Induction of mesenchymal to endothelial transformation of adipose-derived stem cells

Adipose tissue is a readily available source of multipotent adult stem cells for use in tissue engineering and regenerative medicine. Adipose-derived stem cells (ADSCs) are currently being investigated as a source of interstitial cells to populate tissue-engineered heart valve constructs. However, the ability of these cells to differentiate into endothelial cells that would be required to cover the surface of the valve cusps has not been fully investigated.

ADSCs were isolated and characterized using immunofluorescence and flow cytometry. Endothelial differentiation was promoted by culturing confluent cells in the presence of 2% fetal calf serum and 50 ng/ml vascular endothelial growth factor. Differentiation was evaluated by immunofluorescence staining for endothelial markers, and an analysis of acetylated low-density lipoprotein (Ac-LDL) uptake. An assessment of tubular formation was performed using an in vitro angiogenesis assay.

Isolated ADSCs were positive for the mesenchymal markers CD105, CD73, CD29, CD90 and CD44, and negative for hematopoietic and endothelial markers. After a seven-day treatment period, approximately 15% of ADSCs expressed the endothelial marker von Willebrand factor, and 70% had lost the expression of smooth muscle a-actin. Treated cells also were able to incorporate Ac-LDL, and also to form tubular structures on Matrigel, unlike control cells.

Based on these results, ADSCs are capable of differentiating into cells with phenotypic and functional features of endothelial cells. These predifferentiated cells provide new options for the tissue engineering of heart valves, based on autologous mesenchymal stem cells.