Interleukin-6 induced astrocytic differentiation modulates Mannose Binding Lectin (MBL)-Associated Serine Protease (MASP)-1 and MASP-3 expression in C6 glioma cells

Among inflammatory cytokines, Interleukin-6 (IL-6) shows a pleiotropic nature acting as a mediator in differentiation, immune response and diseases within the Central Nervous System (CNS). Exposure to exogenous or autocrine IL-6, induced by cAMP, promotes astrocytic differentiation of glioma C6 cells which assume an astrocytic phenotype correlated to the expression of glial fibrillary acidic protein (GFAP). In addition, in several mouse models of brain injury, the up-regulation of IL-6 expression was correlated to the innate and acquired immunity. Glioma cells also express Mannose-Binding Lectin (MBL)-Associated Serine Proteases (MASP)-1 and 3, involved in the activation of the lectin complement pathway (LCP) in innate immunity. We investigated MASP-1 and MASP-3 expression during IL-6 and dibutyryl cAMP (dbcAMP) induced astrocytic differentiation in C6 cells. As previously reported, IL-6 or dbcAMP promoted a change in C6 cell morphology towards an astrocytic phenotype, as confirmed by the increase in GFAP expression levels. During this differentiation process, we observed a highly increase in MASP-1 and MASP-3 mRNA and protein expression levels compared to untreated cells. To investigate the involvement of protein kinase A (PKA) signalling pathway in IL-6 induced effects, C6 cells were pre-treated with the H89 (PKA) inhibitor. This exposure caused an inhibition in the astrocytic differentiation and a decrease both in STAT3 phosphorylation levels and MASP-1/MASP-3 expression levels. Taken together, these results strongly suggest that IL-6 might act as a regulatory cytokine in innate immunity enhancing MASP-1 and MASP-3 expression level through PKA signalling in C6 cells.