Caveolar ultrastructural changes of the trabecular meshwork in primary open-angle glaucoma

Abstract

Purpose : Caveolae are abundant in Schlemm’s canal (SC) and trabecular meshwork (TM). One key function of caveolae is to respond to mechanosensitive stress and fluid pressure, resulting in remodeling of the extracellular environment and intraocular pressure (IOP) regulation. Our findings of lower expression of SDPR, a caveolae-related gene, in primary open angle glaucoma (POAG) led us to prospectively study caveolar ultrastructural changes in TM in comparison to healthy TM.

Methods :
The study was approved by the Institutional Review Board at Washington University. We collected TM specimens from POAG patients undergoing trabeculectomy surgery and healthy TM from donor residual corneoscleral rims after corneal transplant surgery. Standard transmission electron microscopy (TEM) was conducted (JEM 1400-EX) to evaluate ultrastructural changes. Immunolabeling TEM was performed to precisely identify and quantify TM caveolae with SDPR (rabbit polyclonal) and secondary antibodies (anti-rabbit gold nanoparticles; 10nm). Unpaired T-Test was used for data analysis.

Results :
In healthy donor TM (n=5), typical single and clustered caveolae (size 50~100 nm) were abundant in Schlemm’s canal (SC) and corneoscleral/uveoscleral TM regions. Numerous invaginated plasmalemmal and caveolar vesicles in the cytoplasm were identified. In POAG TM (n=3), caveolar structures on the plasma membrane and in the cytoplasm were difficult to identify. Caveolae counts (30 images per specimen), demonstrated significantly fewer caveolae in POAG TM (P=0.02). To further quantitate caveolar changes, immunogold-labeling TEM for SDPR indicated SDPR-specific labeling in caveolae, as both single and clustered structures on or near TM cell membrane at the inner endothelial wall of SC and corneoscleral meshwork.

Conclusions :
We report caveolar ultrastructural changes in POAG versus healthy TM. The significant decrease in caveolae in POAG may provide initial evidence for a novel mechanism for IOP dysregulation in glaucoma pathogenesis.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Figure 1. Transmission electron microscopy of caveolae in healthy donor trabecular meshwork (50~100 nm, red stars). Abundant invaginated plasmalemmal and caveolar vesicles in the cytoplasm are identified.
Figure 2. SDPR immunogold TEM labeling at the inner wall of Schlemm's canal (SC, Black dots, ~10nm).