Extracellular protease activation and unraveling of the myocardial interstitium: critical steps toward clinical applications

Infliximab Limits Injury in Myocardial Infarction

BACKGROUND

The purpose of this study was to investigate a therapeutic approach targeting the inflammatory response and consequent remodeling from ischemic myocardial injury.

METHODS AND RESULTS

Coronary thrombus aspirates were collected from patients at the time of ST-segment-elevation myocardial infarction and subjected to array-based proteome analysis. Clinically indistinguishable at myocardial infarction (MI), patients were stratified into vulnerable and resilient on the basis of 1-year left ventricular ejection fraction and death. Network analysis from coronary aspirates revealed prioritization of tumor necrosis factor-α signaling in patients with worse clinical outcomes. Infliximab, a tumor necrosis factor-α inhibitor, was infused intravenously at reperfusion in a porcine MI model to assess whether infliximab-mediated immune modulation impacts post-MI injury. At 3 days after MI (n=7), infliximab infusion increased proregenerative M2 macrophages in the myocardial border zone as quantified by immunofluorescence (24.1%±23.3% in infliximab versus 9.29%±8.7% in sham; P<0.01). Concomitantly, immunoassays of coronary sinus samples quantified lower troponin I levels (41.72±7.34 pg/mL versus 58.11±10.75 pg/mL; P<0.05) and secreted protein analysis revealed upregulation of injury-modifying interleukin-2, -4, -10, -12, and -18 cytokines in the infliximab-treated cohort. At 4 weeks (n=12), infliximab treatment resulted in significant protective influence, improving left ventricular ejection fraction (53.9%±5.4% versus 36.2%±5.3%; P<0.001) and reducing scar size (8.31%±10.9% versus 17.41%±12.5%; P<0.05).

CONCLUSIONS

Profiling of coronary thrombus aspirates in patients with ST-segment-elevation MI revealed highest association for tumor necrosis factor-α in injury risk. Infliximab-mediated immune modulation offers an actionable pathway to alter MI-induced inflammatory response, preserving contractility and limiting adverse structural remodeling.

Association of matrix metalloproteinase‐9 and nitric oxide with hypertension in obstructive sleep apnea

Background

Patients with obstructive sleep apnea (OSA) are more likely to suffer from hypertension. At the same time, the serum levels of matrix metalloproteinase‐9 (MMP‐9) and nitric oxide (NO) in patients with OSA are also changed in OSA patients. We investigated the correlation between serum levels of MMP‐9, NO in patients with OSA and their association with hypertension in those patients, and the effects of continuous positive airway pressure therapy (CPAP) on these serum biomarkers and blood pressure.

Methods

Serum MMP‐9 and NO levels and blood pressure of 57 patients with newly diagnosed OSA and 30 controls were measured; among them, 30 patients with moderate to severe OSA underwent 3‐month CPAP treatment.

Results

In comparison to the control group, the MMP‐9 serum levels were higher (232.8 ± 103.2 ng/ml versus 161.6 ± 56.5 ng/ml, p < .001*), there was no statistical significance difference among serum NO (26.7 ± 9.1 IU/ml versus 31.0 ± 11.7 IU/ml, p = .06), and MMP‐9 was negatively correlated to NO, especially in patients with hypertension (r = −.644, p = .02*). MMP‐9, NO, and blood pressure were significantly recovered in the patients with OSA after CPAP treatment for 3 months (p < .05*).

Conclusion

The MMP‐9 level and the NO level were altered in OSA patients. The relationship between the two especially in patients with hypertension suggests the potential mechanism of OSA‐induced hypertension.

Heart Failure in Women with Congenital Heart Disease

Heart failure remains the most common cause of morbidity and mortality in adults with congenital heart disease (CHD). Although gender-specific outcomes are not robust, it seems that women with CHD may be more affected by late heart failure (HF) than men. A specialized and experienced adult CHD team is required to care for these women as they age, including assessment for reversible causes of HF and in the management of pregnancy, labor, and delivery.

Proteinases, Their Extracellular Targets, and Inflammatory Signaling

Given that over 2% of the human genome codes for proteolytic enzymes and their inhibitors, it is not surprising that proteinases serve many physiologic-pathophysiological roles. In this context, we provide an overview of proteolytic mechanisms regulating inflammation, with a focus on cell signaling stimulated by the generation of inflammatory peptides; activation of the proteinase-activated receptor (PAR) family of G protein-coupled receptors (GPCR), with a mechanism in common with adhesion-triggered GPCRs (ADGRs); and by proteolytic ion channel regulation. These mechanisms are considered in the much wider context that proteolytic mechanisms serve, including the processing of growth factors and their receptors, the regulation of matrix-integrin signaling, and the generation and release of membrane-tethered receptor ligands. These signaling mechanisms are relevant for inflammatory, neurodegenerative, and cardiovascular diseases as well as for cancer. We propose that the inflammation-triggering proteinases and their proteolytically generated substrates represent attractive therapeutic targets and we discuss appropriate targeting strategies.

Differential membrane type 1 matrix metalloproteinase substrate processing with ischemia-reperfusion: relationship to interstitial microRNA dynamics and myocardial function

OBJECTIVES

Membrane type 1 matrix metalloproteinase (MT1-MMP) is critical to a number of proteolytic and profibrotic events. However, upstream regulation of MT1-MMP with myocardial ischemia-reperfusion remains poorly understood. MicroRNAs regulate post-transcriptional events, and in silico mapping has identified a conserved sequence in MT1-MMP for microRNA-133a. This study tested the hypothesis that changes in microRNA-133a regulation occur with myocardial ischemia-reperfusion, which contributes to time- and region-dependent changes in MT1-MMP activity and processing of MT1-MMP substrates.

METHODS

Yorkshire pigs (n = 12) underwent ischemia-reperfusion (90 minutes ischemia and 120 minutes reperfusion), where regional preload recruitable stroke work (sonomicrometry), interstitial MT1-MMP activity (microdialysis), Smad2 abundance (immunoblotting), and interstitial microRNA-133a (polymerase chain reaction) were determined within the ischemia-reperfusion and remote regions. Human left ventricular fibroblasts were transduced with microRNA-133a and anti-microRNA-133a (lentivirus) to determine the effects on MT1-MMP protein abundance.

RESULTS

With ischemia-reperfusion, regional preload recruitable stroke work decreased from steady state (139 ± 20 mm Hg to 44 ± 11 mm Hg, P < .05) within the ischemia-reperfusion region. MT1-MMP activity increased in both regions. Phosphorylated Smad2 increased within the ischemia-reperfusion region. Both in vitro and in vivo interstitial levels of microRNA-133a decreased with ischemia and returned to steady-state levels with reperfusion. In vitro transduction of microRNA-133a in left ventricular fibroblasts decreased MT1-MMP levels.

CONCLUSIONS

Modulation of MT1-MMP activity and microRNA-133a exportation into the myocardial interstitium occurred in the setting of acute myocardial ischemia-reperfusion. In addition, changes in microRNA-133a expression in left ventricular fibroblasts resulted in an inverse modulation of MT1-MMP abundance. Therefore, targeting of microRNA-133a represents a potentially novel means for regulating the cascade of profibrotic events after ischemia-reperfusion.

Changes in the myocardial interstitium and contribution to the progression of heart failure

The myocardial interstitium is highly organized and orchestrated, whereby small disruptions in composition, spatial relationships, or content lead to altered myocardial systolic and/or diastolic performance. These changes in extracellular matrix structure and function are important in the progression to heart failure in pressure overload hypertrophy, dilated cardiomyopathy, and ischemic heart disease. The myocardial interstitium is not a passive entity, but rather a complex and dynamic microenvironment that represents an important structural and signaling system within the myocardium.

Genetic polymorphisms and plasma levels of matrix metalloproteinases and their relationships with developing acute myocardial infarction

OBJECTIVES

Matrix metalloproteinases (MMPs) play an important role in early atherosclerosis, plaque rupture, extracellular matrix remodeling, and myocardial infarction (MI). MMP gene polymorphisms contribute to the risk of developing cardiovascular disease. We designed to investigate the association of acute MI (AMI) with a polymorphism in the human MMP-1, 2, 3, and 9 genes in Iranian patients with AMI.

METHODS

Genomic DNA of 400 enrolled patients with AMI and 200 controls was extracted from their blood samples. The -1607 1G/2G MMP-1, -1306 C/T MMP-2, -1171 5A/6A MMP-3, -1562 C/T MMP-9 polymorphisms were detected. Plasma levels of MMPs were analyzed.

RESULTS

There are significant differences in MMP-3 '5A' allele and genotype in the patients with AMI comparing with controls. However, no significant differences were observed in MMP-1, 2, and 9 allele frequencies between the patients and controls. Differences between plasma levels of MMPs were significant in the patients than in controls. There were statistically significant differences between plasma MMP-3 in carriers of 5A allele compared with 6A allele. MMP-9 plasma levels were significantly higher in the carriers of -1306 TT and -1306 CT than CC. However, there were no statistically significant association between genetic variation of MMP-1, 2, and 3 in the patients and their plasma levels.

CONCLUSION

These data suggest that MMP genotyping such as genetic polymorphism in MMP-3 might be helpful in determining susceptibility to AMI in Iranian patients. In addition, susceptibility to AMI might be related to MMP-9 gene expression, which affects its plasma levels.

Serum levels of large tenascin-C variants, matrix metalloproteinase-9, and tissue inhibitors of matrix metalloproteinases in concentric versus eccentric left ventricular hypertrophy

AIMS

Chronic hypertension may cause left ventricular hypertrophy (LVH). The role of matrix metalloproteinases (MMPs), tissue inhibitors of matrix metalloproteinases (TIMPs), and tenascin-C (Tn-C) splice variants in concentric vs. eccentric left ventricular remodelling has not been investigated.

METHODS AND RESULTS

Serum levels of B or C domain containing Tn-C, MMP-9, TIMP-1, -2, and -4 were determined in concentric (left ventricular posterior wall thickness >13 mm and intraventricular septum >13 mm, n = 61) and eccentric (end-diastolic left ventricular diameter >55 mm or end-systolic left ventricular diameter >40 mm, n = 34) LVH by enzyme-linked immunoassays. Levels of B domain containing Tn-C were higher in patients with LVH than in normal volunteers (P = 0.020) and higher in eccentric LVH (EH) compared with concentric LVH (CH) (P = 0.003). A cut-off value of 900 ng/mL might discriminate between these different forms of LVH. Matrix metalloproteinase-9 was higher in patients with LVH than in normal volunteers (P = 0.042), and levels were decreased in EH compared with CH (P = 0.028). Patients with LVH had higher levels of TIMP-1 (P = 0.059), TIMP-2 (P = 0.043), and TIMP-4 (P = 0.163) than normal volunteers, but there were no differences between the LVH groups.

CONCLUSION

Our data suggest that myocardial remodelling in LVH is associated with changes in serum levels of MMP-9, TIMP-1, -2, -4, and Tn-C splice variants. In addition, B domain containing Tn-C discriminated EH from CH and might be suggested as a potential diagnostic marker.

TORAFIC study protocol: torasemide prolonged release versus furosemide in patients with chronic heart failure

Loop diuretics, such as torasemide and furosemide, are important agents in the treatment of chronic heart failure. Beneficial effects of torasemide immediate-release formulation beyond diuresis have been documented as the ability of this compound to inhibit myocardial synthesis and deposition of collagen type I in patients with chronic heart failure. In addition, torasemide-treated patients, but not furosemide-treated patients, showed decreased serum concentrations of the C-terminal propeptide of procollagen type I, a biochemical marker of myocardial fibrosis. The aim of the TORAFIC study is to test the efficacy of torasemide prolonged-release formulation (PR) in reducing myocardial fibrosis in chronic heart failure in a large, randomized clinical trial.

METHODS

This prospective, Phase IV, randomized, blinded end point, active-controlled clinical trial will randomize 142 patients with chronic heart failure in New York Heart Association functional class II-IV to 8 months treatment with either torasemide-PR (10-40 mg daily) or furosemide (40-160 mg daily). The primary objective is to test the hypothesis that torasemide-PR is superior to furosemide in reducing myocardial fibrosis. The primary outcome measure is the difference in the change of serum propeptide of procollagen type I concentration from the initial to the final visit between both study groups. Secondary outcome measures include all efficacy variables related to heart failure (signs and symptoms, ECG, echocardiogram and serum levels of N-terminal brain natriuretic propeptide). Secondary safety variables are heart rate, blood pressure, laboratory data, adverse events, cardiovascular events (hospital admission, emergency department visits) and quality of life (Minnesota questionnaire).

DISCUSSION

This trial will test whether torasemide-PR possesses antifibrotic properties, which may provide an additional benefit beyond diuresis in patients with chronic heart failure.

Matrix metalloproteinase therapy in heart failure

Milestones in the progression to heart failure following myocardial infarction (MI) are changes in left ventricular (LV) geometry and function, termed post-MI remodeling. Critical to this adverse remodeling process are changes in the expression, synthesis, and degradation of myocardial extracellular matrix (ECM) proteins. The myocardial ECM is not a passive entity but a complex and dynamic microenvironment that represents an important structural and signaling system within the myocardium. In particular, basic and clinical studies have provided conclusive evidence that abnormal and persistent activation of the ECM degradation pathway, notably through the matrix metalloproteinases (MMPs), contribute to adverse post-MI remodeling. This review examines recent clinical studies that provide further support to the hypothesis that a specific portfolio of MMPs are diagnostic and likely contributory to LV remodeling and the progression to heart failure after MI. Future translational and clinical research focused on the molecular and cellular mechanisms regulating ECM structure and function likely will contribute to an improved understanding of post-MI LV remodeling and yield novel therapeutic targets.

Inhibition of matrix metalloproteinases improves left ventricular function in mice lacking osteopontin after myocardial infarction

Osteopontin (OPN) plays an important role in left ventricular (LV) remodeling after myocardial infarction (MI) by promoting collagen synthesis and accumulation. This study tested the hypothesis that MMP inhibition modulates post-MI LV remodeling in mice lacking OPN. Wild-type (WT) and OPN knockout (KO) mice were treated daily with MMP inhibitor (PD166793, 30 mg/kg/day) starting 3 days post-MI. LV functional and structural remodeling was measured 14 days post-MI. Infarct size was similar in WT and KO groups with or without MMP inhibition. M-mode echocardiography showed greater increase in LV end-diastolic (LVEDD) and end-systolic diameters (LVESD) and decrease in percent fractional shortening (%FS) and ejection fraction in KO-MI versus WT-MI. MMP inhibition decreased LVEDD and LVESD, and increased %FS in both groups. Interestingly, the effect was more pronounced in KO-MI group versus WT-MI (P < 0.01). MMP inhibition significantly decreased post-MI LV dilation in KO-MI group as measured by Langendorff-perfusion analysis. MMP inhibition improved LV developed pressures in both MI groups. However, the improvement was significantly higher in KO-MI group versus WT-MI (P < 0.05). MMP inhibition increased heart weight-to-body weight ratio, myocyte cross-sectional area, fibrosis and septal wall thickness only in KO-MI. Percent apoptotic myocytes in the non-infarct area was not different between the treatment groups. Expression and activity of MMP-2 and MMP-9 in the non-infarct area was higher in KO-MI group 3 days post-MI. MMP inhibition reduced MMP-2 activity in KO-MI with no effect on the expression of TIMP-2 and TIMP-4 14 days post-MI. Thus, activation of MMPs contributes to reduced fibrosis and LV dysfunction in mice lacking OPN.

Effects of age on plasma matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinases (TIMPs)

BACKGROUND

The mechanisms causing age-dependent changes in left ventricular (LV) structure and function are not completely understood. Matrix metalloproteinase (MMPs) and tissue inhibitor of metalloproteinases (TIMPs) constitute one important proteolytic pathway affecting LV remodeling. However, whether these determinants of extracellular matrix (ECM) composition change as a function of age has not been examined in an aging population free of clinically significant cardiovascular disease.

METHODS AND RESULTS

Subjects (n = 77, age 20-90 years) with no evidence of cardiovascular disease underwent echocardiography and measurement of plasma MMP-2, 7, 8, and 9 and TIMP-1, 2, and 4 (enzyme-linked immunosorbent assay). As subject age increased, volume/mass ratio decreased and mitral E/A ratio decreased. As subject age increased, MMP-2 increased (from 1188 +/- 99 ng/mL to 1507 +/- 76 ng/mL), MMP-7 increased (from 1.2 +/- 0.1 ng/mL to 3.1 +/- 0.6 ng/mL), MMP-9 decreased (from 29 +/- 7 ng/mL to 8 +/- 2 ng/mL), and TIMP-1, 2, and 4 increased (from 728 +/- 46 ng/mL to 1093 +/- 73 ng/mL, from 34 +/- 5 ng/mL to 53 +/- 6 ng/mL, and from 1.26 +/- 0.22 ng/mL to 2.34 +/- 0.30 ng/mL, respectively) (all P < .05). There were significant correlations between decreased LV volume/mass and E/A ratio and increased MMP-7 and TIMP-1 and 4.

CONCLUSIONS

MMPs and TIMPs changed as a function of age in the absence of clinically significant cardiovascular disease. These age-dependent alterations in MMP and TIMP profiles favor ECM accumulation and were associated with concentric remodeling and decreased LV diastolic function. Because of these age-dependent changes in this proteolytic system, the superimposition of disease processes such as myocardial infarction or hypertensive heart disease in the older subject may result in different myocardial ECM remodeling than that seen in a younger subject.

MMPs as therapeutic targets--still a viable option?

Matrix metalloproteinases (MMPs) appear to be ideal drug targets--they are disease-associated, extracellular enzymes with a dependence on zinc for activity. This apparently straightforward target, however, is much more complex than initially realized. Although disease associated, the roles for particular enzymes may be healing rather than harmful making broad-spectrum inhibition unwise; targeting the catalytic zinc with specificity is difficult, since other related proteases as well as non-related proteins can be affected by some chelating groups. While the failure of early-generation MMP inhibitors dampened enthusiasm for this type of drug, there has recently been a wealth of studies examining the basic biology of MMPs which will greatly inform new drug trials in this field.

Intracellular targets of matrix metalloproteinase-2 in cardiac disease: rationale and therapeutic approaches

A new paradigm of matrix metalloproteinase-2 (MMP-2) action in the heart undergoing oxidative stress has emerged. Although best known for its role in the proteolysis of extracellular protein targets, MMP-2 is also localized to the sarcomere within the cardiomyocyte. Oxidative stress activates full-length MMP-2 without need for proteolytic processing and inactivates an endogenous inhibitor, tissue inhibitor of metalloproteinase-4. MMP-2 proteolyzes specific targets within the cell to cause acute, reversible contractile dysfunction. Inhibitors of MMPs are discussed and their possible use for the therapy of acute heart injury caused by oxidative stress is examined.

Long-term treatment of glucagon-like peptide-1 analog exendin-4 ameliorates diabetic nephropathy through improving metabolic anomalies in db/db mice

Glucagon-like peptide-1 (GLP-1) is a gut incretin hormone and is a new clinically available class of agents for improving of insulin resistance in both animals and humans with type 2 diabetes. These studies aimed to determine whether long-term treatment with a long-acting GLP-1 analog, exendin-4, delayed the progression of diabetes. Male db/db mice and db/m mice at 8 wk of age were treated with exendin-4 for 8 wk, whereas the control db/db mice received only vehicle. Urinary albumin excretion was significantly decreased in db/db mice that were treated with 1 nmol/kg exendin-4 compared with those in db/db mice that were treated with 0.5 nmol/kg exendin-4 and control db/db mice (P < 0.005). Intraperitoneal glucose tolerance test was improved in db/db mice that were treated with 1 nmol/kg exendin-4 compared with other groups (P < 0.05). Despite this, fasting blood glucose, glycated hemoglobin, and creatinine concentrations were not significantly different among db/db mice. Renal histology studies further demonstrated that glomerular hypertrophy, mesangial matrix expansion, TGF-beta1 expression, and type IV collagen accumulation and associated glomerular lipid accumulation were significantly decreased in db/db mice that were treated with 1 nmol/kg exendin-4. Furthermore, there were fewer infiltrating inflammatory cells and apoptotic cells in the glomeruli of db/db mice that were treated with 1 nmol/kg exendin-4 compared with those in the other groups accompanied by an increase in the renal immunoreactivity of peroxisome proliferator-activated receptor alpha and GLP-1 receptor-positive cells and a decrease in 24-h urinary 8-hydroxy-deoxyguanosine levels (P < 0.01, respectively) along with decreases in lipid content. Taken together, exendin-4 treatment seems to ameliorate diabetic nephropathy together with improvement of the metabolic anomalies. These results suggest that exendin-4 could provide a therapeutic role in diabetic nephropathy that results from type 2 diabetes.

Differential expression of MMPs and TIMPs in moderate and severe heart failure in a transgenic model

BACKGROUND

Altered expression of matrix metalloproteinases (MMPs) and their endogenous inhibitors (TIMPs) accompanies the development of heart failure (HF). However, changes in MMP and TIMP protein levels or activity during the progression from compensated to decompensated failure remains incompletely examined.

METHODS AND RESULTS

Transgenic mice (Tg) with cardiac-specific overexpression of tumor necrosis factor-alpha (TNF1.6) develop a sex-related, progressive cardiac dilation and HF. Echocardiographic measures were used to categorize HF severity in male (M) and female (F) Tg and wild-type (WT) mice between 4 and 50 weeks of age. Cardiac TIMPs-1, TIMPs-2, and MMP-3 (enzyme-linked immunosorbent assay), and potential (APMA-activated) MMP-9 activity were measured at similar ages. In situ zymography assessed tissue gelatinase activity. Systolic function, ventricular dimensions, and presence of pleural effusions identified severe HF in younger M Tg mice (by 18 weeks) and older F Tg (>34 weeks). Regardless of age, sex, or HF severity, Tg mice expressed significantly more TIMP-1 (Tg 119-193 pg/mg vs. WT 13-24 pg/mg, P < .001) and potential MMP-9 activity (Tg 0.41-0.58 ng/mg vs. WT 0.015-0.028 ng/mg, P < .002). M Tg expressed elevated MMP-3 (4 weeks, 0.16 +/- 0.1 ng/mg protein vs. WT 0.04 +/- 0.01 ng/mg, P < .003), which increased with age and HF severity (18 weeks, 0.51 +/- 0.3 ng/mg P < .01). F Tg showed no increase in MMP-3 at 4 weeks but a progressive increase with age and HF severity (18 weeks 0.09 +/- 0.04 ng/mg, P < .02 vs. Tg M or WT; 34 weeks 0.13 +/- 0.02 ng/mg, P < .001 vs. WT). To test the hypothesis that increased MMP-3 may differentially activate MMP-9 in M Tg, in situ zymography was performed and revealed a significant increase in gelatinase activity in M Tg mice relative to both WT and F Tg.

CONCLUSION

MMP-3 may regulate activation of MMP-9/gelatinase, the progression of cardiac remodeling, and development of decompensated heart failure.

La insuficiencia cardíaca en el año 2005

This article is a review of developments reported in the field of heart failure in the last year. It covers advances in epidemiology, pathophysiology and therapy, including cardiac resynchronization therapy and heart transplantation. Today, management of heart failure is complex. It depends on the participation of numerous health professionals under the guidance of a cardiologist. The increasing prevalence of heart failure means that continuing research is mandatory.

Specific serine proteases selectively damage KCNH2 (hERG1) potassium channels and I(Kr)

KCNH2 (hERG1) encodes the alpha-subunit proteins for the rapidly activating delayed rectifier K+ current (I(Kr)), a major K+ current for cardiac myocyte repolarization. In isolated myocytes I(Kr) frequently is small in amplitude or absent, yet KCNH2 channels and I(Kr) are targets for drug block or mutations to cause long QT syndrome. We hypothesized that KCNH2 channels and I(Kr) are uniquely sensitive to enzymatic damage. To test this hypothesis, we studied heterologously expressed K+, Na+, and L-type Ca2+ channels, and in ventricular myocytes I(Kr), slowly activating delayed rectifier K+ current (I(Ks)), and inward rectifier K+ current (I(K1)), by using electrophysiological and biochemical methods. 1) Specific exogenous serine proteases (protease XIV, XXIV, or proteinase K) selectively degraded KCNH2 current (I(KCNH2)) and its mature channel protein without damaging cell integrity and with minimal effects on the other channel currents; 2) immature KCNH2 channel protein remained intact; 3) smaller molecular mass KCNH2 degradation products appeared; 4) protease XXIV selectively abolished I(Kr); and 5) reculturing HEK-293 cells after protease exposure resulted in the gradual recovery of I(KCNH2) and its mature channel protein over several hours. Thus the channel protein for I(KCNH2) and I(Kr) is uniquely sensitive to proteolysis. Analysis of the degradation products suggests selective proteolysis within the S5-pore extracellular linker, which is structurally unique among Kv channels. These data provide 1) a new mechanism to account for low I(Kr) density in some isolated myocytes, 2) evidence that most complexly glycosylated KCNH2 channel protein is in the plasma membrane, and 3) new insight into the rate of biogenesis of KCNH2 channel protein within cells.

Loss or inhibition of uPA or MMP-9 attenuates LV remodeling and dysfunction after acute pressure overload in mice

Left ventricular (LV) hypertrophy is a natural response of the heart to increased pressure loading, but accompanying fibrosis and dilatation may result in irreversible life-threatening heart failure. Matrix metalloproteinases (MMPs) have been invoked in various cardiac diseases, however, direct genetic evidence for a role of the plasminogen activator (PA) and MMP systems in pressure overload-induced LV hypertrophy and in heart failure is lacking. Therefore, the consequences of transverse aortic banding (TAB) were analyzed in mice lacking tissue-type PA (t-PA(-/-)), urokinase-type PA (u-PA(-/-)), or gelatinase-B (MMP-9(-/-)), and in wild-type (WT) mice after adenoviral gene transfer of the PA-inhibitor PAI-1 or the MMP-inhibitor TIMP-1. TAB elevated LV pressure comparably in all genotypes. In WT and t-PA(-/-) mice, cardiomyocyte hypertrophy was associated with myocardial fibrosis, LV dilatation and dysfunction, and pump failure after 7 weeks. In contrast, in u-PA(-/-) mice or in WT mice after PAI-1- and TIMP-1-gene transfer, cardiomyocyte hypertrophy was moderate and only minimally associated with cardiac fibrosis and LV dilatation, resulting in better preservation of pump function. Deficiency of MMP-9 had an intermediate effect. These findings suggest that the use of u-PA- or MMP-inhibitors might preserve cardiac pump function in LV pressure overloading.

Murine models for the study of congestive heart failure: Implications for understanding molecular mechanisms and for drug discovery

Congestive heart failure (CHF) is a complex illness of diverse aetiology. Despite the current multiple therapies, the prognosis for CHF patients remains poor, and new therapeutic targets need to be identified. With the advent of the genetic era, the mouse has become an increasingly valuable animal species in experimental CHF research. A large number of murine models of cardiac hypertrophy and CHF have been created by genetic engineering. Meanwhile, traditional CHF models created by coronary artery ligation, cardiac pressure, or volume overload have been adapted to mice. The present review categorizes and highlights the value of these murine models of cardiac hypertrophy and CHF. These models, combined with sophisticated physiological measurements of cardiac haemodynamics, are expected to yield more and valuable information regarding the molecular mechanisms of CHF and aid in the discovery of novel therapeutic targets.