MicroRNA Regulation of Human Embryonic Stem Cell Self-Renewal and Differentiation

MicroRNA Regulation of Human Embryonic Stem Cell Self-Renewal and Differentiation

Funding Type: 
SEED Grant
Grant Number: 
RS1-00161
Award Value: 
$605,886
Stem Cell Use: 
Embryonic Stem Cell
Status: 
Closed
Public Abstract: 
A major hurdle for regenerative medicine is the safe transplantation of human embryonic stem (ES) cells or their derivatives into patients. While the unlimited growth potential of ES cells is a major asset for their potential in tissue replacement, it is also a major risk for tumorigenesis. Therefore, it is critical to determine what molecules are responsible for silencing the tumorigenic risk of embryonic stem cell derivatives as occurs during the process of normal development. Identification of such molecules should provide both markers for tumorigenic risk as well as potential targets for therapeutic intervention when tumors do develop from transplanted tissue. We now know that most, if not all adult cells can revert to an early stem cell phenotype. This has been proven by a technique called somatic cell nuclear transfer, where adult cell nuclei are transferred into oocytes and allowed to develop as early embryos. These embryos reactivate the embryonic stem cell program within the adult nuclei. Cells derived from these embryos, the embryonic stem cells, have regained the ability to proliferate indefinitely, a property termed self-renewal. Therefore, considering there is in the order of one hundred trillion cells in the adult human, it is amazing that some fraction of cells do not commonly reactivate the stem cell program by chance. This is because human have evolved an amazing and complex network of molecules whose main purpose is to permanently silence critical components of the embryonic stem cell program. Unfortunately, this network is poorly understood. The aim of our laboratory and of this research proposal is to identify these factors and use them to our advantage. We have discovered in the mouse model that small RNA molecules called microRNAs are essential for the silencing of the embryonic stem cell’s capacity to self-renew. In this grant, we propose to confirm a similar role for microRNAs in human ES cell differentiation. Furthermore, we propose to identify the molecular nature of the specific microRNAs responsible for this function. These miRNAs could then be used as markers for both the developmental potential of embryonic stem cells derived by various means as well as a marker for the appropriate silencing of self-renewal in ES cell derived tissues prior to transplant in patients. Furthermore, they could provide targets for therapeutic intervention in the unfortunate scenario of tumor formation from transplanted tissues that had failed to fully silence the stem cell program.
Statement of Benefit to California: 
This grant proposes to identify the molecules that normally silence the potential of human embryonic stem cells to proliferate indefinitely. Identification of such molecules should benefit California in at least two ways. First, understanding the mechanisms our cells have evolved to silence indefinite proliferation would provide novel targets for therapeutic interventions in cancers either resulting spontaneously or from transplanted embryonic stem cell derivatives. Second, expression of these molecules should provide markers and, therefore, tests for analyzing the developmental and tumorigenic potential of embryonic stem cell derivatives pre- and post-transplant of these cells into patients. Such advances would benefit the health as well as the economy of the state of California.
Progress Report: 

Year 1

Public Progress Report A major risk in the regenerative medicine field is the potential of tumorigenesis in transplanted tissues. To minimize this risk, it is essential that we understand the mechanisms that normally suppress tumorigenesis in adult tissues. When transplanted, human embryonic stems invariably form tumors showing the natural tendency of these cells for uncontrolled cell growth. However, the natural counterparts of these cells that occur during human embryonic development rarely ever form tumors. This suggests that there are powerful embryonic programs that suppress unwanted cell growth as these cells differentiate into adult tissues. We have established a likely role for small molecules called microRNAs in this process. In the absence of microRNAs, the embryonic stem cells fail to differentiate into adult tissues and hence proliferate indefinitely. The goals of our CIRM grant are to uncover the specific microRNAs that are responsible for differentiation and the suppression of cell growth. In the past year, we have made significant progress toward this goal. First, we have completed studies from the previous year and have now published one and have another press, both in high impact journals. One study was published in Nature Biotechnology where we show that a family of microRNAs can promote the de-differentiation of specialized cells back to unspecialized embryonic cells that than can be differentiated to all adult cell types. The other study is in press in Nature and shows how another family promotes differentiation and suppresses proliferation of embryonic stem cells. Furthermore, it shows that the two families: one promoting de-differentiaton and the other promoting differentiation antagonize one another in the decision of whether to continue to remain undifferentiated and proliferate. Second, we have performed large screens to identify many other miRNAs that promote differentiation both in mouse and human ES cells. We are now following the promising miRNAs and expect to uncover various different means of promoting ES cell differentiation and suppressing their tumor forming potential. Our findings provide insights into how one might use small RNAs to clinically manipulate cells in order to expand stem cells or promote their differentiation as needed to produce stable replacement tissues with diminished risk for tumor growth.

Year 2

A major risk in the regenerative medicine field is the potential of tumorigenesis in transplanted tissues. When transplanted, human embryonic stems invariably form tumors showing the natural tendency of these cells for uncontrolled cell growth. However, the natural counterparts of these cells that occur during human embryonic development rarely ever form tumors. This suggests that there are powerful embryonic programs that suppress unwanted cell growth as these cells differentiate into adult tissues. We have established a likely role for small molecules called microRNAs in this process. In the absence of microRNAs, the embryonic stem cells fail to differentiate into adult tissues and hence proliferate indefinitely. The goals of our CIRM grant are to uncover the specific microRNAs that are responsible for differentiation and the suppression of cell growth. During the period of this grant, we have made significant progress toward this goal. We have published two manuscripts on this work, both in high impact journals. One study was published in Nature Biotechnology where we show that a family of microRNAs can promote the de-differentiation of specialized cells back to unspecialized embryonic cells that than can be differentiated to all adult cell types. This work also led to a submission of a patent. The other study in Nature shows how another family promotes differentiation and suppresses proliferation of embryonic stem cells. Furthermore, it shows that the two families: one promoting de-differentiaton and the other promoting differentiation antagonize one another in the decision of whether to continue to remain undifferentiated and proliferate. Second, we have performed large screens to identify many other miRNAs that promote differentiation and de-differentiation both in mouse and human ES cells. We are now trying to complete these stories and prepare them for publication. Our findings provide insights into how one might use small RNAs to clinically manipulate cells in order to expand stem cells or promote their differentiation as needed to produce stable replacement tissues with diminished risk for tumor growth.

Publications

© 2013 California Institute for Regenerative Medicine