The impact of reduction of cellular senescence on age-related epigenetic heterogeneity

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PROJECT SUMMARY This application is being submitted in response to the Notice of Special Interest (NOSI) identified as NOT-CA- 23-045. The decline in hematopoietic stem and progenitor cell (HSPC) function with aging can lead to improper blood and immune cell production, contributing to reduced health and life span. Aged HSPCs accumulate somatic mutations that confer a selective fitness advantage, leading to clonal hematopoiesis (CH), a blood phenotype that increases the risk of leukemia and various diseases of aging including cardiovascular diseases. Cellular senescence, a hallmark of aging, is another potent extrinsic candidate driver for age-related CH in the bone marrow microenvironment. Senescent cells secrete inflammatory factors that can influence the function and differentiation of surrounding cells, including cytokines that are crucial for driving CH. Determining the impact of reducing cellular senescence on the epigenetic heterogeneity of HSPC in aged bone marrow of mice is significant for aging and cancer research, given that greater epigenetic heterogeneity of HSPC with age should alter both stem cell functionality in hematopoiesis and increase the odds of leukemic progression. We will test the hypothesis that rejuvenating the bone marrow microenvironment by reducing senescence will reduce epigenetic heterogeneity of HSPC. This knowledge can contribute to the development of novel therapeutic and preventative strategies for mitigating age-related blood disorders, ultimately benefiting prevention of both hematopoietic decline and increased blood malignancy risk in the elderly. To follow the fate of specific subclones of HSCs, we will uniquely barcode thousands of HSC from old wildtype mice, which will be transplanted into three groups of host mice with vehicle or senolytic treatment to determine how aged vs. rejuvenated BM microenvironment influences HSPC heterogeneity. We will use scRNA-seq and snATAC-seq analysis to identify cell cluster-associated epigenetic and transcriptomic signatures and associated heterogeneity for expanded vs. contracted HSC clones. We will also identify senescence-dependent epigenetic signatures and associated heterogeneity from post-transplantation snATAC-seq data. The expected outcomes of this research will be to determine the impact of cellular senescence reduction on the epigenetic heterogeneity of HSPC in aged bone marrow of mice and identify the specific pathways that are modulated given the rejuvenated, less inflammatory microenvironment. This work can provide a mechanistic foundation for understanding the initiation of age-related blood disorders.