Scientists at the Centre for Genomic Regulation (CRG) in Barcelona say they have taken a significant step toward understanding cellular reprogramming and its efficiency by means of their discovery of the major role of the Wnt signaling pathway in transforming adult cells into induced pluripotent stem cells (iPS cells, or iPSCs). They report their work ("Temporal Perturbation of the Wnt Signaling Pathway in the Control of Cell Reprogramming Is Modulated by TCF1") in Stem Cell Reports.
"Generally, transcription factors are used to try to increase or decrease the cell reprogramming process. We have discovered that we can increase the efficiency of the process by inhibiting the Wnt route," explained Francesco Aulicino, a Ph.D. student in the reprogramming and regeneration group, led by Maria Pia Cosma, Ph.D., and co-author of the study.
The Wnt signaling pathway is a series of biochemical reactions that are produced in cells. In frogs or lizards, for example, these reactions are those that allow their extremities to regenerate if the animal suffers an injury. Although in general humans and mammals have lost this regenerative capacity, the Wnt pathway is involved in numerous processes during embryonic development and cell fusion.
The researchers have studied how the Wnt route behaves throughout the entire process of transforming cells into iPS cells, which usually lasts two weeks. It is a very dynamic process that produces oscillations from the pathway, which is not active all the time.
"We show that Wnt/beta-catenin signaling needs to be off during the early reprogramming phases of mouse embryonic fibroblasts (MEFs) into iPSCs. In MEFs undergoing reprogramming, senescence genes are repressed and mesenchymal-to-epithelial transition is favored," wrote the investigators. "This is correlated with a repressive activity of TCF1, which contributes to the silencing of Wnt/beta-catenin signaling at the onset of reprogramming. In contrast, the Wnt pathway needs to be active in the late reprogramming phases to achieve successful reprogramming. In conclusion, continued activation or inhibition of the Wnt/beta-catenin signaling pathway is detrimental to the reprogramming of MEFs; instead, temporal perturbation of the pathway is essential for efficient reprogramming, and the ‘Wnt-off’ state can be considered an early reprogramming marker."
To artificially control the pathway, the group has employed a chemical molecule, Iwp2, which is a Wnt secretion inhibitor that does not permanently alter the cells, something which other research into reprogramming using different factors has still has not been able to achieve.
"It is a very important and an innovative advance in the field of cell reprogramming, because until now this was a very inefficient process. There are many groups trying to understand the mechanism by which adult cells become pluripotent, and what blocks that process and makes only a small percentage of cells end up being reprogrammed. We are providing information on why it happens," noted Ilda Theka, also a Ph.D. student in the Cosma group and a co-author of the article.
The team believes their study opens the way to new advances in regenerative medicine and sheds light on certain types of tumors involving the Wnt pathway. Other labs are also working on ways to increase efficiency when inducing pluripotency in these cells.