Human pluripotent stem cell culture density modulates YAP signaling

Ferroptosis in cancer (Review)

Ferroptosis is a type of programmed cell death depending on iron and reactive oxygen species. This unique cell death process has attracted a great deal of attention in the field of cancer research over the past decade. Research on the association of ferroptosis signal pathways and cancer development indicated that targeting ferroptosis has great potential for cancer therapy. In the present study, the latest research progress of ferroptosis was reviewed, focusing on the relationship between ferroptosis and the development of cancer, in order to further promote the clinical application of ferroptosis in cancer.

Assessment of human embryonic stem cells differentiation into definitive endoderm lineage on the soft substrates

Pluripotent stem cells (PSCs) hold enormous potential for treating multiple diseases owing to their ability to self-renew and differentiate into any cell type. Albeit possessing such promising potential, controlling their differentiation into a desired cell type continues to be a challenge. Recent studies suggest that PSCs respond to different substrate stiffness and, therefore, can differentiate towards some lineages via Hippo pathway. Human PSCs can also differentiate and self-organize into functional cells, such as organoids. Traditionally, human PSCs are differentiated on stiff plastic or glass plates towards definitive endoderm and then into functional pancreatic progenitor cells in the presence of soluble growth factors. Thus, whether stiffness plays any role in differentiation towards definitive endoderm from human pluripotent stem cells (hPSCs) remains unclear. Our study found that the directed differentiation of human embryonic stem cells towards endodermal lineage on the varying stiffness did not differ from the differentiation on stiff plastic dishes. We also observed no statistical difference between the expression of yes-associated protein (YAP) and phosphorylated YAP. Furthermore, we demonstrate that lysophosphatidic acid, a YAP activator, enhanced definitive endoderm formation, whereas verteporfin, a YAP inhibitor, did not have the significant effect on the differentiation. In summary, our results suggest that human embryonic stem cells may not differentiate in response to changes in stiffness, and that such cues may not have as significant impact on the level of YAP. Our findings indicate that more research is needed to understand the direct relationship between biophysical forces and hPSCs differentiation.

A simple tool for the synchronous differentiation of human induced pluripotent stem cells into pancreatic progenitors

Efficient differentiation of human induced pluripotent stem cells (hiPSCs) into functional pancreatic cells holds great promise for diabetes research and treatment. However, a robust culture strategy for producing pancreatic progenitors with high homogeneity is lacking. Here, we established a simple differentiation strategy for generating synchronous iPSC-derived pancreatic progenitors via a two-step method of sequential cell synchronization using botulinum hemagglutinin (HA), an E-cadherin function-blocking agent. Of the various methods tested, the first-step synchronization method with HA exposure induces a synchronous switch from E- to N-cadherin and N- to E-cadherin expression by spatially controlling heterogeneous cell distribution, subsequently improving their competency for directed differentiation into definitive endodermal cells from iPSCs. The iPSC-derived definitive endodermal cells can efficiently generate PDX1+ and NKX6.1+ pancreatic progenitor cells in high yields. The PDX1+ and PDX1+ /NKX6.1+ cell densities showed 1.6- and 2.2-fold increases, respectively, compared with those from unsynchronized cultures. The intra-run and inter-run coefficient of variation were below 10%, indicating stable and robust differentiation across different cultures and runs. Our approach is a simple and efficient strategy to produce large quantities of differentiated cells with the highest homogeneity during multistage pancreatic progenitor differentiation, providing a potential tool for guided differentiation of iPSCs to functional insulin-producing cells.

Parametric modeling of mechanical effects on circadian oscillators

Circadian rhythms are archetypal examples of nonlinear oscillations. While these oscillations are usually attributed to circuits of biochemical interactions among clock genes and proteins, recent experimental studies reveal that they are also affected by the cell's mechanical environment. Here, we extend a standard biochemical model of circadian rhythmicity to include mechanical effects in a parametric manner. Using experimental observations to constrain the model, we suggest specific ways in which the mechanical signal might affect the clock. Additionally, a bifurcation analysis of the system predicts that these mechanical signals need to be within an optimal range for circadian oscillations to occur.

The ad hoc chemical design of random PBS-based copolymers influences the activation of cardiac differentiation while altering the HYPPO pathway target genes in hiPSCs

Cardiac tissue engineering is a cutting-edge technology aiming to replace irreversibly damaged cardiac tissue and restore contractile functionality. However, cardiac tissue engineering porous and perfusable scaffolds to enable oxygen supply in vitro and eventually promote angiogenesis in vivo are still desirable. Two fully-aliphatic random copolymers of poly(butylene succinate) (PBS), poly(butylene succinate/Pripol), P(BSBPripol), and poly(butylene/neopentyl glycol succinate), P(BSNS), containing two different subunits, neopentyl glycol and Pripol 1009, were successfully synthesized and then electrospun in tridimentional fibrous mats. The copolymers show different thermal and mechanical behaviours as result of their chemical structure. In particular, copolymerization led to a reduction in crystallinity and consequently PBS stiffness, reaching values of elastic modulus very close to those of soft tissues. Then, to check the biological suitability, human induced Pluripotent Stem Cells (hiPSCs) were directly seeded on both PBS-based copolymeric scaffolds. The results confirmed the ability of both the scaffolds to sustain cell viability and to maintain their stemness during cell expansion. Furthermore, gene expression and immunofluorescence analysis showed that P(BSBPripol) scaffold promoted an upregulation of the early cardiac progenitor and later-stage markers with a simultaneously upregulation of HYPPO pathway gene expression, crucial for mechanosensing of cardiac progenitor cells. These results suggest that the correct ad-hoc chemical design and, in turn, the mechanical properties of the matrix, such as substrate stiffness, together with surface porosity, play a critical role in regulating the behaviour of cardiac progenitors, which ultimately offers valuable insights into the development of novel bio-inspired scaffolds for cardiac tissue regeneration.

Hypoxia-induced YAP activation and focal adhesion turnover to promote cell migration in mesenchymal TNBC cells

BACKGROUND

Hypoxia is commonly characterized by malignant tumors that promote the aggressiveness and metastatic potential of cancer. Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer, with approximately 46% capacity related to distant metastasis. Transcriptional factor yes-associated protein (YAP), a core component of the Hippo pathway, is associated with poor prognosis and outcome in cancer metastasis. Here, we explored the effect of hypoxia-mediated YAP activation and focal adhesions (FAs) turnover in mesenchymal TNBC cell migration.

METHODS

We characterized the effect of hypoxia on YAP in different breast cancer cell lines using a hypoxia chamber and CoCl₂ .

RESULTS

Hypoxia-induced YAP nuclear translocation is significantly observed in normal breast epithelial cells, non-TNBC cells, mesenchymal TNBC cells, but not in basal-like TNBC cells. Functionally, we demonstrated that YAP activation was required for hypoxia to promote mesenchymal TNBC cell migration. Furthermore, hypoxia induced the localization of FAs at the leading edge of mesenchymal TNBC cells. In contrast, verteporfin (VP), a YAP inhibitor, significantly reduced the migration and the recruitment of nascent FAs at the cell periphery under hypoxia conditions, which only showed in mesenchymal TNBC cells.

CONCLUSIONS

Our data support the hypothesis that YAP is novel factor and positively responsible for hypoxia-promoting mesenchymal TNBC cell migration. Our findings provide further evidence and outcomes to help prevent the progression of TNBC.

Cell-surface contacts determine volume and mechanical properties of human embryonic kidney 293 T cells

Alterations in the organization of the cytoskeleton precede the escape of adherent cells from the framework of cell-cell and cell-matrix interactions into suspension. With cytoskeletal dynamics being linked to cell mechanical properties, many studies elucidated this relationship under either native adherent or suspended conditions. In contrast, tethered cells that mimic the transition between both states have not been the focus of recent research. Using human embryonic kidney 293 T cells we investigated all three conditions in the light of alterations in cellular shape, volume, as well as mechanical properties and relate these findings to the level, structure, and intracellular localization of filamentous actin (F-actin). For cells adhered to a substrate, our data shows that seeding density affects cell size but does not alter their elastic properties. Removing surface contacts leads to cell stiffening that is accompanied by changes in cell shape, and a reduction in cellular volume but no alterations in F-actin density. Instead, we observe changes in the organization of F-actin indicated by the appearance of blebs in the semi-adherent state. In summary, our work reveals an interplay between molecular and mechanical alterations when cells detach from a surface that is mainly dominated by cell morphology.

Role of YAP as a Mechanosensing Molecule in Stem Cells and Stem Cell-Derived Hematopoietic Cells

Yes-associated protein (YAP) and WW domain-containing transcription regulator protein 1 (WWTR1, also known as TAZ) are transcriptional coactivators in the Hippo signaling pathway. Both are well-known regulators of cell proliferation and organ size control, and they have significant roles in promoting cell proliferation and differentiation. The roles of YAP and TAZ in stem cell pluripotency and differentiation have been extensively studied. However, the upstream mediators of YAP and TAZ are not well understood. Recently, a novel role of YAP in mechanosensing and mechanotransduction has been reported. The present review updates information on the regulation of YAP by mechanical cues such as extracellular matrix stiffness, fluid shear stress, and actin cytoskeleton tension in stem cell behaviors and differentiation. The review explores mesenchymal stem cell fate decisions, pluripotent stem cells (PSCs), self-renewal, pluripotency, and differentiation to blood products. Understanding how cells sense their microenvironment or niche and mimic those microenvironments in vitro could improve the efficiency of producing stem cell products and the efficacy of the products.

Cell Behavioral Dynamics as a Cue in Optimizing Culture Stabilization in the Bioprocessing of Pluripotent Stem Cells

Pluripotent stem cells (PSCs) are important for future regenerative medicine therapies. However, in the production of PSCs and derivatives, the control of culture-induced fluctuations in the outcome of cell quality remains challenging. A detailed mechanistic understanding of how PSC behaviors are altered in response to biomechanical microenvironments within a culture is necessary for rational bioprocessing optimization. In this review, we discuss recent insights into the role of cell behavioral and mechanical homeostasis in modulating the states and functions of PSCs during culture processes. We delineate promising ways to manipulate the culture variability through regulating cell behaviors using currently developed tools. Furthermore, we anticipate their potential implementation for designing a culture strategy based on the concept of Waddington's epigenetic landscape that may provide a feasible solution for tuning the culture quality and stability in the bioprocessing space.

Soft substrate maintains stemness and pluripotent stem cell-like phenotype of human embryonic stem cells under defined culture conditions

Human embryonic stem cells (hESCs) are derived from the inner cell mass (ICM) of the pre-implantation blastocyst. Prior to embryo implantation, the ICM cells are surrounded by trophoblasts which have mechanical stiffness ranging from Pascal (Pa) to kilopascal (kPa). However, under in vitro conditions these cells are cultured on stiff tissue culture treated plastic plates (TCP) which have stiffness of approximately 1 gigapascal (GPa). This obvious dichotomy motivated us to investigate the fate of hESCs cultured on softer substrate, and to probe if the hESCs undergo differentiation or they retain pluripotency on soft substrates. We investigated the expression of pluripotency markers, and lineage-specific markers; we particularly looked at the expression of transcriptional coactivator YAP (Yes-associated protein), an important mediator of extracellular matrix (ECM) mechanical cues and a known downstream transducer of Hippo pathway. Downregulation of YAP has been correlated to the loss of multipotency of human mesenchymal stem cells (hMSCs) and pluripotency in mouse ESCs (mESCs); but we report that hESCs maintain their stemness on soft substrate of varying stiffness. Our findings revealed that on soft substrate hESCs express pluripotency markers and does not undergo substrate-mediated differentiation. Interestingly we show that hESCs maintained basal level of YAP expression for cell survival and proliferation, but YAP expression does not correlate directly with pluripotency in hESCs. To summarize, our results show that hESCs retain their stemness on soft substrate despite downregulation of YAP.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-022-00537-z.

SDHA/B reduction promotes hepatocellular carcinoma by facilitating the deNEDDylation of cullin1 and stabilizing YAP/TAZ

BACKGROUND AND AIMS

Succinate dehydrogenase enzyme (SDH) is frequently diminished in samples from patients with hepatocellular carcinoma (HCC), and SDH reduction is associated with elevated succinate level and poor prognosis in patients with HCC. However, the underlying mechanisms of how impaired SDH activity promotes HCC remain unclear.

APPROACH AND RESULTS

In this study, we observed remarkable downregulations of SDH subunits A and B (SDHA/B) in chronic liver injury-induced murine HCC models and patient samples. Subsequent RNA sequencing, hematoxylin and eosin staining, and immunohistochemistry analyses of HCC samples revealed that Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) were significantly upregulated in HCC, with their levels inversely correlating with that of SDHA/B. YAP/TAZ stability was greatly enhanced in SDHA/B-depleted HCC cells along with accumulation of succinate. Further mechanistic analyses demonstrated that impaired activity of SDHA/B resulted in succinate accumulation, which facilitated the deNEDDylation of cullin1 and therefore disrupted the E3 ubiquitin ligase SCF^β-TrCP complex, consequently leading to YAP/TAZ stabilization and activation in HCC cells. The accelerated in vitro cell proliferation and in vivo tumor growth caused by SDHA/B reduction or succinate exposure were largely dependent on the aberrant activation of YAP/TAZ.

CONCLUSIONS

Our study demonstrated that SDHA/B reduction promotes HCC proliferation by preventing the proteasomal degradation of YAP/TAZ through modulating cullin1 NEDDylation, thus binding SDH-deficient HCC cells to YAP/TAZ pathway and rendering these cells vulnerable to YAP/TAZ inhibition. Our findings warrant further investigation on the therapeutic effects of targeting YAP/TAZ in patients with HCC displaying reduced SDHA/B or elevated succinate levels.

YAP/TAZ in Bone and Cartilage Biology

YAP and TAZ were initially described as the main regulators of organ growth during development and more recently implicated in bone biology. YAP and TAZ are regulated by mechanical and cytoskeletal cues that lead to the control of cell fate in response to the cellular microenvironment. The mechanical component represents a major signal for bone tissue adaptation and remodelling, so YAP/TAZ contributes significantly in bone and cartilage homeostasis. Recently, mice and cellular models have been developed to investigate the precise roles of YAP/TAZ in bone and cartilage cells, and which appear to be crucial. This review provides an overview of YAP/TAZ regulation and function, notably providing new insights into the role of YAP/TAZ in bone biology.

Metabolic regulation of ferroptosis in the tumor microenvironment

Ferroptosis is an iron-dependent, non-apoptotic form of regulated cell death triggered by impaired redox and antioxidant machinery and propagated by the accumulation of toxic lipid peroxides. A compendium of experimental studies suggest that ferroptosis is tumor-suppressive. Sensitivity or resistance to ferroptosis can be regulated by cell-autonomous and non-cell-autonomous metabolic mechanisms. This includes a role for ferroptosis that extends beyond the tumor cells themselves, mediated by components of the tumor microenvironment, including T cells and other immune cells. Herein, we review the intrinsic and extrinsic factors that promote the sensitivity of cancer cells to ferroptosis and conclude by describing approaches to harness the full utility of ferroptotic agents as therapeutic options for cancer therapy.

Mechanics-driven nuclear localization of YAP can be reversed by N-cadherin ligation in mesenchymal stem cells

Mesenchymal stem cells adopt differentiation pathways based upon cumulative effects of mechanosensing. A cell's mechanical microenvironment changes substantially over the course of development, beginning from the early stages in which cells are typically surrounded by other cells and continuing through later stages in which cells are typically surrounded by extracellular matrix. How cells erase the memory of some of these mechanical microenvironments while locking in memory of others is unknown. Here, we develop a material and culture system for modifying and measuring the degree to which cells retain cumulative effects of mechanosensing. Using this system, we discover that effects of the RGD adhesive motif of fibronectin (representative of extracellular matrix), known to impart what is often termed "mechanical memory" in mesenchymal stem cells via nuclear YAP localization, are erased by the HAVDI adhesive motif of the N-cadherin (representative of cell-cell contacts). These effects can be explained by a motor clutch model that relates cellular traction force, nuclear deformation, and resulting nuclear YAP re-localization. Results demonstrate that controlled storage and removal of proteins associated with mechanical memory in mesenchymal stem cells is possible through defined and programmable material systems.

Spatiotemporal model of cellular mechanotransduction via Rho and YAP

How cells sense and respond to mechanical stimuli remains an open question. Recent advances have identified the translocation of Yes-associated protein (YAP) between nucleus and cytoplasm as a central mechanism for sensing mechanical forces and regulating mechanotransduction. We formulate a spatiotemporal model of the mechanotransduction signalling pathway that includes coupling of YAP with the cell force-generation machinery through the Rho family of GTPases. Considering the active and inactive forms of a single Rho protein (GTP/GDP-bound) and of YAP (non-phosphorylated/phosphorylated), we study the cross-talk between cell polarization due to active Rho and YAP activation through its nuclear localization. For fixed mechanical stimuli, our model predicts stationary nuclear-to-cytoplasmic YAP ratios consistent with experimental data at varying adhesive cell area. We further predict damped and even sustained oscillations in the YAP nuclear-to-cytoplasmic ratio by accounting for recently reported positive and negative YAP-Rho feedback. Extending the framework to time-varying mechanical stimuli that simulate cyclic stretching and compression, we show that the YAP nuclear-to-cytoplasmic ratio's time dependence follows that of the cyclic mechanical stimulus. The model presents one of the first frameworks for understanding spatiotemporal YAP mechanotransduction, providing several predictions of possible YAP localization dynamics, and suggesting new directions for experimental and theoretical studies.

An Updated Understanding of the Role of YAP in Driving Oncogenic Responses

Simple Summary

In 2020, the global cancer database GLOBOCAN estimated 19.3 million new cancer cases worldwide. The discovery of targeted therapies may help prognosis and outcome of the patients affected, but the understanding of the plethora of highly interconnected pathways that modulate cell transformation, proliferation, invasion, migration and survival remains an ambitious goal. Here we propose an updated state of the art of YAP as the key protein driving oncogenic response via promoting all those steps at multiple levels. Of interest, the role of YAP in immunosuppression is a field of evolving research and growing interest and this summary about the current pharmacological therapies impacting YAP serves as starting point for future studies.

Abstract

Yes-associated protein (YAP) has emerged as a key component in cancer signaling and is considered a potent oncogene. As such, nuclear YAP participates in complex and only partially understood molecular cascades that are responsible for the oncogenic response by regulating multiple processes, including cell transformation, tumor growth, migration, and metastasis, and by acting as an important mediator of immune and cancer cell interactions. YAP is finely regulated at multiple levels, and its localization in cells in terms of cytoplasm–nucleus shuttling (and vice versa) sheds light on interesting novel anticancer treatment opportunities and putative unconventional functions of the protein when retained in the cytosol. This review aims to summarize and present the state of the art knowledge about the role of YAP in cancer signaling, first focusing on how YAP differs from WW domain-containing transcription regulator 1 (WWTR1, also named as TAZ) and which upstream factors regulate it; then, this review focuses on the role of YAP in different cancer stages and in the crosstalk between immune and cancer cells as well as growing translational strategies derived from its inhibitory and synergistic effects with existing chemo-, immuno- and radiotherapies.

Revisiting the role of lysophosphatidic acid in stem cell biology

Stem cells possess unique biological characteristics such as the ability to self-renew and to undergo multilineage differentiation into specialized cells. Whereas embryonic stem cells (ESC) can differentiate into all cell types of the body, somatic stem cells (SSC) are a population of stem cells located in distinct niches throughout the body that differentiate into the specific cell types of the tissue in which they reside in. SSC function mainly to restore cells as part of normal tissue homeostasis or to replenish cells that are damaged due to injury. Cancer stem-like cells (CSC) are said to be analogous to SSC in this manner where tumor growth and progression as well as metastasis are fueled by a small population of CSC that reside within the corresponding tumor. Moreover, emerging evidence indicates that CSC are inherently resistant to chemo- and radiotherapy that are often the cause of cancer relapse. Hence, major research efforts have been directed at identifying CSC populations in different cancer types and understanding their biology. Many factors are thought to regulate and maintain cell stemness, including bioactive lysophospholipids such as lysophosphatidic acid (LPA). In this review, we discuss some of the newly discovered functions of LPA not only in the regulation of CSC but also normal SSC, the similarities in these regulatory functions, and how these discoveries can pave way to the development of novel therapies in cancer and regenerative medicine.

Decreased YAP activity reduces proliferative ability in human induced pluripotent stem cell of duchenne muscular dystrophy derived cardiomyocytes

Duchenne muscular dystrophy (DMD) is characterized by progressive muscle degeneration accompanied by dilated cardiomyopathy. Recently, abnormality of yes-associated protein (YAP) has been reported as the pathogenesis of muscle degeneration of DMD; however YAP activity remains unclear in dystrophic heart of DMD. Herein, we investigated YAP activity using disease-specific induced pluripotent stem cell (iPSC) derived cardiomyocytes (CMs) in DMD. DMD-iPSCs were generated from DMD patient with exon 48–54 deletion in DMD, and genome-edited (Ed)-DMD-iPSCs with in-frame (Ed-DMD-iPSCs) were created using CRISPR/Cas9. Nuclear translocation of YAP [nuclear (N)/cytoplasmic (C) ratio] was significantly lower in DMD-iPSC-CMs than in Ed-DMD-iPSC-CMs. In addition, Ki67 expression, indicating proliferative ability, was significantly lower in DMD-iPSC-CMs than Ed-DMD-iPSC-CMs. Therefore, immunofluorescent staining showed that actin stress fibers associated with YAP activity by mechanotransduction were disorganized in DMD-iPSC-CMs. Lysophosphatidic acid (LPA), a known lipid mediator on induction of actin polymerization, significantly increased YAP activity and actin dynamics in DMD-iPSC-CMs using live cell imaging. These results suggested that altered YAP activity due to impaired actin dynamics reduced proliferative ability in DMD-iPSC-CMs. Hence, decreased YAP activity in dystrophic heart may contribute to DMD-cardiomyopathy pathogenesis.

Controlled aggregation enhances immunomodulatory potential of mesenchymal stromal cell aggregates

Human mesenchymal stromal cells (MSCs) are promising candidates for cell therapy due to their ease of isolation and expansion and their ability to secrete antiapoptotic, pro‐angiogenic, and immunomodulatory factors. Three‐dimensional (3D) aggregation “self‐activates” MSCs to augment their pro‐angiogenic and immunomodulatory potential, but the microenvironmental features and culture parameters that promote optimal MSC immunomodulatory function in 3D aggregates are poorly understood. Here, we generated MSC aggregates via three distinct methods and compared them with regard to their (a) aggregate structure and (b) immunomodulatory phenotype under resting conditions and in response to inflammatory stimulus. Methods associated with fast aggregation kinetics formed aggregates with higher cell packing density and reduced extracellular matrix (ECM) synthesis compared to those with slow aggregation kinetics. While all three methods of 3D aggregation enhanced MSC expression of immunomodulatory factors compared to two‐dimensional culture, different aggregation methods modulated cells' temporal expression of these factors. A Design of Experiments approach, in which aggregate size and aggregation kinetics were systematically covaried, identified a significant effect of both parameters on MSCs' ability to regulate immune cells. Compared to small aggregates formed with fast kinetics, large aggregates with slow assembly kinetics were more effective at T‐cell suppression and macrophage polarization toward anti‐inflammatory phenotypes. Thus, culture parameters including aggregation method, kinetics, and aggregate size influence both the structural properties of aggregates and their paracrine immunomodulatory function. These findings underscore the utility of engineering strategies to control properties of 3D MSC aggregates, which may identify new avenues for optimizing the immunomodulatory function of MSC‐based cell therapies.

YAP and TAZ Mediators at the Crossroad between Metabolic and Cellular Reprogramming

Cell reprogramming can either refer to a direct conversion of a specialized cell into another or to a reversal of a somatic cell into an induced pluripotent stem cell (iPSC). It implies a peculiar modification of the epigenetic asset and gene regulatory networks needed for a new cell, to better fit the new phenotype of the incoming cell type. Cellular reprogramming also implies a metabolic rearrangement, similar to that observed upon tumorigenesis, with a transition from oxidative phosphorylation to aerobic glycolysis. The induction of a reprogramming process requires a nexus of signaling pathways, mixing a range of local and systemic information, and accumulating evidence points to the crucial role exerted by the Hippo pathway components Yes-Associated Protein (YAP) and Transcriptional Co-activator with PDZ-binding Motif (TAZ). In this review, we will first provide a synopsis of the Hippo pathway and its function during reprogramming and tissue regeneration, then we introduce the latest knowledge on the interplay between YAP/TAZ and metabolism and, finally, we discuss the possible role of YAP/TAZ in the orchestration of the metabolic switch upon cellular reprogramming.

Two distinct trophectoderm lineage stem cells from human pluripotent stem cells

The trophectoderm layer of the blastocyst-stage embryo is the precursor for all trophoblast cells in the placenta. Human trophoblast stem (TS) cells have emerged as an attractive tool for studies on early trophoblast development. However, the use of TS cell models is constrained by the limited genetic diversity of existing TS cell lines and restrictions on using human fetal tissue or embryos needed to generate additional lines. Here we report the derivation of two distinct stem cell types of the trophectoderm lineage from human pluripotent stem cells. Analogous to villous cytotrophoblasts in vivo, the first is a CDX2^- stem cell comparable with placenta-derived TS cells—they both exhibit identical expression of key markers, are maintained in culture and differentiate under similar conditions, and share high transcriptome similarity. The second is a CDX2⁺ stem cell with distinct cell culture requirements, and differences in gene expression and differentiation, relative to CDX2^- stem cells. Derivation of TS cells from pluripotent stem cells will significantly enable construction of in vitro models for normal and pathological placental development.

Transcriptomic Analysis of Naïve Human Embryonic Stem Cells Cultured in Three-Dimensional PEG Scaffolds

Naïve human embryonic stem cells (ESCs) are characterized by improved viability, proliferation, and differentiation capacity in comparison to traditionally derived primed human ESCs. However, currently used two-dimensional (2-D) cell culture techniques fail to mimic the three-dimensional (3-D) in vivo microenvironment, altering morphological and molecular characteristics of ESCs. Here, we describe the use of 3-D self-assembling scaffolds that support growth and maintenance of the naïve state characteristics of ESC line, Elf1. Scaffolds were formed via a Michael addition reaction upon the combination of two 8-arm polyethylene glycol (PEG) polymers functionalized with thiol (PEG-8-SH) and acrylate (PEG-8-Acr) end groups. 3-D scaffold environment maintained the naïve state and supported the long-term growth of ESCs. RNA-sequencing demonstrated significant changes in gene expression profiles between 2-D and 3-D grown cells. Gene ontology analysis revealed upregulation of biological processes involved in the regulation of transcription and translation, extracellular matrix organization, and chromatin remodeling in 3-D grown cells. 3-D culture conditions also induced upregulation of genes associated with Wnt and focal adhesion signaling, while p53 signaling pathway associated genes were downregulated. Our findings, for the first time, provide insight into the possible mechanisms of self-renewal of naïve ESCs stimulated by the transduction of mechanical signals from the 3-D microenvironment.

Developmental deficits and early signs of neurodegeneration revealed by PD patient derived dopamine neurons

Parkinson's disease (PD) is the second most common neurodegenerative disease affecting millions of elder people due to the degeneration of dopamine neurons in the striatum and substantia nigra. The clinical manifestations of PD include tremor, rigidity, bradykinesia and postural instability. Studying PD is challenging due to two obstacles: 1) disease models such as primary neurons or animal models usually couldn't recapitulate the disease phenotype, and 2) accessibility of human autopsied brain samples is very limited if not impossible. Induced pluripotent stem cells (iPSCs)-derived neuronal cells from patients emerge as an ideal in vitro model for disease modeling and drug development. Here we describe a cell density-dependent method for preparing functional hiPSC-derived dopamine neurons (iDAs) with ~90% purity (TH-positive cells). iDAs derived from PD patient exhibit the disease-related phenotypes, for example, slowed morphogenesis, reduced dopamine release, impaired mitochondrial function, and α-synuclein accumulation as early as 35 days after induction. Furthermore, we found that the effects of cell density are different between iDA development stages, whereas high cell density increases stress for early neural progenitor cells (NPCs), but are neural-protective for mature iDAs, high density also favors morphogenesis. Hence, using stage and density-dependent strategies we can obtain high quality iDAs, which are critical for disease modeling, drug development and cell replacement therapy.

Concerted localization-resets precede YAP-dependent transcription

Yes-associated protein 1 (YAP) is a transcriptional regulator with critical roles in mechanotransduction, organ size control, and regeneration. Here, using advanced tools for real-time visualization of native YAP and target gene transcription dynamics, we show that a cycle of fast exodus of nuclear YAP to the cytoplasm followed by fast reentry to the nucleus ("localization-resets") activates YAP target genes. These "resets" are induced by calcium signaling, modulation of actomyosin contractility, or mitosis. Using nascent-transcription reporter knock-ins of YAP target genes, we show a strict association between these resets and downstream transcription. Oncogenically-transformed cell lines lack localization-resets and instead show dramatically elevated rates of nucleocytoplasmic shuttling of YAP, suggesting an escape from compartmentalization-based control. The single-cell localization and transcription traces suggest that YAP activity is not a simple linear function of nuclear enrichment and point to a model of transcriptional activation based on nucleocytoplasmic exchange properties of YAP.

Consistent apparent Young's modulus of human embryonic stem cells and derived cell types stabilized by substrate stiffness regulation promotes lineage specificity maintenance

BACKGROUND

Apparent Young's modulus (AYM), which reflects the fundamental mechanical property of live cells measured by atomic force microscopy and is determined by substrate stiffness regulated cytoskeletal organization, has been investigated as potential indicators of cell fate in specific cell types. However, applying biophysical cues, such as modulating the substrate stiffness, to regulate AYM and thereby reflect and/or control stem cell lineage specificity for downstream applications, remains a primary challenge during in vitro stem cell expansion. Moreover, substrate stiffness could modulate cell heterogeneity in the single-cell stage and contribute to cell fate regulation, yet the indicative link between AYM and cell fate determination during in vitro dynamic cell expansion (from single-cell stage to multi-cell stage) has not been established.

RESULTS

Here, we show that the AYM of cells changed dynamically during passaging and proliferation on substrates with different stiffness. Moreover, the same change in substrate stiffness caused different patterns of AYM change in epithelial and mesenchymal cell types. Embryonic stem cells and their derived progenitor cells exhibited distinguishing AYM changes in response to different substrate stiffness that had significant effects on their maintenance of pluripotency and/or lineage-specific characteristics. On substrates that were too rigid or too soft, fluctuations in AYM occurred during cell passaging and proliferation that led to a loss in lineage specificity. On a substrate with 'optimal' stiffness (i.e., 3.5 kPa), the AYM was maintained at a constant level that was consistent with the parental cells during passaging and proliferation and led to preservation of lineage specificity. The effects of substrate stiffness on AYM and downstream cell fate were correlated with intracellular cytoskeletal organization and nuclear/cytoplasmic localization of YAP.

CONCLUSIONS

In summary, this study suggests that optimal substrate stiffness regulated consistent AYM during passaging and proliferation reflects and contributes to hESCs and their derived progenitor cells lineage specificity maintenance, through the underlying mechanistic pathways of stiffness-induced cytoskeletal organization and the downstream YAP signaling. These findings highlighted the potential of AYM as an indicator to select suitable substrate stiffness for stem cell specificity maintenance during in vitro expansion for regenerative applications.

Role of YAP/TAZ in Cell Lineage Fate Determination and Related Signaling Pathways

The penultimate effectors of the Hippo signaling pathways YAP and TAZ, are transcriptional co-activator proteins that play key roles in many diverse biological processes, ranging from cell proliferation, tumorigenesis, mechanosensing and cell lineage fate determination, to wound healing and regeneration. In this review, we discuss the regulatory mechanisms by which YAP/TAZ control stem/progenitor cell differentiation into the various major lineages that are of interest to tissue engineering and regenerative medicine applications. Of particular interest is the key role of YAP/TAZ in maintaining the delicate balance between quiescence, self-renewal, proliferation and differentiation of endogenous adult stem cells within various tissues/organs during early development, normal homeostasis and regeneration/healing. Finally, we will consider how increasing knowledge of YAP/TAZ signaling might influence the trajectory of future progress in regenerative medicine.

The Role of Lysophosphatidic Acid in Adult Stem Cells

Stem cells are undifferentiated multipotent precursor cells that are capable both of perpetuating themselves as stem cells (self-renewal) and of undergoing differentiation into one or more specialized types of cells. And these stem cells have been reported to reside within distinct anatomic locations termed “niches”. The long-term goals of stem cell biology range from an understanding of cell-lineage determination and tissue organization to cellular therapeutics for degenerative diseases. Stem cells maintain tissue function throughout an organism’s lifespan by replacing differentiated cells. To perform this function, stem cells provide a unique combination of multilineage developmental potential and the capacity to undergo self-renewing divisions. The loss of self-renewal capacity in stem cells underlies certain degenerative diseases and the aging process. This self-renewal regulation must balance the regenerative needs of tissues that persist throughout life. Recent evidence suggests lysophosphatidic acid (LPA) signaling pathway plays an important role in the regulation of a variety of stem cells. In this review, we summarize the evidence linking between LPA and stem cell regulation. The LPA-induced signaling pathway regulates the proliferation and survival of stem cells and progenitors, and thus are likely to play a role in the maintenance of stem cell population in the body. This lipid mediator regulatory system can be a novel potential therapeutics for stem cell maintenance.

Lysophosphatidic Acid and Hematopoiesis: From Microenvironmental Effects to Intracellular Signaling

Vertebrate hematopoiesis is a complex physiological process that is tightly regulated by intracellular signaling and extracellular microenvironment. In recent decades, breakthroughs in lineage-tracing technologies and lipidomics have revealed the existence of numerous lipid molecules in hematopoietic microenvironment. Lysophosphatidic acid (LPA), a bioactive phospholipid molecule, is one of the identified lipids that participates in hematopoiesis. LPA exhibits various physiological functions through activation of G-protein-coupled receptors. The functions of these LPARs have been widely studied in stem cells, while the roles of LPARs in hematopoietic stem cells have rarely been examined. Nonetheless, mounting evidence supports the importance of the LPA-LPAR axis in hematopoiesis. In this article, we have reviewed regulation of hematopoiesis in general and focused on the microenvironmental and intracellular effects of the LPA in hematopoiesis. Discoveries in these areas may be beneficial to our understanding of blood-related disorders, especially in the context of prevention and therapy for anemia.

A TAZ-ANGPTL4-NOX2 Axis Regulates Ferroptotic Cell Death and Chemoresistance in Epithelial Ovarian Cancer

Ovarian cancer is the deadliest gynecologic cancer. Despite recent advances, clinical outcomes remain poor, necessitating novel therapeutic approaches. To investigate metabolic susceptibility, we performed nutrigenetic screens on a panel of clear cell and serous ovarian cancer cells and identified cystine addiction and vulnerability to ferroptosis, a novel form of regulated cell death. Our results may have therapeutic potential, but little is known about the determinants of ferroptosis susceptibility in ovarian cancer. We found that vulnerability to ferroptosis in ovarian cancer cells is enhanced by lower cell confluency. Because the Hippo pathway effectors Yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ) are recognized as sensors of cell density, and TAZ is the predominant effector in the tested ovarian cancer cell lines, we investigated the role of TAZ in ferroptosis of ovarian cancer. TAZ removal confers ferroptosis resistance, while TAZS89A overexpression sensitizes cells to ferroptosis. In addition, we found that lower TAZ level in chemo-resistant recurrent ovarian cancer is responsible for reduced ferroptosis susceptibility. The integrative genomic analysis identified ANGPTL4 as a direct TAZ-regulated target gene that sensitizes ferroptosis by activating NOX2. Collectively, cell density-regulated ferroptosis in ovarian cancer is mediated by TAZ through the regulation of the ANGPTL4-NOX2 axis, suggesting therapeutic potentials for ovarian cancers and other TAZ-activated tumors. IMPLICATIONS: This study reveals that TAZ promotes ferroptosis in ovarian cancers by regulating ANGPTL4 and NOX, offering a novel therapeutic potential for ovarian tumors with TAZ activation.

Increased Neuronal Differentiation Efficiency in High Cell Density-Derived Induced Pluripotent Stem Cells

Human pluripotent stem cells (hPSCs), including induced pluripotent stem cells (iPSCs), provide access to hard-to-obtain cells for studies under physiological and disease conditions. For the study of neurodegenerative diseases, especially sporadic cases where the “disease condition” might be restricted towards the neuroectodermal lineage, obtaining the affected neurons is important to help unravel the underlying molecular mechanism leading to the diseases. Although differentiation of iPSCs to neural lineage allows acquisition of cell types of interest, the technology suffers from low efficiency leading to low yield of neurons. Here, we investigated the potential of adult neuroprogenitor cells (aNPCs) for iPSC derivation and possible confounders such as cell density of infected NPCs on their subsequent neuronal differentiation potential from reprogrammed cells under isogenic conditions. Characterized hiPSCs of defined cell densities generated from aNPCs were subjected to neuronal differentiation on PA6 stromal cells. The results showed that hiPSC clones obtained from low seeding density (iPSC-aNPC_Low) differentiated less efficiently compared to those from higher density (iPSC-aNPC_High). Our findings might help to further improve the yield and quality of neurons for in vitro modelling of neurodegenerative diseases.

Self-Assembling Scaffolds Supported Long-Term Growth of Human Primed Embryonic Stem Cells and Upregulated Core and Naïve Pluripotent Markers

The maintenance and expansion of human embryonic stem cells (ESCs) in two-dimensional (2-D) culture is technically challenging, requiring routine manipulation and passaging. We developed three-dimensional (3-D) scaffolds to mimic the in vivo microenvironment for stem cell proliferation. The scaffolds were made of two 8-arm polyethylene glycol (PEG) polymers functionalized with thiol (PEG-8-SH) and acrylate (PEG-8-Acr) end groups, which self-assembled via a Michael addition reaction. When primed ESCs (H9 cells) were mixed with PEG polymers, they were encapsulated and grew for an extended period, while maintaining their viability, self-renewal, and differentiation potential both in vitro and in vivo. Three-dimensional (3-D) self-assembling scaffold-grown cells displayed an upregulation of core pluripotency genes, OCT4, NANOG, and SOX2. In addition, the expression of primed markers decreased, while the expression of naïve markers substantially increased. Interestingly, the expression of mechanosensitive genes, YAP and TAZ, was also upregulated. YAP inhibition by Verteporfin abrogated the increased expression of YAP/TAZ as well as core and naïve pluripotent markers. Evidently, the 3-D culture conditions induced the upregulation of makers associated with a naïve state of pluripotency in the primed cells. Overall, our 3-D culture system supported the expansion of a homogenous population of ESCs and should be helpful in advancing their use for cell therapy and regenerative medicine.

The Hippo Pathway Effector TAZ Regulates Ferroptosis in Renal Cell Carcinoma

Despite recent advances, the poor outcomes in renal cell carcinoma (RCC) suggest novel therapeutics are needed. Ferroptosis is a form of regulated cell death, which may have therapeutic potential toward RCC; however, much remains unknown about the determinants of ferroptosis susceptibility. We found that ferroptosis susceptibility is highly influenced by cell density and confluency. Because cell density regulates the Hippo-YAP/TAZ pathway, we investigated the roles of the Hippo pathway effectors in ferroptosis. TAZ is abundantly expressed in RCC and undergoes density-dependent nuclear or cytosolic translocation. TAZ removal confers ferroptosis resistance, whereas overexpression of TAZS89A sensitizes cells to ferroptosis. Furthermore, TAZ regulates the expression of Epithelial Membrane Protein 1 (EMP1), which, in turn, induces the expression of nicotinamide adenine dinucleotide phosphate (NADPH) Oxidase 4 (NOX4), a renal-enriched reactive oxygen species (ROS)-generating enzyme essential for ferroptosis. These findings reveal that cell density-regulated ferroptosis is mediated by TAZ through the regulation of EMP1-NOX4, suggesting its therapeutic potential for RCC and other TAZ-activated tumors.

Effect of inoculum density on human-induced pluripotent stem cell expansion in 3D bioreactors

Objective

For optimized expansion of human‐induced pluripotent stem cells (hiPSCs) with regards to clinical applications, we investigated the influence of the inoculum density on the expansion procedure in 3D hollow‐fibre bioreactors.

Materials and Methods

Analytical‐scale bioreactors with a cell compartment volume of 3 mL or a large‐scale bioreactor with a cell compartment volume of 17 mL were used and inoculated with either 10 × 10⁶ or 50 × 10⁶ hiPSCs. Cells were cultured in bioreactors over 15 days; daily measurements of biochemical parameters were performed. At the end of the experiment, the CellTiter‐Blue^® Assay was used for culture activity evaluation and cell quantification. Also, cell compartment sections were removed for gene expression and immunohistochemistry analysis.

Results

The results revealed significantly higher values for cell metabolism, cell activity and cell yields when using the higher inoculation number, but also a more distinct differentiation. As large inoculation numbers require cost and time‐extensive pre‐expansion, low inoculation numbers may be used preferably for long‐term expansion of hiPSCs. Expansion of hiPSCs in the large‐scale bioreactor led to a successful production of 5.4 × 10⁹ hiPSCs, thereby achieving sufficient cell amounts for clinical applications.

Conclusions

In conclusion, the results show a significant effect of the inoculum density on cell expansion, differentiation and production of hiPSCs, emphasizing the importance of the inoculum density for downstream applications of hiPSCs. Furthermore, the bioreactor technology was successfully applied for controlled and scalable production of hiPSCs for clinical use.

Cell population balance of cardiovascular spheroids derived from human induced pluripotent stem cells

Stem cell-derived cardiomyocytes and vascular cells can be used for a variety of applications such as studying human heart development and modelling human disease in culture. In particular, protocols based on modulation of Wnt signaling were able to produce high quality of cardiomyocytes or vascular cells from human pluripotent stem cells (hPSCs). However, the mechanism behind the development of 3D cardiovascular spheroids into either vascular or cardiac cells has not been well explored. Hippo/Yes-associated protein (YAP) signaling plays important roles in the regulation of organogenesis, but its impact on cardiovascular differentiation has been less evaluated. In this study, the effects of seeding density and a change in YAP signaling on 3D cardiovascular spheroids patterning from hPSCs were evaluated. Compared to 2D culture, 3D cardiovascular spheroids exhibited higher levels of sarcomeric striations and higher length-to-width ratios of α-actinin⁺ cells. The spheroids with high seeding density exhibited more α-actinin⁺ cells and less nuclear YAP expression. The 3D cardiovascular spheroids were also treated with different small molecules, including Rho kinase inhibitor (Y27632), Cytochalasin D, Dasatinib, and Lysophosphatidic acid to modulate YAP localization. Nuclear YAP inhibition resulted in lower expression of active β-catenin, vascular marker, and MRTF, the transcription factor mediated by RhoGTPases. Y27632 also promoted the gene expression of MMP-2/-3 (matrix remodeling) and Notch-1 (Notch signaling). These results should help our understanding of the underlying effects for the efficient patterning of cardiovascular spheroids after mesoderm formation from hPSCs.

Roles of lysophosphatidic acid and sphingosine-1-phosphate in stem cell biology

Stem cells are unique in their ability to self-renew and differentiate into various cell types. Because of these features, stem cells are key to the formation of organisms and play fundamental roles in tissue regeneration and repair. Mechanisms controlling their fate are thus fundamental to the development and homeostasis of tissues and organs. Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are bioactive phospholipids that play a wide range of roles in multiple cell types, during developmental and pathophysiological events. Considerable evidence now demonstrates the potent roles of LPA and S1P in the biology of pluripotent and adult stem cells, from maintenance to repair. Here we review their roles for each main category of stem cells and explore how those effects impact development and physiopathology.

The Suppression of Medium Acidosis Improves the Maintenance and Differentiation of Human Pluripotent Stem Cells at High Density in Defined Cell Culture Medium

Cell density has profound impacts on the cell culture practices of human pluripotent stem cells. The regulation of cell growth, cell death, pluripotency and differentiation converge at high density, but it is largely unknown how different regulatory mechanisms act at this stage. We use a chemically defined medium to systemically examine cellular activities and the impact of medium components in high-density culture. We show that medium acidosis is the main factor that alters cell cycle, gene expression and cellular metabolism at high cell density. The low medium pH leads to inhibition of glucose consumption, cell cycle arrest, and subsequent cell death. At high cell density, the suppression of medium acidosis with sodium bicarbonate (NaHCO₃) significantly increases culture capacity for stem cell survival, derivation, maintenance and differentiation. Our study provides a simple and effective tool to improve stem cell maintenance and applications.

Wnt/Yes-Associated Protein Interactions During Neural Tissue Patterning of Human Induced Pluripotent Stem Cells

Human induced pluripotent stem cells (hiPSCs) have special ability to self-assemble into neural spheroids or mini-brain-like structures. During the self-assembly process, Wnt signaling plays an important role in regional patterning and establishing positional identity of hiPSC-derived neural progenitors. Recently, the role of Wnt signaling in regulating Yes-associated protein (YAP) expression (nuclear or cytoplasmic), the pivotal regulator during organ growth and tissue generation, has attracted increasing interests. However, the interactions between Wnt and YAP expression for neural lineage commitment of hiPSCs remain poorly explored. The objective of this study is to investigate the effects of Wnt signaling and YAP expression on the cellular population in three-dimensional (3D) neural spheroids derived from hiPSCs. In this study, Wnt signaling was activated using CHIR99021 for 3D neural spheroids derived from human iPSK3 cells through embryoid body formation. Our results indicate that Wnt activation induces nuclear localization of YAP and upregulates the expression of HOXB4, the marker for hindbrain/spinal cord. By contrast, the cells exhibit more rostral forebrain neural identity (expression of TBR1) without Wnt activation. Cytochalasin D was then used to induce cytoplasmic YAP and the results showed the decreased HOXB4 expression. In addition, the incorporation of microparticles in the neural spheroids was investigated for the perturbation of neural patterning. This study may indicate the bidirectional interactions of Wnt signaling and YAP expression during neural tissue patterning, which have the significance in neurological disease modeling, drug screening, and neural tissue regeneration.

Mechanobiology of YAP and TAZ in physiology and disease

A growing body of evidence suggests that mechanical signals emanating from the cell's microenvironment are fundamental regulators of cell behaviour. Moreover, at the macroscopic scale, the influence of forces, such as the forces generated by blood flow, muscle contraction, gravity and overall tissue rigidity (for example, inside of a tumour lump), is central to our understanding of physiology and disease pathogenesis. Still, how mechanical cues are sensed and transduced at the molecular level to regulate gene expression has long remained enigmatic. The identification of the transcription factors YAP and TAZ as mechanotransducers started to fill this gap. YAP and TAZ read a broad range of mechanical cues, from shear stress to cell shape and extracellular matrix rigidity, and translate them into cell-specific transcriptional programmes. YAP and TAZ mechanotransduction is critical for driving stem cell behaviour and regeneration, and it sheds new light on the mechanisms by which aberrant cell mechanics is instrumental for the onset of multiple diseases, such as atherosclerosis, fibrosis, pulmonary hypertension, inflammation, muscular dystrophy and cancer.

Effect of YAP Inhibition on Human Leukemia HL-60 Cells

Background: Yes-associated protein (YAP), the nuclear effector of the Hippo pathway, is a candidate oncoprotein and participates in the progression of various malignancies. However, few reports have examined the effect of YAP inhibition in human leukemia HL-60 cells. Methods: We examined the effects of YAP knockdown or inhibition using short hairpin RNA (shRNA) or verteporfin (VP), respectively. Western blot assays were used to determine the expression levels of YAP, Survivin, cyclinD1, PARP, Bcl-2, and Bax. Cell proliferation was assessed using the cell counting kit (CCK-8) assay. Cell cycle progression and apoptosis were evaluated by flow cytometry, and apoptotic cell morphology was observed by Hoechst 33342 staining. Results: Knockdown or inhibition of YAP led to cell cycle arrest at the G0/G1 phase and increased apoptosis, inhibited cell proliferation, increased levels of Bax and cleaved PARP, and decreased levels of PARP, Bcl-2, Survivin, and cyclinD1. Moreover, Hoechst 33342 staining revealed increased cell nuclear fragmentation. Conclusion: Collectively, these results show that inhibition of YAP inhibits proliferation and induces apoptosis in HL-60 cells. Therefore, a novel treatment regime involving genetic or pharmacological inhibition of YAP could be established for acute promyelocytic leukemia.