S100B-RAGE induces changes in astrocyte shape and proliferation towards a reactive state in vivo and in vitro.

ALEJANDRO VILLARREAL; SEOANE R; ANGELO MF; BARKER PA; RAMOS AJ

Barcelona

Congreso; VIII FENS Forum of Neuroscience.; 2012

Federation of European Neuroscience Societies

Title: S100B-RAGE induces changes in astrocyte shape and proliferation towards a reactive state in vivo and in vitro. Authors: Villarreal Alejandro, Seoane Rocio, Angelo Maria Florencia, Barker Philip, Ramos Alberto Javier. Understanding autocrine glial crosstalk after brain injury has become important to comprehend the mechanisms that propagate damage in the injured brain. After ischemic injury a plethora of neuronal and glial molecules are released, collectively known as DAMP (Damage Associated Molecular Pattern) proteins. S100B that is released by reactive astrocytes surrounding brain lesions signals in a paracrine (to neurons) and autocrine way (to astroglia and microglia). Here we show that S100B signals through RAGE (Receptor for Advanced Glycosilated End products) and activates NFkB promoting morphological changes resembling reactive gliosis in vivo and in vitro. Our in vitro studies using primary cultures showed that S100B induces proliferation (evidenced by BrdU incorporation) and increases astrocytic branching. The increased branching was blocked by RAGE neutralizing antibody or by the transfection of a RAGE-cyto (dominant negative) and exacerbated by RAGEwt overexpression. Downstream signaling seems to involve Cdc42 but not RhoA since the transfection of a DN-Cdc42 but not the overexpression of active RhoA blocks the S100B-induced branching. Indeed, astrocytic protrusion into an artificial wound in vitro is promoted by S100B and reduced when astrocytes were transfected with the DN-Cdc42. S100B exposure also induced a dose-dependent activation of NFkB as shown by the activation of a reporter plasmid and nuclear p65 localization. Expression of RAGE was also promoted by S100B, an effect partially abolished by chemical NFkB blockage. In vivo, infusion of S100B using 50um diameter glass pipettes in adult rats showed that increased focal release of S100B reproduces many features of ischemia-induced reactive gliosis with the extension of glial projections to the site of injection. Together these results suggest molecular mechanisms by that S100B>RAGE pathway is able to induce many morphological features of reactive gliosis and activates an autocrine loop that may sustain NFkB activity after brain injury.