Activated glycogen synthase-3 beta suppresses cardiac hypertrophy in vivo

Molecular gatekeepers of endogenous adult mammalian cardiomyocyte proliferation

Irreversible cardiac fibrosis, cardiomyocyte death and chronic cardiac dysfunction after myocardial infarction pose a substantial global health-care challenge, with no curative treatments available. To regenerate the injured heart, cardiomyocytes must proliferate to replace lost myocardial tissue - a capability that adult mammals have largely forfeited to adapt to the demanding conditions of life. Using various preclinical models, our understanding of cardiomyocyte proliferation has progressed remarkably, leading to the successful reactivation of cell cycle induction in adult animals, with functional recovery after cardiac injury. Central to this success is the targeting of key pathways and structures that drive cardiomyocyte maturation after birth - nucleation and ploidy, sarcomere structure, developmental signalling, chromatin and epigenetic regulation, the microenvironment and metabolic maturation - forming a complex regulatory framework that allows efficient cellular contraction but restricts cardiomyocyte proliferation. In this Review, we explore the molecular pathways underlying these core mechanisms and how their manipulation can reactivate the cell cycle in cardiomyocytes, potentially contributing to cardiac repair.

Lipid Emulsion Mitigates the Cardiotoxic Effects of Labetalol in Rat Cardiomyoblasts

Lipid emulsion has recently emerged as an effective agent for improving the cardiotoxicity of highly lipophilic drugs. However, its effect on cardiotoxicity induced by labetalol, a nonselective beta-blocker, remains unknown. In this study, we investigated the effects of lipid emulsion on the cardiotoxicity of labetalol in rat cardiomyoblasts and tried to decipher the underlying mechanisms. The effects of lipid emulsion on labetalol-induced changes in cell viability, expression of Bax/Bcl-2, cleaved caspase-3, and cleaved caspase-9, and phosphorylation of GSK-3β, Akt, and PI3K were examined. Lipid emulsion inhibited labetalol-induced decrease in cell viability, whereas LY294002, MK2206, and SB216763, the inhibitors of phosphoinositide 3-kinase (PI3K), Akt, glycogen synthase kinase-3β (GSK-3β), respectively, partially attenuated this restoration of cell viability. Lipid emulsion reversed the increase in expression of cleaved caspase-3, cleaved caspase-9, and Bax/Bcl-2 and decrease in the phosphorylation of GSK-3β, Akt, and PI3K by labetalol. Lipid emulsion and cyclosporin, a mitochondrial permeability transition pore (MPTP) inhibitor, reduced the labetalol-induced increase in the number of TUNEL-positive cells and promoted late-stage apoptosis. Overall, lipid emulsion inhibited apoptotic cell death caused by labetalol toxicity via the inhibition of intrinsic apoptotic pathway and MPTP in rat cardiomyoblasts, which appears to involve PI3K, Akt, and GSK-3β signaling pathways.

Targeting Wnt Pathways with Small Molecules as New Approach in Cardiovascular Disease

The increasing incidences of morbidity and mortality associated with cardiovascular diseases represent significant difficulties for clinical treatment and have a major impact on patient health. Wnt signaling pathways are highly conserved and are well known for their regulatory roles in embryonic development, tissue regeneration, and adult tissue homeostasis. Wnt signaling is classified into two distinct pathways: canonical Wnt/β-catenin signaling and noncanonical pathways, including planar cell polarity and Wnt/Ca2+ pathways. A growing body of experimental evidence suggests the involvement of both canonical and non-canonical Wnt signaling pathways in the development of cardiovascular diseases, including myocardial hypertrophy, arrhythmias, diabetic cardiomyopathy, arrhythmogenic cardiomyopathy, and myocardial infarction. Thus, to enhance patient quality of life, diagnosing and treating cardiac illnesses may require a thorough understanding of the molecular functions played by the Wnt pathway in these disorders. Many small-molecule inhibitors specifically target various components within the Wnt signaling pathways, such as Frizzled, Disheveled, Porcupine, and Tankyrase. This study aims to present an overview of the latest findings regarding the functions of Wnt signaling in human cardiac disorders and possible inhibitors of Wnt, which could lead to novel approaches for treating cardiac ailments.

Targeting GSK-3β for adipose dysfunction and cardiovascular complications of metabolic disease: An entangled WNT/β-catenin question

Individuals with metabolic syndrome have a high risk of developing cardiovascular disorders that is closely tied to visceral adipose tissue dysfunction, as well as an altered interaction between adipose tissue and the cardiovascular system. In metabolic syndrome, adipose tissue dysfunction is associated with increased hypertrophy, reduced vascularization, and hypoxia of adipocytes, leading to a pro-oxidative and pro-inflammatory environment. Among the pathways regulating adipose tissue homeostasis is the wingless-type mammary tumor virus integration site family (Wnt) signaling pathway, with both its canonical and non-canonical arms. Various modulators of the Wnt signaling have been identified to contribute to the development of metabolic diseases and their cardiovascular complications, with a particularly significant role played by Glycogen Synthase Kinase-3β (GSK-3β). GSK-3β levels and activities have various and often contrasting roles in obesity and related metabolic disorders, as well as their cardiovascular sequelae. Here, we explore the possibility that altered Wnt signaling and GSK-3β activities could serve as a connection between adipose tissue dysfunction and the development of cardiovascular disease in individuals with metabolic syndrome. We attempt to define a context-specific approach for intervention, which could possibly serve as a novel disease modifying therapy for the mitigation of such complications.

Accumulated β-catenin is associated with human atrial fibrosis and atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is associated with increased risk of stroke and mortality. It has been reported that the process of atrial fibrosis was regulated by β-catenin in rats with AF. However, pathophysiological mechanisms of this process in human with AF remain unclear. This study aims to investigate the possible mechanisms of β-catenin in participating in the atrial fibrosis using human right atrial appendage (hRAA) tissues .

METHODS

We compared the difference of β-catenin expression in hRAA tissues between the patients with AF and sinus rhythm (SR). The possible function of β-catenin in the development of AF was also explored in mice and primary cells.

RESULTS

Firstly, the space between the membrane of the gap junctions of cardiomyocytes was wider in the AF group. Secondly, the expression of the gap junction function related proteins, Connexin40 and Connexin43, was decreased, while the expression of β-catenin and its binding partner E-cadherin was increased in hRAA and cardiomyocytes of the AF group. Thirdly, β-catenin colocalized with E-cadherin on the plasma membrane of cardiomyocytes in the SR group, while they were dissociated and accumulated intracellularly in the AF group. Furthermore, the expression of glycogen synthase kinase 3β (GSK-3β) and Adenomatous Polyposis Coli (APC), which participated in the degradation of β-catenin, was decreased in hRAA tissues and cardiomyocytes of the AF group. Finally, the development of atrial fibrosis and AF were proved to be prevented after inhibiting β-catenin expression in the AF model mice.

CONCLUSIONS

Based on human atrial pathological and molecular analyses, our findings provided evidence that β-catenin was associated with atrial fibrosis and AF progression.

Early- to mid-gestational testosterone excess leads to adverse cardiac outcomes in postpartum sheep

Cardiovascular dysfunctions complicate 10-20% of pregnancies, increasing the risk for postpartum mortality. Various gestational insults, including preeclampsia are reported to be associated with adverse maternal cardiovascular outcomes. One such insult, gestational hyperandrogenism increases the risk for preeclampsia and other gestational morbidities but its impact on postpartum maternal health is not well known. We hypothesize that gestational hyperandrogenism such as testosterone (T) excess will adversely impact the maternal heart in the postpartum period. Pregnant ewes were injected with T propionate from day 30 to day 90 of gestation (term 147 days). Three months postpartum, echocardiograms, plasma cytokine profiles, cardiac morphometric, and molecular analysis were conducted [control (C) n = 6, T-treated (T) n = 7 number of animals]. Data were analyzed by two-tailed Student's t test and Cohen's effect size (d) analysis. There was a nonsignificant large magnitude decrease in cardiac output (7.64 ± 1.27 L/min vs. 10.19 ± 1.40, P = 0.22, d = 0.81) and fractional shortening in the T ewes compared with C (35.83 ± 2.33% vs. 41.50 ± 2.84, P = 0.15, d = 0.89). T treatment significantly increased 1) left ventricle (LV) weight-to-body weight ratio (2.82 ± 0.14 g/kg vs. 2.46 ± 0.08) and LV thickness (14.56 ± 0.52 mm vs. 12.50 ± 0.75), 2) proinflammatory marker [tumor necrosis factor-alpha (TNF-α)] in LV (1.66 ± 0.35 vs. 1.06 ± 0.18), 3) LV collagen (Masson's Trichrome stain: 3.38 ± 0.35 vs. 1.49 ± 0.15 and Picrosirius red stain: 5.50 ± 0.32 vs. 3.01 ± 0.23), 4) markers of LV apoptosis, including TUNEL (8.3 ± 1.1 vs. 0.9 ± 0.18), bcl-2-associated X protein (Bax)+-to-b-cell lymphoma 2 (Bcl2)+ ratio (0.68 ± 0.30 vs. 0.13 ± 0.02), and cleaved caspase 3 (15.4 ± 1.7 vs. 4.4 ± 0.38). These findings suggest that gestational testosterone excess adversely programs the maternal LV, leading to adverse structural and functional consequences in the postpartum period.NEW & NOTEWORTHY Using a sheep model of human translational relevance, this study provides evidence that excess gestational testosterone exposure such as that seen in hyperandrogenic disorders adversely impacts postpartum maternal hearts.

Loss of ADAM15 in female mice does not worsen pressure overload cardiomyopathy, independent of ovarian hormones

Cardiac hypertrophy is a common feature in several cardiomyopathies. We previously reported that loss of ADAM15 (disintegrin and metalloproteinase 15) worsened cardiac hypertrophy and dilated cardiomyopathy following cardiac pressure overload. Here, we investigated the impact of ADAM15 loss in female mice following cardiac pressure overload induced by transverse aortic constriction (TAC). Female Adam15-/- mice developed the same degree of cardiac hypertrophy, dilation, and dysfunction as the parallel female wild-type (WT) mice at 6 wk post-TAC. To determine if this is due to the protective effects of estrogen, which could mask the negative impact of Adam15 loss, WT and Adam15-/- mice underwent ovariectomy (OVx) 2 wk before TAC. Cardiac structure and function analyses were performed at 6 wk post-TAC. OVx similarly impacted females of both genotypes post-TAC. Calcineurin (Cn) activity was increased post-OVx-TAC, and more in Adam15-/- mice; however, this increase was not reflected in the total-to-phospho-NFAT levels. Integrin-α7 expression, which was upstream of Cn activation in male Adam15-/- -TAC mice, remained unchanged in female mice. However, activation of the mitogen-activated protein kinases (ERK, JNK, P38) was greater in Adam15-/--OVx-TAC than in WT-OVx-TAC mice. In addition, ADAM15 protein levels were significantly increased post-TAC in male but not in female WT mice. Myocardial fibrosis was comparable in non-OVx WT-TAC and Adam15-/- -TAC mice. OVx increased the perivascular fibrosis more in Adam15-/- compared with WT mice post-TAC. Our data demonstrate that loss of ovarian hormones did not fully replicate the male phenotype in the female Adam15-/- mice post-TAC. As ADAM15 levels were increased in males but not in females post-TAC, it is plausible that ADAM15 does not play a prominent role in post-TAC events in female mice. Our findings highlight the significance of factors other than sex hormones in mediating cardiomyopathies in females, which require a more thorough understanding.NEW & NOTEWORTHY Loss of ADAM15 in female mice, unlike the male mice, does not worsen the cardiomyopathy following cardiac pressure overload. Ovariectomy does not worsen the post-TAC cardiomyopathy in female Adam15-/- mice compared with female WT mice. Lack of deleterious impact of Adam15 deficiency in female mice is not because of the protective effects of ovarian hormones but could be due to a less prominent role of ADAM15 in cardiac response to post-TAC remodeling in female mice.

Mitochondrial Kinase Signaling for Cardioprotection

Myocardial ischemia/reperfusion injury is reduced by cardioprotective adaptations such as local or remote ischemic conditioning. The cardioprotective stimuli activate signaling cascades, which converge on mitochondria and maintain the function of the organelles, which is critical for cell survival. The signaling cascades include not only extracellular molecules that activate sarcolemmal receptor-dependent or -independent protein kinases that signal at the plasma membrane or in the cytosol, but also involve kinases, which are located to or within mitochondria, phosphorylate mitochondrial target proteins, and thereby modify, e.g., respiration, the generation of reactive oxygen species, calcium handling, mitochondrial dynamics, mitophagy, or apoptosis. In the present review, we give a personal and opinionated overview of selected protein kinases, localized to/within myocardial mitochondria, and summarize the available data on their role in myocardial ischemia/reperfusion injury and protection from it. We highlight the regulation of mitochondrial function by these mitochondrial protein kinases.

The role of deubiquitinases in cardiac disease

Deubiquitinases are a group of proteins that identify and digest monoubiquitin chains or polyubiquitin chains attached to substrate proteins, preventing the substrate protein from being degraded by the ubiquitin-proteasome system. Deubiquitinases regulate cellular autophagy, metabolism and oxidative stress by acting on different substrate proteins. Recent studies have revealed that deubiquitinases act as a critical regulator in various cardiac diseases, and control the onset and progression of cardiac disease through a board range of mechanism. This review summarizes the function of different deubiquitinases in cardiac disease, including cardiac hypertrophy, myocardial infarction and diabetes mellitus-related cardiac disease. Besides, this review briefly recapitulates the role of deubiquitinases modulators in cardiac disease, providing the potential therapeutic targets in the future.

Sacubitril/valsartan attenuates myocardial inflammation, hypertrophy, and fibrosis in rats with heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) represents a multifaceted syndrome related to complex pathologic mechanisms. Sacubitril/valsartan (Sac/val) has demonstrated therapeutic efficacy in HFpEF treatment. However, additional research is required to elucidate its pharmacological mechanisms. Accordingly, this study aimed to explore the potential therapeutic effects of Sac/val in HFpEF rats and the underlying molecular mechanisms. In this study, rats with HFpEF were induced by subjecting spontaneously hypertensive rats to a diet rich in fats, salts, and sugars, along with administering streptozotocin. Subsequently, they were administered Sac/val at a daily dosage of 18 mg/kg. Finally, cardiac structure and function were assessed using echocardiography; Hematoxylin and eosin staining and Masson's trichrome staining were employed to evaluate the pathological changes; Quantitative real-time polymerase chain reaction and Western blot analysis were conducted to determine the expression of pertinent mRNA and proteins. Sac/val treatment attenuated left ventricular (LV) remodeling and diastolic dysfunction in HFpEF rats, possibly related to its anti-inflammatory, anti-hypertrophic, and anti-fibrotic efficacy. Mechanistically, Sac/val might inhibit inflammation by down-regulating cell adhesion molecule (intercellular adhesion molecule-1 (ICAM-1) and vascular endothelial cell adhesion molecule-1 (VCAM-1)) expression. Additionally, it blocked the phosphorylation of glycogen synthase kinase 3β (GSK-3β) to prevent cardiomyocyte hypertrophy. Furthermore, it effectively suppressed myocardial fibrosis by inhibiting the transforming growth factor-beta1 (TGF-β1)/Smads pathway. Our findings suggest that Sac/val improved LV remodeling and diastolic dysfunction, potentially attributed to its anti-inflammatory, anti-hypertrophic, and anti-fibrotic effects. These results provide a sound theoretical rationale for the clinical application of Sac/val in patients with HFpEF.

GSK-3 at the heart of cardiometabolic diseases: Isoform-specific targeting is critical to therapeutic benefit

Glycogen synthase kinase-3 (GSK-3) is a family of serine/threonine kinases. The GSK-3 family has 2 isoforms, GSK-3α and GSK-3β. The GSK-3 isoforms have been shown to play overlapping as well as isoform-specific-unique roles in both, organ homeostasis and the pathogenesis of multiple diseases. In the present review, we will particularly focus on expanding the isoform-specific role of GSK-3 in the pathophysiology of cardiometabolic disorders. We will highlight recent data from our lab that demonstrated the critical role of cardiac fibroblast (CF) GSK-3α in promoting injury-induced myofibroblast transformation, adverse fibrotic remodeling, and deterioration of cardiac function. We will also discuss studies that found the exact opposite role of CF-GSK-3β in cardiac fibrosis. We will review emerging studies with inducible cardiomyocyte (CM)-specific as well as global isoform-specific GSK-3 KOs that demonstrated inhibition of both GSK-3 isoforms provides benefits against obesity-associated cardiometabolic pathologies. The underlying molecular interactions and crosstalk among GSK-3 and other signaling pathways will be discussed. We will briefly review the specificity and limitations of the available small molecule inhibitors targeting GSK-3 and their potential applications to treat metabolic disorders. Finally, we will summarize these findings and offer our perspective on envisioning GSK-3 as a therapeutic target for the management of cardiometabolic diseases.

A rat model of metabolic syndrome-related heart failure with preserved ejection fraction phenotype: pathological alterations and possible molecular mechanisms

Background

Heart failure with preserved ejection fraction (HFpEF) represents a syndrome involving multiple pathophysiologic disorders and clinical phenotypes. This complexity makes it challenging to develop a comprehensive preclinical model, which presents an obstacle to elucidating disease mechanisms and developing new drugs. Metabolic syndrome (MetS) is a major phenotype of HFpEF. Thus, we produced a rat model of the MetS-related HFpEF phenotype and explored the molecular mechanisms underpinning the observed pathological changes.

Methods

A rat model of the MetS-related HFpEF phenotype was created by feeding spontaneously hypertensive rats a high-fat-salt-sugar diet and administering streptozotocin solution intraperitoneally. Subsequently, pathological changes in the rat heart and their possible molecular mechanisms were explored.

Results

The HFpEF rats demonstrated primary features of MetS, such as hypertension, hyperglycemia, hyperlipidemia, insulin resistance, and cardiac anomalies, such as left ventricular (LV) remodeling and diastolic impairment, and left atrial dilation. Additionally, inflammation, myocardial hypertrophy, and fibrosis were observed in LV myocardial tissue, which may be associated with diverse cellular and molecular signaling cascades. First, the inflammatory response might be related to the overexpression of inflammatory regulators (growth differentiation factor 15 (GDF-15), intercellular adhesion molecule-1 (ICAM-1), and vascular endothelial cell adhesion molecule-1 (VCAM-1)). Secondly, phosphorylated glycogen synthase kinase 3β (GSK-3β) may stimulate cardiac hypertrophy, which was regulated by activated -RAC-alpha serine/threonine-protein kinase (AKT). Finally, the transforming growth factor-β1 (TGF-β1)/Smads pathway might regulate collagen production and fibroblast activation, promoting myocardial fibrosis.

Conclusion

The HFpEF rat replicates the pathology and clinical presentation of human HFpEF with MetS and may be a reliable preclinical model that helps elucidate HFpEF pathogenesis and develop effective treatment strategies.

O-GlcNAcylation-induced GSK-3β activation deteriorates pressure overload-induced heart failure via lack of compensatory cardiac hypertrophy in mice

O-GlcNAc transferase (OGT) modulates many functions of proteins via O-GlcNAcylation that adds O-linked β-N-acetylglucosamine (O-GlcNAc) to the serine/threonine residues of proteins. However, the role of O-GlcNAcylation in cardiac remodeling and function is not fully understood. To examine the effect of O-GlcNAcylation on pressure overload-induced cardiac hypertrophy and subsequent heart failure, transverse aortic constriction (TAC) surgery was performed in wild type (WT) and Ogt transgenic (Ogt-Tg) mice. Four weeks after TAC (TAC4W), the heart function of Ogt-Tg mice was significantly lower than that of WT mice (reduced fractional shortening and increased ANP levels). The myocardium of left ventricle (LV) in Ogt-Tg mice became much thinner than that in WT mice. Moreover, compared to the heart tissues of WT mice, O-GlcNAcylation of GSK-3β at Ser9 was increased and phosphorylation of GSK-3β at Ser9 was reduced in the heart tissues of Ogt-Tg mice, resulting in its activation and subsequent inactivation of nuclear factor of activated T cell (NFAT) activity. Finally, the thinned LV wall and reduced cardiac function induced by TAC4W in Ogt-Tg mice was reversed by the treatment of a GSK-3β inhibitor, TDZD-8. These results imply that augmented O-GlcNAcylation exacerbates pressure overload-induced heart failure due to a lack of compensatory cardiac hypertrophy via O-GlcNAcylation of GSK-3β, which deprives the phosphorylation site of GSK-3β to constantly inactivate NFAT activity to prevent cardiac hypertrophy. Our findings may provide a new therapeutic strategy for cardiac hypertrophy and subsequent heart failure.

A remarkable adaptive paradigm of heart performance and protection emerges in response to marked cardiac-specific overexpression of ADCY8

Adult (3 month) mice with cardiac-specific overexpression of adenylyl cyclase (AC) type VIII (TGAC8) adapt to an increased cAMP-induced cardiac workload (~30% increases in heart rate, ejection fraction and cardiac output) for up to a year without signs of heart failure or excessive mortality. Here, we show classical cardiac hypertrophy markers were absent in TGAC8, and that total left ventricular (LV) mass was not increased: a reduced LV cavity volume in TGAC8 was encased by thicker LV walls harboring an increased number of small cardiac myocytes, and a network of small interstitial proliferative non-cardiac myocytes compared to wild type (WT) littermates; Protein synthesis, proteosome activity, and autophagy were enhanced in TGAC8 vs WT, and Nrf-2, Hsp90α, and ACC2 protein levels were increased. Despite increased energy demands in vivo LV ATP and phosphocreatine levels in TGAC8 did not differ from WT. Unbiased omics analyses identified more than 2,000 transcripts and proteins, comprising a broad array of biological processes across multiple cellular compartments, which differed by genotype; compared to WT, in TGAC8 there was a shift from fatty acid oxidation to aerobic glycolysis in the context of increased utilization of the pentose phosphate shunt and nucleotide synthesis. Thus, marked overexpression of AC8 engages complex, coordinate adaptation "circuity" that has evolved in mammalian cells to defend against stress that threatens health or life (elements of which have already been shown to be central to cardiac ischemic pre-conditioning and exercise endurance cardiac conditioning) that may be of biological significance to allow for proper healing in disease states such as infarction or failure of the heart.

Calcineurin-NFAT dynamics correspond to cardiac remodeling during aortic banding and debanding, mimicking aortic valve replacement

Aortic valve stenosis (AS) is a major health problem. Extensive myocardial remodeling increases operative risk and might lead to incomplete reverse remodeling with persistent symptoms after aortic valve replacement (AVR); this makes the optimal timing of AVR a clinical challenge. The pathogenesis behind incomplete reverse remodeling is unclear. Central among signaling pathways in the remodeling heart is the pro-hypertrophic Ca2+-activated calcineurin and its downstream nuclear factor of activated T-cell (NFATc1-c4) transcription factors. We investigated calcineurin-NFATc dynamics in patient and mouse hearts during remodeling and reverse remodeling. Myocardial biopsies were obtained from AS patients during AVR and left ventricles harvested from mice subjected to aortic banding (AB) and debanding (DB). The transcript and protein of the NFATc-responsive gene regulator of calcineurin 1-4 (RCAN1-4) and luciferase activity in NFAT-luciferase mice were used as read-outs for calcineurin-NFATc activity. Calcineurin-NFATc activation was sustained through AB 24 h to 18 weeks and elevated in AS patients. All four NFATc isoforms were elevated in AS, while NFATc4 was persistently elevated during chronic remodeling after AB in mice. NFAT activation remained reversible when 1 week's AB was followed by 1 week's DB and accompanied functional improvement. However, when DB for 1 week followed AB for 4 weeks, NFAT activation was not reversed. In conclusion, calcineurin-NFAT dynamics correspond with cardiac remodeling and reverse remodeling during experimental AB and DB. Our data suggest that calcineurin-NFATc attenuation is important for reverse remodeling and outcomes after AVR for AS.

Novel GSK-3β Inhibitor Neopetroside A Protects Against Murine Myocardial Ischemia/Reperfusion Injury

Recent trends suggest novel natural compounds as promising treatments for cardiovascular disease. The authors examined how neopetroside A, a natural pyridine nucleoside containing an α-glycoside bond, regulates mitochondrial metabolism and heart function and investigated its cardioprotective role against ischemia/reperfusion injury. Neopetroside A treatment maintained cardiac hemodynamic status and mitochondrial respiration capacity and significantly prevented cardiac fibrosis in murine models. These effects can be attributed to preserved cellular and mitochondrial function caused by the inhibition of glycogen synthase kinase-3 beta, which regulates the ratio of nicotinamide adenine dinucleotide to nicotinamide adenine dinucleotide, reduced, through activation of the nuclear factor erythroid 2-related factor 2/NAD(P)H quinone oxidoreductase 1 axis in a phosphorylation-independent manner.

N6-Methyladenosine RNA Methylation in Cardiovascular Diseases

N6-methyladenosine (m6A) modification is the most universal and abundant post-transcriptional modification of eukaryotic RNA and occurs mainly at the consensus motif RR (m6A) CH (R = A or G, H = A, C, or U) in long internal exons, near stop codons, or in the 3' untranslated region (UTR). "Writers," "erasers," and "readers" are responsible for the occurrence, removal, and recognition of m6A modification, respectively. Substantial evidence has shown that m6A RNA modification can exert important functions in physiological and pathological processes. Cardiovascular diseases (CVDs) are a wide array of disorders affecting heart or vessels, including atherosclerosis (AS), hypertension (HT), ischemia/reperfusion (I/R) injury, myocardial infarction (MI), stroke, cardiac hypertrophy, heart failure (HF), and so on. Despite the advances in lipid-lowering drugs, antihypertensives, antiplatelet agents, and anticoagulation therapy, CVDs are still the leading cause of death worldwide. Recent studies have suggested that m6A modification of RNA may contribute to the pathogenesis of CVDs, providing a novel research insight for CVDs. Herein, we provide an up-of-date summarization of the molecular mechanism of m6A and the roles of m6A in different types of CVDs. At last, we propose that m6A might be a potiential biomarker or therapeutic target for CVDs.

Signaling cascades in the failing heart and emerging therapeutic strategies

Chronic heart failure is the end stage of cardiac diseases. With a high prevalence and a high mortality rate worldwide, chronic heart failure is one of the heaviest health-related burdens. In addition to the standard neurohormonal blockade therapy, several medications have been developed for chronic heart failure treatment, but the population-wide improvement in chronic heart failure prognosis over time has been modest, and novel therapies are still needed. Mechanistic discovery and technical innovation are powerful driving forces for therapeutic development. On the one hand, the past decades have witnessed great progress in understanding the mechanism of chronic heart failure. It is now known that chronic heart failure is not only a matter involving cardiomyocytes. Instead, chronic heart failure involves numerous signaling pathways in noncardiomyocytes, including fibroblasts, immune cells, vascular cells, and lymphatic endothelial cells, and crosstalk among these cells. The complex regulatory network includes protein-protein, protein-RNA, and RNA-RNA interactions. These achievements in mechanistic studies provide novel insights for future therapeutic targets. On the other hand, with the development of modern biological techniques, targeting a protein pharmacologically is no longer the sole option for treating chronic heart failure. Gene therapy can directly manipulate the expression level of genes; gene editing techniques provide hope for curing hereditary cardiomyopathy; cell therapy aims to replace dysfunctional cardiomyocytes; and xenotransplantation may solve the problem of donor heart shortages. In this paper, we reviewed these two aspects in the field of failing heart signaling cascades and emerging therapeutic strategies based on modern biological techniques.

Different activation of MAPKs and Akt/GSK3β after preload vs. afterload elevation

Aims

Pressure overload (PO) and volume overload (VO) lead to concentric or eccentric hypertrophy. Previously, we could show that activation of signalling cascades differ in in vivo mouse models. Activation of these signal cascades could either be induced by intrinsic load sensing or neuro‐endocrine substances like catecholamines or the renin‐angiotensin‐aldosterone system.

Methods and results

We therefore analysed the activation of classical cardiac signal pathways [mitogen‐activated protein kinases (MAPKs) (ERK, p38, and JNK) and Akt‐GSK3β] in in vitro of mechanical overload (ejecting heart model, rabbit and human isolated muscle strips). Selective elevation of preload in vitro increased AKT and GSK3β phosphorylation after 15 min in isolated rabbit muscles strips (AKT 49%, GSK3β 26%, P < 0.05) and in mouse ejecting hearts (AKT 51%, GSK49%, P < 0.05), whereas phosphorylation of MAPKs was not influenced by increased preload. Selective elevation of afterload revealed an increase in ERK phosphorylation in the ejecting heart (43%, P < 0.05), but not in AKT, GSK3β, and the other MAPKs. Elevation of preload and afterload in the ejecting heart induced a significant phosphorylation of ERK (95%, P < 0.001) and showed a moderate increased AKT (P = 0.14) and GSK3β (P = 0.21) phosphorylation, which did not reach significance. Preload and afterload elevation in muscles strips from human failing hearts showed neither AKT nor ERK phosphorylation changes.

Conclusions

Our data show that preload activates the AKT–GSK3β and afterload the ERK pathway in vitro, indicating an intrinsic mechanism independent of endocrine signalling.

GSK-3β Localizes to the Cardiac Z-Disc to Maintain Length Dependent Activation

BACKGROUND

Altered kinase localization is gaining appreciation as a mechanism of cardiovascular disease. Previous work suggests GSK-3β (glycogen synthase kinase 3β) localizes to and regulates contractile function of the myofilament. We aimed to discover GSK-3β's in vivo role in regulating myofilament function, the mechanisms involved, and the translational relevance.

METHODS

Inducible cardiomyocyte-specific GSK-3β knockout mice and left ventricular myocardium from nonfailing and failing human hearts were studied.

RESULTS

Skinned cardiomyocytes from knockout mice failed to exhibit calcium sensitization with stretch indicating a loss of length-dependent activation (LDA), the mechanism underlying the Frank-Starling Law. Titin acts as a length sensor for LDA, and knockout mice had decreased titin stiffness compared with control mice, explaining the lack of LDA. Knockout mice exhibited no changes in titin isoforms, titin phosphorylation, or other thin filament phosphorylation sites known to affect passive tension or LDA. Mass spectrometry identified several z-disc proteins as myofilament phospho-substrates of GSK-3β. Agreeing with the localization of its targets, GSK-3β that is phosphorylated at Y216 binds to the z-disc. We showed pY216 was necessary and sufficient for z-disc binding using adenoviruses for wild-type, Y216F, and Y216E GSK-3β in neonatal rat ventricular cardiomyocytes. One of GSK-3β's z-disc targets, abLIM-1 (actin-binding LIM protein 1), binds to the z-disc domains of titin that are important for maintaining passive tension. Genetic knockdown of abLIM-1 via siRNA in human engineered heart tissues resulted in enhancement of LDA, indicating abLIM-1 may act as a negative regulator that is modulated by GSK-3β. Last, GSK-3β myofilament localization was reduced in left ventricular myocardium from failing human hearts, which correlated with depressed LDA.

CONCLUSIONS

We identified a novel mechanism by which GSK-3β localizes to the myofilament to modulate LDA. Importantly, z-disc GSK-3β levels were reduced in patients with heart failure, indicating z-disc localized GSK-3β is a possible therapeutic target to restore the Frank-Starling mechanism in patients with heart failure.

State of Knowledge on Molecular Adaptations to Exercise in Humans: Historical Perspectives and Future Directions

For centuries, regular exercise has been acknowledged as a potent stimulus to promote, maintain, and restore healthy functioning of nearly every physiological system of the human body. With advancing understanding of the complexity of human physiology, continually evolving methodological possibilities, and an increasingly dire public health situation, the study of exercise as a preventative or therapeutic treatment has never been more interdisciplinary, or more impactful. During the early stages of the NIH Common Fund Molecular Transducers of Physical Activity Consortium (MoTrPAC) Initiative, the field is well-positioned to build substantially upon the existing understanding of the mechanisms underlying benefits associated with exercise. Thus, we present a comprehensive body of the knowledge detailing the current literature basis surrounding the molecular adaptations to exercise in humans to provide a view of the state of the field at this critical juncture, as well as a resource for scientists bringing external expertise to the field of exercise physiology. In reviewing current literature related to molecular and cellular processes underlying exercise-induced benefits and adaptations, we also draw attention to existing knowledge gaps warranting continued research effort. © 2021 American Physiological Society. Compr Physiol 12:3193-3279, 2022.

When one says yes and the other says no; does calcineurin participate in physiologic cardiac hypertrophy?

Developing engaging activities that build skills for understanding and appreciating research is important for undergraduate and postgraduate science students. Comparing and contrasting opposing research studies does this, and more: it also appropriately for these cohorts challenges higher level cognitive processing. Here, we present and discuss one such scenario, that of calcineurin in the heart and its response to exercise training. This scenario is further accentuated by the existence of only two studies. The background is that regular aerobic endurance exercise training stimulates the heart to physiologically adapt to chronically increase its ability to produce a greater cardiac output to meet the increased demand for oxygenated blood in working muscles, and this happens by two main mechanisms: 1) increased cardiac contractile function and 2) physiologic hypertrophy. The major underlying mechanisms have been delineated over the last decades, but one aspect has not been resolved: the potential role of calcineurin in modulating physiologic hypertrophy. This is partly because the existing research has provided opposing and contrasting findings, one line showing that exercise training does activate cardiac calcineurin in conjunction with myocardial hypertrophy, but another line showing that exercise training does not activate cardiac calcineurin even if myocardial hypertrophy is blatantly occurring. Here, we review and present the current evidence in the field and discuss reasons for this controversy. We present real-life examples from physiology research and discuss how this may enhance student engagement and participation, widen the scope of learning, and thereby also further facilitate higher level cognitive processing.

GSK3β Serine 389 Phosphorylation Modulates Cardiomyocyte Hypertrophy and Ischemic Injury

Prior studies show that glycogen synthase kinase 3β (GSK3β) contributes to cardiac ischemic injury and cardiac hypertrophy. GSK3β is constitutionally active and phosphorylation of GSK3β at serine 9 (S9) inactivates the kinase and promotes cellular growth. GSK3β is also phosphorylated at serine 389 (S389), but the significance of this phosphorylation in the heart is not known. We analyzed GSK3β S389 phosphorylation in diseased hearts and utilized overexpression of GSK3β carrying ser→ala mutations at S9 (S9A) and S389 (S389A) to study the biological function of constitutively active GSK3β in primary cardiomyocytes. We found that phosphorylation of GSK3β at S389 was increased in left ventricular samples from patients with dilated cardiomyopathy and ischemic cardiomyopathy, and in hearts of mice subjected to thoracic aortic constriction. Overexpression of either GSK3β S9A or S389A reduced the viability of cardiomyocytes subjected to hypoxia-reoxygenation. Overexpression of double GSK3β mutant (S9A/S389A) further reduced cardiomyocyte viability. Determination of protein synthesis showed that overexpression of GSK3β S389A or GSK3β S9A/S389A increased both basal and agonist-induced cardiomyocyte growth. Mechanistically, GSK3β S389A mutation was associated with activation of mTOR complex 1 signaling. In conclusion, our data suggest that phosphorylation of GSK3β at S389 enhances cardiomyocyte survival and protects from cardiomyocyte hypertrophy.

Emerging roles of Sirtuin 2 in cardiovascular diseases

Sirtuins are a family of NAD⁺ -dependent deacetylases implicated in a wide variety of age-associated pathologies, including cardiovascular disorders. Among the seven mammalian sirtuins, SIRT2 modulates various cellular processes through the deacetylation or deacylation of their target proteins. Notably, the levels of SIRT2 in the heart decline with age and other pathological conditions, leading to cardiovascular dysfunction. In the present review, we discuss the emerging roles of SIRT2 in cardiovascular dysfunction and heart failure associated with factors like age, hypertension, oxidative stress, and diabetes. We also discuss the potential of using inhibitors to study the unexplored role of SIRT2 in the heart. While SIRT2 undoubtedly plays a crucial role in the cardiovascular system, its functions are only beginning to be understood, making it an attractive candidate for further research in the field.

mRNA modifications in cardiovascular biology and disease: with a focus on m6A modification

Among several known RNA modifications, N6-methyladenosine (m6A) is the most studied RNA epitranscriptomic modification and controls multiple cellular functions during development, differentiation, and disease. Current research advancements have made it possible to examine the regulatory mechanisms associated with RNA methylation and reveal its functional consequences in the pathobiology of many diseases, including heart failure. m6A methylation has been described both on coding (mRNA) and non-coding RNA species including rRNA, tRNA, small nuclear RNA and circular RNAs. The protein components which catalyze the m6A methylation are termed methyltransferase or "m6A writers." The family of proteins that recognize this methylation are termed "m6A readers" and finally the enzymes involved in the removal of a methyl group from RNA are known as demethylases or "m6A erasers." At the cellular level, different components of methylation machinery are tightly regulated by many factors to maintain the m6A methylation dynamics. The m6A methylation process impacts different stages of mRNA metabolism and the biogenesis of long non-coding RNA and miRNA. Although, mRNA methylation was initially described in the 1970s, its regulatory roles in various diseases, including cardiovascular diseases are broadly unexplored. Recent investigations suggest the important role of m6A mRNA methylation in both hypertrophic and ischemic heart diseases. In the present review, we evaluate the significance of m6A methylation in the cardiovascular system, in cardiac homeostasis and disease, all of which may help to improve therapeutic intervention for the treatment of heart failure.

Protein acetylation in cardiac aging

Biological aging is attributed to progressive dysfunction in systems governing genetic and metabolic integrity. At the cellular level, aging is evident by accumulated DNA damage and mutation, reactive oxygen species, alternate lipid and protein modifications, alternate gene expression programs, and mitochondrial dysfunction. These effects sum to drive altered tissue morphology and organ dysfunction. Protein-acylation has emerged as a critical mediator of age-dependent changes in these processes. Despite decades of research focus from academia and industry, heart failure remains a leading cause of death in the United States while the 5 year mortality rate for heart failure remains over 40%. Over 90% of heart failure deaths occur in patients over the age of 65 and heart failure is the leading cause of hospitalization in Medicare beneficiaries. In 1931, Cole and Koch discovered age-dependent accumulation of phosphates in skeletal muscle. These and similar findings provided supporting evidence for, now well accepted, theories linking metabolism and aging. Nearly two decades later, age-associated alterations in biochemical molecules were described in the heart. From these small beginnings, the field has grown substantially in recent years. This growing research focus on cardiac aging has, in part, been driven by advances on multiple public health fronts that allow population level clinical presentation of aging related disorders. It is estimated that by 2030, 25% of the worldwide population will be over the age of 65. This review provides an overview of acetylation-dependent regulation of biological processes related to cardiac aging and introduces emerging non-acetyl, acyl-lysine modifications in cardiac function and aging.

Linking metabolic dysfunction with cardiovascular diseases: Brn-3b/POU4F2 transcription factor in cardiometabolic tissues in health and disease

Metabolic and cardiovascular diseases are highly prevalent and chronic conditions that are closely linked by complex molecular and pathological changes. Such adverse effects often arise from changes in the expression of genes that control essential cellular functions, but the factors that drive such effects are not fully understood. Since tissue-specific transcription factors control the expression of multiple genes, which affect cell fate under different conditions, then identifying such regulators can provide valuable insight into the molecular basis of such diseases. This review explores emerging evidence that supports novel and important roles for the POU4F2/Brn-3b transcription factor (TF) in controlling cellular genes that regulate cardiometabolic function. Brn-3b is expressed in insulin-responsive metabolic tissues (e.g. skeletal muscle and adipose tissue) and is important for normal function because constitutive Brn-3b-knockout (KO) mice develop profound metabolic dysfunction (hyperglycaemia; insulin resistance). Brn-3b is highly expressed in the developing hearts, with lower levels in adult hearts. However, Brn-3b is re-expressed in adult cardiomyocytes following haemodynamic stress or injury and is necessary for adaptive cardiac responses, particularly in male hearts, because male Brn-3b KO mice develop adverse remodelling and reduced cardiac function. As a TF, Brn-3b regulates the expression of multiple target genes, including GLUT4, GSK3β, sonic hedgehog (SHH), cyclin D1 and CDK4, which have known functions in controlling metabolic processes but also participate in cardiac responses to stress or injury. Therefore, loss of Brn-3b and the resultant alterations in the expression of such genes could potentially provide the link between metabolic dysfunctions with adverse cardiovascular responses, which is seen in Brn-3b KO mutants. Since the loss of Brn-3b is associated with obesity, type II diabetes (T2DM) and altered cardiac responses to stress, this regulator may provide a new and important link for understanding how pathological changes arise in such endemic diseases.

The nutrient sensing pathways FoxO1/3 and mTOR in the heart are coordinately regulated by central leptin through PPARβ/δ. Implications in cardiac remodeling

BACKGROUND

Cardiovascular disease in obese individuals with type 2 diabetes is often associated with hyperleptinemia and leptin resistance, while other studies support that leptin has cardioprotective effects. Besides, the role of leptin in regulating cardiac atrophy or hypertrophy remains to be clearly defined. In fact, in rats with normal leptin sensitivity, the molecular underpinnings of the effects of central leptin regulating cardiac structural pathways remain poorly understood.

OBJECTIVE

Hence, we assessed the effects of intracerebroventricular (icv) leptin infusion on cardiac remodeling analyzing FOXO1/3 and mTORC1 pathways, focusing special attention to PPARβ/δ as mediator of central leptin's effects on cardiac metabolism.

METHODS

Male 3-months-old Wistar rats, infused with icv leptin (0.2 μg/day) for 7 days, were daily co-treated intraperitoneally with the specific PPARβ/δ antagonist GSK0660, at 1 mg/kg per day along leptin treatment.

RESULTS

Central leptin regulated dynamically, in an opposite manner, the network between FOXOs and mTORC1 and induced an atrophy-related gene program in cardiac tissue. Leptin activated the anti-hypertrophic kinase GSK3β and increased the protein levels of muscle-specific ubiquitin ligases, muscle RING finger 1 (MuRF1) and muscle atrophy F-box (MAFbx)/Atrogin-1 involved in limiting cardiac hypertrophy. FOXO1 activity and the expression of their target genes, Sod2 and Lpl, were also increased in the heart upon central leptin infusion. Besides, Beclin-1 and LC3B-II, gene products of the autophagic pathway response, were upregulated, while the content and expression levels of phenotypic markers of cardiac hypertrophy as ANP and β-myosin heavy chain, gene product of Myh7 were significantly decreased. On the other hand, mTORC1 activity and OXPHOS protein levels were decreased suggesting a key role of central leptin preventing cardiac oxidative stress. In fact, the content of carbonylated proteins, TBARS and ROS/RSN were not increased in cardiac tissue in response to central leptin infusion. Finally, the pharmacological inhibition of PPARβ/δ, via in vivo administration of the selective antagonist GSK0660, blunted the induction of FOXO1/3, Atrogin-1, MuRF1 and GSK3β in the heart mediated by icv leptin infusion.

CONCLUSIONS

Our results demonstrate that, in lean rats with normal leptin sensitivity, central leptin regulates nutrient sensing pathways in heart contributing to balance cardiac remodeling through the anti- and pro-hypertrophic programs, and in this process is involved PPARβ/δ.

Physiological And Pathological Roles Of Protein Kinase A In The Heart

Protein kinase A (PKA) is a central regulator of cardiac performance and morphology. Myocardial PKA activation is induced by a variety of hormones, neurotransmitters and stress signals, most notably catecholamines secreted by the sympathetic nervous system. Catecholamines bind β-adrenergic receptors to stimulate cAMP-dependent PKA activation in cardiomyocytes. Elevated PKA activity enhances Ca2+ cycling and increases cardiac muscle contractility. Dynamic control of PKA is essential for cardiac homeostasis, as dysregulation of PKA signaling is associated with a broad range of heart diseases. Specifically, abnormal PKA activation or inactivation contributes to the pathogenesis of myocardial ischemia, hypertrophy, heart failure, as well as diabetic, takotsubo, or anthracycline cardiomyopathies. PKA may also determine sex-dependent differences in contractile function and heart disease predisposition. Here, we describe the recent advances regarding the roles of PKA in cardiac physiology and pathology, highlighting previous study limitations and future research directions. Moreover, we discuss the therapeutic strategies and molecular mechanisms associated with cardiac PKA biology. In summary, PKA could serve as a promising drug target for cardioprotection. Depending on disease types and mechanisms, therapeutic intervention may require either inhibition or activation of PKA. Therefore, specific PKA inhibitors or activators may represent valuable drug candidates for the treatment of heart diseases.

The piRNA CHAPIR regulates cardiac hypertrophy by controlling METTL3-dependent N6-methyladenosine methylation of Parp10 mRNA

PIWI-interacting RNAs (piRNAs) are abundantly expressed during cardiac hypertrophy. However, their functions and molecular mechanisms remain unknown. Here, we identified a cardiac-hypertrophy-associated piRNA (CHAPIR) that promotes pathological hypertrophy and cardiac remodelling by targeting METTL3-mediated N⁶-methyladenosine (m⁶A) methylation of Parp10 mRNA transcripts. CHAPIR deletion markedly attenuates cardiac hypertrophy and restores heart function, while administration of a CHAPIR mimic enhances the pathological hypertrophic response in pressure-overloaded mice. Mechanistically, CHAPIR-PIWIL4 complexes directly interact with METTL3 and block the m⁶A methylation of Parp10 mRNA transcripts, which upregulates PARP10 expression. The CHAPIR-dependent increase in PARP10 promotes the mono-ADP-ribosylation of GSK3β and inhibits its kinase activity, which results in the accumulation of nuclear NFATC4 and the progression of pathological hypertrophy. Hence, our findings reveal that a piRNA-mediated RNA epigenetic mechanism is involved in the regulation of cardiac hypertrophy and that the CHAPIR-METTL3-PARP10-NFATC4 signalling axis could be therapeutically targeted for treating pathological hypertrophy and maladaptive cardiac remodelling.

The restoration of Wnt/β-catenin signalling activity by a tuna backbone-derived peptide ameliorates hypoxia-induced cardiomyocyte injury

Myocardial infarction (MI) is a serious disease with high morbidity and mortality worldwide. Reducing myocardial reperfusion injury in MI patients remains a challenge. The generation of excessive reactive oxygen species (ROS) during reperfusion is known to be responsible for injury. A peptide from tuna backbone protein (APTBP) captured our attention due to its strong antioxidant activity. Here, we aimed to assess the function of APTBP in protecting against myocardial ischaemia-reperfusion (I/R) injury and to clarify the associated mechanism. Two in vitro models generated by hypoxia and cobalt chloride treatment were used to determine the effect of APTBP on cardiomyocytes under hypoxic stress. In vivo, a rat model of I/R was generated to evaluate APTBP functions. As a result, APTBP attenuated hypoxia- or cobalt chloride-induced injury to H9C2 cells and primary cardiomyocytes. Moreover, hypoxia-induced apoptosis, ROS generation and impaired mitochondrial function were also suppressed by APTBP administration. In vivo, tail vein injection of APTBP ameliorated pathological damage and mildly restored cardiac function. To clarify the mechanism, RNA-seq was performed and revealed that the Wnt signalling pathway may be associated with this mechanism. Rescue analysis showed that β-catenin knockdown diminished the protective effect of APTBP and that the expression of an ROS generator abolished the restoration of Wnt/β-catenin signalling induced by APTBP. Collectively, our findings suggest that APTBP reduces cardiomyocyte apoptosis and protects against myocardial ischaemia-reperfusion injury by scavenging ROS and subsequently restoring Wnt/β-catenin signalling.

Isoform- and Cell Type-Specific Roles of Glycogen Synthase Kinase 3 N-Terminal Serine Phosphorylation in Liver Ischemia Reperfusion Injury

Glycogen synthase kinase 3 (Gsk3) α and β are both constitutively active and inhibited upon stimulation by N-terminal serine phosphorylation. Although roles of active Gsk3 in liver ischemia reperfusion injury (IRI) have been well appreciated, whether Gsk3 N-terminal serine phosphorylation has any functional significance in the disease process remains unclear. In a murine liver partial warm ischemia model, we studied Gsk3 N-terminal serine mutant knock-in (KI) mice and showed that liver IRI was decreased in Gsk3αS21A but increased in Gsk3βS9A mutant KI mice. Bone marrow chimeric experiments revealed that the Gsk3α, but not β, mutation in liver parenchyma protected from IRI, and both mutations in bone marrow-derived cells exacerbated liver injuries. Mechanistically, mutant Gsk3α protected hepatocytes from inflammatory (TNF-α) cell death by the activation of HIV-1 TAT-interactive protein 60 (TIP60)-mediated autophagy pathway. The pharmacological inhibition of TIP60 or autophagy diminished the protection of the Gsk3α mutant hepatocytes from inflammatory cell death in vitro and the Gsk3α mutant KI mice from liver IRI in vivo. Thus, Gsk3 N-terminal serine phosphorylation inhibits liver innate immune activation but suppresses hepatocyte autophagy in response to inflammation. Gsk3 αS21, but not βS9, mutation is sufficient to sustain Gsk4 activities in hepatocytes and protect livers from IRI via TIP60 activation.

Sedentary and Trained Older Men Have Distinct Circulating Exosomal microRNA Profiles at Baseline and in Response to Acute Exercise

Exercise has multi-systemic benefits and attenuates the physiological impairments associated with aging. Emerging evidence suggests that circulating exosomes mediate some of the beneficial effects of exercise via the transfer of microRNAs between tissues. However, the impact of regular exercise and acute exercise on circulating exosomal microRNAs (exomiRs) in older populations remains unknown. In the present study, we analyzed circulating exomiR expression in endurance-trained elderly men (n = 5) and age-matched sedentary males (n = 5) at baseline (Pre), immediately after a forty minute bout of aerobic exercise on a cycle ergometer (Post), and three hours after this acute exercise (3hPost). Following the isolation and enrichment of exosomes from plasma, exosome-enriched preparations were characterized and exomiR levels were determined by sequencing. The effect of regular exercise on circulating exomiRs was assessed by comparing the baseline expression levels in the trained and sedentary groups. The effect of acute exercise was determined by comparing baseline and post-training expression levels in each group. Regular exercise resulted in significantly increased baseline expression of three exomiRs (miR-486-5p, miR-215-5p, miR-941) and decreased expression of one exomiR (miR-151b). Acute exercise altered circulating exomiR expression in both groups. However, exomiRs regulated by acute exercise in the trained group (7 miRNAs at Post and 8 at 3hPost) were distinct from those in the sedentary group (9 at Post and 4 at 3hPost). Pathway analysis prediction and reported target validation experiments revealed that the majority of exercise-regulated exomiRs are targeting genes that are related to IGF-1 signaling, a pathway involved in exercise-induced muscle and cardiac hypertrophy. The immediately post-acute exercise exomiR signature in the trained group correlates with activation of IGF-1 signaling, whereas in the sedentary group it is associated with inhibition of IGF-1 signaling. While further validation is needed, including measurements of IGF-1/IGF-1 signaling in blood or skeletal muscle, our results suggest that training status may counteract age-related anabolic resistance by modulating circulating exomiR profiles both at baseline and in response to acute exercise.

Pregnancy-associated cardiac dysfunction and the regulatory role of microRNAs

Many crucial cardiovascular adaptations occur in the body during pregnancy to ensure successful gestation. Maladaptation of the cardiovascular system during pregnancy can lead to complications that promote cardiac dysfunction and may lead to heart failure (HF). About 12% of pregnancy-related deaths in the USA have been attributed to HF and the detrimental effects of cardiovascular complications on the heart can be long-lasting, pre-disposing the mother to HF later in life. Indeed, cardiovascular complications such as gestational diabetes mellitus, preeclampsia, gestational hypertension, and peripartum cardiomyopathy have been shown to induce cardiac metabolic dysfunction, oxidative stress, fibrosis, apoptosis, and diastolic and systolic dysfunction in the hearts of pregnant women, all of which are hallmarks of HF. The exact etiology and cardiac pathophysiology of pregnancy-related complications is not yet fully deciphered. Furthermore, diagnosis of cardiac dysfunction in pregnancy is often made only after clinical symptoms are already present, thus necessitating the need for novel diagnostic and prognostic biomarkers. Mounting data demonstrates an altered expression of maternal circulating miRNAs during pregnancy affected by cardiovascular complications. Throughout the past decade, miRNAs have become of growing interest as modulators and biomarkers of pathophysiology, diagnosis, and prognosis in cardiac dysfunction. While the association between pregnancy-related cardiovascular complications and cardiac dysfunction or HF is becoming increasingly evident, the roles of miRNA-mediated regulation herein remain poorly understood. Therefore, this review will summarize current reports on pregnancy-related cardiovascular complications that may lead to cardiac dysfunction and HF during and after pregnancy in previously healthy women, with a focus on the pathophysiological role of miRNAs.

Cell-to-cell lactate shuttle operates in heart and is important in age-related heart failure

Recent studies have revealed a resemblance of a HIF-regulated heart and brain glycolytic profiles prompting the hypothesis that the classical cell-to-cell lactate shuttle observed between astrocytes and neurons operates also in heart - between cardiac fibroblasts and cardiomyocytes. Here, we demonstrate that co-culturing of cardiomyocytes with cardiac fibroblasts leads to orchestrated changes in expression and/or localization pattern of glucose metabolism enzymes and lactate transport proteins in both cell types. These changes are regulated by paracrine signaling using microvesicle-packed and soluble factors released to the culture medium and, taken together, they concur with the cardiac lactate shuttle hypothesis. The results presented here show that similarity of heart and brain proteomes demonstrated earlier extend to physiological level and provide a theoretical rationale for designing novel therapeutic strategies for treatment of cardiomyopathies resulting from disruption of the maturation of cardiac metabolic pathways, and of heart failure associated with metabolic complications and age-related heart failure linked with extracellular matrix deposition and hypoxia.

Mechanical Regulation of Protein Translation in the Cardiovascular System

The cardiovascular system can sense and adapt to changes in mechanical stimuli by remodeling the physical properties of the heart and blood vessels in order to maintain homeostasis. Imbalances in mechanical forces and/or impaired sensing are now not only implicated but are, in some cases, considered to be drivers for the development and progression of cardiovascular disease. There is now growing evidence to highlight the role of mechanical forces in the regulation of protein translation pathways. The canonical mechanism of protein synthesis typically involves transcription and translation. Protein translation occurs globally throughout the cell to maintain general function but localized protein synthesis allows for precise spatiotemporal control of protein translation. This Review will cover studies on the role of biomechanical stress -induced translational control in the heart (often in the context of physiological and pathological hypertrophy). We will also discuss the much less studied effects of mechanical forces in regulating protein translation in the vasculature. Understanding how the mechanical environment influences protein translational mechanisms in the cardiovascular system, will help to inform disease pathogenesis and potential areas of therapeutic intervention.

Sodium Selenate Ameliorates Cardiac Injury Developed from High-Fat Diet in Mice through Regulation of Autophagy Activity

Obesity is often accompanied by dyslipidemia, high blood glucose, hypertension, atherosclerosis, and myocardial dysfunction. Selenate is a vital antioxidant in the cardiovascular system. The beneficial effects of selenate on obesity-associated cardiac dysfunction and potential molecular mechanism were identified in both H9C2 cells and C57BL/6J mice hearts. The cardiac histological preformation in C57BL/6J mice were evaluated by cross-sectional area (CSA) of cardiomyocytes and percent area of fibrosis in the left ventricles. The cardiac autophagy flux in H9C2 cells and C57BL/6J mice hearts was analyzed by Western blots and the number of autophagosomes and autolysosome in H9C2 cells. In the present study, we found that lipid overload caused increases in serum lipid, CSA, and percent area of fibrosis. We further found that lipid-induced accumulation of autophagosomes  was due to depressed autophagy degradation, which was not restored in the pretreatment with 3-methyladenine and chloroquine, whereas, it was improved by rapamycin. Moreover, we demonstrated that increased levels of serum lipid, CSA, percent area of fibrosis and mRNA expression related to cardiomyocytes hypertrophy and fibrosis were significantly reduced after selenate treatments of mice. We also found selenate treatment significantly down-regulated activity of the Akt pathway, which was activated in response to lipid-overload. Furthermore, selenate dramatically improved cardiac autophagic degradation which was suppressed after exposure to lipid-overload in both H9C2 cells and C57BL/6J mice hearts. Taken together, selenate offers therapeutic intervention in lipid-related metabolic disorders, and protection against cardiac remodeling, likely through regulation of the activity of autophagic degradation and Akt pathway.

Sex Differences in Morphological and Functional Aspects of Exercise-Induced Cardiac Hypertrophy in a Rat Model

Background: Recent evidences suggest that sex hormones may be involved in the regulation of exercise-induced left ventricular (LV) hypertrophy. However, the sex-specific functional consequences of exercise-induced myocardial hypertrophy is still not investigated in detail. We aimed at understanding the sex-specific functional and morphological alterations in the LV and the underlying molecular changes in a rat model of athlete’s heart.

Methods: We divided our young, adult male and female rats into control and exercised groups. Athlete’s heart was induced by a 12-week long swim training. Following the training period, we assessed LV hypertrophy with echocardiography, while pressure-volume analysis was performed to investigate in vivo LV function. After in vivo experiments, molecular biological studies and histological investigations were performed.

Results: Echocardiography and post-mortem measured heart weight data indicated LV hypertrophy in both genders, nevertheless it was more pronounced in females. Despite the more significant relative hypertrophy in females, characteristic functional parameters did not show notable differences between the genders. LV pressure-volume analysis showed increased stroke volume, improved contractility and stroke work and unaltered LV stiffness in both male and female exercised rats, while active relaxation was ameliorated solely in male animals. The induction of Akt signaling was more significant in females compared to males. There was also a characteristic difference in the mitogen-activated protein kinase pathway as suppressed phosphorylation of p44/42 MAPK (Erk) and mTOR was observed in female exercised rats, but not in male ones. Myosin heavy chain α (MHC)/β-MHC ratio did not differ in males, but increased markedly in females.

Conclusion: Our results confirm that there is a more pronounced exercise-induced LV hypertrophy in females as compared to the males, however, there are only minor differences regarding LV function. There are characteristic molecular differences between male and female animals, that can explain different degrees of LV hypertrophy.

GSK3β inhibition and canonical Wnt signaling in mice hearts after myocardial ischemic damage

Aims

Myocardial infarction induces myocardial injury and tissue damage. During myocardial infarction strong cellular response is initiated to salvage the damaged tissues. This response is associated with the induction of different signaling pathways. Of these, the canonical Wnt signaling is increasingly important for its prosurvival cellular role, making it a good candidate for the search of new molecular targets to develop therapies to prevent heart failure in infarcted patients.

Methods

Herein we report that GSK3β regulates the canonical Wnt signaling in C57Bl6 mice hearts. GSK3β is a canonical Wnt pathway inhibitor. Using GSK3β inhibitors and inducing myocardial injury (MI) in Lrp5^-/- mice model we show that GSK3β phosphorylation levels regulate downstream canonical Wnt pathway genes in the ischemic heart. In the setting of MI, myocardial damage assessment usually correlates with functional and clinical outcomes. Therefore, we measured myocardial injury size in Wt and Lrp5^-/- mice in the presence and absence of two different GSK3 inhibitors prior to MI. Myocardial injury was independent of GSK3 inhibitor treatments and GSK3β expression levels.

Results

These studies support a central role for GSK3β in the activation of the canonical Wnt pathway in the Wt heart. Although LRP5 is protective against myocardial injury, GSK3β expression levels do not regulate heart damage.

OBG-like ATPase 1 inhibition attenuates angiotensin II-induced hypertrophic response in human ventricular myocytes via GSK-3beta/beta-catenin signalling

Obg-like ATPase 1 (OLA1) that possesses both GTP and ATP hydrolyzing activities has been shown to be involved in translational regulation of cancer cell growth and survival. Also, GSK3β signalling has been implicated in cardiac development and disease. However, the role of OLA1 in pathological cardiac hypertrophy is unknown. We sought to understand the mechanism by which OLA1 regulates GSK3β-β-Catenin signalling and its functional significance in angiotensin-II (ANG II)-induced cardiac hypertrophic response. OLA1 function and its endogenous interaction with GSK3β/β-catenin signalling in cultured human ventricular cardiomyocytes (AC16 cells) and mouse hearts (in vivo) was evaluated with/without ANG II-stimulated hypertrophic response. ANG II administration in mice increases myocardial OLA1 protein expression with a corresponding increase in GSK3β phosphorylation and decrease in β-Catenin phosphorylation. Cultured cardiomyocytes treated with ANG II show endogenous interaction between OLA1 and GSK3β, nuclear accumulation of β-Catenin and significant increase in cell size and expression of hypertrophic marker genes such as atrial natriuretic factor (ANF; NPPA) and β-myosin heavy chain (MYH7). Intriguingly, OLA1 inhibition attenuates the above hypertrophic response in cardiomyocytes. Taken together, our data suggest that OLA1 plays a detrimental role in hypertrophic response via GSK3β/β-catenin signalling. Translation strategies to target OLA1 might potentially limit the underlying molecular derangements leading to left ventricular dysfunction in patients with maladaptive cardiac hypertrophy.

Fructose-1,6-bisphosphatase: From a glucose metabolism enzyme to multifaceted regulator of a cell fate

Fructose-1,6-bisphosphatase (FBPase) is one of the ancient, evolutionarily conserved enzymes of carbohydrate metabolism. It has been described for a first time in 1943, however, for the next half a century mostly kinetic and structural parameters of animal FBPases have been studied. Discovery of ubiquitous expression of the muscle isozyme of FBPase, thus far considered to merely regulate glycogen synthesis from carbohydrate precursors, and its nuclear localisation in several cell types has risen new interest in the protein, resulting in numerous publications revealing complex functions/properties of FBPase. This review summarises the current knowledge of FBPase in animal cells providing evidence that the enzyme merits the name of moonlighting protein.

Programmed Cell Death 5 Provides Negative Feedback on Cardiac Hypertrophy Through the Stabilization of Sarco/Endoplasmic Reticulum Ca2+-ATPase 2a Protein

PDCD5 (programmed cell death 5) is ubiquitously expressed in tissues, including the heart; however, the mechanism underlying the cardiac function of PDCD5 has not been understood. We investigated the mechanisms of PDCD5 in the pathogenesis of cardiac hypertrophy. Cardiac-specific PDCD5 knockout mice developed severe cardiac hypertrophy and impaired cardiac function, whereas PDCD5 protein was significantly increased in transverse aortic constriction mouse hearts and phenylephrine-stimulated cardiomyocytes. Overexpression of PDCD5 inhibited phenylephrine-induced cardiomyocyte hypertrophy, and knockdown of PDCD5 induced cardiomyocyte hypertrophy and aggravated phenylephrine-induced hypertrophy. The expression of PDCD5 protein was regulated by NFATc2 (nuclear factor of activated T cells c2) during hypertrophy. SERCA2a (sarco/endoplasmic reticulum Ca²⁺-ATPase 2a) expression was decreased in PDCD5-deficient mouse hearts because of increased ubiquitination. PDCD5-deficient cardiomyocytes displayed decreased calcium uptake rate, slowed decay of Ca²⁺ transients, decreased calcium stores, and diastolic dysfunction. Moreover, reintroduction of PDCD5 in PDCD5-deficient mouse hearts reserved SERCA2a protein, suppressed NFATc2 protein, and rescued the hypertrophy and cardiac dysfunction. Our results revealed that PDCD5 is a novel target of NFATc2 in the hypertrophic heart and provides negative feedback to protect the heart against excessive hypertrophy via the stabilization of SERCA2a protein.

Cardiomyocyte-GSK-3α promotes mPTP opening and heart failure in mice with chronic pressure overload

Chronic pressure-overload (PO)- induced cardiomyopathy is one of the leading causes of left ventricular (LV) remodeling and heart failure. The role of the α isoform of glycogen synthase kinase-3 (GSK-3α) in PO-induced cardiac remodeling is unclear and its downstream molecular targets are largely unknown. To investigate the potential roles of GSK-3α, cardiomyocyte-specific GSK-3α conditional knockout (cKO) and control mice underwent trans-aortic constriction (TAC) or sham surgeries. Cardiac function in the cKOs and littermate controls declined equally up to 2 weeks of TAC. At 4 week, cKO animals retained concentric LV remodeling and showed significantly less decline in contractile function both at systole and diastole, vs. controls which remained same until the end of the study (6 wk). Histological analysis confirmed preservation of LV chamber and protection against TAC-induced cellular hypertrophy in the cKO. Consistent with attenuated hypertrophy, significantly lower level of cardiomyocyte apoptosis was observed in the cKO. Mechanistically, GSK-3α was found to regulate mitochondrial permeability transition pore (mPTP) opening and GSK-3α-deficient mitochondria showed delayed mPTP opening in response to Ca²⁺ overload. Consistently, overexpression of GSK-3α in cardiomyocytes resulted in elevated Bax expression, increased apoptosis, as well as a reduction of maximum respiration capacity and cell viability. Taken together, we show for the first time that GSK-3α regulates mPTP opening under pathological conditions, likely through Bax overexpression. Genetic ablation of cardiomyocyte GSK-3α protects against chronic PO-induced cardiomyopathy and adverse LV remodeling, and preserves contractile function. Selective inhibition of GSK-3α using isoform-specific inhibitors could be a viable therapeutic strategy to limit PO-induced heart failure.

Roles of Glycogen Synthase Kinase-3 (GSK-3) in Cardiac Development and Heart Disease

Glycogen synthase kinase-3 (GSK-3) is a cytoplasmic serine/threonine protein kinase which is known to regulate a variety of cellular processes through a number of signaling pathways important for cell proliferation, stem cell renewal, apoptosis and development. Although GSK-3 exists in a variety of tissues, this kinase plays very important roles in the heart to control its development through the formation of heart and cardiomyocyte proliferation. GSK-3 is also recognized as one of the main molecules that control cardiac hypertrophy and fibrosis. Therefore, GSK-3 could be an attractive target for the development of new drugs to cure cardiac diseases. The present review summarizes the roles of GSK-3 in the signaling pathways and the heart, and discusses the possibility of new drug development targeting this kinase.

Characterization of biventricular alterations in myocardial (reverse) remodelling in aortic banding-induced chronic pressure overload

Aortic Stenosis (AS) is the most frequent valvulopathy in the western world. Traditionally aortic valve replacement (AVR) has been recommended immediately after the onset of heart failure (HF) symptoms. However, recent evidence suggests that AVR outcome can be improved if performed earlier. After AVR, the process of left ventricle (LV) reverse remodelling (RR) is variable and frequently incomplete. In this study, we aimed at detecting mechanism underlying the process of LV RR regarding myocardial structural, functional and molecular changes before the onset of HF symptoms. Wistar-Han rats were subjected to 7-weeks of ascending aortic-banding followed by a 2-week period of debanding to resemble AS-induced LV remodelling and the early events of AVR-induced RR, respectively. This resulted in 3 groups: Sham (n = 10), Banding (Ba, n = 15) and Debanding (Deb, n = 10). Concentric hypertrophy and diastolic dysfunction (DD) were patent in the Ba group. Aortic-debanding induced RR, which promoted LV functional recovery, while cardiac structure did not normalise. Cardiac parameters of RV dysfunction, assessed by echocardiography and at the cardiomyocyte level prevailed altered after debanding. After debanding, these alterations were accompanied by persistent changes in pathways associated to myocardial hypertrophy, fibrosis and LV inflammation. Aortic banding induced pulmonary arterial wall thickness to increase and correlates negatively with effort intolerance and positively with E/e′ and left atrial area. We described dysregulated pathways in LV and RV remodelling and RR after AVR. Importantly we showed important RV-side effects of aortic constriction, highlighting the impact that LV-reverse remodelling has on both ventricles.

Molecular mechanism involved in cyclophosphamide-induced cardiotoxicity: Old drug with a new vision

Cyclophosphamide (CP) is an important anticancer drug which belongs to the class of alkylating agent. Cyclophosphamide is mostly used in bone marrow transplantation, rheumatoid arthritis, lupus erythematosus, multiple sclerosis, neuroblastoma and other types of cancer. Dose-related cardiotoxicity is a limiting factor for its use. CP-induced cardiotoxicity ranges from 7 to 28% and mortality ranges from 11 to 43% at the therapeutic dose of 170-180 mg/kg, i.v. CP undergoes hepatic metabolism that results in the production of aldophosphamide. Aldophosphamide decomposes into phosphoramide mustard & acrolein. Phosphoramide is an active neoplastic agent, and acrolein is a toxic metabolite which acts on the myocardium and endothelial cells. This is the first review article that talks about cyclophosphamide-induced cardiotoxicity and the different signaling pathways involved in its pathogenicity. Based on the available literature, CP is accountable for cardiomyocytes energy pool alteration by affecting the heart fatty acid binding proteins (H-FABP). CP has been found associated with cardiomyocytes apoptosis, inflammation, endothelial dysfunction, calcium dysregulation, endoplasmic reticulum damage, and mitochondrial damage. Molecular mechanism of cardiotoxicity has been discussed in detail through crosstalk of Nrf2/ARE, Akt/GSK-3β/NFAT/calcineurin, p53/p38MAPK, NF-kB/TLR-4, and Phospholamban/SERCA-2a signaling pathway. Based on the available literature we support the fact that metabolites of CP are responsible for cardiotoxicity due to depletion of antioxidants/ATP level, altered contractility, damaged endothelium and enhanced pro-inflammatory/pro-apoptotic activities resulting into cardiomyopathy, myocardial infarction, and heart failure. Dose adjustment, elimination/excretion of acrolein and maintenance of endogenous antioxidant pool could be the therapeutic approach to mitigate the toxicities.

Chronic β-adrenergic stimulation reverses depressed Ca handling in mice overexpressing inhibitor-2 of protein phosphatase 1

RATIONALE

A higher expression/activity of type 1 serine/threonine protein phosphatase 1 (PP1) may contribute to dephosphorylation of cardiac regulatory proteins triggering the development of heart failure.

OBJECTIVE

Here, we tested the putatively protective effects of PP1 inhibitor-2 (I₂) overexpression using a heart failure model induced by chronic β-adrenergic stimulation.

METHODS AND RESULTS

Transgenic (TG) and wild-type (WT) mice were subjected to isoprenaline (ISO) or isotonic NaCl solution supplied via osmotic minipumps for 7 days. I₂ overexpression was associated with a depressed PP1 activity. Basal contractility was unchanged in catheterized mice and isolated cardiomyocytes between TG^NaCl and WT^NaCl. TG^ISO mice exhibited more fibrosis and a higher expression of hypertrophy marker proteins as compared to WT^ISO. After acute administration of ISO, the contractile response was accompanied by a higher sensitivity in TG^ISO as compared to WT^ISO. In contrast to basal contractility, the peak amplitude of [Ca]_i and SR Ca load were reduced in TG^NaCl as compared to WT^NaCl. These effects were normalized to WT levels after chronic ISO stimulation. Cardiomyocyte relaxation and [Ca]_i decay kinetics were hastened in TG^ISO as compared to WT^ISO, which can be explained by a higher phospholamban phosphorylation at Ser¹⁶. Chronic catecholamine stimulation was followed by an enhanced expression of GSK3β, whereas the phosphorylation at Ser⁹ was lower in TG as compared to the corresponding WT group. This resulted in a higher I₂ phosphorylation that may reactivate PP1.

CONCLUSION

Our findings suggest that the basal desensitization of β-adrenergic signaling and the depressed Ca handling in TG by inhibition of PP1 is restored by a GSK3β-dependent phosphorylation of I₂.