Membrane-potential compensation reveals mitochondrial volume expansion during HSC commitment

Proper control of mitochondrial function is a key factor in the maintenance of hematopoietic stem cells (HSCs). Mitochondrial content is commonly measured by staining with fluorescent cationic dyes. However, dye staining can be affected, not only by xenobiotic efflux pumps, but also by dye intake, which is dependent on the negative charge of mitochondria. Therefore, mitochondrial membrane potential (Delta psi(mt)) must be considered in these measurements because a high Allf.t due to respiratory chain activity can enhance dye intake, leading to the overestimation of mitochondrial volume. Here, we show that HSCs exhibit the highest AlIfint of the hematopoietic lineages and, as a result, Allimrindependent methods most accurately assess the relatively low mitochondrial volumes and DNA amounts of HSC mitochondria. Multipotent progenitor stage or active HSCs display expanded mitochondrial volumes, which decline again with further maturation. Further characterization of the controlled remodeling of the mitochondrial landscape at each hematopoietic stage will contribute to a deeper understanding of the mitochondrial role in HSC homeostasis. (C) 2018 Published by Elsevier Inc. on behalf of ISEH Society for Hematology and Stem Cells.