Sulfated glycosaminoglycans in Alzheimer's disease

Heparan sulfate proteoglycans: Mediators of cellular and molecular Alzheimer's disease pathogenic factors via tunnelling nanotubes?

Neurological disorders impact around one billion individuals globally (15 % approx.), with significant implications for disability and mortality with their impact in Australia currently amounts to 6.8 million deaths annually. Heparan sulfate proteoglycans (HSPGs) are complex extracellular molecules implicated in promoting Tau fibril formation resulting in Tau tangles, a hallmark of Alzheimer's disease (AD). HSPG-Tau protein interactions contribute to various AD stages via aggregation, toxicity, and clearance, largely via interactions with the glypican 1 and syndecan 3 core proteins. The tunnelling nanotubes (TNTs) pathway is emerging as a facilitator of intercellular molecule transport, including Tau and Amyloid β proteins, across extensive distances. While current TNT-associated evidence primarily stems from cancer models, their role in Tau propagation and its effects on recipient cells remain unclear. This review explores the interplay of TNTs, HSPGs, and AD-related factors and proposes that HSPGs influence TNT formation in neurodegenerative conditions such as AD.

The Role of Extracellular Matrix in Human Neurodegenerative Diseases

The dense neuropil of the central nervous system leaves only limited space for extracellular substances free. The advent of immunohistochemistry, soon followed by advanced diagnostic tools, enabled us to explore the biochemical heterogeneity and compartmentalization of the brain extracellular matrix in exploratory and clinical research alike. The composition of the extracellular matrix is critical to shape neuronal function; changes in its assembly trigger or reflect brain/spinal cord malfunction. In this study, we focus on extracellular matrix changes in neurodegenerative disorders. We summarize its phenotypic appearance and biochemical characteristics, as well as the major enzymes which regulate and remodel matrix establishment in disease. The specifically built basement membrane of the central nervous system, perineuronal nets and perisynaptic axonal coats can protect neurons from toxic agents, and biochemical analysis revealed how the individual glycosaminoglycan and proteoglycan components interact with these molecules. Depending on the site, type and progress of the disease, select matrix components can either proactively trigger the formation of disease-specific harmful products, or reactively accumulate, likely to reduce tissue breakdown and neuronal loss. We review the diagnostic use and the increasing importance of medical screening of extracellular matrix components, especially enzymes, which informs us about disease status and, better yet, allows us to forecast illness.

The Unifying Hypothesis of Alzheimer's Disease: Heparan Sulfate Proteoglycans/Glycosaminoglycans Are Key as First Hypothesized Over 30 Years Ago

The updated "Unifying Hypothesis of Alzheimer's disease" (AD) is described that links all the observed neuropathology in AD brain (i.e., plaques, tangles, and cerebrovascular amyloid deposits), as well as inflammation, genetic factors (involving ApoE), "AD-in-a-Dish" studies, beta-amyloid protein (Aβ) as a microbial peptide; and theories that bacteria, gut microflora, gingivitis and viruses all play a role in the cause of AD. The common link is the early accumulation of heparan sulfate proteoglycans (HSPGs) and heparan sulfate glycosaminoglycans (GAGs). HS GAG accumulation and/or decreased HS GAG degradation is postulated to be the key initiating event. HS GAGs and highly sulfated macromolecules induce Aβ 1-40 (but not 1-42) to form spherical congophilic maltese-cross star-like amyloid core deposits identical to those in the AD brain. Heparin/HS also induces tau protein to form paired helical filaments (PHFs). Increased sulfation and/or decreased degradation of HSPGs and HS GAGs that occur due to brain aging leads to the formation of plaques and tangles in AD brain. Knockout of HS genes markedly reduce the accumulation of Aβ fibrils in the brain demonstrating that HS GAGs are key. Bacteria and viruses all use cell surface HS GAGs for entry into cells, including SARS-CoV-2. Bacteria and viruses cause HS GAGs to rapidly increase to cause near-immediate aggregation of Aβ fibrils. "AD-in-a-dish" studies use "Matrigel" as the underlying scaffold that spontaneously causes plaque, and then tangle formation in a dish. Matrigel mostly contains large amounts of perlecan, the same specific HSPG implicated in AD and amyloid disorders. Mucopolysaccharidoses caused by lack of specific HS GAG enzymes lead to massive accumulation of HS in lysosomal compartments in neurons and contribute to cognitive impairment in children. Neurons full of HS demonstrate marked accumulation and fibrillization of Aβ, tau, α-synuclein, and prion protein (PrP) in mucopolysaccharidosis animal models demonstrating that HS GAG accumulation is a precursor to Aβ accumulation in neurons. Brain aging leads to changes in HSPGs, including newly identified splice variants leading to increased HS GAG sulfation in the AD brain. All of these events lead to the new "Unifying Hypothesis of Alzheimer's disease" that further implicates HSPGs /HS GAGs as key (as first hypothesized by Snow and Wight in 1989).

Molecular Pathogenesis and Interventional Strategies for Alzheimer's Disease: Promises and Pitfalls

Alzheimer's disease (AD) is a debilitating disorder characterized by age-related dementia, which has no effective treatment to date. β-Amyloid depositions and hyperphosphorylated tau proteins are the main pathological hallmarks, along with oxidative stress, N-methyl-d-aspartate (NMDA) receptor-mediated excitotoxicity, and low levels of acetylcholine. Current pharmacotherapy for AD only provides symptomatic relief and limited improvement in cognitive functions. Many molecules have been explored that show promising outcomes in AD therapy and can regulate cellular survival through different pathways. To have a vivid approach to strategize the treatment regimen, AD physiopathology should be better explained considering diverse etiological factors in conjunction with biochemical disturbances. This Review attempts to discuss different disease modification approaches and address the novel therapeutic targets of AD that might pave the way for new drug discovery using the well-defined targets for therapy of the disease.

APP processing and metabolism in corneal fibroblasts and epithelium as a potential biomarker for Alzheimer's disease

Alzheimer's disease (AD) primarily affects the brain and is the most common form of dementia worldwide. Despite more than a century of research, there are still no early biomarkers for AD. It has been reported that AD affects the eye, which is more accessible for imaging than the brain; however, links with the cornea have not been evaluated. To investigate whether the cornea could be used to identify possible diagnostic indicators of AD, we analyzed the proteolytic processing and isoforms of amyloid precursor protein (APP) and evaluated the expression of AD-related genes and proteins in corneal fibroblasts from wild-type (WT) corneas and corneas from patients with granular corneal dystrophy type 2 (GCD2), which is related to amyloid formation in the cornea. Reverse transcription polymerase chain reaction (RT-PCR) analysis was used to assess the expression of AD-related genes, i.e., APP, ADAM10, BACE1, BACE2, PSEN1, NCSTN, IDE, and NEP. RT-PCR and DNA sequencing analysis demonstrated that isoforms of APP770 and APP751, but not APP695, were expressed in corneal fibroblasts. Moreover, the mRNA ratio of APP770/APP751 isoforms was approximately 4:1. Western blot analysis also demonstrated the expression of a disintegrin and metalloprotease domain-containing protein 10 (ADAM10), beta-site APP-cleaving enzyme 1 (BACE1), nicastrin, insulin degradation enzyme, and neprilysin in corneal fibroblasts. Among these targets, the levels of immature ADAM10 and BACE1 protein were significantly increased in GCD2 cells. The expression levels of APP, ADAM10, BACE1, and transforming growth factor-beta-induced protein (TGFBIp) were also detected by western blot in human corneal epithelium. We also investigated the effects of inhibition of the autophagy-lysosomal and ubiquitin-proteasomal proteolytic systems (UPS) on APP processing and metabolism. These pathway inhibitors accumulated APP, α-carboxy-terminal fragments (CTFs), β-CTFs, and the C-terminal APP intracellular domain (AICD) in corneal fibroblasts. Analysis of microRNAs (miRNAs) revealed that miR-9 and miR-181a negatively coregulated BACE1 and TGFBIp, which was directly associated with the pathogenesis of AD and GCD2, respectively. Immunohistochemical analysis indicated that APP and BACE1 were distributed in corneal stroma cells, epithelial cells, and the retinal layer in mice. Collectively, we propose that the cornea, which is the transparent outermost layer of the eye and thus offers easy accessibility, could be used as a potential biomarker for AD diagnosis and progression.

Cell surface proteoglycan-mediated uptake and accumulation of the Alzheimer's disease peptide Aβ(1-42)

Proteoglycans (PGs) have been found in Alzheimer's disease amyloid-β (Aβ) plaques and their glycosaminoglycan chains reportedly influence Aβ aggregation, neurotoxicity and intracellular accumulation in cell and animal models, but their exact pathophysiological role(s) remain unclear. We have studied the cellular uptake of fluorescently labelled Aβ(1-42) and Aβ(1-40) peptides in normal CHO cells (K1) and the mutant cell line (pgsA-745) which lacks all protein-attached heparan and chondroitin sulfate chains. After 24 h of incubation, CHO-K1 accumulates more Aβ(1-42) and Aβ(1-40) compared with CHO-pgsA-745, consistent with the suggested role of PGs in Aβ uptake. However, after short incubation times (≤3 h) there was no difference; moreover, the time evolution of Aβ(1-42) accumulation in CHO-K1 followed an unusual sigmoidal-like trend, indicating a possible involvement of PG-mediated peptide aggregation in Aβ endocytosis. Neither Aβ(1-42) nor Aβ(1-40) could stimulate uptake of a 10 kDa dextran (a general endocytosis marker) suggesting that Aβ-induced upregulation of endocytosis does not occur. CHO-K1 cells contained a higher number of Aβ(1-42)-positive vesicles, but the intensity difference per vesicle was only marginal suggesting that the superior accumulation of Aβ(1-42) stems from a higher number of endocytic events. FRET imaging support that intracellular Aβ(1-42) is aggregated in both cell types. We also report that CHO-pgsA-745 cells perform less endocytosis than CHO-K1 and, albeit this does not explain their difference in Aβ internalisation, we discuss a general method for data compensation. Altogether, this study contributes new insights into the mechanisms of PG-mediated Aβ uptake that may be relevant for our understanding of their role in AD pathology.

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.

Critical Influence of Cosolutes and Surfaces on the Assembly of Serpin-Derived Amyloid Fibrils

Many proteins and peptides self-associate into highly ordered and structurally similar amyloid cross-β aggregates. This fibrillation is critically dependent on properties of the protein and the surrounding environment that alter kinetic and thermodynamic equilibria. Here, we report on dominating surface and solution effects on the fibrillogenic behavior and amyloid assembly of the C-36 peptide, a circulating bioactive peptide from the α₁-antitrypsin serine protease inhibitor. C-36 converts from an unstructured peptide to mature amyloid twisted-ribbon fibrils over a few hours when incubated on polystyrene plates under physiological conditions through a pathway dominated by surface-enhanced nucleation. In contrast, in plates with nonbinding surfaces, slow bulk nucleation takes precedence over surface catalysis and leads to fibrillar polymorphism. Fibrillation is strongly ion-sensitive, underlining the interplay between hydrophilic and hydrophobic forces in molecular self-assembly. The addition of exogenous surfaces in the form of silica glass beads and polyanionic heparin molecules potently seeds the amyloid conversion process. In particular, heparin acts as an interacting template that rapidly forces β-sheet aggregation of C-36 to distinct amyloid species within minutes and leads to a more homogeneous fibril population according to solid-state NMR analysis. Heparin's template effect highlights its role in amyloid seeding and homogeneous self-assembly, which applies both in vitro and in vivo, where glycosaminoglycans are strongly associated with amyloid deposits. Our study illustrates the versatile thermodynamic landscape of amyloid formation and highlights how different experimental conditions direct C-36 into distinct macromolecular structures.

Amyloid plaque structure and cell surface interactions of β-amyloid fibrils revealed by electron tomography

The deposition of amyloid fibrils as plaques is a key feature of several neurodegenerative diseases including in particular Alzheimer’s. This disease is characterized, if not provoked, by amyloid aggregates formed from Aβ peptide that deposit inside the brain or are toxic to neuronal cells. We here used scanning transmission electron microscopy (STEM) to determine the fibril network structure and interactions of Aβ fibrils within a cell culture model of Alzheimer’s disease. STEM images taken from the formed Aβ amyloid deposits revealed three main types of fibril network structures, termed amorphous meshwork, fibril bundle and amyloid star. All three were infiltrated by different types of lipid inclusions from small-sized exosome-like structures (50–100 nm diameter) to large-sized extracellular vesicles (up to 300 nm). The fibrils also presented strong interactions with the surrounding cells such that fibril bundles extended into tubular invaginations of the plasma membrane. Amyloid formation in the cell model was previously found to have an intracellular origin and we show here that it functionally destroys the integrity of the intracellular membranes as it leads to lysosomal leakage. These data provide a mechanistic link to explain why intracellular fibril formation is toxic to the cell.

Amyloid formation of growth hormone in presence of zinc: Relevance to its storage in secretory granules

Amyloids are cross-β-sheet fibrillar aggregates, associated with various human diseases and native functions such as protein/peptide hormone storage inside secretory granules of neuroendocrine cells. In the current study, using amyloid detecting agents, we show that growth hormone (GH) could be stored as amyloid in the pituitary of rat. Moreover, to demonstrate the formation of GH amyloid in vitro, we studied various conditions (solvents, glycosaminoglycans, salts and metal ions) and found that in presence of zinc metal ions (Zn(II)), GH formed short curvy fibrils. The amyloidogenic nature of these fibrils was examined by Thioflavin T binding, Congo Red binding, transmission electron microscopy and X-ray diffraction. Our biophysical studies also suggest that Zn(II) initiates the early oligomerization of GH that eventually facilitates the fibrillation process. Furthermore, using immunofluorescence study of pituitary tissue, we show that GH in pituitary significantly co-localizes with Zn(II), suggesting the probable role of zinc in GH aggregation within secretory granules. We also found that GH amyloid formed in vitro is capable of releasing monomers. The study will help to understand the possible mechanism of GH storage, its regulation and monomer release from the somatotrophs of anterior pituitary.

Aging and cerebrovascular dysfunction: contribution of hypertension, cerebral amyloid angiopathy, and immunotherapy

Age-related cerebrovascular dysfunction contributes to ischemic stroke, intracerebral hemorrhages (ICHs), microbleeds, cerebral amyloid angiopathy (CAA), and cognitive decline. Importantly, there is increasing recognition that this dysfunction plays a critical secondary role in many neurodegenerative diseases, including Alzheimer's disease (AD). Atherosclerosis, hypertension, and CAA are the most common causes of blood-brain barrier (BBB) lesions. The accumulation of amyloid beta (Aβ) in the cerebrovascular system is a significant risk factor for ICH and has been linked to endothelial transport failure and blockage of perivascular drainage. Moreover, recent anti-Aβ immunotherapy clinical trials demonstrated efficient clearance of parenchymal amyloid deposits but have been plagued by CAA-associated adverse events. Although management of hypertension and atherosclerosis can reduce the incidence of ICH, there are currently no approved therapies for attenuating CAA. Thus, there is a critical need for new strategies that improve BBB function and limit the development of β-amyloidosis in the cerebral vasculature.

Suppression of LPS-induced matrix-metalloproteinase responses in macrophages exposed to phenytoin and its metabolite, 5-(p-hydroxyphenyl-), 5-phenylhydantoin

BACKGROUND

Phenytoin (PHT) has been reported to induce gingival (gum) overgrowth (GO) in approximately 50% of patients taking this medication. While most studies have focused on the effects of PHT on the fibroblast in the pathophysiology underlying GO, few studies have investigated the potential regulatory role of macrophages in extracellular matrix (ECM) turnover and secretion of proinflammatory mediators. The aim of this study was to evaluate the effects of PHT and its metabolite, 5-(p-hydroxyphenyl-), 5-phenylhydantoin (HPPH) on LPS-elicited MMP, TIMP, TNF-α and IL-6 levels in macrophages.

METHODS

Human primary monocyte-derived macrophages (n = 6 independent donors) were pretreated with 15-50 μg/mL PHT-Na+ or 15-50 μg/mL HPPH for 1 hour. Cells were then challenged with 100 ng/ml purified LPS from the periodontal pathogen, Aggregatibacter actinomycetemcomitans. Supernatants were collected after 24 hours and levels of MMP-1, MMP-2, MMP-3, MMP-9, MMP-12, TIMP-1, TIMP-2, TIMP-3, TIMP-4, TNF-α and IL-6 determined by multiplex analysis or enzyme-linked immunoadsorbent assay.

RESULTS

A dose-dependent inhibition of MMP-1, MMP-3, MMP-9, TIMP-1 but not MMP-2 was noted in culture supernatants pretreated with PHT or HPPH prior to LPS challenge. MMP-12, TIMP-2, TIMP-3 and TIMP-2 were not detected in culture supernatants. High concentrations of PHT but not HPPH, blunted LPS-induced TNF-α production although neither significantly affected IL-6 levels.

CONCLUSION

The ability of macrophages to mediate turnover of ECM via the production of metalloproteinases is compromised not only by PHT, but its metabolite, HPPH in a dose-dependent fashion. Further, the preferential dysregulation of macrophage-derived TNF-α but not IL-6 in response to bacterial challenge may provide an inflammatory environment facilitating collagen accumulation without the counteracting production of MMPs.

Heparan sulfate proteoglycans in amyloidosis

Amyloidosis is a generic term for a group of diseases characterized by deposits in different organ systems of insoluble materials composed mainly of distinct fibrillar proteins named amyloid. Besides amyloid, heparan sulfate proteoglycan (HSPG), is commonly found in most amyloid deposits, suggesting that HS/HSPG may be functionally involved in the pathogenesis of amyloidosis. HS or HSPG is found to interact with a number of amyloid proteins, displaying a promoting effect on amyloid fibrilization in vitro. In addition, HS is reported to be involved in processing amyloid precursor proteins and mediate amyloid toxicity. Although little is known about the in vivo mechanisms regarding the codeposition of HS with amyloid proteins in different amyloid diseases, experiments carried out in animal models, especially in transgenic mouse model where HS molecular structure is modified, support an active role for HS in amyloidogenesis. Further experimental evidence is required to strengthen these in vivo findings at a molecular level. Animal models that express mutant forms of HS due to knockout of the enzymes involved in glycosaminoglycan (GAG) biosynthesis are expected to provide valuable tools for studying the implications of HS, as well as other GAGs, in amyloid disorders.

Interactions between heparan sulfate and proteins-design and functional implications

Heparan sulfate (HS) proteoglycans at cell surfaces and in the extracellular matrix of most animal tissues are essential in development and homeostasis, and variously implicated in disease processes. Functions of HS polysaccharide chains depend on ionic interactions with a variety of proteins including growth factors and their receptors. Negatively charged sulfate and carboxylate groups are arranged in various types of domains, generated through strictly regulated biosynthetic reactions and with enormous potential for structural variability. The level of specificity of HS-protein interactions is assessed through binding experiments in vitro using saccharides of defined composition, signaling assays in cell culture, and targeted disruption of genes for biosynthetic enzymes followed by phenotype analysis. While some protein ligands appear to require strictly defined HS structure, others bind to variable saccharide domains without any apparent dependence on distinct saccharide sequence. These findings raise intriguing questions concerning the functional significance of regulation in HS biosynthesis.

Heat shock proteins and amateur chaperones in amyloid-Beta accumulation and clearance in Alzheimer's disease

The pathologic lesions of Alzheimer’s disease (AD) are characterized by accumulation of protein aggregates consisting of intracellular or extracellular misfolded proteins. The amyloid-β (Aβ) protein accumulates extracellularly in senile plaques and cerebral amyloid angiopathy, whereas the hyperphosphorylated tau protein accumulates intracellularly as neurofibrillary tangles. “Professional chaperones”, such as the heat shock protein family, have a function in the prevention of protein misfolding and subsequent aggregation. “Amateur” chaperones, such as apolipoproteins and heparan sulfate proteoglycans, bind amyloidogenic proteins and may affect their aggregation process. Professional and amateur chaperones not only colocalize with the pathological lesions of AD, but may also be involved in conformational changes of Aβ, and in the clearance of Aβ from the brain via phagocytosis or active transport across the blood–brain barrier. Thus, both professional and amateur chaperones may be involved in the aggregation, accumulation, persistence, and clearance of Aβ and tau and in other Aβ-associated reactions such as inflammation associated with AD lesions, and may, therefore, serve as potential targets for therapeutic intervention.

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.

Small heat shock protein HspB8: its distribution in Alzheimer's disease brains and its inhibition of amyloid-beta protein aggregation and cerebrovascular amyloid-beta toxicity

Alzheimer's disease (AD) is characterized by pathological lesions, such as senile plaques (SPs) and cerebral amyloid angiopathy (CAA), both predominantly consisting of a proteolytic cleavage product of the amyloid-beta precursor protein (APP), the amyloid-beta peptide (Abeta). CAA is also the major pathological lesion in hereditary cerebral hemorrhage with amyloidosis of the Dutch type (HCHWA-D), caused by a mutation in the gene coding for the Abeta peptide. Several members of the small heat shock protein (sHsp) family, such as alphaB-crystallin, Hsp27, Hsp20 and HspB2, are associated with the pathological lesions of AD, and the direct interaction between sHsps and Abeta has been demonstrated in vitro. HspB8, also named Hsp22 of H11, is a recently discovered member of the sHsp family, which has chaperone activity and is observed in neuronal tissue. Furthermore, HspB8 affects protein aggregation, which has been shown by its ability to prevent formation of mutant huntingtin aggregates. The aim of this study was to investigate whether HspB8 is associated with the pathological lesions of AD and HCHWA-D and whether there are effects of HspB8 on Abeta aggregation and Abeta-mediated cytotoxicity. We observed the expression of HspB8 in classic SPs in AD brains. In addition, HspB8 was found in CAA in HCHWA-D brains, but not in AD brains. Direct interaction of HspB8 with Abeta(1-42), Abeta(1-40) and Abeta(1-40) with the Dutch mutation was demonstrated by surface plasmon resonance. Furthermore, co-incubation of HspB8 with D-Abeta(1-40) resulted in the complete inhibition of D-Abeta(1-40)-mediated death of cerebrovascular cells, likely mediated by a reduction in both the beta-sheet formation of D-Abeta(1-40) and its accumulation at the cell surface. In contrast, however, with Abeta(1-42), HspB8 neither affected beta-sheet formation nor Abeta-mediated cell death. We conclude that HspB8 might play an important role in regulating Abeta aggregation and, therefore, the development of classic SPs in AD and CAA in HCHWA-D.

Heparan sulphate proteoglycans in Alzheimer's disease and amyloid-related disorders

Proteoglycans are associated with all kinds of amyloid deposits in the human body. These complex macromolecules, in particular heparan sulphate proteoglycans, have also been implicated in several features of the pathogenesis of Alzheimer's disease (AD), including the genesis of senile plaques, cerebrovascular amyloid, and neurofibrillary tangles. In this review we focus on the role of proteoglycans and glycosaminoglycans in amyloidogenesis in general and in AD in particular. Heparan sulphate proteoglycans may promote amyloid-beta peptide (Abeta) or tau fibrillisation on the one hand, and provide resistance against proteolytic breakdown on the other. Knowledge about the role of proteoglycans in AD pathology may eventually be of therapeutic use, because small polysulphated compounds, which can interfere with the interaction between proteoglycan and Abeta, have been shown to stop or even prevent amyloidogenesis.

Establishment of a first-order kinetic model of light chain-associated amyloid fibril extension in vitro

Light chain-associated (AL) amyloidosis is a common and fatal systemic amyloidosis. AL amyloid fibrils (fAL) are composed of intact or fragmental monoclonal light chains (AL proteins). To elucidate the molecular mechanisms of fAL formation from AL proteins, we purified fAL and AL proteins from the amyloid-deposited organs of five AL amyloidosis patients. By electron microscopy and fluorometric thioflavin T method, we observed optimal fibril extension at pH 2.0-3.5 for the fibrils obtained from four patients, while at pH 7.5-8.0 for those obtained from one patient. Fragmental AL proteins were more efficient in the extension reaction than intact AL proteins. The fibrils obtained from all five patients showed clear fibril extension electron microscopically at pH 7.5. The extension of the fibrils obtained from all five patients could be explained by a first-order kinetic model, i.e., fibril extension proceeds via the consecutive association of AL proteins onto the ends of existing fibrils. Fibril extension was accelerated by dermatan sulfate proteoglycan, and inhibited by apolipoprotein E, alpha1-microglobulin, fibronectin, and an antioxidant nordihydroguaiaretic acid. These findings contribute to our understanding of the molecular mechanism underlying the pathogenesis of AL amyloidosis, and will be useful for developing a therapeutic strategy against the disease.

Low molecular weight glycosaminoglycan blockade of beta-amyloid induced neuropathology

Previous studies have shown different roles for proteoglycans and glycosaminoglycans (GAGs) in Alzheimer's disease (AD) neuropathology. Using a rat model of beta-amyloid induced neuropathology, we tested whether low molecular weight glycosaminoglycans (Certoparin and C6) could be useful as preventative agents and/or as a potential therapeutic treatment for AD. Chronic subcutaneous low molecular weight glycosaminoglycan injections beginning either before or after an intra-amygdaloid beta-amyloid-(25-35) injection blocked abnormal intracellular tau changes and reactive astrocytosis but did not affect beta-amyloid's aggregation state. Also, low molecular weight glycosaminoglycan injections beginning 1 day prior to sacrifice did not block the effects of beta-amyloid nor did injections of a disaccharide, suggesting chronic low molecular weight glycosaminoglycan treatment is needed to block the effects of beta-amyloid. Furthermore, these data indicate that there is a molecular weight range of active low molecular weight glycosaminoglycans in this model; and supports the investigation of low molecular weight glycosaminoglycans as a preventative and/or therapeutic treatment of beta-amyloid induced neuropathology.

Structure and location of amyloid beta peptide chains and arrays in Alzheimer's disease: new findings require reevaluation of the amyloid hypothesis and of tests of the hypothesis

New in situ high resolution electronmicroscopic examination of amyloid fibrils in situ indicate that in Alzheimer's disease these fibrils are not simply long chains of self aggregated amyloid beta peptide. The amyloid beta is not only associated with P protein and glycans, as was well known from previous immunohistologic studies, but is arranged in the form of short chains at right angles to a P protein backbone with the glycans wrapped around that backbone. These findings suggest that the hypothesis causally relating simple, fibrillar amyloid beta to Alzheimer's disease must be reevaluated since such simple fibrils may be absent, or not the major form of the amyloid beta in the brain. Other data shows that shorter multimers, so-called protofibrils, or dimers of amyloid beta or molecules cleaved from it can be highly toxic. Some of these may be in the soluble amyloid beta fraction. Shorter multimers or dimers of amyloid beta, either extra or intracellular, may be the real links between amyloid beta production and Alzheimer's disease. Toxicity studies employing fibrillar amyloid beta may not be relevant, even if they produce lesions, because they do not employ amyloid beta in the form in which it actually exists in the Alzheimer brain. Studies of treatments designed to remove fibrils or to prevent their formation may be ineffective or suboptimal in effectiveness because they do not reduce the relevant amyloid burden and/or fail to alter the arrangement of shorter multimers of amyloid beta around its P-protein and glycan core.

Tau protein isoforms, phosphorylation and role in neurodegenerative disorders

Tau proteins belong to the family of microtubule-associated proteins. They are mainly expressed in neurons where they play an important role in the assembly of tubulin monomers into microtubules to constitute the neuronal microtubules network. Microtubules are involved in maintaining the cell shape and serve as tracks for axonal transport. Tau proteins also establish some links between microtubules and other cytoskeletal elements or proteins. Tau proteins are translated from a single gene located on chromosome 17. Their expression is developmentally regulated by an alternative splicing mechanism and six different isoforms exist in the human adult brain. Tau proteins are the major constituents of intraneuronal and glial fibrillar lesions described in Alzheimer's disease and numerous neurodegenerative disorders referred to as 'tauopathies'. Molecular analysis has revealed that an abnormal phosphorylation might be one of the important events in the process leading to their aggregation. Moreover, a specific set of pathological tau proteins exhibiting a typical biochemical pattern, and a different regional and laminar distribution could characterize each of these disorders. Finally, a direct correlation has been established between the progressive involvement of the neocortical areas and the increasing severity of dementia, suggesting that pathological tau proteins are reliable marker of the neurodegenerative process. The recent discovery of tau gene mutations in frontotemporal dementia with parkinsonism linked to chromosome 17 has reinforced the predominant role attributed to tau proteins in the pathogenesis of neurodegenerative disorders, and underlined the fact that distinct sets of tau isoforms expressed in different neuronal populations could lead to different pathologies.

Oligomerizaiton and fibril asssembly of the amyloid-beta protein

In this chapter, we attempt to analyze the evolution of the amyloid-beta (Abeta) molecular structure from its inception as part of the Abeta precursor protein to its release by the secretases and its extrusion from membrane into an aqueous environment. Biophysical studies suggest that the Abeta peptide sustains a series of transitions from a molecule rich in alpha-helix to a molecule in which beta-strands prevail. It is proposed that initially the extended C-termini of two opposing Abeta dimers form an antiparallel beta-sheet and that the subsequent addition of dimers generates a helical Abeta protofilament. Two or more protofilaments create a strand in which the hydrophobic core of the beta-sheets is shielded from the aqueous environment by the N-terminal polar domains of the Abeta dimers. Once the nucleation has occurred, the Abeta filament grows in length by the addition of dimers or tetramers.

Synthesis of 4-deoxy analogues of 2-acetamido-2-deoxy-D-glucose and 2-acetamido-2-deoxy-D-xylose and their effects on glycoconjugate biosynthesis

4-Deoxy analogues of 2-acetamido-2-deoxy-D-glucose and 2-acetamido-2-deoxy-D-xylose were synthesized and evaluated as inhibitors of glycoconjugate biosynthesis. Methyl 2-acetamido-2,4-dideoxy-beta-D-xylo-hexopyranoside (11) showed a reduction in [3H]GlcN and [14C]Leu incorporation into hepatocyte cellular glycoconjugates by 89 and 88%, of the control cells, respectively, at 20 mM, whereas the free sugars, 2-acetamido-2,4-dideoxy-alpha,beta-D-xylo-hexopyranoses (15), showed a reduction of [3H]GlcN and [14C]Leu incorporation by 75 and 64%, respectively, at 20 mM. The acetylated analogues of 11 and 15, namely methyl 2-acetamido-3,6-di-O-acetyl-2,4-dideoxy-beta-D-xylo-hexopyranoside and 2-acetamido-1,3,6-tri-O-acetyl-2,4-dideoxy-alpha,beta-D-xylo-hexopyra noses, showed a greater inhibition of [3H]GlcN and [14C]Leu incorporation at 1 mM compared with their non-acetylated counterparts, but were toxic to hepatocytes at concentrations of 10 and 20 mM. Corresponding derivatives of 2-acetamido-2,4-dideoxy-L-threo-pentopyranose showed no biological effect up to 20 mM, suggesting that the C-6 substituent is important for the biological activity.

A beta amyloidogenesis: unique, or variation on a systemic theme?

For more than a century amyloid was considered to be an interesting, unique, but inconsequential pathologic entity that rarely caused significant clinical problems. We now recognize that amyloid is not one entity. In vivo it is a uniform organization of a disease, or process, specific protein co-deposited with a set of common structural components. Amyloid has been implicated in the pathogenesis of diseases affecting millions of patients. These range from Alzheimer's disease, adult-onset diabetes, consequences of prolonged renal dialysis, to the historically recognized systemic forms associated with inflammation and plasma cell disturbances. Strong evidence is emerging that even when deposited in local organ sites significant physiologic effects may ensue. With emphasis on A beta amyloid, we review the present definition, classification, and general in vivo pathogenetic events believed to be involved in the deposition of amyloids. This encompasses the need for an adequate amyloid precursor protein pool, whether precursor proteolysis is required prior to deposition, amyloidogenic amino acid sequences, fibrillogenic nucleating particles, and an in vivo microenvironment conducive to fibrillogenesis. The latter includes several components that seem to be part of all amyloids. The role these common components may play in amyloid accumulation, why amyloids tend to be associated with basement membranes, and how one may use these findings for anti-amyloid therapeutic strategies is also examined.

Brain microvascular changes in Alzheimer's disease and other dementias

Vasculopathy in Alzheimer's disease (AD) may represent an important pathogenetic factor of this disorder. In the present study, microvasculature was studied by immunohistochemistry using a monoclonal antibody against a vascular heparan sulfate proteoglycan. Vascular changes were consistently observed in AD and included decrease in vascular density, presence of atrophic and coiling vessels, and glomerular loop formations. The laminar and regional distribution of these vascular alterations was correlated with the presence of neurofibrillary tangles. However, vascular changes may also follow neuronal loss. Vascular density may be related to a decrease in brain metabolism. Furthermore, one of the main features of AD is the presence of amyloid deposits within brain parenchyma and blood vessel walls. It is not yet clear whether amyloid components are derived from the blood or the central nervous system. Because AD is clearly heterogeneous, based on clinical and genetic data, evidence for either a brain or peripheral origin is discussed. Microvasculature was also analyzed in other neurodegenerative disorders devoid of amyloid deposits including amyotrophic lateral sclerosis/parkinsonism-dementia complex of Guam and Pick's disease. In conclusion, if vasculopathy in neurodegenerative disorders is not directly involved in pathogenesis, it may act synergistically with other pathogenetic mechanisms including genetic and environmental factors. This aspect of pathology is particularly interesting in view of its accessibility to therapeutic interventions.

Growth cone behavior in the presence of soluble chondroitin sulfate proteoglycan (CSPG), compared to behavior on CSPG bound to laminin or fibronectin

Proteoglycans (PGs) are complex macromolecules of the extracellular matrix (ECM) that have a wide variety of effects on developing and regenerating neurons in vivo and in vitro. One hypothesis regarding the mechanisms of PG regulation of neuronal behavior states that the conformation of PGs may be critical, and thus that ECM- or cell surface-bound PGs may operate differently than secreted (soluble) PGs. Therefore, this study examined differences between the effects of soluble chondroitin sulfate proteoglycan (CSPG) and substratum-bound CSPG on neuronal growth cone behavior. Dissociated chicken dorsal root ganglion (DRG) neurons were cultured on either laminin (LN) or fibronectin (FN), both sensory neurite outgrowth-promotin glycoproteins. CSPG (or chondroitin sulfate alone) was either bound to FN or LN, or was added to the culture media. Subsequently, using time lapse video microscopy and image analysis, this study measured: (1) neuronal attachment, (2) neurite outgrowth, (3) rate of neurite elongation, and (4) filopodial length and lifespan. To determine the site of CSPG action, DRG neurons were grown on either: CS-1, a FN peptide [Humphries M. J. et al. (1987) J. biol. Chem. 262, 6886-6892], or a recombinant FN protein, RFNIIIcs (Maejne, submitted), both of which permit DRG attachment and outgrowth but do not have recognized CSPG binding sites, and the resulting neuronal behavior was compared to that of DRG neurons grown on intact FN. The results of these studies confirm that the effect of CSPG on DRG neurons is concentration-, conformation- and substratum-dependent. On I.N, soluble CSPG had little to no effect on neurite initiation or outgrowth, while substratum-bound CSPG inhibited neurite outgrowth. In contrast, on FN, soluble CSPG inhibited neurite outgrowth and decreased the rate of neurite elongation. Soluble CSPG did not affect the length of sensory growth cone filopodia or filopodial lifespan on either LN or FN. From the FN fragment experiments, we found that: (1) soluble CSPG reduces neurite outgrowth on FN or FN fragments, but not on LN, up to 80%, and reduces elongation rate on FN up to 50%, and (2) soluble CSPG regulates neuronal behavior by binding directly to growth cones elongating on FN. Given that substratum-bound CSPG from a variety of sources is inhibitory to neurite outgrowth and to the rate of neurite elongation, while soluble CSPG often has different effects on growth cone behavior, the regulation of growth cone behavior by CSPGs may be dependent upon CSPG conformation. Further, CSPG may affect growth cone behavior by either binding to the substratum or by binding directly to growth cones.

Heparan sulfate and chondroitin sulfate glycosaminoglycan attenuate beta-amyloid(25-35) induced neurodegeneration in cultured hippocampal neurons

beta-Amyloid peptide has been reported to be toxic to neurons in vitro and in vivo. The fragment of the beta 1-42 peptide believed to be responsible for this toxicity consists of amino acids 25 to 35. beta-amyloid protein, heparan sulfate (HS) glycosaminoglycan (GAG), and proteoglycan (PG) are all localized throughout the senile plaques found in Alzheimer's disease. Chondroitin sulfate (CS) and dermatan sulfate have also been found at the periphery of senile plaques. We have found that both HS and CS prevented neurite fragmentation and toxicity normally induced by beta 25-35. HS and CS by themselves did not have a significant influence on cell viability, indicating that their protective actions were not due to a general trophic effect. In contrast, cultures treated with HS and beta 1-42 did not show significantly reduced toxicity compared to cultures treated with beta 1-42 alone despite specific binding interactions. These data indicate that one function of GAGs in the brain may be to protect neurons from select toxic insults and injury, and additionally suggest that HS interacts differently with different beta-amyloid fragments. These data further suggest that different beta-amyloid fragments may induce distinct mechanisms of toxicity in vitro.

Chondroitin sulfate proteoglycans are a common component of neuronal inclusions and astrocytic reaction in neurodegenerative diseases

Previously, we showed three differentially sulfated forms of chondroitin sulfate proteoglycans (CSPG) associated with senile plaques, astrocytes and neurofibrillary tangles in Alzheimer's disease. Here, monoclonal antibodies were used to demonstrate CSPGs in other neurodegenerative diseases. CSPGs were found associated with inclusions of Parkinson's, diffuse Lewy body, Pick's diseases, and progressive supranuclear palsy. Reacting astrocytes in each of these neurodegenerative diseases and Huntington's disease showed immunoreactivity for CSPG. CSPG distribution in a variety of neurodegenerative diseases suggests that similar mechanisms may be involved in the accumulation of proteoglycans in a number of filamentous inclusions.

Proteoglycans and the acute-phase response in Alzheimer's disease brain

Alzheimer's disease is a dementing disorder affecting increasingly large numbers of individuals in the aging population. The characteristic neuropathologic changes of Alzheimer's disease are the deposition of extracellular amyloid plaques, neurons containing neurofibrillary tangles, and neuronal cell loss. The A4 amyloid peptide is the major constituent of senile plaques. In addition to the A4 peptide, senile plaques contain a variety of molecular species, including proteoglycans and inflammatory components. The presence of proteoglycans in the amyloid deposits of Alzheimer's disease and of systemic amyloidoses suggests that these molecules play an active role in the pathogenesis of amyloidosis. However, the molecular mechanisms that lead to the codeposition of amyloid peptide with proteoglycans is still unknown. Recent evidence suggests that the metabolism of proteoglycans is altered in Alzheimer's disease patients. The acute-phase response observed in the brain of patients affected by Alzheimer's disease may be responsible for this effect. In this article, we discuss the role of proteoglycans in Alzheimer's disease, and the possible interactions between factors involved in brain inflammatory mechanisms and proteoglycans in the pathogenesis of Alzheimer's disease.

Pathological alterations of the cerebral microvasculature in Alzheimer's disease and related dementing disorders

Alterations of the cerebral microvasculature have been reported in aging and in neurodegenerative disorders such as Alzheimer's disease. However, the exact role of microvascular alterations in the pathogenesis of neurodegeneration remains unknown. In the present report, the cerebral cortex microvasculature was studied by immunohistochemistry using a monoclonal antibody against vascular heparan sulfate proteoglycan protein core in normal aging controls. Alzheimer's disease, Down syndrome, Guam amyotrophic lateral sclerosis/parkinsonian dementia complex, Pick's disease and dementia pugilistica. In all dementing illnesses, increased microvascular pathology was evident compared to normal controls. Decreased microvascular density and numerous atrophic vessels were the primary abnormalities observed in all dementing disorders. These microvascular abnormalities demonstrated regional and laminar selectivity, and were primarily found in layers III and V of frontal and temporal cortex. Quantitative analysis employing computer-assisted microscopy demonstrated that the decrease in microvascular density in Alzheimer's disease was statistically significant compared to age-matched controls. In addition, extracellular heparan sulfate proteoglycan deposits were observed which colocalized with thioflavine S-positive senile plaques in Alzheimer's disease, Down syndrome and selected Guam dementia cases. In some cases, heparan sulfate proteoglycan was seen in senile plaques that appeared to be diffuse or primitive plaques that stained weakly with thioflavine. Heparan sulfate proteoglycan-containing neurons were also observed in Alzheimer's disease, as well as in Down syndrome and Guam cases. Glial staining for heparan sulfate proteoglycan was never observed. Our data support previous observations that microvascular pathology is found in aging and in Alzheimer's disease. The changes in Alzheimer's disease exceed those found in normal aging controls. We also found microvascular pathology in all other dementing disorders studied. Our studies further demonstrated that the microvascular pathology displays regional and laminar patterns which parallel patterns of neuronal loss. Finally, we also found that heparan sulfate proteoglycan is present in senile plaques and neurons not only as previously reported in Alzheimer's disease, but also in Down syndrome and Guam cases. Heparan sulfate proteoglycan in senile plaques may be derived from either the degenerating microvasculature or from degenerating neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Binding of vascular heparan sulfate proteoglycan to Alzheimer's amyloid precursor protein is mediated in part by the N-terminal region of A4 peptide

The exact mechanisms of deposition and accumulation of amyloid in senile plaques and in blood vessels in Alzheimer's disease remain unknown. Heparan sulfate proteoglycans may play an important role in amyloid deposition in Alzheimer's disease. Previous investigations have demonstrated high affinity binding between heparan sulfate proteoglycans and the amyloid precursor, as well as with the A4 peptide. In the current studies, a specific vascular heparan sulfate proteoglycan found in senile plaques bound with high affinity to two amyloid protein precursors (APP695 and APP770). Vascular heparan sulfate proteoglycan also bound the Alzheimer's amyloid A4 peptide, and not other amyloid protein precursor regions studied, with high affinity. Both heparan sulfate glycosaminoglycan chains and chemically deglycosylated vascular heparan sulfate proteoglycan protein core bound to A4. High affinity interactions between vascular heparan sulfate proteoglycan and the A4 peptide may play a role in the process of amyloidogenesis in Alzheimer's disease, by localizing the site of deposition of A4, protecting A4 from further proteolysis, or by promoting aggregation and fibril formation.

Morphological and biochemical analyses of amyloid plaque core proteins purified from Alzheimer disease brain tissue

Amyloid plaque cores were purified from Alzheimer disease brain tissue. Plaque core proteins were solubilized in formic acid which upon dialysis against guanidinium hydrochloride (GuHCl) partitioned into soluble (approximately 15%) and insoluble (approximately 85%) components. The GuHCl-soluble fraction contained beta-amyloid1-40, whereas the GuHCl-insoluble fraction was fractionated into six components by size exclusion HPLC: S1 (> 200 kDa), S2 (200 kDa), S3 (45 kDa), S4 (15 kDa), S5 (10 kDa), and S6 (5 kDa). Removal of the GuHCl reconstituted 10-nm filaments composed of two intertwined 5-nm strands. Fractions S5 and S6 also yielded filamentous structures when treated similarly, whereas fractions S1-S4 yielded amorphous aggregates. Chemical analysis identified S4-S6 as multimeric and monomeric beta-amyloid. Immunochemical analyses revealed alpha 1-antichymotrypsin and non-beta-amyloid segments of the beta-amyloid precursor protein within fractions S1 and S2. Several saccharide components were identified within plaque core protein preparations by fluorescence and electron microscopy, as seen with fluorescein isothiocyanate- and colloidal gold-conjugated lectins. We have shown previously that this plaque core protein complex is more toxic to neuronal cultures than beta-amyloid. The non-beta-amyloid components likely mediate this additional toxicity, imposing a significant influence on the pathophysiology of Alzheimer disease.

Binding of secreted human neuroblastoma proteoglycans to the Alzheimer's amyloid A4 peptide

Proteoglycans (PGs) may play a fundamental role in all forms of amyloidosis. In Alzheimer's disease, proteoglycans are found deposited in senile plaques and in neurofibrillary tangles. However, the cellular source of these deposited PGs and their role in amyloidosis in Alzheimer's disease is unknown. Proteoglycans were purified from conditioned medium of human neuroblastoma cells (SKNSH-SY 5Y). Two species of proteoglycans were identified by enzyme susceptibility including a heparan sulfate proteoglycan and a dermatan sulfate proteoglycan. A monoclonal antibody to the protein core of a vascular basement membrane heparan sulfate proteoglycan found in senile plaques in Alzheimer's disease cross-reacted with the proteoglycans secreted by human neuroblastoma cells. Binding between 35SO4-labelled neuroblastoma proteoglycans and the Alzheimer amyloid (A4) peptide was demonstrated by affinity chromatography. Specificity studies demonstrated that binding of human neuroblastoma proteoglycans to the amyloid peptide was specific for a heparan sulfate glycosaminoglycan, with some binding to a dermatan sulfate proteoglycan. Binding to A4 was also demonstrated by a chemically deglycosylated protein core preparation. No significant binding of neuroblastoma proteoglycans was found to two other basic peptides derived from the extracellular domain of the beta-amyloid precursor, demonstrating the specificity of proteoglycan binding to the A4 peptide. Human neuroblastoma proteoglycans may bind to the-Alzheimer amyloid A4 peptide in a region with a heparin binding consensus sequence [VHHQKL] which also contains the cleavage site of the beta-amyloid precursor protein. Neuronal proteoglycans may either regulate the secretion of the amyloid protein precursor or modify the binding of the amyloid protein precursor to other cellular adhesion molecules. Alterations in this binding may be related to the pathogenesis of amyloid deposition in Alzheimer's disease.

Effects of 4-deoxy-L-threo-pentose, a novel carbohydrate, on neural cell proteoglycan synthesis and function

A novel carbohydrate, 4-deoxy-L-threo-pentose (4-deoxyxylose), was synthesized by way of reductive dechlorination of a chlorodeoxy sugar. This carbohydrate, an analogue of xylose which is required for the initiation of glycosaminoglycan (GAG) synthesis, was used to explore the function of GAG side chains in neurite outgrowth on a laminin substrate. 4-Deoxyxylose inhibited the incorporation of 35SO4 into the GAGs of neuronal and astrocytic proteoglycans, with no effect being seen on the incorporation of [3H]glucosamine into proteoglycan. Direct analysis of the heparan sulphate fraction from such cells using nitrous acid digestion confirmed that the GAGs were undersulphated. No inhibition of either 35SO4 or [3H]glucosamine incorporation was observed in primary mouse hepatocytes exposed to 4-deoxyxylose. 4-Deoxyxylose produced a direct dose-dependent inhibition of neurite outgrowth by sensory neurons, and medium conditioned by neurons or astrocytes in the presence of 4-deoxyxylose displayed less laminin-complexed neurite-promoting activity than medium conditioned in its absence. These data suggest that 4-deoxyxylose inhibits neurite outgrowth by altering the sulphation of the GAGs of heparan sulphate proteoglycans.

Localization of heparan sulfate glycosaminoglycan and proteoglycan core protein in aged brain and Alzheimer's disease

Two monoclonal antibodies, one which recognizes a glycosaminoglycan epitope present in heparan sulfate glycosaminoglycan and another which recognizes the core protein of a basement membrane heparan sulfate proteoglycan, were used to study the distribution and localization of these components in Alzheimer's disease and control brain. The cytoplasm of neurons, and occasional neurofibrillary tangles, senile plaques and astrocytes were immunopositive for the heparan sulfate glycosaminoglycan antibody in control brains. In Alzheimer's tissue, however, the number and intensity of these elements was more extensive than in control brains. In addition, within the Alzheimer's brains studied, the nuclei of select neurons and a small number of microglia were also immunopositive for heparan sulfate glycosaminoglycan in contrast to controls, where nuclei and neuroglia were immuno-negative. Some senile plaques in Alzheimer's tissue also contained strong heparan sulfate glycosaminoglycan-positive neurites which were not seen in controls. In Alzheimer's tissue, double labeling for heparan sulfate glycosaminoglycans and the beta-amyloid protein in adjacent sections revealed that, in general, heparan sulfate glycosaminoglycan- and beta-amyloid protein-immunopositive plaques were co-localized. Occasionally, however, beta-amyloid-positive plaques were seen without heparan sulfate glycosaminoglycan immunoreactivity and vice versa. Heparan sulfate glycosaminoglycan immunoreactivity and Tau immunoreactivity co-localized in many neurofibrillary tangles; however a small number of heparan sulfate glycosaminoglycan-positive neurofibrillary tangles did not co-localize with Tau-positive neurofibrillary tangles. In contrast, the heparan sulfate proteoglycan antibody immunostained only the walls of blood vessels and a few senile plaques in Alzheimer's brains and primarily blood vessels in control brains. Heparan sulfate glycosaminoglycan immunostaining was present within neurons, glia, neurofibrillary tangles and senile plaques in Alzheimer's tissue. These results suggest that heparan sulfate-like molecules play an important role in the pathogenesis of the characteristic lesions of Alzheimer's disease and could serve as a marker reflecting early pathological changes.

Selective and differential binding of interleukin (IL)-1 alpha, IL-1 beta, IL-2 and IL-6 to glycosaminoglycans

The binding of interleukin (IL)-1 alpha, IL-1 beta, IL-2 and IL-6 to acidic polysaccharides was investigated by affinity chromatography of the recombinant, radioiodinated interleukins on columns of immobilized polysaccharide. Each interleukin showed selective binding retention. Overall heparin bound all four interleukins significantly, whereas chondroitin sulfate provided little retention. IL-1 alpha and IL-1 beta showed differential binding, with only the latter binding to hyaluronic acid. IL-2 was virtually completely retained on fucoidan. Noniodinated recombinant IL-2 bound similarly to fucoidan, and fucoidan was found to sequester IL-2 activity in a bioassay employing IL-2-dependent CTLL cells. In all other cases tested, interleukin retention was partial, implying that interleukin binding sites are sparsely distributed along the polysaccharide chains. These findings suggest that during the immune response, interleukins will tend to be retained at sites of secretion by interaction with glycosaminoglycans in the extracellular matrix and on cell surfaces.

Characterization of proteoglycans in Alzheimer's disease fibroblasts

Skin fibroblasts lines established from patients with Alzheimer's disease and old normal individuals were cultured with 35S-sodium sulfate and 3H-glucosamine. Proteoglycans were isolated and characterized. Sulfate incorporation into proteoglycans increased in Alzheimer's disease fibroblasts relative to normal controls. These increases changed the ratio of chondroitin sulfate to heparan sulfate proteoglycan from 1.4 to 1.7 (p = 0.0012) and decreased the ratio of cell to medium proteoglycans from 0.32 to 0.26 in normal and Alzheimer fibroblasts (p = 0.006), respectively. HPLC analysis of the disaccharides produced by chondroitinase ABC revealed no differences in composition between proteoglycans of Alzheimer and normal fibroblasts in either the cell or medium fraction. However, analysis of disaccharides produced by heparinase plus heparitinase showed differences in composition in the medium but not the cell fraction. delta UA-GlcNS was increased by 30% while delta UA-GlcNS-6S was reduced by 40% in Alzheimer's disease.

Astroglia in Alzheimer's disease

Amyloid deposits are characteristic of Alzheimer's Disease (AD) and there is growing evidence that amyloid may play an important role in the genesis of this neurodegenerative disease. This review discusses data which suggests that reactive astrocytes and microglia may be a necessary concomitant with amyloid to produce the neuropathology which manifests as AD. Several hypotheses and supporting data for mechanisms by which reactive astrocytes may mediate this neuropathology are presented. These include the possibility that amyloid induces excitotoxicity by interferring with astrocytic glutamate uptake, the possibility that amyloid has this effect via an action on a tachykinin-related receptor and the possibility that proteoglycans released by astrocytes may facilitate the deposition of amyloid plaques. Both symptomatic treatment to enhance cognitive function and treatment to stop the progression of AD are needed. It is hoped that answers to some of the unique questions raised here may provide new insight into the etiology and treatment of AD.

APP-collagen interaction is mediated by a heparin bridge mechanism

The amyloid precursor protein (APP) is a glycoprotein consisting of at least four isoforms derived from a single gene by a process of alternative splicing. The membrane-bound forms of APP have been suggested to have adhesive properties and to mediate neural cell adhesion. Previous studies have demonstrated the ability of Fab' fragments of antibodies to extracellular domains of APP to inhibit neural cell binding to a collagen substrate, suggesting a physiological role for the collagen-binding properties of APP. The binding of APP has been demonstrated to be specific for type IV collagen, and no binding to other extracellular matrix components, including fibronectin and laminin, was detected. The APP-collagen binding appeared to be mediated by a heparin-bridge mechanism, since the binding was abolished by the addition of excess heparan or heparinase. These results were observed by both a homogenate-collagen binding assay and a cell-surface adhesion assay, thus providing further evidence for the adhesion role of APP. They also pose the question of the possible role of the heparin-binding properties of APP in the genesis of the neuritic plaques characteristic of Alzheimer's disease.

Developmental expression of alpha 1-antichymotrypsin in brain may be related to astrogliosis

In the brains of individuals with Alzheimer's disease (AD) and aged monkeys, the serine protease inhibitor alpha 1-antichymotrypsin (ACT) is selectively associated with deposits of amyloid found in senile plaques and in the walls of blood vessels. The origin of ACT in the brains of these aged subjects is unclear. In this study, ribonucleic acid (RNA) blots of human brains show that ACT messenger RNA (mRNA) increases during development. Levels of mRNA were negligible in fetuses and young adults but were increased slightly in normal aged individuals and highest in individuals with AD. In situ hybridization detected ACT transcripts in astrocytes of the cortex, subependymal region, and superficial white matter. The expression of ACT mRNA was highest in subjects with AD, in an adult with Down's syndrome, in an individual with Pick's disease, and in cases of Huntington's disease. In the brains of adult monkeys, ACT expression was detected primarily in astrocytes of the subependyma and white matter. Thus the presence of ACT appears to be related to the response of astrocytes to the brain abnormalities seen in these conditions.

Distribution pattern and functional state of alpha 1-antichymotrypsin in plaques and vascular amyloid in Alzheimer's disease. A immunohistochemical study with monoclonal antibodies against native and inactivated alpha 1-antichymotrypsin

Monoclonal antibodies (mAbs) were raised against inactivated alpha 1-antichymotrypsin (ACT) to study the presence and functional state of the serine protease inhibitor alpha 1-antichymotrypsin in cerebral amyloid deposits in Alzheimer's disease. A panel of seven different mAbs was obtained; six of them were directed against neoepitopes that are expressed on ACT after interaction with proteases (inactivated ACT) and one mAb was directed against an epitope that is exposed both on native and inactivated ACT. The mAbs against neoepitopes could discriminate native ACT from complexed and inactivated ACT in vitro as shown in binding experiments in the presence of either native or inactivated ACT. With the mAbs against ACT we found that: (a) besides classical congophilic plaques, amorphous noncongophilic beta/A4-positive plaques were stained; (b) amorphous and classical plaques reacted with both types of mAbs against ACT indicating that this ACT was either complexed to a protease or proteolytically inactivated; (c) vascular amyloid was not stained for ACT. The presence of ACT in amorphous and classical plaques and its absence in vascular amyloid may indicate differences in the proteolytic degradation of preamyloid into amyloid fibrils. Our study strongly suggests that ACT is biologically active in amyloid plaques from an early stage.

New biochemical insights to unravel the pathogenesis of Alzheimer's lesions

Purification of amyloid plaque core proteins (APCP) from Alzheimer's disease brains to complete homogeneity and in high yield permitted its chemical fractionation and characterization of its components. APCP is mainly made of beta-amyloid (beta A) and an assortment of glycoproteins (accounting for 20%) rich in carbohydrates compatible with N- and O-linked saccharides. When added to tissue culture of sympathetic and sensory neurons APCP and beta A inhibited neuritic sprouting, a reversible phenomenon at low doses. Higher concentrations of both substances kill the neurons in culture. APCP is significantly more toxic than beta A, suggesting the minor components may play an important role in increasing the toxicity of beta A. If the observed toxic effects of APCP in situ are occurring in vivo during the course of AD, then the accumulation of these extracellular proteins could be largely responsible for some of the neuronal death observed in this neuropathology.