Inhibition of the uric acid efflux transporter ABCG2 enhances stimulating effect of soluble uric acid on IL-1β production in murine macrophage-like J774.1 cells

Soluble uric acid (UA) absorbed by cells through UA transporters (UATs) accumulates intracellularly, activates the NLRP3 inflammasome and thereby increases IL-1β secretion. ABCG2 transporter excludes intracellular UA. However, it remains unknown whether ABCG2 inhibition leads to intracellular accumulation of UA and increases IL-1β production. In this study, we examined whether genetic and pharmacological inhibition of ABCG2 could increase IL-1β production in mouse macrophage-like J774.1 cells especially under hyperuricemic conditions. We determined mRNA and protein levels of pro-IL-1β, mature IL-1β, caspase-1 and several UATs in culture supernatants and lysates of J774.1 cells with or without soluble UA pretreatment. Knockdown experiments using an shRNA against ABCG2 and pharmacological experiments with an ABCG2 inhibitor were conducted. Extracellularly applied soluble UA increased protein levels of pro-IL-1β, mature IL-1β and caspase-1 in the culture supernatant from lipopolysaccharide (LPS)-primed and monosodium urate crystal (MSU)-stimulated J774.1 cells. J774.1 cells expressed UATs of ABCG2, GLUT9 and MRP4, and shRNA knockdown of ABCG2 increased protein levels of pro-IL-1β and mature IL-1β in the culture supernatant. Soluble UA increased mRNA and protein levels of ABCG2 in J774.1 cells without either LPS or MSU treatment. An ABCG2 inhibitor, febuxostat, but not a urate reabsorption inhibitor, dotinurad, enhanced IL-1β production in cells pretreated with soluble UA. In conclusion, genetic and pharmacological inhibition of ABCG2 enhanced IL-1β production especially under hyperuricemic conditions by increasing intracellularly accumulated soluble UA that activates the NLRP3 inflammasome and pro-IL-1β transcription in macrophage-like J774.1 cells.

Deep learning-based identification of sinoatrial node-like pacemaker cells from SHOX2/HCN4 double-positive cells differentiated from human iPS cells

BACKGROUND

Cardiomyocytes derived from human iPS cells (hiPSCs) include cells showing SAN- and non-SAN-type spontaneous APs.

OBJECTIVES

To examine whether the deep learning technology could identify hiPSC-derived SAN-like cells showing SAN-type-APs by their shape.

METHODS

We acquired phase-contrast images for hiPSC-derived SHOX2/HCN4 double-positive SAN-like and non-SAN-like cells and made a VGG16-based CNN model to classify an input image as SAN-like or non-SAN-like cell, compared to human discriminability.

RESULTS

All parameter values such as accuracy, recall, specificity, and precision obtained from the trained CNN model were higher than those of human classification.

CONCLUSIONS

Deep learning technology could identify hiPSC-derived SAN-like cells with considerable accuracy.

Effects of Conditioned Medium of Adipose-Derived Stem Cells Exposed to Platelet-Rich Plasma on the Expression of Endothelial Nitric Oxide Synthase and Angiogenesis by Endothelial Cells

ABSTRACT

Platelet-rich plasma (PRP) and adipose-derived stem cells (ADSCs) are known to secrete angiogenic factors that contribute to the treatment of intractable ulcers. The combination of PRP and ADSCs may enhance their angiogenic effects. However, it remains unclear whether treatment of ADSCs with PRP influences angiogenesis. We studied whether the conditioned medium from PRP-treated ADSCs under hypoxic conditions exerts angiogenic effects. Although PRP stimulated the proliferation of ADSCs obtained from rats, it decreased the mRNA levels of vascular endothelial growth factor, hepatocyte growth factor, and TGF-β1, but not of basic fibroblast growth factor, under hypoxia. The conditioned medium of PRP-treated ADSCs inhibited endothelial nitric oxide synthase phosphorylation, decreased NO production, and suppressed tube formation in human umbilical vein endothelial cells. Transplantation of ADSCs alone increased both blood flow and capillary density of the ischemic limb; however, its combination with PRP did not further improve blood flow or capillary density. This suggests that both conditioned medium of ADSCs treated with PRP and combination of PRP with ADSCs transplantation may attenuate the phosphorylation of endothelial nitric oxide synthase and angiogenesis.

Kv1.5 channel mediates monosodium urate-induced activation of NLRP3 inflammasome in macrophages and arrhythmogenic effects of urate on cardiomyocytes

BACKGROUND

Gout is usually found in patients with atrial fibrillation (AF). K+ efflux is a common trigger of NLRP3 inflammasome activation which is involved in the pathogenesis of AF. We investigated the role of the K+ channel Kv1.5 in monosodium urate crystal (MSU)-induced activation of the NLRP3 inflammasome and electrical remodeling in mouse and human macrophages J774.1 and THP-1, and mouse atrial myocytes HL-1.

METHODS AND RESULTS

Macrophages, primed with lipopolysaccharide (LPS), were stimulated by MSU. HL-1 cells were incubated with the conditioned medium (CM) from MSU-stimulated macrophages. Western blot, ELISA and patch clamp were used. MSU induced caspase-1 expression in LPS-primed J774.1 cells and IL-1β secretion, suggesting NLRP3 inflammasome activation. A selective Kv1.5 inhibitor, diphenyl phosphine oxide-1 (DPO-1), and siRNAs against Kv1.5 suppressed the levels of caspase-1 and IL-1β. MSU reduced intracellular K+ concentration which was prevented by DPO-1 and siRNAs against Kv1.5. MSU increased expression of Hsp70, and Kv1.5 on the plasma membrane. siRNAs against Hsp70 were suppressed but heat shock increased the expression of Hsp70, caspase-1, IL-1β, and Kv1.5 in MSU-stimulated J774.1 cells. The CM from MSU-stimulated macrophages enhanced the expression of caspase-1, IL-1β and Kv1.5 with increased Kv1.5-mediated currents that shortened action potential duration in HL-1 cells. These responses were abolished by DPO-1 and a siRNA against Kv1.5.

CONCLUSIONS

Kv1.5 regulates MSU-induced activation of NLRP3 inflammasome in macrophages. MSUrelated activation of NLRP3 inflammasome and electrical remodeling in HL-1 cells are via macrophages. Kv1.5 may have therapeutic value for diseases related to gout-induced activation of the NLRP3 inflammsome, including AF.

Hsp70 promotes maturation of uromodulin mutants that cause familial juvenile hyperuricemic nephropathy and suppresses cellular damage

BACKGROUND

Familial juvenile hyperuricemic nephropathy (FJHN) is an autosomal dominant disorder caused by mutations in UMOD. Here we studied effects of genetic expression and pharmacological induction of Hsp70 on the UMOD mutants C112Y and C217G.

METHODS

We expressed wild type (WT), C112Y and C217G in HEK293 cells and studied their maturation and cellular damage using western blot and flow cytometry.

RESULTS

Expression of C112Y or C217G increased pro-apoptotic proteins, decreased anti-apoptotic proteins, and induced cellular apoptosis as examined by annexin V staining and flow cytometry. Overexpression of Hsp70 or administration of an Hsp70 inducer geranylgeranylacetone (GGA) promoted maturation of the mutant proteins, increased their secreted forms, normalized the levels of pro- and anti-apoptotic proteins and suppressed apoptosis.

CONCLUSION

These findings indicated that Hsp70 enhanced maturation of C112Y and C217G and reduced cellular apoptosis, suggesting that Hsp70 induction might be of a therapeutic value for treatment of FJHN.

α1-Adrenergic receptor mediates adipose-derived stem cell sheet-induced protection against chronic heart failure after myocardial infarction in rats

Cell-based therapy using adipose-derived stem cells (ADSCs) has emerged as a novel therapeutic approach to treat heart failure after myocardial infarction (MI). The purpose of this study was to determine whether inhibition of α1-adrenergic receptors (α1-ARs) in ADSCs attenuates ADSC sheet-induced improvements in cardiac functions and inhibition of remodeling after MI. ADSCs were isolated from fat tissues of Lewis rats. In in vitro studies using cultured ADSCs, we determined the mRNA levels of vascular endothelial growth factor (VEGF)-A and α1-AR under normoxia or hypoxia and the effects of norepinephrine and an α1-blocker, doxazosin, on the mRNA levels of angiogenic factors. Hypoxia increased α1-AR and VEGF mRNA levels in ADSCs. Norepinephrine further increased VEGF mRNA expression under hypoxia; this effect was abolished by doxazosin. Tube formation of human umbilical vein endothelial cells was promoted by conditioned media of ADSCs treated with the α1 stimulant phenylephrine under hypoxia but not by those of ADSCs pretreated with phenylephrine plus doxazosin. In in vivo studies using rats with MI, transplanted ADSC sheets improved cardiac functions, facilitated neovascularization, and suppressed fibrosis after MI. These effects were abolished by doxazosin treatment. Pathway analysis from RNA sequencing data predicted significant upregulation of α1-AR mRNA expression in transplanted ADSC sheets and the involvement of α1-ARs in angiogenesis through VEGF. In conclusion, doxazosin abolished the beneficial effects of ADSC sheets on rat MI hearts as well as the enhancing effect of norepinephrine on VEGF expression in ADSCs, indicating that ADSC sheets promote angiogenesis and prevent cardiac dysfunction and remodeling after MI via their α1-ARs.

Esm1 and Stc1 as Angiogenic Factors Responsible for Protective Actions of Adipose-Derived Stem Cell Sheets on Chronic Heart Failure After Rat Myocardial Infarction

BACKGROUND

Although adipose-derived stem cell (ADSC) sheets improve the cardiac function after myocardial infarction (MI), underlying mechanisms remain to be elucidated. The aim of this study was to determine the fate of transplanted ADSC sheets and candidate angiogenic factors released from ADSCs for their cardiac protective actions.Methods and Results:MI was induced by ligation of the left anterior descending coronary artery. Sheets of transgenic (Tg)-ADSCs expressing green fluorescence protein (GFP) and luciferase or wild-type (WT)-ADSCs were transplanted 1 week after MI. Both WT- and Tg-ADSC sheets improved cardiac functions evaluated by echocardiography at 3 and 5 weeks after MI. Histological examination at 5 weeks after MI demonstrated that either sheet suppressed fibrosis and increased vasculogenesis. Luciferase signals from Tg-ADSC sheets were detected at 1 and 2 weeks, but not at 4 weeks, after transplantation. RNA sequencing of PKH (yellow-orange fluorescent dye with long aliphatic tails)-labeled Tg-ADSCs identified mRNAs of 4 molecules related to angiogenesis, including those of Esm1 and Stc1 that increased under hypoxia. Administration of Esm1 or Stc1 promoted tube formation by human umbilical vein endothelial cells.

CONCLUSIONS

ADSC sheets improved cardiac contractile functions after MI by suppressing cardiac fibrosis and enhancing neovascularization. Transplanted ADSCs existed for >2 weeks on MI hearts and produced the angiogenic factors Esm1 and Stc1, which may improve cardiac functions after MI.

Evidence for Urate Uptake Through Monocarboxylate Transporter 9 Expressed in Mammalian Cells and Its Enhancement by Heat Shock

Background: Monocarboxylate transporter 9 (MCT9), an orphan transporter member of the solute carrier family 16 (SLC16), possibly reabsorbs uric acid in the renal tubule and has been suggested by genome-wide association studies to be involved in the development of hyperuricemia and gout. In this study we investigated the mechanisms regulating the expression of human (h) MCT9, its degradation, and physiological functions. Methods and Results: hMCT9-FLAG was stably expressed in HEK293 cells and its degradation, intracellular localization, and urate uptake activities were assessed by pulse-chase analysis, immunofluorescence, and [¹⁴C]-urate uptake experiments, respectively. hMCT9-FLAG was localized on the plasma membrane as well as in the endoplasmic reticulum and Golgi apparatus. The proteasome inhibitors MG132 and lactacystine increased levels of hMCT9-FLAG protein expression with enhanced ubiquitination, prolonged their half-life, and decreased [¹⁴C]-urate uptake. [¹⁴C]-urate uptake was increased by both heat shock (HS) and the HS protein inducer geranylgeranylacetone (GGA). Both HS and GGA restored the [¹⁴C]-urate uptake impaired by MG132. Conclusions: hMCT9 does transport urate and is degraded by a proteasome, inhibition of which reduces hMCT9 expression on the cell membrane and urate uptake. HS enhanced urate uptake through hMCT9.

Pretreatment with cilnidipine attenuates hypoxia/reoxygenation injury in HL-1 cardiomyocytes through enhanced NO production and action potential shortening

Myocardial ischemia/reperfusion injury worsens in the absence of nitric oxide synthase (NOS). Cilnidipine, a Ca²⁺ channel blocker, has been reported to activate endothelial NOS (eNOS) and increases nitric oxide (NO) in vascular endothelial cells. We examined whether pretreatment with cilnidipine could attenuate cardiac cell deaths including apoptosis caused by hypoxia/reoxygenation (H/R) injury. HL-1 mouse atrial myocytes as well as H9c2 rat ventricular cells were exposed to H/R, and cell viability was evaluated by an autoanalyzer and flow cytometry; eNOS expression, NO production, and electrophysiological properties were also evaluated by western blotting, colorimetry, and patch clamping, respectively, in the absence and presence of cilnidipine. Cilnidipine enhanced phosphorylation of eNOS and NO production in a concentration-dependent manner, which was abolished by siRNAs against eNOS or an Hsp90 inhibitor, geldanamycin. Pretreatment with cilnidipine attenuated cell deaths including apoptosis during H/R; this effect was reproduced by an NO donor and a xanthine oxidase inhibitor. The NOS inhibitor L-NAME abolished the protective action of cilnidipine. Pretreatment with cilnidipine also attenuated H9c2 cell death during H/R. Additional cilnidipine treatment during H/R did not significantly enhance its protective action. There was no significant difference in the protective effect of cilnidipine under normal and high Ca²⁺ conditions. Action potential duration (APD) of HL-1 cells was shortened by cilnidipine, with this shortening augmented after H/R. L-NAME attenuated the APD shortening caused by cilnidipine. These findings indicate that cilnidipine enhances NO production, shortens APD in part by L-type Ca²⁺ channel block, and thereby prevents HL-1 cell deaths during H/R.

β-Adrenergic Blocker, Carvedilol, Abolishes Ameliorating Actions of Adipose-Derived Stem Cell Sheets on Cardiac Dysfunction and Remodeling After Myocardial Infarction

BACKGROUND

Treatment of myocardial infarction (MI) includes inhibition of the sympathetic nervous system (SNS). Cell-based therapy using adipose-derived stem cells (ASCs) has emerged as a novel therapeutic approach to treat heart failure in MI. The purpose of this study was to determine whether a combination of ASC transplantation and SNS inhibition synergistically improves cardiac functions after MI.Methods and Results:ASCs were isolated from fat tissues of Lewis rats. In in vitro studies using cultured ASC cells, mRNA levels of angiogenic factors under normoxia or hypoxia, and the effects of norepinephrine and a β-blocker, carvedilol, on the mRNA levels were determined. Hypoxia increased vascular endothelial growth factor (VEGF) mRNA in ASCs. Norepinephrine further increased VEGF mRNA; this effect was unaffected by carvedilol. VEGF promoted VEGF receptor phosphorylation and tube formation of human umbilical vein endothelial cells, which were inhibited by carvedilol. In in vivo studies using a rat MI model, transplanted ASC sheets improved contractile functions of MI hearts; they also facilitated neovascularization and suppressed fibrosis after MI. These beneficial effects of ASC sheets were abolished by carvedilol. The effects of ASC sheets and carvedilol on MI heart functions were confirmed by Langendorff perfusion experiments using isolated hearts.

CONCLUSIONS

ASC sheets prevented cardiac dysfunctions and remodeling after MI in a rat model via VEGF secretion. Inhibition of VEGF effects by carvedilol abolished their beneficial effects.

Novel dual-reporter transgenic rodents enable cell tracking in animal models of stem cell transplantation

In the present study, we have established a novel transgenic mouse and transgenic rats with dual reporters of EGFP and ELuc. In these transgenic (Tg) rodents, both GFP fluorescent and luciferase luminescent signals were ubiquitously detected in the heart, liver, kidney and testis, while only the GFP signal was detected in the brain. This expression system is based on a P2A linked EGFP/ELuc protein allowing both signals to be generated simultaneously. Microscopy experiments, FCM, and luciferase assays showed strong expression in freshly isolated ADSCs from Tg rodents upon transplantation of Tg rat-derived ADSCs into wild-type-mice. The ELuc transgene signal was observed and traced in vivo, and EGFP positive cells could be recovered from ELuc positive tissues in engraftment sites of wild-type mice for multiple analysis. These dual reporter Tg rodents are a useful reconstituted model system of regenerative medicine and are a valuable tool to study stem cells.

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Establishment of dual reporter transgenic mice and rats, which express luciferase and GFP in all organs.

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Both luciferase and GFP signals were detected by in vivo imaging using their respective antibodies.

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Isolated mesenchymal stem cells from transgenic rodents showed both luciferase and GFP signals.

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Implantation of transgenic mesenchymal stem cells enables cell tracking in vivo.

Inhibitory effects of class I antiarrhythmic agents on Na+ and Ca2+ currents of human iPS cell-derived cardiomyocytes

INTRODUCTION

Human induced pluripotent stem cells (hiPSCs) harboring cardiac myosin heavy chain 6 promoter can differentiate into functional cardiomyocytes called "iCell cardiomyocytes" under blasticidin treatment condition. While iCell cardiomyocytes are expected to be used for predicting cardiotoxicity of drugs, their responses to antiarrhythmic agents remain to be elucidated. We first examined electrophysiological properties of iCell cardiomyocytes and mRNA levels of ion channels and Ca handling proteins, and then evaluated effects of class I antiarrhythmic agents on their Na+ and Ca2+ currents.

METHODS

iCell cardiomyocytes were cultured for 8-14 days (38-44 days after inducing their differentiation), according to the manufacturer's protocol. We determined their action potentials (APs) and sarcolemmal ionic currents using whole-cell patch clamp techniques, and also mRNA levels of ion channels and Ca handling proteins by RT-PCR. Effects of three class I antiarrhythmic agents, pirmenol, pilsicainide and mexiletine, on Na+ channel current (INa) and L-type Ca2+ channel current (ICaL) were evaluated by the whole-cell patch clamp.

RESULTS

iCell cardiomyocytes revealed sinoatrial node-type (18%), atrial-type (18%) and ventricular-type (64%) spontaneous APs. The maximum peak amplitudes of INa, ICaL, and rapidly-activating delayed-rectifier K+ channel current were -62.7 ± 13.7, -8.1 ± 0.7, and 3.0 ± 1.0 pA/pF, respectively. The hyperpolarization-activated cation channel and inward-rectifier K+ channel currents were observed, whereas the T-type Ca2+ channel or slowly-activating delayed-rectifier K+ channel current was not detectable. mRNAs of Nav1.5, Cav1.2, Kir2.1, HCN4, KvLQT1, hERG and SERCA2 were detected, while that of HCN1, minK or MiRP was not. The class Ia antiarrhythmic agent pirmenol and class Ic agent pilsicainide blocked INa in a concentration-dependent manner with IC50 of 0.87 ± 0.37 and 0.88 ± 0.16 μM, respectively; the class Ib agent mexiletine revealed weak INa block with a higher IC50 of 30.0 ± 3.0 μM. Pirmenol, pilsicainide and mexiletine blocked ICaL with IC50 of 2.00 ± 0.39, 7.7 ± 2.5 and 5.0 ± 0.1 μM, respectively.

CONCLUSIONS

In iCell cardiomyocytes, INa was blocked by the class Ia and Ic antiarrhythmic agents and ICaL was blocked by all the class I agents within the ranges of clinical concentrations, suggesting their cardiotoxicity.

Pretreatment with an angiotensin II receptor blocker abolished ameliorating actions of adipose-derived stem cell sheets on cardiac dysfunction and remodeling after myocardial infarction

Introduction

Cell sheets using myoblasts have been developed for the treatment of heart failure after myocardial infarction (MI) bridging to heart transplantation. Stem cells are supposed to be better than myoblasts as a source of cells, since they possess a potential to proliferate and differentiate into cardiomyocytes, and also have capacity to secrete angiogenic factors. Adipose-derived stem cells (ASCs) obtained from fat tissues are expected to be a new cell source for ASC sheet therapies. Administration of angiotensin II receptor blockers (ARBs) is a standard therapy for heart failure after MI. However, it is not known whether ARBs affect the cell sheet therapy. This study aimed to examine ameliorating effects of ASC sheets on heart failure and remodeling after MI, and how pretreatment with ARBs prior to the creation of MI and ASC sheet transplantation modifies the effects of ASC sheets.

Methods

ASCs were isolated from fat tissues of wild-type rats, and ASC sheets were engineered on temperature-responsive dishes. In in vitro studies using cultured cells, mRNA levels of vascular endothelial growth factor (VEGF) in ASCs were determined by RT-PCR in the presence of angiotensin II and/or an ARB, irbesartan, under normoxia and hypoxia; mRNA and protein levels of angiotensin II receptor type 1a (AT1aR), type 1b (AT1bR) and type 2 (AT2R) were also determined by RT-PCR and western blotting. In in vivo studies using a rat MI model, effects of transplanted ASC sheets and/or irbesartan on cardiac functions and remodeling after MI were evaluated by echocardiography, histological analysis and molecular biological techniques.

Results

In the in vitro studies, ASCs expressed higher levels of VEGF mRNA under hypoxia. They also expressed mRNA and protein of AT1aR but not AT1bR or AT2R. Under normoxia, angiotensin II increased the level of VEGF mRNA in ASCs, which was abolished by irbesartan. Under hypoxia, irbesartan reduced the level of VEGF mRNA in ASCs regardless of whether angiotensin II was present or not. In the in vivo studies, ASC sheets improved cardiac functions after MI, leading to decreased interstitial fibrosis and increased capillary density in border zones. These effects of ASC sheets were abolished by oral administration of irbesartan before MI and their transplantation.

Conclusions

ASC sheets ameliorated cardiac dysfunctions and remodeling after MI via increasing VEGF expression, which was abolished by pretreatment with irbesartan before the creation of MI and transplantation.

Tbx18-positive cells differentiated from murine ES cells serve as proepicardial progenitors to give rise to vascular smooth muscle cells and fibroblasts

Proepicardium (PE) cells generate cardiac fibroblasts, smooth muscle cells (SMCs) and endothelial cells that form coronary arteries. T-box18 (Tbx18) is a well-known marker of PE cells and epicardium. We examined whether Tbx18-positive cells differentiated from murine embryonic stem (ES) cells serve as PE progenitors to give rise to vascular SMCs and fibroblasts. To collect Tbx18-positive cells, we established Tbx18-EGFP knock-in mouse ES cells using the CRISPR/Cas9 system. We harvested the Tbx18-EGFP-positive cells on day 8, 10 and 14 after the initiation of differentiation; Tbx18 mRNA was enriched on day 8 to 14 and Snai2 mRNA was enriched on day 8 and 10, indicating successful collection of Tbx18-positive cells. Tbx18-EGFP-positive cells expressed the PE marker WT1 on day 8 and 10. They also expressed the SMC marker Acta2 and fibroblast markers Thy1 and Fsp1 on day 8 to 14, but did not express the endothelial cell marker PECAM or the cardiac cell marker CD166 or Myh7. In conclusion, Tbx18-positive cells represent a part of PE cells in the initial phase of differentiation and subsequently include SMCs as well as fibroblasts. These results indicate that Tbx18-positive cells serve as a PE progenitor to supply a variety of cells that contribute to the formation of coronary arteries.

Protective Effects of Topiroxostat on an Ischemia-Reperfusion Model of Rat Hearts

BACKGROUND

Ischemia/reperfusion (I/R) injury triggers cardiac dysfunctions via creating reactive oxygen species (ROS). Because xanthine oxidase (XO) is one of the major enzymes that generate ROS, inhibition of XO is expected to suppress ROS-induced I/R injury. However, it remains unclear whether XO inhibition really yields cardioprotection during I/R. The protective effects of the XO inhibitors, topiroxostat and allopurinol, on cardiac I/R injury were evaluated.Methods and Results:Using isolated rat hearts, ventricular functions, occurrence of arrhythmias, XO activities and thiobarbituric acid reactive substances (TBARS) productions and myocardial levels of adenine nucleotides before and after I/R, and cardiomyocyte death markers during reperfusion, were evaluated. Topiroxostat prevented left ventricular dysfunctions and facilitated recovery from arrhythmias during I/R. Allopurinol and the antioxidant, N-acetylcysteine (NAC), exhibited similar effects at higher concentrations. Topiroxostat inhibited myocardial XO activities and TBARS productions after I/R. I/R decreased myocardial levels of ATP, ADP and AMP, but increased that of xanthine. While topiroxostat, allopurinol or NAC did not change myocardial levels of ATP, ADP or AMP after I/R, all of the agents decreased the level of xanthine. They also decreased releases of CPK and LDH during reperfusion.

CONCLUSIONS

Topiroxostat showed protective effects against I/R injury with higher potency than allopurinol or NAC. It dramatically inhibited XO activity and TBARS production, suggesting suppression of ROS generation.

Restoration of mutant hERG stability by inhibition of HDAC6

The human ether-a-go-go-related gene (hERG) encodes the α subunit of a rapidly activating delayed-rectifier potassium (I_Kr) channel. Mutations of the hERG cause long QT syndrome type 2 (LQT2). Acetylation of lysine residues occurs in a subset of non-histone proteins and this modification is controlled by both histone acetyltransferases and deacetylases (HDACs). The aim of this study was to clarify effects of HDAC(s) on wild-type (WT) and mutant hERG proteins. WThERG and two trafficking-defective mutants (G601S and R752W) were transiently expressed in HEK293 cells, which were treated with a pan-HDAC inhibitor Trichostatin A (TSA) or an isoform-selective HDAC6 inhibitor Tubastatin A (TBA). Both TSA and TBA increased protein levels of WThERG and induced expression of mature forms of the two mutants. Immunoprecipitation showed an interaction between HDAC6 and immature forms of hERG. Coexpression of HDAC6 decreased acetylation and, reciprocally, increased ubiquitination of hERG, resulting in its decreased expression. siRNA against HDAC6, as well as TBA, exerted opposite effects. Immunochemistry revealed that HDAC6 knockdown increased expression of the WThERG and two mutants both in the endoplasmic reticulum and on the cell surface. Electrophysiology showed that HDAC6 knockdown or TBA treatment increased the hERG channel current corresponding to the rapidly activating delayed-rectifier potassium current (I_Kr) in HEK293 cells stably expressing the WT or mutants. Three lysine residues (K116, K495 and K757) of hERG were predicted to be acetylated. Substitution of these lysine residues with arginine eliminated HDAC6 effects. In HL-1 mouse cardiomyocytes, TBA enhanced endogenous ERG expression, increased I_Kr, and shortened action potential duration. These results indicate that hERG is a substrate of HDAC6. HDAC6 inhibition induced acetylation of hERG which counteracted ubiquitination leading its stabilization. HDAC6 inhibition may be a novel therapeutic option for LQT2.

Isolation and characterization of ventricular-like cells derived from NKX2-5eGFP/w and MLC2vmCherry/w double knock-in human pluripotent stem cells

Human pluripotent stem cell (hPSC)-derived cardiomyocytes (CMs) are a promising source for cell transplantation into the damaged heart, which has limited regenerative ability. Many methods have been developed to obtain large amounts of functional CMs from hPSCs for therapeutic applications. However, during the differentiation process, a mixed population of various cardiac cells, including ventricular, atrial, and pacemaker cells, is generated, which hampers the proper functional analysis and evaluation of cell properties. Here, we established NKX2-5^eGFP/w and MLC2v^mCherry/w hPSC double knock-ins that allow for labeling, tracing, purification, and analysis of the development of ventricular cells from early to late stages. As with the endogenous transcriptional activities of these genes, MLC2v-mCherry expression following NKX2-5-eGFP expression was observed under previously established culture conditions, which mimic the in vivo cardiac developmental process. Patch-clamp and microelectrode array electrophysiological analyses showed that the NKX2-5 and MLC2v double-positive cells possess ventricular-like properties. The results demonstrate that the NKX2-5^eGFP/w and MLC2v^mCherry/w hPSCs provide a powerful model system to capture region-specific cardiac differentiation from early to late stages. Our study would facilitate subtype-specific cardiac development and functional analysis using the hPSC-derived sources.

Molecular mechanisms underlying the pilsicainide-induced stabilization of hERG proteins in transfected mammalian cells

Background

Pilsicainide, classified as a relatively selective Na⁺ channel blocker, also has an inhibitory action on the rapidly-activating delayed-rectifier K⁺ current (I_Kr) through human ether-a-go-go-related gene (hERG) channels. We studied the effects of chronic exposure to pilsicainide on the expression of wild-type (WT) hERG proteins and WT-hERG channel currents, as well as on the expression of mutant hERG proteins, in a heterologous expression system.

Methods

HEK293 cells stably expressing WT or mutant hERG proteins were subjected to Western blotting, immunofluorescence microscopy and patch-clamp experiments.

Results

Acute exposure to pilsicainide at 0.03–10 μM influenced neither the expression of WT-hERG proteins nor WT-hERG channel currents. Chronic treatment with 0.03–10 μM pilsicainide for 48 h, however, increased the expression of WT-hERG proteins and channel currents in a concentration-dependent manner. Chronic treatment with 3 μM pilsicainide for 48 h delayed degradation of WT-hERG proteins and increased the channels expressed on the plasma membrane. A cell membrane-impermeant pilsicainide derivative did not influence the expression of WT-hERG, indicating that pilsicainide stabilized the protein inside the cell. Pilsicainide did not influence phosphorylation of Akt (protein kinase B) or expression of heat shock protein families such as HSF-1, hsp70 and hsp90. E4031, a chemical chaperone for hERG, abolished the pilsicainide effect on hERG. Chronic treatment with pilsicainide could also increase the protein expression of trafficking-defective mutant hERG, G601S and R752W.

Conclusions

Pilsicainide penetrates the plasma membrane, stabilizes WT-hERG proteins by acting as a chemical chaperone, and enhances WT-hERG channel currents. This mechanism could also be applicable to modulations of certain mutant-hERG proteins.

Characterization of the novel mutant A78T-HERG from a long QT syndrome type 2 patient: Instability of the mutant protein and stabilization by heat shock factor 1

BACKGROUND

The human ether-a-go-go-related gene (HERG) encodes the α-subunit of rapidly activating delayed-rectifier potassium channels. Mutations in this gene cause long QT syndrome type 2 (LQT2). In most cases, mutations reduce the stability of the channel protein, which can be restored by heat shock (HS).

METHODS

We identified the novel mutant A78T-HERG in a patient with LQT2. The purpose of the current study was to characterize this mutant protein and test whether HS and heat shock factors (HSFs) could stabilize the mutant protein. A78T-HERG and wild-type HERG (WT-HERG) were expressed in HEK293 cells and analyzed by immunoblotting, immunoprecipitation, immunofluorescence, and whole-cell patch clamping.

RESULTS

When expressed in HEK293 cells, WT-HERG gave rise to immature and mature forms of the protein at 135 and 155 kDa, respectively. A78T-HERG gave rise only to the immature form, which was heavily ubiquitinated. The proteasome inhibitor MG132 increased the expression of immature A78T-HERG and increased both the immature and mature forms of WT-HERG. WT-HERG, but not A78T-HERG, was expressed on the plasma membrane. In whole-cell patch clamping experiments, depolarizing pulses evoked E4031-sensitive HERG channel currents in cells transfected with WT-HERG, but not in cells transfected with A78T-HERG. The A78V mutant, but not A78G mutant, remained in the immature form similarly to A78T. Maturation of the A78T-HERG protein was facilitated by HS, expression of HSF-1, or exposure to geranyl geranyl acetone.

CONCLUSIONS

A78T-HERG was characterized by protein instability and reduced expression on the plasma membrane. The stability of the mutant was partially restored by HSF-1, indicating that HSF-1 is a target for the treatment for LQT2 caused by the A78T mutation in HERG.

Prion Protein and Stage Specific Embryo Antigen 1 as Selection Markers to Enrich the Fraction of Murine Embryonic Stem Cell-Derived Cardiomyocytes

BACKGROUND

The prion protein (PrP) might be useful as a tool to collect cardiac progenitor cells derived from embryonic stem (ES) cells. It is also possible that PrP(+) cells include undifferentiated cells with a capacity to develop into tumors.

METHODS

PrP(+) cells isolated from embryoid bodies (EB) formed by mouse AB1 ES cells were examined using RT-PCR analysis and clonogeneic cell assay. To assess their potential to differentiate into cardiomyocytes, Nkx2.5(GFP/+) (hcgp7) cells, another ES cell line that carries the GFP reporter gene in the Nkx2.5 loci, were used.

RESULTS

PrP(+) cells isolated from EB of day 7 and 14 did not express pluripotency markers, but expressed cardiac cell markers, while PrP(+) cells isolated from EB of day 21 expressed pluripotency markers. Cultured PrP(+) cells isolated from EB of day 21 expressed pluripotency markers to form colonies, whereas those isolated from EB of day 7 and 14 did not. To exclude proliferating cells from PrP(+) cells, stage specific embryo antigen 1 (SSEA1) was employed as a second marker. PrP(+)/SSEA1(-) cells did not proliferate and expressed cardiac cell markers, while PrP(+)/SSEA1(+) did proliferate.

CONCLUSION

PrP(+) cells isolated from EB included undifferentiated cells in day 21. PrP(+)/SSEA1(-) cells included cardiomyoctes, suggesting PrP and SSEA1 may be useful as markers to enrich the fraction of cardiomyocytes.

Electrophysiological properties of iPS cell-derived cardiomyocytes from a patient with long QT syndrome type 1 harboring the novel mutation M437V of KCNQ1

Introduction

Long QT syndrome type 1 (LQT1) is caused by mutations in KCNQ1 coding slowly-activating delayed-rectifier K⁺ channels. We identified the novel missense mutation M437V of KCNQ1 in a LQT1 patient. Here, we employed iPS cell (iPSC)-derived cardiomyocytes to investigate electrophysiological properties of the mutant channel and LQT1 cardiomyocytes.

Methods

To generate iPSCs from the patient and a healthy subject, peripheral blood T cells were reprogrammed by Sendai virus vector encoding human OCT3/4, SOX2, KLF4, and c-MYC. Cardiomyocytes were prepared from iPSCs and human embryonic stem cells using a cytokine-based two-step differentiation method and were subjected to patch clamp experiments.

Results

LQT1 iPSC-derived cardiomyocytes exhibited prolongation of action potential duration (APD), which was due to a reduction of the KCNQ1-mediated current I_Ks; Na⁺, Ca²⁺ and other K⁺ channel currents were comparable. When expressed in HEK293 and COS7 cells, the mutant KCNQ1 was normally expressed in the plasma membrane but generated smaller currents than the wild type. Isoproterenol significantly prolonged APDs of LQT1 cardiomyocytes, while shortening those of healthy ones. A mathematical model for I_Ks-reduced human ventricular myocytes reproduced APD prolongation and generation of early afterdepolarizations (EADs) under β-adrenergic stimulation.

Conclusions

QT prolongation of the LQT1 patient with the mutation M437V of KCNQ1 was caused by I_Ks reduction, which may render the patient vulnerable to generation of EADs and arrhythmias.

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M437V mutation of KCNQ1 reduces channel conductance without trafficking defect.

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Reduced I_Ks of the mutant channel accounts for the prolongation of APD and QTc.

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Lack of medical history in this case is due to relatively small reduction in I_Ks.

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The patient is more vulnerable to generation of EAD and TdP than healthy subjects.

VEGF secretion by adipose tissue-derived regenerative cells is impaired under hyperglycemic conditions via glucose transporter activation and ROS increase

Transplantation of cultured adipose-derived regenerative cells (ADRCs) into ischemic tissues promotes neovascularization and blood perfusion recovery. These effects are attenuated in diabetes patients. We examined the effects of hyperglycemia on the angiogenic capacity of ADRCs derived from Wistar rats both in vivo and in vitro. Cultured ADRCs were predominantly composed of CD90 positive cells; prevalence of CD90 positive cells was not affected by hyperglycemia. mRNA and protein levels of vascular endothelial growth factor (VEGF) were significantly decreased in ADRCs under hyperglycemic conditions independent of osmolarity, whereas mRNA levels of hepatocyte growth factor and fibroblast growth factor were unaffected. Since ADRCs express glucose transporter proteins GLUT1, 3 and 4, we examined the effects of the glucose transporter inhibitor phloretin on reactive oxygen species (ROS) and angiogenic factors. Phloretin decreased the glucose uptake rate, reduced ROS, and increased VEGF mRNA in ADRCs exposed to a hyperglycemic condition. In vivo transplantation of ADRCs cultured under hyperglycemic conditions into mouse ischemic limbs resulted in significantly decreased blood perfusion and capillary density in ischemic regions compared with transplantation of ADRCs cultured under normoglycemic conditions. These results suggest that hyperglycemia impaired VEGF production in ADRCs via an increase of ROS, impairing the angiogenic capacity of ADRCs transplanted into ischemic limbs.

Carvedilol Suppresses Apoptosis and Ion Channel Remodelling of HL-1 Cardiac Myocytes Expressing E334K cMyBPC

BACKGROUND

Besides its antiarrhythmic action, carvedilol has an activity to suppress cardiac tissue damage. However, it is unknown whether it has any effect on cellular apoptosis and ion channel remodelling.

PURPOSE

To know whether carvedilol has any effect on apoptosis and ion channel remodeling of HL-1 cells expressing E334K MyBPC, and comparing it with bisoprolol.

METHOD

We examined effects of carvedilol and bisoprolol on the levels of pro- and anti-apoptotic proteins and ion channels as well as apoptosis of HL-1 cells transfected with E334K MyBPC using Western blot and flow cytometry.

RESULTS

Carvedilol decreased the protein levels of p53, Bax and cytochrome c and increased that of Bcl-2 in HL-1 cells expressing E334K MyBPC. Bisoprolol failed to affect the protein levels. Both carvedilol and bisoprolol increased the protein levels of Cav1.2 but not that of Nav1.5. Carvedilol was stronger than bisoprolol at decreasing the number of annexin-V positive cells in HL-1 cells expressing E334K MyBPC.

CONCLUSION

Carvedilol suppressed apoptosis of HL-1 cells expressing E334K MyBPC through modification of pro- and anti-apoptotic proteins, whose was associated with an increase of Cav 1.2 protein expression.

Molecular Mechanisms Underlying Urate-Induced Enhancement of Kv1.5 Channel Expression in HL-1 Atrial Myocytes

BACKGROUND

Hyperuricemia induces endothelial dysfunction, oxidative stress and inflammation, increasing cardiovascular morbidities. It also raises the incidence of atrial fibrillation; however, underlying mechanisms are unknown.

METHODS AND RESULTS

The effects of urate on expression of Kv1.5 in cultured mouse atrial myocytes (HL-1 cells) using reverse transcriptase-PCR, immunoblots, flow cytometry and patch-clamp experiments were studied. Treatment with urate at 7 mg/dl for 24 h increased the Kv1.5 protein level, enhanced ultra-rapid delayed-rectifier K(+)channel currents and shortened action potential duration in HL-1 cells. HL-1 cells expressed the influx uric acid transporter (UAT), URATv1, and the efflux UATs, ABCG2 and MRP4. An inhibitor against URATv1, benzbromarone, abolished the urate effects, whereas an inhibitor against ABCG2, KO143, augmented them. Flow cytometry showed that urate induced an increase in reactive oxygen species, which was abolished by the antioxidant, N-acetylcysteine (NAC), and the NADPH-oxidase inhibitor, apocynin. Both NAC and apocynin abolished the enhancing effects of urate on Kv1.5 expression. A urate-induced increase in the Kv1.5 proteins was accompanied by phosphorylation of extracellular signal-regulated kinase (ERK), and was abolished by an ERK inhibitor, PD98059. NAC abolished phosphorylation of ERK by urate.

CONCLUSIONS

Intracellular urate taken up by UATs enhanced Kv1.5 protein expression and function in HL-1 atrial myocytes, which could be attributable to ERK phosphorylation and oxidative stress derived from nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase.

E3 ligase CHIP and Hsc70 regulate Kv1.5 protein expression and function in mammalian cells

Kv1.5 confers ultra-rapid delayed-rectifier potassium channel current (IKur) which contributes to repolarization of the atrial action potential. Kv1.5 proteins, degraded via the ubiquitin-proteasome pathway, decreased in some atrial fibrillation patients. Carboxyl-terminus heat shock cognate 70-interacting protein (CHIP), an E3 ubiquitin ligase, is known to ubiquitinate short-lived proteins. Here, we investigated the roles of CHIP in Kv1.5 degradation to provide insights into the mechanisms of Kv1.5 decreases and treatments targeting Kv1.5 for atrial fibrillation. Coexpression of CHIP with Kv1.5 in HEK293 cells increased Kv1.5 protein ubiquitination and decreased the protein level. Immunofluorescence revealed decreases of Kv1.5 proteins in the endoplasmic reticulum and on the cell membrane. A siRNA against CHIP suppressed Kv1.5 protein ubiquitination and increased its protein level. CHIP mutants, lacking either the N-terminal tetratricopeptide region domain or the C-terminal U-box domain, failed to exert these effects on Kv1.5 proteins. Immunoprecipitation showed that CHIP formed complexes with Kv1.5 proteins and heat shock cognate protein 70 (Hsc70). Effects of Hsc70 on Kv1.5 were similar to CHIP by altering interaction of CHIP with Kv1.5 protein. Coexpression of CHIP and Hsc70 with Kv1.5 additionally enhanced Kv1.5 ubiquitination. Kv1.5 currents were decreased by overexpression of CHIP or Hsc70 but were increased by knockdown of CHIP or Hsc70 in HEK 293 cells stably expressing Kv1.5. These effects of CHIP and Hsc70 were also observed on endogenous Kv1.5 in HL-1 mouse cardiomyocytes, decreasing IKur and prolonging action potential duration. These results indicate that CHIP decreases the Kv1.5 protein level and functional channel by facilitating its degradation in concert with chaperone Hsc70.

P19 Cells Overexpressing Lhx1 Differentiate into the Definitive Endoderm by Recapitulating an Embryonic Developmental Pathway

BACKGROUND

Epiblasts occur at the last pluripotent stage of embryonic development and are important in elucidating how the three germ layers are formed. However, little is known of the molecular mechanisms of their development. We have shown that LIM homeobox 1 (Lhx1) was involved in epiblast development in embryonic stem cells, especially meso- and endodermal differentiation. However, since epiblasts in embryoid bodies spontaneously develop into a further stage, it is difficult to study their development in this system.

METHODS

Mouse embryonal carcinoma P19 cells which have properties similar to those of epiblasts provided new avenues of investigation into the regulatory mechanism of epiblasts.

RESULTS

Overexpression of Lhx1 in P19 cells induced expression of organizer marker genes (Cer1, Gsc) and endoderm marker genes (Gata6, Foxa2, Sox17) but not extra-embryonic endoderm marker genes (Sox7 or Hnf4alpha).

CONCLUSION

This study suggested that Lhx1 overexpression caused P19 cells to differentiate into an endodermal lineage. Thus, P19 cells and their derivatives can be a useful model system to study how the three germ layers are formed.

Bepridil Suppresses Apoptosis in HL-1 Cardiac Atrial Myocytes Expressing Mutant E334K cMyBPC

Besides its antiarrhythmic effect on atrial fibrillation, bepridil protects tissue, yet its effect on apoptosis has never been fully tested. We examine the effect of bepridil on apoptosis of HL-1 cells expressing E334K myosin-binding protein C (MyBPC), a model cell of apoptosis. Bepridil was compared with amiodarone, and its effects on the expression of pro- and anti-apoptotic protein and apoptosis of HL-1 cells expressing mutant E334K MyBPC-green fluorescent protein (GFP) was analyzed using Western blot and a flow cytometer. Bepridil decreased the protein levels of both Bax and cytochrome c of cells expressing E334K MyBPC-GFP with no changes in p53 and Bcl-2, while amiodarone decreased cytochrome c but did not influence Bax except in its highest concentration. It also decreased the number of Annexin-V positive cells of HL-1 cells expressing E334K MyBPC-GFP, and decreased apoptosis of HL-1 cells expressing E334K MyBPC-GFP.

Hsp90 prevents interaction between CHIP and HERG proteins to facilitate maturation of wild-type and mutant HERG proteins

AIMS

We examined the role of Hsp90 in expression and maturation of wild-type (WT) and mutant ether-a-go-go related gene (HERG) proteins by using Hsp90 inhibitors, geldanamycin (GA) and radicicol, and Hsp90 overexpression.

METHODS AND RESULTS

The proteins were expressed in HEK293 cells or collected from HL-1 mouse cardiomyocytes, and analysed by western blotting, immunoprecipitation, immunofluorescence, and whole-cell patch-clamp techniques. GA and radicicol suppressed maturation of HERG-FLAG proteins and increased their immature forms. Co-expression of Hsp90 counteracted the effects of Hsp90 inhibitors and suppressed ubiquitination of HERG proteins. Overexpressed Hsp90 also inhibited the binding of endogenous C-terminus of Hsp70-interacting protein (CHIP) to HERG-FLAG proteins. Hsp90-induced increase of functional HERG proteins was verified by their increased expression on the cell surface and enhanced HERG channel currents. CHIP overexpression decreased both mature and immature forms of HERG-FLAG proteins in cells treated with GA. Hsp90 facilitated maturation of endogenous ERG proteins, whereas CHIP decreased both forms of ERG proteins in HL-1 cells. Mutant HERG proteins harbouring disease-causing missense mutations were mainly in the immature form and had a higher binding capacity to CHIP than the WT; Hsp90 overexpression suppressed this association. Overexpressed Hsp90 increased the mature form of HERG(1122fs/147) proteins, reduced its ubiquitinated form, increased its immunoreactivity in the endoplasmic reticulum and on the plasma membrane, and increased the mutant-mediated membrane current. CHIP overexpression decreased the immature form of HERG(1122fs/147) proteins.

CONCLUSION

Enhancement of HERG protein expression through Hsp90 inhibition of CHIP binding might be a novel therapeutic strategy for long QT syndrome 2 caused by trafficking abnormalities of HERG proteins.

AMP deaminase 3 plays a critical role in remote reperfusion lung injury

Remote reperfusion lung injury following skeletal muscle ischemia and reperfusion accounts for high morbidity and mortality. AMP deaminase (AMPD), a key enzyme for nucleotide cycle, has been implicated in the regulation of this phenomenon. However, the function of Ampd2 and Ampd3 subtype has not been elucidated in remote reperfusion rodent lung injury. We utilized AMPD3 and AMPD2-deficient mice. The two types of AMPD-deficient mice and wild-type (WT) littermates were subjected to ischemia-reperfusion injury. After 3h bilateral hind-limb ischemia and reperfusion, AMPD3 mRNA, AMPD activity and inosine monophosphate (IMP) increased significantly in WT and AMPD2-deficient mice lungs, while they did not show significant alterations in AMPD3-deficient mice lungs. Genetic inactivation of Ampd3 resulted in markedly accelerated myeloperoxidase (MPO) activity along with exaggerated neutrophils infiltration and hemorrhage in the lungs compared to WT and AMPD2-deficient mice, furthermore, IMP treatment significantly attenuated MPO activity and neutrophils infiltration in WT and the two types of AMPD-deficient mice lungs after 3h reperfusion. These findings demonstrate for the first time in AMP-deficient mice models that AMPD3 plays a critical role in remote reperfusion lung injury via generation of IMP and validate the potential to use IMP into the clinical arena to attenuate remote ischemia-reperfusion lung injury.

Heterochromatin protein 1γ overexpression in P19 embryonal carcinoma cells elicits spontaneous differentiation into the three germ layers

P19 embryonal carcinoma (EC) cells are pluripotent stem cells and have numerous morphological and biochemical properties in common with embryonic stem (ES) cells. However, P19 cells differentiate very ineffectively as embryoid bodies (EBs) without the specific chemical inducers whereas ES cells exhibit spontaneous differentiation to the three germ layers. Recently the heterochromatin protein 1 (HP1) family protein HP1γ, which is an epigenetic modulator that binds histone H3 methylated at lysine 9, is shown to be associated with the progression from pluripotent to differentiated status in ES cells. Therefore, to study the role of HP1γ in the differentiation capacity of P19 cells, we have established a HP1γ-overexpressing P19 cell line (HPlγ-P19). Similar to the parental P19 cells, undifferentiated HP1γ-P19 cells continued to express pluripotency marker genes. However, HP1γ-P19 cells exhibited significant morphological differentiation including beating cardiomyocytes, as well as Tuj1-positive neuronal cells and Sox17-positive endodermal cells after EB formation under a normal culture condition. Moreover, real-time RT-qPCR analysis revealed that HP1γ-P19 EB cells expressed various differentiation marker genes. Thus, HP1γ-P19 cells could give rise to all three germ layers in EBs without any drug treatment. Therefore, HP1γ affects the spontaneous differentiation potential of P19 cells, and might play major roles in the decision of cell fates in pluripotent stem cells.

Stabilization of Kv1.5 channel protein by bepridil through its action as a chemical chaperone

While bepridil has been reported to alter the stability of ion channel proteins, the precise mechanism of action remains unclear. We examined the effect of bepridil on the stability of Kv1.5 channel proteins expressed in COS7 cells. Bepridil at 0.3-30 μM increased the protein level of Kv1.5 channels in a concentration-dependent manner. Chase experiments showed that bepridil delayed the degradation process of Kv1.5 channel proteins in the same manner as a proteasomal inhibitor, MG132, did. Bepridil increased the immunofluorescent signal of Kv1.5 channel proteins in the endoplasmic reticulum (ER) and Golgi apparatus and on the cell surface. The cell fraction experiment also showed bepridil-induced increases in Kv1.5 in the ER, Golgi apparatus, and the cell membrane. Bepridil at a lower concentration of 1 μM had no effect on the proteasome activity in vitro. A blocker of the ultrarapid delayed-rectifier K(+) channel current, 4-aminopyridine (4AP), abolished bepridil-induced increases in Kv1.5. Kv1.5-medicated membrane currents measured as 4AP-sensitive currents were increased by bepridil. Taken together, we conclude that bepridil stabilizes Kv1.5 proteins at the ER through an action as a chemical chaperone, thereby increasing the density of Kv1.5 channels in the cell membrane.

Electrophysiological properties of prion-positive cardiac progenitors derived from murine embryonic stem cells

BACKGROUND

The prion protein (PrP) has been reported to serve as a surface maker for isolation of cardiomyogenic progenitors from murine embryonic stem (ES) cells. Although PrP-positive cells exhibited automaticity, their electrophysiological characteristics remain unresolved. The aim of the present study was therefore to investigate the electrophysiological properties of PrP-positive cells in comparison with those of HCN4p-or Nkx2.5-positive cells.

METHODS AND RESULTS

Differentiation of AB1, HCN5p-EGFP and hcgp7 ES cells into cardiac progenitors was induced by embryoid body (EB) formation. EBs were dissociated and cells expressing PrP, HCN4-EGFP and/or Nkx2.5-GFP were collected via flow cytometry. Sorted cells were subjected to reverse transcriptase-polymerase chain reaction, immunostaining and patch-clamp experiments. PrP-positive cells expressed mRNA of undifferentiation markers, first and second heart field markers, and cardiac-specific genes and ion channels, indicating their commitment to cardiomyogenic progenitors. PrP-positive cells with automaticity showed positive and negative chronotropic responses to isoproterenol and carbamylcholine, respectively. Hyperpolarization-activated cation current (I(f)) was barely detectable, whereas Na(+) and L-type Ca(2+) channel currents were frequently observed. Their spontaneous activity was slowed by inhibition of sarcoplasmic reticulum Ca(2+) uptake and release but not by blocking I(f). The maximum diastolic potential of their spontaneous firings was more depolarized than that of Nkx2.5-GFP-positive cells.

CONCLUSIONS

PrP-positive cells contained cardiac progenitors that separated from the lineage of sinoatrial node cells. PrP can be used as a marker to enrich nascent cardiac progenitors.

Novel effects of extracts from poisonous mushrooms on expression and function of the human ether-a-go-go-related gene channel

The human ether-a-go-go-related gene (hERG) encodes the α subunit of the potassium current I(Kr), which plays a pivotal role in cardiac action potential repolarization. Inherited mutations of this gene cause Long QT syndrome type 2. hERG expression is altered by several types of drugs as well as by temperature. Heat shock protein 70 (Hsp70) and Heat shock cognate protein 70 (Hsc70) have reciprocal effects on hERG proteins. We examined the effects of poisonous mushrooms on hERG protein expression and its channel function.

METHODS

We evaluated the effects of several types of poisonous mushrooms on the expression and function of wild-type hERG by Western blotting, reverse transcription polymerase chain reaction (PCR), and patch clamping in transfected HEK293 cells and mouse HL-1 cardiomyocytes.

RESULTS

Extracts of Gymnopilus junonius (junonius) increased expression of both hERG and Hsp70 in HEK293 cells with concomitant decrease in Hsc70, whereas extracts of Amanita ibotengutake (ibotengutake) decreased hERG proteins with increase in Hsc70. Knockdown of Hsp70 and Hsc70 by small interfering RNA abolished the effects of the two mushrooms on hERG, respectively. Certain fractions of junonius increased expression of hERG proteins. hERG currents were increased by extracts of junonius, resulting in shortening of action potential duration (APD). In contrast, hERG currents were decreased and APD was prolonged by extracts of ibotengutake.

CONCLUSION

junonius enhanced the expression and function of hERG by increasing Hsp70 and decreasing Hsc70. Ibotengutake decreased hERG expression via increase in Hsc70. Constituents of junonius may have the potential for use in treatment of arrhythmia.

Enhancing effects of salicylate on quinidine-induced block of human wild type and LQT3 related mutant cardiac Na+ channels

It is unknown whether salicylate enhances the action of antiarrhythmic agents on human Na+ channels with state dependency and tissue specificity. We therefore investigated effects of salicylate on quinidine-induced block of human cardiac and skeletal muscle Na+ channels. Human cardiac wild-type (hH1), LQT3-related mutant (ΔKPQ), and skeletal muscle (hSkM1) Na+ channel α subunits were expressed in COS7 cells. Effects of salicylate on quinidine-induced tonic and use-dependent block of Na+ channel currents were examined by the whole-cell patch-clamp technique. Salicylate enhanced the quinidine-induced tonic and use-dependent block of both hH1 and hSkM1 currents at a holding potential (HP) of -100 mV but not at -140 mV. Salicylate decreased the IC50 value for the quinidine-induced tonic block of hH1 at an HP of -100 mV, and produced a negative shift in the steady-state inactivation curve of hH1 in the presence of quinidine. According to the modulated receptor theory, it is probable that salicylate decreases the dissociation constant for quinidine binding to inactivated-state channels. Furthermore, salicylate significantly enhanced the quinidine-induced tonic and use-dependent block of the peak and steady-state ΔKPQ channel currents. The results suggest that salicylate enhances quinidine-induced block of Na+ channels via increasing the affinity of quinidine to inactivated state channels.

Transcriptional activation of the anchoring protein SAP97 by heat shock factor (HSF)-1 stabilizes K(v) 1.5 channels in HL-1 cells

BACKGROUND AND PURPOSE

The expression of voltage-dependent K⁺ channels (K_v) 1.5 is regulated by members of the heat shock protein (Hsp) family. We examined whether the heat shock transcription factor 1 (HSF-1) and its inducer geranylgeranylacetone (GGA) could affect the expression of K_v1.5 channels and its anchoring protein, synapse associated protein 97 (SAP97).

EXPERIMENTAL APPROACH

Transfected mouse atrial cardiomyocytes (HL-1 cells) and COS7 cells were subjected to luciferase reporter gene assay and whole-cell patch clamp. Protein and mRNA extracts were subjected to Western blot and quantitative real-time polymerase chain reaction.

KEY RESULTS

Heat shock of HL-1 cells induced expression of Hsp70, HSF-1, SAP97 and K_v1.5 proteins. These effects were reproduced by wild-type HSF-1. Both heat shock and expression of HSF-1, but not the R71G mutant, increased the SAP97 mRNA level. Small interfering RNA (siRNA) against SAP97 abolished HSF-1-induced increase of K_v1.5 and SAP97 proteins. A luciferase reporter gene assay revealed that the SAP97 promoter region (from −919 to −740) that contains heat shock elements (HSEs) was required for this induction. Suppression of SIRT1 function either by nicotinamide or siRNA decreased the level of SAP97 mRNA. SIRT1 activation by resveratrol had opposing effects. A treatment of the cells with GGA increased the level of SAP97 mRNA, K_v1.5 proteins and I_Kur current, which could be modified with either resveratrol or nicotinamide.

CONCLUSIONS AND IMPLICATIONS

HSF-1 induced transcription of SAP97 through SIRT1-dependent interaction with HSEs; the increase in SAP97 resulted in stabilization of K_v1.5 channels. These effects were mimicked by GGA.

Different distribution of Cav3.2 and Cav3.1 transcripts encoding T-type Ca(2+) channels in the embryonic heart of mice

We investigated the distribution of T-type Ca(2+) channel mRNAs in the mouse embryonic heart. Cav3.2, but not Cav3.1, was expressed in the E8.5 embryonic heart along with cardiac progenitor markers (Nkx2.5, Tbx5, Isl-1) and contractile proteins (alpha and beta MHC). In the E10.5 heart, the distribution of Cav3.1 mRNA was confirmed in the AV-canal and overlapped with that of MinK or Tbx2. Cav3.2 mRNA was observed not only in the AV-canal but also in the outflow tract, along with MinK and Isl-1, indicating the expression of Cav3.2 in the secondary heart field. Thus, Cav3.2 may contribute to the development of the outflow tract from the secondary heart field in the embryonic heart, whereas Cav3.1 may be involved in the development of the cardiac conduction-system together with Cav3.2.

Reciprocal control of hERG stability by Hsp70 and Hsc70 with implication for restoration of LQT2 mutant stability

RATIONALE

The human ether-a-go-go-related gene (hERG) encodes the α subunit of the potassium current I(Kr). It is highly expressed in cardiomyocytes and its mutations cause long QT syndrome type 2. Heat shock protein (Hsp)70 is known to promote maturation of hERG. Hsp70 and heat shock cognate (Hsc70) 70 has been suggested to play a similar function. However, Hsc70 has recently been reported to counteract Hsp70.

OBJECTIVE

We investigated whether Hsc70 counteracts Hsp70 in the control of wild-type and mutant hERG stability.

METHODS AND RESULTS

Coexpression of Hsp70 with hERG in HEK293 cells suppressed hERG ubiquitination and increased the levels of both immature and mature forms of hERG. Immunocytochemistry revealed increased levels of hERG in the endoplasmic reticulum and on the cell surface. Electrophysiological studies showed increased I(Kr). All these effects of Hsp70 were abolished by Hsc70 coexpression. Heat shock treatment of HL-1 mouse cardiomyocytes induced endogenous Hsp70, switched mouse ERG associated with Hsc70 to Hsp70, increased I(Kr), and shortened action potential duration. Channels with disease-causing missense mutations in intracellular domains had a higher binding capacity to Hsc70 than wild-type channels and channels with mutations in the pore region. Knockdown of Hsc70 by small interfering RNA or heat shock prevented degradation of mutant hERG proteins with mutations in intracellular domains.

CONCLUSIONS

These results indicate reciprocal control of hERG stability by Hsp70 and Hsc70. Hsc70 is a potential target in the treatment of LQT2 resulting from missense hERG mutations.

Refined human artificial chromosome vectors for gene therapy and animal transgenesis

Human artificial chromosomes (HACs) have several advantages as gene therapy vectors, including stable episomal maintenance, and the ability to carry large gene inserts. We previously developed HAC vectors from the normal human chromosomes using a chromosome engineering technique. However, endogenous genes were remained in these HACs, limiting their therapeutic applications. In this study, we refined a HAC vector without endogenous genes from human chromosome 21 in homologous recombination-proficient chicken DT40 cells. The HAC was physically characterized using a transformation-associated recombination (TAR) cloning strategy followed by sequencing of TAR-bacterial artificial chromosome clones. No endogenous genes were remained in the HAC. We demonstrated that any desired gene can be cloned into the HAC using the Cre-loxP system in Chinese hamster ovary cells, or a homologous recombination system in DT40 cells. The HAC can be efficiently transferred to other type of cells including mouse ES cells via microcell-mediated chromosome transfer. The transferred HAC was stably maintained in vitro and in vivo. Furthermore, tumor cells containing a HAC carrying the suicide gene, herpes simplex virus thymidine kinase (HSV-TK), were selectively killed by ganciclovir in vitro and in vivo. Thus, this novel HAC vector may be useful not only for gene and cell therapy, but also for animal transgenesis.

Identification, isolation and characterization of HCN4-positive pacemaking cells derived from murine embryonic stem cells during cardiac differentiation

BACKGROUND

Development of biological pacemaker is a potential treatment for bradyarrhythmias. Pacemaker cells could be extracted from differentiated embryonic stem (ES) cells based on their specific cell marker hyperpolarization-activated cyclic nucleotide-gated (HCN)4. The goal of this study was to develop a method of identification, isolation, and characterization of pacemaking cells derived from differentiated ES cells with GFP driven by HCN4 promoter.

METHODS AND RESULTS

Polymerase chain reaction (PCR) screening and southern blot analysis revealed that HCN4p-EGFP trans-gene was stably integrated into the chromosome of mouse AB1 ES cells. RT-PCR and immunostaining results showed similar expression of the specific cardiac pacemaker markers of the HCN4p-EGFP ES cells and its parental AB1 ES cell lines. Although HCN4p-EGFP trans-gene may have slight effect on the general mesodermal differentiation, it had no effect on the pluripotency of ES cells, on the transcription of cardiac specific factors and cardiac contractile proteins, and on the capability of ES cells to differentiate into pacemaker cells. Electrophysiological study indicated that HCN4p-GFP-positive cells revealed the spontaneous action potential, which was slowed by the treatment with 2 mM Cs(+), and expressed the hyperpolarization-activeted cation current I(f) encoded by HCN4 gene.

CONCLUSION

By the approach of using stable transfectant of HCN4p-EGFP gene, the identification, isolation, and characterization of ES cell-derived pacemaking cells could be carried out.

Pendrin is a novel autoantigen recognized by patients with autoimmune thyroid diseases

CONTEXT

Pendrin is an apical protein of thyroid follicular cells, responsible for the efflux of iodide into the follicular lumen via an iodide-chloride transport mechanism. It is unknown whether pendrin is recognized by autoantibodies.

OBJECTIVE

Our objective was to examine the prevalence of pendrin antibodies in autoimmune thyroid diseases and compare with that of thyroglobulin, thyroperoxidase, TSH receptor, and sodium iodide symporter antibodies.

DESIGN

In a prevalent case-control study, we analyzed the sera of 140 autoimmune thyroid disease cases (100 with Graves' disease and 40 with Hashimoto's thyroiditis) and 80 controls (50 healthy subjects, 10 patients with papillary thyroid cancer, 10 with systemic lupus erythematosus, and 10 with rheumatoid arthritis). Pendrin antibodies were measured by immunoblotting using extract of COS-7 cells transfected with pendrin and a rabbit polyclonal pendrin antibody.

RESULTS

Pendrin antibodies were found in 81% of the cases and 9% of controls (odds ratio = 44; P < 0.0001). Among cases, pendrin antibodies were more frequent and of higher titers in Hashimoto's thyroiditis than in Graves' disease. Pendrin antibodies correlated significantly with thyroglobulin, thyroperoxidase, and sodium iodide symporter antibodies but not with TSH receptor antibodies. Pendrin antibodies were equally effective as thyroglobulin and thyroperoxidase antibodies in diagnosis of autoimmune thyroid diseases, especially Hashimoto's thyroiditis.

CONCLUSIONS

The study identifies pendrin as a novel autoantigen recognized by patients with autoimmune thyroid diseases and proposes the use of pendrin antibodies as an accurate diagnostic tool.