PAD4 mediated histone hypercitrullination induces heterochromatin decondensation and chromatin unfolding to form neutrophil extracellular trap-like structures

Abstract

NETosis, the process wherein neutrophils release highly decondensed chromatin called neutrophil extracellular traps (NETs), has gained much attention as an alternative means of killing bacteria. In vivo, NETs are induced by bacteria and pro-inflammatory cytokines. We have reported that peptidylarginine deiminase 4 (PAD4), an enzyme that converts Arg or monomethyl-Arg to citrulline in histones, is essential for NET formation. The areas of extensive chromatin decondensation along the NETs were rich in histone citrullination. Here, upon investigating the effect of global citrullination in cultured cells, we discovered that PAD4 overexpression in osteosarcoma U2OS cells induces extensive chromatin decondensation independent of apoptosis. The highly decondensed chromatin is released to the extracellular space and stained strongly by a histone citrulline-specific antibody. The structure of the decondensed chromatin is reminiscent of NETs but is unique in that it occurs without stimulation of cells with pro-inflammatory cytokines and bacteria. Furthermore, histone citrullination during chromatin decondensation can dissociate heterochromatin protein 1 beta (HP1β) thereby offering a new molecular mechanism for understanding how citrullination regulates chromatin function. Taken together, our study suggests that PAD4 mediated citrullination induces chromatin decondensation, implicating its essential role in NET formation under physiological conditions in neutrophils.

Nanoparticles size-dependently initiate self-limiting NETosis-driven inflammation

“…NETosis can be induced by incubation with crystals or bacteria (7,12) and is characterized by extracellular DNA decorated with NE, histones, or MPO (26). AggNET formation was observed at high granulocyte densities.…”

A molecular signature of preclinical rheumatoid arthritis triggered by dysregulated PTPN22

“…Indeed, citrullination critically regulates embryogenesis (21,22), epithelial-to-mesenchymal transformation (23), and pluripotency of embryonic stem cells (24). In addition, PAD4-mediated citrullination of histones is essential for the formation of neutrophil extracellular traps (NETs) (25)(26)(27), which can induce the expression of inflammatory cytokines, such as IL-6 and IL-18, as well as CCL20 and ICAM-1 from fibroblast-like synoviocytes (28). NETs are also a rich source of citrullinated antigens.…”

Is the neutrophil extracellular trap-driven microvascular inflammation essential for diabetes vasculopathy?

“…1). The NETosis is the post-translational regulated process forming deiminated chromatin, which is not only able to capture bacterial pathogens and bacterial cell adjuvants, but it may regulate inflammation and tissue damage via indirect mechanisms (Dwivedi et al, 2014;Dwivedi and Radic, 2013;Leshner et al, 2012) including free radical production, forming of immune complexes, autoantibodies, inducing inflammatory cytokines release from competent cells (Fig. 2).…”