Profile of classical or alternative activation and acquired deactivation markers in postnatal microglia of C57/Bl6 mice brain

CHERTOFF, MARIELA; SHRIVASTAVA KALPANA; GIMENEZ LLORT LYDIA; ACARIN LAIA

Congreso; The 24th Biennial Joint Meeting of the International Sociey for Neurochemistry and American Society of Neurochemistry; 2013

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In rodents, during the early postnatal period, neuronal and glial differentiation has still not been achieved, neuronal dendritic arborisation is still poor, axonal growth and myelination are taking place and neuronal circuits are not yet well established, with synaptic contacts still in formation. These events are accompanied for blood brain barrier formation, entrance of microglia and distinct expression and release of a wide variety of molecules including growth factors, adhesion molecules, inhibitors of axonal growth and cytokines. Microglia is immerse in these physiological changes and they must deal with them. The aim of this study is to analyze the profile of markers in microglia during postnatal development. C57/Bl6 mice, from postnatal day 1 to 12, were i.p. anaesthetized  and intracardially perfused using 4% paraformaldehyde. Subsequently, brains were removed, postfixed for 4 hours in the same fixative, cryoprotected in 30% sucrose, frozen with dry CO2. Brains were serially cut in a cryostat in 30µm thick sections, mounted  and stored in       -20ºC. Double or triple immunofluorescence were performed for several markers of classical activation, alternative activation and acquired deactivation. Confocal images were analyzed in order to study the colocalization pattern between them. Immunohistochemistry of acquired deactivation marker TREM2 were also performed. Almost no staining of classical activation markers were observed in postnatal brain. Interestingly, we observed that microglia in postnatal brain share markers of alternative activation, such as Arginase-1 and CD206, with the acquired deactivation TREM2. Moreover, the TREM2 expression is maximum at P1, decreasing during postnatal development. In P10 mice, TREM2 is only present in corpus callosum. To conclude, the postnatal microglia expressed an specific arrange of markers, sharing alternative activation and acquired deactivation status. With age, the acquired deactivation marker TREM2 decreased and only alternative activation markers are present at P12. This results show that postnatal microglia belongs to alternative activation profile, but also  express acquired deactivation markers. This special characteristics need to be taken into account for future immunomodulatory therapies in neonatal brain.