Diabetes- and angiotensin II-induced cardiac endoplasmic reticulum stress and cell death: metallothionein protection

Inhibition of JNK by novel curcumin analog C66 prevents diabetic cardiomyopathy with a preservation of cardiac metallothionein expression

The development of diabetic cardiomyopathy is attributed to diabetic oxidative stress, which may be related to the mitogen-activated protein kinase (MAPK) c-Jun NH2-terminal kinase (JNK) activation. The present study tested a hypothesis whether the curcumin analog C66 [(2E,6E)-2,6-bis(2-(trifluoromethyl)benzylidene) cyclohexanone] as a potent antioxidant can protect diabetes-induced cardiac functional and pathogenic changes via inhibition of JNK function. Diabetes was induced with a single intraperitoneal injection of streptozotocin in male C57BL/6 mice. Diabetic and age-matched control mice were randomly divided into three groups, each group treated with C66, JNK inhibitor (JNKi, SP600125), or vehicle (1% CMC-Na solution) by gavage at 5 mg/kg every other day for 3 mo. Neither C66 nor JNKi impacted diabetic hyperglycemia and inhibition of body-weight gain, but both significantly prevented diabetes-induced JNK phosphorylation in the heart. Compared with basal line, cardiac function was significantly decreased in diabetic mice at 3 mo of diabetes but not in C66- or JNKi-treated diabetic mice. Cardiac fibrosis, oxidative damage, endoplasmic reticulum stress, and cell apoptosis, examined by Sirius red staining, Western blot, and thiobarbituric acid assay, were also significantly increased in diabetic mice, all which were prevented by C66 or JNKi treatment under diabetic conditions. Cardiac metallothionein expression was significantly decreased in diabetic mice but was almost normal in C66- or JNKi-treated diabetic mice. These results suggest that, like JNKi, C66 is able to prevent diabetic upregulation of JNK function, resulting in a prevention of diabetes-induced cardiac fibrosis, oxidative stress, endoplasmic reticulum stress, and cell death, along with a preservation of cardiac metallothionein expression.

Metallothionein prevents cardiac pathological changes in diabetes by modulating nitration and inactivation of cardiac ATP synthase

Mitochondrial ATP production is the main energy source for the cell. Diabetes reduces the efficient generation of ATP, possibly due to the inactivation of ATP synthase. However, the exact mechanism by which diabetes induces inactivation of ATP synthase remains unknown, as well as whether such inactivation has a role in the development of pathological abnormalities of the diabetic heart. To address these issues, we used cardiac metallothionein-transgenic (MT-TG) and wild-type (WT) mice with streptozotocin-induced diabetes, since we have demonstrated previously that diabetes-induced cardiac damage and remodeling were found in WT diabetic mice, but not in MT-TG diabetic mice. Immunohistochemical and biochemical assays were used to compare pathological and biochemical changes of the heart between MT-TG and WT diabetic mice, and a proteomic assay to evaluate ATP synthase expression and tyrosine nitration, with its activity. LC/MS analysis revealed that diabetes increased tyrosine nitration of the ATP synthase α subunit at Tyr(271), Tyr(311), and Tyr(476), and the β subunit at Tyr(269) and Tyr(508), and also significantly reduced ATP synthase activity by ~32%. These changes were not observed in MT-TG diabetic mice. Furthermore, parallel experiments with induced expression of cardiac MT by zinc supplementation in diabetic mice produced similar effects. These results suggest that MT can preserve ATP synthase activity in streptozotocin-induced diabetes, probably through the inhibition of ATP synthase nitration.

Molecular mechanisms of diabetic cardiomyopathy

In recent years, diabetes mellitus has become an epidemic and now represents one of the most prevalent disorders. Cardiovascular complications are the major cause of mortality and morbidity in diabetic patients. While ischaemic events dominate the cardiac complications of diabetes, it is widely recognised that the risk for developing heart failure is also increased in the absence of overt myocardial ischaemia and hypertension or is accelerated in the presence of these comorbidities. These diabetes-associated changes in myocardial structure and function have been called diabetic cardiomyopathy. Numerous molecular mechanisms have been proposed to contribute to the development of diabetic cardiomyopathy following analysis of various animal models of type 1 or type 2 diabetes and in genetically modified mouse models. The steady increase in reports presenting novel mechanistic data on this subject expands the list of potential underlying mechanisms. The current review provides an update on molecular alterations that may contribute to the structural and functional alterations in the diabetic heart.

The role of cardiac lipotoxicity in the pathogenesis of diabetic cardiomyopathy

Cardiomyopathy, the presence of cardiac dysfunction independent of ischemic heart disease and/or hypertension, is becoming a more prominent condition in our diabetic patient population. Unfortunately, we do not yet understand the mechanism(s) responsible for causing diabetic cardiomyopathy. With the recent explosion in the obesity and Type 2 diabetes epidemic, our understanding of dyslipidemia and the adverse effects of lipid surplus on cellular and organ function has grown considerably. Numerous studies now illustrate that excess lipid accumulation may exert direct toxic effects on cellular function, a term coined 'lipotoxicity'. As obesity and Type 2 diabetes are significant risk factors for cardiovascular disease, cardiac lipotoxicity may represent a significant component mediating the diabetic cardiomyopathy phenotype. Therefore, a more complete understanding of how cardiac lipotoxicity is regulated and how different lipid metabolites cause cellular dysfunction may lead to the discovery of novel targets to treat cardiomyopathy in our diabetic patient population.

Selenium deficiency is associated with endoplasmic reticulum stress in a rat model of cardiac malfunction

The relationship between selenium (Se) deficiency-induced cardiac malfunction and endoplasmic reticulum (ER) stress is poorly understood. In the present study, 18 weaning Sprague Dawley rats were randomly fed with three different Se diets, and myocardial glutathione peroxidase (GPx) activity was measured by an enzyme activity assay. Cardiac function was evaluated by hemodynamic parameters. ER stress markers immunoglobulin-binding protein (BiP)/glucose-regulated protein 78 (GRP78) and C/EBP homologous protein (CHOP) were detected by western blotting. Our data showed that myocardial GPx activity and cardiac function were conspicuously impaired in Se-deficient rats. Expression of GRP78 and CHOP was significantly upregulated by treatment of Se deficiency. Improvements in myocardial GPx activity and cardiac function, as well as decreases in expression of GRP78 and CHOP, were observed after Se supplementation. Consequently, our data show that ER stress was involved in Se deficiency-induced cardiac dysfunction.

Toxicological profile of small airway epithelial cells exposed to gold nanoparticles

Gold nanoparticles (AuNPs) have diverse applications in the biomedical industry such as in diagnosis, labeling, delivering and sensing. Despite their prevalent medical use, nanotoxicity induced by AuNPs is still largely unknown. We have previously shown that AuNPs could exert cytotoxic effects on lung fibroblasts. In this study, we investigated the in vitro toxicological effects of AuNPs in small airway epithelial cells (SAECs) which are the first cells of contact for inhaled NPs and compared expression of metallothionein (MT), a reactive oxygen species scavenger, in SAECs and lung fibroblasts in vitro. Transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) spectroscopy study revealed cellular uptake of aggregates of AuNPs into the cytoplasm at the ultrastructural level. A significant increase in lipid peroxide as well as substantial DNA damage and cytotoxicity was observed in AuNP-treated cells. For MT expression, AuNPs induced down-regulation of the MT-1X isoform in SAECs, but up-regulation of the MT-1X and MT-2 A isoforms in MRC5 lung fibroblasts. The present study suggests that AuNPs could induce oxidative stress-related cytotoxicity and genotoxicity in SAECs.

Icariin protects rat cardiac H9c2 cells from apoptosis by inhibiting endoplasmic reticulum stress

Endoplasmic reticulum stress (ERS) is one of the mechanisms of apoptotic cell death. Inhibiting the apoptosis induced by ERS may be a novel therapeutic target in cardiovascular diseases. Icariin, a flavonoid isolated from Epimedium brevicornum Maxim, has been demonstrated to have cardiovascular protective effects, but its effects on ERS are unknown. In the present study, we focused on icariin and investigated whether it might protect the cardiac cell from apoptosis via inhibition of ERS. In H9c2 rat cardiomyoblast cells, pretreatment of icariin significantly inhibited cell apoptosis by tunicamycin, an ERS inducer. Icariin also decreased generation of reactive oxygen species (ROS), loss of mitochondrial membrane potential and activation of caspase-3. Moreover, icariin inhibited upregulation of endoplasmic reticulum markers, GRP78, GRP94 and CHOP, elicited by tunicamycin. These results indicated that icariin could protect H9c2 cardiomyoblast cells from ERS-mitochondrial apoptosis in vitro, the mechanisms may be associated with its inhibiting of GRP78, GRP94 and CHOP and decreasing ROS generation directly. It may be a potential agent for treating cardiovascular disease.

Carbamylated erythropoietin attenuates cardiomyopathy via PI3K/Akt activation in rats with diabetic cardiomyopathy

The aim of the present study was to investigate the protective effect of carbamylated erythropoietin (CEPO) against cardiomyopathy in high-fat, high-carbohydrate diet-fed rats with streptozotocin (STZ)-induced diabetic cardiomyopathy (DCM). Healthy male Wistar rats were fed a high-fat, high-carbohydrate diet for four weeks, and then were injected with STZ twice (50 mg/kg, intraperitoneally). Once DCM was confirmed, the rats were divided randomly into the following groups: DCM without treatment, CEPO treatment at different dosages (500, 1,000 or 2,000 IU/kg) or recombinant human erythropoietin (rhEPO) treatment (1,000 IU/kg), for a four-week short intervention or an eight-week long intervention protocol. Healthy rats were used as normal controls. Venous blood samples were drawn for routine hematological examinations, and heart tissues were collected for histological analysis, as well as the determination of myocardial apoptosis and phosphatidylinositol-3-kinase (PI3K)/Akt signaling. CEPO treatment had no significant effect on the erythrocyte or hemoglobin levels in the rats with DCM; however, it reduced myocardial cell apoptosis in the rats and protected the cellular ultrastructure. In addition, CEPO treatment inhibited caspase-3 and increased Bcl-xl protein expression (P<0.05). It also increased PI3K (p85) and Akt1 expression at the mRNA and protein levels in the hearts of the rats with DCM, with a dose-response relationship. An eight-week treatment using CEPO, in comparison with a four-week protocol, marginally increased PI3K (p85) and Akt1 expression, and did not demonstrate significant benefit. The study indicated that CEPO protects against DCM, without markedly affecting erythropoiesis, and that the activation of PI3K/Akt may be a key mechanism in the protection conferred by CEPO.

Activation of ErbB2 and Downstream Signalling via Rho Kinases and ERK1/2 Contributes to Diabetes-Induced Vascular Dysfunction

Diabetes mellitus leads to vascular complications but the underlying signalling mechanisms are not fully understood. Here, we examined the role of ErbB2 (HER2/Neu), a transmembrane receptor tyrosine kinase of the ErbB/EGFR (epidermal growth factor receptor) family, in mediating diabetes-induced vascular dysfunction in an experimental model of type 1 diabetes. Chronic treatment of streptozotocin-induced diabetic rats (1 mg/kg/alt diem) or acute, ex-vivo (10(-6), 10(-5) M) administration of AG825, a specific inhibitor of ErbB2, significantly corrected the diabetes-induced hyper-reactivity of the perfused mesenteric vascular bed (MVB) to the vasoconstrictor, norephinephrine (NE) and the attenuated responsiveness to the vasodilator, carbachol. Diabetes led to enhanced phosphorylation of ErbB2 at multiple tyrosine (Y) residues (Y1221/1222, Y1248 and Y877) in the MVB that could be attenuated by chronic AG825 treatment. Diabetes- or high glucose-mediated upregulation of ErbB2 phosphorylation was coupled with activation of Rho kinases (ROCKs) and ERK1/2 in MVB and in cultured vascular smooth muscle cells (VSMC) that were attenuated upon treatment with either chronic or acute AG825 or with anti-ErbB2 siRNA. ErbB2 likley heterodimerizes with EGFR, as evidenced by increased co-association in diabetic MVB, and further supported by our finding that ERK1/2 and ROCKs are common downstream effectors since their activation could also be blocked by AG1478. Our results show for the first time that ErbB2 is an upstream effector of ROCKs and ERK1/2 in mediating diabetes-induced vascular dysfunction. Thus, potential strategies aimed at modifying actions of signal transduction pathways involving ErbB2 pathway may prove to be beneficial in treatment of diabetes-induced vascular complications.

Depressed calcium-handling proteins due to endoplasmic reticulum stress and apoptosis in the diabetic heart are attenuated by argirein

Diabetic cardiomyopathy (DC) is a unique disease frequently complicated to diabetes mellitus, manifesting endoplasmic reticulum (ER) stress and depressed calcium-handling proteins. We hypothesized that the abnormal FKBP12.6, SERCA2a, and CASQ2 are consequent to ER stress and apoptosis that are likely due to an entity of inflammation. These abnormalities may be attributed to reactive oxygen species genesis from activated NADPH oxidase which could respond to argirein (AR) through its anti-inflammatory activity. Sprague Dawley rats were randomly divided into six groups. Except the normal group, rats were injected with streptozotocin (STZ; 60 mg/kg, i.p.) once. During weeks 5 to 8 following STZ injection, rats were treated (in milligrams per kilogram per day, i.g.) with aminoguanidine (AMG, 100; an inducible nitric oxide synthase and AGEs inhibitor) or three doses of AR (50, 100, and 200). FKBP12.6, SERCA2a, and CASQ2 and ER stress chaperones Bip and PERK and apoptotic molecules were monitored in vivo and in vitro. Impaired cardiac performance and downregulated FKBP12.6, SERCA2a, and CASQ2 were significant in DC in vivo, and abnormal calcium-handling proteins were also found in high-glucose-incubated myocytes in vitro. ER stress manifested by upregulated Bip and PERK was predominant in association with DNA ladder and upregulated Bax and downregulated BCL-2 in vivo and in vitro. AR is effective to attenuate these abnormalities compared to AMG. Diabetic myocardium has inflammatory entity expressed as ER stress contributing to downregulated calcium-handling proteins. AR has potential in managing DC through attenuating depressed calcium-handling proteins, activated ER stress, and apoptosis in the myocardium.

Oxidative activation of Ca(2+)/calmodulin-activated kinase II mediates ER stress-induced cardiac dysfunction and apoptosis

Endoplasmic reticulum (ER) stress elicits oxidative stress and intracellular Ca(2+) derangement via activation of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). This study was designed to examine the role of CaMKII in ER stress-induced cardiac dysfunction and apoptosis as well as the effect of antioxidant catalase. Wild-type FVB and transgenic mice with cardiac-specific overexpression of catalase were challenged with the ER stress inducer tunicamycin (3 mg/kg ip for 48 h). Presence of ER stress was verified using the ER stress protein markers immunoglobulin binding protein (BiP) and C/EBP homologous protein (CHOP), the effect of which was unaffected by catalase overexpression. Echocardiographic assessment revealed that tunicamycin elicited cardiac remodeling (enlarged end-systolic diameter without affecting diastolic and ventricular wall thickness), depressed fractional shortening, ejection fraction, and cardiomyocyte contractile capacity, intracellular Ca(2+) mishandling, accumulation of reactive oxygen species (superoxide production and NADPH oxidase p47phox level), CaMKII oxidation, and apoptosis (evidenced by Bax, Bcl-2/Bax ratio, and TUNEL staining), the effects of which were obliterated by catalase. Interestingly, tunicamycin-induced cardiomyocyte mechanical anomalies and cell death were ablated by the CaMKII inhibitor KN93, in a manner reminiscent of catalase. These data favored a permissive role of oxidative stress and CaMKII activation in ER stress-induced cardiac dysfunction and cell death. Our data further revealed the therapeutic potential of antioxidant or CaMKII inhibition in cardiac pathological conditions associated with ER stress. This research shows for the first time that contractile dysfunction caused by ER stress is a result of the oxidative activation of the CaMKII pathway.

Zinc homeostasis in the metabolic syndrome and diabetes

Zinc (Zn) is an essential mineral that is required for various cellular functions. Zn dyshomeostasis always is related to certain disorders such as metabolic syndrome, diabetes and diabetic complications. The associations of Zn with metabolic syndrome, diabetes and diabetic complications, thus, stem from the multiple roles of Zn: (1) a constructive component of many important enzymes or proteins, (2) a requirement for insulin storage and secretion, (3) a direct or indirect antioxidant action, and (4) an insulin-like action. However, whether there is a clear cause-and-effect relationship of Zn with metabolic syndrome, diabetes, or diabetic complications remains unclear. In fact, it is known that Zn deficiency is a common phenomenon in diabetic patients. Chronic low intake of Zn was associated with the increased risk of diabetes and diabetes also impairs Zn metabolism. Theoretically Zn supplementation should prevent the metabolic syndrome, diabetes, and diabetic complications; however, limited available data are not always supportive of the above notion. Therefore, this review has tried to summarize these pieces of available information, possible mechanisms by which Zn prevents the metabolic syndrome, diabetes, and diabetic complications. In the final part, what are the current issues for Zn supplementation were also discussed.

The role of epidermal growth factor receptor in diabetes-induced cardiac dysfunction

The incidence of diabetes mellitus is increasing rapidly and set to reach near epidemic proportions with the latest estimates suggesting that by 2030 there will be over 550 million people with this debilitating disease. Cardiovascular complications and dysfunctions are three- to eight-folds more likely in diabetic patients and are major causes of increased mortality. The exact underlying mechanisms for the development of complications of the diabetic heart are poorly understood and may involve multiple signaling pathways that are affected by hyperglycemia. This focused article reviews the recent evidence for a possible dual role of epidermal growth factor receptor signaling in diabetes-induced cardiac dysfunction.

Diabetes-induced hepatic pathogenic damage, inflammation, oxidative stress, and insulin resistance was exacerbated in zinc deficient mouse model

OBJECTIVES

Zinc (Zn) deficiency often occurs in the patients with diabetes. Effects of Zn deficiency on diabetes-induced hepatic injury were investigated.

METHODS

Type 1 diabetes was induced in FVB mice with multiple low-dose streptozotocin. Hyperglycemic and age-matched control mice were treated with and without Zn chelator, N,N,N',N'-tetrakis (2-pyridylemethyl) ethylenediamine (TPEN), at 5 mg/kg body-weight daily for 4 months. Hepatic injury was examined by serum alanine aminotransferase (ALT) level and liver histopathological and biochemical changes.

RESULTS

Hepatic Zn deficiency (lower than control level, p<0.05) was seen in the mice with either diabetes or TPEN treatment and more evident in the mice with both diabetes and TPEN. Zn deficiency exacerbated hepatic injuries, shown by further increased serum ALT, hepatic lipid accumulation, inflammation, oxidative damage, and endoplasmic reticulum stress-related cell death in Diabetes/TPEN group compared to Diabetes alone. Diabetes/TPEN group also showed a significant decrease in nuclear factor-erythroid 2-related factor 2 (Nrf2) expression and transcription action along with significant increases in Akt negative regulators, decrease in Akt and GSK-3β phosphorylation, and increase in nuclear accumulation of Fyn (a Nrf2 negative regulator). In vitro study with HepG2 cells showed that apoptotic effect of TPEN at 0.5-1.0 µM could be completely prevented by simultaneous Zn supplementation at the dose range of 30-50 µM.

CONCLUSIONS

Zn is required for maintaining Akt activation by inhibiting the expression of Akt negative regulators; Akt activation can inhibit Fyn nuclear translocation to export nuclear Nrf2 to cytoplasm for degradation. Zn deficiency significantly enhanced diabetes-induced hepatic injury likely through down-regulation of Nrf2 function.

Ghrelin protects H9c2 cardiomyocytes from angiotensin II-induced apoptosis through the endoplasmic reticulum stress pathway

Ghrelin, a gastric hormone, exerts cardioprotective function by increasing myocardial contractility and vasodilation. Previous studies have reported that angiotensin II (Ang II) production increased in heart failure, which can induce cardiomyocyte apoptosis. In this study, we investigated the effect of ghrelin on Ang II-induced H9c2 cardiomyocyte apoptosis. The results showed that Ang II inhibited H9c2 cell viability, which was blocked by ghrelin. By annexin V-propidium iodide dual staining and 2'-deoxyuridine 5'-triphosphate nick end-labeling analysis, we found that Ang II induced H9c2 cell apoptosis, whereas coincubation of ghrelin with Ang II significantly reduced H9c2 cell apoptosis induced by Ang II. Simultaneously, the results revealed that ghrelin regulated the Ang II-induced imbalance of Bax and Bcl-2 expression and reduced Ang II-induced caspase-3 expression. Moreover, mRNA expressions of endoplasmic reticulum stress-related molecules GRP78, caspase-12, and C/EBP homologous protein were significantly upregulated by Ang II. However, their expressions were significantly inhibited by ghrelin. In addition, we found that ghrelin markedly inhibited Ang II-induced Ang II type 1 receptor expression. These data suggest that ghrelin may play an antagonistic role in Ang II-induced cardiomyocyte apoptosis via decreasing Ang II type 1 receptor expression and inhibiting the activation of endoplasmic reticulum stress pathway.

A thrombospondin-dependent pathway for a protective ER stress response

Thrombospondin (Thbs) proteins are induced in sites of tissue damage or active remodeling. The endoplasmic reticulum (ER) stress response is also prominently induced with disease where it regulates protein production and resolution of misfolded proteins. Here we describe a function for Thbs as ER-resident effectors of an adaptive ER stress response. Thbs4 cardiac-specific transgenic mice were protected from myocardial injury, whereas Thbs4(-/-) mice were sensitized to cardiac maladaptation. Thbs induction produced a unique profile of adaptive ER stress response factors and expansion of the ER and downstream vesicles. Thbs bind the ER lumenal domain of activating transcription factor 6α (Atf6α) to promote its nuclear shuttling. Thbs4(-/-) mice showed blunted activation of Atf6α and other ER stress-response factors with injury, and Thbs4-mediated protection was lost upon Atf6α deletion. Hence, Thbs can function inside the cell during disease remodeling to augment ER function and protect through a mechanism involving regulation of Atf6α.

Role of ER stress in ventricular contractile dysfunction in type 2 diabetes

Background

Diabetes mellitus (DM) is associated with an increased risk of ischemic heart disease and of adverse outcomes following myocardial infarction (MI). Here we assessed the role of endoplasmic reticulum (ER) stress in ventricular dysfunction and outcomes after MI in type 2 DM (T2DM).

Methodology and Principal Findings

In hearts of OLETF, a rat model of T2DM, at 25∼30 weeks of age, GRP78 and GRP94, markers of ER stress, were increased and sarcoplasmic reticulum calcium ATPase (SERCA)2a protein was reduced by 35% compared with those in LETO, a non-diabetic control. SERCA2a mRNA levels were similar, but SERCA2a protein was more ubiquitinated in OLETF than in LETO. Left ventricular (LV) end-diastolic elastance (Eed) was higher in OLETF than in LETO (53.9±5.2 vs. 20.2±5.6 mmHg/µl), whereas LV end-systolic elastance and positive inotropic responses to β-adrenergic stimulation were similar in OLETF and LETO. 4-Phenylbutyric acid (4-PBA), an ER stress modulator, suppressed both GRP up-regulation and SERCA2a ubiquitination and normalized SERCA2a protein level and Eed in OLETF. Sodium tauroursodeoxycholic acid, a structurally different ER stress modulator, also restored SERCA2a protein level in OLETF. Though LV dysfunction was modest, mortality within 48 h after coronary occlusion was markedly higher in OLETF than in LETO (61.3% vs. 7.7%). Telemetric recording showed that rapid progression of heart failure was responsible for the high mortality rate in OLETF. ER stress modulators failed to reduce the mortality rate after MI in OLETF.

Conclusions

ER stress reduces SERCA2a protein via its augmented ubiquitination and degradation, leading to LV diastolic dysfunction in T2DM. Even at a stage without systolic LV dysfunction, susceptibility to lethal heart failure after infarction is markedly increased, which cannot be explained by ER stress or change in myocardial response to sympathetic nerve activation.

A novel role for epidermal growth factor receptor tyrosine kinase and its downstream endoplasmic reticulum stress in cardiac damage and microvascular dysfunction in type 1 diabetes mellitus

Epidermal growth factor receptor tyrosine kinase (EGFRtk) and endoplasmic reticulum (ER) stress are important factors in cardiovascular complications. Understanding whether enhanced EGFRtk activity and ER stress induction are involved in cardiac damage, and microvascular dysfunction in type 1 diabetes mellitus is an important question that has remained unanswered. Cardiac fibrosis and microvascular function were determined in C57BL/6J mice injected with streptozotocin only or in combination with EGFRtk inhibitor (AG1478), ER stress inhibitor (Tudca), or insulin for 2 weeks. In diabetic mice, we observed an increase in EGFRtk phosphorylation and ER stress marker expression (CHOP, ATF4, ATF6, and phosphorylated-eIF2α) in heart and mesenteric resistance arteries, which were reduced with AG1478, Tudca, and insulin. Cardiac fibrosis, enhanced collagen type I, and plasminogen activator inhibitor 1 were decreased with AG1478, Tudca, and insulin treatments. The impaired endothelium-dependent relaxation and -independent relaxation responses were also restored after treatments. The inhibition of NO synthesis reduced endothelium-dependent relaxation in control and treated streptozotocin mice, whereas the inhibition of NADPH oxidase improved endothelium-dependent relaxation only in streptozotocin mice. Moreover, in mesenteric resistance arteries, the mRNA levels of Nox2 and Nox4 and the NADPH oxidase activity were augmented in streptozotocin mice and reduced with treatments. This study unveiled novel roles for enhanced EGFRtk phosphorylation and its downstream ER stress in cardiac fibrosis and microvascular endothelial dysfunction in type 1 diabetes mellitus.

Endoplasmic reticulum stress and the on site function of resident PTP1B

Growing evidence links the stress at the endoplasmic reticulum (ER) to pathologies such as diabetes mellitus, obesity, liver, heart, renal and neurodegenerative diseases, endothelial dysfunction, atherosclerosis, and cancer. Therefore, identification of molecular pathways beyond ER stress and their appropriate modulation might alleviate the stress, and direct toward novel tools to fight this disturbance. An interesting resident of the ER membrane is protein tyrosine phosphatase 1B (PTP1B), an enzyme that negatively regulates insulin and leptin signaling, contributing to insulin and leptin resistance. Recently, new functions of PTP1B have been established linked to ER stress response. This review evaluates the novel data on ER stressors, discusses the mechanisms beyond PTP1B function in the ER stress response, and emphasizes the potential therapeutic exploitation of PTP1B to relieve ER stress.

Endoplasmic reticulum stress is involved in cardiac damage and vascular endothelial dysfunction in hypertensive mice

OBJECTIVE

Cardiac damage and vascular dysfunction are major causes of morbidity and mortality in hypertension. In the present study, we explored the beneficial therapeutic effect of endoplasmic reticulum (ER) stress inhibition on cardiac damage and vascular dysfunction in hypertension.

METHODS AND RESULTS

Mice were infused with angiotensin II (400 ng/kg per minute) with or without ER stress inhibitors (taurine-conjugated ursodeoxycholic acid and 4-phenylbutyric acid) for 2 weeks. Mice infused with angiotensin II displayed an increase in blood pressure, cardiac hypertrophy and fibrosis associated with enhanced collagen I content, transforming growth factor-β1 (TGF-β1) activity, and ER stress markers, which were blunted after ER stress inhibition. Hypertension induced ER stress in aorta and mesenteric resistance arteries (MRA), enhanced TGF-β1 activity in aorta but not in MRA, and reduced endothelial NO synthase phosphorylation and endothelium-dependent relaxation (EDR) in aorta and MRA. The inhibition of ER stress significantly reduced TGF-β1 activity, enhanced endothelial NO synthase phosphorylation, and improved EDR. The inhibition of TGF-β1 pathway improved EDR in aorta but not in MRA, whereas the reduction in reactive oxygen species levels ameliorated EDR in MRA only. Infusion of tunicamycin in control mice induced ER stress in aorta and MRA, and reduced EDR by a TGF-β1-dependent mechanism in aorta and reactive oxygen species-dependent mechanism in MRA.

CONCLUSIONS

ER stress inhibition reduces cardiac damage and improves vascular function in hypertension. Therefore, ER stress could be a potential target for cardiovascular diseases.

Β-adrenergic receptor stimulation induces endoplasmic reticulum stress in adult cardiac myocytes: role in apoptosis

Accumulation of misfolded proteins and alterations in calcium homeostasis induces endoplasmic reticulum (ER) stress, leading to apoptosis. In this study, we tested the hypothesis that β-AR stimulation induces ER stress, and induction of ER stress plays a pro-apoptotic role in cardiac myocytes. Using thapsigargin and brefeldin A, we demonstrate that ER stress induces apoptosis in adult rat ventricular myocytes (ARVMs). β-AR-stimulation (isoproterenol; 3h) significantly increased expression of ER stress proteins, such as GRP-78, Gadd-153, and Gadd-34, while activating caspase-12 in ARVMs. In most parts, these effects were mimicked by thapsigargin. β-AR stimulation for 15 min increased PERK and eIF-2α phosphorylation. PERK phosphorylation remained higher, while eIF-2α phosphorylation declined thereafter, reaching to ~50% below basal levels at 3 h after β-AR stimulation. This decline in eIF-2α phosphorylation was prevented by β1-AR, not by β2-AR antagonist. Forskolin, adenylyl cyclase activator, simulated the effects of ISO on eIF-2α phosphorylation. Salubrinal (SAL), an ER stress inhibitor, maintained eIF-2α phosphorylation and inhibited β-AR-stimulated apoptosis. Furthermore, inhibition of caspase-12 using z-ATAD inhibited β-AR-stimulated and thapsigargin-induced apoptosis. In vivo, β-AR stimulation induced ER stress in the mouse heart as evidenced by increased expression of GRP-78 and Gadd-153, activation of caspase-12, and dephosphorylation of eIF-2α. SAL maintained phosphorylation of eIF-2α, inhibited activation of caspase-12, and decreased β-AR-stimulated apoptosis in the heart. Thus, β-AR stimulation induces ER stress in cardiac myocytes and in the heart, and induction of ER stress plays a pro-apoptotic role.

Dietary nitrite attenuates oxidative stress and activates antioxidant genes in rat heart during hypobaric hypoxia

The nitrite anion represents the circulatory and tissue storage form of nitric oxide (NO) and a signaling molecule, capable of conferring cardioprotection and many other health benefits. However, molecular mechanisms for observed cardioprotective properties of nitrite remain largely unknown. We have evaluated the NO-like bioactivity and cardioprotective efficacies of sodium nitrite supplemented in drinking water in rats exposed to short-term chronic hypobaric hypoxia. We observed that, nitrite significantly attenuates hypoxia-induced oxidative stress, modulates HIF-1α stability and promotes NO-cGMP signaling in hypoxic heart. To elucidate potential downstream targets of nitrite during hypoxia, we performed a microarray analysis of nitrite supplemented hypoxic hearts and compared with both hypoxic and nitrite supplemented normoxic hearts respectively. The analysis revealed a significant increase in the expression of many antioxidant genes, transcription factors and cardioprotective signaling pathways which was subsequently confirmed by qRT-PCR and Western blotting. Conversely, hypoxia exposure increased oxidative stress, activated inflammatory cytokines, downregulated ion channels and altered expression of both pro- and anti-oxidant genes. Our results illustrate the physiological function of nitrite as an eNOS-independent source of NO in heart profoundly modulating the oxidative status and cardiac transcriptome during hypoxia.

Endoplasmic reticulum stress and diabetic cardiomyopathy

The endoplasmic reticulum (ER) is an organelle entrusted with lipid synthesis, calcium homeostasis, protein folding, and maturation. Perturbation of ER-associated functions results in an evolutionarily conserved cell stress response, the unfolded protein response (UPR) that is also called ER stress. ER stress is aimed initially at compensating for damage but can eventually trigger cell death if ER stress is excessive or prolonged. Now the ER stress has been associated with numerous diseases. For instance, our recent studies have demonstrated the important role of ER stress in diabetes-induced cardiac cell death. It is known that apoptosis has been considered to play a critical role in diabetic cardiomyopathy. Therefore, this paper will summarize the information from the literature and our own studies to focus on the pathological role of ER stress in the development of diabetic cardiomyopathy. Improved understanding of the molecular mechanisms underlying UPR activation and ER-initiated apoptosis in diabetic cardiomyopathy will provide us with new targets for drug discovery and therapeutic intervention.

Modulation of AT-1R/CHOP-JNK-Caspase12 pathway by olmesartan treatment attenuates ER stress-induced renal apoptosis in streptozotocin-induced diabetic mice

There is evidence that the activation of renal angiotensin (Ang)-II plays a critical role in the pathogenesis of diabetic kidney diseases (DN) via the ER stress-induced renal apoptosis. Since, the potential negative role of Ang-II in the pathogenesis of ER stress-mediated apoptosis is poorly understood; we evaluated whether treatment of mice with AT-1R specific blocker, olmesartan is associated with the reduction of ER stress-induced renal apoptosis in streptozotocin (STZ)-induced diabetic animal model. We employed western blot analysis to measure the renal protein expressions level of NADPH oxidase subunits, ER chaperone GRP78 and the ER-associated apoptosis proteins. Furthermore, TUNEL staining was used to measure the renal apoptosis. Additionally, dihydroethidium staining and TBARS assay, and immunohistochemistry were performed to measure the renal superoxide radical production and lipid peroxidation, and activation of an Ang-II, respectively. The diabetic kidney mice were found to have increased protein expressions of NADPH oxidase subunits, GRP78 and ER-associated apoptosis proteins, such as TRAF2, IRE-1α, CHOP, p-JNK and procaspase-12, in comparison to normal mice, and which were significantly blunted by the olmesartan treatment in diabetic kidney mice. Furthermore, the diabetic kidney mice were found to have significant increment in renal apoptosis, superoxide radical production, MDA level and activation of an Ang-II and which were also attenuated by the olmesartan treatment. Considering all the findings, it is suggested that the AT-1R specific blocker-olmesartan treatment could be a potential therapy in treating ER stress-induced renal apoptosis via the modulation of AT-1R/CHOP-JNK-Caspase12 pathway in STZ-induced diabetic mice.

Altered oxido-reductive state in the diabetic heart: loss of cardioprotection due to protein disulfide isomerase

Diabetes is associated with an increased risk of heart failure, in part explained by endoplasmic reticulum stress and apoptosis. Protein disulfide isomerase (PDI) prevents stressed cardiomyocytes apoptosis. We hypothesized that diabetes impairs PDI function by an alteration in its oxido-reductive state. Myocardial biopsies harvested from the anterolateral left ventricular wall from diabetic (n = 7) and nondiabetic (n = 8) patients were used to assess PDI expression and cardiomyocyte death. A mouse model of diabetes (streptozotocin injection, 130 mg/mL) was used to study PDI expression and its redox state after ischemia/reperfusion injury induced by 30-min occlusion of the left anterior coronary artery followed by reperfusion. Transthoracic echocardiography was performed to assess cardiac remodeling after 1 wk. Western blot analysis was used to analyze PDI expression, and methoxy-polyethyleneglycol-maleimide was used to assess its redox state. Dehydroascorbate (DHA) administration was used to restore the PDI redox state. Diabetic patients had a greater number of transferase-mediated dUTP nick-end labeling (TUNEL)-positive cells than nondiabetic patients despite a greater myocardial PDI expression suggesting altered PDI function. Diabetic mice had a worse postinfarction remodeling associated with an altered PDI redox state. DHA treatment restored functional PDI redox state and ameliorated post-myocardial infarction remodeling. An increase in PDI levels with a paradoxical decrease of its active form occurs in the diabetic heart after ischemia and may explain the lack of protective effects of PDI in diabetes. Restoration of PDI redox state prevents adverse remodeling. The potential significance of these findings deserves to be validated in a clinical setting.

Activin A levels are associated with abnormal glucose regulation in patients with myocardial infarction: potential counteracting effects of activin A on inflammation

OBJECTIVE

On the basis of the role of activin A in inflammation, atherogenesis, and glucose homeostasis, we investigated whether activin A could be related to glucometabolic abnormalities in patients with acute myocardial infarction (MI).

RESEARCH DESIGN AND METHODS

Activin A measurement and oral glucose tolerance tests (OGTTs) were performed in patients (n = 115) with acute MI, without previously known diabetes, and repeated after 3 months. Release of activin A and potential anti-inflammatory effects of activin A were measured in human endothelial cells. Activin A effects on insulin secretion and inflammation were tested in human pancreatic islet cells.

RESULTS

1) In patients with acute MI, serum levels of activin A were significantly higher in those with abnormal glucose regulation (AGR) compared with those with normal glucose regulation. Activin A levels were associated with the presence of AGR 3 months later (adjusted odds ratio 5.1 [95% CI 1.73-15.17], P = 0.003). 2) In endothelial cells, glucose enhanced the release of activin A, whereas activin A attenuated the release of interleukin (IL)-8 and enhanced the mRNA levels of the antioxidant metallothionein. 3) In islet cells, activin A attenuated the suppressive effect of inflammatory cytokines on insulin release, counteracted the ability of these inflammatory cytokines to induce mRNA expression of IL-8, and induced the expression of transforming growth factor-β.

CONCLUSIONS

We found a significant association between activin A and newly detected AGR in patients with acute MI. Our in vitro findings suggest that this association represents a counteracting mechanism to protect against inflammation, hyperglycemia, and oxidative stress.

Novel development in extraintestinal manifestations and spondylarthropathy

The important co-existence of spondylarthritis (SpA) and inflammatory bowel disease (IBD) within the same individual suggests common etiopathogenic mechanisms. This is supported by intriguing similarities between both diseases at the subclinical and molecular level. The recent advances in IBD genetics have led to the identification of common pathways involved in both IBD and SpA, including bacterial recognition and ER stress. This offers the opportunity to develop potential new therapeutic strategies for both diseases. Transgenic animals which develop both joint and gut inflammation (like the TNF(ΔARE) mice and the HLA-B27 transgenic rats) are a very useful tool to test such novel therapeutics and to get further mechanistic insight into the pathogenetic link between SpA and IBD. This review will focus on the recent scientific progress in our understanding of the link between SpA and IBD. Based on this, potential novel therapeutic strategies are discussed.

The role of PDI as a survival factor in cardiomyocyte ischemia

Acute myocardial infarction (AMI) leads to activation of unfolded protein response (UPR) following endoplasmic reticulum (ER) stress. Failing in the restoration of the proper folding activity in the ER can lead to apoptosis and cell death. While it can be easy to detect transcripts and proteins expression alterations during a pathological state, it can be difficult to address the importance of changes in protein expression in the physiopathological context. We found protein disulfide isomerase (PDI) increased expression in human autoptic heart samples correlating with cell survival following AMI. PDI enzymatic activity resulted to be important to achieve cardiomyocyte protection from hypoxic stress, dependent on its ability to relieve ER stress preventing accumulation of nonfolded proteins in the ER, and to enhance superoxide dismutase 1 (SOD-1) activity. Furthermore, adenoviral-mediated PDI overexpression in an in vivo mouse model of AMI prevented adverse cardiac remodeling reducing cardiomyocyte apoptosis. Finally, we suggest a method to detect alterations in normal redox state in PDI (and eventually in the PDI family's proteins) during pathologies in which ER stress is induced. Diabetes pathology correlates with increased risk of AMI and worse cardiac remodeling. We found an alteration in PDI redox state in the diabetic heart and suggest using this system for the detection of the redox state alteration to screen for therapies able to restore the proper redox state.

Deficiency of rac1 blocks NADPH oxidase activation, inhibits endoplasmic reticulum stress, and reduces myocardial remodeling in a mouse model of type 1 diabetes

OBJECTIVE

Our recent study demonstrated that Rac1 and NADPH oxidase activation contributes to cardiomyocyte apoptosis in short-term diabetes. This study was undertaken to investigate if disruption of Rac1 and inhibition of NADPH oxidase would prevent myocardial remodeling in chronic diabetes.

RESEARCH DESIGN AND METHODS

Diabetes was induced by injection of streptozotocin in mice with cardiomyocyte-specific Rac1 knockout and their wild-type littermates. In a separate experiment, wild-type diabetic mice were treated with vehicle or apocynin in drinking water. Myocardial hypertrophy, fibrosis, endoplasmic reticulum (ER) stress, inflammatory response, and myocardial function were investigated after 2 months of diabetes. Isolated adult rat cardiomyocytes were cultured and stimulated with high glucose.

RESULTS

In diabetic hearts, NADPH oxidase activation, its subunits' expression, and reactive oxygen species production were inhibited by Rac1 knockout or apocynin treatment. Myocardial collagen deposition and cardiomyocyte cross-sectional areas were significantly increased in diabetic mice, which were accompanied by elevated expression of pro-fibrotic genes and hypertrophic genes. Deficiency of Rac1 or apocynin administration reduced myocardial fibrosis and hypertrophy, resulting in improved myocardial function. These effects were associated with a normalization of ER stress markers' expression and inflammatory response in diabetic hearts. In cultured cardiomyocytes, high glucose-induced ER stress was inhibited by blocking Rac1 or NADPH oxidase.

CONCLUSIONS

Rac1 via NADPH oxidase activation induces myocardial remodeling and dysfunction in diabetic mice. The role of Rac1 signaling may be associated with ER stress and inflammation. Thus, targeting inhibition of Rac1 and NADPH oxidase may be a therapeutic approach for diabetic cardiomyopathy.

Activation of AMP-activated protein kinase inhibits oxidized LDL-triggered endoplasmic reticulum stress in vivo

OBJECTIVE

The oxidation of LDLs is considered a key step in the development of atherosclerosis. How LDL oxidation contributes to atherosclerosis remains poorly defined. Here we report that oxidized and glycated LDL (HOG-LDL) causes aberrant endoplasmic reticulum (ER) stress and that the AMP-activated protein kinase (AMPK) suppressed HOG-LDL-triggered ER stress in vivo.

RESEARCH DESIGN AND METHODS

ER stress markers, sarcoplasmic/endoplasmic reticulum Ca(2+) ATPase (SERCA) activity and oxidation, and AMPK activity were monitored in cultured bovine aortic endothelial cells (BAECs) exposed to HOG-LDL or in isolated aortae from mice fed an atherogenic diet.

RESULTS

Exposure of BAECs to clinically relevant concentrations of HOG-LDL induced prolonged ER stress and reduced SERCA activity but increased SERCA oxidation. Chronic administration of Tempol (a potent antioxidant) attenuated both SERCA oxidation and aberrant ER stress in mice fed a high-fat diet in vivo. Likewise, AMPK activation by pharmacological (5'-aminoimidazole-4-carboxymide-1-beta-d-ribofuranoside, metformin, and statin) or genetic means (adenoviral overexpression of constitutively active AMPK mutants) significantly mitigated ER stress and SERCA oxidation and improved the endothelium-dependent relaxation in isolated mouse aortae. Finally, Tempol administration markedly attenuated impaired endothelium-dependent vasorelaxation, SERCA oxidation, ER stress, and atherosclerosis in ApoE(-/-) and ApoE(-/-)/AMPKalpha2(-/-) fed a high-fat diet.

CONCLUSION

We conclude that HOG-LDL, via enhanced SERCA oxidation, causes aberrant ER stress, endothelial dysfunction, and atherosclerosis in vivo, all of which are inhibited by AMPK activation.

Sent to destroy: the ubiquitin proteasome system regulates cell signaling and protein quality control in cardiovascular development and disease

The ubiquitin proteasome system (UPS) plays a crucial role in biological processes integral to the development of the cardiovascular system and cardiovascular diseases. The UPS prototypically recognizes specific protein substrates and places polyubiquitin chains on them for subsequent destruction by the proteasome. This system is in place to degrade not only misfolded and damaged proteins, but is essential also in regulating a host of cell signaling pathways involved in proliferation, adaptation to stress, regulation of cell size, and cell death. During the development of the cardiovascular system, the UPS regulates cell signaling by modifying transcription factors, receptors, and structural proteins. Later, in the event of cardiovascular diseases as diverse as atherosclerosis, cardiac hypertrophy, and ischemia/reperfusion injury, ubiquitin ligases and the proteasome are implicated in protecting and exacerbating clinical outcomes. However, when misfolded and damaged proteins are ubiquitinated by the UPS, their destruction by the proteasome is not always possible because of their aggregated confirmations. Recent studies have discovered how these ubiquitinated misfolded proteins can be destroyed by alternative "specific" mechanisms. The cytosolic receptors p62, NBR, and histone deacetylase 6 recognize aggregated ubiquitinated proteins and target them for autophagy in the process of "selective autophagy." Even the ubiquitination of multiple proteins within whole organelles that drive the more general macro-autophagy may be due, in part, to similar ubiquitin-driven mechanisms. In summary, the crosstalk between the UPS and autophagy highlight the pivotal and diverse roles the UPS plays in maintaining protein quality control and regulating cardiovascular development and disease.