The long-term goal of this proposal is to identify and characterize molecules and pathways that impact the metabolism and function of hematopoietic stem cells (HSCs). Specifically, the application will test the hypothesis that branched-chain amino acid/fatty acid (BCAA/FA) oxidation plays a critical role in controlling HSC functions. HSCs are defined by their ability to self-renew and to give rise to multi-lineages of blood cells. n adults, the HSC population resides in the hypoxic bone marrow microenvironment and remains relatively quiescent. How HSCs remain quiescent, but can rapidly reprogram themselves to be metabolically ready for subsequent differentiation and mobilization to maintain homeostasis is totally unknown. Although several studies have begun to investigate the relationship between metabolism and HSC function, most of the studies focused on glycolysis and energy homeostasis but not the contribution of lipid and amino acid catabolism on HSC functions. We have previously shown that conditional knockout (KO) of Cited2 [CBP/p300-interacting transactivators with glutamic acid (E) and aspartic acid (D)-rich tail 2] in the mouse results in increased HSC apoptosis, loss of quiescence and increased cycling, thus leading to severely impaired hematopoietic reconstitution capacity. Our recent global metabolomics analysis using LT-HSCs isolated from WT and Cited2 KO mice identified branched-chain amino acid/fatty acid (BCAA/FA) metabolism as one of the major metabolic differences between WT and Cited2 KO HSCs. Recently, a previously unknown promyelocytic leukemia (PML)-perioxisome proliferator-activated receptor ? (PPAR?)-fatty acid oxidation (FAO) pathway was shown to be crucial for the maintenance of HSCs and the control of asymmetric cell division. Interestingly, others have shown that Cited2 interacts with PPAR family of nuclear receptors that control lipid metabolism. In addition, Cited2 plays a role in gluconeogenesis through its regulation of PGC-1? (PPAR gamma coactivator-1?)actions and could be a novel therapeutic target for type II diabetes. Because of the molecular and biological link of Cited2 to PPAR and overlapping phenotypes of Cited2 and PML knockout mice (FAO), this multi-PI application intends to test the hypothesis that Cited2 acts as a functional node to modulate branched-chain amino acid and fatty acid metabolism in controlling HSC functions by two subaims: 1: To identify intermediates within the branched-chain amino acid and fatty acid metabolism that impact the function of HSCs from Cited2 knockout mice. 2: To determine mechanistically how Cited2 modulates the BCAA/FA oxidation in HSCs. The current application represents a focused synergistic new collaboration between Drs. Yang and Hoppel to investigate the role of Cited2 in BCAA/FA oxidation in HSCs, an under-explored research area in hematopoiesis. The findings may provide new means of controlling HSC cell fate with future therapeutic implications. The study therefore is "tightly focused and directed at validating novel concepts and approaches that promise to open up new pathways for discovery" and fits the mission of the SHINE-II program at NIDDK.
Our study in which we propose to study the role of Cited2/PML/PPAR in lipid and amino acid metabolism and HSC quiescence therefore explores an under-chartered area of research in hematopoiesis and has high significance in our basic understanding of HSC biology with translational potential in regenerative medicine and in treating blood diseases in general.