In vitro study of the attachment of neural retina to RPE in the vitiligo (mivit/mivit) mutant mouse

Purpose: The vitiligo mouse has a slowly progressing photoreceptor cell (PRC) loss accompanied by disrupted outer segments (OS). The vitiligo mouse RPE is unevenly pigmented, has reduced phagocytosis and malformed microvillous processes in some regions. The OS separate from the RPE at an early age. The purpose of this study was to assess the ability of the mutant neural retina and RPE to reattach in vitro. Methods: 33 vitiligo (vit) and 37 age-matched control (con) eyes (ages 2-36 wk) were dissected in BSS. Retinas were removed from original eyecups and recombined with other eyecups (vit RPE/con retina, con RPE/vit retina, vit RPE/vit retina, con RPE/con retina). Recombined eyes were incubated 3h, 37°C in 50:50 F-12:DMEM and processed for histology. The percent of RPE attached to neural retina was determined by light microscopy in JB-4 embedded sections. Attachment was defined as direct contact between RPE and retina. Results: Control eyecups demonstrated about 50% reattachment to control retinas regardless of age, but progressively less attachment to vitiligo retinas as PRC degeneration progressed (45% at 10 wks; 28% al 20 wks). Surprisingly, under in vitro conditions, the vitiligo RPE demonstrated attachment to control retinas, although attachment to age-matched mutant neural retinas declined precipitously as PRC degeneration progressed (66% at 16 wks, 14% at 36 wks). Conclusions: When the vitiligo RPE is removed from its physiological milieu and incubated under controlled conditions, it appears to be able to attach to control neural retinas but is less able to attach to vitiligo retinas as degeneration advances. It remains to be determined whether the in vitro attachment constitutes a true attachment and whether there are factors lacking (or present) in vivo that limit retina/RPE adhesion in this mutant.