LPS-stimulated Cardiomyocytes Research Articles

Pretreatment with interleukin-15 attenuates inflammation and apoptosis by inhibiting NF-κB signaling in sepsis-induced myocardial dysfunction.

Sepsis-induced myocardial dysfunction (SIMD) is associated with poor prognosis and increased mortality in patients with sepsis. Cytokines are important regulators of both the initiation and progression of sepsis. Interleukin-15 (IL-15), a pro-inflammatory cytokine, has been linked to protective effects against myocardial infarction and myocarditis. However, the role of IL-15 in SIMD remains unclear. We established a mouse model of SIMD via cecal ligation puncture (CLP) surgery and a cell model of myocardial injury via lipopolysaccharide (LPS) stimulation. IL-15 expression was prominently upregulated in septic hearts as well as cardiomyocytes challenged with LPS. IL-15 pretreatment attenuated cardiac inflammation and cell apoptosis and improved cardiac function in the CLP model. Similar cardioprotective effects of IL-15 pretreatment were observed in vitro. As expected, IL-15 knockdown had the opposite effect on LPS-stimulated cardiomyocytes. Mechanistically, we found that IL-15 pretreatment reduced the expression of the pro-apoptotic proteins cleaved caspase-3 and Bax and upregulated the anti-apoptotic protein Bcl-2. RNA sequencing and Western blotting further confirmed that IL-15 pretreatment suppressed the activation of nuclear factor kappa B (NF-κB) signaling in mice with sepsis. Besides, the addition of NF-κB inhibitor can significantly attenuate cardiomyocyte apoptosis compared to the control findings. Our results suggest that IL-15 pretreatment attenuated the cardiac inflammatory responses and reduced cardiomyocyte apoptosis by partially inhibiting NF-κB signaling in vivo and in vitro, thereby improving cardiac function in mice with sepsis. These findings highlight a promising therapeutic strategy for SIMD.

RIP2 inhibition alleviates lipopolysaccharide-induced septic cardiomyopathy via regulating TAK1 signaling

PurposeRIP2 is a member of the receptor-interacting protein family that has been associated with various pathophysiological processes, including immunity, apoptosis, and autophagy. However, no studies have hitherto reported the role of RIP2 in lipopolysaccharide (LPS)-induced septic cardiomyopathy (SCM). This study was designed to illustrate the role of RIP2 in LPS-induced SCM. MethodsC57 and RIP2 knockout mice received intraperitoneal injections of LPS to establish models of SCM. Echocardiography was used to assess the cardiac function of the mice. Real-time-PCR, cytometric bead array and immunohistochemical staining were used to detect the inflammatory response. Immunoblotting was used to determine the protein expression of relevant signaling pathways. Our findings were validated by treatment with a RIP2 inhibitor. Neonatal rats cardiomyocytes (NRCMs) and cardiac fibroblasts (CFs) were transfected with Ad-RIP2 to further explore the role of RIP2 in vitro. ResultsRIP2 expression was upregulated in our mice models of septic cardiomyopathy and LPS-stimulated cardiomyocytes and fibroblasts. RIP2 knockout or RIP2 inhibitors attenuated LPS-induced cardiac dysfunction and reduced the inflammatory response in mice. Overexpression of RIP2 in vitro enhanced the inflammatory response, and TAK1 inhibitors attenuated the inflammatory response caused by overexpression of RIP2. ConclusionOur findings substantiate that RIP2 induces an inflammatory response by regulating the TAK1/IκBα/NF-κB signaling pathway. RIP2 inhibition by genetic or pharmacological approaches has huge prospects for application as a potential treatment strategy for inhibiting inflammation, alleviating cardiac dysfunction, and improving survival.

Macrophage-Derived Exosomes in TLR9-/- Mice Ameliorate Sepsis-Induced Mitochondrial Oxidative Stress and Apoptosis in Cardiomyocytes.

Objective To explore the mechanisms of TLR9 from macrophages on mitochondrial apoptosis in cardiomyocytes at early stage of sepsis. Methods The in vivo and in vitro sepsis mice were bone marrow transplantation (BMT) with wild type (WT) or (toll-like receptor 9) TLR9 knockout (−/− or KO) myeloid cells and then constructed by cecum ligation and puncture (CLP) as vivo experiment and cardiomyocytes cocultured with WT or TLR9-deficient macrophages treated with LPS as vitro experiment, respectively. Sepsis model were performed by CLP. The expression levels of exosome, PI3K/AKT, and ERK1/2, inflammatory factors, and apoptotic proteins were tested by western blot in vivo. Besides, associated apoptotic proteins and JC-1 fluorescence assay were tested in vitro. Results The expressions of p-PI3K, p-AKT, exosome markers (CD9, CD63, and TSG101), p-ERK1/2, TNF-α, IFN-γ, IL-1β, and cleaved-caspase-3/-9 were significantly increased in septic mice vs. control mice, and these proteins were declined dramatically in TLR9−/− BMT mice vs. WT BMT mice in sepsis mice models. Meanwhile, the protein expression of cytochrome C, cleaved-caspase-3, and cleaved-caspase-9 increased significantly in primary mouse myocardial cells cocultured with TLR9−/− or WT macrophages stimulated with LPS, and these mitochondrial apoptotic proteins as well as the green 5,5',6,6'-tetrachloro-1,1',3,3'- tetraethylbenzimidazolcarbocyanine iodide (JC-1) fluorescence were dramatically lower in LPS-stimulated cardiomyocytes cocultured with TLR9−/− than with WT macrophages. Conclusion TLR9−/− in macrophages suppressed the inflammatory reaction as well as the exosome secretion and resulted in the inhibition of apoptosis and oxidative stress in sepsis-induced cardiomyopathy.

Abstract 12470: miR-187 Mimic Targets Pro-Inflammatory Cytokynes in Cardiomyocytes Treated With Bacterial Endotoxin

Introduction: 1 in 18 Canadians dies from sepsis, a life-threatening dysfunction caused by a dysregulated host response to infection which can lead to sepsis-induced Cardiac dysfunction. In the past, we have shown that administration of mesenchymal stem cells (MSCs) in the cecal ligation and puncture (CLP) model of polybacterial sepsis leads to the mitigation of sepsis-induced cardiac dysfunction by modulating microRNAs in the septic heart. Differential expression of miRNAs alters mRNA expression profile leading to a change in cellular response. In our CLP model, we identified miR-187 as a host-derived MSC-regulated miRNA. Hypothesis: Here we investigate the broader immunoregulatory of miR-187. Therefore, we tested the hypothesis that miRNA-187 inversely regulates sepsis-induced cardiac dysfunction by attenuating pro-inflammatory gene expression. Methods: Primary cardiomyocytes were isolated from 1-2 days old CD1 neonates. Cultured cells were transfected with miR-187 mimic (25 nM/mL) for 24 hours. Transfected cells were then subsequentially exposed to lipopolysaccharide (LPS, 1 μg/mL) for an additional 24 hours post-transfection. We chose to measure the expression of pro and anti-inflammatory cytokines and some cardiac injury markers via Real-Time Polymerase Chain Reaction (RT-qPCR). Results: Cardiomyocytes treated with bacterial LPS showed a significant decline in expression of miR-187 (n=4, p<0.05) and a significant surge (n=4, p<0.05) in the expression of pro-inflammatory cytokines such as IL-1β, IL-6, TNFα and IL-12 in comparison to untreated cells. Conversely, LPS-stimulated cardiomyocytes transfected with exogenous miR-187 mimic versus non-transfected LPS-stimulated cardiomyocytes demonstrated reduced expression of IL-1β, IL-6, and IL-12 (n=3, p<0.05) and Fasl, S100A4 and S100A9 (n=3, p<0.05). Conclusions: Transfecting neonatal cardiomyocytes with mimic miR-187 in the presence of LPS decreases the production of key inflammatory genes involved in sepsis-induced cardiac dysfunction. Our findings show miR-187 to be a potential therapeutic target to improve cardiac function in a pre-clinical model of sepsis by reducing pro-inflammatory cytokine expression.

Irisin Attenuates Oxidative Stress, Mitochondrial Dysfunction, and Apoptosis in the H9C2 Cellular Model of Septic Cardiomyopathy through Augmenting Fundc1-Dependent Mitophagy.

In the present study, we used lipopolysaccharide- (LPS-) stimulated H9C2 cardiomyocytes to investigate whether irisin treatment attenuates septic cardiomyopathy via Fundc1-related mitophagy. Fundc1 levels and mitophagy were significantly reduced in LPS-stimulated H9C2 cardiomyocytes but were significantly increased by irisin treatment. Irisin significantly increased ATP production and the activities of mitochondrial complexes I and III in the LPS-stimulated cardiomyocytes. Irisin also improved glucose metabolism and significantly reduced LPS-induced levels of reactive oxygen species by increasing the activities of antioxidant enzymes, glutathione peroxidase (GPX), and superoxide dismutase (SOD), as well as levels of reduced glutathione (GSH). TUNEL assays showed that irisin significantly reduced LPS-stimulated cardiomyocyte apoptosis by suppressing the activation of caspase-3 and caspase-9. However, the beneficial effects of irisin on oxidative stress, mitochondrial metabolism, and viability of LPS-stimulated H9C2 cardiomyocytes were abolished by silencing Fundc1. These results demonstrate that irisin abrogates mitochondrial dysfunction, oxidative stress, and apoptosis through Fundc1-related mitophagy in LPS-stimulated H9C2 cardiomyocytes. This suggests irisin is a potentially useful treatment for septic cardiomyopathy, though further investigations are necessary to confirm our findings.

Kcnh2 mediates FAK/AKT‐FOXO3A pathway to attenuate sepsis‐induced cardiac dysfunction

ObjectivesMyocardial dysfunction is a significant manifestation in sepsis, which results in high mortality. Even Kcnh2 has been hinted to associate with the pathological process, its involved signalling is still elusive.Materials and methodsThe caecal ligation puncture (CLP) surgery or lipopolysaccharide (LPS) injection was performed to induce septic cardiac dysfunction. Western blotting was used to determine KCNH2 expression. Cardiac function was examined by echocardiography 6 hours after CLP and LPS injection in Kcnh2 knockout (Kcnh2+/‐) and NS1643 injection rats (n ≥ 6/group). Survival was monitored following CLP‐induced sepsis (n ≥ 8/group).ResultsSepsis could downregulate KCNH2 level in the rat heart, as well as in LPS‐stimulated cardiomyocytes but not cardiac fibroblast. Defect of Kcnh2 (Kcnh2+/‐) significantly aggravated septic cardiac dysfunction, exacerbated tissue damage and increased apoptosis under LPS challenge. Fractional shortening and ejection fraction values were significantly decreased in Kcnh2+/‐ group than Kcnh2+/+ group. Survival outcome in Kcnh2+/‐ septic rats was markedly deteriorated, compared with Kcnh2+/+ rats. Activated Kcnh2 with NS1643, however, resulted in opposite effects. Lack of Kcnh2 caused inhibition of FAK/AKT signalling, reflecting in an upregulation for FOXO3A and its downstream targets, which eventually induced cardiomyocyte apoptosis and heart tissue damage. Either activation of AKT by activator or knockdown of FOXO3A with si‐RNA remarkably attenuated the pathological manifestations that Kcnh2 defect mediated.ConclusionKcnh2 plays a protection role in sepsis‐induced cardiac dysfunction (SCID) via regulating FAK/AKT‐FOXO3A to block LPS‐induced myocardium apoptosis, indicating a potential effect of the potassium channels in pathophysiology of SCID.

MiR-16 exhibits protective function in LPS-treated cardiomyocytes by targeting DOCK2 to repress cell apoptosis and exert anti-inflammatory effect.

This study aims to investigate the effects of microRNA (miR)-16/dedicator of cytokinesis 2 (DOCK2) on myocarditis. The differences in the expression of genes in acute myocarditis were filtered out across Gene Expression Omnibus (GEO) database. Myocarditis cell model was established by lipopolysaccharide (LPS) stimulation in cardiomyocytes. The association between miR-16 and DOCK2 was predicted by bioinformatics software and confirmed by dual-luciferase assay. Polymerase chain reaction and western blot analysis were employed to assess the expression levels of miR-16 and DOCK2 under different conditions. Cells viability, apoptosis, and inflammatory reaction were evaluated by Cell Counting Kit-8, flow cytometry, and enzyme-linked immunosorbent assays. miR-16, as an upstream regulator of DOCK2, exhibited lower expression in LPS-induced myocarditis model. More importantly, we revealed that a marked augmentation of miR-16 promoted the growth of LPS-stimulated cardiomyocytes, and attenuated cell apoptosis and inflammatory response. However, an increasing expression of DOCK2 inhibited the remission of LPS-induced myocardial injury caused by miR-16 mimic. Herein, our results highlighted that upregulation of miR-16 resulted in the protective effects on LPS-induced myocardial injury by reducing DOCK2 expression, affording a pair of novel target molecules for ameliorating the symptoms of myocarditis.

CTRP12 Ameliorated Lipopolysaccharide-Induced Cardiomyocyte Injury.

C1q/tumor necrosis factor (TNF)-related protein 12 (CTRP12) is a secretory protein that participates in the regulation of glucose and lipid metabolism in obesity and diabetes. Its role in cardiovascular disease, particularly sepsis-induced cardiac injury, is unclear. Here, we stimulated cardiomyocytes with lipopolysaccharide (LPS) to establish an in vitro cardiomyocyte injury model and CTRP12 was overexpressed with an adenovirus delivery system. Overexpression of CTRP12 reduced the transcription and release of pro-inflammatory cytokines from LPS-stimulated cardiomyocytes, including TNFα, interleukin-1 (IL-1), and IL-6. Reactive oxygen species (ROS) level increased and the oxidation/redox system was disturbed in LPS-stimulated cardiomyocytes, as evident from the decrease in superoxide dismutase activity and an increase in reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity and malondialdehyde level. CTRP12 overexpression decreased the increasing level of ROS and ameliorated the unbalance in the oxidation/redox system in LPS-stimulated cardiomyocytes. The viability of cardiomyocytes decreased after LPS stimulation, and the cells underwent apoptosis. CTRP12-overexpressing cardiomyocytes showed a decrease in the number of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL)-positive cells, and the ratio of B cell lymphoma (Bcl)-1/Bax in these cells was recovered. In comparison with the control group, LPS-stimulated cardiomyocytes showed reduced expression of nuclear factor E2-related factor 2 (NRF2), while CTRP12-overexpressing cardiomyocytes showed elevated NRF2 expression. Small-interfering RNA-mediated silencing of NRF2 expression in cardiomyocytes resulted in the inhibition of the protective effects of CTRP12. Thus, CTRP12 ameliorated injury in LPS-stimulated cardiomyocytes in an NRF2-dependent manner.

MiR-93-3p alleviates lipopolysaccharide-induced inflammation and apoptosis in H9c2 cardiomyocytes by inhibiting toll-like receptor 4

BackgroundmiR-93 is recently recognized to perform anti-inflammatory action in the pathological process of cardiomyocytes dysfunction. However, it remains unclear whether miR-93-3p involves in lipopolysaccharide (LPS)-induced inflammation and apoptosis in H9c2 cells. The present study aimed to investigate the functions of miR-93-3p and its target, toll-like receptor 4 (TLR4), in LPS-stimulated cardiomyocytes. Material and methodsCell viability was analyzed by CCK-8 assay. AnnexinV-FITC/PI staining and lactate dehydrogenase (LDH) assay were used to evaluate the cell death. The mRNA and protein levels were assayed by RT-qPCR and western blotting, respectively. The targeted gene was predicted by a bioinformatics algorithm and confirmed by a dual luciferase reporter assay. ResultsLDH stimulation resulted in the suppression of cell viability and the increase in apoptosis rate, inflammatory cytokines and LDH levels, while inhibition of TLR4 with TAK-242 or overexpression of miR-93-3p dramatically blocked LPS-induced inflammation and apoptosis in cardiomyocytes. Intriguingly, bioinformatics analysis and experimental data suggested that TLR4 was a direct target of miR-93-3p, which could inhibit TLR4 expression by transfected with miR-93-3p mimics or elevate the expression of TLR4 by transfected with miR-93-3p inhibitors. Overexpression of TLR4 carried out an opposite effect to miR-93-3p and positively regulated LPS-induced inflammation and apoptosis in cardiomyocytes. ConclusionmiR-93-3p showed the protective effects against LPS-induced inflammation and apoptosis in cardiomyocytes by inhibiting TLR4 expression.

Puerarin attenuates the inflammatory response and apoptosis in LPS-stimulated cardiomyocytes.

Patients with septic shock suffer from high mortality rates, particularly when complicated by severe myocardial depression which is characterized by hypotension and a reduction in cardiac output. Inflammation is an important factor involved in the early stages of sepsis. The aim of the present study was to investigate the effect of the Chinese herbal compound puerarin (1, 5, 10, 20 and 40 µM) on cardiomyocyte inflammatory response in a sepsis model using H9c2 cardiomyocytes stimulated with 1 µg/ml lipopolysaccharide (LPS). The mRNA expression levels of tumor necrosis factor (TNF)-α and interleukin (IL)-β were evaluated using reverse transcription-quantitative polymerase chain reaction. In addition, the protein expression levels of various factors were determined using western blot analysis. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling was used to evaluate the apoptosis rates in the various groups, and immunocytochemical analysis was employed to determine the effect of puerarin on the nuclear translocation of p65 protein. The present study demonstrated that LPS stimulation increased IL-1β and TNF-α mRNA expression levels, as compared with the controls (P<0.05). Following treatment with various concentrations of puerarin, the expression levels of IL-1β and TNF-α were markedly blunted, particularly in the LPS + 40 µM puerarin group (P<0.05 vs. the LPS group). Furthermore, puerarin administration significantly inhibited LPS-induced apoptosis in H9c2 cardiomyocytes, as determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining (TUNEL positive cells: LPS + 40 µM puerarin group, 5.5% vs. LPS group, 10.5%; P<0.01). In addition, puerarin significantly decreased LPS-induced phosphorylated nuclear factor (p-NF)-κB p65 and Bax expression levels, and increased the expression levels of Bcl-2, as compared with the LPS group (P<0.05). These data indicated that puerarin may serve as a valuable protective agent against cardiovascular inflammatory diseases.

β₁-adrenoceptor stimulation promotes LPS-induced cardiomyocyte apoptosis through activating PKA and enhancing CaMKII and IκBα phosphorylation.

IntroductionCaspase activation and cardiomyocyte apoptosis have been implicated in lipopolysaccharide (LPS)-induced cardiac contractile dysfunction. We have recently demonstrated that β1-adrenoceptor (AR) activation by endogenous norepinephrine contributes to cardiomyocyte apoptosis in endotoxemic mice. Here, we further investigated the molecular mechanisms for the enhancing effect of β1-AR activation on LPS-induced cardiomyocyte apoptosis.MethodsThe adult mouse ventricular myocytes were exposed to LPS, dobutamine, protein kinase A (PKA) inhibitor or/and nifedipine, an L-type Ca2+ channel blocker. Male BALB/c mice were treated with LPS or/ and β1-AR antagonist, atenolol. Cardiomyocyte apoptosis was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeling (TUNEL) assay and apoptosis-associated molecules were detected.ResultsLPS induced apoptosis in adult mouse ventricular myocytes, dobutamine (DOB), a β1-AR agonist, promoted apoptosis, caspase-8, 9 and 3 activation and increased cytosolic Ca2+ concentration in LPS-challenged cardiomyocytes. DOB also up-regulated TNF-α expression, decreased Bcl-2 levels, promoted Bax translocation to mitochondria, mitochondrial membrane potential loss and cytochrome c release as well as IκBα, p38 MAPK, JNK and Ca2+/calmodulin-dependent protein kinase II (CaMKII) phosphorylation in LPS-treated cardiomyocytes. PKA inhibitor abolished the effects of DOB on caspase-9 activation, Bcl-2 levels as well as JNK and p38 MAPK phosphorylation, but not on IκBα phosphorylation, TNF-α expression and caspase-8 activation in LPS-stimulated cardiomyocytes. Pretreatment with nifedipine not only significantly blocked the enhancing effects of DOB on LPS-induced elevation in cytosolic Ca2+ concentration and CaMKII phosphorylation in cardiomyocytes, but also partly reversed the effects of DOB on caspase-9 and caspase-3/7 activities in LPS-treated cardiomyocytes. Furthermore, atenolol suppressed TNF-α expression, JNK, p38 MAPK and CaMKII phosphorylation, increased Bcl-2 expression, and inhibited cytochrome c release and cardiomyocyte apoptosis in the myocardium of endotoxemic mice.Conclusionsβ1-AR activation promotes LPS-induced apoptosis through activating PKA, increasing CaMKII phosphorylation as well as enhancing IκBα phosphorylation and TNF-α expression in cardiomyocytes.

MAPK Signaling Drives Inflammation in LPS-Stimulated Cardiomyocytes: The Route of Crosstalk to G-Protein-Coupled Receptors

Profound cardiovascular dysfunction is an important cause of mortality from septic shock. The molecular underpinnings of cardiac dysfunction during the inflammatory surge of early sepsis are not fully understood. MAPKs are important signal transducers mediating inflammation whereas G-protein signaling pathways modulate the cardiac response to stress. Using H9c2 cardiomyocytes, we investigated the interaction of MAPK and G-protein signaling in a sepsis model to test the hypothesis that the cardiomyocyte inflammatory response is controlled by MAPKs via G-protein-mediated events. We found that LPS stimulated proinflammatory cytokine production was markedly exacerbated by siRNA knockdown of the MAPK negative regulator Mkp-1. Cytokine production was blunted when cells were treated with p38 inhibitor. Two important cellular signaling molecules typically regulated by G-protein-coupled receptors, cAMP and PKC activity, were also stimulated by LPS and inflammatory cytokines TNF-α and IL-6, through a process regulated by Mkp-1 and p38. Interestingly, neutralizing antibodies against Gαs and Gαq blocked the increase in cellular cAMP and PKC activation, respectively, in response to inflammatory stimuli, indicating a critical role of G-protein coupled receptors in this process. LPS stimulation increased COX-2 in H9c2 cells, which also express prostaglandin receptors. Blockade of G-protein-coupled EP4 prostaglandin receptor by AH 23848 prevented LPS-induced cAMP increase. These data implicate MAPKs and G-proteins in the cardiomyocyte inflammatory response to LPS as well as crosstalk via COX-2-generated PGE2. These data add to our understanding of the pathogenesis of septic shock and have the potential to guide the selection of future therapeutics.

Over-expression of calpastatin inhibits calpain activation and attenuates myocardial dysfunction during endotoxaemia

Lipopolysaccharide (LPS) induces cardiomyocyte caspase-3 activation and proinflammatory factors, in particular tumour necrosis factor-alpha (TNF-alpha) production, both of which contribute to myocardial dysfunction during sepsis. The present study was to investigate the roles of calpain/calpastatin system in cardiomyocyte caspase-3 activation, TNF-alpha expression, and myocardial dysfunction during LPS stimulation. In cultured adult rat cardiomyocytes, LPS (1 microg/mL) induced calpain and caspase-3 activity, and up-regulated TNF-alpha expression. These effects of LPS were abrogated by over-expression of calpastatin, an endogenous calpain inhibitor, transfection of calpain-1 siRNA, or various pharmacological calpain inhibitors. Furthermore, blocking gp91(phox)-NADPH oxidase prevented calpain and caspase-3 activation and decreased TNF-alpha expression in LPS-stimulated cardiomyocytes. To investigate the role of calpastatin in endotoxaemia, transgenic mice with calpastatin over-expression (CAST-Tg) and wild-type mice were treated with LPS (4 mg/kg, i.p.) or saline in the presence of calpain inhibitor-III (10 mg/kg, i.p.) for 4 h, and their heart function was measured with a Langendorff system. Over-expression of calpastatin significantly attenuated myocardial dysfunction (P < 0.05). Consistently, calpain activity, caspase-3 activity, and TNF-alpha expression were also reduced in CAST-Tg and calpain inhibitor-III compared with wild-type and vehicle-treated hearts, respectively. gp91(phox)-NADPH oxidase-mediated calpain-1 activation induces caspase-3 activation and TNF-alpha expression in cardiomyocytes during LPS stimulation. Over-expression of calpastatin inhibits calpain activation and improves myocardial function in endotoxaemia. The present study suggests that targeting calpain/calpastatin system may be a potential therapeutic intervention for septic hearts.

JNK1/c-fos inhibits cardiomyocyte TNF- expression via a negative crosstalk with ERK and p38 MAPK in endotoxaemia

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. 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. JNK1/c-fos inhibits ERK1/2 and p38 MAPK signalling, leading to decreased cardiomyocyte TNF-alpha expression and improvements in cardiac function during endotoxaemia.

Glycogen synthase kinase‐3beta suppresses tumor necrosis factor‐alpha expression in cardiomyocytes during lipopolysaccharide stimulation

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.

Phospholipase Cγ1 signalling regulates lipopolysaccharide-induced cyclooxygenase-2 expression in cardiomyocytes

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 Cγ1 (PLCγ1) in cardiac COX-2 expression in vitro and in vivo. In cultured mouse neonatal cardiomyocytes, LPS increased PLCγ1 phosphorylation and COX-2 expression. Knockdown of PLCγ1 with specific siRNA or inhibition of PI-PLC with U73122 attenuated COX-2 mRNA and protein expression induced by LPS (1 μg/ml). PLCγ1 activation by LPS also increased ERK1/2 MAPK phosphorylation, and inhibition of ERK1/2 MAPK blocked the effect of PLCγ1 on COX-2 expression. Furthermore, activation of PLCγ1 is a consequence of the Src family activation since inhibition of Src abrogated whereas over-expression of Src enhanced PLCγ1 phosphorylation and COX-2 expression in LPS-stimulated cardiomyocytes. To investigate the role of PLCγ1 in endotoxemia, wild-type and PLCγ1 +/− 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 PLCγ1 decreased cardiac COX-2 expression. The phosphorylation of ERK1/2 MAPK induced by LPS was also attenuated in U73122- or PLCγ1 +/− compared to U73343-treated or wild-type littermate hearts, respectively. In conclusion, our study suggests that PLCγ1 signalling represents a novel pathway regulating cardiac COX-2 expression during LPS stimulation. The Src family is responsible for PLCγ1 activation, which signals the ERK1/2 MAPK pathway, resulting in COX-2 production in LPS-stimulated cardiomyocytes.

Activation of GSK‐3β inhibited TNF‐α expression in cardiomyocytes during LPS stimulation

This study was to investigate the role of glycogen synthase kinase (GSK)-3β in cardiomyocyte TNF-α expression induced by lipopolysaccharides (LPS). Neonatal mouse cardiomyocytes were cultured and incubated with LPS in the presence of SB216763, a specific inhibitor of GSK-3β, or DMSO for 4 hours. SB216763 increased both TNF-α protein and mRNA expression, suggesting an inhibitory role of GSK-3β. To substantiate the role of GSK-3β, cardiomyocytes were infected with recombinant adenoviruses containing GSK-3β(Ad-GSK) or dominant active mutant of GSK-3β (Ad-AC-GSK) or dominant negative mutant of GSK-3β(Ad-DN-GSK) or Green Fluorescent Protein (GFP) (Ad-GFP) for 24 hours, followed by incubation with LPS for 4 hours. Both Ad-GSK and Ad-AC-GSK infection decreased whereas Ad-DN-GSK increased TNF-α protein and mRNA expression, compared to Ad-GFP. This result supported the inhibitory role of GSK-3β in TNF-α expression in LPS-stimulated cardiomyocytes. In addition, inhibition of protein kinase B activation (AKT) by either LY294002 or over-expression of dominant negative mutant of AKT significantly decreased TNF-α protein and mRNA expression in LPS-stimulated cardiomyocytes. As AKT suppresses GSK-3β activation, our data further supports the notion that GSK-3β inhibits TNF-α expression. In conclusion, our study demonstrated an inhibitory role of GSK-3β in LPS-stimulated TNF-α expression, suggesting that GSK-3β may be a therapeutic target for sepsis.