HL-1 mouse cardiomyocyte injury and death after simulated ischemia and reperfusion: roles of pH, Ca2+-independent phospholipase A2, and Na+/H+ exchange

Lysophosphatidylserine induces necrosis in pressure overloaded male mouse hearts via G protein coupled receptor 34

Heart failure is a leading cause of mortality in developed countries. Cell death is a key player in the development of heart failure. Calcium-independent phospholipase A₂β (iPLA₂β) produces lipid mediators by catalyzing lipids and induces nuclear shrinkage in caspase-independent cell death. Here, we show that lysophosphatidylserine generated by iPLA₂β induces necrotic cardiomyocyte death, as well as contractile dysfunction mediated through its receptor, G protein-coupled receptor 34 (GPR34). Cardiomyocyte-specific iPLA₂β-deficient male mice were subjected to pressure overload. While control mice showed left ventricular systolic dysfunction with necrotic cardiomyocyte death, iPLA₂β-deficient mice preserved cardiac function. Lipidomic analysis revealed a reduction of 18:0 lysophosphatidylserine in iPLA₂β-deficient hearts. Knockdown of Gpr34 attenuated 18:0 lysophosphatidylserine-induced necrosis in neonatal male rat cardiomyocytes, while the ablation of Gpr34 in male mice reduced the development of pressure overload-induced cardiac remodeling. Thus, the iPLA₂β-lysophosphatidylserine-GPR34-necrosis signaling axis plays a detrimental role in the heart in response to pressure overload.

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.

Plasma exosomes characterization reveals a perioperative protein signature in older patients undergoing different types of on-pump cardiac surgery

Although exosomes are extracellular nanovesicles mainly involved in cardioprotection, it is not known whether plasma exosomes of older patients undergoing different types of on-pump cardiac surgery protect cardiomyocytes from apoptosis. Since different exosomal proteins confer pro-survival effects, we have analyzed the protein cargo of exosomes circulating early after aortic unclamping. Plasma exosomes and serum cardiac troponin I levels were measured in older cardiac surgery patients (NYHA II-III) who underwent first-time on-pump coronary artery bypass graft (CABG; n = 15) or minimally invasive heart valve surgery (mitral valve repair, n = 15; aortic valve replacement, n = 15) at induction of anesthesia (T0, baseline), 3 h (T1) and 72 h (T2) after aortic unclamping. Anti-apoptotic role of exosomes was assessed in HL-1 cardiomyocytes exposed to hypoxia/re-oxygenation (H/R) by TUNEL assay. Protein exosomal cargo was characterized by mass spectrometry approach. Exosome levels increased at T1 (P < 0.01) in accord with troponin values in all groups. In CABG group, plasma exosomes further increased at T2 (P < 0.01) whereas troponin levels decreased. In vitro, all T1-exosomes prevented H/R-induced apoptosis. A total of 340 exosomal proteins were identified in all groups, yet 10% of those proteins were unique for each surgery type. In particular, 22 and 12 pro-survival proteins were detected in T1-exosomes of heart valve surgery and CABG patients, respectively. Our results suggest that endogenous intraoperative cardioprotection in older cardiac surgery patients is early mediated by distinct exosomal proteins regardless of surgery type.

Recovery from hypoxia-induced internalization of cardiac Na+ /H + exchanger 1 requires an adequate intracellular store of antioxidants

The heart is highly active metabolically but relatively underperfused and, therefore, vulnerable to ischemia. In addition to acidosis, a key component of ischemia is hypoxia that can modulate gene expression and protein function as part of an adaptive or even maladaptive response. Here, using cardiac-derived HL-1 cells, we investigate the effect of various hypoxic stimuli on the expression and activity of Na⁺ /H ⁺ exchanger 1 (NHE1), a principal regulator of intracellular pH. Acute (10 min) anoxia produced a reversible decrease in the sarcolemmal NHE1 activity attributable to NHE1 internalization. Treatment with either 1% O ₂ or dimethyloxaloylglycine (DMOG; 1 mM) for 48-hr stabilized hypoxia-inducible factor 1 and reduced the sarcolemmal NHE1 activity by internalization, but without a change in total NHE1 immunoreactivity or message levels of the coding gene ( SLC9A1) determined in whole-cell lysates. Unlike the effect of DMOG, which was rapidly reversed on washout, reoxygenation after a prolonged period of hypoxia did not reverse the effects on NHE1, unless media were also supplemented with a membrane-permeant derivative of glutathione (GSH). Without a prior hypoxic episode, GSH supplementation had no effect on the NHE1 activity. Thus, posthypoxic NHE1 reinsertion can only take place if cells have a sufficient reservoir of a reducing agent. We propose that oxidative stress under prolonged hypoxia depletes intracellular GSH to an extent that curtails NHE1 reinsertion once the hypoxic stimulus is withdrawn. This effect may be cardioprotective, as rapid postischaemic restoration of the NHE1 activity is known to trigger reperfusion injury by producing an intracellular Na ⁺ -overload, which is proarrhythmogenic.

Single glucose molecule transport process revealed by force tracing and molecular dynamics simulations

Transporting individual molecules across cell membranes is a fundamental process in cellular metabolism. Although the crystal diffraction technique has greatly contributed to our understanding of the structures of the involved transporters, a description of the dynamic transport mechanism at the single-molecule level has been extremely elusive. In this study, we applied atomic force microscopy (AFM)-based force tracing to directly monitor the transport of a single molecule, d-glucose, across living cell membranes. Our results show that the force to transport a single molecule of d-glucose across cell membranes is 37 ± 9 pN, and the corresponding transport interval is approximately 20 ms, while the average speed is approximately 0.3 μm s^-1. Furthermore, our calculated force profile from molecular dynamics simulations showed quantitatively good agreement with the force tracing observation and revealed detailed information regarding the glucose transport path, indicating that two salt bridges, K38/E299 and K300/E426, play critical roles during glucose transport across glucose transporter 1 (GLUT1). This role was further verified using biological experiments that disrupted these two bridges and measured the uptake of glucose into the cells. Our approaches led to the first unambiguous description of the glucose transport process across cell membranes at the single-molecule level and demonstrated the biological importance of the two salt bridges for transporting glucose across GLUT1.

Tumor microenvironment conditions alter Akt and Na+/H+ exchanger NHE1 expression in endothelial cells more than hypoxia alone: implications for endothelial cell function in cancer

BACKGROUND

Chronic angiogenesis is a hallmark of most tumors and takes place in a hostile tumor microenvironment (TME) characterized by hypoxia, low nutrient and glucose levels, elevated lactate and low pH. Despite this, most studies addressing angiogenic signaling use hypoxia as a proxy for tumor conditions. Here, we compared the effects of hypoxia and TME conditions on regulation of the Na⁺/H⁺ exchanger NHE1, Ser/Thr kinases Akt1-3, and downstream effectors in endothelial cells.

METHODS

Human umbilical vein endothelial cells (HUVEC) and Ea.hy926 endothelial cells were exposed to simulated TME (1% hypoxia, low serum, glucose, pH, high lactate) or 1% hypoxia for 24 or 48 h, with or without NHE1 inhibition or siRNA-mediated knockdown. mRNA and protein levels of NHE1, Akt1-3, and downstream effectors were assessed by qPCR and Western blotting, vascular endothelial growth factor (VEGF) release by ELISA, and motility by scratch assay.

RESULTS

Within 24 h, HIF-1α level and VEGF mRNA level were increased robustly by TME and modestly by hypoxia alone. The NHE1 mRNA level was decreased by both hypoxia and TME, and NHE1 protein was reduced by TME in Ea.hy926 cells. Akt1-3 mRNA was detected in HUVEC and Ea.hy926 cells, Akt1 most abundantly. Akt1 protein expression was reduced by TME yet unaffected by hypoxia, while Akt phosphorylation was increased by TME. The Akt loss was partly reversed by MCF-7 human breast cancer cell conditioned medium, suggesting that in vivo, the cancer cell secretome may compensate for adverse effects of TME on endothelial cells. TME, yet not hypoxia, reduced p70S6 kinase activity and ribosomal protein S6 phosphorylation and increased eIF2α phosphorylation, consistent with inhibition of protein translation. Finally, TME reduced Retinoblastoma protein phosphorylation and induced poly-ADP-ribose polymerase (PARP) cleavage consistent with inhibition of proliferation and induction of apoptosis. NHE1 knockdown, mimicking the effect of TME on NHE1 expression, reduced Ea.hy926 migration. TME effects on HIF-1α, VEGF, Akt, translation, proliferation or apoptosis markers were unaffected by NHE1 knockdown/inhibition.

CONCLUSIONS

NHE1 and Akt are downregulated by TME conditions, more potently than by hypoxia alone. This inhibits endothelial cell migration and growth in a manner likely modulated by the cancer cell secretome.

Moderate therapeutic hypothermia induces multimodal protective effects in oxygen-glucose deprivation/reperfusion injured cardiomyocytes

OBJECTIVE

Therapeutic hypothermia has been shown to attenuate myocardial cell death due to ischemia/reperfusion injury. However, cellular mechanisms of cooling remain to be elucidated. Especially during reperfusion, mitochondrial dysfunction contributes to cell death by releasing apoptosis inductors. The aim of the present study was to investigate the effects of moderate therapeutic hypothermia (33.5°C) on mitochondrial mediated apoptosis in ischemia/reperfusion-injured cardiomyocytes.

METHODS

Ischemic injury was simulated by oxygen-glucose deprivation for 6h in glucose/serum-free medium at 0.2% O₂ in mouse atrial HL-1 cardiomyocytes. Simulation of reperfusion was achieved by restoration of nutrients in complete supplemented medium and incubation at 21% O₂. Early application of therapeutic hypothermia, cooling during the oxygen-glucose deprivation phase, was initiated after 3h of oxygen-glucose deprivation and maintained for 24h. Mitochondrial membrane integrity was assessed by cytochrome c and AIF protein releases. Furthermore, mitochondria were stained with MitoTracker Red and intra-cellular cytochrome c localization was visualized by immunofluorescence staining. Moreover, anti-apoptotic Bcl-2 and Hsp70 as well as phagophore promoting LC3-II protein expressions were analyzed by Western-blot analysis.

RESULTS

Therapeutic hypothermia initiated during oxygen-glucose deprivation significantly reduced mitochondrial release of cytochrome c and AIF in cardiomyocytes during reperfusion. Secondly, anti-apoptotic Bcl-2/Bax ratio and Hsp70 protein expressions were significantly upregulated due to hypothermia, indicating an inhibition of both caspase-dependent and -independent apoptosis. Furthermore, cardiomyocytes treated with therapeutic hypothermia showed increased LC3-II protein levels associated with the mitochondria during the first 3h of reperfusion, indicating the initiation of phagophores formation and sequestration of presumably damaged mitochondrion.

CONCLUSION

Early application of therapeutic hypothermia effectively inhibited cardiomyocyte cell death due to oxygen-glucose deprivation/reperfusion-induced injury via multiple pathways. As hypothermia preserved mitochondrial membrane integrity, which resulted in reduced cytochrome c and AIF releases, induction of both caspase-dependent and -independent apoptosis was minimized. Secondly, cooling attenuated intrinsic apoptosis via Hsp70 upregulation and increasing anti-apoptotic Bcl-2/Bax ratio. Moreover, therapeutic hypothermia promoted mitochondrial associated LC3-II during the early phase of reperfusion, possibly leading to the sequestration and degradation of damaged mitochondrion to attenuate the activation of cell death.

MitoNEET Protects HL-1 Cardiomyocytes from Oxidative Stress Mediated Apoptosis in an In Vitro Model of Hypoxia and Reoxygenation

The iron-sulfur cluster containing protein mitoNEET is known to modulate the oxidative capacity of cardiac mitochondria but its function during myocardial reperfusion injury after transient ischemia is unknown. The purpose of this study was to analyze the impact of mitoNEET on oxidative stress induced cell death and its relation to the glutathione-redox system in cardiomyocytes in an in vitro model of hypoxia and reoxygenation (H/R). Our results show that siRNA knockdown (KD) of mitoNEET caused an 1.9-fold increase in H/R induced apoptosis compared to H/R control while overexpression of mitoNEET caused a 53% decrease in apoptosis. Necrosis was not affected. Apoptosis of both, mitoNEET-KD and control cells was diminished to comparable levels by using the antioxidants Tiron and glutathione compound glutathione reduced ethyl ester (GSH-MEE), indicating that mitoNEET-dependent apoptosis is mediated by oxidative stress. The interplay between mitoNEET and glutathione redox system was assessed by treating cardiomyocytes with 2-acetylamino-3-[4-(2-acetylamino-2-carboxyethylsulfanylthio-carbonylamino) phenylthiocarbamoylsulfanyl] propionic acid (2-AAPA), known to effectively inhibit glutathione reductase (GSR) and to decrease the GSH/GSSG ratio. Surprisingly, inhibition of GSR-activity to 20% by 2-AAPA decreased apoptosis of control and mitoNEET-KD cells to 23% and 25% respectively, while at the same time mitoNEET-protein was increased 4-fold. This effect on mitoNEET-protein was not accessible by mitoNEET-KD but was reversed by GSH-MEE. In conclusion we show that mitoNEET protects cardiomyocytes from oxidative stress-induced apoptosis during H/R. Inhibition of GSH-recycling, GSR-activity by 2-AAPA increased mitoNEET-protein, accompanied by reduced apoptosis. Addition of GSH reversed these effects suggesting that mitoNEET can in part compensate for imbalances in the antioxidative glutathione-system and therefore could serve as a potential therapeutic approach for the oxidatively stressed myocardium.

Mitochondrial events responsible for morphine's cardioprotection against ischemia/reperfusion injury

Morphine may induce cardioprotection by targeting mitochondria, but little is known about the exact mitochondrial events that mediate morphine's protection. We aimed to address the role of the mitochondrial Src tyrosine kinase in morphine's protection. Isolated rat hearts were subjected to 30 min ischemia and 2h of reperfusion. Morphine was given before the onset of ischemia. Infarct size and troponin I release were measured to evaluate cardiac injury. Oxidative stress was evaluated by measuring mitochondrial protein carbonylation and mitochondrial ROS generation. HL-1 cells were subjected to simulated ischemia/reperfusion and LDH release and mitochondrial membrane potential (ΔΨm) were measured. Morphine reduced infarct size as well as cardiac troponin I release which were aborted by the selective Src tyrosine kinase inhibitors PP2 and Src-I1. Morphine also attenuated LDH release and prevented a loss of ΔΨm at reperfusion in a Src tyrosine kinase dependent manner in HL-1 cells. However, morphine failed to reduce LDH release in HL-1 cells transfected with Src siRNA. Morphine increased mitochondrial Src phosphorylation at reperfusion and this was abrogated by PP2. Morphine attenuated mitochondrial protein carbonylation and mitochondrial superoxide generation at reperfusion through Src tyrosine kinase. The inhibitory effect of morphine on the mitochondrial complex I activity was reversed by PP2. These data suggest that morphine induces cardioprotection by preventing mitochondrial oxidative stress through mitochondrial Src tyrosine kinase. Inhibition of mitochondrial complex I at reperfusion by Src tyrosine kinase may account for the prevention of mitochondrial oxidative stress by morphine.

Maintenance of HL-1 cardiomyocyte functional activity in PEGylated fibrin gels

Successful cellular cardiomyoplasty is dependent on biocompatible materials that can retain the cells in the myocardium in order to promote host tissue repair following myocardial infarction. A variety of methods have been explored for incorporating a cell-seeded matrix into the heart, the most popular options being direct application of an injectable system or surgical implantation of a patch. Fibrin-based gels are suitable for either of these approaches, as they are biocompatible and have mechanical properties that can be tailored by adjusting the initial fibrinogen concentration. We have previously demonstrated that conjugating amine-reactive homo-bifunctional polyethylene glycol (PEG) to the fibrinogen prior to crosslinking with thrombin can increase stability both in vivo and in vitro. Similarly, when mesenchymal stem cells are combined with PEGylated fibrin and injected into the myocardium, cell retention can be significantly increased and scar tissue reduced following myocardial infarction. We hypothesized that this gel system could similarly promote cardiomyocyte viability and function in vitro, and that optimizing the mechanical properties of the hydrogel would enhance contractility. In this study, we cultured HL-1 cardiomyocytes either on top of plated PEGylated fibrin (2D) or embedded in 3D gels and evaluated cardiomyocyte function by assessing the expression of cardiomyocyte specific markers, sarcomeric α-actin, and connexin 43, as well as contractile activity. We observed that the culture method can drastically affect the functional phenotype of HL-1 cardiomyocytes, and we present data suggesting the potential use of PEGylated fibrin gel layers to prepare a sheet-like construct for myocardial regeneration.

Cardiac thromboxane A2 receptor activation does not directly induce cardiomyocyte hypertrophy but does cause cell death that is prevented with gentamicin and 2-APB

Background

We have previously shown that the thromboxane (TXA2) receptor agonist, U46619, can directly induce ventricular arrhythmias that were associated with increases in intracellular calcium in cardiomyocytes. Since TXA2 is an inflammatory mediator and induces direct calcium changes in cardiomyocytes, we hypothesized that TXA2 released during ischemia or inflammation could also cause cardiac remodeling.

Methods

U46619 (0.1-10 μM) was applied to isolated adult mouse ventricular primary cardiomyocytes, mouse ventricular cardiac muscle strips, and cultured HL-1 cardiomyocytes and markers of hypertrophy and cell death were measured.

Results

We found that TXA2 receptors were expressed in ventricular cardiomyocytes and were functional via calcium imaging. U46619 treatment for 24 h did not increase expression of pathological hypertrophy genes (atrial natriuretic peptide, β-myosin heavy chain, skeletal muscle α-actin) and it did not increase protein synthesis. There was also no increase in cardiomyocyte size after 48 h treatment with U46619 as measured by flow cytometry. However, U46619 (0.1-10 μM) caused a concentration-dependent increase in cardiomyocyte death (trypan blue, MTT assays, visual cell counts and TUNEL stain) after 24 h. Treatment of cells with the TXA2 receptor antagonist SQ29548 and inhibitors of the IP3 pathway, gentamicin and 2-APB, eliminated the increase in cell death induced by U46619.

Conclusions

Our data suggests that TXA2 does not induce cardiac hypertrophy, but does induce cell death that is mediated in part by IP3 signaling pathways. These findings may provide important therapeutic targets for inflammatory-induced cardiac apoptosis that can lead to heart failure.

Group VIA phospholipase A2 mitigates palmitate-induced β-cell mitochondrial injury and apoptosis

Palmitate (C16:0) induces apoptosis of insulin-secreting β-cells by processes that involve generation of reactive oxygen species, and chronically elevated blood long chain free fatty acid levels are thought to contribute to β-cell lipotoxicity and the development of diabetes mellitus. Group VIA phospholipase A2 (iPLA2β) affects β-cell sensitivity to apoptosis, and here we examined iPLA2β effects on events that occur in β-cells incubated with C16:0. Such events in INS-1 insulinoma cells were found to include activation of caspase-3, expression of stress response genes (C/EBP homologous protein and activating transcription factor 4), accumulation of ceramide, loss of mitochondrial membrane potential, and apoptosis. All of these responses were blunted in INS-1 cells that overexpress iPLA2β, which has been proposed to facilitate repair of oxidized mitochondrial phospholipids, e.g. cardiolipin (CL), by excising oxidized polyunsaturated fatty acid residues, e.g. linoleate (C18:2), to yield lysophospholipids, e.g. monolysocardiolipin (MLCL), that can be reacylated to regenerate the native phospholipid structures. Here the MLCL content of mouse pancreatic islets was found to rise with increasing iPLA2β expression, and recombinant iPLA2β hydrolyzed CL to MLCL and released oxygenated C18:2 residues from oxidized CL in preference to native C18:2. C16:0 induced accumulation of oxidized CL species and of the oxidized phospholipid (C18:0/hydroxyeicosatetraenoic acid)-glycerophosphoethanolamine, and these effects were blunted in INS-1 cells that overexpress iPLA2β, consistent with iPLA2β-mediated removal of oxidized phospholipids. C16:0 also induced iPLA2β association with INS-1 cell mitochondria, consistent with a role in mitochondrial repair. These findings indicate that iPLA2β confers significant protection of β-cells against C16:0-induced injury.

Murine atrial HL-1 cell line is a reliable model to study drug metabolizing enzymes in the heart

HL-1 cells are currently the only cells that spontaneously contract while maintaining a differentiated cardiac phenotype. Thus, our objective was to examine murine HL-1 cells as a new in vitro model to study drug metabolizing enzymes. We examined the expression of cytochrome P450s (Cyps), phase II enzymes, and nuclear receptors and compared their levels to mice hearts. Our results demonstrated that except for Cyp4a12 and Cyp4a14 all Cyps, phase II enzymes: glutathione-S-transferases (Gsts), heme oxygenase-1 (HO-1), and NAD(P)H: quinone oxidoreductase (Nqo1), nuclear receptors: aryl hydrocarbon receptor (AhR), constitutive androstane receptor (CAR), pregnane X receptor (PXR), and peroxisome proliferator activated receptor (PPAR-alpha) were all constitutively expressed in HL-1 cells. Cyp2b19, Cyp2c29, Cyp2c38, Cyp2c40, and Cyp4f16 mRNA levels were higher in HL-1 cells compared to mice hearts. Cyp2b9, Cyp2c44, Cyp2j9, Cyp2j11, Cyp2j13, Cyp4f13, Cyp4f15 mRNA levels were expressed to the same extent to that of mice hearts. Cyp1a1, Cyp1a2, Cyp1b1, Cyp2b10, Cyp2d10, Cyp2d22, Cyp2e1, Cyp2j5, Cyp2j6, Cyp3a11, Cyp4a10, and Cyp4f18 mRNA levels were lower in HL-1 cells compared to mice hearts. Moreover, 3-methylcholanthrene induced Cyp1a1 while fenofibrate induced Cyp2j9 and Cyp4f13 mRNA levels in HL-1 cells. Examining the metabolism of arachidonic acid (AA) by HL-1 cells, our results demonstrated that HL-1 cells metabolize AA to epoxyeicosatrienoic acids, dihydroxyeicosatrienoic acids, and 20-hydroxyeicosatetraenoic acids. In conclusion, HL-1 cells provide a valuable in vitro model to study the role of Cyps and their associated AA metabolites in addition to phase II enzymes in cardiovascular disease states.

Impact of hypoxia, simulated ischemia and reperfusion in HL-1 cells on the expression of FKBP12/FKBP12.6 and intracellular calcium dynamics

AIMS

To establish a cardiac cell culture model for simulated ischemia and reperfusion and in this model investigate the impact of simulated ischemia and reperfusion on expression of the calcium handling proteins FKBP12 and FKBP12.6, and intracellular calcium dynamics.

METHODS

HL-1 cell cultures were exposed to normoxia (as control), hypoxia, simulated ischemia (HEDA) or HEDA+reactive oxygen species (ROS) for up to 24 h and after HEDA, with or without ROS, followed or not by simulated reperfusion (REPH) for 6 h. Viability was analyzed with a trypan blue exclusion method. Cell lysates were analyzed with real-time PCR and Western blot (WB) for FKBP12 and FKBP12.6. Intracellular Ca(2+)measurements were performed using dual-wavelength ratio imaging in fura-2 loaded cells.

RESULTS

A time-dependent drop in viability was shown after HEDA (P<0.001). Viability was not further influenced by addition of ROS or REPH. The general patterns of FKBP12 and FKBP12.6 mRNA expression showed upregulation after hypoxia, downregulation after ischemia and normalization after reperfusion, which was partially attenuated if ROS was added during HEDA. The protein contents were unaffected after hypoxia, tended to increase after ischemia and, for FKBP12.6, a further increase after reperfusion was shown. Hypoxia or HEDA, with or without REPH, resulted in a decreased amplitude of the Ca(2+) peak in response to caffeine. In addition, cells subjected to HEDA for 3 h or HEDA for 3 h followed by 6 h of REPH displayed irregular Ca(2+) oscillations with a decreased frequency.

CONCLUSION

A threshold for cell survival with respect to duration of ischemia was established in our cell line model. Furthermore, we could demonstrate disturbances of calcium handling in the sarcoplasmic reticulum as well as alterations in the expressions of the calcium handling proteins FKBP12 and FKBP12.6, why this model may be suitable for further studies on ischemia and reperfusion with respect to calcium handling of the sarcoplasmic reticulum.

Long-term culture of HL-1 cardiomyocytes in modular poly(ethylene glycol) microsphere-based scaffolds crosslinked in the phase-separated state

Poly(ethylene glycol) (PEG) microspheres were assembled around HL-1 cardiomyocytes to produce highly porous modular scaffolds. In this study we took advantage of the immiscibility of PEG and dextran to improve upon our previously described modular scaffold fabrication methods. Phase separating the PEG microspheres in dextran solutions caused them to rapidly deswell and crosslink together, eliminating the need for serum protein-based crosslinking. This also led to a dramatic increase in the stiffness of the scaffolds and greatly improved the handling characteristics. HL-1 cardiomyocytes were present during microsphere crosslinking in the cytocompatible dextran solution, exhibiting high cell viability following scaffold formation. Over the course of 2 weeks a 9-fold expansion in cell number was observed. The cardiac functional markers sarcomeric α-actinin and connexin 43 were expressed at 13 and 24 days after scaffold formation. HL-1 cells were spontaneously depolarizing 38 days after scaffold formation, which was visualized by confocal microscopy using a calcium-sensitive dye. Electrical stimulation resulted in synchronization of activation peaks throughout the scaffolds. These findings demonstrate that PEG microsphere scaffolds fabricated in the presence of dextran can support the long-term three-dimensional culture of cells, suggesting applications in cardiovascular tissue engineering.

The Arabidopsis sn-1-specific mitochondrial acylhydrolase AtDLAH is positively correlated with seed viability

Lipid-derived molecules produced by acylhydrolases play important roles in the regulation of diverse cellular functions in plants. In Arabidopsis, the DAD1-like phospholipase A1 family consists of 12 members, all of which possess a lipase 3 domain. In this study, the biochemical and cellular functions of AtDLAH, an Arabidopsis thaliana DAD1-like acylhydrolase, were examined. Bacterially expressed AtDLAH contained phospholipase A1 activity for catalysing the hydrolysis of phospholipids at the sn-1 position. However, AtDLAH displayed an even stronger preference for 1-lysophosphatidylcholine, 1-monodiacylglycerol, and phosphatidic acid, suggesting that AtDLAH is a sn-1-specific acylhydrolase. The AtDLAH gene was highly expressed in young seedlings, and its encoded protein was exclusively localized to the mitochondria. AtDLAH-overexpressing transgenic seeds (35S:AtDLAH) were markedly tolerant to accelerated-ageing treatment and thus had higher germination percentages than wild-type seeds. In contrast, the atdlah loss-of-function knockout mutant seeds were hypersusceptible to accelerated-ageing conditions. The 35S:AtDLAH seeds, as opposed to the atdlah seeds, exhibited a dark red staining pattern following tetrazolium treatment under both normal and accelerated-ageing conditions, suggesting that AtDLAH expression is positively correlated with seed viability. The enhanced viability of 35S:AtDLAH seeds was accompanied by more densely populated epidermal cells, lower levels of accumulated lipid hydroperoxides, and higher levels of polar lipids as compared with wild-type and atdlah mutant seeds. These results suggest that AtDLAH, a mitochondrial-localized sn-1-specific acylhydrolase, plays an important role in Arabidopsis seed viability.

Intestinal lipid alterations occur prior to antibody-induced prostaglandin E2 production in a mouse model of ischemia/reperfusion

Ischemia/reperfusion (IR) induced injury results in significant tissue damage in wild-type, but not antibody-deficient, Rag-1(-/-) mice. However, Rag-1(-/-) mice sustain intestinal damage after administration of wild-type antibodies or naturally occurring, specific anti-phospholipid related monoclonal antibodies, suggesting involvement of a lipid antigen. We hypothesized that IR initiates metabolism of cellular lipids, resulting in production of an antigen recognized by anti-phospholipid antibodies. At multiple time points after Sham or IR treatment, lipids extracted from mouse jejunal sections were analyzed by electrospray ionization triple quadrupole mass spectrometry. Within 15min of reperfusion, IR induced significantly more lysophosphatidylcholine (lysoPC), lysophosphatidylglycerol (lysoPG) and free arachidonic acid (AA) production than Sham treatment. While lysoPC, lysoPG, and free AA levels were similar in C57Bl/6 (wild-type) and Rag-1(-/-) mice, IR led to Cox-2 activation and prostaglandin E(2) (PGE(2)) production in wild-type, but not in the antibody-deficient, Rag-1(-/-) mice. Administration of wild-type antibodies to Rag-1(-/-) mice restored PGE(2) production and intestinal damage. These data indicate that IR-induced intestinal damage requires antibodies for Cox-2 stimulated PGE(2) production but not for production of lysoPC and free AA.

Rosuvastatin attenuates Ang II--mediated cardiomyocyte hypertrophy via inhibition of LOX-1

3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase inhibitors, also known as statins, have been shown to reduce cardiac remodeling. Angiotensin II (Ang II) type 1 receptor (AT1R) and oxidized low-density lipoprotein (ox-LDL) via its lectin-like ox-LDL receptor (LOX-1) are major stimuli for cardiomyocyte growth. We postulated that rosuvastatin, a potent HMG-CoA reductase inhibitor, may reduce Ang II-mediated cardiomyocyte growth via AT1R and LOX-1 inhibition. HL-1 adult mouse cardiomyocytes were incubated overnight in serum-free medium, and then treated with rosuvastatin, the AT1R inhibitor losartan or anti-LOX-1 antibody for 3 hours. The cells were then stimulated with Ang II. We measured cardiomyocyte growth, and associated intracellular redox signals using reverse transcription- polymerase chain reaction (RT-PCR) and real-time quantitative PCR. Losartan and anti-LOX-1 antibody markedly attenuated Ang II-mediated oxidant stress, and the expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (p40(phox) and gp91(phox) subunits) and nuclear factor-kappaB (NF-kappaB). Rosuvastatin attenuated the Ang II-mediated upregulation of both subunits of NAPDH oxidase as well as NF-kappaB. Rosuvastatin also reduced Ang II-mediated upregulation of AT1R and LOX-1. In other experiments, LOX-1 was upregulated in cardiomyocytes by transfection with pCI-neo/LOX-1, which also enhanced the expression AT1R messenger RNA (mRNA), and rosuvastatin pretreatment reduced the expression of both LOX-1 and AT1R in this system. Thus, rosuvastatin attenuates Ang II-mediated cardiomyocyte growth by inhibiting LOX-1 and AT1R expression and suppressing the heightened intracellular redox state.