A large-scale functional high-throughput screening identifies miR-515 and miR-519e as potent inducers of human iPSC-cardiomyocyte proliferation

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.

Calcium supplementation of bioinks reduces shear stress-induced cell damage during bioprinting

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.

XePhIR: the zebrafish xenograft phenotype interactive repository

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

Enhancement of engineered cardiac tissues by promotion of hiPSC-cardiomyocyte proliferation

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

Gpr126 domains control different cellular mechanisms of ventricular chamber development

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

Direct 3D printing of hiPSC-cardiomyocytes in collagen-based bioinks

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

Cardiomyocyte binucleation is associated with aberrant mitotic microtubule distribution, mislocalization of RhoA and IQGAP3, as well as defective actomyosin ring anchorage and cleavage furrow ingression

Aims

After birth mammalian cardiomyocytes initiate a last cell cycle which results in binucleation due to cytokinesis failure. Despite its importance for cardiac regenerative therapies, this process is poorly understood. Here, we aimed at a better understanding of the difference between cardiomyocyte proliferation and binucleation and providing a new tool to distinguish these two processes.

Methods and results

Monitoring of cell division by time-lapse imaging revealed that rat cardiomyocyte binucleation stems from a failure to properly ingress the cleavage furrow. Astral microtubule required for actomyosin ring anchorage and thus furrow ingression were not symmetrically distributed at the periphery of the equatorial region during anaphase in binucleating cardiomyocytes. Consequently, RhoA, the master regulator of actomyosin ring formation and constriction, non-muscle myosin IIB, a central component of the actomyosin ring, as well as IQGAP3 were abnormally localized during cytokinesis. In agreement with improper furrow ingression, binucleation in vitro and in vivo was associated with a failure of RhoA and IQGAP3 to localize to the stembody of the midbody.

Conclusion

Taken together, these results indicate that naturally occurring cytokinesis failure in primary cardiomyocytes is due to an aberrant mitotic microtubule apparatus resulting in inefficient anchorage of the actomyosin ring to the plasma cell membrane. Thus, cardiomyocyte binucleation and division can be discriminated by the analysis of RhoA as well as IQGAP3 localization.

Extracellular vesicles in diagnostics and therapy of the ischaemic heart: Position Paper from the Working Group on Cellular Biology of the Heart of the European Society of Cardiology

Extracellular vesicles (EVs)—particularly exosomes and microvesicles (MVs)—are attracting considerable interest in the cardiovascular field as the wide range of their functions is recognized. These capabilities include transporting regulatory molecules including different RNA species, lipids, and proteins through the extracellular space including blood and delivering these cargos to recipient cells to modify cellular activity. EVs powerfully stimulate angiogenesis, and can protect the heart against myocardial infarction. They also appear to mediate some of the paracrine effects of cells, and have therefore been proposed as a potential alternative to cell-based regenerative therapies. Moreover, EVs of different sources may be useful biomarkers of cardiovascular disease identities. However, the methods used for the detection and isolation of EVs have several limitations and vary widely between studies, leading to uncertainties regarding the exact population of EVs studied and how to interpret the data. The number of publications in the exosome and MV field has been increasing exponentially in recent years and, therefore, in this ESC Working Group Position Paper, the overall objective is to provide a set of recommendations for the analysis and translational application of EVs focussing on the diagnosis and therapy of the ischaemic heart. This should help to ensure that the data from emerging studies are robust and repeatable, and optimize the pathway towards the diagnostic and therapeutic use of EVs in clinical studies for patient benefit.

Epigenomic and transcriptomic approaches in the post-genomic era: path to novel targets for diagnosis and therapy of the ischaemic heart? Position Paper of the European Society of Cardiology Working Group on Cellular Biology of the Heart

Despite advances in myocardial reperfusion therapies, acute myocardial ischaemia/reperfusion injury and consequent ischaemic heart failure represent the number one cause of morbidity and mortality in industrialized societies. Although different therapeutic interventions have been shown beneficial in preclinical settings, an effective cardioprotective or regenerative therapy has yet to be successfully introduced in the clinical arena. Given the complex pathophysiology of the ischaemic heart, large scale, unbiased, global approaches capable of identifying multiple branches of the signalling networks activated in the ischaemic/reperfused heart might be more successful in the search for novel diagnostic or therapeutic targets. High-throughput techniques allow high-resolution, genome-wide investigation of genetic variants, epigenetic modifications, and associated gene expression profiles. Platforms such as proteomics and metabolomics (not described here in detail) also offer simultaneous readouts of hundreds of proteins and metabolites. Isolated omics analyses usually provide Big Data requiring large data storage, advanced computational resources and complex bioinformatics tools. The possibility of integrating different omics approaches gives new hope to better understand the molecular circuitry activated by myocardial ischaemia, putting it in the context of the human ‘diseasome’. Since modifications of cardiac gene expression have been consistently linked to pathophysiology of the ischaemic heart, the integration of epigenomic and transcriptomic data seems a promising approach to identify crucial disease networks. Thus, the scope of this Position Paper will be to highlight potentials and limitations of these approaches, and to provide recommendations to optimize the search for novel diagnostic or therapeutic targets for acute ischaemia/reperfusion injury and ischaemic heart failure in the post-genomic era.

Persistent scarring and dilated cardiomyopathy suggest incomplete regeneration of the apex resected neonatal mouse myocardium--A 180 days follow up study

Heart damage in mammals is generally considered to result in scar formation, whereas zebrafish completely regenerate their hearts following an intermediate and reversible state of fibrosis after apex resection (AR). Recently, using the AR procedure, one-day-old mice were suggested to have full capacity for cardiac regeneration as well. In contrast, using the same mouse model others have shown that the regeneration process is incomplete and that scarring still remains 21 days after AR. The present study tested the hypothesis that like in zebrafish, fibrosis in neonatal mammals could be an intermediate response before the onset of complete heart regeneration. Myocardial damage was performed by AR in postnatal day 1 C57BL/6 mice, and myocardial function and scarring assessed at day 180 using F-18-fluorodeoxyglucose positron emission tomography (FDG-PET) and histology, respectively. AR mice exhibited decreased ejection fraction and wall motion with increased end-diastolic and systolic volumes compared to sham-operated mice. Scarring with collagen accumulation was still substantial, with increased heart size, while cardiomyocyte size was unaffected. In conclusion, these data thus show that apex resection in mice results in irreversible fibrosis and dilated cardiomyopathy suggesting that cardiac regeneration is limited in neonatal mammals and thus distinct from the regenerative capacity seen in zebrafish.

A mammalian myocardial cell-free system to study cell cycle reentry in terminally differentiated cardiomyocytes

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.