Human Stem Cell-derived Cardiomyocytes Research Articles

Comparison of the Simulated Response of Three in Silico Human Stem Cell-Derived Cardiomyocytes Models and in Vitro Data Under 15 Drug Actions.

Objectives: Improvements in human stem cell-derived cardiomyocyte (hSC-CM) technology have promoted their use for drug testing and disease investigations. Several in silico hSC-CM models have been proposed to augment interpretation of experimental findings through simulations. This work aims to assess the response of three hSC-CM in silico models (Koivumäki2018, Kernik2019, and Paci2020) to simulated drug action, and compare simulation results against in vitro data for 15 drugs. Methods: First, simulations were conducted considering 15 drugs, using a simple pore-block model and experimental data for seven ion channels. Similarities and differences were analyzed in the in silico responses of the three models to drugs, in terms of Ca2+ transient duration (CTD90) and occurrence of arrhythmic events. Then, the sensitivity of each model to different degrees of blockage of Na+ (INa), L-type Ca2+ (ICaL), and rapid delayed rectifying K+ (IKr) currents was quantified. Finally, we compared the drug-induced effects on CTD90 against the corresponding in vitro experiments. Results: The observed CTD90 changes were overall consistent among the in silico models, all three showing changes of smaller magnitudes compared to the ones measured in vitro. For example, sparfloxacin 10 µM induced +42% CTD90 prolongation in vitro, and +17% (Koivumäki2018), +6% (Kernik2019), and +9% (Paci2020) in silico. Different arrhythmic events were observed following drug application, mainly for drugs affecting IKr. Paci2020 and Kernik2019 showed only repolarization failure, while Koivumäki2018 also displayed early and delayed afterdepolarizations. The spontaneous activity was suppressed by Na+ blockers and by drugs with similar effects on ICaL and IKr in Koivumäki2018 and Paci2020, while only by strong ICaL blockers, e.g. nisoldipine, in Kernik2019. These results were confirmed by the sensitivity analysis. Conclusion: To conclude, The CTD90 changes observed in silico are qualitatively consistent with our in vitro data, although our simulations show differences in drug responses across the hSC-CM models, which could stem from variability in the experimental data used in their construction.

20902 Elucidation of Cardioprotective Mechanisms via Human Models of Chemotherapy-Induced Cardiotoxicity

ABSTRACT IMPACT: This work should provide further insights to mechanisms of the negative consequences of chemotherapy drugs, specifically in the cardiovascular system. OBJECTIVES/GOALS: Cardiotoxicity remains a safety concern in the development or utilization of chemotherapeutics largely due to the gap in knowledge of the mechanisms of toxicity. The pathophysiology of this cardiotoxicity has not been fully elucidated but data from our lab as well as other recent studies hint toward implications of mitochondrial (mito) biogenesis. METHODS/STUDY POPULATION: Prophylactic use of the beta-blocker carvedilol as well as the ACE inhibitor enalapril have been shown to inhibit the development of anthracycline-induced toxicity, but the mechanism of this cardio-protection remains elusive. To explore this, human stem cell-derived cardiomyocytes and endothelial cells will be either treated with the anthracycline doxorubicin or pretreated with carvedilol or enalapril followed by doxorubicin treatment before cellular lysates are harvested. Western blotting and qPCR will be performed to determine the expression of mito biogenesis markers including Nrf1, TFAM and the master regulator of mito biogenesis, PGC-1α. RESULTS/ANTICIPATED RESULTS: We anticipate that doxorubicin treatment alone will result in decreased expression of the mito biogenesis markers Nrf1, TFAM and PGC-1α and that pretreatment with either carvedilol and/or enalapril prior to doxorubicin treatment will either prevent or reverse this. DISCUSSION/SIGNIFICANCE OF FINDINGS: Doxorubicin’s role in causing mitochondrial dysfunction as well as suppression of biogenesis has already been established. Ideally, generation of new mitochondria would offset the occurrence of dysfunctional mitochondria. Confirming carvedilol/enalapril’s involvement with mito biogenesis would provide a mechanism of cardio-protection.

Regenerative potential of epicardium-derived extracellular vesicles mediated by conserved miRNA transfer.

AimsAfter a myocardial infarction, the adult human heart lacks sufficient regenerative capacity to restore lost tissue, leading to heart failure progression. Finding novel ways to reprogram adult cardiomyocytes into a regenerative state is a major therapeutic goal. The epicardium, the outermost layer of the heart, contributes cardiovascular cell types to the forming heart and is a source of trophic signals to promote heart muscle growth during embryonic development. The epicardium is also essential for heart regeneration in zebrafish and neonatal mice and can be reactivated after injury in adult hearts to improve outcome. A recently identified mechanism of cell–cell communication and signalling is that mediated by extracellular vesicles (EVs). Here, we aimed to investigate epicardial signalling via EV release in response to cardiac injury and as a means to optimize cardiac repair and regeneration.Methods and resultsWe isolated epicardial EVs from mouse and human sources and targeted the cardiomyocyte population. Epicardial EVs enhanced proliferation in H9C2 cells and in primary neonatal murine cardiomyocytes in vitro and promoted cell cycle re-entry when injected into the injured area of infarcted neonatal hearts. These EVs also enhanced regeneration in cryoinjured engineered human myocardium (EHM) as a novel model of human myocardial injury. Deep RNA-sequencing of epicardial EV cargo revealed conserved microRNAs (miRs) between human and mouse epicardial-derived exosomes, and the effects on cell cycle re-entry were recapitulated by administration of cargo miR-30a, miR-100, miR-27a, and miR-30e to human stem cell-derived cardiomyocytes and cryoinjured EHM constructs.ConclusionHere, we describe the first characterization of epicardial EV secretion, which can signal to promote proliferation of cardiomyocytes in infarcted mouse hearts and in a human model of myocardial injury, resulting in enhanced contractile function. Analysis of exosome cargo in mouse and human identified conserved pro-regenerative miRs, which in combination recapitulated the therapeutic effects of promoting cardiomyocyte proliferation.

Investigating the Role of Contraction during Myofibril Formation using Human Stem Cell-Derived Cardiomyocytes

Mechanical contraction is thought to play an essential role during cardiomyocyte development, including formation of contractile elements and cellular hypertrophy. However, the mechanisms by which contraction impacts sarcomere assembly and maturation of developing cardiomyocytes are unknown. To understand the role of contraction during myofibril development in cardiomyocytes, we used CRISPR Cas9 to generate a non-contractile human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) model by introducing the point mutation D65A into the cardiac troponin C (cTnC D65A) gene. The D65A mutation prevents calcium binding to site II of cTnC, thereby preventing activation of sarcomere contraction. Previous studies have reported complete sarcomere disassembly when contraction was inhibited. Therefore, we hypothesized that these non-contracting cardiomyocytes would not form myofibrils or that myofibrils would be more like stress fibers. However, upon cardiomyocyte differentiation, immune-fluorescent staining of alpha actinin showed cTnC D65A-CMs form and maintain myofibrils (> 60 days) with the full complement of sarcomere proteins, including all three troponin subunits. cTnC D65A-CMs had spontaneous and stimulated calcium transients (in the absence of contraction) and matured at a similar timescale as wild type (WT) cells, as demonstrated by the isoform changes from myosin heavy chain 6 to 7. When cTnC D65A-CMs were transduced with adenoviral vectors (AVs) to express WT cTnC, contraction was initiated within a few days. Conversely, when WT hiPSC-CMs were transduced with AVs to express cTnC D65A, contraction was inhibited. hiPSC-CMs containing WT or D65A cTnC had elongated morphology when cultured on nanopatterned surfaces with improved myofibrillar alignment, directionality, and bundling. Inhibition of contraction by expression of D65A cTnC resulted in complete myofibrillar disarray, with the emergence of muscle stress fibers in the cellular periphery. Thus, cTnC D65A hiPSC-CMs are an exciting new tool to study cardiomyocyte development.

Precise engineering of iron oxide nanoparticle-encapsulated protein hydrogel: Implications for cardiac toxicity and ultrasound contrast agents

In the present study, we developed and assessed novel injectable hydrogel matrices combined with nanoparticles and secretome biomolecules to reduce Doxorubicin (DOX)- induced cytotoxicity in human stem cell-derived cardiomyocytes. A Fe2O3 nanoparticle-loaded biocompatible silk sericin (MSS) nanocomposite form was fabricated and used as an injectable carrier for secretome for in vivo cardiomyocyte metabolism. Biological analyses revealed that the secretome-encapsulated Fe3O2-Silk sericin (Sec@MSS) hydrogel markedly reduced acridine orange/ethidium bromide (AOEB) dual staining in cardiomyocytes, revealing significantly induced apoptosis. Furthermore, we evaluated the mitochondrial membrane potential for DOX and Sec@MSS hydrogel, and demonstrated apoptosis of the cardiomyocytes in the DOX-alone and Sec@MSS groups. However, the cardiotoxicity of Sec@MSS sericin was much lower than that in the DOX group. The acoustic behaviors of the functionalized Sec@MSS were examined. The results indicate that Sec@MSS hydrogel might serve as an effective treatment agent in cardiac diseases in the future.

Thymosin β4 increases cardiac cell proliferation, cell engraftment, and the reparative potency of human induced-pluripotent stem cell-derived cardiomyocytes in a porcine model of acute myocardial infarction.

Rationale: Previous studies have shown that human embryonic stem cell-derived cardiomyocytes improved myocardial recovery when administered to infarcted pig and non-human primate hearts. However, the engraftment of intramyocardially delivered cells is poor and the effectiveness of clinically relevant doses of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) in large animal models of myocardial injury remains unknown. Here, we determined whether thymosin β4 (Tb4) could improve the engraftment and reparative potency of transplanted hiPSC-CMs in a porcine model of myocardial infarction (MI).Methods: Tb4 was delivered from injected gelatin microspheres, which extended the duration of Tb4 administration for up to two weeks in vitro. After MI induction, pigs were randomly distributed into 4 treatment groups: the MI Group was injected with basal medium; the Tb4 Group received gelatin microspheres carrying Tb4; the CM Group was treated with 1.2 × 108 hiPSC-CMs; and the Tb4+CM Group received both the Tb4 microspheres and hiPSC-CMs. Myocardial recovery was assessed by cardiac magnetic resonance imaging (MRI), arrhythmogenesis was monitored with implanted loop recorders, and tumorigenesis was evaluated via whole-body MRI.Results: In vitro, 600 ng/mL of Tb4 protected cultured hiPSC-CMs from hypoxic damage by upregulating AKT activity and BcL-XL and promoted hiPSC-CM and hiPSC-EC proliferation. In infarcted pig hearts, hiPSC-CM transplantation alone had a minimal effect on myocardial recovery, but co-treatment with Tb4 significantly enhanced hiPSC-CM engraftment, induced vasculogenesis and the proliferation of cardiomyocytes and endothelial cells, improved left ventricular systolic function, and reduced infarct size. hiPSC-CM implantation did not increase incidence of ventricular arrhythmia and did not induce tumorigenesis in the immunosuppressed pigs.Conclusions: Co-treatment with Tb4-microspheres and hiPSC-CMs was safe and enhanced the reparative potency of hiPSC-CMs for myocardial repair in a large-animal model of MI.

Microgravity-Induced Senescence Mechanisms in Human Stem Cell-Derived Cardiomyocytes

Exposure to outer space microgravity poses a risk for the development of various pathologies including cardiovascular disease. To study this, we derived cardiomyocytes (CMs) from human induced pluripotent stem cells and exposed them to simulated microgravity (SMG). We combined different “omics” and chromosome conformation capture technologies with live-cell imaging of various transgenic lines to discover that SMG impacts on the contractile velocity and function of CMs via the induction of senescence processes. This is linked to SMG-induced changes on reactive oxygen species (ROS) generation and energy metabolism by mitochondria. Taken together, we uncover a microgravity-controlled axis causing contractile dysfunctions to CMs. Our findings can contribute to the design of preventive and therapeutic strategies against senescence-associated disease.

Improving cardiotoxicity prediction in cancer treatment: integration of conventional circulating biomarkers and novel exploratory tools.

Early detection strategies and improvements in cancer treatment have dramatically reduced the cancer mortality rate in the United States (US). However, cardiovascular (CV) side effects of cancer therapy are frequent among the 17 million cancer survivors in the US today, and cardiovascular disease (CVD) has become the second leading cause of morbidity and mortality among cancer survivors. Circulating biomarkers are ideal for detecting and monitoring CV side effects of cancer therapy. Here, we summarize the current state of clinical studies on conventional serum and plasma CVD biomarkers to detect and prevent cardiac injury during cancer treatment. We also review how novel exploratory tools such as genetic testing, human stem cell-derived cardiomyocytes, Omics technologies, and artificial intelligence can elucidate underlying molecular and genetic mechanisms of CV injury and to improve predicting cancer therapy-related cardiotoxicity (CTRC). Current regulatory requirements for biomarker qualifications are also addressed. We present generally applicable lessons learned from published studies, particularly on how to improve reproducibility. The combination of conventional circulating biomarkers and novel exploratory tools will pave the way for precision medicine and improve the clinical practice of prediction, detection, and management of CTRC.

Hit-to-lead optimization and discovery of a potent, and orally bioavailable G protein coupled receptor kinase 2 (GRK2) inhibitor

G-protein coupled receptor kinase 2 (GRK2), which is upregulated in the failing heart, appears to play a critical role in heart failure (HF) progression in part because enhanced GRK2 activity promotes dysfunction of β-adrenergic signaling and myocyte death. An orally bioavailable GRK2 inhibitor could offer unique therapeutic outcomes that cannot be attained by current heart failure treatments that directly target GPCRs or angiotensin-converting enzyme. Herein, we describe the discovery of a potent, selective, and orally bioavailable GRK2 inhibitor, 8h, through high-throughput screening, hit-to-lead optimization, structure-based design, molecular modelling, synthesis, and biological evaluation. In the cellular target engagement assays, 8h enhances isoproterenol-mediated cyclic adenosine 3′,5′-monophosphate (cAMP) production in HEK293 cells overexpressing GRK2. Compound 8h was further evaluated in a human stem cell-derived cardiomyocyte (HSC-CM) contractility assay and potentiated isoproterenol-induced beating rate in HSC-CMs.

Scalable Biomimetic Coaxial Aligned Nanofiber Cardiac Patch: A Potential Model for "Clinical Trials in a Dish".

Recent advances in cardiac tissue engineering have shown that human induced-pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) cultured in a three-dimensional (3D) micro-environment exhibit superior physiological characteristics compared with their two-dimensional (2D) counterparts. These 3D cultured hiPSC-CMs have been used for drug testing as well as cardiac repair applications. However, the fabrication of a cardiac scaffold with optimal biomechanical properties and high biocompatibility remains a challenge. In our study, we fabricated an aligned polycaprolactone (PCL)-Gelatin coaxial nanofiber patch using electrospinning. The structural, chemical, and mechanical properties of the patch were assessed by scanning electron microscopy (SEM), immunocytochemistry (ICC), Fourier-transform infrared spectroscopy (FTIR)-spectroscopy, and tensile testing. hiPSC-CMs were cultured on the aligned coaxial patch for 2 weeks and their viability [lactate dehydrogenase (LDH assay)], morphology (SEM, ICC), and functionality [calcium cycling, multielectrode array (MEA)] were assessed. Furthermore, particle image velocimetry (PIV) and MEA were used to evaluate the cardiotoxicity and physiological functionality of the cells in response to cardiac drugs. Nanofibers patches were comprised of highly aligned core-shell fibers with an average diameter of 578 ± 184 nm. Acellular coaxial patches were significantly stiffer than gelatin alone with an ultimate tensile strength of 0.780 ± 0.098 MPa, but exhibited gelatin-like biocompatibility. Furthermore, hiPSC-CMs cultured on the surface of these aligned coaxial patches (3D cultures) were elongated and rod-shaped with well-organized sarcomeres, as observed by the expression of cardiac troponin-T and α-sarcomeric actinin. Additionally, hiPSC-CMs cultured on these coaxial patches formed a functional syncytium evidenced by the expression of connexin-43 (Cx-43) and synchronous calcium transients. Moreover, MEA analysis showed that the hiPSC-CMs cultured on aligned patches showed an improved response to cardiac drugs like Isoproterenol (ISO), Verapamil (VER), and E4031, compared to the corresponding 2D cultures. Overall, our results demonstrated that an aligned, coaxial 3D cardiac patch can be used for culturing of hiPSC-CMs. These biomimetic cardiac patches could further be used as a potential 3D in vitro model for “clinical trials in a dish” and for in vivo cardiac repair applications for treating myocardial infarction.

Detecting drug-induced delayed cardiac effects using human stem cell-derived cardiomyocytes

Detecting drug-induced delayed cardiac effects using human stem cell-derived cardiomyocytes

The carbon source in the culture media modulates the cardiotoxic effects of doxorubicin on human stem cell-derived cardiomyocytes

The carbon source in the culture media modulates the cardiotoxic effects of doxorubicin on human stem cell-derived cardiomyocytes

In vitro assessments of drug-induced delayed cardiotoxicity using human stem cell-derived cardiomyocytes

In vitro assessments of drug-induced delayed cardiotoxicity using human stem cell-derived cardiomyocytes

Development and evaluation of next-generation cardiotoxicity assay based on embryonic stem cell-derived cardiomyocytes

In accordance with requirements of the ICH S7B safety pharma-cology guidelines, numerous next-generation cardiotoxicity studies using human stem cell-derived cardiomyocytes (CMs) are being conducted globally. Although several stem cell-derived CMs are being developed for commercialization, there is insufficient research to verify if these CMs can replace animal experiments. In this study, in vitro high-efficiency CMs derived from human embryonic stem cells (hESC-CMs) were compared with Sprague-Dawley rats as in vivo experimental animals, and primary cultured in vitro rat-CMs for cardiotoxicity tests. In vivo rats were administrated with two consecutive injections of 100 mg/kg isoproterenol, 15 mg/kg doxorubicin, or 100 mg/kg nifedipine, while in vitro rat-CMs and hESC-CMs were treated with 5 µM isoproterenol, 5 µM doxorubicin, and 50 µM nifedipine. We have verified the equivalence of hESC-CMs assessments over various molecular biological markers, morphological analysis. Also, we have identified the advantages of hESC-CMs, which can distinguish between species variability, over electrophysiological analysis of ion channels against cardiac damage. Our findings demonstrate the possibility and advantage of high-effi-ciency hESC-CMs as next-generation cardiotoxicity assessment.

Label-free conduction velocity mapping and gap junction assessment of functional iPSC-Cardiomyocyte monolayers

Cardiac conduction is an important function of the heart. To date, accurate measurement of conduction velocity (CV) in vitro is hindered by the low spatial resolution and poor signal-to-noise ratio of microelectrode arrays (MEAs), or the cytotoxicity and end-point analysis of fluorescence optical imaging. Here, we have developed a new label-free method based on defocused brightfield imaging to quantify CV by analyzing centroid displacements and contraction trajectories of each cardiomyocyte in a monolayer of human stem cell-derived cardiomyocytes (iPSC-CMs). Our data revealed that the time delay between intracellular calcium release and the initiation of cell contraction is highly consistent across cardiomyocytes; however, the duration a cell takes to reach its maximum beating magnitude varies significantly, proving that the time delay in excitation-contraction coupling is largely constant in iPSC-CMs. Standard calcium imaging of the same iPSC-CM populations (~106 cells) was conducted for comparison with our label-free method. The results confirmed that our label-free method was capable of achieving highly accurate CV mapping (17.64 ± 0.89 cm/s vs. 17.95 ± 2.29 cm/s, p-value>0.1). Additionally, our method effectively revealed various shapes in cell beating pattern. We also performed label-free CV mapping on disease-specific iPSC-CM monolayers with plakophilin-2 (PKP2) knockdown, which effectively quantified their low CV values and further validated the arrhythmogenic role of PKP2 mutation in arrhythmogenic right ventricular cardiomyopathy (ARVC) through the disruption of cardiac conduction. The label-free method offers a cytotoxic-free technique for long-term measurement of dynamic beating trajectories, beating propagation and conduction velocities of cardiomyocyte monolayers.

Abstract 102: Sympathetic Innervation Negatively Regulates Postnatal Cardiomyocyte Proliferation Through Circadian Genes

Sympathetic neurons (SNs) regulate heart rate, conduction velocity, contractility and relaxation of the myocardium. Disruption of SNs in adult cardiac disease, leads to arrhythmias, myocardial dysfunction and sudden cardiac death. However, the role of SNs during cardiac development and whether disruption of cardiac SNs at embryonic stages is associated with disease progression in adult life is unknown. Moreover, controversy exists regarding the effect of SNs on neonatal myocardial regeneration after injury. As the heart is innervated by SNs from mid-gestation and the innervation continues through the neonatal stage, we generated genetically modified mice with profoundly reduced cardiac-specific sympathetic innervation starting at embryonic stages. Inhibition of sympathetic innervation resulted in larger heart size with increased number of myocytes that were smaller and more mononuclear. Analysis also confirmed increased cardiomyocyte proliferation. Interestingly, transcriptomic analysis of P7 and P14 hearts verified dysregulated cell cycle, calcium homeostasis and circadian genes. Remarkably, this led to persistently increased heart size and reduced function at adult stages. To investigate the mechanism whereby SNs, affect cardiomyocyte proliferation, we first co-cultured human stem cell-derived or mouse cardiomyocytes with ganglionic SNs and confirmed similar gene expression patterns. Moreover, alpha1 and beta2-specific adrenergic receptor agonists and norepinephrine, reduced cell cycle genes and myocyte proliferation and upregulated circadian genes such as Period1 and Period2. As circadian genes have been linked with regulation of cell cycle and apoptosis, we analyzed neonatal hearts from Period1/Period2 DKO mice and curiously discovered increased heart size, cardiomyocyte proliferation and cell cycle genes, and suppression of the Wee1 kinase an inhibitor of cell mitosis. More importantly, norepinephrine did not alter cardiomyocyte proliferation and cell cycle genes in Period1/Period2 DKO myocytes. To our knowledge this is the first study to provide direct evidence of the effect of SNs in the regulation of circadian genes in the heart and their role on neonatal cardiomyocyte proliferation.

Targeting muscle-enriched long non-coding RNA H19 reverses pathological cardiac hypertrophy

AimsPathological cardiac remodelling and subsequent heart failure represents an unmet clinical need. Long non-coding RNAs (lncRNAs) are emerging as crucial molecular orchestrators of disease processes, including that of heart diseases. Here, we report on the powerful therapeutic potential of the conserved lncRNA H19 in the treatment of pathological cardiac hypertrophy.Method and resultsPressure overload-induced left ventricular cardiac remodelling revealed an up-regulation of H19 in the early phase but strong sustained repression upon reaching the decompensated phase of heart failure. The translational potential of H19 is highlighted by its repression in a large animal (pig) model of left ventricular hypertrophy, in diseased human heart samples, in human stem cell-derived cardiomyocytes and in human engineered heart tissue in response to afterload enhancement. Pressure overload-induced cardiac hypertrophy in H19 knock-out mice was aggravated compared to wild-type mice. In contrast, vector-based, cardiomyocyte-directed gene therapy using murine and human H19 strongly attenuated heart failure even when cardiac hypertrophy was already established. Mechanistically, using microarray, gene set enrichment analyses and Chromatin ImmunoPrecipitation DNA-Sequencing, we identified a link between H19 and pro-hypertrophic nuclear factor of activated T cells (NFAT) signalling. H19 physically interacts with the polycomb repressive complex 2 to suppress H3K27 tri-methylation of the anti-hypertrophic Tescalcin locus which in turn leads to reduced NFAT expression and activity.ConclusionH19 is highly conserved and down-regulated in failing hearts from mice, pigs and humans. H19 gene therapy prevents and reverses experimental pressure-overload-induced heart failure. H19 acts as an anti-hypertrophic lncRNA and represents a promising therapeutic target to combat pathological cardiac remodelling.

Fluorescent Magnetic Iron Oxide NanoparticleEncapsulated Protein Hydrogel Against Doxorubicin-Associated Cardiotoxicity and for Enhanced Cardiomyocyte Survival

Doxorubicin (DOX) is a widely used and effective anticancer drug. However, it shows high cardiotoxicity in several patients. The exact biological mechanisms of DOX-induced cardiotoxicity remain unclear. In the present study, we developed and assessed novel injectable hydrogel matrices combined with nanoparticles and secretome biomolecules to reduce DOXinduced cytotoxicity in human stem cell-derived cardiomyocytes. A Fe₂O₃ nanoparticle-loaded biocompatible silk sericin nanocomposite form was fabricated and used as an injectable carrier for secretome for in vivo cardiomyocyte metabolism. The formulated hydrogels carrying secretome were analyzed in vitro for proliferation, migration, and tube formation of human stem cell-derived cardiomyocytes. Biological analyses revealed that the secretome-encapsulated florescent Fe₃O₂ Silk sericin (Sec@MSS) hydrogel markedly reduced calcein-PI dual staining in cardiomyocytes, revealing significantly induced apoptosis. Furthermore, we evaluated the mitochondrial membrane potential for DOX and Sec@MSS hydrogel, and demonstrated apoptosis of the cardiomyocytes in the DOX-alone and Sec@MSS groups. However, the cardiotoxicity of Sec@MSS sericin was much lower than that in the DOX group, and was further evaluated via VEGFR and TUNEL analyses. The results indicate that Sec@MSS hydrogel might serve as an effective treatment agent in cardiac diseases in the future.

Hypertrophic Cardiomyopathy: Prolonged Twitch, Calcium Transients and Action Potentials in Human Stem Cell-Derived Cardiomyocytes with β-Myosin Mutation R723G

Hypertrophic cardiomyopathy (HCM) is the most frequent monogenetic cardiac disease. In mutation-positive patients one third of the mutations are located in the β-cardiac myosin heavy chain protein (β-MyHC). We recently showed that high functional heterogeneity among individual cardiomyocytes obtained from HCM patients is associated with cell-to-cell variation in expression of mutant/wildtype β-MyHC mRNA (MYH7). We hypothesized that functional heterogeneity might lead to contractile imbalance with myocyte disarray and activate profibrotic and hypertrophic pathways in HCM. Due to the limited availability of patient's tissue, cardiomyocytes differentiated from induced pluripotent stem cells (hiPSC-CMs) appear attractive to investigate the pathomechanisms and the direct effects of HCM mutations. Here we developed an in vitro disease model using HCM-patient-derived hiPSC-CMs carrying mutation Arg723Gly in β-MyHC. We characterized the impact of the mutation on twitch contractions, intracellular calcium transients and action potential shapes of Arg723Gly-β-MyHC vs wildtype (WT) CMs with pure β-MyHC expression. We further quantified mutated vs. wildtype MYH7-mRNA fractions in individual cardiomyocytes via single cell RT-PCR with subsequent allele specific restriction analysis. Arg723Gly-β-MyHC CMs in comparison to WT-CMs showed significantly longer time to peak and half relaxation time of electrically evoked twitch contractions, longer time courses of calcium transients with arrhythmias in up to ∼ 20 % of the CMs, and significantly prolonged APD50 values. These features may be related to the often observed ventricular tachycardias in this family. How these features are caused by β-MyHC-mutations is not clear. Mutant/wildtype mRNA ratios in individual Arg723Gly-β-MyHC CMs were highly heterogeneous from cell to cell, with a variation comparable to that in cardiomyocytes isolated from patients tissue. Taken together, hiPSC-Arg723Gly-β-MyHC CMs provide a promising model to study functional effects of HCM mutations and potential underlying pathomechanisms.

Sonic Hedgehog upregulation does not enhance the survival and engraftment of stem cell-derived cardiomyocytes in infarcted hearts.

The engraftment of human stem cell-derived cardiomyocytes (hSC-CMs) is a promising treatment for remuscularizing the heart wall post-infarction, but it is plagued by low survival of transplanted cells. We hypothesize that this low survival rate is due to continued ischemia within the infarct, and that increasing the vascularization of the scar will ameliorate the ischemia and improve hSC-CM survival and engraftment. An adenovirus expressing the vascular growth factor Sonic Hedgehog (Shh) was injected into the infarcted myocardium of rats immediately after ischemia/reperfusion, four days prior to hSC-CM injection. By two weeks post-cell injection, Shh treatment had successfully increased capillary density outside the scar, but not within the scar. In addition, there was no change in vessel size or percent vascular volume when compared to cell injection alone. Micro-computed tomography revealed that Shh failed to increase the number and size of larger vessels. It also had no effect on graft size or heart function when compared to cell engraftment alone. Our data suggests that, when combined with the engraftment of hSC-CMs, expression of Shh within the infarct scar and surrounding myocardium is unable to increase vascularization of the infarct scar, and it does not improve survival or function of hSC-CM grafts.