Bioengineering an Artificial Stem Cell Niche to Facilitate the Nuclear Reprogramming of Ipsc (I)

The fate of stem cell is tightly regulated through the concerted action of stem cell-intrinsic factors as well as signals derived from the residing milieu, niche. The function of stem cell niche not only serves as a development and regeneration unit in many tissues, but also nourishes stem cell resided within and provides local or systemic instruction for immediately response to body’s needs. Thus, the fate decision of a stem cell counts on the neighboring tissues, extrinsic signals, and intrinsic properties of itself. This context-dependent combinatorial complexity of stem cell niche poses an enormous challenge to studying the underlying mechanism of stem cell biology. To unravel the interplay signals that derived from intrinsic and extrinsic factors, there is a need to reconstruct the stem cell niche in in-vitro system which recapitulates the dynamic features of these interactions between stem cell and their microenvironment. Traditional stem cell culture system applied the cell cycle arrested feeder cells to provide an artificial environment for the growth of stem cell. Such system only offers a homeostatic microenvironment for maintaining pluripotency of stem cell without revealing the dynamic status of the pluripotent circuitry which may play a pivotal role in the fate decision of stem cell. In this study, I therefore propose to adopt the dynamic process of iPSC (induced pluripotency stem cell) formation to dissect the signal transduction pathways between the provided artificial microenvironments and the stemness acquisition. To this end, an artificial stem cell niche will be constructed to allow us to customize in-vitro cellular microenvironments with defined factors. With such an in-vitro culture system, it allows interrogating participants in a versatile and quantitative fashion. Meanwhile, to have a measureable response from a formulated stem cell niche, a read-out from the cell dwelled within the bioengineered niche is required. Utilizing the process of nuclear reprogramming of iPSC (induced pluripotent stem cell) formation as a pluripotency read-out should provide a sensitive measurement for interrogating each component in the bioengineered niches. Given our recent success in generating iPSC from mouse MEF, my lab have established a triple iPS transgenic mouse line, the “All-iPSC” mouse strain named MOG, which is capable to provide a quantitative readout for indicating the interplay between iPSC formation and the formulated niches. The All-iPSC mouse carried the rtTA, GFP, and tetO-regulated iPSC quartet factors knocked-in to the ROSA26, OCT4, and Col1a locus, respectively. Regardless the somatic cell types, MOG provides an identical genetic background for every single iPSC clones formed after doxycycline induction, and thus avoids the heterogeneity in the population of cells derived from the vector-mediated iPSC generation strategies. As individual iPSC clones represent independent reprogramming events of its original cell type, our formulated niche system is capable of providing the connection between the observed pluripotent phenotype and the interrogated factors at the clonal resolution for each stage of iPSC formation. The unique features of stem cell pose a tremendous potential for cell replacement therapy in regeneration medicine. Performing a cell replacement therapy, however, needs to understand the biology of different niches to avoid the depletion of the transplanted stem cells. In addition, unraveling how the niche forms, which signals provide for each stem cell in different tissues, and how the specific intrinsic and extrinsic signals interplay determine the action of stem cell shall ameliorate age-dependent stem cell loss and increase the homing efficiency of transplanted stem cells for future stem cell therapy.

Project ID:PA10210-0015
External Project ID:NSC102-2633-B182-001