Mitochondrial regulation of self-renewal and differentiation potential of human embryonic stem cells
Human embryonic stem cells, by virtue of their capacity to proliferate indefinitely and to differentiate into almost all types of somatic cells, hold the potential to help us understand and cure, some of our most devastating diseases. The nucleus of a cell controls the expression of its genes and is responsible or the eventual coding of all the proteins that make up the different kinds of functionalities attributed to such a cell. However, each of our cells also contains a large number of copies of mitochondria, which contain their own DNA and proteins responsible for generating most of the energy needed for the functioning of these cells. In addition to energy generation, the mitochondrion is also the site of much biosynthesis. This explains why, even after millions of years of evolution, human cells have learnt to coexist with the mitochondrion, which are derived from bacteria, rather than take on the task of energy generation as part of their nuclear function.
Under normal circumstances, we assume that each cell will contain a perfectly functioning set of mitochondria. A cell will then possess normal metabolism similar to the other cells found within our body. When we talk about transplanting stem cells that have grown on a dish for a while, or when we derive hIPS cells from mature skin cells that are reprogrammed, we test the cells repeatedly for their nuclear coding capacity before use in therapy. Less attention, we believe, has been paid to the metabolic status and the mitochondrial function of the cell. We find it critical that each cell line be given a “metabolic health check” before its use in therapy.
This is important from many standpoints. Mutations in mitochondrial DNA can cause disease, so we intend looking for such changes in the stem cell lines being used. Our studies suggest that the mitochondria are highly dynamic and their morphology varies from one cell line to another although each of these lines is considered virtually synonymous with the other in all other aspects. Our collaborator, [REDACTED} finds that the greatest variation between an ES and an IPS cell line is in the expression of mitochondrial genes. Finally, we find that stem cells in which we induce mitochondrial defects will cause tumors in mice under circumstances where normal stem cells will not. All these issues suggest that the metabolic status of a cell needs to be thoroughly examined before its use in therapy. The problem is in defining what the range of “normal” states is going to be. For this, we need to do controlled experiments with large numbers of lines that we query through many experimental paradigms. From this basic scientific interrogation will result the Standard Operating Procedure for assessing the metabolic component of an acceptable stem cell line. Creating such a protocol based on initial mechanistic studies is the central focus of this proposal.
California is at the forefront of Stem Cell and Regenerative Medicine Research. At [REDACTED], under the auspices of the [REDACTED] we wish to move the basic science of stem cells from the bench to the clinic as efficiently and as safely as possible. This proposal furthers these goals in two ways. As a basic science proposal, it seeks to ask mechanistic questions about the role of metabolism in stem cell function. As importantly, its more practical goal is to ensure safety in the procedures followed. We hope that with the guidelines that we will develop as a result of this proposal, all scientists, particularly those in California, will have a rapid access to obtain a “metabolic check” on the lines that they anticipate using in therapy. In conjunction with our [REDACTED}, we hope, for the future, to be able to push the limits of such detection to a finer scale. This will be a critical step in achieving California’s goal in setting operating procedures and setting guidelines for stem cell research around the world.