The involvement of PPARα in epoxide‐induced activation of adenosine receptors in angiogenesis

Abstract

The role of peroxisome proliferator‐activated receptor alpha (PPARα) in angiogenesis is controversial. However, many studies showed that epoxyeisatrienoic acids (EETs), downstream mediators of adenosine A2B receptor (A2BR) and PPARα ligand are proangiogenic. Using the Zebrafish (Danio rerio) embryo, we here propose that EET‐induced PPARα activation is involved in A2BR‐mediated angiogenesis under hypoxic condition. Angiogenesis was evaluated at 24, 48, 72 hpf using alkaline phosphatase activity (APA). Under normoxic conditions, APA increased in a time‐dependent manner at 24, 48 (132 %) and 72 hpf (200 %). Clofibrate (10–200 μM) or fenofibrate (10–50 μM); PPARα ligands, NECA (0.1–100 μM), a non selective adenosine receptor agonist, or hydralazine (0.5–1mM), inhibitor of degradation of HIF‐1α did not affect angiogenesis at any of the time points. Compared to normoxia, hypoxia for 24 h reduced angiogenesis by 85 % (p<0.01), but not at 48 or 72 hpf. Using transgenic Tg(fli‐1:EGFP) embryos and epifluorescence microscopy, angiogenesis increased under normoxic conditions in response to clofibrate (50 μM), NECA (10 μM) or hydralazine (0.5 mM), but not to fenofibrate. Epifluorescence microscopy but not APA data demonstrate the possible involvement of PPARα in angiogenesis in the Zebrafish embryo model. However, APA data do not support hypoxia‐induced angiogenesis in Zebrafish embryo.