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 4

TTP controls antimicrobial activation of the neutrophil transcriptome.

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TTP controls antimicrobial activation of the neutrophil transcriptome. P...
Peritoneal neutrophils (>95% Ly6G+) from TTPΔM and TTPfl/fl mice were stimulated with 10 ng/ml LPS for 4 hours, and differential expression was analyzed. (A) Volcano plot showing the statistical significance of different expression levels (FDR) against fold changes (FC) of expression between TTPΔM and TTPfl/fl neutrophils. Dots represent genes color-coded according to expression levels (FPKM). Horizontal dashed line indicates an FDR of 0.05. Cxcl2, Il1b, Csf2, Il6, Mcl1, and Tnf represent examples of differently expressed genes. (B) Box-and-whisker plots show the FC in gene expression between TTPΔM and TTPfl/fl neutrophils dependent on AUUUA numbers in 3′-UTRs (FPKM >10). (C) Correlation plots for TTP-dependent differential gene expression in neutrophils and macrophages. Differential gene expression in TTPΔM and TTPfl/fl neutrophils (y axis) and TTPΔM and TTPfl/fl macrophages (x axis) after LPS treatment is shown as the LFC. No correlation between differential gene expression in neutrophils or macrophages was observed (Pearson’s R = –0.005; 95% CI, –0.052 to 0.040; P = 0.8242). (D) GO enrichment in the category “biological process” for significantly upregulated genes in TTPΔM neutrophils (FPKM >10). Edges connect GO terms sharing multiple genes (Jaccard distance ≤0.8); line width indicates the Jaccard distance. Circle size shows term enrichment; circle color shows the P value (from blue to white, P value is shown as –log10). Note the clustering of terms for the negative regulation of programmed cell death (top left), cell migration (top middle), and cytoskeletal rearrangement (bottom right).