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Malia Michelle Edwards, Scott D McLeod, Imran Ahmed Bhutto, Amanda Hardin, Johanna Seddon, Gerard A Lutty, RC; Idiopathic glial blooms in aged human retinas. Invest. Ophthalmol. Vis. Sci. 2014;55(13):826.
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© ARVO (1962-2015); The Authors (2016-present)
Four decades ago, Foos discovered glial protrusions into the vitreous and epiretinal glial membranes using electron microscopy (1). The present study used wholemount immunohistochemistry to characterize what appear to be similar glial structures, termed glial blooms herein, in age-related macular degeneration (AMD) and aged control retinas.
Retinal wholemounts from donors with and without AMD were stained with markers for retinal astrocytes and activated Müller cells (GFAP), Müller cells (vimentin, glutamine synthetase) and microglia (IBA-1). Retinal vessels were labeled with UEA lectin. Imaged retinas were cryopreserved and sections labeled with laminin to determine the location of glial blooms in relation to the inner limiting membrane (ILM). Images were collected using a Zeiss 710 Meta confocal microscope.
Epiretinal glial blooms of varying size were observed in all retinas regardless of disease state. In some retinas, only focal tufts of glial processes were noted on the vitreal surface over large vessels. Others contained large, multicellular glial blooms that extended radially in the vitreous. The most extreme cases had complete epiretinal glial membranes with compact networks of cells and processes creating multiple layers. While blooms were observed in all areas of the retina, they were most prominent over large vessels and in the peripapillary region. All epirteinal glial blooms and membranes contained vimentin and GFAP-positive cells although these proteins were seldom co-localized and vimentin staining extended beyond that for GFAP. While glutamine synthetase was prominent in Müller cells within the retina, labeling in blooms was confined to fine processes at the base. Microglia were found in blooms but did not concentrate in the retina below them. The astrocyte template was normal below some blooms but attenuated below others. Cross sections identified small breaks in the ILM above large vessels through which glial cells entered the vitreous.
Epiretinal glial blooms are a common occurrence in aged retinas and, in many cases, subclinical. While all retinal glia are found in blooms, the extension of vimentin labeling beyond that of GFAP suggests that Müller cells form the leading edge. Although these structures may be benign, their increased growth and spread along the vitreal/retinal interface could exert tractional forces on the retina. 1. Foos, 1972, Investigative Ophthalmology 11, 801-808.
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