TNF and myocardial ischemia: Although cardiac fibroblasts are not a primary source for Mmp9 production [23], moderately increased expression of Mmp9 can, however, be observed in experimentally-induced myocardial ischemia model studies using hypoxia, oxidative stress, and cytokines such as interleukin-1β and tumor necrosis factor-alpha [20,25-27].