Functional responses and molecular mechanisms involved in histone-mediated platelet activation

Abstract

Histones are highly alkaline proteins found in cell nuclei and they can be released by either dying or inflammatory cells. The recent observations that histones are major components of neutrophil extracellular traps and promote platelet aggregation and platelet-dependent thrombin generation have shown that these proteins are potent prothrombotic molecules. Because the mechanism(s) of platelet activation by histones are not completely understood, we explored the ability of individual recombinant human histones H1, H2A, H2B, H3 and H4 to induce platelet activation as well as the possible molecular mechanisms involved. All histones were substrates for platelet adhesion and spreading and triggered fibrinogen binding, aggregation, von Willebrand factor release, P-selectin and phosphatidylserine (PS) exposure and the formation of platelet-leukocyte aggregates; however, H4 was the most potent. Histone-mediated fibrinogen binding, P-selectin and PS exposure and the formation of mixed aggregates were potentiated by thrombin. Histones induced the activation of ERK, Akt, p38 and NFκB. Accordingly, histone-induced platelet activation was significantly impaired by pretreatment of platelets with inhibitors of ERK (U 0126), PI3K/Akt (Ly 294002), p38 (SB 203580) and NFκB (BAY 11-7082 and Ro 106-9920). Preincubation of platelets with either aspirin or dexamethasone markedly decreased fibrinogen binding and the adhesion mediated by histones without affecting P-selectin exposure. Functional platelet responses induced by H3 and H4, but not H1, H2A and H2B, were partially mediated through interaction with Toll-like receptors -2 and -4. Our data identify histones as important triggers of haemostatic and proinflammatory platelet responses, and only haemostatic responses are partially inhibited by anti-inflammatory drugs.

NETosis before and after Hyperglycemic Control in Type 2 Diabetes Mellitus Patients

“…Plasmatic levels of nucleosomal DNA, human IL-6 and TNFα were measured using commercial ELISA kits (Cell death, ELISAPLUS Roche Diagnostic and eBioscience) and vWF levels were measured as previously described [19]. …”

Platelet–neutrophil interactions under thromboinflammatory conditions

“…It was reported that p38 MAPK is not important for Ca 2+ mobilization, P-selectin exposure and αIIbβ3 integrin activation in response to thrombin [150]. In contrast, recent studies showed that inhibition of extracellular signal-regulated kinases (ERK) and p38 MAPK significantly impairs P-selectin exposure and αIIbβ3 integrin activation in histone-stimulated platelets [151]. Treatment of neutrophils with platelet-activating factor (PAF) up-regulates αMβ2 integrin expression and stimulates β2 integrin-dependent adhesion through ERK, but not PI3K [152].…”

“…It was reported that IκBα is phosphorylated and degraded in thrombin-activated platelets and that IκB kinase inhibitors impair P-selectin exposure, αIIbβ3 integrin activation, and ERK phosphorylation in activated platelets [151, 155, 156]. Recent studies suggested that treatment of platelets with TLR2 and 4 agonists triggers P-selectin exposure through NF-κB signaling [157].…”

Fetuin-A associates with histones intracellularly and shuttles them to exosomes to promote focal adhesion assembly resulting in rapid adhesion and spreading in breast carcinoma cells

“…Even though histones have not been established as bonafide adhesion molecules, their extracellular appearance and suggested roles in this microenvironment have provoked interest in biology [21,22]. For example, a recent report indicated that extracellular histones activated a number of adhesion related signals such as PI3 kinase/Akt in platelets [23]. …”