Hypoxia and
adenosine are known to upregulate angiogenesis; however, the role of
peroxisome proliferator-activated receptor alpha (PPARα) in angiogenesis is controversial. Using transgenic Tg(fli-1:EGFP) zebrafish embryos, interactions of PPARα and
adenosine receptors in angiogenesis were evaluated under hypoxic conditions. Epifluorescent microscopy was used to assess angiogenesis by counting the number of intersegmental (ISV) and dorsal longitudinal anastomotic vessel (DLAV) at 28 h post-fertilization (hpf).
Hypoxia (6h) stimulated angiogenesis as the number of ISV and DLAV increased by 18-fold (p<0.01) and 100 ± 8% (p<0.001), respectively, at 28 hpf. Under normoxic and hypoxic conditions,
WY-14643 (10 μM), a PPARα activator, stimulated angiogenesis at 28 hpf, while
MK-886 (0.5 μM), an antagonist of PPARα, attenuated these effects. Compared to normoxic condition,
adenosine receptor activation with
NECA (10 μM) promoted angiogenesis more effectively under hypoxic conditions. Involvement of A2B receptor was implied in
hypoxia-induced angiogenesis as
MRS-1706 (10nM), a selective A2B antagonist attenuated
NECA (10 μM)-induced angiogenesis.
NECA- or WY-14643-induced angiogenesis was also inhibited by
miconazole (0.1 μM), an inhibitor of epoxygenase dependent production of eicosatrienoic
acid (EET)
epoxide. Thus, we conclude that: activation of PPARα promoted angiogenesis just as activation of A2B receptors through an
epoxide dependent mechanism.