Neutrophil Cerebrovascular Transmigration Triggers Rapid Neurotoxicity through Release of Proteases Associated with Decondensed DNA

Abstract

Cerebrovascular inflammation contributes to diverse central nervous system (CNS) disorders through mechanisms that are incompletely understood. The recruitment of neutrophils to the brain can contribute to neurotoxicity, particularly during acute brain injuries such as cerebral ischaemia, trauma and seizures. However, the regulatory and effector mechanisms that underlie neutrophil-mediated neurotoxicity are poorly understood. Here we show that mouse neutrophils are not inherently toxic to neurons but that trans-endothelial migration across IL-1 stimulated brain endothelium triggers neutrophils to acquire a neurotoxic phenotype that causes rapid death of cultured neurons. Neurotoxicity was induced by addition of transmigrated neutrophils or conditioned medium taken from transmigrated neutrophils to neurons, and was partially mediated by excitotoxic mechanisms and soluble proteins. Transmigrated neutrophils also released de-condensed DNA associated with proteases, which are known as neutrophil extracellular traps (NETs). The blockade of histone-DNA complexes attenuated transmigrated neutrophil-induced neuronal death, whilst the inhibition of key neutrophil proteases in the presence of transmigrated neutrophils rescued neuronal viability. We also show that neutrophil recruitment in the brain is IL-1 dependent and release of proteases and de-condensed DNA from recruited neutrophils in the brain occurs in several in vivo experimental models of neuroinflammation. These data reveal new regulatory and effector mechanisms of neutrophil-mediated neurotoxicity, namely the release of proteases and de-condensed DNA triggered by phenotypic transformation during cerebrovascular transmigration. Such mechanisms have important implications for neuroinflammatory disorders, notably in the development of anti-leukocyte therapies.

Neutrophils Mediate Blood–Spinal Cord Barrier Disruption in Demyelinating Neuroinflammatory Diseases

“…The authors postulated that neutrophils promote this phenomenon, thereby facilitating massive leukocyte influx through the compromised BSCB. In support of this hypothesis, in vitro experiments by Allen et al (89) demonstrated that neutrophils acquire a neurotoxic phenotype upon cerebrovascular transendothelial migration, releasing soluble factors and proinflammatory cytokines, which could facilitate such an influx into the CNS. Interestingly, this neurotoxic phenotype of neutrophils was acquired when neutrophils transmigrated across an IL-1-stimulated brain endothelium.…”

IgA Enhances NETosis and Release of Neutrophil Extracellular Traps by Polymorphonuclear Cells via Fcα Receptor I

“…Aberrant NET formation has been associated with tissue damage, autoimmunity, and cancer development (45)(46)(47)(48). It was recently demonstrated that NETs were involved in transfusionrelated acute lung injury (46), neurotoxicity (47), and thrombosis (48).…”

“…It was recently demonstrated that NETs were involved in transfusionrelated acute lung injury (46), neurotoxicity (47), and thrombosis (48). Histones, which are major components of NETs, were furthermore shown to induce epithelial and endothelial cell death (49).…”

Streptococcus pneumoniae worsens cerebral ischemia via interleukin 1 and platelet glycoprotein Ibα

“…Granulocyte numbers were not increased in infected mice independently of infarct size either. Although after IL-1-mediated cerebrovascular transmigration granulocytes acquire a neurotoxic phenotype, and IL-1 actions can worsen injury in the brain via granulocytes in vivo, 30,39 increased numbers of parenchymal granulocytes in the current experimental model might be indirectly associated with infection status and thus bigger infarcts. Nevertheless, systemic or perivascular granulocyte responses might mediate brain injury independently of the cells in the brain parenchyma, although this was not tested experimentally in the present study.…”