Hypoxia-Inducible Factor-1α and-2α Additively Promote Endothelial Vasculogenic Properties

Objective: While both play a role in the transcriptional response of hypoxic endothelial cells (ECs), hypoxia- inducible factor-1 alpha (HIF-1 alpha) and HIF-2 alpha differ in their transactivation sites, pointing at potentially different target genes. We studied the discrete and common effects of HIF-1 alpha and HIF-2 alpha on the cytokine expression and vasculogenic properties of ECs. Methods and Results: H5V and bovine aortic ECs were transfected to express HIF-1 alpha, HIF-2 alpha or both. Overexpression of HIF-1 alpha or HIF-2 alpha and, to a greater extent, cotransfection of HIF-1 alpha and HIF-2 alpha resulted in EC activation, as revealed by analysis of the adhesion capacities and adhesion molecule surface expression of ECs. From the paracrine aspect, conditioned medium from HIF-expressing ECs was found to promote the migration and tube formation capacity of wild-type ECs, mostly following HIF-1 alpha and HIF-2 alpha co-expression. Antibody arrays revealed altered expression of multiple cytokines, pointing at consistent additive effects of HIF-1 alpha and HIF-2 alpha on angiogenic protein expression. Finally, HIF-1 alpha and HIF-2 alpha additively promoted vessel formation in vivo, as demonstrated by a Matrigel angiogenesis assay. Conclusion: Our results further clarify the functional roles of HIF-1 alpha and HIF-2 alpha in ECs and for the first time demonstrate a common contribution of HIF-1 alpha and HIF-2 alpha to vasculogenesis. Copyright (C) 2009 S. Karger AG, Basel