Tissue factor variants induce monocyte transformation and transdifferentiation into endothelial cell-like cells

Background: Monocytes (Mo) increase neovascularization by releasing proangiogenic mediators and/or transdifferentiating into endothelial cell-like (ECL) cells. Recently, we have reported that Mo-microvascular endothelial cells (mECs) crosstalk induces mEC-tissue factor (TF) expression and promotes angiogenesis. However, the effect of TF on Mo remains unknown. Objective: Here, we analyzed whether TF might exert angiogenic effects by inducing transdifferentiation of Mo. Methods: Full-length TF (flTF) and alternatively spliced TF (asTF) were overexpressed in mECs, and their supernatants were added to Mo cultures. CD16 positivity and expression of vascular endothelial cell (VEC) markers in Mo were analyzed by fluorescence activated cell sorting. The capacity to form tube-like structures were visualized in three-dimensional cultures. Results: In mECs flTF and asTF expression and release were increased in cultures with Mo-conditioned media. TF variants induced expansion of a CD16(+) Mo subset and Mo transdifferentiation into ECL-cells expressing VEC markers that can form new microvessels. CD16(+) Mo exposed to TF showed an increased expression of VE-cadherin, von Willebrand factor (VWF) and eNOS. Mo cultured with supernatants obtained from TF-silenced mECs did not transdifferentiate to ECL-cells or expressed VEC markers. Blocking 1-integrin in Mo significantly blocked the effects of the TF variants. Conclusions: Mo induce mECs to express and release TF, which drives CD16(-) Mo to transform into CD16(+) Mo and to transdifferentiate into ECL-cells that can form new microvessels. Our results reveal a TF-mediated positive feedback between mECs and Mo that stimulates Mo differentiation and induces angiogenesis.