Activation of Lysophosphatidic Acid Receptor 3 Inhibits Megakaryopoiesis in Human Hematopoietic Stem Cells and Zebrafish

Lysophosphatidic acid (LPA) is a membrane-derived lysophospholipid that exists in the plasma and platelets. It exerts its functions through activation of various LPA receptors (LPARs), which belong to the family of G protein-coupled receptors (GPCRs). Activation of LPARs has important roles in stem cell differentiation. However, how LPA affects human hematopoietic stem cell (HSC) differentiation remains elusive. In our previous studies, we have suggested that LPA receptor 2 (LPA₂) and LPA receptor 3 (LPA₃) play opposing roles, and may act as a molecular switch during megakaryocytic differentiation in K562 cells. In this study, human CD34⁺ hematopoietic stem cell (HSCs) and zebrafish are adopted to investigate the roles of LPA₃ during megakaryopoiesis/thrombopoiesis <i>in vitro</i> and <i>in vivo</i>. Our results show that <i>LPAR3</i> mRNA expression level is decreased upon induction by thrombopoietin and stem cell factor in human HSCs. Using pharmacological activators and shRNA knockdown experiments, we demonstrate that activation of LPA₃ inhibits megakaryopoiesis in human HSCs. In addition, pharmacological activation of LPA₃ suppressed thrombopoiesis in zebrafish. Furthermore, blockage of LPA₃ translation by morpholino increased the number of CD41-GFP⁺ cells in Tg(CD41:eGFP) zebrafish. Moreover, the mRNA expression level of <i>zCD41</i> increased significantly in LPA₃-knockout zebrafish. These results clarify the negative role of LPA₃ during megakaryopoiesis and provide important information for potential treatments of related diseases, such as megakaryopenia.