PhD Scientific Days 2022

Neurosciences I. (Poster discussion will take place in the Aula during the Coffee Break)

Microglia-neuron interactions in developing brain

Text of the abstract

Microglia, the resident immune cells of the brain, play important roles in physiological and pathological processes. In the last years, breakthrough discoveries demonstrated the importance of microglia in the developing brain. Appearing in the CNS in the early embryonic days, they contribute to synaptogenesis, phagocytosis of synapses, and also neuronal differentiation, the structural basis of which remains elusive. These complex actions require multilevel communication between microglia and neurons, including those through soluble factors, and direct membrane-membrane contact.
Our lab recently discovered a direct contact between microglial processes and neuronal cell bodies in adult, called somatic junctions. We examined the possible presence, prevalence and structure and dynamics of these somatic junctions in neurogenesis.
To assess microglia-neuron interactions, we used brain samples from embryonic E15 (subventricular zone), postnatal P1, P8, P15 (neocortex) and adult P90 (dentate gyrus) mice. We applied immunfluorescent staining against doublecortin (DCX) to mark postmitotic neurons, Iba1 and P2Y12R markers to stain microglia. We examined the slices with confocal laser scanning microscope and found that somatic junctions are already present in the embryonic samples and the number of the connections increased throughout the development. With correlated light and electronmicroscopy we verified that these junctions are indeed direct contacts, and using STORM superresolution microscopy we demonstrated the contact-specific enrichment of microglial P2Y12 receptors in the contact sites. We also confirmed mitochondrial enrichment in neurons at somatic junctions, using TOM20 mitochondrial staining, examined in CLSM. To investigate the dynamics of somatic junctions we performed in vitro 2-photon imaging on acute slices, and found that selective inhibition of P2Y12 receptors caused a significant decrease of microglial coverage on developing neuronal cell bodies.
These results confirm that somatic junctions are also present and functional in the case of developing neurons. We suggest that microglia can monitor and regulate developing neurons through these connections.