Recently, it was reported that the expression levels of SIRT1 and SIRT3 mRNA and protein were decreased in the retinas of rats with early-stage diabetes; however, after injection treatment with an antioxidant glucagon-like peptide 1 analog, exendin-4 (EX4), the expression of both SIRT1 and SIRT3 was restored to normal levels [36]. This evidence concerns the gene GCG and diabetes mellitus.