p38 Kinase rescues failing myocardium after myocardial infarction: evidence for angiogenic and anti-apoptotic mechanisms

Adaptor protein HIP-55-mediated signalosome protects against ferroptosis in myocardial infarction

Ischemic heart disease is a leading cause of death worldwide. Myocardial infarction (MI) results in cardiac damage due to cell death and insufficient cardiomyocyte self-renewal. Ferroptosis, a novel type of cell death, has recently been shown as a key cause of cardiomyocyte death after MI. However, the complicated regulation mechanisms involved in ferroptosis, especially how ferroptosis is integrated into classical cell survival/death pathways, are still unclear. Here, we discovered that HIP-55, a novel adaptor protein, acts as a hub protein for the integration of the ferroptosis mechanism into the classical AKT cell survival and MAP4K1 cell death pathways for MI injury. The expression of HIP-55 is induced in MI. Genetic deletion of HIP-55 increased cardiomyocyte ferroptosis and MI injury, whereas cardiac-specific overexpression of HIP-55 significantly alleviated cardiomyocyte ferroptosis and MI injury. Mechanistically, HIP-55 was identified as a new AKT substrate. AKT phosphorylates HIP-55 at S269/T291 sites and further HIP-55 directs AKT signaling to negatively regulate the MAP4K1 pathway against MI injury in a site-specific manner. S269A/T291A-mutated HIP-55 (HIP-55AA), which is defective in AKT phosphorylation and significantly decreases the interaction between HIP-55 and MAP4K1, failed to inhibit the MAP4K1/GPX4 ferroptosis pathway. In line with this mechanism, cardiac-specific overexpression of HIP-55WT mice, but not cardiac-specific overexpression of HIP-55AA mice, protected cardiomyocytes against MI-induced ferroptosis and cardiac injury in vivo. These findings suggest that HIP-55 rewired the classical AKT (cell survival) and MAPK (cell death) pathways into ferroptosis mechanism in MI injury. HIP-55 may be a new therapeutic target for myocardial damage.

Factor Xa Inhibition with Apixaban Does Not Influence Cardiac Remodelling in Rats with Heart Failure After Myocardial Infarction

Background

Heart failure (HF) is considered to be a prothrombotic condition and it has been suggested that coagulation factors contribute to maladaptive cardiac remodelling via activation of the protease-activated receptor 1 (PAR1). We tested the hypothesis that anticoagulation with the factor Xa (FXa) inhibitor apixaban would ameliorate cardiac remodelling in rats with HF after myocardial infarction (MI).

Methods and Results

Male Sprague-Dawley rats were either subjected to permanent ligation of the left ascending coronary artery (MI) or sham surgery. The MI and sham animals were randomly allocated to treatment with placebo or apixaban in the chow (150 mg/kg/day), starting 2 weeks after surgery. Cardiac function was assessed using echocardiography and histological and molecular markers of cardiac hypertrophy were assessed in the left ventricle (LV). Apixaban resulted in a fivefold increase in anti-FXa activity compared with vehicle, but no overt bleeding was observed and haematocrit levels remained similar in apixaban- and vehicle-treated groups. After 10 weeks of treatment, LV ejection fraction was 42 ± 3% in the MI group treated with apixaban and 37 ± 2 in the vehicle-treated MI group (p > 0.05). Both vehicle- and apixaban-treated MI groups also displayed similar degrees of LV dilatation, LV hypertrophy and interstitial fibrosis. Histological and molecular markers for pathological remodelling were also comparable between groups, as was the activity of signalling pathways downstream of the PAR1 receptor.

Conclusion

FXa inhibition with apixaban does not influence pathological cardiac remodelling after MI. These data do not support the use of FXa inhibitor in HF patients with the aim to amend the severity of HF.

Phosphorylation of GATA4 at serine 105 is required for left ventricular remodelling process in angiotensin II-induced hypertension in rats

In this study, we investigated whether local intramyocardial GATA4 overexpression affects the left ventricular (LV) remodelling process and the importance of phosphorylation at serine 105 (S105) for the actions of GATA4 in an angiotensin II (AngII)‐induced hypertension rat model. Adenoviral constructs overexpressing wild‐type GATA4 or GATA4 mutated at S105 were delivered into the anterior LV free wall. AngII (33.3 µg/kg/h) was administered via subcutaneously implanted minipumps. Cardiac function and structure were examined by echocardiography, followed by histological immunostainings of LV sections and gene expression measurements by RT‐qPCR. The effects of GATA4 on cultured neonatal rat ventricular fibroblasts were evaluated. In AngII‐induced hypertension, GATA4 overexpression repressed fibrotic gene expression, reversed the hypertrophic adult‐to‐foetal isoform switch of myofibrillar genes and prevented apoptosis, whereas histological fibrosis was not affected. Overexpression of GATA4 mutated at S105 resulted in LV chamber dilatation, cardiac dysfunction and had minor effects on expression of myocardial remodelling genes. Fibrotic gene expression in cardiac fibroblasts was differently affected by overexpression of wild‐type or mutated GATA4. Our results indicate that GATA4 reduces AngII‐induced responses by interfering with pro‐fibrotic and hypertrophic gene expressions. GATA4 actions on LV remodelling and fibroblasts are dependent on phosphorylation site S105.

Molecular mechanism involved in cyclophosphamide-induced cardiotoxicity: Old drug with a new vision

Cyclophosphamide (CP) is an important anticancer drug which belongs to the class of alkylating agent. Cyclophosphamide is mostly used in bone marrow transplantation, rheumatoid arthritis, lupus erythematosus, multiple sclerosis, neuroblastoma and other types of cancer. Dose-related cardiotoxicity is a limiting factor for its use. CP-induced cardiotoxicity ranges from 7 to 28% and mortality ranges from 11 to 43% at the therapeutic dose of 170-180 mg/kg, i.v. CP undergoes hepatic metabolism that results in the production of aldophosphamide. Aldophosphamide decomposes into phosphoramide mustard & acrolein. Phosphoramide is an active neoplastic agent, and acrolein is a toxic metabolite which acts on the myocardium and endothelial cells. This is the first review article that talks about cyclophosphamide-induced cardiotoxicity and the different signaling pathways involved in its pathogenicity. Based on the available literature, CP is accountable for cardiomyocytes energy pool alteration by affecting the heart fatty acid binding proteins (H-FABP). CP has been found associated with cardiomyocytes apoptosis, inflammation, endothelial dysfunction, calcium dysregulation, endoplasmic reticulum damage, and mitochondrial damage. Molecular mechanism of cardiotoxicity has been discussed in detail through crosstalk of Nrf2/ARE, Akt/GSK-3β/NFAT/calcineurin, p53/p38MAPK, NF-kB/TLR-4, and Phospholamban/SERCA-2a signaling pathway. Based on the available literature we support the fact that metabolites of CP are responsible for cardiotoxicity due to depletion of antioxidants/ATP level, altered contractility, damaged endothelium and enhanced pro-inflammatory/pro-apoptotic activities resulting into cardiomyopathy, myocardial infarction, and heart failure. Dose adjustment, elimination/excretion of acrolein and maintenance of endogenous antioxidant pool could be the therapeutic approach to mitigate the toxicities.

Cardiac Actions of a Small Molecule Inhibitor Targeting GATA4-NKX2-5 Interaction

Transcription factors are fundamental regulators of gene transcription, and many diseases, such as heart diseases, are associated with deregulation of transcriptional networks. In the adult heart, zinc-finger transcription factor GATA4 is a critical regulator of cardiac repair and remodelling. Previous studies also suggest that NKX2-5 plays function role as a cofactor of GATA4. We have recently reported the identification of small molecules that either inhibit or enhance the GATA4–NKX2-5 transcriptional synergy. Here, we examined the cardiac actions of a potent inhibitor (3i-1000) of GATA4–NKX2-5 interaction in experimental models of myocardial ischemic injury and pressure overload. In mice after myocardial infarction, 3i-1000 significantly improved left ventricular ejection fraction and fractional shortening, and attenuated myocardial structural changes. The compound also improved cardiac function in an experimental model of angiotensin II -mediated hypertension in rats. Furthermore, the up-regulation of cardiac gene expression induced by myocardial infarction and ischemia reduced with treatment of 3i-1000 or when micro- and nanoparticles loaded with 3i-1000 were injected intramyocardially or intravenously, respectively. The compound inhibited stretch- and phenylephrine-induced hypertrophic response in neonatal rat cardiomyocytes. These results indicate significant potential for small molecules targeting GATA4–NKX2-5 interaction to promote myocardial repair after myocardial infarction and other cardiac injuries.

Different Sequences of Fractionated Low-Dose Proton and Single Iron-Radiation-Induced Divergent Biological Responses in the Heart

Deep-space travel presents risks of exposure to ionizing radiation composed of a spectrum of low-fluence protons (¹H) and high-charge and energy (HZE) iron nuclei (e.g., ⁵⁶Fe). When exposed to galactic cosmic rays, each cell in the body may be traversed by ¹H every 3-4 days and HZE nuclei every 3-4 months. The effects of low-dose sequential fractionated ¹H or HZE on the heart are unknown. In this animal model of simulated ionizing radiation, middle-aged (8-9 months old) male C57BL/6NT mice were exposed to radiation as follows: group 1, nonirradiated controls; group 2, three fractionated doses of 17 cGy ¹H every other day (¹H × 3); group 3, three fractionated doses of 17 cGy ¹H every other day followed by a single low dose of 15 cGy ⁵⁶Fe two days after the final ¹H dose (¹H × 3 + ⁵⁶Fe); and group 4, a single low dose of 15 cGy ⁵⁶Fe followed (after 2 days) by three fractionated doses of 17 cGy ¹H every other day (⁵⁶Fe + ¹H × 3). A subgroup of mice from each group underwent myocardial infarction (MI) surgery at 28 days postirradiation. Cardiac structure and function were assessed in all animals at days 7, 14 and 28 after MI surgery was performed. Compared to the control animals, the treatments that groups 2 and 3 received did not induce negative effects on cardiac function or structure. However, compared to all other groups, the animals in group 4, showed depressed left ventricular (LV) functions at 1 month with concomitant enhancement in cardiac fibrosis and induction of cardiac hypertrophy signaling at 3 months. In the irradiated and MI surgery groups compared to the control group, the treatments received by groups 2 and 4 did not induce negative effects at 1 month postirradiation and MI surgery. However, in group 3 after MI surgery, there was a 24% increase in mortality, significant decreases in LV function and a 35% increase in post-infarction size. These changes were associated with significant decreases in the angiogenic and cell survival signaling pathways. These data suggest that fractionated doses of radiation induces cellular and molecular changes that result in depressed heart functions both under basal conditions and particularly after myocardial infarction.

Mitogen-activated protein kinase p38 target regenerating islet-derived 3γ expression is upregulated in cardiac inflammatory response in the rat heart

Regenerating islet‐derived 3γ (Reg3γ) is a multifunctional protein, associated with various tissue injuries and inflammatory states. Since chronic inflammation is characteristics also for heart failure, the aim of this study was to characterize Reg3γ expression in cardiac inflammatory conditions. Reg3γ expression was studied in experimental rat models of myocardial infarction (MI) and pressure overload in vivo. For cell culture studies neonatal rat cardiac myocytes (NRCMs) were used. In addition, adenovirus‐mediated gene transfer of upstream mitogen‐activated protein kinase (MAPK) kinase 3b and p38α MAPK in vivo and in vitro was performed. Reg3γ mRNA (12.8‐fold, P < 0.01) and protein (5.8‐fold, P < 0.001) levels were upregulated during the postinfarction remodeling at day 1 after MI, and angiotensin II (Ang II) markedly increased Reg3γ mRNA levels from 6 h to 2 weeks. Immunohistochemistry revealed that the Ang II‐induced expression of Reg3γ was localized into the cardiac fibroblasts and myofibroblasts of the proliferating connective tissue in the heart. Stretching and treatments with endothelin‐1, lipopolysaccharide (LPS), and fibroblast growth factor‐1 increased Reg3γ mRNA levels in NRCMs. SB203580, a selective p38 MAPK inhibitor, markedly attenuated LPS and mechanical stretch‐induced upregulation of Reg3γ gene expression. Moreover, combined overexpression of MKK3bE and WT p38α increased Reg3γ gene expression in cultured cardiomyocytes in vitro and in the rat heart in vivo. Our study shows that cardiac stress activates Reg3γ expression and p38 MAPK is an upstream regulator of Reg3γ gene expression in heart. Altogether our data suggest Reg3γ is associated with cardiac inflammatory signaling.

TSC-22 up-regulates collagen 3a1 gene expression in the rat heart

BACKGROUND

The transforming growth factor (TGF)-β is one of the key mediators in cardiac remodelling occurring after myocardial infarction (MI) and in hypertensive heart disease. The TGF-β-stimulated clone 22 (TSC-22) is a leucine zipper protein expressed in many tissues and possessing various transcription-modulating activities. However, its function in the heart remains unknown.

METHODS

The aim of the present study was to characterize cardiac TSC-22 expression in vivo in cardiac remodelling and in myocytes in vitro. In addition, we used TSC-22 gene transfer in order to examine the effects of TSC-22 on cardiac gene expression and function.

RESULTS

We found that TSC-22 is rapidly up-regulated by multiple hypertrophic stimuli, and in post-MI remodelling both TSC-22 mRNA and protein levels were up-regulated (4.1-fold, P <0.001 and 3.0-fold, P <0.05, respectively) already on day 1. We observed that both losartan and metoprolol treatments reduced left ventricular TSC-22 gene expression. Finally, TSC-22 overexpression by local intramyocardial adenovirus-mediated gene delivery showed that TSC-22 appears to have a role in regulating collagen type IIIα1 gene expression in the heart.

CONCLUSIONS

These results demonstrate that TSC-22 expression is induced in response to cardiac overload. Moreover, our data suggests that, by regulating collagen expression in the heart in vivo, TSC-22 could be a potential target for fibrosis-preventing therapies.

The Early-Onset Myocardial Infarction Associated PHACTR1 Gene Regulates Skeletal and Cardiac Alpha-Actin Gene Expression

The phosphatase and actin regulator 1 (PHACTR1) locus is a very commonly identified hit in genome-wide association studies investigating coronary artery disease and myocardial infarction (MI). However, the function of PHACTR1 in the heart is still unknown. We characterized the mechanisms regulating Phactr1 expression in the heart, used adenoviral gene delivery to investigate the effects of Phactr1 on cardiac function, and analyzed the relationship between MI associated PHACTR1 allele and cardiac function in human subjects. Phactr1 mRNA and protein levels were markedly reduced (60%, P<0.01 and 90%, P<0.001, respectively) at 1 day after MI in rats. When the direct myocardial effects of Phactr1 were studied, the skeletal α-actin to cardiac α-actin isoform ratio was significantly higher (1.5-fold, P<0.05) at 3 days but 40% lower (P<0.05) at 2 weeks after adenovirus-mediated Phactr1 gene delivery into the anterior wall of the left ventricle. Similarly, the skeletal α-actin to cardiac α-actin ratio was lower at 2 weeks in infarcted hearts overexpressing Phactr1. In cultured neonatal cardiac myocytes, adenovirus-mediated Phactr1 overexpression for 48 hours markedly increased the skeletal α-actin to cardiac α-actin ratio, this being associated with an enhanced DNA binding activity of serum response factor. Phactr1 overexpression exerted no major effects on the expression of other cardiac genes or LV structure and function in normal and infarcted hearts during 2 weeks’ follow-up period. In human subjects, MI associated PHACTR1 allele was not associated significantly with cardiac function (n = 1550). Phactr1 seems to regulate the skeletal to cardiac α-actin isoform ratio.

WDR12, a Member of Nucleolar PeBoW-Complex, Is Up-Regulated in Failing Hearts and Causes Deterioration of Cardiac Function

Aims

In a recent genome-wide association study, WD-repeat domain 12 (WDR12) was associated with early-onset myocardial infarction (MI). However, the function of WDR12 in the heart is unknown.

Methods and Results

We characterized cardiac expression of WDR12, used adenovirus-mediated WDR12 gene delivery to examine effects of WDR12 on left ventricular (LV) remodeling, and analyzed relationship between MI associated WDR12 allele and cardiac function in human subjects. LV WDR12 protein levels were increased in patients with dilated cardiomyopathy and rats post-infarction. In normal adult rat hearts, WDR12 gene delivery into the anterior wall of the LV decreased interventricular septum diastolic and systolic thickness and increased the diastolic and systolic diameters of the LV. Moreover, LV ejection fraction (9.1%, P<0.05) and fractional shortening (12.2%, P<0.05) were declined. The adverse effects of WDR12 gene delivery on cardiac function were associated with decreased cellular proliferation, activation of p38 mitogen–activated protein kinase (MAPK)/heat shock protein (HSP) 27 pathway, and increased protein levels of Block of proliferation 1 (BOP1), essential for ribosome biogenesis. Post-infarction WDR12 gene delivery decreased E/A ratio (32%, P<0.05) suggesting worsening of diastolic function. In human subjects, MI associated WDR12 allele was associated significantly with diastolic dysfunction and left atrial size.

Conclusions

WDR12 triggers distinct deterioration of cardiac function in adult rat heart and the MI associated WDR12 variant is associated with diastolic dysfunction in human subjects.

p38 MAPK in cardioprotection - are we there yet?

PKs transfer a phosphate from ATP to the side-chain hydroxyl group of a serine, threonine or tyrosine residue of a substrate protein. This in turn can alter that protein's function; modulating fundamental cellular processes including, metabolism, transcription, growth, division, differentiation, motility and survival. PKs are subdivided into families based on homology. One such group are the stress-activated kinases, which as the name suggests, are activated in response to cellular stresses such as toxins, cytokines, mechanical deformation and osmotic stress. Members include the p38 MAPK family, which is composed of α, β, γ and δ, isoforms which are encoded by separate genes. These kinases transduce extracellular signals and coordinate the cellular responses needed for adaptation and survival. However, in cardiovascular and other disease states, these same systems can trigger maladaptive responses that aggravate, rather than alleviate, the disease. This situation is analogous to adrenergic, angiotensin and aldosterone signalling in heart failure, where inhibition is beneficial despite the importance of these hormones to homeostasis. The question is whether similar benefits could accrue from p38 inhibition? In this review, we will discuss the structure and function of p38, the history of p38 inhibitors and their use in preclinical studies. Finally, we will summarize the results of recent cardiovascular clinical trials with p38 inhibitors.

Cardiovascular risks associated with low dose ionizing particle radiation

Previous epidemiologic data demonstrate that cardiovascular (CV) morbidity and mortality may occur decades after ionizing radiation exposure. With increased use of proton and carbon ion radiotherapy and concerns about space radiation exposures to astronauts on future long-duration exploration-type missions, the long-term effects and risks of low-dose charged particle irradiation on the CV system must be better appreciated. Here we report on the long-term effects of whole-body proton (¹H; 0.5 Gy, 1 GeV) and iron ion (⁵⁶Fe; 0.15 Gy, 1GeV/nucleon) irradiation with and without an acute myocardial ischemia (AMI) event in mice. We show that cardiac function of proton-irradiated mice initially improves at 1 month but declines by 10 months post-irradiation. In AMI-induced mice, prior proton irradiation improved cardiac function restoration and enhanced cardiac remodeling. This was associated with increased pro-survival gene expression in cardiac tissues. In contrast, cardiac function was significantly declined in ⁵⁶Fe ion-irradiated mice at 1 and 3 months but recovered at 10 months. In addition, ⁵⁶Fe ion-irradiation led to poorer cardiac function and more adverse remodeling in AMI-induced mice, and was associated with decreased angiogenesis and pro-survival factors in cardiac tissues at any time point examined up to 10 months. This is the first study reporting CV effects following low dose proton and iron ion irradiation during normal aging and post-AMI. Understanding the biological effects of charged particle radiation qualities on the CV system is necessary both for the mitigation of space exploration CV risks and for understanding of long-term CV effects following charged particle radiotherapy.

Characterization of the regulatory mechanisms of activating transcription factor 3 by hypertrophic stimuli in rat cardiomyocytes

Aims

Activating transcription factor 3 (ATF3) is a stress-activated immediate early gene suggested to have both detrimental and cardioprotective role in the heart. Here we studied the mechanisms of ATF3 activation by hypertrophic stimuli and ATF3 downstream targets in rat cardiomyocytes.

Methods and Results

When neonatal rat cardiomyocytes were exposed to endothelin-1 (ET-1, 100 nM) and mechanical stretching in vitro, maximal increase in ATF3 expression occurred at 1 hour. Inhibition of extracellular signal-regulated kinase (ERK) by PD98059 decreased ET-1– and stretch–induced increase of ATF3 protein but not ATF3 mRNA levels, whereas protein kinase A (PKA) inhibitor H89 attenuated both ATF3 mRNA transcription and protein expression in response to ET-1 and stretch. To characterize further the regulatory mechanisms upstream of ATF3, p38 mitogen-activated protein kinase (MAPK) signaling was investigated using a gain-of-function approach. Adenoviral overexpression of p38α, but not p38β, increased ATF3 mRNA and protein levels as well as DNA binding activity. To investigate the role of ATF3 in hypertrophic process, we overexpressed ATF3 by adenovirus-mediated gene transfer. In vitro, ATF3 gene delivery attenuated the mRNA transcription of interleukin-6 (IL-6) and plasminogen activator inhibitor-1 (PAI-1), and enhanced nuclear factor-κB (NF-κB) and Nkx-2.5 DNA binding activities. Reduced PAI-1 expression was also detected in vivo in adult rat heart by direct intramyocardial adenovirus-mediated ATF3 gene delivery.

Conclusions

These data demonstrate that ATF3 activation by ET-1 and mechanical stretch is partly mediated through ERK and cAMP-PKA pathways, whereas p38 MAPK pathway is involved in ATF3 activation exclusively through p38α isoform. ATF3 activation caused induction of modulators of the inflammatory response NF-κB and Nkx-2.5, as well as attenuation of pro-fibrotic and pro-inflammatory proteins IL-6 and PAI-1, suggesting cardioprotective role for ATF3 in the heart.

In vivo biocompatibility of porous silicon biomaterials for drug delivery to the heart

Myocardial infarction (MI), commonly known as a heart attack, is the irreversible necrosis of heart muscle secondary to prolonged ischemia, which is an increasing problem in terms of morbidity, mortality and healthcare costs worldwide. Along with the idea to develop nanocarriers that efficiently deliver therapeutic agents to target the heart, in this study, we aimed to test the in vivo biocompatibility of different sizes of thermally hydrocarbonized porous silicon (THCPSi) microparticles and thermally oxidized porous silicon (TOPSi) micro and nanoparticles in the heart tissue. Despite the absence or low cytotoxicity, both particle types showed good in vivo biocompatibility, with no influence on hematological parameters and no considerable changes in cardiac function before and after MI. The local injection of THCPSi microparticles into the myocardium led to significant higher activation of inflammatory cytokine and fibrosis promoting genes compared to TOPSi micro and nanoparticles; however, both particles showed no significant effect on myocardial fibrosis at one week post-injection. Our results suggest that THCPSi and TOPSi micro and nanoparticles could be applied for cardiac delivery of therapeutic agents in the future, and the PSi biomaterials might serve as a promising platform for the specific treatment of heart diseases.

Inhibition of Let-7 microRNA attenuates myocardial remodeling and improves cardiac function postinfarction in mice

The members of lethal-7 (Let-7) microRNA (miRNA) family are involved in regulation of cell differentiation and reprogramming of somatic cells into induced pluripotent stem cells. However, their function in the heart is not known. In this study, we examined the effect of inhibiting the function of Let-7c miRNA on the progression of postinfarction left ventricular (LV) remodeling in mice. Myocardial infarction was induced with permanent ligation of left anterior descending coronary artery with a 4-week follow-up period. Let-7c miRNA was inhibited with a specific antagomir administered intravenously. The inhibition of Let-7c miRNA downregulated the levels of mature Let-7c miRNA and its other closely related members of Let-7 family in the heart and resulted in increased expression of pluripotency-associated genes Oct4 and Sox2 in cardiac fibroblasts in vitro and in adult mouse heart in vivo. Importantly, Let-7c inhibitor prevented the deterioration of cardiac function postinfarction, as demonstrated by preserved LV ejection fraction and elevated cardiac output. Improvement in cardiac function by Let-7c inhibitor postinfarction was associated with decreased apoptosis, reduced fibrosis, and reduction in the number of discoidin domain receptor 2–positive fibroblasts, while the number of c-kit⁺ cardiac stem cells and Ki-67⁺ proliferating cells remained unaltered. In conclusion, inhibition of Let-7 miRNA may be beneficial for the prevention of postinfarction LV remodeling and progression of heart failure.

Ginsenoside RK3 Prevents Hypoxia-Reoxygenation Induced Apoptosis in H9c2 Cardiomyocytes via AKT and MAPK Pathway

Reperfusion therapy is widely utilized for acute myocardial infarction (AMI), but further injury induced by rapidly initiating reperfusion of the heart is often encountered in clinical practice. Ginsenoside RK3 (RK3) is reportedly present in the processed Radix notoginseng that is often used as a major ingredient of the compound preparation for ischemic heart diseases. This study aimed to investigate the possible protective effect of RK3 against hypoxia-reoxygenation (H/R) induced H9c2 cardiomyocytes damage and its underlying mechanisms. Our results showed that RK3 pretreatment caused increased cell viability and decreased levels of LDH leakage compared with the H/R group. Moreover, RK3 pretreatment inhibited cell apoptosis, as evidenced by decreased caspase-3 activity, TUNEL-positive cells, and Bax expression, as well as increased Bcl-2 level. Further mechanism investigation revealed that RK3 prevented H9c2 cardiomyocytes injury and apoptosis induced by H/R via AKT/Nrf-2/HO-1 and MAPK pathways. These observations indicate that RK3 has the potential to exert cardioprotective effects against H/R injury, which might be of great importance to clinical efficacy for AMI treatment.

LY2228820 dimesylate, a selective inhibitor of p38 mitogen-activated protein kinase, reduces angiogenic endothelial cord formation in vitro and in vivo

LY2228820 dimesylate is a highly selective small molecule inhibitor of p38α and p38β mitogen-activated protein kinases (MAPKs) that is currently under clinical investigation for human malignancies. p38 MAPK is implicated in a wide range of biological processes, in particular those that support tumorigenesis. One such process, angiogenesis, is required for tumor growth and metastasis, and many new cancer therapies are therefore directed against the tumor vasculature. Using an in vitro co-culture endothelial cord formation assay, a surrogate of angiogenesis, we investigated the role of p38 MAPK in growth factor- and tumor-driven angiogenesis using LY2228820 dimesylate treatment and by shRNA gene knockdown. p38 MAPK was activated in endothelial cells upon growth factor stimulation, with inhibition by LY2228820 dimesylate treatment causing a significant decrease in VEGF-, bFGF-, EGF-, and IL-6-induced endothelial cord formation and an even more dramatic decrease in tumor-driven cord formation. In addition to involvement in downstream cytokine signaling, p38 MAPK was important for VEGF, bFGF, EGF, IL-6, and other proangiogenic cytokine secretion in stromal and tumor cells. LY2228820 dimesylate results were substantiated using p38α MAPK-specific shRNA and shRNA against the downstream p38 MAPK effectors MAPKAPK-2 and HSP27. Using in vivo models of functional neoangiogenesis, LY2228820 dimesylate treatment reduced hemoglobin content in a plug assay and decreased VEGF-A-stimulated vascularization in a mouse ear model. Thus, p38α MAPK is implicated in tumor angiogenesis through direct tumoral effects and through reduction of proangiogenic cytokine secretion via the microenvironment.

Changes in cell autophagy and apoptosis during age-related left ventricular remodeling in mice and their potential mechanisms

Cardiac structures and functions change with advanced age, but the underlying mechanisms are not well understood. Autophagy and apoptosis play important roles in the process of cardiac remodeling. This study was designed to explore changes in cell autophagy and apoptosis during age-related left ventricular remodeling and to determine whether the mitogen-activated protein kinase (MAPK) pathway is an underlying mechanism. Eight 5-month-old (adult group) and eight 24-month-old male C57bl/6 mice (aged group) were studied. The heart mass index, left ventricular mass index and hydroxyproline content of both groups were compared. Western Blotting was used to quantitate the protein expression of microtubule-associated protein 1 light chain 3 (LC3), Beclin-1, caspase-3, B-cell leukemia-2 (Bcl-2) and MAPKs in the left ventricles of adult and aged mice. Our results showed that the heart mass index, left ventricular mass index and hydroxyproline content in the left ventricles of the aged mice were increased significantly compared with the adult mice, indicating that left ventricular remodeling occurs with aging. The expression of LC3 and Beclin-1 in the left ventricles of aged mice were decreased significantly compared to adult mice. Meanwhile, the level of myocardial caspase-3 in adult mice remained the same in aged mice, and the level of myocardial Bcl-2 increased significantly in aged mice. There were no differences in the expression level of myocardial extracellular signal-regulated kinase 1/2 (ERK1/2), activated/phospho-ERK1/2, c-Jun N-terminal kinase 1/2 (JNK1/2) and p38 between aged and adult mice. However, the expression of myocardial activated/phospho-JNK1/2 increased significantly in aged mice, while activated/phospho-p38 decreased significantly. These findings indicate that autophagy decreases without a concurrent change in apoptosis during age-related left ventricular remodeling in mice. The MAPK pathway may be involved in the regulation of age-related left ventricular remodeling by modulating autophagy.

Rac-induced left ventricular dilation in thyroxin-treated ZmRacD transgenic mice: role of cardiomyocyte apoptosis and myocardial fibrosis

The pathways inducing the critical transition from compensated hypertrophy to cardiac dilation and failure remain poorly understood. The goal of our study is to determine the role of Rac-induced signaling in this transition process. Our previous results showed that Thyroxin (T4) treatment resulted in increased myocardial Rac expression in wild-type mice and a higher level of expression in Zea maize RacD (ZmRacD) transgenic mice. Our current results showed that T4 treatment induced physiologic cardiac hypertrophy in wild-type mice, as demonstrated by echocardiography and histopathology analyses. This was associated with significant increases in myocardial Rac-GTP, superoxide and ERK1/2 activities. Conversely, echocardiography and histopathology analyses showed that T4 treatment induced dilated cardiomyopathy along with compensatory cardiac hypertrophy in ZmRacD mice. These were linked with further increases in myocardial Rac-GTP, superoxide and ERK1/2 activities. Additionally, there were significant increases in caspase-8 expression and caspase-3 activity. However, there was a significant decrease in p38-MAPK activity. Interestingly, inhibition of myocardial Rac-GTP activity and superoxide generation with pravastatin and carvedilol, respectively, attenuated all functional, structural, and molecular changes associated with the T4-induced cardiomyopathy in ZmRacD mice except the compensatory cardiac hypertrophy. Taken together, T4-induced ZmRacD is a novel mouse model of dilated cardiomyopathy that shares many characteristics with the human disease phenotype. To our knowledge, this is the first study to show graded Rac-mediated O(2)·(-) results in cardiac phenotype shift in-vivo. Moreover, Rac-mediated O(2)·(-) generation, cardiomyocyte apoptosis, and myocardial fibrosis seem to play a pivotal role in the transition from cardiac hypertrophy to cardiac dilation and failure. Targeting Rac signaling could represent valuable therapeutic strategy not only in saving the failing myocardium but also to prevent this transition process.

(Pro)renin receptor triggers distinct angiotensin II-independent extracellular matrix remodeling and deterioration of cardiac function

Background

Activation of the renin-angiotensin-system (RAS) plays a key pathophysiological role in heart failure in patients with hypertension and myocardial infarction. However, the function of (pro)renin receptor ((P)RR) is not yet solved. We determined here the direct functional and structural effects of (P)RR in the heart.

Methodology/Principal Findings

(P)RR was overexpressed by using adenovirus-mediated gene delivery in normal adult rat hearts up to 2 weeks. (P)RR gene delivery into the anterior wall of the left ventricle decreased ejection fraction (P<0.01), fractional shortening (P<0.01), and intraventricular septum diastolic and systolic thickness, associated with approximately 2–fold increase in left ventricular (P)RR protein levels at 2 weeks. To test whether the worsening of cardiac function and structure by (P)RR gene overexpression was mediated by angiotensin II (Ang II), we infused an AT₁ receptor blocker losartan via osmotic minipumps. Remarkably, cardiac function deteriorated in losartan-treated (P)RR overexpressing animals as well. Intramyocardial (P)RR gene delivery also resulted in Ang II-independent activation of extracellular-signal-regulated kinase1/2 phosphorylation and myocardial fibrosis, and the expression of transforming growth factor-β1 and connective tissue growth factor genes. In contrast, activation of heat shock protein 27 phosphorylation and apoptotic cell death by (P)RR gene delivery was Ang II-dependent. Finally, (P)RR overexpression significantly increased direct protein–protein interaction between (P)RR and promyelocytic zinc-finger protein.

Conclusions/Significance

These results indicate for the first time that (P)RR triggers distinct Ang II-independent myocardial fibrosis and deterioration of cardiac function in normal adult heart and identify (P)RR as a novel therapeutic target to optimize RAS blockade in failing hearts.

Left ventricular periostin gene expression is associated with fibrogenesis in experimental renal insufficiency

BACKGROUND

Cardiovascular diseases are the most important cause of death in patients with impaired kidney function. Left ventricular hypertrophy (LVH), cardiac interstitial fibrosis and cardiovascular calcifications are characteristic of chronic renal insufficiency (CRI). Periostin is a fibrogenesis- and calcification-related matricellular protein re-expressed in adult tissues undergoing remodelling in response to pathological stimuli. The role of periostin in CRI-induced LVH is unknown.

METHODS

Rats were 5/6-nephrectomized (NX), and after 15 weeks of disease progression high-calcium, high-phosphate or paricalcitol treatment was given for 12 weeks. Cardiac tissue and blood samples were taken to study periostin gene expression and to determine factors contributing to its reactivation, respectively. Left ventricular (LV) periostin expression was also examined in response to angiotensin II or arginine(8)-vasopressin (AVP)-induced pressure overload and in spontaneously hypertensive rats.

RESULTS

CRI resulted in a 6.5-fold increase in LV periostin messenger RNA (mRNA) levels. Positive extracellular immunostaining for periostin was detected in areas of infiltrated inflammatory cells and fibrotic lesions. There was a significant correlation between LV periostin mRNA levels and plasma biomarkers of impaired kidney function, LVH, fibrogenesis-related proteins osteopontin and osteoactivin, and anti-calcific matrix Gla protein. Moreover, LV periostin gene expression in CRI correlated positively with systolic blood pressure (BP) and was activated rapidly in response to angiotensin II or AVP infusions.

CONCLUSIONS

Periostin is involved in fibrotic cardiac remodelling in CRI. The re-expression of periostin is localized to the fibrotic and inflammatory lesions and is most likely the consequence of elevated BP.

Distinct regulation of B-type natriuretic peptide transcription by p38 MAPK isoforms

Persistent controversy underlies the functional roles of specific p38 MAPK isoforms in cardiac biology and regulation of hypertrophy-associated genes. Here we show that adenoviral gene transfer of p38β but not p38α increased B-type natriuretic peptide (BNP) mRNA levels in vitro as well as atrial natriuretic peptide mRNA levels both in vitro and in vivo. Overexpression of p38α, in turn, augmented the expression fibrosis-related genes connective tissue growth factor, basic fibroblast growth factor and matrix metalloproteinase-9 both in vitro and in vivo. p38β-induced BNP transcription was diminished by mutation of GATA-4 binding site, whereas overexpression of MKK6b, an upstream regulator of p38α and p38β, activated BNP transcription through both GATA-4 and AP-1. Overexpression of MKK3, upstream regulator of p38α, induced BNP transcription independently from AP-1 and GATA-4. These data provide new evidence for diversity in downstream targets and functional roles of p38 pathway kinases in regulation of hypertrophy-associated cardiac genes.

Intramyocardial BNP gene delivery improves cardiac function through distinct context-dependent mechanisms

BACKGROUND

B-type natriuretic peptide (BNP) is an endogenous peptide produced under physiological and pathological conditions mainly by ventricular myocytes. It has natriuretic, diuretic, blood pressure-lowering, and antifibrotic actions that could mediate cardiorenal protection in cardiovascular diseases. In the present study, we used BNP gene transfer to examine functional and structural effects of BNP on left ventricular (LV) remodeling.

METHODS AND RESULTS

Human BNP was overexpressed by using adenovirus-mediated gene delivery in normal rat hearts and in hearts during the remodeling process after infarction and in an experimental model of angiotensin II-mediated hypertension. In healthy hearts, BNP gene delivery into the anterior wall of the LV decreased myocardial fibrosis (P<0.01, n=7 to 8) and increased capillary density (P<0.05, n=7 to 8) associated with a 7.3-fold increase in LV BNP peptide levels. Overexpression of BNP improved LV fractional shortening by 22% (P<0.05, n=6 to 7) and ejection fraction by 19% (P<0.05, n=6 to 7) after infarction. The favorable effect of BNP gene delivery on cardiac function after infarction was associated with normalization of cardiac sarcoplasmic reticulum Ca(2+)-ATPase expression and phospholamban Thr17-phosphorylation. BNP gene delivery also improved fractional shortening and ejection fraction in angiotensin II-mediated hypertension as well as decreased myocardial fibrosis and LV collagen III mRNA levels but had no effect on angiogenesis or Ca(2+)-ATPase expression and phospholamban phosphorylation.

CONCLUSIONS

Local intramyocardial BNP gene delivery improves cardiac function and attenuates adverse postinfarction and angiotensin II-induced remodeling. These results also indicate that myocardial BNP has pleiotropic, context-dependent, favorable actions on cardiac function and suggest that BNP acts locally as a key mechanical load-activated regulator of angiogenesis and fibrosis.

Characterization of Molecular Forms of N-Terminal B-Type Natriuretic Peptide In Vitro

BACKGROUND

The heterogeneity of circulating peptides may influence the interpretation of results from N-terminal profragment of BNP (NT-proBNP) assays. Our objective was to characterize the heterogeneity for better usability of the assays.

METHODS

Endogenous proBNP was purified from patient samples and treated with trifluoromethanesulfonic acid (chemical deglycosylation). The human proBNP gene was introduced into rat hearts by adenoviral transfer. Cell lysates and plasma samples containing proBNP-derived peptides were analyzed by chromatography. The fate of exogenous recombinant NT-proBNP added to fresh whole blood samples was followed by immunoassays and chromatography. The main NT-proBNP components were isolated and identified by mass spectrometry.

RESULTS

Immunoreactive NT-proBNP in human plasma comprised several molecular forms, as did circulating immunoreactive human NT-proBNP after adenoviral transfer of human proBNP cDNA into rat ventricular myocardium. Incubation of recombinant NT-proBNP1–76 in human plasma or serum resulted in multiple components with the 2 major components identified as NT-proBNP1–36 and NT-proBNP1–62/64. Profiling by different antisera and chromatography indicated masking of the non–mid-region epitopes likely due to formation of oligomers. More than 75% of the original immunoreactivity in the mid-region epitope was retained after 3-week storage of plasma samples at room temperature.

CONCLUSIONS

There is marked heterogeneity in immunoreactive NT-proBNP in plasma not related to glycosylation. The mid-region epitope of NT-proBNP is stable even in harsh storage conditions. Careful choice of antibody epitopes can yield extraordinarily robust assays.

Collagen XV Is Necessary for Modeling of the Extracellular Matrix and Its Deficiency Predisposes to Cardiomyopathy

Rationale:

The extracellular matrix (ECM) is a major determinant of the structural integrity and functional properties of the myocardium in common pathological conditions, and changes in vasculature contribute to cardiac dysfunction. Collagen (Col) XV is preferentially expressed in the ECM of cardiac muscle and microvessels.

Objective:

We aimed to characterize the ECM, cardiovascular function and responses to elevated cardiovascular load in mice lacking Col XV ( Col15a1 −/− ) to define its functional role in the vasculature and in age- and hypertension-associated myocardial remodeling.

Methods and Results:

Cardiac structure and vasculature were analyzed by light and electron microscopy. Cardiac function, intraarterial blood pressure, microhemodynamics, and gene expression profiles were studied using echocardiography, telemetry, intravital microscopy, and PCR, respectively. Experimental hypertension was induced with angiotensin II or with a nitric oxide synthesis inhibitor. Under basal conditions, lack of Col XV resulted in increased permeability and impaired microvascular hemodynamics, distinct early-onset and age-dependent defects in heart structure and function, a poorly organized fibrillar collagen matrix with marked interstitial deposition of nonfibrillar protein aggregates, increased tissue stiffness, and irregularly organized cardiomyocytes. In response to experimental hypertension, Col15a1 gene expression was increased in the left ventricle of wild-type mice, and mRNA expression of natriuretic peptides (ANP and BNP) and ECM modeling were abnormal in Col15a1 −/− mice.

Conclusions:

Col XV is necessary for ECM organization in the heart, and for the structure and functions of microvessels. Col XV deficiency leads to a complex cardiac phenotype and predisposes the subject to pathological responses under cardiac stress.

Divergent effects of losartan and metoprolol on cardiac remodeling, c-kit+ cells, proliferation and apoptosis in the left ventricle after myocardial infarction

There is strong evidence for the use of angiotensin converting enzyme inhibitors and beta-blockers to reduce morbidity and mortality in patients with myocardial infarction (MI), whereas the effect of angiotensin receptor blockers is less clear. We evaluated the effects of an angiotensin receptor blocker losartan and a beta-blocker metoprolol on left ventricular (LV) remodeling, c-kit+ cells, proliferation, fibrosis, apoptosis, and angiogenesis using a model of coronary ligation in rats. Metoprolol treatment for 2 weeks improved LV systolic function. In contrast, losartan triggered deleterious structural remodeling and functional deterioration of LV systolic function, ejection fraction being 41% and fractional shortening 47% lower in losartan group than in controls 2 weeks after MI. The number of c-kit+ cells as well as expression of Ki-67 was increased by metoprolol. Losartan-induced thinning of the anterior wall and ventricular dilation were associated with increased apoptosis and fibrosis, while losartan had no effect on the expression of c-kit or Ki-67. Metoprolol or losartan had no effect on microvessel density. These results demonstrate that beta-blocker treatment attenuated adverse remodeling via c-kit+ cells and proliferation, whereas angiotensin receptor blocker-induced worsening of LV systolic function was associated with increased apoptosis and fibrosis in the peri-infarct region.

The effects of intra-cage aspen tube on cardiac morphology and gene expression

According to the European recommendations rodents should be provided with a nest box if there is insufficient nesting material to build a complete, covered nest. Rats are generally poor nest builders; hence an additional structure is needed. Optimally, housing refinement may be combined with better science; at least it should not detract from the scientific integrity. In order to evaluate these options, there is a need to assess the items used in individual research projects. Studies investigating molecular mechanisms of cardiac hypertrophy and heart failure are typically long-lasting studies; therefore, refinement of the housing of rats in these studies is important. The aim of this study was to evaluate in rats whether a wooden tube has any impact on cardiac morphology or on basal gene expression of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP); known markers of cardiac overload, hypertrophy and heart failure. The experimental protocol simulated cardiovascular studies, but without any surgical operations. A total of 42 male Hsd:SD rats were used in an eight-week experiment. After weaning, the experimental group was provided with a rectangular aspen tube and nesting material, and the control group with only nesting material. ANP and BNP gene expression were measured from the left ventricles with Northern blot analysis postmortem along with the absolute weights of the whole heart, left and right atria and left and right chambers. The weights of the whole heart and left chamber were also analysed in relation to body weight. No statistically significant differences were observed in any of these variables. The inter-individual variation was also unchanged by the cage item. In conclusion, the aspen tube does not disrupt research results or alter the number of animals needed and can therefore be recommended for enrichment purposes in cardiovascular studies.

Gene therapy for ischemic heart disease

Current pharmacologic therapy for ischemic heart disease suffers multiple limitations such as compliance issues and side effects of medications. Revascularization procedures often end with need for repeat procedures. Patients remain symptomatic despite maximal medical therapy. Gene therapy offers an attractive alternative to current pharmacologic therapies and may be beneficial in refractory disease. Gene therapy with isoforms of growth factors such as VEGF, FGF and HGF induces angiogenesis, decreases apoptosis and leads to protection in the ischemic heart. Stem cell therapy augmented with gene therapy used for myogenesis has proven to be beneficial in numerous animal models of myocardial ischemia. Gene therapy coding for antioxidants, eNOS, HSP, mitogen-activated protein kinase and numerous other anti apoptotic proteins have demonstrated significant cardioprotection in animal models. Clinical trials have demonstrated safety in humans apart from symptomatic and objective improvements in cardiac function. Current research efforts are aimed at refining various gene transfection techniques and regulation of gene expression in vivo in the heart and circulation to improve clinical outcomes in patients that suffer from ischemic heart disease. In this review article we will attempt to summarize the current state of both preclinical and clinical studies of gene therapy to combat myocardial ischemic disease. This article is part of a Special Section entitled "Special Section: Cardiovascular Gene Therapy".

A novel p38 MAPK target dyxin is rapidly induced by mechanical load in the heart

Dyxin is a novel LIM domain protein acting as a transcriptional cofactor with GATA transcription factors. Here, we characterized dyxin as a p38 mitogen-activated protein kinase (MAPK) regulated gene, since combined upstream MAPK kinase 3b and wild-type p38 alpha MAPK gene transfer increased left ventricular dyxin mRNA and protein levels in vivo. We also studied cardiac dyxin expression in experimental models of pressure overload and myocardial infarction (MI) in vivo. Angiotensin II infusion increased left ventricular dyxin mRNA levels (9.4-fold, p<0.001) rapidly at 6 h followed by induction of protein levels. Furthermore, simultaneous administration of p38 MAPK inhibitor SB203580 abolished angiotensin II-induced activation of dyxin gene expression. During the post-infarction remodeling process, increased dyxin mRNA levels (7.7-fold, p<0.01) were noted at day 1 followed by the increase in proteins levels at 2 weeks after MI (1.5-fold, p<0.05). Moreover, direct wall stretch by using isolated rat heart preparation as well as direct mechanical stretch of cardiomyocytes in vitro activated dyxin gene expression within 1 h. Our results indicate that dyxin expression is rapidly upregulated in response to mechanical load, this increase being at least partly mediated by p38 MAPK. These results suggest that dyxin may play an important role in regulating hypertrophic process.

Metoprolol treatment lowers thrombospondin-4 expression in rats with myocardial infarction and left ventricular hypertrophy

Thrombospondins are matrix proteins linked to extracellular matrix remodelling but their precise role in the heart is not known. In this study, we characterised left ventricular thrombospondin-1 and -4 expression in rats treated with a beta-blocker metoprolol during the remodelling process in response to pressure overload and acute myocardial infarction. Left ventricular thrombospondin-1 and thrombospondin-4 mRNA levels increased 8.4-fold (p < 0.001) and 7.3-fold (p < 0.001) post-infarction, respectively. Metoprolol infusion by osmotic minipumps (1.5 mg/kg/hr) for 2 weeks after myocardial infarction decreased thrombospondin-1 and thrombospondin-4 mRNA levels (55% and 50%, respectively), improved left ventricular function, and attenuated left ventricular remodelling with reduction of left ventricular atrial natriuretic peptide and brain natriuretic peptide gene expression. Thrombospondin-1 and -4 mRNA levels correlated positively with echocardiographic parameters of left ventricular remodelling as well as with atrial natriuretic peptide and brain natriuretic peptide gene expression. Moreover, there was a negative correlation between left ventricular ejection fraction and thrombospondin-1 mRNA levels. In 12-month-old spontaneously hypertensive rats with left ventricular hypertrophy, metoprolol decreased left ventricular thrombospondin-4 levels and attenuated remodelling while thrombospondin-1, atrial natriuretic peptide and brain natriuretic peptide mRNA levels as well as left ventricular function remained unchanged. In metoprolol-treated spontaneously hypertensive rats, thrombospondin-4 gene expression correlated with parameters of left ventricular remodelling, while no correlations between thrombospondins and natriuretic peptides were observed. These results indicate that thrombospondin-1 expression is linked exclusively to left ventricular remodelling process post-infarction while thrombospondin-4 associates with myocardial remodelling both after myocardial infarction and in hypertensive heart disease suggesting that thrombospondins may have unique roles in extracellular matrix remodelling process.

Growth differentiation factor 5 regulates cardiac repair after myocardial infarction

OBJECTIVES

The aim of this study was to examine the function of the bone morphogenic protein growth differentiation factor 5 (Gdf5) in a mouse model of myocardial infarction (MI).

BACKGROUND

The Gdf5 has been implicated in skeletal development, but a potential role in the heart had not been studied.

METHODS

The Gdf5-knockout (KO) and wild-type (WT) mice were subjected to permanent left anterior descending coronary artery (LAD) ligation. Cardiac pathology, function, gene expression levels, and signaling pathways downstream of Gdf5 were examined. Effects of recombinant Gdf5 (rGdf5) were tested in primary cardiac cell cultures.

RESULTS

The WT mice showed increased cardiac Gdf5 levels after MI, with increased expression in peri-infarct cardiomyocytes and myofibroblasts. At 1 and 7 days after MI, no differences were observed in ischemic or infarct areas between WT and Gdf5-KO mice. However, by 28 days after MI, Gdf5-KO mice exhibited increased infarct scar expansion and thinning with decreased arteriolar density compared with WT. The Gdf5-KO hearts also displayed increased left ventricular dilation, with decreased contractility after MI. At 4 days after MI, Gdf5-KO mice exhibited increased cardiomyocyte apoptosis and decreased expression of anti-apoptotic genes Bcl2 and Bcl-xL compared with WT. Unexpectedly, Gdf5-KO hearts displayed increased Smad 1/5/8 phosphorylation but decreased p38-mitogen-activated protein kinase (MAPK) phosphorylation versus WT. The latter was associated with increased collagen gene (Col1a1, Col3a1) expression and fibrosis. In cultures, rGdf5 induced p38-MAPK phosphorylation in cardiac fibroblasts and Smad-dependent increases in Bcl2 and Bcl-xL in cardiomyocytes.

CONCLUSIONS

Increased expression of Gdf5 after MI limits infarct scar expansion in vivo. These effects might be mediated by Gdf5-induced p38-MAPK signaling in fibroblasts and Gdf5-driven Smad-dependent pro-survival signaling in cardiomyocytes.

GATA-4 is an angiogenic survival factor of the infarcted heart

BACKGROUND

Recent data suggest that GATA-4 is an antiapoptotic factor required for adaptive responses and a key regulator of hypertrophy and hypertrophy-associated genes in the heart. As a leading cause of chronic heart failure, reversal of postinfarction left ventricular remodeling represents an important target for therapeutic interventions. Here, we studied the role of GATA-4 as a mediator of postinfarction remodeling in rats.

METHODS AND RESULTS

Myocardial infarction, caused by ligating the left anterior descending coronary artery, significantly decreased the DNA binding activity of GATA-4 at day 1, whereas at 2 weeks the GATA-4 DNA binding was significantly upregulated. To determine the functional role of GATA-4, peri-infarct intramyocardial delivery of adenoviral vector expressing GATA-4 was done before left anterior descending coronary artery ligation. Hearts treated with GATA-4 gene transfer exhibited significantly increased ejection fraction and fractional shortening. Accordingly, infarct size was significantly reduced. To determine the cardioprotective mechanisms of GATA-4, myocardial angiogenesis, rate of apoptosis, c-kit+ cardiac stemlike cells, and genes regulated by GATA-4 were studied. The number of capillaries and stemlike cells was significantly increased, and decreased apoptosis was observed.

CONCLUSION

These results indicate that the reversal of reduced GATA-4 activity prevents adverse postinfarction remodeling through myocardial angiogenesis, antiapoptosis, and stem cell recruitment. GATA-4-based gene transfer may represent a novel, efficient therapeutic approach for heart failure.

Ligand-directed signalling at beta-adrenoceptors

beta-Adrenoceptors (ARs) classically mediate responses to the endogenous ligands adrenaline and noradrenaline by coupling to Gsalpha and stimulating cAMP production; however, drugs designed as beta-AR agonists or antagonists can activate alternative cell signalling pathways, with the potential to influence clinical efficacy. Furthermore, drugs acting at beta-ARs have differential capacity for pathway activation, described as stimulus trafficking, biased agonism, functional selectivity or ligand-directed signalling. These terms refer to responses where drug A has higher efficacy than drug B for one signalling pathway, but a lower efficacy than drug B for a second pathway. The accepted explanation for such responses is that drugs A and B have the capacity to induce or stabilize distinct active conformations of the receptor that in turn display altered coupling efficiency to different effectors. This is consistent with biophysical studies showing that drugs can indeed promote distinct conformational states. Agonists acting at beta-ARs display ligand-directed signalling, but many drugs acting as cAMP antagonists are also able to activate signalling pathways central to cell survival and proliferation or cell death. The observed complexity of drug activity at beta-ARs, prototypical G protein-coupled receptors, necessitates rethinking of the approaches used for screening and characterization of novel therapeutic agents. Most studies of ligand-directed signalling employ recombinant cell systems with high receptor abundance. While such systems are valid for examining upstream signalling events, such as receptor conformational changes and G protein activation, they are less robust when comparing downstream signalling outputs as these are likely to be affected by complex pathway interactions.

Engineered early embryonic cardiac tissue increases cardiomyocyte proliferation by cyclic mechanical stretch via p38-MAP kinase phosphorylation

Cardiomyocyte (CM) transplantation is one therapeutic option for cardiac repair. Studies suggest that fetal CMs display the best cell type for cardiac repair, which can finitely proliferate, integrate with injured host myocardium, and restore cardiac function. We have recently developed an engineered early embryonic cardiac tissue (EEECT) using embryonic cardiac cells and have shown that EEECT contractile properties and cellular proliferative response to cyclic mechanical stretch stimulation mimic developing fetal myocardium. However, it remains unknown whether cyclic mechanical stretch-mediated high cellular proliferation activity within EEECT reflects CM or non-CM population. Studies have shown that p38-mitogen-activated protein kinase (p38MAPK) plays an important role in both cyclic mechanical stretch stimulation and cellular proliferation. Therefore, in the present study, we tested the hypothesis that cyclic mechanical stretch (0.5 Hz, 5% strain for 48 h) specifically increases EEECT CM proliferation mediated by p38MAPK activity. Cyclic mechanical stretch increased CM, but not non-CM, proliferation and increased p38MAPK phosphorylation. Treatment of EEECT with the p38MAPK inhibitor, SB202190, reduced CM proliferation. The negative CM proliferation effects of SB202190 were not reversed by concurrent stretch stimulation. Results suggest that immature CM proliferation within EEECT can be positively regulated by mechanical stretch and negatively regulated by p38MAPK inhibition.

Upregulation of cardiac matrix Gla protein expression in response to hypertrophic stimuli

Matrix Gla protein (MGP) expression is increased in cardiac hypertrophy, but the precise mechanisms regulating its expression are unknown. Here we characterized the effect of pressure overload and myocardial infarction in vivo as well as mechanical stretch and hypertrophic agonists in vitro on MGP expression. When angiotensin II (Ang II) was administered by osmotic minipumps, left ventricular (LV) MGP mRNA levels increased significantly from 6 h to 2 weeks, whereas intravenous arginine(8)-vasopressin increased LV MGP mRNA levels within 4 h. During post-infarction remodeling process, MGP mRNA levels were elevated at 24 h (1.3-fold, p<0.05) and the maximal increase was observed at 4 weeks (2.8-fold, p<0.01). Ang II increased MGP mRNA levels 20% (p<0.05) in neonatal rat cardiac myocytes and 40% (p<0.05) in cardiac fibroblasts, whereas endothelin-1 decreased MGP mRNA levels 30% (p<0.01) in myocytes and had no effect in fibroblasts. Cyclic mechanical stretch resulted in reduction of MGP gene expression in both cardiac myocytes and fibroblasts. These results demonstrate that MGP is rapidly upregulated in response to cardiac overload well before the development of LV hypertrophy and post-infarction remodeling process. Our results also suggest that Ang II may be involved in mediating load-induced activation of MGP expression.

Renin Inhibition Improves Cardiac Function and Remodeling After Myocardial Infarction Independent of Blood Pressure

Pharmacological renin inhibition with aliskiren is an effective antihypertensive drug treatment, but it is currently unknown whether aliskiren is able to attenuate cardiac failure independent of its blood pressure–lowering effects. We investigated the effect of aliskiren on cardiac remodeling, apoptosis, and left ventricular (LV) function after experimental myocardial infarction (MI). C57J/bl6 mice were subjected to coronary artery ligation and were treated for 10 days with vehicle or aliskiren (50 mg/kg per day via an SC osmopump), whereas sham-operated animals served as controls. This dose of aliskiren, which did not affect systemic blood pressure, improved systolic and diastolic LV function, as measured by the assessment of pressure-volume loops after MI. Furthermore, after MI LV dilatation, cardiac hypertrophy and lung weights were decreased in mice treated with aliskiren compared with placebo-treated mice after MI. This was associated with a normalization of the mitogen-activated protein kinase P38 and extracellular signal-regulated kinases 1/2, AKT, and the apoptotic markers bax and bcl-2 (all measured by Western blots), as well as the number of TUNEL-positive cells in histology. LV dilatation, as well as the associated upregulation of gene expression (mRNA abundance) and activity (by zymography) of the cardiac metalloproteinase 9 in the placebo group after MI, was also attenuated in the aliskiren-treated group. Aliskiren improved LV dysfunction after MI in a dose that did not affect blood pressure. This was associated with the amelioration of cardiac remodelling, hypertrophy, and apoptosis.

MAPK signalling in cardiovascular health and disease: molecular mechanisms and therapeutic targets

Intracellular MAPK (mitogen-activated protein kinase) signalling cascades probably play an important role in the pathogenesis of cardiac and vascular disease. A substantial amount of basic science research has defined many of the details of MAPK pathway organization and activation, but the role of individual signalling proteins in the pathogenesis of various cardiovascular diseases is still being elucidated. In the present review, the role of the MAPKs ERK (extracellular signal-regulated kinase), JNK (c-Jun N-terminal kinase) and p38 MAPK in cardiac hypertrophy, cardiac remodelling after myocardial infarction, atherosclerosis and vascular restenosis will be examined, with attention paid to genetically modified murine model systems and to the use of pharmacological inhibitors of protein kinases. Despite the complexities of this field of research, attractive targets for pharmacological therapy are emerging.

Thrombospondin-4 expression is rapidly upregulated by cardiac overload

The precise mechanisms regulating gene expression of thrombospondins (TSPs) in the heart remain incompletely understood. Here we characterized cardiac TSP-4 expression in response to pressure overload and myocardial infarction in vivo. Arginine(8)-vasopressin (AVP) infusion increased left ventricular (LV) TSP-4 mRNA levels within 30 min. Also angiotensin II infusion rapidly activated LV TSP-4 expression, TSP-4 mRNA levels being highest at 6h and protein at 72 h and 2 weeks. During remodeling process following myocardial infarction, LV TSP-4 mRNA levels increased at day one, as studied by quantitative RT-PCR. TSP-4 immunostaining was localized to endothelial cells in hypertrophied hearts of spontaneously hypertensive rats. AVP-infusion increased LV TSP-1 mRNA levels similarly to TSP-4 within 30 min showing that rapid induction of gene expression, well before the development of cardiac hypertrophy, is typical for the thrombospondin family. These results further suggest that TSP-4 may be an endothelial specific marker of cardiac overload.

An LRP8 variant is associated with familial and premature coronary artery disease and myocardial infarction

Our previous genomewide linkage scan of 428 nuclear families (GeneQuest) identified a significant genetic susceptibility locus for premature myocardial infarction (MI) on chromosome 1p34-36. We analyzed candidate genes in the locus with a population-based association study involving probands with premature coronary artery disease (CAD) and/or MI from the GeneQuest families (381 cases) and 560 controls without stenosis detectable by coronary angiography. A nonconservative substitution, R952Q, in LRP8 was significantly associated with susceptibility to premature CAD and/or MI by use of both population-based and family-based designs. Three additional white populations were used for follow-up replication studies: another independent cohort of CAD- and/or MI-affected families (GeneQuest II: 441 individuals from 22 pedigrees), an Italian cohort with familial MI (248 cases) and 308 Italian controls, and a separate Cleveland GeneBank cohort with sporadic MI (1,231 cases) and 560 controls. The association was significantly replicated in two independent populations with a family history of CAD and/or MI, the GeneQuest II family-based replication cohort and the Italian cohort, but not in the population with sporadic disease. The R952Q variant of LRP8 increased activation of p38 mitogen-activated protein kinase by oxidized low-density lipoprotein. This extensive study, involving multiple independent populations, provides the first evidence that genetic variants in LRP8 may contribute to the development of premature and familial CAD and MI.

Ligand-Directed Signaling at the β3-Adrenoceptor Produced by 3-(2-Ethylphenoxy)-1-[(1,S)-1,2,3,4-tetrahydronapth-1-ylamino]-2S-2-propanol oxalate (SR59230A) Relative to Receptor Agonists

This study examines signaling pathways activated by the mouse beta(3)-adrenoceptor (AR) expressed in Chinese hamster ovary cells at high (CHObeta(3)H) or low (CHObeta(3)L) levels. Functional responses included extracellular acidification rate (ECAR), cAMP accumulation, and p38 mitogen-activated protein kinase (MAPK) or extracellular signal-regulated protein kinase 1/2 (Erk1/2) phosphorylation. (-)-Isoproterenol and the beta(3)-AR agonist (R, R)-5-[2-[[2-(3-chlorophenyl)-2-hydroxyethyl]-amino]-propyl]1,3-benzodioxole-2,2-decarboxylate (CL316243) caused concentration-dependent increases in cAMP accumulation and ECAR in CHObeta(3)H and CHObeta(3)L cells. For cAMP accumulation, the beta(3)-AR ligand SR59230A was a partial agonist in CHObeta(3)H and an antagonist in CHObeta(3)L cells but for ECAR was an agonist at both expression levels. This suggested that SR59230A, which is normally regarded as an antagonist, can selectively activate pathways leading to ECAR. Examination of the pathways stimulated by (-)-isoproterenol, CL316243, and SR59230A for both ECAR and cAMP accumulation suggested that the cAMP pathway predominates in CHObeta(3)H cells, whereas p38 MAPK is a major contributor to ECAR in CHObeta(3)L cells and was the sole contributor to responses to SR59230A. Western blots of p38 MAPK and Erk1/2 phosphorylation confirmed that MAPKs are activated in CHObeta(3)H and CHObeta(3)L cells by CL316243 and SR59230A but that SR59230A has much higher efficacy. In addition, p38 MAPK phosphorylation displayed differences in drug potency and efficacy between CHObeta(3)H and CHObeta(3)L cells related to inhibition of the response by cAMP. Thus, CL316243 and SR59230A display reversed orders of efficacy for cAMP accumulation compared with Erk1/2 and p38 MAPK phosphorylation, providing a strong indication of ligand-directed signaling.

Current Status of Cardiovascular Gene Therapy

Gene transfer for the therapeutic modulation of cardiovascular diseases is an expanding area of gene therapy. During the last decade several approaches have been designed for the treatment of hyperlipidemias, post-angioplasty restenosis, hypertension, and heart failure, and for protection of vascular by-pass grafts and promotion of therapeutic angiogenesis. Adenoviruses (Ads) and adeno-associated viruses (AAVs) are currently the most efficient vectors for delivering therapeutic genes into the cardiovascular system. Gene transfer using local gene delivery techniques have been shown to be superior to less-targeted intra-arterial or intra-venous applications. To date, no gene therapy drugs have been approved for clinical use in cardiovascular applications. In preclinical studies of therapeutic angiogenesis, various growth factors such as vascular endothelial growth factors (VEGFs) and fibroblast growth factors (FGFs), have shown positive results. Gene therapy also appears to have potential clinical applications in improving the patency of vascular grafts and in treating heart failure. Post-angioplasty restenosis, hypertension, and hyperlipidemias (excluding homozygotic familial hypercholesterolemia) can usually be managed satisfactorily by conventional approaches, and are therefore less favored areas for gene therapy. The development of technologies that can ensure long-term, targeted, and regulated gene transfer, and a careful selection of target patient populations, will be very important for the progress of cardiovascular gene therapy in clinical applications.

Time course of changes in the expression of DHPR, RyR(2), and SERCA2 after myocardial infarction in the rat left ventricle

Postinfarction left ventricular remodeling leads to the functional decline of the left ventricle (LV). Since dihydropyridine receptor (DHPR), ryanodine receptor (RyR(2)), and sarco-endoplasmic reticulum (SR) Ca(2+)-ATPase2 (SERCA2a) play a major role in the contractility of the heart, the aim of our study was to evaluate the time course of changes in the expression of these proteins 1 day, 2 weeks and 4 weeks after myocardial infarction (MI). Myocardial infarction was produced by ligation of left anterior descending coronary artery of the rat. Transthoracic echocardiography was performed to characterize structural and functional changes after MI. To evaluate protein mRNA levels and the relative amount of proteins, real-time quantitative RT-PCR and Western blotting were used. LV ejection fraction and fractional shortening decreased significantly during the 4-week follow-up period (P < 0.001). Typical features of LV remodeling after MI were seen, with a decrease in anterior wall thickness (P < 0.001) and dilatation of the LV (P < 0.001). Expression of DHPR and RyR(2) mRNAs decreased and Serca2a mRNA tended to decrease 1 day after MI (P < 0.001, P < 0.01 and P = 0.06, respectively), followed by recovery of the expression during the next 4 weeks. In the infarcted hearts the quantities of SERCA2 proteins in the LV were significantly decreased at the time of 4 weeks. In conclusion, MI was associated with transient decrease in the expression of the DHPR and RyR(2) mRNAs and a reduced quantity of SERCA2 proteins in the LV. Since they have a key role in the contraction of the heart, changes in the expression of these proteins may be important regulators of LV systolic function after MI.

Can the cardiomyocyte cell cycle be reprogrammed?

Cardiac repair following myocardial injury is restricted due to the limited proliferative potential of adult cardiomyocytes. The ability of mammalian cardiomyocytes to proliferate is lost shortly after birth as cardiomyocytes withdraw from the cell cycle and differentiate. We do not fully understand the molecular and cellular mechanisms that regulate this cell cycle withdrawal, although if we could it might lead to the discovery of novel therapeutic targets for improving cardiac repair following myocardial injury. For the last decade, researchers have investigated cardiomyocyte cell cycle control, commonly using transgenic mouse models or recombinant adenoviruses to manipulate cell cycle regulators in vivo or in vitro. This review discusses cardiomyocyte cell cycle regulation and summarises recent data from studies manipulating the expressions and activities of cell cycle regulators in cardiomyocytes. The validity of therapeutic strategies that aim to reinstate the proliferative potential of cardiomyocytes to improve myocardial repair following injury will be discussed.