Endoplasmic Reticulum Chaperone GRP78 Protects Heart From Ischemia/Reperfusion Injury Through Akt Activation

Direct Endoplasmic Reticulum Targeting by the Selective Alkylphospholipid Analog and Antitumor Ether Lipid Edelfosine as a Therapeutic Approach in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC), the most common malignancy of the pancreas, shows a dismal and grim overall prognosis and survival rate, which have remained virtually unchanged for over half a century. PDAC is the most lethal of all cancers, with the highest mortality-to-incidence ratio. PDAC responds poorly to current therapies and remains an incurable malignancy. Therefore, novel therapeutic targets and drugs are urgently needed for pancreatic cancer treatment. Selective induction of apoptosis in cancer cells is an appealing approach in cancer therapy. Apoptotic cell death is highly regulated by different signaling routes that involve a variety of subcellular organelles. Endoplasmic reticulum (ER) stress acts as a double-edged sword at the interface of cell survival and death. Pancreatic cells exhibit high hormone and enzyme secretory functions, and thereby show a highly developed ER. Thus, pancreatic cancer cells display a prominent ER. Solid tumors have to cope with adverse situations in which hypoxia, lack of certain nutrients, and the action of certain antitumor agents lead to a complex interplay and crosstalk between ER stress and autophagy-the latter acting as an adaptive survival response. ER stress also mediates cell death induced by a number of anticancer drugs and experimental conditions, highlighting the pivotal role of ER stress in modulating cell fate. The alkylphospholipid analog prototype edelfosine is selectively taken up by tumor cells, accumulates in the ER of a number of human solid tumor cells-including pancreatic cancer cells-and promotes apoptosis through a persistent ER-stress-mediated mechanism both in vitro and in vivo. Here, we discuss and propose that direct ER targeting may be a promising approach in the therapy of pancreatic cancer, opening up a new avenue for the treatment of this currently incurable and deadly cancer. Furthermore, because autophagy acts as a cytoprotective response to ER stress, potentiation of the triggering of a persistent ER response by combination therapy, together with the use of autophagy blockers, could improve the current gloomy expectations for finding a cure for this type of cancer.

Mutation in FBXO32 causes dilated cardiomyopathy through up-regulation of ER-stress mediated apoptosis

Endoplasmic reticulum (ER) stress induction of cell death is implicated in cardiovascular diseases. Sustained activation of ER-stress induces the unfolded protein response (UPR) pathways, which in turn activate three major effector proteins. We previously reported a missense homozygous mutation in FBXO32 (MAFbx, Atrogin-1) causing advanced heart failure by impairing autophagy. In the present study, we performed transcriptional profiling and biochemical assays, which unexpectedly revealed a reduced activation of UPR effectors in patient mutant hearts, while a strong up-regulation of the CHOP transcription factor and of its target genes are observed. Expression of mutant FBXO32 in cells is sufficient to induce CHOP-associated apoptosis, to increase the ATF2 transcription factor and to impair ATF2 ubiquitination. ATF2 protein interacts with FBXO32 in the human heart and its expression is especially high in FBXO32 mutant hearts. These findings provide a new underlying mechanism for FBXO32-mediated cardiomyopathy, implicating abnormal activation of CHOP. These results suggest alternative non-canonical pathways of CHOP activation that could be considered to develop new therapeutic targets for the treatment of FBXO32-associated DCM.

Al-Yacoub et al. investigate the consequences of FBXO32 mutation on dilated cardiomyopathy. ER stress, abnormal CHOP activation and CHOP-induced apoptosis with no UPR effector activation are found to underlie the FBXO32 mutation induced cardiomyopathy, suggesting an alternative pathway that can be considered to develop new therapeutic targets for its treatment.

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.

Heat Shock Proteins: Potential Modulators and Candidate Biomarkers of Peripartum Cardiomyopathy

Peripartum cardiomyopathy (PPCM) is a potentially life-threatening condition in which heart failure and systolic dysfunction occur late in pregnancy or within months following delivery. To date, no reliable biomarkers or therapeutic interventions for the condition exist, thus necessitating an urgent need for identification of novel PPCM drug targets and candidate biomarkers. Leads for novel treatments and biomarkers are therefore being investigated worldwide. Pregnancy is generally accompanied by dramatic hemodynamic changes, including a reduced afterload and a 50% increase in cardiac output. These increased cardiac stresses during pregnancy potentially impair protein folding processes within the cardiac tissue. The accumulation of misfolded proteins results in increased toxicity and cardiac insults that trigger heart failure. Under stress conditions, molecular chaperones such as heat shock proteins (Hsps) play crucial roles in maintaining cellular proteostasis. Here, we critically assess the potential role of Hsps in PPCM. We further predict specific associations between the Hsp types Hsp70, Hsp90 and small Hsps with several proteins implicated in PPCM pathophysiology. Furthermore, we explore the possibility of select Hsps as novel candidate PPCM biomarkers and drug targets. A better understanding of how these Hsps modulate PPCM pathogenesis holds promise in improving treatment, prognosis and management of the condition, and possibly other forms of acute heart failure.

Electroacupuncture Pretreatment Mitigates Myocardial Ischemia/Reperfusion Injury via XBP1/GRP78/Akt Pathway

Myocardial ischemia/reperfusion injury is a common clinical problem and can result in severe cardiac dysfunction. Previous studies have demonstrated the protection of electroacupuncture against myocardial ischemia/reperfusion injury. However, the role of X-box binding protein I (XBP1) signaling pathway in the protection of electroacupuncture was still elusive. Thus, we designed this study and demonstrated that electroacupuncture significantly improved cardiac function during myocardial ischemia/reperfusion injury and reduced cardiac infarct size. Electroacupuncture treatment further inhibited cardiac injury manifested by the decrease of the activities of serum lactate dehydrogenase and creatine kinase-MB. The results also revealed that electroacupuncture elevated the expressions of XBP1, glucose-regulated protein 78 (GRP78), Akt, and Bcl-2 and decreased the Bax and cleaved Caspase 3 expressions. By using the inhibitor of XBP1 in vitro, the results revealed that suppression of XBP1 expression could markedly increase the activities of lactate dehydrogenase and creatine kinase-MB and cell apoptosis, thus exacerbating stimulated ischemia/reperfusion-induced H9c2 cell injury. Compared with stimulated ischemia/reperfusion group, inhibition of XBP1 inhibited the downstream GRP78 and Akt expressions during stimulated ischemia/reperfusion injury. Collectively, our data demonstrated that electroacupuncture treatment activated XBP1/GRP78/Akt signaling to protect hearts from myocardial ischemia/reperfusion injury. These findings revealed the underlying mechanisms of electroacupuncture protection against myocardial ischemia/reperfusion injury and may provide novel therapeutic targets for the clinical treatment of myocardial ischemia/reperfusion injury.

iPLA2β Contributes to ER Stress-Induced Apoptosis during Myocardial Ischemia/Reperfusion Injury

Both calcium-independent phospholipase A2 beta (iPLA2β) and endoplasmic reticulum (ER) stress regulate important pathophysiological processes including inflammation, calcium homeostasis and apoptosis. However, their roles in ischemic heart disease are poorly understood. Here, we show that the expression of iPLA2β is increased during myocardial ischemia/reperfusion (I/R) injury, concomitant with the induction of ER stress and the upregulation of cell death. We further show that the levels of iPLA2β in serum collected from acute myocardial infarction (AMI) patients and in samples collected from both in vivo and in vitro I/R injury models are significantly elevated. Further, iPLA2β knockout mice and siRNA mediated iPLA2β knockdown are employed to evaluate the ER stress and cell apoptosis during I/R injury. Additionally, cell surface protein biotinylation and immunofluorescence assays are used to trace and locate iPLA2β. Our data demonstrate the increase of iPLA2β augments ER stress and enhances cardiomyocyte apoptosis during I/R injury in vitro and in vivo. Inhibition of iPLA2β ameliorates ER stress and decreases cell death. Mechanistically, iPLA2β promotes ER stress and apoptosis by translocating to ER upon myocardial I/R injury. Together, our study suggests iPLA2β contributes to ER stress-induced apoptosis during myocardial I/R injury, which may serve as a potential therapeutic target against ischemic heart disease.

Integrated signaling system under endoplasmic reticulum stress in eukaryotic microorganisms

The endoplasmic reticulum (ER) is a multifunctional organelle, which is crucial for correct folding and assembly of secretory and transmembrane proteins. Perturbations of ER function can cause ER stress. ER stress can activate the unfolded protein response (UPR) to cope with the accumulation of misfolded proteins and protein toxicity. UPR is a coordination system that regulates transcription and translation, leading to the recovery of ER homeostasis or cell death. However, cells have an integrated signaling system to cope with ER stress, which helps cells to restore and balance their ER function. The main components of this system are ER-associated degradation (ERAD), autophagy, hypoxia signaling, and mitochondrial biogenesis. If the balance cannot be restored, the imbalance will lead to cell death or apoptosis, or even to a series of diseases. In this review, a series of activities to restore the homeostasis of cells during ER stress are discussed. KEY POINTS: • Endoplasmic reticulum (ER) plays a key role in the biological process of cells. • Perturbations of ER function can cause ER stress, including the ER overload response (EOR), sterol-regulated cascade reaction, and the UPR. • Cells have an integrated signaling system (ERAD, autophagy, hypoxia signaling, and mitochondrial biogenesis) to cope with the adverse impact caused by ER stress.

Autophagy Blockade by Ai Du Qing Formula Promotes Chemosensitivity of Breast Cancer Stem Cells Via GRP78/β-Catenin/ABCG2 Axis

Accumulating evidence suggests that the root of drug chemoresistance in breast cancer is tightly associated with subpopulations of cancer stem cells (CSCs), whose activation is largely dependent on taxol-promoting autophagy. Our pilot study identified GRP78 as a specific marker for chemoresistance potential of breast CSCs by regulating Wnt/β-catenin signaling. Ai Du Qing (ADQ) is a traditional Chinese medicine formula that has been utilized in the treatment cancer, particularly during the consolidation phase. In the present study, we investigated the regulatory effects and molecular mechanisms of ADQ in promoting autophagy-related breast cancer chemosensitivity. ADQ with taxol decreasing the cell proliferation and colony formation of breast cancer cells, which was accompanied by suppressed breast CSC ratio, limited self-renewal capability, as well as attenuated multi-differentiation. Furthermore, autophagy in ADQ-treated breast CSCs was blocked by taxol via regulation of β-catenin/ABCG2 signaling. We also validated that autophagy suppression and chemosensitizing activity of this formula was GRP78-dependent. In addition, GRP78 overexpression promoted autophagy-inducing chemoresistance in breast cancer cells by stabilizing β-catenin, while ADQ treatment downregulated GRP78, activated the Akt/GSK3β-mediated proteasome degradation of β-catenin via ubiquitination activation, and consequently attenuated the chemoresistance-promoted effect of GRP78. In addition, both mouse breast cancer xenograft and zebrafish xenotransplantation models demonstrated that ADQ inhibited mammary tumor growth, and the breast CSC subpopulation showed obscure adverse effects. Collectively, this study not only reveals the chemosensitizating mechanism of ADQ in breast CSCs, but also highlights the importance of GRP78 in mediating autophagy-promoting drug resistance via β-catenin/ABCG2 signaling.

Therapies to prevent post-infarction remodelling: From repair to regeneration

Myocardial infarction is the first cause of worldwide mortality, with an increasing incidence also reported in developing countries. Over the past decades, preclinical research and clinical trials continually tested the efficacy of cellular and acellular-based treatments. However, none of them resulted in a drug or device currently used in combination with either percutaneous coronary intervention or coronary artery bypass graft. Inflammatory, proliferation and remodelling phases follow the ischaemic event in the myocardial tissue. Only recently, single-cell sequencing analyses provided insights into the specific cell populations which determine the final fibrotic deposition in the affected region. In this review, ischaemia, inflammation, fibrosis, angiogenesis, cellular stress and fundamental cellular and molecular components are evaluated as therapeutic targets. Given the emerging evidence of biomaterial-based systems, the increasing use of injectable hydrogels/scaffolds and epicardial patches is reported both as acellular and cellularised/functionalised treatments. Since several variables influence the outcome of any experimented treatment, we return to the pathological basis with an unbiased view towards any specific process or cellular component. Thus, by evaluating the benefits and limitations of the approaches based on these targets, the reader can weigh the rationale of each of the strategies that reached the clinical trials stage. As recent studies focused on the relevance of the extracellular matrix in modulating ischaemic remodelling and enhancing myocardial regeneration, we aim to portray current trends in the field with this review. Finally, approaches towards feasible translational studies that are as yet unexplored are also suggested.

Lactate Dehydrogenase A Governs Cardiac Hypertrophic Growth in Response to Hemodynamic Stress

The heart manifests hypertrophic growth in response to high blood pressure, which may decompensate and progress to heart failure under persistent stress. Metabolic remodeling is an early event in this process. However, its role remains to be fully characterized. Here, we show that lactate dehydrogenase A (LDHA), a critical glycolytic enzyme, is elevated in the heart in response to hemodynamic stress. Cardiomyocyte-restricted deletion of LDHA leads to defective cardiac hypertrophic growth and heart failure by pressure overload. Silencing of LDHA in cultured cardiomyocytes suppresses cell growth from pro-hypertrophic stimulation in vitro, while overexpression of LDHA is sufficient to drive cardiomyocyte growth. Furthermore, we find that lactate is capable of rescuing the growth defect from LDHA knockdown. Mechanistically, lactate stabilizes NDRG3 (N-myc downregulated gene family 3) and stimulates ERK (extracellular signal-regulated kinase). Our results together suggest that the LDHA/NDRG3 axis may play a critical role in adaptive cardiomyocyte growth in response to hemodynamic stress.

Dai et al. find that LDHA is significantly increased in the heart under hemodynamic stress, and cardiomyocyte-specific deletion of LDHA leads to severe cardiac dysfunction in response to pressure overload. LDHA may govern adaptive growth through elevation of NDRG3 and activation of ERK.

Mitochondria-associated membrane-modulated Ca2+ transfer: A potential treatment target in cardiac ischemia reperfusion injury and heart failure

Effective Ca²⁺ dependent mitochondrial energy supply is imperative for proper cardiac contractile activity, while disruption of Ca²⁺ homeostasis participates in the pathogenesis of multiple human diseases. This phenomenon is particularly prominent in cardiac ischemia and reperfusion (I/R) and heart failure, both of which require strict clinical intervention. The interface between endoplasmic reticula (ER) and mitochondria, designated the mitochondria-associated membrane (MAM), is now regarded as a crucial mediator of Ca²⁺ transportation. Thus, interventions targeting this physical and functional coupling between mitochondria and the ER are highly desirable. Increasing evidence supports the notion that restoration, and maintenance, of the physiological contact between these two organelles can improve mitochondrial function, while inhibiting cell death, thereby sufficiently ameliorating I/R injury and heart failure development. A better understanding regarding the underlying mechanism of MAM-mediated transport will pave the way for identification of novel treatment approaches for heart disease. Therefore, in this review, we summarize the crucial functions and potential mechanisms of MAMs in the pathogenesis of I/R and heart failure.

Paeoniflorin and Hydroxysafflor Yellow A in Xuebijing Injection Attenuate Sepsis-Induced Cardiac Dysfunction and Inhibit Proinflammatory Cytokine Production

Sepsis-induced myocardial dysfunction is a major contributor to the poor outcomes of septic shock. As an add-on with conventional sepsis management for over 15 years, the effect of Xuebijing injection (XBJ) on the sepsis-induced myocardial dysfunction was not well understood. The material basis of Xuebijing injection (XBJ) in managing infections and infection-related complications remains to be defined. A murine cecal ligation and puncture (CLP) model and cardiomyocytes in vitro culture were adopted to study the influence of XBJ on infection-induced cardiac dysfunction. XBJ significantly improved the survival of septic-mice and rescued cardiac dysfunction in vivo. RNA-seq revealed XBJ attenuated the expression of proinflammatory cytokines and related signalings in the heart which was further confirmed on the mRNA and protein levels. Xuebijing also protected cardiomyocytes from LPS-induced mitochondrial calcium ion overload and reduced the LPS-induced ROS production in cardiomyocytes. The therapeutic effect of XBJ was mediated by the combination of paeoniflorin and hydroxysafflor yellow A (HSYA) (C0127-2). C0127-2 improved the survival of septic mice, protected their cardiac function and cardiomyocytes while balancing gene expression in cytokine-storm-related signalings, such as TNF-α and NF-κB. In summary, Paeoniflorin and HSYA are key active compounds in XBJ for managing sepsis, protecting cardiac function, and controlling inflammation in the cardiac tissue partially by limiting the production of IL-6, IL-1β, and CXCL2.

Vascular Stress Signaling in Hypertension

Cells respond to stress by activating a variety of defense signaling pathways, including cell survival and cell death pathways. Although cell survival signaling helps the cell to recover from acute insults, cell death or senescence pathways induced by chronic insults can lead to unresolved pathologies. Arterial hypertension results from chronic physiological maladaptation against various stressors represented by abnormal circulating or local neurohormonal factors, mechanical stress, intracellular accumulation of toxic molecules, and dysfunctional organelles. Hypertension and aging share common mechanisms that mediate or prolong chronic cell stress, such as endoplasmic reticulum stress and accumulation of protein aggregates, oxidative stress, metabolic mitochondrial stress, DNA damage, stress-induced senescence, and proinflammatory processes. This review discusses common adaptive signaling mechanisms against these stresses including unfolded protein responses, antioxidant response element signaling, autophagy, mitophagy, and mitochondrial fission/fusion, STING (signaling effector stimulator of interferon genes)-mediated responses, and activation of pattern recognition receptors. The main molecular mechanisms by which the vasculature copes with hypertensive and aging stressors are presented and recent advancements in stress-adaptive signaling mechanisms as well as potential therapeutic targets are discussed.

Endoplasmic reticulum stress and unfolded protein response in cardiovascular diseases

Cardiovascular diseases (CVDs), such as ischaemic heart disease, cardiomyopathy, atherosclerosis, hypertension, stroke and heart failure, are among the leading causes of morbidity and mortality worldwide. Although specific CVDs and the associated cardiometabolic abnormalities have distinct pathophysiological and clinical manifestations, they often share common traits, including disruption of proteostasis resulting in accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER). ER proteostasis is governed by the unfolded protein response (UPR), a signalling pathway that adjusts the protein-folding capacity of the cell to sustain the cell's secretory function. When the adaptive UPR fails to preserve ER homeostasis, a maladaptive or terminal UPR is engaged, leading to the disruption of ER integrity and to apoptosis. ER stress functions as a double-edged sword, with long-term ER stress resulting in cellular defects causing disturbed cardiovascular function. In this Review, we discuss the distinct roles of the UPR and ER stress response as both causes and consequences of CVD. We also summarize the latest advances in our understanding of the importance of the UPR and ER stress in the pathogenesis of CVD and discuss potential therapeutic strategies aimed at restoring ER proteostasis in CVDs.

SOCS3 Negatively Regulates Cardiac Hypertrophy via Targeting GRP78-Mediated ER Stress During Pressure Overload

Pressure overload-induced hypertrophic remodeling is a critical pathological process leading to heart failure (HF). Suppressor of cytokine signaling-3 (SOCS3) has been demonstrated to protect against cardiac hypertrophy and dysfunction, but its mechanisms are largely unknown. Using primary cardiomyocytes and cardiac-specific SOCS3 knockout (SOCS3cko) or overexpression mice, we demonstrated that modulation of SOCS3 level influenced cardiomyocyte hypertrophy, apoptosis and cardiac dysfunction induced by hypertrophic stimuli. We found that glucose regulatory protein 78 (GRP78) was a direct target of SOCS3, and that overexpression of SOCS3 inhibited cardiomyocyte hypertrophy and apoptosis through promoting proteasomal degradation of GRP78, thereby inhibiting activation of endoplasmic reticulum (ER) stress and mitophagy in the heart. Thus, our results uncover SOCS3-GRP78-mediated ER stress as a novel mechanism in the transition from cardiac hypertrophy to HF induced by sustained pressure overload, and suggest that modulating this pathway may provide a new therapeutic approach for hypertrophic heart diseases.

ER stress preconditioning ameliorates liver damage after hemorrhagic shock and reperfusion

The mismatch of oxygen supply and demand during hemorrhagic shock disturbs endoplasmic reticulum (ER) homeostasis. The resulting accumulation of unfolded proteins in the ER lumen, which is a condition that is defined as ER stress, triggers the unfolded protein response (UPR). Since the UPR influences the extent of organ damage following hemorrhagic shock/reperfusion (HS/R) and mediates the protective effects of stress preconditioning before ischemia-reperfusion injury, the current study investigated the mechanisms of ER stress preconditioning and its impact on post-hemorrhagic liver damage. Male C56BL/6-mice were injected intraperitoneally with the ER stress inductor tunicamycin (TM) or its drug vehicle 48 h prior to being subjected to a 90 min pressure-controlled hemorrhagic shock (30±5 mmHg). A period of 14 h after hemorrhagic shock induction, mice were sacrificed. Hepatocellular damage was quantified by analyzing hepatic transaminases and hematoxylin-eosin stained liver tissue sections. Additionally, the topographic expression patterns of the ER stress marker binding immunoglobulin protein (BiP), UPR signaling pathways, and the autophagy marker Beclin1 were evaluated. TM injection significantly increased BiP expression and modified the topographic expression patterns of the UPR signaling proteins. In addition, immunohistochemical analysis of Beclin1 revealed an increased pericentral staining intensity following TM pretreatment. The histologic analysis of hepatocellular damage demonstrated a significant reduction in cell death areas in HS/R+TM (P=0.024). ER stress preconditioning influences the UPR and alleviates post-hemorrhagic liver damage. The beneficial effects were, at least partially, mediated by the upregulation of BiP and autophagy induction. These results underscore the importance of the UPR in the context of HS/R and may help identify novel therapeutic targets.

Resolution-Based Therapies: The Potential of Lipoxins to Treat Human Diseases

Inflammation is an a physiological response instead an essential response of the organism to injury and its adequate resolution is essential to restore homeostasis. However, defective resolution can be the precursor of severe forms of chronic inflammation and fibrosis. Nowadays, it is known that an excessive inflammatory response underlies the most prevalent human pathologies worldwide. Therefore, great biomedical research efforts have been driven toward discovering new strategies to promote the resolution of inflammation with fewer side-effects and more specificity than the available anti-inflammatory treatments. In this line, the use of endogenous specialized pro-resolving mediators (SPMs) has gained a prominent interest. Among the different SPMs described, lipoxins stand out as one of the most studied and their deficiency has been widely associated with a wide range of pathologies. In this review, we examined the current knowledge on the therapeutic potential of lipoxins to treat diseases characterized by a severe inflammatory background affecting main physiological systems, paying special attention to the signaling pathways involved. Altogether, we provide an updated overview of the evidence suggesting that increasing endogenously generated lipoxins may emerge as a new therapeutic approach to prevent and treat many of the most prevalent diseases underpinned by an increased inflammatory response.

Prolonged preoperative fasting induces postoperative insulin resistance by ER-stress mediated Glut4 down-regulation in skeletal muscles

Preoperative fasting aims to prevent pulmonary aspiration and improve bowel preparation, but it may induce profound systemic catabolic responses that lead to protein breakdown and insulin-resistant hyperglycemia after operation. However, the molecular mechanisms of catabolic reaction induced by prolonged preoperative fasting and surgical stress are undetermined. In this study, anesthetized rats were randomly assigned to receive a sham operation or laparotomy cecectomy. Fasting groups were restricted from food and water for 12 h before operation, while the feeding group had free access to food throughout the study period. Twenty-four hours after operation, the animals were sacrificed to collect blood samples and soleus muscles for analysis. Postoperative blood glucose level was significantly increased in the fasting group with elevated serum insulin and C-peptide. Continuous feeding reduced serum myoglobin and lactate dehydrogenase concentrations. Preoperative fasting activated inositol-requiring transmembrane kinase/endoribonuclease (IRE)-1α and c-Jun N-terminal kinase (JNK) mediated endoplasmic reticulum (ER)-stress, and reduced glucose transporter type 4 (Glut4) expression in the soleus muscle. Phospholamban phosphorylation was reduced and intracellular calcium levels were increased in the isolated skeletal muscle cells. Similar results were found in ER stress-induced C1C12 myoblasts. The expression of Glut4 was suppressed in the stressed C1C12, but was potentiated following inhibition of ER stress and chelation of intracellular free calcium. This study provides evidence demonstrating that prolonged preoperative fasting induces ER stress and generates insulin resistance in the skeletal muscle through suppression of Glut4 and inactivation of Ca²⁺-ATPase, leading to intracellular calcium homeostasis disruption and peripheral insulin resistance.

Astragaloside and/or Hydroxysafflor Yellow A Attenuates Oxygen-Glucose Deprivation-Induced Cultured Brain Microvessel Endothelial Cell Death through Downregulation of PHLPP-1

The incidence of ischemic stroke, a life-threatening condition in humans, amongst Asians is high and the prognosis is poor. In the absence of effective therapeutics, traditional Chinese medicines have been used that have shown promising results. It is crucial to identify traditional Chinese medicine formulas that protect the blood-brain barrier, which is damaged by an ischemic stroke. In this study, we aimed to elucidate such formulas. Brain microvascular endothelial cells (BMECs) were used to establish an in vitro ischemia-reperfusion model for oxygen-glucose deprivation (OGD) experiments to evaluate the function of two traditional Chinese medicines, namely, astragaloside (AS-IV) and hydroxysafflor yellow A (HSYA), in protecting against BMEC. Our results revealed that AS-IV and HSYA attenuated the cell loss caused by OGD by increasing cell proliferation and inhibiting cell apoptosis. In addition, these compounds promoted the migration and invasion of BMECs in vitro. Furthermore, we found that BMECs rescued by AS-IV and HSYA could be functionally activated in vitro, with AS-IV and HSYA showing synergetic effects in rescuing BMECs survival in vitro by reducing the expression of PHLPP-1 and activating Akt signaling. Our results elucidated the potential of AS-IV and HSYA in the prevention and treatment of stroke by protecting against cerebral ischemia-reperfusion injury.

Dexmedetomidine at a dose of 1 µM attenuates H9c2 cardiomyocyte injury under 3 h of hypoxia exposure and 3 h of reoxygenation through the inhibition of endoplasmic reticulum stress

Myocardial ischemia-reperfusion injury (MIRI) has been confirmed to induce endoplasmic reticulum stress (ERS) during downstream cascade reactions after the sufficient deterioration of cardiomyocyte function. However, clinically outcomes have been inconsistent with experimental findings because the mechanism has not been entirely elucidated. Dexmedetomidine (DEX), an α² adrenergic receptor agonist with anti-inflammatory and organ-protective activity, has been shown to attenuate IRI in the heart. The present study aimed to determine whether DEX is able to protect injured cardiomyocytes under in vitro hypoxia/reoxygenation (H/R) conditions and evaluate the conditions under which ERS is efficiently ameliorated. The cytotoxicity of DEX in H9c2 cells was evaluated 24 h after treatment with several different concentrations of DEX. The most appropriate H/R model parameters were determined by the assessment of cell viability and injury with Cell Counting Kit-8 and lactate dehydrogenase (LDH) release assays after incubation under hypoxic conditions for 3 h and reoxygenation conditions for 3, 6, 12 and 24 h. Additionally, the aforementioned methods were used to assess cardiomyocytes cultured with various concentrations of DEX under H/R conditions. Furthermore, the degree of apoptosis and the mRNA and protein expression levels of glucose-regulated protein 78 (GRP78), C/EBP homologous protein (CHOP) and caspase-12 were evaluated in all groups. The addition of 1, 5 and 10 µM DEX to the cell culture significantly increased the proliferation of H9c2 cells by >80% under normal culture conditions. In the H/R model assessment, following 3 h of anoxia exposure, H9c2 cell viability decreased to 62.67% with 3 h of reoxygenation and to 36% with 6 h of reoxygenation compared with the control. The viability of H9c2 cells subjected to hypoxia for 3 h and reoxygenation for 3 h increased by 61.3% when pretreated with 1 µM DEX, and the LDH concentration in the supernatant was effectively decreased by 13.7%. H/R significantly increased the percentage of apoptotic cells, as detected by flow cytometry, and increased the expression levels of GRP78, CHOP and caspase-12, while treatment with either DEX or 4-phenylbutyric acid (4-PBA) significantly attenuated these effects. Additionally, despite the protective effect of DEX against H/R injury, 4-PBA attenuated the changes induced by DEX and H/R. In conclusion, treatment with 1 µM DEX alleviated cell injury, apoptosis and the increases in GRP78, CHOP and caspase-12 expression levels in H9c2 cells induced by 3 h of hypoxia and 3 h of reoxygenation.

Syntaxin 17 inhibits ischemic neuronal injury by resuming autophagy flux and ameliorating endoplasmic reticulum stress

Previous studies have shown that syntaxin 17 (STX17) is involved in mediating the fusion of autophagosomes and lysosomes. This study aimed to investigate the role and mechanism of STX17 in neuronal injury following cerebral ischemia/reperfusion. The ischemia/reperfusion (I/R) models were established by transient middle cerebral artery occlusion (tMCAO) in mice and oxygen glucose deprivation/reperfusion (O/R) in primary cultured cortical neurons and HT22 cells. Cerebral ischemia/reperfusion significantly up-regulated the expression of STX17 in neurons. Lentivirus mediated knockdown of STX17 in neurons reduced neuronal viability and increased LDH leakage. Injection of AAV9-shSTX17 into the brain of mice then subjected to tMCAO also significantly augmented the infarct area and exacerbated neurobehavioral deficits and mortality. Depletion of STX17 caused accumulation of autophagic marker/substrate LC3 II and p62, blockade of the autophagic flux, and the accumulation of dysfunctional lysosomes. Knockdown of STX17 also aggravated endoplasmic reticulum (ER) stress-dependent neuronal apoptosis induced by ischemia/reperfusion. Importantly, induction of autophagy-lysosomal pathway and alleviation of ER stress partially rescued STX17 knockdown-induced neuronal damage. These results suggest that STX17 may ameliorate ischemia/reperfusion-induced neuronal damage by enhancing autophagy flux and reducing ER stress-dependent neuronal apoptosis.

Sevoflurane postconditioning reduces myocardial ischemia reperfusion injury-induced necroptosis by up-regulation of OGT-mediated O-GlcNAcylated RIPK3

Inhalation anesthetics have been demonstrated to have protective effects against myocardial ischemia reperfusion injury (MIRI). O-linked GlcNAcylation (O-GlcNAc) modifications have been shown to protect against MIRI. This study aimed to investigate whether O-GlcNAcylation and necroptosis signaling were important for sevoflurane postconditioning (SPC) induced cardioprotective effects. Apart from rats in the SHAM and sevoflurane (SEVO) group, rats underwent 30 min ischemia followed by 2 h reperfusion. Cardiac hemodynamics and function were determined. In addition, myocardial infarction size, cardiac function parameters, myocardial lactic dehydrogenase (LDH) content, myocardium histopathological changes, necrotic myocardium, O-GlcNAcylation, and protein expression levels of necroptosis biomarkers were measured, together with co-immunoprecipitation experiments using proteins associated with the necroptosis pathway and O-GlcNAcylation. SPC reduced myocardial infarction size, ameliorated cardiac function, restored hemodynamic performance, improved histopathological changes, and reduced receptor-interacting protein kinase 1 (RIPK1)/receptor-interacting protein kinase 3 (RIPK3)/mixed lineage kinase domain-like (MLKL) mediated necroptosis. In addition, SPC up-regulated O-GlcNAc transferase (OGT) mediated O-GlcNAcylation, increased O-GlcNAcylated RIPK3, and inhibited the association of RIPK3 and MLKL. However, OSMI-1, an OGT inhibitor, abolished SPC mediated cardioprotective effects and inhibited OGT mediated up-regulation of O-GlcNAcylation and down-regulation of RIPK3 and MLKL proteins induced by SPC. Our study demonstrated that SPC restrained MIRI induced necroptosis via regulating OGT mediated O-GlcNAcylation of RIPK3 and lessening the formulation of RIPK3/MLKL complex.

Cellular Protein Quality Control in Diabetic Cardiomyopathy: From Bench to Bedside

Heart failure is a serious comorbidity and the most common cause of mortality in diabetes patients. Diabetic cardiomyopathy (DCM) features impaired cellular structure and function, culminating in heart failure; however, there is a dearth of specific clinical therapy for treating DCM. Protein homeostasis is pivotal for the maintenance of cellular viability under physiological and pathological conditions, particularly in the irreplaceable cardiomyocytes; therefore, it is tightly regulated by a protein quality control (PQC) system. Three evolutionarily conserved molecular processes, the unfolded protein response (UPR), the ubiquitin-proteasome system (UPS), and autophagy, enhance protein turnover and preserve protein homeostasis by suppressing protein translation, degrading misfolded or unfolded proteins in cytosol or organelles, disposing of damaged and toxic proteins, recycling essential amino acids, and eliminating insoluble protein aggregates. In response to increased cellular protein demand under pathological insults, including the diabetic condition, a coordinated PQC system retains cardiac protein homeostasis and heart performance, on the contrary, inappropriate PQC function exaggerates cardiac proteotoxicity with subsequent heart dysfunction. Further investigation of the PQC mechanisms in diabetes propels a more comprehensive understanding of the molecular pathogenesis of DCM and opens new prospective treatment strategies for heart disease and heart failure in diabetes patients. In this review, the function and regulation of cardiac PQC machinery in diabetes mellitus, and the therapeutic potential for the diabetic heart are discussed.

Dexmedetomidine Attenuates Cellular Injury and Apoptosis in H9c2 Cardiomyocytes by Regulating p-38MAPK and Endoplasmic Reticulum Stress

Background

Myocardial ischaemia-reperfusion injury (IRI) has been confirmed to induce endoplasmic reticulum stress (ERS) when myocardial cell function continues to deteriorate to a certain degree. The clinical applications of effective tested strategies are sometimes inconsistent with the applications evaluated in experiments, although reasonable mechanisms and diverse signalling pathways have been broadly explored. Dexmedetomidine (DEX) has been shown to attenuate IRI of the heart in animal studies. This study aimed to determine whether DEX can protect injured cardiomyocytes under hypoxia/reoxygenation (H/R) at the cellular level and whether the mechanism is related to ERS and the p38 MAPK pathway.

Methods

H9c2 cells were subjected to H/R or thapsigargin (TG) to build a model. DEX or 4-PBA was added to the medium either 1 h or 24 h before modelling, respectively. Model parameters were determined by assessing cell viability and injury, which were measured by assessing cell counting kit-8 (CCK8), lactate dehydrogenase (LDH) release and flow cytometry results, and the expression of GRP78, CHOP and caspase-12. In addition, the protein expression of p38MAPK and p-p38MAPK was examined, and SB202190, a negative regulator, was also preincubated in medium.

Results

Compared to that of cells in the control group, the activity of cells in the H/R and TG groups was decreased dramatically, and the LDH concentration and proportion of apoptotic cells were increased. DEX could correspondingly reverse the changes induced by H/R or TG. Additionally, DEX effectively attenuated ERS defined as increased expression of GRP78, CHOP and caspase-12. Additionally, DEX could obviously depress the P38 MAPK phosphorylation and high p-p38 MAPK expression in the TG group, indicating DEX has a function similar to that of SB202190.

Conclusion

H/R injury in H9c2 cells can lead to abnormal ERS and apoptosis, as well as activation of the p38MAPK signalling pathway. DEX can protect cardiomyocytes by intervening in ERS, regulating p38MAPK and the downstream apoptotic signalling pathway.

Ischemic dilated cardiomyopathy pathophysiology through microRNA-16-5p

INTRODUCTION AND OBJECTIVES

The expression levels of microRNA-16-5p (miR-16) are upregulated in ischemic cardiomyopathy and in animal models of ischemic dilated cardiomyopathy (iDCM), inducing myocardial apoptosis. We investigated the role of miR-16 in the adaptive cellular response associated with endoplasmic reticulum (ER) stress and autophagy in the apoptotic iDCM environment.

METHODS

We quantified the miR-16 plasma levels of 168 participants-76 controls, 60 iDCM patients, and 32 familial DCM patients with the pathogenic variant of BAG3-by quantitative real-time polymerase chain reaction and correlated the levels with patient variables. The effects of intracellular miR-16 overexpression were analyzed in a human cardiac cell line. Apoptosis and cell viability were measured, as well as the levels of markers associated with ER stress, cardiac injury, and autophagy.

RESULTS

Plasma miR-16 levels were upregulated in iDCM patients (P=.039). A multivariate logistic regression model determined the association of miR-16 with iDCM clinical variables (P <.001). In vitro, miR-16 overexpression increased apoptosis (P=.02) and reduced cell viability (P=.008). Furthermore, it induced proapoptotic components of ER stress, based on upregulation of the PERK/CHOP pathway. However, we observed augmentation of autophagic flux (P <.001) without lysosomal blockade by miR-16 as a possible cytoprotective mechanism.

CONCLUSIONS

MiR-16 is specifically associated with iDCM. In an ischemic setting, miR-16 activates ER stress and promotes inflammation followed by autophagy in human cardiac cells. Thus, autophagy may be an attempt to maintain cellular homeostasis in response to misfolded/aggregated proteins related to ER stress, prior to apoptosis.

Pharmacologic IRE1/XBP1s activation confers targeted ER proteostasis reprogramming

Activation of the IRE1/XBP1s signaling arm of the unfolded protein response (UPR) is a promising strategy to correct defects in endoplasmic reticulum (ER) proteostasis implicated in diverse diseases. However, no pharmacologic activators of this pathway identified to date are suitable for ER proteostasis remodeling through selective activation of IRE1/XBP1s signaling. Here, we use high-throughput screening to identify non-toxic compounds that induce ER proteostasis remodeling through IRE1/XBP1s activation. We employ transcriptional profiling to stringently confirm that our prioritized compounds selectively activate IRE1/XBP1s signaling without activating other cellular stress-responsive signaling pathways. Furthermore, we demonstrate that our compounds improve ER proteostasis of destabilized variants of amyloid precursor protein (APP) through an IRE1-dependent mechanism and reduce APP-associated mitochondrial toxicity in cellular models. These results establish highly selective IRE1/XBP1s activating compounds that can be widely employed to define the functional importance of IRE1/XBP1s activity for ER proteostasis regulation in the context of health and disease.

Laquinimod exerts anti-inflammatory and antiapoptotic effects in retinal ischemia/reperfusion injury

Retinal ischemia/reperfusion (I/R) occurs in various vision disabled ocular diseases, involved in acute glaucoma, diabetic retinopathy, ischemic optic neuropathy, hypertensive retinopathy and retinal vascular occlusion. Laquinimod (LQ), a new type of immunosuppressant, has been reported to exert anti-inflammatory effects on autoimmune diseases. This research aims to investigate the protective effect of LQ on I/R damage by focusing on inhibiting dysregulated neuroinflammation and neuronal apoptosis. In our study, mice were treated with LQ after high intraocular pressure (IOP)-induced retinal I/R injury. The data showed that LQ significantly attenuated high IOP-induced retinal ganglion cell (RGC) death and inner plexiform layer (IPL) thinning and inhibited microglial activation. The results of qRT-PCR, flow cytometry and Luminex multiplex assays demonstrated the anti-inflammatory action of LQ in BV2 cells stimulated with lipopolysaccharide (LPS). In addition, primary RGC apoptosis induced by oxygen-glucose deprivation/reperfusion (OGD/R) was also directly suppressed by LQ. Importantly, LQ inhibited the expression of cleaved caspase-8 and the downstream NLRP3 inflammasome and IL-1β. In conclusion, our findings offer the first evidence that LQ treatment prevents retinal I/R damage. Furthermore, LQ could directly inhibit RGC apoptosis. Caspase-8 activation and subsequent inflammation can also be suppressed by LQ, which suggests that LQ may act through inhibiting the caspase-8 pathway. This study demonstrates a new mechanism of LQ and provides beneficial preclinical data for the clinical application of LQ.

Rosuvastatin and simvastatin attenuate cisplatin-induced cardiotoxicity via disruption of endoplasmic reticulum stress-mediated apoptotic death in rats: targeting ER-Chaperone GRP78 and Calpain-1 pathways

Cisplatin (CP) is a powerful antineoplastic chemotherapeutic agent with broad-spectrum properties. Acute and cumulative cardiotoxicity are major limiting factors for CP therapy. Various pathogenic pathways have been suggested to CP-induced cardiotoxicity; oxidative damage, ER stress, and programmed cell death/apoptosis. The present study aimed to assess the signaling mechanisms related to the advantageous effects of rosuvastatin (RSV) and simvastatin (SMV) against CP-related cardiac ER stress dependent apoptotic death in rats. Acute cardiotoxicity was induced by a single dose of CP (10 mg/kg, i.p.) on the 10th day of the experiment. RSV (10 mg/ kg/day) and SMV (10 mg/kg/day) were orally administered for 15 days. CP-treated rats showed significant alterations in electrocardiographic recordings and elevation in serum cardiac function biomarkers; troponin T content, lactate dehydrogenase and creatine kinase-MB levels as well as boost in the cardiac oxidative stress biomarkers. In addition, CP exposure resulted in GRP78 induction; an ER stress and elevation marker at calpain-1 content as well as activation of activated caspase-3 (ACASP3) and caspase-12 were reflected on CP-triggered apoptosis evidenced by elevation in the Bax/Bcl-2 ratio. However, RSV and SMV administration mitigate those adverse CP effects. Statins administration prominently alleviated CP-induced cardiac abnormalities exerting improvement in the ECG pattern and cardiac enzyme biomarkers. Interestingly, statins; RSV and SMV, disrupted CP-induced ER stress and the consequent apoptotic cell death evidenced by downregulation of ER-chaperone GRP78, calpain-1, ACASP3 and caspase-12 as well as decline in the Bax/Bcl-2 ratio. From all the previous findings, it can be suggested that statins namely; RSV and SMV, play protective role against CP-induced cardiac injury by regulating ER stress-mediated apoptotic pathways.

ER Stress-Induced Secretion of Proteins and Their Extracellular Functions in the Heart

Endoplasmic reticulum (ER) stress is a result of conditions that imbalance protein homeostasis or proteostasis at the ER, for example ischemia, and is a common event in various human pathologies, including the diseased heart. Cardiac integrity and function depend on the active secretion of mature proteins from a variety of cell types in the heart, a process that requires an intact ER environment for efficient protein folding and trafficking to the secretory pathway. As a consequence of ER stress, most protein secretion by the ER secretory pathway is decreased. Strikingly, there is a select group of proteins that are secreted in greater quantities during ER stress. ER stress resulting from the dysregulation of ER Ca²⁺ levels, for instance, stimulates the secretion of Ca²⁺-binding ER chaperones, especially GRP78, GRP94, calreticulin, and mesencephalic astrocyte-derived neurotrophic factor (MANF), which play a multitude of roles outside the cell, strongly depending on the cell type and tissue. Here we review current insights in ER stress-induced secretion of proteins, particularly from the heart, and highlight the extracellular functions of these proteins, ranging from the augmentation of cardiac cell viability to the modulation of pro- and anti-apoptotic, oncogenic, and immune-stimulatory cell signaling, cell invasion, extracellular proteostasis, and more. Many of the roles of ER stress-induced protein secretion remain to be explored in the heart. This article is part of a special issue entitled “The Role of Proteostasis Derailment in Cardiac Diseases.”

A module of multifactor-mediated dysfunction guides the molecular typing of coronary heart disease

Background

Coronary atherosclerotic heart disease (CHD) is the most common cardiovascular disease and has become a leading cause of death globally. Various molecular typing methods are available for the diagnosis and treatment of tumors. However, molecular typing results are not routinely used for CHD.

Methods and Results

Aiming to uncover the underlying molecular features of different types of CHD, we screened the differentially expressed genes (DEGs) associated with CHD based on the Gene Expression Omnibus (GEO) data and expanded those with the NCBI‐gene and OMIM databases to finally obtain 2021 DEGs. The weighted gene co‐expression analysis (WGCNA) was performed on the candidate genes, and six distinctive WGCNA modules were identified, two of which were associated with CHD. Moreover, DEGs were mined as key genes for co‐expression based on the module network relationship. Furthermore, the differentially expressed miRNAs in CHD and interactions in the database were mined in the GEO data set to build a multifactor regulatory network of key genes for co‐expression. Based on the network, the CHD samples were further classified into five clusters and we defined FTH1, HCAR3, RGS2, S100A9, and TYROBP as the top genes of the five subgroups. Finally, the mRNA levels of FTH1, S100A9, and TYROBP were found to be significantly increased, while the expression of HCAR3 was decreased in the blood of CHD patients. We did not detect measurable levels of RGS2.

Conclusion

The screened core clusters of genes may be a target for the diagnosis and treatment of CHD as a molecular typing module.

Protective Effects of Glucose-Related Protein 78 and 94 on Cisplatin-Mediated Ototoxicity

Cisplatin is a widely used chemotherapeutic drug for treating various solid tumors. Ototoxicity is a major dose-limiting side effect of cisplatin, which causes progressive and irreversible sensorineural hearing loss. Here, we examined the protective effects of glucose-related protein (GRP) 78 and 94, also identified as endoplasmic reticulum (ER) chaperone proteins, on cisplatin-induced ototoxicity. Treating murine auditory cells (HEI-OC1) with 25 μM cisplatin for 24 h increased cell death resulting from excessive intracellular reactive oxygen species (ROS) accumulation and caspase-involved apoptotic signaling pathway activation with subsequent DNA fragmentation. GRP78 and GRP94 expression was increased in cells treated with 3 nM thapsigargin or 0.1 μg/mL tunicamycin for 24 h, referred to as mild ER stress condition. This condition, prior to cisplatin exposure, attenuated cisplatin-induced ototoxicity. The involvement of GRP78 and GRP94 induction was demonstrated by the knockdown of GRP78 or GRP94 expression using small interfering RNAs, which abolished the protective effect of mild ER stress condition on cisplatin-induced cytotoxicity. These results indicated that GRP78 and GRP94 induction plays a protective role in remediating cisplatin-ototoxicity.

Icariside II ameliorates myocardial ischemia and reperfusion injury by attenuating inflammation and apoptosis through the regulation of the PI3K/AKT signaling pathway

Icariside II (ICAII) is a bioflavonoid compound which has demonstrated anti-oxidative, anti-inflammatory and anti-apoptotic biological activities. However, to the best of our knowledge, whether ICAII can alleviate myocardial ischemia and reperfusion injury (MIRI) remains unknown. The aim of the present study was to determine whether ICAII exerted a protective effect on MIRI and to investigate the potential underlying mechanism of action. A rat MIRI model was established by ligation of the left anterior descending coronary artery for 30 min, followed by a 24 h reperfusion. Pretreatment with ICAII with or without a PI3K/AKT inhibitor was administered at the beginning of reperfusion. Morphological and histological analyses were detected using hematoxylin and eosin staining; the infarct size was measured using Evans blue and 2,3,5-triphenyltetrazolium chloride staining; and plasma levels of lactate dehydrogenase (LDH) and creatine kinase-myocardial band (CK-MB) were analyzed using commercialized assay kits. In addition, the cardiac function was evaluated by echocardiography and the levels of cardiomyocyte apoptosis were determined using a TUNEL staining. The protein expression levels of Bax, Bcl-2, cleaved caspase-3, interleukin-6, tumor necrosis factor-α, PI3K, phosphorylated (p)-PI3K, AKT and p-AKT were analyzed using western blotting analysis. ICAII significantly reduced the infarct size, decreased the release of LDH and CK-MB and improved the cardiac function induced by IR injury. Moreover, ICAII pretreatment significantly inhibited myocardial apoptosis and the inflammatory response. ICAII also upregulated the expression levels of p-PI3K and p-AKT. However, the protective effects of ICAII were abolished by an inhibitor (LY294002) of the PI3K/AKT signaling pathway. In conclusion, the findings of the present study suggested that ICAII may mitigate MIRI by activating the PI3K/AKT signaling pathway.

78 kDa Glucose-Regulated Protein Attenuates Protein Aggregation and Monocyte Adhesion Induced by Angiotensin II in Vascular Cells

Investigations of vascular smooth muscle cell (VSMC) phenotypic modulation due to angiotensin II (AngII) stimulation are important for understanding molecular mechanisms contributing to hypertension and associated vascular pathology. AngII induces endoplasmic reticulum (ER) stress in VSMCs, which has been implicated in hypertensive vascular remodeling. Under ER stress, 78 kDa glucose-regulated protein (GRP78) acts as an endogenous chaperone, as well as a master controller of unfolded protein response (UPR) to maintain protein quality control. However, the potential downstream consequences of ER stress induced by AngII on protein quality control and pro-inflammatory phenotype in VSMCs remain elusive. This study aims to identify protein aggregation as evidence of the disruption of protein quality control in VSMCs, and to test the hypothesis that preservation of proteostasis by overexpression of GRP78 can attenuate the AngII-induced pro-inflammatory phenotype in VSMCs. Increases in protein aggregation and enhanced UPR were observed in VSMCs exposed to AngII, which were mitigated by overexpression of GRP78. Moreover, GRP78 overexpression attenuated enhanced monocyte adhesion to VSMCs induced by AngII. Our results thus indicate that the prevention of protein aggregation can potentially mitigate an inflammatory phenotype in VSMCs, which may suggest an alternative therapy for the treatment of AngII-associated vascular disorders.

GRP78 effectively protect hypoxia/reperfusion-induced myocardial apoptosis via promotion of the Nrf2/HO-1 signaling pathway

Myocardial infarction is a major cause of death worldwide. Despite our understanding of the pathophysiology of myocardial infarction and the therapeutic options for treatment have improved substantially, acute myocardial infarction remains a leading cause of morbidity and mortality. Recent findings revealed that GRP78 could protect myocardial cells against ischemia reperfusion injury‐induced apoptosis, but the exact function and molecular mechanism remains unclear. In this study, we aimed to explore the effects of GRP78 on hypoxia/reperfusion (H/R)‐induced cardiomyocyte injury. Intriguingly, we first observed that GRP78 overexpression significantly protected myocytes from H/R‐induced apoptosis. On mechanism, our work revealed that GRP78 protected myocardial cells from hypoxia/reperfusion‐induced apoptosis via the activation of the Nrf2/HO‐1 signaling pathway. We observed the enhanced expression of Nrf2/HO‐1 in GRP78 overexpressed H9c2 cell, while GRP78 deficiency dramatically antagonized the expression of Nrf2/HO‐1. Furthermore, we found that blocked the Nrf2/HO‐1 signaling by the HO‐1 inhibitor zinc protoporphyrin IX (Znpp) significantly retrieved H9c2 cells apoptosis that inhibited by GRP78 overexpression. Taken together, our findings revealed a new mechanism by which GRP78 alleviated H/R‐induced cardiomyocyte apoptosis in H9c2 cells via the promotion of the Nrf2/HO‐1 signaling pathway.

Levosimendan Protects against Doxorubicin-Induced Cardiotoxicity by Regulating the PTEN/Akt Pathway

BACKGROUND AND AIMS

Myocyte apoptosis plays a critical role in the development of doxorubicin- (DOX-) induced cardiotoxicity. In addition to its cardiotonic effect, laboratory evidence indicates that levosimendan can inhibit apoptosis, but its role in DOX-induced cardiac injury remains unclear. Therefore, the present study is aimed at exploring whether levosimendan could attenuate DOX-induced cardiotoxicity.

METHODS

Levosimendan (1 mg/kg) was administered to mice through oral gavage once daily for 4 weeks, and the mice were also subjected to an intraperitoneal injection of DOX (5 mg/kg) or saline, once a week for 4 weeks, to create a chronic model of DOX-induced cardiotoxicity. A morphological examination and biochemical analysis were used to evaluate the effects of levosimendan. H9C2 cells were used to verify the protective role of levosimendan in vitro. And an Akt inhibitor was utilized to verify the cardioprotection of levosimendan.

RESULTS

Levosimendan reduced the cardiac dysfunction and attenuated the myocardial apoptosis induced by DOX in vivo and in vitro. Levosimendan also inhibited the activation of phosphatase and tensin homolog (PTEN) and upregulated P-Akt expression both in vivo and in vitro. And inhibition of Akt abolished the cardioprotection of levosimendan in vitro.

CONCLUSION

Levosimendan may protect against DOX-induced cardiotoxicity via modulation of the PTEN/Akt signaling pathway.

Membrane-Associated Heat Shock Proteins in Oncology: From Basic Research to New Theranostic Targets

Heat shock proteins (HSPs) constitute a large family of conserved proteins acting as molecular chaperones that play a key role in intracellular protein homeostasis, regulation of apoptosis, and protection from various stress factors (including hypoxia, thermal stress, oxidative stress). Apart from their intracellular localization, members of different HSP families such as small HSPs, HSP40, HSP60, HSP70 and HSP90 have been found to be localized on the plasma membrane of malignantly transformed cells. In the current article, the role of membrane-associated molecular chaperones in normal and tumor cells is comprehensively reviewed with implications of these proteins as plausible targets for cancer therapy and diagnostics.

Proteomic analysis of the cardiac myocyte secretome reveals extracellular protective functions for the ER stress response

The effects of ER stress on protein secretion by cardiac myocytes are not well understood. In this study, the ER stressor thapsigargin (TG), which depletes ER calcium, induced death of cultured neonatal rat ventricular myocytes (NRVMs) in high media volume but fostered protection in low media volume. In contrast, another ER stressor, tunicamycin (TM), a protein glycosylation inhibitor, induced NRVM death in all media volumes, suggesting that protective proteins were secreted in response to TG but not TM. Proteomic analyses of TG- and TM-conditioned media showed that the secretion of most proteins was inhibited by TG and TM; however, secretion of several ER-resident proteins, including GRP78 was increased by TG but not TM. Simulated ischemia, which decreases ER/SR calcium also increased secretion of these proteins. Mechanistically, secreted GRP78 was shown to enhance survival of NRVMs by collaborating with a cell-surface protein, CRIPTO, to activate protective AKT signaling and to inhibit death-promoting SMAD2 signaling. Thus, proteins secreted during ER stress mediated by ER calcium depletion can enhance cardiac myocyte viability.

Mesencephalic astrocyte-derived neurotrophic factor is an ER-resident chaperone that protects against reductive stress in the heart

We have previously demonstrated that ischemia/reperfusion (I/R) impairs endoplasmic reticulum (ER)-based protein folding in the heart and thereby activates an unfolded protein response sensor and effector, activated transcription factor 6α (ATF6). ATF6 then induces mesencephalic astrocyte-derived neurotrophic factor (MANF), an ER-resident protein with no known structural homologs and unclear ER function. To determine MANF's function in the heart in vivo, here we developed a cardiomyocyte-specific MANF-knockdown mouse model. MANF knockdown increased cardiac damage after I/R, which was reversed by AAV9-mediated ectopic MANF expression. Mechanistically, MANF knockdown in cultured neonatal rat ventricular myocytes (NRVMs) impaired protein folding in the ER and cardiomyocyte viability during simulated I/R. However, this was not due to MANF-mediated protection from reactive oxygen species generated during reperfusion. Because I/R impairs oxygen-dependent ER protein disulfide formation and such impairment can be caused by reductive stress in the ER, we examined the effects of the reductive ER stressor DTT. MANF knockdown in NRVMs increased cell death from DTT-mediated reductive ER stress, but not from nonreductive ER stresses caused by thapsigargin-mediated ER Ca²⁺ depletion or tunicamycin-mediated inhibition of ER protein glycosylation. In vitro, recombinant MANF exhibited chaperone activity that depended on its conserved cysteine residues. Moreover, in cells, MANF bound to a model ER protein exhibiting improper disulfide bond formation during reductive ER stress but did not bind to this protein during nonreductive ER stress. We conclude that MANF is an ER chaperone that enhances protein folding and myocyte viability during reductive ER stress.

Chronic activation of hexosamine biosynthesis in the heart triggers pathological cardiac remodeling

The hexosamine biosynthetic pathway (HBP) plays critical roles in nutrient sensing, stress response, and cell growth. However, its contribution to cardiac hypertrophic growth and heart failure remains incompletely understood. Here, we show that the HBP is induced in cardiomyocytes during hypertrophic growth. Overexpression of Gfat1 (glutamine:fructose-6-phosphate amidotransferase 1), the rate-limiting enzyme of HBP, promotes cardiomyocyte growth. On the other hand, Gfat1 inhibition significantly blunts phenylephrine-induced hypertrophic growth in cultured cardiomyocytes. Moreover, cardiac-specific overexpression of Gfat1 exacerbates pressure overload-induced cardiac hypertrophy, fibrosis, and cardiac dysfunction. Conversely, deletion of Gfat1 in cardiomyocytes attenuates pathological cardiac remodeling in response to pressure overload. Mechanistically, persistent upregulation of the HBP triggers decompensated hypertrophy through activation of mTOR while Gfat1 deficiency shows cardioprotection and a concomitant decrease in mTOR activity. Taken together, our results reveal that chronic upregulation of the HBP under hemodynamic stress induces pathological cardiac hypertrophy and heart failure through persistent activation of mTOR.

Metabolic remodeling plays an important role in pathological cardiac hypertrophy. Here, the authors show that hexosamine biosynthetic pathway is elevated in the heart by pressure overload, which contributes to heart failure by persistent activation of mTOR.

The Long Noncoding RNA Hotair Regulates Oxidative Stress and Cardiac Myocyte Apoptosis during Ischemia-Reperfusion Injury

Oxidative stress and subsequent cardiac myocyte apoptosis play central roles in the initiation and progression of myocardial ischemia-reperfusion (I/R) injury. Homeobox transcript antisense intergenic RNA (Hotair) was previously implicated in various heart diseases, yet its role in myocardial I/R injury has not been clearly demonstrated. Mice with cardiac-restricted knockdown or overexpression of Hotair were exposed to I/R surgery. H9c2 cells were cultured and subjected to hypoxia/reoxygenation (H/R) stimulation to further verify the role and underlying mechanisms of Hotair in vitro. Histological examination, molecular detection, and functional parameters were determined in vivo and in vitro. In response to I/R or H/R treatment, Hotair expression was increased in a bromodomain-containing protein 4-dependent manner. Cardiac-restricted knockdown of Hotair exacerbated, whereas Hotair overexpression prevented I/R-induced oxidative stress, cardiac myocyte apoptosis, and cardiac dysfunction. Mechanistically, we observed that Hotair exerted its beneficial effects via activating AMP-activated protein kinase alpha (AMPKα). Further detection revealed that Hotair activated AMPKα through regulating the enhancer of zeste homolog 2/microRNA-451/calcium-binding protein 39 (EZH2/miR-451/Cab39) axis. We provide the evidence that endogenous lncRNA Hotair is an essential negative regulator for oxidative stress and cardiac myocyte apoptosis in myocardial I/R injury, which is dependent on AMPKα activation via the EZH2/miR-451/Cab39 axis.

Designing Novel Therapies to Mend Broken Hearts: ATF6 and Cardiac Proteostasis

The heart exhibits incredible plasticity in response to both environmental and genetic alterations that affect workload. Over the course of development, or in response to physiological or pathological stimuli, the heart responds to fluctuations in workload by hypertrophic growth primarily by individual cardiac myocytes growing in size. Cardiac hypertrophy is associated with an increase in protein synthesis, which must coordinate with protein folding and degradation to allow for homeostatic growth without affecting the functional integrity of cardiac myocytes (i.e., proteostasis). This increase in the protein folding demand in the growing cardiac myocyte activates the transcription factor, ATF6 (activating transcription factor 6α, an inducer of genes that restore proteostasis. Previously, ATF6 has been shown to induce ER-targeted proteins functioning primarily to enhance ER protein folding and degradation. More recent studies, however, have illuminated adaptive roles for ATF6 functioning outside of the ER by inducing non-canonical targets in a stimulus-specific manner. This unique ability of ATF6 to act as an initial adaptive responder has bolstered an enthusiasm for identifying small molecule activators of ATF6 and similar proteostasis-based therapeutics.

Green Tea Polyphenols Modulated Cerebral SOD Expression and Endoplasmic Reticulum Stress in Cardiac Arrest/Cardiopulmonary Resuscitation Rats

BACKGROUND

Reducing cerebral ischemia-reperfusion injury is crucial for improving survival and neurologic outcomes after cardiac arrest/cardiopulmonary resuscitation (CA/CPR). The purpose of this study is to investigate the neuroprotective effects of green tea polyphenols (GTPs) concern with the modulation of endogenous antioxidation and endoplasmic reticulum stress.

METHODS

After subjecting to CA/CPR, rats were randomized into the saline group (NS, n = 40) and the GTPs group (GTPs, n = 40) and the GTPs group (GTPs, n = 40) and the GTPs group (GTPs.

RESULTS

Comparing with that in NS group, GTPs increased the expression of SOD1 and SOD2 at 12 h, 24 h, 48 h, 72 h, and the expression of GRP78 at 24 h and 48 h (p < 0.05) butdecreased caspase-12, CHOP, caspase-3 level, and apoptotic number of neurons (p < 0.05) butdecreased caspase-12, CHOP, caspase-3 level, and apoptotic number of neurons (.

CONCLUSION

GTPs exert neuroprotective effects via mechanisms that may be related to the enhancement of endogenous antioxidant capacity and inhibition of endoplasmic reticulum stress in CA/CPR rat models.

Downregulation of miR-3568 Protects Against Ischemia/Reperfusion-Induced Cardiac Dysfunction in Rats and Apoptosis in H9C2 Cardiomyocytes Through Targeting TRIM62

microRNA-3568 (miR-3568) has been reported to be associated with atherosclerosis. Only few data describe the expression and underlying mechanism of miR-3568 in regulating cardiac ischemia-reperfusion (I/R) injury such as apoptosis. In this study, we therefore sought to investigate the potential function of miR-3568 in simulated I/R-induced apoptosis in H9C2 cardiomyocytes and related signaling pathways involved. Flow cytometry was performed to examine the cell apoptosis. The expression of miR-3568, Survivin, Bcl-2, ERK, JNK, p38, AKT, and STAT3 was measured by western blot and quantitative real-time PCR. The correlation between TRIM62 and p-STAT3 was measured by co-immunoprecipitation and ubiquitination. We found that miR-3568 expression in simulated I/R-induced H9C2 cardiomyocytes was increased in a time-dependent manner. miR-3568 mimic transfection in H9C2 cardiomyocytes significantly enhanced cell apoptosis, decreased the expression of Bcl-2 and Survivin, and activated STAT3 signaling, which were reversed by miR-3568 inhibitor. The direct interaction between miR-3568 and the 3'-untranslated region (UTR) of TRIM62 mRNA was confirmed by dual-luciferase reporter assay. TRIM62 overexpression or AG490, a selective inhibitor of JAK2/STAT3 significantly, significantly inhibited I/R and miR-3568 mimic induced cell apoptosis and STAT3 activation. TRIM62 was found to interact with and induce ubiquitination of p-STAT3. The facilitating role of miR-3568 in I/R injury was also observed in our in vivo rat models. In conclusion, our study suggests that miR-3568 promotes simulated I/R-induced apoptosis in H9C2 cardiomyocytes through targeting TRIM62.

Endoplasmic reticulum stress and focused drug discovery in cardiovascular disease

Endoplasmic reticulum (ER) is an intracellular membranous organelle involved in the synthesis, folding, maturation and post-translation modification of secretory and transmembrane proteins. Therefore, ER is closely related to the maintenance of intracellular homeostasis and the good balance between health and diseases. Endoplasmic reticulum stress (ERS) occurs when unfolded/misfolded proteins accumulate after disturbance of ER environment. In response to ERS, cells trigger an adaptive response called the Unfolded protein response (UPR), which helps cells cope with the stress. In recent years, a large number of studies show that ERS can aggravate cardiovascular diseases. ERS-related proteins expression in cardiovascular diseases is on the rise. Therefore, down-regulation of ERS is critical for alleviating symptoms of cardiovascular diseases, which may be used in the near future to treat cardiovascular diseases. This article reviews the relationship between ERS and cardiovascular diseases and drugs that inhibit ERS. Furthermore, we detail the role of ERS inhibitors in the treatment of cardiovascular disease. Drugs that inhibit ERS are considered as promising strategies for the treatment of cardiovascular diseases.

Crocetin alleviates myocardial ischemia/reperfusion injury by regulating inflammation and the unfolded protein response

Crocetin, a natural compound, has been demonstrated to exhibit beneficial effects in cardiovascular diseases. Previous studies demonstrated that crocetin reduced ischemia/reperfusion (I/R) injury by attenuating cytotoxicity and cellular apoptosis. However, the previous mechanistic studies did not fully elucidate its pharmacological effects on cardiac damage, especially I/R injury. The present study verified its cardioprotective effects in a Langendorff perfusion system, an ex vivo model of I/R. It was demonstrated that crocetin significantly attenuated the activities of pro-inflammatory cytokines and nuclear factor erythroid-2 related factor 2 (Nrf2)/heme oxygenase-1 signaling. The present study provided novel insight that crocetin regulated the unfolded protein response (UPR) and decreased associated protein levels to protect the heart. Furthermore, it was identified that Nrf2 played a key role in the cardioprotective effect of crocetin by attenuating inflammation and the UPR.

GRP78 (Glucose-Regulated Protein of 78 kDa) Promotes Cardiomyocyte Growth Through Activation of GATA4 (GATA-Binding Protein 4)

The heart manifests hypertrophic growth in response to elevation of afterload pressure. Cardiac myocyte growth involves new protein synthesis and membrane expansion, of which a number of cellular quality control machineries are stimulated to maintain function and homeostasis. The unfolded protein response is potently induced during cardiac hypertrophy to enhance protein-folding capacity and eliminate terminally misfolded proteins. However, whether the unfolded protein response directly regulates cardiac myocyte growth remains to be fully determined. Here, we show that GRP78 (glucose-regulated protein of 78 kDa)-an endoplasmic reticulum-resident chaperone and a critical unfolded protein response regulator-is induced by cardiac hypertrophy. Importantly, overexpression of GRP78 in cardiomyocytes is sufficient to potentiate hypertrophic stimulus-triggered growth. At the in vivo level, TG (transgenic) hearts overexpressing GRP78 mount elevated hypertrophic growth in response to pressure overload. We went further to show that GRP78 increases GATA4 (GATA-binding protein 4) level, which may stimulate Anf (atrial natriuretic factor) expression and promote cardiac hypertrophic growth. Silencing of GATA4 in cultured neonatal rat ventricular myocytes significantly diminishes GRP78-mediated growth response. Our results, therefore, reveal that protein-folding chaperone GRP78 may directly enhance cardiomyocyte growth by stimulating cardiac-specific transcriptional factor GATA4.

microRNAs in Cardiovascular Disease: Small Molecules but Big Roles

microRNAs (miRNAs) are an evolutionarily conserved class of small single-stranded noncoding RNAs. The aberrant expression of specific miRNAs has been implicated in the development and progression of diverse cardiovascular diseases. For many decades, miRNA therapeutics has flourished, taking advantage of the fact that miRNAs can modulate gene expression and control cellular phenotypes at the posttranscriptional level. Genetic replacement or knockdown of target miRNAs by chemical molecules, referred to as miRNA mimics or inhibitors, has been used to reverse their abnormal expression as well as their adverse biological effects in vitro and in vivo in an effort to fully implement the therapeutic potential of miRNA-targeting treatment. However, the limitations of the chemical structure and delivery systems are hindering progress towards clinical translation. Here, we focus on the regulatory mechanisms and therapeutic trials of several representative miRNAs in the context of specific cardiovascular diseases; from this basic perspective, we evaluate chemical modifications and delivery vectors of miRNA-based chemical molecules and consider the underlying challenges of miRNA therapeutics as well as the clinical perspectives on their applications.