Interleukin-6 involvement in brain arteriovenous malformations

We recently reported that the GG genotype of the interleukin-6 (IL-6)-174G > C promoter polymorphism is associated with clinical presentation of intracranial hemorrhage in brain arteriovenous malformation (AVM) patients. In this study, we investigated whether tissue IL-6 expression was associated with IL-6-174G > C genotype, and whether IL-6 was linked to downstream targets involved in angiogenesis and vascular instability. Our results showed that the highest IL-6 protein levels in brain AVM tissue were associated with IL-6-174GG genotype (GG: 57.7 +/- 20.2; GC: 35.6 +/- 26.6; CC: 13.9 +/- 10.2pg/mg; p = 0.001). IL-6 protein levels were increased in AVM tissue from patients with hemorrhagic presentation compared with patients without hemorrhage (55 +/- 22 vs 40 +/- 27pg/mg, p = 0.038). IL-6 messenger RNA expression strongly correlated with messenger RNA levels of IL-1 beta, tumor necrosis factor-alpha, IL-8, matrix metalloproteinase-3 (MMP-3), MMP-9, and MMP-12. We further investigated the plausibility of IL-6 being an upstream cytokine responsible for initiating the angiogenic cascade by cell culture and animal experiments. IL-6 induced MMP-3 and MMP-9 expression and activity in mouse brain and increased proliferation and migration of cerebral endothelial cells. Together, our results suggest that the IL-6 genotype associated with intracranial hemorrhage modulates IL-6 expression in brain AVM tissue, which is consistent with the hypothesis that inflammatory processes induce angiogenic activity possibly contributory to brain AVM intracranial hemorrhage.