Immunohistochemistry and Spatial Density of Müller Cells in the Human Fovea.

Purpose: Previous evidence indicates that molecular properties of foveal Müller cells are different from those in the peripheral retina. Here we aimed to characterize Müller cells in the human fovea (including the foveal floor) with specific focus on their spatial density and immunohistochemistry. Methods: Human retinas were obtained postmortem from male and female donors with no known eye disease (aged 31-56 years) or after exenteration (one 75-year-old patient with no retinal disease and one 86-year-old patient with reticular pseudodrusen). Vertical sections through the macula were processed for immunofluorescence using antibodies against cellular retinaldehyde binding protein (CRALBP), glutamine synthetase (GS), glial fibrillary acidic protein (GFAP), transient receptor potential vanilloid 4 (TRPV4), excitatory amino acid transporter 4 (EAAT4), calbindin, and RNA-binding protein with multiple splicing. Sections were imaged using high-resolution, multichannel confocal microscopy. Results: Immunofluorescence for CRALBP and GS was found in Müller cells, including their processes throughout the retina. GFAP expression was found in astrocytes outside the fovea and in some foveal somas. Müller cell nuclei had a peak density of about 35,000 cells/mm2 at 500 µm eccentricity. Calbindin was coexpressed with CRALBP in up to 96% of Müller cells in the fovea, but at eccentricities beyond about 1.5 mm calbindin was not expressed by Müller cells. Conversely, calbindin expression in cone photoreceptors was absent in foveal but present in peripheral retina. Conclusions: This study supports the hypothesis that Müller cells in the macula have distinct structural, functional, and immunohistochemical properties compared to their peripheral counterparts.