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Frequent release of low amounts of herpes simplex virus from neurons: results of a mathematical model.

ABSTRACT: Herpes simplex virus-2 (HSV-2) is a sexually transmitted infection that is the leading cause of genital ulcers worldwide. Infection is life long and is characterized by repeated asymptomatic and symptomatic shedding episodes of virus that are initiated when virus is released from neurons into the genital tract. The pattern of HSV-2 release from neurons into the genital tract is poorly understood. We fit a mathematical model of HSV-2 pathogenesis to curves generated from daily quantification of HSV in mucosal swabs performed from patients with herpetic genital ulcers. We used virologic parameters derived from model fitting for stochastic model simulations. These simulations reproduced previously documented estimates for shedding frequency, and herpetic lesion diameter and frequency. The most realistic model output occurred when we assumed minimal amounts of daily neuronal virus introduction. In our simulations, small changes in average total quantity of HSV-2 released from neurons influenced detectable shedding frequency, while changes in frequency of neuronal HSV-2 release had little effect. Frequent HSV-2 shedding episodes in humans are explained by nearly constant release of small numbers of viruses from neurons that terminate in the genital tract.

SUBMITTER: Schiffer JT

PROVIDER: S-EPMC2818652 | biostudies-literature | 2009 Nov

REPOSITORIES: biostudies-literature

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Frequent release of low amounts of herpes simplex virus from neurons: results of a mathematical model.

Schiffer Joshua T JT Abu-Raddad Laith L Mark Karen E KE Zhu Jia J Selke Stacy S Magaret Amalia A Wald Anna A Corey Lawrence L

Science translational medicine 20091101 7

Herpes simplex virus-2 (HSV-2) is a sexually transmitted infection that is the leading cause of genital ulcers worldwide. Infection is life long and is characterized by repeated asymptomatic and symptomatic shedding episodes of virus that are initiated when virus is released from neurons into the genital tract. The pattern of HSV-2 release from neurons into the genital tract is poorly understood. We fit a mathematical model of HSV-2 pathogenesis to curves generated from daily quantification of H ...[more]

PMID: 20161655

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Project description:Herpes simplex virus-1 (HSV-1) has evolved mechanisms to evade the host immune system and limit the antiviral effects induced by interferon (IFN) produced by local epithelial and immune cells. In this study, we determined the effects of type I, II, and III IFNs on HSV-1 release from sensory axons. Using compartmentalized microfluidic devices separating axons from the neuronal cell bodies, we showed that treating axons with type I (IFNα and IFNβ), type II (IFNγ), and type III (IFNλ) IFNs inhibited the release of HSV-1 from axons, without altering the anterograde axonal transport of viral components. Furthermore, we showed that only type II IFN induced a cell-wide response following axonal treatment, with phosphorylated STAT1 and STAT3 present along axons and in the neuronal cell body, whereas type I and III IFNs only induced a local STAT1 and STAT3 response in axons. We also showed that HSV-1 infection alone, in the absence of exogenous IFN, activated STAT1 and STAT3 in both neuronal cell bodies and along axons. However, HSV-1 infection restricted the translocation of pSTAT1 and pSTAT3 to the nucleus even in the presence of IFNs, suggesting viral evasion mechanisms are involved in limiting the IFN response in the neuronal cell body. Overall, our study indicates a key and greater antiviral role of IFNs in inhibiting HSV-1 release from axon termini than in the ganglia during recurrent infections and identifies a novel intervention site, the neuro-epidermal junction, for the development of new immunotherapies. IMPORTANCE Herpes simplex virus-1 (HSV-1) is a human pathogen known to cause cold sores and genital herpes. HSV-1 establishes lifelong infections in our sensory neurons, with no cure or vaccine available. HSV-1 can reactivate sporadically and travel back along sensory nerves, where it can form lesions in the oral and genital mucosa, eye, and skin, or be shed asymptomatically. New treatment options are needed as resistance is emerging to current antiviral therapies. Here, we show that interferons (IFNs) are capable of blocking virus release from nerve endings, potentially stopping HSV-1 transmission into the skin. Furthermore, we show that IFNγ has the potential to have widespread antiviral effects in the neuron and may have additional effects on HSV-1 reactivation. Together, this study identifies new targets for the development of immunotherapies to stop the spread of HSV-1 from the nerves into the skin.

Project description:Expression of viral genes and activation of innate antiviral responses during infection result in an increase in reactive oxygen species (ROS) and toxic by-products of energy metabolism which can lead to cell death. The mitochondrion and its associated proteins are crucial regulators of these responses and related pathways such as autophagy and apoptosis. Through a mass spectrometry approach, we have shown that the herpes simplex virus 1 (HSV-1) neurovirulence- and autophagy-modulating protein ICP34.5 interacts with numerous mitochondrion-associated factors. Specifically, we showed that amino acids 68 to 87 of ICP34.5, the domain that binds beclin1 and controls neurovirulence, are necessary for interactions with PGAM5, KEAP1, and other regulators of the antioxidant response, mitochondrial trafficking, and programmed cell death. We further show that while this domain interacts with multiple cellular stress response factors, it does not alter apoptosis or antioxidant gene expression. That said, the attenuated replication of a recombinant virus lacking residues 68 to 87 (termed Δ68-87) in primary human fibroblasts was restored by addition of ferric nitrate. Furthermore, in primary mouse neurons, the perinuclear localization of mitochondria that follows infection with HSV-1 was notably absent following Δ68-87 infection. Through this 20-amino-acid domain, ICP34.5 significantly reduces mitochondrial motility in axons of neurons. We propose the hypothesis that ICP34.5 promotes perinuclear mitochondrial localization by modulating transport of mitochondria through interaction with PGAM5. These data expand upon previous observations of altered mitochondrial dynamics following alphaherpesvirus infections and identify a key determinant of this activity during HSV-1 infections.IMPORTANCE Herpes simplex virus persists lifelong in neurons and can reactivate to cause recurrent lesions in mucosal tissues. A key determinant of virulence is the viral protein ICP34.5, of which residues 68 to 87 significantly contribute to neurovirulence through an unknown mechanism. Our report provides evidence that residues 68 to 87 of ICP34.5 are required for binding mitochondrion-associated factors. These interactions alter mitochondrial dynamics in neurons, thereby facilitating viral replication and pathogenesis.

Project description:UnlabelledHerpes simplex virus 1 (HSV-1) establishes lifelong infection in the neurons of trigeminal ganglia (TG), cycling between productive infection and latency. Neuronal antiviral responses are driven by type I interferon (IFN) and are crucial to controlling HSV-1 virulence. Autophagy also plays a role in this neuronal antiviral response, but the mechanism remains obscure. In this study, HSV-1 infection of murine TG neurons triggered unusual clusters of autophagosomes, predominantly in neurons lacking detectable HSV-1 antigen. Treatment of neurons with IFN-β induced a similar response, and cluster formation by infection or IFN treatment was dependent upon an intact IFN-signaling pathway. The autophagic clusters were decorated with both ISG15, an essential effecter of the antiviral response, and p62, a selective autophagy receptor. The autophagic clusters were not induced by rapamycin or starvation, consistent with a process of selective autophagy. While clusters were triggered by other neurotropic herpesviruses, infection with unrelated viruses failed to induce this response. Following ocular infection in vivo, clusters formed exclusively in the infected ophthalmic branch of the TG. Taken together, our results show that infection with HSV and antiviral signaling in TG neurons produce an unorthodox autophagic response. This autophagic clustering is associated with antiviral signaling, the presence of viral genome, and the absence of HSV protein expression and may therefore represent an important neuronal response to HSV infection and the establishment of latency.ImportanceHerpes simplex virus type 1 (HSV-1) is a ubiquitous virus and a significant cause of morbidity and some mortality. It is the causative agent of benign cold sores, but it can also cause blindness and life-threatening encephalitis. The success of HSV-1 is largely due to its ability to establish lifelong latent infections in neurons and to occasionally reactivate. The exact mechanisms by which neurons defend against virus infection is poorly understood, but such defense is at least partially mediated by autophagy, an intracellular pathway by which pathogens and other unwanted cargoes are degraded. The study demonstrates and investigates a new autophagic structure that appears to be specific to the interaction between neurotropic herpesviruses and murine primary sensory neurons. This work may therefore have important implications for our understanding of latency and reactivation.

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Frequent release of low amounts of herpes simplex virus from neurons: results of a mathematical model.

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Frequent release of low amounts of herpes simplex virus from neurons: results of a mathematical model.

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