Neuroinflammation after acute brain injury: the role of interleukin-1 actions on non-neuronal cells

UoM administered thesis: Phd

  • Authors:
  • Fiona Britton

Abstract

The neuroinflammatory response involves a complex network of interactions between multiple cell types and a number of inflammatory mediators. There is substantial evidence for a central role of interleukin-1 (IL-1) in the neuroinflammatory response to cerebral ischaemia. IL-1 exacerbates damage in animal models of ischaemia, and can also be neurotoxic in vitro. Matrix metalloproteinase-9 (MMP-9) is a key mediator of blood-brain barrier (BBB) disruption, and increased MMP-9 activity is associated with a worsened outcome in animal models of cerebral ischaemia. In vitro IL-1 induces astrocytic MMP-9 activity which is neurotoxic in neuronal-glial co-cultures. This study aimed to identify key mediators up-regulated in response to IL-1 in glial and endothelial cells and to study the role of the endothelial IL-1 receptor type 1 (IL-1R1) in cerebral ischaemia. Primary mixed glial cultures and neuronal-glial co-cultures were prepared from rats and mice, and primary endothelial cultures were prepared from mice. Cell cultures were treated with recombinant IL-1alpha or IL-1β, and the production of inflammatory mediators was assayed. The role of endothelial IL-1R1 in cerebral ischaemia was assessed using endothelial specific IL-1R1 knockdown (eIL-1R1 KD) mice. eIL-1R1 KD and wildtype (WT) mice were subjected to 60 min middle cerebral artery occlusion (MCAo) and 24 h reperfusion. Initial findings in this thesis show marked differences in IL-1-induced MMP-9 activity in mixed glial cultures prepared from rat and mouse, which account for the species dependent nature of IL-1-induced neurotoxicity observed. IL-1 induced a concentration-dependent increase in MMP-9 in rat glial cultures, although this effect was not present in mouse glial cultures. Tissue inhibitor of MMP (TIMP)-1 levels were elevated to a greater extent in mouse cultures providing evidence that increased TIMP-1 expression masks IL 1 induced MMP-9 activity, and protects mouse neuronal-glial co cultures from MMP-9 mediated neurotoxicity. Endothelial activation is a key step for leukocyte recruitment and infiltration and many mediators present after an ischaemic insult may induce endothelial activation. Up regulation of vascular cell adhesion molecule (VCAM)-1 was observed after 4 h treatment with IL-1alpha or IL-1β, followed by the up regulation of intracellular cell adhesion molecule (ICAM)-1 after 8 h treatment. Chemokines, monocyte chemoattractant protein (MCP)-1 and keratinocyte-derived chemokine (KC), were released after 8 h treatment followed by release of regulated on activation, normal T cell, expressed and secreted (RANTES) and granulocyte colony stimulating factor (G-CSF) at 24 h. These data suggest that IL 1 activation of the endothelium could be the primary stimulus for peripheral cell infiltration after cerebral ischaemia. To investigate this further MCAo was performed in eIL-1R1 KD and WT mice and lesion volumes and peripheral immune populations were studied. There was no difference in lesion volumes in eIL-1R1 KD mice compared to WT. Flow cytometric analysis of blood, bone marrow and spleen identified no genotype dependent changes in peripheral immune cell populations. In conclusion, IL-1 acts on multiple CNS cell types to induce cell specific responses. These studies provide evidence that IL-1-induced neurotoxicity is a species dependent mechanism, observed in rat cultures but not in mouse cultures. Furthermore, IL-1 activates endothelial cells and induced the up-regulation of adhesion molecules and controlled release of chemokines, facilitating the recruitment of peripheral immune populations. Data obtained from eIL-1R1 KD mice were unable to confirm a role of endothelial IL-1R1 in cerebral ischaemia. Thus, the interaction between multiple cell types and differential responses to IL 1 must be considered in unison. The IL-1 system remains an attractive therapeutic target for the treatment of cerebral ischaemia.

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Original languageEnglish
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Award date31 Dec 2013