Upregulation Of Atrial Natriuretic Peptide Research Articles

Abstract Mo008: Sub-strain Dependent Vulnerability to Psychosocial Stress Exacerbates Doxorubicin-induced Cardiotoxicity in Adult Male Mice

Introduction: Psychosocial stress is a significant cardiovascular risk factor and an enormous burden on cancer patients. However, limited knowledge is available on the underlying mechanisms at least in part because of lack of translationally relevant animal models. Previous work from our lab established that adult exposure to social stress can exacerbate the cardiovascular effect of juvenile doxorubicin (DOX) exposure. However, the effect of concomitant DOX and stress exposure in adult mice is unknown. Methods: In this study, a ‘two-hit’ mouse model was established, in which chronic subordination stress (CSS) and DOX treatment were given simultaneously. Twelve-week-old male C57BL/6N (6N) and C57BL/6J (6J) mice were subjected to daily episodes of social defeat by dominant CD1 mice with whom they remained in continuous sensory contact with for 28 days, thus establishing social subordination. One week after the start of CSS, mice were administered DOX (8 mg/kg/week) for 3 weeks. Thereafter, cardiac function was assessed by echocardiography and gene expression of inflammatory and pro-fibrotic markers were determined by real-time PCR. Cardiac fibrosis and inflammation were assessed by histopathologic analysis. Results: Cardiac dysfunction and significant cardiac fibrosis were observed in 6N but not in 6J mice that were exposed to both DOX and CSS, as evidenced by reduced ejection fraction, cardiac output, and increased trichrome staining, respectively. Additionally, gene expression analysis demonstrated significant upregulation of atrial natriuretic peptide and interleukin-6 in 6N mice exposed to both DOX and CSS compared to 6J mice. Finally, DOX caused cardiac atrophy and abrogated CSS-induced cardiac hypertrophy in 6N but not in 6J mice, as evidenced by measuring left ventricular mass and heart weight/tibia length. Conclusion: Exposure to CSS exacerbated the cardiotoxic effects of DOX in a sub-strain dependent manner. These findings highlight psychosocial stress as a risk factor for worse cardiovascular outcome in cancer patients receiving cardiotoxic regimens. The study underscores sub-strain differences in the cardiac responses of 6N and 6J mouse to CSS alone and CSS/DOX treatment that may serve as a discovery platform for the identification of genetic biomarkers of resilience.

LongShengZhi alleviated cardiac remodeling via upregulation microRNA-150-5p with matrix metalloproteinase 14 as the target

Ethnopharmacological relevanceLongShengZhi capsule (LSZ), a traditional Chinese medicine, is used for treatment of patients with vascular diseases. LSZ reduced doxorubicin-induced heart failure by reducing production of reactive oxygen species and inhibiting inflammation and apoptosis. Aim of the studyThis study was to explore whether LSZ could alleviate cardiac remodeling via upregulation of microRNA (miR)-150-5p and the downstream target. Cardiac remodeling was induced by Ang II in vivo and in vitro. ResultsLSZ attenuated Ang II-induced cardiac hypertrophy and fibrosis in rats, and in primary cardiomyocytes (CMs) and primary cardiac fibroblasts (CFs). MiR-150-5p was downregulated in Ang II-induced rat heart, CMs and CFs, and these decreases were reserved by LSZ. In vivo overexpression of miR-150-5p by transfection of miR-150-5p agomiR protected Ang II-induced cardiac hypertrophy and fibrosis in rats. Meanwhile, its overexpression also reversed Ang II-induced upregulation of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and β-myosin heavy chain (β-MHC) in rat hearts and primary CMs, as well as upregulation of collagen I, collagen III and transforming growth factor-β (TGF-β) in rat hearts and primary CFs. Matrix metalloproteinase 14 (MMP14) was validated as the target gene of miR-150-5p, which was overexpressed in Ang II-induced rat heart, rat primary CMs and primary CFs. Notably, overexpression of MMP14 induced cardiac remodeling, and reversed the protective role of miR-150-5p in downregulating Ang II-induced upregulation of hypertrophy and fibrosis markers in vitro. ConclusionCollectively, LSZ protects Ang II-induced cardiac dysfunction and remodeling via upregulation of miR-150-5p to target MMP14. Administration of LSZ, upregulation of miR-150-5p or targeting of MMP14 may be strategies for cardiac remodeling therapy.

Cardio-renal Protective Role of Alpha Lipoic Acid Against Mesterolone in Relation to ANP, Nrf2 and TSPO genes

The protective role of Alpha Lipoicacide on cardio_renal function in rabbits subjected to Mesterolone wasstudied. A total of twenty adult female rabbits was divided into fourgroups:Control,Mesterolone(0.65mg/kg B.w),Lipoic acid(10 mg/kg B.w) and Mesterolone +Lipoic acid.All animals received treatment everyday for 60 days by oral administration during the period from 1stAugust 2018 to 1st June 2019. At theend of the experiment, animals were anesthetized by double dose anesthesia, heart and kidney tissues forRNA isolation were taken.This retrospective study was carried out in Department of physiology/College ofVeterinary Medicine/University of Baghdad/Iraq. The heart and kidney tissue were isolated for the expressionof atrial natriuretic peptide,nuclear factor erythroid 2 related factor 2 and Translocator protein genes.Theresults showed a significant increase in the expression of the genes in Mesterolonegroup.Whereas, Lipoicavid supplementation decreases them. These results indicate the important effect of Alpha lipoic acid oncardiorenal function. These anabolic androgenic steroids such as Mesterolone exert an up regulation of atrialnatriuretic peptide,nuclear factor erythroid 2 related factor 2 and Translocator protein genes expression toovercome the damage of heart and kidney tissue induced by them.

Cinacalcet as a surrogate therapy for diabetic cardiomyopathy in rats through AMPK-mediated promotion of mitochondrial and autophagic function

Decreased activity of AMP-activated protein kinase (AMPK) is implicated in the pathogenesis of diabetic cardiomyopathy (DCM). Recent evidence suggests a crosstalk between cinacalcet and AMPK activation. This study investigated the effects of cinacalcet on cardiac remodeling and dysfunction in type 2 diabetic rats (T2DM). High fat diet for 4 weeks combined with single intraperitoneal injection of streptozotocin (30 mg/kg) was used to induce type 2 diabetes in rats. Diabetic rats were either orally treated with vehicle, 5 or 10 mg/kg cinacalcet for 4 weeks. Control rats were fed standard chow diet and intraperitoneally injected with citrate buffer. T2DM rats showed lower body weight (BW), hyperglycemia and dyslipidemia, along with increased heart weight (HW) and HW/BW ratio. Masson's trichrome stained cardiac sections revealed massive fibrosis in T2DM rats. There were increased TGF-β1 and hydroxyproline levels, coupled with up-regulation of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) in hearts of T2DM rats. These alterations were associated with redox imbalance and impaired cardiac functions. Decreased phosphorylation of AMPK at threonine172 residue was found in T2DM hearts. Cinacalcet for 4 weeks significantly activated AMPK and alleviated cardiac remodeling and dysfunction in a dose-dependent manner, without affecting blood glucose, serum calcium and phosphorus levels. Cinacalcet increased the mitochondrial DNA content, and expressions of PGC-1α, UCP-3, beclin-1 and LC3-II/LC3-I ratio. Cinacalcet decreased the pro-apoptotic Bax, while increased the anti-apoptotic Bcl-2 in cardiac tissue of T2DM rats. These findings might highlight cinacalcet as an alternative therapy to combat the development and progression of DCM.

Anti-fibrotic Actions of Roselle Extract in Rat Model of Myocardial Infarction.

Heart failure-associated morbidity and mortality is largely attributable to extensive and unregulated cardiac remodelling. Roselle (Hibiscus sabdariffa) calyces are enriched with natural polyphenols known for antioxidant and anti-hypertensive effects, yet its effects on early cardiac remodelling in post myocardial infarction (MI) setting are still unclear. Thus, the aim of this study was to investigate the actions of roselle extract on cardiac remodelling in rat model of MI. Male Wistar rats (200-300g) were randomly allotted into three groups: Control, MI, and MI + Roselle. MI was induced with isoprenaline (ISO) (85mg/kg, s.c) for two consecutive days followed by roselle treatment (100mg/kg, orally) for 7days. Isoprenaline administration showed changes in heart weight to body weight (HW/BW) ratio. MI was especially evident by the elevated cardiac injury marker, troponin-T, and histological observation. Upregulation of plasma levels and cardiac gene expression levels of inflammatory cytokines such as interleukin (IL)-6 and IL-10 was seen in MI rats. A relatively high percentage of fibrosis was observed in rat heart tissues with over-expression of collagen (Col)-1 and Col-3 genes following isoprenaline-induced MI. On top of that, cardiomyocyte areas were larger in heart tissues of MI rats with upregulation of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) gene expression, indicating cardiac hypertrophy. Interestingly, roselle supplementation attenuated elevation of plasma troponin-T, IL-6, IL10, and gene expression level of IL-10. Furthermore, reduction of cardiac fibrosis and hypertrophy were observed. In conclusion, roselle treatment was able to limit early cardiac remodelling in MI rat model by alleviating inflammation, fibrosis, and hypertrophy; hence, the potential application of roselle in early adjunctive treatment to prevent heart failure.

Mesenchymal Stem Cells and Cardiomyocytes Interplay to Prevent Myocardial Hypertrophy

Bone marrow-derived mesenchymal stem cells (BMSCs) have emerged as a promising therapeutic strategy for cardiovascular disease. However, there is no evidence so far that BMSCs can heal pathological myocardial hypertrophy. In this study, BMSCs were indirectly cocultured with neonatal rat ventricular cardiomyocytes (NRVCs) in vitro or intramyocardially transplanted into hypertrophic hearts in vivo. The results showed that isoproterenol (ISO)-induced typical hypertrophic characteristics of cardiomyocytes were prevented by BMSCs in the coculture model in vitro and after BMSC transplantation in vivo. Furthermore, activation of the Ca(2+)/calcineurin/nuclear factor of activated T cells cytoplasmic 3 (NFATc3) hypertrophic pathway in NRVCs was abrogated in the presence of BMSCs both in vitro and in vivo. Interestingly, inhibition of vascular endothelial growth factor (VEGF) release from BMSCs, but not basic fibroblast growth factor and insulin-like growth factor 1, abolished the protective effects of BMSCs on cardiomyocyte hypertrophy. Consistently, VEGF administration attenuated ISO-induced enlargement of cellular size; the upregulation of atrial natriuretic peptide, brain natriuretic peptide, and β-myosin heavy chain expression; and the activation of Ca²⁺/calcineurin/NFATc3 hypertrophic pathways, and these pathways can be abrogated by blocking VEGFR-1 in cardiomyocytes, indicating that VEGF receptor 1 is involved in the antihypertrophic role of VEGF. We further found that the ample VEGF secretion contributing to the antihypertrophic effects of BMSCs originates from the crosstalk of BMSCs and cardiac cells but not BMSCs or cardiomyocytes alone. Interplay of mesenchymal stem cells with cardiomyocytes produced synergistic effects on VEGF release. In summary, crosstalk between mesenchymal stem cells and cardiomyocytes contributes to the inhibition of myocardial hypertrophy via inhibiting Ca²⁺/calcineurin/NFATc3 hypertrophic pathways in cardiac cells. These results provide the first evidence for the treatment of myocardial hypertrophy using BMSCs. This study found that mesenchymal stem cells may crosstalk with cardiomyocytes, which causes a synergistic vascular endothelial growth factor (VEGF) release from both kinds of cells and then inhibits pathological cardiac remodeling following hypertrophic stimulation in cardiomyocytes in vitro and in vivo. Blockage of VEGF release from bone marrow-derived mesenchymal stem cells (BMSCs) abolishes the antihypertrophic actions of BMSCs in vitro and in vivo. On the contrary, VEGF administration attenuates hypertrophic signaling of calcineurin/ nuclear factor of activated T cell cytoplasmic 3 signal pathways. This study provides the first evidence for the treatment of myocardial hypertrophy using BMSCs.

Cytosolic CARP promotes angiotensin II- or pressure overload-induced cardiomyocyte hypertrophy through calcineurin accumulation.

The gene ankyrin repeat domain 1 (Ankrd1) is an enigmatic gene and may exert pleiotropic function dependent on its expression level, subcellular localization and even types of pathological stress, but it remains unclear how these factors influence the fate of cardiomyocytes. Here we attempted to investigate the role of CARP on cardiomyocyte hypertrophy. In neonatal rat ventricular cardiomyocytes (NRVCs), angiotensin II (Ang II) increased the expression of both calpain 1 and CARP, and also induced cytosolic translocation of CARP, which was abrogated by a calpain inhibitor. In the presence of Ang-II in NRVCs, infection with a recombinant adenovirus containing rat Ankrd1 cDNA (Ad-Ankrd1) enhanced myocyte hypertrophy, the upregulation of atrial natriuretic peptide and β-myosin heavy chain genes and calcineurin proteins as well as nuclear translocation of nuclear factor of activated T cells. Cyclosporin A attenuated Ad-Ankrd1-enhanced cardiomyocyte hypertrophy. Intra-myocardial injection of Ad-Ankrd1 in mice with transverse aortic constriction (TAC) markedly increased the cytosolic CARP level, the heart weight/body weight ratio, while short hairpin RNA targeting Ankrd1 inhibited TAC-induced hypertrophy. The expression of calcineurin was also significantly increased in Ad-Ankrd1-infected TAC mice. Olmesartan (an Ang II receptor antagonist) prevented the upregulation of CARP in both Ang II-stimulated NRVCs and hearts with pressure overload. These findings indicate that overexpression of Ankrd1 exacerbates pathological cardiac remodeling through the enhancement of cytosolic translocation of CARP and upregulation of calcineurin.

HDAC4 controls histone methylation in response to elevated cardiac load

In patients with heart failure, reactivation of a fetal gene program, including atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), is a hallmark for maladaptive remodeling of the LV. The mechanisms that regulate this reactivation are incompletely understood. Histone acetylation and methylation affect the conformation of chromatin, which in turn governs the accessibility of DNA for transcription factors. Using human LV myocardium, we found that, despite nuclear export of histone deacetylase 4 (HDAC4), upregulation of ANP and BNP in failing hearts did not require increased histone acetylation in the promoter regions of these genes. In contrast, di- and trimethylation of lysine 9 of histone 3 (H3K9) and binding of heterochromatin protein 1 (HP1) in the promoter regions of these genes were substantially reduced. In isolated working murine hearts, an acute increase of cardiac preload induced HDAC4 nuclear export, H3K9 demethylation, HP1 dissociation from the promoter region, and activation of the ANP gene. These processes were reversed in hearts with myocyte-specific deletion of Hdac4. We conclude that HDAC4 plays a central role for rapid modifications of histone methylation in response to variations in cardiac load and may represent a target for pharmacological interventions to prevent maladaptive remodeling in patients with heart failure.

Silibinin protects H9c2 cardiac cells from oxidative stress and inhibits phenylephrine-induced hypertrophy: potential mechanisms

Cardiac hypertrophy is the main response of the heart to various extrinsic and intrinsic stimuli, and it is characterized by specific molecular and phenotypic changes. Recent in vitro and in vivo studies indicate the involvement of reactive oxygen species in the hypertrophic response. In this study, silibinin, a plant flavonolignan extracted from milk thistle with potent antioxidant activity, was evaluated for its effects in (a) preventing hydrogen peroxide (H2O2)-induced cellular damage and (b) blocking the phenylephrine-induced hypertrophic response. Using the in vitro model of embryonic rat heart-derived H9c2 cells, we showed that silibinin has a rather safe profile as concentrations up to 200μM did not affect cell viability. Pretreatment of H9c2 cells with silibinin resulted in better protection of H9c2 cells under conditions of H2O2-induced cellular stress compared to untreated cells as indicated by cell viability and DNA fragmentation assays. Furthermore, silibinin attenuated the phenylephrine-induced hypertrophic response as evidenced by the measurement of cell surface, up-regulation of atrial natriuretic peptide and increase of cellular protein levels. Moreover, silibinin repressed the phenylephrine-induced phosphorylation of ERK1/2 kinases, while it appeared to inhibit the weakly activated by phenylephrine phosphorylation of Akt. Based on our results, silibinin may attenuate the phenylephrine-induced hypertrophic response of H9c2 cells via antioxidant mechanisms involving mainly the inhibition of the intracellular signaling pathways mediated by ERK1/2 MAPKs and Akt.

Depletion of 14-3-3 Protein Exacerbates Cardiac Oxidative Stress, Inflammation and Remodeling Process via Modulation of MAPK/NF-ĸB Signaling Pathways after Streptozotocin-induced Diabetes Mellitus

Diabetic cardiomyopathy is associated with increased oxidative stress and inflammation. Mammalian 14-3-3 proteins are dimeric phosphoserine-binding proteins that participate in signal transduction and regulate several aspects of cellular biochemistry. The aim of the study presented here was to clarify the role of 14-3-3 protein in the mitogen activated protein kinase (MAPK) and nuclear factor-kB (NF-ĸB) signaling pathway after experimental diabetes by using transgenic mice with cardiac-specific expression of a dominant-negative 14-3-3 protein mutant (DN 14-3-3). Significant p-p38 MAPK activation in DN 14-3-3 mice compared to wild type mice (WT) after diabetes induction and with a corresponding up regulation of its downstream effectors, p-MAPK activated protein kinase 2 (MAPKAPK-2). Marked increases in cardiac hypertrophy, fibrosis and inflammation were observed with a corresponding up-regulation of atrial natriuretic peptide, osteopontin, connective tissue growth factor, tumor necrosis factor α, interleukin (IL)-1β, IL-6 and cellular adhesion molecules. Moreover, reactive oxygen species, left ventricular expression of NADPH oxidase subunits, p22 phox, p67 phox, and Nox4, and lipid peroxidation levels were significantly increased in diabetic DN 14-3-3mice compared to diabetic WT mice. Furthermore, myocardial NF-ĸB activation, inhibitor of kappa B-α degradation and mRNA expression of proinflammatory cytokines were significantly increased in DN 14-3-3 mice compared to WT mice after diabetes induction. In conclusion, our data suggests that depletion of 14-3-3 protein induces cardiac oxidative stress, inflammation and remodeling after experimental diabetes induction mediated through p38 MAPK, MAPKAPK-2 and NF-ĸB signaling.

Upregulation of ANP and NPR-C mRNA in the kidney and heart of eNOS knockout mice

The aim of the present studywas to examine the question of whether the atrial natriuretic peptide (ANP) system is altered by endothelial nitric-oxide synthase (eNOS). Male eNOS-deficient mice (eNOS-/-) and wild type control mice (eNOS+/+, C57B1/6J) were used. Blood pressure was measured in anesthetized mice by tail cuff plethysmography and renal function was measured. Expression of ANP, natriuretic peptide receptor (NPR)-A, NPR-C, and tonicity-responsive enhancer binding protein (TonEBP) mRNA was determined by real-time PCR. Localization of (125)I-ANP binding sites was measured using in vitro autoradiography. In eNOS-/- mice, systolic blood pressure increased and left ventricular hypertrophy was observed. Urine volume and osmolarity did not change. Expression of ANP markedly increased in the heart and kidney of eNOS-/- mice. Expression of NPR-A and NPR-C increased in the heart and tended to increase in the kidney of eNOS-/- mice. In the renal medulla in particular, increased expression of NPR-C was more prominent. Expression of TonEBP mRNA was markedly decreased in the renal medulla, but not in the renal cortex. Maximum binding capacity (B(max)) of ANP and C-ANP increased in the renal medulla in eNOS-/- mice. These results suggest that the eNOS-NO system may be partly involved in regulation of ANP, NPR-A, -C, and TonEBP mRNA expression in the kidney.

Local action of endogenous renal tubular atrial natriuretic peptide

Up-regulation of atrial natriuretic peptide (ANP) mRNA in the kidneys in several disorders has been demonstrated; however, evidence that ANP synthesized by the kidney exerts a local function has never been produced. Therefore, we investigated whether endogenous ANP could modulate high glucose-stimulated TGF-beta1, collagen type I and nuclear factor-kappaB (NF-kappaB) in NRK-52E cells using transfection of ANP and ANP small interfering RNA (siANP). NRK-52E cells were grown with or without transfection with ANP plasmid; cells were also transfected with ANP siRNA or control siRNA. These cells were then stimulated with a high glucose concentration to modulate ANP, TGF-beta1, collagen type I, NF-kappaB and IkappaB-alpha, and the results showed that ANP, TGF-beta1, collagen type I and NF-kappaB significantly increased in untransfected cells, and the transfection of ANP significantly attenuated high glucose-activated TGF-beta1, collagen I and NF-kappaB expression. ANP siRNA knocked-down ANP but significantly increased TGF-beta1 and collagen I under normal glucose conditions; ANP siRNA decreased IkappaB-alpha but strongly enhanced high glucose-activated TGF-beta1, collagen type I and NF-kappaB. In contrast, medium from ANP-transfected cells attenuated high glucose-activated TGF-beta1 and collagen type I expression in NRK-52E cells transfected with siANP. In conclusion, our results demonstrated that siANP increased activation of TGF-beta1, collagen type I and NF-kappaB in NRK-52E cells under high glucose conditions, and medium from ANP-transfected cells attenuated high glucose-activated TGF-beta1 and collagen type I. This is the first study to demonstrate the auto/paracrine action of endogenous ANP in renal tubular cells on the attenuation of hyperglycemia-activated TGF-beta1 and NF-kappaB expression. J. Cell. Physiol. 219: 776-786, 2009. (c) 2009 Wiley-Liss, Inc.

IGF-II/mannose-6-phosphate receptor signaling induced cell hypertrophy and atrial natriuretic peptide/BNP expression via Gαq interaction and protein kinase C-α/CaMKII activation in H9c2 cardiomyoblast cells

The role played by IGF-II in signal transduction through the IGF-II/mannose-6-phosphate receptor (IGF2R) in heart tissue has been poorly understood. In our previous studies, we detected an increased expression of IGF-II and IGF2R in cardiomyocytes that had undergone pathological hypertrophy. We hypothesized that after binding with IGF-II, IGF2R may trigger intracellular signaling cascades involved in the progression of pathologically cardiac hypertrophy. In this study, we used immunohistochemical analysis of the human cardiovascular tissue array to detect expression of IGF2R. In our study of H9c2 cardiomyoblast cell cultures, we used the rhodamine phalloidin staining to measure the cell hypertrophy and western blot to measure the expression of cardiac hypertrophy markers atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) in cells treated with IGF-II. We found that a significant association between IGF2R overexpression and myocardial infarction. The treatment of H9c2 cardiomyoblast cells with IGF-II not only induced cell hypertrophy but also increased the protein level of ANP and BNP. Using Leu27IGF-II, an analog of IGF-II which interacts selectively with the IGF2R, to specifically activate IGF2R signaling cascades, we found that binding of Leu27IGF-II to IGF2R led to an increase in the phosphorylation of protein Kinase C (PKC)-alpha and calcium/calmodulin-dependent protein kinase II (CaMKII) in a Galphaq-dependent manner. By the inhibition of PKC-alpha/CaMKII activity, we found that IGF-II and Leu27IGF-II-induced cell hypertrophy and upregulation of ANP and BNP were significantly suppressed. Taken together, this study provides a new insight into the effects of the IGF2R and its downstream signaling in cardiac hypertrophy. The suppression of IGF2R signaling pathways may be a good strategy to prevent the progression of pathological hypertrophy.

14-3-3 protein regulates Ask1 signaling and protects against diabetic cardiomyopathy

Mammalian 14-3-3 proteins are dimeric phosphoserine-binding proteins that participate in signal transduction and regulate several aspects of cellular biochemistry. Diabetic cardiomyopathy is associated with increased oxidative stress and inflammation. In order to study the pathogenic changes underlying diabetic cardiomyopathy, we examined the role of 14-3-3 protein and apoptosis signal-regulating kinase 1 (Ask1) signaling by using transgenic mice with cardiac-specific expression of a dominant-negative 14-3-3η protein mutant (DN 14-3-3η) after induction of experimental diabetes. The elevation in blood glucose was comparable between wild type (WT) and DN 14-3-3η mice. However, a marked downregulation of thioredoxin reductase was apparent in DN 14-3-3η mice compared to WT mice after induction of diabetes. Significant Ask1 activation in DN 14-3-3η after diabetes induction was evidenced by pronounced de-phosphorylation at Ser-967 and intense immunofluorescence observed in left ventricular (LV) sections. Echocardiographic analysis revealed that cardiac functions were notably impaired in diabetic DN 14-3-3η mice compared to diabetic WT mice. Marked increases in myocardial apoptosis, cardiac hypertrophy, and fibrosis were observed with a corresponding up-regulation of atrial natriuretic peptide and galectin-3, as well as a downregulation of sarcoendoplasmic reticulum Ca 2+ ATPase2 expression. Furthermore, diabetic DN 14-3-3η mice displayed significant reductions of platelet-endothelial cell adhesion molecule-1 staining as well as endothelial nitric acid synthase and vascular endothelial growth factor expression. In conclusion, our data suggests that enhancement of 14-3-3 protein could provide a novel therapeutic strategy against hyperglycemia-induced left ventricular dysfunction and can limit the progression of diabetic cardiomyopathy by regulating Ask1 signaling.

Involvement of endogenous ouabain-like compound in the cardiac hypertrophic process in vivo

The Na +/K +-ATPase inhibitor ouabain has been shown to trigger hypertrophic growth of cultured cardiomyocytes; however, the significance of endogenous ouabain-like compound (OLC) in the hypertrophic process in vivo is unknown. Here we characterized the involvement of OLC in left ventricular (LV) hypertrophy induced by norepinephrine (NE) and angiotensin II (Ang II) infusions in rats. Administration of NE (300 μg/kg/h) via subcutanously implanted osmotic minipumps for 72 h resulted in a significant increase in left ventricular weight to body weight (LVW/BW) ratio ( P < 0.001) and a substantial up-regulation of atrial natriuretic peptide (ANP) gene expression (13.2-fold, P < 0.001). NE infusion induced a transient increase in plasma OLC levels at 12 h ( P < 0.05), which returned to control levels by 72 h. Adrenalectomy markedly reduced both basal and NE-induced increase in plasma OLC levels. LVW/BW ratio was not modulated by adrenalectomy; however, ANP gene expression was blunted by 44% ( P < 0.01) and 47% ( P < 0.05) at 12 and 72 h, respectively. In agreement, adrenalectomy reduced up-regulation of ANP without affecting LV mass in rats infused with Ang II (33 μg/kg/h). Administration of exogenous ouabain (1 nM to 100 μM) for 24 h had no effect on ANP gene expression in cultured neonatal rat ventricular myocytes. However, the up-regulation of ANP mRNA levels induced by the α-adrenergic agonist phenylephrine (1 μM) was markedly enhanced by ouabain (100 μM) (5.6-fold vs. 9.6-fold, P < 0.01). These data show that OLC as an adrenal-derived factor may be required for the induction LV ANP gene expression during the hypertrophic process.

Chronic treatment with trimetazidine reduces the upregulation of atrial natriuretic peptide in heart failure

Trimetazidine (TMZ) is effective for the treatment of ischemic cardiomyopathy; however, little is known about the effect of TMZ in established injury-induced heart failure. When rats with established infarct-induced heart failure were treated for 12 weeks with TMZ there was no effect on left ventricular function or dilation, or on mRNA expression of fatty acid oxidation enzymes. On the other hand, TMZ significantly reduced atrial natriuretic peptide mRNA levels compared with untreated rats.

Preface

We observed that heterozygous knockout (+/-, KO) of either endothelin-A- (ET(A)) or -B- (ET(B)) receptors significantly reduced the pressor responses to systemically administered endothelin-1 (ET-1) in ET(A) or ET(B) (+/-) KO mice when compared to wild-type (WT) mice (data not shown). Also, we observed that basal mean arterial pressure (MAP) is significantly higher in ET(B) (+/-) (92.7 +/- 1.2 mmHg) (n = 53, p < 0.05) but not ET(A) (+/-) KO mice (70.6 +/- 1.8 mmHg) (n = 23) when compared to their anaesthetized WT littermates (70.1 +/- 0.7 mmHg) (n = 118). A 90 min treatment with either BQ-123 (10 mg/kg), an ET(A)-selective antagonist, or BQ-928 (10 mg/kg), a mixed ET(A)/ET(B) antagonist, administered intraperitoneally, significantly reduced basal MAP of ET(B) (+/-) KO mice almost to the level of their WT treated counterparts (94.9 +/- 4.9 mmHg) (n = 6) vs (+ BQ-123: 59.7 +/- 0.3 mmHg, n = 8); (+ BQ-928: 72.4 +/- 2.6 mmHg, n = 5). It is worthy of note that BQ-123 significantly reduced basal MAP in WT mice but to a lesser extent than in ET(B) (+/-) KO mice (69.6 +/- 2.3 mmHg, n = 8) vs (+ BQ-123: 57.3 +/- 1.4 mmHg, n = 8). In contrast, the ET(B)-selective antagonist, BQ-788 (10 mg/kg i.p.), had no significant effect on MAP even after 90 min of treatment (ET(B) (+/-) KO: (92.3 +/- 2.3 mmHg, n = 6) vs (+ BQ-788: 89.7 +/- 3.1 mmHg, n = 6); WT: (70.5 +/- 3.7 mmHg, n = 7) vs (+ BQ-788: 71.2 +/- 2.0 mmHg, n = 6). Therefore heterozygous KO of either ET(A)- or ET(B)-receptors significantly alters the phenotypic pressor properties of ET-1. We also suggest that there is less ET clearance in ET(B) (+/-) KO mice than in WT mice, which can explain the ET(A)-dependent hypertensive state of the former strain.

Neuregulin in cardiac hypertrophy in rats with aortic stenosis. Differential expression of erbB2 and erbB4 receptors.

Neuregulins are a family of peptide growth factors that promote cell growth and viability. The potential role of neuregulin-erbB signaling in hypertrophic growth and later failure in the adult heart in vivo is not known. We used ribonuclease protection assays to quantify mRNA levels of neuregulin, erbB2, and erbB4 in left ventricular (LV) tissue and myocytes of normal rats and rats with aortic stenosis with pressure-overload hypertrophy 6 and 22 weeks after banding. At both stages of hypertrophy, Northern blot analyses of mRNA from LV myocytes showed upregulation of atrial natriuretic peptide, a molecular marker of hypertrophy (P<0.05). LV tissue neuregulin message levels were similar in animals with aortic stenosis compared with controls (P=NS) and were not detectable in myocytes. LV erbB2 and erbB4 message levels in LV tissue and myocytes were maintained during early compensatory hypertrophy in 6-week aortic stenosis animals compared with age-matched controls; in contrast, erbB2 and erbB4 message levels were depressed in 22-week aortic stenosis animals at the stage of early failure (both P<0.01 vs age-matched controls). Immunoblotting of erbB2 and erbB4 also showed normal protein levels in 6-week aortic stenosis animals compared with controls; however, erbB2 and erbB4 protein levels were depressed in 22-week aortic stenosis animals (48% decrease in erbB2, P<0.05, and 43% decrease in erbB4, P<0.01) relative to age-matched controls. The neuregulin receptors erbB2 and erbB4 are downregulated at both the message and protein levels at the stage of early failure in animals with chronic hypertrophy secondary to aortic stenosis. These data suggest a role for disabled erbB receptor signaling in the transition from compensatory hypertrophy to failure.

ANP gene expression in rat hearts during hypoxia.

It is unclear whether the increase in plasma atrial natriuretic peptide (ANP) concentration during hypoxia is due to direct, hypoxia-induced upregulation of ANP secretion in the heart, or to pressure overload of the right ventricle (RV) following hypoxia-induced pulmonary hypertension. To test the hypothesis that hypoxia leads to an early upregulation of the ANP gene, we examined the influence of acute and prolonged inspiratory hypoxia (6 h, 1 or 3 weeks) on the expression of ANP messenger ribonucleic acid (mRNA) in rat heart and compared the results with the expression of the ANP gene after acute pressure overload induced by experimental coarctation of the main pulmonary artery. As a molecular marker for hypertrophy we determined the ratio of alpha- and beta-myosin gene expression. Hypoxia increased systolic RV pressure from 20.0 +/- 1.6 mmHg to 27.8 +/- 1.6 mmHg (P < 0.01) and 41.6 +/- 2.1 mmHg (P < 0. 05) after 1 and 3 weeks hypoxia respectively. The ANP plasma concentration did not change significantly after 6 h or 1 week: 232 +/- 21 pg/ml (control), 246 +/- 25 pg/ml (6 h), 268 +/- 25 pg/ml (1 week), but increased significantly after 3 weeks hypoxia (446.8 +/- 99.56 pg/ml; P < 0.05). ANP mRNA levels in different regions of the heart did not change after 6 h or 1 week hypoxia. After 3 weeks hypoxia ANP mRNA had increased 2.7-fold in the RV (P < 0.05), 4. 2-fold in the left ventricle (LV, P < 0.05), 3.5-fold in the septum (S, P < 0.05) and about 1.4-fold in the right (n.s.) and left atrium (n.s.). Relative ventricular masses increased significantly only for the RV (190%, P < 0.05) during hypoxia. The beta/alpha-myosin mRNA ratio did not change after 6 h hypoxia but, contrary to ANP gene expression, increased after just 1 week (6.1-fold in RV, 7.8-fold in LV, 6-fold in S; P < 0.05) and was more pronounced in the RV after 3 weeks (9.4-fold in RV, 7.6-fold in LV, 9.1-fold in S; P < 0.05). The increase in the beta/alpha-myosin mRNA ratio in the LV contrasts with a lack of increase in relative ventricular mass. Acute pressure overload in the RV after pulmonary arterial banding significantly increased ANP-mRNA and the beta/alpha-myosin mRNA ratio after 1 day in the RV. In the LV ANP mRNA was unchanged. The delayed upregulation of the ANP gene suggests that hypoxia per se is not a significant stimulus for ANP gene expression in the heart and that hypoxia-induced ANP-gene expression in the heart is regulated predominantly by the increase in RV afterload due to hypoxia-induced increased pulmonary pressure. The upregulation of ANP and beta-myosin mRNA in the LV during chronic hypoxia has yet to be elucidated.