Heparan Sulfate: Biosynthesis, Structure, and Function

Cellular SLC35B4 promotes internalization during influenza A virus entry

SLC35B4, a nucleotide sugar transporter that mediates the transport of UDP-GlcNAc and UDP-xylose, was found to be required for the replication of influenza A virus (IAV) of the H5N1 subtype in our genome-wide siRNA library screen. We found that defective IAV replication in SLC35B4-deficient A549 cells was independent of virus strain specificity, and the virulence of IAV in Slc35b4 knockdown mice was also decreased. By examining the individual stages of the IAV replication cycle, we discovered that the amount of internalized IAV was significantly reduced in SLC35B4-knockout A549 cells. Mechanistically, SLC35B4 facilitated IAV replication by transporting UDP-xylose, which attaches to the serine residue of heparan sulfate proteoglycans (HSPGs) in the heparan sulfate (HS) biosynthesis pathway. Knockdown of associated host factors (i.e., XYLT2, B4GALT7, EXT1, and EXT2) in the HS biosynthesis pathway also impaired IAV replication. Furthermore, we revealed that AGRN, a unique HSPG family member, was important for the endocytosis of IAV in A549 cells. Moreover, we found that the homeostasis of the AGRN protein was regulated by HS modification mediated by the initial UDP-xylose transporter SLC35B4, thereby affecting the expression level of endocytic adapter AP2B1 to influence IAV internalization. Collectively, these findings establish that SLC35B4 is an important regulator of IAV replication and uncover the underlying mechanisms by which SLC35B4 employs UDP-xylose transport activity to promote IAV internalization.IMPORTANCEThe entry process of IAV represents a favorable target for drug development. In this study, we identified SLC35B4 as an important host factor for the efficient replication of different subtypes of IAV in vitro and for the virulence of IAV in mice. We revealed that SLC35B4 employed its UDP-xylose transport activity to promote the HS biosynthesis pathway, thereby assisting IAV internalization into target cells in the early stage of viral infection. Consistently, several downstream factors in the HS biosynthesis pathway, i.e., XYLT2, B4GALT7, EXT1, and EXT2, as well as a specific HSPG member AGRN were also important for the replication of IAV. Furthermore, the UDP-xylose-transporting activity of SLC35B4 was involved in the regulation of the homeostasis of the AGRN protein by HS modification, which influenced virus internalization by affecting the expression levels of AP2B1. Together, the identification of the SLC35B4-XYLT2-B4GALT7-EXT1-EXT2-AGRN-AP2B1 axis may shed light on the development of potential anti-IAV therapeutics.

Involvement of GTPases and vesicle adapter proteins in Heparan sulfate biosynthesis: role of Rab1A, Rab2A and GOLPH3

Vesicle trafficking is pivotal in heparan sulfate (HS) biosynthesis, influencing its spatial and temporal regulation within distinct Golgi compartments. This regulation modulates the sulfation pattern of HS, which is crucial for governing various biological processes. Here, we investigate the effects of silencing Rab1A and Rab2A expression on the localisation of 3-O-sulfotransferase-5 (3OST5) within Golgi compartments and subsequent alterations in HS structure and levels. Interestingly, silencing Rab1A led to a shift in 3OST5 localization towards the trans-Golgi, resulting in increased HS levels within 24 and 48 h, while silencing Rab2A caused 3OST5 accumulation in the cis-Golgi, with a delayed rise in HS content observed after 48 h. Furthermore, a compensatory mechanism was evident in Rab2A-silenced cells, where increased Rab1A protein expression was detected. This suggests a dynamic interplay between Rab1A and Rab2A in maintaining the fine balance of vesicle trafficking processes involved in HS biosynthesis. Additionally, we demonstrate that the trafficking of 3OST5 in COPI vesicles is facilitated by GOLPH3 protein. These findings identify novel vesicular transport mechanisms regulating HS biosynthesis and reveal a compensatory relationship between Rab1A and Rab2A in maintaining baseline HS production.

Untangling Heparan Sulfate 3-O-Sulfation Using a Novel Offline Cationic-Peptide Affinity Enrichment, Followed by HILIC-cIM-MS

Heparan sulfate (HS) is a linear polysaccharide that modifies proteoglycans. HS biosynthesis is regulated in a spatiotemporal manner, leading to structural diversity, including variable de-N-acetylation, N-sulfation, hexuronic acid C5 epimerization, and 2-O-, 6-O-, and 3-O-sulfation. Specific structural motifs within HS chains offer multiple specific binding sites for protein partners. The occurrence of HS 3-O-sulfation is relatively rare; however, there is accumulating evidence identifying the importance of this low-abundance modification in many different biological scenarios. Initially described as a key determinant for binding and activation of antithrombin, and more recently, as a coreceptor for viral infection, 3-O-sulfation has been associated with the progression of several neurological disorders. The analytical ability to study the biological roles of HS 3-O-sulfation is hindered by its low abundance within HS chains and the complex isomeric nature of highly sulfated HS, which places a burden on the tandem mass spectrometry step for assigning saccharide structures. In this context, we developed a specific cationic peptide-affinity method for 3-O-sulfation enrichment, followed by hydrophilic interaction liquid chromatography-cyclic ion mobility mass spectrometry analysis (HILIC-cIM-MS). We first demonstrated the high specificity of this approach to capture 3-O-sulfated HS oligosaccharides within complex mixtures. We next showed the influence of specific sulfate and epimerization patterns on HS binding selectivity. Finally, we used the enrichment strategy to analyze 3-O-sulfated HS oligosaccharides from heparin lyase III-digested HS from porcine intestinal mucosa (HSPIM). We concluded that this enrichment method was useful to guide new studies to reveal the biological roles of 3-O-sulfation and to elucidate new HS structural motifs.

Substrate reduction using a glucosamine analogue in Drosophila melanogaster and mouse models of Sanfilippo syndrome

Mucopolysaccharidosis (MPS) types III A and C are inherited neurodegenerative disorders resulting from the lack of a specific enzyme involved in heparan sulfate (HS) catabolism, leading to the accumulation of partially-degraded HS fragments. At present, there are no approved treatments and death is commonly in the second decade of life. Several therapies have undergone pre-clinical evaluation for these conditions, including substrate reduction therapy, with the most studied compound of this class being the isoflavone genistein. However, findings from a Phase III clinical trial demonstrated that high dose oral genistein did not significantly improve neurodevelopmental outcomes in patients with MPS III (Sanfilippo syndrome). Here, we have tested an N-acetylglucosamine analogue, 4-deoxy-N-acetylglucosamine peracetate, as a novel substrate reduction therapy for HS-storing lysosomal storage disorders such as MPS III. Treatment with this compound significantly reduced HS levels in cultured MPS IIIA patient and mouse fibroblasts in a time- and dose-dependent manner. MPS IIIC Drosophila fed 4-deoxy-N-acetylglucosamine peracetate contained significantly less HS relative to those raised on control diets. Likewise, improvements in HS load within the MPS IIIA mouse brain suggests that the compound crossed the blood-brain barrier after oral administration. Although long-term studies are needed, these findings indicate that 4-deoxy-GlcNAc peracetate may be beneficial in slowing the accumulation of HS and may represent a novel substrate reduction therapeutic for MPS III and potentially other HS-storing disorders.

Expanding the Role of Heparin Derivatives in Oncology: From Anticoagulation to Antitumor Activity

Current research demonstrates the expanding therapeutic potential of heparin derivatives in oncology, extending beyond traditional anticoagulation mechanisms. This systematic analysis examines the structural characteristics, molecular mechanisms, and therapeutic applications of heparin-based compounds in malignancy treatment. The essential antithrombin binding pentasaccharide sequence has enabled development of specialized molecular variants, particularly fractionated heparins and their non-anticoagulant counterparts. These agents exert antineoplastic effects via multiple pathways, particularly through modulation of heparanase enzymatic activity and specific protein-glycosaminoglycan interactions. Evidence from pivotal clinical trials (FRAGMATIC, MAGNOLIA, GASTRANOX) confirms efficacy in managing cancer-associated thrombosis while indicating potential enhancement of chemotherapeutic outcomes. The preparation methods utilize enzymatic cleavage reactions and selective chemical derivatization to generate structurally modified heparins exhibiting unique molecular characteristics and biological activities. Analysis of the glycosaminoglycan analog dociparstat sodium reveals significant activity in myeloid malignancies, mediated by specific interference with CXCL12/CXCR4 signaling cascades. Significant challenges remain in manufacturing scale-up, analytical validation, and long-term safety assessment. Future studies must address dose optimization, combination strategies, and controlled clinical trials to determine the full therapeutic potential of these compounds in clinical oncology.

Synthetic heparan sulfate mimics based on chitosan derivatives show broad-spectrum antiviral activity

Enveloped viruses enter cells by binding to receptors present on host cell membranes, which trigger internalization and membrane fusion. For many viruses, this either directly or indirectly involves interaction with membrane-anchored carbohydrates, such as heparan sulfate, providing a potential target for a broad-spectrum antiviral approach. Based on this hypothesis, we screened a library of functionalized chitosan sulfates that mimic heparan sulfate in cellular membranes for inhibition of SARS-CoV-2 and respiratory syncytial virus (RSV) entry. An array of compounds blocking SARS-CoV-2 and RSV were identified, with the lead compound displaying broad-spectrum activity against multiple viral strains and clinical isolates. Mechanism of action studies showed the drug to block viral entry irreversibly, likely via a virucidal mechanism. Importantly, the drug was non-toxic in vivo and showed potent post-exposure therapeutic activity against both SARS-CoV-2 and RSV. Together, these results highlight the potential of functionalized carbohydrates as broad-spectrum antivirals targeting respiratory viruses.

Variant-Specific Interactions at the Plasma Membrane: Heparan Sulfate's Impact on SARS-CoV-2 Binding Kinetics

The spread of SARS-CoV-2 led to the emergence of several variants of concern (VOCs). The spike glycoprotein, responsible for engaging the viral receptor, exhibits the highest density of mutations, suggesting an ongoing evolution to optimize viral entry. This study characterizes the bond formed by virion mimics carrying the SARS-CoV-2 spike protein and the plasma membrane of host cells in the early stages of virus entry. Contrary to the traditional analysis of isolated ligand-receptor pairs, we utilized well-defined biomimetic models and biochemical and biophysical techniques to characterize the multivalent interaction of VOCs with the complex cell membrane. We observed an overall increase in the binding affinity for newer VOCs. By progressively reducing the system complexity, we identify heparan sulfate (HS) as a main driver of this variation, with a 10-fold increase in affinity for Omicron BA.1 over that of the original strain. These results demonstrate the essential role of coreceptors, particularly HS, in the modulation of SARS-CoV-2 infection and highlight the importance of multiscale biophysical and biochemical assays that account for membrane complexity to fully characterize and understand the role of molecular components and their synergy in viral attachment and entry.

Cloning, expression, and characterization of a heparinase III coupled with heparinase I for enzymatic depolymerization of heparin

A heparinase III (NsHep-III) from Niabella sp. was identified, cloned, and expressed as soluble form in E. coli BL21 (DE3). With heparin as substrate, the maximum activity of NsHep-III of 90.0 U·mg- 1 was achieved at pH 7.1 Tris-HCl (containing 15 mM Mg2+) and 30oC. The half-life of NsHep-III was determined to be 5 h at 30oC. The interactions between NsHep-III and substrates were studied by molecular docking. The combination of NsHep-III and a heparinase I from Bacteroides eggthii (BeHep-I) was employed to cleave heparin. Analysis of the enzymatic products of NsHep-III by SAX-HPLC showed seven different modified disaccharides, indicating that NsHep-III has a wide range of substrate specificity. The results of GPC analysis demonstrated that the average molecular weight of the product of heparin cleavage by the combination of NsHep-III/BeHep-I was reduced to 3969 Da, which accounted for 90% of all the components, and complied with the requirements of the European Pharmacopoeia. NsHep-III has notable activity and efficiency in cleaving heparin, which is potentially useful for the industrial production of low molecular weight heparin.

Docking heparan sulfate-based ligands as a promising inhibitor for SARS-CoV-2

CONTEXT

Heparan sulfate (HS) linear polysaccharide glycosaminoglycan compound is linked to components from the cell surface and the extracellular matrix. HS mediates SARS-CoV-2 infection through spike protein binding to cell surface receptors and is required to bind ACE2, prompting the need for electronic structure and molecular docking evaluation of this core system to exploit this attachment in developing new derivatives. Therefore, we have studied five molecules based on HS using molecular docking and electronic structure analysis. Non-covalent interaction analysis shows hydrogen bonding and van der Waals interactions in the binding to RBD-ACE2 interface and 3CLpro. SDM3 and SDM1 molecules present the lowest gap, including solvent effect under 154.6 kcal/mol, and exhibit the most reactivity behavior in this group, potentially leading to enhanced interaction in docking studies.

METHODS

Heparan sulfate and four derivatives were optimized using B3LYP functional with two basis sets 6-31 + G(d,p) and def2SVP. Electronic structure was used to explore the main interactions and the reactivity of these molecules, and these optimized structures were used in the molecular docking study against 3CLpro, RBD, and ACE2.

Synthesis of a deuterated disaccharide internal standard for LC-MS/MS quantitation of heparan sulfate in biological samples

High levels of heparan sulfate (HS) are a marker for several mucopolysaccharidosis (MPS) disorders which are lysosomal storage diseases caused by genetic defects in HS-degrading enzymes. Quantitation of HS in biological samples is therefore critical for diagnosis and evaluating the efficacy of new therapies. Herein we present the efficient synthesis of a butylated GlcN-GlcA disaccharide and its deuterated derivative for use as an internal standard in a quantitative mass spectrometry-based assay for analysis of HS following butanolysis. The synthesis features the stereoselective 1,2-cis glycosylation of a GlcA acceptor with a 6-O-benzoyl-2-deoxy-2-azido thioglucoside donor.

Novel simultaneous analysis of 18 types of glycosaminoglycan-derived disaccharides using 4-aminobenzoic acid ethyl ester derivatization by HPLC with fluorescence detection

Glycosaminoglycans (GAGs), including hyaluronic acid (HA), chondroitin sulfate (CS)/dermatan sulfate (DS), heparan sulfate (HS)/heparin (HP), and keratan sulfate (KS), play pivotal roles in living organisms. Generally, GAGs are analyzed after enzymatic digestion into unsaturated or saturated disaccharides. Due to high structural similarity between disaccharides, however, separation during analysis is challenging. Additionally, little is known about the structures of GAGs and their functional relationships. Elucidating the function of GAGs requires highly sensitive quantitative analytical methods. We developed a method for the simultaneous analysis of 18 types of disaccharides derived from HA (1 type), CS/DS (7 types), HS/HP (8 types), and KS (2 types) potentially detectable in analyses of human urine. The simple method involves HPLC separation with fluorescence detection following derivatization of GAG-derived disaccharides using 4-aminobenzoic acid ethyl ester (ABEE) as a pre-labeling agent and 2-picoline borane as a reductant. The ABEE derivatization reaction can be performed under aqueous conditions, and excess derivatization reagents can be easily, rapidly, and safely removed. This method enables highly sensitive simultaneous analysis of the 18 abovementioned types of GAG-derived disaccharides using HPLC with fluorescence detection in small amounts of urine (1 mL) in a single run. The versatile method described here could be applied to the analysis of GAGs in other biological samples.

Differential regulation of heparan sulfate biosynthesis in fibroblasts cocultured with normal vs. cancerous prostate cells

Heparan sulfate proteoglycans (HSPGs) regulate a wide range of biological activities in both physiological and pathological conditions. Altered expression or deregulated function of HSPGs and their heparan sulfate (HS) chains significantly contribute to carcinogenesis as well and crucially depends on the functioning of the complex system of HS biosynthetic/modifying enzymes termed as "GAGosome". Here, we aimed at investigating the expression profile of the system in a cell culture model of stroma-epithelial crosstalk and searching for transcription factors potentially related to the regulation of expression of the genes involved. Coculture of BjTERT-fibroblasts with normal PNT2 human prostate epithelial cells resulted in significant downregulation (2-4-fold) of transcriptional activity of HS metabolism-involved genes (EXT1/2, NDST1/2, GLCE, HS2ST1, HS3ST1/2, HS6ST1/2, SULF1/2, HPSE) in both cell types, whereas coculture with prostate cancer cells (LNCaP, PC3, DU145) demonstrated no significant interchanges. Human Transcription Factor RT2 Profiler PCR array and manual RT-PCR verification supposed FOS, MYC, E2F, SRF, NR3C1 as potential candidates for regulation and/or coordination of HS biosynthesis. Taken together, transcriptional activity of HS biosynthetic system in normal fibroblasts and prostate epithelial cells during their coculture might be controlled by their intercellular communication, reflecting of adaptation of these cells to each other. The regulation is attenuated or abrogated if normal fibroblasts interact with prostate cancer cells making the cancer cells independent of the limiting effects of fibroblasts, thus contributing to possibility of unlimited growth and progression. Overall, these data demonstrate an ability of cell-cell interactions to affect transcriptional activity of HS biosynthesis-involved genes.

Thromboembolic and bleeding risk in cardiac amyloidosis

Cardiac amyloidosis represents a spectrum of conditions characterized by the accumulation of insoluble fibrils, resulting in progressive deposition and myocardial dysfunction. The exact mechanisms contributing to the heightened risk of thromboembolic events and bleeding tendencies in cardiac amyloidosis remain unclear. Proteins such as transthyretin in transthyretin amyloidosis and light chains in light-chain amyloidosis, along with acute phase proteins in amyloid A (AA) amyloidosis, play complex roles in the coagulation cascade, affecting both coagulation initiation and fibrinolysis regulation. The increased occurrence of atrial fibrillation, systolic and diastolic left ventricular dysfunction, and atrial myopathy in patients with cardiac amyloidosis may predispose them to thrombus formation. This predisposition can occur regardless of sinus rhythm status or even with proper anticoagulant management. Bleeding events are often linked to amyloid deposits around blood vessels, which may increase capillary fragility and cause coagulation disturbances, leading to unstable international normalized ratio levels during anticoagulant therapy. Thus, comprehensive risk assessment for both thrombotic and hemorrhagic complications, especially before commencing anticoagulant therapy, is imperative. This review will explore the essential pathophysiological, epidemiologic, and clinical aspects of thromboembolic and bleeding risk in cardiac amyloidosis, evaluating the existing evidence and uncertainties regarding thrombotic and bleeding risk assessment and antithrombotic treatment.

Overview of the current procedures in synthesis of heparin saccharides

Natural heparin, a glycosaminoglycan consisting of repeating hexuronic acid and glucosamine linked by 1 → 4 glycosidic bonds, is the most widely used anticoagulant. To subvert the dependence on animal sourced heparin, alternative methods to produce heparin saccharides, i.e., either heterogenous sugar chains similar to natural heparin, or structurally defined oligosaccharides, are becoming hot subjects. Although the success by chemical synthesis of the pentasaccharide, fondaparinux, encourages to proceed through a chemical approach generating homogenous product, synthesizing larger oligos is still cumbersome and beyond reach so far. Alternatively, the chemoenzymatic pathway exhibited exquisite stereoselectivity of glycosylation and regioselectivity of modification, with the advantage to skip the tedious protection steps unavoidable in chemical synthesis. However, to a scale of drug production needed today is still not in sight. In comparison, a procedure of de novo biosynthesis in an organism could be an ultimate goal. The main purpose of this review is to summarize the current available/developing strategies and techniques, which is expected to provide a comprehensive picture for production of heparin saccharides to replenish or eventually to replace the animal derived products. In chemical and chemoenzymatic approaches, the methodologies are discussed according to the synthesis procedures: building block preparation, chain elongation, and backbone modification.

Investigation of sample handling steps for accurate heparan sulphate disaccharide analysis using HPLC-MS

Heparan sulphates (HSs), a specific class of glycosaminoglycans (GAGs), are important participants of cellular signalling. Analytical characterization of GAGs requires a complex sample preparation workflow. Although a detailed stability and recovery study is available for the chondroitin sulphate GAG class, the literature concerning HS is incomplete in this regard. Therefore, our aim was to systematically investigate various parameters that could potentially influence the stability and recovery of HS samples when performing disaccharide analysis using high-performance liquid chromatography-mass spectrometry. First, effects concerning vacuum evaporation and freezing were investigated. Next, the storage stability of the HS disaccharides was analysed under several conditions such as temperature, pH, digestion buffers, injection solvents and storage vessels. We have identified several critical parameters influencing the stability and recovery of HS disaccharides. We concluded that major sample loss is expected when Tris-HCl is used as digestion buffer, followed by vacuum evaporation at elevated temperatures, or samples are stored under alkaline conditions. Following the practical considerations of this paper can contribute to increasing the reliability of future analytical measurements.

The extracellular heparan sulfatase SULF2 limits myeloid IFNβ signaling and Th17 responses in inflammatory arthritis

Heparan sulfate (HS) proteoglycans are important regulators of cellular responses to soluble mediators such as chemokines, cytokines and growth factors. We profiled changes in expression of genes encoding HS core proteins, biosynthesis enzymes and modifiers during macrophage polarisation, and found that the most highly regulated gene was Sulf2, an extracellular HS 6-O-sulfatase that was markedly downregulated in response to pro-inflammatory stimuli. We then generated Sulf2+/- bone marrow chimeric mice and examined inflammatory responses in antigen-induced arthritis, as a model of rheumatoid arthritis. Resolution of inflammation was impaired in myeloid Sulf2+/- chimeras, with elevated joint swelling and increased abundance of pro-arthritic Th17 cells in synovial tissue. Transcriptomic and in vitro analyses indicated that Sulf2 deficiency increased type I interferon signaling in bone marrow-derived macrophages, leading to elevated expression of the Th17-inducing cytokine IL6. This establishes that dynamic remodeling of HS by Sulf2 limits type I interferon signaling in macrophages, and so protects against Th17-driven pathology.

Epigenetic Targeting of Heparan Sulfate 3-O- and 6-O-Sulfation in Breast Cancer Cells: Prospects for Attenuating Prothrombotic Tumor Cell Activities

The deregulation of cell surface heparan sulfate proteoglycans (HSPGs) is a main issue of cancer cells for increasing their malignancy. In these terms, the sulfation pattern of HS, created by an orchestrated activity of enzymes balancing a site-specific sulfation, is of key importance. These enzymes are often deregulated by epigenetic processes in cancer, e.g., being silenced by DNA hypermethylation. Here, we address this issue in human breast cancer cell lines aiming to target epigenetic processes to reactivate HS sulfation, shifting HS into an antithrombotic phenotype for which 3-O-sulfation is particularly important. Treatment of MCF-7 and MDA-MB-231 cells with nontoxic concentrations of 5-azacytidine (azacytidine) and 5-fluoro-2'-deoxycytidine (FdCyd) as DNMT inhibitors or vorinostat for targeting HDAC increased HS3-O-sulfation remarkably, as confirmed by fluorescence microscopy, by upregulating HS3-O-sulfotransferases, detected by quantitative real-time polymerase chain reaction and Western blot. Flow cytometry and microscopic approaches confirm that upon inhibitor treatment, increased HS3-O-sulfation improves cell binding to antithrombin, leading to an antithrombotic activity. Nevertheless, only azacytidine- and vorinostat-treated cells display anticoagulative properties, represented by attenuated thrombin formation, a lower activation of human platelet aggregation, or ATP release. In contrast, FdCyd additionally upregulated tissue factor expression in both cell lines, overshadowing the anticoagulant effects of HS, leading to an overall prothrombotic phenotype. Our data provide evidence for the first time that targeting epigenetic processes in HS sulfation is a valuable means to foster anticoagulative cell properties for decreasing malignancy and metastatic potency. These data warrant further investigations to fine-tune epigenetic targeting and to search for potential biomarkers attributed to these activities.

A biological guide to glycosaminoglycans: current perspectives and pending questions

Mammalian glycosaminoglycans (GAGs), except hyaluronan (HA), are sulfated polysaccharides that are covalently attached to core proteins to form proteoglycans (PGs). This article summarizes key biological findings for the most widespread GAGs, namely HA, chondroitin sulfate/dermatan sulfate (CS/DS), keratan sulfate (KS), and heparan sulfate (HS). It focuses on the major processes that remain to be deciphered to get a comprehensive view of the mechanisms mediating GAG biological functions. They include the regulation of GAG biosynthesis and postsynthetic modifications in heparin (HP) and HS, the composition, heterogeneity, and function of the tetrasaccharide linkage region and its role in disease, the functional characterization of the new PGs recently identified by glycoproteomics, the selectivity of interactions mediated by GAG chains, the display of GAG chains and PGs at the cell surface and their impact on the availability and activity of soluble ligands, and on their move through the glycocalyx layer to reach their receptors, the human GAG profile in health and disease, the roles of GAGs and particular PGs (syndecans, decorin, and biglycan) involved in cancer, inflammation, and fibrosis, the possible use of GAGs and PGs as disease biomarkers, and the design of inhibitors targeting GAG biosynthetic enzymes and GAG-protein interactions to develop novel therapeutic approaches.

Significance of Artificial Intelligence in the Study of Virus-Host Cell Interactions

A highly critical event in a virus's life cycle is successfully entering a given host. This process begins when a viral glycoprotein interacts with a target cell receptor, which provides the molecular basis for target virus-host cell interactions for novel drug discovery. Over the years, extensive research has been carried out in the field of virus-host cell interaction, generating a massive number of genetic and molecular data sources. These datasets are an asset for predicting virus-host interactions at the molecular level using machine learning (ML), a subset of artificial intelligence (AI). In this direction, ML tools are now being applied to recognize patterns in these massive datasets to predict critical interactions between virus and host cells at the protein-protein and protein-sugar levels, as well as to perform transcriptional and translational analysis. On the other end, deep learning (DL) algorithms-a subfield of ML-can extract high-level features from very large datasets to recognize the hidden patterns within genomic sequences and images to develop models for rapid drug discovery predictions that address pathogenic viruses displaying heightened affinity for receptor docking and enhanced cell entry. ML and DL are pivotal forces, driving innovation with their ability to perform analysis of enormous datasets in a highly efficient, cost-effective, accurate, and high-throughput manner. This review focuses on the complexity of virus-host cell interactions at the molecular level in light of the current advances of ML and AI in viral pathogenesis to improve new treatments and prevention strategies.

Glycosaminoglycans in mucopolysaccharidoses and other disorders

Glycosaminoglycans (GAGs) are sulfated polysaccharides comprising repeating disaccharides, uronic acid (or galactose) and hexosamines, including chondroitin sulfate, dermatan sulfate, heparan sulfate, and keratan sulfate. Hyaluronan is an exception in the GAG family because it is a non-sulfated polysaccharide. Lysosomal enzymes are crucial for the stepwise degradation of GAGs to provide a normal function of tissues and extracellular matrix (ECM). The deficiency of one or more lysosomal enzyme(s) results in the accumulation of undegraded GAGs, causing cell, tissue, and organ dysfunction. Accumulation of GAGs in various tissues and ECM results in secretion into the circulation and then excretion in urine. GAGs are biomarkers of certain metabolic disorders, such as mucopolysaccharidoses (MPS) and mucolipidoses. GAGs are also elevated in patients with various conditions such as respiratory and renal disorders, fatty acid metabolism disorders, viral infections, vomiting disorders, liver disorders, epilepsy, hypoglycemia, myopathy, developmental disorders, hyperCKemia, heart disease, acidosis, and encephalopathy. MPS are a group of inherited metabolic diseases caused by the deficiency of enzymes required to degrade GAGs in the lysosome. Eight types of MPS are categorized based on lack or defect in one of twelve specific lysosomal enzymes and are described as MPS I through MPS X (excluding MPS V and VIII). Clinical features vary with the type of MPS and clinical severity of the disease. This chapter addresses the historical overview, synthesis, degradation, distribution, biological role, and method for measurement of GAGs.

Excess Dally-like Induces Malformation of Drosophila Legs

Glypicans are closely associated with organ development and tumorigenesis in animals. Dally-like (Dlp), a membrane-bound glypican, plays pivotal roles in various biological processes in Drosophila. In this study, we observed that an excess of Dlp led to the malformation of legs, particularly affecting the distal part. Accordingly, the leg disc was shrunken and frequently exhibited aberrant morphology. In addition, elevated Dlp levels induced ectopic cell death with no apparent cell proliferation changes. Furthermore, Dlp overexpression in the posterior compartment significantly altered Wingless (Wg) distribution. We observed a marked expansion of Wg distribution within the posterior compartment, accompanied by a corresponding decrease in the anterior compartment. It appears that excess Dlp guides Wg to diffuse to cells with higher Dlp levels. In addition, the distal-less (dll) gene, which is crucial for leg patterning, was up-regulated significantly. Notably, dachshund (dac) and homothorax (hth) expression, also essential for leg patterning and development, only appeared to be negligibly affected. Based on these findings, we speculate that excess Dlp may contribute to malformations of the distal leg region of Drosophila, possibly through its influence on Wg distribution, dll expression and induced cell death. Our research advances the understanding of Dlp function in Drosophila leg development.

Diverse Responses of Oligodendrocytes to Different FGF-Family Members: Uncoupling Structure-Function Relationship Within FGF Subfamilies

The fifteen canonical paracrine fibroblast growth factors (FGFs) are organized in five subfamilies that interact with four FGF-receptors (FGFRs) and heparan sulfate proteoglycan (HSPG) co-receptors. Many of these FGFs are expressed in CNS regions where oligodendrocyte (OL) progenitors originate, migrate or differentiate. FGF2 (basic FGF) is considered a prototype FGF and the information about the effects of FGF signaling on OL-lineage cells has evolved largely from the study of FGF2. However, other FGFs from four subfamilies ((FGF1 (FGF1,-2), FGF4 (FGF4,-5,-6), FGF8 (FGF8,-17,-18) and FGF9 (FGF9,-16,-20)) that can interact with the isoforms of FGFRs expressed in OL-lineage cells may also play important roles. We previously reported OL-responses to FGF8 family members. Here, we investigate the effects of members of the FGF1,-4, and -9 subfamilies on proliferation and differentiation of OL progenitors (OPCs), and on cell cycle re-entry and down-regulation of myelin proteins by mature OLs. We found that while FGF2 induced all these responses strongly, FGF4,-6,-9 could do so only transiently and in the presence of exogenous HSPGs, and that FGF5,-16,-20 could not do so even in the presence of heparin or at higher concentrations. Furthermore, we noted that structurally similar FGFs within subfamilies did not always show similarities in their biological effects on OL-lineage cells. Taken together, these studies reveal that FGFs differ in the way they regulate the OL-lineage cells, emphasizes the selectivity and importance of HSPGs as FGF co-receptors in OL-lineage cells and suggests that structural similarity among FGF-subfamily members may not always predict their overlapping biological functions.

MEG3-Mediated Oral Squamous-Cell-Carcinoma-Derived Exosomal miR-421 Activates Angiogenesis by Targeting HS2ST1 in Vascular Endothelial Cells

Exosomal microRNAs (miRNAs) from cancer cells play a key role in mediating the oral squamous cell carcinoma (OSCC) microenvironment. The objective of this study was to investigate how the long non-coding RNA (lncRNA) MEG3 affects OSCC angiogenesis through exosomal miR-421. Global miRNA microarray analysis and quantitative real-time PCR (qRT-PCR) were performed to determine the level of miRNAs in OSCC cell-derived exosomes. Cell migration, invasion, tube formation, immunohistochemistry, and hemoglobin concentrations were used to study the effects of exosomal miR-421 in angiogenesis. Western blotting was used to determine the expression level of HS2ST1 and VEGFR2-related downstream proteins. MiRNA array and qRT-PCR identified the upregulation of miR-421 in OSCC cell-derived exosomes. Furthermore, exosomal miR-421 can be taken up by human umbilical vein endothelial cells (HUVECs) and then target HS2ST1 through VEGF-mediated ERK and AKT phosphorylation, thereby promoting HUVEC migration, invasion, and tube formation. Additionally, forced expression of the lncRNA MEG3 in OSCC cells reduced exosomal miR-421 levels and then increased HS2ST1 expression, thereby reducing the VEGF/VEGFR2 pathway in HUVECs. Our results demonstrate a novel mechanism by which lncRNA MEG3 can act as a tumor suppressor and regulate endothelial angiogenesis through the exosomal miR-421/HS2ST1 axis, which provides a potential therapeutic strategy for OSCC angiogenesis.

Glycosaminoglycans: Participants in Microvascular Coagulation of Sepsis

Sepsis represents a syndromic response to infection and frequently acts as a common pathway leading to fatality in the context of various infectious diseases globally. The pathology of severe sepsis is marked by an excess of inflammation and activated coagulation. A substantial contributor to mortality in sepsis patients is widespread microvascular thrombosis-induced organ dysfunction. Multiple lines of evidence support the notion that sepsis induces endothelial damage, leading to the release of glycosaminoglycans, potentially causing microvascular dysfunction. This review aims to initially elucidate the relationship among endothelial damage, excessive inflammation, and thrombosis in sepsis. Following this, we present a summary of the involvement of glycosaminoglycans in coagulation, elucidating interactions among glycosaminoglycans, platelets, and inflammatory cells. In this section, we also introduce a reasoned generalization of potential signal pathways wherein glycosaminoglycans play a role in clotting. Finally, we discuss current methods for detecting microvascular conditions in sepsis patients from the perspective of glycosaminoglycans. In conclusion, it is imperative to pay closer attention to the role of glycosaminoglycans in the mechanism of microvascular thrombosis in sepsis. Dynamically assessing glycosaminoglycan levels in patients may aid in predicting microvascular conditions, enabling the monitoring of disease progression, adjustment of clinical treatment schemes, and mitigation of both acute and long-term adverse outcomes associated with sepsis.

Glycosylation of FGF/FGFR: An underrated sweet code regulating cellular signaling programs

Fibroblast growth factors (FGFs) and their receptors (FGFRs) constitute plasma-membrane localized signaling hubs that transmit signals from the extracellular environment to the cell interior, governing pivotal cellular processes like motility, metabolism, differentiation, division and death. FGF/FGFR signaling is critical for human body development and homeostasis; dysregulation of FGF/FGFR units is observed in numerous developmental diseases and in about 10% of human cancers. Glycosylation is a highly abundant posttranslational modification that is critical for physiological and pathological functions of the cell. Glycosylation is also very common within FGF/FGFR signaling hubs. Vast majority of FGFs (15 out of 22 members) are N-glycosylated and few FGFs are O-glycosylated. Glycosylation is even more abundant within FGFRs; all FGFRs are heavily N-glycosylated in numerous positions within their extracellular domains. A growing number of studies points on the multiple roles of glycosylation in fine-tuning FGF/FGFR signaling. Glycosylation modifies secretion of FGFs, determines their stability and affects interaction with FGFRs and co-receptors. Glycosylation of FGFRs determines their intracellular sorting, constitutes autoinhibitory mechanism within FGFRs and adjusts FGF and co-receptor recognition. Sugar chains attached to FGFs and FGFRs constitute also a form of code that is differentially decrypted by extracellular lectins, galectins, which transform FGF/FGFR signaling at multiple levels. This review focuses on the identified functions of glycosylation within FGFs and FGFRs and discusses their relevance for the cell physiology in health and disease.

Chemo-enzymatic synthesis of tetrasaccharide linker peptides to study the divergent step in glycosaminoglycan biosynthesis

Glycosaminoglycans are extended linear polysaccharides present on cell surfaces and within the extracellular matrix that play crucial roles in various biological processes. Two prominent glycosaminoglycans, heparan sulfate and chondroitin sulfate, are covalently linked to proteoglycan core proteins through a common tetrasaccharide linker comprising glucuronic acid, galactose, galactose, and xylose moities. This tetrasaccharide linker is meticulously assembled step by step by four Golgi-localized glycosyltransferases. The addition of the fifth sugar moiety, either N-acetylglucosamine or N-acetylgalactosamine, initiates further chain elongation, resulting in the formation of heparan sulfate or chondroitin sulfate, respectively. Despite the fundamental significance of this step in glycosaminoglycan biosynthesis, its regulatory mechanisms have remained elusive. In this study, we detail the expression and purification of the four linker-synthesizing glycosyltransferases and their utilization in the production of fluorescent peptides carrying the native tetrasaccharide linker. We generated five tetrasaccharide peptides, mimicking the core proteins of either heparan sulfate or chondroitin sulfate proteoglycans. These peptides were readily accepted as substrates by the EXTL3 enzyme, which adds an N-acetylglucosamine moiety, thereby initiating heparan sulfate biosynthesis. Importantly, EXTL3 showed a preference towards peptides mimicking the core proteins of heparan sulfate proteoglycans over the ones from chondroitin sulfate proteoglycans. This suggests that EXTL3 could play a role in the decision-making step during glycosaminoglycan biosynthesis. The innovative strategy for chemo-enzymatic synthesis of fluorescent-labeled linker-peptides promises to be instrumental in advancing future investigations into the initial steps and the divergent step of glycosaminoglycan biosynthesis.

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.

Complex N-glycosylation of mGluR6 is required for trans-synaptic interaction with ELFN adhesion proteins

Synaptic transmission from retinal photoreceptors to downstream ON-type bipolar cells (BCs) depends on the postsynaptic metabotropic glutamate receptor mGluR6, located at the BC dendritic tips. Glutamate binding to mGluR6 initiates G-protein signaling that ultimately leads to BC depolarization in response to light. The mGluR6 receptor also engages in trans-synaptic interactions with presynaptic ELFN adhesion proteins. The roles of post-translational modifications in mGluR6 trafficking and function are unknown. Treatment with glycosidase enzymes PNGase F and Endo H demonstrated that both endogenous and heterologously expressed mGluR6 contain complex N-glycosylation acquired in the Golgi. Pull-down experiments with ELFN1 and ELFN2 extracellular domains revealed that these proteins interact exclusively with the complex glycosylated form of mGluR6. Mutation of the four predicted N-glycosylation sites, either singly or in combination, revealed that all four sites are glycosylated. Single mutations partially reduced, but did not abolish, surface expression in heterologous cells, while triple mutants had little or no surface expression, indicating that no single glycosylation site is necessary or sufficient for plasma membrane trafficking. Mutation at N445 severely impaired both ELFN1 and ELFN2 binding. All single mutants exhibited dendritic tip enrichment in rod BCs, as did the triple mutant with N445 as the sole N-glycosylation site, demonstrating that glycosylation at N445 is sufficient but not necessary for dendritic tip localization. The quadruple mutant was completely mislocalized. These results reveal a key role for complex N-glycosylation in regulating mGluR6 trafficking and ELFN binding, and by extension, function of the photoreceptor synapses.

Structure and function of Semaphorin-5A glycosaminoglycan interactions

Integration of extracellular signals by neurons is pivotal for brain development, plasticity, and repair. Axon guidance relies on receptor-ligand interactions crosstalking with extracellular matrix components. Semaphorin-5A (Sema5A) is a bifunctional guidance cue exerting attractive and inhibitory effects on neuronal growth through the interaction with heparan sulfate (HS) and chondroitin sulfate (CS) glycosaminoglycans (GAGs), respectively. Sema5A harbors seven thrombospondin type-1 repeats (TSR1-7) important for GAG binding, however the underlying molecular basis and functions in vivo remain enigmatic. Here we dissect the structural basis for Sema5A:GAG specificity and demonstrate the functional significance of this interaction in vivo. Using x-ray crystallography, we reveal a dimeric fold variation for TSR4 that accommodates GAG interactions. TSR4 co-crystal structures identify binding residues validated by site-directed mutagenesis. In vitro and cell-based assays uncover specific GAG epitopes necessary for TSR association. We demonstrate that HS-GAG binding is preferred over CS-GAG and mediates Sema5A oligomerization. In vivo, Sema5A:GAG interactions are necessary for Sema5A function and regulate Plexin-A2 dependent dentate progenitor cell migration. Our study rationalizes Sema5A associated developmental and neurological disorders and provides mechanistic insights into how multifaceted guidance functions of a single transmembrane cue are regulated by proteoglycans.

EXT2: a novel prognostic and predictive biomarker for head and neck squamous cell carcinoma

OBJECTIVE

This study focused on EXT2, a member of the EXT family involved in heparan sulfate synthesis, to evaluate its potential as a prognostic and predictive biomarker in head-neck squamous cell carcinoma (HNSCC).

MATERIALS AND METHODS

The present study used the cancer genome atlas head-neck squamous cell carcinoma (TCGA-HNSC) dataset-based UALCAN database to analyze the EXT2 expression and its clinicopathological features. In addition, we recruited 51 oral squamous cell carcinoma patients (OSCC), the most common HNSCC subtype, to validate the EXT2 mRNA expression analysis. In addition, we identified the role of EXT2 in prognosis using a Kaplan-Meier plot and immune signature using the tumor infiltration level. Furthermore, functional roles were analyzed using the EXT2 gene and protein networks.

RESULTS

The expression of EXT2 mRNA was significantly upregulated in OSCC tumors, which is consistent with the UALCAN-based results. EXT2 protein was also significantly overexpressed in HNSCC samples and was correlated with clinicopathological features. High EXT2 expression is associated with poor survival outcomes in HNSCC patients. Functional analysis of EXT2 using in silico tools revealed its involvement in critical pathways, including Wnt signaling, proteoglycans in cancer, and cellular responses to fibroblast growth and inflammation.

CONCLUSION

These findings highlight the potential of EXT2 as a prognostic and predictive biomarker of HNSCC.

A glycosylation-related gene signature predicts prognosis, immune microenvironment infiltration, and drug sensitivity in glioma

Glioma represents the most common primary cancer of the central nervous system in adults. Glycosylation is a prevalent post-translational modification that occurs in eukaryotic cells, leading to a wide array of modifications on proteins. We obtained the clinical information, bulk RNA-seq data, and single-cell RNA sequencing (scRNA-seq) from The Cancer Genome Atlas (TCGA), Chinese Glioma Genome Atlas (CGGA), Gene Expression Omnibus (GEO), and Repository of Molecular Brain Neoplasia Data (Rembrandt) databases. RNA sequencing data for normal brain tissues were accessed from the Genotype-Tissue Expression (GTEx) database. Then, the glycosylation genes that were differentially expressed were identified and further subjected to variable selection using a least absolute shrinkage and selection operator (LASSO)-regularized Cox model. We further conducted enrichment analysis, qPCR, nomogram, and single-cell transcriptome to detect the glycosylation signature. Drug sensitivity analysis was also conducted. A five-gene glycosylation signature (CHPF2, PYGL, GALNT13, EXT2, and COLGALT2) classified patients into low- or high-risk groups. Survival analysis, qPCR, ROC curves, and stratified analysis revealed worse outcomes in the high-risk group. Furthermore, GSEA and immune infiltration analysis indicated that the glycosylation signature has the potential to predict the immune response in glioma. In addition, four drugs (crizotinib, lapatinib, nilotinib, and topotecan) showed different responses between the two risk groups. Glioma cells had been classified into seven lines based on single-cell expression profiles. The five-gene glycosylation signature can accurately predict the prognosis of glioma and may offer additional guidance for immunotherapy.

The exostosin glycosyltransferase 1/STAT3 axis is a driver of breast cancer aggressiveness

The epithelial-mesenchymal transition (EMT) program is crucial for transforming carcinoma cells into a partially mesenchymal state, enhancing their chemoresistance, migration, and metastasis. This shift in cell state is tightly regulated by cellular mechanisms that are not yet fully characterized. One intriguing EMT aspect is the rewiring of the proteoglycan landscape, particularly the induction of heparan sulfate proteoglycan (HSPG) biosynthesis. This proteoglycan functions as a co-receptor that accelerates cancer-associated signaling pathways through its negatively-charged residues. However, the precise mechanisms through which EMT governs HSPG biosynthesis and its role in cancer cell plasticity remain elusive. Here, we identified exostosin glycosyltransferase 1 (EXT1), a central enzyme in HSPG biosynthesis, to be selectively upregulated in aggressive tumor subtypes and cancer cell lines, and to function as a key player in breast cancer aggressiveness. Notably, ectopic expression of EXT1 in epithelial cells is sufficient to induce HSPG levels and the expression of known mesenchymal markers, subsequently enhancing EMT features, including cell migration, invasion, and tumor formation. Additionally, EXT1 loss in MDA-MB-231 cells inhibits their aggressiveness-associated traits such as migration, chemoresistance, tumor formation, and metastasis. Our findings reveal that EXT1, through its role in HSPG biosynthesis, governs signal transducer and activator of transcription 3 (STAT3) signaling, a known regulator of cancer cell aggressiveness. Collectively, we present the EXT1/HSPG/STAT3 axis as a central regulator of cancer cell plasticity that directly links proteoglycan synthesis to oncogenic signaling pathways.

The Pathogenesis of Foot-and-Mouth Disease Virus Infection: How the Virus Escapes from Immune Recognition and Elimination

Foot-and-mouth disease virus (FMDV) is a highly contagious and economically devastating pathogen that affects cloven-hoofed animals worldwide. FMDV infection causes vesicular lesions in the mouth, feet, and mammary glands, as well as severe systemic symptoms such as fever, salivation, and lameness. The pathogenesis of FMDV infection involves complex interactions between the virus and the host immune system, which determine the outcome of the disease. FMDV has evolved several strategies to evade immune recognition and elimination, such as antigenic variation, receptor switching, immune suppression, and subversion of innate and adaptive responses. This review paper summarizes the current knowledge on the pathogenesis of FMDV infection and the mechanisms of immune evasion employed by the virus. It also discusses the challenges and opportunities for developing effective vaccines and therapeutics against this important animal disease.

Differential heparan sulfate dependency of the Drosophila glypicans

Heparan sulfate proteoglycans (HSPGs) are composed of a core protein and glycosaminoglycan (GAG) chains and serve as coreceptors for many growth factors and morphogens. To understand the molecular mechanisms by which HSPGs regulate morphogen gradient formation and signaling, it is important to determine the relative contributions of the carbohydrate and protein moieties to the proteoglycan function. To address this question, we generated ΔGAG alleles for dally and dally-like protein (dlp), two Drosophila HSPGs of the glypican family, in which all GAG-attachment serine residues are substituted to alanine residues using CRISPR/Cas9 mutagenesis. In these alleles, the glypican core proteins are expressed from the endogenous loci with no GAG modification. Analyses of the dallyΔGAG allele defined Dally functions that do not require heparan sulfate (HS) chains and that need both core protein and HS chains. We found a new, dallyΔGAG-specific phenotype, the formation of a posterior ectopic vein, which we have never seen in the null mutants. Unlike dallyΔGAG, dlpΔGAG mutants do not show most of the dlp null mutant phenotypes, suggesting that HS chains are dispensable for these dlp functions. As an exception, HS is essentially required for Dlp's activity at the neuromuscular junction. Thus, Drosophila glypicans show strikingly different levels of HS dependency. The ΔGAG mutant alleles of the glypicans serve as new molecular genetic toolsets highly useful to address important biological questions, such as molecular mechanisms of morphogen gradient formation.

In vivo activities of heparan sulfate differentially modified by NDSTs during development

Heparan sulfate proteoglycans (HSPGs) serve as co-receptors for growth factor signaling during development. It is well known that the level and patterns of sulfate groups of heparan sulfate (HS) chains, or HS fine structures, have a major impact on HSPG function. On the other hand, the physiological significance of other structural features of HS, including NS/NA domain organization, remains to be elucidated. A blueprint of the HS domain structures is mainly controlled by HS N-deacetylase/N-sulfotransferases (NDSTs). To analyze in vivo activities of differentially modified HS, we established two knock-in (KI) Drosophila strains with the insertion of mouse Ndst1 (mNdst1) or Ndst2 (mNdst2) in the locus of sulfateless (sfl), the only Drosophila NDST. In these KI lines, mNDSTs are expressed from the sfl locus, in the level and patterns identical to the endogenous sfl gene. Thus, phenotypes of Ndst1 KI and Ndst2KI animals reflect the ability of HS structures made by these enzymes to rescue sfl mutation. Remarkably, we found that mNdst1 completely rescued the loss of sfl. mNdst2 showed a limited rescue ability, despite a higher level of HS sulfation compared to HS in mNdst1 KI. Our study suggests that independent of sulfation levels, additional HS structural features controlled by NDSTs play key roles during tissue patterning.

Human extracellular sulfatases use a dual mechanism for regulation of growth factor interactions with heparan sulfate proteoglycans

Membrane-associated heparan sulfate (HS) proteoglycans (PGs) contribute to the regulation of extracellular cellular signaling cues, such as growth factors (GFs) and chemokines, essential for normal organismal functions and implicated in various pathophysiologies. PGs accomplish this by presenting high affinity binding sites for GFs and their receptors through highly sulfated regions of their HS polysaccharide chains. The composition of HS, and thus GF-binding specificity, are determined during biosynthetic assembly prior to installation at the cell surface. Two extracellular 6- O -endosulfatase enzymes (Sulf-1 and Sulf-2) can uniquely further edit mature HS and alter its interactions with GFs by removing specific sulfation motifs from their recognition sequence on HS. Despite being implicated as signaling regulators during development and in disease, the Sulfs have resisted structural characterization, and their substrate specificity and effects on GF interactions with HS are still poorly defined. Using a panel of PG-mimetics comprising compositionally-defined bioengineered recombinant HS (rHS) substrates in combination with GF binding and enzyme activity assays, we have discovered that Sulfs control GF-HS interactions through a combination of catalytic processing and competitive blocking of high affinity GF-binding sites, providing a new conceptual framework for understanding the functional impact of these enzymes in biological context. Although the contributions from each mechanism are both Sulf- and GF-dependent, the PG-mimetic platform allows for rapid analysis of these complex relationships.

Significance Statement

Cells rely on extracellular signals such as growth factors (GFs) to mediate critical biological functions. Membrane-associated proteins bearing negatively charged heparan sulfate (HS) sugar chains engage with GFs and present them to their receptors, which regulates their activity. Two extracellular sulfatase (Sulf) enzymes can edit HS and alter GF interactions and activity, although the precise mechanisms remain unclear. By using chemically defined HS-mimetics as probes, we have discovered that Sulfs can modulate HS by means of catalytic alterations and competitive blocking of GF-binding sites. These unique dual activities distinguish Sulfs from other enzymes and provide clues to their roles in development and disease.

Topoisomeric Membrane-Active Peptides: A Review of the Last Two Decades

In recent decades, bioactive peptides have been gaining recognition in various biomedical areas, such as intracellular drug delivery (cell-penetrating peptides, CPPs) or anti-infective action (antimicrobial peptides, AMPs), closely associated to their distinct mode of interaction with biological membranes. Exploiting the interaction of membrane-active peptides with diverse targets (healthy, tumoral, bacterial or parasitic cell membranes) is opening encouraging prospects for peptides in therapeutics. However, ordinary peptides formed by L-amino acids are easily decomposed by proteases in biological fluids. One way to sidestep this limitation is to use topoisomers, namely versions of the peptide made up of D-amino acids in either canonic (enantio) or inverted (retroenantio) sequence. Rearranging peptide sequences in this fashion provides a certain degree of native structure mimicry that, in appropriate contexts, may deliver desirable biological activity while avoiding protease degradation. In this review, we will focus on recent accounts of membrane-active topoisomeric peptides with therapeutic applications as CPP drug delivery vectors, or as antimicrobial and anticancer candidates. We will also discuss the most common modes of interaction of these peptides with their membrane targets.

Attachment, Entry, and Intracellular Trafficking of Classical Swine Fever Virus

Classical swine fever virus (CSFV), which is a positive-sense, single-stranded RNA virus with an envelope, is a member of the Pestivirus genus in the Flaviviridae family. CSFV causes a severe and highly contagious disease in pigs and is prevalent worldwide, threatening the pig farming industry. The detailed mechanisms of the CSFV life cycle have been reported, but are still limited. Some receptors and attachment factors of CSFV, including heparan sulfate (HS), laminin receptor (LamR), complement regulatory protein (CD46), MER tyrosine kinase (MERTK), disintegrin, and metalloproteinase domain-containing protein 17 (ADAM17), were identified. After attachment, CSFV internalizes via clathrin-mediated endocytosis (CME) and/or caveolae/raft-dependent endocytosis (CavME). After internalization, CSFV moves to early and late endosomes before uncoating. During this period, intracellular trafficking of CSFV relies on components of the endosomal sorting complex required for transport (ESCRT) and Rab proteins in the endosome dynamics, with a dependence on the cytoskeleton network. This review summarizes the data on the mechanisms of CSFV attachment, internalization pathways, and intracellular trafficking, and provides a general view of the early events in the CSFV life cycle.

Chondroitin sulfate is required for follicle epithelial integrity and organ shape maintenance in Drosophila

Heparan sulfate (HS) and chondroitin sulfate (CS) are evolutionarily conserved glycosaminoglycans that are found in most animal species, including the genetically tractable model organism Drosophila. In contrast to extensive in vivo studies elucidating co-receptor functions of Drosophila HS proteoglycans (PGs), only a limited number of studies have been conducted for those of CSPGs. To investigate the global function of CS in development, we generated mutants for Chondroitin sulfate synthase (Chsy), which encodes the Drosophila homolog of mammalian chondroitin synthase 1, a crucial CS biosynthetic enzyme. Our characterizations of the Chsy mutants indicated that a fraction survive to adult stage, which allowed us to analyze the morphology of the adult organs. In the ovary, Chsy mutants exhibited altered stiffness of the basement membrane and muscle dysfunction, leading to a gradual degradation of the gross organ structure as mutant animals aged. Our observations show that normal CS function is required for the maintenance of the structural integrity of the ECM and gross organ architecture.

Prognostic value of GLCE and infiltrating immune cells in Ewing sarcoma

Background

The prognostic value of D-glucuronyl C5-epimerase (GLCE) and mast cell infiltration in Ewing sarcoma (ES) has not been well specified and highlighted, which may facilitate survival prediction and treatment.

Methods

Several qualified datasets were downloaded from the GEO website. Common differentially expressed genes between normal subjects and ES patients in GSE17679, GSE45544, and GSE68776 were identified and screened by multiple algorithms to find hub genes with prognostic value. The prognostic value of 64 infiltrating cells was also explored. A prognostic model was established and then validated with GSE63155 and GSE63156. Finally, functional analysis was performed.

Results

GLCE and mast cell infiltration were screened as two indicators for a prognostic model. The Kaplan‒Meier analysis showed that patients in the low GLCE expression, mast cell infiltration and risk score groups had poorer outcomes than patients in the high GLCE expression, mast cell infiltration and risk score groups, both in the training and validation sets. Scatter plots and heatmaps also indicated the same results. The concordance indices and calibration analyses indicated a high prediction accuracy of the model in the training and validation sets. The time-dependent receiver operating characteristic analyses suggested high sensitivity and specificity of the model, with area under the curve values between 0.76 and 0.98. The decision curve analyses suggested a significantly higher net benefit by the model than the treat-all and treat-none strategies. Functional analyses suggested that glycosaminoglycan biosynthesis-heparan sulfate/heparin, the cell cycle and microRNAs in cancer were upregulated in ES patients.

Conclusions

GLCE and mast cell infiltration are potential prognostic indicators in ES. GLCE may affect the proliferation, angiogenesis and metastasis of ES by affecting the biosynthesis of heparan sulfate and heparin.

Mapping the Acetylamino and Carboxyl Groups on Glycans by Engineered α-Hemolysin Nanopores

Glycan is a crucial class of biological macromolecules with important biological functions. Functional groups determine the chemical properties of glycans, which further affect their biological activities. However, the structural complexity of glycans has set a technical hurdle for their direct identification. Nanopores have emerged as highly sensitive biosensors that are capable of detecting and characterizing various analytes. Here, we identified the functional groups on glycans with a designed α-hemolysin nanopore containing arginine mutations (M113R), which is specifically sensitive to glycans with acetamido and carboxyl groups. Molecular dynamics simulations indicated that the acetamido and carboxyl groups of the glycans produce unique electrical signatures by forming polar and electrostatic interactions with the M113R nanopores. Using these electrical features as the fingerprints, we mapped the length of the glycans containing acetamido and carboxyl groups at the monosaccharide, disaccharide, and trisaccharide levels. This proof-of-concept study provides a promising foundation for developing single-molecule glycan fingerprinting libraries and demonstrates the capability of biological nanopores in glycan sequencing.

Computational studies on glycosaminoglycan recognition of sialyl transferases

Despite decades of research, glycosaminoglycans (GAGs) have not been known to interact with sialyl transferases (STs). Using our in-house combinatorial virtual library screening (CVLS) technology, we studied seven human isoforms, including ST6GAL1, ST6GAL2, ST3GAL1, ST3GAL3, ST3GAL4, ST3GAL5, and ST3GAL6, and predicted that GAGs, especially heparan sulfate (HS), are likely to differentially bind to STs. Exhaustive CVLS and molecular dynamics studies suggested that the common hexasaccharide sequence of HS preferentially recognized ST6GAL1 in a site overlapping the binding site of the donor substrate CMP-Sia. Interestingly, CVLS did not ascribe any special role for the rare 3-O-sulfate modification of HS in ST6GAL1 recognition. The computational predictions were tested using spectrofluorimetric studies, which confirmed preferential recognition of HS over other GAGs. A classic chain length-dependent binding of GAGs to ST6GAL1 was observed with polymeric HS displaying a tight affinity of ~65 nM. Biophysical studies also confirmed a direct competition between CMP-Sia and an HS oligosaccharide and CS polysaccharide for binding to ST6GAL1. Overall, our novel observation that GAGs bind to ST6GAL1 with high affinity and compete with the donor substrate is likely to be important because modulation of sialylation of glycan substrates on cells has considerable physiological/pathological consequences. Our work also brings forth the possibility of developing GAG-based chemical probes of ST6GAL1.

Phage-based peptides for pancreatic cancer diagnosis and treatment: alternative approach

Pancreatic cancer is a devastating disease with a high mortality rate and a lack of effective therapies. The challenges associated with early detection and the highly aggressive nature of pancreatic cancer have limited treatment options, underscoring the urgent need for better disease-modifying therapies. Peptide-based biotherapeutics have become an attractive area of research due to their favorable properties such as high selectivity and affinity, chemical modifiability, good tissue permeability, and easy metabolism and excretion. Phage display, a powerful technique for identifying peptides with high affinity and specificity for their target molecules, has emerged as a key tool in the discovery of peptide-based drugs. Phage display technology involves the use of bacteriophages to express peptide libraries, which are then screened against a target of interest to identify peptides with desired properties. This approach has shown great promise in cancer diagnosis and treatment, with potential applications in targeting cancer cells and developing new therapies. In this comprehensive review, we provide an overview of the basic biology of phage vectors, the principles of phage library construction, and various methods for binding affinity assessment. We then describe the applications of phage display in pancreatic cancer therapy, targeted drug delivery, and early detection. Despite its promising potential, there are still challenges to be addressed, such as optimizing the selection process and improving the pharmacokinetic properties of phage-based drugs. Nevertheless, phage display represents a promising approach for the development of novel targeted therapies in pancreatic cancer and other tumors.

HS6ST1 overexpressed in cancer-associated fibroblast and inhibited cholangiocarcinoma progression

BACKGROUD

Fibroblasts turn into cancer associated fibroblasts (CAFs) in the tumor microenvironment, which play an important role in tumor progression. However, the mechanism is unclear.

AIMS

To investigate the role of CAFs with HS6ST1-overexpression in cell migration and invasion effects.

METHODS

Human primary CAFs were isolated and identified from intrahepatic cholangiocarcinoma. mRNA profiles differences between CAFs and NFs were examined by using transcriptome sequencing. Using Transwell® migration assays, ICCA cells (RBE and HUCCT1) with NF-CM, CAF-CM, CAFsNC-CM, and CAFsHS6ST1-CM were analyzed. Immunohistochemical staining were used to analyze the expression of HS6ST1 in CAF in 152 patients with ICCA. Overall survival (OS) was compared based on CAF HS6ST1 expression were analysed. The relationship between clinicopathological parameters and survival was also examined.

RESULTS

Successfully isolated CAFs is positive staining with αSMA, FSP-1, FAP, and PDGFR-β. Transcriptome sequencing showed that differently expressed genes were enriched in the function of the extracellular matrix and chemokine signaling pathway. HS6ST1 is differentially expressed between CAFs and NFs, and associated with the migration and invasion of ICCA cells. Moreover, HS6ST1 positive expression of CAFs predicted unfavorable prognosis in patients with intrahepatic cholangiocarcinoma and showed correlation with the presence of lymph node metastasis.

CONCLUSION

HS6ST1 is new possibilities for targeting the CAFs to reduce cholangiocarcinoma growth and metastasis.

Targeting the Conformational Change in ArnA Dehydrogenase for Selective Inhibition of Polymyxin Resistance

Polymyxins are important last resort antibiotics for the treatment of infections caused by multidrug-resistant Gram-negative pathogens. However, pathogens have acquired resistance to polymyxins through a pathway that modifies lipid A with 4-amino-4-deoxy-l-arabinose (Ara4N). Inhibition of this pathway is, therefore, a desirable strategy to combat polymyxin resistance. The first pathway-specific reaction is an NAD+-dependent oxidative decarboxylation of UDP-glucuronic acid (UDP-GlcA) catalyzed by the dehydrogenase domain of ArnA (ArnA_DH). We present the crystal structure of Salmonella enterica serovar typhimurium ArnA in complex with UDP-GlcA showing that binding of the sugar nucleotide is sufficient to trigger a conformational change conserved in bacterial ArnA_DHs but absent in its human homologs, as confirmed by structure and sequence analysis. Ligand binding assays show that the conformational change is essential for NAD+ binding and catalysis. Enzyme activity and binding assays show that (i) UDP-GlcA analogs lacking the 6' carboxylic acid bind the enzyme but fail to trigger the conformational change, resulting in poor inhibition, and (ii) the uridine monophosphate moiety of the substrate provides most of the ligand binding energy. Mutation of asparagine 492 to alanine (N492A) disrupts the ability of ArnA_DH to undergo the conformational change while retaining substrate binding, suggesting that N492 is involved in sensing the 6' carboxylate in the substrate. These results identify the UDP-GlcA-induced conformational change in ArnA_DH as an essential mechanistic step in bacterial enzymes, providing a platform for selective inhibition.

The heparan sulfate mimetic Muparfostat aggravates steatohepatitis in obese mice due to its binding affinity to lipoprotein lipase

BACKGROUND AND PURPOSE

Heparanase is the only confirmed endoglycosidase that cleaves heparan sulfate (HS), a ubiquitous glycosaminoglycan with various essential roles in multiple pathological processes. Thus, the development of heparanase inhibitors has become an attractive strategy for drug discovery, especially in tumour therapy, in which HS mimetics are the most promising compounds. The various biological effects of heparanase also suggest a role for HS mimetics in many non-cancer indications, such as type 1 diabetes. However, the potential benefits of HS mimetics in obesity-related type 2 diabetes have not been elucidated.

EXPERIMENTAL APPROACH

In this study, we investigated muparfostat (PI-88), a developed HS mimetic currently enrolled in Phase III clinical trials, in obese mouse models and in vitro cultured murine hepatocytes.

KEY RESULTS

Daily administration of muparfostat for 4 weeks caused hyperlipidaemia and aggravated hepatic steatosis in obese mice models, but not in lean animals. In cultured hepatocytes, muparfostat did not alter lipid accumulation. Acute tests suggested that muparfostat binds to lipoprotein lipase in competition with HS on vascular endothelial cell surfaces, thereby reducing the degradation of circulating triglycerides by lipoprotein lipase and subsequent uptake of fatty acids into vascular endothelial cells and causing hyperlipidaemia. This hyperlipidaemia aggravates hepatic steatosis and causes liver injury in muparfostat-treated obese mice.

CONCLUSIONS AND IMPLICATIONS

The binding activity of HS mimetics to lipoprotein lipase should be investigated as an additional pharmacological effect during heparanase inhibitor drug discovery. This study also provides novel evidence for an increased risk of drug-induced liver injury in obese individuals.

The prevalence of foot-and-mouth disease in Asia

Foot-and-mouth disease (FMD) is listed among the highly contagious diseases in animals and is endemic throughout the Asian continent. The disease is caused by the Foot-and-mouth disease virus (FMDV) and affects a wide variety of domesticated animals as well as wild ungulates. Clinically, the disease is described as a vesicular lesion on the tongue, muzzle, lips, gum, dental pad, interdigital cleft, coronary band, and heel of the foot. Sometimes these lesions give rise to lameness. Mastitis is also caused due to teat lesions. A biochemical test reveals that during FMD infection, there are elevated levels of interleukin-1 (IL-1), tumor necrosis factor-alpha, interferon-gamma (IFN-γ), interleukin-6, serum amyloid A protein, lactoferrin, mannose-binding lectin, and monocytes chemo-attractant protein-1 in the serum of infected animals. There is no specific treatment for FMD although some antivirals are given as prophylaxis and antibiotics are given to prevent secondary bacterial infection. This review presents comprehensive data on the prevalence of FMD and serotypes of FMDV that are attributable to the cause of FMD from a regional point of view. It also explains the worldwide dynamics of the seven serotypes of FMD and tries to identify epidemiological clusters of FMD in various geographical areas. Furthermore, the pathology associated with the foot and mouth disease virus along with the pathophysiology is discussed. The continent-wide prevalence and diversity patterns of FMD suggest that there is a need for stringent policies and legislation implementation regarding research and development aimed at manufacturing strain-specific vaccination, infection prevention, and control of the disease.

Heparin-resistance in AL amyloidosis: a case report

BACKGROUND

Non-AT-III mediated heparin-resistance during CPB occurs by complex-forming with heparin-binding proteins. Currently, there are no specific recommendations for non-AT-III mediated heparin-resistance.

CASE PRESENTATION

We present a fatal case of a 70-yr-old male-patient undergoing cardiac-surgery in which refractory heparin-resistance was observed. The massive AL amyloidosis found at autopsy is thought to be responsible and illustrates that awareness and knowledge of the etiology and perioperative strategies of non-AT-III mediated heparin-resistance is important.

CONCLUSION

For anticoagulation during cardiopulmonary bypass surgery in case of a non-AT-III medicated heparin resistance, we refer to the decision tree added to this manuscript and if necessary to consider direct thrombin inhibitors, such as bivalirudin or argatroban, as it bypasses the complexing pathway.

Apolipoprotein E Recognizes Alzheimer's Disease Associated 3-O Sulfation of Heparan Sulfate

Apolipoprotein E (ApoE)'s ϵ4 alle is the most important genetic risk factor for late onset Alzheimer's Disease (AD). Cell-surface heparan sulfate (HS) is a cofactor for ApoE/LRP1 interaction and the prion-like spread of tau pathology between cells. 3-O-sulfo (3-O-S) modification of HS has been linked to AD through its interaction with tau, and enhanced levels of 3-O-sulfated HS and 3-O-sulfotransferases in the AD brain. In this study, we characterized ApoE/HS interactions in wildtype ApoE3, AD-linked ApoE4, and AD-protective ApoE2 and ApoE3-Christchurch. Glycan microarray and SPR assays revealed that all ApoE isoforms recognized 3-O-S. NMR titration localized ApoE/3-O-S binding to the vicinity of the canonical HS binding motif. In cells, the knockout of HS3ST1-a major 3-O sulfotransferase-reduced cell surface binding and uptake of ApoE. 3-O-S is thus recognized by both tau and ApoE, suggesting that the interplay between 3-O-sulfated HS, tau and ApoE isoforms may modulate AD risk.

Crosstalk between Circulating Tumor Cells and Plasma Proteins-Impact on Coagulation and Anticoagulation

Cancer metastasis is a complex process. After their intravasation into the circulation, the cancer cells are exposed to a harsh environment of physical and biochemical hazards. Whether circulating tumor cells (CTCs) survive and escape from blood flow defines their ability to metastasize. CTCs sense their environment with surface-exposed receptors. The recognition of corresponding ligands, e.g., fibrinogen, by integrins can induce intracellular signaling processes driving CTCs' survival. Other receptors, such as tissue factor (TF), enable CTCs to induce coagulation. Cancer-associated thrombosis (CAT) is adversely connected to patients' outcome. However, cancer cells have also the ability to inhibit coagulation, e.g., through expressing thrombomodulin (TM) or heparan sulfate (HS), an activator of antithrombin (AT). To that extent, individual CTCs can interact with plasma proteins, and whether these interactions are connected to metastasis or clinical symptoms such as CAT is largely unknown. In the present review, we discuss the biological and clinical relevance of cancer-cell-expressed surface molecules and their interaction with plasma proteins. We aim to encourage future research to expand our knowledge of the CTC interactome, as this may not only yield new molecular markers improving liquid-biopsy-based diagnostics but also additional targets for better cancer therapies.