TOLL-LIKE RECEPTORS IN THE PROPAGATION OF REACTIVE GLIOSIS IN THE INJURED BRAIN

ROSCISZEWSKI G; RAMOS AJ; CADENA V; AUZMENDI J; CIERI MB

BUENOS AIRES

Congreso; 2° Reunión Conjunta de Biociencias.; 2017

Following brain injury astrocytes undergo phenotypic changes collectivelyknown as reactive gliosis. Detrimental effects of reactive gliosis for neuronalsurvival occur when astrocytes polarize to the A2 phenotype expressingproinflammatory genes. We previously shown that TLR4 and NF-kB signalingare required the A2 polarization. However, it is still unknown how reactivegliosis propagates to reach distal brain regions. It is proposed that damageassociated proteins released by dying neurons acting on TLR are probablyinvolved. To address this question, we here performed a penetrating traumaticbrain injury in rodents by stab wound in wild type, TLR4KO and TLR2KOanimals. In vitro, we studied the downstream signaling pathways involved in thereactive gliosis propagation by using the scratch wound healing assay. Stabwoundedanimals showed a gradient of reactive gliosis analyzed by GFAPimmunostaining morphometry that was present at 3-7 days post-injury (DPI),and then at 14 DPI, the gradient was lost and reactive gliosis propagated by theentire hemisphere. At 7 DPI, the TLR4KO, but not TLR2KO, animals showed adecreased gradient of reactive gliosis. In vitro, scratch wounds also produced agradient of reactive gliosis either in purified astrocytic culture or in mixedmicroglial-astroglial culture. In astroglial-enriched cultures, but not in mixedculture, the gradient was prevented by the NFkB chemical blocker BAY117082(10 µM), by Ca2+ chelating agent EGTA (20 µM) or by the gap-junction blockerMFA (100 µM). On the other hand, the exposure to the TLR4 agonist LPSexacerbated the reactive gliosis gradient. Taken together these results showthat reactive gliosis propagation is a phenomenon that involves both astrocytesand microglia and seems to require TLR4.