Brain-IL-1 beta triggers astrogliosis through induction of IL-6: inhibition by propranolol and IL-10

Gliosis is a characteristic pathology in many central nervous system (CNS) diseases. Cytokines are considered to be effectors of gliosis. It has been shown that pro-inflammatory cytokines such as interleukin (IL)-1 and IL-6 boost glia scar formation. On the other hand, anti-inflammatory cytokines, such as IL-10 and IL-1 receptor antagonist (ra), can act neuroprotectively. Furthermore, various immune mediators and neurotransmitters can modulate the onset of gliosis. We used 100 male Sprague-Dawley rats to investigate the mechanisms of brain-cytokine-induced astrogliosis using an in vivo model of convection-enhanced delivery of cytokines (IL-beta, IL-6, tumor necrosis factor (TNF)-alpha) into the cerebro-ventricular system. The protective effects of the anti-inflammatory cytokine IL-10 and the neurotransmitter propranolol were also investigated. With this paradigm, we could clearly demonstrate that IL-6 is a key cytokine mediating astrogliosis, noticeable in the increased expression of glial fibrillary acidic protein (GFAP). Thus intra-cerebroventricular infusion of IL-6 increased GFAP expression in a dose-dependent manner. Furthermore, GFAP expression was also increased by IL-beta, which correspondingly triggered an IL-6 release into the CSF. Accordingly, TNF-alpha, which did not induce IL-6 release, also did not induce gliosis. On the other hand, substances which decrease IL-beta-induced IL-6 production, such as propranolol and IL-10, also dramatically decreased IL-beta triggered gliosis. IL-6 infusion, as well as IL-beta-induced IL-6 release into the CSF, increase GFAP expression in the cerebral cortex and hippocampus. Accordingly, blockade of the IL-beta-induced IL-6 release by IL-10 and propranolol decreases GFAP expression.