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

Abstract

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

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

“…19,40 In contrast, hESCs and hiPSCs barely respond to IFNβ as judged by their lack of ISG expression. 20 The lack of response to these agents is also reported by other investigators in mESCs 12,13 and in miPSCs. 44 In addition to inducing IFN response, viral RNA can directly activate double-stranded (ds) RNA-activated protein kinase (PKR) and cause inhibition of both cellular and viral protein synthesis, thereby repressing viral replication as a separate antiviral mechanism.…”

“…Studies from other investigators have reported similar findings in several types of tissue cells differentiated from both hESCs and mESCs, including endothelial cells, smooth muscle cells, cardiomyocytes, and osteoblasts 12,13,16,64,65. This is elegantly demonstrated with a co-culture model in which mESCs and mESC-FBs are cultured in the same dish and subjected to identical experimental conditions 19,20,40. 19,40 At the molecular level, cytokine receptors and PRRs, such as TNFR1, TLR3, and MDA5, are upregulated in ESC-differentiated cells.…”

“…19,40 At the molecular level, cytokine receptors and PRRs, such as TNFR1, TLR3, and MDA5, are upregulated in ESC-differentiated cells. This is, at least partly, due to the lack of expression of a functional TLR4 at the protein level 12,16,20. This is elegantly demonstrated with a co-culture model in which mESCs and mESC-FBs are cultured in the same dish and subjected to identical experimental conditions 19,20,40.…”

“…5 While genetic abnormalities of the embryo are the major cause of implantation failure, dysregulated immunological and inflammatory responses are also important contributing factors. 8,9 Successful derivation of various cell types from ESCs has now demonstrated the principle and feasibility of their therapeutic application; however, recent studies of both mESCs and hESCs, [10][11][12][13][14][15][16] including a series of studies from our laboratory, [17][18][19][20][21] have revealed that they have attenuated innate immune responses to bacterial and viral pathogens and inflammatory cytokines. The blastocyst is the structure developed from a fertilized egg before implantation (embryonic days 3.5-4.5 [E3.…”

“…These studies proved the concept that innate immunity in somatic cells is acquired during organismal development.It is noted that although mESC-EBs have gained the ability to respond to viral stimuli and inflammatory cytokines, their levels of responsiveness are substantially lower than their naturally differen-tiated counterparts but can be further developed along with their continued in vitro propagation. However, mESC-FBs, mESC-differentiated smooth muscle cells, and hESC-differentiated endothelial cells still do not respond to LPS 12,16,20,21. 13,20,40 A defining feature after differentiation is the transition of NFκB from the inactive state in mESCs to the active state in mESC-FBs in response to viral infection and TNFα.…”