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Zebrafish hearts can regenerate by replacing damaged tissue with new cardiomyocytes. Although the steps leading up to the proliferation of surviving cardiomyocytes have been extensively studied, little is known about the mechanisms that control proliferation and redifferentiation to a mature state. We found that the cardiac dyad, a structure that regulates calcium handling and excitation-contraction coupling, played a key role in the redifferentiation process. A component of the cardiac dyad called leucine-rich repeat–containing 10 (Lrrc10) acted as a negative regulator of proliferation, prevented cardiomegaly, and induced redifferentiation. We found that its function was conserved in mammalian cardiomyocytes. This study highlights the importance of the underlying mechanisms required for heart regeneration and their application to the generation of fully functional cardiomyocytes.

The ability of human pluripotent stem cells to form all cells of the body has provided many opportunities to study disease and produce cells that can be used for therapy in regenerative medicine. Even though beating cardiomyocytes were among the first cell types to be differentiated from human pluripotent stem cell, cardiac applications have advanced more slowly than those, for example, for the brain, eye, and pancreas. This is, in part, because simple 2-dimensional human pluripotent stem cell cardiomyocyte cultures appear to need crucial functional cues normally present in the 3-dimensional heart structure. Recent tissue engineering approaches combined with new insights into the dialogue between noncardiomyocytes and cardiomyocytes have addressed and provided solutions to issues such as cardiomyocyte immaturity and inability to recapitulate adult heart values for features like contraction force, electrophysiology, or metabolism. Three-dimensional bioengineered heart tissues are thus poised to contribute significantly to disease modeling, drug discovery, and safety pharmacology, as well as provide new modalities for heart repair. Here, we review the current status of 3-dimensional engineered heart tissues.

Aims Human-induced pluripotent stem cell-cardiomyocytes (hiPSC-CMs) are widely used to study arrhythmia-associated mutations in ion channels. Among these, the cardiac sodium channel SCN5A undergoes foetal-to-adult isoform switching around birth. Conventional hiPSC-CM cultures, which are phenotypically foetal, have thus far been unable to capture mutations in adult gene isoforms. Here, we investigated whether tri-cellular cross-talk in a three-dimensional (3D) cardiac microtissue (MT) promoted post-natal SCN5A maturation in hiPSC-CMs. Methods and results We derived patient hiPSC-CMs carrying compound mutations in the adult SCN5A exon 6B and exon 4. Electrophysiological properties of patient hiPSC-CMs in monolayer were not altered by the exon 6B mutation compared with isogenic controls since it is not expressed; further, CRISPR/Cas9-mediated excision of the foetal exon 6A did not promote adult SCN5A expression. However, when hiPSC-CMs were matured in 3D cardiac MTs, SCN5A underwent isoform switch and the functional consequences of the mutation located in exon 6B were revealed. Up-regulation of the splicing factor muscleblind-like protein 1 (MBNL1) drove SCN5A post-natal maturation in microtissues since its overexpression in hiPSC-CMs was sufficient to promote exon 6B inclusion, whilst knocking-out MBNL1 failed to foster isoform switch. Conclusions Our study shows that (i) the tri-cellular cardiac microtissues promote post-natal SCN5A isoform switch in hiPSC-CMs, (ii) adult splicing of SCN5A is driven by MBNL1 in these tissues, and (iii) this model can be used for examining post-natal cardiac arrhythmias due to mutations in the exon 6B. Translational perspective The cardiac sodium channel is essential for conducting the electrical impulse in the heart. Postnatal alternative splicing regulation causes mutual exclusive inclusion of fetal or adult exons of the corresponding gene, SCN5A. Typically, immature hiPSCCMs fall short in studying the effect of mutations located in the adult exon. We describe here that an innovative tri-cellular three-dimensional cardiac microtissue culture promotes hiPSC-CMs maturation through upregulation of MBNL1, thus revealing the effect of a pathogenic genetic variant located in the SCN5A adult exon. These results help advancing the use of hiPSC-CMs in studying adult heart disease and for developing personalized medicine applications.

We synthesized and evaluated three novel series of substituted benzophenones for their allosteric modulation of the human K(v)11.1 (hERG) channel. We compared their effects with reference compound LUF7346 previously shown to shorten the action potential of cardiomyocytes derived from human stem cells. Most compounds behaved as negative allosteric modulators (NAMs) of [H-3]dofetilide binding to the channel. Compound 9i was the most potent amongst all ligands, remarkably reducing the affinity of dofetilide in competitive displacement assays. One of the other derivatives (6k) tested in a second radioligand binding set-up, displayed unusual displacement characteristics with a pseudo-Hill coefficient significantly distinct from unity, further indicative of its allosteric effects on the channel. Some compounds were evaluated in a more physiologically relevant context in beating cardiomyocytes derived from human induced pluripotent stem cells. Surprisingly, the compounds tested showed effects quite different from the reference NAM LUF7346. For instance, compound 5e prolonged, rather than shortened, the field potential duration, while it did not influence this parameter when the field potential was already prolonged by dofetilide. In subsequent patch clamp studies on HEK293 cells expressing the hERG channel the compounds behaved as channel blockers. In conclusion, we successfully synthesized and identified new allosteric modulators of the hERG channel. Unexpectedly, their effects differed from the reference compound in functional assays on hERG-HEK293 cells and human cardiomyocytes, to the extent that the compounds behaved as stand-alone channel blockers. (C) 2020 The Author(s). Published by Elsevier Masson SAS.

Tissue-like structures from human pluripotent stem cells containing multiple cell types are transforming our ability to model and understand human development and disease. Here we describe a protocol to generate cardiomyocytes (CMs), cardiac fibroblasts (CFs) and cardiac endothelial cells (ECs), the three principal cell types in the heart, from human induced pluripotent stem cells (hiPSCs) and combine them in three-dimensional (3D) cardiac microtissues (MTs). We include details of how to differentiate, isolate, cryopreserve and thaw the component cells and how to construct and analyze the MTs. The protocol supports hiPSC-CM maturation and allows replacement of one or more of the three heart cell types in the MTs with isogenic variants bearing disease mutations. Differentiation of each cell type takes similar to 30 d, while MT formation and maturation requires another 20 d. No specialist equipment is needed and the method is inexpensive, requiring just 5,000 cells per MT.

Properties of the funny current (If) have been studied in several animal and cellular models, but so far little is known concerning its properties in human pacemaker cells. This work provides a detailed characterization of If in human-induced pluripotent stem cell (iPSC)–derived pacemaker cardiomyocytes (pCMs), at different time points. Patch-clamp analysis showed that If density did not change during differentiation; however, after day 30, it activates at more negative potential and with slower time constants. These changes are accompanied by a slowing in beating rate. If displayed the voltage-dependent block by caesium and reversed (Erev) at − 22 mV, compatibly with the 3:1 K+/Na+ permeability ratio. Lowering [Na+]o (30 mM) shifted the Erev to − 39 mV without affecting conductance. Increasing [K+]o (30 mM) shifted the Erev to − 15 mV with a fourfold increase in conductance. pCMs express mainly HCN4 and HCN1 together with the accessory subunits CAV3, KCR1, MiRP1, and SAP97 that contribute to the context-dependence of If. Autonomic agonists modulated the diastolic depolarization, and thus rate, of pCMs. The adrenergic agonist isoproterenol induced rate acceleration and a positive shift of If voltage-dependence (EC50 73.4 nM). The muscarinic agonists had opposite effects (Carbachol EC50, 11,6 nM). Carbachol effect was however small but it could be increased by pre-stimulation with isoproterenol, indicating low cAMP levels in pCMs. In conclusion, we demonstrated that pCMs display an If with the physiological properties expected by pacemaker cells and may thus represent a suitable model for studying human If-related sinus arrhythmias.

We synthesized and evaluated three novel series of substituted benzophenones for their allosteric modulation of the human K

Introduction: We recently demonstrated in a large multicentre study that sGA can identify fit older patients with aggressive lymphoma able to tolerate first-line intensive treatment with curative intent and to obtain similar results than younger people (Merli at al JCO 2021). Regardless of age, about 40% of patients with aggressive lymphoma are either refractory or will eventually relapse after treatment with curative intent. Salvage platinum-based regimens followed by ASCT in responsive disease is a standard of care to obtain longer second remission. However, in many case series, patients over 65 years are excluded from the transplant approach because of potential severe toxicities of high-dose therapy in older patients. This study was designed to evaluate the feasibility and activity of high-dose treatment followed by ASCT in older FIT patients with R/R aggressive lymphoma selected with a sGA. Methods: Patients with R/R aggressive lymphoma after one line of treatment, aged between 65 and 75, and FIT to sGA were eligible for the study. Salvage treatment could be chosen between R-DHAP, R-ICE or other platinum or gemcitabine-containing regimens and stem cells were mobilized after 1 or 2 cycles. Patients achieving at least partial response after 3 courses and who remained FIT to sGA evaluation were eligible for ASCT and were conditioned with either BEAM or FEAM. Results: From May 2014 to August 2019, seventy-five patients from 16 FIL centres were enrolled and 70 were eligible for the study. Sixty-six of them had a diffuse large B-cell lymphoma, one had follicular 3b, 2 mantle cell and 1 Burkitt histology. Salvage treatment was R-DHAP in 48 patients, R-ICE in seven and gemcitabine or oxalyplatinum containing regimens in the remaining ones. Overall response rate after three courses was 44% (21 complete and 10 partial remission). Among the 39 unresponsive patients, 29 had progressive and 4 stable disease, 2 patients died of septic shock and heart failure during salvage and 4 patients withdrew their consent to ASCT. Four patients relapsed soon after response achievement before undergoing the transplant. ASCT was performed in 27 patients with a median of 5.6 x 10 6 CD34/Kg reinfused. No differences emerged in demographic and clinical characteristics between patients reaching the ASCT timepoint or not (Tab 1a). By intention to treat analysis, 2-y overall survival (OS) and PFS of the entire intention-to-treat population were 65% (95%CI: 50-76%) and 34% (95%CI: 22-46%) respectively, without differences according to age (Tab 1b). After a median of 27 months, 2-y OS was 79% (95CI: 51-86%) and EFS 56% (95CI: 32-75%). Twenty-four patients obtained a complete remission (CR) and 20 of them are in continuous CR after more than 12 months. Three patients progressed 1-8 months after ASCT and died. Most common non-hematologic grade 3-4 adverse events were gastrointestinal (10%) and infectious (8%). Conclusion: This study shows that sGA can identify older patients with R/R aggressive lymphoma who are able to tolerate and can benefit from high-dose therapy and ASCT. The poor response to second-line immunochemotherapy remains the major drawback of this approach since less than 50% of patients could actually receive ASCT. Nevertheless the 2-y survival of 65% in the intention to treat population is remarkable and sets the stage for the evaluation of new approaches such as CAR-T or bispecific antibodies also in older patients. A next step should be to explore the usefulness of sGA in the selection of candidates to these innovative treatments. Figure 1 Figure 1. Disclosures Tucci: Takeda: Membership on an entity's Board of Directors or advisory committees; Gentili: Membership on an entity's Board of Directors or advisory committees; janssen: Membership on an entity's Board of Directors or advisory committees. Musuraca: janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; incyte: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Cavallo: ROCHE: Membership on an entity's Board of Directors or advisory committees; Servier: Speakers Bureau; Gilead: Speakers Bureau. Zilioli: Roche, Italfarmaco: Consultancy, Honoraria; MSD, Janssen: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accommodations; Gentili, Takeda, Gilead, Servier: Consultancy, Speakers Bureau; Takeda: Other: travel expenses, accommodation. Merli: EUSA Pharma: Other: Travel, Accomodations, Expenses; Roche: Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accomodations, Expenses; Takeda: Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accomodations, Expenses; MSD: Membership on an entity's Board of Directors or advisory committees; Gilead Science: Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accomodations, Expenses; Janssen: Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accomodations, Expenses; Celgene: Other: Travel, Accomodations, Expenses. Marcheselli: sandoz: Membership on an entity's Board of Directors or advisory committees. Rossi: Abbvie: Membership on an entity's Board of Directors or advisory committees; Alexion: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Consultancy, Honoraria; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Jazz: Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria; Takeda: Membership on an entity's Board of Directors or advisory committees.

The identification of new molecular insights always drove the research. Data from genetic, molecular biology and biochemistry suggest new directions, open new fields and lead to new discoveries. The significance of these data is, in certain situation, difficult to envision. In this view, physiology could represent one of the possible read-out of the overall complex modifications inside the cell. In particular, electrophysiological analysis shed light on both physiological and pathological conditions in excitable and non-excitable cells. In excitable cell, ion channels, cellular microenvironment, transcription factors and accessory proteins shape the electric profile of the cell. In my PhD, I mainly used this approach to test the effect of mutations associated with arrhythmic diseases (in both cardiac arrhythmia and epilepsy) and of physiopathological remodeling in response to endurance training. In particular, I performed the following projects concerning: - Characterization of the biophysical properties of the hHCN1 L157V mutation found in a patient affected by idiopathic generalized epilepsy. This mutation resulted to decrease the current density and leading to an increased excitability in single neonatal rat cortical neurons. - Analysis of the cardiac endurance training-associated microRNAs (miRNAs) in a trained mouse model and of the role of the muscle-specific miRNAs in modulating membrane excitability in the neonatal rat ventricular cardiomyocytes. These results highlights new miRNAs potentially involved in the cardiac electrical remodeling associated with endurance training. - Characterization of the impact of the T78M cav-3 variant found in a cohort of arrhythmic patients. This variant induces modification of several ionic currents leading to a pro-arrhythmogenic profile. The leitmotiv of these projects is the identification of the causes underlying the pathophysiological modification of excitable cells by ion channels, membrane proteins and post-transcriptional molecules.

Introduction: We have previously reported short-term efficacy of six courses of R-DA-EPOCH in patients with aggressive B cell lymphomas carrying concomitant MYC and BCL-2 and/or BCL-6 rearrangement (DHL/THL) or gene increase copy number (ICN) (Tucci et al. Blood S1: 4154, 2017). Further experience with the same program has been described in the meantime in patients with aggressive lymphoma and c-MYC rearrangement, either as single hit or DHL/THL (Dunleavy et al. Lancet Haematol, 2018). We report here long-term results in a larger unselected series of DHL/THL with the aim to confirm our preliminary results and to define the role of consolidation with autologous stem cell transplantation (ASCT) after R-DA-EPOCH remission induction. Methods: The study includes patients consecutively seen in four Italian centres. From January 2014, fit patients aged less than 80 years, with diffuse large B cell lymphoma (DLBCL), lymphoma with intermediate features between DLBCL and Burkitt (BCLU) or high grade lymphoma (HGBCL) histology, diagnosed as DHL or THL by fluorescent in situ hybridization (FISH), were treated with R-DA-EPOCH and central nervous system prophylaxis. Patients with MYC -ICN (three or more extra signals in more than 30% of nuclei, Schieppati et al. Haematologica, 2019) plus BCL-2 and/or BCL-6 gene rearrangement or ICN were also included. Pre-treatment with one cycle of R-CHOP was allowed in patients in need of urgent treatment, pending the results of FISH analysis. Consolidation with ASCT was planned in three of the four centres for stage II-IV patients aged less than 71 who reached at least a partial remission (PR) after six R-DA-EPOCH courses. Immunohistochemistry (IHC) was used to define cell of origin (COO) according to Hans' algorithm, double expressor cases (MYC and BCL-2 protein >40% and 50% respectively) and Ki67 expression. Results: Sixty-three patients were treated (51 DLBCL, 5 BCLU, 7 HGBCL, including 16 with histologic transformation from an indolent lymphoma). Their median age was 63 years (range 23-79) and 43 (68%) were males. Fifty-four (86%) had Ann-Arbor stage III/IV, 18 (28%) B symptoms and 41 (65%) high-intermediate/high risk score according to International Prognostic Index (IPI), with extranodal disease in 79% of patients, mainly in bone and gastrointestinal tract. According to FISH analysis, 34 cases were DHL, 10 THL and 19 c-MYC-ICN. According to IHC, 81% were of germinal center origin, 73% were double expressors and median Ki-67 was 91% (range 35-100%). Patients received a median of six courses of R-DA-EPOCH (range 1-6). Twelve patients were pre-treated with one R-CHOP course and 24 patients (17 in complete remission, 6 in PR and 1 with disease progression) received transplant consolidation (allogeneic SCT in one PR patient), according to the policy of the centre and eligibility criteria. In the entire cohort, the overall response rate was 81%, including 68% complete responses (CR) and 3y-PFS and OS were 67% and 69% respectively. Two patients died of infectious complications during chemotherapy. Of the 10 chemo-refractory patients, all have died of lymphoma. Median length of follow-up was 32 months. At univariate analysis, IPI > 3 and THL were significantly associated with a worse outcome while cMYC-ICN and ASCT with a better OS. At multivariate analysis, only ASCT remained significantly associated with better survival (HR 0.146, IC 95% 0.032-0.667, p 0.013). Focusing on patients who achieved CR with R-DA-EPOCH, all 17 patients who underwent transplantation (100%) are alive (after a median of 27 months from transplant), versus 19 out of 24 patients (79%) who did not. Only one patient relapsed after ASCT and is alive after receiving CAR-T cells. 3y-OS and PFS of patients in CR after induction therapy who received or not ASCT consolidation were 100% vs 76% and 94% vs 72% respectively (Fig.1). Clinical characteristics of the two subgroups were similar except for median age that was lower in the former one (59 vs 69 years). Conclusions: These results confirm the favourable outcome of patients with MYC and BCL-2 and/or BCL-6 rearrangements or gene ICN with R-DA-EPOCH therapy. The role of consolidative ASCT and its usefulness seems encouraging, but remains to be proven by prospective randomized studies. The poor outcome of chemo-refractory patients represents an unmet need and greater expansion of CAR-T cell programs could improve these results in the near future. Disclosures Tucci: Amgen: Consultancy. Carlo-Stella:Boehringer Ingelheim and Sanofi: Consultancy; Servier, Novartis, Genenta Science srl, ADC Therapeutics, F. Hoffmann-La Roche, Karyopharm, Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb, Merck Sharp & Dohme, Janssen Oncology, AstraZeneca: Honoraria; ADC Therapeutics and Rhizen Pharmaceuticals: Research Funding. Corradini:Takeda: Consultancy, Honoraria, Other; BMS: Other; Janssen: Consultancy, Honoraria; Kite: Consultancy, Honoraria; KiowaKirin: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Other: Travel and accommodations paid by for; F. Hoffman-La Roche Ltd: Consultancy, Honoraria; Sanofi: Consultancy, Honoraria; Servier: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Other: Travel and accommodations paid by for; Amgen: Consultancy, Honoraria, Other: Travel and accommodations paid by for; Daiichi Sankyo: Consultancy, Honoraria; Gilead: Consultancy, Honoraria, Other: Travel and accommodations paid by for; Incyte: Consultancy; AbbVie: Consultancy, Honoraria, Other: Travel and accommodations paid by for. Rossi:Janssen: Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Consultancy, Honoraria; Celgene: Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Other: Advisory board; Abbvie: Membership on an entity's Board of Directors or advisory committees; Alexion: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Sanofi: Honoraria; Jazz: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria.

Ten years ago Yamanaka's lab identified a way to reprogram terminally differentiated cells to a pluripotent state, similar to that of embryonic stem cell. This procedure opened the road for the generation of postmitotic human cells, that have completely lost the replication potential. The initial excitement waned when it was observed that the cells produced by this method are somehow immature and do not resemble the adult phenotype. In the absence of cellular markers that recognize the various maturation steps of induced pluripotent stem cell-derived human cardiomyocytes, we propose to follow their maturation looking at their electrophysiological profile. For this reason, we are first reviewing the most common methods of differentiation, from the preliminary complex procedures to the newly-identified two-step protocols and, second, we report the electrical characteristics of the cells, through electrophysiological analysis of ionic currents that give rise to the action potential. We are aware that each protocol leads to the generation of different cardiomyocyte precursors, thus suggesting the need for a wider standardization. The identification of the electrophysiological characteristics of the cells could help in identifying the type and the maturation stage of the obtained cardiomyocyte, thus compensating for the lack of specific markers. Developmental Dynamics 245:1145-1158, 2016. © 2016 Wiley Periodicals, Inc.

Atrial fibrillation (AF) is characterized by electrical, contractile, and structural remodeling mediated by interstitial fibrosis. It has been shown that human cardiac mesenchymal progenitor cells (CMPCs) can be differentiated into endothelial, smooth muscle, and fibroblast cells. Here, we have investigated, for the first time, the contribution of CMPCs in the fibrotic process occurring in AF. As expected, right auricolae samples displayed significantly higher fibrosis in AF vs control (CTR) patients. In tissue samples of AF patients only, double staining for c-kit and the myofibroblast marker α-smooth muscle actin (α-SMA) was detected. The number of c-kit-positive CMPC was higher in atrial subepicardial regions of CTR than AF cells. AF-derived CMPC (AF-CMPC) and CTR-derived CMPC (Ctr-CMPC) were phenotypically similar, except for CD90 and c-kit, which were significantly more present in AF and CTR cells, respectively. Moreover, AF showed a lower rate of population doubling and fold enrichment vs Ctr-CMPC. When exogenously challenged with the profibrotic transforming growth factor-β1 (TGF-β1), AF-CMPC showed a significantly higher nuclear translocation of SMAD2 than Ctr-CMPC. In addition, TGF-β1 treatment induced the upregulation of COL1A1 and COL1A2 in AF-CMPC only. Further, both a marked production of soluble collagen and α-SMA upregulation have been observed in AF-CMPC only. Finally, electrophysiological studies showed that the inwardly rectifying potassium current (IK1) was evenly present in AF- and Ctr-CMPC in basal conditions and similarly disappeared after TGF-β1 exposure. All together, these data suggest that AF steers the resident atrial CMPC compartment toward an electrically inert profibrotic phenotype.

Mineralocorticoid receptor (MR) signaling is pivotal for numerous physiological processes and implicated in various pathological conditions concerning among others, tight epithelia, central nervous and cardiovascular systems. For decades, the pleiotropic actions of MR have been investigated using animal and cellular models as well as by clinical studies. Here is reviewed and contextualized the utilization of a strategy that recently emerged to analyze the complexity of MR signaling: the derivation and differentiation of mouse embryonic stem (ES) cell models. ES cells were derived from wild-type or transgenic MR overexpressing animals. Undifferentiated ES cells were differentiated into cardiomyocytes, neurons and adipocytes, these cell types being important pathophysiological targets of MR. These approaches have already brought new insights concerning MR effect on cardiomyocyte contractility and ionic channel remodeling, in the regulation of neuronal MR expression and its positive role on neuron survival. Differentiated ES cell models thus constitute powerful and promising tools to further decipher the molecular mechanisms of cell-specific MR actions.

The epigenetics of early commitment to embryonal cardiomyocyte is poorly understood. In this work, we compared the effect of thyroid hormone and that of anacardic acid, a naturally occurring histone acetylase inhibitor, or both in combination, on mouse embryonic stem cells (mES) differentiating into embryonal cardiomyocyte by embryoid bodies (EBs) formation. Although the results indicated that anacardic acid (AA) and thyroid hormone were both efficient in promoting cardiomyocyte differentiation, we noticed that a transient exposure of mES to AA alone was sufficient to enlarge the beating areas of EBs compared to those of untreated controls. This effect was associated with changes in the chromatin structure at the promoters of specific cardiomyogenic genes. Among them, a rapid induction of the transcription factor Castor 1 (CASZ1), important for cardiomyocytes differentiation and maturation during embryonic development, was observed in the presence of AA. In contrast, thyroid hormone (T 3) was more effective in stimulating spontaneous firing, thus suggesting a role in the production of a population of cardiomyocyte with pacemaker properties. In conclusion, AA and thyroid hormone both enhanced cardiomyocyte formation along in apparently distinct pathways.

Rationale: A cell-based biological pacemaker is based on the differentiation of stem cells and the selection of a population displaying the molecular and functional properties of native sinoatrial node (SAN) cardiomyocytes. So far, such selection has been hampered by the lack of proper markers. CD166 is specifically but transiently expressed in the mouse heart tube and sinus venosus, the prospective SAN. Objective: We have explored the possibility of using CD166 expression for isolating SAN progenitors from differentiating embryonic stem cells. Methods and Results: We found that in embryonic day 10.5 mouse hearts, CD166 and HCN4, markers of the pacemaker tissue, are coexpressed. Sorting embryonic stem cells for CD166 expression at differentiation day 8 selects a population of pacemaker precursors. CD166 + cells express high levels of genes involved in SAN development (Tbx18, Tbx3, Isl-1, Shox2) and function (Cx30.2, HCN4, HCN1, CaV1.3) and low levels of ventricular genes (Cx43, Kv4.2, HCN2, Nkx2.5). In culture, CD166 + cells form an autorhythmic syncytium composed of cells morphologically similar to and with the electrophysiological properties of murine SAN myocytes. Isoproterenol increases (+57%) and acetylcholine decreases (−23%) the beating rate of CD166-selected cells, which express the β-adrenergic and muscarinic receptors. In cocultures, CD166-selected cells are able to pace neonatal ventricular myocytes at a rate faster than their own. Furthermore, CD166 + cells have lost pluripotency genes and do not form teratomas in vivo. Conclusions: We demonstrated for the first time the isolation of a nonteratogenic population of cardiac precursors able to mature and form a fully functional SAN-like tissue.

Prior studies have demonstrated that founder cell type could influence induced pluripotent stem cells (iPSCs) molecular and developmental properties at early passages after establishing their pluripotent state. Herein, we evaluated the persistence of a functional memory related to the tissue of origin in iPSCs from syngeneic cardiac (CStC) vs skin stromal cells (SStCs). We found that, at passages greater than 15, iPSCs from cardiac stromal cells (C-iPSCs) produced a higher number of beating embryoid bodies than iPSCs from skin stromal cells (S-iPSCs). Flow cytometry analysis revealed that dissected beating areas from C-iPSCs exhibited more Troponin-T positive cells compared to S-iPSCs. Beating areas derived from C-iPSCs displayed higher expression of cardiac markers, more hyperpolarized diastolic potentials, larger action potential amplitude and higher contractility than beaters from skin. Also, different microRNA subsets were differentially modulated in CStCs vs SStCs during the reprogramming process, potentially accounting for the higher cardiogenic potentials of C-iPSCs vs S-iPSCs. Therefore, the present work supports the existence of a founder organ memory in iPSCs obtained from the stromal component of the origin tissue.