Project Summary Aging and the chronic diseases associated with aging place a tremendous burden on our healthcare system. As our world population ages dramatically over the next three decades, this burden will only increase. Hence, there is a great need to discover fundamental mechanisms of aging to develop rationale strategies for minimizing the impact of aging on our health and economy. There is general agreement that cell autonomous mechanisms contribute to aging. As cells accrue damage over time, they respond by triggering individual cell fate decisions (e.g., senescence and apoptosis) that ultimately disrupt tissue homeostasis and thereby increase risk of morbidity. However, more recently, there are numerous lines of evidence indicating that cell non-autonomous mechanisms are critically important as well. These cell non-autonomous mechanisms are likely much easier and safer to target therapeutically. Therefore identifying and characterizing these mechanisms is a priority. To ask if ?aging? just one tissue in mice is sufficient to drive systemic aging, we generated a series of seven tissue-specific mutant animals in which DNA damage, senescence and tissue dysfunction were increased in only one cell type or tissue at a time. Our preliminary data indicate that ?aged? immune cells play a key role in driving aging non-autonomously. Only in the hematopoietic cell mutant mice were non-targeted, peripheral tissues dramatically affected in the first year of life, showing increased senescence, inflammation and loss of homeostasis. The goal of this project is to fully define this novel mechanism of immune cell-mediated, non- autonomous aging in vivo. The aims of the project are to: 1. Define the full extent to which an ?aged? immune system can drive systemic aging through a cell non-autonomous mechanism. This will be accomplished by fully characterizing the temporal decline in immune function in the hematopoietic mutant mice via comparison to normal sibling controls, and to determine which peripheral tissues undergo premature aging as a consequence of immune dysregulation. 2. Identify the immune cell type(s) that is most potent at driving systemic aging in mice. This will be accomplished by transplanting splenocytes and isolated immune cell populations into young senescence reporter mice, followed by generation and characterization of cell-type specific mutant mice (e.g., T cell, B cell, NK cell transfer and mutant strains). 3. Identify the mechanism by which ?aged? immune cells drive systemic aging. This will be accomplished by serum transfer from the hematopoietic mutant mice into young senescence reporter mice followed by transcriptomic analysis of isolated immune cell populations to identify secreted factors. These putative pro-geronic factors will be validated by proteomics. Completion of these aims will identify and characterize a novel mechanism(s) of cell non-autonomous aging driven by an aged immune system, which will lend itself to therapeutic targeting for extending human healthspan.