Damage to the central nervous system (CNS) causes significant loss of function, reduced quality of life, and substantial cost to society. Damage can be caused by disease, stroke, or trauma. After CNS injury, there may be some recovery, which arises by the formation of new connections in the brain. An approach to improving recovery is to stimulate the mechanisms that form these new connections. Stem cell therapy is a promising avenue for promoting recovery of CNS function. An important goal of this area of research is to identify which stem cells are most effective and to understand how they promote recovery. An obstacle to achieving these goals is that lesions are variable and it is difficult to quantify the formation of new connections. We have developed a lesion model that takes advantage of a pathway containing large, distinct synaptic terminations. This model permits quantitative, robust assessment of lesion-induced sprouting. The lesion is highly reproducible and the number and precision of induced connections can be determined accurately. We propose to use this system to test the effectiveness of stem cell grafts. This model will enable us to compare different types of stem cells and characterize their effects on damaged tissue. Our approach will provide a way to understand the mechanisms by which stem cells effect tissue repair and ultimately lead to the development of new treatments for human diseases and disorders.
Statement of Benefit to California:
Central nervous system injury and stroke are the leading causes of disability in California. Current medical care relies on immediate treatment to lessen the extent of damage. However, there is no known cure that restores function. Stem cell therapy is a promising approach based on several studies in disease and injury models, but more information is needed on how stem cells work in promoting recovery. The proposed studies will provide a tool for assessing stem cell efficacy and for understanding mechanisms by which stem cells promote reorganization of neural circuits. The results will help identify optimal stem cell therapies that will alleviate effects of stroke and traumatic central nervous system injury in Californians. In addition, the project will create new jobs in California and stimulate the state’s economy. It will provide training in stem cell research to new trainees, who will further develop our knowledge in this area, and stimulate further interaction between academic institutions and biomedical technology.
This project is focused on determining the mechanisms underlying repair of the damaged nervous system following cellular transplantation. The applicant proposes to determine whether transplanted stem cells can enhance neuronal sprouting and the formation of new synaptic connections in a lesion model that takes advantage of a pathway containing large, distinct synaptic terminations. S/he will also determine whether or not transplanted stem cells can prolong the time period following injury that is permissive for regeneration. Finally, the applicant will attempt to understand the basis for axon guidance following lesion to promote recovery and the influence that different stem cell populations may have on this process.
This project proposes to use a novel model of unilateral lesion that results in highly specific neuronal sprouting. The model has been well characterized in the applicant’s lab, and reviewers commented that the research plan is carefully devised, clearly written, and could potentially result in critical new information about regenerative capacity of the pathway in response to stem cell transplantation. In spite of these strengths, reviewers were concerned with the applicant’s lack of experience in stem cell biology, which was evident in the superficial experimental design. In addition, they were critical of the fact that the PI does not propose to assess functional recovery after lesion, and does not consider the extent to which the injury seen in this model is indicative of other types of neuronal damage, for instance following stroke or neural degeneration.
Reviewers strongly supported the research approach. One reviewer commented that the characterization of changes in axon guidance signals alone is worth doing, since all too often research in CNS recovery has focused on cellular replacement with little or no attention to the need for neuroanatomically correct circuit reconstruction. However, with regards to the lesion model, reviewers questioned whether this type of injury following transection in the brainstem is representative of the type of injury seen in other parts of the CNS, as the issue was not discussed. For this reason, the real significance of the proposed work could not be properly assessed. In addition, reviewers were concerned by the lack of any functional or behavioral analysis of experimental model following implantation. The application is based solely on morphological data that may have little or no relevance to functional improvement following cellular implantation. Reviewers commented that there are numerous instances where transplanted cells can display significant morphological survival, differentiation, and integration into the brain and yet do not induce significant functional benefit. Reviewers also commented that the applicant treats stem cells as a generic entity without any discussion of the major cell intrinsic differences between the target cells, and does not discuss issues of cell differentiation that could have an important impact on the project’s success. Without differentiation into a somatic stem cell population and extensive propagation in conditions that do not support hES cell pluripotency, the transplanted cells are likely to generate teratomas in the brain of experimental animals.
The main weakness of this proposal, according to reviewers, is the applicant’s poor background in stem cells, which is not sufficiently counterbalanced by the mentoring plan. Although reviewers were very supportive of the applicant, a highly respected developmental neuroscientist who has already made substantive contributions to our understanding of the auditory pathways in avian and mammalian brain and is well-funded by NIH, they were uncomfortable with the way that the applicant is moving into the field. The issues raised above with the research plan and the superficial identification of pitfalls and alternative approaches reflects the applicant’s inexperience with stem cells. The mentoring plan was considered generic and not sufficient to overcome the applicant’s lack of experience in the field.
The applicant’s research institution has established a stem cell research center and has attracted several prominent stem cell biologists to lead it. Institutional support for the applicant, in terms of space and equipment, is excellent. However, the letter of support from the institution is fairly impersonal and very generic. It does not address in any way how the institution proposes to assist the applicant in his/her long-term future. There is no mention of whether the applicant’s percent effort will be adjusted if a CIRM award is made.
In conclusion, this was considered an interesting proposal from a strong investigator. The main weaknesses of the proposal are the applicant’s lack of experience with stem cells, a lack of data on the relevance of this model to other types of neuronal damage, and the absence of functional analysis. Reviewers felt that this application did not merit funding unless there were clear programmatic reasons to do so.