Novel Contribution of Myeloperoxidase‐derived Hypochlorous Acid to 20‐HETE Production Post‐Ischemia
Authors: Azcona Juan Arturo , Tang Samantha , Jeitner Thomas , Guo Austin Meng , Schwartzman Michal Laniado 
Published: June 2021

Ischemia‐induced angiogenesis occurs as a mechanism to minimize the tissue damage caused by atherosclerotic diseases but is often insufficient to maintain adequate tissue perfusion and results in critical limb ischemia and amputation. The discovery of novel factors that increase angiogenesis in response to ischemia is therefore of clinical relevance.Recently, we discovered that 20‐hydroxy‐eicosatetraenoic acid (20‐HETE), an arachidonic acid metabolite produced by a cytochrome P450 (CYP) 4A/F ω‐hydroxylases, is a novel contributor of ischemia‐induced angiogenesis based on the following two major findings: 1) pharmacological interference of the CYP4A/20‐HETE axis attenuates ischemic‐induced angiogenesis; and 2) the expression of cyp4a12a and its product, 20‐HETE are both elevated in ischemic tissues of mice models. The resulting increase in 20‐HETE is endothelial in origin. However, the factors that cause endothelial cells (EC) to produce 20‐HETE following ischemia are largely unknown. The aim of these studies was to investigate the mechanism of post‐ischemic endothelial 20‐HETE increases. Inflammatory cells such as macrophages and neutrophils are the first responders to ischemia injury. Thus, we hypothesized that inflammatory cells contribute to post‐ischemic endothelial increases of 20‐HETE.We first examined the potential contribution of inflammatory response to hindlimb ischemia‐induced angiogenesis using immune‐deficient SCID mice. Following a femoral artery ligation and comparing SCID mice to Balb/C control mice, SCID mice exhibited impaired blood perfusion (55 ± 9% vs 89 ± 10%), decreased micro‐vessel counts (capillary:fiber ratio of 1.5 ± .25 vs 2.5 ± 3.75), as well as an inability to produce 20‐HETE (7.5 ± 2.5 vs 29 ± 5 pg/mg of protein).Furthermore, immune‐competent Balb/c mice depleted of macrophages or neutrophils showed that ischemia failed to induce 20‐HETE production in Balb/c depleted of neutrophils (13 ± 1.5 vs 35 ± 5 pg/mg of protein), accompanied with compromised blood perfusion (58 ± 10% vs 82 ± 9%), but not those depleted of macrophages. Neutrophils are known to release Myeloperoxidase (MPO) at sites of inflammation. The possibility that MPO contributes to ischemia‐induced 20‐HETE production was investigated using MPO−/− mice. Remarkably, the ischemic hind limb tissues of MPO−/− mice produce negligible amount of 20‐HETE (~2 ± .25 vs 35 ± 5 pg/mg of protein). MPO is known to produce hypochlorous acid (HOCl). Therefore, we further studied the role of MPO‐derived HOCl in 20‐HETE production in cultured human EC. The addition of physiological amounts of either MPO or HOCl markedly stimulated the expression of 20‐HETE synthase CYP4A11 and production of 20‐HETE (40 ± 12 vs 8 ± 5 pg/mg of protein); potentially via a HIF1‐a dependent mechanism.These observations suggest for the first time that neutrophil‐derived MPO critically contributes to the 20‐HETE increases post‐ischemia via a mechanism involving the generation of HOCl and activation of the HIF pathway in endothelium.Support or Funding InformationAHA [11SDG6870004(AMG), 17GRNT33430003(AMG)]NIH [HL34300(MLS), DK38226(JRF)]RA Welch Foundation [GL625910(JRF)]This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.