Selective activation of the prostaglandin E2 circuit in chronic injury-induced pathologic angiogenesis

Cyclooxygenase (COX)-derived prostaglandin E(2) (PGE(2)) is a prevalent and established mediator of inflammation and pain in numerous tissues and diseases. Distribution and expression of the four PGE(2) receptors (EP1-EP4) can dictate whether PGE(2) exerts an anti-inflammatory or a proinflammatory and/or a proangiogenic effect. The role and mechanism of endogenous PGE(2) in the cornea, and the regulation of EP expression during a dynamic and complex inflammatory/reparative response remain to be clearly defined.

Chronic or acute self-resolving inflammation was induced in mice by corneal suture or epithelial abrasion, respectively. Reepithelialization was monitored by fluorescein staining and neovascularization quantified by CD31/PECAM-1 immunofluorescence. PGE(2) formation was analyzed by lipidomics and polymorphonuclear leukocyte (PMN) infiltration quantified by myeloperoxidase activity. Expression of EPs and inflammatory/angiogenic mediators was assessed by real-time PCR and immunohistochemistry. Mice eyes were treated with PGE(2) (100 ng topically, three times a day) for up to 7 days.

COX-2, EP-2, and EP-4 expression was upregulated with chronic inflammation that correlated with increased corneal PGE(2) formation and marked neovascularization. In contrast, acute abrasion injury did not alter PGE(2) or EP levels. PGE(2) treatment amplified PMN infiltration and the angiogenic response to chronic inflammation but did not affect wound healing or PMN infiltration after epithelial abrasion. Exacerbated inflammatory neovascularization with PGE(2) treatment was independent of the VEGF circuit but was associated with a significant induction of the eotaxin-CCR3 axis.

These findings place the corneal PGE(2) circuit as an endogenous mediator of inflammatory neovascularization rather than general inflammation and demonstrate that chronic inflammation selectively regulates this circuit at the level of biosynthetic enzyme and receptor expression.