High-density lipoproteins augment hypoxia-induced angiogenesis via regulation of post-translational modulation of hypoxia-inducible factor 1alpha

Increasing evidence suggests that high-density lipoproteins (HDLs) promote hypoxia-induced angiogenesis. The hypoxia-inducible factor 1α (HIF-1α)/vascular endothelial growth factor (VEGF) pathway is important in hypoxia and is modulated post-translationally by prolyl hydroxylases (PHD1−PHD3) and E3 ubiquitin ligases (Siah1 and Siah2). We aimed to elucidate the mechanisms by which HDLs augment hypoxia-induced angiogenesis. Preincubation (16 h) of human coronary artery endothelial cells with reconstituted high-density lipoprotein (rHDL) containing apolipoprotein A-I (apoA-I) and phosphatidylcholine (20 μM, final apoA-I concentration), before hypoxia, increased Siah1 (58%) and Siah2 (88%) mRNA levels and suppressed PHD2 (32%) and PHD3 (45%) protein levels compared with hypoxia-induced control levels. After Siah1/2 small interfering RNA knockdown, rHDL was unable to suppress PHD2/3 and failed to induce HIF-1α, VEGF, and tubulogenesis in hypoxia. Inhibition of the upstream phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway also abrogated the effects of rHDL. Furthermore, knockdown of the scavenger receptor SR-BI attenuated rHDL-induced elevations in Siah1/2 and tubulogenesis in hypoxia, indicating that SR-BI plays a key role. Finally, the importance of VEGF in mediating the ability of rHDL to drive hypoxia-induced angiogenesis was confirmed using a VEGF-neutralizing antibody. In summary, rHDL augments the HIF-1α/VEGF pathway via SR-BI and modulation of the post-translational regulators of HIF-1α (PI3K/Siahs/PHDs). HDL-induced augmentation of angiogenesis in hypoxia may have implications for therapeutic modulation of ischemic injury.Joanne T. M. Tan, Hamish C. G. Prosser, Laura Z. Vanags, Steven A. Monger, Martin K. C. Ng, and Christina A. Bursil