HSV latency and reactivation in a human sensory neuronal model system

The human pathogen, Herpes Simplex Virus-1 (HSV-1), establishes latency in neurons and can reactivate, resulting in the production of infectious virus for transmission to a new host. Reactivation can result in lesions at the body surface and encephalitis. In addition, HSV-1 infection in North American is shifting to become more associated with genital infection, which results in painful lesions, sexual transmission and an enhanced risk of transmission to neonates. There are currently no therapies that target the latent or reactivation stage of HSV-1 infection. In addition, there is increased viral resistance to current therapeutics along with toxicity associated with their use. Therefore, new therapies are required that can prevent HSV reactivation. However, to develop new therapies we need a better understanding of the molecular basis of HSV latency and reactivation. Because HSV establishes latency in neurons, developing model systems has been a challenge. Current models largely rely on murine primary neurons, which, while informative, have limitations; they are not easily scalable and are not of the same host species. Our lab has considerable expertise in creating and characterizing in vitro models of HSV latency, including the development of a recombinant Stayput-GFP virus model that allows latency to be established in murine in vitro neurons without requiring anti-viral drugs. We have also characterized the nature of the chromatin on viral genomes during latency and investigated a biphasic wave of viral gene expression that is unique to reactivation. Therefore, the goals of this project are to use our expertise to develop and characterize a model of HSV-1 latency in human sensory neurons differentiated from a cell line derived from the dorsal root ganglion. Notably, genital HSV-1 infection results in latency in dorsal root ganglia neurons. The aims are based on our preliminary data indicating that we can establish latency in this system using Stayput-GFP and induce reactivation using a combination of triggers. In the first aim, we will comprehensively characterize the system, focusing on viral gene expression, the epigenetic composition of the viral genome, and the role of a known cell stress pathway in inducing a reactivation-specific biphasic wave of viral gene expression. In the second aim, we will fully determine the type of sensory neurons produced and use the system to investigate the epigenetic structures of HSV genomes and differing abilities to reactivate from different neuronal subtypes. In conclusion, this proposal will result in the creation of an easily scalable model in human sensory neurons that does not require antiviral drugs to promote latency establishment. We will also, for the first time, define the epigenetic structure of the viral genome in human neurons. Finally, we will use clinically relevant inhibitors to determine the contribution of a neuronal cell stress pathway in exit of HSV from latency in human neurons. Therefore, the work outlined in this proposal will fill major gaps in the field of Alphaherpesvirus latency by fully characterizing a model system and also identify a potential therapeutic strategy to prevent reactivation from occurring.