1008 – INTERFERON GAMMA-MEDIATED REGULATION OF HSCS: MECHANISMS AND ROLE IN CLONAL HEMATOPOIESIS.

Abstract

Inflammatory conditions such as chronic infection or autoimmune disease are frequently associated with impaired hematopoiesis. Chronic interferon gamma (IFNγ)-mediated inflammatory signaling damages hematopoietic stem cells (HSC) by disrupting quiescence, promoting excessive terminal differentiation, and increasing the propensity for secondary stress-induced apoptosis. In recent studies, we examined the mechanisms underlying IFNγ-mediated HSC activation. Using intravital three-dimensional microscopy, we found that IFNγ disrupts the normally close interaction between HSCs and CXCL12-abundant reticular (CAR) cells in the HSC niche. IFNγ-dependent relocalization and HSC activation are dependent on the cell surface protein BST2, which is induced by IFNγ. HSCs from mice lacking BST2 were more quiescent and resistant to depletion upon chronic infection. Thus, BST2 is a key regulator of HSC quiescence that promotes inflammation-induced niche relocalization and activation. Given that prolonged IFNγ signaling can lead to the depletion of HSCs, we examined the impact of IFNγ-mediated HSC responses on clonal hematopoiesis (CH), with particular attention to loss of function (LOF) mutations in <i>Dnmt3a</i>, the most commonly mutated gene in CH. We used a murine model to investigate the prediction that infection provides selective pressure favoring expansion of <i>Dnmt3a</i>-knock out HSCs. We created <i>Dnmt3a</i> mosaic mice by transplanting a mixed population of Dnmt3a-KO and WT HSCs into WT mice and observed substantial expansion of Dnmt3a-KO HSCs during chronic mycobacterial infection. Transcriptional profiling and functional studies indicate reduced differentiation and reduced secondary stress-induced apoptosis account for <i>Dnmt3a</i> KO clonal expansion during infection. Whole genome bisulfite sequencing reveals possible mechanisms for these effects. Thus, we demonstrate that IFNg signaling during chronic infection can drive DNMT3A-mutant CH. Our future work will continue to elucidate the avenues by which infections and inflammation alter primitive hematopoiesis.