GM-CSF signaling strength determines opposing innate memory phenotypes at different stages of myelopoiesis
Inflammatory responses must be tightly coordinated with the activation of emergency myelopoiesis to produce potent myeloid cells that fight infection without causing self-damage. Here we show that GM-CSF programs myeloid committed progenitors to produce trained macrophages (increased cytokine response), but programs the upstream non-committed LKS+ progenitors to produce tolerized macrophages (decreased cytokine response). In myeloid progenitors, GM-CSF strongly activates STAT5, ERK and Akt-mTOR signaling pathways which are essential to establish a training program, whereas in LKS+ progenitors GM-CSF induces NF-?B translocation to the nucleus to establish a tolerization program. These differences arise from higher GM-CSF receptor expression in myeloid progenitors compared to LKS+ cells. We demonstrate that ß-catenin regulation of NF-?B nuclear translocation is central in this process. Glycogen synthase kinase 3 (GSK3) inactivation by strong ERK and PI3K-Akt signaling increases cytoplasmic ß-catenin levels to block NF-?B nuclear translocation in myeloid progenitors. In contrast, when ERK and PI3K-Akt signaling is weak, active GSK3 decreases ß-catenin to allow NF-?B nuclear translocation in LKS+ progenitors. Finally, GM-CSF-induced LKS+ tolerization can be reversed and takes place in several murine models of trained immunity and in human CD34+ CD38– progenitors. Our study reveals that in addition to activating myelopoiesis, GM-CSF also programs early and immediate myeloid progenitors to produce opposing immune memory phenotypes. We propose that the inflammatory response from immediate myeloid progenitors may be balanced by the tolerized phenotype of early progenitors, thus providing a mechanism for appropriate resolution of inflammation and protection against prolonged cytokine storm. Overall design: 10X Genomics single-cell ATAC-seq from two murine hematopoietic stem cell populations (LKS progenitors and CD34+ myeloid progenitors) treated with two conditions for 24h (M-CSF and M-CSF + GM-CSF)