Endogenous LXA4 circuits are determinants of pathological angiogenesis in response to chronic injury

Abstract

Inflammation and angiogenesis are intimately linked, and their dysregulation leads to pathological angiogenesis in human diseases. 15-lipoxygenase (15-LOX) and lipoxin A4 receptors (ALX) constitute a LXA4 circuit that is a key feature of inflammatory resolution. LXA4 analogs have been shown to regulate vascular endothelial growth factor (VEGF)-A-induced angiogenic response in vitro. 15-LOX and ALX are highly expressed in the avascular and immune-privileged cornea. However, the role of this endogenous LXA4 circuit in pathological neovascularization has not been determined. We report that suture-induced chronic injury in the cornea triggered polymorphonuclear leukocytes (PMN) infiltration, pathological neovascularization, and up-regulation of mediators of inflammatory angiogenesis, namely VEGF-A and the VEGF-3 receptor (FLT4). Up-regulation of the VEGF circuit and neovascularization correlated with selective changes in both 15-LOX (Alox15) and ALX (Fprrs2) expression and a temporally defined increase in basal 15-LOX activity. More importantly, genetic deletion of 15-LOX or 5-LOX, key and obligatory enzymes in the formation of LXA4, respectively, led to exacerbated inflammatory neovascularization coincident with increased VEGF-A and FLT4 expression. Direct topical treatment with LXA4, but not its metabolic precursor 15-hydroxyeicosatetraenoic acid, reduced expression of VEGF-A and FLT4 and inflammatory angiogenesis and rescued 15-LOX knockout mice from exacerbated angiogenesis. In summary, our findings and the prominent expression of 15-LOX and ALX in epithelial cells and macrophages place the LXA4 circuit as an endogenous regulator of pathological angiogenesis. Copyright © American Society for Investigative Pathology.