Zebrafish as a new model for herpes simplex virus type 1 infection

Role of Filopodia in HSV-1 Entry into Zebrafish 3-O-Sulfotransferase-3-Expressing Cells

Background:

Heparan sulfate proteoglycans (HSPGs) modified by zebrafish (ZF) encoded glucosaminyl 3-O sulfotransferase-3 (3-OST-3) generate a receptor for herpes simplex virus type-1 (HSV-1) entry and spread. In order to elucidate the mechanism by which HSV-1 enters into ZF-3-OST-3 cells, we investigated the mode of viral entry.

Results:

Under high resolution scanning electron microscopy (SEM), actin cytoskeleton changes were observed by a dramatic increase in the number of filopodia formed during early interactions of HSV-1 with the target cells. While the increase in number was common among all the infected cells, the highest numbers of filopodia was observed in cells expressing the 3-OST-3 modified form of heparan sulfate (HS) encoded either by human or ZF. The levels of viral infection and filopodia induction were reduced with the actin polymerization inhibitors, Cytochalasin-D and Lantriculin B, suggesting an important role for actin reorganization during ZF-3-OST-3 mediated HSV-1 entry. Supporting an interesting possibility of filopodia usage during HSV-1 spread, pre-treatment of cytochalasin D in ZF-3-OST-3 cells drastically reduced virus glycoprotein induced cell fusion.

Conclusions:

Taken together, our results provide new evidence on the involvement of filopodia during HSV-1 infection of ZF-3-OST-3 cells and confirm a role for modified heparan sulfate in cytoskeleton rearrangement during HSV-1 entry.

Zebrafish encoded 3-O-sulfotransferase-2 generated heparan sulfate serves as a receptor during HSV-1 entry and spread

Previously we reported the role of zebrafish (ZF) encoded glucosaminyl 3-O-sulfotransferase-3 (3-OST-3) isoform in assisting herpes simplex virus type-1 (HSV-1) entry and spread by generating an entry receptor to HSV-1 envelope glycoprotein D (gD). However, the ability of ZF encoded 3-OST-2 isoform to participate in HSV-1 entry has not been determined although it is predominantly expressed in ZF brain, a prime target for HSV-1 to infect and establish lifelong latency. Here we report the expression cloning of ZF encoded 3-OST-2 isoform and demonstrate HSV-1 entry into resistant Chinese hamster ovary (CHO-K1) cells expressing the clone. Additional significance of ZF encoded 3-OST-2 receptor was demonstrated using medically important isolates of HSV-1. In addition, interference to HSV-1 entry was observed upon co-expression of HSV-1 gD and ZF 3-OST-2. Similarly HSV-1 entry was significantly inhibited by the pre-treatment of cells with enzyme HS lyases (heparinase II/III). Finally, ZF-3-OST-2 expressing CHO-K1 was able to fuse with HSV-1 glycoprotein expressing cells suggesting their role in HSV-1 spread. Taken together our result demonstrates a role for ZF 3-OST-2 in HSV-1 pathogenesis.

The zebrafish as a model for paediatric diseases

The rapid increase in information about genes and their associations with human diseases has highlighted the need for model organisms suitable for genetic manipulation and drug testing. The zebrafish is a valuable vertebrate animal model that offers many advantages, including the relative ease of husbandry and genetic manipulation and the capacity for high-throughput screens. In this review, we describe the zebrafish as a model for paediatric diseases, with particular emphasis on haematopoietic and infectious diseases.

CONCLUSION

The zebrafish has become an established vertebrate model in which to elucidate the molecular mechanisms of various human diseases.

Members of 3-O-Sulfotransferases (3-OST) Family: A Valuable Tool from Zebrafish to Humans for Understanding Herpes Simplex Virus Entry

The journey of many viruses to infect cells begins when the virus first binds to cell surface heparan sulfate (HS). The initial step of cell attachment or binding during herpes simplex virus type-1 (HSV-1) entry is mediated by envelope glycoprotein B (gB) and C (gC). The binding is followed by fusion between virus envelope and cell membrane during which HSV-1 glycoprotein D (gD) interacts with a modified form of HS know as 3-O-sulfated heparan sulfate (3-OS HS). The rare modification of 3-O-sulfation on HS chain is governed by enzymes known as 3-O-sulfotransferase (3-OST). Currently, there are seven isoforms of human 3-OSTs that have been identified, and with the exception of 3-OST-1, all other 3-OST isoforms allow HSV-1 entry and spread. Recently, the product of the zebrafish (ZF)-encoded 3-OST-3 was also recognized as a gD receptor, which mediates HSV-1 entry and cell-cell fusion similar to human 3-OST-3. Interestingly, the ZF system expresses multiple isoforms of 3-OST which could be very useful for studying the involvement of HS and 3-OS HS in virus tropism and virus-induced inflammation. In addition, therapeutic targeting of 3-OST generated HS is likely to bring about novel interventions against HSV-1. In this review we have taken a closer look at the potential of both human and ZF encoded 3-OSTs as valuable tools in HSV entry and inflammation studies.

The viral TRAF protein (ORF111L) from infectious spleen and kidney necrosis virus interacts with TRADD and induces caspase 8-mediated apoptosis

Infectious spleen and kidney necrosis virus (ISKNV) is the type species of the Megalocytivirus genus of the Iridoviridae family. It causes a serious and potentially pandemic disease in wild and cultured fishes. ISKNV infection induces evident apoptosis in mandarin fish (Siniperca chuatsi) and zebrafish (Danio renio). However, the mechanism is still unknown. After a genome-wide bioinformatics analysis of ISKNV-encoded proteins, the ISKNV open reading frame 111L (ORF111L) shows a high similarity to the tumour necrosis factor receptor-associated factor (TRAF) encoded by fish, mice and mammals, which is essential for apoptotic signal transduction. Moreover, ORF111L was verified to directly interact with the zebrafish TNF receptor type 1 associated death domain protein (TRADD). A recombinant plasmid containing the DNA sequence of ORF111L was constructed and microinjected into zebrafish embryos at the 1–2 cell stage to investigate its biological function in vivo. ORF111L overexpression in the embryos resulted in increased apoptosis. ORF111L-induced apoptosis was clearly associated with significant caspase 8 upregulation and activation. The knockdown of zebrafish caspase 8 expression effectively blocked the apoptosis induced by ORF111L overexpression. Significantly, ORF111L overexpression resulted in much stronger effect on caspase 8 and caspase 3 upregulation compared to zebrafish TRAF2. This is the first report of a viral protein similar to TRAF that interacts with TRADD and induces caspase 8-mediated apoptosis, which may provide novel insights into the pathogenesis of ISKNV infection.

Herpes simplex virus infects most cell types in vitro: clues to its success

Herpes simplex virus (HSV) type-1 and type-2 have evolved numerous strategies to infect a wide range of hosts and cell types. The result is a very successful prevalence of the virus in the human population infecting 40-80% of people worldwide. HSV entry into host cell is a multistep process that involves the interaction of the viral glycoproteins with various cell surface receptors. Based on the cell type, HSV enter into host cell using different modes of entry. The combination of various receptors and entry modes has resulted in a virus that is capable of infecting virtually all cell types. Identifying the common rate limiting steps of the infection may help the development of antiviral agents that are capable of preventing the virus entry into host cell. In this review we describe the major features of HSV entry that have contributed to the wide susceptibility of cells to HSV infection.

Virostatic potential of micro-nano filopodia-like ZnO structures against herpes simplex virus-1

Herpes simplex virus type-1 (HSV-1) entry into target cell is initiated by the ionic interactions between positively charged viral envelop glycoproteins and a negatively charged cell surface heparan sulfate (HS). This first step involves the induction of HS-rich filopodia-like structures on the cell surface that facilitate viral transport during cell entry. Targeting this initial first step in HSV-1 pathogenesis, we generated different zinc oxide (ZnO) micro-nano structures (MNSs) that were capped with multiple nanoscopic spikes mimicking cell induced filopodia. These MNSs were predicted to target the virus to compete for its binding to cellular HS through their partially negatively charged oxygen vacancies on their nanoscopic spikes, to affect viral entry and subsequent spread. Our results demonstrate that the partially negatively charged ZnO-MNSs efficiently trap the virions via a novel virostatic mechanism rendering them unable to enter into human corneal fibroblasts - a natural target cell for HSV-1 infection. The anti-HSV-1 activity of ZnO MNSs was drastically enhanced after creating additional oxygen vacancies under UV-light illumination. Our results provide a novel insight into the significance of ZnO MNSs as the potent HSV-1 inhibitor and rationalize their development as a novel topical agent for the prevention of HSV-1 infection.

Drug tolerance in replicating mycobacteria mediated by a macrophage-induced efflux mechanism

Treatment of tuberculosis, a complex granulomatous disease, requires long-term multidrug therapy to overcome tolerance, an epigenetic drug resistance that is widely attributed to nonreplicating bacterial subpopulations. Here, we deploy Mycobacterium marinum-infected zebrafish larvae for in vivo characterization of antitubercular drug activity and tolerance. We describe the existence of multidrug-tolerant organisms that arise within days of infection, are enriched in the replicating intracellular population, and are amplified and disseminated by the tuberculous granuloma. Bacterial efflux pumps that are required for intracellular growth mediate this macrophage-induced tolerance. This tolerant population also develops when Mycobacterium tuberculosis infects cultured macrophages, suggesting that it contributes to the burden of drug tolerance in human tuberculosis. Efflux pump inhibitors like verapamil reduce this tolerance. Thus, the addition of this currently approved drug or more specific efflux pump inhibitors to standard antitubercular therapy should shorten the duration of curative treatment.

Study of host-microbe interactions in zebrafish

All animals are ecosystems, home to diverse microbial populations. Animal-associated microbes play important roles in the normal development and physiology of their hosts, but can also be agents of infectious disease. Traditionally, mice have been used to study pathogenic and beneficial associations between microbes and vertebrate animals. The zebrafish is emerging as a valuable new model system for host-microbe interaction studies, affording researchers with the opportunity to survey large populations of hosts and to visualize microbe-host associations at a cellular level in living animals. This chapter provides detailed protocols for the analysis of zebrafish-associated microbial communities, the derivation and husbandry of germ-free zebrafish, and the modeling of infectious disease in different stages of zebrafish development via different routes of inoculation. These protocols offer a starting point for researchers to address a multitude of questions about animals' coexistence with microorganisms.

Zebrafish-encoded 3-O-sulfotransferase-3 isoform mediates herpes simplex virus type 1 entry and spread

Heparan sulfate proteoglycans modified by human glucosaminyl 3-O-sulfotransferase-3 (3-OST-3) isoform generates the cellular receptor for herpes simplex virus type 1 (HSV-1). Interestingly, the ability of zebrafish (ZF)-encoded 3-OST-3 isoform to modify heparan sulfate to mediate HSV-1 entry and cell-cell fusion has not been determined although it is predominantly expressed in ZF, a popular model organism to study viral infections. Here, we demonstrate that expression of ZF-encoded 3-OST-3 isoform renders the resistant Chinese hamster ovary (CHO-K1) cells to become susceptible for HSV-1 entry. The following lines of evidence support the important role of ZF-encoded 3-OST-3 isoform as the mediator of HSV-1 entry into CHO-K1 cells: (1) ZF 3-OST-3-expressing CHO-K1 cells were able to preferentially bind HSV-1 glycoprotein D, and (2) CHO-K1 cells expressing ZF-encoded 3-OST-3 acquire the ability to fuse with cells expressing HSV-1 glycoproteins. Finally, knocking down 3-OST-3 receptor by siRNA in ZF fibroblasts cells significantly reduced HSV-1 entry and glycoprotein D binding to cells. Taken together, our results provide novel insight into the significance of ZF 3-OST-3 isoform as an HSV-1 entry and fusion receptor and its potential involvement in the HSV-1 disease model of ZF.

Host-microbe interactions in the developing zebrafish

The amenability of the zebrafish to in vivo imaging and genetic analysis has fueled expanded use of this vertebrate model to investigate the molecular and cellular foundations of host-microbe relationships. Study of microbial encounters in zebrafish hosts has concentrated on developing embryonic and larval stages, when the advantages of the zebrafish model are maximized. A comprehensive understanding of these host-microbe interactions requires appreciation of the developmental context into which a microbe is introduced, as well as the effects of that microbial challenge on host ontogeny. In this review, we discuss how in vivo imaging and genetic analysis in zebrafish has advanced our knowledge of host-microbe interactions in the context of a developing vertebrate host. We focus on recent insights into immune cell ontogeny and function, commensal microbial relationships in the intestine, and microbial pathogenesis in zebrafish hosts.

Non-mammalian animal models to study infectious disease: worms or fly fishing?

A major challenge in studying human infectious diseases is to understand in detail the molecular bases, including both pathogen and host-related factors, which contribute to disease development. Non-mammalian models have proven to be of great value for our understanding of disease and have shown conservation in fundamental virulence mechanisms for the infection of evolutionary divergent hosts. In this review we describe recent advances with three major non-mammalian models used for analysis of infectious disease in humans; the nematode Caenorhabditis elegans, the fruit fly Drosophila melanogaster and the zebrafish Danio rerio.

Effective polyethyleneimine-mediated gene transfer into zebrafish cells

Polyethyleneimine (PEI) has been broadly studied as a leading nonviral gene delivery carrier because of its relatively high transfection efficiency in a wide range of cell types. Here, we report gene transfer in zebrafish cells (ZF4) using PEI as a gene carrier and lipofectamine as a control. Formations of PEI-DNA complexes were characterized by a series of measurements. The particle size of PEI-DNA complexes decreased from 274 to 132 nm, the surface charge gradually increased from -26 to 29 mV, and the cytotoxicity for zebrafish cells was observed with increasing proportion of PEI. Gel retardation assay showed that DNA was completely bound by PEI with a negative-to-positive charge ratio of 4. It was observed by transmission electron microscopy that the morphology of PEI-DNA complexes was spherical with smooth surfaces. Flow cytometry revealed that the optimum transfection efficiency (27%) mediated by PEI was obtained at an negative-to-positive charge ratio of 8, which was higher than that with lipofectamine. Luciferase activity assay confirmed the increase in reporter gene expression probably due to a more efficient formation of complex between DNA and PEI than DNA and lipofectamine. In conclusion, our study demonstrates that PEI may be applied as an effective gene carrier to mediate gene transfer into zebrafish cells.

Evaluation of the possible transmission of BSE and scrapie to gilthead sea bream (Sparus aurata)

In transmissible spongiform encephalopathies (TSEs), a group of fatal neurodegenerative disorders affecting many species, the key event in disease pathogenesis is the accumulation of an abnormal conformational isoform (PrP(Sc)) of the host-encoded cellular prion protein (PrP(C)). While the precise mechanism of the PrP(C) to PrP(Sc) conversion is not understood, it is clear that host PrP(C) expression is a prerequisite for effective infectious prion propagation. Although there have been many studies on TSEs in mammalian species, little is known about TSE pathogenesis in fish. Here we show that while gilthead sea bream (Sparus aurata) orally challenged with brain homogenates prepared either from a BSE infected cow or from scrapie infected sheep developed no clinical prion disease, the brains of TSE-fed fish sampled two years after challenge did show signs of neurodegeneration and accumulation of deposits that reacted positively with antibodies raised against sea bream PrP. The control groups, fed with brains from uninfected animals, showed no such signs. Remarkably, the deposits developed much more rapidly and extensively in fish inoculated with BSE-infected material than in the ones challenged with the scrapie-infected brain homogenate, with numerous deposits being proteinase K-resistant. These plaque-like aggregates exhibited congophilia and birefringence in polarized light, consistent with an amyloid-like component. The neurodegeneration and abnormal deposition in the brains of fish challenged with prion, especially BSE, raises concerns about the potential risk to public health. As fish aquaculture is an economically important industry providing high protein nutrition for humans and other mammalian species, the prospect of farmed fish being contaminated with infectious mammalian PrP(Sc), or of a prion disease developing in farmed fish is alarming and requires further evaluation.