Abstract
Purpose :
Choroidoremia (CHM) is a rare disease caused by loss of function mutations in the Rab Escort Protein 1 gene that leads to early onset blindness. The present study analyzed Müller cell (MC) and choroidal changes in the eyes of a donor with CHM.
Methods :
Human donor eyes with no eye disease or CHM were imaged then fixed and processed for either flatmount or cryosection analysis. A portion of the eyecup was also prepared for transmission electron microscopy (TEM). The retinas were stained with GFAP (astrocytes and activated MCs), vimentin (MC) and UEA lectin (blood vessels). A subretinal scar prevented dissection of the CHM posterior pole so the retina and choroid were processed together. Control choroids were stained with UEA lectin. Cryosections were stained with rhodopsin (rods), vimentin, GFAP, IBA1 (microglia) and UEA lectin.
Results :
Control retinas displayed organized GFAP+ astrocytes surrounding retinal vessels and vimentin+ MC endfeet. UEA lectin revealed the uniform choriocapillaris (CC). By contrast, a membrane of GFAP and vimentin-double-positive cells covered almost the entire CHM retina. MCs were disorganized and positive for GFAP throughout the retina. MC processes extended through the external limiting membrane to the choroid creating a membrane-like structure. Confocal Z-stacks through the retina and choroid confirmed that this membrane extended exactly over the area of CC and RPE loss. The CC persisted only in the far periphery. Cross sections showed vimentin+/GFAP+ MCs occupying a majority of the CHM retina. The linear MC morphology observed in controls was completely lost. Retinal lamination was largely lost. Rhodopsin+ cells and debris mislocalized to the inner retina were observed in the CHM retina. Interestingly, rhodopsin+ cells appeared to be double positive for GFAP and vimentin. IBA1+ microglia were present throughout the retina but a majority of the rhodopsin staining was not associated with these cells. TEM analysis confirmed that MCs occupied most of the CHM retina. MCs were observed enwrapping cells and appeared to contain photoreceptor outer segment debris. Junctions were evident between MCs. Extracellular vesicles/exosomes were also observed within MCs, within retina and in the vitreous.
Conclusions :
MCs remodel and constitute much of the retina in advanced CHM. The presence of outer segment debris suggests that MCs phagocytose dying photoreceptors. TEM indicates that MCs produce and release exosomes
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.