Over-Expression of Sphingosine Kinase-1 Enhances a Progenitor Phenotype in Human Endothelial Cells

Objectives: The use of endothelial progenitor cells in vascular therapies has been limited due to their low numbers present in the bone marrow and peripheral blood. The aim of this study was to investigate the effect of sphingosine kinase on the de-differentiation of mature human endothelial cells toward a progenitor phenotype. Methods: The lipid enzyme sphingosine kinase-1 was lentivirally over-expressed in human umbilical vein endothelial cells and cells were analyzed for progenitor phenotype and function. Results: Sphingosine kinase-1 mRNA expression was induced approximately 150-fold with a resultant 20-fold increase in sphingosine kinase-1 enzymatic activity. The mRNA expression of the progenitor cell markers CD34, CD133, and CD117 and transcription factor NANOG increased, while the endothelial cell markers analyzed were largely unchanged. The protein level of mature endothelial cell surface markers CD31, CD144, and von Willebrand factor significantly decreased compared to controls. In addition, functional assays provided further evidence for a dedifferentiated phenotype with increased viability, reduced uptake of acetylated low-density lipoprotein and decreased tube formation in Matrigel in the cells over-expressing sphingosine kinase-1. Conclusions: These findings suggest that over-expression of sphingosine kinase-1 in human endothelial cells promotes, in part, their de-differentiation to a progenitor cell phenotype, and is thus a potential tool for the generation of a large population of vascular progenitor cells for therapeutic use.