PROJECT SUMMARY/ABSTRACT Age is one of the most clearly defined risk factors for cancer. As the incidence of cancer increases with age, rising more rapidly beginning in mid-life (ages 45-64 years), cancer can be considered an age-related disease. Recent studies have identified age-dependent somatic mutations, including alleles with a role in cancer initiation, in a spectrum of human tissues. In the hematopoietic system this is termed clonal hematopoiesis (CH) and is most commonly caused by mutations in the epigenetic regulators DNMT3A, TET2, and ASXL1 within the hematopoietic stem and progenitor cell (HSPC) compartment. How the aging process promotes clonal selection, expansion, and transformation from CH to acute myeloid leukemia (AML) is poorly understood. The long-term goal of this research is to understand the mechanisms by which aging promotes transformation causing hematologic malignancies. The overall objective of this proposal is to elucidate the mechanisms by which increased inflammation observed during aging promotes expansion of CH-mutant HSPCs, and the extent to which this fitness advantage is provided by altered epigenetic regulation occurring as a direct consequence of CH mutations. Preliminary data show that CH-mutant HSPCs have a more potent selective advantage and undergo more rapid malignant transformation in aged compared to young mice. Mechanistically, increased inflammation in aged mice is a driver of this phenotype and epigenetic alterations are found to accumulate in CH-mutant HSPCs with aging. These data support the central hypothesis that aging-associated inflammation is a selective pressure favoring CH-mutant HSPC expansion and malignant transformation, and that clonal expansion, epigenetic alterations, and risk of transformation caused by CH mutations are dependent upon sustained CH-mutant allele expression. This project will use cellular and molecular biological approaches in aged mice integrated with studies using primary human CH samples to achieve the following specific aims: AIM 1. Determine the extent to which clonal hematopoietic expansion and leukemic transformation in the aging context is due to inflammation; and AIM 2. Determine the mechanisms by which, and extent to which, reversion of a CH mutation during aging alters clonal evolution and risk of leukemia initiation. The proposed research is conceptually innovative because it is the first to determine how inflammation and epigenetic dysregulation conspire during the aging process to expand, evolve and transform CH-mutant clones. The proposed research is technically innovative as it incorporates novel co-culture systems and therapeutic studies to assess key inflammatory drivers, as well as a novel murine model with CH-mutant induction and reversion capabilities to investigate CH mutant allele dependencies in clonal expansion, epigenetic alterations, and leukemic transformation. This study is significant because understanding the mechanisms by which aging contributes to clonal expansion and transformation will provide insights into effective therapeutic strategies targeting clonal evolution, attenuate pathophysiology promoted by clonal expansion, and intercept malignant transformation.

RELEVANCE TO PUBLIC HEALTH Aging is a complex process that drives increased cancer risk in tissues throughout the body, including the blood system. To understand why aged individuals have higher risk of developing blood cancers, there is a vital need to understand the mechanisms by which aging contributes to clonal expansion and transformation. This research is relevant to public health because it will provide mechanistic insights into effective therapeutic strategies to target clonal evolution, attenuate pathophysiology promoted by clonal expansion, and intercept malignant transformation.