Left Ventricular Weight/body Weight Research Articles

Simvastatin Improves Cardiac Hypertrophy in Diabetic Rats by Attenuation of Oxidative Stress and Inflammation Induced by Calpain-1-Mediated Activation of Nuclear Factor-κB (NF-κB).

BackgroundSimvastatin, an HMG-CoA reductase inhibitor, has been reported to exert multiple protective effects on the cardiovascular system. However, the molecular mechanism remains to be examined. The present study was designed to study the effects of simvastatin on cardiac hypertrophy in diabetic rats and to explore its potential mechanism.Material/MethodsSprague-Dawley rats were assigned into a control (Con) group, a streptozotocin (STZ) group, and a STZ+simvastatin (STZ+SIM) group. The level of reactive oxygen species (ROS) was measured by using dihydroethidium (DHE) staining. The protein expressions of p65, IκBα, vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), interleukin-6 (IL-6), tumor necrosis factor α (TNF-α), calpain-1, and endothelial nitric oxide synthase (eNOS) were examined by Western blot analysis. qPCR was used to detect the levels of brain natriuretic peptide (BNP) and atrial natriuretic peptide (ANP).ResultsSimvastatin improved the cardiac hypertrophy of diabetic rats, as demonstrated by decreases in the ratios of left ventricular weight/body weight (LVW/BW) and heart weight/body weight (HW/BW) and by the downregulation of mRNA expression of BNP and ANP in the heart tissue. Simvastatin decreased the protein expressions of VCAM-1, ICAM-1, IL-6, and TNF-α, increased eNOS protein expression, and limited an increase in ROS levels in the heart tissue. Simvastatin increased IκBα protein expression in cytoplasm and inhibited the translocation of p65, the subunit of nuclear factor-κB (NF-κB) to the nucleus from the cytoplasm of the heart tissue. Furthermore, simvastatin attenuated the activity of calpain and calpain-1 protein expression in heart tissue.ConclusionsSimvastatin attenuates cardiac hypertrophy in diabetic rats, which might be due to the attenuation of oxidative stress and inflammation induced by calpain-1-mediated activation of NF-κB.

Sodium Houttuyfonate Alleviates Post-infarct Remodeling in Rats via AMP-Activated Protein Kinase Pathway.

With the chronic ischemia persisting after acute myocardial infarction, the accompanying low-degree inflammation and subsequent fibrosis result in progression of cardiac remodeling and heart failure. Recently, Sodium Houttuyfonate (SH), a pure compound extracted from Houttuynia cordata, has been confirmed exerting anti-inflammatory and anti-fibrotic effects under diseased situations. Here, we aimed to investigate whether SH could reverse the cardiac remodeling post-myocardial infarction by alleviating cardiac inflammation and fibrosis. Left anterior descending coronary artery of adult male Sprague-Dawley rats was ligated to elicit myocardial infarction. Low and high dose of SH was administered by oral gavage for four consecutive weeks post-myocardial infarction. Long-term SH treatment decreased heart rate, heart weight/ body weight (HW/BW), and left ventricle weight/body weight (LVW/BW), reduced cardiac expression of brain natriuretic peptide (BNP), improved left ventricular heart function, and ameliorated the histopathological changes caused by myocardial infarction. Western blotting revealed the expression of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), transforming growth factor-β (TGF-β), collagen I, and collagen III of the infarcted ventricle were reduced by SH treatment. Meanwhile, we found that SH treatment post-myocardial infarction activated AMP-activated protein kinase (AMPK) and suppressed nuclear factor-κB p65 (NF-κB p65). Furthermore, on H9C2 cells induced hypoxic injury with cobalt chloride (CoCl2), the reduction of inflammatory cytokines (IL-6, TNF-α, and TGF-β), activation of AMPK, and suppression of NF-κB p65 were also observed by SH treatment. However, transfection of H9C2 with AMPKα siRNA blunted the suppression of NF-κB p65 and inflammatory cytokines (IL-6, TNF-α, and TGF-β) by SH post-hypoxia. Taken together, these findings suggested that long-term administration of SH post-myocardial infarction reduced cardiac inflammatory and fibrotic responses, and reversed cardiac remodeling process. The underlying mechanism may be activating AMPK and suppressing NF-κB pathway.

MicroRNA Profile in Swimming Trained Female Rats and its Therapeutic Potential in Spontaneously Hypertensive Rats

IntroductionBoth aerobic exercise training (ET) and Hypertension (HY) induce different cardiac hypertrophy (CH) phenotypes which molecular differences and may lead to new targets for therapies in cardiovascular disease, as microRNAs (miRNAs).MethodsWe selected 15 miRNAs that were differentially expressed by ET from miRNAarray data and compared them with other from SHR (Spontaneously Hypertensive Rats) miRNAarray data. Four miRNAs were selected for qRT‐PCR confirmation: miRNA‐27a, 27b, 126 e 29c. Among then, miRNA 29c was chosen to be modulated by lentiviral vector due its role in fibrosis regulation. Intramuscular cardiac injection of the lentiviral vector particles 0.6×109 vp/was performed for two different times (7 and 14 days) (SHR7 and SHR14). The transduction efficiency was assessed by GFP expression by Western Blot. Blood pressure (BP) was measured by caudal plethysmography, CH was analyzed by ratio LVW/BW (left ventricle weight/body weight), HW/BW (heart weight/body weight) and by cardiomyocytes diameter (dCMO). qRT‐PCR was used to assess miRNA‐29c expression and its targets COLIAI and COLIIIAI gene expression. The LV collagen content was assessed by histology (Picrossirius red), by collagen volume fraction, and by hydroxiproline concentration.ResultsBoth groups that received the low doses were GFP positive in the heart and liver tissue. BP was increased to SHR7, but it was prevented by miR‐29c lentivirus treatment to SHR14. The miRNA‐29c expression increased in all treated groups versus their control (CSI). COLIAI expression decreased in treated groups, while COLIIIAI did not change. Collagen volume fraction decreased in all treated groups, which shows that the treatment was efficient to decrease the cardiac collagen. HW/BW ratio decreased 7–11% in SHR14, while the dCMO was increased in all treated groups.ConclusionsThese results suggest that miR‐29c lentivirus treatment induces beneficial cardiac remodeling in SHR, increasing dCMO and decreasing cardiac fibrosis. These results open perspective for further investigation of antifibrotic therapies for cardiovascular diseases.Support or Funding InformationFAPESP, CNPq, CAPES and NAPmirThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Inhibition of TNF-α-mediated NF-κB Activation by Ginsenoside Rg1 Contributes the Attenuation of Cardiac Hypertrophy Induced by Abdominal Aorta Coarctation.

Ginsenoside Rg1 (Rg1), a protopanaxadiol saponin extracted from Chinese medicine Panax ginseng C.A. Meyer, has been demonstrated to inhibit the cardiac hypertrophy. However, the molecular mechanisms underlying the inhibition remain poorly understood. Activation of nuclear factor-kappa B (NF-κB) mediated by tumor necrosis factor α (TNF-α) gets involved in the cardiac hypertrophy. This study is designed to investigate the effects and the potential mechanism of Rg1 on the abdominal aorta coarctation (AAC)-induced cardiac hypertrophy with focus on TNF-α/NF-κB signaling pathway. The results showed that oral administration of Rg1 dose-dependently improved the pathological changes, decreased the ratios of left ventricular weight/body weight (LVW/BW) and heart weight/BW (HW/BW), corrected the dysfunction of the cardiac hemodynamics by decreasing the left ventricular systolic pressure and left ventricular end-diastolic pressure and increasing the maximal rate of left ventricular systolic and diastolic pressure (±dp/dtmax) compared with the AAC alone. Rg1 also downregulated the atrial natriuretic peptide mRNA expression and decreased the mRNA and protein expression of TNF-α in the heart tissue of rats compared with the AAC alone. In addition, Rg1 and BAY, the specific inhibitor of NF-κB, decreased the protein content and downregulated the mRNA expression of atrial natriuretic peptide in neonatal rat ventricular myocytes treated with TNF-α. Furthermore, Rg1 increased the protein expression of p65, the subunit of NF-κB, in cytoplasm and decreased the expression p65 in nucleus of the heart tissue of rats undergoing the AAC and of neonatal rat ventricular myocytes treated with TNF-α. The results suggested that Rg1 attenuates the AAC-induced cardiac hypertrophy through inhibition of TNF-α/NF-κB signaling pathway.

Protective effect and mechanism of Ginkgo biloba extract-EGb 761 on STZ-induced diabetic cardiomyopathy in rats.

Diabetes mellitus (DM) is a complex metabolic disorder which leads to development of various long-term complications including cardiomyopathy. Oxidative stress due to hyperglycemia plays a key role in the development and progression of diabetic cardiomyopathy (DC). Oxidative stress causes the opening of mitochondrial permeability transition pore (mPTP) eventually leading to myocardium dysfunction. The Ginkgo biloba extract (EGb 761) has antioxidant and mitochondrial membrane potential stabilizing property. Therefore, this study was designed to evaluate the effect of EGb 761 and its possible mechanism of action in DC.Materials and Methods:DM was induced by single injection of Streptozotocin (STZ) (50 mg/kg, i.p.) and cardiac dysfunction was developed on 8th weeks after STZ injection. Cardiac dysfunction was assessed by measuring left ventricle weight/body weight (LVW/BW) ratio, left ventricle (LV) collagen content, LV protein content, serum lactate dehydrogenase (LDH) level.Results:EGb 761 treatment (started after 7th week of STZ injection and continued for 3 weeks) attenuated cardiac dysfunction in diabetic rats as evidenced by a decrease in LV collagen content, protein content, LVW/BW ratio, serum LDH level. Moreover, EGb 761 attenuated the oxido-nitrosative stress (thiobarbituric acid reactive substances, superoxide anion generation, myocardium nitrite) and concomitantly improved the antioxidant enzyme (reduced glutathione) level as compared to untreated diabetic rats. However, protective effect of EGb 761 was inhibited by atractyloside (mPTP opener) that was given for 3 weeks, 30 min before the EGb 761 treatment. These results indicate that EGb 761 corrects diabetic cardiac dysfunction probably by its direct radical scavenging activity and its ability to inhibit the opening of mPTP channel since the cardioprotective effect of EGb 761 was completely abolished by atractyloside.

GW24-e2448 Knockdown of farnesyl pyrophosphate synthase prevents cardiac fibrosis of spontaneously hypertensive rats in vivo

ObjectivesPrevious studies show farnesyl pyrophosphate synthase (FPPS) inhibitor prevents cardiac hypertrophy and fibrosis induced by angiotensin II (Ang II). In this study, we examined the effect of lentivirus against FPPS...

Effects of the Supercritical Fluid Extraction of Dahurian Angelica Root and Szechwan Lovage Rhizome on Spontaneous Hypertension Rats

The supercritical fluid extraction of Dahurian Angelica Root (Bai Zhi) and Szechwan Lovage Rhizome (Chuan Xiong) was named as BCC. In the study, we investigated whether BCC had effects on left ventricular hypertrophy (LVH) and myocardial fibrosis in spontaneous hypertensive rats (SHR). For SHR + BCC group, BCC (0.3 g/kg) was orally administered daily for 12 weeks. The SHR group and the Wistar Kyoto rats (WKY, normal control) group, the equal volume of 5‰ CMC-Na distilled water. After 12 weeks, left ventricle was segregated from each rat in the groups, and the left ventricle weight/body weight (LVW/BW) calculated. The volume fraction of collagen (VFC) in myocardium and the diameter of cardiac muscle cell (DCMC) were examined by histological staining. Biochemical indicators of blood sample such as Angiotensin II (Ang II), Aldosterone (ALD), Hyaluronic Acid (HA), Laminin (LN), Procollagen III (PC III) and Collagen type IV (CIV) levels were detected by using radioimmunoassay (RIA). And also NOS and iNOS levels were measured by means of ultra-violet spectroscopy (UV). The results shown that in SHR + BCC group, the LVW/BW, DCMC and VFC decreased significantly versus SHR group, the same as biochemical indicators except NOS and iNOS. All of above index was similar to WKY group. Statistically significant correlations were found among the plasma Ang II level, the mean systolic blood pressure (SBP), and the NOS level of the three groups. Our study indicates that the BCC can control the LVH and myocardial fibrosis in SHR.

Antioxidant and cardioprotective effects of Danshensu (3-(3, 4-dihydroxyphenyl)-2-hydroxy-propanoic acid from Salvia miltiorrhiza) on isoproterenol-induced myocardial hypertrophy in rats

Myocardial hypertrophy has been linked to the development of a variety of cardiovascular diseases, and is a risk factor for myocardial ischemia, arrhythmias, and sudden cardiac death. The objective of the present study was to evaluate the cardioprotective effects of Danshensu (DSS), a water-soluble active component of Danshen, on cardiac hypertrophy in rats. We are the first to report that DSS reversed Cx43 down-regulation in ventricular tissue. Cardiomyopathy in rats was produced using isoproterenol (Iso) treatment (2.5 mg/kg/d, s.c.) for seven days. DSS (3 and 10 mg/kg/d, i.p.) and Valsartan (Val) (10 mg/kg, i.g.) were administered on days 4-7 of Iso-treatment. Heart weight index, hemodynamic parameters, and ECG II parameters were monitored and recorded; protein expression of left ventricular connexin 43 (Cx43) and the activity of the redox system were assayed, and arrhythmias were produced using a coronary ligation/reperfusion procedure. The results demonstrated that DSS treatment significantly decreased heart weight/body weight (HW/BW) and left ventricular weight/body weight (LVW/BW) ratios. The protective role of DSS against Iso-induced myocardial hypertrophy was further confirmed using ECG. The incidences of ventricular tachycardia and ventricular fibrillation (VT, VF) and arrhythmic scores were higher in the model group and were suppressed by DSS. DSS decreased the serum and myocardium levels of creatine kinase, lactate dehydrogenase, and malondialdehyde (CK, LDH, and MDA) and increased serum activity of superoxide dismutase (SOD) in a dose-dependent manner. Cx43 expression in the left ventricle was down-regulated, and there was significant oxidative stress in this model of cardiomyopathy. DSS reversed the down-regulated Cx43 protein levels and showed potent anti-oxidative activities and cellular protection. These data demonstrate that DSS can prevent cardiac I/R injury and improve cardiac function in a rat model of hypertrophy, the effects partially resulting from antioxidants and the protection from Cx43 expression.

Beneficial effects of angiotensin (1–7) in diabetic rats with cardiomyopathy

This study was designed to investigate the effect of angiotensin (1-7), a Mas receptor agonist, and A-779, a Mas receptor antagonist, in rats with diabetic cardiomyopathy (DC). Rats treated with a single injection of streptozotocin (50 mg/kg, intraperitoneal), developed DC after 8 weeks. The extent of DC was assessed by measuring the left ventricular weight/body weight (LVW/BW) ratio, absolute LVW, left ventricular developed pressure (LVDP), maximum change in left ventricular pressure over time (dp/dtmax), minimum change in left ventricular pressure over time (dp/dtmin), left ventricular (LV) protein content, LV collagen content, lipid profile, and serum nitrite/nitrate concentration. Test drug treatment was given from week 4 to week 8. Angiotensin (1-7) treatment attenuated DC by significantly increasing LVDP, dp/dtmax, dp/dtmin, serum nitrite/nitrate concentration and significantly decreasing the LVW/BW ratio and LV collagen content. For the first time, this study has documented that endogenous angiotensin (1-7) regulates lipid profile in rats, and that treatment with angiotensin (1-7) significantly attenuates diabetes-induced changes in lipid profile. However, LV protein content and absolute LVW remain unaffected after treatment. Angiotensin (1-7) significantly attenuates DC in rats because of vasodilatory, antiproliferative and anifibrotic properties but also because of a significant decrease in dyslipidemia, the major culprit for cardiac dysfunctions in diabetes.

Activation of liver X receptors with T0901317 attenuates cardiac hypertrophy in vivo

Liver X receptor (LXR) is a nuclear receptor regulating cholesterol metabolism. Liver X receptor has also been shown to exert anti-proliferative and anti-inflammatory properties. In this study, we evaluated the effect of LXR activation on cardiac hypertrophy in vitro and in vivo. Treatment with the synthetic LXR agonist T0901317 (T09) attenuated the hypertrophic response of cultured cardiomyocytes to endothelin-1 almost to control levels. siRNA interference showed that this effect was indeed LXR specific. To corroborate these findings in vivo, abdominal aortic constriction (AC) was used as a pressure overload model to induce cardiac hypertrophy in wild-type and LXR-α-deficient (LXR-α(-/-)) mice. In wild-type mice, T09 treatment resulted in a decrease of cardiac wall thickening 4 and 7 weeks after AC. Also, after 7 weeks of AC, mean arterial blood pressure and left ventricular weight/body weight (LVW/BW) ratios were decreased in T09 treated mice. These effects were not observed in LXR-α(-/-) mice, indicating that the beneficial effect of LXR activation on cardiac hypertrophy is attributable to the LXR-α isoform. T09 induced robust cardiac expression of metabolic genes which are downstream of LXR-α, such as SREBP-1c, ABCA1, and ABCG1. Together these results indicate that LXR exerts salutary effects in cardiac hypertrophy, possibly via metabolic remodelling.

Knockdown of farnesylpyrophosphate synthase prevents angiotensin II-mediated cardiac hypertrophy

The Rho guanosine triphosphatases (Rho GTPases) family, including RhoA, plays an important role in angiotensin II (Ang II)-mediated cardiac hypertrophy. Farnesylpyrophosphate synthase (FPPS)-catalyzed isoprenoid intermediates are vital for activation of RhoA. The present study was designed to investigate the role of FPPS in myocardial hypertrophy mediated with Ang II. First, we demonstrated that FPPS expression was elevated both in cultured neonatal cardiomyocytes (NCMs) following Ang II treatment and in the hypertrophic myocardium of 18-week-old spontaneously hypertensive rats (SHRs). Then, the importance of FPPS was assessed by RNA interference (RNAi) against FPPS in NCMs. Successful FPPS silencing in NCMs completely inhibited the hypertrophy marker genes of β-myosin heavy chain (β-MHC) and brain natriuretic peptide (BNP), as well as cell surface area. Furthermore, FPPS knockdown prevented elevated RhoA activity compared with non-silenced controls. Similarly, increased-phosphorylation of p-38 and c-Jun N-terminal kinase (JNK) mitogen-activated protein kinases (MAPK) by Ang II was attenuated. In vivo gene transfer also attenuated hypertrophic responses as indexed by left ventricular weight/body weight (LVW/BW), heart weight/body weight (HW/BW), and echocardiography, as well as expression of β-MHC and BNP mRNA in SHRs. In conclusion, FPPS with RhoA associated p-38 and JNK MAPK signaling might play an important role in Ang II-induced cardiac hypertrophy.

Role of Rho kinase and oxidative stress in cardiac fibrosis induced by aldosterone and salt in angiotensin type 1a receptor knockout mice

Large clinical trials have shown that mineralocorticoid receptor (MR) antagonists improve cardiovascular or total mortality in patients with heart failure or myocardial infarction even though the patients were taking angiotensin-converting enzyme inhibitors or angiotensin II receptor (AT1R) antagonists. We previously reported that cardiac fibrosis induced by aldosterone and salt (Ald–NaCl) was exaggerated in AT1aR knockout mice (AT1aR-KOs). As the association of Rho kinase and oxidative stress was reported in Ald–NaCl-induced hypertension of rats, we investigated the effects of an MR antagonist (eplerenone) and a Rho kinase inhibitor (fasudil) on Ald–NaCl-induced cardiac fibrosis in AT1aR-KOs. AT1aR-KOs were administered aldosterone (0.15 μg/h) subcutaneously using an osmotic minipump and were provided with 1% NaCl drinking water for 4 weeks. AT1aR-KOs receiving Ald–NaCl were treated with a low (30 mg/kg/day) or high (100 mg/kg/day) dose of eplerenone or a fasudil (100 mg/kg/day). Systolic blood pressure (SBP), left ventricular weight/body weight (LVW/BW), histological examination and cardiac gene expression were evaluated on day 28. Ald–NaCl treatment caused increases in SBP and LVW/BW in AT1aR-KOs, and eplerenone dose-dependently decreased SBP, LVW/BW and cardiac fibrosis. Fasudil decreased LVW/BW and cardiac fibrosis without affecting SBP. The expressions of connecting tissue growth factor (CTGF) and nicotinamide adenine dinucleotide phosphate (NADPH) components (p22phox, p47phox and p67phox) were increased in Ald–NaCl-treated AT1aR-KOs, and eplerenone or fasudil decreased the expression of CTGF and NADPH components. Phosphorylated ERM (a marker of the phosphorylation of Rho kinase) was increased in Ald–NaCl-treated AT1aR-KOs and was decreased by eplerenone. Nitrotyrosine and 4-hydroxy-2-nonenal, which indicate tissue damage via oxidative stress, were increased in AT1aR-KO and were apparently attenuated by eplerenone or fasudil. These results suggested that the Rho kinase pathway was activated to induce cardiac fibrosis by Ald–NaCl via MR in AT1aR-KOs. A Rho kinase inhibitor as well as eplerenone might be useful for cardiac damage by Ald–NaCl.

Crucial Role of Interleukin-6 in the Development of Norepinephrine-induced Left Ventricular Remodeling in Mice

Background: Elevated serum concentration of interleukin (IL)-6 is a predictor for poor prognosis in congestive heart failure. It was shown previously in rats, that IL-6 expression in the left ventricle (LV) was followed by LV hypertrophy. Methods: Using IL-6 deficient mice (IL-6^-/-), we studied the role of IL-6 in a model of norepinephrine (NE)-induced LV hypertrophy. Results: In wild type (WT) mice, IL-6 mRNA expression and its concentration in the serum were elevated after 4 h of NE-treatment (s.c. 0.25 mg/kg·h). Further, NE-induced LV hypertrophy was detected: LV weight/body weight (LVW/BW) ratio (+12.3±3%, p < 0.05) and mRNA expression of atrial natriuretic peptide (ANP) in WT mice (+120±25%, p < 0.05) after 3 days were increased. In contrast, NE did not induce elevation of LVW/BW ratio and ANP expression in IL-6^-/- mice. Replacement with recombinant IL-6 restored the hypertrophy-inducing effect of NE in IL-6^-/- mice. As to the extracellular matrix (ECM) proteins, NE increased collagen type I and III expression only in WT mice and not in IL-6^-/- mice. The addition of recombinant IL-6 elevated the expression of the ECM proteins to the WT level. Conclusion: IL-6 is a major player in the development of NE-induced LV hypertrophy in mice.

Higher Physiological Doses of Nandrolone Decanoate Do Not Influence the Bezold-Jarish Reflex Control of Bradycardia

We investigated the influence of short-term treatment with supraphysiological doses of an anabolic-androgenic steroid on the Bezold-Jarisch reflex (BJR) control of heart rate (HR) and whether this treatment induced cardiac hypertrophy and anabolic effects in rats. Male rats were treated with nandrolone decanoate (10 mg/kg(-1) body weight/4 weeks; DECA) or vehicle control (CON). After 4 weeks of treatment, BJR was evaluated by bradycardia responses that were elicited by serotonin administration (2-32 microg/kg(-1)). Mean arterial pressure (MAP) was assessed and cardiac hypertrophy was determined by the left ventricle weight/body weight (LVW/BW) ratio. Histological analyses of LV and the measurement of the total body protein content of the animals were performed. Nandrolone decanoate (ND) treatment had no effect on the MAP (CON=105+/-5; DECA=110+/-3 mmHg). However, the mean basal HR of DECA animals was significantly lower than that of control animals (CON = 381+/-14; DECA=324+/-12 bpm; p<0.01). ND did not change the sensitivity of the BJR. The LVW/BW ratio indicated significant hypertrophy of the LV in DECA animals (CON=1.76+/-0.04; DECA=2.0+/-0.04 mg/g; p<0.01). Histological and morphometrical analyses demonstrate that there is also modest myocyte hypertrophy (CON=14.5+/-1.5; DECA=20.0 +/- 0.9 myocyte nuclei/field; p<0.05). However, the Masson-trichromic-stained samples showed an enhancement of collagen deposits on the LV matrix. We concluded that 4 weeks ND treatment induced an anabolic effect and the beginnings of LV remodeling, mainly due to excessive collagen deposition in the cardiac extracellular matrix. However, the treatment did not influence BJR control of bradycardia, an effect that could be explained by an enhanced efferent vagal tonus in DECA animals.

Abstract 534: Large Tumor Suppressor 2 (Lats2), a Downstream Target of Mammalian Sterile 20 Like Kinase 1 (Mst1), Negatively Regulates Ventricular Mass.

Mst1 is an evolutionarily conserved serine threonine kinase which is a critical regulator of growth and death in cardiac myocytes. Mst1 forms a complex with hWW45 and Lats2, thereby activating Lats2. Lats2 partially mediates the proapoptotic effect of Mst1 in cardiac myocytes in vitro . In order to elucidate the cardiac function of Lats2 in vivo , we generated transgenic mice with cardiac specific expression of Lats2 (Tg-Lats2, line #8) and dominant negative Lats2 (Tg-DN-Lats2). At 5– 6 months of age, Tg-Lats2 exhibited a greater left ventricular (LV) end-diastolic dimension (4.3 vs 3.7 mm, n = 8, n = 7, p &lt; 0.05) and lower LV ejection fraction (EF, 63 vs 72 %, p &lt; 0.05) than wild type (WT) mice. In addition, many Tg-Lats2 exhibited a remarkably enlarged right atrium with mural thrombus. Although LV weight /body weight (LVW/BW) in Tg-Lats2 was not significantly different from that in WT, right ventricular weight (RVW)/BW in Tg-Lats2 was significantly smaller than that in WT (0.65 vs 0.96, p &lt; 0.05). The LV myocyte cross sectional area (CSA) was significantly smaller in Tg-Lats2 than in WT (82 vs 100%, p &lt; 0.05) and the RV myocyte CSA showed a similar tendency. Significantly reduced RVW/BW and LVEF were also observed in Tg-Lats2 line #20 (milder expression). Tg-Lats2 exhibited greater levels of interstitial fibrosis (13.0 vs 3.4%, p &lt; 0.05) at baseline. Although the number of TUNEL positive myocytes was not different between Tg-Lats2 and WT at baseline, it was significantly greater in Tg-Lats2 after transverse aortic constriction for 4 weeks (0.12 vs 0.09%, p &lt; 0.05). In contrast, Tg-DN-Lats2 exhibited significantly greater LVW/BW (3.88 vs 3.27, n = 10, n = 10, p &lt; 0.05) and RVW/BW (0.96 vs 0.73, p &lt; 0.05), and normal LV function. Furthermore, adenovirally expressed Lats2 reduced both the relative cell size and protein/DNA content in cultured neonatal rat cardiac myocytes (53.5%, 63.2% vs LacZ control virus, n = 3, p &lt; 0.05). Conversely, DN-Lats2 virus transduction significantly increased the cell size and protein/DNA content of cardiac myocytes (125.0%, 121.1% vs LacZ control virus, n = 3, p &lt; 0.05). These results suggest that Lats2 is a critical negative regulator of ventricular mass and that stimulation of Lats2 leads to increases in cell death, fibrosis and cardiac dysfunction.

Abstract 339: Endogenous Muscle Atrophy F-box is a Positive Mediator of Cardiac Hypertrophy and Dysfunction in Response to Pressure Overload

Muscle atrophy F-box (MAFbx, Atrogin-1) is an E3 ubiquitin ligase which plays a critical role in mediating skeletal muscle atrophy. It has been shown that cardiac specific expression of MAFbx inhibits pressure overload-induced cardiac hypertrophy, suggesting that MAFbx negatively regulates cardiac mass when overexpressed. To elucidate the role of endogenous MAFbx in regulating cardiac mass, we applied transverse aortic constriction (TAC) to MAFbx −/− and wild type (WT) mice. Pressure gradients in both groups were comparable (MAFbx −/− 90.4 mmHg vs WT 79.3 mmHg). In WT mice, protein expression of MAFbx in the heart was significantly increased (3.5 fold) after 2 weeks of TAC. Unexpectedly, left ventricular weight/body weight (LVW/BW) was significantly smaller in MAFbx −/− than in WT mice (4.49 vs 5.58, p &lt; 0.01). The echocardiographically determined LV posterior wall thickness (1.00 vs 1.13 mm, p &lt; 0.05) and LV mass index (151 vs 193, p &lt; 0.05) after TAC were significantly smaller in MAFbx −/− than in WT mice, consistent with the notion that MAFbx −/− mice develop less hypertrophy in response to TAC. Lung weight/BW after TAC was significantly increased compared with the sham operated group in WT (10.1 vs 5.1, p &lt; 0.01) but not in MAFbx −/− mice (6.0 vs 4.9, NS), suggesting that LV dysfunction after TAC was inhibited in MAFbx −/− mice. Furthermore, picric acid-Sirius red staining revealed that there was significantly less interstitial fibrosis after TAC in MAFbx −/− than in WT mice. These results suggest that MAFbx is up-regulated in response to pressure overload, and that the absence of endogenous MAFbx decreases hypertrophy and interstitial fibrosis and maintains cardiac function. In conclusion, distinct from its essential role in skeletal muscle atrophy, and also in direct contrast to the results seen with mice overexpressing MAFbx, endogenous MAFbx in the heart promotes cardiac hypertrophy and dysfunction during pressure overload.

Tissue Inhibitor of Matrix Metalloproteinase-1 in Norepinephrine-Induced Remodeling of the Mouse Heart

Background: Matrix metalloproteinases (MMPs) play an important role in myocardial remodeling. Their activity is regulated by the tissue inhibitors of metalloproteinases (TIMPs). The present study analyzed the contribution of changes in functional and molecular parameters to early cardiac remodeling in mice hearts. The role that TIMPs might play in this process was specially acknowledged. Methods: The remodeling was induced by norepinephrine (NE) given sc in balb/c mice. Varying concentrations, time and the addition of a neutralizing TIMP-1 antibody were evaluated. Results: High dose NE led to insufficiency of the left ventricle (LV) as evidenced by reduced NE-induced elevation of LV systolic pressure, contractility and relaxation. Further, signs of lung congestion were seen. NE induced a concentration-dependent increase of LV weight/body weight (LVW/BW) ratio and elevated mRNA expression of atrial natriuretic peptide (ANP). This was accompanied by induction of collagen type I and III, as well as TIMP-1 expression. Conclusions: The NE-induced increase of TIMP-1 expression may induce the elevation of the antihypertrophic cardiac factor ANP since NE-induced increase of ANP expression was abolished by neutralizing TIMP-1 antibody. Thus, TIMP-1 may mediate ANP-induced attenuation of NE-induced hypertrophy in the mouse heart.

Norepinephrine-induced cardiac hypertrophy and fibrosis are not due to mast cell degranulation.

The norepinephrine (NE)-induced hypertrophy of the left ventricle (LV) in the rat is preceded by increased interleukin (IL)-6 expression and associated with LV fibrosis. We have examined whether the elevated level of IL-6 may be due to mast cell degranulation. Therefore we tested the effect of cromoglycate sodium salt (cromolyn), an inhibitor of mast cell degranulation with anti-inflammatory and membrane-stabilizing activity, on the increased expression of IL-6 mRNA and of mRNAs of proteins involved in the remodelling of the extracellular matrix (ECM) which is induced by NE (0.1 mg/kg x h). After 4 h, the NE-induced increase in IL-6 mRNA expression was not influenced by cromolyn (20 mg/kg x h). Cromolyn-infusion for 3 days did not affect the extent of LV hypertrophy induced by NE, as measured by the LV weight/body weight (LVW/BW) ratio and by atrial natriuretic peptide (ANP) expression. Cromolyn induced a slight depression of the NE-induced elevation of the matrix metalloproteinase (MMP)-2. However, it did not affect the NE-induced elevated levels of mRNAs of collagen I and III and the tissue inhibitor of matrix metalloproteinase (TIMP)-2. Since cromolyn did not reduce the NE-effects in rat hearts in vivo we conclude that mast cell degranulation seems not to be involved in them.

Late Breaking Basic Science Abstracts

Late Breaking Basic Science Abstracts

Pressure-independent enhancement of cardiac hypertrophy in natriuretic peptide receptor A-deficient mice.

Mice lacking natriuretic peptide receptor A (NPRA) have marked cardiac hypertrophy and chamber dilatation disproportionate to their increased blood pressure (BP), suggesting, in support of previous in vitro data, that the NPRA system moderates the cardiac response to hypertrophic stimuli. Here, we have followed the changes in cardiac function in response to altered mechanical load on the heart of NPRA-null mice (Npr1-/-). Chronic treatment with either enalapril, furosemide, hydralazine, or losartan were all effective in reducing and maintaining BP at normal levels without affecting heart weight/body weight. In the reverse direction, we used transverse aortic constriction (TAC) to induce pressure overload. In the Npr1-/- mice, TAC resulted in a 15-fold increase in atrial natriuretic peptide (ANP) expression, a 55% increase in left ventricular weight/body weight (LV/BW), dilatation of the LV, and significant decline in cardiac function. In contrast, banded Npr1+/+ mice showed only a threefold increase in ANP expression, an 11% increase in LV/BW, a 0.2 mm decrease in LV end diastolic dimension, and no change in fractional shortening. The activation of mitogen-activated protein kinases that occurs in response to TAC did not differ in the Npr1+/+ and Npr1-/- mice. Taken together, these results suggest that the NPRA system has direct antihypertrophic actions in the heart, independent of its role in BP control.