Mechanisms Of Cardiac Hypertrophy Research Articles

Synaptotagmin-7 mediates cardiac hypertrophy by targeting autophagy.

Sustained cardiac hypertrophy damages the heart and weakens cardiac function, often leading to heart failure and even death. Pathological cardiac hypertrophy has become a central therapeutic target for many heart diseases including heart failure. However, the underlying mechanisms of cardiac hypertrophy, especially the involvement of autophagy program, are still ill-understood. Synaptotagmin-7 (Syt7), a multifunctional and high-affinity calcium sensor, plays a pivotal role in asynchronous neurotransmitter release, synaptic facilitation, and vesicle pool regulation during synaptic transmission. However, little is known about whether Syt7 is expressed in the myocardium and involved in the pathogenesis of heart diseases. Here we showed that Syt7 was significantly upregulated in Ang II-treated hearts and cardiomyocytes. Homozygous syt7 knockout (syt7-/-) mice exhibited significantly attenuated cardiac hypertrophy and fibrosis and improved cardiac function. We further found that Syt7 exerted a pro-hypertrophic effect by suppressing the autophagy process. In exploring the upstream mechanisms, microRNA (miR)-93 was identified to participate in the regulation of Syt7 expression. miR-93 protected hearts against Ang II-induced hypertrophy through targeting Syt7-autophagy pathway. In summary, our data reveal a new cardiac hypertrophy regulator and a novel hypertrophy regulating model composed of miR-93, Syt7 and autophagy program. These molecules may serve as potential therapeutic targets in the treatment of cardiac hypertrophy and heart failure.

The potential protective effects of nintedanib against cardiac hypertrophy in vitro and in vivo

IntroductionCardiac hypertrophy is an independent risk factor for heart failure. However, the underlying mechanisms of cardiac hypertrophy are still unclear. Nintedanib is a Food and Drug Administration (FDA) approved therapeutic agent for the treatment of progressive fibrosing lung diseases.Material and methodsIn this study, we examined the effects of nintedanib on cardiac hypertrophy using an in vivo murine model with the transverse aortic constriction (TAC) operation and an in vitro cardiomyocytes model stimulated with Ang II.ResultsNintedanib has a protective effect on cardiac function in TAC mice with decreased heart rates, heart weight/body weight (HW/BW), and reduced plasma levels of creatine kinase-MB (CK-MB) and aspartate aminotransferase (AST). Wheat germ agglutinin (WGA) staining proved that the increased cardiomyocytes sizes in TAC mice were restored by nintedanib treatment. Nintedanib also reversed the decreased plasma levels of oxidative markers nuclear factor erythroid-2-related factor 2 (Nrf2), lipid peroxidation products thiobarbituric acid reactive substances (TBARS), and GSH, as well the increased homocysteine (Hcy) levels in TAC mice. In the in vitro cardiomyocytes model, cells were treated with nintedanib, followed by Ang II stimulation. Nintedanib improved Ang II induction-caused cell injury and oxidative stress in H9C2 cells, as shown by the decreased release of lactate dehydrogenase (LDH), and elevated mRNA levels of GPX1 and HO-1. Mechanistically, we prove that the protective effect of nintedanib is mediated by SIRT1.ConclusionsIn conclusion, this study demonstrates the protective effects of nintedanib on cardiac hypertrophy both in vivo and in vitro, which was attributed to its anti-oxidative activity through regulating SIRT1 expression.

The lncRNA MIAT regulates CPT-1a mediated cardiac hypertrophy through m6A RNA methylation reading protein Ythdf2

sPathological cardiac hypertrophy is a key contributor in heart failure (HF). Long non-coding RNAs (lncRNAs) and N6-methyladenosine (m6A) modification play a vital role in cardiac hypertrophy respectively. Nevertheless, the interaction between lncRNA and m6A methylase in cardiac hypertrophy is scarcely reported. Here, we constructed a cardiac hypertrophy mouse model by transverse aortic constriction (TAC) surgery and H9c2 cell model by stimulating with AngII. We found that lncRNA MIAT mRNA level, and m6A RNA methylation reading protein Ythdf2 mRNA and protein levels, were significantly increased in the cardiac hypertrophy model both in vivo and vitro. MIAT or Ythdf2 overexpression aggravated cardiac hypertrophy, and vice versa. Through bioinformatics prediction, western blotting, FISH, RNA pull-down, and RIP, we found that MIAT bound to Ythdf2 and regulated its expression. Furthermore, we discovered that Ythdf2 function was a downstream of MIAT in cardiac hypertrophy. Finally, we found that MIAT was a necessary regulator of cardiac hypertrophy due to its regulation of the Ythdf2/PPARα/CPT-1a axis. This study indicated a new hypertrophic signaling pathway: MIAT/Ythdf2/PPARα/CPT-1a. The results provided a new understanding of the MIAT and m6A RNA methylation reading protein, Ythdf2, function and mechanism in cardiac hypertrophy and highlighted the potential therapeutic benefits in the heart.

Maslinic acid protects against pressure-overload-induced cardiac hypertrophy by blocking METTL3-mediated m6A methylation.

Coordinated response of the heart to physiological stressors (including stress overload, ischemia, hypothyroidism, and metabolic signals) is a hallmark of heart disease. However, effective treatment and its molecular targets are unknown. Although Maslinic Acid (MA) has been shown to inhibit inflammatory responses with strong anti-tumor, anti-bacterial, and antioxidant effects, information on its role and underlying mechanism in cardiac hypertrophy are scanty. The present study revealed that 10-103 μg/ml MA treatment significantly inhibited Ang-II induced hypertrophy in NMCMs and the dosage did not influence the cell viability of H9C2 and NCMCs. Moreover, the anti-hypertrophy effect of MA (30 mg/kg·day) was verified in the TAC-induced hypertrophy mouse model in vivo. Further analysis showed that MA administration decreased the total RNA m6A methylation and METTL3 levels in Ang-II treated NMCMs and TAC stressed hearts. Rescue experiments under adenovirus-mediated myocardial METTL3 overexpression confirmed that METTL3-mediated m6A methylation is essential in M-driven inhibition of myocardial hypertrophy. Collectively, MA exerts a significant anti-hypertrophy effect by regulating the modification of METTL3-mediated m6A methylation in vitro and in vivo. These findings may provide a platform for establishing a new target and strategy for cardiac hypertrophy treatment.

Transient Post-Natal Exposure to Xenoestrogens Induces Long-Term Alterations in Cardiac Calcium Signaling

Today, non-communicable disorders are widespread worldwide. Among them, cardiovascular diseases represent the main cause of death. At the origin of these diseases, exposure to challenges during developmental windows of vulnerability (peri-conception, in utero, and early infancy periods) have been incriminated. Among the challenges that have been described, endocrine disruptors are of high concern because of their omnipresence in the environment. Worrisomely, since birth, children are exposed to a significant number of endocrine disruptors. However, the role of such early exposure on long-term cardiac health is poorly described. In this context, based on a model of rats exposed postnatally and transiently to an estrogenic compound prototype (estradiol benzoate, EB), we aimed to delineate the effects on the adult heart of such transient early exposure to endocrine disruptors and identify the underlying mechanisms involved in the potential pathogenesis. We found that this transient post-natal exposure to EB induced cardiac hypertrophy in adulthood, with increased cardiomyocyte size. The evaluation of cardiac calcium signaling, through immunoblot approaches, highlighted decreased expression of the sarcoplasmic reticulum calcium ATPase 2 (SERCA2) and decreased Nuclear Factor of Activated T Cells (NFAT3) phosphorylation as a potential underlying mechanism of cardiac hypertrophy. Furthermore, the treatment of cardiomyocytes with EB in vitro induced a decrease in SERCA2 protein levels. Overall, our study demonstrates that early transient exposure to EB induces permanent cardiac alterations. Together, our data highlight SERCA2 down-regulation as a potential mechanism involved in the cardiac pathogenesis induced by EB. These results suggest programming of adult heart dysfunctions such as arrhythmia and heart failures by early exposure to endocrine disruptors and could open new perspectives for treatment and prevention.

Asiatic acid alleviates Ang-II induced cardiac hypertrophy and fibrosis via miR-126/PIK3R2 signaling

BackgroundCardiac hypertrophy is an independent risk factor of many cardiovascular diseases. Studies have demonstrated that microRNA-126 (miR-126) was involved in angiogenesis during physiological and pathological process. However, its role in cardiac hypertrophy has not been known clearly. Our previous study demonstrated that asiatic acid (AA) has obvious protective effect on cardiac hypertrophy. Here, this study aimed to discover the regulatory role of miR-126 and its mechanism in cardiac hypertrophy, and to determine whether AA’s anti-hypertrophy effect is partially miR-126 dependent.MethodsMale Sprague Dawley rats were AngII infused via osmotic minipumps for 4 weeks and were treated with AA (20 mg/kg/day) by oral gavage. Cardiac hypertrophy was assessed using the echocardiography and histological analysis. In vitro studies,cardiomyocyte and cardiac fibroblasts (CF) were treted with AngII and AngII plus AA. And, the effect of AA on miR-126 and PI3K/AKT signaling pathway was investigated.ResultsTreatment of rats with AA decreased the ratio of heart weight to tibia length and hypertrophy markers. In vitro exprements demonstrated that AA significantly attenuated AngII-induced cardiac growth and cardiac fibroblast collagen expression. Moreover, our results found downregulation of miR-126 and activation of PI3K/AKT signaling pathway in AngII infusion induced cardiac hypertrophy model. It was also determined that miR-126 targets PIK3R2 directly.ConclusionsAA supplementation upregulated the expression of miR-126 and conferred cardio-protection effect against AngII induced cardiac hypertrophy.

KLK11 promotes the activation of mTOR and protein synthesis to facilitate cardiac hypertrophy

BackgroundCardiovascular diseases have become the leading cause of death worldwide, and cardiac hypertrophy is the core mechanism underlying cardiac defect and heart failure. However, the underlying mechanisms of cardiac hypertrophy are not fully understood. Here we investigated the roles of Kallikrein 11 (KLK11) in cardiac hypertrophy.MethodsHuman and mouse hypertrophic heart tissues were used to determine the expression of KLK11 with quantitative real-time PCR and western blot. Mouse cardiac hypertrophy was induced by transverse aortic constriction (TAC), and cardiomyocyte hypertrophy was induced by angiotensin II. Cardiac function was analyzed by echocardiography. The signaling pathway was analyzed by western blot. Protein synthesis was monitored by the incorporation of [3H]-leucine. Gene expression was analyzed by quantitative real-time PCR.ResultsThe mRNA and protein levels of KLK11 were upregulated in human hypertrophic hearts. We also induced cardiac hypertrophy in mice and observed the upregulation of KLK11 in hypertrophic hearts. Our in vitro experiments demonstrated that KLK11 overexpression promoted whereas KLK11 knockdown repressed cardiomyocytes hypertrophy induced by angiotensin II, as evidenced by cardiomyocyte size and the expression of hypertrophy-related fetal genes. Besides, we knocked down KLK11 expression in mouse hearts with adeno-associated virus 9. Knockdown of KLK11 in mouse hearts inhibited TAC-induced decline in fraction shortening and ejection fraction, reduced the increase in heart weight, cardiomyocyte size, and expression of hypertrophic fetal genes. We also observed that KLK11 promoted protein synthesis, the key feature of cardiomyocyte hypertrophy, by regulating the pivotal machines S6K1 and 4EBP1. Mechanism study demonstrated that KLK11 promoted the activation of AKT-mTOR signaling to promote S6K1 and 4EBP1 pathway and protein synthesis. Repression of mTOR with rapamycin blocked the effects of KLK11 on S6K1 and 4EBP1 as well as protein synthesis. Besides, rapamycin treatment blocked the roles of KLK11 in the regulation of cardiomyocyte hypertrophy.ConclusionsOur findings demonstrated that KLK11 promoted cardiomyocyte hypertrophy by activating AKT-mTOR signaling to promote protein synthesis.

MicroRNA-27 attenuates pressure overload-Induced cardiac hypertrophy and dysfunction by targeting galectin-3

Cardiac hypertrophy is an adaptive response to hemodynamic stress to compensate for cardiac dysfunction. MicroRNAs can regulate cardiac function and play a vital role in the regulation of cardiac hypertrophy. In the current study, in vivo and vitro hypertrophy models are established to explore the role of miR-27b and to elucidate the underlying mechanism in cardiac hypertrophy. Expression of miR-27b was down-regulated in mice with cardiac hypertrophy. The cardiac function of the mice with cardiac hypertrophy could be restored with the overexpression of miR-27b, this is observed in terms of decreasing LVEDd, LVESd, and increasing LVFS, LVEF. This study also predicted and confirmed that galectin-3 is a target gene of miR-27b. Depletion of galectin-3 significantly attenuated hypertrophy of hearts in both in vitro and in vivo tests. In conclusion, MiR-27b be used to exert a protective role against cardiac dysfunction and hypertrophy by decreasing the expression level of galectin-3. The methodology suggested in this study provides a novel therapeutic strategy against cardiac hypertrophy.

Imine stilbene analog ameliorate isoproterenol-induced cardiac hypertrophy and hydrogen peroxide-induced apoptosis

Cardiac hypertrophy is an adaptive response to stress, in order to maintain proper cardiac function. However, sustained stress leads to pathological hypertrophy accompanied by maladaptive responses and ultimately heart failure. At the cellular level, cardiomyocyte hypertrophy is characterized by an increase in myocyte size, reactivation of the fetal gene markers, disassembly of the sarcomere and transcriptional remodelling which are regulated by heart-specific transcription factors like MEF2, GATA4 and immediate early genes like c-jun and c-fos.2. It has been explored and established that the hypertrophic process is associated by oxidative stress and mediated by pathways involving several terminal stress kinases like P38, JNK and ERK1/2. Stilbenoids are bioactive polyphenols and earlier studies have shown that imine stilbene exert cardioprotective and anti aging effects by acting as modulators of Sirt1. The present study was aimed at designing and synthesizing a series of imine stilbene analogs and investigate its anti hypertrophic effects and regulatory mechanism in cardiac hypertrophy and apoptosis. Interestingly one of the analog, compound 3e (10 μM) alleviated isoproterenol (ISO, 25 μM) induced hypertrophy in rat cardiomyocyte (H9c2) cells by showing a marked decrease in the myocyte size. Further, compound 3e also restored the cardiac function by activating the metabolic stress sensor, AMPK. Moreover, molecular docking studies showed stable binding between compound 3e and GSK3β suggesting that compound 3e may directly regulate GSK3β activity and ameliorate ISO-induced cardiac hypertrophy. In agreement with this, compound 3e also modulated the crosstalk of all the hypertrophy inducing terminal Kinases by bringing down the expression to near control conditions. The compound also relieved H2O2 (100 μM) mediated ROS and normalized abnormal mitochondrial oxygen demand in hypertrophic conditions indicating the possibility of the compound to show promise in playing a role in cardiac hypertrophy.

Inhibiting SLC26A4 reverses cardiac hypertrophy in H9C2 cells and in rats.

BackgroundIt has been confirmed that mutations in solute carrier family 26 member 4 (SLC26A4) contribute to pendred syndrome. However, the role of SLC26A4 in cardiac hypertrophy and the signaling pathways remain unclear.MethodsCardiomyocytes were treated by 200 µM phenylephrine (PE) to induce cardiac hypertrophy. Also, the expression of SLC26A4, GSK3, cardiac hypertrophy markers including atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) was detected through real-time quantitative polymerase chain reaction (RT-qPCR). Flow cytometry assay was used to test the apoptosis of PE-induced cardiomyocytes transfected by small interfere RNA (siRNA)-SLC26A4. Furthermore, we detected the expression of autophagy-related markers including light chain 3 (LC3) and P62. Finally, we established a rat model of abdominal aortic constriction (AAC)-induced cardiac hypertrophy in vivo.ResultsRT-qPCR results showed that the mRNA expression of SLC26A4 was significantly up-regulated in PE-induced cardiac hypertrophy. After inhibiting SLC26A4, the release of ANP and BNP was significantly decreased and GSK3β was elevated in vivo and in vitro. Furthermore, inhibiting SLC26A4 promoted apoptosis of cardiac hypertrophy cells. In addition, LC3 was down-regulated and P62 was enhanced after transfection of siRNA-SLC26A4.ConclusionOur findings revealed that SLC26A4 increases cardiac hypertrophy, and inhibiting SLC26A4 could decrease the release of ANP/BNP and promote the expression of GSK-3β in vitro and in vivo. Moreover, SLC26A4 silencing inhibits autophagy of cardiomyocytes and induces apoptosis of cardiomyocytes. Therefore, SLC26A4 possesses potential value to be a therapeutic target of cardiac hypertrophy, and our study provides new insights into the mechanisms of cardiac hypertrophy.

The Antagonism of β3-AR and MICU1 Forms the Key Pathological Mechanism in Cardiac Hypertrophy

Mitochondrial calcium uptake 1 (MICU1) serves as a pivotal molecule in maintaining mitochondrial homeostasis, but its concrete role in cardiac hypertrophy remains elusive yet. The β3-adrenergic receptor (β3-AR) has received considerable attention of the world in cardiac hypertrophy, whether it possesses mutual restriction relation with MICU1 deserves further investigation. Specific small interfering RNAs against MICU1 or adenovirus-based plasmid with MICU1 were delivered into left ventricles or incubated with neonatal murine ventricular myocytes (NMVMs) for 48 h. Then, mice were rendered to cardiac hypertrophy by chronic infusion of angiotensin II (Ang-II) with a mini-osmotic pump for 28 days, meanwhile NMVMs were cultured with Ang-II for 48 h. Finally, MICU1 expression was downregulated in hypertrophic myocardium. MICU1 ablation aggravated cardiac hypertrophy both in vivo and in vitro, evidenced by impaired cardiac function, enlarged cardiomyocytes, increased hypertrophic maker genes and enhanced reactive oxygen species (ROS) generation. Moreover, excessive ROS accumulation following MICU1 deficiency increased β3-AR expression, which was reversed by N-acetyl-L-cysteine (NAC). In addition, β3-AR agonists BRL37344 depressed expression of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) and MICU1, leading to aggravated cardiac hypertrophy. However, MICU1 supplementation eliminated those detrimental effects of BRL37344, and decreased the susceptibility of cardiomyocytes to hypertrophic stress. Furthermore, in hypertrophicmyocardium, melatonin alone, but not when combined with luzindole, inhibited β3-AR expression, accompanied with increased expression of PGC-1α/MICU1 and decreased generation of ROS, finally contributing to alleviated cardiac hypertrophy. Conclusively, the mutual antagonism of β3-AR and MICU1 gives rise to pathologic development of cardiac hypertrophy, and melatonin protects against hypertrophic stress by negative regulating the abovementioned pathway. Funding Statement: This work was supported by grants from National Science Funds of China (No.81500208; 81670419), Science Fund for Distinguished Young Scholars of Sichuan Province (No.2017JQ0012), China Postdoctoral Science Foundation (No.2017M613429). Declaration of Interests: The authors state: No competing financial interests exist. Ethics Approval Statement: All experiments performed in adherence to the National Institutes of Health Guidelines on the Use of Laboratory Animals (Bethesda, MD, USA) and conformed to the Institutional Animal Care and Use Committee of Chengdu Military General Hospital.

The Antagonism of ß3-AR and MICU1 Forms the Key Pathological Mechanism in Cardiac Hypertrophy

The Antagonism of ß3-AR and MICU1 Forms the Key Pathological Mechanism in Cardiac Hypertrophy

Abstract P234: CTMP Negatively Regulates Pathological Cardiac Hypertrophy via Akt-dependent Manner

Pathological cardiac hypertrophy which represents a leading cause of morbidity and mortality worldwide is a pathological process related to multifactorial and multiple molecules and regulated by numerous signaling pathways. Deregulation of AKT signaling is important in cardiac hypertrophy and cardiac dysfunction, but the underlying mechanism is not fully understood. In this study, we identified carboxy-terminal modulator protein (CTMP), an endogenous AKT inhibitor, as a key regulator of cardiac hypertrophy in response to pressure overload. Our results demonstrated that CTMP levels were downregulated by about 40% in aortic banding (AB)–induced hypertrophied mice hearts and 50% in failing human hearts compared to their controls respectively. Mice overexpressing CTMP specifically in the heart were resistant to AB-induced cardiac hypertrophy, whereas cardiac-specific conditional CTMP-knockout mice exhibited an aggravated phenotype induced by pressure overload. Additionally, gain-or-loss of function experiments mediated by adenovirus demonstrated that CTMP also prevented an angiotensin II–induced hypertrophic response in isolated cardiomyocytes in vitro . Mechanistically, we discovered that AKT signaling was significantly activated in AB-treated WT hearts, which was blocked by cardiac overexpression of CTMP, whereas being enhanced by loss of CTMP in response to chronic pressure overload and agonist stimulation. Moreover, rescue-experiments revealed that inhibition of AKT activation through LY294002 ameliorated the cardiac abnormalities in CTMP-knockout mice after AB. Taken together, our present study provides both in vitro and in vivo evidences that CTMP functions as a novel negative regulator factor of pathological cardiac hypertrophy. The underlying mechanisms responsible for CTMP-elicited effects are dependent on the inhibition of AKT signaling. The above-mentioned findings also expand our knowledge of the mechanisms of cardiac hypertrophy and provide potential therapeutic targets for pathological cardiac hypertrophy and heart failure.

Serum uric acid level and left ventricular hypertrophy in elderly male patients with nonvalvular atrial fibrillation

Background and aimsRecent studies have suggested that serum uric acid (SUA) induces oxidative stress and inflammation, which are involved in the mechanism of cardiac hypertrophy. In patients with atrial fibrillation (AF), comorbidity of left ventricular hypertrophy (LVH) exacerbates cardiac function. In this study, we investigated the association between SUA and cardiac hypertrophy in AF patients. Methods and resultsInitially, 1296 consecutive elderly patients (age >60) with nonvalvular AF were retrospectively selected from the inpatient clinic between January 2012 and April 2015. Demographic, clinical, and echocardiographic characteristics were carefully recorded. The final study population was 577 patients. The mean SUA level was significantly higher in patients with LVH than those without LVH. Compared with the non-LVH group, the LVH group was older, had a higher percentage of female patients, and had lower hemoglobin levels and estimated glomerular filtration rates. Patients in the LVH group also had a higher rate of coronary heart disease and fewer had history of radiofrequency ablation compared with the non-LVH group. In the hyperuricemia group, B-type natriuretic peptide levels, left atrial diameter, left ventricular mass index, and percentage of NYHA (New York Heart Association) class III/IV were significantly higher than the SUA normal group. Multivariate logistic regression analysis indicated the independent risk factors for LVH in elderly AF patients included SUA, age, male sex, the presence of coronary heart disease, and diuretic therapy. Subgroup analysis identified SUA as a significant risk factor associated with LVH in men. ConclusionsSUA was independently associated with LVH in elderly male patients with nonvalvular AF.

Membrane Stretch and Angiotensin II type 1a Receptor: Causes and Role in the Myogenic Response

The ligand-independent activation of Angiotensin II type 1 receptors following vascular stretch plays very important (patho) physiological roles. Indeed, recent studies have implicated this mechanism in cardiac hypertrophy under conditions of pressure overload and it has shown to be indispensable in the regulation of the myogenic response in smooth muscle cells of small resistance arteries, as well as mesenteric and renal resistance arteries. The information discussed in here will highlight the involvement of the mechanoactivation of the Angiotensin II type I receptors in the development of the myogenic response and the molecular mechanisms modulating them following activation.

Potential mechanisms of cardiac hypertrophy in mice with a null deletion of MAFbx (1164.7)

The E3 ubiquitin ligase, MAFbx, has been shown to target specific proteins for degradation through poly‐ubiquitination and the ubiquitin proteasome system. A null deletion of MAFbx reveals no cardiac phenotype in young unchallenged knock out (KO) mice, but leads to the development of congestive heart failure and sudden death (at 18 months) in unchallenged aging mice. The aim of this study was to determine potential mechanisms underlying the development of congestive heart failure in MAFbx KO animals. Echocardiograms demonstrated functional changes (reduced fractional shortening and left ventricular ejection fraction) in KO animals beginning at 11 months and markers for multiple growth pathways were elevated in KO mice at 14 months of age. Calcineurin expression was elevated above wildtype (WT) at 14 months and remained elevated at 18 months. Phosphorylated Akt (S473) and GSK3β (S9) expression were also elevated at 14 months. Markers of the proteasome system demonstrated altered expression and activity relative to WT animals. Expression of 19 and 20S proteasome subunits (RPT1, α3, β5) were elevated in KO mice at 14 months, but only the 26S β1 subunit showed higher activity, with no change in β2 or β5 activity. The 14 month mice also had elevated total ubiquitinated proteins and reduced free ubiquitin. Together, these findings suggest that MAFbx deletion results in a progressive disruption of protein quality control (increased protein synthesis and limited increase in protein degradation) leading to activation of pathological signaling pathways and the development of cardiomyopathy.Grant Funding Source: Muscular Dystrophy Association

GW24-e3524 PARTIAL AORTIC CONSTRICTION IN RATS INCREASES THE EXPRESSION OF (PRO)RENIN RECEPTOR AND PLC-b3 IN THE HEART

ObjectivesRecent studies have shown that (pro)renin receptor (P)RR), a newly identified member of the renin-angiotensin system, was associated with organ damage in the kidney. However, there has been less information...

Role of serotonin 5-HT2A receptors in the development of cardiac hypertrophy in response to aortic constriction in mice

Serotonin, in addition to its fundamental role as a neurotransmitter, plays a critical role in the cardiovascular system, where it is thought to be involved in the development of cardiac hypertrophy and failure. Indeed, we recently found that mice with deletion of monoamine oxidase A had enhanced levels of blood and cardiac 5-HT, which contributed to exacerbation of hypertrophy in a model of experimental pressure overload. 5-HT2A receptors are expressed in the heart and mediate a hypertrophic response to 5-HT in cardiac cells. However, their role in cardiac remodeling in vivo and the signaling pathways associated are not well understood. In the present study, we evaluated the effect of a selective 5-HT2A receptor antagonist, M100907, on the development of cardiac hypertrophy induced by transverse aortic constriction (TAC). Cardiac 5-HT2A receptor expression was transiently increased after TAC, and was recapitulated in cardiomyocytes, as observed with 5-HT2A in situ labeling by immunohistochemistry. Selective blockade of 5-HT2A receptors prevented the development of cardiac hypertrophy, as measured by echocardiography, cardiomyocyte area and heart weight-to-body weight ratio. Interestingly, activation of calmodulin kinase (CamKII), which is a core mechanism in cardiac hypertrophy, was reduced in cardiac samples from M100907-treated TAC mice compared to vehicle-treated mice. In addition, phosphorylation of histone deacetylase 4 (HDAC4), a downstream partner of CamKII was significantly diminished in M100907-treated TAC mice. Thus, our results show that selective blockade of 5-HT2A receptors has beneficial effect in the development of cardiac hypertrophy through inhibition of the CamKII/HDAC4 pathway.

O-GlcNAc signaling is essential for NFAT-mediated transcriptional reprogramming during cardiomyocyte hypertrophy

The regulation of cardiomyocyte hypertrophy is a complex interplay among many known and unknown processes. One specific pathway involves the phosphatase calcineurin, which regulates nuclear translocation of the essential cardiac hypertrophy transcription factor, nuclear factor of activated T-cells (NFAT). Although metabolic dysregulation is frequently described during cardiac hypertrophy, limited insights exist regarding various accessory pathways. One metabolically derived signal, beta-O-linked N-acetylglucosamine (O-GlcNAc), has emerged as a highly dynamic posttranslational modification of serine and threonine residues regulating physiological and stress processes. Given the metabolic dysregulation during hypertrophy, we hypothesized that NFAT activation is dependent on O-GlcNAc signaling. Pressure overload-induced hypertrophy (via transverse aortic constriction) in mice or treatment of neonatal rat cardiac myocytes with phenylephrine significantly enhanced global O-GlcNAc signaling. NFAT-luciferase reporter activity revealed O-GlcNAc-dependent NFAT activation during hypertrophy. Reversal of enhanced O-GlcNAc signaling blunted cardiomyocyte NFAT-induced changes during hypertrophy. Taken together, these results demonstrate a critical role of O-GlcNAc signaling in NFAT activation during hypertrophy and provide evidence that O-GlcNAc signaling is coordinated with the onset and progression of cardiac hypertrophy. This represents a potentially significant and novel mechanism of cardiac hypertrophy, which may be of particular interest in future in vivo studies of hypertrophy.

Abstract 3: Interaction Between NFκB and NFAT Coordinates Cardiac Hypertrophy and Pathological Remodeling

Both NFAT and NFkB are Rel homology domain-containing family members of transcription factors whose independent activities are critically involved in regulating cardiac hypertrophy and failure. Here we identified a novel transcriptional regulatory mechanism whereby NFkB and NFAT directly interact and synergistically promote transcriptional activation of one another in cardiomyoctes. We showed that NFkB-p65 co-immunoprecipitates with NFAT isoforms in cardiomyocytes, and this interaction is mapped to the Rel homology domain (RHD) within p65. Intriguingly, overexpression of p65-RHD disrupts the association between endogenous p65 and NFATc1, leading to reduced NFAT luciferase activity. Overexpression of p65-RHD or IKKβ leads to significant nuclear translocation of NFATc1, and expression of a constitutively nuclear NFATc1-SA similarly facilitated p65 nuclear translocation, further suggesting a physical interaction between p65 and NFATc1. Indeed, we observed that combined overexpression of p65 and NFAT leads to synergistic activation of NFAT transcriptional activity in cardiomyocytes. Conversely, NFAT transcriptional activity in cardiomyocytes is significantly reduced by inhibition of NFkB with IkBαM or dominant negative IKKβ. Importantly, hypertrophic agonist-induced NFAT activity is also significantly reduced in NFkB-p65 null MEFs compared to wild-type MEFs, while adenoviral-mediated expression of p65 restored NFAT luciferase activity in p65 null MEFs. In vivo, cardiac-specific deletion of NFkB-p65 using a Cre-LoxP system caused a ∼ 50% reduction in NFAT activity in NFAT-luciferase reporter mice. Moreover, ablation of p65 in the mouse heart decreased the hypertrophic response following pressure overload stimulation, reduced the degree of pathological remodeling, and preserved contractile function. Taken together, our results suggest a direct interaction between NFAT and NFkB pathways that may serve as a novel signaling mechanism in cardiac hypertrophy and failure.