Molecular profile and partial functional analysis of novel endothelial cell derived growth factors that regulate hematopoiesis

¹ Duke University, Durham, North Carolina
² Predictive Diagnostics Incorporated, Vacaville, California
³ Duke University Medical Center, Durham, North Carolina

^* To whom correspondence should be addressed. E-mail: john.chute{at}duke.edu.

	Abstract

Recent progress has been made in the identification of the osteoblastic cellular niche for hematopoietic stem cells (HSCs) within the bone marrow (BM). Attempts to identify the soluble factors that regulate HSC self-renewal have been less successful. We have demonstrated that primary human brain endothelial cells (HUBECs) support the ex vivo amplification of primitive human BM and cord blood (CB) SCID-repopulating cells (SRCs). In this study, we sought to characterize the soluble hematopoietic activity produced by HUBECs and to identify the growth factors secreted by HUBECs that contribute to this HSCsupportive effect. Extended non-contact HUBEC cultures supported an 8-fold increase in SRCs when combined with thrombopoietin, stem cell factor, and flt3-ligand (TSF) compared to input CD34⁺ cells or cytokines alone. Gene expression analysis of HUBEC biological replicates identified 65 differentially expressed, non-redundant transcripts without annotated hematopoietic activity. Gene ontology studies of the HUBEC transcriptome revealed a high concentration of genes encoding extracellular proteins with cell-cell signaling function. Functional analyses demonstrated that adrenomedullin, a vasodilatory hormone, synergized with SCF and Flt-3 ligand to induce the proliferation of primitive human CD34⁺CD38^-lin^- cells and promoted the expansion of CD34⁺ progenitors in culture. These data demonstrate the potential of primary HUBECs as a reservoir for the discovery of novel secreted proteins that regulate human hematopoiesis.