Targeted inhibition of p38 MAPK promotes hypertrophic cardiomyopathy through upregulation of calcineurin-NFAT signaling

Role of Mitogen-Activated Protein (MAP) Kinase Pathways in Metabolic Diseases

Physiological processes that govern the normal functioning of mammalian cells are regulated by a myriad of signalling pathways. Mammalian mitogen-activated protein (MAP) kinases constitute one of the major signalling arms and have been broadly classified into four groups that include extracellular signal-regulated protein kinase (ERK), c-Jun N-terminal kinase (JNK), p38, and ERK5. Each signalling cascade is governed by a wide array of external and cellular stimuli, which play a critical part in mammalian cells in the regulation of various key responses, such as mitogenic growth, differentiation, stress responses, as well as inflammation. This evolutionarily conserved MAP kinase signalling arm is also important for metabolic maintenance, which is tightly coordinated via complicated mechanisms that include the intricate interaction of scaffold proteins, recognition through cognate motifs, action of phosphatases, distinct subcellular localisation, and even post-translational modifications. Aberration in the signalling pathway itself or their regulation has been implicated in the disruption of metabolic homeostasis, which provides a pathophysiological foundation in the development of metabolic syndrome. Metabolic syndrome is an umbrella term that usually includes a group of closely associated metabolic diseases such as hyperglycaemia, hyperlipidaemia, and hypertension. These risk factors exacerbate the development of obesity, diabetes, atherosclerosis, cardiovascular diseases, and hepatic diseases, which have accounted for an increase in the worldwide morbidity and mortality rate. This review aims to summarise recent findings that have implicated MAP kinase signalling in the development of metabolic diseases, highlighting the potential therapeutic targets of this pathway to be investigated further for the attenuation of these diseases.

MKK6 deficiency promotes cardiac dysfunction through MKK3-p38γ/δ-mTOR hyperactivation

Stress-activated p38 kinases control a plethora of functions, and their dysregulation has been linked to the development of steatosis, obesity, immune disorders, and cancer. Therefore, they have been identified as potential targets for novel therapeutic strategies. There are four p38 family members (p38α, p38β, p38γ, and p38δ) that are activated by MKK3 and MKK6. Here, we demonstrate that lack of MKK6 reduces the lifespan in mice. Longitudinal study of cardiac function in MKK6 KO mice showed that young mice develop cardiac hypertrophy which progresses to cardiac dilatation and fibrosis with age. Mechanistically, lack of MKK6 blunts p38α activation while causing MKK3-p38γ/δ hyperphosphorylation and increased mammalian target of rapamycin (mTOR) signaling, resulting in cardiac hypertrophy. Cardiac hypertrophy in MKK6 KO mice is reverted by knocking out either p38γ or p38δ or by inhibiting the mTOR pathway with rapamycin. In conclusion, we have identified a key role for the MKK3/6-p38γ/δ pathway in the development of cardiac hypertrophy, which has important implications for the clinical use of p38α inhibitors in the long-term treatment since they might result in cardiotoxicity.

Cardiomyocyte p38 MAPKα suppresses a heart-adipose tissue-neutrophil crosstalk in heart failure development

Although p38 MAP Kinase α (p38 MAPKα) is generally accepted to play a central role in the cardiac stress response, to date its function in maladaptive cardiac hypertrophy is still not unambiguously defined. To induce a pathological type of cardiac hypertrophy we infused angiotensin II (AngII) for 2 days via osmotic mini pumps in control and tamoxifen-inducible, cardiomyocyte (CM)-specific p38 MAPKα KO mice (iCMp38αKO) and assessed cardiac function by echocardiography, complemented by transcriptomic, histological, and immune cell analysis. AngII treatment after inactivation of p38 MAPKα in CM results in left ventricular (LV) dilatation within 48 h (EDV: BL: 83.8 ± 22.5 µl, 48 h AngII: 109.7 ± 14.6 µl) and an ectopic lipid deposition in cardiomyocytes, reflecting a metabolic dysfunction in pressure overload (PO). This was accompanied by a concerted downregulation of transcripts for oxidative phosphorylation, TCA cycle, and fatty acid metabolism. Cardiac inflammation involving neutrophils, macrophages, B- and T-cells was significantly enhanced. Inhibition of adipose tissue lipolysis by the small molecule inhibitor of adipocytetriglyceride lipase (ATGL) Atglistatin reduced cardiac lipid accumulation by 70% and neutrophil infiltration by 30% and went along with an improved cardiac function. Direct targeting of neutrophils by means of anti Ly6G-antibody administration in vivo led to a reduced LV dilation in iCMp38αKO mice and an improved systolic function (EF: 39.27 ± 14%). Thus, adipose tissue lipolysis and CM lipid accumulation augmented cardiac inflammation in iCMp38αKO mice. Neutrophils, in particular, triggered the rapid left ventricular dilatation. We provide the first evidence that p38 MAPKα acts as an essential switch in cardiac adaptation to PO by mitigating metabolic dysfunction and inflammation. Moreover, we identified a heart-adipose tissue-immune cell crosstalk, which might serve as new therapeutic target in cardiac pathologies.

Effects of Various Muscle Disuse States and Countermeasures on Muscle Molecular Signaling

Skeletal muscle is capable of changing its structural parameters, metabolic rate and functional characteristics within a wide range when adapting to various loading regimens and states of the organism. Prolonged muscle inactivation leads to serious negative consequences that affect the quality of life and work capacity of people. This review examines various conditions that lead to decreased levels of muscle loading and activity and describes the key molecular mechanisms of muscle responses to these conditions. It also details the theoretical foundations of various methods preventing adverse muscle changes caused by decreased motor activity and describes these methods. A number of recent studies presented in this review make it possible to determine the molecular basis of the countermeasure methods used in rehabilitation and space medicine for many years, as well as to identify promising new approaches to rehabilitation and to form a holistic understanding of the mechanisms of gravity force control over the muscular system.

Nicotinamide promotes cardiomyocyte derivation and survival through kinase inhibition in human pluripotent stem cells

Nicotinamide, the amide form of Vitamin B3, is a common nutrient supplement that plays important role in human fetal development. Nicotinamide has been widely used in clinical treatments, including the treatment of diseases during pregnancy. However, its impacts during embryogenesis have not been fully understood. In this study, we show that nicotinamide plays multiplex roles in mesoderm differentiation of human embryonic stem cells (hESCs). Nicotinamide promotes cardiomyocyte fate from mesoderm progenitor cells, and suppresses the emergence of other cell types. Independent of its functions in PARP and Sirtuin pathways, nicotinamide modulates differentiation through kinase inhibition. A KINOMEscan assay identifies 14 novel nicotinamide targets among 468 kinase candidates. We demonstrate that nicotinamide promotes cardiomyocyte differentiation through p38 MAP kinase inhibition. Furthermore, we show that nicotinamide enhances cardiomyocyte survival as a Rho-associated protein kinase (ROCK) inhibitor. This study reveals nicotinamide as a pleiotropic molecule that promotes the derivation and survival of cardiomyocytes, and it could become a useful tool for cardiomyocyte production for regenerative medicine. It also provides a theoretical foundation for physicians when nicotinamide is considered for treatments for pregnant women.

A Review of Calcineurin Biophysics with Implications for Cardiac Physiology

Calcineurin, also known as protein phosphatase 2B, is a heterodimeric serine threonine phosphatase involved in numerous signaling pathways. During the past 50 years, calcineurin has been the subject of extensive investigation. Many of its cellular and physiological functions have been described, and the underlying biophysical mechanisms are the subject of active investigation. With the abundance of techniques and experimental designs utilized to study calcineurin and its numerous substrates, it is difficult to reconcile the available information. There have been a plethora of reports describing the role of calcineurin in cardiac disease. However, a physiological role of calcineurin in healthy cardiomyocyte function requires clarification. Here, we review the seminal biophysical and structural details that are responsible for the molecular function and inhibition of calcineurin. We then focus on literature describing the roles of calcineurin in cardiomyocyte physiology and disease.

Maternal Fructose Intake Exacerbates Cardiac Remodeling in Offspring with Ventricular Pressure Overload

Recent studies demonstrated that metabolic syndrome and cardiovascular diseases could be elicited by developmental programming, which is regulated by prenatal nutritional and environmental stress. In this study, we utilized a rat model to examine the effect of excessive maternal fructose intake during pregnancy and lactation on cardiac development and progression of pressure overload-induced cardiac hypertrophy in offspring. Transverse aortic constriction (TAC) was performed on 3-month-old male offspring to induce ventricular pressure overload. Four weeks post-TAC, echocardiographic assessment as well as histopathological and biochemical examinations were performed on the myocardium of the offspring. Echocardiographic and gross examinations showed that heart weight, interventricular septal thickness in diastole (IVD; d), and left ventricular posterior wall thickness in diastole (LVPW; d) were elevated in offspring with TAC and further increased by maternal fructose exposure (MFE). However, the left ventricular ejection function was not significantly affected. Myocardial histopathological examination revealed that the indices of fibrosis and oxidative stress were higher in offspring with MFE and TAC than those in animals receiving either treatment. Molecular examinations on the myocardium demonstrated an MFE-induced upregulation of p38-MAPK signaling. Next generation sequence (NGS) analysis indicated a modulation of the expression levels of several cardiac hypertrophy-associated genes, including GPR22, Myh7, Nppa, P2RX4, and Npy by MFE. Subsequent RT-PCR indicated that MFE regulated the expression levels of genes responsive to cardiac hypertrophy (i.e., Myh-7, ANP) and oxidative stress (i.e., GR, GPx, and NQO-1). In conclusion, MFE during pregnancy and lactation modulated myocardial gene expression, increased oxidative stress, and exacerbated ventricular pressure overload-induced cardiac remodeling in rat offspring.

Meteorin-like/Meteorin-β protects heart against cardiac dysfunction

Meteorin-like/Meteorin-β (Metrnl/Metrnβ) is a secreted protein produced by skeletal muscle and adipose tissue that exerts metabolic actions that improve glucose metabolism. The role of Metrnβ in cardiac disease is completely unknown. Here, we show that Metrnβ-null mice exhibit asymmetrical cardiac hypertrophy, fibrosis, and enhanced signs of cardiac dysfunction in response to isoproterenol-induced cardiac hypertrophy and aging. Conversely, adeno-associated virus-mediated specific overexpression of Metrnβ in the heart prevents the development of cardiac remodeling. Furthermore, Metrnβ inhibits cardiac hypertrophy development in cardiomyocytes in vitro, indicating a direct effect on cardiac cells. Antibody-mediated blockage of Metrnβ in cardiomyocyte cell cultures indicated an autocrine action of Metrnβ on the heart, in addition to an endocrine action. Moreover, Metrnβ is highly produced in the heart, and analysis of circulating Metrnβ concentrations in a large cohort of patients reveals that it is a new biomarker of heart failure with an independent prognostic value.

Molecular regulation of myocardial proliferation and regeneration

Heart regeneration is a fascinating and complex biological process. Decades of intensive studies have revealed a sophisticated molecular network regulating cardiac regeneration in the zebrafish and neonatal mouse heart. Here, we review both the classical and recent literature on the molecular and cellular mechanisms underlying heart regeneration, with a particular focus on how injury triggers the cell-cycle re-entry of quiescent cardiomyocytes to replenish their massive loss after myocardial infarction or ventricular resection. We highlight several important signaling pathways for cardiomyocyte proliferation and propose a working model of how these injury-induced signals promote cardiomyocyte proliferation. Thus, this concise review provides up-to-date research progresses on heart regeneration for investigators in the field of regeneration biology.

Branched-chain α-ketoacids are preferentially reaminated and activate protein synthesis in the heart

Branched-chain amino acids (BCAA) and their cognate α-ketoacids (BCKA) are elevated in an array of cardiometabolic diseases. Here we demonstrate that the major metabolic fate of uniformly-¹³C-labeled α-ketoisovalerate ([U-¹³C]KIV) in the heart is reamination to valine. Activation of cardiac branched-chain α-ketoacid dehydrogenase (BCKDH) by treatment with the BCKDH kinase inhibitor, BT2, does not impede the strong flux of [U-¹³C]KIV to valine. Sequestration of BCAA and BCKA away from mitochondrial oxidation is likely due to low levels of expression of the mitochondrial BCAA transporter SLC25A44 in the heart, as its overexpression significantly lowers accumulation of [¹³C]-labeled valine from [U-¹³C]KIV. Finally, exposure of perfused hearts to levels of BCKA found in obese rats increases phosphorylation of the translational repressor 4E-BP1 as well as multiple proteins in the MEK-ERK pathway, leading to a doubling of total protein synthesis. These data suggest that elevated BCKA levels found in obesity may contribute to pathologic cardiac hypertrophy via chronic activation of protein synthesis.

Systemic modulation of branched-chain keto acid (BCKA) metabolism alters cardiac health. Here, the authors define the major fates of BCKA in the heart and demonstrate that acute exposure to BCKA levels found in obesity activates cardiac protein synthesis and markedly alters the heart phosphoproteome.

MK2-Deficient Mice Are Bradycardic and Display Delayed Hypertrophic Remodeling in Response to a Chronic Increase in Afterload

Background

Mitogen‐activated protein kinase–activated protein kinase‐2 (MK2) is a protein serine/threonine kinase activated by p38α/β. Herein, we examine the cardiac phenotype of pan MK2‐null (MK2^−/−) mice.

Methods and Results

Survival curves for male MK2^+/+ and MK2^−/− mice did not differ (Mantel‐Cox test, P=0.580). At 12 weeks of age, MK2^−/− mice exhibited normal systolic function along with signs of possible early diastolic dysfunction; however, aging was not associated with an abnormal reduction in diastolic function. Both R‐R interval and P‐R segment durations were prolonged in MK2‐deficient mice. However, heart rates normalized when isolated hearts were perfused ex vivo in working mode. Ca²⁺ transients evoked by field stimulation or caffeine were similar in ventricular myocytes from MK2^+/+ and MK2^−/− mice. MK2^−/− mice had lower body temperature and an age‐dependent reduction in body weight. mRNA levels of key metabolic genes, including Ppargc1a, Acadm, Lipe, and Ucp3, were increased in hearts from MK2^−/− mice. For equivalent respiration rates, mitochondria from MK2^−/− hearts showed a significant decrease in Ca²⁺ sensitivity to mitochondrial permeability transition pore opening. Eight weeks of pressure overload increased left ventricular mass in MK2^+/+ and MK2^−/− mice; however, after 2 weeks the increase was significant in MK2^+/+ but not MK2^−/− mice. Finally, the pressure overload–induced decrease in systolic function was attenuated in MK2^−/− mice 2 weeks, but not 8 weeks, after constriction of the transverse aorta.

Conclusions

Collectively, these results implicate MK2 in (1) autonomic regulation of heart rate, (2) cardiac mitochondrial function, and (3) the early stages of myocardial remodeling in response to chronic pressure overload.

Plantar Mechanical Stimulation Maintains Slow Myosin Expression in Disused Rat Soleus Muscle via NO-Dependent Signaling

It was observed that gravitational unloading during space missions and simulated microgravity in ground-based studies leads to both transformation of slow-twitch muscle fibers into fast-twitch fibers and to the elimination of support afferentation, leading to the "switching-off" of postural muscle motor units electrical activity. In recent years, plantar mechanical stimulation (PMS) has been found to maintain the neuromuscular activity of the hindlimb muscles. Nitric oxide (NO) was shown to be one of the mediators of muscle fiber activity, which can also promote slow-type myosin expression. We hypothesized that applying PMS during rat hindlimb unloading would lead to NO production upregulation and prevention of the unloading-induced slow-to-fast fiber-type shift in rat soleus muscles. To test this hypothesis, Wistar rats were hindlimb suspended and subjected to daily PMS, and one group of PMS-subjected animals was also treated with nitric oxide synthase inhibitor (L-NAME). We discovered that PMS led to sustained NO level in soleus muscles of the suspended animals, and NOS inhibitor administration blocked this effect, as well as the positive effects of PMS on myosin I and IIa mRNA transcription and slow-to-fast fiber-type ratio during rat hindlimb unloading. The results of the study indicate that NOS activity is necessary for the PMS-mediated prevention of slow-to-fast fiber-type shift and myosin I and IIa mRNA transcription decreases during rat hindlimb unloading.

Therapeutic effects of histone deacetylase inhibitors on heart disease

A wide range of histone deacetylase (HDAC) inhibitors have been studied for their therapeutic potential because the excessive activity and expression of HDACs have been implicated in the pathogenesis of cardiac diseases. An increasing number of preclinical studies have demonstrated the cardioprotective effects of numerous HDAC inhibitors, suggesting a wide variety of mechanisms by which the inhibitors protect against cardiac stress, such as the suppression of cardiac fibrosis and fetal gene expression, enhancement of angiogenesis and mitochondrial biogenesis, prevention of electrical remodeling, and regulation of apoptosis, autophagy, and cell cycle arrest. For the development of isoform-selective HDAC inhibitors with high efficacy and low toxicity, it is important to identify and understand the mechanisms responsible for the effects of the inhibitors. This review highlights the preclinical effects of HDAC inhibitors that act against Zn²⁺-dependent HDACs and the underlying mechanisms of their protective effects against cardiac hypertrophy, hypertension, myocardial infarction, heart failure, and atrial fibrillation.

p38 MAPK Pathway in the Heart: New Insights in Health and Disease

The p38 mitogen-activated kinase (MAPK) family controls cell adaptation to stress stimuli. p38 function has been studied in depth in relation to cardiac development and function. The first isoform demonstrated to play an important role in cardiac development was p38α; however, all p38 family members are now known to collaborate in different aspects of cardiomyocyte differentiation and growth. p38 family members have been proposed to have protective and deleterious actions in the stressed myocardium, with the outcome of their action in part dependent on the model system under study and the identity of the activated p38 family member. Most studies to date have been performed with inhibitors that are not isoform-specific, and, consequently, knowledge remains very limited about how the different p38s control cardiac physiology and respond to cardiac stress. In this review, we summarize the current understanding of the role of the p38 pathway in cardiac physiology and discuss recent advances in the field.

NO-Dependent Mechanisms of Myosin Heavy Chain Transcription Regulation in Rat Soleus Muscle After 7-Days Hindlimb Unloading

It is known that nitric oxide (NO) may affect myosin heavy chain (MyHC) isoform mRNA transcription in skeletal muscles. The content of NO in soleus muscles decreases during rat hindlimb unloading as well as slow MyHC mRNA transcription. We aimed to detect which signaling pathways are involved in NO-dependent prevention of hindlimb-suspension (HS)-induced changes in MyHCs’ expression pattern. Male Wistar rats were divided into four groups: cage control group (C), hindlimb suspended for 7 days (7HS), hindlimb suspended for 7 days with L-arginine administration (7HS+A) (500 mg/kg body mass), and hindlimb suspended for 7 days with both L-arginine (500 mg/kg) and NO-synthase inhibitor L-NAME administration (50 mg/kg) (7HS+A+N). L-arginine treatment during 7 days of rat HS prevented HS-induced NO content decrease and slow MyHC mRNA transcription decrease and attenuated fast MyHC IIb mRNA transcription increase; it also prevented NFATc1 nuclear content decrease, calsarcin-2 expression increase, and GSK-3β Ser 9 phosphorylation decrease. Moreover, L-arginine administration prevented the HS-induced myh7b and PGC1α mRNAs content decreases and slow-type genes repressor SOX6 mRNA transcription increase. All these slow fiber-type protective effects of L-arginine were blocked in HS+A+N group, indicating that these effects were NO-dependent. Thus, NO decrease prevention during HS restores calcineurin/NFATc1 and myh7b/SOX6 signaling.

Reviewing the Limitations of Adult Mammalian Cardiac Regeneration: Noncoding RNAs as Regulators of Cardiomyogenesis

The adult mammalian heart is incapable of regeneration following cardiac injury, leading to a decline in function and eventually heart failure. One of the most evident barriers limiting cardiac regeneration is the inability of cardiomyocytes to divide. It has recently become clear that the mammalian heart undergoes limited cardiomyocyte self-renewal throughout life and is even capable of modest regeneration early after birth. These exciting findings have awakened the goal to promote cardiomyogenesis of the human heart to repair cardiac injury or treat heart failure. We are still far from understanding why adult mammalian cardiomyocytes possess only a limited capacity to proliferate. Identifying the key regulators may help to progress towards such revolutionary therapy. Specific noncoding RNAs control cardiomyocyte division, including well explored microRNAs and more recently emerged long noncoding RNAs. Elucidating their function and molecular mechanisms during cardiomyogenesis is a prerequisite to advance towards therapeutic options for cardiac regeneration. In this review, we present an overview of the molecular basis of cardiac regeneration and describe current evidence implicating microRNAs and long noncoding RNAs in this process. Current limitations and future opportunities regarding how these regulatory mechanisms can be harnessed to study myocardial regeneration will be addressed.

The POU4F2/Brn-3b transcription factor is required for the hypertrophic response to angiotensin II in the heart

Adult hearts respond to increased workload such as prolonged stress or injury, by undergoing hypertrophic growth. During this process, the early adaptive responses are important for maintaining cardiac output whereas at later stages, pathological responses such as cardiomyocyte apoptosis and fibrosis cause adverse remodelling, that can progress to heart failure. Yet the factors that control transition from adaptive responses to pathological remodelling in the heart are not well understood. Here we describe the POU4F2/Brn-3b transcription factor (TF) as a novel regulator of adaptive hypertrophic responses in adult hearts since Brn-3b mRNA and protein are increased in angiotensin-II (AngII) treated mouse hearts with concomitant hypertrophic changes [increased heart weight:body weight (HW:BW) ratio]. These effects occur specifically in cardiomyocytes because Brn-3b expression is increased in AngII-treated primary cultures of neonatal rat ventricular myocytes (NRVM) or foetal heart-derived H9c2 cells, which undergo characteristic sarcomeric re-organisation seen in hypertrophic myocytes and express hypertrophic markers, ANP/βMHC. The Brn-3b promoter is activated by known hypertrophic signalling pathways e.g. p42/p44 mitogen-activated protein kinase (MAPK/ERK1/2) or calcineurin (via NFAT). Brn-3b target genes, e.g. cyclin D1, GLUT4 and Bax, are increased at different stages following AngII treatment, supporting distinct roles in cardiac responses to stress. Furthermore, hearts from male Brn-3b KO mutant mice display contractile dysfunction at baseline but also attenuated hypertrophic responses to AngII treatment. Hearts from AngII-treated male Brn-3b KO mice develop further contractile dysfunction linked to extensive fibrosis/remodelling. Moreover, known Brn-3b target genes, e.g. GLUT4, are reduced in AngII-treated Brn-3b KO hearts, suggesting that Brn-3b and its target genes are important in driving adaptive hypertrophic responses in stressed heart.

Cardiac Fibroblast p38 MAPK: A Critical Regulator of Myocardial Remodeling

The cardiac fibroblast is a remarkably versatile cell type that coordinates inflammatory, fibrotic and hypertrophic responses in the heart through a complex array of intracellular and intercellular signaling mechanisms. One important signaling node that has been identified involves p38 MAPK; a family of kinases activated in response to stress and inflammatory stimuli that modulates multiple aspects of cardiac fibroblast function, including inflammatory responses, myofibroblast differentiation, extracellular matrix turnover and the paracrine induction of cardiomyocyte hypertrophy. This review explores the emerging importance of the p38 MAPK pathway in cardiac fibroblasts, describes the molecular mechanisms by which it regulates the expression of key genes, and highlights its potential as a therapeutic target for reducing adverse myocardial remodeling.

Protective transcriptional mechanisms in cardiomyocytes and cardiac fibroblasts

Heart failure is the leading cause of morbidity and mortality worldwide. Several lines of evidence suggest that physical activity and exercise can pre-condition the heart to improve the response to acute cardiac injury such as myocardial infarction or ischemia/reperfusion injury, preventing the progression to heart failure. It is becoming more apparent that cardioprotection is a concerted effort between multiple cell types and converging signaling pathways. However, the molecular mechanisms of cardioprotection are not completely understood. What is clear is that the mechanisms underlying this protection involve acute activation of transcriptional activators and their corresponding gene expression programs. Here, we review the known stress-dependent transcriptional programs that are activated in cardiomyocytes and cardiac fibroblasts to preserve function in the adult heart after injury. Focus is given to prominent transcriptional pathways such as mechanical stress or reactive oxygen species (ROS)-dependent activation of myocardin-related transcription factors (MRTFs) and transforming growth factor beta (TGFβ), and gene expression that positively regulates protective PI3K/Akt signaling. Together, these pathways modulate both beneficial and pathological responses to cardiac injury in a cell-specific manner.

JDP2 and ATF3 deficiencies dampen maladaptive cardiac remodeling and preserve cardiac function

c-Jun dimerization protein (JDP2) and Activating Transcription Factor 3 (ATF3) are closely related basic leucine zipper proteins. Transgenic mice with cardiac expression of either JDP2 or ATF3 showed maladaptive remodeling and cardiac dysfunction. Surprisingly, JDP2 knockout (KO) did not protect the heart following transverse aortic constriction (TAC). Instead, the JDP2 KO mice performed worse than their wild type (WT) counterparts. To test whether the maladaptive cardiac remodeling observed in the JDP2 KO mice is due to ATF3, ATF3 was removed in the context of JDP2 deficiency, referred as double KO mice (dKO). Mice were challenged by TAC, and followed by detailed physiological, pathological and molecular analyses. dKO mice displayed no apparent differences from WT mice under unstressed condition, except a moderate better performance in dKO male mice. Importantly, following TAC the dKO hearts showed low fibrosis levels, reduced inflammatory and hypertrophic gene expression and a significantly preserved cardiac function as compared with their WT counterparts in both genders. Consistent with these data, removing ATF3 resumed p38 activation in the JDP2 KO mice which correlates with the beneficial cardiac function.

Collectively, mice with JDP2 and ATF3 double deficiency had reduced maladaptive cardiac remodeling and lower hypertrophy following TAC. As such, the worsening of the cardiac outcome found in the JDP2 KO mice is due to the elevated ATF3 expression. Simultaneous suppression of both ATF3 and JDP2 activity is highly beneficial for cardiac function in health and disease.

Exercise promotes a cardioprotective gene program in resident cardiac fibroblasts

Exercise and heart disease both induce cardiac remodeling, but only disease causes fibrosis and compromises heart function. The cardioprotective benefits of exercise have been attributed to changes in cardiomyocyte physiology, but the impact of exercise on cardiac fibroblasts (CFs) is unknown. Here, RNA-sequencing reveals rapid divergence of CF transcriptional programs during exercise and disease. Among the differentially expressed programs, NRF2-dependent antioxidant genes - including metallothioneins (Mt1 and Mt2) - are induced in CFs during exercise and suppressed by TGF-β/p38 signaling in disease. In vivo, mice lacking Mt1/2 exhibit signs of cardiac dysfunction in exercise, including cardiac fibrosis, vascular rarefaction, and functional decline. Mechanistically, exogenous MTs derived from fibroblasts are taken up by cultured cardiomyocytes, reducing oxidative damage-dependent cell death. Importantly, suppression of MT expression is conserved in human heart failure. Taken together, this study defines the acute transcriptional response of CFs to exercise and disease and reveals a cardioprotective mechanism that is lost in disease.

The Crosstalk between Acetylation and Phosphorylation: Emerging New Roles for HDAC Inhibitors in the Heart

Approximately five million United States (U.S.) adults are diagnosed with heart failure (HF), with eight million U.S. adults projected to suffer from HF by 2030. With five-year mortality rates following HF diagnosis approximating 50%, novel therapeutic treatments are needed for HF patients. Pre-clinical animal models of HF have highlighted histone deacetylase (HDAC) inhibitors as efficacious therapeutics that can stop and potentially reverse cardiac remodeling and dysfunction linked with HF development. HDACs remove acetyl groups from nucleosomal histones, altering DNA-histone protein electrostatic interactions in the regulation of gene expression. However, HDACs also remove acetyl groups from non-histone proteins in various tissues. Changes in histone and non-histone protein acetylation plays a key role in protein structure and function that can alter other post translational modifications (PTMs), including protein phosphorylation. Protein phosphorylation is a well described PTM that is important for cardiac signal transduction, protein activity and gene expression, yet the functional role for acetylation-phosphorylation cross-talk in the myocardium remains less clear. This review will focus on the regulation and function for acetylation-phosphorylation cross-talk in the heart, with a focus on the role for HDACs and HDAC inhibitors as regulators of acetyl-phosphorylation cross-talk in the control of cardiac function.

Cardiac fibroblast-specific p38α MAP kinase promotes cardiac hypertrophy via a putative paracrine interleukin-6 signaling mechanism

Recent studies suggest that cardiac fibroblast-specific p38α MAPK contributes to the development of cardiac hypertrophy, but the underlying mechanism is unknown. Our study used a novel fibroblast-specific, tamoxifen-inducible p38α knockout (KO) mouse line to characterize the role of fibroblast p38α in modulating cardiac hypertrophy, and we elucidated the mechanism. Myocardial injury was induced in tamoxifen-treated Cre-positive p38α KO mice or control littermates via chronic infusion of the β-adrenergic receptor agonist isoproterenol. Cardiac function was assessed by pressure-volume conductance catheter analysis and was evaluated for cardiac hypertrophy at tissue, cellular, and molecular levels. Isoproterenol infusion in control mice promoted overt cardiac hypertrophy and dysfunction (reduced ejection fraction, increased end systolic volume, increased cardiac weight index, increased cardiomyocyte area, increased fibrosis, and up-regulation of myocyte fetal genes and hypertrophy-associated microRNAs). Fibroblast-specific p38α KO mice exhibited marked protection against myocardial injury, with isoproterenol-induced alterations in cardiac function, histology, and molecular markers all being attenuated. In vitro mechanistic studies determined that cardiac fibroblasts responded to damaged myocardium by secreting several paracrine factors known to induce cardiomyocyte hypertrophy, including IL-6, whose secretion was dependent upon p38α activity. In conclusion, cardiac fibroblast p38α contributes to cardiomyocyte hypertrophy and cardiac dysfunction, potentially via a mechanism involving paracrine fibroblast-to-myocyte IL-6 signaling.-Bageghni, S. A., Hemmings, K. E., Zava, N., Denton, C. P., Porter, K. E., Ainscough, J. F. X., Drinkhill, M. J., Turner, N. A. Cardiac fibroblast-specific p38α MAP kinase promotes cardiac hypertrophy via a putative paracrine interleukin-6 signaling mechanism.

Mitochondrial ROS Drive Sudden Cardiac Death and Chronic Proteome Remodeling in Heart Failure

RATIONALE

Despite increasing prevalence and incidence of heart failure (HF), therapeutic options remain limited. In early stages of HF, sudden cardiac death (SCD) from ventricular arrhythmias claims many lives. Reactive oxygen species (ROS) have been implicated in both arrhythmias and contractile dysfunction. However, little is known about how ROS in specific subcellular compartments contribute to HF or SCD pathophysiology. The role of ROS in chronic proteome remodeling has not been explored.

OBJECTIVE

We will test the hypothesis that elevated mitochondrial ROS (mROS) is a principal source of oxidative stress in HF and in vivo reduction of mROS mitigates SCD.

METHODS AND RESULTS

Using a unique guinea pig model of nonischemic HF that recapitulates important features of human HF, including prolonged QT interval and high incidence of spontaneous arrhythmic SCD, compartment-specific ROS sensors revealed increased mROS in resting and contracting left ventricular myocytes in failing hearts. Importantly, the mitochondrially targeted antioxidant (MitoTEMPO) normalized global cellular ROS. Further, in vivo MitoTEMPO treatment of HF animals prevented and reversed HF, eliminated SCD by decreasing dispersion of repolarization and ventricular arrhythmias, suppressed chronic HF-induced remodeling of the expression proteome, and prevented specific phosphoproteome alterations. Pathway analysis of mROS-sensitive networks indicated that increased mROS in HF disrupts the normal coupling between cytosolic signals and nuclear gene programs driving mitochondrial function, antioxidant enzymes, Ca²⁺ handling, and action potential repolarization, suggesting new targets for therapeutic intervention.

CONCLUSIONS

mROS drive both acute emergent events, such as electrical instability responsible for SCD, and those that mediate chronic HF remodeling, characterized by suppression or altered phosphorylation of metabolic, antioxidant, and ion transport protein networks. In vivo reduction of mROS prevents and reverses electrical instability, SCD, and HF. Our findings support the feasibility of targeting the mitochondria as a potential new therapy for HF and SCD while identifying new mROS-sensitive protein modifications.

Subcellular compartmentalization of proximal Gαq-receptor signaling produces unique hypertrophic phenotypes in adult cardiac myocytes

G protein-coupled receptors that signal through Gα_q (G_q receptors), such as α₁-adrenergic receptors (α₁-ARs) or angiotensin receptors, share a common proximal signaling pathway that activates phospholipase Cβ1 (PLCβ1), which cleaves phosphatidylinositol 4,5-bisphosphate (PIP₂) to produce inositol 1,4,5-trisphosphate (IP₃) and diacylglycerol. Despite these common proximal signaling mechanisms, G_q receptors produce distinct physiological responses, yet the mechanistic basis for this remains unclear. In the heart, G_q receptors are thought to induce myocyte hypertrophy through a mechanism termed excitation-transcription coupling, which provides a mechanistic basis for compartmentalization of calcium required for contraction versus IP₃-dependent intranuclear calcium required for hypertrophy. Here, we identified subcellular compartmentalization of G_q-receptor signaling as a mechanistic basis for unique G_q receptor-induced hypertrophic phenotypes in cardiac myocytes. We show that α₁-ARs co-localize with PLCβ1 and PIP₂ at the nuclear membrane. Further, nuclear α₁-ARs induced intranuclear PLCβ1 activity, leading to histone deacetylase 5 (HDAC5) export and a robust transcriptional response (i.e. significant up- or down-regulation of 806 genes). Conversely, we found that angiotensin receptors localize to the sarcolemma and induce sarcolemmal PLCβ1 activity, but fail to promote HDAC5 nuclear export, while producing a transcriptional response that is mostly a subset of α₁-AR-induced transcription. In summary, these results link G_q-receptor compartmentalization in cardiac myocytes to unique hypertrophic transcription. They suggest a new model of excitation-transcription coupling in adult cardiac myocytes that accounts for differential G_q-receptor localization and better explains distinct physiological functions of G_q receptors.

A-Kinase Anchoring Protein-Lbc: A Molecular Scaffold Involved in Cardiac Protection

Heart failure is a lethal disease that can develop after myocardial infarction, hypertension, or anticancer therapy. In the damaged heart, loss of function is mainly due to cardiomyocyte death and associated cardiac remodeling and fibrosis. In this context, A-kinase anchoring proteins (AKAPs) constitute a family of scaffolding proteins that facilitate the spatiotemporal activation of the cyclic adenosine monophosphate (AMP)-dependent protein kinase (PKA) and other transduction enzymes involved in cardiac remodeling. AKAP-Lbc, a cardiac enriched anchoring protein, has been shown to act as a key coordinator of the activity of signaling pathways involved in cardiac protection and remodeling. This review will summarize and discuss recent advances highlighting the role of the AKAP-Lbc signalosome in orchestrating adaptive responses in the stressed heart.

Heat stress prevents lipopolysaccharide-induced apoptosis in pulmonary microvascular endothelial cells by blocking calpain/p38 MAPK signalling

Pulmonary microvascular endothelial cells (PMECs) injury including apoptosis plays an important role in the pathogenesis of acute lung injury during sepsis. Our recent study has demonstrated that calpain activation contributes to apoptosis in PMECs under septic conditions. This study investigated how calpain activation mediated apoptosis and whether heat stress regulated calpain activation in lipopolysaccharides (LPS)-stimulated PMECs. In cultured mouse primary PMECs, incubation with LPS (1 μg/ml, 24 h) increased active caspase-3 fragments and DNA fragmentation, indicative of apoptosis. These effects of LPS were abrogated by pre-treatment with heat stress (43 °C for 2 h). LPS also induced calpain activation and increased phosphorylation of p38 MAPK. Inhibition of calpain and p38 MAPK prevented apoptosis induced by LPS. Furthermore, inhibition of calpain blocked p38 MAPK phosphorylation in LPS-stimulated PMECs. Notably, heat stress decreased the protein levels of calpain-1/2 and calpain activities, and blocked p38 MAPK phosphorylation in response to LPS. Additionally, forced up-regulation of calpain-1 or calpain-2 sufficiently induced p38 MAPK phosphorylation and apoptosis in PMECs, both of which were inhibited by heat stress. In conclusion, heat stress prevents LPS-induced apoptosis in PMECs. This effect of heat stress is associated with down-regulation of calpain expression and activation, and subsequent blockage of p38 MAPK activation in response to LPS. Thus, blocking calpain/p38 MAPK pathway may be a novel mechanism underlying heat stress-mediated inhibition of apoptosis in LPS-stimulated endothelial cells.

ASK family in cardiovascular biology and medicine

Cardiovascular disease is a major cause of death worldwide. Mitogen-activated protein kinase (MAPK) signal cascades signaling pathways play crucial roles in cardiovascular pathophysiology. Apoptosis signal-regulating kinase (ASK) family members ASK1, ASK2 and ASK3 are the key molecules in MAPK signal cascades and are activated by various stresses. ASK1 is the most extensively studied MAPKKK and is involved in regulation of the cellular functions such as cell survival, proliferation, inflammation and apoptosis. The current review focuses on the relationship between ASK1 and cardiovascular disease, while exploring the novel therapeutic strategies for cardiovascular disease involved in the ASK1 signal pathway.

Aerobic performance in tinamous is limited by their small heart. A novel hypothesis in the evolution of avian flight

Some biomechanical studies from fossil specimens suggest that sustained flapping flight of birds could have appeared in their Mesozoic ancestors. We challenge this idea because a suitable musculoskeletal anatomy is not the only requirement for sustained flapping flight. We propose the “heart to fly” hypothesis that states that sustained flapping flight in modern birds required an enlargement of the heart for the aerobic performance of the flight muscles and test it experimentally by studying tinamous, the living birds with the smallest hearts. The small ventricular size of tinamous reduces cardiac output without limiting perfusion pressures, but when challenged to fly, the heart is unable to support aerobic metabolism (quick exhaustion, larger lactates and post-exercise oxygen consumption and compromised thermoregulation). At the same time, cardiac growth shows a crocodilian-like pattern and is correlated with differential gene expression in MAPK kinases. We integrate this physiological evidence in a new evolutionary scenario in which the ground-up, short and not sustained flapping flight displayed by tinamous represents an intermediate step in the evolution of the aerobic sustained flapping flight of modern birds.

DUSP1 alleviates cardiac ischemia/reperfusion injury by suppressing the Mff-required mitochondrial fission and Bnip3-related mitophagy via the JNK pathways

Mitochondrial fission and selective mitochondrial autophagy (mitophagy) form an essential axis of mitochondrial quality control that plays a critical role in the development of cardiac ischemia-reperfusion (IR) injury. However, the precise upstream molecular mechanism of fission/mitophagy remains unclear. Dual-specificity protein phosphatase1 (DUSP1) regulates cardiac metabolism, but its physiological contribution in the reperfused heart, particularly its influence on mitochondrial homeostasis, is unknown. Here, we demonstrated that cardiac DUSP1 was downregulated following acute cardiac IR injury. In vivo, compared to wild-type mice, DUSP1 transgenic mice (DUSP1^TG mice) demonstrated a smaller infarcted area and the improved myocardial function. In vitro, the IR-induced DUSP1 deficiency promoted the activation of JNK which upregulated the expression of the mitochondrial fission factor (Mff). A higher expression level of Mff was associated with elevated mitochondrial fission and mitochondrial apoptosis. Additionally, the loss of DUSP1 also amplified the Bnip3 phosphorylated activation via JNK, leading to the activation of mitophagy. Increased mitophagy overtly consumed mitochondrial mass resulting into the mitochondrial metabolism disorder. However, the reintroduction of DUSP1 blunted Mff/Bnip3 activation and therefore alleviated the fatal mitochondrial fission/mitophagy by inactivating the JNK pathway, providing a survival advantage to myocardial tissue following IR stress. The results of our study suggest that DUSP1 and its downstream JNK pathway are therapeutic targets for conferring protection against IR injury by repressing Mff-mediated mitochondrial fission and Bnip3-required mitophagy.

Effect of α7 nicotinic acetylcholine receptor activation on cardiac fibroblasts: a mechanism underlying RV fibrosis associated with cigarette smoke exposure

Right ventricular (RV) dysfunction is associated with numerous smoking-related illnesses, including chronic obstructive pulmonary disease (COPD), in which it is present even in the absence of pulmonary hypertension. It is unknown whether exposure to cigarette smoke (CS) has direct effects on RV function and cardiac fibroblast (CF) proliferation or collagen synthesis. In this study, we evaluated cardiac function and fibrosis in mice exposed to CS and determined mechanisms of smoke-induced changes in CF signaling and fibrosis. AKR mice were exposed to CS for 6 wk followed by echocardiography and evaluation of cardiac hypertrophy, collagen content, and pulmonary muscularization. Proliferation and collagen content were evaluated in primary isolated rat CFs exposed to CS extract (CSE) or nicotine. Markers of cell proliferation, fibrosis, and proliferative signaling were determined by immunoblot or Sircol collagen assay. Mice exposed to CS had significantly decreased RV function, as determined by tricuspid annular plane systolic excursion. There were no changes in left ventricular parameters. RV collagen content was significantly elevated, but there was no change in RV hypertrophy or pulmonary vascular muscularization. CSE directly increased CF proliferation and collagen content in CF. Nicotine alone reproduced these effects. CSE and nicotine-induced fibroblast proliferation and collagen content were mediated through α7 nicotinic acetylcholine receptors and were dependent on PKC-α, PKC-δ, and reduced p38-MAPK phosphorylation. CS and nicotine have direct effects on CFs to induce proliferation and fibrosis, which may negatively affect right heart function.

Cardiac Fibroblast-Specific Activating Transcription Factor 3 Protects Against Heart Failure by Suppressing MAP2K3-p38 Signaling

BACKGROUND

Hypertensive ventricular remodeling is a common cause of heart failure. However, the molecular mechanisms regulating ventricular remodeling remain poorly understood.

METHODS

We used a discovery-driven/nonbiased approach to identify increased activating transcription factor 3 (ATF3) expression in hypertensive heart. We used loss/gain of function approaches to understand the role of ATF3 in heart failure. We also examined the mechanisms through transcriptome, chromatin immunoprecipitation sequencing analysis, and in vivo and in vitro experiments.

RESULTS

ATF3 expression increased in murine hypertensive heart and human hypertrophic heart. Cardiac fibroblast cells are the primary cell type expressing high ATF3 levels in response to hypertensive stimuli. ATF3 knockout (ATF3KO) markedly exaggerated hypertensive ventricular remodeling, a state rescued by lentivirus-mediated/miRNA-aided cardiac fibroblast-selective ATF3 overexpression. Conversely, conditional cardiac fibroblast cell-specific ATF3 transgenic overexpression significantly ameliorated ventricular remodeling and heart failure. We identified Map2K3 as a novel ATF3 target. ATF3 binds with the Map2K3 promoter, recruiting HDAC1, resulting in Map2K3 gene-associated histone deacetylation, thereby inhibiting Map2K3 expression. Genetic Map2K3 knockdown rescued the profibrotic/hypertrophic phenotype in ATF3KO cells. Last, we demonstrated that p38 is the downstream molecule of Map2K3 mediating the profibrotic/hypertrophic effects in ATF3KO animals. Inhibition of p38 signaling reduced transforming growth factor-β signaling-related profibrotic and hypertrophic gene expression, and blocked exaggerated cardiac remodeling in ATF3KO cells.

CONCLUSIONS

Our study provides the first evidence that ATF3 upregulation in cardiac fibroblasts in response to hypertensive stimuli protects the heart by suppressing Map2K3 expression and subsequent p38-transforming growth factor-β signaling. These results suggest that positive modulation of cardiac fibroblast ATF3 may represent a novel therapeutic approach against hypertensive cardiac remodeling.

Redirecting cardiac growth mechanisms for therapeutic regeneration

Heart failure is a major source of morbidity and mortality. Replacing lost myocardium with new tissue is a major goal of regenerative medicine. Unlike adult mammals, zebrafish and neonatal mice are capable of heart regeneration following cardiac injury. In both contexts, the regenerative program echoes molecular and cellular events that occur during cardiac development and morphogenesis, notably muscle creation through division of cardiomyocytes. Based on studies over the past decade, it is now accepted that the adult mammalian heart undergoes a low grade of cardiomyocyte turnover. Recent data suggest that this cardiomyocyte turnover can be augmented in the adult mammalian heart by redeployment of developmental factors. These findings and others suggest that stimulating endogenous regenerative responses can emerge as a therapeutic strategy for human cardiovascular disease.

NFATc3 and VIP in Idiopathic Pulmonary Fibrosis and Chronic Obstructive Pulmonary Disease

Idiopathic pulmonary fibrosis (IPF) and chronic obstructive pulmonary disease (COPD) are both debilitating lung diseases which can lead to hypoxemia and pulmonary hypertension (PH). Nuclear Factor of Activated T-cells (NFAT) is a transcription factor implicated in the etiology of vascular remodeling in hypoxic PH. We have previously shown that mice lacking the ability to generate Vasoactive Intestinal Peptide (VIP) develop spontaneous PH, pulmonary arterial remodeling and lung inflammation. Inhibition of NFAT attenuated PH in these mice suggesting a connection between NFAT and VIP. To test the hypotheses that: 1) VIP inhibits NFAT isoform c3 (NFATc3) activity in pulmonary vascular smooth muscle cells; 2) lung NFATc3 activation is associated with disease severity in IPF and COPD patients, and 3) VIP and NFATc3 expression correlate in lung tissue from IPF and COPD patients. NFAT activity was determined in isolated pulmonary arteries from NFAT-luciferase reporter mice. The % of nuclei with NFAT nuclear accumulation was determined in primary human pulmonary artery smooth muscle cell (PASMC) cultures; in lung airway epithelia and smooth muscle and pulmonary endothelia and smooth muscle from IPF and COPD patients; and in PASMC from mouse lung sections by fluorescence microscopy. Both NFAT and VIP mRNA levels were measured in lungs from IPF and COPD patients. Empirical strategies applied to test hypotheses regarding VIP, NFATc3 expression and activity, and disease type and severity. This study shows a significant negative correlation between NFAT isoform c3 protein expression levels in PASMC, activity of NFATc3 in pulmonary endothelial cells, expression and activity of NFATc3 in bronchial epithelial cells and lung function in IPF patients, supporting the concept that NFATc3 is activated in the early stages of IPF. We further show that there is a significant positive correlation between NFATc3 mRNA expression and VIP RNA expression only in lungs from IPF patients. In addition, we found that VIP inhibits NFAT nuclear translocation in primary human pulmonary artery smooth muscle cells (PASMC). Early activation of NFATc3 in IPF patients may contribute to disease progression and the increase in VIP expression could be a protective compensatory mechanism.

Regulation of cardiac hypertrophy and remodeling through the dual-specificity MAPK phosphatases (DUSPs)

Mitogen-activated protein kinases (MAPKs) play a critical role in regulating cardiac hypertrophy and remodeling in response to increased workload or pathological insults. The spatiotemporal activities and inactivation of MAPKs are tightly controlled by a family of dual-specificity MAPK phosphatases (DUSPs). Over the past 2 decades, we and others have determined the critical role for selected DUSP family members in controlling MAPK activity in the heart and the ensuing effects on ventricular growth and remodeling. More specifically, studies from mice deficient for individual Dusp genes as well as heart-specific inducible transgene-mediated overexpression have implicated select DUSPs as essential signaling effectors in the heart that function by dynamically regulating the level, subcellular and temporal activities of the extracellular signal-regulated kinases (ERKs), c-Jun N-terminal kinases (JNKs) and p38 MAPKs. This review summarizes recent literature on the physiological and pathological roles of MAPK-specific DUSPs in regulating MAPK signaling in the heart and the effect on cardiac growth and remodeling.

Update on novel targets and potential treatment avenues in pulmonary hypertension

Pulmonary hypertension (PH) is a condition marked by a combination of constriction and remodeling within the pulmonary vasculature. It remains a disease without a cure, as current treatments were developed with a focus on vasodilatory properties but do not reverse the remodeling component. Numerous recent advances have been made in the understanding of cellular processes that drive pathologic remodeling in each layer of the vessel wall as well as the accompanying maladaptive changes in the right ventricle. In particular, the past few years have yielded much improved insight into the pathways that contribute to altered metabolism, mitochondrial function, and reactive oxygen species signaling and how these pathways promote the proproliferative, promigratory, and antiapoptotic phenotype of the vasculature during PH. Additionally, there have been significant advances in numerous other pathways linked to PH pathogenesis, such as sex hormones and perivascular inflammation. Novel insights into cellular pathology have suggested new avenues for the development of both biomarkers and therapies that will hopefully bring us closer to the elusive goal: a therapy leading to reversal of disease.

The Emerging Roles of the Calcineurin-Nuclear Factor of Activated T-Lymphocytes Pathway in Nervous System Functions and Diseases

The ongoing epidemics of metabolic diseases and increase in the older population have increased the incidences of neurodegenerative diseases. Evidence from murine and cell line models has implicated calcineurin-nuclear factor of activated T-lymphocytes (NFAT) signaling pathway, a Ca²⁺/calmodulin-dependent major proinflammatory pathway, in the pathogenesis of these diseases. Neurotoxins such as amyloid-β, tau protein, and α-synuclein trigger abnormal calcineurin/NFAT signaling activities. Additionally increased activities of endogenous regulators of calcineurin like plasma membrane Ca²⁺-ATPase (PMCA) and regulator of calcineurin 1 (RCAN1) also cause neuronal and glial loss and related functional alterations, in neurodegenerative diseases, psychotic disorders, epilepsy, and traumatic brain and spinal cord injuries. Treatment with calcineurin/NFAT inhibitors induces some degree of neuroprotection and decreased reactive gliosis in the central and peripheral nervous system. In this paper, we summarize and discuss the current understanding of the roles of calcineurin/NFAT signaling in physiology and pathologies of the adult and developing nervous system, with an emphasis on recent reports and cutting-edge findings. Calcineurin/NFAT signaling is known for its critical roles in the developing and adult nervous system. Its role in physiological and pathological processes is still controversial. However, available data suggest that its beneficial and detrimental effects are context-dependent. In view of recent reports calcineurin/NFAT signaling is likely to serve as a potential therapeutic target for neurodegenerative diseases and conditions. This review further highlights the need to characterize better all factors determining the outcome of calcineurin/NFAT signaling in diseases and the downstream targets mediating the beneficial and detrimental effects.

Single Muscle Immobilization Decreases Single-Fibre Myosin Heavy Chain Polymorphism: Possible Involvement of p38 and JNK MAP Kinases

PURPOSE

Muscle contractile phenotype is affected during immobilization. Myosin heavy chain (MHC) isoforms are the major determinant of the muscle contractile phenotype. We therefore sought to evaluate the effects of muscle immobilization on both the MHC composition at single-fibre level and the mitogen-activated protein kinases (MAPK), a family of intracellular signaling pathways involved in the stress-induced muscle plasticity.

METHODS

The distal tendon of female Wistar rat Peroneus Longus (PL) was cut and fixed to the adjacent bone at neutral muscle length. Four weeks after the surgery, immobilized and contralateral PL were dissociated and the isolated fibres were sampled to determine MHC composition. Protein kinase 38 (p38), extracellular signal-regulated kinases (ERK1/2), and c-Jun- NH2-terminal kinase (JNK) phosphorylations were measured in 6- and 15-day immobilized and contralateral PL.

RESULTS

MHC distribution in immobilized PL was as follows: I = 0%, IIa = 11.8 ± 2.8%, IIx = 53.0 ± 6.1%, IIb = 35.3 ± 7.3% and I = 6.1 ± 3.9%, IIa = 22.1 ± 3.4%, IIx = 46.6 ± 4.5%, IIb = 25.2 ± 6.6% in contralateral muscle. The MHC composition in immobilized muscle is consistent with a faster contractile phenotype according to the Hill's model of the force-velocity relationship. Immobilized and contralateral muscles displayed a polymorphism index of 31.1% (95% CI 26.1-36.0) and 39.3% (95% CI 37.0-41.5), respectively. Significant increases in p38 and JNK phosphorylation were observed following 6 and 15 days of immobilization.

CONCLUSIONS

Single muscle immobilization at neutral length induces a shift of MHC composition toward a faster contractile phenotype and decreases the polymorphic profile of single fibres. Activation of p38 and JNK could be a potential mechanism involved in these contractile phenotype modifications during muscle immobilization.

Cardiomyocyte-Specific Human Bcl2-Associated Anthanogene 3 P209L Expression Induces Mitochondrial Fragmentation, Bcl2-Associated Anthanogene 3 Haploinsufficiency, and Activates p38 Signaling

The Bcl2-associated anthanogene (BAG) 3 protein is a member of the BAG family of cochaperones, which supports multiple critical cellular processes, including critical structural roles supporting desmin and interactions with heat shock proteins and ubiquitin ligases intimately involved in protein quality control. The missense mutation P209L in exon 3 results in a primarily cardiac phenotype leading to skeletal muscle and cardiac complications. At least 10 other Bag3 mutations have been reported, nine resulting in a dilated cardiomyopathy for which no specific therapy is available. We generated αMHC-human Bag3 P209L transgenic mice and characterized the progressive cardiac phenotype in vivo to investigate its utility in modeling human disease, understand the underlying molecular mechanisms, and identify potential therapeutic targets. We identified a progressive heart failure by echocardiography and Doppler analysis and the presence of pre-amyloid oligomers at 1 year. Paralleling the pathogenesis of neurodegenerative diseases (eg, Parkinson disease), pre-amyloid oligomers-associated alterations in cardiac mitochondrial dynamics, haploinsufficiency of wild-type BAG3, and activation of p38 signaling were identified. Unexpectedly, increased numbers of activated cardiac fibroblasts were identified in Bag3 P209L Tg+ hearts without increased fibrosis. Together, these findings point to a previously undescribed therapeutic target that may have application to mutation-induced myofibrillar myopathies as well as other common causes of heart failure that commonly harbor misfolded proteins.

DUSP8 Regulates Cardiac Ventricular Remodeling by Altering ERK1/2 Signaling

RATIONALE

Mitogen-activated protein kinase (MAPK) signaling regulates the growth response of the adult myocardium in response to increased cardiac workload or pathological insults. The dual-specificity phosphatases (DUSPs) are critical effectors, which dephosphorylate the MAPKs to control the basal tone, amplitude, and duration of MAPK signaling.

OBJECTIVE

To examine DUSP8 as a regulator of MAPK signaling in the heart and its impact on ventricular and cardiac myocyte growth dynamics.

METHODS AND RESULTS

Dusp8 gene-deleted mice and transgenic mice with inducible expression of DUSP8 in the heart were used here to investigate how this MAPK-phosphatase might regulate intracellular signaling and cardiac growth dynamics in vivo. Dusp8 gene-deleted mice were mildly hypercontractile at baseline with a cardiac phenotype of concentric ventricular remodeling, which protected them from progressing towards heart failure in 2 surgery-induced disease models. Cardiac-specific overexpression of DUSP8 produced spontaneous eccentric remodeling and ventricular dilation with heart failure. At the cellular level, adult cardiac myocytes from Dusp8 gene-deleted mice were thicker and shorter, whereas DUSP8 overexpression promoted cardiac myocyte lengthening with a loss of thickness. Mechanistically, activation of extracellular signal-regulated kinases 1/2 were selectively increased in Dusp8 gene-deleted hearts at baseline and following acute pathological stress stimulation, whereas p38 MAPK and c-Jun N-terminal kinases were mostly unaffected.

CONCLUSIONS

These results indicate that DUSP8 controls basal and acute stress-induced extracellular signal-regulated kinases 1/2 signaling in adult cardiac myocytes that then alters the length-width growth dynamics of individual cardiac myocytes, which further alters contractility, ventricular remodeling, and disease susceptibility.

p38γ and δ promote heart hypertrophy by targeting the mTOR-inhibitory protein DEPTOR for degradation

Disrupted organ growth leads to disease development. Hypertrophy underlies postnatal heart growth and is triggered after stress, but the molecular mechanisms involved in these processes are largely unknown. Here we show that cardiac activation of p38γ and p38δ increases during postnatal development and by hypertrophy-inducing stimuli. p38γ/δ promote cardiac hypertrophy by phosphorylating the mTORC1 and mTORC2 inhibitor DEPTOR, which leads to its degradation and mTOR activation. Hearts from mice lacking one or both kinases are below normal size, have high levels of DEPTOR, low activity of the mTOR pathway and reduced protein synthesis. The phenotype of p38γ/δ^−/− mice is reverted by overactivation of mTOR with amino acids, shRNA-mediated knockdown of Deptor, or cardiomyocyte overexpression of active p38γ and p38δ. Moreover, in WT mice, heart weight is reduced by cardiac overexpression of DEPTOR. Our results demonstrate that p38γ/δ control heart growth by modulating mTOR pathway through DEPTOR phosphorylation and subsequent degradation.

mTOR signalling pathway is a critical regulator of cardiac hypertrophy. Here the authors show that two kinases, p38γ and p38δ, control heart growth by promoting mTOR activity via phosphorylation and consequent proteasome degradation of mTOR inhibitor DEPTOR, extending our knowledge of cardiac hypertrophy regulation.

Overexpression of protein kinase C ɛ improves retention and survival of transplanted mesenchymal stem cells in rat acute myocardial infarction

We assessed the effects of protein kinase C ɛ (PKCɛ) for improving stem cell therapy for acute myocardial infarction (AMI). Primary mesenchymal stem cells (MSCs) were harvested from rat bone marrow. PKCɛ-overexpressed MSCs and control MSCs were transplanted into infarct border zones in a rat AMI model. MSCs and PKCɛ distribution and expression of principal proteins involved in PKCɛ signaling through the stromal cell-derived factor 1 (SDF-1)/CXC chemokine receptor type 4 (CXCR4) axis and the phosphatidylinositol 3 kinase (PI3K)/protein kinase B (AKT) pathway were analyzed by immunofluorescence and western blot 1 day after transplantation. Echocardiographic measurements and histologic studies were performed at 4 weeks after transplantation, and MSC survival, expression of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), transforming growth factor β (TGFβ), cardiac troponin I (cTnI), von Willebrand factor (vWF), smooth muscle actin (SMA) and factor VIII and apoptosis in infarct border zones were assessed. Rat heart muscles retained more MSCs and SDF-1, CXCR4, PI3K and phosphorylated AKT increased with PKCɛ overexpression 1 day after transplantation. MSC survival and VEGF, bFGF, TGFβ, cTnI, vWF, SMA and factor VIII expression increased in animals with PKCɛ-overexpressed MSCs at 4 weeks after transplantation and cardiac dysfunction and remodeling improved. Infarct size and apoptosis decreased as well. Inhibitory actions of CXCR4 or PI3K partly attenuated the effects of PKCɛ. Activation of PKCɛ may improve retention, survival and differentiation of transplanted MSCs in myocardia. Augmentation of PKCɛ expression may enhance the therapeutic effects of stem cell therapy for AMI.

Myozap Deficiency Promotes Adverse Cardiac Remodeling via Differential Regulation of Mitogen-activated Protein Kinase/Serum-response Factor and β-Catenin/GSK-3β Protein Signaling

The intercalated disc (ID) is a "hot spot" for heart disease, as several ID proteins have been found mutated in cardiomyopathy. Myozap is a recent addition to the list of ID proteins and has been implicated in serum-response factor signaling. To elucidate the cardiac consequences of targeted deletion of myozap in vivo, we generated myozap-null mutant (Mzp(-/-)) mice. Although Mzp(-/-) mice did not exhibit a baseline phenotype, increased biomechanical stress due to pressure overload led to accelerated cardiac hypertrophy, accompanied by "super"-induction of fetal genes, including natriuretic peptides A and B (Nppa/Nppb). Moreover, Mzp(-/-) mice manifested a severe reduction of contractile function, signs of heart failure, and increased mortality. Expression of other ID proteins like N-cadherin, desmoplakin, connexin-43, and ZO-1 was significantly perturbed upon pressure overload, underscored by disorganization of the IDs in Mzp(-/-) mice. Exploration of the molecular causes of enhanced cardiac hypertrophy revealed significant activation of β-catenin/GSK-3β signaling, whereas MAPK and MKL1/serum-response factor pathways were inhibited. In summary, myozap is required for proper adaptation to increased biomechanical stress. In broader terms, our data imply an essential function of the ID in cardiac remodeling beyond a mere structural role and emphasize the need for a better understanding of this molecular structure in the context of heart disease.

Low-dose radiation affects cardiac physiology: gene networks and molecular signaling in cardiomyocytes

There are 160,000 cancer patients worldwide treated with particle radiotherapy (RT). With the advent of proton, and high (H) charge (Z) and energy (E) HZE ionizing particle RT, the cardiovascular diseases risk estimates are uncertain. In addition, future deep space exploratory-type missions will expose humans to unknown but low doses of particle irradiation (IR). We examined molecular responses using transcriptome profiling in left ventricular murine cardiomyocytes isolated from mice that were exposed to 90 cGy, 1 GeV proton ((1)H) and 15 cGy, 1 GeV/nucleon iron ((56)Fe) over 28 days after exposure. Unsupervised clustering analysis of gene expression segregated samples according to the IR response and time after exposure, with (56)Fe-IR showing the greatest level of gene modulation. (1)H-IR showed little differential transcript modulation. Network analysis categorized the major differentially expressed genes into cell cycle, oxidative responses, and transcriptional regulation functional groups. Transcriptional networks identified key nodes regulating expression. Validation of the signal transduction network by protein analysis and gel shift assay showed that particle IR clearly regulates a long-lived signaling mechanism for ERK1/2, p38 MAPK signaling and identified NFATc4, GATA4, STAT3, and NF-κB as regulators of the response at specific time points. These data suggest that the molecular responses and gene expression to (56)Fe-IR in cardiomyocytes are unique and long-lasting. Our study may have significant implications for the efforts of National Aeronautics and Space Administration to develop heart disease risk estimates for astronauts and for patients receiving conventional and particle RT via identification of specific HZE-IR molecular markers.

The calcineurin-NFAT pathway controls activity-dependent circadian gene expression in slow skeletal muscle

Objective

Physical activity and circadian rhythms are well-established determinants of human health and disease, but the relationship between muscle activity and the circadian regulation of muscle genes is a relatively new area of research. It is unknown whether muscle activity and muscle clock rhythms are coupled together, nor whether activity rhythms can drive circadian gene expression in skeletal muscle.

Methods

We compared the circadian transcriptomes of two mouse hindlimb muscles with vastly different circadian activity patterns, the continuously active slow soleus and the sporadically active fast tibialis anterior, in the presence or absence of a functional skeletal muscle clock (skeletal muscle-specific Bmal1 KO). In addition, we compared the effect of denervation on muscle circadian gene expression.

Results

We found that different skeletal muscles exhibit major differences in their circadian transcriptomes, yet core clock gene oscillations were essentially identical in fast and slow muscles. Furthermore, denervation caused relatively minor changes in circadian expression of most core clock genes, yet major differences in expression level, phase and amplitude of many muscle circadian genes.

Conclusions

We report that activity controls the oscillation of around 15% of skeletal muscle circadian genes independently of the core muscle clock, and we have identified the Ca²⁺-dependent calcineurin-NFAT pathway as an important mediator of activity-dependent circadian gene expression, showing that circadian locomotor activity rhythms drive circadian rhythms of NFAT nuclear translocation and target gene expression.

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Activity is a major extrinsic factor driving ∼15% of muscle circadian genes.

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Calcineurin-NFAT drives activity-dependent circadian gene expression in muscle.

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The majority of skeletal muscle circadian genes are muscle type-specific.

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A common set of skeletal muscle circadian genes are clock-dependent.

p38 MAP kinases in the heart

p38 kinases are members of the mitogen-activated protein kinases (MAPK) with established contribution to a wide range of signaling pathways and different biological processes. The prototypic p38 MAPK, p38α was originally identified as an essential signaling kinase for inflammatory cytokine production Extensive studies have now revealed that p38s have critical roles in many different tissues far beyond immune regulation and inflammatory responses. In this review, we will focus on the structure and molecular biology of p38s, and their specific roles in heart, especially regarding myocyte proliferation, apoptosis, and hypertrophic responses.

Orphan Nuclear Receptor Nur77 Inhibits Cardiac Hypertrophic Response to Beta-Adrenergic Stimulation

The orphan nuclear receptor Nur77 plays critical roles in cardiovascular diseases, and its expression is markedly induced in the heart after beta-adrenergic receptor (β-AR) activation. However, the functional significance of Nur77 in β-AR signaling in the heart remains unclear. By using Northern blot, Western blot, and immunofluorescent staining assays, we showed that Nur77 expression was markedly upregulated in cardiomyocytes in response to multiple hypertrophic stimuli, including isoproterenol (ISO), phenylephrine (PE), and endothelin-1 (ET-1). In a time- and dose-dependent manner, ISO increases Nur77 expression in the nuclei of cardiomyocytes. Overexpression of Nur77 markedly inhibited ISO-induced cardiac hypertrophy by inducing nuclear translocation of Nur77 in cardiomyocytes. Furthermore, cardiac overexpression of Nur77 by intramyocardial injection of Ad-Nur77 substantially inhibited cardiac hypertrophy and ameliorated cardiac dysfunction after chronic infusion of ISO in mice. Mechanistically, we demonstrated that Nur77 functionally interacts with NFATc3 and GATA4 and inhibits their transcriptional activities, which are critical for the development of cardiac hypertrophy. These results demonstrate for the first time that Nur77 is a novel negative regulator for the β-AR-induced cardiac hypertrophy through inhibiting the NFATc3 and GATA4 transcriptional pathways. Targeting Nur77 may represent a potentially novel therapeutic strategy for preventing cardiac hypertrophy and heart failure.

The case for inhibiting p38 mitogen-activated protein kinase in heart failure

This minireview discusses the evidence that the inhibition of p38 mitogen-activated protein kinases (p38 MAPKs) maybe of therapeutic value in heart failure. Most previous experimental studies, as well as past and ongoing clinical trials, have focussed on the role of p38 MAPKs in myocardial infarction and acute coronary syndromes. There is now growing evidence that these kinases are activated within the myocardium of the failing human heart and in the heart and blood vessels of animal models of heart failure. Furthermore, from a philosophical viewpoint the chronic activation of the adaptive stress pathways that lead to the activation of p38 MAPKs in heart failure is analogous to the chronic activation of the sympathetic, renin-aldosterone-angiotensin and neprilysin systems. These have provided some of the most effective therapies for heart failure. This minireview questions whether similar and synergistic advantages would follow the inhibition of p38 MAPKs.

p38 MAPK in cardioprotection - are we there yet?

PKs transfer a phosphate from ATP to the side-chain hydroxyl group of a serine, threonine or tyrosine residue of a substrate protein. This in turn can alter that protein's function; modulating fundamental cellular processes including, metabolism, transcription, growth, division, differentiation, motility and survival. PKs are subdivided into families based on homology. One such group are the stress-activated kinases, which as the name suggests, are activated in response to cellular stresses such as toxins, cytokines, mechanical deformation and osmotic stress. Members include the p38 MAPK family, which is composed of α, β, γ and δ, isoforms which are encoded by separate genes. These kinases transduce extracellular signals and coordinate the cellular responses needed for adaptation and survival. However, in cardiovascular and other disease states, these same systems can trigger maladaptive responses that aggravate, rather than alleviate, the disease. This situation is analogous to adrenergic, angiotensin and aldosterone signalling in heart failure, where inhibition is beneficial despite the importance of these hormones to homeostasis. The question is whether similar benefits could accrue from p38 inhibition? In this review, we will discuss the structure and function of p38, the history of p38 inhibitors and their use in preclinical studies. Finally, we will summarize the results of recent cardiovascular clinical trials with p38 inhibitors.

PKC δ and βII regulate angiotensin II-mediated fibrosis through p38: a mechanism of RV fibrosis in pulmonary hypertension

Pulmonary hypertension (PH) eventually leads to right ventricular (RV) fibrosis and dysfunction that is associated with increased morbidity and mortality. Although angiotensin II plays an important role in RV remodeling associated with hypoxic PH, the molecular mechanisms underlying RV fibrosis in PH largely remain unresolved. We hypothesized that PKC-p38 signaling is involved in RV collagen accumulation in PH and in response to angiotensin II stimulation. Adult male Sprague-Dawley rats were exposed to 3 wk of normoxia or hypoxia (10% FiO2 ) as a model of PH. Hypoxic rats developed RV hypertrophy and fibrosis associated with an increase in PKC βII and δ protein expression and p38 dephosphorylation in freshly isolated RV cardiac fibroblasts. Further mechanistic studies were performed in cultured primary cardiac fibroblasts stimulated with angiotensin II, a key activator of ventricular fibrosis in PH. Angiotensin II induced a reduction in p38 phosphorylation that was attenuated following chemical inhibition of PKC βII and δ. Molecular and chemical inhibition of PKC βII and δ abrogated angiotensin II-induced cardiac fibroblast proliferation and collagen deposition in vitro. The effects of PKC inhibition on proliferation and fibrosis were reversed by chemical inhibition of p38. Conversely, constitutive activation of p38 attenuated angiotensin II-induced increase of cardiac fibroblast proliferation and collagen accumulation. PKC βII- and δ-dependent inactivation of p38 regulates cardiac fibroblast proliferation and collagen deposition in response to angiotensin II, which suggests that the PKC-p38 signaling in cardiac fibroblasts may be involved and important in the pathophysiology of RV fibrosis in PH.