Cardiac sarcomeric proteins: novel intracellular targets of matrix metalloproteinase-2 in heart disease

Matrix metalloproteinases (MMPs) have been almost exclusively thought to be secreted proteases (with the exception of the membrane-type MMPs) that exert diverse biological actions in health and disease via proteolyzing substrates outside the cell. However, recent evidence has demonstrated that the role of MMPs goes far beyond their proteolytic activity in the extracellular matrix. MMP-2 is arguably the most ubiquitous member of the 23 member MMP family and is expressed in all cells of the heart and vasculature. In the past 10 years, MMP-2 was shown to change the bioactivity of a growing list of specific, non-extracellular matrix proteins both outside and inside the cell. There is clear evidence of its intracellular localization to the cardiac sarcomere, nucleus, and mitochondria and that during early phases of oxidative stress injury to the heart, MMP-2 proteolyzes specific sarcomeric and cytoskeletal proteins to cause contractile dysfunction. In this review we discuss this novel intracellular biology of MMP-2 and the potential use of MMP inhibitors for the therapy of heart injury caused by oxidative stress.