Reperfusion-activated Akt kinase prevents apoptosis in transgenic mouse hearts overexpressing insulin-like growth factor-1

Loss of Cavin-2 destabilizes phosphatase and tensin homologue and enhances Akt signalling pathway in cardiomyocytes

AIMS

Specific cavins and caveolins, known as caveola-related proteins, have been implicated in cardiac hypertrophy and myocardial injury. Cavin-2 forms complexes with other caveola-related proteins, but the role of Cavin-2 in cardiomyocytes (CMs) is poorly understood. Here, we investigated an unknown function of Cavin-2 in CMs.

METHODS AND RESULTS

Under cardiac stress-free conditions, systemic Cavin-2 knockout (KO) induced mild and significant CM hypertrophy. Cavin-2 KO suppressed phosphatase and tensin homologue (PTEN) associated with Akt signalling, whereas there was no difference in Akt activity between the hearts of the wild-type and the Cavin-2 KO mice under cardiac stress-free conditions. However, after swim training, CM hypertrophy was more facilitated with enhanced phosphoinositide 3-kinase (PI3K)-Akt activity in the hearts of Cavin-2 KO mice. Cavin-2 knockdown neonatal rat CMs (NRCMs) using adenovirus expressing Cavin-2 short hairpin RNA were hypertrophied and resistant to hypoxia and H2O2-induced apoptosis. Cavin-2 knockdown increased Akt phosphorylation in NRCMs, and an Akt inhibitor inhibited Cavin-2 knockdown-induced anti-apoptotic responses in a dose-dependent manner. Cavin-2 knockdown increased phosphatidylinositol-3,4,5-triphosphate production and attenuated PTEN at the membrane fraction of NRCMs. Immunostaining and immunoprecipitation showed that Cavin-2 was associated with PTEN at the plasma membrane of NRCMs. A protein stability assay showed that Cavin-2 knockdown promoted PTEN destabilization in NRCMs. In an Angiotensin II (2-week continuous infusion)-induced pathological cardiac hypertrophy model, CM hypertrophy and CM apoptosis were suppressed in CM-specific Cavin-2 conditional KO (Cavin-2 cKO) mice. Because Cavin-2 cKO mouse hearts showed increased Akt activity but not decreased extracellular signal-regulated kinase activity, suppression of pathological hypertrophy by Cavin-2 loss may be due to increased survival of healthy CMs.

CONCLUSION

Cavin-2 plays a negative regulator in the PI3K-Akt signalling in CMs through interaction with PTEN. Loss of Cavin-2 enhances Akt activity by promoting PTEN destabilization, which promotes physiological CM hypertrophy and may enhance Akt-mediated cardioprotective effects against pathological CM hypertrophy.

Blocking RIPK2 Function Alleviates Myocardial Ischemia/Reperfusion Injury by Regulating the AKT and NF-κB Pathways

OBJECTIVE

Inflammation and oxidation brought on by myocardial ischemia-reperfusion (MI/R) injury lead to cardiomyocyte apoptosis and necrosis. The receptor interacting serine/threonine kinase 2 (RIPK2) plays significant roles in oxidative stress and excessive inflammation. The purpose of this research is to examine the roles of RIPK2 in MI/R injury.

METHODS

The in vivo animal model was constructed by acute coronary I/R, and the in vitro cell model was established by oxygen and glucose deprivation/reperfusion (OGD/R)-stimulated cardiomyocyte injury. RIPK2 expression was examined using qRT-PCR and Western blot. CCK-8 was proposed as a method for detecting cell proliferation. ELISA was utilized to measure inflammatory cytokines (TNF-α, IL-6, and IL-1β) and myocardial injury indicators (CK-MB, Mb, cTnI, and LDH). The levels of MDA and ROS were determined by the kit and fluorescent probe. H&E was conducted to assess MI/R injury after silencing of RIPK2.

RESULTS

In MI/R rats and OGD/R-treated H9C2 cardiomyocytes, RIPK2 was overexpressed at both the mRNA and protein levels. RIPK2 inhibition promoted cell proliferation while inhibiting apoptosis, as evidenced by decreased TUNEL-positive cells and cleaved caspase-3. RIPK2 inhibition reduced MDA and ROS levels, as well as the contents of inflammatory factors. RIPK2 silencing reduced CK-MB, Mb, cTnI, and LDH levels in rat serum and alleviated MI/R injury. Furthermore, RIPK2 inhibition increased p-AKT while decreasing NF-B p-p65 expression.

CONCLUSION

Silencing of RIPK2 reduced apoptosis, proinflammatory factors, and oxidative stress in MI/R by activating AKT and suppressing NF-κB signals, suggesting a potential therapeutic strategy for MI/R injury.

Myocardial IGF2R is a critical mediator of inflammation and fibrosis after ischemia-reperfusion injury

Ischemia-reperfusion (I/R) injury is a common occurrence in various surgical procedures used to treat heart diseases. However, the role of insulin-like growth factor 2 receptor (IGF2R) during the process of myocardial I/R remains unclear. Therefore, this study aims to investigate the expression, distribution, and functionality of IGF2R in various I/R-associated models (such as reoxygenation, revascularization, and heart transplant). Loss-of-function studies (including myocardial conditional knockout and CRISPR interference) were performed to clarify the role of IGF2R in I/R injuries. Following hypoxia, IGF2R expression increased, but this effect was reversed upon restoration of oxygen levels. Loss of myocardial IGF2R was found to enhance the cardiac contractile functions, and reduced cell infiltration or cardiac fibrosis of I/R mouse models compared to the genotype control. CRISPR-inhibition of IGF2R decreased cell apoptotic death under hypoxia. RNA sequencing analysis indicated that myocardial IGF2R played a critical role in regulating the inflammatory response, innate immune response, and apoptotic process following I/R. Integrated analysis of the mRNA profiling, pulldown assays, and mass spectrometry identified granulocyte-specific factors as potential targets of myocardial IGF2R in the injured heart. In conclusion, myocardial IGF2R emerges as a promising therapeutic target to ameliorate inflammation or fibrosis following I/R injuries.

PHLPPs: Emerging players in metabolic disorders

That reversible protein phosphorylation by kinases and phosphatases occurs in metabolic disorders is well known. Various studies have revealed that a multi-faceted and tightly regulated phosphatase, pleckstrin homology domain leucine-rich repeat protein phosphatase (PHLPP)-1/2 displays robust effects in cardioprotection, ischaemia/reperfusion (I/R), and vascular remodelling. PHLPP1 promotes foamy macrophage development through ChREBP/AMPK-dependent pathways. Adipocyte-specific loss of PHLPP2 reduces adiposity, improves glucose tolerance,and attenuates fatty liver via the PHLPP2-HSL-PPARα axis. Discoveries of PHLPP1-mediated insulin resistance and pancreatic β cell death via the PHLPP1/2-Mst1-mTORC1 triangular loop have shed light on its significance in diabetology. PHLPP1 downregulation attenuates diabetic cardiomyopathy (DCM) by restoring PI3K-Akt-mTOR signalling. In this review, we summarise the functional role of, and cellular signalling mediated by, PHLPPs in metabolic tissues and discuss their potential as therapeutic targets.

Exogenous ANP Treatment Ameliorates Myocardial Insulin Resistance and Protects against Ischemia-Reperfusion Injury in Diet-Induced Obesity

Increasing evidence suggests natriuretic peptides (NPs) coordinate interorgan metabolic crosstalk. We recently reported exogenous ANP treatment ameliorated systemic insulin resistance by inducing adipose tissue browning and attenuating hepatic steatosis in diet-induced obesity (DIO). We herein investigated whether ANP treatment also ameliorates myocardial insulin resistance, leading to cardioprotection during ischemia-reperfusion injury (IRI) in DIO. Mice fed a high-fat diet (HFD) or normal-fat diet for 13 weeks were treated with or without ANP infusion subcutaneously for another 3 weeks. Left ventricular BNP expression was substantially reduced in HFD hearts. Intraperitoneal-insulin-administration-induced Akt phosphorylation was impaired in HFD hearts, which was restored by ANP treatment, suggesting that ANP treatment ameliorated myocardial insulin resistance. After ischemia-reperfusion using the Langendorff model, HFD impaired cardiac functional recovery with a corresponding increased infarct size. However, ANP treatment improved functional recovery and reduced injury while restoring impaired IRI-induced Akt phosphorylation in HFD hearts. Myocardial ultrastructural analyses showed increased peri-mitochondrial lipid droplets with concomitantly decreased ATGL and HSL phosphorylation levels in ANP-treated HFD, suggesting that ANP protects mitochondria from lipid overload by trapping lipids. Accordingly, ANP treatment attenuated mitochondria cristae disruption after IRI in HFD hearts. In summary, exogenous ANP treatment ameliorates myocardial insulin resistance and protects against IRI associated with mitochondrial ultrastructure modifications in DIO. Replenishing biologically active NPs substantially affects HFD hearts in which endogenous NP production is impaired.

Uncovering the Effect and Mechanism of Rhizoma Corydalis on Myocardial Infarction Through an Integrated Network Pharmacology Approach and Experimental Verification

Background: Myocardial infarction (MI), characterized by reduced blood flow to the heart, is a coronary artery disorder with the highest morbidity and mortality among cardiovascular diseases. Consequently, there is an urgent need to identify effective drugs to treat MI. Rhizoma Corydalis (RC) is the dry tuber of Corydalis yanhusuo W.T. Wang, and is extensively applied in treating MI clinically in China. Its underlying pharmacological mechanism remains unknown. This study aims to clarify the molecular mechanism of RC on MI by utilizing network pharmacology and experimental verification.

Methods: Based on network pharmacology, the potential targets of the RC ingredients and MI-related targets were collected from the databases. Furthermore, core targets of RC on MI were identified by the protein-protein interaction (PPI) network and analyzed with Gene Ontology (GO) analysis and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis. Molecular docking was used to validate the binding affinity between the core targets and the bioactive components. Oxygen-glucose deprivation (OGD) was performed on H9c2 cells to mimic MI in vitro. A Cell Counting Kit-8 assay was used to assess the cardioprotective effect of the active ingredient against OGD. Western blot analysis and RT-qPCR were used to measure the cell apoptosis and inflammation level of H9c2 cells.

Results: The network pharmacology obtained 60 bioactive components of RC, 431 potential targets, and 1131 MI-related targets. In total, 126 core targets were screened according to topological analysis. KEGG results showed that RC was closely related to the phosphatidylinositol 3-kinase (PI3K)/Protein kinase B (PKB, also called Akt) signaling pathway. The experimental validation data showed that tetrahydropalmatine (THP) pretreatment preserved cell viability after OGD exposure. THP suppressed cardiomyocyte apoptosis and inflammation induced by OGD, while LY294002 blocked the inhibition effect of THP on OGD-induced H9c2 cell injury. Moreover, the molecular docking results indicated that THP had the strongest binding affinity with Akt over berberine, coptisine, palmatine, and quercetin.

Conclusion: THP, the active ingredient of RC, can suppress OGD-induced H9c2 cell injury by activating the PI3K/Akt pathway, which in turn provides a scientific basis for a novel strategy for MI therapy and RC application.

Potential Role of Exercise in Regulating YAP and TAZ During Cardiomyocytes Aging

Adaptation of cardiac muscle to regular exercise results in morphological and structural changes known as physiological cardiac hypertrophy, to which the Hippo signaling pathway might have contributed. Two major terminal effectors in the Hippo signaling pathway are Yes-associated protein (YAP) and its homolog transcriptional coactivator with PDZ-binding motif (TAZ). The latest studies have reported the role of YAP and TAZ in different life stages, such as in fetal, neonatal, and adult hearts. Their regulation might involve several mechanisms and effectors. One of the possible coregulators is exercise. Exercise plays a role in cardiomyocyte hypertrophic changes during different stages of life, including in aged hearts. YAP/TAZ signaling pathway has a role in physiological cardiac hypertrophy induced by exercise and is associated with cardiac remodelling. Thus, it can be believed that exercise has roles in activating the signaling pathway of YAP and TAZ in aged cardiomyocytes. However, the studies regarding the roles of YAP and TAZ during cardiomyocyte aging are limited. The primary purpose of this review is to explore the response of cardiovascular aging to exercise via signaling pathway of YAP and TAZ.

Unfolded protein response during cardiovascular disorders: a tilt towards pro-survival and cellular homeostasis

The endoplasmic reticulum (ER) is an organelle that orchestrates the production and proper assembly of an extensive types of secretory and membrane proteins. Endoplasmic reticulum stress is conventionally related to prolonged disruption in the protein folding machinery resulting in the accumulation of unfolded proteins in the ER. This disruption is often manifested due to oxidative stress, Ca²⁺ leakage, iron imbalance, disease conditions which in turn hampers the cellular homeostasis and induces cellular apoptosis. A mild ER stress is often reverted back to normal. However, cells retaliate to acute ER stress by activating the unfolded protein response (UPR) which comprises three signaling pathways, Activating transcription factor 6 (ATF6), inositol requiring enzyme 1 alpha (IRE1α), and protein kinase RNA-activated-like ER kinase (PERK). The UPR response participates in both protective and pro-apoptotic responses and not much is known about the mechanistic aspects of the switch from pro-survival to pro-apoptosis. When ER stress outpaces UPR response then cell apoptosis prevails which often leads to the development of various diseases including cardiomyopathies. Therefore, it is important to identify molecules that modulate the UPR that may serve as promising tools towards effective treatment of cardiovascular diseases. In this review, we elucidated the latest advances in construing the contribution imparted by the three arms of UPR to combat the adverse environment in the ER to restore cellular homeostasis during cardiomyopathies. We also summarized the various therapeutic agents that plays crucial role in tilting the UPR response towards pro-survival.

Cardiomyocyte protective effects of thyroid hormone during hypoxia/reoxygenation injury through activating of IGF-1-mediated PI3K/Akt signalling

Ischaemia/reperfusion (I/R) injury is a common clinical condition that results in apoptosis and oxidative stress injury. Thyroid hormone was previously reported to elicit cardiac myocyte hypertrophy and promote cardiac function after cardiac injury. We used an in vivo mouse model of I/R injury and in vitro primary cardiomyocyte culture assays to investigate the effects of thyroid hormone on cardiomyocytes during hypoxia/reoxygenation (H/R) injury. The results showed that T3 pretreatment in vivo significantly improved left ventricular function after I/R injury. In vitro, T3 pretreatment decreased cell apoptosis rate, inhibited caspase‐3 activity and decreased the Bax/Bcl‐2 ration induced by H/R injury. T3 pretreatment significantly attenuated the loss of mitochondrial membrane potential. Furthermore, it was observed that T3 diminished the expression of NCX1 protein and decreased SERCA2a protein expression in H/R‐induced cardiomyocytes, and T3 prevented intracellular Ca²⁺ increase during H/R injury. Also, T3 increased the expression of IGF‐1, and PI3K/Akt signalling in cardiomyocytes under H/R‐induced injury, and that the protective effect of T3 against H/R‐induced injury was blocked by the PI3K inhibitor LY294002. IGF‐1 receptor (IGF‐1R) inhibitor GSK1904529A significantly inhibited the expression of IGF‐1R and PI3K/Akt signalling. In summary, T3 pretreatment protects cardiomyocytes against H/R‐induced injury by activating the IGF‐1‐mediated PI3K/Akt signalling pathway.

Research progress of IGF-1 and cerebral ischemia

Cerebral ischemic disease is a group of diseases that cause insufficient blood supply to the cerebrum, cerebellum or brain stem for different reasons, resulting in corresponding nervous system symptoms. Cardiovascular disease is the leading cause of death in the world. Among them, the death caused by cerebral ischemia accounts for the vast majority, and it is one of the fatal diseases in the middle-aged and elderly at present. Epidemiologic studies have projected increasing mortality due to cardiovascular disease worldwide (about 23.3 million people by 2030) because of the aging population. However, related studies have shown that insulin-like growth factor I (IGF-1) is a multifunctional cell proliferation regulator. It plays an important role in cerebral ischemia. It is effective in promoting cell differentiation, proliferation and individual development. Studies have shown that IGF-1 signaling pathway is a key pathway controlling cell growth and survival. There may be five mechanisms in cerebral ischemia: prevention of intracellular calcium overload, inhibition of the upregulation of nNOS, IGF-1upregulations activating HIF-1α, regulation of Bcl-2 to resist apoptosis, and enhancement of vascular endothelial function. Three critical nodes in the IGF-1 signaling pathway have been described in cardiomyocytes: protein kinase Akt/mammalian target of rapamycin (mTOR), Ras/Raf/extracellular signal-regulated kinase (ERK), and phospholipase C (PLC)/inositol 1,4,5-triphosphate (InsP3)/Ca2+. IGF-1 plays an important role in cerebral ischemia and myocardial ischemia, mainly by activating downstream of IGF-1, controlling cell death and differentiation or transcription work, improving the function of heart muscle cells, reducing the myocardial cell apoptosis induced by myocardial infarction, regulating endogenous protection and restoration of cerebral ischemia injury, thus protecting cerebral and myocardial injury. Related studies have shown that bcl-2 exerts great influence on both cerebral ischemia and myocardial ischemia. Therefore, the relevant pathways and targets of cerebral ischemia and myocardial ischemia and the role of IGF-1 in protecting the heart are reviewed in this paper.

Modulatory Effect of Myokines on Reactive Oxygen Species in Ischemia/Reperfusion

There is a growing body of evidence showing the importance of physical activity against acute ischemic events in various organs. Ischemia/reperfusion injury (I/R) is characterized by tissue damage as a result of restriction and subsequent restoration of blood supply to an organ. Oxidative stress due to increased reactive oxygen species formation and/or insufficient antioxidant defense is considered to play an important role in I/R. Physical activity not only decreases the general risk factors for ischemia but also confers direct anti-ischemic protection via myokine production. Myokines are skeletal muscle-derived cytokines, representing multifunctional communication channels between the contracting skeletal muscle and other organs through an endocrine manner. In this review, we discuss the most prominent members of the myokines (i.e., brain-derived neurotrophic factor (BDNF), cathepsin B, decorin, fibroblast growth factors-2 and -21, follistatin, follistatin-like, insulin-like growth factor-1; interleukin-6, interleukin-7, interleukin-15, irisin, leukemia inhibitory factor, meteorin-like, myonectin, musclin, myostatin, and osteoglycin) with a particular interest in their potential influence on reactive oxygen and nitrogen species formation or antioxidant capacity. A better understanding of the mechanism of action of myokines and particularly their participation in the regulation of oxidative stress may widen their possible therapeutic use and, thereby, may support the fight against I/R.

Effects of GH/IGF on the Aging Mitochondria

The mitochondria are key organelles regulating vital processes in the eukaryote cell. A decline in mitochondrial function is one of the hallmarks of aging. Growth hormone (GH) and the insulin-like growth factor-1 (IGF-1) are somatotropic hormones that regulate cellular homeostasis and play significant roles in cell differentiation, function, and survival. In mammals, these hormones peak during puberty and decline gradually during adulthood and aging. Here, we review the evidence that GH and IGF-1 regulate mitochondrial mass and function and contribute to specific processes of cellular aging. Specifically, we discuss the contribution of GH and IGF-1 to mitochondrial biogenesis, respiration and ATP production, oxidative stress, senescence, and apoptosis. Particular emphasis was placed on how these pathways intersect during aging.

Cardioprotective effect of IGF-1 against myocardial ischemia/reperfusion injury through activation of PI3K/Akt pathway in rats in vivo

Objective

It remains unknown whether insulin-like growth factor-1 (IGF-1) can attenuate myocardial ischemia/reperfusion (I/R) injury in vivo by activating the phosphoinositide 3-kinase/protein kinase B (PI3K/Akt) pathway. This study investigated the possible interaction of IGF-1 with the PI3K/Akt pathway in cardioprotection against in vivo myocardial I/R injury in rats.

Methods

We established a myocardial I/R model in rats through left anterior descending artery ligation for 40 minutes followed by 6 hours reperfusion. The PI3K/Akt inhibitor, LY294002 (0.3 mg/kg), was injected through the caudal vein 30 minutes before myocardial ischemia, and IGF-1 (1 µg/kg or 5 µg/kg) was injected through the caudal vein 10 minutes before myocardial ischemia.

Results

IGF-1 treatment decreased myocardial infarct size; myocardial cell apoptosis; and serum lactate dehydrogenase, creatine kinase MB, and cardiac troponin I levels in rats with myocardial I/R in vivo. Moreover, IGF-1 treatment led to significant increases in expression levels of p-Akt (Ser473) and B cell lymphoma 2, while reducing expression levels of caspase-9 mRNA and cleaved caspase-9 protein in rats with myocardial I/R. However, pretreatment with LY294002 significantly reduced the cardioprotective effects of IGF-1.

Conclusion

Treatment with IGF-1 may confer cardiac protection against in vivo myocardial I/R injury via the PI3K/Akt pathway in rats.

Proteostasis and Beyond: ATF6 in Ischemic Disease

Endoplasmic reticulum (ER) stress is a pathological hallmark of numerous ischemic diseases, including stroke and myocardial infarction (MI). In these diseases, ER stress leads to activation of the unfolded protein response (UPR) and subsequent adaptation of cellular physiology in ways that dictate cellular fate following ischemia. Recent evidence highlights a protective role for the activating transcription factor 6 (ATF6) arm of the UPR in mitigating adverse outcomes associated with ischemia/reperfusion (I/R) injury in multiple disease models. This suggests ATF6 as a potential therapeutic target for intervening in diverse ischemia-related disorders. Here, we discuss the evidence demonstrating the importance of ATF6 signaling in protecting different tissues against ischemic damage and discuss preclinical results focused on defining the potential for pharmacologically targeting ATF6 to intervene in such diseases.

Mitochondrial Function Is Compromised in Cortical Bone Osteocytes of Long-Lived Growth Hormone Receptor Null Mice

Despite increased longevity and resistance to multiple stressors, growth hormone receptor null (GHRKO) mice exhibit severe skeletal impairment. The role of GHR in maintaining osteocyte mitochondrial function is unknown. We found that GHR ablation was detrimental to osteocyte mitochondrial function. In vivo multiphoton microscopy revealed significant reductions of >10% in mitochondrial membrane potential (MMP) in GHRKO osteocytes and reduced mitochondrial volumetric density. Reductions in MMP were accompanied by reductions in glucose transporter-1 levels, steady state ATP, NADH redox index, oxygen consumption rate, and mitochondrial reserve capacity in GHRKO osteocytes. Glycolytic capacity did not differ between control and GHRKO males' osteocytes. However, osteocytes from aged female GHRKO mice exhibited reductions in glycolytic parameters, indicating impairments in glucose metabolism, which may be sex dependent. GHRKO osteocytes exhibited increased levels of cytoplasmic reactive oxygen species (ROS) (both basal and in response to high glucose), insulin-like growth factor-1 (IGF-1), and insulin. Mitochondrial ROS levels were increased and correlated with reduced glutathione in GHRKO osteocytes. Overall, the compromised osteocyte mitochondrial function and responses to metabolic insults strongly correlated with skeletal impairments, suggesting that despite increased life span of the GHRKO mice, skeletal health span is decreased. © 2018 American Society for Bone and Mineral Research.

Umbilical cord blood-mesenchymal stem cells and carvedilol reduce doxorubicin- induced cardiotoxicity: Possible role of insulin-like growth factor-1

In this study, we tried to demonstrate the effects of adding human umbilical cord blood mesenchymal stem cells (hUCB-MSCs) to carvedilol in improving the doxorubicin- induced cardiotoxicity in rats. Rats were randomly divided into four groups: group 1: control group, group 2: doxorubicin untreated group, group 3: rats injected with doxorubicin and received carvedilol, and group 4: rats injected with doxorubicin and received carvedilol and stem cell-treated. Electrocardiography (ECG) was performed to assess cardiac function after animals were sacrificed. Cardiac muscle sections were examined histologically using H&E, Masson trichrome and immunohistochemically using caspase 3 immunostaining. The morphometric and statistical analysis was performed. Levels of malondialdehyde (MDA), superoxide dismutase (SOD), insulin-like growth factor (IGF-1), and vascular endothelial growth factor (VEGF) were measured. We concluded that combination of hUCB-MSCs and carvedilol markedly improves histological and immunohistochemical structure of cardiac muscle fibers and restores cardiac function in doxorubicin- induced cardiotoxicity in rats.

Endoplasmic Reticulum Chaperone GRP78 Protects Heart From Ischemia/Reperfusion Injury Through Akt Activation

RATIONALE

Restoration of coronary artery blood flow is the most effective means of ameliorating myocardial damage triggered by ischemic heart disease. However, coronary reperfusion elicits an increment of additional injury to the myocardium. Accumulating evidence indicates that the unfolded protein response (UPR) in cardiomyocytes is activated by ischemia/reperfusion (I/R) injury. Xbp1s (spliced X-box binding protein 1), the most highly conserved branch of the unfolded protein response, is protective in response to cardiac I/R injury. GRP78 (78 kDa glucose-regulated protein), a master regulator of the UPR and an Xbp1s target, is upregulated after I/R. However, its role in the protective response of Xbp1s during I/R remains largely undefined.

OBJECTIVE

To elucidate the role of GRP78 in the cardiomyocyte response to I/R using both in vitro and in vivo approaches.

METHODS AND RESULTS

Simulated I/R injury to cultured neonatal rat ventricular myocytes induced apoptotic cell death and strong activation of the UPR and GRP78. Overexpression of GRP78 in neonatal rat ventricular myocytes significantly protected myocytes from I/R-induced cell death. Furthermore, cardiomyocyte-specific overexpression of GRP78 ameliorated I/R damage to the heart in vivo. Exploration of underlying mechanisms revealed that GRP78 mitigates cellular damage by suppressing the accumulation of reactive oxygen species. We go on to show that the GRP78-mediated cytoprotective response involves plasma membrane translocation of GRP78 and interaction with PI3 kinase, culminating in stimulation of Akt. This response is required as inhibition of the Akt pathway significantly blunted the antioxidant activity and cardioprotective effects of GRP78.

CONCLUSIONS

I/R induction of GRP78 in cardiomyocytes stimulates Akt signaling and protects against oxidative stress, which together protect cells from I/R damage.

Oleuropein Protects Cardiomyocyte against Apoptosis via Activating the Reperfusion Injury Salvage Kinase Pathway In Vitro

Oleuropein, the main glycoside present in olives, has been reported to have cardioprotective effect, but the exact mechanism has not been clearly elucidated. This study attempted to clarify the cardioprotective effect of oleuropein against simulated ischemia/reperfusion- (SI/R-) induced cardiomyocyte injury in vitro and further explore the underlying mechanism. Here we confirmed that oleuropein reduced the cell injury in neonatal rat cardiomyocyte induced by SI/R evidenced by decreasing MTT dye reduction and LDH activity in the culture medium. Meanwhile, the compound also inhibited reactive oxygen species excessive generation and stabilized mitochondrial membrane potential after SI/R. The flow cytometry assessment results indicated the inhibition of cellular apoptosis with oleuropein treatment. Furthermore, western blot analysis showed that oleuropein attenuated the expression of Cyt-C, c-caspase-3, and c-caspase-9, increased the Bcl-2/Bax ratio, and enhanced the phosphorylation of ERK1/2 and Akt after SI/R. However, the phosphorylation enhancement was partially abolished in the presence of LY294002 (PI3K inhibitor) and U0126 (ERK inhibitor). All these findings indicate that oleuropein has the protective potential against SI/R-induced injury and its protective effect may be partly due to the attenuation of apoptosis via the activation of the PI3K/Akt and ERK1/2 signaling pathways.

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

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

Insulin-like growth factor-1 improves diabetic cardiomyopathy through antioxidative and anti-inflammatory processes along with modulation of Akt/GSK-3β signaling in rats

Diabetic cardiomyopathy (DCM), a serious complication of diabetes mellitus, is associated with changes in myocardial structure and function. This study sought to explore the ability of insulin-like growth factor-1 (IGF-1) to modulate DCM and its related mechanisms. Twenty-four male Wistar rats were injected with streptozotocin (STZ, 60 mg/kg) to mimic diabetes mellitus. Myocardial fibrosis and apoptosis were evaluated by histopathologic analyses, and relevant proteins were analyzed by Western blotting. Inflammatory factors were assessed by ELISA. Markers of oxidative stress were tested by colorimetric analysis. Rats with DCM displayed decreased body weight, metabolic abnormalities, elevated apoptosis (as assessed by the bcl-2/bax ratio and TUNEL assays), increased fibrosis, increased markers of oxidative stress (MDA and SOD) and inflammatory factors (TNF-α and IL-1β), and decreased phosphorylation of Akt and glycogen synthase kinase (GSK-3β). IGF-1 treatment, however, attenuated the metabolic abnormalities and myocardial apoptosis, interstitial fibrosis, oxidative stress and inflammation seen in diabetic rats, while also increasing the phosphorylation levels of Akt and GSK-3β. These findings suggest that IGF-1 ameliorates the pathophysiological progress of DCM along with an activation of the Akt/GSK-3β signaling pathway. Our findings suggest that IGF-1 could be a potential therapeutic choice for controlling DCM.

The Role of Exercise in Cardiac Aging: From Physiology to Molecular Mechanisms

Aging induces structural and functional changes in the heart that are associated with increased risk of cardiovascular disease and impaired functional capacity in the elderly. Exercise is a diagnostic and therapeutic tool, with the potential to provide insights into clinical diagnosis and prognosis, as well as the molecular mechanisms by which aging influences cardiac physiology and function. In this review, we first provide an overview of how aging impacts the cardiac response to exercise, and the implications this has for functional capacity in older adults. We then review the underlying molecular mechanisms by which cardiac aging contributes to exercise intolerance, and conversely how exercise training can potentially modulate aging phenotypes in the heart. Finally, we highlight the potential use of these exercise models to complement models of disease in efforts to uncover new therapeutic targets to prevent or treat heart disease in the aging population.

Physiological and pathological cardiac hypertrophy

The heart must continuously pump blood to supply the body with oxygen and nutrients. To maintain the high energy consumption required by this role, the heart is equipped with multiple complex biological systems that allow adaptation to changes of systemic demand. The processes of growth (hypertrophy), angiogenesis, and metabolic plasticity are critically involved in maintenance of cardiac homeostasis. Cardiac hypertrophy is classified as physiological when it is associated with normal cardiac function or as pathological when associated with cardiac dysfunction. Physiological hypertrophy of the heart occurs in response to normal growth of children or during pregnancy, as well as in athletes. In contrast, pathological hypertrophy is induced by factors such as prolonged and abnormal hemodynamic stress, due to hypertension, myocardial infarction etc. Pathological hypertrophy is associated with fibrosis, capillary rarefaction, increased production of pro-inflammatory cytokines, and cellular dysfunction (impairment of signaling, suppression of autophagy, and abnormal cardiomyocyte/non-cardiomyocyte interactions), as well as undesirable epigenetic changes, with these complex responses leading to maladaptive cardiac remodeling and heart failure. This review describes the key molecules and cellular responses involved in physiological/pathological cardiac hypertrophy.

Altered Phosphatidylinositol 3-Kinase and Calcium Signaling in Cardiac Dysfunction After Brain Death in Rats

BACKGROUND

Phosphatidylinositol 3-kinase is involved in myocardial function, including contractility. To date, myocardial regulation by phosphatidylinositol 3-kinase after brain death has not been investigated. The present study using a brain death model was designed to examine the role of phosphatidylinositol 3-kinase in myocardial function after brain death.

METHODS

After anesthesia with sevoflurane, a Fogarty catheter was placed intracranially for induction of brain death. A conductance catheter was inserted into the left ventricle for measurement of myocardial function. Rats were assigned to the following groups: one group undergoing sham operation (with catheter placement but no brain death introduction); one group receiving saline before brain death; and one group receiving wortmannin, an inhibitor of phosphatidylinositol 3-kinase, before brain death. Various measurements, including mean blood pressure, heart rate, maximal rate of rise of left ventricular pressure, and ejection fraction, were obtained every 30 minutes for 6 hours after brain death. The phosphorylation status of Akt and phospholamban was determined 360 minutes after brain death.

RESULTS

After induction of brain death, rats showed significant decreases in blood pressure, maximal rate of rise of left ventricular pressure, and ejection fraction. Inhibition of phosphatidylinositol 3-kinase using wortmannin significantly improved these measurements, resulting in increased survival. Western blot analysis demonstrated that brain death increased Akt phosphorylation and decreased phospholamban phosphorylation; these effects were abolished by wortmannin.

CONCLUSIONS

Inhibition of phosphatidylinositol 3-kinase prevented myocardial dysfunction after brain death in association with inhibition of the decrease in phosphorylation of myocardial phospholamban, characteristic of brain death.

Influence of Physical Activity on Hypertension and Cardiac Structure and Function

The global burden of hypertension is rising and accounts for substantial morbidity and mortality. Lifestyle factors such as diet and physical inactivity contribute to this burden, further highlighting the need for prevention efforts to curb this public health epidemic. Regular physical activity is associated with lower blood pressure, reduced cardiovascular risk, and cardiac remodeling. While exercise and hypertension can both be associated with the development of left ventricular hypertrophy (LVH), the cardiac remodeling from hypertension is pathologic with an associated increase in myocyte hypertrophy, fibrosis, and risk of heart failure and mortality, whereas LVH in athletes is generally non-pathologic and lacks the fibrosis seen in hypertension. In hypertensive patients, physical activity has been associated with paradoxical regression or prevention of LVH, suggesting a mechanism by which exercise can benefit hypertensive patients. Further studies are needed to better understand the mechanisms underlying the benefits of physical activity in the hypertensive heart.

Toll-interacting protein contributes to mortality following myocardial infarction through promoting inflammation and apoptosis

BACKGROUND AND PURPOSE

Toll-interacting protein (Tollip) is an endogenous inhibitor of toll-like receptors, a superfamily that plays a pivotal role in various pathological conditions, including myocardial infarction (MI). However, the exact role of Tollip in MI remains unknown.

EXPERIMENTAL APPROACH

MI models were established in Tollip knockout (KO) mice, mice with cardiac-specific overexpression of human Tollip gene and in their Tollip(+/+) and non-transgenic controls respectively. The effects of Tollip on MI were evaluated by mortality, infarct size and cardiac function. Hypoxia-induced cardiomyocyte damage was investigated in vitro to confirm the role of Tollip in heart damage.

KEY RESULTS

Tollip expression was dramatically up-regulated in human ischaemic hearts and infarcted mice hearts. MI-induced mortality, infarct size and cardiac dysfunction were decreased in Tollip-KO mice compared with Tollip(+/+) controls. Ischaemic hearts from Tollip-KO mice exhibited decreased inflammatory cell infiltration and reduced NF-κB activation. Tollip depletion also alleviated myocardial apoptosis by down-regulating pro-apoptotic protein levels and up-regulating anti-apoptotic protein expressions in infarct border zone. Conversely, MI effects were exacerbated in mice with cardiac-specific Tollip overexpression. This aggravated MI injury by Tollip in vivo was confirmed with in vitro assays. Inhibition of Akt signalling was associated with the detrimental effects of Tollip on MI injury; activation of Akt largely reversed the deleterious effects of Tollip on MI-induced cardiomyocyte death.

CONCLUSIONS AND IMPLICATIONS

Tollip promotes inflammatory and apoptotic responses after MI, leading to increased mortality and aggravated cardiac dysfunction. These findings suggest that Tollip may serve as a novel therapeutic target for the treatment of MI.

Using exercise to measure and modify cardiac function

Exercise is the archetype of physiologic demands placed on the cardiovascular system. Acute responses provide an informative assessment of cardiovascular function and fitness, while repeated exercise promotes cardiovascular health and evokes important molecular, structural, and functional changes contributing to its effects in primary and secondary prevention. Here we examine the use of exercise in murine models, both as a phenotypic assay and as a provocative intervention. We first review the advantages and limitations of exercise testing for assessing cardiac function, then highlight the cardiac structural and cellular changes elicited by chronic exercise and key molecular pathways that mediate these effects.

Physiological activation of Akt by PHLPP1 deletion protects against pathological hypertrophy

AIMS

To examine the role of physiological Akt signalling in pathological hypertrophy through analysis of PHLPP1 (PH domain leucine-rich repeat protein phosphatase) knock-out (KO) mice.

METHODS AND RESULTS

To investigate the in vivo requirement for 'physiological' control of Akt activation in cardiac growth, we examined the effect of deleting the Akt phosphatase, PHLPP, on the induction of cardiac hypertrophy. Basal Akt phosphorylation increased nearly two-fold in the cardiomyocytes from PHLPP1 KO mice and physiological hypertrophy induced by swimming exercise was accentuated as assessed by increased heart size and myocyte cell area. In contrast, the development of pathophysiological hypertrophy induced by pressure overload and assessed by increases in heart size, myocyte cell area, and hypertrophic gene expression was attenuated. This attenuation coincided with decreased fibrosis and cell death in the KO mice. Cast moulding revealed increased capillary density basally in the KO hearts, which was further elevated relative to wild-type mouse hearts in response to pressure overload. In vitro studies with isolated myocytes in co-culture also demonstrated that PHLPP1 deletion in cardiomyocytes can enhance endothelial tube formation. Expression of the pro-angiogenic factor VEGF was also elevated basally and accentuated in response to transverse aortic constriction in hearts from KO mice.

CONCLUSION

Our data suggest that enhancing Akt activity by inhibiting its PHLPP1-mediated dephosphorylation promotes processes associated with physiological hypertrophy that may be beneficial in attenuating the development of pathological hypertrophy.

Mitochondrial membrane permeabilization and cell death during myocardial infarction: roles of calcium and reactive oxygen species

Excess generation of reactive oxygen species (ROS) and cytosolic calcium accumulation play major roles in the initiation of programmed cell death during acute myocardial infarction. Cell death may include necrosis, apoptosis and autophagy, and combinations thereof. During ischemia, calcium handling between the sarcoplasmic reticulum and myofilament is disrupted and calcium is diverted to the mitochondria causing swelling. Reperfusion, while essential for survival, reactivates energy transduction and contractility and causes the release of ROS and additional ionic imbalance. During acute ischemia-reperfusion, the principal death pathways are programmed necrosis and apoptosis through the intrinsic pathway, initiated by the opening of the mitochondrial permeability transition pore and outer mitochondrial membrane permeabilization, respectively. Despite intense investigation, the mechanisms of action and modes of regulation of mitochondrial membrane permeabilization are incompletely understood. Extrinsic apoptosis, necroptosis and autophagy may also contribute to ischemia-reperfusion injury. In this review, the roles of dysregulated calcium and ROS and the contributions of Bcl-2 proteins, as well as mitochondrial morphology in promoting mitochondrial membrane permeability change and the ensuing cell death during myocardial infarction are discussed.

Dual role of cyclic GMP in cardiac cell survival

It is well known that cyclic guanosine 3',5'-monophosphate plays an important role in cardioprotection against ischemia/reperfusion injury through activation of protein kinase G (PKG). We found that cGMP prevents the mitochondrial permeability transition pore (mPTP) opening by inactivating glycogen synthase kinase 3β (GSK-3β) via protein kinase G (PKG) in cardiac H9c2 cells. While GSK-3β and its major upstream regulator phosphoinositide 3-kinase (PI3K)/Akt are critical for acute cardioprotection, an excessive activation of PI3K/Akt or GSK-3β inactivation can also lead to cardiac hypertrophy. Here, we show that cGMP not only inactivates GSK-3β through PKG (this leads to acute cardioprotection) but also negatively regulates Akt activity (this may lead to prevention of hypertrophy and heart failure, and the regulation of NO synthesis) in cardiac cells. We further found that the negative regulatory effect of cGMP on Akt activity is not mediated by PKG but may be through up-regulation of protein phosphatase PP2A activity. We propose that cGMP is a versatile signal with dual beneficial role in cardiac cell survival.

Enhanced recovery from ischemia-reperfusion injury in PI3Kα dominant negative hearts: investigating the role of alternate PI3K isoforms, increased glucose oxidation and MAPK signaling

Classical ischemia-reperfusion (IR) preconditioning relies on phosphatidylinositol 3-kinase (PI3K) for protective signaling. Surprisingly, inhibition of PI3Kα activity using a dominant negative (DN) strategy protected the murine heart from IR injury. It has been proposed that increased signaling through PI3Kγ may contribute to the improved recovery of PI3KαDN hearts following IR. To investigate the mechanism by which PI3KαDN hearts are protected from IR injury, we created a double mutant (PI3KDM) model by crossing p110γ(-/-) (PI3KγKO) with cardiac-specific PI3KαDN mice. The PI3KDM model has morphological and hemodynamic features that are characteristic of both PI3Kγ(-/-) and PI3KαDN mice. Interestingly, when subjected to IR using ex vivo Langendorff perfusion, PI3KDM hearts showed significantly enhanced functional recovery when compared to wildtype (WT) hearts. However, signaling downstream of PI3K through Akt and GSK3β, which has been associated with IR protection, was reduced in PI3KDM hearts. Using ex vivo working heart perfusion, we found no difference in functional recovery after IR between PI3KDM and PI3KαDN; also, glucose oxidation rates were significantly increased in PI3KαDN hearts when compared to WT, and this metabolic shift has been associated with enhanced IR recovery. However, we found that PI3KαDN hearts still had enhanced recovery when perfused exclusively with fatty acids (FA). We then investigated parallel signaling pathways, and found that mitogen-activated protein kinase signaling was increased in PI3KαDN hearts, possibly through the inhibition of negative feedback loops downstream of PI3Kα.

Lysophospholipid receptor activation of RhoA and lipid signaling pathways

The lysophospholipids sphingosine 1-phosphate (S1P) and lysophosphatidic acid (LPA) signal through G-protein coupled receptors (GPCRs) which couple to multiple G-proteins and their effectors. These GPCRs are quite efficacious in coupling to the Gα(12/13) family of G-proteins, which stimulate guanine nucleotide exchange factors (GEFs) for RhoA. Activated RhoA subsequently regulates downstream enzymes that transduce signals which affect the actin cytoskeleton, gene expression, cell proliferation and cell survival. Remarkably many of the enzymes regulated downstream of RhoA either use phospholipids as substrates (e.g. phospholipase D, phospholipase C-epsilon, PTEN, PI3 kinase) or are regulated by phospholipid products (e.g. protein kinase D, Akt). Thus lysophospholipids signal from outside of the cell and control phospholipid signaling processes within the cell that they target. Here we review evidence suggesting an integrative role for RhoA in responding to lysophospholipids upregulated in the pathophysiological environment, and in transducing this signal to cellular responses through effects on phospholipid regulatory or phospholipid regulated enzymes. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.

Characterization of superoxide dismutases in cardiac progenitor cells demonstrates a critical role for manganese superoxide dismutase

Transplantation of cardiac progenitor cells (CPCs) is currently in early clinical testing as a potential therapeutic strategy. Superoxide is increased in the ischemic myocardium and poor survival of cells is one of the major limitations of cell transplantation therapy. Superoxide dismutase (SOD) levels were analyzed in c-kit-positive CPCs isolated from rat myocardium to identify their roles in protection against oxidative stress-induced apoptosis in vitro. CPCs were subjected to oxidative stress using xanthine/xanthine oxidase (XXO) and little apoptosis was detected. CPCs contained significantly higher levels of SOD1 and SOD2 as compared with adult cardiac cell types, both at the protein and activity levels. Both SOD1 and SOD2 were increased by XXO at the mRNA and protein level, suggesting compensatory adaptation. Only knockdown of SOD2 and not SOD1 with siRNA sensitized the cells to XXO-apoptosis, despite only accounting for 10% of total SOD levels. Finally, we found XXO activated Akt within 10 min, and this regulated both SOD2 gene expression and protection against apoptosis. Rat CPCs are resistant to superoxide-induced cell death, primarily through higher levels of SOD2 compared to adult cardiac-derived cells. Exposure to superoxide increases expression of SOD2 in an Akt-dependent manner and regulates CPC survival during oxidative stress.

Optimization of cardiac metabolism in heart failure

The derangement of the cardiac energy substrate metabolism plays a key role in the pathogenesis of heart failure. The utilization of non-carbohydrate substrates, such as fatty acids, is the predominant metabolic pathway in the normal heart, because this provides the highest energy yield per molecule of substrate metabolized. In contrast, glucose becomes an important preferential substrate for metabolism and ATP generation under specific pathological conditions, because it can provide greater efficiency in producing high energy products per oxygen consumed compared to fatty acids. Manipulations that shift energy substrate utilization away from fatty acids toward glucose can improve the cardiac function and slow the progression of heart failure. However, insulin resistance, which is highly prevalent in the heart failure population, impedes this adaptive metabolic shift. Therefore, the acceleration of the glucose metabolism, along with the restoration of insulin sensitivity, would be the ideal metabolic therapy for heart failure. This review discusses the therapeutic potential of modifying substrate utilization to optimize cardiac metabolism in heart failure.

Panax notoginseng saponins inhibit ischemia-induced apoptosis by activating PI3K/Akt pathway in cardiomyocytes

AIM OF THIS STUDY

The panax notoginseng saponins (PNS) have been clinically used for the treatment of cardiovascular diseases and stroke in China. Evidences demonstrated that PNS could protect cardiomyocytes from injury induced by ischemia, but the underlying molecular mechanisms of this protective effect are still unclear. This study was aimed to investigate the protective effect and potential molecular mechanisms of PNS on apoptosis in H9c2 cells in vitro and rat myocardial ischemia injury model in vivo.

MATERIALS AND METHODS

H9c2 cells subjected to serum, glucose and oxygen deprivation (SGOD) were used as in vitro models and SD rats subjected to left anterior descending (LAD) coronary artery ligation were used as in vivo models. The anti-apoptotic effect of PNS was evaluated by Annexin V/PI analysis or TUNEL assay. Mitochondrial membrane potential (Δψm) was detected by JC-1 analysis. The expression of Akt and phosphorylated Akt (p-Akt) were detected by western blot assay.

RESULTS

PNS exhibited anti-apoptotic effect both in H9c2 cells and in ischemic myocardial tissues. However, the effect was blocked in vitro by LY294002, a specific PI3K inhibitor. The anti-apoptotic effect of PNS was mediated by stabilizing Δψm in H9c2 cells. Furthermore the indices of the left ventricular ejection fractions (EF), left ventricular fractional shortening (FS), left ventricular dimensions at end diastole (LVDd) and left ventricular dimensions at end systole (LVDs) suggested that PNS improved rats cardiac function. PNS significantly increased p-Akt both in H9c2 cells and in ischemic myocardial tissues and this effect was also blocked by LY294002 in H9c2 cells.

CONCLUSION

Results of this study suggested that PNS could protect myocardial cells from apoptosis induced by ischemia in both the in vitro and in vivo models through activating PI3K/Akt signaling pathway.

Myocardial AKT: the omnipresent nexus

One of the greatest examples of integrated signal transduction is revealed by examination of effects mediated by AKT kinase in myocardial biology. Positioned at the intersection of multiple afferent and efferent signals, AKT exemplifies a molecular sensing node that coordinates dynamic responses of the cell in literally every aspect of biological responses. The balanced and nuanced nature of homeostatic signaling is particularly essential within the myocardial context, where regulation of survival, energy production, contractility, and response to pathological stress all flow through the nexus of AKT activation or repression. Equally important, the loss of regulated AKT activity is primarily the cause or consequence of pathological conditions leading to remodeling of the heart and eventual decompensation. This review presents an overview compendium of the complex world of myocardial AKT biology gleaned from more than a decade of research. Summarization of the widespread influence that AKT exerts upon myocardial responses leaves no doubt that the participation of AKT in molecular signaling will need to be reckoned with as a seemingly omnipresent regulator of myocardial molecular biological responses.

IGF-1 and atherothrombosis: relevance to pathophysiology and therapy

IGF-1 (insulin-like growth factor-1) plays a unique role in the cell protection of multiple systems, where its fine-tuned signal transduction helps to preserve tissues from hypoxia, ischaemia and oxidative stress, thus mediating functional homoeostatic adjustments. In contrast, its deprivation results in apoptosis and dysfunction. Many prospective epidemiological surveys have associated low IGF-1 levels with late mortality, MI (myocardial infarction), HF (heart failure) and diabetes. Interventional studies suggest that IGF-1 has anti-atherogenic actions, owing to its multifaceted impact on cardiovascular risk factors and diseases. The metabolic ability of IGF-1 in coupling vasodilation with improved function plays a key role in these actions. The endothelial-protective, anti-platelet and anti-thrombotic activities of IGF-1 exert critical effects in preventing both vascular damage and mechanisms that lead to unstable coronary plaques and syndromes. The pro-survival and anti-inflammatory short-term properties of IGF-1 appear to reduce infarct size and improve LV (left ventricular) remodelling after MI. An immune-modulatory ability, which is able to suppress 'friendly fire' and autoreactivity, is a proposed important additional mechanism explaining the anti-thrombotic and anti-remodelling activities of IGF-1. The concern of cancer risk raised by long-term therapy with IGF-1, however, deserves further study. In the present review, we discuss the large body of published evidence and review data on rhIGF-1 (recombinant human IGF-1) administration in cardiovascular disease and diabetes, with a focus on dosage and safety issues. Perhaps the time has come for the regenerative properties of IGF-1 to be assessed as a new pharmacological tool in cardiovascular medicine.

c-Jun N-terminal kinase (JNK-1) confers protection against brief but not extended ischemia during acute myocardial infarction

Brief periods of ischemia do not damage the heart and can actually protect against reperfusion injury caused by extended ischemia. It is not known what causes the transition from protection to irreversible damage as ischemia progresses. c-Jun N-terminal kinase-1 (JNK-1) is a stress-regulated kinase that is activated by reactive oxygen and thought to promote injury during severe acute myocardial infarction. Because some reports suggest that JNK-1 can also be protective, we hypothesized that the function of JNK-1 depends on the metabolic state of the heart at the time of reperfusion, a condition that changes progressively with duration of ischemia. Mice treated with JNK-1 inhibitors or transgenic mice wherein the JNK-1 gene was ablated were subjected to 5 or 20 min of ischemia followed by reperfusion. When JNK-1 was inactive, ischemia of only 5 min duration caused massive apoptosis, infarction, and negative remodeling that was equivalent to or greater than extended ischemia. Conversely, when ischemia was extended JNK-1 inactivation was protective. Mechanisms of the JNK-1 switch in function were investigated in vivo and in cultured cardiac myocytes. In vitro there was a comparable switch in the function of JNK-1 from protective when ATP levels were maintained during hypoxia to injurious when reoxygenation followed glucose and ATP depletion. Both apoptotic and necrotic death pathways were affected and responded reciprocally to JNK-1 inhibitors. JNK-1 differentially regulated Akt phosphorylation of the regulatory sites Ser-473 and Thr-450 and the catalytic Thr-308 site in vivo. The studies define a novel role for JNK-1 as a conditional survival kinase that protects the heart against brief but not protracted ischemia.

Improved rat steatotic and nonsteatotic liver preservation by the addition of epidermal growth factor and insulin-like growth factor-I to University of Wisconsin solution

This study examined the effects of epidermal growth factor (EGF) and insulin-like growth factor-I (IGF-I) supplementation to University of Wisconsin solution (UW) in steatotic and nonsteatotic livers during cold storage. Hepatic injury and function were evaluated in livers preserved for 24 hours at 4 degrees C in UW and in UW with EGF and IGF-I (separately or in combination) and then perfused ex vivo for 2 hours at 37 degrees C. AKT was inhibited pharmacologically. In addition, hepatic injury and survival were evaluated in recipients who underwent transplantation with steatotic and nonsteatotic livers preserved for 6 hours in UW and UW with EGF and IGF-I (separately or in combination). The results, based on isolated perfused liver, indicated that the addition of EGF and IGF-I (separately or in combination) to UW reduced hepatic injury and improved function in both liver types. A combination of EGF and IGF-I resulted in hepatic injury and function parameters in both liver types similar to those obtained by EGF and IGF-I separately. EGF increased IGF-I, and both additives up-regulated AKT in both liver types. This was associated with glycogen synthase kinase-3beta (GSK3(beta)) inhibition in nonsteatotic livers and PPAR gamma overexpression in steatotic livers. When AKT was inhibited, the effects of EGF and IGF-I on GSK3(beta), PPAR gamma, hepatic injury and function disappeared. The benefits of EGF and IGF-I as additives in UW solution were also clearly seen in the liver transplantation model, because the presence of EGF and IGF-I (separately or in combination) in UW solution reduced hepatic injury and improved survival in recipients who underwent transplantation with steatotic and nonsteatotic liver grafts. In conclusion, EGF and IGF-I may constitute new additives to UW solution in steatotic and nonsteatotic liver preservation, whereas a combination of both seems unnecessary.

PHLPP-1 negatively regulates Akt activity and survival in the heart

RATIONALE

The recently discovered PHLPP-1 (PH domain leucine-rich repeat protein phosphatase-1) selectively dephosphorylates Akt at Ser473 and terminates Akt signaling in cancer cells. The regulatory role of PHLPP-1 in the heart has not been considered.

OBJECTIVE

To test the hypothesis that blockade/inhibition of PHLPP-1 could constitute a novel way to enhance Akt signals and provide cardioprotection.

METHODS AND RESULTS

PHLPP-1 is expressed in neonatal rat ventricular myocytes (NRVMs) and in adult mouse ventricular myocytes (AMVMs). PHLPP-1 knockdown by small interfering RNA significantly enhances phosphorylation of Akt (p-Akt) at Ser473, but not at Thr308, in NRVMs stimulated with leukemia inhibitory factor (LIF). The increased phosphorylation is accompanied by greater Akt catalytic activity. PHLPP-1 knockdown enhances LIF-mediated cardioprotection against doxorubicin and also protects cardiomyocytes against H(2)O(2). Direct Akt effects at mitochondria have been implicated in cardioprotection and mitochondria/cytosol fractionation revealed a significant enrichment of PHLPP-1 at mitochondria. The ability of PHLPP-1 knockdown to potentiate LIF-mediated increases in p-Akt at mitochondria and an accompanying increase in mitochondrial hexokinase-II was demonstrated. We generated PHLPP-1 knockout (KO) mice and demonstrate that AMVMs isolated from KO mice show potentiated p-Akt at Ser473 in response to agonists. When isolated perfused hearts are subjected to ischemia/reperfusion, p-Akt in whole-heart homogenates and in the mitochondrial fraction is significantly increased. Additionally in PHLPP-1 KO hearts, the increase in p-Akt elicited by ischemia/reperfusion is potentiated and, concomitantly, infarct size is significantly reduced.

CONCLUSIONS

These results implicate PHLPP-1 as an endogenous negative regulator of Akt activity and cell survival in the heart.

Pretreatment with a traditional Chinese formula, guanxin II, reduces cardiac apoptosis via the Akt survival pathway in rats with myocardial ischemia

Guanxin II (GXII) is a traditional Chinese formula to treat coronary heart disease in China. Previous studies indicate cardioprotection of GXII are related to cardiomyocyte apoptosis. Akt is necessary and sufficient for inhibition of apoptosis in cardiomyocytes. Our aim was to examine whether or not the antiapoptotic mechanisms of GXII are related to the Akt pathway. Male Sprague-Dawley rats were randomly assigned to four groups: GXII administered at 2.5 or 0.5 g raw materials/kg, the vehicle control and sham-operated oral 0.9% NaCl. They were pretreated once a day for 15 consecutive days by gavage. Thirty min after the last administration, the left anterior descending coronary artery was occluded to induce myocardial ischemia except for the sham-operated rats. Compared with rats receiving vehicle, those rats pretreated with GXII at 2.5 g/kg significantly reduced infarct size and decrease apoptosis. Furthermore, GXII (2.5 g/kg) significantly activated Akt kinase, increased the Bcl-2/Bax ratio, inhibited cytochrome c release, reduced caspase-9 activation, and attenuated subsequent caspase-3 activation. GXII at 0.5 g/kg have no noticeable effect on these parameters. Meanwhile, GXII at 2.5 g/kg did not change myocardial blood flow of ischemic zone, indicating a direct action on cardiomyocytes. These results suggest GXII at 2.5 g/kg ensures the survival of myocardium by enhancing the Akt-mediated antiapoptosis pathway. The findings provide new evidence of the effective and safe therapy with GXII for patients with chronic coronary heart disease.

Pharmacological strategies against cold ischemia reperfusion injury

IMPORTANCE OF THE FIELD

Good organ preservation is a determinant of graft outcome after revascularization. The necessity of increasing the quality of organ preservation, as well as of extending cold storage time, has made it necessary to consider the use of pharmacological additives.

AREAS COVERED IN THIS REVIEW

The complex physiopathology of cold-ischemia-reperfusion (I/R) injury--and in particular cell death, mitochondrial injury and endoplasmic reticulum stress--are reviewed. Basic principles of the formulation of the different preservation solutions are discussed.

WHAT THE READER WILL GAIN

Current strategies and new trends in static organ preservation using additives such as trimetazidine, polyethylene glycols, melatonin, trophic factors and endothelin antagonists in solution are presented and discussed. The benefits and mechanisms responsible for enhancing organ protection against I/R injury are also discussed. Graft preservation was substantially improved when additives were added to the preservation solutions.

TAKE HOME MESSAGE

Enrichment of preservation solutions by additives is clinically useful only for short periods. For longer periods of cold ischemia, the use of such additives becomes insufficient because graft function deteriorates as a result of ischemia. In such conditions, the preservation strategy should be changed by the use of machine perfusion in normothermic conditions.

Cardiac regulation by phosphoinositide 3-kinases and PTEN

The diverse effects mediated by PI3K/PTEN (phosphoinositide 3-kinase/phosphatase and tensin homologue deleted on chromosome 10) signalling in the heart clearly support an important biological and pathophysiological role for this signalling cascade. PI3Ks are a family of evolutionarily conserved lipid kinases that mediate many cellular responses to physiological and pathophysiological stimuli. Class I PI3K can be activated by either receptor tyrosine kinase/cytokine receptor activation (class IA) or G-protein-coupled receptors (class IB), leading to the generation of phosphatidyl inositol (3,4,5)P3 and recruitment and activation of Akt/protein kinase B, 3'-phosphoinositide-dependent kinase-1 (PDK1), or monomeric G-proteins, and phosphorylation of a wide range of downstream targets including glycogen synthase kinase 3beta (GSK3beta), mTOR (mammalian target of rapamycin), p70S6 kinase, endothelial nitric oxide synthase, and several anti-apoptotic effectors. Class IA (PI3Kalpha, beta, and delta) and class IB (PI3Kgamma) PI3Ks mediate distinct phenotypes in the heart under negative control by the 3'-lipid phosphatase PTEN, which dephosphorylates PtdIns(3,4,5)P3 to generate PtdIns(4,5)P2. PI3Kalpha, PI3Kgamma, and PTEN are expressed in cardiomyocytes, fibroblasts, endothelial cells, and vascular smooth muscle cells, where they modulate cell survival, hypertrophy, contractility, metabolism, and mechanotransduction. The PI3K/PTEN signalling pathways are involved in a wide variety of diseases including myocardial hypertrophy and contractility, heart failure, and preconditioning. In this review, we discuss the signalling pathways mediated by PI3K class I isoforms and PTEN and their roles in cardiac structure and function.