Human ALDH-Bright Bone Marrow Cells Produce Paracrine Factors That Protect Endothelial Cells From Hypoxic and Nutritional Stress.

Abstract 3056

Poster Board II-1032

Human bone marrow cell populations isolated by sorting cells on the basis of high aldehyde dehydrogenase expression (ALDHbr cells) include endothelial, mesenchymal, and other progenitor cells (Gentry et al, 2007, Cytotherapy 9, 259). These cell populations home to and are retained at ischemic endothelium, induce angiogenesis, and effect restoration of tissue perfusion in a mouse hind limb ischemia model (Cappoccia et al, 2009 Blood 113, 5340.) Critical limb ischemia patients treated with ALDHbr cells in a Phase I/II clinical trial showed increased limb perfusion. We are studying paracrine and contact dependent mechanisms by which ALDHbr cells may repair damaged endothelium by measuring the protective effects of ALDHbr cells on early passage human umbilical vein endothelial cells (HUVEC) exposed to hypoxic and nutritional stress. ALDHbr cells migrated through membrane filters in response to supernatants conditioned by hypoxic HUVECs more rapidly than to normoxic HUVEC supernatants. ALDHbr cells attached to HUVECs that had been induced to form tubular structures on Matrigel®, and more ALDHbr cells decorated HUVEC tubules under hypoxic than normoxic conditions. ALDHbr cells and HUVECs expressed several adhesion molecule-ligand pairs, including VLA-1/VCAM, that are regulated by hypoxia and could mediate these interactions. While HUVEC tubules fell apart under hypoxic conditions, adding ALDHbr cells in a transwell culture system for 24 hours preserved the branching structure of hypoxic HUVEC tubule networks. Gene array studies demonstrated that ALDHbr cells highly express several angiogenic growth factors, cytokines and matrix remodeling molecules. Expression of proteins corresponding to many of these gene products, including members of the ephrin-Eph receptor family that can direct endothelial growth, has been confirmed by flow cytometry. Additionally, 29 angiogenic factors including angiopoietin 2, VEGF-A,C, and D, and MMP2 were upregulated under hypoxic conditions. Gene array and flow cytometry showed that hypoxic HUVECs expressed surface receptors for many of the angiogenic factors expressed by ALDHbr cells. In hypoxic transwell cultures, ALDHbr cells specifically induced HUVECs to express six angiogenic factors that were not induced by hypoxia alone. ALDHbr cells protected HUVECs from apoptosis and necrosis induced by serum starvation when added to cultures at the time of or 24 hours following medium shift. Thus, in addition to providing progenitor cells that can potentially participate in angiogenesis, ALDHbr cell populations can mediate repair of ischemic injury by releasing a variety of angiogenic and protective factors at sites of endothelial damage.