Abstract 240: High-Density Lipoproteins Augment Hypoxia-Induced Angiogenic Regulation via Mediators in the HIF-1α Signaling Pathway
Background: Angiogenesis plays a critical role in tissue neovascularization in response to ischemia, particularly in collateral vessel development following myocardial infarction (MI). One of the key pathways involved in hypoxia-induced angiogenesis is the HIF-1α/VEGF pathway. High-density lipoproteins (HDL) are associated with improved survival and prognosis following MI, suggesting that it may play a role in hypoxia-induced angiogenic regulation. We assessed the hypothesis that HDL regulates the HIF-1α/VEGF pathway in vitro.
Methods: Human coronary artery endothelial cells (HCAECs) were pre-incubated with PBS (control) or reconstituted HDL (rHDL) for 24 hrs then subjected to either normoxic or hypoxic conditions for a further 6 hrs. Protein and gene expression of key mediators in the HIF-1α/VEGF pathway were investigated.
Results: As expected, hypoxia elevated HIF-1α protein levels (49%, p<0.05), which was augmented by a further 30% (p<0.05) in rHDL-treated HCAECs. Consistent with this, rHDL increased VEGF mRNA levels above hypoxia-induced increases (23%, p<0.05). Prolyl hydroxylases (PHD 1-3) hydroxylate HIF-1α, targeting it for degradation. rHDL pre-incubation inhibited hypoxia-induced increases in PHD2 and PHD3 levels (32% and 45%, respectively, p<0.05), indicating that rHDL may protect against HIF-1α degradation and explains the rHDL-induced elevation in HIF-1α protein levels. Furthermore, the mRNA levels of Siah-1 and Siah-2, which promote PHD degradation, were increased in rHDL-treated HCAECs (58% and 88% respectively, p<0.05). To determine the importance of Siah-1 and Siah-2 in the HDL-induced modulation of the HIF-1α/VEGF pathway, a siRNA knockdown approach was used. When cells had low levels of Siah-1 and -2, HDL’s ability to induce VEGF was completely attenuated.
Conclusion: In conclusion, we found that HDL is able to augment the HIF-1α/VEGF pathway through the stabilization of HIF-1α protein via a decrease in PHD2/3 and increase in Siah1/2. These findings suggest that rHDL may stimulate hypoxia-induced angiogenic regulation via the HIF-1α pathway, which may have implications for preventing ischemic injury following MI.
- © 2012 by American Heart Association, Inc.