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Julia Lai, Yanfeng Su, Davy Huang, Haiyan Gong; The role of cellular connections in Schlemm’s canal endothelial cells in regulating segmental aqueous outflow. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1077.
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Aqueous outflow is segmental. Increased outflow facility by Rho-kinase inhibitors was found to be associated with increased high-flow areas, which was in turn associated with expansion of juxtacanalicular connective tissue (JCT) and disconnections between Schlemm’s canal (SC) inner wall endothelium and JCT. This suggests that changes in cellular connectivity may play a role in segmental outflow regulation. This study aimed to determine whether there are differences in cellular connections, giant vacuoles (GVs), and pores between high-flow and non-flow areas of normal eyes.
Two normal human eyes were perfused at 15 mmHg and exchanged with fluorescent tracer to establish high- and non-flow areas based on tracer distributions in global imaging. Radial sections of SC from high-flow and non-flow areas were processed for serial block-face scanning electron microscopy (SBF-SEM). SC cells were 3D-reconstructed based on SBF-SEM images of high-flow areas (N=11 cells) and non-flow areas (N=11 cells). GVs, transcellular I-pores, and paracellular B-pores were reconstructed for geometric and volumetric analyses. In each SC cell, the number of cellular connections with its underlying JCT cells/matrix was determined. Overlap length was measured to determine the overlap amount between adjacent SC cell borders. Data were compared between high- and non-flow areas using unpaired t-test.
The number of SC/JCT connections significantly decreased in high-flow (72±10, N=11 cells) vs. non-flow areas (107±10, N=11 cells; p<0.01). Summed GV volume in individual SC cells significantly increased in high-flow (251.01±31.06 μm3) vs. non-flow areas (98.15±14.92 μm3; p<0.01). I-pores were found only in larger GVs (≧42 μm3). Overlap length between SC cells significantly decreased in high-flow (0.70±0.22 μm) vs. non-flow areas (1.07±0.20 μm; p<0.03). B-pores were found only in regions of zero overlap. More pores were found in high-flow (13 I-pores;8 B-pores) vs. non-flow areas (3 I-pores;0 B-pores).
3D-EM reconstruction allowed us to reliably quantify cellular connections, GV size, and pore count that no 2D-imaging methods currently can. Our data suggest that decreased SC/JCT connectivity and SC endothelial cells connectivity in high-flow areas may promote GV and pore formations, thereby contributing to the regulation of segmental aqueous outflow.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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