Targeted Lipidomic Analysis of Aqueous Humor Reveals Signaling Lipid-Mediated Pathways in Primary Open-Angle Glaucoma

Abstract

Primary open-angle glaucoma (POAG) is characterized by degeneration of retinal ganglion cells associated with an increase in intraocular pressure (IOP) due to hindered aqueous humor (AH) drainage through the trabecular meshwork and uveoscleral pathway. Polyunsaturated fatty acids and oxylipins are signaling lipids regulating neuroinflammation, neuronal survival and AH outflow. Among them, prostaglandins have been previously implicated in glaucoma and employed for its treatment. This study addressed the role of signaling lipids in glaucoma by determining their changes in AH accompanying IOP growth and progression of the disease. Eye liquids were collected from patients with POAG of different stages and cataract patients without glaucoma. Lipids were identified and quantified by UPLC-MS/MS. The compounds discriminating glaucoma groups were recognized using ANCOVA and PLS-DA statistic approaches and their biosynthetic pathways were predicted by bioinformatics. Among 22 signaling lipids identified in AH, stage/IOP-dependent alterations in glaucoma were provided by a small set of mediators, including 12,13-DiHOME, 9- and 13-HODE/KODE, arachidonic acid and lyso-PAF. These observations correlated with the expression of cytochromes P450 (CYPs) and phospholipases A2 in the ocular tissues. Interestingly, tear fluid exhibited similar lipidomic alterations in POAG. Overall, POAG may involve arachidonic acid/PAF-dependent pathways and oxidative stress as evidenced from an increase in its markers, KODEs and 12,13-DiHOME. The latter is a product of CYPs, one of which, CYP1B1, is known as POAG and primary congenital glaucoma-associated gene. These data provide novel targets for glaucoma treatment. Oxylipin content of tear fluid may have diagnostic value in POAG.

Analyses of pseudoexfoliation aqueous humor lipidome

“…25 Targeted lipidomic analysis has been performed for POAG but not for PEX or PEXG. 24 Another independent lipidomic study revealed significant increases in the concentrations of 14 sphingomyelin (SM) and 5 cholesteryl ester (ChoE) species from open angle glaucoma (OAG) AH samples. 9 The univariate analysis of the profile showed that 37 out of 110 lipids to undergo statistically significant concentration changes in OAG compared to controls, with most of the species belonging to chemical groups diacylglycerophosphocholines (DAPCs) and 1-ether, 2-acylglycerophosphocholines (MEMAPCs).…”

“…20 Lipidomic studies previously published have focused on sphingolipids, phospholipids, cholesterol, and glycosphingolipids of glaucomatous tissues (i.e., POAG) and the AH. [21][22][23][24] In this study, we expanded our analysis to include PEX, PEXG, POAG and controls with the inclusion of additional lipids like cholesterol esters, TGs, diacylglycerols, and ceramides. Currently, there is not enough available research to provide a definitive answer to explain how the proteome, lipidome, and metabolome converge.…”

Clinical Tear Fluid Proteomics—A Novel Tool in Glaucoma Research

“…Studies of small extracellular vesicles (sEVs) also enable further morphologic examination of the tear fluid [ 31 ]. Lipidomic and metabolomic tear analyses are also being carried out and produce complementary information about the tear fluid state and composition [ 4 , 21 , 32 ].…”

“…These proteins in the aqueous layer make up the majority of the proteins identified in tear fluid, although the mucins from the mucin layer can also be detected. The outermost lipid layer, which can be studied with tear lipidomics [ 4 ], “seals” the tear film and prevents its evaporation from the ocular surface in-between blinks.…”

Identification of the novel role of sterol regulatory element binding proteins (SREBPs) in mechanotransduction and intraocular pressure regulation

“…Cellular lipids play important roles in tissue biomechanics by modulating the plasma membrane remodeling, signal transduction cascades, and actin cytoskeleton-cell adhesions linked to the ECM (26). Moreover various lipids found in TM and AH are known to impact IOP homeostasis (27)(28)(29). This is attributed via modulating the signaling events including altering the TM contractility and tissue stiffness.…”