Re-expression Of Fetal Genes Research Articles

Conditional ablation of MCU exacerbated cardiac pathology in a genetic arrhythmic model of CPVT

BackgroundCatecholaminergic polymorphic ventricular tachycardia (CPVT) is a genetic arrhythmic syndrome caused by mutations in the calcium (Ca2+) release channel ryanodine receptor (RyR2) and its accessory proteins. These mutations make the channel leaky, resulting in Ca2+-dependent arrhythmias. Besides arrhythmias, CPVT hearts typically lack structural cardiac remodeling, a characteristic often observed in other cardiac conditions (heart failure, prediabetes) also marked by RyR2 leak. Recent studies suggest that mitochondria are able to accommodate more Ca2+ influx to inhibit arrhythmias in CPVT. Thus, we hypothesize that CPVT mitochondria can absorb diastolic Ca2+ to protect the heart from cardiac remodeling. Methods and resultsThe Mitochondrial Ca2+ uniporter (MCU), the main mitochondrial Ca2+ uptake protein, was conditionally knocked out in a CPVT model of calsequestrin 2 (CASQ2) KO. In vivo cardiac function was impaired in the CASQ2−/−-MCUCKO model as assessed by echocardiography. Cardiac dilation and cellular hypertrophy were also observed in the CASQ2−/−-MCUCKO hearts. Live-cell imaging identified altered Ca2+ handling and increased oxidative stress in CASQ2−/−-MCUCKO myocytes. The activation status of Ca2+-dependent remodeling pathways (CaMKII, Calcineurin) was not altered in the CASQ2−/−-MCUCKO model. RNAseq identified changes in the transcriptome of the CASQ2−/−-MCUCKO hearts, distinct from the classic cardiac remodeling program of fetal gene re-expression. ConclusionsWe present genetic evidence that mitochondria play a protective role in CPVT. MCU-dependent Ca2+ uptake is crucial for preventing pathological cardiac remodeling in CPVT.

Cardiac Na/K-ATPase alpha1 isoform-specific role in hypertrophic response: role of metabolic and oxidative signaling

Cardiac Na/K-ATPase (NKA) inhibition by cardiotonic steroids (CTS) modulates intracellular Na + and Ca 2+ , leading to increased force of contraction. In contrast, hypertrophy of cardiomyocytes (CM) is triggered by CTS through stimulation of reactive oxygen species (ROS) and fetal gene re-expression independently of changes in intracellular Na + or Ca 2+ . Based on recent evidence that NKAα1 serves an isoform-specific function in the regulation of oxidative metabolism and ROS generation, we used a genetic approach in the mouse and in human cardiac cells (AC16) to test the hypothesis that NKAα1 is required for cardiac hypertrophy. Cardio α1 -/- mice, a conditional KO of NKAα1 in the heart, were viable without overt abnormality of cardiac structure or function. NKAα1 was undetectable in heart lysates or isolated CM of adult cardio α1 -/- mice. Despite a compensatory upregulation of NKAα2, Na/K-ATPase activity in crude heart homogenates and NKA currents in CM were reduced by about 60%. Decreased ROS (assessed by total protein carbonylation) and reduced fatty acid oxidation (FAO) and oxidative phosphorylation pathways (revealed by RNA-seq analysis) were noted at baseline. RT-qPCR revealed downregulated genes involved with FAO and the electron transport chain (such as, Acadl and Ndufa9, about 20% decrease, n=6) in cardio α1 -/- hearts. The activity of the electron transport chain complex I was decreased in cardio α1 -/- hearts (0.3354 vs 0.2732 mOD/min/mg of protein, p<0.05). When 3-month-old male mice were challenged with angiotensin II (1.5 mg.kg -1 .day -1 for 1 week, n=6-15), cardio α1 -/- mice did not develop cardiac hypertrophy, as assessed by heart weight to tibia length ratio, but displayed exacerbated cardiac fibrosis, revealed by Trichrome staining, consistent with the postulated role of CM NKAα1 isoform-specific function in cardiac hypertrophy in vivo. In vitro, CRISPR-Cas9-mediated KO of NKAα1 in AC16 cells led to a drastic downregulation of NKAα1 compared to WT AC16 cells. In contrast to WT AC16 cells, NKAα1 KO cells did not respond to the α-adrenergic agonist phenylephrine (50 μM for 24h) with the expected increase in cell area (2243 vs 3520 μm 2 for WT, p<0.05; 2454 vs 2563 μm 2 for KO, p>0.05). These data suggest that NKAα1 isoform-specific function is required for cardiac hypertrophy. Mechanistically, our data support an isoform-specific regulatory function of NKAα1 in normal FAO, electron transport chain activity, and ROS generation, which are critical for CM hypertrophy. Supported by NIH Grant R15 HL145666 and American Heart Association Grant 22POST917776 (Marco T. Pessoa) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Multiomic analyses reveal enriched glycolytic processes in β-myosin heavy chain-expressed cardiomyocytes in early cardiac hypertrophy

Cardiac pressure overload induces cardiac hypertrophy and eventually leads to heart failure. One distinct feature of pathological cardiac hypertrophy is fetal-gene re-expression, but not every cardiomyocyte exhibits fetal gene re-expression in the diseased heart. Adult cardiomyocytes are terminally differentiated cells, so we do not know how the heterogeneity is determined and whether the differential fetal-gene reprogramming indicates a different degree of remodeling among cardiomyocytes. We hypothesized that fetal gene-expressed cardiomyocytes show more pathological features in the pressure-overloaded heart. We induced pressure overload in mice by transverse aortic constriction (TAC) and observed a cardiomyocyte population with expression of β-myosin heavy chain (βMHC, a fetal gene encoded by Myh7 ) after TAC for 3 days. On transcriptomic and proteomic analyses, βMHC-expressed cardiomyocytes of 3-day TAC hearts were enriched in genes in cardiomyopathy-associated pathways and glycolytic processes. Moreover, results of immunoblotting and enzyme activity assay suggested higher glycolytic activity in βMHC-expressed than non-expressed cardiomyocytes. When we inhibited the glycolytic flux by 2-deoxy- d -glucose, a widely used glycolysis inhibitor, the number of βMHC-expressed cardiomyocytes was reduced, and the level of TEA domain family member 1 (TEAD1), a transcriptional enhancer, was decreased. Also, our spatial transcriptomic results demonstrated that naïve and 3-day TAC hearts had fetal-gene–rich tissue domains that were enriched in pathways in extracellular matrix organization and tissue remodeling. As well, gene levels of glycolytic enzymes were higher in Myh7 -positive than Myh7 -negative domains. Our data suggest that βMHC-expressed cardiomyocytes progress to pathological remodeling in the early stages of cardiac hypertrophy. In addition, the diverse glycolytic activity among cardiomyocytes might play a role in regulating gene expression via TEAD1 signaling. • Cardiomyocytes with and without βMHC expression have different cell properties. • Pathological features are enriched in the βMHC-positive cardiomyocytes. • Cardiomyocytes with βMHC expression prefer glycolysis. • Inhibit glycolysis by 2-DG could reduce the number of βMHC-positive cardiomyocytes.

Calcium Signaling, Calcineurin and NFAT3 Molecular Pathway in Reprogramming of Fetal Gene (BNP) Expression in Cardiac Hypertrophy and Inhibitors of Cardiac Hypertrophy-Review

G-Protein Coupled Receptor (GPCR) plays a major role in cardiac hypertrophy. Isoproterenol is an agonist which binds to GPCR. This results in the activation of GS subunit. Activated Gs subunit stimulates cAMP mediated pathway. This activates the calcium signaling and elevates the calcium level. Increased calcium activates the phosphatase activity of calcineurin. Activated calcineurin dephosphorylates NFAT in cytoplasm. Dephosphorylated NFAT translocates to nucleus and binds to target region in DNA and activates re-expression of fetal genes in synergy with GATA-4 trascription factor. Reprogramming of fetal genes by NFAT- 3 and GATA-4 results in cardiac hypertrophy. Calcineurin inhibitors and rephosphorylation of NFAT can prevent cardiac hypertrophy.

Sinapic Acid Inhibits Cardiac Hypertrophy via Activation of Mitochondrial Sirt3/SOD2 Signaling in Neonatal Rat Cardiomyocytes.

Sinapic acid (SA) is a naturally occurring phenolic compound with antioxidant properties. It also has a wide range of pharmacological properties, such as anti-inflammatory, anticancer, and hepatoprotective properties. The present study aimed to evaluate the potential pharmacological effects of SA against hypertrophic responses in neonatal rat cardiomyocytes. In order to evaluate the preventive effect of SA on cardiac hypertrophy, phenylephrine (PE)-induced hypertrophic cardiomyocytes were treated with subcytotoxic concentrations of SA. SA effectively suppressed hypertrophic responses, such as cell size enlargement, sarcomeric rearrangement, and fetal gene re-expression. In addition, SA significantly inhibited the expression of mitogen-activated protein kinase (MAPK) proteins as pro-hypertrophic factors and protected the mitochondrial functions from hypertrophic stimuli. Notably, SA activated Sirt3, a mitochondrial deacetylase, and SOD2, a mitochondrial antioxidant, in hypertrophic cardiomyocytes. SA also inhibited oxidative stress in hypertrophic cardiomyocytes. However, the protective effect of SA was significantly reduced in Sirt3-silenced hypertrophic cardiomyocytes, indicating that SA exerts its beneficial effect through Sirt3/SOD signaling. In summary, this is the first study to reveal the potential pharmacological action and inhibitory mechanism of SA as an antioxidant against cardiac hypertrophy, suggesting that SA could be utilized for the treatment of cardiac hypertrophy.

Pressure overload by suprarenal aortic constriction in mice leads to left ventricular hypertrophy without c-Kit expression in cardiomyocytes

Animal models of pressure overload are valuable for understanding hypertensive heart disease. We characterised a surgical model of pressure overload-induced hypertrophy in C57BL/6J mice produced by suprarenal aortic constriction (SAC). Compared to sham controls, at one week post-SAC systolic blood pressure was significantly elevated and left ventricular (LV) hypertrophy was evident by a 50% increase in the LV weight-to-tibia length ratio due to cardiomyocyte hypertrophy. As a result, LV end-diastolic wall thickness-to-chamber radius (h/R) ratio increased, consistent with the development of concentric hypertrophy. LV wall thickening was not sufficient to normalise LV wall stress, which also increased, resulting in LV systolic dysfunction with reductions in ejection fraction and fractional shortening, but no evidence of heart failure. Pathological LV remodelling was evident by the re-expression of fetal genes and coronary artery perivascular fibrosis, with ischaemia indicated by enhanced cardiomyocyte Hif1a expression. The expression of stem cell factor receptor, c-Kit, was low basally in cardiomyocytes and did not change following the development of robust hypertrophy, suggesting there is no role for cardiomyocyte c-Kit signalling in pathological LV remodelling following pressure overload.

Abstract MP171: Transcription Start Site Profiling Defines Promoter and Enhancer Regions for Cardiomyopathy Genes

Background: Mutations in more than 100 genes lead to dilated, hypertrophic and other forms of cardiomyopathy. Autosomal dominant mutations in the MYH7 and LMNA genes cause autosomal dominant hypertrophic and dilated cardiomyopathy, respectively. Individual mutations display a range of clinical expression from severe early onset disease to minimal or no symptoms. Genetic variation in noncoding gene regulatory regions including enhancers is expected to modify expression of cardiomyopathy genes and disease expressivity. In addition, heart failure is associated a fetal gene re-expression program, mediated by genetic regulatory regions. The contribution of noncoding genetic variation to cardiomyopathy and heart failure has been hampered by limited genome wide descriptions of human cardiac regulatory regions. Methods and Results: We used C ap A nalysis of G ene E xpression by sequencing (CAGE-seq) to profile the transcriptional start sites in healthy and failed human hearts. CAGE-seq detects the unidirectional signals of gene promoters and the bidirectional signal of transcribed enhancer regions. We identified ~17,000 transcriptional start sites associated with gene promoters and ~1,500 putative enhancer regions active in cardiac tissue. These CAGE-defined regulatory regions carried histone modifications and transcription factor binding properties characteristic of enhancers or promoters. We specifically identified promoter switching and differential enhancer usage between healthy and failed hearts. We intersected CAGE-defined enhancers with additional epigenomic datasets to identify regulatory regions for MYH7 and LMNA genes. We identified 13 putative enhancer regions and validated the functionality of a subset of these regulatory regions using reporter assays and gene editing. Conclusions: This CAGE-seq dataset defines the regulatory environment for heart failure. These promoter and enhancer regions could be used to target heart-failure associated gene expression changes. Additionally, this data can be used to identify enhancer regions regulating cardiomyopathy genes.

BNP as a New Biomarker of Cardiac Thyroid Hormone Function.

BackgroundCardiac re-expression of fetal genes in patients with heart failure (HF) suggests the presence of low cardiac tissue thyroid hormone (TH) function. However, serum concentrations of T3 and T4 are often normal or subclinically low, necessitating an alternative serum biomarker for low cardiac TH function to guide treatment of these patients. The clinical literature suggests that serum Brain Natriuretic Peptide (BNP) levels are inversely associated with serum triiodo-L-thyronine (T3) levels. The objective of this study was to investigate BNP as a potential serum biomarker for TH function in the heart.MethodsTwo animal models of thyroid hormone deficiency: (1) 8-weeks of propyl thiouracil-induced hypothyroidism (Hypo) in adult female rats were subsequently treated with oral T3 (10 μg/kg/d) for 3, 6, or 14 days; (2) HF induced by coronary artery ligation (myocardial infarction, MI) in adult female rats was treated daily with low dose oral T3 (5 μg/kg/d) for 8 or 16 wks.ResultsSix days of T3 treatment of Hypo rats normalized most cardiac functional parameters. Serum levels of BNP increased 5-fold in Hypo rats, while T3 treatment normalized BNP by day 14, showing a significant inverse relationship between serum BNP and free or total T3 concentrations. Myocardial BNP mRNA was increased 2.5-fold in Hypo rats and its expression was decreased to normal values by 14 days of T3 treatment. Measurements of hemodynamic function showed significant dysfunction in MI rats after 16 weeks, with serum BNP increased by 4.5-fold and serum free and total T3 decreased significantly. Treatment with T3 decreased serum BNP while increasing total T3 indicating an inverse correlation between these two biologic factors (r2 = 0.676, p < 0.001). Myocardial BNP mRNA was increased 5-fold in MI rats which was significantly decreased by T3 over 8 to 16 week treatment periods.ConclusionsResults from the two models of TH dysfunction confirmed an inverse relationship between tissue and serum T3 and BNP, such that the reduction in serum BNP could potentially be utilized to monitor efficacy and dosing of T3 treatment. Thus, serum BNP may serve as a reliable biomarker for cardiac TH function.

Abstract 311: In vitro Regulation of G-protein Coupled Receptor Kinase 5 (GRK5) Induced Cardiac Hypertrophy by a Novel Interaction With the Phosphatase PHLPP2

PHLPP is a Ser/Thr phosphatase that has been shown to directly dephosphorylate several members of the AGC family of kinases, which are important regulators of cell growth, proliferation, and survival. We have previously demonstrated that removal of PHLPP1 increases Akt activity in neonatal rat ventricular myocytes (NRVMs) (Miyamoto et al 2010) as well as the heart (Moc et al 2015) leading to protection from pathological hypertrophy and damage, however the effects of PHLPP2 removal on cardiomyocyte hypertrophic growth are unknown. In NRVMs, we found that removal of PHLPP2 induced hypertrophic growth basally without altering Akt activity and immunoprecipitation experiments revealed a novel interaction with an AGC kinase, G-protein coupled receptor kinase 5 (GRK5). GRK5 acts as an HDAC kinase downstream of phenylephrine (PE) to regulate hypertrophy in NRVMs. Thus, our objective was to determine whether PHLPP2 regulates PE-induced cardiomyocyte hypertrophy through its interaction with GRK5. We found that knockdown of PHLPP2, not PHLPP1, potentiated PE-induced hypertrophy (siPH2+PE (109 ± 3.5μm) vs. siCon+PE (88 ± 1.9μm)), and increased mRNA expression of fetal genes (i.e. ANF and BNP). Conversely, overexpression of PHLPP2 attenuated PE-induced hypertrophic growth (PH2+PE (66.6 ±7.7μm) vs. GFP+PE (95.5 ± 2.7μm)) as well as fetal gene re-expression. This inhibition of hypertrophic growth was dependent on phosphatase activity since a PHLPP2 mutant lacking the phosphatase domain (αPP2C) reversed the effect of PHLPP2 overexpression. To determine whether removal of PHLPP2 alters GRK5 translocation, cells were fractionated, and we found that PHLPP2 removal significantly increased basal and PE-induced nuclear accumulation of GRK5 that was blocked by overexpression of PHLPP2. Finally, knockdown studies with siGRK5 revealed that GRK5 was indeed required for the hypertrophic response elicited by PHLPP2 removal. Overall, our data revealed for the first time that PHLPP2 plays a role in regulating PE-induced cardiac hypertrophy via a GRK5 dependent pathway. Understanding the biological function and signaling pathways altered by PHLPP2 in cardiomyocytes may help delineate therapeutic targets for cardiac hypertrophy.

Maternal exercise intervention in obese pregnancy improves the cardiovascular health of the adult male offspring

ObjectiveObesity during pregnancy is associated with an elevated risk of cardiovascular disease in the offspring. With increased numbers of women entering pregnancy overweight or obese, there is a requirement for targeted interventions to reduce disease risk in future generations. Using an established murine model of maternal obesity during pregnancy, we investigated if a treadmill exercise intervention in the mother could improve offspring cardiac health and explored potential underlying mechanisms. MethodsA 20-minute treadmill exercise intervention protocol was performed 5 days a week in diet-induced obese female C57BL/6 mice 1 week prior to, and up to E17 of pregnancy. All male offspring were weaned onto a control diet and studied at 8 weeks of age when their cardiovascular physiology was assessed by in vivo echocardiography and non-invasive tail cuff plethysmography. Cardiomyocyte cell area, re-expression of fetal genes and the expression of calcium handling and sympathetic activation proteins were determined. ResultsAt 8 weeks, there was no difference in bodyweight or fat mass between groups. Offspring of obese dams developed pathologic cardiac hypertrophy, hypertension and cardiac dysfunction characterized by reduced ejection fraction (p < 0.001). Maternal exercise prevented cardiac hypertrophy and dysfunction but failed to prevent hypertension. These offspring of exercised dams also had enhanced (p < 0.001) levels of calcium handling proteins and a sympathetic-activated inotropic response. ConclusionsExercise in obese pregnancy was beneficial to offspring cardiac function and structure but did not influence hypertension suggesting they are programmed by separate mechanistic pathways. These data suggest combination interventions in obese pregnancies will be required to improve all aspects of the cardiovascular health of the next generation.

PH domain leucine-rich repeat protein phosphatase 2 (PHLPP2) regulates G-protein–coupled receptor kinase 5 (GRK5)-induced cardiac hypertrophy in vitro

PH domain leucine-rich repeat protein phosphatase (PHLPP) is a serine/threonine phosphatase that has been shown to regulate cell growth and survival through dephosphorylation of several members of the AGC family of kinases. G-protein-coupled receptor kinase 5 (GRK5) is an AGC kinase that regulates phenylephrine (PE)-induced cardiac hypertrophy through its noncanonical function of directly targeting proteins to the nucleus to regulate transcription. Here we investigated the possibility that the PHLPP2 isoform can regulate GRK5-induced cardiomyocyte hypertrophy in neonatal rat ventricular myocytes (NRVMs). We show that removal of PHLPP2 by siRNA induces hypertrophic growth of NRVMs as measured by cell size changes at baseline, potentiated PE-induced cell size changes, and re-expression of fetal genes atrial natriuretic factor and brain natriuretic peptide. Endogenous GRK5 and PHLPP2 were found to interact in NRVMs, and PE-induced nuclear accumulation of GRK5 was enhanced upon down-regulation of PHLPP2. Conversely, overexpression of PHLPP2 blocked PE-induced hypertrophic growth, re-expression of fetal genes, and nuclear accumulation of GRK5, which depended on its phosphatase activity. Finally, using siRNA against GRK5, we found that GRK5 was necessary for the hypertrophic response induced by PHLPP2 knockdown. Our findings demonstrate for the first time a novel regulation of GRK5 by the phosphatase PHLPP2, which modulates hypertrophic growth. Understanding the signaling pathways affected by PHLPP2 has potential for new therapeutic targets in the treatment of cardiac hypertrophy and failure.

Loss of KCNK3 is a hallmark of RV hypertrophy/dysfunction associated with pulmonary hypertension.

Mutations in the KCNK3 gene, which encodes for an outward-rectifier K+ channel, have been identified in patients suffering from pulmonary arterial hypertension (PAH), and constitute the first described channelopathy in PAH. In human PAH and experimental pulmonary hypertension (PH), we demonstrated that KCNK3 expression and function are severely reduced in pulmonary vascular cells, promoting PH-like phenotype at the morphologic and haemodynamic levels. Since KCNK3 channel is also expressed in both the human and rodent heart, we aimed to elucidate the pathophysiological role of KCNK3 channel in right ventricular (RV) hypertrophy (RVH) related to PH. Using whole-cell Patch-clamp technique, we demonstrated that KCNK3 is predominantly expressed in adult rat RV cardiomyocytes compared to the left ventricle cardiomyocytes and participates in the repolarizing phase of the RV action potential. We revealed a reduction in KCNK3 function prior to development of RVH and the rise of pulmonary vascular resistance. KCNK3 function is severely reduced in RV cardiomyocytes during the development of RVH in several rat models of PH (exposure to monocrotaline, chronic hypoxia, and Sugen/hypoxia) and chronic RV pressure overload (pulmonary artery banding). In experimental PH, we revealed a reduction in KCNK3 function before any rise in pulmonary vascular resistance and the development of RVH. KCNK3 mRNA level is also reduced in human RV tissues from PAH patients compared to non-PAH patients. In line with these findings, chronic inhibition of KCNK3 in rats with the specific inhibitor (A293) induces RV hypertrophy which is associated with the re-expression of foetal genes, RV fibrosis, RV inflammation, and subsequent loss of RV performance as assessed by echocardiography. Our data indicate that loss of KCNK3 function and expression is a hallmark of the RV hypertrophy/dysfunction associated with PH.

The H3K9 dimethyltransferases EHMT1/2 protect against pathological cardiac hypertrophy.

Cardiac hypertrophic growth in response to pathological cues is associated with reexpression of fetal genes and decreased cardiac function and is often a precursor to heart failure. In contrast, physiologically induced hypertrophy is adaptive, resulting in improved cardiac function. The processes that selectively induce these hypertrophic states are poorly understood. Here, we have profiled 2 repressive epigenetic marks, H3K9me2 and H3K27me3, which are involved in stable cellular differentiation, specifically in cardiomyocytes from physiologically and pathologically hypertrophied rat hearts, and correlated these marks with their associated transcriptomes. This analysis revealed the pervasive loss of euchromatic H3K9me2 as a conserved feature of pathological hypertrophy that was associated with reexpression of fetal genes. In hypertrophy, H3K9me2 was reduced following a miR-217-mediated decrease in expression of the H3K9 dimethyltransferases EHMT1 and EHMT2 (EHMT1/2). miR-217-mediated, genetic, or pharmacological inactivation of EHMT1/2 was sufficient to promote pathological hypertrophy and fetal gene reexpression, while suppression of this pathway protected against pathological hypertrophy both in vitro and in mice. Thus, we have established a conserved mechanism involving a departure of the cardiomyocyte epigenome from its adult cellular identity to a reprogrammed state that is accompanied by reexpression of fetal genes and pathological hypertrophy. These results suggest that targeting miR-217 and EHMT1/2 to prevent H3K9 methylation loss is a viable therapeutic approach for the treatment of heart disease.

Cardiac-restricted Overexpression of TRAF3 Interacting Protein 2 (TRAF3IP2) Results in Spontaneous Development of Myocardial Hypertrophy, Fibrosis, and Dysfunction

TRAF3IP2 (TRAF3 interacting protein 2; previously known as CIKS or Act1) is a key intermediate in the normal inflammatory response and the pathogenesis of various autoimmune and inflammatory diseases. Induction of TRAF3IP2 activates IκB kinase (IKK)/NF-κB, JNK/AP-1, and c/EBPβ and stimulates the expression of various inflammatory mediators with negative myocardial inotropic effects. To investigate the role of TRAF3IP2 in heart disease, we generated a transgenic mouse model with cardiomyocyte-specific TRAF3IP2 overexpression (TRAF3IP2-Tg). Echocardiography, magnetic resonance imaging, and pressure-volume conductance catheterization revealed impaired cardiac function in 2-month-old male transgenic (Tg) mice as evidenced by decreased ejection fraction, stroke volume, cardiac output, and peak ejection rate. Moreover, the male Tg mice spontaneously developed myocardial hypertrophy (increased heart/body weight ratio, cardiomyocyte cross-sectional area, GATA4 induction, and fetal gene re-expression). Furthermore, TRAF3IP2 overexpression resulted in the activation of IKK/NF-κB, JNK/AP-1, c/EBPβ, and p38 MAPK and induction of proinflammatory cytokines, chemokines, and extracellular matrix proteins in the heart. Although myocardial hypertrophy decreased with age, cardiac fibrosis (increased number of myofibroblasts and enhanced expression and deposition of fibrillar collagens) increased progressively. Despite these adverse changes, TRAF3IP2 overexpression did not result in cell death at any time period. Interestingly, despite increased mRNA expression, TRAF3IP2 protein levels and activation of its downstream signaling intermediates remained unchanged in the hearts of female Tg mice. The female Tg mice also failed to develop myocardial hypertrophy. In summary, these results demonstrate that overexpression of TRAF3IP2 in male mice is sufficient to induce myocardial hypertrophy, cardiac fibrosis, and contractile dysfunction.

Abstract 18835: Chromatin Gene Cohorts, Not Individual Cardiac Genes, Modulate Cardiac Phenotype in a Genetically Diverse Population

Re-expression of fetal genes is a hallmark of transcriptome change in models of cardiac hypertrophy, but how this remodeling is affected by the common genetic variation present in populations is unknown. We examined gene expression in 86 strains of control and isoproterenol (ISO)-treated mice, which exhibited varying degrees of disease. Correlations between individual fetal genes (Anf, Serca2a, alpha-MHC, beta-MHC) and hypertrophic phenotypes were not significant. Expanded analysis of 37 fetal genes showed sparse correlation (at p&lt;0.05) between expression of individual genes with one or more of 52 systemic phenotypes. We next tested the hypothesis that groups of genes exhibit emergent association with phenotype not observed with individual transcripts. Examining the fetal genes as a group unmasked a correlation with left atrial mass (enriched 3.04-fold vs transcriptome, p&lt;0.001). Grouping cardiac transcription factors (n=31 genes) or genes shown by gain/loss of function studies to contribute to hypertrophic signaling (n=142) revealed no correlation to cardiac phenotypes, whereas chromatin regulators (n=124) were associated with right ventricular mass (1.55-fold, p&lt;0.01), fractional shortening (1.52-fold, p&lt;0.05) and ejection fraction (1.50-fold, p&lt;0.05). We next analyzed histone genes. HOPACH clustering generated 39 clusters of strains based on the basal transcriptome that collapsed to 13 clusters after ISO, suggesting that adrenergic stress entrains gene expression. We observed transcriptional co-regulation of H2A with H2B, and H3 with H4 (the other pairings did not show correlation), mirroring the protein level assembly, which proceeds via pairs of dimers according to the same logic. Comparison of strain grouping based on partitioning clustering using histone stoichiometry or phenotype revealed that hypertrophic mice were enriched in histone cluster 4, marked by minimal change to histone variant expression (enriched 2.27-fold, p&lt;0.01). The two novel conclusions are: fetal gene regulation is buffered within populations by common genetic variation and is not a good predictor of disease; and cardiac phenotype is influenced in the basal and disease states through global changes in chromatin.

Abstract 227: The Effect of PHLPP2 Removal on Cardiomyocyte Hypertrophy

Crucial cellular decisions that lead to cell growth, metabolism, proliferation, and survival are all dependent on the precise control of the phosphorylation state of proteins. The serine/threonine phosphatase, PHLPP (PH domain leucine-rich repeat protein phosphatase) has been shown to directly dephosphorylate several members of the AGC family of kinases. Knockdown of PHLPP1 by siRNA in neonatal cardiomyocytes potentiates Akt activity and phosphorylation specifically at Ser473 basally and following agonist stimulation while, the removal of PHLPP2 in cardiomyocytes does not affect Akt phosphorylation as previously reported in other cells. We hypothesize that PHLPP2 may target other AGC kinases in cardiomyocytes to regulate cardiac hypertrophy. Preliminary data suggests that removal of PHLPP2 activates fetal gene re-expression at baseline and potentiates phenylephrine (PE) induced gene expression 2 fold over siControl. Recently, G protein-coupled receptor kinase 5 (GRK5), which is an AGC kinase, has been shown to regulate cardiac hypertrophy through HDAC5 phosphorylation and de-repression of gene transcription. We wanted to determine whether PHLPP2 regulates GRK5 phosphorylation and localization in cardiomyocytes. GRK5 translocates to the nucleus following hypertrophic stimulation and we found that removal of PHLPP2 increased GRK5 translocation to the nucleus at baseline and with PE treatment compared to siControl cells. Also, removal of PHLPP2 increased nuclear export of HDAC5 at baseline and following PE treatment. Conversely, overexpression of PHLPP2 blocked nuclear translocation of GRK5 following PE treatment. Ongoing studies will determine whether PHLPP acts as a scaffold or if its phosphatase activity is necessary for inhibition of GRK5 translocation by directly measuring the phosphorylation of GRK5 in the presence and absence of PHLPP2 following hypertrophic stimulation. Our preliminary data is the first to uncover GRK5 as a novel PHLPP2 target in cardiomyocytes. Since little is known about the non-canonical regulation of GRK5, understanding whether phosphorylation and localization is regulated within the cardiomyocyte by PHLPP has potential for new therapeutic targets in the treatment of cardiac hypertrophy and failure.

Pressure overload-induced cardiac hypertrophy response requires janus kinase 2-histone deacetylase 2 signaling.

Pressure overload induces cardiac hypertrophy through activation of Janus kinase 2 (Jak2), however, the underlying mechanisms remain largely unknown. In the current study, we tested whether histone deacetylase 2 (HDAC2) was involved in the process. We found that angiotensin II (Ang-II)-induced re-expression of fetal genes (Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP)) in cultured cardiomyocytes was prevented by the Jak2 inhibitor AG-490 and HDAC2 inhibitor Trichostatin-A (TSA), or by Jak2/HDAC2 siRNA knockdown. On the other hand, myocardial cells with Jak2 or HDAC2 over-expression were hyper-sensitive to Ang-II. In vivo, pressure overload by transverse aorta binding (AB) induced a significant cardiac hypertrophic response as well as re-expression of ANP and BNP in mice heart, which were markedly reduced by AG-490 and TSA. Significantly, AG-490, the Jak2 inhibitor, largely suppressed pressure overload-/Ang-II-induced HDAC2 nuclear exportation in vivo and in vitro. Meanwhile, TSA or HDAC2 siRNA knockdown reduced Ang-II-induced ANP/BNP expression in Jak2 over-expressed H9c2 cardiomyocytes. Together, these results suggest that HDAC2 might be a downstream effector of Jak2 to mediate cardiac hypertrophic response by pressure overload or Ang-II.

The Huntington's disease-related cardiomyopathy prevents a hypertrophic response in the R6/2 mouse model.

Huntington's disease (HD) is neurodegenerative disorder for which the mutation results in an extra-long tract of glutamines that causes the huntingtin protein to aggregate. It is characterized by neurological symptoms and brain pathology that is associated with nuclear and cytoplasmic aggregates and with transcriptional deregulation. Despite the fact that HD has been recognized principally as a neurological disease, there are multiple epidemiological studies showing that HD patients exhibit a high rate of cardiovascular events leading to heart failure. To unravel the mechanistic basis of cardiac dysfunction in HD, we employed a wide range of molecular techniques using the well-established genetic R6/2 mouse model that develop a considerable degree of the cardiac atrophy at end stage disease. We found that chronic treatment with isoproterenol, a potent beta-adrenoreceptor agonist, did not change the overall gross morphology of the HD murine hearts. However, there was a partial response to the beta-adrenergenic stimulation by the further re-expression of foetal genes. In addition we have profiled the expression level of Hdacs in the R6/2 murine hearts and found that the isoproterenol stimulation of Hdac expression was partially blocked. For the first time we established the Hdac transcriptional profile under hypertrophic conditions and found 10 out of 18 Hdacs to be markedly deregulated. Therefore, we conclude that R6/2 murine hearts are not able to respond to the chronic isoproterenol treatment to the same degree as wild type hearts and some of the hypertrophic signals are likely attenuated in the symptomatic HD animals.

B44 The Cns-heart Axis Is A Source Of Cardiac Dysfunction In Mouse Models Of Huntington's Disease

<h3></h3> Cardiac remodelling and contractile dysfunction occur during both acute and chronic disease processes including the accumulation of insoluble aggregates of misfolded amyloid proteins that are typical features of Alzheimer’s, Parkinson’s and Huntington’s disease (HD). while HD has been described mainly as a neurological disease, multiple epidemiological studies have shown that hd patients exhibit a high incidence of cardiovascular events leading to heart failure, and that this is the second highest cause of death. Given that huntingtin is ubiquitously expressed, cardiomyocytes may be at risk of an HD-related dysfunction. In mice, the forced expression of an expanded Polyq repeat under the control of a cardiac specific promoter led to severe heart failure followed by reduced lifespan. However the mechanism leading to cardiac dysfunction in the clinical and pre-clinical hd settings remains unknown. To unravel this mechanism, we employed the R6/2 transgenic and HdhQ150 knock-in mouse models of hd. we found that pre-symptomatic animals developed connexin-43 relocation and a significant deregulation of hypertrophic markers and bdnf transcripts. In the symptomatic animals, pronounced functional changes were visualised by cardiac mri revealing a contractile dysfunction, which might be a part of dilatated cardiomyopathy (dcm). This was accompanied by the re-expression of foetal genes, apoptotic cardiomyocyte loss and a moderate degree of interstitial fibrosis. To our surprise, we could identify neither mutant htt aggregates in cardiac tissue nor a hd-specific transcriptional dysregulation, even at the end stage of disease. We postulate that the hd-related cardiomyopathy is caused by altered central autonomic pathways although the pathogenic effects of mutant htt acting intrinsically in the heart may also be a contributing factor.

Dysfunction of the CNS-heart axis in mouse models of Huntington's disease.

Cardiac remodelling and contractile dysfunction occur during both acute and chronic disease processes including the accumulation of insoluble aggregates of misfolded amyloid proteins that are typical features of Alzheimer's, Parkinson's and Huntington's disease (HD). While HD has been described mainly as a neurological disease, multiple epidemiological studies have shown that HD patients exhibit a high incidence of cardiovascular events leading to heart failure, and that this is the second highest cause of death. Given that huntingtin is ubiquitously expressed, cardiomyocytes may be at risk of an HD-related dysfunction. In mice, the forced expression of an expanded polyQ repeat under the control of a cardiac specific promoter led to severe heart failure followed by reduced lifespan. However the mechanism leading to cardiac dysfunction in the clinical and pre-clinical HD settings remains unknown. To unravel this mechanism, we employed the R6/2 transgenic and HdhQ150 knock-in mouse models of HD. We found that pre-symptomatic animals developed connexin-43 relocation and a significant deregulation of hypertrophic markers and Bdnf transcripts. In the symptomatic animals, pronounced functional changes were visualised by cardiac MRI revealing a contractile dysfunction, which might be a part of dilatated cardiomyopathy (DCM). This was accompanied by the re-expression of foetal genes, apoptotic cardiomyocyte loss and a moderate degree of interstitial fibrosis. To our surprise, we could identify neither mutant HTT aggregates in cardiac tissue nor a HD-specific transcriptional dysregulation, even at the end stage of disease. We postulate that the HD-related cardiomyopathy is caused by altered central autonomic pathways although the pathogenic effects of mutant HTT acting intrinsically in the heart may also be a contributing factor.