Increased protein kinase C activity in myotrophin-induced myocyte growth

Aqueous extract of Solanum nigrum attenuates Angiotensin-II induced cardiac hypertrophy and improves cardiac function by repressing protein kinase C-ζ to restore HSF2 deSUMOlyation and Mel-18-IGF-IIR signaling suppression

ETHNOPHARMACOLOGICAL RELEVANCE

Solanum nigrum, commonly known as Makoi or black shade has been traditionally used in Asian countries and other regions of world to treat liver disorders, diarrhoea, inflammatory conditions, chronic skin ailments (psoriasis and ringworm), fever, hydrophobia, painful periods, eye diseases, etc. It has been observed that S. nigrum contains substances, like steroidal saponins, total alkaloid, steroid alkaloid, and glycoprotein, which show anti-tumor activity. However; there is no scientific evidence of the efficacy of S. nigrum in the treatment of cardiac hypertrophy.

AIM

To investigate the ability of S. nigrum to attenuate Angiotensin II - induced cardiac hypertrophy and improve cardiac function through the suppression of protein kinase PKC-ζ and Mel-18-IGF-IIR signaling leading to the restoration of HSF2 desumolyation.

MATERIALS AND METHODS

Cardiomyoblast cells (H9c2) were challenged with 100 nM Angiotensin-II (AngII) for 24 h and were then treated with different concentration of S.nigrum or Calphostin C for 24 h. The hypertrophic effect in cardiomyoblast cells were determined by immunofluorescence staining and the modulations in hypertrophic protein marker along with Protein Kinase C-ζ, MEL18, HSF2, and Insulin like growth factor II (IGFIIR), markers were analyzed by western blotting. In vivo experiments were performed using 12 week old male Wistar Kyoto rats (WKY) and Spontaneously hypertensive rats (SHR) separated into five groups. [1]Control WKY, [2] WKY -100 mg/kg of S.nigrum treatment, [3] SHR, [4] SHR-100 mg/kg of S.nigrum treatment, [5] SHR-300 mg/kg of S.nigrum treatment. S. nigrum was administered intraperitoneally for 8 week time interval.

RESULTS

Western blotting results indicate that S. nigrum significantly attenuates AngII induced cardiac hypertrophy. Furthermore, actin staining confirmed the ability of S. nigrum to ameliorate AngII induced cardiac hypertrophy. Moreover, S. nigrum administration suppressed the hypertrophic signaling mediators like Protein Kinase C-ζ, Mel-18, and IGFIIR in a dose-dependent manner and HSF2 activation (restore deSUMOlyation) that leads to downregulation of IGF-IIR expression. Additionally in vivo experiments demonstrate the reduced heart sizes of S. nigrum treated SHRs rats when compared to control WKY rats.

CONCLUSION

Collectively, the data reveals the cardioprotective effect of S. nigrum inhibiting PKC-ζ with alleviated IGF IIR level in the heart that profoundly remits cardiac hypertrophy for hypertension-induced heart failure.

PRKCE gene encoding protein kinase C-epsilon-Dual roles at sarcomeres and mitochondria in cardiomyocytes

Protein kinase C-epsilon (PKCε) is an isoform of a large PKC family of enzymes that has a variety of functions in different cell types. Here we discuss two major roles of PKCε in cardiac muscle cells; specifically, its role in regulating cardiac muscle contraction via targeting the sarcomeric proteins, as well as modulating cardiac cell energy production and metabolism by targeting cardiac mitochondria. The importance of PKCε action is described within the context of intracellular localization, as substrate selectivity and specificity is achieved through spatiotemporal targeting of PKCε. Accordingly, the role of PKCε in regulating myocardial function in physiological and pathological states has been documented in both cardioprotection and cardiac hypertrophy.

Differential and conditional activation of PKC-isoforms dictates cardiac adaptation during physiological to pathological hypertrophy

A cardiac hypertrophy is defined as an increase in heart mass which may either be beneficial (physiological hypertrophy) or detrimental (pathological hypertrophy). This study was undertaken to establish the role of different protein kinase-C (PKC) isoforms in the regulation of cardiac adaptation during two types of cardiac hypertrophy. Phosphorylation of specific PKC-isoforms and expression of their downstream proteins were studied during physiological and pathological hypertrophy in 24 week male Balb/c mice (Mus musculus) models, by reverse transcriptase-PCR, western blot analysis and M-mode echocardiography for cardiac function analysis. PKC-δ was significantly induced during pathological hypertrophy while PKC-α was exclusively activated during physiological hypertrophy in our study. PKC-δ activation during pathological hypertrophy resulted in cardiomyocyte apoptosis leading to compromised cardiac function and on the other hand, activation of PKC-α during physiological hypertrophy promoted cardiomyocyte growth but down regulated cellular apoptotic load resulting in improved cardiac function. Reversal in PKC-isoform with induced activation of PKC-δ and simultaneous inhibition of phospho-PKC-α resulted in an efficient myocardium to deteriorate considerably resulting in compromised cardiac function during physiological hypertrophy via augmentation of apoptotic and fibrotic load. This is the first report where PKC-α and -δ have been shown to play crucial role in cardiac adaptation during physiological and pathological hypertrophy respectively thereby rendering compromised cardiac function to an otherwise efficient heart by conditional reversal of their activation.

βIIPKC and εPKC isozymes as potential pharmacological targets in cardiac hypertrophy and heart failure

Cardiac hypertrophy is a complex adaptive response to mechanical and neurohumoral stimuli and under continual stressor, it contributes to maladaptive responses, heart failure and death. Protein kinase C (PKC) and several other kinases play a role in the maladaptative cardiac responses, including cardiomyocyte hypertrophy, myocardial fibrosis and inflammation. Identifying specific therapies that regulate these kinases is a major focus of current research. PKC, a family of serine/threonine kinases, has emerged as potential mediators of hypertrophic stimuli associated with neurohumoral hyperactivity in heart failure. In this review, we describe the role of PKC isozymes that is involved in cardiac hypertrophy and heart failure. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure".

The protective role of arjunolic acid against doxorubicin induced intracellular ROS dependent JNK-p38 and p53-mediated cardiac apoptosis

In spite of tremendous demand for the development and implementation of effective therapeutic strategies, limitations are still associated with doxorubicin-induced cardiotoxicity. Arjunolic acid (AA) has been shown to possess a multitude of biological functions. The purpose of the present study was to explore whether AA plays any protective role against doxorubicin-induced cardiotoxicity; and if so, what molecular mechanism it utilizes for its protective action. In rat cardiomyocytes, doxorubicin administration activated the proapoptotic p53, p38 and JNK MAPKs, Bax translocation, disrupted mitochondrial membrane potential, precipitated mitochondrion mediated caspase-dependent apoptotic signalling and reduced viability of cardiomyocytes. Doxorubicin exposure increases dichlorofluorescein (DCF) intensity corresponding to the intracellular H(2)O(2) generation in myocytes; catalase (CAT) treatment, however, reduced this intensity and preserves cell viability. Intracellular H(2)O(2) thus produced now activates the p38-JNK and p53-mediated pathways. CAT treatment also markedly decreased the doxorubicin-mediated activation of p38 and JNK, suggesting that H(2)O(2) is involved in the activation of MAPKs. Blockage of p53 and p38-JNK by pharmacological inhibitors also suppressed the doxorubicin-induced apoptosis with the concomitant inhibition of anti-apoptotic Bcl-2 family proteins. AA treatment ameliorates nearly all of these apoptotic actions of doxorubicin and preserves cell viability. Similarly, rats treated with doxorubicin displayed retarded growth of body and heart as well as elevated apoptotic indices in heart tissue, whereas AA treatment effectively neutralised all these doxorubicin-induced cardiac-abnormalities. Combining all, our results suggest that doxorubicin induces cardiac apoptosis via the activation of JNK-p38 and p53-mediated signalling pathways, where H(2)O(2) acts as the mediators of these pathways. AA can effectively and extensively counteract this action of doxorubicin, and may potentially protect the heart and cardiomyocytes from the severe doxorubicin-induced cardiovascular burden.

Taurine suppresses doxorubicin-triggered oxidative stress and cardiac apoptosis in rat via up-regulation of PI3-K/Akt and inhibition of p53, p38-JNK

The objective of the present study was to investigate the signaling mechanisms involved in the beneficial role of taurine against doxorubicin-induced cardiac oxidative stress. Male rats were administered doxorubicin. Hearts were collected 3 weeks after the last dose of doxorubicin and were analyzed. Doxorubicin administration retarded the growth of the body and the heart and caused injury in the cardiac tissue because of increased oxidative stress. Similar experiments with doxorubicin showed reduced cell viability, increased ROS generation, intracellular Ca(2+) and DNA fragmentation, disrupted mitochondrial membrane potential and apoptotic cell death in primary cultured neonatal rat cardiomyocytes. Signal transduction studies showed that doxorubicin increased p53, JNK, p38 and NFκB phosphorylation; decreased the levels of phospho ERK and Akt; disturbed the Bcl-2 family protein balance; activated caspase 12, caspase 9 and caspase 3; and induced cleavage of the PARP protein. However, taurine treatment or cardiomyocyte incubation with taurine suppressed all of the adverse effects of doxorubicin. Studies with several inhibitors, including PS-1145 (an IKK inhibitor), SP600125 (a JNK inhibitor), SB203580 (a p38 inhibitor) and LY294002 (a PI3-K/Akt inhibitor), demonstrated that the mechanism of taurine-induced cardio protection involves activation of specific survival signals and PI3-K/Akt as well as the inhibition of p53, JNK, p38 and NFκB. These novel findings suggest that taurine might have clinical implications for the prevention of doxorubicin-induced cardiac oxidative stress.

Anchoring skeletal muscle development and disease: the role of ankyrin repeat domain containing proteins in muscle physiology

The ankyrin repeat is a protein module with high affinity for other ankyrin repeats based on strong Van der Waals forces. The resulting dimerization is unusually resistant to both mechanical forces and alkanization, making this module exceedingly useful for meeting the extraordinary demands of muscle physiology. Many aspects of muscle function are controlled by the superfamily ankyrin repeat domain containing proteins, including structural fixation of the contractile apparatus to the muscle membrane by ankyrins, the archetypical member of the family. Additionally, other ankyrin repeat domain containing proteins critically control the various differentiation steps during muscle development, with Notch and developmental stage-specific expression of the members of the Ankyrin repeat and SOCS box (ASB) containing family of proteins controlling compartment size and guiding the various steps of muscle specification. Also, adaptive responses in fully formed muscle require ankyrin repeat containing proteins, with Myotrophin/V-1 ankyrin repeat containing proteins controlling the induction of hypertrophic responses following excessive mechanical load, and muscle ankyrin repeat proteins (MARPs) acting as protective mechanisms of last resort following extreme demands on muscle tissue. Knowledge on mechanisms governing the ordered expression of the various members of superfamily of ankyrin repeat domain containing proteins may prove exceedingly useful for developing novel rational therapy for cardiac disease and muscle dystrophies.

Taurine prevents arsenic-induced cardiac oxidative stress and apoptotic damage: role of NF-kappa B, p38 and JNK MAPK pathway

Cardiac dysfunction is a major cause of morbidity and mortality worldwide due to its complex pathogenesis. However, little is known about the mechanism of arsenic-induced cardiac abnormalities and the use of antioxidants as the possible protective agents in this pathophysiology. Conditionally essential amino acid, taurine, accounts for 25% to 50% of the amino acid pool in myocardium and possesses antioxidant properties. The present study has, therefore, been carried out to investigate the underlying mechanism of the beneficial role of taurine in arsenic-induced cardiac oxidative damage and cell death. Arsenic reduced cardiomyocyte viability, increased reactive oxygen species (ROS) production and intracellular calcium overload, and induced apoptotic cell death by mitochondrial dependent caspase-3 activation and poly-ADP ribose polymerase (PARP) cleavage. These changes due to arsenic exposure were found to be associated with increased IKK and NF-kappaB (p65) phosphorylation. Pre-exposure of myocytes to an IKK inhibitor (PS-1145) prevented As-induced caspase-3 and PARP cleavage. Arsenic also markedly increased the activity of p38 and JNK MAPKs, but not ERK to that extent. Pre-treatment with SP600125 (JNK inhibitor) and SB203580 (p38 MAPK inhibitor) attenuated NF-kappaB and IKK phosphorylation indicating that p38 and JNK MAPKs are mainly involved in arsenic-induced NF-kappaB activation. Taurine treatment suppressed these apoptotic actions, suggesting that its protective role in arsenic-induced cardiomyocyte apoptosis is mediated by attenuation of p38 and JNK MAPK signaling pathways. Similarly, arsenic intoxication altered a number of biomarkers related to cardiac oxidative stress and other apoptotic indices in vivo and taurine supplementation could reduce it. Results suggest that taurine prevented arsenic-induced myocardial pathophysiology, attenuated NF-kappaB activation via IKK, p38 and JNK MAPK signaling pathways and could possibly provide a protection against As-induced cardiovascular burden.

Protein kinase C in heart failure: a therapeutic target?

Heart failure (HF) afflicts about 5 million people and causes 300,000 deaths a year in the United States alone. An integral part of the pathogenesis of HF is cardiac remodelling, and the signalling events that regulate it are a subject of intense research. Cardiac remodelling is the sum of responses of the heart to causes of HF, such as ischaemia, myocardial infarction, volume and pressure overload, infection, inflammation, and mechanical injury. These responses, including cardiomyocyte hypertrophy, myocardial fibrosis, and inflammation, involve numerous cellular and structural changes and ultimately result in a progressive decline in cardiac performance. Pharmacological and genetic manipulation of cultured heart cells and animal models of HF and the analysis of cardiac samples from patients with HF are all used to identify the molecular and cellular mechanisms leading to the disease. Protein kinase C (PKC) isozymes, a family of serine-threonine protein kinase enzymes, were found to regulate a number of cardiac responses, including those associated with HF. In this review, we describe the PKC isozymes that play critical roles in specific aspects of cardiac remodelling and dysfunction in HF.

Nuclear co-translocation of myotrophin and p65 stimulates myocyte growth. Regulation by myotrophin hairpin loops

Myotrophin, a 12-kDa ankyrin repeat protein, stimulates protein synthesis and cardiomyocyte growth to initiate cardiac hypertrophy by activating the NF-kappaB signaling cascade. We found that, after internalization into myocytes, myotrophin cotranslocates into the nucleus with p65 to stimulate myocyte growth. We used structure-based mutations on the hairpin loops of myotrophin to determine the effect of the loops on myotrophin and p65 localization, induction of protein synthesis, and cardiac hypertrophy. Loop mutants, most prominently glutamic acid 33-->alanine (E33A), stimulated protein synthesis much less than wild type. Myotrophin-E33A internalized into myocytes but did not translocate into the nucleus and failed to promote nuclear translocation of p65. In addition, two cardiac hypertrophy marker genes, atrial natriuretic factor and beta-myosin heavy chain, were not up-regulated in E33A-treated cells. Myotrophin-induced myocyte growth and initiation of hypertrophy thus require nuclear co-translocation of myotrophin and p65, in a manner that depends crucially on the myotrophin hairpin loops.

Cardiac hypertrophy: mechanisms and therapeutic opportunities

Cardiac hypertrophy and heart failure are major causes of morbidity and mortality in Western societies. Many factors have been implicated in cardiac remodeling, including alterations in gene expression in myocytes, cardiomyocytes apoptosis, cytokines and growth factors that influence cardiac dynamics, and deficits in energy metabolism as well as alterations in cardiac extracellular matrix composition. Many therapeutic means have been shown to prevent or reverse cardiac hypertrophy. New concepts for characterizing the pathophysiology of cardiac hypertrophy have been drawn from various aspects, including medical therapy and gene therapy, or use of stem cells for tissue regeneration. In this review, we focus on various types of cardiac hypertrophy, defining the causes of hypertrophy, describing available animal models of hypertrophy, discussing the mechanisms for development of hypertrophy and its transition to heart failure, and presenting the potential use of novel promising therapeutic strategies derived from new advances in basic scientific research.

Differential expression of oxygen-regulated genes in bovine blastocysts

Low oxygen conditions (2%) during post-compaction culture of bovine blastocysts improve embryo quality, which is associated with a small yet significant increase in the expression of glucose transporter 1 (GLUT-1), suggesting a role of oxygen in embryo development mediated through oxygen-sensitive gene expression. However, bovine embryos to at least the blastocyst stage lack a key regulator of oxygen-sensitive gene expression, hypoxia-inducible factor 1alpha (HIF1alpha). A second, less well-characterized protein (HIF2alpha) is, however, detectable from the 8-cell stage of development. Here we use differential display to determine additional gene targets in bovine embryos in response to low oxygen conditions. While development to the blastocyst stage was unaffected by the oxygen concentration used during post-compaction culture, differential display identified oxygen-regulation of myotrophin and anaphase promoting complex 1 expression, with significantly lower levels observed following culture under 20% oxygen than 2% oxygen. These results further support the hypothesis that the level of gene expression of specific transcripts by bovine embryos alters in response to changes in the oxygen environment post-compaction. Specifically, we have identified two oxygen-sensitive genes that are potentially regulated by HIF2 in the bovine blastocyst.

Myotrophin is a more powerful predictor of major adverse cardiac events following acute coronary syndrome than N-terminal pro-B-type natriuretic peptide

Myotrophin is a 12 kDa protein initially isolated from hypertrophied hearts of spontaneously hypertensive rats and acts by modulating NF-kappaB (nuclear factor kappaB) activity. We have reported previously the presence of myotrophin in patients with human systolic heart failure; however, its role as a predictor of MACE (major adverse cardiac events) in patients with ACS (acute coronary syndrome) is unclear. In the present study, we sought to investigate this and compared myotrophin with NTproBNP (N-terminal pro-B-type natriuretic peptide), a marker of MACE. We studied 356 patients with ACS {276 men; mean age, 63.0+/-12.8 years; 80.6% STEMI [ST segment elevation MI (myocardial infarction)]; and 19.4% NSTEMI (non-STEMI)}. Blood measurement was made at 25-48 h after the onset of chest pain. The plasma concentration of myotrophin and NTproBNP was determined using in-house non-competitive immunoassays. Patients were followed-up for the combined end point of death, MI or need for urgent revascularization. Over the median follow-up period of 355 (range 0-645) days, there were 28 deaths, 27 non-fatal MIs and 73 patients required urgent revascularization. Myotrophin was raised in patients with MACE compared with survivors [510.7 (116.0-7445.6) fmol/ml compared with 371.5 (51.8-6990.4) fmol/ml respectively; P=0.001; values are medians (range)]. Using a Cox proportional hazards model, myotrophin {HR (hazard ratio), 1.64 [95% CI (confidence interval), 0.97-2.76]; P=0.05} and Killip class above 1 [HR, 1.52 (95% CI, 0.93-2.42); P=0.10] were the only independent predictors of MACE. A Kaplan-Meier survival curve revealed a significantly better clinical outcome in patients with myotrophin below the median compared with those with myotrophin above the median (log rank, 7.63; P=0.006). In conclusion, after an ACS, levels of myotrophin are more informative at predicting MACE than NTproBNP and may be useful to risk stratify patients.

Regional and modular expression of morphogenetic factors in the demosponge Lubomirskia baicalensis

Some sponges [phylum Porifera], e.g. the demosponges Lubomirskia baicalensis or Axinella polypoides, show an arborescent growth form. In the freshwater sponge L. baicalensis this morphotype is seen mostly in depths below 4m while in more shallow regions it grows as a crust. The different growth forms are determined in nature very likely by water current and/or light. The branches of this species are composed of modules, arranged along the apical-basal axis. The modules are delimited by a precise architecture of the spicule bundles; longitudinal bundles originate from the apex of the earlier module, while at the basis of each module these bundles are cross-linked by traverse bundles under formation of annuli. Genes encoding putative morphogenetic factors, myotrophin and epidermal growth factor (EGF)-like molecules, and one gene of an antagonist for the Wnt signaling pathway, the soluble frizzled molecule, have been identified and characterized. Their expression levels as well as those of silicatein, one major spicule-forming molecule, have been studied in the crusts and the modules. The data revealed that at the apices of each module higher level of expression of myotrophin and EGF can be detected, while the base of each module is characterized by a high steady-state expression level of soluble frizzled molecule. These results suggest that module formation in L. baicalensis is controlled by a tuned interaction of agonistic (e.g., myotrophin and EGF) as well as antagonistic morphogenetic factors (e.g., soluble frizzled molecule).

Meal feeding stimulates phosphorylation of multiple effector proteins regulating protein synthetic processes in rat hearts

Feeding promotes protein synthesis in cardiac muscle through a stimulation of the mRNA translation initiation phase of protein synthesis either secondary to nutrient-induced rises in insulin or because of direct effects of nutrients themselves. The present set of experiments establishes the effects of meal feeding on the potential signal transduction pathways that may be important in accelerating mRNA translation initiation. Hearts were obtained from male Sprague Dawley rats that had been trained to consume a meal consisting of nonpurified diet prior to, during, and following the test meal. Meal feeding raised the extent of phosphorylation of eukaryotic initiation factor (eIF)4G (Ser(1108)), which returned to basal levels within 3 h of removal of food. Likewise, meal feeding was associated with an increase in phosphorylation of eIF4E binding protein-1(4EBP1) in the gamma-form during feeding. Phosphorylation of mammalian target of rapamycin (mTOR) on Ser(2448) or Ser(2481) or 70-kDa ribosomal protein S6 kinase (S6K1) on Thr(389) was not affected by meal feeding or following removal of food. Likewise, the extent of phosphorylation of TSC2, a potential upstream regulator of mTOR, was not significantly altered during meal feeding. Phosphorylation of protein kinase B (PKB) (Thr(308)) was elevated at all time points after initiating meal feeding. Similarly, the phosphorylation of protein kinase C(PKC)-epsilon but not PKC-delta was elevated at all time points after initiating meal feeding. We conclude from these studies that meal feeding stimulates at least 2 signal pathways in cardiac muscle that raises phosphorylation of eIF4G and 4EBP1 during meal feeding and results in sustained increases in phosphorylation of PKB and PKC-epsilon.

The stem cell concept in sponges (Porifera): Metazoan traits

Sponges are considered the oldest living animal group and provide important insights into the earliest evolutionary processes in the Metazoa. This paper reviews the evidence that sponge stem cells have essential roles in cellular specialization, embryogenesis and Bauplan formation. Data indicate that sponge archaeocytes not only represent germ cells but also totipotent stem cells. Marker genes have been identified which are expressed in totipotent stem cells and gemmule cells. Furthermore, genes are described for the three main cell lineages in sponge, which share a common origin from archaeocytes and result in the differentiation of skeletal, epithelial, and contractile cells.

Characterization and functional significance of myotrophin: a gene with multiple transcripts

The underlying mechanism for the development of cardiac hypertrophy that advances to heart failure is not known. Many factors have been implied to play a role in this process. Among others, we have isolated and identified myotrophin, a factor that stimulates myocytes growth, from spontaneously hypertensive rat (SHR) heart and patients with dilated cardiomyopathy. The gene encoding myotrophin has been cloned and expressed in E. coli. Recently, myotrophin gene has been mapped and shown to be a novel gene localized in human chromosome 7q-33. To define the characteristics of each transcript and its pathophysiological significance, we examined transcripts of myotrophin in SHR heart during progression of hypertrophy. Northern blot analysis of myotrophin mRNA showed multiple transcripts. We isolated and characterized various myotrophin cDNA clones corresponding to the multiple transcripts by 5' "stretch plus" rat heart cDNA library screening. Sequence analysis of these cDNA clones indicates that each clone has a unique 5' UTR and multiple 3' UTR with varying lengths, repeated ATTTA motifs and many polyadenylation signals. In vitro transcripts generated from all these myotrophin-specific cDNA clones translate in vitro to a 12-kD protein. Among pathophysiological significance, we determined mRNA expression in 9 days old, 3 weeks old and 31 weeks old and observed a linear increased during the progression of hypertrophy. In WKY, this mRNA level remained the same throughout the growth and development of hypertrophy. Our data strongly suggest that myotrophin appears to be a candidate gene for cardiac hypertrophy and heart failure.

Docosahexaenoic acid inhibits protein kinase C translocation/activation and cardiac hypertrophy in rat cardiomyocytes

Phenylephrine (PE) induces cardiac hypertrophy through multiple signaling pathways including pathways involving protein kinase C (PKC) activation. Docosahexaenoic acid (DHA), an omega-3 fatty acid, has been shown to reduce the PE-induced hypertrophic responses. However, the effects of DHA on PKC activation and translocation are controversial. The present study investigates the effect of DHA on PE-induced activation of PKC. The results indicate that PE induces PKCalpha translocation (from cytosol to plasma membranes) and activation in cardiomyocytes during the hypertrophic responses. Although DHA itself has no significant effect on basal PKC translocation and activation, it effectively reduced PE-stimulated PKC translocation and activation. The results of the present study suggest a possible mechanism explaining how dietary fish oil may inhibit development of cardiac hypertrophy and therefore may be an attractive dietary agent for preventing cardiac hypertrophy in patients with heart failure.

Matrix-mediated canal formation in primmorphs from the sponge Suberites domuncula involves the expression of a CD36 receptor-ligand system

Sponges (Porifera), represent the phylogenetically oldest metazoan phylum still extant today. Recently, molecular biological studies provided compelling evidence that these animals share basic receptor/ligand systems, especially those involved in bodyplan formation and in immune recognition, with the higher metazoan phyla. An in vitro cell/organ-like culture system, the primmorphs, has been established that consists of proliferating and differentiating cells, but no canals of the aquiferous system. We show that after the transfer of primmorphs from the demosponge Suberites domuncula to a homologous matrix (galectin), canal-like structures are formed in these 3D-cell aggregates. In parallel with the formation of these structures a gene is expressed whose deduced protein falls into the CD36/LIMPII receptor family. The receptor was cloned and found to be strongly expressed after adhesion to the galectin matrix. This process was suppressed if primmorphs were co-incubated with a homologous polypeptide containing the CSVTCG domain, as found in thrombospondin-1 (and related) molecules of vertebrates. In situ hybridization studies revealed that the S. domuncula CD36/LIMPII receptor is localized in the pinacocytes that surround the canals of the sponge. Furthermore, a secondary metabolite from a sponge-associated bacterium was isolated and characterized, the 2-methylthio-1,4-naphthoquinone (MTN). MTN causes inhibition of cell proliferation of vertebrate tumor cells at concentrations of >80 ng/ml. However, doses of only 2 ng are required to potently inhibit angiogenesis in the chick chorio-allantoic membrane assay. At concentrations of 10 ng/ml this compound was also found to suppress the expression of the S. domuncula CD36/LIMPII; this result is a first indication that this secondary metabolite has a conserved functional activity: the suppression of the formation of the circulation system, from sponges to vertebrates.

Myocardial cell death and regeneration during progression of cardiac hypertrophy to heart failure

Cardiac hypertrophy and ensuing heart failure are among the most common causes of mortality worldwide, yet the triggering mechanisms for progression of hypertrophy to failure are not fully understood. Tissue homeostasis depends on proper relationships between cell proliferation, differentiation, and death and any imbalance between them results in compromised cardiac function. Recently, we developed a transgenic (Tg) mouse model that overexpress myotrophin (a 12-kDa protein that stimulates myocyte growth) in heart resulting in hypertrophy that progresses to heart failure. This provided us an appropriate model to study the disease process at any point from initiation of hypertrophy end-stage heart failure. We studied detailed apoptotic signaling and regenerative pathways and found that the Tg mouse heart undergoes myocyte loss and regeneration, but only at a late stage (during transition to heart failure). Several apoptotic genes were up-regulated in 9-month-old Tg hearts compared with age-matched wild type or 4-week-old Tg hearts. Cardiac cell death during heart failure involved activation of Fas, tumor necrosis factor-alpha, and caspases 9, 8, and 3 and poly(ADP-ribose) polymerase cleavage. Tg mice with hypertrophy associated with compromised function showed significant up-regulation of cyclins,cyclin-dependent kinases (Cdks), and cell regeneration markers in myocytes. Furthermore, in human failing and nonfailing hearts, similar observations were documented including induction of active caspase 3 and Ki-67 proteins in dilated cardiomyopathic myocytes. Taken together, our data suggest that the stress of extensive myocardial damage from longstanding hypertrophy may cause myocytes to reenter the cell cycle. We demonstrate, for the first time in an animal model, that cell death and regeneration occur simultaneously in myocytes during end-stage heart failure, a phenomenon not observed at the onset of the disease process.

Influence of cytokines and growth factors in ANG II-mediated collagen upregulation by fibroblasts in rats: role of myocytes

Abnormal stiffness and altered cardiac function arising from abnormal collagen deposition occur in hypertrophy and heart failure. ANG II has been shown to play a role in this process. To evaluate the mechanism, we developed an in vitro model by subjecting fibroblasts to ANG II treatment in the presence or absence of myocytes in coculture (25). Employing this model, we demonstrated that ANG II-induced collagen gene transcription in cardiac fibroblasts was potentiated by myocyte-derived factors. In attempting to identify mechanisms of collagen upregulation and to define the role of myocytes, we found that interleukin (IL)-6, tumor necrosis factor (TNF)-alpha, and the transforming growth factor (TGF)-beta superfamily were also involved in collagen upregulation. Collagen transcripts were increased after fibroblasts were treated with IL-6 (20-50 ng/ml) and TNF-alpha (0.1-0.5 ng/ml). In this study, we show that cardiomyocytes induce secretion of active TGF-beta in the presence of ANG II and that a paracrine action of TGF-beta subsequently induces different cytokines (IL-6) in fibroblasts, thereby promoting collagen synthesis. The cross-talk between myocytes and fibroblasts and involvement of these cytokines in the upregulation of collagen transcript levels are novel findings that may explain their possible roles in the upregulation of collagen.

Cardiac overexpression of myotrophin triggers myocardial hypertrophy and heart failure in transgenic mice

Cardiac hypertrophy and heart failure remain leading causes of death in the United States. Many studies have suggested that, under stress, myocardium releases factors triggering protein synthesis and stimulating myocyte growth. We identified and cloned myotrophin, a 12-kDa protein from hypertrophied human and rat hearts. Myotrophin (whose gene is localized on human chromosome 7q33) stimulates myocyte growth and participates in cellular interaction that initiates cardiac hypertrophy in vitro. In this report, we present data on the pathophysiological significance of myotrophin in vivo, showing the effects of overexpression of cardio-specific myotrophin in transgenic mice in which cardiac hypertrophy occurred by 4 weeks of age and progressed to heart failure by 9-12 months. This hypertrophy was associated with increased expression of proto-oncogenes, hypertrophy marker genes, growth factors, and cytokines, with symptoms that mimicked those of human cardiomyopathy, functionally and morphologically. This model provided a unique opportunity to analyze gene clusters that are differentially up-regulated during initiation of hypertrophy versus transition of hypertrophy to heart failure. Importantly, changes in gene expression observed during initiation of hypertrophy were significantly different from those seen during its transition to heart failure. Our data show that overexpression of myotrophin results in initiation of cardiac hypertrophy that progresses to heart failure, similar to changes in human heart failure. Knowledge of the changes that take place as a result of overexpression of myotrophin at both the cellular and molecular levels will suggest novel strategies for treatment to prevent hypertrophy and its progression to heart failure.

Myotrophin in human heart failure

OBJECTIVES

The goal of this study was to investigate plasma levels of myotrophin in heart failure (HF) and their relationship to gender and disease severity.

BACKGROUND

Myotrophin is a myocardial hypertrophy-inducing factor initially demonstrated in hypertrophied and cardiomyopathic hearts. Recent evidence suggests an interaction with the transcription factor nuclear factor kappa B (NFkappaB), which is activated in HF and modulates myocardial protein expression. It is unknown whether this peptide has an endocrine/paracrine role in man. We hypothesized that it may have a role in HF and would be raised in plasma.

METHODS

We developed a competitive binding assay specific for human myotrophin. Myotrophin was measured in plasma extracts of 120 HF patients and 130 age- and gender-matched normal controls.

RESULTS

Myotrophin in plasma existed as the full-length 12 kD form with also a 2.7 kD form (possibly a degradation product). Log normalized myotrophin levels were significantly elevated in HF patients (mean +/- SEM [geometric mean, range], 2.402 +/- 0.021 [252, 72 to 933] vs. 2.268 +/- 0.021 [185, 28 to 501] fmol/ml, p < 0.0005). There was no relationship between myotrophin and age or gender in controls. However, males with HF had higher levels of myotrophin than females (p < 0.001). There was an inverse relationship of myotrophin levels with New York Heart Association class in patients with no gender difference in the relationship.

CONCLUSIONS

There is evidence of early activation of the myotrophin system in HF, which is more evident in males. This response is attenuated in more severe disease. The contribution of myotrophin to NFkappaB-mediated gene transcription and preservation of cardiac muscle mass remains to be investigated further.

V-1, a protein expressed transiently during murine cerebellar development, regulates actin polymerization via interaction with capping protein

V-1 is a 12-kDa protein consisting of three consecutive ANK repeats, which are believed to serve as the surface for protein-protein interactions. It is thought to have a role in neural development for its temporal profile of expression during murine cerebellar development, but its precise role remains unknown. Here we applied the proteomic approach to search for protein targets that interact with V-1. The V-1 cDNA attached with a tandem affinity purification tag was expressed in the cultured 293T cells, and the protein complex formed within the cells were captured and characterized by mass spectrometry. We detected two polypeptides specifically associated with V-1, which were identified as the alpha and beta subunits of the capping protein (CP, alternatively called CapZ or beta-actinin). CP regulates actin polymerization by capping the barbed end of the actin filament. The V-1.CP complex was detected not only in cultured cells transfected with the V-1 cDNA but also endogenously in cells as well as in murine cerebellar extracts. An analysis of the V-1/CP interaction by surface plasmon resonance spectroscopy showed that V-1 formed a stable complex with the CP heterodimer with a dissociation constant of 1.2 x 10(-7) m and a molecular stoichiometry of approximately 1:1. In addition, V-1 inhibited the CP-regulated actin polymerization in vitro in a dose-dependent manner. Thus, our results suggest that V-1 is a novel component that regulates the dynamics of actin polymerization by interacting with CP and thereby participates in a variety of cellular processes such as actin-driven cell movements and motility during neuronal development.

The Chemokine Networks in Sponges: Potential Roles in Morphogenesis, Immunity and Stem Cell Formation

Porifera (sponges) are now well accepted as the phylum which branched off first from the common ancestor of all metazoans, the Urmetazoa. The transition to the Metazoa became possible because during this phase, cell-cell as well as cell-matrix adhesion molecules evolved which allowed the formation of a colonial stage of animals. The next prerequisite for the evolution to the Urmetazoa was the establishment of an effective immune system which, flanked by apoptosis, allowed the formation of a first level of individuation. In sponges (with the model Suberites domuncula and Geodia cydonium), the main mediators of the immune responses are the chemokines. Since sponges lack a vascular system and consequently blood cells (in the narrow sense), we have used the term chemokines (in a broad sense) to highlight that the complex network of intercellular mediators initiates besides differentiation processes also cell movement. In the present review, the cDNAs encoding the following chemokines were described and the roles of their deduced proteins during self-self and nonself recognition outlined: the allograft inflammatory factor, the glutathione peroxidase, the endothelial-monocyte-activating polypeptide, the pre-B-cell colony-enhancing factor and the myotrophin as well as an enzyme, the (2-5)A synthetase, which is involved in cytokine response in vertebrates. A further step required to reach the evolutionary step of the integrated stage of the Urmetazoa was the acquisition of a stem cell system. In this review, first markers for stem cells (mesenchymal stem cell-like protein) as well as for chemokines involved in the maintenance of stem cells (noggin and glia maturation factor) are described at the molecular level, and a first functional analysis is approached. Taken together, it is outlined that the chemokine network was essential for the establishment of metazoans, which evolved approximately 600 to 800 million years ago.

Activation of nuclear factor-kappaB is necessary for myotrophin-induced cardiac hypertrophy

The transcription factor nuclear factor-kappaB (NF-kappaB) regulates expression of a variety of genes involved in immune responses, inflammation, proliferation, and programmed cell death (apoptosis). Here, we show that in rat neonatal ventricular cardiomyocytes, activation of NF-kappaB is involved in the hypertrophic response induced by myotrophin, a hypertrophic activator identified from spontaneously hypertensive rat heart and cardiomyopathic human hearts. Myotrophin treatment stimulated NF-kappaB nuclear translocation and transcriptional activity, accompanied by IkappaB-alpha phosphorylation and degradation. Consistently, myotrophin-induced NF-kappaB activation was enhanced by wild-type IkappaB kinase (IKK) beta and abolished by the dominant-negative IKKbeta or a general PKC inhibitor, calphostin C. Importantly, myotrophin-induced expression of two hypertrophic genes (atrial natriuretic factor [ANF] and c-myc) and also enhanced protein synthesis were partially inhibited by a potent NF-kappaB inhibitor, pyrrolidine dithio-carbamate (PDTC), and calphostin C. Expression of the dominant-negative form of IkappaB-alpha or IKKbeta also partially inhibited the transcriptional activity of ANF induced by myotrophin. These findings suggest that the PKC-IKK-NF-kappaB pathway may play a critical role in mediating the myotrophin-induced hypertrophic response in cardiomyocytes.

Identification of PKCalpha isoform-specific effects in cardiac myocytes using antisense phosphorothioate oligonucleotides

Members of the mammalian protein kinase C (PKC) superfamily play key regulatory roles in multiple cellular processes. In the heart, PKC signaling is involved in hypertrophic agonist-induced gene expression and hypertrophic growth. To investigate the specific function of PKC signaling in regulating cardiomyocyte growth, we used antisense oligonucleotides to inhibit PKC alpha, the major isozyme present in the neonatal heart. Transfection of cultured neonatal cardiomyocytes with antisense PKCalpha oligonucleotides resulted in a marked reduction in both PKCalpha mRNA and protein levels. PKCalpha antisense treatment also reduced phenylephrine (PE)-induced PKC activity and perinuclear translocation of PKCalpha. Antisense inhibition of PKCalpha led to reduction of PE-induced increase in skeletal alpha-actin mRNA levels and atrial natriuretic peptide (ANP) secretion but had no significant effects on PE-induced beta-myosin heavy chain, ANP, or B-type natriuretic peptide (BNP) gene expression. On the other hand, antisense PKCalpha treatment attenuated endothelin-1-induced increase in ANP and BNP peptide secretion, whereas endothelin-1-induced gene expression of ANP and BNP remained unchanged. The hypertrophic agonist-induced growth of cardiomyocytes, characterized by increased [(3)H]leucine incorporation, was not affected with antisense PKCalpha treatment. Furthermore, we found that PE-induced increase in extracellular signal-regulated kinase (ERK) activity was partially inhibited by antisense PKCalpha treatment, implicating ERK as a downstream mediator for PKCalpha signaling. These results indicate that PKCalpha isozyme is involved in hypertrophic signaling in cardiomyocytes and provide novel strategies for future studies to identify other cellular targets controlled selectively by PKCalpha or other PKC isozymes.

Role of protein kinase C alpha in primary human osteoblast proliferation

Protein kinase C (PKC) isoforms have been shown to have specific expression profiles and individual isoforms are believed to play distinct roles in the cells in which they are found. The goal here was to determine which specific isoform(s) is involved in proliferation of primary human osteoblasts. In primary human osteoblasts, 10 microM of acute sphingosine-1-phosphate (S1P) treatment induced an increase in proliferation that correlated with an increase in PKCalpha and PKCiota expression. To further delineate which isoforms are involved in osteoblastic cell proliferation, the effect of low versus high serum culture conditions on PKC isoform expression was determined. Likewise, the effect of antisense oligodeoxynucleotides (ODNs) to specific PKC isoforms on proliferation and MAPK activation was studied. The effect of S1P on intracellular translocation of activated PKC isoforms was also evaluated. The results indicated that in primary human osteoblasts, PKCalpha was not expressed under conditions of low proliferative rate while PKCdelta and PKCiota expression was not affected. The specific inhibition of PKCalpha by antisense ODNs resulted in inhibition of MAPK activity leading to a significant decrease in proliferation. S1P up-regulated antisense ODN inhibited PKCalpha expression and MAPK activity and led to an increase in proliferation. Subsequent experiments using platelet-derived growth factor (PDGF) as an additional mitogen generated similar data. PDGF stimulation resulted in a significant increase in proliferation that correlated with an up-regulation of inhibited PKCalpha expression in antisense ODN-treated cells. Immunofluorescence methods showed that mitogenic stimulation of PKCa resulted in nuclear translocation. Our findings present original data that PKCalpha is the isoform specifically involved in the proliferation of primary human osteoblasts.

Myotrophin-kappaB DNA interaction in the initiation process of cardiac hypertrophy

To investigate how cardiac hypertrophy and heart failure develop, we isolated and characterized a candidate initiator, the soluble 12-kDa protein myotrophin, from rat and human hearts. Myotrophin stimulates protein synthesis and myocardial cell growth associated with increased levels of hypertrophy marker genes. Recombinant myotrophin from the cloned gene showed structural/functional motifs, including ankyrin repeats and putative phosphorylation sites for protein kinase C (PKC) and casein kinase II. One repeat, homologous with I kappaB, interacts with rel/NF-kappaB in vitro. We analyzed the interaction of recombinant myotrophin and nuclear extracts prepared from neonatal and adult cardiomyocytes; gel mobility shift assay showed that myotrophin bound to kappaB DNA. To define PKC's role in myotrophin-induced myocyte growth, we incubated neonatal rat myocytes (normal and stretch) with specific inhibitors and found that myotrophin inhibits [3H]leucine incorporation into myocytes and different hypertrophic gene expression in neonatal myocytes. Using confocal microscopy, we observed that a basal level of myotrophin was present in both cytoplasm and nucleus under normal conditions, but under cyclic stretch, myotrophin levels became elevated in the nucleus. Myotrophin gene levels were upregulated when myocytes underwent cyclic stretch or were treated with tumor necrosis factor-alpha (TNF-alpha) or interleukin-1beta and also when excised beating hearts were exposed to high pressure. Our data showed that the myotrophin-kappaB interaction was increased with age in spontaneously hypertensive rats (SHRs) only. Our data provide evidence that myotrophin-kappaB DNA interaction may be an important step in initiating cardiac hypertrophy.

PKC alpha regulates the hypertrophic growth of cardiomyocytes through extracellular signal-regulated kinase1/2 (ERK1/2)

Members of the protein kinase C (PKC) isozyme family are important signal transducers in virtually every mammalian cell type. Within the heart, PKC isozymes are thought to participate in a signaling network that programs developmental and pathological cardiomyocyte hypertrophic growth. To investigate the function of PKC signaling in regulating cardiomyocyte growth, adenoviral-mediated gene transfer of wild-type and dominant negative mutants of PKC alpha, beta II, delta, and epsilon (only wild-type zeta) was performed in cultured neonatal rat cardiomyocytes. Overexpression of wild-type PKC alpha, beta II, delta, and epsilon revealed distinct subcellular localizations upon activation suggesting unique functions of each isozyme in cardiomyocytes. Indeed, overexpression of wild-type PKC alpha, but not betaI I, delta, epsilon, or zeta induced hypertrophic growth of cardiomyocytes characterized by increased cell surface area, increased [(3)H]-leucine incorporation, and increased expression of the hypertrophic marker gene atrial natriuretic factor. In contrast, expression of dominant negative PKC alpha, beta II, delta, and epsilon revealed a necessary role for PKC alpha as a mediator of agonist-induced cardiomyocyte hypertrophy, whereas dominant negative PKC epsilon reduced cellular viability. A mechanism whereby PKC alpha might regulate hypertrophy was suggested by the observations that wild-type PKC alpha induced extracellular signal-regulated kinase1/2 (ERK1/2), that dominant negative PKC alpha inhibited PMA-induced ERK1/2 activation, and that dominant negative MEK1 (up-stream of ERK1/2) inhibited wild-type PKC alpha-induced hypertrophic growth. These results implicate PKC alpha as a necessary mediator of cardiomyocyte hypertrophic growth, in part, through a ERK1/2-dependent signaling pathway.

Sphingosine-1-phosphate effects on PKC isoform expression in human osteoblastic cells

Sphingosine-1-phosphate (S1P) has been shown to participate in the proliferative process in human osteoblasts.(1) The mitogenic effect of S1P has been postulated to involve two signaling pathways, the Gi linked protein receptor pathway and the PKC pathway. To define the possible role of PKC isoforms in osteoblastic cell proliferation, the effects of S1P on PKC isoform expression was determined. While PKC lambda was minimally detected, the isoforms alpha, delta and iota were all found to be highly expressed by the human osteoblast. In human osteoblastic cells, S1P induced a 25% increase in the expression of PKC alpha and approximately a 30% increase in the expression of PKC iota. S1P did not have an effect on PKC delta expression. Pretreatment with pertussis toxin (PT) led to an inhibition of the observed S1P effects on the expression of the alpha and iota isoforms.

Localization, anchoring, and functions of protein kinase C isozymes in the heart

Although protein kinase C (PKC) was identified more than 20 years ago, and is involved in a wide variety of essential cellular processes, assigning specific roles to each PKC isozyme has proved difficult. Results over the last few years have suggested that much of the specificity of activated PKC isozymes is attributed to their subcellular localization bringing them into close proximity to a subset of substrates. Our laboratory has taken advantage of the importance of PKC localization and studied the way in which PKC isozymes are anchored. We have identified PKC anchoring proteins (RACKs or Receptors for Activated C Kinase) and used information about interaction sites between PKC isozymes and their respective RACKs to design peptides which modulate translocation of specific PKC isozymes to the functional site. These isozyme-specific peptides can be delivered into isolated or cultured cells or expressed in transgenic mice to determine the role of specific PKC isozymes in particular functions. Here we will describe the isozymes-specific peptide activators and inhibitors that we have developed and the specific functions of each isozyme in cardiac ventricular tissue.

Stimulation of protein (collagen) synthesis in sponge cells by a cardiac myotrophin-related molecule from Suberites domuncula

The body wall of sponges (Porifera), the lowest metazoan phylum, is formed by two epithelial cell layers of exopinacocytes and endopinacocytes, both of which are associated with collagen fibrils. Here we show that a myotrophin-like polypeptide from the sponge Suberites domuncula causes the expression of collagen in cells from the same sponge in vitro. The cDNA of the sponge myotrophin was isolated; the potential open reading frame of 360 nt encodes a 120 aa long protein (Mr of 12,837). The sequence SUBDOMYOL shares high similarity with the known metazoan myotrophin sequences. The expression of SUBDOMYOL is low in single cells but high after formation of primmorph aggregates as well as in intact animals. Recombinant myotrophin was found to stimulate protein synthesis by fivefold, as analyzed by incorporation studies using [3H] lysine. In addition, it is shown that after incubation of single cells with myotrophin, the primmorphs show an unusual elongated, oval-shaped appearance. It is demonstrated that in the presence of recombinant myotrophin, the cells up-regulate the expression of the collagen gene. The cDNA for S. domuncula collagen was isolated; the deduced aa sequence shows that the collagenous internal domain is rather short, with only 24 G-x-y collagen triplets. We conclude that the sponge myotrophin causes in homologous cells the same/similar effect as the cardiac myotrophin in mammalian cells, where it is involved in initiation of cardial ventricular hypertrophy. We assume that an understanding of sponge molecular cell biology will also contribute to a further elucidation of human diseases, here of the cardiovascular system.

AT1-receptor blockade enhances ischemic preconditioning in hypertrophied rat myocardium

The purpose of this study was to determine whether ischemic preconditioning protects contractile function in hypertrophied rat myocardium from ischemia-reperfusion (I/R) injury. Male salt-sensitive rats were fed a high-salt diet for 2 wk to induce myocardial hypertrophy. Nonhypertrophied hearts were obtained from age-matched Sprague-Dawley (SD) rats fed a regular diet. Heart weight-to-body weight ratios were higher in salt-sensitive rats than in SD rats (6.9 +/- 0.2 vs. 4.7 +/- 0.2 g/kg, P < 0.01). A second group of salt-sensitive and SD rats was administered losartan (10 mg. kg(-1). day(-1)), an AT(1)-receptor blocker, for 1 wk before the study. Isolated hearts were preconditioned with transient ischemia before global I/R. After I/R, preconditioned hypertrophied hearts exhibited greater recovery of left ventricular developed pressure compared with that of preconditioned normal hearts (73 +/- 8 vs. 18 +/- 8%, P < 0.01). Left ventricular developed pressure was further enhanced by losartan in both hypertrophied and normal myocardium (99 +/- 5 vs. 73 +/- 8%, P < 0.05 and 97 +/- 15 vs. 18 +/- 8%, P < 0.01). Hypertrophied rat myocardium can be protected from I/R-induced contractile dysfunction by ischemic preconditioning. Losartan improves the ischemic tolerance of normal and hypertrophied myocardium.