Transcriptomic analysis of 3D Cardiac Differentiation of Human Induced Pluripotent Stem Cells Reveals Faster Cardiomyocyte Maturation Compared to 2D Culture

Hydrogel microsphere stem cell encapsulation enhances cardiomyocyte differentiation and functionality in scalable suspension system

A reliable suspension-based platform for scaling engineered cardiac tissue (ECT) production from human induced pluripotent stem cells (hiPSCs) is crucial for regenerative therapies. Here, we compared the production and functionality of ECTs formed using our scaffold-based, engineered tissue microsphere differentiation approach with those formed using the prevalent scaffold-free aggregate platform. We utilized a microfluidic system for the rapid (1 million cells/min), high density (30, 40, 60 million cells/ml) encapsulation of hiPSCs within PEG-fibrinogen hydrogel microspheres. HiPSC-laden microspheres and aggregates underwent suspension-based cardiac differentiation in chemically defined media. In comparison to aggregates, microspheres maintained consistent size and shape initially, over time, and within and between batches. Initial size and shape coefficients of variation for microspheres were eight and three times lower, respectively, compared to aggregates. On day 10, microsphere cardiomyocyte (CM) content was 27 % higher and the number of CMs per initial hiPSC was 250 % higher than in aggregates. Contraction and relaxation velocities of microspheres were four and nine times higher than those of aggregates, respectively. Microsphere contractile functionality also improved with culture time, whereas aggregate functionality remained unchanged. Additionally, microspheres displayed improved β-adrenergic signaling responsiveness and uniform calcium transient propagation. Transcriptomic analysis revealed that while both microspheres and aggregates demonstrated similar gene regulation patterns associated with cardiomyocyte differentiation, heart development, cardiac muscle contraction, and sarcomere organization, the microspheres exhibited more pronounced transcriptional changes over time. Taken together, these results highlight the capability of the microsphere platform for scaling up biomanufacturing of ECTs in a suspension-based culture platform.

Patient-derived induced pluripotent stem cells to study non-canonical splicing variants associated with Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most prevalent inherited cardiomyopathy and a leading cause of sudden death. Genetic testing and familial cascade screening play a pivotal role in the clinical management of HCM patients. However, conventional genetic tests primarily focus on the detection of exonic and canonical splice site variation. Oversighting intronic non-canonical splicing variants potentially contributes to a proportion of HCM patients remaining genetically undiagnosed. Here, using a non-integrative reprogramming strategy, we generated induced pluripotent stem cell (iPSC) lines from four individuals carrying one of two variants within intronic regions of MYBPC3: c.1224-52G > A and c.1898-23A > G. Upon differentiation to iPSC-derived cardiomyocytes (iPSC-CMs), mis-spliced mRNAs were identified in cells harbouring these variants. Both abnormal mRNAs contained a premature termination codon (PTC), fitting the criteria for activation of nonsense mediated decay (NMD). However, the c.1898-23A > G transcripts escaped this mRNA quality control mechanism, while the c.1224-52G > A transcripts were degraded. The newly generated iPSC lines represent valuable tools for studying the functional consequences of intronic variation and for translational research aimed at reversing splicing abnormalities to prevent disease progression.

Chemically defined production of engineered cardiac tissue microspheres from hydrogel-encapsulated pluripotent stem cells

Chemically defined, suspension culture conditions are a key requirement in realizing clinical translation of engineered cardiac tissues (ECTs). Building on our previous work producing functional ECT microspheres through differentiation of biomaterial encapsulated human induced pluripotent stem cells (hiPSCs), here we establish the ability to use chemically defined culture conditions, including stem cell media (E8) and cardiac differentiation media (chemically defined differentiation media with three components, CDM3). A custom microfluidic cell encapsulation system was used to encapsulate hiPSCs at a range of initial cell concentrations and diameters in the hybrid biomaterial, poly(ethylene glycol)-fibrinogen (PF), for the formation of highly spherical and uniform ECT microspheres for subsequent cardiac differentiation. Initial microsphere diameter could be tightly controlled, and microspheres could be produced with an initial diameter between 400 and 800 µm. Three days after encapsulation, cardiac differentiation was initiated through small molecule modulation of Wnt signaling in CDM3. Cardiac differentiation occurred resulting in in situ ECT formation; results showed that this differentiation protocol could be used to achieve cardiomyocyte (CM) contents greater than 90%, although there was relatively high variability in CM content and yield between differentiation batches. Spontaneous contraction of ECT microspheres initiated between Days 7 and 10 of differentiation and ECT microspheres responded to electrical pacing up to 1.5 Hz. Resulting CMs had well-defined sarcomeres and the gap junction protein, connexin 43, and had appropriate temporal changes in gene expression. In summary, this study demonstrated the proof-of-concept to produce functional ECT microspheres with chemically defined media in suspension culture in combination with biomaterial support of microsphere encapsulated hiPSCs.

Pathway-Based Similarity Measurement to Quantify Transcriptomics Similarity Between Human Tissues and Preclinical Models

Accurate clinical translation of preclinical research remains challenging, primarily due to species-specific differences and disease and patient heterogeneity. An important recent advancement has been development of microphysiological systems that consist of multiple human cell types that recapitulate key characteristics of their respective human systems, allowing essential physiologic processes to be accurately assessed during drug development. However, an unmet need remains regarding a quantitative method to evaluate the similarity between diverse sample types for various contexts of use (CoU)-specific pathways. To address this gap, this study describes the development of pathway-based similarity measurement (PBSM), which leverages RNA-seq data and pathway-based information to assess the human relevance of preclinical models for specific CoU. PBSM offers a quantitative method to compare the transcriptomic similarity of preclinical models to human tissues, shown here as proof of concept for liver and cardiac tissues, enabling improved model selection and validation. Thus, PBSM can successfully support CoU selection for preclinical models, assess the impact of different gene sets on similarity calculations, and differentiate among various in vitro and in vivo models. PBSM has the potential to reduce the translational gap in drug development by allowing quantitative evaluation of the similarity of preclinical models to human tissues, facilitating model selection, and improving understanding of context-specific applications. PBSM can serve as a foundation for enhancing the physiological relevance of in vitro models and supporting the development of more effective therapeutic interventions.

Progress of organoid platform in cardiovascular research

Cardiovascular disease is a significant cause of death in humans. Various models are necessary for the study of cardiovascular diseases, but once cellular and animal models have some defects, such as insufficient fidelity. As a new technology, organoid has certain advantages and has been used in many applications in the study of cardiovascular diseases. This article aims to summarize the application of organoid platforms in cardiovascular diseases, including organoid construction schemes, modeling, and application of cardiovascular organoids. Advances in cardiovascular organoid research have provided many models for different cardiovascular diseases in a variety of areas, including myocardium, blood vessels, and valves. Physiological and pathological models of different diseases, drug research models, and methods for evaluating and promoting the maturation of different kinds of organ tissues are provided for various cardiovascular diseases, including cardiomyopathy, myocardial infarction, and atherosclerosis. This article provides a comprehensive overview of the latest research progress in cardiovascular organ tissues, including construction protocols for cardiovascular organoid tissues and their evaluation system, different types of disease models, and applications of cardiovascular organoid models in various studies. The problems and possible solutions in organoid development are summarized.

Improving human cardiac organoid design using transcriptomics

Cardiovascular disease (CVD) is the leading cause of death worldwide. To this end, human cardiac organoids (hCOs) have been developed for improved organotypic CVD modeling over conventional in vivo animal models. Utilizing human cells, hCOs hold great promise to bridge key gaps in CVD research pertaining to human-specific conditions. hCOs are multicellular 3D models which resemble heart structure and function. Varying hCOs fabrication techniques leads to functional and phenotypic differences. To investigate heterogeneity across hCO platforms, we performed a transcriptomic analysis utilizing bulk RNA-sequencing from four previously published unique hCO studies. We further compared selected hCOs to 2D and 3D hiPSC-derived cardiomyocytes (hiPSC-CMs), as well as fetal and adult human myocardium bulk RNA-sequencing samples. Upon investigation utilizing Principal Component Analysis, K-means clustering analysis of key genes, and further downstream analyses such as Gene Set Enrichment (GSEA), Gene Set Variation (GSVA), and GO term enrichment, we found that hCO fabrication method influences maturity and cellular heterogeneity across models. Thus, we propose that adjustment of fabrication method will result in an hCO with a defined maturity and transcriptomic profile to facilitate its specified applications, in turn maximizing its modeling potential.

Advances in induced pluripotent stem cell-derived cardiac myocytes: technological breakthroughs, key discoveries and new applications

A transformation is underway in precision and patient-specific medicine. Rapid progress has been enabled by multiple new technologies including induced pluripotent stem cell-derived cardiac myocytes (iPSC-CMs). Here, we delve into these advancements and their future promise, focusing on the efficiency of reprogramming techniques, the fidelity of differentiation into the cardiac lineage, the functional characterization of the resulting cardiac myocytes, and the many applications of in silico models to understand general and patient-specific mechanisms controlling excitation-contraction coupling in health and disease. Furthermore, we explore the current and potential applications of iPSC-CMs in both research and clinical settings, underscoring the far-reaching implications of this rapidly evolving field.

Deep learning based characterization of human organoids using optical coherence tomography

Organoids, derived from human induced pluripotent stem cells (hiPSCs), are intricate three-dimensional in vitro structures that mimic many key aspects of the complex morphology and functions of in vivo organs such as the retina and heart. Traditional histological methods, while crucial, often fall short in analyzing these dynamic structures due to their inherently static and destructive nature. In this study, we leveraged the capabilities of optical coherence tomography (OCT) for rapid, non-invasive imaging of both retinal, cerebral, and cardiac organoids. Complementing this, we developed a sophisticated deep learning approach to automatically segment the organoid tissues and their internal structures, such as hollows and chambers. Utilizing this advanced imaging and analysis platform, we quantitatively assessed critical parameters, including size, area, volume, and cardiac beating, offering a comprehensive live characterization and classification of the organoids. These findings provide profound insights into the differentiation and developmental processes of organoids, positioning quantitative OCT imaging as a potentially transformative tool for future organoid research.

Myoglobin modulates the Hippo pathway to promote cardiomyocyte differentiation

The endogenous mechanisms that propagate cardiomyocyte differentiation and prevent de-differentiation remain unclear. While the expression of the heme protein myoglobin increases by over 50% during cardiomyocyte differentiation, a role for myoglobin in regulating cardiomyocyte differentiation has not been tested. Here, we show that deletion of myoglobin in cardiomyocyte models decreases the gene expression of differentiation markers and stimulates cellular proliferation, consistent with cardiomyocyte de-differentiation. Mechanistically, the heme prosthetic group of myoglobin catalyzes the oxidation of the Hippo pathway kinase LATS1, resulting in phosphorylation and inactivation of yes-associated protein (YAP). In vivo, myoglobin-deficient zebrafish hearts show YAP dephosphorylation and accelerated cardiac regeneration after apical injury. Similarly, myoglobin knockdown in neonatal murine hearts shows increased YAP dephosphorylation and cardiomyocyte cycling. These data demonstrate a novel role for myoglobin as an endogenous driver of cardiomyocyte differentiation and highlight myoglobin as a potential target to enhance cardiac development and improve cardiac repair and regeneration.

Strengthening cardiac therapy pipelines using human pluripotent stem cell-derived cardiomyocytes

Advances in hiPSC isolation and reprogramming and hPSC-CM differentiation have prompted their therapeutic application and utilization for evaluating potential cardiovascular safety liabilities. In this perspective, we showcase key efforts toward the large-scale production of hiPSC-CMs, implementation of hiPSC-CMs in industry settings, and recent clinical applications of this technology. The key observations are a need for traceable gender and ethnically diverse hiPSC lines, approaches to reduce cost of scale-up, accessible clinical trial datasets, and transparent guidelines surrounding the safety and efficacy of hiPSC-based therapies.

Guided Differentiation of Pluripotent Stem Cells for Cardiac Cell Diversity

We have developed a guided differentiation protocol for induced pluripotent stem cells (iPSCs) that rapidly generates a temporally and functionally diverse set of cardiac-relevant cell types. By leveraging techniques used in embryoid body and cardiac organoid generation, we produce both progenitor and terminal cardiac cell types concomitantly in just 10 days. Our results show that guided differentiation generates functionally relevant cardiac cell types that closely align with the transcriptional profiles of cells from differentiation time-course collections, mature cardiac organoids, and in vivo heart tissue. Guided differentiation prioritizes simplicity by minimizing the number of reagents and steps required, thereby enabling rapid and cost-effective experimental throughput. We expect this approach will provide a scalable cardiac model for population-level studies of gene regulatory variation and gene-by-environment interactions.

Unsupervised analysis of whole transcriptome data from human pluripotent stem cells cardiac differentiation

The main objective of the present work was to highlight differences and similarities in gene expression patterns between different pluripotent stem cell cardiac differentiation protocols, using a workflow based on unsupervised machine learning algorithms to analyse the transcriptome of cells cultured as a 2D monolayer or as 3D aggregates. This unsupervised approach effectively allowed to portray the transcriptomic changes that occurred throughout the differentiation processes, with a visual representation of the entire transcriptome. The results allowed to corroborate previously reported data and also to unveil new gene expression patterns. In particular, it was possible to identify a correlation between low cardiomyocyte differentiation efficiencies and the early expression of a set of non-mesodermal genes, which can be further explored as predictive markers of differentiation efficiency. The workflow here developed can also be applied to analyse other stem cell differentiation transcriptomic datasets, envisaging future clinical implementation of cellular therapies.

Stem Cell-Derived Cardiomyocyte-Like Cells in Myocardial Regeneration

Myocardial infarction results in the significant loss of cardiomyocytes (CMs) due to the ischemic injury following coronary occlusion leading to impaired contractility, fibrosis, and ultimately heart failure. Stem cell therapy emerged as a promising regenerative strategy to replenish the otherwise terminally differentiated CM to restore cardiac function. Multiple strategies have been applied to successfully differentiate diverse stem cell populations into CM-like phenotypes characterized by the expression status of signature biomarkers and observable spontaneous contractions. This article discusses the current understanding and applications of various stem cell phenotypes to drive the differentiation machinery toward CM-like lineage. Impact Statement Ischemic heart disease (IHD) extensively affects a large proportion of the population worldwide. Unfortunately, current treatments for IHD are insufficient to restore cardiac effectiveness and functionality. A growing field in regenerative cardiology explores the potential for stem cell therapy following cardiovascular ischemic episodes. The thorough understanding regarding the potential and shortcomings of translational approaches to drive versatile stem cells to cardiomyocyte lineage paves the way for multiple opportunities for next-generation cardiac management.

Pluripotent stem cell-based cardiac regenerative therapy for heart failure

Cardiac regenerative therapy using human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) is expected to become an alternative to heart transplantation for severe heart failure. It is now possible to produce large numbers of human pluripotent stem cells (hPSCs) and eliminate non-cardiomyocytes, including residual undifferentiated hPSCs, which can cause teratoma formation after transplantation. There are two main strategies for transplanting hPSC-CMs: injection of hPSC-CMs into the myocardium from the epicardial side, and implantation of hPSC-CM patches or engineered heart tissues onto the epicardium. Transplantation of hPSC-CMs into the myocardium of large animals in a myocardial infarction model improved cardiac function. The engrafted hPSC-CMs matured, and microvessels derived from the host entered the graft abundantly. Furthermore, as less invasive methods using catheters, injection into the coronary artery and injection into the myocardium from the endocardium side have recently been investigated. Since transplantation of hPSC-CMs alone has a low engraftment rate, various methods such as transplantation with the extracellular matrix or non-cardiomyocytes and aggregation of hPSC-CMs have been developed. Post-transplant arrhythmias, imaging of engrafted hPSC-CMs, and immune rejection are the remaining major issues, and research is being conducted to address them. The clinical application of cardiac regenerative therapy using hPSC-CMs has just begun and is expected to spread widely if its safety and efficacy are proven in the near future.

Perlecan (HSPG2) promotes structural, contractile, and metabolic development of human cardiomyocytes

Perlecan (HSPG2), a heparan sulfate proteoglycan similar to agrin, is key for extracellular matrix (ECM) maturation and stabilization. Although crucial for cardiac development, its role remains elusive. We show that perlecan expression increases as cardiomyocytes mature in vivo and during human pluripotent stem cell differentiation to cardiomyocytes (hPSC-CMs). Perlecan-haploinsuffient hPSCs (HSPG2+/-) differentiate efficiently, but late-stage CMs have structural, contractile, metabolic, and ECM gene dysregulation. In keeping with this, late-stage HSPG2+/- hPSC-CMs have immature features, including reduced ⍺-actinin expression and increased glycolytic metabolism and proliferation. Moreover, perlecan-haploinsuffient engineered heart tissues have reduced tissue thickness and force generation. Conversely, hPSC-CMs grown on a perlecan-peptide substrate are enlarged and display increased nucleation, typical of hypertrophic growth. Together, perlecan appears to play the opposite role of agrin, promoting cellular maturation rather than hyperplasia and proliferation. Perlecan signaling is likely mediated via its binding to the dystroglycan complex. Targeting perlecan-dependent signaling may help reverse the phenotypic switch common to heart failure.

Single-Step Biofabrication of In Situ Spheroid-Forming Compartmentalized Hydrogel for Clinical-Sized Cartilage Tissue Formation

3D cellular spheroids offer more biomimetic microenvironments than conventional 2D cell culture technologies, which has proven value for many tissue engineering applications. Despite beneficiary effects of 3D cell culture, clinical translation of spheroid tissue engineering is challenged by limited scalability of current spheroid formation methods. Although recent adoption of droplet microfluidics can provide a continuous production process, use of oils and surfactants, generally low throughput, and requirement of additional biofabrication steps hinder clinical translation of spheroid culture. Here, the use of clean (e.g., oil-free and surfactant-free), ultra-high throughput (e.g., 8.5 mL min-1 , 10 000 spheroids s-1 ), single-step, in-air microfluidic biofabrication of spheroid forming compartmentalized hydrogels is reported. This novel technique can reliably produce 1D fibers, 2D planes, and 3D volumes compartmentalized hydrogel constructs, which each allows for distinct (an)isotropic orientation of hollow spheroid-forming compartments. Spheroids produced within ink-jet bioprinted compartmentalized hydrogels outperform 2D cell cultures in terms of chondrogenic behavior. Moreover, the cellular spheroids can be harvested from compartmentalized hydrogels and used to build shape-stable centimeter-sized biomaterial-free living tissues in a bottom-up manner. Consequently, it is anticipated that in-air microfluidic production of spheroid-forming compartmentalized hydrogels can advance production and use of cellular spheroids for various biomedical applications.

Application of Human Induced Pluripotent Stem Cells for Tissue Engineered Cardiomyocyte Modelling

Purpose

Cardiac tissue engineering opens up opportunities for regenerative therapy in heart diseases. Current technologies improve engineered cardiac tissue characteristics by combining human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) with non-cardiomyocytes, selective biomaterials, and additional growth factors. Animal models are still required to determine cardiac patches’ overall in vivo effect before initiating human trials. Here, we review the current in vivo studies of cardiac patches using hiPSC-CMs.

Methods

We performed a literature search for studies on cardiac patch in vivo application and compared outcomes based on cell engraftment, functional changes, and safety profiles.

Results

Present studies confirm the beneficial results of combining hiPSC-CMs with other cardiac cell lineages and biomaterials. They improved the functional capacity of the heart, showed a reduction in infarct size, and initiated an adaptive inflammatory process through neovascularisation.

Conclusion

The cardiac patch is currently the most effective delivery system, proving safety and improvements in animal models, which are suggested to be the role of the paracrine mechanism. Further studies should focus on honing in vitro patch characteristics to achieve ideal results.

Lay Summary

Cardiac tissue engineering answers the demand for regenerative therapy in heart diseases. Combining human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) with biomaterials and growth factors in cardiac patches improves the heart’s structural and functional characteristics. This delivery system is safe and efficient for delivering many cells and minimising cellular loss in vivo. Rat and porcine models of ischemic and non-ischemic heart diseases demonstrated the benefits of this therapy, which include cell engraftment, reduced infarct size, and increased left ventricular (LV) systolic function, with no reported critical adverse events. These reports sufficiently provide evidence of feasible improvements to proceed towards further trials.

Metabolic Remodeling during Early Cardiac Lineage Specification of Pluripotent Stem Cells

Growing evidence indicates that metabolites and energy metabolism play an active rather than consequential role in regulating cellular fate. Cardiac development requires dramatic metabolic remodeling from relying primarily on glycolysis in pluripotent stem cells (PSCs) to oxidizing a wide array of energy substrates to match the high bioenergetic demands of continuous contraction in the developed heart. However, a detailed analysis of how remodeling of energy metabolism contributes to human cardiac development is lacking. Using dynamic multiple reaction monitoring metabolomics of central carbon metabolism, we evaluated temporal changes in energy metabolism during human PSC 3D cardiac lineage specification. Significant metabolic remodeling occurs during the complete differentiation, yet temporal analysis revealed that most changes occur during transitions from pluripotency to mesoderm (day 1) and mesoderm to early cardiac (day 5), with limited maturation of cardiac metabolism beyond day 5. Real-time metabolic analysis demonstrated that while hPSC cardiomyocytes (hPSC-CM) showed elevated rates of oxidative metabolism compared to PSCs, they still retained high glycolytic rates, confirming an immature metabolic phenotype. These observations support the opportunity to metabolically optimize the differentiation process to support lineage specification and maturation of hPSC-CMs.

Three-Dimensional Matrix Stiffness Activates the Piezo1-AMPK-Autophagy Axis to Regulate the Cellular Osteogenic Differentiation

Extracellular matrix (ECM) stiffness is a key stimulus affecting cellular differentiation, and osteoblasts are also in a three-dimensional (3D) stiff environment during the formation of bone tissues. However, it remains unclear how cells perceive matrix mechanical stiffness stimuli and translate them into intracellular signals to affect differentiation. Here, for the first time, we constructed a 3D culture environment by GelMA hydrogels with different amino substitution degrees and found that Piezo1 expression was significantly stimulated by the stiff matrix with high substitution; meanwhile, the expressions of osteogenic markers OSX, RUNX2, and ALP were also observably improved. Moreover, knockdown of Piezo1 in the stiff matrix revealed significant reduction of the abovementioned osteogenic markers. In addition, in this 3D biomimetic ECM, we also observed that Piezo1 can be activated by the static mechanical conditions of the stiff matrix, leading to the increase of the intracellular calcium content and accompanied with a continuous change in cellular energy levels as ATP was consumed during cellular differentiation. More surprisingly, we found that in the 3D stiff matrix, intracellular calcium as a second messenger promoted the activation of the AMP-activated protein kinase (AMPK) and unc-51-like autophagy-activated kinase 1 (ULK1) axis and modestly modulated the level of autophagy, bringing it more similar to differentiated osteoblasts, with increased ATP energy metabolism consumption. Our study innovatively clarifies the regulatory role of the mechanosensitive ion channel Piezo1 in a static mechanical environment on cellular differentiation and verifies the activation of the AMPK-ULK1 axis in the cellular ATP energy metabolism and autophagy level. Collectively, our research develops the understanding of the interaction mechanisms of biomimetic extracellular matrix biomaterials and cells from a novel perspective and provides a theoretical basis for bone regeneration biomaterials design and application.

APLNR marks a cardiac progenitor derived with human induced pluripotent stem cells

Cardiomyocytes can be readily derived from human induced pluripotent stem cell (hiPSC) lines, yet its efficacy varies across different batches of the same and different hiPSC lines. To unravel the inconsistencies of in vitro cardiac differentiation, we utilized single cell transcriptomics on hiPSCs undergoing cardiac differentiation and identified cardiac and extra-cardiac lineages throughout differentiation. We further identified APLNR as a surface marker for in vitro cardiac progenitors and immunomagnetically isolated them. Differentiation of isolated in vitro APLNR+ cardiac progenitors derived from multiple hiPSC lines resulted in predominantly cardiomyocytes accompanied with cardiac mesenchyme. Transcriptomic analysis of differentiating in vitro APLNR+ cardiac progenitors revealed transient expression of cardiac progenitor markers before further commitment into cardiomyocyte and cardiac mesenchyme. Analysis of in vivo human and mouse embryo single cell transcriptomic datasets have identified APLNR expression in early cardiac progenitors of multiple lineages. This platform enables generation of in vitro cardiac progenitors from multiple hiPSC lines without genetic manipulation, which has potential applications in studying cardiac development, disease modelling and cardiac regeneration.

Cellular reprogramming of fibroblasts in heart regeneration

Myocardial infarction causes the loss of cardiomyocytes and the formation of cardiac fibrosis due to the activation of cardiac fibroblasts, leading to cardiac dysfunction and heart failure. Unfortunately, current therapeutic interventions can only slow the disease progression. Furthermore, they cannot fully restore cardiac function, likely because the adult human heart lacks sufficient capacity to regenerate cardiomyocytes. Therefore, intensive efforts have focused on developing therapeutics to regenerate the damaged heart. Several strategies have been intensively investigated, including stimulation of cardiomyocyte proliferation, transplantation of stem cell-derived cardiomyocytes, and conversion of fibroblasts into cardiac cells. Resident cardiac fibroblasts are critical in the maintenance of the structure and contractility of the heart. Fibroblast plasticity makes this type of cells be reprogrammed into many cell types, including but not limited to induced pluripotent stem cells, induced cardiac progenitor cells, and induced cardiomyocytes. Fibroblasts have become a therapeutic target due to their critical roles in cardiac pathogenesis. This review summarizes the reprogramming of fibroblasts into induced pluripotent stem cell-derived cardiomyocytes, induced cardiac progenitor cells, and induced cardiomyocytes to repair a damaged heart, outlines recent findings in utilizing fibroblast-derived cells for heart regeneration, and discusses the limitations and challenges.

Systematic discovery of transcription factors that improve hPSC-derived cardiomyocyte maturation via temporal analysis of bioengineered cardiac tissues

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) have the potential to become powerful tools for disease modeling, drug testing, and transplantation; however, their immaturity limits their applications. Transcription factor (TF) overexpression can improve hPSC-CM maturity, but identifying these TFs has been elusive. Toward this, we establish here an experimental framework for systematic identification of maturation enhancing factors. Specifically, we performed temporal transcriptome RNAseq analyses of progressively matured hPSC-derived cardiomyocytes across 2D and 3D differentiation systems and further compared these bioengineered tissues to native fetal and adult-derived tissues. These analyses revealed 22 TFs whose expression did not increase in 2D differentiation systems but progressively increased in 3D culture systems and adult mature cell types. Individually overexpressing each of these TFs in immature hPSC-CMs identified five TFs (KLF15, ZBTB20, ESRRA, HOPX, and CAMTA2) as regulators of calcium handling, metabolic function, and hypertrophy. Notably, the combinatorial overexpression of KLF15, ESRRA, and HOPX improved all three maturation parameters simultaneously. Taken together, we introduce a new TF cocktail that can be used in solo or in conjunction with other strategies to improve hPSC-CM maturation and anticipate that our generalizable methodology can also be implemented to identify maturation-associated TFs for other stem cell progenies.

An Efficient and Reproducible Method for the Isolation and Culture of Primary Cardiomyocytes from Adult Zebrafish

Zebrafish is a popular animal model in regeneration studies due to their ability to regenerate the heart. Primary cardiomyocytes could be an alternative tool for studying the intrinsic mechanisms of cardiovascular disease in vitro. Thus, our objective is to develop an efficient protocol to isolate primary cardiomyocytes from zebrafish hearts. Low concentration of digestive enzyme (0.5 mg/mL collagenase type II) was utilized in our protocol to obtain single-cell suspension. The ventricles were fragmented, mechanically pipetted, and constantly shaken to ensure adequate contact between the tissues and the enzyme. Preplating the cell suspension onto culture plates for 2 h helped remove cardiac fibroblasts. The purity of isolated cells was validated by flow cytometry analysis of transgenic zebrafish with cardiomyocyte-specific expression of enhanced green fluorescent protein (EGFP) or endothelial cell-specific expression of mCherry. Quantitative real-time PCR analysis revealed a high level of the purity, with cardiac fibroblasts, endothelial cells, and epicardial cell markers scarcely detected in the purified cells. Altogether, this study established a reproducible protocol for isolating primary cardiomyocytes with high purity and activity from adult zebrafish hearts that can be cultured in vitro for up to 4 weeks. This protocol provides a valuable tool for studying the intrinsic mechanisms of cardiovascular disease in vitro using primary cardiomyocytes.

Trajectory reconstruction identifies dysregulation of perinatal maturation programs in pluripotent stem cell-derived cardiomyocytes

A limitation in the application of pluripotent stem cell-derived cardiomyocytes (PSC-CMs) is the failure of these cells to achieve full functional maturity. The mechanisms by which directed differentiation differs from endogenous development, leading to consequent PSC-CM maturation arrest, remain unclear. Here, we generate a single-cell RNA sequencing (scRNA-seq) reference of mouse in vivo CM maturation with extensive sampling of previously difficult-to-isolate perinatal time periods. We subsequently generate isogenic embryonic stem cells to create an in vitro scRNA-seq reference of PSC-CM-directed differentiation. Through trajectory reconstruction, we identify an endogenous perinatal maturation program that is poorly recapitulated in vitro. By comparison with published human datasets, we identify a network of nine transcription factors (TFs) whose targets are consistently dysregulated in PSC-CMs across species. Notably, these TFs are only partially activated in common ex vivo approaches to engineer PSC-CM maturation. Our study can be leveraged toward improving the clinical viability of PSC-CMs.

Generation of left ventricle-like cardiomyocytes with improved structural, functional, and metabolic maturity from human pluripotent stem cells

Decreased left ventricle (LV) function caused by genetic mutations or injury often leads to debilitating and fatal cardiovascular disease. LV cardiomyocytes are, therefore, a potentially valuable therapeutical target. Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) are neither homogeneous nor functionally mature, which reduces their utility. Here, we exploit cardiac development knowledge to instruct differentiation of hPSCs specifically toward LV cardiomyocytes. Correct mesoderm patterning and retinoic acid pathway blocking are essential to generate near-homogenous LV-specific hPSC-CMs (hPSC-LV-CMs). These cells transit via first heart field progenitors and display typical ventricular action potentials. Importantly, hPSC-LV-CMs exhibit increased metabolism, reduced proliferation, and improved cytoarchitecture and functional maturity compared with age-matched cardiomyocytes generated using the standard WNT-ON/WNT-OFF protocol. Similarly, engineered heart tissues made from hPSC-LV-CMs are better organized, produce higher force, and beat more slowly but can be paced to physiological levels. Together, we show that functionally matured hPSC-LV-CMs can be obtained rapidly without exposure to current maturation regimes.

Developmental Toxicity Studies: The Path towards Humanized 3D Stem Cell-Based Models

Today, it is recognized that medicines will eventually be needed during pregnancy to help prevent to, ameliorate or treat an illness, either due to gestation-related medical conditions or pre-existing diseases. Adding to that, the rate of drug prescription to pregnant women has increased over the past few years, in accordance with the increasing trend to postpone childbirth to a later age. However, in spite of these trends, information regarding teratogenic risk in humans is often missing for most of the purchased drugs. So far, animal models have been the gold standard to obtain teratogenic data, but inter-species differences have limited the suitability of those models to predict human-specific outcomes, contributing to misidentified human teratogenicity. Therefore, the development of physiologically relevant in vitro humanized models can be the key to surpassing this limitation. In this context, this review describes the pathway towards the introduction of human pluripotent stem cell-derived models in developmental toxicity studies. Moreover, as an illustration of their relevance, a particular emphasis will be placed on those models that recapitulate two very important early developmental stages, namely gastrulation and cardiac specification.

Scalable fabrication, compartmentalization and applications of living microtissues

Living microtissues are used in a multitude of applications as they more closely resemble native tissue physiology, as compared to 2D cultures. Microtissues are typically composed of a combination of cells and materials in varying combinations, which are dictated by the applications' design requirements. Their applications range wide, from fundamental biological research such as differentiation studies to industrial applications such as cruelty-free meat production. However, their translation to industrial and clinical settings has been hindered due to the lack of scalability of microtissue production techniques. Continuous microfluidic processes provide an opportunity to overcome this limitation as they offer higher throughput production rates as compared to traditional batch techniques, while maintaining reproducible control over microtissue composition and size. In this review, we provide a comprehensive overview of the current approaches to engineer microtissues with a focus on the advantages of, and need for, the use of continuous processes to produce microtissues in large quantities. Finally, an outlook is provided that outlines the required developments to enable large-scale microtissue fabrication using continuous processes.

Cost-Effective Mechanical Aggregation of Cardiac Progenitors and Encapsulation in Matrigel Support Self-Organization in a Dynamic Culture Environment

Human iPSC-derived self-organized cardiac tissues can be valuable for the development of platforms for disease modeling and drug screening, enhancing test accuracy and reducing pharmaceutical industry financial burden. However, current differentiation systems still rely on static culture conditions and specialized commercial microwells for aggregation, which hinders the full potential of hiPSC-derived cardiac tissues. Herein, we integrate cost-effective and reproducible manual aggregation of hiPSC-derived cardiac progenitors with Matrigel encapsulation and a dynamic culture to support hiPSC cardiac differentiation and self-organization. Manual aggregation at day 7 of cardiac differentiation resulted in 97% of beating aggregates with 78% of cTnT-positive cells. Matrigel encapsulation conjugated with a dynamic culture promoted cell migration and the creation of organized structures, with observed cell polarization and the creation of lumens. In addition, encapsulation increased buoyancy and decreased coalescence of the hiPSC-derived cardiac aggregates. Moreover, VEGF supplementation increased over two-fold the percentage of CD31-positive cells resulting in the emergence of microvessel-like structures. Thus, this study shows that the explored culture parameters support the self-organization of hiPSC-derived cardiac microtissues containing multiple cardiac cell types. Additional stimuli (e.g., BMP) in long-term scalable and fully automatized cultures can further potentiate highly structured and mature hiPSC-derived cardiac models, contributing to the development of reliable platforms for high-throughput drug screening and disease modeling.

Xeno-Free Integrated Platform for Robust Production of Cardiomyocyte Sheets from hiPSCs

Human induced pluripotent stem cells (hiPSCs) can be efficiently differentiated into cardiomyocytes (CMs), which can be used for cardiac disease modeling, for drug screening, and to regenerate damaged myocardium. Implementation of xeno-free culture systems is essential to fully explore the potential of these cells. However, differentiation using xeno-free adhesion matrices often results in low CM yields and lack of functional CM sheets, capable of enduring additional maturation stages. Here, we established a xeno-free CM differentiation platform using TeSR/Synthemax, including a replating step and integrated with two versatile purification/enrichment metabolic approaches. Results showed that the replating step was essential to reestablish a fully integrated, closely-knit CM sheet. In addition, replating contributed to increase the cTnT expression from 65% to 75% and the output from 2.2 to 3.1 CM per hiPSC, comparable with the efficiency observed when using TeSR/Matrigel. In addition, supplementation with PluriSin1 and Glu-Lac+ medium allowed increasing the CM content over 80% without compromising CM sheet integrity or functionality. Thus, this xeno-free differentiation platform is a reliable and robust method to produce hiPSC-derived CMs, increasing the possibility of using these cells safely for a wide range of applications.

Differentiating Human Pluripotent Stem Cells to Cardiomyocytes Using Purified Extracellular Matrix Proteins

Human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) can be differentiated into cardiomyocytes (hESC-CMs and iPSC-CMs, respectively), which hold great promise for cardiac regenerative medicine and disease modeling efforts. However, the most widely employed differentiation protocols require undefined substrates that are derived from xenogeneic (animal) products, contaminating resultant hESC- and iPSC-CM cultures with xenogeneic proteins and limiting their clinical applicability. Additionally, typical hESC- and iPSC-CM protocols produce CMs that are significantly contaminated by non-CMs and that are immature, requiring lengthy maturation procedures. In this review, we will summarize recent studies that have investigated the ability of purified extracellular matrix (ECM) proteins to support hESC- and iPSC-CM differentiation, with a focus on commercially available ECM proteins and coatings to make such protocols widely available to researchers. The most promising of the substrates reviewed here include laminin-521 with laminin-221 together or Synthemax (a synthetic vitronectin-based peptide coating), which both resulted in highly pure CM cultures. Future efforts are needed to determine whether combinations of specific purified ECM proteins or derived peptides could further improve CM maturation and culture times, and significantly improve hESC- and iPSC-CM differentiation protocols.

Cell Behavioral Dynamics as a Cue in Optimizing Culture Stabilization in the Bioprocessing of Pluripotent Stem Cells

Pluripotent stem cells (PSCs) are important for future regenerative medicine therapies. However, in the production of PSCs and derivatives, the control of culture-induced fluctuations in the outcome of cell quality remains challenging. A detailed mechanistic understanding of how PSC behaviors are altered in response to biomechanical microenvironments within a culture is necessary for rational bioprocessing optimization. In this review, we discuss recent insights into the role of cell behavioral and mechanical homeostasis in modulating the states and functions of PSCs during culture processes. We delineate promising ways to manipulate the culture variability through regulating cell behaviors using currently developed tools. Furthermore, we anticipate their potential implementation for designing a culture strategy based on the concept of Waddington's epigenetic landscape that may provide a feasible solution for tuning the culture quality and stability in the bioprocessing space.

Combination of mesenchymal stem cells and three-dimensional collagen scaffold preserves ventricular remodeling in rat myocardial infarction model

BACKGROUND

Cardiovascular diseases are the major cause of mortality worldwide. Regeneration of the damaged myocardium remains a challenge due to mechanical constraints and limited healing ability of the adult heart tissue. Cardiac tissue engineering using biomaterial scaffolds combined with stem cells and bioactive molecules could be a highly promising approach for cardiac repair. Use of biomaterials can provide suitable microenvironment to the cells and can solve cell engraftment problems associated with cell transplantation alone. Mesenchymal stem cells (MSCs) are potential candidates in cardiac tissue engineering because of their multilineage differentiation potential and ease of isolation. Use of DNA methyl transferase inhibitor, such as zebularine, in combination with three-dimensional (3D) scaffold can promote efficient MSC differentiation into cardiac lineage, as epigenetic modifications play a fundamental role in determining cell fate and lineage specific gene expression.

AIM

To investigate the role of collagen scaffold and zebularine in the differentiation of rat bone marrow (BM)-MSCs and their subsequent in vivo effects.

METHODS

MSCs were isolated from rat BM and characterized morphologically, immunophenotypically and by multilineage differentiation potential. MSCs were seeded in collagen scaffold and treated with 3 μmol/L zebularine in three different ways. Cytotoxicity analysis was done and cardiac differentiation was analyzed at the gene and protein levels. Treated and untreated MSC-seeded scaffolds were transplanted in the rat myocardial infarction (MI) model and cardiac function was assessed by echocardiography. Cell tracking was performed by DiI dye labeling, while regeneration and neovascularization were evaluated by histological and immunohistochemical analysis, respectively.

RESULTS

MSCs were successfully isolated and seeded in collagen scaffold. Cytotoxicity analysis revealed that zebularine was not cytotoxic in any of the treatment groups. Cardiac differentiation analysis showed more pronounced results in the type 3 treatment group which was subsequently chosen for the transplantation in the in vivo MI model. Significant improvement in cardiac function was observed in the zebularine treated MSC-seeded scaffold group as compared to the MI control. Histological analysis also showed reduction in fibrotic scar, improvement in left ventricular wall thickness and preservation of ventricular remodeling in the zebularine treated MSC-seeded scaffold group. Immunohistochemical analysis revealed significant expression of cardiac proteins in DiI labeled transplanted cells and a significant increase in the number of blood vessels in the zebularine treated MSC-seeded collagen scaffold transplanted group.

CONCLUSION

Combination of 3D collagen scaffold and zebularine treatment enhances cardiac differentiation potential of MSCs, improves cell engraftment at the infarcted region, reduces infarct size and improves cardiac function.

Polycaprolactone-co-polylactic acid nanofiber scaffold in combination with 5-azacytidine and transforming growth factor-β to induce cardiomyocyte differentiation of adipose-derived mesenchymal stem cells

Adipose-derived mesenchymal stem cells (Ad-MSCs) are promising candidates for cardiac repair/regeneration. The application of copolymer nanoscaffolds has received great attention in tissue engineering to support differentiation and functional tissue organization toward effective tissue regeneration. The objective of the current study was to develop functional and bioactive scaffolds by combining polycaprolactone (PCL) and polylactic acid (PLA) for cardiomyocyte differentiation of human Ad-MSC (hAd-MSCs) in the absence or presence of 5-azacytidine and transforming growth factor-β (TGF-β). To that end, the human MSCs were extracted from human adipose tissue (AD). The cardiomyocyte differentiation potency of hAd-MSCs was evaluated on the novel synthetic PCL/PLA nanofiber scaffolds prepared in the absence and presence of 5-azacytidine and TGF-β supplements. A PCL/PLA nanofibrous scaffold was fabricated using the electrospinning method and its nanotopography and porous structure were characterized using scanning electron microscopy. In addition, the attachment of hAd-MSCs on the PCL/PLA scaffolds was semiquantitatively investigated. Compared with other treatments, the PCL/PLA nanofibrous scaffold supplemented with both 5-azacytidine and TGF-β was observed to differentiate hAd-MSCs into cardiomyocytes at Day 21 as evidenced by real-time PCR for cardiac-specific genes including cardiac troponin I (cTnI), GATA4, MYH7, and NKX2.5. In addition, flow cytometric analysis of cTnI-positive cells demonstrated that the cardiomyocyte differentiation of hAd-MSCs was more efficient on the PCL/PLA nanofibrous scaffold supplemented with both 5-azacytidine and TGF-β than it was in the other treatment groups. Generally speaking, the results show that PCL/PLA nanofibrous scaffolds may be applied as a platform for efficient differentiation of hAd-MSCs into functional cardiomyocytes.

Opportunities and challenges in cardiac tissue engineering from an analysis of two decades of advances

Engineered human cardiac tissues facilitate progress in regenerative medicine, disease modelling and drug development. In this Perspective, we reflect on the most notable advances in cardiac tissue engineering from the past two decades by analysing pivotal studies and critically examining the most consequential developments. This retrospective analysis led us to identify key milestones and to outline a set of opportunities, along with their associated challenges, for the further advancement of engineered human cardiac tissues.

Computational profiling of hiPSC-derived heart organoids reveals chamber defects associated with NKX2-5 deficiency

Heart organoids have the potential to generate primary heart-like anatomical structures and hold great promise as in vitro models for cardiac disease. However, their properties have not yet been fully studied, which hinders their wide spread application. Here we report the development of differentiation systems for ventricular and atrial heart organoids, enabling the study of heart diseases with chamber defects. We show that our systems generate chamber-specific organoids comprising of the major cardiac cell types, and we use single cell RNA sequencing together with sample multiplexing to characterize the cells we generate. To that end, we developed a machine learning label transfer approach leveraging cell type, chamber, and laterality annotations available for primary human fetal heart cells. We then used this model to analyze organoid cells from an isogeneic line carrying an Ebstein’s anomaly associated genetic variant in NKX2-5, and we successfully recapitulated the disease’s atrialized ventricular defects. In summary, we have established a workflow integrating heart organoids and computational analysis to model heart development in normal and disease states.

A human cardiac organoid system, coupled with single cell RNA sequencing and machine learning for transcriptional phenotyping, was developed. This allowed investigation of a genetic variant associated with Ebstein’s Anomaly, a congenital heart disease with chamber defects.

Bioengineering Strategies to Create 3D Cardiac Constructs from Human Induced Pluripotent Stem Cells

Human induced pluripotent stem cells (hiPSCs) can be used to generate various cell types in the human body. Hence, hiPSC-derived cardiomyocytes (hiPSC-CMs) represent a significant cell source for disease modeling, drug testing, and regenerative medicine. The immaturity of hiPSC-CMs in two-dimensional (2D) culture limit their applications. Cardiac tissue engineering provides a new promise for both basic and clinical research. Advanced bioengineered cardiac in vitro models can create contractile structures that serve as exquisite in vitro heart microtissues for drug testing and disease modeling, thereby promoting the identification of better treatments for cardiovascular disorders. In this review, we will introduce recent advances of bioengineering technologies to produce in vitro cardiac tissues derived from hiPSCs.

High temporal resolution proteome and phosphoproteome profiling of stem cell-derived hepatocyte development

Primary human hepatocytes are widely used to evaluate liver toxicity of drugs, but they are scarce and demanding to culture. Stem cell-derived hepatocytes are increasingly discussed as alternatives. To obtain a better appreciation of the molecular processes during the differentiation of induced pluripotent stem cells into hepatocytes, we employ a quantitative proteomic approach to follow the expression of 9,000 proteins, 12,000 phosphorylation sites, and 800 acetylation sites over time. The analysis reveals stage-specific markers, a major molecular switch between hepatic endoderm versus immature hepatocyte-like cells impacting, e.g., metabolism, the cell cycle, kinase activity, and the expression of drug transporters. Comparing the proteomes of two- (2D) and three-dimensional (3D)-derived hepatocytes with fetal and adult liver indicates a fetal-like status of the in vitro models and lower expression of important ADME/Tox proteins. The collective data enable constructing a molecular roadmap of hepatocyte development that serves as a valuable resource for future research.

A Dynamic 3D Aggregate-Based System for the Successful Expansion and Neural Induction of Human Pluripotent Stem Cells

The demand for large cell numbers for cellular therapies and drug screening applications requires the development of scalable platforms capable of generating high-quality populations of tissue-specific cells derived from human pluripotent stem cells (hPSCs). Here, we studied the ability of Gibco StemScale PSC Suspension Medium to promote the efficient expansion of hPSC cultures as aggregates grown in suspension. We tested human induced pluripotent stem cell (hiPSC) growth in 6-well plates (on orbital shaker platforms) and single-use vertical-wheel bioreactors for a total of three consecutive passages. Up to a 9-fold increase in cell number was observed over 5 days per passage, with a cumulative fold change up to 600 in 15 days. Additionally, we compared neural induction of hiPSCs by using a dual SMAD inhibition protocol with a commercially available neural induction medium, which can potentially yield more than a 30-fold change, including neural progenitor induction and expansion. This system can also be adapted toward the generation of floor plate progenitors, which yields up to an 80-fold change in cell number and generates FOXA2-positive populations. In summary, we developed platforms for hiPSC expansion and neural induction into different brain regions that provide scalability toward producing clinically relevant cell numbers.

Conditional immortalization of human atrial myocytes for the generation of in vitro models of atrial fibrillation

The lack of a scalable and robust source of well-differentiated human atrial myocytes constrains the development of in vitro models of atrial fibrillation (AF). Here we show that fully functional atrial myocytes can be generated and expanded one-quadrillion-fold via a conditional cell-immortalization method relying on lentiviral vectors and the doxycycline-controlled expression of a recombinant viral oncogene in human foetal atrial myocytes, and that the immortalized cells can be used to generate in vitro models of AF. The method generated 15 monoclonal cell lines with molecular, cellular and electrophysiological properties resembling those of primary atrial myocytes. Multicellular in vitro models of AF generated using the immortalized atrial myocytes displayed fibrillatory activity (with activation frequencies of 6-8 Hz, consistent with the clinical manifestation of AF), which could be terminated by the administration of clinically approved antiarrhythmic drugs. The conditional cell-immortalization method could be used to generate functional cell lines from other human parenchymal cells, for the development of in vitro models of human disease.

Capturing the third dimension in drug discovery: Spatially-resolved tools for interrogation of complex 3D cell models

Advanced three-dimensional (3D) cell models have proven to be capable of depicting architectural and microenvironmental features of several tissues. By providing data of higher physiological and pathophysiological relevance, 3D cell models have been contributing to a better understanding of human development, pathology onset and progression mechanisms, as well as for 3D cell-based assays for drug discovery. Nonetheless, the characterization and interrogation of these tissue-like structures pose major challenges on the conventional analytical methods, pushing the development of spatially-resolved technologies. Herein, we review recent advances and pioneering technologies suitable for the interrogation of multicellular 3D models, while capable of retaining biological spatial information. We focused on imaging technologies and omics tools, namely transcriptomics, proteomics and metabolomics. The advantages and shortcomings of these novel methodologies are discussed, alongside the opportunities to intertwine data from the different tools.

Human Atrial Cardiac Microtissues for Chamber-Specific Arrhythmic Risk Assessment

Introduction

Although atrial fibrillation is the most prevalent disorder of electrical conduction, the mechanisms behind atrial arrhythmias remain elusive. To address this challenge, we developed a robust in vitro model of 3D atrial microtissue from human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes and evaluated chamber-specific chemical responses experimentally and computationally.

Methods

We differentiated atrial and ventricular cardiomyocytes (aCMs/vCMs) from GCaMP6f-expressing hiPSCs and assessed spontaneous AP activity using fluorescence imaging. Self-assembling 3D microtissues were formed with lactate purified CMs and 5% human cardiac fibroblasts and electrically stimulated for one week before high resolution action potential (AP) optical mapping. AP responses to the atrial-specific potassium repolarizing current I _Kur-blocker 4-Aminopyridine (4-AP) and funny current I _f-blocker Ivabradine were characterized within their therapeutic window. Finally, we expanded upon a published hiPSC-CM computational model by incorporating the atrial-specific I _Kur current, modifying ion channel conductances to match the AP waveforms of our microtissues, and employing the updated model to reinforce our experimental findings.

Results

High purity CMs (> 75% cTnT⁺) demonstrated subtype specification by MLC2v expression. Spontaneous beating rates significantly decreased following 3D microtissue formation, with atrial microtissues characterized by their faster spontaneous beating rate, slower AP rise time, and shorter AP duration (APD) compared to ventricular microtissues. We measured atrial-specific responses, including dose-dependent APD prolongation with 4-AP treatment and dose-dependent reduction in spontaneous activity post-Ivabradine treatment.

Conclusion

The presented in vitro platform for screening atrial-specific responses is both robust and sensitive, with high throughput, enabling studies focused at elucidating the mechanisms underlying atrial arrhythmias.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-021-00703-x.

Tissue engineering techniques for iPSC derived three-dimensional cardiac constructs

Recent developments in applied developmental physiology have provided well-defined methodologies for producing human stem cell derived cardiomyocytes. Cardiomyocytes produced in this way have become commonplace as cardiac physiology research models. This accessibility has also allowed for the development of tissue engineered human heart constructs for drug screening, surgical intervention, and investigating cardiac pathogenesis. However, cardiac tissue engineering is an interdisciplinary field that involves complex engineering and physiological concepts, which limits its accessibility. This review provides a readable, broad reaching, and thorough discussion of major factors to consider for the development of cardiovascular tissues from stem cell derived cardiomyocytes. This review will examine important considerations in undertaking a cardiovascular tissue engineering project, and will present, interpret, and summarize some of the recent advancements in this field. This includes reviewing different forms of tissue engineered constructs, a discussion on cardiomyocyte sources, and an in-depth discussion of the fabrication and maturation procedures for tissue engineered heart constructs.

Bioengineering platforms for cell therapeutics derived from pluripotent and direct reprogramming

Pluripotent and direct reprogramming technologies hold great potential for tissue repair and restoration of tissue and organ function. The implementation of induced pluripotent stem cells and directly reprogrammed cells in biomedical research has resulted in a significant leap forward in the highly promising area of regenerative medicine. While these therapeutic strategies are promising, there are several obstacles to overcome prior to the introduction of these therapies into clinical settings. Bioengineering technologies, such as biomaterials, bioprinting, microfluidic devices, and biostimulatory systems, can enhance cell viability, differentiation, and function, in turn the efficacy of cell therapeutics generated via pluripotent and direct reprogramming. Therefore, cellular reprogramming technologies, in combination with tissue-engineering platforms, are poised to overcome current bottlenecks associated with cell-based therapies and create new ways of producing engineered tissue substitutes.

Transcriptome analysis of non human primate-induced pluripotent stem cell-derived cardiomyocytes in 2D monolayer culture vs. 3D engineered heart tissue

AIMS

Stem cell therapy has shown promise for treating myocardial infarction via re-muscularization and paracrine signalling in both small and large animals. Non-human primates (NHPs), such as rhesus macaques (Macaca mulatta), are primarily utilized in preclinical trials due to their similarity to humans, both genetically and physiologically. Currently, induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) are delivered into the infarcted myocardium by either direct cell injection or an engineered tissue patch. Although both approaches have advantages in terms of sample preparation, cell-host interaction, and engraftment, how the iPSC-CMs respond to ischaemic conditions in the infarcted heart under these two different delivery approaches remains unclear. Here, we aim to gain a better understanding of the effects of hypoxia on iPSC-CMs at the transcriptome level.

METHODS AND RESULTS

NHP iPSC-CMs in both monolayer culture (2D) and engineered heart tissue (EHT) (3D) format were exposed to hypoxic conditions to serve as surrogates of direct cell injection and tissue implantation in vivo, respectively. Outcomes were compared at the transcriptome level. We found the 3D EHT model was more sensitive to ischaemic conditions and similar to the native in vivo myocardium in terms of cell-extracellular matrix/cell-cell interactions, energy metabolism, and paracrine signalling.

CONCLUSION

By exposing NHP iPSC-CMs to different culture conditions, transcriptome profiling improves our understanding of the mechanism of ischaemic injury.

Engineered cardiac tissue microsphere production through direct differentiation of hydrogel-encapsulated human pluripotent stem cells

Engineered cardiac tissues that can be directly produced from human induced pluripotent stem cells (hiPSCs) in scalable, suspension culture systems are needed to meet the demands of cardiac regenerative medicine. Here, we demonstrate successful production of functional cardiac tissue microspheres through direct differentiation of hydrogel encapsulated hiPSCs. To form the microspheres, hiPSCs were suspended within the photocrosslinkable biomaterial, PEG-fibrinogen (25 million cells/mL), and encapsulated at a rate of 420,000 cells/minute using a custom microfluidic system. Even at this high cell density and rapid production rate, high intra-batch and batch-to-batch reproducibility was achieved. Following microsphere formation, hiPSCs maintained high cell viability and continued to grow within and beyond the original PEG-fibrinogen matrix. These initially soft microspheres (<250 Pa) supported efficient cardiac differentiation; spontaneous contractions initiated by differentiation day 8, and the microspheres contained >75% cardiomyocytes (CMs). CMs responded appropriately to pharmacological stimuli and exhibited 1:1 capture up to 6.0 Hz when electrically paced. Over time, cells formed cell-cell junctions and aligned myofibril fibers; engineered cardiac microspheres were maintained in culture over 3 years. The capability to rapidly generate uniform cardiac microsphere tissues is critical for advancing downstream applications including biomanufacturing, multi-well plate drug screening, and injection-based regenerative therapies.

Human-induced pluripotent stem cell-derived cardiomyocytes, 3D cardiac structures, and heart-on-a-chip as tools for drug research

Development of new drugs is of high interest for the field of cardiac and cardiovascular diseases, which are a dominant cause of death worldwide. Before being allowed to be used and distributed, every new potentially therapeutic compound must be strictly validated during preclinical and clinical trials. The preclinical studies usually involve the in vitro and in vivo evaluation. Due to the increasing reporting of discrepancy in drug effects in animal and humans and the requirement to reduce the number of animals used in research, improvement of in vitro models based on human cells is indispensable. Primary cardiac cells are difficult to access and maintain in cell culture for extensive experiments; therefore, the human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) became an excellent alternative. This technology enables a production of high number of patient- and disease-specific cardiomyocytes and other cardiac cell types for a large-scale research. The drug effects can be extensively evaluated in the context of electrophysiological responses with a use of well-established tools, such as multielectrode array (MEA), patch clamp, or calcium ion oscillation measurements. Cardiotoxicity, which is a common reason for withdrawing drugs from marketing or rejection at final stages of clinical trials, can be easily verified with a use of hiPSC-CM model providing a prediction of human-specific responses and higher safety of clinical trials involving patient cohort. Abovementioned studies can be performed using two-dimensional cell culture providing a high-throughput and relatively lower costs. On the other hand, more complex structures, such as engineered heart tissue, organoids, or spheroids, frequently applied as co-culture systems, represent more physiological conditions and higher maturation rate of hiPSC-derived cells. Furthermore, heart-on-a-chip technology has recently become an increasingly popular tool, as it implements controllable culture conditions, application of various stimulations and continuous parameters read-out. This paper is an overview of possible use of cardiomyocytes and other cardiac cell types derived from hiPSC as in vitro models of heart in drug research area prepared on the basis of latest scientific reports and providing thorough discussion regarding their advantages and limitations.

Impairment of the ER/mitochondria compartment in human cardiomyocytes with PLN p.Arg14del mutation

The phospholamban (PLN) p.Arg14del mutation causes dilated cardiomyopathy, with the molecular disease mechanisms incompletely understood. Patient dermal fibroblasts were reprogrammed to hiPSC, isogenic controls were established by CRISPR/Cas9, and cardiomyocytes were differentiated. Mutant cardiomyocytes revealed significantly prolonged Ca2+ transient decay time, Ca2+ -load dependent irregular beating pattern, and lower force. Proteomic analysis revealed less endoplasmic reticulum (ER) and ribosomal and mitochondrial proteins. Electron microscopy showed dilation of the ER and large lipid droplets in close association with mitochondria. Follow-up experiments confirmed impairment of the ER/mitochondria compartment. PLN p.Arg14del end-stage heart failure samples revealed perinuclear aggregates positive for ER marker proteins and oxidative stress in comparison with ischemic heart failure and non-failing donor heart samples. Transduction of PLN p.Arg14del EHTs with the Ca2+ -binding proteins GCaMP6f or parvalbumin improved the disease phenotype. This study identified impairment of the ER/mitochondria compartment without SR dysfunction as a novel disease mechanism underlying PLN p.Arg14del cardiomyopathy. The pathology was improved by Ca2+ -scavenging, suggesting impaired local Ca2+ cycling as an important disease culprit.

Bioengineering Clinically Relevant Cardiomyocytes and Cardiac Tissues from Pluripotent Stem Cells

The regenerative capacity of cardiomyocytes is insufficient to functionally recover damaged tissue, and as such, ischaemic heart disease forms the largest proportion of cardiovascular associated deaths. Human-induced pluripotent stem cells (hiPSCs) have enormous potential for developing patient specific cardiomyocytes for modelling heart disease, patient-based cardiac toxicity testing and potentially replacement therapy. However, traditional protocols for hiPSC-derived cardiomyocytes yield mixed populations of atrial, ventricular and nodal-like cells with immature cardiac properties. New insights gleaned from embryonic heart development have progressed the precise production of subtype-specific hiPSC-derived cardiomyocytes; however, their physiological immaturity severely limits their utility as model systems and their use for drug screening and cell therapy. The long-entrenched challenges in this field are being addressed by innovative bioengingeering technologies that incorporate biophysical, biochemical and more recently biomimetic electrical cues, with the latter having the potential to be used to both direct hiPSC differentiation and augment maturation and the function of derived cardiomyocytes and cardiac tissues by mimicking endogenous electric fields.

Validation of a multicellular tumor microenvironment system for modeling patient tumor biology and drug response

Lung cancer rates are rising globally and non-small cell lung cancer (NSCLC) has a five year survival rate of only 24%. Unfortunately, the development of drugs to treat cancer is severely hampered by the inefficiency of translating pre-clinical studies into clinical benefit. Thus, we sought to apply a tumor microenvironment system (TMES) to NSCLC. Using microvascular endothelial cells, lung cancer derived fibroblasts, and NSCLC tumor cells in the presence of in vivo tumor-derived hemodynamic flow and transport, we demonstrate that the TMES generates an in-vivo like biological state and predicts drug response to EGFR inhibitors. Transcriptomic and proteomic profiling indicate that the TMES recapitulates the in vivo and patient molecular biological state providing a mechanistic rationale for the predictive nature of the TMES. This work further validates the TMES for modeling patient tumor biology and drug response indicating utility of the TMES as a predictive tool for drug discovery and development and potential for use as a system for patient avatars.