Inflammatory landscapes shaped by bone marrow cavities define hematopoietic response to stress and clonal selection

About This Grant

(PLEASE KEEP IN WORD, DO NOT PDF) Clonal hematopoiesis (CH) is driven by mutated hematopoietic stem cells (HSCs) that expand in the bone marrow. Inflammation has been shown to drive CH progression; however, despite the presence of systemic inflammation, we showed that HSCs exclusively expanded in the marrow cavities with bone resorptive activities. These results raised questions of whether CH clonal development also depends on physiological bone turnover (a process initiated by bone resorption) and emphasizes the importance of establishing a robust methodology to track the CH clones along with the skeletal dynamics in live animals. To address the knowledge gap, we recently developed an intravital imaging protocol to visualize engraftment of non-malignant clones in a functional microenvironment that only received ultralow-dose (0.5 - 2 Gy) irradiation. Leveraging this model, we propose to determine the causality of bone turnover, local inflammatory profiles, and expansion of CH clones via longitudinal imaging, and further assess and optimize its applicability for tracking CH progression to clonal cytopenia or advanced clonal disorders. In Aim1, we will perform longitudinal imaging and functional assays to determine immune cell phenotypes altered by physiological bone remodeling within a marrow cavity. Imaging will be performed at a two-day interval to follow changes induced by a bone resorption cycle. The experiments will be performed at the steady state and in animals transplanted with CH clones to further delineate contributions from the mutant cells. In Aim2, niche occupancy and lineage contribution of the mutant clones will be characterized in the ultralow-dose irradiated model over the course of one year. Additionally, microenvironment cells surrounding the CH clones will be harvested at distinct disease stages for transcriptomic assays to delineate overlapping and differential microenvironment factors over disease evolution. Taken together, currently, the dynamic niches in the marrow microenvironment responsible for expansion of CH clones are not well defined, and the experimental tools to pinpoint the niches remain to be tested. The proposed work will address these knowledge gaps and provide the field with validated technology for therapeutic discovery leveraging the bone marrow microenvironment.