Dysregulated Retinoic Acid Signaling in the Pathogenesis of Pseudoexfoliation Syndrome

Abstract

Pseudoexfoliation (PEX) syndrome, a stress-induced fibrotic matrix process, is the most common recognizable cause of open-angle glaucoma worldwide. The recent identification of PEX-associated gene variants uncovered the vitamin A metabolic pathway as a factor influencing the risk of disease. In this study, we analyzed the role of the retinoic acid (RA) signaling pathway in the PEX-associated matrix metabolism and evaluated its targeting as a potential candidate for an anti-fibrotic intervention. We provided evidence that decreased expression levels of RA pathway components and diminished RA signaling activity occur in an antagonistic crosstalk with TGF-β1/Smad signaling in ocular tissues and cells from PEX patients when compared with age-matched controls. Genetic and pharmacologic modes of RA pathway inhibition induced the expression and production of PEX-associated matrix components by disease-relevant cell culture models in vitro. Conversely, RA signaling pathway activation by natural and synthetic retinoids was able to suppress PEX-associated matrix production and formation of microfibrillar networks via antagonization of Smad-dependent TGF-β1 signaling. The findings indicate that deficient RA signaling in conjunction with hyperactivated TGF-β1/Smad signaling is a driver of PEX-associated fibrosis, and that restoration of RA signaling may be a promising strategy for anti-fibrotic intervention in patients with PEX syndrome and glaucoma.

Genome-Wide RNA Sequencing of Human Trabecular Meshwork Cells Treated with TGF-β1: Relevance to Pseudoexfoliation Glaucoma

“…Retinoic acid signalling has been reported to play a role in XFG and XFS [ 12 ] but our enrichment analysis did not reveal any enrichment terms directly associated with retinoic acid signalling, metabolism or transport; although some genes that are important in retinoic acid pathways (such as STRA6) did appear in other enrichment terms such as “eye development” and “artery development”. To investigate retinoic acid pathways in our dataset, a custom gene list was created by combining gene lists of Reactome pathways R-HSA-5362517 Signaling by Retinoic Acid and GO:0001523 retinoid metabolic process resulting in a list of 118 unique genes in total.…”

“…Retinoic acid signalling has been reported to play a role in the pathogenesis of XFG and to modulate the activated TGF-β pathway by changing levels of phosphorylation [ 12 ]. Our results showed differential expression of several genes involved in retinoic acid transport and signalling.…”

“…XFS and XFG are highly associated with single nucleotide polymorphisms of lysyl oxidase like 1 (LOXL1) [ 7 ], a gene which is involved in crosslinking collagen and elastin, and which is also a component of the XFM [ 5 ]. Certain risk-alleles in LOXL1 that are highly associated with XFS/XFG are also common in unaffected individuals indicating that other risk-factors play a role in the development of XFS/XFG, such as, older age, exposure to UV radiation [ 8 ], reactive oxygen species [ 9 ], homocysteinaemia [ 10 ] and folate intake [ 11 ], dysregulated retinoic acid signalling [ 12 ], latitude probably related to UV exposure [ 8 ], impaired autophagy [ 13 ] and elevation of several signal molecules such as transforming growth factor beta 1 (TGF-β1) in the aqueous humour (AH) [ 14 ]. In XFG, TGF-β1 is upregulated both in active form in the AH and in its latent form as part of the large latent complex which binds to the extracellular matrix (ECM) [ 14 ].…”

“…There is significant overlap between biological processes known to be activated by TGF-β1 [ 21 ] and pathological fibrotic changes in XFG such as XFM production [ 5 , 14 ], oxidative stress [ 6 , 22 ], unfolded protein response [ 23 ], dysregulated retinoic acid signalling [ 12 ] and fibrotic ECM remodelling [ 20 ] suggesting that TGF-β1 plays an important role in the pathogenesis of XFG [ 20 ]. Therefore, the main purpose of this study was to perform a hypothesis-independent RNA sequencing analysis to investigate genome-wide alterations in the transcriptome of normal HTMs stimulated with TGF-β1 and investigate possible pathophysiological mechanisms driving XFG.…”

All-trans Retinoic Acids Synergistically and Beneficially Affect In Vitro Glaucomatous Trabecular Meshwork (TM) Models Using 2D and 3D Cell Cultures of Human TM Cells

“…In addition, Nishikiori et al reported an interesting result in terms of the relationship between RA and BRB. That is, RAR alpha caused significant reductions in vascular leakage in the diabetic retina by antagonizing the loss of tight junction integrity that is induced by diabetes [ 38 ]. These observations corresponded well with our current results, which show that ATRA exerts synergistic and beneficial effects in TGF-β2-treated 2D- and 3D-cultured HTM cells; our results were found through in vitro models that replicate the single- and multiple-sheet barrier structures of the HTM [ 25 , 26 , 39 , 40 , 41 ].…”