Signaling network crosstalk in human pluripotent cells: a Smad2/3-regulated switch that controls the balance between self-renewal and differentiation

The Fibrotic Effects of TMAO on Human Renal Fibroblasts Is Mediated by NLRP3, Caspase-1 and the PERK/Akt/mTOR Pathway

Trimethylamine N-oxide (TMAO), a product of gut microbiota metabolism, has previously been shown to be implicated in chronic kidney disease. A high TMAO-containing diet has been found to cause tubulointerstitial renal fibrosis in mice. However, today there are no data linking specific molecular pathways with the effect of TMAO on human renal fibrosis. The aim of this study was to investigate the fibrotic effects of TMAO on renal fibroblasts and to elucidate the molecular pathways involved. We found that TMAO promoted renal fibroblast activation and fibroblast proliferation via the PERK/Akt/mTOR pathway, NLRP3, and caspase-1 signaling. We also found that TMAO increased the total collagen production from renal fibroblasts via the PERK/Akt/mTOR pathway. However, TMAO did not induce fibronectin or TGF-β1 release from renal fibroblasts. We have unraveled that the PERK/Akt/mTOR pathway, NLRP3, and caspase-1 mediates TMAO’s fibrotic effect on human renal fibroblasts. Our results can pave the way for future research to further clarify the molecular mechanism behind TMAO’s effects and to identify novel therapeutic targets in the context of chronic kidney disease.

Oxygen and metabolic reprogramming in the tumor microenvironment influences metastasis homing

Tumor metastasis is the leading cause of cancer mortality, often characterized by abnormal cell growth and invasion to distant organs. The cancer invasion due to epithelial to mesenchymal transition is affected by metabolic and oxygen availability in the tumor-associated micro-environment. A precise alteration in oxygen and metabolic signaling between healthy and metastatic cells is a substantial probe for understanding tumor progression and metastasis. Molecular heterogeneity in the tumor microenvironment help to sustain the metastatic cell growth during their survival shift from low to high metabolic-oxygen-rich sites and reinforces the metastatic events. This review highlighted the crucial role of oxygen and metabolites in metastatic progression and exemplified the role of metabolic rewiring and oxygen availability in cancer cell adaptation. Furthermore, we have also addressed potential applications of altered oxygen and metabolic networking with tumor type that could be a signature pattern to assess tumor growth and chemotherapeutics efficacy in managing cancer metastasis.

Sulfarotene, a synthetic retinoid, overcomes stemness and sorafenib resistance of hepatocellular carcinoma via suppressing SOS2-RAS pathway

BACKGROUND

Recurrent hepatocellular carcinoma (HCC) shows strong resistance to sorafenib, and the tumor-repopulating cells (TRCs) with cancer stem cell-like properties are considered a driver for its high recurrent rate and drug resistance.

METHODS

Suppression of TRCs may thus be an effective therapeutic strategy for treating this fatal disease. We evaluated the pharmacology and mechanism of sulfarotene, a new type of synthetic retinoid, on the cancer stem cell-like properties of HCC TRCs, and assessed its preclinical efficacy in models of HCC patient-derived xenografts (PDXs).

RESULTS

Sulfarotene selectively inhibited the growth of HCC TRCs in vitro and significantly deterred TRC-mediated tumor formation and lung metastasis in vivo without apparent toxicity, with an IC₅₀ superior to that of acyclic retinoid and sorafenib, to which the recurrent HCC exhibits significant resistance at advanced stage. Sulfarotene promoted the expression and activation of RARα, which down-regulated SOS2, a key signal mediator associated with RAS activation and signal transduction involved in multiple downstream pathways. Moreover, sulfarotene selectively inhibited tumorigenesis of HCC PDXs with high expression for SOS2.

CONCLUSIONS

Our study identified sulfarotene as a selective inhibitor for the TRCs of HCC, which targets a novel RARα-SOS2-RAS signal nexus, shedding light on a new, promising strategy of target therapy for advanced liver cancer.

Disruption of RING and PHD Domains of TRIM28 Evokes Differentiation in Human iPSCs

TRIM28, a multi-domain protein, is crucial in the development of mouse embryos and the maintenance of embryonic stem cells’ (ESC) self-renewal potential. As the epigenetic factor modulating chromatin structure, TRIM28 regulates the expression of numerous genes and is associated with progression and poor prognosis in many types of cancer. Because of many similarities between highly dedifferentiated cancer cells and normal pluripotent stem cells, we applied human induced pluripotent stem cells (hiPSC) as a model for stemness studies. For the first time in hiPSC, we analyzed the function of individual TRIM28 domains. Here we demonstrate the essential role of a really interesting new gene (RING) domain and plant homeodomain (PHD) in regulating pluripotency maintenance and self-renewal capacity of hiPSC. Our data indicate that mutation within the RING or PHD domain leads to the loss of stem cell phenotypes and downregulation of the FGF signaling. Moreover, impairment of RING or PHD domain results in decreased proliferation and impedes embryoid body formation. In opposition to previous data indicating the impact of phosphorylation on TRIM28 function, our data suggest that TRIM28 phosphorylation does not significantly affect the pluripotency and self-renewal maintenance of hiPSC. Of note, iPSC with disrupted RING and PHD functions display downregulation of genes associated with tumor metastasis, which are considered important targets in cancer treatment. Our data suggest the potential use of RING and PHD domains of TRIM28 as targets in cancer therapy.

Discovering the role of VEGF signaling pathway in mesendodermal induction of human embryonic stem cells

Human embryonic stem cells (hESCs) have the unique feature of unlimited self-renewal and differentiation into derivatives of all three germ layers in human body, providing a powerful in vitro model for studying cell differentiation. FGF2, BMP4 and TGF-β signaling have been shown to play crucial roles in mesendodermal differentiation of hESCs. However, their underlying molecular mechanisms and other signaling pathways potentially involved in mesendodermal differentiation of hESCs remain to be further investigated. In this study, we uncover that VEGF signaling pathway plays a critical role in the mesendodermal induction of hESCs. Treating hESCs with Lenvatinib, a pan-inhibitor of VEGF receptors (VEGFRs), impedes their mesendodermal induction. Conversely, overexpression of VEGFA165, a major human VEGF isoform, promotes the mesendodermal differentiation. Similar to the VEGFR inhibitor, MEK inhibitor PD0325901 hinders mesendodermal induction of hESCs. In contrast, overexpression of ERK2^GOF, an intrinsically active ERK2 mutant, markedly reduces the inhibitory effect of the VEGFR inhibitor. Thus, the MEK-ERK cascade plays an important role for the function of VEGF signaling pathway in the mesendodermal induction of hESCs. All together, this study identifies the critical role of VEGF signaling pathway as well as potential crosstalk of VEGF signaling pathway with other known signaling pathways in mesendodermal differentiation of hESCs.

Endogenous suppression of WNT signalling in human embryonic stem cells leads to low differentiation propensity towards definitive endoderm

Low differentiation propensity towards a targeted lineage can significantly hamper the utility of individual human pluripotent stem cell (hPSC) lines in biomedical applications. Here, we use monolayer and micropatterned cell cultures, as well as transcriptomic profiling, to investigate how variability in signalling pathway activity between human embryonic stem cell lines affects their differentiation efficiency towards definitive endoderm (DE). We show that endogenous suppression of WNT signalling in hPSCs at the onset of differentiation prevents the switch from self-renewal to DE specification. Gene expression profiling reveals that this inefficient switch is reflected in NANOG expression dynamics. Importantly, we demonstrate that higher WNT stimulation or inhibition of the PI3K/AKT signalling can overcome the DE commitment blockage. Our findings highlight that redirection of the activity of Activin/NODAL pathway by WNT signalling towards mediating DE fate specification is a vulnerable spot, as disruption of this process can result in poor hPSC specification towards DE.

Defective insulin receptor signaling in hPSCs skews pluripotency and negatively perturbs neural differentiation

Human embryonic stem cells are a type of pluripotent stem cells (hPSCs) that are used to investigate their differentiation into diverse mature cell types for molecular studies. The mechanisms underlying insulin receptor (IR)-mediated signaling in the maintenance of human pluripotent stem cell (hPSC) identity and cell fate specification are not fully understood. Here, we used two independent shRNAs to stably knock down IRs in two hPSC lines that represent pluripotent stem cells and explored the consequences on expression of key proteins in pathways linked to proliferation and differentiation. We consistently observed lowered pAKT in contrast to increased pERK1/2 and a concordant elevation in pluripotency gene expression. ERK2 chromatin immunoprecipitation, luciferase assays, and ERK1/2 inhibitors established direct causality between ERK1/2 and OCT4 expression. Of importance, RNA sequencing analyses indicated a dysregulation of genes involved in cell differentiation and organismal development. Mass spectrometry–based proteomic analyses further confirmed a global downregulation of extracellular matrix proteins. Subsequent differentiation toward the neural lineage reflected alterations in SOX1⁺PAX6⁺ neuroectoderm and FOXG1⁺ cortical neuron marker expression and protein localization. Collectively, our data underscore the role of IR-mediated signaling in maintaining pluripotency, the extracellular matrix necessary for the stem cell niche, and regulating cell fate specification including the neural lineage.

Both Hypoxia-Inducible Factor 1 and MAPK Signaling Pathway Attenuate PI3K/AKT via Suppression of Reactive Oxygen Species in Human Pluripotent Stem Cells

Mild hypoxia (5% O₂) as well as FGFR1-induced activation of phosphatidylinositol-4,5-bisphosphate 3-kinase/protein kinase B (PI3K/AKT) and MAPK signaling pathways markedly support pluripotency in human pluripotent stem cells (hPSCs). This study demonstrates that the pluripotency-promoting PI3K/AKT signaling pathway is surprisingly attenuated in mild hypoxia compared to the 21% O₂ environment. Hypoxia is known to be associated with lower levels of reactive oxygen species (ROS), which are recognized as intracellular second messengers capable of upregulating the PI3K/AKT signaling pathway. Our data denote that ROS downregulation results in pluripotency upregulation and PI3K/AKT attenuation in a hypoxia-inducible factor 1 (HIF-1)-dependent manner in hPSCs. Using specific MAPK inhibitors, we show that the MAPK pathway also downregulates ROS and therefore attenuates the PI3K/AKT signaling—this represents a novel interaction between these signaling pathways. This inhibition of ROS initiated by MEK1/2–ERK1/2 may serve as a negative feedback loop from the MAPK pathway toward FGFR1 and PI3K/AKT activation. We further describe the molecular mechanism resulting in PI3K/AKT upregulation in hPSCs—ROS inhibit the PI3K's primary antagonist PTEN and upregulate FGFR1 phosphorylation. These novel regulatory circuits utilizing ROS as second messengers may contribute to the development of enhanced cultivation and differentiation protocols for hPSCs. Since the PI3K/AKT pathway often undergoes an oncogenic transformation, our data could also provide new insights into the regulation of cancer stem cell signaling.

Targeting transforming growth factor-β signaling for enhanced cancer chemotherapy

During the past decades, drugs targeting transforming growth factor-β (TGFβ) signaling have received tremendous attention for late-stage cancer treatment since TGFβ signaling has been recognized as a prime driver for tumor progression and metastasis. Nonetheless, in healthy and pre-malignant tissues, TGFβ functions as a potent tumor suppressor. Furthermore, TGFβ signaling plays a key role in normal development and homeostasis by regulating cell proliferation, differentiation, migration, apoptosis, and immune evasion, and by suppressing tumor-associated inflammation. Therefore, targeting TGFβ signaling for cancer therapy is challenging. Recently, we and others showed that blocking TGFβ signaling increased chemotherapy efficacy, particularly for nanomedicines. In this review, we briefly introduce the TGFβ signaling pathway, and the multifaceted functions of TGFβ signaling in cancer, including regulating the tumor microenvironment (TME) and the behavior of cancer cells. We also summarize TGFβ targeting agents. Then, we highlight TGFβ inhibition strategies to restore the extracellular matrix (ECM), regulate the tumor vasculature, reverse epithelial-mesenchymal transition (EMT), and impair the stemness of cancer stem-like cells (CSCs) to enhance cancer chemotherapy efficacy. Finally, the current challenges and future opportunities in targeting TGFβ signaling for cancer therapy are discussed.

Combined transcriptomic and phosphoproteomic analysis of BMP4 signaling in human embryonic stem cells

Human embryonic stem cells (hESCs) are an invaluable tool in the fields of embryology and regenerative medicine. Activin A and BMP4 are well-characterised growth factors implicated in pluripotency and differentiation. In the current study, hESCs are cultured in a modified version of mTeSR1, where low concentrations of ActivinA substitute for TGFβ. This culture system is further used to investigate the changes induced by BMP4 on hESCs by employing a combination of transcriptomic and phosphoproteomic approaches. Results indicate that in a pluripotent state, hESCs maintain WNT signaling under negative regulation by expressing pathway inhibitors. Initial stages of differentiation are characterized by upregulation of WNT pathway ligands, TGFβ pathway inhibitors which have been shown in Xenopus to expand the BMP signaling range essential for embryonic patterning, and mesendodermal transcripts. Moreover, BMP4 enhances the phosphorylation of proteins associated with migration and transcriptional regulation. Results further indicate the vital regulatory role of Activin A and BMP4 in crucial fate decisions in hESCs.

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

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

Inhibition of protein kinase D by CID755673 promotes maintenance of the pluripotency of embryonic stem cells

The identification of novel mechanisms to maintain embryonic stem cell (ESC) pluripotency is of crucial importance, because the currently used culture conditions are not suitable for ESCs from all species. In this study, we show that the protein kinase D (PKD) inhibitor CID755673 (CID) is able to maintain the undifferentiated state of mouse ESCs in combination with the mitogen-activated protein kinase kinase (MEK) inhibitor. The expression levels of PKD members, including PKD1, PKD2 and PKD3, were low in mouse ESCs but significantly increased under differentiation conditions. Therefore, depletion of three PKD genes was able to phenocopy PKD inhibition. Mechanistically, PKD inhibition activated PI3K/AKT signaling by increasing the level of AKT phosphorylation, and the addition of a PI3K/AKT signaling pathway inhibitor partially reduced the cellular response to PKD inhibition. Importantly, the self-renewal-promoting effect of CID was maintained in human ESCs. Simultaneous knockdown of the three human PKD isoforms enabled short-term self-renewal in human ESCs, whereas PI3K/AKT signaling inhibition eliminated this self-renewal ability downstream of the PKD inhibitor. These findings expand our understanding of the gene regulatory network of ESC pluripotency.

The Role of SMAD2/3 in Human Embryonic Stem Cells

Human embryonic stem cells (hESCs) possess the potential of long-term self-renewal and three primary germ layers differentiation, and thus hESCs are expected to have broad applications in cell therapy, drug screening and basic research on human early embryonic development. Many efforts have been put to dissect the regulation of pluripotency and direct differentiation of hESCs. TGFβ/Activin/Nodal signal pathway critically regulates pluripotency maintenance and cell differentiation through the main signal transducer SMAD2/3 in hESCs, but the action manners of SMAD2/3 in hESCs are sophisticated and not documented yet. Here we review and discuss the roles of SMAD2/3 in hESC pluripotency maintenance and differentiation initiation separately. We summarize that SMAD2/3 regulates pluripotency and differentiation mainly through four aspects, (1) controlling divergent transcriptional networks of pluripotency and differentiation; (2) interacting with chromatin modifiers to make the chromatin accessible or recruiting METTL3-METTL14-WTAP complex and depositing m6A to the mRNA of pluripotency genes; (3) acting as a transcription factor to activate endoderm-specific genes to thus initiate definitive endoderm differentiation, which happens as cyclin D/CDK4/6 downstream target in later G1 phase as well; (4) interacting with endoderm specific lncRNAs to promote differentiation.

CXCL14 Maintains hESC Self-Renewal through Binding to IGF-1R and Activation of the IGF-1R Pathway

Human embryonic stem cells (hESCs) have important roles in regenerative medicine, but only a few studies have investigated the cytokines secreted by hESCs. We screened and identified chemokine (C-X-C motif) ligand 14 (CXCL14), which plays crucial roles in hESC renewal. CXCL14, a C-X-C motif chemokine, is also named as breast and kidney-expressed chemokine (BRAK), B cell and monocyte-activated chemokine (BMAC), and macrophage inflammatory protein-2γ (MIP-2γ). Knockdown of CXCL14 disrupted the hESC self-renewal, changed cell cycle distribution, and further increased the expression levels of mesoderm and endoderm differentiated markers. Interestingly, we demonstrated that CXCL14 is the ligand for the insulin-like growth factor 1 receptor (IGF-1R), and it can activate IGF-1R signal transduction to support hESC renewal. Currently published literature indicates that all receptors in the CXCL family are G protein-coupled receptors (GPCRs). This report is the first to demonstrate that a CXCL protein can bind to and activate a receptor tyrosine kinase (RTK), and also the first to show that IGF-1R has another ligand in addition to IGFs. These findings broaden our understanding of stem cell biology and signal transduction.

Signaling Inhibitors Accelerate the Conversion of mouse iPS Cells into Cancer Stem Cells in the Tumor Microenvironment

Cancer stem cells (CSCs) are a class of cancer cells characterized by self-renewal, differentiation and tumorigenic potential. We previously established a model of CSCs by culturing mouse induced pluripotent stem cells (miPSCs) for four weeks in the presence of a conditioned medium (CM) of cancer cell lines, which functioned as the tumor microenvironment. Based on this methodology of developing CSCs from miPSCs, we assessed the risk of 110 non-mutagenic chemical compounds, most of which are known as inhibitors of cytoplasmic signaling pathways, as potential carcinogens. We treated miPSCs with each compound for one week in the presence of a CM of Lewis lung carcinoma (LLC) cells. However, one-week period was too short for the CM to convert miPSCs into CSCs. Consequently, PDO325901 (MEK inhibitor), CHIR99021 (GSK-3β inhibitor) and Dasatinib (Abl, Src and c-Kit inhibitor) were found to confer miPSCs with the CSC phenotype in one week. The tumor cells that survived exhibited stemness markers, spheroid formation and tumorigenesis in Balb/c nude mice. Hence, we concluded that the three signal inhibitors accelerated the conversion of miPSCs into CSCs. Similarly to our previous study, we found that the PI3K-Akt signaling pathway was upregulated in the CSCs. Herein, we focused on the expression of relative genes after the treatment with these three inhibitors. Our results demonstrated an increased expression of pik3ca, pik3cb, pik3r5 and pik3r1 genes indicating class IA PI3K as the responsible signaling pathway. Hence, AKT phosphorylation was found to be up-regulated in the obtained CSCs. Inhibition of Erk1/2, tyrosine kinase, and/or GSK-3β was implied to be involved in the enhancement of the PI3K-AKT signaling pathway in the undifferentiated cells, resulting in the sustained stemness, and subsequent conversion of miPSCs into CSCs in the tumor microenvironment.

SHP2 mutations induce precocious gliogenesis of Noonan syndrome-derived iPSCs during neural development in vitro

Background

Noonan syndrome (NS) is a developmental disorder caused by mutations of Src homology 2 domain-containing protein tyrosine phosphatase 2 (SHP2). Although NS patients have diverse neurological manifestations, the mechanisms underlying the involvement of SHP2 mutations in neurological dysfunction remain elusive.

Methods

Induced pluripotent stem cells generated from dermal fibroblasts of three NS-patients (NS-iPSCs) differentiated to the neural cells by using two different culture systems, 2D- and 3D-cultured systems in vitro.

Results

Here we represent that SHP2 mutations cause aberrant neural development. The NS-iPSCs exhibited impaired development of EBs in which BMP and TGF-β signalings were activated. Defective early neuroectodermal development of NS-iPSCs recovered by inhibition of both signalings and further differentiated into NPCs. Intriguingly, neural cells developed from NS-NPCs exhibited abundancy of the glial cells, neurites of neuronal cells, and low electrophysiological property. Those aberrant phenotypes were also detected in NS-cerebral organoids. SHP2 inhibition in the NS-NPCs and NS-cerebral organoids ameliorated those anomalies such as biased glial differentiation and low neural activity.

Conclusion

Our findings demonstrate that SHP2 mutations contribute to precocious gliogenesis in NS-iPSCs during neural development in vitro.

Human beige adipocytes for drug discovery and cell therapy in metabolic diseases

Human beige adipocytes (BAs) have potential utility for the development of therapeutics to treat diabetes and obesity-associated diseases. Although several reports have described the generation of beige adipocytes in vitro, their potential utility in cell therapy and drug discovery has not been reported. Here, we describe the generation of BAs from human adipose-derived stem/stromal cells (ADSCs) in serum-free medium with efficiencies >90%. Molecular profiling of beige adipocytes shows them to be similar to primary BAs isolated from human tissue. In vitro, beige adipocytes exhibit uncoupled mitochondrial respiration and cAMP-induced lipolytic activity. Following transplantation, BAs increase whole-body energy expenditure and oxygen consumption, while reducing body-weight in recipient mice. Finally, we show the therapeutic utility of BAs in a platform for high-throughput drug screening (HTS). These findings demonstrate the potential utility of BAs as a cell therapeutic and as a tool for the identification of drugs to treat metabolic diseases.

Methods to generate beige adipocytes from a human cell source are inefficient. Here, the authors present a protocol that efficiently generates beige adipocytes from human adipose-derived stem cells (ADSCs), which have potential utility in therapeutic development relating to metabolic diseases such as type 2 diabetes.

WNT signalling supported by MEK/ERK inhibition is essential to maintain pluripotency in bovine preimplantation embryo

Capturing stable embryonic stem cell (ESC) lines from domesticated animals still remains one of the challenges of non-rodent embryology. The stake is high, as stable ESCs derived from species such as cattle present high economic and scientific value. Understanding of the processes leading to the embryonic lineage segregation is crucial to provide species-orientated molecular environment capable of supporting self-renewal and pluripotency. Therefore, the aim of this study was to validate the action of the two core regulatory pathways (WNT and MEK/ERK) during bovine embryo development. In vitro produced bovine embryos were obtained in the presence of inhibitors (i), which enable activation of the WNT pathway (via GSK3i, CHIR99021) and suppression of MEK signalling by PD0325901 in the 2i system and PD184325 and SU5402 in the 3i system. We have followed the changes in the distribution of the key lineage specific markers both at the transcript and protein level. Our results showed that WNT signalling promotes the expression of key inner cell mass (ICM) specific markers in bovine embryos, regardless of the MEK/ERK inhibitor cocktail used. MEK/ERK downregulation is crucial to maintain OCT4 and NANOG expression within the ICM and to prevent their exclusion from the trophectoderm (TE). At the same time, the classical TE marker (CDX2) was downregulated at the mRNA and protein level. As a follow up for the observed pluripotency stimulating effect of the inhibitors, we have tested the potential of the 2i and the 3i culture conditions (supported by LIF) to derive primary bovine ESC lines. As a result, we propose a model in which all of the primary signalling pathways determining embryonic cell fate are active in bovine embryos, yet the requirement for pluripotency maintenance in cattle may differ from the described standards. WNT activation leads to the formation (and stabilisation of the ICM) and MEK/ERK signalling is maintained at low levels. Unlike in the mouse, GATA6 is expressed in both ICM and TE. MEK/ERK signalling affects HP formation in cattle, but this process is activated at the post-blastocyst stage. With regard to self-renewal, 2i is preferable, as 3i also blocks the FGF receptor, what may prevent PI3K signalling, important for pluripotency and self-renewal.

Derivation of induced pluripotent stem cells from ferret somatic cells

Ferrets are an attractive mammalian model for several diseases, especially those affecting the lungs, liver, brain, and kidneys. Many chronic human diseases have been difficult to model in rodents due to differences in size and cellular anatomy. This is particularly the case for the lung, where ferrets provide an attractive mammalian model of both acute and chronic lung diseases, such as influenza, cystic fibrosis, A1A emphysema, and obliterative bronchiolitis, closely recapitulating disease pathogenesis, as it occurs in humans. As such, ferrets have the potential to be a valuable preclinical model for the evaluation of cell-based therapies for lung regeneration and, likely, for other tissues. Induced pluripotent stem cells (iPSCs) provide a great option for provision of enough autologous cells to make patient-specific cell therapies a reality. Unfortunately, they have not been successfully created from ferrets. In this study, we demonstrate the generation of ferret iPSCs that reflect the primed pluripotent state of human iPSCs. Ferret fetal fibroblasts were reprogrammed and acquired core features of pluripotency, having the capacity for self-renewal, multilineage differentiation, and a high-level expression of the core pluripotency genes and pathways at both the transcriptional and protein level. In conclusion, we have generated ferret pluripotent stem cells that provide an opportunity for advancing our capacity to evaluate autologous cell engraftment in ferrets.

The Solo Play of TERT Promoter Mutations

The reactivation of telomerase reverse transcriptase (TERT) protein is the principal mechanism of telomere maintenance in cancer cells. Mutations in the TERT promoter (TERTp) are a common mechanism of TERT reactivation in many solid cancers, particularly those originating from slow-replicating tissues. They are associated with increased TERT levels, telomere stabilization, and cell immortalization and proliferation. Much effort has been invested in recent years in characterizing their prevalence in different cancers and their potential as biomarkers for tumor stratification, as well as assessing their molecular mechanism of action, but much remains to be understood. Notably, they appear late in cell transformation and are mutually exclusive with each other as well as with other telomere maintenance mechanisms, indicative of overlapping selective advantages and of a strict regulation of TERT expression levels. In this review, we summarized the latest literature on the role and prevalence of TERTp mutations across different cancer types, highlighting their biased distribution. We then discussed the need to maintain TERT levels at sufficient levels to immortalize cells and promote proliferation while remaining within cell sustainability levels. A better understanding of TERT regulation is crucial when considering its use as a possible target in antitumor strategies.

Yes-Associated Protein and PDZ Binding Motif: A Critical Signaling Pathway in the Control of Human Pluripotent Stem Cells Self-Renewal and Differentiation

Human pluripotent stem cells (hPSCs) can self-renew indefinitely to generate cells like themselves with a normal karyotype and differentiate into other types of cells when stimulated with a proper set of internal and external signals. hPSCs including human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) are an alternative approach toward stem cell biology, drug discovery, disease modeling, and regenerative medicine. hESCs are commonly derived from the inner cell mass of preimplantation embryos and can maintain their pluripotency in appropriate culture media. The Hippo pathway is a major integrator of cell surface-mediated signals and plays an essential role in regulating hESCs function. Yes-associated protein (YAP) and TAZ (PDZ binding motif) are critical downstream transcriptional coactivators in the Hippo pathway. The culture conditions have effects on the cytoplasmic or nuclear YAP/TAZ localization. Also, the activity of Hippo pathway is influenced by cell density, mechanical tension, and biochemical signals. In this review article, we summarize the function of YAP/TAZ and focus on the regulation of YAP/TAZ in self-renewal and differentiation of hESCs.

PI3K in stemness regulation: from development to cancer

The PI3K/AKT pathway is a key target in oncology where most efforts are focussed on phenotypes such as cell proliferation and survival. Comparatively, little attention has been paid to PI3K in stemness regulation, despite the emerging link between acquisition of stem cell-like features and therapeutic failure in cancer. The aim of this review is to summarise current known and unknowns of PI3K-dependent stemness regulation, by integrating knowledge from the fields of developmental, signalling and cancer biology. Particular attention is given to the role of the PI3K pathway in pluripotent stem cells (PSCs) and the emerging parallels to dedifferentiated cancer cells with stem cell-like features. Compelling evidence suggests that PI3K/AKT signalling forms part of a 'core molecular stemness programme' in both mouse and human PSCs. In cancer, the oncogenic PIK3CAH1047R variant causes constitutive activation of the PI3K pathway and has recently been linked to increased stemness in a dose-dependent manner, similar to observations in mouse PSCs with heterozygous versus homozygous Pten loss. There is also evidence that the stemness phenotype may become 'locked' and thus independent of the original PI3K activation, posing limitations for the success of PI3K monotherapy in cancer. Ongoing therapeutic developments for PI3K-associated cancers may therefore benefit from a better understanding of the pathway's two-layered and highly context-dependent regulation of cell growth versus stemness.

FGF Signaling Pathway: A Key Regulator of Stem Cell Pluripotency

Pluripotent stem cells (PSCs) isolated in vitro from embryonic stem cells (ESCs), induced PSC (iPSC) and also post-implantation epiblast-derived stem cells (EpiSCs) are known for their two unique characteristics: the ability to give rise to all somatic lineages and the self-renewal capacity. Numerous intrinsic signaling pathways contribute to the maintenance of the pluripotency state of stem cells by tightly controlling key transcriptional regulators of stemness including sex determining region Y box 2 (Sox-2), octamer-binding transcription factor (Oct)3/4, krueppel-like factor 4 (Klf-4), Nanog, and c-Myc. Signaling by fibroblast growth factor (FGF) is of critical importance in regulating stem cells pluripotency. The FGF family is comprised of 22 ligands that interact with four FGF receptors (FGFRs). FGF/FGFR signaling governs fundamental cellular processes such as cell survival, proliferation, migration, differentiation, embryonic development, organogenesis, tissue repair/regeneration, and metabolism. FGF signaling is mediated by the activation of RAS - mitogen-activated protein kinase (MAPK), phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)-AKT, Phospholipase C Gamma (PLCγ), and signal transducers and activators of transcription (STAT), which intersects and synergizes with other signaling pathways such as Wnt, retinoic acid (RA) and transforming growth factor (TGF)-β signaling. In the current review, we summarize the role of FGF signaling in the maintenance of pluripotency state of stem cells through regulation of key transcriptional factors.

A cytokine screen using CRISPR-Cas9 knock-in reporter pig iPS cells reveals that Activin A regulates NANOG

BACKGROUND

NANOG functions as the gateway for the generation of pluripotent stem cells (PSCs) in mice and humans. NANOG is a transcription factor highly expressed in pig pre-implantation embryos, indicating that it is a conserved pluripotency-associated factor. However, pig NANOG reporter PSCs have yet to be established, and the regulation of pluripotency by NANOG is not fully understood in this animal.

METHODS

In this study, pig NANOG tdTomato knock-in reporter positive PC-iPS cells were established using CRISPR/Cas9. The resulting cell line was treated with several cytokines and their corresponding inhibitors to identify pathways that regulate NANOG expression. The pathways examined were LIF (leukemia inhibitory factor)/IL6 (interleukin 6)-STAT3, FGF (fibroblast growth factor)/ERK, IGF1 (insulin-like growth factor 1)/PIP3 (phosphoinositide 3-kinase)-AKT, Activin A/SMAD, and BMP4 (bone morphogenetic proteins)/SMAD.

RESULTS

Our experiments showed that the Activin A/SMAD pathway is directly associated with activation of NANOG expression in the pig, as is also the case in mice and humans. Activin A directly regulates the expression of pig NANOG via SMAD2/3; inhibition of this pathway by SB431542 resulted in inhibition of NANOG expression.

CONCLUSIONS

Our results show that Activin A plays an important regulatory role in NANOG-mediated pluripotency in pig iPS cells. Activin A treatment may be therefore an effective method for de novo derivation of authentic embryonic stem cells (ESCs) from pig pre-implantation embryos.

Negligible-Cost and Weekend-Free Chemically Defined Human iPSC Culture

Human induced pluripotent stem cell (hiPSC) culture has become routine, yet the cost of pluripotent cell media, frequent medium changes, and the reproducibility of differentiation have remained restrictive. Here, we describe the formulation of a hiPSC culture medium (B8) as a result of the exhaustive optimization of medium constituents and concentrations, establishing the necessity and relative contributions of each component to the pluripotent state and cell proliferation. The reagents in B8 represent only 3% of the costs of commercial media, made possible primarily by the in-lab generation of three E. coli-expressed, codon-optimized recombinant proteins: fibroblast growth factor 2, transforming growth factor β3, and neuregulin 1. We demonstrate the derivation and culture of 34 hiPSC lines in B8 as well as the maintenance of pluripotency long term (over 100 passages). This formula also allows a weekend-free feeding schedule without sacrificing capacity for differentiation.

IGF1-mediated human embryonic stem cell self-renewal recapitulates the embryonic niche

Our understanding of the signalling pathways regulating early human development is limited, despite their fundamental biological importance. Here, we mine transcriptomics datasets to investigate signalling in the human embryo and identify expression for the insulin and insulin growth factor 1 (IGF1) receptors, along with IGF1 ligand. Consequently, we generate a minimal chemically-defined culture medium in which IGF1 together with Activin maintain self-renewal in the absence of fibroblast growth factor (FGF) signalling. Under these conditions, we derive several pluripotent stem cell lines that express pluripotency-associated genes, retain high viability and a normal karyotype, and can be genetically modified or differentiated into multiple cell lineages. We also identify active phosphoinositide 3-kinase (PI3K)/AKT/mTOR signalling in early human embryos, and in both primed and naïve pluripotent culture conditions. This demonstrates that signalling insights from human blastocysts can be used to define culture conditions that more closely recapitulate the embryonic niche.

Inhibition Of Glycogen Synthase Kinase 3 Beta Suppresses The Growth And Survival Of Skull Base Chordoma Cells By Downregulating Brachyury Expression

Purpose

Chordomas are locally aggressive tumors arising from notochordal remnants. Brachyury, a protein coded by T-gene, is crucial for chordoma cell proliferation. The aim of this study was to evaluate the effects of glycogen synthase kinase 3 beta (GSK3β) activity on brachyury expression and on the growth and survival of skull base chordoma cells.

Patients and methods

In this study, 16 paraffin-embedded specimens of primary skull base chordomas were analyzed for the expression of phosphorylated GSK3β and brachyury using immunohistochemistry. The UM-Chor1 cell line derived from a clival chordoma was treated with AR-A014418 (AR), an inhibitor of GSK3β, and brachyury expression was analyzed by qRT-PCR and Western blotting. The possible mechanism by which brachyury regulates the Wnt/β-catenin signaling pathway was investigated by immunocytochemistry. The effects of AR on cell proliferation as well as sensitivity to chemotherapeutic drugs were also examined.

Results

The results suggested that phosphorylated GSK3β and brachyury were upregulated in chordoma tissues. The GSK3β inhibitor (AR) decreased brachyury expression and suppressed the growth and survival of the chordoma cells, possibly via regulation of the Wnt/β-catenin signaling pathway. Moreover, AR increased the sensitivity of chordoma cells to chemotherapeutic drugs in vitro.

Conclusion

This study provides evidence for the clinical development of the GSK3β inhibitor (AR-A014418) as a potential chemotherapeutic adjuvant for the treatment of chordoma.

TGFβ Family Signaling Pathways in Pluripotent and Teratocarcinoma Stem Cells' Fate Decisions: Balancing Between Self-Renewal, Differentiation, and Cancer

The transforming growth factor-β (TGFβ) family factors induce pleiotropic effects and are involved in the regulation of most normal and pathological cellular processes. The activity of different branches of the TGFβ family signaling pathways and their interplay with other signaling pathways govern the fine regulation of the self-renewal, differentiation onset and specialization of pluripotent stem cells in various cell derivatives. TGFβ family signaling pathways play a pivotal role in balancing basic cellular processes in pluripotent stem cells and their derivatives, although disturbances in their genome integrity induce the rearrangements of signaling pathways and lead to functional impairments and malignant transformation into cancer stem cells. Therefore, the identification of critical nodes and targets in the regulatory cascades of TGFβ family factors and other signaling pathways, and analysis of the rearrangements of the signal regulatory network during stem cell state transitions and interconversions, are key issues for understanding the fundamental mechanisms of both stem cell biology and cancer initiation and progression, as well as for clinical applications. This review summarizes recent advances in our understanding of TGFβ family functions in naїve and primed pluripotent stem cells and discusses how these pathways are involved in perturbations in the signaling network of malignant teratocarcinoma stem cells with impaired differentiation potential.

Adenomatous Polyposis Coli as a Major Regulator of Human Embryonic Stem Cells Self-Renewal

Human embryonic stem cells (hESCs) provide an essential tool to investigate early human development, study disease pathogenesis, and examine therapeutic interventions. Adenomatous polyposis coli (APC) is a negative regulator of Wnt/β-catenin signaling, implicated in the majority of sporadic colorectal cancers and in the autosomal dominant inherited syndrome familial adenomatous polyposis (FAP). Studies into the role of Wnt/β-catenin signaling in hESCs arrived at conflicting results, due at least in part to variations in culture conditions and the use of external inhibitors and agonists. Here, we directly targeted APC in hESCs carrying a germline APC mutation, derived from affected blastocysts following preimplantation genetic diagnosis (PGD) for FAP, in order to answer open questions regarding the role of APC in regulating pluripotency and differentiation potential of hESCs. Using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9), we generated second hit APC mutations in FAP-hESCs. Despite high CRISPR/Cas9 targeting efficiency and the successful isolation of many clones, none of the isolated clones carried a loss of function mutation in the wild-type (WT) APC allele. Using a fluorescent β-catenin reporter and analysis of mutated-allele frequencies in the APC locus, we show that APC double mutant hESCs robustly activate Wnt/β-catenin signaling that results in rapid differentiation to endodermal and mesodermal lineages. Here, we provide direct evidence for a strict requirement for constant β-catenin degradation through the APC destruction complex in order to maintain pluripotency, highlighting a fundamental role for APC in self-renewal of hESCs. Stem Cells 2019;37:1505-1515.

CDK11 safeguards the identity of human embryonic stem cells via fine-tuning signaling pathways

Signaling pathways transmit extracellular cues into cells and regulate transcriptome and epigenome to maintain or change the cell identity. Protein kinases and phosphatases are critical for signaling transduction and regulation. Here, we report that CDK11, a member of the CDK family, is required for the maintenance of human embryonic stem cell (hESC) self-renewal. Our results show that, among the three main isoforms of CDK11, CDK11^p46 is the main isoform safeguarding the hESC identity. Mechanistically, CDK11 constrains two important mitogen-activated protein kinase (MAPK) signaling pathways (JNK and p38 signaling) through modulating the activity of protein phosphatase 1. Furthermore, CDK11 knockdown activates transforming growth factor β (TGF-β)/SMAD2/3 signaling and upregulates certain nonneural differentiation-associated genes. Taken together, this study uncovers a kinase required for hESC self-renewal through fine-tuning MAPK and TGF-β signaling at appropriate levels. The kinase-phosphatase axis reported here may shed new light on the molecular mechanism sustaining the identity of hESCs.

Defining early hematopoietic-fated primitive streak specification of human pluripotent stem cells by the orchestrated balance of Wnt, activin, and BMP signaling

Distinct regions of the primitive streak (PS) have diverse potential to differentiate into several tissues, including the hematopoietic lineage originated from the posterior region of PS. Although various signaling pathways have been identified to promote the development of PS and its mesoderm derivatives, there is a large gap in our understanding of signaling pathways that regulate the hematopoietic fate of PS. Here, we defined the roles of Wnt, activin, and bone morphogenetic protein (BMP) signaling pathways in generating hematopoietic-fated PS from human pluripotent stem cells (hPSCs). We found that the synergistic balance of these signaling pathways was crucial for controlling the PS fate determination towards hematopoietic lineage via mesodermal progenitors. Although the induction of PS depends largely on the Wnt and activin signaling, the PS generated without BMP4 lacks the hematopoietic potential, indicating that the BMP signaling is necessary for the PS to acquire hematopoietic property. Appropriate levels of Wnt signaling is crucial for the development of PS and its specification to the hematopoietic lineage. Although the development of PS is less sensitive to activin or BMP signaling, the fate of PS to mesoderm progenitors and subsequent hematopoietic lineage is determined by appropriate levels of activin or BMP signaling. Collectively, our study demonstrates that Wnt, activin, and BMP signaling pathways play cooperative and distinct roles in regulating the fate determination of PS for hematopoietic development. Our understanding of the regulatory networks of hematopoietic-fated PS would provide important insights into early hematopoietic patterning and possible guidance for generating functional hematopoietic cells from hPSCs in vitro.

Multifactorial Modeling Reveals a Dominant Role of Wnt Signaling in Lineage Commitment of Human Pluripotent Stem Cells

The human primed pluripotent state is maintained by a complex balance of several signaling pathways governing pluripotency maintenance and commitment. Here, we explore a multiparameter approach using a full factorial design and a simple well-defined culture system to assess individual and synergistic contributions of Wnt, FGF and TGFβ signaling to pluripotency and lineage specification of human induced pluripotent stem cells (hiPSC). Hierarchical clustering and quadratic models highlighted a dominant effect of Wnt signaling over FGF and TGFβ signaling, drawing hiPSCs towards mesendoderm lineages. In addition, a synergistic effect between Wnt signaling and FGF was observed to have a negative contribution to pluripotency maintenance and a positive contribution to ectoderm and mesoderm commitment. Furthermore, FGF and TGFβ signaling only contributed significantly for negative ectoderm scores, suggesting that the effect of both factors for pluripotency maintenance resides in a balance of inhibitory signals instead of proactive stimulation of hiPSC pluripotency. Overall, our dry-signaling multiparameter modeling approach can contribute to elucidate individual and synergistic inputs, providing an additional degree of comprehension of the complex regulatory mechanisms of human pluripotency and commitment.

Human Pluripotent Stem Cell-Derived Endoderm for Modeling Development and Clinical Applications

The liver, lung, pancreas, and digestive tract all originate from the endoderm germ layer, and these vital organs are subject to many life-threatening diseases affecting millions of patients. However, primary cells from endodermal organs are often difficult to grow in vitro. Human pluripotent stem cells thus hold great promise for generating endoderm cells and their derivatives as tools for the development of new therapeutics against a variety of global healthcare challenges. Here we describe recent advances in methods for generating endodermal cell types from human pluripotent stem cells and their use for disease modeling and cell-based therapy.

Restoration of primary cilia in obese adipose-derived mesenchymal stem cells by inhibiting Aurora A or extracellular signal-regulated kinase

BACKGROUND

Obesity impairs a variety of cell types including adipose-derived mesenchymal stem cells (ASCs). ASCs are indispensable for tissue homeostasis/repair, immunomodulation, and cell renewal. It has been demonstrated that obese ASCs are defective in differentiation, motility, immunomodulation, and replication. We have recently reported that some of these defects are linked to impaired primary cilia, which are unable to properly convey and coordinate a variety of signaling pathways. We hypothesized that the rescue of the primary cilium in obese ASCs would restore their functional properties.

METHODS

Obese ASCs derived from subcutaneous and visceral adipose tissues were treated with a specific inhibitor against Aurora A or with an inhibitor against extracellular signal-regulated kinase 1/2 (Erk1/2). Multiple molecular and cellular assays were performed to analyze the altered functionalities and their involved pathways.

RESULTS

The treatment with low doses of these inhibitors extended the length of the primary cilium, restored the invasion and migration potential, and improved the differentiation capacity of obese ASCs. Associated with enhanced differentiation ability, the cells displayed an increased expression of self-renewal/stemness-related genes like SOX2, OCT4, and NANOG, mediated by reduced active glycogen synthase kinase 3 β (GSK3β).

CONCLUSION

This work describes a novel phenomenon whereby the primary cilium of obese ASCs is rescuable by the low-dose inhibition of Aurora A or Erk1/2, restoring functional ASCs with increased stemness. These cells might be able to improve tissue homeostasis in obese patients and thereby ameliorate obesity-associated diseases. Additionally, these functionally restored obese ASCs could be useful for novel autologous mesenchymal stem cell-based therapies.

Mitochondrial Akt Signaling Modulated Reprogramming of Somatic Cells

The signaling mechanisms controlling somatic cell reprogramming are not fully understood. In this study, we report a novel role for mitochondrial Akt1 signaling that enhanced somatic cell reprogramming efficiency. The role of mitochondrial Akt1 in somatic cell reprogramming was investigated by transducing fibroblasts with the four reprogramming factors (Oct4, Sox2, Klf4, c-Myc) in conjunction with Mito-Akt1, Mito-dnAkt1, or control virus. Mito-Akt1 enhanced reprogramming efficiency whereas Mito-dnAkt1 inhibited reprogramming. The resulting iPSCs formed embryoid bodies in vitro and teratomas in vivo. Moreover, Oct4 and Nanog promoter methylation was reduced in the iPSCs generated in the presence of Mito-Akt1. Akt1 was activated and translocated into mitochondria after growth factor stimulation in embryonic stem cells (ESCs). To study the effect of mitochondrial Akt in ESCs, a mitochondria-targeting constitutively active Akt1 (Mito-Akt1) was expressed in ESCs. Gene expression profiling showed upregulation of genes that promote stem cell proliferation and survival and down-regulation of genes that promote differentiation. Analysis of cellular respiration indicated similar metabolic profile in the resulting iPSCs and ESCs, suggesting comparable bioenergetics. These findings showed that activation of mitochondrial Akt1 signaling was required during somatic cell reprogramming.

R-spondin2 promotes hematopoietic differentiation of human pluripotent stem cells by activating TGF beta signaling

BACKGROUND

Human pluripotent stem cells (hPSCs) provide supplies of potential functional blood cells to suffice the clinical needs. However, the underlying mechanism of generating genuine hematopoietic stem cells (HSCs) and functional blood cells from hPSCs remains largely elusive.

METHOD

In this study, we supplied R-spondin2 exogenously during hematopoietic differentiation of hPSCs under various culture conditions and analyzed the production of hematopoietic progenitor cells (HPCs). We further added R-spondin2 at different temporal window to pin down the stage at which R-spondin2 conferred its effects. RNA-SEQ-based gene profiling was applied to analyze genes with significantly altered expression and altered signaling pathways. Finally, megakaryocytic differentiation and platelet generation were determined using HPCs with R-spondin2 treatment.

RESULTS

We found that R-spondin2 generated by hematopoiesis-supporting stromal cells significantly enhances hematopoietic differentiation of hPSCs. Supply of R-spondin2 exogenously at the early stage of mesoderm differentiation elevates the generation of APLNR⁺ cells. Furthermore, early treatment of cells with R-spondin2 enables us to increase the output of hPSC-derived platelet-like particles (PLPs) with intact function. At the mechanistic level, R-spondin2 activates TGF-β signaling to promote the hematopoietic differentiation.

CONCLUSIONS

Our results demonstrate that a transient supply of R-spondin2 can efficiently promote hematopoietic development by activating both WNT and TGF-β signaling. R-spondin2 can be therefore used as a powerful tool for large-scale generation of functional hematopoietic progenitors and platelets for translational medicine.

Cell quality control mechanisms maintain stemness and differentiation potential of P19 embryonic carcinoma cells

Given the relatively long life of stem cells (SCs), efficient mechanisms of quality control to balance cell survival and resistance to external and internal stress are required. Our objective was to test the relevance of cell quality control mechanisms for SCs maintenance, differentiation and resistance to cell death. We compared cell quality control in P19 stem cells (P19SCs) before and after differentiation (P19dCs). Differentiation of P19SCs resulted in alterations in parameters involved in cell survival and protein homeostasis, including the redox system, cardiolipin and lipid profiles, unfolded protein response, ubiquitin-proteasome and lysosomal systems, and signaling pathways controlling cell growth. In addition, P19SCs pluripotency was correlated with stronger antioxidant protection, modulation of apoptosis, and activation of macroautophagy, which all contributed to preserve SCs quality by increasing the threshold for cell death activation. Furthermore, our findings identify critical roles for the PI3K-AKT-MTOR pathway, as well as autophagic flux and apoptosis regulation in the maintenance of P19SCs pluripotency and differentiation potential.Abbreviations: 3-MA: 3-methyladenine; AKT/protein kinase B: thymoma viral proto-oncogene; AKT1: thymoma viral proto-oncogene 1; ATG: AuTophaGy-related; ATF6: activating transcription factor 6; BAX: BCL2-associated X protein; BBC3/PUMA: BCL2 binding component 3; BCL2: B cell leukemia/lymphoma 2; BNIP3L: BCL2/adenovirus E1B interacting protein 3-like; CASP3: caspase 3; CASP8: caspase 8; CASP9: caspase 9; CL: cardiolipin; CTSB: cathepsin B; CTSD: cathepsin D; DDIT3/CHOP: DNA-damage inducible transcript 3; DNM1L/DRP1: dynamin 1-like; DRAM1: DNA-damage regulated autophagy modulator 1; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 3; EIF2S1/eIF2α: eukaryotic translation initiation factor 2, subunit alpha; ERN1/IRE1α: endoplasmic reticulum to nucleus signaling 1; ESCs: embryonic stem cells; KRT8/TROMA-1: cytokeratin 8; LAMP2A: lysosomal-associated membrane protein 2A; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; NANOG: Nanog homeobox; NAO: 10-N-nonyl acridine orange; NFE2L2/NRF2: nuclear factor, erythroid derived 2, like 2; OPA1: OPA1, mitochondrial dynamin like GTPase; P19dCs: P19 differentiated cells; P19SCs: P19 stem cells; POU5F1/OCT4: POU domain, class 5, transcription factor 1; PtdIns3K: phosphatidylinositol 3-kinase; RA: retinoic acid; ROS: reactive oxygen species; RPS6KB1/p70S6K: ribosomal protein S6 kinase, polypeptide 1; SCs: stem cells; SOD: superoxide dismutase; SHC1-1/p66SHC: src homology 2 domain-containing transforming protein C1, 66 kDa isoform; SOX2: SRY (sex determining region Y)-box 2; SQSTM1/p62: sequestosome 1; SPTAN1/αII-spectrin: spectrin alpha, non-erythrocytic 1; TOMM20: translocase of outer mitochondrial membrane 20; TRP53/p53: transformation related protein 53; TUBB3/betaIII-tubulin: tubulin, beta 3 class III; UPR: unfolded protein response; UPS: ubiquitin-proteasome system.

Phosphoinositide 3 Kinase Signaling in Human Stem Cells from Reprogramming to Differentiation: A Tale in Cytoplasmic and Nuclear Compartments

Stem cells are undifferentiated cells that can give rise to several different cell types and can self-renew. Given their ability to differentiate into different lineages, stem cells retain huge therapeutic potential for regenerative medicine. Therefore, the understanding of the signaling pathways involved in stem cell pluripotency maintenance and differentiation has a paramount importance in order to understand these biological processes and to develop therapeutic strategies. In this review, we focus on phosphoinositide 3 kinase (PI3K) since its signaling pathway regulates many cellular processes, such as cell growth, proliferation, survival, and cellular transformation. Precisely, in human stem cells, the PI3K cascade is involved in different processes from pluripotency and induced pluripotent stem cell (iPSC) reprogramming to mesenchymal and oral mesenchymal differentiation, through different and interconnected mechanisms.

Oncogenic PIK3CA promotes cellular stemness in an allele dose-dependent manner

The PIK3CA gene, which encodes the p110α catalytic subunit of PI3 kinase (PI3K), is mutationally activated in cancer and in overgrowth disorders known as PIK3CA-related overgrowth spectrum (PROS). To determine the consequences of genetic PIK3CA activation in a developmental context of relevance to both PROS and cancer, we engineered isogenic human induced pluripotent stem cells (iPSCs) with heterozygous or homozygous knockin of PIK3CAH1047R While heterozygous iPSCs remained largely similar to wild-type cells, homozygosity for PIK3CAH1047R caused widespread, cancer-like transcriptional remodeling, partial loss of epithelial morphology, up-regulation of stemness markers, and impaired differentiation to all three germ layers in vitro and in vivo. Genetic analysis of PIK3CA-associated cancers revealed that 64% had multiple oncogenic PIK3CA copies (39%) or additional PI3K signaling pathway-activating "hits" (25%). This contrasts with the prevailing view that PIK3CA mutations occur heterozygously in cancer. Our findings suggest that a PI3K activity threshold determines pathological consequences of oncogenic PIK3CA activation and provide insight into the specific role of this pathway in human pluripotent stem cells.

Transforming growth factor-β (TGF-β)-induced up-regulation of TGF-β receptors at the cell surface amplifies the TGF-β response

Functional activation of the transforming growth factor-β (TGF-β) receptors (TGFBRs) is carefully regulated through integration of post-translational modifications, spatial regulation at the cellular level, and TGFBR availability at the cell surface. Although the bulk of TGFBRs resides inside the cells, AKT Ser/Thr kinase (AKT) activation in response to insulin or other growth factors rapidly induces transport of TGFBRs to the cell surface, thereby increasing the cell's responsiveness to TGF-β. We now demonstrate that TGF-β itself induces a rapid translocation of its own receptors to the cell surface and thus amplifies its own response. This mechanism of response amplification, which hitherto has not been reported for other cell-surface receptors, depended on AKT activation and TGF-β type I receptor kinase. In addition to an increase in cell-surface TGFBR levels, TGF-β treatment promoted TGFBR internalization, suggesting an overall amplification of TGFBR cycling. The TGF-β-induced increase in receptor presentation at the cell surface amplified TGF-β-induced SMAD family member (SMAD) activation and gene expression. Furthermore, bone morphogenetic protein 4 (BMP-4), which also induces AKT activation, increased TGFBR levels at the cell surface, leading to enhanced autocrine activation of TGF-β-responsive SMADs and gene expression, providing context for the activation of TGF-β signaling in response to BMP during development. In summary, our results indicate that TGF-β- and BMP-induced activation of low levels of cell surface-associated TGFBRs rapidly mobilizes additional TGFBRs from intracellular stores to the cell surface, increasing the abundance of cell-surface TGFBRs and cells' responsiveness to TGF-β signaling.

DRUGPATH - a novel bioinformatic approach identifies DNA-damage pathway as a regulator of size maintenance in human ESCs and iPSCs

Genetic and biochemical screening approaches often fail to identify functionally relevant pathway networks because many signaling proteins contribute to multiple gene ontology pathways. We developed a DRUGPATH-approach to predict pathway-interactomes from high-content drug screen data. DRUGPATH is based upon combining z-scores of effective inhibitors with their corresponding and validated targets. We test DRUGPATH by comparing homeostatic pathways in human embryonic stem cells (hESCs), human induced pluripotent stem cells (hiPSCs) and human amniotic fluid stem cells (hAFSCs). We show that hAFSCs utilize distinct interactomes compared to hESCs/hiPSCs and that pathways orchestrating cell cycle and apoptosis are strongly interconnected, while pathways regulating survival and size are not. Interestingly, hESCs/hiPSCs regulate their size by growing exact additional sizes during each cell cycle. Chemical and genetic perturbation studies show that this “adder-model” is dependent on the DNA-damage pathway. In the future, the DRUGPATH-approach may help to predict novel pathway interactomes from high-content drug screens.

An Efficient Protocol for Single-Cell Cloning Human Pluripotent Stem Cells

Genomic manipulation of human pluripotent stem cells (hPSCs) has become essential to introduce genetic modifications and transgenes, and develop reporter lines. One of the major bottlenecks in gene editing is at the stage of single-cell cloning, which is thought to be variable across hPSC lines and is substantially reduced following a transfection. Due to the difficulty of performing fluorescent-assisted cell sorting (FACS) for single-cell isolation of hPSCs, previous approaches rely on manual colony picking, which is both time-consuming and labor-intensive. In this protocol, I provide a method for utilizing FACS to generate single-cell clones of hPSCs with efficiencies approaching 40% within 7–10 days. This can be achieved by sorting cells onto a feeder layer of MEFs in a stem cell defined medium with KSR and a Rock inhibitor, as early as 1–2 days following a transfection, streamlining the gene editing process. The approach described here provides a fundamental method for all researchers utilizing hPSCs for scientific studies.

Cell Surface Antigen Display for Neuronal Differentiation-Specific Tracking

Cell therapeutic agents for treating degenerative brain diseases using neural stem cells are actively being developed. However, few systems have been developed to monitor in real time whether the transplanted neural stem cells are actually differentiated into neurons. Therefore, it is necessary to develop a technology capable of specifically monitoring neuronal differentiation in vivo. In this study, we established a system that expresses cell membrane-targeting red fluorescent protein under control of the Synapsin promoter in order to specifically monitor differentiation from neural stem cells into neurons. In order to overcome the weak expression level of the tissue-specific promoter system, the partial 5′ UTR sequence of Creb was added for efficient expression of the cell surface-specific antigen. This system was able to track functional neuronal differentiation of neural stem cells transplanted in vivo, which will help improve stem cell therapies.

Functional and molecular mechanism of intracellular pH regulation in human inducible pluripotent stem cells

AIM

To establish a functional and molecular model of the intracellular pH (pH_i) regulatory mechanism in human induced pluripotent stem cells (hiPSCs).

METHODS

hiPSCs (HPS0077) were kindly provided by Dr. Dai from the Tri-Service General Hospital (IRB No. B-106-09). Changes in the pH_i were detected either by microspectrofluorimetry or by a multimode reader with a pH-sensitive fluorescent probe, BCECF, and the fluorescent ratio was calibrated by the high K⁺/nigericin method. NH₄Cl and Na-acetate prepulse techniques were used to induce rapid intracellular acidosis and alkalization, respectively. The buffering power (β) was calculated from the ΔpH_i induced by perfusing different concentrations of (NH₄)₂SO₄. Western blot techniques and immunocytochemistry staining were used to detect the protein expression of pH_i regulators and pluripotency markers.

RESULTS

In this study, our results indicated that (1) the steady-state pH_i value was found to be 7.5 ± 0.01 (n = 20) and 7.68 ± 0.01 (n =20) in HEPES and 5% CO₂/HCO₃^--buffered systems, respectively, which were much greater than that in normal adult cells (7.2); (2) in a CO₂/HCO₃^--buffered system, the values of total intracellular buffering power (β) can be described by the following equation: β_tot = 107.79 (pH_i)² - 1522.2 (pH_i) + 5396.9 (correlation coefficient R² = 0.85), in the estimated pH_i range of 7.1-8.0; (3) the Na⁺/H⁺ exchanger (NHE) and the Na⁺/HCO₃^- cotransporter (NBC) were found to be functionally activated for acid extrusion for pH_i values less than 7.5 and 7.68, respectively; (4) V-ATPase and some other unknown Na⁺-independent acid extruder(s) could only be functionally detected for pH_i values less than 7.1; (5) the Cl^-/ OH^- exchanger (CHE) and the Cl^-/HCO₃^- anion exchanger (AE) were found to be responsible for the weakening of intracellular proton loading; (6) besides the CHE and the AE, a Cl^--independent acid loading mechanism was functionally identified; and (7) in hiPSCs, a strong positive correlation was observed between the loss of pluripotency and the weakening of the intracellular acid extrusion mechanism, which included a decrease in the steady-state pH_i value and diminished the functional activity and protein expression of the NHE and the NBC.

CONCLUSION

For the first time, we established a functional and molecular model of a pH_i regulatory mechanism and demonstrated its strong positive correlation with hiPSC pluripotency.

A transient DMSO treatment increases the differentiation potential of human pluripotent stem cells through the Rb family

The propensity for differentiation varies substantially across human pluripotent stem cell (hPSC) lines, greatly restricting the use of hPSCs for cell replacement therapy or disease modeling. Here, we investigate the underlying mechanisms and demonstrate that activation of the retinoblastoma (Rb) pathway in a transient manner is important for differentiation. In prior work, we demonstrated that pre-treating hPSCs with dimethylsulfoxide (DMSO) before directed differentiation enhanced differentiation potential across all three germ layers. Here, we show that exposure to DMSO improves the efficiency of hPSC differentiation through Rb and by repressing downstream E2F-target genes. While transient inactivation of the Rb family members (including Rb, p107, and p130) suppresses DMSO’s capacity to enhance differentiation across all germ layers, transient expression of a constitutively active (non-phosphorylatable) form of Rb increases the differentiation efficiency similar to DMSO. Inhibition of downstream targets of Rb, such as E2F signaling, also promotes differentiation of hPSCs. More generally, we demonstrate that the duration of Rb activation plays an important role in regulating differentiation capacity.

bFGF-mediated pluripotency maintenance in human induced pluripotent stem cells is associated with NRAS-MAPK signaling

BACKGROUND

Human pluripotent stem cells (PSCs) open new windows for basic research and regenerative medicine due to their remarkable properties, i.e. their ability to self-renew indefinitely and being pluripotent. There are different, conflicting data related to the role of basic fibroblast growth factor (bFGF) in intracellular signal transduction and the regulation of pluripotency of PSCs. Here, we investigated the effect of bFGF and its downstream pathways in pluripotent vs. differentiated human induced (hi) PSCs.

METHODS

bFGF downstream signaling pathways were investigated in long-term culture of hiPSCs from pluripotent to differentiated state (withdrawing bFGF) using immunoblotting, immunocytochemistry and qPCR. Subcellular distribution of signaling components were investigated by simple fractionation and immunoblotting upon bFGF stimulation. Finally, RAS activity and RAS isoforms were studied using RAS assays both after short- and long-term culture in response to bFGF stimulation.

RESULTS

Our results revealed that hiPSCs were differentiated into the ectoderm lineage upon withdrawing bFGF as an essential pluripotency mediator. Pluripotency markers OCT4, SOX2 and NANOG were downregulated, following a drastic decrease in MAPK pathway activity levels. Notably, a remarkable increase in phosphorylation levels of p38 and JAK/STAT3 was observed in differentiated hiPSCs, while the PI3K/AKT and JNK pathways remained active during differentiation. Our data further indicate that among the RAS paralogs, NRAS predominantly activates the MAPK pathway in hiPSCs.

CONCLUSION

Collectively, the MAPK pathway appears to be the prime signaling pathway downstream of bFGF for maintaining pluripotency in hiPSCs and among the MAPK pathways, the activity of NRAS-RAF-MEK-ERK is decreased during differentiation, whereas p38 is activated and JNK remains constant.

Rapamycin rescues BMP mediated midline craniosynostosis phenotype through reduction of mTOR signaling in a mouse model

Craniosynostosis is defined as congenital premature fusion of one or more cranial sutures. While the genetic basis for about 30% of cases is known, the causative genes for the diverse presentations of the remainder of cases are unknown. The recently discovered cranial suture stem cell population affords an opportunity to identify early signaling pathways that contribute to craniosynostosis. We previously demonstrated that enhanced BMP signaling in neural crest cells (caA3 mutants) leads to premature cranial suture fusion resulting in midline craniosynostosis. Since enhanced mTOR signaling in neural crest cells leads to craniofacial bone lesions, we investigated the extent to which mTOR signaling is involved in the pathogenesis of BMP-mediated craniosynostosis by affecting the suture stem cell population. Our results demonstrate a loss of suture stem cells in the caA3 mutant mice by the newborn stage. We have found increased activation of mTOR signaling in caA3 mutant mice during embryonic stages, but not at the newborn stage. Our study demonstrated that inhibition of mTOR signaling via rapamycin in a time specific manner partially rescued the loss of the suture stem cell population. This study provides insight into how enhanced BMP signaling regulates suture stem cells via mTOR activation.

Multi-faceted computational assessment of risk and progression in oligodendroglioma implicates NOTCH and PI3K pathways

Oligodendrogliomas are diffusely infiltrative gliomas defined by IDH-mutation and co-deletion of 1p/19q. They have highly variable clinical courses, with survivals ranging from 6 months to over 20 years, but little is known regarding the pathways involved with their progression or optimal markers for stratifying risk. We utilized machine-learning approaches with genomic data from The Cancer Genome Atlas to objectively identify molecular factors associated with clinical outcomes of oligodendroglioma and extended these findings to study signaling pathways implicated in oncogenesis and clinical endpoints associated with glioma progression. Our multi-faceted computational approach uncovered key genetic alterations associated with disease progression and shorter survival in oligodendroglioma and specifically identified Notch pathway inactivation and PI3K pathway activation as the most strongly associated with MRI and pathology findings of advanced disease and poor clinical outcome. Our findings that Notch pathway inactivation and PI3K pathway activation are associated with advanced disease and survival risk will pave the way for clinically relevant markers of disease progression and therapeutic targets to improve clinical outcomes. Furthermore, our approach demonstrates the strength of machine learning and computational methods for identifying genetic events critical to disease progression in the era of big data and precision medicine.