Integration between Abutting Retinas: Role of Glial Structures and Associated Molecules at the Interface

Abstract

Integration between subretinal grafts and the host retina is limited in part by the presence of a barrier at the graft-host interface. This study was conducted to identify factors that may contribute to this barrier, by examining the distribution of glial structures and associated molecules in different setups of overlapping retinal pieces. Neuroretinal tissue derived from mice that express green fluorescent protein (GFP) was fragmented and transplanted into the subretinal space of adult rd1 mice. In an in vitro system, two retinal pieces, derived from GFP and rd1 mice, respectively, were placed overlapping each other and forming either laminar-laminar pairs or fragment-laminar pairs. The glia-associated markers analyzed included glial fibrillary acidic protein (GFAP), cellular retinaldehyde-binding protein (CRALBP), and two molecules known to inhibit neurite outgrowth: CD44 and neurocan. Bridging fibers and migrated cells were visualized with GFP fluorescence and retinal cell markers. A thick CRALBP-immunolabeled band was observed in the interface in cultured laminar-laminar pairs, whereas a thinner band was seen in cultured fragment-laminar pairs and in transplants. Accumulation of CD44 and neurocan was also observed in the interface between abutting retinal pieces in all setups. GFP(+) bridging fibers and GFP(+) cells (some of which coexpressed neuronal markers) were observed within the abutting rd1 retina in some areas. However, such integration occurred exclusively where CRALBP, CD44, and neurocan immunolabeling appeared disrupted in the interface, but coincided with high GFAP expression within the rd1 retina. The results demonstrate that, on the one hand, an accumulation of glial-associated inhibitory molecules in the interface correlates with limited integration between overlapping retinal pieces. On the other hand, glial reactivity within the rd1 retina does not appear to be incompatible with integration.