Approaches to repair the injured brain or even prevent age-related neurodegeneration are in their infancy but there is growing interest in the role of neural stem cells in these conditions. Indeed, there is hope that some day stem cells can be used for the treatment of spinal cord injury, stroke, or Parkinson’s disease and stem cells are even mentioned in the public with respect to Alzheimer’s disease. To utilize stem cells for these conditions and, equally important to avoid potential adverse events in premature clinical trials, we need to understand the environment that supports and controls neural stem cell survival, proliferation, and functional integration into the brain. This “neurogenic” environment is controlled by local cues in the neurogenic niche, by cell-intrinsic factors, and by soluble factors which can act as mitogens or inhibitory factors potentially over longer distances. While some of these factors are starting to be identified very little is known why neurogenesis decreases so dramatically with age and what factors might mediate these changes. Because exercise or diet can increase stem cell activity even in old animals and lead to the formation of new neurons there is hope that neurogenesis in the aged brain could be restored to that seen in younger brains and that stem cell transplants could survive in an old brain given the right “young” environmental factors. Indeed, our preliminary data demonstrate that systemic factors circulating in the blood are potent regulators of neurogenesis. By studying how the most promising of these factors influence key aspects of the neurogenic niche in vitro and in vivo we hope to gain an understanding about the molecular interactions that support stem cell activity and the generation of new neurons in the brain. The experiments supported under this grant will help us to identify and understand the minimal signals required to regulate adult neurogenesis. These findings could be highly significant for human health and biomedical applications if they ultimately allow us to stimulate neurogenesis in a controlled way to repair, augment, or replace neural networks that are damaged or lost due to injury and degeneration.
In California there are hundreds of thousands of elderly individuals with age-related debilitating brain injuries, ranging from stroke to Alzheimer’s and Parkinson’s disease. Approaches to repair the injured brain or even prevent age-related neurodegeneration are in their infancy but there is growing interest in the role of neural stem cells in these conditions. However, to potentially utilize such stem cells we need to understand the basic mechanisms that control their activity in the aging brain. The proposed research will start to address this problem using a novel and innovative approach and characterize protein factors in blood that regulate stem cell activity in the old brain. Such factors could be used in the future to support stem cell transplants into the brain or to increase the activity of the brain’s own stem cells.
This proposal is designed to investigate the role of the microenvironment in regulating neural stem cell (NSC) fate and is focused on identifying soluble protein factors that inhibit or enhance neurogenesis. Aging is a systemic event and neurogenic niches are intimately connected with blood vessels, therefore, the applicant hypothesizes that soluble systemic factors in blood have direct effects on the decline of neurogenesis in the aging brain. The applicant proposes the use of a parabiotic rodent screening protocol to interrogate the role of soluble factors in promoting or inhibiting neurogenesis. The study plan builds upon preliminary data where the parabiotic screen was used to identify soluble factors that inhibit neurogenesis in aged mice. In Aim 1, the applicant proposes to investigate the effects of these factors on proliferation, differentiation or survival of human neural progenitor cells (NPCs). In Aim 2, the applicant expands upon the parabiotic screen by planning to perform a more comprehensive screen of secreted factors in parabionts to try to identify factors that are pro-neurogenic and will test candidate factors on human NPCs. Finally, in Aim 3, the applicant proposes to test the effect of the identified pro-neurogenic and inhibitory factors in vivo on endogenous and engrafted NPCs in a young versus old brain environment.
Reviewers found the significance and innovation of this application to be strong. The survival of stem cell (SC) transplants will likely depend on an appropriate microenvironment. Understanding the nature of these microenvironmental signals is an essential component of efforts to advance SC therapeutics; thus knowledge gained from the work proposed here could impact treatment of Parkinson's disease, neurodegenerative dementias such as Alzheimer’s and age-related declines in cognition. Although the use of parabiotic mice is an old tool of endocrinology research, most reviewers considered clever and innovative the use of parabionts for an entry-level screen for age-related factors that regulate growth and differentiation of hNSCs. Reviewers commented that the study plan has a "high risk/high gain" nature.
In general, reviewers found the preliminary data to be persuasive and the study plan to be well written and carefully considered. Reviewers had a few minor suggestions that if addressed could strengthen the experimental design. One reviewer suggested that the Principal Investigator (PI) consider the model by which circulating factors influence neurogenesis across the blood brain barrier. This is more than a theoretical issue as application of this knowledge to stem cell therapeutics in the CNS may require an understanding of this pathway. One feasibility concern was that the biological effects of the inhibitory factors shown in the applicant’s studies are rather nuanced and RNA knockdown experiments proposed might not be robust enough due to the signal-to-noise ratio. While these minor concerns did not detract from the reviewers’ enthusiasm for this proposal, Aim 3 was slightly problematic. Here, the applicant focuses on utilizing the anti-neurogenic proteins identified in their preliminary studies and pro-neurogenic factors they hope to identify in Aims 2 for in vivo studies. This aim would obviously be stronger if these pro-neurogenic factors were already in hand and the realistic limitation that no pro-neurogenic factors may be identified is not adequately addressed within the potential pitfalls. Additionally, one reviewer felt that the proposal is primarily a mouse study and therefore not particularly responsive to the RFA. While noting that the mouse studies are both necessary and informative, reviewers agreed that the applicant ignored opportunities for additional human studies such as screening human plasma samples, and including human transplantation experiments in the study plan. Despite these concerns, reviewers appreciated the otherwise logical and achievable aims that address the central focus of the application.
Reviewers praised the PI’s proposed significant commitment, experience, and qualifications and commented that the PI’s productive collaboration with his/her Co-PI would increase the likelihood that the team would be successful in achieving the aims of the present study. Moreover, reviewers found the scientific environment for neuroscience research at the applicant institution to be outstanding.
Overall, the reviewers considered this proposal from a strong PI to be highly innovative and significant and achievable despite some concerns regarding the study plan and some concerns as to balance of murine and human focused studies.