Regulating Cardiomyocyte Survival Research Articles

Connexin 43 dephosphorylation at serine 282 induces spontaneous arrhythmia and increases susceptibility to ischemia/reperfusion injury

BackgroundConnexin 43 (Cx43), the predominant gap junction protein in hearts, is modified by specific (de)phosphorylation events under physiological and pathological states to affect myocardium function and structure. Previously we found that deficiency in Cx43 S282 phosphorylation could impair intercellular communication and contribute to cardiomyocyte apoptosis by activating p38 mitogen-activated protein kinase (p38 MAPK)/factor-associated suicide (Fas)/Fas-associating protein with a novel death domain (FADD) pathway, which is involved in myocardium injury in ischemia/reperfusion (I/R) heart. In addition, mutant at Cx43 S282 substituted with alanine heterozygous mice (S282A+/−) exhibited different degrees of ventricular arrhythmias and only some underwent myocardium apoptosis. In this study, we aimed to investigate the role of Cx43 pS282 in different cardiac pathological phenotypes. MethodsWe examined cardiac function, structure, and relevant protein expression in S282A+/− mice (aged 2, 10 and 30 weeks) by electrocardiograph, echocardiography, histological staining, and co-immunoprecipitation followed by Western blot. Intraperitoneal isoprenaline injection and I/R surgery were applied in S282A+/− mice as external stimulus. 2,3,5-triphenyltetrazolium chloride staining was used for myocardium infarction evaluation. ResultsAdult S282A+/− mice (aged 10 and 30 weeks) still exhibited spontaneous arrhythmia. Unlike neonatal stage (aged around 2 weeks), no apoptosis-related manifestations and the activation of p38 MAPK-Fas-FADD apoptotic pathway were observed in adult S282A+/− hearts. S282A+/− neonatal mice with cardiomyocytes apoptosis exhibited more than 60% dephosphorylation at Cx43 S282 than WT mice, while less than 40% S282 dephosphorylation were found in adult S282A+/− mice. In addition, although S282A+/− mice displayed normal cardiac function, they were highly susceptible to isoproterenol-induced ECG alternans and prone to cardiac injury and deaths upon I/R attack. ConclusionsThese results reinforce that Cx43 S282 dephosphorylation acts as a susceptibility factor in regulating cardiomyocyte survival and cardiac electrical homeostasis in basal conditions and contributes to myocardium injury in the setting of I/R. Cx43 S282 phosphorylation was competent to induce spontaneous arrhythmias, cardiomyocyte apoptosis and deaths based on the degree of S282 dephosphorylation.

Insulin-like growth factor-1 levels are associated with interventricular septal thickening.

Insulin-like growth factor-1 (IGF-1) regulates cardiomyocyte survival, hypertrophy, and ageing. We aimed to investigate the potential correlation between IGF-1 and interventricular septal (IVS) thickening. Medical record data were obtained from patients hospitalized between May 1, 2012 and April 30, 2022. All patients underwent echocardiography and had laboratory data on plasma IGF-1. We analyzed the relationship between IGF-1 levels and IVS thickening based on logistic regression models. Propensity score matching at 1:4 ratio was performed for 180 patients with IVS thickening and 1,964 patients without IVS thickening. Finally, 180 (case group) and 623 (control group) patients were enrolled. Of the total 803 patients, the mean age was 59 years, and 59.7% were male. In multivariate-adjusted models that adjusted for propensity scores, the risk of IVS thickening increased with increasing IGF-1 levels; specifically, the risk of IVS thickening increased per 1 ng/mL [odds ratio (OR) 1.003; 95% confidence interval (CI): 1.002-1.004; P < 0.001], per 5 ng/mL (OR, 1.016; 95% CI, 1.010-1.022; P < 0.001), and per 10 ng/mL(OR, 1.032; 95% CI, 1.019-1.045; P < 0.001) increase in IGF-1 levels. When the IGF-1 levels were expressed as a categorical variable, the increased levels of IGF-1 led to an increased risk of IVS thickening; specifically, the OR of IVS thickening for T3 >152.00 ng/mL was 2.020 (95% CI: 1.310-3.115, P < 0.01) compared with T1 <102.00 ng/mL. We performed restricted cubic splines, and it showed a linear association between IGF-1 levels and the risk of IVS thickening. In splines for the age and sex subgroups, different IGF-1 levels increased the risk of IVS thickening among different age groups in male patients: 18-44 years when IGF-1 value >164.00 ng/mL, 45-60 years when IGF-1 value > 140.34 ng/mL and ≥ 60 years when IGF-1 value >108.20 ng/mL. In female patients aged 45-60 years, the risk of IVS thickening increased when the IGF-1 levels were >207.45 ng/mL. However, IGF-1 was not significantly correlated with IVS thickening in female patients aged 18-45 and ≥60 years. Sensitivity analysis by excluding those with acromegaly did not change the relationship between IGF-1 and the risk of IVS thickening. The plasma IGF-1 levels were related to the risk of IVS thickening irrespective of blood pressure.

Upregulation of FAM129B protects cardiomyocytes from hypoxia/reoxygenation-induced injury by inhibiting apoptosis, oxidative stress, and inflammatory response via enhancing Nrf2/ARE activation.

Family with sequence similarity 129, member B (FAM129B) has been identified as a novel cytoprotective protein that facilitates the survival of detrimentally stimulated cells. However, whether FAM129B is involved in regulating cardiomyocyte survival after myocardial ischemia-reperfusion injury is unknown. The goal of this work was to evaluate the potential role of FAM129B in regulating hypoxia/reoxygenation (H/R)-induced cardiomyocyte injury in vitro. We demonstrated that exposure to H/R markedly downregulated the expression of FAM129B in cardiomyocytes. Functional experiments revealed that the upregulation of FAM129B improved H/R-exposed cardiomyocyte viability, and ameliorated H/R-induced cardiomyocyte apoptosis, the generation of reactive oxygen species (ROS), and pro-inflammatory cytokine release. The upregulation of FAM129B significantly increased the nuclear expression of nuclear factor-erythroid 2-related factor 2 (Nrf2), and reinforced Nrf2/antioxidant response element (ARE) activation in H/R-exposed cardiomyocytes. Moreover, FAM129B modulates Nrf2/ARE signaling in a Kelchlike ECH-associated protein 1-dependent manner. Notably, the inhibition of Nrf2 significantly blocked FAM129B-overexpression-induced cardioprotective effects in H/R-exposed cardiomyocytes. In summary, the findings of our work demonstrate that the upregulation of FAM129B ameliorates H/R-induced cardiomyocyte injury via enhancing Nrf2/ARE activation. Thus, our study indicates that FAM129B may play a role in myocardial ischemia-reperfusion injury and has the potential to be used as a cardioprotective target.

Downregulation of circ-ZNF609 Promotes Heart Repair by Modulating RNA N6-Methyladenosine-Modified Yap Expression.

Circular RNAs take crucial roles in several pathophysiological processes. The regulatory role and its underlying mechanisms of circ-ZNF609 in the heart remains largely unknown. Here, we report that circ-ZNF609 is upregulated during myocardial ischemia/reperfusion (I/R) remodeling. Knockdown of circ-ZNF609 protects against acute I/R injury and attenuates left ventricle dysfunction after I/R remodeling in vivo. In vitro, circ-ZNF609 regulates cardiomyocyte survival and proliferation via modulating the crosstalk between Hippo-YAP and Akt signaling. Mechanically, N6-methyladenosine-modification is involved in the regulatory role of circ-ZNF609 on YAP. An in-depth study indicates that knockdown of circ-ZNF609 decreases the expression of YTHDF3 and further fine-tuned the accessibility of Yap mRNA to YTHDF1 and YTHDF2 to regulate YAP expression. circ-ZNF609 knockdown represents a promising therapeutic strategy to combat the pathological process of myocardial I/R injury.

HIPK2 overexpression relieves hypoxia/reoxygenation-induced apoptosis and oxidative damage of cardiomyocytes through enhancement of the Nrf2/ARE signaling pathway

Homeodomain interacting protein kinase-2 (HIPK2) has emerged as a crucial stress-responsive kinase that plays a critical role in regulating cell survival and apoptosis. However, whether HIPK2 participates in regulating cardiomyocyte survival during myocardial ischemia/reperfusion injury remains unclear. Here, we investigated the regulatory effect of HIPK2 on hypoxia/reoxygenation (H/R)-induced cardiomyocyte injury and its potential underlying molecular mechanism. We found that HIPK2 expression was induced in response to H/R exposure. HIPK2 depletion by small interfering RNA (siRNA)-mediated gene silencing significantly decreased the viability and exacerbated H/R-induced apoptosis and reactive oxygen species (ROS) production in cardiomyocytes. Comparatively, HIPK2 overexpression effectively rescued H/R-impaired viability and repressed H/R-induced apoptosis and ROS production in cardiomyocytes. HIPK2 overexpression significantly increased the nuclear expression of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and enhanced Nrf2-mediated transcriptional activity. Moreover, HIPK2 overexpression significantly increased the transcription of Nrf2/ARE target genes. Additionally, Nrf2 inhibition partially reversed the HIPK2-mediated protective effect. Overall, these results demonstrate that HIPK2 overexpression protects cardiomyocytes from H/R-induced injury by enhancing Nrf2/ARE antioxidant signaling, data that suggest HIPK2 is a potential target for cardioprotection.

Novel Screening Method Identifies PI3Kα, mTOR, and IGF1R as Key Kinases Regulating Cardiomyocyte Survival.

BackgroundSmall molecule kinase inhibitors (KIs) are a class of agents currently used for treatment of various cancers. Unfortunately, treatment of cancer patients with some of the KIs is associated with cardiotoxicity, and there is an unmet need for methods to predict their cardiotoxicity. Here, we utilized a novel computational method to identify protein kinases crucial for cardiomyocyte viability.Methods and ResultsOne hundred forty KIs were screened for their toxicity in cultured neonatal cardiomyocytes. The kinase targets of KIs were determined based on integrated data from binding assays. The key kinases mediating the toxicity of KIs to cardiomyocytes were identified by using a novel machine learning method for target deconvolution that combines the information from the toxicity screen and from the kinase profiling assays. The top kinases identified by the model were phosphoinositide 3‐kinase catalytic subunit alpha, mammalian target of rapamycin, and insulin‐like growth factor 1 receptor. Knockdown of the individual kinases in cardiomyocytes confirmed their role in regulating cardiomyocyte viability.ConclusionsCombining the data from analysis of KI toxicity on cardiomyocytes and KI target profiling provides a novel method to predict cardiomyocyte toxicity of KIs.

TLR9 is essential for HMGB1-mediated post-myocardial infarction tissue repair through affecting apoptosis, cardiac healing, and angiogenesis

The poor prognosis of patients with acute myocardial infarction is partially attributed to a large number of cardiomyocyte apoptosis, necrosis, limited cardiac healing and angiogenesis, and cardiac dysfunction. Immune cells dysfunction leads to nonhealing or poor healing of wounds after acute myocardial infarction. Toll-like receptor 9 (TLR9) as an essential part of the innate immune system plays a vital role in regulating cardiomyocyte survival and wound healing. During hypoxia, High Mobility Group Box 1 (HMGB1), as the typical damage-associated molecular patterns (DAMPs) or alarmin, is rapidly released extracellularly and translocates from the nucleus to bind with cytoplasmic TLR9. However, the mechanism by which TLR9 interacts with HMGB1 and regulates myocardial damage remains unclear. Our current study found that the survival rate of TLR9KO mice with a higher rate of cardiac rupture was significantly lower than that in WT mice after 28 days post-operation. The effect of TLR9 knockout on insufficient wound healing in experimental MI was caused by a diminished number of myofibroblast and defective matrix synthetic capability. Moreover, the increased myocardial apoptotic cells and decreased angiogenic capacity were found in TLR9 knockout mice after MI. The results showed contrary in Recombinant Human High Mobility Group Box 1 (rhHMGB1) treated WT mice and similarity after applying rhHMGB1 in TLR9KO mice. This study demonstrates that TLR9 is essential for the repair of infarcted myocardium and interaction of HMGB1 and TLR9 is involved in the survival of myocardial cells, wound healing, and angiogenesis after myocardial infarction.

Connexin 43-serine 282 modulates serine 279 phosphorylation in cardiomyocytes

Connexin 43 (Cx43) phosphorylation plays a pivotal role in cardiac electrical and contractile performance. In a previous study we have found that Cx43 phosphorylation at serine 282 (pS282) regulates cardiomyocyte survival. Considering that both sites are altered simultaneously in many studies, we designed this study to identify the status of S279 phosphorylation upon pS282 manipulation. In heterozygous mice with S282 gene substituted with alanine (S282A), we found ventricular arrhythmias with inhibition of Cx43 phosphorylation at both S282 and S279 in the hearts. In cultured neonatal rat ventricular myocytes (NRVMs), transfection of virus carrying S282A mutant also blocked Cx43 phosphorylation at both S279/282 and gap junction coupling, while expression of wild-type Cx43 or S279A did not. Further, NRVMs transfected with S282 phospho-mimicking mutant substituted with aspartate or treated with ATP exhibited promotions of Cx43 phosphorylation at S279/282 and intercellular communication. Therefore, this study demonstrated a regulatory role of Cx43-S282 on S279 phosphorylation in cardiomyocytes, and suggested an involvement of S279 in the Cx43-S282 mediated cardiomyocyte homeostasis.

TLR9-HIF-1α-VEGF Axis Is Essential for HMGB1-Mediate Post-Myocardial Infarction Tissue Repair

Background: Toll-like receptor 9 (TLR9) as an essential part of the innate immune system plays a vital role in regulating cardiomyocyte survival and wound healing. During hypoxia, High Mobility Group Box 1 (HMGB1) is rapidly released extracellularly and translocates from the nucleus to bind with cytoplasmic TLR9. However, the mechanism by which TLR9 interacts with HMGB1 and regulates myocardial damage remains unclear. Our current study investigated the effects of TLR9 and HMGB1 on experimental MI. Methods: Experimental MI was induced by left anterior descending (LAD) ligation in wild type (WT) or TLR9 knockout (TLR9KO)mice, to delineate the functional effects of TLR9 on cardiac healing, apoptosis, angiogenesis. Left ventricular injection of recombination human HMGB1(rhHMGB1)was performed to explore the mechanism of TLR9 and HMGB1 in MI. Findings: The survival rate of TLR9KO mice with a higher rate of cardiac rupture was significantly lower than that in WT mice after 28-days postoperation. The effect of TLR9 knockout on insufficient wound healing in experimental MI is caused by a diminished number of myofibroblasts and defective matrix synthetic capability. Moreover, the increased myocardial apoptotic cells and decreased angiogenic capacity were found in TLR9 knockout mice after MI. The results showed contrary in rhHMGB1 (Recombinant Human High Mobility Group Box 1) treated WT mice and similarity after applying rhHMGB1 in TLR9KO mice. Interpretation: Our study demonstrates that TLR9 is essential for the repair of infarcted myocardium and interaction of HMGB1 and TLR9 is involved in the survival and wound healing of myocardial cells after myocardial infarction. Funding Statement: This work was supported by grants from the National Natural Science Foundation of China (No: 81470402, 81800216, 81700218, 81770399 and 81700254), the Key Project of the National Natural Science Foundation (No. 81530012) and the Fundamental Research Funds for the Central Universities (No. 2042017kf0085, 2042018kf1032 and 2042015kf0073). Declaration of Interests: The authors declare: None. Ethics Approval Statement: All human heart samples are dedicated for research purposes only, approved by the Renmin Hospital of Wuhan University Review Board, according to the Helsinki Declaration. All animal care and experimental procedures were approved by the Animal Care and Use Committee of Renmin Hospital of Wuhan University (approval no. 2016005) in accordance with the guidelines for the Care and Use of Laboratory Animals published by the United States National Institutes of Health (NIH).

Connexin43 dephosphorylation at serine 282 is associated with connexin43-mediated cardiomyocyte apoptosis

Gap junction protein connexin 43 (Cx43) plays an important role in regulating cardiomyocyte survival in addition to regulating electrical coordination. Cx43 dephosphorylation, found in severe cardiac pathologies, is thought to contribute to myocardial injury. However, the mechanisms underlying Cx43 mediation of cell survival and myocardial lesions remain unknown. Here, we found that transfecting an adenovirus carrying a mutant gene of Cx43-serine 282 substituted with alanine (S282A) into neonatal rat ventricular myocytes (NRVMs) induced cell apoptosis and Ca2+ transient desynchronization, whereas using gap junction inhibitor or knocking down Cx43 expression with Cx43-miRNA caused uncoupled Ca2+ signaling without cell death. Similarly, while Cx43-S282A+/+ failed in generation, Cx43-S282A+/- mice exhibited cardiomyocyte apoptosis and ventricular arrhythmias dependent on S282 dephosphorylation. Further, Cx43 dephosphorylation at S282 activated p38 mitogen-activated protein kinase (p38 MAPK), factor-associated suicide and the caspase-8 apoptotic pathway by physically interacting with p38 MAPK. These findings uncovered a specific Cx43 phosphorylation residue involved in regulating cardiomyocyte homeostasis. S282 phosphorylation deficiency acts as a trigger inducing cardiomyocyte apoptosis and cardiac arrhythmias, providing a potential mechanism for Cx43-mediated myocardial injury in severe cardiac diseases.

Mir-215-5p induces autophagy by targeting PI3K and activating ROS-mediated MAPK pathways in cardiomyocytes of chicken

Our previous study revealed that selenium (Se) deficiency can cause myocardial injury through triggering autophagy. MicroRNAs (miRNAs) play crucial roles in autophagic cell death. However, the relationship between miRNAs and myocardial autophagy injury caused by Se deficiency remains unclear. We selected differential microRNA-215-5p (miR-215-5p) in Se-deficient myocardial tissue using high-throughput miRNA-sequencing. To further explore the role of miR-215-5p in myocardial injury, overexpression/knockdown of miR-215-5p in primary cardiomyocyte model was established by miRNAs interference technology. In this study, we report that miR-215-5p can promote myocardial autophagy by directly binding to the 3′untranslated region (3′UTR) of phosphatidylinositol-4, 5-bisphosphate 3-kinase (PI3K). Its target gene PI3K was confirmed by dual luciferase reporter assay, quantitative real-time polymerase chain reaction (qRT-PCR) and western blot in cardiomyocytes. Our results showed that overexpression of miR-215-5p could trigger myocardial autophagy through PI3K-threonine-protein kinase (AKT)-target of rapamycin (TOR) pathway. Further studies revealed that autophagic cell death was dependent on the activation of extracellular signal-regulated kinase1/2 (ERK1/2), c-Jun N-terminal kinase (JNK), p38 kinase (p38) and generation of reactive oxygen species (ROS) in overexpression of miR-215-5p in cardiomyocytes. On the contrary, miR-215-5p inhibitor can enhance cell survival capacity against autophagy by inhibiting ROS-mitogen-activated protein kinase (MAPK) pathways and activating the PI3K/AKT/TOR pathway in cardiomyocytes. Together, our findings support that miR-215-5p may modulate cell survival programs by regulating autophagy, and miR-215-5p acts as an autophagic regulator in the regulatory feedback loop that regulates cardiomyocyte survival by modulating the PI3K/AKT/TOR pathway and ROS-dependent MAPK pathways.

Multiprotein Complex With TRPC (Transient Receptor Potential-Canonical) Channel, PDE1C (Phosphodiesterase 1C), and A2R (Adenosine A2 Receptor) Plays a Critical Role in Regulating Cardiomyocyte cAMP and Survival.

cAMP plays a critical role in regulating cardiomyocyte survival. Various cAMP signaling pathways behave distinctly or in opposition. We have previously reported that activation of cAMP hydrolysis by cyclic nucleotide phosphodiesterase 1C (PDE1C) promotes cardiomyocytes death/apoptosis, yet the underlying molecular mechanism remains unknown. In this study, we aimed to identify the specific cAMP signaling pathway modulated by PDE1C and determine the mechanism by which Ca2+/calmodulin-stimulated PDE1C is activated. To study cardiomyocyte death/apoptosis, we used both isolated mouse adult cardiomyocytes in vitro and doxorubicin-induced cardiotoxicity in vivo. We used a variety of pharmacological activators and inhibitors as well as genetically engineered molecular tools to manipulate the expression and activity of proteins of interest. We found that the protective effect of PDE1C inhibition/deficiency on Ang II or doxorubicin-induced cardiomyocyte death/apoptosis is dependent on cAMP-generating adenosine A2 receptors (A2Rs), suggesting that PDE1C's cAMP-hydrolyzing activity selectively modulates A2R-cAMP signaling in cardiomyocytes. In addition, we found that the effects of PDE1C activation on Ang II-mediated cAMP reduction and cardiomyocyte death are dependent on transient receptor potential-canonical (TRPC) channels, in particular TRPC3. We also observed synergistic protective effects on cardiomyocyte survival from the combination of A2R stimulation together with PDE1 or TRPC inhibition. Coimmunostaining and coimmunoprecipitation studies showed that PDE1C is localized in proximity with A2R and TRPC3 in the plasma membrane and perhaps T tubules. It is important to note that we found that doxorubicin-induced cardiac toxicity and dysfunction in mice are attenuated by the PDE1 inhibitor IC86340 or in PDE1C knockout mice, and this protective effect is significantly diminished by A2R antagonism. We have characterized a novel multiprotein complex comprised of A2R, PDE1C, and TRPC3, in which PDE1C is activated by TRPC3-derived Ca2+, thereby antagonizing A2R-cAMP signaling and promoting cardiomyocyte death/apoptosis. Targeting these molecules individually or in combination may represent a compelling therapeutic strategy for potentiating cardiomyocyte survival.

MiR-381 negatively regulates cardiomyocyte survival by suppressing Notch signaling.

The mechanisms for cardiomyocyte death in cardiovascular diseases are incompletely understood. The aim of this study is to reveal the function of miR-381 in myocardium infarction (MI)-induced cardiomyocyte apoptosis. We established mouse model of MI and cellular models of apoptosis induced by oxidative stress (H2O2 and hypoxia/reoxygenation (H/R)). The expression of miR-381 in these models was assessed by quantitative reverse transcription polymerase chain reaction (qRT-PCR); we employed approaches including cell counting kit-8 (CCK-8) assay and flow cytometry to evaluate the cell viability and apoptosis. Notch signaling was determined by western blot analysis of key signaling components including Notch1 intracellular domain (ICD), Jag1, and Hes1. The predicted binding of miR-381 to Jag1 3' untranslated region (UTR) was validated by luciferase assay. Following MI, miR-381 expression was upregulated time dependently in the border zone of ischemic area but not in the non-ischemic area. MiR-381 expression was also upregulated in cardiomyocytes treated with H2O2 and H/R. Overexpression of miR-381 exacerbated H2O2- and H/R-induced apoptosis of cardiomyocytes; in contrast, inhibition of miR-381 attenuated apoptosis in these conditions. Importantly, in vivo delivery of miR-381 antagomir significantly reduced infarction size. Moreover, miR-381 negatively regulates the cardioprotective Notch signaling in vivo and in vitro, which might be an effect of targeted inhibition of Jag1 by itself. These data indicate an essential role of miR-381/Jag1 pathway in regulating Notch signaling-mediated cardioprotective effect in cardiomyocytes. Our study also provides a potential therapeutic target for cardiovascular diseases.

Downregulation of Akt2 attenuates ER stress-induced cytotoxicity through JNK-Wnt pathway in cardiomyocytes

Akt, also known as protein kinase B (PKB), is a serine/threonine kinase that promotes survival and growth in response to extracellular signals. Akt1 has been demonstrated to play vital roles in cardiovascular diseases, but the role of Akt2 in cardiomyocytes is not fully understood. This study investigated the effect of Akt2 knockdown on tunicamycin (TM)-induced cytotoxicity in cardiomyocytes and the underlying mechanisms with a focus on the JNK-Wnt pathway. TM treatment significantly increased the expression of Akt2 at both mRNA and protein levels, which was shown to be mediated by the induction of reactive oxygen species (ROS). Knockdown of Akt2 expression via siRNA transfection markedly increased cell viability, decreased lactate dehydrogenase (LDH) release and reduced cell apoptosis after TM exposure. The results of western blot showed that downregulation of Akt2 also attenuated the TM-induced activation of the unfolded protein response (UPR) factors and ER stress associated pro-apoptotic proteins. In addition, Si-Akt2 transfection partially prevented the TM-induced decrease in nuclear localization of β-catenin. By using the selective inhibitor SP-600,125 to inhibit JNK phosphorylation, we found that knockdown of Akt2-induced protection and inhibition of ER stress was mediated by reversing TM-induced decrease of Wnt through the JNK pathway. In summary, these data suggested that Akt2 play a pivotal role in regulating cardiomyocyte survival during ER stress by modulating the JNK-Wnt pathway.

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.

Bridging the Gap between Translational and Outcome Research in Cardiovascular Disease

Bridging the Gap between Translational and Outcome Research in Cardiovascular Disease

2010 Riley Heart Center Symposium on Cardiac Development: Cardiomyocyte Injury and Protection

2010 Riley Heart Center Symposium on Cardiac Development: Cardiomyocyte Injury and Protection

FAK regulates cardiomyocyte survival following ischemia/reperfusion

FAK regulates cardiomyocyte survival following ischemia/reperfusion

FAK regulates cardiomyocyte survival following ischemia/reperfusion

Myocyte apoptosis is central to myocardial dysfunction following ischemia/reperfusion (I/R) and during the transition from hypertrophy to heart failure. Focal adhesion kinase (FAK), a non-receptor tyrosine kinase regulates adhesion-dependent survival signals and unopposed FAK activation has been linked to tumor development. We previously showed that conditional myocyte-specific deletion of FAK (MFKO) in the adult heart did not affect basal cardiomyocyte survival or cardiac function but led to dilated cardiomyopathy and heart failure following pressure overload. In the present study, we sought to determine if FAK functions to limit stress-induced cardiomyocyte apoptosis. We reasoned that (I/R), which stimulates robust apoptotic cell death, might uncover an important cardioprotective function for FAK. We found that depletion of FAK markedly exacerbates hypoxia/re-oxygenation-induced cardiomyocyte cell death in vitro. Moreover, deletion of FAK in the adult myocardium resulted in significant increases in I/R-induced infarct size and cardiomyocyte apoptosis with a concomitant reduction in left ventricular function. Finally, our results suggest that NF-κB signaling may play a key role in modulating FAK-dependent cardioprotection, since FAK inactivation blunted activation of the NF-κB survival signaling pathway and reduced levels of the NF-κB target genes, Bcl2 and Bcl-xl. Since the toggling between pro-survival and pro-apoptotic signals remains central to preventing irreversible damage to the heart, we conclude that targeted FAK activation may be beneficial for protecting stress-dependent cardiac remodeling.

A Nucleolar Weapon in Our Fight for Regenerating Adult Hearts

See related article, pages 89–97 Ischemic diseases and heart failure remain the major causes of morbidity and mortality in the industrialized world. Several new therapeutic modalities have been developed to interfere with the response to injury and to improve cardiac function after ischemia or cardiomyopathy. Experimental and clinical studies demonstrated that the transplantation of bone marrow–derived or tissue-resident stem/progenitor cells in diseased hearts improves neovascularization and functional recovery.1 However, the recent discovery of cardiac stem cells (CSCs) in the adult heart poses the question whether activation of the endogenous pool of these resident stem cells may compensate for the loss of cardiac tissue after injury and improve functional recovery. Indeed, a genetic fate-mapping study elegantly demonstrated that stem cells or precursor cells significantly contributed to the replacement of adult mammalian cardiomyocytes after injury.2 Although it remains unclear to what extent cardiac regeneration in this genetic model was mediated by CSCs or circulating progenitor cell populations being attracted to the heart after injury, mounting evidence suggests that injury-associated signals activate CSCs in situ, which subsequently contribute to the refreshment of the injured heart.3 Obviously, to play a significant role in endogenous cardiac regeneration, the relatively small number of endogenous CSCs needs to be expanded after injury before differentiating into cardiac myocytes. However, the molecular mechanisms underlying the activation, expansion, and recruitment of resident CSCs after injury remain unclear. In the current issue of Circulation Research , Siddiqi et al provide an intriguing concept, which might help to mechanistically explain how proliferation of CSCs is regulated in response to injury.4 The authors investigated the cardiac expression of stem cell specific genes, involved in self-renewal and proliferation, during cardiomyopathic injuries and found increased expression of the nucleolar protein nucleostemin—recently discovered in embryonic and adult stem cells as well …