Efficient differentiation of human pluripotent stem cells to endothelial progenitors via small-molecule activation of WNT signaling

Bioengineering methods for vascularizing organoids

Organoids, self-organizing three-dimensional (3D) structures derived from stem cells, offer unique advantages for studying organ development, modeling diseases, and screening potential therapeutics. However, their translational potential and ability to mimic complex in vivo functions are often hindered by the lack of an integrated vascular network. To address this critical limitation, bioengineering strategies are rapidly advancing to enable efficient vascularization of organoids. These methods encompass co-culturing organoids with various vascular cell types, co-culturing lineage-specific organoids with vascular organoids, co-differentiating stem cells into organ-specific and vascular lineages, using organoid-on-a-chip technology to integrate perfusable vasculature within organoids, and using 3D bioprinting to also create perfusable organoids. This review explores the field of organoid vascularization, examining the biological principles that inform bioengineering approaches. Additionally, this review envisions how the converging disciplines of stem cell biology, biomaterials, and advanced fabrication technologies will propel the creation of increasingly sophisticated organoid models, ultimately accelerating biomedical discoveries and innovations.

Direct programming of human pluripotent stem cells into endothelial progenitors with SOX17 and FGF2

Transcription factors (TFs) are pivotal in guiding stem cell behavior, including their maintenance and differentiation. Using single-cell RNA sequencing, we investigated TFs expressed in endothelial progenitors (EPs) derived from human pluripotent stem cells (hPSCs) and identified upregulated expression of SOXF factors SOX7, SOX17, and SOX18 in the EP population. To test whether overexpression of these factors increases differentiation efficiency, we established inducible hPSC lines for each SOXF factor and found only SOX17 overexpression robustly increased the percentage of cells expressing CD34 and vascular endothelial cadherin (VEC). Conversely, SOX17 knockdown via CRISPR-Cas13d significantly compromised EP differentiation. Intriguingly, we discovered SOX17 overexpression alone was sufficient to generate CD34+VEC+CD31- cells, and, when combined with FGF2 treatment, more than 90% of CD34+VEC+CD31+ EP was produced. These cells are capable of further differentiating into endothelial cells. These findings underscore an undiscovered role of SOX17 in programming hPSCs toward an EP lineage, illuminating pivotal mechanisms in EP differentiation.

SARS-CoV-2 spike protein induces endothelial dysfunction in 3D engineered vascular networks

With new daily discoveries about the long-term impacts of COVID-19, there is a clear need to develop in vitro models that can be used to better understand the pathogenicity and impact of COVID-19. Here, we demonstrate the utility of developing a model of endothelial dysfunction that utilizes human induced pluripotent stem cell-derived endothelial progenitors encapsulated in collagen hydrogels to study the effects of COVID-19 on the endothelium. These cells form capillary-like vasculature within 1 week after encapsulation and treating these cell-laden hydrogels with SARS-CoV-2 spike protein resulted in a significant decrease in the number of vessel-forming cells as well as vessel network connectivity quantified by our computational pipeline. This vascular dysfunction is a unique phenomenon observed upon treatment with SARS-CoV-2 SP and is not seen upon treatment with other coronaviruses, indicating that these effects were specific to SARS-CoV-2. We show that this vascular dysfunction is caused by an increase in inflammatory cytokines, associated with the COVID-19 cytokine storm, released from SARS-CoV-2 spike protein treated endothelial cells. Following treatment with the corticosteroid dexamethasone, we were able to prevent SARS-CoV-2 spike protein-induced endothelial dysfunction. Our results highlight the importance of understanding the interactions between SARS-CoV-2 spike protein and the endothelium and show that even in the absence of immune cells, the proposed 3D in vitro model for angiogenesis can reproduce COVID-19-induced endothelial dysfunction seen in clinical settings. This model represents a significant step in creating physiologically relevant disease models to further study the impact of long COVID and potentially identify mitigating therapeutics.

SOX17/ETV2 improves the direct reprogramming of adult fibroblasts to endothelial cells

An autologous source of vascular endothelial cells (ECs) is valuable for vascular regeneration and tissue engineering without the concern of immune rejection. The transcription factor ETS variant 2 (ETV2) has been shown to directly convert patient fibroblasts into vascular EC-like cells. However, reprogramming efficiency is low and there are limitations in EC functions, such as eNOS expression. In this study, we directly reprogram adult human dermal fibroblasts into reprogrammed ECs (rECs) by overexpressing SOX17 in conjunction with ETV2. We find several advantages to rEC generation using this approach, including improved reprogramming efficiency, increased enrichment of EC genes, formation of large blood vessels carrying blood from the host, and, most importantly, expression of eNOS in vivo. From these results, we present an improved method to reprogram adult fibroblasts into functional ECs and posit ideas for the future that could potentially further improve the reprogramming process.

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.

Building human artery and vein endothelial cells from pluripotent stem cells, and enduring mysteries surrounding arteriovenous development

Owing to their manifold roles in health and disease, there have been intense efforts to synthetically generate blood vessels in vitro from human pluripotent stem cells (hPSCs). However, there are multiple types of blood vessel, including arteries and veins, which are molecularly and functionally different. How can we specifically generate either arterial or venous endothelial cells (ECs) from hPSCs in vitro? Here, we summarize how arterial or venous ECs arise during embryonic development. VEGF and NOTCH arbitrate the bifurcation of arterial vs. venous ECs in vivo. While manipulating these two signaling pathways biases hPSC differentiation towards arterial and venous identities, efficiently generating these two subtypes of ECs has remained challenging until recently. Numerous questions remain to be fully addressed. What is the complete identity, timing and combination of extracellular signals that specify arterial vs. venous identities? How do these extracellular signals intersect with fluid flow to modulate arteriovenous fate? What is a unified definition for endothelial progenitors or angioblasts, and when do arterial vs. venous potentials segregate? How can we regulate hPSC-derived arterial and venous ECs in vitro, and generate organ-specific ECs? In turn, answers to these questions could avail the production of arterial and venous ECs from hPSCs, accelerating vascular research, tissue engineering, and regenerative medicine.

Bioengineering Cell Therapy for Treatment of Peripheral Artery Disease

Peripheral artery disease is an atherosclerotic disease associated with limb ischemia that necessitates limb amputation in severe cases. Cell therapies comprised of adult mononuclear or stromal cells have been clinically tested and show moderate benefits. Bioengineering strategies can be applied to modify cell behavior and function in a controllable fashion. Using mechanically tunable or spatially controllable biomaterials, we highlight examples in which biomaterials can increase the survival and function of the transplanted cells to improve their revascularization efficacy in preclinical models. Biomaterials can be used in conjunction with soluble factors or genetic approaches to further modulate the behavior of transplanted cells and the locally implanted tissue environment in vivo. We critically assess the advances in bioengineering strategies such as 3-dimensional bioprinting and immunomodulatory biomaterials that can be applied to the treatment of peripheral artery disease and then discuss the current challenges and future directions in the implementation of bioengineering strategies.

Advances in the differentiation of pluripotent stem cells into vascular cells

Blood vessels constitute a closed pipe system distributed throughout the body, transporting blood from the heart to other organs and delivering metabolic waste products back to the lungs and kidneys. Changes in blood vessels are related to many disorders like stroke, myocardial infarction, aneurysm, and diabetes, which are important causes of death worldwide. Translational research for new approaches to disease modeling and effective treatment is needed due to the huge socio-economic burden on healthcare systems. Although mice or rats have been widely used, applying data from animal studies to human-specific vascular physiology and pathology is difficult. The rise of induced pluripotent stem cells (iPSCs) provides a reliable in vitro resource for disease modeling, regenerative medicine, and drug discovery because they carry all human genetic information and have the ability to directionally differentiate into any type of human cells. This review summarizes the latest progress from the establishment of iPSCs, the strategies for differentiating iPSCs into vascular cells, and the in vivo transplantation of these vascular derivatives. It also introduces the application of these technologies in disease modeling, drug screening, and regenerative medicine. Additionally, the application of high-tech tools, such as omics analysis and high-throughput sequencing, in this field is reviewed.

Host-microbe interactions at the blood-brain barrier through the lens of induced pluripotent stem cell-derived brain-like endothelial cells

Microbe-induced meningoencephalitis/meningitis is a life-threatening infection of the central nervous system (CNS) that occurs when pathogens are able to cross the blood-brain barrier (BBB) and gain access to the CNS. The BBB consists of highly specialized brain endothelial cells that exhibit specific properties to allow tight regulation of CNS homeostasis and prevent pathogen crossing. However, during meningoencephalitis/meningitis, the BBB fails to protect the CNS. Modeling the BBB remains a challenge due to the specialized characteristics of these cells. In this review, we cover the induced pluripotent stem cell-derived, brain-like endothelial cell model during host-pathogen interaction, highlighting the strengths and recent work on various pathogens known to interact with the BBB. As stem cell technologies are becoming more prominent, the stem cell-derived, brain-like endothelial cell model has been able to reveal new insights in vitro, which remain challenging with other in vitro cell-based models consisting of primary human brain endothelial cells and immortalized human brain endothelial cell lines.

Review: Human stem cell-based 3D in vitro angiogenesis models for preclinical drug screening applications

Vascular diseases are the underlying pathology in many life-threatening illnesses. Human cellular and molecular mechanisms involved in angiogenesis are complex and difficult to study in current 2D in vitro and in vivo animal models. Engineered 3D in vitro models that incorporate human pluripotent stem cell (hPSC) derived endothelial cells (ECs) and supportive biomaterials within a dynamic microfluidic platform provide a less expensive, more controlled, and reproducible platform to better study angiogenic processes in response to external chemical or physical stimulus. Current studies to develop 3D in vitro angiogenesis models aim to establish single-source systems by incorporating hPSC-ECs into biomimetic extracellular matrices (ECM) and microfluidic devices to create a patient-specific, physiologically relevant platform that facilitates preclinical study of endothelial cell-ECM interactions, vascular disease pathology, and drug treatment pharmacokinetics. This review provides a detailed description of the current methods used for the directed differentiation of human stem cells to endothelial cells and their use in engineered 3D in vitro angiogenesis models that have been developed within the last 10 years.

Engineered T cells from induced pluripotent stem cells: from research towards clinical implementation

Induced pluripotent stem cell (iPSC)-derived T (iT) cells represent a groundbreaking frontier in adoptive cell therapies with engineered T cells, poised to overcome pivotal limitations associated with conventional manufacturing methods. iPSCs offer an off-the-shelf source of therapeutic T cells with the potential for infinite expansion and straightforward genetic manipulation to ensure hypo-immunogenicity and introduce specific therapeutic functions, such as antigen specificity through a chimeric antigen receptor (CAR). Importantly, genetic engineering of iPSC offers the benefit of generating fully modified clonal lines that are amenable to rigorous safety assessments. Critical to harnessing the potential of iT cells is the development of a robust and clinically compatible production process. Current protocols for genetic engineering as well as differentiation protocols designed to mirror human hematopoiesis and T cell development, vary in efficiency and often contain non-compliant components, thereby rendering them unsuitable for clinical implementation. This comprehensive review centers on the remarkable progress made over the last decade in generating functional engineered T cells from iPSCs. Emphasis is placed on alignment with good manufacturing practice (GMP) standards, scalability, safety measures and quality controls, which constitute the fundamental prerequisites for clinical application. In conclusion, the focus on iPSC as a source promises standardized, scalable, clinically relevant, and potentially safer production of engineered T cells. This groundbreaking approach holds the potential to extend hope to a broader spectrum of patients and diseases, leading in a new era in adoptive T cell therapy.

TGF-β and SHH Regulate Pluripotent Stem Cell Differentiation into Brain Microvascular Endothelial Cells in Generating an In Vitro Blood-Brain Barrier Model

Blood-brain barrier (BBB) models are important tools for studying CNS drug delivery, brain development, and brain disease. In vitro BBB models have been obtained from animals and immortalized cell lines; however, brain microvascular endothelial cells (BMECs) derived from them have several limitations. Furthermore, obtaining mature brain microvascular endothelial-like cells (BME-like cells) from human pluripotent stem cells (hPSCs) with desirable properties for establishing BBB models has been challenging. Here, we developed an efficient method for differentiating hPSCs into BMECs that are amenable to the development and application of human BBB models. The established conditions provided an environment similar to that occurring during BBB differentiation in the presence of the co-differentiating neural cell population by the modulation of TGF-β and SHH signaling. The developed BME-like cells showed well-organized tight junctions, appropriate expression of nutrient transporters, and polarized efflux transporter activity. In addition, BME-like cells responded to astrocytes, acquiring substantial barrier properties as measured by transendothelial electrical resistance. Moreover, the BME-like cells exhibited an immune quiescent property of BBB endothelial cells by decreasing the expression of adhesion molecules. Therefore, our novel cellular platform could be useful for drug screening and the development of brain-permeable pharmaceuticals.

Stem cell pathology: histogenesis of malignant fibrous histiocytoma and characterization of myofibroblasts appearing in fibrotic lesions

The concept of "stem cell pathology" is to establish the role of the stem cells by exploring their contribution to lesion development. The somatic stem cells are present in the body. Malignant fibrous histiocytoma (MFH; recently named "undifferentiated pleomorphic sarcoma") includes pluripotential undifferentiated mesenchymal stem cells as a cell element. An antibody (A3) generated by using rat MFH cells as the antigen labels somatic stem cells such as bone marrow stem cells and immature endothelial cells and pericytes, as well as immature epithelial cells in epithelialization. By using A3 and other antibodies recognizing somatic stem cells, it is considered that myofibroblasts appearing in rat fibrotic lesions are developed partly from immature hepatic stellate cells in hepatic fibrosis, immature pancreatic stellate cells in pancreatic fibrosis, pericytes/endothelial cells in neovascularization in injured tissues, as well as via the epithelial-mesenchymal transition. These progenitors may be in the stem cell lineage. In this review, the author introduces the histogenesis of MFH and the characteristics of myofibroblasts appearing in fibrosis, based mainly on the author's studies.

Direct differentiation of human pluripotent stem cells into vascular network along with supporting mural cells

During embryonic development, endothelial cells (ECs) undergo vasculogenesis to form a primitive plexus and assemble into networks comprised of mural cell-stabilized vessels with molecularly distinct artery and vein signatures. This organized vasculature is established prior to the initiation of blood flow and depends on a sequence of complex signaling events elucidated primarily in animal models, but less studied and understood in humans. Here, we have developed a simple vascular differentiation protocol for human pluripotent stem cells that generates ECs, pericytes, and smooth muscle cells simultaneously. When this protocol is applied in a 3D hydrogel, we demonstrate that it recapitulates the dynamic processes of early human vessel formation, including acquisition of distinct arterial and venous fates, resulting in a vasculogenesis angiogenesis model plexus (VAMP). The VAMP captures the major stages of vasculogenesis, angiogenesis, and vascular network formation and is a simple, rapid, scalable model system for studying early human vascular development in vitro.

Extracellular matrix cues regulate the differentiation of pluripotent stem cell-derived endothelial cells

The generation of endothelial cells (ECs) from human pluripotent stem cells (PSCs) has been a promising approach for treating cardiovascular diseases for several years. Human PSCs, particularly induced pluripotent stem cells (iPSCs), are an attractive source of ECs for cell therapy. Although there is a diversity of methods for endothelial cell differentiation using biochemical factors, such as small molecules and cytokines, the efficiency of EC production varies depending on the type and dose of biochemical factors. Moreover, the protocols in which most EC differentiation studies have been performed were in very unphysiological conditions that do not reflect the microenvironment of native tissue. The microenvironment surrounding stem cells exerts variable biochemical and biomechanical stimuli that can affect stem cell differentiation and behavior. The stiffness and components of the extracellular microenvironment are critical inducers of stem cell behavior and fate specification by sensing the extracellular matrix (ECM) cues, adjusting the cytoskeleton tension, and delivering external signals to the nucleus. Differentiation of stem cells into ECs using a cocktail of biochemical factors has been performed for decades. However, the effects of mechanical stimuli on endothelial cell differentiation remain poorly understood. This review provides an overview of the methods used to differentiate ECs from stem cells by chemical and mechanical stimuli. We also propose the possibility of a novel EC differentiation strategy using a synthetic and natural extracellular matrix.

Chronic nicotine impairs the angiogenic capacity of human induced pluripotent stem cell-derived endothelial cells in a murine model of peripheral arterial disease

Objective

Lifestyle choices such as tobacco and e-cigarette use are a risk factor for peripheral arterial disease (PAD) and may influence therapeutic outcomes. The effect of chronic nicotine exposure on the angiogenic capacity of human induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) was assessed in a murine model of PAD.

Methods

Mice were exposed to nicotine or phosphate-buffered saline (PBS) for 28 days, followed by induction of limb ischemia and iPSC-EC transplantation. Cells were injected into the ischemic limb immediately after induction of hindlimb ischemia and again 7 days later. Limb perfusion was assessed by laser Doppler spectroscopy, and transplant cell survival was monitored for 14 days afterward using bioluminescence imaging, followed by histological analysis of angiogenesis.

Results

Transplant cell retention progressively decreased over time after implantation based on bioluminescence imaging, and there were no significant differences in cell survival between mice with chronic exposure to nicotine or PBS. However, compared with mice without nicotine exposure, mice with prior nicotine exposure had had an impaired therapeutic response to iPSC-EC therapy based on decreased vascular perfusion recovery. Mice with nicotine exposure, followed by cell transplantation, had significantly lower mean perfusion ratio after 14 days (0.47 ± 0.07) compared with mice undergoing cell transplantation without prior nicotine exposure (0.79 ± 0.11). This finding was further supported by histological analysis of capillary density, in which animals with prior nicotine exposure had a lower capillary density (45.9 ± 4.7 per mm2) compared with mice without nicotine exposure (66.5 ± 8.1 per mm2). Importantly, the ischemic limbs mice exposed to nicotine without cell therapy also showed significant impairment in perfusion recovery after 14 days, compared with mice that received PBS + iPSC-EC treatment. This result suggested that mice without chronic nicotine exposure could respond to iPSC-EC implantation into the ischemic limb by inducing perfusion recovery, whereas mice with chronic nicotine exposure did not respond to iPSC-EC therapy.

Conclusions

Together, these findings show that chronic nicotine exposure adversely affects the ability of iPSC-EC therapy to promote vascular perfusion recovery and angiogenesis in a murine PAD model.

Engineered anti-prostate cancer CAR-neutrophils from human pluripotent stem cells

Immunotherapy is a powerful technique where immune cells are modified to improve cytotoxicity against cancerous cells to treat cancers that do not respond to surgery, chemotherapy, or radiotherapy. Expressing chimeric antigen receptor (CAR) in immune cells, typically T lymphocytes, is a practical modification that drives an immune response against cancerous tissue. CAR-T efficacy is suboptimal in solid tumors due to the tumor microenvironment (TME) that limits T lymphocyte cytotoxicity. In this study, we demonstrate that neutrophils differentiated from human pluripotent stem cells modified with AAVS1-inserted CAR constructs showed a robust cytotoxic effect against prostate-specific membrane antigen (PSMA) expressing LNCaP cells as a model for prostate cancer in vitro. Our results suggest that engineered CAR can significantly enhance the neutrophil anti-tumor effect, providing a new avenue in treating prostate cancers.

Role of MEF2C in the Endothelial Cells Derived from Human Induced Pluripotent Stem Cells

Human induced pluripotent stem cells (hiPSCs) not only provide an abundant source of vascular cells for potential therapeutic applications in vascular disease but also constitute an excellent model for understanding the mechanisms that regulate the differentiation and the functionality of vascular cells. Here, we reported that myocyte enhancer factor 2C (MEF2C) transcription factor, but not any other members of the MEF2 family, was robustly upregulated during the differentiation of vascular progenitors and endothelial cells (ECs) from hiPSCs. Vascular endothelial growth factors (VEGF) strongly induced MEF2C expression in endothelial lineage cells. The specific upregulation of MEF2C during the commitment of endothelial lineage was dependent on the extracellular signal regulated kinase (ERK). Moreover, knockdown of MEF2C with shRNA in hiPSCs did not affect the differentiation of ECs from these hiPSCs, but greatly reduced the migration and tube formation capacity of the hiPSC-derived ECs. Through a chromatin immunoprecipitation-sequencing, genome-wide RNA-sequencing, quantitative RT-PCR, and immunostaining analyses of the hiPSC-derived endothelial lineage cells with MEF2C inhibition or knockdown compared to control hiPSC-derived ECs, we identified TNF-related apoptosis inducing ligand (TRAIL) and transmembrane protein 100 (TMEM100) as novel targets of MEF2C. This study demonstrates an important role for MEF2C in regulating human EC functions and highlights MEF2C and its downstream effectors as potential targets to treat vascular malfunction-associated diseases.

Enriched environment as a nonpharmacological neuroprotective strategy

The structure and functions of the central nervous system are influenced by environmental stimuli, which also play an important role in brain diseases. Enriched environment (EE) consists of producing modifications in the environment of standard laboratory animals to induce an improvement in their biological conditions. This paradigm promotes transcriptional and translational effects that result in ameliorated motor, sensory, and cognitive stimulation. EE has been shown to enhance experience-dependent cellular plasticity and cognitive performance in animals housed under these conditions compared with animals housed under standard conditions. In addition, several studies claim that EE induces nerve repair by restoring functional activities through morphological, cellular, and molecular adaptations in the brain that have clinical relevance in neurological and psychiatric disorders. In fact, the effects of EE have been studied in different animal models of psychiatric and neurological diseases, such as Alzheimer's disease, Parkinson's disease, schizophrenia, ischemic brain injury, or traumatic brain injury, delaying the onset and progression of a wide variety of symptoms of these disorders. In this review, we analyze the action of EE focused on diseases of the central nervous system and the translation to humans to develop a bridge to its application.

Chemically defined generation of human definitive hematopoietic stem and progenitor cells

Here, we present a protocol to efficiently direct human pluripotent stem cells (hPSCs) into hematopoietic stem and progenitor cells (HSPCs) under a chemically defined, albumin-free system. We describe the induction of aorta-gonad-mesonephros-like hematopoiesis from hPSCs into SOX17+ hemogenic endothelium and then into CD34+CD45+ HSPCs via application of Wnt activator and TGFβ inhibitor, respectively. The generated HSPCs, characterized by flow cytometry and colony-forming unit assay, express definitive hematopoiesis markers and exhibit multilineage differentiation potential and the capacity to expand. For complete details on the use and execution of this protocol, please refer to Chang et al. (2022a, 2022b).1,2.

Extracellular matrix proteins in construction and function of in vitro blood-brain barrier models

The blood-brain barrier (BBB) is a highly impermeable barrier separating circulating blood and brain tissue. A functional BBB is critical for brain health, and BBB dysfunction has been linked to the pathophysiology of diseases such as stroke and Alzheimer’s disease. A variety of models have been developed to study the formation and maintenance of the BBB, ranging from in vivo animal models to in vitro models consisting of primary cells or cells differentiated from human pluripotent stem cells (hPSCs). These models must consider the composition and source of the cellular components of the neurovascular unit (NVU), including brain microvascular endothelial cells (BMECs), brain pericytes, astrocytes, and neurons, and how these cell types interact. In addition, the non-cellular components of the BBB microenvironment, such as the brain vascular basement membrane (BM) that is in direct contact with the NVU, also play key roles in BBB function. Here, we review how extracellular matrix (ECM) proteins in the brain vascular BM affect the BBB, with a particular focus on studies using hPSC-derived in vitro BBB models, and discuss how future studies are needed to advance our understanding of how the ECM affects BBB models to improve model performance and expand our knowledge on the formation and maintenance of the BBB.

High and low permeability of human pluripotent stem cell-derived blood-brain barrier models depend on epithelial or endothelial features

The search for reliable human blood-brain barrier (BBB) models represents a challenge for the development/testing of strategies aiming to enhance brain delivery of drugs. Human-induced pluripotent stem cells (hiPSCs) have raised hopes in the development of predictive BBB models. Differentiating strategies are thus required to generate endothelial cells (ECs), a major component of the BBB. Several hiPSC-based protocols have reported the generation of in vitro models with significant differences in barrier properties. We studied in depth the properties of iPSCs byproducts from two protocols that have been established to yield these in vitro barrier models. Our analysis/study reveals that iPSCs derivatives endowed with EC features yield high permeability models while the cells that exhibit outstanding barrier properties show principally epithelial cell-like (EpC) features. We found that models containing EpC-like cells express tight junction proteins, transporters/efflux pumps and display a high functional tightness with very low permeability, which are features commonly shared between BBB and epithelial barriers. Our study demonstrates that hiPSC-based BBB models need extensive characterization beforehand and that a reliable human BBB model containing EC-like cells and displaying low permeability is still needed.

Experimental Models of In Vitro Blood-Brain Barrier for CNS Drug Delivery: An Evolutionary Perspective

Central nervous system (CNS) disorders represent one of the leading causes of global health burden. Nonetheless, new therapies approved against these disorders are among the lowest compared to their counterparts. The absence of reliable and efficient in vitro blood-brain barrier (BBB) models resembling in vivo barrier properties stands out as a significant roadblock in developing successful therapy for CNS disorders. Therefore, advancement in the creation of robust and sensitive in vitro BBB models for drug screening might allow us to expedite neurological drug development. This review discusses the major in vitro BBB models developed as of now for exploring the barrier properties of the cerebral vasculature. Our main focus is describing existing in vitro models, including the 2D transwell models covering both single-layer and co-culture models, 3D organoid models, and microfluidic models with their construction, permeability measurement, applications, and limitations. Although microfluidic models are better at recapitulating the in vivo properties of BBB than other models, significant gaps still exist for their use in predicting the performance of neurotherapeutics. However, this comprehensive account of in vitro BBB models can be useful for researchers to create improved models in the future.

Defined Differentiation of Human Pluripotent Stem Cells to Brain Microvascular Endothelial-Like Cells for Modeling the Blood-Brain Barrier

The blood-brain barrier (BBB) comprises brain microvascular endothelial cells (BMECs) that form a high-resistance cellular interface that separates the blood compartment from the brain parenchyma. An intact BBB is pivotal to maintaining brain homeostasis but also impedes the entry of neurotherapeutics. There are limited options for human-specific BBB permeability testing, however. Human pluripotent stem cell models offer a powerful tool for dissecting components of this barrier in vitro, including understanding mechanisms of BBB function, and developing strategies to improve the permeability of molecular and cellular therapeutics targeting the brain. Here, we provide a detailed, step-by-step protocol for differentiation of human pluripotent stem cells (hPSCs) to cells exhibiting key characteristics of BMECs, including paracellular and transcellular transport resistance and transporter function that enable modeling the human BBB.

Engineering approaches for cardiac organoid formation and their characterization

Cardiac organoids are 3-dimensional (3D) structures composed of tissue or niche-specific cells, obtained from diverse sources, encapsulated in either a naturally derived or synthetic, extracellular matrix scaffold, and include exogenous biochemical signals such as essential growth factors. The overarching goal of developing cardiac organoid models is to establish a functional integration of cardiomyocytes with physiologically relevant cells, tissues, and structures like capillary-like networks composed of endothelial cells. These organoids used to model human heart anatomy, physiology, and disease pathologies in vitro have the potential to solve many issues related to cardiovascular drug discovery and fundamental research. The advent of patient-specific human-induced pluripotent stem cell-derived cardiovascular cells provide a unique, single-source approach to study the complex process of cardiovascular disease progression through organoid formation and incorporation into relevant, controlled microenvironments such as microfluidic devices. Strategies that aim to accomplish such a feat include microfluidic technology-based approaches, microphysiological systems, microwells, microarray-based platforms, 3D bioprinted models, and electrospun fiber mat-based scaffolds. This article discusses the engineering or technology-driven practices for making cardiac organoid models in comparison with self-assembled or scaffold-free methods to generate organoids. We further discuss emerging strategies for characterization of the bio-assembled cardiac organoids including electrophysiology and machine-learning and conclude with prospective points of interest for engineering cardiac tissues in vitro.

SARS-CoV-2 spike protein induces endothelial dysfunction in 3D engineered vascular networks

With new daily discoveries about the long-term impacts of COVID-19 there is a clear need to develop in vitro models that can be used to better understand the pathogenicity and impact of COVID-19. Here we demonstrate the utility of developing a model of endothelial dysfunction that utilizes induced pluripotent stem cell-derived endothelial progenitors encapsulated in collagen hydrogels to study the effects of COVID-19 on the endothelium. We found that treating these cell-laden hydrogels with SARS-CoV-2 spike protein resulted in a significant decrease in the number of vessel-forming cells as well as vessel network connectivity. Following treatment with the anti-inflammatory drug dexamethasone, we were able to prevent SARS-CoV-2 spike protein-induced endothelial dysfunction. In addition, we confirmed release of inflammatory cytokines associated with the COVID-19 cytokine storm. In conclusion, we have demonstrated that even in the absence of immune cells, we are able to use this 3D in vitro model for angiogenesis to reproduce COVID-19 induced endothelial dysfunction seen in clinical settings.

Robust genome editing via modRNA-based Cas9 or base editor in human pluripotent stem cells

CRISPR systems have revolutionized biomedical research because they offer an unprecedented opportunity for genome editing. However, a bottleneck of applying CRISPR systems in human pluripotent stem cells (hPSCs) is how to deliver CRISPR effectors easily and efficiently. Here, we developed modified mRNA (modRNA)-based CRIPSR systems that utilized Cas9 and p53DD or a base editor (ABE8e) modRNA for the purposes of knocking out genes in hPSCs via simple lipid-based transfection. ABE8e modRNA was employed to disrupt the splice donor site, resulting in defective splicing of the target transcript and ultimately leading to gene knockout. Using our modRNA CRISPR systems, we achieved 73.3% ± 11.2% and 69.6 ± 3.8% knockout efficiency with Cas9 plus p53DD modRNA and ABE8e modRNA, respectively, which was significantly higher than the plasmid-based systems. In summary, we demonstrate that our non-integrating modRNA-based CRISPR methods hold great promise as more efficient and accessible techniques for genome editing of hPSCs.

Challenges and opportunities for the next generation of cardiovascular tissue engineering

Engineered cardiac tissues derived from human induced pluripotent stem cells offer unique opportunities for patient-specific disease modeling, drug discovery and cardiac repair. Since the first engineered hearts were introduced over two decades ago, human induced pluripotent stem cell-based three-dimensional cardiac organoids and heart-on-a-chip systems have now become mainstays in basic cardiovascular research as valuable platforms for investigating fundamental human pathophysiology and development. However, major obstacles remain to be addressed before the field can truly advance toward commercial and clinical translation. Here we provide a snapshot of the state-of-the-art methods in cardiac tissue engineering, with a focus on in vitro models of the human heart. Looking ahead, we discuss major challenges and opportunities in the field and suggest strategies for enabling broad acceptance of engineered cardiac tissues as models of cardiac pathophysiology and testbeds for the development of therapies.

Enhancement strategy for effective vascular regeneration following myocardial infarction through a dual stem cell approach

Since an impaired coronary blood supply following myocardial infarction (MI) negatively affects heart function, therapeutic neovascularization is considered one of the major therapeutic strategies for cell-based cardiac repair. Here, to more effectively achieve therapeutic neovascularization in ischemic hearts, we developed a dual stem cell approach for effective vascular regeneration by utilizing two distinct types of stem cells, CD31⁺-endothelial cells derived from human induced pluripotent stem cells (hiPSC-ECs) and engineered human mesenchymal stem cells that continuously secrete stromal derived factor-1α (SDF-eMSCs), to simultaneously promote natal vasculogenesis and angiogenesis, two core mechanisms of neovascularization. To induce more comprehensive vascular regeneration, we intramyocardially injected hiPSC-ECs to produce de novo vessels, possibly via vasculogenesis, and a 3D cardiac patch encapsulating SDF-eMSCs (SDF-eMSC-PA) to enhance angiogenesis through prolonged secretion of paracrine factors, including SDF-1α, was implanted into the epicardium of ischemic hearts. We verified that hiPSC-ECs directly contribute to de novo vessel formation in ischemic hearts, resulting in enhanced cardiac function. In addition, the concomitant implantation of SDF1α-eMSC-PAs substantially improved the survival, retention, and vasculogenic potential of hiPSC-ECs, ultimately achieving more comprehensive neovascularization in the MI hearts. Of note, the newly formed vessels through the dual stem cell approach were significantly larger and more functional than those formed by hiPSC-ECs alone. In conclusion, these results provide compelling evidence that our strategy for effective vascular regeneration can be an effective means to treat ischemic heart disease.

A treatment involving two different types of stem cells leads to repairing failed hearts by making new functional blood vessels. Researchers at the City University of Hong Kong and the Catholic University of Korea induced heart attacks in rats before injecting the hearts with endothelial cells derived from human induced pluripotent stem cells, specialized to form blood vessels. These cells successfully induced the formation of new blood vessels in the damaged hearts. The researchers combined this treatment with a cardiac patch containing engineered human adult stem cells, which improved the survival and performance of the endothelial cells. And this dual stem cell treatment resulted in enhanced cardiac function and a higher number of larger and stronger new blood vessels than those produced by the single-cell treatment suggesting an effective way to repair failed hearts.

Timely delivery of cardiac mmRNAs in microfluidics enhances cardiogenic programming of human pluripotent stem cells

In the last two decades lab-on-chip models, specifically heart-on-chip, have been developed as promising technologies for recapitulating physiological environments suitable for studies of drug and environmental effects on either human physiological or patho-physiological conditions. Most human heart-on-chip systems are based on integration and adaptation of terminally differentiated cells within microfluidic context. This process requires prolonged procedures, multiple steps, and is associated with an intrinsic variability of cardiac differentiation. In this view, we developed a method for cardiac differentiation-on-a-chip based on combining the stage-specific regulation of Wnt/β-catenin signaling with the forced expression of transcription factors (TFs) that timely recapitulate hallmarks of the cardiac development. We performed the overall cardiac differentiation from human pluripotent stem cells (hPSCs) to cardiomyocytes (CMs) within a microfluidic environment. Sequential forced expression of cardiac TFs was achieved by a sequential mmRNAs delivery of first MESP1, GATA4 followed by GATA4, NKX2.5, MEF2C, TBX3, and TBX5. We showed that this optimized protocol led to a robust and reproducible approach to obtain a cost-effective hiPSC-derived heart-on-chip. The results showed higher distribution of cTNT positive CMs along the channel and a higher expression of functional cardiac markers (TNNT2 and MYH7). The combination of stage-specific regulation of Wnt/β-catenin signaling with mmRNAs encoding cardiac transcription factors will be suitable to obtain heart-on-chip model in a cost-effective manner, enabling to perform combinatorial, multiparametric, parallelized and high-throughput experiments on functional cardiomyocytes.

An in vitro model of glucose transporter 1 deficiency syndrome at the blood-brain barrier using induced pluripotent stem cells

Glucose is an important source of energy for the central nervous system. Its uptake at the blood-brain barrier (BBB) is mostly mediated via glucose transporter 1 (GLUT1), a facilitated transporter encoded by the SLC2A1 gene. GLUT1 Deficiency Syndrome (GLUT1DS) is a haploinsufficiency characterized by mutations in the SLC2A1 gene, resulting in impaired glucose uptake at the BBB and clinically characterized by epileptic seizures and movement disorder. A major limitation is an absence of in vitro models of the BBB reproducing the disease. This study aimed to characterize an in vitro model of GLUT1DS using human pluripotent stem cells (iPSCs). Two GLUT1DS clones were generated (GLUT1-iPSC) from their original parental clone iPS(IMR90)-c4 by CRISPR/Cas9 and differentiated into brain microvascular endothelial cells (iBMECs). Cells were characterized in terms of SLC2A1 expression, changes in the barrier function, glucose uptake and metabolism, and angiogenesis. GLUT1DS iPSCs and iBMECs showed comparable phenotype to their parental control, with exception of reduced GLUT1 expression at the protein level. Although no major disruption in the barrier function was reported in the two clones, a significant reduction in glucose uptake accompanied by an increase in glycolysis and mitochondrial respiration was reported in both GLUT1DS-iBMECs. Finally, impaired angiogenic features were reported in such clones compared to the parental clone. Our study provides the first documented characterization of GLUT1DS-iBMECs generated by CRISPR-Cas9, suggesting that GLUT1 truncation appears detrimental to brain angiogenesis and brain endothelial bioenergetics, but maybe not be detrimental to iBMECs differentiation and barriergenesis. Our future direction is to further characterize the functional outcome of such truncated product, as well as its impact on other cells of the neurovascular unit.

Chromosome silencing in vitro reveals trisomy 21 causes cell-autonomous deficits in angiogenesis and early dysregulation in Notch signaling

Despite the prevalence of Down syndrome (DS), little is known regarding the specific cell pathologies that underlie this multi-system disorder. To understand which cell types and pathways are more directly affected by trisomy 21 (T21), we used an inducible-XIST system to silence one chromosome 21 in vitro. T21 caused the dysregulation of Notch signaling in iPSCs, potentially affecting cell-type programming. Further analyses identified dysregulation of pathways important for two cell types: neurogenesis and angiogenesis. Angiogenesis is essential to many bodily systems, yet is understudied in DS; therefore, we focused next on whether T21 affects endothelial cells. An in vitro assay for microvasculature formation revealed a cellular pathology involving delayed tube formation in response to angiogenic signals. Parallel transcriptomic analysis of endothelia further showed deficits in angiogenesis regulators. Results indicate a direct cell-autonomous impact of T21 on endothelial function, highlighting the importance of angiogenesis, with wide-reaching implications for development and disease progression.

Moon and Lawrence examine the immediate effects of trisomy 21 silencing and find angiogenesis and neurogenesis pathways, including Notch signaling, affected as early as pluripotency. In endothelial cells, functional analyses show that trisomy delays the angiogenic response for microvessel formation and transcriptomics show a parallel impact on angiogenic regulators and signal-response and cytoskeleton processes.

Engineering chimeric antigen receptor neutrophils from human pluripotent stem cells for targeted cancer immunotherapy

Neutrophils, the most abundant white blood cells in circulation, are closely related to cancer development and progression. Healthy primary neutrophils present potent cytotoxicity against various cancer cell lines through direct contact and via generation of reactive oxygen species. However, due to their short half-life and resistance to genetic modification, neutrophils have not yet been engineered with chimeric antigen receptors (CARs) to enhance their antitumor cytotoxicity for targeted immunotherapy. Here, we genetically engineered human pluripotent stem cells with synthetic CARs and differentiated them into functional neutrophils by implementing a chemically defined platform. The resulting CAR neutrophils present superior and specific cytotoxicity against tumor cells both in vitro and in vivo. Collectively, we established a robust platform for massive production of CAR neutrophils, paving the way to myeloid cell-based therapeutic strategies that would boost current cancer-treatment approaches.

Neutrophils are important innate immune cells that mediate both protumor and antitumor activities. Chang et al. genetically engineer human pluripotent stem cells to produce chimeric antigen receptor (CAR) neutrophils that display superior antitumor activities and improve survival in an in situ glioblastoma xenograft model.

Generating human artery and vein cells from pluripotent stem cells highlights the arterial tropism of Nipah and Hendra viruses

Stem cell research endeavors to generate specific subtypes of classically defined "cell types." Here, we generate >90% pure human artery or vein endothelial cells from pluripotent stem cells within 3-4 days. We specified artery cells by inhibiting vein-specifying signals and vice versa. These cells modeled viral infection of human vasculature by Nipah and Hendra viruses, which are extraordinarily deadly (∼57%-59% fatality rate) and require biosafety-level-4 containment. Generating pure populations of artery and vein cells highlighted that Nipah and Hendra viruses preferentially infected arteries; arteries expressed higher levels of their viral-entry receptor. Virally infected artery cells fused into syncytia containing up to 23 nuclei, which rapidly died. Despite infecting arteries and occupying ∼6%-17% of their transcriptome, Nipah and Hendra largely eluded innate immune detection, minimally eliciting interferon signaling. We thus efficiently generate artery and vein cells, introduce stem-cell-based toolkits for biosafety-level-4 virology, and explore the arterial tropism and cellular effects of Nipah and Hendra viruses.

High-efficient serum-free differentiation of endothelial cells from human iPS cells

Introduction

Endothelial cells (ECs) form the inner lining of all blood vessels of the body play important roles in vascular tone regulation, hormone secretion, anticoagulation, regulation of blood cell adhesion and immune cell extravasation. Limitless ECs sources are required to further in vitro investigations of ECs’ physiology and pathophysiology as well as for tissue engineering approaches. Ideally, the differentiation protocol avoids animal-derived components such as fetal serum and yields ECs at efficiencies that make further sorting obsolete for most applications.

Method

Human induced pluripotent stem cells (hiPSCs) are cultured under serum-free conditions and induced into mesodermal progenitor cells via stimulation of Wnt signaling for 24 h. Mesodermal progenitor cells are further differentiated into ECs by utilizing a combination of human vascular endothelial growth factor A165 (VEGF), basic fibroblast growth factor (bFGF), 8-Bromoadenosine 3′,5′-cyclic monophosphate sodium salt monohydrate (8Bro) and melatonin (Mel) for 48 h.

Result

This combination generates hiPSC derived ECs (hiPSC-ECs) at a fraction of 90.9 ± 1.5% and is easily transferable from the two-dimensional (2D) monolayer into three-dimensional (3D) scalable bioreactor suspension cultures. hiPSC-ECs are positive for CD31, VE-Cadherin, von Willebrand factor and CD34. Furthermore, the majority of hiPSC-ECs express the vascular endothelial marker CD184 (CXCR4).

Conclusion

The differentiation method presented here generates hiPSC-ECs in only 6 days, without addition of animal sera and at high efficiency, hence providing a scalable source of hiPSC-ECs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02924-x.

Cellular and Engineered Organoids for Cardiovascular Models

An ensemble of in vitro cardiac tissue models has been developed over the past several decades to aid our understanding of complex cardiovascular disorders using a reductionist approach. These approaches often rely on recapitulating single or multiple clinically relevant end points in a dish indicative of the cardiac pathophysiology. The possibility to generate disease-relevant and patient-specific human induced pluripotent stem cells has further leveraged the utility of the cardiac models as screening tools at a large scale. To elucidate biological mechanisms in the cardiac models, it is critical to integrate physiological cues in form of biochemical, biophysical, and electromechanical stimuli to achieve desired tissue-like maturity for a robust phenotyping. Here, we review the latest advances in the directed stem cell differentiation approaches to derive a wide gamut of cardiovascular cell types, to allow customization in cardiac model systems, and to study diseased states in multiple cell types. We also highlight the recent progress in the development of several cardiovascular models, such as cardiac organoids, microtissues, engineered heart tissues, and microphysiological systems. We further expand our discussion on defining the context of use for the selection of currently available cardiac tissue models. Last, we discuss the limitations and challenges with the current state-of-the-art cardiac models and highlight future directions.

Temporal Expression of Transcription Factor ID2 Improves Natural Killer Cell Differentiation from Human Pluripotent Stem Cells

Natural killer (NK) cells are one type of innate lymphoid cells, and NK cell-based immunotherapy serves as a potentially curative therapy for cancers. However, the lack of reliable resources for a large amount of NK cells required for clinical infusion has limited the broader application of NK cells in targeted immunotherapy. Substantial effort has thus been made to generate NK-like cells from human pluripotent stem cells (hPSCs), but detailed molecular mechanisms regulating NK cell differentiation remain elusive, preventing us from developing robust strategies for NK cell production. Here, we genetically engineered hPSCs with inducible overexpression of transcription factors NFIL3, ID2, or SPI1 via CRISPR/Cas9-mediated gene knock-in and investigated their temporal roles during NK cell differentiation. Our results demonstrated ID2 overexpression significantly promoted NK cell generation compared with NFIL3 and SPI1 overexpression under a chemically defined, feeder-free culture condition. The resulting ID2 hPSC-derived NK cells exhibited various mature NK-specific markers and displayed effective tumor-killing activities, comparable to NK cells derived from wildtype hPSCs. Our study provides a new platform for efficient NK cell production, serving as a realistic off-the-shelf cell source for targeted cancer immunotherapy.

Modularizable Liquid-Crystal-Based Open Surfaces Enable Programmable Chemical Transport and Feeding using Liquid Droplets

Droplet-based miniature reactors have attracted interest in both fundamental studies, for the unique reaction kinetics they enable, and applications in bio-diagnosis and material synthesis. However, the precise and automatic feeding of chemicals, important for the delicate reactions in these miniaturized chemical reactors, either requires complex, high-cost microfluidic devices or lacks the capability to maintain a pinning-free droplet movement. Here, the design and synthesis of a new class of liquid crystal (LC)-based open surfaces, which enable a controlled chemical release via a programmable LC phase transition without sacrificing the free transport of the droplets, are reported. It is demonstrated that their intrinsic slipperiness and self-healing properties enable a modularizable assembly of LC surfaces that can be loaded with different chemicals to achieve a wide range of chemical reactions carried out within the droplets, including sequential and parallel chemical reactions, crystal growth, and polymer synthesis. Finally, an LC-based chemical feeding device is developed that can automatically control the release of chemicals to direct the simultaneous differentiation of human induced pluripotent stem cells into endothelial progenitor cells and cardiomyocytes. Overall, these LC surfaces exhibit desirable levels of automation, responsiveness, and controllability for use in miniature droplet carriers and reactors.

Chemically-defined generation of human hemogenic endothelium and definitive hematopoietic progenitor cells

Human hematopoietic stem cells (HSCs), which arise from aorta-gonad-mesonephros (AGM), are widely used to treat blood diseases and cancers. However, a technique for their robust generation in vitro is still missing. Here we show temporal manipulation of Wnt signaling is sufficient and essential to induce AGM-like hematopoiesis from human pluripotent stem cells. TGFβ inhibition at the stage of aorta-like SOX17⁺CD235a^- hemogenic endothelium yielded AGM-like hematopoietic progenitors, which closely resembled primary cord blood HSCs at the transcriptional level and contained diverse lineage-primed progenitor populations via single cell RNA-sequencing analysis. Notably, the resulting definitive cells presented lymphoid and myeloid potential in vitro; and could home to a definitive hematopoietic site in zebrafish and rescue bloodless zebrafish after transplantation. Engraftment and multilineage repopulating activities were also observed in mouse recipients. Together, our work provided a chemically-defined and feeder-free culture platform for scalable generation of AGM-like hematopoietic progenitor cells, leading to enhanced production of functional blood and immune cells for various therapeutic applications.

Metabolically driven maturation of human-induced-pluripotent-stem-cell-derived cardiac microtissues on microfluidic chips

The immature physiology of cardiomyocytes derived from human induced pluripotent stem cells (hiPSCs) limits their utility for drug screening and disease modelling. Here we show that suitable combinations of mechanical stimuli and metabolic cues can enhance the maturation of hiPSC-derived cardiomyocytes, and that the maturation-inducing cues have phenotype-dependent effects on the cells' action-potential morphology and calcium handling. By using microfluidic chips that enhanced the alignment and extracellular-matrix production of cardiac microtissues derived from genetically distinct sources of hiPSC-derived cardiomyocytes, we identified fatty-acid-enriched maturation media that improved the cells' mitochondrial structure and calcium handling, and observed divergent cell-source-dependent effects on action-potential duration (APD). Specifically, in the presence of maturation media, tissues with abnormally prolonged APDs exhibited shorter APDs, and tissues with aberrantly short APDs displayed prolonged APDs. Regardless of cell source, tissue maturation reduced variabilities in spontaneous beat rate and in APD, and led to converging cell phenotypes (with APDs within the 300-450 ms range characteristic of human left ventricular cardiomyocytes) that improved the modelling of the effects of pro-arrhythmic drugs on cardiac tissue.

An efficient method of inducing differentiation of mouse embryonic stem cells into primitive endodermal cells

Primitive Endoderm (PrE) is an extraembryonic structure derived from inner cell mass (ICM) in the blastocysts. Its interaction with the epiblast is critical to sustain embryonic growth and embryonic pattern. In this study, we reported a simple and efficient method to induce the differentiation of mouse Embryonic Stem Cells (mESCs) into PrE cells. In the process of ESC monolayer adherent culture, 1 μM atRA and 10 μM CHIR inducers were used to activate RA and Wnt signaling pathways respectively. After 9 days of differentiation, the proportion of PrE cells was up to 85%. Further studies indicated that Wnt signaling pathway acted as a switch that RA induces mESCs differentiation between SMC and PrE cell. In the presence of only RA signaling, mESCs adopted the fate of smooth muscle cells (SMCs); Simultaneous activation of the Wnt signaling pathway changed the differentiation fate of mESCs into PrE cells. This efficient induction method can provide new cellular resources and models for relevant studies of PrE.

Pacemaker translocations and power laws in 2D stem cell-derived cardiomyocyte cultures

Power laws are of interest to several scientific disciplines because they can provide important information about the underlying dynamics (e.g. scale invariance and self-similarity) of a given system. Because power laws are of increasing interest to the cardiac sciences as potential indicators of cardiac dysfunction, it is essential that rigorous, standardized analytical methods are employed in the evaluation of power laws. This study compares the methods currently used in the fields of condensed matter physics, geoscience, neuroscience, and cardiology in order to provide a robust analytical framework for evaluating power laws in stem cell-derived cardiomyocyte cultures. One potential power law-obeying phenomenon observed in these cultures is pacemaker translocations, or the spatial and temporal instability of the pacemaker region, in a 2D cell culture. Power law analysis of translocation data was performed using increasingly rigorous methods in order to illustrate how differences in analytical robustness can result in misleading power law interpretations. Non-robust methods concluded that pacemaker translocations adhere to a power law while robust methods convincingly demonstrated that they obey a doubly truncated power law. The results of this study highlight the importance of employing comprehensive methods during power law analysis of cardiomyocyte cultures.

Laminin 411 mediates endothelial specification via multiple signaling axes that converge on β-catenin

The extracellular matrix (ECM) provides essential cues to promote endothelial specification during tissue development in vivo; correspondingly, ECM is considered essential for endothelial differentiation outside of the body. However, systematic studies to assess the precise contribution of individual ECM proteins to endothelial differentiation have not been conducted. Further, the multi-component nature of differentiation protocols makes it challenging to study the underlying mechanisms by which the ECM contributes to cell fate. In this study, we determined that Laminin 411 alone increases endothelial differentiation of induced pluripotent stem cells over collagen I or Matrigel. The effect of ECM was shown to be independent of vascular endothelial growth factor (VEGF) binding capacity. We also show that ECM-guided endothelial differentiation is dependent on activation of focal adhesion kinase (FAK), integrin-linked kinase (ILK), Notch, and β-catenin pathways. Our results indicate that ECM contributes to endothelial differentiation through multiple avenues, which converge at the expression of active β-catenin.

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

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

Differentiation and Characterization of Human Pluripotent Stem Cell-Derived Cardiac Endothelial Cells for In Vitro Applications

Various protocols have been developed to generate endothelial cells for disease modeling, angiogenesis, vascular regeneration, and drug screening. These protocols often require cell sorting, as most differentiation strategies result in a heterogenous population of endothelial cells (ECs). For any given model system, one important consideration is choosing the appropriate EC subtype, as different EC populations have unique molecular signatures.Herein, we describe a protocol for cardiac EC differentiation and a protocol for endothelial cell characterization. This protocol is aimed at investigating differentiation efficiency by measuring endothelial lineage markers, CD31, VE-Cadherin, and VEGFR2 by flow cytometry. Collectively, these protocols comprise the tools required to generate cardiac ECs efficiently and reproducibly from different hPSC lines without the need for cell sorting. Our protocol adds to the panel of hPSCs for cardiac EC differentiation and addresses reproducibility concerns of hPSC-based experiments. The approaches described are also applicable for complex model generation where multiple cardiovascular cell types are involved and may assist in optimizing differentiations for different cell lineages, including cardiomyocytes, cardiac endothelial cells, and cardiac fibroblasts.

A High-Efficiency Method for the Production of Endothelial Cells from Human Induced Pluripotent Stem Cells

Endothelial cells (ECs) are important components of the circulatory system. These cells can be used for in vitro modeling of cardiovascular diseases and in regenerative medicine to promote vascularization of engineered tissue constructs. However, low proliferative capacity and patient-to-patient variability limit the use of primary ECs in the clinic and disease modeling. ECs differentiated from human induced pluripotent stem cells (iPSCs) can serve as a viable alternative to primary ECs for these applications. This is because human iPSCs can proliferate indefinitely and have the potential to differentiate into a variety of somatic cell lines, providing a renewable source of patient-specific cells. Here, we present an optimized, highly reproducible method for the differentiation of human iPSCs toward vascular ECs. The protocol relies on the activation of the WNT signaling pathway and the use of growth factors and small molecules. The resulting iPSC-derived ECs can be cultured for multiple passages without losing their functionality and are suitable for both in vitro and in vivo studies.

Engineering the multiscale complexity of vascular networks

The survival of vertebrate organisms depends on highly regulated delivery of oxygen and nutrients through vascular networks that pervade nearly all tissues in the body. Dysregulation of these vascular networks is implicated in many common human diseases such as hypertension, coronary artery disease, diabetes and cancer. Therefore, engineers have sought to create vascular networks within engineered tissues for applications such as regenerative therapies, human disease modelling and pharmacological testing. Yet engineering vascular networks has historically remained difficult, owing to both incomplete understanding of vascular structure and technical limitations for vascular fabrication. This Review highlights the materials advances that have enabled transformative progress in vascular engineering by ushering in new tools for both visualizing and building vasculature. New methods such as bioprinting, organoids and microfluidic systems are discussed, which have enabled the fabrication of 3D vascular topologies at a cellular scale with lumen perfusion. These approaches to vascular engineering are categorized into technology-driven and nature-driven approaches. Finally, the remaining knowledge gaps, emerging frontiers and opportunities for this field are highlighted, including the steps required to replicate the multiscale complexity of vascular networks found in nature.

Differentiating Human Pluripotent Stem Cells to Vascular Endothelial Cells for Regenerative Medicine, Tissue Engineering, and Disease Modeling

Vasculature plays a vital role in human biology as blood vessels transport nutrients and oxygen throughout the body. Endothelial cells (ECs), specifically, are key as they maintain barrier functions between the circulating blood and the surrounding tissues. ECs derived from human pluripotent stem cells (hPSCs) are utilized to study vascular development and disease mechanisms within in vitro models. Additionally, ECs derived from induced pluripotent stem cells (iPSCs) hold great promise for advancing personalized medicine, cell therapies, and tissue-engineered constructs by creating patient-specific cell populations. Here, we describe a xeno-free, serum-free differentiation protocol for deriving ECs from hPSCs. In brief, mesoderm progenitor cells are derived via WNT pathway activation. Following this, EC maturation is achieved with exogenous vascular endothelial growth factor A (VEGFA) and basic fibroblast growth factor 2 (bFGF2). We have characterized these cells as expressing mature EC markers and have illustrated their functionality in vitro.