[Regulation of hematopoietic stem cell homeostasis by Spred1]

Various types of stresses account for the dysregulation of the self-renewal activity of stem cells, resulting in the functional failure of tissues or tumorigenesis promotion. Although diets also affect our health, the effect of harmful dietary stresses on the tissue or stem cell homeostasis remains unclear. Recent research has revealed that Spred1, which negatively regulates RAS-MAPK signaling, protects hematopoietic stem cell (HSC) homeostasis against high-fat diet (HFD) -induced systemic stress. In steady-state conditions, Spred1 negatively regulates HSC self-renewal in a manner supported by the Rho kinase (ROCK) activity. In addition, Spred1 deficiency in mice mitigates HSC dysfunction induced by aging or lipopolysaccharide treatment, enhances the HSC self-renewal capacity, and prolongs HSC lifespan, but does not induce leukemia because of the compensatory upregulation of Spred2-the other Spred family member. Conversely, HFD triggers ERK hyperactivation and aberrant self-renewal in Spred1-deficient HSCs, resulting in HSC dysfunction, severe anemia, and the development of lethal myeloproliferative neoplasm-like disease. The depletion of the gut microbiota by antibiotics restored myeloproliferation, anemia, and HSC reconstitution ability in HFD-fed Spred1-deficient mice, suggesting that HFD-induced hematopoietic abnormalities were partially because of alterations in the gut microbiota composition. Thus, HFD-induced systemic stress affects the regulation of HSC self-renewal, and Spred1 safeguards HSC homeostasis against the diet-induced systemic stress.