Matrix metalloproteinase-1 mitral expression and -1607 1G/2G gene promoter polymorphism in mitral chordae tendinae rupture.

Understanding the pathogenesis of mitral chordae tendinae rupture (MCTR) is essential for identification of risk factors. Mitral matrix metalloproteinase (MMP) triggers the signal cascade that instigates cardiac fibrosis, which may be a predisposing factor in MCTR. We investigated associations among MMP1 expression, MMP1 -1607 1G/2G polymorphism and mitral chordae tendinae rupture (MCTR). This study enrolled 185 patients (group A) receiving mitral valve replacement. Group A included 65 patients with MCTR and 120 controls without MCTR. MMP1 was assessed on a semiquantitative scale (0-3) by immunohistochemical staining. For genetic association study, another 227 subjects were recruited for group B, including 75 with MCTR and 152 controls. The gene polymorphisms were analyzed by polymerase chain reaction. In group A, MCTR patients had a higher MMP1 expression compared to controls (P < 0.001). Binary regression analysis showed the variation in the MCTR patients was independently explained by MMP1 (P = 0.027). Hypertension and MMP1 staining had a synergistic effect on the MCTR occurrence (P < 0.001). In group B, MMP1 -1607 1G allele was increased in patients with MCTR compared to controls (P = 0.014). The odds ratio for the 1G/1G genotype to the 2G/2G genotype was 3.22 (P = 0.009). Univariate and logistic regression analysis showed an independent association between MCTR and MMP1 -1607 1G/2G polymorphism (P = 0.028 and 0.032, respectively). Since MMP1 mitral expression and -1607 1G/2G polymorphism were associated with MCTR independently of other baseline characteristics, MMP1 may play a role in the individual susceptibility to MCTR.

Matrix metalloproteinase-28 deletion exacerbates cardiac dysfunction and rupture after myocardial infarction in mice by inhibiting M2 macrophage activation.

RATIONALE: Matrix metalloproteinase (MMP)-28 regulates the inflammatory and extracellular matrix responses in cardiac aging, but the roles of MMP-28 after myocardial infarction (MI) have not been explored. OBJECTIVE: To determine the impact of MMP-28 deletion on post-MI remodeling of the left ventricle (LV). METHODS AND RESULTS: Adult C57BL/6J wild-type (n=76) and MMP null (MMP-28((-/-)), n=86) mice of both sexes were subjected to permanent coronary artery ligation to create MI. MMP-28 expression decreased post-MI, and its cell source shifted from myocytes to macrophages. MMP-28 deletion increased day 7 mortality because of increased cardiac rupture post-MI. MMP-28(-/-) mice exhibited larger LV volumes, worse LV dysfunction, a worse LV remodeling index, and increased lung edema. Plasma MMP-9 levels were unchanged in the MMP-28((-/-)) mice but increased in wild-type mice at day 7 post-MI. The mRNA levels of inflammatory and extracellular matrix proteins were attenuated in the infarct regions of MMP-28(-/-) mice, indicating reduced inflammatory and extracellular matrix responses. M2 macrophage activation was impaired when MMP-28 was absent. MMP-28 deletion also led to decreased collagen deposition and fewer myofibroblasts. Collagen cross-linking was impaired as a result of decreased expression and activation of lysyl oxidase in the infarcts of MMP-28(-/-) mice. The LV tensile strength at day 3 post-MI, however, was similar between the 2 genotypes. CONCLUSIONS: MMP-28 deletion aggravated MI-induced LV dysfunction and rupture as a result of defective inflammatory response and scar formation by suppressing M2 macrophage activation.

Glycogen synthase kinase-3α limits ischemic injury, cardiac rupture, post-myocardial infarction remodeling and death.

BACKGROUND: The molecular pathways that regulate the extent of ischemic injury and post-myocardial infarction (MI) remodeling are not well understood. We recently demonstrated that glycogen synthase kinase-3α (GSK-3α) is critical to the heart's response to pressure overload. However, the role, if any, of GSK-3α in regulating ischemic injury and its consequences is not known. METHODS AND RESULTS: MI was induced in wild-type (WT) versus GSK-3α((-/-)) (KO) littermates by left anterior descending coronary artery ligation. Pre-MI, WT, and KO hearts had comparable chamber dimensions and ventricular function, but as early as 1 week post-MI, KO mice had significantly more left ventricular dilatation and dysfunction than WT mice. KO mice also had increased mortality during the first 10 days post-MI (43% versus 22%; P=0.04), and postmortem examination confirmed cardiac rupture as the cause of most of the deaths. In the mice that survived the first 10 days, left ventricular dilatation and dysfunction remained worse in the KO mice throughout the study (8 weeks). Hypertrophy, fibrosis, and heart failure were all increased in the KO mice. Given the early deaths due to rupture and the significant reduction in left ventricular function evident as early as 1 week post-MI, we examined infarct size following a 48-hour coronary artery ligation and found it to be increased in the KO mice. This was accompanied by increased apoptosis in the border zone of the MI. This increased susceptibility to ischemic injury-induced apoptosis was also seen in cardiomyocytes isolated from the KO mice that were exposed to hypoxia. Finally, Bax translocation to the mitochondria and cytochrome C release into the cytosol were increased in the KO mice. CONCLUSION: GSK-3α confers resistance to ischemic injury, at least in part, via limiting apoptosis. Loss of GSK-3α promotes ischemic injury, increases risk of cardiac rupture, accentuates post-MI remodeling and left ventricular dysfunction, and increases the progression to heart failure. These findings are in striking contrast to multiple previous reports in which deletion or inhibition of GSK-3ß is protective.

Critical role for white blood cell NAD(P)H oxidase-mediated plasminogen activator inhibitor-1 oxidation and ventricular rupture following acute myocardial infarction.

Plasminogen activator inhibitor-1 (PAI-1) is an oxidant-sensitive protease inhibitor that is inactivated by oxidation and has a critical role in ventricular remodeling post myocardial infarction (MI). PAI-1 knockout (KO) mice die within 7days of myocardial infarction post MI due to increased plasmin activity leading to ventricular rupture. The goal of this study was to assess the relevant pathways of leukocyte-derived oxidants post MI that alter PAI-1 activity. Transplantation of wild-type (WT) bone marrow into PAI-1 null mice prolonged survival after MI (WT marrow: 41.66% vs. PAI-1 KO marrow: 0% in PAI-1 KO mice at day 7 (p<0.02). To determine relevant enzyme systems, we transplanted marrow from mice with specific deletions relevant to leukocyte-derived oxidants (NAD(P)H oxidase, iNOS, myeloperoxidase (MPO)) to determine which deletion controls PAI-1 oxidative inactivation and prolongs survival. MI was induced by ligation of the left anterior descending artery (LAD) and the incidence of cardiac rupture was monitored. PAI-1 KO transplanted with MPO KO, or iNOS KO bone marrow died within 9 days after MI. PAI-1 KO mice transplanted with p47(phox) KO marrow exhibited prolonged survival 21 days after MI (30% survival, p<0.03, n=10) compared to WT marrow (8.3%, n=12). Three days after MI, PAI-1 KO mice transplanted with p47(phox) KO marrow had increased PAI-1 activity and decreased nitration of PAI-1 in myocardial tissue compared to PAI-1 KO mice transplanted with WT marrow. These data suggest that modulating O(2)(•-) generation by NAD(P)H oxidase appears to be a therapeutically relevant target for increasing myocardial PAI-1 levels after MI, whereas downstream enzymes like MPO and iNOS may not be.