Human Extracellular-Matrix Functionalization of 3D hiPSC-Based Cardiac Tissues Improves Cardiomyocyte Maturation

Versatile human cardiac tissues engineered with perfusable heart extracellular microenvironment for biomedical applications

Engineered human cardiac tissues have been utilized for various biomedical applications, including drug testing, disease modeling, and regenerative medicine. However, the applications of cardiac tissues derived from human pluripotent stem cells are often limited due to their immaturity and lack of functionality. Therefore, in this study, we establish a perfusable culture system based on in vivo-like heart microenvironments to improve human cardiac tissue fabrication. The integrated culture platform of a microfluidic chip and a three-dimensional heart extracellular matrix enhances human cardiac tissue development and their structural and functional maturation. These tissues are comprised of cardiovascular lineage cells, including cardiomyocytes and cardiac fibroblasts derived from human induced pluripotent stem cells, as well as vascular endothelial cells. The resultant macroscale human cardiac tissues exhibit improved efficacy in drug testing (small molecules with various levels of arrhythmia risk), disease modeling (Long QT Syndrome and cardiac fibrosis), and regenerative therapy (myocardial infarction treatment). Therefore, our culture system can serve as a highly effective tissue-engineering platform to provide human cardiac tissues for versatile biomedical applications.

ECM-derived biomaterials for regulating tissue multicellularity and maturation

Recent breakthroughs in developing human-relevant organotypic models led to the building of highly resemblant tissue constructs that hold immense potential for transplantation, drug screening, and disease modeling. Despite the progress in fine-tuning stem cell multilineage differentiation in highly controlled spatiotemporal conditions and hosting microenvironments, 3D models still experience naive and incomplete morphogenesis. In particular, existing systems and induction protocols fail to maintain stem cell long-term potency, induce high tissue-level multicellularity, or drive the maturity of stem cell-derived 3D models to levels seen in their in vivo counterparts. In this review, we highlight the use of extracellular matrix (ECM)-derived biomaterials in providing stem cell niche-mimicking microenvironment capable of preserving stem cell long-term potency and inducing spatial and region-specific differentiation. We also examine the maturation of different 3D models, including organoids, encapsulated in ECM biomaterials and provide looking-forward perspectives on employing ECM biomaterials in building more innovative, transplantable, and functional organs.

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.

Recent advances in soluble decellularized extracellular matrix for heart tissue engineering and organ modeling

Despite the advent of tissue engineering (TE) for the remodeling, restoring, and replacing damaged cardiovascular tissues, the progress is hindered by the optimal mechanical and chemical properties required to induce cardiac tissue-specific cellular behaviors including migration, adhesion, proliferation, and differentiation. Cardiac extracellular matrix (ECM) consists of numerous structural and functional molecules and tissue-specific cells, therefore it plays an important role in stimulating cell proliferation and differentiation, guiding cell migration, and activating regulatory signaling pathways. With the improvement and modification of cell removal methods, decellularized ECM (dECM) preserves biochemical complexity, and bio-inductive properties of the native matrix and improves the process of generating functional tissue. In this review, we first provide an overview of the latest advancements in the utilization of dECM in in vitro model systems for disease and tissue modeling, as well as drug screening. Then, we explore the role of dECM-based biomaterials in cardiovascular regenerative medicine (RM), including both invasive and non-invasive methods. In the next step, we elucidate the engineering and material considerations in the preparation of dECM-based biomaterials, namely various decellularization techniques, dECM sources, modulation, characterizations, and fabrication approaches. Finally, we discuss the limitations and future directions in fabrication of dECM-based biomaterials for cardiovascular modeling, RM, and clinical translation.

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.

Synergistic effects of hormones on structural and functional maturation of cardiomyocytes and implications for heart regeneration

The limited endogenous regenerative capacity of the human heart renders cardiovascular diseases a major health threat, thus motivating intense research on in vitro heart cell generation and cell replacement therapies. However, so far, in vitro-generated cardiomyocytes share a rather fetal phenotype, limiting their utility for drug testing and cell-based heart repair. Various strategies to foster cellular maturation provide some success, but fully matured cardiomyocytes are still to be achieved. Today, several hormones are recognized for their effects on cardiomyocyte proliferation, differentiation, and function. Here, we will discuss how the endocrine system impacts cardiomyocyte maturation. After detailing which features characterize a mature phenotype, we will contemplate hormones most promising to induce such a phenotype, the routes of their action, and experimental evidence for their significance in this process. Due to their pleiotropic effects, hormones might be not only valuable to improve in vitro heart cell generation but also beneficial for in vivo heart regeneration. Accordingly, we will also contemplate how the presented hormones might be exploited for hormone-based regenerative therapies.

High-throughput longitudinal electrophysiology screening of mature chamber-specific hiPSC-CMs using optical mapping

hiPSC-CMs are being considered by the Food and Drug Administration and other regulatory agencies for in vitro cardiotoxicity screening to provide human-relevant safety data. Widespread adoption of hiPSC-CMs in regulatory and academic science is limited by the immature, fetal-like phenotype of the cells. Here, to advance the maturation state of hiPSC-CMs, we developed and validated a human perinatal stem cell-derived extracellular matrix coating applied to high-throughput cell culture plates. We also present and validate a cardiac optical mapping device designed for high-throughput functional assessment of mature hiPSC-CM action potentials using voltage-sensitive dye and calcium transients using calcium-sensitive dyes or genetically encoded calcium indicators (GECI, GCaMP6). We utilize the optical mapping device to provide new biological insight into mature chamber-specific hiPSC-CMs, responsiveness to cardioactive drugs, the effect of GCaMP6 genetic variants on electrophysiological function, and the effect of daily β-receptor stimulation on hiPSC-CM monolayer function and SERCA2a expression.

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.

Insight into Heart-Tailored Architectures of Hydrogel to Restore Cardiac Functions after Myocardial Infarction

With permanent heart muscle injury or death, myocardial infarction (MI) is complicated by inflammatory, proliferation and remodeling phases from both the early ischemic period and subsequent infarct expansion. Though in situ re-establishment of blood flow to the infarct zone and delays of the ventricular remodeling process are current treatment options of MI, they fail to address massive loss of viable cardiomyocytes while transplanting stem cells to regenerate heart is hindered by their poor retention in the infarct bed. Equipped with heart-specific mimicry and extracellular matrix (ECM)-like functionality on the network structure, hydrogels leveraging tissue-matching biomechanics and biocompatibility can mechanically constrain the infarct and act as localized transport of bioactive ingredients to refresh the dysfunctional heart under the constant cyclic stress. Given diverse characteristics of hydrogel including conductivity, anisotropy, adhesiveness, biodegradability, self-healing and mechanical properties driving local cardiac repair, we aim to investigate and conclude the dynamic balance between ordered architectures of hydrogels and the post-MI pathological milieu. Additionally, our review summarizes advantages of heart-tailored architectures of hydrogels in cardiac repair following MI. Finally, we propose challenges and prospects in clinical translation of hydrogels to draw theoretical guidance on cardiac repair and regeneration after MI.

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.

Cardiac Tissue-like 3D Microenvironment Enhances Route towards Human Fibroblast Direct Reprogramming into Induced Cardiomyocytes by microRNAs

The restoration of cardiac functionality after myocardial infarction represents a major clinical challenge. Recently, we found that transient transfection with microRNA combination (miRcombo: miR-1, miR-133, miR-208 and 499) is able to trigger direct reprogramming of adult human cardiac fibroblasts (AHCFs) into induced cardiomyocytes (iCMs) in vitro. However, achieving efficient direct reprogramming still remains a challenge. The aim of this study was to investigate the influence of cardiac tissue-like biochemical and biophysical stimuli on direct reprogramming efficiency. Biomatrix (BM), a cardiac-like extracellular matrix (ECM), was produced by in vitro culture of AHCFs for 21 days, followed by decellularization. In a set of experiments, AHCFs were transfected with miRcombo and then cultured for 2 weeks on the surface of uncoated and BM-coated polystyrene (PS) dishes and fibrin hydrogels (2D hydrogel) or embedded into 3D fibrin hydrogels (3D hydrogel). Cell culturing on BM-coated PS dishes and in 3D hydrogels significantly improved direct reprogramming outcomes. Biochemical and biophysical cues were then combined in 3D fibrin hydrogels containing BM (3D BM hydrogel), resulting in a synergistic effect, triggering increased CM gene and cardiac troponin T expression in miRcombo-transfected AHCFs. Hence, biomimetic 3D culture environments may improve direct reprogramming of miRcombo-transfected AHCFs into iCMs, deserving further study.

Enhancement of cardiac contractility using gold-coated SU-8 cantilevers and their application to drug-induced cardiac toxicity tests

Herein, we propose an array of gold (Au)-coated SU-8 cantilevers with microgrooves for improved maturation of cardiomyocytes and describe its applications to drug-induced cardiac toxicity tests. Firstly, we evaluated the effect of cell culture substrates such as polydimethylsiloxane (PDMS), polyimide (PI), and SU-8 on the cardiomyocyte's maturation. Among these, the SU-8 with microgroove structures exhibits improved cardiomyocyte maturation. Further, thin layers of graphene and Au are coated on SU-8 substrates and the effects of these materials on cardiomyocyte maturation are evaluated by analyzing the expression of proteins such as alpha-actinin, Connexin 43 (Cx43), and Vinculin. While both conductive materials enhanced protein expression when compared to bare SU-8, the Au-coated SU-8 substrates demonstrated superior cardiomyocyte maturation. The cantilever structure is constructed using microgroove patterned SU-8 with and without an Au coating. The Au-coated SU-8 cantilever showed maximum displacement of 17.6 ± 0.3 μm on day 21 compared to bare SU-8 (14.2 ± 0.4 μm) owing to improved cardiomyocytes maturation. Verapamil and quinidine are used to characterize drug-induced changes in the contraction characteristics of cardiomyocytes on bare and Au-coated SU-8 cantilevers. The relative contraction forces and beat rates changed according to the calcium and sodium channel related drugs. Matured cardiomyocytes are less influenced by the drugs compared to immature cardiomyocytes and showed reliable IC₅₀ values. These results indicate that the proposed Au-coated SU-8 cantilever array could help improve the accuracy of toxicity screening results by allowing for the use of cardiomyocytes that have been matured on the drug screening platform.

Interindividual heterogeneity affects the outcome of human cardiac tissue decellularization

The extracellular matrix (ECM) of engineered human cardiac tissues corresponds to simplistic biomaterials that allow tissue assembly, or animal derived off-the-shelf non-cardiac specific matrices. Decellularized ECM from human cardiac tissue could provide a means to improve the mimicry of engineered human cardiac tissues. Decellularization of cardiac tissue samples using immersion-based methods can produce acceptable cardiac ECM scaffolds; however, these protocols are mostly described for animal tissue preparations. We have tested four methods to decellularize human cardiac tissue and evaluated their efficiency in terms of cell removal and preservation of key ECM components, such as collagens and sulfated glycosaminoglycans. Extended exposure to decellularization agents, namely sodium dodecyl sulfate and Triton-X-100, was needed to significantly remove DNA content by approximately 93% in all human donors. However, the biochemical composition of decellularized tissue is affected, and the preservation of ECM architecture is donor dependent. Our results indicate that standardization of decellularization protocols for human tissue is likely unfeasible, and a compromise between cell removal and ECM preservation must be established in accordance with the scaffold's intended application. Notwithstanding, decellularized human cardiac ECM supported human induced pluripotent-derived cardiomyocyte (hiPSC-CM) attachment and retention for up to 2 weeks of culture, and promoted cell alignment and contraction, providing evidence it could be a valuable tool for cardiac tissue engineering.

The Use of Stem Cell-Derived Organoids in Disease Modeling: An Update

Organoids represent one of the most important advancements in the field of stem cells during the past decade. They are three-dimensional in vitro culturing models that originate from self-organizing stem cells and can mimic the in vivo structural and functional specificities of body organs. Organoids have been established from multiple adult tissues as well as pluripotent stem cells and have recently become a powerful tool for studying development and diseases in vitro, drug screening, and host-microbe interaction. The use of stem cells-that have self-renewal capacity to proliferate and differentiate into specialized cell types-for organoids culturing represents a major advancement in biomedical research. Indeed, this new technology has a great potential to be used in a multitude of fields, including cancer research, hereditary and infectious diseases. Nevertheless, organoid culturing is still rife with many challenges, not limited to being costly and time consuming, having variable rates of efficiency in generation and maintenance, genetic stability, and clinical applications. In this review, we aim to provide a synopsis of pluripotent stem cell-derived organoids and their use for disease modeling and other clinical applications.