Calnexin Silencing in Mouse Neonatal Cardiomyocytes Induces Ca2+Cycling Defects, ER Stress, and Apoptosis

Crosstalk between endoplasmic reticulum stress and non-coding RNAs in cardiovascular diseases

Cells are exposed to various pathological stimulus within the cardiovascular system that challenge cells to adapt and survive. Several of these pathological stimulus alter the normal function of the endoplasmic reticulum (ER), leading to the accumulation of unfolded and misfolded proteins, thus triggering the unfolded protein response (UPR) to cope with the stress or trigger apoptosis of damaged cells. Downstream components of the UPR regulate transcription and translation reprogramming to ensure selective gene expression in response to pathological stimulus, including the expression of non-coding RNAs (ncRNAs). The ncRNAs play crucial roles in regulating transcription and translation, and their aberrant expression is associated with the development of cardiovascular disease (CVD). Notably, ncRNAs and ER stress can modulate each other and synergistically affect the development of CVD. Therefore, studying the interaction between ER stress and ncRNAs is necessary for effective prevention and treatment of CVD. In this review, we discuss the UPR signaling pathway and ncRNAs followed by the interplay regulation of ER stress and ncRNAs in CVD, which provides further insights into the understanding of the pathogenesis of CVD and therapeutic strategies. This article is categorized under: RNA in Disease and Development > RNA in Disease.

Incretin Mimetics Restore the ER-Mitochondrial Axis and Switch Cell Fate Towards Survival in LUHMES Dopaminergic-Like Neurons: Implications for Novel Therapeutic Strategies in Parkinson's Disease

BACKGROUND

Parkinson's disease (PD) is a progressive neurodegenerative movement disorder that afflicts more than 10 million people worldwide. Available therapeutic interventions do not stop disease progression. The etiopathogenesis of PD includes unbalanced calcium dynamics and chronic dysfunction of the axis of the endoplasmic reticulum (ER) and mitochondria that all can gradually favor protein aggregation and dopaminergic degeneration.

OBJECTIVE

In Lund Human Mesencephalic (LUHMES) dopaminergic-like neurons, we tested novel incretin mimetics under conditions of persistent, calcium-dependent ER stress.

METHODS

We assessed the pharmacological effects of Liraglutide-a glucagon-like peptide-1 (GLP-1) analog-and the dual incretin GLP-1/GIP agonist DA3-CH in the unfolded protein response (UPR), cell bioenergetics, mitochondrial biogenesis, macroautophagy, and intracellular signaling for cell fate in terminally differentiated LUHMES cells. Cells were co-stressed with the sarcoplasmic reticulum calcium ATPase (SERCA) inhibitor, thapsigargin.

RESULTS

We report that Liraglutide and DA3-CH analogs rescue the arrested oxidative phosphorylation and glycolysis. They mitigate the suppressed mitochondrial biogenesis and hyper-polarization of the mitochondrial membrane, all to re-establish normalcy of mitochondrial function under conditions of chronic ER stress. These effects correlate with a resolution of the UPR and the deficiency of components for autophagosome formation to ultimately halt the excessive synaptic and neuronal death. Notably, the dual incretin displayed a superior anti-apoptotic effect, when compared to Liraglutide.

CONCLUSIONS

The results confirm the protective effects of incretin signaling in ER and mitochondrial stress for neuronal degeneration management and further explain the incretin-derived effects observed in PD patients.

ER stress and calcium-dependent arrhythmias

The sarcoplasmic reticulum (SR) plays the key role in cardiac function as the major source of Ca²⁺ that activates cardiomyocyte contractile machinery. Disturbances in finely-tuned SR Ca²⁺ release by SR Ca²⁺ channel ryanodine receptor (RyR2) and SR Ca²⁺ reuptake by SR Ca²⁺-ATPase (SERCa2a) not only impair contraction, but also contribute to cardiac arrhythmia trigger and reentry. Besides being the main Ca²⁺ storage organelle, SR in cardiomyocytes performs all the functions of endoplasmic reticulum (ER) in other cell types including protein synthesis, folding and degradation. In recent years ER stress has become recognized as an important contributing factor in many cardiac pathologies, including deadly ventricular arrhythmias. This brief review will therefore focus on ER stress mechanisms in the heart and how these changes can lead to pro-arrhythmic defects in SR Ca²⁺ handling machinery.

Balancing energy and protein homeostasis at ER-mitochondria contact sites

The endoplasmic reticulum (ER) is the largest organelle of the cell and participates in multiple essential functions, including the production of secretory proteins, lipid synthesis, and calcium storage. Sustaining proteostasis requires an intimate coupling with energy production. Mitochondrial respiration evolved to be functionally connected to ER physiology through a physical interface between both organelles known as mitochondria-associated membranes. This quasi-synaptic structure acts as a signaling hub that tunes the function of both organelles in a bidirectional manner and controls proteostasis, cell death pathways, and mitochondrial bioenergetics. Here, we discuss the main signaling mechanisms governing interorganellar communication and their putative role in diseases including cancer and neurodegeneration.

Protein palmitoylation-mediated palmitic acid sensing causes blood-testis barrier damage via inducing ER stress

Blood-testis barrier (BTB) damage promotes spermatogenesis dysfunction, which is a critical cause of male infertility. Dyslipidemia has been correlated with male infertility, but the major hazardous lipid and the underlying mechanism remains unclear. In this study, we firstly discovered an elevation of palmitic acid (PA) and a decrease of inhibin B in patients with severe dyszoospermia, which leaded us to explore the effects of PA on Sertoli cells. We observed a damage of BTB by PA. PA penetration to endoplasmic reticulum (ER) and its damage to ER structures were exhibited by microimaging and dynamic observation, and consequent ER stress was proved to mediate PA-induced Sertoli cell barrier disruption. Remarkably, we demonstrated a critical role of aberrant protein palmitoylation in PA-induced Sertoli cell barrier dysfunction. An ER protein, Calnexin, was screened out and was demonstrated to participate in this process, and suppression of its palmitoylation showed an ameliorating effect. We also found that ω-3 poly-unsaturated fatty acids down-regulated Calnexin palmitoylation, and alleviated BTB dysfunction. Our results indicate that dysregulated palmitoylation induced by PA plays a pivotal role in BTB disruption and subsequent spermatogenesis dysfunction, suggesting that protein palmitoylation might be therapeutically targetable in male infertility.

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An elevation of circulating PA was identified in patients with severe dyszoospermia.

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PA-induced over-palmitoylation in Sertoli cells leads to ER stress and BTB damage.

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The palmitoylation of the ER protein Calnexin regulates Sertoli cell barrier function.

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ω-3 PUFAs ameliorate PA-induced damage and over-palmitoylation in Sertoli cells.

DNA methylation analyses identify an intronic ZDHHC6 locus associated with time to recurrent stroke in the Vitamin Intervention for Stroke Prevention (VISP) clinical trial

Aberrant DNA methylation profiles have been implicated in numerous cardiovascular diseases; however, few studies have investigated how these epigenetic modifications contribute to stroke recurrence. The aim of this study was to identify methylation loci associated with the time to recurrent cerebro- and cardiovascular events in individuals of European and African descent. DNA methylation profiles were generated for 180 individuals from the Vitamin Intervention for Stroke Prevention clinical trial using Illumina HumanMethylation 450K BeadChip microarrays, resulting in beta values for 470,871 autosomal CpG sites. Ethnicity-stratified survival analyses were performed using Cox Proportional Hazards regression models for associations between each methylation locus and the time to recurrent stroke or composite vascular event. Results were validated in the Vall d’Hebron University Hospital cohort from Barcelona, Spain. Network analyses of the methylation loci were generated using weighted gene coexpression network analysis. Primary analysis identified four significant loci, cg04059318, ch.2.81927627R, cg03584380, and cg24875416, associated with time to recurrent stroke. Secondary analysis identified three loci, cg00076998, cg16758041, and cg02365967, associated with time to composite vascular endpoint. Locus cg03584380, which is located in an intron of ZDHHC6, was replicated in the Vall d’Hebron University Hospital cohort. The results from this study implicate the degree of methylation at cg03584380 is associated with the time of recurrence for stroke or composite vascular events across two ethnically diverse groups. Furthermore, modules of loci were associated with clinical traits and blood biomarkers including previous number of strokes, prothrombin fragments 1 + 2, thrombomodulin, thrombin-antithrombin complex, triglyceride levels, and tissue plasminogen activator. Ultimately, these loci could serve as potential epigenetic biomarkers that could identify at-risk individuals in recurrence-prone populations.

Seipin Deficiency Accelerates Heart Failure Due to Calcium Handling Abnormalities and Endoplasmic Reticulum Stress in Mice

Seipin deficiency can induce hypertrophic cardiomyopathy and heart failure, which often leads to death in humans. To explore the effects and the possible mechanisms of Seipin deficiency in myocardial remodeling, Seipin knockout (SKO) mice underwent transverse aortic constriction (TAC) for 12 weeks. We found a more severe left ventricular hypertrophy and diastolic heart failure and increases in inflammatory cell infiltration, collagen deposition, and apoptotic bodies in the SKO group compared to those in the wild type (WT) group after TAC. Electron microscopy also showed a more extensive sarcoplasmic reticulum expansion, deformation of microtubules, and formation of mitochondrial lesions in the cardiomyocytes of SKO mice than in those of WT mice after TAC. Compared with the WT group, the SKO group showed increases in endoplasmic reticulum (ER) stress-, inflammation-, and fibrosis-related gene expression, while calcium ion-related factors, such as Serca2a and Ryr, were decreased in the SKO group after TAC. Increased levels of the ER stress-related protein GRP78 and decreased SERCA2a and P-RYR protein levels were detected in the SKO group compared with the WT group after TAC. Slowing of transient Ca²⁺ current decay and an increased SR Ca²⁺ content in myocytes were detected in the cardiomyocytes of SKO mice. Adipose tissue transplantation could not rescue the cardiac hypertrophy after TAC in SKO mice. In conclusion, we found that Seipin deficiency could promote cardiac hypertrophy and diastolic heart failure after TAC in mice. These changes may be related to the impairment of myocardial calcium handling, ER stress, inflammation, and apoptosis.

Role of Hydrogen Sulfide and 3-Mercaptopyruvate Sulfurtransferase in the Regulation of the Endoplasmic Reticulum Stress Response in Hepatocytes

It is estimated that over 1.5 billion people suffer from various forms of chronic liver disease worldwide. The emerging prevalence of metabolic syndromes and alcohol misuse, along with the lack of disease-modifying agents for the therapy of many severe liver conditions predicts that chronic liver disease will continue to be a major problem in the future. Better understanding of the underlying pathogenetic mechanisms and identification of potential therapeutic targets remains a priority. Herein, we explored the potential role of the 3-mercaptopyruvate sulfurtransferase/hydrogen sulfide (H₂S) system in the regulation of the endoplasmic reticulum (ER) stress and of its downstream processes in the immortalized hepatic cell line HepG2 in vitro. ER stress suppressed endogenous H₂S levels and pharmacological supplementation of H₂S with sodium hydrogen sulfide (NaHS) mitigated many aspects of ER stress, culminating in improved cellular bioenergetics and prevention of autophagic arrest, thereby switching cells’ fate towards survival. Genetic silencing of 3-MST or pharmacological inhibition of the key enzymes involved in hepatocyte H₂S biosynthesis exacerbated many readouts related to ER-stress or its downstream functional responses. Our findings implicate the 3-MST/H₂S system in the intracellular network that governs proteostasis and ER-stress adaptability in hepatocytes and reinforce the therapeutic potential of pharmacological H₂S supplementation.

Phosphoproteomic analysis identifies phospho-Threonine-17 site of phospholamban important in low molecular weight isoform of fibroblast growth factor 2-induced protection against post-ischemic cardiac dysfunction

RATIONALE

Among its many biological roles, fibroblast growth factor 2 (FGF2) protects the heart from dysfunction and damage associated with an ischemic attack. Our laboratory demonstrated that its protection against myocardial dysfunction occurs by the low molecular weight (LMW) isoform of FGF2, while the high molecular weight (HMW) isoforms are associated with a worsening in post-ischemic recovery of cardiac function. LMW FGF2-mediated cardioprotection is facilitated by activation of multiple kinases, including PKCalpha, PKCepsilon, and ERK, and inhibition of p38 and JNK.

OBJECTIVE

Yet, the substrates of those kinases associated with LMW FGF2-induced cardioprotection against myocardial dysfunction remain to be elucidated.

METHODS AND RESULTS

To identify substrates in LMW FGF2 improvement of post-ischemic cardiac function, mouse hearts expressing only LMW FGF2 were subjected to ischemia-reperfusion (I/R) injury and analyzed by a mass spectrometry (MS)-based quantitative phosphoproteomic strategy. MS analysis identified 50 phosphorylation sites from 7 sarcoendoplasmic reticulum (SR) proteins that were significantly altered in I/R-treated hearts only expressing LMW FGF2 compared to those hearts lacking FGF2. One of those phosphorylated SR proteins identified was phospholamban (PLB), which exhibited rapid, increased phosphorylation at Threonine-17 (Thr17) after I/R in hearts expressing only LMW FGF2; this was further validated using Selected Reaction Monitoring-based MS workflow. To demonstrate a mechanistic role of phospho-Thr17 PLB in LMW FGF2-mediated cardioprotection, hearts only expressing LMW FGF2 and those expressing only LMW FGF2 with a mutant PLB lacking phosphorylatable Thr17 (Thr17Ala PLB) were subjected to I/R. Hearts only expressing LMW FGF2 showed significantly improved recovery of cardiac function following I/R (p < 0.05), and this functional improvement was significantly abrogated in hearts expressing LMW FGF2 and Thr17Ala PLB (p < 0.05).

CONCLUSION

The findings indicate that LMW FGF2 modulates intracellular calcium handling/cycling via regulatory changes in SR proteins essential for recovery from I/R injury, and thereby protects the heart from post-ischemic cardiac dysfunction.

An activating transcription factor 6 beta (ATF6β) regulates apoptosis of hemocyte during immune response in Crassostrea gigas

The homeostasis of immune cells during immune response is vital for hosts to defend against invaders. Activating transcription factor 6 (ATF6) is an important transcription factor in the unfolded protein response (UPR) to maintaining cellular homeostasis. In the present study, one ATF6 homologue was identified from Pacific oyster Crassostrea gigas (designated as CgATF6β). The full length cDNA of CgATF6β was of 2645 bp with a 1596 bp open reading frame (ORF) encoding a polypeptide of 531 amino acids. The deduced amino acid sequence of CgATF6β was predicted to contain a transmembrane region, a conserved basic leucine zipper (bZIP) domain, a site 1 protease cleavage site, a site 2 protease cleavage site, and a Golgi localization signal. CgATF6β mRNA was constitutively expressed in hemocytes, gill, mantle, gonad, hepatopancreas and labial palp, with a slightly higher expression level in muscle (2.45-fold of that in gill, p < 0.05). After oysters were challenged with Vibrio splendidus, the mRNA expression levels of CgATF6β in hemocytes were significantly up-regulated at 3 h (2.68-fold of that in seawater group, p < 0.01) and peaked at 12 h (3.14-fold of that in seawater group, p < 0.01). The endogenic CgATF6β protein was mainly located in the cytoplasm of oyster hemocytes, and it was significantly transported into the nuclei of hemocytes at 1.5 h after the challenge with V. splendidus. After an injection with CgATF6β dsRNA, the mRNA expression of CgATF6β was knocked down to 0.26-fold of that in dsGFP group (p < 0.01). In CgATF6β dsRNA-injected oysters, the mRNA expressions of glucose-regulated protein 78 (GRP78), calnexin (CNX) and anti-apoptotic B-cell lymphoma-2 (Bcl-2) in hemocytes were significantly decreased at 12 h after V. splendidus challenge, which were 0.65-fold (p < 0.01), 0.54-fold (p < 0.01) and 0.17-fold (p < 0.01) of that in dsGFP-injected oysters, while the apoptotic rate of hemocytes was significantly up-regulated (1.97-fold of that in dsGFP group, p < 0.05). Collectively, these results suggested that CgATF6β was involved in apoptosis inhibition of oyster hemocytes upon V. splendidus challenge by regulating the expression of CgGRP78, CgCNX and CgBcl-2.

Progerin in muscle leads to thermogenic and metabolic defects via impaired calcium homeostasis

Mutations in lamin A (LMNA) are responsible for a variety of human dystrophic and metabolic diseases. Here, we created a mouse model in which progerin, the lamin A mutant protein that causes Hutchinson–Gilford progeria syndrome (HGPS), can be inducibly overexpressed. Muscle‐specific overexpression of progerin was sufficient to induce muscular dystrophy and alter whole‐body energy expenditure, leading to premature death. Intriguingly, sarcolipin (Sln), an endoplasmic reticulum (ER)‐associated protein involved in heat production, is upregulated in progerin‐expressing and Lmna knockout (Lmna^−/−) skeletal muscle. The depletion of Sln accelerated the early death of Lmna^−/− mice. An examination at the molecular level revealed that progerin recruits Sln and Calnexin to the nuclear periphery. Furthermore, progerin‐expressing myoblasts presented enhanced store‐operated Ca²⁺ entry, as well as increased co‐localization of STIM1 and ORAI1. These findings suggest that progerin dysregulates calcium homeostasis through an interaction with a subset of ER‐associated proteins, resulting in thermogenic and metabolic abnormalities.

Unraveling oxidative stress response in the cestode parasite Echinococcus granulosus

Cystic hydatid disease (CHD) is a worldwide neglected zoonotic disease caused by Echinococcus granulosus. The parasite is well adapted to its host by producing protective molecules that modulate host immune response. An unexplored issue associated with the parasite's persistence in its host is how the organism can survive the oxidative stress resulting from parasite endogenous metabolism and host defenses. Here, we used hydrogen peroxide (H₂O₂) to induce oxidative stress in E. granulosus protoescoleces (PSCs) to identify molecular pathways and antioxidant responses during H₂O₂ exposure. Using proteomics, we identified 550 unique proteins; including 474 in H₂O₂-exposed PSCs (H-PSCs) samples and 515 in non-exposed PSCs (C-PSCs) samples. Larger amounts of antioxidant proteins, including GSTs and novel carbonyl detoxifying enzymes, such as aldo-keto reductase and carbonyl reductase, were detected after H₂O₂ exposure. Increased concentrations of caspase-3 and cathepsin-D proteases and components of the 26S proteasome were also detected in H-PSCs. Reduction of lamin-B and other caspase-substrate, such as filamin, in H-PSCs suggested that molecular events related to early apoptosis were also induced. We present data that describe proteins expressed in response to oxidative stress in a metazoan parasite, including novel antioxidant enzymes and targets with potential application to treatment and prevention of CHD.

N-acetyl-seryl-aspartyl-lysyl-proline treatment protects heart against excessive myocardial injury and heart failure in mice

Myocardial infarction (MI) in mice results in cardiac rupture at 4-7 days after MI, whereas cardiac fibrosis and dysfunction occur later. N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) has anti-inflammatory, anti-fibrotic, and pro-angiogenic properties. We hypothesized that Ac-SDKP reduces cardiac rupture and adverse cardiac remodeling, and improves function by promoting angiogenesis and inhibiting detrimental reactive fibrosis and inflammation after MI. C57BL/6J mice were subjected to MI and treated with Ac-SDKP (1.6 mg/kg per day) for 1 or 5 weeks. We analyzed (1) intercellular adhesion molecule-1 (ICAM-1) expression; (2) inflammatory cell infiltration and angiogenesis; (3) gelatinolytic activity; (4) incidence of cardiac rupture; (5) p53, the endoplasmic reticulum stress marker CCAAT/enhancer binding protein homology protein (CHOP), and cardiomyocyte apoptosis; (6) sarcoplasmic reticulum Ca2+ ATPase (SERCA2) expression; (7) interstitial collagen fraction and capillary density; and (8) cardiac remodeling and function. Acutely, Ac-SDKP reduced cardiac rupture, decreased ICAM-1 expression and the number of infiltrating macrophages, decreased gelatinolytic activity, p53 expression, and myocyte apoptosis, but increased capillary density in the infarction border. Chronically, Ac-SDKP improved cardiac structures and function, reduced CHOP expression and interstitial collagen fraction, and preserved myocardium SERCA2 expression. Thus, Ac-SDKP decreased cardiac rupture, ameliorated adverse cardiac remodeling, and improved cardiac function after MI, likely through preserved SERCA2 expression and inhibition of endoplasmic reticulum stress.

Liraglutide restores chronic ER stress, autophagy impairments and apoptotic signalling in SH-SY5Y cells

Growing evidence suggests that agonists of glucagon-like peptide (GLP-1) receptor exert neuroprotective and neurorestorative effects across a range of experimental models of neuronal degeneration, and, recently, a pilot clinical trial of Liraglutide in Alzheimer’s disease patients showed improvements in cerebral glucose consumption that signifies disease progression. However, the exact underlying mechanism of action remains unclear. Chronic endoplasmic reticulum (ER) stress has recently emerged as a mechanism for neuronal injury, rendering it a potent therapeutic target for acute and chronic neurodegenerative disorders. Here, we investigate the neuroprotective effects of Liraglutide along with the signalling network against prolong ER stress and autophagy impairments induced by the non-competitive inhibitor of sarco/ER Ca²⁺-ATPase, thapsigargin. We show that Liraglutide modulates the ER stress response and elicits ER proteostasis and autophagy machinery homeostasis in human SH-SY5Y neuroblastoma cell line. These effects correlate with resolution of hyper-activity of the antioxidant Nrf2 factor and restoration of the impaired cell viability and proliferation. Mechanistically, Liraglutide engages Akt and signal transducer and activator of transcription 3 (STAT3) signalling to favour adaptive responses and shift cell fate from apoptosis to survival under chronic stress conditions in SH-SY5Y cells.

Calcium signaling at the endoplasmic reticulum: fine-tuning stress responses

Endoplasmic reticulum (ER) calcium signaling is implicated in a myriad of coordinated cellular processes. The ER calcium content is tightly regulated as it allows a favorable environment for protein folding, in addition to operate as a major reservoir for fast and specific release of calcium. Altered ER homeostasis impacts protein folding, activating the unfolded protein response (UPR) as a rescue mechanism to restore proteostasis. ER calcium release impacts mitochondrial metabolism and also fine-tunes the threshold to undergo apoptosis under chronic stress. The global coordination between UPR signaling and energetic demands takes place at mitochondrial associated membranes (MAMs), specialized subdomains mediating interorganelle communication. Here we discuss current models explaining the functional relationship between ER homeostasis and various cellular responses to coordinate proteostasis and metabolic maintenance.

SERCA control of cell death and survival

Intracellular calcium (Ca²⁺⁾ is a critical coordinator of various aspects of cellular physiology. It is increasingly apparent that changes in cellular Ca²⁺ dynamics contribute to the regulation of normal and pathological signal transduction that controls cell growth and survival. Aberrant perturbations in Ca²⁺ homeostasis have been implicated in a range of pathological conditions, such as cardiovascular diseases, diabetes, tumorigenesis and steatosis hepatitis. Intracellular Ca²⁺ concentrations are therefore tightly regulated by a number of Ca²⁺ handling enzymes, proteins, channels and transporters located in the plasma membrane and in Ca²⁺ storage organelles, which work in concert to fine tune a temporally and spatially precise Ca²⁺ signal. Chief amongst them is the sarco/endoplasmic reticulum (SR/ER) Ca²⁺ ATPase pump (SERCA) which actively re-accumulates released Ca²⁺ back into the SR/ER, therefore maintaining Ca²⁺ homeostasis. There are at least 14 different SERCA isoforms encoded by three ATP2A1-3 genes whose expressions are species- and tissue-specific. Altered SERCA expression and activity results in cellular malignancy and induction of ER stress and ER stress-associated apoptosis. The role of SERCA misregulation in the control of apoptosis in various cell types and disease setting with prospective therapeutic implications is the focus of this review. Ca²⁺ is a double edge sword for both life as well as death, and current experimental evidence supports a model in which Ca²⁺ homeostasis and SERCA activity represent a nodal point that controls cell survival. Pharmacological or genetic targeting of this axis constitutes an incredible therapeutic potential to treat different diseases sharing similar biological disorders.

Endoplasmic reticulum chaperones tweak the mitochondrial calcium rheostat to control metabolism and cell death

The folding of secretory proteins is a well-understood mechanism, based on decades of research on endoplasmic reticulum (ER) chaperones. These chaperones interact with newly imported polypeptides close to the ER translocon. Classic examples for these proteins include the immunoglobulin binding protein (BiP/GRP78), and the lectins calnexin and calreticulin. Although not considered chaperones per se, the ER oxidoreductases of the protein disulfide isomerase (PDI) family complete the folding job by catalyzing the formation of disulfide bonds through cysteine oxidation. Research from the past decade has demonstrated that ER chaperones are multifunctional proteins. The regulation of ER-mitochondria Ca²⁺ crosstalk is one of their additional functions, as shown for calnexin, BiP/GRP78 or the oxidoreductases Ero1α and TMX1. This function depends on interactions of this group of proteins with the ER Ca²⁺ handling machinery. This novel function makes perfect sense for two reasons: i. It allows ER chaperones to control mitochondrial apoptosis instantly without a lengthy bypass involving the upregulation of pro-apoptotic transcription factors via the unfolded protein response (UPR); and ii. It allows the ER protein folding machinery to fine-tune ATP import via controlling the speed of mitochondrial oxidative phosphorylation. Therefore, the role of ER chaperones in regulating ER-mitochondria Ca²⁺ flux identifies the progression of secretory protein folding as a central regulator of cell survival and death, at least in cell types that secrete large amount of proteins. In other cell types, ER protein folding might serve as a sentinel mechanism that monitors cellular well-being to control cell metabolism and apoptosis. The selenoprotein SEPN1 is a classic example for such a role. Through the control of ER-mitochondria Ca²⁺-flux, ER chaperones and folding assistants guide cellular apoptosis and mitochondrial metabolism.

Effects of gene polymorphisms in the endoplasmic reticulum stress pathway on clinical outcomes of chemoradiotherapy in Chinese patients with nasopharyngeal carcinoma

There is considerable inter-individual variabil¬ity in chemoradiotherapy responses in nasopharyngeal carcinoma (NPC) patients receiv¬ing the same or similar treatment protocols. In this study we evaluated the association between the gene polymorphisms in endoplasmic reticulum (ER) stress pathway and chemoradiation responses in Chinese NPC patients. A total of 150 patients with histopathologically conformed NPC and treated with concurrent chemoradiotherapy were enrolled. Genotypes in ER stress pathway genes, including VCP (valosin-containing protein) rs2074549, HSP90B1 rs17034943, CANX (calnexin) rs7566, HSPA5 [heat shock protein family A (Hsp70) member 5] rs430397, CALCR (calcitonin receptor) rs2528521, and XBP1 (X-box binding protein 1) rs2269577 were analyzed by Sequenom MassARRAY system. The short-term effects of primary tumor and lymph node after radiotherapy were assessed based on the Response Evaluation Criteria in Solid Tumors (RECIST) of WHO. And acute radiation-induced toxic reactions were evaluated according to the Radiation Therapy Oncology Group or European Organization for Research and Treatment of Cancer (RTOG/EORTC). The effects of gene polymorphisms on clinical outcomes of chemoradiotherapy were assessed by chi-square test, univariate and multivariate logistic regression analyses. We found that CT and CT+CC genotypes of CANX rs7566 was significantly correlated with primary tumor treatment efficacy at 3 months after chemoradiotherapy and with occurrence of radiation-induced myelosuppression in Chinese NPC patients. CT and CT+CC genotypes of CALCR rs2528521 were significantly correlated with cervical lymph node efficacy at 3 months after chemoradiotherapy. And CC and CT+CC genotypes of VCP rs2074549 were significantly associated with occurrence of myelosuppression. In conclusion, SNPs of VCP rs2074549, CANX rs7566 and CALCR rs2528521 in ER stress pathway genes may serve as predictors for clinical outcomes of chemoradiotherapy in Chinese NPC patients.

Cardiac Overexpression of S100A6 Attenuates Cardiomyocyte Apoptosis and Reduces Infarct Size After Myocardial Ischemia-Reperfusion

Background

Cardiomyocyte‐specific transgenic mice overexpressing S100A6, a member of the family of EF‐hand calcium‐binding proteins, develop less cardiac hypertrophy, interstitial fibrosis, and myocyte apoptosis after permanent coronary ligation, findings that support S100A6 as a potential therapeutic target after acute myocardial infarction. Our purpose was to investigate S100A6 gene therapy for acute myocardial ischemia‐reperfusion.

Methods and Results

We first performed in vitro studies to examine the effects of S100A6 overexpression and knockdown in rat neonatal cardiomyocytes. S100A6 overexpression improved calcium transients and protected against apoptosis induced by hypoxia‐reoxygenation via enhanced calcineurin activity, whereas knockdown of S100A6 had detrimental effects. For in vivo studies, human S100A6 plasmid or empty plasmid was delivered to the left ventricular myocardium by ultrasound‐targeted microbubble destruction in Fischer‐344 rats 2 days prior to a 30‐minute ligation of the left anterior descending coronary artery followed by reperfusion. Control animals received no therapy. Pretreatment with S100A6 gene therapy yielded a survival advantage compared to empty‐plasmid and nontreated controls. S100A6‐pretreated animals had reduced infarct size and improved left ventricular systolic function, with less myocyte apoptosis, attenuated cardiac hypertrophy, and less cardiac fibrosis.

Conclusions

S100A6 overexpression by ultrasound‐targeted microbubble destruction helps ameliorate myocardial ischemia‐reperfusion, resulting in lower mortality and improved left ventricular systolic function post–ischemia‐reperfusion via attenuation of apoptosis, reduction in cardiac hypertrophy, and reduced infarct size. Our results indicate that S100A6 is a potential therapeutic target for acute myocardial infarction.

Calbindin-D9k Ablation Disrupt Glucose/Pancreatic Insulin Homeostasis

It has been proposed that cellular Ca²⁺ signals activate hormone secretion. In pancreatic β cells, which produce insulin, Ca²⁺ signals have been known to contribute to insulin secretion. Prior to this study, we confirmed that insulin-secreting β cells express CaBP-9k, and assumed that CaBP-9k play a role in β cell insulin synthesis or secretion. Using CaBP-9k knock out (KO) mice, we demonstrated that ablation of CaBP-9k causes reducing insulin secretion and increasing serum glucose. To compare the role of CaBP-9k with pathophysiological conditions, we exposed wild-type and CaBP-9k KO mice to hypoxic conditions for 10 days. Hypoxia induced endoplasmic reticulum (ER) stress, increasing both insulin signaling and insulin resistance. By exposing hypoxia, CaBP-9k KO mice showed an increased level of ER stress marker protein relative to wild type mice. Without hypoxic conditions, CaBP-9K ablation regulates calcium channels and causes ER stress in a CaBP-9K specific manner. Ablation of CaBP-9k also showed decreased levels of sulfonylurea receptor1 (SUR1) and inward-rectifier potassium ion channel 6.2 (K_ir6.2), which are insulin secretion marker genes. Overall, the results of the present study demonstrated that CaBP-9k regulates synthesis of insulin and is part of the insulin-secreting calcium signaling.

Hepatic Macrosteatosis Is Partially Converted to Microsteatosis by Melatonin Supplementation in ob/ob Mice Non-Alcoholic Fatty Liver Disease

Background

Obesity is a common risk factor for non-alcoholic fatty liver disease (NAFLD). Currently, there are no specific treatments against NAFLD. Thus, examining any molecule with potential benefits against this condition emerged melatonin as a molecule that influences metabolic dysfunctions. The aim of this study was to determine whether melatonin would function against NAFDL, studying morphological, ultrastuctural and metabolic markers that characterize the liver of ob/ob mice.

Methods

Lean and ob/ob mice were supplemented with melatonin in the drinking water for 8 weeks. Histology and stereology were performed to assess hepatic steatosis and glycogen deposition. Ultrastructural features of mitochondria, endoplasmic reticulum (ER) and their juxtapositions were evaluated in livers of all experimental groups. Furthermore, hepatic distribution and expression of markers of ER and mitochondria (calnexin, ATP sintase β, GRP78 and CHOP) and metabolic dysfunction (RPB4, β-catenin) and cellular longevity (SIRT1) were analyzed.

Results

Melatonin significantly reduced glycemia, identified also by a decrease of hepatic RBP4 expression, reversed macrosteatosis in microsteatosis at the hepatic pericentral zone, enlarged ER-mitochondrial distance and ameliorated the morphology and organization of these organelles in ob/ob mouse liver. Furthermore, in ob/ob mice, calnexin and ATP synthase β were partially restored, GRP78 and CHOP decreased in periportal and midzonal hepatocytes and β-catenin expression was, in part, restored in peripheral membranes of hepatocytes. Melatonin supplementation to ob/ob mice improves hepatic morphological, ultrastructural and metabolic damage that occurs as a result of NAFLD.

Conclusions

Melatonin may be a potential adjuvant treatment to limit NAFLD and its progression into irreversible complications.

Weight loss-induced stress in subcutaneous adipose tissue is related to weight regain

Initial successful weight loss is often followed by weight regain after the dietary intervention. Compared with lean people, cellular stress in adipose tissue is increased in obese subjects. However, the relation between cellular stress and the risk for weight regain after weight loss is unclear. Therefore, we determined the expression levels of stress proteins during weight loss and weight maintenance in relation to weight regain. In vivo findings were compared with results from in vitro cultured human Simpson-Golabi-Behmel syndrome (SGBS) adipocytes. In total, eighteen healthy subjects underwent an 8-week diet programme with a 10-month follow-up. Participants were categorised as weight maintainers or weight regainers (WR) depending on their weight changes during the intervention. Abdominal subcutaneous adipose tissue biopsies were obtained before and after the diet and after the follow-up. In vitro differentiated SGBS adipocytes were starved for 96 h with low (0·55 mm) glucose. Levels of stress proteins were determined by Western blotting. WR showed increased expressions of β-actin, calnexin, heat shock protein (HSP) 27, HSP60 and HSP70. Changes of β-actin, HSP27 and HSP70 are linked to HSP60, a proposed key factor in weight regain after weight loss. SGBS adipocytes showed increased levels of β-actin and HSP60 after 96 h of glucose restriction. The increased level of cellular stress proteins in the adipose tissue of WR probably resides in the adipocytes as shown by in vitro experiments. Cellular stress accumulated in adipose tissue during weight loss may be a risk factor for weight regain.

Inhibition of Receptor Interacting Protein Kinases Attenuates Cardiomyocyte Hypertrophy Induced by Palmitic Acid

Palmitic acid (PA) is known to cause cardiomyocyte dysfunction. Cardiac hypertrophy is one of the important pathological features of PA-induced lipotoxicity, but the mechanism by which PA induces cardiomyocyte hypertrophy is still unclear. Therefore, our study was to test whether necroptosis, a receptor interacting protein kinase 1 and 3 (RIPK1 and RIPK3-) dependent programmed necrosis, was involved in the PA-induced cardiomyocyte hypertrophy. We used the PA-treated primary neonatal rat cardiac myocytes (NCMs) or H9c2 cells to study lipotoxicity. Our results demonstrated that cardiomyocyte hypertrophy was induced by PA treatment, determined by upregulation of hypertrophic marker genes and cell surface area enlargement. Upon PA treatment, the expression of RIPK1 and RIPK3 was increased. Pretreatment with the RIPK1 inhibitor necrostatin-1 (Nec-1), the PA-induced cardiomyocyte hypertrophy, was attenuated. Knockdown of RIPK1 or RIPK3 by siRNA suppressed the PA-induced myocardial hypertrophy. Moreover, a crosstalk between necroptosis and endoplasmic reticulum (ER) stress was observed in PA-treated cardiomyocytes. Inhibition of RIPK1 with Nec-1, phosphorylation level of AKT (Ser473), and mTOR (Ser2481) was significantly reduced in PA-treated cardiomyocytes. In conclusion, RIPKs-dependent necroptosis might be crucial in PA-induced myocardial hypertrophy. Activation of mTOR may mediate the effect of necroptosis in cardiomyocyte hypertrophy induced by PA.

The unfolded protein response in the therapeutic effect of hydroxy-DHA against Alzheimer's disease

The unfolded protein response (UPR) and autophagy are two cellular processes involved in the clearing of intracellular misfolded proteins. Both pathways are targets for molecules that may serve as treatments for several diseases, including neurodegenerative disorders like Alzheimer's disease (AD). In the present work, we show that 2-hydroxy-DHA (HDHA), a docosahexaenoic acid (DHA) derivate that restores cognitive function in a transgenic mouse model of AD, modulates UPR and autophagy in differentiated neuron-like SH-SY5Y cells. Mild therapeutic HDHA exposure induced UPR activation, characterized by the up-regulation of the molecular chaperone Bip as well as PERK-mediated stimulation of eIF2α phosphorylation. Key proteins involved in initiating autophagy, such as beclin-1, and several Atg proteins involved in autophagosome maturation (Atg3, Atg5, Atg12 and Atg7), were also up-regulated on exposure to HDHA. Moreover, when HDHA-mediated autophagy was studied after amyloid-β peptide (Aβ) stimulation to mimic the neurotoxic environment of AD, it was associated with increased cell survival, suggesting that HDHA driven modulation of this process at least in part mediates the neuroprotective effects of this new anti-neurodegenerative drug. The present results in part explain the pharmacological effects of HDHA inducing full recovery of the cognitive scores in murine models of AD.

Streptozotocin induces endoplasmic reticulum stress and apoptosis via disruption of calcium homeostasis in mouse pancreas

Calcium homeostasis refers to the regulation of calcium ion concentration in the body. This concentration is tightly controlled by a stabilizing system consisting of calcium channels and calcium buffering proteins. Calcium homeostasis is crucial for cell survival. Various forms of cell death (e.g., necrosis and apoptosis) also share calcium signaling pathways and molecular effectors. Calcium acts not only as a ubiquitous second messenger involved in apoptosis along with various cell death inducers but also a regulator for the synthesis of enzymes/hormones such as insulin. We hypothesized that streptozotocin disrupts calcium homeostasis and the altered intracellular calcium levels may induce cell death. After streptozotocin administration, blood glucose level was increased while insulin levels decreased. The expression of insulin response markers also decreased relative to the vehicle group. L-type voltage-gated calcium channel expression and sarcoplasmic reticulum Ca(2+) ATPase were increased by streptozotocin. Calcium buffering protein calbindin-D9k and calmodulin family members were also increased. The expression of genes involved in transporting calcium ions to the endoplasmic reticulum (ER) was decrease while the expression of those affecting the removal of calcium from the ER was increased. Depletion of calcium from the ER leads to ER-stress and can induce apoptosis. In the streptozotocin-treatment group, apoptosis markers were increased. Taken together, these results imply that the disruption of calcium homeostasis by streptozotocin induces ER-stress and leads to the apoptosis of pancreatic cells. Additionally, findings from this study suggest that imbalances in calcium homeostasis could promote pancreatic beta cell death and result in type I diabetes.

Metformin increases degradation of phospholamban via autophagy in cardiomyocytes

Phospholamban (PLN) is an effective inhibitor of the sarco(endo)plasmic reticulum Ca(2+) ATPase (SERCA). Here, we examined PLN stability and degradation in primary cultured mouse neonatal cardiomyocytes (CMNCs) and mouse hearts using immunoblotting, molecular imaging, and [(35)S]methionine pulse-chase experiments, together with lysosome (chloroquine and bafilomycin A1) and autophagic (3-methyladenine and Atg5 siRNA) antagonists. Inhibiting lysosomal and autophagic activities promoted endogenous PLN accumulation, whereas accelerating autophagy with metformin enhanced PLN degradation in CMNCs. This reduction in PLN levels was functionally correlated with an increased rate of SERCA2a activity, accounting for an inotropic effect of metformin. Metabolic labeling reaffirmed that metformin promoted wild-type and R9C PLN degradation. Immunofluorescence showed that PLN and the autophagy marker, microtubule light chain 3, became increasingly colocalized in response to chloroquine and bafilomycin treatments. Mechanistically, pentameric PLN was polyubiquitinylated at the K3 residue and this modification was required for p62-mediated selective autophagy trafficking. Consistently, attenuated autophagic flux in HECT domain and ankyrin repeat-containing E3 ubiquitin protein ligase 1-null mouse hearts was associated with increased PLN levels determined by immunoblots and immunofluorescence. Our study identifies a biological mechanism that traffics PLN to the lysosomes for degradation in mouse hearts.

The Protective Effect of Lacidipine on Myocardial Remodeling Is Mediated by the Suppression in Expression of GPR78 and CHOP in Rats

Lacidipine (LAC) is now widely used for the treatment of hypertension and further can prevent cardiac hypertrophy and remodeling. However, the underlying mechanism has not been fully understood. In this study, we examined the protective effects of LAC on cardiac remodeling in spontaneously hypertensive rats (SHR) and investigated the possible mechanism. Four weeks after administration of the designated drugs, blood pressure, left ventricular mass index (LVMI), and rterial pressure (MAP) were measured. The endoplasmic reticulum stress (ERS) parameters such as GRP78 and CHOP expressions in cardiomyocytes were also detected by immunohistochemistry. Results showed that the MAP in 0.36 and 0.72 mg/kg LAC groups was markedly lowered compared with that of the SHR control group (P < 0.01 or P < 0.05). Moreover, 0.72 mg/kg LAC could also significantly decrease the LVMI (P < 0.05). Simultaneously, the results of immunohistochemistry demonstrated that the expression of GRP78 and CHOP was significantly decreased by 0.72 mg/kg LAC (P < 0.05), respectively. Our present study suggested that LAC could lower blood pressure and could prevent left ventricular hypertrophy accompanied by inhibiting expression of GRP78 and CHOP in ERS.

Hydrogen sulfide attenuates high fat diet-induced cardiac dysfunction via the suppression of endoplasmic reticulum stress

Diabetic cardiomyopathy is a significant contributor to the morbidity and mortality associated with diabetes and metabolic syndrome. However, the underlying molecular mechanisms that lead to its development have not been fully elucidated. Hydrogen sulfide (H2S) is an endogenously produced signaling molecule that is critical for the regulation of cardiovascular homeostasis. Recently, therapeutic strategies aimed at increasing its levels have proven cardioprotective in models of acute myocardial ischemia-reperfusion injury and heart failure. The precise role of H2S in the pathogenesis of diabetic cardiomyopathy has not yet been established. Therefore, the goal of the present study was to evaluate circulating and cardiac H2S levels in a murine model of high fat diet (HFD)-induced cardiomyopathy. Diabetic cardiomyopathy was produced by feeding mice HFD (60% fat) chow for 24 weeks. HFD feeding reduced both circulating and cardiac H2S and induced hallmark features of type-2 diabetes. We also observed marked cardiac dysfunction, evidence of cardiac enlargement, cardiac hypertrophy, and fibrosis. H2S therapy (SG-1002, an orally active H2S donor) restored sulfide levels, improved some of the metabolic perturbations stemming from HFD feeding, and attenuated HFD-induced cardiac dysfunction. Additional analysis revealed that H2S therapy restored adiponectin levels and suppressed cardiac ER stress stemming from HFD feeding. These results suggest that diminished circulating and cardiac H2S levels play a role in the pathophysiology of HFD-induced cardiomyopathy. Additionally, these results suggest that H2S therapy may be of clinical importance in the treatment of cardiovascular complications stemming from diabetes.

New insights into the roles of CHOP-induced apoptosis in ER stress

Endoplasmic reticulum stress (ER stress) is triggered due to a loss of homeostasis in the ER, resulting in accumulation of misfolded proteins in the ER lumen. ER stress activates a series of adaptive mechanisms known as the unfolded protein response. Perturbation of the ER is a powerful inducer of the transcription factor C/EBP homologous protein (CHOP). Although it has been proved that excessive or adverse stress to the ER triggers apoptosis, the specific mechanisms underlying these processes induced by CHOP remain unclear. By now, CHOP-induced apoptosis in ER stress has been implicated in numerous human diseases, such as neurodegenerative diseases, diabetes, ischemic diseases, tumor, and so on. In this review, we summarized the current understanding of the roles of CHOP in the development of several diseases from the laboratory to the clinic.

Insight into genetic determinants of resting heart rate

BACKGROUND

Recent studies suggested that resting heart rate (RHR) might be an independent predictor of cardiovascular mortality and morbidity. Nonetheless, the interrelation between RHR and cardiovascular diseases is not clear. In order to resolve this puzzle, the importance of genetic determinants of RHR has been recently suggested, but it needs to be further investigated.

OBJECTIVE

The aim of this study was to estimate the contribution of common genetic variations on RHR using Genome Wide Association Study.

METHODS

We performed a Genome Wide Association Study in an isolated population cohort of 1737 individuals, the Italian Network on Genetic Isolates - Friuli Venezia Giulia (INGI-FVG). Moreover, a haplotype analysis was performed. A regression tree analysis was run to highlight the effect of each haplotype combination on the phenotype.

RESULTS

A significant level of association (p<5 × 10(-8)) was detected for Single Nucleotide Polymorphisms (SNPs) in two genes expressed in the heart: MAML1 and CANX. Founding that the three different variants of the haplotype, which encompass both genes, yielded a phenotypic correlation. Indeed, a haplotype in homozygosity is significantly associated with the lower quartile of RHR (RHR ≤ 58 bpm). Moreover no significant association was found between cardiovascular risk factors and the different haplotype combinations.

CONCLUSION

Mastermind-like 1 and Calnexin were found to be associated with RHR. We demonstrated a relation between a haplotype and the lower quartile of RHR in our populations. Our findings highlight that genetic determinants of RHR may be implicated in determining cardiovascular diseases and could allow a better risk stratification.