Intermediate filament expression in human retinal macroglia. Histopathologic changes associated with age-related macular degeneration.

PURPOSE: Intermediate filament expression by retinal macroglia was studied in normal eyes, normal eyes of older subjects, and eyes of subjects with age-related macular degeneration (AMD), classified on the basis of histopathologic assessment of the retinal pigment epithelium (RPE), choroid, and donor age.
METHODS: Adult human retinae (N = 43) were divided into three groups: normal (< 50 years of age, with normal RPE and choroid); normal eyes of older subjects (> 50 years with normal RPE and choroid); and eyes of subjects with AMD (> 50 years with histopathologic findings indicative of AMD), on the basis of histopathologic assessment of the RPE/choroid and donor age. Intermediate filament expression by retinal macroglia was studied in cryostat sections and in retinal flatmounts using avidin-biotin-peroxidase immunolabeling of antibodies to glial fibrillary acidic protein (GFAP) and vimentin. RESULTS. Analyses of immunohistochemically labeled retinal sections revealed similar distributions of vimentin reactivity in retinae of each group. Distributions of GFAP in normal and normal aged retinae were similar, but sections of AMD-affected retinae showed evidence of GFAP expression by Müller cells. In flatmounts, vimentin distribution was similar in the three groups, but GFAP labeling revealed hypertrophic astrocytes, which were absent from normal retinae, in 17% of aged retinae and 55% of AMD-affected retinae. Deeply penetrating, GFAP-positive processes were observed in 17%, 27%, and 55% of normal, normal aged, and AMD-affected retinae, respectively.
CONCLUSIONS: Variation in GFAP and vimentin expression in retinal macroglia is affected by increasing age, and a distinctive variation of intermediate filament expression in retinal macroglia is associated with the pathogenesis of AMD.