2V Aβ1–40 specifically reduced the nematodes lifespan, causing behavioral defects and neurotransmission impairment which were worse in A2V worms. Mutant animals were more resistant than WT to paralysis induced by the cholinergic agonist levamisole, indicating that the locomotor defect was specifically linked to postsynaptic dysfunctions. The toxicity caused by the mutated protein was associated with a high propensity to form oligomeric assemblies which accumulate in the neurons, suggesting this to be the central event involved in the postsynaptic damage and early onset of the disease in homozygous human A673V carriers.

Infectivity in Skeletal Muscle of Cattle with Atypical Bovine Spongiform Encephalopathy

The amyloidotic form of bovine spongiform encephalopathy (BSE) termed BASE is caused by a prion strain whose biological properties differ from those of typical BSE, resulting in a clinically and pathologically distinct phenotype. Whether peripheral tissues of BASE-affected cattle contain infectivity is unknown. This is a critical issue since the BASE prion is readily transmissible to a variety of hosts including primates, suggesting that humans may be susceptible. We carried out bioassays in transgenic mice overexpressing bovine PrP (Tgbov XV) and found infectivity in a variety of skeletal muscles from cattle with natural and experimental BASE. Noteworthy, all BASE muscles used for inoculation transmitted disease, although the attack rate differed between experimental and natural cases (∼70% versus ∼10%, respectively). This difference was likely related to different prion titers, possibly due to different stages of disease in the two conditions, i.e. terminal stage in experimental BASE and pre-symptomatic stage in natural BASE. The neuropathological phenotype and PrPres type were consistent in all affected mice and matched those of Tgbov XV mice infected with brain homogenate from natural BASE. The immunohistochemical analysis of skeletal muscles from cattle with natural and experimental BASE showed the presence of abnormal prion protein deposits within muscle fibers. Conversely, Tgbov XV mice challenged with lymphoid tissue and kidney from natural and experimental BASE did not develop disease. The novel information on the neuromuscular tropism of the BASE strain, efficiently overcoming species barriers, underlines the relevance of maintaining an active surveillance.

Familial frontotemporal dementia associated with the novel MAPT mutation T427M

Sirs: Mutations of the microtubule-associated protein tau (MAPT) lead to a clinically heterogeneous disorder called “Frontotemporal dementia and parkinsonism linked to chromosome 17” (FTDP-17) [1–4]. The clinical phenotype is characterised by behavioural, cognitive and motor disturbances and the neuropathology by intracellular tau-positive inclusions involving neurons and glial cells [5]. More than 30 different mutations of the MAPT gene have been identified. Here we report the novel genetic variation T427M of the MAPT gene in an Italian patient with family history of dementia and clinical, neuroradiological and neuropsychological features typical of frontotemporal dementia (FTD). The proband (Fig. 1, patient III1) had 3 years of formal education and her medical history was unremarkable. Starting at age 60, she developed language disturbance and personality change with apathy and inappropriate social and eating behaviour. The spontaneous conversation was reduced, the speech was characterized by frequent anomias and semantic paraphrasis and there were difficulties in comprehension of the language. She became impulsive, had antisocial behaviour and attention deficit. After a short period of decreased appetite, she became bulimic with a tendency to crave sweet food and gained about 30 kg in a period of two years. The anterograde and retrograde memory, visual perception, praxis, visuospatial abilities and familiar face recognition were spared. At age 62, neurological examination was unremarkable and the MMSE was 19. At age 64, she was unable to carry on her ordinary housework because of further decline in cognitive functions. At this time, language dysfunction was severe, but memory and orientation were relatively preserved. The patient performed below the cut-off (adjusted score 38.8 with normal value > 89.5) in a screening for global cognitive deterioration, the Milan Overall Dementia Assessment [6]. A formal battery assessing language was in the pathological range, while tests of executive functions were unrevealing since the patient was not able to understand the task. MRI showed moderate fronto-temporal atrophy, more evident on the left side, associated with signal abnormality of the subcortical white matter. As the disease progressed the patient became mute, disoriented and unable to communicate, but not bedridden. At age 66, MRI showed progression of the fronto-temporal atrophy that was still asymmetrical, more severe on the left side, and diffuse abnormal signal intensity of the fronto-temporal white matter that was also reduced in extension (Fig. 2). The patient died at age 67 from pneumonia and autopsy was not performed. The father of the proband (II-1) died at age 79 after an 8-year history of dementia with prominent behavioural disturbances. The paternal grandfather (I-1) and a paternal aunt (II-3) were reported demented during aging, but no further details are available about their medical history. Two paternal aunts died without signs of dementia, one at age 78 and one at age unknown, but older than 65. A brother of the proband (III-4) died at age 52 from neoplasia. No data are available for an uncle (II-5) and a brother (III-5) since they have moved to Australia (Fig. 1). DNA of the proband and her unaffected sisters (III-2 and III-3) was extracted from peripheral leukocytes. In the proband, sequencing of exons 9 to 13 of the MAPT gene revealed a C to T substitution at the second position of codon 427, resulting in threonine to methionine mutation. This mutation was absent in 150 normal individuals and in 150 demented patients that we have previously screened, as well as in the two nonaffected sisters of the proband, who are 64 and 53 years old, the latter being, however, under the age of onset of disease in the proband. The clinical picture of the proband, characterized by personality changes and language disturbances with relative sparing of memory, spatial skills and praxis, meets the current criteria for FTD [7]. These features are consistent with the MRI findings of asymmetrical atrophy of the frontal, insular and temporal regions, but the lack LETTER TO THE EDITORS

Tackling amyloidogenesis in Alzheimer's disease with A2V variants of Amyloid-β

We developed a novel therapeutic strategy for Alzheimer’s disease (AD) exploiting the properties of a natural variant of Amyloid-β (Aβ) carrying the A2V substitution, which protects heterozygous carriers from AD by its ability to interact with wild-type Aβ, hindering conformational changes and assembly thereof. As prototypic compound we designed a six-mer mutated peptide (Aβ1-6A2V), linked to the HIV-related TAT protein, which is widely used for brain delivery and cell membrane penetration of drugs. The resulting molecule [Aβ1-6A2VTAT(D)] revealed strong anti-amyloidogenic effects in vitro and protected human neuroblastoma cells from Aβ toxicity. Preclinical studies in AD mouse models showed that short-term treatment with Aβ1-6A2VTAT(D) inhibits Aβ aggregation and cerebral amyloid deposition, but a long treatment schedule unexpectedly increases amyloid burden, although preventing cognitive deterioration. Our data support the view that the AβA2V-based strategy can be successfully used for the development of treatments for AD, as suggested by the natural protection against the disease in human A2V heterozygous carriers. The undesirable outcome of the prolonged treatment with Aβ1-6A2VTAT(D) was likely due to the TAT intrinsic attitude to increase Aβ production, avidly bind amyloid and boost its seeding activity, warning against the use of the TAT carrier in the design of AD therapeutics.