title: High-density lipoproteins augment hypoxia-induced angiogenesis via regulation of post-translational modulation of hypoxia-inducible factor 1α.
abstract: 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.
authors.affiliation: 1Heart Research Institute, 7 Eliza Street, Newtown, NSW 2042, Australia. joanne.tan@hri.org.au.
authors.forename: Joanne T M
authors.initials: JT
authors.lastname: Tan
authors.forename: Hamish C G
authors.initials: HC
authors.lastname: Prosser
authors.forename: Laura Z
authors.initials: LZ
authors.lastname: Vanags
authors.forename: Steven A
authors.initials: SA
authors.lastname: Monger
authors.forename: Martin K C
authors.initials: MK
authors.lastname: Ng
authors.forename: Christina A
authors.initials: CA
authors.lastname: Bursill
mesh_terms: D015687:Cell Hypoxia / Q000502:physiology*; D002478:Cells, Cultured; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases / Q000235:genetics / Q000378:metabolism; D008075:Lipoproteins, HDL / Q000494:pharmacology*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism; D000098563:Seven in Absentia Proteins
chemical_list: D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008075:Lipoproteins, HDL; D009687:Nuclear Proteins; D064799:Hypoxia-Inducible Factor-Proline Dioxygenases; D044767:Ubiquitin-Protein Ligases; D000098563:Seven in Absentia Proteins
keywords: PI3K/Akt pathway; Siah ubiquitin ligases; endothelial cells; phosphatidylinositol 3-kinase; prolyl hydroxylase domain proteins; scavenger receptor BI