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RN1-00542-1: Role of Apolipoprotein E in Hippocampal Neurogenesis and Its Therapeutic Potential in Alzheimer's Disease
Recommendation: Not recommended for funding
Public Abstract (provided by applicant)
GOALS I propose (1) to determine the molecular and cellular mechanisms by which apolipoprotein (apo) E4 impairs the generation of new neurons in the hippocampus of mice and (2) to explore whether apoE4-induced learning and memory impairments in mice can be rescued by stimulating the generation of new neurons or transplanting mouse or human neural stem cells expressing apoE3 into the hippocampus.
RATIONALE AND SIGNIFICANCE In many mammals, including humans, new neurons are generated throughout life in the subgranular zone (SGZ) of the dentate gyrus in the hippocampus and may participate in learning and memory formation. Alzheimer’s disease (AD) causes progressive and irreversible cognitive loss, and there is no effective treatment. Since early loss of neurons in the hippocampus is a major pathological feature of AD, transplantation of neural stem cells into the hippocampus might be an effective treatment.
Among its neurobiological functions, apoE distributes lipids in the central nervous system for normal lipid metabolism and participates in neuronal repair and remodeling. However, its three isoforms (apoE2, apoE3, and apoE4) differ in their ability to accomplish these critical tasks. ApoE4 is a major risk factor for AD, is associated with a smaller hippocampus in humans, and impairs learning and memory in mice carrying human apoE4 gene.
This proposal builds on novel findings suggesting that apoE modulates the generation of new neurons in the hippocampus and that apoE4 contributes to the development of AD by impairing this process. Stimulating the generation of new neurons in the hippocampus or transplanting neural stem cells expressing apoE3 into the hippocampus might rescue the learning and memory impairments associated with apoE4 in AD. The outcome of the proposed studies will shed light on the cause of AD and will provide a foundation for the development of stem cell therapy in AD patients carrying the apoE4 gene, who account for ~50% of total AD cases.
SPECIFIC AIMS Aim 1. To determine the molecular and cellular mechanisms by which apoE deficiency and apoE4 impair the generation of new neurons in the hippocampus in mice. Aim 2. To test whether stimulating the generation of new neurons in the hippocampus improves the learning and memory deficits associated with apoE4 in mice. Aim 3. To explore whether transplanting mouse or human neural stem cells expressing apoE3 into the hippocampus rescues the learning and memory impairments associated with apoE4 in mice.
Statement of Benefit to California (provided by applicant)
CONTRIBUTION TO THE CALFORNIA ECONOMY: A major goal of regenerative medicine is to repair damaged cells or tissue. My research focuses on (1) understanding the role of neuronal regeneration in learning and memory and (2) developing stem cell therapy for Alzheimer’s disease. Alzheimer’s disease is the leading cause of dementia and is the fastest growing form of cognitive impairment in California, in the USA, and worldwide. My research could benefit the California economy by creating jobs in the biomedical sector. Ultimately, this study could help reduce the adverse impact of neurodegenerative diseases. Thereby, I hope to increase the productivity and enhance the quality of life for Californians.
The results of my studies will also help develop new technology that could contribute to the California biotechnology industry. The studies will characterize multiple lines of neural stem cells carrying apoE3, a protein protective to the brain, or apoE4, which is detrimental to the brain and is associated with increased risk of Alzheimer’s disease. These cell lines could be valuable for biotechnology companies and researchers who are screening for drug compounds targeting Alzheimer’s disease.
CONTRIBUTION TO THE HEALTH OF CALFORNIANS: The most important contribution of the studies will be to improve the health of Californians. Diseases that are the target of regenerative medicine, such as Alzheimer’s disease, are major causes of mortality and morbidity, resulting in billions of dollars in healthcare costs and lost productivity. As we continue our efforts in medical research, we hope to one day unlock the secrets of brain development and repair. This knowledge will help medical researchers develop beneficial therapies beyond what is currently available and potentially improve the quality of life and life expectancy of patients with neurodegenerative diseases, such as Alzheimer’s disease.
Review
SYNOPSIS: Three isoforms of apolipoprotein E (apoE) play broad-based roles in lipid homeostasis, neuronal repair and neuronal remodeling. However, these three isoforms differ in their ability to accomplish these tasks and one of them, apolipoprotein E4 (apoE4), is a major risk factor for Alzheimer’s disease (AD, 50% of all cases). The proposal is to identify the molecular and cellular mechanisms by which apoE4 appears to impair hippocampal neurogenesis in vitro and in vivo, and to determine if apoE4-induced learning and memory deficits in mice can be rescued by stimulating endogenous hippocampal neurogenesis or by transplanting mouse or human neural stem cells (NSCs) expressing apoE3 into the hippocampus. This proposal is based on the PI’s potentially interesting preliminary results from studying adult forebrain neurogenesis in mice. These studies show that apoE4 modulates hippocampal neurogenesis in complex ways. The proposed studies could shed light on the pathogenesis of AD and establish a foundation for developing stem cell therapy for AD patients that carry the apoE4 gene, as well as possibly other brain disorders/injury.
STRENGTHS AND WEAKNESSES OF THE RESEARCH PLAN: The studies address the important question of how apoE4 is detrimental to the brain, both in AD and other brain disorders. Since apoE4 is also associated with poor clinical outcome and with earlier onset, progression, or severity of head trauma, stroke, Parkinson’s disease, multiple sclerosis and amyotrophic lateral sclerosis (ALS), the proposed studies could also provide important information for the development of stem cell therapies for neurological diseases other than AD. The concept is one the PI has worked on for many years and the approaches use standard techniques.
The first specific aim addresses the molecular mechanisms whereby changes in apoE4 expression can impair hippocampal neurogenesis. A number of different experiments are embedded within this first aim. Given that most of these studies are performed in vivo, it is difficult to assess whether an observed effect is directly related to apoE. This first aim alone is complex enough that it could have been fleshed out to be the basis of an entire grant proposal. The point was made that without establishing this first aim, the rest of the proposal might not be significant.
The second specific aim is to determine whether stimulating endogenous hippocampal neurogenesis improves learning and memory defects associated with apoE4 expression in mice. In preliminary studies, the applicant rescued impairment of hippocampal neurogenesis observed in apoE4 mice with a specific treatment. The applicant proposes to induce hippocampal neurogenesis via a variety of tactics and monitor performance by conventional behavioral methods.
The point was made that the preliminary study showing rescue of impairment of neuronal maturation is difficult to understand as written. Given that this was the major finding supporting the proposed studies for this aim, a reviewer would have liked the facts of this study to be more clearly conveyed. Also, one reviewer found it hard to believe that a one-time treatment causes these dramatic changes and wondered how many times the animals were treated and how many animals were used in this preliminary study. Also, many of the studies proposed in this aim to induce hippocampal neurogenesis have nothing to do with the proposal’s hypothesis regarding the mechanism of action of apoE4 in AD pathogenesis.
The final specific aim is to determine if learning and memory defects associated with apoE4 in mice can be rescued by transplanting neural stem cells that express apoE3 into the hippocampus. Mouse neural stem cells expressing human apoE3 will be cultured and transplanted. Their human counterparts will be developed in vitro from embryonic stem cells that have been screened for the apoE genotype and also transplanted. This aim is the most difficult.
At a global level, reviewers struggled with several aspects of the proposal. The proposal was based on potentially interesting preliminary results. The applicant has the expertise, with help of colleagues, to carry out the studies. However, the innovation level is not that high, and the techniques proposed are all standard. Also, the behavioral assays of improved learning and memory deficits may not be sensitive enough to identify positive effects. The biggest concern was that the reviewers found the proposed research diffuse, very broad, and overly ambitious. They indicated that the first one or two aims could easily be turned into an entire grant proposal if better organized and described.
QUALIFICATIONS AND POTENTIAL OF THE PRINCIPAL INVESTIGATOR: The applicant received M.D. and Ph.D. degrees in Asia. The applicant has been studying apoE biology for many years since receipt of a PhD – first in Germany and since then in a lab whose focus in on apoE and its role in disease, at what is now the home institution. The applicant has received numerous prizes and awards for scholarship during postdoctoral training periods, has risen through the ranks at the institution, and has been an Assistant Professor since 2005. While at the institution, the applicant developed mouse and rabbit models to study apoE3/4 function in neurodegeneration and more recently in neurogenesis.
A reviewer noted that the preliminary data for this proposal was presented at a recent meeting and has not been published in a peer reviewed journal. Since starting his/her own independent laboratory in 2004, the applicant has been senior author of seven research articles on the role of apoE4 in AD pathogenesis and on evaluating apoE4-related targets for AD drug development. These articles have appeared in well-regarded journals. The applicant is a Co-PI on two grants; was invited to chair scientific sessions at two international meetings and to present at eight international or national scientific meetings. The applicant is also an inventor on seven issued or pending patent applications.
The applicant has provided an acceptable outline for career development in the years ahead. Based on the preliminary findings, the applicant has decided to redirect his/her research toward stem cell biology and therapy, still focusing on apoE4-related AD pathogenesis and treatment. The applicant’s key goals are: (1) to become an established stem cell biologist, (2) to advance stem cell therapy for neurodegenerative diseases, and (3) to train the next generation of biomedical scientists in stem cell research. The applicant has asked two senior investigators at the institution, both internationally recognized experts in stem cell research, to serve as mentors. They will have periodic meetings with the applicant to review and evaluate the progress of his/her stem cell research program and to provide suggestions and comments on future directions and plans. The milestones are realistic and achievable.
INSTITUTIONAL COMMITMENT TO PRINCIPAL INVESTIGATOR: The Director has provided a letter documenting the institutional commitments. Some of the reviewers thought that the letter was less than clear as exactly how the institution would support the applicant’s development in stem cell research. Based on the applicant’s achievements during the past 3 years, the institution recently approved an accelerated promotion on the Assistant Professor ladder. The applicant is provided with adequate laboratory space (~800 sq. ft.), office space, and administrative support in the institution’s new research facility, plus access to embryonic stem cell and neurobehavioral shared core facilities as well as access to a range of other pertinent cores and services, including a pathogen-free animal care facility. The applicant has all the equipment necessary to successfully complete the proposed studies. The director states that the applicant’s formal teaching and administrative requirements are minimal, which will allow time to be used for research and hands-on mentoring in the laboratory.
Over 60% of the institution’s laboratories are engaged in some aspect of stem cell research. A neighboring institution also has research programs related to stem cell research or regenerative medicine. The institution is slated for significant growth in human ESC research over the next five years. Within the applicant’s home institute there are several scientists who have focused their ESC research on neurodegeneration and repair.
DISCUSSION: The reviewers all felt that the proposed research was diffuse and overly ambitious for the proposed time period and not very innovative, although all acknowledged that the animal model was an interesting model for the study of AD. The applicant was considered good and productive but not outstanding.
The following Working Group members had a conflict of interest with this application and were therefore recused from participating in review of, discussion of, and voting on the application:
- None