Proteomic Analysis of Human Conjunctival Cells and Tears Collected with Schirmer Strips Using TimsTOF Pro

This study aimed to investigate the human tear proteins extracted from whole (W) Schirmer strips (ScS) and their two parts, the bulb (B) and the rest of the strip (R) with a comprehensive proteomic approach using a trapped ion mobility mass spectrometer, the timsTOF Pro. Eight ScS were collected from two healthy subjects at 4 different visits to be separated into three batches: 4W, 4B and 4R. In total, 1582 proteins were identified in the W, B and R batches. Among all iden-tified proteins, binding proteins (43.4%) and those with catalytic activity (42.2%) constituted more than 80% of the molecular functions. The most represented biological processes were cel-lular processes (31.2%), metabolic processes (20.8%) and biological regulation (13.1%). Enzymes were the most represented protein class (41 %), consisting mainly of hydrolases (47.5%), oxi-doreductases (22.1%) and transferases (16.7%). The bulb (B), which is in contact with the conjunc-tiva, might collect both tear and cell proteins and therefore promote identification of more pro-teins. Processing B and R separately before MS analysis, combined with the high data acquisition speed and the addition of ion-mobility-based separation in timsTOF Pro, can bring a new dimension to biomarker investigations of a limited sample such as tear fluid.