Palmitate alters neuregulin signaling and biology in cardiac myocytes

Neuregulin-1β increases glucose uptake and promotes GLUT4 translocation in palmitate-treated C2C12 myotubes by activating PI3K/AKT signaling pathway

Insulin resistance (IR) is a feature of type 2 diabetes (T2DM) accompanied by reduced glucose uptake and glucose transporter 4 (GLUT4) translocation by skeletal muscle. Neuregulin-1β (NRG-1β) is essential for myogenesis and the regulation of skeletal muscle metabolism. Neuregulin-1β increases insulin sensitivity, promotes glucose uptake and glucose translocation in normal skeletal muscle. Here, we explored whether Neuregulin-1β increased glucose uptake and GLUT4 translocation in palmitate (PA)-treated C2C12 myotubes. After C2C12 myoblasts differentiated into myotubes, we used palmitate to induce cellular insulin resistance. Cells were incubated with or without Neuregulin-1β and glucose uptake was determined using the 2-NBDG assay. The expression level of glucose transporter 4 (GLUT4) was measured via immunofluorescence and Western blotting. MK2206, an inhibitor of AKT, was employed to reveal the important role played by AKT signaling in PA-treated C2C12 myotubes. We then established an animal model with T2DM and evaluated the effects of Neuregulin-1β on body weight and the blood glucose level. The GLUT4 level in the gastrocnemius of T2DM mice was also measured. NRG-1β not only increased glucose uptake by PA-treated myotubes but also promoted GLUT4 translocation to the plasma membrane. The effect of NRG-1β on PA-treated C2C12 myotubes was associated with AKT activation. In T2DM mice, Neuregulin-1β not only improved diabetes-induced weight loss and diabetes-induced hyperglycemia, but also promoted GLUT4 translocation in the gastrocnemius. In summary, Neuregulin-1β increased glucose uptake and promoted translocation of GLUT4 to the plasma membrane in PA-treated C2C12 myotubes by activating the PI3K/AKT signaling pathway.

Decreased expression of ErbB2 on left ventricular epicardial cells in patients with diabetes mellitus

We investigated the cell surface expression of ErbB receptors on left ventricular (LV) epicardial endothelial cells and CD105⁺ cells obtained from cardiac biopsies of patients undergoing coronary artery bypass grafting surgery (CABG). Endothelial cells and CD105⁺ non-endothelial cells were freshly isolated from LV epicardial biopsies obtained from 15 subjects with diabetes mellitus (DM) and 8 controls. The expression of ErbB receptors was examined using flow cytometry. We found that diabetes mellitus (DM) and high levels of hemoglobin A1C are associated with reduced expression of ErbB2. To determine if the expression of ErbB2 receptors is regulated by glucose levels, we examined the effect of high Glucose in human microvascular endothelial cells (HMEC-1) and CD105⁺ non-endothelial cells, using a novel flow cytometric approach to simultaneously determine the total level, cell surface expression, and phosphorylation of ErbB2. Incubation of cells in the presence of 25 mM d-glucose resulted in decreased cell surface but not total levels of ErbB2. The level of ErbB2 at the cell surface is controlled by disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) that is expressed on LV epicardial cells. Inhibition of ADAM10 prevented the high glucose-dependent decrease in the cell surface expression of ErbB2. We suggest that high Glucose depresses ErbB receptor signaling in endothelial cells and cardiac progenitor cells via the promotion of ADAM10-dependent cleavage of ErbB2 at the cell surface, thus contributing to vascular dysfunction and adverse remodeling seen in diabetic patients.

Short-term exposure to an obesogenic diet during adolescence elicits anxiety-related behavior and neuroinflammation: modulatory effects of exogenous neuregulin-1

Childhood obesity leads to hippocampal atrophy and altered cognition. However, the molecular mechanisms underlying these impairments are poorly understood. The neurotrophic factor neuregulin-1 (NRG1) and its cognate ErbB4 receptor play critical roles in hippocampal maturation and function. This study aimed to determine whether exogenous NRG1 administration reduces hippocampal abnormalities and neuroinflammation in rats exposed to an obesogenic Western-like diet (WD). Lewis rats were randomly divided into four groups (12 rats/group): (1) control diet+vehicle (CDV); (2) CD + NRG1 (CDN) (daily intraperitoneal injections: 5 μg/kg/day; between postnatal day, PND 21-PND 41); (3) WD + VEH (WDV); (4) WD + NRG1 (WDN). Neurobehavioral assessments were performed at PND 43-49. Brains were harvested for MRI and molecular analyses at PND 49. We found that NRG1 administration reduced hippocampal volume (7%) and attenuated hippocampal-dependent cued fear conditioning in CD rats (56%). NRG1 administration reduced PSD-95 protein expression (30%) and selectively reduced hippocampal cytokine levels (IL-33, GM-CSF, CCL-2, IFN-γ) while significantly impacting microglia morphology (increased span ratio and reduced circularity). WD rats exhibited reduced right hippocampal volume (7%), altered microglia morphology (reduced density and increased lacunarity), and increased levels of cytokines implicated in neuroinflammation (IL-1α, TNF-α, IL-6). Notably, NRG1 synergized with the WD to increase hippocampal ErbB4 phosphorylation and the tumor necrosis alpha converting enzyme (TACE/ADAM17) protein levels. Although the results did not provide sufficient evidence to conclude that exogenous NRG1 administration is beneficial to alleviate obesity-related outcomes in adolescent rats, we identified a potential novel interaction between obesogenic diet exposure and TACE/ADAM17-NRG1-ErbB4 signaling during hippocampal maturation. Our results indicate that supraoptimal ErbB4 activities may contribute to the abnormal hippocampal structure and cognitive vulnerabilities observed in obese individuals.

Alteration of serum neuregulin 4 and neuregulin 1 in gestational diabetes mellitus

CONTEXT

Neuregulin 4 (Nrg4) and neuregulin 1 (Nrg1) have been shown to play vital roles in several disorders of glucose metabolism. The pathophysiological role of Nrg4 and Nrg1 in gestational diabetes mellitus (GDM), however, remains poorly understood. We assessed the clinical relevance of the two cytokines in patients with GDM.

METHODS

The study recruited 36 GDM patients and 38 age-matched, gestational age (24-28 weeks of gestation)-matched, and BMI (during pregnancy)-matched controls in this study. Serum Nrg4 and Nrg1 were measured using ELISA. Inflammatory factors such as IL-6, IL-1β, leptin, TNF-α, and monocyte chemotactic protein 1 (MCP-1) were determined via Luminex technique.

RESULTS

Serum Nrg4 in GDM patients was significantly lower than that in the controls, while Nrg1 was significantly higher in the GDM group (p < 0.01). Inflammatory factors such as IL-6, leptin, and TNF-α were significantly increased in GDM patients, while MCP-1 and IL-1β were not significantly different between the two groups. In addition, serum Nrg4 was negatively correlated with fasting glucose (r = -0.438, p = 0.008), HOMA-IR (r = -0.364, p = 0.029), IL-6 (r = -0.384, p = 0.021), leptin (r = -0.393, p = 0.018), TNF-α (r = -0.346, p = 0.039), and MCP-1 (r = -0.342, p = 0.041), and positively correlated with high-density lipoprotein cholesterol (HDL-C) (r = -0.357, p = 0.033) in GDM group. Serum Nrg1 was positively correlated with BMI (r = 0.452, p = 0.006), fasting glucose (r = 0.424, p = 0.010), HOMA-IR (r = 0.369, p = 0.027), and triglyceride (r = 0.439, p = 0.007). The decrease of Nrg4 and the increase of Nrg1 were significantly related to the increased prevalence of GDM. Finally, ROC curve results indicated that Nrg1 combined with IL-6 and TNF-α might be an effective means for GDM screening.

CONCLUSIONS

Lower circulating Nrg4 and higher circulating Nrg1 serve risk factors of GDM. Nrg1 combined with IL-6 and TNF-α might be a potential tool for GDM screening.

Mechanisms of the Multitasking Endothelial Protein NRG-1 as a Compensatory Factor During Chronic Heart Failure

Heart failure is a complex syndrome whose phenotypic presentation and disease progression depends on a complex network of adaptive and maladaptive responses. One of these responses is the endothelial release of NRG (neuregulin)-1—a paracrine growth factor activating ErbB2 (erythroblastic leukemia viral oncogene homolog B2), ErbB3, and ErbB4 receptor tyrosine kinases on various targets cells. NRG-1 features a multitasking profile tuning regenerative, inflammatory, fibrotic, and metabolic processes. Here, we review the activities of NRG-1 on different cell types and organs and their implication for heart failure progression and its comorbidities. Although, in general, effects of NRG-1 in heart failure are compensatory and beneficial, translation into therapies remains unaccomplished both because of the complexity of the underlying pathways and because of the challenges in the development of therapeutics (proteins, peptides, small molecules, and RNA-based therapies) for tyrosine kinase receptors. Here, we give an overview of the complexity to be faced and how it may be tackled.

Cardiomyocyte-specific deletion of GSK-3β leads to cardiac dysfunction in a diet induced obesity model

BACKGROUND AND RATIONALE

Obesity, an independent risk factor for the development of myocardial diseases is a growing healthcare problem worldwide. It's well established that GSK-3β is critical to cardiac pathophysiology. However, the role cardiomyocyte (CM) GSK-3β in diet-induced cardiac dysfunction is unknown.

METHODS

CM-specific GSK-3β knockout (CM-GSK-3β-KO) and littermate controls (WT) mice were fed either a control diet (CD) or high-fat diet (HFD) for 55weeks. Cardiac function was assessed by transthoracic echocardiography.

RESULTS

At baseline, body weights and cardiac function were comparable between the WT and CM-GSK-3β-KOs. However, HFD-fed CM-GSK-3β-KO mice developed severe cardiac dysfunction. Consistently, both heart weight/tibia length and lung weight/tibia length were significantly elevated in the HFD-fed CM-GSK-3β-KO mice. The impaired cardiac function and adverse ventricular remodeling in the CM-GSK-3β-KOs were independent of body weight or the lean/fat mass composition as HFD-fed CM-GSK-3β-KO and controls demonstrated comparable body weight and body masses. At the molecular level, on a CD, CM-GSK-3α compensated for the loss of CM-GSK-3β, as evident by significantly reduced GSK-3αs21 phosphorylation (activation) resulting in a preserved canonical β-catenin ubiquitination pathway and cardiac function. However, this protective compensatory mechanism is lost with HFD, leading to excessive accumulation of β-catenin in HFD-fed CM-GSK-3β-KO hearts, resulting in adverse ventricular remodeling and cardiac dysfunction.

CONCLUSION

In summary, these results suggest that cardiac GSK-3β is crucial to protect against obesity-induced adverse ventricular remodeling and cardiac dysfunction.

Neuregulin 1 Improves Glucose Tolerance in db/db Mice

In vitro experiments using rodent skeletal muscle cells suggest that neuregulin 1 (NRG1) is involved in glucose metabolism regulation, although no study has evaluated the role of NRG1 in systemic glucose homeostasis. The purpose of this study was to investigate the effect of chronic and acute NRG1 treatment on glucose homeostasis in db/db mice. To this aim, glucose tolerance tests were performed in 8-week-old male db/db mice after treatment with NRG1 (50μg.kg^-1) or saline 3 times per week for 8 weeks. In other experiments, glucose tolerance and pyruvate tolerance tests were performed in db/db mice 15 minutes after a single NRG1 (50μg.kg^-1) or saline injection. Liver, adipose tissue, hypothalamus and skeletal muscle were also collected 30 minutes after acute NRG1 (50μg.kg^-1) or saline treatment, and the phosphorylation status of the ERBB receptors, AKT (on Ser473) and FOXO1 (on Ser256) was assessed by western blotting. Chronic treatment (8 weeks) with NRG1 improved glucose tolerance in db/db mice. Acute treatment also lowered glycemia and insulinemia during glucose or pyruvate tolerance tests. NRG1 acute injection induced activation of ERBB3 receptors and phosphorylation of AKT and FOXO1 only in liver. Altogether, this study shows that acute and chronic NRG1 treatments improve glucose tolerance in db/db mice. This effect could be mediated through inhibition of hepatic gluconeogenesis.

Exercise training and return to a well-balanced diet activate the neuregulin 1/ErbB pathway in skeletal muscle of obese rats

KEY POINTS

Some studies suggest that neuregulin 1 (NRG1) could be involved in the regulation of skeletal muscle energy metabolism in rodents. Here we assessed whether unbalanced diet is associated with alterations of the NRG1 signalling pathway and whether exercise and diet might restore NRG1 signalling in skeletal muscle of obese rats. We show that diet-induced obesity does not impair NRG1 signalling in rat skeletal muscle. We also report that endurance training and a well-balanced diet activate the NRG1 signalling in skeletal muscle of obese rats, possibly via a new mechanism mediated by the protease ADAM17. These results suggest that some beneficial effects of physical activity and diet in obese rats could be partly explained by stimulation of the NRG1 signalling pathway.

ABSTRACT

Some studies suggest that the signalling pathway of neuregulin 1 (NRG1), a protein involved in the regulation of skeletal muscle metabolism, could be altered by nutritional and exercise interventions. We hypothesized that diet-induced obesity could lead to alterations of the NRG1 signalling pathway and that chronic exercise could improve NRG1 signalling in rat skeletal muscle. To test this hypothesis, male Wistar rats received a high fat/high sucrose (HF/HS) diet for 16 weeks. At the end of this period, NRG1 and ErbB expression/activity in skeletal muscle was assessed. The obese rats then continued the HF/HS diet or were switched to a well-balanced diet. Moreover, in both groups, half of the animals also performed low intensity treadmill exercise training. After another 8 weeks, NRG1 and ErbB expression/activity in skeletal muscle were tested again. The 16 week HF/HS diet induced obesity, but did not significantly affect the NRG1/ErbB signalling pathway in rat skeletal muscle. Conversely, after the switch to a well-balanced diet, NRG1 cleavage ratio and ErbB4 amount were increased. Chronic exercise training also promoted NRG1 cleavage, resulting in increased ErbB4 phosphorylation. This result was associated with increased protein expression and phosphorylation ratio of the metalloprotease ADAM17, which is involved in NRG1 shedding. Similarly, in vitro stretch-induced activation of ADAM17 in rat myoblasts induced NRG1 cleavage and ErbB4 activation. These results show that low intensity endurance training and well-balanced diet activate the NRG1-ErbB4 pathway, possibly via the metalloprotease ADAM17, in skeletal muscle of diet-induced obese rats.

Astragalus polysaccharide suppresses palmitate-induced apoptosis in human cardiac myocytes: the role of Nrf1 and antioxidant response

OBJECTIVE

Previous studies have shown that Astragalus polysaccharides (APS) can be used to ameliorate cardiotoxicity due to chemotherapy and improve the cardiac function. However, the mechanism by which APS mediate this effect is unclear. In the present study, the effects of APS, which suppressed ROS-mediated apoptosis through Nrf1 accumulation in human cardiac myocytes (HCMs), was investigated.

METHODS

The cell viability was detected by the CCK8 assay. The cell apoptosis was assessed by annexin V-PI double-labeling staining. Expression of genes and proteins were analyzed by real-time PCR and western blotting respectively. Nrf1 gene was overexpressed using a lentiviral expression vector in HCMs in vitro, in order to explore the mechanism by which the Nrf1 promoted cell growth.

RESULTS

CCK8 and Annexin V-PI double-labeling showed that PAL induced cell death in a concentration-dependent manner, and suppressed HCMs proliferation. The combination PAL with APS was significantly decreased the percentage of the early phase of apoptosis cells. ROS levels were increased in HCMs by exposure to PAL. APS treatment significantly inhibited generation of ROS in response to palmitate. Moreover, PAL administration significantly decreased the mRNA and proteins expression of Bcl-2 as well as increased the mRNA expression of BAX and the protein expression of caspase-3 and caspase-8 as compare to those of control group, but APS treatment could reverse PA-induced HCMs apoptosis. The levels of reactive oxygen species (ROS), which was an oxidative stress marker, was significantly increased in cardiomyocytes by exposure to PAL, but overexpressing Nrf1 could ameliorate ROS-induced cardiomyocyte toxicity and increase the expression of SOD1 and SOD2 in HCMs by overexpressing Nrf1.

CONCLUSIONS

This study demonstrated that the PAL could induce HCMs apoptosis. However, APS could reverse PAL-induced cardiomyocyte toxicity, at least partially, through suppression ROS and Nrf1 accumulation in HCMs.

Neuregulin 1 affects leptin levels, food intake and weight gain in normal-weight, but not obese, db/db mice

AIM

Studies in vitro have highlighted the potential involvement of neuregulin 1 (NRG1) in the regulation of energy metabolism. This effect has also been suggested in vivo, as intracerebroventricular injection of NRG1 reduces food intakes and weight gain in rodents. Thus, it was hypothesised that NRG1 might affect serum leptin levels in mice.

METHODS

Weight, food intakes, energy expenditure, spontaneous physical activity and serum leptin levels were evaluated in normal-weight C57BL/6JRJ mice following intraperitoneal administration of NRG1 (50 μg/kg, three times/week) or saline for 8 weeks. Based on the results of this first experiment, leptin-resistant obese db/db mice were then given NRG1 for 8 weeks.

RESULTS

Leptin serum concentrations were six times higher in C57BL/6JRJ mice treated with NRG1 than in the animals given saline. NRG1 treatment also reduced weight gain by 10% and food intakes by 15% compared with saline treatment, while energy expenditure remained unchanged. In db/db mice, serum leptin concentrations, weight gain, food intakes, energy expenditure and spontaneous physical activity were not altered by NRG1 treatment.

CONCLUSION

The decrease in food intakes and weight gain associated with NRG1 treatment in C57BL/6JRJ mice may be partly explained by increased leptin levels, whereas db/db mice were not affected by the treatment, suggesting resistance to NRG1 in this pathological state.

Neuregulin as a heart failure therapy and mediator of reverse remodeling

The beta isoform of Neuregulin-1 (NRG-1β), along with its receptors (ErbB2-4), is required for cardiac development. NRG-1β, as well as the ErbB2 and ErbB4 receptors, is also essential for maintenance of adult heart function. These observations have led to its evaluation as a therapeutic for heart failure. Animal studies and ongoing clinical trials have demonstrated beneficial effects of two forms of recombinant NRG-1β on cardiac function. In addition to the possible role for recombinant NRG-1βs as heart failure therapies, endogenous NRG-1β/ErbB signaling appears to play a role in restoring cardiac function after injury. The potential mechanisms by which NRG-1β may act as both a therapy and a mediator of reverse remodeling remain incompletely understood. In addition to direct effects on cardiac myocytes NRG-1β acts on the vasculature, interstitium, cardiac fibroblasts, and hematopoietic and immune cells, which, collectively, may contribute to NRG-1β's role in maintaining cardiac structure and function, as well as mediating reverse remodeling.

Type 1 diabetes mellitus abrogates compensatory augmentation of myocardial neuregulin-1β/ErbB in response to myocardial infarction resulting in worsening heart failure

Background

Diabetes mellitus (DM) patients surviving myocardial infarction (MI) exhibit a substantially higher incidence of subsequent heart failure (HF). Neuregulin (NRG)-1 and erythroblastic leukemia viral oncogene homolog (ErbB) receptors have been shown to play a critical role in maintenance of cardiac function. However, whether myocardial NRG-1/ErbB is altered during post-MI HF associated with DM remains unknown. The aim of this study was to determine the impact of type 1 DM on the myocardial NRG-1/ErbB system following MI in relation to residual left ventricular (LV) function.

Methods

Type 1 DM was induced in rats via administration of streptozotocin (65 mg/kg, i.p.). Control rats were injected with citrate buffer (vehicle) only. Two weeks after induction of type 1 DM, MI was produced in DM and non-DM rats by ligation of the left coronary artery. Sham MI rats underwent the same surgical procedure with the exception that the left coronary artery was not ligated. At 4 weeks after surgery, residual in vivo LV function was assessed via echocardiography. Myocardial protein expression of NRG-1β, ErbB2 and ErbB4 receptors, and MDM2 (a downstream signaling pathway induced by NRG-1 that has been implicated in cell survival) was assessed in the remaining, viable LV myocardium by Western blotting. Changes in ErbB receptor localization in the surviving LV myocardium of diabetic and non-diabetic post-MI rats was determined using immunohistochemistry techniques.

Results

At 4 weeks post-MI, echocardiography revealed that LV fractional shortening (FS) and LV ejection fraction (EF) were significantly lower in the DM + MI group compared to the MI group (LVFS: 17.9 ± 0.7 vs. 25.2 ± 2.2; LVEF: 35.5 ± 1.4 vs. 47.5 ± 3.5, respectively; P < 0.05), indicating an increased functional severity of HF among the DM + MI rats. Up-regulation of NRG-1β and ErbB2 protein expression in the MI group was abrogated in the DM + MI group concurrent with degradation of MDM2, a downstream negative regulator of p53. ErbB2 and ErbB4 receptors re-localized to cardiac myocyte nuclei in failing type 1 diabetic post-MI hearts.

Conclusions

Type 1 DM prevents compensatory up-regulation of myocardial NRG-1/ErbB after MI coincident with an increased severity of HF.

Intravenous glial growth factor 2 (GGF2) isoform of neuregulin-1β improves left ventricular function, gene and protein expression in rats after myocardial infarction

AIMS

Recombinant Neuregulin (NRG)-1β has multiple beneficial effects on cardiac myocytes in culture, and has potential as a clinical therapy for heart failure (HF). A number of factors may influence the effect of NRG-1β on cardiac function via ErbB receptor coupling and expression. We examined the effect of the NRG-1β isoform, glial growth factor 2 (GGF2), in rats with myocardial infarction (MI) and determined the impact of high-fat diet as well as chronicity of disease on GGF2 induced improvement in left ventricular systolic function. Potential mechanisms for GGF2 effects on the remote myocardium were explored using microarray and proteomic analysis.

METHODS AND RESULTS

Rats with MI were randomized to receive vehicle, 0.625 mg/kg, or 3.25 mg/kg GGF2 in the presence and absence of high-fat feeding beginning at day 7 post-MI and continuing for 4 weeks. Residual left ventricular (LV) function was improved in both of the GGF2 treatment groups compared with the vehicle treated MI group at 4 weeks of treatment as assessed by echocardiography. High-fat diet did not prevent the effects of high dose GGF2. In experiments where treatment was delayed until 8 weeks after MI, high but not low dose GGF2 treatment was associated with improved systolic function. mRNA and protein expression analysis of remote left ventricular tissue revealed a number of changes in myocardial gene and protein expression altered by MI that were normalized by GGF2 treatment, many of which are involved in energy production.

CONCLUSIONS

This study demonstrates that in rats with MI induced systolic dysfunction, GGF2 treatment improves cardiac function. There are differences in sensitivity of the myocardium to GGF2 effects when administered early vs. late post-MI that may be important to consider in the development of GGF2 in humans.

Neuregulin in cardiovascular development and disease

Studies in genetically modified mice have demonstrated that neuregulin-1 (NRG-1), along with the erythroblastic leukemia viral oncogene homolog (ErbB) 2, 3, and 4 receptor tyrosine kinases, is necessary for multiple aspects of cardiovascular development. These observations stimulated in vitro and in vivo animal studies, implicating NRG-1/ErbB signaling in the regulation of cardiac cell biology throughout life. Cardiovascular effects of ErbB2-targeted cancer therapies provide evidence in humans that ErbB signaling plays a role in the maintenance of cardiac function. These and other studies suggest a conceptual model in which a key function of NRG-1/ErbB signaling is to mediate adaptations of the heart to physiological and pathological stimuli through activation of intracellular kinase cascades that regulate tissue plasticity. Recent work implicates NRG-1/ErbB signaling in the regulation of multiple aspects of cardiovascular biology, including angiogenesis, blood pressure, and skeletal muscle responses to exercise. The therapeutic potential of recombinant NRG-1 as a potential treatment for heart failure has been demonstrated in animal models and is now being explored in clinical studies. NRG-1 is found in human serum and plasma, and it correlates with some clinical parameters, suggesting that it may have value as an indicator of prognosis. In this review, we bring together this growing literature on NRG-1 and its significance in cardiovascular development and disease.

Dual pathways of p53 mediated glucolipotoxicity-induced apoptosis of rat cardiomyoblast cell: activation of p53 proapoptosis and inhibition of Nrf2-NQO1 antiapoptosis

Reactive oxygen species (ROS), driven by excessive levels of glucose and free fatty acids, appears to induce cell apoptosis. However, the underlying molecular mechanism of this process remains unclear in cardiac myocytes. We investigated the glucolipotoxicity effects of high glucose and palmitic acid (C16:0) on the rat cardiomyoblast cell line (H9c2) focusing on tumor suppressor p53. Cultured H9c2 rat cardiomyoblasts were exposed to palmitate and /or to an elevated glucose concentration for 18 hours. Only the glucolipotoxic condition of 30 mM glucose in combination with 250 μM palmitate resulted in significant generation of ROS and upregulation of p53 which caused to an increased cleavage of caspase-3. On the other hand, the expression of NF-E2-related factor 2 (Nrf2) showed increased tendency while the expression of NAD(P)H: quinone oxidoreductase-1 (NQO1) was decreased. N-acetyl L cysteins and pifithrin-α, an inhibitor of p53 abrogated glucolipotoxicity-induced ROS generation and p53 expression. Chromatin immunoprecipitation analysis revealed that p53 interacted antioxidant responsive elements (ARE)-containing promoter of NQO1. Upregulated p53 counteracted the Nrf2-induced transcription of ARE-containing promoter of NQO1 gene and leaded to decrease in NQO1 expression. We demonstrated that the elevated p53 mediated glucolipotoxicity-induced apoptosis of rat cardiomyoblast cell through dual pathways: stimulating pro-apoptosis signaling as well as suppressing anti-apoptosis pathway of Nrf2-NQO1 signaling.

PPARα agonist prevented the apoptosis induced by glucose and fatty acid in neonatal cardiomyocytes

OBJECTIVE

We investigated the effect of peroxisome proliferator activator receptors α (PPARα) on cardiomyocyte apoptosis induced by glucose and fatty acid, and if high glucose levels could increase fatty acid-induced apoptosis.

METHODS

Cardiomyocytes were maintained in Dulbecco's Modified Eagle Medium and divided into 5 groups: Group N (control Group); Group G (exposed to 25.5 mmol/l glucose); Group L (exposed to 5 mmol/l glucose, fatty acid); Group H (exposed to 25.5 mmol/l glucose and fatty acid); Group I (exposed to 25.5 mmol/l glucose, fatty acid and Wy14643). Apoptosis was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling. Immunocytochemistry staining detected PPARα's expressing, and western blotting detected PPARα and nuclear factor κB's (NF-κB) protein level.

RESULTS

Exposure to fatty acid resulted in a significant increase of cardiomyocytes apoptosis, with the extension of NF-κB formation, whereas exposure to 25.5 mmol/l glucose had no influence on the apoptosis rate. However, combination with fatty acid and high glucose concentration had induced more apoptosis with the up-regulation of NF-κB formation. The fatty acid and glucose-induced effects were improved by Wy14643, with down-regulation of NF-κB formation.

CONCLUSION

These results suggested that in neonatal cardiomyocytes, fatty acid and glucose in combination with fatty acid induced apoptosis via NF-κB formation and activation of apoptosis pathways; glucose in combination with fatty acid induce more apoptosis rate for the more NF- κB formation, activation of the PPARα can reverse such apoptosis effect. The results also suggest that gluco-lipotoxicity may play a central role in the development of diabetic cardiomyopathy, and PPARα-agonist may be an effective drug in treating the diabetic cardiomyopathy.