Pathogen-Induced TLR4-TRIF Innate Immune Signaling in Hematopoietic Stem Cells Promotes Proliferation but Reduces Competitive Fitness

Publication date: Available online 20 July 2017
Source:Cell Stem Cell
Author(s): Hitoshi Takizawa, Kristin Fritsch, Larisa V. Kovtonyuk, Yasuyuki Saito, Chakradhar Yakkala, Kurt Jacobs, Akshay K. Ahuja, Massimo Lopes, Annika Hausmann, Wolf-Dietrich Hardt, Álvaro Gomariz, César Nombela-Arrieta, Markus G. Manz
Bacterial infection leads to consumption of short-lived innate immune effector cells, which then need to be replenished from hematopoietic stem and progenitor cells (HSPCs). HSPCs express pattern recognition receptors, such as Toll-like receptors (TLRs), and ligation of these receptors induces HSPC mobilization, cytokine production, and myeloid differentiation. The underlying mechanisms involved in pathogen signal transduction in HSCs and the resulting biological consequences remain poorly defined. Here, we show that in vivo lipopolysaccharide (LPS) application induces proliferation of dormant HSCs directly via TLR4 and that sustained LPS exposure impairs HSC self-renewal and competitive repopulation activity. This process is mediated via TLR4-TRIF-ROS-p38, but not MyD88 signaling, and can be inhibited pharmacologically without preventing emergency granulopoiesis. Live Salmonella Typhimurium infection similarly induces proliferative stress in HSCs, in part via TLR4-TRIF signals. Thus, while direct TLR4 activation in HSCs might be beneficial for controlling systemic infection, prolonged TLR4 signaling has detrimental effects and may contribute to inflammation-associated HSPC dysfunction.

Graphical abstract

Teaser

Takizawa et al. show that self-renewing hematopoietic cells directly sense gram-negative bacterial infection through Toll-like receptor 4 (TLR4) activation, which leads to impaired function via proliferative stress. Genetic and pharmacological blockage of the TLR4-TRIF-ROS-p38 axis can maintain HSC function without disrupting emergency granulopoietic responses to infection.


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