Intermittent hypoxia: Friend or foe on endothelial repair in mouse model

Aim of the study: Obstructive sleep apnea, which is characterized by intermittent hypoxia (IH), is a common respiratory disease. The aim of the present study was to explore the relationship between hypoxia and endothelial progenitor cell (EPC) function, and explain the role of IH in endothelial repair.Materials and methods: Peripheral blood mononuclear cells (PBMCs) were isolated from a mouse model of IH. The number of CD133⁺ kinase insert domain receptor (KDR)⁺, CD133⁺CD34⁺, CD34⁺KDR⁺ and ALDH^lowCD34⁺KDR⁺ EPCs was determined by flow cytometry. HIF-1α, stromal-derived factor-1 (SDF-1) α and VEGF were measured by ELISA. The proliferative ability of PBMCs was determined. EPC migration was assessed by Transwell assay and surface proteins by western blot analysis. EPCs were co-cultured with mouse brain endothelial cells and their angiogenic ability was analyzed.Results: The number of CD133⁺KDR⁺, CD133⁺CD34⁺ and CD34⁺KDR⁺ EPCs increased with IH ingravescence. The number of ALDH^lowCD34⁺KDR⁺ EPCs with mild IH stimulation was higher and gradually decreased in the moderate and severe IH groups. The release of HIF-1α, SDF-1α and VEGF in the serum increased with the increase in the degree of IH. In the mild IH treatment, the migration and angiogenesis of EPCs, as well as the expression of vascular endothelial growth factor receptor 2 and cysteine-X-cysteine receptor 4, were higher than those in the control group, but progressively decreased in the groups with moderate and severe IH.Conclusion: Increased levels of IH accelerated the increase in vasoactive factors in peripheral blood, thereby mobilizing a large number of EPCs. Increasing of IH diminished the mobilization, chemotactic and angiogenetic ability of EPCs.