Targeted Disruption ofSmad4in Cardiomyocytes Results in Cardiac Hypertrophy and Heart Failure

MicroRNA-34a regulates cardiac fibrosis after myocardial infarction by targeting Smad4

BACKGROUND

Although few microRNAs (miRNAs) have been involved in the regulation of post-ischemic cardiac fibrosis, the exact effect and underlying mechanism of miRNAs in cardiac fibrosis remains unclear. Here, we sought to investigate whether microRNA-34 (miR-34) plays a role in the pathogenic development of myocardial fibrosis.

METHODS

The myocardial infarction (MI) mice model was induced and cardiac fibroblasts were cultured. Histological analyses, quantitative real-time polymerase chain reaction and Western blotting analysis were used.

RESULTS

We found that the miR-34 cluster, especially miR-34a, was upregulated in the MI heart. In vivo, inhibition of miR-34a reduces the severity of experimental cardiac fibrosis in mice. TGF-β1 increased miR-34a expression in cardiac fibroblasts. Overexpressing miR-34a levels increased the profibrogenic activity of TGF-β1 in cardiac fibroblast, whereas inhibition miR-34a levels weakened the activity. Finally, we showed that miR-34a's underlying mechanism during cardiac fibrosis occurs through the targeting of Smad4 expression.

CONCLUSIONS

Our findings provide evidence that miR-34a plays a critical role in the progression of cardiac tissue fibrosis by directly targeting Smad4, which suggests that miR-34a may be new marker for cardiac fibrosis progression and that inhibition of miR-34a may be a promising strategy in the treatment of cardiac fibrosis.

Bone Morphogenetic Protein (BMP) signaling in development and human diseases

Bone Morphogenetic Proteins (BMPs) are a group of signaling molecules that belongs to the Transforming Growth Factor-β (TGF-β) superfamily of proteins. Initially discovered for their ability to induce bone formation, BMPs are now known to play crucial roles in all organ systems. BMPs are important in embryogenesis and development, and also in maintenance of adult tissue homeostasis. Mouse knockout models of various components of the BMP signaling pathway result in embryonic lethality or marked defects, highlighting the essential functions of BMPs. In this review, we first outline the basic aspects of BMP signaling and then focus on genetically manipulated mouse knockout models that have helped elucidate the role of BMPs in development. A significant portion of this review is devoted to the prominent human pathologies associated with dysregulated BMP signaling.

Echocardiographic assessment of β-adrenoceptor stimulation-induced heart failure with reduced heart rate in mice

1. Chronic injection with the β-adrenoceptor (β-AR) agonist isoproterenol (ISO) has been commonly used as an animal model of β-AR-induced cardiac remodelling and heart failure. This ISO-treated model usually exhibits significantly decreased conscious heart rate (HR). However, the HR in treatment groups is usually adjusted to the same levels by anaesthesia to assess cardiac geometry and function. In the present study, we report a method of echocardiographic assessment that represents the true cardiac geometry and function under conditions of ISO withdrawal. 2. Briefly, C57BL/6 mice were treated with 5 mg/kg per day ISO for 12 weeks. Cardiac geometry and function were assessed by high-resolution echocardiography in vehicle (saline) - and ISO-treated mice that were either conscious or anaesthetized using different concentrations of isoflurane. 3. The cardiac β-AR response was decreased in ISO-treated mice, as evidenced by markedly decreased conscious HR. Vehicle- and ISO-treated mice did not differ in terms of cardiac geometry or function when HR was adjusted to the same level (400 b.p.m.) in both treatment groups, but cardiac geometry and function did differ when a low (1%) rather than high (1.5% or 2%) isoflurane concentration was used to adjust HR. Furthermore, 3 day ISO withdrawal eliminated the difference in conscious HR between the two groups. In addition, the groups differed in cardiac geometry and function regardless of the isoflurane concentration used. 4. In conclusion, using isoflurane to decrease the HR of treated groups to the same level may mask left ventricular dysfunction in ISO-treated mice. Withdrawal of ISO eliminated the difference in basal HR between the ISO-treated and control groups on echocardiography, allowing a more accurate assessment of cardiac pathological and functional changes.

Inhibition of platelet activation by clopidogrel prevents hypertension-induced cardiac inflammation and fibrosis

Purpose

Platelets are essential for primary hemostasis; however, platelet activation also plays an important proinflammatory role. Inflammation promotes the development of cardiac fibrosis and heart failure induced by hypertension. In this study, we aimed to determine whether inhibiting platelet activation using clopidogrel could inhibit hypertension-induced cardiac inflammation and fibrosis.

Methods

Using a mouse model of angiotensin II (Ang II) infusion (1,500 ng/[kg·min] for 7 days), we determined the role of platelet activation in Ang II infusion-induced cardiac inflammation and fibrosis using a P2Y₁₂ receptor inhibitor, clopidogrel (50 mg/[kg·day]).

Results

CD41 staining showed that platelets accumulated in Ang II-infused hearts. Clopidogrel treatment inhibited Ang II infusion-induced accumulation of α-SMA⁺ myofibroblasts and cardiac fibrosis (4.17 ± 1.26 vs. 1.46 ± 0.81, p < 0.05). Infiltration of inflammatory cells, including Mac-2⁺ macrophages and CD45⁺Ly6G⁺ neutrophils (30.38 ± 4.12 vs. 18.7 ± 2.38, p < 0.05), into Ang II-infused hearts was also suppressed by platelet inhibition. Real-time PCR and immunohistochemical staining showed that platelet inhibition significantly decreased the expression of interleukin-1β and transforming growth factor-β. Acute injection of Ang II or PE stimulated platelet activation and platelet-leukocyte conjugation, which were abolished by clopidogrel treatment.

Conclusion

Thus, inhibition of platelet activation by clopidogrel prevents cardiac inflammation and fibrosis in response to Ang II. Taken together, our results indicate Ang II infusion-induced hypertension stimulated platelet activation and platelet-leukocyte conjugation, which initiated inflammatory responses that contributed to cardiac fibrosis.

Grb2-associated binder 1 is essential for cardioprotection against ischemia/reperfusion injury

We have shown recently that endothelial Grb-2-associated binder 1 (Gab1), an intracellular scaffolding adaptor, has a protective effect against limb ischemia via mediating angiogenic signaling pathways. However, the role of Gab1 in cardiac ischemia/reperfusion (I/R) injury remains unknown. In this study, we show that Gab1 is required for cardioprotection against I/R injury. I/R injury led to remarkable phosphorylation of Gab1 in cardiomyocytes. Compared with controls, the mice with cardiomyocyte-specific deletion of Gab1 gene (CGKO mice) exhibited an increase in infarct size and a decrease in cardiac function after I/R injury. Consistently, in hearts of CGKO mice subjected to I/R, the activation of caspase 3 and myocardial apoptosis was markedly enhanced whereas the activation of protein kinase B (Akt) and mitogen-activated protein kinase (MAPK), which are critical for cardiomyocyte survival, was attenuated. Oxidative stress is regarded as a major contributor to myocardial I/R injury. To examine the role of Gab1 in oxidative stress directly, isolated adult cardiomyocytes were subject to oxidant hydrogen peroxide and the cardioprotective effects of Gab1 were confirmed. Furthermore, we found that the phosphorylation of Gab1 and Gab1-mediated activation of Akt and MAPK by oxidative stress was suppressed by ErbB receptor and Src kinase inhibitors, accompanied by an increase in apoptotic cell death. In conclusion, our results suggest that Gab1 is essential for cardioprotection against I/R oxidative injury via mediating survival signaling.

A cardiomyocyte-specific Wdr1 knockout demonstrates essential functional roles for actin disassembly during myocardial growth and maintenance in mice

Actin dynamics are critical for muscle development and function, and mutations leading to deregulation of actin dynamics cause various forms of heritable muscle diseases. AIP1 is a major cofactor of the actin depolymerizing factor/cofilin in eukaryotes, promoting actin depolymerizing factor/cofilin-mediated actin disassembly. Its function in vertebrate muscle has been unknown. To investigate functional roles of AIP1 in myocardium, we generated conditional knockout (cKO) mice with cardiomyocyte-specific deletion of Wdr1, the mammalian homolog of yeast AIP1. Wdr1 cKO mice began to die at postnatal day 13 (P13), and none survived past P24. At P12, cKO mice exhibited cardiac hypertrophy and impaired contraction of the left ventricle. Electrocardiography revealed reduced heart rate, abnormal P wave, and abnormal T wave at P10 and prolonged QT interval at P12. Actin filament (F-actin) accumulations began at P10 and became prominent at P12 in the myocardium of cKO mice. Within regions of F-actin accumulation in myofibrils, the sarcomeric components α-actinin and tropomodulin-1 exhibited disrupted patterns, indicating that F-actin accumulations caused by Wdr1 deletion result in disruption of sarcomeric structure. Ectopic cofilin colocalized with F-actin aggregates. In adult mice, Wdr1 deletion resulted in similar but much milder phenotypes of heart hypertrophy, F-actin accumulations within myofibrils, and lethality. Taken together, these results demonstrate that AIP1-regulated actin dynamics play essential roles in heart function in mice.

Bone Morphogenetic Protein 9 and 13 Induce C3H10T1/2 Cell Differentiation to Cardiomyocyte-Like Cells In Vitro

The present study aimed to evaluate the effect of bone morphogenetic protein 9 (BMP9) and BMP13 on cardiac differentiation of C3H10T1/2 cells in vitro and to characterize the differentiated cells on their ultrastructure and transmembrane electrophysiological features. C3H10T1/2 cells were transfected with the vectors for BMP9 or BMP13 and differentiated into cardiomyocytes in vitro for up to 28 days. The expression of cardiac-specific genes Gata4 and Mef2c and proteins troponin T (cTnT) and connexin 43 (Cx43) was significantly increased in the cells transfected with BMP9 or BMP13 after differentiation over the controls as evaluated using quantitative RT-PCR, Western blotting, and immunofluorescence staining. Transmission electron microscopy and Masson trichrome staining showed that the specific myocardial leap dish and myofilament-like structure were present in the cells overexpressing BMP9 or BMP13, not in the control cells. Whole-cell patch-clamping study demonstrated the presence of delayed rectifier potassium current, inward rectifier potassium current, and T-type calcium current in the cells overexpressing BMP9 or BMP13. Sodium current was detected in a small number of cells overexpressing BMP9, not in the BMP13-transfected cells or the control cells. The expression of Mef2c gene and Cx43 and cTnT proteins was also significantly higher in the cells overexpressing BMP9 than those overexpressing BMP13. Our data indicate that BMP9 and BMP13 (BMP9 might be more effective) promoted the differentiation of C3H10T1/2 cells into cardiomyocyte-like cells with cellular ultrastructures and ion channel currents similar to mature cardiomyocytes in vitro.

Effects of wenxin keli on the action potential and L-type calcium current in rats with transverse aortic constriction-induced heart failure

Objective. We investigated the effects of WXKL on the action potential (AP) and the L-type calcium current (I_Ca-L) in normal and hypertrophied myocytes. Methods. Forty male rats were randomly divided into two groups: the control group and the transverse aortic constriction- (TAC-) induced heart failure group. Cardiac hypertrophy was induced by TAC surgery, whereas the control group underwent a sham operation. Eight weeks after surgery, single cardiac ventricular myocytes were isolated from the hearts of the rats. The APs and I_Ca-L were recorded using the whole-cell patch clamp technique. Results. The action potential duration (APD) of the TAC group was prolonged compared with the control group and was markedly shortened by WXKL treatment in a dose-dependent manner. The current densities of the I_Ca-L in the TAC group treated with 5 g/L WXKL were significantly decreased compared with the TAC group. We also determined the effect of WXKL on the gating mechanism of the I_Ca-L in the TAC group. We found that WXKL decreased the I_Ca-L by accelerating the inactivation of the channels and delaying the recovery time from inactivation. Conclusions. The results suggest that WXKL affects the AP and blocked the I_Ca-L, which ultimately resulted in the treatment of arrhythmias.

Regulation of fetal gene expression in heart failure

During the processes leading to adverse cardiac remodeling and heart failure, cardiomyocytes react to neurohumoral stimuli and biomechanical stress by activating pathways that induce pathological hypertrophy. The gene expression patterns and molecular changes observed during cardiac hypertrophic remodeling bare resemblance to those observed during fetal cardiac development. The re-activation of fetal genes in the adult failing heart is a complex biological process that involves transcriptional, posttranscriptional and epigenetic regulation of the cardiac genome. In this review, the mechanistic actions of transcription factors, microRNAs and chromatin remodeling processes in regulating fetal gene expression in heart failure are discussed.

TNNI3K, a cardiac-specific kinase, promotes physiological cardiac hypertrophy in transgenic mice

Purpose

Protein kinase plays an essential role in controlling cardiac growth and hypertrophic remodeling. The cardiac troponin I-interacting kinase (TNNI3K), a novel cardiac specific kinase, is associated with cardiomyocyte hypertrophy. However, the precise function of TNNI3K in regulating cardiac remodeling has remained controversial.

Methods and Results

In a rat model of cardiac hypertrophy generated by transverse aortic constriction, myocardial TNNI3K expression was significantly increased by 1.62 folds (P<0.05) after constriction for 15 days. To investigate the role of TNNI3K in cardiac hypertrophy, we generated transgenic mouse lines with overexpression of human TNNI3K specifically in the heart. At the age of 3 months, the high-copy-number TNNI3K transgenic mice demonstrated a phenotype of concentric hypertrophy with increased heart weight normalized to body weight (1.31 fold, P<0.01). Echocardiography and non-invasive hemodynamic assessments showed enhanced cardiac function. No necrosis or myocyte disarray was observed in the heart of TNNI3K transgenic mice. This concentric hypertrophy maintained up to 12 months of age without cardiac dysfunction. The phospho amino acid analysis revealed that TNNI3K is a protein-tyrosine kinase. The yeast two-hybrid screen and co-immunoprecipitation assay identified cTnI as a target for TNNI3K. Moreover, TNNI3K overexpression induced cTnI phosphorylation at Ser22/Ser23 in vivo and in vitro, suggesting that TNNI3K is a novel upstream regulator for cTnI phosphorylation.

Conclusion

TNNI3K promotes a concentric hypertrophy with enhancement of cardiac function via regulating the phosphorylation of cTnI. TNNI3K could be a potential therapeutic target for preventing from heart failure.

The function of miRNA in cardiac hypertrophy

Cardiac hypertrophy is an adaptive enlargement of the myocardium in response to altered stress or injury. The cellular responses of cardiomyocytes and non-cardiomyocytes to various signaling pathways should be tightly and delicately regulated to maintain cardiac homeostasis and prevent pathological cardiac hypertrophy. MicroRNAs (miRNAs) are endogenous, single-stranded, short non-coding RNAs that act as regulators of gene expression by promoting the degradation or inhibiting the translation of target mRNAs. Recent studies have revealed expression signatures of miRNAs associated with pathological cardiac hypertrophy and heart failure in humans and mouse models of heart diseases. Increasing evidence indicates that dysregulation of specific miRNAs could alter the cellular responses of cardiomyocytes and non-cardiomyocytes to specific signaling upon the pathological hemodynamic overload, leading to cardiac hypertrophy and heart failure. This review summarizes the cell-autonomous functions of cardiomyocyte miRNAs regulated by different pathways and the roles of non-cardiomyocyte miRNAs in cardiac hypertrophy. The therapeutic effects of a number of miRNAs in heart diseases are also discussed.

TGFβ and BMP signaling in cardiac cushion formation: lessons from mice and chicken

Cardiac cushion formation is crucial for both valvular and septal development. Disruption in this process can lead to valvular and septal malformations, which constitute the largest part of congenital heart defects. One of the signaling pathways that is important for cushion formation is the TGFβ superfamily. The involvement of TGFβ and BMP signaling pathways in cardiac cushion formation has been intensively studied using chicken in vitro explant assays and in genetically modified mice. In this review, we will summarize and discuss the role of TGFβ and BMP signaling components in cardiac cushion formation.

Reduced endoglin activity limits cardiac fibrosis and improves survival in heart failure

BACKGROUND

Heart failure is a major cause of morbidity and mortality worldwide. The ubiquitously expressed cytokine transforming growth factor-β1 (TGFβ1) promotes cardiac fibrosis, an important component of progressive heart failure. Membrane-associated endoglin is a coreceptor for TGFβ1 signaling and has been studied in vascular remodeling and preeclampsia. We hypothesized that reduced endoglin expression may limit cardiac fibrosis in heart failure.

METHODS AND RESULTS

We first report that endoglin expression is increased in the left ventricle of human subjects with heart failure and determined that endoglin is required for TGFβ1 signaling in human cardiac fibroblasts using neutralizing antibodies and an siRNA approach. We further identified that reduced endoglin expression attenuates cardiac fibrosis, preserves left ventricular function, and improves survival in a mouse model of pressure-overload-induced heart failure. Prior studies have shown that the extracellular domain of endoglin can be cleaved and released into the circulation as soluble endoglin, which disrupts TGFβ1 signaling in endothelium. We now demonstrate that soluble endoglin limits TGFβ1 signaling and type I collagen synthesis in cardiac fibroblasts and further show that soluble endoglin treatment attenuates cardiac fibrosis in an in vivo model of heart failure.

CONCLUSION

Our results identify endoglin as a critical component of TGFβ1 signaling in the cardiac fibroblast and show that targeting endoglin attenuates cardiac fibrosis, thereby providing a potentially novel therapeutic approach for individuals with heart failure.

[Cardiomycyte overexpression of miR-27b resulted in cardiac fibrosis and mitochondria injury in mice]

Previous microRNA (miRNA) array results have shown that the expression of miR-27b is upregulated in heart tissues from human cardiomyopathy and pressure-overloaded hypertrophic mouse model, implying that miR-27b might play an important role in heart diseases. To study the in vivo function of miR-27b, we generated a transgenic mouse line overexpressing miR-27b under the control of the 5.5 kb promoter of a-myosin heavy chain (a-MHC). Real-time PCR results demonstrated that miR-27b precursor and mature miR-27b were significantly increased in the heart tissues of miR-27b transgenic mice. miR-27b transgenic mice not only displayed cardiac hypertrophy, but also exhibited significant cardiac fibrosis. Further study showed that matrix metalloproteinase 13 (MMP13), a key regulator involved in cardiac fibrosis, was the target of miR-27b. The expression of MMP13 was decreased and the expression of Col I and III was increased in miR-27b transgenic mice.. In addition, defects in ultrastructral architecture were also found in miR-27b trans-genic mice. The above results demonstrated that miR-27b might promote cardiac fibrosis through inhibiting MMP13.

Epigenetic regulation of cardiac development and function by polycomb group and trithorax group proteins

Heart disease is a leading cause of death and disability in developed countries. Heart disease includes a broad range of diseases that affect the development and/or function of the cardiovascular system. Some of these diseases, such as congenital heart defects, are present at birth. Others develop over time and may be influenced by both genetic and environmental factors. Many of the known heart diseases are associated with abnormal expression of genes. Understanding the factors and mechanisms that regulate gene expression in the heart is essential for the detection, treatment, and prevention of heart diseases. Polycomb Group (PcG) and Trithorax Group (TrxG) proteins are special families of chromatin factors that regulate developmental gene expression in many tissues and organs. Accumulating evidence suggests that these proteins are important regulators of development and function of the heart as well. A better understanding of their roles and functional mechanisms will translate into new opportunities for combating heart disease.

Cardiac lineage protein-1 (CLP-1) regulates cardiac remodeling via transcriptional modulation of diverse hypertrophic and fibrotic responses and angiotensin II-transforming growth factor β (TGF-β1) signaling axis

It is well known that the renin-angiotensin system contributes to left ventricular hypertrophy and fibrosis, a major determinant of myocardial stiffness. TGF-β1 and renin-angiotensin system signaling alters the fibroblast phenotype by promoting its differentiation into morphologically distinct pathological myofibroblasts, which potentiates collagen synthesis and fibrosis and causes enhanced extracellular matrix deposition. However, the atrial natriuretic peptide, which is induced during left ventricular hypertrophy, plays an anti-fibrogenic and anti-hypertrophic role by blocking, among others, the TGF-β-induced nuclear localization of Smads. It is not clear how the hypertrophic and fibrotic responses are transcriptionally regulated. CLP-1, the mouse homolog of human hexamethylene bis-acetamide inducible-1 (HEXIM-1), regulates the pTEFb activity via direct association with pTEFb causing inhibition of the Cdk9-mediated serine 2 phosphorylation in the carboxyl-terminal domain of RNA polymerase II. It was recently reported that the serine kinase activity of Cdk9 not only targets RNA polymerase II but also the conserved serine residues of the polylinker region in Smad3, suggesting that CLP-1-mediated changes in pTEFb activity may trigger Cdk9-dependent Smad3 signaling that can modulate collagen expression and fibrosis. In this study, we evaluated the role of CLP-1 in vivo in induction of left ventricular hypertrophy in angiotensinogen-overexpressing transgenic mice harboring CLP-1 heterozygosity. We observed that introduction of CLP-1 haplodeficiency in the transgenic α-myosin heavy chain-angiotensinogen mice causes prominent changes in hypertrophic and fibrotic responses accompanied by augmentation of Smad3/Stat3 signaling. Together, our findings underscore the critical role of CLP-1 in remodeling of the genetic response during hypertrophy and fibrosis.

GATA4 regulates ANF expression synergistically with Sp1 in a cardiac hypertrophy model

Cardiac hypertrophy in response to multiple stimuli has important physiological and pathological significances. GATA4 serves as a nuclear integrator of several signalling pathways during cardiac hypertrophy. Sp1 and Sp3 are also reported to be involved in this process. However, the mechanism by which GATA4 acts as a mediator, integrating these ubiquitously expressed transcriptional factors, is poorly understood. We found that the expression of GATA4 and Sp1 was up-regulated in the myocardium of a pressure overload hypertrophy rat model, as well in phenylephrine-induced (PE-induced) hypertrophic growth of neonatal cardiomyocytes. GST pull-down assays demonstrated that GATA4 could interact with Sp1 in vitro. Therefore, we proposed that GATA4 cooperates with Sp1 in regulating ANF expression, as its reactivation is closely linked with hypertrophy. Further studies demonstrated that GATA4 could activate the ANF promoter synergistically with Sp1 through direct interaction. In contrast, Sp3 exhibited antagonistic function, and overexpression of Sp3 repressed the transcriptional synergy between Sp1 and GATA4. We also found that Sp1 alone could activate the ANF promoter in cardiomyocytes, whereas Sp3 exerted negative effects on ANF expression. Bioinformatics analysis revealed novel Sp-binding sites on the ANF promoter. The recruitment of GATA4 and Sp1 on the ANF promoter was enhanced during phenylephrine-mediated hypertrophy, whereas the recruitment of Sp3 was reduced. The phosphorylation of GATA4 by ERK1/2 kinase could enhance the affinity between GATA4 and Sp1. Thus, our findings revealed the critical interaction of GATA4 and Sp1 in modulating ANF expression, indicating their involvement in cardiac hypertrophy.

Angiotensin II-induced cardiomyocyte hypertrophy in vitro is TAK1-dependent and Smad2/3-independent

Cardiac hypertrophy occurs as an adaptation to hypertension but a sustained hypertrophic response can ultimately lead to heart failure. Angiotensin-II (Ang II) is released following hemodynamic overload and stimulates a cardiac hypertrophic response. AngII also increases expression of the regulatory cytokine, transforming growth factor-β1 (TGFβ1), which is also implicated in the cardiac hypertrophic response and can stimulate activation of Smad2/3 as well as TGFβ-activated kinase 1 (TAK1) signaling mediators. To better understand the downstream signaling events in cardiac hypertrophy, we therefore investigated activation of Smad2/3 and TAK1 signaling pathways in response to Ang II and TGFβ1 using primary neonatal rat cardiomyocytes to model cardiac hypertrophic responses. Small interfering RNA (siRNA) knockdown of Smad 2/3 or TAK1 protein or addition of the TGFβ type I receptor inhibitor, SB431542, were used to investigate the role of downstream mediators of TGFβ signaling in the hypertrophic response. Our data revealed that TGFβ1 stimulation leads to cardiomyocyte hypertrophic phenotypes that were indistinguishable from those occurring in response to Ang II. In addition, inhibition of the TGFβ1 type receptor abolished Ang II-induced hypertrophic changes. Furthermore, the hypertrophic response was also prevented following siRNA knockdown of TAK1 protein, but was unaffected by knockdown of Smad2/3 proteins. We conclude that Ang II-induced cardiomyocyte hypertrophy in vitro occurs in a TAK1-dependent, but Smad-independent, manner.

Disruption of Smad4 impairs TGF-β/Smad3 and Smad7 transcriptional regulation during renal inflammation and fibrosis in vivo and in vitro

The mechanism by which TGF-β regulates renal inflammation and fibrosis is largely unclear; however, it is well accepted that its biological effects are mediated through Smad2 and Smad3 phosphorylation. Following activation, these Smads form heteromeric complex with Smad4 and translocate into the nucleus to bind and regulate the expression of target genes. Here we studied the roles of Smad4 to regulate TGF-β signaling in a mouse model of unilateral ureteral obstruction using conditional Smad4 knockout mice and in isolated Smad4 mutant macrophages and fibroblasts. Disruption of Smad4 significantly enhanced renal inflammation as evidenced by a greater CD45(+) leukocyte and F4/80(+) macrophage infiltration and upregulation of IL-1β, TNF-α, MCP-1, and ICAM-1 in the obstructed kidney and in IL-1β-stimulated macrophages. In contrast, deletion of Smad4 inhibited renal fibrosis and TGF-β1-induced collagen I expression by fibroblasts. Further studies showed that the loss of Smad4 repressed Smad7 transcription, leading to a loss of functional protein. This, in turn, inhibited IκBα expression but enhanced NF-κB activation, thereby promoting renal inflammation. Interestingly, deletion of Smad4 influenced Smad3-mediated promoter activities and the binding of Smad3 to the COL1A2 promoter, but not Smad3 phosphorylation and nuclear translocation, thereby inhibiting the fibrotic response. Thus, Smad4 may be a key regulator for the diverse roles of TGF-β1 in inflammation and fibrogenesis by interacting with Smad7 and Smad3 to influence their transcriptional activities in renal inflammation and fibrosis.

TRB3 gene silencing alleviates diabetic cardiomyopathy in a type 2 diabetic rat model

OBJECTIVE

Tribbles 3 (TRB3) is associated with insulin resistance, an important trigger in the development of diabetic cardiomyopathy (DCM). We sought to determine whether TRB3 plays a major role in modulating DCM and the mechanisms involved.

RESEARCH DESIGN AND METHODS

The type 2 diabetic rat model was induced by high-fat diet and low-dose streptozotocin. We evaluated the characteristics of type 2 DCM by serial echocardiography and metabolite tests, Western blot analysis for TRB3 expression, and histopathologic analyses of cardiomyocyte density, lipids accumulation, cardiac inflammation, and fibrosis area. We then used gene silencing to investigate the role of TRB3 in the pathophysiologic features of DCM.

RESULTS

Rats with DCM showed severe insulin resistance, left ventricular dysfunction, aberrant lipids deposition, cardiac inflammation, fibrosis, and TRB3 overexpression. We found that the silencing of TRB3 ameliorated metabolic disturbance and insulin resistance; myocardial hypertrophy, lipids accumulation, inflammation, fibrosis, and elevated collagen I-to-III content ratio in DCM rats were significantly decreased. These anatomic findings were accompanied by significant improvements in cardiac function. Furthermore, with TRB3 gene silencing, the inhibited phosphorylation of Akt was restored and the increased phosphorylation of extracellular signal-regulated kinase 1/2 and Jun NH(2)-terminal kinase in DCM was significantly decreased.

CONCLUSIONS

TRB3 gene silencing may exert a protective effect on DCM by improving selective insulin resistance, implicating its potential role for treatment of human DCM.

Fasudil hydrochloride hydrate, a Rho-kinase inhibitor, suppresses isoproterenol-induced heart failure in rats via JNK and ERK1/2 pathways

The Rho-kinase (ROCK) plays an important role in the pathogenesis of heart injury. Recent cellular and molecular biology studies indicated a pivotal role of the RhoA/ROCK cascade in many aspects of cardiovascular function such as heart failure, cardiac hypertrophy, and ventricular remodeling following myocardial infarction. However, the signal transduction of RhoA/ROCK and its down-stream signaling pathways remains elusive, and the mechanism of ROCK-mediated isoproterenol (ISO)-induced heart failure is still not thoroughly understood. In the present study, we investigated the effect of the ROCK inhibitor, fasudil hydrochloride hydrate, on ISO-induced heart failure and the potential relationship of RhoA/ROCK to the extracellular signal-regulated kinases (ERK) and the c-jun NH 2-terminal kinase (JNK) pathways. Male Sprague-Dawley (SD) rats, maintained on a normal diet, were randomly divided into four groups given control, ISO alone, ISO with low-dose fasudil, or ISO with high-dose fasudil treatments. Fasudil effectively inhibited ISO-induced heart failure, as evaluated by biometric, hemodynamic, and histological examinations. Consistently, ISO-induced ROCK-1 mRNA expression and myosin phosphatase target subunit-1 (MYPT-1) phosphorylation were markedly suppressed by fasudil. In addition, fasudil significantly decreased ISO-induced JNK activation, ERK translocation to the nucleus and subsequent c-fos, c-jun expression and upregulated c-FLIP(L) expression. Taken together, these results indicate that the RhoA/ROCK pathway is essential for ISO induced heart failure, which can be effectively suppressed by fasudil.

Transforming growth factor beta signaling in adult cardiovascular diseases and repair

The majority of children with congenital heart disease now live into adulthood due to the remarkable surgical and medical advances that have taken place over the past half century. Because of this, adults now represent the largest age group with adult cardiovascular diseases. It includes patients with heart diseases that were not detected or not treated during childhood, those whose defects were surgically corrected but now need revision due to maladaptive responses to the procedure, those with exercise problems and those with age-related degenerative diseases. Because adult cardiovascular diseases in this population are relatively new, they are not well understood. It is therefore necessary to understand the molecular and physiological pathways involved if we are to improve treatments. Since there is a developmental basis to adult cardiovascular disease, transforming growth factor beta (TGFβ) signaling pathways that are essential for proper cardiovascular development may also play critical roles in the homeostatic, repair and stress response processes involved in adult cardiovascular diseases. Consequently, we have chosen to summarize the current information on a subset of TGFβ ligand and receptor genes and related effector genes that, when dysregulated, are known to lead to cardiovascular diseases and adult cardiovascular deficiencies and/or pathologies. A better understanding of the TGFβ signaling network in cardiovascular disease and repair will impact genetic and physiologic investigations of cardiovascular diseases in elderly patients and lead to an improvement in clinical interventions.

Cardiomyocyte overexpression of miR-27b induces cardiac hypertrophy and dysfunction in mice

Recent studies have begun to reveal critical roles of microRNAs (miRNAs) in the pathogenesis of cardiac hypertrophy and dysfunction. In this study, we tested whether a transforming growth factor-β (TGF-β)-regulated miRNA played a pivotal role in the development of cardiac hypertrophy and heart failure (HF). We observed that miR-27b was upregulated in hearts of cardiomyocyte-specific Smad4 knockout mice, which developed cardiac hypertrophy. In vitro experiments showed that the miR-27b expression could be inhibited by TGF-β1 and that its overexpression promoted hypertrophic cell growth, while the miR-27b suppression led to inhibition of the hypertrophic cell growth caused by phenylephrine (PE) treatment. Furthermore, the analysis of transgenic mice with cardiomyocyte-specific overexpression of miR-27b revealed that miR-27b overexpression was sufficient to induce cardiac hypertrophy and dysfunction. We validated the peroxisome proliferator-activated receptor-γ (PPAR-γ) as a direct target of miR-27b in cardiomyocyte. Consistently, the miR-27b transgenic mice displayed significantly lower levels of PPAR-γ than the control mice. Furthermore, in vivo silencing of miR-27b using a specific antagomir in a pressure-overload-induced mouse model of HF increased cardiac PPAR-γ expression, attenuated cardiac hypertrophy and dysfunction. The results of our study demonstrate that TGF-β1-regulated miR-27b is involved in the regulation of cardiac hypertrophy, and validate miR-27b as an efficient therapeutic target for cardiac diseases.

Metformin attenuates pressure overload-induced cardiac hypertrophy via AMPK activation

AIM

To identify the role of metformin in cardiac hypertrophy and investigate the possible mechanism underlying this effect.

METHODS

Wild type and AMPKα2 knockout (AMPKα2⁻/⁻) littermates were subjected to left ventricular pressure overload caused by transverse aortic constriction. After administration of metformin (200 mg·kg⁻¹·d⁻¹) for 6 weeks, the degree of cardiac hypertrophy was evaluated using echocardiography and anatomic and histological methods. The antihypertrophic mechanism of metformin was analyzed using Western blotting.

RESULTS

Metformin significantly attenuated cardiac hypertrophy induced by pressure overload in wild type mice, but the antihypertrophic actions of metformin were ablated in AMPKα2⁻/⁻ mice. Furthermore, metformin suppressed the phosphorylation of Akt/protein kinase B (AKT) and mammalian target of rapamycin (mTOR) in response to pressure overload in wild type mice, but not in AMPKα2⁻/⁻ mice.

CONCLUSION

Long-term administration of metformin may attenuate cardiac hypertrophy induced by pressure overload in nondiabetic mice, and this attenuation is highly dependent on AMPK activation. These findings may provide a potential therapy for patients at risk of developing pathological cardiac hypertrophy.

Caveolin-1 modulates TGF-β1 signaling in cardiac remodeling

The cardiac response to myocardial injury includes fibrotic and hypertrophic processes and a key mediator in this response is transforming growth factor-β1 (TGF-β1). Caveolin-1 (cav1), the main structural protein of caveolae, is an inhibitor of the TGF-β1 signaling pathway. To examine the role of cav1 in cardiac repair, cav1 deficient (Cav1(-/-)) and wild type (WT) mice were subjected to cryoinjury of the left ventricle (LV). At baseline the two groups exhibited no inflammation, similar collagen content, and similar cardiac function. After injury, Cav1(-/-) animals displayed enhanced TGF-β1 signaling, as reflected by a 3-fold increase in the activation of the Smad2-dependent pathway and more widespread collagen deposition in the heart. Qualitative and quantitative analyses indicated that collagen deposition peaked in the WT LV 14days after injury, accompanied by increased mRNA abundance for procol1a2 (2-fold) and procol3a1 (3-fold). Collagen deposition was further enhanced in Cav1(-/-) mice, which was accompanied by reduced expression of matrix metalloproteinases MMP-8 (3-fold) and -13 mRNA (2-fold). The levels of expression of inflammatory markers of acute phase were similar between the strains However, macrophage clearance in the damaged region was delayed in Cav1(-/-) mice. We observed a 4-fold decrease in collagen deposition in Cav1(-/-) mice injected with a cav1 scaffolding domain peptide (CSD) and a 2-fold decrease in WT mice treated with the CSD. We conclude that cav1 has a direct role in reducing TGF-β1 signaling and as such might be an appropriate target for therapies to influence cardiac remodeling.

Pivotal role of cardiomyocyte TGF-β signaling in the murine pathological response to sustained pressure overload

The cardiac pathological response to sustained pressure overload involves myocyte hypertrophy and dysfunction along with interstitial changes such as fibrosis and reduced capillary density. These changes are orchestrated by mechanical forces and factors secreted between cells. One such secreted factor is TGF-β, which is generated by and interacts with multiple cell types. Here we have shown that TGF-β suppression in cardiomyocytes was required to protect against maladaptive remodeling and involved noncanonical (non-Smad-related) signaling. Mouse hearts subjected to pressure overload and treated with a TGF-β-neutralizing Ab had suppressed Smad activation in the interstitium but not in myocytes, and noncanonical (TGF-β-activated kinase 1 [TAK1]) activation remained. Although fibrosis was greatly reduced, chamber dysfunction and dilation persisted. Induced myocyte knockdown of TGF-β type 2 receptor (TβR2) blocked all maladaptive responses, inhibiting myocyte and interstitial Smad and TAK1. Myocyte knockdown of TβR1 suppressed myocyte but not interstitial Smad, nor TAK1, modestly reducing fibrosis without improving chamber function or hypertrophy. Only TβR2 knockdown preserved capillary density after pressure overload, enhancing BMP7, a regulator of the endothelial-mesenchymal transition. BMP7 enhancement also was coupled to TAK1 suppression. Thus, myocyte targeting is required to modulate TGF-β in hearts subjected to pressure overload, with noncanonical pathways predominantly affecting the maladaptive hypertrophy/dysfunction.

BMP signaling in congenital heart disease: new developments and future directions

Congenital heart malformations are the most common of all congenital human birth anomalies. During the past decade, research with zebrafish, chick, and mouse models have elucidated many fundamental genetic pathways that govern early cardiac patterning and differentiation. This review highlights the roles of the bone morphogenetic protein (BMP) signaling pathway in cardiogenesis and how defective BMP signals can disrupt the intricate steps of cardiac formation and cause congenital heart defects.

Single-molecule imaging revealed enhanced dimerization of transforming growth factor β type II receptors in hypertrophic cardiomyocytes

Transforming growth factor β (TGF-β) signaling plays an important role in the pathogenesis of cardiac hypertrophy. However, the molecular mechanism of TGF-β signaling during the process of cardiac remodeling remains poorly understood. In the present study, by employing single-molecule fluorescence imaging approach, we demonstrated that in neonatal rat cardiomyocytes, TGF-β type II receptors (TβRII) existed as monomers at the low expression level, and dimerized upon TGF-β1 stimulation. Importantly, for the first time, we found the increased dimerization of TβRII in hypertrophic cardiomyocytes comparing to the normal cardiomyocytes. The enhanced TβRII dimerization was correlated with the enhanced Smad3 phosphorylation levels. These results provide new information on the mechanism of TGF-β signaling in cardiac remodeling.

Cardiac myocyte-specific ablation of follistatin-like 3 attenuates stress-induced myocardial hypertrophy

Transforming growth factor-β family cytokines have diverse actions in the maintenance of cardiac homeostasis. Follistatin-like 3 (Fstl3) is an extracellular regulator of certain TGF-β family members, including activin A. The aim of this study was to examine the role of Fstl3 in cardiac hypertrophy. Cardiac myocyte-specific Fstl3 knock-out (KO) mice and control mice were subjected to pressure overload induced by transverse aortic constriction (TAC). Cardiac hypertrophy was assessed by echocardiography and histological and biochemical methods. KO mice showed reduced cardiac hypertrophy, pulmonary congestion, concentric LV wall thickness, LV dilatation, and LV systolic dysfunction after TAC compared with control mice. KO mice displayed attenuated increases in cardiomyocyte cell surface area and interstitial fibrosis following pressure overload. Although activin A was similarly up-regulated in KO and control mice after TAC, a significant increase in Smad2 phosphorylation only occurred in KO mice. Knockdown of Fstl3 in cultured cardiomyocytes inhibited PE-induced cardiac hypertrophy. Conversely, adenovirus-mediated Fstl3 overexpression blocked the inhibitory action of activin A on hypertrophy and Smad2 activation. Transduction with Smad7, a negative regulator of Smad2 signaling, blocked the antihypertrophic actions of activin A stimulation or Fstl3 ablation. These findings identify Fstl3 as a stress-induced regulator of hypertrophy that controls myocyte size via regulation of Smad signaling.

Mitofusin 2 inhibits angiotensin II-induced myocardial hypertrophy

BACKGROUND AND OBJECTIVES

Myocardial hypertrophy is a common clinical finding leading to heart failure and sudden death. Mitofusin 2 (Mfn2), a hyperplasia suppressor protein, is downregulated in hypertrophic heart. This study examined the role of Mfn2 in myocardial hypertrophy and its potential signal pathway.

METHODS AND RESULTS

In in vitro studies, neonatal cardiac myocytes were isolated and cultured. Incubation of cultured cardiomycytes with angiotensin II (Ang II) inhibited gene expression of Mfn2; induced cell hypertrophy and protein synthesis; and activated protein kinase Akt. Pretreatment of cells with AdMfn2-a replication-deficient adenoviral vector encoding rat Mfn2 gene-upregulated Mfn2 expression and subsequently attenuated Ang II-induced cell hypertrophy; protein synthesis; and Akt activation. In in vivo studies, direct gene delivery of AdMfn2 into myocardium decreased the infusion of Ang II-induced atrial natriuretic factor (ANF, a hypertrophic marker) expression and cardiomyocyte cross-sectional area. Consistently, upregulation of Mfn2 in myocardium decreased the thicknesses of anterior and posterior walls of left ventricle (LV) and the ratio of LV mass/body weight in Ang II-treated rats. Of note, AdGFP (control for AdMfn2) did not affect the effects of Ang II in vitro or in vivo.

CONCLUSIONS

Upregulation of Mfn2 inhibits Ang II-induced myocardial hypertrophy. In this process, inhibition of Akt activation seems to play a significant role. These findings indicate Mfn2 is a critical protein in modulating myocyte hypertrophy.

Myocardial deletion of Smad4 using a novel α skeletal muscle actin Cre recombinase transgenic mouse causes misalignment of the cardiac outflow tract

SMAD4 acts as the converging point for TGFβ and BMP signaling in heart development. Here, we investigated the role of SMAD4 in heart development using a novel α skeletal muscle actin Cre recombinase (MuCre) transgenic mouse strain. Lineage tracing using MuCre/ROSA26^LacZ reporter mice indicated strong Cre-recombinase expression in developing and adult heart and skeletal muscles. In heart development, significant MuCre expression was noted at E11.5 in the atrial, ventricular, outflow tract and atrioventricular canal myocardium, but not in the endocardial cushions. MuCre-driven conditional deletion of Smad4 in mice caused double outlet right ventricle (DORV), ventricular septal defect (VSD), impaired trabeculation and thinning of ventricular myocardium, and mid-gestational embryonic lethality. In conclusion, MuCre mice effectively delete genes in both heart and skeletal muscles, thus enabling the discovery that myocardial Smad4 deletion causes misalignment of the outflow tract and DORV.

Biomarkers in acute myocardial infarction

Myocardial infarction causes significant mortality and morbidity. Timely diagnosis allows clinicians to risk stratify their patients and select appropriate treatment. Biomarkers have been used to assist with timely diagnosis, while an increasing number of novel markers have been identified to predict outcome following an acute myocardial infarction or acute coronary syndrome. This may facilitate tailoring of appropriate therapy to high-risk patients. This review focuses on a variety of promising biomarkers which provide diagnostic and prognostic information. Heart-type Fatty Acid Binding Protein and copeptin in combination with cardiac troponin help diagnose myocardial infarction or acute coronary syndrome in the early hours following symptoms. An elevated N-Terminal Pro-B-type Natriuretic Peptide has been well validated to predict death and heart failure following a myocardial infarction. Similarly other biomarkers such as Mid-regional pro-Atrial Natriuretic Peptide, ST2, C-Terminal pro-endothelin 1, Mid-regional pro-Adrenomedullin and copeptin all provide incremental information in predicting death and heart failure. Growth differentiation factor-15 and high-sensitivity C-reactive protein predict death following an acute coronary syndrome. Pregnancy associated plasma protein A levels following chest pain predicts risk of myocardial infarction and revascularisation. Some biomarkers such as myeloperoxidase and high-sensitivity C-reactive protein in an apparently healthy population predicts risk of coronary disease and allows clinicians to initiate early preventative treatment. In addition to biomarkers, various well-validated scoring systems based on clinical characteristics are available to help clinicians predict mortality risk, such as the Thrombolysis In Myocardial Infarction score and Global Registry of Acute Coronary Events score. A multimarker approach incorporating biomarkers and clinical scores will increase the prognostic accuracy. However, it is important to note that only troponin has been used to direct therapeutic intervention and none of the new prognostic biomarkers have been tested and proven to alter outcome of therapeutic intervention. Novel biomarkers have improved prediction of outcome in acute myocardial infarction, but none have been demonstrated to alter the outcome of a particular therapy or management strategy. Randomised trials are urgently needed to address this translational gap before the use of novel biomarkers becomes common practice to facilitate tailored treatment following an acute coronary event.

Growth differentiation factor 15 acts anti-apoptotic and pro-hypertrophic in adult cardiomyocytes

Growth differentiation factor 15 (GDF15) is induced during heart failure development, and may influence different processes in cardiac remodeling. While its anti-apoptotic action under conditions of ischemia-reperfusion have been shown, it remained unclear if this is a broadly protective effect applicable to other apoptotic stimuli. Furthermore, effects on cardiac hypertrophy remained obscure. Therefore, we investigated the effects of GDF15 on induction of hypertrophy and apoptosis in ventricular cardiomyocytes. GDF15 (3 ng/ml) enhanced hypertrophic growth of cardiomyocytes as determined by an increase in cell size by 27 +/- 5% and rate of protein synthesis by 47 +/- 15%. In addition, a time and dose-dependent increase in SMAD-binding affinity was found, as well as enhanced phosphorylation of R-SMAD1. Inhibition of SMADs by transformation of cardiomyocytes with SMAD-decoy oligonucleotides abolished the hypertrophic growth effect. Specific inhibitors of PI3K (10 microM LY290042 or 10 nM wortmannin) or ERK (10 microM PD98059) also blocked GDF15-induced hypertrophy and SMAD activation. Apoptosis induction by three different agents, 100 nM angiotensin II, 1 ng/ml TGFbeta(1), or the NO-donor SNAP (100 microM) was blocked by addition of GDF15 (3 ng/ml). Scavenging of SMADs by transformation of cardiomyocytes with SMAD-decoy oligonucleotides abolished the anti-apoptotic effect of GDF15. In conclusion, GDF15 protects ventricular cardiomyocytes against different apoptotic stimuli and enhances hypertrophic growth. Hypertrophic signaling is thereby mediated via the kinases PI3K and ERK and the transcription factor R-SMAD1. Thus, GDF15 may influence cardiac remodeling via two different mechanisms, apoptosis protection and induction of hypertrophy.

Impairment of ultrastructure and cytoskeleton during progression of cardiac hypertrophy to heart failure

Studies at the morphological and molecular level have found that transgenic (Tg) mice that overexpress myotrophin in the heart develop hypertrophy at the early age of 4 weeks; this condition worsens to heart failure (HF) at approximately 36 weeks. However, how the sustained effects of alteration in cytoarchitecture of the contractile machinery lead to malfunction of the normal heart remains unclear. Our data have shown that at 4 weeks, the cytoarchitecture observed in left ventricular (LV) tissue samples of Tg mice is similar to that of wild-type (WT) mice. However, as the disease progresses, cardiomyocytes show deterioration in some mitochondrial as well as myofibril features, evidenced by swelling of mitochondria, misalignment of myofibril structure, and blurring as well as breakage of Z-lines. At 36 weeks of age, Tg mice (the group in transition from hypertrophy to HF) show significant degenerative changes in cardiomyocytes, including swelling of mitochondria, disruption of the nuclear membrane, and absence of myofibril structure. Besides these, formation of myelin bodies was also observed, a feature typically found in human hearts with HF. Changes in Z-line architecture were further confirmed by alteration in the gene expression profile of desmin and tubulin, the two main cytoskeletal proteins. We thus conclude that Tg mice overexpressing myotrophin show no visible changes in the initiation phase (4 weeks); however, as the disease progresses, alterations in the cytoskeleton are found during the transition phase from hypertrophy to HF (36 weeks onward). Our data suggest that treatment for prevention/reversal of hypertrophy should start at the early stage of hypertrophy to prevent its transition to HF.

Metformin attenuates cardiac fibrosis by inhibiting the TGFbeta1-Smad3 signalling pathway

AIMS

The mechanism of the cardioprotective action of metformin is incompletely understood. We determined the role of metformin in cardiac fibrosis and investigated the mechanism.

METHODS AND RESULTS

Ten-week-old male mice (C57BL/6) were subjected to left ventricular pressure overload by transverse aortic constriction. Mice received metformin (200 mg/kg/day) or normal saline for 6 weeks. Metformin inhibited cardiac fibrosis (fibrosis area/total heart area: 0.6 +/- 0.3 vs. 3.6 +/- 0.9%, P < 0.01) induced by pressure overload and improved cardiac diastolic function (left ventricular end-diastolic pressure: 5.2 +/- 0.9 vs. 11.0 +/- 1.6 mmHg, P < 0.05). Metformin inhibited the pressure overload-induced transforming growth factor (TGF)-beta(1) production in mouse hearts and the TGF-beta(1)-induced collagen synthesis in cultured adult mouse cardiac fibroblasts (CFs). Metformin suppressed the phosphorylation of Smad3 in response to TGF-beta(1) in CFs. Metformin also inhibited the nuclear translocation and transcriptional activity of Smad3 in CFs.

CONCLUSION

Metformin inhibited cardiac fibrosis induced by pressure overload in vivo and inhibited collagen synthesis in CFs probably via inhibition of the TGF-beta(1)-Smad3 signalling pathway. These findings provide a new mechanism for the cardioprotective effects of metformin.

Functional role of KLF10 in multiple disease processes

Since the discovery by this laboratory of the zinc finger transcription factor, KLF10, a member of the Krüppel-like family of transcription factors, there have been multiple publications regarding its functions and its immediate family members, in numerous cell types. KLF10 has been shown to be rapidly induced by TGFbeta1, 2, 3, E(2), epidermal growth factor, and bone morphogenetic protein-2. TGFbeta inducible early gene-1 activates the TGFbeta-Smad signaling pathway via repression of Smad 7 expression and activation of Smad 2 expression and activity. Overall, KLF10 has been implicated in cell differentiation, as a target gene for a variety of signaling pathways, and in serving as a potential marker for human diseases such as breast cancer, cardiac hypertrophy, and osteoporosis. Like other KLF members, KLF10 is expressed in specific cell types in numerous tissues and is known to be involved in repressing cell proliferation and inflammation as well as inducing apoptosis similar to that of TGFbeta. KLF10 binds to Sp-1-GC rich DNA sequences and can activate or repress the transcription of a number of genes. Overall, KLF10 has been shown to play a major role in the TGFbeta inhibition of cell proliferation and inflammation and induction of apoptosis, and its overexpression in human osteoblasts and pancreatic carcinoma cells mimics the actions of TGFbeta.

Smad4-dependent pathways control basement membrane deposition and endodermal cell migration at early stages of mouse development

Background

Smad4 mutant embryos arrest shortly after implantation and display a characteristic shortened proximodistal axis, a significantly reduced epiblast, as well as a thickened visceral endoderm layer. Conditional rescue experiments demonstrate that bypassing the primary requirement for Smad4 in the extra-embryonic endoderm allows the epiblast to gastrulate. Smad4-independent TGF-β signals are thus sufficient to promote mesoderm formation and patterning. To further analyse essential Smad4 activities contributed by the extra-embryonic tissues, and characterise Smad4 dependent pathways in the early embryo, here we performed transcriptional profiling of Smad4 null embryonic stem (ES) cells and day 4 embryoid bodies (EBs).

Results

Transcripts from wild-type versus Smad4 null ES cells and day 4 EBs were analysed using Illumina arrays. In addition to several known TGF-β/BMP target genes, we identified numerous Smad4-dependent transcripts that are mis-expressed in the mutants. As expected, mesodermal cell markers were dramatically down-regulated. We also observed an increase in non-canonical potency markers (Pramel7, Tbx3, Zscan4), germ cell markers (Aire, Tuba3a, Dnmt3l) as well as early endoderm markers (Dpp4, H19, Dcn). Additionally, expression of the extracellular matrix (ECM) remodelling enzymes Mmp14 and Mmp9 was decreased in Smad4 mutant ES and EB populations. These changes, in combination with increased levels of laminin alpha1, cause excessive basement membrane deposition. Similarly, in the context of the Smad4 null E6.5 embryos we observed an expanded basement membrane (BM) associated with the thickened endoderm layer.

Conclusion

Smad4 functional loss results in a dramatic shift in gene expression patterns and in the endodermal cell lineage causes an excess deposition of, or an inability to breakdown and remodel, the underlying BM layer. These structural abnormalities probably disrupt reciprocal signalling between the epiblast and overlying visceral endoderm required for gastrulation.

Adaptive and maladptive effects of SMAD3 signaling in the adult heart after hemodynamic pressure overloading

BACKGROUND

Previous studies suggest that transforming growth factor-beta provokes cardiac hypertrophy and myocardial fibrosis; however, it is unclear whether the deleterious effects of transforming growth factor-beta signaling are conveyed through SMAD-dependent or SMAD-independent signaling pathways.

METHODS AND RESULTS

To determine the contribution of SMAD-dependent signaling to cardiac remodeling, we performed transaortic constriction in SMAD3 null (SMAD3(-/-)) and littermate control mice (age, 10 to 12 weeks). Cumulative survival 20 days after transaortic constriction was significantly less in the SMAD3(-/-) mice when compared with littermate controls (43.6% versus 90.9%, P<0.01). Transaortic constriction resulted in a significant increase in cardiac hypertrophy in the SMAD3(-/-) mice, denoted by an increase in the heart weight to tibial length ratio and increased myocyte cross-sectional area. Loss of SMAD3 signaling also resulted in a significant 60% decrease in myocardial fibrosis (P<0.05). A microRNA microarray showed that 55 microRNAs were differentially expressed in littermate and SMAD3(-/-) mice and that 10 of these microRNAs were predicted to bind to genes that regulate the extracellular matrix. Of these 10 candidate microRNAs, both miR-25 and miR-29a were sufficient to decrease collagen gene expression when transfected into isolated cardiac fibroblasts in vitro.

CONCLUSIONS

The results suggest that SMAD3 signaling plays dual roles in the heart: one beneficial role by delimiting hypertrophic growth and the other deleterious by modulating myocardial fibrosis, possibly through a pathway that entails accumulation of microRNAs that decrease collagen gene expression.

Developmental signaling in myocardial progenitor cells: a comprehensive view of Bmp- and Wnt/beta-catenin signaling

The tight regulation of different signaling systems and the transcriptional and translational networks during embryonic development have been the focus of embryologists in recent decades. Defective developmental signaling due to genetic mutation or temporal and region-specific alteration of gene expression causes embryonic lethality or accounts for birth defects (e.g., congenital heart disease). The formation of the heart requires the coordinated integration of multiple cardiac progenitor cell populations derived from the first and second heart fields and from cardiac neural crest cells. This article summarizes what has been learned from conditional mutagenesis of Bmp pathway components and the Wnt effector, beta-catenin, in the developing heart of mice. Although Bmp signaling is required for cardiac progenitor cell specification, proliferation, and differentiation, recent studies have demonstrated distinct functions of Wnt/beta-catenin signaling at various stages of heart development.

SMAD-proteins as a molecular switch from hypertrophy to apoptosis induction in adult ventricular cardiomyocytes

Heart failure development goes along with a transition from hypertrophic growth to apoptosis induction. In adult cardiomyocytes SMAD proteins are only activated under apoptotic, but not under hypertrophic conditions and are increased at the transition to heart failure. Therefore, SMADs could be candidates that turn the balance from hypertrophic growth to apoptosis resulting in heart failure development. To test this hypothesis we infected isolated rat ventricular cardiomyocytes with adenovirus encoding SMAD4 (AdSMAD4) and investigated the impact of SMAD4 overexpression on the development of apoptosis and hypertrophy under stimulation with phenylephrine (PE). Infection of cardiomyocytes with AdSMAD4 significantly enhanced SMAD-binding activity while apoptosis after 24 and 36 h infection did not rise. But when SMAD4 overexpressing cardiomyocytes were incubated with PE (10 microM), the number of apoptotic cells increased (Ctrl: 94.97 +/- 6.91%; PE: 102.48 +/- 4.78% vs. AdSMAD4 + PE: 118.64 +/- 3.28%). Furthermore expression of caspase 3 as well as bax/bcl2 ratio increased in SMAD4 overexpressing, PE-stimulated cardiomyocytes. In addition, the effects of SMAD4 overexpression on PE-induced hypertrophic growth were analyzed. Protein synthesis 36 h after AdSMAD4 infection was comparable to control cells, whereas the increase in protein synthesis stimulated by phyenylephrine was significantly reduced in SMAD4 overexpressing cells (134.28 +/- 10.02% vs. 100.57 +/- 8.86%). SMAD4 triggers the transition from hypertrophy to apoptosis in ventricular cardiomyocytes. Since SMADs are increased under several pathophysiological conditions in the heart, it can be assumed that it triggers apoptosis induction and therefore contributes to negative remodeling and heart failure progression.

Inhibition of extracellular signal-regulated kinase signaling to prevent cardiomyopathy caused by mutation in the gene encoding A-type lamins

Autosomal Emery-Dreifuss muscular dystrophy and related disorders with dilated cardiomyopathy and variable skeletal muscle involvement are caused by mutations in LMNA, which encodes A-type nuclear lamins. How alterations in A-type lamins, intermediate filament proteins of the nuclear envelope expressed in most differentiated somatic cells, cause cardiomyopathy is only poorly understood. We demonstrated previously abnormal activation of the extracellular signal-regulated kinase (ERK) branch of the mitogen-activated protein kinase (MAPK) signaling cascade in hearts of Lmna H222P 'knock in' mice, a model of autosomal Emery-Dreifuss muscular dystrophy. We therefore treated Lmna(H222P/H222P) mice that develop cardiomyopathy with PD98059, an inhibitor of ERK activation. Systemic treatment of Lmna(H222P/H222P) mice with PD98059 inhibited ERK phosphorylation and blocked the activation of downstream genes in heart. It also blocked increased expression of RNAs encoding natriuretic peptide precursors and proteins involved in sarcomere organization that occurred in placebo-treated mice. Histological analysis and echocardiography demonstrated that treatment with PD98059 delayed the development of left ventricular dilatation. PD98059-treated Lmna(H222P/H222P) mice had normal cardiac ejection fractions assessed by echocardiography when placebo-treated mice had a 30% decrease. These results emphasize the role of ERK activation in the development of cardiomyopathy caused by LMNA mutations. They further provide proof of principle for ERK inhibition as a therapeutic option to prevent or delay heart failure in humans with Emery-Dreifuss muscular dystrophy and related disorders caused by mutations in LMNA.

TGFbeta in Cancer

The transforming growth factor beta (TGFbeta) signaling pathway is a key player in metazoan biology, and its misregulation can result in tumor development. The regulatory cytokine TGFbeta exerts tumor-suppressive effects that cancer cells must elude for malignant evolution. Yet, paradoxically, TGFbeta also modulates processes such as cell invasion, immune regulation, and microenvironment modification that cancer cells may exploit to their advantage. Consequently, the output of a TGFbeta response is highly contextual throughout development, across different tissues, and also in cancer. The mechanistic basis and clinical relevance of TGFbeta's role in cancer is becoming increasingly clear, paving the way for a better understanding of the complexity and therapeutic potential of this pathway.

Transforming growth factor beta inhibition increases mortality and left ventricular dilatation after myocardial infarction

BACKGROUND

Transforming growth factor (TGF)-beta is a locally generated cytokine involved in healing processes and tissue fibrosis, all relevant for cardiac remodeling and the development of heart failure after myocardial infarction (MI). However, data regarding the function of TGF-beta after ischemic injury are inconclusive.

METHODS AND RESULTS

We tested the effect of TGF-beta inhibition by application of a blocking antibody in mice with MI. Starting 1 week before or 5 days after coronary artery ligation mice were treated with intraperitoneal injections of an anti-TGF-beta (5 mg/kg bodyweight 1D11, Genzyme) or control antibody. Mortality over 8 weeks was significantly higher in the groups treated with the anti-TGF-beta antibody. Both, pre or post MI treatments were associated with increased left ventricular dilatation after MI as determined by serial echocardiography. In anti-TGF-beta treated mice collagen production decreased and matrix-metalloproteinase expression increased. However, the expression of TGF pro-inflammatory cytokine TNF-alpha was not altered by the treatment. Anti-TGF-beta treatment before or after coronary artery ligation increases mortality and worsens left ventricular remodeling in mice with non-reperfused MI. The detrimental effects of TGF-beta inhibition may be mediated by alterations in extracellular matrix remodeling.

Transforming growth factor-beta-regulated miR-24 promotes skeletal muscle differentiation

MicroRNAs (miRNAs) have recently been proposed as a versatile class of molecules involved in regulation of a variety of biological processes. However, the role of miRNAs in TGF-beta-regulated biological processes is poorly addressed. In this study, we found that miR-24 was upregulated during myoblast differentiation and could be inhibited by TGF-beta1. Using both a reporter assay and Northern blot analysis, we showed that TGF-beta1 repressed miR-24 transcription which was dependent on the presence of Smad3 and a Smads binding site in the promoter region of miR-24. TGF-beta1 was unable to inhibit miR-24 expression in Smad3-deficient myoblasts, which exhibited accelerated myogenesis. Knockdown of miR-24 led to reduced expression of myogenic differentiation markers in C2C12 cells, while ectopic expression of miR-24 enhanced differentiation, and partially rescued inhibited myogenesis by TGF-beta1. This is the first study demonstrating a critical role for miRNAs in modulating TGF-beta-dependent inhibition of myogenesis, and provides a novel mechanism of the genetic regulation of TGF-beta signaling during skeletal muscle differentiation.