BLOOD MONOCYTES MIMIC ENDOTHELIAL PROGENITOR CELLS

¹ Department of Blood Group Serology and Transfusion Medicine, Medical University, Graz, Austria
² Department of Internal Medicine, Division of Hematology and Stem Cell Cluster, Medical University, Graz, Austria
³ Department of Internal Medicine, Medical University, Graz, Austria
⁴ Center for Medical Research, Medical University Graz, Austria
⁵ Department of Internal Medicine, Division of Hematology, Medical University, Graz, Austria

^* To whom correspondence should be addressed. E-mail: dirk.strunk{at}klinikum-graz.at.

	Abstract

The generation of endothelial progenitor cells (EPC) from blood monocytes has been propagated as a novel approach in the diagnosis and treatment of cardiovascular diseases. LDL uptake and lectin binding together with endothelial marker expression are commonly used to define these EPC. Considerable controversy exists regarding their nature, in particular, because myelomonocytic cells share a number of properties with endothelial cells (EC). This study was performed to elucidate whether the commonly used endothelial marker determination is sufficient to distinguish supposed EPC from monocytes. We measured endothelial, hematopoietic and progenitor cell marker expression of monocytes before and after angiogenic culture by fluorescence microscopy, flow cytometry and real-time RT-PCR. The function of primary monocytes and monocyte-derived supposed EPC were investigated during vascular network formation and EC colony forming unit (CFU-EC) development. Monocytes cultured for 4-6 days under angiogenic conditions lost CD14/CD45 and displayed a commonly accepted EPC phenotype including LDL uptake and lectin binding, CD31/CD105/CD144 reactivity and formation of cord-like structures. Strikingly, primary monocytes already expressed most tested endothelial genes and proteins at even higher levels than their supposed EPC progeny. Neither fresh nor cultured monocytes formed vascular networks but CFU-EC formation was strictly dependent on monocyte presence. LDL uptake, lectin binding and CD31/CD105/CD144 expression are inherent features of monocytes cells making them phenotypically indistinguishable from putative EPC. In consequence monocytes and their progeny can phenotypically mimic EPC in various experimental models.

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