Functionality of Endothelial Cells and Pericytes From Human Pluripotent Stem Cells Demonstrated in Cultured Vascular Plexus and Zebrafish Xenografts

The lncRNA DSCR9 is modulated in pulmonary arterial hypertension endothelial cell models and is associated with alterations in the nitric oxide pathway

Long non-coding RNA (lncRNA) may be involved in dysfunction of pulmonary artery endothelial cells (PAEC) and, thus, in pulmonary arterial hypertension (PAH) pathobiology. We screened the RNA expression profile of commercial human PAEC (hPAEC) exposed to increased hydrostatic pressure, and found that the lncRNA Down syndrome critical region 9 (DSCR9) was the most regulated transcript (log2FC 1.89 vs control). We confirmed by RT-qPCR that DSCR9 levels were higher in PAEC isolated from patients with idiopathic PAH (iPAH-PAEC), as well as in induced pluripotent stem cell-derived endothelial cells (iPSC-EC) from a patient with BMPR2-mutated PAH, than in relevant controls. Moreover, a re-analysis of the publicly available GSE117261 microarray dataset revealed that DSCR9 was upregulated in the lung tissue of PAH patients. In silico simulation indicated that DSCR9 would be mainly located in the nucleus and could interact with calcium/calmodulin-dependent protein kinase II beta (CAMK2B) and nitric oxide synthase 3 (NOS3, encoding eNOS). CAMK2B levels resulted 3.4-fold higher (p < 0.05) in iPAH-PAEC transfected with a DSCR9-GFP carrying plasmid than with a GFP-only-carrying one. A trend for higher NOS3 expression was also noted. GFP immunostaining was predominantly nuclear and cytoplasmic upon DSCR9-GFP or GFP-only transfection, respectively. CAMK2B and NOS3 mRNA were also higher in iPAH-PAEC than control-PAEC in basal conditions. Instead, variations in total and phosphorylated CAMK2B, eNOS, and NO synthesis were inconsistent. We conclude that DSCR9 is upregulated in PAH-related endothelial cell models and influences CAMK2B and NOS3 expression. Future studies are necessary to determine whether DSCR9 affects NO availability, including in PAH.

A guide for blood-brain barrier models

Understanding the intricate mechanisms underlying brain-related diseases hinges on unraveling the pivotal role of the blood-brain barrier (BBB), an essential dynamic interface crucial for maintaining brain equilibrium. This review offers a comprehensive analysis of BBB physiology, delving into its cellular and molecular components while exploring a wide range of in vivo and in vitro BBB models. Notably, recent advancements in 3D cell culture techniques are explicitly discussed, as they have significantly improved the fidelity of BBB modeling by enabling the replication of physiologically relevant environments under flow conditions. Special attention is given to the cellular aspects of in vitro BBB models, alongside discussions on advances in stem cell technologies, providing valuable insights into generating robust cellular systems for BBB modeling. The diverse array of cell types used in BBB modeling, depending on their sources, is meticulously examined in this comprehensive review, scrutinizing their respective derivation protocols and implications. By synthesizing diverse approaches, this review sheds light on the improvements of BBB models to capture physiological conditions, aiding in understanding BBB interactions in health and disease conditions to foster clinical developments.

The Rise of Pluripotent Stem Cell-Derived Glia Models of Neuroinflammation

Neuroinflammation is a blanket term that describes the body's complex inflammatory response in the central nervous system (CNS). It encompasses a phenotype shift to a proinflammatory state, the release of cytokines, the recruitment of peripheral immune cells, and a wide variety of other processes. Neuroinflammation has been implicated in nearly every major CNS disease ranging from Alzheimer's disease to brain cancer. Understanding and modeling neuroinflammation is critical for the identification of novel therapeutic targets in the treatment of CNS diseases. Unfortunately, the translation of findings from non-human models has left much to be desired. This review systematically discusses the role of human pluripotent stem cell (hPSC)-derived glia and supporting cells within the CNS, including astrocytes, microglia, oligodendrocyte precursor cells, pericytes, and endothelial cells, to describe the state of the field and hope for future discoveries. hPSC-derived cells offer an expanded potential to study the pathobiology of neuroinflammation and immunomodulatory cascades that impact disease progression. While much progress has been made in the development of models, there is much left to explore in the application of these models to understand the complex inflammatory response in the CNS.

NOS3 regulates angiogenic potential of human induced pluripotent stem cell-derived endothelial cells

Incorporation of blood capillaries in engineered tissues and their functional connection to host blood vessels is essential for success in engineering vascularized tissues, a process which involves spatial patterning of endothelial cells (ECs) to form functional and integrated vascular networks. Different types of ECs have been employed for vascular network formation and each source offers advantages and disadvantages. While ECs derived from induced pluripotent stem cells (iPSC-ECs) offer advantages over primary ECs in that they can be generated in large quantities for autologous applications, their suitability for disease modelling and cell replacement therapies is not well-explored. The present study compares the angiogenic capacity of iPSC-ECs and primary ECs (cardiac microvascular ECs and lymphatic microvascular ECs) using an in vitro tubulogenesis assay, revealing comparable performance in forming a pseudo-capillary network on Matrigel. Analysis of genes encoding angiogenic factors (VEGFA, VEGFC, VEGFD and ANG), endothelial cell markers (PECAM1, PCDH12 and NOS3) and proliferation markers (AURKB and MKI67) indicates a significant positive correlation between NOS3 mRNA expression levels and various tubulogenic parameters. Further experimentation using a CRISPR activation system demonstrates a positive impact of NOS3 on tubulogenic activity of ECs, suggesting that iPSC-ECs can be enhanced with endogenous NOS3 activation. Collectively, these findings highlight the potential of iPSC-ECs in generating vascularized tissues and advancing therapeutic vascularization.

Inhibition of the E3 ligase UBR5 stabilizes TERT and protects vascular organoids from oxidative stress

BACKGROUND

Excessive oxidative stress is known to cause endothelial dysfunction and drive cardiovascular diseases (CVD). While telomerase reverse transcriptase (TERT) shows protective effects against oxidative stress in rodents and is associated to human flow-mediated dilation in CVD, its regulatory mechanisms in human vascular systems under pathological oxidative stress require further investigation.

METHODS

Human induced pluripotent stem cells (hiPSCs) were used to create vascular organoids (VOs). These VOs and human umbilical vein endothelial cells (HUVECs) were subjected to oxidative stress through both hydrogen peroxide (H2O2) and oxidized low-density lipoprotein (oxLDL) models. The effects of TERT overexpression by inhibition of the ubiquitin protein ligase E3 component N-recognin 5 (UBR5) on reactive oxygen species (ROS)-induced vascular injury and cellular senescence were assessed using neovascular sprouting assays, senescence-associated β-galactosidase (SA-β-Gal) staining, and senescence-associated secretory phenotype (SASP) assays.

RESULTS

ROS significantly impaired VO development and endothelial progenitor cell (EPC) angiogenesis, evidenced by reduced neovascular sprouting and increased senescence markers, including elevated SA-β-Gal activity and SASP-related cytokine levels. Overexpression of TERT counteracted these effects, restoring VO development and EPC function. Immunoprecipitation-mass spectrometry identified UBR5 as a critical TERT regulator, facilitating its degradation. Inhibition of UBR5 stabilized TERT, improving VO angiogenic capacity, and reducing SA-β-Gal activity and SASP cytokine levels.

CONCLUSIONS

Inhibiting UBR5 stabilizes TERT, which preserves EPC angiogenic capacity, reduces VO impairment, and delays endothelial cell senescence under oxidative stress. These findings highlight the potential of targeting UBR5 to enhance vascular health in oxidative stress-related conditions.

An Endothelial Cell Is Not Simply an Endothelial Cell

Endothelial cells (ECs) are a multifaceted component of the vascular system with roles in immunity, maintaining tissue fluid balance, and vascular tone. Dysregulation or dysfunction of ECs can have far-reaching implications, leading pathologies ranging from cardiovascular diseases, such as hypertension and atherosclerosis, ischemia, chronic kidney disease, blood-brain barrier integrity, dementia, and tumor metastasis. Recent advancements in regenerative medicine have highlighted the potential of stem cell-derived ECs, particularly from induced pluripotent stem cells, to treat ischemic tissues, as well as models of vascular integrity. This review summarizes what is known in the generation of ECs with an emphasis on tissue-specific ECs and EC subphenotypes important in the development of targeted cell-based therapies for patient treatment.

Robust differentiation of human pluripotent stem cells into mural progenitor cells via transient activation of NKX3.1

Mural cells are central to vascular integrity and function. In this study, we demonstrate the innovative use of the transcription factor NKX3.1 to guide the differentiation of human induced pluripotent stem cells into mural progenitor cells (iMPCs). By transiently activating NKX3.1 in mesodermal intermediates, we developed a method that diverges from traditional growth factor-based differentiation techniques. This approach efficiently generates a robust iMPC population capable of maturing into diverse functional mural cell subtypes, including smooth muscle cells and pericytes. These iMPCs exhibit key mural cell functionalities such as contractility, deposition of extracellular matrix, and the ability to support endothelial cell-mediated vascular network formation in vivo. Our study not only underscores the fate-determining significance of NKX3.1 in mural cell differentiation but also highlights the therapeutic potential of these iMPCs. We envision these insights could pave the way for a broader use of iMPCs in vascular biology and regenerative medicine.

Sources and applications of endothelial seed cells: a review

Endothelial cells (ECs) are widely used as donor cells in tissue engineering, organoid vascularization, and in vitro microvascular model development. ECs are invaluable tools for disease modeling and drug screening in fundamental research. When treating ischemic diseases, EC engraftment facilitates the restoration of damaged blood vessels, enhancing therapeutic outcomes. This article presents a comprehensive overview of the current sources of ECs, which encompass stem/progenitor cells, primary ECs, cell lineage conversion, and ECs derived from other cellular sources, provides insights into their characteristics, potential applications, discusses challenges, and explores strategies to mitigate these issues. The primary aim is to serve as a reference for selecting suitable EC sources for preclinical research and promote the translation of basic research into clinical applications.

Induced pluripotent stem cell derived pericytes respond to mediators of proliferation and contractility

BACKGROUND

Pericytes are multifunctional contractile cells that reside on capillaries. Pericytes are critical regulators of cerebral blood flow and blood-brain barrier function, and pericyte dysfunction may contribute to the pathophysiology of human neurological diseases including Alzheimers disease, multiple sclerosis, and stroke. Induced pluripotent stem cell (iPSC)-derived pericytes (iPericytes) are a promising tool for vascular research. However, it is unclear how iPericytes functionally compare to primary human brain vascular pericytes (HBVPs).

METHODS

We differentiated iPSCs into iPericytes of either the mesoderm or neural crest lineage using established protocols. We compared iPericyte and HBVP morphologies, quantified gene expression by qPCR and bulk RNA sequencing, and visualised pericyte protein markers by immunocytochemistry. To determine whether the gene expression of neural crest iPericytes, mesoderm iPericytes or HBVPs correlated with their functional characteristics in vitro, we quantified EdU incorporation following exposure to the key pericyte mitogen, platelet derived growth factor (PDGF)-BB and, contraction and relaxation in response to the vasoconstrictor endothelin-1 or vasodilator adenosine, respectively.

RESULTS

iPericytes were morphologically similar to HBVPs and expressed canonical pericyte markers. However, iPericytes had 1864 differentially expressed genes compared to HBVPs, while there were 797 genes differentially expressed between neural crest and mesoderm iPericytes. Consistent with the ability of HBVPs to respond to PDGF-BB signalling, PDGF-BB enhanced and a PDGF receptor-beta inhibitor impaired iPericyte proliferation. Administration of endothelin-1 led to iPericyte contraction and adenosine led to iPericyte relaxation, of a magnitude similar to the response evoked in HBVPs. We determined that neural crest iPericytes were less susceptible to PDGFR beta inhibition, but responded most robustly to vasoconstrictive mediators.

CONCLUSIONS

iPericytes express pericyte-associated genes and proteins and, exhibit an appropriate physiological response upon exposure to a key endogenous mitogen or vasoactive mediators. Therefore, the generation of functional iPericytes would be suitable for use in future investigations exploring pericyte function or dysfunction in neurological diseases.

The role of cardiac pericytes in health and disease: therapeutic targets for myocardial infarction

Millions of cardiomyocytes die immediately after myocardial infarction, regardless of whether the culprit coronary artery undergoes prompt revascularization. Residual ischaemia in the peri-infarct border zone causes further cardiomyocyte damage, resulting in a progressive decline in contractile function. To date, no treatment has succeeded in increasing the vascularization of the infarcted heart. In the past decade, new approaches that can target the heart's highly plastic perivascular niche have been proposed. The perivascular environment is populated by mesenchymal progenitor cells, fibroblasts, myofibroblasts and pericytes, which can together mount a healing response to the ischaemic damage. In the infarcted heart, pericytes have crucial roles in angiogenesis, scar formation and stabilization, and control of the inflammatory response. Persistent ischaemia and accrual of age-related risk factors can lead to pericyte depletion and dysfunction. In this Review, we describe the phenotypic changes that characterize the response of cardiac pericytes to ischaemia and the potential of pericyte-based therapy for restoring the perivascular niche after myocardial infarction. Pericyte-related therapies that can salvage the area at risk of an ischaemic injury include exogenously administered pericytes, pericyte-derived exosomes, pericyte-engineered biomaterials, and pharmacological approaches that can stimulate the differentiation of constitutively resident pericytes towards an arteriogenic phenotype. Promising preclinical results from in vitro and in vivo studies indicate that pericytes have crucial roles in the treatment of coronary artery disease and the prevention of post-ischaemic heart failure.

A novel human iPSC model of COL4A1/A2 small vessel disease unveils a key pathogenic role of matrix metalloproteinases

Cerebral small vessel disease (SVD) affects the small vessels in the brain and is a leading cause of stroke and dementia. Emerging evidence supports a role of the extracellular matrix (ECM), at the interface between blood and brain, in the progression of SVD pathology, but this remains poorly characterized. To address ECM role in SVD, we developed a co-culture model of mural and endothelial cells using human induced pluripotent stem cells from patients with COL4A1/A2 SVD-related mutations. This model revealed that these mutations induce apoptosis, migration defects, ECM remodeling, and transcriptome changes in mural cells. Importantly, these mural cell defects exert a detrimental effect on endothelial cell tight junctions through paracrine actions. COL4A1/A2 models also express high levels of matrix metalloproteinases (MMPs), and inhibiting MMP activity partially rescues the ECM abnormalities and mural cell phenotypic changes. These data provide a basis for targeting MMP as a therapeutic opportunity in SVD.

Bioprinted vascular tissue: Assessing functions from cellular, tissue to organ levels

3D bioprinting technology is widely used to fabricate various tissue structures. However, the absence of vessels hampers the ability of bioprinted tissues to receive oxygen and nutrients as well as to remove wastes, leading to a significant reduction in their survival rate. Despite the advancements in bioinks and bioprinting technologies, bioprinted vascular structures continue to be unsuitable for transplantation compared to natural blood vessels. In addition, a complete assessment index system for evaluating the structure and function of bioprinted vessels in vitro has not yet been established. Therefore, in this review, we firstly highlight the significance of selecting suitable bioinks and bioprinting techniques as they two synergize with each other. Subsequently, focusing on both vascular-associated cells and vascular tissues, we provide a relatively thorough assessment of the functions of bioprinted vascular tissue based on the physiological functions that natural blood vessels possess. We end with a review of the applications of vascular models, such as vessel-on-a-chip, in simulating pathological processes and conducting drug screening at the organ level. We believe that the development of fully functional blood vessels will soon make great contributions to tissue engineering and regenerative medicine.

A review of the evidence to support electrical stimulation-induced vascularization in engineered tissue

Tissue engineering presents a promising solution for regenerative medicine and the success depends on the supply of oxygen/nutrients to the cells by rapid vascularization. More and more technologies are being developed to facilitate vascularization of engineered tissues. In this review, we indicated that a regulatory system which influences all angiogenesis associated cells to achieve their desired functional state is ideal for the construction of vascularized engineered tissues in vitro. We presented the evidence that electrical stimulation (ES) enhances the synergistic promotion of co-cultured angiogenesis associated cells and its potential regulatory mechanisms, highlighted the potential advantages of a combination of mesenchymal stem cells (MSCs), endothelial cells (ECs) and ES to achieve tissue vascularization, with particular emphasis on the different biological pathways of ES-regulated ECs. Finally, we proposed the future direction of using ES to reconstruct engineered tissue blood vessels, pointed out the potential advantages and disadvantages of ES application on tissue vascularization.

Clonal and Scalable Endothelial Progenitor Cell Lines from Human Pluripotent Stem Cells

Human pluripotent stem cells (hPSCs) can be used as a renewable source of endothelial cells for treating cardiovascular disease and other ischemic conditions. Here, we present the derivation and characterization of a panel of distinct clonal embryonic endothelial progenitor cells (eEPCs) lines that were differentiated from human embryonic stem cells (hESCs). The hESC line, ESI-017, was first partially differentiated to produce candidate cultures from which eEPCs were cloned. Endothelial cell identity was assessed by transcriptomic analysis, cell surface marker expression, immunocytochemical marker analysis, and functional analysis of cells and exosomes using vascular network forming assays. The transcriptome of the eEPC lines was compared to various adult endothelial lines as well as various non-endothelial cells including both adult and embryonic origins. This resulted in a variety of distinct cell lines with functional properties of endothelial cells and strong transcriptomic similarity to adult endothelial primary cell lines. The eEPC lines, however, were distinguished from adult endothelium by their novel pattern of embryonic gene expression. We demonstrated eEPC line scalability of up to 80 population doublings (pd) and stable long-term expansion of over 50 pd with stable angiogenic properties at late passage. Taken together, these data support the finding that hESC-derived clonal eEPC lines are a potential source of scalable therapeutic cells and cell products for treating cardiovascular disease. These eEPC lines offer a highly promising resource for the development of further preclinical studies aimed at therapeutic interventions.

Human iPSCs as Model Systems for BMP-Related Rare Diseases

Disturbances in bone morphogenetic protein (BMP) signalling contribute to onset and development of a number of rare genetic diseases, including Fibrodysplasia ossificans progressiva (FOP), Pulmonary arterial hypertension (PAH), and Hereditary haemorrhagic telangiectasia (HHT). After decades of animal research to build a solid foundation in understanding the underlying molecular mechanisms, the progressive implementation of iPSC-based patient-derived models will improve drug development by addressing drug efficacy, specificity, and toxicity in a complex humanized environment. We will review the current state of literature on iPSC-derived model systems in this field, with special emphasis on the access to patient source material and the complications that may come with it. Given the essential role of BMPs during embryonic development and stem cell differentiation, gain- or loss-of-function mutations in the BMP signalling pathway may compromise iPSC generation, maintenance, and differentiation procedures. This review highlights the need for careful optimization of the protocols used. Finally, we will discuss recent developments towards complex in vitro culture models aiming to resemble specific tissue microenvironments with multi-faceted cellular inputs, such as cell mechanics and ECM together with organoids, organ-on-chip, and microfluidic technologies.

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.

Induced pluripotent stem cells for cardiovascular therapeutics: Progress and perspectives

The discovery of methods for reprogramming adult somatic cells into induced pluripotent stem cells (iPSCs) opens up prospects of developing personalized cell-based therapy options for a variety of human diseases as well as disease modeling and new drug discovery. Like embryonic stem cells, iPSCs can give rise to various cell types of the human body and are amenable to genetic correction. This allows usage of iPSCs in the development of modern therapies for many virtually incurable human diseases. The review summarizes progress in iPSC research in the context of application in the cardiovascular field including modeling cardiovascular disease, drug study, tissue engineering, and perspectives for personalized cardiovascular medicine.

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.

3D Human iPSC Blood Vessel Organoids as a Source of Flow-Adaptive Vascular Cells for Creating a Human-Relevant 3D-Scaffold Based Macrovessel Model

3D-scaffold based in vitro human tissue models accelerate disease studies and screening of pharmaceutics while improving the clinical translation of findings. Here is reported the use of human induced pluripotent stem cell (hiPSC)-derived vascular organoid cells as a new cell source for the creation of an electrospun polycaprolactone-bisurea (PCL-BU) 3D-scaffold-based, perfused human macrovessel model. A separation protocol is developed to obtain monocultures of organoid-derived endothelial cells (ODECs) and mural cells (ODMCs) from hiPSC vascular organoids. Shear stress responses of ODECs versus HUVECs and barrier function (by trans endothelial electrical resistance) are measured. PCL-BU scaffolds are seeded with ODECs and ODMCs, and tissue organization and flow adaptation are evaluated in a perfused bioreactor system. ODECs and ODMCs harvested from vascular organoids can be cryopreserved and expanded without loss of cell purity and proliferative capacity. ODECs are shear stress responsive and establish a functional barrier that self-restores after the thrombin challenge. Static bioreactor culture of ODECs/ODMCs seeded scaffolds results in a biomimetic vascular bi-layer hierarchy, which is preserved under laminar flow similar to scaffolds seeded with primary vascular cells. HiPSC-derived vascular organoids can be used as a source of functional, flow-adaptive vascular cells for the creation of 3D-scaffold based human macrovascular models.

Three-Dimensional Vessels-on-a-Chip Based on hiPSC-derived Vascular Endothelial and Smooth Muscle Cells

Blood vessels are composed of endothelial cells (ECs) that form the inner vessel wall and mural cells that cover the ECs to mediate their stabilization. Crosstalk between ECs and VSMCs while the ECs undergo microfluidic flow is vital for the function and integrity of blood vessels. Here, we describe a protocol to generate three-dimensional (3D) engineered vessels-on-chip (VoCs) composed of vascular cells derived from human induced pluripotent stem cells (hiPSCs). We first describe protocols for robust differentiation of vascular smooth muscle cells (hiPSC-VSMCs) from hiPSCs that are effective across multiple hiPSC lines. Second, we describe the fabrication of a simple microfluidic device consisting of a single collagen lumen that can act as a cell scaffold and support fluid flow using the viscous finger patterning (VFP) technique. After the channel is seeded sequentially with hiPSC-derived ECs (hiPSC-ECs) and hiPSC-VSMCs, a stable EC barrier covered by VSMCs lines the collagen lumen. We demonstrate that this 3D VoC model can recapitulate physiological cell-cell interaction and can be perfused under physiological shear stress using a microfluidic pump. The uniform geometry of the vessel lumens allows precise control of flow dynamics. We have thus developed a robust protocol to generate an entirely isogenic hiPSC-derived 3D VoC model, which could be valuable for studying vessel barrier function and physiology in healthy or disease states. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Differentiation of hiPSC-VSMCs Support Protocol 1: Characterization of hiPSC-NCCs and hiPSC-VSMCs Support Protocol 2: Preparation of cryopreserved hiPSC-VSMCs and hiPSC-ECs for VoC culture Basic Protocol 2: Generation of 3D VoC model composed of hiPSC-ECs and hiPSC-VSMCs Support Protocol 3: Structural characterization of 3D VoC model.

Flow-induced glycocalyx formation and cell alignment of HUVECs compared to iPSC-derived ECs for tissue engineering applications

The relevance of cellular in vitro models highly depends on their ability to mimic the physiological environment of the respective tissue or cell niche. Static culture conditions are often unsuitable, especially for endothelial models, since they completely neglect the physiological surface shear stress and corresponding reactions of endothelial cells (ECs) such as alignment in the direction of flow. Furthermore, formation and maturation of the glycocalyx, the essential polysaccharide layer covering all endothelial surfaces and regulating diverse processes, is highly dependent on applied fluid flow. This fragile but utterly important macromolecular layer is hard to analyze, its importance is often underestimated and accordingly neglected in many endothelial models. Therefore, we exposed human umbilical vein ECs (HUVECs) and human induced pluripotent stem cell-derived ECs (iPSC-ECs) as two relevant EC models in a side-by-side comparison to static and physiological dynamic (6.6 dyn cm-2) culture conditions. Both cell types demonstrated an elongation and alignment along the flow direction, some distinct changes in glycocalyx composition on the surface regarding the main glycosaminoglycan components heparan sulfate, chondroitin sulfate or hyaluronic acid as well as an increased and thereby improved glycocalyx thickness and functionality when cultured under homogeneous fluid flow. Thus, we were able to demonstrate the maturity of the employed iPSC-EC model regarding its ability to sense fluid flow along with the general importance of physiological shear stress for glycocalyx formation. Additionally, we investigated EC monolayer integrity with and without application of surface shear stress, revealing a comparable existence of tight junctions for all conditions and a reorganization of the cytoskeleton upon dynamic culture leading to an increased formation of focal adhesions. We then fabricated cell sheets of EC monolayers after static and dynamic culture via non-enzymatic detachment using thermoresponsive polymer coatings as culture substrates. In a first proof-of-concept we were able to transfer an aligned iPSC-EC sheet to a 3D-printed scaffold thereby making a step in the direction of vascular modelling. We envision these results to be a valuable contribution to improvements of in vitro endothelial models and vascular engineering in the future.

RNA-Binding Proteins: Emerging Therapeutics for Vascular Dysfunction

Vascular diseases account for a significant number of deaths worldwide, with cardiovascular diseases remaining the leading cause of mortality. This ongoing, ever-increasing burden has made the need for an effective treatment strategy a global priority. Recent advances in regenerative medicine, largely the derivation and use of induced pluripotent stem cell (iPSC) technologies as disease models, have provided powerful tools to study the different cell types that comprise the vascular system, allowing for a greater understanding of the molecular mechanisms behind vascular health. iPSC disease models consequently offer an exciting strategy to deepen our understanding of disease as well as develop new therapeutic avenues with clinical translation. Both transcriptional and post-transcriptional mechanisms are widely accepted to have fundamental roles in orchestrating responses to vascular damage. Recently, iPSC technologies have increased our understanding of RNA-binding proteins (RBPs) in controlling gene expression and cellular functions, providing an insight into the onset and progression of vascular dysfunction. Revelations of such roles within vascular disease states have therefore allowed for a greater clarification of disease mechanisms, aiding the development of novel therapeutic interventions. Here, we discuss newly discovered roles of RBPs within the cardio-vasculature aided by iPSC technologies, as well as examine their therapeutic potential, with a particular focus on the Quaking family of isoforms.

Vascular defects associated with hereditary hemorrhagic telangiectasia revealed in patient-derived isogenic iPSCs in 3D vessels on chip

Hereditary hemorrhagic telangiectasia (HHT) is a genetic disease characterized by weak blood vessels. HHT1 is caused by mutations in the ENDOGLIN (ENG) gene. Here, we generated induced pluripotent stem cells (hiPSCs) from a patient with rare mosaic HHT1 with tissues containing both mutant (ENG^c.1678C>T) and normal cells, enabling derivation of isogenic diseased and healthy hiPSCs, respectively. We showed reduced ENG expression in HHT1 endothelial cells (HHT1-hiPSC-ECs), reflecting haploinsufficiency. HHT1^c.1678C>T-hiPSC-ECs and the healthy isogenic control behaved similarly in two-dimensional (2D) culture, forming functionally indistinguishable vascular networks. However, when grown in 3D organ-on-chip devices under microfluidic flow, lumenized vessels formed in which defective vascular organization was evident: interaction between inner ECs and surrounding pericytes was decreased, and there was evidence for vascular leakage. Organs on chip thus revealed features of HHT in hiPSC-derived blood vessels that were not evident in conventional 2D assays.

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Vessels from isogenic hiPSCs from HHT1 patients compared

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HHT1-hiPSC-ECs show defective vascular organization in 3D microfluidic chips

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HHT1-hiPSC-ECs show defective EC-pericyte interaction

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.

Intrinsic epigenetic control of angiogenesis in induced pluripotent stem cell-derived endothelium regulates vascular regeneration

Human-induced pluripotent stem cell-derived endothelial cells (iECs) provide opportunities to study vascular development and regeneration, develop cardiovascular therapeutics, and engineer model systems for drug screening. The differentiation and characterization of iECs are well established; however, the mechanisms governing their angiogenic phenotype remain unknown. Here, we aimed to determine the angiogenic phenotype of iECs and the regulatory mechanism controlling their regenerative capacity. In a comparative study with HUVECs, we show that iECs increased expression of vascular endothelial growth factor receptor 2 (VEGFR2) mediates their highly angiogenic phenotype via regulation of glycolysis enzymes, filopodia formation, VEGF mediated migration, and robust sprouting. We find that the elevated expression of VEGFR2 is epigenetically regulated via intrinsic acetylation of histone 3 at lysine 27 by histone acetyltransferase P300. Utilizing a zebrafish xenograft model, we demonstrate that the ability of iECs to promote the regeneration of the amputated fin can be modulated by P300 activity. These findings demonstrate how the innate epigenetic status of iECs regulates their phenotype with implications for their therapeutic potential.

Single-Cell Analysis Reveals Transcriptomic Reprogramming in Aging Cardiovascular Endothelial Cells

The senescence of cardiovascular endothelial cells (ECs) is a major risk factor in the development of aging-related cardiovascular diseases. However, the molecular dynamics in cardiovascular EC aging are poorly understood. Here, we characterized the transcriptomic landscape of cardiovascular ECs during aging and observed that ribosome biogenesis, inflammation, apoptosis and angiogenesis-related genes and pathways changed with age. We also highlighted the importance of collagen genes in the crosstalk between ECs and other cell types in cardiovascular aging. Moreover, transcriptional regulatory network analysis revealed Jun as a candidate transcription factor involved in murine cardiovascular senescence and we validated the upregulation of Jun in aged cardiovascular ECs both in vitro and in vivo. Altogether, our study reveals the transcriptomic reprogramming in the aging murine cardiovascular ECs, which deepens the understanding of the molecular mechanisms of cardiovascular aging and provides new insights into potential therapeutic targets against age-related cardiovascular diseases.

Aneurysm-on-a-Chip: Setting Flow Parameters for Microfluidic Endothelial Cultures Based on Computational Fluid Dynamics Modeling of Intracranial Aneurysms

Intracranial aneurysms are pouch-like extrusions from the vessels at the base of the brain which can rupture and cause a subarachnoid hemorrhage. The pathophysiological mechanism of aneurysm formation is thought to be a consequence of blood flow (hemodynamic) induced changes on the endothelium. In this study, the results of a personalized aneurysm-on-a-chip model using patient-specific flow parameters and patient-specific cells are presented. CT imaging was used to calculate CFD parameters using an immersed boundary method. A microfluidic device either cultured with human umbilical vein endothelial cells (HUVECs) or human induced pluripotent stem cell-derived endothelial cells (hiPSC-EC) was used. Both types of endothelial cells were exposed for 24 h to either 0.03 Pa or 1.5 Pa shear stress, corresponding to regions of low shear and high shear in the computational aneurysm model, respectively. As a control, both cell types were also cultured under static conditions for 24 h as a control. Both HUVEC and hiPSC-EC cultures presented as confluent monolayers with no particular cell alignment in static or low shear conditions. Under high shear conditions HUVEC elongated and aligned in the direction of the flow. HiPSC-EC exhibited reduced cell numbers, monolayer gap formation and cells with aberrant, spread-out morphology. Future research should focus on hiPSC-EC stabilization to allow personalized intracranial aneurysm models.

Updated perspectives on vascular cell specification and pluripotent stem cell-derived vascular organoids for studying vasculopathies

Vasculopathy is a pathological process occurring in the blood vessel wall, which could affect the haemostasis and physiological functions of all the vital tissues/organs and is one of the main underlying causes for a variety of human diseases including cardiovascular diseases. Current pharmacological interventions aiming to either delay or stop progression of vasculopathies are suboptimal, thus searching novel, targeted, risk-reducing therapeutic agents, or vascular grafts with full regenerative potential for patients with vascular abnormalities are urgently needed. Since first reported, pluripotent stem cells (PSCs), particularly human-induced PSCs, have open new avenue in all research disciplines including cardiovascular regenerative medicine and disease remodelling. Assisting with recent technological breakthroughs in tissue engineering, in vitro construction of tissue organoid made a tremendous stride in the past decade. In this review, we provide an update of the main signal pathways involved in vascular cell differentiation from human PSCs and an extensive overview of PSC-derived tissue organoids, highlighting the most recent discoveries in the field of blood vessel organoids as well as vascularization of other complex tissue organoids, with the aim of discussing the key cellular and molecular players in generating vascular organoids.

Recent Advances on Cell-Based Co-Culture Strategies for Prevascularization in Tissue Engineering

Currently, the fabrication of a functional vascular network to maintain the viability of engineered tissues is a major bottleneck in the way of developing a more advanced engineered construct. Inspired by vasculogenesis during the embryonic period, the in vitro prevascularization strategies have focused on optimizing communications and interactions of cells, biomaterial and culture conditions to develop a capillary-like network to tackle the aforementioned issue. Many of these studies employ a combination of endothelial lineage cells and supporting cells such as mesenchymal stem cells, fibroblasts, and perivascular cells to create a lumenized endothelial network. These supporting cells are necessary for the stabilization of the newly developed endothelial network. Moreover, to optimize endothelial network development without impairing biomechanical properties of scaffolds or differentiation of target tissue cells, several other factors, including target tissue, endothelial cell origins, the choice of supporting cell, culture condition, incorporated pro-angiogenic factors, and choice of biomaterial must be taken into account. The prevascularization method can also influence the endothelial lineage cell/supporting cell co-culture system to vascularize the bioengineered constructs. This review aims to investigate the recent advances on standard cells used in in vitro prevascularization methods, their co-culture systems, and conditions in which they form an organized and functional vascular network.

Human Induced Pluripotent Stem Cell-Derived Vascular Cells: Recent Progress and Future Directions

Human induced pluripotent stem cells (hiPSCs) hold great promise for cardiovascular regeneration following ischemic injury. Considerable effort has been made toward the development and optimization of methods to differentiate hiPSCs into vascular cells, such as endothelial and smooth muscle cells (ECs and SMCs). In particular, hiPSC-derived ECs have shown robust potential for promoting neovascularization in animal models of cardiovascular diseases, potentially achieving significant and sustained therapeutic benefits. However, the use of hiPSC-derived SMCs that possess high therapeutic relevance is a relatively new area of investigation, still in the earlier investigational stages. In this review, we first discuss different methodologies to derive vascular cells from hiPSCs with a particular emphasis on the role of key developmental signals. Furthermore, we propose a standardized framework for assessing and defining the EC and SMC identity that might be suitable for inducing tissue repair and regeneration. We then highlight the regenerative effects of hiPSC-derived vascular cells on animal models of myocardial infarction and hindlimb ischemia. Finally, we address several obstacles that need to be overcome to fully implement the use of hiPSC-derived vascular cells for clinical application.

Recent progress and new challenges in modeling of human pluripotent stem cell-derived blood-brain barrier

The blood-brain barrier (BBB) is a semipermeable unit that serves to vascularize the central nervous system (CNS) while tightly regulating the movement of molecules, ions, and cells between the blood and the brain. The BBB precisely controls brain homeostasis and protects the neural tissue from toxins and pathogens. The BBB is coordinated by a tight monolayer of brain microvascular endothelial cells, which is subsequently supported by mural cells, astrocytes, and surrounding neuronal cells that regulate the barrier function with a series of specialized properties. Dysfunction of barrier properties is an important pathological feature in the progression of various neurological diseases. In vitro BBB models recapitulating the physiological and diseased states are important tools to understand the pathological mechanism and to serve as a platform to screen potential drugs. Recent advances in this field have stemmed from the use of pluripotent stem cells (PSCs). Various cell types of the BBB such as brain microvascular endothelial cells (BMECs), pericytes, and astrocytes have been derived from PSCs and synergistically incorporated to model the complex BBB structure in vitro. In this review, we summarize the most recent protocols and techniques for the differentiation of major cell types of the BBB. We also discuss the progress of BBB modeling by using PSC-derived cells and perspectives on how to reproduce more natural BBBs in vitro.

Engineered models of the human heart: Directions and challenges

Human heart (patho)physiology is now widely studied using human pluripotent stem cells, but the immaturity of derivative cardiomyocytes has largely limited disease modeling to conditions associated with mutations in cardiac ion channel genes. Recent advances in tissue engineering and organoids have, however, created new opportunities to study diseases beyond "channelopathies." These synthetic cardiac structures allow quantitative measurement of contraction, force, and other biophysical parameters in three-dimensional configurations, in which the cardiomyocytes in addition become more mature. Multiple cardiac-relevant cell types are also often combined to form organized cardiac tissue mimetic constructs, where cell-cell, cell-extracellular matrix, and paracrine interactions can be mimicked. In this review, we provide an overview of some of the most promising technologies being implemented specifically in personalized heart-on-a-chip models and explore their applications, drawbacks, and potential for future development.

Engineered 3D vessel-on-chip using hiPSC-derived endothelial- and vascular smooth muscle cells

Crosstalk between endothelial cells (ECs) and pericytes or vascular smooth muscle cells (VSMCs) is essential for the proper functioning of blood vessels. This balance is disrupted in several vascular diseases but there are few experimental models which recapitulate this vascular cell dialogue in humans. Here, we developed a robust multi-cell type 3D vessel-on-chip (VoC) model based entirely on human induced pluripotent stem cells (hiPSCs). Within a fibrin hydrogel microenvironment, the hiPSC-derived vascular cells self-organized to form stable microvascular networks reproducibly, in which the vessels were lumenized and functional, responding as expected to vasoactive stimulation. Vascular organization and intracellular Ca²⁺ release kinetics in VSMCs could be quantified using automated image analysis based on open-source software CellProfiler and ImageJ on widefield or confocal images, setting the stage for use of the platform to study vascular (patho)physiology and therapy.

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3D VoC formed by hiPSC-ECs and hiPSC-VSMCs

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Vascular organization in 3D VoC formed by hiPSC-VSMC and primary mural cells

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Functional responses of hiPSC-VSMCs in 3D VoC

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Automated analysis of microvascular network morphology and Ca²⁺ release in VSMCs

Quantitative Evaluation of Human Umbilical Vein and Induced Pluripotent Stem Cell-Derived Endothelial Cells as an Alternative Cell Source to Skin-Specific Endothelial Cells in Engineered Skin Grafts

Objective: We compared the capability of human umbilical vein endothelial cells (HUVECs), induced pluripotent stem cell (iPSC)-derived endothelial cells (iECs), and human dermal blood endothelial cells (HDBECs) to effectively vascularize engineered human skin constructs (HSCs) in vitro and on immunodeficient mice. Approach: We quantified the angiogenesis within HSCs both in vitro and in vivo through computational analyses of immunofluorescent (IF) staining. We assayed with real-time quantitative PCR (RT-qPCR) the expression of key endothelial, dermal, and epidermal genes in 2D culture and HSCs. Epidermal integrity and proliferation were also evaluated through haematoxylin and eosin staining, and IF staining. Results: IF confirmed iEC commitment to endothelial phenotype. RT-qPCR showed HUVECs and iECs immaturity compared with HDBECs. In vitro, the vascular network extension was comparable for HDBECs and HUVECs despite differences in vascular diameter, whereas iECs formed unorganized rudimentary tubular structures. In vivo, all ECs produced discrete vascular networks of varying dimensions. HUVECs and HDBECs maintained a higher proliferation of basal keratinocytes. HDBECs had the best impact on extracellular matrix expression, and epidermal proliferation and differentiation. Innovation: To our knowledge, this study represents the first direct and quantitative comparison of HDBECs, HUVECs, and iECs angiogenic performance in HSCs. Conclusions: Our data indicate that HUVECs and iECs can be an alternative cell source to HDBEC to promote the short-term viability of prevascularized engineered grafts. Nevertheless, HDBECs maintain their capillary identity and outperform other EC types in promoting the maturation of the dermis and epidermis. These intrinsic characteristics of HDBECs may influence the long-term function of skin grafts.

Building a stem cell-based primate uterus

The uterus is the organ for embryo implantation and fetal development. Most current models of the uterus are centred around capturing its function during later stages of pregnancy to increase the survival in pre-term births. However, in vitro models focusing on the uterine tissue itself would allow modelling of pathologies including endometriosis and uterine cancers, and open new avenues to investigate embryo implantation and human development. Motivated by these key questions, we discuss how stem cell-based uteri may be engineered from constituent cell parts, either as advanced self-organising cultures, or by controlled assembly through microfluidic and print-based technologies.

Generation and Functional Characterization of Monocytes and Macrophages Derived from Human Induced Pluripotent Stem Cells

Monocytes and macrophages are essential for immune defense and tissue hemostasis. They are also the underlying trigger of many diseases. The availability of robust and short protocols to induce monocytes and macrophages from human induced pluripotent stem cells (hiPSCs) will benefit many applications of immune cells in biomedical research. Here, we describe a protocol to derive and functionally characterize these cells. Large numbers of hiPSC‐derived monocytes (hiPSC‐mono) could be generated in just 15 days. These monocytes were fully functional after cryopreservation and could be polarized to M1 and M2 macrophage subtypes. hiPSC‐derived macrophages (iPSDMs) showed high phagocytotic uptake of bacteria, apoptotic cells, and tumor cells. The protocol was effective across multiple hiPSC lines. In summary, we developed a robust protocol to generate hiPSC‐mono and iPSDMs which showed phenotypic features of macrophages and functional maturity in different bioassays. © 2020 The Authors.

Basic Protocol 1: Differentiation of hiPSCs toward monocytes

Support Protocol 1: Isolation and cryopreservation of monocytes

Support Protocol 2: Characterization of monocytes

Basic Protocol 2: Differentiation of different subtypes of macrophages

Support Protocol 3: Characterization of hiPSC‐derived macrophages (iPSDMs)

Support Protocol 4: Functional characterization of different subtypes of macrophages

In vitro and in vivo study on angiogenesis of porcine induced pluripotent stem cell-derived endothelial cells

Pluripotent stem cells (PSCs) are a promising source of endothelial cells (ECs) for the treatment of cardiovascular diseases. Since clinical application of embryo stem cells (ESCs) involves issues of medical ethics and risk of immune rejection, induced pluripotent stem cells (iPSCs) will facilitate cell transplantation therapy for the cardiovascular diseases. Swine is identified as an ideal large-animal model for human, because of its similar organ size and physiological characteristics. However, there are very few studies on EC differentiation of porcine iPSCs (piPSCs). In recent study, we provided an efficient protocol to differentiate piPSCs into ECs with the purity of 19.76% CD31 positive cells within 16 days. Passaging of these cells yielded a nearly pure population, which also expressed other endothelial markers such as CD144, eNOS and vWF. Besides, these cells exhibited functions of ECs such as uptake of low-density lipoprotein and formation of tubes in vitro or blood vessels in vivo. Our study successfully obtained ECs from piPSCs via a feeder- and serum-free monolayer system and demonstrated their angiogenic function in vivo and in vitro. piPSC-ECs derivation is not only potential for the autologous cell transplantation and cardiovascular drug screening, but also for the mechanistic studies on EC differentiation and endothelial dysfunction.

The next generation of endothelial differentiation: Tissue-specific ECs

Endothelial cells (ECs) sense and respond to fluid flow and regulate immune cell trafficking in all organs. Despite sharing the same mesodermal origin, ECs exhibit heterogeneous tissue-specific characteristics. Human pluripotent stem cells (hPSCs) can potentially be harnessed to capture this heterogeneity and further elucidate endothelium behavior to satisfy the need for increased accuracy and breadth of disease models and therapeutics. Here, we review current strategies for hPSC differentiation to blood vascular ECs and their maturation into continuous, fenestrated, and sinusoidal tissues. We then discuss the contribution of hPSC-derived ECs to recent advances in organoid development and organ-on-chip approaches.

Reconstructing the heart using iPSCs: Engineering strategies and applications

Induced pluripotent stem cells (iPSCs) have emerged as a key component of cardiac tissue engineering, enabling studies of cardiovascular disease mechanisms, drug responses, and developmental processes in human 3D tissue models assembled from isogenic cells. Since the very first engineered heart tissues were introduced more than two decades ago, a wide array of iPSC-derived cardiac spheroids, organoids, and heart-on-a-chip models have been developed incorporating the latest available technologies and materials. In this review, we will first outline the fundamental biological building blocks required to form a functional unit of cardiac muscle, including iPSC-derived cells differentiated by soluble factors (e.g., small molecules), extracellular matrix scaffolds, and exogenous biophysical maturation cues. We will then summarize the different fabrication approaches and strategies employed to reconstruct the heart in vitro at varying scales and geometries. Finally, we will discuss how these platforms, with continued improvements in scalability and tissue maturity, can contribute to both basic cardiovascular research and clinical applications in the future.

Stem cell-based vascularization of microphysiological systems

Microphysiological systems (MPSs) (i.e., tissue or organ chips) exploit microfluidics and 3D cell culture to mimic tissue and organ-level physiology. The advent of human induced pluripotent stem cell (hiPSC) technology has accelerated the use of MPSs to study human disease in a range of organ systems. However, in the reduction of system complexity, the intricacies of vasculature are an often-overlooked aspect of MPS design. The growing library of pluripotent stem cell-derived endothelial cell and perivascular cell protocols have great potential to improve the physiological relevance of vasculature within MPS, specifically for in vitro disease modeling. Three strategic categories of vascular MPS are outlined: self-assembled, interface focused, and 3D biofabricated. This review discusses key features and development of the native vasculature, linking that to how hiPSC-derived vascular cells have been generated, the state of the art in vascular MPSs, and opportunities arising from interdisciplinary thinking.

Endothelial Cells Differentiated from Porcine Epiblast Stem Cells

Pluripotent stem cells (PSCs) have the ability of self-renewal that can retain the characteristics of the mother cell, and of pluripotency that can differentiate into several body types. PSCs typically include embryonic stem cells (ESCs) derived from the inner cell mass of the preimplantation embryo, and epiblast stem cells (EpiSCs) derived from the epiblast of postimplantation embryo. Although PSCs are able to be used by differentiation into endothelial cells as a potential treatment for vascular diseases, human ESCs and induced PSCs (iPSCs) are followed by ethical and safety issues. Pigs are anatomically and physiologically similar to humans. Therefore, the goal of this study was to establish an efficient protocol that differentiates porcine EpiSCs (pEpiSCs) into the endothelial cells for applying the treatment of human vascular diseases. As a result, alkaline phosphatase (AP)-negative (-) pEpiSCs cultured in endothelial cell growth basal medium-2 (EBM-2) differentiation medium in association with 50 ng/mL of vascular endothelial growth factor (VEGF) for 8 days were changed morphologically like the feature of endothelial cells, and expression of pluripotency-associated markers (OCT-3/4, NANOG, SOX2, and C-MYC) in porcine differentiated cells was significantly decreased (p < 0.05). Additionally, when pEpiSCs were cultured in EBM-2 + 50 ng/mL of VEGF, porcine differentiated cells represented a common endothelial cell marker positive (CD31+) but monocytes and lymphocytes marker negative (CD45-). Therefore, these results indicated that pEpiSCs cultured in EBM-2 + 50 ng/mL of VEGF culture condition were efficiently differentiated into endothelial cells for the treatment of blood vessel diseases.

Induced Pluripotent Stem Cells (iPSCs) in Vascular Research: from Two- to Three-Dimensional Organoids

Stem cell technology has been around for almost 30 years and in that time has grown into an enormous field. The stem cell technique progressed from the first successful isolation of mammalian embryonic stem cells (ESCs) in the 1990s, to the production of human induced-pluripotent stem cells (iPSCs) in the early 2000s, to finally culminate in the differentiation of pluripotent cells into highly specialized cell types, such as neurons, endothelial cells (ECs), cardiomyocytes, fibroblasts, and lung and intestinal cells, in the last decades. In recent times, we have attained a new height in stem cell research whereby we can produce 3D organoids derived from stem cells that more accurately mimic the in vivo environment. This review summarizes the development of stem cell research in the context of vascular research ranging from differentiation techniques of ECs and smooth muscle cells (SMCs) to the generation of vascularized 3D organoids. Furthermore, the different techniques are critically reviewed, and future applications of current 3D models are reported.

Differentiation and characterization of human iPSC-derived vascular endothelial cells under physiological shear stress

Induced pluripotent stem cells (iPSCs) offer a potentially unlimited source to generate endothelial cells (ECs) for numerous applications. Here, we describe a 7-day protocol to differentiate up to 55 million vascular endothelial cells (viECs) from 3.5 million human iPSCs using small molecules to regulate specific transcription factors. We also describe a parallel-plate flow chamber system to study EC behavior under physiological shear stress.

For complete details on the use and execution of this protocol, please refer to Atchison et al. (2020).

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A protocol for differentiating vascular endothelial cells (viECs) from human iPSCs

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Generation of up to 55 million viECs from 3.5 million iPSCs within 7 days

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Design and use of parallel-plate flow chamber to study EC behavior under flow

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viECs express EC markers, upregulate flow-sensitive genes, and align to flow direction

Pluripotent stem cell-derived epithelium misidentified as brain microvascular endothelium requires ETS factors to acquire vascular fate

Cells derived from pluripotent sources in vitro must resemble those found in vivo as closely as possible at both transcriptional and functional levels in order to be a useful tool for studying diseases and developing therapeutics. Recently, differentiation of human pluripotent stem cells (hPSCs) into brain microvascular endothelial cells (ECs) with blood-brain barrier (BBB)-like properties has been reported. These cells have since been used as a robust in vitro BBB model for drug delivery and mechanistic understanding of neurological diseases. However, the precise cellular identity of these induced brain microvascular endothelial cells (iBMECs) has not been well described. Employing a comprehensive transcriptomic metaanalysis of previously published hPSC-derived cells validated by physiological assays, we demonstrate that iBMECs lack functional attributes of ECs since they are deficient in vascular lineage genes while expressing clusters of genes related to the neuroectodermal epithelial lineage (Epi-iBMEC). Overexpression of key endothelial ETS transcription factors (ETV2, ERG, and FLI1) reprograms Epi-iBMECs into authentic endothelial cells that are congruent with bona fide endothelium at both transcriptomic as well as some functional levels. This approach could eventually be used to develop a robust human BBB model in vitro that resembles the human brain EC in vivo for functional studies and drug discovery.

A protocol for rapid pericyte differentiation of human induced pluripotent stem cells

Pericytes play a critical role in promoting, regulating, and maintaining numerous vascular functions. Their dysfunction is a major contributor to the progression of vascular and neurodegenerative diseases, making them an ideal candidate for large-scale production for disease modeling and regenerative cell therapy. This protocol describes the rapid and robust differentiation of pericytes from human induced pluripotent stem cells (hiPSCs) while simultaneously generating a population of hiPSC-derived endothelial progenitor cells. For complete details on the use and execution of this protocol, please refer to Zhang et al. (2017).

Endothelial Cells as Tools to Model Tissue Microenvironment in Hypoxia-Dependent Pathologies

Endothelial cells (ECs) lining the blood vessels are important players in many biological phenomena but are crucial in hypoxia-dependent diseases where their deregulation contributes to pathology. On the other hand, processes mediated by ECs, such as angiogenesis, vessel permeability, interactions with cells and factors circulating in the blood, maintain homeostasis of the organism. Understanding the diversity and heterogeneity of ECs in different tissues and during various biological processes is crucial in biomedical research to properly develop our knowledge on many diseases, including cancer. Here, we review the most important aspects related to ECs’ heterogeneity and list the available in vitro tools to study different angiogenesis-related pathologies. We focus on the relationship between functions of ECs and their organo-specificity but also point to how the microenvironment, mainly hypoxia, shapes their activity. We believe that taking into account the specific features of ECs that are relevant to the object of the study (organ or disease state), especially in a simplified in vitro setting, is important to truly depict the biology of endothelium and its consequences. This is possible in many instances with the use of proper in vitro tools as alternative methods to animal testing.

Generation of Functional Vascular Endothelial Cells and Pericytes from Keratinocyte Derived Human Induced Pluripotent Stem Cells

Human induced pluripotent stem cell (hiPSC)-derived endothelial cells (ECs) and pericytes provide a powerful tool for cardiovascular disease modelling, personalized drug testing, translational medicine, and tissue engineering. Here, we report a novel differentiation protocol that results in the fast and efficient production of ECs and pericytes from keratinocyte-derived hiPSCs. We found that the implementation of a 3D embryoid body (EB) stage significantly improves the differentiation efficiency. Compared with the monolayer-based technique, our protocol yields a distinct EC population with higher levels of EC marker expression such as CD31 and vascular endothelial cadherin (VE-cadherin). Furthermore, the EB-based protocol allows the generation of functional EC and pericyte populations that can promote blood vessel-like structure formation upon co-culturing. Moreover, we demonstrate that the EB-based ECs and pericytes can be successfully used in a microfluidic chip model, forming a stable 3D microvascular network. Overall, the described protocol can be used to efficiently differentiate both ECs and pericytes with distinct and high marker expression from keratinocyte-derived hiPSCs, providing a potent source material for future cardiovascular disease studies.

Vascular Tumor Recapitulated in Endothelial Cells from hiPSCs Engineered to Express the SERPINE1-FOSB Translocation

Chromosomal translocations are prevalent among soft tissue tumors, including those of the vasculature such as pseudomyogenic hemangioendothelioma (PHE). PHE shows endothelial cell (EC) features and has a tumor-specific t(7;19)(q22;q13) SERPINE1-FOSB translocation, but is difficult to study as no primary tumor cell lines have yet been derived. Here, we engineer the PHE chromosomal translocation into human induced pluripotent stem cells (hiPSCs) using CRISPR/Cas9 and differentiate these into ECs (hiPSC-ECs) to address this. Comparison of parental with PHE hiPSC-ECs shows (1) elevated expression of FOSB, (2) higher proliferation and more tube formation but lower endothelial barrier function, (3) invasive growth and abnormal vessel formation in mice after transplantation, and (4) specific transcriptome alterations reflecting PHE and indicating PI3K-Akt and MAPK signaling pathways as possible therapeutic targets. The modified hiPSC-ECs thus recapitulate functional features of PHE and demonstrate how these translocation models can be used to understand tumorigenic mechanisms and identify therapeutic targets.

SERPINE1-FOSB translocation in hiPSC to model the vascular tumor PHE

CRISPR/Cas9-mediated gene targeting to engineer hiPSC^{SERPINE1-FOSB}

hiPSC-ECs^{SERPINE1-FOSB} show increased FOSB expression

Functional features of PHE recapitulated by hiPSC-ECs^{SERPINE1-FOSB}

Dual Function of iPSC-Derived Pericyte-Like Cells in Vascularization and Fibrosis-Related Cardiac Tissue Remodeling In Vitro

Myocardial interstitial fibrosis (MIF) is characterized by excessive extracellular matrix (ECM) deposition, increased myocardial stiffness, functional weakening, and compensatory cardiomyocyte (CM) hypertrophy. Fibroblasts (Fbs) are considered the principal source of ECM, but the contribution of perivascular cells, including pericytes (PCs), has gained attention, since MIF develops primarily around small vessels. The pathogenesis of MIF is difficult to study in humans because of the pleiotropy of mutually influencing pathomechanisms, unpredictable side effects, and the lack of available patient samples. Human pluripotent stem cells (hPSCs) offer the unique opportunity for the de novo formation of bioartificial cardiac tissue (BCT) using a variety of different cardiovascular cell types to model aspects of MIF pathogenesis in vitro. Here, we have optimized a protocol for the derivation of hPSC-derived PC-like cells (iPSC-PCs) and present a BCT in vitro model of MIF that shows their central influence on interstitial collagen deposition and myocardial tissue stiffening. This model was used to study the interplay of different cell types-i.e., hPSC-derived CMs, endothelial cells (ECs), and iPSC-PCs or primary Fbs, respectively. While iPSC-PCs improved the sarcomere structure and supported vascularization in a PC-like fashion, the functional and histological parameters of BCTs revealed EC- and PC-mediated effects on fibrosis-related cardiac tissue remodeling.