Elastin modulation and modification by homocysteine: a key factor in the pathogenesis of Pseudoexfoliation syndrome?

Abstract

BackgroundPseudoexfoliation syndrome (PXF) is an idiopathic, elastogenesis-associated systemic disease characterised by amyloid-like material aggregates in the eye. Elevated plasma and aqueous humour (aqH) homocysteine (Hcy) is reportedly associated with PXF. This study is aimed to probe Hcy-mediated alterations in elastin expression.MethodologyLens level of Hcy (total Hcy (tHcy)), mRNA expression of Eln, CBS and MTR in lens capsule, protein expression of elastin in aqH were estimated by enzyme immunoassay, quantitative PCR and western blot, respectively in PXF, PXF with glaucoma (PXF-G) cases, in comparison with cataract-alone disease controls. Human lens epithelial cells (hLECs) were exposed to Hcy and homocysteine thiolactone (HCTL) to evaluate elastin expression in vitro. Furthermore, elastin recombinant protein was incubated with Hcy and HCTL to assess secondary and tertiary structural modifications based on circular dichroism spectroscopy, spectrophotometric and SEM studies.ResultsThe lens tHcy was significantly high in PXF (p=0.02) and PXF-G (p=0.009). Eln expression was elevated in PXF and PXF-G (p=0.0007). Elastin level in aqH was elevated in PXF (p=0.01) and PXF-G (p=0.002). Hcy (200 µM) and HCTL (1 µM) promoted elastin expression at mRNA level by 36-fold (p=0.02) and 10-fold (p=0.05), respectively, and at protein level by nearly two-fold in cultured hLECs. Secondary structure changes in elastin protein caused by Hcy were evident from 34.11% drop in α-helix and 6.17% gain in β-sheet. Fluorescence, spectral assays and SEM analyses showed aggregation and amyloid formation of elastin with homocysteinylation.ConclusionThe study reveals that lens accumulation of Hcy associated with hyperhomocysteinaemia is characteristic of PXF that augments elastin expression. Hcy causes structural changes promoting elastin aggregation, thereby contributing to defective elastin in PXF and PXF-G.

Automated AI labelling of optic nerve head enables new insights into cross-ancestry glaucoma risk and genetic discovery in over 280,000 images from the UK Biobank and Canadian Longitudinal Study on Aging

“…We use transfer learning to train three CNN models for image gradability, VCDR, and vertical disc diameter (VDD) values from ~70,000 UKB fundus images graded by clinicians. These models were then applied to all UKB fundus images (85,736 participants and 175,770 images in total) and another independent cohort -the Canadian Longitudinal Study on Aging (CLSA, 29,635 participants and 106,330 images in total). We performed the largest AI-based GWAS for VCDR and VDD, and replicated novel genetic discoveries in clinician-graded fundus images from International Glaucoma Genetics Consortium (IGGC) and in glaucoma case-control studies (UKB and the Australian and New Zealand Registry of Advanced Glaucoma; ANZRAG).…”

Analysis of Genetically Determined Gene Expression Suggests Role of Inflammatory Processes in Etiology of Exfoliation Syndrome

“…1,2 It is the most common cause of secondary glaucoma, resulting in widespread global blindness. 3 In addition to ocular manifestations, exfoliation syndrome deposits have been observed in visceral organs, such as the lung, kidney, liver and gallbladder. 2,4 In addition to elastic tissue disorders, XFS has also been associated with increased risk of vascular diseases.…”

“…[5][6][7] Associations of XFS to several systemic biomarkers of inflammation, including complement components and homocysteine, have also been reported. 3,8,9 Genetic mechanisms have substantial influence on XFS etiology as evidenced in family and twin studies. 10,11 There have been eight genome-wide association studies (GWAS) of XFS, 7,[12][13][14][15][16][17][18] three of which include meta-analysis, 7,12,13 that have cumulatively identified >60 associated genetic variants.…”

Analysis of Genetically Determined Gene Expression Suggests Role of Inflammatory Processes in Exfoliation Syndrome

“…1,2 It is the most common cause of secondary glaucoma, resulting in widespread global blindness. 3 In addition to ocular manifestations, exfoliation syndrome deposits have been observed in visceral organs, such as the lung, kidney, liver and gallbladder. 2,4 In addition to elastic tissue disorders, XFS has also been associated with increased risk of vascular diseases.…”

“…[5][6][7] Associations of XFS to several systemic biomarkers of inflammation, including complement components and homocysteine, have also been reported. 3,8,9 Genetic mechanisms have substantial influence on XFS etiology as evidenced in family and twin studies. 10,11 There have been eight genome-wide association studies (GWAS) of XFS, 7,[12][13][14][15][16][17][18] three of which include meta-analysis, 7,12,13 that have cumulatively identified >60 associated genetic variants.…”