Differential Sensitivity of HSV-1 and PRV to IFN-{lambda} Reveals a Neuron-Specific Antiviral Role for RSAD2

Technical Summary: Differential Sensitivity of HSV-1 and PRV to IFN-{lambda} Reveals a Neuron-Specific Antiviral Role for RSAD2

Problem Statement
Alpha herpesviruses (-HV) exhibit a distinct pathogenesis involving initial infection of mucosal epithelial cells followed by the establishment of lifelong latency within the peripheral nervous system (PNS). While Herpes simplex virus-1 (HSV-1) is a human pathogen persisting in the majority of the adult population, Pseudorabies virus (PRV), a swine -HV, serves as a critical model for studying neuroinvasive properties. Previous work by the authors established that IFN-{lambda} pre-treatment significantly reduced PRV yields in primary peripheral neuronal cultures. However, the specific mechanisms governing the differential sensitivity of human HSV-1 versus model PRV to IFN-{lambda} within neuronal environments, and the specific host factors mediating this response, remained to be fully characterized.

Methodology
This study employed primary peripheral neuronal cultures derived from both murine and human sources to investigate early and late neuronal responses to IFN-{lambda}. The authors utilized RNA-sequencing (RNA-seq) to profile transcriptional changes induced by IFN-{lambda} treatment. To dissect the molecular basis of viral resistance, the study compared wild-type HSV-1 against an ICP34.5-deficient mutant ({Delta}34.5). Viral replication and protein synthesis were assessed in the presence and absence of IFN-{lambda} pre-treatment. Furthermore, the study utilized siRNA-mediated knockdown to functionally validate the role of specific host factors, specifically RSAD2, in restricting viral replication. Subcellular localization of RSAD2 was also examined to determine its site of action.

Key Results
The investigation revealed a striking neuron-specific resistance of wild-type HSV-1 to IFN-{lambda} mediated antiviral responses, a phenotype observed in both murine primary neurons and human neuronal cells. In contrast, PRV remained sensitive to IFN-{lambda}. This resistance was found to be dependent on the viral protein ICP34.5; the {Delta}34.5 mutant, which replicates normally in untreated neurons, became highly sensitive to IFN-{lambda} mediated restriction in the neuronal environment.

Transcriptional analysis identified RSAD2 as a host factor strongly induced by IFN-{lambda} specifically in neurons. RSAD2 was observed to localize to ER-associated membranes. Functionally, RSAD2 was shown to effectively restrict -HV protein synthesis, but only in the absence of the viral antagonist ICP34.5. Crucially, siRNA-mediated knockdown of RSAD2 in IFN-{lambda}-primed primary neurons largely restored the replication capacity of the {Delta}34.5 HSV-1 mutant, confirming that RSAD2 is the primary effector of the IFN-{lambda} induced antiviral state in this context.

Significance and Claims
The paper posits that the interplay between neuronal IFN-{lambda}-induced RSAD2 and the viral protein HSV-1 ICP34.5 constitutes a neuron-specific antagonistic mechanism. This dynamic defines the replication efficiency of HSV-1 within the peripheral nervous system. The study concludes that while IFN-{lambda} induces a potent antiviral state via RSAD2 in neurons, HSV-1 has evolved to counteract this specific defense through ICP34.5, thereby securing its ability to persist and replicate in the PNS. This work delineates a specific molecular axis determining the outcome of alpha herpesvirus infection in neuronal tissues.