P81	Endothelial progenitor cell transdifferentiation into smooth muscle cells: impact on vascular lesion formation.
D.Sedding, D.Hess, H.Brunsch, H.Tillmanns, R.Braun-Dullaeus
Cardiology - Giessen University Clinic, Gießen, DE.

Background: Endothelial progenitor cells (EPC) significantly contribute to vessel regeneration, and clinical application of EPC emerges as therapeutic option to restore blood supply to ischemic tissue. However, further transdifferentiation of EPC into other lineages may modulate the beneficial or adverse effects of cell therapy. We therefore sought to determine the potential of EPC to transdifferentiate into vascular smooth muscle cells (VSMC) and their impact on neointimal lesion formation. Methods and Results: EPCs were obtained from peripheral blood mononuclear cells by cultivation with endothelial cell medium and growth factors. After 3 days, more than 95% of adherent cells show endothelial characteristics, as demonstrated by Dil-acetylated LDL uptake, lectin binding and the expression of VEGFR2, von Willebrand factor and VE-Cadherin. EPC were then co-cultivated with freshly isolated rat VSMC for 7 days. Co-cultivated EPC increased in size and developed a smooth muscle cell like phenotype. After 6 days of co-culture, 16.7 ± 3.8% of EPCs expressed alpha smooth muscle actin as determined by FACS analysis. Transdifferentiated EPCs also expressed calponin and smooth muscle myosin heavy chain. Furthermore, VSMC specific mRNA expression (calponin and h-caldesmon) was detected in co-cultured EPCs using human-specific primers. Importantly, the angiotensin II-induced contractile response of co-cultured EPCs was similar to VSMC, indicating functional activity. Transdifferentiation of EPCs into VSMC was not detected in EPC cultured in conditioned medium, suggesting an essential role of cell-cell contacts. As determined by co-cultivation with GFP-expressing VSMC, phenotypical changes are due to transdifferentiation rather than fusion. To follow EPC transdifferentiation in vivo, spleen-derived EPC from GFP+/- mice were administered after dilation of the mouse femoral artery. Two weeks after dilation, GFP(+) cells expressing smooth muscle cell markers were detected in the neointima. Conclusion: As demonstrated by morphological, histochemical and functional parameters, adult human EPC can transdifferentiate into functionally active smooth muscle cells in vitro and in vivo. Transdifferentiation of EPC to VSMC may improve vessel maturation during vasculogenesis or plaque stabilisation but may also contribute to vascular lesion formation.

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