Multifunctional Regulation of Angiogenesis by High Density Lipoproteins

Abstract

Introduction: Angiogenesis is a key biological process in both physiological and pathological states. It is critical for neovascularisation in response to ischaemia; however, excessive inflammatory-driven angiogenesis accelerates atherosclerotic plaque growth. High-density lipoproteins (HDL) are associated with improved prognosis following myocardial infarction, and with reduced atherogenesis. We hypothesised that HDL may regulate angiogenesis in a multifunctional manner: by augmenting hypoxia-mediated angiogenesis while inhibiting inflammation-driven angiogenesis. Methods and results: Treatment of human coronary artery endothelial cells (ECs) with reconstituted HDL (rHDL, 600 μg/mL) augmented hypoxia (1%O2, 6 h)-mediated stimulation of EC proliferation (53%) and tubulogenesis in matrigel (14%) (p < 0.05). These rHDL-mediated effects were associated with augmentation of hypoxia-related induction of hypoxia inducible factor-1α (HIF1α) (39%) by downregulation of prolyl hydroxylase 2 & 3 (30% & 52%) and induction of Siah 1 & 2 (36% & 60%), post-translational regulators of HIF1α stability. Consistent with HIF1α induction, rHDL stimulated EC protein expression of the key proangiogenic factors vascular endothelial growth factor (VEGF) (50%) and stromal cell-derived factor-1α in hypoxia (p < 0.05). In contrast to hypoxia, rHDL significantly inhibited EC tubulogenesis (75% & 70%), proliferation (47% & 39%) and migration (37% & 55%), following exposure to two inflammatory stimuli: tumour necrosis factor-α (TNFα) and macrophage-conditioned media (CM) (p < 0.05). The anti-angiogenic effects of rHDL in inflammation were associated with reduced pro-angiogenic inflammatory mediators: p65 (43% & 52%) and monocyte chemoattractant protein (33% & 30%) (p < 0.05). Strikingly, under inflammation, rHDL reduced HIF1α and VEGF protein expression: 36% & 34% (TNFα), 37% & 19% (CM) (p < 0.05). rHDL increased hemeoxygenase-1 expression, a multi-functional regulator of angiogenesis, under both hypoxic & inflammatory conditions (p < 0.05). Conclusions: HDL uniquely regulates angiogenesis in a multifunctional manner, characterised by enhancement of hypoxia-mediated angiogenesis and, conversely, marked suppression of inflammation-associated angiogenesis.