Herpes Simplex Virus-2 Variation Contributes to Neurovirulence During Neonatal Infection.

Herpes simplex virus (HSV) infection of the neonatal brain causes severe encephalitis and permanent neurologic deficits. However, infants infected with HSV at the time of birth follow varied clinical courses, with approximately half of infants experiencing only external infection of the skin rather than invasive neurologic disease. Understanding the cause of these divergent outcomes is essential to developing neuroprotective strategies. To directly assess the contribution of viral variation to neurovirulence, independent of human host factors, we evaluated clinical HSV isolates from neonates with different neurologic outcomes in neurologically relevant in vitro and in vivo models. We found that isolates taken from neonates with encephalitis are more neurovirulent in human neuronal culture and mouse models of HSV encephalitis, as compared to isolates collected from neonates with skin-limited disease. These findings suggest that inherent characteristics of the infecting HSV strain contribute to disease outcome following neonatal infection.

Comparative proteomics identifies Schlafen 5 (SLFN5) as a herpes simplex virus restriction factor that suppresses viral transcription.

Intrinsic antiviral host factors confer cellular defence by limiting virus replication and are often counteracted by viral countermeasures. We reasoned that host factors that inhibit viral gene expression could be identified by determining proteins bound to viral DNA (vDNA) in the absence of key viral antagonists. Herpes simplex virus 1 (HSV-1) expresses E3 ubiquitin-protein ligase ICP0 (ICP0), which functions as an E3 ubiquitin ligase required to promote infection. Cellular substrates of ICP0 have been discovered as host barriers to infection but the mechanisms for inhibition of viral gene expression are not fully understood. To identify restriction factors antagonized by ICP0, we compared proteomes associated with vDNA during HSV-1 infection with wild-type virus and a mutant lacking functional ICP0 (ΔICP0). We identified the cellular protein Schlafen family member 5 (SLFN5) as an ICP0 target that binds vDNA during HSV-1 ΔICP0 infection. We demonstrated that ICP0 mediates ubiquitination of SLFN5, which leads to its proteasomal degradation. In the absence of ICP0, SLFN5 binds vDNA to repress HSV-1 transcription by limiting accessibility of RNA polymerase II to viral promoters. These results highlight how comparative proteomics of proteins associated with viral genomes can identify host restriction factors and reveal that viral countermeasures can overcome SLFN antiviral activity.

Genotypic and Phenotypic Diversity of Herpes Simplex Virus 2 within the Infected Neonatal Population.

More than 14,000 neonates are infected with herpes simplex virus (HSV) annually. Approximately half display manifestations limited to the skin, eyes, or mouth (SEM disease). The rest develop invasive infections that spread to the central nervous system (CNS disease or encephalitis) or throughout the infected neonate (disseminated disease). Invasive HSV disease is associated with significant morbidity and mortality, but the viral and host factors that predispose neonates to these forms are unknown. To define viral diversity within the infected neonatal population, we evaluated 10 HSV-2 isolates from newborns with a range of clinical presentations. To assess viral fitness independently of host immune factors, we measured viral growth characteristics in cultured cells and found diverse in vitro phenotypes. Isolates from neonates with CNS disease were associated with larger plaque size and enhanced spread, with the isolates from cerebrospinal fluid (CSF) exhibiting the most robust growth. We sequenced complete viral genomes of all 10 neonatal viruses, providing new insights into HSV-2 genomic diversity in this clinical setting. We found extensive interhost and intrahost genomic diversity throughout the viral genome, including amino acid differences in more than 90% of the viral proteome. The genes encoding glycoprotein G (gG; US4), glycoprotein I (gI; US7), and glycoprotein K (gK; UL53) and viral proteins UL8, UL20, UL24, and US2 contained variants that were found in association with CNS isolates. Many of these viral proteins are known to contribute to cell spread and neurovirulence in mouse models of CNS disease. This report represents the first application of comparative pathogen genomics to neonatal HSV disease.IMPORTANCE Herpes simplex virus (HSV) causes invasive disease in half of infected neonates, resulting in significant mortality and permanent cognitive morbidity. The factors that contribute to invasive disease are not understood. This study revealed diversity among HSV isolates from infected neonates and detected the first associations between viral genetic variations and clinical disease manifestations. We found that viruses isolated from newborns with encephalitis showed enhanced spread in culture. These viruses contained protein-coding variations not found in viruses causing noninvasive disease. Many of these variations were found in proteins known to impact neurovirulence and viral spread between cells. This work advances our understanding of HSV diversity in the neonatal population and how it may impact disease outcome.

Viral genetic diversity and its potential contributions to the development and progression of neonatal herpes simplex virus (HSV) disease.

PURPOSE OF REVIEW: Neonatal infection by herpes simplex virus (HSV) 1 or 2 presents a devastating burden to new parents, due to the unpredictability of severe clinical outcomes, as well as the potential for lifelong reactivation. While just under half of neonatal HSV infections have mild clinical impacts akin to those observed in adults, the other half experience viral spread throughout the body (disseminated infection) and/or the brain (central nervous system infection). SUMMARY: Here we summarize current data on clinical diagnostic measures, antiviral therapy, and known factors of human host biology that contribute to the distinct neonatal outcomes of HSV infection. RECENT FINDINGS: We then explore recent new data on how viral genetic diversity between infections may impact clinical outcomes. Further research will be critical to build upon these early findings and to provide statistical power to our ability to discern and/or predict the potential clinical path of a given neonatal infection.

Identifying Host Factors Associated with DNA Replicated During Virus Infection.

Viral DNA genomes replicating in cells encounter a myriad of host factors that facilitate or hinder viral replication. Viral proteins expressed early during infection modulate host factors interacting with viral genomes, recruiting proteins to promote viral replication, and limiting access to antiviral repressors. Although some host factors manipulated by viruses have been identified, we have limited knowledge of pathways exploited during infection and how these differ between viruses. To identify cellular processes manipulated during viral replication, we defined proteomes associated with viral genomes during infection with adenovirus, herpes simplex virus and vaccinia virus. We compared enrichment of host factors between virus proteomes and confirmed association with viral genomes and replication compartments. Using adenovirus as an illustrative example, we uncovered host factors deactivated by early viral proteins, and identified a subgroup of nucleolar proteins that aid virus replication. Our data sets provide valuable resources of virus-host interactions that affect proteins on viral genomes.