Altered balance between matrix gelatinases (MMP-2 and MMP-9) and their tissue inhibitors in human dilated cardiomyopathy: potential role of MMP-9 in myosin-heavy chain degradation

Background: End-stage of human dilated cardiomyopathy (DCM) is characterize d by myocyte loss and fibrosis, and associated with ventricular dilatation and reduced cardiac function. Matrix metalloproteinases (MMPs) and their na tural tissue inhibitors (TIMPs) have been involved in the myocardial remode ling. Aims: To evaluate the potential role of matrix gelatinases (MMP-2 and MMP-9) in DCM, the balance between gelatinases and TIMPs and the gelatinas e localization were investigated in left free wall ventricles from six norm al donors and six patients with DCM at the transplantation time. Methods: T IMP-(1, 2, 3 and 4) mRNAs were analyzed by quantitative reverse transcripti on-polymerase chain reaction (RT-PCR). TIMP-1 and -2 protein content was as sessed by ELISA. MMP-2 and MMP-9 expression were examined by zymography and immunological techniques. Results: All TIMPs were down-regulated in DCM he arts, especially TIMP-1 (reduced by 80%). Gel zymography revealed similar a ctivity of MMP-2 and MMP-9 in both tissues. By in situ zymography and immun ohistochemistry, active and immunoreactive gelatinases were pericardiomyocy te in control hearts and intracardiomyocyte in DCM hearts. Intracellular MM Ps were associated with sarcomeric structure in DCM. To estimate a putative role of these gelatinases, several sarcomeric contractile proteins were di gested in vitro by purified active MMP-9. Only myosin-heavy chain was cleav ed in vitro giving 180-, 120-, 80- and 20-kDa proteolytic fragments. In viv o, two major myosin-heavy chain proteolytic fragments (80 and 20 kDa) were detected by specific monoclonal antibody against myosin-heavy chain in DCM left ventricular homogenates, only. Conclusions: Taken together, these data highly suggest that MMP-2 and MMP-9 may be involved in the disorganization of the contractile apparatus in DCM hearts. (C) 1999 European Society of C ardiology. All rights reserved.