S100B stimulates IL–6 and TNF-alpha secretion of astrocytes mediated by RAGE

S100B is a Calcium-binding protein constitutively released by astrocytes evolving autocrine and paracrine effects on astrocytes and neurons. S100B exerts a dual effect depending on its concentration. Nanomolar levels are growth promoting and protective whereas micromolar concentrations are toxic. Binding to the receptor for advanced glycation end products (RAGE) on neurons has been involved in both neurotrophic and neurotoxic effects of S100B. Excessive production of astrocytic IL–6 and TNF-alpha may cause damage emphasizing the need for tight regulation to maintain beneficial functions and prevent potentially detrimental effects.

To characterize the role of S100B in the immunity of the CNS we investigated the capacity of astrocytes to upregulate the expression of IL–6 and TNF-alpha by stimulation with S100B mediated by RAGE. The subcellular localization of RAGE expression at the cell surface membrane of cultured astrocytes were depicted by immunofluorescence microscopy, flow cytometry and Western Blotting. S100B as well as anti-RAGE antibody were able to stimulate IL–6 and TNF-alpha secretion in cultured astrocytes in a concentration and time dependent way shown by ELISA. S100B induced IL–6 and TNF-alpha secretion was blocked by the use of RAGE specific siRNA for knocking down RAGE expression.

Our data indicate a novel autocrine inflammatory pathway in which S100B upregulates IL–6 and TNF-alpha secretion mediated by RAGE expressed on astrocytes.