Pluripotent stem cells are insensitive to the cytotoxicity of TNFα and IFNγ

Equine Embryonic Stem Cell-Derived Tenocytes are Insensitive to a Combination of Inflammatory Cytokines and Have Distinct Molecular Responses Compared to Primary Tenocytes

Tissue fibrosis following tendon injury is a major clinical problem due to the increased risk of re-injury and limited treatment options; however, its mechanism remains unclear. Evidence suggests that insufficient resolution of inflammation contributes to fibrotic healing by disrupting tenocyte activity, with the NF-κB pathway being identified as a potential mediator. Equine embryonic stem cell (ESC) derived tenocytes may offer a potential cell-based therapy to improve tendon regeneration, but how they respond to an inflammatory environment is largely unknown. Our findings reveal for the first time that, unlike adult tenocytes, ESC-tenocytes are unaffected by IFN-γ, TNFα, and IL-1β stimulation; producing minimal changes to tendon-associated gene expression and generating 3-D collagen gel constructs indistinguishable from unstimulated controls. Inflammatory pathway analysis found these inflammatory cytokines failed to activate NF-κB in the ESC-tenocytes. However, NF-κB could be activated to induce changes in gene expression following stimulation with NF-κB pharmaceutical activators. Transcriptomic analysis revealed differences between cytokine and NF-κB signalling components between adult and ESC-tenocytes, which may contribute to the mechanism by which ESC-tenocytes escape inflammatory stimuli. Further investigation of these molecular mechanisms will help guide novel therapies to reduce fibrosis and encourage superior tendon healing.

Mouse Trophoblast Cells Have Attenuated Responses to TNF-α and IFN-γ and Can Avoid Synergic Cytotoxicity of the Two Cytokines

TNF-α and IFN-γ are two inflammatory cytokines that play critical roles in immune responses, but they can also negatively affect cell proliferation and viability. In particular, the combination of the two cytokines (TNF-α/IFN-γ) synergistically causes cytotoxicity in many cell types. We recently reported that mouse embryonic stem cells (ESCs) isolated from the blastocyst stage embryo do not respond to TNF-α and have limited response to IFN-γ, thereby avoiding TNF-α/IFN-γ cytotoxicity. The current study expanded our investigation to mouse trophoblast stem cells (TSCs) and their differentiated trophoblasts (TSC-TBs), the precursors and the differentiated cells of the placenta, respectively. In this study, we report that the combination of TNF-α/IFN-γ does not show the cytotoxicity to TSCs and TSC-TBs that otherwise effectively kills fibroblasts, similar to ESCs. Although ESCs, TSCs, and TSC-TBs are dramatically different in their growth rate, morphology, and physiological functions, they nevertheless share a similarity in being able to avoid TNF-α/IFN-γ cytotoxicity. We propose that this unique immune property may serve as a protective mechanism that limits cytokine cytotoxicity in the blastocyst. With molecular and cellular approaches and genome-wide transcriptomic analysis, we have demonstrated that the attenuated NF-κB and STAT1 transcription activation is a limiting factor that restricts the effect of TNF-α/IFN-γ on TSCs and TSC-TBs.

Toll-like receptor expression profile of stem/progenitor cells from human exfoliated deciduous teeth

BACKGROUND

Stem/progenitor cells from human exfoliated deciduous teeth (SHED) show remarkable pluripotent, regenerative, and immunological capacities. During in vivo regenerative processes, there could be the presence of SHED in the surrounding inflammatory microenvironment, through toll-like receptors (TLRs).

AIM

The aim of this paper was to present a characteristic TLR expression profile on SHED for the first time.

DESIGN

Cells were harvested from extracted primary teeth (n = 10), anti-STRO-1 immunomagnetically sorted and cultivated, through colony-forming units (CFUs). SHED were examined for mesenchymal stem/progenitor cell traits, including the expression of clusters of differentiation (CDs) 14, 34, 45, 73, 90, 105, and 146, and their multilineage differentiation aptitude. TLRs 1-10 expression was investigated for SHED in uninflamed and inflamed (25 ng/mL IL-1β, 103 U/mL IFN-γ, 50 ng/mL TNF-α, and 3 × 103  U/mL IFN-α; SHED-i) microenvironmental conditions.

RESULTS

SHED were negative for CDs 14, 34, and 45, but were positive for CDs 73, 90, 105, and 146, and demonstrated characteristic multilineage differentiation. In an uninflamed microenvironment, SHED expressed TLRs 1, 2, 3, 4, 6, 8, 9, and 10. The inflammatory microenvironment downregulated TLR7 significantly on gene level and upregulated TLR8 on gene and protein levels (p < .05; Wilcoxon signed-rank test).

CONCLUSION

There appears to be a unique TLR expression profile on SHED, which could modulate their immunological and regenerative abilities in oral tissue engineering approaches.

Equine induced pluripotent stem cells are responsive to inflammatory cytokines before and after differentiation into musculoskeletal cell types

Persistent inflammation is associated with the poor regeneration of musculoskeletal tissues. Embryonic stem cells (ESCs) have an attenuated response to inflammatory cytokines, but there are mixed reports on the response of induced pluripotent stem cells (iPSCs) to inflammation. Horses provide a relevant large animal model for studying musculoskeletal tissue diseases and the testing of novel therapies. The aim of this study was to determine if equine iPSCs are responsive to the inflammatory cytokines IL-1β, TNFα and IFN-γ in their undifferentiated state, or following differentiation into tendon and cartilage-like cells. We demonstrated that in undifferentiated iPSCs, the cytokines induce NF-κB P65 and STAT1 nuclear translocation which leads to cell death, decreased OCT4 expression and increased expression of inflammatory genes. Following differentiation towards cartilage-like cells exposure to the cytokines resulted in STAT1 nuclear translocation, changes in cartilage gene expression and increased expression of matrix metalloproteinases (MMPs) and inflammatory genes. Exposure of iPSC-derived tendon-like cells to the cytokines resulted nuclear translocation of NF-κB P65 and STAT1, altered tendon gene expression, increased MMP expression and increased expression of inflammatory genes. Equine iPSCs are therefore capable of responding to inflammatory stimulation and this may have relevance for their future clinical application.

Transient upregulation of IRF1 during exit from naive pluripotency confers viral protection

Stem cells intrinsically express a subset of genes which are normally associated with interferon stimulation and the innate immune response. However, the expression of these interferon-stimulated genes (ISG) in stem cells is independent from external stimuli such as viral infection. Here, we show that the interferon regulatory factor 1, Irf1, is directly controlled by the murine formative pluripotency gene regulatory network and transiently upregulated during the transition from naive to formative pluripotency. IRF1 binds to regulatory regions of a conserved set of ISGs and is required for their faithful expression upon exit from naive pluripotency. We show that in the absence of IRF1, cells exiting the naive pluripotent stem cell state are more susceptible to viral infection. Irf1 therefore acts as a link between the formative pluripotency network, regulation of innate immunity genes, and defense against viral infections during formative pluripotency.

Mouse Trophoblast Cells Can Provide IFN-Based Antiviral Protection to Embryonic Stem Cells via Paracrine Signaling

The blastocyst is the preimplantation stage embryo that consists of two major components: the inner cell mass (ICM) and the trophectoderm (TE). The ICM gives rise to the fetus and some extraembryonic tissues whereas the TE contributes to development of the placenta. Previous studies have demonstrated that both human and mouse embryonic stem cells (ESCs) derived from the ICM are deficient in expressing type I IFNs in response to viral infection. In this study, we investigated the IFN response in mouse trophoblast stem cells (TSCs) and their in vitro differentiated trophoblasts (TSC-TBs). In this study, we report that, unlike ESCs, TSCs have a functional IFN system. They can express type I IFNs in response to viral stimuli and express IFN-stimulated genes in response to type I IFNs. TSC-TBs have a further developed IFN system and acquired the ability to express specialized type III IFN-λ. Furthermore, TSCs and TSC-TBs can provide ESCs with antiviral activity against Chikungunya, West Nile, and Zika virus infection, as demonstrated with a novel coculture model that simulates the temporal and spatial relationship between the ICM and the TE in a blastocyst. Taken together, our data demonstrate that mouse ESCs can respond to type I IFNs and gain IFN-based antiviral protection from TSCs and TSC-TBs via paracrine signaling mechanisms even though they themselves are unable to express type I IFNs.

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.