Single Cell Proteomics Reveals Novel Cytokine-Producing Function of Hematopoietic Stem and Progenitor Cells

Abstract

During infection, hematopoietic stem and progenitor cells (HSPCs) are called upon to proliferate and differentiate to produce more innate and adaptive immune cells to combat infection. Traditionally, HSPCs are thought to respond to depletion of downstream hematopoietic cells during infection. More recent evidence suggests that HSPCs may respond directly to infection and pro-inflammatory cytokines. However, little is known about the direct immune response of HSPCs and the molecular signaling regulating this response upon sensing an infection. In this study, we have combined transgenic and genetic knockout mouse models with a novel single cell barcode proteomics microchip technology to tackle these questions. We show that although long-term hematopoietic stem cells (HSCs) (defined by Lineage-cKit+Sca1+CD150+CD48-) do not secrete cytokines upon toll-like receptor (TLR) stimulation, short-term HSCs and multipotent progenitor cells (MPPs) (defined by Lineage-cKit+Sca1+, referred to as LKS thereafter) can produce copious amounts of cytokines upon direct TLR-4 and TLR-2 stimulation, indicating that LKS cells can directly participate in an immune response by producing a myriad of cytokines, upon a bacterial infection. Within the population of LKS cells we detect multiple functional subsets of cells, specialized in producing myeloid-like, lymphoid-like or both types of cytokines. Moreover, we show that the cytokine production by LKS cells is regulated by the NF-κB activity, as p50-deficient LKS cells show reduced cytokine production while microRNA-146a (miR-146a)-deficient LKS cells show significantly increased cytokine production.

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