Laying the foundation for building a tooth: analysis of mammalian dental epithelial stem cells.

Funding Type: 
New Faculty I
Grant Number: 
RN1-00544-A
ICOC Funds Committed: 
$0
Stem Cell Use: 
Embryonic Stem Cell
Public Abstract: 
To fix a broken car, the mechanic either repairs or replaces the defective part. Similarly, one of the most promising approaches physicians foresee for treating human disease and ameliorating the aging process is regenerative medicine. One of the major aims of this field is to restore function by repairing or replacing damaged organs. Scientists envision a day when people with heart failure can be cured with hearts grown from their own cells, and a future in which dialysis machines are not needed because patients with damaged kidneys can be furnished with new ones. However, organ engineering is highly complex, and the field of regenerative biology is still in its early stages. Therefore, it is important to provide proof of principle and lay the foundation for creation of new organs by first using as simple a system as possible, and teeth provide an excellent model system for organ replacement. Their physiology is less complex than many other organs, but their development has much in common with that of other organs. This means that much of the information obtained from studying tooth regeneration will be generally applicable for building other organs. Teeth are a relatively safe prototype for organ regeneration, and there is a significant need for replacement teeth, as those born without teeth due to genetic defects, as well as elderly patients, patients with caries and periodontal disease, and victims of physical trauma all need new teeth. Our ultimate goal is to take advantage of basic biological principles in order to develop new therapeutic approaches. As such, we seek to help lay the groundwork for the formation of new teeth that can replace missing teeth, in the same way that permanent teeth replace the primary teeth formed in early childhood. This ambitious goal must be built on the proper foundation if it is to succeed. Therefore, we will first concentrate on a more readily achievable objective, which is to understand a naturally occurring version of regeneration by studying the continuous growth of the mouse incisor. This unusual tooth depends on the presence of adult stem cells to constantly produce all the cell types of the mature organ. Toward this end, we propose in this application to first analyze the biological processes that regulate the stem cells in this remarkable tooth. We will develop tools to grow the mouse stem cells outside of the animal in order to better understand them. Subsequently, we propose to translate what we have learned from the mouse model into human cells by learning how to induce human embryonic stem cells, fetal cells, or adult cells to become tooth progenitor cells. This last step will help lay the necessary groundwork for growing human teeth and blaze the trail for regeneration of larger organs.
Statement of Benefit to California: 
The promise of stem cell biology for regenerative medicine lies in the ability of these remarkable cells to give rise to more differentiated cell types that, individually or as part of a bioengineered organ, can replace structures that have been damaged by disease or aging. We propose to help lay the groundwork for organ regeneration by focusing on the tooth as a prototype organ. In addition to addressing the health issues posed by dental decay and tooth loss, which require prosthetic replacements that are functionally inferior to natural teeth, our project will help to pave the way for safe clinical applications of human embryonic stem cells in regeneration of larger organs, such as hearts or lungs. We anticipate that our research will be a significant step towards making the promise of regenerative medicine from adult stem cells and human embryonic stem cells a reality. Our studies will provide a much-needed model system that will allow us to study the basic mechanisms underlying guided development of organs from stem cells, which will be central to fulfilling the therapeutic potential of stem cell-based organ regeneration. Eventually, stem cell-based therapies will reduce health care costs for Californians by improving treatment for diseases for which we currently do not have effective therapies. Our work could provide economic benefits to the state by helping to lay the groundwork for commercial efforts to regenerate teeth as well as other solid organs, such as the heart and pancreas. Such developments would be of great benefit to California by making the state a leader in a field that is poised to become economically important in the future. The State of California will also stand to benefit from the intellectual property generated by this research, as generalizable principles regarding the use of stem cells, in vitro differentiation of cells, scaffolding materials, and organ bioengineering may be patentable.
Progress Report: 
  • Stem cells are the building blocks during development of organisms as varied as plants and humans. In addition, adult or “tissue” stem cells provide for the maintenance and regeneration of tissues, such as blood and skin throughout the lifetime of an individual. The ability of stem cells to contribute to these processes depends on their unique ability to divide and generate both new stem cells (self-renewal) as well as specialized cell types (differentiation).
  • In some tissues, cells that have already begun to specialize can revert or “de-differentiate” and assume stem cell properties, including the ability to self-renew. De-differentiation of specialized cells could provide a “reservoir” of cells that could act to replace stem cells lost due to wounding or aging. This proposal seeks to uncover the mechanisms that are utilized to regulate the process of de-differentiation and to compare these to the mechanisms that endow stem cells with the ability to self-renew. Understanding the mechanisms by which partially differentiated cells can reacquire self-renewal potential and how these programs are utilized during the normal course of tissue maintenance and repair could provide powerful strategies for regenerative medicine by stimulating inherent self-repair programs normally present within tissues and organs.
  • In the most recent funding period, we have focused primarily on understanding the role of a candidate protein, human Igf-II mRNA binding protein (hIMP1), that likely plays a role in enhancing the de-differentiation of committed cells back to a pluripotent stem cell state in mammalian systems. Published data indicate that hIMP1 is highly expressed in most tissue during development and that IMP1 is reportedly down-regulated in all tissues, except gonads, after birth. In contrast, our preliminary data suggest that IMP1 is highly expressed in human pluripotent stem cells as well as in some adult tissue stem and progenitor cells. Our focus in the coming year will be to address the role of hIMP1 in regulating the proliferation and differentiation of human stem cells.
  • Stem cells are the building blocks during development of organisms as varied as plants and humans. In addition, adult or “tissue” stem cells provide for the maintenance and regeneration of tissues, such as blood and skin throughout the lifetime of an individual. The ability of stem cells to contribute to these processes depends on their unique ability to divide and generate both new stem cells (self-renewal) as well as specialized cell types (differentiation).
  • A thorough understanding of the factors that regulate self-renewal programs will be essential for the expansion and long-term maintenance of adult stem cells in culture, a necessary step towards the successful use of stem cells in regenerative medicine and tissue replacement therapies. In some tissues, cells that have already begun to specialize can revert or “de-differentiate” and assume stem cell properties, including the ability to self-renew. De-differentiation of specialized cells could provide a “reservoir” of cells that could act to replace stem cells lost due to wounding or aging. This proposal seeks to uncover the mechanisms that are utilized to regulate the process of de-differentiation and to compare these to the mechanisms that endow stem cells with the ability to self-renew using the fruit fly Drosophila melanogaster as well as pluripotent human cells. Understanding the mechanisms by which partially differentiated cells can re-acquire self-renewal potential and how these programs are utilized during the normal course of tissue maintenance and repair could provide powerful strategies for regenerative medicine by stimulating inherent self-repair programs normally present within tissues and organs.
  • In the most recent funding period, we have characterized the role of a gene called multiple sex combs (msx), which plays a role in regulating the switch between proliferation and differentiation via control of proteins that are essential for proper DNA compaction and, consequently gene expression. Because the function of this gene is conserved in human cells, we speculate that understanding the function of this gene will provide insight into additional mechanisms that regulate the behavior of human stem cells. IN addition, we have characterized the role of human Igf-II mRNA binding protein 1 (hIMP1) in pluripotent human cells and during early neural differentiation. Lastly, we have developed a system for investigating maintenance and regeneration of specialized stem cell microenvironments in the Drosophila male germ line. Regeneration of stem cell environments (also known as ‘niches’) must accompany the expansion of stem cells required for tissue repair. Thus, investigating this process will lead to the identification of genes and pathways that regulate regeneration of stem cells in more complex mammalian tissues.
  • Stem cells are the building blocks during development of organisms as varied as plants and humans. In addition, adult or “tissue” stem cells provide for the maintenance and regeneration of tissues, such as blood and skin throughout the lifetime of an individual. The ability of stem cells to contribute to these processes depends on their unique ability to divide and generate both new stem cells (self-renewal) as well as specialized cell types (differentiation). A thorough understanding of the factors that regulate self-renewal programs will be essential for the expansion and long-term maintenance of adult stem cells in culture, a necessary step towards the successful use of stem cells in regenerative medicine and tissue replacement therapies. This proposal seeks to uncover the mechanisms that endow stem cells with the ability to self-renew using the fruit fly Drosophila melanogaster as well as pluripotent human cells.
  • In the most recent funding period, we have characterized the role of a gene called multiple sex combs (mxc), which plays a role in regulating the switch between proliferation and differentiation via control of proteins that are essential for proper DNA compaction and, consequently, gene expression; these genes are called histones. However, we have made the surprising finding that the protein encoded by mxc can regulate the expression of genes, in addition to histones. We have shown that this gene is required for maintenance of three different stem cell populations in flies; however, the mechanism by which Mxc regulates stem cell maintenance varies for each stem cell population. Because the function of this gene is conserved in human cells, we speculate that understanding the function of this gene will provide insight into additional mechanisms that regulate the behavior of human stem cells.
  • In addition, we have characterized the role of human Igf-II mRNA binding protein 1 (hIMP1) in pluripotent human cells and found that it regulates the expression of key proteins that maintain the pluripotent state and, thus, regulates the ability of these cells to give rise to specific tissues during development.
  • Lastly, we have developed a system for investigating maintenance and regeneration of specialized stem cell microenvironments in the Drosophila male germ line. Regeneration of stem cell environments (also known as ‘niches’) must accompany the expansion of stem cells required for tissue repair. Thus, investigating this process will lead to the identification of genes and pathways that regulate regeneration of stem cells in more complex mammalian tissues.

© 2013 California Institute for Regenerative Medicine