Bone marrow stroma-derived prolactin is involved in basal and platelet activating factor-stimulated in vitro erythropoiesis

Abstract

Blood cell development occurs in close association with bone marrow stroma cells (BMSC), which provide nutritive and adhesive support for stem cell survival, proliferation, and differentiation through cell-cell interaction and production of short-range acting hemopoietic growth factors (HGF). Cooperation between exogenous prolactin (Prl) and HGF at an early step of in vitro erythroid differentiation has been shown in a previous study To gain more insight into the role of Prl in in vivo hemopoiesis, we have now addressed the involvement of endogenous Prl in the growth of hemopoietic progenitors (HP) in a BMSC environment. We found that development of burst-forming unit-erythroid (BFUE) colonies from CD34+ HP cultured on a autologous BMSC layer was slightly, but significantly reduced in the presence of an antihuman Prl antibody. Pre-treatment of BMSC with Platelet activating factor (PAF), a potent inflammatory mediator, specifically increased the BFU-E colony efficiency of co-cultured CD34+ cells, through the release of Prl by BMSC, as demonstrated by immunoprecipitation and western blotting, enzyme-linked-immunospot (Elispot), and RT-PCR experiments. Lastly, responsiveness of BMSC to PAF was substantiated by the presence of the PAF receptor mRNA on these cells. These findings, together with our previous observation of a synergistic effect of exogenous Prl on GM-CSF, IL-3 and Erythropoietin-driven BFU-E colony formation, suggest an interactive role for Prl and other HGF in vivo at the sites of hemopoiesis. In addition, the present data reinforce the modulatory role of PAF in hemopoiesis and indicate that Prl may be one of the mediators of its effect.