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Cardiac cells can adapt to pathological stress-induced energy crisis by shifting from fatty acid oxidation to glycolysis. However, the use of glucose-insulin-potassium (GIK) solution in patients undergoing cardiac surgery does not alleviate ischemia/reperfusion (I/R)-induced energy shortage. This indicates that insulin-mediated translocation of glucose transporter-4 (Glut-4) is impaired in ischemic hearts. Indeed, cardiac myocytes contain two intracellular populations of Glut-4: an insulin-dependent non-endosomal pool (also referred to as Glut-4 storage vesicles, GSVs) and an insulin-independent endosomal pool. Tumor susceptibility gene 101 (Tsg101) has been implicated in the endosomal recycling of membrane proteins. In this study, we aimed to examine whether Tsg101 regulated the sorting and re-distribution of Glut-4 to the sarcolemma membrane of cardiomyocytes under basal and ischemic conditions, using gain- and loss-of-function approaches. Forced overexpression of Tsg101 in mouse hearts and isolated cardiomyocytes could promote Glut-4 re-distribution to the sarcolemma, leading to enhanced glucose entry and adenosine triphosphate (ATP) generation in I/R hearts which in turn, attenuation of I/R-induced cardiac dysfunction. Conversely, knockdown of Tsg101 in cardiac myocytes exhibited opposite effects. Mechanistically, we identified that Tsg101 could interact and co-localize with Glut-4 in the sarcolemma membrane of cardiomyocytes. Our findings define Tsg101 as a novel regulator of cardiac Glut-4 trafficking, which may provide a new therapeutic strategy for the treatment of ischemic heart disease.

Background: Spaceflight or microgravity conditions cause myocardial atrophy and dysfunction, contributing to post-flight orthostatic intolerance. However, the underlying mechanisms remain incompletely understood and preventive approaches are limited. This study investigated whether and how losartan, a blocker of angiotensin-II receptor, preserved cardiomyocyte size and prevented myocardial dysfunction during microgravity., Method: Adult male mice were suspended with their tails to simulate microgravity. Echocardiography was performed to assess myocardial function. Heart weight and cardiomyocyte size were measured. NADPH oxidase activation was determined by analyzing membrane translocation of its cytosolic subunits including p47 phox , p67 phox and Rac1. Heart tissues were also assayed for oxidative stress, p47 phox phosphorylation (Ser345), MuRF1 protein levels and angiotensin-II production., Results: Tail-suspension for 28 days increased angiotensin-II production in hearts, decreased cardiomyocyte size and heart weight, and induced myocardial dysfunction. Administration of losartan preserved cardiomyocyte size and heart weight, and prevented myocardial dysfunction in tail-suspended mice. These cardioprotective effects of losartan were associated with inhibition of p47 phox phosphorylation (Ser345), NADPH oxidase and oxidative stress in tail-suspended mouse hearts. Additionally, the NADPH oxidase inhibitor, apocynin, also reduced oxidative stress, preserved cardiomyocyte size and heart weight, and improved myocardial function in tail-suspended mice. Furthermore, losartan but not apocynin attenuated tail-suspension-induced up-regulation of MuRF1 protein in mouse hearts., Conclusions: Administration of losartan preserves cardiomyocyte size and prevents myocardial dysfunction under microgravity by blocking p47 phox phosphorylation and NADPH oxidase activation, and by inhibiting MuRF1 expression. Thus, losartan may be a useful drug to prevent microgravity-induced myocardial abnormalities.

Doxorubicin (DOX) is widely used as a first-line chemotherapeutic drug for various malignancies. However, DOX causes severe cardiotoxicity, which limits its clinical uses. Oxidative stress is one of major contributors to DOX-induced cardiotoxicity. While autophagic flux serves as an important defense mechanism against oxidative stress in cardiomyocytes, recent studies have demonstrated that DOX induces the blockage of autophagic flux, which contributes to DOX cardiotoxicity. The present study investigated whether nicotinamide riboside (NR), a precursor of nicotinamide adenine dinucleotide (NAD) + , prevents DOX cardiotoxicity by improving autophagic flux. We report that administration of NR elevated NAD + levels, and reduced cardiac injury and myocardial dysfunction in DOX-injected mice. These protective effects of NR were recapitulated in cultured cardiomyocytes upon DOX treatment. Mechanistically, NR prevented the blockage of autophagic flux, accumulation of autolysosomes, and oxidative stress in DOX-treated cardiomyocytes, the effects of which were associated with restoration of lysosomal acidification. Furthermore, inhibition of lysosomal acidification or SIRT1 abrogated these protective effects of NR during DOX-induced cardiotoxicity. Collectively, our study shows that NR enhances autolysosome clearance via the NAD + /SIRT1 signaling, thereby preventing DOX-triggered cardiotoxicity., (© 2019 The Author(s). Published by Portland Press Limited on behalf of the Biochemical Society.)

Cardiovascular dysfunction is a common complication among heatstroke patients, but its underlying mechanism is unclear. This study was designed to investigate the role of calpain-2 and its downstream signal pathway in heat stress-induced cardiomyocyte apoptosis and heart dysfunction. In cultured primary mouse neonatal cardiomyocytes (MNCs), heat stress (43°C for 2 hr) induced a heat-shock response, as indicated by upregulated heat-shock protein 27 (HSP27) expression and cellular apoptosis, as indicated by increased caspase-3 activity, DNA fragmentation and decreased cell viability. Meanwhile, heat stress decreased calpain activity, which was accompanied by downregulated calpain-2 expression and increased phosphorylation of p38, extraceIIuIar signaI-reguIated protein kinase (ERK1/2) and c-Jun N-terminaI kinase (JNK). Calpain-2 overexpression abrogated heat stress-induced apoptosis and phosphorylation of p38 and JNK, but not of ERK1/2. Blocking only p38 prevented heat stress-induced apoptosis in MNCs. In cardiac-specific calpain-2 overexpressing transgenic mice, p38 phosphorylation and cardiomyocyte apoptosis were decreased in the heart tissue of heatstroke mice, as revealed by western blot and terminal deoxynucleotidyl transferase dUTP nick end labelling assays, respectively. M-mode echocardiography also demonstrated that calpain-2 overexpression significantly improved heatstroke-induced decreases in ventricular end-diastolic volume and cardiac output. In conclusion, our study suggests that heat stress reduces calpain-2 expression, which then activates p38, leading to cardiomyocyte apoptosis and heart dysfunction., (© 2018 Wiley Periodicals, Inc.)

We recently reported that doxorubicin decreased the expression of calpain-1/2, while inhibition of calpain activity promoted doxorubicin-induced cardiac injury in mice. In this study, we investigated whether and how elevation of calpain-2 could affect doxorubicin-triggered cardiac injury. Transgenic mice with inducible cardiomyocyte-specific expression of calpain-2 were generated. An acute cardiotoxicity was induced in both transgenic mice and their relevant wild-type littermates by injection of a single dose of doxorubicin (20 mg/kg) and cardiac injury was analyzed 5 days after doxorubicin injection. Cardiomyocyte-specific up-regulation of calpain-2 did not induce any adverse cardiac phenotypes under physiological conditions by age 3 months, but significantly reduced myocardial injury and improved myocardial function in doxorubicin-treated mice. Cardiac protection of calpain-2 up-regulation was also observed in a mouse model of chronic doxorubicin cardiotoxicity. Up-regulation of calpain-2 increased the protein levels of mitogen activated protein kinase phosphatase-1 (MKP-1) in cultured mouse cardiomyocytes and heart tissues. Over-expression of MKP-1 prevented, whereas knockdown of MKP-1 augmented doxorubicin-induced apoptosis in cultured cardiomyocytes. Moreover, knockdown of MKP-1 offset calpain-2-elicited protective effects against doxorubicin-induced injury in cultured cardiomyocytes. Mechanistically, up-regulation of calpain-2 reduced the protein levels of phosphatase and tensin homolog and consequently promoted Akt activation, leading to increased MKP-1 protein steady-state levels by inhibiting its degradation. Collectively, this study reveals a new role of calpain-2 in promoting MKP-1 expression via phosphatase and tensin homolog/Akt signaling. This study also suggests that calpain-2/MKP-1 signaling may represent new therapeutic targets for doxorubicin-induced cardiac injury.

Decreased heat shock protein (Hsp) expression in type 1 and type 2 diabetes has been implicated as a primary factor contributing to diabetes-induced organ damage. We recently showed that diabetic cardiomyocytes could release detrimental exosomes, which contain lower levels of Hsp20 than normal ones. To investigate whether such detrimental exosomes could be modified in cardiomyocytes by raising Hsp20 levels to become protective, we used a transgenic (TG) mouse model with cardiac-specific overexpression of Hsp20. TG and control wild-type (WT) mice were injected with streptozotocin (STZ) to induce diabetes. We observed that overexpression of Hsp20 significantly attenuated STZ-caused cardiac dysfunction, hypertrophy, apoptosis, fibrosis, and microvascular rarefaction. Moreover, Hsp20-TG cardiomyocytes exhibited an increased generation/secretion of exosomes by direct interaction of Hsp20 with Tsg101. Of importance, exosomes derived from TG cardiomyocytes encased higher levels of Hsp20, p-Akt, survivin, and SOD1 than WT exosomes and protected against in vitro hyperglycemia-triggered cell death, as well as in vivo STZ-induced cardiac adverse remodeling. Last, blockade of exosome generation by GW4869 remarkably offset Hsp20-mediated cardioprotection in diabetic mice. Our results indicate that elevation of Hsp20 in cardiomyocytes can offer protection in diabetic hearts through the release of instrumental exosomes. Thus, Hsp20-engineered exosomes might be a novel therapeutic agent for diabetic cardiomyopathy., (© 2016 by the American Diabetes Association.)

Calpain plays a critical role in cardiomyopathic changes in type 1 diabetes (T1D). This study investigated how calpain regulates mitochondrial reactive oxygen species (ROS) generation in the development of diabetic cardiomyopathy. T1D was induced in transgenic mice overexpressing calpastatin, in mice with cardiomyocyte-specific capn4 deletion, or in their wild-type littermates by injection of streptozotocin. Calpain-1 protein and activity in mitochondria were elevated in diabetic mouse hearts. The increased mitochondrial calpain-1 was associated with an increase in mitochondrial ROS generation and oxidative damage and a reduction in ATP synthase-α (ATP5A1) protein and ATP synthase activity. Genetic inhibition of calpain or upregulation of ATP5A1 increased ATP5A1 and ATP synthase activity, prevented mitochondrial ROS generation and oxidative damage, and reduced cardiomyopathic changes in diabetic mice. High glucose concentration induced ATP synthase disruption, mitochondrial superoxide generation, and cell death in cardiomyocytes, all of which were prevented by overexpression of mitochondria-targeted calpastatin or ATP5A1. Moreover, upregulation of calpain-1 specifically in mitochondria induced the cleavage of ATP5A1, superoxide generation, and apoptosis in cardiomyocytes. In summary, calpain-1 accumulation in mitochondria disrupts ATP synthase and induces ROS generation, which promotes diabetic cardiomyopathy. These findings suggest a novel mechanism for and may have significant implications in diabetic cardiac complications., (© 2016 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.)

Background: Our recent study has demonstrated that inhibition of calpain by transgenic overexpression of calpastatin reduces myocardial proinflammatory response and dysfunction in endotoxemia. However, the underlying mechanisms remain to be determined. In this study, we used cardiomyocyte-specific capn4 knockout mice to investigate whether and how calpain disrupts ATP synthase and induces mitochondrial superoxide generation during endotoxemia., Methods and Results: Cardiomyocyte-specific capn4 knockout mice and their wild-type littermates were injected with lipopolysaccharides. Four hours later, calpain-1 protein and activity were increased in mitochondria of endotoxemic mouse hearts. Mitochondrial calpain-1 colocalized with and cleaved ATP synthase-α (ATP5A1), leading to ATP synthase disruption and a concomitant increase in mitochondrial reactive oxygen species generation during lipopolysaccharide stimulation. Deletion of capn4 or upregulation of ATP5A1 increased ATP synthase activity, prevented mitochondrial reactive oxygen species generation, and reduced proinflammatory response and myocardial dysfunction in endotoxemic mice. In cultured cardiomyocytes, lipopolysaccharide induced mitochondrial superoxide generation that was prevented by overexpression of mitochondria-targeted calpastatin or ATP5A1. Upregulation of calpain-1 specifically in mitochondria sufficiently induced superoxide generation and proinflammatory response, both of which were attenuated by ATP5A1 overexpression or mitochondria-targeted superoxide dismutase mimetics., Conclusions: Cardiomyocyte-specific capn4 knockout protects the heart against lipopolysaccharide-induced injury in endotoxemic mice. Lipopolysaccharides induce calpain-1 accumulation in mitochondria. Mitochondrial calpain-1 disrupts ATP synthase, leading to mitochondrial reactive oxygen species generation, which promotes proinflammatory response and myocardial dysfunction during endotoxemia. These findings uncover a novel mechanism by which calpain mediates myocardial dysfunction in sepsis., (© 2015 American Heart Association, Inc.)

Junctophilin-2 (JP2), a membrane-binding protein that provides a structural bridge between the plasmalemma and sarcoplasmic reticulum, is essential for precise Ca(2+)-induced Ca(2+) release during excitation-contraction coupling in cardiomyocytes. In animal and human failing hearts, expression of JP2 is decreased markedly, but the molecular mechanisms underlying JP2 down-regulation remain incompletely defined. In mouse hearts, ischemia/reperfusion injury resulted in acute JP2 down-regulation, which was attenuated by pretreatment with the calpain inhibitor MDL-28170 or by transgenic overexpression of calpastatin, an endogenous calpain inhibitor. Using a combination of computational analysis to predict calpain cleavage sites and in vitro calpain proteolysis reactions, we identified four putative calpain cleavage sites within JP2 with three N-terminal and one C-terminal cleavage sites. Mutagenesis defined the C-terminal region of JP2 as the predominant calpain cleavage site. Exogenous expression of putative JP2 cleavage fragments was not sufficient to rescue Ca(2+) handling in JP2-deficient cardiomyocytes, indicating that cleaved JP2 is non-functional for normal Ca(2+)-induced Ca(2+) release. These data provide new molecular insights into the posttranslational regulatory mechanisms of JP2 in cardiac diseases., (© 2015 by The American Society for Biochemistry and Molecular Biology, Inc.)

Both calpain activation and endoplasmic reticulum (ER) stress are implicated in ischemic heart injury. However, the role of calpain in ER stress remains largely elusive. This study investigated whether calpain activation causes ER stress, thereby mediating cardiomyocyte apoptosis in an in vitro model of hypoxia/re-oxygenation (H/R). In neonatal mouse cardiomyocytes and rat cardiomyocyte-like H9c2 cells, up-regulation of calpain-1 sufficiently induced ER stress, c-Jun N-terminal protein kinase1/2 (JNK1/2) activation and apoptosis. Inhibition of ER stress or JNK1/2 prevented apoptosis induced by calpain-1. In an in vitro model of H/R-induced injury in cardiomyocytes, H/R was induced by a 24-hour hypoxia followed by a 24-hour re-oxygenation. H/R activated calpain-1, induced ER stress and JNK1/2 activation, and triggered apoptosis. Inhibition of calpain and ER stress blocked JNK1/2 activation and prevented H/R-induced apoptosis. Furthermore, blockade of JNK1/2 signaling inhibited apoptosis following H/R. The role of calpain in ER stress was also demonstrated in an in vivo model of ischemia/reperfusion using transgenic mice over-expressing calpastatin. In summary, calpain-1 induces ER stress and JNK1/2 activation, thereby mediating apoptosis in cardiomyocytes. Accordingly, inhibition of calpain prevents ER stress, JNK1/2 activation and apoptosis in H/R-induced cardiomyocytes. Thus, ER stress/JNK1/2 activation may represent an important mechanism linking calpain-1 to ischemic injury., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Exosomes, nano-vesicles naturally released from living cells, have been well recognized to play critical roles in mediating cell-to-cell communication. Given that diabetic hearts exhibit insufficient angiogenesis, it is significant to test whether diabetic cardiomyocyte-derived exosomes possess any capacity in regulating angiogenesis. In this study, we first observed that both proliferation and migration of mouse cardiac endothelial cells (MCECs) were inhibited when co-cultured with cardiomyocytes isolated from adult Goto-Kakizaki (GK) rats, a commonly used animal model of type 2 diabetes. However, GK-myocyte-mediated anti-angiogenic effects were negated upon addition of GW4869, an inhibitor of exosome formation/release, into the co-cultures. Next, exosomes were purified from the myocyte culture supernatants by differential centrifugation. While exosomes derived from GK myocytes (GK-exosomes) displayed similar size and molecular markers (CD63 and CD81) to those originated from the control Wistar rat myocytes (WT-exosomes), their regulatory role in angiogenesis is opposite. We observed that the MCEC proliferation, migration and tube-like formation were inhibited by GK-exosomes, but were promoted by WT-exosomes. Mechanistically, we found that GK-exosomes encapsulated higher levels of miR-320 and lower levels of miR-126 compared to WT-exosomes. Furthermore, GK-exosomes were effectively taken up by MCECs and delivered miR-320. In addition, transportation of miR-320 from myocytes to MCECs could be blocked by GW4869. Importantly, the exosomal miR-320 functionally down-regulated its target genes (IGF-1, Hsp20 and Ets2) in recipient MCECs, and overexpression of miR-320 inhibited MCEC migration and tube formation. GK exosome-mediated inhibitory effects on angiogenesis were removed by knockdown of miR-320. Together, these data indicate that cardiomyocytes exert an anti-angiogenic function in type 2 diabetic rats through exosomal transfer of miR-320 into endothelial cells. Thus, our study provides a novel mechanism underlying diabetes mellitus-induced myocardial vascular deficiency which may be caused by secretion of anti-angiogenic exosomes from cardiomyocyes., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Aims: Doxorubicin causes damage to the heart, which may present as cardiomyopathy. However, the mechanisms by which doxorubicin induces cardiotoxicity remain not fully understood and no effective prevention for doxorubicin cardiomyopathy is available. Calpains, a family of calcium-dependent thiol-proteases, have been implicated in cardiovascular diseases. Their activities are tightly controlled by calpastatin. This study employed transgenic mice over-expressing calpastatin to investigate the role of calpain in doxorubicin-induced cardiotoxicity., Methods and Results: Doxorubicin treatment decreased calpain activities in cultured neonatal mouse cardiomyocytes and in vivo mouse hearts, which correlated with down-regulation of calpain-1 and calpain-2 proteins. Over-expression of calpastatin or incubation with pharmacological calpain inhibitors enhanced apoptosis in neonatal and adult cardiomyocytes induced by doxorubicin. In contrast, over-expression of calpain-2 but not calpain-1 attenuated doxorubicin-induced apoptosis in cardiomyocytes. The pro-apoptotic effects of calpain inhibition were associated with down-regulation of protein kinase B (AKT) protein and mRNA expression, and a concomitant reduction in glycogen synthase kinase-3beta (GSK-3β) phosphorylation (Ser9) in doxorubicin-treated cardiomyocytes. Blocking AKT further increased doxorubicin-induced cardiac injuries, suggesting the effects of calpain inhibition may be mediated by inactivating the AKT signalling. In an in vivo model of doxorubicin-induced cardiotoxicity, over-expression of calpastatin exacerbated myocardial dysfunction as assessed by echocardiography and haemodynamic measurement in transgenic mice 5 days after doxorubicin injection. The 5-day mortality was higher in transgenic mice (29.16%) compared with their wild-type littermates (8%) after doxorubicin treatment., Conclusion: Over-expression of calpastatin enhances doxorubicin-induced cardiac injuries through calpain inhibition and thus, calpains may protect cardiomyocytes against doxorubicin-induced cardiotoxicity.

Aims: Doxorubicin causes damage to the heart, often leading to irreversible cardiomyopathy, which is fatal. Reactive oxygen species (ROS) or oxidative stress is involved in cardiomyocyte death, contributing to doxorubicin-induced cardiotoxicity. This study investigated the role of Rac1, an important subunit of NADPH oxidase, in doxorubicin-induced cardiotoxicity and the underlying mechanisms., Methods and Results: In a mouse model of acute doxorubicin-induced cardiotoxicity, cardiomyocyte-specific deletion of Rac1 inhibited NADPH oxidase activation and ROS production, prevented cardiac cell death, and improved myocardial function in Rac1 knockout mice. Therapeutic administration of the specific Rac1 inhibitor NSC23766 achieved similar cardio-protective effects in doxorubicin-stimulated mice. In rat cardiomyoblasts (H9c2 cells) and cultured neonatal mouse cardiomyocytes, Rac1 inhibition attenuated apoptosis as evidenced by decreases in caspase-3 activity and DNA fragmentation in response to doxorubicin, which correlated with a reduction in ROS production and down-regulation of p53 acetylation and histone H2AX phosphorylation. In contrast, overexpression of Rac1 enhanced apoptosis. Doxorubicin also inhibited the activity of classical histone deacetylases (HDAC), which was preserved by Rac1 inhibition and further decreased by Rac1 overexpression. Interestingly, scavenging ROS mitigated apoptosis but did not change HDAC activity and p53 acetylation stimulated by doxorubicin, suggesting both ROS-dependent and -independent pathways are involved in Rac1-mediated cardiotoxicity. Furthermore, the HDAC inhibitor trichostatin A enhanced apoptosis, p53 acetylation and H2AX phosphorylation in doxorubicin-treated cardiomyocytes., Conclusions: Rac1 signalling contributes to doxorubicin-induced cardiotoxicity through both a ROS-dependent mechanism and ROS-independent HDAC/p53 signalling in cardiomyocytes. Thus, inhibition of Rac1 may be a useful therapy for doxorubicin-induced cardiotoxicity.

Calpain has been implicated in acute myocardial injury after myocardial infarction (MI). However, the causal relationship between calpain and post-MI myocardial remodeling has not been fully understood. This study examined whether deletion of Capn4, essential for calpain-1 and calpain-2 activities, reduces myocardial remodeling and dysfunction following MI, and if yes, whether these effects of Capn4 deletion are associated with NF-κB signaling and inflammatory responses in the MI heart. A novel mouse model with cardiomyocyte-specific deletion of Capn4 (Capn4-ko) was employed. MI was induced by left coronary artery ligation. Deficiency of Capn4 dramatically reduced the protein levels and activities of calpain-1 and calpain-2 in the Capn4-ko heart. In vivo cardiac function was relatively improved in Capn4-ko mice at 7 and 30 days after MI when compared with their wild-type littermates. Deletion of Capn4 reduced apoptosis, limited infarct expansion, prevented left ventricle dilation, and reduced mortality in Capn4-ko mice. Furthermore, cardiomyocyte cross-sectional areas and myocardial collagen deposition were significantly attenuated in Capn4-ko mice, which were accompanied by down-regulation of hypertrophic genes and profibrotic genes. These effects of Capn4 knock-out correlated with restoration of IκB protein and inhibition of NF-κB activation, leading to suppression of proinflammatory cytokine expression and inflammatory cell infiltration in the Capn4-ko heart after MI. In conclusion, deficiency of Capn4 reduces adverse myocardial remodeling and myocardial dysfunction after MI. These effects of Capn4 deletion may be mediated through prevention of IκB degradation and NF-κB activation, resulting in inhibition of inflammatory responses.

Aims: Free fatty acids induce apoptosis in cardiomyocytes, which is implicated in lipotoxic cardiomyopathy. However, the underlying mechanisms remain not fully understood. MicroRNAs (miRNAs) are non-coding small RNAs that control gene expression at the post-transcriptional level. Dysregulated miRNAs have been shown to be involved in heart diseases. This study was to examine whether miR-195 regulates palmitate-induced cardiomyocyte apoptosis by targeting Sirt1, a known anti-apoptotic protein., Methods and Results: In cultured neonatal mouse cardiomyocytes, palmitate up-regulated miR-195 expression, increased reactive oxygen species (ROS) production, and induced apoptosis as determined by up-regulation of caspase-3 activity and DNA fragmentation. Inhibition of miR-195 decreased ROS production and apoptosis in palmitate-stimulated cardiomyocytes. In contrast, a miR-195 mimic enhanced palmitate-induced ROS production and apoptosis. The induction of miR-195 correlated with a reduction in Sirt1 and Bcl-2. We further showed that miR-195 targeted and inhibited Sirt1 expression through two target sites located in the 3' un-translational region of Sirt1 mRNA. In concordance, inhibition of miR-195 increased Sirt1 protein in cardiomyocytes whereas the miR-195 mimic reduced it. Activation of Sirt1 or overexpression of Bcl-2 inhibited palmitate-induced apoptosis. On the other hand, inhibition of Sirt1 enhanced apoptosis. The inhibitory effect of Sirt1 on apoptosis was associated with a reduction in ROS., Conclusions: This study demonstrates a pro-apoptotic role of miR-195 in cardiomyocytes and identifies Sirt1 as a direct target of miR-195. The effect of miR-195 on apoptosis is mediated through down-regulation of Sirt1 and Bcl-2 and ROS production. Thus, miR-195 may be a new therapeutic target for lipotoxic cardiomyopathy.

Lipopolysaccharides (LPS) induce tumor necrosis factor-alpha (TNF-alpha) production in cardiomyocytes, which contributes to myocardial depression during sepsis. However, the underlying mechanisms remain not fully understood. This study was undertaken to investigate the contribution of histone deacetylase (HDAC) to TNF-alpha expression in cardiomyocytes and the signaling mechanism of LPS-induced HDAC activation. Here, we show for the first time that LPS increases HDAC activity and that inhibition of HDAC decreases LPS-stimulated TNF-alpha expression via the accumulation of NF-kappaB/p65 at the TNF-alpha promoter in cardiomyocytes. Using a positive screen, we have further identified HDAC3 as a specific member of the HDAC family able to regulate TNF-alpha production. Furthermore, our data reveal that LPS-induced HDAC activity is mediated through reactive oxygen species from mitochondria and c-Src signaling. In summary, this study demonstrates a novel signaling mechanism by which LPS via mitochondrial reactive oxygen species/c-Src/HDAC3 pathways mediate TNF-alpha expression in cardiomyocytes.

Aims: Cardiomyocyte apoptosis contributes to cardiac complications of diabetes. The aim of this study was to investigate the role of calpain in cardiomyocyte apoptosis induced by hyperglycaemia., Methods and Results: In cultured adult rat ventricular cardiomyocytes, high glucose (33 mM) increased calpain activity and induced apoptosis, concomitant with the impairment of Na+/K+ ATPase activity. These effects of high glucose on cardiomyocytes were abolished by various pharmacological calpain inhibitors, knockdown of calpain-1 but not calpain-2 using siRNA, or over-expression of calpastatin, a specific endogenous calpain inhibitor. The effect of calpain inhibition on cardiomyocyte apoptosis was abrogated by ouabain, a selective inhibitor of Na+/K+ ATPase. Furthermore, blocking gp91(phox)-NADPH oxidase activation, L-type calcium channels, or ryanodine receptors prevented calpain activation and apoptosis in high glucose-stimulated cardiomyocytes. In a mouse model of streptozotocin-induced diabetes, administration of different calpain inhibitors blocked calpain activation, increased the Na+/K+ ATPase activity, and decreased apoptosis in the heart., Conclusion: Calpain-1 activation induces apoptosis through down-regulation of the Na+/K+ ATPase activity in high glucose-stimulated cardiomyocytes and in vivo hyperglycaemic hearts. High glucose-induced calpain-1 activation is mediated through the NADPH oxidase-dependent pathway and associated with activation of L-type calcium channels and ryanodine receptors. Our data suggest that calpain activation may be important in the development of diabetic cardiomyopathy and thus may represent a potential therapeutic target for diabetic heart diseases.

Objective: Hyperglycemia induces reactive oxygen species (ROS) and apoptosis in cardiomyocytes, which contributes to diabetic cardiomyopathy. The present study was to investigate the role of Rac1 in ROS production and cardiomyocyte apoptosis during hyperglycemia., Research Design and Methods: Mice with cardiomyocyte-specific Rac1 knockout (Rac1-ko) were generated. Hyperglycemia was induced in Rac1-ko mice and their wild-type littermates by injection of streptozotocin (STZ). In cultured adult rat cardiomyocytes, apoptosis was induced by high glucose., Results: The results showed a mouse model of STZ-induced diabetes, 7 days of hyperglycemia-upregulated Rac1 and NADPH oxidase activation, elevated ROS production, and induced apoptosis in the heart. These effects of hyperglycemia were significantly decreased in Rac1-ko mice or wild-type mice treated with apocynin. Interestingly, deficiency of Rac1 or apocynin treatment significantly reduced hyperglycemia-induced mitochondrial ROS production in the heart. Deficiency of Rac1 also attenuated myocardial dysfunction after 2 months of STZ injection. In cultured cardiomyocytes, high glucose upregulated Rac1 and NADPH oxidase activity and induced apoptotic cell death, which were blocked by overexpression of a dominant negative mutant of Rac1, knockdown of gp91(phox) or p47(phox), or NADPH oxidase inhibitor. In type 2 diabetic db/db mice, administration of Rac1 inhibitor, NSC23766, significantly inhibited NADPH oxidase activity and apoptosis and slightly improved myocardial function., Conclusions: Rac1 is pivotal in hyperglycemia-induced apoptosis in cardiomyocytes. The role of Rac1 is mediated through NADPH oxidase activation and associated with mitochondrial ROS generation. Our study suggests that Rac1 may serve as a potential therapeutic target for cardiac complications of diabetes.

Aims: Myocardial tumour necrosis factor-alpha (TNF-alpha) production plays an important role in cardiac dysfunction during sepsis. The aim of this study was to investigate the role of c-Jun NH2-terminal kinases (JNK) signalling in cardiomyocyte TNF-alpha expression during lipopolysaccharide (LPS) stimulation and myocardial function in endotoxaemic mice., Methods and Results: In cultured neonatal mouse cardiomyocytes, deficiency of JNK1 or selective inhibition of JNK1 signalling by over-expression of a dominant negative mutant of JNK1 enhanced LPS-induced TNF-alpha expression, which was associated with elevations in phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein kinase (MAPK). At the organ level, LPS-induced TNF-alpha expression was significantly increased in JNK1(-/-) compared with wild-type hearts. JNK1 activation by LPS also induced immediate c-fos expression in cardiomyocytes, which was blocked by inhibition of JNK1 signalling. The role of c-fos expression in LPS-induced TNF-alpha expression was investigated in both cultured c-fos(-/-) cardiomyocytes and isolated c-fos(-/-) hearts. Deficiency of c-fos significantly enhanced LPS-induced TNF-alpha expression in cardiomyocytes and isolated hearts. Over-expression of c-fos decreased TNF-alpha expression in LPS-stimulated cardiomyocytes, which was associated with a decrease in phosphorylation of ERK1/2 and p38. In mice with endotoxaemia, deficiency of either JNK1 or c-fos further decreased cardiac function compared with corresponding wild-type controls., Conclusion: JNK1/c-fos inhibits ERK1/2 and p38 MAPK signalling, leading to decreased cardiomyocyte TNF-alpha expression and improvements in cardiac function during endotoxaemia.

Taurine has been shown to prevent cardiomyocyte apoptosis. This study investigated the effects of taurine on NADPH oxidase and calpain activation in mediating apoptosis in cardiomyocytes. Apoptosis was induced by norepinephrine (NE) in cultured adult rat ventricular cardiomyocytes. NE (5 microM) increased NADPH oxidase activation and reactive oxygen species (ROS) production and induced apoptosis. These effects of NE on cardiomyocytes were diminished by taurine (0.5 mg/kg) but not beta-alanine. Inhibition of gp91(phox)-NADPH oxidase or ROS production protected cardiomyocytes from apoptosis. NE also induced calpain-1 activation in cardiomyocytes. This effect of NE on calpain was abrogated by gp91(phox)-NADPH oxidase inhibition or ROS scavengers and was mimicked by H(2)O(2) (25 microM) in cardiomyocytes. Pharmacological inhibitors of calpain or overexpression of calpastatin, a specific calpain inhibitor, blocked calpain activation and prevented cardiomyocyte apoptosis during NE stimulation. Furthermore, taurine treatment inhibited NE- or H(2)O(2)-induced calpain activation in cardiomyocytes. In conclusion, NADPH oxidase induces calpain activation, leading to apoptosis in NE-induced cardiomyocytes. Taurine inhibits NADPH oxidase and calpain activation. Thus, inhibition of NADPH oxidase-mediated calpain activation may be an important mechanism for taurine's antiapoptotic action in cardiomyocytes.

This study was to investigate the role of glycogen synthase kinase-3beta (GSK-3beta) in cardiomyocyte tumor necrosis factor-alpha (TNF-alpha) expression induced by lipopolysaccharide (LPS). In cultured neonatal mouse cardiomyocytes, LPS induced TNF-alpha expression and increased GSK-3beta activation. Inhibition of GSK-3beta by SB216763 or by over-expression of a dominant negative mutant of GSK-3beta significantly enhanced TNF-alpha expression in LPS-stimulated cardiomyocytes, in association with an increase in p65 phosphorylation. In contrast, over-expression of GSK-3beta by adenoviral vectors containing wild-type GSK-3beta or a constitutively active GSK-3beta attenuated TNF-alpha expression induced by LPS. Further evidence to support the inhibitory role of GSK-3beta in TNF-alpha expression is that protein kinase B (Akt) signaling, an upstream inhibitor of GSK-3beta, promotes TNF-alpha expression in LPS-stimulated cardiomyocytes and this action of Akt signaling can be mimicked by GSK-3beta inactivation. Our study demonstrates that GSK-3beta plays an inhibitory role in cardiomyocyte TNF-alpha expression during LPS stimulation, and it may be a potential therapeutic target for sepsis.

Aims: Lipopolysaccharide (LPS) induces tumor necrosis factor-alpha (TNF-alpha) expression in cardiomyocytes, which contributes to myocardial dysfunction during sepsis. The purpose of this study was to investigate the role of phosphatidylinositol (PI) phospholipase Cgamma1 (PLCgamma1) in cardiac TNF-alpha expression, and myocardial dysfunction during endotoxemia., Methods and Results: In cultured mouse neonatal cardiomyocytes, LPS increased PLCgamma1 phosphorylation. Knockdown of PLCgamma1 with specific siRNA or inhibition of PLCgamma1 with U73122 attenuated TNF-alpha expression induced by LPS. This action of PLCgamma1 was mediated through inositol-1,4,5-trisphosphate (IP3)/IP3 receptor (IP3R) pathways since blocking either IP3 or IP3R decreased LPS-induced TNF-alpha expression. In contrast, neither diacylglycerol agonist nor antagonist had any evident effect on LPS-induced TNF-alpha expression in cardiomyocytes. To investigate the role of PLCgamma1 in endotoxemia in vivo, wild-type and heterozygous PLCgamma1 knockout (PLCgamma1(+/-)) mice were pre-treated with either U73122, or its inactive analog U73343, or vehicle for 15 min, followed by LPS for 4 h. Inhibition of PLCgamma1 by U73122 or by heterozygous deletion of the PLCgamma1 gene decreased cardiac TNF-alpha expression. More importantly, LPS-induced myocardial dysfunction was also attenuated in PLCgamma1(+/-) mice or by U73122 treatment., Conclusion: PLCgamma1 signalling induces cardiac TNF-alpha expression and myocardial dysfunction during LPS stimulation. The action of PLCgamma1 on TNF-alpha expression is mediated through IP3/IP3R pathways. The present results suggest that PLCgamma1 may be a potential therapeutic target for myocardial dysfunction in sepsis.

Lipopolysaccharide (LPS) induces cyclooxygenase-2 (COX-2) expression in cardiomyocytes, which plays a role in myocardial depression during endotoxemia. The purpose of this study was to investigate the role of phosphatidylinositol (PI)-phospholipase Cgamma1 (PLCgamma1) in cardiac COX-2 expression in vitro and in vivo. In cultured mouse neonatal cardiomyocytes, LPS increased PLCgamma1 phosphorylation and COX-2 expression. Knockdown of PLCgamma1 with specific siRNA or inhibition of PI-PLC with U73122 attenuated COX-2 mRNA and protein expression induced by LPS (1 microg/ml). PLCgamma1 activation by LPS also increased ERK1/2 MAPK phosphorylation, and inhibition of ERK1/2 MAPK blocked the effect of PLCgamma1 on COX-2 expression. Furthermore, activation of PLCgamma1 is a consequence of the Src family activation since inhibition of Src abrogated whereas over-expression of Src enhanced PLCgamma1 phosphorylation and COX-2 expression in LPS-stimulated cardiomyocytes. To investigate the role of PLCgamma1 in endotoxemia, wild-type and PLCgamma1(+/-) adult mice were pre-treated with U73122, or its inactive analog, U73343 (9 mg/kg, i.p.), or vehicle for 15 min followed by LPS (4 mg/kg, i.p.) for 4 h. U73122 or heterozygous deletion of PLCgamma1 decreased cardiac COX-2 expression. The phosphorylation of ERK1/2 MAPK induced by LPS was also attenuated in U73122- or PLCgamma1(+/-) compared to U73343-treated or wild-type littermate hearts, respectively. In conclusion, our study suggests that PLCgamma1 signalling represents a novel pathway regulating cardiac COX-2 expression during LPS stimulation. The Src family is responsible for PLCgamma1 activation, which signals the ERK1/2 MAPK pathway, resulting in COX-2 production in LPS-stimulated cardiomyocytes.

Objective: Neuronal nitric oxide synthase (nNOS) has been shown to regulate intracellular calcium in cardiomyocytes. Calcium in turn modulates extracellular signal-related kinase (ERK) signaling, which is important in tumor necrosis factor-alpha (TNF-alpha) expression during lipopolysaccharide (LPS) stimulation. However, the role of nNOS in LPS-induced TNF-alpha expression is not known. We hypothesized that nNOS suppresses LPS-induced TNF-alpha expression by inhibiting the calcium/ERK signaling pathway., Methods and Results: Cultured neonatal mouse cardiomyocytes were challenged with LPS for 4 h. While there was no change in the basal Ca(2+) concentration, LPS increased peak Ca(2+) levels. LPS stimulation increased TNF-alpha mRNA and protein levels in wild-type cells however, the responses were enhanced in nNOS(-/-) cardiomyocytes. Treatment with an antisense oligonucleotide against nNOS also significantly enhanced TNF-alpha expression during LPS stimulation. Furthermore, LPS-induced ERK phosphorylation was significantly increased in the nNOS(-/-) compared to wild-type cardiomyocytes. The enhanced TNF-alpha expression in nNOS(-/-) cardiomyocytes was abrogated by an L-type calcium channel blocker verapamil or ERK1 siRNA. Finally, myocardial ERK phosphorylation and TNF-alpha expression were increased while cardiac function was decreased in endotoxemia in nNOS(-/-) compared to wild-type mice., Conclusions: nNOS inhibits LPS-induced TNF-alpha expression in cardiomyocytes and improves cardiac function in endotoxemia. The inhibitory role of nNOS is mediated by a reduction in L-type calcium channel-dependent ERK signaling in cardiomyocytes.

Cyclooxygenase-2 (COX-2) is induced in response to lipopolysaccharide (LPS). However, the signaling mechanisms of LPS-induced COX-2 expression in cardiomyocytes are not well understood. The aim of this study was to investigate the role of gp91(phox)-containing NADH oxidase signaling pathway in LPS-induced COX-2 expression in cardiomyocytes. Cultured neonatal mouse cardiomyocytes showed basal COX-2 expression and PGE2 production. In response to LPS, COX-2 expression and PGE2 production increased by two- to four-fold, which were completely blocked by a selective COX-2 inhibitor NS398. LPS also increased NADH oxidase (gp91(phox) and p47(phox) subunits) expression and superoxide generation. Deficiency of gp91(phox) or suppression of p22(phox) expression decreased NADH oxidase activity and down-regulated COX-2 expression and PGE2 production stimulated by LPS. Pharmacological inhibitors of NADH oxidase prevented LPS-induced COX-2 expression and PGE2 production. The effect of NADH oxidase was mediated through MAPK activation, since inhibition of NADH-oxidase activity prevented phosphorylation of ERK1/2, p38, and JNK1/2, as well as selective inhibition of each subfamily of MAPK by siRNAs and a dominant negative mutant of JNK1 decreased COX-2 expression and completely abrogated PGE2 production in response to LPS. Furthermore, LPS-induced NF-kappaB activation was decreased by inhibition of NADH oxidase, ERK1/2 or JNK1/2 activation, suggesting that LPS increases NF-kappaB activity and COX-2 expression via NADH oxidase-dependent activation of ERK1/2 and JNK1/2. In conclusion, NADH oxidase signaling represents a novel pathway leading to COX-2 expression via MAPK/NF-kappaB-dependent mechanisms in cardiomyocytes during LPS stimulation. Our study suggests that gp91(phox)-containing NADH oxidase is a potential therapeutic target of sepsis.