S1PR1 and proliferative diabetic retinopathy: For individuals who are suffering from proliferative diabetic retinopathy (PDR), the Müller cells exert control over endothelial cells via exosomes, focusing on the S1P1/AKT/VEGFR2 pathway, activating VEGFR2 phosphorylation and internalization, thereby promoting abnormal vascular growth (27).