Upregulation of NF-kappaB upon differentiation of mouse embryonic stem cells

Dicer and PKR as Novel Regulators of Embryonic Stem Cell Fate and Antiviral Innate Immunity

Embryonic stem cells (ESCs) represent a unique cell population in the blastocyst stage embryo. They have been intensively studied as a promising cell source for regenerative medicine. Recent studies have revealed that both human and mouse ESCs are deficient in expressing IFNs and have attenuated inflammatory responses. Apparently, the ability to express IFNs and respond to certain inflammatory cytokines is not "innate" to ESCs but rather is developmentally acquired by somatic cells during differentiation. Accumulating evidence supports a hypothesis that the attenuated innate immune response may serve as a protective mechanism allowing ESCs to avoid immunological cytotoxicity. This review describes our current understanding of the molecular basis that shapes the immune properties of ESCs. We highlight the recent findings on Dicer and dsRNA-activated protein kinase R as novel regulators of ESC fate and antiviral immunity and discuss how ESCs use alternative mechanisms to accommodate their stem cell properties.

The FOXO signaling axis displays conjoined functions in redox homeostasis and stemness

Previous views of reactive oxygen species (ROS) depicted them as harmful byproducts of metabolism as uncontrolled levels of ROS can lead to DNA damage and cell death. However, recent studies have shed light into the key role of ROS in the self-renewal or differentiation of the stem cell. The interplay between ROS levels, metabolism, and the downstream redox signaling pathways influence stem cell fate. In this review we will define ROS, explain how they are generated, and how ROS signaling can influence transcription factors, first and foremost forkhead box-O transcription factors, that shape not only the cellular redox state, but also stem cell fate. Now that studies have illustrated the importance of redox homeostasis and the role of redox signaling, understanding the mechanisms behind this interplay will further shed light into stem cell biology.

Inhibition of MUC1-C Increases ROS and Cell Death in Mouse Embryonic Stem Cells

Background and Objectives

Embryonic stem (ES) cells have the capacity to self-renew and generate all types of cells. MUC1-C, a cytoplasmic subunit of MUC1, is overexpressed in various carcinomas and mediates signaling pathways to regulate intracellular metabolic processes and gene expression involved in the maintenance of cancer cells. However, the functional role of MUC1-C in ES cells is not well understood. In this study, we investigated the role of MUC1-C on growth, survival, and differentiation of mouse ES (mES) cells.

Methods and Results

Undifferentiated mES cells expressed the MUC1-C protein and the expression level was decreased during differentiation. Inhibition of MUC1-C, by the specific inhibitor GO201, reduced proliferation of mES cells. However, there was no prominent effect on pluripotent markers such as Oct4 expression and STAT3 signaling, and MUC1-C inhibition did not induce differentiation. Inhibition of MUC1-C increased the G1 phase population, decreased the S phase population, and increased cell death. Furthermore, inhibition of MUC1-C induced disruption of the ROS balance in mES cells.

Conclusions

These results suggest that MUC1-C is involved in the growth and survival of mES cells.

A Matter of Choice: Inhibition of c-Rel Shifts Neuronal to Oligodendroglial Fate in Human Stem Cells

The molecular mechanisms underlying fate decisions of human neural stem cells (hNSCs) between neurogenesis and gliogenesis are critical during neuronal development and neurodegenerative diseases. Despite its crucial role in the murine nervous system, the potential role of the transcription factor NF-κB in the neuronal development of hNSCs is poorly understood. Here, we analyzed NF-κB subunit distribution during glutamatergic differentiation of hNSCs originating from neural crest-derived stem cells. We observed several peaks of specific NF-κB subunits. The most prominent nuclear peak was shown by c-REL subunit during a period of 2–5 days after differentiation onset. Furthermore, c-REL inhibition with pentoxifylline (PTXF) resulted in a complete shift towards oligodendroglial fate, as demonstrated by the presence of OLIG2⁺/O4⁺-oligodendrocytes, which showed PDGFRα, NG2 and MBP at the transcript level. In addition c-REL impairment further produced a significant decrease in neuronal survival. Transplantation of PTXF-treated predifferentiated hNSCs into an ex vivo oxidative-stress-mediated demyelination model of mouse organotypic cerebellar slices further led to integration in the white matter and differentiation into MBP⁺ oligodendrocytes, validating their functionality and therapeutic potential. In summary, we present a human cellular model of neuronal differentiation exhibiting a novel essential function of NF-κB-c-REL in fate choice between neurogenesis and oligodendrogenesis which will potentially be relevant for multiple sclerosis and schizophrenia.

The underdeveloped innate immunity in embryonic stem cells: The molecular basis and biological perspectives from early embryogenesis

Embryonic stem cells (ESCs) have been intensively studied as a promising cell source for regenerative medicine. The rapid advancements in the field have not only proven the feasibility of ESC-based cell therapy, but also led to a better understanding of pluripotent stem cells (PSCs) as a unique cell population at an early stage of embryogenesis. Recent studies have revealed that both human and mouse ESCs have attenuated innate immune responses to infectious agents and inflammatory cytokines. These findings raise interesting questions about the rationale for ESCs, the PSCs experimentally derived from preimplantation stage embryos, to not have an innate defense mechanism that has been adapted so well in somatic cells. All somatic cells have innate immune systems that can be activated by pathogen-associated molecular patterns (PAMPs) or cellular damage-associated molecular patterns (DAMPs), leading to production of cytokines. The underdeveloped innate immunity represents a unique property of PSCs that may have important implications. This review discusses the immunological properties of PSCs, the molecular basis underlying their diminished innate immune responses, and the hypothesis that the attenuated innate immune responses could be an adaptive mechanism that allows PSCs to avoid cytotoxicity associated with inflammation and immune responses during early embryogenesis.

The Molecular Basis for the Lack of Inflammatory Responses in Mouse Embryonic Stem Cells and Their Differentiated Cells

We reported previously that mouse embryonic stem cells do not have a functional IFN-based antiviral mechanism. The current study extends our investigation to the inflammatory response in mouse embryonic stem cells and mouse embryonic stem cell-differentiated cells. We demonstrate that LPS, TNF-α, and viral infection, all of which induce robust inflammatory responses in naturally differentiated cells, failed to activate NF-κB, the key transcription factor that mediates inflammatory responses, and were unable to induce the expression of inflammatory genes in mouse embryonic stem cells. Similar results were obtained in human embryonic stem cells. In addition to the inactive state of NF-κB, the deficiency in the inflammatory response in mouse embryonic stem cells is also attributed to the lack of functional receptors for LPS and TNF-α. In vitro differentiation can trigger the development of the inflammatory response mechanism, as indicated by the transition of NF-κB from its inactive to active state. However, a limited response to TNF-α and viral infection, but not to LPS, was observed in mouse embryonic stem cell-differentiated fibroblasts. We conclude that the inflammatory response mechanism is not active in mouse embryonic stem cells, and in vitro differentiation promotes only partial development of this mechanism. Together with our previous studies, the findings described in this article demonstrate that embryonic stem cells are fundamentally different from differentiated somatic cells in their innate immunity, which may have important implications in developmental biology, immunology, and embryonic stem cell-based regenerative medicine.

Utilization of different anti-viral mechanisms by mammalian embryonic stem cells and differentiated cells

Embryonic stem cells (ESCs) have received tremendous attention because of their potential applications in regenerative medicine. Over the past two decades, intensive research has not only led to the generation of various types of cells from ESCs that can be potentially used for the treatment of human diseases but also led to the formation of new concepts and breakthroughs that have significantly impacted our understanding of basic cell biology and developmental biology. Recent studies have revealed that ESCs and other types of pluripotent cells do not have a functional interferon (IFN)-based anti-viral mechanism, challenging the idea that the IFN system is developed as the central component of anti-viral innate immunity in all types of cells in vertebrates. This finding also provided important insight into a question that has been uncertain for a long time: whether or not the RNA interference (RNAi) anti-viral mechanism operates in mammalian cells. An emerging paradigm is that mammals may have adapted distinct anti-viral mechanisms at different stages of organismal development; the IFN-based system is mainly used by differentiated somatic cells, while the RNAi anti-viral mechanism may be used in ESCs. This paper discusses the molecular basis and biological implications for mammals to have different anti-viral mechanisms during development.

c-Rel Regulates Inscuteable Gene Expression during Mouse Embryonic Stem Cell Differentiation

Inscuteable (Insc) regulates cell fate decisions in several types of stem cells. Although it is recognized that the expression levels of mouse INSC govern the balance between symmetric and asymmetric stem cell division, regulation of mouse Insc gene expression remains poorly understood. Here, we showed that mouse Insc expression transiently increases at an early stage of differentiation, when mouse embryonic stem (mES) cells differentiate into bipotent mesendoderm capable of producing both endoderm and mesoderm in defined culture conditions. We identified the minimum transcriptional regulatory element (354 bases) that drives mouse Insc transcription in mES cells within a region >5 kb upstream of the mouse Insc transcription start site. We found that the transcription factor reticuloendotheliosis oncogene (c-Rel) bound to the minimum element and promoted mouse Insc expression in mES cells. In addition, short interfering RNA-mediated knockdown of either mouse INSC or c-Rel protein decreased mesodermal cell populations without affecting differentiation into the mesendoderm or endoderm. Furthermore, overexpression of mouse INSC rescued the mesoderm-reduced phenotype induced by knockdown of c-Rel. We propose that regulation of mouse Insc expression by c-Rel modulates cell fate decisions during mES cell differentiation.

Granulosa cell-derived induced pluripotent stem cells exhibit pro-trophoblastic differentiation potential

Introduction

Human induced pluripotent stem cells (hiPSCs) have been derived from various somatic cell types. Granulosa cells, a group of cells which surround oocytes and are obtained from the (normally discarded) retrieved egg follicles of women undergoing infertility treatment, are a possible cell source for induced pluripotent stem cell (iPSC) generation. Here, we explored the possibility of using human granulosa cells as a donor cell type for iPSC reprogramming, and compared granulosa cell-derived iPSCs (iGRAs) with those derived from other cell sources, to determine the potential ability of iGRA differentiation.

Methods

Granulosa cells were collected from egg follicles retrieved from women undergoing infertility treatment. After short-term culture, the granulosa cells derived from different patients were mixed in culture, and infected with retroviruses encoding reprogramming factors. The resulting iPSC clones were selected and subjected to microsatellite DNA analysis to determine their parental origin. IGRAs were subjected to RT-PCR, immunofluorescence staining, and in vitro and in vivo differentiation assays to further establish their pluripotent characteristics.

Results

Microsatellite DNA analysis was used to demonstrate that hiPSCs with different parental origins can be simultaneously reprogrammed by retroviral transfection of a mixed human granulosa cell population obtained from multiple individuals. The iGRAs resemble human embryonic stem cells (hESCs) in many respects, including morphological traits, growth requirements, gene and marker expression profiles, and in vitro and in vivo developmental propensities. We also demonstrate that the iGRAs express low levels of NLRP2, and differentiating iGRAs possess a biased differentiation potential toward the trophoblastic lineage. Although NLRP2 knockdown in hESCs promotes trophoblastic differentiation of differentiating hESCs, it does not result in exit from pluripotency. These results imply that NLRP2 may play a role in regulating the trophoblastic differentiation of human pluripotent stem cells.

Conclusions

These findings provide a means of generating iPSCs from multiple granulosa cell populations with different parental origins. The ability to generate iPSCs from granulosa cells not only enables modeling of infertility-associated disease, but also provides a means of identifying potential clinical interventions through iPSC-based drug screening.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0005-5) contains supplementary material, which is available to authorized users.

Comparison of osteogenic differentiation of embryonic stem cells and primary osteoblasts revealed by responses to IL-1β, TNF-α, and IFN-γ

There are well-established approaches for osteogenic differentiation of embryonic stem cells (ESCs), but few show direct comparison with primary osteoblasts or demonstrate differences in response to external factors. Here, we show comparative analysis of in vitro osteogenic differentiation of mouse ESC (osteo-mESC) and mouse primary osteoblasts. Both cell types formed mineralized bone nodules and produced osteogenic extracellular matrix, based on immunostaining for osteopontin and osteocalcin. However, there were marked differences in the morphology of osteo-mESCs and levels of mRNA expression for osteogenic genes. In response to the addition of proinflammatory cytokines interleukin-1β, tumor necrosis factor-α, and interferon-γ to the culture medium, primary osteoblasts showed increased production of nitric oxide (NO) and prostaglandin E2 (PGE2) at early time points and decreases in cell viability. In contrast, osteo-mESCs maintained viability and did not produce NO and PGE2 until day 21. The formation of bone nodules by primary osteoblasts was reduced markedly after cytokine stimulation but was unaffected in osteo-mESCs. Cell sorting of osteo-mESCs by cadherin-11 (cad-11) showed clear osteogenesis of cad-11(+) cells compared to unsorted osteo-mESCs and cad-11(-) cells. Moreover, the cad-11(+) cells showed a significant response to cytokines, similar to primary osteoblasts. Overall, these results show that while osteo-mESC cultures, without specific cell sorting, show characteristics of osteoblasts, there are also marked differences, notably in their responses to cytokine stimuli. These findings are relevant to understanding the differentiation of stem cells and especially developing in vitro models of disease, testing new drugs, and developing cell therapies.

Knockdown of IKK1/2 promotes differentiation of mouse embryonic stem cells into neuroectoderm at the expense of mesoderm

Activation of nuclear factor kappa B (NF-κB) is accomplished by a specific kinase complex (IKK-complex), phosphorylating inhibitors of NF-κB (IκB). In embryonic stem cells (ESCs), NF-κB signaling causes loss of pluripotency and promotes differentiation towards a mesodermal phenotype. Here we show that NF-κB signaling is involved in cell fate determination during retinoic acid (RA) mediated differentiation of ESCs. Knockdown of IKK1 and IKK2 promotes differentiation of ESCs into neuroectoderm at the expense of neural crest derived myofibroblasts. Our data indicate that RA is not only able to induce neuronal differentiation in vitro but also drives ESCs into a neural crest cell lineage represented by differentiation towards peripheral neurons and myofibroblasts. The NC is a transiently existing, highly multipotent embryonic cell population generating a wide range of different cell types. During embryonic development the NC gives rise to distinct precursor lineages along the anterior-posterior axis determining differentiation towards specific derivates. Retinoic acid (RA) signaling provides essential instructive cues for patterning the neuroectoderm along the anterior-posterior axis. The demonstration of RA as a sufficient instructive signal for the differentiation of pluripotent cells towards NC and the involvement of NF-κB during this process provides useful information for the generation of specific NC-lineages, which are valuable for studying NC development or disease modeling.

The role of NF-κB signaling in the maintenance of pluripotency of human induced pluripotent stem cells

NF-κB signaling plays an essential role in maintaining the undifferentiated state of embryonic stem (ES) cells. However, opposing roles of NF-κB have been reported in mouse and human ES cells, and the role of NF-κB in human induced pluripotent stem (iPS) cells has not yet been clarified. Here, we report the role of NF-κB signaling in maintaining the undifferentiated state of human iPS cells. Compared with differentiated cells, undifferentiated human iPS cells showed an augmentation of NF-κB activity. During differentiation induced by the removal of feeder cells and FGF2, we observed a reduction in NF-κB activity, the expression of the undifferentiation markers Oct3/4 and Nanog, and the up-regulation of the differentiated markers WT-1 and Pax-2. The specific knockdown of NF-κB signaling using p65 siRNA also reduced the expression of Oct3/4 and Nanog and up-regulated WT-1 and Pax-2 but did not change the ES-like colony formation. Our results show that the augmentation of NF-κB signaling maintains the undifferentiated state of human iPS and suggest the importance of this signaling pathway in maintenance of human iPS cells.

High sensitivity of embryonic stem cells to proteasome inhibitors correlates with low expression of heat shock protein and decrease of pluripotent cell marker expression

The ubiquitin-proteasome system is a major proteolytic system for nonlysosomal degradation of cellular proteins. Here, we investigated the response of mouse embryonic stem (ES) cells under proteotoxic stress. Proteasome inhibitors induced expression of heat shock protein 70 (HSP70) in a concentration- and time-dependent manner, and also induced apoptosis of ES cells. Importantly, more apoptotic cells were observed in ES cells compared with other somatic cells. To understand this phenomenon, we further investigated the expression of HSP70 and pluripotent cell markers. HSP70 expression was more significantly increased in somatic cells than in ES cells, and expression levels of pluripotent cell markers such as Oct4 and Nanog were decreased in ES cells. These results suggest that higher sensitivity of ES cells to proteotoxic stress may be related with lower capacity of HSP70 expression and decreased pluripotent cell marker expression, which is essential for the survival of ES cells.

NFκB signaling regulates embryonic and adult neurogenesis

Both embryonic and adult neurogenesis involves the self-renewal/proliferation, survival, migration and lineage differentiation of neural stem/progenitor cells. Such dynamic process is tightly regulated by intrinsic and extrinsic factors and complex signaling pathways. Misregulated neurogenesis contributes much to a large range of neurodevelopmental defects and neurodegenerative diseases. The signaling of NFκB regulates many genes important in inflammation, immunity, cell survival and neural plasticity. During neurogenesis, NFκB signaling mediates the effect of numerous niche factors such as cytokines, chemokines, growth factors, extracellular matrix molecules, but also crosstalks with other signaling pathways such as Notch, Shh, Wnt/β-catenin. This review summarizes current progress on the NFκB signaling in all aspects of neurogenesis, focusing on the novel role of NFκB signaling in initiating early neural differentiation of neural stem cells and embryonic stem cells.

Innate immunity in human embryonic stem cells: comparison with adult human endothelial cells

Treatment of human disease with human embryonic stem cell (hESC)-derived cells is now close to reality, but little is known of their responses to physiological and pathological insult. The ability of cells to respond via activation of Toll like receptors (TLR) is critical in innate immune sensing in most tissues, but also extends to more general danger sensing, e.g. of oxidative stress, in cardiomyocytes. We used biomarker release and gene-array analysis to compare responses in hESC before and after differentiation, and to those in primary human endothelial cells. The presence of cardiomyocytes and endothelial cells was confirmed in differentiated cultures by immunostaining, FACS-sorting and, for cardiomyocytes, beating activity. Undifferentiated hESC did not respond with CXCL8 release to Gram positive or Gram negative bacteria, or a range of PAMPs (pathogen associated molecular patterns) for TLRs 1-9 (apart from flagellin, an activator of TLR5). Surprisingly, lack of TLR-dependent responses was maintained over 4 months of differentiation of hESC, in cultures which included cardiomyocytes and endothelial cells. In contrast, primary cultures of human aortic endothelial cells (HAEC) demonstrated responses to a broad range of PAMPs. Expression of downstream TLR signalling pathways was demonstrated in hESC, and IL-1beta, TNFalpha and INFgamma, which bypass the TLRs, stimulated CXCL8 release. NFkappaB pathway expression was also present in hESC and NFkappaB was able to translocate to the nucleus. Low expression levels of TLRs were detected in hESC, especially TLRs 1 and 4, explaining the lack of response of hESC to the main TLR signals. TLR5 levels were similar between differentiated hESC and HAEC, and siRNA knockdown of TLR5 abolished the response to flagellin. These findings have potential implications for survival and function of grafted hESC-derived cells.