Mitochondrial Responses to Sublethal Doxorubicin in H9c2 Cardiomyocytes: The Role of Phosphorylated CaMKII

Background

Doxorubicin (Dox) is effective against different types of cancers, but it poses cardiotoxic side effects, frequently resulting in irreversible heart failure. However, the complexities surrounding this cardiotoxicity, especially at sublethal dosages, remain to be fully elucidated. We investigated early cellular disruptions in response to sublethal Dox, with a specific emphasis on the role of phosphorylated calcium/calmodulin-dependent protein kinase II (CaMKII) in initiating mitochondrial dysfunction.

Methods

This study utilized the H9c2 cardiomyocyte model to identify a sublethal concentration of Dox and investigate its impact on mitochondrial health using markers such as mitochondrial membrane potential (MMP), mitophagy initiation, and mitochondrial calcium dynamics. We examined the roles of and interactions between CaMKII, dynamin-related protein 1 (Drp1), and the mitochondrial calcium uniporter (MCU) in Dox-induced mitochondrial disruption using specific inhibitors, such as KN-93, Mdivi-1, and Ru360, respectively.

Results

Exposure to a sublethal dose of Dox reduced the MMP red-to-green fluorescence ratio in H9c2 cells by 40.6% compared with vehicle, and increased the proportion of cells undergoing mitophagy from negligible levels compared with vehicle to 62.2%. Mitochondrial calcium levels also increased by 8.7-fold compared with the vehicle group. Notably, the activation of CaMKII, particularly its phosphorylated form, was pivotal in driving these mitochondrial changes, as inhibition using KN-93 restored MMP and decreased mitophagy. However, inhibition of Drp1 and MCU functions had a limited impact on the observed mitochondrial disruptions.

Conclusion

Sublethal administration of Dox is closely linked to CaMKII activation through phosphorylation, emphasizing its pivotal role in early mitochondrial disruption. These findings present a promising direction for developing therapeutic strategies that may alleviate the cardiotoxic effects of Dox, potentially increasing its clinical efficacy.

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.

Impact of Hyper- and Hypo-Uricemia on Kidney Function

Uric acid (UA) forms monosodium urate (MSU) crystals to exert proinflammatory actions, thus causing gout arthritis, urolithiasis, kidney disease, and cardiovascular disease. UA is also one of the most potent antioxidants that suppresses oxidative stress. Hyper andhypouricemia are caused by genetic mutations or polymorphism. Hyperuricemia increases urinary UA concentration and is frequently associated with urolithiasis, which is augmented by low urinary pH. Renal hypouricemia (RHU) is associated with renal stones by increased level of urinary UA, which correlates with the impaired tubular reabsorption of UA. Hyperuricemia causes gout nephropathy, characterized by renal interstitium and tubular damage because MSU precipitates in the tubules. RHU is also frequently associated with tubular damage with elevated urinary beta2-microglobulin due to increased urinary UA concentration, which is related to impaired tubular UA reabsorption through URAT1. Hyperuricemia could induce renal arteriopathy and reduce renal blood flow, while increasing urinary albumin excretion, which is correlated with plasma xanthine oxidoreductase (XOR) activity. RHU is associated with exercise-induced kidney injury, since low levels of SUA could induce the vasoconstriction of the kidney and the enhanced urinary UA excretion could form intratubular precipitation. A U-shaped association of SUA with organ damage is observed in patients with kidney diseases related to impaired endothelial function. Under hyperuricemia, intracellular UA, MSU crystals, and XOR could reduce NO and activate several proinflammatory signals, impairing endothelial functions. Under hypouricemia, the genetic and pharmacological depletion of UA could impair the NO-dependent and independent endothelial functions, suggesting that RHU and secondary hypouricemia might be a risk factor for the loss of kidney functions. In order to protect kidney functions in hyperuricemic patients, the use of urate lowering agents could be recommended to target SUA below 6 mg/dL. In order to protect the kidney functions in RHU patients, hydration and urinary alkalization may be recommended, and in some cases an XOR inhibitor might be recommended in order to reduce oxidative stress.

Epstein-Barr virus reactivation in peripheral B lymphocytes induces IgM-type thyrotropin receptor autoantibody production in patients with Graves' disease

Epstein-Barr virus (EBV) is a human herpes virus that latently infects B lymphocytes. When EBV is reactivated, host B cells differentiate into plasma cells and produce IgM-dominant antibodies as well as many progeny virions. The aims of the present study were to confirm the IgM dominance of thyrotropin-receptor antibodies (TRAbs) produced by EBV reactivation and investigate the roles of TRAb-IgM in Graves' disease. Peripheral blood mononuclear cells (PBMCs) containing TRAb-producing cells were stimulated for EBV reactivation, and TRAb-IgM and TRAb-IgG were measured by ELISA. TRAb-IgM were purified and TSH-binding inhibitory activities were assessed using a radio-receptor assay. Porcine thyroid follicular epithelial cells were cultured with TRAb-IgM and/or complements to measure the intracellular levels of cAMP and the amount of LDH released. TRAb-IgM/TRAb-IgG (the MG ratio) was examined in sequential serum samples of Graves' disease and compared among groups of thyroid function. The results obtained showed that IgM-dominant TRAb production was induced by EBV reactivation. TRAb-IgM did not inhibit TSH binding to TSH receptors and did not transduce hormone-producing signals. However, it destroyed thyroid follicular epithelial cells with complements. The MG ratio was significantly higher in samples of hyperthyroidism or hypothyroidism than in those with normal function or in healthy controls. A close relationship was observed between TRAb-IgM produced by EBV reactivation and the development and exacerbation of Graves' disease. The present results provide novel insights for the development of prophylaxis and therapeutics for Graves' disease.

[Gut microbiota and cardiovascular disease-insights into the potential and challenges of drug discovery]

Cardiovascular disease is a major cause of death worldwide, with high prevalence and morbidity. Recent advances in technology have reported that abnormalities in the gut microbiota are associated with a variety of diseases, including cardiovascular diseases. The gut microbiota is a complex ecosystem that plays an important role in maintaining host health. It has been reported that the imbalance of gut microbiota causes changes in the production of substances derived from gut bacteria, such as short-chain fatty acids, trimethylamine-N-oxide, and lipopolysaccharide, and contributes to the development of cardiovascular diseases. In the drug discovery, it is a promising approach to prevention and therapy of the cardiovascular disease to focus on the relation between gut and heart, such as gut bacteria. However, there are challenges that must be overcome to convert this approach into effective therapy. In this review, we focus on cardiovascular diseases, particularly atherosclerotic disease, heart failure, and atrial fibrillation, and discuss the relationship between gut bacteria and substances derived from gut bacteria in cardiovascular disease. We also discuss the challenges and potential of drug discovery targeting the gut-heart relationship for the treatment and prevention of cardiovascular disease.

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.

MicroRNA-494-3p inhibits formation of fast oxidative muscle fibres by targeting E1A-binding protein p300 in human-induced pluripotent stem cells

MYOD-induced microRNA-494-3p expression inhibits fast oxidative myotube formation by downregulating myosin heavy chain 2 (MYH2) in human induced pluripotent stem cells (hiPSCs) during skeletal myogenesis. However, the molecular mechanisms regulating MYH2 expression via miR-494-3p remain unknown. Here, using bioinformatic analyses, we show that miR-494-3p potentially targets the transcript of the E1A-binding protein p300 at its 3'-untranslated region (UTR). Myogenesis in hiPSCs with the Tet/ON-myogenic differentiation 1 (MYOD1) gene (MyoD-hiPSCs) was induced by culturing them in doxycycline-supplemented differentiation medium for 7 days. p300 protein expression decreased after transient induction of miR-494-3p during myogenesis. miR-494-3p mimics decreased the levels of p300 and its downstream targets MYOD and MYH2 and myotube formation efficiency. p300 knockdown decreased myotube formation efficiency, MYH2 expression, and basal oxygen consumption rate. The binding of miR-494-3p to the wild type p300 3'-UTR, but not the mutated site, was confirmed using luciferase assay. Overexpression of p300 rescued the miR-494-3p mimic-induced phenotype in MyoD-hiPSCs. Moreover, miR-494-3p mimic reduced the levels of p300, MYOD, and MYH2 in skeletal muscles in mice. Thus, miR-494-3p might modulate MYH2 expression and fast oxidative myotube formation by directly regulating p300 levels during skeletal myogenesis in MyoD-hiPSCs and murine skeletal muscle tissues.

A Novel Treatment for Arrhythmias via the Control of the Degradation of Ion Channel Proteins

Although there are many reports on the regulation of ion channel expression in transcription and translation, few drugs have been studied to influence post-translational modification of ion channel proteins. The Kv1.5 channel is a potassium ion channel expressed in atrial muscle, belongs to the voltage-gated K⁺ channel superfamily, and forms an ultrarapid delayed rectifier potassium ion current. It is important to understand the fate of these channel proteins, as cardiac Kv1.5 mutations can cause arrhythmias. Disruption of quantitative and qualitative control mechanisms of channels leads to stagnation and degradation of intracellular channel proteins. As a result, ion channel proteins are not transported to the cell membrane and are involved in the development of atrial fibrillation. This review takes the Kv1.5 channel as an example and focuses on the degradation mechanism of ion channel proteins, and discusses its application to the treatment of arrhythmia by drugs that control the mechanism of ion channel protein degradation.

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.

Hyperuricemia as a Risk Factor for Atrial Fibrillation Due to Soluble and Crystalized Uric Acid

Among the several independent risk factors for atrial fibrillation (AF), hyperuricemia has been widely accepted as associated with the incidence of paroxysmal or persistent AF, as well as with the risk of AF in patients undergoing cardiovascular surgery. The electrophysiological mechanism of AF involves electrical remodeling of the arrhythmogenic substrate and abnormal automaticity as trigger. Both electrical and structural remodeling mediated by oxidative stress derived from either xanthine oxidoreductase (XOR), soluble uric acid (UA) or monosodium urate (MSU) crystals might be plausible explanations for the association of AF with hyperuricemia. XOR generates reactive oxygen species (ROS) that lead to atrial structural remodeling via inflammation. Soluble UA accumulates intracellularly through UA transporters (UAT), shortening the atrial action potential via enhanced expression and activity of Kv1.5 channel proteins. Intracellular accumulation of soluble UA generates ROS in atrial myocytes via nicotinamide adenine dinucleotide phosphate oxidase, which phosphorylates ERK/Akt and heat shock factor 1 (HSF1), thereby increasing transcription and translation of Hsp70, which stabilizes Kv1.5. In macrophages, MSU activates the NLRP3 inflammasome and proteolytic processing mediated by caspase-1 with enhanced interleukin (IL)-1β and IL-18 secretion. Use of an XOR inhibitor, antioxidants, a UAT inhibitor such as a uricosuric agent, and an NLRP3 inflammasome inhibitor, might become a potential strategy to reduce the risk of hyperuricemia-induced AF, and control serum UA level.

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.

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.

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.

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.

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.

•

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.

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.

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.

Isolation and expansion of functionally-competent cardiac progenitor cells directly from heart biopsies

The adult heart contains reservoirs of progenitor cells that express embryonic and stem cell-related antigens. While these antigenically-purified cells are promising candidates for autologous cell therapy, clinical application is hampered by their limited abundance and tedious isolation methods. Methods that involve an intermediate cardiosphere-forming step have proven successful and are being tested clinically, but it is unclear whether the cardiosphere step is necessary. Accordingly, we investigated the molecular profile and functional benefit of cells that spontaneously emigrate from cardiac tissue in primary culture. Adult Wistar-Kyoto rat hearts were minced, digested and cultured as separate anatomical regions. Loosely-adherent cells that surround the plated tissue were harvested weekly for a total of five harvests. Genetic lineage tracing demonstrated that a small proportion of the direct outgrowth from cardiac samples originates from myocardial cells. This outgrowth contains sub-populations of cells expressing embryonic (SSEA-1) and stem cell-related antigens (c-Kit, abcg2) that varied with time in culture but not with the cardiac chamber of origin. This direct outgrowth, and its expanded progeny, underwent marked in vitro angiogenic/cardiogenic differentiation and cytokine secretion (IGF-1, VGEF). In vivo effects included long-term functional benefits as gauged by MRI following cell injection in a rat model of myocardial infarction. Outgrowth cells afforded equivalent functional benefits to cardiosphere-derived cells, which require more processing steps to manufacture. These results provide the basis for a simplified and efficient process to generate autologous cardiac progenitor cells (and mesenchymal supporting cells) to augment clinically-relevant approaches for myocardial repair.

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.