MMP9 and diabetic cardiomyopathy: Moreover, we also found that fibrosis was involved in the development of diabetic cardiomyopathy, including collagen accumulation in the myocardial interstitium; increased expression of COL1, COL3, or CTGF at the transcriptional and protein levels; and reduced activity of MMP9, which were consistent with previous studies (Fein, 1990; Shimizu, 1993; Mizushige et al., 2000: Westermann et al., 2007; Linthout et al., 2008; Braga et al., 2014; Huynh et al., 2014).