Heparanase is a host enzyme required for herpes simplex virus-1 release from cells

Herpes simplex virus 1 glycoprotein C promotes virus penetration from endosomes during entry, independent of interaction with heparan sulfate

Herpes simplex virus 1 (HSV-1) gC is a multi-functional glycoprotein present in the viral envelope and on the surface of infected cells. Virion gC, and to a lesser extent the fusion protein gB, interacts with host heparan sulfate to mediate HSV-1 attachment to the cell surface. Virion gC selectively facilitates HSV-1 entry into cells that support entry by a low pH-dependent endocytic pathway. gC regulates fusion-associated conformational changes in gB. Here we investigated the mechanism by which gC plays a post-attachment role in HSV-1 entry into cells. HSV-1 entered HS-deficient cells by a low pH-dependent route. Similarly, HSV-1 deleted for HS-binding domains entered HS-bearing cells by a low pH pathway. Thus, the presence of HS on cells and the ability of HSV-1 to engage HS do not direct HSV-1 to a pH-dependent entry pathway. HSV-1 lacking gC accumulated in endosomes during viral entry, supporting the notion that gC influences viral penetration from endosomes. Interestingly, the pH-neutral cell-cell fusion mediated by HSV-1 glycoproteins gB, gD, and gH/gL was not altered by gC. Soluble heparin inhibited cell-cell fusion regardless of the presence of gC or heparan sulfate. The kinetics of endocytic uptake of gC-null HSV-1 was rapid and very similar to wild type virus. Thus, the role of gC in regulating low pH entry of HSV-1 occurs downstream of internalization of enveloped particles from the plasma membrane. Together, the results presented here and elsewhere support a post-attachment, post-internalization function for gC in HSV-1 entry that is independent of HS.

HPSE-mediated proinflammatory signaling contributes to neurobehavioral deficits following intranasal HSV-1 infection

Herpes simplex virus-1 (HSV-1) is a neurotropic virus that can infect the brain, and an uncontrolled infection can lead to a range of diseases, including chronic nerve pain, encephalitis, and neurobehavioral abnormalities. These outcomes are often severe and have lasting consequences, highlighting the need to identify host factors that contribute to disease severity. In this study, we report that intranasal HSV-1 infection in murine model, which promotes viral dissemination into the brain, implicates the host protein heparanase (HPSE) as a key mediator of neuroinflammation. Specifically, we observed that the HPSE activity during HSV-1 infection in naïve animals promotes the upregulation of proinflammatory cytokines, enhances microglial activity in the brain, and contributes to cognitive impairment, anxiety, and motor coordination deficits. Such effects are significantly less detectable in heparanase deficient (Hpse-/-) mice. Additionally, we found that moderate activation of toll-like receptors (TLRs), particularly in Hpse+/+ mice, may contribute to the activation of the inflammasome pathway. This, in turn, leads to the activation of caspase-1 (Casp1) and caspase-3 (Casp3), which may play a role in nerve function loss. Our findings position HPSE as a potential therapeutic target for mitigating virus-induced neuroinflammation and neurobehavioral defects.

IMPORTANCE

Herpes simplex virus-1 (HSV-1) infection in the brain can lead to severe and often permanent neurological consequences. Host factors influence disease outcomes in response to infection, and understanding these factors is crucial for developing effective therapies. This study identifies the host protein HPSE as a key mediator of neuroinflammation in response to HSV-1 infection. We demonstrate that the HPSE activity drives proinflammatory cytokine expression and microglial activation and promotes a signaling cascade involving toll-like receptors and caspase activation, potentially intensifying neuroinflammatory responses. These findings implicate HPSE as an important player in HSV-1 pathogenesis in the central nervous system and suggest that targeting HPSE could provide a novel therapeutic strategy to mitigate virus-induced neuroinflammation and neurobehavioral disturbance.

Herpesvirus Infections of the Corneal Endothelium

Corneal endotheliitis is an inflammatory process, most commonly of viral etiology, that manifests clinically with features including corneal edema, keratic precipitates, and a mild anterior chamber reaction. Several studies have implicated human herpesviruses from the Herpesviridae family as primary causes of corneal endotheliitis, including cytomegalovirus (CMV), varicella zoster virus (VZV), and herpes simplex viruses 1 and 2 (HSV-1 and HSV-2). This review critically evaluates the present literature surrounding herpesvirus infections of the corneal endothelium.

Oral SARS-CoV-2 Infection and Risk for Long Covid

SARS-CoV-2 is an oral pathogen that infects and replicates in mucosal and salivary epithelial cells, contributing to oral post-acute sequelae COVID-19 (PASC) and other oral and non-oral pathologies. While pre-existing inflammatory oral diseases provides a conducive environment for the virus, acute infection and persistence of SARS-CoV-2 can also results in oral microbiome dysbiosis that further worsens poor oral mucosal health. Indeed, oral PASC includes periodontal diseases, dysgeusia, xerostomia, pharyngitis, oral keratoses, and pulpitis suggesting significant bacterial contributions to SARS-CoV-2 and oral tissue tropism. Dysbiotic microbiome-induced inflammation can promote viral entry via angiotensin-converting enzyme receptor-2 (ACE2), serine transmembrane TMPRSS2 and possibly other non-canonical pathways. Additionally, metabolites derived from a dysbiotic microbiome can alter the physiological and biochemical pathways related to the metabolism of lipids, carbohydrates, and amino acids. This may promote a pro-inflammatory microenvironment, leading to immune exhaustion, loss of tolerance, and susceptibility to a variety of oral pathogens, causing acute and later chronic inflammation. Microbial release of mimics of host metallopeptidases related to furin, ADAM17 (A disintegrin and metalloproteinase 17), and glycoprotein metabolites can further aid viral attachment to T cell immunoglobulin-like (TIMs), enhancing viral entry while simultaneously depressing oral mucosal immune resistance and clearance. Membrane reorganization characterised by neuroproteins, such as neuropilins, also functionally assists with SARS-CoV-2 entry and extends the pathogenesis of PASC from the oral cavity to the brain, gut, or other non-oral tissues. Thus, poor oral health, characterised by disrupted oral microbiomes can promote viral tropism, weaken antiviral resistance, and heightens susceptibility to SARS-CoV-2 infection. This immune dysfunction also increases the risk of additional viral infections, exacerbating oral conditions like periodontal and endodontic diseases. These persistent oral health issues can contribute to systemic inflammation, creating bidirectional effects between oral and non-oral tissues, potentially leading to Post-Acute Sequelae of COVID-19 (PASC).

Recruitment of apolipoprotein E facilitates Herpes simplex virus 1 attachment and release

Human apolipoprotein E (ApoE) has been shown to play important roles during primary infection and pathogenesis of several viruses. Furthermore, epidemiological studies suggest that interactions between ApoE 4 and herpes simplex virus type-1 (HSV1) could associate with higher risk of Alzheimer's disease. Nevertheless, little is known about the ApoE-HSV1 interactions at molecular levels. Here, we investigate the effects of ApoE on HSV1 infection in vitro. Our results show that ApoE promotes HSV1 growth, which is attributed to the incorporation of ApoE into HSV1 particles. Using both biological and biophysical approaches, we conclude that ApoE-coated HSV1 demonstrates a more efficient attachment to and faster release from the cell surface. Mechanistic studies reveal that ApoE modifies HSV1 interactions with heparan sulfate, thereby modulating interactions between HSV1 and the cell surface. Overall, our results provide new insights into the roles of ApoE during HSV1 infections which may inspire future studies on Alzheimer's disease etiology.

Global MicroRNA Profiling of HSV-1 Infected Cornea Identifies miR-329 as a Novel Regulator of Virus Infection

Purpose

Although the mechanisms underlying herpes simplex virus type-1 (HSV-1) ocular infection have been extensively studied, the role of host microRNAs (miRNAs) in the pathobiology of herpetic keratitis (HK) is not well understood. The aim of this study was to identify endogenous miRNA regulators involved in the progression of HSV-1 ocular infection.

Methods

C57BL/6 mice were infected with HSV-1 strain McKrae following epithelial debridement, and corneal miRNA profiles were analyzed at various time points using miRNA sequencing (miRNA-seq). The miRNA expression was measured at 2, 4, 6, and 10 days post-infection. Ingenuity Pathway Analysis (IPA) was used to identify immune pathways potentially targeted by differentially expressed miRNAs. The role of selected miRNAs in viral entry and replication was assessed by overexpression in murine embryonic fibroblasts (MEFs) and human corneal epithelial cells (HCEs).

Results

A total of 32 miRNAs at 2 days post-infection, 21 miRNAs at 4 days post-infection, 140 miRNAs at 6 days post-infection, and 27 miRNAs at 10 days post-infection showed significant changes in expression. IPA revealed that differentially expressed miRNAs targeted several immune pathways, including TLR and interferon signaling. Notably, mmu-miR-184-3p and mmu-let-7d-5p were upregulated, whereas mmu-miR-329-3p was down-regulated during infection. Functional assays demonstrated that overexpression of miR-329, but not miR-184-3p or miR-let-7d-5p, increased HSV-1 viral entry and replication in a dose-dependent manner. In contrast, miR-329 inhibition reversed these effects, suggesting its role as a pro-viral miRNA. Increased plaque formation and viral gB expression further confirmed miR-329's pro-viral role.

Conclusions

Our findings suggest that miR-329 functions as a pro-viral miRNA by disrupting TLR9 signaling, thus facilitating HSV-1 replication. Inhibition of miR-329 enhances TLR9-mediated antiviral responses, highlighting the potential of targeting host miRNAs as a novel therapeutic strategy for managing viral keratitis.

Heparanase 2 Modulation Inhibits HSV-2 Replication by Regulating Heparan Sulfate

The host enzyme heparanase (HPSE) facilitates the release of herpes simplex virus type 2 (HSV-2) from target cells by cleaving the viral attachment receptor heparan sulfate (HS) from infected cell surfaces. HPSE 2, an isoform of HPSE, binds to but does not possess the enzymatic activity needed to cleave cell surface HS. Our study demonstrates that HSV-2 infection significantly elevates HPSE 2 protein levels, impacting two distinct stages of viral replication. We show that higher HPSE 2 negatively affects HSV-2 replication which may be through the regulation of cell surface HS. By acting as a competitive inhibitor of HPSE, HPSE 2 may be interfering with HPSE's interactions with HS. We demonstrate that the enhanced expression of HPSE 2, either via viral infection or plasmid transfection, reduces HPSE's ability to cleave HS, thereby hindering viral egress. Conversely, low HPSE 2 levels achieved through siRNA transfection allow HPSE to cleave more HS, reducing viral entry. Altogether, we propose a hypothetical model in which the modulation of HPSE 2 impedes HSV-2 replication by regulating HS availability on the cell surface. This dual role of HPSE 2 in viral replication and potential tumor suppression underscores its significance in cellular processes and viral pathogenesis.

Intervention strategies targeting virus and host factors against porcine reproductive and respiratory syndrome virus: A systematic review

Porcine reproductive and respiratory syndrome (PRRS) caused by porcine reproductive and respiratory syndrome virus (PRRSV) causes considerable economic losses to the global swine industry every year and seriously hinders the healthy development of this industry. Although tremendous efforts have been made over the past 30 years toward the development of prevention and control strategies against PRRSV infection, to date, treatments with proven efficacy have yet to be available due to our incomplete understanding of the molecular basis and complexity of the infection machinery. This review systematically discusses recent advances in the research and development of anti-PRRSV therapies targeting different stages of the viral life cycle. Furthermore, this review puts forward novel intervention targets and research approaches based on our in-depth exploration of virus-host interactions and the latest biological technologies, which have the potential to complement or transform current anti-PRRSV strategies and become breakthrough points for the control of PRRS in the future.

The immunobiology of corneal HSV-1 infection and herpetic stromal keratitis

SUMMARYHuman alphaherpesvirus 1 (HSV-1) is a highly successful neurotropic pathogen that primarily infects the epithelial cells lining the orofacial mucosa. After primary lytic replication in the oral, ocular, and nasal mucosal epithelial cells, HSV-1 establishes life-long latency in neurons within the trigeminal ganglion. Patients with compromised immune systems experience frequent reactivation of HSV-1 from latency, leading to virus entry in the sensory neurons, followed by anterograde transport and lytic replication at the innervated mucosal epithelial surface. Although recurrent infection of the corneal mucosal surface is rare, it can result in a chronic immuno-inflammatory condition called herpetic stromal keratitis (HSK). HSK leads to gradual vision loss and can cause permanent blindness in severe untreated cases. Currently, there is no cure or successful vaccine to prevent latent or recurrent HSV-1 infections, posing a significant clinical challenge to managing HSK and preventing vision loss. The conventional clinical management of HSK primarily relies on anti-virals to suppress HSV-1 replication, anti-inflammatory drugs (such as corticosteroids) to provide symptomatic relief from pain and inflammation, and surgical interventions in more severe cases to replace damaged cornea. However, each clinical treatment strategy has limitations, such as local and systemic drug toxicities and the emergence of anti-viral-resistant HSV-1 strains. In this review, we summarize the factors and immune cells involved in HSK pathogenesis and highlight alternate therapeutic strategies for successful clinical management of HSK. We also discuss the therapeutic potential of immunoregulatory cytokines and immunometabolism modulators as promising HSK therapies against emerging anti-viral-resistant HSV-1 strains.

Enhancement of HSV-1 cell-free virion release by the envelope protein gC

Glycoprotein C (gC), one of ∼12 HSV-1 envelope glycoproteins, carries out several important functions during infection, including the enhancement of virion attachment by binding to host cell heparan sulfate proteoglycans (HSPG). Here we report that gC can also enhance the release of cell-free progeny virions at the end of the infectious cycle. This activity was observed in multiple cellular contexts including Vero cells and immortalized human keratinocytes. In the absence of gC, progeny virions bound more tightly to infected cells, suggesting that gC promotes the detachment of virions from the infected cell surface. Given this finding, we analyzed the biochemical interactions that tether progeny virions to cells and report evidence for two distinct modes of binding. One is consistent with a direct interaction between gC and HSPG, whereas the other is gC-independent and likely does not involve HSPG. Together, our results i) identify a novel function for a long-studied HSV-1 glycoprotein, and ii) demonstrate that the extracellular release of HSV-1 virions is a dynamic process involving multiple viral and host components.

Aspergillus Fumigatus Spore Proteases Alter the Respiratory Mucosa Architecture and Facilitate Equine Herpesvirus 1 Infection

Numerous Aspergillus fumigatus (Af) airborne spores are inhaled daily by humans and animals due to their ubiquitous presence. The interaction between the spores and the respiratory epithelium, as well as its impact on the epithelial barrier function, remains largely unknown. The epithelial barrier protects the respiratory epithelium against viral infections. However, it can be compromised by environmental contaminants such as pollen, thereby increasing susceptibility to respiratory viral infections, including alphaherpesvirus equine herpesvirus type 1 (EHV-1). To determine whether Af spores disrupt the epithelial integrity and enhance susceptibility to viral infections, equine respiratory mucosal ex vivo explants were pretreated with Af spore diffusate, followed by EHV-1 inoculation. Spore proteases were characterized by zymography and identified using mass spectrometry-based proteomics. Proteases of the serine protease, metalloprotease, and aspartic protease groups were identified. Morphological analysis of hematoxylin-eosin (HE)-stained sections of the explants revealed that Af spores induced the desquamation of epithelial cells and a significant increase in intercellular space at high and low concentrations, respectively. The increase in intercellular space in the epithelium caused by Af spore proteases correlated with an increase in EHV-1 infection. Together, our findings demonstrate that Af spore proteases disrupt epithelial integrity, potentially leading to increased viral infection of the respiratory epithelium.

Hypoxia-induced activation of HIF-1alpha/IL-1beta axis in microglia promotes glioma progression via NF-κB-mediated upregulation of heparanase expression

BACKGROUND

Glioma is a common tumor that occurs in the brain and spinal cord. Hypoxia is a crucial feature of the tumor microenvironment. Tumor-associated macrophages/microglia play a crucial role in the advancement of glioma. This study aims to illuminate the detailed mechanisms by which hypoxia regulates microglia and, consequently, influences the progression of glioma.

METHODS

The glioma cell viability and proliferation were analyzed by cell counting kit-8 assay and 5-ethynyl-2'-deoxyuridine assay. Wound healing assay and transwell assay were implemented to detect glioma cell migration and invasion, respectively. Enzyme-linked immunosorbent assay was conducted to detect protein levels in cell culture medium. The protein levels in glioma cells and tumor tissues were evaluated using western blot analysis. The histological morphology of tumor tissue was determined by hematoxylin-eosin staining. The protein expression in tumor tissues was determined using immunohistochemistry. Human glioma xenograft in nude mice was employed to test the influence of hypoxic microglia-derived interleukin-1beta (IL-1β) and heparanase (HPSE) on glioma growth in vivo.

RESULTS

Hypoxic HMC3 cells promoted proliferation, migration, and invasion abilities of U251 and U87 cells by secreting IL-1β, which was upregulated by hypoxia-induced activation of hypoxia inducible factor-1alpha (HIF-1α). Besides, IL-1β from HMC3 cells promoted glioma progression and caused activation of nuclear factor-κB (NF-κB) and upregulation of HPSE in vivo. We also confirmed that IL-1β facilitated HPSE expression in U251 and U87 cells by activating NF-κB. Hypoxic HMC3 cells-secreted IL-1β facilitated the proliferation, migration, and invasion of U251 and U87 cells via NF-κB-mediated upregulation of HPSE expression. Finally, we revealed that silencing HPSE curbed the proliferation and metastasis of glioma in mice.

CONCLUSION

Hypoxia-induced activation of HIF-1α/IL-1β axis in microglia promoted glioma progression via NF-κB-mediated upregulation of HPSE expression.

The underlying mechanisms of arenaviral entry through matriglycan

Matriglycan, a recently characterized linear polysaccharide, is composed of alternating xylose and glucuronic acid subunits bound to the ubiquitously expressed protein α-dystroglycan (α-DG). Pathogenic arenaviruses, like the Lassa virus (LASV), hijack this long linear polysaccharide to gain cellular entry. Until recently, it was unclear through what mechanisms LASV engages its matriglycan receptor to initiate infection. Additionally, how matriglycan is synthesized onto α-DG by the Golgi-resident glycosyltransferase LARGE1 remained enigmatic. Recent structural data for LARGE1 and for the LASV spike complex informs us about the synthesis of matriglycan as well as its usage as an entry receptor by arenaviruses. In this review, we discuss structural insights into the system of matriglycan generation and eventual recognition by pathogenic viruses. We also highlight the unique usage of matriglycan as a high-affinity host receptor compared with other polysaccharides that decorate cells.

Exploring Heparanase Levels in Tears: Insights From Herpes Simplex Virus-1 Keratitis Patients and Animal Studies

Purpose

Heparanase (HPSE) cleaves heparan sulfate proteoglycans during herpes simplex virus-1 (HSV-1) infection, aiding in viral egress and disease progression. Its action has been well established in in vitro and in vivo models, but its relevance in human patients remains unclear. This study aimed to specifically evaluate tear HPSE levels of patients with herpes simplex keratitis (HSK) and to correlate these findings with a commonly used murine model.

Methods

Tear samples from patient and mice samples were collected at LV Prasad Eye Institute, Hyderabad, India, and at the University of Illinois, Chicago, IL, respectively. Tears were collected from HSV-1 patients, bacterial/fungal keratitis cases, and healthy individuals. For in vivo study, C57BL/6 mice were infected with HSV-1 (McKrae strain) followed by tear fluid collection at various time points (0-10 days).

Results

The HSV-1, bacterial keratitis, fungal keratitis, and healthy control groups each had 30 patients. There was a significant difference in HPSE expression in the HSV-1 infected eyes (1.55 ± 0.19 units/mL) compared to HSV-1 contralateral eyes (1.23 ± 0.13 units/mL; P = 0.82), bacterial keratitis eyes (0.87 ± 0.15 units/mL; P = 0.0078), fungal keratitis eyes (0.64 ± 0.09 units/mL; P < 0.00001), and normal controls (0.53 ± 0.06 units/mL; P < 0.00001). C57BL/6 mice tear HPSE expression in infected eyes was 0.66 to 5.57 ng heparan sulfate (HS) removed per minute when compared to non-infected eye (range, 0.70-3.67 ng HS removed per minute).

Conclusions

To the best of our knowledge, this study is the first to report elevated HPSE levels in the tears of patients with different forms of HSV-1 keratitis, and it confirms similar findings in a murine model, providing a valuable basis for future in vivo and clinical research on HSV-1 ocular infection.

A Fluorogenic Green Merocyanine-Based Probe to Detect Heparanase-1 Activity

Heparanase-1 (HPSE-1), an endo-β-D-glucuronidase, is an extracellular matrix (ECM) remodeling enzyme that degrades heparan sulfate (HS) chains of heparan sulfate proteoglycans (HSPGs). HPSE-1 functions to remodel the ECM and thereby disseminate cells, liberate HS-bound bioactive molecules, and release biologically active HS fragments. Being the only known enzyme for the cleavage of HS, HPSE-1 regulates a number of fundamental cellular processes including cell migration, cytokine regulation, angiogenesis, and wound healing. Overexpression of HPSE-1 has been discovered in most cancers, inflammatory diseases, viral infections, among others. As an emerging therapeutic target, the biological role of HPSE-1 remains to be explored but is hampered by a lack of research tools. To expand the chemical tool-kit of fluorogenic probes to interrogate HPSE-1 activity, we design and synthesized a fluorogenic green disaccharide-based HPSE-1 probe using our design strategy of tuning the electronic effect of the aryl aglycon. The novel probe exhibits a highly sensitive 278-fold fluorescence turn-on response in the presence of recombinant human HPSE-1, while emitting green light at 560 nm, enabling the fluorescence imaging of HPSE-1 activity in cells.

Validation of Candidate Host Cell Entry Factors for Bovine Herpes Virus Type-1 Based on a Genome-Wide CRISPR Knockout Screen

To identify host factors that affect Bovine Herpes Virus Type 1 (BoHV-1) infection we previously applied a genome wide CRISPR knockout screen targeting all bovine protein coding genes. By doing so we compiled a list of both pro-viral and anti-viral proteins involved in BoHV-1 replication. Here we provide further analysis of those that are potentially involved in viral entry into the host cell. We first generated single cell knockout clones deficient in some of the candidate genes for validation. We provide evidence that Polio Virus Receptor-related protein (PVRL2) serves as a receptor for BoHV-1, mediating more efficient entry than the previously identified Polio Virus Receptor (PVR). By knocking out two enzymes that catalyze HSPG chain elongation, HST2ST1 and GLCE, we further demonstrate the significance of HSPG in BoHV-1 entry. Another intriguing cluster of candidate genes, COG1, COG2 and COG4-7 encode six subunits of the Conserved Oligomeric Golgi (COG) complex. MDBK cells lacking COG6 produced fewer but bigger plaques compared to control cells, suggesting more efficient release of newly produced virions from these COG6 knockout cells, due to impaired HSPG biosynthesis. We further observed that viruses produced by the COG6 knockout cells consist of protein(s) with reduced N-glycosylation, potentially explaining their lower infectivity. To facilitate candidate validation, we also detailed a one-step multiplex CRISPR interference (CRISPRi) system, an orthogonal method to KO that enables quick and simultaneous deployment of three CRISPRs for efficient gene inactivation. Using CRISPR3i, we verified eight candidates that have been implicated in the synthesis of surface heparan sulfate proteoglycans (HSPGs). In summary, our experiments confirmed the two receptors PVR and PVRL2 for BoHV-1 entry into the host cell and other factors that affect this process, likely through the direct or indirect roles they play during HSPG synthesis and glycosylation of viral proteins.

Signaling network analysis reveals fostamatinib as a potential drug to control platelet hyperactivation during SARS-CoV-2 infection

Introduction

Pro-thrombotic events are one of the prevalent causes of intensive care unit (ICU) admissions among COVID-19 patients, although the signaling events in the stimulated platelets are still unclear.

Methods

We conducted a comparative analysis of platelet transcriptome data from healthy donors, ICU, and non-ICU COVID-19 patients to elucidate these mechanisms. To surpass previous analyses, we constructed models of involved networks and control cascades by integrating a global human signaling network with transcriptome data. We investigated the control of platelet hyperactivation and the specific proteins involved.

Results

Our study revealed that control of the platelet network in ICU patients is significantly higher than in non-ICU patients. Non-ICU patients require control over fewer proteins for managing platelet hyperactivity compared to ICU patients. Identification of indispensable proteins highlighted key subnetworks, that are targetable for system control in COVID-19-related platelet hyperactivity. We scrutinized FDA-approved drugs targeting indispensable proteins and identified fostamatinib as a potent candidate for preventing thrombosis in COVID-19 patients.

Discussion

Our findings shed light on how SARS-CoV-2 efficiently affects host platelets by targeting indispensable and critical proteins involved in the control of platelet activity. We evaluated several drugs for specific control of platelet hyperactivity in ICU patients suffering from platelet hyperactivation. The focus of our approach is repurposing existing drugs for optimal control over the signaling network responsible for platelet hyperactivity in COVID-19 patients. Our study offers specific pharmacological recommendations, with drug prioritization tailored to the distinct network states observed in each patient condition. Interactive networks and detailed results can be accessed at https://fostamatinib.bioinfo-wuerz.eu/.

Glycoengineered keratinocyte library reveals essential functions of specific glycans for all stages of HSV-1 infection

Viral and host glycans represent an understudied aspect of host-pathogen interactions, despite potential implications for treatment of viral infections. This is due to lack of easily accessible tools for analyzing glycan function in a meaningful context. Here we generate a glycoengineered keratinocyte library delineating human glycosylation pathways to uncover roles of specific glycans at different stages of herpes simplex virus type 1 (HSV-1) infectious cycle. We show the importance of cellular glycosaminoglycans and glycosphingolipids for HSV-1 attachment, N-glycans for entry and spread, and O-glycans for propagation. While altered virion surface structures have minimal effects on the early interactions with wild type cells, mutation of specific O-glycosylation sites affects glycoprotein surface expression and function. In conclusion, the data demonstrates the importance of specific glycans in a clinically relevant human model of HSV-1 infection and highlights the utility of genetic engineering to elucidate the roles of specific viral and cellular carbohydrate structures.

Synthetic Heparanase Inhibitors Can Prevent Herpes Simplex Viral Spread

Herpes simplex virus (HSV-1) employs heparan sulfate (HS) as receptor for cell attachment and entry. During late-stage infection, the virus induces the upregulation of human heparanase (Hpse) to remove cell surface HS allowing viral spread. We hypothesized that inhibition of Hpse will prevent viral release thereby representing a new therapeutic strategy for HSV-1. A range of HS-oligosaccharides was prepared to examine the importance of chain length and 2-O-sulfation of iduronic moieties for Hpse inhibition. It was found that hexa- and octasaccharides potently inhibited the enzyme and that 2-O-sulfation of iduronic acid is tolerated. Computational studies provided a rationale for the observed structure-activity relationship. Treatment of human corneal epithelial cells (HCEs) infected with HSV-1 with the hexa- and octasaccharide blocked viral induced shedding of HS which significantly reduced spread of virions. The compounds also inhibited migration and proliferation of immortalized HCEs thereby providing additional therapeutic properties.

Several Alphaherpesviruses Interact Similarly with the NF-κB Pathway and Suppress NF-κB-Dependent Gene Expression

Alphaherpesvirus infection is associated with attenuation of different aspects of the host innate immune response that is elicited to confine primary infections at the mucosal epithelia. Here, we report that infection of epithelial cells with several alphaherpesviruses of different species, including herpes simplex virus 1 and 2 (HSV-1 and HSV-2), feline alphaherpesvirus 1 (FHV-1), and bovine alphaherpesvirus 1 (BoHV-1) results in the inactivation of the responses driven by the nuclear factor kappa B (NF-κB) pathway, considered a pillar of the innate immune response. The mode to interact with and circumvent NF-κB-driven responses in infected epithelial cells is seemingly conserved in human, feline, and porcine alphaherpesviruses, consisting of a persistent activation of the NF-κB cascade but a potent repression of NF-κB-dependent transcription activity, which relies on replication of viral genomes. However, BoHV-1 apparently deviates from the other investigated members of the taxon in this respect, as BoHV-1-infected epithelial cells do not display the persistent NF-κB activation observed for the other alphaherpesviruses. In conclusion, this study suggests that inhibition of NF-κB transcription activity is a strategy used by several alphaherpesviruses to prevent NF-κB-driven responses in infected epithelial cells. IMPORTANCE The current study provides a side-by-side comparison of the interaction of different alphaherpesviruses with NF-κB, a key and central player in the (proinflammatory) innate host response, in infected nontransformed epithelial cell lines. We report that all studied viruses prevent expression of the hallmark NF-κB-dependent gene IκB, often but not always via similar strategies, pointing to suppression of NF-κB-dependent host gene expression in infected epithelial cells as a common and therefore likely important aspect of alphaherpesviruses.

Heparanase-A single protein with multiple enzymatic and nonenzymatic functions

Heparanase (Hpa1) is expressed by tumor cells and cells of the tumor microenvironment and functions extracellularly to remodel the extracellular matrix (ECM) and regulate the bioavailability of ECM-bound factors, augmenting, among other effects, gene transcription, autophagy, exosome formation, and heparan sulfate (HS) turnover. Much of the impact of heparanase on tumor progression is related to its function in mediating tumor-host crosstalk, priming the tumor microenvironment to better support tumor growth, metastasis, and chemoresistance. The enzyme appears to fulfill some normal functions associated, for example, with vesicular traffic, lysosomal-based secretion, autophagy, HS turnover, and gene transcription. It activates cells of the innate immune system, promotes the formation of exosomes and autophagosomes, and stimulates signal transduction pathways via enzymatic and nonenzymatic activities. These effects dynamically impact multiple regulatory pathways that together drive tumor growth, dissemination, and drug resistance as well as inflammatory responses. The emerging premise is that heparanase expressed by tumor cells, immune cells, endothelial cells, and other cells of the tumor microenvironment is a key regulator of the aggressive phenotype of cancer, an important contributor to the poor outcome of cancer patients and a valid target for therapy. So far, however, antiheparanase-based therapy has not been implemented in the clinic. Unlike heparanase, heparanase-2 (Hpa2), a close homolog of heparanase (Hpa1), does not undergo proteolytic processing and hence lacks intrinsic HS-degrading activity, the hallmark of heparanase. Hpa2 retains the capacity to bind heparin/HS and exhibits an even higher affinity towards HS than heparanase, thus competing for HS binding and inhibiting heparanase enzymatic activity. It appears that Hpa2 functions as a natural inhibitor of Hpa1 regulates the expression of selected genes that maintain tissue hemostasis and normal function, and plays a protective role against cancer and inflammation, together emphasizing the significance of maintaining a proper balance between Hpa1 and Hpa2.

Pathophysiology of reinfection by exogenous HSV-1 is driven by heparanase dysfunction

Limited knowledge exists on exogenous DNA virus reinfections. Herpes simplex virus-1 (HSV-1), a prototype DNA virus, causes multiple human diseases including vision-threatening eye infections. While reinfection with an exogenous HSV-1 strain is considered plausible, little is known about the underlying mechanisms governing its pathophysiology in a host. Heparanase (HPSE), a host endoglycosidase, when up-regulated by HSV-1 infection dictates local inflammatory response by destabilizing tissue architecture. Here, we demonstrate that HSV-1 reinfection in mice causes notable pathophysiology in wild-type controls compared to the animals lacking HPSE. The endoglycosidase promotes infected cell survival and supports a pro-disease environment. In contrast, lack of HPSE strengthens intrinsic immunity by promoting cytokine expression, inducing necroptosis of infected cells, and decreasing leukocyte infiltration into the cornea. Collectively, we report that immunity from a recent prior infection fails to abolish disease manifestation during HSV-1 reinfection unless HPSE is rendered inactive.

Heparanase-1: From Cancer Biology to a Future Antiviral Target

Heparan sulfate proteoglycans (HSPGs) are a major constituent of the extracellular matrix (ECM) and are found to be implicated in viral infections, where they play a role in both cell entry and release for many viruses. The enzyme heparanase-1 is the only known endo-beta-D-glucuronidase capable of degrading heparan sulphate (HS) chains of HSPGs and is thus important for regulating ECM homeostasis. Heparanase-1 expression is tightly regulated as the uncontrolled cleavage of HS may result in abnormal cell activation and significant tissue damage. The overexpression of heparanase-1 correlates with pathological scenarios and is observed in different human malignancies, such as lymphoma, breast, colon, lung, and hepatocellular carcinomas. Interestingly, heparanase-1 has also been documented to be involved in numerous viral infections, e.g., HSV-1, HPV, DENV. Moreover, very recent reports have demonstrated a role of heparanase-1 in HCV and SARS-CoV-2 infections. Due to the undenied pro-carcinogenic role of heparanase-1, multiple inhibitors have been developed, some reaching phase II and III in clinical studies. However, the use of heparanase inhibitors as antivirals has not yet been proposed. If it can be assumed that heparanase-1 is implicated in numerous viral life cycles, its inhibition by specific heparanase-acting compounds should result in a blockage of viral infection. This review addresses the perspectives of using heparanase inhibitors, not only for cancer treatment, but also as antivirals. Eventually, the development of a novel class antivirals targeting a cellular protein could help to alleviate the resistance problems seen with some current antiretroviral therapies.

Heparanase: A Novel Therapeutic Target for the Treatment of Atherosclerosis

Cardiovascular disease (CVD) is the leading cause of death and disability worldwide, and its management places a huge burden on healthcare systems through hospitalisation and treatment. Atherosclerosis is a chronic inflammatory disease of the arterial wall resulting in the formation of lipid-rich, fibrotic plaques under the subendothelium and is a key contributor to the development of CVD. As such, a detailed understanding of the mechanisms involved in the development of atherosclerosis is urgently required for more effective disease treatment and prevention strategies. Heparanase is the only mammalian enzyme known to cleave heparan sulfate of heparan sulfate proteoglycans, which is a key component of the extracellular matrix and basement membrane. By cleaving heparan sulfate, heparanase contributes to the regulation of numerous physiological and pathological processes such as wound healing, inflammation, tumour angiogenesis, and cell migration. Recent evidence suggests a multifactorial role for heparanase in atherosclerosis by promoting underlying inflammatory processes giving rise to plaque formation, as well as regulating lesion stability. This review provides an up-to-date overview of the role of heparanase in physiological and pathological processes with a focus on the emerging role of the enzyme in atherosclerosis.

Role of Heparanase and Syndecan-1 in HSV-1 Release from Infected Cells

Herpes Simplex Virus 1 (HSV-1) is a neurotropic human virus that belongs to the Alphaherpesvirinae subfamily of Herpesviridae. Establishment of its productive infection and progression of disease pathologies depend largely on successful release of virions from the virus-producing cells. HSV-1 is known to exploit many host factors for its release. Recent studies have shown that heparanase (HPSE) is one such host enzyme that is recruited for this purpose. It is an endoglycosidase that cleaves heparan sulfate (HS) from the surface of infected cells. HS is a virus attachment coreceptor that is commonly found on cell surfaces as HS proteoglycans e.g., syndecan-1 (SDC-1). The current model suggests that HSV-1 during the late stage of infection upregulates HPSE, which in turn enhances viral release by removing the virus-trapping HS moieties. In addition to its role in directly enabling viral release, HPSE accelerates the shedding of HS-containing ectodomains of SDC-1, which enhances HSV-1 release via a similar mechanism by upregulating CREB3 and COPII proteins. This review outlines the role of HPSE and SDC-1 as newly assigned host factors that facilitate HSV-1 release during a lytic infection cycle.

Efficient production of inhibitor-free foamy virus glycoprotein-containing retroviral vectors by proteoglycan-deficient packaging cells

Foamy viruses (FVs) or heterologous retroviruses pseudotyped with FV glycoprotein enable transduction of a great variety of target tissues of disparate species. Specific cellular entry receptors responsible for this exceptionally broad tropism await their identification. Though, ubiquitously expressed heparan sulfate proteoglycan (HS-PG) is known to serve as an attachment factor of FV envelope (Env)-containing virus particles, greatly enhancing target cell permissiveness. Production of high-titer, FV Env-containing retroviral vectors is strongly dependent on the use of cationic polymer-based transfection reagents like polyethyleneimine (PEI). We identified packaging cell-surface HS-PG expression to be responsible for this requirement. Efficient release of FV Env-containing virus particles necessitates neutralization of HS-PG binding sites by PEI. Remarkably, remnants of PEI in FV Env-containing vector supernatants, which are not easily removable, negatively impact target cell transduction, in particular those of myeloid and lymphoid origin. To overcome this limitation for production of FV Env-containing retrovirus supernatants, we generated 293T-based packaging cell lines devoid of HS-PG by genome engineering. This enabled, for the first, time production of inhibitor-free, high-titer FV Env-containing virus supernatants by non-cationic polymer-mediated transfection. Depending on the type of virus, produced titers were 2- to 10-fold higher compared with those obtained by PEI transfection.

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.

Cellular Chondroitin Sulfate and the Mucin-like Domain of Viral Glycoprotein C Promote Diffusion of Herpes Simplex Virus 1 While Heparan Sulfate Restricts Mobility

The diffusion of viruses at the cell membrane is essential to reach a suitable entry site and initiate subsequent internalization. Although many viruses take advantage of glycosaminoglycans (GAG) to bind to the cell surface, little is known about the dynamics of the virus–GAG interactions. Here, single-particle tracking of the initial interaction of individual herpes simplex virus 1 (HSV-1) virions reveals a heterogeneous diffusive behavior, regulated by cell-surface GAGs with two main diffusion types: confined and normal free. This study reports that different GAGs can have competing influences in mediating diffusion on the cells used here: chondroitin sulfate (CS) enhances free diffusion but hinders virus attachment to cell surfaces, while heparan sulfate (HS) promotes virus confinement and increases entry efficiency. In addition, the role that the viral mucin-like domains (MLD) of the HSV-1 glycoprotein C plays in facilitating the diffusion of the virus and accelerating virus penetration into cells is demonstrated. Together, our results shed new light on the mechanisms of GAG-regulated virus diffusion at the cell surface for optimal internalization. These findings may be extendable to other GAG-binding viruses.

The Key Role of Lysosomal Protease Cathepsins in Viral Infections

Cathepsins encompass a family of lysosomal proteases that mediate protein degradation and turnover. Although mainly localized in the endolysosomal compartment, cathepsins are also found in the cytoplasm, nucleus, and extracellular space, where they are involved in cell signaling, extracellular matrix assembly/disassembly, and protein processing and trafficking through the plasma and nuclear membrane and between intracellular organelles. Ubiquitously expressed in the body, cathepsins play regulatory roles in a wide range of physiological processes including coagulation, hormone secretion, immune responses, and others. A dysregulation of cathepsin expression and/or activity has been associated with many human diseases, including cancer, diabetes, obesity, cardiovascular and inflammatory diseases, kidney dysfunctions, and neurodegenerative disorders, as well as infectious diseases. In viral infections, cathepsins may promote (1) activation of the viral attachment glycoproteins and entry of the virus into target cells; (2) antigen processing and presentation, enabling the virus to replicate in infected cells; (3) up-regulation and processing of heparanase that facilitates the release of viral progeny and the spread of infection; and (4) activation of cell death that may either favor viral clearance or assist viral propagation. In this review, we report the most relevant findings on the molecular mechanisms underlying cathepsin involvement in viral infection physiopathology, and we discuss the potential of cathepsin inhibitors for therapeutical applications in viral infectious diseases.

Pseudorabies Virus Infection Results in a Broad Inhibition of Host Gene Transcription

Pseudorabies virus (PRV) is a porcine alphaherpesvirus that belongs to the Herpesviridae family. We showed earlier that infection of porcine epithelial cells with PRV triggers activation of the nuclear factor κB (NF-κB) pathway, a pivotal signaling axis in the early immune response. However, PRV-induced NF-κB activation does not lead to NF-κB-dependent gene expression. Here, using electrophoretic mobility shift assays (EMSAs), we show that PRV does not disrupt the ability of NF-κB to interact with its κB target sites. Assessing basal cellular transcriptional activity in PRV-infected cells by quantitation of prespliced transcripts of constitutively expressed genes uncovered a broad suppression of cellular transcription by PRV, which also affects the inducible expression of NF-κB target genes. Host cell transcription inhibition was rescued when viral genome replication was blocked using phosphonoacetic acid (PAA). Remarkably, we found that host gene expression shutoff in PRV-infected cells correlated with a substantial retention of the NF-κB subunit p65, the TATA box binding protein, and RNA polymerase II-essential factors required for (NF-κB-dependent) gene transcription-in expanding PRV replication centers in the nucleus and thereby away from the host chromatin. This study reveals a potent mechanism used by the alphaherpesvirus PRV to steer the protein production capacity of infected cells to viral proteins by preventing expression of host genes, including inducible genes involved in mounting antiviral responses. IMPORTANCE Herpesviruses are highly successful pathogens that cause lifelong persistent infections of their host. Modulation of the intracellular environment of infected cells is imperative for the success of virus infections. We reported earlier that a DNA damage response in epithelial cells infected with the alphaherpesvirus pseudorabies virus (PRV) results in activation of the hallmark proinflammatory NF-κB signaling axis but, remarkably, that this activation does not lead to NF-κB-induced (proinflammatory) gene expression. Here, we report that PRV-mediated inhibition of host gene expression stretches beyond NF-κB-dependent gene expression and in fact reflects a broad inhibition of host gene transcription, which correlates with a substantial recruitment of essential host transcription factors in viral replication compartments in the nucleus, away from the host chromatin. These data uncover a potent alphaherpesvirus mechanism to interfere with production of host proteins, including proteins involved in antiviral responses.

Heparanase-1 is upregulated by hepatitis C virus and favors its replication

BACKGROUND & AIMS

Over time, chronic HCV infection can lead to hepatocellular carcinoma (HCC), a process that involves changes to the liver extracellular matrix (ECM). However, the exact mechanisms by which HCV induces HCC remain unclear. Therefore, we sought to investigate the impact of HCV on the liver ECM, with a focus on heparanase-1 (HPSE).

METHODS

HPSE expression was assessed by quantitative reverse-transcription PCR, immunoblotting and immunofluorescence in liver biopsies infected or not with HCV, and in 10-day-infected hepatoma Huh7.5 cells. Cell lines deficient for or overexpressing HPSE were established to study its role during infection.

RESULTS

HCV propagation led to significant HPSE induction, in vivo and in vitro. HPSE enhanced infection when exogenously expressed or supplemented as a recombinant protein. Conversely, when HPSE expression was downregulated or its activity blocked, HCV infection dropped, suggesting a role of HPSE in the HCV life cycle. We further studied the underlying mechanisms of such observations and found that HPSE favored HCV release by enhancing CD63 synthesis and exosome secretion, but not by stimulating HCV entry or genome replication. We also showed that virus-induced oxidative stress was involved in HPSE induction, most likely through NF-κB activation.

CONCLUSIONS

We report for the first time that HCV infection is favored by HPSE, and upregulates HPSE expression and secretion, which may result in pathogenic alterations of the ECM.

LAY SUMMARY

Chronic hepatitis C virus (HCV) infection can lead to hepatocellular carcinoma development in a process that involves derangement of the extracellular matrix (ECM). Herein, we show that heparanase-1, a protein involved in ECM degradation and remodeling, favors HCV infection and is upregulated by HCV infection; this upregulation may result in pathogenic alterations of the ECM.

Heparanase Is a Putative Mediator of Endothelial Glycocalyx Damage in COVID-19 - A Proof-of-Concept Study

Coronavirus disease 2019 (COVID-19) is a systemic disease associated with injury (thinning) of the endothelial glycocalyx (eGC), a protective layer on the vascular endothelium. The aim of this translational study was to investigate the role of the eGC-degrading enzyme heparanase (HPSE), which is known to play a central role in the destruction of the eGC in bacterial sepsis. Excess activity of HPSE in plasma from COVID-19 patients correlated with several markers of eGC damage and perfused boundary region (PBR, an inverse estimate of glycocalyx dimensions of vessels with a diameter 4-25 µm). In a series of translational experiments, we demonstrate that the changes in eGC thickness of cultured cells exposed to COVID-19 serum correlated closely with HPSE activity in concordant plasma samples (R = 0.82, P = 0.003). Inhibition of HPSE by a nonanticoagulant heparin fragment prevented eGC injury in response to COVID-19 serum, as shown by atomic force microscopy and immunofluorescence imaging. Our results suggest that the protective effect of heparin in COVID-19 may be due to an eGC-protective off-target effect.

CREB3 Plays an Important Role in HPSE-Facilitated HSV-1 Release in Human Corneal Epithelial Cells

Herpes simplex virus type-1 (HSV-1) exploits several host factors to enhance its replication and release from infected cells. It induces the production of host enzyme heparanase (HPSE) to aid in egress. While the mechanism by which HPSE assists in viral release is well-characterized, other host factors that are recruited along with HPSE for viral release are less well understood. In this study, we identify cyclic-AMP-responsive element-binding protein3 (CREB3) as a key player in HPSE-facilitated HSV-1 egress. When CREB3 is transiently upregulated in human corneal epithelial cells, HSV-1 release from the infected cells is correspondingly enhanced. This activity is linked to HPSE expression such that HPSE-transfected corneal epithelial (HCE) cells more highly express CREB3 than wild-type cells while the cells knocked out for HPSE show very little CREB3 expression. CREB3-transfected HCE cells showed significantly higher export of HPSE upon infection than wild-type cells. Our data suggests that coat protein complex II (COPII), which mediates HPSE trafficking, is also upregulated via a CREB3-dependent pathway during HSV-1 infection. Finally, the co-transfection of CREB3 and HPSE in HCE cells shows the highest viral release compared to either treatment alone, establishing CREB3 as a key player in HPSE-facilitated HSV-1 egress.

Heparanase Blockade as a Novel Dual-Targeting Therapy for COVID-19

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has caused over 5 million deaths worldwide. Pneumonia and systemic inflammation contribute to its high mortality. Many viruses use heparan sulfate proteoglycans as coreceptors for viral entry, and heparanase (HPSE) is a known regulator of both viral entry and inflammatory cytokines. We evaluated the heparanase inhibitor Roneparstat, a modified heparin with minimum anticoagulant activity, in pathophysiology and therapy for COVID-19. We found that Roneparstat significantly decreased the infectivity of SARS-CoV-2, SARS-CoV-1, and retroviruses (human T-lymphotropic virus 1 [HTLV-1] and HIV-1) in vitro. Single-cell RNA sequencing (scRNA-seq) analysis of cells from the bronchoalveolar lavage fluid of COVID-19 patients revealed a marked increase in HPSE gene expression in CD68+ macrophages compared to healthy controls. Elevated levels of HPSE expression in macrophages correlated with the severity of COVID-19 and the expression of inflammatory cytokine genes, including IL6, TNF, IL1B, and CCL2. In line with this finding, we found a marked induction of HPSE and numerous inflammatory cytokines in human macrophages challenged with SARS-CoV-2 S1 protein. Treatment with Roneparstat significantly attenuated SARS-CoV-2 S1 protein-mediated inflammatory cytokine release from human macrophages, through disruption of NF-κB signaling. HPSE knockdown in a macrophage cell line also showed diminished inflammatory cytokine production during S1 protein challenge. Taken together, this study provides a proof of concept that heparanase is a target for SARS-CoV-2-mediated pathogenesis and that Roneparstat may serve as a dual-targeted therapy to reduce viral infection and inflammation in COVID-19. IMPORTANCE The complex pathogenesis of COVID-19 consists of two major pathological phases: an initial infection phase elicited by SARS-CoV-2 entry and replication and an inflammation phase that could lead to tissue damage, which can evolve into acute respiratory failure or even death. While the development and deployment of vaccines are ongoing, effective therapy for COVID-19 is still urgently needed. In this study, we explored HPSE blockade with Roneparstat, a phase I clinically tested HPSE inhibitor, in the context of COVID-19 pathogenesis. Treatment with Roneparstat showed wide-spectrum anti-infection activities against SARS-CoV-2, HTLV-1, and HIV-1 in vitro. In addition, HPSE blockade with Roneparstat significantly attenuated SARS-CoV-2 S1 protein-induced inflammatory cytokine release from human macrophages through disruption of NF-κB signaling. Together, this study provides a proof of principle for the use of Roneparstat as a dual-targeting therapy for COVID-19 to decrease viral infection and dampen the proinflammatory immune response mediated by macrophages.

Optineurin in ocular herpes infection

Herpes Simplex Virus-1 (HSV-1) is a neurotropic virus that can infect humans in the eye and travel to the trigeminal ganglion to establish latency. HSV-1 causes various disease states in both the primary and secondary sites of infection including the eye and the nervous system. This DNA virus exploits various adaptive measures to infect host cells, hijack host cell proteins, evade host immune response and spread from cell-to-cell to avoid immune detection. Recent data suggest that Optineurin (OPTN), a host protein, is a key restriction factor that prevents cell-to-cell spread of HSV-1 and guards against serious damage to the nervous system during infection. In recent years OPTN has gained increased attention because of its involvement in cellular mechanisms that promote homeostasis and prevent neurodegeneration. At the center of it all is the role OPTN plays as a receptor for selective autophagy. This review summarizes our latest understanding of the viral lifecycle, disease pathologies, and OPTN-mediated protective mechanisms during HSV-1 infection of the eye and the nervous system. We specifically highlight recent discoveries that implicate OPTN as crucial in the prevention of ocular and neurodegenerative diseases.

Host Molecules That Promote Pathophysiology of Ocular Herpes

Herpes simplex virus type-1 (HSV-1) is a human virus that causes lifelong infections in a large population worldwide. Recurrence of HSV-1 from latency in trigeminal ganglion (TG) is the trigger of the morbidities seen with this virus. In addition to causing fever blisters and cold sores, occasionally the virus can also cause corneal lesions resulting in blindness in untreated individuals. Several host cell proteins play important roles in HSV-1 infection of the eye. HSV-1 enters into the corneal epithelial cells via its interactions with cell surface receptors. In parallel, the Toll-like receptors sense viral invasion and activate defense mechanisms to fight the infection. New data shows that Optineurin, a host autophagy receptor is also activated to degrade viral particles. In contrast, activation of heparanase, a host enzyme, induces an immune-inflammatory response, which triggers pro-inflammatory and pro-angiogenic environment and ultimately results in many of the clinical features seen with HSV-1 infection of the cornea. Rarely, HSV-1 can also spread to the central nervous system causing serious diseases. In this review, we summarize the latest knowledge on host molecules that promote pathophysiological aspects of ocular herpes.

Intrinsic Antiviral Activity of Optineurin Prevents Hyperproliferation of a Primary Herpes Simplex Virus Type 2 Infection

Very little knowledge exists on virus-specific host cell intrinsic mechanisms that prevent hyperproliferation of primary HSV type 2 (HSV-2) genital infections. In this study, we provide evidence that the Nemo-related protein, optineurin (OPTN), plays a key role in restricting HSV-2 infection both in vitro and in vivo. Contrary to previous reports regarding the proviral role of OPTN during Sendai virus infection, we demonstrate that lack of OPTN in cells causes enhanced virus production. OPTN deficiency negatively affects the host autophagy response and results in a marked reduction of CCL5 induction. OPTN knockout (OPTN^-/-) mice display exacerbated genital disease and dysregulated T cell frequencies in infected tissues and lymph nodes. A human transcriptomic profile dataset provides further credence that a strong positive correlation exists between CCL5 upregulation and OPTN expression during HSV-2 genital infection. Our findings underscore a previously unknown OPTN/CCL5 nexus that restricts hyperproliferative spread of primary HSV-2 infection, which may constitute an intrinsic host defense mechanism against herpesviruses in general.

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.

Release of HSV-1 Cell-Free Virions: Mechanisms, Regulation, and Likely Role in Human-Human Transmission

Herpes simplex virus type 1, or HSV-1, is a widespread human pathogen that replicates in epithelial cells of the body surface and then establishes latent infection in peripheral neurons. When HSV-1 replicates, viral progeny must be efficiently released to spread infection to new target cells. Viral spread occurs via two major routes. In cell-cell spread, progeny virions are delivered directly to cellular junctions, where they infect adjacent cells. In cell-free release, progeny virions are released into the extracellular milieu, potentially allowing the infection of distant cells. Cell-cell spread of HSV-1 has been well studied and is known to be important for in vivo infection and pathogenesis. In contrast, HSV-1 cell-free release has received less attention, and its significance to viral biology is unclear. Here, I review the mechanisms and regulation of HSV-1 cell-free virion release. Based on knowledge accrued in other herpesviral systems, I argue that HSV-1 cell-free release is likely to be tightly regulated in vivo. Specifically, I hypothesize that this process is generally suppressed as the virus replicates within the body, but activated to high levels at sites of viral reactivation, such as the oral mucosa and skin, in order to promote efficient transmission of HSV-1 to new human hosts.

Pseudorabies Virus Infection Triggers NF-κB Activation via the DNA Damage Response but Actively Inhibits NF-κB-Dependent Gene Expression

The nuclear factor kappa B (NF-κB) pathway is known to integrate signaling associated with very diverse intra- and extracellular stressors, including virus infections, and triggers a powerful (proinflammatory) response through the expression of NF-κB-regulated genes. Typically, the NF-κB pathway collects and transduces threatening signals at the cell surface or in the cytoplasm leading to nuclear import of activated NF-κB transcription factors. In the current work, we demonstrate that the swine alphaherpesvirus pseudorabies virus (PRV) induces a peculiar mode of NF-κB activation known as "inside-out" NF-κB activation. We show that PRV triggers the DNA damage response (DDR) and that this DDR response drives NF-κB activation since inhibition of the nuclear ataxia telangiectasia-mutated (ATM) kinase, a chief controller of DDR, abolished PRV-induced NF-κB activation. Initiation of the DDR-NF-κB signaling axis requires viral protein synthesis but occurs before active viral genome replication. In addition, the initiation of the DDR-NF-κB signaling axis is followed by a virus-induced complete shutoff of NF-κB-dependent gene expression that depends on viral DNA replication. In summary, the results presented in this study reveal that PRV infection triggers a noncanonical DDR-NF-κB activation signaling axis and that the virus actively inhibits the (potentially antiviral) consequences of this pathway, by inhibiting NF-κB-dependent gene expression. IMPORTANCE The NF-κB signaling pathway plays a critical role in coordination of innate immune responses that are of vital importance in the control of infections. The current report generates new insights into the interaction of the alphaherpesvirus pseudorabies virus (PRV) with the NF-κB pathway, as they reveal that (i) PRV infection leads to NF-κB activation via a peculiar "inside-out" nucleus-to-cytoplasm signal that is triggered via the DNA damage response (DDR), (ii) the DDR-NF-κB signaling axis requires expression of viral proteins but is initiated before active PRV replication, and (iii) late viral factor(s) allow PRV to actively and efficiently inhibit NF-κB-dependent (proinflammatory) gene expression. These data suggest that activation of the DDR-NF-κB during PRV infection is host driven and that its potential antiviral consequences are actively inhibited by the virus.

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.

Heparanase-Induced Activation of AKT Stabilizes β-Catenin and Modulates Wnt/β-Catenin Signaling during Herpes Simplex Virus 1 Infection

Under pathological conditions like herpes simplex virus 1 (HSV-1) infection, host-pathogen interactions lead to major reconstruction of the host protein network, which contributes to the dysregulation of signaling pathways and disease onset. Of note is the upregulation of a multifunctional host protein, heparanase (HPSE), following infection, which serves as a mediator in HSV-1 replication. In this study, we identify a novel function of HPSE and highlight it as a key regulator of β-catenin signal transduction. The regulatory role of HPSE on the activation, nuclear translocation, and signal transduction of β-catenin disrupts cellular homeostasis and establishes a pathogenic environment that promotes viral replication. Under normal physiological conditions, β-catenin is bound to a group of proteins, referred to as the destruction complex, and targeted for ubiquitination and, ultimately, degradation. We show that virus-induced upregulation of HPSE leads to the activation of Akt and subsequent stabilization and activation of β-catenin through (i) the release of β-catenin from the destruction complex, and (ii) direct phosphorylation of β-catenin at Ser552. This study also provides an in-depth characterization of the proviral role of β-catenin signaling during HSV-1 replication using physiologically relevant cell lines and in vivo models of ocular infection. Furthermore, pharmacological inhibitors of this pathway generated a robust antiviral state against multiple laboratory and clinical strains of HSV-1. Collectively, our findings assign a novel regulatory role to HPSE as a driver of β-catenin signaling in HSV-1 infection. IMPORTANCE Heparanase (HPSE) and β-catenin have independently been implicated in regulating key pathophysiological processes, including neovascularization, angiogenesis, and inflammation; however, the relationship between the two proteins has remained elusive thus far. For that reason, characterizing this relationship is crucial and can lead to the development of novel therapeutics. For HSV-1 specifically, current antivirals are not able to abolish the virus from the host, leaving patients susceptible to episodes of viral reactivation. Identifying a host-based intervention can provide a better alternative with enhanced efficacy and sustained relief.

Receptors and ligands for herpes simplex viruses: Novel insights for drug targeting

Human herpes simplex viruses (HSVs) belong to the Herpesviridae family. At present, no vaccine or curative treatment is available for the prevention of HSV infections. Here, we review the cell surface receptors that are recognized by HSV's glycoprotein B, glycoprotein C, glycoprotein D, and the glycoprotein H - glycoprotein L complex to facilitate entry into host cells. These receptors include heparan sulfate (HS), herpesvirus entry mediator (HVEM), and nectin-1/-2, 3-O-sulfated heparan sulfate (3-OS HS).

The Heparanase Regulatory Network in Health and Disease

The extracellular matrix (ECM) is a structural framework that has many important physiological functions which include maintaining tissue structure and integrity, serving as a barrier to invading pathogens, and acting as a reservoir for bioactive molecules. This cellular scaffold is made up of various types of macromolecules including heparan sulfate proteoglycans (HSPGs). HSPGs comprise a protein core linked to the complex glycosaminoglycan heparan sulfate (HS), the remodeling of which is important for many physiological processes such as wound healing as well as pathological processes including cancer metastasis. Turnover of HS is tightly regulated by a single enzyme capable of cleaving HS side chains: heparanase. Heparanase upregulation has been identified in many inflammatory diseases including atherosclerosis, fibrosis, and cancer, where it has been shown to play multiple roles in processes such as epithelial-mesenchymal transition, angiogenesis, and cancer metastasis. Heparanase expression and activity are tightly regulated. Understanding the regulation of heparanase and its downstream targets is attractive for the development of treatments for these diseases. This review provides a comprehensive overview of the regulators of heparanase as well as the enzyme's downstream gene and protein targets, and implications for the development of new therapeutic strategies.

Aptamers in Virology-A Consolidated Review of the Most Recent Advancements in Diagnosis and Therapy

The use of short oligonucleotide or peptide molecules as target-specific aptamers has recently garnered substantial attention in the field of the detection and treatment of viral infections. Based on their high affinity and high specificity to desired targets, their use is on the rise to replace antibodies for the detection of viruses and viral antigens. Furthermore, aptamers inhibit intracellular viral transcription and translation, in addition to restricting viral entry into host cells. This has opened up a plethora of new targets for the research and development of novel vaccines against viruses. Here, we discuss the advances made in aptamer technology for viral diagnosis and therapy in the past decade.

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

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

The Epithelial Cell Glycocalyx in Ocular Surface Infection

The glycocalyx is the main component of the transcellular barrier located at the interface between the ocular surface epithelia and the external environment. This barrier extends up to 500 nm from the plasma membrane and projects into the tear fluid bathing the surface of the eye. Under homeostatic conditions, defense molecules in the glycocalyx, such as transmembrane mucins, resist infection. However, many pathogenic microorganisms have evolved to exploit components of the glycocalyx in order to gain access to epithelial cells and consequently exert deleterious effects. This manuscript reviews the implications of the ocular surface epithelial glycocalyx to bacterial, viral, fungal and parasitic infection. Moreover, it presents some ongoing controversies surrounding the functional relevance of the epithelial glycocalyx to ocular infectious disease.

Protease, Growth Factor, and Heparanase-Mediated Syndecan-1 Shedding Leads to Enhanced HSV-1 Egress

Heparan sulfate (HS) and heparan sulfate proteoglycans (HSPGs) are considered important for the entry of many different viruses. Previously, we demonstrated that heparanase (HPSE), the host enzyme responsible for cleaving HS chains, is upregulated by herpes simplex virus-1 (HSV-1) infection. Higher levels of HPSE accelerate HS removal from the cell surface, facilitating viral release from infected cells. Here, we study the effects of overexpressing HPSE on viral entry, cell-to-cell fusion, plaque formation, and viral egress. We provide new information that higher levels of HPSE reduce syncytial plaque formation while promoting egress and extracellular release of the virions. We also found that transiently enhanced expression of HPSE did not affect HSV-1 entry into host cells or HSV-1-induced cell-to-cell fusion, suggesting that HPSE activation is tightly regulated and facilitates extracellular release of the maturing virions. We demonstrate that an HSPG-shedding agonist, PMA; a protease, thrombin; and a growth factor, EGF as well as bacterially produced recombinant heparinases resulted in enhanced HSV-1 release from HeLa and human corneal epithelial (HCE) cells. Our findings here underscore the significance of syndecan-1 functions in the HSV-1 lifecycle, provide evidence that the shedding of syndecan-1 ectodomain is another way HPSE works to facilitate HSV-1 release, and add new evidence on the significance of various HSPG shedding agonists in HSV-1 release from infected cells.

Antiviral strategies targeting herpesviruses

Herpesviruses, known as large DNA viruses, have a wide host range. In addition to human beings, cattle, and horses, even carp can be hosts for herpesvirus infection. Herpesviruses are pathogens possessing elaborate mechanisms that regulate host cell components for its replication, assembly and generating mature virus particles that can infect humans and most animals, usually causing multiple and lifelong infections. In addition, several human diseases, such as genital or mouth herpes, mononucleosis, and Burkitt lymphoma, are usually associated with herpesvirus infection. Blocking the steps of viral infection, such as entry, replication and assembly, may be an effective way for many different herpes viruses and their related diseases. Therefore, we aim to describe antiviral agents that are able to prevent herpesvirus entry, replication and assembly in host cells. We summarize antiviral strategies, including certain small molecular drugs, RNA interference and CRISPR/Cas9 system-based antiviral approaches, which represent promising approaches.

Effect of Anticoagulant Administration on the Mortality of Hospitalized Patients With COVID-19: An Updated Systematic Review and Meta-Analysis

Background: Anticoagulation is generally used in hospitalized patients with coronavirus disease 2019 (COVID-19) as thromboprophylaxis. However, results from different studies comparing the effect of anticoagulation on the mortality of COVID-19 patients with non-anticoagulation are inconclusive.

Methods: Our systematic review included observational trials if they studied anticoagulant therapy in hospitalized patients with COVID-19 for mortality or bleeding events. Dichotomous variables from individual studies were pooled by risk ratio (RR) and their 95% confidence interval (95% CI) using the random-effects model. Grading of Recommendations Assessment, Development and Evaluation was used to assess the quality of evidence.

Results: A total of 11 observational studies enrolling 20,748 hospitalized COVID-19 patients overall were included. A pooled meta-analysis of these studies showed that anticoagulation therapy, compared with non-anticoagulation therapy, was associated with lower mortality risk (RR 0.70, 95% CI 0.52–0.93, p = 0.01). The evidence of benefit was stronger among critically ill COVID-19 patients in the intensive care units (RR 0.59, 95% CI 0.43–0.83, p = 0.002). Additionally, severe bleeding events were not associated with the administration of anticoagulants (RR 0.93, 95% CI 0.71–1.23, p = 0.63).

Conclusion: Among patients with COVID-19 admitted to hospital, the administration of anticoagulants was associated with a decreased mortality without increasing the incidence of bleeding events.