Title: P158 Endothelial progenitor cells form biological exclusion barriers similar to that of mature endothelial cells- A therapeutic potential in systemic sclerosis?
Abstract: <h3>Abstract</h3> Vascular complications associated with systemic sclerosis (SSc) including pulmonary arterial hypertension (PAH-SSc), result from endothelial damage and loss of barrier function. Endothelial progenitor cells (EPCs) express endothelial (VEGFR2<sup>+</sup>, CD31<sup>+</sup> ) and haematopoietic (CD133<sup>+</sup> ) markers. They home to sites of vascular injury and differentiate into endothelial cells restoring the endothelium. In SSc patients circulating levels of EPCs are reduced. This study aimed to develop a robust method to grow EPCs from peripheral blood mononuclear cells (PBMCs) and to compare cellular functions to mature endothelial cells. <h3>Methods</h3> EPCs and human pulmonary artery endothelial cells (hPAECs) were seeded into transwell inserts and grown to confluence. Cells were incubated with TNFa (50ng/ml), and their capacity to form biological barriers assessed using FITC-albumin (5mg/ml). FITC-albumin ‘leak’ was quantified by fluorescent absorbance over time. We further assessed the responses of EPCs to TNFa stimulation by ELISA to quantify pro-inflammatory cytokine release. <h3>Results</h3> EPCs form a biological exclusion barrier with similar capabilities as mature hPAECs. TNFa significantly enhanced the permeability of EPCs (P < 0.05) and hPAECs (P < 0.05) monolayers. There is no difference in EPC colony formation between HC and SSc EPCs. <h3>Discussion</h3> We developed a robust method for isolating EPCs from PBMCs. We have demonstrated that EPCs can maintain an endothelial barrier consistent with that observed by mature hPAECs <i>in vitro</i>. We have established that EPCs respond to TNFa in a similar manner to mature PAECs. We have shown no significant difference in the capacity of PBMCs from SSc patients to form EPC colonies compared to HCs.