Chromatin remodelling and autocrine TNFα are required for optimal interleukin-6 expression in activated human neutrophils

Abstract

Controversy currently exists about the ability of human neutrophils to produce IL-6. Here, we show that the chromatin organization of the IL-6 genomic locus in human neutrophils is constitutively kept in an inactive configuration. However, we also show that upon exposure to stimuli that trigger chromatin remodelling at the IL-6 locus, such as ligands for TLR8 or, less efficiently, TLR4, highly purified neutrophils express and secrete IL-6. In TLR8-activated neutrophils, but not monocytes, IL-6 expression is preceded by the induction of a latent enhancer located 14 kb upstream of the IL-6 transcriptional start site. In addition, IL-6 induction is potentiated by endogenous TNFa, which prolongs the synthesis of the IkBz co-activator and sustains C/EBPb recruitment and histone acetylation at IL-6 regulatory regions. Altogether, these data clarify controversial literature on the ability of human neutrophils to generate IL-6 and uncover chromatin-dependent layers of regulation of IL-6 in these cells.

Neutrophil heterogeneity: implications for homeostasis and pathogenesis

“…Interestingly, interleukin (IL)-6 expression by human neutrophils after exposure to Toll-like receptor (TLR)-8 ligands involved chromatin remodeling and increased activity of noncoding regulatory elements (eg, enhancers). 23 Thus, this evidence supports an inducible epigenetic and genetic regulation of neutrophil gene expression. Moreover, the association between genetic variants 24 and altered methylation profiles 25 in neutrophils associated with disease susceptibility emphasizes the importance of understanding how gene expression is controlled in neutrophils.…”

“…In line with the ability of neutrophils to synthesize de novo proteins, recent studies report an active chromatin remodeling and a fine regulation of mRNA expression. On one side, neutrophil gene expression is controlled on an epigenetic level by chromatin histone modification such as methylation 22 or acetylation, 23 processes that tightly influence gene transcription. On the other side, neutrophils display a cell-specific pattern of noncoding regulatory regions, 24 elements that are involved in the regulation of gene expression.…”

Mature CD10+ and immature CD10− neutrophils present in G-CSF–treated donors display opposite effects on T cells

“…NDNs were also isolated from the granulocyte fraction by negative selection using immunomagnetic beads as previously described. 30 Cell purity of all sorted populations was always .98%, as determined by flow cytometry.…”

“…Moreover, none of the isolation methods caused an activation of neutrophils (as revealed by eventual changes in CD11b, CD16, and CD62L expression), and/or an alteration of their vitality, as compared with the negative selection purification procedure (supplemental Figure 4B-C). 30 Finally, unfractionated CD10…”

Feedback Amplification of Neutrophil Function

“…receptors [57]. In addition, neutrophil-derived TNF-α has been shown to contribute to the amplification of IL-6 production by human neutrophils stimulated by a TLR8 ligand [58].…”