Hendra and Nipah Virus Infection in Cultured Human Olfactory Epithelial Cells

Pathogenicity and virulence of henipaviruses

Paramyxoviruses are a family of single-stranded negative-sense RNA viruses, many of which are responsible for a range of respiratory and neurological diseases in humans and animals. Among the most notable are the henipaviruses, which include the deadly Nipah (NiV) and Hendra (HeV) viruses, the causative agents of outbreaks of severe disease and high case fatality rates in humans and animals. NiV and HeV are maintained in fruit bat reservoirs primarily in the family Pteropus and spillover into humans directly or by an intermediate amplifying host such as swine or horses. Recently, non-chiropteran associated Langya (LayV), Gamak (GAKV), and Mojiang (MojV) viruses have been discovered with confirmed or suspected ability to cause disease in humans or animals. These viruses are less genetically related to HeV and NiV yet share many features with their better-known counterparts. Recent advances in surveillance of wild animal reservoir viruses have revealed a high number of henipaviral genome sequences distributed across most continents, and mammalian orders previously unknown to harbour henipaviruses. In this review, we summarize the current knowledge on the range of pathogenesis observed for the henipaviruses as well as their replication cycle, epidemiology, genomics, and host responses. We focus on the most pathogenic viruses, including NiV, HeV, LayV, and GAKV, as well as the experimentally non-pathogenic CedV. We also highlight the emerging threats posed by these and potentially other closely related viruses.

Primary Culture of the Human Olfactory Neuroepithelium and Utilization for Henipavirus Infection In Vitro

The olfactory receptor neurons (ORNs) are a unique cell type involved in the initial perception of odors. These specialized epithelial cells are located in the neuroepithelium of the nasal cavities and directly connect the nasal cavity with the central nervous system (CNS) via axons, which traverse the cribriform plate to synapse within the olfactory bulb. ORNs are derived from precursor cells that lie adjacent to the basal lamina of the olfactory epithelium. These precursor cells divide several times and their progeny differentiate into mature sensory neurons throughout life. In addition to its major and critical role in sensory transduction, the olfactory neuroepithelium may be an important tissue for viral replication and represents a potential site for viral entry into the CNS. In general, to gain access to the CNS, neurotropic viruses such as henipaviruses can use peripheral neural pathways or the circulatory system. However, the olfactory system has been reported to provide a portal of entry to the CNS for henipaviruses. The ability to obtain biopsies from living human subjects and culture these cells in the laboratory provides the opportunity to examine viral replication and effects on a neuronal cell population. As the most exposed and unprotected segment of the nervous system, the olfactory neuroepithelium may have an important role in neuropathology and systemic dissemination of viruses with established CNS effects. This chapter presents methods for primary culture of human ORNs, which have been used successfully by multiple investigators. The protocol provides a consistent, heterogeneous olfactory epithelial cell population, which demonstrates functional responses to odorant mixtures and exhibits several key features of the olfactory receptor neuron phenotype, encompassing olfactory receptors and signaling pathways.

Isolation of Primary Porcine Bronchial Epithelial Cells for Nipah Virus Infections

The Malaysian strain of Nipah virus (NiV) first emerged in 1998/99 and caused a major disease outbreak in pigs and humans. While humans developed fatal encephalitis due to a prominent infection of brain microvessels, NiV-infected pigs mostly suffered from an acute respiratory disease and efficiently spread the infection via airway secretions. To elucidate the molecular basis of the highly productive NiV replication in porcine airways in vitro, physiologically relevant cell models that have maintained functional characteristics of airway epithelia in vivo are needed. Here, we describe in detail the method of isolating bronchial epithelial cells (PBEpC) from pig lungs that can be used for NiV infection studies. After the dissection of primary bronchia and removal of the mucus and protease digestion, bronchi segments are cut open and epithelial cells are scraped off and seeded on collagen-coated cell culture flasks. With this method, it is possible to isolate about 2 × 106 primary cells from the primary bronchi of one pig lung which can be cryopreserved or further subcultured. PBEpC form polarized monolayers on Transwell membrane inserts as controlled by immunostainings of epithelial marker proteins. NiV infection causes rapid formation of syncytia, allowing productive NiV infections in living PBEpC cultures to be monitored by phase-contrast microscopy.

The Importance of Lipid Conjugation on Anti-Fusion Peptides against Nipah Virus

Nipah virus (NiV) is a recently emerging zoonotic virus that belongs to the Paramyxoviridae family and the Henipavirus genus. It causes a range of conditions, from asymptomatic infection to acute respiratory illness and fatal encephalitis. The high mortality rate of 40 to 90% ranks these viruses among the deadliest viruses known to infect humans. Currently, there is no antiviral drug available for Nipah virus disease and treatment is only supportive. Thus, there is an urgent demand for efficient antiviral therapies. NiV F protein, which catalyzes fusion between the viral and host membranes, is a potential target for antiviral drugs, as it is a key protein in the initial stages of infection. Fusion inhibitor peptides derived from the HRC-domain of the F protein are known to bind to their complementary domain in the protein’s transient intermediate state, preventing the formation of a six-helix bundle (6HB) thought to be responsible for driving the fusion of the viral and cell membranes. Here, we evaluated the biophysical and structural properties of four different C-terminal lipid-tagged peptides. Different compositions of the lipid tags were tested to search for properties that might promote efficacy and broad-spectrum activity. Fluorescence spectroscopy was used to study the interaction of the peptides with biomembrane model systems and human blood cells. In order to understand the structural properties of the peptides, circular dichroism measurements and molecular dynamics simulations were performed. Our results indicate a peptide preference for cholesterol-enriched membranes and a lipid conjugation-driven stabilization of the peptide α-helical secondary structure. This work may contribute for the development of highly effective viral fusion against NiV inhibitors.

Drivers and Distribution of Henipavirus-Induced Syncytia: What Do We Know?

Syncytium formation, i.e., cell-cell fusion resulting in the formation of multinucleated cells, is a hallmark of infection by paramyxoviruses and other pathogenic viruses. This natural mechanism has historically been a diagnostic marker for paramyxovirus infection in vivo and is now widely used for the study of virus-induced membrane fusion in vitro. However, the role of syncytium formation in within-host dissemination and pathogenicity of viruses remains poorly understood. The diversity of henipaviruses and their wide host range and tissue tropism make them particularly appropriate models with which to characterize the drivers of syncytium formation and the implications for virus fitness and pathogenicity. Based on the henipavirus literature, we summarized current knowledge on the mechanisms driving syncytium formation, mostly acquired from in vitro studies, and on the in vivo distribution of syncytia. While these data suggest that syncytium formation widely occurs across henipaviruses, hosts, and tissues, we identified important data gaps that undermined our understanding of the role of syncytium formation in virus pathogenesis. Based on these observations, we propose solutions of varying complexity to fill these data gaps, from better practices in data archiving and publication for in vivo studies, to experimental approaches in vitro.

Zika virus infection in chemosensory cells

Zika virus (ZIKV) is an emerging virus belonging to the genus Flavivirus. ZIKV infection is a significant health concern, with increasing numbers of reports of microcephaly cases in fetuses and Guillain-Barré syndrome (GBS) in adults. Interestingly, chemosensory disturbances are also reported as one of the manifestations of GBS. ZIKV infects several human tissues and cell types in vitro and in vivo. However, there is no study demonstrating ZIKV infection and replication in chemosensory cells, including olfactory and taste cells. Taste papilla and olfactory cells are chemosensory receptor cells with unique histological, molecular, and physiological characteristics. Here we examined ZIKV infection (PRVABC59) in cultured human olfactory epithelial cells (hOECs) and fungiform taste papilla (HBO) cells in vitro, as well as in vivo mouse taste and olfactory epithelial and olfactory bulb tissues. Interestingly, while HBO cells showed resistance to ZIKV replication, hOECs were highly susceptible for ZIKV infection and replication. Further, we demonstrated the presence of ZIKV particles and expression of viral proteins in olfactory epithelium, as well as in olfactory bulb, but not in taste papillae, of immunocompromised mice (ifnar^/-) infected with the PRVABC59 strain of ZIKV. These observations suggest that chemosensory cells in the olfactory neuroepithelium and olfactory bulb may be important tissues for ZIKV replication and dissemination.

Henipavirus infection of the central nervous system

Nipah virus (NiV) and Hendra virus are highly pathogenic zoonotic viruses of the genus Henipavirus, family Paramyxoviridae. These viruses were first identified as the causative agents of severe respiratory and encephalitic disease in the 1990s across Australia and Southern Asia with mortality rates reaching up to 75%. While outbreaks of Nipah and Hendra virus infections remain rare and sporadic, there is concern that NiV has pandemic potential. Despite increased attention, little is understood about the neuropathogenesis of henipavirus infection. Neuropathogenesis appears to arise from dual mechanisms of vascular disease and direct parenchymal brain infection, but the relative contributions remain unknown while respiratory disease arises from vasculitis and respiratory epithelial cell infection. This review will address NiV basic clinical disease, pathology and pathogenesis with a particular focus on central nervous system (CNS) infection and address the necessity of a model of relapsed CNS infection. Additionally, the innate immune responses to NiV infection in vitro and in the CNS are reviewed as it is likely linked to any persistent CNS infection.