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THE STEM CELL NICHE

Molecular Profile and Partial Functional Analysis of Novel Endothelial Cell-Derived Growth Factors that Regulate Hematopoiesis

^a Division of Cellular Therapy, Department of Internal Medicine,
^b Institute for Genome Sciences and Policy, Department of Molecular Genetics and Microbiology,
^d Department of Bioinformatics and Biostatistics, Duke University, Durham, North Carolina, USA;
^c Predictive Diagnostics Incorporated, Vacaville, California, USA

Key Words. Endothelial cell • Stem cell expansion • Hematopoietic stem cell

Correspondence: John P. Chute, M.D., Division of Cellular Therapy, Duke University, 2400 Pratt Street, Suite 1100, Box 3961, Durham, North Carolina 27710, USA. Telephone: 919-668-4706; Fax: 919-668-1091; e-mail: john.chute{at}duke.edu

Received January 21, 2005; accepted for publication December 14, 2005.
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 cells capable of repopulating non-obese diabetic/severe combined immunodeficient repopulating (SCID) mice (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 HSC-supportive effect. Extended noncontact HUBEC cultures supported an eight-fold increase in SRCs when combined with thrombopoietin, stem cell factor, and Flt-3 ligand compared with input CD34⁺ cells or cytokines alone. Gene expression analysis of HUBEC biological replicates identified 65 differentially expressed, nonredundant 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 stem cell factor 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.