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      Programming and Isolation of Highly Pure Physiologically and Pharmacologically Functional Sinus-Nodal Bodies from Pluripotent Stem Cells

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          Summary

          Therapeutic approaches for “sick sinus syndrome” rely on electrical pacemakers, which lack hormone responsiveness and bear hazards such as infection and battery failure. These issues may be overcome via “biological pacemakers” derived from pluripotent stem cells (PSCs). Here, we show that forward programming of PSCs with the nodal cell inducer TBX3 plus an additional Myh6-promoter-based antibiotic selection leads to cardiomyocyte aggregates consisting of >80% physiologically and pharmacologically functional pacemaker cells. These induced sinoatrial bodies (iSABs) exhibited highly increased beating rates (300–400 bpm), coming close to those found in mouse hearts, and were able to robustly pace myocardium ex vivo. Our study introduces iSABs as highly pure, functional nodal tissue that is derived from PSCs and may be important for future cell therapies and drug testing in vitro.

          Highlights

          • TBX3 plus Myh6-promoter antibiotic selection yields pacemaker cells from PSCs

          • Induced sinoatrial bodies (iSABs) consist of >80% functional pacemaker cells

          • iSABs showed highly increased beating rates and were able to pace myocardium ex vivo

          • iSABs represent highly pure functional nodal tissue derived from PSCs

          Abstract

          David and colleagues describe how forward programming of PSCs with TBX3 plus additional Myh6-promoter-based antibiotic selection yielded cardiomyocyte aggregates consisting of >80% physiologically and pharmacologically functional pacemaker cells. These induced sinoatrial bodies (iSABs) exhibited highly increased beating rates (300–400 bpm) and were able to pace myocardium ex vivo. Their study introduces iSABs as highly pure functional nodal tissue derived from PSCs.

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          Most cited references30

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          Direct conversion of quiescent cardiomyocytes to pacemaker cells by expression of Tbx18.

          The heartbeat originates within the sinoatrial node (SAN), a small structure containing <10,000 genuine pacemaker cells. If the SAN fails, the ∼5 billion working cardiomyocytes downstream of it become quiescent, leading to circulatory collapse in the absence of electronic pacemaker therapy. Here we demonstrate conversion of rodent cardiomyocytes to SAN cells in vitro and in vivo by expression of Tbx18, a gene critical for early SAN specification. Within days of in vivo Tbx18 transduction, 9.2% of transduced, ventricular cardiomyocytes develop spontaneous electrical firing physiologically indistinguishable from that of SAN cells, along with morphological and epigenetic features characteristic of SAN cells. In vivo, focal Tbx18 gene transfer in the guinea-pig ventricle yields ectopic pacemaker activity, correcting a bradycardic disease phenotype. Myocytes transduced in vivo acquire the cardinal tapering morphology and physiological automaticity of native SAN pacemaker cells. The creation of induced SAN pacemaker (iSAN) cells opens new prospects for bioengineered pacemakers.
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            Generation of functional murine cardiac myocytes from induced pluripotent stem cells.

            The recent breakthrough in the generation of induced pluripotent stem (iPS) cells, which are almost indistinguishable from embryonic stem (ES) cells, facilitates the generation of murine disease- and human patient-specific stem cell lines. The aim of this study was to characterize the cardiac differentiation potential of a murine iPS cell clone in comparison to a well-established murine ES cell line. With the use of a standard embryoid body-based differentiation protocol for ES cells, iPS cells as well as ES cells were differentiated for 24 days. Although the analyzed iPS cell clone showed a delayed and less efficient formation of beating embryoid bodies compared with the ES cell line, the differentiation resulted in an average of 55% of spontaneously contracting iPS cell embryoid bodies. Analyses on molecular, structural, and functional levels demonstrated that iPS cell-derived cardiomyocytes show typical features of ES cell-derived cardiomyocytes. Reverse transcription polymerase chain reaction analyses demonstrated expression of marker genes typical for mesoderm, cardiac mesoderm, and cardiomyocytes including Brachyury, mesoderm posterior factor 1 (Mesp1), friend of GATA2 (FOG-2), GATA-binding protein 4 (GATA4), NK2 transcription factor related, locus 5 (Nkx2.5), T-box 5 (Tbx5), T-box 20 (Tbx20), atrial natriuretic factor (ANF), myosin light chain 2 atrial transcripts (MLC2a), myosin light chain 2 ventricular transcripts (MLC2v), alpha-myosin heavy chain (alpha-MHC), and cardiac troponin T in differentiation cultures of iPS cells. Immunocytology confirmed expression of cardiomyocyte-typical proteins including sarcomeric alpha-actinin, titin, cardiac troponin T, MLC2v, and connexin 43. iPS cell cardiomyocytes displayed spontaneous rhythmic intracellular Ca(2+) fluctuations with amplitudes of Ca(2+) transients comparable to ES cell cardiomyocytes. Simultaneous Ca(2+) release within clusters of iPS cell-derived cardiomyocytes indicated functional coupling of the cells. Electrophysiological studies with multielectrode arrays demonstrated functionality and presence of the beta-adrenergic and muscarinic signaling cascade in these cells. iPS cells differentiate into functional cardiomyocytes. In contrast to ES cells, iPS cells allow derivation of autologous functional cardiomyocytes for cellular cardiomyoplasty and myocardial tissue engineering.
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              Formation of the sinus node head and differentiation of sinus node myocardium are independently regulated by Tbx18 and Tbx3.

              The sinus node (or sinoatrial node [SAN]), the pacemaker of the heart, is a functionally and structurally heterogeneous tissue, which consists of a large "head" within the right caval vein myocardium and a "tail" along the terminal crest. Here, we investigated its cellular origin and mechanism of formation. Using genetic lineage analysis and explant assays, we identified T-box transcription factor Tbx18-expressing mesenchymal progenitors in the inflow tract region that differentiate into pacemaker myocardium to form the SAN. We found that the head and tail represent separate regulatory domains expressing distinctive gene programs. Tbx18 is required to establish the large head structure, as seen by the existence of a very small but still functional tail piece in Tbx18-deficient fetuses. In contrast, Tbx3-deficient embryos formed a morphologically normal SAN, which, however, aberrantly expressed Cx40 and other atrial genes, demonstrating that Tbx3 controls differentiation of SAN head and tail cardiomyocytes but also demonstrating that Tbx3 is not required for the formation of the SAN structure. Our data establish a functional order for Tbx18 and Tbx3 in SAN formation, in which Tbx18 controls the formation of the SAN head from mesenchymal precursors, on which Tbx3 subsequently imposes the pacemaker gene program.
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                Author and article information

                Contributors
                Journal
                Stem Cell Reports
                Stem Cell Reports
                Stem Cell Reports
                Elsevier
                2213-6711
                17 April 2014
                17 April 2014
                06 May 2014
                : 2
                : 5
                : 592-605
                Affiliations
                [1 ]Referenz und Translationszentrum für Kardiale Stammzelltherapie (RTC) der Universität Rostock, 18057 Rostock, Germany
                [2 ]Universitätsklinik für Innere Medizin III, Kardiologie und Angiologie, 6020 Innsbruck, Austria
                [3 ]Gene Center Munich, LMU Munich, 81377 Munich, Germany
                [4 ]Institut für Experimentelle und Klinische Pharmakologie und Toxikologie der FAU Erlangen-Nürnberg, 91054 Erlangen, Germany
                [5 ]Walter Brendel Centre, LMU Munich, 81377 Munich, Germany
                [6 ]German Center for Cardiovascular Research (DZHK), partner site Munich Heart Alliance, Munich, Germany
                Author notes
                []Corresponding author robert.david@ 123456med.uni-rostock.de
                [7]

                These authors contributed equally to this work

                Article
                S2213-6711(14)00085-X
                10.1016/j.stemcr.2014.03.006
                4050488
                60ab5e1c-48c3-40a8-a790-009462311150
                © 2014 The Authors

                This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

                History
                : 28 February 2014
                : 17 March 2014
                : 18 March 2014
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