Activation of Innate Immunity Is Required for Efficient Nuclear Reprogramming

Abstract

Retroviral overexpression of reprogramming factors (Oct4, Sox2, Klf4, c-Myc) generates induced pluripotent stem cells (iPSCs). However, the integration of foreign DNA could induce genomic dysregulation. Cell-permeant proteins (CPPs) could overcome this limitation. To date this approach has proved exceedingly inefficient. We discovered a striking difference in the pattern of gene expression induced by viral versus CPP-based delivery of the reprogramming factors, suggesting that a signaling pathway required for efficient nuclear reprogramming was activated by the retroviral, but not CPP approach. In gain- and loss-of function studies, we find that the toll-like receptor 3 (TLR3) pathway enables efficient induction of pluripotency by viral or mmRNA approaches. Stimulation of TLR3 causes rapid and global changes in the expression of epigenetic modifiers to enhance chromatin remodeling and nuclear reprogramming. Activation of inflammatory pathways are required for efficient nuclear reprogramming in the induction of pluripotency.

Type-I-interferons in infection and cancer: Unanticipated dynamics with therapeutic implications

“…69 In addition, it was recently shown that TLR3 stimulation on somatic cells caused global changes in the expression of epigenetic modifiers leading to enhanced chromatin remodeling, nuclear reprogramming, cell plasticity, pluripotentiality, transdifferentiation and even malignant transformation. 70 In line with these data, experiments in breast cancer cells put in evidence that NF-kB and b-catenin signaling downstream of TLR3 promoted the enrichment of a subset of cells with CSC phenotype. 71 Similarly, in the haematopoietic stem/progenitor cell (HSPC) compartment, chronic Type-I-IFN stimulation resulted in HSPC loss of quiescence and dysfunction.…”

Evading innate immunity in nonviral mRNA delivery: don’t shoot the messenger

“…Stimulation of TLR3 seems to affect the expression and/or distribution of epigenetic modifiers promoting an open chromatin configuration and thus nuclear reprogramming. Although these findings recommend stimulation of the innate immune system for efficient mRNA-based iPSC generation, the authors also note that the level of TLR3 should be balanced, as further stimulation can cause cell death [144].…”

Direct reprogramming of somatic cells: an update

“…Therefore, iPSCs must be screened to select free cells for further applications (Gonzalez et al, 2009). To date, the safest technique of iPSC production is induction of pluripotency via mRNA (Warren et al, 2012;Yoshioka et al, 2013) or protein (Kim et al, 2009;Lee et al, 2012). These iPSCs are called "clean" iPSCs.…”