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

Glycosaminoglycans' for brain health: Harnessing glycosaminoglycan based biomaterials for treating central nervous system diseases and in-vitro modeling

Dysfunction of the central nervous system (CNS) following traumatic brain injuries (TBI), spinal cord injuries (SCI), or strokes remains challenging to address using existing medications and cell-based therapies. Although therapeutic cell administration, such as stem cells and neuronal progenitor cells (NPCs), have shown promise in regenerative properties, they have failed to provide substantial benefits. However, the development of living cortical tissue engineered grafts, created by encapsulating these cells within an extracellular matrix (ECM) mimetic hydrogel scaffold, presents a promising functional replacement for damaged cortex in cases of stroke, SCI, and TBI. These grafts facilitate neural network repair and regeneration following CNS injuries. Given that natural glycosaminoglycans (GAGs) are a major constituent of the CNS, GAG-based hydrogels hold potential for the next generation of CNS healing therapies and in vitro modeling of CNS diseases. Brain-specific GAGs not only offer structural and biochemical signaling support to encapsulated neural cells but also modulate the inflammatory response in lesioned brain tissue, facilitating host integration and regeneration. This review briefly discusses different roles of GAGs and their related proteoglycan counterparts in healthy and diseases brain and explores current trends and advancements in GAG-based biomaterials for treating CNS injuries and modeling diseases. Additionally, it examines injectable, 3D bioprintable, and conductive GAG-based scaffolds, highlighting their clinical potential for in vitro modeling of patient-specific neural dysfunction and their ability to enhance CNS regeneration and repair following CNS injury in vivo.

Probing Protein Structural Changes in Alzheimer's Disease via Quantitative Cross-linking Mass Spectrometry

Alzheimer's disease (AD) is a progressive neurological disorder featuring abnormal protein aggregation in the brain, including the pathological hallmarks of amyloid plaques and hyperphosphorylated tau. Despite extensive research efforts, understanding the molecular intricacies driving AD development remains a formidable challenge. This study focuses on identifying key protein conformational changes associated with the progression of AD. To achieve this, we employed quantitative cross-linking mass spectrometry (XL-MS) to elucidate conformational changes in the protein networks in cerebrospinal fluid (CSF). By using isotopically labeled cross-linkers BS3d0 and BS3d4, we reveal a dynamic shift in protein interaction networks during AD progression. Our comprehensive analysis highlights distinct alterations in protein-protein interactions within mild cognitive impairment (MCI) states. This study accentuates the potential of cross-linked peptides as indicators of AD-related conformational changes, including previously unreported site-specific binding between α-1-antitrypsin (A1AT) and complement component 3 (CO3). Furthermore, this work enables detailed structural characterization of apolipoprotein E (ApoE) and reveals modifications within its helical domains, suggesting their involvement in MCI pathogenesis. The quantitative approach provides insights into site-specific interactions and changes in the abundance of cross-linked peptides, offering an improved understanding of the intricate protein-protein interactions underlying AD progression. These findings lay a foundation for the development of potential diagnostic or therapeutic strategies aimed at mitigating the negative impact of AD.

Kallikrein-related peptidase's significance in Alzheimer's disease pathogenesis: A comprehensive survey

Alzheimer's disease (AD) and related dementias constitute an important global health challenge. Detailed understanding of the multiple molecular mechanisms underlying their pathogenesis constitutes a clue for the management of the disease. Kallikrein-related peptidases (KLKs), a lead family of serine proteases, have emerged as potential biomarkers and therapeutic targets in the context of AD and associated cognitive decline. Hence, KLKs were proposed to display multifaceted impacts influencing various aspects of neurodegeneration, including amyloid-beta aggregation, tau pathology, neuroinflammation, and synaptic dysfunction. We propose here a comprehensive survey to summarize recent findings, providing an overview of the main kallikreins implicated in AD pathophysiology namely KLK8, KLK6 and KLK7. We explore the interplay between KLKs and key AD molecular pathways, shedding light on their significance as potential biomarkers for early disease detection. We also discuss their pertinence as therapeutic targets for disease-modifying interventions to develop innovative therapeutic strategies aimed at halting or ameliorating the progression of AD and associated dementias.

Vascular Heparan Sulfate and Amyloid-β in Alzheimer's Disease Patients

Alzheimer's disease (AD) is a debilitating neurodegenerative disease characterized by the accumulation of extracellular amyloid-β peptides (Aβ) within the cerebral parenchyma and vasculature, which is known as cerebral amyloid angiopathy (CAA). This study utilized confocal imaging to investigate heparan sulfate (HS) expression within the cerebrovasculature and its associations with Aβ, gender, and ApoE4 genotype in AD. Our investigation revealed elevated levels of HS in the cerebrovasculature of AD patients with severe CAA. Additionally, these patients exhibited higher HS colocalization with Aβ in the cerebrovasculature, including both endothelial and vascular smooth muscle cell compartments. Intriguingly, a reversal in the polarized expression of HS within the cerebrovasculature was detected in AD patients with severe CAA. Furthermore, male patients exhibited lower levels of both parenchymal and cerebrovascular HS. Additionally, ApoE4 carriers displayed heightened cerebrovascular Aβ expression and a tendency of elevated cerebrovascular HS levels in AD patients with severe CAA. Overall, these findings reveal potential intricate interplay between HS, Aβ, ApoE, and vascular pathology in AD, thereby underscoring the potential roles of cerebrovascular HS in CAA development and AD pathology. Further study of the underlying mechanisms may present novel therapeutic avenues for AD treatment.

Lung endothelium, tau, and amyloids in health and disease

Lung endothelia in the arteries, capillaries, and veins are heterogeneous in structure and function. Lung capillaries in particular represent a unique vascular niche, with a thin yet highly restrictive alveolar-capillary barrier that optimizes gas exchange. Capillary endothelium surveys the blood while simultaneously interpreting cues initiated within the alveolus and communicated via immediately adjacent type I and type II epithelial cells, fibroblasts, and pericytes. This cell-cell communication is necessary to coordinate the immune response to lower respiratory tract infection. Recent discoveries identify an important role for the microtubule-associated protein tau that is expressed in lung capillary endothelia in the host-pathogen interaction. This endothelial tau stabilizes microtubules necessary for barrier integrity, yet infection drives production of cytotoxic tau variants that are released into the airways and circulation, where they contribute to end-organ dysfunction. Similarly, beta-amyloid is produced during infection. Beta-amyloid has antimicrobial activity, but during infection it can acquire cytotoxic activity that is deleterious to the host. The production and function of these cytotoxic tau and amyloid variants are the subject of this review. Lung-derived cytotoxic tau and amyloid variants are a recently discovered mechanism of end-organ dysfunction, including neurocognitive dysfunction, during and in the aftermath of infection.

Exploring Heparan Sulfate Proteoglycans as Mediators of Human Mesenchymal Stem Cell Neurogenesis

Alzheimer's disease (AD) and traumatic brain injury (TBI) are major public health issues worldwide, with over 38 million people living with AD and approximately 48 million people (27-69 million) experiencing TBI annually. Neurodegenerative conditions are characterised by the accumulation of neurotoxic amyloid beta (Aβ) and microtubule-associated protein Tau (Tau) with current treatments focused on managing symptoms rather than addressing the underlying cause. Heparan sulfate proteoglycans (HSPGs) are a diverse family of macromolecules that interact with various proteins and ligands and promote neurogenesis, a process where new neural cells are formed from stem cells. The syndecan (SDC) and glypican (GPC) HSPGs have been implicated in AD pathogenesis, acting as drivers of disease, as well as potential therapeutic targets. Human mesenchymal stem cells (hMSCs) provide an attractive therapeutic option for studying and potentially treating neurodegenerative diseases due to their relative ease of isolation and subsequent extensive in vitro expansive potential. Understanding how HSPGs regulate protein aggregation, a key feature of neurodegenerative disorders, is essential to unravelling the underlying disease processes of AD and TBI, as well as any link between these two neurological disorders. Further research may validate HSPG, specifically SDCs or GPCs, use as neurodegenerative disease targets, either via driving hMSC stem cell therapy or direct targeting.

Heparin-enriched plasma proteome is significantly altered in Alzheimer's Disease

Introduction

Heparin binding proteins (HBPs) with roles in extracellular matrix assembly are strongly correlated to β-amyloid (Aβ) and tau pathology in Alzheimer's disease (AD) brain and cerebrospinal fluid (CSF). However, it remains challenging to detect these proteins in plasma using standard mass spectrometry-based proteomic approaches.

Methods

We employed heparin affinity chromatography, followed by off-line fractionation and tandem mass tag mass spectrometry (TMT-MS), to capture and enrich HBPs in plasma obtained from AD (n=62) and control (n=47) samples. These profiles were then correlated to a consensus AD brain proteome, as well as with Aβ, tau and phosphorylated tau (pTau) CSF biomarkers from the same individuals. We then leveraged published human postmortem brain proteome datasets to assess the overlap with the heparin-enriched plasma proteome.

Results

Heparin-enrichment from plasma was highly reproducible, enriched well-known HBPs like APOE and thrombin, and depleted high-abundance proteins such as albumin. A total of 2865 proteins, spanning 10 orders of magnitude were detectable. Utilizing a consensus AD brain protein co-expression network, we observed that specific plasma HBPs exhibited consistent direction of change in both brain and plasma, whereas others displayed divergent changes highlighting the complex interplay between the two compartments. Elevated HBPs in AD plasma, when compared to controls, included members of the matrisome module in brain that accumulate within Aβ deposits, such as SMOC1, SMOC2, SPON1, MDK, OLFML3, FRZB, GPNMB, and APOE. Additionally, heparin enriched plasma proteins demonstrated significant correlations with conventional AD CSF biomarkers, including Aβ, total tau, pTau, and plasma pTau from the same individuals.

Conclusion

These findings support the utility of a heparin-affinity approach for enriching amyloid-associated proteins, as well as a wide spectrum of plasma biomarkers that reflect pathological changes in the AD brain.

Heparan sulfate modified proteins affect cellular processes central to neurodegeneration and modulate presenilin function

Mutations in presenilin-1 (PSEN1) are the most common cause of familial, early-onset Alzheimer's disease (AD), typically producing cognitive deficits in the fourth decade. A variant of APOE, APOE3 Christchurch (APOE3ch) , was found associated with protection from both cognitive decline and Tau accumulation in a 70-year-old bearing the disease-causing PSEN1-E280A mutation. The amino acid change in ApoE3ch is within the heparan sulfate (HS) binding domain of APOE, and purified APOEch showed dramatically reduced affinity for heparin, a highly sulfated form of HS. The physiological significance of ApoE3ch is supported by studies of a mouse bearing a knock-in of this human variant and its effects on microglia reactivity and Aβ-induced Tau deposition. The studies reported here examine the function of heparan sulfate-modified proteoglycans (HSPGs) in cellular and molecular pathways affecting AD-related cell pathology in human cell lines and mouse astrocytes. The mechanisms of HSPG influences on presenilin- dependent cell loss and pathology were evaluated in Drosophila using knockdown of the presenilin homolog, Psn , together with partial loss of function of sulfateless (sfl) , a homolog of NDST1 , a gene specifically affecting HS sulfation. HSPG modulation of autophagy, mitochondrial function, and lipid metabolism were shown to be conserved in cultured human cell lines, Drosophila , and mouse astrocytes. RNAi of Ndst1 reduced intracellular lipid levels in wild-type mouse astrocytes or those expressing humanized variants of APOE, APOE3 , and APOE4 . RNA-sequence analysis of human cells deficient in HS synthesis demonstrated effects on the transcriptome governing lipid metabolism, autophagy, and mitochondrial biogenesis and showed significant enrichment in AD susceptibility genes identified by GWAS. Neuron-directed knockdown of Psn in Drosophila produced cell loss in the brain and behavioral phenotypes, both suppressed by simultaneous reductions in sfl mRNA levels. Abnormalities in mitochondria, liposome morphology, and autophagosome-derived structures in animals with Psn knockdown were also rescued by simultaneous reduction of sfl. sfl knockdown reversed Psn- dependent transcript changes in genes affecting lipid transport, metabolism, and monocarboxylate carriers. These findings support the direct involvement of HSPGs in AD pathogenesis.

Genetic associations with longevity are on average stronger in females than in males

It is long observed that females tend to live longer than males in nearly every country. However, the underlying mechanism remains elusive. In this study, we discovered that genetic associations with longevity are on average stronger in females than in males through bio-demographic analyses of genome-wide association studies (GWAS) dataset of 2178 centenarians and 2299 middle-age controls of Chinese Longitudinal Healthy Longevity Study (CLHLS). This discovery is replicated across North and South regions of China, and is further confirmed by North-South discovery/replication analyses of different and independent datasets of Chinese healthy aging candidate genes with CLHLS participants who are not in CLHLS GWAS, including 2972 centenarians and 1992 middle-age controls. Our polygenic risk score analyses of eight exclusive groups of sex-specific genes, analyses of sex-specific and not-sex-specific individual genes, and Genome-wide Complex Trait Analysis using all SNPs all reconfirm that genetic associations with longevity are on average stronger in females than in males. Our discovery/replication analyses are based on genetic datasets of in total 5150 centenarians and compatible middle-age controls, which comprises the worldwide largest sample of centenarians. The present study's findings may partially explain the well-known male-female health-survival paradox and suggest that genetic variants may be associated with different reactions between males and females to the same vaccine, drug treatment and/or nutritional intervention. Thus, our findings provide evidence to steer away from traditional view that "one-size-fits-all" for clinical interventions, and to consider sex differences for improving healthcare efficiency. We suggest future investigations focusing on effects of interactions between sex-specific genetic variants and environment on longevity as well as biological function.

Aβ Amyloid Scaffolds the Accumulation of Matrisome and Additional Proteins in Alzheimer's Disease

We report a highly significant correlation in brain proteome changes between Alzheimers disease (AD) and CRND8 APP695NL/F transgenic mice. However, integrating protein changes observed in the CRND8 mice with co-expression networks derived from human AD, reveals both conserved and divergent module changes. For the most highly conserved module (M42, matrisome) we find many proteins accumulate in plaques, cerebrovascular amyloid (CAA), dystrophic processes, or a combination thereof. Overexpression of two M42 proteins, midkine (Mdk) and pleiotrophin (PTN), in CRND8 mice brains leads to increased accumulation of A β ; in plaques and in CAA; further, recombinant MDK and PTN enhance A β ; aggregation into amyloid. Multiple M42 proteins, annotated as heparan sulfate binding proteins, bind to fibrillar A β 42 and a non-human amyloid fibril in vitro. Supporting this binding data, MDK and PTN co-accumulate with transthyretin (TTR) amyloid in the heart and islet amyloid polypeptide (IAPP) amyloid in the pancreas. Our findings establish several critical insights. Proteomic changes in modules observed in human AD brains define an A β ; amyloid responsome that is well conserved from mouse model to human. Further, distinct amyloid structures may serve as scaffolds, facilitating the co-accumulation of proteins with signaling functions. We hypothesize that this co-accumulation may contribute to downstream pathological sequalae. Overall, this contextualized understanding of proteomic changes and their interplay with amyloid deposition provides valuable insights into the complexity of AD pathogenesis and potential biomarkers and therapeutic targets.

Global impact of proteoglycan science on human diseases

In this comprehensive review, we will dissect the impact of research on proteoglycans focusing on recent developments involved in their synthesis, degradation, and interactions, while critically assessing their usefulness in various biological processes. The emerging roles of proteoglycans in global infections, specifically the SARS-CoV-2 pandemic, and their rising functions in regenerative medicine and biomaterial science have significantly affected our current view of proteoglycans and related compounds. The roles of proteoglycans in cancer biology and their potential use as a next-generation protein-based adjuvant therapy to combat cancer is also emerging as a constructive and potentially beneficial therapeutic strategy. We will discuss the role of proteoglycans in selected and emerging areas of proteoglycan science, such as neurodegenerative diseases, autophagy, angiogenesis, cancer, infections and their impact on mammalian diseases.

Sulfated Polysaccharides as a Fighter with Protein Non-Physiological Aggregation: The Role of Polysaccharide Flexibility and Charge Density

Proteins can lose native functionality due to non-physiological aggregation. In this work, we have shown the power of sulfated polysaccharides as a natural assistant to restore damaged protein structures. Protein aggregates enriched by cross-β structures are a characteristic of amyloid fibrils related to different health disorders. Our recent studies demonstrated that model fibrils of hen egg white lysozyme (HEWL) can be disaggregated and renatured by some negatively charged polysaccharides. In the current work, using the same model protein system and FTIR spectroscopy, we studied the role of conformation and charge distribution along the polysaccharide chain in the protein secondary structure conversion. The effects of three carrageenans (κ, ι, and λ) possessing from one to three sulfate groups per disaccharide unit were shown to be different. κ-Carrageenan was able to fully eliminate cross-β structures and complete the renaturation process. ι-Carrageenan only initiated the formation of native-like β-structures in HEWL, retaining most of the cross-β structures. In contrast, λ-carrageenan even increased the content of amyloid cross-β structures. Furthermore, κ-carrageenan in rigid helical conformation loses its capability to restore protein native structures, largely increasing the amount of amyloid cross-β structures. Our findings create a platform for the design of novel natural chaperons to counteract protein unfolding.

The Glycosaminoglycan Side Chains and Modular Core Proteins of Heparan Sulphate Proteoglycans and the Varied Ways They Provide Tissue Protection by Regulating Physiological Processes and Cellular Behaviour

This review examines the roles of HS-proteoglycans (HS-PGs) in general, and, in particular, perlecan and syndecan as representative examples and their interactive ligands, which regulate physiological processes and cellular behavior in health and disease. HS-PGs are essential for the functional properties of tissues both in development and in the extracellular matrix (ECM) remodeling that occurs in response to trauma or disease. HS-PGs interact with a biodiverse range of chemokines, chemokine receptors, protease inhibitors, and growth factors in immune regulation, inflammation, ECM stabilization, and tissue protection. Some cell regulatory proteoglycan receptors are dually modified hybrid HS/CS proteoglycans (betaglycan, CD47). Neurexins provide synaptic stabilization, plasticity, and specificity of interaction, promoting neurotransduction, neurogenesis, and differentiation. Ternary complexes of glypican-1 and Robbo-Slit neuroregulatory proteins direct axonogenesis and neural network formation. Specific neurexin-neuroligin complexes stabilize synaptic interactions and neural activity. Disruption in these interactions leads to neurological deficits in disorders of functional cognitive decline. Interactions with HS-PGs also promote or inhibit tumor development. Thus, HS-PGs have complex and diverse regulatory roles in the physiological processes that regulate cellular behavior and the functional properties of normal and pathological tissues. Specialized HS-PGs, such as the neurexins, pikachurin, and Eyes-shut, provide synaptic stabilization and specificity of neural transduction and also stabilize the axenome primary cilium of phototoreceptors and ribbon synapse interactions with bipolar neurons of retinal neural networks, which are essential in ocular vision. Pikachurin and Eyes-Shut interactions with an α-dystroglycan stabilize the photoreceptor synapse. Novel regulatory roles for HS-PGs controlling cell behavior and tissue function are expected to continue to be uncovered in this fascinating class of proteoglycan.

Genetic associations with age at dementia onset in the PSEN1 E280A Colombian kindred

INTRODUCTION

Genetic associations with Alzheimer's disease (AD) age at onset (AAO) could reveal genetic variants with therapeutic applications. We present a large Colombian kindred with autosomal dominant AD (ADAD) as a unique opportunity to discover AAO genetic associations.

METHODS

A genetic association study was conducted to examine ADAD AAO in 340 individuals with the PSEN1 E280A mutation via TOPMed array imputation. Replication was assessed in two ADAD cohorts, one sporadic early-onset AD study and four late-onset AD studies.

RESULTS

13 variants had p<1×10-7 or p<1×10-5 with replication including three independent loci with candidate associations with clusterin including near CLU. Other suggestive associations were identified in or near HS3ST1, HSPG2, ACE, LRP1B, TSPAN10, and TSPAN14.

DISCUSSION

Variants with suggestive associations with AAO were associated with biological processes including clusterin, heparin sulfate, and amyloid processing. The detection of these effects in the presence of a strong mutation for ADAD reinforces their potentially impactful role.

Increased Cerebral Serum Amyloid A2 and Parameters of Oxidation in Arylsulfatase B (N-Acetylgalactosamine-4-Sulfatase)-Null Mice

Background

Chondroitin sulfate and chondroitin sulfate proteoglycans have been associated with Alzheimer's disease (AD), and the impact of modified chondroitin sulfates is being investigated in several animal and cell-based models of AD. Published reports have shown the role of accumulation of chondroitin 4-sulfate and decline in Arylsulfatase B (ARSB; B-acetylgalactosamine-4-sulfatase) in other pathology, including nerve injury, traumatic brain injury, and spinal cord injury. However, the impact of ARSB deficiency on AD pathobiology has not been reported, although changes in ARSB were associated with AD in two prior reports. The enzyme ARSB removes 4-sulfate groups from the non-reducing end of chondroitin 4-sulfate and dermatan sulfate and is required for their degradation. When ARSB activity declines, these sulfated glycosaminoglycans accumulate, as in the inherited disorder Mucopolysaccharidosis VI.

Objective

Reports about chondroitin sulfate, chondroitin sulfate proteoglycans, and chondroitin sulfatases in AD were reviewed.

Methods

Measurements of SAA2, iNOS, lipid peroxidation, chondroitin sulfate proteoglycan 4 (CSPG4), and other parameters were performed in cortex and hippocampus from ARSB-null mice and controls by QRT-PCR, ELISA, and other standard assays.

Results

SAA2 mRNA expression and protein, CSPG4 mRNA, chondroitin 4-sulfate, and iNOS were increased significantly in ARSB-null mice. Measures of lipid peroxidation and redox state were significantly modified.

Conclusion

Findings indicate that decline in ARSB leads to changes in expression of parameters associated with AD in the hippocampus and cortex of the ARSB-deficient mouse. Further investigation of the impact of decline in ARSB on the development of AD may provide a new approach to prevent and treat AD.

The fusiform gyrus exhibits differential gene-gene co-expression in Alzheimer's disease

Alzheimer's Disease (AD) is an irreversible neurodegenerative disease clinically characterized by the presence of β-amyloid plaques and tau deposits in various regions of the brain. However, the underlying factors that contribute to the development of AD remain unclear. Recently, the fusiform gyrus has been identified as a critical brain region associated with mild cognitive impairment, which may increase the risk of AD development. In our study, we performed gene co-expression and differential co-expression network analyses, as well as gene-expression-based prediction, using RNA-seq transcriptome data from post-mortem fusiform gyrus tissue samples collected from both cognitively healthy individuals and those with AD. We accessed differential co-expression networks in large cohorts such as ROSMAP, MSBB, and Mayo, and conducted over-representation analyses of gene pathways and gene ontology. Our results comprise four exclusive gene hubs in co-expression modules of Alzheimer's Disease, including FNDC3A, MED23, NRIP1, and PKN2. Further, we identified three genes with differential co-expressed links, namely FAM153B, CYP2C8, and CKMT1B. The differential co-expressed network showed moderate predictive performance for AD, with an area under the curve ranging from 0.71 to 0.76 (+/- 0.07). The over-representation analysis identified enrichment for Toll-Like Receptors Cascades and signaling pathways, such as G protein events, PIP2 hydrolysis and EPH-Epherin mechanism, in the fusiform gyrus. In conclusion, our findings shed new light on the molecular pathophysiology of AD by identifying new genes and biological pathways involved, emphasizing the crucial role of gene regulatory networks in the fusiform gyrus.

Increased Cerebral Serum Amyloid A2 and Parameters of Oxidation in Arylsulfatase B (N-Acetylgalactosamine-4-Sulfatase)-Null Mice

Introduction

Chondroitin sulfate and chondroitin sulfate proteoglycans have been associated with Alzheimer's Disease (AD), and the impact of modified chondroitin sulfates is being investigated in several animal and cell-based models of AD. Published reports have shown the role of accumulation of chondroitin 4-sulfate and decline in Arylsulfatase B (ARSB; B-acetylgalactosamine-4-sulfatase) in other pathology, including nerve injury, traumatic brain injury, and spinal cord injury. However, the impact of ARSB deficiency on AD pathobiology has not been reported, although changes in ARSB were associated with AD in two prior reports. The enzyme ARSB removes 4-sulfate groups from the non-reducing end of chondroitin 4-sulfate and dermatan sulfate and is required for their degradation. When ARSB activity declines, these sulfated glycosaminoglycans accumulate, as in the inherited disorder Mucopolysaccharidosis VI.

Methods

Reports about chondroitin sulfate, chondroitin sulfate proteoglycans and chondroitin sulfatases in Alzheimer's Disease were reviewed. Measurements of SAA2, iNOS, lipid peroxidation, chondroitin sulfate proteoglycan 4, and other parameters were performed in cortex and hippocampus from ARSB-null mice and controls by QRT-PCR, ELISA, and other standard assays.

Results

SAA2 mRNA expression and protein, CSPG4 mRNA, chondroitin 4-sulfate and i-NOS were increased significantly in ARSB-null mice. Measures of lipid peroxidation and redox state were significantly modified.

Discussion

Findings indicate that decline in ARSB leads to changes in expression of parameters associated with AD in the hippocampus and cortex of the ARSB-deficient mouse.

Conclusions

Further investigation of the impact of decline in ARSB on the development of AD may provide a new approach to prevent and treat AD.

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 therapeutic potential of the neuroactive peptides of soluble amyloid precursor protein-alpha in Alzheimer's disease and related neurological disorders

Soluble amyloid precursor protein-alpha (sAPPα) is a multi-functional brain-derived protein that has neuroprotective, neurogenic and neurotropic properties. Moreover, it is known to facilitate synaptic function and promote neural repair. These properties suggest sAPPα may be useful as a therapeutic agent for the treatment of neurological diseases characterized by synaptic failure and neuronal loss, such as occurs in Alzheimer's disease, and for neural repair following traumatic brain injury and stroke. However, sAPPα's relatively large size and the difficulty of ongoing delivery of therapeutics to the brain mean this is not currently practicable. Importantly, however, sAPPα is composed of several neuroactive domains that each possess properties that collectively are remarkably similar to those of sAPPα itself. Here, we review the molecular structure of sAPPα and identify the domains that contribute to its overall functionality. Four peptide motifs present as possible targets for therapeutic development. We review their physiochemical and neuroactive properties, both within sAPPα and as isolated peptides, and discuss their potential for future development as multipurpose therapeutic agents for the treatment of Alzheimer's disease and other disorders of neuronal function. Further, we discuss the role of heparin binding sites, found within sAPPα's structure and overlapping with the neuroactive domains, as sites for interactions with effector proteins and synaptic receptors. The potential role of the neuroactive peptides known as Cationic Arginine-Rich Peptides (CARPs) as neuroprotective motifs is also reviewed. Mechanisms of peptide delivery to the brain are briefly discussed. Finally, we summarise the potential benefits and pitfalls of using the isolated peptides, either individually or in combination, for the treatment of neurological diseases.

Unravelling the mechanotransduction pathways in Alzheimer's disease

Alzheimer's disease (AD) represents one of the most common and debilitating neurodegenerative disorders. By the end of 2040, AD patients might reach 11.2 million in the USA, around 70% higher than 2022, with severe consequences on the society. As now, we still need research to find effective methods to treat AD. Most studies focused on the tau and amyloid hypothesis, but many other factors are likely involved in the pathophysiology of AD. In this review, we summarize scientific evidence dealing with the mechanotransduction players in AD to highlight the most relevant mechano-responsive elements that play a role in AD pathophysiology. We focused on the AD-related role of extracellular matrix (ECM), nuclear lamina, nuclear transport and synaptic activity. The literature supports that ECM alteration causes the lamin A increment in the AD patients, leading to the formation of nuclear blebs and invaginations. Nuclear blebs have consequences on the nuclear pore complexes, impairing nucleo-cytoplasmic transport. This may result in tau hyperphosphorylation and its consequent self-aggregation in tangles, which impairs the neurotransmitters transport. It all exacerbates in synaptic transmission impairment, leading to the characteristic AD patient's memory loss. Here we related for the first time all the evidence associating the mechanotransduction pathway with neurons. In addition, we highlighted the entire pathway influencing neurodegenerative diseases, paving the way for new research perspectives in the context of AD and related pathologies.

circRNA from APP Gene Changes in Alzheimer's Disease Human Brain

Alzheimer's disease (AD) is the most common cause of age-related dementia. Amyloid precursor protein (APP) is the precursor of Aβ peptides, and its role in AD has been widely investigated. Recently, it has been reported that a circular RNA (circRNA) originated from APP gene can serve as a template for Aβ synthesis, postulating it as an alternative pathway for the Aβ biogenesis. Moreover, circRNAs play important roles in brain development and in neurological diseases. Therefore, our aim was to study the expression of a circAPP (hsa_circ_0007556) and its linear cognate in AD human entorhinal cortex, a brain region most vulnerable to AD pathology. First, we confirmed the presence of circAPP (hsa_circ_0007556) in human entorhinal cortex samples using RT-PCR and Sanger sequencing of PCR products. Next, a 0.49-fold decrease in circAPP (hsa_circ_0007556) levels was observed in entorhinal cortex of AD cases compared to controls (p-value < 0.05) by qPCR. In contrast, APP mRNA expression did not show changes in the entorhinal cortex between AD cases and controls (Fold-change = 1.06; p-value = 0.81). A negative correlation was found between Aβ deposits and circAPP (hsa_circ_0007556) and APP expression levels (Rho Spearman = -0.56, p-value < 0.001 and Rho Spearman = -0.44, p-values < 0.001, respectively). Finally, by using bioinformatics tools, 17 miRNAs were predicted to bind circAPP (hsa_circ_0007556), and the functional analysis predicted that they were involved in some pathways, such as the Wnt-signaling pathway (p = 3.32 × 10^-6). Long-term potentiation (p = 2.86 × 10^-5), among others, is known to be altered in AD. To sum up, we show that circAPP (hsa_circ_0007556) is deregulated in the entorhinal cortex of AD patients. These results add to the notion that circAPP (hsa_circ_0007556) could be playing a role in the pathogenesis of AD disease.

The Ability of Some Polysaccharides to Disaggregate Lysozyme Amyloid Fibrils and Renature the Protein

The deposition of proteins in the form of insoluble amyloid fibril aggregates is linked to a range of diseases. The supramolecular architecture of such deposits is governed by the propagation of β-strands in the direction of protofilament growth. In the present study, we analyze the structural changes of hen egg-white lysozyme fibrils upon their interactions with a range of polysaccharides, using AFM and FTIR spectroscopy. Linear anionic polysaccharides, such as κ-carrageenan and sodium alginate, are shown to be capable to disaggregate protofilaments with eventual protein renaturation. The results help to understand the mechanism of amyloid disaggregation and create a platform for both the development of new therapeutic agents for amyloidose treatment, and the design of novel functional protein-polysaccharide complex-based nanomaterials.

Regulation of autophagy, lipid metabolism, and neurodegenerative pathology by heparan sulfate proteoglycans

Heparan sulfate modified proteins or proteoglycans (HSPGs) are an abundant class of cell surface and extracellular matrix molecules. They serve important co-receptor functions in the regulation of signaling as well as membrane trafficking. Many of these activities directly affect processes associated with neurodegeneration including uptake and export of Tau protein, disposition of Amyloid Precursor Protein-derived peptides, and regulation of autophagy. In this review we focus on the impact of HSPGs on autophagy, membrane trafficking, mitochondrial quality control and biogenesis, and lipid metabolism. Disruption of these processes are a hallmark of Alzheimer's disease (AD) and there is evidence that altering heparan sulfate structure and function could counter AD-associated pathological processes. Compromising presenilin function in several systems has provided instructive models for understanding the molecular and cellular underpinnings of AD. Disrupting presenilin function produces a constellation of cellular deficits including accumulation of lipid, disruption of autophagosome to lysosome traffic and reduction in mitochondrial size and number. Inhibition of heparan sulfate biosynthesis has opposing effects on all these cellular phenotypes, increasing mitochondrial size, stimulating autophagy flux to lysosomes, and reducing the level of intracellular lipid. These findings suggest a potential mechanism for countering pathology found in AD and related disorders by altering heparan sulfate structure and influencing cellular processes disrupted broadly in neurodegenerative disease. Vertebrate and invertebrate model systems, where the cellular machinery of autophagy and lipid metabolism are conserved, continue to provide important translational guideposts for designing interventions that address the root cause of neurodegenerative pathology.

HS, an Ancient Molecular Recognition and Information Storage Glycosaminoglycan, Equips HS-Proteoglycans with Diverse Matrix and Cell-Interactive Properties Operative in Tissue Development and Tissue Function in Health and Disease

Heparan sulfate is a ubiquitous, variably sulfated interactive glycosaminoglycan that consists of repeating disaccharides of glucuronic acid and glucosamine that are subject to a number of modifications (acetylation, de-acetylation, epimerization, sulfation). Variable heparan sulfate chain lengths and sequences within the heparan sulfate chains provide structural diversity generating interactive oligosaccharide binding motifs with a diverse range of extracellular ligands and cellular receptors providing instructional cues over cellular behaviour and tissue homeostasis through the regulation of essential physiological processes in development, health, and disease. heparan sulfate and heparan sulfate-PGs are integral components of the specialized glycocalyx surrounding cells. Heparan sulfate is the most heterogeneous glycosaminoglycan, in terms of its sequence and biosynthetic modifications making it a difficult molecule to fully characterize, multiple ligands also make an elucidation of heparan sulfate functional properties complicated. Spatio-temporal presentation of heparan sulfate sulfate groups is an important functional determinant in tissue development and in cellular control of wound healing and extracellular remodelling in pathological tissues. The regulatory properties of heparan sulfate are mediated via interactions with chemokines, chemokine receptors, growth factors and morphogens in cell proliferation, differentiation, development, tissue remodelling, wound healing, immune regulation, inflammation, and tumour development. A greater understanding of these HS interactive processes will improve therapeutic procedures and prognoses. Advances in glycosaminoglycan synthesis and sequencing, computational analytical carbohydrate algorithms and advanced software for the evaluation of molecular docking of heparan sulfate with its molecular partners are now available. These advanced analytic techniques and artificial intelligence offer predictive capability in the elucidation of heparan sulfate conformational effects on heparan sulfate-ligand interactions significantly aiding heparan sulfate therapeutics development.

Synthesis of a Systematic 64-Membered Heparan Sulfate Tetrasaccharide Library

Heparan sulfate (HS) has multifaceted biological activities. To date, no libraries of HS oligosaccharides bearing systematically varied sulfation structures are available owing to the challenges in synthesizing a large number of HS oligosaccharides. To overcome the obstacles and expedite the synthesis, a divergent approach was designed, where 64 HS tetrasaccharides covering all possible structures of 2-O-, 6-O- and N-sulfation with the glucosamine-glucuronic acid-glucosamine-iduronic acid backbone were successfully produced from a single strategically protected tetrasaccharide intermediate. This extensive library helped identify the structural requirements for HS sequences to have strong fibroblast growth factor-2 binding but a weak affinity for platelet factor-4. Such a strategy to separate out these two interactions could lead to new HS-based potential therapeutics without the dangerous adverse effect of heparin-induced thrombocytopenia.

Heparan Sulfate Proteoglycans in Tauopathy

Tauopathies are a class of neurodegenerative diseases, including Alzheimer's disease, and are characterized by intraneuronal tau inclusion in the brain and the patient's cognitive decline with obscure pathogenesis. Heparan sulfate proteoglycans, a major type of extracellular matrix, have been believed to involve in tauopathies. The heparan sulfate proteoglycans co-deposit with tau in Alzheimer's patient brain, directly bind to tau and modulate tau secretion, internalization, and aggregation. This review summarizes the current understanding of the functions and the modulated molecular pathways of heparan sulfate proteoglycans in tauopathies, as well as the implication of dysregulated heparan sulfate proteoglycan expression in tau pathology and the potential of targeting heparan sulfate proteoglycan-tau interaction as a novel therapeutic option.

Molecular determinants of the interaction between HSV-1 glycoprotein D and heparan sulfate

Literature has well-established the importance of 3-O-sulfation of neuronal cell surface glycan heparan sulfate (HS) to its interaction with herpes simplex virus type 1 glycoprotein D (gD). Previous investigations of gD to its viral receptors HVEM and nectin-1 also highlighted the conformational dynamics of gD's N- and C-termini, necessary for viral membrane fusion. However, little is known on the structural interactions of gD with HS. Here, we present our findings on this interface from both the glycan and the protein perspective. We used C-terminal and N-terminal gD variants to probe the role of their respective regions in gD/HS binding. The N-terminal truncation mutants (with Δ1-22) demonstrate equivalent or stronger binding to heparin than their intact glycoproteins, indicating that the first 22 amino acids are disposable for heparin binding. Characterization of the conformational differences between C-terminal truncated mutants by sedimentation velocity analytical ultracentrifugation distinguished between the "open" and "closed" conformations of the glycoprotein D, highlighting the region's modulation of receptor binding. From the glycan perspective, we investigated gD interacting with heparin, heparan sulfate, and other de-sulfated and chemically defined oligosaccharides using surface plasmon resonance and glycan microarray. The results show a strong preference of gD for 6-O-sulfate, with 2-O-sulfation becoming more important in the presence of 6-O-S. Additionally, 3-O-sulfation shifted the chain length preference of gD from longer chain to mid-chain length, reaffirming the sulfation site's importance to the gD/HS interface. Our results shed new light on the molecular details of one of seven known protein-glycan interactions with 3-O-sulfated heparan sulfate.

Metal Binding to Sodium Heparin Monitored by Quadrupolar NMR

Heparins and heparan sulfate polysaccharides are negatively charged glycosaminoglycans and play important roles in cell-to-matrix and cell-to-cell signaling processes. Metal ion binding to heparins alters the conformation of heparins and influences their function. Various experimental techniques have been used to investigate metal ion-heparin interactions, frequently with inconsistent results. Exploiting the quadrupolar 23Na nucleus, we herein develop a 23Na NMR-based competition assay and monitor the binding of divalent Ca2+ and Mg2+ and trivalent Al3+ metal ions to sodium heparin and the consequent release of sodium ions from heparin. The 23Na spin relaxation rates and translational diffusion coefficients are utilized to quantify the metal ion-induced release of sodium ions from heparin. In the case of the Al3+ ion, the complementary approach of 27Al quadrupolar NMR is employed as a direct probe of ion binding to heparin. Our NMR results demonstrate at least two metal ion-binding sites with different affinities on heparin, potentially undergoing dynamic exchange. For the site with lower metal ion binding affinity, the order of Ca2+ > Mg2+ > Al3+ is obtained, in which even the weakly binding Al3+ ion is capable of displacing sodium ions from heparin. Overall, the multinuclear quadrupolar NMR approach employed here can monitor and quantify metal ion binding to heparin and capture different modes of metal ion-heparin binding.

Transcriptional profiles in olfactory pathway-associated brain regions of African green monkeys: Associations with age and Alzheimer's disease neuropathology

Introduction

Olfactory impairment in older individuals is associated with an increased risk of Alzheimer's disease (AD). Characterization of age versus neuropathology‐associated changes in the brain olfactory pathway may elucidate processes underlying early AD pathogenesis. Here, we report age versus AD neuropathology–associated differential transcription in four brain regions in the olfactory pathway of 10 female African green monkeys (vervet, Chlorocebus aethiops sabaeus), a well‐described model of early AD‐like neuropathology.

Methods

Transcriptional profiles were determined by microarray in the olfactory bulb (OB), piriform cortex (PC), temporal lobe white matter (WM), and inferior temporal cortex (ITC). Amyloid beta (Aβ) plaque load in parietal and temporal cortex was determined by immunohistochemistry, and concentrations of Aβ42, Aβ40, and norepinephrine in ITC were determined by enzyme‐linked immuosorbent assay (ELISA). Transcriptional profiles were compared between middle‐aged and old animals, and associations with AD‐relevant neuropathological measures were determined.

Results

Transcriptional profiles varied by brain region and age group. Expression levels of TRO and RNU4‐1 were significantly lower in all four regions in the older group. An additional 29 genes were differentially expressed by age in three of four regions. Analyses of a combined expression data set of all four regions identified 77 differentially expressed genes (DEGs) by age group. Among these DEGs, older subjects had elevated levels of CTSB, EBAG9, LAMTOR3, and MRPL17, and lower levels of COMMD10 and TYW1B. A subset of these DEGs was associated with neuropathology biomarkers. Notably, CTSB was positively correlated with Aβ plaque counts, Aβ42:Aβ40 ratios, and norepinephrine levels in all brain regions.

Discussion

These data demonstrate age differences in gene expression in olfaction‐associated brain regions. Biological processes exhibiting age‐related enrichment included the regulation of cell death, vascular function, mitochondrial function, and proteostasis. A subset of DEGs was specifically associated with AD phenotypes. These may represent promising targets for future mechanistic investigations and perhaps therapeutic intervention.

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.

A Method for Bridging Population-Specific Genotypes to Detect Gene Modules Associated with Alzheimer's Disease

BACKGROUND

Genome-wide association studies have successfully identified variants associated with multiple conditions. However, generalizing discoveries across diverse populations remains challenging due to large variations in genetic composition. Methods that perform gene expression imputation have attempted to address the transferability of gene discoveries across populations, but with limited success.

METHODS

Here, we introduce a pipeline that combines gene expression imputation with gene module discovery, including a dense gene module search and a gene set variation analysis, to address the transferability issue. Our method feeds association probabilities of imputed gene expression with a selected phenotype into tissue-specific gene-module discovery over protein interaction networks to create higher-level gene modules.

RESULTS

We demonstrate our method's utility in three case-control studies of Alzheimer's disease (AD) for three different race/ethnic populations (Whites, African descent and Hispanics). We discovered 182 AD-associated genes from gene modules shared between these populations, highlighting new gene modules associated with AD.

CONCLUSIONS

Our innovative framework has the potential to identify robust discoveries across populations based on gene modules, as demonstrated in AD.

Molecular Dynamics Approaches Dissect Molecular Mechanisms Underlying Methylene Blue-Glycosaminoglycan Interactions

Glycosaminoglycans (GAGs) are a class of periodic anionic linear polysaccharides involved in a number of biologically relevant processes in the extracellular matrix via interactions with various types of molecules including proteins, peptides and small organic molecules. The metachromatic dye methylene blue (MB) is a GAG binding agent. This molecule possesses a tricyclic, monocationic phenothiazine ring system, while the terminal methyl groups attached to the nitrogen atoms bear the most positive charges of the cation and, therefore, represent potential binding sites for negatively charged GAGs. In this study, we rigorously explored molecular mechanisms underlying these interactions for several GAG types: heparin, heparan and chondroitin sulfates. We found that GAG-MB interactions are predominantly electrostatically driven, with the particularly important role of sulfate groups. MB oligomeric stack formation was favored in the presence of GAGs. Furthermore, the impact of MB binding on the conformation of GAGs was also evaluated. The novel results allow for better quantitative analytics of GAG composition in the studied biochemical systems using MB dye as a GAG-specific marker. Our data add to the knowledge on small molecule-GAG interactions and could be potentially useful for novel developments in drug design and putative disease therapies in which GAGs are involved.

Perlecan, A Multi-Functional, Cell-Instructive, Matrix-Stabilizing Proteoglycan With Roles in Tissue Development Has Relevance to Connective Tissue Repair and Regeneration

This review highlights the multifunctional properties of perlecan (HSPG2) and its potential roles in repair biology. Perlecan is ubiquitous, occurring in vascular, cartilaginous, adipose, lymphoreticular, bone and bone marrow stroma and in neural tissues. Perlecan has roles in angiogenesis, tissue development and extracellular matrix stabilization in mature weight bearing and tensional tissues. Perlecan contributes to mechanosensory properties in cartilage through pericellular interactions with fibrillin-1, type IV, V, VI and XI collagen and elastin. Perlecan domain I - FGF, PDGF, VEGF and BMP interactions promote embryonic cellular proliferation, differentiation, and tissue development. Perlecan domain II, an LDLR-like domain interacts with lipids, Wnt and Hedgehog morphogens. Perlecan domain III binds FGF-7 and 18 and has roles in the secretion of perlecan. Perlecan domain IV, an immunoglobulin repeat domain, has cell attachment and matrix stabilizing properties. Perlecan domain V promotes tissue repair through interactions with VEGF, VEGF-R2 and α2β1 integrin. Perlecan domain-V LG1-LG2 and LG3 fragments antagonize these interactions. Perlecan domain V promotes reconstitution of the blood brain barrier damaged by ischemic stroke and is neurogenic and neuroprotective. Perlecan-VEGF-VEGFR2, perlecan-FGF-2 and perlecan-PDGF interactions promote angiogenesis and wound healing. Perlecan domain I, III and V interactions with platelet factor-4 and megakaryocyte and platelet inhibitory receptor promote adhesion of cells to implants and scaffolds in vascular repair. Perlecan localizes acetylcholinesterase in the neuromuscular junction and is of functional significance in neuromuscular control. Perlecan mutation leads to Schwartz-Jampel Syndrome, functional impairment of the biomechanical properties of the intervertebral disc, variable levels of chondroplasia and myotonia. A greater understanding of the functional working of the neuromuscular junction may be insightful in therapeutic approaches in the treatment of neuromuscular disorders. Tissue engineering of salivary glands has been undertaken using bioactive peptides (TWSKV) derived from perlecan domain IV. Perlecan TWSKV peptide induces differentiation of salivary gland cells into self-assembling acini-like structures that express salivary gland biomarkers and secrete α-amylase. Perlecan also promotes chondroprogenitor stem cell maturation and development of pluripotent migratory stem cell lineages, which participate in diarthrodial joint formation, and early cartilage development. Recent studies have also shown that perlecan is prominently expressed during repair of adult human articular cartilage. Perlecan also has roles in endochondral ossification and bone development. Perlecan domain I hydrogels been used in tissue engineering to establish heparin binding growth factor gradients that promote cell migration and cartilage repair. Perlecan domain I collagen I fibril scaffolds have also been used as an FGF-2 delivery system for tissue repair. With the availability of recombinant perlecan domains, the development of other tissue repair strategies should emerge in the near future. Perlecan co-localization with vascular elastin in the intima, acts as a blood shear-flow endothelial sensor that regulates blood volume and pressure and has a similar role to perlecan in canalicular fluid, regulating bone development and remodeling. This complements perlecan’s roles in growth plate cartilage and in endochondral ossification to form the appendicular and axial skeleton. Perlecan is thus a ubiquitous, multifunctional, and pleomorphic molecule of considerable biological importance. A greater understanding of its diverse biological roles and functional repertoires during tissue development, growth and disease will yield valuable insights into how this impressive proteoglycan could be utilized successfully in repair biology.

Syndecan-3 as a Novel Biomarker in Alzheimer's Disease

Early diagnosis of Alzheimer’s disease (AD) is of paramount importance in preserving the patient’s mental and physical health in a fairly manageable condition for a longer period. Reliable AD detection requires novel biomarkers indicating central nervous system (CNS) degeneration in the periphery. Members of the syndecan family of transmembrane proteoglycans are emerging new targets in inflammatory and neurodegenerative disorders. Reviewing the growing scientific evidence on the involvement of syndecans in the pathomechanism of AD, we analyzed the expression of the neuronal syndecan, syndecan-3 (SDC3), in experimental models of neurodegeneration. Initial in vitro studies showed that prolonged treatment of tumor necrosis factor-alpha (TNF-α) increases SDC3 expression in model neuronal and brain microvascular endothelial cell lines. In vivo studies revealed elevated concentrations of TNF-α in the blood and brain of APPSWE-Tau transgenic mice, along with increased SDC3 concentration in the brain and the liver. Primary brain endothelial cells and peripheral blood monocytes isolated from APPSWE-Tau mice exhibited increased SDC3 expression than wild-type controls. SDC3 expression of blood-derived monocytes showed a positive correlation with amyloid plaque load in the brain, demonstrating that SDC3 on monocytes is a good indicator of amyloid pathology in the brain. Given the well-established role of blood tests, the SDC3 expression of monocytes could serve as a novel biomarker for early AD detection.