Study of N-Linked Glycoproteins in Tears From Patients With Climatic Droplet Keratopathy in Argentina

Abstract

Purpose: : Climatic droplet keratopathy (CDK) is a degenerative corneal disease with a high prevalence in a region of the Argentina Patagonia, characterized by accumulation of proteins in the anterior stroma and Bowman membrane which cause progressive opacity of these layers. Although the causes of this disease remain unknown, it is considered a multifactorial disease related to environmental factors. Since glycoproteins are potentially biomarkers of diseases we decided to investigate N-linked glycoproteins in tears of CDK patients and compare these profiles with tears from normal individuals.

Methods: : 13 CDK patients and 11 control subjects with clinically normal eyes and no history of eye disease or eye surgery were recruited for this study.Tear samples were pre-fractionated using a hydrazide-resin capture method, and the previously N-glycosylated peptides were then subjected to two-dimensional nano-LC-nano-ESI-MS/MS analysis to obtain peptide fragmentation patterns for identification through protein database searches. Quantitative comparisons of N-glycoprotein profiles in tear fluid of patients with CDK and to that of non-diseased controls used glycopeptide capture, iTRAQ labeling and 2D nano-LC-nano-ESI-MS/MS analysis.

Results: : From 43 unique N-glycoproteins we identified 19 not previously described in tears. More over, when we quantitatively compared N-glycoprotein profiles in tear fluid from CDK patients with non-diseased controls we found that five N-glycosylated proteins were differentially expressed in CDK patients. Four of them (haptoglobin, polymeric immunoglobulin receptor, immunoglobulin J chain and an uncharacterized protein) were up-regulated in tears from CDK patients whereas lacritin was down-regulated.

Conclusions: : The significant up-regulation of N-glycosylated haptoglobin in CDK, which is related to exposure to ultraviolet irradiation, could be clinically significant in terms of disease etiology and biomarker discovery. Further analysis of the biochemical pathways of significant proteins should improve our understanding of CDK

Keywords: pathology: human • cornea: tears/tear film/dry eye • proteomics