Response to Letter Regarding Article “Transdifferentiation of Human Fibroblasts to Endothelial Cells: Role of Innate Immunity”

Abstract

Background-Cell fate is fluid and may be altered experimentally by the forced expression of master regulators mediating cell lineage. Such reprogramming has been achieved with the use of viral vectors encoding transcription factors. We recently discovered that the viral vectors are more than passive vehicles for transcription factors because they participate actively in the process of nuclear reprogramming to pluripotency by increasing epigenetic plasticity. On the basis of this recognition, we hypothesized that small-molecule activators of toll-like receptor 3, together with external microenvironmental cues that drive endothelial cell (EC) specification, might be sufficient to induce transdifferentiation of fibroblasts into ECs (induced ECs). Methods and Results-We show that toll-like receptor 3 agonist Poly I:C, combined with exogenous EC growth factors, transdifferentiated human fibroblasts into ECs. These induced ECs were comparable to human dermal microvascular ECs in immunohistochemical, genetic, and functional assays, including the ability to form capillary-like structures and to incorporate acetylated low-density lipoprotein. Furthermore, induced ECs significantly improved limb perfusion and neovascularization in the murine ischemic hindlimb. Finally, using genetic knockdown studies, we found that the effective transdifferentiation of human fibroblasts to ECs requires innate immune activation. Conclusions-This study suggests that manipulation of innate immune signaling may be generally used to modify cell fate. Because similar signaling pathways are activated by damage-associated molecular patterns, epigenetic plasticity induced by innate immunity may play a fundamental role in transdifferentiation during wound healing and regeneration. Finally, this study is a first step toward development of a small-molecule strategy for therapeutic transdifferentiation for vascular disease.

Senescence-Inflammatory Regulation of Reparative Cellular Reprogramming in Aging and Cancer

“…Beyond an optimal threshold zone of optimally and transiently activated transflammation, a successful augmentation of epigenetic and phenotypic tissue plasticity would be minimal or totally absent despite damage/disease-driven activation of cellular reprogramming-like processes (Figure 1). Reaching into an optimal zone of transflammation-initiated cellular reprogramming-like phenomena, followed by re-acquisition of the original or alternative cell fate, might allow tissue repair via replenishment or transdifferentiation of the original damaged/lost cells (Lee et al, 2012; O'Neill, 2012; Cooke et al, 2014, 2015; Sayed et al, 2015). Conversely, a chronic, cell-autonomous hyperactivation of comparable inflammation-epigenetic axes (e.g., NF-κB), rather than establishing stem-like epigenetic states, will position the damaged/stressed cell outside the optimal zone for cellular reprogramming, impeding tissue rejuvenation and generating an aging phenotype (Figure 1).…”

“…At sites of transient inflammation, acute resolution of inflammatory response mediated by IL-6 (and downstream activation of NF-κB) could be accompanied by beneficial tissue regeneration (Cressman et al, 1996; Taub et al, 1999; Lasry and Ben-Neriah, 2015; Chiche et al, 2017), or reparative transdifferentiation (e.g., conversion of fibroblasts into endothelial cells to increase microvascular density in response to myocardial infarction-induced ischemic injury; Cooke et al, 2015; Sayed et al, 2015). At sites of chronic inflammation, if the culmination of transient reprogramming to stem-like epigenetic states is not accompanied by a committed re-acquisition of the original or alternative (but beneficial) differentiated cell fate, unrestrained nuclear reprogramming-driven tissue plasticity might impair the repair or replacement of damaged cells and at the same time generate cancer-like cellular states.…”