ANGPT1 and obstructive sleep apnea syndrome: OSA-induced hypoxemia enhances production of several pro-angiogenic factors in MSCs, including vascular endothelial growth factor (VEGF), placental growth factor (PLGF), angiopoietin-1 (Ang1), interleukin (IL)-6, platelet-derived endothelial cell growth factor (PD-ECGF), stromal derived factor 1 (SDF-1), hepatocyte growth factor (HGF) [7,11].