Much attention has focused in recent years on the promise of using embryonic stem (ES) cells and their differentiated progeny to regenerate various adult tissues. We believe, however, that for the foreseeable future, a far more viable and attainable strategy will derive, at least in the case of epithelial tissues, from experimental protocols designed to induce the reprogramming of differentiated adult cells into committed progenitors and stem cells, which can then serve as vehicles for the regeneration of adult tissues depleted by aging or by various pathological processes. For this purpose, we intend to develop a cocktail of signaling agents that can be applied to differentiated epithelial cells in order to reprogram them to lineage-committed epithelial stem cells. Our strategy is to re-activate a latent developmental program, termed the Epithelial-Mesenchymal Transition (EMT). We have previously shown that induction into EMT confers on differentiated mammary epithelial cells many of the traits associated with epithelial stem cells. Importantly, we believe that our rationale is applicable to a wide range of differentiated epithelial cells, including stratified squamous epithelia, such as the mucosa of the mouth. EMTs effect key morphogenetic steps during various steps of embryonic development. In general, research has focused on the ability of EMTs to switch cellular fate from epithelial to mesenchymal, thereby causing profound changes in cell morphology and function. However, our recent findings indicate a novel physiological role for EMTs in stem-cell self-renewal and thus in tissue homeostasis. Reinforcing this association between the products of EMT and the stem-cell state is the finding that putative human and mouse mammary stem cells have been shown to possess mesenchymal traits, further linking EMT to stem cell biology. Importantly, the close parallels between EMT and the stem-cell state do not appear to be an idiosyncrasy of the mammary epithelium: emerging evidence suggests an essential role for the EMT-inducing Transcription Factors (TF) Snail and Slug in skin morphogenesis. During the course of development, epithelial-mesenchymal transitions (EMTs) are induced and coordinated by contextual signals received by individual cells from adjacent cell layers. Thus, the convergence of several paracrine signals on an embryonic epithelial cell induces that epithelial cell to undergo an EMT. Based on these observations, we have hypothesized that the initial triggering of an EMT program within a cell depends on concomitant stimulation of that cell by a defined set of such paracrine signals, and that maintenance of the resulting mesenchymal/stem-cell state depends subsequently on the activation of autocrine signaling loops involving the same factors that previously triggered entrance into the EMT. Indeed, our preliminary data are in concordance with this model, underscoring the importance of the extracellular signaling environment for regulating EMTs, and reinforcing our rationale to develop an experimental protocol with a cocktail of signaling agents as a means to dedifferentiate and reprogram differentiated epithelial cells to a stem cell-like state. In the longer term, we intend to develop a protocol for inducing the controlled dedifferentiation of a number of distinct adult epithelial cell types into their corresponding stem cells. Such protocols have the potential of generating large numbers of committed epithelial stem cells that hold promise for the regeneration of a variety of depleted adult epithelial tissues.
Much attention has focused in recent years on the promise of using embryonic stem (ES) cells to regenerate various adult tissues. We believe, however, that for the foreseeable future, a far more viable and attainable strategy will derive from experimental protocols designed to induce the reprogramming of differentiated adult cells into committed progenitors and stem cells. These reprogrammed cells can then serve as vehicles for the regeneration of adult tissues depleted by aging or by various pathological processes. For this purpose, we intend to develop a cocktail of signaling agents that can be applied to in vitro cultures of differentiated epithelial cells in order to reprogram them to committed epithelial stem cells via activation of a latent developmental program. We believe that this strategy can be applied to many epithelial tissues, such as the skin or mouth mucosa.
|Scheel, Christina; Weinberg, Robert A (2012) Cancer stem cells and epithelial-mesenchymal transition: concepts and molecular links. Semin Cancer Biol 22:396-403|
|Li, Hua-Jung; Reinhardt, Ferenc; Herschman, Harvey R et al. (2012) Cancer-stimulated mesenchymal stem cells create a carcinoma stem cell niche via prostaglandin E2 signaling. Cancer Discov 2:840-55|
|Scheel, Christina; Eaton, Elinor Ng; Li, Sophia Hsin-Jung et al. (2011) Paracrine and autocrine signals induce and maintain mesenchymal and stem cell states in the breast. Cell 145:926-40|
|Scheel, Christina; Weinberg, Robert A (2011) Phenotypic plasticity and epithelial-mesenchymal transitions in cancer and normal stem cells? Int J Cancer 129:2310-4|