S100B exposure improves astrocytic survival to oxidative stress and induces changes in glial morphology towards a reactive state

VILLARREAL ALEJANDRO, SEOANE ROCIO, ÁNGELO MARÍA FLORENCIA, ROSSI ALICIA, RAMOS ALBERTO JAVIER

Buenos Aires

Simposio; 2nd French-Argentinean Symposium In Neuroscience; 2012

Understanding the glial autocrine proinflammatory response that takes place after brain damage is key for the development of neuroprotective strategies. The soluble protein S100B is secreted from reactive astrocytes after brain injury acting as a DAMP (Damage Associated Molecular Pattern) molecule inducing effects on neurons, microglial cells and astrocytes as well. In this way, S100B might be contributing to the damage propagation of focal injuries such as brain focal ischemia. We have previously shown than S100B has neuroprotective effects on glutamate stressed neurons at nanomolar concentrations; but induces death at micromolar levels. These effects are mediated by the surface receptor RAGE and nuclear factor NFκB (Villarreal et al, 2011). In this work, we show that S100B exposure induces astrocyte proliferation (evidenced by BrdU incorporation) and increases astrocytic branching. The increased branching effect is RAGE dependent being 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 small GTPases Cdc42 and Rac1 since their blockage abolished the S100B-induced branching. S100B exposure also induced a dose-dependent activation of NFkB in astrocytes as shown by the activation of NFkB reporter plasmid and nuclear p65 localization. Increased survival to oxidative stress was also observed in S100B exposed astrocytes, an effect blocked by PD98059 or LY294002 (Erk and AKT kinases inhibitors respectively) thus being Erk/Akt dependent. In vivo, intracortical release of S100B by direct infusion of S100B using 50um diameter glass pipettes in adult rats (Wistar) showed that increased focal release of S100B reproduces many features of ischemia-induced reactive gliosis including the extension of glial projections to the site of injection and increased proliferation evidenced by the analysis of GFAP and Vimentin expression. Oxidative stress is one of the mayor causes of cell malfunction after brain ischemia and we provide evidence on how S100B, which is released in those conditions, may protect astrocytes from damage, probably by activating them since we show that direct infusion of S100B is capable of inducing gliosis in vivo. Together these results suggest that S100B controls an autocrine loop in astrocytes that induce many morphological features of reactive gliosis and improves glial survival to the detrimental environment found in brain lesions.