Knockout of cyclophilin D in Ppif⁻/⁻ mice increases stability of brain mitochondria against Ca²⁺ stress

The mitochondrial peptidyl prolyl isomerase cyclophilin D (CypD) activates permeability transition (PT). To study the role of CypD in this process we compared the functions of brain mitochondria isolated from wild type (BMWT) and CypD knockout (Ppif(-/-)) mice (BMKO) with and without CypD inhibitor Cyclosporin A (CsA) under normal and Ca(2+) stress conditions. Our data demonstrate that BMKO are characterized by higher rates of glutamate/malate-dependent oxidative phosphorylation, higher membrane potential and higher resistance to detrimental Ca(2+) effects than BMWT. Under the elevated Ca(2+) and correspondingly decreased membrane potential the dose response in BMKO shifts to higher Ca(2+) concentrations as compared to BMWT. However, significantly high Ca(2+) levels result in complete loss of membrane potential in BMKO, too. CsA diminishes the loss of membrane potential in BMWT but has no protecting effect in BMKO. The results are in line with the assumption that PT is regulated by CypD under the control of matrix Ca(2+). Due to missing of CypD the BMKO can favor PT only at high Ca(2+) concentrations. It is concluded that CypD sensitizes the brain mitochondria to PT, and its inhibition by CsA or CypD absence improves the complex I-related mitochondrial function and increases mitochondria stability against Ca(2+) stress.

Genetic evidence in the mouse solidifies the calcium hypothesis of myofiber death in muscular dystrophy

Muscular dystrophy (MD) refers to a clinically and genetically heterogeneous group of degenerative muscle disorders characterized by progressive muscle wasting and often premature death. Although the primary defect underlying most forms of MD typically results from a loss of sarcolemmal integrity, the secondary molecular mechanisms leading to muscle degeneration and myofiber necrosis is debated. One hypothesis suggests that elevated or dysregulated cytosolic calcium is the common transducing event, resulting in myofiber necrosis in MD. Previous measurements of resting calcium levels in myofibers from dystrophic animal models or humans produced equivocal results. However, recent studies in genetically altered mouse models have largely solidified the calcium hypothesis of MD, such that models with artificially elevated calcium in skeletal muscle manifest fulminant dystrophic-like disease, whereas models with enhanced calcium clearance or inhibited calcium influx are resistant to myofiber death and MD. Here, we will review the field and the recent cadre of data from genetically altered mouse models, which we propose have collectively mostly proven the hypothesis that calcium is the primary effector of myofiber necrosis in MD. This new consensus on calcium should guide future selection of drugs to be evaluated in clinical trials as well as gene therapy-based approaches.

Calcineurin deficiency decreases inflammatory lesions in transforming growth factor beta1-deficient mice

Transforming growth factor (TGF) beta1) is an immunoregulatory cytokine involved in self-tolerance and lymphocyte homeostasis. Tgfb1 knock-out (KO) mice develop severe multi-focal autoimmune inflammatory lesions due to [Ca(2+)]i deregulation in T cells, and die within 3 weeks after birth. Because the calcineurin inhibitor FK506 inhibits the hyperresponsiveness of Tgfb1(-/-) thymocytes, and because calcineurin Abeta (CNAbeta)-deficient mice do not reject allogenic tumours, we have generated Tgfb1(-/-) Cnab(-/-) mice to address whether CNAbeta deficiency prevents T cell activation and inflammation in Tgfb1(-/-) mice. Here we show that in Tgfb1(-/-) Cnab(-/-) mice inflammation is reduced significantly relative to that in Tgfb1(-/-) mice. However, both CD4(+) and CD8(+) T cells in double knock-out (DKO) mice are activated, as revealed by up-regulation of CD11a lymphocyte function-associated antigen-1 (LFA-1), CD44 and CD69 and down-regulation of CD62L. These data suggest that deficiency of CNAbeta decreases inflammatory lesions but does not prevent activation of autoreactive T cells. Also Tgfb1(-/-) T cells can undergo activation in the absence of CNAbeta, probably by using the other isoform of calcineurin (CNAalpha) in a compensatory manner. CNAbeta-deficient T cells undergo spontaneous activation in vivo and are activated upon anti-T cell receptor stimulation in vitro. Understanding the role of calcineurin in T cell regulation should open up new therapeutic opportunities for inflammation and cancer.

Periostin facilitates eosinophil tissue infiltration in allergic lung and esophageal responses

Periostin is an extracellular matrix protein that has been primarily studied in the context of the heart, where it has been shown to promote cardiac repair and remodeling. In this study, we focused on the role of periostin in an allergic eosinophilic inflammatory disease (eosinophilic esophagitis (EE)) known to involve extensive tissue remodeling. Periostin was indeed markedly overexpressed (35-fold) in the esophagus of EE patients, particularly in the papillae, compared with control individuals. Periostin expression was downstream from transforming growth factor-beta and interleukin-13, as these cytokines were elevated in EE esophageal samples and markedly induced periostin production by primary esophageal fibroblasts (107- and 295-fold, respectively, at 10 ng ml(-1)). A functional role for periostin in eliciting esophageal eosinophilia was demonstrated, as periostin-null mice had a specific defect in allergen-induced eosinophil recruitment to the lungs and esophagus (66 and 72% decrease, respectively). Mechanistic analyses revealed that periostin increased (5.8-fold) eosinophil adhesion to fibronectin. As such, these findings extend the involvement of periostin to esophagitis and uncover a novel role for periostin in directly regulating leukocyte (eosinophil) accumulation in T helper type 2-associated mucosal inflammation in both mice and humans.

Time-dependent systolic and diastolic function in mice overexpressing calcineurin

Echocardiograms have been assessed only at 56 days in mice overexpressing calcineurin (CN mice). Age-dependent echocardiographic changes were evaluated because the development of sudden death is time dependent. Because cyclosporin A (CsA) reverses hypertrophy in CN mice, its effects on the time course of the development of sudden death and cardiac dysfunction were assessed. In wild-type (WT) mice, the left ventricular (LV) internal end-diastolic dimension (LVIDd) increased and the LV mass index (LVMI) decreased with age. In CN mice, two distinct phases of pathophysiology were found. After 14 days, in CN mice, the LVIDd and LVMI were significantly increased, but sudden death had not occurred. After 28 days, in CN mice, relative dilation of the left ventricle occurred, whereas the LVMI decreased. Sudden death developed during progressive dilation associated with systolic and diastolic dysfunction. CsA treatment reversed hypertrophy in CN mice but did not reverse systolic and diastolic dysfunction and exaggerated sudden death. Sudden cardiac death was associated with systolic and diastolic dysfunction but was not related to isolated cardiac hypertrophy in CN mice.

The transcription factor GATA4 is activated by extracellular signal-regulated kinase 1- and 2-mediated phosphorylation of serine 105 in cardiomyocytes

The zinc finger-containing transcription factor GATA4 has been implicated as a critical regulator of multiple cardiac-expressed genes as well as a regulator of inducible gene expression in response to hypertrophic stimulation. Here we demonstrate that GATA4 is itself regulated by the mitogen-activated protein kinase signaling cascade through direct phosphorylation. Site-directed mutagenesis and phospho-specific GATA4 antiserum revealed serine 105 as the primary site involved in agonist-induced phosphorylation of GATA4. Infection of cultured cardiomyocytes with an activated MEK1-expressing adenovirus induced robust phosphorylation of serine 105 in GATA4, while a dominant-negative MEK1-expressing adenovirus blocked agonist-induced phosphorylation of serine 105, implicating extracellular signal-regulated kinase (ERK) as a GATA4 kinase. Indeed, bacterially purified ERK2 protein directly phosphorylated purified GATA4 at serine 105 in vitro. Phosphorylation of serine 105 enhanced the transcriptional potency of GATA4, which was sensitive to U0126 (MEK1 inhibitor) but not SB202190 (p38 inhibitor). Phosphorylation of serine 105 also modestly enhanced the DNA binding activity of bacterially purified GATA4. Finally, induction of cardiomyocyte hypertrophy with an activated MEK1-expressing adenovirus was blocked with a dominant-negative GATA4-engrailed-expressing adenovirus. These results suggest a molecular pathway whereby MEK1-ERK1/2 signaling regulates cardiomyocyte hypertrophic growth through the transcription factor GATA4 by direct phosphorylation of serine 105, which enhances DNA binding and transcriptional activation.

Tissue-specific GATA factors are transcriptional effectors of the small GTPase RhoA

Rho-like GTPases play a pivotal role in the orchestration of changes in the actin cytoskeleton in response to receptor stimulation, and have been implicated in transcriptional activation, cell growth regulation, and oncogenic transformation. Recently, a role for RhoA in the regulation of cardiac contractility and hypertrophic cardiomyocyte growth has been suggested but the mechanisms underlying RhoA function in the heart remain undefined. We now report that transcription factor GATA-4, a key regulator of cardiac genes, is a nuclear mediator of RhoA signaling and is involved in the control of sarcomere assembly in cardiomyocytes. Both RhoA and GATA-4 are essential for sarcomeric reorganization in response to hypertrophic growth stimuli and overexpression of either protein is sufficient to induce sarcomeric reorganization. Consistent with convergence of RhoA and GATA signaling, RhoA potentiates the transcriptional activity of GATA-4 via a p38 MAPK-dependent pathway that phosphorylates GATA-4 activation domains and GATA binding sites mediate RhoA activation of target cardiac promoters. Moreover, a dominant-negative GATA-4 protein abolishes RhoA-induced sarcomere reorganization. The identification of transcription factor GATA-4 as a RhoA mediator in sarcomere reorganization and cardiac gene regulation provides a link between RhoA effects on transcription and cell remodeling.

Deoxycholic acid (DCA) causes ligand-independent activation of epidermal growth factor receptor (EGFR) and FAS receptor in primary hepatocytes: inhibition of EGFR/mitogen-activated protein kinase-signaling module enhances DCA-induced apoptosis

Previous studies have argued that enhanced activity of the epidermal growth factor receptor (EGFR) and the mitogen-activated protein kinase (MAPK) pathway can promote tumor cell survival in response to cytotoxic insults. In this study, we examined the impact of MAPK signaling on the survival of primary hepatocytes exposed to low concentrations of deoxycholic acid (DCA, 50 microM). Treatment of hepatocytes with DCA caused MAPK activation, which was dependent upon ligand independent activation of EGFR, and downstream signaling through Ras and PI(3) kinase. Neither inhibition of MAPK signaling alone by MEK1/2 inhibitors, nor exposure to DCA alone, enhanced basal hepatocyte apoptosis, whereas inhibition of DCA-induced MAPK activation caused approximately 25% apoptosis within 6 h. Similar data were also obtained when either dominant negative EGFR-CD533 or dominant negative Ras N17 were used to block MAPK activation. DCA-induced apoptosis correlated with sequential cleavage of procaspase 8, BID, procaspase 9, and procaspase 3. Inhibition of MAPK potentiated bile acid-induced apoptosis in hepatocytes with mutant FAS-ligand, but did not enhance in hepatocytes that were null for FAS receptor expression. These data argues that DCA is causing ligand independent activation of the FAS receptor to stimulate an apoptotic response, which is counteracted by enhanced ligand-independent EGFR/MAPK signaling. In agreement with FAS-mediated cell killing, inhibition of caspase function with the use of dominant negative Fas-associated protein with death domain, a caspase 8 inhibitor (Ile-Glu-Thr-Asp-p-nitroanilide [IETD]) or dominant negative procaspase 8 blocked the potentiation of bile acid-induced apoptosis. Inhibition of bile acid-induced MAPK signaling enhanced the cleavage of BID and release of cytochrome c from mitochondria, which were all blocked by IETD. Despite activation of caspase 8, expression of dominant negative procaspase 9 blocked procaspase 3 cleavage and the potentiation of DCA-induced apoptosis. Treatment of hepatocytes with DCA transiently increased expression of the caspase 8 inhibitor proteins c-FLIP-(S) and c-FLIP-(L) that were reduced by inhibition of MAPK or PI(3) kinase. Constitutive overexpression of c-FLIP-(s) abolished the potentiation of bile acid-induced apoptosis. Collectively, our data argue that loss of DCA-induced EGFR/Ras/MAPK pathway function potentiates DCA-stimulated FAS-induced hepatocyte cell death via a reduction in the expression of c-FLIP isoforms.

Comparative studies on individual isomeric 18:1 acids in cow, goat, and ewe milk fats by low-temperature high-resolution capillary gas-liquid chromatography

The trans- as well as the cis-18:1 isomer profiles were established in cow, goat, and ewe cheese fats, with the assumption that these are representative of the corresponding milks. Argentation thin-layer chromatography was combined with low-temperature high-resolution gas-liquid chromatography on 100-m highly polar capillary columns, thus adding precision to earlier data for these species. Despite differences in the absolute content of trans-18:1 isomers between species, the relative profiles were essentially similar. Except for the minor trans delta6-delta8 group, all trans-18:1 isomers with their ethylenic bonds between positions delta4 and delta16 (including the resolved critical pair delta13/delta14) were separated and quantitated individually. As expected, vaccenic (trans delta9-18:1) acid was the main isomer, accounting for as much as 37 to 50% of the total fraction. It was observed that the goat trans-18:1 isomer profile was usually rather close to that of cows in winter (barn feeding), whereas that of the ewe shows a seasonal dependence. The trans-18:1 profile of ewe milk fats from this study resembles that of cows in the transition period between winter and summer (pasture) feeding. Regarding the cis-18:1 acid fraction, two isomers (oleic and cis-vaccenic acids) accounted for ca. 97% of that fraction for the three species, with the cis-delta12 isomer ranked third. The analytical procedure employed here appears a convenient alternative to oxidative-based procedures (generally ozonolysis), taking less time and alleviating some drawbacks of the latter procedure.

Temporally regulated and tissue-specific gene manipulations in the adult and embryonic heart using a tamoxifen-inducible Cre protein

The advent of conditional and tissue-specific recombination systems in gene-targeted or transgenic mice has permitted an assessment of single gene function in a temporally regulated and cell-specific manner. Here we generated transgenic mice expressing a tamoxifen-inducible Cre recombinase protein fused to two mutant estrogen-receptor ligand-binding domains (MerCreMer) under the control of the alpha-myosin heavy chain promoter. These transgenic mice were crossed with the ROSA26 lacZ-flox-targeted mice to examine Cre recombinase activity and the fidelity of the system. The data demonstrate essentially no Cre-mediated recombination in the embryonic, neonatal, or adult heart in the absence of inducing agent but >80% recombination after only four tamoxifen injections. Expression of the MerCreMer fusion protein within the adult heart did not affect cardiac performance, cellular architecture, or expression of hypertrophic marker genes, demonstrating that the transgene-encoded protein is relatively innocuous. In summary, MerCreMer transgenic mice represent a tool for temporally regulated inactivation of any loxP-targeted gene within the developing and adult heart or for specifically directing recombination and expression of a loxP-inactivated cardiac transgene in the heart.

Cytoplasmic signaling pathways that regulate cardiac hypertrophy

This review discusses the rapidly progressing field of cardiomyocyte signal transduction and the regulation of the hypertrophic response. When stimulated by a wide array of neurohumoral factors or when faced with an increase in ventricular-wall tension, individual cardiomyocytes undergo hypertrophic growth as an adaptive response. However, sustained cardiac hypertrophy is a leading predictor of future heart failure. A growing number of intracellular signaling pathways have been characterized as important transducers of the hypertrophic response, including specific G protein isoforms, low-molecular-weight GTPases (Ras, RhoA, and Rac), mitogen-activated protein kinase cascades, protein kinase C, calcineurin, gp130-signal transducer and activator of transcription, insulin-like growth factor I receptor pathway, fibroblast growth factor and transforming growth factor beta receptor pathways, and many others. Each of these signaling pathways has been implicated as a hypertrophic transducer, which collectively suggests an emerging paradigm whereby multiple pathways operate in concert to orchestrate a hypertrophic response

Divergent transcriptional responses to independent genetic causes of cardiac hypertrophy

To define molecular mechanisms of cardiac hypertrophy, genes whose expression was perturbed by any of four different transgenic mouse hypertrophy models [protein kinase C-epsilon activation peptide (PsiepsilonRACK), calsequestrin (CSQ), calcineurin (CN), and Galpha(q)] were compared by DNA microarray analyses using the approximately 8,800 genes present on the Incyte mouse GEM1. The total numbers of regulated genes (tens to hundreds) correlated with phenotypic severity of the model (Galpha(q) > CN > CSQ > PsiepsilonRACK), but demonstrated that no single gene was consistently upregulated. Of the three models exhibiting pathological hypertrophy, only atrial natriuretic peptide was consistently upregulated, suggesting that transcriptional alterations are highly specific to individual genetic causes of hypertrophy. However, hierarchical-tree and K-means clustering analyses revealed that subsets of the upregulated genes did exhibit coordinate regulatory patterns that were unique or overlapping across the different hypertrophy models. One striking set consisted of apoptotic genes uniquely regulated in the apoptosis-prone Galpha(q) model. Thus, rather than identifying a single common hypertrophic cardiomyopathy gene program, these data suggest that extensive groups of genes may be useful for the prediction of specific underlying genetic determinants and condition-specific therapeutic approaches.

The transcription factors GATA4 and GATA6 regulate cardiomyocyte hypertrophy in vitro and in vivo

The zinc finger-containing transcription factors GATA4 and GATA6 are important regulators of basal and inducible gene expression in cardiac and smooth muscle cell types. Here we demonstrate a direct functional role for GATA4 and GATA6 as regulators of cardiomyocyte hypertrophic growth and gene expression. To model the increase in endogenous GATA4 and GATA6 transcriptional activity that occurs in response to hypertrophic stimulation, each factor was overexpressed in cardiomyocytes using recombinant adenovirus. Overexpression of either GATA4 or GATA6 was sufficient to induce cardiomyocyte hypertrophy characterized by enhanced sarcomeric organization, a greater than 2-fold increase in cell surface area, and a significant increase in total protein accumulation. In vivo, transgenic mice with 2.5-fold overexpression of GATA4 within the adult heart demonstrated a slowly progressing increase in heart to body weight ratio, histological features of cardiomyopathy, and activation of hypertrophy-associated genes, suggesting that GATA factors are sufficient regulators of cardiomyocyte hypertrophy in vitro and in vivo. To evaluate the requirement of GATA factors as downstream transcriptional mediators of hypertrophy, a dominant negative GATA4-engrailed repressor fusion-encoding adenovirus was generated. Expression of GATA4-engrailed blocked GATA4- and GATA6-directed transcriptional responses and agonist-induced cardiomyocyte hypertrophy, demonstrating that cardiac-expressed GATA factors are necessary mediators of this process.

Calcineurin enhances MAPK phosphatase-1 expression and p38 MAPK inactivation in cardiac myocytes

Multiple intracellular signaling pathways have been shown to regulate the hypertrophic growth of cardiac myocytes including mitogen-activated protein kinase (MAPK) and calcineurin-nuclear factor of activated T-cells. However, it is uncertain if individual regulatory pathways operate in isolation or if interconnectivity between unrelated pathways is required for the orchestration of the entire hypertrophic response. To this end, we investigated the interconnectivity between calcineurin-mediated cardiac myocyte hypertrophy and p38 MAPK signaling in vitro and in vivo. We show that calcineurin promotes down-regulation of p38 MAPK activity and enhances expression of the dual specificity phosphatase MAPK phosphatase-1 (MKP-1). Transgenic mice expressing activated calcineurin in the heart were characterized by inactivation of p38 and increased MKP-1 expression during early postnatal development, before the onset of cardiac hypertrophy. In vitro, cultured neonatal cardiomyocytes infected with a calcineurin-expressing adenovirus and stimulated with phenylephrine demonstrated reduced p38 phosphorylation and increased MKP-1 protein levels. Activation of endogenous calcineurin with the calcium ionophore decreased p38 phosphorylation and increased MKP-1 protein levels. Inhibition of endogenous calcineurin with cyclosporin A decreased MKP-1 protein levels and increased p38 activation in response to agonist stimulation. To further investigate potential cross-talk between calcineurin and p38 through alteration in MKP-1 expression, the MKP-1 promoter was characterized and determined to be calcineurin-responsive. These data suggest that calcineurin enhances MKP-1 expression in cardiac myocytes, which is associated with p38 inactivation.

Retinoic acid inhibits cardiac neural crest migration by blocking c-Jun N-terminal kinase activation

Retinoic acid (RA), a potent teratogen, produces a characteristic set of embryonic cardiovascular malformations similar to those observed in neural crest ablated avians. While the effects of RA on neural crest are well described, the molecular mechanism(s) of RA action on these cells is less clear. The present study examines the relationship between RA and mitogen-activated protein kinase signaling in neural crest cells and demonstrates that c-Jun N-terminal kinase (JNK) activation is severely repressed by RA. RA suppressed migration and proliferation of primary cultures of mouse neural crest cells treated in vitro as well as from animals treated in vivo. On Western blots, JNK activation/phosphorylation in neural crest cultures was reduced, while neither extracellular signal-regulated kinase (ERK) nor p38 pathways were affected. Both the dose-dependent stimulation of neural crest outgrowth and JNK phosphorylation by platelet-derived growth factor AA, which promotes outgrowth but not proliferation of neural crest cultures, were completely abrogated by RA. To establish the relevance of the JNK signaling pathway to cardiac neural crest migration, dominant negative adenoviral constructs were used to inhibit upstream activation of JNK or c-Jun downstream responses. Both adenoviral constructs markedly reduced neural crest cell outgrowth, while a dominant negative inhibitor of the p38 pathway had no effect. These data demonstrate that the JNK signaling pathway and c-Jun activation are critical for cardiac neural crest outgrowth and are potential targets for the action of RA.

Proper coronary vascular development and heart morphogenesis depend on interaction of GATA-4 with FOG cofactors

GATA-family transcription factors are critical to the development of diverse tissues. In particular, GATA-4 has been implicated in formation of the vertebrate heart. As the mouse Gata-4 knock-out is early embryonic lethal because of a defect in ventral morphogenesis, the in vivo function of this factor in heart development remains unresolved. To search for a requirement for Gata4 in heart development, we created mice harboring a single amino acid replacement in GATA-4 that impairs its physical interaction with its presumptive cardiac cofactor FOG-2. Gata4(ki/ki) mice die just after embryonic day (E) 12.5 exhibiting features in common with Fog2(-/-) embryos as well as additional semilunar cardiac valve defects and a double-outlet right ventricle. These findings establish an intrinsic requirement for GATA-4 in heart development. We also infer that GATA-4 function is dependent on interaction with FOG-2 and, very likely, an additional FOG protein for distinct aspects of heart formation.

Targeted inhibition of calcineurin attenuates cardiac hypertrophy in vivo

The Ca(2+)-calmodulin-activated Ser/Thr protein phosphatase calcineurin and the downstream transcriptional effectors of calcineurin, nuclear factor of activated T cells, have been implicated in the hypertrophic response of the myocardium. Recently, the calcineurin inhibitory agents cyclosporine A and FK506 have been extensively used to evaluate the importance of this signaling pathway in rodent models of cardiac hypertrophy. However, pharmacologic approaches have rendered equivocal results necessitating more specific or genetic-based inhibitory strategies. In this regard, we have generated Tg mice expressing the calcineurin inhibitory domains of Cain/Cabin-1 and A-kinase anchoring protein 79 specifically in the heart. DeltaCain and DeltaA-kinase-anchoring protein Tg mice demonstrated reduced cardiac calcineurin activity and reduced hypertrophy in response to catecholamine infusion or pressure overload. In a second approach, adenoviral-mediated gene transfer of DeltaCain was performed in the adult rat myocardium to evaluate the effectiveness of an acute intervention and any potential species dependency. DeltaCain adenoviral gene transfer inhibited cardiac calcineurin activity and reduced hypertrophy in response to pressure overload without reducing aortic pressure. These results provide genetic evidence implicating calcineurin as an important mediator of the cardiac hypertrophic response in vivo.

Differential activation of signal transduction pathways in human hearts with hypertrophy versus advanced heart failure

BACKGROUND

Left ventricular failure is commonly preceded by a period of hypertrophy. Intriguingly, many of the signaling pathways that have been implicated in the regulation of hypertrophy, including the 3 mitogen-activated protein kinases (MAPKs: extracellular signal-regulated kinase, stress-activated protein kinase, and p38), protein phosphatase, calcineurin, and the protein kinase Akt and its target glycogen synthase kinase-3 (GSK-3), also regulate the apoptotic response.

METHODS AND RESULTS

To understand the mechanisms that might regulate the progression of heart failure, we analyzed the activity of these signaling pathways in the hearts of patients with advanced heart failure, patients with compensated cardiac hypertrophy, and normal subjects. In patients with hypertrophy, neither the MAPK nor the Akt/GSK-3 pathways were activated, and the dominant signaling pathway was calcineurin. In failing hearts, calcineurin activity was increased but less so than in the hypertrophied hearts, and all 3 MAPKs and Akt were activated (and, accordingly, GSK-3ss was inhibited), irrespective of whether the underlying diagnosis was ischemic or idiopathic cardiomyopathy.

CONCLUSIONS

In the failing heart, there is a clear prohypertrophic activity profile, likely occurring in response to increased systolic wall stress and neurohormonal mediators. However, with the activation of these hypertrophic pathways, potent proapoptotic and antiapoptotic signals may also be generated. Therapies directed at altering the balance of activity of these signaling pathways could potentially alter the progression of heart failure.

Enhanced Ca2+ channel currents in cardiac hypertrophy induced by activation of calcineurin-dependent pathway

Cardiac-specific expression of an activated calcineurin protein in the hearts of transgenic (CLN) mice produces a profound hypertrophy that rapidly progresses to heart failure. While calcineurin is regulated by Ca2+, the potential effects of calcineurin on cardiac myocyte Ca2+ handling has not been evaluated. To this end, we examined L-type Ca2+ currents (I(Ca)) in left ventricular myocytes. CLN myocytes had larger (approximately 80%) cell capacitance and enhanced I(Ca) density (approximately 20%) compared with non-transgenic (NTG) littermates, but no change in the current-voltage relationship, single-channel conductance or protein levels of alpha 1 or beta 2 subunit of L-type Ca2+ channels. Interestingly, the kinetics of I(Ca) inactivation was faster (approximately two-fold) in CLN myocytes compared with NTG myocytes. Ryanodine application slowed the rate of I(Ca) inactivation in both groups and abolished the kinetic difference, suggesting that Ca2+ dependent inactivation is increased in CLN myocytes due to altered SR Ca2+ release. Treatment of CLN mice with Cyclosporine A (CsA), a calcineurin inhibitor, prevented myocyte hypertrophy and changes in I(Ca) activity and inactivation kinetics. However, there was no direct effect of CsA on I(Ca) in either NTG or CLN myocytes, suggesting that endogenous calcineurin activity does not directly regulate Ca2+ channel activity. This interpretation is consistent with the observation that I(Ca) density, inactivation kinetics and regulation by isoproterenol were normal in cardiac-specific transgenic mice expressing calcineurin inhibitory protein domains from either Cain or AKAP79. Taken together these data suggest that chronic activation of calcineurin is associated with myocyte hypertrophy and a secondary enhancement of intracellular Ca2+ handling that is tied to the hypertrophy response itself.

The dual-specificity phosphatase MKP-1 limits the cardiac hypertrophic response in vitro and in vivo

Mitogen-activated protein kinase (MAPK) signaling pathways are important regulators of cell growth, proliferation, and stress responsiveness. A family of dual-specificity MAP kinase phosphatases (MKPs) act as critical counteracting factors that directly regulate the magnitude and duration of p38, c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK) activation. Here we show that constitutive expression of MKP-1 in cultured primary cardiomyocytes using adenovirus-mediated gene transfer blocked the activation of p38, JNK1/2, and ERK1/2 and prevented agonist-induced hypertrophy. Transgenic mice expressing physiological levels of MKP-1 in the heart showed (1) no activation of p38, JNK1/2, or ERK1/2; (2) diminished developmental myocardial growth; and (3) attenuated hypertrophy in response to aortic banding and catecholamine infusion. These results provide further evidence implicating MAPK signaling factors as obligate regulators of cardiac growth and hypertrophy and demonstrate the importance of dual-specificity phosphatases as counterbalancing regulatory factors in the heart.

The MEK1-ERK1/2 signaling pathway promotes compensated cardiac hypertrophy in transgenic mice

Members of the mitogen-activated protein kinase (MAPK) cascade such as extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and p38 are implicated as important regulators of cardiomyocyte hypertrophic growth in culture. However, the role that individual MAPK pathways play in vivo has not been extensively evaluated. Here we generated nine transgenic mouse lines with cardiac-restricted expression of an activated MEK1 cDNA in the heart. MEK1 transgenic mice demonstrated concentric hypertrophy without signs of cardiomyopathy or lethality up to 12 months of age. MEK1 transgenic mice showed a dramatic increase in cardiac function, as measured by echocardiography and isolated working heart preparation, without signs of decompensation over time. MEK1 transgenic mice and MEK1 adenovirus-infected neonatal cardiomyocytes each demonstrated ERK1/2, but not p38 or JNK, activation. MEK1 transgenic mice and MEK1 adenovirus-infected cultured cardiomyocytes were also partially resistant to apoptotic stimuli. The results of the present study indicate that the MEK1-ERK1/2 signaling pathway stimulates a physiologic hypertrophy response associated with augmented cardiac function and partial resistance to apoptotsis.

Occurrence and biochemical characteristics of natural bioactive substances in bovine milk lipids

Bovine milk lipids (BML) contain a number of bioactive substances with positive as well as negative properties, mainly in the class of fatty acids. Besides trans fatty acids (TFA), conjugated linoleic acids (CLA) are of particular interest. Apart from ruminant meat products the main source of CLA in food are BML. Although TFA as well as saturated fatty acids (12:0-16:0) are thought to be positively correlated with atherosclerosis and coronary heart disease, CLA are considered antiatherogenic. Further, CLA are reported to reduce adipose fat and to have anticarcinogenic properties. The varying CLA and TFA contents of lipids from milk and dairy products are positively correlated with one another. However, TFA are also negatively correlated with 12:0-16:0 in BML. Anticarcinogenic effects are also ascribed to butyric acid as well as to some phospholipids and ether lipids present in BML. Moreover, the essential fatty acids 18:2n-6 and 18:3n-3 are found in BML which are involved in a variety of biochemical processes and thus have numerous functions in human metabolism. Contents of the individual bioactive components of BML are summarised taking into account also seasonal variations. The total content of bioactive substances in BML is approximately 75 % but their overall impact on human health considering benefits and drawbacks is difficult to assess.

Calcineurin and beyond: cardiac hypertrophic signaling

In response to increased ventricular wall tension or neurohumoral stimuli, the myocardium undergoes an adaptive hypertrophy response that temporarily augments pump function. Although initially beneficial, sustained cardiac hypertrophy can lead to decompensation and cardiomyopathy. Recent studies have focused on characterizing the molecular mechanisms that underlie cardiac hypertrophy. An increasing number of signal transduction pathways have been identified as important regulators of the hypertrophic response, including the low-molecular weight GTPases (Ras, RhoA, and Rac), mitogen-activated protein kinases, protein kinase C, and calcineurin. This review will discuss an emerging body of evidence that implicates the calcium-calmodulin-activated protein phosphatase calcineurin as a physiological regulator of the cardiac hypertrophic response. Although the sufficiency of calcineurin to promote cardiomyocyte hypertrophy in vivo and in vitro is established, its overall necessity as a hypertrophic mediator is currently an area of ongoing debate. The use of the calcineurin-inhibitory agents cyclosporine A and FK506 have suggested a necessary role for calcineurin in many, but not all, animal models of hypertrophy or cardiomyopathy. The evidence implicating a role for calcineurin signaling in the heart will be weighed against a growing body of literature suggesting necessary roles for a diverse array of intracellular signaling pathways, highlighting the multifactorial nature of the hypertrophic program.

Glycogen synthase kinase-3beta is a negative regulator of cardiomyocyte hypertrophy

Hypertrophy is a basic cellular response to a variety of stressors and growth factors, and has been best characterized in myocytes. Pathologic hypertrophy of cardiac myocytes leads to heart failure, a major cause of death and disability in the developed world. Several cytosolic signaling pathways have been identified that transduce prohypertrophic signals, but to date, little work has focused on signaling pathways that might negatively regulate hypertrophy. Herein, we report that glycogen synthase kinase-3beta (GSK-3beta), a protein kinase previously implicated in processes as diverse as development and tumorigenesis, is inactivated by hypertrophic stimuli via a phosphoinositide 3-kinase-dependent protein kinase that phosphorylates GSK-3beta on ser 9. Using adenovirus-mediated gene transfer of GSK-3beta containing a ser 9 to alanine mutation, which prevents inactivation by hypertrophic stimuli, we demonstrate that inactivation of GSK-3beta is required for cardiomyocytes to undergo hypertrophy. Furthermore, our data suggest that GSK-3beta regulates the hypertrophic response, at least in part, by modulating the nuclear/cytoplasmic partitioning of a member of the nuclear factor of activated T cells family of transcription factors. The identification of GSK-3beta as a transducer of antihypertrophic signals suggests that novel therapeutic strategies to treat hypertrophic diseases of the heart could be designed that target components of the GSK-3 pathway.

Study of individual trans- and cis-16:1 isomers in cow, goat, and ewe cheese fats by gas-liquid chromatography with emphasis on the trans-delta3 isomer

Low-temperature gas-liquid chromatography (GLC) was applied to study the distribution profiles of isomeric trans- and cis-hexadecenoic acids in ruminant (cow, goat, and ewe) milk fat after their fractionation by argentation thin-layer chromatography (Ag-TLC). The fat was extracted from cheeses (12 samples of each species), the most common foods made with goat and ewe milks. The predominant trans-16:1 isomer is palmitelaidic acid (the delta9 isomer), but it does not exceed one-third of the total group, which itself represents 0.17% (cow), 0.16% (goat), and 0.26% (ewe) of the total fatty acids. The trans-delta3 16:1 isomer, which is reported for the first time in ruminant lipids and which likely comes from the animals' feed, is present at a level of ca. 10% of the trans-16:1 acid group. Otherwise, all isomers with their ethylenic bond between positions delta4 and delta14 are observed in the three species studied, roughly showing the same relative distribution pattern. Quantitatively, the trans-16:1 isomers only represent ca. 5% of the sum of the trans-16:1 plus trans-18:1 isomers, and they appear of little importance in comparison. It is inferred from this and recent studies that some previously reported data that were established for consumption assessments dealt in fact mainly with iso-17:0 acid, which was confused with (and added to) trans-delta9 (palmitelaidic) acid; consequently, these results were large over-estimates. Regarding the cis-16:1 acids, the delta9 isomer is the prominent constituent as expected, but the second-most important isomer is the delta13 isomer. It does not appear that trans-16:1 isomers are from ruminant milk fats of great nutritional importance as compared with trans-18:1 isomeric acids. As for trans18:1 isomers, the combination Ag-TLC/GLC is a necessary procedure to quantitate trans-16:1 acids accurately and reliably. Ag-TLC allows removal of interfering branched 17:0 acids and cis-16:1 acids, and low-temperature GLC permits an accurate measurement of all individual isomers most of which with baseline resolution.

A calcineurin-NFATc3-dependent pathway regulates skeletal muscle differentiation and slow myosin heavy-chain expression

The differentiation and maturation of skeletal muscle cells into functional fibers is coordinated largely by inductive signals which act through discrete intracellular signal transduction pathways. Recently, the calcium-activated phosphatase calcineurin (PP2B) and the family of transcription factors known as NFAT have been implicated in the regulation of myocyte hypertrophy and fiber type specificity. Here we present an analysis of the intracellular mechanisms which underlie myocyte differentiation and fiber type specificity due to an insulinlike growth factor 1 (IGF-1)-calcineurin-NFAT signal transduction pathway. We demonstrate that calcineurin enzymatic activity is transiently increased during the initiation of myogenic differentiation in cultured C2C12 cells and that this increase is associated with NFATc3 nuclear translocation. Adenovirus-mediated gene transfer of an activated calcineurin protein (AdCnA) potentiates C2C12 and Sol8 myocyte differentiation, while adenovirus-mediated gene transfer of noncompetitive calcineurin-inhibitory peptides (cain or DeltaAKAP79) attenuates differentiation. AdCnA infection was also sufficient to rescue myocyte differentiation in an IGF-depleted myoblast cell line. Using 10T1/2 cells, we demonstrate that MyoD-directed myogenesis is dramatically enhanced by either calcineurin or NFATc3 cotransfection, while a calcineurin inhibitory peptide (cain) blocks differentiation. Enhanced myogenic differentiation directed by calcineurin, but not NFATc3, preferentially specifies slow myosin heavy-chain expression, while enhanced differentiation through mitogen-activated protein kinase kinase 6 (MKK6) promotes fast myosin heavy-chain expression. These data indicate that a signaling pathway involving IGF-calcineurin-NFATc3 enhances myogenic differentiation whereas calcineurin acts through other factors to promote the slow fiber type program.

Recent trends in the fatty acid composition of German sunflower margarines, shortenings and cooking fats with emphasis on individual C16:1, C18:1, C18:2, C18:3 and C20:1 trans isomers

In some countries the content of trans fatty acids (TFA) in margarines has strongly decreased as a result of the continuous discussion on their disadvantages regarding aspects of nutritional physiology. However, still in 1994 almost 1/3 of total fatty acids in part of German sunflower margarines, shortenings and cooking fats comprised these unfavourable TFA. In the present study the main interest was laid on trans-C16:1, trans-C18:1, trans-C20:1, trans-C18:2 and trans-C18:3 fatty acids and particularly their individual isomers, as negative metabolic activity of TFA possibly might only be attributable to certain isomers. By combining argentation thin-layer chromatography with gas chromatography using a 100-m capillary column (CP-Sil 88) trans fatty acid contents were determined in nearly all German brands of sunflower margarines (SFM; n = 9) and of cooking fats and shortenings (CFS; n = 10). Concerning the above-mentioned groups of isomers mean TFA contents of 0.01, 4.88, 0.00, 0.45 and 0.03% for SFM as well as of 0.01, 5.02, 0.03, 0.70 and 0.17% for CFS were established, respectively. The re-evaluation of samples from 1994 and 1996 exhibited that the total TFA content (sum of all mentioned isomers) in SFM decreased from 21.77% (range: 13.78-26.29; n = 11) to 5.37% (1.98-6.15%; n = 9) between 1994 and 1999. Also the total TFA content in CFS on average strongly decreased from 11.77% (0.08-33.63; n = 16) in 1994 and 12.52% (1.61-26.79%; n = 7) in 1996 to 5.91% (0.43-19.72%; n = 10) in 1999. However, even the newest CFS samples partly exhibited relative high TFA contents. In addition to the total TFA contents all positional isomers of trans-C18:1, trans-C18:2 and trans-C18:3 in SFM and CFS were quantified and compared between different years. The conjugated linoleic acid (cis delta 9, trans delta 11) occurred only in small amounts of 0.03% and 0.02% in current SFM and CFS.

Follow-up of the delta4 to delta16 trans-18:1 isomer profile and content in French processed foods containing partially hydrogenated vegetable oils during the period 1995-1999. Analytical and nutritional implications

A survey of the total content of trans-18:1 acids and their detailed profile in French food lipids was conducted in 1995-1996, and 1999. For this purpose, 37 food items were chosen from their label indicating the presence of partially hydrogenated vegetable oils (PHVO) in their ingredients. The content as well as the detailed profile of these isomers was established by a combination of argentation thin-layer chromatography and gas liquid chromatography (GLC) on long polar capillary columns. With regard to the mean trans-18:1 acid contents of extracted PHVO, a significant decrease was observed between the two periods, i.e., from 26.9 to 11.8% of total fatty acids. However, only minor differences were noted in the mean relative distribution profiles of individual trans-18:1 isomers with ethylenic bonds between positions delta4 and delta16 for the two periods. The predominant isomer was delta9-18:1 (elaidic) acid, in the wide range 15.2-46.1% (mean, 27.9+/-7.2%) of total trans-18:1 acids, with the delta10 isomer ranked second, with a mean of 21.3% (range, 11.6 to 27.4%). The content of the unresolved delta6 to delta8 isomer group was higher than the delta11 isomer (vaccenic acid), representing on average 17.5 and 13.3%, respectively. Other isomers delta4, delta5, delta12, delta13/delta14, delta15, and delta16, were less than 10% each: 1.0, 1.6, 7.4, 7.1, 1.8, and 1.0%, respectively. However, considering individual food items, it was noted that none of the extracted PHVO were identical to one another, indicating a considerable diversity of such fats available to the food industry. A comparison of data for French foods with similar data recently established for Germany indicates that no gross differences occur in PHVO used by food industries in both countries. Estimates for the absolute mean consumption of individual isomers from ruminant fats and PHVO are made for the French population and compared to similarly reconstructed hypothetical profiles for Germany and North America. Differences occur in the total intake of trans-18:1 acids, but most important, in individual trans-18:1 isomer intake, with a particular increase of the delta6-delta8 to delta10 isomers with increasing consumption of PHVO. It is inferred from the present and earlier data that direct GLC of fatty acids is a faulty procedure that results (i) in variable underestimates of total trans-18:1 acids, (ii) in a loss of information as regards the assessment of individual isomeric trans-18:1 acids, and (iii) in the impossibility of comparing data obtained from human tissues if the relative contribution of dietary PHVO and ruminant fats is not known.

Abnormalities of the genitourinary tract in female mice lacking GATA5

Members of the GATA family of transcription factors play important roles in cell fate specification, differentiation, and morphogenesis during mammalian development. GATA5, the only one of the six vertebrate GATA factor genes not yet inactivated in mice, is expressed in a pattern that overlaps with but is distinct from that of other GATA factor genes. During mouse embryogenesis, GATA5 is expressed first in the developing heart and subsequently in the lung, vasculature, and genitourinary system. To investigate the function of GATA5 in vivo, we created mice homozygous for a GATA5 null allele. Homozygous mutants were viable and fertile, but females exhibited pronounced genitourinary abnormalities that included vaginal and uterine defects and hypospadias. In contrast, the genitourinary system was unaffected in male GATA5 mutants. These results reveal a specific role of GATA5 in development of the female genitourinary system and suggest that other GATA factors may have functions overlapping those of GATA5 in other tissues.

Calcineurin expression, activation, and function in cardiac pressure-overload hypertrophy

BACKGROUND

Vascular hypertension resulting in increased cardiac load is associated with left ventricular hypertrophy and is a leading predicator for progressive heart disease. The molecular signaling pathways that respond to increases in cardiac load are poorly understood. One potential regulator of the hypertrophic response is the calcium-sensitive phosphatase calcineurin.

METHODS AND RESULTS

We showed that calcineurin enzymatic activity is increased 3. 2-fold in the heart in response to pressure-overload hypertrophy induced by abdominal aortic banding in the rat. Western blot analysis further demonstrates that calcineurin A (catalytic subunit) protein content and association with calmodulin are increased in response to pressure-overload hypertrophy. This increase in calcineurin protein content was prevented by administration of the calcineurin inhibitor cyclosporine A (CsA). CsA administration attenuated load-induced cardiac hypertrophy in a dose-dependent manner over a 14-day treatment protocol. CsA administration also partially reversed pressure-overload hypertrophy in aortic-banded rats after 14 days. CsA also attenuated the histological and molecular indexes of pressure-overload hypertrophy.

CONCLUSIONS

These data suggest that calcineurin is an important upstream regulator of load-induced hypertrophy.

Calcineurin promotes protein kinase C and c-Jun NH2-terminal kinase activation in the heart. Cross-talk between cardiac hypertrophic signaling pathways

Multiple intracellular signaling pathways have been shown to regulate the hypertrophic growth of cardiomyocytes. Both necessary and sufficient roles have been described for the mitogen activated protein kinase(1) (MAPK) signaling pathway, specific protein kinase C (PKC) isoforms, and calcineurin. Here we investigate the interdependence between calcineurin, MAPK, and PKC isoforms in regulating cardiomyocyte hypertrophy using three separate approaches. Hearts from hypertrophic calcineurin transgenic mice were characterized for PKC and MAPK activation. Transgenic hearts demonstrated activation of c-Jun NH(2)-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK1/2), but not p38 MAPK factors. Calcineurin transgenic hearts demonstrated increased activation of PKCalpha, beta(1), and theta, but not of epsilon, beta(2), or lambda. In a second approach, cultured cardiomyocytes were infected with a calcineurin adenovirus to induce hypertrophy and the effects of pharmacologic inhibitors or co-infection with a dominant negative adenovirus were examined. Calcineurin-mediated hypertrophy was prevented with PKC inhibitors, Ca(2+) chelation, and attenuated with a dominant negative SEK-1 (MKK4) adenovirus, but inhibitors of ERK or p38 activation had no effect. In a third approach, we examined the activation of MAPK factors and PKC isoforms during the progression of load-induced hypertrophy in aortic banded rats with or without cyclosporine. We determined that inhibition of calcineurin activity with cyclosporine prevented PKCalpha, theta, and JNK activation, but did not affect PKCepsilon, beta, lambda, ERK1/2, or p38 activation. Collectively, these data indicate that calcineurin hypertrophic signaling is interconnected with PKCalpha, theta, and JNK in the heart, while PKCepsilon, beta, lambda, p38, and ERK1/2 are not involved in calcineurin-mediated hypertrophy.

Hypertrophic defect unmasked by calcineurin expression in asymptomatic tropomodulin overexpressing transgenic mice

OBJECTIVE

Dilation and hypertrophy often occur concurrently in cardiomyopathy, yet the interaction between these two functionally distinct conditions remains unknown.

METHODS

Combinatorial effects of hypertrophy and dilation were investigated by cross-breeding of two cardiomyopathic transgenic mouse lines which develop either hypertrophy (calcineurin-mediated) or dilation (tropomodulin-mediated).

RESULTS

Altering the intensity of signals driving hypertrophy and dilation in cross-bred litters resulted in novel disease phenotypes different from either parental line. Augmenting the calcineurin-dependent hypertrophic stimulus in tropomodulin overexpressing transgenics elevated heart:body weight ratios, increased ventricular wall thickness, and significantly accelerated mortality. These effects were evident in calcineurin cross-breeding to tropomodulin backgrounds of transgene homozygosity (severe dilation) or heterozygosity (mild dilation to asymptomatic). Molecular analyses indicated that tropomodulin and calcineurin signaling events in the first week after birth were critical for determination of disease outcome, substantiated by demonstration that temporary neonatal inhibition of tropomodulin expression prevents dilation.

CONCLUSIONS

This study shows that postnatal timing of altered signaling in cardiomyopathic transgenic mouse models is a pivotal part of determining outcome. In addition, intensifying hypertrophic stimulation exacerbates dilated cardiomyopathy, supporting the concept of shared molecular signaling between hypertrophy and dilation.

Reversal of cardiac hypertrophy in transgenic disease models by calcineurin inhibition

Heart disease remains one of the leading causes of morbidity and mortality in the industrialized nations of the world. Intense investigation has centered around identifying and manipulating intracellular signaling pathways that direct hypertrophic and myopathic responses in an attempt to intervene in the progression or reverse certain forms of heart disease. We show here that cyclosporin A-mediated inhibition of the calcium-regulated phosphatase, calcineurin (PP2B), reverses cardiac hypertrophy and myopathic dilation in two transgenic mouse models of cardiomyopathy. Reversal was demonstrated by gravimetric analysis, echocardiography, histological analysis, and molecular analysis of hypertrophy-associated gene expression. In contrast, a third mouse model of hypertrophic cardiomyopathy due to activated NFAT3 cardiac-specific expression was not affected by cyclosporin A. These results suggest that calcineurin may function in the long-term maintenance of cardiac hypertrophy or myopathic disease states.

Calcineurin-mediated hypertrophy protects cardiomyocytes from apoptosis in vitro and in vivo: An apoptosis-independent model of dilated heart failure

We have previously shown that the calcium-calmodulin-regulated phosphatase calcineurin (PP2B) is sufficient to induce cardiac hypertrophy that transitions to heart failure in transgenic mice. Given the rapid onset of heart failure in these mice, we hypothesized that calcineurin signaling would stimulate myocardial cell apoptosis. However, utilizing multiple approaches, we determined that calcineurin-mediated hypertrophy protected cardiac myocytes from apoptosis, suggesting a model of heart failure that is independent of apoptosis. Adenovirally mediated gene transfer of a constitutively active calcineurin cDNA (AdCnA) was performed in cultured neonatal rat cardiomyocytes to elucidate the mechanism whereby calcineurin affected myocardial cell viability. AdCnA infection, which induced myocyte hypertrophy and atrial natriuretic factor expression, protected against apoptosis induced by 2-deoxyglucose or staurosporine, as assessed by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling (TUNEL) labeling, caspase-3 activation, DNA laddering, and cellular morphology. The level of protection conferred by AdCnA was similar to that of adenoviral Bcl-x(L) gene transfer or hypertrophy induced by phenylephrine. In vivo, failing hearts from calcineurin-transgenic mice did not demonstrate increased TUNEL labeling and, in fact, demonstrated a resistance to ischemia/reperfusion-induced apoptosis. We determined that the mechanism whereby calcineurin afforded protection from apoptosis was partially mediated by nuclear factor of activated T cells (NFAT3) signaling and partially by Akt/protein kinase B (PKB) signaling. Although calcineurin activation protected myocytes from apoptosis, inhibition of calcineurin with cyclosporine was not sufficient to induce TUNEL labeling in Gqalpha-transgenic mice or in cultured cardiomyocytes. Collectively, these data identify a calcineurin-dependent mouse model of dilated heart failure that is independent of apoptosis.

Targeted inhibition of calcineurin prevents agonist-induced cardiomyocyte hypertrophy

Cardiac hypertrophy is a major predictor of future morbidity and mortality. Recent investigation has centered around identifying the molecular signaling pathways that regulate cardiac myocyte reactivity with the goal of modulating pathologic hypertrophic programs. One potential regulator of cardiomyocyte hypertrophy is the calcium-sensitive phosphatase calcineurin. We show here that calcineurin enzymatic activity, mRNA, and protein levels are increased in cultured neonatal rat cardiomyocytes by hypertrophic agonists such as angiotensin II, phenylephrine, and 1% fetal bovine serum. This induction of calcineurin activity was associated with an increase in calcineurin Abeta (CnAbeta) mRNA and protein, but not in CnAalpha or CnAgamma. Agonist-dependent increases in calcineurin enzymatic activity were specifically inhibited with an adenovirus expressing a noncompetitive peptide inhibitor of calcineurin known as cain [Lai, M. M., Burnett, P. E., Wolosker, H., Blackshaw, S. & Snyder, S. H. (1998) J. Biol. Chem. 273, 18325-18331]. Targeted inhibition of calcineurin with cain or an adenovirus expressing only the calcineurin inhibitory domain of AKAP79 attenuated cardiomyocyte hypertrophy and atrial natriuretic factor expression in response to angiotensin II, phenylephrine, and 1% fetal bovine serum. These data demonstrate that calcineurin is an important regulator of cardiomyocyte hypertrophy in response to certain agonists and suggest that cyclosporin A and FK506 function to attenuate cardiac hypertrophy by specifically inhibiting calcineurin.

Direct activation of a GATA6 cardiac enhancer by Nkx2.5: evidence for a reinforcing regulatory network of Nkx2.5 and GATA transcription factors in the developing heart

The zinc finger transcription factors GATA4, -5, and -6 and the homeodomain protein Nkx2.5 are expressed in the developing heart and have been shown to activate a variety of cardiac-specific genes. To begin to define the regulatory relationships between these cardiac transcription factors and to understand the mechanisms that control their expression during cardiogenesis, we analyzed the mouse GATA6 gene for regulatory elements sufficient to direct cardiac expression during embryogenesis. Using beta-galactosidase fusion constructs in transgenic mice, a 4.3-kb 5' regulatory region that directed transcription specifically in the cardiac lineage, beginning at the cardiac crescent stage, was identified. Thereafter, transgene expression became compartmentalized to the outflow tract, a portion of the right ventricle, and a limited region of the common atrial chamber of the embryonic heart. Further dissection of this regulatory region identified a 1.8-kb cardiac-specific enhancer that recapitulated the expression pattern of the larger region when fused to a heterologous promoter and a smaller 500-bp subregion that retained cardiac expression, but was quantitatively weaker. The GATA6 cardiac enhancer contained a binding site for Nkx2.5 that was essential for cardiac-specific expression in transgenic mice. These studies demonstrate that GATA6 is a direct target gene for Nkx2.5 in the developing heart and reveal a mutually reinforcing regulatory network of Nkx2.5 and GATA transcription factors during cardiogenesis.

Regulation of MEF2 by p38 MAPK and its implication in cardiomyocyte biology

Myocyte enhancer factor-2 (MEF2), transcription factors and mitogen-activated protein kinase (MAPK) p38 are regulators of cardiac development and various pathophysiologic processes. The recent finding that p38 can directly regulate MEF2 transcription factors suggests a novel mechanism for reprogramming cardiac gene expression in response to neuroendocrine and/or stress stimulation. This review weighs the accumulating evidence for a p38 MAPK-MEF2 signal transduction cascade and discusses its role in cardiac myocyte biology.

The zinc finger proteins Pannier and GATA4 function as cardiogenic factors in Drosophila

The regulation of cardiac gene expression by GATA zinc finger transcription factors is well documented in vertebrates. However, genetic studies in mice have failed to demonstrate a function for these proteins in cardiomyocyte specification. In Drosophila, the existence of a cardiogenic GATA factor has been implicated through the analysis of a cardial cell enhancer of the muscle differentiation gene D-mef2. We show that the GATA gene pannier is expressed in the dorsal mesoderm and required for cardial cell formation while repressing a pericardial cell fate. Ectopic expression of Pannier results in cardial cell overproduction, while co-expression of Pannier and the homeodomain protein Tinman synergistically activate cardiac gene expression and induce cardial cells. The related GATA4 protein of mice likewise functions as a cardiogenic factor in Drosophila, demonstrating an evolutionarily conserved function between Pannier and GATA4 in heart development.

Pathogenesis of dilated cardiomyopathy: molecular, structural, and population analyses in tropomodulin-overexpressing transgenic mice

Dilated cardiomyopathy is characterized by decreased contractile function and loss of myofibril organization. Previously unexplored structural and molecular events that precede and initiate dilation can now be studied in tropomodulin-overexpressing transgenic (TOT) mice exhibiting progressive dilated cardiomyopathy. Onset of dilation did not correspond to a change in transgene expression levels, which were more than threefold above normal at birth and remained elevated throughout postnatal life. Similarly, mitogen-activated protein kinase activation (p38, ERK1/ERK2, JNK1/JNK2) was not associated with dilation. In contrast, calcineurin was activated before dilation, presumably due to doubling of intracellular diastolic calcium levels in TOT cardiomyocytes. Amplitude of systolic calcium transients was greatly increased as well, demonstrating the novel and unique calcium handling profile of TOT cardiomyocytes. Loss of myofibril organization was not apparent by confocal microscopy until over 1 week after birth, although neonatal sarcomeric abnormalities were revealed by ultrastructural analysis. Rapid postnatal increases in heart:body weight ratio at 1.5 weeks were followed by two waves of mortality between 2 and 3 weeks after birth coincident with maturational stress. Ultimately, TOT pathogenesis is a compensatory response to altered sarcomeric structure driven by calcineurin activation within days after birth, making TOTs an excellent paradigm for studying the role of calcium overload in dilated cardiomyopathy.

C18:1, C18:2 and C18:3 trans and cis fatty acid isomers including conjugated cis delta 9, trans delta 11 linoleic acid (CLA) as well as total fat composition of German human milk lipids

In particular with respect to infant nutrition knowledge of the current contents of trans fatty acids (TFA) and of conjugated linoleic acid (CLA in human milk lipids is of interest. After pre-separation by Ag-TLC 11 trans-C18:1 isomers could be quantified by GC with a mean total content of 2.40 +/- 0.60 wt% in samples from 40 German women. For the positional isomers t4, t5, t6-8, t9, t10, t11, t12, t13, t14, t15 and t16 contents of 0.02, 0.02, 0.21, 0.37, 0.32, 0.68, 0.23, 0.15, 0.18, 0.09 and 0.14 wt% were established, with vaccenic acid being the predominant isomer. Further, small trans-C14:1 and trans-C16:1 contents of 0.08% and 0.15% on average were found. As the trans-C18:1 isomers also the trans-C16:1 isomers of human milk lipids could for the first time be baseline-resolved by GC to a great extent. Moreover, besides a mean CLA (c9,t11) content of 0.40 +/- 0.09% further 6 cis/trans isomers of linoleic acid with a total content of 1.07 +/- 0.56% on average (w/o CLA) were determined. Further, 4 trans isomers of alpha-linolenic acid could be baseline-resolved exhibiting a total content of 0.11%. Altogether German human milk lipids on average were found to contain 3.81 +/- 0.97% TFA with a range of 2.38-6.03%. Direct connections between the dietary intake of trans-C18:1 isomers and the composition of human milk lipids could be established. The major fatty acids exhibited the following contents (wt%): C4: 0.16, C6: 0.18, C8: 0.06, C10: 0.58, C12: 3.12, C14: 6.43, C16: 25.28, C18: 7.41, C18: 1 (total): 33.67, C18: 2 (total): 10.63 and alpha-C18: 3:0.87.

Bioactive lipids naturally occurring in bovine milk

Bioactive properties of food components increasingly gain in importance in the modern diet. Bovine milk fat (BMF) exhibits bioactive substances mainly in the class of fatty acids. Currently, most interest is addressed to trans fatty acids (TFA) and particularly conjugated linoleic acids (CLA) with BMF being the main source of CLA in food. Whereas saturated fatty acids (C12-C16) and TFA are reported to be positively correlated (negatively for oleic acid) with atherosclerosis and coronary heart disease, CLA are regarded as potent anticarcinogens. Also butyric acid (C4) as well as some phospholipids and either lipids present in BMF are thought to have anticarcinogenic properties. Furthermore, BMF contains the essential fatty acids C18:2 n-6 and C18:3 n-3 that have many and diverse functions in human metabolism and, thus, control a variety of biochemical and physiological processes. Altogether, BMF contains approximately 75 wt% of bioactive substances. However, the overall impact on human health can hardly be assessed.

Activated notch inhibits myogenic activity of the MADS-Box transcription factor myocyte enhancer factor 2C

Skeletal muscle gene expression is dependent on combinatorial associations between members of the MyoD family of basic helix-loop-helix (bHLH) transcription factors and the myocyte enhancer factor 2 (MEF2) family of MADS-box transcription factors. The transmembrane receptor Notch interferes with the muscle-inducing activity of myogenic bHLH proteins, and it has been suggested that this inhibitory activity of Notch is directed at an essential cofactor that recognizes the DNA binding domains of the myogenic bHLH proteins. Given that MEF2 proteins interact with the DNA binding domains of myogenic bHLH factors to cooperatively regulate myogenesis, we investigated whether members of the MEF2 family might serve as targets for the inhibitory effects of Notch on myogenesis. We show that a constitutively activated form of Notch specifically blocks DNA binding by MEF2C, as well as its ability to cooperate with MyoD and myogenin to activate myogenesis. Responsiveness to Notch requires a 12-amino-acid region of MEF2C immediately adjacent to the DNA binding domain that is unique to this MEF2 isoform. Two-hybrid assays and coimmunoprecipitations show that this region of MEF2C interacts directly with the ankyrin repeat region of Notch. These findings reveal a novel mechanism for Notch-mediated inhibition of myogenesis and demonstrate that the Notch signaling pathway can discriminate between different members of the MEF2 family.