Title : Amyloid associated protein misfolding and structural alterations in human cataractous lenses
Abstract:
Cataract, opacification of the lens, is a multifactorial eye disease affecting millions of people globally. However, its underlying etiology remains unclear despite progress in surgical methods. Although researchers have implicated oxidative stress and post- translational modifications, the fundamental mechanisms leading to the loss of lens transparency remain unclear. Recent studies have suggested that amyloidogenic protein aggregation may underlie lens opacification by disrupting the ordered packing of crystallins. To address this gap, the present study utilises histology, raman spectroscopic imaging, and laser microdissection-based tandem mass spectrometry to elucidate the molecular mechanism of amyloidogenesis in human cataractous lenses. Lens samples were collected from patients exhibiting nuclear, cortical, posterior subcapsular, and mixed cataracts (Emery-Little grade II–IV). The Congo-Red staining indicated the presence of amyloid in certain lenses, particularly nuclear cataracts, which exhibited apple-green birefringence when observed under polarised light. A proteomic analysis of amyloid-positive regions using LMD-MS/MS identified the presence of α-, β-, and γ-crystallins, heat shock proteins, and extracellular matrix components, highlighting the compositional diversity of lens amyloid aggregates. Raman spectroscopy revealed structural alteration in protein peaks associated with cataract formation. In advanced cataracts, there was a gradual burying of tyrosine residues and a rise in β-sheet formation. This was shown by the fact that the tyrosine doublet intensity ratio (I~852/I~830 cm?¹) went from 0.9 to 0.6 (r = -0.805). The decrease in tryptophan-associated peaks in amyloid-positive regions significantly corroborates the destabilisation of crystallin structure. The amide I (1670 cm?¹) and III (1246 cm?¹) bands correlated with LMD-MS/MS-derived crystallin and heat shock protein profiles, confirming the structural-proteomic correlation. Together, these findings support the concept that cataract is marked by amyloidogenic misfolding pathways. The combination of multimodal molecular imaging and proteomics establishes a robust framework for understanding the biological basis of cataract formation. This approach offers potential for identifying early biomarkers and and aggregation-prone crystallin isoforms to deepen understanding of cataract pathogenesis and facilitate the development of pharmacological strategies to prevent or slow disease progression.
