Quantitative Glycoproteomic Analysis Identifies Platelet-Induced Increase of Monocyte Adhesion via the Up-Regulation of Very Late Antigen 5

Physiological
stimuli, such as thrombin, or pathological stimuli,
such as lysophosphatidic acid (LPA), activate platelets circulating
in blood. Once activated, platelets bind to monocytes via P-selectin–PSGL-1
interactions but also release the stored contents of their granules.
These platelet releasates, in addition to direct platelet binding,
activate monocytes and facilitate their recruitment to atherosclerotic
sites. Consequently, understanding the changes platelet releasates
induce in monocyte membrane proteins is critical. We studied the glyco-proteome
changes of THP-1 monocytic cells affected by LPA- or thrombin-induced
platelet releasates. We employed lectin affinity chromatography combined
with filter aided sample preparation to achieve high glyco- and membrane
protein and protein sequence coverage. Using stable isotope labeling
by amino acids in cell culture, we quantified 1715 proteins, including
852 membrane and 500 glycoproteins, identifying the up-regulation
of multiple proteins involved in monocyte extracellular matrix binding
and transendothelial migration. Flow cytometry indicated expression
changes of integrin α5, integrin β1, PECAM-1, and PSGL-1.
The observed increase in monocyte adhesion to fibronectin was determined
to be mediated by the up-regulation of very late antigen 5 via a P-selectin–PSGL-1
independent mechanism. This novel aspect could be validated on CD14+
human primary monocytes, highlighting the benefits of the improved
enrichment method regarding high membrane protein coverage and reliable
quantification.