S1PR1 and proliferative diabetic retinopathy: A significant increase in the expression of S1P1 and S1P lyase is detected in the vitreous of patients with proliferative diabetic retinopathy (Abu El-Asrar et al., 2014) whereas S1P signaling through S1P1/S1P3 promotes angiogenesis in vitro, participating in the changes affecting pericytes and endothelial cells (Durham et al., 2015).