Degenerative diseases, such as Parkinson’s, Alzheimer’s and muscle atrophy, in which the bodies capacity to regenerate new tissue can no longer keep up with tissue death often accompany human aging, are debilitating for individuals and represent a major problem for society. One intriguing possibility is that stem cells residing in aged organs retain their intrinsic ability to regenerate but are not properly triggered in when surrounded by old tissue. Specifically, productive responses of aged stem cells and repair of old tissues can be rescued in an animal model, when young and old mice share blood circulation. These findings, and their more recent extrapolation, strongly suggest that the development of effective hESC-based therapies in old people critically requires much improved understanding of why stem cells do not repair older organs even when they have the capacity to do so. In this respect, our current scientific evidence strongly suggests that any stem cell: local or transplanted, adult or embryonic will not efficiently work in older individuals, unless these cells are provided with a “youthful” surroundings, which protect them form the negative signals emanating from an aged body. More specifically, our most recent work suggests that it is not simply the lack of “positive” factors in an old body that causes a decreased regeneration with age or simply the presence of these factors in young organism that causes “youthful” tissue repair. In contrast, we provide evidence that aged circulation-blood and aged organs contain factors that inhibit the ability of any stem cell to engage in tissue repair; and this negative influence of aged body applies to all cell subsets currently hoped to be used for therapeutic purposes, e.g. embryonic stem cells and their derivatives, adult stem cells and entirely differentiated tissue containing a resource of dedicated stem cells. These findings mean that in order to capture the tremendous therapeutic potential of human embryonic stem cells in the elderly, it is necessary to understand the nature of the inhibitory “culprits” typical of aged body and to design molecular devices that would protect these cells and thus, would enable productive tissue repair in the old. These aims will be approached in the proposed study with the goal to restore the activity of the key determinants of stem cell regenerative potential back to those typical of a young organism and thus, to enable therapeutic applications based on hESC in older people afflicted by degenerative disorders.
Statement of Benefit to California:
Degenerative diseases in which the bodies capacity to regenerate new tissue can no longer keep up with tissue death is a major problem for society in general and for State of California in particular. The lack of tissue repair that eventually leads to the loss of organ function is undeniable and devastating trait of aging that causes many degenerative disorders, exemplified by Parkinson’s, Alzheimer’s and muscle atrophy. Therefore, Californians with life-long skills, expertise and invaluable knowledge can no longer contribute to society and do not enjoy life fully. In recent years biologists and clinicians realized that practical therapies would only emerge when the balance between the regenerative and the degenerative processes were properly understood in biomedical terms. The development of effective therapies for age-related degenerative diseases critically requires much improved understanding of why stem cells in older tissue are not engaging in tissue repair even when the have the capacity to do so. Current work suggests that it is not simply the lack of “positive” external factors that causes a decreased regeneration with age, but that there is an elevation in dominant “negative” factors in the old, and thus the regenerative responses of stem cells and their derivatives (including hESC-based approaches) will be incapacitated in old organism, unless these cells are provided with a “youthful” environment. This proposal describes steps to rejuvenate stem cell responses in the old, to insure that the health prognosis is significantly improved for older Californians, especially those afflicted with degenerative disorders, and that the results of these studies are translated as rapidly as possible to the clinical setting where their practical benefit can be fully utilized. Thus this work seeks not only to improve the quality of life for our older citizens, but also to reduce the health-cost associated with treating currently incurable degenerative diseases.
SYNOPSIS: The specific aims in this proposal are to “(1) Define the affects of aged niches on the self-renewal, “stemness” and myogenic potential of multiple therapeutically relevant hESC lines in vitro and in vivo and to reveal when systemic and local organ environments first become inhibitory with advancing age; (2) To identify key signaling networks altered by the aged niches in multiple therapeutically relevant hESC lines and to create a data-base of dynamic changes in stem cell gene regulatory circuitry as a function of age progression within systemic and organ niches; and (3) To design synthetic “youthful” stem cell niches enabling the efficient regenerative potential of therapeutically relevant hESC and their progeny in physiologically old environments.” In Aim 1, the niches are mouse serum from different aged animals and an aged leg muscle environment. The second aim uses microarrays to look at signaling changes in hESC as a consequence of cultivation in an old environment. SIGNIFICANCE AND INNOVATION: Some of the planned therapeutic uses of hESCs involve transplantation into old hosts. One hurdle to translation of stem cell therapies is an understanding of the aged or pathologic environment into which the cells will be placed. Since this transplantation seems to preserve “stemness” less well in older than younger animals, the plan to investigate the mechanisms by which age affects “stemness” is very relevant and important. The hypotheses in this proposal are novel, i.e., that the age of the environment influences the outcome of the transplant, and the methods by which the PI aims to gain new information are rather contemporary and creative. STRENGTHS: The idea of studying the aged environment is a good one. This is a provocative proposal that attempts to test hypotheses in a logical way to explore the importance of age in the environment. The PI describes potential problems that might arise and alternative directions that would be taken to deal with them. The preliminary data of the PI also are provocative. The PI, an Assistant Professor in the Department of BioEngineering at UC Berkeley since 2004, is an expert on the subject of the inhibition of stem cells' regenerative potential by aged environments. The background (post-doctoral) work of the PI in identifying signaling changes in adult stem cells is also a strength. WEAKNESSES: This was a chance to go for an innovative look into the aged environment, but the details of the methods and studies chosen are disappointing. The use of all the mouse materials and models is internally inconsistent with the PIs justification for using the new hES cell lines (non-approved). Since the translatability of the new hES cell lines is the major reason these were chosen for this work, the work would be considerably more translation-oriented if human serum was used for the first experiments. Also, the cells are growing on Matrigel. Why not grow on some other human substrate for cleaner work? Similarly, Aim 3 does not use human material to make the ECMs characteristic of youthful animals. What about secreted molecules as in the earlier aim? The markers of muscle differentiation will be sought only after 48 hours, and this time course is unrealistically short. One wonders whether Aim III would be more comprehensive if there was a more unbiased screen to identify rejuvenating factors. In addition, as noted below, the findings of gene expression differences in hESC cultures may not be the same as those seen following transplantation in hosts of different ages. The microarray data gleaned in Aim II may difficult to interpret for many reasons, such as the variability of the hESCs and the multitude of differences that is sometimes seen. Affymetrix chips may not be the best way to looks for signal transduction cascades unless the time-course is very dense. But the time course is not stated, except that it occurs within 48 hours. How many time points and how many replicates will be tested? One wonders whether Aim II could be strengthened by crudely or more finely purifying the factor in the “old” serum. Dr. Conboy has an enormous amount of funding for a young investigator and there is considerable overlap with this CIRM grant and her other funding sources. Basically, the CIRM funding would superimpose a high-throughput approach on top of other funded grants to look at particular pathways that are changed in the environment and expression of aged stem cells. Given her success rate at NIH and NSF, she has enormous potential for future funding. Thus, the use of non-approved lines is not necessary for her research (at least a strong case has not been made). DISCUSSION: Reviewers found that the ideas presented in this grant were good, but that there was no real background research on how the PI would do the work. The applicant is encouraged to think more specifically about hESC, such as building on the Notch work for senescence. Reviewers were very impressed by the publications on transplanting muscle into young versus old hosts, and thought that the transplantation of hESC into older individuals would benefit from these studies. There appears to be an issue of overlap with other grants as well. This young investigator just embarking on her career as an independent scientist is strongly encouraged to resubmit as future funding opportunities arise with the appropriate human embryonic stem cell biology background and expertise included.