MEK inhibitor PD0325901 upregulates CD34 expression in endothelial cells via inhibition of ERK phosphorylation.

Introduction: CD34-positive endothelial progenitor cells (EPCs) promote angiogenesis and are a promising tool for regenerative cell therapy of ischemic diseases. However, the number and quality of CD34-positive cells decrease owing to various external and internal factors; thus, an efficient method is needed to establish CD34-positive EPCs. The generation of functional cells by reprogramming, that is, manipulating cell fate via gene transfer and/or treatment with chemical compounds, has recently been reported. Therefore, we aimed to generate CD34-positive cells by the reprogramming of endothelial cells (ECs). Methods: Based on previous reports, seven candidate chemical compounds were selected to reprogram human umbilical vein ECs (HUVECs) to CD34-positive cells. Following stimulation with the chemical compounds, the expression of CD34 was evaluated using quantitative PCR, flow cytometry, and immunocytochemistry. Results: HUVECs treated with the compounds exhibited increased CD34 expression. We cultured cells in alternate media lacking one of the seven compounds and found no CD34 expression in cells treated with PD0325901-free media, suggesting that PD0325901-a MEK inhibitor-mainly contributed to the increase in CD34 expression. We found that 98% of cells were CD34-positive after PD0325901 treatment alone for 7 d. Western blotting revealed that the phosphorylation of ERK was suppressed in PD0325901-treated cells. No upregulation of CD34 was observed in fibroblast cell lines, even after PD0325901 treatment. These results suggested that PD0325901 induces CD34-positive cells by inhibiting ERK phosphorylation in ECs. Conclusions: CD34 expression was strongly induced in ECs by treatment with the MEK inhibitor PD0325901 in vitro. Our study provides a useful reference for the establishment of CD34-positive EPCs and will contribute to the development of regenerative therapies, especially for ischemic diseases.