SUCNR1 and diabetic retinopathy: Once outside the cell, it can bind to the succinate receptor SUCNR1/GPR91, a G-protein–coupled cell surface sensor for extracellular succinate (113) expressed in many cell types, that is known to be activated in diabetic retinopathy (108), diabetic renal disease (114), hypertension (113, 115), and atherothrombosis (116).