Abstract P767: Understanding the Role of Microglial Il-1α After Stroke

Abstract

The role of inflammation driven by the pro-inflammatory cytokine interleukin-1 (IL-1) during poststroke injury has been the focus of intense research. Indeed, pre-clinical studies have demonstrated the deleterious actions of IL-1 after stroke, whilst blocking its actions is beneficial in pre-clinical and clinical settings. Whilst most studies have focused on the role of IL-1β, the role of IL-1α during poststroke inflammation has been largely overlooked and very little has been done to examine the selective contribution of each IL-1 isoform in ischaemic stroke. In this study, we have investigated the contribution of IL-1α to ischaemic and haemorrhagic stroke. Methods : in vivo model of middle cerebral artery thrombosis through topical application of FeCl3 (40%) (n=4/group (4, 24, 72h) histology, n=6 /group (4, 24, 72 ) qPCR) in vivo model of haemorrhagic stroke induced by using the collagenase model (intra-striatal injection of collagenase VII-S, 0.045U) (n=4/group (4, 24h) histology). We first investigated the spatio-temporal expression of IL-1 in the brain after ischaemic stroke using an in vivo model of middle cerebral artery thrombosis through topical application of FeCl3 (n=4-6/group). We observed IL-1α positive microglia as early as 4 hours after ischaemic stroke. At 24 hours we observed IL-1α and also IL-1β positive microglia, moreover, IL-1β was also expressed by neutrophils and monocytes. These results have been confirmed by qPCR. Interestingly, we observed similar results after haemorrhagic stroke, induced by using the collagenase model, whereby IL-1α expression in microglia precedes IL-1β expression (n=4/group). The early expression of IL-1α in microglia in both models suggest a critical role for the microglial response during sterile inflammation. To further investigate the role of microglial IL-1α, we have generated a conditional IL-1α mouse mutant crossed with CX3CR1 Cre-ERT2 mice to induce a specific deletion of IL-1α in microglia. Future experiments using this genetic model will clarify the role of IL-1α during the acute phase of strokes.