Lysophosphatidic acid induced red blood cell aggregation in vitro

Under physiological conditions healthy RBCs do not adhere to each other. There are indications that RBCs display an intercellular adhesion under certain (pathophysiological) conditions. Therefore we investigated signaling steps starting with transmembrane calcium transport by means of calcium imaging. We found a lysophosphatidic acid (LPA) concentration dependent calcium influx with an EC50 of 5 μM LPA. Downstream signaling was investigated by flow cytometry as well as by video-imaging comparing LPA induced with “pure” calcium mediated phosphatidylserine exposure and concluded the coexistence of two branches of the signaling pathway. Finally we performed force measurements with holographic optical tweezers (HOT): The intercellular adhesion of RBCs (aggregation) exceeds a force of 25 pN. These results support (i) earlier data of a RBC associated component in thrombotic events under certain pathophysiological conditions and (ii) the concept to use RBCs in studies of cellular adhesion behavior, especially in combination with HOT. The latter paves the way to use RBCs as model cells to investigate molecular regulation of cellular adhesion processes.

► Lysophosphatidic acid leads to concentration dependent Ca2+ entry in red blood cells.
► Lysophosphatidic acid induces phosphatydylserine exposure via 2 alternative pathways.
► Lysophosphatidic acid triggered intercellular red blood cell adhesion exceeds 25 pN.
► Red blood cells and laser tweezers are a good model system to investigate adhesion.
► Red blood cell adhesion/aggregation has most likely a pathophysiological relevance.