Cardioids reveal self-organizing principles of human cardiogenesis

Human brain organoid: trends, evolution, and remaining challenges

Advanced brain organoids provide promising platforms for deciphering the cellular and molecular processes of human neural development and diseases. Although various studies and reviews have described developments and advancements in brain organoids, few studies have comprehensively summarized and analyzed the global trends in this area of neuroscience. To identify and further facilitate the development of cerebral organoids, we utilized bibliometrics and visualization methods to analyze the global trends and evolution of brain organoids in the last 10 years. First, annual publications, countries/regions, organizations, journals, authors, co-citations, and keywords relating to brain organoids were identified. The hotspots in this field were also systematically identified. Subsequently, current applications for brain organoids in neuroscience, including human neural development, neural disorders, infectious diseases, regenerative medicine, drug discovery, and toxicity assessment studies, are comprehensively discussed. Towards that end, several considerations regarding the current challenges in brain organoid research and future strategies to advance neuroscience will be presented to further promote their application in neurological research.

Dynamic microphysiological system chip platform for high-throughput, customizable, and multi-dimensional drug screening

Spheroids and organoids have attracted significant attention as innovative models for disease modeling and drug screening. By employing diverse types of spheroids or organoids, it is feasible to establish microphysiological systems that enhance the precision of disease modeling and offer more dependable and comprehensive drug screening. High-throughput microphysiological systems that support optional, parallel testing of multiple drugs have promising applications in personalized medical treatment and drug research. However, establishing such a system is highly challenging and requires a multidisciplinary approach. This study introduces a dynamic Microphysiological System Chip Platform (MSCP) with multiple functional microstructures that encompass the mentioned advantages. We developed a high-throughput lung cancer spheroids model and an intestine-liver-heart-lung cancer microphysiological system for conducting parallel testing on four anti-lung cancer drugs, demonstrating the feasibility of the MSCP. This microphysiological system combines microscale and macroscale biomimetics to enable a comprehensive assessment of drug efficacy and side effects. Moreover, the microphysiological system enables evaluation of the real pharmacological effect of drug molecules reaching the target lesion after absorption by normal organs through fluid-based physiological communication. The MSCP could serves as a valuable platform for microphysiological system research, making significant contributions to disease modeling, drug development, and personalized medical treatment.

Three-dimensional cardiac models: a pre-clinical testing platform

Major advancements in human pluripotent stem cell (hPSC) technology over recent years have yielded valuable tools for cardiovascular research. Multi-cell type 3-dimensional (3D) cardiac models in particular, are providing complementary approaches to animal studies that are better representatives than simple 2-dimensional (2D) cultures of differentiated hPSCs. These human 3D cardiac models can be broadly divided into two categories; namely those generated through aggregating pre-differentiated cells and those that form self-organizing structures during their in vitro differentiation from hPSCs. These models can either replicate aspects of cardiac development or enable the examination of interactions among constituent cell types, with some of these models showing increased maturity compared with 2D systems. Both groups have already emerged as physiologically relevant pre-clinical platforms for studying heart disease mechanisms, exhibiting key functional attributes of the human heart. In this review, we describe the different cardiac organoid models derived from hPSCs, their generation methods, applications in cardiovascular disease research and use in drug screening. We also address their current limitations and challenges as pre-clinical testing platforms and propose potential improvements to enhance their efficacy in cardiac drug discovery.

Protocol for quantifying stem-cell-derived cardiomyocyte maturity using transcriptomic entropy score

The inability to quantify cardiomyocyte (CM) maturation remains a significant barrier to evaluating the effects of ongoing efforts to produce adult-like CMs from pluripotent stem cells (PSCs). Here, we present a protocol to quantify stem-cell-derived CM maturity using a single-cell RNA sequencing-based metric "entropy score." We describe steps for generating an entropy score using customized R code. This tool can be used to quantify maturation levels of PSC-CMs and potentially other cell types. For complete details on the use and execution of this protocol, please refer to Kannan et al.1.

Cardiac organoids do not warrant additional moral scrutiny

Certain organoid subtypes are particularly sensitive. We explore whether moral intuitions about the heartbeat warrant unique moral consideration for newly advanced contracting cardiac organoids. Despite the heartbeat's moral significance in organ procurement and abortion discussions, we argue that this significance should not translate into moral implications for cardiac organoids.

Discovery platforms for RNA therapeutics

RNA therapeutics are emerging as a unique opportunity to drug currently "undruggable" molecules and diseases. While their advantages over conventional, small molecule drugs, their therapeutic implications and the tools for their effective in vivo delivery have been extensively reviewed, little attention has been so far paid to the technological platforms exploited for the discovery of RNA therapeutics. Here, we provide an overview of the existing platforms and ex vivo assays for RNA discovery, their advantages and disadvantages, as well as their main fields of application, with specific focus on RNA therapies that have reached either phase 3 or market approval.

Exploring the prospects, advancements, and challenges of in vitro modeling of the heart-brain axis

Research on bidirectional communication between the heart and brain has often relied on studies involving nonhuman animals. Dependance on animal models offer limited applicability to humans and a lack of high-throughput screening. Recently, the field of 3D cell biology, specifically organoid technology, has rapidly emerged as a valuable tool for studying interactions across organ systems, i.e., gut-brain axis. The initial success of organoid models indicates the usefulness of 3D cultures for elucidating the intricate interactivity of the autonomic nervous system and overall health. This perspective aims to explore the potential of advancing in vitro modeling of the heart-brain axis by discussing the benefits, applications, and adaptability of organoid technologies. We closely examine the current state of brain organoids in conjunction with the advancements of cardiac organoids. Moreover, we explore the use of combined organoid systems to investigate pathophysiology and provide a platform for treatment discovery. Finally, we address the challenges that accompany the use of 3D models for studying the heart-brain axis with an emphasis on generating tailored engineering strategies for further refinement of dynamic organ system modeling in vitro.

Modeling acute myocardial infarction and cardiac fibrosis using human induced pluripotent stem cell-derived multi-cellular heart organoids

Heart disease involves irreversible myocardial injury that leads to high morbidity and mortality rates. Numerous cell-based cardiac in vitro models have been proposed as complementary approaches to non-clinical animal research. However, most of these approaches struggle to accurately replicate adult human heart conditions, such as myocardial infarction and ventricular remodeling pathology. The intricate interplay between various cell types within the adult heart, including cardiomyocytes, fibroblasts, and endothelial cells, contributes to the complexity of most heart diseases. Consequently, the mechanisms behind heart disease induction cannot be attributed to a single-cell type. Thus, the use of multi-cellular models becomes essential for creating clinically relevant in vitro cell models. This study focuses on generating self-organizing heart organoids (HOs) using human-induced pluripotent stem cells (hiPSCs). These organoids consist of cardiomyocytes, fibroblasts, and endothelial cells, mimicking the cellular composition of the human heart. The multi-cellular composition of HOs was confirmed through various techniques, including immunohistochemistry, flow cytometry, q-PCR, and single-cell RNA sequencing. Subsequently, HOs were subjected to hypoxia-induced ischemia and ischemia-reperfusion (IR) injuries within controlled culture conditions. The resulting phenotypes resembled those of acute myocardial infarction (AMI), characterized by cardiac cell death, biomarker secretion, functional deficits, alterations in calcium ion handling, and changes in beating properties. Additionally, the HOs subjected to IR efficiently exhibited cardiac fibrosis, displaying collagen deposition, disrupted calcium ion handling, and electrophysiological anomalies that emulate heart disease. These findings hold significant implications for the advancement of in vivo-like 3D heart and disease modeling. These disease models present a promising alternative to animal experimentation for studying cardiac diseases, and they also serve as a platform for drug screening to identify potential therapeutic targets.

Proposal for considerations during human iPSC-derived cardiac organoid generation for cardiotoxicity drug testing

Human iPSC-derived cardiac organoids (hiPSC-COs) for cardiotoxicity drug testing via the variety of cell lines and unestablished protocols may lead to differences in response results due to a lack of criteria for generation period and size. To ensure reliable drug testing, it is important for researchers to set optimal generation period and size of COs according to the cell line and protocol applied in their studies. Hence, we sought to propose a process to establish minimum criteria for the generation duration and size of hiPSC-COs for cardiotoxic drug testing. We generated hiPSC-COs of different sizes based on our protocol and continuously monitored organoids until they indicated a minimal beating rate change as a control that could lead to more accurate beating rate changes on drug testing. Calcium transients and physiological tests to assess the functionality of hiPSC-COs on selected generation period, which showed regular cardiac beating, and immunostaining assays to compare characteristics were performed. We explained the generation period and size that exhibited and maintained regular beating rate changes on hiPSC-COs, and lead to reliable response results to cardiotoxicity drugs. We anticipate that this study will offer valuable insights into considering the appropriate generation period and size of hiPSC-COs ensuring reliable outcomes in cardiotoxicity drug testing.

Targeting Interactions between Fibroblasts and Macrophages to Treat Cardiac Fibrosis

Excessive extracellular matrix (ECM) deposition is a defining feature of cardiac fibrosis. Most notably, it is characterized by a significant change in the concentration and volume fraction of collagen I, a disproportionate deposition of collagen subtypes, and a disturbed ECM network arrangement, which directly affect the systolic and diastolic functions of the heart. Immune cells that reside within or infiltrate the myocardium, including macrophages, play important roles in fibroblast activation and consequent ECM remodeling. Through both direct and indirect connections to fibroblasts, monocyte-derived macrophages and resident cardiac macrophages play complex, bidirectional, regulatory roles in cardiac fibrosis. In this review, we discuss emerging interactions between fibroblasts and macrophages in physiology and pathologic conditions, providing insights for future research aimed at targeting macrophages to combat cardiac fibrosis.

Induced pluripotent stem cells (iPSCs): molecular mechanisms of induction and applications

The induced pluripotent stem cell (iPSC) technology has transformed in vitro research and holds great promise to advance regenerative medicine. iPSCs have the capacity for an almost unlimited expansion, are amenable to genetic engineering, and can be differentiated into most somatic cell types. iPSCs have been widely applied to model human development and diseases, perform drug screening, and develop cell therapies. In this review, we outline key developments in the iPSC field and highlight the immense versatility of the iPSC technology for in vitro modeling and therapeutic applications. We begin by discussing the pivotal discoveries that revealed the potential of a somatic cell nucleus for reprogramming and led to successful generation of iPSCs. We consider the molecular mechanisms and dynamics of somatic cell reprogramming as well as the numerous methods available to induce pluripotency. Subsequently, we discuss various iPSC-based cellular models, from mono-cultures of a single cell type to complex three-dimensional organoids, and how these models can be applied to elucidate the mechanisms of human development and diseases. We use examples of neurological disorders, coronavirus disease 2019 (COVID-19), and cancer to highlight the diversity of disease-specific phenotypes that can be modeled using iPSC-derived cells. We also consider how iPSC-derived cellular models can be used in high-throughput drug screening and drug toxicity studies. Finally, we discuss the process of developing autologous and allogeneic iPSC-based cell therapies and their potential to alleviate human diseases.

Engineered platforms for mimicking cardiac development and drug screening

Congenital heart defects are associated with significant health challenges, demanding a deep understanding of the underlying biological mechanisms and, thus, better devices or platforms that can recapitulate human cardiac development. The discovery of human pluripotent stem cells has substantially reduced the dependence on animal models. Recent advances in stem cell biology, genetic editing, omics, microfluidics, and sensor technologies have further enabled remarkable progress in the development of in vitro platforms with increased fidelity and efficiency. In this review, we provide an overview of advancements in in vitro cardiac development platforms, with a particular focus on technological innovation. We categorize these platforms into four areas: two-dimensional solid substrate cultures, engineered substrate architectures that enhance cellular functions, cardiac organoids, and embryos/explants-on-chip models. We conclude by addressing current limitations and presenting future perspectives.

Unveiling new horizons in heart research: the promise of multi-chamber cardiac organoids

Human cardiac and other organoids have recently emerged as a groundbreaking tool for advancing our understanding the developmental biology of human organs. A recent paper from Sasha Mendjan's laboratory published in the journal Cell on December 7, 2023, reported the generation of multi-chamber cardioids from human pluripotent stem cells, a transformative technology in the field of cardiology. In this short highlight paper, we summarize their findings. Their cardioids remarkably recapitulate the complexity of the human embryonic heart, including tissue architecture, cellular diversity, and functionality providing an excellent in vitro model for investigation of human heart development, disease modeling, precision medicine, and regenerative medicine. Thus, generating cardioids is an important step forward for understanding human heart development and developing potential therapies for heart diseases.

Methods for Generating Self-Organizing Human Patterned Heart Organoids Using Pluripotent Stem Cells

Organoids derived from pluripotent stem cells exhibit notable similarities to organ development in vitro. Nonetheless, cardiac organoids generated to date possess immature phenotypes and are unable to model the full spectrum of heart development and disease. Here, we describe the developmental maturation of human heart organoids by controlled exposure to metabolic and hormonal factors over a 10-day period, mirroring key stages of human cardiac development and resulting in significant molecular, cellular, morphological, and functional changes. Overall, our findings represent a significant advancement in synthetic human heart development, offering a valuable platform for studying cardiac disease states and conducting pharmacological research.

Methodology and Characterization of a 3D Bone Organoid Model Derived from Murine Cells

Here, we report on the development of a cost-effective, well-characterized three-dimensional (3D) model of bone homeostasis derived from commonly available stocks of immortalized murine cell lines and laboratory reagents. This 3D murine-cell-derived bone organoid model (3D-mcBOM) is adaptable to a range of contexts and can be used in conjunction with surrogates of osteoblast and osteoclast function to study cellular and molecular mechanisms that affect bone homeostasis in vitro or to augment in vivo models of physiology or disease. The 3D-mcBOM was established using a pre-osteoblast murine cell line, which was seeded into a hydrogel extracellular matrix (ECM) and differentiated into functional osteoblasts (OBs). The OBs mineralized the hydrogel ECM, leading to the deposition and consolidation of hydroxyapatite into bone-like organoids. Fourier-transform infrared (FTIR) spectroscopy confirmed that the mineralized matrix formed in the 3D-mcBOM was bone. The histological staining of 3D-mcBOM samples indicated a consistent rate of ECM mineralization. Type I collagen C-telopeptide (CTX1) analysis was used to evaluate the dynamics of OC differentiation and activity. Reliable 3D models of bone formation and homeostasis align with current ethical trends to reduce the use of animal models. This functional model of bone homeostasis provides a cost-effective model system using immortalized cell lines and easily procured supplemental compounds, which can be assessed by measuring surrogates of OB and OC function to study the effects of various stimuli in future experimental evaluations of bone homeostasis.

A versatile high-throughput assay based on 3D ring-shaped cardiac tissues generated from human induced pluripotent stem cell-derived cardiomyocytes

We developed a 96-well plate assay which allows fast, reproducible, and high-throughput generation of 3D cardiac rings around a deformable optically transparent hydrogel (polyethylene glycol [PEG]) pillar of known stiffness. Human induced pluripotent stem cell-derived cardiomyocytes, mixed with normal human adult dermal fibroblasts in an optimized 3:1 ratio, self-organized to form ring-shaped cardiac constructs. Immunostaining showed that the fibroblasts form a basal layer in contact with the glass, stabilizing the muscular fiber above. Tissues started contracting around the pillar at D1 and their fractional shortening increased until D7, reaching a plateau at 25±1%, that was maintained up to 14 days. The average stress, calculated from the compaction of the central pillar during contractions, was 1.4±0.4 mN/mm2. The cardiac constructs recapitulated expected inotropic responses to calcium and various drugs (isoproterenol, verapamil) as well as the arrhythmogenic effects of dofetilide. This versatile high-throughput assay allows multiple in situ mechanical and structural readouts.

Organoids as preclinical models of human disease: progress and applications

In the field of biomedical research, organoids represent a remarkable advancement that has the potential to revolutionize our approach to studying human diseases even before clinical trials. Organoids are essentially miniature 3D models of specific organs or tissues, enabling scientists to investigate the causes of diseases, test new drugs, and explore personalized medicine within a controlled laboratory setting. Over the past decade, organoid technology has made substantial progress, allowing researchers to create highly detailed environments that closely mimic the human body. These organoids can be generated from various sources, including pluripotent stem cells, specialized tissue cells, and tumor tissue cells. This versatility enables scientists to replicate a wide range of diseases affecting different organ systems, effectively creating disease replicas in a laboratory dish. This exciting capability has provided us with unprecedented insights into the progression of diseases and how we can develop improved treatments. In this paper, we will provide an overview of the progress made in utilizing organoids as preclinical models, aiding our understanding and providing a more effective approach to addressing various human diseases.

Polyoxyethylene tallow amine and glyphosate exert different developmental toxicities on human pluripotent stem cells-derived heart organoid model

The early stage of heart development is highly susceptible to various environmental factors. While the use of animal models has aided in identifying numerous environmental risk factors, the variability between species and the low throughput limit their translational potential. Recently, a type of self-assembling cardiac structures, known as human heart organoids (hHOs), exhibits a remarkable biological consistency with human heart. However, the feasibility of hHOs for assessing cardiac developmental risk factors remains unexplored. Here, we focused on the cardiac developmental effects of core components of Glyphosate-based herbicides (GBHs), the most widely used herbicides, to evaluate the reliability of hHOs for the prediction of possible cardiogenesis toxicity. GBHs have been proven toxic to cardiac development based on multiple animal models, with the mechanism remaining unknown. We found that polyoxyethylene tallow amine (POEA), the most common surfactant in GBHs formulations, played a dominant role in GBHs' heart developmental toxicity. Though there were a few differences in transcriptive features, hHOs exposed to sole POEA and combined POEA and Glyphosate would suffer from both disruption of heart contraction and disturbance of commitment in cardiomyocyte isoforms. By contrast, Glyphosate only caused mild epicardial hyperplasia. This study not only sheds light on the toxic mechanism of GBHs, but also serves as a methodological demonstration, showcasing its effectiveness in recognizing and evaluating environmental risk factors, and deciphering toxic mechanisms.

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.

Micro-Engineered Heart Tissues On-Chip with Heterotypic Cell Composition Display Self-Organization and Improved Cardiac Function

Advanced in vitro models that recapitulate the structural organization and function of the human heart are highly needed for accurate disease modeling, more predictable drug screening, and safety pharmacology. Conventional 3D Engineered Heart Tissues (EHTs) lack heterotypic cell complexity and culture under flow, whereas microfluidic Heart-on-Chip (HoC) models in general lack the 3D configuration and accurate contractile readouts. In this study, an innovative and user-friendly HoC model is developed to overcome these limitations, by culturing human pluripotent stem cell (hPSC)-derived cardiomyocytes (CMs), endothelial (ECs)- and smooth muscle cells (SMCs), together with human cardiac fibroblasts (FBs), underflow, leading to self-organized miniaturized micro-EHTs (µEHTs) with a CM-EC interface reminiscent of the physiological capillary lining. µEHTs cultured under flow display enhanced contractile performance and conduction velocity. In addition, the presence of the EC layer altered drug responses in µEHT contraction. This observation suggests a potential barrier-like function of ECs, which may affect the availability of drugs to the CMs. These cardiac models with increased physiological complexity, will pave the way to screen for therapeutic targets and predict drug efficacy.

ER stress and lipid imbalance drive diabetic embryonic cardiomyopathy in an organoid model of human heart development

Congenital heart defects are the most prevalent human birth defects, and their incidence is exacerbated by maternal health conditions, such as diabetes during the first trimester (pregestational diabetes). Our understanding of the pathology of these disorders is hindered by a lack of human models and the inaccessibility of embryonic tissue. Using an advanced human heart organoid system, we simulated embryonic heart development under pregestational diabetes-like conditions. These organoids developed pathophysiological features observed in mouse and human studies before, including ROS-mediated stress and cardiomyocyte hypertrophy. scRNA-seq revealed cardiac cell-type-specific dysfunction affecting epicardial and cardiomyocyte populations and alterations in the endoplasmic reticulum and very-long-chain fatty acid lipid metabolism. Imaging and lipidomics confirmed these findings and showed that dyslipidemia was linked to fatty acid desaturase 2 mRNA decay dependent on IRE1-RIDD signaling. Targeting IRE1 or restoring lipid levels partially reversed the effects of pregestational diabetes, offering potential preventive and therapeutic strategies in humans.

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

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

Differentiation of Pluripotent Stem Cells for Disease Modeling: Learning from Heart Development

Heart disease is a pressing public health problem and the leading cause of death worldwide. The heart is the first organ to gain function during embryogenesis in mammals. Heart development involves cell determination, expansion, migration, and crosstalk, which are orchestrated by numerous signaling pathways, such as the Wnt, TGF-β, IGF, and Retinoic acid signaling pathways. Human-induced pluripotent stem cell-based platforms are emerging as promising approaches for modeling heart disease in vitro. Understanding the signaling pathways that are essential for cardiac development has shed light on the molecular mechanisms of congenital heart defects and postnatal heart diseases, significantly advancing stem cell-based platforms to model heart diseases. This review summarizes signaling pathways that are crucial for heart development and discusses how these findings improve the strategies for modeling human heart disease in vitro.

Innovative explorations: unveiling the potential of organoids for investigating environmental pollutant exposure

As the economy rapidly develops, chemicals are widely produced and used. This has exacerbated the problems associated with environmental pollution, raising the need for efficient toxicological evaluation techniques to investigate the toxic effects and mechanisms of toxicity of environmental pollutants. The progress in the techniques of cell culture in three dimensions has resulted in the creation of models that are more relevant in terms of biology and physiology. This enables researchers to study organ development, toxicology, and drug screening. Adult stem cells (ASCs) and induced pluripotent stem cells (iPSCs) can be obtained from various mammalian tissues, including cancerous and healthy tissues. Such stem cells exhibit a significant level of tissue memory and ability to self-assemble. When cultivated in 3D in vitro environments, the resulting organoids demonstrate a remarkable capacity to recapitulate the cellular composition and function of organs in vivo. Recently, many tumors' tissue-derived organoids have been widely used in research on tumor pathogenesis, drug development, precision medicine, and other fields, including those derived from colon cancer, cholangiocarcinoma, liver cancer, and gastric cancer. However, the application of organoid models for evaluating the toxicity of environmental pollutants is still in its infancy. This review introduces the characteristics of the toxicity responses of organoid models upon exposure to pollutants from the perspectives of organoid characteristics, tissue types, and their applications in toxicology; discusses the feasibility of using organoid models in evaluating the toxicity of pollutants; and provides a reference for future toxicological studies on environmental pollutants based on organoid models.

Overexpression of multidrug resistance-associated protein 1 protects against cardiotoxicity by augmenting the doxorubicin efflux from cardiomyocytes

Doxorubicin is a commonly used anti-cancer drug used in treating a variety of malignancies. However, a major adverse effect is cardiotoxicity, which is dose dependent and can be either acute or chronic. Doxorubicin causes injury by DNA damage, the formation of free reactive oxygen radicals and induction of apoptosis. Our aim is to induce expression of the multidrug resistance-associated protein 1 (MRP1) in cardiomyocytes derived from human iPS cells (hiPSC-CM), to determine whether this will allow cells to effectively remove doxorubicin and confer cardioprotection. We generated a lentivirus vector encoding MRP1 (LV.MRP1) and validated its function in HEK293T cells and stem cell-derived cardiomyocytes (hiPSC-CM) by quantitative PCR and western blot analysis. The activity of the overexpressed MRP1 was also tested, by quantifying the amount of fluorescent dye exported from the cell by the transporter. We demonstrated reduced dye sequestration in cells overexpressing MRP1. Finally, we demonstrated that hiPSC-CM transduced with LV.MRP1 were protected against doxorubicin injury. In conclusion, we have shown that we can successfully overexpress MRP1 protein in hiPSC-CM, with functional transporter activity leading to protection against doxorubicin-induced toxicity.

Assessing Cardiac Contractility From Single Molecules to Whole Hearts

Fundamentally, the heart needs to generate sufficient force and power output to dynamically meet the needs of the body. Cardiomyocytes contain specialized structures referred to as sarcomeres that power and regulate contraction. Disruption of sarcomeric function or regulation impairs contractility and leads to cardiomyopathies and heart failure. Basic, translational, and clinical studies have adapted numerous methods to assess cardiac contraction in a variety of pathophysiological contexts. These tools measure aspects of cardiac contraction at different scales ranging from single molecules to whole organisms. Moreover, these studies have revealed new pathogenic mechanisms of heart disease leading to the development of novel therapies targeting contractility. In this review, the authors explore the breadth of tools available for studying cardiac contractile function across scales, discuss their strengths and limitations, highlight new insights into cardiac physiology and pathophysiology, and describe how these insights can be harnessed for therapeutic candidate development and translational.

Application Prospect of Induced Pluripotent Stem Cells in Organoids and Cell Therapy

Since its inception, induced pluripotent stem cell (iPSC) technology has been hailed as a powerful tool for comprehending disease etiology and advancing drug screening across various domains. While earlier iPSC-based disease modeling and drug assessment primarily operated at the cellular level, recent years have witnessed a significant shift towards organoid-based investigations. Organoids derived from iPSCs offer distinct advantages, particularly in enabling the observation of disease progression and drug metabolism in an in vivo-like environment, surpassing the capabilities of iPSC-derived cells. Furthermore, iPSC-based cell therapy has emerged as a focal point of clinical interest. In this review, we provide an extensive overview of non-integrative reprogramming methods that have evolved since the inception of iPSC technology. We also deliver a comprehensive examination of iPSC-derived organoids, spanning the realms of the nervous system, cardiovascular system, and oncology, as well as systematically elucidate recent advancements in iPSC-related cell therapies.

Cardiac construction-Recent advances in morphological and transcriptional modeling of early heart development

During human embryonic development the early establishment of a functional heart is vital to support the growing fetus. However, forming the embryonic heart is an extremely complex process, requiring spatiotemporally controlled cell specification and differentiation, tissue organization, and coordination of cardiac function. These complexities, in concert with the early and rapid development of the embryonic heart, mean that understanding the intricate interplay between these processes that help shape the early heart remains highly challenging. In this review I focus on recent insights from animal models that have shed new light on the earliest stages of heart development. This includes specification and organization of cardiac progenitors, cell and tissue movements that make and shape the early heart tube, and the initiation of the first beat in the developing heart. In addition I highlight relevant in vitro models that could support translation of findings from animal models to human heart development. Finally I discuss challenges that are being addressed in the field, along with future considerations that together may help move us towards a deeper understanding of how our hearts are made.

Patient-derived organoids in human cancer: a platform for fundamental research and precision medicine

Cancer is associated with a high degree of heterogeneity, encompassing both inter- and intra-tumor heterogeneity, along with considerable variability in clinical response to common treatments across patients. Conventional models for tumor research, such as in vitro cell cultures and in vivo animal models, demonstrate significant limitations that fall short of satisfying the research requisites. Patient-derived tumor organoids, which recapitulate the structures, specific functions, molecular characteristics, genomics alterations and expression profiles of primary tumors. They have been efficaciously implemented in illness portrayal, mechanism exploration, high-throughput drug screening and assessment, discovery of innovative therapeutic targets and potential compounds, and customized treatment regimen for cancer patients. In contrast to conventional models, tumor organoids offer an intuitive, dependable, and efficient in vitro research model by conserving the phenotypic, genetic diversity, and mutational attributes of the originating tumor. Nevertheless, the organoid technology also confronts the bottlenecks and challenges, such as how to comprehensively reflect intra-tumor heterogeneity, tumor microenvironment, tumor angiogenesis, reduce research costs, and establish standardized construction processes while retaining reliability. This review extensively examines the use of tumor organoid techniques in fundamental research and precision medicine. It emphasizes the importance of patient-derived tumor organoid biobanks for drug development, screening, safety evaluation, and personalized medicine. Additionally, it evaluates the application of organoid technology as an experimental tumor model to better understand the molecular mechanisms of tumor. The intent of this review is to explicate the significance of tumor organoids in cancer research and to present new avenues for the future of tumor research.

The new era of cardiovascular research: revolutionizing cardiovascular research with 3D models in a dish

Cardiovascular research has heavily relied on studies using patient samples and animal models. However, patient studies often miss the data from the crucial early stage of cardiovascular diseases, as obtaining primary tissues at this stage is impracticable. Transgenic animal models can offer some insights into disease mechanisms, although they usually do not fully recapitulate the phenotype of cardiovascular diseases and their progression. In recent years, a promising breakthrough has emerged in the form of in vitro three-dimensional (3D) cardiovascular models utilizing human pluripotent stem cells. These innovative models recreate the intricate 3D structure of the human heart and vessels within a controlled environment. This advancement is pivotal as it addresses the existing gaps in cardiovascular research, allowing scientists to study different stages of cardiovascular diseases and specific drug responses using human-origin models. In this review, we first outline various approaches employed to generate these models. We then comprehensively discuss their applications in studying cardiovascular diseases by providing insights into molecular and cellular changes associated with cardiovascular conditions. Moreover, we highlight the potential of these 3D models serving as a platform for drug testing to assess drug efficacy and safety. Despite their immense potential, challenges persist, particularly in maintaining the complex structure of 3D heart and vessel models and ensuring their function is comparable to real organs. However, overcoming these challenges could revolutionize cardiovascular research. It has the potential to offer comprehensive mechanistic insights into human-specific disease processes, ultimately expediting the development of personalized therapies.

Bone Organoids: Recent Advances and Future Challenges

Bone defects stemming from tumorous growths, traumatic events, and diverse conditions present a profound conundrum in clinical practice and research. While bone has the inherent ability to regenerate, substantial bone anomalies require bone regeneration techniques. Bone organoids represent a new concept in this field, involving the 3D self-assembly of bone-associated stem cells guided in vitro with or without extracellular matrix material, resulting in a tissue that mimics the structural, functional, and genetic properties of native bone tissue. Within the scientific panorama, bone organoids ascend to an esteemed status, securing significant experimental endorsement. Through a synthesis of current literature and pioneering studies, this review offers a comprehensive survey of the bone organoid paradigm, delves into the quintessential architecture and ontogeny of bone, and highlights the latest progress in bone organoid fabrication. Further, existing challenges and prospective directions for future research are identified, advocating for interdisciplinary collaboration to fully harness the potential of this burgeoning domain. Conclusively, as bone organoid technology continues to mature, its implications for both clinical and research landscapes are poised to be profound.

Advances in the Generation of Constructed Cardiac Tissue Derived from Induced Pluripotent Stem Cells for Disease Modeling and Therapeutic Discovery

The human heart lacks significant regenerative capacity; thus, the solution to heart failure (HF) remains organ donation, requiring surgery and immunosuppression. The demand for constructed cardiac tissues (CCTs) to model and treat disease continues to grow. Recent advances in induced pluripotent stem cell (iPSC) manipulation, CRISPR gene editing, and 3D tissue culture have enabled a boom in iPSC-derived CCTs (iPSC-CCTs) with diverse cell types and architecture. Compared with 2D-cultured cells, iPSC-CCTs better recapitulate heart biology, demonstrating the potential to advance organ modeling, drug discovery, and regenerative medicine, though iPSC-CCTs could benefit from better methods to faithfully mimic heart physiology and electrophysiology. Here, we summarize advances in iPSC-CCTs and future developments in the vascularization, immunization, and maturation of iPSC-CCTs for study and therapy.

Unlocking cardiac motion: assessing software and machine learning for single-cell and cardioid kinematic insights

The heart coordinates its functional parameters for optimal beat-to-beat mechanical activity. Reliable detection and quantification of these parameters still represent a hot topic in cardiovascular research. Nowadays, computer vision allows the development of open-source algorithms to measure cellular kinematics. However, the analysis software can vary based on analyzed specimens. In this study, we compared different software performances in in-silico model, in-vitro mouse adult ventricular cardiomyocytes and cardioids. We acquired in-vitro high-resolution videos during suprathreshold stimulation at 0.5-1-2 Hz, adapting the protocol for the cardioids. Moreover, we exposed the samples to inotropic and depolarizing substances. We analyzed in-silico and in-vitro videos by (i) MUSCLEMOTION, the gold standard among open-source software; (ii) CONTRACTIONWAVE, a recently developed tracking software; and (iii) ViKiE, an in-house customized video kinematic evaluation software. We enriched the study with three machine-learning algorithms to test the robustness of the motion-tracking approaches. Our results revealed that all software produced comparable estimations of cardiac mechanical parameters. For instance, in cardioids, beat duration measurements at 0.5 Hz were 1053.58 ms (MUSCLEMOTION), 1043.59 ms (CONTRACTIONWAVE), and 937.11 ms (ViKiE). ViKiE exhibited higher sensitivity in exposed samples due to its localized kinematic analysis, while MUSCLEMOTION and CONTRACTIONWAVE offered temporal correlation, combining global assessment with time-efficient analysis. Finally, machine learning reveals greater accuracy when trained with MUSCLEMOTION dataset in comparison with the other software (accuracy > 83%). In conclusion, our findings provide valuable insights for the accurate selection and integration of software tools into the kinematic analysis pipeline, tailored to the experimental protocol.

Single-cell RNA sequencing reveals the role of mitochondrial dysfunction in the cardiogenic toxicity of perfluorooctane sulfonate in human embryonic stem cells

Perfluorooctane sulfonate (PFOS), an endocrine-disrupting chemical pollutant, affects embryonic heart development; however, the mechanisms underlying its toxicity have not been fully elucidated. Here, Single-cell RNA sequencing (scRNA-seq) was used to investigate the overall effects of PFOS on myocardial differentiation from human embryonic stem cells (hESCs). Additionally, apoptosis, mitochondrial membrane potential, and ATP assays were performed. Downregulated cardiogenesis-related genes and inhibited cardiac differentiation were observed after PFOS exposure in vitro. The percentages of cardiomyocyte and cardiac progenitor cell clusters decreased significantly following exposure to PFOS, while the proportion of primitive endoderm cell was increased in PFOS group. Moreover, PFOS inhibited myocardial differentiation and blocked cellular development at the early- and middle-stage. A Gene Ontology analysis and pseudo-time trajectory illustrated that PFOS disturbed multiple processes related to cardiogenesis and oxidative phosphorylation in the mitochondria. Furthermore, PFOS decreased mitochondrial membrane potential and induced apoptosis. These results offer meaningful insights into the cardiogenic toxicity of PFOS exposure during heart formation as well as the adverse effects of PFOS on mitochondria.

Skeletal Muscle Spheroids as Building Blocks for Engineered Muscle Tissue

Spheroids exhibit enhanced cell-cell interactions that facilitate improved survival and mimic the physiological cellular environment in vivo. Cell spheroids have been successfully used as building blocks for engineered tissues, yet the viability of this approach with skeletal muscle spheroids is poorly understood, particularly when incorporated into three-dimensional (3D) constructs. Bioprinting is a promising strategy to recapitulate the hierarchical organization of native tissue that is fundamental to its function. However, the influence of bioprinting on skeletal muscle cell spheroids and their function are yet to be interrogated. Using C2C12 mouse myoblasts and primary bovine muscle stem cells (MuSCs), we characterized spheroid formation as a function of duration and cell seeding density. We then investigated the potential of skeletal muscle spheroids entrapped in alginate bioink as tissue building blocks for bioprinting myogenic tissue. Both C2C12 and primary bovine MuSCs formed spheroids of similar sizes and remained viable after bioprinting. Spheroids of both cell types fused into larger tissue clusters over time within alginate and exhibited tissue formation comparable to monodisperse cells. Compared to monodisperse cells in alginate gels, C2C12 spheroids exhibited greater MyHC expression after 2 weeks, while cells within bovine MuSC spheroids displayed increased cell spreading. Both monodisperse and MuSC spheroids exhibited increased expression of genes denoting mid- and late-stage myogenic differentiation. Together, these data suggest that skeletal muscle spheroids have the potential for generating myogenic tissue via 3D bioprinting and reveal areas of research that could enhance myogenesis and myogenic differentiation in future studies.

Organoids in COVID-19: can we break the glass ceiling?

COVID-19 emerged in September 2020 as a disease caused by the virus SARS-CoV-2. The disease presented as pneumonia at first but later was shown to cause multisystem infections and long-term complications. Many efforts have been put into discovering the exact pathogenesis of the disease. In this review, we aim to discuss an emerging tool in disease modeling, organoids, in the investigation of COVID-19. This review will introduce some methods and breakthroughs achieved by organoids and the limitations of this system.

Development of heart organoid cryopreservation method through Fe3 O4 nanoparticles based nanowarming system

Beyond single cell two-dimensional (2D) culture, research on organoids that can mimic human organs is rapidly developing. However, there are still problems in commercialization and joint research using organoids due to the lack of technology to safely store organoids. Since organoids are 3D complex structures with a certain size (0.1-5 mm) beyond the size of cells, the conventional cell-level cryopreservation method using cryoprotectant (CPA) cannot overcome the damage caused by volume change due to osmotic pressure difference and ice nucleation. Herein, we attempted to solve such limitations by applying a nanowarming system using CPA with high cell permeability and Fe3 O4 nanoparticles. By performing beat rate measurement, histological analysis, contractility analysis, and multi-electrode array, it was verified that the developed method could significantly improve functional recovery and survival of heart organoids after freezing and thawing. In this study, we demonstrated a successful organoid cryopreservation method based on a Fe3 O4 nanowarming system. The developed technology will provide clues to the field of tissue cryopreservation and spur the application of organoids.

Embryonic exposure of polystyrene nanoplastics affects cardiac development

Micro- and nanoplastics have recently been detected in human blood and placentas, indicating inevitable embryonic exposure to these particles. However, their influence on human embryogenesis and the underlying mechanisms are still unknown. In this study, the effects of polystyrene nanoplastics (PS-NPs) exposure on cardiac differentiation of human embryonic stem cells (hESCs) were evaluated. Uptake of PS-NPs not only caused cellular injury, but also regulated cardiac-related pathways as revealed by RNA-sequencing. Consequently, the efficiency of cardiomyocyte differentiation from hESCs was compromised, leading to immature of cardiomyocytes and smaller cardiac organoids with impaired contractility. Mechanistically, PS-NPs promoted mitochondrial oxidative stress, activated P38/Erk MAPK signaling pathway, blocked autophagy flux, and eventually reduced the pluripotency of hESCs. Consistently, in vivo exposure of PS-NPs from cleavage to gastrula period of zebrafish embryo led to reduced cardiac contraction and blood flow. Collectively, this study suggests that PS-NPs is a risk factor for fetal health, especially for heart development.

Embryonic Spinal Cord Innervation in Human Trunk Organogenesis Gastruloids: Cardiac Versus Enteric Customization and Beyond

Trunk-biased human gastruloids provide the ability to couple developmentally relevant spinal neurogenesis and organ morphogenesis via spatiotemporal self-organization events from derivatives of the three germ layers. The multi-lineage nature of gastruloids provides the full complexity of regulatory signaling cues that surpasses directed organoids and lays the foundation for an ex vivo self-evolving system. Here we detail two distinct protocols for trunk-biased gastruloids from an elongated, polarized structure with coordinated organ-specific neural patterning. Following an induction phase to caudalize iPSCs to trunk phenotype, divergent features of organogenesis and end-organ innervation yield separate models of enteric and cardiac nervous system formation. Both protocols are permissive to multi-lineage development and allow the study of neural integration events within a native, embryo-like context. We discuss the customizability of human gastruloids and the optimization of initial and extended conditions that maintain a permissive environment for multi-lineage differentiation and integration.

Construction of millimeter-scale vascularized engineered myocardial tissue using a mixed gel

Engineering myocardium has shown great clinal potential for repairing permanent myocardial injury. However, the lack of perfusing blood vessels and difficulties in preparing a thick-engineered myocardium result in its limited clinical use. We prepared a mixed gel containing fibrin (5 mg/ml) and collagen I (0.2 mg/ml) and verified that human umbilical vein endothelial cells (HUVECs) and human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) could form microvascular lumens and myocardial cell clusters by harnessing the low-hardness and hyperelastic characteristics of fibrin. hiPSC-CMs and HUVECs in the mixed gel formed self-organized cell clusters, which were then cultured in different media using a three-phase approach. The successfully constructed vascularized engineered myocardial tissue had a spherical structure and final diameter of 1-2 mm. The tissue exhibited autonomous beats that occurred at a frequency similar to a normal human heart rate. The internal microvascular lumen could be maintained for 6 weeks and showed good results during preliminary surface re-vascularization in vitro and vascular remodeling in vivo. In summary, we propose a simple method for constructing vascularized engineered myocardial tissue, through phased cultivation that does not rely on high-end manufacturing equipment and cutting-edge preparation techniques. The constructed tissue has potential value for clinical use after preliminary evaluation.

The sinoatrial node extracellular matrix promotes pacemaker phenotype and protects automaticity in engineered heart tissues from cyclic strain

The composite material-like extracellular matrix (ECM) in the sinoatrial node (SAN) supports the native pacemaking cardiomyocytes (PCMs). To test the roles of SAN ECM in the PCM phenotype and function, we engineered reconstructed-SAN heart tissues (rSANHTs) by recellularizing porcine SAN ECMs with hiPSC-derived PCMs. The hiPSC-PCMs in rSANHTs self-organized into clusters resembling the native SAN and displayed higher expression of pacemaker-specific genes and a faster automaticity compared with PCMs in reconstructed-left ventricular heart tissues (rLVHTs). To test the protective nature of SAN ECMs under strain, rSANHTs and rLVHTs were transplanted onto the murine thoracic diaphragm to undergo constant cyclic strain. All strained-rSANHTs preserved automaticity, whereas 66% of strained-rLVHTs lost their automaticity. In contrast to the strained-rLVHTs, PCMs in strained-rSANHTs maintained high expression of key pacemaker genes (HCN4, TBX3, and TBX18). These findings highlight the promotive and protective roles of the composite SAN ECM and provide valuable insights for pacemaking tissue engineering.

The application of quantitative telomerase activity measurement as an important indicator to monitor the cardiomyocyte differentiation process of human induced pluripotent stem cells under defined conditions

The construction of an in vitro differentiation system for human induced pluripotent stem cells (hiPSCs) has made exciting progress, but it is still of great significance to clarify the differentiation process. The use of conventional genetic and protein-labeled microscopes to observe or detect different stages of hiPSC differentiation is not specific enough and is cumbersome and time-consuming. In this study, in addition to analyzing the expression of gene/protein-related markers, we used a previously reported simple and excellent quantitative method of cellular telomerase activity based on a quartz crystal microbalance (TREAQ) device to monitor the dynamic changes in cellular telomerase activity in hiPSCs during myocardial differentiation under chemically defined conditions. Finally, by integrating these results, we analyzed the relationship between telomerase activity and the expression of marker genes/proteins as well as the cell type at each study time point. This dynamic quantitative measurement of cellular telomerase activity should be a promising indicator for monitoring dynamic changes in a stage of hiPSC differentiation and inducing cell types. This study provided a quantitative, dynamic and simple monitoring index for the in vitro differentiation process of hiPSC-CMs, which was a certain reference value for the optimization and improvement of the induction system.

A patterned human primitive heart organoid model generated by pluripotent stem cell self-organization

Pluripotent stem cell-derived organoids can recapitulate significant features of organ development in vitro. We hypothesized that creating human heart organoids by mimicking aspects of in utero gestation (e.g., addition of metabolic and hormonal factors) would lead to higher physiological and anatomical relevance. We find that heart organoids produced using this self-organization-driven developmental induction strategy are remarkably similar transcriptionally and morphologically to age-matched human embryonic hearts. We also show that they recapitulate several aspects of cardiac development, including large atrial and ventricular chambers, proepicardial organ formation, and retinoic acid-mediated anterior-posterior patterning, mimicking the developmental processes found in the post-heart tube stage primitive heart. Moreover, we provide proof-of-concept demonstration of the value of this system for disease modeling by exploring the effects of ondansetron, a drug administered to pregnant women and associated with congenital heart defects. These findings constitute a significant technical advance for synthetic heart development and provide a powerful tool for cardiac disease modeling.

Modeling cardiac fibroblast heterogeneity from human pluripotent stem cell-derived epicardial cells

Cardiac fibroblasts play an essential role in the development of the heart and are implicated in disease progression in the context of fibrosis and regeneration. Here, we establish a simple organoid culture platform using human pluripotent stem cell-derived epicardial cells and ventricular cardiomyocytes to study the development, maturation, and heterogeneity of cardiac fibroblasts under normal conditions and following treatment with pathological stimuli. We demonstrate that this system models the early interactions between epicardial cells and cardiomyocytes to generate a population of fibroblasts that recapitulates many aspects of fibroblast behavior in vivo, including changes associated with maturation and in response to pathological stimuli associated with cardiac injury. Using single cell transcriptomics, we show that the hPSC-derived organoid fibroblast population displays a high degree of heterogeneity that approximates the heterogeneity of populations in both the normal and diseased human heart. Additionally, we identify a unique subpopulation of fibroblasts possessing reparative features previously characterized in the hearts of model organisms. Taken together, our system recapitulates many aspects of human cardiac fibroblast specification, development, and maturation, providing a platform to investigate the role of these cells in human cardiovascular development and disease.

Multi-chamber cardioids unravel human heart development and cardiac defects

The number one cause of human fetal death are defects in heart development. Because the human embryonic heart is inaccessible and the impacts of mutations, drugs, and environmental factors on the specialized functions of different heart compartments are not captured by in vitro models, determining the underlying causes is difficult. Here, we established a human cardioid platform that recapitulates the development of all major embryonic heart compartments, including right and left ventricles, atria, outflow tract, and atrioventricular canal. By leveraging 2D and 3D differentiation, we efficiently generated progenitor subsets with distinct first, anterior, and posterior second heart field identities. This advance enabled the reproducible generation of cardioids with compartment-specific in vivo-like gene expression profiles, morphologies, and functions. We used this platform to unravel the ontogeny of signal and contraction propagation between interacting heart chambers and dissect how mutations, teratogens, and drugs cause compartment-specific defects in the developing human heart.

Nkx2.5: a crucial regulator of cardiac development, regeneration and diseases

Cardiomyocytes fail to regenerate after birth and respond to mitotic signals through cellular hypertrophy rather than cellular proliferation. Necrotic cardiomyocytes in the infarcted ventricular tissue are eventually replaced by fibroblasts, generating scar tissue. Cardiomyocyte loss causes localized systolic dysfunction. Therefore, achieving the regeneration of cardiomyocytes is of great significance for cardiac function and development. Heart development is a complex biological process. An integral cardiac developmental network plays a decisive role in the regeneration of cardiomyocytes. During this process, genetic epigenetic factors, transcription factors, signaling pathways and small RNAs are involved in regulating the developmental process of the heart. Cardiomyocyte-specific genes largely promote myocardial regeneration, among which the Nkx2.5 transcription factor is one of the earliest markers of cardiac progenitor cells, and the loss or overexpression of Nkx2.5 affects cardiac development and is a promising candidate factor. Nkx2.5 affects the development and function of the heart through its multiple functional domains. However, until now, the specific mechanism of Nkx2.5 in cardiac development and regeneration is not been fully understood. Therefore, this article will review the molecular structure, function and interaction regulation of Nkx2.5 to provide a new direction for cardiac development and the treatment of heart regeneration.

Induced pluripotent stem cell-derived cardiomyocytes-more show than substance?

Cardiomyocytes that are derived from human-induced pluripotent stem cells (iPSC-CM) are an exciting tool to investigate cardiomyopathy disease mechanisms at the cellular level as well as to screen for potential side effects of novel drugs. However, currently their benefit is limited due to their fairly immature differentiation status under conventional culture conditions. This review is mainly aimed at researchers outside of the iPSC-CM field and will describe potential pitfalls and which features at the level of the myofibrils would be desired to make them a more representative model system. We will also discuss different strategies that may help to achieve these.

Engineering Biomimetic Microenvironment for Organoid

Organoid is an emerging frontier technology in the field of life science, in which pluripotent stem cells or tissue-derived differentiated/progenitor cells form 3D structures according to their multi-directional differentiation potential and self-assembly ability. Nowadays, although various types of organoids are widely investigated, their construction is still complicated in operation, uncertain in yield, and poor in reproducibility for the structure and function of native organs. Constructing a biomimetic microenvironment for stem cell proliferation and differentiation in vitro is recognized as a key to driving this field. This review reviews the recent development of engineered biomimetic microenvironments for organoids. First, the composition of the matrix for organoid culture is summarized. Then, strategies for engineering the microenvironment from biophysical, biochemical, and cellular perspectives are discussed in detail. Subsequently, the newly developed monitoring technologies are also reviewed. Finally, a brief conclusion and outlook are presented for the inspiration of future research.

The PERK Branch of the Unfolded Protein Response Safeguards Protein Homeostasis and Mesendoderm Specification of Human Pluripotent Stem Cells

Cardiac development involves large-scale rearrangements of the proteome. How the developing cardiac cells maintain the integrity of the proteome during the rapid lineage transition remains unclear. Here it is shown that proteotoxic stress visualized by the misfolded and/or aggregated proteins appears during early cardiac differentiation of human pluripotent stem cells and is resolved by activation of the PERK branch of unfolded protein response (UPR). PERK depletion increases misfolded and/or aggregated protein accumulation, leading to pluripotency exit defect and impaired mesendoderm specification of human pluripotent stem cells. Mechanistically, it is found that PERK safeguards mesendoderm specification through its conserved downstream effector ATF4, which subsequently activates a novel transcriptional target WARS1, to cope with the differentiation-induced proteotoxic stress. The results indicate that protein quality control represents a previously unrecognized core component of the cardiogenic regulatory network. Broadly, these findings provide a framework for understanding how UPR is integrated into the developmental program by activating the PERK-ATF4-WARS1 axis.