MMP9 and diabetes mellitus: Histone methylation and DNA methylation are considered to be tightly coordinated; methylation of lysine can initiate, target, or maintain DNA methylation, and this is true vice versa as well.29,30 Our recent work has shown that the methylation status of MMP-9 promoter is altered in diabetes, despite increased recruitment of Dnmt1 at the MMP-9 promoter, 5mC levels are decreased.