Morphological factors associated with giant vacuoles with I-pores in Schlemm's canal endothelial cells of human eyes: A serial block-face scanning electron microscopy study. (April 2021)

• Record Type: Journal Article
• Authors: Swain, David L.; Le, Thuy Duong; Yasmin, Senila; Fernandes, Beatriz; Lamaj, Ganimete; Dasgupta, Indira; Gao, Yanyun; Gong, Haiyan
• Is Part Of: Experimental eye research. Volume 205(2021)
• Publication Date: 2021-04
• Subjects: Human eye anatomy -- Schlemm's canal endothelium -- Giant vacuoles -- Pores -- Segmental aqueous outflow -- Serial block-face scanning electron microscopy -- 3D electron microscopy; AH aqueous humor -- CSA cross-sectional area -- GV giant vacuole -- I-pore intracellular pore -- IOP intraocular pressure -- IW inner wall -- JCT juxtacanalicular connective tissue -- POAG primary open-angle glaucoma -- SBF-SEM serial block-face scanning electron microscopy -- SC Schlemm's canal -- SEM scanning electron microscopy -- TM trabecular meshwork; Ophthalmology -- Periodicals; Eye -- Periodicals; Œil -- Périodiques; Ophthalmology; Periodicals; Electronic journals; 612.8405
• DOI: 10.1016/j.exer.2021.108488
• Languages: English
• ISSNs: 0014-4835

Abstract

Abstract: Increased intraocular pressure (IOP) is the main risk factor for primary open-angle glaucoma and results from impaired drainage of aqueous humor (AH) through the trabecular outflow pathway. AH must pass the inner wall (IW) endothelium of Schlemm's canal (SC), which is a monolayer held together by tight junctions, to exit the eye. One route across the IW is through giant vacuoles (GVs) with their basal openings and intracellular pores (I-pores). AH drainage through the trabecular outflow pathway is segmental. Whether more GVs with both basal openings and I-pores are present in the active flow areas and factors that may influence formation of GVs with I-pores have not been fully elucidated due to limitations in imaging methods. In this study, we applied a relatively new technique, serial block-face scanning electron microscopy (SBF-SEM), to investigate morphological factors associated with GVs with I-pores in different flow areas. Two normal human donor eyes were perfused at 15 mmHg with fluorescent tracers to label the outflow pattern followed by perfusion-fixation. Six radial wedges of trabecular meshwork including SC (2 each from high-, low-, and non-flow areas) were imaged using SBF-SEM (total: 9802 images). Total GVs, I-pores, basal openings, and four types of GVs were identified. Percentages of GVs with I-pores and basal openings and number of I-pores/GV were determined. Overall, 14.4% (477/3302) of GVs had I-pores. Overall percentage of GVs with both I-pores and basal openings was higher in high- (15.7%), than low- (12.6%) or non-flow (7.3%) areas. Of GVs with I-pores, 83.2% had a single I-pore; 16.8% had multiple I-pores (range: 2–6). Additionally, 180 GVs (90 with I-pores and 90 without I-pores) were randomly selected, manually segmented, and three-dimensionally (3D) reconstructed to determine size, shape, and thickness of the cellular lining. Size of GVs (including median volume, surface area, and maximal cross-sectional area) with I-pores ( n = 90) was significantly larger than GVs without I-pores ( n = 90) using 3D-reconstructed GVs ( P ≤ 0.01). Most I-pores (73.3%; 66/90) were located on or close to GV's maximal cross-sectional area with significant thinning of the cellular lining. Our results suggest that larger size and thinner cellular lining of GVs may contribute to formation of GVs with I-pores. More GVs with I-pores and basal openings were observed in high-flow areas, suggesting these GVs do provide a channel through which AH passes into SC and that increasing this type of GV may be a potential strategy to increase aqueous outflow for glaucoma treatment. Highlights: Serial block-face scanning electron microscopy study of Schlemm's canal endothelium. More giant vacuoles with both I-pores and basal openings found in high-flow areas. Giant vacuoles with I-pores were larger in size than those without I-pores. Larger size and thinner cellular lining of giant vacuoles associated with I-pores.