Functional vascular smooth muscle cells derived from human induced pluripotent stem cells via mesenchymal stem cell intermediates

Engineered Extracellular Vesicles from Antler Blastema Progenitor Cells: A Therapeutic Choice for Spinal Cord Injury

Deer antler blastema progenitor cells (ABPCs) are promising for regenerative medicine due to their role in annual antler regeneration, the only case of complete organ regeneration in mammals. ABPC-derived signals show great potential for promoting regeneration in tissues with limited natural regenerative ability. Our findings demonstrate the capability of extracellular vesicles from ABPCs (EVsABPC) to repair spinal cord injury (SCI), a condition with low regenerative capacity. EVsABPC significantly enhanced the proliferation of neural stem cells (NSCs) and activated neuronal regenerative potential, resulting in a 5.2-fold increase in axonal length. Additionally, EVsABPC exhibited immunomodulatory effects, shifting macrophages from M1 to M2. Engineered with activated cell-penetrating peptides (ACPPs), EVsABPC significantly outperformed EVs from rat bone marrow stem cells (EVsBMSC) and neural stem cells (EVsNSC), promoting a 1.3-fold increase in axonal growth, a 30.6% reduction in neuronal apoptosis, and a 2.6-fold improvement in motor function recovery. These findings support ABPC-derived EVs as a promising therapeutic candidate for SCI repair.

Tissue-Engineered Microvessels: A Review of Current Engineering Strategies and Applications

Microvessels, including arterioles, capillaries, and venules, play an important role in regulating blood flow, enabling nutrient and waste exchange, and facilitating immune surveillance. Due to their important roles in maintaining normal function in human tissues, a substantial effort has been devoted to developing tissue-engineered models to study endothelium-related biology and pathology. Various engineering strategies have been developed to recapitulate the structural, cellular, and molecular hallmarks of native human microvessels in vitro. In this review, recent progress in engineering approaches, key components, and culture platforms for tissue-engineered human microvessel models is summarized. Then, tissue-specific models, and the major applications of tissue-engineered microvessels in development, disease modeling, drug screening and delivery, and vascularization in tissue engineering, are reviewed. Finally, future research directions for the field are discussed.

Evaluation of Antibodies for Vascular Smooth Muscle Cell Characterization

Flow cytometry, paired with fluorescent antibodies, is a popular method for characterizing cell phenotypes. Our laboratory is interested in deriving and characterizing vascular smooth muscle cells from embryonic and induced pluripotent stem cells, one of the few stem cell differentiation methods that remain underdeveloped. In our studies, we found that most commercially available antibodies advertised for smooth muscle cell identification using flow-activated cell scanning (FACS) were, in fact, not able to distinguish between positive and negative controls. Attempts to resolve the issues included exploring a range of incubation times, blocking reagents, staining kits, and titrating dilutions against both positive and negative control cells. In the end, we found that only the smooth muscle myosin heavy chain (SMMHC) antibody at a narrow titrating dilution range could distinctly bind to its intended epitope. Moreover, without more adequate and specific antibodies for labelling smooth muscle cells, we were not able to continue with our studies on smooth muscle cell fate.

Advances in the differentiation of pluripotent stem cells into vascular cells

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

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.

A genome-wide genetic screen uncovers determinants of human pigmentation

Skin color, one of the most diverse human traits, is determined by the quantity, type, and distribution of melanin. In this study, we leveraged the light-scattering properties of melanin to conduct a genome-wide screen for regulators of melanogenesis. We identified 169 functionally diverse genes that converge on melanosome biogenesis, endosomal transport, and gene regulation, of which 135 represented previously unknown associations with pigmentation. In agreement with their melanin-promoting function, the majority of screen hits were up-regulated in melanocytes from darkly pigmented individuals. We further unraveled functions of KLF6 as a transcription factor that regulates melanosome maturation and pigmentation in vivo, and of the endosomal trafficking protein COMMD3 in modulating melanosomal pH. Our study reveals a plethora of melanin-promoting genes, with broad implications for human variation, cell biology, and medicine.

Differentiation and Engineering of Human Stem Cells for Smooth Muscle Generation

Cardiovascular diseases are responsible for 31% of global deaths and are considered the main cause of death and disability worldwide. Stem cells from various sources have become attractive options for a range of cell-based therapies for smooth muscle tissue regeneration. However, for efficient myogenic differentiation, the stem cell characteristics, cell culture conditions, and their respective microenvironments need to be carefully assessed. This review covers the various approaches involved in the regeneration of vascular smooth muscles by conditioning human stem cells. This article delves into the different sources of stem cells used in the generation of myogenic tissues, the role of soluble growth factors, use of scaffolding techniques, biomolecular cues, relevance of mechanical stimulation, and key transcription factors involved, aimed at inducing myogenic differentiation. Impact statement The review article's main goal is to discuss the recent advances in the field of smooth muscle tissue regeneration. We look at various cell sources, growth factors, scaffolds, mechanical stimuli, and factors involved in smooth muscle formation. These stem cell-based approaches for vascular muscle formation will provide various options for cell-based therapies with long-term beneficial effects on patients.

Bioengineering strategies for 3D bioprinting of tubular construct using tissue-specific decellularized extracellular matrix

The goal of the current study is to develop an extracellular matrix bioink that could mimic the biochemical components present in natural blood vessels. Here, we have used an innovative approach to recycle the discarded varicose vein for isolation of endothelial cells and decellularization of the same sample to formulate the decellularized extracellular matrix (dECM) bioink. The shift towards dECM bioink observed as varicose vein dECM provides the tissue-specific biochemical factors that will enhance the regeneration capability. Interestingly, the encapsulated umbilical cord mesenchymal stem cells expressed the markers of vascular smooth muscle cells because of the cues present in the vein dECM. Further, in vitro immunological investigation of dECM revealed a predominant M2 polarization which could further aid in tissue remodeling. A novel approach was used to fabricate vascular construct using 3D bioprinting without secondary support. The outcomes suggest that this could be a potential approach for patient- and tissue-specific blood vessel regeneration.

Comparative study of differentiating human pluripotent stem cells into vascular smooth muscle cells in hydrogel-based culture methods

Vascular smooth muscle cells (VSMCs), which provides structural integrity and regulates the diameter of vasculature, are of great potential for modeling vascular-associated diseases and tissue engineering. Here, we presented a detailed comparison of differentiating human pluripotent stem cells (hPSCs) into VSMCs (hPSCs-VSMCs) in four different culture methods, including 2-dimensional (2D) culture, 3-dimensional (3D) PNIPAAm-PEG hydrogel culture, 3-dimensional (3D) alginate hydrogel culture, and transferring 3-dimensional alginate hydrogel culture to 2-dimensional (2D) culture. Both hydrogel-based culture methods could mimic in vivo microenvironment to protect cells from shear force, and avoid cells agglomeration, resulting in the extremely high culture efficiency (e.g., high viability, high purity and high yield) compared with 2D culture. We demonstrated hPSC-VSMCs produced from hydrogel-based culture methods had better contractile phenotypes and the potential of vasculature formation. The transcriptome analysis showed the hPSC-VSMCs derived from hydrogel-based culture methods displayed more upregulated genes in vasculature development, angiogenesis and blood vessel development, extracellular matrix compared with 2D culture. Taken together, hPSC-VSMCs produced from hydrogel-based culture system could be applied in various biomedical fields, and further indicated the suitable development of alginate hydrogel for industrial production by taking all aspects into consideration.

Electrospun Biodegradable α-Amino Acid-Substituted Poly(organophosphazene) Fiber Mats for Stem Cell Differentiation towards Vascular Smooth Muscle Cells

Mesenchymal stem cells, derived from human-induced pluripotent stem cells (iPSC), are valuable for generating smooth muscle cells (SMCs) for vascular tissue engineering applications. In this study, we synthesized biodegradable α-amino acid-substituted poly(organophosphazene) polymers and electrospun nano-fibrous scaffolds (~200 nm diameter) to evaluate their suitability as a matrix for differentiation of iPSC-derived mesenchymal stem cells (iMSC) into mature contractile SMCs. Both the polymer synthesis approach and the electrospinning parameters were optimized. Three types of cells, namely iMSC, bone marrow derived mesenchymal stem cells (BM-MSC), and primary human coronary artery SMC, attached and spread on the materials. Although L-ascorbic acid (AA) and transforming growth factor-beta 1 (TGF-β1) were able to differentiate iMSC along the smooth muscle lineage, we showed that the electrospun fibrous mats provided material cues for the enhanced differentiation of iMSCs. Differentiation of iMSC to SMC was characterized by increased transcriptional levels of early to late-stage smooth muscle marker proteins on electrospun fibrous mats. Our findings provide a feasible strategy for engineering functional vascular tissues.

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.

Wnt-mediated endothelial transformation into mesenchymal stem cell-like cells induces chemoresistance in glioblastoma

Therapeutic resistance remains a persistent challenge for patients with malignant tumors. Here, we reveal that endothelial cells (ECs) acquire transformation into mesenchymal stem cell (MSC)-like cells in glioblastoma (GBM), driving tumor resistance to cytotoxic treatment. Transcriptome analysis by RNA sequencing (RNA-seq) revealed that ECs undergo mesenchymal transformation and stemness-like activation in GBM microenvironment. Furthermore, we identified a c-Met-mediated axis that induces β-catenin phosphorylation at Ser⁶⁷⁵ and Wnt signaling activation, inducing multidrug resistance-associated protein-1(MRP-1) expression and leading to EC stemness-like activation and chemoresistance. Last, genetic ablation of β-catenin in ECs overcome GBM tumor resistance to temozolomide (TMZ) chemotherapy in vivo. Combination of Wnt inhibition and TMZ chemotherapy eliminated tumor-associated ECs, inhibited GBM growth, and increased mouse survival. These findings identified a cell plasticity-based, microenvironment-dependent mechanism that controls tumor chemoresistance, and suggest that targeting Wnt/β-catenin-mediated EC transformation and stemness activation may overcome therapeutic resistance in GBM.

Generation of Vascular Smooth Muscle Cells From Induced Pluripotent Stem Cells: Methods, Applications, and Considerations

The developmental origin of vascular smooth muscle cells (VSMCs) has been increasingly recognized as a major determinant for regional susceptibility or resistance to vascular diseases. As a human material-based complement to animal models and human primary cultures, patient induced pluripotent stem cell iPSC-derived VSMCs have been leveraged to conduct basic research and develop therapeutic applications in vascular diseases. However, iPSC-VSMCs (induced pluripotent stem cell VSMCs) derived by most existing induction protocols are heterogeneous in developmental origins. In this review, we summarize signaling networks that govern in vivo cell fate decisions and in vitro derivation of distinct VSMC progenitors, as well as key regulators that terminally specify lineage-specific VSMCs. We then highlight the significance of leveraging patient-derived iPSC-VSMCs for vascular disease modeling, drug discovery, and vascular tissue engineering and discuss several obstacles that need to be circumvented to fully unleash the potential of induced pluripotent stem cells for precision vascular medicine.

Tools, techniques, and future opportunities for characterizing the mechanobiology of uterine myometrium

The myometrium is the smooth muscle layer of the uterus that generates the contractions that drive processes such as menstruation and childbirth. Aberrant contractions of the myometrium can result in preterm birth, insufficient progression of labor, or other difficulties that can lead to maternal or fetal complications or even death. To investigate the underlying mechanisms of these conditions, the most common model systems have conventionally been animal models and human tissue strips, which have limitations mostly related to relevance and scalability, respectively. Myometrial smooth muscle cells have also been isolated from patient biopsies and cultured in vitro as a more controlled experimental system. However, in vitro approaches have focused primarily on measuring the effects of biochemical stimuli and neglected biomechanical stimuli, despite the extensive evidence indicating that remodeling of tissue rigidity or excessive strain is associated with uterine disorders. In this review, we first describe the existing approaches for modeling human myometrium with animal models and human tissue strips and compare their advantages and disadvantages. Next, we introduce existing in vitro techniques and assays for assessing contractility and summarize their applications in elucidating the role of biochemical or biomechanical stimuli on human myometrium. Finally, we conclude by proposing the translation of "organ on chip" approaches to myometrial smooth muscle cells as new paradigms for establishing their fundamental mechanobiology and to serve as next-generation platforms for drug development.

Xenogeneic-free generation of vascular smooth muscle cells from human induced pluripotent stem cells for vascular tissue engineering

Development of mechanically advanced tissue-engineered vascular grafts (TEVGs) from human induced pluripotent stem cell (hiPSC)-derived vascular smooth muscle cells (hiPSC-VSMCs) offers an innovative approach to replace or bypass diseased blood vessels. To move current hiPSC-TEVGs toward clinical application, it is essential to obtain hiPSC-VSMC-derived tissues under xenogeneic-free conditions, meaning without the use of any animal-derived reagents. Many approaches in VSMC differentiation of hiPSCs have been reported, although a xenogeneic-free method for generating hiPSC-VSMCs suitable for vascular tissue engineering has yet to be established. Based on our previously established standard method of xenogeneic VSMC differentiation, we have replaced all animal-derived reagents with functional counterparts of human origin and successfully derived functional xenogeneic-free hiPSC-VSMCs (XF-hiPSC-VSMCs). Next, our group developed tissue rings via cellular self-assembly from XF-hiPSC-VSMCs, which exhibited comparable mechanical strength to those developed from xenogeneic hiPSC-VSMCs. Moreover, by seeding XF-hiPSC-VSMCs onto biodegradable polyglycolic acid (PGA) scaffolds, we generated engineered vascular tissues presenting effective collagen deposition which were suitable for implantation into an immunodeficient mice model. In conclusion, our xenogeneic-free conditions for generating hiPSC-VSMCs produce cells with the comparable capacity for vascular tissue engineering as standard xenogeneic protocols, thereby moving the hiPSC-TEVG technology one step closer to safe and efficacious clinical translation.

Human hair follicle-derived mesenchymal stem cells: Isolation, expansion, and differentiation

Hair follicles are easily accessible skin appendages that protect against cold and potential injuries. Hair follicles contain various pools of stem cells, such as epithelial, melanocyte, and mesenchymal stem cells (MSCs) that continuously self-renew, differentiate, regulate hair growth, and maintain skin homeostasis. Recently, MSCs derived from the dermal papilla or dermal sheath of the human hair follicle have received attention because of their accessibility and broad differentiation potential. In this review, we describe the applications of human hair follicle-derived MSCs (hHF-MSCs) in tissue engineering and regenerative medicine. We have described protocols for isolating hHF-MSCs from human hair follicles and their culture condition in detail. We also summarize strategies for maintaining hHF-MSCs in a highly proliferative but undifferentiated state after repeated in vitro passages, including supplementation of growth factors, 3D suspension culture technology, and 3D aggregates of MSCs. In addition, we report the potential of hHF-MSCs in obtaining induced smooth muscle cells and tissue-engineered blood vessels, regenerated hair follicles, induced red blood cells, and induced pluripotent stem cells. In summary, the abundance, convenient accessibility, and broad differentiation potential make hHF-MSCs an ideal seed cell source of regenerative medical and cell therapy.

Generation of myogenic progenitor cell-derived smooth muscle cells for sphincter regeneration

BACKGROUND

Degeneration of smooth muscles in sphincters can cause debilitating diseases such as fecal incontinence. Skeletal muscle-derived cells have been effectively used in clinics for the regeneration of the skeletal muscle sphincters, such as the external anal or urinary sphincter. However, little is known about the in vitro smooth muscle differentiation potential and in vivo regenerative potential of skeletal muscle-derived cells.

METHODS

Myogenic progenitor cells (MPC) were isolated from the skeletal muscle and analyzed by flow cytometry and in vitro differentiation assays. The differentiation of MPC to smooth muscle cells (MPC-SMC) was evaluated by immunofluorescence, flow cytometry, patch-clamp, collagen contraction, and microarray gene expression analysis. In vivo engraftment of MPC-SMC was monitored by transplanting reporter protein-expressing cells into the pyloric sphincter of immunodeficient mice.

RESULTS

MPC derived from human skeletal muscle expressed mesenchymal surface markers and exhibit skeletal myogenic differentiation potential in vitro. In contrast, they lack hematopoietic surface marker, as well as adipogenic, osteogenic, and chondrogenic differentiation potential in vitro. Cultivation of MPC in smooth muscle differentiation medium significantly increases the fraction of alpha smooth muscle actin (aSMA) and smoothelin-positive cells, while leaving the number of desmin-positive cells unchanged. Smooth muscle-differentiated MPC (MPC-SMC) exhibit increased expression of smooth muscle-related genes, significantly enhanced numbers of CD146- and CD49a-positive cells, and in vitro contractility and express functional Cav and Kv channels. MPC to MPC-SMC differentiation was also accompanied by a reduction in their skeletal muscle differentiation potential. Upon removal of the smooth muscle differentiation medium, a major fraction of MPC-SMC remained positive for aSMA, suggesting the definitive acquisition of their phenotype. Transplantation of murine MPC-SMC into the mouse pyloric sphincter revealed engraftment of MPC-SMC based on aSMA protein expression within the host smooth muscle tissue.

CONCLUSIONS

Our work confirms the ability of MPC to give rise to smooth muscle cells (MPC-SMC) with a well-defined and stable phenotype. Moreover, the engraftment of in vitro-differentiated murine MPC-SMC into the pyloric sphincter in vivo underscores the potential of this cell population as a novel cell therapeutic treatment for smooth muscle regeneration of sphincters.

Human pluripotent stem cell-derived cardiac stromal cells and their applications in regenerative medicine

Coronary heart disease is one of the leading causes of death in the United States. Recent advances in stem cell biology have led to the development and engineering of human pluripotent stem cell (hPSC)-derived cardiac cells and tissues for application in cellular therapy and cardiotoxicity studies. Initial studies in this area have largely focused on improving differentiation efficiency and maturation states of cardiomyocytes. However, other cell types in the heart, including endothelial and stromal cells, play crucial roles in cardiac development, injury response, and cardiomyocyte function. This review discusses recent advances in differentiation of hPSCs to cardiac stromal cells, identification and classification of cardiac stromal cell types, and application of hPSC-derived cardiac stromal cells and tissues containing these cells in regenerative and drug development applications.

Efficient differentiation of vascular smooth muscle cells from Wharton's Jelly mesenchymal stromal cells using human platelet lysate: A potential cell source for small blood vessel engineering

BACKGROUND

The development of fully functional small diameter vascular grafts requires both a properly defined vessel conduit and tissue-specific cellular populations. Mesenchymal stromal cells (MSCs) derived from the Wharton's Jelly (WJ) tissue can be used as a source for obtaining vascular smooth muscle cells (VSMCs), while the human umbilical arteries (hUAs) can serve as a scaffold for blood vessel engineering.

AIM

To develop VSMCs from WJ-MSCs utilizing umbilical cord blood platelet lysate.

METHODS

WJ-MSCs were isolated and expanded until passage (P) 4. WJ-MSCs were properly defined according to the criteria of the International Society for Cell and Gene Therapy. Then, these cells were differentiated into VSMCs with the use of platelet lysate from umbilical cord blood in combination with ascorbic acid, followed by evaluation at the gene and protein levels. Specifically, gene expression profile analysis of VSMCs for ACTA2, MYH11, TGLN, MYOCD, SOX9, NANOG homeobox, OCT4 and GAPDH, was performed. In addition, immunofluorescence against ACTA2 and MYH11 in combination with DAPI staining was also performed in VSMCs. HUAs were decellularized and served as scaffolds for possible repopulation by VSMCs. Histological and biochemical analyses were performed in repopulated hUAs.

RESULTS

WJ-MSCs exhibited fibroblastic morphology, successfully differentiating into "osteocytes", "adipocytes" and "chondrocytes", and were characterized by positive expression (> 90%) of CD90, CD73 and CD105. In addition, WJ-MSCs were successfully differentiated into VSMCs with the proposed differentiation protocol. VSMCs successfully expressed ACTA2, MYH11, MYOCD, TGLN and SOX9. Immunofluorescence results indicated the expression of ACTA2 and MYH11 in VSMCs. In order to determine the functionality of VSMCs, hUAs were isolated and decellularized. Based on histological analysis, decellularized hUAs were free of any cellular or nuclear materials, while their extracellular matrix retained intact. Then, repopulation of decellularized hUAs with VSMCs was performed for 3 wk. Decellularized hUAs were repopulated efficiently by the VSMCs. Biochemical analysis revealed the increase of total hydroyproline and sGAG contents in repopulated hUAs with VSMCs. Specifically, total hydroxyproline and sGAG content after the 1st, 2nd and 3rd wk was 71 ± 10, 74 ± 9 and 86 ± 8 μg hydroxyproline/mg of dry tissue weight and 2 ± 1, 3 ± 1 and 3 ± 1 μg sGAG/mg of dry tissue weight, respectively. Statistically significant differences were observed between all study groups (P < 0.05).

CONCLUSION

VSMCs were successfully obtained from WJ-MSCs with the proposed differentiation protocol. Furthermore, hUAs were efficiently repopulated by VSMCs. Differentiated VSMCs from WJ-MSCs could provide an alternative source of cells for vascular tissue engineering.

Tissue-Engineered Vascular Grafts with Advanced Mechanical Strength from Human iPSCs

Vascular smooth muscle cells (VSMCs) can be derived in large numbers from human induced pluripotent stem cells (hiPSCs) for producing tissue-engineered vascular grafts (TEVGs). However, hiPSC-derived TEVGs are hampered by low mechanical strength and significant radial dilation after implantation. Here, we report generation of hiPSC-derived TEVGs with mechanical strength comparable to native vessels used in arterial bypass grafts by utilizing biodegradable scaffolds, incremental pulsatile stretching, and optimal culture conditions. Following implantation into a rat aortic model, hiPSC-derived TEVGs show excellent patency without luminal dilation and effectively maintain mechanical and contractile function. This study provides a foundation for future production of non-immunogenic, cellularized hiPSC-derived TEVGs composed of allogenic vascular cells, potentially serving needs to a considerable number of patients whose dysfunctional vascular cells preclude TEVG generation via other methods.

Generation of blood vessel organoids from human pluripotent stem cells

Blood vessels are fundamental to animal life and have critical roles in many diseases, such as stroke, myocardial infarction and diabetes. The vasculature is formed by endothelial cells that line the vessel and are covered with mural cells, specifically pericytes in smaller vessels and vascular smooth muscle cells (vSMCs) in larger-diameter vessels. Both endothelial cells and mural cells are essential for proper blood vessel function and can be derived from human pluripotent stem cells (hPSCs). Here, we describe a protocol to generate self-organizing 3D human blood vessel organoids from hPSCs that exhibit morphological, functional and molecular features of human microvasculature. These organoids are differentiated via mesoderm induction of hPSC aggregates and subsequent differentiation into endothelial networks and pericytes in a 3D collagen I-Matrigel matrix. Blood vessels form within 2-3 weeks and can be further grown in scalable suspension culture. Importantly, in vitro-differentiated human blood vessel organoids transplanted into immunocompromised mice gain access to the mouse circulation and specify into functional arteries, arterioles and veins.

A Human Pluripotent Stem Cell-Based Screen for Smooth Muscle Cell Differentiation and Maturation Identifies Inhibitors of Intimal Hyperplasia

Contractile to synthetic phenotypic switching of smooth muscle cells (SMCs) contributes to stenosis in vascular disease and vascular transplants. To generate more contractile SMCs, we performed a high-throughput differentiation screen using a MYH11-NLuc-tdTomato human embryonic stem cell reporter cell line. We identified RepSox as a factor that promotes differentiation of MYH11-positive cells by promoting NOTCH signaling. RepSox induces SMCs to exhibit a more contractile phenotype than SMCs generated using PDGF-BB and TGF-β1, two factors previously used for SMC differentiation but which also cause intimal hyperplasia. In addition, RepSox inhibited intimal hyperplasia caused by contractile to synthetic phenotypic switching of SMCs in a rat balloon injury model. Thus, in addition to providing more contractile SMCs that could prove useful for constructing artificial blood vessels, this study suggests a strategy for identifying drugs for inhibiting intimal hyperplasia that act by driving contractile differentiation rather than inhibiting proliferation non-specifically.

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Fully defined differentiation of contractile (95% MYH11⁺) smooth muscle cells (SMCs)

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RepSox-NOTCH signal promotes SMC differentiation and inhibits intimal hyperplasia

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RepSox-SMCs could reduce the risk of intimal hyperplasia compared with PDGF/TGF-SMCs

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Applying SMC differentiation for high-throughput screening of anti-restenosis drugs

Non-invasive functional molecular phenotyping of human smooth muscle cells utilized in cardiovascular tissue engineering

Smooth muscle cell (SMC) diversity and plasticity are limiting factors in their characterization and application in cardiovascular tissue engineering. This work aimed to evaluate the potential of Raman microspectroscopy and Raman imaging to distinguish SMCs of different tissue origins and phenotypes. Cultured human SMCs isolated from different vascular and non-vascular tissues as well as fixed human SMC-containing tissues were analyzed. In addition, Raman spectra and images of tissue-engineered SMC constructs were acquired. Routine techniques such as qPCR, histochemistry, histological and immunocytological staining were performed for comparative gene and protein expression analysis. We identified that SMCs of different tissue origins exhibited unique spectral information that allowed a separation of all groups of origin by multivariate data analysis (MVA). We were further able to non-invasively monitor phenotypic switching in cultured SMCs and assess the impact of different culture conditions on extracellular matrix remodeling in the tissue-engineered ring constructs. Interestingly, we identified that the Raman signature of the human SMC-based ring constructs was similar to the one obtained from native aortic tissue. We conclude that Raman microspectroscopic methods are promising tools to characterize cells and define cellular and extracellular matrix components on a molecular level. In this study, in situ measurements were marker-independent, fast, and identified cellular differences that were not detectable by established routine techniques. Perspectively, Raman microspectroscopy and MVA in combination with artificial intelligence can be suitable for automated quality monitoring of (stem) cell and cell-based tissue engineering products. STATEMENT OF SIGNIFICANCE: The accessibility of autologous blood vessels for surgery is limited. Tissue engineering (TE) aims to develop functional vascular replacements; however, no commercially available TE vascular graft (TEVG) exists to date. One limiting factor is the availability of a well-characterized and safe cell source. Smooth muscle cells (SMCs) are generally used for TEVGs. To engineer a TEVG, proliferating SMCs of the synthesizing phenotype are essential, whereas functional, sustainable TEVGs require SMCs of the contractile phenotype. SMC diversity and plasticity are therefore limiting factors, also for their quality monitoring and application in TE. In this study, Raman microspectroscopy and imaging combined with machine learning tools allowed the non-destructive, marker-independent characterization of SMCs, smooth muscle tissues and TE SMC-constructs. The spectral information was specific enough to distinguish for the first time the phenotypic switching in SMCs in real-time, and monitor the impact of culture conditions on ECM remodeling in the TE SMC-constructs.

Bioengineering human vascular networks: trends and directions in endothelial and perivascular cell sources

Tissue engineering holds great promise in regenerative medicine. However, the field of tissue engineering faces a myriad of difficulties. A major challenge is the necessity to integrate vascular networks into bioengineered constructs to enable physiological functions including adequate oxygenation, nutrient delivery, and removal of waste products. The last two decades have seen remarkable progress in our collective effort to bioengineer human-specific vascular networks. Studies have included both in vitro and in vivo investigations, and multiple methodologies have found varying degrees of success. What most approaches to bioengineer human vascular networks have in common, however, is the synergistic use of both (1) endothelial cells (ECs)-the cells used to line the lumen of the vascular structures and (2) perivascular cells-usually used to support EC function and provide perivascular stability to the networks. Here, we have highlighted trends in the use of various cellular sources over the last two decades of vascular network bioengineering research. To this end, we comprehensively reviewed all life science and biomedical publications available at the MEDLINE database up to 2018. Emphasis was put on selective studies that definitively used human ECs and were specifically related to bioengineering vascular networks. To facilitate this analysis, all papers were stratified by publication year and then analyzed according to their use of EC and perivascular cell types. This study provides an illustrating discussion on how each alternative source of cells has come to be used in the field. Our intention was to reveal trends and to provide new insights into the trajectory of vascular network bioengineering with regard to cellular sources.

Engineered Microenvironment for Manufacturing Human Pluripotent Stem Cell-Derived Vascular Smooth Muscle Cells

Human pluripotent stem cell-derived vascular smooth muscle cells (hPSC-VSMCs) are of great value for disease modeling, drug screening, cell therapies, and tissue engineering. However, producing a high quantity of hPSC-VSMCs with current cell culture technologies remains very challenging. Here, we report a scalable method for manufacturing hPSC-VSMCs in alginate hydrogel microtubes (i.e., AlgTubes), which protect cells from hydrodynamic stresses and limit cell mass to <400 μm to ensure efficient mass transport. The tubes provide cells a friendly microenvironment, leading to extremely high culture efficiency. We have shown that hPSC-VSMCs can be generated in 10 days with high viability, high purity, and high yield (∼5.0 × 108 cells/mL). Phenotype and gene expression showed that VSMCs made in AlgTubes and VSMCs made in 2D cultures were similar overall. However, AlgTube-VSMCs had higher expression of genes related to vasculature development and angiogenesis, and 2D-VSMCs had higher expression of genes related to cell death and biosynthetic processes.

Do Induced Pluripotent Stem Cell Characteristics Correlate with Efficient In Vitro Smooth Muscle Cell Differentiation? A Comparison of Three Patient-Derived Induced Pluripotent Stem Cell Lines

Human induced pluripotent stem cells (iPSCs) have the potential to repair/regenerate smooth muscle cells (SMCs) in different organs. However, there are many challenges in their translation to clinical therapies. In this study, we describe our observations of in vitro SMC differentiation in three iPSC lines derived from human fibroblasts using retroviral, episomal, and mRNA/miRNA reprogramming methods. We sought to elucidate correlations between differentiation characteristics and efficiencies that can facilitate large-scale production of differentiated cells for clinical applications, and to report differences in pluripotency marker expression in differentiated cells from different iPSC lines. A standardized SMC differentiation protocol was used to induce the CD31⁺/CD34⁺ vascular progenitor cell phenotype. These were sorted by magnetic-activated (MACS) and fluorescence-activated cell sorting (FACS), and then treated with PDGF-BB and smooth muscle growth medium for further differentiation into smooth muscle progenitor cells (pSMCs). The expression of SMC and pluripotency markers in early- and late-passage (P1 and P4) pSMCs was analyzed. A total of 36 differentiation runs was performed on the three patient iPSC lines. All pSMC populations expressed SMC markers and Ki67 consistent with the progenitor phenotype. Initial iPSC density correlated positively with the sorted cell FACS efficiency, and this correlation could be fit to a quadratic equation. We also observed that a specific "honeycomb" pattern of the starting cultured iPSCs cultured correlated with higher efficiency in all three iPSC lines. Pluripotency marker expression decreased significantly to nearly undetectable levels in all three lines. There was no significant change in SMC and pluripotent marker expression between passage 1 and 4. In summary, our observations suggest that the method of iPSC reprogramming does not affect iPSC differentiation into pSMCs. Protocol efficiency can be modeled mathematically and coupled with the initial "honeycomb" cell pattern to optimize production of large cell numbers for clinical therapies.

Human induced pluripotent stem cell-derived vascular smooth muscle cells: differentiation and therapeutic potential

Cardiovascular diseases remain the leading cause of death worldwide and current treatment strategies have limited effect of disease progression. It would be desirable to have better models to study developmental and pathological processes and model vascular diseases in laboratory settings. To this end, human induced pluripotent stem cells (hiPSCs) have generated great enthusiasm, and have been a driving force for development of novel strategies in drug discovery and regenerative cell-therapy for the last decade. Hence, investigating the mechanisms underlying the differentiation of hiPSCs into specialized cell types such as cardiomyocytes, endothelial cells, and vascular smooth muscle cells (VSMCs) may lead to a better understanding of developmental cardiovascular processes and potentiate progress of safe autologous regenerative therapies in pathological conditions. In this review, we summarize the latest trends on differentiation protocols of hiPSC-derived VSMCs and their potential application in vascular research and regenerative therapy.

Human iPSC-derived mesenchymal stem cells encapsulated in PEGDA hydrogels mature into valve interstitial-like cells

Despite recent advances in tissue engineered heart valves (TEHV), a major challenge is identifying a cell source for seeding TEHV scaffolds. Native heart valves are durable because valve interstitial cells (VICs) maintain tissue homeostasis by synthesizing and remodeling the extracellular matrix. This study demonstrates that induced pluripotent stem cells (iPSC)-derived mesenchymal stem cells (iMSCs) can be derived from iPSCs using a feeder-free protocol and then further matured into VICs by encapsulation within 3D hydrogels. The differentiation efficiency was characterized using flow cytometry, immunohistochemistry staining, and trilineage differentiation. Using our feeder-free differentiation protocol, iMSCs were differentiated from iPSCs and had CD90+, CD44+, CD71+, αSMA+, and CD45- expression. Furthermore, iMSCs underwent trilineage differentiation when cultured in induction media for 21 days. iMSCs were then encapsulated in poly(ethylene glycol)diacrylate (PEGDA) hydrogels grafted with adhesion peptide (RGDS) to promote remodeling and further maturation into VIC-like cells. VIC phenotype was assessed by the expression of alpha-smooth muscle actin (αSMA), vimentin, and collagen production after 28 days. When MSC-derived cells were encapsulated in PEGDA hydrogels that mimic the leaflet modulus, a decrease in αSMA expression and increase in vimentin was observed. In addition, iMSCs synthesized collagen type I after 28 days in 3D hydrogel culture. Thus, the results from this study suggest that iMSCs may be a promising cell source for TEHV.

STATEMENT OF SIGNIFICANCE

Developing a suitable cell source is a critical component for the success and durability of tissue engineered heart valves. The significance of this study is the generation of iPSCs-derived mesenchymal stem cells (iMSCs) that have the capacity to mature into valve interstitial-like cells when introduced into a 3D cell culture designed to mimic the layers of the valve leaflet. iMSCs were generated using a feeder-free protocol, which is one major advantage over other methods, as it is more clinically relevant. In addition to generating a potential new cell source for heart valve tissue engineering, this study also highlights the importance of a 3D culture environment to influence cell phenotype and function.

Specification and Diversification of Pericytes and Smooth Muscle Cells from Mesenchymoangioblasts

Elucidating the pathways that lead to vasculogenic cells, and being able to identify their progenitors and lineage-restricted cells, is critical to the establishment of human pluripotent stem cell (hPSC) models for vascular diseases and development of vascular therapies. Here, we find that mesoderm-derived pericytes (PCs) and smooth muscle cells (SMCs) originate from a clonal mesenchymal progenitor mesenchymoangioblast (MB). In clonogenic cultures, MBs differentiate into primitive PDGFRβ⁺ CD271⁺CD73⁻ mesenchymal progenitors, which give rise to proliferative PCs, SMCs, and mesenchymal stem/stromal cells. MB-derived PCs can be further specified to CD274⁺ capillary and DLK1⁺ arteriolar PCs with a proinflammatory and contractile phenotype, respectively. SMC maturation was induced using a MEK inhibitor. Establishing the vasculogenic lineage tree, along with identification of stage- and lineage-specific markers, provides a platform for interrogating the molecular mechanisms that regulate vasculogenic cell specification and diversification and manufacturing well-defined mural cell populations for vascular engineering and cellular therapies from hPSCs.

Kumar et al. find that mesodermal pericytes and smooth muscle cells in human pluripotent stem cell cultures originate from a common endothelial and mesenchymal cell precursor, the mesenchymoangioblast. They show how different lineages of mural cells are specified from mesenchymoangioblasts and define stage- and lineage-specific markers for vasculogenic cells.

Tissue-Engineered Vascular Rings from Human iPSC-Derived Smooth Muscle Cells

There is an urgent need for an efficient approach to obtain a large-scale and renewable source of functional human vascular smooth muscle cells (VSMCs) to establish robust, patient-specific tissue model systems for studying the pathogenesis of vascular disease, and for developing novel therapeutic interventions. Here, we have derived a large quantity of highly enriched functional VSMCs from human induced pluripotent stem cells (hiPSC-VSMCs). Furthermore, we have engineered 3D tissue rings from hiPSC-VSMCs using a facile one-step cellular self-assembly approach. The tissue rings are mechanically robust and can be used for vascular tissue engineering and disease modeling of supravalvular aortic stenosis syndrome. Our method may serve as a model system, extendable to study other vascular proliferative diseases for drug screening. Thus, this report describes an exciting platform technology with broad utility for manufacturing cell-based tissues and materials for various biomedical applications.

Differentiation and Application of Induced Pluripotent Stem Cell–Derived Vascular Smooth Muscle Cells

Vascular smooth muscle cells (VSMCs) play a role in the development of vascular disease, for example, neointimal formation, arterial aneurysm, and Marfan syndrome caused by genetic mutations in VSMCs, but little is known about the mechanisms of the disease process. Advances in induced pluripotent stem cell technology have now made it possible to derive VSMCs from several different somatic cells using a selection of protocols. As such, researchers have set out to delineate key signaling processes involved in triggering VSMC gene expression to grasp the extent of gene regulatory networks involved in phenotype commitment. This technology has also paved the way for investigations into diseases affecting VSMC behavior and function, which may be treatable once an identifiable culprit molecule or gene has been repaired. Moreover, induced pluripotent stem cell–derived VSMCs are also being considered for their use in tissue-engineered blood vessels as they may prove more beneficial than using autologous vessels. Finally, while several issues remains to be clarified before induced pluripotent stem cell–derived VSMCs can become used in regenerative medicine, they do offer both clinicians and researchers hope for both treating and understanding vascular disease. In this review, we aim to update the recent progress on VSMC generation from stem cells and the underlying molecular mechanisms of VSMC differentiation. We will also explore how the use of induced pluripotent stem cell–derived VSMCs has changed the game for regenerative medicine by offering new therapeutic avenues to clinicians, as well as providing researchers with a new platform for modeling of vascular disease.

Deriving vascular smooth muscle cells from mesenchymal stromal cells: Evolving differentiation strategies and current understanding of their mechanisms

Vascular smooth muscle cells (VSMCs) play essential roles in regulating blood vessel form and function. Regeneration of functional vascular smooth muscle tissue to repair vascular diseases is an area of intense research in tissue engineering and regenerative medicine. For functional vascular smooth muscle tissue regeneration to become a practical therapy over the next decade, the field will need to have access to VSMC sources that are effective, robust and safe. While pluripotent stem cells hold good future promise to this end, more immediate translation is expected to come from approaches that generate functional VSMCs from adult sources of multipotent adipose-derived and bone marrow-derived mesenchymal stromal cells (ASCs and BMSCs). The research to this end is extensive and is dominated by studies relating to classical biochemical signalling molecules used to induce differentiation of ASCs and BMSCs. However, prolonged use of the biochemical induction factors is costly and can cause potential endotoxin contamination in the culture. Over recent years several non-traditional differentiation approaches have been devised to mimic defined aspects of the native micro-environment in which VSMCs reside to contribute to the differentiation of VSMC-like cells from ASCs and BMSCs. In this review, the promises and limitations of several non-traditional culture approaches (e.g., co-culture, biomechanical, and biomaterial stimuli) targeting VSMC differentiation are discussed. The extensive crosstalk between the underlying signalling cascades are delineated and put into a translational context. It is expected that this review will not only provide significant insight into VSMC differentiation strategies for vascular smooth muscle tissue engineering applications, but will also highlight the fundamental importance of engineering the cellular microenvironment on multiple scales (with consideration of different combinatorial pathways) in order to direct cell differentiation fate and obtain cells of a desired and stable phenotype. These strategies may ultimately be applied to different sources of stem cells in the future for a range of biomaterial and tissue engineering disciplines.

Flow induced adherens junction remodeling driven by cytoskeletal forces

Adherens junctions (AJs) are a key structural component for tissue organization and function. Under fluid shear stress, AJs exhibit dynamic assembly/disassembly, but how shear stress couples to AJs is unclear. In MDCK cells we measured simultaneously the forces in cytoskeletal α-actinin and the density and length of AJs using a genetically coded optical force sensor, actinin-sstFRET, and fluorescently labeled E-cadherin (E-cad). We found that shear stress of 0.74dyn/cm² for 3h significantly enhanced E-cad expression at cell-cell contacts and this phenomenon has two phases. The initial formation of segregated AJ plaques coincided with a decrease in cytoskeletal tension, but an increase in tension was necessary for expansion of the plaques and the formation of continuous AJs in the later phase. The changes in cytoskeletal tension and reorganization appear to be an upstream process in response to flow since it occurred in both wild type and dominant negative E-cad cells. Disruption of F-actin with a Rho-ROCK inhibitor eliminated AJ growth under flow. These results delineate the shear stress transduction paths in cultured cells, which helps to understand pathology of a range of diseases that involve dysfunction of E-cadherin.

Application of induced pluripotent stem cells to model smooth muscle cell function in vascular diseases

Vascular smooth muscle cells (SMC) play an essential role in remodeling the vasculature during disease progression. Induced pluripotent stem cells (iPSC) provide an attractive approach to obtain autologous SMC source for patient-specific disease modeling. Here we discuss the current methods to 1) derive functional SMC from iPSC, 2) model vascular diseases using SMC generated from patient-derived iPSC, and 3) modulate microenvironmental cues to enhance cellular differentiation and functionality and better mimic the physiological environment. We emphasize that continuous exploration of biomaterial technologies to engineer a more SMC-specific microenvironment will provide further insight on complex vascular diseases.

Reprogramming Postnatal Human Epidermal Keratinocytes Toward Functional Neural Crest Fates

During development, neural crest (NC) cells are induced by signaling events at the neural plate border of all vertebrate embryos. Initially arising within the central nervous system, NC cells subsequently undergo an epithelial to mesenchymal transition to migrate into the periphery, where they differentiate into diverse cell types. Here we provide evidence that postnatal human epidermal keratinocytes (KC), in response to fibroblast growth factor 2 and insulin like growth factor 1 signals, can be reprogrammed toward a NC fate. Genome-wide transcriptome analyses show that keratinocyte-derived NC cells are similar to those derived from human embryonic stem cells. Moreover, they give rise in vitro and in vivo to NC derivatives such as peripheral neurons, melanocytes, Schwann cells and mesenchymal cells (osteocytes, chondrocytes, adipocytes, and smooth muscle cells). By demonstrating that human keratin-14+ KC can form NC cells, even from clones of single cells, our results have important implications in stem cell biology and regenerative medicine. Stem Cells 2017;35:1402-1415.

TGF-β1-induced differentiation of SHED into functional smooth muscle cells

BACKGROUND

Adequate vascularization is crucial for supplying nutrition and discharging metabolic waste in freshly transplanted tissue-engineered constructs. Obtaining the appropriate building blocks for vascular tissue engineering (i.e. endothelial and mural cells) is a challenging task for tissue neovascularization. Hence, we investigated whether stem cells from human exfoliated deciduous teeth (SHED) could be induced to differentiate into functional vascular smooth muscle cells (vSMCs).

METHODS

We utilized two cytokines of the TGF-β family, transforming growth factor beta 1 (TGF-β1) and bone morphogenetic protein 4 (BMP4), to induce SHED differentiation into SMCs. Quantitative real-time polymerase chain reaction (RT-qPCR) was used to assess mRNA expression, and protein expression was analyzed using flow cytometry, western blot and immunostaining. Additionally, to examine whether these SHED-derived SMCs possess the same function as primary SMCs, in vitro Matrigel angiogenesis assay, fibrin gel bead assay, and functional contraction study were used here.

RESULTS

By analyzing the expression of specific markers of SMCs (α-SMA, SM22α, Calponin, and SM-MHC), we confirmed that TGF-β1, and not BMP4, could induce SHED differentiation into SMCs. The differentiation efficiency was relatively high (α-SMA+ 86.1%, SM22α+ 93.9%, Calponin+ 56.8%, and SM-MHC+ 88.2%) as assessed by flow cytometry. In vitro Matrigel angiogenesis assay showed that the vascular structures generated by SHED-derived SMCs and human umbilical vein endothelial cells (HUVECs) were comparable to primary SMCs and HUVECs in terms of vessel stability. Fibrin gel bead assay showed that SHED-derived SMCs had a stronger capacity for promoting vessel formation compared with primary SMCs. Further analyses of protein expression in fibrin gel showed that cultures containing SHED-derived SMCs exhibited higher expression levels of Fibronectin than the primary SMCs group. Additionally, it was also confirmed that SHED-derived SMCs exhibited functional contractility. When SB-431542, a specific inhibitor of ALK5 was administered, TGF-β1 stimulation could not induce SHED into SMCs, indicating that the differentiation of SHED into SMCs is somehow related to the TGF-β1-ALK5 signaling pathway.

CONCLUSIONS

SHED could be successfully induced into functional SMCs for vascular tissue engineering, and this course could be regulated through the ALK5 signaling pathway. Hence, SHED appear to be a promising candidate cell type for vascular tissue engineering.

3D Cell Culturing and Possibilities for Myometrial Tissue Engineering

Research insights into uterine function and the mechanisms of labour have been hindered by the lack of suitable animal and cellular models. The use of traditional culturing methods limits the exploration of complex uterine functions, such as cell interactions, connectivity and contractile behaviour, as it fails to mimic the three-dimensional (3D) nature of uterine cell interactions in vivo. Animal models are an option, however, use of these models is constrained by ethical considerations as well as translational limitations to humans. Evidence indicates that these limitations can be overcome by using 3D culture systems, or 3D Bioprinters, to model the in vivo cytological architecture of the tissue in an in vitro environment. 3D cultured or 3D printed cells can be used to form an artificial tissue. This artificial tissue can not only be used as an appropriate model in which to study cellular function and organisation, but could also be used for regenerative medicine purposes including organ or tissue transplantation, organ donation and obstetric care. The current review describes recent developments in cell culture that can facilitate the development of myometrial 3D structures and tissue engineering applications.

Vascular diseases await translation of blood vessels engineered from stem cells

The discovery of human induced pluripotent stem cells (hiPSCs) might pave the way toward a long-sought solution for obtaining sufficient numbers of autologous cells for tissue engineering. Several methods exist for generating endothelial cells or perivascular cells from hiPSCs in vitro for use in the building of vascular tissue. We discuss current developments in the generation of vascular progenitor cells from hiPSCs and the assessment of their functional capacity in vivo, opportunities and challenges for the clinical translation of engineered vascular tissue, and modeling of vascular diseases using hiPSC-derived vascular progenitor cells.

Full biological characterization of human pluripotent stem cells will open the door to translational research

Since the discovery of human embryonic stem cells (hESC) and human-induced pluripotent stem cells (hiPSC), great hopes were held for their therapeutic application including disease modeling, drug discovery screenings, toxicological screenings and regenerative therapy. hESC and hiPSC have the advantage of indefinite self-renewal, thereby generating an inexhaustible pool of cells with, e.g., specific genotype for developing putative treatments; they can differentiate into derivatives of all three germ layers enabling autologous transplantation, and via donor-selection they can express various genotypes of interest for better disease modeling. Furthermore, drug screenings and toxicological screenings in hESC and hiPSC are more pertinent to identify drugs or chemical compounds that are harmful for human, than a mouse model could predict. Despite continuing research in the wide field of therapeutic applications, further understanding of the underlying basic mechanisms of stem cell function is necessary. Here, we summarize current knowledge concerning pluripotency, self-renewal, apoptosis, motility, epithelial-to-mesenchymal transition and differentiation of pluripotent stem cells.

Pulmonary Arterial Stiffness: Toward a New Paradigm in Pulmonary Arterial Hypertension Pathophysiology and Assessment

Stiffening of the pulmonary arterial bed with the subsequent increased load on the right ventricle is a paramount feature of pulmonary hypertension (PH). The pathophysiology of vascular stiffening is a complex and self-reinforcing function of extracellular matrix remodeling, driven by recruitment of circulating inflammatory cells and their interactions with resident vascular cells, and mechanotransduction of altered hemodynamic forces throughout the ventricular-vascular axis. New approaches to understanding the cell and molecular determinants of the pathophysiology combine novel biopolymer substrates, controlled flow conditions, and defined cell types to recapitulate the biomechanical environment in vitro. Simultaneously, advances are occurring to assess novel parameters of stiffness in vivo. In this comprehensive state-of-art review, we describe clinical hemodynamic markers, together with the newest translational echocardiographic and cardiac magnetic resonance imaging methods, to assess vascular stiffness and ventricular-vascular coupling. Finally, fluid-tissue interactions appear to offer a novel route of investigating the mechanotransduction processes and disease progression.

Advancing cardiovascular tissue engineering

Cardiovascular tissue engineering offers the promise of biologically based repair of injured and damaged blood vessels, valves, and cardiac tissue. Major advances in cardiovascular tissue engineering over the past few years involve improved methods to promote the establishment and differentiation of induced pluripotent stem cells (iPSCs), scaffolds from decellularized tissue that may produce more highly differentiated tissues and advance clinical translation, improved methods to promote vascularization, and novel in vitro microphysiological systems to model normal and diseased tissue function. iPSC technology holds great promise, but robust methods are needed to further promote differentiation. Differentiation can be further enhanced with chemical, electrical, or mechanical stimuli.

Pluripotent stem cells: An in vitro model for nanotoxicity assessments

The advent of technology has led to an established range of engineered nanoparticles that are used in diverse applications, such as cell-cell interactions, cell-material interactions, medical therapies and the target modulation of cellular processes. The exponential increase in the utilization of nanomaterials and the growing number of associated criticisms has highlighted the potential risks of nanomaterials to human health and the ecosystem. The existing in vivo and in vitro platforms show limitations, with fluctuations being observed in the results of toxicity assessments. Pluripotent stem cells (PSCs) are viable source of cells that are capable of developing into specialized cells of the human body. PSCs can be efficiently used to screen new biomaterials/drugs and are potential candidates for studying impairments of biophysical morphology at both the cellular and tissue levels during interactions with nanomaterials and for diagnosing toxicity. Three-dimensional in vitro models obtained using PSC-derived cells would provide a realistic, patient-specific platform for toxicity assessments and in drug screening applications. The current review focuses on PSCs as an alternative in vitro platform for assessing the hazardous effects of nanomaterials on health systems and highlights the importance of PSC-derived in vitro platforms. Copyright © 2016 John Wiley & Sons, Ltd.

Cell-based strategies for vascular regeneration

Vascular regeneration is known to play an essential role in the repair of injured tissues mainly through accelerating the repair of vascular injury caused by vascular diseases, as well as the recovery of ischemic tissues. However, the clinical vascular regeneration is still challenging. Cell-based therapy is thought to be a promising strategy for vascular regeneration, since various cells have been identified to exert important influences on the process of vascular regeneration such as the enhanced endothelium formation on the surface of vascular grafts, and the induction of vessel-like network formation in the ischemic tissues. Here are a vast number of diverse cell-based strategies that have been extensively studied in vascular regeneration. These strategies can be further classified into three main categories, including cell transplantation, construction of tissue-engineered grafts, and surface modification of scaffolds. Cells used in these strategies mainly refer to terminally differentiated vascular cells, pluripotent stem cells, multipotent stem cells, and unipotent stem cells. The aim of this review is to summarize the reported research advances on the application of various cells for vascular regeneration, yielding insights into future clinical treatment for injured tissue/organ.

A Novel Selectable Islet 1 Positive Progenitor Cell Reprogrammed to Expandable and Functional Smooth Muscle Cells

Disorders affecting smooth muscle structure/function may require technologies that can generate large scale, differentiated and contractile smooth muscle cells (SMC) suitable for cell therapy. To date no clonal precursor population that provides large numbers of differentiated SMC in culture has been identified in a rodent. Identification of such cells may also enhance insight into progenitor cell fate decisions and the relationship between smooth muscle precursors and disease states that implicate differentiated SMC.  In this study, we used classic clonal expansion techniques to identify novel self-renewing Islet 1 (Isl-1) positive primitive progenitor cells (PPC) within rat bone marrow that exhibited canonical stem cell markers and preferential differentiation towards a smooth muscle-like fate. We subsequently used molecular tagging to select Isl-1 positive clonal populations from expanded and de novo marrow cell populations. We refer to these previously undescribed cells as the PPC given its stem cell marker profile, and robust self-renewal capacity. PPC could be directly converted into induced smooth muscle cells (iSMC) using single transcription factor (Kruppel-like factor 4) knockdown or transactivator (myocardin) overexpression in contrast to three control cells (HEK 293, endothelial cells and mesenchymal stem cells) where such induction was not possible. iSMC exhibited immuno- and cytoskeletal-phenotype, calcium signaling profile and contractile responses similar to bona fide SMC. Passaged iSMC could be expanded to a scale sufficient for large scale tissue replacement.  PPC and reprogramed iSMC so derived may offer future opportunities to investigate molecular, structure/function and cell-based replacement therapy approaches to diverse cardiovascular, respiratory, gastrointestinal, and genitourinary diseases that have as their basis smooth muscle cell functional aberrancy or numerical loss. Stem Cells 2016;34:1354-1368.

Transdifferentiation of human endothelial progenitors into smooth muscle cells

Access to smooth muscle cells (SMC) would create opportunities for tissue engineering, drug testing, and disease modeling. Herein we report the direct conversion of human endothelial progenitor cells (EPC) to induced smooth muscle cells (iSMC) by induced expression of MYOCD. The EPC undergo a cytoskeletal rearrangement resembling that of mesenchymal cells within 3 days post initiation of MYOCD expression. By day 7, the reprogrammed cells show upregulation of smooth muscle markers ACTA2, MYH11, and TAGLN by qRT-PCR and ACTA2 and MYH11 expression by immunofluorescence. By two weeks, they resemble umbilical artery SMC in microarray gene expression analysis. The iSMC, in contrast to EPC control, show calcium transients in response to phenylephrine stimulation and a contractility an order of magnitude higher than that of EPC as determined by traction force microscopy. Tissue-engineered blood vessels constructed using iSMC show functionality with respect to flow- and drug-mediated vasodilation and vasoconstriction.

G-protein Coupled Receptor Signaling in Pluripotent Stem Cell-derived Cardiovascular Cells: Implications for Disease Modeling

Human pluripotent stem cell derivatives show promise as an in vitro platform to study a range of human cardiovascular diseases. A better understanding of the biology of stem cells and their cardiovascular derivatives will help to understand the strengths and limitations of this new model system. G-protein coupled receptors (GPCRs) are key regulators of stem cell maintenance and differentiation and have an important role in cardiovascular cell signaling. In this review, we will therefore describe the state of knowledge concerning the regulatory role of GPCRs in both the generation and function of pluripotent stem cell derived-cardiomyocytes, -endothelial, and -vascular smooth muscle cells. We will consider how far the in vitro disease models recapitulate authentic GPCR signaling and provide a useful basis for discovery of disease mechanisms or design of therapeutic strategies.