Hypothalamic Corticotropin-Releasing Hormone Contributes to Hypertension in Spontaneously Hypertensive Rats.

Corticotropin-releasing hormone (CRH) is a neuropeptide regulating neuroendocrine and autonomic function. CRH mRNA and protein levels in the hypothalamic paraventricular nucleus (PVN) are increased in primary hypertension. However, the role of CRH in elevated sympathetic outflow in primary hypertension remains unclear. CRHR1 proteins were distributed in retrogradely labeled PVN presympathetic neurons with an increased level in the PVN tissue in adult spontaneously hypertensive rats (SHRs) compared with age-matched male Wistar-Kyoto (WKY) rats. CRH induced a more significant increase in the firing rate of PVN-rostral ventrolateral medulla (RVLM) neurons and sympathoexcitatory response in SHRs than in WKY rats, an effect that was blocked by preapplication of NMDA receptors (NMDARs) antagonist AP5 and PSD-95 inhibitor, Tat-N-dimer. Blocking CRHRs with astressin or CRHR1 with NBI35965 significantly decreased the firing rate of PVN-RVLM output neurons and reduced arterial blood pressure (ABP) and renal sympathetic nerve activity (RSNA) in SHRs but not in WKY, whereas blocking CRHR2 with antisauvagine-30 did not. Furthermore, Immunocytochemistry staining revealed that CRHR1 colocalized with NMDARs in PVN presympathetic neurons. Blocking CRHRs significantly decreased the NMDA currents in labeled PVN neurons. PSD-95-bound CRHR1 and PSD-95-bound GluN2A in the PVN were increased in SHRs. These data suggested that the upregulation of CRHR1 in the PVN is critically involved in the hyperactivity of PVN presympathetic neurons and elevated sympathetic outflow in primary hypertension.SIGNIFICANCE STATEMENT Our study found that corticotropin-releasing hormone receptor (CRHR)1 protein levels were increased in the paraventricular nucleus (PVN), and CRHR1 interacts with NMDA receptors (NMDARs) through postsynaptic density protein (PSD)-95 in the PVN neurons in primary hypertension. The increased CRHR1 and CRHR1-NMDAR-PSD-95 complex in the PVN contribute to the hyperactivity of the PVN presympathetic neurons and elevated sympathetic vasomotor tone in hypertension in SHRs. Thus, the antagonism of CRHR1 decreases sympathetic outflow and blood pressure in hypertension. These findings determine a novel role of CRHR1 in elevated sympathetic vasomotor tone in hypertension, which is useful for developing novel therapeutics targeting CRHR1 to treat elevated sympathetic outflow in primary hypertension. The CRHR1 receptor antagonists, which are used to treat health consequences resulting from chronic stress, are candidates to treat primary hypertension.

Signaling pathways involved in NMDA-induced suppression of M-channels in corticotropin-releasing hormone neurons in central amygdala.

Glutamate N-methyl-d-aspartate (NMDA) receptors (NMDARs) and Kv7/M channels are importantly involved in regulating neuronal activity involved in various physiological and pathological functions. Corticotropin-releasing hormone (CRH)-expressing neurons in the central nucleus of the amygdala (CeA) critically mediate autonomic response during stress. However, the interaction between NMDA receptors and Kv7/M channels in the CRHCeA neurons remains unclear. In this study, we identified rat CRHCeA neurons through the expression of an AAV viral vector-mediated enhanced green fluorescent protein (eGFP) driven by the rat CRH promoter. M-currents carried by Kv7/M channels were recorded using the whole-cell patch-clamp approach in eGFP-tagged CRHCeA neurons in brain slices. Acute exposure to NMDA significantly reduced M-currents recorded from the CRHCeA neurons. NMDA-induced suppression of M-currents was eliminated by chelating intracellular Ca2+ , supplying phosphatidylinositol 4,5-bisphosphate (PIP2) intracellularly, or blocking phosphoinositide3-kinase (PI3K). In contrast, inhibiting protein kinase C (PKC) or calmodulin did not alter NMDA-induced suppression of M-currents. Sustained exposure of NMDA decreased Kv7.3 membrane protein levels and suppressed M-currents, while the Kv7.2 expression levels remained unaltered. Pre-treatment of brain slices with PKC inhibitors alleviated the decreases in Kv7.3 and reduction of M-currents in CRHCeA neurons induced by NMDA. PKC inhibitors did not alter Kv7.2 and Kv7.3 membrane protein levels and M-currents in CRHCeA neurons. These data suggest that transient activation of NMDARs suppresses M-currents through the Ca2+ -dependent PI3K-PIP2 signaling pathway. In contrast, sustained activation of NMDARs reduces Kv7.3 protein expression and suppresses M-currents through a PKC-dependent pathway.

Tr-Predictior: An Ensemble Transfer Learning Model for Small-Sample Cloud Workload Prediction.

Accurate workload prediction plays a key role in intelligent scheduling decisions on cloud platforms. There are massive amounts of short-workload sequences in the cloud platform, and the small amount of data and the presence of outliers make accurate workload sequence prediction a challenge. For the above issues, this paper proposes an ensemble learning method based on sample weight transfer and long short-term memory (LSTM), termed as Tr-Predictor. Specifically, a selection method of similar sequences combining time warp edit distance (TWED) and transfer entropy (TE) is proposed to select a source domain dataset with higher similarity for the target workload sequence. Then, we upgrade the basic learner of the ensemble model two-stage TrAdaBoost.R2 to LSTM in the deep model and enhance the ability of the ensemble model to extract sequence features. To optimize the weight adjustment strategy, we adopt a two-stage weight adjustment strategy and select the best weight for the learner according to the sample error and model error. Finally, the above process determines the parameters of the target model and uses the target model to predict the short-task sequences. In the experimental validation, we arbitrarily select nine sets of short-workload data from the Google dataset and three sets of short-workload data from the Alibaba cluster to verify the prediction effectiveness of the proposed algorithm. The experimental results show that compared with the commonly used cloud workload prediction methods Tr-Predictor has higher prediction accuracy on the small-sample workload. The prediction indicators of the ablation experiments show the performance gain of each part in the proposed method.

Human CD34+ cells in experimental myocardial infarction: long-term survival, sustained functional improvement, and mechanism of action.

RATIONALE: Human CD34(+) cells have been used in clinical trials for treatment of myocardial infarction (MI). However, it is unknown how long the CD34(+) cells persist in hearts, whether the improvement in cardiac function is sustained, or what are the underlying mechanisms. OBJECTIVE: We sought to track the fate of injected human CD34(+) cells in the hearts of severe combined immune deficiency (SCID) mice after experimental MI and to determine the mechanisms of action. METHODS AND RESULTS: We used multimodality molecular imaging to track the fate of injected human CD34(+) cells in the hearts of SCID mice after experimental MI, and used selective antibody blocking to determine the mechanisms of action. Bioluminescence imaging showed that injected CD34(+) cells survived in the hearts for longer than 12 months. The PET signal from the injected cells was detected in the wall of the left ventricle. Cardiac MRI showed that left ventricular ejection fraction was significantly improved in the treated mice compared to the control mice for up to 52 weeks (P<0.05). Furthermore, treatment with anti-alpha4beta1 showed that generation of human-derived cardiomyocytes was inhibited, whereas anti-vascular endothelial growth factor (VEGF) treatment blocked the production of human-derived endothelial cells. However, the improvement in cardiac function was abolished only in the anti-VEGF, but not anti-alpha4beta1, treated group. CONCLUSIONS: Angiogenesis and/or paracrine effect, but not myogenesis, is responsible for functional improvement following CD34(+) cells therapy.

Potential therapeutic value of antioxidants for abnormal prolongation of QT interval and the associated arrhythmias in a rabbit model of diabetes.

Abnormal QT prolongation is the major cardiac electrical disorder and a predictor of mortality in diabetic patients. Our previous studies suggest that dysfunction of delayed rectifier K(+) current (I(Kr)) is the main cause for the problem. Here we report the potential therapeutic role and mechanisms of vitamin E in the rabbit model of diabetes. The QT interval and action potential duration were considerably prolonged with frequent occurrence of ventricular tachyarrhythmias in diabetic rabbits. Administration of vitamin E corrected the abnormal QT prolongation and abolished the arrhythmic incidence. I(Kr) was found markedly reduced resulting in slowing of cardiac repolarization thereby QT prolongation in diabetic hearts. The diabetic depression of I(Kr) is primarily ascribed to oxidative damages to the cardiac membrane and proteins, as indicated by the overproduction of reactive oxygen species leading to severe lipid peroxidation and protein oxidation. Moreover, I(Kr) depression is most likely due to the dysfunction of HERG K(+) channel, the major subunit underlying native I(Kr), in response to oxidative stress, for peroxide anion-generating system produced similar depression of HERG channels. Vitamin E restored the depressed I(Kr) and HERG by its antioxidant actions which likely underlie its beneficial effects on diabetic QT prolongation and the associated arrhythmias. The data indicate that an antioxidant is sufficient for reversing the I(Kr)/I(HERG) dysfunction and the consequent electrical disorders in diabetic hearts. Our study also conceptually simplifies the complex nature of diabetic electrical disorders to primarily oxidative stress, and should stimulate interest in antioxidants as a therapeutic strategy for diabetic QT prolongation.

HERG K+ channel, a regulator of tumor cell apoptosis and proliferation.

The human ether-a-go-go related gene (HERG) encodes K+ channel identified as a molecular target for mutations underlying some forms of the long Q-T syndrome, a lethal cardiac arrhythmia. Recent studies revealed that HERG is abundantly expressed in a variety of tumor cells. Yet, the role of HERG in tumor cells had remained unclear. Here, we show that HERG conductance markedly promotes H2O2-induced apoptosis of various tumor cells, whereas HERG expression facilitates the tumor cell proliferation caused by tumor necrosis factor (TNF) ligand (TNF-alpha). Immunostaining and immunocoprecipitation reveal coexpression of HERG and TNF receptor 1 on the cytoplasmic membrane, which is correlated with greater activities of nuclear transcription factor, nuclear factor-kappaB, in HERG-expressing tumor cells. Our data suggest that HERG K+ channel is a regulator of tumor cell proliferation and apoptosis and provide a potential new target for cancer therapy.

Prostacyclin-producing human mesenchymal cells target H19 lncRNA to augment endogenous progenitor function in hindlimb ischaemia.

Promoting the paracrine effects of human mesenchymal stem cell (hMSC) therapy may contribute to improvements in patient outcomes. Here we develop an innovative strategy to enhance the paracrine effects of hMSCs. In a mouse hindlimb ischaemia model, we examine the effects of hMSCs in which a novel triple-catalytic enzyme is introduced to stably produce prostacyclin (PGI2-hMSCs). We show that PGI2-hMSCs facilitate perfusion recovery and enhance running capability as compared with control hMSCs or iloprost (a stable PGI2 analogue). Transplanted PGI2-hMSCs do not incorporate long term into host tissue, but rather they mediate host regeneration and muscle mass gain in a paracrine manner. Mechanistically, this involves long noncoding RNA H19 in promoting PGI2-hMSC-associated survival and proliferation of host progenitor cells under hypoxic conditions. Together, our data reveal the novel ability of PGI2-hMSCs to stimulate host regenerative processes and improve physical function by regulating long noncoding RNA in resident progenitor cells.

Normal function of HERG K+ channels expressed in HEK293 cells requires basal protein kinase B activity.

The potential role of protein kinase B (PKB), a serine/threonine protein kinase, in regulating HERG (human ether-a-go-go related gene) K(+) channel function was investigated. Wortmannin (a phosphoinositide 3-kinase (PI3K) inhibitor) caused approximately 30% reduction of HERG current (I(HERG)) stably expressed in HEK293 cells. Transient transfection with the constitutively active PI3K in HERG-expressing HEK293 cells slightly increased ( approximately 7%) I(HERG) while a dominant negative PI3K significantly reduced I(HERG) ( approximately 25%) relative to results in vehicle-transfected cells. I(HERG) was approximately 35% greater in cells transfected with the constitutively activated PKB (caPKB), whereas it was approximately 47% smaller in cells transfected with dominant negative PKB (dnPKB). Basal activation of PKB was detected by immunocytochemistry. PKB activity was significantly enhanced in caPKB-transfected cells and nearly abolished in dnPKB-transfected cells. We conclude that normal HERG function in HEK293 cells requires basal activity of PKB. Our data represent the first evidence that PKB phosphorylation regulates K(+) channels.

Potential mechanisms for the enhancement of HERG K+ channel function by phospholipid metabolites.

1. Phospholipid metabolites lysophospholipids cause extracellular K(+) accumulation and action potential shortening with increased risk of arrhythmias during myocardial ischemia. Here we studied effects of several lysophospholipids with different lengths of hydrocarbon chains and charged headgroups on HERG K(+) currents (I(HERG)) expressed in HEK293 cells and the potential mechanisms using whole-cell patch-clamp techniques. 2. Only the lipids with 16 hydrocarbons such as 1-palmitoyl-lysophosphatidylcholine (LPC-16) and 1-palmitoyl-lysophosphatidylglycerol (LPG-16) were found to produce significant enhancement of I(HERG) and negative shifts of HERG activation, although the voltage dependence of the effects was different between LPC-16 and LPG-16 which have differently charged headgroups. The lipid with 18 hydrocarbons modestly increased I(HERG). The lipids with 6 or 24 hydrocarbons had no effect or slightly decreased I(HERG). 3. Inhibition or activation of protein kinase C did not alter the effects of LPC-16 and LPG-16. Participation of phosphatidylinositol-4,5-bisphosphate in I(HERG) enhancement by LPC-16/LPG-16 was also excluded. 4. Vitamin E augmented the effects of LPC-16/LPG-16 whereas xanthine/xanthine oxidase reduced I(HERG): indicating that LPC-16/LPG-16 produced dual effects on I(HERG): direct enhancement of I(HERG) and indirect suppression via production of superoxide anion. 5. We conclude that enhancement of HERG function by lysophospholipids is specific to the lipids with 16-hydrocarbon chain structure and the pattern of voltage dependence is determined by the polar headgroups. The increase in I(HERG) is best described by direct interactions between lipid molecules and HERG proteins, which is consistent with lack of effects via membrane destabilization or modulation by intracellular signaling pathways.

Hyper-SUMOylation of the Kv7 potassium channel diminishes the M-current leading to seizures and sudden death.

Sudden unexplained death in epilepsy (SUDEP) is the most common cause of premature mortality in epilepsy and was linked to mutations in ion channels; however, genes within the channel protein interactome might also represent pathogenic candidates. Here we show that mice with partial deficiency of Sentrin/SUMO-specific protease 2 (SENP2) develop spontaneous seizures and sudden death. SENP2 is highly enriched in the hippocampus, often the focus of epileptic seizures. SENP2 deficiency results in hyper-SUMOylation of multiple potassium channels known to regulate neuronal excitability. We demonstrate that the depolarizing M-current conducted by Kv7 channel is significantly diminished in SENP2-deficient hippocampal CA3 neurons, primarily responsible for neuronal hyperexcitability. Following seizures, SENP2-deficient mice develop atrioventricular conduction blocks and cardiac asystole. Both seizures and cardiac conduction blocks can be prevented by retigabine, a Kv7 channel opener. Thus, we uncover a disease-causing role for hyper-SUMOylation in the nervous system and establish an animal model for SUDEP.

Molecular imaging of mesenchymal stem cell: mechanistic insight into cardiac repair after experimental myocardial infarction.

BACKGROUND: Mesenchymal stem cells (MSCs) can differentiate into endothelial cells in vivo. However, it is unknown if the differentiated MSCs persist in vivo and if this potential persistence contributes to functional improvement after experimental myocardial infarction. METHODS AND RESULTS: We generated a lentivector encoding 2 distinct reporter genes, one driven by a constitutive murine stem cell virus promoter and the other driven by an endothelial-specific Tie-2 promoter. The endothelial specificity of the lentivector was validated by its expression in endothelial cells but not in human MSCs (hMSCs). The lentivirus-transduced hMSCs were injected into peri-infarct areas of the hearts of severe combined immune-deficient mice. Persistence of injected cells was tracked by bioluminescence imaging (BLI) and verified by immunohistochemical staining. The BLI signal from the endothelial-specific reporter revealed that hMSCs differentiated into endothelial cells 48 hours after injection. However, both the constitutive and endothelial-specific BLI signals disappeared by day 50. Nonetheless, the improvement in left ventricle ejection fraction with hMSC therapy persisted for up to 6 months. Immunohistochemical staining showed that hMSC-derived endothelial cells integrated into endogenous CD31(+) vessels. Furthermore, hMSC-transplanted hearts had more CD31(+) vessels and a lesser degree of cardiac fibrosis compared with the controls at 6 months. CONCLUSIONS: hMSCs differentiated into endothelial cells and integrated into blood vessels after experimental myocardial infarction. The differentiated hMSCs only lasted for up to 50 days in vivo, but improvement in cardiac function persisted for up to 6 months. Increased angiogenesis and decreased fibrosis were associated with cardiac functional improvement after hMSC transplantation.

Phospholipid lysophosphatidylcholine as a metabolic trigger and HERG as an ionic pathway for extracellular K accumulation and "short QT syndrome" in acute myocardial ischemia.

The most profound abnormalities during acute myocardial ischemia are extracellular K(+) accumulation ([K(+)](o)- upward arrow) and shortening of action potential duration or QT interval (APD- downward arrow or QT- downward arrow), which are pivotal in the genesis of ischemic arrhythmias and sudden cardiac death. The ionic mechanisms however remained obscured. We performed studies in a rabbit model of acute global myocardial ischemia in order to explore ionic and metabolic mechanisms for ischemic [K(+)](o)- upward arrow and QT- downward arrow. Exogenous 1-palmitoyl-lysophosphatidylcholine (LPC-16) mimicked the low-perfusion ischemia to produce significant [K(+)](o)- upward arrow and QT- downward arrow. The [K(+)](o)- upward arrow and QT- downward arrow induced by either LPC-16 or ischemia were prevented by dofetilide, a blocker of rapid delayed rectifier K(+) current (I(Kr)), but not by blockers for other K(+) channels. Consistently, dofetilide efficiently abolished the ventricular tachy-arrhythmias induced by ischemia or LPC-16. LPC-16 remarkably shortened APD and enhanced the function of I(Kr) and HERG (the pore-forming subunit of I(Kr)). The effects of LPC-16 manifested with shorter APD (faster repolarization rate) and at more negative potential (membrane repolarization). Dofetilide abolished the I(Kr)/HERG enhancing and APD shortening effects of LPC-16. Our results suggest that LPC-16 accumulation/HERG enhancement may be a link between metabolic trigger and ionic pathway for ischemic [K(+)](o)- upward arrow and QTc- downward arrow. This represents the first documentation of I(Kr)/HERG as the ionic mechanism in ischemic [K(+)](o)- upward arrow and QTc- downward arrow. Inhibition of LPC-16 production and accumulation and/or of I(Kr)/HERG may be a promising therapeutic strategy to attenuate the incidence of lethal arrhythmias associated with ischemic heart disease.

Sphingolipid metabolite ceramide causes metabolic perturbation contributing to HERG K+ channel dysfunction.

Ceramide, a sphingolipid metabolite, has emerged as a key second messenger molecule that mediates multiple cellular functions. Its de nova synthesis and accumulation in ischemic myocardium, congestive heart failure and diabetic cardiomyopathy is associated with the abnormalities such as abnormal QT prolongation and increased risk of arrhythmias. To investigate how ceramide is involved in modulating cardiac repolarization, we performed whole-cell patch-clamp studies on HERG current (I(HERG)), a critical determinant of cardiac repolarization, expressed in HEK293 cells. Acute application (superfusion for 25 min) of membrane permeable ceramide (C2, 5 microM) did not alter I(HERG). Prolonged incubation with C2 for 10 hrs caused pronounced I(HERG) inhibition in a concentration-dependent and voltage-independent fashion and positive shift of voltage-dependent HERG activation. The IC(50) for I(HERG) suppression was 19.5 microM. C2 did not affect the inactivation property and time-dependent kinetics of I(HERG). Similar effects were observed with production of endogenous ceramide catalyzed by sphingomyelinase. Tyrosine kinase inhibitors failed to reverse C2-induced suppression of HERG function, and PKA and PKC inhibitors only slightly reversed the I(HERG) depression. Western blotting and immunocytochemical analyses indicate that C2 does not alter HERG protein expression on the cytoplasmic membrane. The inhibitory effect of C2 on I(HERG) was reversed by antioxidants vitamin E or MnTBAP. C2 caused considerable production of intracellular reactive oxygen species (ROS), which was prevented by vitamin E or MnTBAP. We conclude that ceramide depresses I(HERG) mainly via ROS overproduction and ceramide-induced I(HERG) impairment may contribute to QT prolongation in prolonged myocardial ischemia, heart failure and diabetic cardiomyopathy.

Ionic mechanisms underlying abnormal QT prolongation and the associated arrhythmias in diabetic rabbits: a role of rapid delayed rectifier K+ current.

Abnormal QT prolongation with the associated arrhythmias is considered the major cardiac electrical disorder and a significant predictor of mortality in diabetic patients. The precise ionic mechanisms for diabetic QT prolongation remained unclear. We performed whole-cell patch-clamp studies in a rabbit model of alloxan-induced insulin-dependent diabetes mellitus. We demonstrated that heart rate-corrected QT interval and action potential duration (APD) were prolonged by approximately 20% with frequent occurrence of ventricular tachyarrhythmias. Several K(+) currents were found decreased in diabetic rabbits including transient outward K(+)current (I(to)) that was reduced by approximately 60%, rapid delayed rectifier K(+) current (I(Kr)) reduced by approximately 70% and slow delayed rectifier K(+) current (I(Ks)) reduced by approximately 40%. The time-dependent kinetics of these currents remained unaltered. The peak amplitude of L-type Ca% current (I(CaL)) was reduced by approximately 22% and the inactivation kinetics was slowed; the integration of these two effects yielded approximately 15% reduction of I(CaL). The inward rectifier K(+) current (I(K1)) and fast sodium current (I(Na)) were unaffected. Simulation with LabHEART, a computer model of rabbit ventricular action potentials, revealed that inhibition of I(to) or I(Ks) alone fails to alter APD whereas inhibition of I(Kr) alone results in 30% APD prolongation and inhibition of I(CaL) alone causes 10% APD shortening. Integration of changes of all these currents leads to approximately 20% APD lengthening. Protein levels of the pore-forming subunits for these ion channels were decreased to varying extents, as revealed by immunoblotting analysis. Our study represents the first documentation of I(Kr) channelopathy as the major ionic mechanism for diabetic QT prolongation.

Restoring depressed HERG K+ channel function as a mechanism for insulin treatment of abnormal QT prolongation and associated arrhythmias in diabetic rabbits.

Abnormal QT prolongation (QT-P) in diabetic patients has become a nonnegligible clinical problem and has attracted increasing attention from basic scientists, because it increases the risk of lethal ventricular arrhythmias. Correction of QT-P may be an important measure in minimizing sudden cardiac death in diabetic patients. Here we report the efficacy of insulin in preventing QT-P and the associated arrhythmias and the mechanisms underlying the effects in a rabbit model of type 1 insulin-dependent diabetes mellitus (IDDM). The heart rate-corrected QT (QTc) interval and action potential duration were considerably prolonged, with frequent ventricular tachycardias. The rapid delayed rectifier K+ current (IKr) was markedly reduced in IDDM hearts, and hyperglycemia depressed the function of the human ether-a-go-go-related gene (HERG), which conducts IKr. The impairment was primarily ascribed to the enhanced oxidative damage to the myocardium, as indicated by the increased intracellular level of reactive oxygen species and simultaneously decreased endogenous antioxidant reserve and by the increased lipid peroxidation and protein oxidation. Moreover, IDDM or hyperglycemia resulted in downregulation of HERG protein level. Insulin restored the depressed IKr/HERG and prevented QTc/action potential duration prolongation and the associated arrhythmias, and the beneficial actions of insulin are partially due to its antioxidant ability. Our study represents the first documentation of oxidative stress as the major metabolic mechanism for HERG K+ dysfunction, which causes diabetic QT-P, and suggests IKr/HERG as a potential therapeutic target for treatment of the disorder.

Impairment of human ether-à-go-go-related gene (HERG) K+ channel function by hypoglycemia and hyperglycemia. Similar phenotypes but different mechanisms.

Hyperglycemia and hypoglycemia both can cause prolongation of the Q-T interval and ventricular arrhythmias. Here we studied modulation of human ether-à-go-go-related gene (HERG) K(+) channel, the major molecular component of delayed rectifier K(+) current responsible for cardiac repolarization, by glucose in HEK293 cells using whole-cell patch clamp techniques. We found that both hyperglycemia (extracellular glucose concentration [Glu](o) = 10 or 20 mm) and hypoglycemia ([Glu](o) = 2.5, 1, or 0 mm) impaired HERG function by reducing HERG current (I(HERG)) density, as compared with normoglycemia ([Glu](o) = 5 mm). Complete inhibition of glucose metabolism (glycolysis and oxidative phosphorylation) by 2-deoxy-d-glucose mimicked the effects of hypoglycemia, but inhibition of glycolysis or oxidative phosphorylation alone did not cause I(HERG) depression. Depletion of intracellular ATP mimicked the effects of hypoglycemia, and replacement of ATP by GTP or non-hydrolysable ATP failed to prevent the effects. Inhibition of oxidative phosphorylation by NaCN or application of antioxidants vitamin E or superoxide dismutase mimetic (Mn(III) tetrakis(4-benzoic acid) porphyrin chloride) abrogated and incubation with xanthine/xanthine oxidase mimicked the effects of hyperglycemia. Hyperglycemia or xanthine/xanthine oxidase markedly increased intracellular levels of reactive oxygen species, as measured by 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate (CM-H(2)DCFDA) fluorescence dye, and this increase was prevented by NaCN, vitamin E, or Mn(III) tetrakis(4-benzoic acid) porphyrin chloride. We conclude that ATP, derived from either glycolysis or oxidative phosphorylation, is critical for normal HERG function; depression of I(HERG) in hypoglycemia results from underproduction of ATP and in hyperglycemia from overproduction of reactive oxygen species. Impairment of HERG function might contribute to Q-T prolongation caused by hypoglycemia and hyperglycemia.

Impairment of HERG K(+) channel function by tumor necrosis factor-alpha: role of reactive oxygen species as a mediator.

Congestive heart failure (CHF) is associated with susceptibility to lethal arrhythmias and typically increases levels of tumor necrosis factor-alpha (TNF-alpha) and its receptor, TNFR1. CHF down-regulates rapid delayed-rectifier K(+) current (I(Kr)) and delays cardiac repolarization. We studied the effects of TNF-alpha on cloned HERG K(+) channel (human ether-a-go-go-related gene) in HEK293 cells and native I(Kr) in canine cardiomyocytes with whole-cell patch clamp techniques. TNF-alpha consistently and reversibly decreased HERG current (I(HERG)). Effects of TNF-alpha were concentration-dependent, increased with longer incubation period, and occurred at clinically relevant concentrations. TNF-alpha had similar inhibitory effects on I(Kr) and markedly prolonged action potential duration (APD) in canine cardiomyocytes. Immunoblotting analysis demonstrated that HERG protein level was slightly higher in canine hearts with tachypacing-induced CHF than in healthy hearts, and TNF-alpha slightly increased HERG protein level in CHF but not in healthy hearts. In cells pretreated with the inhibitory anti-TNFR1 antibody, TNF-alpha lost its ability to suppress I(HERG), indicating a requirement of TNFR1 activation for HERG suppression. Vitamin E or MnTBAP (Mn(III) tetrakis(4-benzoic acid) porphyrin chloride), a superoxide dismutase mimic) prevented, whereas the superoxide anion generating system xanthine/xanthine oxidase mimicked, TNF-alpha-induced I(HERG) depression. TNF-alpha caused robust increases in intracellular reactive oxygen species, and vitamin E and MnTBAP abolished the increases, in both HEK293 cells and canine ventricular myocytes. We conclude that the TNF-alpha/TNFR1 system impairs HERG/I(Kr) function mainly by stimulating reactive oxygen species, particularly superoxide anion, but not by altering HERG expression; the effect may contribute to APD prolongation by TNF-alpha and may be a novel mechanism for electrophysiological abnormalities and sudden death in CHF.

Progressive apoptotic cell death triggered by transient oxidative insult in H9c2 rat ventricular cells: a novel pattern of apoptosis and the mechanisms.

Many pathophysiological processes are associated with oxidative stress and progressive cell death. Oxidative stress is an apoptotic inducer that is known to cause rapid cell death. Here we show that a brief oxidative insult (5-min exposure to 400 microM H(2)O(2)), although it did not kill H9c2 rat ventricular cells during the exposure, triggered an intracellular death cascade leading to delayed time-dependent cell death starting from 1 h after the insult had been withdrawn, and this post-H(2)O(2) cell death cumulated gradually, reaching a maximum level 8 h after H(2)O(2) withdrawal. By comparison, sustained exposure to H(2)O(2) caused complete cell death within a narrow time frame (2 h). The time-dependent post-H(2)O(2) cell death was typical of apoptosis, both morphologically (cell shrinkage and nuclear condensation) and biochemically (DNA fragmentation, extracellular exposure of phosphatidylserines, and caspase-3 activation). A dichlorofluorescein fluorescent signal showed a time-dependent endogenous increase of reactive oxygen species (ROS) production, which was almost abolished by inhibition of the mitochondrial electron transport chain. Application of antioxidants (vitamin E or DTT) before H(2)O(2) addition or after H(2)O(2) withdrawal prevented the H(2)O(2)-triggered progressive ROS production and apoptosis. Sequential appearance of events associated with activation of the mitochondrial death pathway was found, including progressive dissipation of mitochondrial membrane potential, cytochrome c release, and late activation of caspase-3. In conclusion, transient oxidative stress triggers an intrinsic program leading to self-sustained apoptosis in H9c2 cells via cumulative production of mitochondrial ROS and subsequent activation of the mitochondrial death pathway. This pattern of apoptosis may contribute to the progressive and long-lasting cell loss in some degenerative diseases.

HERG K channel conductance promotes H2O2-induced apoptosis in HEK293 cells: cellular mechanisms.

The human ether-a-go-go-related gene (HERG) encodes a delayed rectifier K(+) channel, which is expressed in a variety of tissues and cells. Besides its well-recognized function in cellular electrophysiology, HERG channels have also been implicated in neuronal differentiation and cell cycle regulation. We have recently found that HERG regulates apoptosis. To elucidate the signaling pathways, we performed studies in HEK293 cells stably expressing HERG channels. ELISA was used to quantify DNA fragmentation, a biochemical hallmark of apoptosis. In HERG-transfected HEK cells, the degree of DNA fragmentation was found consistently higher (approximately 4-times) than in non-transfected cells. Correspondingly, remarkable activation of caspase 3, caspase 9 and cleavage of PARP were seen in HERG-expressing cells, which were otherwise minimal in non-transfected cells. Exposure of cells to H(2)O(2) (10 hrs) at concentrations up to 1 mM, which is known to induce apoptosis in a variety of cells, caused minimal DNA fragmentation in non-transfected cells. HERG expression facilitates DNA fragmentation induced by H(2)O(2) at a concentration-dependent fashion, starting at 200 microM and reaching maximum at 1 mM. Selective HERG channel inhibitors, dofetilide or E-4031 (5 microM) prevented DNA fragmentation. Inhibition of p38 by SB-203580 alleviated DNA-F and PD-98059, which inhibited activation of ERKs, nearly abolished DNA-F. Immunoblotting analysis demonstrated that p38, SAPKs and ERKs MAP kinases were all substantially activated (>10-fold higher) in HERG-expressing cells vs. non-transfected cells. Akt activity was approximately 4-fold lower in HERG cells vs. non-transfected cells in the absence of H(2)O(2) and was slightly increased (approximately 2-fold) after H(2)O(2) exposure. We conclude that HERG channels facilitate cellular DNA fragmentation in HEK cells via concomitant activation of MAP kinases and inactivation of Akt.