Ectopic automaticity induced in ventricular myocytes by transgenic overexpression of HCN2

Oshita, Kensuke; Itoh, Masayuki; Hirashima, Shingo; Kuwabara, Yoshihiro; Ishihara, Keiko; Kuwahara, Koichiro; Nakao, Kazuwa; Kimura, Takeshi; Nakamura, Kei‐ichiro; Ushijima, Kazuo; Takano, Makoto

doi:10.1016/j.yjmcc.2014.12.019

Cited by 15 publications

(17 citation statements)

References 30 publications

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“…Furthermore, APD 20 and APD 50 were shorter compared to WT, while APD 90 was similar. This in parts is consistent with previous data obtained from cardiomyocytes overexpressing HCN2 37 , which showed that outward tail current of I f shortened APD at membrane potentials more positive than reversal potential (~−35 mV for HCN4 38 ), while inward tail current of I f prolonged APD at membrane potentials more negative than reversal potential. However, prolongation of APD 90 was not observed in our model, most likely due to the repolarizing driving force of the electrogenic ‘reverse mode’ NCX, known to effectively shorten AP duration when [Na + ] i is increased 39 .…”

Section: Discussionsupporting

confidence: 93%

Augmentation of myocardial If dysregulates calcium homeostasis and causes adverse cardiac remodeling

et al. 2019

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HCN channels underlie the depolarizing funny current (I f ) that contributes importantly to cardiac pacemaking. I f is upregulated in failing and infarcted hearts, but its implication in disease mechanisms remained unresolved. We generated transgenic mice ( HCN4 tg/wt ) to assess functional consequences of HCN4 overexpression-mediated I f increase in cardiomyocytes to levels observed in human heart failure. HCN4 tg/wt animals exhibit a dilated cardiomyopathy phenotype with increased cellular arrhythmogenicity but unchanged heart rate and conduction parameters. I f augmentation induces a diastolic Na + influx shifting the Na + /Ca 2+ exchanger equilibrium towards ‘reverse mode’ leading to increased [Ca 2+ ] i . Changed Ca 2+ homeostasis results in significantly higher systolic [Ca 2+ ] i transients and stimulates apoptosis. Pharmacological inhibition of I f prevents the rise of [Ca 2+ ] i and protects from ventricular remodeling. Here we report that augmented myocardial I f alters intracellular Ca 2+ homeostasis leading to structural cardiac changes and increased arrhythmogenicity. Inhibition of myocardial I f per se may constitute a therapeutic mechanism to prevent cardiomyopathy.

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Section: Discussionsupporting

confidence: 93%

Augmentation of myocardial If dysregulates calcium homeostasis and causes adverse cardiac remodeling

et al. 2019

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“…The transgenic mouse overexpressing HCN2 specifically in the heart reportedly showed tachycardia, but PR and QRS durations were not shortened (Oshita et al . ). At present, the reasons for these discrepancies remain unclear; electrophysiological mechanisms regulating conduction velocity in the CCS should be explored in future research.…”

Section: Discussionmentioning

confidence: 97%

HCN4 pacemaker channels attenuate the parasympathetic response and stabilize the spontaneous firing of the sinoatrial node

Kozasa

Nakashima

Itô

et al. 2018

The Journal of Physiology

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Key points The contribution of HCN4 pacemaker channels in the autonomic regulation of the sino‐atrial node (SAN) has been a matter of debate.The transgenic overexpression of HCN4 did not induce tachycardia, but reduced heart rate variability, while the conditional knockdown of HCN4 gave rise to sinus arrhythmia.The response of the SAN to β‐adrenergic stimulation was not affected by overexpression or knockdown of HCN4 channels.When HCN4 channels were knocked down, the parasympathetic response examined by cervical vagus nerve stimulation (CVNS) was enhanced; the CVNS induced complete sinus pause. The overexpression of HCN4 attenuated bradycardia induced by CVNS only during β‐adrenergic stimulation.We concluded that HCN4 pacemaker channels stabilize the spontaneous firing by attenuating the parasympathetic response of the SAN. AbstractThe heart rate is dynamically controlled by the sympathetic and parasympathetic nervous systems that regulate the sinoatrial node (SAN). HCN4 pacemaker channels are the well‐known causative molecule of congenital sick sinus syndrome. Although HCN4 channels are activated by cAMP, the sympathetic response of the SAN was preserved in patients carrying loss‐of‐function mutations of the HCN4 gene. In order to clarify the contribution of HCN4 channels in the autonomic regulation of the SAN, we developed novel gain‐of‐function mutant mice in which the expression level of HCN4 channels could be reversibly changed from zero to ∼3 times that in wild‐type mice, using tetracycline transactivator and the tetracycline responsive element. We recorded telemetric ECGs in freely moving conscious mice and analysed the heart rate variability. We also evaluated the response of the SAN to cervical vagus nerve stimulation (CVNS). The conditional overexpression of HCN4 did not induce tachycardia, but reduced heart rate variability. The HCN4 overexpression also attenuated bradycardia induced by the CVNS only during the β‐adrenergic stimulation. In contrast, the knockdown of HCN4 gave rise to sinus arrhythmia, and enhanced the parasympathetic response; complete sinus pause was induced by the CVNS. In vitro, we compared the effects of acetylcholine on the spontaneous action potentials of single pacemaker cells, and found that similar phenotypic changes were induced by genetic manipulation of HCN4 expression both in the presence and absence of β‐adrenergic stimulation. Our study suggests that HCN4 channels attenuate the vagal response of the SAN, and thereby stabilize the spontaneous firing of the SAN.

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“…Moreover, ion channel-associated proteins, mainly hyperpolarization-activated cyclic nucleotide-gated channel 4 (HCN4), are related to the diastolic depolarization process of SAN [7]. In vitro and in vivo studies of gene manipulation for rodent neonatal rat cardiomyocytes to restore the ectopic pacing region by overexpressing embryonic transcription factors and ion channel-associated proteins have been proved to be successful [8–12]. Kapoor et al have proved that Tbx18 was the most effective transcription factor with the ability to transform neonatal ventricular myocytes into SAN-like cells by transducing a panel of transcription factors individually, including Shox2, Tbx3, Tbx5, Tbx18, and Tbx20 [11].…”

Section: Introductionmentioning

confidence: 99%

Genetically Modified Porcine Mesenchymal Stem Cells by Lentiviral Tbx18 Create a Biological Pacemaker

Liu

et al. 2019

Stem Cells International

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Background Tbx18 is a vital transcription factor involved in embryonic sinoatrial node (SAN) formation process but is gradually vanished after birth. Myocardial injection of lentiviral Tbx18 converts cardiomyocytes into pacemaker-like cells morphologically and functionally. In this in vitro and in vivo study, genetical modification of porcine bone mesenchymal stem cells (BMSCs) by recapturing the Tbx18 expression creates a biological pacemaker which was examined. Methods The isolated porcine BMSCs were transfected with lentiviral Tbx18, and the induced pacemaker-like cells were analyzed using real-time polymerase chain reaction and western blotting to investigate the efficiency of transformation. Then, the induced pacemaker-like cells were implanted into the right ventricle of the SAN dysfunction porcine model after the differentiation process. Biological pacemaker activity and ectopic pacing region were tested by an electrocardiograph (ECG) monitor. Results The isolated porcine BMSCs expressed specific surface markers of stem cells; meanwhile, the expression of myocardial markers was upregulated significantly after lentiviral Tbx18 transfection. The porcine SAN dysfunction model was constructed by electrocoagulation using a surgical electrotome. The results showed that the mean heart beat (HR) of BMSCs-Tbx18 was significantly higher than that of BMSCs-GFP. An ectopic pacing region was affirmed into the right ventricle by ECG after implantation of BMSCs-Tbx18. Conclusion It was verified that Lenti-Tbx18 is capable of transducing porcine BMSCs into pacemaker-like cells. Genetically modified porcine BMSCs by lentiviral Tbx18 could create a biological pacemaker. However, further researches in large-scale animals are required to rule out unexpected complications prior to application in clinical practice.

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Ectopic automaticity induced in ventricular myocytes by transgenic overexpression of HCN2

Cited by 15 publications

References 30 publications

Augmentation of myocardial If dysregulates calcium homeostasis and causes adverse cardiac remodeling

Augmentation of myocardial If dysregulates calcium homeostasis and causes adverse cardiac remodeling

HCN4 pacemaker channels attenuate the parasympathetic response and stabilize the spontaneous firing of the sinoatrial node

Genetically Modified Porcine Mesenchymal Stem Cells by Lentiviral Tbx18 Create a Biological Pacemaker

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