Herpes Simplex Virus Type 2 Counteracts Neurite Outgrowth Repulsion During Infection In A Nerve Growth Factor-Dependent Manner.

During primary infection, herpes simplex virus type 2 (HSV-2) replicates in epithelial cells and enters neurites to infect neurons of the peripheral nervous system. Growth factors, attractive and repulsive directional cues influence neurite outgrowth and neuronal survival. We hypothesised that HSV-2 modulates the activity of such cues to increase neurite outgrowth. To test this hypothesis we exposed sensory neurons to nerve growth factor (NGF) and mock or HSV-2-infected HEK-293T cells, since they express repellents of neurite outgrowth. We show that HEK-293T cells secreted factors that inhibit neurite outgrowth, while infection with HSV-2 strains MS and 333 reduced this repelling phenotype, increasing neurite numbers. The HSV-2 mediated restoration of neurite outgrowth required the activity of NGF. In the absence of infection, however, NGF did not overcome the repulsion mediated by HEK-293T cells. We previously showed that recombinant, soluble glycoprotein G of HSV-2 (rSgG2) binds and enhances NGF activity, increasing neurite outgrowth. However, the effect of gG2 during infection had not been investigated. Therefore, we addressed whether gG2 contributed to overcoming neurite outgrowth repulsion. To do so, we generated viruses lacking gG2 expression and complemented them by exogenous expression of gG2. Overall, our results suggest that HSV-2 infection of non-neuronal cells reduced their repelling effect on neurite outgrowth in an NGF-dependent manner. gG2 contributed to this phenotype but it was not the only factor. The enhanced neurite outgrowth may facilitate HSV-2 spread from epithelial cells into neurons expressing NGF receptors and increase HSV-2 mediated pathogenesis.Importance: Herpes simplex virus type 2 (HSV-2) is a prevalent human pathogen that establishes life-long latency in neurons of the peripheral nervous system. Colonization of neurons is required for HSV-2 persistence and pathogenesis. The viral and cellular factors required for efficient infection of neurons are not fully understood. We show here that non-neuronal cells repel neurite outgrowth of sensory neurons, while HSV-2 infection overcomes this inhibition, and rather stimulates neurite outgrowth. HSV-2 glycoprotein G and nerve growth factor contribute to this phenotype, which may attract neurites to sites of infection and facilitate virus spread to neurons. Understanding the mechanisms that modulate neurite outgrowth and facilitate HSV-2 infection of neurons might foster the development of therapeutics to reduce HSV-2 colonization of the nervous system and provide insights on neurite outgrowth and regeneration.