Bioactive epoxy-fatty acid levels are determined by the activity of the cytochrome P450 enzyme that generates them and the soluble epoxide hydrolase (sEH) which metabolizes them to diols. To investigate the role of epoxides and diols in postnatal retinal vascularization we studied responses in sEH^-/- mice.

Retinal vascularisation was markedly delayed in sEH^-/- mice 2 and 5 days after birth, and was associated with reduced tip cell numbers and filipodia extensions, the induction of the Notch-dependent transcription factors Hes1 and Hey1 and attenuated endothelial cell (EC) proliferation. The sEH was mainly expressed in Müller glia cells and Müller cell-specific sEH^-/- mice displayed a similar delayed vascularisation phenotype. sEH expression was maintained in cultured murine Müller cells and conditioned medium from wild-type (WT) Müller cells stimulated EC proliferation while that from sEH^-/- cells increased Hes1 and Hey1 expression and decreased EC proliferation. The impaired Notch signaling in EC could be rescued by the depletion of lipids from the conditioned medium. We found a particularly marked difference in levels of 19,20-dihydroxydocosapentaenoic acid (DiHDPA) in WT versus sEH^-/- retina and we observed that 19,20-DiHDPA significantly decreased the Dll4-induced cleavage of the Notch intracellular domain indicating an effect on the g-secretase. Intravitreal injection of 19,20-DiHDPA dramatically enhanced primary network density and tip cell and filipodia number in sEH^-/- retina.

This is the first indication that a lipid mediator from Müller glia cells play an important role in the development of the retinal vasculature and that a sEH metabolite is essential for normal vascularization.