Cardiomyocyte maturation: advances in knowledge and implications for regenerative medicine

Advances in human induced pluripotent stem cell (hiPSC)-based disease modelling in cardiogenetics

Human induced pluripotent stem cell (hiPSC)-based disease modelling has significantly advanced the field of cardiogenetics, providing a precise, patient-specific platform for studying genetic causes of heart diseases. Coupled with genome editing technologies such as CRISPR/Cas, hiPSC-based models not only allow the creation of isogenic lines to study mutation-specific cardiac phenotypes, but also enable the targeted modulation of gene expression to explore the effects of genetic and epigenetic deficits at the cellular and molecular level. hiPSC-based models of heart disease range from two-dimensional cultures of hiPSC-derived cardiovascular cell types, such as various cardiomyocyte subtypes, endothelial cells, pericytes, vascular smooth muscle cells, cardiac fibroblasts, immune cells, etc., to cardiac tissue cultures including organoids, microtissues, engineered heart tissues, and microphysiological systems. These models are further enhanced by multi-omics approaches, integrating genomic, transcriptomic, epigenomic, proteomic, and metabolomic data to provide a comprehensive view of disease mechanisms. In particular, advances in cardiovascular tissue engineering enable the development of more physiologically relevant systems that recapitulate native heart architecture and function, allowing for more accurate modelling of cardiac disease, drug screening, and toxicity testing, with the overall goal of personalised medical approaches, where therapies can be tailored to individual genetic profiles. Despite significant progress, challenges remain in the maturation of hiPSC-derived cardiomyocytes and the complexity of reproducing adult heart conditions. Here, we provide a concise update on the most advanced methods of hiPSC-based disease modelling in cardiogenetics, with a focus on genome editing and cardiac tissue engineering.

Injectable myocardium-derived hydrogels with SDF-1α releasing for cardiac repair

Myocardial infarction (MI) is a predominant cause of morbidity and mortality globally. Therapeutic chemokines, such as stromal cell-derived factor 1α (SDF-1α), present a promising opportunity to treat the profibrotic remodeling post-MI if they can be delivered effectively to the injured tissue. However, direct injection of SDF-1α or physical entrapment in a hydrogel has shown limited efficacy. Here, we developed a sustained-release system consisting of SDF-1α loaded poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs) and an injectable porcine cardiac decellularized extracellular matrix (cdECM) hydrogel. This system demonstrated a sustained release of SDF-1α over four weeks while there is one week release for SDF-1α directly encapsulated in the cdECM hydrogel during in vitro testing. The incorporation of PLGA NPs into the cdECM hydrogel significantly enhanced its mechanical properties, increasing the Young's modulus from 561 ± 228 kPa to 1007 ± 2 kPa and the maximum compressive strength from 639 ± 42 kPa to 1014 ± 101 kPa. This nanocomposite hydrogel showed good cell compatibility after 7 days of culture with H9C2 cells, while the released SDF-1α retained its bioactivity, as evidenced by its chemotactic effects in vitro. Furthermore, in vivo studies further highlighted its significant ability to promote angiogenesis in the infarcted area and improve cardiac function after intramyocardial injection. These results demonstrated the therapeutic potential of combining local release of SDF-1α with the cdECM hydrogel for MI treatment.

Construction of engineered cardiac tissue on a heart-on-a-chip device enables modeling of arrhythmogenic right ventricular cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a progressive cardiac disorder characterized by the replacement of the right ventricular myocardium with fibrofatty tissue, with an incidence rate of approximately 1 in 5000. To advance our understanding of its pathology and facilitate drug screening, there is an urgent need for myocardial models that closely replicate human physiological conditions. In this study, we developed an engineered cardiac tissue (ECT) model on a chip using cardiomyocytes differentiated from induced pluripotent stem cells (iPSCs) derived from ARVC patients. The disease ECT model successfully recapitulated key phenotypic features of ARVC, including reduced contractility, arrhythmic events, and abnormal calcium transients. We further assessed the drug responses of the model to isoproterenol and amiodarone, confirming increased sensitivity to isoproterenol in the ARVC model, while amiodarone effectively alleviated the arrhythmic events. In conclusion, our ECT model successfully reproduced ARVC phenotypes, providing a novel platform for drug screening and pathological studies.

Integrin stimulation by collagen I at the progenitor stage accelerates maturation of human iPSC-derived cardiomyocytes

Cell manufacturing challenges have hampered effective preclinical evaluations of mature cardiac cells derived from human-induced pluripotent stem cells (hiPSCs). These challenges mainly stem from standard differentiation methods yielding cardiac cells of an immature phenotype, low cell yields and the need for extended culture for enhanced maturation. Although the intricate relationship between extracellular matrix (ECM) components and integrin expression levels plays a pivotal role during heart development, the impact of differentiation and maturation of cardiac cells on integrin behavior has not been thoroughly studied. This study postulates that cardiac cell maturation is significantly influenced by the timing of integrin stimulation via cell-matrix interactions. We profiled integrin expression levels throughout the differentiation process of cardiac cells and assessed the effects of utilizing defined ECM components as culture substrates on cell adhesion, proliferation, differentiation, and maturation. Our findings reveal that integrins facilitate hiPSC adhesion to ECM coated culture surfaces and underscores dynamic alterations in integrin expression during cardiac cell differentiation. Remarkably, we observed significant enrichments in α2 and β1 collagen integrin levels at the progenitor and differentiated stages. These shifts in collagen integrin levels were associated with enhanced cell seeding efficiency on collagen-type I surfaces and altered population doubling times. The stimulation of collagen integrins at the progenitor stage markedly boosted cardiac cell maturation, demonstrated by a significant (∼3-fold) increase in cardiac troponin I expression compared to the standard method after 15 days of culture. Enhanced maturation levels were further supported by significant increases in sarcomere development, maturation gene expression, morphological features, improved beating potency, and fatty acid metabolism dependency. Cardiac maturation driven by collagen was abrogated upon inhibition of collagen integrins targeted with selective pharmacological blockers, affirming their indispensable role in maturation without affecting cardiac differentiation levels. Our work confirms that stimulating collagen integrins at the progenitor stage is a potential strategy to achieve rapid maturation of hiPSC-derived cardiac cells. STATEMENT OF SIGNIFICANCE: This study offers a novel strategy guided by integrin expression levels for generating hiPSC-CMs with improved maturation features in a short culture period (<16 days). The improvements in cardiac cell maturation were achieved by stimulating collagen type 1 integrin at the progenitor stage. The potential benefits of this method for regenerative cardiac repair will pave the way for the preclinical examination of mature cardiac cells in tissues to advance cell manufacturing and cardiac toxicity studies.

Advances in humanoid organoid-based research on inter-organ communications during cardiac organogenesis and cardiovascular diseases

The intimate correlation between cardiovascular diseases and other organ pathologies, such as metabolic and kidney diseases, underscores the intricate interactions among these organs. Understanding inter-organ communications is crucial for developing more precise drugs and effective treatments for systemic diseases. While animal models have traditionally been pivotal in studying these interactions, human-induced pluripotent stem cells (hiPSCs) offer distinct advantages when constructing in vitro models. Beyond the conventional two-dimensional co-culture model, hiPSC-derived humanoid organoids have emerged as a substantial advancement, capable of replicating essential structural and functional attributes of internal organs in vitro. This breakthrough has spurred the development of multilineage organoids, assembloids, and organoids-on-a-chip technologies, which allow for enhanced physiological relevance. These technologies have shown great potential for mimicking coordinated organogenesis, exploring disease pathogenesis, and facilitating drug discovery. As the central organ of the cardiovascular system, the heart serves as the focal point of an extensively studied network of interactions. This review focuses on the advancements and challenges of hiPSC-derived humanoid organoids in studying interactions between the heart and other organs, presenting a comprehensive exploration of this cutting-edge approach in systemic disease research.

Foxk1 and Foxk2 promote cardiomyocyte proliferation and heart regeneration

Promoting endogenous cardiomyocyte proliferation is a promising strategy for cardiac repair. Identifying key factors that regulate cardiomyocyte proliferation can advance the development of novel therapies for heart regeneration. Here, we identify Foxk1 and Foxk2 as key regulators of cardiomyocyte proliferation, whose expression declines during postnatal heart development. Cardiomyocyte-specific knockout of Foxk1 or Foxk2 impairs neonatal heart regeneration after myocardial infarction (MI) injury. AAV9-mediated Foxk1 or Foxk2 overexpression extends the postnatal cardiomyocyte proliferative window and enhances cardiac repair in adult mice after MI. Mechanistically, Foxk1 and Foxk2 drive cardiomyocyte cell cycle progression by directly activating CCNB1 and CDK1 expression, forming the CCNB1/CDK1 complex that facilitates G2/M transition. Moreover, Foxk1 and Foxk2 promote cardiomyocyte proliferation by upregulating HIF1α expression, which enhances glycolysis and the pentose phosphate pathway (PPP), which further favors cardiomyocyte proliferation. These findings establish Foxk1 and Foxk2 as promising therapeutic targets for cardiac injury.

Harnessing native blueprints for designing bioinks to bioprint functional cardiac tissue

Cardiac tissue lacks regenerative capacity, making heart transplantation the primary treatment for end-stage heart failure. Engineered cardiac tissues developed through three-dimensional bioprinting (3DBP) offer a promising alternative. However, reproducing the native structure, cellular diversity, and functionality of cardiac tissue requires advanced cardiac bioinks. Major obstacles in CTE (cardiac tissue engineering) include accurately characterizing bioink properties, replicating the cardiac microenvironment, and achieving precise spatial organization. Optimizing bioink properties to closely mimic the extracellular matrix (ECM) is essential, as deviations may result in pathological effects. This review encompasses the rheological and electromechanical properties of bioinks and the function of the cardiac microenvironment in the design of functional cardiac constructs. Furthermore, it focuses on improving the rheological characteristics, printability, and functionality of bioinks, offering valuable perspectives for developing new bioinks especially designed for CTE.

Calcium-Activated Sarcomere Contractility Drives Cardiomyocyte Maturation and the Response to External Mechanical Cues but is Dispensable for Sarcomere Formation

Background

Understanding the mechanisms of cardiomyocyte development is critical for fulfilling the potential of induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). Although myocyte development is known to depend on internal and external mechanical cues, further investigation is required to understand the contributions of different signals and how they are integrated together to generate an adult cardiomyocyte. Here, we address this gap by examining the role of calcium-activated contractility in sarcomere formation and maturation and its influence on the iPSC-CM response to nanopatterns.

Methods

We generated iPSCs with homozygous D65A cardiac troponin C (cTnC) mutations. This mutation prevents calcium binding to site II of cTnC, resulting in tropomyosin blocking strong myosin binding to the thin filament and inhibiting sarcomere contraction. The iPSCs were differentiated into cardiomyocytes and matured in culture over 60 days. Cells were characterized via fluorescence imaging and calcium transient analysis. WT and mutant proteomes were examined via mass spectrometry throughout differentiation and maturation. We also replated partially matured cardiomyocytes onto nanopatterned surfaces to investigate how external mechanical signals affect maturation in contractile versus non-contractile cells.

Results

Surprisingly, we found that sarcomeres formed in the cTnC D65A cardiomyocytes, though these sarcomeres were underdeveloped and disorganized. Mutant cardiomyocytes also exhibited significant proteomic maturation defects and abnormal calcium transients. Plating D65A cardiomyocytes on nanopatterns improved structural and proteomic maturation. However, plating WT cardiomyocytes on nanopatterns led to a reduction in sarcomeric and oxidative phosphorylation protein content.

Conclusions

Calcium-activated contractility is dispensable for sarcomerogenesis but critical for cardiomyocyte maturation. In non-contractile, mutant cardiomyocytes, nanopatterns enhance maturation, suggesting that external mechanical cues may partially compensate for defective contractility. However, nanopatterns did not facilitate WT maturation and may have hindered it. In addition to these novel findings, these large mass spectrometry datasets cataloging iPSC-CM maturation represent a useful resource for the cardiovascular community.

A systematic review and embryological perspective of pluripotent stem cell-derived autonomic postganglionic neuron differentiation for human disease modeling

Human autonomic neuronal cell models are emerging as tools for modeling diseases such as cardiac arrhythmias. In this systematic review, we compared 33 articles applying 14 different protocols to generate sympathetic neurons and 3 different procedures to produce parasympathetic neurons. All methods involved the differentiation of human pluripotent stem cells, and none employed permanent or reversible cell immortalization. Almost all protocols were reproduced in multiple pluripotent stem cell lines, and over half showed evidence of neural firing capacity. Common limitations in the field are a lack of three-dimensional models and models that include multiple cell types. Sympathetic neuron differentiation protocols largely mirrored embryonic development, with the notable absence of migration, axon extension, and target-specificity cues. Parasympathetic neuron differentiation protocols may be improved by including several embryonic cues promoting cell survival, cell maturation, or ion channel expression. Moreover, additional markers to define parasympathetic neurons in vitro may support the validity of these protocols. Nonetheless, four sympathetic neuron differentiation protocols and one parasympathetic neuron differentiation protocol reported more than two-thirds of cells expressing autonomic neuron markers. Altogether, these protocols promise to open new research avenues of human autonomic neuron development and disease modeling.

α-Catenin force-sensitive binding and sequestration of LZTS2 leads to cytokinesis failure

Epithelial cells can become polyploid upon tissue injury, but mechanosensitive cues that trigger this state are poorly understood. Using an Madin Darby Canine Kidney (MDCK) cell knock-out/reconstitution system, we show that α-catenin mutants that alter force-sensitive binding to F-actin or middle (M)-domain promote cytokinesis failure and binucleation, particularly near epithelial wound-fronts. We identified Leucine Zipper Tumor Suppressor 2 (LZTS2), a factor previously implicated in abscission, as a conformation sensitive proximity partner of α-catenin. We show that LZTS2 enriches not only at midbody/intercellular bridges but also at apical adhering junctions. α-Catenin mutants with persistent M-domain opening show elevated junctional enrichment of LZTS2 compared with wild-type cells. LZTS2 knock-down leads to elevated rates of binucleation. These data implicate LZTS2 as a mechanosensitive effector of α-catenin that is critical for cytokinetic fidelity. This model rationalizes how persistent mechanoactivation of α-catenin may drive tension-induced polyploidization of epithelia after injury and suggests an underlying mechanism for how pathogenic α-catenin M-domain mutations drive macular dystrophy.

Self-organization of conducting pathways explains complex wave trajectories in procedurally interpolated fibrotic cardiac tissue: A virtual replica study

In precision cardiology, virtual replicas (VRs) hold promise for predicting arrhythmias by leveraging patient-specific data and biophysics knowledge. A crucial first step is creating VRs of cardiac tissue based on retrospective patient data. However, VRs aim to replicate biopotential conduction directly, whereas only non-invasive methods are feasible for clinical use on real organs and tissues. This discrepancy challenges our understanding of VR applicability limits. This study aims to enhance the mathematical template of VR by developing an in vitro validation complement. We performed a frame-by-frame comparison of in vitro optical mapping of biopotential conduction with VR predictions. Patient-specific self-organized tissue samples from human induced pluripotent stem cell-derived cardiomyocytes (CMs) with diffuse fibrosis were utilized as VR prototypes. High-resolution optical mapping recordings (Δx = 117 ± 4 μm, Δt = 7.69 ms) and immunostaining were used to reproduce fibrotic samples of linear size 7.5 mm. We applied data-driven Bayesian optimization of the Cellular Potts model (CPM) to study wave propagation at the subcellular level. The modified CPM accurately reflected the "perinatal window" until the 20th day of differentiation, affecting CMs' self-organization. The percolation threshold of virtual conductive pathways reached 0.26 (0.27 ± 0.03 of CMs in vitro), yielding a spatial correlation of amplitude maps with Pearson's coefficients of 0.83 ± 0.02. As a proof-of-concept, we demonstrated that CPM-enhanced VR could predict wavefront trajectories in optical mapping recordings, showing that approximating fibrosis distribution is crucial for improving VR prediction accuracy.

Integrating melt electrospinning writing and microfluidics to engineer a human cardiac microenvironment for high-fidelity drug screening

The preclinical evaluation of drug-induced cardiotoxicity is critical for developing novel drug, helping to avoid drug wastage and post-marketing withdrawal. Although human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) and the engineered heart organoid have been used for drug screening and mimicking disease models, they are always limited by the immaturity and lack of functionality of the cardiomyocytes. In this study, we constructed a Cardiomyocytes-on-a-Chip (CoC) that combines micro-grooves (MGs) and circulating mechanical stimulation to recapitulate the well-organized structure and stable beating of myocardial tissue. The phenotypic changes and maturation of CMs cultured on the CoC have been verified and can be used for the evaluation of cardiotoxicity and cardioprotective drug responses. Taken together, these results highlight the ability of our myocardial microarray platform to accurately reflect clinical behaviour, underscoring its potential as a powerful pre-clinical tool for assessing drug response and toxicity.

Molecular and cellular neurocardiology in heart disease

This paper updates and builds on a previous White Paper in this journal that some of us contributed to concerning the molecular and cellular basis of cardiac neurobiology of heart disease. Here we focus on recent findings that underpin cardiac autonomic development, novel intracellular pathways and neuroplasticity. Throughout we highlight unanswered questions and areas of controversy. Whilst some neurochemical pathways are already demonstrating prognostic viability in patients with heart failure, we also discuss the opportunity to better understand sympathetic impairment by using patient specific stem cells that provides pathophysiological contextualization to study 'disease in a dish'. Novel imaging techniques and spatial transcriptomics are also facilitating a road map for target discovery of molecular pathways that may form a therapeutic opportunity to treat cardiac dysautonomia.

Engineering Highly Aligned and Densely Populated Cardiac Muscle Bundles via Fibrin Remodeling in 3D-Printed Anisotropic Microfibrous Lattices

Replicating the structural and functional features of native myocardium, particularly its high-density cellular alignment and efficient electrical connectivity, is essential for engineering functional cardiac tissues. Here, novel electrohydrodynamically printed InterPore microfibrous lattices with anisotropic architectures are introduced to promote high-density cellular alignment and enhanced tissue interconnectivity. The interconnected pores in the microfibrous lattice enable dynamic, cell-mediated remodeling of fibrous hydrogels, resulting in continuous, mechanically stable tissue bundles. Compared to lattices with isolated pores, the engineered aligned cardiac tissues from neonatal rat cardiomyocytes exhibit improved electrophysiological properties and synchronous contractions. Using a multiseeding strategy, an equivalent cell seeding density of 8 × 107 cells mL-1, facilitating the formation of multicellular, vascularized cardiac structures with maintained tissue viability and integrity, is achieved. As a demonstration, human-induced pluripotent stem cell-derived cardiac tissues are engineered with progressive maturation and functional integration over time. These findings underscore the potential of InterPore microfibrous lattices for applications in cardiac tissue engineering, drug discovery, and therapeutic development.

3D-Printed Myocardium-Specific Structure Enhances Maturation and Therapeutic Efficacy of Engineered Heart Tissue in Myocardial Infarction

Despite advancements in engineered heart tissue (EHT), challenges persist in achieving accurate dimensional accuracy of scaffolds and maturing human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), a primary source of functional cardiac cells. Drawing inspiration from cardiac muscle fiber arrangement, a three-dimensional (3D)-printed multi-layered microporous polycaprolactone (PCL) scaffold is created with interlayer angles set at 45° to replicate the precise structure of native cardiac tissue. Compared with the control group and 90° PCL scaffolds, the 45° PCL scaffolds exhibited superior biocompatibility for cell culture and improved hiPSC-CM maturation in calcium handling. RNA sequencing demonstrated that the 45° PCL scaffold promotes the mature phenotype in hiPSC-CMs by upregulating ion channel genes. Using the 45° PCL scaffold, a multi-cellular EHT is successfully constructed, incorporating human cardiomyocytes, endothelial cells, and mesenchymal stem cells. These complex EHTs significantly enhanced hiPSC-CM engraftment in vivo, attenuated ventricular remodeling, and improved cardiac function in mouse myocardial infarction. In summary, the myocardium-specific structured EHT developed in this study represents a promising advancement in cardiovascular regenerative medicine.

TAOK1 suppression improves doxorubicin-induced cardiomyopathy by preventing cardiomyocyte death and dysfunction

AIMS

Doxorubicin (DOX) is one of the most effective chemotherapeutic agents for various types of cancers. However, DOX often causes cardiotoxicity, which is referred to as DOX-induced cardiomyopathy (DIC). Despite extensive research, only a limited number of effective treatments are currently available. In this study, we aimed to identify a potential therapeutic target for DIC by preventing DOX-induced cell injury in cardiomyocytes.

METHODS AND RESULTS

We performed a kinome-wide CRISPR gene knockout screen in human cardiomyocytes derived from pluripotent stem cells (hPSC-CMs) and identified a member of the STE20 kinase family, thousand and one amino acid protein kinase 1 (TAOK1) as a potential regulator of DOX-induced cardiomyocyte death. Using CRISPR-mediated gene knockout and siRNA-mediated gene knockdown, we demonstrated that TAOK1 suppression improved DOX-induced cardiomyocyte death and dysfunction, including sarcomere disarray, contractile dysfunction, DNA damage, and mitochondrial dysfunction in hPSC-CMs. Transcriptome analysis using RNA-Seq also showed that DOX-induced mitochondrial dysfunction was attenuated by TAOK1 suppression. In contrast to the protective role of TAOK1 against DOX toxicity in cardiomyocytes, TAOK1 suppression did not induce DOX resistance in human cancer cell lines. DOX-induced activation of p38 MAPK was markedly attenuated in TAOK1-knockout hPSC-CMs. Furthermore, DOX-induced cardiomyocyte death and disruption of mitochondrial membrane potential were augmented by TAOK1 overexpression, which was partially attenuated by an inhibitor or knockdown of p38 MAPK or an apoptosis inhibitor. Finally, we demonstrated that TAOK1 suppression using AAV-mediated gene silencing attenuated DOX-induced myocardial damage, including myocardial fibrosis, apoptosis, and cardiomyocyte atrophy, resulting in improved cardiac function in a mouse model of DIC.

CONCLUSION

Our results indicate that TAOK1 suppression is a promising therapeutic approach for treating DIC in patients with cancer and highlight the advantages of hPSC-CMs as a platform to study drug-induced cardiotoxicity.

Clinical and Genetic Heterogeneity of HCM: The Possible Role of a Deletion Involving MYH6 and MYH7

BACKGROUND/OBJECTIVES

Pediatric hypertrophic cardiomyopathy (HCM) is the most common genetic myocardial disorder in children and a leading cause of sudden cardiac death (SCD) among the young. Its phenotypic variability, driven by incomplete penetrance and variable expressivity, presents significant challenges in diagnosis and clinical management.

METHODS

In this study, we report a unique case of a 16-month-old female diagnosed with HCM caused by a rare genetic deletion. Molecular analysis was performed using a multigene panel and chromosomal microarray analysis (CMA).

RESULTS

Molecular tests identified a 30 kb deletion encompassing the MYH6 and MYH7 genes. These genes are critical components of sarcomeric architecture, with known associations to HCM and other cardiomyopathies.

CONCLUSIONS

This case underscores the clinical and genetic heterogeneity of HCM, highlighting the importance of considering genomic deletions involving key sarcomeric genes in the diagnostic evaluation.

Cardiomyocytes in Hypoxia: Cellular Responses and Implications for Cell-Based Cardiac Regenerative Therapies

Myocardial infarction (MI) is a severe hypoxic event, resulting in the loss of up to one billion cardiomyocytes (CMs). Due to the limited intrinsic regenerative capacity of the heart, cell-based regenerative therapies, which feature the implantation of stem cell-derived cardiomyocytes (SC-CMs) into the infarcted myocardium, are being developed with the goal of restoring lost muscle mass, re-engineering cardiac contractility, and preventing the progression of MI into heart failure (HF). However, such cell-based therapies are challenged by their susceptibility to oxidative stress in the ischemic environment of the infarcted heart. To maximize the therapeutic benefits of cell-based approaches, a better understanding of the heart environment at the cellular, tissue, and organ level throughout MI is imperative. This review provides a comprehensive summary of the cardiac pathophysiology occurring during and after MI, as well as how these changes define the cardiac environment to which cell-based cardiac regenerative therapies are delivered. This understanding is then leveraged to frame how cell culture treatments may be employed to enhance SC-CMs' hypoxia resistance. In this way, we synthesize both the complex experience of SC-CMs upon implantation and the engineering techniques that can be utilized to develop robust SC-CMs for the clinical translation of cell-based cardiac therapies.

Enhancing Cardiomyocyte Purity through Lactate-Based Metabolic Selection

BACKGROUND

Direct reprogramming of fibroblasts into chemically induced cardiomyocyte-like cells (CiCMs) through small molecules presents a promising cell source for cardiac regeneration and therapeutic development. However, the contaminating non-cardiomyocytes, primarily unconverted fibroblasts, reduce the effectiveness of CiCMs in various applications. This study investigated a metabolic selection approach using lactate to enrich CiCMs by exploiting the unique metabolic capability of cardiomyocytes to utilize lactate as an alternative energy source.

METHODS

Primary mouse embryonic fibroblasts (pMEFs) were reprogrammed into CiCMs and subjected to a glucose-depleted, lactate-supplemented medium for 4 days. Afterward, cell viability was analyzed, and cardiomyocyte efficiency was assessed through the expression of cardiac-specific markers. Additionally, electrophysiological function was evaluated by examining drug-induced responses.

RESULTS

The lactate treatment led to a significant decrease in the viability of non-cardiomyocytes (pMEF-LAC), while CiCMs (CiCM-LAC) showed minimal cell death. Specifically, the expression of all cardiac-related markers was increased in CiCM-LAC. Metabolically purified CiCMs exhibited enhanced contractile force and increased contraction frequency compared to non-purified CiCMs, as well as an elevated responsiveness to drugs.

CONCLUSION

This study demonstrates that lactate-based metabolic selection is an effective and practical approach for enriching CiCMs, offering a cost-effective alternative to other purification methods. The application of this strategy could potentially broaden the accessibility and utility of reprogrammed cardiomyocytes in cardiac regeneration and therapeutic development.

Applications of carbon dot-mediated cardiomyocyte maturation in regenerative medicine: a review

The maturation of cardiomyocytes (CMs) plays key roles in regenerative medicine and the treatment of cardiovascular diseases via stem cell-derived CMs. Carbon dots (CDs) have good biocompatibility, optical properties, and electrophysical properties and have been widely applied in bioimaging, biosensors, and biotherapy. In this review, we comprehensively summarize recent advances in promoting the maturation of CMs, mainly human pluripotent stem cell-derived CMs, and related regenerative medicine. Moreover, we explore the innovative application of CDs to enhance the maturation of these CMs. Finally, we look forward to the future design and application of CDs in the maturation of CMs in terms of cell therapies.

Heart-on-a-chip: a revolutionary organ-on-chip platform for cardiovascular disease modeling

Heart-on-a-chip (HoC) devices have emerged as a powerful tool for studying the human heart's intricate functions and dysfunctions in vitro. Traditional preclinical models, such as 2D cell cultures model and animal model, have limitations in accurately predicting human response to cardiovascular diseases and treatments. The HoC approach addresses these shortcomings by recapitulating the microscale anatomy, physiology, and biomechanics of the heart, thereby providing a more clinically relevant platform for drug testing, disease modeling, and personalized therapy. Recent years have seen significant strides in HoC technology, driven by advancements in biomaterials, bioelectronics, and tissue engineering. Here, we first review the construction and on-chip detection in HoC. Then we introduce the current proceedings of in vitro models for studying cardiovascular diseases (CVD) based on the HoC platform, including ischemia and myocardial infarction, cardiac fibrosis, cardiac scar, myocardial hypertrophy and other CVD models. Finally, we discuss the future directions of HoC and related emerging technologies.

Aromatherapy and Essential Oils: Holistic Strategies in Complementary and Alternative Medicine for Integral Wellbeing

Complementary and alternative medicine (CAM) encompasses a variety of ancient therapies with origins in cultures such as those of China, Egypt, Greece, Iran, India, and Rome. The National Institutes of Health (NIH) classifies these integrative therapies into five categories: (1) mind-body therapies, (2) biological practices, (3) manipulative and body practices, (4) energy medicine, and (5) whole medical systems, including traditional Chinese medicine and Ayurvedic medicine. This review explores the role of biological practices utilizing aromatic plants, particularly through inhalation aromatherapy and massage with essential oils, as effective complementary strategies within health systems. The review compiles information on the most commonly used plants and essential oils for holistic health maintenance from a complementary and alternative perspective. Given their accessibility and relative safety compared to conventional treatments, these therapies have gained popularity worldwide. Furthermore, the integration of essential oils has been shown to alleviate various psychological and physiological symptoms, including anxiety, depression, fatigue, sleep disorders, neuropathic pain, nausea, and menopausal symptoms. Among the studied plants, lavender has emerged as being particularly notable due to its broad spectrum of therapeutic effects and its designation by the US Food and Drug Administration (FDA) as "Generally Recognized as Safe". Other essential oils under investigation include eucalyptus, damask rose, sandalwood, vetiver, calamus, frankincense, chamomile, lemon, grapefruit, tangerine, orange, sage, rosemary, garlic, and black pepper. This study emphasizes the potential benefits of these aromatic plants in enhancing patient well-being. Additionally, it underscores the importance of conducting further research to ensure the safety and efficacy of these therapies.

Molecular Regulation of Cardiomyocyte Maturation

PURPOSE OF THE REVIEW

This review aims to discuss the process of cardiomyocyte maturation, with a focus on the underlying molecular mechanisms required to form a fully functional heart. We examine both long-standing concepts associated with cardiac maturation and recent developments, and the overall complexity of molecularly integrating all the processes that lead to a mature heart.

RECENT FINDINGS

Cardiac maturation, defined here as the sequential changes that occurring before the heart reaches full maturity, has been a subject of investigation for decades. Recently, there has been a renewed, highly focused interest in this process, driven by clinically motivated research areas where enhancing maturation may lead to improved therapeutic opportunities. These include using pluripotent stem cell models for cell therapy and disease modeling, as well as recent advancements in adult cardiac regeneration approaches. We highlight key processes underlying maturation of the heart, including cellular and organ growth, and electrophysiological, metabolic, and contractile maturation. We further discuss how these processes integrate and interact to contribute to the overall complexity of the developing heart. Finally, we emphasize the transformative potential for translating relevant maturation concepts to emerging models of heart disease and regeneration.

Bioprinting approaches in cardiac tissue engineering to reproduce blood-pumping heart function

The heart, with its complex structural and functional characteristics, plays a critical role in sustaining life by pumping blood throughout the entire body to supply nutrients and oxygen. Engineered heart tissues have been introduced to reproduce heart functions to understand the pathophysiological properties of the heart and to test and develop potential therapeutics. Although numerous studies have been conducted in various fields to increase the functionality of heart tissue to be similar to reality, there are still many difficulties in reproducing the blood-pumping function of the heart. In this review, we discuss advancements in cells, biomaterials, and biofabrication in cardiac tissue engineering to achieve cardiac models that closely mimic the pumping function. Moreover, we provide insight into future directions by proposing future perspectives to overcome remaining challenges, such as scaling up and biomimetic patterning of blood vessels and nerves through bioprinting.

Deubiquitinase MYSM1 drives myocardial ischemia/reperfusion injury by stabilizing STAT1 in cardiomyocytes

Rationale: Myocardial ischemia/reperfusion (I/R) injury leads to irreversible cardiomyocyte death and aggravates myocardial infarction. Deubiquitinating enzymes (DUBs) are essential for maintaining substrate protein stability and functionality, playing significant roles in cardiac pathophysiology. In this study, we aimed to clarify the regulatory role of a DUB, Myb-like, SWIRM, and MPN domains 1 protein (MYSM1), in myocardial I/R injury and explore the molecular mechanism behind. Methods and Results: Firstly, it was found that the expression of MYSM1 positively correlates with myocardial I/R injury. Genetic knockdown of MYSM1 significantly conferred protection against I/R injury in hearts. Correspondingly, AAV9-mediated cardiomyocyte-specific knockdown of MYSM1 had a therapeutic effect on myocardial I/R injury. Through a comprehensive proteome-wide quantitative analysis, we identified signal transducer and activator of transcription 1 (STAT1) as the direct substrate of MYSM1. Mechanistically, MYSM1 mediated the K63-linked deubiquitination and stabilization of STAT1 at position K379 via its MPN metalloprotease domain. Additionally, MYSM1 initiates the expression of necroptosis-related genes by promoting the transcription factor function of STAT1. Conclusion: This study illustrated a MYSM1-STAT1 axis in regulating myocardial I/R injury and identified MYSM1 as a pharmacological target for myocardial I/R injury.

Pluripotent stem-cell-derived therapies in clinical trial: A 2025 update

Since the first derivation of human pluripotent stem cells (hPSCs) 27 years ago, technologies to control their differentiation and manufacturing have advanced immensely, enabling increasing numbers of clinical trials with hPSC-derived products. Here, we revew the landscape of interventional hPSC trials worldwide, highlighting available data on clinical safety and efficacy. As of December 2024, we identify 116 clinical trials with regulatory approval, testing 83 hPSC products. The majority of trials are targeting eye, central nervous system, and cancer. To date, more than 1,200 patients have been dosed with hPSC products, accumulating to >1011 clinically administered cells, so far showing no generalizable safety concerns.

Wearable electrodriven switch actively delivers macromolecular drugs to fundus in non-invasive and controllable manners

Current treatments for fundus disorders, such as intravitreal injections, pose risks, including infection and retinal detachment, and are limited in their ability to deliver macromolecular drugs across the blood‒retinal barrier. Although non-invasive methods are safer, their delivery efficiency remains suboptimal (<5%). We have developed a wearable electrodriven switch (WES) that improves the non-invasive delivery of macromolecules to the fundus. The WES system, which integrates an electrodriven drug delivery lens with a square wave generator, leverages electrical stimulation to enhance drug penetration through the sclera-choroid-retina pathway. In our study, WES achieved a delivery efficiency of 14% for immunoglobulin G, comparable to that of intravitreal injection (16%). Moreover, WES-enhanced anti-VEGF administration resulted in an 86% inhibition of choroidal neovascularization, and anti-PDL1 delivery inhibited choroidal melanoma growth more effectively than intravenous injections, with no adverse effects on ocular health. These findings suggest that WES holds transformative potential for the non-invasive treatment of chronic fundus diseases.

Induced pluripotent stem cell-derived cardiomyocyte in vitro models: benchmarking progress and ongoing challenges

Recent innovations in differentiating cardiomyocytes from human induced pluripotent stem cells (hiPSCs) have unlocked a viable path to creating in vitro cardiac models. Currently, hiPSC-derived cardiomyocytes (hiPSC-CMs) remain immature, leading many in the field to explore approaches to enhance cell and tissue maturation. Here, we systematically analyzed 300 studies using hiPSC-CM models to determine common fabrication, maturation and assessment techniques used to evaluate cardiomyocyte functionality and maturity and compiled the data into an open-access database. Based on this analysis, we present the diversity of, and current trends in, in vitro models and highlight the most common and promising practices for functional assessments. We further analyzed outputs spanning structural maturity, contractile function, electrophysiology and gene expression and note field-wide improvements over time. Finally, we discuss opportunities to collectively pursue the shared goal of hiPSC-CM model development, maturation and assessment that we believe are critical for engineering mature cardiac tissue.

Conductive Microfibers Improve Stem Cell-Derived Cardiac Spheroid Maturation

Conventional two-dimensional (2D) cardiomyocyte differentiation protocols create cells with limited maturity, which impairs their predictive capacity and has driven interest in three-dimensional (3D) engineered cardiac tissue models of varying maturity and scalability. Cardiac spheroids are attractive high-throughput models that have demonstrated improved functional and transcriptional maturity over conventional 2D differentiations. However, these 3D models still tend to have limited contractile and electrical maturity compared to highly engineered cardiac tissues; hence, we incorporated a library of conductive polymer microfibers in cardiac spheroids to determine if fiber properties could accelerate maturation. Conductive microfibers improved contractility parameters of cardiac spheroids over time versus nonconductive fibers, specifically, when they were short, for example, 5 μm, and when there was moderate fiber mass per spheroid, for example, 20 μg. Spheroids with optimal conductive microfiber length and concentration developed a thicker ring-like perimeter and a less compacted cavity, improving their contractile work compared to control cardiac spheroids. Functional improvements correlated with increased expression of contractility and calcium handling-related cardiac proteins, as well as improved calcium handling abilities and drug response. Taken together, these data suggest that conductive microfibers can improve cardiac spheroid performance to improve cardiac disease modeling.

Global Knowledge Map and Emerging Research Trends in Induced Pluripotent Stem Cells and Hereditary Diseases: A CiteSpace-based Visualization and Analysis

The rise of induced pluripotent stem cells (iPSCs) technology has ushered in a landmark shift in the study of hereditary diseases. However, there is a scarcity of reports that offer a comprehensive and objective overview of the current state of research at the intersection of iPSCs and hereditary diseases. Therefore, this study endeavors to categorize and synthesize the publications in this field over the past decade through bibliometric methods and visual knowledge mapping, aiming to visually analyze their research focus and clinical trends. The English language literature on iPSCs and hereditary diseases, published from 2014 to 2023 in the Web of Science Core Collection (WoSCC), was examined. The CiteSpace (version 6.3.R1) software was utilized to visualize and analyze country/region, institution, scholar, co-cited authors, and co-cited journals. Additionally, the co-occurrence, clustering, and bursting of co-cited references were displayed. Analysis of 347 articles that met the inclusion criteria revealed a steady increase in the number of published articles and citation frequency in the field over the past decade. With regard to the countries/regions, institutions, scholars, and journals where the articles were published, the highest numbers were found in the USA, the University of California System, Suren M. Zakian, and Stem Cell Research, respectively. The current research is focused on the construction of disease models, both before and after correction, as well as drug target testing for single-gene hereditary diseases. Chromosome transplantation genomic therapy for hereditary diseases with abnormal chromosome structures may emerge as a future research hotspot in this field.

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.

The Future of Biohybrid Regenerative Bioelectronics

Biohybrid regenerative bioelectronics are an emerging technology combining implantable devices with cell transplantation. Once implanted, biohybrid regenerative devices integrate with host tissue. The combination of transplant and device provides an avenue to both replace damaged or dysfunctional tissue, and monitor or control its function with high precision. While early challenges in the fusion of the biological and technological components limited development of biohybrid regenerative technologies, progress in the field has resulted in a rapidly increasing number of applications. In this perspective the great potential of this emerging technology for the delivery of therapy is discussed, including both recent research progress and potential new directions. Then the technology barriers are discussed that will need to be addressed to unlock the full potential of biohybrid regenerative devices.

Deubiquitinase MYSM1 promotes doxorubicin-induced cardiotoxicity by mediating TRIM21-ferroptosis axis in cardiomyocytes

Anthracycline antitumor drug doxorubicin (DOX) induces severe cardiotoxicity. Deubiquitinating enzymes (DUBs) are crucial for protein stability and function and play a significant role in cardiac pathophysiology. By comparing RNA sequencing datasets and conducting functional screening, we determined that Myb-like, SWIRM, and MPN domains 1 (MYSM1) is a key regulator of DOX-induced cardiotoxicity. In this study, we aimed to explore the function and regulatory mechanisms of MYSM1 in DOX-induced cardiotoxicity. Genetic knockdown of MYSM1 significantly mitigated DOX-induced cardiomyopathy. Correspondingly, cardiomyocyte-specific knockdown of MYSM1 by AAV9 protected the heart from DOX-induced cardiotoxicity. Gain- and loss-of-function analysis verified that MYSM1 mediated DOX-induced cardiomyocyte injury in vitro. Through a Co-IP combined with LC-MS/MS analysis, we discovered that MYSM1 directly interacted with tripartite motif-containing protein 21 (TRIM21). Mechanistic investigations revealed that MYSM1 regulates the deubiquitination and the stability of TRIM21 via its MPN domain. Furthermore, MYSM1 exacerbated DOX-induced cardiotoxicity by enhancing ferroptosis. This study identified MYSM1 as a potential therapeutic target for DOX-induced cardiotoxicity and illustrated a MYSM1-TRIM21-ferroptosis axis in regulating DOX-induced cardiotoxicity.

The Wilms' Tumor Suppressor WT1 in Cardiomyocytes: Implications for Cardiac Homeostasis and Repair

The Wilms' tumor suppressor WT1 is essential for the development of the heart, among other organs such as the kidneys and gonads. The Wt1 gene encodes a zinc finger transcription factor that regulates proliferation, cellular differentiation processes, and apoptosis. WT1 is also involved in cardiac homeostasis and repair. In adulthood, WT1-expression levels are lower compared to those observed through development, and WT1 expression is restricted to a few cell types. However, its systemic deletion in adult mice is lethal, demonstrating that its presence is also key for organ maintenance. In response to injury, the epicardium re-activates the expression of WT1, but little is known about the roles it plays in cardiomyocytes, which are the main cell type affected after myocardial infarction. The fact that cardiomyocytes exhibit a low proliferation rate in the adult heart in mammals highlights the need to explore new approaches for cardiac regeneration. The aim of this review is to emphasize the functions carried out by WT1 in cardiomyocytes in cardiac homeostasis and heart regeneration.

Enhancing the Maturation of Human Pluripotent Stem Cell-Derived Cardiomyocytes with an n-Type Organic Semiconductor Coating

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) are a promising cell source for cardiac regenerative medicine and in vitro modeling. However, hPSC-CMs exhibit immature structural and functional properties compared with adult cardiomyocytes. Various electrical, mechanical, and biochemical cues have been applied to enhance hPSC-CM maturation but with limited success. In this work, we investigated the potential application of the semiconducting polymer poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2)) as a light-sensitive material to stimulate hPSC-CMs optically. Our results indicated that P(NDI2OD-T2)-mediated photostimulation caused cell damage at irradiances applied long-term above 36 μW/mm2 and did not regulate cardiac monolayer beating (after maturation) at higher intensities applied in a transient fashion. However, we discovered that the cells grown on P(NDI2OD-T2)-coated substrates showed significantly enhanced expression of cardiomyocyte maturation markers in the absence of a light exposure stimulus. A combination of techniques, such as atomic force microscopy, scanning electron microscopy, and quartz crystal microbalance with dissipation monitoring, which we applied to investigate the interface of the cell with the n-type coating, revealed that P(NDI2OD-T2) impacted the nanostructure, adsorption, and viscoelasticity of the Matrigel coating used as a cell adhesion promoter matrix. This modified cellular microenvironment promoted the expression of cardiomyocyte maturation markers related to contraction, calcium handling, metabolism, and conduction. Overall, our findings demonstrate that conjugated polymers such as P(NDI2OD-T2) can be used as passive coatings to direct stem cell fate through interfacial engineering of cell growth substrates.

Fabrication of chitin-fibrin hydrogels to construct the 3D artificial extracellular matrix scaffold for vascular regeneration and cardiac tissue engineering

As the cornerstone of tissue engineering and regeneration medicine research, developing a cost-effective and bionic extracellular matrix (ECM) that can precisely modulate cellular behavior and form functional tissue remains challenging. An artificial ECM combining polysaccharides and fibrillar proteins to mimic the structure and composition of natural ECM provides a promising solution for cardiac tissue regeneration. In this study, we developed a bionic hydrogel scaffold by combining a quaternized β-chitin derivative (QC) and fibrin-matrigel (FM) in different ratios to mimic a natural ECM. We evaluated the stiffness of those composite hydrogels with different mixing ratios and their effects on the growth of human umbilical vein endothelial cells (HUVECs). The optimal hydrogels, QCFM1 hydrogels were further applied to load HUVECs into nude mice for in vivo angiogenesis. Besides, we encapsulated human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) into QCFM hydrogels and employed 3D bioprinting to achieve batch fabrication of human-engineered heart tissue (hEHT). Finally, the myocardial structure and electrophysiological function of hEHT were evaluated by immunofluorescence and optical mapping. Designed artificial ECM has a tunable modulus (220-1380 Pa), which determines the different cellular behavior of HUVECs when encapsulated in these. QCFM1 composite hydrogels with optimal stiffness (800 Pa) and porous architecture were finally identified, which could adapt for in vitro cell spreading and in vivo angiogenesis of HUVECs. Moreover, QCFM1 hydrogels were applied in 3D bioprinting successfully to achieve batch fabrication of both ring-shaped and patch-shaped hEHT. These QCFM1 hydrogels-based hEHTs possess organized sarcomeres and advanced function characteristics comparable to reported hEHTs. The chitin-derived hydrogels are first used for cardiac tissue engineering and achieve the batch fabrication of functionalized artificial myocardium. Specifically, these novel QCFM1 hydrogels provided a reliable and economical choice serving as ideal ECM for application in tissue engineering and regeneration medicine.

The importance of matrix in cardiomyogenesis: Defined substrates for maturation and chamber specificity

Human embryonic stem cell-derived cardiomyocytes (hESC-CM) are a promising source of cardiac cells for disease modelling and regenerative medicine. However, current protocols invariably lead to mixed population of cardiac cell types and often generate cells that resemble embryonic phenotypes. Here we developed a combinatorial approach to assess the importance of extracellular matrix proteins (ECMP) in directing the differentiation of cardiomyocytes from human embryonic stem cells (hESC). We did this by focusing on combinations of ECMP commonly found in the developing heart with a broad goal of identifying combinations that promote maturation and influence chamber specific differentiation. We formulated 63 unique ECMP combinations fabricated from collagen 1, collagen 3, collagen 4, fibronectin, laminin, and vitronectin, presented alone and in combinations, leading to the identification of specific ECMP combinations that promote hESC proliferation, pluripotency, and germ layer specification. When hESC were subjected to a differentiation protocol on the ECMP combinations, it revealed precise protein combinations that enhance differentiation as determined by the expression of cardiac progenitor markers kinase insert domain receptor (KDR) and mesoderm posterior transcription factor 1 (MESP1). High expression of cardiac troponin (cTnT) and the relative expression of myosin light chain isoforms (MLC2a and MLC2v) led to the identification of three surfaces that promote a mature cardiomyocyte phenotype. Action potential morphology was used to assess chamber specificity, which led to the identification of matrices that promote chamber-specific cardiomyocytes. This study provides a matrix-based approach to improve control over cardiomyocyte phenotypes during differentiation, with the scope for translation to cardiac laboratory models and for the generation of functional chamber specific cardiomyocytes for regenerative therapies.

Improving cardiac differentiation of human pluripotent stem cells by targeting ferroptosis

Generation of cardiomyocytes from human pluripotent stem cells (hPSCs) is of high interest for disease modelling and regenerative medicine. hPSCs can provide an unlimited source of patient-specific cardiomyocytes that are otherwise difficult to obtain from individuals. Moreover, the low proliferation rate of adult cardiomyocytes and low viability ex vivo limits the quantity of study material. Most protocols for the differentiation of cardiomyocytes from hPSCs are based on the temporal modulation of the Wnt pathway. However, during the initial stage of GSK-3 inhibition, a substantial number of cells are lost due to detachment. In this study, we aimed to increase the efficiency of generating cardiomyocytes from hPSCs. We identified cell death as a detrimental factor during this initial stage of in vitro cardiomyocyte differentiation. Through pharmacological targeting of different types of cell death, we discovered that ferroptosis was the main cell death type during the first 48 h of the in vitro differentiation procedure. Inhibiting ferroptosis using ferrostatin-1 during cardiomyocyte differentiation resulted in increased robustness and cell yield.

The tRNA methyltransferase Mettl1 governs ketogenesis through translational regulation and drives metabolic reprogramming in cardiomyocyte maturation

After birth, the heart undergoes a shift in energy metabolism and cytoarchitecture to enhance efficient energy production and cardiac contraction, which is essential for postnatal development and growth. However, the precise mechanisms regulating this process remain elusive. Here we show that the RNA modification enzyme Mettl1 is a critical regulator of postnatal metabolic reprogramming and cardiomyocyte maturation in mice, primarily through its influence on the translation of the rate-limiting ketogenesis enzyme Hmgcs2. Our findings reveal that ketogenesis is vital for the postnatal transition of fuel from glucose to fatty acids in cardiomyocytes, achieved by modulating tricarboxylic acid cycle-related enzymatic activity via lysine β-hydroxybutyrylation protein modification. Loss of Mettl1 results in aberrant metabolic reprogramming and cardiomyocyte immaturity, leading to heart failure, although some clinical features can be rescued by β-hydroxybutyrate supplementation. Our study provides mechanistic insights into how Mettl1 regulates metabolic reprogramming in neonatal cardiomyocytes and highlights the importance of ketogenesis in cardiomyocyte maturation.

MitoMAMMAL: a genome scale model of mammalian mitochondria predicts cardiac and BAT metabolism

Motivation

Mitochondria are essential for cellular metabolism and are inherently flexible to allow correct function in a wide range of tissues. Consequently, dysregulated mitochondrial metabolism affects different tissues in different ways leading to challenges in understanding the pathology of mitochondrial diseases. System-level metabolic modelling is useful in studying tissue-specific mitochondrial metabolism, yet despite the mouse being a common model organism in research, no mouse specific mitochondrial metabolic model is currently available.

Results

Building upon the similarity between human and mouse mitochondrial metabolism, we present mitoMammal, a genome-scale metabolic model that contains human and mouse specific gene-product reaction rules. MitoMammal is able to model mouse and human mitochondrial metabolism. To demonstrate this, using an adapted E-Flux algorithm, we integrated proteomic data from mitochondria of isolated mouse cardiomyocytes and mouse brown adipocyte tissue, as well as transcriptomic data from in vitro differentiated human brown adipocytes and modelled the context specific metabolism using flux balance analysis. In all three simulations, mitoMammal made mostly accurate, and some novel predictions relating to energy metabolism in the context of cardiomyocytes and brown adipocytes. This demonstrates its usefulness in research in cardiac disease and diabetes in both mouse and human contexts.

Availability and implementation

The MitoMammal Jupyter Notebook is available at: https://gitlab.com/habermann_lab/mitomammal.

In situ reprogramming of cardiac fibroblasts into cardiomyocytes in mouse heart with chemicals

Cardiomyocytes are terminal differentiated cells and have limited ability to proliferate or regenerate. Condition like myocardial infarction causes massive death of cardiomyocytes and is the leading cause of death. Previous studies have demonstrated that cardiac fibroblasts can be induced to transdifferentiate into cardiomyocytes in vitro and in vivo by forced expression of cardiac transcription factors and microRNAs. Our previous study have demonstrated that full chemical cocktails could also induce fibroblast to cardiomyocyte transdifferentiation both in vitro and in vivo. With the development of tissue clearing techniques, it is possible to visualize the reprogramming at the whole-organ level. In this study, we investigated the effect of the chemical cocktail CRFVPTM in inducing in situ fibroblast to cardiomyocyte transdifferentiation with two strains of genetic tracing mice, and the reprogramming was observed at whole-heart level with CUBIC tissue clearing technique and 3D imaging. In addition, single-cell RNA sequencing (scRNA-seq) confirmed the generation of cardiomyocytes from cardiac fibroblasts which carries the tracing marker. Our study confirms the use of small molecule cocktails in inducing in situ fibroblast to cardiomyocyte reprogramming at the whole-heart level and proof-of-conceptly providing a new source of naturally incorporated cardiomyocytes to help heart regeneration.

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.

A critical review on advances and challenges of bioprinted cardiac patches

Myocardial infarction (MI), which causes irreversible myocardium necrosis, affects 0.25 billion people globally and has become one of the most significant epidemics of our time. Over the past few years, bioprinting has moved beyond a concept of simply incorporating cells into biomaterials, to strategically defining the microenvironment (e.g., architecture, biomolecular signalling, mechanical stimuli, etc.) within which the cells are printed. Among the different bioprinting applications, myocardial repair is a field that has seen some of the most significant advances towards the management of the repaired tissue microenvironment. This review critically assesses the most recent biomedical innovations being carried out in cardiac patch bioprinting, with specific considerations given to the biomaterial design parameters, growth factors/cytokines, biomechanical and bioelectrical conditioning, as well as innovative biomaterial-based "4D" bioprinting (3D scaffold structure + temporal morphology changes) of myocardial tissues, immunomodulation and sustained delivery systems used in myocardium bioprinting. Key challenges include the ability to generate large quantities of cardiac cells, achieve high-density capillary networks, establish biomaterial designs that are comparable to native cardiac extracellular matrix, and manage the sophisticated systems needed for combining cardiac tissue microenvironmental cues while simultaneously establishing bioprinting technologies yielding both high-speed and precision. This must be achieved while considering quality assurance towards enabling reproducibility and clinical translation. Moreover, this manuscript thoroughly discussed the current clinical translational hurdles and regulatory issues associated with the post-bioprinting evaluation, storage, delivery and implantation of the bioprinted myocardial patches. Overall, this paper provides insights into how the clinical feasibility and important regulatory concerns may influence the design of the bioink (biomaterials, cell sources), fabrication and post-fabrication processes associated with bioprinting of the cardiac patches. This paper emphasizes that cardiac patch bioprinting requires extensive collaborations from imaging and 3D modelling technical experts, biomaterial scientists, additive manufacturing experts and healthcare professionals. Further, the work can also guide the field of cardiac patch bioprinting moving forward, by shedding light on the potential use of robotics and automation to increase productivity, reduce financial cost, and enable standardization and true commercialization of bioprinted cardiac patches. STATEMENT OF SIGNIFICANCE: The manuscript provides a critical review of important themes currently pursued for heart patch bioprinting, including critical biomaterial design parameters, physiologically-relevant cardiac tissue stimulations, and newly emerging cardiac tissue bioprinting strategies. This review describes the limited number of studies, to date in the literature, that describe systemic approaches to combine multiple design parameters, including capabilities to yield high-density capillary networks, establish biomaterial composite designs similar to native cardiac extracellular matrix, and incorporate cardiac tissue microenvironmental cues, while simultaneously establishing bioprinting technologies that yield high-speed and precision. New tools such as artificial intelligence may provide the analytical power to consider multiple design parameters and identify an optimized work-flow(s) for enabling the clinical translation of bioprinted cardiac patches.

Compact lens-free imager using a thin-film transistor for long-term quantitative monitoring of stem cell culture and cardiomyocyte production

With advancements in human induced pluripotent stem cell (hiPSC) technology, there is an increasing demand for quality control techniques to manage the long-term process of target cell production effectively. While monitoring systems designed for use within incubators are promising for assessing culture quality, existing systems still face challenges in terms of compactness, throughput, and available metrics. To address these limitations, we have developed a compact and high-throughput lens-free imaging device named INSPCTOR. The device is as small as a standard culture plate, which allows for the installation of multiple units within an incubator. INSPCTOR utilises a large thin-film transistor image sensor, enabling simultaneous observation of six independent culture environments, each approximately 1 cm2. With this device, we successfully monitored the confluency of hiPSC cultures and identified the onset timing of epithelial-to-mesenchymal transition during mesodermal induction. Additionally, we quantified the beating frequency and conduction of hiPSC-derived cardiomyocytes by using high-speed imaging modes. This enabled us to identify the onset of spontaneous beating during differentiation and assess chronotropic responses in drug evaluations. Moreover, by tracking beating frequency over 10 days of cardiomyocyte maturation, we identified week-scale and daily-scale fluctuations, the latter of which correlated with cellular metabolic activity. The metrics derived from this device would enhance the reproducibility and quality of target cell production.

Exosomes Induce Crosstalk Between Multiple Types of Cells and Cardiac Fibroblasts: Therapeutic Potential for Remodeling After Myocardial Infarction

Recanalization therapy can significantly improve the prognosis of patients with acute myocardial infarction (AMI). However, infarction or reperfusion-induced cardiomyocyte death, immune cell infiltration, fibroblast proliferation, and scarring formation lead to cardiac remodeling and gradually progress to heart failure or arrhythmia, resulting in a high mortality rate. Due to the inability of cardiomyocytes to regenerate, the healing of infarcted myocardium mainly relies on the formation of scars. Cardiac fibroblasts, as the main effector cells involved in repair and scar formation, play a crucial role in maintaining the structural integrity of the heart after MI. Recent studies have revealed that exosome-mediated intercellular communication plays a huge role in myocardial repair and signaling transduction after myocardial infarction (MI). Exosomes can regulate the biological behavior of fibroblasts by activating or inhibiting the intracellular signaling pathways through their contents, which are derived from cardiomyocytes, immune cells, endothelial cells, mesenchymal cells, and others. Understanding the interactions between fibroblasts and other cell types during cardiac remodeling will be the key to breakthrough therapies. This review examines the role of exosomes from different sources in the repair process after MI injury, especially the impacts on fibroblasts during myocardial remodeling, and explores the use of exosomes in the treatment of myocardial remodeling after MI.

Near-infrared-triggered plasmonic regulation and cardiomyocyte-based biosensing system for in vitro bradyarrhythmia treatment

Bradyarrhythmia, a life-threatening cardiovascular disease, is an increasing burden for the healthcare system. Currently, surgery, implanted device, and drug are introduced to treat the bradyarrhythmia in clinical practice. However, these conventional therapeutic strategies suffer from the invasive surgery, power supply, or drug side effect, respectively, hence developing the alternative therapeutic strategy is necessarily imperative. Here, a convenient and effective strategy to treat the bradyarrhythmia is proposed using near-infrared-triggered Au nanorod (NR) based plasmonic photothermal effect (PPE). Moreover, electrophysiology of cardiomyocytes is dynamically monitored by the integrated biosensing-regulating system during and after the treatment. Cardiomyocyte-based bradyarrhythmia recover rhythmic for a long time by regulating plasmonic photothermal effect. Furthermore, the regulatory mechanism is qualitatively investigated to verify the significant thermal stimulation in the recovery process. This study establishes a reliable platform for long-term recording and evaluation of mild photothermal therapy for bradyarrhythmia in vitro, offering an efficient and non-invasive strategy for the potential clinical applications.

Extracellular vesicles from human cardiac stromal cells up-regulate cardiomyocyte protective responses to hypoxia

BACKGROUND

Cell therapy can protect cardiomyocytes from hypoxia, primarily via paracrine secretions, including extracellular vesicles (EVs). Since EVs fulfil specific biological functions based on their cellular origin, we hypothesised that EVs from human cardiac stromal cells (CMSCLCs) obtained from coronary artery bypass surgery may have cardioprotective properties.

OBJECTIVES

This study characterises CMSCLC EVs (C_EVs), miRNA cargo, cardioprotective efficacy and transcriptomic modulation of hypoxic human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). C_EVs are compared to bone marrow mesenchymal stromal cell EVs (B_EVs) which are a known therapeutic EV type.

METHODS

Cells were characterised for surface markers, gene expression and differentiation potential. EVs were compared for yield, phenotype, and ability to protect hiPSC-CMs from hypoxia/reoxygenation injury. EV dose was normalised by both protein concentration and particle count, allowing direct comparison. C_EV and B_EV miRNA cargo was profiled and RNA-seq was performed on EV-treated hypoxic hiPSC-CMs, then data were integrated by multi-omics. Confirmatory experiments were carried out using miRNA mimics.

RESULTS

At the same dose, C_EVs were more effective than B_EVs at protecting CM integrity, reducing apoptotic markers, and cell death during hypoxia. While C_EVs and B_EVs shared 70-77% similarity in miRNA content, C_EVs contained unique miRNAs, including miR-202-5p, miR-451a and miR-142-3p. Delivering miRNA mimics confirmed that miR-1260a and miR-202/451a/142 were cardioprotective, and the latter upregulated protective pathways similar to whole C_EVs.

CONCLUSIONS

This study demonstrates the potential of cardiac tissues, routinely discarded following surgery, as a valuable source of EVs for myocardial infarction therapy. We also identify miR-1260a as protective of CM hypoxia.

Mechanical stimulation promotes the maturation of cardiomyocyte-like cells from P19 cells and the function in a mouse model of myocardial infarction

In this study, we aimed to promote the maturation of cardiomyocytes-like cells by mechanical stimulation, and evaluate their therapeutic potential against myocardial infarction. The cyclic tensile strain was used to induce the maturation of cardsiomyocyte-like cells from P19 cells in vitro. Western blot and qPCR assays were performed to examine protein and gene expression, respectively. High-resolution respirometry was used to assay cell function. The induced cells were then evaluated for their therapeutic effect. In vitro, we observed cyclic tensile strain induced P19 cell differentiation into cardiomyocyte-like cells, as indicated by the increased expression of cardiomyocyte maturation-related genes such as Myh6, Myl2, and Gja1. Furthermore, cyclic tensile strain increased the antioxidant capacity of cardiomyocytes by upregulating the expression Sirt1, a gene important for P19 maturation into cardiomyocyte-like cells. High-resolution respirometry analysis of P19 cells following cyclic tensile strain showed enhanced metabolic function. In vivo, stimulated P19 cells enhanced cardiac function in a mouse model of myocardial infarction, and these mice showed decreased infarction-related biomarkers. The current study demonstrates a simple yet effective mean to induce the maturation of P19 cells into cardiomyocyte-like cells, with a promising therapeutic potential for the treatment of myocardial infarction.