Discovery and Verification of Sjögren’s Syndrome Protein Biomarkers in Tears by Targeted LC-MRM

Sjögren’s syndrome (SS) is an autoimmune
rheumatic disorder characterized by exocrine gland dysfunction, mainly
from the lacrimal and salivary glands. The disease causes severe aqueous
dry eye syndrome (DED) and is associated with high rates of complications,
including corneal ulceration, scaring, and perforation. Systemic complications
may occur as well as a higher risk of developing lymphoma. Diagnosis
of SS-DED is often delayed and difficult to establish. With the aim
of discovering biomarkers to help discriminate SS-DED patients, a
combination of untargeted and targeted LC-MS/MS analyses were performed
on tear samples collected on Schirmer strips and subjected to tryptic
digestion. Following the analysis of three cohorts and the development
of two targeted LC-sMRM methods for the verification of putative biomarkers
found in the first cohort of samples, 64 proteins could be linked
to Sjögren’s syndrome, in the hopes of helping to confirm
diagnoses as well as potentially stratifying the severity of disease
in these patients. Proteins that were increased in SS-DED showed activation
of the immune system and alterations in homeostasis. Several proteases
and protease inhibitors were found to be significantly changing in
SS-DED, as well as a consistent decrease in specific proteins known
to be secreted by the lacrimal gland.