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  • Non-missense variants of KCNH2 show better outcomes in type 2 long QT syndrome. Europace : European pacing, arrhythmias, and cardiac electrophysiology : journal of the working groups on cardiac pacing, arrhythmias, and cardiac cellular electrophysiology of the European Society of Cardiology Aizawa, T., Wada, Y., Hasegawa, K., Huang, H., Imamura, T., Gao, J., Kashiwa, A., Kohjitani, H., Fukuyama, M., Kato, K., Kato, E. T., Hisamatsu, T., Ohno, S., Makiyama, T., Kimura, T., Horie, M. 2023; 25 (4): 1491-1499


    More than one-third of type 2 long QT syndrome (LQT2) patients carry KCNH2 non-missense variants that can result in haploinsufficiency (HI), leading to mechanistic loss-of-function. However, their clinical phenotypes have not been fully investigated. The remaining two-thirds of patients harbour missense variants, and past studies uncovered that most of these variants cause trafficking deficiency, resulting in different functional changes: either HI or dominant-negative (DN) effects. In this study, we examined the impact of altered molecular mechanisms on clinical outcomes in LQT2 patients.We included 429 LQT2 patients (234 probands) carrying a rare KCNH2 variant from our patient cohort undergoing genetic testing. Non-missense variants showed shorter corrected QT (QTc) and less arrhythmic events (AEs) than missense variants. We found that 40% of missense variants in this study were previously reported as HI or DN. Non-missense and HI-groups had similar phenotypes, while both exhibited shorter QTc and less AEs than the DN-group. Based on previous work, we predicted the functional change of the unreported variants-whether they cause HI or DN via altered functional domains-and stratified them as predicted HI (pHI)- or pDN-group. The pHI-group including non-missense variants exhibited milder phenotypes compared to the pDN-group. Multivariable Cox model showed that the functional change was an independent risk of AEs (P = 0.005).Stratification based on molecular biological studies enables us to better predict clinical outcomes in the patients with LQT2.

    View details for DOI 10.1093/europace/euac269

    View details for PubMedID 36861347

    View details for PubMedCentralID PMC10105889

  • Novel Calmodulin Variant p.E46K Associated With Severe Catecholaminergic Polymorphic Ventricular Tachycardia Produces Robust Arrhythmogenicity in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes. Circulation. Arrhythmia and electrophysiology Gao, J., Makiyama, T., Yamamoto, Y., Kobayashi, T., Aoki, H., Maurissen, T. L., Wuriyanghai, Y., Kashiwa, A., Imamura, T., Aizawa, T., Huang, H., Kohjitani, H., Nishikawa, M., Chonabayashi, K., Fukuyama, M., Manabe, H., Nakau, K., Wada, T., Kato, K., Toyoda, F., Yoshida, Y., Makita, N., Woltjen, K., Ohno, S., Kurebayashi, N., Murayama, T., Sakurai, T., Horie, M., Kimura, T. 2023: e011387


    BACKGROUND: CaM (calmodulin) is a ubiquitously expressed, multifunctional Ca2+ sensor protein that regulates numerous proteins. Recently, CaM missense variants have been identified in patients with malignant inherited arrhythmias, such as long QT syndrome and catecholaminergic polymorphic ventricular tachycardia (CPVT). However, the exact mechanism of CaM-related CPVT in human cardiomyocytes remains unclear. In this study, we sought to investigate the arrhythmogenic mechanism of CPVT caused by a novel variant using human induced pluripotent stem cell (iPSC) models and biochemical assays.METHODS: We generated iPSCs from a patient with CPVT bearing CALM2 p.E46K. As comparisons, we used 2 control lines including an isogenic line, and another iPSC line from an patient with long QT syndrome bearing CALM2 p.N98S (also reported in CPVT). Electrophysiological properties were investigated using iPSC-cardiomyocytes. We further examined the cardiac RyR2 (ryanodine receptor) and Ca2+ affinities of CaM using recombinant proteins.RESULTS: We identified a novel de novo heterozygous variant, CALM2 p.E46K, in 2 unrelated patients with CPVT accompanied by neurodevelopmental disorders. The E46K-cardiomyocytes exhibited more frequent abnormal electrical excitations and Ca2+ waves than the other lines in association with increased Ca2+ leakage from the sarcoplasmic reticulum via RyR2. Furthermore, the [3H]ryanodine binding assay revealed that E46K-CaM facilitated RyR2 function especially by activating at low [Ca2+] levels. The real-time CaM-RyR2 binding analysis demonstrated that E46K-CaM had a 10-fold increased RyR2 binding affinity compared with wild-type CaM which may account for the dominant effect of the mutant CaM. Additionally, the E46K-CaM did not affect CaM-Ca2+ binding or L-type calcium channel function. Finally, antiarrhythmic agents, nadolol and flecainide, suppressed abnormal Ca2+ waves in E46K-cardiomyocytes.CONCLUSIONS: We, for the first time, established a CaM-related CPVT iPSC-CM model which recapitulated severe arrhythmogenic features resulting from E46K-CaM dominantly binding and facilitating RyR2. In addition, the findings in iPSC-based drug testing will contribute to precision medicine.

    View details for DOI 10.1161/CIRCEP.122.011387

    View details for PubMedID 36866681

  • Disrupted CaV1.2 selectivity causes overlapping long QT and Brugada syndrome phenotypes in the CACNA1C-E1115K iPS cell model. Heart rhythm Kashiwa, A., Makiyama, T., Kohjitani, H., Maurissen, T. L., Ishikawa, T., Yamamoto, Y., Wuriyanghai, Y., Gao, J., Huang, H., Imamura, T., Aizawa, T., Nishikawa, M., Chonabayashi, K., Mishima, H., Ohno, S., Toyoda, F., Sato, S., Yoshiura, K., Takahashi, K., Yoshida, Y., Woltjen, K., Horie, M., Makita, N., Kimura, T. 2023; 20 (1): 89-99


    BACKGROUND: A missense mutation in the alpha1c subunit of voltage-gated L-type Ca2+ channel-coding CACNA1C-E1115K, located in the Ca2+ selectivity site, causes a variety of arrhythmogenic phenotypes.OBJECTIVE: We aimed to investigate the electrophysiological features and pathophysiological mechanisms of CACNA1C-E1115K in patient-specific induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CMs).METHODS: We generated iPSCs from a patient carrying heterozygous CACNA1C-E1115K with overlapping phenotypes of long QT syndrome, Brugada syndrome, and mild cardiac dysfunction. Electrophysiological properties were investigated using iPSC-CMs. We used iPSCs from a healthy individual and an isogenic iPSC line corrected using CRISPR-Cas9-mediated gene editing as controls. A mathematical E1115K-CM model was developed using a human ventricular cell model.RESULTS: Patch-clamp analysis revealed that E1115K-iPSC-CMs exhibited reduced peak Ca2+ current density and impaired Ca2+ selectivity with an increased permeability to monovalent cations. Consequently, E1115K-iPSC-CMs showed decreased action potential plateau amplitude, longer action potential duration (APD), and a higher frequency of early afterdepolarization compared with controls. In optical recordings examining the antiarrhythmic drug effect, late Na+ channel current (INaL) inhibitors (mexiletine and GS-458967) shortened APDs specifically in E1115K-iPSC-CMs. The AP-clamp using a voltage command obtained from E1115K-iPSC-CMs with lower action potential plateau amplitude and longer APD confirmed the upregulation of INaL. An in silico study recapitulated the invitro electrophysiological properties.CONCLUSION: Our iPSC-based analysis in CACNA1C-E1115K with disrupted CaV1.2 selectivity demonstrated that the aberrant currents through the mutant channels carried by monovalent cations resulted in specific action potential changes, which increased endogenous INaL, thereby synergistically contributing to the arrhythmogenic phenotype.

    View details for DOI 10.1016/j.hrthm.2022.08.021

    View details for PubMedID 36007726

  • Oral Adrenergic Agents Produced Ventricular Fibrillation and QT Prolongation in an Elderly Patient Carrying an RYR2 Variant. International heart journal Hasegawa, K., Gao, J., Ohno, S., Ishida, K., Miyazaki, S., Makiyama, T., Horie, M., Uzui, H., Tada, H. 2022; 63 (2): 398-403


    Mutant cardiac ryanodine receptor channels (RyR2) are "leaky," and spontaneous Ca2+ release through these channels causes delayed afterdepolarizations that can deteriorate into ventricular fibrillation. Some patients carrying RYR2 mutations in type 1 catecholaminergic polymorphic ventricular tachycardia exhibit QT prolongation and are initially diagnosed with long QT syndrome. However, none have been reported to cause drug-induced ventricular fibrillation in patients with RYR2 variants. We describe the first case of an elderly woman with drug-induced QT prolongation and ventricular fibrillation who carried a novel RYR2 variant but no other mutations related to long QT syndrome. Oral adrenergic agents might induce QT prolongation and subsequent ventricular fibrillation in patients carrying an RYR2 variant. Screening for RYR2 could be valuable in patients with suspected drug-induced long QT syndrome.

    View details for DOI 10.1536/ihj.21-543

    View details for PubMedID 35354758

  • Clinical aspects of pediatric Brugada syndrome Imamura, T., Makiyama, T., Huang, H., Aizawa, T., Gao, J., Kashiwa, A., Wuriyanghai, Y., Yamamoto, Y., Kohjitani, Y., Kato, K., Ohno, S., Sumitomo, N., Horie, M. OXFORD UNIV PRESS. 2020: 738
  • Preclinical proof-of-concept study: antisense-mediated knockdown of CALM as a therapeutic strategy for calmodulinopathy Yamamoto, Y., Makiyama, T., Wuriyanghai, Y., Kohjitani, H., Gao, J., Kashiwa, A., Hai, H., Aizawa, T., Imamura, T., Ishikawa, T., Yoshida, Y., Ohno, S., Horie, M., Makita, N., Kimura, T. OXFORD UNIV PRESS. 2020: 3688
  • Propranolol Attenuates Late Sodium Current in a Long QT Syndrome Type 3-Human Induced Pluripotent Stem Cell Model FRONTIERS IN CELL AND DEVELOPMENTAL BIOLOGY Hirose, S., Makiyama, T., Melgari, D., Yamamoto, Y., Wuriyanghai, Y., Yokoi, F., Nishiuchi, S., Harita, T., Hayano, M., Kohjitani, H., Gao, J., Kashiwa, A., Nishikawa, M., Wu, J., Yoshimoto, J., Chonabayashi, K., Ohno, S., Yoshida, Y., Horie, M., Kimura, T. 2020; 8: 761


    Long QT syndrome type 3 (LQT3) is caused by gain-of-function mutations in the SCN5A gene, which encodes the α subunit of the cardiac voltage-gated sodium channel. LQT3 patients present bradycardia and lethal arrhythmias during rest or sleep. Further, the efficacy of β-blockers, the drug used for their treatment, is uncertain. Recently, a large multicenter LQT3 cohort study demonstrated that β-blocker therapy reduced the risk of life-threatening cardiac events in female patients; however, the detailed mechanism of action remains unclear.This study aimed to establish LQT3-human induced pluripotent stem cells (hiPSCs) and to investigate the effect of propranolol in this model.An hiPSCs cell line was established from peripheral blood mononuclear cells of a boy with LQT3 carrying the SCN5A-N1774D mutation. He had suffered from repetitive torsades de pointes (TdPs) with QT prolongation since birth (QTc 680 ms), which were effectively treated with propranolol, as it suppressed lethal arrhythmias. Furthermore, hiPSCs were differentiated into cardiomyocytes (CMs), on which electrophysiological functional assays were performed using the patch-clamp method.N1774D-hiPSC-CMs exhibited significantly prolonged action potential durations (APDs) in comparison to those of the control cells (N1774D: 440 ± 37 ms vs. control: 272 ± 22 ms; at 1 Hz pacing; p < 0.01). Furthermore, N1774D-hiPSC-CMs presented gain-of-function features: a hyperpolarized shift of steady-state activation and increased late sodium current compared to those of the control cells. 5 μM propranolol shortened APDs and inhibited late sodium current in N1774D-hiPSC-CMs, but did not significantly affect in the control cells. In addition, even in the presence of intrapipette guanosine diphosphate βs (GDPβs), an inhibitor of G proteins, propranolol reduced late sodium current in N1774D cells. Therefore, these results suggested a unique inhibitory effect of propranolol on late sodium current unrelated to β-adrenergic receptor block in N1774D-hiPSC-CMs.We successfully recapitulated the clinical phenotype of LQT3 using patient-derived hiPSC-CMs and determined that the mechanism, by which propranolol inhibited the late sodium current, was independent of β-adrenergic receptor signaling pathway.

    View details for DOI 10.3389/fcell.2020.00761

    View details for Web of Science ID 000566255400001

    View details for PubMedID 32903469

    View details for PubMedCentralID PMC7438478

  • Complex aberrant splicing in the induced pluripotent stem cell-derived cardiomyocytes from a patient with long QT syndrome carrying KCNQ1-A344Aspl mutation HEART RHYTHM Wuriyanghai, Y., Makiyama, T., Sasaki, K., Kamakura, T., Yamamoto, Y., Hayano, M., Harita, T., Nishiuchi, S., Chen, J., Kohjitani, H., Hirose, S., Yokoi, F., Gao, J., Chonabayashi, K., Watanabe, K., Ohno, S., Yoshida, Y., Kimura, T., Horie, M. 2018; 15 (10): 1566-1574


    Long QT syndrome type 1 (LQT1) is caused by mutations in KCNQ1, which encodes the α subunit of the slow delayed rectifier potassium current channel. We previously reported that a synonymous mutation, c.1032G>A, p.A344Aspl, in KCNQ1 is most commonly identified in genotyped patients with LQT1 in Japan and the aberrant splicing was analyzed in the lymphocytes isolated from patients' blood samples. However, the mechanisms underlying the observed processes in human cardiomyocytes remain unclear.The purpose of this study was to establish and analyze patient-specific human-induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) model carrying KCNQ1-A344Aspl.We generated hiPSCs from the peripheral blood mononuclear cells obtained from a patient with LQT1 carrying KCNQ1-A344Aspl. Using the differentiated cardiomyocytes, we analyzed splicing variants and performed electrophysiology studies.We identified 7 aberrant RNA variants in A344Aspl hiPSC-CMs, which were more complex compared with those in peripheral lymphocytes. Multielectrode array analysis revealed that 1 μM isoproterenol significantly prolonged the duration of the corrected field potential in A344Aspl hiPSC-CMs as compared with that in control hiPSC-CMs. In addition, 100 nM E-4031, which inhibits the rapid component of the delayed rectifier potassium current, was shown to induce early afterdepolarization-like waveforms in A344Aspl hiPSC-CMs. Action potential durations (APDs) did not significantly differ between the hiPSC-CM groups. After administering 500 nM isoproterenol, APDs of A344Aspl hiPSC-CMs were significantly longer than those of the controls. (R)-N-(4-(4-Methoxyphenyl)thiazol-2-yl)-1-tosylpiperidine-2-carboxamide and phenylboronic acid, slow delayed rectifier potassium current activators, ameliorated the APDs of hiPSC-CMs.We identified complex aberrant messenger RNA variants in the A344Aspl hiPSC-CM model and successfully recapitulated the clinical phenotypes of the patient with concealed LQT1. This model allows the investigation of the underlying mechanisms and development of novel therapies.

    View details for DOI 10.1016/j.hrthm.2018.05.028

    View details for Web of Science ID 000445914700028

    View details for PubMedID 29857160

  • Analysis of mutation of the c-Kit gene and <i>PDGFRA</i> in gastrointestinal stromal tumors EXPERIMENTAL AND THERAPEUTIC MEDICINE Xu, C., Lin, S., Wang, W., Gao, W., Lv, J., Gao, J., Zhang, L., Li, Y., Wang, L., Zhang, Y., Tian, Y. 2015; 10 (3): 1045-1051


    The aim of the present study was to investigate mutation status of the c-Kit gene (KIT) and PDGFRA in patients with a gastrointestinal stromal tumor (GIST). In total, 93 patients with a GIST were included in the study, in which polymerase chain reaction amplification and gene sequencing were used to detect the sequences of exons 9, 11, 13 and 17 in KIT and exons 12 and 18 in PDGFRA. KIT mutations were detected in 64 cases (68.82%), of which exon 11 mutations were detected in 56 cases (60.22%), exon 13 mutations were detected in three cases (3.23%) and one case (1.08%) was shown to have a mutation in exon 17. The most common mutation in exon 11 was a deletion, which accounted for 55.36% (31/56) of the cases, followed by a point mutation observed in 26.79% (15/56) of the cases, while an insertion (tandem repeats) was identified in 14.29% (8/56) of the cases, and 3.57% (2/56) of the exon 11 mutations were deletions associated with a point mutation. The majority of the mutations were heterozygous, with only a few homozygous mutations. Mutational analysis revealed the mutations to be more concentrated in the classic hot zone at the 5'-end, followed by the tandem repeat frame at the 3'-end. In four cases, a mutation was detected in exon 18 of PDGFRA, of which one was associated with a mutation in KIT. The remaining three cases (10.34%, 3/29) were not associated with mutations in KIT and accounted for 37.5% (3/8) of the CD117-negative GIST cases. Therefore, the majority of the GIST cases were characterized by mutations in KIT or PDGFRA, which were directly associated with the disease. Pairs of different mutations in the same exon of KIT, or KIT mutations coupled with pairs of mutations in PDGFRA, were detected in a small number of patients. Imatinib is a small molecule tyrosine kinase inhibitor and is the first line targeted treatment for GIST, resulting in markedly improved survival rates. Thus, gene mutation genotyping may provide inspiration and guidance for imatinib-based targeted cancer therapy.

    View details for DOI 10.3892/etm.2015.2613

    View details for Web of Science ID 000361148800035

    View details for PubMedID 26622437

    View details for PubMedCentralID PMC4533144

  • Association between EML4-ALK fusion gene and thymidylate synthase mRNA expression in non-small cell lung cancer tissues EXPERIMENTAL AND THERAPEUTIC MEDICINE Xu, C., Wang, G., Wang, W., Gao, W., Han, C., Gao, J., Zhang, L., Li, Y., Wang, L., Zhang, Y., Tian, Y., Qi, D. 2015; 9 (6): 2151-2154


    This study aimed to investigate the association of the mRNA expression of the echinoderm microtubule-associated protein-like 4 (EML4)-anaplastic lymphoma kinase (ALK) fusion gene with that of thymidylate synthase (TYMS) in non-small cell lung cancer (NSCLC) tissues. Quantitative polymerase chain reaction was used to detect the expression of EML4-ALK fusion gene and TYMS mRNA in 257 cases of NSCLC. The positive rate of EML4-ALK fusion gene was 4.28% in the NSCLC tissues (11/257), and was higher in nonsmokers than in smokers (P<0.05); TYMS mRNA expression was detected in 63.42% (163/257) of cases. An association of the EML4-ALK fusion gene with TYMS expression was detected; a low expression level of TYMS mRNA was observed more frequently when the EML4-ALK fusion gene was present than when it was not detected (P<0.05). In conclusion, patients positive for the EML4-ALK fusion gene in NSCLC tissues are likely to have a low expression level of TYMS, and may benefit from the first-line chemotherapy drug pemetrexed.

    View details for DOI 10.3892/etm.2015.2372

    View details for Web of Science ID 000355496800017

    View details for PubMedID 26136951

    View details for PubMedCentralID PMC4473652

  • Association between epidermal growth factor receptor mutations and the expression of excision repair cross-complementing protein 1 and ribonucleotide reductase subunit M1 mRNA in patients with non-small cell lung cancer EXPERIMENTAL AND THERAPEUTIC MEDICINE Xu, C., Wang, G., Wang, W., Gao, W., Han, C., Gao, J., Li, Y., Wang, L., Zhang, L., Zhang, Y., Tian, Y., Fang, J. 2015; 9 (3): 880-884


    The present study aimed to investigate the association between epidermal growth factor receptor (EGFR) gene mutations and excision repair cross-complementing protein 1 (ERCC1) and ribonucleotide reductase subunit M1 (RRM1) mRNA expression in non-small cell lung cancer (NSCLC) tissue. The quantitative polymerase chain reaction was used to detect EGFR mutations, and ERCC1 and RRM1 mRNA expression in 257 cases of NSCLC. In the NSCLC samples the EGFR mutation rate was 49.03% (126/257). The rate was higher in females and non-smoking patients (P<0.05). High expression of ERCC1 mRNA was observed in 47.47% of the samples (122/257), while a high RRM1 mRNA expression was observed in 61.87% of the samples (159/257). In comparison with patients with NSCLC without EGFR mutations, patients with EGFR mutations had significantly lower levels of ERCC1 mRNA expression (P<0.05); however, EGFR mutations and expression levels of RRM1 mRNA were not correlated in NSCLC tissues (P>0.05). In addition, ERCC1 mRNA expression was not correlated with the expression levels of RRM1 mRNA (P>0.05). In conclusion, patients with NSCLC with EGFR mutations tend to have a low expression of ERCC1 mRNA and may potentially benefit from platinum-based chemotherapy.

    View details for DOI 10.3892/etm.2015.2196

    View details for Web of Science ID 000350917900039

    View details for PubMedID 25667646

    View details for PubMedCentralID PMC4316980