ACE2 and SCARF expression in human dorsal root ganglion nociceptors: implications for SARS-CoV-2 virus neurological effects

SARS-CoV-2 has created a global crisis. COVID-19, the disease caused by the virus, is characterized by pneumonia, respiratory distress, and hypercoagulation and can be fatal. An early sign of infection is loss of smell, taste, and chemesthesis-loss of chemical sensation. Other neurological effects of the disease have been described, but not explained. It is now apparent that many of these neurological effects (for instance joint pain and headache) can persist for at least months after infection, suggesting a sensory neuronal involvement in persistent disease. We show that human dorsal root ganglion (DRG) neurons express the SARS-CoV-2 receptor, angiotensin-converting enzyme 2 at the RNA and protein level. We also demonstrate that SARS-CoV-2 and coronavirus-associated factors and receptors are broadly expressed in human DRG at the lumbar and thoracic level as assessed by bulk RNA sequencing. ACE2 mRNA is expressed by a subset of nociceptors that express MRGPRD mRNA, suggesting that SARS-CoV-2 may gain access to the nervous system through entry into neurons that form free nerve endings at the outermost layers of skin and luminal organs. Therefore, DRG sensory neurons are a potential target for SARS-CoV-2 invasion of the peripheral nervous system, and viral infection of human nociceptors may cause some of the persistent neurological effects seen in COVID-19.

RUNX Binding Sites Are Enriched in Herpesvirus Genomes, and RUNX1 Overexpression Leads to Herpes Simplex Virus 1 Suppression

Herpes simplex virus 1 (HSV-1) and HSV-2 can efficiently establish lifelong, transcriptionally silent latency states in sensory neurons to escape host detection. While host factors have previously been associated with long-range insulators in the viral genome, it is still unknown whether host transcription factors can repress viral genes more proximately to promote latency in dorsal root ganglion (DRG) neurons. Here, we assessed whether RUNX (runt-related transcription factor) transcription factors, which are critical in the development of sensory neurons, could be binding HSV-1 genome directly to suppress viral gene expression and lytic infection. Using previously published transcriptome sequencing data, we confirmed that mouse DRG neurons highly express Runx1 mRNA. Through computational analysis of HSV-1 and HSV-2 genomes, we observed that putative RUNX consensus binding sites (CBSs) were more enriched and more closely located to viral gene transcription start sites than would be expected by chance. We further found that RUNX CBSs were significantly more enriched among genomes of herpesviruses compared to those of nonherpesviruses. Utilizing an in vitro model of HSV-1 infection, we found that overexpressed RUNX1 could bind putative binding sites in the HSV-1 genome, repress numerous viral genes spanning all three kinetic classes, and suppress productive infection. In contrast, knockdown of RUNX1 in neuroblastoma cells induced viral gene expression and increased HSV-1 infection in vitro In sum, these data support a novel role for RUNX1 in directly binding herpesvirus genome, silencing the transcription of numerous viral genes, and ultimately limiting overall infection.IMPORTANCE Infecting 90% of the global population, HSV-1 and HSV-2 represent some of the most prevalent viruses in the world. Much of their success can be attributed to their ability to establish lifelong latent infections in the dorsal root ganglia (DRG). It is still largely unknown, however, how host transcription factors are involved in establishing this latency. Here, we report that RUNX1, expressed highly in DRG, binds HSV-1 genome, represses transcription of numerous viral genes, and suppresses productive in vitro infection. Our computational work further suggests this strategy may be used by other herpesviruses to reinforce latency in a cell-specific manner.

The round trip model for severe herpes zoster caused by live attenuated varicella vaccine virus

Varicella vaccine is a live attenuated varicella‐zoster virus. Varicella vaccine can enter latency and later reactivate as herpes zoster. Pseudorabies virus is another herpesvirus closely related to varicella‐zoster virus. The round trip model for pseudorabies virus explains pathogenesis of herpes zoster from vaccine virus.

Deletion of Herpes Simplex Virus 1 MicroRNAs miR-H1 and miR-H6 Impairs Reactivation

During all stages of infection, herpes simplex virus 1 (HSV-1) expresses viral microRNAs (miRNAs). There are at least 20 confirmed HSV-1 miRNAs, yet the roles of individual miRNAs in the context of viral infection remain largely uncharacterized. We constructed a recombinant virus lacking the sequences for miR-H1-5p and miR-H6-3p (17dmiR-H1/H6). The seed sequences for these miRNAs are antisense to each other and are transcribed from divergent noncoding RNAs in the latency-associated transcript (LAT) promoter region. Comparing phenotypes exhibited by the recombinant virus lacking these miRNAs to the wild type (17syn+), we found that during acute infection in cell culture, 17dmiR-H1/H6 exhibited a modest increase in viral yields. Analysis of pathogenesis in the mouse following footpad infection revealed a slight increase in virulence for 17dmiR-H1/H6 but no significant difference in the establishment or maintenance of latency. Strikingly, explant of latently infected dorsal root ganglia revealed a decreased and delayed reactivation phenotype. Further, 17dmiR-H1/H6 was severely impaired in epinephrine-induced reactivation in the rabbit ocular model. Finally, we demonstrated that deletion of miR-H1/H6 increased the accumulation of the LAT as well as several of the LAT region miRNAs. These results suggest that miR-H1/H6 plays an important role in facilitating efficient reactivation from latency.IMPORTANCE While HSV antivirals reduce the severity and duration of clinical disease in some individuals, there is no vaccine or cure. Therefore, understanding the mechanisms regulating latency and reactivation as a potential to elucidate targets for better therapeutics is important. There are at least 20 confirmed HSV-1 miRNAs, yet the roles of individual miRNAs in the context of viral infection remain largely uncharacterized. The present study focuses on two of the miRNAs (miR-H1/H6) that are encoded within the latency-associated transcript (LAT) region, a portion of the genome that has been associated with efficient reactivation. Here, we demonstrate that the deletion of the seed sequences of these miRNAs results in a severe reduction in reactivation of HSV-1 in the mouse and rabbit models. These results suggest a linkage between these miRNAs and reactivation.

Pulsed radiofrequency of dorsal root ganglion of upper thoracic segment for herpes zoster neuralgia: Case report

RATIONALE

Pulsed radiofrequency (PRF) therapy of dorsal root ganglion is effective in treating acute stage shingles neuralgia of chest and back. Herein, a case of herpetic neuralgia with difficult puncture of dorsal root ganglion of upper thoracic segment is report.

PATIENT CONCERNS

A 62-year-old male patient was admitted to the hospital for 2 days for herpes zoster with paroxysmal needle-like pain in the left chest and back. The skin lesion area of herpes zoster and the superficial location of neuralgia was left T2-4, and visual analog scale (VAS) score was 6 points.

DIAGNOSIS

Two days ago, the patient had paroxysmal needle-like pain in the left chest and back, without herpes, and was admitted to the hospital for emergency treatment. Chest pain and myocardial infarction were considered; however, troponin, myocardial enzyme spectrum, and blood amylase were in the normal range. On the evening of the same day, the patient presented green bean-sized blisters distributed in clusters along the left T2-4 nerve as a banded pattern. Thus, the patient was diagnosed as shingles.

INTERVENTION

Oral gabapentin capsules, varaciclovir tablets, mecobalamine tablets, and amitriptyline hydrochloride tablets were administered, and topical aciclovir cream was applied. The VAS score after the above treatment was 5 points. The patient underwent computed tomography-guided PRF surgery on the dorsal root ganglion.

OUTCOME

Postoperative pain was relieved. One month post-surgery, no oral analgesic drugs were administered. The VAS score was 1 point, and the pain completely disappeared at 3 months post-surgery.

CONCLUSIONS

Herpes zoster is most common in the chest and back. The PRF of dorsal root ganglion cannot access the target by conventional puncture, and can be completed by thoracic sympathetic nerve radiofrequency puncture path.

The Use of Microfluidic Neuronal Devices to Study the Anterograde Axonal Transport of Herpes Simplex Virus-1

Understanding how herpes simplex virus-1 (HSV-1) interacts with different parts of the neuron is fundamental in understanding the mechanisms behind HSV-1 transport during primary and recurrent infections. In this chapter, we describe a unique neuronal culture system that is capable of compartmentalizing neuronal cell bodies from their axons to study the transport of HSV-1 along axons. The ability to separate neuronal cell bodies and axons provides a unique model to investigate the mechanisms used by HSV-1 for viral transport, assembly, and exit from different parts of the neuron.

Cryopreservation of Canine Primary Dorsal Root Ganglion Neurons and Its Impact upon Susceptibility to Paramyxovirus Infection

Canine dorsal root ganglion (DRG) neurons, isolated post mortem from adult dogs, could provide a promising tool to study neuropathogenesis of neurotropic virus infections with a non-rodent host spectrum. However, access to canine DRG is limited due to lack of donor tissue and the cryopreservation of DRG neurons would greatly facilitate experiments. The present study aimed (i) to establish canine DRG neurons as an in vitro model for canine distemper virus (CDV) infection; and (ii) to determine whether DRG neurons are cryopreservable and remain infectable with CDV. Neurons were characterized morphologically and phenotypically by light microscopy, immunofluorescence, and functionally, by studying their neurite outgrowth and infectability with CDV. Cryopreserved canine DRG neurons remained in culture for at least 12 days. Furthermore, both non-cryopreserved and cryopreserved DRG neurons were susceptible to infection with two different strains of CDV, albeit only one of the two strains (CDV R252) provided sufficient absolute numbers of infected neurons. However, cryopreserved DRG neurons showed reduced cell yield, neurite outgrowth, neurite branching, and soma size and reduced susceptibility to CDV infection. In conclusion, canine primary DRG neurons represent a suitable tool for investigations upon the pathogenesis of neuronal CDV infection. Moreover, despite certain limitations, cryopreserved canine DRG neurons generally provide a useful and practicable alternative to address questions regarding virus tropism and neuropathogenesis.

Botulinum Neurotoxin Light Chains Expressed by Defective Herpes Simplex Virus Type-1 Vectors Cleave SNARE Proteins and Inhibit CGRP Release in Rat Sensory Neurons

A set of herpes simplex virus type 1 (HSV-1) amplicon vectors expressing the light chains (LC) of botulinum neurotoxins (BoNT) A, B, C, D, E and F was constructed. Their properties have been assessed in primary cultures of rat embryonic dorsal root ganglia (DRG) neurons, and in organotypic cultures of explanted DRG from adult rats. Following infection of primary cultures of rat embryonic DRG neurons, the different BoNT LC induced efficient cleavage of their corresponding target Soluble N-ethylmaleimide-sensitive-factor Attachment protein Receptor (SNARE) protein (VAMP, SNAP25, syntaxin). A similar effect was observed following infection by BoNT-A LC of organotypic cultures of adult rat DRG. To quantify and compare the functional activities of the different BoNT LC, the inhibition of calcitonin gene-related protein (CGRP) secretion was assessed in DRG neurons following infection by the different vectors. All BoNT-LC were able to inhibit CGRP secretion although to different levels. Vectors expressing BoNT-F LC displayed the highest inhibitory activity, while those expressing BoNT-D and -E LC induced a significantly lower CGRP release inhibition. Cleavage of SNARE proteins and inhibition of CGRP release could be detected in neuron cultures infected at less than one transducing unit (TU) per neuron, showing the extreme efficacy of these vectors. To our knowledge this is the first study investigating the impact of vector-expressed transgenic BoNT LC in sensory neurons.

Inner tegument proteins of Herpes Simplex Virus are sufficient for intracellular capsid motility in neurons but not for axonal targeting

Upon reactivation from latency and during lytic infections in neurons, alphaherpesviruses assemble cytosolic capsids, capsids associated with enveloping membranes, and transport vesicles harboring fully enveloped capsids. It is debated whether capsid envelopment of herpes simplex virus (HSV) is completed in the soma prior to axonal targeting or later, and whether the mechanisms are the same in neurons derived from embryos or from adult hosts. We used HSV mutants impaired in capsid envelopment to test whether the inner tegument proteins pUL36 or pUL37 necessary for microtubule-mediated capsid transport were sufficient for axonal capsid targeting in neurons derived from the dorsal root ganglia of adult mice. Such neurons were infected with HSV1-ΔUL20 whose capsids recruited pUL36 and pUL37, with HSV1-ΔUL37 whose capsids associate only with pUL36, or with HSV1-ΔUL36 that assembles capsids lacking both proteins. While capsids of HSV1-ΔUL20 were actively transported along microtubules in epithelial cells and in the somata of neurons, those of HSV1-ΔUL36 and -ΔUL37 could only diffuse in the cytoplasm. Employing a novel image analysis algorithm to quantify capsid targeting to axons, we show that only a few capsids of HSV1-ΔUL20 entered axons, while vesicles transporting gD utilized axonal transport efficiently and independently of pUL36, pUL37, or pUL20. Our data indicate that capsid motility in the somata of neurons mediated by pUL36 and pUL37 does not suffice for targeting capsids to axons, and suggest that capsid envelopment needs to be completed in the soma prior to targeting of herpes simplex virus to the axons, and to spreading from neurons to neighboring cells.

Zika virus tropism and interactions in myelinating neural cell cultures: CNS cells and myelin are preferentially affected

The recent global outbreak of Zika virus (ZIKV) infection has been linked to severe neurological disorders affecting the peripheral and central nervous systems (PNS and CNS, respectively). The pathobiology underlying these diverse clinical phenotypes are the subject of intense research; however, even the principal neural cell types vulnerable to productive Zika infection remain poorly characterised. Here we used CNS and PNS myelinating cultures from wild type and Ifnar1 knockout mice to examine neuronal and glial tropism and short-term consequences of direct infection with a Brazilian variant of ZIKV. Cell cultures were infected pre- or post-myelination for various intervals, then stained with cell-type and ZIKV-specific antibodies. In bypassing systemic immunity using ex vivo culture, and the type I interferon response in Ifnar1 deficient cells, we were able to evaluate the intrinsic infectivity of neural cells. Through systematic quantification of ZIKV infected cells in myelinating cultures, we found that ZIKV infection is enhanced in the absence of the type I interferon responses and that CNS cells are considerably more susceptible to infection than PNS cells. In particular, we demonstrate that CNS axons and myelinating oligodendrocytes are especially vulnerable to injury. These results have implications for understanding the pathobiology of neurological symptoms associated with ZIKV infection. Furthermore, we provide a quantifiable ex vivo infection model that can be used for fundamental and therapeutic studies on viral neuroinvasion and its consequences.

Elevated PrPC Expression Predisposes to Increased HSV-1 Pathogenicity

PrPC is a ubiquitously expressed glycophos-phatidylinositol-linked cell-surface glycoprotein found primarily in neural tissue. Although its normal function has not been established, there is evidence suggesting that PrPC is involved in cell signalling and cellular homeostasis. This suggests that variation in neuronal expression levels of this protein contributes towards pathogenicity induced by neurotropic agents. We have investigated the pathological response to infection with herpes simplex virus type-1 (HSV-1) in strains of mice that express different levels of PrPC. Prnp−/− mice fail to express PrPC due to an interruption in the open reading frame of the Prnp gene, whilst tg19 and tga20 mice express approximately 5 and 10 times more PrPC protein, respectively, than wild-type animals. Mice that express normal or increased levels of PrPC protein were more susceptible to acute HSV-1 infection than Prnp−/− mice. Following ear pinna inoculation with HSV-1 SC16, the order of susceptibility was tga20>tg19>wild-type> Prnp−/−. This trend was reversed when latent virus was assessed. Prnp−/− mice expressed significantly higher levels of latency-associated transcript-positive neurons in various tissues when compared with wild-type, tg19 and tga20 mice. Collectively, our data show that acute HSV-1 replication proceeds more efficiently in neuronal tissue that expresses PrPC protein and lends support to the view that this protein is involved in regulation of neurotropic viral pathogenesis. This suggests that interference of PrPC expression, or possible biochemical pathways associated with its function, may serve as an effective means of limiting the pathogenesis of acute HSV-1 infection.

Viral Spread to Enteric Neurons Links Genital HSV-1 Infection to Toxic Megacolon and Lethality

Herpes simplex virus 1 (HSV-1), a leading cause of genital herpes, infects oral or genital mucosal epithelial cells before infecting the peripheral sensory nervous system. The spread of HSV-1 beyond the sensory nervous system and the resulting broader spectrum of disease are not well understood. Using a mouse model of genital herpes, we found that HSV-1-infection-associated lethality correlated with severe fecal and urinary retention. No inflammation or infection of the brain was evident. Instead, HSV-1 spread via the dorsal root ganglia to the autonomic ganglia of the enteric nervous system (ENS) in the colon. ENS infection led to robust viral gene transcription, pathological inflammatory responses, and neutrophil-mediated destruction of enteric neurons, ultimately resulting in permanent loss of peristalsis and the development of toxic megacolon. Laxative treatment rescued mice from lethality following genital HSV-1 infection. These results reveal an unexpected pathogenesis of HSV associated with ENS infection.

Neuronal Subtype and Satellite Cell Tropism Are Determinants of Varicella-Zoster Virus Virulence in Human Dorsal Root Ganglia Xenografts In Vivo

Varicella zoster virus (VZV), a human alphaherpesvirus, causes varicella during primary infection. VZV reactivation from neuronal latency may cause herpes zoster, post herpetic neuralgia (PHN) and other neurologic syndromes. To investigate VZV neuropathogenesis, we developed a model using human dorsal root ganglia (DRG) xenografts in immunodeficient (SCID) mice. The SCID DRG model provides an opportunity to examine characteristics of VZV infection that occur in the context of the specialized architecture of DRG, in which nerve cell bodies are ensheathed by satellite glial cells (SGC) which support neuronal homeostasis. We hypothesized that VZV exhibits neuron-subtype specific tropism and that VZV tropism for SGC contributes to VZV-related ganglionopathy. Based on quantitative analyses of viral and cell protein expression in DRG tissue sections, we demonstrated that, whereas DRG neurons had an immature neuronal phenotype prior to implantation, subtype heterogeneity was observed within 20 weeks and SGC retained the capacity to maintain neuronal homeostasis longterm. Profiling VZV protein expression in DRG neurons showed that VZV enters peripherin+ nociceptive and RT97+ mechanoreceptive neurons by both axonal transport and contiguous spread from SGC, but replication in RT97+ neurons is blocked. Restriction occurs even when the SGC surrounding the neuronal cell body were infected and after entry and ORF61 expression, but before IE62 or IE63 protein expression. Notably, although contiguous VZV spread with loss of SGC support would be predicted to affect survival of both nociceptive and mechanoreceptive neurons, RT97+ neurons showed selective loss relative to peripherin+ neurons at later times in DRG infection. Profiling cell factors that were upregulated in VZV-infected DRG indicated that VZV infection induced marked pro-inflammatory responses, as well as proteins of the interferon pathway and neuroprotective responses. These neuropathologic changes observed in sensory ganglia infected with VZV may help to explain the neurologic sequelae often associated with zoster and PHN.

Varicella zoster virus (VZV) causes varicella; herpes zoster results from VZV reactivation and is associated with post herpetic neuralgia (PHN). We hypothesized that VZV exhibits neuron-subtype specific tropism and that VZV tropism for satellite glial cells (SGC) results in loss of SGC functions that support neurons and contributes to VZV-related ganglionopathy. Using human DRG xenografts in SCID mice, we demonstrated that initial VZV access to neuronal cell bodies occurs by the axonal route, followed by axonal and contiguous spread between neuron-satellite cell complexes. VZV replication is restricted in mechanoreceptive neurons compared to nociceptive neurons. Despite restricted infection, mechanoreceptive neurons were selectively depleted in association with SGC loss following acute DRG infection. VZV infection of DRG triggers release of pro-inflammatory cytokines that cause neuronal damage. These observations may help to explain the neurologic sequelae often associated with herpes zoster and PHN.

In vivo gene knockdown in rat dorsal root ganglia mediated by self-complementary adeno-associated virus serotype 5 following intrathecal delivery

We report here in adult rat viral vector mediate-gene knockdown in the primary sensory neurons and the associated cellular and behavior consequences. Self-complementary adeno-associated virus serotype 5 (AAV5) was constructed to express green fluorescent protein (GFP) and a small interfering RNA (siRNA) targeting mammalian target of rapamycin (mTOR). The AAV vectors were injected via an intrathecal catheter. We observed profound GFP expression in lumbar DRG neurons beginning at 2-week post-injection. Of those neurons, over 85% were large to medium-diameter and co-labeled with NF200, a marker for myelinated fibers. Western blotting of mTOR revealed an 80% reduction in the lumbar DRGs (L4–L6) of rats treated with the active siRNA vectors compared to the control siRNA vector. Gene knockdown became apparent as early as 7-day post-injection and lasted for at least 5 weeks. Importantly, mTOR knockdown occurred in large (NF200) and small-diameter neurons (nociceptors). The viral administration induced an increase of Iba1 immunoreactivity in the DRGs, which was likely attributed to the expression of GFP but not siRNA. Rats with mTOR knockdown in DRG neurons showed normal general behavior and unaltered responses to noxious stimuli. In conclusion, intrathecal AAV5 is a highly efficient vehicle to deliver siRNA and generate gene knockdown in DRG neurons. This will be valuable for both basic research and clinic intervention of diseases involving primary sensory neurons.

Latency of varicella zoster virus in dorsal root, cranial, and enteric ganglia in vaccinated children

Despite vaccination, varicella-zoster virus (VZV) remains an important pathogen. We investigated VZV latency in autopsy specimens from vaccinees, in gastrointestinal tissue removed surgically, and in a guinea pig model. We propose that retrograde transport from infected skin and viremia deliver VZV to neurons in which it becomes latent. Wild type (WT) VZV was found to be latent in many ganglia of vaccinated children with no history of varicella, suggesting that subclinical infection with WT-VZV occurs with subsequent viremic dissemination. The 30% to 40% rate of WT-VZV zoster reported in vaccinees and occasional trigeminal zoster due to vaccine type VZV (vOka) are consistent with viremic delivery of VZV to multiple ganglia. Most human intestinal specimens contained latent VZV within neurons of the enteric nervous system (ENS). Induction of viremia in guinea pigs led to VZV latency throughout the ENS. The possibility VZV reactivation in the ENS is an unsuspected cause of gastrointestinal disease requires future investigation.

Varicella zoster virus-induced pain and post-herpetic neuralgia in the human host and in rodent animal models

Pain and post-herpetic neuralgia (PHN) are common and highly distressing complications of herpes zoster that remain a significant public health concern and in need of improved therapies. Zoster results from reactivation of the herpesvirus varicella zoster virus (VZV) from a neuronal latent state established at the primary infection (varicella). PHN occurs in some one fifth to one third of zoster cases with severity, incidence, and duration of pain increasing with rising patient age. While VZV reactivation and the ensuing ganglionic damage trigger the pain response, the mechanisms underlying protracted PHN are not understood, and the lack of an animal model of herpes zoster (reactivation) makes this issue more challenging. A recent preclinical rodent model has developed that opens up the potential to allow the exploration of the underlying mechanisms and treatments for VZV-induced pain. Rats inoculated with live cell-associated human VZV into the hind paw reliably demonstrate thermal hyperalgesia and mechanical allodynia for extended periods and then spontaneously recover. Dorsal root ganglia express a limited VZV gene subset, including the IE62 regulatory protein, and upregulate expression of markers suggesting a neuropathic pain state. The model has been used to investigate treatment modalities and aspects of pain signaling and is under investigation by the authors to delineate VZV genetics involved in the induction of pain. This article compares human zoster-associated pain and PHN to the pain indicators in the rat and poses important questions that, if answered, could be the basis for new treatments.

Molecular studies of the Oka varicella vaccine

Varicella zoster virus (VZV) is one of eight members of the Herpesviridae family for which humans are the primary host; it causes two distinct diseases, varicella (chickenpox) and zoster (shingles). Varicella results from primary infection, during which the virus establishes latency in sensory neurons, a characteristic of all members of the Alphaherpesvirinae subfamily. Zoster is caused by reactivation of latent virus, which typically occurs when cellular immunity is impaired. VZV is the first human herpesvirus for which a vaccine has been licensed. The vaccine preparation, v-Oka, is a live-attenuated virus stock produced by the classic method of tissue culture passage in animal and human cell lines. Over 90 million doses of the vaccine have been administered in countries worldwide, including the USA, where varicella morbidity and mortality has declined dramatically. Over the last decade, several laboratories have been committed to investigating the mechanism by which the Oka vaccine is attenuated. Mutations have accumulated across the genome of the vaccine during the attenuation process; however, studies of the contribution of these changes to vaccine attenuation have been hampered by the lack of a suitable animal model of VZV disease and by the heterogeneity that exists among the viral population within the vaccine preparation. Notwithstanding, a wealth of data has been generated using various laboratory methodologies. Studies of the vaccine virus in human xenografts implanted in severe combined immunodeficiency-hu mice, have enabled analyses of the replication dynamics of the vaccine in dorsal root ganglia, T lymphocytes and skin. In vitro assays have been used to investigate the effect of vaccine mutations on viral gene expression and sequence analysis of vaccine rash viruses has permitted investigations into spread of the vaccine virus in a human host. We present here a review of what has been learned thus far about the molecular and phenotypic characteristics of the Oka vaccine.

Viral genome silencing by neuronal sirtuin 1

Neurotropic viruses remain dormant in sensory neurons for years, but upon reactivation, they can produce multiple disease states including pain symptoms. Latent viral DNA is extrachromosomal, maintained as a circular episome bound to histones. Here, we show the regulation of an adenoviral genome by the nicotinamide adenine dinucleotide (NAD(+))-dependent histone deacetylator Sirt1 in dorsal root ganglion neurons. Pharmacological modulation of Sirt1 and Sirt1 overexpression both affected viral transgene expression. We propose that age or stress-related neuronal NAD(+) depletion may be a trigger for viral reactivation.

Efficient retrograde transport of adeno-associated virus type 8 to spinal cord and dorsal root ganglion after vector delivery in muscle

The peripheral nervous system (PNS), including peripheral nerves and dorsal root ganglion (DRG), is involved in numerous neurological disorders, such as peripheral neuropathies (diabetic neuropathy, chronic pain, etc.) and demyelination diseases (multiple sclerosis, congenital muscular dystrophy, Charcot-Marie-Tooth disease, etc.). Effective clinical interventions for those diseases are very limited. Gene therapy represents a novel therapeutic strategy for the PNS diseases, especially with simply and minimally invasive delivery methods. Previously, we have shown that adeno-associated virus type 8 (AAV8) can efficiently transduce muscles body wide by a simple intraperitoneal injection in neonatal mice. In this study, we investigated the capacity of AAV8 in transducing PNS in neonatal mice by intraperitoneal injection and also in adult mice by intramuscular injection. Efficient and long-term gene transfer was found in the white matter of the spinal cord, DRG neurons, and peripheral nerves in both groups, treated either as neonates or as adults, particularly neonates. In the adult mice injected with AAV8 in tibialis anterior and gastrocnemius muscles in one of the hind legs, more neurons were transduced in the lower part of the spinal cord than in the upper part; the DRG neurons were transduced more on the vector-injected side than in the contralateral uninjected side. Few cells in the gray matter of the spinal cord were transduced regardless of the delivery methods and age of the mice. These results support the mechanism of vector retrograde transport and suggest that AAV8 crosses blood-nerve barrier poorly. Our finding should have important implications in gene therapy for peripheral neurological disorders.

CAR-associated vesicular transport of an adenovirus in motor neuron axons

Axonal transport is responsible for the movement of signals and cargo between nerve termini and cell bodies. Pathogens also exploit this pathway to enter and exit the central nervous system. In this study, we characterised the binding, endocytosis and axonal transport of an adenovirus (CAV-2) that preferentially infects neurons. Using biochemical, cell biology, genetic, ultrastructural and live-cell imaging approaches, we show that interaction with the neuronal membrane correlates with coxsackievirus and adenovirus receptor (CAR) surface expression, followed by endocytosis involving clathrin. In axons, long-range CAV-2 motility was bidirectional with a bias for retrograde transport in nonacidic Rab7-positive organelles. Unexpectedly, we found that CAR was associated with CAV-2 vesicles that also transported cargo as functionally distinct as tetanus toxin, neurotrophins, and their receptors. These results suggest that a single axonal transport carrier is capable of transporting functionally distinct cargoes that target different membrane compartments in the soma. We propose that CAV-2 transport is dictated by an innate trafficking of CAR, suggesting an unsuspected function for this adhesion protein during neuronal homeostasis.

Adenoviruses commonly cause subclinical morbidity in the ocular, respiratory, and gastrointestinal tracts, and less frequently, adenovirus-induced disease can be fatal for newborns and immunocompromised hosts. In addition, adenoviruses can reach the central nervous system (CNS) and cause associated encephalitis and tumours. On the flip side, during the last two decades, adenovirus vectors have become powerful tools to treat and address diseases of the CNS. Despite the fact that axonal transport of adenoviruses was reported more than 15 years ago, nothing was known concerning how adenoviruses access the CNS. The characterization of their interactions with brain cells was therefore long overdue. In this study, we describe the axonal trafficking of an adenovirus that preferentially infects neurons and reaches the CNS through long-range axonal transport. We show that this adenovirus exploits an endogenous vesicular pathway used by the adhesion molecule CAR (coxsackievirus and adenovirus receptor). Our study characterizes this endogenous route of access, which is likely to be crucial to neuronal survival, neurodegenerative diseases, gene transfer vectors, and adenovirus-induced morbidity.

In vitro propagation of rabies virus in mouse dorsal root ganglia cells

Rabies virus (RV) is highly neurotropic and migrates to the neuronal soma by retrograde axonal transport from nerve terminals, after which it is taken by anterograde axonal transport to be finally released into the central nervous system (CNS) from which it disseminates, resulting in lethal encephalitis. Dorsal root ganglia (DRG) are crucial in the initial events of the infection by RV since they can act as a gate for the viral entrance into the CNS. In the present study, we examined cell tropism of RV and the roles of neuronal cytoskeletal components in the production of viral nucleoprotein (N protein) using cultured nerve cells and non-neuronal cells from DRG of newborn mice. Our in vitro study demonstrated a low propagation rate of RV in nerve cells, susceptibility of non-neuronal cells to RV, and independence of cytoplasmic synthesis of viral N protein from the neuronal cytoskeleton. The present study also suggests that Schwann cells should be considered as another possible candidate supporting RV propagation.

The rabies virus glycoprotein receptor p75NTR is not essential for rabies virus infection

Rabies virus glycoprotein (RVG) is known to be the only factor that mediates rabies infection. The neurotrophin receptor (p75(NTR)), through its cysteine-rich domain 1, is a specific receptor for RVG and neutralizes virus infectivity, but its role in virus infection has remained obscure. We used adult mouse dorsal root ganglion (DRG) neurons as a model to study the role of p75(NTR) in RV infection of primary neurons. We show that RV infects around 20% of DRG neurons, of which more than 80% are p75(NTR) positive, have large diameters, and are capsaicin insensitive. Surprisingly, RV binding and infection are absent in about half of the p75(NTR)-expressing DRG neurons which have small diameters and are often capsaicin sensitive. This indicates that p75(NTR) is not sufficient to mediate RV interaction in sensory neurons. The rate and specificity of neural infection are unchanged in RV-infected p75(NTRExonIV-/-) mice that lack all extracellular receptor domains and in wild-type mice infected with two independent RV mutants that lack p75(NTR) binding. Accordingly, the mortality rate is unchanged in the absence of RV-p75(NTR) interaction. We conclude that although p75(NTR) is a receptor for soluble RVG in transfected cells of heterologous expression systems, an RVG-p75(NTR) interaction is not necessary for RV infection of primary neurons. This means that other receptors are required to mediate RV infection in vivo and in vitro.

Morphological and biochemical characterisation of sensory neurons infected in vitro with rabies virus

This work was aimed at the morphological and biochemical characterisation of the most susceptible neuronal subpopulation to rabies virus (RABV) infection. Adult mouse DRG cultures were infected with RABV and double-processed for viral antigen detection and neuropeptides: calcitonin gene-related peptide (CGRP), galanin (GAL), substance P (SP), neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP). It was found that 56% of the neurons in culture were small (diameter < 20 microm) but, in spite of this, 69% of the infected neurons had intermediate and large diameters (> or = 20 microm). More than 50% of infected neurons expressed NPY, VIP or SP, whereas no association was found between infected neurons and the presence of CGRP or GAL. Despite SP having been shown to be a small neuron marker, it was found that RABV infects medium and large-sized SP positive cells. RABV preference for larger neurons could explain part of the neuropathogenesis since it can be suggested that, following a rabid accident, the virus uses large neurons (mainly innervating muscle and joints) in vivo to be transported later on to the central nervous system.

Aberrant infection and persistence of varicella-zoster virus in human dorsal root ganglia in vivo in the absence of glycoprotein I

Varicella-zoster virus (VZV) causes varicella, establishes latency in sensory ganglia, and reactivates as herpes zoster. Human dorsal root ganglia (DRGs) xenografts in immunodeficient mice provide a model for evaluating VZV neuropathogenesis. Our investigation of the role of glycoprotein I (gI), which is dispensable in vitro, examines the functions of a VZV gene product during infection of human neural cells in vivo. Whereas intact recombinant Oka (rOka) initiated a short replicative phase followed by persistence in DRGs, the gI deletion mutant, rOkaDeltagI, showed prolonged replication with no transition to persistence up to 70 days after infection. Only a few varicella-zoster nucleocapsids and cytoplasmic virions were observed in neurons, and the major VZV glycoprotein, gE, was retained in the rough endoplasmic reticulum in the absence of gI. VZV neurotropism was not disrupted when DRG xenografts were infected with rOka mutants lacking gI promoter elements that bind cellular transactivators, specificity factor 1 (Sp1) and upstream stimulatory factor (USF). Because gI is essential and Sp1 and USF contribute to VZV pathogenesis in skin and T cells in vivo, these DRG experiments indicate that the genetic requirements for VZV infection are less stringent in neural cells in vivo. The observations demonstrate that gI is important for VZV neurotropism and suggest that a strategy to reduce neurovirulence by deleting gI could prolong active infection in human DRGs.

Herpes simplex virus vector-mediated delivery of glial cell line-derived neurotrophic factor rescues erectile dysfunction following cavernous nerve injury

Erectile dysfunction (ED) is frequently associated with injury to the cavernous nerve sustained during pelvic surgery. Functional recovery from cavernous nerve injury is generally incomplete and occurs over an extended time frame. We employed a therapeutic gene transfer approach with herpes simplex virus (HSV) vector expressing glial cell line-derived neurotrophic factor (GDNF). Rat cavernous nerve was injured bilaterally using a clamp and dry ice. For HSV-treated groups, 20 microl of purified vector stock was administered directly to and around the damaged nerve. Delivery of an HSV vector expressing both green fluorescent protein (GFP) and lacZ (HSV-LacZ) was used as a control. Intracavernous pressure along with systemic arterial pressure (ICP/AP) was measured 2 and 4 weeks after the nerve injury. Fluorogold (FG) was injected into the penile crus 7 days before killing to assess nerve survival. Approximately 60% of major pelvic ganglion (MPG) cells were GFP positive after viral administration. At 4 weeks after nerve injury, rats treated with HSV-GDNF exhibited significant recovery of ICP/AP compared with control vector or untreated groups. The HSV-GDNF group also yielded more FG-positive MPG cells than the control vector group. HSV vector-mediated delivery of GDNF presents a viable approach for the treatment of ED following cavernous nerve injury.

NK cell-mediated destruction of influenza A virus-infected peripheral but not central neurones

Peripheral neurones have the potential to transmit infectious agents to the central nervous system (CNS). This raises the possibility of existing host defence mechanisms that may prevent such spread. Natural killer (NK) cells can target infected cells, and by this ability serve to limit spread of infection prior to the development of adaptive immune responses. To address directly if NK cells can target infected peripheral neurones, we examined the expression of NK cell-activating ligands and susceptibility to NK cell-mediated cytolytic effects in ex vivo cultures of mouse peripheral dorsal root ganglia (DRG) neurones prior to and after infection with a neurotropic strain of influenza A virus, WSN/33. In infected DRG cultures, retinoic acid early inducible gene-1 (RAE-1) transcripts were induced and exposure to interleukin (IL)-2-activated NK cells resulted in a total destruction of neurites. Studies on cultures from interferon (IFN)-alpha/betaR-deficient mice suggest that the infection engages an IFN-alpha/beta-dependent signalling pathway to induce RAE-1 transcripts. In contrast, induction of RAE-1 transcripts or NK cell-mediated neurite destructions was not observed in central hippocampal neurones. This reveals distinct properties between peripheral DRG and central hippocampal neurones with respect to the ability to signal for immune destruction following infection.

Diverse herpes simplex virus type 1 thymidine kinase mutants in individual human neurons and Ganglia

Mutations in the thymidine kinase gene (tk) of herpes simplex virus type 1 (HSV-1) explain most cases of virus resistance to acyclovir (ACV) treatment. Mucocutaneous lesions of patients with ACV resistance contain mixed populations of tk mutant and wild-type virus. However, it is unknown whether human ganglia also contain mixed populations since the replication of HSV tk mutants in animal neurons is impaired. Here we report the detection of mutated HSV tk sequences in human ganglia. Trigeminal and dorsal root ganglia were obtained at autopsy from an immunocompromised woman with chronic mucocutaneous infection with ACV-resistant HSV-1. The HSV-1 tk open reading frames from ganglia were amplified by PCR, cloned, and sequenced. tk mutations were detected in a seven-G homopolymer region in 11 of 12 ganglia tested, with clonal frequencies ranging from 4.2 to 76% HSV-1 tk mutants per ganglion. In 8 of 11 ganglia, the mutations were heterogeneous, varying from a deletion of one G to an insertion of one to three G residues, with the two-G insertion being the most common. Each ganglion had its own pattern of mutant populations. When individual neurons from one ganglion were analyzed by laser capture microdissection and PCR, 6 of 14 HSV-1-positive neurons were coinfected with HSV tk mutants and wild-type virus, 4 of 14 were infected with wild-type virus alone, and 4 of 14 were infected with tk mutant virus alone. These data suggest that diverse tk mutants arise independently under drug selection and establish latency in human sensory ganglia alone or together with wild-type virus.

Ultrastructural description of rabies virus infection in cultured sensory neurons

Primary cultures were made from adult mouse spinal ganglia for depicting an ultrastructural description of rabies virus (RABV) infection in adult mouse sensory neuron cultures; they were infected with rabies virus for 24, 36, and 48 h. The monolayers were processed for transmission electron microscopy and immunochemistry studies at the end of each period. As previously reported, sensory neurons showed great susceptibility to infection by RABV; however, in none of the periods evaluated were assembled virions observed in the cytoplasm or seen to be associated with the cytoplasmic membrane. Instead, fibril matrices of aggregated ribonucleoprotein were detected in the cytoplasm. When infected culture lysate were inoculated into normal animals via intra-cerebral route it was observed that these animals developed clinical symptoms characteristic of infection and transmission electron microscopy revealed assembled virions in the cerebral cortex and other areas of the brain. Sensory neurons infected in vitro by RABV produced a large amount of unassembled viral ribonucleoprotein. However, this intracellular material was able to produce infection and virions on being intra-cerebrally inoculated. It can thus be suggested that the lack of intracellular assembly in sensory neurons forms part of an efficient dissemination strategy.

Herpes simplex virus latency-associated transcript sequence downstream of the promoter influences type-specific reactivation and viral neurotropism

Herpes simplex virus (HSV) establishes latency in sensory nerve ganglia during acute infection and may later periodically reactivate to cause recurrent disease. HSV type 1 (HSV-1) reactivates more efficiently than HSV-2 from trigeminal ganglia while HSV-2 reactivates more efficiently than HSV-1 from lumbosacral dorsal root ganglia (DRG) to cause recurrent orofacial and genital herpes, respectively. In a previous study, a chimeric HSV-2 that expressed the latency-associated transcript (LAT) from HSV-1 reactivated similarly to wild-type HSV-1, suggesting that the LAT influences the type-specific reactivation phenotype of HSV-2. To further define the LAT region essential for type-specific reactivation, we constructed additional chimeric HSV-2 viruses by replacing the HSV-2 LAT promoter (HSV2-LAT-P1) or 2.5 kb of the HSV-2 LAT sequence (HSV2-LAT-S1) with the corresponding regions from HSV-1. HSV2-LAT-S1 was impaired for reactivation in the guinea pig genital model, while its rescuant and HSV2-LAT-P1 reactivated with a wild-type HSV-2 phenotype. Moreover, recurrences of HSV-2-LAT-S1 were frequently fatal, in contrast to the relatively mild recurrences of the other viruses. During recurrences, HSV2-LAT-S1 DNA increased more in the sacral cord compared to its rescuant or HSV-2. Thus, the LAT sequence region, not the LAT promoter region, provides essential elements for type-specific reactivation of HSV-2 and also plays a role in viral neurotropism. HSV-1 DNA, as quantified by real-time PCR, was more abundant in the lumbar spinal cord, while HSV-2 DNA was more abundant in the sacral spinal cord, which may provide insights into the mechanism for type-specific reactivation and different patterns of central nervous system infection of HSV-1 and HSV-2.

Productive varicella-zoster virus infection of cultured intact human ganglia

Varicella-zoster virus (VZV) is a species-specific herpesvirus which infects sensory ganglia. We have developed a model of infection of human intact explant dorsal root ganglia (DRG). Following exposure of DRG to VZV, viral antigens were detected in neurons and nonneuronal cells. Enveloped virions were visualized by transmission electron microscopy in neurons and nonneuronal cells and within the extracellular space. Moreover, rather than remaining highly cell associated during infection of cultured cells, such as fibroblasts, cell-free VZV was released from infected DRG. This model enables VZV infection of ganglionic cells to be studied in the context of intact DRG.

Two alphaherpesvirus latency-associated gene products influence calcitonin gene-related peptide levels in rat trigeminal neurons

Herpes simplex virus type-1 (HSV-1) initially infects mucoepithelial tissues of the eye and the orofacial region. Subsequently, the virus is retrogradely transported through the axons of the trigeminal sensory neurons. HSV-1 establishes a life-long latent infection in these neurons, during which the transcription of the viral genome is silent, except for the sequences encoding the latency-associated transcript (LAT). To determine if HSV-1 latency might affect calcitonin gene-related peptide (CGRP) expression in trigeminal sensory neurons, we transfected primary neuronal cultures of trigeminal ganglia from rat embryos with plasmids expressing LAT. In the presence of Bone Morphogenetic Protein-7 (BMP7), CGRP was expressed in 49% of sensory neurons. However, this percentage was reduced to 19% in neurons transfected with LAT expressing plasmids. We also found that transfection of the IE63 gene of varicella-zoster virus (VZV) reduced the percentage of trigeminal neurons containing CGRP. However, the observed effect of IE63 in contrast to that of LAT was completely reversed by treatment of cultures with MgCl2, which indicates that the effect of IE63 was due to increased release of CGRP from trigeminal neurons. We provide here the first evidence that HSV-1 LAT decreases the level of CGRP in trigeminal neurons. These effects may be important for reducing the neuroinflammatory response, thus protecting host neuronal cells during HSV-1 latency in trigeminal neurons. In contrast, increased release of CGRP in the presence of IE63 protein may contribute to the neuralgias associated with VZV infection.

Pathogenesis of cytomegalovirus-associated labyrinthitis in a guinea pig model

Cytomegalovirus infects fetuses through the placenta, resulting in various congenital disorders in newborns, including hearing loss. We developed a monoclonal antibody to guinea pig cytomegalovirus (GPCMV) that was available for immunohistochemistry, and investigated the expression of the GPCMV antigen in animal models of direct and congenital infections. Injection of GPCMV, directly to the inner ear, increased the sound pressure level and resulted in labyrinthitis with severe inflammation. Immunohistochemistry detected GPCMV-infected cells mainly in the scala tympani, scala vestibule and spinal ganglion, but rarely in the cochlear duct. Injection of GPCMV to 5-week pregnant guinea pigs resulted in severe labyrinthitis in fetuses. Immunohistochemistry detected GPCMV-infected cells in the perilymph area and spinal ganglion, but not in the endolymph area, including hair cells. These data suggest that the virus spreads via the perilymph and neural routes in the inner ear of both models of direct and congenital infections.

Latency of alpha-herpes viruses is accompanied by a chronic inflammation in human trigeminal ganglia but not in dorsal root ganglia

The immune response to latent herpesvirus infections was compared in human trigeminal ganglia (TG) and dorsal root ganglia (DRG) of 15 dead individuals. On the basis of our previous findings, we hypothesized that T-cells would be attracted to sensory neurons latently infected with herpes simplex virus type 1 (HSV-1), but not to those harboring latent varicella zoster virus (VZV). We showed that the TG contain a positive hybridization signal for HSV-1 latency-associated transcript (LAT), whereas the DRG from the same individuals lack detectable LAT. In contrast, immunohistochemistry revealed that latent VZV protein 62 stained positive in the vast majority of all tested TG and DRG. T-cell infiltrates prominently surrounded individual neurons in the TG but not in the DRG. TaqMan polymerase chain reaction also showed higher expression of CD8 and RANTES transcripts in the TG versus DRG. Only the infiltrates in the TG, but not in the DRG, produced RANTES at the protein level. Because it has been shown that RANTES protein is produced only after T-cell receptor stimulation, we assume that T-cell infiltration is associated with antigen recognition in the TG but not in the DRG.

The cycle of human herpes simplex virus infection: virus transport and immune control

After infection of skin or mucosa, herpes simplex virus enters the sensory nerve endings and is conveyed by retrograde axonal transport to the dorsal root ganglion, where the virus develops lifelong latency. Intermittent reactivation, which is spontaneous in humans, leads to anterograde transport of virus particles and proteins to the skin or mucosa, where the virus is shed and/or causes disease. Immune control of viral infection and replication occurs at the level of skin or mucosa during initial or recurrent infection and also within the dorsal root ganglion, where immune mechanisms control latency and reactivation. This article examines current views on the mechanisms of retrograde and anterograde transport of the virus in axons and the mechanisms of innate and adaptive immunity that control infection in the skin or mucosa and in the dorsal root ganglion--in particular, the role of interferons, myeloid and plasmacytoid dendritic cells, CD4(+) and CD8(+) T cells, and interferon- gamma and other cytokines, including their significance in the development of vaccines for genital herpes.

Temporal analyses of the neuropathogenesis of a West Nile virus infection in mice

A West Nile virus (WNV) infection in humans can produce neurological symptoms including acute flaccid paralysis, encephalitis, meningitis and myelitis. To investigate the pathogenesis of WNV in the peripheral and the central nervous system (PNS and CNS), the authors used a murine footpad inoculation model of WNV infection. Survival curves of virus-infected animals of ages 4- to 6-weeks-old demonstrated age-dependent mortality where older animals (6-weeks-old) had a higher mortality rate compared to younger animals (4- and 5-weeks-old). The mice that survived the virus infection formed WNV-reactive antibodies, confirming viral infection and clearance. The localization of viral RNA (vRNA) and antigen in infected murine tissues was investigated using TaqMan and immunohistochemistry (IHC) respectively. During a nine day infection, vRNA levels in the spinal cord and brainstem fluctuated, suggesting early viral clearance from these tissues by days 3-4 p.i. with later re-introduction. Viral antigens detected using IHC were primarily observed in three main regions of the brain: cortex, hippocampus and brainstem. Additionally, the dorsal root ganglion neurons of the PNS stained positive for viral antigens. These data are consistent with multiple routes of neuroinvasion following a peripheral inoculation of virus and do not preclude the previous observation that virus-infected peripheral neurons can introduce virus into the CNS by a retrograde transport mechanism.

Major histocompatibility complex haplotype is associated with postherpetic pain in mice

BACKGROUND

Postherpetic neuralgia is one of the major complications of herpes zoster caused by the reactivation of varicella-zoster virus and is characterized by severe pain. The authors previously showed the association of a human major histocompatibility complex (MHC) haplotype with postherpetic neuralgia. This study was performed to experimentally confirm the role of MHC haplotype in the development of postherpetic pain using a mouse model of postherpetic pain, which corresponds to postherpetic neuralgia.

METHODS

BALB/c mice (MHC haplotype: H-2), C57BL/6 mice (MHC haplotype: H-2), and BALB/b mice, a congenic BALB/c strain with H-2, were used. Herpes simplex virus type I was transdermally inoculated on the hind paw. Unilaterally zosteriform skin lesion and pain-related responses (acute herpetic pain) were caused, and some mice showed pain-related responses (postherpetic pain) after the cure of skin lesions. Herpes simplex virus type I antigen and CD3-positive cells were immunostained in the dorsal root ganglion in the acute phase.

RESULTS

The incidence (78%) of postherpetic pain in C57BL/6 mice was significantly higher than that (35%) in BALB/c mice (P = 0.004, odds ratio = 6.7). Furthermore, the incidence of postherpetic pain in BALB/b (H-2) was similar to that in C57BL/6. Herpes simplex virus type I antigen-positive cells were less in the dorsal root ganglion of C57BL/6 mice than that of BALB/c mice. CD3-positive T cells were more in the dorsal root ganglion of C57BL/6 mice than BALB/c mice.

CONCLUSIONS

These results suggest that the MHC haplotype (H-2) is involved in the incidence of postherpetic pain, and CD3-positive T cells may play a role in its pathogenesis.

Downregulation of varicella-zoster virus (VZV) immediate-early ORF62 transcription by VZV ORF63 correlates with virus replication in vitro and with latency

Varicella-zoster virus (VZV) open reading frame 63 (ORF63) protein is expressed during latency in human sensory ganglia. Deletion of ORF63 impairs virus replication in cell culture and establishment of latency in cotton rats. We found that cells infected with a VZV ORF63 deletion mutant yielded low titers of cell-free virus and produced very few enveloped virions detectable by electron microscopy compared with those infected with parental virus. Microarray analysis of cells infected with a recombinant adenovirus expressing ORF63 showed that transcription of few human genes was affected by ORF63; a heat shock 70-kDa protein gene was downregulated, and several histone genes were upregulated. In experiments using VZV transcription arrays, deletion of ORF63 from VZV resulted in a fourfold increase in expression of ORF62, the major viral transcriptional activator. A threefold increase in ORF62 protein was observed in cells infected with the ORF63 deletion mutant compared with those infected with parental virus. Cells infected with ORF63 mutants impaired for replication and latency (J. I. Cohen, T. Krogmann, S. Bontems, C. Sadzot-Delvaux, and L. Pesnicak, J. Virol. 79:5069-5077, 2005) showed an increase in ORF62 transcription compared with those infected with parental virus. In contrast, cells infected with an ORF63 mutant that is not impaired for replication or latency showed ORF62 RNA levels equivalent to those in cells infected with parental virus. The ability of ORF63 to downregulate ORF62 transcription may play an important role in virus replication and latency.

Herpes simplex virus type 1 accumulation, envelopment, and exit in growth cones and varicosities in mid-distal regions of axons

The mechanism of anterograde transport of alphaherpesviruses in axons remains controversial. This study examined the transport, assembly, and egress of herpes simplex virus type 1 (HSV-1) in mid- and distal axons of infected explanted human fetal dorsal root ganglia using confocal microscopy and transmission electron microscopy (TEM) at 19, 24, and 48 h postinfection (p.i.). Confocal-microscopy studies showed that although capsid (VP5) and tegument (UL37) proteins were not uniformly present in axons until 24 h p.i., they colocalized with envelope (gG) proteins in axonal varicosities and in growth cones at 24 and 48 h p.i. TEM of longitudinal sections of axons in situ showed enveloped and unenveloped capsids in the axonal varicosities and growth cones, whereas in the midregion of the axons, predominantly unenveloped capsids were observed. Partially enveloped capsids, apparently budding into vesicles, were observed in axonal varicosities and growth cones, but not during viral attachment and entry into axons. Tegument proteins (VP22) were found associated with vesicles in growth cones, either alone or together with envelope (gD) proteins, by transmission immunoelectron microscopy. Extracellular virions were observed adjacent to axonal varicosities and growth cones, with some virions observed in crescent-shaped invaginations of the axonal plasma membrane, suggesting exit at these sites. These findings suggest that varicosities and growth cones are probable sites of HSV-1 envelopment of at least a proportion of virions in the mid- to distal axon. Envelopment probably occurs by budding of capsids into vesicles with associated tegument and envelope proteins. Virions appear to exit from these sites by exocytosis.

Deacetylation of the herpes simplex virus type 1 latency-associated transcript (LAT) enhancer and a decrease in LAT abundance precede an increase in ICP0 transcriptional permissiveness at early times postexplant

Only the latency-associated transcript (LAT) of the herpes simplex virus type 1 (HSV-1) genome is transcribed during latency, while the lytic genes are suppressed, possibly by LAT antisense mechanisms and/or chromatin modifications. In the present study, latently infected dorsal root ganglia were explanted to assess both relative levels of LAT and histone H3 (K9, K14) acetylation of the LAT locus and ICP0 promoter at early times postexplant. We observed that a decrease in both LAT enhancer histone H3 (K9, K14) acetylation and LAT RNA abundance occurs prior to an increase in acetylation, or transcriptional permissiveness, at the ICP0 promoter.

HSV-mediated expression of interleukin-4 in dorsal root ganglion neurons reduces neuropathic pain

BACKGROUND

To examine the role of inflammatory mediators in neuropathic pain, we used a replication-defective genomic herpes simplex virus (HSV)-based vector containing the coding sequence for the anti-inflammatory peptide interleukin (IL)-4 under the transcriptional control of the HSV ICP4 immediate early promoter, vector S4IL4, to express IL-4 in dorsal root ganglion (DRG) neurons in vivo.

RESULTS

Subcutaneous inoculation of S4IL4 in the foot transduced lumbar DRG to produce IL-4. Transgene-mediated expression of IL-4 did not alter thermal latency or tactile threshold in normal animals, but inoculation of S4IL4 1 week after spinal nerve ligation (SNL) reduced mechanical allodynia and reversed thermal hyperalgesia resulting from SNL. Inoculation of S4IL4 1 week before SNL delayed the development of thermal hyperalgesia and tactile allodynia, but did not prevent the ultimate development of these manifestations of neuropathic pain. S4IL4 inoculation suppressed non-noxious-induced expression of c-Fos immunoreactivity in dorsal horn of spinal cord and reversed the upregulation of spinal IL-1beta, PGE2, and phosphorylated-p38 MAP kinase, characteristic of neuropathic pain.

CONCLUSION

HSV-mediated expression of IL-4 effectively reduces the behavioral manifestations of neuropathic pain, and reverses some of the biochemical and histologic correlates of neuropathic pain at the spinal level.

Markers of immune activation and viral load in HIV-associated sensory neuropathy

BACKGROUND

HIV infection is associated with a painful distal sensory polyneuropathy (DSP) that can severely limit the quality of life of affected subjects. The pathogenesis of DSP is unknown, although both HIV proteins and products of immune activation triggered by HIV infection have been implicated.

OBJECTIVE

To assess the association between baseline markers of immune activation and HIV RNA levels (viral load) and time to symptomatic DSP (SDSP).

METHODS

A cohort of 376 subjects, most receiving highly active antiretroviral therapy (HAART), were followed semiannually for up to 48 months. Blood and CSF levels of HIV viral load, monocyte chemotactic protein-1, macrophage colony-stimulating factor (M-CSF), matrix metalloproteinase-2, and tumor necrosis factor-alpha were measured in addition to CD4 lymphocyte cell count.

RESULTS

In subjects without SDSP at baseline (62.5% of the cohort), among the virologic and immunologic markers, only baseline CSF M-CSF levels were associated with time to SDSP (hazard ratio = 2.97, p = 0.05). The Kaplan-Meier estimate of the 1-year incidence of SDSP was 21%, a 15% decrease from that observed in the Dana cohort, a pre-HAART cohort enrolled with the same inclusion/exclusion criteria.

CONCLUSION

Highly active retroviral therapy (HAART) has changed the natural history of HIV-associated symptomatic distal sensory polyneuropathy (SDSP), which may explain, in contrast with studies from the pre-HAART era, the lack of association between SDSP and baseline HIV viral load and CD4 cell count.

HSV-mediated gene transfer of vascular endothelial growth factor to dorsal root ganglia prevents diabetic neuropathy

We examined the utility of herpes simplex virus (HSV) vector-mediated gene transfer of vascular endothelial growth factor (VEGF) in a mouse model of diabetic neuropathy. A replication-incompetent HSV vector with VEGF under the control of the HSV ICP0 promoter (vector T0VEGF) was constructed. T0VEGF expressed and released VEGF from primary dorsal root ganglion (DRG) neurons in vitro, and following subcutaneous inoculation in the foot, expressed VEGF in DRG and nerve in vivo. At 2 weeks after induction of diabetes, subcutaneous inoculation of T0VEGF prevented the reduction in sensory nerve amplitude characteristic of diabetic neuropathy measured 4 weeks later, preserved autonomic function measured by pilocarpine-induced sweating, and prevented the loss of nerve fibers in the skin and reduction of neuropeptide calcitonin gene-related peptide and substance P in DRG neurons of the diabetic mice. HSV-mediated transfer of VEGF to DRG may prove useful in treatment of diabetic neuropathy.

Adenoviral gene transfer in the peripheral nervous system

BACKGROUND

Viral vectors have gained widespread use as vehicles for somatic gene transfer, and the targeted expression of foreign proteins by these vectors offers advantages over the systemic administration of the drugs in some therapeutic situations. Selective virus-mediated gene transfer to the peripheral nervous system (PNS), however, remains to be established. There are no data showing efficiency of protein transduction in the PNS, which consists of a variety of cell types, many of which are postmitotic.

METHODS

We prepared the first-generation replication-deficient recombinant adenovirus vectors engineered to express LacZ. Eight-week-old Wister rats were used in this study. Adenovirus vector (5 microl) containing the LacZ gene (5 x 10(8) pfu) was injected into rat sciatic nerves or the dorsal root ganglia at the level of L5. The sciatic nerves, the dorsal root ganglia, and the spinal cords were obtained 7, 14, 21, and 28 days after injection. Expression of LacZ was assessed by X-gal histochemistry and beta-gal immunohistochemistry.

RESULTS

Following injection of the adenovirus carrying the LacZ gene into the sciatic nerve, LacZ expression was seen mainly in the Schwann cells and the small neurons in the dorsal root ganglion. In contrast, expression was observed in the primary nerve terminals of the spinal dorsal horn and the small to large dorsal root ganglion neurons and the Schwann cells after injection of the vectors into the L5 dorsal root ganglion. There were no side effects in rats with injection in the dorsal root ganglia or the sciatic nerve.

CONCLUSIONS

The present study shows efficient protein transduction by adenovirus vectors in the PNS. It is noted that injection of the virus into the dorsal root ganglia leads to extensive expression of LacZ in the spinal cord, the dorsal root ganglia, and the sciatic nerves.

Varicella zoster virus induces neuropathic changes in rat dorsal root ganglia and behavioral reflex sensitisation that is attenuated by gabapentin or sodium channel blocking drugs

Reactivation of latent varicella zoster virus (VZV) within sensory trigeminal and dorsal root ganglia (DRG) neurons produces shingles (zoster), often accompanied by a chronic neuropathic pain state, post-herpetic neuralgia (PHN). PHN persists despite latency of the virus within human sensory ganglia and is often unresponsive to current analgesic or antiviral agents. To study the basis of varicella zoster-induced pain, we have utilised a recently developed model of chronic VZV infection in rodents. Immunohistochemical analysis of DRG following VZV infection showed the presence of a viral immediate early gene protein (IE62) co-expressed with markers of A- (neurofilament-200; NF-200) and C- (peripherin) afferent sensory neurons. There was increased expression of neuropeptide Y (NPY) in neurons co-expressing NF-200. In addition, there was an increased expression of alpha2delta1 calcium channel, Na(v)1.3 and Na(v)1.8 sodium channels, the neuropeptide galanin and the nerve injury marker, Activating Transcription Factor-3 (ATF-3) as determined by Western blotting in DRG of VZV-infected rats. VZV infection induced increased behavioral reflex responsiveness to both noxious thermal and mechanical stimuli ipsilateral to injection (lasting up to 10 weeks post-infection) that is mediated by spinal NMDA receptors. These changes were reversed by systemic administration of gabapentin or the sodium channel blockers, mexiletine and lamotrigine, but not by the non-steroidal anti-inflammatory agent, diclofenac. This is the first time that the profile of VZV infection-induced phenotypic changes in DRG has been shown in rodents and reveals that this profile appears to be broadly similar (but not identical) to changes in other neuropathic pain models.

Lentivirus infection causes neuroinflammation and neuronal injury in dorsal root ganglia: pathogenic effects of STAT-1 and inducible nitric oxide synthase

Distal sensory polyneuropathy (DSP) is currently the most common neurological complication of HIV infection in the developed world and is characterized by sensory neuronal injury accompanied by inflammation, which is clinically manifested as disabling pain and gait instability. We previously showed that feline immunodeficiency virus (FIV) infection of cats caused DSP together with immunosuppression in cats, similar to that observed in HIV-infected humans. In this study, we investigated the pathogenic mechanisms underlying the development of FIV-induced DSP using feline dorsal root ganglia (DRG) cultures, consisting of neurons, Schwann cells, and macrophages. FIV-infected cultures exhibited viral Ags (p24 and envelope) in macrophages accompanied by neuronal injury, indicated by neurite retraction, neuronal loss and decreased soma size, compared with mock-infected (control) cultures. FIV infection up-regulated inducible NO synthase (iNOS), STAT-1, and TNF-alpha mRNA levels in DRG cultures. Increased STAT-1 and iNOS mRNA levels were also observed in DRGs from FIV-infected animals relative to mock-infected controls. Similarly, immunolabeling studies of DRGs from FIV-infected animals showed that macrophages were the principal sources of STAT-1 and iNOS protein production. The iNOS inhibitor aminoguanidine reduced nitrotyrosine and protein carbonyl levels, together with preventing neuronal injury in FIV-infected DRG cultures. The present studies indicate that FIV infection of DRGs directly contributes to axonal and neuronal injury through a mechanism involving macrophage immune activation, which is mediated by STAT-1 and iNOS activation.

A combination of mutations enhances the neurotropism of AAV-2

There is strong interest in developing practical strategies for gene delivery to the central nervous system (CNS). Direct delivery into the brain or spinal cord is highly invasive as well as inefficient or hazardous using most current vector systems. Our objective was to generate innocuous gene vehicles that would be effectively taken up by axons and then home to the neuron cell bodies. Vectors derived from Adeno-Associated Virus (AAV), a harmless human parvovirus, offer strong starting candidates for deriving such vehicles. Enhancing the axonal uptake of AAV, and conferring more efficient retrograde transport capabilities upon the virus, should produce near ideal gene transfer vehicles for the CNS. To enhance retrograde transport of the virus, peptides mimicking binding domains for cytoplasmic dynein were inserted in the capsid by directed mutagenesis. In separate clones, peptides derived from an NMDA receptor antagonist were also introduced to provide a specific affinity for this receptor. When combined, these two functionally distinct classes of mutation enabled efficient gene transfer into neurons under conditions not permissive for standard AAV-2 vectors prepared under the same conditions. These results hold strong promise for the development of safe, convenient vehicles to target genes and other sequences to neurons, enabling new and novel approaches for the treatment of multiple neurological disorders.

Characterization of West Nile viral replication and maturation in peripheral neurons in culture

The North American West Nile virus (WNV), New York 1999 strain, appears to be highly neurotropic, and its neuroinvasiveness is an important aspect of human disease. The authors have developed an in vitro model to study WNV replication and protein processing in neurons. They compared WNV infection of the dorsal root ganglion (DRG) neurons (sensory neurons) and PC-12 cells (sympathetic neurons) to WNV infection of the mosquito cell line, C6/36, and Vero cells. WNV infection of both neuronal cell types and C6/36 cells was not cytopathic up to 30 days post infection, and continual viral shedding was observed during this period. However, WNV infection of Vero cells was lytic. Interestingly, WNV infection of neurons was not efficient, requiring a high multiplicity of infection of > or = 10. Indirect immunofluorescence assays using normal and confocal microscopy with flavivirus-reactive antibodies and WNV-infected neurons demonstrated viral antigen mostly associated with the plasma membrane and in the neurite processes. Treatment of WNV-infected C6/36, PC-12, or DRG cells with brefeldin A (BFA; a trans-Golgi inhibitor) or nocadazole (a beta-tubulin inhibitor) had little effect on viral maturation and secretion. Treatment of WNV-infected Vero cells with BFA resulted in a 1000-fold decrease in viral titer, but nocodazole had no effect. Our studies suggest that even though PC-12 and DRG neurons are mammalian cells, viral protein processing and maturation in these cells more closely resembles replication in C6/36 insect cells than in mammalian Vero cells.

Varicella-zoster virus infection of human dorsal root ganglia in vivo

Varicella-zoster virus (VZV) causes varicella and establishes latency in sensory ganglia. VZV reactivation results in herpes zoster. We developed a model using human dorsal root ganglion (DRG) xenografts in severe combined immunodeficient (SCID) mice to investigate VZV infection of differentiated neurons and satellite cells in vivo. DRG engrafted under the kidney capsule and contained neurons and satellite cells within a typical DRG architecture. VZV clinical isolates infected the neurons within DRG. At 14 days postinfection, VZ virions were detected by electron microscopy in neuronal cell nuclei and cytoplasm but not in satellite cells. The VZV genome copy number was 7.1 x 10(7) to 8.0 x 10(8) copies per 10(5) cells, and infectious virus was recovered. This initial phase of viral replication was followed within 4-8 weeks by a transition to VZV latency, characterized by the absence of infectious virus release, the cessation of virion assembly, and a reduction in VZV genome copies to 3.7 x 10(5) to 4.7 x 10(6) per 10(5) cells. VZV persistence in DRG was achieved without any requirement for VZV-specific adaptive immunity and was associated with continued transcription of the ORF63 regulatory gene. The live attenuated varicella vaccine virus exhibited the same pattern of short-term replication, persistence of viral DNA, and prominent ORF63 transcription as the clinical isolates. VZV-infected T cells transferred virus from the circulation into DRG, suggesting that VZV lymphotropism facilitates its neurotropism. DRG xenografts may be useful for investigating neuropathogenic mechanisms of other human viruses.