[Thesis]. Manchester, UK: The University of Manchester; 2010.
IL-1α and IL-1β are two IL-1 agonists which signals at the same receptor complex
composed of IL-1R1/IL-1RAcP. However, IL-1α and IL-1β exert differential actions.
A recent CNS-specific IL-1 receptor accessory protein, called IL-1RAcPb, has been
characterised but its actions are unknown. In T cell line, over expression of IL-1RAcPb
negatively regulate IL-1 action (Smith et al, 2009), but over-expression of IL-1RAcPb
in HEK cell line induces IL-1 signaling (Lu et al, 2008). The role of IL-1RAcPb has
not been studied in primary cells. The aim of this project was to investigate the
role of IL-1RAcPb in IL-1-induced actions in neurones and glia, and to determine IL-1α
and IL-1β differential actions in these two cell types. The role of IL-1RAcPb in IL-1-induced
protein expression and IL 1α and IL-1β differential effects were investigated by treating
WT and IL 1RAcPb-/- neurones and glia with IL-1α or IL-1β in the presence or absence
of IL-1RA for 24 h followed by assessment of IL-6 induction by ELISA. The mechanism
of IL-1RAcPb actions were studied by examining the effects of IL-1α or IL-1β on p38,
ERK1/2 and Src kinase activation in neurones and glia by Western blot analysis. SB203580
(p38 inhibitor), UO126 (ERK1/2 inhibitor), and PP2 (Src kinase inhibitor) were used
to determine the contribution of p38, ERK1/2 and Src kinase activation to IL-1-induced
IL-6 synthesis in neuronal cultures. In WT neurones, IL-1α and IL-1β were equipotent
at inducing IL-6 synthesis and p38 activation, whilst both ligands failed to induce
ERK1/2 or Src kinase activation. In IL-1RAcPb-/- neurones, IL-1α and IL-1β induced
similar levels of IL-6, but IL-1β was more potent than IL-1α at inducing p38 activation.
IL-1α-induced p38 activation was reduced in IL-1RAcPb-/- neurones compared to WT neurones.
In contrast to WT neurones, ERK1/2 was activated in IL-1RAcPb-/- neurones in response
to IL-1α, whilst Src kinase was not activated by IL-1α or IL 1β. IL-1-induced IL-6
synthesis was abolished by IL-1RA, SB203580, UO126 and PP2. Interestingly PP2, a specific
Src kinase inhibitor also partially inhibited basal ERK1/2 activity. In WT glial
cells, IL-1α was more potent than IL-1β at inducing IL-6 synthesis but both cytokines
induced ERK1/2 activation with equal potency. In IL-1RAcPb-/- glia, IL-1α and IL-1β
were equally potent at inducing IL-6 synthesis and ERK1/2 activation. However, IL-α-induced-IL-6
synthesis was reduced in IL 1RAcPb-/- glia compared to WT glia. In both WT and IL-1RAcPb-/-
glia, IL-1α and IL-1β induced p38 activation but not Src kinase activation . In
conclusion, this study showed that in neurones, IL-1RAcPb may contribute to IL-1α-induced
p38 activation but negatively regulates IL-1-induced ERK1/2 activation, therefore
IL-1RAcPb may have specific effects on different signalling pathways. The effect of
IL-1RAcPb could also be cell specific, as IL 1RAcPb contributed to IL-1α-induced p38
signalling in neurones but IL-6 production in glia. The role of IL-1RAcPb remains
largely unknown and more investigations are required to elucidate its role in IL-1
signalling in the brain.