Understanding fundamental aspects of stem cell biology is essential to develop regenerative medicine therapies. Unacceptable outcomes include inadequate functionality, exhaustion, immune rejection, cancer development, and others. Recent studies strongly support our core hypothesis that mitochondrial function determines stem cell quality and safety. Dysfunctional mitochondria foster cancer, diabetes, obesity, neurodegeneration, immunodeficiency, and cardiomyopathy. Unlike whole genome approaches, methodological hurdles for evaluating mitochondria in human embryonic stem cells (hESCs) and in reprogrammed human induced pluripotent stem cells (hiPSCs) are significant and techniques developed or adapted for stem cells are almost non-existent. With a 2-year CIRM Seed Grant, we developed new approaches for analyzing respiration (oxygen consumption that drives energy production) in hESCs in a series of 4 invited publications for the stem cell scientific community (www.JoVE.com; 2008). We also now have a CIRM-supported manuscript under review describing the function of stem cell mitochondria in low oxygen (hypoxia), in normoxia (room air), and during differentiation. Building on these early studies, we have now determined that mitochondria are an essential component of stem cell differentiation and reprogramming. Specifically, we find that the mitochondria network structure changes between fragmented and fused appearances with differentiation or reprogramming, and that a mitochondrial quality control system is activated as hESCs differentiate. Essential metabolic changes are also required during differentiation, and these changes affect how mitochondria function to consume or generate cell energy. Our studies are providing new basic and clinical insights into stem cell biology and hold promise for developing applications to common diseases, such as Parkinson and Alzheimer neurodegenerative disorders and cancer. These CIRM-supported advances provide the underpinnings for our current proposal.
We propose two main aims to address fundamental questions in mitochondrial biology and the safety of stem cells. In Aim 1, we will characterize components that regulate the mitochondrial quality control system and network dynamics. These studies will delineate a system that ensures that healthy mitochondria are propagated, which is likely critical for successful regenerative medicine therapies. In Aim 2, we will establish the metabolic profiles of hESCs and hiPSCs in comparison to non-stem cells. Our early work suggests that a precise metabolic program for mitochondria is required for proper differentiation. Combined, we continue to build upon successful CIRM-funded work by moving into functional analyses of mitochondria that support stem cell self-renewal, survival, and differentiation, with major economic and social implications for new-age cellular therapies in medicine.
Statement of Benefit to California:
This proposal benefits California by adding new knowledge about the influence of mitochondria in metabolic functions of human embryonic stem cells (hESCs), human induced pluripotent stem cells (hiPSCs), and their lineage differentiated derivatives, which will support the California peoples' and taxpayers' commitment to personalized cell therapies. This new work builds on a highly successful two-year CIRM Seed Grant [REDACTED] that provided one of the first systematic characterizations of stem cell mitochondria. CIRM funds supported 1) four published protocols (www. JoVE.com) on growing pure stem cells to characterize mitochondria, 2) the first report of high-resolution genome differences between hESCs derived from different individuals, and 3) now complete studies that characterize the functional capabilities of hESC mitochondria that are under review. This completed study, and the new mechanism-driven studies in our current proposal, will help clinician/scientists select the best possible stem cells for investigation and therapy development in our major academic centers and will provide information to many of California's biotechnology and pharmaceutical companies in the ever growing stem cell industry, whose success will propel hiring and increased economic prosperity for the state. Our ongoing CIRM-funded work will provide additional information to patient advocates, ethicists, and medical geneticists to help select the optimal course for developing and modifying stem cell usage policies and infrastructure within California. This proposal will provide information for patients and their physicians that may, at some future time, impact the selection of particular stem cell attributes for specific types of therapeutic applications. In sum, added knowledge provided by our new studies on mitochondrial factors that control stem cell metabolism and mitochondrial dynamics will help drive successful differentiation of hESCs, will propel the most complete cellular reprogramming to hiPSCs, and will generate cell therapies with reduced risk, increased safety, and limited cancer potential. Understanding mitochondrial biology in stem cells is particularly important when considering stem cell therapeutics because mitochondrial energy production is required for functional stem cell differentiation (paper under review, 2011). A faulty or sub-optimal energy generation system may severely impact the success of developing stem cell-derived therapies, or cause therapies that appear initially successful to fail over time. With success in this proposal, tangible health and economic impact on California, its academic institutions and biotechnology/pharmaceutical companies, and the rest of the nation will be achieved as California and its people lead the way forward with personalized medicine for the 21st century and beyond.
The goal of the proposed research is to evaluate the role of changes in mitochondrial morphology and mitochondrial metabolism in determining stem cell fate. Mitochondria are the cellular centers of energy metabolism, but their contribution to the regulation of stem cell self-renewal and differentiation is poorly understood. The first specific aim is to investigate how changes in morphology of the dynamic mitochondrial network and mechanisms that regulate quality control of mitochondria affect the differentiation of human pluripotent stem cells (hPSC). The second specific aim is to characterize changes in mitochondrial bioenergetics during stem cell self-renewal and differentiation.
Significance and Innovation:
- The proposal focuses on an important yet relatively neglected area of stem cell biology.
- The significance of the proposed study is unclear; mitochondrial activities might be deterministic for stem cell fate decisions, or mitochondrial changes could be a consequence of differentiation.
- Reviewers questioned the project’s novelty, as others have proposed key roles for mitochondria in stem cell differentiation.
Feasibility and Experimental Design:
- The proposed investigation is based on promising but essentially correlative preliminary data, much of which has yet to be published.
- Reviewer enthusiasm was diminished by an absence of key experimental details and inadequate information about experimental methods.
- Reviewers found that those portions of the study focused on mitochondrial quality control and on metabolomic analysis were vague and incomplete.
Principal Investigator (PI) and Research Team:
- The principal investigator (PI) and co-investigator have excellent track records, appropriate expertise, and together represent a major strength of the proposal.
- Reviewers considered the research team to be strong, although they expressed concern that the number of personnel on the project was excessive.
Responsiveness to the RFA:
- This proposal is entirely responsive to the RFA, as it investigates molecular mechanisms underlying fundamental aspects of proliferation and differentiation of human embryonic stem cells and hPSC.