Neuronal Sorting of Herpes Simplex Virus Components in Mature Mouse Visual System

Abstract

Abstract: : Purpose: Our information about the neuropathogenesis of Herpes simplex virus (HSV) infections is incomplete. For example, HSV infection results in alterations in the synthesis and maintenance of host cell proteins, but specific details about how this alteration affects viral maturation and egress are lacking. Mature axons do not contain endogenous protein synthesizing machinery; axonal transport provides the major means by which the axon is supplied with new endogenous proteins. In the course of examining the timing of delivery of a subset of HSV envelope and nucleocapsid proteins to the axon compartment of infected retinal ganglion cell in adult mice, we found a 48 hr delay in appearance of the capsid protein as compared to the envelope protein. Since infection of retinal ganglion cells with HSV might disrupt the normal segregation of viral transcriptional machinery within the host neurons, we tested that viral mRNA is transported to axons. If not, then other mechanisms than mRNA delivery must account for the difference in time of appearance of the viral proteins in the axon. Methods: Mice were infected with HSV by intravitreal injection. Twenty-four hrs later, the mice were treated with valacyclovir. Without treatment, viral spread and replication in periaxonal glial cells counfound the study of axonal transport. Additional mice were infected but were not treated with the drug. Five days after infection, the mice were killed and retinas and optic tracts (OT) were isolated. RNA was extracted, DNAase treated and the RNA was used for cDNA synthesis and amplification by RT-PCR using viral glycoprotein D (gD) primers. Results: Five days after infection, gD mRNA was present in infected retina and OT of mice that were not treated with valacyclovir; it was absent in retina and OT from mice that were treated with the drug. Tissues from animals with no infection were also negative. Conclusions: We found no evidence of gD mRNA in the axons of HSV infected retinal ganglion cells from mice that had been treated with valacyclovir. We assume that the gD mRNA that is found in OT of infected animals that received no drug is the result of secondary viral infection of glial cells in the nerve. Thus, the expression of this viral glycoprotein is limited to the retina, and it is subsequently targeted to the axon for assembly and release.

Keywords: herpes simplex virus • pathobiology • retina