The RNA-binding protein tristetraprolin schedules apoptosis of pathogen-engaged neutrophils during bacterial infection
Florian Ebner, … , Michael Sixt, Pavel Kovarik
Florian Ebner, … , Michael Sixt, Pavel Kovarik
Published May 15, 2017
Citation Information: J Clin Invest. 2017;127(6):2051-2065. https://doi.org/10.1172/JCI80631.
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Research Article Immunology Infectious disease

The RNA-binding protein tristetraprolin schedules apoptosis of pathogen-engaged neutrophils during bacterial infection

Abstract

Protective responses against pathogens require a rapid mobilization of resting neutrophils and the timely removal of activated ones. Neutrophils are exceptionally short-lived leukocytes, yet it remains unclear whether the lifespan of pathogen-engaged neutrophils is regulated differently from that in the circulating steady-state pool. Here, we have found that under homeostatic conditions, the mRNA-destabilizing protein tristetraprolin (TTP) regulates apoptosis and the numbers of activated infiltrating murine neutrophils but not neutrophil cellularity. Activated TTP-deficient neutrophils exhibited decreased apoptosis and enhanced accumulation at the infection site. In the context of myeloid-specific deletion of Ttp, the potentiation of neutrophil deployment protected mice against lethal soft tissue infection with Streptococcus pyogenes and prevented bacterial dissemination. Neutrophil transcriptome analysis revealed that decreased apoptosis of TTP-deficient neutrophils was specifically associated with elevated expression of myeloid cell leukemia 1 (Mcl1) but not other antiapoptotic B cell leukemia/lymphoma 2 (Bcl2) family members. Higher Mcl1 expression resulted from stabilization of Mcl1 mRNA in the absence of TTP. The low apoptosis rate of infiltrating TTP-deficient neutrophils was comparable to that of transgenic Mcl1-overexpressing neutrophils. Our study demonstrates that posttranscriptional gene regulation by TTP schedules the termination of the antimicrobial engagement of neutrophils. The balancing role of TTP comes at the cost of an increased risk of bacterial infections.

Authors

Florian Ebner, Vitaly Sedlyarov, Saren Tasciyan, Masa Ivin, Franz Kratochvill, Nina Gratz, Lukas Kenner, Andreas Villunger, Michael Sixt, Pavel Kovarik

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Figure 2

Bone marrow and circulating neutrophils and monocytes are not regulated by TTP during bacterial infection.

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Bone marrow and circulating neutrophils and monocytes are not regulated ...
(A and B) Neutrophil and inflammatory monocyte populations in the bone marrow and blood of TTPfl/fl and TTPΔM animals. Bone marrow and blood of untreated or infected animals were analyzed by flow cytometry 48 hours p.i. Cells were subgated for CD11b+Siglec-F–FcεRI– cell populations, and neutrophils and inflammatory monocytes were detected as Ly6G+Ly6C+ or Ly6G–Ly6Chi cells, respectively. Dot plots of neutrophil and inflammatory monocytes in bone marrow (A, upper panel) and blood (A, lower panel) of untreated (n = 4/genotype) and infected animals (n = 9/genotype). Representative flow plots of bone marrow (B, upper panel) and blood (B, lower panel) 48 hours p.i. Numbers indicate the percentages in the outlined area. (C) CMPs (Lin–Sca-1–c-KithiCD16/32loCD34+) and GMPs (Lin–Sca-1–c-KithiCD16/32hiCD34+) in the bone marrow of untreated and infected (48 hours p.i.) TTPfl/fl and TTPΔM mice were analyzed by flow cytometry. (D) Mature neutrophils (c-Kit–Ly6G+) and (E) immature neutrophils (c-Kit+Ly6G+) in the bone marrow and blood of untreated and infected (48 hours p.i.) TTPfl/fl and TTPΔM mice were analyzed by flow cytometry. n = 5 untreated TTPfl/fl; n = 5 untreated TTPΔM mice; n = 6 infected TTPfl/fl mice; and n = 6 infected TTPΔM mice were used in C, D, and E. Error bars represent the mean. *P < 0.05 and **P < 0.01, by unpaired Student’s t test.