DNMT1 and diabetes mellitus: Consistently with increase in the activities of Dnmts and Tets, the binding of both Dnmt1 and Tet2 (the only isoforms activated in the retina in diabetes [19], at the MMP-9 promoter was further exacerbated in the HG/Hcy group, and 5-hydroxymethyl cytosine (5hmC) levels were significantly higher compared to those in the HG group (Figure 4a–c).