1. ¹Stem Cell Biology Program, James Graham Brown Cancer Center, University of Louisville, Louisville, KY, USA
2. ²Jagiellominan University, Krakow, Poland
3. ³Department of Molecular Embryology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Brno, Czech Republic

Correspondence: Professor MZ Ratajczak, Director of Stem Cell Biology Program, James Graham Brown Cancer Center, University of Louisville, KY 40202, USA. E-mail: mzrata01@louisville.edu

Received 16 November 2005; Revised 21 December 2005; Accepted 26 December 2005; Published online 2 February 2006.

Abstract

Membrane-derived vesicles (MV) are released from the surface of activated eucaryotic cells and exert pleiotropic effects on surrounding cells. Since the maintenance of pluripotency and undifferentiated propagation of embryonic stem (ES) cells in vitro requires tight cell to cell contacts and effective intercellular signaling, we hypothesize that MV derived from ES cells (ES-MV) express stem cell-specific molecules that may also support self-renewal and expansion of adult stem cells. To address this hypothesis, we employed expansion of hematopoietic progenitor cells (HPC) as a model. We found that ES-MV (10 g/ml) isolated from murine ES cells (ES-D3) in serum-free cultures significantly (i) enhanced survival and improved expansion of murine HPC, (ii) upregulated the expression of early pluripotent (Oct-4, Nanog and Rex-1) and early hematopoietic stem cells (Scl, HoxB4 and GATA 2) markers in these cells, and (iii) induced phosphorylation of MAPK p42/44 and serine-threonine kinase AKT. Furthermore, molecular analysis revealed that ES-MV express Wnt-3 protein and are selectively highly enriched in mRNA for several pluripotent transcription factors as compared to parental ES cells. More important, this mRNA could be delivered by ES-MV to target cells and translated into the corresponding proteins. The biological effects of ES-MV were inhibited after heat inactivation or pretreatment with RNAse, indicating a major involvement of protein and mRNA components of ES-MV in the observed phenomena. We postulate that ES-MV may efficiently expand HPC by stimulating them with ES-MV expressed ligands (e.g., Wnt-3) as well as increase their pluripotency after horizontal transfer of ES-derived mRNA.