SERPINF1 and diabetic retinopathy: In early stages of diabetic retinopathy, downregulation of key factors such as pigment epithelium-derived factor (PEDF), somatostatin, glucagon-like peptide 1 (GLP-1) and other neurotrophic factors is counterbalanced by an upregulation of VEGF and erythropoietin [4, 5].