Abstract
Purpose :
There is a lack of mechanistic understanding of how deposits form in pseudoexfoliative glaucoma (PEX). This study tested the hypotheses that high vitamin D binding protein (GC) levels, linked to increased solar exposure, provide a nucleation center that promotes the formation of PEX deposits and that GC overexpression in mice leads to anterior chamber deposit formation.
Methods :
We collected ~100 µl of aqueous humor (AH) by performing paracentesis on PEX, primary open-angle glaucoma, and cataract patients (n=12 per group). All patients were Caucasian, aged 65±5, 67±4, and 66±6 in the PEXG, POAG, and cataract groups, respectively. The patients were evenly distributed by sex and had no other ocular diseases. In order to test if GC provides a nucleation center for deposit formation in vitro, 10 µl of AH from each group were seeded with and without 1 µl GC, covered with a coverslip, sealed with an insert, and incubated for five days. The slides were observed daily and imaged with confocal microscopy. 10 out of 20 C57BL/6J mice (4-month-old, even sex distribution) were subjected to lentiviral overexpression of GC protein via a CMV promoter with IRES GFP expression. In contrast, the other ten were subjected to an empty vector with the same promoter and expression. The mice's anterior chambers were evaluated for deposit formation 45 days after overexpression. Detection of green fluorescence, a sign of GFP expression, was done using an anterior segment microscope. Intraocular pressure (IOP) was measured using a Tonolab, and the results were analyzed.
Results :
By day five, all PEX patient AH samples seeded with GC displayed deposit formation. Incubation beyond seven days led to crystal formation in 30% of PEX AH. None of the POAG and cataract AH samples formed deposits. Furthermore, 6/10 GC overexpression mice had IOP measurements of 22±3 mmHg compared to 15±2 mmHg in 10/10 control mice. In our endpoint analysis, all GC overexpression mice developed deposits in their anterior segments.
Conclusions :
Our results are consistent with our hypothesis that GC serves as a nucleation center that promotes the formation of PEX deposits. These results provide insight into the molecular aspect of PEX deposit formation, which can lay the foundation for creating molecularly targeted treatment for this type of glaucoma.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.