The degree of polymerization and sulfation patterns in heparan sulfate are critical determinants of cytomegalovirus entry into host cells

Glycosaminoglycan microarrays for studying glycosaminoglycan-protein systems

More than 3000 proteins are now known to bind to glycosaminoglycans (GAGs). Yet, GAG-protein systems are rather poorly understood in terms of selectivity of recognition, molecular mechanism of action, and translational promise. High-throughput screening (HTS) technologies are critically needed for studying GAG biology and developing GAG-based therapeutics. Microarrays, developed within the past two decades, have now improved to the point of being the preferred tool in the HTS of biomolecules. GAG microarrays, in which GAG sequences are immobilized on slides, while similar to other microarrays, have their own sets of challenges and considerations. GAG microarrays are rapidly becoming the first choice in studying GAG-protein systems. Here, we review different modalities and applications of GAG microarrays presented to date. We discuss advantages and disadvantages of this technology, explain covalent and non-covalent immobilization strategies using different chemically reactive groups, and present various assay formats for qualitative and quantitative interpretations, including selectivity screening, binding affinity studies, competitive binding studies etc. We also highlight recent advances in implementing this technology, cataloging of data, and project its future promise. Overall, the technology of GAG microarray exhibits enormous potential of evolving into more than a mere screening tool for studying GAG - protein systems.

Phagocyte-expressed glycosaminoglycans promote capture of alphaviruses from the blood circulation in a host species-specific manner

The magnitude and duration of vertebrate viremia are critical determinants of arbovirus transmission, geographic spread, and disease severity-yet, mechanisms determining arbovirus viremia levels are poorly defined. Previous studies have drawn associations between in vitro virion-glycosaminoglycan (GAG) interactions and in vivo clearance kinetics of virions from blood circulation. From these observations, it is commonly hypothesized that GAG-binding virions are rapidly removed from circulation due to ubiquitous expression of GAGs by vascular endothelial cells, thereby limiting viremia. Using an in vivo model for viremia, we compared the vascular clearance of low and enhanced GAG-binding viral variants of chikungunya, eastern- (EEEV), and Venezuelan- (VEEV) equine encephalitis viruses. We find GAG-binding virions are more quickly removed from circulation than their non-GAG-binding variant; however individual clearance kinetics vary between GAG-binding viruses, from swift (VEEV) to slow removal from circulation (EEEV). Remarkably, we find phagocytes are required for efficient vascular clearance of some enhanced GAG-binding virions. Moreover, transient depletion of vascular heparan sulfate impedes vascular clearance of only some GAG-binding viral variants and in a phagocyte-dependent manner, implying phagocytes can mediate vascular GAG-virion interactions. Finally, in direct contrast to mice, we find enhanced GAG-binding EEEV is resistant to vascular clearance in avian hosts, suggesting the existence of species-specificity in virion-GAG interactions. In summary, these data support a role for GAG-mediated clearance of some viral particles from the blood circulation, illuminate the potential of blood-contacting phagocytes as a site for GAG-virion binding, and suggest a role for species-specific GAG structures in arbovirus ecology.

Human induced pluripotent stem cells are resistant to human cytomegalovirus infection primarily at the attachment level due to the reduced expression of cell-surface heparan sulfate

Cytomegalovirus (CMV), a type of herpes virus, is the predominant cause of congenital anomalies due to intrauterine infections in humans. Adverse outcomes related to intrauterine infections with human cytomegalovirus (HCMV) vary widely, depending on factors such as fetal infection timing, infection route, and viral virulence. The precise mechanism underlying HCMV susceptibility remains unclear. In this study, we compared the susceptibility of neonatal human dermal fibroblast cells (NHDFCs) and human induced pluripotent stem cells (hiPSCs) derived from NHDFCs, which are genetically identical to HCMV, using immunostaining, microarray, in situ hybridization, quantitative PCR, and scanning electron microscopy. These cells were previously used to compare CMV susceptibility, but the underlying mechanisms were not fully elucidated. HCMV susceptibility of hiPSCs was significantly lower in the earliest phase. No shared gene ontologies were observed immediately post-infection between the two cell types using microarray analysis. Early-stage expression of HCMV antigens and the HCMV genome was minimal in immunostaining and in in situ hybridization in hiPSCs. This strongly suggests that HCMV does not readily bind to hiPSC surfaces. Scanning electron microscopy performed using the NanoSuit method confirmed the scarcity of HCMV particles on hiPSC surfaces. The zeta potential and charge mapping of the charged surface in NHDFCs and hiPSCs exhibited minimal differences when assessed using zeta potential analyzer and scanning ion conductance microscopy; however, the expression of heparan sulfate (HS) was significantly lower in hiPSCs compared with that in NHDFCs. Thus, HS expression could be a primary determinant of HCMV resistance in hiPSCs at the attachment level.

IMPORTANCE

Numerous factors such as attachment, virus particle entry, transcription, and virus particle egress can affect viral susceptibility. Since 1984, pluripotent cells are known to be CMV resistant; however, the exact mechanism underlying this resistance remains elusive. Some researchers suggest inhibition in the initial phase of HCMV binding, while others have suggested the possibility of a sufficient amount of HCMV entering the cells to establish latency. This study demonstrates that HCMV particles rarely attach to the surfaces of hiPSCs. This is not due to limitations in the electrostatic interactions between the surface of hiPSCs and HCMV particles, but due to HS expression. Therefore, HS expression should be recognized as a key factor in determining the susceptibility of HCMV in congenital infection in vitro and in vivo. In the future, drugs targeting HS may become crucial for the treatment of congenital CMV infections. Thus, further research in this area is warranted.

Myocardial Oedema as a Consequence of Viral Infection and Persistence-A Narrative Review with Focus on COVID-19 and Post COVID Sequelae

Microvascular integrity is a critical factor in myocardial fluid homeostasis. The subtle equilibrium between capillary filtration and lymphatic fluid removal is disturbed during pathological processes leading to inflammation, but also in hypoxia or due to alterations in vascular perfusion and coagulability. The degradation of the glycocalyx as the main component of the endothelial filtration barrier as well as pericyte disintegration results in the accumulation of interstitial and intracellular water. Moreover, lymphatic dysfunction evokes an increase in metabolic waste products, cytokines and inflammatory cells in the interstitial space contributing to myocardial oedema formation. This leads to myocardial stiffness and impaired contractility, eventually resulting in cardiomyocyte apoptosis, myocardial remodelling and fibrosis. The following article reviews pathophysiological inflammatory processes leading to myocardial oedema including myocarditis, ischaemia-reperfusion injury and viral infections with a special focus on the pathomechanisms evoked by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. In addition, clinical implications including potential long-term effects due to viral persistence (long COVID), as well as treatment options, are discussed.

Phagocyte-expressed glycosaminoglycans promote capture of alphaviruses from the blood circulation in a host species-specific manner

The magnitude and duration of vertebrate viremia are critical determinants of arbovirus transmission, geographic spread, and disease severity-yet, mechanisms determining arbovirus viremia levels are poorly defined. Previous studies have drawn associations between in vitro virion-glycosaminoglycan (GAG) interactions and in vivo clearance kinetics of virions from blood circulation. From these observations, it is commonly hypothesized that GAG-binding virions are rapidly removed from circulation due to ubiquitous expression of GAGs by vascular endothelial cells, thereby limiting viremia. Using an in vivo model for viremia, we compared the vascular clearance of low and enhanced GAG-binding viral variants of chikungunya (CHIKV), eastern-(EEEV), and Venezuelan-(VEEV) equine encephalitis viruses. We find GAG-binding virions are more quickly removed from circulation than their non-GAG-binding variant; however individual clearance kinetics vary between GAG-binding viruses, from swift (VEEV) to slow removal from circulation (EEEV). Remarkably, we find phagocytes are required for efficient vascular clearance of some enhanced GAG-binding virions. Moreover, transient depletion of vascular heparan sulfate (HS) impedes vascular clearance of only some GAG-binding viral variants and in a phagocyte-dependent manner, implying phagocytes can mediate vascular GAG-virion interactions. Finally, in direct contrast to mice, we find enhanced GAG-binding EEEV is resistant to vascular clearance in avian hosts, suggesting the existence of species-specificity in virion-GAG interactions. In summary, these data support a role for GAG-mediated clearance of some viral particles from the blood circulation, illuminate the potential of blood-contacting phagocytes as a site for GAG-virion binding, and suggest a role for species-specific GAG structures in arbovirus ecology.

Significance Statement

Previously, evidence of arbovirus-GAG interactions in vivo has been limited to associations between viral residues shown to promote enhanced GAG-binding phenotypes in vitro and in vivo phenotypes of viral dissemination and pathogenesis. By directly manipulating host GAG expression, we identified virion-GAG interactions in vivo and discovered a role for phagocyte-expressed GAGs in viral vascular clearance. Moreover, we observe species-specific differences in viral vascular clearance of enhanced GAG-binding virions between murine and avian hosts. These data suggest species-specific variation in GAG structure is a mechanism to distinguish amplifying from dead-end hosts for arbovirus transmission.

Inhibition of Cytomegalovirus by Pentacta pygmaea Fucosylated Chondroitin Sulfate Depends on Its Molecular Weight

Many viruses attach to host cells by first interacting with cell surface proteoglycans containing heparan sulfate (HS) glycosaminoglycan chains and then by engaging with specific receptor, resulting in virus entry. In this project, HS–virus interactions were targeted by a new fucosylated chondroitin sulfate from the sea cucumber Pentacta pygmaea (PpFucCS) in order to block human cytomegalovirus (HCMV) entry into cells. Human foreskin fibroblasts were infected with HCMV in the presence of PpFucCS and its low molecular weight (LMW) fractions and the virus yield at five days post-infection was assessed. The virus attachment and entry into the cells were visualized by labeling the purified virus particles with a self-quenching fluorophore octadecyl rhodamine B (R18). The native PpFucCS exhibited potent inhibitory activity against HCMV specifically blocking virus entry into the cell and the inhibitory activities of the LMW PpFucCS derivatives were proportional to their chain lengths. PpFucCS and the derived oligosaccharides did not exhibit any significant cytotoxicity; moreover, they protected the infected cells from virus-induced lytic cell death. In conclusion, PpFucCS inhibits the entry of HCMV into cells and the high MW of this carbohydrate is a key structural element to achieve the maximal anti-viral effect. This new marine sulfated glycan can be developed into a potential prophylactic and therapeutic antiviral agent against HCMV infection.

PCV2 Uptake by Porcine Monocytes Is Strain-Dependent and Is Associated with Amino Acid Characteristics on the Capsid Surface

Porcine circovirus type 2 (PCV2) is associated with several economically important diseases that are described as PCV2-associated diseases (PCVADs). PCV2 is replicating in lymphoblasts, and PCV2 particles are taken up by monocytes without effective replication or complete degradation. Glycosaminoglycans (GAGs) have been demonstrated to be important receptors for PCV2 binding and entry in T-lymphocytes and continuous cell lines. The objective of this study was to determine whether differences exist in viral uptake and outcome among six PCV2 strains from different disease outbreaks in primary porcine monocytes: Stoon-1010 (PCV2a; PMWS), 1121 (PCV2a; abortion), 1147 (PCV2b; PDNS), 09V448 (PCV2d-1; PCVAD with high viral load in lymphoid tissues [PCVADhigh]), DE222-13 (PCV2d-2; PCVADhigh), and 19V245 (PCV2d-2; PCVADhigh). The uptake of PCV2 in peripheral blood monocytes was different among the PCV2 strains. A large number of PCV2 particles were found in the monocytes for Stoon-1010, DE222-13, and 19V245, while a low number was found for 1121, 1147, and 09V448. Competition with, and removal of GAGs on the cell surface, demonstrated an important role of chondroitin sulfate (CS) and dermatan sulfate (DS) in PCV2 entry into monocytes. The mapping of positively/negatively charged amino acids exposed on the surface of PCV2 capsids revealed that their number and distribution could have an impact on the binding of the capsids to GAGs, and the internalization into monocytes. Based on the distribution of positively charged amino acids on PCV2 capsids, phosphacan was hypothesized, and further demonstrated, as an effective candidate to mediate virus attachment to, and internalization in, monocytes. IMPORTANCE PCV2 is present on almost every pig farm in the world and is associated with a high number of diseases (PCV2-associated diseases [PCVADs]). It causes severe economic losses. Although vaccination is successfully applied in the field, there are still a lot of unanswered questions on the pathogenesis of PCV2 infections. This article reports on the uptake difference of various PCV2 strains by peripheral blood monocytes, and reveals the mechanism of the strong viral uptake ability of monocytes of Piétrain pigs. We further demonstrated that: (i) GAGs mediate the uptake of PCV2 particles by monocytes, (ii) positively charged three-wings-windmill-like amino acid patterns on the capsid outer surface are activating PCV2 uptake, and (iii) phosphacan is one of the potential candidates for PCV2 internalization. These results provide new insights into the mechanisms involved in PCVAD and contribute to a better understanding of PCV2 evolution. This may lead to the development of resistant pigs.

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.

Calcium dobesilate reduces SARS-CoV-2 entry into endothelial cells by inhibiting virus binding to heparan sulfate

Recent reports demonstrate that SARS-CoV-2 utilizes cell surface heparan sulfate as an attachment factor to facilitate the initial interaction with host cells. Heparan sulfate interacts with the receptor binding domain of SARS-CoV-2 spike glycoprotein, and blocking this interaction can decrease cell infection. We and others reported recently that the family of compounds of 2,5-dihydroxyphenylic acid interferes with the binding of the positively charged groove in growth factor molecules to negatively charged cell surface heparan sulfate. We hypothesized that Calcium Dobesilate (CaD)-calcium salt of 2,5-dihydroxyphenylic acid-may also interfere with the binding of SARS-CoV-2 spike protein to heparan sulfate. Using lentiviral SARS-CoV-2 spike protein pseudotyped particles we show that CaD could significantly reduce pseudovirus uptake into endothelial cells. On the contrary, CaD did not affect cell infection with VSVG-expressing lentivirus. CaD could also prevent retention of SARS-CoV-2 spike protein in ex vivo perfused mouse kidney. Using microfluidic culture of endothelial cells under flow, we show that CaD prevents spike protein interaction with heparan sulfate glycocalyx. Since CaD has no adverse side effects and is approved in humans for other medical indications, our findings can rapidly translate into clinical studies.

Charge-based drug delivery to cartilage: Hydrophobic and not electrostatic interactions are the dominant cause of competitive binding of cationic carriers in synovial fluid

Charge-based drug delivery has proven to be effective for targeting negatively charged cartilage for the treatment of osteoarthritis. Cartilage is surrounded by synovial fluid (SF), which is comprised of negatively charged hyaluronic acid and hydrophobic proteins that can competitively bind cationic carriers and prevent their transport into cartilage. Here we investigate the relative contributions of charge and hydrophobic effects on the binding of cationic carriers within healthy and arthritic SF by comparing the transport of arginine-rich cartilage targeting cationic peptide carriers with hydrophilic (CPC +14N) or hydrophobic property (CPC +14A). CPC +14N had significantly greater intra-cartilage uptake in presence of SF compared to CPC +14A in-vitro and in vivo. In presence of individual anionic SF constituents, both CPCs maintained similar high intra-cartilage uptake while in presence of hydrophobic constituents, CPC +14N had greater uptake confirming that hydrophobic and not charge interactions are the dominant cause of competitive binding within SF. Results also demonstrate that short-range effects can synergistically stabilize intra-cartilage charge-based binding - a property that can be utilized for enhancing drug-carrier residence time in arthritic cartilage with diminished negative fixed charge density. The work provides a framework for the rational design of cationic carriers for developing targeted therapies for another complex negatively charged environments. STATEMENT OF SIGNIFICANCE: This work demonstrates that hydrophobic and not charge interactions are the dominant cause of the binding of cationic carriers in synovial fluid. Therefore, cationic carriers can be effectively used for cartilage targeting if they are made hydrophilic. This can facilitate clinical translation of various osteoarthritis drugs for cartilage repair that have failed due to a lack of effective cartilage targeting methods. It also demonstrates that short-range hydrogen bonds can synergistically stabilize electrostatic binding in cartilage offering a method for enhancing the targeting and residence time of cationic carriers within arthritic cartilage with reduced charge density. Finally, the cartilage-synovial fluid unit provides an excellent model of a complex negatively charged environment and allows us to generalize these findings and develop targeted therapies for other charged tissue-systems.

Heparan Sulfate and Sialic Acid in Viral Attachment: Two Sides of the Same Coin?

Sialic acids and heparan sulfates make up the outermost part of the cell membrane and the extracellular matrix. Both structures are characterized by being negatively charged, serving as receptors for various pathogens, and are highly expressed in the respiratory and digestive tracts. Numerous viruses use heparan sulfates as receptors to infect cells; in this group are HSV, HPV, and SARS-CoV-2. Other viruses require the cell to express sialic acids, as is the case in influenza A viruses and adenoviruses. This review aims to present, in a general way, the participation of glycoconjugates in viral entry, and therapeutic strategies focused on inhibiting the interaction between the virus and the glycoconjugates. Interestingly, there are few studies that suggest the participation of both glycoconjugates in the viruses addressed here. Considering the biological redundancy that exists between heparan sulfates and sialic acids, we propose that it is important to jointly evaluate and design strategies that contemplate inhibiting the interactions of both glycoconjugates. This approach will allow identifying new receptors and lead to a deeper understanding of interspecies transmission.

Glycosaminoglycan Mimetic Precision Glycomacromolecules with Sequence-Defined Sulfation and Rigidity Patterns

Sulfated glycosaminoglycans (sGAGs) such as heparan sulfate (HS) are structurally diverse linear polysaccharides that are involved in many biological processes and have gained interest as antiviral compounds. Their recognition is driven by a complex orchestra of structural parameters that are still under intense investigation. One distinct characteristic is the incorporation of sulfation patterns including highly sulfated and non-sulfated sequences that provide variations in flexibility and conformation, which in turn impact the biological function of sGAGs. However, these distinct features have not yet been fully realized in the synthetic preparation of sGAG mimetics. Here, we present the synthesis of three groups of sulfated glycomacromolecules as sGAG mimetics: (i) globally sulfated glycooligomers, (ii) glycooligomers with sequence-defined sulfation patterns, and (iii) a globally sulfated glycooligomer-oligo-L-proline hybrid structure. The complete synthesis, including chemical sulfation, was conducted on solid support, enabled by the introduction of a commercially available photocleavable linker allowing for the preservation of sensitive sulfates during cleavage of the products. Structures were obtained in good purity and with high degrees of sulfation demonstrating the wide applicability of this methodology to prepare tailor-made sulfated glycomacromolecules and similar sGAG mimetics. Structures were tested for their anticoagulant properties showing activity similar to their natural HS counterpart and significantly lower than HP.

Harnessing Human Papillomavirus’ Natural Tropism to Target Tumors

Human papillomaviruses (HPV) are small non-enveloped DNA tumor viruses established as the primary etiological agent for the development of cervical cancer. Decades of research have elucidated HPV’s primary attachment factor to be heparan sulfate proteoglycans (HSPG). Importantly, wounding and exposure of the epithelial basement membrane was found to be pivotal for efficient attachment and infection of HPV in vivo. Sulfation patterns on HSPG’s become modified at the site of wounds as they serve an important role promoting tissue healing, cell proliferation and neovascularization and it is these modifications recognized by HPV. Analogous HSPG modification patterns can be found on tumor cells as they too require the aforementioned processes to grow and metastasize. Although targeting tumor associated HSPG is not a novel concept, the use of HPV to target and treat tumors has only been realized in recent years. The work herein describes how decades of basic HPV research has culminated in the rational design of an HPV-based virus-like infrared light activated dye conjugate for the treatment of choroidal melanoma.

Protection is not always a good thing: The immune system's impact on gene therapy

There are many clinical trials underway for the development of gene therapies, and some have resulted in gene therapy products being commercially approved already. Significant progress was made to develop safer and more effective strategies to deliver and regulate genetic products. An unsolved aspect is the immune system, which can affect the efficiency of gene therapy in different ways. Here we present an overview of approved gene therapy products and the immune response elicited by gene delivery systems. These include responses against the vector or its content after delivery and against the product of the corrected gene. Strategies to overcome the hurdles include hiding the vector or/and the transgene product from the immune system and hiding the immune system from the vector/transgene product. Combining different strategies, such as patient screening and intelligent vector design, gene therapy is set to make a difference in the life of patients with severe genetic diseases.

CMV Seropositive Status Increases Heparanase SNPs Regulatory Activity, Risk of Acute GVHD and Yield of CD34+ Cell Mobilization

Heparanase is an endo-β-glucuronidase that is best known for its pro-cancerous effects but is also implicated in the pathogenesis of various viruses. Activation of heparanase is a common strategy to increase viral spread and trigger the subsequent inflammatory cascade. Using a Single Nucleotide Polymorphisms (SNP)-associated approach we identified enhancer and insulator regions that regulate HPSE expression. Although a role for heparanase in viral infection has been noticed, the impact of HPSE functional SNPs has not been determined. We investigated the effect of cytomegalovirus (CMV) serostatus on the involvement of HPSE enhancer and insulator functional SNPs in the risk of acute graft versus host disease (GVHD) and granulocyte-colony stimulating factor related CD34⁺ mobilization. A significant correlation between the C alleles of insulator rs4364254 and rs4426765 and CMV seropositivity was found in healthy donors and patients with hematological malignancies. The risk of developing acute GVHD after hematopoietic stem cell transplantation was identified only in CMV-seropositive patients. A significant correlation between the enhancer rs4693608 and insulator rs28649799 and CD34⁺ cell mobilization was demonstrated in the CMV-seropositive donors. It is thus conceivable that latent CMV infection modulates heparanase regulatory regions and enhances the effect of functional SNPs on heparanase function in normal and pathological processes.

Tegument Protein pp150 Sequence-Specific Peptide Blocks Cytomegalovirus Infection

Human cytomegalovirus (HCMV) tegument protein pp150 is essential for the completion of the final steps in virion maturation. Earlier studies indicated that three pp150nt (N-terminal one-third of pp150) conformers cluster on each triplex (Tri1, Tri2A and Tri2B), and extend towards small capsid proteins atop nearby major capsid proteins, forming a net-like layer of tegument densities that enmesh and stabilize HCMV capsids. Based on this atomic detail, we designed several peptides targeting pp150nt. Our data show significant reduction in virus growth upon treatment with one of these peptides (pep-CR2) with an IC₅₀ of 1.33 μM and no significant impact on cell viability. Based on 3D modeling, pep-CR2 specifically interferes with the pp150–capsid binding interface. Cells pre-treated with pep-CR2 and infected with HCMV sequester pp150 in the nucleus, indicating a mechanistic disruption of pp150 loading onto capsids and subsequent nuclear egress. Furthermore, pep-CR2 effectively inhibits mouse cytomegalovirus (MCMV) infection in cell culture, paving the way for future animal testing. Combined, these results indicate that CR2 of pp150 is amenable to targeting by a peptide inhibitor, and can be developed into an effective antiviral.