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Early and late processes driving NET formation, and the autocrine/paracrine role of endogenous RAGE ligands

ABSTRACT: Neutrophil extracellular trap (NET) formation has emerged as an important response against various pathogens; it also plays a role in chronic inflammation, autoimmunity, and cancer. Despite a growing understanding of the mechanisms underlying NET formation, much remains to be elucidated. We previously showed that in human neutrophils activated with different classes of physiological stimuli, NET formation features both early and late events that are controlled by discrete signaling pathways. However, the nature of these events has remained elusive. We now report that PAD4 inhibition only affects the early phase of NETosis, as do distinct signaling intermediates (TAK1, MEK, p38 MAPK). Accordingly, the inducible citrullination of residue R2 on histone H3 is an early neutrophil response that is regulated by these kinases; other arginine residues on histones H3 and H4 do not seem to be citrullinated. Conversely, chromatin decondensation is a belated event in NET formation, that is impaired by the inhibition of most signaling pathways known to control the phenomenon. We additionally show that neutrophils can condition themselves to be poised for rapid NET formation, and that this represents another late process. Similarly, activated neutrophils release a number of endogenous proteic factors that promote and largely mediate NET generation, and this is yet another late process. Our data shed new light on the cellular processes underlying NET formation, and unveil some unsuspected facets of the phenomenon. In view of the involvement of NETs in both homeostasis and several pathologies, our findings are of broad relevance.

INSTRUMENT(S): Q Exactive

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Blood

DISEASE(S): Disease Free

SUBMITTER: Francois-Michel Boisvert

LAB HEAD: Patrick McDonald

PROVIDER: PXD027055 | Pride | 2021-10-12

REPOSITORIES: Pride

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Project description:The role of myeloid cells in supporting cancer growth is well established. Most work has focused on myeloid-derived suppressor cells (MDSC) that accumulate in tumor-bearing animals, but tumor-associated neutrophils (TAN) are also known to be capable of augmenting tumor growth. However, little is known about their evolution, phenotype, and relationship to naive neutrophils (NN) and to the granulocytic fraction of MDSC (G-MDSC). In the current study, a transcriptomics approach was used in mice to compare these cell types. Our data show that the three populations of neutrophils are significantly different in their mRNA profiles with NN and G-MDSC being more closely related to each other than to TAN. Structural genes and genes related to cell-cytotoxicity (i.e. respiratory burst) were significantly down-regulated in TAN. In contrast, many immune-related genes and pathways, including genes related to the antigen presenting complex (e.g. all six MHC-II complex genes), and cytokines (e.g. TNF-a, IL-1-a/b), were up-regulated in G-MDSC, and further up-regulated in TAN. Thirteen of the 25 chemokines tested were markedly up-regulated in TAN compared to NN, including striking up-regulation of chemoattractants for T/B-cells, neutrophils and macrophages. This study characterizes different populations of neutrophils related to cancer, pointing out the major differences between TAN and the other neutrophil populations. Various types of myeloid cells have been shown to promote tumor progression by direct immune suppression and by production of angiogenic factors, matrix-degrading enzymes, or growth factors. In untreated tumors, neutrophils have been reported to produce angiogenic factors and matrix-degrading enzymes, support the acquisition of a metastatic phenotype, and suppress the anti-tumor immune response. Neutrophils, like all other leukocytes, move into tissues from the blood under the influence of specific chemokines (e.g. KC/CXCL-1, MIP-2a/CXCL-2 and GCP-2/CXCL-6), cytokines (e.g. TNFa and IFN-x), and cell adhesion molecules located on their own surface (e.g. CD11b) and on the surface of endothelial cells (e.g. selectins, ICAM-1 and PECAM-1). When they traffic into tumors, they are referred to as TAN. In mice, TAN can be defined by the specific surface markers CD11b and Ly6G with low expression of macrophage markers such as F4/80. Myeloid-derived suppressor cells (MDSC) are a heterogeneous population of immune suppressive cells that are produced excessively in cancer. They comprise at least two subsets -granulocytic (Ly6G+, G-MDSC) and monocytic cells (Ly6C+, M-MDSC), potentially with different immunosuppressive properties. It has been previously shown that MDSC can enter tumors and differentiate to mature macrophages (TAM) or neutrophils (TAN). However, since no definitive markers have been established, it is unknown whether intratumoral N2 neutrophils (N2 TAN) are granulocytic MDSC from spleen that are attracted to the tumor or if they are typical blood-derived neutrophils that are then converted to an N2 phenotype by the tumor microenvironment, specifically by the high local concentrations of TGF-b. The purpose of this study was to use a transcriptomics approach to gain further information about TANs by comparing the RNA profile of these cells to naive bone-marrow neutrophils (NN) and to the granulocytic fraction of myeloid derived suppressor cells (G-MDSC). We examined which pathways and gene-groups varied amongst these 3 populations of neutrophils and performed a detailed analysis on pathways related to the main functions of neutrophils, such as respiratory burst, granule proteins, phagocytosis, apoptosis, structural genes, antigen presentation and specific immune effects. Our data defines TAN as a unique population of neutrophils, quite distinct from both NN and G-MDSC.

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Early and late processes driving NET formation, and the autocrine/paracrine role of endogenous RAGE ligands

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