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Renikunta HV, Lazarow K, Gong Y, Shukla PC, Giral H, Kratzer A, Nageswaran V, Opitz L, Engel FB, Haghikia A, Paneni F, Von Kries JP, Streckfuss-Boemeke K, Landmesser U, Jakob P. A large-scale functional high-throughput screening identifies miR-515 and miR-519e as potent inducers of human iPSC-cardiomyocyte proliferation. Eur Heart J 2022. [DOI: 10.1093/eurheartj/ehac544.2881] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Abstract
Introduction
Ischemic heart failure persists as a global health problem despite optimized medical and adjunctive device therapies. Loss of cardiomyocytes in the absence of a proliferative response comprise a major contributor to pathological remodeling and death in this patient population. Experimental studies have shown that microRNAs (miRNAs) may be used as a therapeutic option to reinduce adult cardiomyocyte proliferation.
Purpose
This study thought to evaluate proliferative potential in human cardiomyocytes after overexpression and inhibition of 2019 miRNAs.
Methods
To identify miRNAs that regulate cardiomyocyte proliferation, we performed functional high-throughput screenings in human iPSC-derived cardiomyocytes (hiPSC-CM) after transient hypoxia. Herein, 2019 miRNA-mimics for overexpression and 2019 anti-miRs for inhibition were individually transfected to examine EdU-incorporation in hiPSC-CM. MiR-mimic-515 and miR-mimic-519e that induced the highest EdU-uptake, were further assessed by immunostaining and molecular methods for markers indicative of early and late mitosis. In addition, RNA-Sequencing in hiPSC-CM after overexpression of miR-515 and miR-519e was performed to examine differential gene expression and miRNA-modulated pathways involved in cardiomyocyte proliferation.
Results
Using a functional high-throughput screening, we assessed differential proliferative potential of 2019 miRNAs after transient hypoxia by transfecting both miR-inhibitor and miR-mimic libraries in human iPSC-derived cardiomyocytes (hiPSC-CM). Overexpression of 28 miRNAs substantially induced proliferative activity in hiPSC-CM, with an overrepresentation of miRNAs belonging to the C19MC-cluster and adjacent miR-371–373 family. Two of these miRNAs, miR-515 and miR-519e increased markers of early and late mitosis, with an additive cardiomyocyte turnover after transient hypoxia and substantially increased Aurora B-kinase activity in midbodies, indicative of cell division. These findings were supported by molecular studies using qRT-PCR, Western blot, and RNA-Sequencing after overexpression of miR-515 and miR-519e showing substantial alterations of signaling pathways relevant for cardiomyocytes proliferation in human iPSC-CM.
Conclusion
Collectively, these results support a critical role of miR-515 and miR-519e for induction of proliferation in human cardiomyocytes under hypoxic conditions, such as present in patients with ischemia-driven cardiomyopathy.
Funding Acknowledgement
Type of funding sources: Foundation. Main funding source(s): This work was supported by the German Centre for Cardiovascular Research (DZHK), Deutsche Stiftung für Herzforschung (DSHF) and OPO Foundation.
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Affiliation(s)
- H V Renikunta
- Charite - Campus Benjamin Franklin, Department of Cardiology , Berlin , Germany
| | - K Lazarow
- Max Delbruck Center for Molecular Medicine, Leibniz-Institute for Molecular Pharmacology , Berlin , Germany
| | - Y Gong
- University of Zurich, Center for Molecular Cardiology , Schlieren , Switzerland
| | - P C Shukla
- Charite - Campus Benjamin Franklin, Department of Cardiology , Berlin , Germany
| | - H Giral
- Charite - Campus Benjamin Franklin, Department of Cardiology , Berlin , Germany
| | - A Kratzer
- Charite - Campus Benjamin Franklin, Department of Cardiology , Berlin , Germany
| | - V Nageswaran
- Charite - Campus Benjamin Franklin, Department of Cardiology , Berlin , Germany
| | - L Opitz
- University of Zurich, Functional Genomics Center Zurich UZH/ETH , Zurich , Switzerland
| | - F B Engel
- Friedrich Alexander University, Experimental Renal and Cardiovascular Research, Department of Nephropathology , Erlangen , Germany
| | - A Haghikia
- Charite - Campus Benjamin Franklin, Department of Cardiology , Berlin , Germany
| | - F Paneni
- University of Zurich, Center for Molecular Cardiology , Schlieren , Switzerland
| | - J P Von Kries
- Max Delbruck Center for Molecular Medicine, Leibniz-Institute for Molecular Pharmacology , Berlin , Germany
| | - K Streckfuss-Boemeke
- University Medical Center of Gottingen (UMG), Clinic for Cardiology and Pneumology , Goettingen , Germany
| | - U Landmesser
- Charite - Campus Benjamin Franklin, Department of Cardiology , Berlin , Germany
| | - P Jakob
- University Heart Center, Cardiology, University Hospital Zurich , Zurich , Switzerland
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Fischer L, Nosratlo M, Hast K, Karakaya E, Ströhlein N, Esser TU, Gerum R, Richter S, Engel FB, Detsch R, Fabry B, Thievessen I. Calcium supplementation of bioinks reduces shear stress-induced cell damage during bioprinting. Biofabrication 2022; 14. [PMID: 35896101 DOI: 10.1088/1758-5090/ac84af] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [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: 02/02/2022] [Accepted: 07/27/2022] [Indexed: 11/12/2022]
Abstract
During bioprinting, cells are suspended in a viscous bioink and extruded under pressure through small diameter printing needles. The combination of high pressure and small needle diameter exposes cells to considerable shear stress, which can lead to cell damage and death. Approaches to monitor and control shear stress-induced cell damage are currently not well established. To visualize the effects of printing-induced shear stress on plasma membrane integrity, we add FM 1-43 to the bioink, a styryl dye that becomes fluorescent when bound to lipid membranes, such as the cellular plasma membrane. Upon plasma membrane disruption, the dye enters the cell and also stains intracellular membranes. Extrusion of alginate-suspended NIH/3T3 cells through a 200µm printing needle led to an increased FM 1-43 incorporation at high pressure, demonstrating that typical shear stresses during bioprinting can transiently damage the plasma membrane. Cell imaging in a microfluidic channel confirmed that FM 1-43 incorporation is caused by cell strain. Notably, high printing pressure also impaired cell survival in bioprinting experiments. Using cell types of different stiffnesses, we find that shear stress-induced cell strain, FM 1-43 incorporation and cell death were reduced in stiffer compared to softer cell types and demonstrate that cell damage and death correlate with shear stress-induced cell deformation. Importantly, supplementation of the suspension medium with physiological concentrations of CaCl2greatly reduced shear stress-induced cell damage and death but not cell deformation. As the sudden influx of calcium ions is known to induce rapid cellular vesicle exocytosis and subsequent actin polymerization in the cell cortex, we hypothesize that calcium supplementation facilitates the rapid resealing of plasma membrane damage sites. We recommend that bioinks should be routinely supplemented with physiological concentrations of calcium ions to reduce shear stress-induced cell damage and death during extrusion bioprinting.
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Affiliation(s)
- Lena Fischer
- Department of Physics, University of Erlangen-Nuremberg, Erlangen, Germany
| | - Mojtaba Nosratlo
- Department of Physics, University of Erlangen-Nuremberg, Erlangen, Germany
| | - Katharina Hast
- Department of Physics, University of Erlangen-Nuremberg, Erlangen, Germany
| | - Emine Karakaya
- Institute of Biomaterials, Department of Materials Science and Engineering, University of Erlangen-Nuremberg, Erlangen, Germany
| | - Nadine Ströhlein
- Department of Physics, University of Erlangen-Nuremberg, Erlangen, Germany
| | - Tilman U Esser
- Experimental Renal and Cardiovascular Research, Department of Nephropathology, Institute of Pathology, Friedrich-Alexander-University of Erlangen-Nuremberg, Erlangen, Germany
| | - Richard Gerum
- Department of Physics, University of Erlangen-Nuremberg, Erlangen, Germany.,Department of Physics and Astronomy, York-University Toronto, Ontario, Canada
| | - Sebastian Richter
- Department of Physics, University of Erlangen-Nuremberg, Erlangen, Germany
| | - F B Engel
- Experimental Renal and Cardiovascular Research, Department of Nephropathology, Institute of Pathology, Friedrich-Alexander-University of Erlangen-Nuremberg, Erlangen, Germany
| | - Rainer Detsch
- Institute of Biomaterials, Department of Materials Science and Engineering, University of Erlangen-Nuremberg, Erlangen, Germany
| | - Ben Fabry
- Department of Physics, University of Erlangen-Nuremberg, Erlangen, Germany
| | - Ingo Thievessen
- Department of Physics, University of Erlangen-Nuremberg, Erlangen, Germany
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Groenewoud A, Forn-Cuní G, Engel FB, Snaar-Jagalska BE. XePhIR: the zebrafish xenograft phenotype interactive repository. Database (Oxford) 2022; 2022:6575480. [PMID: 35482537 PMCID: PMC9216515 DOI: 10.1093/database/baac028] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [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: 11/04/2021] [Revised: 01/28/2022] [Accepted: 04/19/2022] [Indexed: 11/14/2022]
Abstract
Abstract
Zebrafish xenografts are an established model in cancer biology, with a steadily rising number of models and users. However, as of yet, there is no platform dedicated to standardizing protocols and sharing data regarding zebrafish xenograft phenotypes. Here, we present the Xenograft Phenotype Interactive Repository (XePhIR, https://www.xephir.org) as an independent data-sharing platform to deposit, share and repurpose zebrafish xenograft data. Deposition of data and publication with XePhIR will be done after the acceptation of the original publication. This will enhance the reach of the original research article, enhance visibility and do not interfere with the publication or copyrights of the original article. With XePhIR, we strive to fulfill these objectives and reason that this resource will enhance reproducibility and showcase the appeal and applicability of the zebrafish xenograft model.
Database URL: https://www.xephir.org
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Affiliation(s)
- A Groenewoud
- Institute of Biology Leiden, Animal Sciences, Leiden University, Einsteinweg 55, CC Leiden 2333, The Netherlands
- Experimental Renal and Cardiovascular Research, Department of Nephropathology, Institute of Pathology, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Schwabachanlage 12, Erlangen 91054, Germany
| | - G Forn-Cuní
- Institute of Biology Leiden, Animal Sciences, Leiden University, Einsteinweg 55, CC Leiden 2333, The Netherlands
| | - F B Engel
- Experimental Renal and Cardiovascular Research, Department of Nephropathology, Institute of Pathology, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Schwabachanlage 12, Erlangen 91054, Germany
- Comprehensive Cancer Center Erlangen-EMN (CCC ER-EMN), Östliche Stadtmauerstraße 30, Erlangen 91054, Germany
| | - B E Snaar-Jagalska
- Institute of Biology Leiden, Animal Sciences, Leiden University, Einsteinweg 55, CC Leiden 2333, The Netherlands
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Hesselbarth R, Esser TU, Roshanbinfar K, Struefer S, Schubert DW, Engel FB. Enhancement of engineered cardiac tissues by promotion of hiPSC-cardiomyocyte proliferation. Eur Heart J 2021. [DOI: 10.1093/eurheartj/ehab724.3234] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Abstract
Background/Introduction
Cardiac tissue engineering is a promising strategy to generate human cardiac tissues for modelling cardiac diseases, screening for therapeutic drugs, and repairing the injured heart. Yet, several issues remain to be resolved including the generation of tissues with high cardiomyocyte density.
Purpose
Determining the effects of the induction of human-induced pluripotent stem cell-derived (hiPSC) cardiomyocyte proliferation post-fabrication.
Methods
hiPSCs were differentiated into cardiomyocytes, embedded with or without CHIR990121 at three concentrations in a collagen pre-gel, and cast. The engineered cardiac tissues were then cultured in the absence or presence of CHIR99021 for up to 35 days. Hydrogels and engineered cardiac tissues were analysed utilizing rheology and assays to determine viability, proliferation, calcium flow, and contractility.
Results
Here, we show that the integration of CHIR99021 in collagen I hydrogels promotes proliferation of hiPSC-cardiomyocytes post-fabrication improving contractility of and calcium flow in engineered cardiac tissues. Presence of CHIR99021 has no effect on the gelation kinetic or the mechanical properties of collagen I hydrogels. Analysis of cell density and proliferation based on Ki-67 staining indicates that integration of CHIR99021 together with external CHIR99021 stimulation increases hiPSC-cardiomyocyte number by ∼2-fold within 7 days post-fabrication. Analysis of the contractility of engineered cardiac tissues after another 3 days in the absence of external CHIR99021 shows that CHIR99021-induced hiPSC-cardiomyocyte proliferation results in synchronized calcium flow, rhythmic beating, increases speed of contraction and contraction amplitude, and reduces peak-to-peak time. The CHIR99021-stimulated engineered cardiac tissues exhibited spontaneous rhythmic contractions for at least 35 days.
Conclusion
Collectively, our data demonstrate the potential of induced cardiomyocyte proliferation to enhance engineered cardiac tissues by increasing cardiomyocyte density and reducing arrhythmia.
Funding Acknowledgement
Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Deutsche Forschungsgemeinschaft
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Affiliation(s)
| | - T U Esser
- University hospital Erlangen, Erlangen, Germany
| | | | - S Struefer
- Friedrich Alexander University, Erlangen, Germany
| | - D W Schubert
- Friedrich Alexander University, Erlangen, Germany
| | - F B Engel
- University hospital Erlangen, Erlangen, Germany
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5
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Srivastava S, Gunanwan F, Guenther S, Ferrazzi F, Gentile A, Monk KM, Stainier DYR, Engel FB. Gpr126 domains control different cellular mechanisms of ventricular chamber development. Eur Heart J 2021. [DOI: 10.1093/eurheartj/ehab724.3180] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Abstract
Introduction
Trabeculation is a crucial process during ventricular chamber development which describes the protrusion of cardiomyocytes into the lumen of the ventricular chamber to form complex muscular structures called trabeculae. Defects in this process results in various human diseases such as left ventricular non compaction cardiomyopathies and other congenital heart defects. Several cellular mechanisms have been identified underlying trabeculation including tension heterogeneity induced cardiomyocyte selection, depolarization and delamination. However, the molecular mechanisms governing trabeculation are still poorly understood.
Purpose
Previously, we have shown that Gpr126 is required for trabeculation and heart development in mice and zebrafish. Gpr126 is an adhesion G-protein coupled receptor which is autoproteolytically cleaved into an N-terminal fragment (NTF) and a C-terminal fragment (CTF). Here, we show that NTF and CTF control different cellular processes during trabeculation.
Methods and results
In-vivo confocal images of hearts of CTF-depleted mutants gpr126st49 (expressing NTF) revealed a multilayered ventricular wall lacking any trabecular projections, which is in contrast to our previous results obtained with morpholinos suggesting that the NTF is sufficient for proper heart development in zebrafish. A molecular characterization of gpr126st49 mutants showed that cardiomyocytes in the multilayer fail to depolarize and relocalize N-cadherin from the lateral to the basal side, indicating that the cardiomyocytes in the multi-layered wall fail to attain a trabecular identity. In addition, these mutants showed significantly upregulated myocardial notch expression, which is known to prevent cardiomyocytes from attaining a trabecular identity. These data suggest that CTF is required for proper formation of trabeculae. We analyzed the full length-depleted mutant gpr126stl47 for trabeculation defects and observed that 17% of gpr126stl47 maternal zygotic mutants exhibited complete absence of trabeculation and 27% hypotrabeculation. Analysis of these mutants revealed that instead of being specifically localized at the junctions, N-cadherin was mainly distributed to the apical and basal side in the compact layer cardiomyocytes. This indicates that the NTF is required for maintaining the cell-cell adhesion in the compact wall. Finally, overexpression of gpr126 in the absence of Erbb2 signaling and blood flow / -or contractility failed to cause multilayering suggesting that Gpr126 is part of the well-established Erbb2 signaling cascade controlling trabeculation.
Conclusion
Collectively, our data support a model with domain-specific functions of Gpr126 in ventricular chamber development, where the NTF of Gpr126 is required for maintaining the compact wall integrity at the onset of trabeculation by maintaining cell-cell junctions, while the CTF helps in providing trabecular identity to cardiomyocytes through modulation of myocardial notch activity.
Funding Acknowledgement
Type of funding sources: Public grant(s) – EU funding. Main funding source(s): DFG
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Affiliation(s)
- S Srivastava
- University hospital Erlangen, Nephropathologie, Erlangen, Germany
| | - F Gunanwan
- Max Planck Institute for Heart and Lung Research, Developmental Genetics, Bad Nauheim, Germany
| | - S Guenther
- Max Planck Institute for Heart and Lung Research, Bioinformatics and Deep Sequencing Platform, Bad Nauheim, Germany
| | - F Ferrazzi
- University hospital Erlangen, Nephropathologie, Erlangen, Germany
| | - A Gentile
- Max Planck Institute for Heart and Lung Research, Developmental Genetics, Bad Nauheim, Germany
| | - K M Monk
- Oregon Health and Science University, The Vollum Institute, Portland, United States of America
| | - D Y R Stainier
- Max Planck Institute for Heart and Lung Research, Developmental Genetics, Bad Nauheim, Germany
| | - F B Engel
- University hospital Erlangen, Nephropathologie, Erlangen, Germany
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6
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Abstract
Abstract
Background
Cardiac tissue engineering is an effective strategy to generate tissues for drug testing and disease modelling as well as for cardiac repair. Tissues produced by casting show good functionality and advanced maturation, but do not replicate the native tissue architecture and hierarchy. Additive manufacturing technologies, such as 3D bioprinting, enable the generation of hierarchically structured tissues with complex geometries. This technology has been used previously to generate models of the heart. However, these approaches either showed limited tissue functionality or required a two-step procedure using a structural and a cell-laden bioink.
Purpose
Here, we aimed to develop a collagen-based bioink, which enables direct 3D-bioprinting of hiPSC-derived cardiomyocytes and supports the formation of functional cardiac tissue.
Methods
To generate cardiac tissues, a commercial pneumatic extrusion bioprinter with custom modifications to enable passive cooling of the bioink was used. Gelatin/gum arabic microparticles were obtained through complex coacervation, compacted by centrifugation and utilized as support bath. Cardiomyocytes were differentiated in 2D monolayer and expanded by CHIR99021-treatment and regular passaging. Cells were encapsulated in a rat collagen-I based bioink and printed into support bath prior to gelation. After bioink gelation at 37°C, support bath was removed, and constructs cultivated free-floating for up to 30 days.
Results
We printed ring-shaped cardiac tissues measuring 5 x 5 x 1 mm, which remained stable over the course of cultivation. First contractions were observed after three days, which increased in magnitude and synchronized across the tissue with prolonged culture. HiPSC-cardiomyocytes displayed striated sarcomeres and were responsive to pharmacological stimulation. In addition, using two distinct bioinks, multi-layered constructs were generated.
Conclusion
3D-bioprinting is a promising tool to generate engineered cardiac tissues with complex geometries and improved functionality through designed hierarchy. Our collagen-based bioink and associated printing strategy enables the fabrication of Collagen-based contractile cardiac tissues in a direct manner.
Funding Acknowledgement
Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Deutsche Forschungsgemeinschaft (DFG) Contractions of printed cardiac tissue
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Affiliation(s)
- T U Esser
- Friedrich Alexander University, Department of Nephropathology, Erlangen, Germany
| | - F B Engel
- Friedrich Alexander University, Department of Nephropathology, Erlangen, Germany
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Becker R, Engel FB. 223CRISPR-mediated fluorescent tagging of endogenous PCM1 enables live cell imaging of non-centrosomal MTOC formation in muscle cells. Cardiovasc Res 2018. [DOI: 10.1093/cvr/cvy060.159] [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] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- R Becker
- University Hospital Erlangen, Nephropathology, Erlangen, Germany
| | - F B Engel
- University Hospital Erlangen, Nephropathology, Erlangen, Germany
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Musa G, Srivastava S, Engel FB. P451The endocardial expression of ADGRG6 (Gpr126) is necessary for survival in mouse and sufficient to drive trabeculation in zebrafish. Cardiovasc Res 2018. [DOI: 10.1093/cvr/cvy060.311] [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] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Affiliation(s)
- G Musa
- University Hospital Erlangen, Nephropathology, Erlangen, Germany
| | - S Srivastava
- University Hospital Erlangen, Nephropathology, Erlangen, Germany
| | - F B Engel
- University Hospital Erlangen, Nephropathology, Erlangen, Germany
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Engel FB, Hauck L, Cardoso MC, Leonhardt H, Dietz R, von Harsdorf R. A mammalian myocardial cell-free system to study cell cycle reentry in terminally differentiated cardiomyocytes. Circ Res 1999; 85:294-301. [PMID: 10436173 DOI: 10.1161/01.res.85.3.294] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Cardiomyocytes withdraw from the cell cycle in the early neonatal period, rendering the adult heart incapable to regenerate after injury. In the present study, we report the establishment of a cell-free system to investigate the control of cell cycle reentry in mammalian ventricular cardiomyocyte nuclei and to specifically address the question of whether nuclei from terminally differentiated cardiomyocytes can be stimulated to reenter S phase when incubated with extracts from S-phase cells. Immobilized cardiomyocyte nuclei were incubated with nuclei and cytoplasmic extract of synchronized H9c2 muscle cells or cardiac nonmyocytes. Ongoing DNA synthesis was monitored by biotin-16-dUTP incorporation as well as proliferating cell nuclear antigen expression and localization. Nuclei and cytoplasmic extract from S-phase H9c2 cells but not from H9c2 myotubes induced DNA synthesis in 92% of neonatal cardiomyocyte nuclei. Coincubation in the presence of cycloheximide indicated that de novo translation is required for the reinduction of S phase. Similar results were obtained with adult cardiomyocyte nuclei. When coincubated with both cytoplasmic extract and nuclei or nuclear extracts of S-phase cells, >70% of adult cardiomyocyte nuclei underwent DNA synthesis. In conclusion, these results demonstrate that postmitotic ventricular myocyte nuclei are responsive to stimuli derived from S-phase cells and can thus bypass the cell cycle block. This cell-free system now makes it feasible to analyze the molecular requirements for the release of the cell cycle block and will help to engineer strategies for regenerative growth in cardiac muscle.
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Affiliation(s)
- F B Engel
- Department of Cardiology, Franz Volhard Clinic, Humboldt University, Berlin, Germany
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