Regulation of Hematopoietic Stem Cell Mitochondrial Metabolism

Hematopoietic stem cells (HSCs) like most, if not all, adult stem cells are primarily quiescent but have the potential to become highly active on demand. HSC quiescence is maintained by glycolytic metabolism and low levels of reactive oxygen species (ROS), which indicate that mitochondria are relatively inactive in quiescent HSC. However, HSC cycling - and exit of quiescence state - require a swift metabolic switch from glycolysis to mitochondrial oxidative phosphorylation. To improve our understanding of mechanisms that integrate energy metabolism with HSC homeostasis, my laboratory has been focused on the transcription factor FOXO3, which is critical for the maintenance of HSC quiescence and redox state and is implicated in HSC aging. We showed recently that FOXO3 is key to HSC mitochondrial metabolism, independent of its inhibition of ROS or mTOR signaling. Mitochondria divide and fuse constantly in part to segregate and dispose of their damaged counterparts. These processes are influenced by and highly linked to mitochondrial metabolism. We have recently developed imaging approaches to study HSC mitochondrial divisions. Mechanisms by which FOXO3 regulates HSC mitochondria and the impact of impaired FOXO3 on the HSC health and activity, and mitochondrial network will be discussed. Detailed understanding of the mitochondrial metabolism and divisions in HSC and their relationship to nuclear transcription are likely to have broad implications for the state of HSC fitness, regenerative capacity and aging.