Regulation of the proapoptotic factor FOXO1 (FKHR) in cardiomyocytes by growth factors and alpha1-adrenergic agonists

Low-Intensity Exercise Affects Cardiac Fatty Acid Oxidation by Increasing the Nuclear Content of PPARα, FOXO1, and Lipin1 in Fructose-Fed Rats

Background and Aim: Excessive fructose consumption along with a sedentary lifestyle provokes metabolic disorders and cardiovascular diseases. Fructose overload causes cardiac insulin resistance and increases reliance on fatty acid (FA) uptake and catabolism. The cardiometabolic benefits of exercise training have long been appreciated. The goal of the presented study is to shed a new light to the preventive role of exercise training on cardiac lipid metabolism in fructose-fed rats. Methods: Male Wistar rats were divided into control (C), sedentary fructose (F), and exercised fructose (EF) groups. Fructose was given as a 10% fructose solution in drinking water for 9 weeks. Low-intensity exercise training was applied for 9 weeks. The protein expression and subcellular localization of Lipin1, peroxisome proliferator-activated receptor α (PPARα), and peroxisome proliferator-activated receptor-γ coactivator 1 α (PGC1) were analyzed in the heart using Western blot. Cardiac forkhead box transcription factor 1 (FOXO1) and sirtuin 1 (SIRT1) protein levels were also evaluated. Gene expression of long-chain acyl-CoA dehydrogenase was analyzed by quantitative polymerase chain reaction. Results: Exercise training has augmented the expression of main regulators of FA oxidation in the heart and achieves its effect by increasing the nuclear content of PPARα, Lipin1, and FOXO1 compared with the fructose group (P = 0.0422, P = 0.000045, P = 0.00958, respectively). In addition, Lipin1, FOXO1, and SIRT1 were increased in nuclear extract after exercise compared with the control group (P = 0.000043, P = 0.0417, P = 0.0329, respectively). In cardiac lysate, low-intensity exercise caused significantly increased protein level of PPARα, PGC1, FOXO1, and SIRT1 compared with control (P = 0.0377, P = 0.0275, P = 0.0096, P = 0.0282, respectively) and PGC1 level compared with the fructose group (P = 0.0417). Conclusion: The obtained results imply that the heart with a metabolic burden additionally relies on FA as an energy substrate after low-intensity running.

FoxO1 is required for physiological cardiac hypertrophy induced by exercise but not by constitutively active PI3K

The insulin-like growth factor 1 receptor (IGF1R) and phosphoinositide 3-kinase p110α (PI3K) are critical regulators of exercise-induced physiological cardiac hypertrophy and provide protection in experimental models of pathological remodeling and heart failure. Forkhead box class O1 (FoxO1) is a transcription factor that regulates cardiomyocyte hypertrophy downstream of IGF1R/PI3K activation in vitro, but its role in physiological hypertrophy in vivo was unknown. We generated cardiomyocyte-specific FoxO1 knockout (cKO) mice and assessed the phenotype under basal conditions and settings of physiological hypertrophy induced by 1) swim training or 2) cardiac-specific transgenic expression of constitutively active PI3K (caPI3KTg+). Under basal conditions, male and female cKO mice displayed mild interstitial fibrosis compared with control (CON) littermates, but no other signs of cardiac pathology were present. In response to exercise training, female CON mice displayed an increase (∼21%) in heart weight normalized to tibia length vs. untrained mice. Exercise-induced hypertrophy was blunted in cKO mice. Exercise increased cardiac Akt phosphorylation and IGF1R expression but was comparable between genotypes. However, differences in Foxo3a, Hsp70, and autophagy markers were identified in hearts of exercised cKO mice. Deletion of FoxO1 did not reduce cardiac hypertrophy in male or female caPI3KTg+ mice. Cardiac Akt and FoxO1 protein expressions were significantly reduced in hearts of caPI3KTg+ mice, which may represent a negative feedback mechanism from chronic caPI3K, and negate any further effect of reducing FoxO1 in the cKO. In summary, FoxO1 contributes to exercise-induced hypertrophy. This has important implications when one is considering FoxO1 as a target for treating the diseased heart.NEW & NOTEWORTHY Regulators of exercise-induced physiological cardiac hypertrophy and protection are considered promising targets for the treatment of heart failure. Unlike pathological hypertrophy, the transcriptional regulation of physiological hypertrophy has remained largely elusive. To our knowledge, this is the first study to show that the transcription factor FoxO1 is a critical mediator of exercise-induced cardiac hypertrophy. Given that exercise-induced hypertrophy is protective, this finding has important implications when one is considering FoxO1 as a target for treating the diseased heart.

Imipridone enhances vascular relaxation via FOXO1 pathway

Cardiovascular complications are a side effect of cancer therapy, potentially through reduced blood vessel function. ONC201 (TIC10) is currently used in phase 2 clinical trials to treat high-grade gliomas. TIC10 is a phosphatidylinositol 3-kinase (PI3K)/AKT/extracellular signal-regulated kinase (ERK) inhibitor that induces apoptosis via upregulation of TNF-related apoptosis-inducing ligand, which via stimulation of FOXO and death receptor could increase eNOS upregulation. This has the potential to improve vascular function through increased NO bioavailability. Our aim was to investigate the role of TIC10 on vascular function to determine if it would affect the risk of CVD. Excised abdominal aorta from White New Zealand male rabbits were cut into rings. Vessels were incubated with TIC10 and AS1842856 (FOXO1 inhibitor) followed by cumulative doses of acetylcholine (Ach) to assess vessel function. Vessels were then processed for immunohistochemistry. Incubation of blood vessels with TIC10 resulted in enhanced vasodilatory capacity. Combination treatment with the FOXO1 inhibitor and TIC10 resulted in reduced vascular function compared to control. Immunohistochemical analysis indicated a 3-fold increase in death receptor 5 (DR5) expression in the TIC10-treated blood vessels but the addition of the FOXO1 inhibitor downregulated DR5 expression. The expression of DR4 receptor was not significantly increased in the presence of TIC10; however, addition of the FOXO1 inhibitor downregulated expression. TIC10 has the capacity to improve the function of healthy vessels when stimulated with the vasodilator Ach. This highlights its therapeutic potential not only in cancer treatment without cardiovascular side effects, but also as a possible drug to treat established CVD.

The impact of FOXO-1 to cardiac pathology in diabetes mellitus and diabetes-related metabolic abnormalities

Diabetic heart pathology has a serious social impact due to high prevalence worldwide and significant mortality/invalidation of diabetic patients suffered from cardiomyopathy. The pathogenesis of diabetic and diabetes-related cardiomyopathy is associated with progressive loss and impairment of cardiac function due to adverse effects of metabolic, prooxidant, proinflammatory, and pro-apoptotic stress factors. In the adult heart, the transcriptional factor forkhead box-1 (FOXO-1) is involved in maintaining cardiomyocytes in the homeostatic state and induction of their adaptation to metabolic and pro-oxidant stress stimuli. Insulin inhibits cardiac FOXO-1 expression/activity through the IRS1/Akt signaling in order to prevent gluconeogenesis. In diabetes and insulin resistance, both insulin production and insulin-dependent signaling is weakened or absent. Indeed, FOXO-1 becomes overproduced/overactivated in response to stress stimuli. In diabetic cardiac tissue, FOXO-1 overactivity induces the metabolic switch from the glucose uptake to the predominant lipid uptake. FOXO-1 limits mitochondrial glucose oxidation by stimulation of pyruvate dehydrogenase kinase 4 (PDK4) and increases the lipid uptake through up-regulation of surface expression of CD36. In cardiac muscle cells, lipid accumulation leads to lipotoxicity via increased lipid oxidation, oxidative stress, and cardiomyocyte apoptosis. Indeed, cardiac FOXO-1 levels and activity should be strictly regulated. FOXO-1 deregulation (that is observed in the diabetic heart) causes detrimental effects that finally lead to heart failure.

Posttranslational modulation of FoxO1 contributes to cardiac remodeling in post-ischemic heart failure

OBJECTIVE

Forkhead box protein O1 (FoxO1) plays a key role in energy homeostasis, stress response and autophagy and is dysregulated in diabetes and ischemia. We investigated cardiac FoxO1 expression and posttranstranslational modifications after myocardial infarction (MI) and further tested if active posttranstranslational modulation of FoxO1 can alter cardiac remodeling in postischemic heart failure.

METHODS

Non-diabetic and diabetic C57BL/6 mice were subjected to MI by ligation of left anterior descending artery. In selected experiments we combined this model with intramyocardial injection of adenovirus expressing different isoforms of FoxO1. We used Millar catheter, histology, Western blot and metabolomics for further analyses.

RESULTS

We show that after MI total cardiac FoxO1 is downregulated and partly recovers after 7 days. This downregulation is accompanied by fundamental posttranslational modifications of FoxO1, particularly acetylation. Adenovirus experiments revealed smaller infarction size and improved heart function in mice expressing a constitutively deacetylated variant of FoxO1 compared to a wild type variant of FoxO1 in both non-diabetic (MI size: -13.4 ± 3.5%; LVDP: +29.1 ± 9.4  mmHg; p < 0.05) and diabetic mice (MI size: -17.6 ± 3.7%; LVDP: +10.9 ± 3.6  mmHg; p < 0.05). Metabolomics analyses showed alterations in metabolites connected to muscle breakdown, collagen/elastin and energy metabolism between the two groups.

CONCLUSION

First, our results demonstrate that myocardial ischemia is associated with downregulation and posttranslational modification of cardiac FoxO1. Second, we show in a mouse model of postischemic heart failure that posttranslational modulation of FoxO1 alters heart function involving collagen and protein metabolism. Therefore, posttranslational modifications of FoxO1 could be an option to target remodeling processes in postischemic heart failure.

Forkhead box transcription factor 1: role in the pathogenesis of diabetic cardiomyopathy

Diabetic cardiomyopathy (DCM) is a disorder of the heart muscle in people with diabetes that can occur independent of hypertension or vascular disease. The underlying mechanism of DCM is incompletely understood. Some transcription factors have been suggested to regulate the gene program intricate in the pathogenesis of diabetes prompted cardiac injury. Forkhead box transcription factor 1 is a pleiotropic transcription factor that plays a pivotal role in a variety of physiological processes. Altered FOXO1 expression and function have been associated with cardiovascular diseases, and the important role of FOXO1 in DCM has begun to attract attention. In this review, we focus on the FOXO1 pathway and its role in various processes that have been related to DCM, such as metabolism, oxidative stress, endothelial dysfunction, inflammation and apoptosis.

Association study to evaluate FoxO1 and FoxO3 gene in CHD in Han Chinese

Background

Coronary heart disease (CHD) is one of the leading causes of mortality and morbidity in China. Genetic factors that predispose individuals to CHD are unclear. In the present study, we aimed to determine whether the variation of FoxOs, a novel genetic factor associated with longevity, was associated with CHD in Han Chinese populations.

Methods

1271 CHD patients and 1287 age-and sex-matched controls from Beijing and Harbin were included. We selected four tagging single nucleotide polymorphisms (SNPs) of FoxO1 (rs2755209, rs2721072, rs4325427 and rs17592371) and two tagging SNPs of FoxO3 (rs768023 and rs1268165). And the genotypes of these SNPs were determined in both CHD patients and non-CHD controls.

Results

For population from Beijing, four SNPs of FoxO1 and two SNPs of FoxO3 were found not to be associated with CHD (p>0.05). And this was validated in the other population from Harbin (p>0.05). After combining the two geographically isolated case-control populations, the results showed that the six SNPs did not necessarily predispose to CHD in Han Chinese(p>0.05). In stratified analysis according to gender, the history of smoking, hypertension, diabetes mellitus, hyperlipidemia and the metabolic syndrome, we further explored that neither the variants of FoxO1 nor the variants of FoxO3 might be associated with CHD (p>0.05).

Conclusion

The variants of FoxO1 and FoxO3 may not increase the prevalence of CHD in Han Chinese population.

Back to your heart: ubiquitin proteasome system-regulated signal transduction

Awareness of the regulation of cell signaling by post-translational ubiquitination has emerged over the past 2 decades. Like phosphorylation, post-translational modification of proteins with ubiquitin can result in the regulation of numerous cellular functions, for example, the DNA damage response, apoptosis, cell growth, and the innate immune response. In this review, we discuss recently published mechanisms by which the ubiquitin proteasome system regulates key signal transduction pathways in the heart, including MAPK JNK, calcineurin, FOXO, p53, and estrogen receptors α and β. We then explore how ubiquitin proteasome system-specific regulation of these signal transduction pathways plays a role in the pathophysiology of common cardiac diseases, such as cardiac hypertrophy, heart failure, ischemia reperfusion injury, and diabetes. This article is part of a Special Section entitled "Post-translational Modification."

RNA binding protein QKI inhibits the ischemia/reperfusion-induced apoptosis in neonatal cardiomyocytes

BACKGROUNDS

RNA-binding protein QKI is abundantly expressed in the brain and heart. The role of QKI in the nervous system has been well characterized, but its function in cardiac muscle is still poorly understood. The present study was to investigate the role of QKI in ischemia/reperfusion-induced apoptosis in cardiomyocytes.

METHODS

A simulated ischemia/reperfusion model was established in neonatal cardiomyocytes and adult rat heart. After QKI5 or QKI6 was expressed by adenovirus and QKI was knocked down QKI by RNAi in the cardiomyocytes, RT-PCR, western blot and immunofluorescence staining were applied to detect gene expression alterations. Apoptosis was evaluated by PARP degradation, DNA fragmentation (DNA laddering) and flow cytometry.

RESULTS

Our study demonstrated that both QKI5 and QKI6 were present in cardiomyocytes, while QKI5 expression was greatly inhibited by simulated ischemia/reperfusion. Knocking down endogenous QKI by RNAi enhanced cell susceptibility to apoptosis, whereas overexpression of either QKI5 or QKI6 suppressed IR-induced apoptosis substantially. The pro-apoptotic transcription factor FoxO1, a potential QKI target, was induced by ischemia/reperfusion at both total amount and nuclear distribution. Accordingly, FOXO1 downstream target genes were negatively affected by the presence of QKI with IR treatment.

CONCLUSION

In summary, our study supports that both QKI-5 and 6 are anti-apoptotic proteins in cardiomyocytes, favoring cardiac survival via antagonizing the elevation of some pro-apoptotic factors in cardiac injury.

β-Adrenergic receptor-PI3K signaling crosstalk in mouse heart: elucidation of immediate downstream signaling cascades

Sustained β-adrenergic receptors (βAR) activation leads to cardiac hypertrophy and prevents left ventricular (LV) atrophy during LV unloading. The immediate signaling pathways downstream from βAR stimulation, however, have not been well investigated. The current study was to examine the early cardiac signaling mechanism(s) following βAR stimulation. In adult C57BL/6 mice, acute βAR stimulation induced significant increases in PI3K activity and activation of Akt and ERK1/2 in the heart, but not in lungs or livers. In contrast, the same treatment did not elicit these changes in β₁/β₂AR double knockout mice. We further showed the specificity of β₂AR in this crosstalk as treatment with formoterol, a β₂AR-selective agonist, but not dobutamine, a predominantly β₁AR agonist, activated cardiac Akt and ERK1/2. Acute βAR stimulation also significantly increased the phosphorylation of mTOR (the mammalian target of rapamycin), P70S6K, ribosomal protein S6, GSK-3α/β (glycogen synthase kinase-3α/β), and FOXO1/3a (the forkhead box family of transcription factors 1 and 3a). Moreover, acute βAR stimulation time-dependently decreased the mRNA levels of the muscle-specific E3 ligases atrogin-1 and muscle ring finger protein-1 (MuRF1) in mouse heart. Our results indicate that acute βAR stimulation in vivo affects multiple cardiac signaling cascades, including the PI3K signaling pathway, ERK1/2, atrogin-1 and MuRF1. These data 1) provide convincing evidence for the crosstalk between βAR and PI3K signaling pathways; 2) confirm the β₂AR specificity in this crosstalk in vivo; and 3) identify novel signaling factors involved in cardiac hypertrophy and LV unloading. Understanding of the intricate interplay between β₂AR activation and these signaling cascades should provide critical clues to the pathogenesis of cardiac hypertrophy and enable identification of targets for early clinical interaction of cardiac lesions.

The role of E2F-1 and downstream target genes in mediating ischemia/reperfusion injury in vivo

E2Fs are a family of transcription factors that regulate proliferation, differentiation and apoptosis in many cell types. E2F-1 is the prototypical E2F and the family member that has most often been implicated in also mediating apoptosis. To better understand the role of E2F-1 in mediating cardiomyocyte injury we initially analyzed E2F family member expression after ischemia/reperfusion (I/R) in vivo or simulated ischemia in vitro. I/R injury in vivo caused a 3.4-fold increase specifically in E2F-1 protein levels. Expression of other E2F family members did not change. To establish the role of E2F-1 in I/R we examined the response of germline deleted E2F-1 mice to I/R injury. Infarct size as a percentage of the area at risk was decreased 39.8% in E2F-1(-/-) mice compared to E2F-1(+/+) controls. Interestingly, expression of classic, E2F-1 apoptotic target genes was not altered in E2F-1 null cardiomyocytes after I/R. However, upregulation of the primary member of the Forkhead family of transcription factors, FoxO-1a, was attenuated. Consistent, with a role for FoxO-1a as an important target of E2F-1 in I/R, a number of proapoptotic FoxO-1a target genes were also altered. These results suggest that E2F-1 and FoxO-1a belong to a complex transcriptional network that may modulate myocardial cell death during I/R injury.

Cardiac triglyceride accumulation following acute lipid excess occurs through activation of a FoxO1-iNOS-CD36 pathway

Obesity due to nutrient excess leads to chronic pathologies including type 2 diabetes and cardiovascular disease. Related to nutrient excess, FoxO1 has a role in regulating fatty acid uptake and oxidation and triglyceride (TG) storage by mechanisms that are largely unresolved. We examined the mechanism behind palmitate (PA)-induced TG accumulation in cardiomyocytes. To mimic lipid excess, rat ventricular myocytes were incubated with albumin-bound PA (1 mM) or rats were administered Intralipid (20%). PA-treated cardiomyocytes showed a substantial increase in TG accumulation, accompanied by amplification of nuclear migration of phospho-p38 and FoxO1, iNOS induction, and translocation of CD36 to the plasma membrane. PA also increased Cdc42 protein and its tyrosine nitration, thereby rearranging the cytoskeleton and facilitating CD36 translocation. These effects were duplicated by TNF-α and reversed by the iNOS inhibitor 1400 W. PA increased the nuclear interaction between FoxO1 and NF-κB, reduced the nuclear presence of PGC-1α, and downregulated expression of oxidative phosphorylation proteins. In vivo a robust increase in cardiac TGs after Intralipid administration was also associated with augmentation of nuclear FoxO1 and iNOS expression. Impeding this FoxO1-iNOS-CD36 pathway could decrease cardiac lipid accumulation and oxidative/nitrosative stress and help ameliorate the cardiovascular complications associated with obesity and diabetes.

Cardiac and neuroprotection regulated by α(1)-adrenergic receptor subtypes

Sympathetic nervous system regulation by the α(1)-adrenergic receptor (AR) subtypes (α(1A), α(1B), α(1D)) is complex, whereby chronic activity can be either detrimental or protective for both heart and brain function. This review will summarize the evidence that this dual regulation can be mediated through the different α(1)-AR subtypes in the context of cardiac hypertrophy, heart failure, apoptosis, ischemic preconditioning, neurogenesis, locomotion, neurodegeneration, cognition, neuroplasticity, depression, anxiety, epilepsy, and mental illness.

A fork in the path: Developing therapeutic inroads with FoxO proteins

Advances in clinical care for disorders involving any system of the body necessitates novel therapeutic strategies that can focus upon the modulation of cellular proliferation, metabolism, inflammation and longevity. In this respect, members of the mammalian forkhead transcription factors of the O class (FoxOs) that include FoxO1, FoxO3, FoxO4 and FoxO6 are increasingly being recognized as exciting prospects for multiple disorders. These transcription factors govern development, proliferation, survival and longevity during multiple cellular environments that can involve oxidative stress. Furthermore, these transcription factors are closely integrated with several novel signal transduction pathways, such as erythropoietin and Wnt proteins, that may influence the ability of FoxOs to act as a “double-edge sword” to sometimes promote cell survival, but at other times lead to cell injury. Here we discuss the fascinating but complex role of FoxOs during cellular injury and oxidative stress, progenitor cell development, fertility, angiogenesis, cardiovascular function, cellular metabolism and diabetes, cell longevity, immune surveillance and cancer.

A hidden incoherent switch regulates RCAN1 in the calcineurin–NFAT signaling network

Regulator of calcineurin 1 (RCAN1) is a key regulator of the calcineurin–NFAT signaling network in organisms ranging from yeast to human, but its functional role is still under debate because different roles of RCAN1 have been suggested under various experimental conditions. To elucidate the mechanisms underlying the RCAN1 regulatory system, we used a systems approach by combining single-cell experimentation with in silico simulations. In particular, we found that the nuclear export of GSK3β, which switches on the facilitative role of RCAN1 in the calcineurin–NFAT signaling pathway, is promoted by PI3K signaling. Based on this, along with integrated information from previous experiments, we developed a mathematical model in which the functional role of RCAN1 changes in a dose-dependent manner: RCAN1 functions as an inhibitor when its levels are low, but as a facilitator when its levels are high. Furthermore, we identified a hidden incoherent regulation switch that mediates this role change, which entails negative regulation through RCAN1 binding to calcineurin and positive regulation through sequential phosphorylation of RCAN1.

Oxidative stress: Biomarkers and novel therapeutic pathways

Oxidative stress significantly impacts multiple cellular pathways that can lead to the initiation and progression of varied disorders throughout the body. It therefore becomes imperative to elucidate the components and function of novel therapeutic strategies against oxidative stress to further clinical diagnosis and care. In particular, both the growth factor and cytokine erythropoietin (EPO) and members of the mammalian forkhead transcription factors of the O class (FoxOs) may offer the greatest promise for new treatment regimens since these agents and the cellular pathways they oversee cover a range of critical functions that directly influence progenitor cell development, cell survival and degeneration, metabolism, immune function, and cancer cell invasion. Furthermore, both EPO and FoxOs function not only as therapeutic targets, but also as biomarkers of disease onset and progression, since their cellular pathways are closely linked and overlap with several unique signal transduction pathways. However, biological outcome with EPO and FoxOs may sometimes be both unexpected and undesirable that can raise caution for these agents and warrant further investigations. Here we present the exciting as well as complicated role EPO and FoxOs possess to uncover the benefits as well as the risks of these agents for cell biology and clinical care in processes that range from stem cell development to uncontrolled cellular proliferation.

Erythropoietin, forkhead proteins, and oxidative injury: biomarkers and biology

Oxidative stress significantly impacts multiple cellular pathways that can lead to the initiation and progression of varied disorders throughout the body. It therefore becomes imperative to elucidate the components and function of novel therapeutic strategies against oxidative stress to further clinical diagnosis and care. In particular, both the growth factor and cytokine erythropoietin (EPO), and members of the mammalian forkhead transcription factors of the O class (FoxOs), may offer the greatest promise for new treatment regimens, since these agents and the cellular pathways they oversee cover a range of critical functions that directly influence progenitor cell development, cell survival and degeneration, metabolism, immune function, and cancer cell invasion. Furthermore, both EPO and FoxOs function not only as therapeutic targets, but also as biomarkers of disease onset and progression, since their cellular pathways are closely linked and overlap with several unique signal transduction pathways. Yet, EPO and FoxOs may sometimes have unexpected and undesirable effects that can raise caution for these agents and warrant further investigations. Here we present the exciting as well as the complex role that EPO and FoxOs possess to uncover the benefits as well as the risks of these agents for cell biology and clinical care in processes that range from stem cell development to uncontrolled cellular proliferation.

ErbB receptors protect the perfused heart against injury induced by epinephrine combined with low-flow ischemia

ErbB receptor tyrosine kinases are important in maintaining the long-term structural integrity of the heart and in the induction of hypertrophy. In addition, in vivo activation of ErbB1 by epidermal growth factor (EGF) protects the heart against acute stress-induced damage. We examined here whether the ErbB sytem acutely protects the isolated heart in which stress was induced in vitro by ischemia combined with epinephrine infusion (EPI). In perfused mouse hearts, EGF induced Tyr-phosphorylation of ErbB1 but not ErbB2. Neuregulin-1beta (NRG-1beta) induced Tyr-phosphorylation of both ErbB4 and ErbB2. We also found differences in the signaling cascades activated by each growth factor. To stress the perfused mouse heart, we combined EPI with low-flow ischemia. This resulted in (i) loss of left ventricle contraction force ( + dP/dt(max)) and developed pressure (LVDP) after a short period of hypercontractility, (ii) enhanced anaerobic metabolism (lactate production), and (iii) myocyte injury (lactate dehydrogenase (LDH) release). EGF and NRG-1beta had different effects on stressed-heart contractility. EGF reduced to a half the loss of both + dP/dt(max) and LVDP. In contrast, NRG-1beta exacerbated the hypercontractility soon after reperfusion. This is coincident with a transient increase in coronary flow after reperfusion. In spite of these differences in contraction, both EGF and NRG-1beta induced similar early protection as shown by the reduction of LDH release. Our results show that the ErbB system protects the perfused heart against damage induced by acute stress. They reinforce the relevance of ErbB receptors and ligands in cardiac physiology.

FoxO proteins: cunning concepts and considerations for the cardiovascular system. Clin Sci (Lond). 2009;116:191-203. [PMID: 19118491 DOI: 10.1042/cs20080113]

Dysfunction in the cardiovascular system can lead to the progression of a number of disease entities that can involve cancer, diabetes, cardiac ischaemia, neurodegeneration and immune system dysfunction. In order for new therapeutic avenues to overcome some of the limitations of present clinical treatments for these disorders, future investigations must focus upon novel cellular processes that control cellular development, proliferation, metabolism and inflammation. In this respect, members of the mammalian forkhead transcription factors of the O class (FoxOs) have increasingly become recognized as important and exciting targets for disorders of the cardiovascular system. In the present review, we describe the role of these transcription factors in the cardiovascular system during processes that involve angiogenesis, cardiovascular development, hypertension, cellular metabolism, oxidative stress, stem cell proliferation, immune system regulation and cancer. Current knowledge of FoxO protein function combined with future studies should continue to lay the foundation for the successful translation of these transcription factors into novel and robust clinical therapies.

FoxO proteins and cardiac pathology

The FoxO family of transcription factors mediate a wide range of cellular responses from cell death to cell survival, growth inhibition and glucose utilization. This complex array of responses is regulated by an equally complex regulatory system, involving phosphorylation, ubiquitinization and acetylation, in addition to interactions with other transcription factors and transcriptional modifiers. In heart, FoxO proteins have been shown to be involved in development in limiting hypertrophic growth responses and in cardioprotection provided by silent information regulator 1 (Sirt1). However, the range of responses mediated by FoxO proteins and the clear evidence for involvement of FoxO regulators in cardiac pathology, suggest that further pathological actions of FoxO family members remain to be elucidated.

Protein O-GlcNAcylation: a new signaling paradigm for the cardiovascular system

The posttranslational modification of serine and threonine residues of nuclear and cytoplasmic proteins by the O-linked attachment of the monosaccharide beta-N-acetylglucosamine (O-GlcNAc) is a highly dynamic and ubiquitous protein modification. Protein O-GlcNAcylation is rapidly emerging as a key regulator of critical biological processes including nuclear transport, translation and transcription, signal transduction, cytoskeletal reorganization, proteasomal degradation, and apoptosis. Increased levels of O-GlcNAc have been implicated as a pathogenic contributor to glucose toxicity and insulin resistance, which are both major hallmarks of diabetes mellitus and diabetes-related cardiovascular complications. Conversely, there is a growing body of data demonstrating that the acute activation of O-GlcNAc levels is an endogenous stress response designed to enhance cell survival. Reports on the effect of altered O-GlcNAc levels on the heart and cardiovascular system have been growing rapidly over the past few years and have implicated a role for O-GlcNAc in contributing to the adverse effects of diabetes on cardiovascular function as well as mediating the response to ischemic injury. Here, we summarize our present understanding of protein O-GlcNAcylation and its effect on the regulation of cardiovascular function. We examine the pathways regulating protein O-GlcNAcylation and discuss, in more detail, our understanding of the role of O-GlcNAc in both mediating the adverse effects of diabetes as well as its role in mediating cellular protective mechanisms in the cardiovascular system. In addition, we also explore the parallels between O-GlcNAc signaling and redox signaling, as an alternative paradigm for understanding the role of O-GlcNAcylation in regulating cell function.

The "O" class: crafting clinical care with FoxO transcription factors

Forkhead Transcription Factors: Vital Elements in Biology and Medicine provides a unique platform for the presentation of novel work and new insights into the vital role that forkhead transcription factors play in both cellular physiology as well as clinical medicine. Internationally recognized investigators provide their insights and perspectives for a number of forkhead genes and proteins that may have the greatest impact for the development of new strategies for a broad array of disorders that can involve aging, cancer, cardiac function, neurovascular integrity, fertility, stem cell differentiation, cellular metabolism, and immune system regulation. Yet, the work clearly sets a precedent for the necessity to understand the cellular and molecular function of forkhead proteins since this family of transcription factors can limit as well as foster disease progression depending upon the cellular environment. With this in mind, our concluding chapter for Forkhead Transcription Factors: Vital Elements in Biology andMedicine offers to highlight both the diversity and complexity of the forkhead transcription family by focusing upon the mammalian forkhead transcription factors of the O class (FoxOs) that include FoxO1, FoxO3, FoxO4, and FoxO6. FoxO proteins are increasingly considered to represent unique cellular targets that can control numerous processes such as angiogenesis, cardiovascular development, vascular tone, oxidative stress, stem cell proliferation, fertility, and immune surveillance. Furthermore, FoxO transcription factors are exciting considerations for disorders such as cancer in light of their pro-apoptotic and inhibitory cell cycle effects as well as diabetes mellitus given the close association FoxOs hold with cellular metabolism. In addition, these transcription factors are closely integrated with several novel signal transduction pathways, such as erythropoietin and Wnt proteins, that may influence the ability of FoxOs to lead to cell survival or cell injury. Further understanding of both the function and intricate nature of the forkhead transcription factor family, and in particular the FoxO proteins, should allow selective regulation of cellular development or cellular demise for the generation of successful future clinical strategies and patient well-being.

Forkhead transcription factors and cardiovascular biology

The Forkhead family of transcription factors modulates a wide variety of cellular functions in cardiovascular tissues. In this review article, we discuss recent advances in our understanding of regulation provided by the forkhead factors in cardiac myocytes and vascular cells.

Identification of the prosurvival activity of nerve growth factor on cardiac myocytes

Neurotrophins (NTs) control neuron survival and regeneration. Recent research showed that NTs possess cardiovascular actions. In this study, we investigated the hypothesis that the NT nerve growth factor (NGF) prevents cardiomyocyte apoptosis. We demonstrated that cultured rat neonatal cardiomyocytes (RNCMs) produce NGF and express its trkA (tropomyosin-related receptor A (NGF high-affinity receptor)) receptor. RNCMs given a neutralizing antibody for NGF or the trkA inhibitor K252a underwent apoptosis, thus suggesting that NGF is an endogenous prosurvival factor for cardiomyocytes. Adenovirus (Ad)-mediated NGF overexpression protected RNCMs from apoptosis induced by either hypoxia/reoxygenation or angiotensin II (AngII). Similarly, recombinant NGF inhibited AngII-induced apoptosis in isolated rat adult cardiomyocytes. Finally, in a rat model of myocardial infarction, NGF gene transfer promoted cardiomyocyte survival. In RNCMs, recombinant NGF induced trkA phosphorylation, followed by Ser473 phosphorylation and nuclear translocation of phospho-protein kinase B (Akt). In response to Akt activation, Forkhead transcription factors Foxo-3a and Foxo-1 were phosphorylated and excluded from the nucleus. The prosurvival effect of adenoviral vector carrying the human NGF gene was inhibited in vitro by K252a, LY294002 (a pan-phosphatidyl inositol 3-kinase - PI3K - inhibitor), an Akt small interfering RNA, and adenoviruses carrying a dominant negative mutant form of Akt (Ad.DN.Akt) or an Akt-resistant Foxo-3a (Ad.AAA-Foxo-3a). These results newly demonstrate the cardiac prosurvival action of NGF and provide mechanistic information on the signaling pathway, which encompasses trkA, PI3K-Akt, and Foxo.

Transcriptional factor FOXL2 interacts with DP103 and induces apoptosis

Blepharophimosis-ptosis-epicanthus inversus syndrome type I is an autosomal disorder caused by mutations in FOXL2 gene and associated with premature ovarian failure in women by a dominant inheritance. FOXL2 is a recently identified protein that belongs to forkhead family transcription factor, of which signaling pathways are still unknown. Here, we show that FOXL2 induces apoptosis in both Chinese hamster ovary cells and rat granulosa cells, and it interacts with DP103, a DEAD box-containing protein. Overexpression of DP103 itself did not affect cell viability while its coexpression with FOXL2 led to the potentiation of cell death. Our results present previously undiscovered functions of these proteins, an apoptotic activity of FOXL2 in the ovary and a modulating activity of DP103 by interacting with FOXL2.