Abstract B031: Accelerated intra-clonal diversification of hematopoietic stem cells during aging fuels leukemia evolution
Authors: Naddaf Lamis , De Dominici Marco , Chen Xiaowen , Kumar Parveen , Chavez James , Roeder Travis , Karmakar Shilpita , Pietras Eric , Oguro Hideyuki , DeGregori James , Li Sheng 
Published: February 2024

Abstract
Cancer are diseases of aging. Many cellular processes characteristic of cancer, e.g., epigenetic dysregulation, are similarly observed during aging. Acute myeloid leukemia (AML) is emblematic of this interplay. As a blood cancer stemming from hematopoietic stem and progenitors (HSPC), the median age of AML diagnosis is 65. This is linked to age-related clonal hematopoiesis (CH), a condition resulting from the expansion of hematopoietic stem and progenitor cells, typically marked by mutations in leukemia-associated genes. Our investigation thus seeks to clarify the intrinsic role of aging in HSPCs as they relate to CH and leukemic transformation. Hypothesis: Aging amplifies the inheritable phenotypic variations in hematopoietic stem cells, enhancing epigenetic heterogeneity. This acts as a substrate for natural selection, driving leukemic transformation. HSPC Epigenomic and transcriptomic heterogeneity increase in old age: we profiled the single-cell transcriptome (scRNA-seq) and single-nuclear ATAC-seq (snATAC-seq) data from Lineage-c-Kit+ HSPCs isolated from mice at two age groups. Applying Shannon entropy, our analysis revealed a significant increase in epigenetic and transcriptomic heterogeneity in middle-aged LT-HSC compared to their younger counterparts. This process occurs in an aged bone marrow (BM) microenvironment characterized by inflammation and altered HSPC support. Interestingly, we previously show that the rise of epigenetic and transcriptomic heterogeneity in HSC with Tet2 loss (Tet2 MT) and Flt3 ITD precedes leukemic transformation. Diversification of LT-HSC Transcriptome: We employed CellTag Indexing to track the fate of specific HSC subclones. With a barcode detection rate of 80%, our findings indicate that a significant majority (97%) of clones emerged from an HSC. Furthermore, we observed that cells of the same clone manifest higher transcriptomic similarities than those from different clones, underscoring the technique's capability in mapping HSPC clonal evolution. Then we applied scRNA-seq to tagged HSPCs after 16 days of ex vivo expansion. We found that LT-HSCs from older mice exhibited greater clonal diversification, evidenced by intra-clonal transcriptomic correlation. ST-HSC and MPP from older mice also exhibt this pattern. Functional Relevance: Our GSEA analysis of genes with increased expression variability in older mice highlighted several pathways pivotal for HSPC fitness, encompassing ribosome synthesis, inflammation response mechanisms (e.g., JAK-STAT), hematopoietic cell lineage, and AML/cancer pathways. Conclusion: our results suggest that the combined effects of aging and somatic mutations in epigenetic regulators may enhance cell-to-cell variations, offering additional heritable phenotypic variations. These, in turn, may facilitate clonal hematopoiesis and leukemic transformation. Future work will delineate specific epigenetic and transcriptomic configurations that enable mutant HSPC clonal expansion. This study provides a cohesive framework, linking the principles governing aging to cancer.
Citation Format: Lamis Naddaf, Marco De Dominici, Xiaowen Chen, Parveen Kumar, James Chavez, Travis Roeder, Shilpita Karmakar, Eric Pietras, Hideyuki Oguro, James DeGregori, Sheng Li. Accelerated intra-clonal diversification of hematopoietic stem cells during aging fuels leukemia evolution [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Translating Cancer Evolution and Data Science: The Next Frontier; 2023 Dec 3-6; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_2):Abstract nr B031.