Interferon dependent immune memory during HSV-1 neuronal latency via increased H3K9me3 and restriction by ATRX

Herpes simplex virus-1 (HSV-1) establishes a latent infection in neurons, periodically reactivating to cause disease. Neuronal conditions, including immune signaling, during initial HSV-1 infection, impact later reactivation. Type I interferon (IFNα) exposure during initial infection results in promyelocytic leukemia nuclear-body (PML-NB) formation and subsequent restriction of reactivation, via mechanisms that were unknown. Here we find that PML-NB formation results in the recruitment of histone chaperones to the viral genome and increased enrichment of the repressive heterochromatin mark, histone H3 lysine 9 tri-methylation (H3K9me3), and its reader, ATRX (alpha-thalassemia/mental retardation, X-linked). ATRX is highly abundant in neurons and prevents reactivation from H3K9me3-bound latent genomes by remaining associated with viral chromatin. Therefore, we demonstrate how immune signaling during initial infection results in an epigenetic memory on HSV-1 genomes and identify ATRX as a neuronal restriction factor against HSV-1 reactivation, elucidating a new potential target for inhibiting HSV-1 reactivation and subsequent human disease. This study uncovers a mechanism for innate immune memory in neurons, demonstrated by a more silent epigenetic structure of the Herpes Simplex Virus genome, resulting in a deep form of latent infection that is restricted for reactivation of the virus.