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Blood monocytes mimic endothelial progenitor cells
Eva Rohde1, Christina Malischnik, Daniela Thaler
1Department of Blood group Serology and Transfusion Medicine, Medical University, Auenbrugger Pl. 38 A-8036, Graz, Austria.
Stem Cells (Dayton, Ohio)
|September 6, 2005
Summary
Monocytes, not just endothelial progenitor cells (EPCs), exhibit markers like LDL uptake and endothelial proteins. This challenges the use of these markers for distinguishing EPCs in cardiovascular disease research and therapy.
Area of Science:
- Cardiovascular Biology
- Cell Biology
- Immunology
Background:
- Endothelial progenitor cells (EPCs) derived from blood monocytes are explored for cardiovascular disease diagnosis and treatment.
- Established markers for EPCs include low-density lipoprotein (LDL) uptake, lectin binding, and endothelial marker expression.
- There is ongoing debate regarding the true nature of EPCs, as myelomonocytic cells share characteristics with endothelial cells (ECs).
Purpose of the Study:
- To determine if standard endothelial marker expression is sufficient to differentiate monocytes from purported EPCs.
- To investigate the phenotypic and functional similarities between primary monocytes and cultured monocyte-derived cells.
- To clarify the role of monocytes in vascular network formation and endothelial colony-forming unit (CFU-EC) development.
Main Methods:
- Monocytes were cultured under angiogenic conditions for 4-6 days.
- Marker expression (endothelial, hematopoietic, progenitor) was analyzed using fluorescence microscopy, flow cytometry, and RT-PCR.
- Functional assays included vascular network formation and CFU-EC development assessment.
Main Results:
- Cultured monocytes acquired an EPC-like phenotype, expressing LDL uptake, lectin binding, and endothelial markers (CD31, CD105, CD144), while downregulating CD14/CD45.
- Primary monocytes expressed many endothelial genes and proteins at levels equal to or higher than their cultured progeny.
- Neither fresh nor cultured monocytes formed vascular networks, but CFU-EC formation was dependent on monocyte presence.
Conclusions:
- Endothelial marker expression, LDL uptake, and lectin binding are inherent properties of monocytes, making them phenotypically indistinguishable from putative EPCs.
- Monocytes and their progeny can mimic EPCs in experimental settings, complicating their use as distinct cell populations.
- The findings necessitate a re-evaluation of current methods for identifying and utilizing EPCs in cardiovascular research and therapeutics.