Using spatial, single-cell genomic recording to investigate age-associated clonal hematopoiesis

Project Summary: Hematopoiesis primarily takes place within the dense milieu of the bone marrow. It is regulated by complex signaling interactions among multiple cell types to maintain a balanced blood pool and to respond to injuries such as bleeding and infection. During aging, hematopoiesis declines and develops clonal dominance, also known as clonal hematopoiesis, where a small number of hematopoietic stem and progenitor cells (HSPCs) produce a disproportionately large amount of blood cells. Clonal hematopoiesis has been associated with various types of hematologic disorders including leukemia. To understand how and why clonal hematopoiesis develops with age, it is crucial to examine the key intercellular communications that regulate hematopoiesis within the bone marrow. This is particularly important because of dramatic age-associated changes to the bone marrow where the cell number substantially decreases and the cell type composition massively shifts, leading to changes in the intercellular signaling network critical for hematopoiesis. Here, we will apply a new genomic recording and imaging technique, MEMOIR (Memory through Enhanced Mutagenesis with Optical In-situ Readout), to analyze how the aging bone marrow environment alters HSPC intercellular signaling and influences clonal hematopoiesis. We will test two opposite hypotheses: (1) clonal hematopoiesis is induced by age-associated changes to the intercellular signaling of HSPCs in the bone marrow; and alternatively (2) clonal hematopoiesis is the result of intrinsic changes in HSPCs that allow them to escape from the control of the intercellular signaling network. We will determine how aging alters the spatial context and intercellular signaling of HSPCs, and influences their clonal expansion. And we will investigate how age-associated spontaneous mutations perturb the spatial context and intercellular signaling of HSPC clonal expansion. Our proposed study will identify the lineage relationships and spatial organization of individual HSPCs as well as their intercellular signaling in the aging bone marrow. Our results can reveal new cellular and molecular players underlying clonal hematopoiesis that could be used as therapeutic targets to control hematopoietic aging and age-related diseases. More generally, this study will provide an experimental and conceptual framework for analyzing spatially defined intercellular communication in hematopoiesis.