GDF5 deficiency prevents cardiac rupture following acute myocardial infarction in mice.

BACKGROUND: We previously showed that growth differentiation factor 5 (GDF5) limits infarct expansion post-myocardial infarction (MI). We now examine the acute post-MI role of GDF5 in cardiac rupture. METHODS AND RESULTS: Following permanent ligation of the left anterior descending artery, GDF5 deficiency (i.e., GDF5 knockout mice) reduced the incidence of cardiac rupture (4/24 vs. 17/24; P < .05), and improved survival over 28-d compared to wild-type (WT) mice (79% vs. 25%; P < .0001). Moreover, at 3-d post-MI, GDF5-deficient mice manifest: (a) reduced heart weight/body weight ratio (P < .0001) without differences in infarct size or cardiomyocyte size; (b) increased infarct zone expression of Col1a1 (P < .05) and Col3a1 (P < .01), suggesting increased myocardial fibrosis; and (c) reduced aortic and left ventricular peak systolic pressures (P ≤ .05), suggesting reduced afterload. Despite dysregulated inflammatory markers and reduced circulating monocytes in GDF5-deficient mice at 3-d post-MI, reciprocal bone marrow transplantation (BMT) failed to implicate GDF5 in BM-derived cells, suggesting the involvement of tissue-resident GDF5 expression in cardiac rupture. CONCLUSIONS: Loss of GDF5 reduces cardiac rupture post-MI with increased myocardial fibrosis and lower afterload, albeit at the cost of chronic adverse remodeling.

Cthrc1 deficiency aggravates wound healing and promotes cardiac rupture after myocardial infarction via non-canonical WNT5A signaling pathway.

Cardiac fibroblasts are crucial for scar formation and cardiac repair after myocardial infarction (MI). Collagen triple helix repeat containing 1 (CTHRC1), an extracellular matrix protein, is involved in the pathogenesis of vascular remodeling, bone formation, and tumor progression. However, the role and underlying mechanism of CTHRC1 in post-MI wound repair are not fully clear. Bioinformatics analysis demonstrated CTHRC1 up-regulation in cardiac fibroblasts after ischemic cardiac injury. Serum levels of CTHRC1 were increased in MI mice and CTHRC1 expression was up-regulated in cardiac fibroblasts after MI. In vitro results showed that the induction of CTHRC1 expression in cardiac fibroblasts was mediated by canonical TGFß1-Smad2/3 signaling axis. Moreover, CTHRC1 improved wound healing and boosted cardiac fibroblast activation in vitro. Cthrc1 deficiency aggravated cardiac function and reduced collagen deposition as well as increased mortality attributable to cardiac rupture after MI. Consistent with above phenotypes, reduced the levels of myocardial CD31, α-smooth muscle actin, collagen I, and collagen III was observed, whereas myocardial expression of matrix metalloproteinase 2 and matrix metalloproteinase 9 were increased in Cthrc1 knockout mice post-MI. Above effects could be partly reversed by rCTHRC1 protein or rWNT5A protein. Our study indicates that cardiac fibroblast-derived, canonical TGFß1-Smad2/3-dependent CTHRC1 could improve wound repair and prevent cardiac rupture after MI via selectively activating non-canonical WNT5A-PCP signaling pathway.

Cardiac Myocyte-Specific Overexpression of FASTKD1 Prevents Ventricular Rupture After Myocardial Infarction.

Background The mitochondrial mRNA-binding protein FASTKD1 (Fas-activated serine/threonine [FAST] kinase domain-containing protein 1) protects myocytes from oxidative stress in vitro. However, the role of FASTKD1 in the myocardium in vivo is unknown. Therefore, we developed cardiac-specific FASTKD1 transgenic mice to test the effects of this protein on experimental myocardial infarction (MI). Methods and Results Transgenic mouse lines with cardiac myocyte-specific overexpression of FASTKD1 to varying degrees were generated. These mice displayed normal cardiac morphological features and function at the gross and microscopic levels. Isolated cardiac mitochondria from all transgenic mouse lines showed normal mitochondrial function, ATP levels, and permeability transition pore activity. Male nontransgenic and transgenic mice from the highest-expressing line were subjected to 8 weeks of permanent coronary ligation. Of nontransgenic mice, 40% underwent left ventricular free wall rupture within 7 days of MI compared with 0% of FASTKD1-overexpressing mice. At 3 days after MI, FASTKD1 overexpression did not alter infarct size. However, increased FASTKD1 resulted in decreased neutrophil and increased macrophage infiltration, elevated levels of the extracellular matrix component periostin, and enhanced antioxidant capacity compared with control mice. In contrast, markers of mitochondrial fusion/fission and apoptosis remained unaltered. Instead, transcriptomic analyses indicated activation of the integrated stress response in the FASTKD1 transgenic hearts. Conclusions Cardiac-specific overexpression of FASTKD1 results in viable mice displaying normal cardiac morphological features and function. However, these mice are resistant to MI-induced cardiac rupture and display altered inflammatory, extracellular matrix, and antioxidant responses following MI. Moreover, these protective effects were associated with enhanced activation of the integrated stress response.

Cardiac Overexpression of Chil1 Improves Wound Healing to Prevent Cardiac Rupture After Myocardial Infarction.

Timely formation of collagen-rich-scar is of importance to prevent ventricular rupture after myocardial infarction (MI). Chil1 (Chitinase 3-like 1) is a secreted protein associated with tissue remodeling response. However, its function in MI progression remains elusive. Chil1 was downregulated in the injured area overall post-MI. Overexpression of Chil1 markedly reduced cardiac rupture, increased wall thickness, and improved cardiac function post-MI due to collagen-rich-scar formation and extracellular matrix remodeling. In vitro, Chil1 induced the transformation of fibroblasts to myofibroblasts. Mechanistically, a phosphoproteomics study revealed that Chil1 binded to the EGFR enhancing RAF/MEK1/ERK signaling pathway to exert cardiac protection function. The effects of Chil1 on fibroblasts transformation and cardiac protections after MI were partially abolished by co-treated with RAF inhibitor. Together, our findings identify Chil1 as a protection factor in MI progression through binding to EGFR which further activates RAF/MEK1/ERK signaling pathway.

Nuclear Receptor Nur77 Controls Cardiac Fibrosis through Distinct Actions on Fibroblasts and Cardiomyocytes.

Fibrosis is a hallmark of adverse cardiac remodeling, which promotes heart failure, but it is also an essential repair mechanism to prevent cardiac rupture, signifying the importance of appropriate regulation of this process. In the remodeling heart, cardiac fibroblasts (CFs) differentiate into myofibroblasts (MyoFB), which are the key mediators of the fibrotic response. Additionally, cardiomyocytes are involved by providing pro-fibrotic cues. Nuclear receptor Nur77 is known to reduce cardiac hypertrophy and associated fibrosis; however, the exact function of Nur77 in the fibrotic response is yet unknown. Here, we show that Nur77-deficient mice exhibit severe myocardial wall thinning, rupture and reduced collagen fiber density after myocardial infarction and chronic isoproterenol (ISO) infusion. Upon Nur77 knockdown in cultured rat CFs, expression of MyoFB markers and extracellular matrix proteins is reduced after stimulation with ISO or transforming growth factor-ß (TGF-ß). Accordingly, Nur77-depleted CFs produce less collagen and exhibit diminished proliferation and wound closure capacity. Interestingly, Nur77 knockdown in neonatal rat cardiomyocytes results in increased paracrine induction of MyoFB differentiation, which was blocked by TGF-ß receptor antagonism. Taken together, Nur77-mediated regulation involves CF-intrinsic promotion of CF-to-MyoFB transition and inhibition of cardiomyocyte-driven paracrine TGF-ß-mediated MyoFB differentiation. As such, Nur77 provides distinct, cell-specific regulation of cardiac fibrosis.

Loss of Protease-Activated Receptor 4 Prevents Inflammation Resolution and Predisposes the Heart to Cardiac Rupture After Myocardial Infarction.

BACKGROUND: Cardiac rupture is a major lethal complication of acute myocardial infarction (MI). Despite significant advances in reperfusion strategies, mortality from cardiac rupture remains high. Studies suggest that cardiac rupture can be accelerated by thrombolytic therapy, but the relevance of this risk factor remains controversial. METHODS: We analyzed protease-activated receptor 4 (Par4) expression in mouse hearts with MI and investigated the effects of Par4 deletion on cardiac remodeling and function after MI by echocardiography, quantitative immunohistochemistry, and flow cytometry. RESULTS: Par4 mRNA and protein levels were increased in mouse hearts after MI and in isolated cardiomyocytes in response to hypertrophic and inflammatory stimuli. Par4-deficient mice showed less myocyte apoptosis, reduced infarct size, and improved functional recovery after acute MI relative to wild-type (WT). Conversely, Par4-/- mice showed impaired cardiac function, greater rates of myocardial rupture, and increased mortality after chronic MI relative to WT. Pathological evaluation of hearts from Par4-/- mice demonstrated a greater infarct expansion, increased cardiac hemorrhage, and delayed neutrophil accumulation, which resulted in impaired post-MI healing compared with WT. Par4 deficiency also attenuated neutrophil apoptosis in vitro and after MI in vivo and impaired inflammation resolution in infarcted myocardium. Transfer of Par4-/- neutrophils, but not of Par4-/- platelets, in WT recipient mice delayed inflammation resolution, increased cardiac hemorrhage, and enhanced cardiac dysfunction. In parallel, adoptive transfer of WT neutrophils into Par4-/- mice restored inflammation resolution, reduced cardiac rupture incidence, and improved cardiac function after MI. CONCLUSIONS: These findings reveal essential roles of Par4 in neutrophil apoptosis and inflammation resolution during myocardial healing and point to Par4 inhibition as a potential therapy that should be limited to the acute phases of ischemic insult and avoided for long-term treatment after MI.

S100A8/A9 promotes MMP-9 expression in the fibroblasts from cardiac rupture after myocardial infarction by inducing macrophages secreting TNFα.

OBJECTIVE: Inflammation and extracellular matrix degradation play a role in cardiac rupture (CR) after myocardial infarction (MI). It has been found that the expression of inflammatory cytokine S100A8/A9 was elevated in acute MI patients, whereas its impact in CR after infarction remains unclear. PATIENTS AND METHODS: Samples from cardiac tissue and peripheral blood of patients with CR after MI, MI, patients without CR, and healthy control (cardiotrauma) were collected to test the expressions of S100A8/A9, p-p65, and MMP-9. Co-culture system for HCF cells and macrophages were established to identify the impact of hypoxia-ischemia on the expressions of S100A8/A9 and TNFα. S100A9 and/or TNFα blocking agent were applied to examine the effect on macrophages migration, expressions of S100A8, S100A9, and TNFα. Western blot was adopted to determine levels of p-p65 and MMP-9 protein after the inhibition of S100A9 and/or TNFα. RESULTS: Compared with healthy control and non-CR patients, serum S100A8/A9 and MMP-9 levels were elevated in cardiac tissues of CR patients, while S100A8/A9, p-p65, and MMP-9 were also overexpressed. Hypoxia-ischemia significantly caused the increasing levels of S100A8/A9 and TNFα in macrophages (p < 0.05). The blockade of S100A9 and/or TNFα suppressed the activation and migration of macrophages. The inhibition of S100A9 expression also decreased the secretion of TNFα in macrophages, while the suppression of TNFα showed no significant impact on S100A8 and S100A9 levels. Downregulation of TNFα or NF-κB markedly declined p-p65 and MMP-9 protein levels in HCF cells from co-culture system or single culture, whereas the blockade of S100A9 only reduced their expressions in co-cultured HCF cells. CONCLUSIONS: The level of S100A8/A9 was upregulated in MI patients with CR. S100A8/A9 induced the activation of NF-κB and expression of MMP-9 protein in HCF cells through facilitating secretion of TNFα from macrophages, which may play a role in triggering extracellular matrix degradation and CR.

Haploinsufficiency of Hand1 improves mice survival after acute myocardial infarction through preventing cardiac rupture.

Previous studies have demonstrated a significantly lower level of Hand1 in ischemic cardiomyopathy than in normal heart tissue. The role of decreased Hand1 in myocardial infarction remains unclear. This study was designed to investigate the effects of haploinsufficiency of Hand1 on mouse heart after myocardial infarction. 8-10 weeks old male heterozygous Hand1-deficient (Hand1(+/-)) mice and wild-type littermates (control) were subjected to sham operation or ligation of the left anterior descending coronary artery to induce acute myocardial infarction (AMI). Hand1(+/-) mice have low incidence of left ventricular free wall rupture in the first week after operation than control mice. Then we found lower MMP9 activity and less cardiomyocytes apoptosis in Hand1(+/-) than in control mice. All of these contribute to the protection role of haploinsufficiency of Hand1 after AMI.

Twinkle overexpression prevents cardiac rupture after myocardial infarction by alleviating impaired mitochondrial biogenesis.

Cardiac rupture is a fatal complication after myocardial infarction (MI). However, the detailed mechanism underlying cardiac rupture after MI remains to be fully elucidated. In this study, we investigated the role of mitochondrial DNA (mtDNA) and mitochondria in the pathophysiology of cardiac rupture by analyzing Twinkle helicase overexpression mice (TW mice). Twinkle overexpression increased mtDNA copy number approximately twofold and ameliorated ischemic cardiomyopathy at day 28 after MI. Notably, Twinkle overexpression markedly prevented cardiac rupture and improved post-MI survival, accompanied by the suppression of MMP-2 and MMP-9 in the MI border area at day 5 after MI when cardiac rupture frequently occurs. Additionally, these cardioprotective effects of Twinkle overexpression were abolished in transgenic mice overexpressing mutant Twinkle with an in-frame duplication of amino acids 353-365, which resulted in no increases in mtDNA copy number. Furthermore, although apoptosis and oxidative stress were induced and mitochondria were damaged in the border area, these injuries were improved in TW mice. Further analysis revealed that mitochondrial biogenesis, including mtDNA copy number, transcription, and translation, was severely impaired in the border area at day 5 In contrast, Twinkle overexpression maintained mtDNA copy number and restored the impaired transcription and translation of mtDNA in the border area. These results demonstrated that Twinkle overexpression alleviated impaired mitochondrial biogenesis in the border area through maintained mtDNA copy number and thereby prevented cardiac rupture accompanied by the reduction of apoptosis and oxidative stress, and suppression of MMP activity.

Bone marrow transplantation modulates tissue macrophage phenotype and enhances cardiac recovery after subsequent acute myocardial infarction.

BACKGROUND: Bone marrow transplantation (BMT) is commonly used in experimental studies to investigate the contribution of BM-derived circulating cells to different disease processes. During studies investigating the cardiac response to acute myocardial infarction (MI) induced by permanent coronary ligation in mice that had previously undergone BMT, we found that BMT itself affects the remodelling response. METHODS AND RESULTS: Compared to matched naive mice, animals that had previously undergone BMT developed significantly less post-MI adverse remodelling, infarct thinning and contractile dysfunction as assessed by serial magnetic resonance imaging. Cardiac rupture in male mice was prevented. Histological analysis showed that the infarcts of mice that had undergone BMT had a significantly higher number of inflammatory cells, surviving cardiomyocytes and neovessels than control mice, as well as evidence of significant haemosiderin deposition. Flow cytometric and histological analyses demonstrated a higher number of alternatively activated (M2) macrophages in myocardium of the BMT group compared to control animals even before MI, and this increased further in the infarcts of the BMT mice after MI. CONCLUSIONS: The process of BMT itself substantially alters tissue macrophage phenotype and the subsequent response to acute MI. An increase in alternatively activated macrophages in this setting appears to enhance cardiac recovery after MI.

Olmesartan prevents cardiac rupture in mice with myocardial infarction by modulating growth differentiation factor 15 and p53.

BACKGROUND AND PURPOSE: Cardiac rupture is a catastrophic complication that occurs after acute myocardial infarction (MI) and, at present, there are no effective pharmacological strategies for preventing this condition. Here we investigated the effect of the angiotensin II receptor blocker olmesartan (Olm) on post-infarct cardiac rupture and its underlying mechanisms of action. EXPERIMENTAL APPROACH: C57Bl/6 mice with MI were treated with Olm, aldosterone (Aldo) or vehicle. Cultured neonatal cardiomyocytes and fibroblasts were exposed to normoxia or anoxia and treated with angiotensin II (Ang II), RNH6270 (active ingredient of Olm) or Aldo. KEY RESULTS: The mortality rate and incidence of cardiac rupture in MI mice during the first week in the Olm-treated group were significantly lower than in the vehicle-treated group. Olm or RNH6270 reduced myeloperoxidase staining in the infarcted myocardium, decreased apoptosis in cultured cardiomyocytes and fibroblasts, as assessed by Hoechst staining and TUNEL assay, attenuated the accumulation of p53 and phosphorylated p53 and cleaved caspase 3 induced by MI or Ang II, as assessed by Western blotting, and up-regulated growth differentiation factor-15 (GDF-15). In cultured cardiomyocytes and fibroblasts, treatment with Ang II, Aldo or anoxia significantly down-regulated the expression of GDF-15. CONCLUSIONS AND IMPLICATIONS: Olm prevents cardiac rupture through inhibition of apoptosis and inflammation, which is attributable to the down-regulation of p53 activity and up-regulation of GDF-15. Our findings suggest that early administration of an AT1 receptor anatagonist to patients with acute MI is a potential preventive approach for cardiac rupture.

Melusin protects from cardiac rupture and improves functional remodelling after myocardial infarction.

AIMS: Melusin is a muscle-specific chaperone protein whose expression is required for a compensatory hypertrophy response to pressure overload. Here, we evaluated the consequences of melusin overexpression in the setting of myocardial infarction (MI) using a comprehensive multicentre approach. METHODS AND RESULTS: Mice overexpressing melusin in the heart (TG) and wild-type controls (WT) were subjected to permanent LAD ligation and both the acute response (Day 3) and subsequent remodelling (2 weeks) were examined. Mortality in wild-type mice was significant between Days 3 and 7, primarily due to cardiac rupture, but melusin's overexpression strongly reduced mortality (43.2% in wild-type vs. 27.3% in melusin-TG, P = 0.005). At Day 3 after MI, a time point preceding the mortality peak, TG hearts had increased heat shock protein 70 expression, increased ERK1/2 signalling, reduced cardiomyocyte hyper-contractility and inflammatory cell infiltrates, and increased matricellular protein expression in the infarcted area. At 2 weeks after MI, melusin overexpression conferred a favourable adaptive remodelling characterized by reduced left ventricle dilatation and better preserved contractility in the presence of a comparable degree of hypertrophy. Adaptive remodelling in melusin TG mice was characterized by reduced apoptosis and fibrosis as well as increased cardiomyocyte contractility. CONCLUSIONS: Consistent with its function as a chaperone protein, melusin overexpression exerts a dual protective action following MI reducing an array of maladaptive processes. In the early phase after MI, reduced inflammation and myocyte remodelling protect against cardiac rupture. Chronically, reduced myocyte loss and matrix remodelling, with preserved myocyte contractility, confer adaptive LV remodelling.

Lack of haptoglobin results in unbalanced VEGFα/angiopoietin-1 expression, intramural hemorrhage and impaired wound healing after myocardial infarction.

Decreased haptoglobin (Hp) functionality due to allelic variations is associated with worsened outcome in patients after myocardial infarction (MI). However, mechanisms through which haptoglobin deficiency impairs cardiac repair remain to be elucidated. In the present study, we identified novel molecular alterations mediated by Hp involved in early and late cardiac repair responses after left coronary artery ligation in Hp(-/-) and wild-type (WT) mice. We observed a higher mortality rate in Hp(-/-) mice despite similar infarct size between groups. Deaths were commonly caused by cardiac rupture in Hp(-/-) animals. Histological analysis of 3 and 7days old non-ruptured infarcted hearts revealed more frequent and more severe intramural hemorrhage and increased leukocyte infiltration in Hp(-/-) mice. Analyses of non-ruptured hearts revealed increased oxidative stress, reduced PAI-1 activity and enhanced VEGFα transcription in Hp(-/-) mice. In line with these observations, we found increased microvascular permeability in Hp(-/-) hearts 3days after infarction. In vitro, haptoglobin prevented hemoglobin-induced oxidative stress and restored VEGF/Ang-1 balance in endothelial cell cultures. During long-term follow-up of the surviving animals, we observed altered matrix turnover, impaired scar formation and worsened cardiac function and geometry in Hp(-/-)mice. In conclusion, haptoglobin deficiency severely deteriorates tissue repair and cardiac performance after experimental MI. Haptoglobin plays a crucial role in both short- and long-term cardiac repair responses by reducing oxidative stress, maintaining microvascular integrity, myocardial architecture and proper scar formation.

Enhanced expression of plasminogen activator inhibitor may prevent cardiac rupture in female and castrated mice after myocardial infarction.

OBJECTIVE: The objective of this study was to test the hypothesis that gender has a significant impact on cardiac inflammation, fibrosis, and survival after myocardial infarction (MI) in a murine model of left coronary artery ligation (CAL) by investigating the underlying cellular-molecular mechanisms. METHODS: Age-matched male and female mice were randomly assigned into 6 groups: sham-operated males, sham-operated females, intact males with CAL, intact females with CAL, castrated males with CAL, and oophorectomized females with CAL. The animals were sacrificed 14 days postoperatively. The hearts from each group were harvested for morphologic studies (n = 6) (infarct and fibrotic area, inflammatory cell markers CD40 and CD68) and mRNA expression analyses (n = 6) of pro- and antiinflammatory molecules, including matrix metalloproteinase (MMP)-9, plasminogen activator inhibitor (PAI)-1, interleukin (IL)-10, transforming growth factor (TGF)-ß, and endothelial nitric oxide synthase (eNOS). RESULTS: Intact males with CAL had significantly lower 14-day survival compared with intact females with CAL. Similarly, the infarct areas in intact males with CAL were largest compared with other CAL animals. The fibrotic area was also larger in intact males with CAL than in intact females with CAL. Numbers of CD40(+)/CD68(+) cells and MMP-9 expression were higher in intact males with CAL than in intact females with CAL and castrated males with CAL. IL-10, eNOS, and TGF-ß were significantly suppressed in oophorectomized females with CAL compared with intact females with CAL. Intact females with CAL and castrated males with CAL exhibited notably enhanced post-MI PAI-1 expression. CONCLUSIONS: Male gender (compared with female) may be an unfavorable prognostic factor after MI in terms of enhanced inflammation and fibrosis in a murine model. Although castration seemed to be significantly antiinflammatory and antifibrotic after MI, oophorectomy had no significant impact on survival, suggesting that factors other than estrogen may account for favorable outcome after MI in the female gender. Furthermore, enhanced postinfarct PAI-1 expression in castrated and female mice may contribute to suppressed MMP-9 expression and survival advantage.

Deficiency in TIMP-3 increases cardiac rupture and mortality post-myocardial infarction via EGFR signaling: beneficial effects of cetuximab.

Cardiac rupture is a fatal complication of myocardial infarction (MI); however, its underlying molecular mechanisms are not fully understood. This study investigated the role of tissue inhibitor of metalloproteinase-3 (TIMP-3)/matrix metalloproteinase (MMP)/epidermal growth factor (EGF)/transforming growth factor (TGF)-ß1 pathway in infarct healing and effects of cetuximab on cardiac rupture after MI. Induction of MI was achieved by left coronary artery ligation in wild-type (WT) and TIMP-3(-/-) mice. TIMP-3 deficiency resulted in a fourfold increase in cardiac rupture and 50% decrease in survival after MI. Hydroxyproline content, collagen synthesis and myofibroblast cell number in the infarct region, and the force required to induce rupture of the infarct scar were significantly decreased, while MMP activity was increased in TIMP-3(-/-) mice. EGF proteins were increased by threefold in TIMP-3(-/-) mice following MI, while TGF-ß1 mRNA levels were decreased by 68%. Cell proliferation of cultured adult cardiac myofibroblasts was significantly decreased in TIMP-3(-/-) compared to WT myofibroblasts. EGF treatment significantly decreased collagen synthesis and TGF-ß1 expression. Conversely, TGF-ß1 treatment increased collagen synthesis in cardiac myofibroblasts. Treatment with cetuximab significantly decreased the incidence of cardiac rupture and improved survival post-MI in TIMP-3(-/-) mice. We conclude that deficiency in TIMP-3 increases cardiac rupture post-MI via EGF/epidermal growth factor receptor (EGFR) signaling which downregulates TGF-ß1 expression and collagen synthesis. Inhibition of EGFR by cetuximab protects against cardiac rupture and improves survival post-MI.

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.

Early activation of matrix metalloproteinases underlies the exacerbated systolic and diastolic dysfunction in mice lacking TIMP3 following myocardial infarction.

Extracellular matrix (ECM) remodeling is a critical aspect of cardiac remodeling following myocardial infarction. Tissue inhibitors of metalloproteinases (TIMPs) are physiological inhibitors of matrix metalloproteinases (MMPs) that degrade the ECM proteins. TIMP3 is highly expressed in the heart, and is markedly downregulated in patients with ischemic cardiomyopathy. We therefore examined the time- and region-dependent role of TIMP3 in the cardiac response to myocardial infarction (MI). TIMP3(-/-) and wild-type (WT) mice were subjected to MI by ligation of the left anterior descending artery. TIMP3(-/-)-MI mice exhibited a significantly compromised rate of survival compared with WT-MI mice, primarily due to increased left ventricular (LV) rupture, greater infarct expansion, exacerbated LV dilation, and greater systolic and diastolic dysfunction. Second harmonic generation imaging of unfixed and unstained hearts revealed greater collagen disarray and reduced density in the TIMP3(-/-) infarct myocardium compared with the WT group. Gelatinolytic and collagenolytic activities increased in TIMP3(-/-) compared with WT hearts at 1 day post-MI but not at 3 days or 1 wk post-MI. Neutrophil infiltration and inflammatory MMPs were significantly increased in the infarct and peri-infarct regions of TIMP3(-/-)-MI hearts. Treatment of TIMP3(-/-) mice with a broad-spectrum MMP inhibitor (PD-166793) for 2 days before and 2 days after MI markedly improved post-MI infarct expansion, LV rupture incident, LV dilation, and systolic dysfunction in these mice up to 1 wk post-MI. Our data demonstrate that the initial rise in proteolytic activities early post-MI is a triggering factor for subsequent LV adverse remodeling, LV rupture, and dilated cardiomyopathy. Hence, timing of treatments to improve cardiac response to MI may be critical in producing favorable outcome.

Synergistic effect of mitral expression of tissue inhibitor of metalloproteinase-2 with hypertension on the occurrence of mitral chordae tendinae rupture.

OBJECTIVES: We previously found the association between mitral chordae tendinae ruptures (MCTR) and hypertension. Tissue inhibitor of metalloproteinase-2 (TIMP2), which expresses differently under pressure loads, could trigger a signal cascade instigating cardiac fibrosis, possibly predisposing to MCTR. We aimed to elucidate the relationship between the TIMP2 and hypertension and the effect they may have on the occurrence of MCTR. METHODS: Using a cross-sectional study in a tertiary medical center in Taiwan, we enrolled 186 patients who had received mitral valve replacements and classified them into two groups: 64 (34%) with MCTR and 122 (66%) without MCTR. Expression of mitral TIMP2 was assessed on a semiquantitative scale (grade 0-3) by immunohistochemical staining using antibodies against TIMP2. RESULTS: TIMP2 expression was significantly higher in MCTR patients (P < 0.001). Multiple logistic regression analysis showed four independent risk factors: TIMP2 [odds ratio (OR) = 1.82, 95% confidence interval (CI) = 1.18-2.81, P = 0.007], hypertension (OR = 2.40, CI = 1.08-5.34, P = 0.032), rheumatic heart disease (OR = 0.18, CI = 0.05-0.70, P = 0.014), and left ventricular end-diastolic dimension (OR = 1.10, CI = 1.05-1.15, P < 0.001). Among nonhypertensive patients, the higher expression of TIMP2 (grade 2 and 3 vs. 0 and 1) was associated with a 3.27-fold risk. However, hypertensive patients with higher TIMP2 expression had a significantly 10-fold higher risk (P < 0.001 for interaction). CONCLUSION: Mitral TIMP2 expression is higher in patients with MCTR and there is a synergistic effect of mitral TIMP2 staining with hypertension on the occurrence of MCTR.