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Paquette SE, Oduor CI, Gaulke A, Stefan S, Bronk P, Dafonseca V, Barulin N, Lee C, Carley R, Morrison AR, Choi BR, Bailey JA, Plavicki JS. Loss of developmentally derived Irf8+ macrophages promotes hyperinnervation and arrhythmia in the adult zebrafish heart. bioRxiv 2024:2024.04.17.589909. [PMID: 38659956 PMCID: PMC11042273 DOI: 10.1101/2024.04.17.589909] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/26/2024]
Abstract
Recent developments in cardiac macrophage biology have broadened our understanding of the critical functions of macrophages in the heart. As a result, there is further interest in understanding the independent contributions of distinct subsets of macrophage to cardiac development and function. Here, we demonstrate that genetic loss of interferon regulatory factor 8 (Irf8)-positive embryonic-derived macrophages significantly disrupts cardiac conduction, chamber function, and innervation in adult zebrafish. At 4 months post-fertilization (mpf), homozygous irf8st96/st96 mutants have significantly shortened atrial action potential duration and significant differential expression of genes involved in cardiac contraction. Functional in vivo assessments via electro- and echocardiograms at 12 mpf reveal that irf8 mutants are arrhythmogenic and exhibit diastolic dysfunction and ventricular stiffening. To identify the molecular drivers of the functional disturbances in irf8 null zebrafish, we perform single cell RNA sequencing and immunohistochemistry, which reveal increased leukocyte infiltration, epicardial activation, mesenchymal gene expression, and fibrosis. Irf8 null hearts are also hyperinnervated and have aberrant axonal patterning, a phenotype not previously assessed in the context of cardiac macrophage loss. Gene ontology analysis supports a novel role for activated epicardial-derived cells (EPDCs) in promoting neurogenesis and neuronal remodeling in vivo. Together, these data uncover significant cardiac abnormalities following embryonic macrophage loss and expand our knowledge of critical macrophage functions in heart physiology and governing homeostatic heart health.
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2
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Kabakov AY, Roder K, Bronk P, Turan NN, Dhakal S, Zhong M, Lu Y, Zeltzer ZA, Najman-Licht YB, Karma A, Koren G. E3 ubiquitin ligase rififylin has yin and yang effects on rabbit cardiac transient outward potassium currents (I to) and corresponding channel proteins. J Biol Chem 2024; 300:105759. [PMID: 38367666 PMCID: PMC10945274 DOI: 10.1016/j.jbc.2024.105759] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2023] [Revised: 01/23/2024] [Accepted: 02/09/2024] [Indexed: 02/19/2024] Open
Abstract
Genome-wide association studies have reported a correlation between a SNP of the RING finger E3 ubiquitin protein ligase rififylin (RFFL) and QT interval variability in humans (Newton-Cheh et al., 2009). Previously, we have shown that RFFL downregulates expression and function of the human-like ether-a-go-go-related gene potassium channel and corresponding rapidly activating delayed rectifier potassium current (IKr) in adult rabbit ventricular cardiomyocytes. Here, we report that RFFL also affects the transient outward current (Ito), but in a peculiar way. RFFL overexpression in adult rabbit ventricular cardiomyocytes significantly decreases the contribution of its fast component (Ito,f) from 35% to 21% and increases the contribution of its slow component (Ito,s) from 65% to 79%. Since Ito,f in rabbits is mainly conducted by Kv4.3, we investigated the effect of RFFL on Kv4.3 expressed in HEK293A cells. We found that RFFL overexpression reduced Kv4.3 expression and corresponding Ito,f in a RING domain-dependent manner in the presence or absence of its accessory subunit Kv channel-interacting protein 2. On the other hand, RFFL overexpression in Kv1.4-expressing HEK cells leads to an increase in both Kv1.4 expression level and Ito,s, similarly in a RING domain-dependent manner. Our physiologically detailed rabbit ventricular myocyte computational model shows that these yin and yang effects of RFFL overexpression on Ito,f, and Ito,s affect phase 1 of the action potential waveform and slightly decrease its duration in addition to suppressing IKr. Thus, RFFL modifies cardiac repolarization reserve via ubiquitination of multiple proteins that differently affect various potassium channels and cardiac action potential duration.
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Affiliation(s)
- Anatoli Y Kabakov
- Division of Cardiology, Department of Medicine, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School, Brown University, Providence, Rhode Island, USA
| | - Karim Roder
- Division of Cardiology, Department of Medicine, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School, Brown University, Providence, Rhode Island, USA
| | - Peter Bronk
- Division of Cardiology, Department of Medicine, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School, Brown University, Providence, Rhode Island, USA
| | - Nilüfer N Turan
- Division of Cardiology, Department of Medicine, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School, Brown University, Providence, Rhode Island, USA
| | - Saroj Dhakal
- Physics Department and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston, Massachusetts, USA
| | - Mingwang Zhong
- Physics Department and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston, Massachusetts, USA
| | - Yichun Lu
- Division of Cardiology, Department of Medicine, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School, Brown University, Providence, Rhode Island, USA
| | - Zachary A Zeltzer
- Division of Cardiology, Department of Medicine, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School, Brown University, Providence, Rhode Island, USA
| | - Yonatan B Najman-Licht
- Division of Cardiology, Department of Medicine, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School, Brown University, Providence, Rhode Island, USA
| | - Alain Karma
- Physics Department and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston, Massachusetts, USA
| | - Gideon Koren
- Division of Cardiology, Department of Medicine, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School, Brown University, Providence, Rhode Island, USA.
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3
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Baggett BC, Murphy KR, Sengun E, Mi E, Cao Y, Turan NN, Lu Y, Schofield L, Kim TY, Kabakov AY, Bronk P, Qu Z, Camelliti P, Dubielecka P, Terentyev D, del Monte F, Choi BR, Sedivy J, Koren G. Myofibroblast senescence promotes arrhythmogenic remodeling in the aged infarcted rabbit heart. eLife 2023; 12:e84088. [PMID: 37204302 PMCID: PMC10259375 DOI: 10.7554/elife.84088] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2022] [Accepted: 05/18/2023] [Indexed: 05/20/2023] Open
Abstract
Progressive tissue remodeling after myocardial infarction (MI) promotes cardiac arrhythmias. This process is well studied in young animals, but little is known about pro-arrhythmic changes in aged animals. Senescent cells accumulate with age and accelerate age-associated diseases. Senescent cells interfere with cardiac function and outcome post-MI with age, but studies have not been performed in larger animals, and the mechanisms are unknown. Specifically, age-associated changes in timecourse of senescence and related changes in inflammation and fibrosis are not well understood. Additionally, the cellular and systemic role of senescence and its inflammatory milieu in influencing arrhythmogenesis with age is not clear, particularly in large animal models with cardiac electrophysiology more similar to humans than previously studied animal models. Here, we investigated the role of senescence in regulating inflammation, fibrosis, and arrhythmogenesis in young and aged infarcted rabbits. Aged rabbits exhibited increased peri-procedural mortality and arrhythmogenic electrophysiological remodeling at the infarct border zone (IBZ) compared to young rabbits. Studies of the aged infarct zone revealed persistent myofibroblast senescence and increased inflammatory signaling over a 12-week timecourse. Senescent IBZ myofibroblasts in aged rabbits appear to be coupled to myocytes, and our computational modeling showed that senescent myofibroblast-cardiomyocyte coupling prolongs action potential duration (APD) and facilitates conduction block permissive of arrhythmias. Aged infarcted human ventricles show levels of senescence consistent with aged rabbits, and senescent myofibroblasts also couple to IBZ myocytes. Our findings suggest that therapeutic interventions targeting senescent cells may mitigate arrhythmias post-MI with age.
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Affiliation(s)
- Brett C Baggett
- Brown UniversityProvidenceUnited States
- Cardiovascular Research Center, Rhode Island HospitalProvidenceUnited States
| | - Kevin R Murphy
- Brown UniversityProvidenceUnited States
- Cardiovascular Research Center, Rhode Island HospitalProvidenceUnited States
| | - Elif Sengun
- Brown UniversityProvidenceUnited States
- Cardiovascular Research Center, Rhode Island HospitalProvidenceUnited States
- Department of Pharmacology, Institute of Graduate Studies in Health Sciences, Istanbul UniversityIstanbulTurkey
| | - Eric Mi
- Brown UniversityProvidenceUnited States
- Cardiovascular Research Center, Rhode Island HospitalProvidenceUnited States
| | - Yueming Cao
- Brown UniversityProvidenceUnited States
- Cardiovascular Research Center, Rhode Island HospitalProvidenceUnited States
| | - Nilufer N Turan
- Cardiovascular Research Center, Rhode Island HospitalProvidenceUnited States
| | - Yichun Lu
- Cardiovascular Research Center, Rhode Island HospitalProvidenceUnited States
| | - Lorraine Schofield
- Cardiovascular Research Center, Rhode Island HospitalProvidenceUnited States
| | - Tae Yun Kim
- Cardiovascular Research Center, Rhode Island HospitalProvidenceUnited States
| | - Anatoli Y Kabakov
- Brown UniversityProvidenceUnited States
- Cardiovascular Research Center, Rhode Island HospitalProvidenceUnited States
| | - Peter Bronk
- Cardiovascular Research Center, Rhode Island HospitalProvidenceUnited States
| | - Zhilin Qu
- School of Medicine, University of California, Los AngelesLos AngelesUnited States
| | - Patrizia Camelliti
- School of Biosciences and Medicine, University of SurreyGuildfordUnited Kingdom
| | - Patrycja Dubielecka
- Brown UniversityProvidenceUnited States
- Department of Hematology, Rhode Island HospitalProvidenceUnited States
| | - Dmitry Terentyev
- Cardiovascular Research Center, Rhode Island HospitalProvidenceUnited States
| | | | - Bum-Rak Choi
- Cardiovascular Research Center, Rhode Island HospitalProvidenceUnited States
| | | | - Gideon Koren
- Brown UniversityProvidenceUnited States
- Cardiovascular Research Center, Rhode Island HospitalProvidenceUnited States
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4
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Bronk P, Yun Kim T, Chun Lu Y, Turan N, Qu Z, Terentyeva R, Terentyev DA, Koren G, Choi BR. Physiological role of SK channels in modulating cardiac repolarization: APD and dispersion at slow heart rate in long QT syndrome. Biophys J 2023; 122:255a. [PMID: 36783254 DOI: 10.1016/j.bpj.2022.11.1473] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/12/2023] Open
Affiliation(s)
- Peter Bronk
- Department of Medicine, Rhode Island Hospital, Providence, RI, USA
| | - Tae Yun Kim
- Department of Pediatrics, Emory University, Atlanta, GA, USA
| | - Yi Chun Lu
- Department of Medicine, Rhode Island Hospital, Providence, RI, USA
| | - Nilufer Turan
- Department of Medicine, Rhode Island Hospital, Providence, RI, USA
| | - Zhilin Qu
- David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA, USA
| | - Radmila Terentyeva
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, USA
| | - Dmitry A Terentyev
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, USA
| | - Gideon Koren
- Department of Medicine, Rhode Island Hospital, Providence, RI, USA
| | - Bum-Rak Choi
- Department of Medicine, Rhode Island Hospital, Providence, RI, USA
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5
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Soepriatna AH, Navarrete-Welton A, Kim TY, Daley MC, Bronk P, Kofron CM, Mende U, Coulombe KLK, Choi BR. Action potential metrics and automated data analysis pipeline for cardiotoxicity testing using optically mapped hiPSC-derived 3D cardiac microtissues. PLoS One 2023; 18:e0280406. [PMID: 36745602 PMCID: PMC9901774 DOI: 10.1371/journal.pone.0280406] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Accepted: 12/28/2022] [Indexed: 02/07/2023] Open
Abstract
Recent advances in human induced pluripotent stem cell (hiPSC)-derived cardiac microtissues provide a unique opportunity for cardiotoxic assessment of pharmaceutical and environmental compounds. Here, we developed a series of automated data processing algorithms to assess changes in action potential (AP) properties for cardiotoxicity testing in 3D engineered cardiac microtissues generated from hiPSC-derived cardiomyocytes (hiPSC-CMs). Purified hiPSC-CMs were mixed with 5-25% human cardiac fibroblasts (hCFs) under scaffold-free conditions and allowed to self-assemble into 3D spherical microtissues in 35-microwell agarose gels. Optical mapping was performed to quantify electrophysiological changes. To increase throughput, AP traces from 4x4 cardiac microtissues were simultaneously acquired with a voltage sensitive dye and a CMOS camera. Individual microtissues showing APs were identified using automated thresholding after Fourier transforming traces. An asymmetric least squares method was used to correct non-uniform background and baseline drift, and the fluorescence was normalized (ΔF/F0). Bilateral filtering was applied to preserve the sharpness of the AP upstroke. AP shape changes under selective ion channel block were characterized using AP metrics including stimulation delay, rise time of AP upstroke, APD30, APD50, APD80, APDmxr (maximum rate change of repolarization), and AP triangulation (APDtri = APDmxr-APD50). We also characterized changes in AP metrics under various ion channel block conditions with multi-class logistic regression and feature extraction using principal component analysis of human AP computer simulations. Simulation results were validated experimentally with selective pharmacological ion channel blockers. In conclusion, this simple and robust automated data analysis pipeline for evaluating key AP metrics provides an excellent in vitro cardiotoxicity testing platform for a wide range of environmental and pharmaceutical compounds.
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Affiliation(s)
- Arvin H. Soepriatna
- Center for Biomedical Engineering, School of Engineering, Brown University, Providence, Rhode Island, United States of America
| | - Allison Navarrete-Welton
- Cardiovascular Research Center, Cardiovascular Institute, Rhode Island Hospital and Alpert Medical School of Brown University, Providence, Rhode Island, United States of America
| | - Tae Yun Kim
- Cardiovascular Research Center, Cardiovascular Institute, Rhode Island Hospital and Alpert Medical School of Brown University, Providence, Rhode Island, United States of America
| | - Mark C. Daley
- Center for Biomedical Engineering, School of Engineering, Brown University, Providence, Rhode Island, United States of America
| | - Peter Bronk
- Cardiovascular Research Center, Cardiovascular Institute, Rhode Island Hospital and Alpert Medical School of Brown University, Providence, Rhode Island, United States of America
| | - Celinda M. Kofron
- Center for Biomedical Engineering, School of Engineering, Brown University, Providence, Rhode Island, United States of America
| | - Ulrike Mende
- Cardiovascular Research Center, Cardiovascular Institute, Rhode Island Hospital and Alpert Medical School of Brown University, Providence, Rhode Island, United States of America
| | - Kareen L. K. Coulombe
- Center for Biomedical Engineering, School of Engineering, Brown University, Providence, Rhode Island, United States of America
| | - Bum-Rak Choi
- Cardiovascular Research Center, Cardiovascular Institute, Rhode Island Hospital and Alpert Medical School of Brown University, Providence, Rhode Island, United States of America
- * E-mail:
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6
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Kabakov AY, Sengun E, Lu Y, Roder K, Bronk P, Baggett B, Turan NN, Moshal KS, Koren G. Corrigendum: Three-week-old rabbit ventricular cardiomyocytes as a novel system to study cardiac excitation and EC coupling. Front Physiol 2023; 14:1157712. [PMID: 36909240 PMCID: PMC9992972 DOI: 10.3389/fphys.2023.1157712] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2023] [Accepted: 02/07/2023] [Indexed: 02/24/2023] Open
Abstract
[This corrects the article DOI: 10.3389/fphys.2021.672360.].
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Affiliation(s)
- Anatoli Y Kabakov
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Elif Sengun
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States.,Department of Pharmacology, Institute of Graduate Studies in Health Sciences, Istanbul University, Istanbul, Türkiye
| | - Yichun Lu
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Karim Roder
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Peter Bronk
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Brett Baggett
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Nilüfer N Turan
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Karni S Moshal
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Gideon Koren
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
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7
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Gupta A, Fei YD, Kim TY, Xie A, Batai K, Greener I, Tang H, Ciftci-Yilmaz S, Juneman E, Indik JH, Shi G, Christensen J, Gupta G, Hillery C, Kansal MM, Parikh DS, Zhou T, Yuan JXJ, Kanthi Y, Bronk P, Koren G, Kittles R, Duarte JD, Garcia JGN, Machado RF, Dudley SC, Choi BR, Desai AA. IL-18 mediates sickle cell cardiomyopathy and ventricular arrhythmias. Blood 2021; 137:1208-1218. [PMID: 33181835 PMCID: PMC7933768 DOI: 10.1182/blood.2020005944] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2020] [Accepted: 10/21/2020] [Indexed: 12/16/2022] Open
Abstract
Previous reports indicate that IL18 is a novel candidate gene for diastolic dysfunction in sickle cell disease (SCD)-related cardiomyopathy. We hypothesize that interleukin-18 (IL-18) mediates the development of cardiomyopathy and ventricular tachycardia (VT) in SCD. Compared with control mice, a humanized mouse model of SCD exhibited increased cardiac fibrosis, prolonged duration of action potential, higher VT inducibility in vivo, higher cardiac NF-κB phosphorylation, and higher circulating IL-18 levels, as well as reduced voltage-gated potassium channel expression, which translates to reduced transient outward potassium current (Ito) in isolated cardiomyocytes. Administering IL-18 to isolated mouse hearts resulted in VT originating from the right ventricle and further reduced Ito in SCD mouse cardiomyocytes. Sustained IL-18 inhibition via IL-18-binding protein resulted in decreased cardiac fibrosis and NF-κB phosphorylation, improved diastolic function, normalized electrical remodeling, and attenuated IL-18-mediated VT in SCD mice. Patients with SCD and either myocardial fibrosis or increased QTc displayed greater IL18 gene expression in peripheral blood mononuclear cells (PBMCs), and QTc was strongly correlated with plasma IL-18 levels. PBMC-derived IL18 gene expression was increased in patients who did not survive compared with those who did. IL-18 is a mediator of sickle cell cardiomyopathy and VT in mice and a novel therapeutic target in patients at risk for sudden death.
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Affiliation(s)
- Akash Gupta
- Department of Medicine, University of Arizona Health Sciences Center, University of Arizona, Tucson, AZ
| | - Yu-Dong Fei
- Department of Medicine, Indiana University, Indianapolis, IN
- Department of Cardiology, XinHua Hospital Affiliated to Shanghai JiaoTong University School of Medicine, Shanghai, China
| | - Tae Yun Kim
- Cardiovascular Research Center, Department of Medicine, Rhode Island Hospital and Alpert Medical School of Brown University, Providence, RI
| | - An Xie
- Department of Medicine, University of Minnesota, Minneapolis, MN
| | - Ken Batai
- Department of Surgery, University of Arizona Health Sciences Center, University of Arizona, Tucson, AZ
| | - Ian Greener
- Department of Medicine, University of Illinois Hospitals and Health Sciences System, Chicago, IL
| | - Haiyang Tang
- Department of Medicine, University of Arizona, Tucson, AZ
| | | | - Elizabeth Juneman
- Department of Medicine, University of Arizona Health Sciences Center, University of Arizona, Tucson, AZ
| | - Julia H Indik
- Department of Medicine, University of Arizona Health Sciences Center, University of Arizona, Tucson, AZ
| | - Guanbin Shi
- Cardiovascular Research Center, Department of Medicine, Rhode Island Hospital and Alpert Medical School of Brown University, Providence, RI
| | - Jared Christensen
- Cardiovascular Research Center, Department of Medicine, Rhode Island Hospital and Alpert Medical School of Brown University, Providence, RI
| | - Geetanjali Gupta
- Department of Medicine, University of Arizona Health Sciences Center, University of Arizona, Tucson, AZ
| | - Cheryl Hillery
- Department of Pediatrics, University of Pittsburgh, Pittsburgh, PA
| | - Mayank M Kansal
- Department of Medicine, University of Illinois Hospitals and Health Sciences System, Chicago, IL
| | - Devang S Parikh
- Department of Medicine, University of Illinois Hospitals and Health Sciences System, Chicago, IL
| | - Tong Zhou
- Department of Physiology and Cell Biology, University of Nevada, Reno, NV
| | - Jason X-J Yuan
- Department of Medicine, University of California, San Diego, La Jolla, CA
| | - Yogendra Kanthi
- Laboratory of Vascular Thrombosis & Inflammation, National Heart, Lung and Blood Institute, Bethesda, MD
| | - Peter Bronk
- Cardiovascular Research Center, Department of Medicine, Rhode Island Hospital and Alpert Medical School of Brown University, Providence, RI
| | - Gideon Koren
- Cardiovascular Research Center, Department of Medicine, Rhode Island Hospital and Alpert Medical School of Brown University, Providence, RI
| | - Rick Kittles
- Department of Population Science, City of Hope Medical Center, Duarte, CA; and
| | - Julio D Duarte
- Department of Pharmacotherapy and Translational Research, University of Florida, Gainesville, FL
| | - Joe G N Garcia
- Department of Medicine, University of Arizona Health Sciences Center, University of Arizona, Tucson, AZ
| | | | - Samuel C Dudley
- Department of Medicine, University of Minnesota, Minneapolis, MN
| | - Bum-Rak Choi
- Cardiovascular Research Center, Department of Medicine, Rhode Island Hospital and Alpert Medical School of Brown University, Providence, RI
| | - Ankit A Desai
- Department of Medicine, Indiana University, Indianapolis, IN
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8
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Kabakov AY, Sengun E, Lu Y, Roder K, Bronk P, Baggett B, Turan NN, Moshal KS, Koren G. Three-Week-Old Rabbit Ventricular Cardiomyocytes as a Novel System to Study Cardiac Excitation and EC Coupling. Front Physiol 2021; 12:672360. [PMID: 34867432 PMCID: PMC8637404 DOI: 10.3389/fphys.2021.672360] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Accepted: 10/06/2021] [Indexed: 01/14/2023] Open
Abstract
Cardiac arrhythmias significantly contribute to cardiovascular morbidity and mortality. The rabbit heart serves as an accepted model system for studying cardiac cell excitation and arrhythmogenicity. Accordingly, primary cultures of adult rabbit ventricular cardiomyocytes serve as a preferable model to study molecular mechanisms of human cardiac excitation. However, the use of adult rabbit cardiomyocytes is often regarded as excessively costly. Therefore, we developed and characterized a novel low-cost rabbit cardiomyocyte model, namely, 3-week-old ventricular cardiomyocytes (3wRbCMs). Ventricular myocytes were isolated from whole ventricles of 3-week-old New Zealand White rabbits of both sexes by standard enzymatic techniques. Using wheat germ agglutinin, we found a clear T-tubule structure in acutely isolated 3wRbCMs. Cells were adenovirally infected (multiplicity of infection of 10) to express Green Fluorescent Protein (GFP) and cultured for 48 h. The cells showed action potential duration (APD90 = 253 ± 24 ms) and calcium transients similar to adult rabbit cardiomyocytes. Freshly isolated and 48-h-old-cultured cells expressed critical ion channel proteins: calcium voltage-gated channel subunit alpha1 C (Cavα1c), sodium voltage-gated channel alpha subunit 5 (Nav1.5), potassium voltage-gated channel subfamily D member 3 (Kv4.3), and subfamily A member 4 (Kv1.4), and also subfamily H member 2 (RERG. Kv11.1), KvLQT1 (K7.1) protein and inward-rectifier potassium channel (Kir2.1). The cells displayed an appropriate electrophysiological phenotype, including fast sodium current (I Na), transient outward potassium current (I to), L-type calcium channel peak current (I Ca,L), rapid and slow components of the delayed rectifier potassium current (I Kr and I Ks), and inward rectifier (I K1). Although expression of the channel proteins and some currents decreased during the 48 h of culturing, we conclude that 3wRbCMs are a new, low-cost alternative to the adult-rabbit-cardiomyocytes system, which allows the investigation of molecular mechanisms of cardiac excitation on morphological, biochemical, genetic, physiological, and biophysical levels.
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Affiliation(s)
- Anatoli Y Kabakov
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Elif Sengun
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States.,Department of Pharmacology, Institute of Graduate Studies in Health Sciences, Istanbul University, Istanbul, Türkiye
| | - Yichun Lu
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Karim Roder
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Peter Bronk
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Brett Baggett
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Nilüfer N Turan
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Karni S Moshal
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Gideon Koren
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
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9
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Hwang J, Kim TY, Terentyev D, Zhong M, Kabakov AY, Bronk P, Arunachalam K, Belardinelli L, Rajamani S, Kunitomo Y, Pfeiffer Z, Lu Y, Peng X, Odening KE, Qu Z, Karma A, Koren G, Choi BR. Late I Na Blocker GS967 Supresses Polymorphic Ventricular Tachycardia in a Transgenic Rabbit Model of Long QT Type 2. Circ Arrhythm Electrophysiol 2020; 13:e006875. [PMID: 32628505 PMCID: PMC10626560 DOI: 10.1161/circep.118.006875] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
BACKGROUND Long QT syndrome has been associated with sudden cardiac death likely caused by early afterdepolarizations (EADs) and polymorphic ventricular tachycardias (PVTs). Suppressing the late sodium current (INaL) may counterbalance the reduced repolarization reserve in long QT syndrome and prevent EADs and PVTs. METHODS We tested the effects of the selective INaL blocker GS967 on PVT induction in a transgenic rabbit model of long QT syndrome type 2 using intact heart optical mapping, cellular electrophysiology and confocal Ca2+ imaging, and computer modeling. RESULTS GS967 reduced ventricular fibrillation induction under a rapid pacing protocol (n=7/14 hearts in control versus 1/14 hearts at 100 nmol/L) without altering action potential duration or restitution and dispersion. GS967 suppressed PVT incidences by reducing Ca2+-mediated EADs and focal activity during isoproterenol perfusion (at 30 nmol/L, n=7/12 and 100 nmol/L n=8/12 hearts without EADs and PVTs). Confocal Ca2+ imaging of long QT syndrome type 2 myocytes revealed that GS967 shortened Ca2+ transient duration via accelerating Na+/Ca2+ exchanger (INCX)-mediated Ca2+ efflux from cytosol, thereby reducing EADs. Computer modeling revealed that INaL potentiates EADs in the long QT syndrome type 2 setting through (1) providing additional depolarizing currents during action potential plateau phase, (2) increasing intracellular Na+ (Nai) that decreases the depolarizing INCX thereby suppressing the action potential plateau and delaying the activation of slowly activating delayed rectifier K+ channels (IKs), suggesting important roles of INaL in regulating Nai. CONCLUSIONS Selective INaL blockade by GS967 prevents EADs and abolishes PVT in long QT syndrome type 2 rabbits by counterbalancing the reduced repolarization reserve and normalizing Nai. Graphic Abstract: A graphic abstract is available for this article.
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Affiliation(s)
- Jungmin Hwang
- Cardiovascular Rsrch Ctr, Division of Cardiology, Rhode Island Hospital, Alpert Medical School of Brown Univ, Providence
- College of Pharmacy, Univ of Rhode Island, Kingstown, RI
| | - Tae Yun Kim
- Cardiovascular Rsrch Ctr, Division of Cardiology, Rhode Island Hospital, Alpert Medical School of Brown Univ, Providence
| | - Dmitry Terentyev
- Cardiovascular Rsrch Ctr, Division of Cardiology, Rhode Island Hospital, Alpert Medical School of Brown Univ, Providence
| | | | - Anatoli Y. Kabakov
- Cardiovascular Rsrch Ctr, Division of Cardiology, Rhode Island Hospital, Alpert Medical School of Brown Univ, Providence
| | - Peter Bronk
- Cardiovascular Rsrch Ctr, Division of Cardiology, Rhode Island Hospital, Alpert Medical School of Brown Univ, Providence
| | - Karuppiah Arunachalam
- Cardiovascular Rsrch Ctr, Division of Cardiology, Rhode Island Hospital, Alpert Medical School of Brown Univ, Providence
| | | | - Sridharan Rajamani
- Former employee: Dept of Biology, Gilead Science, Foster City, CA
- Amgen Inc, South San Francisco, CA
| | - Yukiko Kunitomo
- Cardiovascular Rsrch Ctr, Division of Cardiology, Rhode Island Hospital, Alpert Medical School of Brown Univ, Providence
| | - Zachary Pfeiffer
- Cardiovascular Rsrch Ctr, Division of Cardiology, Rhode Island Hospital, Alpert Medical School of Brown Univ, Providence
| | - Yichun Lu
- Cardiovascular Rsrch Ctr, Division of Cardiology, Rhode Island Hospital, Alpert Medical School of Brown Univ, Providence
| | - Xuwen Peng
- Dept of Comparative Medicine, Pennsylvania State Univ College of Medicine, Hershey, PA
| | - Katja E. Odening
- Dept of Cardiology & Angiology I, Heart Ctr, Univ of Freiburg, Germany
| | - Zhilin Qu
- Dept of Medicine, Univ of California, Los Angeles
| | - Alain Karma
- Dept of Physics, Northeastern Univ, Boston, MA
| | - Gideon Koren
- Cardiovascular Rsrch Ctr, Division of Cardiology, Rhode Island Hospital, Alpert Medical School of Brown Univ, Providence
| | - Bum-Rak Choi
- Cardiovascular Rsrch Ctr, Division of Cardiology, Rhode Island Hospital, Alpert Medical School of Brown Univ, Providence
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10
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Hamilton S, Polina I, Terentyeva R, Bronk P, Kim TY, Roder K, Clements RT, Koren G, Choi BR, Terentyev D. PKA phosphorylation underlies functional recruitment of sarcolemmal SK2 channels in ventricular myocytes from hypertrophic hearts. J Physiol 2019; 598:2847-2873. [PMID: 30771223 PMCID: PMC7496687 DOI: 10.1113/jp277618] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2018] [Accepted: 02/08/2019] [Indexed: 12/11/2022] Open
Abstract
KEY POINTS Small-conductance Ca2+ -activated K+ (SK) channels expressed in ventricular myocytes are dormant in health, yet become functional in cardiac disease. SK channels are voltage independent and their gating is controlled by intracellular [Ca2+ ] in a biphasic manner. Submicromolar [Ca2+ ] activates the channel via constitutively-bound calmodulin, whereas higher [Ca2+ ] exerts inhibitory effect during depolarization. Using a rat model of cardiac hypertrophy induced by thoracic aortic banding, we found that functional upregulation of SK2 channels in hypertrophic rat ventricular cardiomyocytes is driven by protein kinase A (PKA) phosphorylation. Using site-directed mutagenesis, we identified serine-465 as the site conferring PKA-dependent effects on SK2 channel function. PKA phosphorylation attenuates ISK rectification by reducing the Ca2+ /voltage-dependent inhibition of SK channels without changing their sensitivity to activating submicromolar [Ca2+ ]i . This mechanism underlies the functional recruitment of SK channels not only in cardiac disease, but also in normal physiology, contributing to repolarization under conditions of enhanced adrenergic drive. ABSTRACT Small-conductance Ca2+ -activated K+ (SK) channels expressed in ventricular myocytes (VMs) are dormant in health, yet become functional in cardiac disease. We aimed to test the hypothesis that post-translational modification of SK channels under conditions accompanied by enhanced adrenergic drive plays a central role in disease-related activation of the channels. We investigated this phenomenon using a rat model of hypertrophy induced by thoracic aortic banding (TAB). Western blot analysis using anti-pan-serine/threonine antibodies demonstrated enhanced phosphorylation of immunoprecipitated SK2 channels in VMs from TAB rats vs. Shams, which was reversible by incubation of the VMs with PKA inhibitor H89 (1 μmol L-1 ). Patch clamped VMs under basal conditions from TABs but not Shams exhibited outward current sensitive to the specific SK inhibitor apamin (100 nmol L-1 ), which was eliminated by inhibition of PKA (1 μmol L-1 ). Beta-adrenergic stimulation (isoproterenol, 100 nmol L-1 ) evoked ISK in VMs from Shams, resulting in shortening of action potentials in VMs and ex vivo optically mapped Sham hearts. Using adenoviral gene transfer, wild-type and mutant SK2 channels were overexpressed in adult rat VMs, revealing serine-465 as the site that elicits PKA-dependent phosphorylation effects on SK2 channel function. Concurrent confocal Ca2+ imaging experiments established that PKA phosphorylation lessens rectification of ISK via reduction Ca2+ /voltage-dependent inhibition of the channels at high [Ca2+ ] without affecting their sensitivity to activation by Ca2+ in the submicromolar range. In conclusion, upregulation of SK channels in diseased VMs is mediated by hyperadrenergic drive in cardiac hypertrophy, with functional effects on the channel conferred by PKA-dependent phosphorylation at serine-465.
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Affiliation(s)
- Shanna Hamilton
- Department of Medicine, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Cardiovascular Research Center, Providence, RI, USA.,Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University, Columbus, OH, USA.,Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, USA
| | - Iuliia Polina
- Department of Medicine, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Cardiovascular Research Center, Providence, RI, USA.,Medical University of South Carolina, Department of Medicine, Division of Nephrology, Charleston, SC, USA
| | - Radmila Terentyeva
- Department of Medicine, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Cardiovascular Research Center, Providence, RI, USA.,Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University, Columbus, OH, USA.,Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, USA
| | - Peter Bronk
- Department of Medicine, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Cardiovascular Research Center, Providence, RI, USA
| | - Tae Yun Kim
- Department of Medicine, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Cardiovascular Research Center, Providence, RI, USA
| | - Karim Roder
- Department of Medicine, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Cardiovascular Research Center, Providence, RI, USA
| | - Richard T Clements
- Department of Surgery, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Cardiovascular Research Center, Providence, RI, USA.,Vascular Research Laboratory, Providence Veterans Affairs Medical Center, Providence, RI, USA
| | - Gideon Koren
- Department of Medicine, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Cardiovascular Research Center, Providence, RI, USA
| | - Bum-Rak Choi
- Department of Medicine, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Cardiovascular Research Center, Providence, RI, USA
| | - Dmitry Terentyev
- Department of Medicine, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Cardiovascular Research Center, Providence, RI, USA.,Dorothy M. Davis Heart and Lung Research Institute, College of Medicine, The Ohio State University, Columbus, OH, USA.,Department of Physiology and Cell Biology, College of Medicine, The Ohio State University, Columbus, OH, USA
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11
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Hamilton S, Terentyeva R, Yun Kim T, Bronk P, O-Uchi J, Csordas G, Rak Choi B, Terentyev D. Pharmacological Modulation of Mitochondrial Ca2+ Uptake Regulates Sarcoplasmic Reticulum Ca2+ Release via Oxidation of Ryanodine Receptor by Reactive Oxygen Species. Biophys J 2019. [DOI: 10.1016/j.bpj.2018.11.2072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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12
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Hamilton S, Terentyeva R, Kim TY, Bronk P, Clements RT, O-Uchi J, Csordás G, Choi BR, Terentyev D. Pharmacological Modulation of Mitochondrial Ca 2+ Content Regulates Sarcoplasmic Reticulum Ca 2+ Release via Oxidation of the Ryanodine Receptor by Mitochondria-Derived Reactive Oxygen Species. Front Physiol 2018; 9:1831. [PMID: 30622478 PMCID: PMC6308295 DOI: 10.3389/fphys.2018.01831] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2018] [Accepted: 12/06/2018] [Indexed: 01/09/2023] Open
Abstract
In a physiological setting, mitochondria increase oxidative phosphorylation during periods of stress to meet increased metabolic demand. This in part is mediated via enhanced mitochondrial Ca2+ uptake, an important regulator of cellular ATP homeostasis. In a pathophysiological setting pharmacological modulation of mitochondrial Ca2+ uptake or retention has been suggested as a therapeutic strategy to improve metabolic homeostasis or attenuate Ca2+-dependent arrhythmias in cardiac disease states. To explore the consequences of mitochondrial Ca2+ accumulation, we tested the effects of kaempferol, an activator of mitochondrial Ca2+ uniporter (MCU), CGP-37157, an inhibitor of mitochondrial Na+/Ca2+ exchanger, and MCU inhibitor Ru360 in rat ventricular myocytes (VMs) from control rats and rats with hypertrophy induced by thoracic aortic banding (TAB). In periodically paced VMs under β-adrenergic stimulation, treatment with kaempferol (10 μmol/L) or CGP-37157 (1 μmol/L) enhanced mitochondrial Ca2+ accumulation monitored by mitochondrial-targeted Ca2+ biosensor mtRCamp1h. Experiments with mitochondrial membrane potential-sensitive dye TMRM revealed this was accompanied by depolarization of the mitochondrial matrix. Using redox-sensitive OMM-HyPer and ERroGFP_iE biosensors, we found treatment with kaempferol or CGP-37157 increased the levels of reactive oxygen species (ROS) in mitochondria and the sarcoplasmic reticulum (SR), respectively. Confocal Ca2+ imaging showed that accelerated Ca2+ accumulation reduced Ca2+ transient amplitude and promoted generation of spontaneous Ca2+ waves in VMs paced under ISO, suggestive of abnormally high activity of the SR Ca2+ release channel ryanodine receptor (RyR). Western blot analyses showed increased RyR oxidation after treatment with kaempferol or CGP-37157 vs. controls. Furthermore, in freshly isolated TAB VMs, confocal Ca2+ imaging demonstrated that enhancement of mitochondrial Ca2+ accumulation further perturbed global Ca2+ handling, increasing the number of cells exhibiting spontaneous Ca2+ waves, shortening RyR refractoriness and decreasing SR Ca2+ content. In ex vivo optically mapped TAB hearts, kaempferol exacerbated proarrhythmic phenotype. On the contrary, incubation of cells with MCU inhibitor Ru360 (2 μmol/L, 30 min) normalized RyR oxidation state, improved intracellular Ca2+ homeostasis and reduced triggered activity in ex vivo TAB hearts. These findings suggest facilitation of mitochondrial Ca2+ uptake in cardiac disease can exacerbate proarrhythmic disturbances in Ca2+ homeostasis via ROS and enhanced activity of oxidized RyRs, while strategies to reduce mitochondrial Ca2+ accumulation can be protective.
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Affiliation(s)
- Shanna Hamilton
- Department of Medicine, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Cardiovascular Research Center, Providence, RI, United States
| | - Radmila Terentyeva
- Department of Medicine, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Cardiovascular Research Center, Providence, RI, United States
| | - Tae Yun Kim
- Department of Medicine, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Cardiovascular Research Center, Providence, RI, United States
| | - Peter Bronk
- Department of Medicine, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Cardiovascular Research Center, Providence, RI, United States
| | - Richard T. Clements
- Department of Surgery, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Cardiovascular Research Center, Providence, RI, United States
- Vascular Research Laboratory, Providence Veterans Affairs Medical Center, Providence, RI, United States
| | - Jin O-Uchi
- Lillehei Heart Institute University of Minnesota, Cancer and Cardiovascular Research Building, Minneapolis, MN, United States
| | - György Csordás
- Department of Pathology, Anatomy and Cell Biology, Thomas Jefferson University, Philadelphia, PA, United States
| | - Bum-Rak Choi
- Department of Medicine, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Cardiovascular Research Center, Providence, RI, United States
| | - Dmitry Terentyev
- Department of Medicine, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Cardiovascular Research Center, Providence, RI, United States
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13
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Bronk P, Kuklin EA, Gorur-Shandilya S, Liu C, Wiggin TD, Reed ML, Marder E, Griffith LC. Regulation of Eag by Ca 2+/calmodulin controls presynaptic excitability in Drosophila. J Neurophysiol 2018; 119:1665-1680. [PMID: 29364071 PMCID: PMC6008097 DOI: 10.1152/jn.00820.2017] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2017] [Revised: 01/15/2018] [Accepted: 01/16/2018] [Indexed: 11/22/2022] Open
Abstract
Drosophila ether-à-go-go ( eag) is the founding member of a large family of voltage-gated K+ channels, the KCNH family, which includes Kv10, 11, and 12. Concurrent binding of calcium/calmodulin (Ca2+/CaM) to NH2- and COOH-terminal sites inhibits mammalian EAG1 channels at submicromolar Ca2+ concentrations, likely by causing pore constriction. Although the Drosophila EAG channel was believed to be Ca2+-insensitive (Schönherr R, Löber K, Heinemann SH. EMBO J 19: 3263-3271, 2000.), both the NH2- and COOH-terminal sites are conserved. In this study we show that Drosophila EAG is inhibited by high Ca2+ concentrations that are only present at plasma membrane Ca2+ channel microdomains. To test the role of this regulation in vivo, we engineered mutations that block CaM-binding to the major COOH-terminal site of the endogenous eag locus, disrupting Ca2+-dependent inhibition. eag CaMBD mutants have reduced evoked release from larval motor neuron presynaptic terminals and show decreased Ca2+ influx in stimulated adult projection neuron presynaptic terminals, consistent with an increase in K+ conductance. These results are predicted by a conductance-based multicompartment model of the presynaptic terminal in which some fraction of EAG is localized to the Ca2+ channel microdomains that control neurotransmitter release. The reduction of release in the larval neuromuscular junction drives a compensatory increase in motor neuron somatic excitability. This misregulation of synaptic and somatic excitability has consequences for systems-level processes and leads to defects in associative memory formation in adults. NEW & NOTEWORTHY Regulation of excitability is critical to tuning the nervous system for complex behaviors. We demonstrate in this article that the EAG family of voltage-gated K+ channels exhibit conserved gating by Ca2+/CaM. Disruption of this inhibition in Drosophila results in decreased evoked neurotransmitter release due to truncated Ca2+ influx in presynaptic terminals. In adults, disrupted Ca2+ dynamics cripples memory formation. These data demonstrate that the biophysical details of channels have important implications for cell function and behavior.
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Affiliation(s)
- Peter Bronk
- Department of Biology, National Center for Behavioral Genomics and Volen Center for Complex Systems, Brandeis University , Waltham, Massachusetts
| | - Elena A Kuklin
- Department of Biology, National Center for Behavioral Genomics and Volen Center for Complex Systems, Brandeis University , Waltham, Massachusetts
| | - Srinivas Gorur-Shandilya
- Department of Biology, National Center for Behavioral Genomics and Volen Center for Complex Systems, Brandeis University , Waltham, Massachusetts
| | - Chang Liu
- Department of Biology, National Center for Behavioral Genomics and Volen Center for Complex Systems, Brandeis University , Waltham, Massachusetts
| | - Timothy D Wiggin
- Department of Biology, National Center for Behavioral Genomics and Volen Center for Complex Systems, Brandeis University , Waltham, Massachusetts
| | - Martha L Reed
- Department of Biology, National Center for Behavioral Genomics and Volen Center for Complex Systems, Brandeis University , Waltham, Massachusetts
| | - Eve Marder
- Department of Biology, National Center for Behavioral Genomics and Volen Center for Complex Systems, Brandeis University , Waltham, Massachusetts
| | - Leslie C Griffith
- Department of Biology, National Center for Behavioral Genomics and Volen Center for Complex Systems, Brandeis University , Waltham, Massachusetts
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14
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Ni L, Bronk P, Chang EC, Lowell AM, Flam JO, Panzano VC, Theobald DL, Griffith LC, Garrity PA. A gustatory receptor paralogue controls rapid warmth avoidance in Drosophila. Nature 2013; 500:580-4. [PMID: 23925112 PMCID: PMC3758369 DOI: 10.1038/nature12390] [Citation(s) in RCA: 147] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2013] [Accepted: 06/14/2013] [Indexed: 11/09/2022]
Abstract
Behavioural responses to temperature are critical for survival, and animals from insects to humans show strong preferences for specific temperatures. Preferred temperature selection promotes avoidance of adverse thermal environments in the short term and maintenance of optimal body temperatures over the long term, but its molecular and cellular basis is largely unknown. Recent studies have generated conflicting views of thermal preference in Drosophila, attributing importance to either internal or peripheral warmth sensors. Here we reconcile these views by showing that thermal preference is not a singular response, but involves multiple systems relevant in different contexts. We found previously that the transient receptor potential channel TRPA1 acts internally to control the slowly developing preference response of flies exposed to a shallow thermal gradient. We now find that the rapid response of flies exposed to a steep warmth gradient does not require TRPA1; rather, the gustatory receptor GR28B(D) drives this behaviour through peripheral thermosensors. Gustatory receptors are a large gene family, widely studied in insect gustation and olfaction, and are implicated in host-seeking by insect disease vectors, but have not previously been implicated in thermosensation. At the molecular level, GR28B(D) misexpression confers thermosensitivity upon diverse cell types, suggesting that it is a warmth sensor. These data reveal a new type of thermosensory molecule and uncover a functional distinction between peripheral and internal warmth sensors in this tiny ectotherm reminiscent of thermoregulatory systems in larger, endothermic animals. The use of multiple, distinct molecules to respond to a given temperature, as observed here, may facilitate independent tuning of an animal's distinct thermosensory responses.
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Affiliation(s)
- Lina Ni
- National Center for Behavioral Genomics, Brandeis University, Waltham, Massachusetts 02454, USA
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15
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Sharma M, Burré J, Bronk P, Zhang Y, Xu W, Südhof TC. CSPα knockout causes neurodegeneration by impairing SNAP-25 function. EMBO J 2011; 31:829-41. [PMID: 22187053 DOI: 10.1038/emboj.2011.467] [Citation(s) in RCA: 117] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2011] [Accepted: 11/28/2011] [Indexed: 12/31/2022] Open
Abstract
At a synapse, the synaptic vesicle protein cysteine-string protein-α (CSPα) functions as a co-chaperone for the SNARE protein SNAP-25. Knockout (KO) of CSPα causes fulminant neurodegeneration that is rescued by α-synuclein overexpression. The CSPα KO decreases SNAP-25 levels and impairs SNARE-complex assembly; only the latter but not the former is reversed by α-synuclein. Thus, the question arises whether the CSPα KO phenotype is due to decreased SNAP-25 function that then causes neurodegeneration, or due to the dysfunction of multiple as-yet uncharacterized CSPα targets. Here, we demonstrate that decreasing SNAP-25 levels in CSPα KO mice by either KO or knockdown of SNAP-25 aggravated their phenotype. Conversely, increasing SNAP-25 levels by overexpression rescued their phenotype. Inactive SNAP-25 mutants were unable to rescue, showing that the rescue was specific. Under all conditions, the neurodegenerative phenotype precisely correlated with SNARE-complex assembly, indicating that impaired SNARE-complex assembly due to decreased SNAP-25 levels is the ultimate correlate of neurodegeneration. Our findings suggest that the neurodegeneration in CSPα KO mice is primarily produced by defective SNAP-25 function, which causes neurodegeneration by impairing SNARE-complex assembly.
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Affiliation(s)
- Manu Sharma
- Department of Molecular and Cellular Physiology, Howard Hughes Medical Institute, Stanford University, Stanford, CA, USA.
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Bronk P, Deák F, Wilson MC, Liu X, Südhof TC, Kavalali ET. Differential effects of SNAP-25 deletion on Ca2+ -dependent and Ca2+ -independent neurotransmission. J Neurophysiol 2007; 98:794-806. [PMID: 17553942 DOI: 10.1152/jn.00226.2007] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
At the synapse, SNAP-25, along with syntaxin/HPC-1 and synaptobrevin/VAMP, forms SNARE N-ethylmaleimide-sensitive factor [soluble (NSF) attachment protein receptor] complexes that are thought to catalyze membrane fusion. Results from neuronal cultures of synaptobrevin-2 knockout (KO) mice showed that loss of synaptobrevin has a more severe effect on calcium-evoked release than on spontaneous release or on release evoked by hypertonicity. In this study, we recorded neurotransmitter release from neuronal cultures of SNAP-25 KO mice to determine whether they share this property. In neurons lacking SNAP-25, as those deficient in synaptobrevin-2, we found that approximately 10-12% of calcium-independent excitatory and inhibitory neurotransmitter release persisted. However, in contrast to synaptobrevin-2 knockouts, this remaining readily releasable pool in SNAP-25-deficient synapses was virtually insensitive to calcium-dependent-evoked stimulation. Although field stimulation reliably evoked neurotransmitter release in synaptobrevin-2 KO neurons, responses were rare in neurons lacking SNAP-25, and unlike synaptobrevin-2-deficient synapses, SNAP-25-deficient synapses did not exhibit facilitation of release during high-frequency stimulation. This severe loss of evoked exocytosis was matched by a reduction, but not a complete loss, of endocytosis during evoked stimulation. Moreover, synaptic vesicle turnover probed by FM-dye uptake and release during hypertonic stimulation was relatively unaffected by the absence of SNAP-25. This last difference indicates that in contrast to synaptobrevin, SNAP-25 does not directly function in endocytosis. Together, these results suggest that SNAP-25 has a more significant role in calcium-secretion coupling than synaptobrevin-2.
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Affiliation(s)
- Peter Bronk
- Department of Neuroscience, The University of Texas Southwestern Medical Center, Dallas, Texas 75390-9111, USA
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17
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Bronk P, Nie Z, Klose MK, Dawson-Scully K, Zhang J, Robertson RM, Atwood HL, Zinsmaier KE. The multiple functions of cysteine-string protein analyzed at Drosophila nerve terminals. J Neurosci 2006; 25:2204-14. [PMID: 15745946 PMCID: PMC6726096 DOI: 10.1523/jneurosci.3610-04.2005] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The synaptic vesicle-associated cysteine-string protein (CSP) is important for synaptic transmission. Previous studies revealed multiple defects at neuromuscular junctions (NMJs) of csp null-mutant Drosophila, but whether these defects are independent of each other or mechanistically linked through J domain mediated-interactions with heat-shock cognate protein 70 (Hsc70) has not been established. To resolve this issue, we genetically dissected the individual functions of CSP by an in vivo structure/function analysis. Expression of mutant CSP lacking the J domain at csp null-mutant NMJs fully restored normal thermo-tolerance of evoked transmitter release but did not completely restore evoked release at room temperature and failed to reverse the abnormal intraterminal Ca2+ levels. This suggests that J domain-mediated functions are essential for the regulation of intraterminal Ca2+ levels but only partially required for regulating evoked release and not required for protecting evoked release against thermal stress. Hence, CSP can also act as an Hsc70-independent chaperone protecting evoked release from thermal stress. Expression of mutant CSP lacking the L domain restored neurotransmission and partially reversed the abnormal intraterminal Ca2+ levels, suggesting that the L domain is important, although not essential, for the role of CSP in regulating intraterminal Ca2+ levels. We detected no effects of csp mutations on individual presynaptic Ca2+ signals triggered by action potentials, suggesting that presynaptic Ca2+ entry is not primarily impaired. Both the J and L domains were also required for the role of CSP in synaptic growth. Together, these results suggest that CSP has several independent synaptic functions, affecting synaptic growth, evoked release, thermal protection of evoked release, and intraterminal Ca2+ levels at rest and during stimulation.
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Affiliation(s)
- Peter Bronk
- Arizona Research Laboratories Division of Neurobiology, University of Arizona, Tucson, Arizona 85721-0077, USA
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Sun J, Bronk P, Liu X, Han W, Südhof TC. Synapsins regulate use-dependent synaptic plasticity in the calyx of Held by a Ca2+/calmodulin-dependent pathway. Proc Natl Acad Sci U S A 2006; 103:2880-5. [PMID: 16481620 PMCID: PMC1413856 DOI: 10.1073/pnas.0511300103] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Synapsins are abundant synaptic-vesicle phosphoproteins that are known to regulate neurotransmitter release but whose precise function has been difficult to pinpoint. Here, we use knockout mice to analyze the role of synapsins 1 and 2 in the calyx of Held synapse, allowing precise measurements of neurotransmitter release. We find that deletion of synapsins did not induce significant changes in spontaneous release or release evoked by isolated action potentials (APs) and did not alter the size of the readily releasable vesicle pool (RRP), the kinetics of RRP depletion, or the rate of recovery of the RRP after depletion. Deletion of synapsins, however, did increase use-dependent synaptic depression induced by a high-frequency stimulus train (> or = 50 Hz). The increased depression was due to a decrease in the fraction of the RRP, whose release was evoked by APs late in the stimulus train. The effect of synapsin deletions was occluded by intracellular application of the Ca2+-chelator EGTA or of a calmodulin inhibitor. Our results show that synapsins boost the release probability during high-frequency stimulation and suggest that this effect involves Ca2+/calmodulin-dependent phosphorylation of synapsins.
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Affiliation(s)
- Jianyuan Sun
- *Center for Basic Neuroscience
- To whom correspondence may be addressed. E-mail:
or
| | | | - Xinran Liu
- *Center for Basic Neuroscience
- Department of Molecular Genetics, and
| | | | - Thomas C. Südhof
- *Center for Basic Neuroscience
- Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, 6000 Harry Hines Boulevard, Dallas, TX 75390-9111
- To whom correspondence may be addressed. E-mail:
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19
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Song W, Ranjan R, Dawson-Scully K, Bronk P, Marin L, Seroude L, Lin YJ, Nie Z, Atwood HL, Benzer S, Zinsmaier KE. Presynaptic regulation of neurotransmission in Drosophila by the g protein-coupled receptor methuselah. Neuron 2002; 36:105-19. [PMID: 12367510 DOI: 10.1016/s0896-6273(02)00932-7] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Regulation of synaptic strength is essential for neuronal information processing, but the molecular mechanisms that control changes in neuroexocytosis are only partially known. Here we show that the putative G protein-coupled receptor Methuselah (Mth) is required in the presynaptic motor neuron to acutely upregulate neurotransmitter exocytosis at larval Drosophila NMJs. Mutations in the mth gene reduce evoked neurotransmitter release by approximately 50%, and decrease synaptic area and the density of docked and clustered vesicles. Pre- but not postsynaptic expression of normal Mth restored normal release in mth mutants. Conditional expression of Mth restored normal release and normal vesicle docking and clustering but not the reduced size of synaptic sites, suggesting that Mth acutely adjusts vesicle trafficking to synaptic sites.
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Affiliation(s)
- Wei Song
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
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20
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Zinsmaier KE, Bronk P. Molecular chaperones and the regulation of neurotransmitter exocytosis11Abbreviations: SNARE, soluble NSF attachment protein (SNAP) receptor; NSF, N-ethylmaleimide-sensitive factor; Hsc70, 70-kDa heat-shock cognate protein; CSP, cysteine-string protein; VAMP vesicle-associated membrane protein; SNAP-25, synaptosome-associated protein 25 kDa; NEM, N-ethylmaleimide; AAA ATPases, ATPases Associated to a variety of Activities; and Hsp70, Hsp90, and Hsp60, 70-kDa, 90-kDa, and 60-kDa heat-shock protein, respectively. Biochem Pharmacol 2001; 62:1-11. [PMID: 11377391 DOI: 10.1016/s0006-2952(01)00648-7] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Regulated neurotransmitter release depends on a precise sequence of events that lead to repeated cycles of exocytosis and endocytosis. These events are mediated by a series of molecular interactions among vesicular, plasma membrane, and cytosolic proteins. An emerging theme has been that molecular chaperones may guide the sequential restructuring of stable or transient protein complexes to promote a temporal and spatial regulation of the endo- and exocytotic machinery and to ensure a vectorial passage through the vesicle cycle. Chaperones, specialized for a few substrates, are ideally suited to participate in regulatory processes that require some molecular dexterity to rearrange conformational or oligomeric protein structures. This article emphasizes the significance of three molecular chaperone systems in regulated neurotransmitter release: the regulation of soluble NSF attachment protein receptor (SNARE) complexes by N-ethylmaleimide-sensitive factor (NSF) and the soluble NSF attachment protein (SNAP), the uncoating of clathrin-coated vesicles by the 70 kDa heat-shock cognate protein (Hsc70), and the regulation of SNARE complex-associated protein interactions by cysteine-string protein and Hsc70.
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Affiliation(s)
- K E Zinsmaier
- Department of Neuroscience, 234d Stemmler Hall, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6974, USA.
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21
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Abstract
Previous in vitro studies of cysteine-string protein (CSP) imply a potential role for the clathrin-uncoating ATPase Hsc70 in exocytosis. We show that hypomorphic mutations in Drosophila Hsc70-4 (Hsc4) impair nerve-evoked neurotransmitter release, but not synaptic vesicle recycling in vivo. The loss of release can be restored by increasing external or internal Ca(2+) and is caused by a reduced Ca(2+) sensitivity of exocytosis downstream of Ca(2+) entry. Hsc4 and CSP are likely to act in common pathways, as indicated by their in vitro protein interaction, the similar loss of evoked release in individual and double mutants, and genetic interactions causing a loss of release in trans-heterozygous hsc4-csp double mutants. We suggest that Hsc4 and CSP cooperatively augment the probability of release by increasing the Ca(2+) sensitivity of vesicle fusion.
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Affiliation(s)
- P Bronk
- Department of Neuroscience, 234d Stemmler Hall, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
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22
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Dawson-Scully K, Bronk P, Atwood HL, Zinsmaier KE. Cysteine-string protein increases the calcium sensitivity of neurotransmitter exocytosis in Drosophila. J Neurosci 2000; 20:6039-47. [PMID: 10934253 PMCID: PMC6772598] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023] Open
Abstract
Previous studies suggest that the vesicular cysteine-string protein (CSP) may modulate presynaptic Ca(2+) channel activity in fast neurotransmitter release. To test this hypothesis, we analyzed the dynamics of presynaptic Ca(2+) ion influx with the Ca(2+) indicator fluo-4 AM at csp mutant neuromuscular junctions of Drosophila. From 24 to 30 degrees C, stimulus-evoked, relative presynaptic Ca(2+) signals were increasingly larger in csp mutant boutons than in controls. Above 30 degrees C, Ca(2+) signals declined and were similar to controls at 34 degrees C. A prolonged decay of Ca(2+) signals in mutant boutons at high temperatures indicated abnormally slow Ca(2+) clearance. Cytosolic Ca(2+) at rest was determined with the ratiometric Ca(2+) indicator fura-2 AM and was similar in mutant and control boutons at 24 degrees C but higher in mutant boutons at 34 degrees C. Despite larger Ca(2+) signals in mutant boutons, evoked neurotransmitter release was always reduced in csp mutants and exhibited pronounced facilitation. Thus, a lack of Ca(2+) entry cannot explain the reduction of neurotransmitter release in csp mutants. At all temperatures tested, raising extracellular Ca(2+) increased transmitter release elicited by single stimuli in csp mutants. Collectively, these data suggest multiple functions for CSP at synaptic terminals. Increased Ca(2+) signals coupled with reduced release suggest a direct function of CSP in exocytosis downstream from Ca(2+) entry. Because the reduction of evoked release in csp mutants is counteracted by increased Ca(2+) levels, we suggest that CSP primarily increases the Ca(2+) sensitivity of the exocytotic machinery.
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Affiliation(s)
- K Dawson-Scully
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6974, USA
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Frolov VA, Cho MS, Bronk P, Reese TS, Zimmerberg J. Multiple local contact sites are induced by GPI-linked influenza hemagglutinin during hemifusion and flickering pore formation. Traffic 2000; 1:622-30. [PMID: 11208150 DOI: 10.1034/j.1600-0854.2000.010806.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Membrane fusion intermediates induced by the glycosylphosphatidylinositol-linked ectodomain of influenza hemagglutinin (GPI-HA) were investigated by rapid freeze, freeze-substitution, thin section electron microscopy, and with simultaneous recordings of whole-cell admittance and fluorescence. Upon triggering, the previously separated membranes developed numerous hourglass shaped points of membrane contact (approximately 10-130 nm waist) when viewed by electron microscopy. Stereo pairs showed close membrane contact at peaks of complementary protrusions, arising from each membrane. With HA, there were fewer contacts, but wide fusion pores. Physiological measurements showed fast lipid dye mixing between cells after acidification, and either fusion pore formation or the lack thereof (true hemifusion). For the earliest pores, a similar conductance distribution and frequency of flickering pores were detected for both HA and GPI-HA. For GPI-HA, lipid mixing was detected prior to, during, or after pore opening, whereas for HA, lipid mixing is seen only after pore opening. Our findings are consistent with a pathway wherein conformational changes in the ectodomain of HA pull membranes towards each other to form a contact site, then hemifusion and pore formation initiate in a small percentage of these contact sites. Finally, the transmembrane domain of HA is needed to complete membrane fusion for macromolecular content mixing.
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Affiliation(s)
- V A Frolov
- Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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Nie Z, Ranjan R, Wenniger JJ, Hong SN, Bronk P, Zinsmaier KE. Overexpression of cysteine-string proteins in Drosophila reveals interactions with syntaxin. J Neurosci 1999; 19:10270-9. [PMID: 10575024 PMCID: PMC6782430] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/14/2023] Open
Abstract
Cysteine-string proteins (CSPs) are associated with secretory vesicles and critical for regulated neurotransmitter release and peptide exocytosis. At nerve terminals, CSPs have been implicated in the mediation of neurotransmitter exocytosis by modulating presynaptic calcium channels; however, studies of CSPs in peptidergic secretion suggest a direct role in exocytosis independent of calcium transmembrane fluxes. Here we show that the individual expression of various CSP isoforms in Drosophila similarly rescues the loss of evoked neurotransmitter release at csp null mutant motor nerve terminals, suggesting widely overlapping functions for each isoform. Thus, the structural difference of CSP variants may not explain the opposing putative functions of CSP in neurotransmitter and peptide exocytosis. Consistently, the individual overexpression of each CSP isoform in wild-type Drosophila shows similar effects such as impaired viability and interference with wing and eye development. The dominant effects caused by the overexpression of CSP are suppressed by the simultaneous overexpression of syntaxin-1A but not by the coexpression of SNAP-25. Although overexpression of CSP itself has no apparent effect on the synaptic physiology of larval motor nerve terminals, it fully suppresses the decrease of evoked release induced by the overexpression of syntaxin-1A. A direct protein-protein interaction of CSP with syntaxin is further supported by coimmunoprecipitations of syntaxin with CSP and by protein binding assays using recombinant fusion proteins. Together, the genetic and biochemical interactions of CSP and syntaxin-1A suggest that CSP may chaperone or modulate protein-protein interactions of syntaxin-1A with either calcium channels or other components of the regulatory machinery mediating depolarization-dependent neurotransmitter exocytosis.
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Affiliation(s)
- Z Nie
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6974, USA
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25
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Chernomordik LV, Frolov VA, Leikina E, Bronk P, Zimmerberg J. The pathway of membrane fusion catalyzed by influenza hemagglutinin: restriction of lipids, hemifusion, and lipidic fusion pore formation. J Cell Biol 1998; 140:1369-82. [PMID: 9508770 PMCID: PMC2132678 DOI: 10.1083/jcb.140.6.1369] [Citation(s) in RCA: 318] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The mechanism of bilayer unification in biological fusion is unclear. We reversibly arrested hemagglutinin (HA)-mediated cell-cell fusion right before fusion pore opening. A low-pH conformation of HA was required to form this intermediate and to ensure fusion beyond it. We present evidence indicating that outer monolayers of the fusing membranes were merged and continuous in this intermediate, but HA restricted lipid mixing. Depending on the surface density of HA and the membrane lipid composition, this restricted hemifusion intermediate either transformed into a fusion pore or expanded into an unrestricted hemifusion, without pores but with unrestricted lipid mixing. Our results suggest that restriction of lipid flux by a ring of activated HA is necessary for successful fusion, during which a lipidic fusion pore develops in a local and transient hemifusion diaphragm.
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Affiliation(s)
- L V Chernomordik
- Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-1855, USA.
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Ranjan R, Bronk P, Zinsmaier KE. Cysteine string protein is required for calcium secretion coupling of evoked neurotransmission in drosophila but not for vesicle recycling. J Neurosci 1998; 18:956-64. [PMID: 9437017 PMCID: PMC6792780] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The entire deletion of the cysteine string protein (CSP) gene causes a temperature-sensitive (ts) block of evoked neurotransmission in Drosophila. CSP has been found to interact in vitro with the clathrin-uncoating ATPase HSC70, suggesting a potential role of CSP in vesicle recycling. Using FM1-43 imaging, we analyzed whether the ts block of neurotransmission in csp mutants is caused by a defect in vesicle exocytosis or vesicle recycling. We determined that FM1-43-labeled synaptic boutons of csp mutant neuromuscular junctions fail to destain at 32 degrees C after K+ depolarization, and that FM1-43 dye uptake cannot be evoked by K+ stimulation at 32 degrees C. However, when we stimulated dye uptake independent of depolarization by using black widow spider venom (BWSV), we observed endocytotic uptake of FM1-43. This suggests that endocytosis exhibits no primary ts defect. In addition, we found no ts defect of vesicle recycling at 32 degrees C that would correlate with the ts block of neurotransmission. We also discovered that BWSV and the calcium ionophore calcimycin stimulate FM1-43 destaining and quantal release in csp mutants at 32 degrees C when depolarization fails to evoke any response. The wild-type-like, calcimycin-induced response in csp null mutants indicates that some aspect of the depolarization-dependent calcium signaling pathway must be impaired, either calcium entry, calcium action, or both. Collectively, our results indicate that the csp mutation affects calcium secretion coupling of evoked exocytosis but not vesicle recycling. This supports the hypothesis that CSP links synaptic vesicles to calcium secretion coupling.
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Affiliation(s)
- R Ranjan
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6074, USA
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Chernomordik LV, Leikina E, Frolov V, Bronk P, Zimmerberg J. An early stage of membrane fusion mediated by the low pH conformation of influenza hemagglutinin depends upon membrane lipids. J Cell Biol 1997; 136:81-93. [PMID: 9008705 PMCID: PMC2132452 DOI: 10.1083/jcb.136.1.81] [Citation(s) in RCA: 175] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
While the specificity and timing of membrane fusion in diverse physiological reactions, including virus-cell fusion, is determined by proteins, fusion always involves the merger of membrane lipid bilayers. We have isolated a lipid-dependent stage of cell-cell fusion mediated by influenza hemagglutinin and triggered by cell exposure to mildly acidic pH. This stage preceded actual membrane merger and fusion pore formation but was subsequent to a low pH-induced change in hemagglutinin conformation that is required for fusion. A low pH conformation of hemagglutinin was required to achieve this lipid-dependent stage and also, downstream of it, to drive fusion to completion. The lower the pH of the medium applied to trigger fusion and, thus, the more hemagglutinin molecules activated, the less profound was the dependence of fusion on lipids. Membrane-incorporated lipids affected fusion in a manner that correlated with their dynamic molecular shape, a characteristic that determines a lipid monolayer's propensity to bend in different directions. The lipid sensitivity of this stage, i.e., inhibition of fusion by inverted cone-shaped lysophosphatidylcholine and promotion by cone-shaped oleic acid, was consistent with the stalk hypothesis of fusion, suggesting that fusion proteins begin membrane merger by promoting the formation of a bent, lipid-involving, stalk intermediate.
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Affiliation(s)
- L V Chernomordik
- Laboratary of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
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