Müller cell processes occupy the subretinal space in geographic atrophy and Stargardt disease.

Abstract

Purpose : Müller cells create the external limiting membrane (ELM) by forming junctions with photoreceptor cells. This study investigated how the focal loss of photoreceptors and retinal pigment epithelium (RPE) in geographic atrophy (GA) and Stargardt disease (STGD) affects Müller cells and the ELM.

Methods : Human donor eyes with either no retinal disease (N=4), GA (N=4) or STGD (N=2) were obtained through NDRI, the AMD Registry and Biorepository and the Foundation Fighting Blindness Eye Donor Program. Eyes were imaged after retinal dissection with RPE intact and after RPE removal. Retinas were then stained with GFAP (astrocytes and activated Müller cells), vimentin (Müller cells) and UEA lectin (blood vessels) while the submacular choroids were stained with UEA lectin. Choroids and retinas (photoreceptors up) were imaged using a Zeiss 710 confocal microscope. After imaging, retinas were cryopreserved and sectioned to better visualize the Müller cells. Additional cross sections were stained with nestin. Three dimensional images were created using Imaris. Eyes were also processed for transmission electron microscopy (TEM).

Results : Vimentin staining of the control retina revealed a pan retinal cobblestone-like ELM. This pattern was also observed throughout much of the diseased retinas. Areas with vimentin⁺ and vimentin⁺/GFAP⁺ cells were noted subretinally in GA and STGD eyes. Comparison to the gross photos revealed that these subretinal glial membranes very closely correlated with areas of RPE atrophy. In eyes with GA, smaller glial projections were observed beyond the atrophic region which aligned with drusen in gross photos. The presence of glial elaboration into the subretinal space was confirmed by TEM. Cross sectional analysis of eyes with GA demonstrated that Müller cells anterior to atrophy were disorganized and expressed nestin. Choriocapillaris loss was also evident subjacent to these atrophic areas and was more severe in eyes with STGD.

Conclusions : Photoreceptor and RPE cell death appears to stimulate Müller cell remodeling and subretinal membrane formation. These glial membranes likely represent a Müller cell attempt to replace the ELM in regions of degenerated photoreceptors but may interfere with future treatments like photoreceptor or RPE replacement therapy. Subretinal Müller cells may also express VEGF, potentially contributing to the progression from GA to neovascular AMD.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.