Molecular targets and regulators of cardiac hypertrophy

Wnt Signaling in Cardiac Remodeling and Heart Failure

Wnt signaling plays an essential role during development, but is also activated in diseases as diverse as neurodegeneration, osteoporosis, and cancer. Accumulating evidence demonstrates that Wnt signaling is also activated during cardiac remodeling and heart failure. In this chapter, we will provide a brief overview of Wnt signaling in all its complexity. Then we will discuss the evidence for its involvement in the development of cardiac hypertrophy, the wound healing after myocardial infarction (MI) and heart failure. Finally, we will provide an overview of the drugs that are available to target Wnt signaling at different levels of the signaling cascade and the results of these pharmacological interventions in cardiac disease.

The role of autophagy in angiotensin II-induced pathological cardiac hypertrophy

Pathological cardiac hypertrophy is associated with nearly all forms of heart failure. It develops in response to disorders such as coronary artery disease, hypertension and myocardial infarction. Angiotensin II (Ang II) has direct effects on the myocardium and promotes hypertension. Chronic elevation of Ang II can lead to pathological cardiac hypertrophy and cardiac failure. Autophagy is an important process in the pathogenesis of cardiovascular diseases. Under physiological conditions, autophagy is an essential homeostatic mechanism to maintain the global cardiac structure function by ridding damaged cells or unwanted macromolecules and organelles. Dysregulation of autophagy may play an important role in Ang II-induced cardiac hypertrophy although conflicting reports on the effects of Ang II on autophagy and cardiac hypertrophy exist. Some studies showed that autophagy activation attenuated Ang II-induced cardiac dysfunction. Others suggested that inhibition of the Ang II induced autophagy should be protective. The discrepancies may be due to different model systems and different signaling pathway involved. Ang II-induced cardiac hypertrophy may be alleviated through regulation of autophagy. This review focuses on Ang II to highlight the molecular targets and pathways identified in the prevention and treatment of Ang II-induced pathological cardiac hypertrophy by regulating autophagy.

(-)-Epicatechin induces physiological cardiac growth by activation of the PI3K/Akt pathway in mice

SCOPE

The flavanol (-)-epicatechin (Epi) has cardioprotective effects and improves physical capacity in normal mice. In addition, Epi increases nitric oxide (NO) production by activation of both PI3K/Akt or Ca²⁺ /CaMI/CaMKII (where Akt is protein kinase B; PI3K is phosphoinositide 3-kinase; CaMI is calmodulin; CaMKII is Ca²⁺ /calmodulin-dependent protein kinase II) signaling pathways, which have been associated with physiological and pathological cardiac hypertrophy, respectively. Notwithstanding all this information, few studies have been carried out that aimed to determine the potential beneficial effects that Epi may have in normal heart.

METHODS AND RESULTS

Mice were treated by oral gavage with the flavanol Epi. The treatment induced a significant increase in heart weight, size of the free walls, and size of the cardiac fibers. Also, no evidence of cardiac fibrosis was revealed. Furthermore, the phosphorylation level of PI3K/Akt/mTOR/p70S6K (where mTOR is mammalian target of rapamycin; p70S6K is ribosomal protein S6 kinase beta-1) proteins was significantly higher in the heart of Epi-treated animals. In contrast, a significantly decreased level of pathological cardiac hypertrophy markers atrial natriuretic peptide and brain natriuretic peptide was observed along with no modification in the level of β myosin heavy chain beta, calmodulin, and Ca²⁺ /calmodulin-dependent protein kinase II proteins. Hemodynamic parameters indicated an improvement in mechanical heart performance after Epi treatment. Interestingly, morphometric parameters were similar between treated and untreated mice after 4 wk without treatment.

CONCLUSION

These findings indicate that Epi treatment induced physiological cardiac growth in healthy mice by activation of the PI3K/Akt pathway.

Pleiotropic properties of ASK1

BACKGROUND

Apoptosis signal-regulating kinase 1 (ASK1), also known as mitogen-activated protein kinase kinase kinase 5 (MAP3K5), has the potential to induce cellular apoptosis under various physiological conditions. It has long been suggested that ASK1 is highly sensitive to oxidative stress and contributes substantially to apoptosis. However, recent studies have indicated that ASK1 has pleiotropic roles in living organisms through other mechanisms in addition to apoptosis.

SCOPE OF THE REVIEW

This review describes the physiological functions of ASK1 in living organisms, focusing on the regulatory mechanisms of ASK1 activity and its importance in the pathogenesis of various diseases. We also highlight recent works published within the past few years.

MAJOR CONCLUSIONS

ASK1 forms a high-molecular-mass complex within the cell, designated as the ASK1 signalosome. Soon after the discovery of ASK1, several regulatory components of the ASK1 signalosome have been revealed, including thioredoxin (Trx), tumor-necrosis factor α receptor-associated factors (TRAFs) and 14-3-3s. In parallel with the precise analyses unveiling the molecular basis of ASK1 regulation, the physiological or pathophysiological significance of ASK1 in diverse organs has been elucidated. In addition to the generation of global knockout mice or tissue-specific knockout mice, ASK1-specific inhibitors have illuminated the biological roles of ASK1.

GENERAL SIGNIFICANCE

The multi-faceted features of the function of ASK1 have been discovered over the past two decades, revealing that ASK1 is a crucial molecule for maintaining cellular homeostasis, especially under conditions of stress. Based on the results that ASK1 deficiency provides beneficial effects for several diseases, modulating ASK1 activity is a promising method to ameliorate a subset of diseases.

The Importance of Biological Sex and Estrogen in Rodent Models of Cardiovascular Health and Disease

Nearly one-third of deaths in the United States are caused by cardiovascular disease (CVD) each year. In the past, CVD was thought to mainly affect men, leading to the exclusion of women and female animals from clinical studies and preclinical research. In light of sexual dimorphisms in CVD, a need exists to examine baseline cardiac differences in humans and the animals used to model CVD. In humans, sex differences are apparent at every level of cardiovascular physiology from action potential duration and mitochondrial energetics to cardiac myocyte and whole-heart contractile function. Biological sex is an important modifier of the development of CVD with younger women generally being protected, but this cardioprotection is lost later in life, suggesting a role for estrogen. Although endogenous estrogen is most likely a mediator of the observed functional differences in both health and disease, the signaling mechanisms involved are complex and are not yet fully understood. To investigate how sex modulates CVD development, animal models are essential tools and should be useful in the development of therapeutics. This review will focus on describing the cardiovascular sexual dimorphisms that exist both physiologically and in common animal models of CVD.

NMNAT3 is involved in the protective effect of SIRT3 in Ang II-induced cardiac hypertrophy

Pathological cardiac hypertrophy is a maladaptive response in a variety of organic heart disease (OHD), which is characterized by mitochondrial dysfunction that results from disturbed energy metabolism. SIRT3, a mitochondria-localized sirtuin, regulates global mitochondrial lysine acetylation and preserves mitochondrial function. However, the mechanisms by which SIRT3 regulates cardiac hypertrophy remains to be further elucidated. In this study, we firstly demonstrated that expression of SIRT3 was decreased in Angiotension II (Ang II)-treated cardiomyocytes and in hearts of Ang II-induced cardiac hypertrophic mice. In addition, SIRT3 overexpression protected myocytes from hypertrophy, whereas SIRT3 silencing exacerbated Ang II-induced cardiomyocyte hypertrophy. In particular, SIRT3-KO mice exhibited significant cardiac hypertrophy. Mechanistically, we identified NMNAT3 (nicotinamide mononucleotide adenylyltransferase 3), the rate-limiting enzyme for mitochondrial NAD biosynthesis, as a new target and binding partner of SIRT3. Specifically, SIRT3 physically interacts with and deacetylates NMNAT3, thereby enhancing the enzyme activity of NMNAT3 and contributing to SIRT3-mediated anti-hypertrophic effects. Moreover, NMNAT3 regulates the activity of SIRT3 via synthesis of mitochondria NAD. Taken together, these findings provide mechanistic insights into the negative regulatory role of SIRT3 in cardiac hypertrophy.

Danhong injection attenuates isoproterenol-induced cardiac hypertrophy by regulating p38 and NF-κb pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Danhong injection (DHI), derived from Rhizoma Salviae Miltiorrhizae (Salvia miltiorrhiza Bge., Labiatae, Danshen in Chinese) and Flos Carthami (Carthamus tinctorius L., Compositae, Salvia militiorrhiza Bunge), is an extensively-used Chinese material standardized clinical product for treatment of cardiovascular diseases.

AIM OF THE STUDY

Cardiac hypertrophy (CH) is an adaptive response of cardiomyocytes. Long-lasting cardiac hypertrophy results in the loss of compensation by cardiomyocytes which could ultimately develop into heart failure. In the present study, we aimed to investigate the effect and exact mechanisms of DHI on isoproterenol (ISO)-induced CH.

MATERIALS AND METHODS

H9c2 cells and male Wistar rats were stimulated by ISO in the present study to establish CH models in vitro and in vivo. CCk-8 assay, Western blot, real time-polymerase chain reaction (RT-PCR), electrophoretic mobility shift assay (EMSA) and Echocardiography were used in the present study.

RESULTS

DHI significantly attenuated ISO-induced CH of H9c2 cells (p<0.01). DHI decreased ISO-induced atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) elevation both at the mRNA and protein levels (p<0.05 and p<0.01, respectively). Western blot showed that DHI down-regulated the phosphorylation of p38. Furthermore, we found that DHI inhibited the nuclear translocation and activation of NF-κb. Echocardiography from ISO-induced CH rats showed that DHI significantly decreased left ventricle (LV) mass, the thickness of the LV end-systolic posterior wall (LVPWs), and the LV end-diastolic posterior wall (LVPWd) elevated by ISO (p<0.01 and p<0.05, respectively).

CONCLUSION

These data demonstrate that DHI might exert anti-cardiac hypertrophic effects by regulating p38 and NF-κb pathway.

miR-218 Involvement in Cardiomyocyte Hypertrophy Is Likely through Targeting REST

MicroRNAs (miRNAs) have been identified as key players in cardiomyocyte hypertrophy, which is associated with significant risks of heart failure. However, many microRNAs are still not recognized for their functions in pathophysiological processes. In this study, we evaluated effects of miR-218 in cardiomyocyte hypertrophy using both in vitro and in vivo models. We found that miR-218 was evidently downregulated in a transverse aortic constriction (TAC) mouse model. Overexpression of miR-218 is sufficient to reduce hypertrophy, whereas the suppression of miR-218 aggravates hypertrophy in primary cardiomyocytes induced by isoprenaline (ISO). In addition, we identified RE1-silencing transcription factor (REST) as a novel target of miR-218; it negatively regulated the expression of REST in hypertrophic cardiomyocytes and the TAC model. These results showed that miR-218 plays a crucial role in cardiomyocyte hypertrophy, likely via targeting REST, suggesting a potential candidate target for interfering hypertrophy.

Pivotal Role of Regulator of G-protein Signaling 12 in Pathological Cardiac Hypertrophy

Cardiac hypertrophy is a major predictor of heart failure and is regulated by diverse signaling pathways. As a typical multi-domain member of the regulator of G-protein signaling (RGS) family, RGS12 plays a regulatory role in various signaling pathways. However, the precise effect of RGS12 on cardiac hypertrophy remains largely unknown. In this study, we observed increased expression of RGS12 in the development of pathological cardiac hypertrophy and heart failure. We then generated genetically engineered mice and neonatal rat cardiomyocytes to investigate the effects of RGS12 during this pathological process. Four weeks after aortic banding, RGS12-deficient hearts showed decreased cardiomyocyte cross area (374.7±43.2 μm(2) versus 487.1±47.9 μm(2) in controls; P<0.05) with preserved fractional shortening (43.0±3.4% versus 28.4±2.2% in controls; P<0.05), whereas RGS12-overexpressing hearts exhibited increased cardiomyocyte cross area (582.4±46.7 μm(2) versus 474.8±40.0 μm(2) in controls; P<0.05) and reduced fractional shortening (20.8±4.1% versus 28.6±3.2% in controls; P<0.05). RGS12 also contributed to angiotensin II-induced hypertrophy in isolated cardiomyocytes. Mechanistically, our data indicated that the activation of MEK1/2-ERK1/2 signaling may be responsible for the prohypertrophic action of RGS12. In addition, the requirement of the MEK1/2-ERK1/2 signaling for RGS12-mediated cardiac hypertrophy was confirmed in rescue experiments using the MEK1/2-specific inhibitor U0126. In conclusion, our findings provide a novel diagnostic and therapeutic target for pathological cardiac hypertrophy and heart failure.

Wnt Signaling in Cardiac Disease

Wnt signaling encompasses multiple and complex signaling cascades and is involved in many developmental processes such as tissue patterning, cell fate specification, and control of cell division. Consequently, accurate regulation of signaling activities is essential for proper embryonic development. Wnt signaling is mostly silent in the healthy adult organs but a reactivation of Wnt signaling is generally observed under pathological conditions. This has generated increasing interest in this pathway from a therapeutic point of view. In this review article, the involvement of Wnt signaling in cardiovascular development will be outlined, followed by its implication in myocardial infarct healing, cardiac hypertrophy, heart failure, arrhythmias, and atherosclerosis. The initial experiments not always offer consensus on the effects of activation or inactivation of the pathway, which may be attributed to (i) the type of cardiac disease, (ii) timing of the intervention, and (iii) type of cells that are targeted. Therefore, more research is needed to determine the exact implication of Wnt signaling in the conditions mentioned above to exploit it as a powerful therapeutic target.

Abundant and Altered Expression of PIWI-Interacting RNAs during Cardiac Hypertrophy

BACKGROUND

The discovery of PIWI-interacting RNAs (piRNAs) has fundamentally changed our understanding of post transcriptional regulation of transposons and other genes. Unlike miRNA and siRNA, the piRNAs are the most abundant but least studied RNA species in mammals. Although the expression of PIWI proteins and piRNAs has long been regarded as germline specific, increasing evidences suggest the expression of piRNAs in somatic cells.

METHODS

In this study, the small RNA sequencing executed during induction of cardiac hypertrophy in both in vivo and in vitro conditions were annotated for the expression of piRNAs. The expression of piRNAs was validated by qPCR and RNA immunoprecipitation. In addition, the presence of piRNAs in circulation of myocardial infarction patients was studied by qPCR.

RESULTS

We identified an abundant and altered expression of piRNAs during cardiac hypertrophy. The differentially expressed piRNAs was validated by qPCR and RNA immunoprecipitation. The significantly and differentially expressed piRNAs were predicted to target different retrotransposons and mRNAs in the rat genome. The detection of specific piRNA in serum of myocardial infarction patients suggests the potential of piRNA for diagnosis.

CONCLUSION

Overall this study is the first to provide a whole-genome analysis of the large repertoire of piRNAs in the cardiac system and this would pave a new path to understanding the molecular aetiology of piRNA and retrotransposons in the physiology and pathology of the cardiac system.

Mechanism of Taiwan Mingjian Oolong Tea to Inhibit Isoproterenol-Induced Hypertrophy and Apoptosis in Cardiomyoblasts

This study investigates the cardio-protective effect of Nos. 1 and 5 extracts from Taiwan Mingjian Oolong Tea on H9c2 cardiomyoblast cells treated with isoproterenol (ISO). Treatment with Nos. 1 and 5 extracts increased cell viability and blocked apoptosis in ISO exposed H9c2 cells. Moreover, Nos. 1 and 5 extracts blocked hypertrophy markers like G[Formula: see text]s, calcineurin, NFATc3, and BNP, thereby increasing cell proliferation markers -PI3K and AKT in a dose dependent manner. In contrast, apoptotic proteins, such as caspase-3 and cytochrome c were decreased in H9c2 cells treated with Nos. 1 and 5 extracts. We confirmed that the protective effect of No. 1 extract was partially mediated through the expression of ERK and p38, however, the No. 5 extract showed a protective effect via the ERK, JNK, and p38 pathways. This evidence provides new insights into the pharmacological role and therapeutic mechanism of Taiwan Mingjian Oolong Tea in heart diseases.

Tripartite motif 32 prevents pathological cardiac hypertrophy

This study presents the first evidence that TRIM32 protects against pathological cardiac hypertrophy by suppressing Akt-dependent signalling pathways. Therefore TRIM32 might be a potential therapeutic strategy for the prevention and treatment of cardiac hypertrophy and heart failure.

TRIM32 (tripartite motif 32) is widely accepted to be an E3 ligase that interacts with and eventually ubiquitylates multiple substrates. TRIM32 mutants have been associated with LGMD-2H (limb girdle muscular dystrophy 2H). However, whether TRIM32 is involved in cardiac hypertrophy induced by biomechanical stresses and neurohumoral mediators remains unclear. We generated mice and isolated NRCMs (neonatal rat cardiomyocytes) that overexpressed or were deficient in TRIM32 to investigate the effect of TRIM32 on AB (aortic banding) or AngII (angiotensin II)-mediated cardiac hypertrophy. Echocardiography and both pathological and molecular analyses were used to determine the extent of cardiac hypertrophy and subsequent fibrosis. Our results showed that overexpression of TRIM32 in the heart significantly alleviated the hypertrophic response induced by pressure overload, whereas TRIM32 deficiency dramatically aggravated pathological cardiac remodelling. Similar results were also found in cultured NRCMs incubated with AngII. Mechanistically, the present study suggests that TRIM32 exerts cardioprotective action by interruption of Akt- but not MAPK (mitogen-dependent protein kinase)-dependent signalling pathways. Additionally, inactivation of Akt by LY294002 offset the exacerbated hypertrophic response induced by AB in TRIM32-deficient mice. In conclusion, the present study indicates that TRIM32 plays a protective role in AB-induced pathological cardiac remodelling by blocking Akt-dependent signalling. Therefore TRIM32 could be a novel therapeutic target for the prevention of cardiac hypertrophy and heart failure.

Adiponectin downregulation is associated with volume overload-induced myocyte dysfunction in rats

AIM

Adiponectin has been reported to exert protective effects during pathological ventricular remodeling, but the role of adiponectin in volume overload-induced heart failure remains unclear. In this study we investigated the effect of adiponectin on cardiac myocyte contractile dysfunction following volume overload in rats.

METHODS

Volume overload was surgically induced in rats by infrarenal aorta-vena cava fistula. The rats were intravenously administered adenoviral adiponectin at 2-, 6- and 9-weeks following fistula. The protein expression of adiponectin, adiponectin receptors (AdipoR1/R2 and T-cadherin) and AMPK activity were measured using Western blot analyses. Isolated ventricular myocytes were prepared at 12 weeks post-fistula to examine the contractile performance of myocytes and intracellular Ca(2+) transient.

RESULTS

A-V fistula resulted in significant reductions in serum and myocardial adiponectin levels, myocardial adiponectin receptor (AdipoR1/R2 and T-cadherin) levels, as well as myocardial AMPK activity. Consistent with these changes, the isolated myocytes exhibited significant depression in cell shortening and intracellular Ca(2+) transient. Administration of adenoviral adiponectin significantly increased serum adiponectin levels and prevented myocyte contractile dysfunction in fistula rats. Furthermore, pretreatment of isolated myocytes with recombinant adiponectin (2.5 μg/mL) significantly improved their contractile performance in fistula rats, but had no effects in control or adenoviral adiponectin-administered rats.

CONCLUSION

These results demonstrate a positive correlation between adiponectin downregulation and volume overload-induced ventricular remodeling. Adiponectin plays a protective role in volume overload-induced heart failure.

Molecular Mechanisms of Cardioprotective Actions of Tanshinones

Tanshinones are lipophilic compounds derived fromSalvia miltiorrhiza(Danshen) that has been widely used to treat coronary heart diseases in China. The cardioprotective actions of tanshinones have been extensively studied in various models of myocardial infarction, cardiac ischemia reperfusion injury, cardiac hypertrophy, atherosclerosis, hypoxia, and cardiomyopathy. This review outlines the recent development in understanding the molecular mechanisms and signaling pathways involved in the cardioprotective actions of tanshinones, in particular on mitochondrial apoptosis, calcium, nitric oxide, ROS, TNF-α, PKC, PI3K/Akt, IKK/NF-κB, and TGF-β1/Smad mechanisms, which highlights the potential of these compounds as therapeutic agents for treating cardiovascular diseases.

Vitamin D and Cardiac Differentiation

Calcitriol (1,25-dihydroxycholecalciferol or 1,25-D3) is the hormonally active metabolite of vitamin D. Experimental studies of vitamin D receptors and 1,25-D3 establish calcitriol to be a critical regulator of the structure and function of the heart. Clinical studies link vitamin D deficiency with cardiovascular disease (CVD). Emerging evidence demonstrates that calcitriol is highly involved in CVD-related signaling pathways, particularly the Wnt signaling pathway. Addition of 1,25-D3 to cardiomyocyte cells and examination of its effects on cardiomyocytes and mainly Wnt11 signaling allowed the specific characterization of the role of calcitriol in cardiac differentiation. 1,25-D3 is demonstrated to: (i) inhibit cell proliferation without promoting apoptosis; (ii) decrease expression of genes related to the regulation of the cell cycle; (iii) promote formation of cardiomyotubes; (iv) induce expression of casein kinase-1-α1, a negative regulator of the canonical Wnt signaling pathway; and (v) increase expression of noncanonical Wnt11, which has been recognized to induce cardiac differentiation during embryonic development and in adult cells. Thus, it appears that vitamin D promotes cardiac differentiation through negative modulation of the canonical Wnt signaling pathway and upregulation of noncanonical Wnt11 expression. Future work to elucidate the role(s) of vitamin D in cardiovascular disorders will hopefully lead to improvement and potentially prevention of CVD, including abnormal cardiac differentiation in settings such as postinfarction cardiac remodeling.

Exercise preconditioning prevents MCT-induced right ventricle remodeling through the regulation of TNF superfamily cytokines

BACKGROUND

Exercise training has been recognized as a non-pharmacological therapeutic approach in several chronic diseases; however it remains to be tested if exercise preconditioning can positively interfere with the natural history of pulmonary arterial hypertension (PAH). This is important since the majority of these patients are diagnosed at advanced stages of the disease, when right ventricle (RV) impairment is already present.

OBJECTIVES

In the current study, we evaluated the preventive effect of exercise preconditioning on RV failure secondary to PAH, with a focus on the signaling pathways modulated by pro-inflammatory cytokines from TNF superfamily.

METHODS

We analyzed the RV muscle from adult male Wistar rats exposed to a 4-week treadmill exercise training or sedentary regime, prior to the administration of monocrotaline (MCT) to induce PAH or with saline solution (controls).

RESULTS

Data indicate that exercise preconditioning prevented cardiac hypertrophy and RV diastolic dysfunction. At a molecular level, exercise modulated the TWEAK/NF-κB signaling axis and prevented the shift in MHC isoforms towards an increased expression of beta-MHC. Exercise preconditioning also prevented the increase of atrogin-1 expression, and induced a shift of MMP activity from MMP-9 to MMP-2 activity.

CONCLUSIONS

Altogether, data support exercise as a preventive strategy for the management of PAH, which is of particular relevance for the familial form of PAH that is manifested by greater severity or earlier onset.

Peroxisome proliferator-activated receptor gamma coactivator 1 alpha protects cardiomyocytes from hypertrophy by suppressing calcineurin-nuclear factor of activated T cells c4 signaling pathway

Peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) is a crucial coregulator interacting with multiple transcriptional factors in the regulation of cardiac hypertrophy. The present study revealed that PGC-1α protected cardiomyocytes from hypertrophy by suppressing calcineurin-nuclear factor of activated T cells c4 (NFATc4) signaling pathway. Overexpression of PGC-1α by adenovirus infection prevented the increased protein and messenger RNA expression of NFATc4 in phenylephrine (PE)-treated hypertrophic cardiomyocytes, whereas knockdown of PGC-1α by RNA silencing augmented the expression of NFATc4. An interaction between PGC-1α and NFATc4 was observed in both the cytoplasm and nucleus of neonatal rat cardiomyocytes. Adenovirus PGC-1α prevented the nuclear import of NFATc4 and increased its phosphorylation level of NFATc4, probably through repressing the expression and activity of calcineurin and interfering with the interaction between calcineurin and NFATc4. On the contrary, PGC-1α silencing aggravated PE-induced calcineurin activation, NFATc4 dephosphorylation, and nuclear translocation. Moreover, the binding activity and transcription activity of NFATc4 to DNA promoter of brain natriuretic peptide were abrogated by PGC-1α overexpression but were enhanced by PGC-1α knockdown. The effect of PGC-1α on suppressing the calcinuerin-NFATc4 signaling pathway might at least partially contribute to the protective effect of PGC-1α on cardiomyocyte hypertrophy. These findings provide novel insights into the role of PGC-1α in regulation of cardiac hypertrophy.

The Human Myotrophin Variant Attenuates MicroRNA-Let-7 Binding Ability but Not Risk of Left Ventricular Hypertrophy in Human Essential Hypertension

Myotrophin, known as a myocardial hypertrophy-inducing factor, is responsible for the initiation of cardiac hypertrophy that transits to heart failure. MicroRNAs are small noncoding RNAs that down-regulate posttranscriptional expression of target molecules. We investigated the role of variants of the microRNA-binding site in myotrophin in affecting its expression and any association with cardiac hypertrophy. Bioinformatics demonstrated that variant rs17168525 was identified to be located in the let-7/miR-98-binding site of myotrophin. We further experimentally test to effects of the identified variant on myotrophin translation using luciferase reporter assay and Western blotting. We found that the C allele of rs17168525 suppressed myotrophin translation by facilitating let-7c binding, but not the T allele. Let-7c overexpression caused a significant decrease in the level of myotrophin protein. Next, we investigated the association of the variant with cardiac hypertrophy in 1614 hypertensive patients, including 552 with left ventricular hypertrophy and 1062 without left ventricular hypertrophy, as well as 591 healthy control subjects from a Han Chinese population. No significant association between the variant rs17168525 and left ventricular hypertrophy in hypertensive patients in a Han Chinese population (P>0.05). In conclusion, our experimental results provide evidence that the T allele of rs17168525 in the 3'-UTR of myotrophin might influence the level of myotrophin protein by interfering with let-7/miR-98 binding.

Targeting osteopontin, the silent partner of Na+/H+ exchanger isoform 1 in cardiac remodeling

Cardiac hypertrophy (CH), characterized by the enlargement of cardiomyocytes, fibrosis and apoptosis, contributes to cardiac remodeling, which if left unresolved results in heart failure. Understanding the signaling pathways underlying CH is necessary to identify potential therapeutic targets. The Na(+) /H(+) -exchanger isoform I (NHE1), a ubiquitously expressed glycoprotein and cardiac specific isoform, regulates intracellular pH. Recent studies have demonstrated that enhanced expression/activity of NHE1 contributes to cardiac remodeling and CH. Inhibition of NHE1 in both in vitro and in vivo models have suggested that inhibition of NHE1 protects against hypertrophy. However, clinical trials using NHE1 inhibitors have proven to be unsuccessful, suggesting that additional factors maybe contributing to cardiac remodeling. Recent studies have indicated that the upregulation of NHE1 is associated with enhanced levels of osteopontin (OPN) in the setting of CH. OPN has been demonstrated to be upregulated in left ventricular hypertrophy, dilated cardiomyopathy and in diabetic cardiomyopathy. The cellular interplay between OPN and NHE1 in the setting of CH remains unknown. This review focuses on the role of NHE1 and OPN in cardiac remodeling and emphasizes the signaling pathways implicating OPN in the NHE1-induced hypertrophic response.

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.

Relevance of SGK1 in structural, functional and molecular alterations produced by aldosterone in heart

Aldosterone regulates sodium (Na+) and potassium (K+) transports in epithelial cells. Besides, aldosterone participates in cardiac alterations associated with hypertension, heart failure, diabetes, and other pathological alterations. One of the main cardiac alterations induced by aldosterone is cardiac hypertrophy in which different mechanisms are involved such as increased cardiomyocyte, calcium concentration, oxidative stress, and inflammatory and fibrotic mediators stimulation. Many epidemiological studies have demonstrated that left ventricular hypertrophy is associated with significantly increased risk of heart failure and malignant arrhythmias. SGK1 is a member of the serine/threonine kinase gene family that plays an important role in the absorption of Na+ and water through the Na+ channel in the apical membrane of tubular epithelial cells. SGK1 has been related to fibrotic mediator increase such as connective tissue growth factor (CTGF) and transforming growth factor-β (TGF-β) as well as inflammatory [tumor necrosis factor-α (TNF-α) and interleukin (IL)-1β] and oxidative (NADPH oxidase) species. It has been shown that aldosterone induces SGK1 gene expression not only in kidneys but also in the heart. Supporting the central role of SGK1 in cardiac alterations induced by aldosterone, treatment with the mineralocorticoid antagonist spironolactone is able to reduce the gene expression of SGK1 in aldosterone-treated rats. Taken together, data suggest the involvement of SGK1 in a complex intracellular signaling, involving fibrotic, inflammatory, and oxidative pathways, which lead to cardiac hypertrophy and fibrosis induced by aldosterone.

Total glycosides of Ranunculus japonius prevent hypertrophy in cardiomyocytes via alleviating chronic Ca(2+) overload

OBJECTIVE

To evaluate the in vitro anti-hypertrophic effect of total Glycosides of Ranunculus Japonius (TGRJ).

METHODS

Neonatal rat cardiomyocytes were cultured and hypertrophy was induced by administrating isoproterenol (ISO, 10 µmol/L) or angiotensin 2 (Ang 2, 1 µmol/L) for 48 hours. In the treatment groups, cells were pretreated with TGRJ (0.3 g/L) for 30 minutes prior to hypertrophic stimuli. The anti-hypertrophic effects of TGRJ were examined by measuring cell size, total protein content, and protein synthesis. Intracellular free Ca(2+) concentration ([Ca(2+)]i) was evaluated using fluorescence dye Fura-2/AM. Sacroplasmic/endoplasmic reticulum Ca(2+) ATPase 2a (SERCA2a), atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP), and beta-myosin heavy chain (β-MHC) protein expression levels were measured by Western blotting . SERCA2a activity was assayed by p-nitrophenal phosphate disodium salt hexahydrate method.

RESULTS

Increased cell size, total protein content, and protein synthesis following ISO or Ang 2 stimulation were significantly inhibited by pretreatment with TGRJ (all P<0.05). This anti-hypertrophic effect of TGRJ was confirmed by its suppressing effect on elevated expression of the three hypertrophic related genetic markers, ANP, BNP, and β-MHC. In addition, TGRJ inhibited ISO or Ang 2 induced up-regulation of [Ca(2+)]i under chronic but not acute conditions. And ISO or Ang 2 induced down-regulation of SERCA2a expression and activity was also effectively rectified by TGRJ pretreatment.

CONCLUSIONS

The results of present study suggested that TGRJ could prevent ISO or Ang 2 induced cardiac hypertrophy through improving chronic [Ca(2+)]i disorder, might via normalizing SERCA2a expression and activity.

Interplay between the E2F pathway and β-adrenergic signaling in the pathological hypertrophic response of myocardium

The E2F/Pocket protein (Rb) pathway regulates cell growth, differentiation, and death by modulating gene expression. We previously examined this pathway in the myocardium via manipulation of the unique E2F repressor, E2F6, which is believed to repress gene activity independently of Rb. Mice with targeted expression of E2F6 in postnatal myocardium developed dilated cardiomyopathy (DCM) without hypertrophic growth. We assessed the mechanisms of the apparent failure of compensatory hypertrophic growth as well as their response to the β-adrenergic agonist isoproterenol. As early as 2 weeks, E2F6 transgenic (Tg) mice present with dilated thinner left ventricles and significantly reduced ejection fraction and fractional shortening which persists at 6 weeks of age, but with no apparent increase in left ventricle weight: body weight (LVW:BW). E2F6-Tg mice treated with isoproterenol (6.1 mg/kg/day) show double the increase in LVW:BW than their Wt counterparts (32% vs 16%, p-value: 0.007). Western blot analysis revealed the activation of the adrenergic pathway in Tg heart tissue under basal conditions with ~2-fold increase in the level of β2-adrenergic receptors (p-value: 8.9E-05), protein kinase A catalytic subunit (PKA-C) (p-value: 0.0176), activated c-Src tyrosine-protein kinase (p-value: 0.0002), extracellular receptor kinase 2 (ERK2) (p-value: 0.0005), and induction of the anti-apoptotic protein Bcl2 (p-value 0. 0.00001). In contrast, a ~60% decrease in the cardiac growth regulator: AKT1 (p-value 0.0001) and a ~four fold increase in cyclic AMP dependent phosphodiesterase 4D (PDE4D), the negative regulator of PKA activity, were evident in the myocardium of E2F6-Tg mice. The expression of E2F3 was down-regulated by E2F6, but was restored by isoproterenol. Further, Rb expression was down-regulated in Tg mice in response to isoproterenol implying a net activation of the E2F pathway. Thus the unique regulation of E2F activity by E2F6 renders the myocardium hypersensitive to adrenergic stimulus resulting in robust hypertrophic growth. These data reveal a novel interplay between the E2F pathway, β2-adrenergic/PKA/PDE4D, and ERK/c-Src axis in fine tuning the pathological hypertrophic growth response. E2F6 deregulates E2F3 such that pro-hypertrophic growth and survival are enhanced via β2-adrenergic signaling however this response is outweighed by the induction of anti-hypertrophic signals so that left ventricle dilation proceeds without any increase in muscle mass.

Pik3ip1 modulates cardiac hypertrophy by inhibiting PI3K pathway

Cardiac hypertrophy is an adaptive response to various physiological and pathological stimuli. Phosphoinositide-3 kinase (PI3K) is a highly conserved lipid kinase involved in physiological cardiac hypertrophy (PHH). PI3K interacting protein1 (Pik3ip1) shares homology with the p85 regulatory subunit of PI3K and is known to interact with the p110 catalytic subunit of PI3K, leading to attenuation of PI3K activity in liver and immune cells. However, the role of Pik3ip1 in the heart remains unknown. In the present study, the effects of Pik3ip1 on cardiac hypertrophy were examined. We found that the expression level of Pik3ip1 was markedly higher in cardiomyocytes than in fibroblasts. The interaction of Pik3ip1 with the p110a subunit of PI3K in the heart was identified by immunoprecipitation using neonatal rat cardiomyocytes (NRCM). Approximately 35% knockdown of Pik3ip1 was sufficient to induce myocardial hypertrophy. Pik3ip1 deficiency was shown to lead to activation of PI3K/protein kinase B (AKT)/ mammalian target of rapamycin (mTOR) signaling pathway, increasing protein synthesis and cell size. However, adenovirus-mediated overexpression of Pik3ip1 attenuated PI3K-mediated cardiac hypertrophy. Pik3ip1 was upregulated by PHH due to swimming training, but not by pathological cardiac hypertrophy (PAH) due to pressure-overload, suggesting that Pik3ip1 plays a compensatory negative role for PHH. Collectively, our results elucidate the mechanisms for the roles of Pik3ip1 in PI3K/AKT signaling pathway.

Modulation of cellular signaling by herpesvirus-encoded G protein-coupled receptors

Human herpesviruses (HHVs) are widespread infectious pathogens that have been associated with proliferative and inflammatory diseases. During viral evolution, HHVs have pirated genes encoding viral G protein-coupled receptors (vGPCRs), which are expressed on infected host cells. These vGPCRs show highest homology to human chemokine receptors, which play a key role in the immune system. Importantly, vGPCRs have acquired unique properties such as constitutive activity and the ability to bind a broad range of human chemokines. This allows vGPCRs to hijack human proteins and modulate cellular signaling for the benefit of the virus, ultimately resulting in immune evasion and viral dissemination to establish a widespread and lifelong infection. Knowledge on the mechanisms by which herpesviruses reprogram cellular signaling might provide insight in the contribution of vGPCRs to viral survival and herpesvirus-associated pathologies.

Cathepsin B deficiency attenuates cardiac remodeling in response to pressure overload via TNF-α/ASK1/JNK pathway

Cathepsin B (CTSB), a member of the lysosomal cathepsin family that is expressed in both murine and human hearts, was previously shown to participate in apoptosis, autophagy, and the progression of certain types of cancers. Recently, CTSB has been linked to myocardial infarction. Given that cathepsin L, another member of the lysosomal cathepsin family, ameliorates pathological cardiac hypertrophy, we hypothesized that CTSB plays a role in pressure overload-induced cardiac remodeling. Here we report that CTSB was upregulated in cardiomyocytes in response to hypertrophic stimuli both in vivo and in vitro. Moreover, knockout of CTSB attenuated pressure overload-induced cardiac hypertrophy, fibrosis, dysfunction, and apoptosis. Furthermore, the aortic banding-induced activation of TNF-α, apoptosis signal-regulating kinase 1 (ASK1), c-Jun NH2-terminal kinases (JNK), c-Jun, and release of cytochrome c was blunted by CTSB deficiency, which was further confirmed in in vitro studies induced by angiotensin II. In cardiomyocytes pretreatment with SP600125, a JNK inhibitor, suppressed the cardiomyocytes hypertrophy by inhibiting the ASK1/JNK pathway. Altogether, these data indicate that the CTSB protein functions as a necessary modulator of hypertrophic response by regulating TNF-α/ASK1/JNK signaling pathway involved in cardiac remodeling.

Variants in miRNA regulating cardiac growth are not a common cause of hypertrophic cardiomyopathy

OBJECTIVES

A substantial proportion of patients with hypertrophic cardiomyopathy (HCM) do not have causative mutations in the genes for heart sarcomere. The purpose of this study was to evaluate the association between microRNA (miRNA) sequence variants and HCM.

METHODS

We performed genetic testing on 56 HCM patients who had previously been found to be negative for mutations in the 4 major genes for sarcomeric proteins. The coding and adjacent regions (120-220 nt) of selected miRNAs were analyzed for the presence of sequence variants. The testing was based on PCR amplification of DNA-encoding miRNAs and subsequent denaturing capillary electrophoresis.

RESULTS

A total of 3 different variants were detected in the 11 selected miRNAs. These included polymorphisms rs45489294 in miRNA 208b, rs13136737 in miRNA 367 and rs9989532 in miRNA 1-2. In the patient group, the most frequent polymorphism was in miRNA 208b (10 times) followed by miRNA 367 (7 times). Both polymorphisms were found to occur with similar frequencies in the group of healthy controls. The remaining detected variant was not present in the control group, but was not connected with the HCM phenotype in the children of the probands.

CONCLUSION

Sequence variants in miRNAs of patients with HCM are not frequent and the contribution of these variants to the development of this disease was not demonstrated.

1,25-Vitamin D3 promotes cardiac differentiation through modulation of the WNT signaling pathway

Cardiovascular disease (CVD) remains the leading cause of death worldwide. Low levels of vitamin D are associated with high risk of myocardial infarction, even after controlling for factors associated with coronary artery disease. A growing body of evidence indicates that vitamin D plays an important role in CVD-related signaling pathways. However, little is known about the molecular mechanism by which vitamin D modulates heart development. The WNT signaling pathway plays a pivotal role in tissue development by controlling stem cell renewal, lineage selection and, even more importantly, heart development. In this study, we examined the role of 1,25-D3 (the active form of vitamin D) on cardiomyocyte proliferation, apoptosis, cell phenotype, cell cycle progression and differentiation into cardiomyotubes. We determined that the addition of 1,25-D3 to cardiomyocytes cells: i) inhibits cell proliferation without promoting apoptosis; ii) decreases expression of genes related to the regulation of the cell cycle; iii) promotes formation of cardiomyotubes; iv) induces the expression of casein kinase-1-α1, a negative regulator of the canonical WNT signaling pathway; and v) increases the expression of the noncanonical WNT11, which it has been demonstrated to induce cardiac differentiation during embryonic development and in adult cells. In conclusion, we postulate that vitamin D promotes cardiac differentiation through a negative modulation of the canonical WNT signaling pathway and by upregulating the expression of WNT11. These results indicate that vitamin D repletion to prevent and/or improve cardiovascular disorders that are linked with abnormal cardiac differentiation, such as post infarction cardiac remodeling, deserve further study.

Could interferon-gamma be a therapeutic target for treating heart failure?

The cytokine interferon-gamma (IFN-γ) is the only known member of the type II family of interferons, and as such, binds to its own distinct receptor. It is important in host defense against infection, as well as adaptive immune responses. While a wide array of cytokines are known to be involved in adverse remodeling of the heart and the progression to heart failure, the role of IFN-γ is unclear. Recent evidence from clinical studies, animal models of myocarditis and hypertension, as well as isolated cell studies, provide conflicting data as to whether IFN-γ is pathological or protective in the heart. Thus, it is important to highlight these discrepant findings so that areas of future investigation can be identified to more clearly determine the precise role of IFN-γ in the heart. Accordingly, this review will (1) discuss the source of IFN-γ in the diseased heart; (2) summarize the data from animal studies; (3) discuss the effects of IFN-γ on isolated cardiac fibroblasts and cardiomyocytes; (4) identify signaling mechanisms that may be invoked by IFN-γ in the heart; and (5) present the clinical evidence supporting a role for IFN-γ in heart failure.

Oxidation-induced conformational changes in calcineurin determined by covalent labeling and tandem mass spectrometry

The Ca²⁺/calmodulin activated phosphatase, calcineurin, is inactivated by H₂O₂ or superoxide-induced oxidation, both in vivo and in vitro. However, the potential for global and/or local conformation changes occurring within calcineurin as a function of oxidative modification, that may play a role in the inactivation process, has not been examined. Here, the susceptibility of calcineurin methionine residues toward H₂O₂-induced oxidation were determined using a multienzyme digestion strategy coupled with capillary HPLC–electrospray ionization mass spectrometry and tandem mass spectrometry analysis. Then, regions within the protein complex that underwent significant conformational perturbation upon oxidative modification were identified by monitoring changes in the modification rates of accessible lysine residues between native and oxidized forms of calcineurin, using an amine-specific covalent labeling reagent, S,S′-dimethylthiobutanoylhydroxysuccinimide ester (DMBNHS), and tandem mass spectrometry. Importantly, methionine residues found to be highly susceptible toward oxidation, and the lysine residues exhibiting large increases in accessibility upon oxidation, were all located in calcineurin functional domains involved in Ca²⁺/CaM binding regulated calcineurin stimulation. These findings therefore provide initial support for the novel mechanistic hypothesis that oxidation-induced global and/or local conformational changes within calcineurin contribute to inactivation via (i) impairing the interaction between calcineurin A and calcineurin B, (ii) altering the low-affinity Ca²⁺ binding site in calcineurin B, (iii) inhibiting calmodulin binding to calcineurin A, and/or (iv) by altering the affinity between the calcineurin A autoinhibitory domain and the catalytic center.

TRPC1, CaN and NFATC3 signaling pathway in the pathogenesis and progression of left ventricular hypertrophy in spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) was used to study left ventricular hypertrophy (LVH) and its dynamic change after the interventions with Telmisartan and Amlodipine. The results showed that the expression of TRPC1, CaN and NFATC3 increased gradually with the pathogenesis and progression of LVH. Telmisartan reduced blood pressure and LVH, and down-regulated the expression of TRPC1, CaN and NFATC3 in left ventricle of SHR. Amlodipine reduced the blood pressure in SHR but had no impact on the hypertrophy and expression of above factors. Our data suggest that the pathogenesis and progression of LVH in SHR are related to upregulation of TRPC1, CaN and NFATC3 signaling pathway.

Characterization of the PLCB1 promoter and regulation by early growth response transcription factor EGR-1

The Gαq/-Gα11-PLCβ1 pathway is important for intracellular signalling and associated with pathological conditions, such as cardiac hypertrophy. The GNAQ and GNA11 promoters (encoding for Gαq and Gα11) have already been characterized and are both regulated by the transcription factor early growth response 1 (Egr-1). In contrast, the PLCB1 promoter (encoding for the direct downstream effector PLCβ1) has neither been cloned nor characterized. Therefore, the purpose of this study was to 1) characterize the PLCB1 promoter, and 2) assess its potential regulation by Egr-1. By means of 5'- Rapid Amplification of 5'-cDNA ends analysis in human heart tissue we found an initiation of transcription from multiple starting points, the main transcription starting point being located at nt-235 relative to the translation start point. The PLCB1 promoter was cloned and deletion constructs were generated. Luciferase assays were performed in three different cell lines and regulatory regions were identified between nt-595/nt-313 (Hek293: P=0.013; HASMC: P=0.019; H9c2: P=0.005). In electrophoretic mobility shift assays one specific Egr-1 binding site was identified at nt-451/-419 and PLCB1 promoter activity was increased more than 5-fold (Hek293: P=0.0008) and 1,6- fold (H9c2: P=0.0499) following overexpression of Egr-1. Thus, the PLCB1 promoter was characterized for the first time and a specific interaction with the transcription factor Egr-1 was shown. Our data provide a potential molecular mechanism relating to pathophysiological conditions such as cardiac hypertrophy where activation by Egr-1 of Gαq/Gα11-PLCβ1 plays an important role.

Apelin-13 and APJ in paraventricular nucleus contribute to hypertension via sympathetic activation and vasopressin release in spontaneously hypertensive rats

AIMS

Apelin is a specific endogenous ligand of orphan G protein-coupled receptor APJ. This study was designed to determine the roles and mechanisms of apelin-13 and APJ in paraventricular nucleus (PVN) in renal sympathetic nerve activity (RSNA), arginine vasopressin (AVP) release and mean arterial pressure (MAP) in spontaneously hypertensive rats (SHR).

METHOD

Acute experiment was carried out in 13-week-old male SHR and Wistar-Kyoto rats (WKY) under anaesthesia. RSNA and MAP responses to the PVN microinjection were determined. Apelin and APJ expressions were examined with quantitative real-time PCR and Western blot. AVP and noradrenaline were determined with ELISA. Osmotic minipumps were used for chronic PVN infusion in conscious WKY.

RESULTS

Apelin and APJ in the PVN were up-regulated in SHR. The PVN microinjection of apelin-13 increased, but APJ antagonist F13A decreased the RSNA, MAP, plasma noradrenaline and AVP levels in SHR. N-methyl-D-aspartate receptor (NMDAR) antagonist plus non-NMDAR antagonist abolished the apelin-13-induced sympathetic activation rather than AVP release. NMDAR antagonist or non-NMDAR antagonist alone attenuated the apelin-13-induced sympathetic activation. Chronic infusion of apelin-13 into the PVN in normotensive rats induced hypertension, increased plasma noradrenaline and AVP levels and promoted myocardial atrial natriuretic peptide and beta-myosin heavy chain mRNA expressions, two indicative markers of cardiac hypertrophy.

CONCLUSION

Apelin-13 and APJ in the PVN contribute to hypertension via sympathetic activation and AVP release in SHR. The sympatho-excitatory effect of apeline-13 is mediated by both NMDAR and non-NMDAR in the PVN. Persistent activation of APJ in the PVN induces hypertension.

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.

Qishenyiqi protects ligation-induced left ventricular remodeling by attenuating inflammation and fibrosis via STAT3 and NF-κB signaling pathway

AIM

Qi-shen-yi-qi (QSYQ), a formula used for the routine treatment of heart failure (HF) in China, has been demonstrated to improve cardiac function through down-regulating the activation of the Renin-Angiotensin-Aldosterone System (RAAS). However, the mechanisms governing its therapeutic effects are largely unknown. The present study aims to demonstrate that QSYQ treatment can prevent left ventricular remodeling in heart failure by attenuating oxidative stress and inhabiting inflammation.

METHODS

Sprague-Dawley (SD) rats were randomly divided into 6 groups: sham group, model group (LAD coronary artery ligation), QSYQ group with high dosage, middle dosage and low dosage (LAD ligation and treated with QSYQ), and captopril group (LAD ligation and treated with captopril as the positive drug). Indicators of fibrosis (Masson, MMPs, and collagens) and inflammation factors were detected 28 days after surgery.

RESULTS

Results of hemodynamic alterations (dp/dt value) in the model group as well as other ventricular remodeling (VR) markers, such as MMP-2, MMP-9, collagen I and III elevated compared with sham group. VR was accompanied by activation of RAAS (angiotensin II and NADPHoxidase). Levels of pro-inflammatory cytokines (TNF-α, IL-6) in myocardial tissue were also up-regulated. Treatment of QSYQ improved cardiac remodeling through counter-acting the aforementioned events. The improvement of QSYQ was accompanied with a restoration of angiotensin II-NADPHoxidase-ROS-MMPs pathways. In addition, "therapeutic" QSYQ administration can reduce both TNF-α-NF-B and IL-6-STAT3 pathways, respectively, which further proves the beneficial effects of QSYQ.

CONCLUSIONS

Our study demonstrated that QSYQ protected LAD ligation-induced left VR via attenuating AngII -NADPH oxidase pathway and inhabiting inflammation. These findings provide evidence as to the cardiac protective efficacy of QSYQ to HF and explain the beneficial effects of QSYQ in the clinical application for HF.

Cellular FLICE-like inhibitory protein protects against cardiac hypertrophy by blocking ASK1/p38 signaling in mice

Cellular FLICE-like inhibitory protein (Flip) is a negative regulator of nuclear factor κB signaling which has been shown previously to complicate with cardiac hypertrophy. In the present study, we tested the hypothesis that the knockout of Flip would increase cardiac hypertrophy in vivo and in vitro. The effects of Flip knockout on cardiac hypertrophy were investigated using in vitro and in vivo models. Flip was downregulated in transverse aortic constriction (TAC)-induced animal hearts and cardiomyocytes that had been treated with angiotensin II or phenylephrine for 1 h. An in vivo, heart hypertrophy model, was performed by TAC in Flip knockdown and sham mice. The extent of hypertrophy of heart was quantitated by echocardiography, and further confirmed by pathological and molecular examination of heart tissue samples. Conditional knockout of Flip in the murine heart increases the hypertrophic response induced by TAC, whereas cardiac function was preserved with reduced Flip levels in response to hypertrophic stimuli. Western blot experiments further showed Flip knockout activated markedly ASK1/P38 signaling cascades in vivo and in vitro. In conclusion, Flip preserves cardiac functions and inhibits cardiac hypertrophy partially by blocking ASK1/P38 signaling.

Negative feedback regulation of calcineurin-dependent Prz1 transcription factor by the CaMKK-CaMK1 axis in fission yeast

Calcium signals trigger the translocation of the Prz1 transcription factor from the cytoplasm to the nucleus. The process is regulated by the calcium-activated phosphatase calcineurin, which activates Prz1 thereby maintaining active transcription during calcium signalling. When calcium signalling ceases, Prz1 is inactivated by phosphorylation and exported to the cytoplasm. In budding yeast and mammalian cells, different kinases have been reported to counter calcineurin activity and regulate nuclear export. Here, we show that the Ca(2+)/calmodulin-dependent kinase Cmk1 is first phosphorylated and activated by the newly identified kinase CaMKK2 homologue, Ckk2, in response to Ca(2+). Then, active Cmk1 binds, phosphorylates and inactivates Prz1 transcription activity whilst at the same time cmk1 expression is enhanced by Prz1 in response to Ca(2+). Furthermore, Cdc25 phosphatase is also phosphorylated by Cmk1, inducing cell cycle arrest in response to an increase in Ca(2+). Moreover, cmk1 deletion shows a high tolerance to chronic exposure to Ca(2+), due to the lack of cell cycle inhibition and elevated Prz1 activity. This work reveals that Cmk1 kinase activated by the newly identified Ckk2 counteracts calcineurin function by negatively regulating Prz1 activity which in turn is involved in activating cmk1 gene transcription. These results are the first insights into Cmk1 and Ckk2 function in Schizosaccharomyces pombe.

Disruption of tumor necrosis factor receptor associated factor 5 exacerbates pressure overload cardiac hypertrophy and fibrosis

The cytoplasmic signaling protein tumor necrosis factor (TNF) receptor-associated factor 5 (TRAF5), which was identified as a signal transducer for members of the TNF receptor super-family, has been implicated in several biological functions in T/B lymphocytes and the innate immune response against viral infection. However, the role of TRAF5 in cardiac hypertrophy has not been reported. In the present study, we investigated the effect of TRAF5 on the development of pathological cardiac hypertrophy induced by transthoracic aorta constriction (TAC) and further explored the underlying molecular mechanisms. Cardiac hypertrophy and function were evaluated with echocardiography, hemodynamic measurements, pathological and molecular analyses. For the first time, we found that TRAF5 deficiency substantially aggravated cardiac hypertrophy, cardiac dysfunction and fibrosis in response to pressure overload after 4 weeks of TAC compared to wild-type (WT) mice. Moreover, the mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK)-extracellular signal-regulated kinases 1/2 (ERK1/2) signaling pathway was more activated in TRAF5-deficient mice than WT mice. In conclusion, our results suggest that as an intrinsic cardioprotective factor, TRAF5 plays a crucial role in the development of cardiac hypertrophy through the negative regulation of the MEK-ERK1/2 pathway. J. Cell. Biochem. 115: 349-358, 2014. © 2013 Wiley Periodicals, Inc.

Targeted inactivation of Cerberus like-2 leads to left ventricular cardiac hyperplasia and systolic dysfunction in the mouse

Previous analysis of the Cerberus like 2 knockout (Cerl2^−/−) mouse revealed a significant mortality during the first day after birth, mostly due to cardiac defects apparently associated with randomization of the left-right axis. We have however, identified Cerl2-associated cardiac defects, particularly a large increase in the left ventricular myocardial wall in neonates that cannot be explained by laterality abnormalities. Therefore, in order to access the endogenous role of Cerl2 in cardiogenesis, we analyzed the embryonic and neonatal hearts of Cerl2 null mutants that did not display a laterality phenotype. Neonatal mutants obtained from the compound mouse line Cer2^−/−::Mlc1v-nLacZ24⁺, in which the pulmonary ventricle is genetically marked, revealed a massive enlargement of the ventricular myocardium in animals without laterality defects. Echocardiography analysis in Cerl2^−/− neonates showed a left ventricular systolic dysfunction that is incompatible with a long lifespan. We uncovered that the increased ventricular muscle observed in Cerl2^−/− mice is caused by a high cardiomyocyte mitotic index in the compact myocardium which is mainly associated with increased Ccnd1 expression levels in the left ventricle at embryonic day (E) 13. Interestingly, at this stage we found augmented left ventricular expression of Cerl2 levels when compared with the right ventricle, which may elucidate the regionalized contribution of Cerl2 to the left ventricular muscle formation. Importantly, we observed an increase of phosphorylated Smad2 (pSmad2) levels in embryonic (E13) and neonatal hearts indicating a prolonged TGFβs/Nodal-signaling activation. Concomitantly, we detected an increase of Baf60c levels, but only in Cerl2^−/− embryonic hearts. These results indicate that independently of its well-known role in left-right axis establishment Cerl2 plays an important role during heart development in the mouse, mediating Baf60c levels by exerting an important control of the TGFβs/Nodal-signaling pathway.

The PPARβ/δ agonist GW0742 modulates signaling pathways associated with cardiac myocyte growth via a non-genomic redox mechanism

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that belong to the nuclear hormone receptor superfamily and appear to have beneficial effects in the cardiovascular system. PPARβ/δ has been shown previously to exert an inhibitory effect on cardiac myocyte hypertrophy in vivo and in vitro although the exact mechanism is not fully clear yet. The principal signaling pathways that have been involved in triggering cardiac hypertrophic response are mitogen-activated protein kinases (MAPKs) and PI3K/Akt cascades. In this study, we sought to evaluate the potential effects evoked by PPARβ/δ activation on signaling pathways that are implicated in cardiac myocyte growth responses. The selective PPARβ/δ agonist GW0742 attenuated ERK1/2 and Akt phosphorylation that was stimulated by growth promoting agonists (phenylephrine, insulin or IGF-1). This effect was not reversed by the specific PPARβ/δ antagonist, GSK0660, but was inhibited by vanadate, a potent protein tyrosine phosphatase inhibitor. In addition, GW0742 prevented the oxidation and inactivation of PTEN supporting further the notion that its inhibitory action on the agonist-induced kinase phosphorylation is mediated by the modulation of phosphatase activity. Furthermore, GW0742 abolished the agonist-induced intracellular generation of reactive oxygen species, independently of PPARβ/δ activation. Our data reveals a new non-genomic mechanism of GW0742, which ameliorates the generation of reactive oxygen species and attenuates ERK1/2 and PI3K/Akt signaling, with implications in the regulation of cardiac hypertrophic response.