Cancer therapy modulates VEGF signaling and viability in adult rat cardiac microvascular endothelial cells and cardiomyocytes

This work was motivated by the incomplete characterization of the role of vascular endothelial growth factor-A (VEGF-A) in the stressed heart in consideration of upcoming cancer treatment options challenging the natural VEGF balance in the myocardium. We tested, if the cytotoxic cancer therapy doxorubicin (Doxo) or the anti-angiogenic therapy sunitinib alters viability and VEGF signaling in primary cardiac microvascular endothelial cells (CMEC) and adult rat ventricular myocytes (ARVM). ARVM were isolated and cultured in serum-free medium. CMEC were isolated from the left ventricle and used in the second passage. Viability was measured by LDH-release and by MTT-assay, cellular respiration by high-resolution oxymetry. VEGF-A release was measured using a rat specific VEGF-A ELISA-kit. CMEC were characterized by marker proteins including CD31, von Willebrand factor, smooth muscle actin and desmin. Both Doxo and sunitinib led to a dose-dependent reduction of cell viability. Sunitinib treatment caused a significant reduction of complex I and II-dependent respiration in cardiomyocytes and the loss of mitochondrial membrane potential in CMEC. Endothelial cells up-regulated VEGF-A release after peroxide or Doxo treatment. Doxo induced HIF-1α stabilization and upregulation at clinically relevant concentrations of the cancer therapy. VEGF-A release was abrogated by the inhibition of the Erk1/2 or the MAPKp38 pathway. ARVM did not answer to Doxo-induced stress conditions by the release of VEGF-A as observed in CMEC. VEGF receptor 2 amounts were reduced by Doxo and by sunitinib in a dose-dependent manner in both CMEC and ARVM. In conclusion, these data suggest that cancer therapy with anthracyclines modulates VEGF-A release and its cellular receptors in CMEC and ARVM, and therefore alters paracrine signaling in the myocardium.     

Reactive oxygen species modulate endothelin-I-induced c-fos gene expression in cardiomyocytes.

OBJECTIVES: Recent evidence indicates that reactive oxygen species (ROS) may act as second messengers in receptor-mediated signaling pathways. The possible role of ROS during Et-1 stimulation in cardiomyocytes was therefore investigated. METHODS: Intracellular ROS levels were measured with fluorescence probe 2',7'-dichlorofluorescin diacetate by confocal microscopy in cultured neonatal rat cardiomyocytes. The ROS-inducible c-fos expression was analyzed by Northern blotting and promoter activity. RESULTS: Et-1 applied to cardiomyocytes dose-dependently increased intracellular ROS levels. The increase of ROS levels was attenuated by pretreating cardiomyocytes with Et-A receptor antagonist-BQ485, but not with Et-B receptor antagonist. Cardiomyocytes pretreated with catalase or an antioxidant N-acetylcysteine (NAC) reduced Et-1-induced ROS levels. Et-1 or H2O2 treatment of cardiomyocytes rapidly induced the expression of an immediate early gene c-fos. Et-1-treated cardiomyocytes enhanced the c-fos gene expression as revealed by functional analysis using a reporter gene construct containing c-fos promoter region (-2.25 kb) and reporter gene chloramphenicol acetyltransferase. The induction of mRNA levels and the promoter activities of c-fos gene by Et-1 or H2O2 were abolished by pretreating cardiomyocytes with catalase or NAC. Cells transiently transfected with the dominant positive mutant of p21ras (RasL61) led to a significant increase in intracellular ROS. Concomitantly, the mRNA levels and the promoter activities of c-fos were also induced. In contrast, cells transfected with the dominant negative mutant of Ras (RasN17) inhibited Et-1-induced ROS. Consistently, the increase of c-fos mRNA levels and promoter activities by Et-1 were also inhibited. CONCLUSIONS: These findings clearly indicate that Et-1 treatment to cardiomyocytes can induce ROS via Ras pathway and the increased ROS are involved in the increase of c-fos expression. Our studies thus emphasize the importance of ROS as second messengers in Et-1-induced responses on cardiomyocytes.     

Involvement of reactive oxygen species-mediated NF-kappa B activation in TNF-alpha-induced cardiomyocyte hypertrophy

We examined the intracellular signaling mechanism for tumor necrosis factor-alpha (TNF-alpha)-induced cardiac hypertrophy in isolated rat neonatal cardiomyocytes. TNF-alpha enhanced the expression of a kappa B-dependent reporter gene construct in a dose-dependent manner, which was transiently transfected in cardiomyocytes. Electrophoretic mobility shift assay demonstrated that TNF-alpha induced nuclear factor- kappa B (NF-kappa B)-specific DNA binding. Cultured cardiomyocytes were infected with a recombinant adenoviral vector expressing a degradation-resistant mutant of I kappa B alpha (AdI kappa B alpha 32/36A). The I kappa B alpha mutant suppressed NF-kappa B activation induced by TNF- alpha. In cardiomyocytes infected with AdI kappa B alpha 32/36A, TNF-alpha-induced hypertrophic responses, including increases in cell size, protein synthesis and atrial natriuretic factor production and enhancement of sarcomeric organization, were remarkably attenuated compared to the cells infected with an adenovirus expressing bacterial beta-galactosidase. Using a reactive oxygen species (ROS)-sensitive fluorescent dye, 2', 7'-dichlorofluorescin, we observed an increase in fluorescent signal in cardiomyocytes over time, upon addition of TNF-alpha. Preincubation of n-acetyl cysteine (NAC), an antioxidant, prior to TNF-alpha treatment, abolished TNF-alpha -induced ROS generation. NAC abolished TNF-alpha-induced NF-kappa B activation and hypertrophic responses. These findings indicated that TNF-alpha-induced cardiomyocyte hypertrophy is mediated through NF-kappa B activation via the generation of ROS.     

Endothelin-1 prolongs intracellular calcium transient decay in neonatal rat cardiac myocytes

Endothelin-1 (ET-1) is involved in the development of cardiac hypertrophy and heart failure. We investigated the effects of ET-1 on intracellular calcium transient and its mechanisms. Neonatal rat cardiomyocytes were prepared and calcium transient was measured using fura-2. Treatment with ET-1 for 48 h prolonged calcium transient decay. In the presence of thapsigargin, ET-1 did not alter calcium transient decay. On the other hand, the prolonged calcium transient decay was maintained even when sodium was removed from the bath solution. These results indicate that ET-1-induced prolongation of calcium transient decay is mainly due to the suppression of calcium uptake by sarcoplasmic reticulum, but not inhibition of the sodium/calcium exchanger. Northern blotting analysis revealed that sarcoplasmic reticulum ATPase (SERCA2) mRNA was decreased in ET-1-treated cardiomyocytes, and that this decrease was inhibited by BQ-123 but not by BQ-788. Moreover, pretreatment with chelerythrine partially restored the ET-1-induced decrease in SERCA2 mRNA, whereas phorbol 12-myristate 13-acetate markedly reduced SERCA2 gene expression. Real-time RT-PCR analysis showed abundant ETA receptor gene expression in cardiomyocytes. ET-1 reduces SERCA2 gene expression through the ETA receptor and PKC pathway, and prolongs intracellular calcium transient decay. Specific inhibition of the ETA receptor may be a possible therapeutic strategy for improving cardiac performance.     

Formation of reactive oxygen species at increased contraction frequency in rat cardiomyocytes

OBJECTIVE: Reactive oxygen species (ROS) play an ambivalent role in cardiomyocytes: low concentrations are involved in cellular signaling, while higher concentrations contribute to cellular injury. We studied ROS formation during increases in contraction frequency in isolated cardiomyocytes. METHODS: Rat ventricular cardiomyocytes were loaded with dichlorodihydrofluorescein and electrically stimulated (37 degrees C). ROS formation was assessed by the rate of oxidation-dependent fluorescence increase (OxR). Oxygen consumption (VO(2)) and NAD(P)H autofluorescence were measured in parallel experiments. RESULTS: Increases in contraction frequency were accompanied by an increase in VO(2) and a decrease in NAD(P)H fluorescence. OxR increased to 124+/-4%, 146+/-8%, 204+/-25% and 256+/-29% of OxR at baseline during 1, 2, 3 and 4 Hz stimulation, and subsequently returned to baseline values with 0.2 Hz. The OxR increase was dose-dependently inhibited by the antioxidant NAC (10 and 100 mM), but unaffected by the NO synthase inhibitor l-NAME (200 microM and 10 mM). The OxR increase was attenuated when myosin ATPase activity was inhibited by butanedione monoxime (BDM; 5 mM). CONCLUSION: Increased contraction frequency induces ROS formation in rat cardiomyocytes.     

Hypoxia and HIF-1 suppress SERCA2a expression in embryonic cardiac myocytes through two interdependent hypoxia response elements

Sarcoplasmic reticulum (SR) Ca²⁺-ATPase (SERCA2a) is an essential component of cardiomyocyte excitation–contraction (EC)-coupling. Suppression of SERCA2a expression induces contractile dysfunction and has been reported in various forms of ischemic cardiac disease as well as in hypobaric hypoxia. The present study investigated whether SERCA2a expression is regulated by hypoxia in embryonic mouse cardiomyocytes and explored the underlying mechanism. We show that in cultured embryonic cardiomyocytes hypoxia (1% O₂) induce time-dependent downregulation of SERCA2a expression. This mechanism manifested as specific changes in cardiac myocyte calcium signals induced by reduced expression and activity of SERCA2a. Chemical activation of hypoxia-inducible factor-1 (HIF-1) by DFO or overexpression of normoxia-stabile HIF-1α (HIF-1α/VP16) suppressed endogenous SERCA2a expression as well as the activity of the SERCA2a-promoter-luciferase reporter. Analysis of the SERCA2a promoter found two putative HIF-1 binding HRE-sites. Site-specific promoter mutagenesis revealed that co-operative HIF-1 binding to both of these hypoxia response elements on the SERCA2a promoter is required for expressional suppression. This mechanism establishes a link between oxygen supply and calcium activity in embryonic cardiac myocytes that is exploited in cardiac development, and further may offer a possible explanation for the functional depression of SERCA2a seen in ischemic and hypoxic myocardium.     

Melatonin ameliorates calcium homeostasis in myocardial and ischemia-reperfusion injury in chronically hypoxic rats

Chronic hypoxia (CH) leads to the deterioration of myocardial functions with impaired calcium handling in the sarcoplasmic reticulum (SR), which may be mediated by oxidative stress. We hypothesized that administration of antioxidant melatonin would protect against cardiac and ischemia-reperfusion (I/R) injury by ameliorating SR calcium handling. Adult Sprague-Dawley rats that had received a daily injection of melatonin or vehicle were exposed to 10% oxygen for 4 wk. The heart of each rat was then dissected and perfused using a Langendorff apparatus. The ratio of heart-to-body weight, ventricular hypertrophy and hematocrit were increased in the hypoxic rats compared with the normoxic controls. Malondialdehyde levels were also increased in the heart of hypoxic rats and were lowered by the treatment of melatonin. The hearts were subjected to left coronary artery ischemia (30 min) followed by 120-min reperfusion. Lactate dehydrogenase leakage before ischemia, during I/R and infarct size of the isolated perfused hearts were significantly elevated in the vehicle-treated hypoxic rats but not in the melatonin-treated rats. Spectroflurometric studies showed that resting calcium levels and I/R-induced calcium overload in the cardiomyocytes were more significantly altered in the hypoxic rats than the normoxic controls. Also, the hypoxic group had decreased levels of the SR calcium content and reduced amplitude and decay time of electrically induced calcium transients, indicating impaired contractility and SR calcium re-uptake. Moreover, there were reductions in protein expression of calcium handling proteins, markedly shown at the level of SR-Ca(2+) ATPase (SERCA) in the heart of hypoxic rats. Melatonin treatment significantly mitigated the calcium handling in the hypoxic rats by preserving SERCA expression. The results suggest that melatonin is cardioprotective against CH-induced myocardial injury by improving calcium handling in the SR of cardiomyocytes via an antioxidant mechanism.     

Alteration of BACE1-dependent NRG1/ErbB4 signaling and schizophrenia-like phenotypes in BACE1-null mice

beta-Site APP-cleaving enzyme 1 (BACE1) is required for the penultimate cleavage of the amyloid-beta precursor protein (APP) leading to the generation of amyloid-beta peptides that is central to the pathogenesis of Alzheimer's disease. In addition to its role in endoproteolysis of APP, BACE1 participates in the proteolytic processing of neuregulin 1 (NRG1) and influences the myelination of central and peripheral axons. Although NRG1 has been genetically linked to schizophrenia and NRG1(+/-) mice exhibit a number of schizophrenia-like behavioral traits, it is not known whether altered BACE1-dependent NRG1 signaling can cause similar behavioral abnormalities. To test this hypothesis, we analyze the behaviors considered to be rodent analogs of clinical features of schizophrenia in BACE1(-/-) mice with impaired processing of NRG1. We demonstrate that BACE1(-/-) mice exhibit deficits in prepulse inhibition, novelty-induced hyperactivity, hypersensitivity to a glutamatergic psychostimulant (MK-801), cognitive impairments, and deficits in social recognition. Importantly, some of these manifestations were responsive to treatment with clozapine, an atypical antipsychotic drug. Moreover, although the total amount of ErbB4, a receptor for NRG1 was not changed, binding of ErbB4 with postsynaptic density protein 95 (PSD95) was significantly reduced in the brains of BACE1(-/-) mice. Consistent with the role of ErbB4 in spine morphology and synaptic function, BACE1(-/-) mice displayed reduced spine density in hippocampal pyramidal neurons. Collectively, our findings suggest that alterations in BACE1-dependent NRG1/ErbB4 signaling may participate in the pathogenesis of schizophrenia and related psychiatric disorders.     

Role of neuregulin-1/ErbB signaling in cardiovascular physiology and disease: implications for therapy of heart failure

Since the discovery that neuregulin-1 (NRG-1)/ErbB signaling is indispensable in cardiac development, evidence has shown that this system also plays a crucial role in the adult heart. In patients, an inhibitory ErbB2 antibody, trastuzumab, used in the treatment of mammary carcinomas, increases the risk for the development of cardiotoxic cardiomyopathy. Postnatal disruption of NRG-1/ErbB signaling by gene targeting in mice leads to dilated cardiomyopathy. Initially, the search for the mechanisms behind these observations focused mainly on the effects of NRG-1 on cardiomyocyte growth and survival and revealed that NRG-1 has Akt-dependent antiapoptotic effects in cultured cardiomyocytes. In vivo studies, however, did not uniformly reinforce a role for apoptosis in the development of cardiomyopathy induced by impaired NRG-1/ErbB signaling. More recent studies have revealed that NRG-1 is involved in the regulation of cardiac sympathovagal balances by counterbalancing adrenergic stimulation of the adult myocardium and through an obligatory interaction with the muscarinic cholinergic system. NRG-1 is synthesized and released by the endocardial and cardiac microvascular endothelium, dynamically controlled by neurohormonal and biomechanical stimuli. The physiology of the cardiac NRG-1/ErbB system has implications for the treatment of both cancer and heart failure. Clinical studies in breast cancer with novel ErbB inhibitors are currently underway. Novel oncological indications for ErbB inhibition are emerging; cardiovascular side effects need to be carefully monitored. On the other hand, pharmacological activation of ErbB signaling is likely an unrecognized and beneficial effect of currently used drugs in heart failure and a promising therapeutic approach to prevent or reverse myocardial dysfunction.     

Neuregulin-1 and its potential role in the control of cardiac function

The rapidly evolving insights into the protective and modulatory function of neuregulin-1 (NRG-1) in the adult heart are discussed in this review. The actions of NRG-1 in the adult heart have begun to be elucidated following the unexpected clinical observation that trastuzumab can cause ventricular dysfunction and increases the risk of cardiomyopathy induced by anthracyclines. Trastuzumab is an inhibitory antibody against the NRG receptor erythroblastic leukemia viral oncogene homolog 2 (ErbB2) and is used in the treatment of breast cancer. In vitro studies have demonstrated that NRG-1 promotes growth and survival of isolated cardiomyocytes. Ventricular dysfunction following anti-ErbB2 treatment was initially explained by a loss of ErbB2-dependent cell survival pathways in the heart. However, in vivo studies in genetically modified mice did not uniformly confirm this finding. More recent studies have revealed that NRG-1 counterbalances the adrenergic inotropic response of the adult myocardium through an obligatory interaction with the muscarinic cholinergic system. In addition, it was demonstrated that cardiac NRG-1 synthesis and release from the cardiac endothelium, the principal source of NRG-1 in the heart, is dynamically controlled by neurohormonal and biomechanical stimuli, allowing adaptive tuning of ErbB signaling during cardiovascular stress. Cardiac NRG-1 is beginning to emerge as a cardioprotective factor implicated in the physiological regulation of myocardial performance and sympathovagal balances. Cardiac NRG-1/ErbB signaling has implications for the treatment of both cancer and heart failure. As novel ErbB inhibitors are currently being tested in broader oncological indications, there is a need to better understand their cardiovascular side effects. It is possible that pharmacological activation of ErbB signaling is an indirect, beneficial effect of the drugs currently used in heart failure, and this could be a promising therapeutic approach for prevention or reversal of myocardial dysfunction. Heart Fail Monit 2008;5(4):119-24.     

Oxidative stress and protein aggregation during biological aging

Biological aging is a fundamental process that represents the major risk factor with respect to the development of cancer, neurodegenerative, and cardiovascular diseases in vertebrates. It is, therefore, evident that the molecular mechanisms of aging are fundamental to understand many disease processes. In this regard, the oxidation and nitration of intracellular proteins and the formation of protein aggregates have been suggested to underlie the loss of cellular function and the reduced ability of senescent animals to withstand physiological stresses. Since oxidatively modified proteins are thermodynamically unstable and assume partially unfolded tertiary structures that readily form aggregates, it is likely that oxidized proteins are intermediates in the formation of amyloid fibrils. It is, therefore, of interest to identify oxidatively sensitive protein targets that may play a protective role through their ability to down-regulate energy metabolism and the consequent generation of reactive oxygen species (ROS). In this respect, the maintenance of cellular calcium gradients represents a major energetic expense, which links alterations in intracellular calcium levels to ATP utilization and the associated generation of ROS through respiratory control mechanisms. The selective oxidation or nitration of the calcium regulatory proteins calmodulin and Ca-ATPase that occurs in vivo during aging and under conditions of oxidative stress may represent an adaptive response to oxidative stress that functions to down-regulate energy metabolism and the associated generation of ROS. Since these calcium regulatory proteins are also preferentially oxidized or nitrated under in vitro conditions, these results suggest an enhanced sensitivity of these critical calcium regulatory proteins, which modulate signal transduction processes and intracellular energy metabolism, to conditions of oxidative stress. Thus, the selective oxidation of critical signal transduction proteins probably represents a regulatory mechanism that functions to minimize the generation of ROS through respiratory control mechanisms. The reduction of the rate of ROS generation, in turn, will promote cellular survival under conditions of oxidative stress, when reactive oxygen and nitrogen species overwhelm cellular antioxidant defense systems, by minimizing the non-selective oxidation of a range of biomolecules. Since protein aggregation occurs if protein repair and degradative systems are unable to act upon oxidized proteins and restore cellular function, the reduction of the oxidative load on the cell by the down-regulation of the electron transport chain functions to minimize protein aggregation. Thus, ROS function as signaling molecules that fine-tune cellular metabolism through the selective oxidation or nitration of calcium regulatory proteins in order to minimize wide-spread oxidative damage and protein aggregation.Oxidative damage to cellular proteins, the loss of calcium homeostasis and protein aggregation contribute to the formation of amyloid deposits that accumulate during biological aging. Critical to understand the relationship between these processes and biological aging is the identification of oxidatively sensitive proteins that modulate energy utilization and the associated generation of ROS. In this latter respect, oxidative modifications to the calcium regulatory proteins calmodulin (CaM) and the sarco/endoplasmic reticulum Ca-ATPase (SERCA) function to down-regulate ATP utilization and the associated generation of ROS associated with replenishing intracellular ATP through oxidative phosphorylation. Reductions in the rate of ROS generation, in turn, will minimize protein oxidation and facilitate intracellular repair and degradative systems that function to eliminate damaged and partially unfolded proteins. Since the rates of protein repair or degradation compete with the rate of protein aggregation, the modulation of intracellular calcium concentrations and energy metabolism through the selective oxidation or nitration of critical signal transduction proteins (i.e. CaM or SERCA) is thought to maintain cellular function by minimizing protein aggregation and amyloid formation. Age-dependent increases in the rate of ROS generation or declines in cellular repair or degradation mechanisms will increase the oxidative load on the cell, resulting in corresponding increases in the concentrations of oxidized proteins and the associated formation of amyloid.     

Diazoxide-induced cardioprotection requires signaling through a redox-sensitive mechanism

Diazoxide, a selective opener of the mitochondrial ATP-sensitive potassium channel, has been shown to elicit tolerance to ischemia in cardiac myocytes and in perfused heart. However, the mechanism of this cardioprotection is poorly understood. Because reactive oxygen species (ROS) are recognized as important intracellular signaling molecules and have been implicated in ischemic preconditioning, we examined diazoxide-induced ROS production in adult cardiomyocytes. Cells treated with 50 micromol/L diazoxide showed a 173% increase in ROS production relative to baseline. 5-Hydroxydecanoate was found to attenuate the diazoxide-induced increase in ROS generation. The diazoxide-induced increase in ROS also was abrogated by the addition of either the antioxidant N-acetylcysteine (NAC) or N-mercaptopropionylglycine. We also examined the ability of NAC to block the protective effects of diazoxide in the perfused rat heart. After 20 minutes of global ischemia and 20 minutes of reflow, hearts perfused with 100 micromol/L diazoxide before ischemia showed significantly improved postischemic contractile function relative to untreated hearts (84% versus 29% of initial left ventricular developed pressure, respectively). Hearts treated with diazoxide in the presence of 4 mmol/L NAC recovered 53% of initial left ventricular developed pressure, whereas hearts treated with NAC alone recovered 46% of preischemic function. Using (31)P NMR spectroscopy, we found that, similar to preconditioning, diazoxide significantly attenuated ischemia-induced intracellular acidification and enhanced post- ischemic recovery of phosphocreatine levels, both of which were blocked by cotreatment with NAC. These data suggest that the cardioprotective actions of diazoxide are mediated by generation of a pro-oxidant environment.     

Reduced level of serine(16) phosphorylated phospholamban in the failing rat myocardium: a major contributor to reduced SERCA2 activity

OBJECTIVE: Heart failure is associated with alterations in contractile parameters and accompanied by abnormalities in intracellular calcium homeostasis. Sarcoplasmic reticulum Ca(2+) ATPase (SERCA2) and phospholamban (PLB) are important in intracellular calcium cycling. The aim of the present study was to examine mechanisms causing reductions in SERCA2 activity in the failing heart. METHODS: Myocardial infarction (MI) was induced in male Wistar rats, and animals with congestive heart failure were examined 6 weeks after the primary operation. RESULTS: Serine(16) monomeric and pentameric phosphorylated PLB were significantly downregulated (50 and 55%, respectively), whereas threonine(17) phosphorylated PLB was unchanged in failing compared to sham hearts. Protein phosphatases 1 and 2A were significantly upregulated (26 and 42%, respectively) and phosphatase 2C significantly downregulated (29%), whereas the level of protein kinase A regulatory subunit II remained unchanged during heart failure. Increasing PLB phosphorylation by forskolin in isolated cardiomyocytes after inhibition of the Na(+)-Ca(2+) exchanger activity had significantly greater effect on SERCA2 activity in failing than in sham cells (49 and 20% faster transient decline, respectively). Decreasing PLB phosphorylation by the protein kinase A inhibitor H89 had significantly less effect on SERCA2 activity in failing compared to sham cardiomyocytes (20 and 75% slower transient decline, respectively). CONCLUSION: The observed changes in SERCA2 activity after increasing and decreasing serine(16) PLB phosphorylation in cardiomyocytes from sham and failing hearts, suggest that the observed reduction in serine(16) PLB phosphorylation is one major factor determining the reduced SERCA2 activity in heart failure after MI.     

Neuregulin-3 (NRG3): A novel neural tissue-enriched protein that binds and activates ErbB4

We describe the identification of Neuregulin-3 (NRG3), a novel protein that is structurally related to the neuregulins (NRG1). The NRG1/neuregulins are a diverse family of proteins that arise by alternative splicing from a single gene. These proteins play an important role in controlling the growth and differentiation of glial, epithelial, and muscle cells. The biological effects of NRG1 are mediated by receptor tyrosine kinases ErbB2, ErbB3, and ErbB4. However, genetic studies have suggested that the activity of ErbB4 may also be regulated in the central nervous system by a ligand distinct from NRG1. NRG3 is predicted to contain an extracellular domain with an epidermal growth factor (EGF) motif, a transmembrane domain, and a large cytoplasmic domain. We show that the EGF-like domain of NRG3 binds to the extracellular domain of ErbB4 in vitro. Moreover, NRG3 binds to ErbB4 expressed on cells and stimulates tyrosine phosphorylation of this receptor. The expression of NRG3 is highly restricted to the developing and adult nervous system. These data suggest that NRG3 is a novel, neural-enriched ligand for ErbB4.     

Cytostatic Drugs,Neuregulin Activation of ErbB Receptors,and Angiogenesis

Cytostatic drugs were developed to target specific molecular pathways shown to drive tumor growth. Although this approach has been very successful in treating cancers, its use is often hindered by off-target toxic effects. An example of this is trastuzumab, which targets the erbB2 kinase receptor. This drug successfully decreases tumor growth but adversely affects cardiac function. This observation led to important studies elucidating the importance of the erbB pathway in cardioprotection and angiogenesis. This review addresses the problem of off-target effects of cytostatic drugs (specifically trastuzumab) and their effect on cardiac function, summarizes the neuregulin-1 (NRG)/erbB signaling pathway, and discusses its importance in cardiac myocytes. It also highlights important findings showing the role of NRG/erbB signaling in microvascular preservation and angiogenesis, with a brief discussion of preclinical and clinical data regarding treatment of cardiovascular disease with NRG.     

过表达肌浆网钙三磷酸腺苷酶抑制缺氧诱导心肌细胞凋亡的研究

目的研究过表达肌浆网钙ATP酶2a(SERCA2a)能否提高心肌细胞对缺氧的耐受性,评价其对心肌细胞凋亡的影响。方法体外培养的SD乳鼠心肌细胞随机分为对照组、缺氧组、过表达SERCA2a组和SERCA2a+缺氧组,以携带SERCA2a基因的重组腺病毒转染心肌细胞48 h后对其进行缺氧处理。Western blot法检测细胞质内SERCA2a蛋白及Caspase-3表达的变化;膜联蛋白V/碘化丙啶双染色法及流式细胞术检测心肌细胞凋亡率;激光共聚焦显微镜检测细胞质内Ca~(2+)浓度变化。结果与对照组比较,缺氧组SERCA2a蛋白表达水平显著降低,过表达SERCA2a组蛋白含量升高2.5倍(P<0.05),缺氧组Caspase-3蛋白表达升高53.1%,过表达SERCA2a后给予缺氧处理,Caspase-3蛋白表达降低39.7%(P<0.05)。与对照组比较,缺氧组心肌细胞凋亡率显著升高,与缺氧组比较,SERCA2a+缺氧组细胞凋亡率显著下降(P<0.05)。与对照组比较,缺氧组细胞质内Ca~(2+)荧光强度显著升高;与缺氧组比较,SERCA2a+缺氧组细胞质内Ca~(2+)荧光强度显著降低(P<0.05)。结论过表达SERCA2a可减轻细胞内Ca~(2+)超载和抑制Caspase-3激活,进而减少缺氧诱导的心肌细胞凋亡。     

Glucose-6-phosphate dehydrogenase modulates cytosolic redox status and contractile phenotype in adult cardiomyocytes

Reactive oxygen species (ROS)-mediated cell injury contributes to the pathophysiology of cardiovascular disease and myocardial dysfunction. Protection against ROS requires maintenance of endogenous thiol pools, most importantly, reduced glutathione (GSH), by NADPH. In cardiomyocytes, GSH resides in two separate cellular compartments: the mitochondria and cytosol. Although mitochondrial GSH is maintained largely by transhydrogenase and isocitrate dehydrogenase, the mechanisms responsible for sustaining cytosolic GSH remain unclear. Glucose-6-phosphate dehydrogenase (G6PD) functions as the first and rate-limiting enzyme in the pentose phosphate pathway, responsible for the generation of NADPH in a reaction coupled to the de novo production of cellular ribose. We hypothesized that G6PD is required to maintain cytosolic GSH levels and protect against ROS injury in cardiomyocytes. We found that in adult cardiomyocytes, G6PD activity is rapidly increased in response to cellular oxidative stress, with translocation of G6PD to the cell membrane. Furthermore, inhibition of G6PD depletes cytosolic GSH levels and subsequently results in cardiomyocyte contractile dysfunction through dysregulation of calcium homeostasis. Cardiomyocyte dysfunction was reversed through treatment with either a thiol-repleting agent (L-2-oxothiazolidine-4-carboxylic acid) or antioxidant treatment (Eukarion-134), but not with exogenous ribose. Finally, in a murine model of G6PD deficiency, we demonstrate the development of in vivo adverse structural remodeling and impaired contractile function over time. We, therefore, conclude that G6PD is a critical cytosolic antioxidant enzyme, essential for maintenance of cytosolic redox status in adult cardiomyocytes. Deficiency of G6PD may contribute to cardiac dysfunction through increased susceptibility to free radical injury and impairment of intracellular calcium transport. The full text of this article is available online at http://www.circresaha.org.     

Combined phospholamban ablation and SERCA1a overexpression result in a new hyperdynamic cardiac state

OBJECTIVE: Phospholamban ablation or ectopic expression of SERCA1a in the heart results in significant increases in cardiac contractile parameters. The aim of the present study was to determine whether a combination of these two genetic manipulations may lead to further augmentation of cardiac function. METHODS: Transgenic mice with cardiac specific overexpression of SERCA1a were mated with phospholamban deficient mice to generate a model with SERCA1a overexpression in the phospholamban null background (SERCA1(OE)/PLB(KO)). The cardiac phenotype was characterized using quantitative immunoblotting, sarcoplasmic reticulum calcium uptake and single myocyte mechanics and calcium kinetics. RESULTS: Quantitative immunoblotting revealed an increase of 1.8-fold in total SERCA level, while SERCA2 was decreased to 50% of wild types. Isolated myocytes indicated increases in the maximal rates of contraction by 195 and 125%, the maximal rates of relaxation by 200 and 124%, while the time for 80% decay of the Ca(2+)-transient was decreased to 43 and 75%, in SERCA1(OE)/PLB(KO) hearts, compared to SERCA1a overexpressors and phospholamban knockouts, respectively. These mechanical alterations reflected parallel alterations in V(max) and EC(50) for Ca(2+) of the sarcoplasmic reticulum Ca(2+) transport system. Furthermore, there were no significant cardiac histological or pathological alterations, and the myocyte contractile parameters remained enhanced, up to 12 months of age. CONCLUSIONS: These findings suggest that a combination of SERCA1a overexpression and phospholamban ablation results in further enhancement of myocyte contractility over each individual alteration.     

五味子乙素通过半胱天冬酶凋亡途径对抗高糖诱导的心肌细胞氧化应激损伤

目的 研究五味子乙素(Sch.B)是否可通过降低活性氧(ROS)的生成保护糖尿病状态下心肌细胞;是否通过抑制细胞凋亡减轻高糖诱导的心肌细胞损伤.方法 链脲佐菌素诱导Wistar大鼠制备1型糖尿病模型.口服药物Sch.B 4周后进行取材和检测.心肌细胞分为低糖组和高糖组,高糖+Sch.B组和高糖+氧自由基清除剂组.DHE...