The role of PDI as a survival factor in cardiomyocyte ischemia

HDAC3 genetic and pharmacologic inhibition radiosensitizes fusion positive rhabdomyosarcoma by promoting DNA double-strand breaks

Radiotherapy (RT) plays a critical role in the management of rhabdomyosarcoma (RMS), the prevalent soft tissue sarcoma in childhood. The high risk PAX3-FOXO1 fusion-positive subtype (FP-RMS) is often resistant to RT. We have recently demonstrated that inhibition of class-I histone deacetylases (HDACs) radiosensitizes FP-RMS both in vitro and in vivo. However, HDAC inhibitors exhibited limited success on solid tumors in human clinical trials, at least in part due to the presence of off-target effects. Hence, identifying specific HDAC isoforms that can be targeted to radiosensitize FP-RMS is imperative. We, here, found that only HDAC3 silencing, among all class-I HDACs screened by siRNA, radiosensitizes FP-RMS cells by inhibiting colony formation. Thus, we dissected the effects of HDAC3 depletion using CRISPR/Cas9-dependent HDAC3 knock-out (KO) in FP-RMS cells, which resulted in Endoplasmatic Reticulum Stress activation, ERK inactivation, PARP1- and caspase-dependent apoptosis and reduced stemness when combined with irradiation compared to single treatments. HDAC3 loss-of-function increased DNA damage in irradiated cells augmenting H2AX phosphorylation and DNA double-strand breaks (DSBs) and counteracting irradiation-dependent activation of ATM and DNA-Pkcs as well as Rad51 protein induction. Moreover, HDAC3 depletion hampers FP-RMS tumor growth in vivo and maximally inhibits the growth of irradiated tumors compared to single approaches. We, then, developed a new HDAC3 inhibitor, MC4448, which showed specific cell anti-tumor effects and mirrors the radiosensitizing effects of HDAC3 depletion in vitro synergizing with ERKs inhibition. Overall, our findings dissect the pro-survival role of HDAC3 in FP-RMS and suggest HDAC3 genetic or pharmacologic inhibition as a new promising strategy to overcome radioresistance in this tumor.

ERO1-PDI Redox Signaling in Health and Disease

Significance: Protein disulfide isomerase (PDI) and endoplasmic reticulum oxidoreductase 1 (ERO1) are crucial for oxidative protein folding in the endoplasmic reticulum (ER). These enzymes are frequently overexpressed and secreted, and they contribute to the pathology of neurodegenerative, cardiovascular, and metabolic diseases. Recent Advances: Tissue-specific knockout mouse models and pharmacologic inhibitors have been developed to advance our understanding of the cell-specific functions of PDI and ERO1. In addition to their roles in protecting cells from the unfolded protein response and oxidative stress, recent studies have revealed that PDI and ERO1 also function outside of the cells. Critical Issues: Despite the well-known contributions of PDI and ERO1 to specific disease pathology, the detailed molecular and cellular mechanisms underlying these activities remain to be elucidated. Further, although PDI and ERO1 inhibitors have been identified, the results from previous studies require careful evaluation, as many of these agents are not selective and may have significant cytotoxicity. Future Directions: The functions of PDI and ERO1 in the ER have been extensively studied. Additional studies will be required to define their functions outside the ER.

Protein Aggregation in the Pathogenesis of Ischemic Stroke

Despite the distinction between ischemic stroke and neurodegenerative disorders, they share numerous pathophysiologies particularly those mediated by inflammation and oxidative stress. Although protein aggregation is considered to be a hallmark of neurodegenerative diseases, the formation of protein aggregates can be also induced within a short time after cerebral ischemia, aggravating cerebral ischemic injury. Protein aggregation uncovers a previously unappreciated molecular overlap between neurodegenerative diseases and ischemic stroke. Unfortunately, compared with neurodegenerative disease, mechanism of protein aggregation after cerebral ischemia and how this can be averted remain unclear. This review highlights current understanding on protein aggregation and its intrinsic role in ischemic stroke.

Unfolded protein response during cardiovascular disorders: a tilt towards pro-survival and cellular homeostasis

The endoplasmic reticulum (ER) is an organelle that orchestrates the production and proper assembly of an extensive types of secretory and membrane proteins. Endoplasmic reticulum stress is conventionally related to prolonged disruption in the protein folding machinery resulting in the accumulation of unfolded proteins in the ER. This disruption is often manifested due to oxidative stress, Ca²⁺ leakage, iron imbalance, disease conditions which in turn hampers the cellular homeostasis and induces cellular apoptosis. A mild ER stress is often reverted back to normal. However, cells retaliate to acute ER stress by activating the unfolded protein response (UPR) which comprises three signaling pathways, Activating transcription factor 6 (ATF6), inositol requiring enzyme 1 alpha (IRE1α), and protein kinase RNA-activated-like ER kinase (PERK). The UPR response participates in both protective and pro-apoptotic responses and not much is known about the mechanistic aspects of the switch from pro-survival to pro-apoptosis. When ER stress outpaces UPR response then cell apoptosis prevails which often leads to the development of various diseases including cardiomyopathies. Therefore, it is important to identify molecules that modulate the UPR that may serve as promising tools towards effective treatment of cardiovascular diseases. In this review, we elucidated the latest advances in construing the contribution imparted by the three arms of UPR to combat the adverse environment in the ER to restore cellular homeostasis during cardiomyopathies. We also summarized the various therapeutic agents that plays crucial role in tilting the UPR response towards pro-survival.

Crosstalk between endoplasmic reticulum stress and oxidative stress: Focus on protein disulfide isomerase and endoplasmic reticulum oxidase 1

Cellular stress and inflammation, establishing as disease pathology, have reached great heights in the last few decades. Stress conditions such as hyperglycemia, hyperlipidemia and lipoproteins are known to disturb proteostasis resulting in the accumulation of unfolded or misfolded proteins, alteration in calcium homeostasis culminating in unfolded protein response. Protein disulfide isomerase and endoplasmic reticulum oxidase-1 are the key players in protein folding. The protein folding process assisted by endoplasmic reticulum oxidase-1 results in the production of reactive oxygen species in the lumen of the endoplasmic reticulum. Production of reactive oxygen species beyond the quenching capacity of the antioxidant systems perturbs ER homeostasis. Endoplasmic reticulum stress also induces the production of cytokines leading to inflammatory responses. This has been proven to be the major causative factor for various pathophysiological states compared to other cellular triggers in diseases, which further manifests to increased oxidative stress, mitochondrial dysfunction, and altered inflammatory responses, deleterious to cellular physiology and homeostasis. Numerous studies have drawn correlations between the progression of several diseases in association with endoplasmic reticulum stress, redox protein folding, oxidative stress and inflammatory responses. This review aims to provide an insight into the role of protein disulfide isomerase and endoplasmic reticulum oxidase-1 in endoplasmic reticulum stress, unfolded protein response, mitochondrial dysfunction, and inflammatory responses, which exacerbate the progression of various diseases.

Protein Disulfide Isomerase 4 Drives Docetaxel Resistance in Prostate Cancer

BACKGROUND

Protein disulfide isomerase 4 (PDIA4) has been reported to be closely associated with chemoresistance in several types of malignancies. But the pathogenic mechanisms of PDIA4 involved in docetaxel (DTX) resistance in prostate cancer (PCa) are still unknown. Hence, this study was conducted to evaluate the potential effect of PDIA4 on chemoresistance to DTX in PCa cells and to investigate the underlying mechanisms.

METHODS

Two types of DTX-resistant PCa cells, that is, DTX-resistant PC-3 cells (PC-3/DTXR) and C4-2B cells (C4-2B/DTXR) were developed, as well as the parental PC-3 and C4-2B cells were obtained to investigate these issues. Short hairpin RNAs targeting human PDIA4 to knockdown the expression of PDIA4 or PDIA4-expressing adenoviral vectors to overexpress the PDIA4 were transfected into PCa cells to study the underlying mechanisms of PDIA4 involving in PCa DTX resistance.

RESULTS

Results showed that PDIA4 exhibited a dramatic overexpression in PC-3/DTXR and C4-2B/DTXR cells. Down-regulation of PDIA4 by infecting PC-3/DTXR and C4-2B/DTXR cells with shPDIA4 lentivirus stimulated cell death by prompting apoptosis. Up-regulation of PDIA4 by infecting PC-3 and C4-2B cells with PDIA4-expressing adenovirus showed severer resistance to DTX. In addition, PDIA4 up-regulation induced phosphorylated protein kinase B (Akt) expression, while PDIA4 knockdown significantly inhibited the expression in PCa cells.

CONCLUSIONS

Our study indicates that PDIA4 is a negative regulator of PCa cell apoptosis and plays a critical role in PCa DTX resistance by activating the Akt-signaling pathway. Thereby, it implies that targeting PDIA4 could be a potential adjuvant therapeutic approach against DTX resistance in PCa.

Protein disulfide isomerase is regulated in multiple ways: Consequences for conformation, activities, and pathophysiological functions

Protein disulfide isomerase (PDI) is one of the most abundant and critical protein folding catalysts in the endoplasmic reticulum of eukaryotic cells. PDI consists of four thioredoxin domains and interacts with a wide range of substrate and partner proteins due to its intrinsic conformational flexibility. PDI plays multifunctional roles in a variety of pathophysiological events, both as an oxidoreductase and a molecular chaperone. Recent studies have revealed that the conformation and activity of PDI can be regulated in multiple ways, including posttranslational modification and substrate/ligand binding. Here, we summarize recent advances in understanding the function and regulation of PDI in different pathological and physiological events. We propose that the multifunctional roles of PDI are regulated by multiple mechanisms. Furthermore, we discuss future directions for the study of PDI, emphasizing how different regulatory modes are linked to the conformational changes and biological functions of PDI in the context of diverse pathophysiologies.

Protein disulfide isomerase in cardiovascular disease

Protein disulfide isomerase (PDI) participates in the pathogenesis of numerous diseases. Increasing evidence indicates that intravascular cell-derived PDI plays an important role in the initiation and progression of cardiovascular diseases, including thrombosis and vascular inflammation. Recent studies with PDI conditional knockout mice have advanced our understanding of the function of cell-specific PDI in disease processes. Furthermore, the identification and development of novel small-molecule PDI inhibitors has led into a new era of PDI research that transitioned from the bench to bedside. In this review, we will discuss recent findings on the regulatory role of PDI in cardiovascular disease.

Efforts to untangle the functions of a large family of enzymes could lead researchers to new therapies for diverse cardiovascular diseases. Members of the protein disulfide isomerase (PDI) family chemically modify other proteins in ways that can alter both their structure and biological activity. Jaehyung Cho of the University of Illinois at Chicago, USA and coworkers have reviewed numerous studies linking PDI with cardiovascular diseases, including thrombosis, heart attack, vascular inflammation, and stroke. The authors also report progress in developing small-molecule PDI inhibitors that could yield the treatment for these conditions.

Hypoxia evokes increased PDI and PDIA6 expression in the infarcted myocardium of ex-germ-free and conventionally raised mice

The prototypic protein disulfide isomerase (PDI), encoded by the P4HB gene, has been described as a survival factor in ischemic cardiomyopathy. However, the role of protein disulfide isomerase associated 6 (PDIA6) under hypoxic conditions in the myocardium remains enigmatic, and it is unknown whether the gut microbiota influences the expression of PDI and PDIA6 under conditions of acute myocardial infarction. Here, we revealed that, in addition to the prototypic PDI, the PDI family member PDIA6, a regulator of the unfolded protein response, is upregulated in the mouse cardiomyocyte cell line HL-1 when cultured under hypoxia. In vivo, in the left anterior descending artery (LAD) ligation mouse model of acute myocardial infarction, similar to PDI, PDIA6 protein expression was enhanced in the infarcted area (LAD+) relative to uninfarcted sham tissue or the neighbouring area at risk (LAD–) of C57BL/6J mice. Interestingly, we found that ex-germ-free (ex-GF) mice subjected to the LAD ligation model for 24 h had a reduced ejection fraction compared with their conventionally raised (CONV-R) SPF controls. Furthermore, the LAD+ area in the infarcted heart of ex-GF mice showed reduced PDIA6 expression relative to CONV-R controls, suggesting that the presence of a gut microbiota enhanced LAD ligation-triggered PDIA6 expression. Collectively, our results demonstrate that PDIA6 is upregulated in cardiomyocytes as a consequence of hypoxia. In the LAD mouse model, PDIA6 was also increased in the infarcted area under in vivo conditions, but this increase was suppressed in ex-GF mice relative to CONV-R controls.

This article has an associated First Person interview with the first author of the paper.

Summary: We identified PDIA6 as a hypoxia-induced element of the unfolded protein response in cardiomyocytes and infarcted mouse hearts. PDIA6 expression and ejection fractions were reduced in infarcted ex-germ-free mouse hearts.

Effects of hypoestrogenism and/or hyperaldosteronism on myocardial remodeling in female mice

We investigated the potential adverse effects of hyperaldosteronism and/or hypoestrogenism on cardiac phenotype, and examined their combined effects in female mice overexpressing cardiac aldosterone synthase (AS). We focused on some signaling cascades challenging defensive responses to adapt and/or to survive in the face of double deleterious stresses, such as Ca2+ -homeostasis, pro/anti-hypertrophic, endoplasmic reticulum stress (ER stress), pro- or anti-apoptotic effectors, and MAP kinase activation, and redox signaling. These protein expressions were assessed by immunoblotting at 9 weeks after surgery. Female wild type (FWT) and FAS mice were fed with phytoestrogen-free diet; underwent ovariectomy (Ovx) or sham-operation (Sham). Ovx increased gain weight and hypertrophy index. Transthoracic echocardiograghy was performed. Both Ovx-induced heart rate decrease and fractional shortening increase were associated with collagen type III shift. Cardiac estrogen receptor (ERα, ERβ) protein expression levels were downregulated in Ovx mice. Hypoestrogenism increased plasma aldosterone and MR protein expression in FAS mice. Both aldosterone and Ovx played as mirror effects on up and downstream signaling effectors of calcium/redox homeostasis, apoptosis, such as concomitant CaMKII activation and calcineurin down-regulation, MAP kinase inhibition (ERK1/2, p38 MAPK) and Akt activation. The ratio Bcl2/Bax is in favor to promote cell survivor. Finally, myocardium had dynamically orchestrated multiple signaling cascades to restore tolerance to hostile environment thereby contributing to a better maintenance of Ca2+ /redox homeostasis. Ovx-induced collagen type III isoform shift and its upregulation may be important for the biomechanical transduction of the heart and the recovery of cardiac function in FAS mice. OVX antagonized aldosterone signaling pathways.

Gene Therapy Strategies to Restore ER Proteostasis in Disease

Proteostasis alterations are proposed as a transversal hallmark of several pathological conditions, including metabolic disorders, mechanical injury, cardiac malfunction, neurodegeneration, and cancer. Strategies to improve proteostasis aim to reduce the accumulation of specific disease-related misfolded proteins or bolster the endogenous mechanisms to fold and degrade abnormal proteins. Endoplasmic reticulum (ER) stress is a common pathological signature of a variety of diseases, which engages the unfolded protein response (UPR) as a cellular reaction to mitigate ER stress. Pharmacological modulation of the UPR is challenging considering the physiological importance of the pathway in various organs. However, local targeting of ER stress responses in the affected tissue using gene therapy is emerging as a possible solution to overcome side effects. The delivery of ER chaperones or active UPR components using adeno-associated virus (AAV) has demonstrated outstanding beneficial effects in several disease models (e.g., neurodegenerative conditions, eye disorders, and metabolic diseases). Here, we discuss current efforts to design and optimize gene therapy strategies to improve ER proteostasis in different disease contexts.

Protein disulphide-isomerase A2 regulated intracellular tissue factor mobilisation in migrating human vascular smooth muscle cells

Protein-disulphide isomerase family (PDI) are an ER-stress protein that controls TF-procoagulant activity but its role in HVSMC migration and coronary artery disease remains to be elucidated. We aimed to investigate whether in human coronary smooth muscle cells (HVSMC) the ER-stress protein-disulphide isomerase family A member 2 (PDIA2) regulates tissue factor (TF) polarisation during migration and atherosclerotic remodeling. PDIA2 and TF were analysed by confocal microscopy, silenced by small interfering RNAs (siRNA) and their function analysed by transwell and migration assays in vitro and in vivo. PDIA2and TF co-localise in the front edge of motile HVSMC. Silencing PDIA2, as well as silencing TF, reduces migration. PDIA2 silenced cells show increased TF-rich microparticle shedding. In vivo cell-loaded plug implants in nude mice of PDIA2 silenced HVSMC together with microvascular endothelial cells showed a significant impairment in mature microvessel formation. PDIA2 and TF are found in remodelled atherosclerotic plaques but not in healthy coronaries. In conclusion, we demonstrate that TF is chaperoned by PDIA2 to the HVSMC membrane and to the cell migratory front. Absence of PDIA2 impairs TF intracellular trafficking to its membrane docking favoring its uncontrolled release in microparticles. TF-regulated HVSMC migration and microvessel formation is under the control of the ER-protein PDIA2.

Maternal nicotine exposure leads to decreased cardiac protein disulfide isomerase and impaired mitochondrial function in male rat offspring

Smoking throughout pregnancy can lead to complications during gestation, parturition and neonatal development. Thus, nicotine replacement therapies are a popular alternative thought to be safer than cigarettes. However, recent studies in rodents suggest that fetal and neonatal nicotine exposure alone results in cardiac dysfunction and high blood pressure. While it is well known that perinatal nicotine exposure causes increased congenital abnormalities, the mechanisms underlying longer-term deficits in cardiac function are not completely understood. Recently, our laboratory demonstrated that nicotine impairs placental protein disulfide isomerase (PDI) triggering an increase in endoplasmic reticulum stress, leading us to hypothesize that this may also occur in the heart. At 3 months of age, nicotine-exposed offspring had 45% decreased PDI levels in the absence of endoplasmic reticulum stress. Given the association of PDI and superoxide dismutase enzymes, we further observed that antioxidant superoxide dismutase-2 levels were reduced by 32% in these offspring concomitant with a 26-49% decrease in mitochondrial complex proteins (I, II, IV and V) and tissue inhibitor of metalloproteinase-4, a critical matrix metalloprotease for cardiac contractility and health. Collectively, this study suggests that perinatal nicotine exposure decreases PDI, which can promote oxidative damage and mitochondrial damage, associated with a premature decline in cardiac function.

GRP78 Interacting Partner Bag5 Responds to ER Stress and Protects Cardiomyocytes From ER Stress-Induced Apoptosis

Bag5 is a member of the BAG family of molecular chaperone regulators and is unusual in that it consists of five BAG domains, which function as modulators of chaperone activity. Bag family proteins play a key role in cellular as well as in cardiac function and their differential expression is reported in heart failure. In this study, we examined the importance of a Bag family member protein, Bag5, in cardiomyocytes during endoplasmic reticulum (ER) stress. We found that expression of Bag5 in cardiomyocytes is significantly increased with the induction of ER stress in a time dependent manner. We have taken gain-in and loss-of functional approaches to characterize Bag5 protein function in cardiomyocytes. Adenoviral mediated expression of Bag5 significantly decreased cell death as well as improved cellular viability in ER stress. Along with this, ER stress-induced CHOP protein expression is significantly decreased in cells that overexpress Bag5. Conversely, we found that siRNA-mediated knockdown of Bag5 caused cell death, increased cytotoxicity, and decreased cellular viability in cardiomyocytes. Mechanistically, we found that Bag5 protein expression is significantly increased in the ER during ER stress and that this in turn modulates GRP78 protein stability and reduces ER stress. This study suggests that Bag5 is an important regulator of ER function and so could be exploited as a tool to improve cardiomyocyte function under stress conditions. J. Cell. Biochem. 117: 1813-1821, 2016. © 2016 Wiley Periodicals, Inc.

Thioredoxin superfamily and its effects on cardiac physiology and pathology

A precise control of oxidation/reduction of protein thiols is essential for intact cardiac physiology. Irreversible oxidative modifications have been proposed to play a role in the pathogenesis of cardiovascular diseases. An imbalance of redox homeostasis with diminution of antioxidant capacities predisposes the heart to oxidant injury. There is growing interest in endoplasmic reticulum (ER) stress in the cardiovascular field, since perturbation of redox homeostasis in the ER is sufficient to cause ER stress. Because a number of human diseases are related to altered redox homeostasis and defects in protein folding, many research efforts have been devoted in recent years to understanding the structure and enzymatic properties of the thioredoxin superfamily. The thioredoxin superfamily has been well documented as thiol oxidoreductases to exert a role in various cell signaling pathways. The redox properties of the thioredoxin motif account for the different functions of several members of the thioredoxin superfamily. While thioredoxin and glutaredoxin primarily act as antioxidants by reducing protein disulfides and mixed disulfide, another member of the superfamily, protein disulfide isomerase (PDI), can act as an oxidant by forming intrachain disulfide bonds that contribute to proper protein folding. Increasing evidence suggests a pivotal role of PDI in the survival pathway that promotes cardiomyocyte survival and leads to more favorable cardiac remodeling. Thus, the thiol redox state is important for cellular redox signaling and survival pathway in the heart. This review summarizes the key features of major members of the thioredoxin superfamily directly involved in cardiac physiology and pathology.

Regulation of signal transduction by reactive oxygen species in the cardiovascular system

Oxidative stress has long been implicated in cardiovascular disease, but more recently, the role of reactive oxygen species (ROS) in normal physiological signaling has been elucidated. Signaling pathways modulated by ROS are complex and compartmentalized, and we are only beginning to identify the molecular modifications of specific targets. Here, we review the current literature on ROS signaling in the cardiovascular system, focusing on the role of ROS in normal physiology and how dysregulation of signaling circuits contributes to cardiovascular diseases, including atherosclerosis, ischemia-reperfusion injury, cardiomyopathy, and heart failure. In particular, we consider how ROS modulate signaling pathways related to phenotypic modulation, migration and adhesion, contractility, proliferation and hypertrophy, angiogenesis, endoplasmic reticulum stress, apoptosis, and senescence. Understanding the specific targets of ROS may guide the development of the next generation of ROS-modifying therapies to reduce morbidity and mortality associated with oxidative stress.

Cell surface protein disulfide isomerase regulates natriuretic peptide generation of cyclic guanosine monophosphate

Rationale

The family of natriuretic peptides (NPs), including atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP), and C-type natriuretic peptide (CNP), exert important and diverse actions for cardiovascular and renal homeostasis. The autocrine and paracrine functions of the NPs are primarily mediated through the cellular membrane bound guanylyl cyclase-linked receptors GC-A (NPR-A) and GC-B (NPR-B). As the ligands and receptors each contain disulfide bonds, a regulatory role for the cell surface protein disulfide isomerase (PDI) was investigated.

Objective

We utilized complementary in vitro and in vivo models to determine the potential role of PDI in regulating the ability of the NPs to generate its second messenger, cyclic guanosine monophosphate.

Methods and Results

Inhibition of PDI attenuated the ability of ANP, BNP and CNP to generate cGMP in human mesangial cells (HMCs), human umbilical vein endothelial cells (HUVECs), and human aortic smooth muscle cells (HASMCs), each of which were shown to express PDI. In LLC-PK1 cells, where PDI expression was undetectable by immunoblotting, PDI inhibition had a minimal effect on cGMP generation. Addition of PDI to cultured LLC-PK1 cells increased intracellular cGMP generation mediated by ANP. Inhibition of PDI in vivo attenuated NP-mediated generation of cGMP by ANP. Surface Plasmon Resonance demonstrated modest and differential binding of the natriuretic peptides with immobilized PDI in a cell free system. However, PDI was shown to co-localize on the surface of cells with GC-A and GC-B by co-immunoprecpitation and immunohistochemistry.

Conclusion

These data demonstrate for the first time that cell surface PDI expression and function regulate the capacity of natriuretic peptides to generate cGMP through interaction with their receptors.

Protein disulfide isomerase modification and inhibition contribute to ER stress and apoptosis induced by oxidized low density lipoproteins

AIMS

Protein disulfide isomerase (PDI) is an abundant endoplasmic reticulum (ER)-resident chaperone and oxidoreductase that catalyzes formation and rearrangement (isomerization) of disulfide bonds, thereby participating in protein folding. PDI modification by nitrosative stress is known to increase protein misfolding, ER stress, and neuronal apoptosis. As LDL oxidation and ER stress may play a role in atherogenesis, this work was designed to investigate whether PDI was inactivated by oxLDLs, thereby participating in oxLDL-induced ER stress and apoptosis.

RESULTS

Preincubation of human endothelial HMEC-1 and of macrophagic U937 cells with toxic concentration of oxLDLs induced PDI inhibition and modification, as assessed by 4-HNE-PDI adducts formation. PDI inhibition by bacitracin potentiated ER stress (increased mRNA expression of CHOP and sXBP1) and apoptosis induced by oxLDLs. In contrast, increased PDI activity by overexpression of an active wild-type PDI was associated with reduced oxLDL-induced ER stress and toxicity, whereas the overexpression of a mutant inactive form was not protective. These effects on PDI were mimicked by exogenous 4-HNE and prevented by the carbonyl-scavengers N-acetylcysteine and pyridoxamine, which reduced CHOP expression and toxicity by oxLDLs. Interestingly, 4-HNE-modified PDI was detected in the lipid-rich areas of human advanced atherosclerotic lesions. Innovation and

CONCLUSIONS

PDI modification by oxLDLs or by reactive carbonyls inhibits its enzymatic activity and potentiates both ER stress and apoptosis by oxLDLs. PDI modification by lipid peroxidation products in atherosclerotic lesions suggests that a loss of function of PDI may occur in vivo, and may contribute to local ER stress, apoptosis, and plaque progression.

SOD1 aggregation in astrocytes following ischemia/reperfusion injury: a role of NO-mediated S-nitrosylation of protein disulfide isomerase (PDI)

Background

Ubiquitinated-protein aggregates are implicated in cerebral ischemia/reperfusion injury. The very presence of these ubiquitinated-protein aggregates is abnormal and seems to be disease-related. However, it is not clear what leads to aggregate formation and whether the aggregations represent a reaction to aggregate-mediated neurodegeneration.

Methods

To study the nitrosative stress-induced protein aggregation in cerebral ischemia/reperfusion injury, we used primary astrocyte cultures as a cell model, and systematically examined their iNOS expression and consequent NO generation following oxygen glucose deprivation and reperfusion. The expression of protein disulfide isomerase (PDI) and copper-zinc superoxide dismutase (SOD1) were also examined, and the biochemical interaction between PDI and SOD1 was determined by immunoprecipitation. In addition, the levels of S-nitrosylated PDI in cultured astrocytes after oxygen glucose deprivation and reperfusion treatment were measured using the biotin-switch assay. The formation of ubiquitinated-protein aggregates was detected by immunoblot and immunofluorescence staining.

Results

Our data showed that the up-regulation of iNOS expression after oxygen glucose deprivation and reperfusion treatment led to excessive NO generation. Up-regulation of PDI and SOD1 was also identified in cultured astrocytes following oxygen glucose deprivation and reperfusion, and these two proteins were found to bind to each other. Furthermore, the increased nitrosative stress due to ischemia/reperfusion injury was highly associated with NO-induced S-nitrosylation of PDI, and this S-nitrosylation of PDI was correlated with the formation of ubiquitinated-protein aggregates; the levels of S-nitrosylated PDI increased in parallel with the formation of aggregates. When NO generation was pharmacologically inhibited by iNOS specific inhibitor 1400W, S-nitrosylation of PDI was significantly blocked. In addition, the formation of ubiquitinated-protein aggregates in cultured astrocytes following oxygen glucose deprivation and reperfusion was also suppressed by 1400W. Interestingly, these aggregates were colocalized with SOD1, which was found to co-immunoprecipitate with PDI.

Conclusions

NO-mediated S-nitrosylation of PDI may be involved in the formation of the SOD1-linked ubiquitinated-protein aggregates in cerebral ischemia/reperfusion injury.

Coping with endoplasmic reticulum stress in the cardiovascular system

The endoplasmic reticulum (ER) is a multifunctional intracellular organelle, a component of the cellular reticular network that allows cells to adjust to a wide variety of conditions. The cardiomyocyte reticular network is the ideal location of sensors for both intrinsic and extrinsic factors that disrupt energy and/or nutrient homeostasis and lead to ER stress, a disturbance in ER function. ER stress has been linked to both physiological and pathological states in the cardiovascular system; such states include myocardial infarction, oxygen starvation (hypoxia) and fuel starvation, ischemia, pressure overload, dilated cardiomyopathy, hypertrophy, and heart failure. The ER stress coping response (e.g., the unfolded protein response) is composed of discrete pathways that are controlled by a collection of common regulatory components that may function as a single entity involved in reacting to ER stress. These corrective strategies allow the cardiomyocyte reticular network to restore energy and/or nutrient homeostasis and to avoid cell death. Therefore, the identities of the ER stress corrective strategies are important targets for the development of therapeutic approaches for cardiovascular and other acquired disorders.

The endoplasmic reticulum in cardiovascular health and disease

The endoplasmic reticulum has an intricate network of pathways built to deal with the secretory and integral membrane protein synthesis demands of the cell, as well as adaptive responses set up for the endoplasmic reticulum to rely on when stressed. These pathways are both essential and complex, and because of these 2 factors, several situations can lead to a dysfunctional endoplasmic reticulum and result in a dysfunctional cell with the potential to contribute to the progression of disease. The endoplasmic reticulum has been implicated in several metabolic, neurodegenerative, inflammatory, autoimmune, and renal diseases and disorders, and in particular, cardiovascular diseases. The role of the endoplasmic reticulum in cardiovascular disease shows how the change in function of a particular microscopic organelle can lead to macroscopic changes in the form of disease.

Protein disulfide isomerases in neurodegeneration: from disease mechanisms to biomedical applications

Protein disulfide isomerases (PDIs) are a family of foldases and chaperones primarily located at the endoplasmic reticulum that catalyze the formation and isomerization of disulfide bonds thereby facilitating protein folding. PDIs also perform important physiological functions in protein quality control, cell death, and cell signaling. Protein misfolding is involved in the etiology of the most common neurodegenerative diseases, including Alzheimer, Parkinson, amyotrophic lateral sclerosis, Prion-related disorders, among others. Accumulating evidence indicate altered expression of PDIs as a prominent and common feature of these neurodegenerative conditions. Here we overview most recent advances in our understanding of the possible functional contribution of PDIs to neurodegeneration, depicting a complex and poorly understood scenario. Possible therapeutic benefits of targeting PDIs in a disease context and their use as biomarkers are discussed.

Proteomic studies on protective effects of salvianolic acids, notoginsengnosides and combination of salvianolic acids and notoginsengnosides against cardiac ischemic-reperfusion injury

ETHNOPHARMACOLOGICAL RELEVANCE

Salvia miltiorrhiza and Panax notoginseng are popularly used traditional Chinese medicine for cardiovascular disorders and they are often used in the form of combination. However, mechanisms of their cardioprotective effects were still not clear. In the present study, the protective effects of salvianolic acids (SA), notoginsengnosides (NG) and combination of SA and NG (CSN) against rat cardiac ischemia-reperfusion injury were checked and the protein expression profiles of heart tissues were examined to search their possible protein targets.

MATERIALS AND METHODS

The cardioprotective effects of SA, NG and CSN were checked in a rat model of ischemia-reperfusion (IR) by temporarily occluding coronary artery for 20 min followed by reperfusion. Rats were grouped into sham-operation group, IR group, IR+SA group, IR+NG group and IR+CSN group. The plasma creatine kinase (CK) activities were measured using commercial kit and the percentages of infarcted area in total ventricle tissue were calculated after nitroblue-tetrazolium (N-BT) staining of heart tissue slices. Two-dimensional protein electrophoresis (2-DE) was used to check the protein expression profiles of heart tissues. Then, proteins differentially expressed between IR group and sham-operation group were identified using matrix assisted laser desorption ionization-time of flight-mass spectrometry/mass spectrometry (MALDI-TOF MS/MS). The regulative effects of SA, NG and CSN on these IR-related proteins were analyzed.

RESULTS

Treatments including SA, NG and CSN all showed cardioprotective effects against ischemia-reperfusion injury and CSN exhibited to be the best. Eighteen proteins involved in IR injury were found. These proteins are involved in pathways including energy metabolism, lipid metabolism, muscle contraction, heat shock stress, cell survival and proliferation. The regulation of these proteins by SA, NG or CSN suggested possible protein targets in their cardioprotective effects.

CONCLUSIONS

SA and NG showed both similarity and difference in their protein targets involved in cardioprotective effects. The capability of CSN to regulate both protein targets of SA and NG might be the basis of CSN to show cardioprotective effects better than that of SA or NG.

Protein disulfide isomerase-associated 6 is an ATF6-inducible ER stress response protein that protects cardiac myocytes from ischemia/reperfusion-mediated cell death

Proper folding of secreted and transmembrane proteins made in the rough endoplasmic reticulum (ER) requires oxygen for disulfide bond formation. Accordingly, ischemia can impair ER protein folding and initiate the ER stress response, which we previously showed is activated in the ischemic heart and in culture cardiac myocytes subjected to simulated ischemia. ER stress and ischemia activate the transcription factor, activating transcription factor 6 (ATF6), which induces numerous genes, many of which have not been identified, or examined in the heart. Using an ATF6 transgenic mouse model, we previously showed that ATF6 protected the heart from ischemic damage; however, the mechanism of this protection remains to be determined. In this study, we showed that, in the mouse heart, and in cultured cardiac myocytes, ATF6 induced the protein disulfide isomerase associated 6 (PDIA6) gene, which encodes an ER enzyme that catalyzes protein disulfide bond formation. Moreover, in cultured cardiac myocytes, ER stress-mediated PDIA6 promoter activation was ATF6-dependent, and required an ER stress response element (ERSE) and a nearby CCAAT box element. Electromobility shift assays and chromatin immunoprecipitation showed that ATF6 bound to the ERSE in the PDIA6 promoter, in vitro, and in the mouse heart, in vivo. Gain- and loss-of-function studies showed that PDIA6 protected cardiac myocytes against simulated ischemia/reperfusion-induced death in a manner that was dependent on the catalytic activity of PDIA6. Thus, by facilitating disulfide bond formation, and enhanced ER protein folding, PDIA6 may contribute to the protective effects of ATF6 in the ischemic mouse heart.

Serendipitous discovery of a novel protein signaling mechanism in heart failure

A number of protein signaling mechanisms are known to be involved in the progression of heart failure, yet the mechanism(s) by which the heart fails remains poorly understood. Therefore, we undertook a global approach to this question and used an antibody microarray to identify proteins differentially expressed in dysfunctional right ventricles in a bovine model of heart failure and the results were validated using cardiac tissue from both bovine and human heart failure. We found that protein disulfide isomerase 3, PDIA3, a protein that resides in the lumen of the endoplasmic reticulum, is significantly upregulated in both animal and human models of right and left heart failure. Altered expression of this protein has not previously been described in models of heart failure. In our initial microarray analysis, we found that CSK (c-Src kinase) was among the proteins upregulated in failing bovine ventricle. To further elucidate the role of CSK in heart failure, we studied the expression of its downstream target, Src, and found that Src expression and phosphorylation were markedly upregulated in failing ventricles. However, we also noted a smaller immunologically reactive protein that was only seen in experimental animals. In order to positively identify the smaller, Src-reactive protein, we used 2-dimensional gel electrophoresis and mass spectrophotometry. Surprisingly, we identified this protein as PDIA3, a protein that did not belong to the Src family of proteins. Upon sequence examination we found that PDIA3 contains a short C-terminal sequence with strong homology to Src and that it was this short sequence to which the antibody was generated. PDIA3 participates in MHC class I presentation and is implicated in the progression of valvular dysfunction in rheumatic heart disease, as well as calcium modulation in the sarcoplasmic reticulum. The molecule resides in the lumen of the endoplasmic reticulum and participates in disulfide bond formation during protein folding by interacting with calnexin and calreticulin. This interaction may indirectly effect SERCA (sarco/endoplasmic reticulum Ca(2+)-transport ATPase) activity and by extension contribute to the calcium dysregulation that characterizes progressive heart failure. Further studies are needed to elucidate the role that PDIA3 may play in the progression of heart failure.

Inflammation, endoplasmic reticulum stress, autophagy, and the monocyte chemoattractant protein-1/CCR2 pathway

Numerous inflammatory cytokines have been implicated in the pathogenesis of cardiovascular diseases. Monocyte chemoattractant protein (MCP)-1/CCL2 is expressed by mainly inflammatory cells and stromal cells such as endothelial cells, and its expression is upregulated after proinflammatory stimuli and tissue injury. MCP-1 can function as a traditional chemotactic cytokine and also regulates gene transcription. The recently discovered novel zinc-finger protein, called MCPIP (MCP-1-induced protein), initiates a series of signaling events that causes oxidative and endoplasmic reticulum (ER) stress, leading to autophagy that can result in cell death or differentiation, depending on the cellular context. After a brief review of the basic processes involved in inflammation, ER stress, and autophagy, the recently elucidated role of MCP-1 and MCPIP in inflammatory diseases is reviewed. MCPIP was found to be able to control inflammatory response by inhibition of nuclear factor-κB activation through its deubiquitinase activity or by degradation of mRNA encoding a set of inflammatory cytokines through its RNase activity. The potential inclusion of such a novel deubiquitinase in the emerging anti-inflammatory strategies for the treatment of inflammation-related diseases such as cardiovascular diseases and type 2 diabetes is briefly discussed.

Ablation of junctin or triadin is associated with increased cardiac injury following ischaemia/reperfusion

AIMS

Junctin and triadin are calsequestrin-binding proteins that regulate sarcoplasmic reticulum (SR) Ca(2+) release by interacting with the ryanodine receptor. The levels of these proteins are significantly down-regulated in failing human hearts. However, the significance of such decreases is currently unknown. Here, we addressed the functional role of these accessory proteins in the heart's responses to ischaemia/reperfusion (I/R) injury.

METHODS AND RESULTS

Isolated mouse hearts were subjected to global I/R, and contractile parameters were assessed in wild-type (WT), junctin-knockout (JKO), and triadin-knockout (TKO) hearts. Both JKO and TKO were associated with significantly depressed post-I/R contractile recovery. However, ablation of triadin resulted in the most severe post-I/R phenotype. The additional contractile impairment of TKO hearts was not related to a mitochondrial death pathway, but attributed to endoplasmic reticulum (ER) stress-mediated apoptosis. Activation of the X-box-binding protein-1 and transcriptional up-regulation of C/EBP-homologous protein (CHOP) provided a molecular mechanism of caspase-12-dependent apoptosis in myocytes. In addition, elevation of cytosolic Ca(2+) during reperfusion was associated with the activation of calpain proteases and troponin I breakdown. Accordingly, treatment with the calpain inhibitor MDL-28170 significantly ameliorated post-I/R impairment of contractile recovery in intact hearts.

CONCLUSION

These findings indicate that deficiency of either junctin or triadin impairs the contractile recovery in post-ischaemic hearts, which appears to be primarily attributed to increased ER stress and activation of calpain.

Endoplasmic reticulum stress-related inflammation and cardiovascular diseases

The endoplasmic reticulum (ER) is the site of synthesis and maturation of proteins designed for secretion or for localization on the cell membrane. Various types of stress from both inside and outside cells disturb ER function, thus causing unfolded or misfolded proteins to accumulate in the ER. To improve and maintain the ER functions against such stresses, the ER stress response pathway is activated. However, when the stress is prolonged or severe, apoptosis pathways are activated to remove damaged cells. It was recently reported that the ER stress pathway is also involved in the inflammatory response, whereby inflammation induces ER stress, and ER stress induces an inflammatory response. Therefore, the ER stress response pathway is involved in various diseases, including cardiovascular diseases such as atherosclerosis and ischemic diseases, in various ways. The ER stress pathway may represent a novel target for the treatment of these diseases.

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.