Sulfation of heparan sulfate associated with amyloid-beta plaques in patients with Alzheimer's disease

Impact of long-term deltamethrin exposure on Alzheimer's-related neurodegeneration in rats

In recent years, epidemiological studies have emerged indicating a potential association between chronic exposure to pesticides and the development of chronic neurodegenerative nervous system diseases such as Alzheimer's disease. In this study, we aimed to investigate the potential role of long-term nonfatal exposure to Deltamethrin in spreading this disease. To this end, a range of aspects of brain damage were discussed in rats administered deltamethrin in oral doses of 0.65 mg/kg b.w. and 1.3 mg/kg b.w. for 30 days. The activation of beta-amyloid, the primary component of plaques characteristic of Alzheimer's disease, and the NG2, a type 1 transmembrane protein, was assessed by immunohistochemistry and western blot methods in rat brain. In addition, the expression level of the APP, GFAP, NfL, TNF-alpha, CXCL9, CCL5, and IL-1 alpha genes in deltamethrin-exposed brain tissue was measured using qRT-PCR. In addition, levels of pTau181 and Abeta42 were measured with ELISA. A strong positive immunohistochemical reaction for beta-amyloid was detected in the deltamethrin-exposed brain tissues. A decrease in NG2 immunofluorescence positivity was found in the application groups compared to the control group. It was demonstrated that deltamethrin exposure significantly up-regulated the expressions of APP, GFAP, NfL, TNF-alpha, CXCL9, CCL5, and IL-1 alpha genes, also significantly higher the levels of pTau181 and Abeta42 (pg/ml) in rat brain tissues. This study provides scientific evidence that exposure to chronic doses of deltamethrin may play a positive role in the development of diseases such as Alzheimer's. Future studies should investigate similar projects and expand knowledge on the topic.

Multi-omic analysis of meningeal cerebral amyloid angiopathy reveals enrichment of unsubstituted glucosamine and extracellular proteins

Cerebral amyloid angiopathy (CAA) is a common feature of Alzheimer's disease in which amyloid-β (Aβ) deposits in cerebral and leptomeningeal vessel walls, predisposing vessels to micro- and macro-hemorrhages. The vessel walls contain distinct proteins and heparan sulfate (HS), yet how vascular proteins and HS jointly associate with Aβ is unknown. We conducted the first multi-omics study to systematically characterize the proteins as well as the HS abundance, sulfation level, and disaccharide composition of leptomeninges from 23 moderate to severe CAA cases and controls. We then analyzed the associations between Aβ and other proteins, HS, and apolipoprotein E genotype. We found an increase in a minor HS disaccharide containing unsubstituted glucosamine, as well as 6-O sulfated disaccharides; Aβ40 levels positively correlated with unsubstituted glucosamine. There was also an increase in extracellular proteins derived from brain parenchyma or plasma, including olfactomedin-like protein 3, fibrinogen, serum amyloid protein, apolipoprotein E, and secreted frizzled related protein-3. Our findings of vascular HS and protein alterations specific to CAA-affected leptomeningeal vessels provide molecular insight into the extracellular remodeling that co-occurs with Aβ deposits and may indicate a basis for antemortem diagnostic assay development and therapeutic strategies to impede Aβ-HS interactions.

A Single-Domain VNAR Nanobody Binds with High-Affinity and Selectivity to the Heparin Pentasaccharide Fondaparinux

Glycosaminoglycans (GAGs) are key ligands for proteins involved in physiological and pathological processes. Specific GAG-binding patterns are rarely identified, with the heparin pentasaccharide as an Antithrombin-III ligand being the best characterized. Generating glycan-specific antibodies is difficult due to their size, pattern dispersion, and flexibility. Single-domain variable new antigen receptors (VNAR nanobodies) from nurse sharks are highly soluble, stable, and versatile. Their unique properties suggest advantages over conventional antibodies, particularly for challenging biotherapeutic targets. Here we have used VNAR semi-synthetic phage libraries to select high-affinity fondaparinux-binding VNARs that did not show cross-reactivity with other GAG species. Competition ELISA and surface plasmon resonance identified a single fondaparinux-selective VNAR clone. This VNAR exhibited an extraordinarily stable protein fold: the beta-strands are stabilized by a robust hydrophobic network, as revealed by heteronuclear NMR. Docking fondaparinux to the VNAR structure revealed a large contact surface area between the CDR3 loop of the antibody and the glycan. Fusing the VNAR with a human Fc domain resulted in a stable product with a high affinity for fondaparinux (Kd = 9.3 × 10-8 M) that could efficiently discriminate between fondaparinux and other glycosaminoglycans. This novel glycan-targeting screening technology represents a promising therapeutic strategy for addressing GAG-related diseases.

Shared Gene Expression Dysregulation Across Subtypes of Sanfilippo and Morquio Diseases: The Role of PFN1 in Regulating Glycosaminoglycan Levels

BACKGROUND

Mucopolysaccharidosis (MPS) is a class of hereditary metabolic diseases that demonstrate itself by accumulating incompletely degraded glycosaminoglycans (GAGs). MPS are classified according to the kind(s) of stored GAG(s) and specific genetic/enzymatic defects. Despite the accumulation of the same type of GAG, two MPS diseases, Sanfilippo (MPS III) and Morquio (MPS IV), are further distinguished into subclasses based on different enzymes that are deficient. Although genetic defects in MPS are known, molecular mechanisms of particular MPS types are still incomplete. This work aimed to investigate gene expression patterns in MPS III and MPS IV subtypes to identify dysregulated genes that could indicate unidentified molecular mechanisms of the diseases.

METHODS

Transcriptomic analyses were conducted to assess gene expression patterns in MPS and control cells. Western blotting and immunohistochemistry determined selected protein levels (products of the most significantly dysregulated genes). Effects of decreased levels of gene expression were investigated using small interferring RNA (siRNA)-mediated gene silencing.

RESULTS

Transcriptomic analyses indicated 45 commonly dysregulated genes among all MPS III subtypes and as many as 150 commonly dysregulated genes among both MPS IV subtypes. A few genes revealed particularly high levels of dysregulation, including PFN1, MFAP5, and MMP12. Intriguingly, elevated levels of profilin-1 (product of the PFN1 gene) could be reduced by decreasing GAG levels in genistein-treated MPS III and MPS IV cells, while silencing of PFN1 caused a significant decrease in GAG accumulation in these cells, indicating an interdependent correlation between profilin-1 and GAG levels.

CONCLUSIONS

A plethora of commonly dysregulated genes were identified in MPS subtypes III and IV. Some of these genes, like PFN1, MFAP5, and MMP12, revealed highly pronounced changes in expression relative to control cells. An interdependent correlation between GAG levels and the expression of the PFN1 gene was identified. Thus, PFN1 could be suggested as a potential new therapeutic target for MPS III and IV.

Comprehensive evaluation of pathogenic protein accumulation in fibroblasts from all subtypes of Sanfilippo disease patients

Sanfilippo disease is a lysosomal storage disorder from the group of mucopolysaccharidoses (MPS), characterized by storage of glycosaminoglycans (GAGs); thus, it is also called MPS type III. The syndrome is divided into 4 subtypes (MPS III A, B, C and D). Despite the storage of the same GAG, heparan sulfate (HS), the course of these subtypes can vary considerably. Here, we comprehensively evaluated the levels of protein aggregates (APP, β-amyloid, p-tau, α-synuclein, TDP43) in fibroblasts derived from patients with all MPS III subtypes, and tested whether lowering GAG levels results in a decrease in the levels of the investigated proteins and the number of aggregates they form. Elevated levels of APP, β-amyloid, tau, and TDP43 proteins were evident in all MPS III subtypes, and elevated levels of p-tau and α-synuclein were demonstrated in all subtypes except MPS IIIC. These findings were confirmed in the neural tissue of MPS IIIB mice. Fluorescence microscopy studies also indicated a high number of protein aggregates formed by β-amyloid and tau in all cell lines tested, and a high number of aggregates of p-tau, TDP43, and α-synuclein in all lines except MPS IIIC. Reduction of GAG levels by genistein led to the decrease of levels of all tested proteins and their aggregates except α-synuclein, indicating a relationship between GAG levels and those of some protein aggregates. This work describes for the first time the problem of deposited protein aggregates in all subtypes of Sanfilippo disease and suggests that GAGs are partly responsible for the formation of protein aggregates.

Potential Mechanisms of Tunneling Nanotube Formation and Their Role in Pathology Spread in Alzheimer's Disease and Other Proteinopathies

Alzheimer's disease (AD) is the most common type of dementia worldwide. The etiopathogenesis of this disease remains unknown. Currently, several hypotheses attempt to explain its cause, with the most well-studied being the cholinergic, beta-amyloid (Aβ), and Tau hypotheses. Lately, there has been increasing interest in the role of immunological factors and other proteins such as alpha-synuclein (α-syn) and transactive response DNA-binding protein of 43 kDa (TDP-43). Recent studies emphasize the role of tunneling nanotubes (TNTs) in the spread of pathological proteins within the brains of AD patients. TNTs are small membrane protrusions composed of F-actin that connect non-adjacent cells. Conditions such as pathogen infections, oxidative stress, inflammation, and misfolded protein accumulation lead to the formation of TNTs. These structures have been shown to transport pathological proteins such as Aβ, Tau, α-syn, and TDP-43 between central nervous system (CNS) cells, as confirmed by in vitro studies. Besides their role in spreading pathology, TNTs may also have protective functions. Neurons burdened with α-syn can transfer protein aggregates to glial cells and receive healthy mitochondria, thereby reducing cellular stress associated with α-syn accumulation. Current AD treatments focus on alleviating symptoms, and clinical trials with Aβ-lowering drugs have proven ineffective. Therefore, intensifying research on TNTs could bring scientists closer to a better understanding of AD and the development of effective therapies.

Mass spectrometry methods for analysis of extracellular matrix components in neurological diseases

The brain extracellular matrix (ECM) is a highly glycosylated environment and plays important roles in many processes including cell communication, growth factor binding, and scaffolding. The formation of structures such as perineuronal nets (PNNs) is critical in neuroprotection and neural plasticity, and the formation of molecular networks is dependent in part on glycans. The ECM is also implicated in the neuropathophysiology of disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), and Schizophrenia (SZ). As such, it is of interest to understand both the proteomic and glycomic makeup of healthy and diseased brain ECM. Further, there is a growing need for site-specific glycoproteomic information. Over the past decade, sample preparation, mass spectrometry, and bioinformatic methods have been developed and refined to provide comprehensive information about the glycoproteome. Core ECM molecules including versican, hyaluronan and proteoglycan link proteins, and tenascin are dysregulated in AD, PD, and SZ. Glycomic changes such as differential sialylation, sulfation, and branching are also associated with neurodegeneration. A more thorough understanding of the ECM and its proteomic, glycomic, and glycoproteomic changes in brain diseases may provide pathways to new therapeutic options.

Heparan sulfate proteoglycan in Alzheimer's disease: aberrant expression and functions in molecular pathways related to amyloid-β metabolism

Alzheimer's disease (AD) is the most common form of dementia. Currently, there is no effective treatment for AD, as its etiology remains poorly understood. Mounting evidence suggests that the accumulation and aggregation of amyloid-β peptides (Aβ), which constitute amyloid plaques in the brain, is critical for initiating and accelerating AD pathogenesis. Considerable efforts have been dedicated to shedding light on the molecular basis and fundamental origins of the impaired Aβ metabolism in AD. Heparan sulfate (HS), a linear polysaccharide of the glycosaminoglycan family, co-deposits with Aβ in plaques in the AD brain, directly binds and accelerates Aβ aggregation, and mediates Aβ internalization and cytotoxicity. Mouse model studies demonstrate that HS regulates Aβ clearance and neuroinflammation in vivo. Previous reviews have extensively explored these discoveries. Here, this review focuses on the recent advancements in understanding abnormal HS expression in the AD brain, the structural aspects of HS-Aβ interaction, and the molecules involved in modulating Aβ metabolism through HS interaction. Furthermore, this review presents a perspective on the potential effects of abnormal HS expression on Aβ metabolism and AD pathogenesis. In addition, the review highlights the importance of conducting further research to differentiate the spatiotemporal components of HS structure and function in the brain and AD pathogenesis.

The Alterations and Roles of Glycosaminoglycans in Human Diseases

Glycosaminoglycans (GAGs) are a heterogeneous family of linear polysaccharides which are composed of a repeating disaccharide unit. They are also linked to core proteins to form proteoglycans (PGs). GAGs/PGs are major components of the cell surface and the extracellular matrix (ECM), and they display critical roles in development, normal function, and damage response in the body. Some properties (such as expression quantity, molecular weight, and sulfation pattern) of GAGs may be altered under pathological conditions. Due to the close connection between these properties and the function of GAGs/PGs, the alterations are often associated with enormous changes in the physiological/pathological status of cells and organs. Therefore, these GAGs/PGs may serve as marker molecules of disease. This review aimed to investigate the structural alterations and roles of GAGs/PGs in a range of diseases, such as atherosclerosis, cancer, diabetes, neurodegenerative disease, and virus infection. It is hoped to provide a reference for disease diagnosis, monitoring, prognosis, and drug development.

Glycosylated clusterin species facilitate Aβ toxicity in human neurons

Clusterin (CLU) is one of the most significant genetic risk factors for late onset Alzheimer's disease (AD). However, the mechanisms by which CLU contributes to AD development and pathogenesis remain unclear. Studies have demonstrated that the trafficking and localisation of glycosylated CLU proteins is altered by CLU-AD mutations and amyloid-β (Aβ), which may contribute to AD pathogenesis. However, the roles of non-glycosylated and glycosylated CLU proteins in mediating Aβ toxicity have not been studied in human neurons. iPSCs with altered CLU trafficking were generated following the removal of CLU exon 2 by CRISPR/Cas9 gene editing. Neurons were generated from control (CTR) and exon 2 -/- edited iPSCs and were incubated with aggregated Aβ peptides. Aβ induced changes in cell death and neurite length were quantified to determine if altered CLU protein trafficking influenced neuronal sensitivity to Aβ. Finally, RNA-Seq analysis was performed to identify key transcriptomic differences between CLU exon 2  -/- and CTR neurons. The removal of CLU exon 2, and the endoplasmic reticulum (ER)-signal peptide located within, abolished the presence of glycosylated CLU and increased the abundance of intracellular, non-glycosylated CLU. While non-glycosylated CLU levels were unaltered by Aβ_25-35 treatment, the trafficking of glycosylated CLU was altered in control but not exon 2  -/- neurons. The latter also displayed partial protection against Aβ-induced cell death and neurite retraction. Transcriptome analysis identified downregulation of multiple extracellular matrix (ECM) related genes in exon 2  -/- neurons, potentially contributing to their reduced sensitivity to Aβ toxicity. This study identifies a crucial role of glycosylated CLU in facilitating Aβ toxicity in human neurons. The loss of these proteins reduced both, cell death and neurite damage, two key consequences of Aβ toxicity identified in the AD brain. Strikingly, transcriptomic differences between exon 2  -/- and control neurons were small, but a significant and consistent downregulation of ECM genes and pathways was identified in exon 2  -/- neurons. This may contribute to the reduced sensitivity of these neurons to Aβ, providing new mechanistic insights into Aβ pathologies and therapeutic targets for 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.

Design and Synthesis of 6-O-Phosphorylated Heparan Sulfate Oligosaccharides to Inhibit Amyloid β Aggregation

Dysregulation of amyloidogenic proteins and their abnormal processing and deposition in tissues cause systemic and localized amyloidosis. Formation of amyloid β (Aβ) fibrils that deposit as amyloid plaques in Alzheimer's disease (AD) brains is an earliest pathological hallmark. The polysulfated heparan sulfate (HS)/heparin (HP) is one of the non-protein components of Aβ deposits that not only modulates Aβ aggregation, but also acts as a receptor for Aβ fibrils to mediate their cytotoxicity. Interfering with the interaction between HS/HP and Aβ could be a therapeutic strategy to arrest amyloidosis. Here we have synthesized the 6-O-phosphorylated HS/HP oligosaccharides and reported their competitive effects on the inhibition of HP-mediated Aβ fibril formation in vitro using a thioflavin T fluorescence assay and a tapping mode atomic force microscopy.

Circadian control of heparan sulfate levels times phagocytosis of amyloid beta aggregates

Alzheimer's Disease (AD) is a neuroinflammatory disease characterized partly by the inability to clear, and subsequent build-up, of amyloid-beta (Aβ). AD has a bi-directional relationship with circadian disruption (CD) with sleep disturbances starting years before disease onset. However, the molecular mechanism underlying the relationship of CD and AD has not been elucidated. Myeloid-based phagocytosis, a key component in the metabolism of Aβ, is circadianly-regulated, presenting a potential link between CD and AD. In this work, we revealed that the phagocytosis of Aβ42 undergoes a daily circadian oscillation. We found the circadian timing of global heparan sulfate proteoglycan (HSPG) biosynthesis was the molecular timer for the clock-controlled phagocytosis of Aβ and that both HSPG binding and aggregation may play a role in this oscillation. These data highlight that circadian regulation in immune cells may play a role in the intricate relationship between the circadian clock and AD.

Isolation and Characterization of Heparan Sulfate Containing Amyloid Precursor Protein Degradation Products

Numerous studies indicate that heparan sulfate proteoglycans (HSPGs) participate in a network of complex molecular events involving amyloid precursor protein (APP) processing and formation, oligomerization, intracellular targeting, clearance, and propagation of amyloid β in Alzheimer's disease (AD). A mutual functional interplay between recycling glypican-1 and APP processing has been demonstrated where the HS released from glypican-1 by a Cu/NO-ascorbate-dependent reaction forms a conjugate with APP degradation products and undergoes an endosome-nucleus-autophagosome co-trafficking. HS has been shown to display contradictory and dual effects in AD involving both prevention and promotion of amyloid β formation. It is therefore important to identify the source, detailed structural features as well as factors that favor formation of the neuroprotective forms of HS. Here, a method for isolation and identification of HS-containing APP degradation products has been described. The method is based on isolation of radiolabeled HS followed by identification of accompanying APP degradation products by SDS-PAGE and Western blotting.

Disease-specific glycosaminoglycan patterns in the extracellular matrix of human lung and brain

A wide variety of diseases throughout the mammalian organism is characterized by abnormal deposition of various components of the extracellular matrix (ECM), including the heterogeneous family of glycosaminoglycans (GAGs), which contribute considerably to the ECM architecture as part of the so-called proteoglycans. The GAG's unique sulfation pattern, derived from highly dynamic and specific modification processes, has a massive impact on critical mediators such as cytokines and growth factors. Due to the strong connection between the specific sulfation pattern and GAG function, slight alterations of this pattern are often associated with enormous changes at the cell as well as at the organ level. This review aims to investigate the connection between modifications of GAG sulfation patterns and the wide range of pathological conditions, mainly focusing on a range of chronic diseases of the central nervous system (CNS) as well as the respiratory tract.

To target Tau pathologies, we must embrace and reconstruct their complexities

The accumulation of hyperphosphorylated fibrillar Tau aggregates in the brain is one of the defining hallmarks of Tauopathy diseases, including Alzheimer's disease. However, the primary events or molecules responsible for initiation of the pathological Tau aggregation and spreading remain unknown. The discovery of heparin as an effective inducer of Tau aggregation in vitro was instrumental to enabling different lines of research into the role of Tau aggregation in the pathogenesis of Tauopathies. However, recent proteomics and cryogenic electron microscopy (cryo-EM) studies have revealed that heparin-induced Tau fibrils generated in vitro do not reproduce the biochemical and ultrastructural properties of disease-associated brain-derived Tau fibrils. These observations demand that we reassess our current approaches for investigating the mechanisms underpinning Tau aggregation and pathology formation. Our review article presents an up-to-date survey and analyses of 1) the evolution of our understanding of the interactions between Tau and heparin, 2) the various structural and mechanistic models of the heparin-induced Tau aggregation, 3) the similarities and differences between brain-derived and heparin-induced Tau fibrils; and 4) emerging concepts on the biochemical and structural determinants underpinning Tau pathological heterogeneity in Tauopathies. Our analyses identify specific knowledge gaps and call for 1) embracing the complexities of Tau pathologies; 2) reassessment of current approaches to investigate, model and reproduce pathological Tau aggregation as it occurs in the brain; 3) more research towards a better understanding of the naturally-occurring cofactor molecules that are associated with Tau brain pathology initiation and propagation; and 4) developing improved approaches for in vitro production of the Tau aggregates and fibrils that recapitulate and/or amplify the biochemical and structural complexity and diversity of pathological Tau in Tauopathies. This will result in better and more relevant tools, assays, and mechanistic models, which could significantly improve translational research and the development of drugs and antibodies that have higher chances for success in the clinic.

Role of the Extracellular Matrix in Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disease with complex pathological characteristics, whose etiology and pathogenesis are still unclear. Over the past few decades, the role of the extracellular matrix (ECM) has gained importance in neurodegenerative disease. In this review, we describe the role of the ECM in AD, focusing on the aspects of synaptic transmission, amyloid-β-plaque generation and degradation, Tau-protein production, oxidative-stress response, and inflammatory response. The function of ECM in the pathological process of AD will inform future research on the etiology and pathogenesis of AD.

Heparanase overexpression impedes perivascular clearance of amyloid-β from murine brain: relevance to Alzheimer's disease

Defective amyloid-β (Aβ) clearance from the brain is a major contributing factor to the pathophysiology of Alzheimer's disease (AD). Aβ clearance is mediated by macrophages, enzymatic degradation, perivascular drainage along the vascular basement membrane (VBM) and transcytosis across the blood-brain barrier (BBB). AD pathology is typically associated with cerebral amyloid angiopathy due to perivascular accumulation of Aβ. Heparan sulfate (HS) is an important component of the VBM, thought to fulfill multiple roles in AD pathology. We previously showed that macrophage-mediated clearance of intracortically injected Aβ was impaired in the brains of transgenic mice overexpressing heparanase (Hpa-tg). This study revealed that perivascular drainage was impeded in the Hpa-tg brain, evidenced by perivascular accumulation of the injected Aβ in the thalamus of Hpa-tg mice. Furthermore, endogenous Aβ accumulated at the perivasculature of Hpa-tg thalamus, but not in control thalamus. This perivascular clearance defect was confirmed following intracortical injection of dextran that was largely retained in the perivasculature of Hpa-tg brains, compared to control brains. Hpa-tg brains presented with thicker VBMs and swollen perivascular astrocyte endfeet, as well as elevated expression of the BBB-associated water-pump protein aquaporin 4 (AQP4). Elevated levels of both heparanase and AQP4 were also detected in human AD brain. These findings indicate that elevated heparanase levels alter the organization and composition of the BBB, likely through increased fragmentation of BBB-associated HS, resulting in defective perivascular drainage. This defect contributes to perivascular accumulation of Aβ in the Hpa-tg brain, highlighting a potential role for heparanase in the pathogenesis of AD.

Alterations in the Expression of the Genes Responsible for the Synthesis of Heparan Sulfate in Brains With Alzheimer Disease

The saccharide chains of heparan sulfate appear to be involved in several aspects Alzheimer disease (AD) pathogenesis. Their structural complexity is due to the expression of different isoenzymes. We studied the differential transcription of heparan sulfate chain biosynthesis in AD brains, analyzing different brain regions in patients with different extents of AD pathology. The transcriptomic study was performed by RT-PCR using samples of amygdala, anterior hippocampus, posterior hippocampus, claustrum, calcarine fissure, globus pallidus and cerebellum from patients with mild, moderate, or severe AD, as well as healthy individuals. Certain heparan sulfate epitopes were also detected by immunohistochemistry. Several genes, across all stages of heparan sulfate synthesis, showed altered transcription in different brain regions of AD patients. The numbers of alterations were greater in in moderate versus mild AD patients. In severe patients, there were fewer alterations in genes related to early stages of biosynthesis, and overexpression of genes involved in late stages. The alterations correlated with progressive brain atrophy, although alterations were more common in the cerebellum. Detection of some heparan sulfate epitopes by immunohistochemistry was consistent with previous studies. In conclusion, transcriptional alterations in the biosynthetic genes of heparan sulfate depend on the brain region and the degree of AD pathology.

Heparan Sulfate Proteoglycans Undergo Differential Expression Alterations in Alzheimer Disease Brains

Previous studies have reported that heparan sulfate proteoglycans (HSPGs) promote amyloid-beta peptide and tau fibrillization in Alzheimer disease (AD) and provide resistance against proteolytic breakdown. We compared the expression levels of 17 HSPG core proteins in 18 AD cases and 6 controls. RT-PCR was used to analyze transcription levels. Immunohistochemistry was performed to localize HSPGs in the brain tissue. We detected expression of all HSPG genes investigated. SDC1, GPC3, and CD44v3 showed the lowest levels of expression, while SDC3 and GPC1 showed the highest. Remarkably, SDC4 and SRGN were overexpressed in most of the areas analyzed. Immunohistochemistry revealed the presence of both SDC4 and SRGN mostly associated with tau and amyloid-β pathology throughout the AD brains. In conclusion, in view of the involvement of HSPGs in AD pathology, especially SDC4 and SRGN, there would seem to be a relationship between the regulation of core protein expression and the pathological features suggesting HSPGs are potential inducers of the disease.

Implications of Heparan Sulfate and Heparanase in Amyloid Diseases

Amyloidosis refers to a group of diseases characterized by abnormal deposition of denatured endogenous proteins, termed amyloid, in the affected organs. Analysis of biopsy and autopsy tissues from patients revealed the presence of heparan sulfate proteoglycans (HSPGs) along with amyloid proteins in the deposits. For a long time, HSPGs were believed to occur in the deposits as an innocent bystander. Yet, the consistent presence of HSPGs in various deposits, regardless of the amyloid species, led to the hypothesis that these macromolecular glycoconjugates might play functional roles in the pathological process of amyloidosis. In vitro studies have revealed that HSPGs, or more precisely, the heparan sulfate (HS) side chains interact with amyloid peptides, thus promoting amyloid fibrillization. Although information on the mechanisms of HS participation in amyloid deposition is limited, recent studies involving a transgenic mouse model of Alzheimer's disease point to an active role of HS in amyloid formation. Heparanase cleavage alters the molecular structure of HS, and thus modulates the functional roles of HS in homeostasis, as well as in diseases, including amyloidosis. The heparanase transgenic mice have provided models for unveiling the effects of heparanase, through cleavage of HS, in various amyloidosis conditions.

Salt and solvent effects in the microscale chromatographic separation of heparan sulfate disaccharides

The analysis of heparan sulfate disaccharides poses a real challenge both from chromatographic and mass spectrometric point of view. This necessitates the constant improvement of their analytical methodology. In the present study, the chromatographic effects of solvent composition, salt concentration, and salt type were systematically investigated in isocratic HILIC-WAX separations of heparan sulfate disaccharides. The combined use of 75% acetonitrile with ammonium formate had overall benefits regarding intensity, detection limits, and peak shape for all salt concentrations investigated. Results obtained with the isocratic measurements suggested the potential use of a salt gradient method in order to maximize separation efficiency. A 3-step gradient from 14 mM to 65 mM ammonium formate concentration proved to be ideal for separation and quantitation. The LOD of the resulting method was 0.8-1.5 fmol for the individual disaccharides and the LOQ was between 2.5-5 fmol. Outstanding linearity could be observed up to 2 pmol. This novel combination provided sufficient sensitivity for disaccharide analysis, which was demonstrated by the analysis of heparan sulfate samples from porcine and bovine origin.

Contribution of syndecans to cellular internalization and fibrillation of amyloid-β(1-42)

Intraneuronal accumulation of amyloid-β(1-42) (Aβ1-42) is one of the earliest signs of Alzheimer's disease (AD). Cell surface heparan sulfate proteoglycans (HSPGs) have profound influence on the cellular uptake of Aβ1-42 by mediating its attachment and subsequent internalization into the cells. Colocalization of amyloid plaques with members of the syndecan family of HSPGs, along with the increased expression of syndecan-3 and -4 have already been reported in postmortem AD brains. Considering the growing evidence on the involvement of syndecans in the pathogenesis of AD, we analyzed the contribution of syndecans to cellular uptake and fibrillation of Aβ1-42. Among syndecans, the neuron specific syndecan-3 isoform increased cellular uptake of Aβ1-42 the most. Kinetics of Aβ1-42 uptake also proved to be fairly different among SDC family members: syndecan-3 increased Aβ1-42 uptake from the earliest time points, while other syndecans facilitated Aβ1-42 internalization at a slower pace. Internalized Aβ1-42 colocalized with syndecans and flotillins, highlighting the role of lipid-rafts in syndecan-mediated uptake. Syndecan-3 and 4 also triggered fibrillation of Aβ1-42, further emphasizing the pathophysiological relevance of syndecans in plaque formation. Overall our data highlight syndecans, especially the neuron-specific syndecan-3 isoform, as important players in amyloid pathology and show that syndecans, regardless of cell type, facilitate key molecular events in neurodegeneration.

The Accumulation of Heparan Sulfate S-Domains in Kidney Transthyretin Deposits Accelerates Fibril Formation and Promotes Cytotoxicity

The highly sulfated domains of heparan sulfate (HS), alias HS S-domains, are made up of repeated trisulfated disaccharide units [iduronic acid (2S)-glucosamine (NS, 6S)] and are selectively remodeled by extracellular endoglucosamine 6-sulfatases (Sulfs). Although HS S-domains are critical for signal transduction of several growth factors, their roles in amyloidoses are not yet fully understood. Herein, we found HS S-domains in the kidney of a patient with transthyretin amyloidosis. In in vitro assays with cells stably expressing human Sulfs, heparin, a structural analog of HS S-domains, promoted aggregation of transthyretin in an HS S-domain-dependent manner. Interactions of cells with transthyretin fibrils and cytotoxicity of these fibrils also depended on HS S-domains at the cell surface. Furthermore, glypican-5, encoded by the susceptibility gene for nephrotic syndrome GPC5, was found to be accumulated in the transthyretin amyloidosis kidney. Our study, thus, provides a novel insight into the pathologic roles of HS S-domains in amyloidoses, and we propose that enzymatic remodeling of HS chains by Sulfs may offer an effective approach to inhibiting formation and cytotoxicity of amyloid fibrils.

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.

The role of heparan sulfates in protein aggregation and their potential impact on neurodegeneration

Neurodegenerative disorders, such as Alzheimer's, Parkinson's, and prion diseases, are directly linked to the formation and accumulation of protein aggregates in the brain. These aggregates, principally made of proteins or peptides that clamp together after acquisition of β-folded structures, also contain heparan sulfates. Several lines of evidence suggest that heparan sulfates centrally participate in the protein aggregation process. In vitro, they trigger misfolding, oligomerization, and fibrillation of amyloidogenic proteins, such as Aβ, tau, α-synuclein, prion protein, etc. They participate in the stabilization of protein aggregates, protect them from proteolysis, and act as cell-surface receptors for the cellular uptake of proteopathic seeds during their spreading. This review focuses attention on the importance of heparan sulfates in protein aggregation in brain disorders including Alzheimer's, Parkinson's, and prion diseases. The presence of these sulfated polysaccharides in protein inclusions in vivo and their capacity to trigger protein aggregation in vitro strongly suggest that they might play critical roles in the neurodegenerative process. Further advances in glyco-neurobiology will improve our understanding of the molecular and cellular mechanisms leading to protein aggregation and neurodegeneration.

Tau Pathology Promotes the Reorganization of the Extracellular Matrix and Inhibits the Formation of Perineuronal Nets by Regulating the Expression and the Distribution of Hyaluronic Acid Synthases

Hyaluronic acid (HA) is the backbone of the extracellular matrix (ECM) and provides biochemical and physical support to aggrecan-based perineuronal nets (PNNs), which are associated with the selective vulnerability of neurons in Alzheimer's disease (AD). Here, we showed that HA synthases (HASs), including Has1, Has2, and Has3, were widely expressed in murine central nervous system. All types of HASs were localized to cell bodies of neurons; only Has1 existed in the membranes of neural axons. By using TauP301S transgenic (Tg) mouse model, we found that the axonal-localization of Has1 was abolished in TauP301S overexpressed mouse brain, and the redistribution of Has1 was also observed in human AD brains, suggesting that the localization of Has1 is dependent on intact microtubules which are regulated partially by the phosphorylation and dephosphorylation cycles of tau proteins. Furthermore, Has1 was reduced and Has3 was increased in TauP301S Tg mouse brain, resulting in the upregulation of shorter-chain HA in the ECM. These findings suggest that by abolishing the axonal-localization of Has1 and promoting the expression of Has3 and the synthesis of shorter-chain HA, the tau pathology breaks the balance of ECM components, promotes the reorganization of the ECM, and inhibits the formation of PNNs in the hippocampus, and then regulates neuronal plasticity during the progression of AD.

Sensitive method for glycosaminoglycan analysis of tissue sections

A simple, isocratic HPLC method based on HILIC-WAX separation, has been developed for analyzing sulfated disaccharides of glycosaminoglycans (GAGs). To our best knowledge, this is the first successful attempt using this special phase in nano-HPLC-MS analysis. Mass spectrometry was based on negative ionization, improving both sensitivity and specificity. Detection limit for most sulfated disaccharides were approximately 1 fmol; quantitation limits 10 fmol. The method was applied for glycosaminoglycan profiling of tissue samples, using surface digestion protocols. This novel combination provides sufficient sensitivity for GAG disaccharide analysis, which was first performed using prostate cancer tissue microarrays. Preliminary results show that GAG analysis may be useful for identifying cancer related changes in small amounts of tissue samples (ca. 10 μg).

Role of proteoglycans in neuro-inflammation and central nervous system fibrosis

Fibrosis is defined as the thickening and scarring of connective tissue, usually as a consequence of tissue damage. The central nervous system (CNS) is special in the sense that fibrogenic cells are restricted to vascular and meningeal areas. Inflammation and the disruption of the blood-brain barrier can lead to the infiltration of fibroblasts and trigger fibrotic response. While the initial function of the fibrotic tissue is to restore the blood-brain barrier and to limit the site of injury, it also demolishes the structure of extracellular matrix and impedes the healing process by producing inhibitory molecules and forming a physical and biochemical barrier that prevents axon regeneration. As a major constituent in the extracellular matrix, proteoglycans participate in the neuro-inflammation, modulating the fibrotic process. In this review, we will discuss the pathophysiology of fibrosis during acute injuries of the CNS, as well as during chronic neurodegenerative conditions such as Alzheimer's disease, Parkinson's disease, multiple sclerosis and age-related neurodegeneration with focus on the functional roles of proteoglycans.

Heparan Sulfate Proteoglycans as Relays of Neuroinflammation

Heparan sulfate proteoglycans (HSPGs) are implicated as inflammatory mediators in a variety of settings, including chemokine activation, which is required to recruit circulating leukocytes to infection sites. Heparan sulfate (HS) polysaccharide chains are highly interactive and serve co-receptor roles in multiple ligand:receptor interactions. HS may also serve as a storage depot, sequestering ligands such as cytokines and restricting their access to binding partners. Heparanase, through its ability to fragment HS chains, is a key regulator of HS function and has featured prominently in studies of HS's involvement in inflammatory processes. This review focuses on recent discoveries regarding the role of HSPGs, HS, and heparanase during inflammation, with particular focus on the brain. HS chains emerge as critical go-betweens in multiple aspects of the inflammatory response-relaying signals between receptors and cells. The molecular interactions proposed to occur between HSPGs and the pathogen receptor toll-like receptor 4 (TLR4) are discussed, and we summarize some of the contrasting roles that HS and heparanase have been assigned in diseases associated with chronic inflammatory states, including Alzheimer's disease (AD). We conclude by briefly discussing how current knowledge could potentially be applied to augment HS-mediated events during sustained neuroinflammation, which contributes to neurodegeneration in AD.

Decreased Expression of Sulfatase 2 in the Brains of Alzheimer's Disease Patients: Implications for Regulation of Neuronal Cell Signaling

Background:

The human sulfatase 1 (SULF1) and sulfatase 2 (SULF2) genes modulate cell signaling and homeostasis in many tissues. Gene expression analyses have implicated SULF2 in disease pathogenesis, including Alzheimer’s disease (AD), but changes in brain SULF2 expression have not been directly established.

Objective:

To investigate the expression of SULF1 and SULF2 in brain tissues from AD cases and cognitively normal controls.

Methods:

Autopsy tissue from AD cases (n = 20) and age-and gender-matched cognitively normal controls (n = 20) were identified from the Mayo Clinic Alzheimer’s Disease Patient Registry neuropathology database. Tissue slides were stained for SULF1 and SULF2 protein expression in the hippocampus and frontal lobe and an expression score computed from the proportion of cells stained and the intensity of staining (range 0 [no expression] to 9 [marked expression]).

Results:

SULF2 expression was reduced in AD cases. Compared to cognitively normal controls, SULF2 expression in AD cases was significantly decreased in the hippocampal Cornu Ammonis (CA) (mean score of 6.5 in cases versus 8.3 in controls; p = 0.003), in the gray matter of the parahippocampal gyrus (5.6 in cases versus 7.6 in controls; p = 0.003), and in the frontal lobe gray matter (5.4 in cases versus 7.4 in controls; p = 0.002). There was no difference in SULF1 expression in the hippocampus or frontal lobe of AD cases and controls. As expected there were no differences in SULF1 or SULF2 expression in white matter in AD cases compared to cognitively normal controls.

Conclusion:

Decreased SULF2 in specific regions of the brain occurs in AD.

Molecular Origins of the Compatibility between Glycosaminoglycans and Aβ40 Amyloid Fibrils

The Aβ peptide forms extracellular plaques associated with Alzheimer's disease. In addition to protein fibrils, amyloid plaques also contain non-proteinaceous components, including glycosaminoglycans (GAGs). We have shown previously that the GAG low-molecular-weight heparin (LMWH) binds to Aβ40 fibrils with a three-fold-symmetric (3Q) morphology with higher affinity than Aβ40 fibrils in alternative structures, Aβ42 fibrils, or amyloid fibrils formed from other sequences. Solid-state NMR analysis of the GAG-3Q fibril complex revealed an interaction site at the corners of the 3Q fibril structure, but the origin of the binding specificity remained obscure. Here, using a library of short heparin polysaccharides modified at specific sites, we show that the N-sulfate or 6-O-sulfate of glucosamine, but not the 2-O-sulfate of iduronate within heparin is required for 3Q binding, indicating selectivity in the interactions of the GAG with the fibril that extends beyond general electrostatic complementarity. By creating 3Q fibrils containing point substitutions in the amino acid sequence, we also show that charged residues at the fibril three-fold apices provide the majority of the binding free energy, while charged residues elsewhere are less critical for binding. The results indicate, therefore, that LMWH binding to 3Q fibrils requires a precise molecular complementarity of the sulfate moieties on the GAG and charged residues displayed on the fibril surface. Differences in GAG binding to fibrils with distinct sequence and/or structure may thus contribute to the diverse etiology and progression of amyloid diseases.

Extracellular matrix proteomics in schizophrenia and Alzheimer's disease

Brain extracellular matrix (ECM) is a highly organized system that consists of collagens, noncollagenous proteins, glycoproteins, hyaluronan, and proteoglycans. Recognized physiological roles of ECM include developmental regulation, tissue homeostasis, cell migration, cell proliferation, cell differentiation, neuronal plasticity, and neurite outgrowth. Aberrant ECM structure is associated with brain neurodegenerative conditions. This review focuses on two neurodegenerative conditions, schizophrenia and Alzheimer's disease, and summarizes recent findings of altered ECM components, including proteoglycans, glycosaminoglycans, proteins, and glycoproteins, and proteins and genes related to other brain components. The scope includes immunohistochemical, genomics, transcriptomics, proteomics, and glycomics studies, and a critical assessment of current state of proteomic studies for neurodegenerative disorders. The intent is to summarize the ECM molecular alterations associated with neurodegenerative pathophysiology. Graphical Abstract Brain extracellular matrix showing HSPGs, CSPGs, HA, collagens, and other glycoproteins.

The "in and out" of glucosamine 6-O-sulfation: the 6th sense of heparan sulfate

The biological properties of Heparan sulfate (HS) polysaccharides essentially rely on their ability to bind and modulate a multitude of protein ligands. These interactions involve internal oligosaccharide sequences defined by their sulfation patterns. Amongst these, the 6-O-sulfation of HS contributes significantly to the polysaccharide structural diversity and is critically involved in the binding of many proteins. HS 6-O-sulfation is catalyzed by 6-O-sulfotransferases (6OSTs) during biosynthesis, and it is further modified by the post-synthetic action of 6-O-endosulfatases (Sulfs), two enzyme families that remain poorly characterized. The aim of the present review is to summarize the contribution of 6-O-sulfates in HS structure/function relationships and to discuss the present knowledge on the complex mechanisms regulating HS 6-O-sulfation.

How Glycosaminoglycans Promote Fibrillation of Salmon Calcitonin

Glycosaminoglycans (GAGs) bind all known amyloid plaques and help store protein hormones in (acidic) granular vesicles, but the molecular mechanisms underlying these important effects are unclear. Here we investigate GAG interactions with the peptide hormone salmon calcitonin (sCT). GAGs induce fast sCT fibrillation at acidic pH and only bind monomeric sCT at acidic pH, inducing sCT helicity. Increasing GAG sulfation expands the pH range for binding. Heparin, the most highly sulfated GAG, binds sCT in the pH interval 3-7. Small angle x-ray scattering indicates that sCT monomers densely decorate and pack single heparin chains, possibly via hydrophobic patches on helical sCT. sCT fibrillates without GAGs, but heparin binding accelerates the process by decreasing the otherwise long fibrillation lag times at low pH and accelerates fibril growth rates at neutral pH. sCT·heparin complexes form β-sheet-rich heparin-covered fibrils. Solid-state NMR reveals that heparin does not alter the sCT fibrillary core around Lys(11) but makes changes to Val(8) on the exterior side of the β-strand, possibly through contacts to Lys(18) Thus GAGs significantly modulate sCT fibrillation in a pH-dependent manner by interacting with both monomeric and aggregated sCT.

Amyloid-β Precursor Protein Modulates the Sorting of Testican-1 and Contributes to Its Accumulation in Brain Tissue and Cerebrospinal Fluid from Patients with Alzheimer Disease

The mechanisms leading to amyloid-β (Aβ) accumulation in sporadic Alzheimer disease (AD) are unknown but both increased production or impaired clearance likely contribute to aggregation. To understand the potential roles of the extracellular matrix proteoglycan Testican-1 in the pathophysiology of AD, we used samples from AD patients and controls and an in vitro approach. Protein expression analysis showed increased levels of Testican-1 in frontal and temporal cortex of AD patients; histological analysis showed that Testican-1 accumulates and co-aggregates with Aβ plaques in the frontal, temporal and entorhinal cortices of AD patients. Proteomic analysis identified 10 fragments of Testican-1 in cerebrospinal fluid (CSF) from AD patients. HEK293T cells expressing human wild type or mutant Aβ precursor protein (APP) were transfected with Testican-1. The co-expression of both proteins modified the sorting of Testican-1 into the endocytic pathway leading to its transient accumulation in Golgi, which seemed to affect APP processing, as indicated by reduced Aβ40 and Aβ42 levels in APP mutant cells. In conclusion, patient data reflect a clearance impairment that may favor Aβ accumulation in AD brains and our in vitro model supports the notion that the interaction between APP and Testican-1 may be a key step in the production and aggregation of Aβ species.

In Sickness and in Health: Perineuronal Nets and Synaptic Plasticity in Psychiatric Disorders

Rapidly emerging evidence implicates perineuronal nets (PNNs) and extracellular matrix (ECM) molecules that compose or interact with PNNs, in the pathophysiology of several psychiatric disorders. Studies on schizophrenia, autism spectrum disorders, mood disorders, Alzheimer's disease, and epilepsy point to the involvement of ECM molecules such as chondroitin sulfate proteoglycans, Reelin, and matrix metalloproteases, as well as their cell surface receptors. In many of these disorders, PNN abnormalities have also been reported. In the context of the “quadripartite” synapse concept, that is, the functional unit composed of the pre- and postsynaptic terminals, glial processes, and ECM, and of the role that PNNs and ECM molecules play in regulating synaptic functions and plasticity, these findings resonate with one of the most well-replicated aspects of the pathology of psychiatric disorders, that is, synaptic abnormalities. Here we review the evidence for PNN/ECM-related pathology in these disorders, with particular emphasis on schizophrenia, and discuss the hypothesis that such pathology may significantly contribute to synaptic dysfunction.

Role of Factor H and Related Proteins in Regulating Complement Activation in the Macula, and Relevance to Age-Related Macular Degeneration

The recent revolution in age-related macular degeneration (AMD) genetics has demonstrated that genetic alterations affecting the alternative pathway of the complement cascade have a major influence on AMD risk. One of the two most important genetic loci is on chromosome 1 and contains genes encoding complement factor H (FH) and the factor H related proteins (FHR proteins). In macular tissue, especially Bruch’s membrane, relatively high levels of a truncated splice variant of FH called factor H-like protein 1 (FHL-1) are present. Here we discuss how genetic variations may alter the amounts, or by altering their protein sequences, the functions of these proteins. In particular, the common Y402H polymorphism affects the ability of FHL-1 and FH to localize to Bruch’s membrane and the inner choroid because it alters the ability of these complement regulators to bind heparan sulphate (HS) in these structures. In addition, there is an age-related loss of HS from Bruch’s membrane. We hypothesize that a combination of poor binding of the 402H variants of FHL-1 and FH to Bruch’s membrane, combined with a decrease in binding due to age-related HS loss, eventually results in insufficient FHL-1 and FH binding to Bruch’s membrane. This could result in complement activation, inflammation and thereby predispose to AMD.

Complementing the Sugar Code: Role of GAGs and Sialic Acid in Complement Regulation

Sugar molecules play a vital role on both microbial and mammalian cells, where they are involved in cellular communication, govern microbial virulence, and modulate host immunity and inflammatory responses. The complement cascade, as part of a host's innate immune system, is a potent weapon against invading bacteria but has to be tightly regulated to prevent inappropriate attack and damage to host tissues. A number of complement regulators, such as factor H and properdin, interact with sugar molecules, such as glycosaminoglycans (GAGs) and sialic acid, on host and pathogen membranes and direct the appropriate complement response by either promoting the binding of complement activators or inhibitors. The binding of these complement regulators to sugar molecules can vary from location to location, due to their different specificities and because distinct structural and functional subpopulations of sugars are found in different human organs, such as the brain, kidney, and eye. This review will cover recent studies that have provided important new insights into the role of GAGs and sialic acid in complement regulation and how sugar recognition may be compromised in disease.

Identification of factor H-like protein 1 as the predominant complement regulator in Bruch's membrane: implications for age-related macular degeneration

The tight regulation of innate immunity on extracellular matrix (ECM) is a vital part of immune homeostasis throughout the human body, and disruption to this regulation in the eye is thought to contribute directly to the progression of age-related macular degeneration (AMD). The plasma complement regulator factor H (FH) is thought to be the main regulator that protects ECM against damaging complement activation. However, in the present study we demonstrate that a truncated form of FH, called FH-like protein 1 (FHL-1), is the main regulatory protein in the layer of ECM under human retina, called Bruch's membrane. Bruch's membrane is a major site of AMD disease pathogenesis and where drusen, the hallmark lesions of AMD, form. We show that FHL-1 can passively diffuse through Bruch's membrane, whereas the full sized, glycosylated, FH cannot. FHL-1 is largely bound to Bruch's membrane through interactions with heparan sulfate, and we show that the common Y402H polymorphism in the CFH gene, associated with an increased risk of AMD, reduces the binding of FHL-1 to this heparan sulfate. We also show that FHL-1 is retained in drusen whereas FH coats the periphery of the lesions, perhaps inhibiting their clearance. Our results identify a novel mechanism of complement regulation in the human eye, which highlights potential new avenues for therapeutic strategies.

Inactivation of Wnt signaling by a human antibody that recognizes the heparan sulfate chains of glypican-3 for liver cancer therapy

Wnt signaling is important for cancer pathogenesis and is often up-regulated in hepatocellular carcinoma (HCC). Heparan sulfate proteoglycans (HSPGs) function as coreceptors or modulators of Wnt activation. Glypican-3 (GPC3) is an HSPG that is highly expressed in HCC, where it can attract Wnt proteins to the cell surface and promote cell proliferation. Thus, GPC3 has emerged as a candidate therapeutic target in liver cancer. While monoclonal antibodies to GPC3 are currently being evaluated in preclinical and clinical studies, none have shown an effect on Wnt signaling. Here, we first document the expression of Wnt3a, multiple Wnt receptors, and GPC3 in several HCC cell lines, and demonstrate that GPC3 enhanced the activity of Wnt3a/β-catenin signaling in these cells. Then we report the identification of HS20, a human monoclonal antibody against GPC3, which preferentially recognized the heparan sulfate chains of GPC3, both the sulfated and nonsulfated portions. HS20 disrupted the interaction of Wnt3a and GPC3 and blocked Wnt3a/β-catenin signaling. Moreover, HS20 inhibited Wnt3a-dependent cell proliferation in vitro and HCC xenograft growth in nude mice. In addition, HS20 had no detectable undesired toxicity in mice. Taken together, our results show that a monoclonal antibody primarily targeting the heparin sulfate chains of GPC3 inhibited Wnt/β-catenin signaling in HCC cells and had potent antitumor activity in vivo.

CONCLUSION

An antibody directed against the heparan sulfate of a proteoglycan shows efficacy in blocking Wnt signaling and HCC growth, suggesting a novel strategy for liver cancer therapy.

Towards understanding the roles of heparan sulfate proteoglycans in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia, characterized by progressive loss of memory and cognitive dysfunctions. A central pathological event of AD is accumulation and deposition of cytotoxic amyloid-β peptide (Aβ) in the brain parenchyma. Heparan sulfate proteoglycans (HSPGs) and the side chains heparan sulfate (HS) are found associated with Aβ deposits in the brains of AD patients and transgenic animal models of AD. A growing body of evidence from in vitro and in vivo studies suggests functional roles of HSPG/HS in Aβ pathogenesis. Although the question of "how and why HSPG/HS is codeposited with Aβ?" still remains, it is within reach to understand the mechanisms of the events. Recent progress by immunohistochemical examination with advanced antibodies shed light on molecular structures of HS codeposited with Aβ. Several recent reports have provided important new insights into the roles of HSPG in Aβ pathogenesis. Particularly, experiments on mouse models revealed indispensible functions of HSPG in modulating Aβ-associated neuroinflammation and clearance of Aβ from the brain. Application of molecules to interfere with the interaction between HS and Aβ peptides has demonstrated beneficial effects on AD mouse models. Elucidating the functions of HSPG/HS in Aβ deposition and toxicity is leading to further understanding of the complex pathology of AD. The progress is encouraging development of new treatments for AD by targeting HS-Aβ interactions.

Apolipoprotein E increases cell association of amyloid-β 40 through heparan sulfate and LRP1 dependent pathways

The increased risk of Alzheimer's disease (AD) associated with specific apolipoprotein E (ApoE) isoforms appears to relate to altered amyloid-β (Aβ) homeostasis. Clearance of Aβ from the brain is reduced in the presence of the AD-associated ApoE4 isoform, which may contribute to the accumulation of Aβ deposits in the parenchyma and vasculature. The low-density lipoprotein receptor-related protein 1 (LRP1) and heparan sulfate proteoglycans (HSPGs), both established ApoE receptors, are involved in Aβ uptake, with LRP1 additionally implicated in Aβ transcytosis across the blood-brain barrier. In this study, we detected the co-distribution of heparan sulfate (HS), ApoE and LRP1 in Aβ(1-40)-positive brain microvessels from individuals with Down's syndrome diagnosed with AD. In addition, ApoE was pulled-down from AD cerebrospinal fluid with anti-Aβ antibodies. Using Chinese hamster ovary cells deficient in HS or LRP1, we found that ApoE increases cell association of Aβ in a HSPG- and LRP1-dependent manner; and further, ApoE processing is altered in the absence of cellular HS. These interactions may facilitate Aβ clearance from the brain, but if overwhelmed could contribute to Aβ accumulation and the pathogenesis of AD.

Implications of heparan sulfate and heparanase in neuroinflammation

Heparan sulfate proteoglycans (HSPGs), expressed on the cell surface and in the extracellular matrix of most animal tissues, have essential functions in development and homeostasis, and have been implicated in several pathological conditions. The functions of HSPGs are mainly mediated through interactions of the heparan sulfate (HS) polysaccharide side chains with different protein ligands. The molecular structure of HS is highly diverse, expressed in a cell-type specific manner. The flexible yet controlled structure of HS is primarily generated through a strictly regulated biosynthesis process and is further modified post-synthetically, such as desulfation by endosulfatases and fragmentation by heparanase. Heparanase is an endo-glucuronidase expressed in all tissues. The enzyme has been found up-regulated in a number of pathological conditions, implying a role in diseases mainly through degradation of HS. Emerging evidence demonstrates important roles of HS and heparanase in inflammatory reactions, particularly in the regulation of leukocyte activation and extravasation. Neuroinflammation is a common feature of various central nervous system disorders, thus it is a great interest to understand the implications of HS and heparanase in neuroinflammation.