3100 - A Novel G Protein Coupled Receptor Circuit Regulates Hematopoiesis

Abstract

Hematopoietic stem cell (HSC) generation is a complex process that is tightly regulated by a variety of integrated molecular signals. Gpr56, a G-coupled receptor protein, is most highly expressed in HSCs as they are generated. Despite the demonstration that Gpr56 is required for HSC generation in zebrafish, its role in mammalian haematopoiesis remains unclear and controversial. In this study, we examine the function of Gpr56 by taking advantage of our unique mouse Gata2Venus embryonic stem cell line (G2V ESC). G2V ESCs are an excellent tool to examine the role of Gpr56 in hematopoiesis in vitro. In vitro hematopoietic differentiation of mouse G2V ESC showed that Gpr56 is mainly expressed in the Gata2-expressing cell fraction, which is enriched in hematopoietic progenitor cells (HPC). When Gpr56 knockout (G56-/-) G2V ESCs are differentiated, a surprising increase in Gata2 expressing cells and HPCs was found. Preliminary data demonstrate that another G-coupled receptor protein, Gpr97 (located at same locus as Gpr56) is highly expressed when Gpr56 is deleted. A Gpr56 gain-of-function approach is also being taken to explore the mechanism by which this receptor acts in HSCs. To this end, we are using an innovative approach to target mouse and human pluripotent stem cells to ensure the Gpr56 overexpression during the different stages of in vitro differentiation. The data so far collected demonstrate that Gpr56 is required for the maintenance of HSC physiology, and suggest that Gpr97 is a novel molecule that could support a compensatory, and possibly an additional, function in HSCs.