MDH1-mediated malate-aspartate NADH shuttle maintains the activity levels of fetal liver hematopoietic stem cells.

The connections between energy metabolism and stemness of hematopoietic stem cells (HSCs) at different developmental stages remain largely unknown. We herein generate a transgenic mouse line for the genetically encoded NADH/NAD+ sensor (SoNar) and demonstrate that there exist three distinct fetal liver hematopoietic cell populations according to the ratios of SoNar fluorescence. SoNar-low cells have an enhanced level of mitochondrial respiration, but similar glycolytic level to SoNar-high cells. Interestingly, 10% of SoNar-low cells are enriched for 65% of total immunophenotypical fetal liver HSCs (FL-HSCs) and contain approximately 5-fold greater functional HSCs than that of SoNar-high counterparts. SoNar can monitor sensitively the dynamic changes of energy metabolism in HSCs both in vitro and in vivo. Mechanistically, STAT3 transactivates MDH1 to sustain the malate-aspartate NADH shuttle activity and the HSC self-renewal and differentiation. We reveal an unexpected metabolic program of FL-HSCs and provide a powerful genetic tool for metabolic studies of HSCs or other types of stem cells.

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