Zur Amyloidfrage

George Budd and His Contribution to the Early History of Amyloid Disease

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Challenges in sample preparation and structure determination of amyloids by cryo-EM

Amyloids share a common architecture but play disparate biological roles in processes ranging from bacterial defense mechanisms to protein misfolding diseases. Their structures are highly polymorphic, which makes them difficult to study by X-ray diffraction or NMR spectroscopy. Our understanding of amyloid structures is due in large part to recent advances in the field of cryo-EM, which allows for determining the polymorphs separately. In this review, we highlight the main stepping stones leading to the substantial number of high-resolution amyloid fibril structures known today as well as recent developments regarding automation and software in cryo-EM. We discuss that sample preparation should move closer to physiological conditions to understand how amyloid aggregation and disease are linked. We further highlight new approaches to address heterogeneity and polymorphism of amyloid fibrils in EM image processing and give an outlook to the upcoming challenges in researching the structural biology of amyloids.

Hierarchical chemical determination of amyloid polymorphs in neurodegenerative disease

Amyloid aggregation, which disrupts protein homeostasis, is a common pathological event occurring in human neurodegenerative diseases (NDs). Numerous evidences have shown that the structural diversity, so-called polymorphism, is decisive to the amyloid pathology and is closely associated with the onset, progression, and phenotype of ND. But how could one protein form so many stable structures? Recently, atomic structural evidence has been rapidly mounting to depict the involvement of chemical modifications in the amyloid fibril formation. In this Perspective, we aim to present a hierarchical regulation of chemical modifications including covalent post-translational modifications (PTMs) and noncovalent cofactor binding in governing the polymorphic amyloid formation, based mainly on the latest α-synuclein and Tau fibril structures. We hope to emphasize the determinant role of chemical modifications in amyloid assembly and pathology and to evoke chemical biological approaches to lead the fundamental and therapeutic research on protein amyloid state and the associated NDs.

Interactions between Amyloid-Β Proteins and Human Brain Pericytes: Implications for the Pathobiology of Alzheimer's Disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disease that is the most common cause of dementia, especially among aging populations. Despite advances in AD research, the underlying cause and the discovery of disease-modifying treatments have remained elusive. Two key features of AD pathology are the aberrant deposition of amyloid beta (amyloid-β or Aβ) proteins in the brain parenchyma and Aβ toxicity in brain pericytes of the neurovascular unit/blood–brain barrier (NVU/BBB). This toxicity induces oxidative stress in pericytes and leads to capillary constriction. The interaction between pericytes and Aβ proteins results in the release of endothelin-1 in the pericytes. Endothelin-1 interacts with ET_A receptors to cause pericyte contraction. This pericyte-mediated constriction of brain capillaries can cause chronic hypoperfusion of the brain microvasculature, subsequently leading to the neurodegeneration and cognitive decline observed in AD patients. The interaction between Aβ proteins and brain pericytes is largely unknown and requires further investigation. This review provides an updated overview of the interaction between Aβ proteins with pericytes, one the most significant and often forgotten cellular components of the BBB and the inner blood–retinal barrier (IBRB). The IBRB has been shown to be a window into the central nervous system (CNS) that could allow the early diagnosis of AD pathology in the brain and the BBB using modern photonic imaging systems such as optical coherence tomography (OCT) and two-photon microscopy. In this review, I explore the regulation of Aβ proteins in the brain parenchyma, their role in AD pathobiology, and their association with pericyte function. This review discusses Aβ proteins and pericytes in the ocular compartment of AD patients as well as strategies to rescue or protect pericytes from the effects of Aβ proteins, or to replace them with healthy cells.

A new era for understanding amyloid structures and disease

The aggregation of proteins into amyloid fibrils and their deposition into plaques and intracellular inclusions is the hallmark of amyloid disease. The accumulation and deposition of amyloid fibrils, collectively known as amyloidosis, is associated with many pathological conditions that can be associated with ageing, such as Alzheimer disease, Parkinson disease, type II diabetes and dialysis-related amyloidosis. However, elucidation of the atomic structure of amyloid fibrils formed from their intact protein precursors and how fibril formation relates to disease has remained elusive. Recent advances in structural biology techniques, including cryo-electron microscopy and solid-state NMR spectroscopy, have finally broken this impasse. The first near-atomic-resolution structures of amyloid fibrils formed in vitro, seeded from plaque material and analysed directly ex vivo are now available. The results reveal cross-β structures that are far more intricate than anticipated. Here, we describe these structures, highlighting their similarities and differences, and the basis for their toxicity. We discuss how amyloid structure may affect the ability of fibrils to spread to different sites in the cell and between organisms in a prion-like manner, along with their roles in disease. These molecular insights will aid in understanding the development and spread of amyloid diseases and are inspiring new strategies for therapeutic intervention.

Congo Red and amyloids: history and relationship

Staining with Congo Red (CR) is a qualitative method used for the identification of amyloids in vitro and in tissue sections. However, the drawbacks and artefacts obtained when using this dye can be found both in vitro and in vivo. Analysis of scientific data from previous studies shows that CR staining alone is not sufficient for confirmation of the amyloid nature of protein aggregates in vitro or for diagnosis of amyloidosis in tissue sections. In the present paper, we describe the characteristics and limitations of other methods used for amyloid studies. Our historical review on the use of CR staining for amyloid studies may provide insight into the pitfalls and caveats related to this technique for researchers considering using this dye.

Biomolecular Assemblies: Moving from Observation to Predictive Design

Biomolecular assembly is a key driving force in nearly all life processes, providing structure, information storage, and communication within cells and at the whole organism level. These assembly processes rely on precise interactions between functional groups on nucleic acids, proteins, carbohydrates, and small molecules, and can be fine-tuned to span a range of time, length, and complexity scales. Recognizing the power of these motifs, researchers have sought to emulate and engineer biomolecular assemblies in the laboratory, with goals ranging from modulating cellular function to the creation of new polymeric materials. In most cases, engineering efforts are inspired or informed by understanding the structure and properties of naturally occurring assemblies, which has in turn fueled the development of predictive models that enable computational design of novel assemblies. This Review will focus on selected examples of protein assemblies, highlighting the story arc from initial discovery of an assembly, through initial engineering attempts, toward the ultimate goal of predictive design. The aim of this Review is to highlight areas where significant progress has been made, as well as to outline remaining challenges, as solving these challenges will be the key that unlocks the full power of biomolecules for advances in technology and medicine.

Disruptive membrane interactions of alpha-synuclein aggregates

Alpha synuclein (αS) is a ~14 kDa intrinsically disordered protein. Decades of research have increased our knowledge on αS yet its physiological function remains largely elusive. The conversion of monomeric αS into oligomers and amyloid fibrils is believed to play a central role of the pathology of Parkinson's disease (PD). It is becoming increasingly clear that the interactions of αS with cellular membranes are important for both αS's functional and pathogenic actions. Therefore, understanding interactions of αS with membranes seems critical to uncover functional or pathological mechanisms. This review summarizes our current knowledge of how physicochemical properties of phospholipid membranes affect the binding and aggregation of αS species and gives an overview of how post-translational modifications and point mutations in αS affect phospholipid membrane binding and protein aggregation. We discuss the disruptive effects resulting from the interaction of αS aggregate species with membranes and highlight current approaches and hypotheses that seek to understand the pathogenic and/or protective role of αS in PD.

Heparan sulfate S-domains and extracellular sulfatases (Sulfs): their possible roles in protein aggregation diseases

Highly sulfated domains of heparan sulfate (HS), also known as HS S-domains, consist of repeated trisulfated disaccharide units [iduronic acid (2S)-glucosamine (NS, 6S)-]. The expression of HS S-domains at the cell surface is determined by two mechanisms: tightly regulated biosynthetic machinery and enzymatic remodeling by extracellular endoglucosamine 6-sulfatases, Sulf-1 and Sulf-2. Intracellular or extracellular deposits of misfolded and aggregated proteins are characteristic of protein aggregation diseases. Although proteins can aggregate alone, deposits of protein aggregates in vivo contain a number of proteinaceous and non-protein components. HS S-domains are one non-protein component of these aggregated deposits. HS S-domains are considered to be critical for signal transduction of several growth factors and several disease conditions, such as tumor progression, but their roles in protein aggregation diseases are not yet fully understood. This review summarizes the current understanding of the possible roles of HS S-domains and Sulfs in the formation and cytotoxicity of protein aggregates.

Amyloids and prions in plants: Facts and perspectives

Amyloids represent protein fibrils that have highly ordered structure with unique physical and chemical properties. Amyloids have long been considered lethal pathogens that cause dozens of incurable diseases in humans and animals. Recent data show that amyloids may not only possess pathogenic properties but are also implicated in the essential biological processes in a variety of prokaryotes and eukaryotes. Functional amyloids have been identified in archaea, bacteria, fungi, and animals, including humans. Plants are one of the most poorly studied groups of organisms in the field of amyloid biology. Although amyloid properties have not been shown under native conditions for any plant protein, studies demonstrating amyloid properties for a set of plant proteins in vitro or in heterologous systems in vivo have been published in recent years. In this review, we systematize the data on the amyloidogenic proteins of plants and their functions and discuss the perspectives of identifying novel amyloids using bioinformatic and proteomic approaches.

Prions, amyloids, and RNA: Pieces of a puzzle

Amyloids are protein aggregates consisting of fibrils rich in β-sheets. Growth of amyloid fibrils occurs by the addition of protein molecules to the tip of an aggregate with a concurrent change of a conformation. Thus, amyloids are self-propagating protein conformations. In certain cases these conformations are transmissible / infectious; they are known as prions. Initially, amyloids were discovered as pathological extracellular deposits occurring in different tissues and organs. To date, amyloids and prions have been associated with over 30 incurable diseases in humans and animals. However, a number of recent studies demonstrate that amyloids are also functionally involved in a variety of biological processes, from biofilm formation by bacteria, to long-term memory in animals. Interestingly, amyloid-forming proteins are highly overrepresented among cellular factors engaged in all stages of mRNA life cycle: from transcription and translation, to storage and degradation. Here we review rapidly accumulating data on functional and pathogenic amyloids associated with mRNA processing, and discuss possible significance of prion and amyloid networks in the modulation of key cellular functions.

Predicting Amyloidogenic Proteins in the Proteomes of Plants

Amyloids are protein fibrils with characteristic spatial structure. Though amyloids were long perceived to be pathogens that cause dozens of incurable pathologies in humans and mammals, it is currently clear that amyloids also represent a functionally important form of protein structure implicated in a variety of biological processes in organisms ranging from archaea and bacteria to fungi and animals. Despite their social significance, plants remain the most poorly studied group of organisms in the field of amyloid biology. To date, amyloid properties have only been demonstrated in vitro or in heterologous systems for a small number of plant proteins. Here, for the first time, we performed a comprehensive analysis of the distribution of potentially amyloidogenic proteins in the proteomes of approximately 70 species of land plants using the Waltz and SARP (Sequence Analysis based on the Ranking of Probabilities) bioinformatic algorithms. We analyzed more than 2.9 million protein sequences and found that potentially amyloidogenic proteins are abundant in plant proteomes. We found that such proteins are overrepresented among membrane as well as DNA- and RNA-binding proteins of plants. Moreover, seed storage and defense proteins of most plant species are rich in amyloidogenic regions. Taken together, our data demonstrate the diversity of potentially amyloidogenic proteins in plant proteomes and suggest biological processes where formation of amyloids might be functionally important.

Lessons learned from protein aggregation: toward technological and biomedical applications

The close relationship between protein aggregation and neurodegenerative diseases has been the driving force behind the renewed interest in a field where biophysics, neurobiology and nanotechnology converge in the study of the aggregate state. On one hand, knowledge of the molecular principles that govern the processes of protein aggregation has a direct impact on the design of new drugs for high-incidence pathologies that currently can only be treated palliatively. On the other hand, exploiting the benefits of protein aggregation in the design of new nanomaterials could have a strong impact on biotechnology. Here we review the contributions of our research group on novel neuroprotective strategies developed using a purely biophysical approach. First, we examine how doxycycline, a well-known and innocuous antibiotic, can reshape α-synuclein oligomers into non-toxic high-molecular-weight species with decreased ability to destabilize biological membranes, affect cell viability and form additional toxic species. This mechanism can be exploited to diminish the toxicity of α-synuclein oligomers in Parkinson's disease. Second, we discuss a novel function in proteostasis for extracellular glyceraldehyde 3-phosphate dehydrogenase (GAPDH) in combination with a specific glycosaminoglycan (GAG) present in the extracellular matrix. GAPDH, by changing its quaternary structure from a tetramer to protofibrillar assembly, can kidnap toxic species of α-synuclein, and thereby interfere with the spreading of the disease. Finally, we review a brighter side of protein aggregation, that of exploiting the physicochemical advantages of amyloid aggregates as nanomaterials. For this, we designed a new generation of insoluble biocatalysts based on the binding of photo-immobilized enzymes onto hybrid protein:GAG amyloid nanofibrils. These new nanomaterials can be easily functionalized by attaching different enzymes through dityrosine covalent bonds.

Historical and Current Concepts of Fibrillogenesis and In vivo Amyloidogenesis: Implications of Amyloid Tissue Targeting

Historical and current concepts of in vitro fibrillogenesis are considered in the light of disorders in which amyloid is deposited at anatomic sites remote from the site of synthesis of the corresponding precursor protein. These clinical conditions set constraints on the interpretation of information derived from in vitro fibrillogenesis studies. They suggest that in addition to kinetic and thermodynamic factors identified in vitro, fibrillogenesis in vivo is determined by site specific factors most of which have yet to be identified.

Exploring the structure and formation mechanism of amyloid fibrils by Raman spectroscopy: a review

Amyloid fibrils are β-sheet rich protein aggregates that are strongly associated with various neurodegenerative diseases. Raman spectroscopy has been broadly utilized to investigate protein aggregation and amyloid fibril formation and has been shown to be capable of revealing changes in secondary and tertiary structures at all stages of fibrillation. When coupled with atomic force (AFM) and scanning electron (SEM) microscopies, Raman spectroscopy becomes a powerful spectroscopic approach that can investigate the structural organization of amyloid fibril polymorphs. In this review, we discuss the applications of Raman spectroscopy, a unique, label-free and non-destructive technique for the structural characterization of amyloidogenic proteins, prefibrilar oligomers, and mature fibrils.

Divergent effect of glycosaminoglycans on the in vitro aggregation of serum amyloid A

Serum amyloid A (SAA) is an apolipoprotein involved in poorly understood roles in inflammation. Upon trauma, hepatic expression of SAA rises 1000 times the basal levels. In the case of inflammatory diseases like rheumatoid arthritis, there is a risk for deposition of SAA fibrils in various organs leading to Amyloid A (AA) amyloidosis. Although the amyloid deposits in AA amyloidosis accumulate with the glycosaminoglycan (GAG) heparan sulfate, the role GAGs play in the function and pathology of SAA is an enigma. It has been shown that GAG sulfation is a contributing factor in protein fibrillation and for co-aggregating with a plethora of amyloidogenic proteins. Herein, the effects of heparin, heparan sulfate, hyaluronic acid, chondroitin sulfate A, and heparosan on the oligomerization and aggregation properties of pathogenic mouse SAA1.1 were investigated. Delipidated SAA was used to better understand the interactions between SAA and GAGs without the complicating involvement of lipids. The results revealed-to varying degrees-that all GAGs accelerated SAA1.1 aggregation, but had variable effects on its fibrillation. Heparan sulfate, hyaluronic acid, and heparosan did not affect much the fibrillation of SAA1.1. In contrast, chondroitin sulfate A blocked SAA fibril formation and facilitated the formation of spherical aggregates of various sizes. Interestingly, heparin caused formation of spherical SAA1.1 aggregates of various sizes, vast amounts of thin protofibrils, and few long fibrils of various heights. These results suggest that GAGs may have an intrinsic and divergent influence on the aggregation and fibrillation of HDL-free SAA1.1 in vivo, with functional and pathological implications.

Proteins and peptides as biological nanowires: towards biosensing devices

The current landscape of nanotechnology is such that attention is being given to those materials that self-assemble, as a mode of "bottom-up" fabrication of nanomaterials. The field of nanotubes and nanowires has long been dominated by carbon nanotubes and inorganic materials. However in more recent years, the search for materials with desirable properties, such as self-assembly, has unsurprisingly led to the biological world, where functional nanoscale biomolecular assemblies are in abundance.Potential has been seen for a number of these assemblies to be translated into functional nanomaterials. The early days of bionanotechnology saw a lot of attention given to DNA molecules as nanowires, and proteins and peptides have now also been seen to have promise in this area. With most of the biological structures investigated having low conductivity in the native state, the use of biomolecules as templates for the formation of metallic and semiconductor nanowires has been the direction taken.This chapter will discuss the use of various biomolecules and biomolecular assemblies as nanowires, with a particular emphasis on proteins, beginning with an introduction into the field of nanotubes and nanowires. Many applications are now recognized for nanowires, but for brevity, this chapter will focus solely on their use as biosensors, using glucose sensors as a case study.

Amyloid fibrils: abnormal protein assembly

Amyloid refers to the abnormal fibrous, extracellular, proteinaceous deposits found in organs and tissues. Amyloid is insoluble and is structurally dominated by beta-sheet structure. Unlike other fibrous proteins it does not commonly have a structural, supportive or motility role but is associated with the pathology seen in a range of diseases known as the amyloidoses. These diseases include Alzheimer's, the spongiform encephalopathies and type II diabetes, all of which are progressive disorders with associated high morbidity and mortality. Not surprisingly, research into the physicochemical properties of amyloid and its formation is currently intensely pursued. In this chapter we will highlight the key scientific findings and discuss how the stability of amyloid fibrils impacts on bionanotechnology.

The role of novel chitin-like polysaccharides in Alzheimer disease

While controversy over the role of carbohydrates in amyloidosis has existed since the initial recognition of amyloid, current understanding of the role of polysaccharides in the pathogenesis of amyloid deposition of Alzheimer disease and other amyloidoses is limited to studies of glyco-conjugates such as heparin sulfate proteoglycan. We hypothesized that polysaccharides may play a broader role in light of 1) the impaired glucose utilization in Alzheimer disease; 2) the demonstration of amylose in the Alzheimer disease brain; 3) the role of amyloid in Alzheimer disease pathogenesis. Specifically, as with glucose polymers (amyloid), we wanted to explore whether glucosamine polymers such as chitin were being synthesized and deposited as a result of impaired glucose utilization and aberrant hexosamine pathway activation. To this end, using calcofluor histochemistry, we recently demonstrated that amyloid plaques and blood vessels affected by amyloid angiopathy in subjects with sporadic and familial Alzheimer disease elicit chitin-type characteristics. Since chitin is a highly insoluble molecule and a substrate for glycan-protein interactions, chitin-like polysaccharides within the Alzheimer disease brain could provide a scaffolding for amyloid-beta deposition. As such, glucosamine may facilitate the process of amyloidosis, and /or provide neuroprotection in the Alzheimer disease brain.

Nanoimaging in protein-misfolding and -conformational diseases

Protein misfolding and the subsequent assembly of protein molecules into aggregates of various morphologies represent common mechanisms that link a number of important human diseases, known as protein-misfolding diseases. The current list of these disorders includes (but is not limited to) numerous neurodegenerative diseases, cataracts, arthritis, medullary carcinoma of the thyroid, late-onset diabetes mellitus, symptomatic (hemodialysis-related) beta(2)-microglobulin amyloidosis, arthritis and many other systemic, localized and familial amyloidoses. Progress in understanding protein-misfolding pathologies and in potential rational drug design aimed at the inhibition or reversal of protein aggregation depends on our ability to study the details of the misfolding process, to follow the aggregation process and to see and analyze the structure and mechanical properties of the aggregated particles. Nanoimaging provides a method to monitor the aggregation process, visualize protein aggregates and analyze their properties and provides fundamental knowledge of key factors that lead to protein misfolding and self-assembly in various protein-misfolding pathologies, therefore advancing medicine dramatically.

Heparan sulfate as a therapeutic target in amyloidogenesis: prospects and possible complications

Amyloid formation in vivo is a much more complicated process than studies of in vitro protein/peptide fibrillogenesis would lead one to believe. Amyloidogenesis in vivo involves multiple components, some no less important than the amyloidogenic protein/peptides themselves, and each of these components, and its role in the pathogenetic steps toward amyloid deposition could, theoretically, be a therapeutic target. Herein we use the definition of amyloid as it was originally described, discuss the similarities and differences between amyloid in vivo and in vitro, address the potential role of the extracellular matrix in in vivo amyloidogenesis by focusing on a specific component, namely heparan sulfate proteoglycan, and describe studies illustrating that heparan sulfate is a valid target for anti-amyloid therapy. In light of experimental and recent clinical results obtained from studies addressing heparan sulfate's role in amyloid deposition additional novel anti-amyloid therapeutic targets will be proposed. Lastly, given the multiple roles that heparan sulfate plays in organ development, and organ and cell function, potential side effects of targeting heparan sulfate biosynthesis for therapeutic purposes are considered.

Glycosaminoglycans are part of amyloid fibrils: ultrastructural evidence in avian AA amyloid stained with cuprolinic blue and labeled with immunogold

In domestic brown layer fowl, reactive amyloidosis of internal organs, such as liver and spleen, and of the joints is a common disorder. In a variety of amyloid types including the AA-amyloid of the chicken, in addition to amyloid fibrils, proteoglycans and glycosaminoglycans (GAGs) are found on immunohistochemistry or after extraction. The aim of the present report is to study amyloid fibrils for the ultrastructural location of GAGs by cuprolinic blue staining and immunogold labeling. Rabbit antichicken AA antiserum was used for the immunogold labeling on conventionally embedded and cryoembedded liver tissue and revealed similar results. Therefore conventional blocks could be used for further analysis. Cuprolinic blue staining was performed on blocks of joint tissue in which clearly discernable rod-shaped glycoproteins were encountered in between collagen fibrils. Moreover, it appeared to stain larger deposits which might represent amyloid. Postlabeling with the immunogold method of the cuprolinic blue-stained tissue proved that cuprolinic blue positive fibrils represented AA-amyloid fibrils. Therefore, it was concluded that the GAGs which appeared to colocalize with the fibrillar microanatomy of amyloid, represent a structural part of the amyloid fibrils and that the avian amyloid fibrils may be considered as a pathological proteoglycan.

Protein folding pathology in domestic animals

Fibrillar proteins form structural elements of cells and the extracellular matrix. Pathological lesions of fibrillar microanatomical structures, or secondary fibrillar changes in globular proteins are well known. A special group concerns histologically amorphous deposits, amyloid. The major characteristics of amyloid are: apple green birefringence after Congo red staining of histological sections, and non-branching 7-10 nm thick fibrils on electron microscopy revealing a high content of cross beta pleated sheets. About 25 different types of amyloid have been characterised. In animals, AA-amyloid is the most frequent type. Other types of amyloid in animals represent: AIAPP (in cats), AApoAI, AApoAII, localised AL-amyloid, amyloid in odontogenic or mammary tumors and amyloid in the brain. In old dogs Abeta and in sheep APrPsc-amyloid can be encountered. AA-amyloidosis is a systemic disorder with a precursor in blood, acute phase serum amyloid A (SAA). In chronic inflammatory processes AA-amyloid can be deposited. A rapid crystallization of SAA to amyloid fibrils on small beta-sheeted fragments, the 'amyloid enhancing factor' (AEF), is known and the AEF has been shown to penetrate the enteric barrier. Amyloid fibrils can aggregate from various precursor proteins in vitro in particular at acidic pH and when proteolytic fragments are formed. Molecular chaperones influence this process. Tissue data point to amyloid fibrillogenesis in lysosomes and near cell surfaces. A comparison can be made of the fibrillogenesis in prion diseases and in enhanced AA-amyloidosis. In the reactive form, acute phase SAA is the supply of the precursor protein, whereas in the prion diseases, cell membrane proteins form a structural source. Abeta-amyloid in brain tissue of aged dogs showing signs of dementia forms a canine counterpart of senile dementia of the Alzheimer type (ccSDAT) in man. Misfolded proteins remain potential food hazards. Developments concerning prevention of amyloidogenesis and therapy of amyloid deposits are shortly commented.

Cerebral amyloid angiopathy: major contributor or decorative response to Alzheimer’s disease pathogenesis

Amyloid deposition within cerebral vessels, or cerebral amyloid angiopathy (CAA), is common in advanced age and even more common in Alzheimer's disease. CAA may be complicated by lobar intracerebral hemorrhage, while rare kindreds of autosomal dominant CAA also show propensity for intracerebral hemorrhage, due to germline mutations in specific amyloidogenic precursor proteins and apparent compromise of structural integrity of the blood vessel wall due to marked amyloid deposition. The relationship between cerebral amyloid angiopathy and cognitive dysfunction, however, is less clear. While cognitive dysfunction in familial CAA is likely related to prodigious amyloid deposits and vascular luminal compromise (e.g., hereditary cerebral hemorrhage with angiopathy-Dutch type (HCHWA-D)), cerebral amyloid angiopathy with intracerebral hemorrhage often presents sporadically in cognitively intact elderly patients. Moreover, while about 80% of subjects with Alzheimer's disease have demonstrable amyloid beta within blood vessel walls at autopsy, the vast majority of these fail to suffer clinically relevant intracerebral hemorrhage during life. The remaining 20% manage to progress and die of their disease with virtual no amyloid within blood vessels. Thus, the role of amyloid beta deposits in cerebral vessels as regards cognitive function on the one hand, and tendency for hemorrhage on the other, remain to be resolved for sporadic late onset Alzheimer's disease and CAA. Recent studies on transgenic APP23 mice suggest a relationship between passive immunization and amyloid angiopathy-associated cerebral hemorrhage, although the mechanism of hemorrhage was unclear from the data presented. We suggest that amyloid accumulation represents a response to chronic stress, and that the neurodegenerative process occurs at the neuronal level, encompassing oxidative stress and aberrant cell cycle activation. As such, CAA represents tissue homeostasis, such that an abrupt perturbation of this balance (e.g., amyloid beta immunization) is deleterious.

Amyloid in Alzheimer's disease and prion-related encephalopathies: studies with synthetic peptides

Deposition of amyloid-beta protein (beta A) in brain parenchyma and vessel walls is a major pathological feature of Alzheimer's disease (AD). In prion-related encephalopathies (PRE), too, an altered form of prion protein (PrPsc) forms amyloid fibrils and accumulates in the brain. In both conditions the amyloid deposition is accompanied by nerve cell loss, whose pathogenesis and molecular basis are not understood. Neuropathological, genetic and biochemical studies indicate a central role of beta A in the AD pathogenesis. Synthetic peptides homologous to beta A and its fragments contribute to investigate the mechanisms of beta A deposit formation and the role played by beta A in AD pathogenesis. The physicochemical studies on the beta-sheet conformation and self-aggregation properties of beta A peptides indicate the conditions and the factors influencing the formation of beta A deposits. The neurotoxic activity of beta A and its fragments support the causal relationship between beta A deposits and the neuropathological events in AD. Numerous studies were performed to clarify the mechanism of neuronal death induced by exposure to beta A peptides. A similar approach has been used to investigate the role of PrPsc in PRE; in these diseases, the association between accumulation of PrPsc and neuropathology is evident and numerous data indicate that PrPsc itself might be the infectious agent responsible for disease transmission. Thus, PrP peptides were used to investigate the pathogenic role of PrPsc in PRE and the conformational change responsible for the conversion PrPc to PrPsc that makes the molecule apparently infectious. In particular, we synthesized a peptide homologous to residues 106-126, an integral part of all abnormal PrP isoforms that accumulate in the brain of subjects' PRE. This peptide is fibrillogenic, has secondary structure largely composed of beta-sheet and proteinase-resistant properties, is neurotoxic and induces astrogliosis. In this review, we summarize and compare the data obtained with beta A and PrP peptides and analyze the significance in terms of amyloidogenic proteins and neurodegeneration.

Clinical and therapeutic aspects of AA amyloidosis

Approach to the management of AA amyloidosis complicating RA. (A) In case of proteinuria or loss of renal function a rectal biopsy or a subcutaneous fat biopsy is a suitable screening method for the detection of amyloidosis. If in any doubt, try to ascertain the diagnosis by renal biopsy. Adequate staining with alkaline Congo red and preferably immunohistochemical staining with anti-AA antibodies should be performed. Beware of renal pathology other than amyloidosis even in the presence of a positive rectal biopsy. (B) A vigorous attempt to control disease activity of the RA should be made in order to eliminate the production of SAA, an acute phase protein. The response to treatment should be monitored by serial measurements of CRP and preferably SAA. (C) The function of some vital organs should be evaluated: (a) endogenous creatinine clearance and the extent of proteinuria; (b) electrocardiogram and optional echocardiography; (c) thyroid function and adrenocortical function; (d) intestinal absorption tests; (e) optional--SAP scintigraphy and turnover studies. (D) Attention should be given to adequate supportive treatment: (a) blood pressure control; (b) treatment of intercurrent infections; (c) corticosteroids during major surgical procedures; (d) pay attention to the possible effect of NSAID on proteinuria and renal function. (E) In case of total renal failure or uncontrollable proteinuria: (a) consider the possibility of primary renal transplantation; (b) otherwise regular haemodialysis is indicated.

Proteoglycans in the pathogenesis of Alzheimer's disease and other amyloidoses

Proteoglycans and the amyloid P component are two constituents of amyloid that appear to be present regardless of the type of amyloid protein deposited, the extent of amyloid deposition and the tissue or organ involved. This article reviews the literature concerning proteoglycans and/or glycosaminoglycans in amyloidosis and describes recent studies which demonstrate their localization to the characteristic lesions of Alzheimer's disease and the amyloid plaques containing PrP protein in the prion diseases. Additionally, the possible interaction of proteoglycans with various amyloidogenic proteins, including the beta-amyloid protein in Alzheimer's disease is discussed. It is postulated that proteoglycans localized to a number of different amyloids play a common role in the pathogenesis of amyloidosis. Some of these hypothesized roles include 1) inducing amyloidogenic precursor proteins to form amyloid fibrils containing a predominant beta-pleated sheet structure, 2) influencing amyloid deposition to occur at specific anatomical sites within tissues and/or 3) aiding in prevention of amyloid degradation once amyloid has formed.

The potential significance of sulphated glycosaminoglycans as a common constituent of all amyloids: or, perhaps amyloid is not a misnomer

Amyloid is a generic term referring to a group of diseases in which proteinaceous tissue deposits all have in common specific stain affinities, a common appearance in polarized light, common ultrastructure fibrillary characteristics, and uniform x-ray diffraction and infrared spectral properties. Where groups of diseases have a common underlying pathogenetic process the polypeptide responsible for the protein fibril is the same regardless of the specific disease. Where diseases have a different underlying pathogenesis the polypeptide is unique for each disease. The different amyloidogenic polypeptides are clearly not related in terms of amino acid sequence or function, yet they all tend to fold in such a way as to present the same staining, structural or spectral properties. It is proposed that amyloid fibrils are not only composed of the specific amyloidogenic polypeptide but also highly sulphated glycosaminoglycans or proteoglycans which have a profound influence on the manner in which the peptides fold and interact with each other. It is this highly charged carbohydrate which may be common to all amyloids and which plays a determining role in the final appearance of the deposit. Amyloid should therefore be considered as more than simply a protein entity but, as its name originally implied, one related to carbohydrate deposition as well.

[New aspects of amyloidosis (author's transl)]

Amyloid is a substance that has the same composition of the basic qualities even in the different patterns of amyloidosis. Electron microscopic investigations have revealed that all forms of amyloidosis do not only exhibit homogeneous basic qualities but also common principle of accumulation. This may be commented as follows: Fibrils of amyloid are always found in close connection with basement membranes or basement membrane-like substances respectively produced by cells with the property of contracting (myocytic or "myopotent' cells). Collagen fibres of different types do not display a regular relation to the substance of amyloid. The origin and development of the various forms of amyloidosis depends on the three following factors: 1. On the extent of the production of amyloidogenic proteins which may belong to different types of proteins according to the basic disease; 2. On the way of protein silting (hematogenic silting-generalized amyloidosis; local enrichment--local amyloidosis); 3. On the site of predilection of all deposits of amyloid in the areas of basement membranes or basement membrane-like substances resp. produced by cells with the properties of contracting. A new classification should be made on the basis of these principles.

A chemical classification of amyloid. Correlation with different clinical types of amyloidosis

Results of recent research have made it possible to classify amyloidosis by means of the chemical and antigenic characteristics of the amyloid fibrils. The chemical classification of amyloid correlates quite well with the various clinical types of amyloidosis. Monoclonal immunoglobulins constitute a major part of primary amyloid fibrils, while amyloid protein AA plays a similar role in secondary amyloidosis. In addition, structural properties of amyloid fibril proteins derived from medullary carcinoma of the thyroid and from senile cardiac amyloidosis respectively, have been shown to be unique for these clinical types of localized amyloidosis. A protein identical or similar to prealbumin appears to constitute an amyloid fibril subunit in familial amyloidotic polyneuropathy. However, the mechanisms by which the various amyloid precursor proteins are converted to fibrils and deposited in the tissues are still not clear.

The pathogenesis of amyloid deposition: a new hypothesis

Amyloid proteins are probably derived from a variety of precursor glycoproteins. It is postulated that there may be at least two key events in the pathogenesisi of amyloidosis. The first is an increase in the load of glycoprotein being brought to a site of degradation. In the case of myeloma this might be in the form of excess immunoglobulin light chains. In the case of secondary amyloidosis the form taken could be enzyme-alpha-globulin complexes. The second is an inability of the degrading site to handle the arriving substrate at a sufficiently rapid rate, the rate limiting step being at some point along the degradation pathway. We postulate that an acquired enzyme deficiency prevents removal of the carbohydrate moiety of the presented glycoprotein. This results in the accumulation of a normal intermediate (amyloid protein) during the breakdown of the glycoprotein substrate. Evidence for the operation of these mechanisms is discussed and their detailed nature and implications considered.

[Corpora amylacea in the human brain (author's transl)]

130.5 mg of almost pure corpora amylacea was isolated from lyophilized tissue of 35 human brains obtained by autopsy. Staining shaved this material to be homogenous. The greater part of this material is composed of carbohydrates, whereas the protein- and lipid content is small. With regard to composition, one can take for granted that this material is different from amyloid and from the corpora amylacea of the prostatic gland. It may be assumed that corpora amylacea of the brain are caused by the glucose requirement of the brain being reduced, while the supply of glucose for the brain is normal.