Genetic alterations of the BRI2 gene: familial British and Danish dementias

The Dual Role of Amyloid Beta-Peptide in Oxidative Stress and Inflammation: Unveiling Their Connections in Alzheimer's Disease Etiopathology

Alzheimer's disease (AD) is a progressive neurodegenerative disease, and it is currently the seventh leading cause of death worldwide. It is characterized by the extracellular aggregation of the amyloid β-peptide (Aβ) into oligomers and fibrils that cause synaptotoxicity and neuronal death. Aβ exhibits a dual role in promoting oxidative stress and inflammation. This review aims to unravel the intricate connection between these processes and their contribution to AD progression. The review delves into oxidative stress in AD, focusing on the involvement of metals, mitochondrial dysfunction, and biomolecule oxidation. The distinct yet overlapping concept of nitro-oxidative stress is also discussed, detailing the roles of nitric oxide, mitochondrial perturbations, and their cumulative impact on Aβ production and neurotoxicity. Inflammation is examined through astroglia and microglia function, elucidating their response to Aβ and their contribution to oxidative stress within the AD brain. The blood-brain barrier and oligodendrocytes are also considered in the context of AD pathophysiology. We also review current diagnostic methodologies and emerging therapeutic strategies aimed at mitigating oxidative stress and inflammation, thereby offering potential treatments for halting or slowing AD progression. This comprehensive synthesis underscores the pivotal role of Aβ in bridging oxidative stress and inflammation, advancing our understanding of AD and informing future research and treatment paradigms.

Chemical traits of cerebral amyloid angiopathy in familial British-, Danish-, and non-Alzheimer's dementias

Familial British dementia (FBD) and familial Danish dementia (FDD) are autosomal dominant forms of dementia caused by mutations in the integral membrane protein 2B (ITM2B, also known as BRI2) gene. Secretase processing of mutant BRI2 leads to secretion and deposition of BRI2-derived amyloidogenic peptides, ABri and ADan that resemble APP/β-amyloid (Aβ) pathology, which is characteristic of Alzheimer's disease (AD). Amyloid pathology in FBD/FDD manifests itself predominantly in the microvasculature by ABri/ADan containing cerebral amyloid angiopathy (CAA). While ABri and ADan peptide sequences differ only in a few C-terminal amino acids, CAA in FDD is characterized by co-aggregation of ADan with Aβ, while in contrast no Aβ deposition is observed in FBD. The fact that FDD patients display an earlier and more severe disease onset than FBD suggests a potential role of ADan and Aβ co-aggregation that promotes a more rapid disease progression in FDD compared to FBD. It is therefore critical to delineate the chemical signatures of amyloid aggregation in these two vascular dementias. This in turn will increase the knowledge on the pathophysiology of these diseases and the pathogenic role of heterogenous amyloid peptide interactions and deposition, respectively. Herein, we used matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) in combination with hyperspectral, confocal microscopy based on luminescent conjugated oligothiophene probes (LCO) to delineate the structural traits and associated amyloid peptide patterns of single CAA in postmortem brain tissue of patients with FBD, FDD as well as sporadic CAA without AD (CAA+) that show pronounced CAA without parenchymal plaques. The results show that CAA in both FBD and FDD consist of N-terminally truncated- and pyroglutamate-modified amyloid peptide species (ADan and ABri), but that ADan peptides in FDD are also extensively C-terminally truncated as compared to ABri in FBD, which contributes to hydrophobicity of ADan species. Further, CAA in FDD showed co-deposition with Aβ x-42 and Aβ x-40 species. CAA+ vessels were structurally more mature than FDD/FBD CAA and contained significant amounts of pyroglutamated Aβ. When compared with FDD, Aβ in CAA+ showed more C-terminal and less N-terminally truncations. In FDD, ADan showed spatial co-localization with Aβ3pE-40 and Aβ3-40 but not with Aβx-42 species. This suggests an increased aggregation propensity of Aβ in FDD that promotes co-aggregation of both Aβ and ADan. Further, CAA maturity appears to be mainly governed by Aβ content based on the significantly higher 500/580 patterns observed in CAA+ than in FDD and FBD, respectively. Together this is the first study of its kind on comprehensive delineation of Bri2 and APP-derived amyloid peptides in single vascular plaques in both FDD/FBD and sporadic CAA that provides new insight in non-AD-related vascular amyloid pathology. Cover Image for this issue: https://doi.org/10.1111/jnc.15424.

Association of clusterin with the BRI2-derived amyloid molecules ABri and ADan

Familial British and Danish dementias (FBD and FDD) share striking neuropathological similarities with Alzheimer's disease (AD), including intraneuronal neurofibrillary tangles as well as parenchymal and vascular amyloid deposits. Multiple amyloid associated proteins with still controversial role in amyloidogenesis colocalize with the structurally different amyloid peptides ABri in FBD, ADan in FDD, and Aβ in AD. Genetic variants and plasma levels of one of these associated proteins, clusterin, have been identified as risk factors for AD. Clusterin is known to bind soluble Aβ in biological fluids, facilitate its brain clearance, and prevent its aggregation. The current work identifies clusterin as the major ABri- and ADan-binding protein and provides insight into the biochemical mechanisms leading to the association of clusterin with ABri and ADan deposits. Mirroring findings in AD, the studies corroborate clusterin co-localization with cerebral parenchymal and vascular amyloid deposits in both disorders. Ligand affinity chromatography with downstream Western blot and amino acid sequence analyses unequivocally identified clusterin as the major ABri- and ADan-binding plasma protein. ELISA highlighted a specific saturable binding of clusterin to ABri and ADan with low nanomolar Kd values within the same range as those previously demonstrated for the clusterin-Aβ interaction. Consistent with its chaperone activity, thioflavin T binding assays clearly showed a modulatory effect of clusterin on ABri and ADan aggregation/fibrillization properties. Our findings, together with the known multifunctional activity of clusterin and its modulatory activity on the complex cellular pathways leading to oxidative stress, mitochondrial dysfunction, and the induction of cell death mechanisms - all known pathogenic features of these protein folding disorders - suggests the likelihood of a more complex role and a translational potential for the apolipoprotein in the amelioration/prevention of these pathogenic mechanisms.

The presubiculum is preserved from neurodegenerative changes in Alzheimer's disease

In the majority of affected brain regions the pathological hallmarks of Alzheimer’s disease (AD) are β-amyloid (Aβ) deposits in the form of diffuse and neuritic plaques, tau pathology in the form of neurofibrillary tangles, neuropil threads and plaque-associated abnormal neurites in combination with an inflammatory response. However, the anatomical area of the presubiculum, is characterised by the presence of a single large evenly distributed ‘lake-like’ Aβ deposit with minimal tau deposition or accumulation of inflammatory markers. Post-mortem brain samples from sporadic AD (SAD) and familial AD (FAD) and two hereditary cerebral amyloid diseases, familial British dementia (FBD) and familial Danish dementia (FDD) were used to compare the morphology of the extracellular proteins deposited in the presubiculum compared to the entorhinal cortex. The level of tau pathology and the extent of microglial activation were quantitated in the two brain regions in SAD and FAD. Frozen tissue was used to investigate the Aβ species and proteomic differences between the two regions. Consistent with our previous investigations of FBD and FDD cases we were able to establish that the ‘lake-like’ pre-amyloid deposits of the presubiculum were not a unique feature of AD but they also found two non-Aβ amyloidosis. Comparing the presubiculum to the entorhinal cortex the number of neurofibrillary tangles and tau load were significantly reduced; there was a reduction in microglial activation; there were differences in the Aβ profiles and the investigation of the whole proteome showed significant changes in different protein pathways. In summary, understanding why the presubiculum has a different morphological appearance, biochemical and proteomic makeup compared to surrounding brain regions severely affected by neurodegeneration could lead us to understanding protective mechanisms in neurodegenerative diseases.

Neuropathology of cerebrovascular diseases

The chapter describes the epidemiology of cerebrovascular diseases, anatomy of the cerebral blood vessels, pathophysiology of ischemia, hypoxia, hypoxemia, anemic hypoxia, histotoxic hypoxia, carbon monoxide damage, hyperoxid brain damage and decompression sickness, and selective cell and regional vulnerability; diseases of the blood vessels including atherosclerosis, hypertensive angiopathy, small vessel disease, inflammatory vascular diseases, cerebral amyloid angiopathies, CADASIL, CARASIL and other diseases that can lead to cerebrovascular occlusion; intracranial and intraspinal aneurysms and vascular malformations; hematologic disorders that can cause cerebral infarct or hemorrhage; brain ischemic damage; and spontaneous intracranial bleeding. Within ischemic brain damage, focal cerebral ischemia, hemorrhagic infarct, brain edema, penumbra, global cerebral ischemia, venous thrombosis, lacunas and lacunar state, status cribosus, granular atrophy of the cerebral cortex, hippocampal sclerosis, vascular leukoencephalopathy Binswanger type and multi-infarct encephalopathy are discussed in detail. Cognitive impairment of vascular origin deserves an individual section.

Interaction of ApoE3 and ApoE4 isoforms with an ITM2b/BRI2 mutation linked to the Alzheimer disease-like Danish dementia: Effects on learning and memory

Mutations in Amyloid β Precursor Protein (APP) and in genes that regulate APP processing--such as PSEN1/2 and ITM2b/BRI2--cause familial dementia, such Familial Alzheimer disease (FAD), Familial Danish (FDD) and British (FBD) dementias. The ApoE gene is the major genetic risk factor for sporadic AD. Three major variants of ApoE exist in humans (ApoE2, ApoE3, and ApoE4), with the ApoE4 allele being strongly associated with AD. ITM2b/BRI2 is also a candidate regulatory node genes predicted to mediate the common patterns of gene expression shared by healthy ApoE4 carriers and late-onset AD patients not carrying ApoE4. This evidence provides a direct link between ITM2b/BRI2 and ApoE4. To test whether ApoE4 and pathogenic ITM2b/BRI2 interact to modulate learning and memory, we crossed a mouse carrying the ITM2b/BRI2 mutations that causes FDD knocked-in the endogenous mouse Itm2b/Bri2 gene (FDDKI mice) with human ApoE3 and ApoE4 targeted replacement mice. The resultant ApoE3, FDDKI/ApoE3, ApoE4, FDDKI/ApoE4 male mice were assessed longitudinally for learning and memory at 4, 6, 12, and 16-17 months of age. The results showed that ApoE4-carrying mice displayed spatial working/short-term memory deficits relative to ApoE3-carrying mice starting in early middle age, while long-term spatial memory of ApoE4 mice was not adversely affected even at 16-17 months, and that the FDD mutation impaired working/short-term spatial memory in ApoE3-carrying mice and produced impaired long-term spatial memory in ApoE4-carrying mice in middle age. The present results suggest that the FDD mutation may differentially affect learning and memory in ApoE4 carriers and non-carriers.

Oxidative stress and mitochondria-mediated cell death mechanisms triggered by the familial Danish dementia ADan amyloid

Familial Danish Dementia (FDD), an early-onset non-amyloid-β (Aβ) cerebral amyloidosis, is neuropathologically characterized by widespread cerebral amyloid angiopathy, parenchymal amyloid and preamyloid deposits, as well as neurofibrillary degeneration indistinguishable to that seen in Alzheimer's disease (AD). The main amyloid subunit composing FDD lesions, a 34-amino acid de-novo generated peptide ADan, is the direct result of a genetic defect at the 3'-end of the BRI2 gene and the physiologic action of furin-like proteolytic processing at the C-terminal region of the ADan precursor protein. We aimed to study the impact of the FDD mutation, the additional formation of the pyroglutamate (pE) posttranslational modification as well as the relevance of C-terminal truncations -all major components of the heterogeneous FDD deposits- on the structural and neurotoxic properties of the molecule. Our data indicates that whereas the mutation generated a β-sheet-rich hydrophobic ADan subunit of high oligomerization/fibrillization propensity and the pE modification further enhanced these properties, C-terminal truncations had the opposite effect mostly abolishing these features. The potentiation of pro-amyloidogenic properties correlated with the initiation of neuronal cell death mechanisms involving oxidative stress, perturbation of mitochondrial membrane potential, release of mitochondrial cytochrome c, and downstream activation of caspase-mediated apoptotic pathways. The amyloid-induced toxicity was inhibited by targeting specific components of these detrimental cellular pathways, using reactive oxygen scavengers and monoclonal antibodies recognizing the pathological amyloid subunit. Taken together, the data indicate that the FDD mutation and the pE posttranslational modification are both primary elements driving intact ADan into an amyloidogenic/neurotoxic pathway while truncations at the C-terminus eliminate the pro-amyloidogenic characteristics of the molecule, likely reflecting effect of physiologic clearance mechanisms.

The Familial British Dementia Mutation Promotes Formation of Neurotoxic Cystine Cross-linked Amyloid Bri (ABri) Oligomers

Familial British dementia (FBD) is an inherited neurodegenerative disease believed to result from a mutation in the BRI2 gene. Post-translational processing of wild type BRI2 and FBD-BRI2 result in the production of a 23-residue long Bri peptide and a 34-amino acid long ABri peptide, respectively, and ABri is found deposited in the brains of individuals with FBD. Similarities in the neuropathology and clinical presentation shared by FBD and Alzheimer disease (AD) have led some to suggest that ABri and the AD-associated amyloid β-protein (Aβ) are molecular equivalents that trigger analogous pathogenic cascades. But the sequences and innate properties of ABri and Aβ are quite different, notably ABri contains two cysteine residues that can form disulfide bonds. Thus we sought to determine whether ABri was neurotoxic and if this activity was regulated by oxidation and/or aggregation. Crucially, the type of oxidative cross-linking dramatically influenced both ABri aggregation and toxicity. Cyclization of Bri and ABri resulted in production of biologically inert monomers that showed no propensity to assemble, whereas reduced ABri and reduced Bri aggregated forming thioflavin T-positive amyloid fibrils that lacked significant toxic activity. ABri was more prone to form inter-molecular disulfide bonds than Bri and the formation of covalently stabilized ABri oligomers was associated with toxicity. These results suggest that extension of the C-terminal of Bri causes a shift in the type of disulfide bonds formed and that structures built from covalently cross-linked oligomers can interact with neurons and compromise their function and viability.

Proteinopathies, a core concept for understanding and ultimately treating degenerative disorders?

The current review covers proteinopathies an umbrella term for neurodegenerative disorders that are characterized by the accumulation of specific proteins within neurons or in the brain parenchyma. Most prevalent examples for typical proteinopathies are Alzheimer's disease and Parkinson's disease. In healthy brain, these proteins are unstructured as a monomer, serving most likely as the physiological form. In a disease condition, the unstructured proteins experience a conformational change leading to small oligomers that eventually will aggregate into higher order structures. Prion disease is an exception within the family of proteinopathies as the aggregated prion protein is highly infectious and can self-aggregate and propagate. Recent reports might implicate a prion-like spread of misfolded proteins in Alzheimer's and Parkinson's disease; however there are evident differences in comparison to prion diseases. As proteinopathies are caused by the aggregation of disease-typical proteins with an ordered structure, active and passive immunization protocols have been used to expose model systems to therapeutic antibodies that bind to the aggregates thereby inhibiting the prolongation into higher ordered fibrils or dissolving the existing fibrillar structure. While most of the immunization treatments have been only carried out in preclinical model systems overexpressing the disease-relevant aggregating protein, other approaches are already in clinical testing. Taking the core concept of proteinopathies with conformationally altered protein aggregates into account, immunization appears to be a very promising therapeutic option for neurodegenerative disorders.

Recurrence of Lobar Hemorrhage: A Red Flag for Cerebral Amyloid Angiopathy-related Inflammation?

Background. Recurrent lobar intracerebral hemorrhage is more commonly associated with cerebral amyloid angiopathy and less likely associated with hypertension. Cerebral amyloid angiopathy-related inflammation is a subgroup of cerebral amyloid angiopathy that can present with lobar intracerebral hemorrhage, encephalopathy, and seizures; wherein corticosteroids may facilitate favorable outcome. Whether recurrence of lobar intracerebral hemorrhage in cerebral amyloid angiopathy is related to cerebral amyloid angiopathy-related inflammation is unknown. Case presentation. A 68-year-old woman presented with an acute onset of confusion. She was known to have a history of recurrent lobar intracerebral hemorrhage related to cerebral amyloid angiopathy. Brain imaging revealed previous sequelae of cerebral amyloid angiopathy and a new lobar intracerebral hemorrhage. An empirical diagnosis of cerebral amyloid angiopathy-related inflammation was made given the patent's clinical course of recurrence. Utilizing current evidence of criteria used to diagnose cerebral amyloid angiopathy-related inflammation, corticosteroid therapy was initiated with significant improvement in clinical and imaging characteristics. Discussion. Inflammatory pathways incited as a result of cerebrovascular amyloid deposition play a vital role in pathogenesis of cerebral amyloid angiopathy-related inflammation. We highlight the need to consider corticosteroid therapy in patients presenting with recurrent lobar intracerebral hemorrhage in the setting of cerebral amyloid angiopathy since inflammation may play a role in its pathophysiology. Evidence in the literature is sparse to suggest that cerebral amyloid angiopathy-related inflammation might be the root cause for the lobar intracerebral hemorrhage recurrence in cerebral amyloid angiopathy. Further studies are needed to identify mechanisms of recurrent hemorrhage, its correlations with cerebral amyloid angiopathy-related inflammation, and the potential role of corticosteroid therapy.

Metal ion mediated transition from random coil to β-sheet and aggregation of Bri2-23, a natural inhibitor of Aβ aggregation

Soft metal ion binding enforces critical rearrangement of the structure of Bri2-23, a natural inhibitor of Aβ aggregation, thus shifting its solution behavior to a self aggregating system.

Mitochondrial dysfunction induced by a post-translationally modified amyloid linked to a familial mutation in an alternative model of neurodegeneration

Familial British dementia (FBD) is an early-onset non-amyloid-β (Aβ) cerebral amyloidosis that presents with severe cognitive decline and strikingly similar neuropathological features to those present in Alzheimer's disease (AD). FBD is associated with a T to A single nucleotide transition in the stop codon of a gene encoding BRI2, leading to the production of an elongated precursor protein. Furin-like proteolytic processing at its C-terminus releases a longer-than-normal 34 amino acid peptide, ABri, exhibiting amyloidogenic properties not seen in its 23 amino acid physiologic counterpart Bri1-23. Deposited ABri exhibits abundant post-translational pyroglutamate (pE) formation at the N-terminus, a feature seen in truncated forms of Aβ found in AD deposits, and co-exists with neurofibrillary tangles almost identical to those found in AD. We tested the impact of the FBD mutation alone and in conjunction with the pE post-translational modification on the structural properties and associated neurotoxicity of the ABri peptide. The presence of pE conferred to the ABri molecule enhanced hydrophobicity and accelerated aggregation/fibrillization properties. ABri pE was capable of triggering oxidative stress, loss of mitochondrial membrane potential and activation of caspase-mediated apoptotic mechanisms in neuronal cells, whereas homologous peptides lacking the elongated C-terminus and/or the N-terminal pE were unable to induce similar detrimental cellular pathways. The data indicate that the presence of N-terminal pE is not in itself sufficient to induce pathogenic changes in the physiologic Bri1-23 peptides but that its combination with the ABri mutation is critical for the molecular pathogenesis of FBD.

Development of a new DNA vaccine for Alzheimer disease targeting a wide range of aβ species and amyloidogenic peptides

It has recently been determined that not only Aβ oligomers, but also other Aβ species and amyloidogenic peptides are neurotoxic in Alzheimer disease (AD) and play a pivotal role in AD pathogenesis. In the present study, we attempted to develop new DNA vaccines targeting a wide range of Aβ species. For this purpose, we first performed in vitro assays with newly developed vaccines to evaluate Aβ production and Aβ secretion abilities and then chose an IgL-Aβx4-Fc-IL-4 vaccine (designated YM3711) for further studies. YM3711 was vaccinated to mice, rabbits and monkeys to evaluate anti-Aβ species antibody-producing ability and Aβ reduction effects. It was found that YM3711 vaccination induced significantly higher levels of antibodies not only to Aβ1-42 but also to AD-related molecules including AβpE3-42, Aβ oligomers and Aβ fibrils. Importantly, YM3711 significantly reduced these Aβ species in the brain of model mice. Binding and competition assays using translated YM3711 protein products clearly demonstrated that a large part of antibodies induced by YM3711 vaccination are directed at conformational epitopes of the Aβ complex and oligomers. Taken together, we demonstrate that YM3711 is a powerful DNA vaccine targeting a wide range of AD-related molecules and is worth examining in preclinical and clinical trials.

The familial dementia gene revisited: a missense mutation revealed by whole-exome sequencing identifies ITM2B as a candidate gene underlying a novel autosomal dominant retinal dystrophy in a large family

Inherited retinal diseases are a group of clinically and genetically heterogeneous disorders for which a significant number of cases remain genetically unresolved. Increasing knowledge on underlying pathogenic mechanisms with precise phenotype-genotype correlation is, however, critical for establishing novel therapeutic interventions for these yet incurable neurodegenerative conditions. We report phenotypic and genetic characterization of a large family presenting an unusual autosomal dominant retinal dystrophy. Phenotypic characterization revealed a retinopathy dominated by inner retinal dysfunction and ganglion cell abnormalities. Whole-exome sequencing identified a missense variant (c.782A>C, p.Glu261Ala) in ITM2B coding for Integral Membrane Protein 2B, which co-segregates with the disease in this large family and lies within the 24.6 Mb interval identified by microsatellite haplotyping. The physiological role of ITM2B remains unclear and has never been investigated in the retina. RNA in situ hybridization reveals Itm2b mRNA in inner nuclear and ganglion cell layers within the retina, with immunostaining demonstrating the presence of the corresponding protein in the same layers. Furthermore, ITM2B in the retina co-localizes with its known interacting partner in cerebral tissue, the amyloid β precursor protein, critical in Alzheimer disease physiopathology. Interestingly, two distinct ITM2B mutations, both resulting in a longer protein product, had already been reported in two large autosomal dominant families with Alzheimer-like dementia but never in subjects with isolated retinal diseases. These findings should better define pathogenic mechanism(s) associated with ITM2B mutations underlying dementia or retinal disease and add a new candidate to the list of genes involved in inherited retinal dystrophies.

Thinking laterally about neurodegenerative proteinopathies

Many neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, Huntington's disease, and frontotemporal dementia, are proteinopathies that are associated with the aggregation and accumulation of misfolded proteins. While remarkable progress has been made in understanding the triggers of these conditions, several challenges have hampered the translation of preclinical therapies targeting pathways downstream of the initiating proteinopathies. Clinical trials in symptomatic patients using therapies directed toward initiating trigger events have met with little success, prompting concerns that such therapeutics may be of limited efficacy when used in advanced stages of the disease rather than as prophylactics. Herein, we discuss gaps in our understanding of the pathological processes downstream of the trigger and potential strategies to identify common features of the downstream degenerative cascade in multiple CNS proteinopathies, which could potentially lead to the development of common therapeutic targets for multiple disorders.

Abundant pyroglutamate-modified ABri and ADan peptides in extracellular and vascular amyloid deposits in familial British and Danish dementias

Familial British and familial Danish dementia (FDD) are progressive neurodegenerative disorders characterized by cerebral deposition of the amyloidogenic peptides ABri and ADan, respectively. These amyloid peptides start with an N-terminal glutamate residue, which can be posttranslationally converted into a pyroglutamate (pGlu) modified form, a mechanism which has been extensively described to be relevant for amyloid-beta (Aβ) peptides in Alzheimer's disease. Like pGlu-Aβ peptides, pGlu-ABri peptides have an increased aggregation propensity and show higher toxicity on human neuroblastoma cells as their nonmodified counterparts. We have generated novel N-terminal specific antibodies detecting the pGlu-modified forms of ABri and ADan peptides. With these antibodies we were able to identify abundant extracellular amyloid plaques, vascular, and parenchymal deposits in human familial British dementia and FDD brain tissue, and in a mouse model for FDD. Double-stainings using C-terminal specific antibodies in human samples revealed that highly aggregated pGlu-ABri and pGlu-ADan peptides are mainly present in plaque cores and central vascular deposits, leading to the assumption that these peptides have seeding properties. Furthermore, in an FDD-mouse model ADan peptides were detected in presynaptic terminals of the hippocampus where they might contribute to impaired synaptic transmission. These similarities of ABri and ADan to Aβ in Alzheimer's disease suggest that the posttranslational pGlu-modification of amyloid peptides might represent a general pathological mechanism leading to increased aggregation and toxicity in these forms of degenerative dementias.

Proteomic characterization of a mouse model of familial Danish dementia

A dominant mutation in the ITM2B/BRI2 gene causes familial Danish dementia (FDD) in humans. To model FDD in animal systems, a knock-in approach was recently implemented in mice expressing a wild-type and mutant allele, which bears the FDD-associated mutation. Since these FDD(KI) mice show behavioural alterations and impaired synaptic function, we characterized their synaptosomal proteome via two-dimensional differential in-gel electrophoresis. After identification by nanoliquid chromatography coupled to electrospray-linear ion trap tandem mass spectrometry, the differentially expressed proteins were classified according to their gene ontology descriptions and their predicted functional interactions. The Dlg4/Psd95 scaffold protein and additional signalling proteins, including protein phosphatases, were revealed by STRING analysis as potential players in the altered synaptic function of FDD(KI) mice. Immunoblotting analysis finally demonstrated the actual downregulation of the synaptosomal scaffold protein Dlg4/Psd95 and of the dual-specificity phosphatase Dusp3 in the synaptosomes of FDD(KI) mice.

Cerebral amyloid angiopathy: a systematic review

Cerebral amyloid angiopathy (CAA) is a disorder characterized by amyloid deposition in the walls of leptomeningeal and cortical arteries, arterioles, and less often capillaries and veins of the central nervous system. CAA occurs mostly as a sporadic condition in the elderly, its incidence associating with advancing age. All sporadic CAA cases are due to deposition of amyloid-β, originating from proteolytic cleavage of the Amyloid Precursor Protein. Hereditary forms of CAA are generally familial (and therefore rare in the general population), more severe and earlier in onset. CAA-related lobar intracerebral hemorrhage is the most well-studied clinical condition associated with brain amyloid deposition. Despite ever increasing understanding of CAA pathogenesis and availability of reliable clinical and diagnostic tools, preventive and therapeutic options remain very limited. Further research efforts are required in order to identify biological targets for novel CAA treatment strategies. We present a systematic review of existing evidence regarding the epidemiology, genetics, pathogenesis, diagnosis and clinical management of CAA.

Anti-aβ therapeutics in Alzheimer's disease: the need for a paradigm shift

Most current Alzheimer's disease (AD) therapies in advanced phases of development target amyloid β-peptide (Aβ) production, aggregation, or accumulation. Translational models suggest that anti-Aβ therapies may be highly effective if tested as agents to prevent or delay development of the disease or as therapies for asymptomatic patients with very early signs of AD pathology. However, anti-Aβ therapeutics are currently being tested in symptomatic patients where they are likely to be much less effective or ineffective. The lack of alignment between human clinical studies and preclinical studies, together with predictions about optimal trial design based on our understanding of the initiating role of Aβ aggregates in AD, has created a treatment versus prevention dilemma. In this perspective, we discuss why it is imperative to resolve this dilemma and suggest ways for moving forward in the hopes of enhancing the development of truly effective AD therapeutics.

Cognitive impairment of vascular origin: neuropathology of cognitive impairment of vascular origin

The term cognitive impairment of vascular origin is used to designate global cognitive deficits as well as focal neurological deficits such as aphasia, apraxia and agnosia of vascular/circulatory origin. It has been useful for identifying early clinical and neuroradiological alterations that might permit therapeutic strategies geared to curbing the progression of cerebrovascular disease. Multi-infarct encephalopathy, infarcts in strategic areas, lacunae and lacunar status, Binswanger's encephalopathy, hippocampal sclerosis, cortical granular atrophy and watershed infarcts are common lesions. Hypertension and vascular diseases such as arteriosclerosis, small blood vessel disease, inflammatory diseases of the blood vessels, Sneddon syndrome, cerebral amyloid angiopathies, cerebral autosomic dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), and Maeda's syndrome are causative of cognitive impairment of vascular origin. Other less common causes are hereditary endotheliopathy with retinopathy, neuropathy and strokes (HERNS), cerebro-retinian vasculopathy (CRV), hereditary vascular retinopathy (HVR) (all three linked to 3p21.1-p21.3), hereditary infantile hemiparesis with arteriolar retinopathy and leukoencephalopathy (HIHRATL) (not linked to 3p21), fibromuscular dysplasia, and moya-moya disease. Lack of uniformity of clinical manifestations, the variety of vascular diseases and circulatory factors, the diverse, but often convergent, neuropathological substrates, and the common association with unrelated neurodegenerative diseases in the elderly, make it hard to assume a single clinical approach in the diagnosis and treatment of cognitive impairment of vascular origin. Rather, environmental and genetic risk factors, underlying vascular diseases, associated systemic, metabolic and neurodegenerative diseases and identification of extent and distribution of lesions with morphological and functional neuroimaging methods should be applied in every individual patient.

CEREBRAL AMYLOID ANGIOPATHY AND ALZHEIMER'S DISEASE

Cerebral amyloid angiopathy (CAA) is increasingly recognized as a major contributor of Alzheimer's disease (AD) pathogenesis. To date, vascular deposits and not parenchymal plaques appear more sensitive predictors of dementia. Amyloid deposition in and around cerebral blood vessels plays a central role in a series of response mechanisms that lead to changes in the integrity of the blood-brain barrier, extravasations of plasma proteins, edema formation, release of inflammatory mediators and matrix metalloproteases which, in turn, produce partial degradation of the basal lamina with the potential to develop hemorrhagic complications. The progressive buildup of amyloid deposits in and around blood vessels chronically limits blood supply and causes focal deprivation of oxygen, triggering a secondary cascade of metabolic events several of which involve the generation of nitrogen and oxygen free radicals with consequent oxidative stress and cell toxicity. Many aspects of CAA in early- and late-onset AD -the special preference of Aβ40 to deposit in the vessel walls, the favored vascular compromise associated with many Aβ genetic variants, the puzzling observation that some of these vasculotropic variants solely manifest with recurrent hemorrhagic episodes while others are mainly associated with dementia- await clarification. Non-Aβ cerebral amyloidoses reinforce the viewpoint that plaque burden is not indicative of dementia while highlighting the relevance of nonfibrillar lesions and vascular involvement in the disease pathogenesis. The lessons learned from the comparative study of Aβ and non-Aβ cerebral amyloidosis provide new avenues and alternative models to study the role of amyloid in the molecular basis of neurodegeneration.

Cerebral amyloidosis: amyloid subunits, mutants and phenotypes

Cerebral amyloid diseases are part of a complex group of chronic and progressive entities bracketed together under the common denomination of protein folding disorders and characterized by the intra- and extracellular accumulation of fibrillar aggregates. Of the more than 25 unrelated proteins known to produce amyloidosis in humans only about a third of them are associated with cerebral deposits translating in cognitive deficits, dementia, stroke, cerebellar and extrapyramidal signs, or a combination thereof. The familial forms reviewed herein, although infrequent, provide unique paradigms to examine the role of amyloid in the mechanism of disease pathogenesis and to dissect the link between vascular and parenchymal amyloid deposition and their differential contribution to neurodegeneration.

Isolation and biochemical characterization of amyloid plaques and paired helical filaments

Extracellular deposits of amyloid fibrils in the form of parenchymal plaques and cerebrovascular lesions, as well as intracellular accumulation of paired-helical filaments in the form of neurofibrillary tangles (NFT) in selected neuronal populations are the main neuropathologic hallmarks of Alzheimer's disease. Amyloid fibrils composed of polymeric structures of the amyloid-beta (Abeta) concentrate at the center of senile plaques and accumulate in the walls of cerebral blood vessels, exhibiting extensive Congo red/thioflavin S staining. Intraneuronal NFT are composed of building blocks of aberrantly hyperphosphorylated species of the microtubule-associated protein tau, which accumulate in the perinuclear cytoplasm of vulnerable neurons in the form of paired helical filaments (PHF). This unit presents a variety of protocols for the isolation, biochemical analysis, and characterization of amyloid fibrils and neurofibrillary tangles.

Genetics and molecular pathogenesis of sporadic and hereditary cerebral amyloid angiopathies

In cerebral amyloid angiopathy (CAA), amyloid fibrils deposit in walls of arteries, arterioles and less frequently in veins and capillaries of the central nervous system, often resulting in secondary degenerative vascular changes. Although the amyloid-beta peptide is by far the commonest amyloid subunit implicated in sporadic and rarely in hereditary forms of CAA, a number of other proteins may also be involved in rare familial diseases in which CAA is also a characteristic morphological feature. These latter proteins include the ABri and ADan subunits in familial British dementia and familial Danish dementia, respectively, which are also known under the umbrella term BRI2 gene-related dementias, variant cystatin C in hereditary cerebral haemorrhage with amyloidosis of Icelandic-type, variant transthyretins in meningo-vascular amyloidosis, disease-associated prion protein (PrP(Sc)) in hereditary prion disease with premature stop codon mutations and mutated gelsolin (AGel) in familial amyloidosis of Finnish type. In this review, the characteristic morphological features of the different CAAs is described and the implication of the biochemical, genetic and transgenic animal data for the pathogenesis of CAA is discussed.

BRI2 (ITM2b) inhibits Abeta deposition in vivo

Analyses of the biologic effects of mutations in the BRI2 (ITM2b) and the amyloid beta precursor protein (APP) genes support the hypothesis that cerebral accumulation of amyloidogenic peptides in familial British and familial Danish dementias and Alzheimer's disease (AD) is associated with neurodegeneration. We have used somatic brain transgenic technology to express the BRI2 and BRI2-Abeta1-40 transgenes in APP mouse models. Expression of BRI2-Abeta1-40 mimics the suppressive effect previously observed using conventional transgenic methods, further validating the somatic brain transgenic methodology. Unexpectedly, we also find that expression of wild-type human BRI2 reduces cerebral Abeta deposition in an AD mouse model. Additional data indicate that the 23 aa peptide, Bri23, released from BRI2 by normal processing, is present in human CSF, inhibits Abeta aggregation in vitro and mediates its anti-amyloidogenic effect in vivo. These studies demonstrate that BRI2 is a novel mediator of Abeta deposition in vivo.

Preamyloid lesions and cerebrovascular deposits in the mechanism of dementia: lessons from non-beta-amyloid cerebral amyloidosis

The importance of amyloid plaques in the pathogenesis of dementia is usually centered on beta-amyloid (Abeta) and its role in Alzheimer's disease (AD). However, since fibrillar plaques correlate poorly with neurodegeneration, challenging their importance in the mechanism(s) of dementia, investigators turned their focus to the importance of soluble oligomers and the role of preamyloid and cerebrovascular deposits. Two non-Abeta cerebral amyloidoses, familial British and Danish dementias (FBD and FDD), share many aspects of AD, including cognitive impairment and the presence of neurofibrillary tangles in limbic areas. The lack of compact plaques in FDD and in many areas in FBD further questions the importance of these lesions in the mechanism of dementia. The main components of the deposits--ABri and ADan--are structurally unrelated to Abeta and yet they all have a high tendency to oligomerize and assemble into amyloid fibrils in vitro and form ion-like channels in lipid membranes. Thus, different amyloid species have the capability to induce similar neuropathological changes, which are neither exclusive for Abeta nor dependent on the presence of compact plaques. These findings reaffirm the notion that non-Abeta amyloidoses constitute alternative models to study the role of preassembled amyloid subunits in neuronal death.

Expression of BRI2 mRNA and protein in normal human brain and familial British dementia: its relevance to the pathogenesis of disease

INTRODUCTION

Two different disease-specific mutations in the BRI2 gene, situated on chromosome 13, have been identified as giving rise to familial British dementia (FBD) and familial Danish dementia (FDD). Each mutation results in extension of the open reading frame generating the disease-specific precursor proteins which are cleaved by furin-like proteolysis releasing the amyloidogenic C-terminal peptides ABri and ADan in FBD and FDD, respectively.

MATERIAL AND METHODS

To understand the mechanism of the formation of amyloid lesions in FBD, we studied the origin of the precursor proteins and furin in the human brain. We used control brains, cases of sporadic Alzheimer's disease (AD), variant AD with cotton wool plaques and FBD to study BRI2 mRNA expression using in situ hybridization. Furin and BRI2 protein expression was investigated using Western blotting and immunohistochemistry.

RESULTS

BRI2 mRNA and BRI2 protein are widely expressed primarily by neurones and glia and are deposited in the amyloid lesions in FBD. They were, however, not expressed by cerebrovascular components. Furin expression showed a similar pattern except that it was also present in cerebrovascular smooth muscle cells.

CONCLUSIONS

These findings suggest that neurones and glia and are a major source of BRI2 protein and that in FBD, the mutated precursor protein may undergo furin cleavage within neurones to produce the amyloid peptide ABri. The failure to demonstrate BRI2 in blood vessels under the conditions tested suggests that vascular amyloid peptide production does not contribute significantly to cerebral amyloid angiopathy (CAA) in FBD and FDD, lending indirect support to the drainage hypothesis of CAA.

Solubilized cystatin C amyloid is cytotoxic to cultured human cerebrovascular smooth muscle cells

Cerebral amyloid angiopathy (CAA) is characterized by the accumulation of amyloid within arteries of the cerebral cortex and leptomeninges. This condition is age related, especially prevalent in Alzheimer's disease (AD) and the main feature of certain hereditary disorders. The vascular smooth muscle cells (VSMC) appear to play a vital role in the development of CAA and have been found to produce the amyloid beta precursor protein (AbetaPP) and process it to Abeta the major component of most CAA amyloid. Moreover, synthesized Abeta has proven to be toxic to cerebral VSMC in culture possibly explaining the disintegration and disappearance of the muscle cells from affected cerebral blood vessels seen in CAA. An aggressive and extremely rare form of CAA, known as Hereditary Cerebral Hemorrhage With Amyloidosis-Icelandic Type (HCHWA-I), exhibits this withdrawal of VSMC as amyloid accumulates in the vessel wall. However, the amyloid in HCHWA-I is made from a variant of cystatin C (L68Q) instead of the more common Abeta. To evaluate possible cytotoxicity in this condition solubilized cystatin C amyloid extracted from HCHWA-I leptomeninges was applied to cerebral smooth muscle cells in culture and was found to kill the cells.

Las amiloidosis cerebrales y las demencias

Amyloid deposit in the brain causes neurologicaldiseases characterized by dementia. These depositsare constituted by fibrilar proteins with beta-planarshape whose origin is due to mutations, infectionsor exogenous alterations. Treatment of cerebralamyloid angiopathy depends on the cause and atpresent, the manipulation of the synthesis of theresponsible peptides, their chemical solubilizationor extraction outside of the nervous system, arebeing investigated.

Human herpesvirus 6 and multiple sclerosis: a one-year follow-up study

BACKGROUND

This study was undertaken in order to investigate the possible relation of HHV-6 and EBV in relapsing-remitting MS (RRMS).

MATERIALS AND METHODS

A one-year follow up study was performed analysing peripheral blood mononuclear cells and serum samples of 57 patients with RRMS and 57 healthy blood donors (HBD) by a quantitative real time PCR, to detect HHV-6 and EBV. Clinical data (starting age and EDSS increase) were collected.

RESULTS

We did not find any statistically significant difference for EBV between RRMS patients and HBD. Regarding HHV-6: i) There was a higher prevalence of HHV-6 in RRMS patients than in controls: 80.7% versus 29.8% respectively. ii) HHV-6 active replication seems to be related to exacerbations. iii) Only variant A was detected among RRMS patients with HHV-6 active replication. iv) Although some difference was found when we compared clinical data in RRMS patients with and without HHV-6 active replication, the results did not reach statistical significance.

CONCLUSIONS

A higher HHV-6A frequency of active infection (reactivation or new infection) would lead to a more frequent exposure of HHV-6A antigens to the immune system of RRMS patients; this active replication of HHV-6A seems to be specifically related with the exacerbations in a subset of RRMS patients.