Reversal Of Cardiac Hypertrophy Research Articles

Postprandial cardiac hypertrophy is sustained by mechanics, epigenetic, and metabolic reprogramming in pythons

Constricting pythons, known for their ability to consume infrequent, massive meals, exhibit rapid and reversible cardiac hypertrophy following feeding. Our primary goal was to investigate how python hearts achieve this adaptive response after feeding. Isolated myofibrils increased force after feeding without changes in sarcomere ultrastructure and without increasing energy cost. Ca2+ transients were prolonged after feeding with no changes in myofibril Ca2+ sensitivity. Feeding reduced titin-based tension, resulting in decreased cardiac tissue stiffness. Feeding also reduced the activity of sirtuins, a metabolically linked class of histone deacetylases, and increased chromatin accessibility. Transcription factor enrichment analysis on transposase-accessible chromatin with sequencing revealed the prominent role of transcription factors Yin Yang1 and NRF1 in postfeeding cardiac adaptation. Gene expression also changed with the enrichment of translation and metabolism. Finally, metabolomics analysis and adenosine triphosphate production demonstrated that cardiac adaptation after feeding not only increased energy demand but also energy production. These findings have broad implications for our understanding of cardiac adaptation across species and hold promise for the development of innovative approaches to address cardiovascular diseases.

Bioinformatics network analyses of growth differentiation factor 11.

Growth differentiation factor 11 (GDF11) has been implicated in rejuvenating functions in age-related diseases. The molecular mechanisms connecting GDF11 with these anti-aging phenomena, including reverse age-related cardiac hypertrophy and vascular and neurogenic rejuvenation, remain unclear. In this study, we sought to uncover the molecular functions of GDF11 using bioinformatics and network-driven analyses at the human gene and transcription levels using the gene co-expression network analysis, the protein–protein interaction network analysis, and the transcription factor network analysis. Our findings suggested that GDF11 is involved in a variety of functions, such as apoptosis, DNA repair, telomere maintenance, and interaction with key transcription factors, such as MYC proto-oncogene, specificity protein 1, and ETS proto-oncogene 2. The human skin fibroblast premature senescence model was established by UVB. The treatment with 10 ng/mL GDF11 in this cell model could reduce cell damage, reduce the apoptosis rate and the expression of caspase-3, and increase the length of telomeres. Therefore, our findings shed light on the functions of GDF11 and provide insights into the roles of GDF11 in aging.

Combination of 1,8-cineole and beta-caryophyllene synergistically reverses cardiac hypertrophy in isoprenaline-induced mice and H9c2 cells

Combination drug therapy has become an effective strategy for chronic metabolic disease, especially cardiovascular disease. In the present study, possible drug combinations were screened and the mechanism of the combinations against cardiac hypertrophy was examined within 1,8-cineole, β-caryophyllene, linalool, and β-pinene.H9c2 cells were treatment with 1,8-cineole, β-caryophyllene, linalool, and β-pinene individually or in combination for 24 h after isoprenaline stimulation. Cell viability was detected by the MTT assay. Subsequently, bioinformatic analysis and network pharmacology were used to reveal the multi-targeted synergistic therapeutic effect of the combination treatment compounds on cardiac hypertrophy. Ultimately, western blot and elisa was performed to analyses the protein expression in vivo. MTT results found that 1,8-cineole and β-caryophyllene synergistically increased cell viability with CalcuSyn software analyses. Specifically, bioinformatic and network pharmacology analysis showed PTGS2, TNF, IL-6, AKT1, NOS2, and CAT were identified as the key targets. P13K-AKT signaling pathway was involved in the reversal of cardiac hypertrophy by the combination of 1,8-cineole and β-caryophyllene. The in vitro results indicated that the combination synergistically treated the isoprenaline-induced mice against structural and functional myocardial damage via the P13K-AKT signaling pathway. Collectively, the combined application of 1,8-cineole and β-caryophyllene synergistically reverses cardiac hypertrophy in isoprenaline-induced H9c2 cells and mice.

Therapeutic Delivery of Pip4k2c-Modified mRNA Attenuates Cardiac Hypertrophy and Fibrosis in the Failing Heart.

Heart failure (HF) remains a major cause of morbidity and mortality worldwide. One of the risk factors for HF is cardiac hypertrophy (CH), which is frequently accompanied by cardiac fibrosis (CF). CH and CF are controlled by master regulators mTORC1 and TGF‐β, respectively. Type‐2‐phosphatidylinositol‐5‐phosphate‐4‐kinase‐gamma (Pip4k2c) is a known mTORC1 regulator. It is shown that Pip4k2c is significantly downregulated in the hearts of CH and HF patients as compared to non‐injured hearts. The role of Pip4k2c in the heart during development and disease is unknown. It is shown that deleting Pip4k2c does not affect normal embryonic cardiac development; however, three weeks after TAC, adult Pip4k2c−/− mice has higher rates of CH, CF, and sudden death than wild‐type mice. In a gain‐of‐function study using a TAC mouse model, Pip4k2c is transiently upregulated using a modified mRNA (modRNA) gene delivery platform, which significantly improve heart function, reverse CH and CF, and lead to increased survival. Mechanistically, it is shown that Pip4k2c inhibits TGFβ1 via its N‐terminal motif, Pip5k1α, phospho‐AKT 1/2/3, and phospho‐Smad3. In sum, loss‐and‐gain‐of‐function studies in a TAC mouse model are used to identify Pip4k2c as a potential therapeutic target for CF, CH, and HF, for which modRNA is a highly translatable gene therapy approach.

Chronic resveratrol consumption prevents hypertension development altering electrophysiological currents and Ca2+ signaling in chromaffin cells from SHR rats

Resveratrol (RESV) is one of the most abundant polyphenol-stilbene compounds found in red wine with well-established cardioprotective and antihypertensive effects. Hyperactivity of the sympathoadrenal axis seems to be one of the major contributing factors in the pathogenesis of human essential hypertension. Alterations in outward voltage-dependent potassium currents (IK) and inward voltage-dependent sodium (INa), calcium (ICa) and nicotinic (IACh) currents, CCs excitability, Ca2+ homeostasis, and catecholamine exocytosis were previously related to the hypertensive state. This raised the issue of whether in vivo long-term RESV treatment can directly act as a modulator of Ca2+ influx or a regulator of ion channel permeability in CCs. We monitored outward and inward currents, and cytosolic Ca2+ concentrations ([Ca2+]c) using different pharmacological approaches in CCs from normotensive (WKY) and hypertensive (SHR) animals chronically exposed to trans-RESV (50 mg/L/v.o, 28 days). The long-term RESV treatment prevented the increase of the systolic blood pressure (SBP) in SHR, without reversion of cardiac hypertrophy. We also found an increase of the outward IK, reduction in inward INa,ICa, and IACh, and the mitigation of [Ca2+]c overload in CCs from SHR at the end of RESV treatment. Our data revealed that electrophysiological alterations of the CCs and in its Ca2+ homeostasis are potential new targets related to the antihypertensive effects of long-term RESV treatment.

Deficiency of Cardiac Natriuretic Peptide Signaling Promotes Peripartum Cardiomyopathy-Like Remodeling in the Mouse Heart.

The maternal circulatory system and hormone balance both change dynamically during pregnancy, delivery, and the postpartum period. Although atrial natriuretic peptides and brain natriuretic peptides produced in the heart control circulatory homeostasis through their common receptor, NPR1, the physiologic and pathophysiologic roles of endogenous atrial natriuretic peptide/brain natriuretic peptide in the perinatal period are not fully understood. To clarify the physiologic and pathophysiologic roles of the endogenous atrial natriuretic peptide/brain natriuretic peptide-NPR1 system during the perinatal period, the phenotype of female wild-type and conventional or tissue-specific Npr1-knockout mice during the perinatal period was examined, especially focusing on maternal heart weight, blood pressure, and cardiac function. In wild-type mice, lactation but not pregnancy induced reversible cardiac hypertrophy accompanied by increases in fetal cardiac gene mRNAs and ERK1/2 (extracellular signaling-regulated kinase) phosphorylation. Npr1-knockout mice exhibited significantly higher plasma aldosterone level than did wild-type mice, severe cardiac hypertrophy accompanied by fibrosis, and left ventricular dysfunction in the lactation period. Npr1-knockout mice showed a high mortality rate over consecutive pregnancy-lactation cycles. In the hearts of Npr1-knockout mice during or after the lactation period, an increase in interleukin-6 mRNA expression, phosphorylation of signal transducer and activator of transcription 3, and activation of the calcineurin-nuclear factor of the activated T cells pathway were observed. Pharmacologic inhibition of the mineralocorticoid receptor or neuron-specific deletion of the mineralocorticoid receptor gene significantly ameliorated cardiac hypertrophy in lactating Npr1-knockout mice. Anti-interleukin-6 receptor antibody administration tended to reduce cardiac hypertrophy in lactating Npr1-knockout mice. These results suggest that the characteristics of lactation-induced cardiac hypertrophy in wild-type mice are different from exercise-induced cardiac hypertrophy, and that the endogenous atrial natriuretic peptide/brain natriuretic peptide-NPR1 system plays an important role in protecting the maternal heart from interleukin-6-induced inflammation and remodeling in the lactation period, a condition mimicking peripartum cardiomyopathy.

Abstract 011: Cardiovascular Consequences of Cantu Syndrome and Response to Glibenclamide Treatment in Two Novel KATP Channel Mutant Mouse Models

The rare heritable disorder Cantů syndrome (CS) arises from gain-of-function mutations in the genes encoding the cardiovascular KATP channel subunits Kir6.1 and SUR2 ( KCNJ8 and ABCC9 , respectively). CS is characterized by diverse features including hypertrichosis, osteochondrodysplasia and craniofacial dysmorphology. Multiple cardiovascular abnormalities are also reported in CS including vascular dilation and tortuosity, dramatic cardiomegaly, pulmonary hypertension and low systemic blood pressure. We have developed and characterized two novel mouse models of Cantu Syndrome in which disease causing amino acid substitutions have been engineered into either Kir6.1 (p.V65M) or SUR2 (p.A478V) using CRISPR/Cas9 genome editing. Electrophysiological assessment of isolated vascular smooth muscle cells (VSMCs) showed that both mutations result in increased basal activity of VSM KATP channels. Mutant mice also exhibit vascular dilation, low blood pressure, and pulmonary hypertension. In addition, mutant mice exhibited hypertrophic, hyper-contractile hearts. The latter findings are not trivially predictable as a consequence of KATP gain-of-function, but also recapitulates key clinical features of CS. The severity of pathophysiological remodeling correlated with the molecular effects of the substitution. These models provide novel insights to the cardiovascular consequences of KATP over-activity. Little is known about the long-term effects of human CS, nor reversibility of pathophysiological consequences. Chronic administration of the sulfonylurea KATP inhibitor glibenclamide (glyburide) by slow-release pellets implanted under the skin resulted in normalization of vascular consequences and reversal of cardiac hypertrophy in SUR2(A478V) mice over 3 weeks. Kir6.1(V65M) mice are less sensitive to glibenclamide treatment, as predicted from studies of recombinant channels. These results suggest that glibenclamide represents a promising pharmacotherapy for CS (but that sensitivity may be patient- and mutation-dependent), and perhaps for diverse cardiovascular conditions arising from decreased smooth muscle excitability in general.

Memantine, an NMDA Receptor Antagonist, Prevents Thyroxin-induced Hypertension, but Not Cardiac Remodeling.

Stimulation of glutamatergic tone has been causally linked to myocardial pathogenesis and amplified systemic blood pressure (BP). Memantine, a noncompetitive N-methyl-D-aspartate glutamatergic receptor (NMDA-R) antagonist, has been proposed to be an active cardioprotective drug. However, the efficacy of memantine and subsequently the possible involvement of the NMDA-R in the thyroxin (T4)-induced cardiovascular complications have never been investigated. We examined the effect of memantine (30 mg·kg·d) on the T4 (500 μg·kg·d)-provoked increase in mouse BP, cardiac hypertrophy indicated by enlarged overall myocardial mass, and reformed reactions of the contractile myocardium both in vivo and ex vivo after 2 weeks of treatment. Memantine alone did not result in any cardiovascular pathology in mice. Instead, memantine significantly prevented the T4-triggered systemic hypertension. But, it did not reverse cardiac hypertrophy, coupled in vivo left ventricular dysfunction (LV) or ex vivo right ventricular (RV) papillary muscle contractile alterations of the T4-treated mice. Our results openly direct the cardiovascular safety and tolerability of memantine therapy. Yet, extra research is necessary to endorse these prospective advantageous outcomes. Also, we believe that this is the first study to inspect the possible role of NMDA-R in the T4-stimulated cardiovascular disorders and concluded that NMDA-R could play a key role in the T4-induced hypertension.

Size matters: Finding growth pathways that protect the heart.

In a recent paper published in Cell Research, Abdul-Ghani and colleagues show that the cytokine, cardiotrophin-1 (CT1), drives a protective form of reversible cardiac hypertrophy that acts through a nonapoptotic caspase-dependent mechanism. Since CT1 can be delivered as exogenous protein, these studies provide new biological insights and potential translational opportunities.

Diltiazem prevents stress-induced contractile deficits in cardiomyocytes, but does not reverse the cardiomyopathy phenotype in Mybpc3-knock-in mice.

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac illness and can lead to diastolic dysfunction, sudden cardiac death and heart failure. Treatment of HCM patients is empirical and current pharmacological treatments are unable to stop disease progression or reverse hypertrophy. In this study, we tested if the non-dihydropyridine Ca2+ channel blocker diltiazem, which previously showed potential to stop disease progression, can improve the phenotype of a HCM mouse model (Mybpc3-targeted knock-in), which is based on a mutation commonly found in patients. Diltiazem improved contractile function of isolated ventricular cardiomyocytes acutely, but chronic application did not improve the phenotype of adult mice with a fully developed HCM. Our study shows that diltiazem has beneficial effects in HCM, but long-term treatment success is likely to depend on characteristics and cause of HCM and onset of treatment. Left ventricular hypertrophy, diastolic dysfunction and fibrosis are the main features of hypertrophic cardiomyopathy (HCM). Guidelines recommend β-adrenoceptor or Ca2+ channel antagonists as pharmacological treatment. The Ca2+ channel blocker diltiazem recently showed promising beneficial effects in pre-clinical HCM, particularly in patients carrying MYBPC3 mutations. In the present study we evaluated whether diltiazem could ameliorate or reverse the disease phenotype in cells and in vivo in an Mybpc3-targeted knock-in (KI) mouse model of HCM. Sarcomere shortening and Ca2+ transients were measured in KI and wild-type (WT) cardiomyocytes in basal conditions (1-Hz pacing) and under stress conditions (30nm isoprenaline, 5-Hz pacing) with or without pre-treatment with 1μm diltiazem. KI cardiomyocytes exhibited lower diastolic sarcomere length (dSL) at baseline, a tendency to a stronger positive inotropic response to isoprenaline than WT, a marked reduction of dSL and a tendency towards arrhythmias under stress conditions. Pre-treatment of cardiomyocytes with 1μm diltiazem reduced the drop in dSL and arrhythmia frequency in KI, and attenuated the positive inotropic effect of isoprenaline. Furthermore, diltiazem reduced the contraction amplitude at 5Hz but did not affect diastolic Ca2+ load and Ca2+ transient amplitude. Sixmonths of diltiazem treatment of KI mice did not reverse cardiac hypertrophy and dysfunction, activation of the fetal gene program or fibrosis. In conclusion, diltiazem blunted the response to isoprenaline in WT and KI cardiomyocytes and improved diastolic relaxation under stress conditions in KI cardiomyocytes. This beneficial effect of diltiazem in cells did not translate in therapeutic efficacy when applied chronically in KI mice.

Response of the JAK-STAT pathway to mammalian hibernation in 13-lined ground squirrel striated muscle

Over the course of the torpor-arousal cycle, hibernators must make behavioral, physiological, and molecular rearrangements in order to keep a very low metabolic rate and retain organ viability. 13-lined ground squirrels (Ictidomys tridecemlineatus) remain immobile during hibernation, and although the mechanisms of skeletal muscle survival are largely unknown, studies have shown minimal muscle loss in hibernating organisms. Additionally, the ground squirrel heart undergoes cold-stress, reversible cardiac hypertrophy, and ischemia-reperfusion without experiencing fatal impairment. This study examines the role of the Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway in the regulation of cell stress in cardiac and skeletal muscles, comparing euthermic and hibernating ground squirrels. Immunoblots showed a fivefold decrease in JAK3 expression during torpor in skeletal muscle, along with increases in STAT3 and 5 phosphorylation and suppressors of cytokine signaling-1 (SOCS1) protein levels. Immunoblots also showed coordinated increases in STAT1, 3 and 5 phosphorylation and STAT1 inhibitor protein expression in cardiac muscle during torpor. PCR analysis revealed that the activation of these pro-survival signaling cascades did not result in coordinate changes in downstream genes such as anti-apoptotic B-cell lymphoma-2 (Bcl-2) family gene expression. Overall, these results indicate activation of the JAK-STAT pathway in both cardiac and skeletal muscles, suggesting a response to cellular stress during hibernation.

OP.2C.01] TETRAHYDROBIOPTERIN REVERSE LEFT VENTRICULAR HYPERTROPHY AND DIASTOLIC DYSFUNCTION THROUGH THE PI3K/P-AKT PATHWAY IN SPONTANEOUSLY HYPERTENSIVE RATS

Objective: Hypertension induced hypertrophy and diastolic dysfunction and is associated with cardiac oxidation and reduced NO production. We hypothesized that tetrahydrobiopterin (BH4) can regulate the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathway and reverse cardiac hypertrophy and diastolic dysfunction in spontaneously hypertensive rats. Design and method: Ten-week-old male spontaneously hypertensive rats (SHR) and age-matched normotensive control Wistar-Kyoto (WKY) rats were divided into five groups, WKY,WKY + BH4, SHR, SHR + BH4 and SHR + VAL. Diastolic function were assessed by echocardiography and hemodynamics. The expression and phosphorylation level of PI3Kand Akt were assayed with western blot analysis. High performance liquid chromatography (HPLC) analysis was used to measure BH4 and biopterins. Quantitative real-time- Polymerase Chain Reaction (PCR) and immunohistochemistry were used to test cardiac hypertrophic genes and expression of Bax and Bcl-2 in the myocardium. Results: In SHR diastolic dysfunction was accompanied by concentric hypertrophy,cardiac oxidation, a reduction in cardiac BH4 and NO production. Administered with BH4 and Valsartan for four weeks, the data showed that both can reverse hypertrophy and improve diastolic function.BH4 and Valsartan blunted the expression of hypertrophy markers alpha - skeletal actin and beta - myosin heavy chain (beta - MHC), only BH4 reduced hypertension induced myocardial fibrosis and expression of transforming growth factor - beta 1 (TGF - beta1). BH 4 reduced cardiac oxidant stress and increased NO production. Exogenous BH 4 increased the phosphorylated Akt level and enhanced expression of Bcl-2. Conclusions: Less BH4 and reduced NO increases myocardial hypertrophy and cardiac oxidative stress, which exacerbates diastolic dysfunction. Exogenous BH4 ameliorates cardiac hypertrophy and diastolic dysfunction through the PI3K/p-Akt pathway. BH4 may be a potent therapy for hypertension with diastolic dysfunction.

OS 36-05 TETRAHYDROBIOPTERIN REVERSE LEFT VENTRICULAR HYPERTROPHY AND DIASTOLIC DYSFUNCTION THROUGH THE PI3K/p-Akt PATHWAY IN SPONTANEOUSLY HYPERTENSIVE RATS

Objective: Hypertension induced hypertrophy and diastolic dysfunction and is associated with cardiac oxidation and reduced NO production. We hypothesized that tetrahydrobiopterin (BH4) can regulate the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathway and reverse cardiac hypertrophy and diastolic dysfunction in spontaneously hypertensive rats. Design and Method: Ten-week-old male spontaneously hypertensive rats (SHR) and age-matched normotensive control Wistar-Kyoto (WKY) rats were divided into five groups, WKY,WKY + BH4, SHR, SHR + BH4 and SHR + VAL. Diastolic function were assessed by echocardiography and hemodynamics. The expression and phosphorylation level of PI3Kand Akt were assayed with western blot analysis. High performance liquid chromatography (HPLC) analysis was used to measure BH4 and biopterins. Quantitative real-time- Polymerase Chain Reaction (PCR) and immunohistochemistry were used to test cardiac hypertrophic genes and expression of Bax and Bcl-2 in the myocardium. Results: In SHR diastolic dysfunction was accompanied by concentric hypertrophy,cardiac oxidation, a reduction in cardiac BH4 and NO production. Administered with BH4 and Valsartan for four weeks, the data showed that both can reverse hypertrophy and improve diastolic function.BH4 and Valsartan blunted the expression of hypertrophy markers α-skeletal actin (α-SA) and β-myosin heavy chain (β-MHC), only BH4 reduced hypertension induced myocardial fibrosis and expression of transforming growth factor-β1(TGF-β1). BH4 reduced cardiac oxidant stress and increased NO production. Exogenous BH4 increased the phosphorylated Akt level and enhanced expression of Bcl-2. Conclusions: Less BH4 and reduced NO increases myocardial hypertrophy and cardiac oxidative stress, which exacerbates diastolic dysfunction. Exogenous BH4 ameliorates cardiac hypertrophy and diastolic dysfunction through the PI3K/p-Akt pathway. BH4 may be a potent therapy for hypertension with diastolic dysfunction.

Response of the JAK-STAT pathway to mammalian hibernation in 13-lined ground squirrel striated muscle.

Over the course of the torpor-arousal cycle, hibernators must make behavioral, physiological, and molecular rearrangements in order to keep a very low metabolic rate and retain organ viability. 13-lined ground squirrels (Ictidomys tridecemlineatus) remain immobile during hibernation, and although the mechanisms of skeletal muscle survival are largely unknown, studies have shown minimal muscle loss in hibernating organisms. Additionally, the ground squirrel heart undergoes cold-stress, reversible cardiac hypertrophy, and ischemia-reperfusion without experiencing fatal impairment. This study examines the role of the Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway in the regulation of cell stress in cardiac and skeletal muscles, comparing euthermic and hibernating ground squirrels. Immunoblots showed a fivefold decrease in JAK3 expression during torpor in skeletal muscle, along with increases in STAT3 and 5 phosphorylation and suppressors of cytokine signaling-1 (SOCS1) protein levels. Immunoblots also showed coordinated increases in STAT1, 3 and 5 phosphorylation and STAT1 inhibitor protein expression in cardiac muscle during torpor. PCR analysis revealed that the activation of these pro-survival signaling cascades did not result in coordinate changes in downstream genes such as anti-apoptotic B-cell lymphoma-2 (Bcl-2) family gene expression. Overall, these results indicate activation of the JAK-STAT pathway in both cardiac and skeletal muscles, suggesting a response to cellular stress during hibernation.

Reversible cardiac hypertrophy induced by PEG-coated gold nanoparticles in mice.

Gold nanoparticles (GNPs) are attracting more and more attention for their great potential value in biomedical application. Currently, no study has been reported on the chronic cardiac toxicity of GNPs after repeated administration. Here we carried out a comprehensive evaluation of the chronic cardiac toxicity of GNPs to the heart. Polyethylene glycol (PEG) -coated GNPs at three different sizes (10, 30 and 50 nm) or PBS was administrated to mice via tail vein for 14 consecutive days. Then the mice were euthanized at 2 weeks, 4 weeks or 12 weeks after the first injection. The accumulation of GNPs in the mouse heart and their effects on cardiac function, structure, fibrosis and inflammation were analysized. GNPs with smaller size showed higher accumulation and faster elimination. None of the three sizes of GNPs affected cardiac systolic function. The LVIDd (left ventricular end-diastolicinner-dimension), LVMass (left ventricular mass) and HW/BW (heart weight/body weight) were significantly increased in the mice receiving 10 nm PEG-GNPs for 2 weeks, but not for 4 weeks or 12 weeks. These results indicated that the accumulation of small size GNPs can induce reversible cardiac hypertrophy. Our results provide the basis for the further biomedical applications of GNPs in cardiac diseases.

Ranolazine antagonizes catecholamine-induced dysfunction in isolated cardiomyocytes, but lacks long-term therapeutic effects in vivo in a mouse model of hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy (HCM) is often accompanied by increased myofilament Ca(2+) sensitivity and diastolic dysfunction. Recent findings indicate increased late Na(+) current density in human HCM cardiomyocytes. Since ranolazine has the potential to decrease myofilament Ca(2+) sensitivity and late Na(+) current, we investigated its effects in an Mybpc3-targeted knock-in (KI) mouse model of HCM. Unloaded sarcomere shortening and Ca(2+) transients were measured in KI and wild-type (WT) cardiomyocytes. Measurements were performed at baseline (1 Hz) and under increased workload (30 nM isoprenaline (ISO), 5 Hz) in the absence or presence of 10 µM ranolazine. KI myocytes showed shorter diastolic sarcomere length at baseline, stronger inotropic response to ISO, and drastic drop of diastolic sarcomere length under increased workload. Ranolazine attenuated ISO responses in WT and KI cells and prevented workload-induced diastolic failure in KI. Late Na(+) current density was diminished and insensitive to ranolazine in KI cardiomyocytes. Ca(2+) sensitivity of skinned KI trabeculae was slightly decreased by ranolazine. Phosphorylation analysis of cAMP-dependent protein kinase A-target proteins and ISO concentration-response measurements on muscle strips indicated antagonism at β-adrenoceptors with 10 µM ranolazine shifting the ISO response by 0.6 log units. Six-month treatment with ranolazine (plasma level >20 µM) demonstrated a β-blocking effect, but did not reverse cardiac hypertrophy or dysfunction in KI mice. Ranolazine improved tolerance to high workload in mouse HCM cardiomyocytes, not by blocking late Na(+) current, but by antagonizing β-adrenergic stimulation and slightly desensitizing myofilaments to Ca(2+). This effect did not translate in therapeutic efficacy in vivo.

EXPRESSION OF NUCLEAR FACTOR OF ACTIVATED T CELLS (NFAT) AND DOWNSTREAM TARGETS IN GROUND SQUIRREL CARDIAC MUSCLE

13-lined ground squirrels undergo remarkable adaptive changes during hibernation where the animals enter deep torpor and allow body temperature (Tb) to fall as low as 0-5°C. While hibernating, reversible cardiac hypertrophy occurs to increase contractility of the heart; this helps the heart to pump colder and more viscous blood, while avoiding heart failure as a result of sustained or chronic hypertrophy. We were interested in studying the role of the nuclear factor of activated T-cell (NFAT) family of transcription factors and their recently discovered sarcolemmal targets, myoferlin and myomaker, with the adaptations taking place in cardiac muscle during hibernation. Whole heart samples were collected at 6 different time points over the torpor-arousal cycle including euthermic control (EC), entrance into torpor (EN), early torpor (ET), late torpor (LT), early arousal (EA), and interbout arousal (IA) back to euthermia; each stage differs in squirrel Tb and respiration rates. Total protein extracts were prepared and immunoblotting was performed using antibodies specific for mammalian NFATc1, c2, c3, c4, myoferlin, and myomaker. Bioinformatic analysis was conducted on the 1500 bp region upstream of the myomaker transcription start site to identify novel NFAT transcription factor binding sites. DNA-binding enzyme-lined immunosorbent assay (ELISA) was performed over the torpor-arousal timecourse to characterize NFAT-binding to the NFAT-binding sequence identified. In cardiac muscle, NFATc1, c2, and c3 increased during torpor whereas NFATc4 protein levels were elevated throughout the torpor-arousal cycle. A spike in myoferlin protein levels was observed during ET (2.68 fold increase compared to control) with a smaller increase during EA (1.69 fold increase). Myomaker also increased significantly in cardiac muscle during ET (1.88 fold increase) and to a much lesser extent at EA. Bioinformatics analysis and cross-referencing using the NFAT consensus binding sequence resulted in the identification of a putative novel NFAT binding site and DNA-binding ELISAs showed that NFATc1 and c3 were able to bind to this site. This study is the first to observe myomaker expression in cardiac tissue and to identify a possible NFAT-binding region within its promoter. Elevated protein levels of NFATc1-4, myoferlin, and myomaker at selected stages of the torpor-arousal cycle appear to be a regulatory mechanism that contributes to reversible cardiac hypertrophy in response to the changing physiological and environmental stresses encountered during hibernation. The identification of novel targets involved in cardiac hypertrophy provides insight into how heart failure resulting from sustained cardiac overload might be prevented.

Exposure to concentrated ambient particulate matter induces reversible increase of heart weight in spontaneously hypertensive rats

BackgroundExposure to ambient PM2.5 increases cardiovascular mortality and morbidity. To delineate the underlying biological mechanism, we investigated the time dependence of cardiovascular response to chronic exposure to concentrated ambient PM2.5 (CAP).MethodsSpontaneously hypertensive rats (SHR) were exposed to CAP for 15 weeks, and blood pressure (BP), cardiac function and structure, and inflammations of lung, hypothalamus, and heart were measured at different time points.ResultsChronic exposure to CAP significantly increased BP, and withdrawal from CAP exposure restored BP. Consistent with its BP effect, chronic exposure to CAP significantly decreased cardiac stroke volume and output in SHR, accompanied by increased heart weight and increased cardiac expression of hypertrophic markers ACTA1 and MYH7. Withdrawal from CAP exposure restored cardiac function, weight, and expression of hypertrophic markers, supporting the notion that cardiac dysfunction and hypertrophy is subsequent to hypertension. In agreement with the role of systemic inflammation in mediating the cardiovascular effects of CAP exposure, chronic exposure to CAP markedly increased expression of pro-inflammatory cytokines in lung, heart, and hypothalamus. However, withdrawal from exposure resolves inflammation in the heart and hypothalamus, but not in the lung, suggesting that CAP exposure-induced systemic inflammation may be independent of pulmonary inflammation.ConclusionChronic exposure to CAP induces reversible cardiac dysfunction and hypertrophy, which is likely to be subsequent to the elevation in BP and induction of systemic inflammation as evidenced by increased mRNA expression of pro-inflammatory cytokines in diverse tissues.

Tetrahydrobiopterin reverse left ventricular hypertrophy and diastolic dysfunction through the PI3K/p-Akt pathway in spontaneously hypertensive rats

Hypertension induced hypertrophy and diastolic dysfunction and is associated with cardiac oxidation and reduced NO production. We hypothesized that tetrahydrobiopterin (BH4) can regulate the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathway and reverse cardiac hypertrophy and diastolic dysfunction in spontaneously hypertensive rats. Ten-week-old male spontaneously hypertensive rats (SHR) and age-matched normotensive control Wistar-Kyoto (WKY) rats were divided into five groups, WKY, WKY + BH4, SHR, SHR + BH4 and SHR + VAL. In SHR, diastolic dysfunction was accompanied by concentric hypertrophy, cardiac oxidation, and reduced cardiac BH4 and NO production. Four-week BH4 and valsartan administration reversed hypertrophy and improved diastolic function. BH4 and valsartan blunted the expression of hypertrophy markers α-skeletal actin (α-SA) and β-myosin heavy chain (β-MHC). Only BH4 reduced hypertension and induced myocardial fibrosis and expression of transforming growth factor-β1 (TGF-β1). BH4 reduced cardiac oxidant stress and increased NO production. Exogenous BH4 increased phosphorylated Akt levels and increased Bcl-2 expression.In conclusion, less BH4 and reduced NO increases myocardial hypertrophy and cardiac oxidative stress, which exacerbates diastolic dysfunction. Exogenous BH4 ameliorates cardiac hypertrophy and diastolic dysfunction through the PI3K/p-Akt pathway. BH4 may be a potent therapy for hypertension with diastolic dysfunction.

Alcohol-induced histone H3K9 hyperacetylation and cardiac hypertrophy are reversed by a histone acetylases inhibitor anacardic acid in developing murine hearts

The expression of cardiac genes is precisely regulated, and any perturbation may cause developmental defects. In a previous study, we demonstrated that alcohol consumption during pregnancy could lead to uncontrolled expressions of cardiac genes and eventually result in cardiac dysplasia. However, the underlying mechanisms remain unclear. In the present study, we have investigated the alcohol-induced cardiac hypertrophy and its potential mechanisms. Furthermore, the protective effect of anacardic acid against the alcohol-induced cardiac hypertrophy has been explored in experimental mice. C57BL/6 pregnant mice were gavaged with 56% ethanol or saline and the hearts of their fetus were collected for analysis. Binding of p300, CBP, PCAF, SRC1, except GCN5, were increased to the NKX2.5 promoter in fetal mouse hearts exposed to alcohol. Increased acetylation of H3K9 and increased mRNA expression of NKX2.5, β-MHC and Cx43 were observed in the same samples. Treatment with a pan-acetylase inhibitor, anacardic acid, reduced the binding affinity of p300 and PCAF to the NKX2.5, β-MHC, Cx43 promoters and attenuated H3K9 hyperacetylation. Interestingly, anacardic acid down-regulated over-expression of these cardiac genes induced by alcohol and ultimately attenuated ethanol-induced cardiac hypertrophy in fetal mice. Our results indicate that alcohol exposure during pregnancy could lead to fetal cardiac hypertrophy. The over-expression of NKX2.5, β-MHC, Cx43 mediated by p300 and PCAF may be critical mechanisms of alcohol-induced cardiac hypertrophy. Anacardic acid can down-regulate the over-expression of cardiac genes and reverse cardiac hypertrophy caused by alcohol treatment in pregnant mice, suggesting it could be a potential therapeutic agent for the treatment of cardiac hypertrophy.