3055 – MITOCHONDRIAL METABOLISM LINKS HSC DIVISIONAL HISTORY AND CELL FATE

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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 showed 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 doxycycline-inducible promoter. Five months after doxycycline removal, mitochondrial membrane potential (MMP) was examined using TMRE in HSCs with different GFP intensity. HSC were subdivided into GFP high, medium and low. Interestingly, 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 population 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) and transplanted with competitors. 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 were myeloid/lymphoid balanced engraftment whereas G3 graft was myeloid-bias graft. Further, HSC from G1, G2, G3 and G4 groups carry mitochondria that were morphologically different, exhibited distinct metabolomic profiles, proliferated and differentiated into mature lineages at different rate in vitro. These findings suggest that HSC transition into distinct metabolic and functional state with division history that may contribute to HSC cellular memory.