The 5-LOX/COX-2 cross-over metabolite, hemiketal E₂, enhances VEGFR2 activation and promotes angiogenesis

Abstract

Consecutive oxygenation of arachidonic acid by 5-lipoxygenase (5-LOX) and cyclooxygenase-2 (COX-2) yields the hemiketal (HK) eicosanoids, HKE2 and HKD2. HKs stimulate angiogenesis by inducing endothelial cell tubulogenesis in culture; however, how this process is regulated has not been determined. Here, we identify vascular endothelial growth factor receptor 2 (VEGFR2) as a mediator of HKE2-induced angiogenesis in vitro and in vivo. HKE2 treatment of human umbilical vein endothelial cells dose-dependently increased phosphorylation of VEGFR2 and the downstream kinases ERK and Akt that mediated endothelial cell tubulogenesis. In vivo, HKE2 induced the growth of blood vessels into polyacetal sponges implanted in mice. HKE2-mediated effects in vitro and in vivo were blocked by the VEGFR2 inhibitor vatalanib, indicating that the pro-angiogenic effect of HKE2 was mediated by VEGFR2. We found that HKE2 covalently bound and inhibited PTP1B, a protein tyrosine phosphatase that dephosphorylates VEGFR2, thereby providing a possible molecular mechanism for how HKE2 induced pro-angiogenic signaling. Our studies indicate that biosynthetic cross-over of the 5-LOX and COX-2 pathways gives rise to a potent lipid autacoid that regulates endothelial cell function in vitro and in vivo.SignificanceAngiogenesis, the growth of new blood vessels from existing vessels, contributes to both physiological and pathological conditions, including tissue repair after injury and tumorigenesis. Novel approaches to control pathologic angiogenesis are urgently needed since current therapy targeting the pro-angiogenic receptor VEGFR2 has significant side effects. We show that a metabolite of arachidonic acid, formed in a biosynthetic cross-over of the enzymes that generate the pro-inflammatory leukotriene and prostaglandin mediators, respectively, promotes VEGFR2 activation to induce angiogenesis. This finding suggests that common drugs targeting the arachidonic acid pathway may be viewed as valid anti-angiogenic candidates.