Carbon Monoxide Induces Heme Oxygenase-1 via Activation of Protein Kinase R–Like Endoplasmic Reticulum Kinase and Inhibits Endothelial Cell Apoptosis Triggered by Endoplasmic Reticulum Stress

Fibronectin Type III Domain Containing 4 attenuates hyperlipidemia-induced insulin resistance via suppression of inflammation and ER stress through HO-1 expression in adipocytes

Although Fibronectin Type III Domain Containing 4 (FNDC4) has been reported to be involved in the modulation of inflammation in macrophages, its effects on inflammation and insulin resistance in adipose tissue are unknown. In the current study, we investigated the effects of FNDC4 on hyperlipidemia-mediated endoplasmic reticulum (ER) stress, inflammation, and insulin resistance in adipocytes via the AMP-activated protein kinase (AMPK)/heme oxygenase-1 (HO-1)-mediated pathway. Hyperlipidemia-induced nuclear factor κB (NFκB), inhibitory κBα (IκBα) phosphorylation, and pro-inflammatory cytokines such as TNFα and MCP-1 were markedly mitigated by FNDC4. Furthermore, FNDC4 treatment attenuated impaired insulin signaling in palmitate-treated differentiated 3T3-L1 cells and in subcutaneous adipose tissue of HFD-fed mice. FNDC4 administration ameliorated glucose intolerance and reduced HFD-induced body weight gain in mice. However, FNDC4 treatment did not affect calorie intake. Additionally, treatment with FNDC4 attenuated hyperlipidemia-induced phosphorylation or expression of ER stress markers such as IRE-1, eIF2α, and CHOP in 3T3-L1 adipocytes and in subcutaneous adipose tissue of mice. FNDC4 treatment stimulated AMPK phosphorylation and HO-1 expression in 3T3-L1 adipocytes and in subcutaneous adipose tissue of mice. siRNA-mediated suppression of AMPK and HO-1 abrogated the suppressive effects of FNDC4 on palmitate-induced ER stress, inflammation, and insulin resistance. In conclusion, our results show that FNDC4 ameliorates insulin resistance via AMPK/HO-1-mediated suppression of inflammation and ER stress, indicating that FNDC4 may be a novel therapeutic agent for treating insulin resistance and type 2 diabetes.

Carbon Monoxide Inhibits Islet Apoptosis via Induction of Autophagy

AIM

Carbon monoxide (CO) functions as a therapeutic molecule in various disease models because of its anti-inflammatory and antiapoptotic properties. We investigated the capacity of CO to reduce hypoxia-induced islet cell death and dysfunction in human and mouse models.

RESULTS

Culturing islets in CO-saturated medium protected them from hypoxia-induced apoptosis and preserved β cell function by suppressing expression of proapoptotic (Bim, PARP, Cas-3), proinflammatory (TNF-α), and endoplasmic reticulum (ER) stress (glucose-regulated protein 94, grp94, CHOP) proteins. The prosurvival effects of CO on islets were attenuated when autophagy was blocked by specific inhibitors or when either ATG7 or ATG16L1, two essential factors for autophagy, was downregulated by siRNA. In vivo, CO exposure reduced both inflammation and cell death in grafts immediately after transplantation, and enhanced long-term graft survival of CO-treated human and mouse islet grafts in streptozotocin-induced diabetic non-obese diabetic severe combined immunodeficiency (NOD-SCID) or C57BL/6 recipients.

INNOVATION

These findings underline that pretreatment with CO protects islets from hypoxia and stress-induced cell death via upregulation of ATG16L1-mediated autophagy.

CONCLUSION

Our results suggested that CO exposure may provide an effective means to enhance survival of grafts in clinical islet cell transplantation, and may be beneficial in other diseases in which inflammation and cell death pose impediments to achieving optimal therapeutic effects. Antioxid. Redox Signal. 28, 1309-1322.

Endoplasmic Reticulum Stress, a Driver or an Innocent Bystander in Endothelial Dysfunction Associated with Hypertension?

PURPOSE OF REVIEW

Hypertension (htn) is a polygenic disorder that effects up to one third of the US population. The endoplasmic reticulum (ER) stress response is a homeostatic pathway that regulates membrane structure, protein folding, and secretory function. Emerging evidence suggests that ER stress may induce endothelial dysfunction; however, it is unclear whether ER stress-associated endothelial dysfunction modulates htn.

RECENT FINDINGS

Exogenous and endogenous molecules activate ER stress in the endothelium, and ER stress mediates some forms of neurogenic htn, such as angiotensin II-dependent htn. Human studies suggest that ER stress induces endothelial dysfunction, though direct evidence that ER stress augments blood pressure in humans is lacking. However, animal and cellular models demonstrate direct evidence that ER stress influences htn. ER stress is likely one of many players in a complex interplay among molecular pathways that influence the expression of htn. Targeted activation of specific ER stress pathways may provide novel therapeutic opportunities.

On the Structure and Reaction Mechanism of Human Acireductone Dioxygenase

Acireductone dioxygenase (ARD) is an intriguing enzyme from the methionine salvage pathway that is capable of catalysing two different oxidation reactions with the same substrate depending on the type of the metal ion in the active site. To date, the structural information regarding the ARD-acireductone complex is limited and possible reaction mechanisms are still under debate. The results of joint experimental and computational studies undertaken to advance knowledge about ARD are reported. The crystal structure of an ARD from Homo sapiens was determined with selenomethionine. EPR spectroscopy suggested that binding acireductone triggers one protein residue to dissociate from Fe²⁺ , which allows NO (and presumably O₂ ) to bind directly to the metal. Mössbauer spectroscopic data (interpreted with the aid of DFT calculations) was consistent with bidentate binding of acireductone to Fe²⁺ and concomitant dissociation of His88 from the metal. Major features of Fe vibrational spectra obtained for the native enzyme and upon addition of acireductone were reproduced by QM/MM calculations for the proposed models. A computational (QM/MM) study of the reaction mechanisms suggests that Fe²⁺ promotes O-O bond homolysis, which elicits cleavage of the C1-C2 bond of the substrate. Higher M³⁺ /M²⁺ redox potentials of other divalent metals do not support this pathway, and instead the reaction proceeds similarly to the key reaction step in the quercetin 2,3-dioxygenase mechanism.

FGF21 induced by carbon monoxide mediates metabolic homeostasis via the PERK/ATF4 pathway

The prevalence of metabolic diseases, including type 2 diabetes, obesity, and cardiovascular disease, has rapidly increased, yet the molecular mechanisms underlying the metabolic syndrome, a primary risk factor, remain incompletely understood. The small, gaseous molecule carbon monoxide (CO) has well-known anti-inflammatory, antiproliferative, and antiapoptotic effects in a variety of cellular- and tissue-injury models, whereas its potential effects on the complex pathways of metabolic disease remain unknown. We demonstrate here that CO can alleviate metabolic dysfunction in vivo and in vitro. We show that CO increased the expression and section of the fibroblast growth factor 21 (FGF21) in hepatocytes and liver. CO-stimulated PERK activation and enhanced the levels of FGF21 via the eIF2α–ATF4 signaling pathway. The induction of FGF21 by CO attenuated endoreticulum stress- or diet-induced, obesity-dependent hepatic steatosis. Moreover, CO inhalation lowered blood glucose levels, enhanced insulin sensitivity, and promoted energy expenditure by stimulating the emergence of beige adipose cells from white adipose cells. In conclusion, we suggest that CO acts as a potent inducer of FGF21 expression and that CO critically depends on FGF21 to regulate metabolic homeostasis.—Joe, Y., Kim, S., Kim, H. J., Park, J., Chen, Y., Park, H.-J., Jekal, S.-J., Ryter, S. W., Kim, U. H., Chung, H. T. FGF21 induced by carbon monoxide mediates metabolic homeostasis via the PERK/ATF4 pathway.

Hyperhomocysteinaemia and vascular injury: advances in mechanisms and drug targets

Homocysteine is a sulphur-containing non-proteinogenic amino acid. Hyperhomocysteinaemia (HHcy), the pathogenic elevation of plasma homocysteine as a result of an imbalance of its metabolism, is an independent risk factor for various vascular diseases, such as atherosclerosis, hypertension, vascular calcification and aneurysm. Treatments aimed at lowering plasma homocysteine via dietary supplementation with folic acids and vitamin B are more effective in preventing vascular disease where the population has a normally low folate consumption than in areas with higher dietary folate. To date, the mechanisms of HHcy-induced vascular injury are not fully understood. HHcy increases oxidative stress and its downstream signalling pathways, resulting in vascular inflammation. HHcy also causes vascular injury via endoplasmic reticulum stress. Moreover, HHcy up-regulates pathogenic genes and down-regulates protective genes via DNA demethylation and methylation respectively. Homocysteinylation of proteins induced by homocysteine also contributes to vascular injury by modulating intracellular redox state and altering protein function. Furthermore, HHcy-induced vascular injury leads to neuronal damage and disease. Also, an HHcy-activated sympathetic system and HHcy-injured adipose tissue also cause vascular injury, thus demonstrating the interactions between the organs injured by HHcy. Here, we have summarized the recent developments in the mechanisms of HHcy-induced vascular injury, which are further considered as potential therapeutic targets in this condition.

LINKED ARTICLES

This article is part of a themed section on Spotlight on Small Molecules in Cardiovascular Diseases. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.8/issuetoc.

Carbon monoxide protects against hepatic steatosis in mice by inducing sestrin-2 via the PERK-eIF2α-ATF4 pathway

Nonalcoholic fatty liver disease (NAFLD), the hepatic manifestation of the metabolic syndrome, has emerged as one of the most common causes of chronic liver disease in developed countries over the last decade. NAFLD comprises a spectrum of pathological hepatic changes, including steatosis, steatohepatitis, advanced fibrosis, and cirrhosis. Autophagy, a homeostatic process for protein and organelle turnover, is decreased in the liver during the development of NAFLD. Previously, we have shown that carbon monoxide (CO), a reaction product of heme oxygenase (HO) activity, can confer protection in NAFLD, though the molecular mechanisms remain unclear. We therefore investigated the mechanisms underlying the protective effect of CO on methionine/choline-deficient (MCD) diet-induced hepatic steatosis. We found that CO induced sestrin-2 (SESN2) expression through enhanced mitochondrial ROS production and protected against MCD-induced NAFLD progression through activation of autophagy. SESN2 expression was increased by CO or CO-releasing molecule (CORM2), in a manner dependent on signaling through the protein kinase R-like endoplasmic reticulum kinase (PERK), eukaryotic initiation factor-2 alpha (eIF2α)/ activating transcription factor-4 (ATF4)-dependent pathway. CO-induced SESN2 upregulation in hepatocytes contributed to autophagy induction through activation of 5'-AMP-activated protein kinase (AMPK) and inhibition of mechanistic target of rapamycin (mTOR) complex I (mTORC1). Furthermore, we demonstrate that CO significantly induced the expression of SESN2 and enhanced autophagy in the livers of MCD-fed mice or in MCD-media treated hepatocytes. Conversely, knockdown of SESN2 abrogated autophagy activation and mTOR inhibition in response to CO. We conclude that CO ameliorates hepatic steatosis through the autophagy pathway induced by SESN2 upregulation.

The role of carbon monoxide and heme oxygenase in the prevention of sickle cell disease vaso-occlusive crises

Sickle Cell Disease (SCD) is a painful, lifelong hemoglobinopathy inherited as a missense point mutation in the hemoglobin (Hb) beta-globin gene. This disease has significant impact on quality of life and mortality, thus a substantial medical need exists to reduce the vaso-occlusive crises which underlie the pathophysiology of the disease. The concept that a gaseous molecule may exert biological function has been well known for over one hundred years. Carbon monoxide (CO), although studied in SCD for over 50 years, has recently emerged as a powerful cytoprotective biological response modifier capable of regulating a host of physiologic and therapeutic processes that, at low concentrations, exerts key physiological functions in various models of tissue inflammation and injury. CO is physiologically generated by the metabolism of heme by the heme oxygenase enzymes and is measurable in blood. A substantial amount of preclinical and clinical data with CO have been generated, which provide compelling support for CO as a potential therapeutic in a number of pathological conditions. Data underlying the therapeutic mechanisms of CO, including in SCD, have been generated by a plethora of in vitro and preclinical studies including multiple SCD mouse models. These data show CO to have key signaling impacts on a host of metallo-enzymes as well as key modulating genes that in sum, result in significant anti-inflammatory, anti-oxidant and anti-apoptotic effects as well as vasodilation and anti-adhesion of cells to the endothelium resulting in preservation of vascular flow. CO may also have a role as an anti-polymerization HbS agent. In addition, considerable scientific data in the non-SCD literature provide evidence for a beneficial impact of CO on cerebrovascular complications, suggesting that in SCD, CO could potentially limit these highly problematic neurologic outcomes. Research is needed and hopefully forthcoming, to carefully elucidate the safety and benefits of this potential therapy across the age spectrum of patients impacted by the host of pathophysiological complications of this devastating disease.

Anti-Fibrotic Effect of Losartan, an Angiotensin II Receptor Blocker, Is Mediated through Inhibition of ER Stress via Up-Regulation of SIRT1, Followed by Induction of HO-1 and Thioredoxin

Endoplasmic reticulum (ER) stress is increasingly identified as modulator of fibrosis. Losartan, an angiotensin II receptor blocker, has been widely used as the first choice of treatment in chronic renal diseases. We postulated that anti-fibrotic effect of losartan is mediated through inhibition of ER stress via SIRT1 (silent mating type information regulation 2 homolog 1) hemeoxygenase-1 (HO-1)/thioredoxin pathway. Renal tubular cells, tunicamycin (TM)-induced ER stress, and unilateral ureteral obstruction (UUO) mouse model were used. Expression of ER stress was assessed by Western blot analysis and immunohistochemical stain. ER stress was induced by chemical ER stress inducer, tunicamycin, and non-chemical inducers such as TGF-β, angiotensin II, high glucose, and albumin. Losartan suppressed the TM-induced ER stress, as shown by inhibition of TM-induced expression of GRP78 (glucose related protein 78) and p-eIF2α (phosphospecific-eukaryotic translation initiation factor-2α), through up-regulation of SIRT1 via HO-1 and thioredoxin. Losartan also suppressed the ER stress by non-chemical inducers. In both animal models, losartan reduced the tubular expression of GRP78, which were abolished by pretreatment with sirtinol (SIRT1 inhibitor). Sirtinol also blocked the inhibitory effect of losartan on the UUO-induced renal fibrosis. These findings provide new insights into renoprotective effects of losartan and suggest that SIRT1, HO-1, and thioredoxin may be potential pharmacological targets in kidney diseases under excessive ER stress condition.

Benefits of tubular morphologies on electron transfer properties in CNT/TiNT nanohybrid photocatalyst for enhanced H2 production

Beneficial effects of tubular morphologies on electron transfer properties in CNT/TiNT nanohybrid photocatalysts for enhanced H₂ production as both co-catalyst and sensitizer are shown schematically here.

Multifactorial Regulation of G Protein-Coupled Receptor Endocytosis

Endocytosis is a process by which cells absorb extracellular materials via the inward budding of vesicles formed from the plasma membrane. Receptor-mediated endocytosis is a highly selective process where receptors with specific binding sites for extracellular molecules internalize via vesicles. G protein-coupled receptors (GPCRs) are the largest single family of plasma-membrane receptors with more than 1000 family members. But the molecular mechanisms involved in the regulation of GPCRs are believed to be highly conserved. For example, receptor phosphorylation in collaboration with β-arrestins plays major roles in desensitization and endocytosis of most GPCRs. Nevertheless, a number of subsequent studies showed that GPCR regulation, such as that by endocytosis, occurs through various pathways with a multitude of cellular components and processes. This review focused on i) functional interactions between homologous and heterologous pathways, ii) methodologies applied for determining receptor endocytosis, iii) experimental tools to determine specific endocytic routes, iv) roles of small guanosine triphosphate-binding proteins in GPCR endocytosis, and v) role of post-translational modification of the receptors in endocytosis.

Heme oxygenase (HO)-1 induction prevents Endoplasmic Reticulum stress-mediated endothelial cell death and impaired angiogenic capacity

Most of diabetic cardiovascular complications are attributed to endothelial dysfunction and impaired angiogenesis. Endoplasmic Reticulum (ER) and oxidative stresses were shown to play a pivotal role in the development of endothelial dysfunction in diabetes. Hemeoxygenase-1 (HO-1) was shown to protect against oxidative stress in diabetes; however, its role in alleviating ER stress-induced endothelial dysfunction remains not fully elucidated. We aim here to test the protective role of HO-1 against high glucose-mediated ER stress and endothelial dysfunction and understand the underlying mechanisms with special emphasis on oxidative stress, inflammation and cell death. Human Umbilical Vein Endothelial Cells (HUVECs) were grown in either physiological or intermittent high concentrations of glucose for 5days in the presence or absence of Cobalt (III) Protoporphyrin IX chloride (CoPP, HO-1 inducer) or 4-Phenyl Butyric Acid (PBA, ER stress inhibitor). Using an integrated cellular and molecular approach, we then assessed ER stress and inflammatory responses, in addition to apoptosis and angiogenic capacity in these cells. Our results show that HO-1 induction prevented high glucose-mediated increase of mRNA and protein expression of key ER stress markers. Cells incubated with high glucose exhibited high levels of oxidative stress, activation of major inflammatory and apoptotic responses [nuclear factor (NF)-κB and c-Jun N-terminal kinase (JNK)] and increased rate of apoptosis; however, cells pre-treated with CoPP or PBA were fully protected. In addition, high glucose enhanced caspases 3 and 7 cleavage and activity and augmented cleaved poly ADP ribose polymerase (PARP) expression whereas HO-1 induction prevented these effects. Finally, HO-1 induction and ER stress inhibition prevented high glucose-induced reduction in NO release and impaired the angiogenic capacity of HUVECs, and enhanced vascular endothelial growth factor (VEGF)-A expression. Altogether, we show here the critical role of ER stress-mediated cell death in diabetes-induced endothelial dysfunction and impaired angiogenesis and underscore the role of HO-1 induction as a key therapeutic modulator for ER stress response in ischemic disorders and diabetes. Our results also highlight the complex interplay between ER stress response and oxidative stress.

Localized delivery of carbon monoxide

The heme oxygenase (HO)/carbon monoxide (CO) system is a physiological feedback loop orchestrating various cell-protective effects in response to cellular stress. The therapeutic use of CO is impeded by safety challenges as a result of high CO-Hemoglobin formation following non-targeted, systemic administration jeopardizing successful CO therapies as of this biological barrier. Another caveat is the use of CO-Releasing Molecules containing toxicologically critical transition metals. An emerging number of local delivery approaches addressing these issues have recently been introduced and provide exciting new starting points for translating the fascinating preclinical potential of CO into a clinical setting. This review will discuss these approaches and link to future delivery strategies aiming at establishing CO as a safe and effective medication of tomorrow.

Carbon monoxide releasing molecule induces endothelial nitric oxide synthase activation through a calcium and phosphatidylinositol 3-kinase/Akt mechanism

The production of nitric oxide (NO) by endothelial NO synthase (eNOS) plays a major role in maintaining vascular homeostasis. This study elucidated the potential role of carbon monoxide (CO)-releasing molecules (CORMs) in NO production and explored the underlying mechanisms in endothelial cells. We observed that 25μM CORM-2 could increase NO production and stimulate an increase in the intracellular Ca²⁺ level. Furthermore, ethylene glycol-bis(β-aminoethyl ether)-N,N,N',N'-tetra acetic acid caused CORM-2-induced NO production, which was abolished by 1,2-bis(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid tetraacetoxy-methyl ester (BAPTA-AM), indicating that intracellular Ca²⁺ release plays a major role in eNOS activation. The inhibition of the IP3 receptor diminished the CORM-2-induced intracellular Ca²⁺ increase and NO production. Furthermore, CORM-2 induced eNOS Ser¹¹⁷⁹ phosphorylation and eNOS dimerization, but it did not alter eNOS expression. CORM-2 (25μM) also prolonged Akt phosphorylation, lasting for at least 12h. Pretreatment with phosphatidylinositol 3-kinase inhibitors (wortmannin or LY294002) inhibited the increases in NO production and phosphorylation but did not affect eNOS dimerization. CORM-2-induced eNOS Ser¹¹⁷⁹ phosphorylation was intracellularly calcium-dependent, because pretreatment with an intracellular Ca²⁺ chelator (BAPTA-AM) inhibited this process. Although CORM-2 increases intracellular reactive oxygen species (ROS), pretreatment with antioxidant enzyme catalase and N-acetyl-cysteine did not abolish the CORM-2-induced eNOS activity or phosphorylation, signifying that ROS is not involved in this activity. Hence, CORM-2 enhances eNOS activation through intracellular calcium release, Akt phosphorylation, and eNOS dimerization.

The herbal extract KCHO-1 exerts a neuroprotective effect by ameliorating oxidative stress via heme oxygenase-1 upregulation

KCHO-1 is a novel product comprised of 30% ethanol extracts obtained from nine medical herbs, which are commonly used in traditional Korean and Chinese medicine. The nine herbs include Curcuma longa, Salvia miltiorrhiza, Gastrodia elata, Chaenomeles sinensis, Polygala tenuifolia, Paeonia japonica, Glycyrrhiza uralensis, Atractylodes japonica and processed Aconitum carmichaeli. Recent studies have reported the beneficial effects of these herbs. The present study aimed to investigate the direct neuroprotective effects of KCHO‑1 on HT22 mouse hippocampal cells, and to determine the possible underlying mechanisms. KCHO‑1 significantly suppressed glutamate‑ and hydrogen peroxide (H2O2)‑induced cell damage, and reactive oxygen species generation. In addition, KCHO‑1 increased the mRNA and protein expression levels of heme oxygenase (HO)‑1. Tin protoporphyrin, which is an inhibitor of HO activity, partially suppressed the effects of KCHO‑1. Furthermore, KCHO‑1 significantly upregulated nuclear factor erythroid‑derived 2‑related factor‑2 (Nrf2) nuclear translocation. Extracellular signal‑regulated kinase (ERK) activation also appeared to be associated with KCHO‑1‑induced HO‑1 expression, since the ERK inhibitor PD98059 suppressed HO‑1 expression and prevented KCHO‑1‑induced cytoprotection. The results of the present study suggested that KCHO‑1 may effectively prevent glutamate‑ or H2O2‑induced oxidative damage via Nrf2/ERK mitogen‑activated protein kinase‑dependent HO‑1 expression. These data suggest that KCHO‑1 may be useful for the treatment of neurodegenerative diseases.

Porcine Circovirus 2 Deploys PERK Pathway and GRP78 for Its Enhanced Replication in PK-15 Cells

Porcine circovirus type 2 (PCV2) infection induces autophagy and apoptosis. These cellular responses could be connected with endoplasmic reticulum (ER) stress. It remains unknown if PCV2 induces ER stress and if autophagy or apoptosis is primary to PCV2 infection or secondary responses following ER stress. Here, we demonstrate that PCV2 triggered unfolded protein response (UPR) in PK-15 cells by activating the PERK/eIF2α pathway without concomitant activation of IRE1 or ATF6. Since ATF4 and CHOP were induced later than PERK/eIF2α, it is clear that persistent PCV2 infection could lead to selective activation of PERK via the PERK-eIF2α-ATF4-CHOP axis. Therefore, PERK activation could be part of the pro-apoptotic signaling via induced expression of CHOP by PCV2. Since PERK inhibition by GSK2606414 or RNA silencing or suppression of eIF2α dephosphorylation by salubrinal limited viral replication, we suppose that PCV2 deploys UPR to enhance its replication. Over-expression of GRP78 or treatment with tauroursodeoxycholic acid could enhance viral capsid expression and/or viral titers, indicating that these chaperones, endogenous or exogenous, could help correct folding of viral proteins. Our findings provide the first evidence that ER stress plays a role in the pathogenesis of PCV2 infection probably as part of autophagic and apoptotic responses.

Glycolaldehyde induces endoplasmic reticulum stress and apoptosis in Schwann cells

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Glycolaldehyde induces endoplasmic reticulum stress in Schwann cells.

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Glycolaldehyde causes apoptosis in Schwann cells.

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Nrf2 activated by glycolaldehyde plays a protective role in the cytotoxicity.

Schwann cell injury is caused by diabetic neuropathy. The apoptosis of Schwann cells plays a pivotal role in diabetic nerve dysfunction. Glycolaldehyde is a precursor of advanced glycation end products that contribute to the pathogenesis of diabetic neuropathy. In this study, we examined whether glycolaldehyde induces endoplasmic reticulum (ER) stress and apoptosis in rat Schwann cells. Schwann cells treated with 500 μM glycolaldehyde showed morphological changes characteristic of apoptosis. Glycolaldehyde activated apoptotic signals, such as caspase-3 and caspase-8. Furthermore, it induced ER stress response involving RNA-dependent protein kinase-like ER kinase (PERK), inositol-requiring ER-to-nucleus signal kinase 1α (IRE1α), and eukaryotic initiation factor 2α (eIF2α). In addition, glycolaldehyde activated CCAAT/enhancer-binding homologous protein (CHOP), an ER stress response factor crucial to executing apoptosis. Knockdown of nuclear factor E2-related factor 2 (Nrf2), which is involved in the promotion of cell survival following ER stress, enhanced glycolaldehyde-induced cytotoxicity, indicating that Nrf2 plays a protective role in the cytotoxicity caused by glycolaldehyde. Taken together, these findings indicate that glycolaldehyde is capable of inducing apoptosis and ER stress in Schwann cells. The ER stress induced by glycolaldehyde may trigger the glycolaldehyde-induced apoptosis in Schwann cells. This study demonstrated for the first time that glycolaldehyde induced ER stress.

Carbon Monoxide (CO) Released from Tricarbonyldichlororuthenium (II) Dimer (CORM-2) in Gastroprotection against Experimental Ethanol-Induced Gastric Damage

The physiological gaseous molecule, carbon monoxide (CO) becomes a subject of extensive investigation due to its vasoactive activity throughout the body but its role in gastroprotection has been little investigated. We determined the mechanism of CO released from its donor tricarbonyldichlororuthenium (II) dimer (CORM-2) in protection of gastric mucosa against 75% ethanol-induced injury. Rats were pretreated with CORM-2 30 min prior to 75% ethanol with or without 1) non-selective (indomethacin) or selective cyclooxygenase (COX)-1 (SC-560) and COX-2 (celecoxib) inhibitors, 2) nitric oxide (NO) synthase inhibitor L-NNA, 3) ODQ, a soluble guanylyl cyclase (sGC) inhibitor, hemin, a heme oxygenase (HO)-1 inductor or zinc protoporphyrin IX (ZnPPIX), an inhibitor of HO-1 activity. The CO content in gastric mucosa and carboxyhemoglobin (COHb) level in blood was analyzed by gas chromatography. The gastric mucosal mRNA expression for HO-1, COX-1, COX-2, iNOS, IL-4, IL-1β was analyzed by real-time PCR while HO-1, HO-2 and Nrf2 protein expression was determined by Western Blot. Pretreatment with CORM-2 (0.5-10 mg/kg) dose-dependently attenuated ethanol-induced lesions and raised gastric blood flow (GBF) but large dose of 100 mg/kg was ineffective. CORM-2 (5 mg/kg and 50 mg/kg i.g.) significantly increased gastric mucosal CO content and whole blood COHb level. CORM-2-induced protection was reversed by indomethacin, SC-560 and significantly attenuated by celecoxib, ODQ and L-NNA. Hemin significantly reduced ethanol damage and raised GBF while ZnPPIX which exacerbated ethanol-induced injury inhibited CORM-2- and hemin-induced gastroprotection and the accompanying rise in GBF. CORM-2 significantly increased gastric mucosal HO-1 mRNA expression and decreased mRNA expression for iNOS, IL-1β, COX-1 and COX-2 but failed to affect HO-1 and Nrf2 protein expression decreased by ethanol. We conclude that CORM-2 released CO exerts gastroprotection against ethanol-induced gastric lesions involving an increase in gastric microcirculation mediated by sGC/cGMP, prostaglandins derived from COX-1, NO-NOS system and its anti-inflammatory properties.

Ursodeoxycholic Acid (UDCA) Exerts Anti-Atherogenic Effects by Inhibiting Endoplasmic Reticulum (ER) Stress Induced by Disturbed Flow

Disturbed blood flow with low-oscillatory shear stress (OSS) is a predominant atherogenic factor leading to dysfunctional endothelial cells (ECs). Recently, it was found that disturbed flow can directly induce endoplasmic reticulum (ER) stress in ECs, thereby playing a critical role in the development and progression of atherosclerosis. Ursodeoxycholic acid (UDCA), a naturally occurring bile acid, has long been used to treat chronic cholestatic liver disease and is known to alleviate endoplasmic reticulum (ER) stress at the cellular level. However, its role in atherosclerosis remains unexplored. In this study, we demonstrated the anti-atherogenic activity of UDCA via inhibition of disturbed flow-induced ER stress in atherosclerosis. UDCA effectively reduced ER stress, resulting in a reduction in expression of X-box binding protein-1 (XBP-1) and CEBP-homologous protein (CHOP) in ECs. UDCA also inhibits the disturbed flow-induced inflammatory responses such as increases in adhesion molecules, monocyte adhesion to ECs, and apoptosis of ECs. In a mouse model of disturbed flow-induced atherosclerosis, UDCA inhibits atheromatous plaque formation through the alleviation of ER stress and a decrease in adhesion molecules. Taken together, our results revealed that UDCA exerts anti-atherogenic activity in disturbed flow-induced atherosclerosis by inhibiting ER stress and the inflammatory response. This study suggests that UDCA may be a therapeutic agent for prevention or treatment of atherosclerosis.

Avarol induces apoptosis in pancreatic ductal adenocarcinoma cells by activating PERK-eIF2α-CHOP signaling

Avarol is a sesquiterpenoid hydroquinone with potent cytotoxicity. Although resolving endoplasmic reticulum (ER) stress is essential for intracellular homeostasis, erratic or excessive ER stress can lead to apoptosis. Here, we reported that avarol selectively induces cell death in pancreatic ductal adenocarcinomas (PDAC), which are difficult to treat owing to the availability of few chemotherapeutic agents. Analyses of the molecular mechanisms of avarol-induced apoptosis indicated upregulation of ER stress marker BiP and ER stress-dependent apoptosis inducer CHOP in PDAC cells but not in normal cells, suggesting that avarol selectively induces ER stress responses. We also showed that avarol activated the PERK–eIF2α pathway but did not affect the IRE1 and ATF6 pathways. Moreover, CHOP downregulation was significantly suppressed by avarol-induced apoptosis. Thus, the PERK–eIF2α–CHOP signaling pathway may be a novel molecular mechanism of avarol-induced apoptosis. The present data indicate that avarol has potential as a chemotherapeutic agent for PDAC and induces apoptosis by activating the PERK–eIF2α pathway.

Carbon monoxide reverses adipose tissue inflammation and insulin resistance upon loss of ovarian function

We hypothesized that carbon monoxide (CO) might suppress chronic inflammation, which led to metabolic disturbances. Ovariectomy (OVX) was performed in mice to mimic chronic inflammation secondary to loss of ovarian function. OVX increased fat mass and the infiltration of highly inflammatory CD11c cells into adipose tissue (AT), resulting in a disturbance of glucose metabolism. Treatment of CO attenuated these; CO decreased recruitment of CD11c-expressing cells in AT and reduced expression of CD11c in bone marrow-derived macrophages, protecting them from M1 polarization. Upregulated cGMP and decreased reactive oxygen species were responsible for the inhibitory activity of CO on CD11c expression; knockdown of soluble guanylate cyclase or heme oxygenase-1 using small interfering RNAs reduced this inhibition substantially. Improved OVX-induced insulin resistance (IR) by CO was highly associated with its activity to attenuate AT inflammation. Our results suggest a therapeutic value of CO to treat postmenopausal IR by reducing AT inflammation.

Calreticulin protects rat microvascular endothelial cells against microwave radiation-induced injury by attenuating endoplasmic reticulum stress

OBJECTIVE

This study was designed to evaluate whether exogenous CRT was beneficial for alleviating MR-induced injury by suppressing ER stress in rat MMECs.

METHODS

MMECs were pretreated with CRT (25 pg/mL) for 12 hours, followed by the exposure to 2.856 GHz radiation at a mean power density of 30 mW/cm(2) for six minutes. MR-induced injury in MMECs was evaluated by LDH leakage, apoptosis, and cell viability analysis. The expression of GRP78, CRT, CHOP, Bcl-2, and Bax were examined by Western blot analysis to reflect ER stress response and ER stress-related apoptosis.

RESULTS

MR induced marked MMECs injury, as shown by increased LDH leakage and apoptosis rate and decreased cell viability. MR also induced excessive ER stress, characterized by increased expression of GRP78 and CRT, and ER stress-related apoptotic signaling as well, as shown by the upregulation of CHOP and Bax and the downregulation of Bcl-2. Exogenous CRT pretreatment remarkably attenuated MR-induced cell apoptosis and LDH leakage, ER stress, and activation of the ER stress-related apoptotic signaling.

CONCLUSIONS

Exogenous CRT attenuates MR-induced ER stress-related apoptosis by suppressing CHOP-mediated apoptotic signaling pathways in MMECs.

Unspliced X-box-binding protein 1 (XBP1) protects endothelial cells from oxidative stress through interaction with histone deacetylase 3

It is well known that atherosclerosis occurs geographically at branch points where disturbed flow predisposes to the development of plaque via triggering of oxidative stress and inflammatory reactions. In this study, we found that disturbed flow activated anti-oxidative reactions via up-regulating heme oxygenase 1 (HO-1) in an X-box-binding protein 1 (XBP1) and histone deacetylase 3 (HDAC3)-dependent manner. Disturbed flow concomitantly up-regulated the unspliced XBP1 (XBP1u) and HDAC3 in a VEGF receptor and PI3K/Akt-dependent manner. The presence of XBP1 was essential for the up-regulation of HDAC3 protein. Overexpression of XBP1u and/or HDAC3 activated Akt1 phosphorylation, Nrf2 protein stabilization and nuclear translocation, and HO-1 expression. Knockdown of XBP1u decreased the basal level and disturbed flow-induced Akt1 phosphorylation, Nrf2 stabilization, and HO-1 expression. Knockdown of HDAC3 ablated XBP1u-mediated effects. The mammalian target of rapamycin complex 2 (mTORC2) inhibitor, AZD2014, ablated XBP1u or HDAC3 or disturbed flow-mediated Akt1 phosphorylation, Nrf2 nuclear translocation, and HO-1 expression. Neither actinomycin D nor cycloheximide affected disturbed flow-induced up-regulation of Nrf2 protein. Knockdown of Nrf2 abolished XBP1u or HDAC3 or disturbed flow-induced HO-1 up-regulation. Co-immunoprecipitation assays demonstrated that XBP1u physically bound to HDAC3 and Akt1. The region of amino acids 201 to 323 of the HDAC3 protein was responsible for the binding to XBP1u. Double immunofluorescence staining revealed that the interactions between Akt1 and mTORC2, Akt1 and HDAC3, Akt1 and XBP1u, HDAC3, and XBP1u occurred in the cytosol. Thus, we demonstrate that XBP1u and HDAC3 exert a protective effect on disturbed flow-induced oxidative stress via up-regulation of mTORC2-dependent Akt1 phosphorylation and Nrf2-mediated HO-1 expression.

Metformin induces microRNA-34a to downregulate the Sirt1/Pgc-1α/Nrf2 pathway, leading to increased susceptibility of wild-type p53 cancer cells to oxidative stress and therapeutic agents

Sirtuin 1 (Sirt1) plays an important role in cellular redox balance and resistance to oxidative stress. Sirt1 exhibits oncogenic properties in wild-type p53 cancer cells, whereas it acts as a tumor suppressor in p53-mutated cancer cells. Here, we investigated the effects of metformin on Sirt1 expression in several cancer cell lines. Using human cancer cell lines that exhibit differential expression of p53, we found that metformin reduced Sirt1 protein levels in cancer cells bearing wild-type p53, but did not affect Sirt1 protein levels in cancer cell lines harboring mutant forms of p53. Metformin-induced p53 protein levels in wild-type p53 cancer cells resulted in upregulation of microRNA (miR)-34a. The use of a miR-34a inhibitor confirmed that metformin-induced miR-34a was required for Sirt1 downregulation. Metformin suppressed peroxisome proliferator-activated receptor γ (PPARγ) coactivator-1α (Pgc-1α) expression and its downstream target Nrf2 in MCF-7 cells. Genetic tools demonstrated that the reduction of Sirt1 and Pgc-1α by metformin caused Nrf2 downregulation via suppression of PPARγ transcriptional activity. Metformin reduced heme oxygenase-1 and superoxide dismutase 2 but upregulated catalase expression in MCF-7 cells. Metformin-treated MCF-7 cells had no increase in basal levels of reactive oxygen species but were more susceptible to oxidative stress. Furthermore, upregulation of death receptor 5 by metformin-mediated Sirt1 downregulation enhanced the sensitivity of wild-type p53 cancer cells to TRAIL-induced apoptosis. Our results demonstrated that metformin induces miR-34a to suppress the Sirt1/Pgc-1α/Nrf2 pathway and increases susceptibility of wild-type p53 cancer cells to oxidative stress and TRAIL-induced apoptosis.

Carbon monoxide induces heme oxygenase-1 to modulate STAT3 activation in endothelial cells via S-glutathionylation

IL-6/STAT3 pathway is involved in a variety of biological responses, including cell proliferation, differentiation, apoptosis, and inflammation. In our present study, we found that CO releasing molecules (CORMs) suppress IL-6-induced STAT3 phosphorylation, nuclear translocation and transactivity in endothelial cells (ECs). CO is a byproduct of heme degradation mediated by heme oxygenase (HO-1). However, CORMs can induce HO-1 expression and then inhibit STAT3 phosphorylation. CO has been found to increase a low level ROS and which may induce protein glutathionylation. We hypothesized that CORMs increases protein glutathionylation and inhibits STAT3 activation. We found that CORMs increase the intracellular GSSG level and induce the glutathionylation of multiple proteins including STAT3. GSSG can inhibit STAT3 phosphorylation and increase STAT3 glutathionylation whereas the antioxidant enzyme catalase can suppress the glutathionylation. Furthermore, catalase blocks the inhibition of STAT3 phosphorylation by CORMs treatment. The inhibition of glutathione synthesis by BSO was also found to attenuate STAT3 glutathionylation and its inhibition of STAT3 phosphorylation. We further found that HO-1 increases STAT3 glutathionylation and that HO-1 siRNA attenuates CORM-induced STAT3 glutathionylation. Hence, the inhibition of STAT3 activation is likely to occur via a CO-mediated increase in the GSSG level, which augments protein glutathionylation, and CO-induced HO-1 expression, which may enhance and maintain its effects in IL-6-treated ECs.

CO and CO-releasing molecules (CO-RMs) in acute gastrointestinal inflammation

Carbon monoxide (CO) is enzymatically generated in mammalian cells alongside the liberation of iron and the production of biliverdin and bilirubin. This occurs during the degradation of haem by haem oxygenase (HO) enzymes, a class of ubiquitous proteins consisting of constitutive and inducible isoforms. The constitutive HO2 is present in the gastrointestinal tract in neurons and interstitial cells of Cajal and CO released from these cells might contribute to intestinal inhibitory neurotransmission and/or to the control of intestinal smooth muscle cell membrane potential. On the other hand, increased expression of the inducible HO1 is now recognized as a beneficial response to oxidative stress and inflammation. Among the products of haem metabolism, CO appears to contribute primarily to the antioxidant and anti-inflammatory effects of the HO1 pathway explaining the studies conducted to exploit CO as a possible therapeutic agent. This article reviews the effects and, as far as known today, the mechanism(s) of action of CO administered either as CO gas or via CO-releasing molecules in acute gastrointestinal inflammation. We provide here a comprehensive overview on the effect of CO in experimental in vivo models of post-operative ileus, intestinal injury during sepsis and necrotizing enterocolitis. In addition, we will analyse the in vitro data obtained so far on the effect of CO on intestinal epithelial cell lines exposed to cytokines, considering the important role of the intestinal mucosa in the pathology of gastrointestinal inflammation.

Gas what: NO is not the only answer to sexual function

The ability to get and keep an erection is important to men for several reasons and the inability is known as erectile dysfunction (ED). ED has started to be accepted as an early indicator of systemic endothelial dysfunction and subsequently of cardiovascular diseases. The role of NO in endothelial relaxation and erectile function is well accepted. The discovery of NO as a small signalling gasotransmitter led to the investigation of the role of other endogenously derived gases, carbon monoxide (CO) and hydrogen sulphide (H2 S) in physiological and pathophysiological conditions. The role of NO and CO in sexual function and dysfunction has been investigated more extensively and, recently, the involvement of H2 S in erectile function has also been confirmed. In this review, we focus on the role of these three sister gasotransmitters in the physiology, pharmacology and pathophysiology of sexual function in man, specifically erectile function. We have also reviewed the role of soluble guanylyl cyclase/cGMP pathway as a common target of these gasotransmitters. Several studies have proposed alternative therapies targeting different mechanisms in addition to PDE-5 inhibition for ED treatment, since some patients do not respond to these drugs. This review highlights complementary and possible coordinated roles for these mediators and treatments targeting these gasotransmitters in erectile function/ED.

Endoplasmic reticulum stress sensor protein kinase R-like endoplasmic reticulum kinase (PERK) protects against pressure overload-induced heart failure and lung remodeling

Studies have reported that development of congestive heart failure is associated with increased endoplasmic reticulum stress. Double stranded RNA-activated protein kinase R-like endoplasmic reticulum kinase (PERK) is a major transducer of the endoplasmic reticulum stress response and directly phosphorylates eukaryotic initiation factor 2α, resulting in translational attenuation. However, the physiological effect of PERK on congestive heart failure development is unknown. To study the effect of PERK on ventricular structure and function, we generated inducible cardiac-specific PERK knockout mice. Under unstressed conditions, cardiac PERK knockout had no effect on left ventricular mass, or its ratio to body weight, cardiomyocyte size, fibrosis, or left ventricular function. However, in response to chronic transverse aortic constriction, PERK knockout mice exhibited decreased ejection fraction, increased left ventricular fibrosis, enhanced cardiomyocyte apoptosis, and exacerbated lung remodeling in comparison with wild-type mice. PERK knockout also dramatically attenuated cardiac sarcoplasmic reticulum Ca(2+)-ATPase expression in response to aortic constriction. Our findings suggest that PERK is required to protect the heart from pressure overload-induced congestive heart failure.

CO-releasing molecules and increased heme oxygenase-1 induce protein S-glutathionylation to modulate NF-κB activity in endothelial cells

Protein glutathionylation is a protective mechanism that functions in response to mild oxidative stress. Carbon monoxide (CO) can increase the reactive oxygen species concentration from a low level via the inhibition of cytochrome c oxidase. We therefore hypothesized that CO would induce NF-κB-p65 glutathionylation and then show anti-inflammatory effects. In this study, we found that CO-releasing molecules suppress TNFα-induced monocyte adhesion to endothelial cells (ECs) and reduce ICAM-1 expression. Moreover, CO donors were further found to exert their inhibitory effects by blocking NF-κB-p65 nuclear translocation, but do so independent of IκBα degradation, in TNFα-treated ECs. In addition, p65 protein glutathionylation represents the response signal to CO donors and is reversed by the reducing agent dithiothreitol. Thiol modification of the cysteine residue in the p65 RHD region was required for the CO-modulated NF-κB activation. The suppression of p65 glutathionylation by a GSH synthesis inhibitor, BSO, and by catalase could also attenuate TNFα-induced p65 nuclear translocation and ICAM-1 expression. CO donors induce Nrf2 activation and Nrf2 siRNA suppresses CO-induced p65 glutathionylation and inhibition. Furthermore, we found that the CO donors induce heme oxygenase-1 (HO-1) expression, which increases p65 glutathionylation. In contrast, HO-1 siRNA attenuates CO donor- and hemin-induced p65 glutathionylation. Our results thus indicate that the glutathionylation of p65 is likely to be responsible for CO-mediated NF-κB inactivation and that the HO-1-dependent pathway may prolong the inhibitory effects of CO donors upon TNFα treatment of ECs.

Salvianolic acid B protects human endothelial progenitor cells against oxidative stress-mediated dysfunction by modulating Akt/mTOR/4EBP1, p38 MAPK/ATF2, and ERK1/2 signaling pathways

The vascular endothelium is specifically sensitive to oxidative stress, and this is one of the mechanisms that causes widespread endothelial dysfunction in most cardiovascular diseases and disorders. Protection against reactive oxygen species (ROS)-mediated oxidative damage via antioxidant mechanisms is essential for tissue maintenance and shows therapeutic potential for patients suffering from cardiovascular and metabolic disorders. Salvianolic acid B (SalB), a natural bioactive component known from Traditional Chinese Medicine, has been reported to exert cellular protection in various types of cells. However, the underlying mechanisms involved are not fully understood. Here, we showed that SalB significantly promoted the migratory and tube formation abilities of human bone marrow derived-endothelial progenitor cells (BM-EPCs) in vitro, and substantially abrogated hydrogen peroxide (H2O2)-induced cell damage. SalB down-regulated Nox4 and eNOS, as well as nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase expression upon H2O2 induction that in turn prevents oxidative-induced endothelial dysfunction. Moreover, SalB suppressed the Bax/Bcl-xL ratio and caspase-3 activation after H2O2 induction. Furthermore, our results provide mechanistic evidence that activation of the mTOR/p70S6K/4EBP1 pathways is required for both SalB-mediated angiogenic and protective effects against oxidative stress-induced cell injury in BM-EPCs. Suppression of MKK3/6-p38 MAPK-ATF2 and ERK1/2 signaling pathways by SalB significantly protected BM-EPCs against cell injury caused by oxidative stress via reduction of intracellular ROS levels and apoptosis. Taken together, by providing a mechanistic insight into the modulation of redox states in BM-EPCs by SalB, we suggest that SalB has a strong potential of being a new proangiogenic and cytoprotective therapeutic agent with applications in the field of endothelial injury-mediated vascular diseases.

New insights into intracellular locations and functions of heme oxygenase-1

SIGNIFICANCE

Heme oxygenase-1 (HMOX1) plays a critical role in the protection of cells, and the inducible enzyme is implicated in a spectrum of human diseases. The increasing prevalence of cardiovascular and metabolic morbidities, for which current treatment approaches are not optimal, emphasizes the necessity to better understand key players such as HMOX1 that may be therapeutic targets.

RECENT ADVANCES

HMOX1 is a dynamic protein that can undergo post-translational and structural modifications which modulate HMOX1 function. Moreover, trafficking from the endoplasmic reticulum to other cellular compartments, including the nucleus, highlights that HMOX1 may play roles other than the catabolism of heme.

CRITICAL ISSUES

The ability of HMOX1 to be induced by a variety of stressors, in an equally wide variety of tissues and cell types, represents an obstacle for the therapeutic exploitation of the enzyme. Any capacity to modulate HMOX1 in cardiovascular and metabolic diseases should be tempered with an appreciation that HMOX1 may have an impact on cancer. Moreover, the potential for heme catabolism end products, such as carbon monoxide, to amplify the HMOX1 stress response should be considered.

FUTURE DIRECTIONS

A more complete understanding of HMOX1 modifications and the properties that they impart is necessary. Delineating these parameters will provide a clearer picture of the opportunities to modulate HMOX1 in human disease.

Activation of the PKR/eIF2α signaling cascade inhibits replication of Newcastle disease virus

Background

Newcastle Disease virus (NDV) causes severe and economically significant disease in almost all birds. However, factors that affect NDV replication in host cells are poorly understood. NDV generates long double-stranded RNA (dsRNA) molecules during transcription of single-stranded genomic RNA. Protein kinase R (PKR) is activated by dsRNA. The aim of this study was to elucidate the role of PKR in NDV infection.

Results

NDV infection led to the activation of dsRNA-dependent PKR and phosphorylation of its substrate, translation initiation factor eIF2α, in a dose-dependent manner by either the lentogenic strain LaSota or a velogenic strain Herts/33. PKR activation coincided with the accumulation of dsRNA induced by NDV infection. PKR knockdown remarkably decreased eIF2α phosphorylation as well as IFN-β mRNA levels, leading to the augmentation of extracellular virus titer. Furthermore, siRNA knockdown or phosphorylation of eIF2α or okadaic acid treatment significantly impaired NDV replication, indicating the critical role of the PKR/eIF2α signaling cascade in NDV infection.

Conclusion

PKR is activated by dsRNA generated by NDV infection and inhibits NDV replication by eIF2α phosphorylation. This study provides insight into NDV-host interactions for the development of candidate antiviral strategies.

Delayed inhaled carbon monoxide mediates the regression of established neointimal lesions

OBJECTIVE

Intimal hyperplasia (IH) contributes to the failure of vascular interventions. While many investigational therapies inhibit the development of IH in animal models, few of these potential therapies can reverse established lesions. Inhaled carbon monoxide (CO) dramatically inhibits IH in both rats and pigs when given perioperatively. It also prevented the development of pulmonary arterial hypertension in rodents. Interestingly, CO could reverse pulmonary artery structural changes and right heart hemodynamic changes when administered after the establishment of pulmonary hypertension. Thus, we hypothesize that inhaled CO may mediate the regression of established neointimal lesions.

METHODS

Rats underwent carotid artery balloon angioplasty injury. Carotid arteries were collected at 2 and 4 weeks after injury for morphometric analysis of the neointima. Another group was treated with inhaled CO (250 parts per million) for 1 hour daily from week 2 until week 4. Additional rats were sacrificed 3 days after initiating CO treatment, and the carotid arteries were examined for apoptosis by terminal deoxynucleotidyl transferase dUTP nick end-labeling, proliferation by Ki67 staining, and autophagy by microtubule-associated protein light chain 3 I/II staining.

RESULTS

At 2 weeks following injury, sizable neointimal lesions had developed (intimal/media = 0.92 ± 0.22). By 4 weeks, lesion size remained stable (0.80 ± 0.09). Delayed inhaled CO treatment greatly reduced neointimal lesion size vs the 2- and 4-week control mice (0.38 ± 0.05; P < .05). Arteries from the CO-treated rats exhibited significantly reduced apoptosis compared with control vessels (3.18% ± 1.94% vs 16.26% ± 5.91%; P = .036). Proliferation was also dramatically reduced in the CO-treated animals (2.98 ± 1.55 vs 10.37 ± 2.80; P = .036). No difference in autophagy between control and CO-treated rats was detected.

CONCLUSIONS

Delayed administration of inhaled CO reduced established neointimal lesion size. This effect was mediated by the antiproliferative effect of CO on medial and intimal smooth muscle cells without increases in arterial wall apoptosis or autophagy. Future studies will examine additional time points to determine if there is temporal variation in the rates of apoptosis and autophagy.

Endoplasmic reticulum stress is sufficient for the induction of IL-1β production via activation of the NF-κB and inflammasome pathways

The mechanisms underlying pathophysiological states such as metabolic syndrome and obesity include endoplasmic reticulum (ER) stress and aberrant inflammatory responses. ER stress results from the accumulation of misfolded proteins during stress conditions. However, the precise mechanisms by which ER stress modulates inflammation remain incompletely understood. In this study, we hypothesized that ER stress alone could represent a sufficient signal for the modulation of inflammasome-dependent cytokine responses. We found that several ER stress-inducing chemicals and the free fatty acid palmitate can trigger IL-1β secretion in various cell types, including monocytic leukemia cells, primary macrophages and differentiated adipocytes. We show that ER stress primes cells for the expression of pro-IL-1β via NF-κB activation and promotes IL-1β secretion. Enhanced IL-1β secretion depended on the activation of the NLRP3 inflammasome through a mechanism involving reactive oxygen species formation and activation of thioredoxin-interacting protein. Chemical chaperone treatment and the pharmacological application of carbon monoxide inhibited IL-1β secretion in response to ER stress. Our results provide a mechanistic link between ER stress and the regulation of inflammation, and suggest that modulation of ER stress may provide a therapeutic opportunity to block progression of low grade chronic inflammation to metabolic syndrome.

Hypoxic preconditioning protects microvascular endothelial cells against hypoxia/reoxygenation injury by attenuating endoplasmic reticulum stress

Endothelial cells (ECs) are directly exposed to hypoxia and contribute to injury during myocardial ischemia/reperfusion. Hypoxic preconditioning (HPC) protects ECs against hypoxia injury. This study aimed to explore whether HPC attenuates hypoxia/reoxygenation (H/R) injury by suppressing excessive endoplasmic reticulum stress (ERS) in cultured microvascular ECs (MVECs) from rat heart. MVECs injury was measured by lactate dehydrogenase (LDH) leakage, cytoskeleton destruction, and apoptosis. Expression of glucose regulating protein 78 (GRP78) and C/EBP homologous protein (CHOP), activation of caspase-12 (pro-apoptosis factors) and phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK) were detected by western blot analysis. HPC attenuated H/R-induced LDH leakage, cytoskeleton destruction, and cell apoptosis, as shown by flow cytometry, Bax/Bcl-2 ratio, caspase-3 activation and terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end labeling. HPC suppressed H/R-induced ERS, as shown by a decrease in expression of GRP78 and CHOP, and caspase-12 activation. HPC enhanced p38 MAPK phosphorylation but decreased that of protein kinase R-like ER kinase (PERK, upstream regulator of CHOP). SB202190 (an inhibitor of p38 MAPK) abolished HPC-induced cytoprotection, downregulation of GRP78 and CHOP, and activation of caspase-12, as well as PERK phosphorylation. HPC may protect MVECs against H/R injury by suppressing CHOP-dependent apoptosis through p38 MAPK mediated downregulation of PERK activation.

Antidiabetic potential of the heme oxygenase-1 inducer curcumin analogues

Although there is a therapeutic treatment to combat diabetes, the identification of agents that may deal with its more serious aspects is an important medical field for research. Diabetes, which contributes to the risk of cardiovascular disease, is associated with a low-grade chronic inflammation (inflammatory stress), oxidative stress, and endoplasmic reticulum (ER) stress. Because the integration of these stresses is critical to the pathogenesis of diabetes, agents and cellular molecules that can modulate these stress responses are emerging as potential targets for intervention and treatment of diabetic diseases. It has been recognized that heme oxygenase-1 (HO-1) plays an important role in cellular protection. Because HO-1 can reduce oxidative stress, inflammatory stress, and ER stress, in part by exerting antioxidant, anti-inflammatory, and antiapoptotic effects, HO-1 has been suggested to play important roles in pathogenesis of diabetes. In the present review, we will explore our current understanding of the protective mechanisms of HO-1 in diabetes and present some emerging therapeutic options for HO-1 expression in treating diabetic diseases, together with the therapeutic potential of curcumin analogues that have their ability to induce HO-1 expression.

Therapeutic roles of heme oxygenase-1 in metabolic diseases: curcumin and resveratrol analogues as possible inducers of heme oxygenase-1

Metabolic diseases, such as insulin resistance, type II diabetes, and obesity, are associated with a low-grade chronic inflammation (inflammatory stress), oxidative stress, and endoplasmic reticulum (ER) stress. Because the integration of these stresses is critical to the pathogenesis of metabolic diseases, agents and cellular molecules that can modulate these stress responses are emerging as potential targets for intervention and treatment of metabolic diseases. It has been recognized that heme oxygenase-1 (HO-1) plays an important role in cellular protection. Because HO-1 can reduce inflammatory stress, oxidative stress, and ER stress, in part by exerting antioxidant, anti-inflammatory, and antiapoptotic effects, HO-1 has been suggested to play important roles in pathogenesis of metabolic diseases. In the present review, we will explore our current understanding of the protective mechanisms of HO-1 in metabolic diseases and present some emerging therapeutic options for HO-1 expression in treating metabolic diseases, together with the therapeutic potential of curcumin and resveratrol analogues that have their ability to induce HO-1 expression.

Haem catabolism: a novel modulator of inflammation in Gilbert's syndrome

BACKGROUND

Moderately elevated unconjugated bilirubin concentrations protect against inflammatory diseases and are present in individuals with Gilbert's syndrome. This study examined the relationship between circulating haem oxygenase catabolites, unconjugated bilirubin, carboxy haemoglobin, iron and inflammatory parameters.

MATERIALS AND METHODS

Seventy-six matched individuals were allocated to Gilbert's syndrome (GS) or control group (unconjugated bilirubin ≥ or < 17.1 μM). Iron, carboxy haemoglobin and high-sensitivity C-reactive protein were analysed using routine diagnostic tests. Unconjugated bilirubin and haem were analysed using high-performance liquid chromatography. The cytokines IL-1β, TNF-α and IL-6 were assessed using high-sensitivity enzyme-linked immunosorbent assays.

RESULTS

Gilbert's syndrome subjects had significantly greater levels of unconjugated bilirubin (P < 0.05), carboxy haemoglobin (P < 0.05), iron (P < 0.05), IL-1β (P < 0.05), a significantly lower body mass index (P < 0.05) and IL-6 concentrations (P < 0.05) vs. controls. Regression analysis revealed that unconjugated bilirubin mainly explained IL-1β results (16%), and body mass index+IL-6 predicted 26% of the variance in C-reactive protein concentrations.

CONCLUSIONS

A positive relationship between unconjugated bilirubin and free plasma haem, iron and carboxy haemoglobin indicated a positive feedback loop of haem oxygenase induction possibly mediated by unconjugated bilirubin. Furthermore, reduced body mass index in Gilbert's syndrome individuals was linked to reduced inflammation status, which could be influenced by circulating haem oxygenase catabolites and contribute to reduced risk of noncommunicable diseases in this population.

Transforming growth factor-β induces transcription factors MafK and Bach1 to suppress expression of the heme oxygenase-1 gene

Transforming growth factor-β (TGF-β) has multiple functions in embryogenesis, adult homeostasis, tissue repair, and development of cancer. Here, we report that TGF-β suppresses the transcriptional activation of the heme oxygenase-1 (HO-1) gene, which is implicated in protection against oxidative injury and lung carcinogenesis. HO-1 is a target of the oxidative stress-responsive transcription factor Nrf2. TGF-β did not affect the stabilization or nuclear accumulation of Nrf2 after stimulation with electrophiles. Instead, TGF-β induced expression of transcription factors MafK and Bach1. Enhanced expression of either MafK or Bach1 was enough to suppress the electrophile-inducible expression of HO-1 even in the presence of accumulated Nrf2 in the nucleus. Knockdown of MafK and Bach1 by siRNA abolished TGF-β-dependent suppression of HO-1. Furthermore, chromatin immunoprecipitation assays revealed that Nrf2 substitutes for Bach1 at the antioxidant response elements (E1 and E2), which are responsible for the induction of HO-1 in response to oxidative stress. On the other hand, pretreatment with TGF-β suppressed binding of Nrf2 to both E1 and E2 but marginally increased the binding of MafK to E2 together with Smads. As TGF-β is activated after tissue injury and in the process of cancer development, these findings suggest a novel mechanism by which damaged tissue becomes vulnerable to oxidative stress and xenobiotics.

Decursin Isolated from Angelica gigas Nakai Rescues PC12 Cells from Amyloid β-Protein-Induced Neurotoxicity through Nrf2-Mediated Upregulation of Heme Oxygenase-1: Potential Roles of MAPK

Decursin (D), purified from Angelica gigas Nakai, has been proven to exert neuroprotective property. Previous study revealed that D reduced A β 25 ‒ 35-induced cytotoxicity in PC12 cells. Our study explored the underlying mechanisms by which D mediates its therapeutic effects in vitro. Pretreatment of cells with D diminished intracellular generation of ROS in response to A β 25 ‒ 35. Western blot revealed that D significantly increased the expression and activity of HO-1, which was correlated with its protection against A β 25 ‒ 35-induced injury. Addition of ZnPP, an HO-1 competitive inhibitor, significantly attenuated its protective effect in A β 25 ‒ 35-treated cells, indicating the vital role of HO-1 resistance to oxidative injury. Moreover, D induced Nrf2 nuclear translocation, the upstream of HO-1 expression. While investigating the signaling pathways responsible for HO-1 induction, D activated ERK and dephosphorylated p38 in PC12 cells. Addition of U0126, a selective inhibitor of ERK, blocked D-induced Nrf2 activation and HO-1 induction and meanwhile reversed the protection of D against A β 25 ‒ 35-induced cell death. These findings suggest D augments cellular antioxidant defense capacity through both intrinsic free radical scavenging activity and activation of MAPK signal pathways that leads to Nrf2 activation, and subsequently HO-1 induction, thereby protecting the PC12 cells from A β 25 ‒ 35-induced oxidative cytotoxicity.

Carbon monoxide-releasing molecules reverse leptin resistance induced by endoplasmic reticulum stress

Leptin, a circulating hormone, regulates food intake and body weight. While leptin resistance represents a major cause of obesity, the underlying mechanisms remain unclear. Endoplasmic reticulum (ER) stress can contribute to leptin resistance. Carbon monoxide (CO), a gaseous molecule, exerts antiapoptotic and anti-inflammatory effects in animal models of tissue injury. We hypothesized that CO could inhibit leptin resistance during ER stress. Thapsigargin or tunicamycin was used to induce ER stress in human cells expressing the leptin receptor. These agents markedly inhibited leptin-induced STAT3 phosphorylation, confirming that ER stress induces leptin resistance. The CO-releasing molecule CORM-2 blocked the ER stress-dependent inhibition of leptin-induced STAT3 phosphorylation. CORM-2 treatment induced the phosphorylation of protein kinase R-like endoplasmic reticulum kinase (PERK), and eukaryotic translation initiation factor-2α and enhanced PERK phosphorylation during ER stress. Furthermore, CORM-2 inhibited X-box binding protein-1 expression, activating transcription factor-6 cleavage, and inositol-requiring enzyme (IRE)1α phosphorylation induced by ER stress. IRE1α knockdown rescued leptin resistance, whereas PERK knockdown blocked CO-dependent regulation of IRE1α. In vivo, CO inhalation normalized body weight in animals fed high-fat diets. Furthermore, CO modulated ER stress pathways and rescued leptin resistance in vivo. In conclusion, the pathological mechanism of leptin resistance may be ameliorated by the pharmacological application of CO.