Summary Aging human tissues have recently been shown to nearly universally experience clonal evolution, in which their genetic diversity plummets due to selective expansion of specific clones driven by particular somatic mutations. In the hematopoietic system, clonal evolution (or “clonal hematopoiesis” (CH)) has been associated with an increased risk for hematologic malignancies, but also acceleration of other non-hematologic aging-associated diseases. How circulating blood cells derived from aberrant hematopoietic stem cell clones impacts the function of distal tissues and promotes disease is largely unknown. Overall, this project aims to establish the mouse as a model for natural clonal hematopoiesis, and to begin to examine the mechanisms through which CH impacts distal tissues in the context of the most common CH driver- reduced function of DNA Methyltransferase 3A (DNMT3A). Our preliminary data from three distinct mouse strains demonstrates that expansion of clones indicative of natural CH can be observed in mice above 2 years of age, with the most common variants overlapping with those in humans. Here this observation will be extensively verified by testing for CH in mice of multiple ages and under different conditions in collaboration with Projects 1 and 2. We will also determine clone expansion kinetics by serial sampling, and the effect on clones of specific perturbations. This Aim will establish the mouse as the first experimental model for natural clonal hematopoiesis and reveal conditions which enhance or slow its development. Additionally, we will engraft Dnmt3a-mutant cells into murine recipients to mimic CH, and examine the impact on function of distal tissues and their resident stem cells in collaboration with Projects 1 and 2. Using single cell sequencing and tissue-proteomics, we will determine the identity and activity of donor cells infiltrating tissues. A variety of molecular and functional assays will also reveal the impact of this “induced” CH on the tissue stem cells. Finally, our preliminary data suggest aberrant macrophages in the context of CH as a key mediator of the downstream effects of CH. Thus, using multi-omic approaches and candidate gene modulation, we will determine the mechanisms through which natural aging and reduced DNMT3A engender biased myeloid development and altered function that in turn impacts distal tissues. Together, these studies exploit the mouse as a model to study key aspects of CH. Given that CH is ubiquitous in aging humans, and is associated with a growing list of aging-associated diseases, understanding how CH impacts broader aspects of tissue and organismal aging, in collaboration with Projects 1 and 2, will enable us to develop new therapeutic approaches to improve human health-span.