Abstract 289: High Density Lipoproteins Augment Hypoxia-Induced Angiogenesis via Regulation of Post-translational Modification of HIF-1a
Background Angiogenesis plays a critical role in tissue neovascularization in response to ischemia, particularly following myocardial infarction (MI). High-density lipoproteins (HDL) are associated with improved survival following MI, suggesting that it may play a role in hypoxia-induced angiogenic regulation. We have shown previously that in hypoxia, HDL augments angiogenesis and HIF-1α/VEGF expression. HIF-1α is post-translationally regulated by prolyl hydroxylases (PHDs 1-3), which target HIF-1α for degradation following hydroxylation. Furthermore, Siah ubiquitin ligases (Siah1 and Siah2) promote the degradation of PHDs. We aimed to determine if HDL augments HIF-1α/VEGF via modulation of PHDs and Siahs.
Methods Human coronary artery endothelial cells were pre-incubated with PBS (control) or reconstituted HDL (rHDL) for 24 h then subjected to normoxic or hypoxic conditions for 6 h. To determine the importance of Siah1 and Siah2 in the HDL-induced modulation of the HIF-1α/VEGF pathway, a siRNA knockdown approach was used.
Results Pre-incubation with rHDL inhibited the hypoxia-induced increases in PHD2 and PHD3 levels (32% and 45% respectively, p<0.05) while Siah1 and Siah2 mRNA levels were increased (58% and 88% respectively, p<0.05) with rHDL pre-incubation. Following siRNA knockdown of Siah1 and Siah2, HDL lost its ability to induce the expression of HIF-1α (11% reduction, p<0.05) and VEGF (18% reduction, p<0.05). Augmentation of tubulogenesis by HDL was attenuated in Siah siRNA-transfected cells (55% in siSiah1; 40% in siSiah2, p<0.05). Siah knockdown also abrogated HDL inhibition of hypoxia-mediated induction of PHD2 and PHD3 (p<0.05). PI3K and Akt are upstream regulators of HIF-1α/VEGF and also regulate Siahs. Specific inhibition of the PI3K/Akt pathway revealed that it plays a key role in HDL-induced elevations in Siah1 and Siah2 (37% and 20% reduction respectively, p<0.05) as well as HIF-1α and VEGF (65% and 15% reduction respectively, p<0.05).
Conclusion In conclusion, HDL augments the HIF-1α/VEGF pathway by regulation of post-translational modification of HIF-1α via the PI3K/Siah/PHD pathway. HDL induced augmentation of angiogenesis in hypoxia may have implications for preventing ischemic injury following MI.
- © 2013 by American Heart Association, Inc.