Switch from caspase-dependent to caspase-independent death during heart development: essential role of endonuclease G in ischemia-induced DNA processing of differentiated cardiomyocytes

Hypoxia-Induced Myocardial Hypertrophy Companies with Apoptosis Enhancement and p38-MAPK Pathway Activation

Li, Xiaoxu, Zhijun Pu, Gang Xu, Yidong Yang, Yu Cui, Xiaoying Zhou, Chenyuan Wang, Zhifeng Zhong, Simin Zhou, Jun Yin, Fabo Shan, Chengzhong Yang, Li Jiao, Dewei Chen, and Jian Huang. Hypoxia-induced myocardial hypertrophy companies with apoptosis enhancement and p38-MAPK pathway activation. High Alt Med Biol. 00:00-00, 2024. Background: Right ventricular function and remodeling are closely associated with symptom severity and patient survival in hypoxic pulmonary hypertension. However, the detailed molecular mechanisms underlying hypoxia-induced myocardial hypertrophy remain unclear. Methods: In Sprague-Dawley rats, hemodynamics were assessed under both normoxia and hypobaric hypoxia at intervals of 7 (H7), 14 (H14), and 28 (H28) days. Morphological changes in myocardial tissue were examined using hematoxylin and eosin (HE) staining, while myocardial hypertrophy was evaluated with wheat germ agglutinin (WGA) staining. Apoptosis was determined through TUNEL assays. To further understand the mechanism of myocardial hypertrophy, RNA sequencing was conducted, with findings validated via Western blot analysis. Results: The study demonstrated increased hypoxic pulmonary hypertension and improved right ventricular diastolic and systolic function in the rat models. Significant elevations in pulmonary arterial systolic pressure (PASP), mean pulmonary arterial pressure (mPAP), right ventricular mean pressure (RVMP), and the absolute value of +dp/dtmax were observed in the H14 and H28 groups compared with controls. In addition, right ventricular systolic pressure (RVSP), -dp/dtmax, and the mean dp/dt during isovolumetric relaxation period were notably higher in the H28 group. Heart rate increased in the H14 group, whereas the time constant of right ventricular isovolumic relaxation (tau) was reduced in both H14 and H28 groups. Both the right heart hypertrophy index and the heart weight/body weight ratio (HW/BW) were elevated in the H14 and H28 groups. Myocardial cell cross-sectional area also increased, as shown by HE and WGA staining. Western blot results revealed upregulated HIF-1α levels and enhanced HIF-2α expression in the H7 group. In addition, phosphorylation of p38 and c-fos was augmented in the H28 group. The H28 group showed elevated levels of Cytochrome C (Cyto C), whereas the H14 and H28 groups exhibited increased levels of Cleaved Caspase-3 and the Bax/Bcl-2 ratio. TUNEL analysis revealed a rise in apoptosis with the extension of hypoxia duration in the right ventricle. Conclusions: The study established a link between apoptosis and p38-MAPK pathway activation in hypoxia-induced myocardial hypertrophy, suggesting their significant roles in this pathological process.

Mesenchymal stromal cells for improvement of cardiac function following acute myocardial infarction: a matter of timing

Acute myocardial infarction (AMI) is the leading cause of cardiovascular death and remains the most common cause of heart failure. Reopening of the occluded artery, i.e., reperfusion, is the only way to save the myocardium. However, the expected benefits of reducing infarct size are disappointing due to the reperfusion paradox, which also induces specific cell death. These ischemia-reperfusion (I/R) lesions can account for up to 50% of final infarct size, a major determinant for both mortality and the risk of heart failure (morbidity). In this review, we provide a detailed description of the cell death and inflammation mechanisms as features of I/R injury and cardioprotective strategies such as ischemic postconditioning as well as their underlying mechanisms. Due to their biological properties, the use of mesenchymal stromal/stem cells (MSCs) has been considered a potential therapeutic approach in AMI. Despite promising results and evidence of safety in preclinical studies using MSCs, the effects reported in clinical trials are not conclusive and even inconsistent. These discrepancies were attributed to many parameters such as donor age, in vitro culture, and storage time as well as injection time window after AMI, which alter MSC therapeutic properties. In the context of AMI, future directions will be to generate MSCs with enhanced properties to limit cell death in myocardial tissue and thereby reduce infarct size and improve the healing phase to increase postinfarct myocardial performance.

The roles of intracellular proteolysis in cardiac ischemia-reperfusion injury

Ischemic heart disease remains a leading cause of human mortality worldwide. One form of ischemic heart disease is ischemia-reperfusion injury caused by the reintroduction of blood supply to ischemic cardiac muscle. The short and long-term damage that occurs due to ischemia-reperfusion injury is partly due to the proteolysis of diverse protein substrates inside and outside of cardiomyocytes. Ischemia-reperfusion activates several diverse intracellular proteases, including, but not limited to, matrix metalloproteinases, calpains, cathepsins, and caspases. This review will focus on the biological roles, intracellular localization, proteolytic targets, and inhibitors of these proteases in cardiomyocytes following ischemia-reperfusion injury. Recognition of the intracellular function of each of these proteases includes defining their activation, proteolytic targets, and their inhibitors during myocardial ischemia-reperfusion injury. This review is a step toward a better understanding of protease activation and involvement in ischemic heart disease and developing new therapeutic strategies for its treatment.

Pharmacological Cardioprotection against Ischemia Reperfusion Injury-The Search for a Clinical Effective Therapy

Pharmacological conditioning aims to protect the heart from myocardial ischemia-reperfusion injury (IRI). Despite extensive research in this area, today, a significant gap remains between experimental findings and clinical practice. This review provides an update on recent developments in pharmacological conditioning in the experimental setting and summarizes the clinical evidence of these cardioprotective strategies in the perioperative setting. We start describing the crucial cellular processes during ischemia and reperfusion that drive acute IRI through changes in critical compounds (∆G_ATP, Na⁺, Ca²⁺, pH, glycogen, succinate, glucose-6-phosphate, mitoHKII, acylcarnitines, BH₄, and NAD⁺). These compounds all precipitate common end-effector mechanisms of IRI, such as reactive oxygen species (ROS) generation, Ca²⁺ overload, and mitochondrial permeability transition pore opening (mPTP). We further discuss novel promising interventions targeting these processes, with emphasis on cardiomyocytes and the endothelium. The limited translatability from basic research to clinical practice is likely due to the lack of comorbidities, comedications, and peri-operative treatments in preclinical animal models, employing only monotherapy/monointervention, and the use of no-flow (always in preclinical models) versus low-flow ischemia (often in humans). Future research should focus on improved matching between preclinical models and clinical reality, and on aligning multitarget therapy with optimized dosing and timing towards the human condition.

Cardiac fibroblasts display endurance to ischemia, high ROS control and elevated respiration regulated by the JAK2/STAT pathway

Cardiovascular diseases are the leading cause of death globally and more than four out of five cases are due to ischemic events. Cardiac fibroblasts (CF) contribute to normal heart development and function, and produce the post-ischemic scar. Here, we characterize the biochemical and functional aspects related to CF endurance to ischemia-like conditions. Expression data mining showed that cultured human CF (HCF) express more BCL2 than pulmonary and dermal fibroblasts. In addition, gene set enrichment analysis showed overrepresentation of genes involved in the response to hypoxia and oxidative stress, respiration and Janus kinase (JAK)/Signal transducer and Activator of Transcription (STAT) signaling pathways in HCF. BCL2 sustained survival and proliferation of cultured rat CF, which also had higher respiration capacity and reactive oxygen species (ROS) production than pulmonary and dermal fibroblasts. This was associated with higher expression of the electron transport chain (ETC) and antioxidant enzymes. CF had high phosphorylation of JAK2 and its effectors STAT3 and STAT5, and their inhibition reduced viability and respiration, impaired ROS control and reduced the expression of BCL2, ETC complexes and antioxidant enzymes. Together, our results identify molecular and biochemical mechanisms conferring survival advantage to experimental ischemia in CF and show their control by the JAK2/STAT signaling pathway. The presented data point to potential targets for the regulation of cardiac fibrosis and also open the possibility of a general mechanism by which somatic cells required to acutely respond to ischemia are constitutively adapted to survive it.

ENDOG Impacts on Tumor Cell Proliferation and Tumor Prognosis in the Context of PI3K/PTEN Pathway Status

EndoG influences mitochondrial DNA replication and is involved in somatic cell proliferation. Here, we investigated the effect of ENDOG/Endog expression on proliferation in different tumor models. Noteworthy, ENDOG deficiency reduced proliferation of endometrial tumor cells expressing low PTEN/high p-AKT levels, and Endog deletion blunted the growth of PTEN-deficient 3D endometrial cultures. Furthermore, ENDOG silencing reduced proliferation of follicular thyroid carcinoma and glioblastoma cell lines with high p-AKT expression. High ENDOG expression was associated with a short time to treatment in a cohort of patients with chronic lymphocytic leukemia (CLL), a B-cell lymphoid neoplasm with activation of PI3K/AKT. This clinical impact was observed in the less aggressive CLL subtype with mutated IGHV in which high ENDOG and low PTEN levels were associated with worse outcome. In summary, our results show that reducing ENDOG expression hinders growth of some tumors characterized by low PTEN activity and high p-AKT expression and that ENDOG has prognostic value for some cancer types.

Current status of cardiac regenerative medicine; An update on point of view to cell therapy application

Cardiovascular diseases (CVDs) are the leading cause of death globally. Because of the economic and social burden of acute myocardial infarction and its chronic consequences in surviving patients, understanding the pathophysiology of myocardial infarction injury is a major priority for cardiovascular research. MI is defined as cardiomyocytes death caused by an ischemic that resulted from the apoptosis, necrosis, necroptosis, and autophagy. The phases of normal repair following MI including inflammatory, proliferation, and maturation. Normal repair is slow and inefficient generally so that other treatments are required. Because of difficulties, outcomes, and backwashes of traditional therapies including coronary artery bypass grafting, balloon angioplasty, heart transplantation, and artificial heart operations, the novel strategy in the treatment of MI, cell therapy, was newly emerged. In cell therapy, a new population of cells has created that substitute with damaged cells. Different types of stem cell and progenitor cells have been shown to improve cardiac function through various mechanisms, including the formation of new myocytes, endothelial cells, and vascular smooth muscle cells. Bone marrow- and/or adipose tissue-derived mesenchymal stem cells, embryonic stem cells, autologous skeletal myoblasts, induced pluripotent stem cells, endothelial progenitor cells, cardiac progenitor cells and cardiac pericytes considered as a source for cell therapy. In this study, we focused on the point of view of the cell sources.

Autophagy restricts mitochondrial DNA damage-induced release of ENDOG (endonuclease G) to regulate genome stability

Genotoxic insult causes nuclear and mitochondrial DNA damages with macroautophagy/autophagy induction. The role of mitochondrial DNA (mtDNA) damage in the requirement of autophagy for nuclear DNA (nDNA) stability is unclear. Using site-specific DNA damage approaches, we show that specific nDNA damage alone does not require autophagy for repair unless in the presence of mtDNA damage. We provide evidence that after IR exposure-induced mtDNA and nDNA damages, autophagy suppression causes non-apoptotic mitochondrial permeability, by which mitochondrial ENDOG (endonuclease G) is released and translocated to nuclei to sustain nDNA damage in a TET (tet methylcytosine dioxygenase)-dependent manner. Furthermore, blocking lysosome function is sufficient to increase the amount of mtDNA leakage to the cytosol, accompanied by ENDOG-free mitochondrial puncta formation with concurrent ENDOG nuclear accumulation. We proposed that autophagy eliminates the mitochondria specified by mtDNA damage-driven mitochondrial permeability to prevent ENDOG-mediated genome instability. Finally, we showed that HBx, a hepatitis B viral protein capable of suppressing autophagy, also causes mitochondrial permeability-dependent ENDOG mis-localization in nuclei and is linked to hepatitis B virus (HBV)-mediated hepatocellular carcinoma development.Abbreviations: 3-MA: 3-methyladenine; 5-hmC: 5-hydroxymethylcytosine; ACTB: actin beta; ATG5: autophagy related 5; ATM: ATM serine/threonine kinase; DFFB/CAD: DNA fragmentation factor subunit beta; cmtDNA: cytosolic mitochondrial DNA; ConA: concanamycin A; CQ: chloroquine; CsA: cyclosporin A; Dox: doxycycline; DSB: double-strand break; ENDOG: endonuclease G; GFP: green fluorescent protein; Gy: gray; H2AX: H2A.X variant histone; HBV: hepatitis B virus; HBx: hepatitis B virus X protein; HCC: hepatocellular carcinoma; I-PpoI: intron-encoded endonuclease; IR: ionizing radiation; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MOMP: mitochondrial outer membrane permeability; mPTP: mitochondrial permeability transition pore; mtDNA: mitochondrial DNA; nDNA: nuclear DNA; 4-OHT: 4-hydroxytamoxifen; rDNA: ribosomal DNA; ROS: reactive oxygen species; SQSTM1/p62: sequestosome 1; TET: tet methylcytosine dioxygenase; TFAM: transcription factor A, mitochondrial; TOMM20: translocase of outer mitochondrial membrane 20; VDAC: voltage dependent anion channel.

Involvement of the mitochondrial nuclease EndoG in the regulation of cell proliferation through the control of reactive oxygen species

The apoptotic nuclease EndoG is involved in mitochondrial DNA replication. Previous results suggested that, in addition to regulate cardiomyocyte hypertrophy, EndoG could be involved in cell proliferation. Here, by using in vivo and cell culture models, we investigated the role of EndoG in cell proliferation. Genetic deletion of Endog both in vivo and in cultured cells or Endog silencing in vitro induced a defect in rodent and human cell proliferation with a tendency of cells to accumulate in the G₁ phase of cell cycle and increased reactive oxygen species (ROS) production. The defect in cell proliferation occurred with a decrease in the activity of the AKT/PKB-GSK-3β-Cyclin D axis and was reversed by addition of ROS scavengers. EndoG deficiency did not affect the expression of ROS detoxifying enzymes, nor the expression of the electron transport chain complexes and oxygen consumption rate. Addition of the micropeptide Humanin to EndoG-deficient cells restored AKT phosphorylation and proliferation without lowering ROS levels. Thus, our results show that EndoG is important for cell proliferation through the control of ROS and that Humanin can restore cell division in EndoG-deficient cells and counteracts the effects of ROS on AKT phosphorylation.

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Reduced expression of the mitochondrial nuclease EndoG induces ROS production.

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EndoG deficiency hampers cell proliferation through ROS-dependent signaling.

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Increased ROS in EndoG-deficient cells limits the Akt/Gsk3/cyclin axis activity.

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Humanin sustains proliferation despite high ROS levels induced by Endog deficiency.

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Romo-1 deficiency reduces cell proliferation independently of EndoG and ROS.

Cardiomyocyte hypertrophy induced by Endonuclease G deficiency requires reactive oxygen radicals accumulation and is inhibitable by the micropeptide humanin

The endonuclease G gene (Endog), which codes for a mitochondrial nuclease, was identified as a determinant of cardiac hypertrophy. How ENDOG controls cardiomyocyte growth is still unknown. Thus, we aimed at finding the link between ENDOG activity and cardiomyocyte growth. Endog deficiency induced reactive oxygen species (ROS) accumulation and abnormal growth in neonatal rodent cardiomyocytes, altering the AKT-GSK3β and Class-II histone deacethylases (HDAC) signal transduction pathways. These effects were blocked by ROS scavengers. Lack of ENDOG reduced mitochondrial DNA (mtDNA) replication independently of ROS accumulation. Because mtDNA encodes several subunits of the mitochondrial electron transport chain, whose activity is an important source of cellular ROS, we investigated whether Endog deficiency compromised the expression and activity of the respiratory chain complexes but found no changes in these parameters nor in ATP content. MtDNA also codes for humanin, a micropeptide with possible metabolic functions. Nanomolar concentrations of synthetic humanin restored normal ROS levels and cell size in Endog-deficient cardiomyocytes. These results support the involvement of redox signaling in the control of cardiomyocyte growth by ENDOG and suggest a pathway relating mtDNA content to the regulation of cell growth probably involving humanin, which prevents reactive oxygen radicals accumulation and hypertrophy induced by Endog deficiency.

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Endog deficiency induces cardiomyocyte hypertrophy and superoxide accumulation.

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Hypertrophy induced by Endog deficiency requires ROS accumulation.

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ENDOG is involved in mtDNA replication independently of ROS accumulation.

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Electron Transport Chain activity is not affected by Endog deficiency.

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Humanin restricts ROS accumulation and blocks cardiomyocyte growth.

AKT2 deficiency induces retardation of myocyte development through EndoG-MEF2A signaling in mouse heart

Protein kinase B2 (AKT2) is implicated in diverse process of cardiomyocyte signaling including survival and metabolism. However, the role of AKT2 in myocardium development and the signaling pathway is rarely understood. Therefore, we sought to determine the effect of AKT2 deletion on heart development and its downstream targets. By using experimental animal models and neonatal rat cardiomyocytes (NRCMs), we observed that AKT2 deficiency induces retardation of heart development and increased systemic blood pressure (BP) without affecting cardiac function. Further investigation suggested that deficiency of AKT2 in myocardium results in diminished MEF2A abundance, which induced decreased size of cardiomyocytes. We additionally confirmed that EndoG, which is also regulated by AKT2, is a suppressor of MEF2A in myocardium. Finally, our results proved that AKT2 deficiency impairs the response to β-adrenergic stimuli that normally causes hypertrophy in cardiomyocytes by downregulating MEF2A expression. Our data are the first to show the important role of AKT2 in determining the size of myocardium, its deficiency causes retardation of cardiomyocyte development. We also proved a novel pathway of heart development involving EndoG and MEF2A regulated by AKT2.

AKT2 Blocks Nucleus Translocation of Apoptosis-Inducing Factor (AIF) and Endonuclease G (EndoG) While Promoting Caspase Activation during Cardiac Ischemia

The AKT (protein kinase B, PKB) family has been shown to participate in diverse cellular processes, including apoptosis. Previous studies demonstrated that protein kinase B2 (AKT2^−/−) mice heart was sensitized to apoptosis in response to ischemic injury. However, little is known about the mechanism and apoptotic signaling pathway. Here, we show that AKT2 inhibition does not affect the development of cardiomyocytes but increases cell death during cardiomyocyte ischemia. Caspase-dependent apoptosis of both the extrinsic and intrinsic pathway was inactivated in cardiomyocytes with AKT2 inhibition during ischemia, while significant mitochondrial disruption was observed as well as intracytosolic translocation of cytochrome C (Cyto C) together with apoptosis-inducing factor (AIF) and endonuclease G (EndoG), both of which are proven to conduct DNA degradation in a range of cell death stimuli. Therefore, mitochondria-dependent cell death was investigated and the results suggested that AIF and EndoG nucleus translocation causes cardiomyocyte DNA degradation during ischemia when AKT2 is blocked. These data are the first to show a previous unrecognized function and mechanism of AKT2 in regulating cardiomyocyte survival during ischemia by inducing a unique mitochondrial-dependent DNA degradation pathway when it is inhibited.

Role of Endonuclease G in Exogenous DNA Stability in HeLa Cells

Endonuclease G (EndoG) is a well-conserved mitochondrial-nuclear nuclease with dual lethal and vital roles in the cell. The aim of our study was to examine whether EndoG exerts its nuclease activity on exogenous DNA substrates such as plasmid DNA (pDNA), considering their importance in gene therapy applications. The effects of EndoG knockdown on pDNA stability and levels of encoded reporter gene expression were evaluated in the cervical carcinoma HeLa cells. Transfection of pDNA vectors encoding short-hairpin RNAs (shRNAs) reduced levels of EndoG mRNA in HeLa cells. In physiological circumstances, EndoG knockdown did not have an effect on the stability of pDNA or the levels of encoded transgene expression as measured over a four-day time course. However, when endogenous expression of EndoG was induced by an extrinsic stimulus, targeting of EndoG by shRNA improved the perceived stability and transgene expression of pDNA vectors. Therefore, EndoG is not a mediator of exogenous DNA clearance, but in non-physiological circumstances, it may nonspecifically cleave intracellular DNA regardless of its origin. These findings make it unlikely that targeting of EndoG is a viable strategy for improving the duration and level of transgene expression from nonviral DNA vectors in gene therapy efforts.

Myocardial apoptosis in heart disease: does the emperor have clothes?

Since the discovery of a novel mechanism of cell death that differs from traditional necrosis, i.e., apoptosis, there have been numerous studies concluding that increased apoptosis augments myocardial infarction and heart failure and that limiting apoptosis protects the heart. Importantly, the vast majority of cells in the heart are non-myocytes with only roughly 30 % myocytes, yet almost the entire field studying apoptosis in the heart has disregarded non-myocyte apoptosis, e.g., only 4.7 % of 423 studies on myocardial apoptosis in the past 3 years quantified non-myocyte apoptosis. Accordingly, we reviewed the history of apoptosis in the heart focusing first on myocyte apoptosis, followed by the history of non-myocyte apoptosis in myocardial infarction and heart failure. Apoptosis of several of the major non-myocyte cell types in the heart (cardiac fibroblasts, endothelial cells, vascular smooth muscle cells, macrophages and leukocytes) may actually be responsible for affecting the severity of myocardial infarction and heart failure. In summary, even though it is now known that the majority of apoptosis in the heart occurs in non-myocytes, very little work has been done to elucidate the mechanisms by which non-myocyte apoptosis might be responsible for the adverse effects of apoptosis in myocardial infarction and heart failure. The goal of this review is to provide an impetus for future work in this field on non-myocyte apoptosis that will be required for a better understanding of the role of apoptosis in the heart.

Cardiomyocytes display low mitochondrial priming and are highly resistant toward cytotoxic T-cell killing

Following heart transplantation, alloimmune responses can cause graft rejection by damaging donor vascular and parenchymal cells. However, it remains unclear whether cardiomyocytes are also directly killed by immune cells. Here, we used two‐photon microscopy to investigate how graft‐specific effector CD8⁺ T cells interact with cardiomyocytes in a mouse heart transplantation model. Surprisingly, we observed that CD8⁺ T cells are completely impaired in killing cardiomyocytes. Even after virus‐mediated preactivation, antigen‐specific CD8⁺ T cells largely fail to lyse these cells although both cell types engage in dynamic interactions. Furthermore, we established a two‐photon microscopy‐based assay using intact myocardium to determine the susceptibility of cardiomyocytes to undergo apoptosis. This feature, also known as mitochondrial priming reveals an unexpected weak predisposition of cardiomyocytes to undergo apoptosis in situ. These observations together with the early exhaustion phenotype of graft‐infiltrating specific T cells provide an explanation why cardiomyocytes are largely protected from direct CD8⁺ T‐cell‐mediated killing.

Studies on the role of apoptosis after transient myocardial ischemia: genetic deletion of the executioner caspases-3 and -7 does not limit infarct size and ventricular remodeling

Although it is widely accepted that apoptosis may contribute to cell death in myocardial infarction, experimental evidence suggests that adult cardiomyocytes repress the expression of the caspase-dependent apoptotic pathway. The aim of this study was to analyze the contribution of caspase-mediated apoptosis to myocardial ischemia-reperfusion injury. Cardiac-specific caspase-3 deficient/full caspase-7-deficient mice (Casp3/7DKO) and wild type control mice (WT) were subjected to in situ ischemia by left anterior coronary artery ligation for 45 min followed by 24 h or 28 days of reperfusion. Heart function was assessed using M-mode echocardiography. Deletion of caspases did not modify neither infarct size determined by triphenyltetrazolium staining after 24 h of reperfusion (40.0 ± 5.1 % in WT vs. 36.2 ± 3.6 % in Casp3/7DKO), nor the scar area measured by pricosirius red staining after 28 days of reperfusion (41.1 ± 5.4 % in WT vs. 44.6 ± 8.7 % in Casp3/7DKO). Morphometric and echocardiographic studies performed 28 days after the ischemic insult revealed left ventricular dilation and severe cardiac dysfunction without statistically significant differences between WT and Casp3/7DKO groups. These data demonstrate that the executioner caspases-3 and -7 do not significantly contribute to cardiomyocyte death induced by transient coronary occlusion and provide the first evidence obtained in an in vivo model that argues against a relevant role of apoptosis through the canonical caspase pathway in this context.

Effect of superoxide anion scavenger on rat hearts with chronic intermittent hypoxia

Only very limited information regarding the protective effects of the superoxide anion scavenger on chronic intermittent hypoxia-induced cardiac apoptosis is available. The purpose of this study is to evaluate the effects of the superoxide anion scavenger on cardiac apoptotic and prosurvival pathways in rats with sleep apnea. Forty-two Sprague-Dawley rats were divided into three groups, rats with normoxic exposure (Control, 21% O2, 1 mo), rats with chronic intermittent hypoxia exposure (Hypoxia, 3-7% O2vs. 21% O2per 40 s cycle, 8 h per day, 1 mo), and rats with pretreatment of the superoxide anion scavenger and chronic intermittent hypoxia exposure (Hypoxia-O2 (-)-Scavenger, MnTMPyP pentachloride, 1 mg/kg ip per day; 3-7% O2vs. 21% O2per 40 s cycle, 8 h per day, 1 mo) at 5-6 mo of age. After 1 mo, the protein levels and apoptotic cells of excised hearts from three groups were measured by Western blotting and terminal deoxynucleotide transferase-mediated dUTP nick end labeling (TUNEL) assay. The superoxide anion scavenger decreased hypoxia-induced myocardial architecture abnormalities, left ventricular hypertrophy, and TUNEL-positive apoptosis. The superoxide anion scavenger decreased hypoxia-induced Fas ligand, Fas death receptors, Fas-associated death domain (FADD), activated caspase-8, and activated caspase-3 (Fas-dependent apoptotic pathway) as well as Bad, activated caspase-9 and activated caspase-3 (mitochondria-dependent apoptotic pathway), endonuclease G (EndoG), apoptosis-inducing factor (AIF), and TUNEL-positive apoptosis. The superoxide anion scavenger increased IGF-1, IGF-1R, p-PI3k, p-Akt, p-Bad, Bcl-2, and Bcl-xL (survival pathway). Our findings imply that the superoxide anion scavenger might prevent cardiac Fas-mediated and mitochondrial-mediated apoptosis and enhance the IGF-1-related survival pathway in chronic intermittent hypoxia. The superoxide anion scavenger may prevent chronic sleep apnea-enhanced cardiac apoptotic pathways and enhances cardiac survival pathways.

Mechanisms of cyclic AMP/protein kinase A- and glucocorticoid-mediated apoptosis using S49 lymphoma cells as a model system

Cyclic AMP/protein kinase A (cAMP/PKA) and glucocorticoids promote the death of many cell types, including cells of hematopoietic origin. In wild-type (WT) S49 T-lymphoma cells, signaling by cAMP and glucocorticoids converges on the induction of the proapoptotic B-cell lymphoma-family protein Bim to produce mitochondria-dependent apoptosis. Kin(-), a clonal variant of WT S49 cells, lacks PKA catalytic (PKA-Cα) activity and is resistant to cAMP-mediated apoptosis. Using sorbitol density gradient fractionation, we show here that in kin(-) S49 cells PKA-Cα is not only depleted but the residual PKA-Cα mislocalizes to heavier cell fractions and is not phosphorylated at two conserved residues (Ser(338) or Thr(197)). In WT S49 cells, PKA-regulatory subunit I (RI) and Bim coimmunoprecipitate upon treatment with cAMP analogs and forskolin (which increases endogenous cAMP concentrations). By contrast, in kin(-) cells, expression of PKA-RIα and Bim is prominently decreased, and increases in cAMP do not increase Bim expression. Even so, kin(-) cells undergo apoptosis in response to treatment with the glucocorticoid dexamethasone (Dex). In WT cells, glucorticoid-mediated apoptosis involves an increase in Bim, but in kin(-) cells, Dex-promoted cell death appears to occur by a caspase 3-independent apoptosis-inducing factor pathway. Thus, although cAMP/PKA-Cα and PKA-R1α/Bim mediate apoptotic cell death in WT S49 cells, kin(-) cells resist this response because of lower levels of PKA-Cα and PKA-RIα subunits as well as Bim. The findings for Dex-promoted apoptosis imply that these lymphoma cells have adapted to selective pressure that promotes cell death by altering canonical signaling pathways.

Glutathione administration reduces mitochondrial damage and shifts cell death from necrosis to apoptosis in ageing diabetic mice hearts during exercise

BACKGROUND AND PURPOSE

The effect of antioxidants on ageing type 2 diabetic (T2D) hearts during exercise is unclear. We hypothesized that GSH therapy during exercise reduces mitochondrial oxidative stress (mOXS) and cell death in ageing db/db mice hearts.

EXPERIMENTAL APPROACH

The effect of GSH on cardiac mOXS and cell death was evaluated both in vivo and in vitro.

KEY RESULTS

During exercise, GSH treatment protected db/db hearts from exaggerated mOXS without reducing total cell death. Despite similar cell death, investigations on apoptosis-specific single-stranded DNA breaks and necrosis-specific damage provided the first in vivo evidence of a shift from necrosis to apoptosis, with reduced fibrosis following GSH administration in exercised db/db hearts. Further support for a GSH-regulated 'switch' in death phenotypes came from NIH-3T3 fibroblasts and H9c2 cardiomyocytes treated with H2 O2 , a reactive oxygen species (ROS). Similar to in vivo findings, augmenting GSH by overexpressing glutamyl cysteine ligase (GCLc) protected fibroblasts and cardiomyocytes from necrosis induced by H2 O2 , but elevated caspase-3 and apoptosis instead. Similar to in vivo findings, where GSH therapy in normoglycaemic mice suppressed endogenous antioxidants and augmented caspase-3 activity, GCLc overexpression during staurosporine-induced death, which was not characterized by ROS, increased GSH efflux and aggravated death in fibroblasts and cardiomyocytes, confirming that oxidative stress is required for GSH-mediated cytoprotection.

CONCLUSIONS AND IMPLICATIONS

While GSH treatment is useful for reducing mOXS and attenuating necrosis and fibrosis in ageing T2D hearts during exercise, such antioxidant treatment could be counterproductive in the healthy heart during exercise.

Executioner Caspase-3 and 7 Deficiency Reduces Myocyte Number in the Developing Mouse Heart

Executioner caspase-3 and -7 are proteases promoting cell death but non-apoptotic roles are being discovered. The heart expresses caspases only during development, suggesting they contribute to the organ maturation process. Therefore, we aimed at identifying novel functions of caspases in heart development. We induced simultaneous deletion of executioner caspase-3 and -7 in the mouse myocardium and studied its effects. Caspase knockout hearts are hypoplastic at birth, reaching normal weight progressively through myocyte hypertrophy. To identify the molecular pathways involved in these effects, we used microarray-based transcriptomics and multiplexed quantitative proteomics to compare wild type and executioner caspase-deficient myocardium at different developmental stages. Transcriptomics showed reduced expression of genes promoting DNA replication and cell cycle progression in the neonatal caspase-deficient heart suggesting reduced myocyte proliferation, and expression of non-cardiac isoforms of structural proteins in the adult null myocardium. Proteomics showed reduced abundance of proteins involved in oxidative phosphorylation accompanied by increased abundance of glycolytic enzymes underscoring retarded metabolic maturation of the caspase-null myocardium. Correlation between mRNA expression and protein abundance of relevant genes was confirmed, but transcriptomics and proteomics indentified complementary molecular pathways influenced by caspases in the developing heart. Forced expression of wild type or proteolytically inactive caspases in cultured cardiomyocytes induced expression of genes promoting cell division. The results reveal that executioner caspases can modulate heart’s cellularity and maturation during development, contributing novel information about caspase biology and heart development.

Die another way--non-apoptotic mechanisms of cell death

Regulated, programmed cell death is crucial for all multicellular organisms. Cell death is essential in many processes, including tissue sculpting during embryogenesis, development of the immune system and destruction of damaged cells. The best-studied form of programmed cell death is apoptosis, a process that requires activation of caspase proteases. Recently it has been appreciated that various non-apoptotic forms of cell death also exist, such as necroptosis and pyroptosis. These non-apoptotic cell death modalities can be either triggered independently of apoptosis or are engaged should apoptosis fail to execute. In this Commentary, we discuss several regulated non-apoptotic forms of cell death including necroptosis, autophagic cell death, pyroptosis and caspase-independent cell death. We outline what we know about their mechanism, potential roles in vivo and define outstanding questions. Finally, we review data arguing that the means by which a cell dies actually matters, focusing our discussion on inflammatory aspects of cell death.

Enrichment of cardiomyocytes in primary cultures of murine neonatal hearts

In vitro culture of neonatal murine cardiomyocytes is vital for understanding the functions of the heart. Cardiomyocyte cultures are difficult to maintain because they do not proliferate after birth. The maintenance of primary cultures of viable and functional cardiomyocytes is considerably affected by the yield from initial steps of isolation procedures. This protocol describes an efficient and rapid method for isolation and maintenance of long-term cultures of neonatal murine cardiomyocytes by effectively shortening the trypsin enzyme digestion period and the cardiomyocyte enrichment step.

Loss of mitochondrial exo/endonuclease EXOG affects mitochondrial respiration and induces ROS-mediated cardiomyocyte hypertrophy

Recently, a locus at the mitochondrial exo/endonuclease EXOG gene, which has been implicated in mitochondrial DNA repair, was associated with cardiac function. The function of EXOG in cardiomyocytes is still elusive. Here we investigated the role of EXOG in mitochondrial function and hypertrophy in cardiomyocytes. Depletion of EXOG in primary neonatal rat ventricular cardiomyocytes (NRVCs) induced a marked increase in cardiomyocyte hypertrophy. Depletion of EXOG, however, did not result in loss of mitochondrial DNA integrity. Although EXOG depletion did not induce fetal gene expression and common hypertrophy pathways were not activated, a clear increase in ribosomal S6 phosphorylation was observed, which readily explains increased protein synthesis. With the use of a Seahorse flux analyzer, it was shown that the mitochondrial oxidative consumption rate (OCR) was increased 2.4-fold in EXOG-depleted NRVCs. Moreover, ATP-linked OCR was 5.2-fold higher. This increase was not explained by mitochondrial biogenesis or alterations in mitochondrial membrane potential. Western blotting confirmed normal levels of the oxidative phosphorylation (OXPHOS) complexes. The increased OCR was accompanied by a 5.4-fold increase in mitochondrial ROS levels. These increased ROS levels could be normalized with specific mitochondrial ROS scavengers (MitoTEMPO, mnSOD). Remarkably, scavenging of excess ROS strongly attenuated the hypertrophic response. In conclusion, loss of EXOG affects normal mitochondrial function resulting in increased mitochondrial respiration, excess ROS production, and cardiomyocyte hypertrophy.

Histone deacetylase inhibitors promote glioma cell death by G2 checkpoint abrogation leading to mitotic catastrophe

Glioblastoma multiforme is resistant to conventional anti-tumoral treatments due to its infiltrative nature and capability of relapse; therefore, research efforts focus on characterizing gliomagenesis and identifying molecular targets useful on therapy. New therapeutic strategies are being tested in patients, such as Histone deacetylase inhibitors (HDACi) either alone or in combination with other therapies. Here two HDACi included in clinical trials have been tested, suberanilohydroxamic acid (SAHA) and valproic acid (VPA), to characterize their effects on glioma cell growth in vitro and to determine the molecular changes that promote cancer cell death. We found that both HDACi reduce glioma cell viability, proliferation and clonogenicity. They have multiple effects, such as inducing the production of reactive oxygen species (ROS) and activating the mitochondrial apoptotic pathway, nevertheless cell death is not prevented by the pan-caspase inhibitor Q-VD-OPh. Importantly, we found that HDACi alter cell cycle progression by decreasing the expression of G2 checkpoint kinases Wee1 and checkpoint kinase 1 (Chk1). In addition, HDACi reduce the expression of proteins involved in DNA repair (Rad51), mitotic spindle formation (TPX2) and chromosome segregation (Survivin) in glioma cells and in human glioblastoma multiforme primary cultures. Therefore, HDACi treatment causes glioma cell entry into mitosis before DNA damage could be repaired and to the formation of an aberrant mitotic spindle that results in glioma cell death through mitotic catastrophe-induced apoptosis.

Therapeutic use of H2O2-responsive anti-oxidant polymer nanoparticles for doxorubicin-induced cardiomyopathy

Doxorubicin (DOX) is a commonly used anti-neoplastic agent but its clinical use is limited due to serious hepatic and cardiac side effects. DOX-induced toxicity is mainly associated with overproduction of reactive species oxygen (ROS) such as hydrogen peroxide (H2O2). We have recently developed H2O2-responsive anti-oxidant polymer, polyoxalate containing vanillyl alcohol (PVAX), which is designed to rapidly scavenge H2O2 and release vanillyl alcohol with anti-oxidant, anti-inflammatory and anti-apoptotic properties. In this study, we report that PVAX nanoparticles are novel therapeutic agents for treating DOX-induced cardiac and hepatic toxicity. Intraperitoneal injection of PVAX nanoparticles (4 mg/kg/day) resulted in significant inhibition in apoptosis in liver and heart of DOX-treated mice by suppressing the activation of poly (ADP ribose) polymerase 1 (PARP-1) and caspase-3. PVAX treatment also prevented DOX-induced cardiac dysfunction. Furthermore, survival rate (vehicle = 35% vs. PVAX = 75%; p < 0.05) was significantly improved in a PVAX nanoparticles-treated group compared with vehicle treated groups. Taken together, we anticipate that PVAX nanoparticles could be a highly specific and potent treatment modality in DOX-induced cardiac and hepatic toxicity.

Moderate and high amounts of tamoxifen in αMHC-MerCreMer mice induce a DNA damage response, leading to heart failure and death

Numerous mouse models have utilized Cre-loxP technology to modify gene expression. Adverse effects of Cre recombinase activity have been reported, including in the heart. However, the mechanisms associated with cardiac Cre toxicity are largely unknown. Here, we show that expression of Cre in cardiomyocytes induces a DNA damage response, resulting in cardiomyocyte apoptosis, cardiac fibrosis and cardiac dysfunction. In an effort to increase the recombination efficiency of a widely used tamoxifen-sensitive Cre transgene under control of the α-myosin-heavy-chain promoter (αMHC-MerCreMer), we observed myocardial dysfunction and decreased survival, which were dependent on the dose of tamoxifen injected. After excluding a Cre-independent contribution by tamoxifen, we found that Cre induced myocardial fibrosis, activation of pro-fibrotic genes and cardiomyocyte apoptosis. Examination of the molecular mechanisms showed activation of DNA damage response signaling and p53 stabilization in the absence of loxP sites, suggesting that Cre induced illegitimate DNA breaks. Cardiomyocyte apoptosis was also induced by expressing Cre using adenoviral transduction, indicating that the effect was not dependent on genomic integration of the transgene. Cre-mediated homologous recombination at loxP sites was dose-dependent and had a ceiling effect at ∼80% of cardiomyocytes showing recombination. By titrating the amount of tamoxifen to maximize recombination while minimizing animal lethality, we determined that 30 μg tamoxifen/g body weight/day injected on three consecutive days is the optimal condition for the αMHC-MerCreMer system to induce recombination in the Rosa26-lacZ strain. Our results further highlight the importance of experimental design, including the use of appropriate genetic controls for Cre expression.

Protective effect of zinc-N-acetylcysteine on the rat kidney during cold storage

Cold storage of kidneys before transplantation is problematic because of the limited survival time of the allografts. In this study, zinc-N-acetylcysteine (ZnNAC) was shown to be a potent endonuclease inhibitor and antioxidant, and it was tested as a potential additive to a cold storage solution for kidney preservation. Exposure of normal rat kidney NRK-52E cells to ZnNAC resulted in zinc delivery to the cells as determined by TFL-Zn fluorophore and partial protection of the cells against injury by cold storage in University of Wisconsin solution (UWS) as measured by propidium iodide assay. Ex vivo, rat kidneys demonstrated time- and temperature-dependent DNA fragmentation as assessed by TUNEL assay, indicating irreversible cell death. DNA fragmentation was faster in the medulla than in the cortex, and tubules were affected more than glomeruli. Perfusion of rat kidneys with cold ZnNAC solution in UWS significantly inhibited cell death both in the cortex and medulla at concentrations of 0.3-30 mM compared with UWS alone, with a maximum effect at 1-10 mM ZnNAC. Cold storage of the kidney significantly increased quantities of cleaved caspase-3 and endonuclease G (EndoG) in the tissue, which were abolished by 10 mM ZnNAC, indicating its ability to suppress both caspase-dependent and -independent cell death. Therefore, supplementation of UWS with ZnNAC can decrease DNA fragmentation and protect kidney allografts from cell death due to cold storage.

A pathway involving HDAC5, cFLIP and caspases regulates expression of the splicing regulator polypyrimidine tract binding protein in the heart

Polypyrimidine tract binding protein (PTB) regulates pre-mRNA splicing, having special relevance for determining gene expression in the differentiating muscle. We have previously shown that PTB protein abundance is progressively reduced during heart development without reduction of its own transcript. Simultaneous reduction of histone deacetylase (HDAC) expression prompted us to investigate the potential link between these events. HDAC5-deficient mice have reduced cardiac PTB protein abundance, and HDAC inhibition in myocytes causes a reduction in endogenous expression of cellular FLICE-like inhibitory protein (cFLIP) and caspase-dependent cleavage of PTB. In agreement with this, cardiac PTB expression is abnormally high in mice with cardiac-specific executioner caspase deficiency, and cFLIP overexpression prevents PTB cleavage in vitro. Caspase-dependent cleavage triggers further fragmentation of PTB, and these fragments accumulate in the presence of proteasome inhibitors. Experimental modification of the above processes in vivo and in vitro results in coherent changes in the alternative splicing of genes encoding tropomyosin-1 (TPM1), tropomyosin-2 (TPM2) and myocyte enhancer factor-2 (MEF2). Thus, we report a pathway connecting HDAC, cFLIP and caspases regulating the progressive disappearance of PTB, which enables the expression of the adult variants of proteins involved in the regulation of contraction and transcription during cardiac muscle development.

Evidence of early involvement of apoptosis inducing factor-induced neuronal death in Alzheimer brain

Apoptosis inducing factor (AIF) has been proposed to act as a putative reactive oxygen species scavenger in mitochondria. When apoptotic cell death is triggered, AIF translocates to the nucleus, where it leads to nuclear chromatin condensation and large-scale DNA fragmentation which result in caspase-independent neuronal death. We performed this study to investigate the possibility that, in addition to caspase-dependent neuronal death, AIF induced neuronal death could be a cause of neuronal death in Alzheimer's disease (AD). We have found that AIF immunoreactivity was increased in the hippocampal pyramidal neurons in the Alzheimer brains compared to those of healthy, age-matched control brains. Nuclear AIF immunoreactivity was detected in the apoptotic pyramidal CA1 neurons at the early stage of AD and CA2 at the advanced stage. Nuclear AIF positive neurons were also observed in the amygdala and cholinergic neurons of the basal forebrain (BFCN) from the early stages of AD. The results of this study imply that AIF-induced apoptosis may contribute to neuronal death within the hippocampus, amygdala, and BFCN in early of AD.

Downregulation of doxorubicin-induced myocardial apoptosis accompanies postnatal heart maturation

Doxorubicin is a highly effective chemotherapeutic agent used for treating a wide spectrum of tumors, but its usage is limited because of its dose-dependent cardiotoxicity, especially in pediatric patients. Accumulating evidence indicates that caspase-dependent apoptosis contributes to the cardiotoxicity of doxorubicin. However, less attention has been paid to the effects of age on doxorubicin-induced apoptosis signaling in myocardium. This study focused on investigating differential apoptotic sensitivity between neonatal and adult myocardium, in particular, between neonatal and adult cardiomyocytes in vivo. Our results show that caspase-3 activity in normal mouse hearts decreased by ≥ 20-fold within the first 3 wk after birth, associated with a rapid downregulation in the expression of key proapoptotic proteins in intrinsic and extrinsic pathways. This rapid downregulation of caspase-3 activity was confirmed by immunostaining for cleaved caspase-3 and terminal deoxynucleotidyl transferase dUTP-mediated nick-end label staining. Doxorubicin treatment induced a dose-dependent increase in caspase-3 activity and apoptosis in neonatal mouse hearts, and both caspase-8 and caspase-9 activations were involved. Using transgenic mice with a nuclear localized LacZ reporter gene to label cardiomyocytes in vivo, we observed a fourfold higher level of doxorubicin-induced cardiomyocyte apoptosis in 1-wk-old mice compared with that in 3-wk-old mice. This study points to a major difference in apoptotic signaling in doxorubicin cardiotoxicity between neonatal and adult mouse hearts and reveals a critical transition from high to low susceptibility to doxorubicin-induced apoptosis during postnatal heart maturation.

Cardiomyocyte death: mechanisms and translational implications

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality worldwide. Although treatments have improved, development of novel therapies for patients with CVD remains a major research goal. Apoptosis, necrosis, and autophagy occur in cardiac myocytes, and both gradual and acute cell death are hallmarks of cardiac pathology, including heart failure, myocardial infarction, and ischemia/reperfusion. Pharmacological and genetic inhibition of autophagy, apoptosis, or necrosis diminishes infarct size and improves cardiac function in these disorders. Here, we review recent progress in the fields of autophagy, apoptosis, and necrosis. In addition, we highlight the involvement of these mechanisms in cardiac pathology and discuss potential translational implications.

Apoptosis in Anthracycline Cardiomyopathy

Apoptosis is a tightly regulated physiologic process of programmed cell death that occurs in both normal and pathologic tissues. Numerous in vitro or in vivo studies have indicated that cardiomyocyte death through apoptosis and necrosis is a primary contributor to the progression of anthracycline-induced cardiomyopathy. There are now several pieces of evidence to suggest that activation of intrinsic and extrinsic apoptotic pathways contribute to anthracycline-induced apoptosis in the heart. Novel strategies were developed to address a wide variety of cardiotoxic mechanisms and apoptotic pathways by which anthracycline influences cardiac structure and function. Anthracycline-induced apoptosis provides a very valid representation of cardiotoxicity in the heart, an argument which has implications for the most appropriate animal models of damaged heart plus diverse pharmacological effects. In this review we describe various aspects of the current understanding of apoptotic cell death triggered by anthracycline. Differences in the sensitivity to anthracycline-induced apoptosis between young and adult hearts are also discussed.

Endonuclease G is a novel determinant of cardiac hypertrophy and mitochondrial function

Left ventricular mass (LVM) is a highly heritable trait and an independent risk factor for all-cause mortality. So far, genome-wide association studies have not identified the genetic factors that underlie LVM variation, and the regulatory mechanisms for blood-pressure-independent cardiac hypertrophy remain poorly understood. Unbiased systems genetics approaches in the rat now provide a powerful complementary tool to genome-wide association studies, and we applied integrative genomics to dissect a highly replicated, blood-pressure-independent LVM locus on rat chromosome 3p. Here we identified endonuclease G (Endog), which previously was implicated in apoptosis but not hypertrophy, as the gene at the locus, and we found a loss-of-function mutation in Endog that is associated with increased LVM and impaired cardiac function. Inhibition of Endog in cultured cardiomyocytes resulted in an increase in cell size and hypertrophic biomarkers in the absence of pro-hypertrophic stimulation. Genome-wide network analysis unexpectedly implicated ENDOG in fundamental mitochondrial processes that are unrelated to apoptosis. We showed direct regulation of ENDOG by ERR-α and PGC1α (which are master regulators of mitochondrial and cardiac function), interaction of ENDOG with the mitochondrial genome and ENDOG-mediated regulation of mitochondrial mass. At baseline, the Endog-deleted mouse heart had depleted mitochondria, mitochondrial dysfunction and elevated levels of reactive oxygen species, which were associated with enlarged and steatotic cardiomyocytes. Our study has further established the link between mitochondrial dysfunction, reactive oxygen species and heart disease and has uncovered a role for Endog in maladaptive cardiac hypertrophy.

Disintegration of the medial epithelial seam: is cell death important in palatogenesis?

During palatogenesis, the palatal medial edge epithelium (MEE) forms the medial epithelial seam (MES) on adhesion of the opposing palatal shelves. The MES eventually disappears, leading to mesenchymal confluence of the palate and completion of palatogenesis. Failure of these processes results in cleft palate, one of the most common congenital anomalies in human affecting around one case in 500-2500 live births. The cell fate of MEE has been controversial for more than 20 years. Recent studies suggest that the disappearance of MES is a complex process involving cell death, epithelial-mesenchymal transition (EMT) and epithelial migration. Interestingly, transforming growth factor-β3 (Tgf β3) expression in MEE and the tip epithelium of the nasal septum begins just before palatal shelf reorientation and lasts until MES disruption, and several works including targeted disruption of the gene have indicated that the process appears to be regulated mainly by the TGFβ3-TGFβR signaling. However, how MEE cells choose their fate and how the cell fate is altered in response to cellular environment remains to be elucidated.

Ubiquitination of TrkA by Nedd4-2 regulates receptor lysosomal targeting and mediates receptor signaling

The nerve growth factor receptor TrkA (tropomyosin-related kinase receptor) participates in the survival and differentiation of several neuronal populations. The C-terminal tail of TrkA contains a PPXY motif, the binding site of the E3 ubiquitin-ligase Nedd4-2 (neural precursor cell expressed, developmentally down-regulated 4-2). In order to analyze the role of Nedd4-2 ubiquitination on TrkA function, we generated three TrkA mutants, by introducing point mutations on conserved hydrophobic amino acids - Leu784 and Val790 switched to Ala. TrkA mutants co-localized and co-immunoprecipitated more efficiently with Nedd4-2 and consequently a strong increase in the basal multimonoubiquitination of the mutant receptors was observed. In addition, we found a decrease in TrkA abundance because of the preferential sorting of mutant receptors towards the late endosome/lysosome pathway instead of recycling back to the plasma membrane. Despite the reduction in the amount of membrane receptor caused by the C-terminal changes, TrkA mutants were able to activate signaling cascades and were even more efficient in promoting neurite outgrowth than the wild-type receptor. Our results demonstrate that the C-terminal tail hydrophobicity of TrkA regulates Nedd4-2 binding and activity and therefore controls receptor turnover. In addition, TrkA multimonoubiquitination does not interfere with the activation of signaling cascades, but rather potentiates receptor signaling leading to differentiation.

Multiple antimelanoma potential of dry olive leaf extract

Various constituents of the olive tree (Olea europaea) have been traditionally used in the treatment of infection, inflammation, prevention of chronic diseases, cardiovascular disorders and cancer. The anticancer potential of dry olive leaf extract (DOLE) represents the net effect of multilevel interactions between different biologically active compounds from the extract, cancer cells and conventional therapy. In this context, it was of primary interest to evaluate the influence of DOLE on progression of the highly malignant, immuno- and chemoresistant type of skin cancer-melanoma. DOLE significantly inhibited proliferation and subsequently restricted clonogenicity of the B16 mouse melanoma cell line in vitro. Moreover, late phase tumor treatment with DOLE significantly reduced tumor volume in a syngeneic strain of mice. DOLE-treated B16 cells were blocked in the G(0) /G(1) phase of the cell cycle, underwent early apoptosis and died by late necrosis. At the molecular level, the dying process started as caspase dependent, but finalized as caspase independent. In concordance, overexpression of antiapoptotic members of the Bcl-2 family, Bcl-2 and Bcl-XL, and diminished expression of their natural antagonists, Bim and p53, were observed. Despite molecular suppression of the proapoptotic process, DOLE successfully promoted cell death mainly through disruption of cell membrane integrity and late caspase-independent fragmentation of genetic material. Taken together, the results of this study indicate that DOLE possesses strong antimelanoma potential. When DOLE was applied in combination with different chemotherapeutics, various outcomes, including synergy and antagonism, were observed. This requires caution in the use of the extract as a supplementary antitumor therapeutic.

EndoG links Bnip3-induced mitochondrial damage and caspase-independent DNA fragmentation in ischemic cardiomyocytes

Mitochondrial dysfunction, caspase activation and caspase-dependent DNA fragmentation are involved in cell damage in many tissues. However, differentiated cardiomyocytes repress the expression of the canonical apoptotic pathway and their death during ischemia is caspase-independent. The atypical BH3-only protein Bnip3 is involved in the process leading to caspase-independent DNA fragmentation in cardiomyocytes. However, the pathway by which DNA degradation ensues following Bnip3 activation is not resolved. To identify the mechanism involved, we analyzed the interdependence of Bnip3, Nix and EndoG in mitochondrial damage and DNA fragmentation during experimental ischemia in neonatal rat ventricular cardiomyocytes. Our results show that the expression of EndoG and Bnip3 increases in the heart throughout development, while the caspase-dependent machinery is silenced. TUNEL-positive DNA damage, which depends on caspase activity in other cells, is caspase-independent in ischemic cardiomyocytes and ischemia-induced DNA high and low molecular weight fragmentation is blocked by repressing EndoG expression. Ischemia-induced EndoG translocation and DNA degradation are prevented by silencing the expression of Bnip3, but not Nix, or by overexpressing Bcl-x_L. These data establish a link between Bnip3 and EndoG-dependent, TUNEL-positive, DNA fragmentation in ischemic cardiomyocytes in the absence of caspases, defining an alternative cell death pathway in postmitotic cells.

Delayed activation of caspase-independent apoptosis during heart failure in transgenic mice overexpressing caspase inhibitor CrmA

Although caspase activation is generally thought to be necessary to induce apoptosis, recent evidence suggests that apoptosis can be activated in the setting of caspase inhibition. In this study, we tested the hypothesis that caspase-independent apoptotic pathways contribute to the development of heart failure in the absence of caspase activation. Acute cardiomyopathy was induced using a single dose of doxorubicin (Dox, 20 mg/kg) injected into male wild-type (WT) and transgenic (Tg) mice with a cardiac-specific expression of cytokine response modifier A (CrmA), a known caspase inhibitor. Early (6 day) survival was significantly better in CrmA Tg (81%) than WT (38%) mice. Twelve days after Dox injection, however, the mortality benefit had dissipated, and increased cardiac apoptosis was observed in both groups. There was, however, a significantly greater release of apoptosis-inducing factor (AIF) from mitochondria to cytosol in CrmA Tg compared with WT mice, which suggests that an enhancement of activation in caspase-independent apoptotic pathways had occurred. The administration of a poly(ADP-ribose) polymerase-1 inhibitor, 4-amino-1,8-naphthalimide (4-AN), to Dox-treated mice resulted in significantly improved cardiac function, a significant blockade of AIF released from mitochondria, and decreased cardiac apoptosis. There were also significantly improved survival in WT (18% without 4-AN vs. 89% with 4-AN) and CrmA Tg (13% without 4-AN vs. 93% with 4-AN) mice 12 days after Dox injection. In conclusion, these findings suggest that apoptosis can be induced in the heart lacking caspase activation via caspase-independent pathways and that enabling the inhibition of AIF activation may provide a significant cardiac benefit.

Apoptosis in cardiovascular diseases: mechanism and clinical implications

Apoptosis is a tightly regulated, cell deletion process that plays an important role in various cardiovascular diseases, such as myocardial infarction, reperfusion injury, and heart failure. Since cardiomyocyte loss is the most important determinant of patient morbidity and mortality, fully understanding the regulatory mechanisms of apoptotic signaling is crucial. In fact, the inhibition of cardiac apoptosis holds promise as an effective therapeutic strategy for cardiovascular diseases. Caspase, a critical enzyme in the induction and execution of apoptosis, has been the main potential target for achieving anti-apoptotic therapy. Studies suggest, however, that a caspase-independent pathway may also play an important role in cardiac apoptosis, although the mechanism and potential significance of caspase-independent apoptosis in the heart remain poorly understood. Herein we discuss the role of apoptosis in various cardiovascular diseases, provide an update on current knowledge about the molecular mechanisms that govern apoptosis, and discuss the clinical implications of anti-apoptotic therapies.

Therapeutic hypothermia cardioprotection via Akt- and nitric oxide-mediated attenuation of mitochondrial oxidants

Therapeutic hypothermia (TH) is a promising cardioprotective treatment for cardiac arrest and acute myocardial infarction, but its cytoprotective mechanisms remain unknown. In this study, we developed a murine cardiomyocyte model of ischemia-reperfusion injury to better determine the mechanisms of TH cardioprotection. We hypothesized that TH manipulates Akt, a survival kinase that mediates mitochondrial protection by modulating reactive oxygen species (ROS) and nitric oxide (NO) generation. Cardiomyocytes, isolated from 1- to 2-day-old C57BL6/J mice, were exposed to 90 min simulated ischemia and 3 h reperfusion. For TH, cells were cooled to 32 degrees C during the last 20 min of ischemia and the first hour of reperfusion. Cell viability was evaluated by propidium iodide and lactate dehydrogenase release. ROS production was measured by 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate and mitochondrial membrane potential (DeltaPsim) by 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazoly-carbocyanine iodide (JC-1). Phospho (p)-Akt (Thr308), p-Akt (Ser473), and phosphorylated heat shock protein 27 (p-HSP27) (Ser82) were analyzed by Western blot analysis. TH attenuated reperfusion ROS generation, increased NO, maintained DeltaPsim, and decreased cell death [19.3 + or - 3.3% (n = 11) vs. 44.7 + or - 2.7% (n = 10), P < 0.001]. TH also increased p-Akt during ischemia before reperfusion. TH protection and attenuation of ROS were blocked by the inhibition of Akt and NO synthase but not by a cGMP inhibitor. HSP27, a regulator of Akt, also exhibited increased phosphorylation (Ser82) during ischemia with TH. We conclude that TH cardioprotection is mediated by enhanced Akt/HSP27 phosphorylation and enhanced NO generation, resulting in the attenuation of ROS generation and the maintenance of DeltaPsim following ischemia-reperfusion.

p300 plays a critical role in maintaining cardiac mitochondrial function and cell survival in postnatal hearts

RATIONALE

It is known that the transcriptional coactivator p300 is crucially involved in the differentiation and growth of cardiac myocytes during development. However, the physiological function of p300 in the postnatal hearts remains to be characterized.

OBJECTIVE

We have now investigated the physiological function of p300 in adult hearts.

METHODS AND RESULTS

We analyzed transgenic mice exhibiting cardiac-specific overexpression of a dominant-negative p300 mutant lacking the C/H3 domain (p300DeltaC/H3 transgenic [TG] mice). p300DeltaC/H3 significantly inhibited p300-induced activation of GATA- and myocyte enhancer factor 2-dependent promoters in cultured ventricular myocytes, and p300DeltaC/H3-TG mice showed cardiac dysfunction that was lethal by 20 weeks of age. The numbers of mitochondria in p300DeltaC/H3-TG myocytes were markedly increased, but the mitochondria were diminished in size. Moreover, cardiac mitochondrial gene expression, mitochondrial membrane potential and ATP contents were all significantly disrupted in p300DeltaC/H3-TG hearts, suggesting that mitochondrial dysfunction contributes to the progression of the observed cardiomyopathy. Transcription of peroxisome proliferator-activated receptor gamma coactivator (PGC)-1alpha, a master regulator of mitochondrial gene expression, and its target genes was significantly downregulated in p300DeltaC/H3-TG mice, and p300DeltaC/H3 directly repressed myocyte enhancer factor 2C-dependent PGC-1alpha promoter activity and disrupted the transcriptional activity of PGC-1alpha in cultured ventricular myocytes. In addition, myocytes showing features of autophagy were observed in p300DeltaC/H3-TG hearts.

CONCLUSIONS

Collectively, our findings suggest that p300 is essential for the maintenance of mitochondrial integrity and for myocyte survival in the postnatal left ventricular myocardium.

Oxidative stress triggers neuronal caspase-independent death: endonuclease G involvement in programmed cell death-type III

To characterize neuronal death, primary cortical neurons (C57/Black 6 J mice) were exposed to hydrogen peroxide (H2O2) and staurosporine. Both caused cell shrinkage, nuclear condensation, DNA fragmentation and loss of plasma membrane integrity. Neither treatment induced caspase-7 activity, but caspase-3 was activated by staurosporine but not H2O2. Each treatment caused redistribution from mitochondria of both endonuclease G (Endo G) and cytochrome c. Neurons knocked down for Endo G expression using siRNA showed reduction in both nuclear condensation and DNA fragmentation after treatment with H2O2, but not staurosporine. Endo G suppression protected cells against H2O2-induced cell death, while staurosporine-induced death was merely delayed. We conclude that staurosporine induces apoptosis in these neurons, but severe oxidative stress leads to Endo G-dependent death, in the absence of caspase activation (programmed cell death-type III). Therefore, oxidative stress triggers in neurons a form of necrosis that is a systematic cellular response subject to molecular regulation.

Role of apoptosis in cardiovascular disease

Apoptosis plays a key role in the pathogenesis in a variety of cardiovascular diseases due to loss of terminally differentiated cardiac myocytes. Cardiac myocytes undergoing apoptosis have been identified in tissue samples from patients suffering from myocardial infarction, diabetic cardiomyopathy, and end-stage congestive heart failure. Apoptosis is a highly regulated program of cell death and can be mediated by death receptors in the plasma membrane, as well as the mitochondria and the endoplasmic reticulum. The cell death program is activated in cardiac myocytes by various stressors including cytokines, increased oxidative stress and DNA damage. Many studies have demonstrated that inhibition of apoptosis is cardioprotective and can prevent the development of heart failure. This review provides a current overview of the evidence of apoptosis in cardiovascular diseases and discusses the molecular pathways involved in cardiac myocyte apoptosis.

The Drosophila melanogaster Gene cg4930 Encodes a High Affinity Inhibitor for Endonuclease G

Endonuclease G (EndoG) is a mitochondrial enzyme believed to be released during apoptosis to participate in the degradation of nuclear DNA. This paper describes a Drosophila protein, EndoGI, which inhibits EndoG specifically. EndoG and EndoGI associate with subpicomolar affinity, forming a 2:1 complex in which dimeric EndoG is bound by two tandemly repeated homologous domains of monomeric EndoGI. Binding appears to involve the active site of EndoG. EndoGI is present in the cell nucleus at micromolar concentrations. Upon induction of apoptosis, levels of the inhibitor appear to be reduced, and it is relocalized to the cytoplasm. EndoGI, encoded by the predicted open reading frame cg4930, is expressed throughout Drosophila development. Flies homozygous for a hypomorphic EndoGI mutation have a strongly reduced viability, which is modulated by genetic background and diet. We propose that EndoGI protects the cell against low levels of EndoG outside mitochondria.