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.

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The LOXL1 SNPs, rs1048661 and rs3825942, are associated with PXF in the South Indian population correlating with lowered LOX activity in the aqueous humor. The increased level of total TGF-β in the aqueous humor of PXF cases is possibly associated with LOX regulation which needs further investigation.

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