SUMMARY The loss of tissue homeostasis and regenerative capacity with age underlies some of the most challenging health issues in the elderly. A major contributor to age-related decline in the structure and function of many tissues is the loss of stem cell function that occurs during the aging process. To be able slow, arrest, or even reverse those age-related declines in stem cell function holds would represent a major therapeutic advance in the growing field of regenerative medicine. The primary focus of this Program is to understand the molecular basis of age-related changes in stem cell function with the underlying premise that such an understanding is likely to reveal ways to target those changes in order to enhance aged stem cell function. Based largely on the work from the laboratories of this Program, there is increasing evidence of profound epigenetic changes that occur in stem cells as they age and that underlie many functional changes. A central conceptual theme that is woven throughout the proposal is the notion that these changes are not only mediators of cellular function but are amenable to being restored to a more youthful state through the process we call “epigenetic rejuvenation”. In addition, we explore how the epigenetic changes confer upon stem cells the characteristics that may be responsible for selection of subsets of cells across the lifespan by an ever changing adaptive landscape and result in a population of distinct stem cells in the aged milieu. To examine those concepts experimentally, this Program includes three Projects that focus on somatic stem cells from three different tissues that differ in terms of their homeostatic turnover and regenerative capacity – blood (high turnover, highly regenerative), muscle (low turnover, highly regenerative), and brain (low homeostatic, minimally regenerative). The Projects are integrated in their shared approaches to understanding the epigenetics of stem cell aging using cutting-edge technologies, including single cell transcriptome and epigenome analysis, modified CRISPR/cas9 technology for locus-specific epigenetic modifications, and in vivo lineage studies to explore the dynamics of stem cell populations during aging. These Projects are supported by three essential Cores – an Administrative Core to facilitate the interactions among the laboratories, a “Rejuvenation Strategies” Core for our shared animal studies to explore epigenetic rejuvenation, and a Bioinformatics Core to serve as the essential hub for storing, processing, visualizing, analyzing, and sharing data from the three Projects. Overall, the investigators who are Project Leaders and Core Directors are internationally recognized experts in these areas and bring to the Program the full breadth of expertise, creativity, and records of accomplishment to assure an integrated, innovative, and highly successful Program to explore the molecular mechanisms of stem cell aging.
SUMMARY The loss of tissue regenerative capacity is an almost ubiquitous aspect of mammalian aging. Underlying this age-related change is a decline in the potential of tissue-specific stem cells to participate in tissue repair and regeneration. In skeletal muscle, this has been amply demonstrated for the resident muscle stem cells (MuSCs), whose response to injury has been shown to decline with age in response to cell-intrinsic changes and to suppressive activity from the aged systemic milieu, the former perhaps arising from the latter. Nevertheless, the molecular basis of the cellular changes that integrate these diverse inputs to render a MuSC less responsive with age remains to be determined. Likewise, the molecular basis for the cellular memory that persists ex vivo and that can be “reprogrammed” in vivo in response to different environments remain to be elucidated. Understanding these fundamental mechanisms of MuSC aging provide the potential for being able to intervene to restore youthful characteristics to aged stem cells, thus enhancing aged tissue repair and regeneration. Toward these goals, this Project focuses primarily on epigenetic mechanisms based on the hypothesis that it is the epigenome that integrates diverse signals, mediates cellular responses, and is amenable to reprogramming in response to diverse environmental influences. In collaboration with Projects 2 and 3 and with Core C, we will explore the epigenetic features and regulators of young and aged MuSCs, in terms of transcriptome (RNA-seq), epigenome (ChIP-seq), and nucleosome positioning (ATAC-seq). In collaboration with Core B, we and Projects 2 and 3 will explore in more detail the notion of “epigenetic rejuvenation” by studying the epigenetics of aged MuSCs (and other stem cells) exposed to rejuvenating interventions that have been shown to restore youthful function to aged stem cells. We will examine a specific histone mark, trimethylation of lysine 27 on histone 3 (H3K27me3) what we have shown previously to be strikingly enriched in aged MuSCs. We will examine how that pattern changes in response to rejuvenating strategies and how it is regulated by chromatin modifiers. In collaboration with Project 3, we will explore the role of DNA methylation in MuSC aging, also testing how this epigenetic pattern, and resulting cellular function, changes in response to Core B interventions and to alterations in expression of DNA demethylases. We will also use modified CRISP/cas9 technology to modify DNA methylation in a locus-specific manner. Finally, in collaboration with Project 2, we will explore the population dynamics of MuSC aging by using single cell RNA-seq analysis to evaluate changes in clonal diversity and to test for clonal expansion, a process that we will also explore independently using clonal lineage tracing strategies. We will work closely with all members of this Program to integrate our efforts to lead the field of epigenetics of stem cell aging.
SUMMARY The Administrative Core will coordinate the activities of the three Projects and three Cores of this Program Project. The Specific Aims of the Administrative Core are: 1) to provide administrative assistance and fiscal oversight to all Projects and Cores B and C; 2) to facilitate communication both within the Program and between the Program members and other investigators, centers, programs and institutions; and 3) to establish and maintain an Executive Committee, an external Scientific Advisory Committee, and an Internal Advisory Committee. The services offered by the Core will include administrative and secretarial support (ordering of supplies, financial reports, assistance with budget management), organization of regular meetings and of the annual meeting with the Scientific Advisory Committee, and preparation of progress reports and other documents. The Director will oversee and coordinate all activities of the Core. He will meet regularly with the Administrator and with other Project Leaders/Core Directors to discuss administrative and managerial issues to insure that the Program is working effectively and efficiently. The Administrator and the Administrative Assistant will assist the investigators with financial matters, the organization of meetings and conferences, and general needs for the proper functioning of the Program.
