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

Abstract

Recent studies have demonstrated that embryonic stem cells (ESCs) have an underdeveloped innate immune system, but the biological implications of this finding are poorly understood. In this study, we compared the responses of mouse ESCs (mESCs) and mESC differentiated fibroblasts (mESC-FBs) to tumor necrosis factor α (TNFα) and interferons (IFNs). Our data revealed that TNFα, IFNα, IFNβ, or IFNγ alone do not cause apparent effects on mESCs and mESC-FBs, but the combination of TNFα and IFNγ (TNFα/IFNγ) showed toxicity to mESC-FBs as indicated by cell cycle inhibition and reduced cell viability, correlating with the expression of inducible nitric oxide synthase (iNOS). However, none of these effects were observed in mESCs that were treated with TNFα/IFNγ. Furthermore, mESC-FBs, but not mESCs, are vulnerable to cytotoxicity resulting from lipopolysaccharide (LPS)-activated macrophages. The insensitivity of mESCs to cytotoxicity in all cases is correlated with their lack of responses to TNFα and IFNγ. Similar to mESCs, human ESCs (hESCs) and iPSCs (hiPSCs) do not respond to TNFα and are not susceptible to the cytotoxicity of TNFα, IFNβ, or IFNγ alone or in combination that significantly affects human foreskin fibroblast (hFBs) and Hela cells. However, unlike mESCs, hESCs and hiPSCs can respond to IFNγ, but this does not cause significant cytotoxicity in hESCs and hiPSCs. Our findings in both mouse and human PSCs together support the hypothesis that attenuated innate immune responses could be a protective mechanism that limits immunologic cytotoxicity resulting from inflammatory and immune responses.

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

“…TNF-a and IFN-g are known as "embryotoxic cytokines" for their detrimental effect on early embryos when dysregulated (35). Remarkably, mESCs, hESCs, and hiPSCs were insensitive to the cytotoxicity of TNF-a/IFN-g or any of the above-mentioned cytokines alone (9,22,23). Therefore, we proposed that the attenuated innate immune response in ESCs could be an adaptive feature for ESCs to avoid immunological insults in a blastocyst (1).…”

“…The molecular basis underlying the attenuated innate immune response in ESCs is not completely understood. Studies have shown that the major receptors for viral RNA (TLR3, RIG-I, and MDA5), LPS (TLR4), and TNF-a (TNFR1) are either expressed at low levels or not functional in ESCs (6,9,10,23). More importantly, NF-kB, the master transcription factor in mediating many types of immune responses, is inactive in ESCs (8,9,3941).…”

“…Based on the dynamic changes of innate immune responses during in vitro ESC differentiation and iPSC reprogramming, there is an apparent reciprocal inhibition between the pluripotent state and the innate immune response (2). This is illustrated by the fact that differentiating ESCs lose pluripotency while gaining the ability to express IFNs and respond to inflammatory cytokines (7,8,11,23). Conversely, fibroblasts lose the capacity to express IFNs after being reprogrammed into iPSCs (10,11).…”

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

“…The subsets of expressed ISGs are distinct between different stem cell types and change in differentiation (Wu et al , 2018). How these ISGs are regulated is unknown, as mouse ESCs for example do not respond to interferon (IFN) stimulation (Burke et al , 1978; Harada et al , 1990; Wang et al , 2013; Chen et al , 2020). Strikingly, pluripotent stem cells are more resistant against viral infection compared with their differentiated descendants (Swartzendruber & Lehman, 1975; Wolf & Goff, 2009), and this is at least in part due to ISG expression (Wu et al , 2018).…”

Stem cell specific interferon stimulated gene expression is regulated by the formative pluripotency network through IRF1

“…While it is not clear which factors are involved in the formative pluripotency network, stem cells intrinsically express a subset of genes which are referred to as interferon stimulated genes (ISGs) (Wu et al 2018). How these ISGs are regulated is unclear, as stem cells do not respond to interferon stimulation (Burke, Graham, and Lehman 1978; Harada et al 1990; Chen et al 2020). At the same time, stem cells are resistant against viral infection (Swartzendruber and Lehman 1975; Wolf and Goff 2009).…”