Extracellular Chromatin Is an Important Mediator of Ischemic Stroke in Mice

Abstract

Objective Recently, a growing number of studies have revealed a pro-thrombotic and cytotoxic role for extracellular chromatin. Cerebral ischemia/reperfusion injury is characterized by a significant amount of cell death and neutrophil activation, both of which may result in the release of chromatin. The goal of this study was to assess the effect of extracellular chromatin in ischemic stroke using a mouse model of transient middle cerebral artery occlusion. Methods and results Similar to reports in stroke patients, we observed increased levels of circulating nucleosomes and DNA after ischemic stroke in mice. In addition, we observed that general hypoxia also augmented extracellular chromatin. We hypothesized that targeting extracellular chromatin components would be protective in ischemic stroke. Indeed, treatment with recombinant human DNase 1 significantly improved stroke outcome. Neutralization of histones using an anti-histone antibody was also protective as evidenced by smaller infarct volumes, whereas increasing levels of extracellular histones via histone infusion exacerbated stroke outcome by increasing infarct size and worsening functional outcome. Conclusions Our results indicate that extracellular chromatin is generated and is detrimental during cerebral ischemia/reperfusion in mice. Targeting DNA and/or histones may be a new therapeutic strategy to limit injury resulting from ischemic stroke.

Thrombosis: tangled up in NETs

“…59 Ischemic stroke also elevates plasma nucleosome levels, and systemic hypoxia produced by placing animals in a hypoxic chamber results in release of histone-DNA complexes into circulation. 60 After a day in the hypoxic chamber, mice become highly susceptible to IVC thrombus formation. 61 Interestingly, hypoxia induces hypoxia-inducible factor 1a (HIF-1a), which is implicated in NETosis.…”

“…74,110,111 Such nucleases may be good candidates to improve thrombolysis. Administration of DNase I has a protective effect in vivo in murine models of ischemic stroke, 60 myocardial infarction, 105 and DVT. 34,54 Combination therapies including DNase with ADAMTS13 and/or tissue plasminogen activator could allow for more complete penetration of thrombolytic agents within large thrombi.…”

“…30 In mice, infusion of histones precipitates DVT 54 and exacerbates ischemic stroke. 60 Inhibiting the serine proteases on NETs could allow for TFPI activity and decreased TF-promoted coagulation. 33 TF is found on NETs, 34 and it is likely that TF-containing microparticles are recruited to NETs or NET-associated platelets.…”

PAD4-deficiency does not affect bacteremia in polymicrobial sepsis and ameliorates endotoxemic shock

“…There is vast evidence that aberrant NET production has pathological consequences in noninfectious conditions, including thrombosis, 28 autoimmune diseases, 39,40 and ischemia/reperfusion injury. 29,41 Histones are an integral part of NETs 4,30 and are cytotoxic to endothelial and epithelial cells. 9,35 In vivo, histones contribute substantially to mortality in sepsis 9 and can induce thrombocytopenia.…”

VWF-mediated leukocyte recruitment with chromatin decondensation by PAD4 increases myocardial ischemia/reperfusion injury in mice

“…[15][16][17][18][19][20] In fact, NETs are observed in coronary thrombi removed from patients with AMI. 21 Extracellular chromatin and histones exacerbate tissue injury in experimental models of cerebral and hepatic I/R, 22,23 and impair the clearance of apoptotic neutrophils, 24 a process pivotal to the resolution of inflammation. 25,26 Histone citrullination by peptidylarginine deiminase 4 (PAD4) is a posttranslational histone modification process, necessary for chromatin decondensation during NET formation.…”