SOD1 and diabetic retinopathy: In a STZ induced rat model, poor glucose control can lead to retinal key antioxidant gene mitochondrial superoxide dismutase (SOD) downregulation by increased promoter levels of H4K20me3 through increased corresponding methyltransferase SUV4-20H2 recruitment to SOD gene promoter, suggesting that diabetic retinopathy is related with SOD repression in retinal ECs [29].