Post-conditioning protects cardiomyocytes from apoptosis via PKC(epsilon)-interacting with calcium-sensing receptors to inhibit endo(sarco)plasmic reticulum-mitochondria crosstalk

Dapagliflozin attenuates cardiac remodeling and dysfunction in rats with β-adrenergic receptor overactivation through restoring calcium handling and suppressing cardiomyocyte apoptosis

Background: Long-term β-adrenergic receptor (β-AR) activation can impair myocardial structure and function. Dapagliflozin (DAPA) has been reported to improve clinical prognosis in heart failure patients, whereas the exact mechanism remains unclear. Here, we investigated the effects of DAPA against β-AR overactivation toxicity and explored the underlying mechanism.Methods and Results: Rats were randomized to receive saline + placebo, isoproterenol (ISO, 5 mg/kg/day, intraperitoneally) + placebo, or ISO + DAPA (1 mg/kg/day, intragastrically) for 2-week. DAPA treatment improved cardiac function, alleviated myocardial fibrosis, prevented cardiomyocytes (CMs) apoptosis, and decreased the expression of ER stress-mediated apoptosis markers in ISO-treated hearts. In isolated CMs, 2-week ISO stimulation resulted in deteriorated kinetics of cellular contraction and relaxation, increased diastolic intracellular Ca2+ level and decay time constant of Ca2+ transient (CaT) but decreased CaT amplitude and sarcoplasmic reticulum (SR) Ca2+ level. However, DAPA treatment prevented abnormal Ca2+ handling and contractile dysfunction in CMs from ISO-treated hearts. Consistently, DAPA treatment upregulated the expression of SR Ca2+-ATPase protein and ryanodine receptor 2 (RyR2) but reduced the expression of phosphorylated-RyR2, Ca2+/calmodulin-dependent protein kinase II (CaMKII), and phosphorylated-CaMKII in ventricles from ISO-treated rats.Conclusion: DAPA prevented myocardial remodeling and cardiac dysfunction in rats with β-AR overactivation via restoring calcium handling and suppressing ER stress-related CMs apoptosis.

BAP31: Physiological functions and roles in disease

B-cell receptor-associated protein 31 (BAP31 or BCAP31) is a ubiquitously expressed transmembrane protein found mainly in the endoplasmic reticulum (ER), including in mitochondria-associated membranes (MAMs). It acts as a broad-specificity membrane protein chaperone and quality control factor, which can promote different fates for its clients, including ER retention, ER export, ER-associated degradation (ERAD), or evasion of degradation, and it also acts as a MAM tetherer and regulatory protein. It is involved in several cellular processes - it supports ER and mitochondrial homeostasis, promotes proliferation and migration, plays several roles in metabolism and the immune system, and regulates autophagy and apoptosis. Full-length BAP31 can be anti-apoptotic, but can also mediate activation of caspase-8, and itself be cleaved by caspase-8 into p20-BAP31, which promotes apoptosis by mobilizing ER calcium stores at MAMs. BAP31 loss-of-function mutations is the cause of 'deafness, dystonia, and central hypomyelination' (DDCH) syndrome, characterized by severe neurological symptoms and early death. BAP31 is furthermore implicated in a growing number of cancers and other diseases, and several viruses have been found to target it to promote their survival or life cycle progression. The purpose of this review is to provide an overview and examination of the basic properties, functions, mechanisms, and roles in disease of BAP31.

Risk Compounds, Preclinical Toxicity Evaluation, and Potential Mechanisms of Chinese Materia Medica-Induced Cardiotoxicity

Chinese materia medica (CMM) has been applied for the prevention and treatment of diseases for thousands of years. However, arrhythmia, myocardial ischemia, heart failure, and other cardiac adverse reactions during CMM application were gradually reported. CMM-induced cardiotoxicity has aroused widespread attention. Our review aimed to summarize the risk compounds, preclinical toxicity evaluation, and potential mechanisms of CMM-induced cardiotoxicity. All relevant articles published on the PubMed, Embase, and China National Knowledge Infrastructure (CNKI) databases for the latest twenty years were searched and manually extracted. The risk substances of CMM-induced cardiotoxicity are relatively complex. A single CMM usually contains various risk compounds, and the same risk substance may exist in various CMM. The active and risk substances in CMM may be transformed into each other under different conditions, such as drug dosage, medication methods, and body status. Generally, the risk compounds of CMM-induced cardiotoxicity can be classified into alkaloids, terpenoids, steroids, heavy metals, organic acids, toxic proteins, and peptides. Traditional evaluation methods of chemical drug-induced cardiotoxicity primarily include cardiac function monitoring, endomyocardial biopsy, myocardial zymogram, and biomarker determination. In the preclinical stage, CMM-induced cardiotoxicity should be systematically evaluated at the overall, tissue, cellular, and molecular levels, including cardiac function, histopathology, cytology, myocardial zymogram, and biomarkers. Thanks to the development of systematic biology, the higher specificity and sensitivity of biomarkers, such as genes, proteins, and metabolic small molecules, are gradually applied for evaluating CMM-induced cardiotoxicity. Previous studies on the mechanisms of CMM-induced cardiotoxicity focused on a single drug, monomer or components of CMM. The interaction among ion homeostasis (sodium, potassium, and calcium ions), oxidative damage, mitochondrial injury, apoptosis and autophagy, and metabolic disturbance is involved in CMM-induced cardiotoxicity. Clarification on the risk compounds, preclinical toxicity evaluation, and potential mechanisms of CMM-induced cardiotoxicity must be beneficial to guide new CMM development and post-marketed CMM reevaluation.

Activation of the CaR-CSE/H2S pathway confers cardioprotection against ischemia-reperfusion injury

Ischemia-reperfusion (I/R) injury is a multifactorial process triggered when an organ is subjected to transiently reduced blood supply. The result is a cascade of pathological complications and organ damage due to the production of reactive oxygen species following reperfusion. The present study aims to evaluate the role of activated calcium-sensing receptor (CaR)-cystathionine γ-lyase (CSE)/hydrogen sulfide (H2S) pathway in I/R injury. Firstly, an I/R rat model with CSE knockout was constructed. Transthoracic echocardiography, TTC and HE staining were performed to determine the cardiac function of rats following I/R Injury, followed by TUNEL staining observation on apoptosis. Besides, with the attempt to better elucidate how CaR-CSE/H2S affects I/R, in-vitro culture of human coronary artery endothelial cells (HCAECs) was conducted with gadolinium chloride (GdCl3, a CaR agonist), H₂O₂, siRNA against CSE (siCSE), or W7 (a CaM inhibitor). The interaction between CSE and CaM was subsequently detected. Plasma oxidative stress indexes, H2S and CSE, and apoptosis-related proteins were all analyzed following cell apoptosis. We found that H2S elevation led to the improvement whereas CSE knockdown decreased cardiac function in rats with I/R injury. Moreover, oxidative stress injury in I/R rats with CSE knockout was aggravated, while the increased expression of H2S and CSE in the aortic tissues resulted in alleviated the oxidative stress injury. Moreover, increased H2S and CSE levels were found to inhibit cell apoptotic ability in the aortic tissues after I/R injury, thus attenuating oxidative stress injury, accompanied by inhibited expression of apoptosis-related proteins. In HCAECs following oxidative stress treatment, siCSE and CaM inhibitor were observed to reverse the protection of CaR agonist. Coimmunoprecipitation assay revealed the interaction between CSE and CaM. Taken together, all above-mentioned data provides evidence that activation of the CaR-CSE/H2S pathway may confer a potent protective effect in cardiac I/R injury.

Astragaloside IV Reduces Cerebral Ischemia/Reperfusion-Induced Blood-Brain Barrier Permeability in Rats by Inhibiting ER Stress-Mediated Apoptosis

Background

Previous studies proved that AS-IV could prevent blood-brain barrier (BBB) against an increase in permeability. However, its underlying molecular mechanism has not been enlightened yet. The aim of the study is to reveal the potential protective mechanism of astragaloside IV (AS-IV) on the blood-brain barrier after ischemia-reperfusion.

Methods

In vivo, AS-IV neurological protection was measured by Long's five-point scale and 2,3,5-triphenyltetrazolium chloride staining. AS-IV protection for BBB was observed by Evans blue extravasation technique. Endoplasmic reticulum stress and apoptosis-related protein levels were measured by western blot with AS-IV intervention. In vitro, cell apoptosis was analyzed by western blot and flow cytometry.Endoplasmic reticulum stress-related protein levels were quantified through western blot.

Results

AS-IV treatment could decrease the infarct size in rats' brain and protect the BBB against Evans blue permeating through brain, after ischemia/reperfusion, significantly. Further, ischemia/reperfusion or oxygen-glucose deprivation/reperfusion was found to have an increase in endothelial cell apoptosis proteins, such as Bax, Bcl-2, and caspase-3, and endoplasmic reticulum stress-associated proteins, such as phosphorylated PERK and eIF2α, Bip, and CHOP, which were attenuated by AS-IV treatment.

Conclusions

AS-IV can effectively protect the blood-brain barrier and reduce the area of cerebral infarction via inhibiting endoplasmic reticulum stress-mediated apoptosis in endothelial cells.

Sarcoplasmic reticulum and calcium signaling in muscle cells: Homeostasis and disease

The sarco/endoplasmic reticulum is an extensive, dynamic and heterogeneous membranous network that fulfills multiple homeostatic functions. Among them, it compartmentalizes, stores and releases calcium within the intracellular space. In the case of muscle cells, calcium released from the sarco/endoplasmic reticulum in the vicinity of the contractile machinery induces cell contraction. Furthermore, sarco/endoplasmic reticulum-derived calcium also regulates gene transcription in the nucleus, energy metabolism in mitochondria and cytosolic signaling pathways. These diverse and overlapping processes require a highly complex fine-tuning that the sarco/endoplasmic reticulum provides by means of its numerous tubules and cisternae, specialized domains and contacts with other organelles. The sarco/endoplasmic reticulum also possesses a rich calcium-handling machinery, functionally coupled to both contraction-inducing stimuli and the contractile apparatus. Such is the importance of the sarco/endoplasmic reticulum for muscle cell physiology, that alterations in its structure, function or its calcium-handling machinery are intimately associated with the development of cardiometabolic diseases. Cardiac hypertrophy, insulin resistance and arterial hypertension are age-related pathologies with a common mechanism at the muscle cell level: the accumulation of damaged proteins at the sarco/endoplasmic reticulum induces a stress response condition termed endoplasmic reticulum stress, which impairs proper organelle function, ultimately leading to pathogenesis.

CaSR activates PKCδ to induce cardiomyocyte apoptosis via ER stress‑associated apoptotic pathways during ischemia/reperfusion

Endoplasmic reticulum (ER) stress can be activated by ischemia/reperfusion (I/R) injury in cardiomyocytes. Persistent ER stress, with an increase in intracellular Ca2+ ([Ca2+]i) concentration, leads to apoptosis. Protein kinase C (PKC) has a key role in myocardial damage by elevation of [Ca2+]i. The calcium‑sensing receptor (CaSR), a G protein‑coupled receptor, can increase the release of [Ca2+]i from the ER through the inositol triphosphate receptor (IP3R). Intracellular calcium overload has been demonstrated to cause cardiac myocyte apoptosis during I/R. However, the associations between PKC, CaSR and ER stress are not clear. The present study examined the hypothesis that activation of PKCδ by CaSR participates in ER stress‑associated apoptotic pathways within myocardial I/R. Rat hearts were subjected to 30 min of ischemia in vivo, followed by reperfusion for 120 min. GdCl3 (a CaSR activator) was used to elevate the intracellular Ca2+ concentration, but the Ca2+ concentration in the ER was significantly decreased during I/R. Following exposure to GdCl3, expression levels of CaSR, glucose‑regulated protein 78 (GRP78), Caspase‑12, phosphorylated JNK and Caspase‑3 were increased, and the ratios of apoptotic myocardial cells were significantly increased. By contrast, following exposure to rottlerin, a PKCδ inhibitor, the expression levels of these proteins and the ratio of apoptotic myocardial cells were significantly reduced. The present study also demonstrated that PKCδ translocated into the ER to induce an ER stress response and participate in the ER stress‑related apoptosis pathway. These results confirmed that CaSR activated PKCδ to induce cardiomyocyte apoptosis through ER stress‑associated apoptotic pathways during I/R in vivo.

The Cardiotoxicity Induced by Arsenic Trioxide is Alleviated by Salvianolic Acid A via Maintaining Calcium Homeostasis and Inhibiting Endoplasmic Reticulum Stress

Arsenic trioxide (ATO) has been verified as a breakthrough with respect to the management of acute promyelocytic leukemia (APL) in recent decades but associated with some serious adverse phenomena, particularly cardiac functional abnormalities. Salvianolic acid A (Sal A) is a major effective component in treating ATO-induced cardiotoxicity. Therefore, the objective of our study was to assess whether Sal A had protective effects by the regulation of calcium homeostasis and endoplasmic reticulum (ER) stress. For the in vivo study, BALB/c mice were treated with ATO and/or Sal A via daily tail vein injections for two weeks. For the in vitro study, we detected the effects of ATO and/or Sal A in real time using adult rat ventricular myocytes (ARVMs) and an IonOptix MyoCam system. Our results showed that Sal A pretreatment alleviated cardiac dysfunction and Ca²⁺ overload induced by ATO in vivo and vitro. Moreover, Sal A increased sarcoplasmic reticulum (SR) Ca²⁺-ATPase (SERCA) activity and expression, alleviated [Ca²⁺]ER depletion, and decreased ER stress-related protein expression. Sal A protects the heart from ATO-induced injury and its administration correlates with the modulation of SERCA, the recovery of Ca²⁺ homeostasis, and the down-regulation of ER stress-mediated apoptosis.

The Different Facets of Extracellular Calcium Sensors: Old and New Concepts in Calcium-Sensing Receptor Signalling and Pharmacology

The current interest of the scientific community for research in the field of calcium sensing in general and on the calcium-sensing Receptor (CaR) in particular is demonstrated by the still increasing number of papers published on this topic. The extracellular calcium-sensing receptor is the best-known G-protein-coupled receptor (GPCR) able to sense external Ca2+ changes. Widely recognized as a fundamental player in systemic Ca2+ homeostasis, the CaR is ubiquitously expressed in the human body where it activates multiple signalling pathways. In this review, old and new notions regarding the mechanisms by which extracellular Ca2+ microdomains are created and the tools available to measure them are analyzed. After a survey of the main signalling pathways triggered by the CaR, a special attention is reserved for the emerging concepts regarding CaR function in the heart, CaR trafficking and pharmacology. Finally, an overview on other Ca2+ sensors is provided.

Mitochondria in Cardiac Postconditioning

Mitochondria play a pivotal role in cardioprotection. Here we report some fundamental studies which considered the role of mitochondrial components (connexin 43, mitochondrial KATP channels and mitochondrial permeability transition pore) in postconditioning cardioprotection. We briefly discuss the role of mitochondria, reactive oxygen species and gaseous molecules in postconditioning. Also the effects of anesthetics-used as cardioprotective substances-is briefly considered in the context of postconditioning. The role of mitochondrial postconditioning signaling in determining the limitation of cell death is underpinned. Issues in clinical translation are briefly considered. The aim of the present mini-review is to discuss in a historical perspective the role of main mitochondria mechanisms in cardiac postconditioning.

Calcium sensing receptor expression and signalling in cardiovascular physiology and disease

Initially identified in the parathyroidea, the calcium sensing receptor (CaSR) is now recognized as an ubiquitously expressed receptor that exerts specific functions in multiple organs including the cardiovascular system. This review will focus on the role that CaSR plays in vascular and cardiac tissues. In the vasculature, CaSR is expressed in endothelial and smooth muscle cells. CaSR of endothelial cells participates in part to the regulation of local perfusion by linkage of CaSR activation to endothelial hyperpolarization and nitric oxide release. CaSR of smooth muscle cells is involved in the control of proliferation. In the pulmonary vasculature, however, CaSR participates in the onset of pulmonary hypertension, making CaSR antagonism a therapeutic option in this case. In the heart, CaSR is expressed in cardiac fibroblasts and myoyctes, contributing to normal cardiac function and composition of extracellular matrix. More important, activation of CaSR may participate in the cardiac protective effects of ischaemic pre-conditioning. In conclusion, CaSR plays an important physiological role in many regulatory pathways of the cardiovascular system, but due to the complex interaction between various cardiovascular cells and cell-specific effects, use of activators or inhibitors of CaSR for treatment of specific disease forms is yet not on the way.

Vangl2 is essential for myocardial remodeling activated by Wnt/JNK signaling

The Wnt/JNK pathway, responsible for tissue polarity in cardiogenesis in vertebrates, has been shown to play numerous roles during differentiation and development of cardiac myocytes. Van Gogh-like-2 (Vangl2) is a core component that regulates the induction of polarized cellular and tissue morphology during animal development. However, little is known about Wnt/JNK signaling pathway in the process of myocardial remodeling. In present study, we found that activation of Wnt/JNK signaling by Wnt5a stimulates enlargement of cardiomyocyte surface area. The hypertrophic features were inhibited in Vangl2 depleted cells. Meanwhile, Wnt/JNK activation induced cytoskeleton rearrangement but failed to activate these effects in cells lacking Vangl2. Moreover, Wnt/JNK activation significantly increased the cell apoptosis by mediating the mitochondrial permeability transition pore (mPTP) dysfunction, whereas knockdown of Vangl2 partly reversed these effects. These results suggest that activation of Wnt/JNK signaling stimulates myocardial remodeling (cell morphological changes, apoptosis and mitochondrial dysfunction), in which Vangl2 may play an essential role.

Stromal Cell-Derived Factor-1α Alleviates Calcium-Sensing Receptor Activation-Mediated Ischemia/Reperfusion Injury by Inhibiting Caspase-3/Caspase-9-Induced Cell Apoptosis in Rat Free Flaps

Surgical flaps are frequently affected by ischemia/reperfusion (I/R) injury. Calcium-sensing receptor (CaSR) and stromal cell-derived factor-1α (SDF-1α) are closely associated with myocardial I/R injury. This study was performed to evaluate the feasibility of applying SDF-1α to counteract CaSR activation-mediated I/R injury in ischemic free flaps. Free flaps that underwent ischemia for 3 h were equally randomized into five groups: CaCl₂, NPS2143 + CaCl₂, SDF-1α + CaCl₂, AMD3100 + SDF-1α + CaCl₂, and normal saline. The free flaps were harvested to evaluate flap necrosis and neovascularization after 2 h or 7 d of reperfusion. p-CaSR/CaSR was extensively expressed in vascular endothelial cells of free flaps after I/R injury, and activation of the SDF-1α/CXCR4 axis and NPS2143 could reduce the expression of cleaved caspase-3, caspase-9, FAS, Cyt-c, and Bax and increase Bcl-2 expression; the opposite was true after CaSR activation. Interestingly, initiation of the SDF-1α/CXCR4 axis might abrogate CaSR activation-induced I/R injury through enhancement of microvessel density. In conclusion, CaSR might become a novel therapeutic target of free flaps affected by I/R injury. Activation of the SDF-1α/CXCR4 axis and NPS2143 could counteract CaSR activation-mediated I/R injury and promote free flap survival through inhibition of caspase-3/caspase-9-related cell apoptosis and enhancement of neovascularization.

Chronic Intermittent Hypobaric Hypoxia Improves Cardiac Function through Inhibition of Endoplasmic Reticulum Stress

We investigated the role of endoplasmic reticulum stress (ERS) in chronic intermittent hypobaric hypoxia (CIHH)-induced cardiac protection. Adult male Sprague-Dawley rats were exposed to CIHH treatment simulating 5000 m altitude for 28 days, 6 hours per day. The heart was isolated and perfused with Langendorff apparatus and subjected to 30-min ischemia followed by 60-min reperfusion. Cardiac function, infarct size, and lactate dehydrogenase (LDH) activity were assessed. Expression of ERS molecular chaperones (GRP78, CHOP and caspase-12) was assayed by western blot analysis. CIHH treatment improved the recovery of left ventricular function and decreased cardiac infarct size and activity of LDH after I/R compared to control rats. Furthermore, CIHH treatment inhibited over-expression of ERS-related factors including GRP78, CHOP and caspase-12. CIHH-induced cardioprotection and inhibition of ERS were eliminated by application of dithiothreitol, an ERS inducer, and chelerythrine, a protein kinase C (PKC) inhibitor. In conclusion CIHH treatment exerts cardiac protection against I/R injury through inhibition of ERS via PKC signaling pathway.

Effects of Renal Ischemic Postconditioning on Myocardial Ultrastructural Organization and Myocardial Expression of Bcl-2/Bax in Rabbits

We investigated the cardioprotective effect of renal ischemic postconditioning (RI-PostC) and its mechanisms in a rabbit model. Rabbits underwent 60 min of left anterior descending coronary artery occlusion (LADO) and 6 h of reperfusion. The ischemia-reperfusion (IR) group underwent LADO and reperfusion only. In the RI-PostC group, the left renal artery underwent 3 cycles of occlusion for 30 seconds and release for 30 seconds, before the coronary artery was reperfused. In the RI-PostC + GF109203X group, the rabbits received 0.05 mg/kg GF109203X (protein kinase C inhibitor) intravenously for 10 min followed by RI-PostC. Light microscopy and electron microscopy demonstrated that the RI-PostC group showed less pronounced changes, a smaller infarct region, and less apoptosis than the other two groups. Bcl-2 and Bax protein expression did not differ between the IR and RI-PostC + GF109203X groups. However, in the RI-PostC group, Bcl-2 protein expression was significantly higher and Bax protein expression was significantly lower than in the other two groups (P < 0.05). Changes in heart rate and mean arterial pressure were also smaller in the RI-PostC group than in the other two groups. These results indicate that RI-PostC can ameliorate myocardial ischemia-reperfusion injury and increase the Bcl-2/Bax ratio through a mechanism involving protein kinase C.

Signaling Pathways in Cardiac Myocyte Apoptosis

Cardiovascular diseases, the number 1 cause of death worldwide, are frequently associated with apoptotic death of cardiac myocytes. Since cardiomyocyte apoptosis is a highly regulated process, pharmacological intervention of apoptosis pathways may represent a promising therapeutic strategy for a number of cardiovascular diseases and disorders including myocardial infarction, ischemia/reperfusion injury, chemotherapy cardiotoxicity, and end-stage heart failure. Despite rapid growth of our knowledge in apoptosis signaling pathways, a clinically applicable treatment targeting this cellular process is currently unavailable. To help identify potential innovative directions for future research, it is necessary to have a full understanding of the apoptotic pathways currently known to be functional in cardiac myocytes. Here, we summarize recent progress in the regulation of cardiomyocyte apoptosis by multiple signaling molecules and pathways, with a focus on the involvement of these pathways in the pathogenesis of heart disease. In addition, we provide an update regarding bench to bedside translation of this knowledge and discuss unanswered questions that need further investigation.

Ischemic postconditioning and pinacidil suppress calcium overload in anoxia-reoxygenation cardiomyocytes via down-regulation of the calcium-sensing receptor

Ischemic postconditioning (IPC) and ATP sensitive potassium channel (KATP) agonists (e.g. pinacidil and diazoxide) postconditioning are effective methods to defeat myocardial ischemia-reperfusion (I/R) injury, but their specific mechanisms of reducing I/R injury are not fully understood. We observed an intracellular free calcium ([Ca²⁺]_i) overload in Anoxia/reoxygenation (A/R) cardiomyocytes, which can be reversed by KATP agonists diazoxide or pinacidil. The calcium-sensing receptor (CaSR) regulates intracellular calcium homeostasis. CaSR was reported to be involved in the I/R-induced apoptosis in rat cardiomyocytes. We therefore hypothesize that IPC and pinacidil postconditioning (PPC) reduce calcium overload in I/R cardiomyocytes by the down-regulation of CaSR. A/R model was established with adult rat caridomyocyte. mRNA and protein expression of CaSR were detected, IPC, PPC and KATP’s effects on [Ca²⁺]_i concentration was assayed too. IPC and PPC ameliorated A/R insult induced [Ca²⁺]_i overload in cardiomyocytes. In addition, they down-regulated the mRNA and protein level of CaSR as we expected. CaSR agonist spermine and KATP blocker glibenclamide offset IPC’s effects on CaSR expression and [Ca²⁺]_i modulation. Our data indicate that CaSR down-regulation contributes to the mitigation of calcium overload in A/R cardiomyocytes, which may partially represents IPC and KATP’s myocardial protective mechanism under I/R circumstances.

Discrepancy in calcium release from the sarcoplasmic reticulum and intracellular acidic stores for the protection of the heart against ischemia/reperfusion injury

We and others have demonstrated a protective effect of pacing postconditioning (PPC) against ischemia/reperfusion (I/R) injury. However, the mechanisms underlying this protection are not completely clear. In the present study, we evaluated the effects of calcium release from the sarcoplasmic reticulum (SR) and the novel intracellular acidic stores (AS). Isolated rat hearts (n = 6 per group) were subjected to coronary occlusion followed by reperfusion using a modified Langendorff system. Cardiac hemodynamics and contractility were assessed using a data acquisition program, and cardiac injury was evaluated by creatine kinase (CK) and lactate dehydrogenase (LDH) levels. Hearts were subjected to 30 min of regional ischemia, produced by ligation of the left anterior descending (LAD) coronary artery, followed by 30 min of reperfusion. The hearts were also subjected to PPC (3 cycles of 30 s of left ventricle (LV) pacing alternated with 30 s of right atrium (RA) pacing) and/or were treated during reperfusion with agonists or antagonists of release of calcium from SR or AS. PPC significantly (P < 0.05) normalized LV, contractility, and coronary vascular dynamics and significantly (P < 0.001) decreased heart enzyme levels compared to the control treatments. The blockade of SR calcium release resulted in a significant (P < 0.01) recovery in LV function and contractility and a significant reduction in CK and LDH levels (P < 0.01) when applied alone or in combination with PPC. Interestingly, the release of calcium from AS alone or in combination with PPC significantly improved LV function and contractility (P < 0.05) and significantly decreased the CK and LDH levels (P < 0.01) compared to the control treatments. An additive effect was produced when agonism of calcium release from AS or blockade of calcium release from the SR was combined with PPC. Calcium release from AS and blockade of calcium release from the SR protect the heart against I/R. Combining calcium release from acidic stores or blockade of calcium release from the SR with PPC produced a synergistic protective effect.

Exogenous H2S modulates mitochondrial fusion-fission to inhibit vascular smooth muscle cell proliferation in a hyperglycemic state

Aim

Vascular smooth muscle cell (VSMC) proliferation in response to hyperglycemia is an important process in the development of arterial vessel hyperplasia. The shape change of mitochondria is dynamic and closely related to fission and fusion. Hydrogen sulfide (H₂S) was confirmed to have anti-oxidative, anti-inflammatory and anti-proliferative effects. However, little it is known about its effects on mitochondrial morphology induced by hyperglycemia. The aim of the study is to demonstrate that H₂S inhibits VSMC proliferation through regulating mitochondrial fission.

Methods and results

We observe lower H₂S levels as well as higher proliferative protein expression levels for proliferative cell nuclear antigen (PCNA) and cyclin D1 and higher mitochondrial fusion–fission protein expression levels for dynamin-related protein 1 (Drp 1) in human kidney arteries and in db/db mouse aorta. Exogenous H₂S (100 μM NaHS) inhibits vascular smooth muscle cells of human pulmonary aorta(HPASMC) proliferation and migration in response to high glucose using the BrdU and scratch wound repair assays, decreases proliferative protein (PCNA and cyclin D1) expression, and reduces ROS production in the cytoplasm and mitochondria. When HPASMCs proliferate with a high glucose treatment, the mitochondria become small spheres with a short rod-shaped structure, whereas NaHS, a mitochondrial division inhibitor and siDrp prevent VSMC proliferation and maintain mitochondria as stationary and randomly dispersed with fixed structures.

Conclusion

Exogenous H₂S aids in inhibiting mitochondrial fragmentation and affects proliferation in db/db mice and HPASMCs by decreasing Drp 1 expression.

Electronic supplementary material

The online version of this article (doi:10.1186/s13578-016-0102-x) contains supplementary material, which is available to authorized users.

Calcium plays a key role in paraoxon-induced apoptosis in EL4 cells by regulating both endoplasmic reticulum- and mitochondria-associated pathways

CONTEXT AND OBJECTIVE

Paraoxon (POX) is one of the most toxic organophosphorus pesticides, but its toxic mechanisms associated with apoptosis remain unclear. The aim of this study was to investigate calcium-associated mechanisms in POX-induced apoptosis in EL4 cells.

MATERIALS AND METHODS

EL4 cells were exposed to POX for 0-16 h. EGTA was used to chelate Ca(2+ ) in extracellular medium, and heparin and procaine were used to inhibit Ca(2+ )efflux from the endoplasmic reticulum (ER). Z-ATAD-FMK was used to inhibit caspase-12 activity. The apoptotic rate assay, western blotting and immunocytochemistry (ICC) were used to reveal the mechanisms of POX-induced apoptosis.

RESULTS AND DISCUSSION

POX significantly increased the expression and activation of caspase-12 and caspase-3, enhanced expression of calpain 1 and calpain 2, and induced the release of cyt c, but did not change the expression of Grp 78. Inhibiting caspase-12 activity alleviated POX-induced upregulation of calpain 1 and caspase-3, promoted POX-induced upregulation of calpain 2, and reduced POX-induced cyt c release, suggesting that there was a cross-talk between the ER-associated pathway and mitochondria-associated apoptotic signals. Attenuating intracellular calcium concentration with EGTA, heparin or procaine decreased POX-induced upregulation of calpain 1, calpain 2, caspase-12 and caspase-3, and reduced POX-induced cyt c release. After pretreatment with EGTA or procaine, POX significantly promoted expression of Grp 78.

CONCLUSIONS

Calcium played a key role in POX-induced apoptosis in EL4 cells by regulating both ER- and mitochondria-associated pathways. The cross-talk of ER- and mitochondria-associated pathways was accomplished through calcium signal.

Arsenic trioxide triggered calcium homeostasis imbalance and induced endoplasmic reticulum stress-mediated apoptosis in adult rat ventricular myocytes

Arsenic trioxide (ATO) is a potent anticancer drug agent but its clinical use is often limited by severe cardiotoxicity. However, its exact mechanism remains poorly understood. In this study, we simultaneously explored the direct effect of ATO on cardiac contraction in adult rat ventricular myocytes and its effects on Ca²⁺ transient in real time by using an IonOptix MyoCam system. The results showed that ATO increased the amplitude of sarcomere shortening, the maximal velocity of relengthening and shortening (-dL/dt_max and +dL/dt_max), time-to-90% relengthening (TR90), and time-to-peak shortening (TPS), resulting in abnormal cardiomyocyte contraction. Meanwhile, ATO markedly increased the resting Ca²⁺ ratio, amplitude/resting calcium, the maximal velocity of Ca²⁺ shortening and relaxation (+d[Ca²⁺]/dt_max and -d[Ca²⁺]/dt_max), time-to-50% peak [Ca²⁺] _i and the decay rate of [Ca²⁺] _i transients, suggesting that ATO leads to intracellular imbalance of calcium homeostasis. ATO also inhibited sarcoplasmic reticulum Ca²⁺-ATPase 2a (SERCA2a) activity in a time-dependent manner and activated the endoplasmic reticulum (ER) stress reaction. These results revealed that ATO dramatically aggravates Ca²⁺ overload and promotes ER stress, eventually causing abnormal cardiomyocyte contraction in a dose-dependent and time-dependent manner.

Cyclosporine-A mimicked the ischemic pre- and postconditioning-mediated cardioprotection in hypertensive rats: Role of PKCε

Our aim was to assess the action of cyclosporine-A (CsA) against reperfusion injury in spontaneously hypertensive rats (SHR) compared to the effects of ischemic pre- (IP) and postconditioning (IPC), examining the role played by PKCε. Isolated hearts were submitted to the following protocols: IC: 45 min global ischemia (GI) and 1h reperfusion (R); IP: a cycle of 5 min GI and 10 min of R prior to 45 min-GI; and IPC: three cycles of 30s-GI/30s-R at the start of R. Other hearts of the IC, IP and IPC groups received CsA (mitochondrial permeability transition pore inhibitor) or chelerythrine (Che, non-selective PKC inhibitor). Infarct size (IS) was assessed. TBARS and reduced glutathione (GSH) content - as parameters of oxidative damage, the expression of P-Akt, P-GSK-3β, P-PKCε and cytochrome c (Cyc) release - as an index of mitochondrial permeability and the response of isolated mitochondria to Ca(2+) were also measured. IS similarly decreased in preconditioned, postconditioned and CsA treated heart showing the highest values in the combinations IP+CsA and IPC+CsA. TBARS decreased and GSH was partially preserved after all interventions. The content of P-Akt, P-GSK-3β and P-PKCε increased in cytosol and decreased in mitochondria after IP and IPC. In CsA treated hearts these enzymes increased in both fractions reaching the highest values. Cyc release was attenuated and the response of mitochondria to Ca(2+) was improved by the interventions. The beneficial effects of IP and IPC were annulled when PKC was inhibited with Che. A PKCε/VDAC association was also detected. These data show that, in SHR, the CsA treatment mimicked and reinforced the cardioprotective action afforded by IP and IPC in which PKCε-mediated attenuation of mitochondrial permeability appears as the main mechanism involved.

Reduction of Mitochondria–Endoplasmic Reticulum Interactions by Acetylcholine Protects Human Umbilical Vein Endothelial Cells From Hypoxia/Reoxygenation Injury

Objective—

We explored the role of endoplasmic reticulum (ER)–mitochondria Ca 2+ cross talk involving voltage-dependent anion channel-1 (VDAC1)/glucose-regulated protein 75/inositol 1,4,5-trisphosphate receptor 1 complex and mitofusin 2 in endothelial cells during hypoxia/reoxygenation (H/R), and investigated the protective effects of acetylcholine.

Approach and Results—

Acetylcholine treatment during reoxygenation prevented intracellular and mitochondrial Ca 2+ increases and alleviated ER Ca 2+ depletion during H/R in human umbilical vein endothelial cells. Consequently, acetylcholine enhanced mitochondrial membrane potential and inhibited proapoptotic cascades, thereby reducing cell death and preserving endothelial ultrastructure. This effect was likely mediated by the type-3 muscarinic acetylcholine receptor and the phosphatidylinositol 3-kinase/Akt pathway. In addition, interactions among members of the VDAC1/glucose-regulated protein 75/inositol 1,4,5-trisphosphate receptor 1 complex were increased after H/R and were associated with mitochondrial Ca 2+ overload and cell death. Inhibition of the partner of the Ca 2+ channeling complex (VDAC1 siRNA) or a reduction in ER–mitochondria tethering (mitofusin 2 siRNA) prevented the increased protein interaction within the complex and reduced mitochondrial Ca 2+ accumulation and subsequent endothelial cell death after H/R. Intriguingly, acetylcholine could modulate ER–mitochondria Ca 2+ cross talk by inhibiting the VDAC1/glucose-regulated protein 75/inositol 1,4,5-trisphosphate receptor 1 complex and mitofusin 2 expression. Phosphatidylinositol 3-kinase siRNA diminished acetylcholine-mediated inhibition of mitochondrial Ca 2+ overload and VDAC1/glucose-regulated protein 75/inositol 1,4,5-trisphosphate receptor 1 complex formation induced by H/R.

Conclusions—

Our data suggest that ER–mitochondria interplay plays an important role in reperfusion injury in the endothelium and may be a novel molecular target for endothelial protection. Acetylcholine attenuates both intracellular and mitochondrial Ca 2+ overload and protects endothelial cells from H/R injury, presumably by disrupting the ER–mitochondria interaction.

Acetylcholine ameliorates endoplasmic reticulum stress in endothelial cells after hypoxia/reoxygenation via M3 AChR-AMPK signaling

Endoplasmic reticulum (ER) stress is associated with various cardiovascular diseases. However, its pathophysiological relevance and the underlying mechanisms in the context of hypoxia/reoxygenation (H/R) in endothelial cells are not fully understood. Previous findings have suggested that acetylcholine (ACh), the major vagal nerve neurotransmitter, protected against cardiomyocyte injury by activating AMP-activated protein kinase (AMPK). This study investigated the role of ER stress in endothelial cells during H/R and explored the beneficial effects of ACh. Our results showed that H/R triggered ER stress and apoptosis in endothelial cells, evidenced by the elevation of glucose-regulated protein 78, cleaved caspase-12 and C/EBP homologous protein expression. ACh significantly decreased ER stress and terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end labeling positive cells and restored ER ultrastructural changes induced by H/R, possibly via protein kinase-like ER kinase and inositol-requiring kinase 1 pathways. Additionally, 4-diphenylacetoxy-N-methylpiperidine methiodide, a type-3 muscarinic ACh receptor (M3 AChR) inhibitor, abolished ACh-mediated increase in AMPK phosphorylation during H/R. Furthermore, M3 AChR or AMPK siRNA abrogated the ACh-elicited the attenuation of ER stress in endothelial cells, indicating that the salutary effects of ACh were likely mediated by M3 AChR-AMPK signaling. Overall, ACh activated AMPK through M3 AChR, thereby inhibited H/R-induced ER stress and apoptosis in endothelial cells. We have suggested for the first time that AMPK may function as an essential intermediate step between M3 AChR stimulation and inhibition of ER stress-associated apoptotic pathway during H/R, which may help to develop novel therapeutic approaches targeting ER stress to prevent or alleviate ischemia/reperfusion injury.

Elatoside C protects the heart from ischaemia/reperfusion injury through the modulation of oxidative stress and intracellular Ca²⁺ homeostasis

BACKGROUND

We have previously shown that Elatoside C reduces cardiomyocyte apoptosis during ischaemia/reperfusion (I/R). Here, we investigated whether Elatoside C improves heart function in isolated rat hearts subjected to I/R and elucidated the potential mechanisms involved in Elatoside C-induced protection.

METHODS AND RESULTS

Isolated rat hearts were subjected to global ischaemia followed by reperfusion in the absence or presence of Elatoside C. We found that Elatoside C significantly attenuated cardiac dysfunction and depressed oxidative stress induced by I/R. Consistently, Elatoside C prevented I/R-induced mitochondrial dysfunction, which was evident by the inhibition of mitochondrial ROS production, mitochondrial permeability transition pore (mPTP) opening, cytochrome c release from the mitochondria and Bax translocation. Moreover, Elatoside C improved abnormal calcium handling during I/R, including increasing sarcoplasmic reticulum Ca(2+) ATPase (SERCA2) activity, alleviating [Ca(2+)]ER depletion, and reducing the expression levels of ER stress protein markers. All of these protective effects of Elatoside C were partially abolished by the PI3K/Akt inhibitor LY294002, ERK1/2 inhibitor PD98059, and JAK2/STAT3 inhibitor AG490. Further assessment in isolated cardiomyocytes showed that Elatoside C maintained the Ca(2+) transients and cell shortening against I/R.

CONCLUSIONS

Elatoside C protects against cardiac injury during I/R by attenuating oxidative stress and [Ca(2+)]i overload through the activation of both the reperfusion injury salvage kinase (RISK) pathway (including PI3K/Akt and ERK1/2) and the survivor activating factor enhancement (SAFE) pathway (including JAK2/STAT3) and, subsequently, inhibiting the opening of mPTPs.

Anticipatory estrogen activation of the unfolded protein response is linked to cell proliferation and poor survival in estrogen receptor α-positive breast cancer

In response to cell stress, cancer cells often activate the endoplasmic reticulum (EnR) stress sensor, the unfolded protein response (UPR). Little was known about the potential role in cancer of a different mode of UPR activation; anticipatory activation of the UPR prior to accumulation of unfolded protein or cell stress. We show that estrogen, acting via estrogen receptor α (ERα), induces rapid anticipatory activation of the UPR, resulting in increased production of the antiapoptotic chaperone BiP/GRP78, preparing cancer cells for the increased protein production required for subsequent estrogen-ERα induced cell proliferation. In ERα containing cancer cells, the estrogen, 17β-estradiol (E₂) activates the UPR through a phospholipase C γ (PLCγ)-mediated opening of EnR IP₃R calcium channels, enabling passage of calcium from the lumen of the EnR into the cytosol. siRNA knockdown of ERα blocked the estrogen-mediated increase in cytosol calcium and UPR activation. Knockdown or inhibition of PLCγ, or of IP₃R, strongly inhibited the estrogen-mediated increases in cytosol calcium, UPR activation and cell proliferation. E₂-ERα activates all three arms of the UPR in breast and ovarian cancer cells in culture and in a mouse xenograft. Knockdown of ATF6α, which regulates UPR chaperones, blocked estrogen induction of BiP and strongly inhibited E₂-ERα stimulated cell proliferation. Mild and transient UPR activation by estrogen promotes an adaptive UPR response that protects cells against subsequent UPR-mediated apoptosis. Analysis of data from ERα positive breast cancers demonstrates elevated expression of a UPR gene signature that is a powerful new prognostic marker tightly correlated with subsequent resistance to tamoxifen therapy, reduced time to recurrence and poor survival. Thus, as an early component of the E₂-ERα proliferation program, the mitogen estrogen, drives rapid anticipatory activation of the UPR. Anticipatory activation of the UPR is a new role for estrogens in cancer cell proliferation and resistance to therapy.

Silymarin component 2,3-dehydrosilybin attenuates cardiomyocyte damage following hypoxia/reoxygenation by limiting oxidative stress

Ischemic postconditioning and remote conditioning are potentially useful tools for protecting ischemic myocardium. This study tested the hypothesis that 2,3-dehydrosilybin (DHS), a flavonolignan component of Silybum marianum, could attenuate cardiomyocyte damage following hypoxia/reoxygenation by decreasing the generation of reactive oxygen species (ROS). After 5-6 days of cell culture in normoxic conditions the rat neonatal cardiomyocytes were divided into four groups. Control group (9 h at normoxic conditions), hypoxia/reoxygenation group (3 h at 1 % O₂, 94 % N₂and 5 % CO₂followed by 10 min of 10 micromol·l⁻¹DHS and 6 h of reoxygenation in normoxia) and postconditioning group (3 h of hypoxia, three cycles of 5 min reoxygenation and 5 min hypoxia followed by 6 h of normoxia). Cell viability assessed by propidium iodide staining was decreased after DHS treatment consistent with increased levels of lactatedehydrogenase (LDH) after reoxygenation. LDH leakage was significantly reduced when cardiomyocytes in the H/Re group were exposed to DHS. DHS treatment reduced H₂O₂production and also decreased the generation of ROS in the H/Re group as evidenced by a fluorescence indicator. DHS treatment reduces reoxygenation-induced injury in cardiomyocytes by attenuation of ROS generation, H₂O₂and protein carbonyls levels. In addition, we found that both the postconditioning protocol and the DHS treatment are associated with restored ratio of phosphorylated/total protein kinase C epsilon, relative to the H/Re group. In conclusion, our data support the protective role of DHS in hypoxia/reperfusion injury and indicate that DHS may act as a postconditioning mimic.

Simultaneous loss of phospholipase Cδ1 and phospholipase Cδ3 causes cardiomyocyte apoptosis and cardiomyopathy

Phospholipase C (PLC) is a key enzyme in phosphoinositide turnover. Among 13 PLC isozymes, PLCδ1 and PLCδ3 share high sequence homology and similar tissue distribution, and are expected to have functional redundancy in many tissues. We previously reported that the simultaneous loss of PLCδ1 and PLCδ3 caused embryonic lethality because of excessive apoptosis and impaired vascularization of the placenta. Prenatal death of PLCδ1/PLCδ3 double-knockout mice hampered our investigation of the roles of these genes in adult animals. Here, we generated PLCδ1/PLCδ3 double-knockout mice that expressed PLCδ1 in extra-embryonic tissues (cDKO mice) to escape embryonic lethality. The cDKO mice were born at the expected Mendelian ratio, which indicated that the simultaneous loss of PLCδ1 and PLCδ3 in the embryo proper did not impair embryonic development. However, half of the cDKO mice died prematurely. In addition, the surviving cDKO mice spontaneously showed cardiac abnormalities, such as increased heart weight/tibial length ratios, impaired cardiac function, cardiac fibrosis, dilation, and hypertrophy. Predating these abnormalities, excessive apoptosis of their cardiomyocytes was observed. In addition, siRNA-mediated simultaneous silencing of PLCδ1 and PLCδ3 increased apoptosis in differentiated-H9c2 cardiomyoblasts. Activation of Akt and protein kinase C (PKC) θ was impaired in the hearts of the cDKO mice. siRNA-mediated simultaneous silencing of PLCδ1 and PLCδ3 also decreased activated Akt and PKCθ in differentiated-H9c2 cardiomyoblasts. These results indicate that PLCδ1 and PLCδ3 are required for cardiomyocyte survival and normal cardiac function.

Osteopontin stimulates apoptosis in adult cardiac myocytes via the involvement of CD44 receptors, mitochondrial death pathway, and endoplasmic reticulum stress

Increased osteopontin (OPN) expression associates with increased myocyte apoptosis and myocardial dysfunction. The objective of this study was to identify the receptor for OPN and get insight into the mechanism by which OPN induces cardiac myocyte apoptosis. Adult rat ventricular myocytes (ARVMs) and transgenic mice expressing OPN in a myocyte-specific manner were used for in vitro and in vivo studies. Treatment with purified OPN (20 nM) protein or adenoviral-mediated OPN expression induced apoptosis in ARVMs. OPN co-immunoprecipitated with CD44 receptors, not with β1 or β3 integrins. Proximity ligation assay confirmed interaction of OPN with CD44 receptors. Neutralizing anti-CD44 antibodies inhibited OPN-stimulated apoptosis. OPN activated JNKs and increased expression of Bax and levels of cytosolic cytochrome c, suggesting involvement of mitochondrial death pathway. OPN increased endoplasmic reticulum (ER) stress, as evidenced by increased expression of Gadd153 and activation of caspase-12. Inhibition of JNKs using SP600125 or ER stress using salubrinal or caspase-12 inhibitor significantly reduced OPN-stimulated apoptosis. Expression of OPN in adult mouse heart in myocyte-specific manner associated with decreased left ventricular function and increased myocyte apoptosis. In the heart, OPN expression increased JNKs and caspase-12 activities, and expression of Bax and Gadd153. Thus, OPN, acting via CD44 receptors, induces apoptosis in myocytes via the involvement of mitochondrial death pathway and ER stress.

Novel functional role of heat shock protein 90 in protein kinase C-mediated ischemic postconditioning

BACKGROUND

Previous studies have shown that heat shock protein 90 (HSP90) plays a vital role in ischemic preconditioning. The present study was designed to explore whether HSP90 might be responsible for cardioprotection in ischemic postconditioning (PostC).

MATERIALS AND METHODS

Rat hearts underwent 30 min of regional ischemia and 2 h of reperfusion in situ, and PostC was effected with three cycles of 30-s reperfusion and 30-s coronary artery occlusion at the end of ischemia. Ninety rats were randomized into five groups: sham; ischemia-reperfusion (I/R); PostC; 1 mg/kg HSP90 inhibitor geldanamycin (GA) plus PostC (PostC + GA1); and 5 mg/kg GA plus PostC (PostC + GA5). The GA was administered 10 min before reperfusion.

RESULTS

Compared with the I/R group, the PostC group exhibited lower infarct size (46.7 ± 3.0% versus 27.4 ± 4.0%, respectively), release of lactate dehydrogenase and creatine kinase-MB (2252.6 ± 350.8 versus 1713.7 ± 202.4 IU/L, 2804.3 ± 315.7 versus 1846.2 ± 238.0 IU/L, respectively), cardiomyocyte apoptosis (48.4 ± 5.6% versus 27.6 ± 3.8%, respectively), and mitochondrial damage. These beneficial effects were accompanied by an increase in mitochondrial Bcl-2 levels and a decrease in Bax levels. In addition, mitochondrial protein kinase Cepsilon (PKCepsilon) was relatively low in the I/R group but significantly higher in the PostC group, whereas cytosolic PKCepsilon was relatively high in the I/R group but significantly lower in the PostC group, suggesting the translocation of PKCepsilon from cytosol to mitochondria during PostC. However, blocking HSP90 function with GA inhibited the protection of PostC and PKCepsilon mitochondrial translocation.

CONCLUSIONS

HSP90 is critical in PostC-induced cardioprotection, and its activity might be linked to mitochondrial targeting of PKCepsilon, the activation of which results in upregulation of its target gene, Bcl-2, and the inhibition of proapoptotic Bax in mitochondria.

Effect of aqueous extract of sanweitanxiang powder on calcium homeostasis protein expression in ischemic-reperfusion injury rat heart

OBJECTIVE

To investigate the underlying mechanism of reduced myocardial ischemia-reperfusion (I/R) injury in rats using the traditional Tibetan medicine Sanweitanxiang powder (SWTX).

METHODS

Rats were randomly divided into six groups (n = 10) as follows: (a) propranolol dinitrate control group, given propranolol dinitrate 0.02 g/kg for 10 days before I/R, (b) SWTX with a high dose group, given SWTX 1.5 g/kg for 10 days before I/R, (c) SWTX with a medium dose group, given SWTX 1.25 g/kg for 10 days before I/R, (d) sham group (Sham), in which the rat heart was exposed by pericardiotomy but without I/R, (e) SWTX with a low dose group, given SWTX 1.0 g/kg for 10 days before I/R, and (f) I/R injury group. Rats were intragastrically pretreated with propranolol dinitrate or SWTX. After that, the operation to cause ischemia and reperfusion was conducted. The histopathologic changes of rat hearts were observed by hematoxylin and eosin staining and transmission electron microscopy. Ca2+ homeostasis protein expression was determined by western blot.

RESULTS

After SWTX pretreatment, the development of ultrastructural pathological changes from IR injury was attenuated. A decrease in the expression of B-cell lymphoma 2 associated X protein, and an increase in the expression of B-cell lymphoma 2 were observed. An increased activation of extracellular signal regulated kinases were found. Compared with the sham group, the expression of sarcoplasmic reticulum calcium-ATPase, phospholamban, and calsequestrin were all up-regulated after pretreatment with SWTX.

CONCLUSION

The protective mechanism of SWTX pretreatment on myocardial I/R injury might be related to its effect on maintaining the balance of calcium homeostasis in rat heart.

Mitochondria, myocardial remodeling, and cardiovascular disease

The process of muscle remodeling lies at the core of most cardiovascular diseases. Cardiac adaptation to pressure or volume overload is associated with a complex molecular change in cardiomyocytes which leads to anatomic remodeling of the heart muscle. Although adaptive at its beginnings, the sustained cardiac hypertrophic remodeling almost unavoidably ends in progressive muscle dysfunction, heart failure and ultimately death. One of the features of cardiac remodeling is a progressive impairment in mitochondrial function. The heart has the highest oxygen uptake in the human body and accordingly it has a large number of mitochondria, which form a complex network under constant remodeling in order to sustain the high metabolic rate of cardiac cells and serve as Ca(2+) buffers acting together with the endoplasmic reticulum (ER). However, this high dependence on mitochondrial metabolism has its costs: when oxygen supply is threatened, high leak of electrons from the electron transport chain leads to oxidative stress and mitochondrial failure. These three aspects of mitochondrial function (Reactive oxygen species signaling, Ca(2+) handling and mitochondrial dynamics) are critical for normal muscle homeostasis. In this article, we will review the latest evidence linking mitochondrial morphology and function with the process of myocardial remodeling and cardiovascular disease.

Mechanism for reduced pericardial adhesion formation in hypercholesterolemic swine supplemented with alcohol

OBJECTIVE

Previous experiments in Yorkshire swine demonstrated significantly fewer pericardial adhesions and intramyocardial collagen deposition at reoperative sternotomy in animals supplemented with vodka but not with red wine. The purpose of this experiment was to determine a mechanism for adhesion reduction.

METHODS

Twenty-seven male Yorkshire swine were fed a high-cholesterol diet to simulate conditions of coronary artery disease followed by the surgical placement of an ameroid constrictor to the left circumflex coronary artery to induce chronic ischaemia. Postoperatively, control pigs continued their high-fat/cholesterol diet alone, whereas the two experimental groups had diets supplemented with either red wine or vodka for 7 weeks followed by reoperative sternotomy and cardiac harvest.

RESULTS

The expression of related adhesion focal tyrosine kinase (RAFTK) and caspase 3 in the sodium dodecyl sulphate (SDS)-soluble myocardial fraction was significantly higher only in the vodka-supplemented group. In the more soluble fraction, the expression of caspase 3, cleaved caspase 3 and caspase 9 was lower in both the vodka and red wine treatment groups.

CONCLUSIONS

In the SDS-soluble lysate fraction, likely representing the transmembrane/cell-extracellular matrix (ECM), a significant increase in RAFTK and caspase 3 expression was seen only in the vodka-treated animals, which may explain why this group demonstrated significantly fewer pericardial adhesions. Caspase expression/signalling was not increased in the more soluble myocardial lysate, suggesting that the increased apoptotic signalling was specific to the epicardial-ECM.

Phosphorylation of mammalian cytochrome c and cytochrome c oxidase in the regulation of cell destiny: respiration, apoptosis, and human disease

The mitochondrial oxidative phosphorylation (OxPhos) system not only generates the vast majority of cellular energy, but is also involved in the generation of reactive oxygen species (ROS), and apoptosis. Cytochrome c (Cytc) and cytochrome c oxidase (COX) represent the terminal step of the electron transport chain (ETC), the proposed rate-limiting reaction in mammals. Cytc and COX show unique regulatory features including allosteric regulation, isoform expression, and regulation through cell signaling pathways. This chapter focuses on the latter and discusses all mapped phosphorylation sites based on the crystal structures of COX and Cytc. Several signaling pathways have been identified that target COX including protein kinase A and C, receptor tyrosine kinase, and inflammatory signaling. In addition, four phosphorylation sites have been mapped on Cytc with potentially large implications due to its multiple functions including apoptosis, a pathway that is overactive in stressed cells but inactive in cancer. The role of COX and Cytc phosphorylation is reviewed in a human disease context, including cancer, inflammation, sepsis, asthma, and ischemia/reperfusion injury as seen in myocardial infarction and ischemic stroke.

Calcium-mediated cell death during myocardial reperfusion

Reperfusion may induce additional cell death in patients with acute myocardial infarction receiving primary angioplasty or thrombolysis. Altered intracellular Ca(2+) handling was initially considered an essential mechanism of reperfusion-induced cardiomyocyte death. However, more recent studies have demonstrated the importance of Ca(2+)-independent mechanisms that converge on mitochondrial permeability transition (MPT) and are shared by cardiomyocytes and other cell types. This article analyses the importance of Ca(2+)-dependent cell death in light of these new observations. Altered Ca(2+) handling includes increased cytosolic Ca(2+) levels, leading to activation of calpain-mediated proteolysis and sarcoplasmic reticulum-driven oscillations; this can induce hypercontracture, but also MPT due to the privileged Ca(2+) transfer between sarcoplasmic reticulum and mitochondria through cytosolic Ca(2+) microdomains. In the opposite direction, permeability transition can worsen altered Ca(2+) handling and favour hypercontracture. Ca(2+) appears to play an important role in cell death during the initial minutes of reperfusion, particularly after brief periods of ischaemia. Developing effective and safe treatments to prevent Ca(2+)-mediated cardiomyocyte death in patients with transient ischaemia, by targeting Ca(2+) influx, intracellular Ca(2+) handling, or Ca(2+)-induced cell death effectors, is an unmet challenge with important therapeutic implications and large potential clinical impact.

Overexpressing GRP78 influences Ca2+ handling and function of mitochondria in astrocytes after ischemia-like stress

Ca(2+) transfer from endoplasmic reticulum (ER) to mitochondria at contact sites between the organelles can induce mitochondrial dysfunction and programmed cell death after stress. The ER-localized chaperone glucose-regulated protein 78kDa (GRP78/BiP) protects neurons against excitotoxicity and apoptosis. Here we show that overexpressing GRP78 protects astrocytes against ischemic injury, reduces net flux of Ca(2+) from ER to mitochondria, increases Ca(2+) uptake capacity in isolated mitochondria, reduces free radical production, and preserves respiratory activity and mitochondrial membrane potential after stress. We conclude that GRP78 influences ER-mitochondrial Ca(2+) crosstalk to maintain mitochondrial function and protect astrocytes from ischemic injury.