Human Apolipoprotein E (ApoE) Allele 4 Regulates the Resolution and Recurrence of HSV Stromal Keratitis (HSK) in the Mouse Eye

Abstract

Purpose:: To determine the role of human ApoE alleles in resolution and recurrence following primary HSK.

Methods:: Transgenic knock-in mice for human ApoE allele ε3 or ε4 in mouse ApoE null-C57Bl/6 background were used. Controls were ApoE null mice. HSV-1 strain KOS with a repoter gene GFP was used to infect scarified corneas. Mice had corneal GFP expression at 1-9 days post-infection (dpi) with a peak at 2 dpi. Corneas were monitored for HSK development from 1-65 dpi by slit lamp examination (SLE) for quantification of opacity, neovascularization and incidence rate. For each genotype, half of the mice were swabbed to assess tears for infectious HSV-1. At 65 dpi, mice were sacrificed and their corneas, TGs, and brains were harvested to quantitate HSV-1 DNA and host gene expression (ApoE and TLR9).

Results:: Of the ApoE ε4 mice that developed primary HSK and were swabbed, 100% developed HSK which did not resolve. The ApoE ε3 mice that were swabbed had 80% resolution from primary HSK during 33-65 dpi. The group of ε4 mice that were never swabbed, had full recovery; however, spontaneous recurrence of HSK was observed in 20% of the mice. All of the ε4 mice (not previously swabbed) had significantly higher incidence and greater severity of HSK vs. ε3 mice. ApoE ε3 and ApoE ε4 knock-in mice, swabbed for1-14 dpi, had no significant differences in the onset and severity of primary HSK. No significant differences in the HSV-1 DNA load in the cornea, TG, or brains of ε3 and ε4 mice were detected at 65 dpi. Host gene expression analysis of corneas, TG, and brains of mice at 65 dpi revealed higher expression of ApoE and TLR9 in ε4 mice than in ε3 mice.

Conclusions:: Human ApoE ε4 is a risk factor for spontaneous recurrence of HSK. We suggest that swabbing could accelerate the onset and severity of HSK. Human ApoE ε4 blocks the resolution of primary HSK and increases spontaneous recurrence of HSK. TLR-9 could be one pathway involved in HSK pathogenesis in ε4 mice. This is the first report to implicate a human gene as a risk factor for HSK.

Keywords: herpes simplex virus • keratitis • transgenics/knock-outs