Ex-vivo Human Hematopoietic Stem Cell Expansion Requires Coordination of Cellular Reprogramming with Mitochondrial Remodeling and P53 Activation [bulk]

Ex-vivo culture conditions used to expand the numbers of hematopoietic stem cells (HSCs) present within an umbilical cord blood (UCB) unit create cellular stresses leading to loss or at best maintenance of the primitive HSCs. Recently, we have shown that treatment with a histone deacetylase inhibitor, valproic acid (VPA), increases substantially the numbers of transplantable HSCs from UCB-CD34+ cells. In this report, we demonstrate that VPA treatment orchestrates cellular mechanisms that drive UCB-CD34+ cells into a primitive state in which they acquire and retain phenotypic, transcriptomic and primitive mitochondrial profiles, all of which characterize long-term HSCs. Remarkably, our data link the acquisition of the HSC phenotype to the remodeling of the mitochondrial network and p53 activation and establish both as critical regulators of ROS and therefore of HSC fate. VPA treatment leads to restructured mitochondria with reduced mass, membrane potential and ROS levels. p53 activity is critical for the activation of antioxidant defense mechanisms, which rely on magnesium superoxide dismutase (MnSOD) activity. Failure to activate the p53-MnSOD axis compromises both the acquisition and the maintenance of the HSC phenotype. These studies indicate that suppression of ROS through the coordination of p53 activity and mitochondrial remodeling determines the fate of ex-vivo expanded human HSCs