Iontophoresis of lysophosphatidic acid into rabbit cornea induces HSV-1 reactivation: Evidence that neuronal signaling changes after infection

PURPOSE: Lysophosphatidic acid induces neurite retraction; it is also prese nt in tears and aqueous humor. We determined whether lysophosphatidic acid induces HSV-1 reactivation in latently infected rabbits and whether the ner ve growth associated protein GAP-43 undergoes posttranslational modificatio n during the course of HSV-1 infection. METHODS: Rabbits were infected with HSV-1 and acute infection was documente d by slit lamp examination. Corneas of latently infected rabbits were treat ed with lysophosphatidic acid or lysophosphatidylserine (structurally simil ar but lacking biological potency). For application to the cornea, these co mpounds were impregnated into collagen shields, applied as topical drops, o r iontophoresed. In another experiment, corneas of latently infected rabbit s were either untreated or treated iontophoretically with lysophosphatidic acid, lysophosphatidylserine, or saline. Ocular swabs detected shedding of infectious virus. Western blot and immunoprecipitation identified GAP-43 in corneal extracts and densitometry of silver-stained isoelectric focusing g els measured changes in GAP-43 isoform abundance. RESULTS: Iontophoresis of lysophosphatidic acid induced HSV-1 shedding more frequently than lysophosphatidylserine or saline. Viral shedding induced b y collagen shield and topical drop administration was low and not significa ntly different for lysophosphatidic acid and lysophosphatidylserine. Five d iscrete GAP-43 isoforms predominated in the IEF gels. Most abundant were th e pI 4.7 band in uninfected cornea and the pI 5.05 band in latently-infecte d cornea. Compared to latently-infected cornea, there was no significant ch ange in isoform abundance 1 h after lysophosphatidic acid iontophoresis, bu t 24 and 72 h later, the pI 5.05 band was diminished. CONCLUSIONS: Lysophosphatidic acid can induce HSV-1 reactivation and change s in GAP-43 pI suggest that posttranslational modifications, possibly relat ed to phosphorylation and ADP-ribosylation, are occurring during HSV-1 late ncy and after LPA is iontophoretically applied to the cornea. How lysophosp hatidic acid-induced signaling, HSV-1 reactivation, and GAP-43 pI are relat ed remains to be determined.