Dissect the consequences of telomere stress on hematopoietic stem cells

About This Grant

Progressive telomere shortening, which occurs over humans' natural lifespan, is a primary molecular cause of the functional decline of stem cells in high-turnover tissues, including hematopoietic stem cells (HSCs). However, how telomere damage compromises HSCs’ functions is largely unknown. Here, we propose investigating the molecular mechanisms behind telomere damage–induced functional HSCs’ decline to uncover therapeutic strategies to ameliorate bone marrow (BM) failure disorders. In preliminary studies, we demonstrated that telomere damage does not activate programs of apoptosis or senescence in HSCs but instead induces their aberrant activation and differentiation towards the megakaryocytic lineage through the cell-intrinsic upregulation of Ifi20x/IFI16-mediated innate immune signaling response, which directly compromises HSCs’ self-renewal capabilities and eventually leads to their exhaustion. Given that HSCs’ exhaustion in the context of BM failure disorders predisposes to clonal selection, we evaluated whether telomere shortening–induced DNA damage in patients with germline mutations affecting telomere maintenance genes who developed telomere biology disorders (TBDs) is associated with clonal hematopoiesis (CH). We studied the architecture, trajectories, and impact of CH in a cohort of 207 TBD patients. CH was rare in asymptomatic patients but present in 46% of symptomatic patients and involved chromosome 1q aberrations (mainly chromosome 1q gain [Chr1q+]) and recurrent mutations in PPM1D, POT1, TERT promoter, and U2AF1S34. Compared with age-matched healthy controls, patients with TBDs had a significantly higher CH frequency, which increased with age. Regardless of allele burden, Chr1q+ and mutations in U2AF1S34 or TP53 increased the risk of developing myelodysplastic syndromes and acute myeloid leukemia. Further functional studies demonstrated that the U2AF1S34 mutation compensated for the aberrant activation of the TP53 and interferon pathways, which contribute to HSC exhaustion in patients with TBDs. These results suggest that the acquisition of U2AF1S34 mutations in TBDs compensates for the restricted cell fitness caused by germline mutations in telomere maintenance genes, which underscores the importance of understanding the molecular mechanisms of U2AF1S34 mutation–induced tumorigenesis. In this proposal, we will use innovative technologies, such as organoid and induced pluripotent stem cell systems and the MISTRG mouse model to 1) Dissect the IFI16-mediated signaling pathway under telomere attrition and determine the feasibility of targeting IFI16 in humans to rescue telomere-dysfunctional HSC function and 2) Dissect the mechanisms of U2AF1S34 mutation–induced tumorigenesis under telomere stress. The proposed study will expand our understanding of the contribution of telomere damage to HSCs’ functional decline and CH and provide new opportunities for developing strategies to improve the prevention and treatment of hematological disorders associated with telomere dysfunction.