Overcoming the chromatin barrier during reprogramming
Embryonic stem (ES) cells are able to give rise to all the cell types in an organism, a unique property called pluripotency. After ES cells differentiate into adult tissues, they lose the ability to respond to many environmental cues and can not differentiate into other cell types. This lack of plasticity is due to the permanent silencing of critical genes, a fact that in the past has been considered to be irreversible. However, recent achievements show that is possible to reprogram adult somatic cells to pluripotency by the overexpression of critical transcription factors. These induced pluripotent cells have the same properties as embryonic stem cells regarding self-renewal and pluripotency, and are thus of great importance for regenerative medicine.
The process of somatic cell reprogramming is very inefficient because it entails the reactivation of the endogenous pluripotency genes that are permanently silenced in somatic cells and refractory to stimulation. The molecular basis of this silencing is found in the structural organization of DNA around histone proteins, called chromatin. Both DNA and histones can be modified by the action of enzymes and as a result, the chromatin structure changes to facilitate or block the expression of genes. These modifications are inherited from cell to cell in a process that is known as epigenetic memory.
Our main goal is to gain insight into the epigenetic mechanisms that mediate the permanent silencing of pluripotency genes in human somatic cells and that contribute to the establishment of the repressive chromatin environment of these genes during the differentiation of human ES cells. We will address critical questions aimed at the identification of critical chromatin related factors that play a role in this process and to understand how these factors mediate their function.
We anticipate that the knowledge generated from our proposal will shed light on the epigenetic barriers that need to be overcome during somatic cell reprogramming and inspire approaches to make this process more efficient. Ultimately, these new approaches could facilitate the use of induced pluripotent cells for clinical applications. Moreover, understanding the mechanisms of gene silencing will provide basic knowledge about the mechanisms that govern cell plasticity and will also help to understand pathological processes like cancer, in which the epigenetic deregulation of gene silencing plays an important role.
Embryonic stem (ES) cells have the ability to differentiate into a variety of cell types, tissues and organs, which opens the door to the possibility of tissue engineering, replacement, and cell transplant therapies to cure diseases ranging from Parkinson’s, Alzheimer’s, diabetes, blood disorders and a host of other debilitating disorders. Rarely, there comes along a new technology that has the potential to make such a major impact on human health. Recently, researchers have discovered methods to reprogram adult fibroblasts and skin cells back into a cell type referred to as an induced pluripotent stem cell, which appears to be indistinguishable from a pluripotent ES cell. This is accomplished without the need for embryo destruction and offers great potential to alleviate the problems of immune rejection in cell or tissue transplantation by allowing a patient’s own cells to be reprogrammed, expanded and then used in therapeutic applications.
In this study we propose to gain insight into the basic mechanisms of gene silencing in the context of somatic cell reprogramming to pluripotency. Our findings could be used as a basis to enhance new strategies that render the process of reprogramming more efficient. These strategies might favor the generation of improved pluripotent cells that could later be used for therapeutic purposes, or as disease models by the pharmaceutical industry in order to test new drugs.
We anticipate that our work will generate important contributions to understanding the basic mechanisms of gene silencing and epigenetics. This knowledge can be of great importance to uncovering the molecular mechanisms governing pluripotency, cell plasticity and differentiation. Moreover, epigenetic abnormalities have been found to be causative factors in cancer, genetic disorders and pediatric syndromes, as well as contributing factors in autoimmune diseases and aging. We feel confident that the proposal presented here will significantly contribute to understanding diseases characterized by epigenetic deregulation.
Thus, our research will benefit the State of California by generating basic knowledge that will clearly reinforce the scientific leadership of California and that in the long term will inspire strategies applicable to therapeutic approaches that will directly benefit the people of California.