Nuclear targeting of Akt enhances kinase activity and survival of cardiomyocytes

TRAF6-mediated ubiquitination of AKT1 in the nucleus occurs in a β-arrestin2-dependent manner upon insulin stimulation

AKT, also known as protein kinase B (PKB), serves as a crucial regulator of numerous biological functions, including cell growth, metabolism, and tumorigenesis. Increasing evidence suggests that the kinase activity of AKT is regulated via ubiquitination by various E3 ligase enzymes in response to different stimuli. However, the molecular mechanisms underlying insulin-induced AKT ubiquitination are not yet fully understood. Here, we show that activation of the insulin receptor (IR) leads to enhanced ubiquitination of AKT1 at K8 and K14 residues, facilitated by the cytosolic E3 ubiquitin ligase enzyme, TRAF6. Further investigation using AKT1 mutants with modified nucleocytoplasmic shuttling properties reveals that TRAF6-mediated AKT1 ubiquitination occurs within the nucleus in a β-Arr2-dependent manner. The nuclear entry of TRAF6 depends on importin β1, while β-Arr2 regulates this process by facilitating the interaction between TRAF6 and importin β1. Additionally, the ubiquitination of AKT1 is essential for its translocation to the activated IR on the plasma membrane, where it plays a functional role in recruiting Glut4 and facilitating glucose uptake. This study uncovers the cellular components and processes involved in insulin-induced ubiquitination and activation of AKT1, providing insights and detailed strategies for manipulating AKT1.

Lipid transfer proteins and a PI 4-kinase initiate nuclear phosphoinositide signaling

Phosphoinositide (PIP n ) messengers are present in non-membranous regions of nuclei, where they are assembled into a phosphatidylinositol (PI) 3-kinase (PI3K)/Akt pathway that is distinct from the cytosolic membrane-localized pathway. In the nuclear pathway, PI kinases/phosphatases bind the p53 tumor suppressor protein (wild-type and mutant) to generate p53-PIP n complexes that regulate Akt activation. However, this pathway is dependent on poorly characterized nuclear PIP n pools. Here we report that PI transfer proteins (PITPs), which transport PI between membranes to enable membrane-localized PIP n synthesis, accumulate in the nucleoplasm in response to stress and supply nuclear PIP n pools. PITPα/β and the PI 4-kinase PI4KIIα bind p53 and are required to generate p53-PI4P, which is further phosphorylated to synthesize p53-PIP n complexes that regulate nuclear Akt activation and stress-resistance. Remarkably, PITPα/β and PI4KIIα initiate PIP n -linkage to multiple proteins that are detectable by immunoblotting and [ 3 H] myo -inositol metabolic labeling and are resistant to denaturation, suggesting a posttranslational modification.

In brief

Phosphatidylinositol transfer proteins initiate the nuclear PIP n -linked protein network in membrane-free regions.

TRAF6-mediated ubiquitination of AKT in the nucleus is a critical event underlying the desensitization of G protein-coupled receptors

BACKGROUND

Desensitization of G protein-coupled receptors (GPCRs) refers to the attenuation of receptor responsiveness by prolonged or intermittent exposure to agonists. The binding of β-arrestin to the cytoplasmic cavity of the phosphorylated receptor, which competes with the G protein, has been widely accepted as an extensive model for explaining GPCRs desensitization. However, studies on various GPCRs, including dopamine D2-like receptors (D2R, D3R, D4R), have suggested the existence of other desensitization mechanisms. The present study employed D2R/D3R variants with different desensitization properties and utilized loss-of-function approaches to uncover the mechanisms underlying GPCRs homologous desensitization, focusing on the signaling cascade that regulates the ubiquitination of AKT.

RESULTS

AKT undergoes K8/14 ubiquitination by TRAF6, which occurs in the nucleus and promotes its membrane recruitment, phosphorylation and activation under receptor desensitization conditions. The nuclear entry of TRAF6 relies on the presence of the importin complex. Src regulates the nuclear entry of TRAF6 by mediating the interaction between TRAF6 and importin β1. Ubiquitinated AKT translocates to the plasma membrane where it associates with Mdm2 to phosphorylate it at the S166 and S186 residues. Thereafter, phosphorylated Mdm2 is recruited to the nucleus, resulting in the deubiquitination of β-Arr2. The deubiquitinated β-Arr2 then forms a complex with Gβγ, which serves as a biomarker for GPCRs desensitization. Like in D3R, ubiquitination of AKT is also involved in the desensitization of β2 adrenoceptors.

CONCLUSION

Our study proposed that the property of a receptor that causes a change in the subcellular localization of TRAF6 from the cytoplasm to the nucleus to mediate AKT ubiquitination could initiate the desensitization of GPCRs.

Protective role of MG53 against ischemia/reperfusion injury on multiple organs: A narrative review

Ischemia/reperfusion (I/R) injury is a common clinical problem after coronary angioplasty, cardiopulmonary resuscitation, and organ transplantation, which can lead to cell damage and death. Mitsugumin 53 (MG53), also known as Trim72, is a conservative member of the TRIM family and is highly expressed in mouse skeletal and cardiac muscle, with minimal amounts in humans. MG53 has been proven to be involved in repairing cell membrane damage. It has a protective effect on I/R injury in multiple oxygen-dependent organs, such as the heart, brain, lung, kidney, and liver. Recombinant human MG53 also plays a unique role in I/R, sepsis, and other aspects, which is expected to provide new ideas for related treatment. This article briefly reviews the pathophysiology of I/R injury and how MG53 mitigates multi-organ I/R injury.

Exercise training maintains cardiovascular health: signaling pathways involved and potential therapeutics

Exercise training has been widely recognized as a healthy lifestyle as well as an effective non-drug therapeutic strategy for cardiovascular diseases (CVD). Functional and mechanistic studies that employ animal exercise models as well as observational and interventional cohort studies with human participants, have contributed considerably in delineating the essential signaling pathways by which exercise promotes cardiovascular fitness and health. First, this review summarizes the beneficial impact of exercise on multiple aspects of cardiovascular health. We then discuss in detail the signaling pathways mediating exercise's benefits for cardiovascular health. The exercise-regulated signaling cascades have been shown to confer myocardial protection and drive systemic adaptations. The signaling molecules that are necessary for exercise-induced physiological cardiac hypertrophy have the potential to attenuate myocardial injury and reverse cardiac remodeling. Exercise-regulated noncoding RNAs and their associated signaling pathways are also discussed in detail for their roles and mechanisms in exercise-induced cardioprotective effects. Moreover, we address the exercise-mediated signaling pathways and molecules that can serve as potential therapeutic targets ranging from pharmacological approaches to gene therapies in CVD. We also discuss multiple factors that influence exercise's effect and highlight the importance and need for further investigations regarding the exercise-regulated molecules as therapeutic targets and biomarkers for CVD as well as the cross talk between the heart and other tissues or organs during exercise. We conclude that a deep understanding of the signaling pathways involved in exercise's benefits for cardiovascular health will undoubtedly contribute to the identification and development of novel therapeutic targets and strategies for CVD.

Activation of the HSP27-AKT axis contributes to gefitinib resistance in non-small cell lung cancer cells independent of EGFR mutations

PURPOSE

Although epidermal growth factor receptor (EGFR)-activating mutations in non-small cell lung cancer (NSCLC) usually show sensitivity to first-generation EGFR-tyrosine kinase inhibitors (TKIs), most patients relapse because of drug resistance. Heat shock protein 27 (HSP27) has been reported to be involved in the resistance of EGFR-TKIs, although the underlying mechanism is unclear. Here, we explore the mechanisms of HSP27-mediated EGFR TKI resistance and propose novel therapeutic strategies.

METHODS

To determine the mechanism of HSP27 associated gefitinib resistance, differences were assessed using gefitinib-sensitive and -resistant NSCLC cell lines. In vivo xenograft experiments were conducted to elucidate the combinatorial effects of J2, a small molecule HSP27 inhibitor, and gefitinib. Analyses of human NSCLC tissues and PDX tissues were also used for comparison of HSP27 and phosphorylated AKT expression.

RESULTS

Large-scale cohort analysis of NSCLC cases revealed that HSP27 expression correlated well with the incidence of EGFR mutations and affected patient survival. Increased pAKT and HSP27 was observed in gefitinib-resistant cells compared with gefitinib-sensitive cells. Moreover, increased phosphorylation of HSP27 by gefitinib augmented its protein stability and potentiated its binding activity with pAKT, which resulted in increased gefitinib resistance. However, in gefitinib-sensitive cells, stronger binding activity between EGFR and HSP27 was observed. Moreover, these phenomena occurred regardless of EGFR mutation including secondary mutations, such as T790M. AKT knockdown switched HSP27-pAKT binding to HSP27-EGFR, which promoted gefitinib sensitivity in gefitinib-resistant cells. Functional inhibition of HSP27 yielded sensitization to gefitinib in gefitinib-resistant cells by inhibiting the interaction between HSP27 and pAKT.

CONCLUSIONS

Our results indicate that combination of EGFR-TKIs with HSP27 inhibitors may represent a good strategy to overcome resistance to EGFR-TKIs, especially in cancers exhibiting AKT pathway activation.

A p53-phosphoinositide signalosome regulates nuclear AKT activation

The tumour suppressor p53 and PI3K-AKT pathways have fundamental roles in the regulation of cell growth and apoptosis, and are frequently mutated in cancer. Here, we show that genotoxic stress induces nuclear AKT activation through a p53-dependent mechanism that is distinct from the canonical membrane-localized PI3K-AKT pathway. Following genotoxic stress, a nuclear PI3K binds p53 in the non-membranous nucleoplasm to generate a complex of p53 and phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P₃), which recruits AKT, PDK1 and mTORC2 to activate AKT and phosphorylate FOXO proteins, thereby inhibiting DNA damage-induced apoptosis. Wild-type p53 activates nuclear AKT in an on/off fashion following stress, whereas mutant p53 dose-dependently stimulates high basal AKT activity. The p53-PtdIns(3,4,5)P₃ complex is dephosphorylated to p53-phosphatidylinositol 4,5-bisphosphate by PTEN to inhibit AKT activation. The nuclear p53-phosphoinositide signalosome is distinct from the canonical membrane-localized pathway and insensitive to PI3K inhibitors currently in the clinic, which underscores its therapeutic relevance.

LncRNA Chaer Prevents Cardiomyocyte Apoptosis From Acute Myocardial Infarction Through AMPK Activation

Long non-coding RNA (lncRNA) is widely reported to be involved in cardiac (patho)physiology. Acute myocardial infarction, in which cardiomyocyte apoptosis plays an important role, is a life-threatening disease. Here, we report the lncRNA Chaer that is anti-apoptotic in cardiomyocytes during Acute myocardial infarction. Importantly, lncRNA Chaer is significantly downregulated in both oxygen-glucose deprivation (oxygen-glucose deprivation)-treated cardiomyocytes in vitro and AMI heart. In vitro, overexpression of lncRNA Chaer with adeno virus reduces cardiomyocyte apoptosis induced by OGD-treated while silencing of lncRNA Chaer increases cardiomyocyte apoptosis instead. In vivo, forced expression of lncRNA Chaer with AAV9 attenuates cardiac apoptosis, reduces infarction area and improves mice heart function in AMI. Interestingly, overexpression of lncRNA Chaer promotes the phosphorylation of AMPK, and AMPK inhibitor Compound C reverses the overexpression of lncRNA Chaer effect of reducing cardiomyocyte apoptosis under OGD-treatment. In summary, we identify the novel ability of lncRNA Chaer in regulating cardiomyocyte apoptosis by promoting phosphorylation of AMPK in AMI.

Cardiac effects and clinical applications of MG53

Heart disease remains the leading cause of mortality globally, so further investigation is required to identify its underlying mechanisms and potential targets for treatment and prevention. Mitsugumin 53 (MG53), also known as TRIM72, is a TRIM family protein that was found to be involved in cell membrane repair and primarily found in striated muscle. Its role in skeletal muscle regeneration and myogenesis has been well documented. However, accumulating evidence suggests that MG53 has a potentially protective role in heart tissue, including in ischemia/reperfusion injury of the heart, cardiomyocyte membrane injury repair, and atrial fibrosis. This review summarizes the regulatory role of MG53 in cardiac tissues, current debates regarding MG53 in diabetes and diabetic cardiomyopathy, as well as highlights potential clinical applications of MG53 in treating cardiac pathologies.

The traditional Chinese medicine formula Fufang-Zhenzhu-Tiaozhi protects myocardia from injury in diabetic minipigs with coronary heart disease

BACKGROUND AND PURPOSE

Diabetes mellitus (DM) is a major risk factor for coronary heart disease (CHD). Previous research has reported that the Fufang-Zhenzhu-Tiaozhi (FTZ) formula has obvious effects on the treatment of dyslipidemia and hyperglycemia. In the present study, we intended to establish a convenient DM-CHD model in minipigs and investigated the protective effect of FTZ against myocardial injury and its mechanism.

METHODS

The DM-CHD model was established by a high-fat/high-sucrose/high-cholesterol diet (HFSCD) combined with balloon injury in the coronary artery. Subsequently, sixteen Wuzhishan minipigs were assigned to three groups: control group, model group, and FTZ group. The model group and FTZ group were given a HFSCD, while the control group was given a normal diet (ND). FTZ was given with meals in the FTZ group. During this time, biochemical parameters, such as total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein (HDL-C), and fasting blood glucose (FBG), were measured by using testing kits. Insulin (INS) was determined by ELISA, and the homeostasis model assessment index of insulin resistance (HOMA-IR) was calculated to evaluate insulin resistance levels. After FTZ administration, the plasma levels of lactate dehydrogenase (LDH), creatine kinase isoenzyme MB (CK-MB), and cardiac troponin I (cTnI) were measured by using ELISA kits to evaluate myocardial injury. Coronary artery stenosis was analyzed by angiographic and HE staining. Myocardial ischemia was assayed with electrocardiogram (ECG). Moreover, cytokines, including interleukin-6 (IL-6), hypersensitive C-reactive protein (hs-CRP), and tumor necrosis factor-alpha (TNF-α), were measured by ELISA kits to assess inflammation. The myocardial tissue was collected, and the pathological morphology was observed by transmission electron microscopy (TEM), HE staining, and Masson staining. Western blots were used to detect the expression of PI3K, AKT, p-AKT, p-NF-κB, and NF-κB.

RESULTS

A DM-CHD model in minipigs with glucose-lipid metabolism disorder, coronary artery incrassation and myocardial damage was successfully established through balloon injury in the coronary artery combined with HFSCD. FTZ effectively inhibited coronary artery incrassation and protected the myocardium against injury in DM-CHD minipigs. FTZ decreased proinflammatory cytokine levels and upregulated the protein expression of the PI3K/Akt pathway in the myocardium.

CONCLUSIONS

A novel DM-CHD model in minipigs was successfully established through balloon injury in the coronary artery combined with HFSCD. FTZ has a protective effect against myocardial injury in DM-CHD by inhibiting inflammation and activating the PI3K/AKT signaling pathway.

Consistent Long-Term Therapeutic Efficacy of Human Umbilical Cord Matrix-Derived Mesenchymal Stromal Cells After Myocardial Infarction Despite Individual Differences and Transient Engraftment

Human mesenchymal stem cells gather special interest as a universal and feasible add-on therapy for myocardial infarction (MI). In particular, human umbilical cord matrix-derived mesenchymal stromal cells (UCM-MSC) are advantageous since can be easily obtained and display high expansion potential. Using isolation protocols compliant with cell therapy, we previously showed UCM-MSC preserved cardiac function and attenuated remodeling 2 weeks after MI. In this study, UCM-MSC from two umbilical cords, UC-A and UC-B, were transplanted in a murine MI model to investigate consistency and durability of the therapeutic benefits. Both cellular products improved cardiac function and limited adverse cardiac remodeling 12 weeks post-ischemic injury, supporting sustained and long-term beneficial therapeutic effect. Donor associated variability was found in the modulation of cardiac remodeling and activation of the Akt-mTOR-GSK3β survival pathway. In vitro, the two cell products displayed similar ability to induce the formation of vessel-like structures and comparable transcriptome in normoxia and hypoxia, apart from UCM-MSCs proliferation and expression differences in a small subset of genes associated with MHC Class I. These findings support that UCM-MSC are strong candidates to assist the treatment of MI whilst calling for the discussion on methodologies to characterize and select best performing UCM-MSC before clinical application.

SIRT1 promotes pulmonary artery endothelial cell proliferation by targeting the Akt signaling pathway

Pulmonary arterial hypertension (PAH) is a disease characterized by a progressive increase in pulmonary vascular resistance and obliterative pulmonary vascular remodeling; however, the pathogenesis of the disease is not completely understood. Sirtuin 1 (SIRT1) is a histone deacetylase involved in cell survival and metabolism. The present study explored the potential role of SIRT1 in human pulmonary arterial endothelial cells (HPAECs) under hypoxic conditions. In vitro HPAECs were cultured and exposed to hypoxic conditions. Subsequently, SIRT1 expression levels were measured via western blotting, the generation of reactive oxygen species (ROS) was evaluated, and the interaction between SIRT1 and Akt was assessed via reverse transcription-quantitative PCR and western blotting. In addition, the effects of SIRT1 on cell proliferation and apoptosis were also investigated. The results indicated that hypoxia induced SIRT1 expression in pulmonary arterial endothelial cells, which may be associated with ROS generation. SIRT1 expression activated the Akt signaling pathway, which increased the expression levels of Bcl-2 and hypoxia-inducible factor-1 in HPAECs. Moreover, SIRT1 promoted HPAEC proliferation and inhibited HPAEC apoptosis. ROS generation enhanced the SIRT1/Akt axis, which was essential for epithelial cell injury under hypoxic conditions. Therefore, blocking SIRT1 may reduce hypoxia-induced pathological damage in HPAECs.

Control of Akt activity and substrate phosphorylation in cells

Protein kinase B/Akt is a serine/threonine kinase that links receptors coupled to the PI3K lipid kinase to cellular anabolic pathways. Its activity in cells is controlled by reversible phosphorylation and an intramolecular lipid-controlled allosteric switch. In this review, I outline the current progress in understanding Akt regulatory mechanisms, define three models of Akt activation in cells, and highlight how intramolecular allosterism cooperates with cell-autonomous mechanisms to control Akt localization and activity and direct it toward specific sets of substrates in cells.

Cardioprotection of Tetrahedral DNA Nanostructures in Myocardial Ischemia-Reperfusion Injury

Acute myocardial infarction, which can be extremely difficult to treat, is the worst deadly disease around the world. Reperfusion is expedient to reverse myocardial ischemia. However, during reperfusion, reactive oxygen species (ROS) produced by myocardial ischemia-reperfusion injury (MIRI) and further cell apoptosis are the most serious challenges to cardiomyocytes. Therefore, searching for reagents that can simultaneously reduce oxidative damage and MIRI-induced apoptosis is the pivotal strategy to rescue injured cardiomyocytes. Nevertheless, current cardioprotective drugs have some shortcomings, such as cardiotoxicity, inadequate intravenous administration, or immature technology. Previous studies have shown that tetrahedral DNA nanostructures (TDNs) have biological safety with promising anti-inflammatory and antioxidative potential. However, the progress that TDNs have made in the biological behavior of cardiomyocytes has not been explored. In this experiment, a cellular model of MIRI was first established. Then, confirmed by a series of experiments, our study indicates that TDNs can significantly decrease oxidative damage and apoptosis by limiting the overexpression of ROS, along with effecting the expression of apoptosis-related proteins. In addition, Western blot analysis demonstrated that TDNs could activate the Akt/Nrf2 signaling pathway to improve the myocardial injury induced by MIRI. Above all, the antioxidant and antiapoptotic capacities of TDNs make them a potential therapeutic drug for MIRI. This study provides new ideas and directions for more homogeneous diseases induced by oxidative damage.

Myosin 1b Regulates Nuclear AKT Activation by Preventing Localization of PTEN in the Nucleus

Insulin-induced AKT activation is dependent on phosphoinositide 3-kinase and opposed by tumor suppressor phosphatase and tensin homolog (PTEN). Our previous study demonstrates that myosin 1b (MYO1B) mediates arginase-II-induced activation of mechanistic target of rapamycin complex 1 that is regulated by AKT. However, the role of MYO1B in AKT activation is unknown. Here we show that silencing MYO1B in mouse embryonic fibroblasts (MEF) inhibits insulin-induced nuclear but not cytoplasmic AKT activation accompanied by elevated nuclear PTEN level. Co-immunoprecipitation, co-immunostaining, and proximity ligation assay show an interaction of MYO1B and PTEN resulting in reduced nuclear PTEN. Moreover, the elevated nuclear PTEN upon silencing MYO1B promotes apoptosis of MEFs and melanoma B16F10 cells. Taken together, we demonstrate that MYO1B, by interacting with PTEN, prevents nuclear localization of PTEN contributing to nuclear AKT activation and suppression of cell apoptosis. This may present a therapeutic approach for cancer treatment such as melanoma.

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MYO1B, by interacting with PTEN, prevents PTEN localization in the nucleus

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MYO1B prevents nuclear localization of PTEN depending on its motor activity

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This contributes to nuclear AKT activation and suppression of cell apoptosis

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Targeting MYO1B may represent a therapeutic approach for cancer treatment

Endothelial and cardiomyocyte PI3Kβ divergently regulate cardiac remodelling in response to ischaemic injury

AIMS

Cardiac remodelling in the ischaemic heart determines prognosis in patients with ischaemic heart disease (IHD), while enhancement of angiogenesis and cell survival has shown great potential for IHD despite translational challenges. Phosphoinositide 3-kinase (PI3K)/Akt signalling pathways play a critical role in promoting angiogenesis and cell survival. However, the effect of PI3Kβ in the ischaemic heart is poorly understood. This study investigates the role of endothelial and cardiomyocyte (CM) PI3Kβ in post-infarct cardiac remodelling.

METHODS AND RESULTS

PI3Kβ catalytic subunit-p110β level was increased in infarcted murine and human hearts. Using cell type-specific loss-of-function approaches, we reported novel and distinct actions of p110β in endothelial cells (ECs) vs. CMs in response to myocardial ischaemic injury. Inactivation of endothelial p110β resulted in marked resistance to infarction and adverse cardiac remodelling with decreased mortality, improved systolic function, preserved microvasculature, and enhanced Akt activation. Cultured ECs with p110β knockout or inhibition displayed preferential PI3Kα/Akt/endothelial nitric oxide synthase signalling that consequently promoted protective signalling and angiogenesis. In contrast, mice with CM p110β-deficiency exhibited adverse post-infarct ventricular remodelling with larger infarct size and deteriorated cardiac function, which was due to enhanced susceptibility of CMs to ischaemia-mediated cell death. Disruption of CM p110β signalling compromised nuclear p110β and phospho-Akt levels leading to perturbed gene expression and elevated pro-cell death protein levels, increasing the susceptibility to CM death. A similar divergent response of PI3Kβ endothelial and CM mutant mice was seen using a model of myocardial ischaemia-reperfusion injury.

CONCLUSION

These data demonstrate novel, differential, and cell-specific functions of PI3Kβ in the ischaemic heart. While the loss of endothelial PI3Kβ activity produces cardioprotective effects, CM PI3Kβ is protective against myocardial ischaemic injury.

PM2.5-induced ADRB2 hypermethylation contributed to cardiac dysfunction through cardiomyocytes apoptosis via PI3K/Akt pathway

BACKGROUND

Long-term exposure to fine particulate matter (PM_2.5) can causally contribute to progression of atherosclerosis, risk of ischemic heart disease and death, but the underlying mechanism is little known. Since DNA methylation impacts the process of heart disease, it might be useful in exploring potential mechanistic pathways linking PM_2.5 exposure and heart disease.

OBJECTIVES

Here, we investigated the PM_2.5-induced ADRB2 hypermethylation and the involving epigenetic mechanism of PM_2.5-induced cardiomyocytes apoptosis and cardiac dysfunction.

METHODS AND RESULTS

In vitro, PM_2.5 markedly augmented cardiotoxicity including oxidative damage and apoptosis in cardiomyocytes AC16 as well as epigenetic alteration. DNA methylation profiling revealed a significant gene-ADRB2 was involved in the cardiac relative GO and KEGG pathways. Methylation chip and Bisulfite Sequencing PCR (BSP) both identified the hypermethylation status of ADRB2 which encodes β2-Adrenergic receptor (β2AR). Mechanistic study showed ADRB2 hypermethylation-induced down-regulation of β2AR inhibited PI3K/Akt and then activated Bcl-2/BAX and p53 pathway in AC16. The transgenic cell lines showed over-expression of ADRB2 weakened the PM_2.5-induced cardiomyocytes apoptosis in opposite way, but was augmented by PI3K inhibitor (LY294002). In vivo, echocardiography showed the heart contractile function was decreased after SD rats intratracheal instillation of PM_2.5 for 30 days. The myocardial interstitial edema, myocardial gap expansion and myofibril disorder in PM_2.5 treated group were observed in rats heart tissue. What's more, basal expression of β2AR and VEGFR2 decreased in heart tissue as the dosage of PM_2.5 increasing, meanwhile PM_2.5 markedly attenuated PI3K/Akt pathway followed by augmented Bcl-2/BAX and p53 pathway, thus caused a greater number of TUNEL positive cardiomyocytes resulted in cardiac dysfunction in vivo.

CONCLUSIONS

PM_2.5 exposure could cause the myocardial ADRB2 hypermethylation and activate the β2AR/PI3K/Akt pathway, resulted in PM_2.5-induced cardiomyocytes apoptosis and cardiac dysfunction. Our study suggested that the ADRB2 demethylation or ADRB2/β2AR activation may serve as a potential pathway to prevent cardiac dysfunction induced by PM_2.5 exposure.

AKT-dependent phosphorylation of the adenosine deaminases ADAR-1 and -2 inhibits deaminase activity

Murine thymoma viral oncogene homolog (AKT) kinases target both cytosolic and nuclear substrates for phosphorylation. Whereas the cytosolic substrates are known to be closely associated with the regulation of apoptosis and autophagy or metabolism and protein synthesis, the nuclear substrates are, for the most part, poorly understood. To better define the role of nuclear AKT, potential AKT substrates were isolated from the nuclear lysates of leukemic cell lines using a phosphorylated AKT substrate antibody and identified in tandem mass spectrometry. Among the proteins identified was adenosine deaminase acting on RNA (ADAR)1p110, the predominant nuclear isoform of the adenosine deaminase acting on double-stranded RNA. Coimmunoprecipitation studies and in vitro kinase assays revealed that AKT-1, -2, and -3 interact with both ADAR1p110 and ADAR2 and phosphorylate these RNA editases. Using site-directed mutagenesis of suspected AKT phosphorylation sites, AKT was found to primarily phosphorylate ADAR1p110 and ADAR2 on T738 and T553, respectively, and overexpression of the phosphomimic mutants ADAR1p110 (T738D) and ADAR2 (T553D) resulted in a 50-100% reduction in editase activity. Thus, activation of AKT has a direct and major impact on RNA editing.-Bavelloni, A., Focaccia, E., Piazzi, M., Raffini, M., Cesarini, V., Tomaselli, S., Orsini, A., Ratti, S., Faenza, I., Cocco, L., Gallo, A., Blalock, W. L. AKT-dependent phosphorylation of the adenosine deaminases ADAR-1 and -2 inhibits deaminase activity.

Nuclear localized Akt limits skeletal muscle derived fibrotic signaling

Skeletal muscle regeneration following injury is a complex multi-stage process involving the recruitment of inflammatory cells, the activation of muscle resident fibroblasts, and the differentiation of activated myoblasts into myocytes. Dysregulation of these cellular processes is associated with ineffective myofiber repair and excessive deposition of extracellular matrix proteins leading to fibrosis. PI3K/Akt signaling is a critical integrator of intra- and intercellular signals connecting nutrient availability to cell survival and growth. Activation of the PI3K/Akt pathway in skeletal muscle leads to hypertrophic growth and a reversal of the changes in body composition associated with obesity and advanced age. Though the molecular mechanisms mediating these effects are incompletely understood, changes in paracrine signaling are thought to play a key role. Here, we utilized modified RNA to study the biological role of the transient translocation of Akt to the myonuclei of maturing myotubes. Using a conditioned medium model system, we show that ectopic myonuclear Akt suppresses fibrogenic paracrine signaling in response to oxidative stress, and that interventions that increase or restore myonuclear Akt may impair fibrosis.

Understanding Key Mechanisms of Exercise-Induced Cardiac Protection to Mitigate Disease: Current Knowledge and Emerging Concepts

The benefits of exercise on the heart are well recognized, and clinical studies have demonstrated that exercise is an intervention that can improve cardiac function in heart failure patients. This has led to significant research into understanding the key mechanisms responsible for exercise-induced cardiac protection. Here, we summarize molecular mechanisms that regulate exercise-induced cardiac myocyte growth and proliferation. We discuss in detail the effects of exercise on other cardiac cells, organelles, and systems that have received less or little attention and require further investigation. This includes cardiac excitation and contraction, mitochondrial adaptations, cellular stress responses to promote survival (heat shock response, ubiquitin-proteasome system, autophagy-lysosomal system, endoplasmic reticulum unfolded protein response, DNA damage response), extracellular matrix, inflammatory response, and organ-to-organ crosstalk. We summarize therapeutic strategies targeting known regulators of exercise-induced protection and the challenges translating findings from bench to bedside. We conclude that technological advancements that allow for in-depth profiling of the genome, transcriptome, proteome and metabolome, combined with animal and human studies, provide new opportunities for comprehensively defining the signaling and regulatory aspects of cell/organelle functions that underpin the protective properties of exercise. This is likely to lead to the identification of novel biomarkers and therapeutic targets for heart disease.

Empagliflozin Improves Left Ventricular Diastolic Dysfunction in a Genetic Model of Type 2 Diabetes

PURPOSE

Cardiovascular (CV) diseases in type 2 diabetes (T2DM) represent an enormous burden with high mortality and morbidity. Sodium-glucose cotransporter 2 (SGLT2) inhibitors have recently emerged as a new antidiabetic class that improves glucose control, as well as body weight and blood pressure with no increased risk of hypoglycemia. The first CV outcome study terminated with empagliflozin, a specific SGLT2 inhibitor, has shown a reduction in CV mortality and in heart failure hospitalization, suggesting a beneficial impact on cardiac function which remains to be demonstrated. This study was designed to examine the chronic effect of empagliflozin on left ventricular (LV) systolic and diastolic functions in a genetic model of T2DM, ob/ob mice.

METHODS AND RESULTS

Cardiac phenotype was characterized by echocardiography, in vivo hemodynamics, histology, and molecular profiling. Our results demonstrate that empagliflozin significantly lowered HbA1c and slightly reduced body weight compared to vehicle treatment with no obvious changes in insulin levels. Empagliflozin also improved LV maximum pressure and in vivo indices of diastolic function. While systolic function was grossly not affected in both groups at steady state, response to dobutamine stimulation was significantly improved in the empagliflozin-treated group, suggesting amelioration of contractile reserve. This was paralleled by an increase in phospholamban (PLN) phosphorylation and increased SERCA2a/PLN ratio, indicative of enhanced SERCA2a function, further supporting improved cardiac relaxation and diastolic function. In addition, empagliflozin reconciled diabetes-associated increase in MAPKs and dysregulated phosphorylation of IRS1 and Akt, leading to improvement in myocardial insulin sensitivity and glucose utilization.

CONCLUSION

The data show that chronic treatment with empagliflozin improves diastolic function, preserves calcium handling and growth signaling pathways and attenuates myocardial insulin resistance in ob/ob mice, findings suggestive of a potential clinical utility for empagliflozin in the treatment of diastolic dysfunction.

Dhcr24 activates the PI3K/Akt/HKII pathway and protects against dilated cardiomyopathy in mice

BACKGROUND

24-dehydrocholesterol reductase (Dhcr24) catalyzes the last step of cholesterol biosynthesis, which is required for normal development and anti-apoptotic activities of tissues. We found that Dhcr24 expression decreased in the cTnTR 141W dilated cardiomyopathy (DCM) transgenic mice. Therefore, we tested whether rescued expression of Dhcr24 could prevent the development of DCM and its possible mechanism.

METHODS

Heart tissue specific transgenic overexpression mice of Dhcr24 was generated, then was crossed to cTnTR 141W mouse to obtain the double transgenic mouse (DTG). The phenotypes were demonstrated by the survival, cardiac geometry and function analysis, as well as microstructural and ultrastructural observations based on echocardiography and histology examination. The pathway and apoptosis were analysed by western blotting and TUNEL assay in vivo and in vitro.

RESULTS

We find that Dhcr24 decreased in hearts tissues of cTnTR 141W and LMNAE 82K DCM mice. The transgenic overexpression of Dhcr24 significantly improves DCM phenotypes in cTnTR 141W mice, and activates PI3K/Akt/HKII pathway, followed by a reduction of the translocation of Bax and release of cytochrome c, caspase-9 and caspase-3 activation and myocyte apoptosis. Knockdown the expression of Dhcr24 reduces the activation of PI3K/Akt/HKII pathway and inhibition of the mitochondrial-dependent apoptosis. The anti-apoptotic effect of Dhcr24 could be completely removed by the inhibition of PI3K pathway and partly removed by the HKII inhibitor in H9c2 cell line.

CONCLUSION

Compensatory expression of Dhcr24 protect against DCM through activated PI3K/Akt/HKII pathway and reduce Bax translocation. This is the first investigation for the molecular mechanism of Dhcr24 participate in development of DCM.

Combining cell and gene therapy to advance cardiac regeneration

INTRODUCTION

The characterization of multipotent endogenous cardiac stem cells (eCSCs) and the breakthroughs of somatic cell reprogramming to boost cardiomyocyte replacement have fostered the prospect of achieving functional heart repair/regeneration.

AREAS COVERED

Allogeneic CSC therapy through its paracrine stimulation of the endogenous resident reparative/regenerative process produces functional meaningful myocardial regeneration in pre-clinical porcine myocardial infarction models and is currently tested in the first-in-man human trial. The in vivo test of somatic reprogramming and cardioregenerative non-coding RNAs revived the interest in gene therapy for myocardial regeneration. The latter, together with the advent of genome editing, has prompted most recent efforts to produce genetically-modified allogeneic CSCs that secrete cardioregenerative factors to optimize effective myocardial repair.

EXPERT OPINION

The current war against heart failure epidemics in western countries seeks to find effective treatments to set back the failing hearts prolonging human lifespan. Off-the-shelf allogeneic-genetically-modified CSCs producing regenerative agents are a novel and evolving therapy set to be affordable, safe, effective and available at all times for myocardial regeneration to either prevent or treat heart failure.

A novel ventricular restraint device (ASD) repetitively deliver Salvia miltiorrhiza to epicardium have good curative effects in heart failure management

A novel ventricular restraint is the non-transplant surgical option for the management of an end-stage dilated heart failure (HF). To expand the therapeutic techniques we design a novel ventricular restraint device (ASD) which has the ability to deliver a therapeutic drug directly to the heart. We deliver a Traditional Chinese Medicine (TCM) Salvia miltiorrhiza (Danshen Zhusheye) through active hydraulic ventricular support drug delivery system (ASD) and we hypothesize that it will show better results in HF management than the restraint device and drug alone. SD rats were selected and divided into five groups (n=6), Normal, HF, HF+SM (IV), HF+ASD, HF+ASD+SM groups respectively. Post myocardial infarction (MI), electrocardiography (ECG) showed abnormal heart function in all groups and HF+ASD+SM group showed a significant therapeutic improvement with respect to other treatment HF, HF+ASD, and HF+SM (IV) groups on day 30. The mechanical functions of the heart such as heart rate, LVEDP, and LVSP were brought to normal when treated with ASD+SM and show significant (P value<0.01) compared to other groups. BNP significantly declines in HF+ASD+SM group animals compared with other treatment groups. Masson's Trichrome staining was used to study histopathology of cardiac myocytes and quantification of fibrosis was assessed. The large blue fibrotic area was observed in HF, HF+ASD, and HF+SM (IV) groups while HF+ASD+SM showed negligible fibrotic myocyte at the end of study period (30days). This study proves that novel ASD device augments the therapeutic effect of the drug and delivers Salvia miltiorrhiza to the cardiomyocytes significantly as well as provides additional support to the dilated ventricle by the heart failure.

SERCA control of cell death and survival

Intracellular calcium (Ca²⁺⁾ is a critical coordinator of various aspects of cellular physiology. It is increasingly apparent that changes in cellular Ca²⁺ dynamics contribute to the regulation of normal and pathological signal transduction that controls cell growth and survival. Aberrant perturbations in Ca²⁺ homeostasis have been implicated in a range of pathological conditions, such as cardiovascular diseases, diabetes, tumorigenesis and steatosis hepatitis. Intracellular Ca²⁺ concentrations are therefore tightly regulated by a number of Ca²⁺ handling enzymes, proteins, channels and transporters located in the plasma membrane and in Ca²⁺ storage organelles, which work in concert to fine tune a temporally and spatially precise Ca²⁺ signal. Chief amongst them is the sarco/endoplasmic reticulum (SR/ER) Ca²⁺ ATPase pump (SERCA) which actively re-accumulates released Ca²⁺ back into the SR/ER, therefore maintaining Ca²⁺ homeostasis. There are at least 14 different SERCA isoforms encoded by three ATP2A1-3 genes whose expressions are species- and tissue-specific. Altered SERCA expression and activity results in cellular malignancy and induction of ER stress and ER stress-associated apoptosis. The role of SERCA misregulation in the control of apoptosis in various cell types and disease setting with prospective therapeutic implications is the focus of this review. Ca²⁺ is a double edge sword for both life as well as death, and current experimental evidence supports a model in which Ca²⁺ homeostasis and SERCA activity represent a nodal point that controls cell survival. Pharmacological or genetic targeting of this axis constitutes an incredible therapeutic potential to treat different diseases sharing similar biological disorders.

The IGF1-PI3K-Akt Signaling Pathway in Mediating Exercise-Induced Cardiac Hypertrophy and Protection

Regular physical activity or exercise training can lead to heart enlargement known as cardiac hypertrophy. Cardiac hypertrophy is broadly defined as an increase in heart mass. In adults, cardiac hypertrophy is often considered a poor prognostic sign because it often progresses to heart failure. Heart enlargement in a setting of cardiac disease is referred to as pathological cardiac hypertrophy and is typically characterized by cell death and depressed cardiac function. By contrast, physiological cardiac hypertrophy, as occurs in response to chronic exercise training (i.e. the 'athlete's heart'), is associated with normal or enhanced cardiac function. The following chapter describes the morphologically distinct types of heart growth, and the key role of the insulin-like growth factor 1 (IGF1) - phosphoinositide 3-kinase (PI3K)-Akt signaling pathway in regulating exercise-induced physiological cardiac hypertrophy and cardiac protection. Finally we summarize therapeutic approaches that target the IGF1-PI3K-Akt signaling pathway which are showing promise in preclinical models of heart disease.

Signaling Pathways in Cardiac Myocyte Apoptosis

Cardiovascular diseases, the number 1 cause of death worldwide, are frequently associated with apoptotic death of cardiac myocytes. Since cardiomyocyte apoptosis is a highly regulated process, pharmacological intervention of apoptosis pathways may represent a promising therapeutic strategy for a number of cardiovascular diseases and disorders including myocardial infarction, ischemia/reperfusion injury, chemotherapy cardiotoxicity, and end-stage heart failure. Despite rapid growth of our knowledge in apoptosis signaling pathways, a clinically applicable treatment targeting this cellular process is currently unavailable. To help identify potential innovative directions for future research, it is necessary to have a full understanding of the apoptotic pathways currently known to be functional in cardiac myocytes. Here, we summarize recent progress in the regulation of cardiomyocyte apoptosis by multiple signaling molecules and pathways, with a focus on the involvement of these pathways in the pathogenesis of heart disease. In addition, we provide an update regarding bench to bedside translation of this knowledge and discuss unanswered questions that need further investigation.

CYP2J2 and its metabolites (epoxyeicosatrienoic acids) attenuate cardiac hypertrophy by activating AMPKα2 and enhancing nuclear translocation of Akt1

Cytochrome P450 epoyxgenase 2J2 and epoxyeicosatrienoic acids (EETs) are known to protect against cardiac hypertrophy and heart failure, which involve the activation of 5′‐AMP‐activated protein kinase (AMPK) and Akt. Although the functional roles of AMPK and Akt are well established, the significance of cross talk between them in the development of cardiac hypertrophy and antihypertrophy of CYP2J2 and EETs remains unclear. We investigated whether CYP2J2 and its metabolites EETs protected against cardiac hypertrophy by activating AMPKα2 and Akt1. Moreover, we tested whether EETs enhanced cross talk between AMPKα2 and phosphorylated Akt1 (p‐Akt1), and stimulated nuclear translocation of p‐Akt1, to exert their antihypertrophic effects. AMPKα2^−/− mice that overexpressed CYP2J2 in heart were treated with Ang II for 2 weeks. Interestingly, overexpression of CYP2J2 suppressed cardiac hypertrophy and increased levels of atrial natriuretic peptide (ANP) in the heart tissue and plasma of wild‐type mice but not AMPKα2^−/− mice. The CYP2J2 metabolites, 11,12‐EET, activated AMPKα2 to induce nuclear translocation of p‐Akt1 selectively, which increased the production of ANP and therefore inhibited the development of cardiac hypertrophy. Furthermore, by co‐immunoprecipitation analysis, we found that AMPKα2β2γ1 and p‐Akt1 interact through the direct binding of the AMPKγ1 subunit to the Akt1 protein kinase domain. This interaction was enhanced by 11,12‐EET. Our studies reveal a novel mechanism in which CYP2J2 and EETs enhanced Akt1 nuclear translocation through interaction with AMPKα2β2γ1 and protect against cardiac hypertrophy and suggest that overexpression of CYP2J2 might have clinical potential to suppress cardiac hypertrophy and heart failure.

Saffron (Crocus sativus) pretreatment confers cardioprotection against ischemia-reperfusion injuries in isolated rabbit heart

Restoration of blood flow to the ischemic myocardium is imperative to avoid demise of cardiomyocytes, but is paradoxically associated with irreversible damage to cardiac tissues due to the excessive generation of reactive oxygen species (ROS). We have previously reported that saffron, a natural antioxidant, attenuated ischemia-reperfusion (IR) injuries in vitro; however, its role in a meaningful cardiac recovery remains unknown. Here, we show that saffron supplement (oral administration for 6 weeks) reduced myocardial damage and restored cardiac function in an IR model of rabbit hearts. This was evidenced by improved left ventricle pressure, heart rate and coronary flow, and left ventricle end diastolic pressure (LVEDP) in IR hearts (isolated from rabbits pre-exposed to saffron (S/IR)). Electrophysiological recordings revealed a significant decline in both premature ventricle contraction and ventricle tachycardia/fibrillation in S/IR compared to IR hearts. This was paralleled by increased expression of the contractile proteins α-actinin and Troponin C in the myocardium of S/IR hearts. Histological examination combined to biochemical analysis indicated that hearts pre-exposed to saffron exhibited reduced infarct size, lower lipid peroxidation, with increased glutathione peroxidase activity, and oxidation of nitro blue tetrazolium (by reactive oxygen species). Furthermore, in contrast with IR hearts, saffron pretreatment induced restoration of the phosphorylation level of the survival proteins Akt and 4EBP1 and reduced activity of p38. Collectively, our data demonstrate that the natural antioxidant saffron plays a pivotal role in halting IR-associated cardiac injuries and emerges as a novel preventive tool for ischemic heart disease.

Relaxin-2 improves diastolic function of pressure-overloaded rats via phospholamban by activating Akt

BACKGROUND

Relaxin is a peptide hormone which has been demonstrated to be safe and has a therapeutic effect on acute heart failure in clinic trials. However, its effect on diastolic function is still unknown. The aims of the study were to determine whether relaxin could improve the diastolic function in pressure-overloaded rat model and to analyze potential mechanisms.

METHODS AND RESULTS

In the present study, a pressure-overloaded rat model induced by transaortic constriction (TAC) was established. Four weeks after TAC, echocardiography was performed and then all the rat models were randomly divided into 3 groups: models without intramyocardial injection (TAC), with intramyocardial injection of empty adenoviral vector (TAC+GFP) and adenoviral vector overexpression relaxin-2 gene (TAC+RLN2). A sham group was also included. Twelve days after intramyocardial injection, echocardiography and hemodynamics were carried out to evaluate diastolic function in sham, TAC, TAC+GFP and TAC+RLN2 groups. Then hearts were harvested for subsequent examinations. The results indicated that relaxin-2 had ameliorated diastolic function in the pressure-overloaded rats. Compared with the TAC and TAC+GFP groups, the relaxin-2 gene transfer increased phosphorylation of Akt at both the Ser473 and Thr308 sites. Meanwhile, it increased the Ser16 and Thr17- phosphorylation levels of phospholamban (PLB). Furthermore, SERCA2 activity was enhanced in the TAC+RLN2 group more than in the TAC and TAC+GFP groups.

CONCLUSIONS

These results demonstrated that relaxin-2 gene therapy improved diastolic function in pressure-overloaded rats. The potential mechanism may be that relaxin-2 gene transfer enhances SERCA2 activity in hearts by increasing phospholamban phosphorylation through nuclear-targeted Akt phosphorylation.

Stem cell death and survival in heart regeneration and repair

Cardiovascular diseases are major causes of mortality and morbidity. Cardiomyocyte apoptosis disrupts cardiac function and leads to cardiac decompensation and terminal heart failure. Delineating the regulatory signaling pathways that orchestrate cell survival in the heart has significant therapeutic implications. Cardiac tissue has limited capacity to regenerate and repair. Stem cell therapy is a successful approach for repairing and regenerating ischemic cardiac tissue; however, transplanted cells display very high death percentage, a problem that affects success of tissue regeneration. Stem cells display multipotency or pluripotency and undergo self-renewal, however these events are negatively influenced by upregulation of cell death machinery that induces the significant decrease in survival and differentiation signals upon cardiovascular injury. While efforts to identify cell types and molecular pathways that promote cardiac tissue regeneration have been productive, studies that focus on blocking the extensive cell death after transplantation are limited. The control of cell death includes multiple networks rather than one crucial pathway, which underlies the challenge of identifying the interaction between various cellular and biochemical components. This review is aimed at exploiting the molecular mechanisms by which stem cells resist death signals to develop into mature and healthy cardiac cells. Specifically, we focus on a number of factors that control death and survival of stem cells upon transplantation and ultimately affect cardiac regeneration. We also discuss potential survival enhancing strategies and how they could be meaningful in the design of targeted therapies that improve cardiac function.

A Switch in Akt Isoforms Is Required for Notch-Induced Snail1 Expression and Protection from Cell Death

Notch activation in aortic endothelial cells (ECs) takes place at embryonic stages during cardiac valve formation and induces endothelial-to-mesenchymal transition (EndMT). Using aortic ECs, we show here that active Notch expression promotes EndMT, resulting in downregulation of vascular endothelial cadherin (VE-cadherin) and upregulation of mesenchymal genes such as those for fibronectin and Snail1/2. In these cells, transforming growth factor β1 exacerbates Notch effects by increasing Snail1 and fibronectin activation. When Notch-downstream pathways were analyzed, we detected an increase in glycogen synthase kinase 3β (GSK-3β) phosphorylation and inactivation that facilitates Snail1 nuclear retention and protein stabilization. However, the total activity of Akt was downregulated. The discrepancy between Akt activity and GSK-3β phosphorylation is explained by a Notch-induced switch in the Akt isoforms, whereby Akt1, the predominant isoform expressed in ECs, is decreased and Akt2 transcription is upregulated. Mechanistically, Akt2 induction requires the stimulation of the β-catenin/TCF4 transcriptional complex, which activates the Akt2 promoter. Active, phosphorylated Akt2 translocates to the nucleus in Notch-expressing cells, resulting in GSK-3β inactivation in this compartment. Akt2, but not Akt1, colocalizes in the nucleus with lamin B in the nuclear envelope. In addition to promoting GSK-3β inactivation, Notch downregulates Forkhead box O1 (FoxO1), another Akt2 nuclear substrate. Moreover, Notch protects ECs from oxidative stress-induced apoptosis through an Akt2- and Snail1-dependent mechanism.

Deletion of low molecular weight protein tyrosine phosphatase (Acp1) protects against stress-induced cardiomyopathy

The low molecular weight protein tyrosine phosphatase (LMPTP), encoded by the ACP1 gene, is a ubiquitously expressed phosphatase whose in vivo function in the heart and in cardiac diseases remains unknown. To investigate the in vivo role of LMPTP in cardiac function, we generated mice with genetic inactivation of the Acp1 locus and studied their response to long‐term pressure overload. Acp1^−/− mice develop normally and ageing mice do not show pathology in major tissues under basal conditions. However, Acp1^−/− mice are strikingly resistant to pressure overload hypertrophy and heart failure. Lmptp expression is high in the embryonic mouse heart, decreased in the postnatal stage, and increased in the adult mouse failing heart. We also show that LMPTP expression increases in end‐stage heart failure in humans. Consistent with their protected phenotype, Acp1^−/− mice subjected to pressure overload hypertrophy have attenuated fibrosis and decreased expression of fibrotic genes. Transcriptional profiling and analysis of molecular signalling show that the resistance of Acp1^−/− mice to pathological cardiac stress correlates with marginal re‐expression of fetal cardiac genes, increased insulin receptor beta phosphorylation, as well as PKA and ephrin receptor expression, and inactivation of the CaMKIIδ pathway. Our data show that ablation of Lmptp inhibits pathological cardiac remodelling and suggest that inhibition of LMPTP may be of therapeutic relevance for the treatment of human heart failure. © 2015 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Tetrahydrobiopterin reverse left ventricular hypertrophy and diastolic dysfunction through the PI3K/p-Akt pathway in spontaneously hypertensive rats

Hypertension induced hypertrophy and diastolic dysfunction and is associated with cardiac oxidation and reduced NO production. We hypothesized that tetrahydrobiopterin (BH4) can regulate the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathway and reverse cardiac hypertrophy and diastolic dysfunction in spontaneously hypertensive rats. Ten-week-old male spontaneously hypertensive rats (SHR) and age-matched normotensive control Wistar-Kyoto (WKY) rats were divided into five groups, WKY, WKY + BH4, SHR, SHR + BH4 and SHR + VAL. In SHR, diastolic dysfunction was accompanied by concentric hypertrophy, cardiac oxidation, and reduced cardiac BH4 and NO production. Four-week BH4 and valsartan administration reversed hypertrophy and improved diastolic function. BH4 and valsartan blunted the expression of hypertrophy markers α-skeletal actin (α-SA) and β-myosin heavy chain (β-MHC). Only BH4 reduced hypertension and induced myocardial fibrosis and expression of transforming growth factor-β1 (TGF-β1). BH4 reduced cardiac oxidant stress and increased NO production. Exogenous BH4 increased phosphorylated Akt levels and increased Bcl-2 expression. In conclusion, less BH4 and reduced NO increases myocardial hypertrophy and cardiac oxidative stress, which exacerbates diastolic dysfunction. Exogenous BH4 ameliorates cardiac hypertrophy and diastolic dysfunction through the PI3K/p-Akt pathway. BH4 may be a potent therapy for hypertension with diastolic dysfunction.

Nuclear localized Akt enhances breast cancer stem-like cells through counter-regulation of p21(Waf1/Cip1) and p27(kip1)

Cancer stem-like cells (CSCs) are a rare subpopulation of cancer cells capable of propagating the disease and causing cancer recurrence. In this study, we found that the cellular localization of PKB/Akt kinase affects the maintenance of CSCs. When Akt tagged with nuclear localization signal (Akt-NLS) was overexpressed in SKBR3 and MDA-MB468 cells, these cells showed a 10-15% increase in the number of cells with CSCs enhanced ALDH activity and demonstrated a CD44(+High)/CD24(-Low) phenotype. This effect was completely reversed in the presence of Akt-specific inhibitor, triciribine. Furthermore, cells overexpressing Akt or Akt-NLS were less likely to be in G0/G1 phase of the cell cycle by inactivating p21(Waf1/Cip1) and exhibited increased clonogenicity and proliferation as assayed by colony-forming assay (mammosphere formation). Thus, our data emphasize the importance the intracellular localization of Akt has on stemness in human breast cancer cells. It also indicates a new robust way for improving the enrichment and culture of CSCs for experimental purposes. Hence, it allows for the development of simpler protocols to study stemness, clonogenic potency, and screening of new chemotherapeutic agents that preferentially target cancer stem cells.

SUMMARY

The presented data, (i) shows new, stemness-promoting role of nuclear Akt/PKB kinase, (ii) it underlines the effects of nuclear Akt on cell cycle regulation, and finally (iii) it suggests new ways to study cancer stem-like cells.

B-type natriuretic peptide expression and cardioprotection is regulated by Akt dependent signaling at early reperfusion

Exogenously administered B-type natriuretic peptide (BNP) has been shown to offer cardioprotection through activation of particulate guanylyl cyclase (pGC), protein kinase G (PKG) and KATP channel opening. The current study explores if cardioprotection afforded by short intermittent BNP administration involves PI3K/Akt/p70s6k dependent signaling, and whether this signaling pathway may participate in regulation of BNP mRNA expression at early reperfusion. Isolated Langendorff perfused rat hearts were subjected to 30min of regional ischemia and 120min of reperfusion (IR). Applying intermittent 3×30s infusion of BNP peptide in a postconditioning like manner (BNPPost) reduced infarct size by >50% compared to controls (BNPPost 17±2% vs. control 42±4%, p<0.001). Co-treatment with inhibitors of the PI3K/Akt/p70s6k pathway (wortmannin, SH-6 and rapamycin) completely abolished the infarct-limiting effect of BNP postconditioning (BNPPost+Wi 36±5%, BNPPost+SH-6 41±4%, BNPPost+Rap 37±6% vs. BNPPost 17±2%, p<0.001). Inhibition of natriuretic peptide receptors (NPR) by isatin also abrogated BNPPost cardioprotection (BNPPost+isatin 46±2% vs. BNPPost 17±2%, p<0.001). BNPPost also significantly phosphorylated Akt and p70s6k at early reperfusion, and Akt phosphorylation was inhibited by SH-6 and isatin. Myocardial BNP mRNA levels in the area at risk (AA) were significantly elevated at early reperfusion as compared to the non-ischemic area (ANA) (Ctr(AA) 2.7±0.5 vs. Ctr(ANA) 1.2±0.2, p<0.05) and the ischemic control tissue (Ctr(AA) 2.7±0.5 vs. ischemia 1.0±0.1, p<0.05). Additional experiments also revealed a significant higher BNP mRNA level in ischemic postconditioned (IPost) hearts as compared to ischemic controls (IPost 6.7±1.3 vs. ischemia 1.0±0.2, p<0.05), but showed no difference from controls run in parallel (Ctr 5.4±0.8). Akt inhibition by SH-6 completely abrogated this elevation (IPost 6.7±1.3 vs. IPost+SH-6 1.8±0.7, p<0.05) (Ctr 5.4±0.8 vs. SH-6 1.5±0.9, p<0.05). In conclusion, Akt dependent signaling is involved in mediating the cardioprotection afforded by intermittent BNP infusion at early reperfusion, and may also participate in regulation of reperfusion induced BNP expression.

Role of copper in regression of cardiac hypertrophy

Pressure overload causes an accumulation of homocysteine in the heart, which is accompanied by copper depletion through the formation of copper-homocysteine complexes and the excretion of the complexes. Copper supplementation recovers cytochrome c oxidase (CCO) activity and promotes myocardial angiogenesis, along with the regression of cardiac hypertrophy and the recovery of cardiac contractile function. Increased copper availability is responsible for the recovery of CCO activity. Copper promoted expression of angiogenesis factors including vascular endothelial growth factor (VEGF) in endothelial cells is responsible for angiogenesis. VEGF receptor-2 (VEGFR-2) is critical for hypertrophic growth of cardiomyocytes and VEGFR-1 is essential for the regression of cardiomyocyte hypertrophy. Copper, through promoting VEGF production and suppressing VEGFR-2, switches the VEGF signaling pathway from VEGFR-2-dependent to VEGFR-1-dependent, leading to the regression of cardiomyocyte hypertrophy. Copper is also required for hypoxia-inducible factor-1 (HIF-1) transcriptional activity, acting on the interaction between HIF-1 and the hypoxia responsible element and the formation of HIF-1 transcriptional complex by inhibiting the factor inhibiting HIF-1. Therefore, therapeutic targets for copper supplementation-induced regression of cardiac hypertrophy include: (1) the recovery of copper availability for CCO and other critical cellular events; (2) the activation of HIF-1 transcriptional complex leading to the promotion of angiogenesis in the endothelial cells by VEGF and other factors; (3) the activation of VEGFR-1-dependent regression signaling pathway in the cardiomyocytes; and (4) the inhibition of VEGFR-2 through post-translational regulation in the hypertrophic cardiomyocytes. Future studies should focus on target-specific delivery of copper for the development of clinical application.

The heart: mostly postmitotic or mostly premitotic? Myocyte cell cycle, senescence, and quiescence

The concept of myocyte division and myocyte-mediated regeneration has re-emerged in the past 5 years through development of sophisticated transgenic mice and carbon-dating of cells. Although recently, a couple of studies have been conducted as an attempt to intervene in myocyte division, the efficiency in adult animals remains discouragingly low. Re-enforcing myocyte division is a vision that has been desired for decades, leading to years of experience in myocyte resistance to proproliferative stimuli. Previous attempts have indeed provided a platform for basic knowledge on molecular players and signalling in myocytes. However, natural biological processes such as hypertrophy and binucleation provide layers of complexity in interpretation of previous and current findings. A major hurdle in mediating myocyte division is a lack of insight in the myocyte cell cycle. To date, no knowledge is gained on myoycte cell cycle progression and/or duration. This review will include an overview of previous and current literature on myocyte cell cycle and division. Furthermore, the limitations of current approaches and basic questions that might be essential in understanding myocardial resistance to division will be discussed.

Lutein inhibits the migration of retinal pigment epithelial cells via cytosolic and mitochondrial Akt pathways (lutein inhibits RPE cells migration)

During the course of proliferative vitreoretinopathy (PVR), the retinal pigment epithelium (RPE) cells will de-differentiate, proliferate, and migrate onto the surfaces of the sensory retina. Several studies have shown that platelet-derived growth factor (PDGF) can induce migration of RPE cells via an Akt-related pathway. In this study, the effect of lutein on PDGF-BB-induced RPE cells migration was examined using transwell migration assays and Western blot analyses. We found that both phosphorylation of Akt and mitochondrial translocation of Akt in RPE cells induced by PDGF-BB stimulation were suppressed by lutein. Furthermore, the increased migration observed in RPE cells with overexpressed mitochondrial Akt could also be suppressed by lutein. Our results demonstrate that lutein can inhibit PDGF-BB induced RPE cells migration through the inhibition of both cytoplasmic and mitochondrial Akt activation.

Role of biological sex in normal cardiac function and in its disease outcome - a review

Biological sex plays an important role in normal cardiac physiology as well as in the heart's response to cardiac disease. Women generally have better cardiac function and survival than do men in the face of cardiac disease; however, this is progressively lost when comparing postmenopausal women with age matched men. Animal model of cardiac disease mirror what is seen in humans. Sex hormones contribute significantly to sex based difference in cardiac functioning and in its disease outcome. Estrogen is considered to be cardioprotective, whereas testosterone is detrimental to heart function.