Divisional Memory Drives Hematopoietic Stem Cell Functional Diversity

• Published in: Blood 2021-11, Vol.138 (Supplement 1), p.20-20
• Main Authors: Bartram, James, Song, Baobao (Annie), Xu, Juying, Salomonis, Nathan, Grimes, H. Leighton, Filippi, Marie-Dominique
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2021-153296

Hematopoietic stem cells are endowed with high regenerative potential but their actual self-renewal capacity is limited. Studies using the H2B-retention labeling system show HSC functional decline at each round of division (Qiu, Stem Cell Reports 2014). We have shown that mitochondria drive HSC functional decline with division history after transplantation (Cell Stem Cell 2020). Here we examined the link between mitochondrial metabolism, in vivo division at steady state, and HSC functions using the GFP label-Histone 2B (GFP-H2B) mouse model driven by a doxycycline-inducible promoter. Five months after doxycycline removal, mitochondrial membrane potential (MMP) was examined using TMRE in HSC with varying GFP intensity. HSC were separated into an H2B-labeled retention population and an H2B-labeled population. Interestingly, within the H2B-labeled retention population, HSC could be further subdivided into GFP high, medium, and low. MMP increased in a stepwise fashion with GFP dilution in HSC. We noted the presence of 2 TMRE peaks within each GFP high and medium populations leading to 5 populations: GFP-high;MMP-low (G1), GFP-high;MMP-high (G2), GFP-medium;MMP-low (G3), GFP-medium;MMP-high (G4), GFP-low;MMP-high (G5). We examined the repopulation activity of each population in a serial competitive transplant assay. G1 and G2 maintained higher peripheral blood chimerism up to 24 weeks post-transplant than G3 and G4. G5 did not engraft at all. However, only G1 reconstituted high frequency of HSC in primary recipients. In secondary recipients, G1, G2, G3 but not G4 gave rise to positive engraftment. Interestingly, G1 and G2 grafts showed myeloid/lymphoid balanced engraftment whereas the G3 graft was myeloid-bias, suggesting that myeloid skewing can be acquired upon HSC division. We further examined lineage fate maps of bone marrow cells derived from G1 or G3 population in vivo, using single cell RNA sequencing, 10X genomics. Surprisingly, G3-derived bone marrow cells displayed a distinct myeloid cell trajectory from G1-derived bone marrow cells, in which G3 gave rise to increased immature neutrophils but fewer myeloid precursors. Remarkably, each lineage population derived from G3 donor cells had different gene expression signatures than those derived from G1 donor cells. Therefore, HSC that have divided in vivo in the same bone marrow microenvironment are intrinsically and molecularly different such that not only do they exhibit lineage potential differences but