Leptin attenuates hypoxia/reoxygenation-induced activation of the intrinsic pathway of apoptosis in rat H9c2 cells

Cardiomyocyte apoptosis is a component of cardiac remodeling that can contribute to heart failure in obesity. A role for leptin in mediating this process has been suggested and the objective of this work was to investigate the effect of leptin on apoptosis and associated mechanisms in H9c2 cells which were subjected to hypoxia/reoxygenation (HR) to mimic myocardial ischemia/reperfusion. Qualitative immunofluorescent and quantitative laser scanning cytometry approaches demonstrated that exposure of cells to HR increased DNA fragmentation (TUNEL staining) which was attenuated by leptin (6 nM, 1 h) pretreatment. We also found increased annexin-V binding and caspase-3 activity in cells exposed to HR, both of which were attenuated by leptin pretreatment. Leptin reduced HR-induced translocation of the pro-apoptotic protein Bax to the mitochondrial membrane, which provides a mechanism to explain its protective effect. Consequently, leptin attenuated the HR-induced decrease in mitochondrial membrane potential and increase in cytochrome c release from mitochondria. Leptin treatment increased the phosphorylation of p38 MAPK and AMPK and respective inhibitors of these kinases, SB203580 and Compound C, prevented the ability of leptin to decrease HR-induced caspase-3 activity. In conclusion, we establish mechanisms via which leptin exerts anti-apoptotic effects that may be of significance in understanding the development of heart failure in obesity. J. Cell. Physiol. 221: 490–497, 2009. © 2009 Wiley-Liss, Inc.     

类叶升麻苷通过上调miR-204对缺氧/复氧诱导H9C2细胞凋亡的抑制作用

目的探讨类叶升麻苷对缺氧/复氧（H/R）处理大鼠心肌细胞（H9C2）损伤的影响及其分子机制。 方法体外培养H9C2细胞,H/R （4 h/20 h）建立心肌细胞损伤模型,并采用1、10、100 μmol/L类叶升麻苷,转染miR-204模拟物阴性对照（miR-NC）、转染miR-204模拟物（miR-24）,100 μmol/L类叶升麻苷干预+转染miR-204抑制剂阴性对照、100 μmol/L类叶升麻苷+转染miR-204抑制剂干预H/R细胞。分别进行RT-qPCR、MTT、流式细胞术、Western blot检测miR-204表达水平、细胞活力、细胞凋亡率和相关蛋白表达,利用相应试剂盒检测乳酸脱氢酶（LDH）、丙二醛（MDA）、超氧化物歧化酶（SOD）和谷胱甘肽过氧化物酶（GSH-Px）水平,酶联免疫吸附试验（ELISA）检测白细胞介素-6 （IL-6）、白细胞介素-β （IL-β）和肿瘤坏死因子-α （TNF-α）的含量。两组间比较采用独立样本t检验,多组间比较采用单因素方差分析,组间两两比较采用SNK-q检验。 结果与心肌损伤模型比较,10、100 μmol/L类叶升麻苷的细胞凋亡率[（25.62±1.96）%比（18.17±1.27）%,（11.24±0.57）%]、Bax（0.71±0.05比0.51±0.04、0.29±0.03）、LDH [（243.16±11.31）比（121.22±4.52）,（94.39±2.82）U/g]、MDA [（1.82±0.07）比（1.13±0.04）,（0.92±0.04）nmol/mg]、IL-6 [（121.45±6.18）比（87.16±4.53）,（47.11± 2.24）pg/mL]、IL-1β [（229.82±8.48）比（175.32±8.73）,（113.14±5.63）pg/mL]和TNF-α表达水平[（138.18±6.60）比（92.24±4.04）,（61.53±4.17）pg/mL]降低,Bcl-2 （0.18±0.01比0.35± 0.03、0.52±0.04）、SOD [（18.72±1.26）比（38.81±1.51）,（45.43±1.29）U/mg]和GSH-Px表达水平[（58.74±2.28）比（89.24±2.82）,（94.66±3.05）U/mg]升高（P均< 0.05）;与miR-NC比较,转染miR-204的细胞凋亡率[（24.12±1.12）%比（9.26±0.49）%]、Bax （0.62±0.04比0.25±0.02）、LDH [（229.11±8.47）比（86.32±5.92）U/g]、MDA [（1.75±0.08）比（0.85± 0.05）nmol/mg]、IL-6 [（134.47±7.31）比（55.26±2.13）pg/mL]、IL-1β [（211.14±9.70）比（98.11±3.18）pg/mL]和TNF-α表达水平[（152.92±3.49）比（51.34±2.66）pg/mL]降低,Bcl-2 （0.22±0.01比0.57±0.03）、SOD [（20.92±1.38）比（47.68±1.76）U/mg]和GSH-Px表达水平[（62.65±2.76）比（91.13±3.80）U/mg]升高（P < 0.05）;10、100 μmol/L类叶升麻苷可提高H/R诱导H9C2细胞中miR-204的表达水平（P < 0.05）;且下调miR-204逆转了类叶升麻苷对H/R处理H9C2细胞凋亡、氧化应激和炎症因子的影响。 结论类叶升麻苷可能通过上调miR-204表达缓解H/R诱导的H9C2细胞损伤。     

Oxidative stress is involved in the permeabilization of the inner membrane of brain mitochondria exposed to hypoxia/reoxygenation and low micromolar Ca2+

From in vivo models of stroke it is known that ischemia/reperfusion induces oxidative stress that is accompanied by deterioration of brain mitochondria. Previously, we reported that the increase in Ca2+ induces functional breakdown and morphological disintegration in brain mitochondria subjected to hypoxia/reoxygenation (H/R). Protection by ADP indicated the involvement of the mitochondrial permeability transition pore in the mechanism of membrane permeabilization. Until now it has been unclear how reactive oxygen species (ROS) contribute to this process. We now report that brain mitochondria which had been subjected to H/R in the presence of low micromolar Ca2+ display low state 3 respiration (20% of control), loss of cytochrome c, and reduced glutathione levels (75% of control). During reoxygenation, significant mitochondrial generation of hydrogen peroxide (H2O2) was detected. The addition of the membrane permeant superoxide anion scavenger TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl) suppressed the production of H2O2 by brain mitochondria metabolizing glutamate plus malate by 80% under normoxic conditions. TEMPOL partially protected brain mitochondria exposed to H/R and low micromolar Ca2+ from decrease in state 3 respiration (from 25% of control to 60% of control with TEMPOL) and permeabilization of the inner membrane. Membrane permeabilization was obvious, because state 3 respiration could be stimulated by extramitochondrial NADH. Our data suggest that ROS and Ca2+ synergistically induce permeabilization of the inner membrane of brain mitochondria exposed to H/R. However, permeabilization can only partially be prevented by suppressing mitochondrial generation of ROS. We conclude that transient deprivation of oxygen and glucose during temporary ischemia coupled with elevation in cytosolic Ca2+ concentration triggers ROS generation and mitochondrial permeabilization, resulting in neural cell death.     

H2O2-induced filamin redistribution in endothelial cells is modulated by the cyclic AMP-dependent protein kinase pathway

Hypoxia/reoxygenation injury in vitro causes endothelial cell cytoskeletal rearrangement that is related to increased monolayer permeability. Nonmuscle filamin (ABP-280) promotes orthogonal branching of F-actin and links microfilaments to membrane glycoproteins. Human umbilical vein endothelial cell monolayers are exposed to H₂O₂ (100 μM) for 1–60 min, with or without modulators of cAMP-dependent second-messenger pathways, and evaluated for changes in filamin distribution, cAMP levels, and the formation of gaps at interendothelial junctions. Filamin translocates from the membrane-cytoskeletal interface to the cytosol within 1 min of exposure to H₂O₂. This is associated with a decrease in endothelial cell cAMP levels from 83 pmoles/mg protein to 15 pmoles/mg protein. Intercellular gaps form 15 min after H₂O₂ treatment and progressively increase in number and diameter through 60 min. Both filamin redistribution and actin redistribution are associated with decreased phosphorylation of filamin and are prevented by activation of the cAMP-dependent protein kinase pathway. A synthetic peptide corresponding to filamin's C-terminal, cAMP-dependent, protein kinase phosphorylation site effectively induces filamin translocation and intercellular gap formation, which suggests that decreased phosphorylation of filamin at this site causes filamin redistribution and destabilization of junctions. These data indicate that H₂O₂-induced filamin redistribution and interendothelial cell gap formation result from inhibition of the cAMP-dependent protein kinase pathway. J. Cell. Physiol. 172:373–381, 1997. © 1997 Wiley-Liss, Inc.     

Oxidation of cardiolipin is involved in functional impairment and disintegration of liver mitochondria by hypoxia/reoxygenation in the presence of increased Ca2+ concentrations

The aim of this study was to investigate the interrelationship between the mitochondrial phospholipid cardiolipin (CL), mitochondrial respiration and morphology in dependence on hypoxia/reoxygenation and Ca²⁺. Therefore, we subjected rat liver mitochondria to hypoxia/reoxygenation at different extramitochondrial Ca²⁺ concentrations and analysed mitochondrial respiration, morphology, CL content, the composition of molecular CL species, oxidation of CL and two mono-lyso-CL species. Hypoxia/reoxygenation in the presence of elevated extramitochondrial Ca²⁺ concentration caused dramatic impairment of mitochondrial respiration and morphology. Concomitantly, increased amounts of oxidised CL were detected in the incubation medium after the treatment. Hypoxia/reoxygenation alone caused degradation of CL. The treatments had no effect on the composition of molecular CL species. Our data support the hypothesis that CL oxidation and CL degradation are involved in mitochondrial injury caused by hypoxia/reoxygenation and Ca²⁺. Our results further suggest that prevention of CL oxidation by modification of CL composition may support the beneficial action of antioxidants during hypoxia/reoxygenation in the presence of elevated Ca²⁺ concentrations.     

IL-20 promotes hypoxia/reoxygenation-induced mitochondrial dysfunction and apoptosis in cardiomyocytes by upregulating oxidative stress by activating the PKC/NADPH oxidase pathway

Acute myocardial infarction (AMI) is the maximum critical cardiovascular event and causes high morbidity and mortality worldwide. The ischemia and reperfusion that occur in AMI cause apoptosis and cellular dysfunction in cardiomyocytes. IL-20, an IL-10 family member, is involved in various inflammatory diseases. Therefore, we sought to elucidate the role of IL-20 in the infarcted heart following ischemia/reperfusion (I/R) injury. We found that IL-20 and its receptors, IL-20R1 and IL-20R2, were increased in H2C2 cardiomyoblast cells and ventricular tissues subjected to hypoxia/reoxygenation (H/R) stimulation. The presence of IL-20 further inhibited the cell viability of H9C2 cells and primary cardiomyocytes. Our results suggested that IL-20 elicited an increase in Ca²⁺ and activation of the PKC/NADPH oxidase pathway, leading to the elevation of oxidase stress and downregulation of AKT. Furthermore, we demonstrated that IL-20 was able to mediate H/R-induced apoptosis via PKC/NADPH oxidase/AKT signaling. Our findings implied that IL-20 was responsive to H/R stress in vitro and in rat hearts undergoing I/R injury, and this upregulation of IL-20 may contribute to the apoptosis of cardiomyocytes.     

Cryptotanshinone inhibits hypoxia/reoxygenation-induced oxidative stress and apoptosis in renal tubular epithelial cells

Cryptotanshinone (CTS), an active component extracted from the root of Salvia miltiorrhiza Bunge , was reported to attenuate hepatic ischemia/reperfusion (I/R) injury. However, its protective effect against renal I/R injury remains unclear. In this study, the role of CTS in renal I/R injury in vitro and its possible mechanism were investigated. Our results showed that CTS improved cell viability in HK-2 cells exposed to hypoxia/reoxygenation (H/R). CTS also inhibited the H/R-mediated production of reactive oxygen species, as well as increased the activities of superoxide dismutase and catalase in H/R-stimulated HK-2 cells. In addition, CTS dramatically attenuated the induction of bax expression and caspase-3 activity and alleviated the reduction of bcl-2 expression in HK-2 cells cultured with H/R. Furthermore, CTS activated the levels of p-PI3K and p-Akt in H/R-injured HK-2 cells; meanwhile, the renal protective activity of CTS was inhibited by the inhibitor of the (phosphatidylinositol 3 kinase/protein kinase B) PI3K/Akt pathway (LY294002). These findings indicate that CTS can ameliorate renal I/R injury in vitro partly through regulating the PI3K/Akt pathway.     

FoxO4 negatively modulates USP10 transcription to aggravate the apoptosis and oxidative stress of hypoxia/reoxygenation-induced cardiomyocytes by regulating the Hippo/YAP pathway

Journal of Bioenergetics and Biomembranes - Acute myocardial infarction (AMI) is the main cause of death in the whole world. This study aimed to investigate whether forkhead box O4 (FoxO4) could...     

Suppression of rat Frizzled-2 attenuates hypoxia/reoxygenation-induced Ca2+ accumulation in rat H9c2 cells

Growing evidence suggests that Ca(2+) overload is one of the major contributors of myocardial ischemia/reperfusion-induced injury. Since Frizzled-2 receptor, a seven transmembrane protein, transduces downstream signaling by specialized binding of Wnt5a to increase intracellular Ca(2+) release, this work aimed to investigate the effect of Frizzled-2 on Ca(2+) accumulation in H9c2 cells, which were subjected to hypoxia/reoxygenation to mimic myocardial ischemia/reperfusion. After exposing H9c2 cells to hypoxia/reoxygenation, we observed higher expression of Frizzled-2 and Wnt5a as compared to control group cells. Hypoxia/reoxygenation-induced intracellular Ca(2+) accumulation approached that of cells transfected with frizzled-2 plasmid. In cells treated with RNAi specifically designed against frizzled-2, intracellular Ca(2+) in both hypoxia/reoxygenation-treated cells and plasmid-treated cells were decreased. Rats that underwent ischemia/reperfusion injury exhibited increased intracellular Ca(2+) with high expression levels of Frizzled-2 and Wnt5a as compared to the sham group. Our data indicates that upon binding to Wnt5a, increased Frizzled-2 expression after hypoxia/reoxygenation treatment activated intracellular calcium release in H9c2 cells. Our findings provide a new perspective in understanding calcium overload in myocardial ischemia/reperfusion.     

NF-kappaB pathway is involved in griseofulvin-induced G2/M arrest and apoptosis in HL-60 cells

Griseofulvin (GF), an oral antifungal agent, has been shown to exert antitumorigenesis effect through G2/M cell cycle arrest in colon cancer cells. But the underlying mechanisms remained obscure. The purpose of this study is to test the cytotoxic effect of GF on HL-60 and HT-29 cells and elucidate its underlying molecular pathways. Dose-dependent and time-course studies by flow cytometry demonstrated that 30 to 60 microM GF significantly induced G2/M arrest and to a less extend, apoptosis, in HL-60 cells. In contrast, only G2/M arrest was observed in HT-29 cells under similar condition. Pretreatment of 30 microM TPCK, a serine protease inhibitor, completely reversed GF-induced G2/M cell cycle arrest and apoptosis in HL-60 cells but not in HT-29 cells. The GF-induced G2/M arrest in HL-60 cells is reversible. Using EMSA and super-shift analysis, we demonstrated that GF stimulated NF-kappaB binding activity in HL-60 cells, which was completely inhibited by pretreatment of TPCK. Treatment of HL-60 with 30 microM GF activated JNK but not ERK or p38 MAPK and subsequently resulted in phosphorylation of Bcl-2. Pretreatment of TPCK to HL-60 cells blocked the GF-induced Bcl-2 phosphorylation but not JNK activation. Time course study demonstrated that activation of cdc-2 kinase activity by GF correlated with Bcl-2 phosphorylation. Taken together, our results suggest that activation of NF-kappaB pathway with cdc-2 activation and phosphorylation of Bcl-2 might be involved in G2/M cell cycle arrest in HL-60 cells.     

Inhibition of the mitochondrial unfolded protein response by acetylcholine alleviated hypoxia/reoxygenation-induced apoptosis of endothelial cells

The mitochondrial unfolded protein response (UPR^mt) is involved in numerous diseases that have the common feature of mitochondrial dysfunction. However, its pathophysiological relevance in the context of hypoxia/reoxygenation (H/R) in endothelial cells remains elusive. Previous studies have demonstrated that acetylcholine (ACh) protects against cardiomyocyte injury by suppressing generation of mitochondrial reactive oxygen species (mtROS). This study aimed to explore the role of UPR^mt in endothelial cells during H/R and to clarify the beneficial effects of ACh. Our results demonstrated that H/R triggered UPR^mt in endothelial cells, as evidenced by the elevation of heat shock protein 60 and LON protease 1 protein levels, and resulted in release of mitochondrial pro-apoptotic proteins, including cytochrome C, Omi/high temperature requirement protein A 2 and second mitochondrial activator of caspases/direct inhibitor of apoptosis-binding protein with low PI, from the mitochondria to cytosol. ACh administration markedly decreased UPR^mt by inhibiting mtROS and alleviating the mitonuclear protein imbalance. Consequently, ACh alleviated the release of pro-apoptotic proteins and restored mitochondrial ultrastructure and function, thereby reducing the number of terminal deoxynucleotidyl transferase mediated dUTP-biotin nick end labeling (TUNEL)-positive cells. Intriguingly, 4-diphenylacetoxy-N-methylpiperidine methiodide, a type-3 muscarinic ACh receptor (M3AChR) inhibitor, abolished the ACh-elicited attenuation of UPR^mt and TUNEL positive cells, indicating that the salutary effects of ACh were likely mediated by M3AChR in endothelial cells. In conclusion, our studies demonstrated that UPR^mt might be essential for triggering the mitochondrion-associated apoptotic pathway during H/R. ACh markedly suppressed UPR^mt by inhibiting mtROS and alleviating the mitonuclear protein imbalance, presumably through M3AChR.     

Consumption of redox energy by glutathione metabolism contributes to hypoxia/ reoxygenation-induced injury in astrocytes

The assumption of oxidative stress as a mechanism in oxalate induced renal damage suggests that antioxidants might play a beneficial role against oxalate toxicity. An in vivo model was used to investigate the effect of C-phycocyanin (from aquatic micro algae; Spirulina spp.), a known antioxidant, against calcium oxalate urolithiasis. Hyperoxaluria was induced in two of the 4 groups of Wistar albino rats (n = 6 in each) by intraperitoneally injecting sodium oxalate (70,mg/kg body weight). A pretreatment of phycocyanin (100,mg/kg body weight) as a single oral dosage was given, one hour prior to oxalate challenge. An untreated control and drug control (phycocyanin alone) were employed. Phycocyanin administration resulted in a significant improvement (p < 0.001) in the thiol content of renal tissue and RBC lysate via increasing glutathione and reducing malondialdehyde levels in the plasma of oxalate induced rats (p < 0.001), indicating phycocyanin’s antioxidant effect on oxalate mediated oxidative stress. Administering phycocyanin after oxalate treatment significantly increased catalase and glucose-6-phosphate dehydrogenase activity (p < 0.001) in RBC lysate suggesting phycocyanin as a free radical quencher. Assessing calcium oxalate crystal retention in renal tissue using polarization microscopy and renal ultrastructure by electron microscopy reveals normal features in phycocyanin – pretreated groups. Thus the study presents positive pharmacological implications of phycocyanin against oxalate mediated nephronal impairment and warrants further work to tap this potential aquatic resource for its medicinal application. (Mol Cell Biochem xxx: 1–7, 2004)     

Stabilization and translocation of p53 to mitochondria is linked to Bax translocation to mitochondria in simvastatin-induced apoptosis

Statins are cholesterol-lowing drugs with pleiotropic effects including cytotoxicity to cancer cells. In this study, we investigated the signaling pathways leading to apoptosis by simvastatin. Simvastatin induced cardinal features of apoptosis including increased DNA fragmentation, disruption of mitochondrial membrane potential (MMP), and increased caspase-3 activity by depleting isoprenoids in MethA fibrosarcoma cells. Interestingly, the simvastatin-induced apoptosis was accompanied by p53 stabilization involving Mdm2 degradation. The apoptosis was ameliorated in p53 knockdown clones of MethA cells as well as p53^−/− HCT116 cells. The stabilized p53 protein translocated to mitochondria with Bax, and cytochrome c was released into cytosol. Moreover, knockdown or deficiency of p53 expression reduced both Bax translocation to mitochondria and MMP disruption in simvastatin-induced apoptosis. Taken together, these all indicate that stabilization and translocation of p53 to mitochondria is involved in Bax translocation to mitochondria in simvastatin-induced apoptosis.     

Dopamine release in PC12 cells is mediated by Ca(2+)-dependent production of ceramide via sphingomyelin pathway

A presynaptic membrane disturbance is an essential process for the release of various neurotransmitters. Ceramide, which is a tumor suppressive lipid, has been shown to act as a channel-forming molecule and serve as a precursor of ceramide-1-phosphate, which can disturb the cellular membrane. This study found that while permeable ceramide increases the rate of dopamine release in the presence of a Ca(2+)-ionophore, A23187, permeable ceramide-1-phosphate provoked its release even without the ionophore. The treatment of PC12 cells with the ionophore at concentrations < 2 microM produced ceramide via the sphingomyelin (SM) pathway with a concomitant release of dopamine, and no cell damage was observed. The addition of a Ca(2+) chelator, EGTA, to the medium inhibited the increase in the release of both the ceramide and dopamine. This suggests that ceramide might be produced by Ca(2+) and is implicated in the membrane disturbance associated with the release of dopamine as a result of its conversion to ceramide-1-phosphate. Consistent with these results, this study detected a membrane-associated and neutral pH optimum sphingomyelinase (SMase) whose activity was increased by Ca(2+). Together, these results demonstrate that ceramide can be produced via the activation of a neutral form of SMase through Ca(2+), and is involved in the dopamine release in concert with Ca(2+).     

Glutathione peroxidase 2 in Saccharomyces cerevisiae is distributed in mitochondria and involved in sporulation

Gpx2, one of three glutathione peroxidase homologs (Gpx1, Gpx2, and Gpx3) in Saccharomyces cerevisiae, is an atypical 2-Cys peroxiredoxin that prefers to use thioredoxin as a reducing agent in vitro. Despite Gpx2 being an antioxidant, no obvious phenotype of gpx2Δ mutant cells in terms of oxidative stress has yet been found. To gain a clue as to Gpx2’s physiological function in vivo, here we identify its intracellular distribution. Gpx2 was found to exist in the cytoplasm and mitochondria. In mitochondria, Gpx2 was associated with the outer membrane of the cytoplasmic-side, as well as the inner membrane of the matrix-side. The redox state of the mitochondrial Gpx2 was regulated by Trx1 and Trx2 (cytoplasmic thioredoxin), and by Trx3 (mitochondrial matrix thioredoxin). In addition, we found that the disruption of GPX2 reduced the sporulation efficiency of diploid cells.