DAB2IP coordinates both PI3K-Akt and ASK1 pathways for cell survival and apoptosis

In metastatic prostate cancer (PCa) cells, imbalance between cell survival and death signals such as constitutive activation of phosphatidylinositol 3-kinase (PI3K)-Akt and inactivation of apoptosis-stimulated kinase (ASK1)-JNK pathways is often detected. Here, we show that DAB2IP protein, often down-regulated in PCa, is a potent growth inhibitor by inducing G₀/G₁ cell cycle arrest and is proapoptotic in response to stress. Gain of function study showed that DAB2IP can suppress the PI3K-Akt pathway and enhance ASK1 activation leading to cell apoptosis, whereas loss of DAB2IP expression resulted in PI3K-Akt activation and ASK1-JNK inactivation leading to accelerated PCa growth in vivo. Moreover, glandular epithelia from DAB2IP^−/− animal exhibited hyperplasia and apoptotic defect. Structural functional analyses of DAB2IP protein indicate that both proline-rich (PR) and PERIOD-like (PER) domains, in addition to the critical role of C2 domain in ASK1 activity, are important for modulating PI3K-Akt activity. Thus, DAB2IP is a scaffold protein capable of bridging both survival and death signal molecules, which implies its role in maintaining cell homeostasis.     

Heat stress responses modulate calcium regulations and electrophysiological characteristics in atrial myocytes

Heat stress-induced responses change the ionic currents and calcium homeostasis. However, the molecular insights into the heat stress responses on calcium homeostasis remain unclear. The purposes of this study were to examine the mechanisms of heat stress responses on calcium handling and electrophysiological characteristics in atrial myocytes. We used indo-1 fluorimetric ratio technique and whole-cell patch clamp to investigate the intracellular calcium, action potentials, and ionic currents in isolated rabbit single atrial cardiomyocytes with or without (control) exposure to heat stress (43 °C, 15 min) 5 ± 1 h before experiments. The expressions of sarcoplasmic reticulum ATPase (SERCA2a), and Na⁺-Ca²⁺ exchanger (NCX) in the control and heat stress-treated atrial myocytes were evaluated by Western blot and real-time PCR. As compared with control myocytes, the heat stress-treated myocytes had larger sarcoplasmic reticulum calcium content and larger intracellular calcium transient with a shorter decay portion. Heat stress-treated myocytes also had larger L-type calcium currents, transient outward potassium currents, but smaller NCX currents. Heat stress responses increased the protein expressions, SERCA2a, NCX, and heat shock protein. However, heat stress responses did not change the RNA expression of SERCA2a and NCX. In conclusion, heat stress responses change calcium handling through protein but not RNA regulation.     

过表达肌浆网钙三磷酸腺苷酶抑制缺氧诱导心肌细胞凋亡的研究

目的研究过表达肌浆网钙ATP酶2a(SERCA2a)能否提高心肌细胞对缺氧的耐受性,评价其对心肌细胞凋亡的影响。方法体外培养的SD乳鼠心肌细胞随机分为对照组、缺氧组、过表达SERCA2a组和SERCA2a+缺氧组,以携带SERCA2a基因的重组腺病毒转染心肌细胞48 h后对其进行缺氧处理。Western blot法检测细胞质内SERCA2a蛋白及Caspase-3表达的变化;膜联蛋白V/碘化丙啶双染色法及流式细胞术检测心肌细胞凋亡率;激光共聚焦显微镜检测细胞质内Ca~(2+)浓度变化。结果与对照组比较,缺氧组SERCA2a蛋白表达水平显著降低,过表达SERCA2a组蛋白含量升高2.5倍(P<0.05),缺氧组Caspase-3蛋白表达升高53.1%,过表达SERCA2a后给予缺氧处理,Caspase-3蛋白表达降低39.7%(P<0.05)。与对照组比较,缺氧组心肌细胞凋亡率显著升高,与缺氧组比较,SERCA2a+缺氧组细胞凋亡率显著下降(P<0.05)。与对照组比较,缺氧组细胞质内Ca~(2+)荧光强度显著升高;与缺氧组比较,SERCA2a+缺氧组细胞质内Ca~(2+)荧光强度显著降低(P<0.05)。结论过表达SERCA2a可减轻细胞内Ca~(2+)超载和抑制Caspase-3激活,进而减少缺氧诱导的心肌细胞凋亡。     

Excess of glucocorticoid induces myocardial remodeling and alteration of calcium signaling in cardiomyocytes

Ventricular dysfunction is one of the important side effects of the anti-inflammatory agent, glucocorticoid (GC). The present study was undertaken to examine whether abnormal calcium signaling is responsible for cardiac dysfunction due to an excess of GC hormone. The synthetic GC drug, dexamethasone (DEX), significantly (P<0.001, n=20) increased heart weight to body weight ratio, left ventricular remodeling, and fibrosis. The microarray analysis showed altered expression of several genes encoding calcium cycling/ion channel proteins in DEX-treated rat heart. The altered expression of some of the genes was validated by real-time PCR and western blotting analyses. The expression of the L-type calcium channels and calsequestrin was increased, whereas sarcoendoplasmic reticulum calcium transport ATPase 2a (SERCA2a) and junctin mRNAs were significantly reduced in DEX-treated rat left ventricular tissues. In neonatal rat ventricular cardiomyocytes, DEX also increased the level of mRNAs of atrial- and brain natriuretic peptides, L-type calcium channels, and calsequestrin after 24 h of treatment, which were mostly restored by mifepristone. The caffeine-induced calcium release was prolonged by DEX compared to the sharp release in control cardiomyocytes. Taken together, these data show that impaired calcium kinetics may be responsible for cardiac malfunction by DEX. The results are important in understanding the pathophysiology of the heart in patients treated with excess GC.     

肌肉萎缩蛋白Fbox-1基因沉默对糖皮质激素作用下肌管萎缩的影响

目的:研究糖皮质激素地塞米松(dexamethasone,DEX)对体外培养肌管的形态、蛋白质合成/分解代谢及肌肉萎缩蛋白Fbox-1(Atrogin-1)的表达,Atrogin-1基因沉默是否可减轻肌管萎缩.方法:体外培养小鼠肌纤维细胞株C2C12细胞并分化为肌管后,用DEX处理48h,同位素3H-酪氨酸掺入法检测蛋白合成,3H-酪氨酸释放率检测蛋白分解代谢;荧光显微镜观察肌管形态并拍照;Northern blot检测Atrogin-1 mRNA水平;应用小分子干扰RNA片段(siRNA)技术使Atrogin-1基因沉默后,观察DEX作用下肌管形态的改变.结果:DEX 5μmol/L作用后,肌管酪氨酸(tyrosine)掺入率下降17.4%,同时tyrosine释放率升高24.7%,使肌管形态变细、萎缩;剂量依赖性地升高Atroign-1蛋白表达水平,使Atroign-1 mRNA表达升高3倍;Atrogin-1基因沉默可改善DEX引起的肌管萎缩. 结论:DEX促进肌管蛋白质分解代谢,并抑制蛋白合成代谢,导致肌肉萎缩;Atrogin-1基因沉默可改善DEX引起的肌肉萎缩,Atrogin-1基因可能是逆转肌肉消耗性营养不良的有效靶点.     

老年性痴呆致病基因早老素1突变作用机制的研究

目的研究阿尔茨海默病(AD)致病基因早老素(PS)突变导致AD的可能发病机制。方法 利用PS神经细胞模型,应用细胞内钙拮抗剂及抗氧化剂处理细胞后检测细胞凋亡及细胞内钙水平。结果 4种细胞在自然状态下细胞内钙及凋亡程度差异无显著性(P>005) 经β淀粉样蛋白(Aβ)的诱导 含突变PS1细胞凋亡的百分率及细胞内钙浓度较其他3组显著升高(P<001)。4种细胞经金纳多或尼莫地平处理后 含突变的PS1细胞内钙浓度及凋亡率较其他3种细胞差异无显著性(P>005)。突变PS1细胞内钙浓度变化与细胞凋亡程度呈正相关(P<001)。结论 突变PS1导致AD的可能机制是:突变的PS1促进细胞内钙超载、提高细胞内氧化应激反应 从而导致细胞凋亡增加;;加速了老年性痴呆患者细胞的退行性变。细胞内钙拮抗剂及抗氧化剂可以对抗PS突变导致的细胞内钙的水平升高及细胞凋亡程度而减少细胞凋亡     

Interferon-γ potentiates endoplasmic reticulum stress-induced death by reducing pancreatic beta cell defence mechanisms

Aims/hypothesis A tight control of endoplasmic reticulum homeostasis is crucial for beta cell function and survival. We recently described that IL-1β plus IFN-γ deplete endoplasmic reticulum Ca²⁺ stores in beta cells, leading to endoplasmic reticulum stress and apoptosis. IL-1β alone induced endoplasmic reticulum stress but failed to induce beta cell death, while IFN-γ alone neither caused endoplasmic reticulum stress nor induced beta cell death. This suggests that IFN-γ aggravates endoplasmic reticulum stress induced by IL-1β, eventually triggering apoptosis. Here we tested this hypothesis and the mechanisms involved, by investigating the effects of IFN-γ on endoplasmic reticulum-stress-induced beta cell apoptosis caused by a specific blocker of the sarcoendoplasmic-reticulum pump Ca²⁺-ATPase (SERCA).Materials and methods INS-1E cells or beta cells were pretreated with IFN-γ and then exposed to the SERCA blocker cyclopiazonic acid (CPA) for induction of endoplasmic reticulum stress. Cell death was evaluated by Hoechst 342 and propidium iodide staining. Expression of genes related to endoplasmic reticulum stress was determined by real-time RT-PCR, while activation of the endoplasmic reticulum stress response was determined by analysing X-box binding protein-1 (Xbp1) splicing and using a reporter construct containing five copies of the unfolded protein response element (UPRE).Results CPA induces endoplasmic reticulum stress and apoptosis in insulin-producing cells. Pretreatment with IFN-γ decreased the basal level of spliced Xbp1 mRNA, the basal and CPA-induced activity of the UPRE reporter, and the mRNA expression of several endoplasmic reticulum chaperones (Bip, Grp94 and Orp 150) and Sec61a. Furthermore, CPA-induced Chop mRNA expression and beta cell apoptosis were potentiated in cells that had been pretreated with IFN-γ.Conclusions/interpretation CPA-induced endoplasmic reticulum stress and apoptosis is enhanced in IFN-γ-treated beta cells. These effects are mediated via downregulation of the expression of genes involved in beta cell defence against endoplasmic reticulum stress.     

Human immunodeficiency virus protease inhibitors modulate Ca2+ homeostasis and potentiate alcoholic stress and injury in mice and primary mouse and human hepatocytes

A portion of human immunodeficiency virus (HIV)-infected patients undergoing protease inhibitor (PI) therapy concomitantly consume or abuse alcohol leading to hepatic injury. The underling mechanisms are not known. We hypothesize that HIV PIs aggravate alcohol-induced liver injury through an endoplasmic reticulum (ER) stress mechanism. To address this, we treated mice, primary mouse hepatocytes (PMHs), and primary human hepatocytes (PHHs) with alcohol and the HIV PIs ritonavir (RIT) and lopinavir (LOP). In mice, RIT and LOP induced mild ER stress and inhibition of sarco/ER calcium-ATPase (SERCA) without significant increase in serum alanine aminotransferase (ALT) levels. However, a single dose of alcohol plus the two HIV PIs caused a more than five-fold increase in serum ALT, a synergistic increase in alcohol-induced liver lipid accumulation and ER stress response, and a decrease of SERCA. Mice treated with chronic HIV PIs and alcohol developed moderate liver fibrosis. In PMHs, the HIV drugs plus alcohol also inhibited SERCA expression and increased expression of glucose-regulated protein 78, C/EBP homologous protein, sterol regulatory element-binding protein 1c, and phosphorylated c-Jun N-terminal kinase 2, which were accompanied by a synergistic increase in cell death compared with alcohol or the HIV drugs alone. In PHHs, treatment with RIT and LOP or alcohol alone increased messenger RNA of spliced X box-binding protein 1 and decreased SERCA, which were accompanied by reduced levels of intracellular calcium. Alcohol combined with the HIV drugs significantly reduced intracellular calcium levels and potentiated cell death, which was comparable to the cell death caused by the SERCA inhibitor thapsigargin. CONCLUSION: Our findings suggest the possibility that HIV PIs potentiate alcohol-induced ER stress and injury through modulation of SERCA and maintaining calcium homeostasis could be a therapeutic aim for better care of HIV patients.     

Myoglobin‐Induced Apoptosis: Two Pathways Related to Endoplasmic Reticulum Stress

Myoglobin plays an important role in rhabdomyolysis‐induced acute kidney injury (AKI), but the underlying mechanisms are still unclear. The present study investigates myoglobin‐induced apoptosis in HK‐2 cells (human renal proximal tubule cells) to discover some of the mechanisms involved in rhabdomyolysis related AKI. Metmyoglobin is reduced to ferrous myoglobin by ascorbic acid, and then the HK‐2 cells are incubated with ferrous myoglobin. Cell viability is measured by 3‐(4,5)‐dimethylthiahiazo(‐z‐y1)‐3,5‐di‐phenytetrazoliumromide (MTT) assay, and cell injury is tested by supernatant lactose dehydrogenase (LDH). Cell apoptosis is evaluated by fluorescent microscopy of Hoechst staining and by flow cytometry of Annexin V/PI double staining. The apoptosis related protein expression is determined by Western blot. HK‐2 cells were incubated with 200 µM ferrous myoglobin for 24 h, the cell viability decreased and supernatant LDH release increased. Hoechst staining indicated more apoptosis after incubation. Molecular chaperone glucose‐related protein 78 (GRP78), cytochrome C, caspase‐9 started to increase within 3 h after incubation while caspase‐4, caspase‐8 showed no significant change. (iii) When the inositol triphosphate receptor (IP3R) calcium channel was blocked by 2‐aminoethoxydiphenyl‐borinate (2‐APB), caspase‐9 was completely inhibited, GRP78 and caspase‐4 increased dramatically, and caspase‐3 expression was not affected. The apoptosis in HK‐2 cells showed no significant change. Apoptosis in HK‐2 cells incubated with ferrous myoglobin is an endoplasmic reticulum stress induced, IP3R calcium channel mediated, caspase‐9 dependent intrinsic pathway. When the intrinsic pathway was inhibited using an IP3R calcium channel blocker, endoplasmic reticulum stress increased, resulting in the activation of caspase‐4 that cleaved caspase‐3 and generated a substitutive pathway of apoptosis.     

Early Hemodynamic and Biochemical Changes in Overloaded Swine Ventricle

The present study was undertaken to investigate, in an animal model, the relationship between sarcoplasmic reticulum Ca²⁺-ATPase (SERCA2a) activity, phospholamban phosphorylation, acylphosphatase activity, and hemodynamic changes that occur in the early phase of pressure overload.In 54 study-group pigs, weighing 40 ± 5 kg each, an aortic stenosis was created with a band of umbilical tape tied around the aorta; 18 sham-operated pigs formed our control group. Eight animals (6 study and 2 control) were randomly assigned to each experimental time (0.5, 3, 6, 12, 24, 48, 72, 96, and 168 hr).All indices of left ventricular function declined significantly, with a peak at 6 hr and a return to baseline at 168 hr. At each observational time, SERCA2a activity, Ca²⁺ uptake, and acylphosphatase activity rose significantly, with a maximum increase at 6 hr. These changes indicated a higher expression of these proteins; conversely, phospholamban did not show significant changes in its concentration or in its phosphorylation status. Nuclear proto-oncogene c-fos expression rose at 6 hr. A strong inverse correlation was found when Ca²⁺-ATPase activity, Ca²⁺-ATPase expression, Ca²⁺ uptake, and acylphosphatase were compared with indices of systolic function.In our model of induced pressure overload, an initial phase of depressed myocardial contractility was accompanied by an increased sarcoplasmic reticulum function and by higher Ca²⁺-ATPase and Ca²⁺ uptake activities mediated by acylphosphatase. This new finding of Ca²⁺ homeostasis might indicate a compensatory mechanism for mechanical stress. Further studies are needed to confirm our findings.Key words: Aortic valve stenosis/pathology, calcium, calcium-transporting ATP-ases, disease models, animal, hemodynamics, myocardial contraction/physiology, sarcoplasmic reticulum/physiology, sarcoplasmic reticulum calcium-transporting ATPases, swineIn the presence of pressure overload, left ventricular hypertrophy (LVH) is an adaptive mechanism that normalizes parietal wall stress and contributes to the preservation of normal left ventricular (LV) function.^1,2 Myocyte Ca²⁺ handling plays a pivotal role in cardiac excitation-contraction coupling,³ and hypertrophy is associated with changes in sarcoplasmic reticulum (SR) and sarcoplasmic reticulum Ca²⁺-ATPase (SERCA2a) function.⁴ However, changes in SR function have also been observed during the acute phase of pressure overload, when the hypertrophy has not yet fully developed; this results in enhanced SR function with increased levels of acylphosphatase, a cytosolic enzyme well represented in cardiac muscle, which might contribute to this effect.⁵ Furthermore, SERCA2a is regulated by phospholamban (PLB), a membrane protein whose cAMP-dependent phosphorylation leads to an enhancement of Ca²⁺ active transport.The present study was undertaken to investigate, in an animal model, the relationship between SERCA2a activity, PLB phosphorylation, acylphosphatase activity, and hemodynamic changes that occur in the early phase of pressure overload.     

Hyperglycemia-induced cardiac contractile dysfunction in the diabetic heart

The development of a diabetic cardiomyopathy is a multifactorial process, and evidence is accumulating that defects in intracellular free calcium concentration [Ca²⁺]_i or its homeostasis are related to impaired mechanical performance of the diabetic heart leading to a reduction in contractile dysfunction. Defects in ryanodine receptor, reduced activity of the sarcoplasmic reticulum calcium pump (SERCA) and, along with reduced activity of the sodium-calcium exchanger (NCX) and alterations in myofilament, collectively cause a calcium imbalance within the diabetic cardiomyocytes. This in turn is characterized by cytosolic calcium overloading or elevated diastolic calcium leading to heart failure. Numerous studies have been performed to identify the cellular, subcellular, and molecular derangements in diabetes-induced cardiomyopathy (DCM), but the precise mechanism(s) is still unknown. This review focuses on the mechanism behind DCM, the onset of contractile dysfunction, and the associated changes with special emphasis on hyperglycemia, mitochondrial dysfunction in the diabetic heart. Further, management strategies, including treatment and emerging therapeutic modalities, are discussed.     

右美托咪定联合Tol样受体4抑制剂对缺氧复氧心肌细胞凋亡和炎症反应的影响及其机制

目的探讨右美托咪定(DEX)联合Toll样受体4(TLR4)抑制剂TAK-242对缺氧复氧(H/R)心肌细胞凋亡和炎症反应的影响及其机制。方法心肌细胞H9C2分为对照(Con)组、H/R组(H/R损伤)、DEX组(1.0μmol/L DEX,再行H/R损伤)、TAK-242组(30μmol/L TAK-242,再行H/R损伤)和DEX+TAK-242组(30μmol/L TAK-242及1.0μmol/L DEX,再行H/R损伤处理)。各组细胞复氧培养6 h后,采用MTT法、流式细胞仪、试剂盒、酶联免疫吸附法检测细胞增殖、凋亡、乳酸脱氢酶(LDH)释放率、白介素1β(IL-1β)和肿瘤坏死因子-α(TNF-α)含量,Western blot检测B细胞淋巴瘤/白血病-2(Bcl-2)、Bcl-2相关X蛋白(Bax)、裂解的caspase-3(cleaved caspase-3)、TLR4和核因子B p65(NF-κB p65)蛋白表达。结果五组细胞凋亡率、LDH释放率、Bax、Bcl-2、cleaved caspase-3、TLR4、NF-κB p65蛋白表达水平、IL-1β、TNF-α含量比较差异均有统计学意义(F=316.938、330.004、839.933、169.750、378.365、476.535、298.527、99.219、293.498,P<0.05)。与Con组相比,H/R组细胞的凋亡率、LDH释放率、Bax、cleaved caspase-3、TLR4和NF-κB p65蛋白表达水平、细胞上清液中IL-1β和TNF-α含量均明显升高(均P<0.05),Bcl-2蛋白表达水平明显降低(均P<0.05)。与H/R组相比,DEX组、TAK-242组和DEX+TAK-242组的细胞凋亡率、LDH释放率、Bax蛋白、cleaved caspase-3、TLR4和NF-κB p65蛋白、IL-1β、TNF-α的表达水平均明显降低,Bcl-2蛋白表达水平明显升高(均P<0.05)。与DEX组、TAK-242组相比,DEX+TAK-242组的细胞凋亡率、LDH释放率、Bax、cleaved caspase-3、TLR4和NF-κB p65蛋白表达、IL-1β、TNF-α表达水平更低,Bcl-2蛋白的表达更高(均P<0.05)。结论DEX和TAK-242联合可协同抑制H/R引起的心肌细胞凋亡和炎症反应,其作用机制可能与协同抑制TLR4/NF-κB通路有关。     

A peptide inhibitor of cytochrome c/inositol 1,4,5-trisphosphate receptor binding blocks intrinsic and extrinsic cell death pathways

Apoptotic stimuli augment intracellular calcium concentration through inositol 1,4,5-trisphosphate receptors (IP3R) on endoplasmic reticulum calcium stores. We previously discovered an apoptotic cascade wherein cytochrome c binds to IP3R early in apoptosis, resulting in dysregulated calcium release. Here we show that cytochrome c binding to IP3R depends on a cluster of glutamic acid residues within the C terminus of the channel. A cell permeant peptide derived from this sequence displaces cytochrome c from IP3R and abrogates cell death induced by staurosporine treatment of HeLa cells and Fas ligand stimulation of Jurkat cells. Small-molecule inhibitors of cytochrome c/IP3R interactions may prove useful in treating disorders associated with inappropriate intrinsic and extrinsic apoptotic signaling.     

Endothelin-1-induced arrhythmogenic Ca2+ signaling is abolished in atrial myocytes of inositol-1,4,5-trisphosphate(IP3)-receptor type 2-deficient mice

Recent studies have suggested that inositol-1,4,5-trisphosphate-receptor (IP3R)-mediated Ca2+ release plays an important role in the modulation of excitation-contraction coupling (ECC) in atrial tissue and the generation of arrhythmias, specifically chronic atrial fibrillation (AF). IP3R type-2 (IP3R2) is the predominant IP3R isoform expressed in atrial myocytes. To determine the role of IP3R2 in atrial arrhythmogenesis and ECC, we generated IP3R2-deficient mice. Our results revealed that endothelin-1 (ET-1) stimulation of wild-type (WT) atrial myocytes caused an increase in basal [Ca2+]i, an enhancement of action potential (AP)-induced [Ca2+]i transients, an improvement of the efficacy of ECC (increased fractional SR Ca2+ release), and the occurrence of spontaneous arrhythmogenic Ca2+ release events as the result of activation of IP3R-dependent Ca2+ release. In contrast, ET-1 did not alter diastolic [Ca2+]i or cause spontaneous Ca2+ release events in IP3R2-deficient atrial myocytes. Under basal conditions the spatio-temporal properties (amplitude, rise-time, decay kinetics, and spatial spread) of [Ca2+]i transients and fractional SR Ca2+ release were not different in WT and IP3R2-deficient atrial myocytes. WT and IP3R2-deficient atrial myocytes also showed a significant and very similar increase in the amplitude of AP-dependent [Ca2+]i transients and Ca2+ spark frequency in response to isoproterenol stimulation, suggesting that both cell types maintained a strong inotropic reserve. No compensatory changes in Ca2+ regulatory protein expression (IP3R1, IP3R3, RyR2, NCX, SERCA2) or morphology of the atria could be detected between WT and IP3R2-deficient mice. These results show that lack of IP3R2 abolishes the positive inotropic effect of neurohumoral stimulation with ET-1 and protects from its arrhythmogenic effects.