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

miR-375 enhances palmitate-induced lipoapoptosis in insulin-secreting NIT-1 cells by repressing myotrophin (V1) protein expression

Lipoapoptosis of pancreatic beta cells caused by elevated circulating free fatty acids (FFAs) has now been recognized to be a pivotal factor contributing to beta cellular dysfunction and beta-mass lose in type 2 diabetes. Although recent studies suggested an important role for the ceramide pathway in the late destructive phase of lipid overload in the pancreatic beta cells, the overall underlying mechanisms leading to lipoapoptosis, however, remained poorly understood. mir-375 was recently characterized to be a pancreatic islet-specific miRNA implicated in the regulation of insulin secretion and beta-mass turnover. In the present study we further examined its effect on palmitate-induced lipoapoptosis in NIT-1 cells, a NOD-derived beta-cell line. It was found that NIT-1 cells with ectopic mir-375 expression were much more susceptible to palmitate-induced lipoapoptosis. In contrast, knockdown of endogenous pri-mir-375 expression by a modified antisense oligo, 2'-O-me-375, almost completely protected NIT-1 cells from palmitate-induced lipoapoptosis. We further demonstrated that mir-375 could target V1 mRNA and repress its translation. Consistent with this assumption, NIT-1 cells transfected with 2'-O-me-375 showed significant higher levels of V1 protein after palmitate induction. Together, our data suggest that mir-375 could be a potential therapeutic target for prevention and intervention of beta-cell dysfunction and beta-mass lose in type 2 diabetes.

Antioxidant Amelioration of Dilated Cardiomyopathy Caused by Conditional Deletion of NEMO/IKKγ in Cardiomyocytes

Rationale : Insight into the function of nuclear factor (NF)-κB in the adult heart has been hampered by the embryonic lethality of constitutive NF-κB inactivation.

Objective : The goal of the present study was therefore to gain insights into the role of NF-κB pathway specifically in mouse cardiomyocytes by conditional deletion of the NF-κB essential modulator (NEMO).

Methods and Results : Using a Cre/loxP system, we disrupted the Nemo gene in a cardiomyocyte-specific manner in the heart, which simulated gene expression changes underlying human heart failure and caused adult-onset dilated cardiomyopathy accompanied by inflammation and apoptosis. Pressure overload challenges of NEMO-deficient young hearts precociously induced the functional decrements that develop spontaneously in older knockout animals. Moreover, oxidative stress in NEMO-deficient cardiomyocytes is a critical pathological component that can be attenuated with antioxidant diet in vivo.

Conclusions : These results reveal an essential physiological role for NEMO-mediated signaling in the adult heart to maintain cardiac function in response to age-related or mechanical challenges, in part through modulation of oxidative stress.

Isorhamnetin protects rat ventricular myocytes from ischemia and reperfusion injury

Ischemia/reperfusion (I/R) has been known to cause damages to ventricular myocytes. Isorhamnetin, one member of flavonoid compounds, has cardioprotective effect, the effect that suggests a possible treatment for I/R damages. In the present investigation, we found that isorhamnetin could significantly promote the viability of neonatal rat ventricular myocytes that were exposed to ischemia/reperfusion (I/R) in vitro. Ventricular myocytes were obtained from neonatal SD rats, and then were divided randomly into three groups, namely I/R-/isor-, I/R+/isor- and I/R+/isor+ group. Before the whole experiment, the most appropriate concentration of isorhamnetin (4 μM) was determined by MTT assay. Our results showed that isorhamnetin could alleviate the damages of I/R to ventricular myocytes through inhibiting lactate dehydrogenase (LDH) activity, and repressing apoptosis. Compared with the counterpart of the I/R+/isor- group, LDH activity in the isorhamnetin-treated group weakened, halving from 24.1 ± 2.3 to 11.4 ± 1.2U/L. Additionally, flow cytometry showed the apparently increased apoptosis rate induced by I/R, the result that was further confirmed by transmission electron microscope. Administration of isorhamnetin, however, assuaged the apoptosis induced by I/R. Corresponding to the reduced apoptosis rate in the I/R+/isor+ group, western blotting assay showed increased amount of Bcl-2 and p53, decreased amount of Bax, and nuclear accumulation of NF-κB/p65.

Silencing the myotrophin gene by RNA interference leads to the regression of cardiac hypertrophy

Myotrophin-induced activation of NF-kappaB has been shown to be associated with cardiac hypertrophy (CH) that progresses to heart failure (HF). In the present study, we examined the cause-and-effect relationship between myotrophin and NF-kappaB activation using small hairpin RNA (shRNA) against myotrophin both in vitro (using neonatal rat myocytes) and in vivo [using myotrophin transgenic (Myo-Tg) mice, which overexpress myotrophin in the heart, develop CH, and gradually progress to HF]. Among several lentiviral vectors expressing myotrophin shRNAs, L-sh-109 showed the best silencing effect at both the mRNA (155.3 +/- 5.9 vs. 32.5 +/- 5.5, P < 0.001) and protein levels associated with a significant reduction of atrial natriuretic factor (ANF) and NF-kappaB. In vivo, when L-sh-109 was delivered directly into the hearts of 10-wk-old Myo-Tg mice, we observed a significant regression of cardiac mass (8.0 vs. 5.7 mg/g, P < 0.001) and myotrophin gene expression (54.5% over untreated Myo-Tg mice, P < 0.001) associated with a reduction in ANF and NF-kappaB signaling components. Our data suggest that using RNA interference to silence the myotrophin gene prevents NF-kappaB activation, associated with an attenuation of CH. This strategy could be an excellent therapeutic means for the treatment of CH and HF.

Ca2+/calmodulin-dependent kinase II triggers cell membrane injury by inducing complement factor B gene expression in the mouse heart

Myocardial Ca2+/calmodulin-dependent protein kinase II (CaMKII) inhibition improves cardiac function following myocardial infarction (MI), but the CaMKII-dependent pathways that participate in myocardial stress responses are incompletely understood. To address this issue, we sought to determine the transcriptional consequences of myocardial CaMKII inhibition after MI. We performed gene expression profiling in mouse hearts with cardiomyocyte-delimited transgenic expression of either a CaMKII inhibitory peptide (AC3-I) or a scrambled control peptide (AC3-C) following MI. Of the 8,600 mRNAs examined, 156 were substantially modulated by MI, and nearly half of these showed markedly altered responses to MI with CaMKII inhibition. CaMKII inhibition substantially reduced the MI-triggered upregulation of a constellation of proinflammatory genes. We studied 1 of these proinflammatory genes, complement factor B (Cfb), in detail, because complement proteins secreted by cells other than cardiomyocytes can induce sarcolemmal injury during MI. CFB protein expression in cardiomyocytes was triggered by CaMKII activation of the NF-kappaB pathway during both MI and exposure to bacterial endotoxin. CaMKII inhibition suppressed NF-kappaB activity in vitro and in vivo and reduced Cfb expression and sarcolemmal injury. The Cfb-/- mice were partially protected from the adverse consequences of MI. Our findings demonstrate what we believe is a novel target for CaMKII in myocardial injury and suggest that CaMKII is broadly important for the genetic effects of MI in cardiomyocytes.

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.

Blockade of NF-kappaB using IkappaB alpha dominant-negative mice ameliorates cardiac hypertrophy in myotrophin-overexpressed transgenic mice

Nuclear factor-kappaB (NF-kappaB) is a ubiquitous transcription factor that regulates various kinds of genes including inflammatory molecules, macrophage infiltration factors, cell adhesion molecules, and so forth, in various disease processes including cardiac hypertrophy and heart failure. Previously, we have demonstrated that activation of NF-kappaB was required in myotrophin-induced cardiac hypertrophy, in spontaneously hypertensive rats, and in dilated cardiomyopathy human hearts. Moreover, our recent study using the myotrophin-overexpressed transgenic mouse (Myo-Tg) model showed that short hairpin RNA-mediated knockdown of NF-kappaB significantly attenuated cardiac mass associated with improved cardiac function. Although it has been shown that NF-kappaB is substantially involved in cardiovascular remodeling, it is not clear whether the continuous blockade of NF-kappaB is effective in cardiovascular remodeling. To address this question, we took a genetic approach using IkappaB alpha triple mutant mice (3M) bred with Myo-Tg mice (a progressive hypertrophy/heart failure model). The double transgenic mice (Myo-3M) displayed an attenuated cardiac hypertrophy (9.8+/-0.62 versus 5.4+/-0.34, p<0.001) and improved cardiac function associated with significant inhibition of the NF-kappaB signaling cascade, hypertrophy marker gene expression, and inflammatory and macrophage gene expression at 24 weeks of age compared to Myo-Tg mice. NF-kappaB-targeted gene array profiling displayed several important genes that were significantly downregulated in Myo-3M mice compared to Myo-Tg mice. Furthermore, Myo-3M did not show any changes of apoptotic gene expression, indicating that significant inhibition of NF-kappaB activation reduces further proinflammatory reactions without affecting susceptibility to apoptosis. Therefore, development of therapeutic strategies targeting NF-kappaB may provide an effective approach to prevent adverse cardiac pathophysiological consequences.

Specific LPA receptor subtype mediation of LPA-induced hypertrophy of cardiac myocytes and involvement of Akt and NFkappaB signal pathways

Lysophosphatidic acid (LPA) is a bioactive phospholipid with diverse functions mediated via G-protein-coupled receptors (GPCRs). In view of the elevated levels of LPA in acute myocardial infarction (MI) patients we have conducted studies aimed at identifying specific LPA receptor subtypes and signaling events that may mediate its actions in hypertrophic remodeling. Experiments were carried out in cultured neonatal rat cardiomyocytes (NRCMs) exposed to LPA and in a rat MI model. In NRCMs, LPA-induced hypertrophic growth was completely abrogated by DGPP, an LPA1/LPA3 antagonist. The LPA3 agonist OMPT, but not the LPA2 agonist dodecylphosphate, promoted hypertrophy as examined by 3[H]-Leucine incorporation, ANF-luciferase expression and cell area. In in vivo experiments, LPA1, LPA2 and LPA3 mRNA levels as well as LPA1 and LPA3 protein levels increased together with left ventricular remodeling (LVRM) after MI. In addition, LPA stimulated the phosphorylation of Akt and p65 protein and activated NF-kappaB-luciferase expression. Inhibitors of PI3K (wortmannin), mTOR (rapamycin), and NF-kappaB (PDTC or SN50) effectively prevented LPA-induced 3[H]-Leucine incorporation and ANF-luciferase expression. Furthermore, ERK inhibitors (U0126 and PD98059) suppressed LPA-stimulated activation of NF-kappaB and p65 phosphorylation whereas wortmannin showed no effect on NF-kappaB activation. Our findings indicate that LPA3 and/or LPA1 mediate LPA-induced hypertrophy of NRCMs and that LPA1 and LPA3 may be involved in LVRM of MI rats. Moreover, Akt and NF-kappaB signaling pathways independently implicate in LPA-stimulated myocardial hypertrophic growth.

Losartan reduced connexin43 expression in left ventricular myocardium of spontaneously hypertensive rats

OBJECTIVE

To assess the effect of angiotensin II type 1 (AT(1)) receptor antagonist losartan on myocardium connexin43 (Cx43) gap junction (GJ) expression in spontaneously hypertensive rats (SHRs) and investigate possible mechanisms.

METHODS

Sixteen 9-week-old male SHRs and 8 age-matched male Wistar-Kyoto (WKY) rats were included in this study. SHRs were randomly divided into two groups to receive losartan at 30 mg/(kg x d) by oral gavage once daily for 8 weeks (SHR-L) or vehicle (0.9% saline) to act as controls (SHR-V); WKY rats receiving vehicle for 8 weeks served as normotensive controls. At the end of the experiment, rats were sacrificed and the hearts were removed. Expressions of Cx43 and nuclear factor-kappaB p65 (NF-kappaB p65) proteins in all three groups were observed and further investigations on the effect of angiotensin II type 1 receptor antagonist losartan (30 mg/(kg x d), 8 weeks) on Cx43 expression were conducted with Western blot and immunohistochemistry. NF-kappaB p65 protein in nuclear extracts was determined by Western blot.

RESULTS

Left ventricular (LV) hypertrophy was prominent in SHRs, Cx43 and NF-kappaB p65 protein expressions were obviously upregulated and Cx43 distribution was dispersed over the cell surface. Treatment with losarton reduced the over-expressions of Cx43 and NF-kappaB p65 in LV myocardium. The distribution of Cx43 gap junction also became much regular and confined to intercalated disk after losartan treatment.

CONCLUSION

Cx43 level was upregulated in LV myocardium of SHR during early stage of hypertrophy. Angiotensin II type 1 receptor antagonist losartan prevented Cx43 gap junction remodeling in hypertrophied left ventricles, possibly through the NF-kappaB pathway.

Prevention of cardiac hypertrophy and heart failure by silencing of NF-kappaB

Activation of the nuclear factor (NF)-kappaB signaling pathway may be associated with the development of cardiac hypertrophy and its transition to heart failure (HF). The transgenic Myo-Tg mouse develops hypertrophy and HF as a result of overexpression of myotrophin in the heart associated with an elevated level of NF-kappaB activity. Using this mouse model and an NF-kappaB-targeted gene array, we first determined the components of NF-kappaB signaling cascade and the NF-kappaB-linked genes that are expressed during the progression to cardiac hypertrophy and HF. Second, we explored the effects of inhibition of NF-kappaB signaling events by using a gene knockdown approach: RNA interference through delivery of a short hairpin RNA against NF-kappaB p65 using a lentiviral vector (L-sh-p65). When the short hairpin RNA was delivered directly into the hearts of 10-week-old Myo-Tg mice, there was a significant regression of cardiac hypertrophy, associated with a significant reduction in NF-kappaB activation and atrial natriuretic factor expression. Our data suggest, for the first time, that inhibition of NF-kappaB using direct gene delivery of sh-p65 RNA results in regression of cardiac hypertrophy. These data validate NF-kappaB as a therapeutic target to prevent hypertrophy/HF.

Nuclear factor-kappaB signaling contributes to severe, but not moderate, angiotensin II-induced left ventricular remodeling

OBJECTIVE

The transcription factor nuclear factor-kappaB (NF-kappaB) has been implicated in cardiomyocyte hypertrophy in vitro as well as in vivo; however, it is unknown if activation of NF-kappaB plays a mandatory role in the hypertrophic process. Here we characterize the importance of NF-kappaB signaling in moderate and severe left ventricular (LV) hypertrophy in rats with chronic pressure overload induced by angiotensin II (Ang II) infusion.

METHODS AND RESULTS

Electrophoretic mobility shift assay analysis revealed that Ang II infusion (2.5 microg/kg per min) for 6 days increased LV NF-kappaB/DNA-binding activity in a biphasic manner in Sprague-Dawley rats. Pyrrolidine dithiocarbamate (PDTC) (100 mg/kg per day), an NF-kappaB inhibitor, abolished Ang II-induced NF-kappaB activation and concomitant increase in tumor necrosis factor-alpha gene expression, while activator protein-1/DNA binding was not affected. Inhibition of NF-kappaB signaling for 6 days significantly attenuated Ang II-induced increases in LV/body weight ratio, LV mean wall thickness and cardiomyocyte cross-sectional area, without compromising LV systolic function. Moreover, PDTC abolished Ang II-induced cardiomyocyte apoptosis and interstitial fibrosis, and attenuated the gene expression of type I collagen. In contrast, a moderate LV hypertrophy induced by Ang II at a lower dose (0.5 microg/kg per min) was not associated with a significant activation of NF-kappaB, and PDTC treatment had no effect on the hypertrophic indices.

CONCLUSION

Our in-vivo data indicate a critical role of NF-kappaB signaling in the advanced stage of the remodeling process, whereas development of moderate LV hypertrophy is not dependent on NF-kappaB activation.

Noncoding miRNAs as key controllers of pancreatic β-cell functions

miRNAs, a recently discovered family of small noncoding RNAs, are emerging as major controllers of gene expression and key determinants of pancreatic β-cell function. These 19-22-nucleotide molecules govern gene expression by partially pairing to 3´-untranslated regions of target mRNAs and by inhibiting their translation. The elucidation of the role of miRNAs promises to unravel new aspects of β-cell biology and to clarify the mechanisms leading to defective insulin secretion in diabetes mellitus. This information is expected to favor the design of new approaches for preserving functional β-cells in prediabetic stages and the development of strategies for engineering insulin-secreting cells capable of replacing endogenous β-cells in diabetic patients.

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.

Increased susceptibility of MER5 (peroxiredoxin III) knockout mice to LPS-induced oxidative stress

MER5 (also called peroxiredoxin III, PrxIII) is a member of peroxiredoxin family that has antioxidant activity. The present study was performed to investigate its in vivo function using MER5 knockout mice. MER5 knockout mice were born in normal frequency and could grow to maturity, but we found that intracellular ROS levels are significantly higher in the macrophages of the knockout mice. We examined roles of MER5 function for the oxidative stress responses by intratracheal inoculation of lipopolysaccharide (LPS) to the mice. Lung inflammation such as inflammatory cell infiltration and airway wall thickening was more severely detected in the knockout mice. At the same time, oxidative damage on DNA and proteins was more strongly detected in lung tissues of the knockout mice, including 8-hydroxy-2'-deoxyguanosine (8-OHdG) formation and protein carbonylation. The degrees of lung inflammation and oxidative damage were positively related with LPS doses. Our results indicate that MER5 knockout mice accumulated higher intracellular ROS levels, which cause LPS-induced lung injury more severely, and thus, suggested that MER5 acts as an important scavenger of reactive oxygen species (ROS) under oxidative stress.

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.

Prevention and reversal of cardiac hypertrophy by soluble epoxide hydrolase inhibitors

Sustained cardiac hypertrophy represents one of the most common causes leading to cardiac failure. There is emerging evidence to implicate the involvement of NF-kappaB in the development of cardiac hypertrophy. However, several critical questions remain unanswered. We tested the use of soluble epoxide hydrolase (sEH) inhibitors as a means to enhance the biological activities of epoxyeicosatrienoic acids (EETs) to treat cardiac hypertrophy. sEH catalyzes the conversion of EETs to form the corresponding dihydroxyeicosatrienoic acids. Previous data have suggested that EETs may inhibit the activation of NF-kappaB-mediated gene transcription. We directly demonstrate the beneficial effects of several potent sEH inhibitors (sEHIs) in cardiac hypertrophy. Specifically, we show that sEHIs can prevent the development of cardiac hypertrophy using a murine model of pressure-induced cardiac hypertrophy. In addition, sEHIs reverse the preestablished cardiac hypertrophy caused by chronic pressure overload. We further demonstrate that these compounds potently block the NF-kappaB activation in cardiac myocytes. Moreover, by using in vivo electrophysiologic recordings, our study shows a beneficial effect of the compounds in the prevention of cardiac arrhythmias that occur in association with cardiac hypertrophy. We conclude that the use of sEHIs to increase the level of the endogenous lipid epoxides such as EETs may represent a viable and completely unexplored avenue to reduce cardiac hypertrophy by blocking NF-kappaB activation.

Re-employment of developmental transcription factors in adult heart disease

A finite number of transcription factors constitute a combinatorial code that orchestrates cardiac development and the specification and differentiation of myocytes. Many, if not all of these same transcription factors are re-employed in the adult heart in response to disease stimuli that promote hypertrophic enlargement and/or dilated cardiomyopathy, as part of the so-called "fetal gene program". This review will discuss the transcription factors that regulate the hypertrophic growth response of the adult heart, with a special emphasis on those regulators that participate in cardiac development.

FAK-related nonkinase attenuates hypertrophy induced by angiotensin-II in cultured neonatal rat cardiac myocytes

AIM

To examine the inhibitory effect of FAK-related nonkinase (FRNK) in cardiac hypertrophy in vitro and investigate the possible mechanisms.

METHODS

A functional fragment of FRNK cDNA was amplified by reverse transcription-polymerase chain reaction and cloned into the vector pcDNA3.1. Hypertrophy in neonatal rat cardiac myocytes was established with angiotensin-II stimulation. The pcDNA3.1-FRNK or pcDNA3.1 was respectively transfected into cardiomyocytes by Lipofectamine 2000. The surface area and mRNA expression of atrial natriuretic peptide (ANP) of myocytes were employed to detect cardiac hypertrophy. NF-kappaB p65 protein in nuclear extracts, phosphorylation levels of ERK1/2 (p-ERK1/2) and AKT (p-AKT), as well as total ERK1/2, and AKT in variant treated cardiomyocytes were determined by Western blot.

RESULTS

Under the stimulation of angiotensin II, the surface area of myocytes and levels of ANP mRNA were significantly increased. But transient transfection with pcDNA3.1-FRNK in advance may reduce the surface area and expression of ANP mRNA of hypertrophic myocytes. The protein levels of NF-kappaB p65 in nuclear extracts and p-ERK1/2, p-AKT in FRNK treated cardiomyocytes were significantly decreased compared with that in angiotensin-II induced cardiomyocytes, while different treatments had little effect on total ERK1/2 and AKT.

CONCLUSION

FRNK may inhibit angiotensin-II-induced cardiomyocyte hypertrophy via decreasing phosphorylation levels at ERK1/2 and AKT, consequently downregulating nuclear translocation of NF-kappaB p65.

Protective effects of pyrrolidine dithiocarbamate on myocardium apoptosis induced by adriamycin in rats

BACKGROUND

Effects of pyrrolidine dithiocarbamate (PDTC) on programmed cell death are controversial. It is unclear if PDTC has the protective effects on myocardial apoptosis induced by adriamycin (ADR) in rats. The present study was undertaken to study the protective effects of pyrrolidine dithiocarbamate (PDTC) on myocardium apoptosis induced by adriamycin (ADR) in rats and its mechanisms.

METHODS

Forty male Wistar rats were randomly divided into five groups: control, ADR, ADR+PDTC 50 mg/kg, ADR+PDTC 100 mg/kg and ADR+PDTC 200 mg/kg group. Myocardial apoptosis was detected by electron microscopic examination and TUNEL assay. Myocardium p53 gene expression was examined by RT-PCR analysis. Location and distribution of p53 was observed by immunohistochemical assay. Myocardial expression of p53 protein was assessed by Western blot analysis. Activity of NF-kappaB was evaluated by Electrophoretic Mobility Shift Assay.

RESULTS

Myocardial apoptotic index, expression of p53 mRNA, expression of p53 protein and the binding activity of NF-kappaB decreased significantly in ADR+PDTC groups compared with ADR group. All these change were significantly correlated with dose of PDTC.

CONCLUSION

PDTC has preventive effects on myocardial apoptosis induced by ADR, which is probably associated with inhibiting binding activity of NF-kappa B and further regulating apoptosis-related gene expression and translation, and inhibiting myocardial apoptosis.

Epigallocathechin-3 gallate inhibits cardiac hypertrophy through blocking reactive oxidative species-dependent and -independent signal pathways

Cardiac hypertrophy is a major cause of morbidity and mortality worldwide. Recent in vitro and in vivo studies have suggested that reactive oxygen species (ROS) may play an important role in cardiac hypertrophy. It was therefore thought to be of particular value to examine the effects of antioxidants on cardiac hypertrophy. Epigallocatechin-3-gallate (EGCG) is a major bioactive polyphenol present in green tea and a potent antioxidant. The current study was designed to test the hypothesis that EGCG inhibits cardiac hypertrophy in vitro and in vivo. In this study, we investigated the effects of EGCG on angiotensin II- (Ang II) and pressure-overload-induced cardiac hypertrophy. Our results showed that EGCG attenuated Ang II- and pressure-overload-mediated cardiac hypertrophy. Both reactive oxygen species generation and NADPH oxidase expressions induced by Ang II and pressure overload were suppressed by EGCG. The increased hypertension by pressure overload was almost completely blocked after EGCG treatment. Further studies showed that EGCG inhibited Ang II-induced NF-kappaB and AP-1 activation. Inhibition of the activity of NF-kappaB was through blocking ROS-dependent p38 and JNK signaling pathways, whereas inhibition of AP-1 activation was via blocking EGFR transactivation and its downstream events ERKs/PI3K/Akt/mTOR/p70(S6K). The combination of these actions resulted in repressing the reactivation of ANP and BNP, and ultimately preventing the progress of cardiac hypertrophy. These findings indicated that EGCG prevents the development of cardiac hypertrophy through ROS-dependent and -independent mechanisms involving inhibition of different intracellular signaling transductional pathways.

Inhibition of cardiac hypertrophy by triflusal (4-trifluoromethyl derivative of salicylate) and its active metabolite

The nuclear factor (NF)-kappaB signaling pathway is an important intracellular mediator of cardiac hypertrophy. The aim of the present study was to determine whether triflusal (2-acetoxy-4-trifluoromethylbenzoic acid), a salicylate derivative used as antiplatelet agent, and its active metabolite 2-hydroxy-4-trifluoromethylbenzoic acid (HTB) inhibit cardiac hypertrophy in vitro and in vivo by blocking the NF-kappaB signaling pathway. In cultured neonatal rat cardiomyocytes, HTB (300 microM, a concentration reached in clinical use) inhibited phenylephrine (PE)-induced protein synthesis ([3H]leucine uptake), induction of the fetal-type gene atrial natriuretic factor (ANF), and sarcomeric disorganization. Assessment of the effects of triflusal in pressure overload-induced cardiac hypertrophy by aortic banding resulted in a significant reduction in the ratio of heart weight to body weight and in a reduction of the mRNA levels of the cardiac hypertrophy markers ANF and alpha-actinin compared with untreated banded rats. Electrophoretic mobility shift assay revealed an increase in the NF-kappaB binding activity in cardiac nuclear extracts of banded rats that was prevented by triflusal treatment. It is noteworthy that banded rats treated with oral triflusal, compared with untreated rats, showed enhanced protein levels of IkappaBalpha, which forms a cytoplasmic inactive complex with the p65-p50 heterodimeric complex. Finally, HTB increased phospho-IkappaBalpha levels in neonatal cardiomyocytes and inhibited proteosome activity, suggesting that this drug prevented proteosome-mediated degradation of IkappaBalpha. These results indicate that triflusal, a drug with a well characterized pharmacological and safety profile currently used as antiplatelet, inhibits cardiomyocyte growth by interfering with the NF-kappaB signaling pathway through a post-transcriptional mechanism involving reduced-proteosome degradation of IkappaBalpha.

Blockade of MyD88 attenuates cardiac hypertrophy and decreases cardiac myocyte apoptosis in pressure overload-induced cardiac hypertrophy in vivo

In this study, we evaluated whether blocking myeloid differentiation factor-88 (MyD88) could decrease cardiac myocyte apoptosis following pressure overload. Adenovirus expressing dominant negative MyD88 (Ad5-dnMyD88) or Ad5-green fluorescent protein (GFP) (Ad5-GFP) was transfected into rat hearts (n = 8/group) immediately followed by aortic banding for 3 wk. One group of rats (n = 8) was subjected to aortic banding for 3 wk without transfection. Sham surgical operation (n = 8) served as control. The ratios of heart weight to body weight (HW/BW) and heart weight to tibia length (HW/TL) were calculated. Cardiomyocyte size was examined by FITC-labeled wheat germ agglutinin staining of membranes. Cardiac myocyte apoptosis was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay, and myocardial interstitial fibrosis was examined by Masson's Trichrome staining. Aortic banding significantly increased the HW/BW by 41.0% (0.44 +/- 0.013 vs. 0.31 +/- 0.008), HW/TL by 47.2% (42.7 +/- 1.30 vs. 29.0 +/- 0.69), cardiac myocyte size by 49.6%, and cardiac myocyte apoptosis by 11.5%, and myocardial fibrosis and decreased cardiac function compared with sham controls. Transfection of Ad5-dnMyD88 significantly reduced the HW/BW by 18.2% (0.36 +/- 0.006 vs. 0.44 +/- 0.013) and HW/TL by 22.3% (33.2 +/- 0.95 vs. 42.7 +/- 1.30) and decreased cardiomyocyte size by 56.8%, cardiac myocyte apoptosis by 76.2%, as well as fibrosis, and improved cardiac function compared with aortic-banded group. Our results suggest that MyD88 is an important component in the Toll-like receptor-4-mediated nuclear factor-kappaB activation pathway that contributes to the development of cardiac hypertrophy. Blockade of MyD88 significantly reduced cardiac hypertrophy, cardiac myocyte apoptosis, and improved cardiac function in vivo.

Atorvastatin prevents peroxisome proliferator-activated receptor γ coactivator-1 (PGC-1) downregulation in lipopolysaccharide-stimulated H9c2 cells

Although abnormalities in cardiac fatty acid metabolism are involved in the development of several cardiac pathologies, the mechanisms underlying these changes are not well understood. Given the prominent role played by peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta in cardiac fatty acid metabolism, the aim of this study was to examine the effects of nuclear factor (NF)-kappaB activation on the activity of this nuclear receptor. Embryonic rat heart-derived H9c2 cells stimulated with lipopolysaccharide (LPS) showed a reduction (38%, P<0.05) in the mRNA levels of the PPARbeta/delta-target gene pyruvatedehydrogenase kinase 4 (PDK4) that was prevented in the presence of the NF-kappaB inhibitors parthenolide (10 microM) and atorvastatin (10 microM). Electrophoretic mobility shift assay revealed that both parthenolide and atorvastatin significantly decreased LPS-stimulated NF-kappaB binding activity in H9c2 cardiac cells. LPS-stimulation of H9c2 cardiac cells also led to a 30% reduction (P<0.05) in the mRNA levels of PPARgamma Coactivator 1 (PGC-1) that was consistent with the reduction in the protein levels of this coactivator. In the presence of either atorvastatin or parthenolide, the reduction in PGC-1 expression was prevented. Co-immunoprecipitation studies showed that LPS-stimulation led to a reduction in the physical interaction between PGC-1 and PPARbeta/delta and that this reduction was prevented in the presence of atorvastatin. Finally, electrophoretic mobility shift assay revealed that parthenolide and atorvastatin prevented LPS-mediated reduction in PPARbeta/delta binding activity in H9c2 cardiac cells. These results suggest that LPS-mediated NF-kappaB activation inhibits the expression of genes involved in fatty acid metabolism by a mechanism involving reduced expression of PGC-1, which in turn affects the PPARbeta/delta transactivation of target genes involved in cardiac fatty acid oxidation.

Role of the NF-kappaB signaling cascade and NF-kappaB-targeted genes in failing human hearts

Nuclear factor-kappaB (NF-kappaB) is a ubiquitous transcription factor that has been indicated to play a causal role for many pathological states. Heart failure is a major cause of morbidity all over the world. In this study, we examined the role of NF-kappaB in failing (F) human hearts and nonfailing (NF) controls. Our data showed that an enhanced activation of this nuclear factor occurs in the F hearts along with its components, like I-kappaB kinase (IKK)beta and IkappaBalpha, both at transcript and translational levels. To obtain a profile of NF-kappaB-targeted gene expression in F hearts, we profiled, for the first time, the expression analysis of NF-kappaB-linked gene using a TranSignal human NF-kappaB-targeted gene array. Our data suggest that more than 50 genes were consistently upregulated in F hearts more than 1.5-fold (vs NF hearts, p<0.001). Our studies demonstrated that NF-kappaB is specifically and significantly activated via IKKbeta in F hearts. The most intriguing aspects of our studies are molecular profiles of NF-kappaB-linked or targeted gene expression in F hearts. Our data suggest that the regulation and control of NF-kappaB activation is, therefore, a powerful therapeutic strategy for delaying or attenuating such deadly disease.

Inhibition of NF-κB induces regression of cardiac hypertrophy, independent of blood pressure control, in spontaneously hypertensive rats

The transcription factor nuclear factor (NF)-κB plays a leading role in cardiac hypertrophy associated with heart failure, but whether it is involved in cardiac mass reduction is not known. We evaluated whether inhibiting the NF-κB cascade with pyrrolidine dithiocarbamate (PDTC) in spontaneously hypertensive rats (SHRs) and age-matched Wistar-Kyoto rats (WKYs) affected hypertrophy. We measured NF-κB signaling components [NF-κB translocation, IκBα, p65, mRNA and protein levels, and IκB kinase-β (IKKβ) activity] at 12 and 36 wk in WKYs and SHRs and at 10 wk in PDTC-treated rats ( n = 9). NF-κB activation was also evaluated in rats treated for 10 wk with captopril or hydralazine alone or with either drug plus PDTC. All components were increased in SHRs compared with WKYs. After PDTC treatment, NF-κB activity was inhibited, and heart weight-to-body weight ratio in SHRs was significantly attenuated (3.52 ± 0.04 to 3.32 ± 0.05 mg/kg). Captopril treatment significantly reduced cardiac mass (3.5 vs. 3.05 mg/kg; n = 9) and inhibited NF-κB activity (169.71 ± 5.70 to 106.7 ± 12.44). Hydralazine had no effect on cardiac mass (3.5 vs. 3.42 mg/kg) or NF-κB activity (169.71 ± 5.70 to 155.52 ± 6.11). Hydralazine plus PDTC reduced blood pressure (191.16 ± 1.7 to 158.5 ± 2.36 mmHg) and inhibited NF-κB activity (169.71 ± 5.70 to 97.29 ± 3.65). Our data suggest that 1) cardiac hypertrophy in SHRs is partly due to NF-κB activation, 2) inhibition of NF-κB activity by PDTC parallels regression of hypertrophy, and 3) regression of hypertrophy is partly due to inhibition of NF-κB activity, independent of hypertension. The relationship between NF-κB activity and cardiac remodeling is causal, not coincidental.

Cardiac-specific blockade of NF-κB in cardiac pathophysiology: differences between acute and chronic stimuli in vivo

The role of NF-κB in cardiac physiology and pathophysiology has been difficult to delineate due to the inability to specifically block NF-κB signaling in the heart. Cardiac-specific transgenic models have recently been developed that repress NF-κB activation by preventing phosphorylation at specific serine residues of the inhibitory κB (IκB) protein isoform IκBα. However, these models are unable to completely block NF-κB because of a second signaling pathway that regulates NF-κB function via Tyr42 phosphorylation of IκBα. We report the development of transgenic (3M) mouse lines that express the mutant IκBα(S32A,S36A,Y42F)in a cardiac-specific manner. NF-κB activation in cardiomyopathic TNF-1.6 mice is completely blocked by the 3M transgene but only partially blocked (70–80%) by the previously described double-mutant 2M [IκBα(S32A,S36A)] transgene, which demonstrates the action of two proximal pathways for NF-κB activation in TNF-α-induced cardiomyopathy. In contrast, after acute stimuli including administration of TNF-α and ischemia-reperfusion (I/R), NF-κB activation is blocked in both 2M and 3M transgenic mice. This result suggests that phosphorylation of the regulatory Ser32 and Ser36 predominantly mediates NF-κB activation in these situations. We show that infarct size after I/R is reduced by 70% in 3M transgenic mice, which conclusively demonstrates that NF-κB is involved in I/R injury. In summary, we have engineered novel transgenic mice that allow us to distinguish two major proximal pathways for NF-κB activation. Our results demonstrate that the serine and tyrosine phosphorylation pathways are differentially activated during different pathophysiological processes (cardiomyopathy and I/R injury) and that NF-κB contributes to infarct development after I/R.

Lipoxin A4 inhibits TNF-α-induced production of interleukins and proliferation of rat mesangial cells

BACKGROUND

Studies have shown that lipoxin A(4) (LXA(4)) and its analogues inhibited proliferation of glomerular mesangial cells induced by leukotriene D(4) (LTD(4)) or platelet-derived growth factor (PDGF), reduced the production of proinflammatory cytokines such as interleukin (IL)-1beta and IL-6 in renal tissue of ischemic injury. In the present studies, we examine whether LXA(4) have inhibitory effects on tumor necrosis factor-alpha (TNF-alpha)-induced productions of IL-1beta and IL-6 and proliferation of glomerular mesangial cells of rat, and explore the molecular mechanisms of signal pathway of LXA(4).

METHODS

Cultured glomerular mesangial cells were treated with TNF-alpha (10 ng/mL), with or without preincubation with LXA(4) at the different concentrations. Cell proliferation was assessed by [(3)H]-thymidine incorporation. Proteins of IL-1beta and IL-6 in supernatant were analyzed by enzyme-linked immunosorbent assay (ELISA). Expressions of mRNA of IL-1beta and IL-6 were determined by real-time polymerase chain reaction (PCR) and cyclin E by reverse transcription (RT)-PCR. Proteins of cyclin E, threonine phosphorylated Akt(1) at 308 site (Thr(308)) and p27(kip1) were analyzed by Western blotting studies. Activities of signal transducers and activators of transcription-3 (STAT(3)), nuclear factor-kappaB (NF-kappaB) were determined by electrophroretic mobility shift assay (EMSA). Expression of Src homology (SH) 2-containing protein-tyrosine phosphatase (SHP-2) was assessed by immunoprecipitation and immunoblotting.

RESULTS

TNF-alpha-stimulated proliferation, release of proteins and expressions of mRNA of IL-1beta and IL-6 in mesangial cells were inhibited by LXA(4) in a dose-dependent manner. The marked increments in mRNA expression and protein synthesis of cyclin E induced by TNF-alpha in parallel with proliferation of mesangial cells were down-regulated by LXA(4). LXA(4) antagonized the phosphorylation of SHP-2 and activity of NF-kappaB induced by TNF-alpha. Pretreatment of the cells with NF-kappaB inhibitor pyrrolidine dithio-carbamate (PDTC) blocked the productions of IL-1beta, IL-6, and activation of NF-kappaB induced by TNF-alpha. Stimulation of mesangial cells with TNF-alpha resulted in enhanced DNA-binding activity of STAT(3). This increment was inhibited by LXA(4) in a dose-dependent manner. Threonine phosphorylated Akt(1) protein at 308 site stimulated by TNF-alpha was reduced by LXA(4.) TNF-alpha-induced decrement in expression of p27(kip1) protein was ameliorated by LXA(4) in a dose-dependent manner.

CONCLUSION

TNF-alpha-induced proliferation and increment of cyclin E of rat mesangial cells can be inhibited by LXA(4), and these inhibitory effects might be through the mechanisms of STAT(3) and Akt(1)/p27(kip1) pathway-dependent signal transduction. LXA(4) also antagonized TNF-alpha-stimulated IL-1beta and IL-6 synthesis, and these antagonisms were related to SHP-2 and NF-kappaB pathway-dependent signal transduction.

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.

Atorvastatin improves peroxisome proliferator-activated receptor signaling in cardiac hypertrophy by preventing nuclear factor-kappa B activation

Nuclear factor (NF)-kappa B signaling pathway plays a pivotal role in cardiac hypertrophy. Although it has been reported that statins inhibit cardiac hypertrophy by reducing generation of reactive oxygen species, it is not yet known whether statins prevent NF-kappa B activation and whether this effect can be related to the reduction in the peroxisome proliferator-activated receptor (PPAR) pathway. In this study, we examined the role of atorvastatin on NF-kappa B activity and PPAR signaling in pressure overload-induced cardiac hypertrophy. Our findings indicate that atorvastatin inhibits cardiac hypertrophy and prevents the fall in the protein levels of PPAR alpha and PPAR beta/delta. Further, atorvastatin treatment avoided NF-kappa B activation during cardiac hypertrophy, reducing the protein-protein association between these PPAR subtypes and the p65 subunit of NF-kappa B. These findings indicate that negative cross-talk between NF-kappa B and PPARs may interfere with the transactivation capacity of the latter, leading to a fall in the expression of genes involved in fatty acid metabolism, and that these changes are prevented by statin treatment.

Nuclear factor-kappaB activation leads to down-regulation of fatty acid oxidation during cardiac hypertrophy

Little is known about the mechanisms responsible for the fall in fatty acid oxidation during the development of cardiac hypertrophy. We focused on the effects of nuclear factor (NF)-kappaB activation during cardiac hypertrophy on the activity of peroxisome proliferator-activated receptor (PPAR) beta/delta, which is the predominant PPAR subtype in cardiac cells and plays a prominent role in the regulation of cardiac lipid metabolism. Phenylephrine-induced cardiac hypertrophy in neonatal rat cardiomyocytes caused a reduction in the expression of pyruvate dehydrogenase kinase 4 (Pdk4), a target gene of PPARbeta/delta involved in fatty acid utilization, and a fall in palmitate oxidation that was reversed by NF-kappaB inhibitors. Lipopolysaccharide stimulation of NF-kappaB in embryonic rat heart-derived H9c2 myotubes, which only express PPARbeta/delta, caused both a reduction in Pdk4 expression and DNA binding activity of PPARbeta/delta to its response element, effects that were reversed by NF-kappaB inhibitors. Coimmunoprecipitation studies demonstrated that lipopolysaccharide strongly stimulated the physical interaction between the p65 subunit of NF-kappaB and PPARbeta/delta, providing an explanation for the reduced activity of PPARbeta/delta. Finally, we assessed whether this mechanism was present in vivo in pressure overload-induced cardiac hypertrophy. In hypertrophied hearts of banded rats the reduction in the expression of Pdk4 was accompanied by activation of NF-kappaB and enhanced interaction between p65 and PPARbeta/delta. These results indicate that NF-kappaB activation during cardiac hypertrophy down-regulates PPARbeta/delta activity, leading to a fall in fatty acid oxidation, through a mechanism that involves enhanced protein-protein interaction between the p65 subunit of NF-kappaB and PPARbeta/delta.

NF-κB activation is required for the development of cardiac hypertrophy in vivo

In the present study, we examined whether NF-κB activation is required for cardiac hypertrophy in vivo. Cardiac hypertrophy in rats was induced by aortic banding for 1, 3, and 5 days and 1–6 wk, and age-matched sham-operated rats served as controls. In a separate group of rats, an IκB-α dominant negative mutant (IκB-αM), a superrepressor of NF-κB activation, or pyrrolidinedithiocarbamate (PDTC), an antioxidant that can inhibit NF-κB activation, was administered to aortic-banded rats for 3 wk. The heart weight-to-body weight ratio was significantly increased at 5 days after aortic banding, peaked at 4 wk, and remained elevated at 6 wk compared with age-matched sham controls. Atrial natriuretic peptide and brain natriuretic peptide mRNA expressions were significantly increased after 1 wk of aortic banding, reached a maximum between 2 and 3 wk, and remained increased at 6 wk compared with age-matched sham controls. NF-κB activity was significantly increased at 1 day, reached a peak at 3 wk, and remained elevated at 6 wk, and IKK-β activity was significantly increased at 1 day, peaked at 5 days, and then decreased but remained elevated at 6 wk after aortic banding compared with age-matched sham controls. Inhibiting NF-κB activation in vivo by cardiac transfection of IκB-αM or by PDTC treatment significantly attenuated the development of cardiac hypertrophy in vivo with a concomitant decrease in NF-κB activity. Our results suggest that NF-κB activation is required for the development of cardiac hypertrophy in vivo and that NF-κB could be an important target for inhibiting the development of cardiac hypertrophy in vivo.

Regulation of myotrophin gene by pressure overload and stretch

Hemodynamic load is a major determinant of cardiac mass and its phenotype, but very little is known about how mechanical load is converted into intracellular signals of gene expression and regulation. We have shown earlier that factors other than blood pressure control play a role in the mechanism involved in the development or regression of myocardial hypertrophy. We have identified a soluble factor, myotrophin, from the hearts of spontaneously hypertensive rats and dilated cardiomyopathic humans, which stimulates protein synthesis both in neonatal and adult rat cardiac myocytes. Myotrophin gene has been mapped and shown to be a novel gene localized in human chromosome 7q-33. The present study was conducted to evaluate the mechanism by which myotrophin is released and in turn initiates myocardial hypertrophy. We used an in vitro model, where neonatal cardiac myocytes were grown on stretchable plates and examined the effect of stretch on myotrophin gene expression (to mimic pressure overload), an in vivo model using beating non-working hearts exposed to high pressure and three different models of hypertensive rats. Our data showed that both cyclic stretch and exposure to high pressure caused significant increase in the transcript levels of myotrophin followed by expression of beta-myosin heavy chain and atrial natriuretic factor associated with an increase in myocardial protein synthesis. All three models of hypertensive rats also showed a significant increase in myotrophin transcripts. Altogether, our data strongly suggest that stretching of the cells by pressure or volume turns on the myotrophin, which in turn is responsible for the initiation process of myocardial hypertrophy in response to pressure or volume overload.

Nuclear factor-kappaB: its role in health and disease

Nuclear factor-kappaB (NF-kappaB) is a major transcription factor that plays an essential role in several aspects of human health including the development of innate and adaptive immunity. The dysregulation of NF-kappaB is associated with many disease states such as AIDS, atherosclerosis, asthma, arthritis, cancer, diabetes, inflammatory bowel disease, muscular dystrophy, stroke, and viral infections. Recent evidence also suggests that the dysfunction of NF-kappaB is a major mediator of some human genetic disorders. Appropriate regulation and control of NF-kappaB activity, which can be achieved by gene modification or pharmacological strategies, would provide a potential approach for the management of NF-kappaB related human diseases. This review summarizes the current knowledge of the physiological and pathophysiological functions of NF-kappaB and its possible role as a target of therapeutic intervention

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.

Peroxisome Proliferator Activator Receptors (PPAR), Insulin Resistance, and Cardiomyopathy

Diabetes is a risk factor for coronary atherosclerosis, myocardial infarction, and ischemic cardiomyopathy. Insulin resistance is associated with left ventricular (LV) hypertrophy and hypertensive cardiomyopathy. Even in the absence of coronary artery disease or hypertension, "diabetic cardiomyopathy" can develop because of myocardial autonomic dysfunction or impaired coronary flow reserve. The relationship between insulin resistance and cardiomyopathy is bidirectional. Systemic and myocardial glucose uptake is compromised in heart failure independent of etiology. These abnormalities are associated with cellular deficits of insulin signaling. Insulin resistance in heart failure can be detrimental, because transcriptional shifts in metabolic gene expression favor glucose over fat as a substrate for high-energy phosphate production. Although preexisting diabetes accelerates this process of "metabolic death," insulin resistance can also develop secondary to cardiomyopathy-associated overabundance of neurohormones and cytokines. Insulin resistance and fatty acid excess are potential therapeutic targets in heart failure, striving for efficient myocardial substrate utilization. Peroxisome proliferator activator receptor gamma (PPARgamma) agonists are antidiabetic agents with antilipemic and insulin-sensitizing activity. Experimental studies suggest salutary effects in limiting infarct size, attenuating myocardial reperfusion injury, inhibiting hypertrophic signaling and vascular antiinflammatory actions through cytokine inhibition. However, clinical applicability in diabetic patients experiencing heart failure has been hampered because of increased edema and even fewer reports of exacerbation associated with these compounds. Evidence to date argues for peripheral mechanisms of edema unrelated to central hemodynamics. Nevertheless, they are currently contraindicated in New York Heart Association (NYHA) III-IV patients, particularly in combination with insulin. Investigations are underway to decipher mechanisms, risks, and benefits of PPARgamma agonists, as well as the role of the structurally related PPARalpha receptor on cardiovascular metabolism and function.

Modulatory Properties of Various Natural Chemopreventive Agents on the Activation of NF-κB Signaling Pathway

PURPOSE

To study and compare effects of selected natural chemopreventive agents on the transcription activation of nuclear factor-kappa B (NF-kappaB) in human HT-29 colon cancer cells.

METHODS

The natural chemopreventive compounds isothiocyanates (ITCs) found in cruciferous vegetables, flavonoids found in green tea, resveratrol (RES) and procyanidin dimers found in red wine, and curcumin (CUR) found in turmeric curry food were examined in this study. HT-29 cells were stably transfected with NF-kappaB luciferase construct, and stable clones were selected. One of the clones, HT-29 N9 cells, was selected and treated with various concentrations of the natural chemopreventive agents and subsequently challenged with NF-kappaB stimulator lipopolysaccharide (LPS), and the luciferase activities were measured. Western blot analysis of phosphorylated IkappaBalpha was performed after treatments with the natural chemopreventive agents. The effects of these agents on cell viability and apoptosis were also evaluated by a nonradioactive cell proliferation MTS assay [3-(4,5-dimethylthiazol-2-yl)-5-(3-arboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt]. Trypan blue staining, and caspase assay.

RESULTS

Treatments with the natural chemopreventive compounds resulted in different responses in the NF-kappaB-luciferase assay. ITCs such as phenethyl isothiocyanate (PEITC), sulforaphane (SUL), allyl isothiocyanate (AITC), and curcumin (CUR) strongly inhibited LPS-induced NF-kappaB-luciferase activations, whereas RES increased activation at lower dose, but inhibited activation at higher dose, and tea flavonoids and procyanidin dimers had little or no effects. ITCs, CUR, (-)-epigallocatechin-3-gallate (EGCG), and RES reduced LPS-induced IkappaBalpha phosphorylation. Furthermore, in the MTS assay, PEITC, SUL, and CUR also potently inhibited cell growth. Caspase-3 activity was induced by chemopreventive compounds, however, the kinetics of caspase-3 activation varied between these compounds within the 48-h time period.

CONCLUSIONS

These results suggest that natural chemopreventive agents have differential biological functions on the signal transduction pathways in the colon and/or colon cancer.

Reactive oxygen species as mediators of signal transduction in ischemic preconditioning

Ischemic preconditioning (IPC) is a most powerful endogenous mechanism for myocardial protection against ischemia/reperfusion injury. It is now apparent that reactive oxygen species (ROS) generated in the mitochondrial respiratory chain act as a trigger of IPC. ROS mediate signal transduction in the early phase of IPC through the posttranslational modification of redox-sensitive proteins. ROS-mediated activation of Src tyrosine kinases serves a scaffold for interaction of proteins recruited by G protein-coupled receptors and growth factor receptors that is necessary for amplification of cardioprotective signal transduction. Protein kinase C (PKC) plays a central role in this signaling cascade. A crucial target of PKC is the mitochondrial ATP-sensitive potassium channel, which acts as a trigger and a mediator of IPC. Mitogen-activated protein (MAP) kinases (extracellular signal-regulated kinase, p38 MAP kinase, and c-Jun NH(2)-terminal kinase) are thought to exist downstream of the Src-PKC signaling module, although the role of MAP kinases in IPC remains undetermined. The late phase of IPC is mediated by cardioprotective gene expression. This mechanism involves redox-sensitive activation of transcription factors through PKC and tyrosine kinase signal transduction pathways that are in common with the early phase of IPC. The effector proteins then act against myocardial necrosis and stunning presumably through alleviation of oxidative stress and Ca(2+) overload. Elucidation of IPC-mediated complex signaling processes will help in the development of more effective pharmacological approaches for prevention of myocardial ischemia/reperfusion injury.