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The Role of Schlemm's Canal Endothelium Cellular Connectivity in Giant Vacuole Formation: A 3D Electron Microscopy
Julia Lai1, Yanfeng Su1,2, David L Swain1,3
1Department of Ophthalmology, Boston University School of Medicine, Boston, Massachusetts, United States.
Insights
Cellular connections in Schlemm's canal (SC) inner wall (IW) influence giant vacuole (GV) formation and pore development. Reduced IW/JCT and IW/IW connectivity may increase GV volume and promote pore formation, impacting intraocular pressure (IOP).
Area of Science:
- Ocular Physiology
- Cell Biology
- Glaucoma Research
Background:
- Schlemm's canal (SC) inner wall (IW) endothelium and juxtacanalicular connective tissue (JCT) are critical for aqueous humor outflow.
- Giant vacuoles (GVs) and pores within the trabecular meshwork are implicated in regulating intraocular pressure (IOP).
Purpose of the Study:
- To investigate the role of cellular connectivity between SC IW endothelium and JCT, and between IW endothelial cells, in GV and pore formation.
- To compare these cellular connections in perfusion-fixed versus immersion-fixed human donor eyes.
Main Methods:
- Human donor eyes (n=4) were immersion- (0 mm Hg) or perfusion-fixed (15 mm Hg).
- Trabecular meshwork near SC was imaged using scanning electron microscopy.
- 3D reconstructions of 12 IW cells per group were analyzed for IW/JCT and IW/IW connectivity, GV characteristics, and pore formation.
Main Results:
- Perfusion-fixed eyes showed significantly decreased IW/JCT connections and increased GV volume compared to immersion-fixed eyes.
- Intracellular pores were observed in GVs in perfusion-fixed eyes only.
- Decreased IW/IW connectivity correlated with increased GV volume and the presence of paracellular pores.
Conclusions:
- Changes in IW/JCT connectivity may drive larger GV formation.
- Reduced IW/IW connectivity appears to promote paracellular pore formation.
- Targeting IW/JCT and IW/IW connectivity presents a potential strategy for regulating outflow resistance and IOP.
Purpose:
We investigated whether cellular connectivity between Schlemm's canal (SC) inner wall (IW) endothelium, and juxtacanalicular connective tissue (JCT), and between IW endothelial cells, plays a role in giant vacuole (GV) and pore formation by comparing perfusion- and immersion-fixed eyes.
Methods:
Normal human donor eyes (n = 4) were either immersion-fixed (0 mm Hg) or perfusion-fixed (15 mm Hg). Trabecular meshwork near SC was imaged using serial block-face scanning electron microscopy. A total of 12 IW cells from each group were 3D-reconstructed from ∼7040 electron micrographs and compared. In each cell, connections between IW cells and JCT cells/matrix were quantified; IW/IW connectivity was measured by cell border overlap length. GV volume, density, shape, and intracellular and paracellular pores were analyzed.
Results:
The mean number of IW/JCT cell-cell connections per cell significantly decreased (P < 0.01) while the summed GV volume per cell significantly increased (P < 0.01) in perfusion-fixed eyes compared to immersion-fixed eyes. Intracellular pores were observed in 14.6% of GVs in perfusion-fixed eyes and not observed in immersion-fixed eyes. The mean IW/IW overlap length per cell decreased (P < 0.01), and paracellular pores were found only in regions where IW/IW connectivity was minimal (overlap length = 0 μm) in perfusion-fixed eyes and not observed in immersion-fixed eyes.
Conclusions:
Our data suggest that changes in IW/JCT connectivity may be an important factor in the formation of larger GVs, and decreased IW/IW connectivity may promote paracellular pore formation. Targeting the IW/JCT and IW/IW connectivity may therefore be a potential strategy to regulate outflow resistance and IOP. .