Characterization of Innate Immune Responses in Mouse Trophoblast Stem Cells and Their Differentiated Cells

The blastocyst is the preimplantation stage embryo consisting of two major components: the inner cell mass (ICM) and the trophectoderm (TE). The ICM forms the fetus, whereas the TE contributes to the placenta development. Previous studies have demonstrated that human and mouse embryonic stem cells (ESCs) derived from the ICM are deficient in expressing type I IFNs in response to viral infection. This study investigated the innate immune responses in mouse trophoblast stem cells (TSCs) and their in vitro differentiated trophoblasts (TSC-TBs). I report that, unlike ESCs, TSCs have a functional IFN system. They can express and respond to type I IFNs and provide ESCs with antiviral activity against Chikungunya and Zika virus infection. 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 cannot express type I IFNs. TNF⍺ and IFN play an important role in successful implantation. However, the combination of these cytokines can cause cytotoxicity in most of the cells through inducible nitric oxide synthase (iNOS) expression; ESCs are less susceptible to their cytotoxicity due to their lack of ability to express iNOS. Nevertheless, ESCs are sensitive to the cytotoxicity of nitric oxide (NO) in vitro, suggesting that NO can be detrimental to ESCs in the blastocyst cavity if an excessive amount is released from TSCs and TSC-TBs. Interestingly, our data also revealed that, like ESCs, TSCs and TSC-TBs are insensitive to the cytotoxicity of TNFα/IFNγ and do not express iNOS. We analyzed the responses of TSCs and TSC-TBs and mouse embryonic fibroblasts (MEFs) to TNFα, IFNγ, and TNFα/IFNγ with different experimental approaches. We have compared TSCs and TSC-TBs responses with MEFs, which strongly respond to TNFα and IFNγ and express iNOS. Our results show that IFN can weakly activate JAK/STAT1 pathway, and TNF⍺ fails to activate the NFκB pathway in TSCs and TSC-TBs, which explains the lack of inflammatory genes and iNOS induction in these cells. Our studies may provide a critical, new approach to defining the molecular properties of TE cells after in vivo exposure to cytokines or pathogens during implantation