Role of matricellular proteins in cardiac tissue remodeling after myocardial infarction

Figure 1 Phases of cardiac healing and remodeling after myocardial infarction (MI). The cardiac healing and remodeling process after MI can be divided into four phases: (1) death of cardiomyocytes; (2) acute inflammation; (3) formation of granulation tissue; and (4) scar formation. Death of cardiomyocytes starts at approximately 1 h after coronary artery occlusion, and can either be the result of apoptosis or necrosis. During acute inflammation, the influx of inflammatory cells, including neutrophils and monocytes, for phagocytosis and removal of dead cardiomyocytes into the infarcted area and degradation of the extracellular matrix (ECM) by matrix metalloproteinase (MMP) takes place between 1 h and 4 d after MI. MMP also modulates inflammatory cytokine and chemokine activity. Generation of matrix fragments exerts potent inflammatory effects. Thereafter, formation of granulation tissue, characterized by the presence of fibroblasts, macrophages, myofibroblasts, new blood vessels, and ECM proteins, occurs in the infarcted heart between 2 and 14 d after MI. To rescue the loss of the shielding effects of the normal matrix, fibroblasts and myofibroblasts produce ECM. Finally, granulation tissue matures in the infarcted heart between 14 d and 2 mo after MI. The scar is characterized by a cross-linked, collagen-rich region that is induced by lysyl oxidase. In this phase, most infarct myofibroblasts undergo apoptosis and disappear. The time intervals for each phase are dependent on the species, as rodents exhibit an accelerated inflammatory and reparative response following MI as compared with large mammals.