Project Summary Acute myeloid leukemia (AML) is the most common diagnosed adult leukemia, the median age of patients with AML is about 70 years. Although the prognosis for younger adults with AML has improved during the last four decades, there has been little progress in the treatment of older adults. Currently, approximately 90% of adults with AML over the age of 55 will die due to resistance to therapy, relapse, or complications from harsh treatments such as chemotherapy. AML disease progression is heavily influenced by supportive cells in the tumor microenvironment. Bone marrow mesenchymal stromal cells (BMSCs) are an instrumental extrinsic component to normal hematopoiesis which are hijacked by leukemic cells in the process of leukemia development. Based on AML being mainly a disease of older adults and evidence of an accelerated aging phenotype in the (BM) microenvironment of AML, this proposal aims to investigate the role of aging and senescence in AML disease progression and to ultimately identify therapeutic targets and eliminate the leukemia-supportive aging phenotype in the BM. Although epigenetic aging and senescence are two distinct but parallel mechanisms of aging, they have been shown to converge where certain triggers of senescence can affect epigenetic age. The molecular basis for age-related alterations in AML-derived BMSCs are poorly described and if deciphered, could have significant implication on both the prevention and treatment of elderly AML. Moreover, the correlation of epigenetic age in cells of the AML tumor microenvironment with outcome has not been examined. Thus, the specific aims of this proposal are to (1) examine epigenetic, transcriptional and phenotypic differences in BMSCs derived from AML patients, compared to age matched control BSMCs, enabled by the use of methylation studies, sequencing, mass cytometry and biochemical assays (2) determine the epigenetic age via methylation analysis of different components of the tumor microen