DAMAGE ASSOCIATED MOLECULAR PATTERN HMGB1 EFFECTS IN NEURONAL SYNAPTOGENESIS AND PROPAGATION OF REACTIVE GLIOSIS

CADENA, VANESA; ROSCISZEWSKI, GERARDO; RAMOS, ALBERTO JAVIER

Congreso; Reunión Anual de Biociencias; 2017

High-mobility group box-1 (HMGB1) is a DAMP released after focal brain injury that activates local innate immunity cells but also behaves as cytokine acting on the professional immune organs of the periphery. Local brain innate immunity cells are microglia and astrocytes that express pattern recognition receptors such as TLR2-4 and RAGE. We here dissected the HMGB1 effects on astrocytes, microglia and neurons and studied the downstream signaling. Primary astroglial cultures containing different amounts of microglial cells were obtained from postnatal 3-4 days rats or wt/TLR2KO/TLR4KO mice and primary neurons were from E18 rat embryos as described in detail in Rosciszewski et al., Mol.Neurobiol. (2017). In vivo, focal hemorrhagic brain ischemia was induced by cortical devascularization and animals received sulphazalazine (200mg/kg every 12hours) for 3 days. Our results showed that purified primary cortical neurons exposed to 50 or 500 ng/ml HMGB-1, presented a rapid increase in the number of synaptic puncta per neuron without showing significative neuronal loss. However, primary neurons exposed to conditioned medium secreted by 500 ng/ml HMGB1-treated astrocytes showed a reduced survival. In primary astrocytes, HMGB-1 exposure induced a dose-dependent NFkB activation and reactive gliosis; however astroglial response to HMGB1 required the presence of microglia. Loss of function studies showed that the HMGB1 effects are TLR2-TLR4 dependent and partially RAGE-dependent. In addition, HMGB-1 application onastrocytes induced TREM-2 expression. Finally, in vivo NFkB blockage withsulphazalazine significantly reduced reactive gliosis and neuronal degenerationinduced by focal brain ischemia. We conclude that DAMP HMGB-1 has a major role in the propagation of proinflammatory response but also acts directly on the surviving neurons after focal brain injury