Histone H4 directly stimulates neutrophil activation through membrane permeabilization

Abstract

Extracellular histones have been implicated as a cause of tissue inflammatory injury in a variety of disorders including sepsis, lung, and liver diseases. However, little is known about their interactions with neutrophils and how this might contribute to injury. Here, it is shown that histone H4 acts as neutrophil activator by inducing hydrogen peroxide production, degranulation, cell adhesion, and IL-8 generation. Histone H4 caused permeabilization of the neutrophil membrane (a phenomenon described in other cell types) leading to accelerated cell death. H4 caused sustained rise in neutrophil intracellular calcium that is necessary for respiratory burst activation and degranulation. Convincing evidence was not found for TLRs or ATP receptors in H4 mediated activation. However, pertussis toxin and wortmannin (inhibitors of G protein and PI3K) inhibited H4-induced hydrogen peroxide production and degranulation. These studies suggest that release of histone H4 in sites of infection or inflammation may potentiate neutrophil activation and promote additional inflammatory responses. These studies may provide a better basis for developing novel therapeutic strategies to block neutrophil extracellular trap (NET) and H4-related pathology in sepsis and various forms of lung injury including that induced by viruses like influenza or SAR-CoV2.

Histone H4 potentiates neutrophil inflammatory responses to influenza A virus: Down-modulation by H4 binding to C-reactive protein and Surfactant protein D

“…Histone H4 enhances neutrophil respiratory burst responses to IAV. As shown in Fig 2A, Phil82 IAV (MOI = 40) or histone H4 alone caused significant H 2 O 2 production (as previously reported- [20,34]), and pre-incubation of the virus with histone H4 markedly enhanced the response induced by IAV. To determine the role of extracellular and intracellular calcium sources in these responses, we restricted the availability of extracellular calcium by using PBS buffer without calcium and restricted the availability of intracellular calcium by preincubating neutrophils with BAPTA-AM to chelate intracellular calcium.…”

“…Since NETs and histones have been implication in pathogenesis of IAV and likely interact with the virus during severe infection, and IAV induces NET formation in vitro, we studied interaction of histones and IAV with human neutrophils. We recently reported that histone H4 directly activates neutrophils through causing membrane permeabilization leading to sustained calcium influx, respiratory burst activation, degranulation and generation of IL-8 [20].…”

Innate Immunity and Influenza A Virus Pathogenesis: Lessons for COVID-19

“…Studies similar to those of Brandes et al using targeted reduction of myeloid or neutrophil activity can be evaluated in animal models of COVID-19 as well (Brandes et al, 2013). A topic of special interest to us in this regard it the potential role of histones which are a major component of NETs and have been shown to contribute to lung injury in many setting and histone H4 can directly activate neutrophils and monocytes to generate pro-inflammatory cytokines and reactive oxygen species (Hsieh et al, 2020). Various proteins block inflammatory effects of histones including CRP, thrombomodulin, heparin, and anti-histone antibodies, with beneficial effects in mouse models (Hoeksema et al, 2016).…”

“…Histones trigger profound inflammatory responses in the lung and lung injury and also trigger thrombotic events so they may provide a link between inflammatory injury and thrombosis in COVID 19 (Hoeksema et al, 2016;Pulavendran et al, 2019). We have recently shown that free histone H4, which has been found in lung lavage of patients with severe lung inflammation, directly activates neutrophil responses including the respiratory burst, degranulation and cytokine production (Hsieh et al, 2020). The mechanism for this activation involves membrane permeabilization and calcium influx into the cell.…”

Ion and Water Transport in Neutrophil Granulocytes and Its Impairment during Sepsis

“…Important representatives for DAMPs are histones and extracellular ATP. For example, histone H4 causes neutrophil membrane depolarization, a rise in intracellular Ca 2+ and the release of myeloperoxidase and IL-8 [ 122 ]. Interestingly, histone-induced cell death of neutrophils is ameliorated in the presence of fibrinogen, providing a potential therapeutic rationale reducing the detrimental effects of histones on neutrophils by preventing fibrinogen depletion during sepsis [ 123 ].…”