Possible role of differentially expressing novel protein markers (ligatin and fibulin‐7) in human aqueous humor and trabecular meshwork tissue in glaucoma progression

Abstract

The pathological mechanism underlying glaucoma has always been a complex aspect of this permanently blinding disease but proteomic studies have been helpful in elucidating it to a great extent in several studies. This study was designed to evaluate the expression and to get an idea about the function of two novel markers (ligatin and fibulin‐7) identified in human aqueous humor (hAH) in relation to glaucomatous progression. A significant increase in the protein content of glaucomatous hAH compared to that of non‐glaucomatous controls (NG‐Ctrls) was observed. Ligatin, fibulin‐7, and its proteolysis were revealed in hAH of primary open angle glaucoma (POAG), primary angle closure glaucoma (PACG) and NG‐Ctrls. Quantification confirmed no significant difference in expression of ligatin, whereas fibulin‐7 was significantly (P < 0.05) low in hAH of PACG in comparison to NG‐Ctrls and POAG. Importantly the immunohistochemical assay for both indicated their possible involvement in the maintenance of the appropriate structure of TM in vivo. Since oxidative stress is a major contributor to glaucomatous pathogenesis, in vitro analysis of nuclear and cytoplasmic fractions indicated intracellular changes in localization and expression of ligatin upon oxidative insult of human trabecular meshwork (TM) cells. While no such changes were found for fibulin‐7 expression. This was also corroborated with the immunocytochemical assay. Though a study with a small sample size, this is the first report which confirms the presence of ligatin and fibulin‐7 in hAH, quantified their differential expression, and indicated the possibility of their involvement in the maintenance of the TM structure.

The role of adhesion protein Fibulin7 in development and diseases

“…The authors claimed the role of Fbln7 in the TM to be mainly structure related and not in any protective function (Fig. 2a) (Basu et al 2019). Further studies with a larger sample size will determine the potential of Fbln7 to be a biomarker in PACG.…”

“…Glaucoma, a chronic eye disease, involves the apoptosis of retinal ganglion cells and functional loss of the trabecular meshwork (TM) (Basu et al 2019). It is one of the leading causes of permanent blindness affecting more than 60 million people globally (Quigley and Broman 2006).…”

“…It is one of the leading causes of permanent blindness affecting more than 60 million people globally (Quigley and Broman 2006). Very recently, Basu et al reported the existence of Fbln7 in human aqueous humor (hAH) (Basu et al 2019). The study showed that Fbln7 expression in hAH of primary angle-closure glaucoma (PACG) patients is significantly lower as compared to nonglaucomatous controls and primary open-angle glaucoma (POAG) patients.…”

Candidate Glaucoma Biomarkers: From Proteins to Metabolites, and the Pitfalls to Clinical Applications

“…A liquid chromatography tandem mass spectrometry (LC–MS/MS) proteomics analysis carried out in the aqueous humor of POAG (n = 90), PACG (n = 72), and control (n = 78) subjects showed the under-regulation of the extracellular matrix proteins OPN, CD, and cystatin C (CysC), which was further validated by Western blot (WB), with the exception of CD [ 78 ]. Recently, the levels of fibulin (FBLN)-7—an adhesion molecule that interacts with extracellular matrix molecules involved in the maintenance of the trabecular meshwork’s functionality—were found to be downregulated in the aqueous humor of PACG patients when compared with POAG and control subjects [ 79 ]. The same group also determined the concentration of clusterin (CLU) in the aqueous humor and tears of POAG, PEXG, and control subjects via ELISA, observing markedly higher aqueous humor CLU levels in patients with PEXG [ 80 ].…”