Transdifferentiation of Human Endothelial Progenitors into Smooth Muscle Cells

Derivation of induced smooth muscle cells (iSMC) through direct transdifferentiation of a convenient and expandable primary cell source would open a wide range of prospects for their use in tissue engineering, drug testing, and disease modeling. Hypothesizing that MYOCD as a master regulator of smooth muscle gene expression would facilitate the generation of iSMC, we studied the conversion of human endothelial progenitor cells (EPC) into iSMC through the induced expression of by over-expression of MYOCD. A significant cytoskeletal rearrangement of the EPC resembling that of mesenchymal cells occurred within 3 days post initiation of MYOCD expression. This transition was associated with a downregulation of endothelial cell surface markers (CD31, CD105) as determined by flow cytometry. By day 7, iSMC derivation was evident with a significant upregulation of smooth muscle markers ACTA2, MYH11, TAGLN, and downregulation of CD31 and CDH5 as determined by gene expression analysis. Immunofluorescence revealed expression of MYH11 and ACTA2 and absence of endothelial markers VWF and CD31. By two weeks, microarray gene expression analysis demonstrated a significant similarity between iSMC and umbilical artery SMC (UASMC). The iSMC continued to develop toward the SMC lineage after four weeks of MYOCD induced expression. Microarray gene expression analysis showed an upregulation of molecular pathways associated with smooth muscle contraction and cytoskeletal reorganization in iSMC. Calcium transients were detected in iSMC when stimulated with phenylephrine but not in EPC. Contractility of iSMC was also higher than that of EPC as determined by traction force microscopy. Tissue-engineered blood vessels constructed using iSMC showed functionality with respect to flow- and drug- mediated vasodilation and vasoconstriction. We used microarrays to detail the global programme of gene expression underlying the transdifferentiation of endothelial progenitor cells into smooth muscle cells via the transient induced expression of the transcriptional co factor MYOCD To further ascertain the overall effect that the induction of MYOCD expression had on cells undergoing transdifferentiation we performed microarray gene expression analysis on iSMC following 2 weeks of continuous MYOCD expression (iSMC-2w) or 2 weeks of continuous MYOCD expression followed by 2 weeks of culture under standard conditions (iSMC-4w). Control cells included non-transduced EPC and primary human smooth muscle cells isolated from the umbilical artery (UASMC).