The Control of Proliferation, Migration, and Differentiation of Human Pluripotent Stem Cells-Derived Neural Progenitor Cells by MicroRNAs
Basic Biology I
Neurodegenerative diseases such as Alzheimer’s disease, frontotemporal dementia, amyotrophic lateral sclerosis, Parkinson’s disease, Huntington’s disease, as well as stroke and spinal cord injuries, pose a serious challenge to our society. All are characterized by neuronal cell loss in specific regions of the brain or spinal cord. It is conceivable that the functions of these regions could be restored by replacing damaged nerve cells through transplantation of stem cells or stem cell–derived progenitor cells. Such cells could differentiate into the desired cell types and then integrate into functional neuronal circuits. Therefore, human embryonic stem cells (hESCs) and induced pluoripotent stem (iPS) cells offer an exciting new approach for treating brain diseases and injuries. However, before clinical applications become a reality, much more needs to be learned about the cellular behaviors of neural progenitor cells (hNPCs) derived from human pluripotent stem cells (hPSCs). For instance, transplanted stem cells or stem cell–derived hNPCs must be prevented from turning into tumors and they must migrate effectively to injured brain regions and incorporate into the damaged neuronal circuitry. Thus, understanding the basic molecular mechanisms that govern the proliferation, migration, and differentiation of hPSC-derived hNPCs is critically important. The studies proposed here will further our understanding of how microRNAs—a recently identified class of small regulatory RNA molecules—control the cellular behaviors of hPSC-derived hNPCs. These studies will provide important mechanistic insights into the basic molecular pathways relevant to human stem cell biology. Since miRNAs are excellent tools for manipulating cellular behaviors and may become feasible targets for therapeutic approaches, the proposed studies will likely contribute to the development of effective stem cell–based therapies for neurodegenerative diseases and brain and spinal cord injuries.
Statement of Benefit to California:
California is the most populous state in the U.S., and many Californians suffer from neurodegenerative diseases and brain and spinal cord injuries. Unfortunately, these insidious conditions remain incurable, and will become more common as the number of people of advanced age increases. Stem cell–based therapies are a promising new approach for these problems; however, much more need to be done to understand the basic biology of human embryonic and induced pluoripotent stem cells. We propose to investigate the roles of a class of small RNA molecules called microRNAs in controlling the proliferation, migration, and differentiation of human neural progenitor cells derived from human stem cells. These studies will help develop feasible therapeutic approaches that will eventually be used to treat patients in California and around the world.
The goal of this proposal is to understand how specific microRNAs (miRNAs) regulate the proliferation, migration and differentiation of human neural progenitor cells (hNPCs) derived from human embryonic stem cells. The proposal builds on the applicant's recent work showing that a brain-specific miRNA influences the proliferation and migration of hNPCs. In Aim 1, the applicant proposes to study the molecular mechanisms underlying this observation. In Aim 2, the applicant will focus on a closely related miRNA and examine its effects on hNPC proliferation, migration and differentiation. Finally, in Aim 3, the applicant proposes to manipulate these miRNAs in hNPCs prior to transplant into mouse embryos and adult mouse brains and assess their effects on the migratory behavior of these cells in vivo. Reviewers did not believe that this proposal would make a major impact in the field. They noted that the applicant has done outstanding work in Drosophila but that the rationale for moving this work into human cells is not yet compelling. Reviewers suggested that more genetically accessible model organisms, such as mice, might yield results at a faster pace. In addition, they specifically questioned the rationale for Aim 2, noting that the miRNA of interest has no known role in any tissue or organism and its expression in hNPCs can only be inferred from the preliminary data presented. While reviewers appreciated the proposal's focus on mechanism, they did not find the project particularly innovative and felt it would only produce an incremental advance in the field. Reviewers agreed that the research plan is both logical and feasible but they raised a number of issues with the preliminary data. They found some of this data confusing and incomplete. For example, Figure 6, which displays a ratio of miRNA expression, provided no explanation of how these data were obtained or exactly what they represent, yet these are the only data in the proposal suggesting that the miRNA of interest in Aim 2 is expressed in hNPCs. Reviewers found Aim 3 to be poorly written and weakly justified and were unsure what new information it would yield. They noted that the applicant does not describe how migration will be quantified in vivo and that the miRNA knockdown proposed will only last a few days, not long enough to study migration to stroke areas in adult brain. Reviewers described the applicant as a productive investigator with significant experience studying miRNAs. They noted that s/he has an impressive publication record, with many articles published in top-tier journals. Reviewers were concerned that no supporting information or letter from a collaborator who is central to Aim 3 was provided, and a Biosketch for a named postdoc was not supplied. However, in general, reviewers found the research team well-qualified to carry out the proposed research. Overall, reviewers appreciated this proposal's logical, achievable aims and the applicant's considerable expertise. However, they questioned the scientific rationale for the project and did not find it likely to make a significant impact in the field of human stem cell biology.