Expansion and maintenance of human embryonic stem cell-derived endothelial cells by TGFbeta inhibition is Id1 dependent

Bridging the Gap: Advances and Challenges in Heart Regeneration from In Vitro to In Vivo Applications

Cardiovascular diseases, particularly ischemic heart disease, area leading cause of morbidity and mortality worldwide. Myocardial infarction (MI) results in extensive cardiomyocyte loss, inflammation, extracellular matrix (ECM) degradation, fibrosis, and ultimately, adverse ventricular remodeling associated with impaired heart function. While heart transplantation is the only definitive treatment for end-stage heart failure, donor organ scarcity necessitates the development of alternative therapies. In such cases, methods to promote endogenous tissue regeneration by stimulating growth factor secretion and vascular formation alone are insufficient. Techniques for the creation and transplantation of viable tissues are therefore highly sought after. Approaches to cardiac regeneration range from stem cell injections to epicardial patches and interposition grafts. While numerous preclinical trials have demonstrated the positive effects of tissue transplantation on vasculogenesis and functional recovery, long-term graft survival in large animal models is rare. Adequate vascularization is essential for the survival of transplanted tissues, yet pre-formed microvasculature often fails to achieve sufficient engraftment. Recent studies report success in enhancing cell survival rates in vitro via tissue perfusion. However, the transition of these techniques to in vivo models remains challenging, especially in large animals. This review aims to highlight the evolution of cardiac patch and stem cell therapies for the treatment of cardiovascular disease, identify discrepancies between in vitro and in vivo studies, and discuss critical factors for establishing effective myocardial tissue regeneration in vivo.

Advances in Shear Stress Stimulation of Stem Cells: A Review of the Last Three Decades

Stem cells are widely used in scientific research because of their ability to self-renew and differentiate into a variety of specialized cell types needed for body functions. However, the self-renewal and differentiation of stem cells are regulated by various stimuli, with mechanical stimulation being particularly notable due to its ability to mimic the physical environment in the body. This study systematically collected 2638 research papers published between 1994 and 2024, employing tools such as VOSviewer, CiteSpace, and GraphPad Prism to uncover research hotspots, publication trends, and collaboration networks. The results indicate a yearly increase in global research on the shear stress stimulation of stem cells, with significant contributions from the United States and China in terms of research investment and output. Future research directions include a deeper understanding of the mechanisms underlying mechanical stimulation's effects on stem cell differentiation, the development of new materials and scaffold designs to better replicate the natural cellular environment, and advancements in regenerative medicine. Despite considerable progress, challenges remain in translating basic research findings into clinical applications.

Generation and characterisation of scalable and stable human pluripotent stem cell-derived microvascular-like endothelial cells for cardiac applications

Coronary microvascular disease (CMD) and its progression towards major adverse coronary events pose a significant health challenge. Accurate in vitro investigation of CMD requires a robust cell model that faithfully represents the cells within the cardiac microvasculature. Human pluripotent stem cell-derived endothelial cells (hPSC-ECs) offer great potential; however, they are traditionally derived via differentiation protocols that are not readily scalable and are not specified towards the microvasculature. Here, we report the development and comprehensive characterisation of a scalable 3D protocol enabling the generation of phenotypically stable cardiac hPSC-microvascular-like ECs (hPSC-CMVECs) and cardiac pericyte-like cells. These were derived by growing vascular organoids within 3D stirred tank bioreactors and subjecting the emerging 3D hPSC-ECs to high-concentration VEGF-A treatment (3DV). Not only did this promote phenotypic stability of the 3DV hPSC-ECs; single cell-RNA sequencing (scRNA-seq) revealed the pronounced expression of cardiac endothelial- and microvascular-associated genes. Further, the generated mural cells attained from the vascular organoid exhibited markers characteristic of cardiac pericytes. Thus, we present a suitable cell model for investigating the cardiac microvasculature as well as the endothelial-dependent and -independent mechanisms of CMD. Moreover, owing to their phenotypic stability, cardiac specificity, and high angiogenic potential, the cells described within would also be well suited for cardiac tissue engineering applications.

BCL6B-dependent suppression of ETV2 hampers endothelial cell differentiation

BACKGROUND

B-cell CLL/lymphoma 6 member B (BCL6B) operates as a sequence-specific transcriptional repressor within the nucleus, playing crucial roles in various biological functions, including tumor suppression, immune response, stem cell self-renew, and vascular angiogenesis. However, whether BCL6B is involved in endothelial cell (EC) development has remained largely unknown. ETS variant transcription factor 2 (ETV2) is well known to facilitate EC differentiation. This study aims to determine the important role of BCL6B in EC differentiation and its potential mechanisms.

METHODS

Doxycycline-inducible human induced pluripotent stem cell (hiPSC) lines with BCL6B overexpression or BCL6B knockdown were established and subjected to differentiate into ECs and vessel organoids (VOs). RNA sequencing analysis was performed to identify potential signal pathways regulated by BCL6B during EC differentiation from hiPSCs. Quantitative real-time PCR (qRT-PCR) was used to detect the expression of pluripotency and vascular-specific marker genes expression. EC differentiation efficiency was determined by Flow cytometry analysis. The performance of EC was evaluated by in vitro Tube formation assay. The protein expression and the vessel-like structures were assessed using immunofluorescence analysis or western blot. Luciferase reporter gene assay and chromatin immunoprecipitation (ChIP)-PCR analysis were used to determine the regulatory relationship between BCL6B and ETV2.

RESULTS

Functional ECs and VOs were successfully generated from hiPSCs. Notably, overexpression of BCL6B suppressed while knockdown of BCL6B improved EC differentiation from hiPSCs. Additionally, the overexpression of BCL6B attenuated the capacity of derived hiPSC-ECs to form a tubular structure. Furthermore, compared to the control VOs, BCL6B overexpression repressed the growth of VOs, whereas BCL6B knockdown had little effect on the size of VOs. RNA sequencing analysis confirmed that our differentiation protocol induced landscape changes for cell/tissue/system developmental process, particularly vascular development and tube morphogenesis, which were significantly modulated by BCL6B. Subsequent experiments confirmed the inhibitory effect of BCL6B is facilitated by the binding of BCL6B to the promoter region of ETV2, led to the suppression of ETV2's transcriptional activity. Importantly, the inhibitory effect of BCL6B overexpression on EC differentiation from hiPSCs could be rescued by ETV2 overexpression.

CONCLUSIONS

BCL6B inhibits EC differentiation and hinders VO development by repressing the transcriptional activity of ETV2.

Cracking the code of the cardiovascular enigma: hPSC-derived endothelial cells unveil the secrets of endothelial dysfunction

Endothelial dysfunction is a central contributor to the development of most cardiovascular diseases and is characterised by the reduced synthesis or bioavailability of the vasodilator nitric oxide together with other abnormalities such as inflammation, senescence, and oxidative stress. The use of patient-specific and genome-edited human pluripotent stem cell-derived endothelial cells (hPSC-ECs) has shed novel insights into the role of endothelial dysfunction in cardiovascular diseases with strong genetic components such as genetic cardiomyopathies and pulmonary arterial hypertension. However, their utility in studying complex multifactorial diseases such as atherosclerosis, metabolic syndrome and heart failure poses notable challenges. In this review, we provide an overview of the different methods used to generate and characterise hPSC-ECs before comprehensively assessing their effectiveness in cardiovascular disease modelling and high-throughput drug screening. Furthermore, we explore current obstacles that will need to be overcome to unleash the full potential of hPSC-ECs in facilitating patient-specific precision medicine. Addressing these challenges holds great promise in advancing our understanding of intricate cardiovascular diseases and in tailoring personalised therapeutic strategies.

Applications, challenges, and prospects of induced pluripotent stem cells for vascular disease

Vascular disease, including heart disease, stroke, and peripheral arterial disease, is one of the leading causes of death and disability and represents a significant global health issue. Since the development of human induced pluripotent stem cells (hiPSCs) in 2007, hiPSCs have provided unique and tremendous opportunities for studying human pathophysiology, disease modeling, and drug discovery in the field of regenerative medicine. In this review, we discuss vascular physiology and related diseases, the current methods for generating vascular cells (eg, endothelial cells, smooth muscle cells, and pericytes) from hiPSCs, and describe the opportunities and challenges to the clinical applications of vascular organoids, tissue-engineered blood vessels, and vessels-on-a-chip. We then explore how hiPSCs can be used to study and treat inherited vascular diseases and discuss the current challenges and future prospects. In the future, it will be essential to develop vascularized organoids or tissues that can simultaneously undergo shear stress and cyclic stretching. This development will not only increase their maturity and function but also enable effective and innovative disease modeling and drug discovery.

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.

From theory to therapy: a bibliometric and visual study of stem cell advancements in age-related macular degeneration

BACKGROUND AIMS

Human pluripotent stem cells, including embryonic stem cells and induced pluripotent stem cells, offer groundbreaking therapeutic potential for degenerative diseases and cellular repair. Despite their significance, a comprehensive bibliometric analysis in this field, particularly in relation to age-related macular degeneration (AMD), is yet to be conducted. This study aims to map the foundational and emerging areas in stem cell and AMD research through bibliometric analysis.

METHODS

This study analyzed articles and reviews on stem cells and AMD from 2000 to 2022, sourced from the Web of Science Core Collection. We used VOSviewer and CiteSpace for analysis and visualization of data pertaining to countries, institutions, authors, journals, references and key words. Statistical analyses were conducted using R language and Microsoft Excel 365.

RESULTS

In total, 539 publications were included, indicating an increase in global literature on stem cells and AMD from 2000 to 2022. The USA was the leading contributor, with 239 papers and the highest H-index, also the USA had the highest average citation rate per article (59.82). Notably, 50% of the top 10 institutions were from the USA, with the University of California system being the most productive. Key authors included Masayo Takahashi, Michiko Mandai, Dennis Clegg, Pete J. Coffey, Boris Stanzel, and Budd A. Tucker. Investigative Ophthalmology & Visual Science published the majority of relevant papers (n = 27). Key words like "clinical trial," "stem cell therapy," "retinal organoid," and "retinal progenitor cells" were predominant.

CONCLUSIONS

Research on stem cells and AMD has grown significantly, highlighting the need for increased global cooperation. Current research prioritizes the relationship between "ipsc," "induced pluripotent stem cell," "cell culture," and "human embryonic stem cell." As stem cell culture and safety have advanced, focus has shifted to prognosis and complications post-transplantation, signifying the movement of stem cell research from labs to clinical settings.

Advancing cardiac regeneration through 3D bioprinting: methods, applications, and future directions

Cardiovascular diseases (CVDs) represent a paramount global mortality concern, and their prevalence is on a relentless ascent. Despite the effectiveness of contemporary medical interventions in mitigating CVD-related fatality rates and complications, their efficacy remains curtailed by an array of limitations. These include the suboptimal efficiency of direct cell injection and an inherent disequilibrium between the demand and availability of heart transplantations. Consequently, the imperative to formulate innovative strategies for cardiac regeneration therapy becomes unmistakable. Within this context, 3D bioprinting technology emerges as a vanguard contender, occupying a pivotal niche in the realm of tissue engineering and regenerative medicine. This state-of-the-art methodology holds the potential to fabricate intricate heart tissues endowed with multifaceted structures and functionalities, thereby engendering substantial promise. By harnessing the prowess of 3D bioprinting, it becomes plausible to synthesize functional cardiac architectures seamlessly enmeshed with the host tissue, affording a viable avenue for the restitution of infarcted domains and, by extension, mitigating the onerous yoke of CVDs. In this review, we encapsulate the myriad applications of 3D bioprinting technology in the domain of heart tissue regeneration. Furthermore, we usher in the latest advancements in printing methodologies and bioinks, culminating in an exploration of the extant challenges and the vista of possibilities inherent to a diverse array of approaches.

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.

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.

PCSK9 activation promotes early atherosclerosis in a vascular microphysiological system

Atherosclerosis is a primary precursor of cardiovascular disease (CVD), the leading cause of death worldwide. While proprotein convertase subtilisin/kexin 9 (PCSK9) contributes to CVD by degrading low-density lipoprotein receptors (LDLR) and altering lipid metabolism, PCSK9 also influences vascular inflammation, further promoting atherosclerosis. Here, we utilized a vascular microphysiological system to test the effect of PCSK9 activation or repression on the initiation of atherosclerosis and to screen the efficacy of a small molecule PCSK9 inhibitor. We have generated PCSK9 over-expressed (P+) or repressed (P-) human induced pluripotent stem cells (iPSCs) and further differentiated them to smooth muscle cells (viSMCs) or endothelial cells (viECs). Tissue-engineered blood vessels (TEBVs) made from P+ viSMCs and viECs resulted in increased monocyte adhesion compared to the wild type (WT) or P- equivalents when treated with enzyme-modified LDL (eLDL) and TNF-α. We also found significant viEC dysfunction, such as increased secretion of VCAM-1, TNF-α, and IL-6, in P+ viECs treated with eLDL and TNF-α. A small molecule compound, NYX-1492, that was originally designed to block PCSK9 binding with the LDLR was tested in TEBVs to determine its effect on lowering PCSK9-induced inflammation. The compound reduced monocyte adhesion in P+ TEBVs with evidence of lowering secretion of VCAM-1 and TNF-α. These results suggest that PCSK9 inhibition may decrease vascular inflammation in addition to lowering plasma LDL levels, enhancing its anti-atherosclerotic effects, particularly in patients with elevated chronic inflammation.

Development of Reproducible and Scalable Culture Conditions for In Vitro Maintenance of Pig Embryonic Stem Cells Using the Sandoz Inbred Swiss Mouse Thioguanine-Resistant Ouabain-Resistant Cell Line as a Feeder Layer

Feeder cells play a crucial role in maintaining the pluripotency of embryonic stem cells (ESCs) by secreting various extrinsic regulators, such as extracellular matrix (ECM) proteins and growth factors. Although primary mouse embryonic fibroblasts (MEFs) are the most widely used feeder cell type for the culture of ESCs, they have inevitable disadvantages such as batch-to-batch variation and labor-intensive isolation processes. Here, we revealed that the Sandoz inbred Swiss Mouse (SIM) thioguanine-resistant ouabain-resistant (STO) cell line, an immortalized cell line established from mouse SIM embryonic fibroblasts, can be used as a feeder layer for in vitro culture of authentic pig ESCs instead of primary MEFs. First, the expression of genes encoding ECM proteins and growth factors was analyzed to compare their secretory functions as feeder cells. Quantitative real-time polymerase chain reaction (qPCR) showed that the gene expression of these pluripotency-associated factors was downregulated in STO cells compared to primary MEFs of similar density. Therefore, subsequent optimization of the culture conditions was attempted using higher STO cell densities. Notably, pig ESCs cultured on STO cell density of 3 × (187,500 cells/cm2) exhibited the most similar pluripotent state to pig ESCs cultured on primary MEF density of 1 × (62,500 cells/cm2), as determined by alkaline phosphatase staining, qPCR, and immunocytochemistry. In addition, pig ESCs cultured on STO cell density of 3 × formed complex teratoma containing multiple types of tissues derived from all three germ layers. Our culture conditions using optimal STO cell density can be applied to fields requiring reproducible and scalable production of pig ESCs, such as preclinical research and cellular agriculture.

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.

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.

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.

Recent advancements and future requirements in vascularization of cortical organoids

The fields of tissue engineering and disease modeling have become increasingly cognizant of the need to create complex and mature structures in vitro to adequately mimic the in vivo niche. Specifically for neural applications, human brain cortical organoids (COs) require highly stratified neurons and glial cells to generate synaptic functions, and to date, most efforts achieve only fetal functionality at best. Moreover, COs are usually avascular, inducing the development of necrotic cores, which can limit growth, development, and maturation. Recent efforts have attempted to vascularize cortical and other organoid types. In this review, we will outline the components of a fully vascularized CO as they relate to neocortical development in vivo. These components address challenges in recapitulating neurovascular tissue patterning, biomechanical properties, and functionality with the goal of mirroring the quality of organoid vascularization only achieved with an in vivo host. We will provide a comprehensive summary of the current progress made in each one of these categories, highlighting advances in vascularization technologies and areas still under investigation.

Engineering bioactive nanoparticles to rejuvenate vascular progenitor cells

Fetal exposure to gestational diabetes mellitus (GDM) predisposes children to future health complications including type-2 diabetes mellitus, hypertension, and cardiovascular disease. A key mechanism by which these complications occur is through stress-induced dysfunction of endothelial progenitor cells (EPCs), including endothelial colony-forming cells (ECFCs). Although several approaches have been previously explored to restore endothelial function, their widespread adoption remains tampered by systemic side effects of adjuvant drugs and unintended immune response of gene therapies. Here, we report a strategy to rejuvenate circulating vascular progenitor cells by conjugation of drug-loaded liposomal nanoparticles directly to the surface of GDM-exposed ECFCs (GDM-ECFCs). Bioactive nanoparticles can be robustly conjugated to the surface of ECFCs without altering cell viability and key progenitor phenotypes. Moreover, controlled delivery of therapeutic drugs to GDM-ECFCs is able to normalize transgelin (TAGLN) expression and improve cell migration, which is a critical key step in establishing functional vascular networks. More importantly, sustained pseudo-autocrine stimulation with bioactive nanoparticles is able to improve in vitro and in vivo vasculogenesis of GDM-ECFCs. Collectively, these findings highlight a simple, yet promising strategy to rejuvenate GDM-ECFCs and improve their therapeutic potential. Promising results from this study warrant future investigations on the prospect of the proposed strategy to improve dysfunctional vascular progenitor cells in the context of other chronic diseases, which has broad implications for addressing various cardiovascular complications, as well as advancing tissue repair and regenerative medicine.

Drug-loaded liposomal nanoparticles conjugated to endothelial colony-forming cells can improve the vasculogenic potential of vascular progenitor cells exposed to gestational diabetes mellitus.

Challenges and opportunities in the use of transcriptomics characterization for human iPSC-derived BBB models

The blood-brain barrier (BBB) is localized at the brain microvascular endothelial cells. These cells form a tight barrier, limiting the access of cells, pathogens, chemicals, and toxins to the brain due to tight junctions and efflux transporters. As the BBB plays a role in the assessment of neurotoxicity and brain uptake of drugs, human in vitro BBB models are highly needed. They allow to evaluate if compounds could reach the central nervous system across the BBB or can compromise its barrier function. Past decade, multiple induced pluripotent stem cell (iPSC)-derived BBB differentiation protocols emerged. These protocols can be divided in two groups, the one-step protocols, direct differentiation from iPSC to BBB cells, or the two-step protocols, differentiation for iPSC to endothelial (progenitor) cells and further induction of BBB characteristics. While the one-step differentiation protocols display good barrier properties, reports question their endothelial nature and maturation status. Therefore protocol characterization remains important. With transcriptomics becoming cheaper, this may support iPSC-derived model characterization. Because of the constraints in obtaining human brain tissue, good human reference data is scarce and would bear inter-individual variability. Additionally, comparison across studies might be challenging due to variations in sample preparation and analysis. Hopefully, increasing use of transcriptomics will allow in-depth characterization of the current iPSC-BBB models and guide researchers to generate more relevant human BBB models.

Derivation and Characterization of Endothelial Cells from Porcine Induced Pluripotent Stem Cells

Although the study on the regulatory mechanism of endothelial differentiation from the perspective of development provides references for endothelial cell (EC) derivation from pluripotent stem cells, incomplete reprogramming and donor-specific epigenetic memory are still thought to be the obstacles of iPSCs for clinical application. Thus, it is necessary to establish a stable iPSC-EC induction system and investigate the regulatory mechanism of endothelial differentiation. Based on a single-layer culture system, we successfully obtained ECs from porcine iPSCs (piPSCs). In vitro, the derived piPSC-ECs formed microvessel-like structures along 3D gelatin scaffolds. Under pathological conditions, the piPSC-ECs functioned on hindlimb ischemia repair by promoting blood vessel formation. To elucidate the molecular events essential for endothelial differentiation in our model, genome-wide transcriptional profile analysis was conducted, and we found that during piPSC-EC derivation, the synthesis and secretion level of TGF-β as well as the phosphorylation level of Smad2/3 changed dynamically. TGF-β-Smad2/3 signaling activation promoted mesoderm formation and prevented endothelial differentiation. Understanding the regulatory mechanism of iPSC-EC derivation not only paves the way for further optimization, but also provides reference for establishing a cardiovascular drug screening platform and revealing the molecular mechanism of endothelial dysfunction.

Progress in Bioengineering Strategies for Heart Regenerative Medicine

The human heart has the least regenerative capabilities among tissues and organs, and heart disease continues to be a leading cause of mortality in the industrialized world with insufficient therapeutic options and poor prognosis. Therefore, developing new therapeutic strategies for heart regeneration is a major goal in modern cardiac biology and medicine. Recent advances in stem cell biology and biotechnologies such as human pluripotent stem cells (hPSCs) and cardiac tissue engineering hold great promise for opening novel paths to heart regeneration and repair for heart disease, although these areas are still in their infancy. In this review, we summarize and discuss the recent progress in cardiac tissue engineering strategies, highlighting stem cell engineering and cardiomyocyte maturation, development of novel functional biomaterials and biofabrication tools, and their therapeutic applications involving drug discovery, disease modeling, and regenerative medicine for heart disease.

Expanding tubular microvessels on stiff substrates with endothelial cells and pericytes from the same adult tissue

Endothelial cells (ECs) usually form a monolayer on two-dimensional (2D) stiff substrates and a tubular structure with soft hydrogels. The coculture models using ECs and pericytes derived from different adult tissues or pluripotent stem cells cannot mimic tissue-specific microvessels due to vascular heterogeneity. Our study established a method for expanding tubular microvessels on 2D stiff substrates with ECs and pericytes from the same adult tissue. We isolated microvessels from adult rat subcutaneous soft connective tissue and cultured them in the custom-made tubular microvascular growth medium on 2D stiff substrates (TGM2D). TGM2D promoted adult microvessel growth for at least 4 weeks and maintained a tubular morphology, contrary to the EC monolayer in the commercial medium EGM2MV. Transcriptomic analysis showed that TGM2D upregulated angiogenesis and vascular morphogenesis while suppressing oxidation and lipid metabolic pathways. Our method can be applied to other organs for expanding organ-specific microvessels for tissue engineering.

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.

Modeling Transposition of the Great Arteries with Patient-Specific Induced Pluripotent Stem Cells

The dextro-transposition of the great arteries (d-TGA) is one of the most common congenital heart diseases. To identify biological processes that could be related to the development of d-TGA, we established induced pluripotent stem cell (iPSC) lines from two patients with d-TGA and from two healthy subjects (as controls) and differentiated them into endothelial cells (iPSC-ECs). iPSC-EC transcriptome profiling and bioinformatics analysis revealed differences in the expression level of genes involved in circulatory system and animal organ development. iPSC-ECs from patients with d-TGA showed impaired ability to develop tubular structures in an in vitro capillary-like tube formation assay, and interactome studies revealed downregulation of biological processes related to Notch signaling, circulatory system development and angiogenesis, pointing to alterations in vascular structure development. Our study provides an iPSC-based cellular model to investigate the etiology of d-TGA.

The Differentiation of Pluripotent Stem Cells towards Endothelial Progenitor Cells - Potential Application in Pulmonary Arterial Hypertension

Background and Objectives

Endothelial progenitor cells (EPCs) and endothelial cells (ECs) have been applied in the clinic to treat pulmonary arterial hypertension (PAH), a disease characterized by disordered pulmonary vasculature. However, the lack of sufficient transplantable cells before the deterioration of disease condition is a current limitation to apply cell therapy in patients. It is necessary to differentiate pluripotent stem cells (PSCs) into EPCs and identify their characteristics.

Methods and Results

Comparing previously reported methods of human PSCs-derived ECs, we optimized a highly efficient differentiation protocol to obtain cells that match the phenotype of isolated EPCs from healthy donors. The protocol is compatible with chemically defined medium (CDM), it could produce a large number of clinically applicable cells with low cost. Moreover, we also found PSCs-derived EPCs express CD133, have some characteristics of mesenchymal stem cells and are capable of homing to repair blood vessels in zebrafish xenograft assays. In addition, we further revealed that IPAH PSCs-derived EPCs have higher expression of proliferation-related genes and lower expression of immune-related genes than normal EPCs and PSCs-derived EPCs through microarray analysis.

Conclusions

In conclusion, we optimized a highly efficient differentiation protocol to obtain PSCs-derived EPCs with the phenotypic and molecular characteristics of EPCs from healthy donors which distinguished them from EPCs from PAH.

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.

A Modular Differentiation System Maps Multiple Human Kidney Lineages from Pluripotent Stem Cells

Recent studies using human pluripotent stem cells (hPSCs) have developed protocols to induce kidney-lineage cells and reconstruct kidney organoids. However, the separate generation of metanephric nephron progenitors (NPs), mesonephric NPs, and ureteric bud (UB) cells, which constitute embryonic kidneys, in in vitro differentiation culture systems has not been fully investigated. Here, we create a culture system in which these mesoderm-like cell types and paraxial and lateral plate mesoderm-like cells are separately generated from hPSCs. We recapitulate nephrogenic niches from separately induced metanephric NP-like and UB-like cells, which are subsequently differentiated into glomeruli, renal tubules, and collecting ducts in vitro and further vascularized in vivo. Our selective differentiation protocols should contribute to understanding the mechanisms underlying human kidney development and disease and also supply cell sources for regenerative therapies.

Human Induced Pluripotent Stem Cell-Derived Brain Endothelial Cells: Current Controversies

Brain microvascular endothelial cells (BMECs) possess unique properties that are crucial for many functions of the blood-brain-barrier (BBB) including maintenance of brain homeostasis and regulation of interactions between the brain and immune system. The generation of a pure population of putative brain microvascular endothelial cells from human pluripotent stem cell sources (iBMECs) has been described to meet the need for reliable and reproducible brain endothelial cells in vitro. Human pluripotent stem cells (hPSCs), embryonic or induced, can be differentiated into large quantities of specialized cells in order to study development and model disease. These hPSC-derived iBMECs display endothelial-like properties, such as tube formation and low-density lipoprotein uptake, high transendothelial electrical resistance (TEER), and barrier-like efflux transporter activities. Over time, the de novo generation of an organotypic endothelial cell from hPSCs has aroused controversies. This perspective article highlights the developments made in the field of hPSC derived brain endothelial cells as well as where experimental data are lacking, and what concerns have emerged since their initial description.

Comparative Study of Human Pluripotent Stem Cell-Derived Endothelial Cells in Hydrogel-Based Culture Systems

Human pluripotent stem cell (hPSC)-derived endothelial cells (ECs) are promising cell sources for drug discovery, tissue engineering, and studying or treating vascular diseases. However, hPSC-ECs derived from different culture methods display different phenotypes. Herein, we made a detailed comparative study of hPSC-ECs from three different culture systems (e.g., 2D, 3D PNIPAAm-PEG hydrogel, and 3D alginate hydrogel cultures) based on our previous reports. We expanded hPSCs and differentiated them into ECs in three culture systems. Both 3D hydrogel systems could mimic an in vivo physiologically relevant microenvironment to protect cells from shear force and prevent cell agglomeration, leading to a high culture efficiency and a high volumetric yield. We demonstrated that hPSC-ECs produced from both hydrogel systems had similar results as 2D-ECs. The transcriptome analysis showed that PEG-ECs and alginate-ECs displayed a functional phenotype due to their higher gene expressions in vasculature development, extracellular matrix, angiogenesis, and glycolysis, while 2D-ECs showed a proliferative phenotype due to their higher gene expressions in cell proliferation. Taken together, both PEG- and alginate-hydrogel systems will significantly advance the applications of hPSC-ECs in various biomedical fields.

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.

Nuclear IL-33/SMAD signaling axis promotes cancer development in chronic inflammation

Interleukin (IL)-33 cytokine plays a critical role in allergic diseases and cancer. IL-33 also has a nuclear localization signal. However, the nuclear function of IL-33 and its impact on cancer is unknown. Here, we demonstrate that nuclear IL-33-mediated activation of SMAD signaling pathway in epithelial cells is essential for cancer development in chronic inflammation. Using RNA and ChIP sequencing, we found that nuclear IL-33 repressed the expression of an inhibitory SMAD, Smad6, by interacting with its transcription factor, RUNX2. IL-33 was highly expressed in the skin and pancreatic epithelial cells in chronic inflammation, leading to a markedly repressed Smad6 expression as well as dramatically upregulated p-SMAD2/3 and p-SMAD1/5 in the epithelial cells. Blocking TGF-β/SMAD signaling attenuated the IL-33-induced cell proliferation in vitro and inhibited IL-33-dependent epidermal hyperplasia and skin cancer development in vivo. IL-33 and SMAD signaling were upregulated in human skin cancer, pancreatitis, and pancreatitis-associated pancreatic cancer. Collectively, our findings reveal that nuclear IL-33/SMAD signaling is a cell-autonomous tumor-promoting axis in chronic inflammation, which can be targeted by small-molecule inhibitors for cancer treatment and prevention.

Long-term single-cell passaging of human iPSC fully supports pluripotency and high-efficient trilineage differentiation capacity

Objectives:

To establish a straightforward single-cell passaging cultivation method that enables high-quality maintenance of human induced pluripotent stem cells without the appearance of karyotypic abnormalities or loss of pluripotency.

Methods:

Cells were kept in culture for over 50 passages, following a structured chronogram of passage and monitoring cell growth by population doubling time calculation and cell confluence. Standard procedures for human induced pluripotent stem cells monitoring as embryonic body formation, karyotyping and pluripotency markers expression were evaluated in order to assess the cellular state in long-term culture. Cells that underwent these tests were then subjected to differentiation into keratinocytes, cardiomyocytes and definitive endoderm to evaluate its differentiation capacity.

Results:

Human induced pluripotent stem cells clones maintained its pluripotent capability as well as chromosomal integrity and were able to generate derivatives from the three germ layers at high passages by embryoid body formation and high-efficient direct differentiation into keratinocytes, cardiomyocytes and definitive endoderm.

Conclusions:

Our findings support the routine of human induced pluripotent stem cells single-cell passaging as a reliable procedure even after long-term cultivation, providing healthy human induced pluripotent stem cells to be used in drug discovery, toxicity, and disease modeling as well as for therapeutic approaches.

Stepwise differentiation and functional characterization of human induced pluripotent stem cell-derived choroidal endothelial cells

BACKGROUND

Endothelial cells (ECs) are essential regulators of the vasculature, lining arteries, veins, and capillary beds. While all ECs share a number of structural and molecular features, heterogeneity exists depending on their resident tissue. ECs lining the choriocapillaris in the human eye are lost early in the pathogenesis of age-related macular degeneration (AMD), a common and devastating form of vision loss. In order to study the mechanisms leading to choroidal endothelial cell (CEC) loss and to develop reagents for repairing the choroid, a reproducible in vitro model, which closely mimic CECs, is needed. While a number of protocols have been published to direct induced pluripotent stem cells (iPSCs) into ECs, the goal of this study was to develop methods to differentiate iPSCs into ECs resembling those found in the human choriocapillaris specifically.

METHODS

We transduced human iPSCs with a CDH5p-GFP-ZEO lentiviral vector and selected for transduced iPSCs using blasticidin. We generated embryoid bodies (EBs) from expanded iPSC colonies and transitioned from mTESR™1 to EC media. One day post-EB formation, we induced mesoderm fate commitment via addition of BMP-4, activin A, and FGF-2. On day 5, EBs were adhered to Matrigel-coated plates in EC media containing vascular endothelial cell growth factor (VEGF) and connective tissue growth factor (CTGF) to promote CEC differentiation. On day 14, we selected for CECs using either zeocin resistance or anti-CD31 MACS beads. We expanded CECs post-selection and performed immunocytochemical analysis of CD31, carbonic anhydrase IV (CA4), and RGCC; tube formation assays; and transmission electron microscopy to access vascular function.

RESULTS

We report a detailed protocol whereby we direct iPSC differentiation toward mesoderm and utilize CTGF to specify CECs. The CDH5p-GFP-ZEO lentiviral vector facilitated the selection of iPSC-derived ECs that label with antibodies directed against CD31, CA4, and RGCC; form vascular tubes in vitro; and migrate into empty choroidal vessels. CECs selected using either antibiotic selection or CD31 MACS beads showed similar characteristics, thereby making this protocol easily reproducible with or without lentiviral vectors.

CONCLUSION

ECs generated following this protocol exhibit functional and biochemical characteristics of CECs. This protocol will be useful for developing in vitro models toward understanding the mechanisms of CEC loss early in AMD.

Endogenous IGF Signaling Directs Heterogeneous Mesoderm Differentiation in Human Embryonic Stem Cells

During embryogenesis, various cell types emerge simultaneously from their common progenitors under the influence of intrinsic signals. Human embryonic stem cells can differentiate to diverse cell types of three embryonic lineages, making them an excellent system for understanding the regulatory mechanism that maintains the balance of different cell types in embryogenesis. In this report, we demonstrate that insulin-like growth factor (IGF) proteins are endogenously expressed during differentiation, and their temporal expression contributes to the cell fate diversity in mesoderm differentiation. Small molecule LY294002 inhibits the IGF pathway to promote cardiomyocyte differentiation while suppressing epicardial and noncardiac cell fates. LY294002-induced cardiomyocytes demonstrate characteristic cardiomyocyte features and provide insights into the molecular mechanisms underlying cardiac differentiation. We further show that LY294002 induces cardiomyocytes through CK2 pathway inhibition. This study elucidates the crucial roles of endogenous IGF in mesoderm differentiation and shows that the inhibition of the IGF pathway is an effective approach for generating cardiomyocytes.

Cells, Materials, and Fabrication Processes for Cardiac Tissue Engineering

Cardiovascular disease is the number one killer worldwide, with myocardial infarction (MI) responsible for approximately 1 in 6 deaths. The lack of endogenous regenerative capacity, added to the deleterious remodelling programme set into motion by myocardial necrosis, turns MI into a progressively debilitating disease, which current pharmacological therapy cannot halt. The advent of Regenerative Therapies over 2 decades ago kick-started a whole new scientific field whose aim was to prevent or even reverse the pathological processes of MI. As a highly dynamic organ, the heart displays a tight association between 3D structure and function, with the non-cellular components, mainly the cardiac extracellular matrix (ECM), playing both fundamental active and passive roles. Tissue engineering aims to reproduce this tissue architecture and function in order to fabricate replicas able to mimic or even substitute damaged organs. Recent advances in cell reprogramming and refinement of methods for additive manufacturing have played a critical role in the development of clinically relevant engineered cardiovascular tissues. This review focuses on the generation of human cardiac tissues for therapy, paying special attention to human pluripotent stem cells and their derivatives. We provide a perspective on progress in regenerative medicine from the early stages of cell therapy to the present day, as well as an overview of cellular processes, materials and fabrication strategies currently under investigation. Finally, we summarise current clinical applications and reflect on the most urgent needs and gaps to be filled for efficient translation to the clinical arena.

Human pluripotent stem cell-derived chondroprogenitors for cartilage tissue engineering

The cartilage of joints, such as meniscus and articular cartilage, is normally long lasting (i.e., permanent). However, once damaged, especially in large animals and humans, joint cartilage is not spontaneously repaired. Compensating the lack of repair activity by supplying cartilage-(re)forming cells, such as chondrocytes or mesenchymal stromal cells, or by transplanting a piece of normal cartilage, has been the basis of therapy for biological restoration of damaged joint cartilage. Unfortunately, current biological therapies face problems on a number of fronts. The joint cartilage is generated de novo from a specialized cell type, termed a 'joint progenitor' or 'interzone cell' during embryogenesis. Therefore, embryonic chondroprogenitors that mimic the property of joint progenitors might be the best type of cell for regenerating joint cartilage in the adult. Pluripotent stem cells (PSCs) are expected to differentiate in culture into any somatic cell type through processes that mimic embryogenesis, making human (h)PSCs a promising source of embryonic chondroprogenitors. The major research goals toward the clinical application of PSCs in joint cartilage regeneration are to (1) efficiently generate lineage-specific chondroprogenitors from hPSCs, (2) expand the chondroprogenitors to the number needed for therapy without loss of their chondrogenic activity, and (3) direct the in vivo or in vitro differentiation of the chondroprogenitors to articular or meniscal (i.e., permanent) chondrocytes rather than growth plate (i.e., transient) chondrocytes. This review is aimed at providing the current state of research toward meeting these goals. We also include our recent achievement of successful generation of "permanent-like" cartilage from long-term expandable, hPSC-derived ectomesenchymal chondroprogenitors.

Machine learning uncovers cell identity regulator by histone code

Conversion between cell types, e.g., by induced expression of master transcription factors, holds great promise for cellular therapy. Our ability to manipulate cell identity is constrained by incomplete information on cell identity genes (CIGs) and their expression regulation. Here, we develop CEFCIG, an artificial intelligent framework to uncover CIGs and further define their master regulators. On the basis of machine learning, CEFCIG reveals unique histone codes for transcriptional regulation of reported CIGs, and utilizes these codes to predict CIGs and their master regulators with high accuracy. Applying CEFCIG to 1,005 epigenetic profiles, our analysis uncovers the landscape of regulation network for identity genes in individual cell or tissue types. Together, this work provides insights into cell identity regulation, and delivers a powerful technique to facilitate regenerative medicine.

Cyclic Strain Promotes H19 Expression and Vascular Tube Formation in iPSC-Derived Endothelial Cells

Introduction

Induced pluripotent stem cell (iPSC)-derived endothelial cells (ECs) have the potential for therapeutic application in several cardiovascular diseases. Mechanical strain is known to regulate EC behavior and stem cell differentiation and may play a role in directing EC differentiation of iPSCs. H19, a long non-coding RNA (lncRNA), is known to affect ECs in several mechanically relevant pathologies and may play a role in this process as well. Therefore, we investigated expression changes of H19 resulting from mechanical stimulation during EC differentiation, as well as functional effects on EC tube formation.

Methods

iPSCs were subjected to 5% cyclic mechanical strain during EC differentiation. RT-PCR and flow cytometry were used to assess changes in mesoderm differentiation and gene expression in the final ECs as a result of strain. Functional outcomes of mechanically differentiated ECs were assessed with a tube formation assay and changes in H19. H19 was also overexpressed in human umbilical vein endothelial cells (HUVECs) to assess its role in non-H19-expressing ECs.

Results

Mechanical strain promoted mesoderm differentiation, marked by increased expression of brachyury 24 h after initiation of differentiation. Strain also increased expression of H19, CD31, VE-cadherin, and VEGFR2 in differentiated ECs. Strain-differentiated ECs formed tube networks with higher junction and endpoint density than statically-differentiated ECs. Overexpression of H19 in HUVECs resulted in similar patterns of tube formation.

Conclusions

H19 expression is increased by mechanical strain and promotes tube branching in iPSC-derived ECs.

Impairment of hypoxia-induced angiogenesis by LDL involves a HIF-centered signaling network linking inflammatory TNFα and angiogenic VEGF

Hypoxia inducible factors (HIFs) mediate angiogenesis via up-regulation of various pro-angiogenic factors (particularly VEGF) in response to hypoxia. Here, we report that hypoxia unexpectedly induced robust production of the pro-inflammatory factor TNFα by endothelial cells (ECs), suggesting an autocrine loop that in turn activated HIFs via an NF-κB-dependent process, resulting in production of VEGF and thereby promotion of angiogenesis. In contrast, low-density lipoprotein (LDL) prevented expression of HIFs in ECs exposed to either hypoxia or TNFα, while knockdown of either HIF-1α or HIF-2α strikingly attenuated hypoxia-induced production of VEGF by ECs as well as EC colony formation and tube formation. Significantly, LDL attenuated hypoxia-induced angiogenesis by disrupting the TNFα/NF-κB/HIF/VEGF signaling cascade via down-regulation of the TNF receptor TNF-R1, rather than TNFα itself, and multiple key components of both canonical and non-canonical NF-κB pathways. By doing so, LDL was able to either inhibit or down-regulate a wide spectrum of HIF-dependent pro-angiogenic downstream targets and signals. Together, these findings argue existence of a self-regulatory TNFα/NF-κB/HIF/VEGF signaling network in ECs, which mediates and fine-tones angiogenesis, at least in response to hypoxia. They also suggest that LDL impairs angiogenesis by disrupting this network, which might represent a novel mechanism underlying anti-angiogenic property of LDL.

Efficient differentiation and purification of human induced pluripotent stem cell-derived endothelial progenitor cells and expansion with the use of inhibitors of ROCK, TGF-β, and GSK3β

Endothelial cells (ECs) and endothelial progenitor cells (EPCs) play crucial roles in maintaining vascular health and homeostasis. Both cell types have been used in regenerative therapy as well as in various in vitro models; however, the properties of primary human ECs and EPCs are dissimilar owing to differences in genetic backgrounds and sampling techniques. Human induced pluripotent stem cells (hiPSCs) are an alternative cell source of ECs and EPCs. However, owing to the low purity of differentiated cells from hiPSCs, purification via an antigen–antibody reaction, which damages the cells, is indispensable. Besides, owing to limited expandability, it is difficult to produce these cells in large numbers. Here we report the development of relatively simple differentiation and purification methods for hiPSC-derived EPCs (iEPCs). Furthermore, we discovered that a combination of three small molecules, that is, Y-27632 (a selective inhibitor of Rho-associated, coiled-coil containing protein kinase [ROCK]), A 83–01 (a receptor-like kinase inhibitor of transforming growth factor beta [TGF-β]), and CHIR-99021 (a selective inhibitor of glycogen synthase kinase-3β [GSK3β] that also activates Wnt), dramatically stimulated protein synthesis-related pathways and enhanced the proliferative capacity of iEPCs. These findings will help to establish a supply system of EPCs at an industrial scale.

Clonally selected primitive endothelial cells promote occlusive pulmonary arteriopathy and severe pulmonary hypertension in rats exposed to chronic hypoxia

One current concept suggests that unchecked proliferation of clonally selected precursors of endothelial cells (ECs) contribute to severe pulmonary arterial hypertension (PAH). We hypothesized that clonally selected ECs expressing the progenitor marker CD117 promote severe occlusive pulmonary hypertension (PH). The remodelled pulmonary arteries of PAH patients harboured CD117⁺ ECs. Rat lung CD117⁺ ECs underwent four generations of clonal expansion to enrich hyperproliferative ECs. The resulting clonally enriched ECs behaved like ECs, as measured by in vitro and in vivo angiogenesis assays. The same primitive ECs showed a limited ability for mesenchymal lineage differentiation. Endothelial differentiation and function were enhanced by blocking TGF-β signalling, promoting bone morphogenic protein (BMP) signalling. The transplantation of the EC clones caused arterio-occlusive PH in rats exposed to chronic hypoxia. These EC clones engrafted in the pulmonary arteries. Yet cessation of chronic hypoxia promoted lung cell apoptosis and resolution of vascular lesions. In conclusion, this is to the best of our knowledge, the first report that clonally enriched primitive ECs promote occlusive pulmonary arteriopathy and severe PH. These primitive EC clones further give rise to cells of endothelial and mesenchymal lineage as directed by BMP and TGF-β signaling.

Heart regeneration with human pluripotent stem cells: Prospects and challenges

Cardiovascular disease, ranging from congenital heart disease to adult myocardial infarction, is the leading cause of death worldwide. In pursuit of reliable cardiovascular regenerative medicine, human pluripotent stem cells (hPSCs), including human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs), offer plenty of potential cell-based applications. HPSCs are capable of proliferating indefinitely in an undifferentiated state, and are also pluripotent, being able to differentiate into virtually any somatic cell types given specific stepwise cues, thus representing an unlimited source to generate functional cardiovascular cells for heart regeneration. Here we recapitulated current advances in developing efficient protocols to generate hPSC-derived cardiovascular cell lineages, including cardiomyocytes, endothelial cells, and epicardial cells. We also discussed applications of hPSC-derived cells in combination with compatible bioactive materials, promising trials of cell transplantation in animal models of myocardial infarction, and potential hurdles to bring us closer to the ultimate goal of cell-based heart repair.

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HPSCs hold tremendous therapeutic potential for treating CVDs.

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HPSCs could differentiate into multiple cardiovascular cell lineages.

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Transplantation of hPSC-derived cardiovascular cells and biomaterials shows promising results, but challenges still remain.

Bioactive Molecules for Skin Repair and Regeneration: Progress and Perspectives

Skin regeneration is a vexing problem in the field of regenerative medicine. A bioactive molecule-based strategy has been frequently used in skin wound healing in recent years. Bioactive molecules are practical tools for regulating cellular processes and have been applied to control cellular differentiation, dedifferentiation, and reprogramming. In this review, we focus on recent progress in the use of bioactive molecules in skin regenerative medicine, by which desired cell types can be generated in vitro for cell therapy and conventional therapeutics can be developed to repair and regenerate skin in vivo through activation of the endogenous repairing potential. We further prospect that the bioactive molecule-base method might be one of the promising strategies to achieve in situ skin regeneration in the future.

cAMP/EPAC Signaling Enables ETV2 to Induce Endothelial Cells with High Angiogenesis Potential

Although the generation of ETV2-induced endothelial cells (iECs) from human fibroblasts serves as a novel therapeutic strategy in regenerative medicine, the process is inefficient, resulting in incomplete iEC angiogenesis. Therefore, we employed chromatin immunoprecipitation (ChIP) sequencing and identified molecular mechanisms underlying ETV2-mediated endothelial transdifferentiation to efficiently produce iECs retaining appropriate functionality in long-term culture. We revealed that the majority of ETV2 targets in human fibroblasts are related to vasculature development and signaling transduction pathways, including Rap1 signaling. From a screening of signaling pathway modulators, we confirmed that forskolin facilitated efficient and rapid iEC reprogramming via activation of the cyclic AMP (cAMP)/exchange proteins directly activated by cAMP (EPAC)/RAP1 axis. The iECs obtained via cAMP signaling activation showed superior angiogenesis in vivo as well as in vitro. Moreover, these cells could form aligned endothelium along the vascular lumen ex vivo when seeded into decellularized liver scaffold. Overall, our study provided evidence that the cAMP/EPAC/RAP1 axis is required for the efficient generation of iECs with angiogenesis potential.

Application of Human Induced Pluripotent Stem Cells in Generating Tissue-Engineered Blood Vessels as Vascular Grafts

In pace with the advancement of tissue engineering during recent decades, tissue-engineered blood vessels (TEBVs) have been generated using primary seed cells, and their impressive success in clinical trials have demonstrated the great potential of these TEBVs as implantable vascular grafts in human regenerative medicine. However, the production, therapeutic efficacy, and readiness in emergencies of current TEBVs could be hindered by the accessibility, expandability, and donor-donor variation of patient-specific primary seed cells. Alternatively, using human induced pluripotent stem cells (hiPSCs) to derive seed vascular cells for vascular tissue engineering could fundamentally address this current dilemma in TEBV production. As an emerging research field with a promising future, the generation of hiPSC-based TEBVs has been reported recently with significant progress. Simultaneously, to further promote hiPSC-based TEBVs into vascular grafts for clinical use, several challenges related to the safety, readiness, and structural integrity of vascular tissue need to be addressed. Herein, this review will focus on the evolution and role of hiPSCs in vascular tissue engineering technology and summarize the current progress, challenges, and future directions of research on hiPSC-based TEBVs.

Induced Pluripotent Stem Cells as Vasculature Forming Entities

Tissue engineering (TE) pursues the ambitious goal to heal damaged tissues. One of the most successful TE approaches relies on the use of scaffolds specifically designed and fabricated to promote tissue growth. During regeneration the guidance of biological events may be essential to sustain vasculature neoformation inside the engineered scaffold. In this context, one of the most effective strategies includes the incorporation of vasculature forming cells, namely endothelial cells (EC), into engineered constructs. However, the most common EC sources currently available, intended as primary cells, are affected by several limitations that make them inappropriate to personalized medicine. Human induced Pluripotent Stem Cells (hiPSC), since the time of their discovery, represent an unprecedented opportunity for regenerative medicine applications. Unfortunately, human induced Pluripotent Stem Cells-Endothelial Cells (hiPSC-ECs) still display significant safety issues. In this work, we reviewed the most effective protocols to induce pluripotency, to generate cells displaying the endothelial phenotype and to perform an efficient and safe cell selection. We also provide noteworthy examples of both in vitro and in vivo applications of hiPSC-ECs in order to highlight their ability to form functional blood vessels. In conclusion, we propose hiPSC-ECs as the preferred source of endothelial cells currently available in the field of personalized regenerative medicine.

Engineering transferrable microvascular meshes for subcutaneous islet transplantation

The success of engineered cell or tissue implants is dependent on vascular regeneration to meet adequate metabolic requirements. However, development of a broadly applicable strategy for stable and functional vascularization has remained challenging. We report here highly organized and resilient microvascular meshes fabricated through a controllable anchored self-assembly method. The microvascular meshes are scalable to centimeters, almost free of defects and transferrable to diverse substrates, ready for transplantation. They promote formation of functional blood vessels, with a density as high as ~220 vessels mm-2, in the poorly vascularized subcutaneous space of SCID-Beige mice. We further demonstrate the feasibility of fabricating microvascular meshes from human induced pluripotent stem cell-derived endothelial cells, opening a way to engineer patient-specific microvasculature. As a proof-of-concept for type 1 diabetes treatment, we combine microvascular meshes and subcutaneously transplanted rat islets and achieve correction of chemically induced diabetes in SCID-Beige mice for 3 months.