Linking mitochondria, fatty acids and HSC expansion during infection: Implications for aging and metabolic diseases

In steady state, hematopoietic stem cells (HSCs) reside quiescently in their hypoxic niche with minimal mitochondrial activity, maintaining characteristically low levels of reactive oxygen species (ROS) and instead favoring glycolysis to meet their low energy requirements. However, stress, such as acute infection, triggers a state of emergency hematopoiesis during which HSCs expand more rapidly to produce up to 10-fold more downstream differentiated immune cells. To cope with this demand, HSCs increase their energy production by switching from low ATP-yielding glycolysis to high ATP-yielding mitochondrial oxidative phosphorylation. It is this metabolic switch that enables rapid HSC expansion and differentiation into downstream progeny to increase the immune cell pool and effectively clear the infection. This metabolic switch relies on the sufficient availability of healthy mitochondria as well as fuel in the form of free fatty acids to drive the necessary production of cellular components. This concise review aims to focus on how HSCs increase their mitochondrial content and fuel ATP production via fatty acid oxidation and the impact of HSC dysfunction during aging and other metabolic diseases.