Periodic Reporting for period 1 - SinGly (Glycobiology of synaptic pruning in a developing brain)
Reporting period: 2020-11-01 to 2022-10-31
Effective neuron-microglial communication is a prerequisite to achieve the final connectome. It is mediated by both the formation of new synapses and selective removal of unnecessary connections through synaptic pruning. Recent evidences suggest that superfluous connections are eliminated by microglia. Almost 70% of the connections are lost in a primate cortex within six months of life. But what drives this selective elimination of so many synapses is a million-euro question. Identifying neuronal signals that differentiate weak synapses from the strong ones is an emerging frontier in cellular neuroscience. Several eat-me signals in synaptic pruning have been identified, but spare-me signals that limit phagocytic elimination of synapses are yet to be explored. Sialic acids on neuronal glycocalyx acts as spare-me signal and prevents microglial phagocytosis through Siglec receptors. Aberrant regulation of sialic acid caused neuronal loss and embryonic lethality. It is also becoming evident that sialic acid plays a key role in neurodevelopment, but the cellular and molecular mechanisms by which it regulates neurodevelopment is yet to be explored. This makes sialic acid an ideal candidate to evaluate its role in neurodevelopment. Hence, we aimed to interrogate whether sialidases and glycocalyx recognizing targets are developmentally regulated; and also, to define the role of sialic acid during microglial-mediated synaptic pruning in a developmental context. This paves a path to identify cellular and molecular mechanisms by which glycocalyx composition defines neuron-microglia interactions and thus circuit refinement through synaptic pruning. Since Marie Skłodowska-Curie Actions offer attractive career developmental opportunities, the global aim of this EU-funded grant was to also to enhance the researcher’s potential through training in all aspects of scientific research besides neuroscience.
In order to interrogate whether sialidases and glycocalyx-recognizing proteins is developmentally regulated, we investigated the expression of their genes in different brain areas: hippocampus, prefrontal cortex and cerebellum, and at different developmental stage: from 1 to 40 days after birth. As recent reports indicate sex-specific differences in brain development, experiments were performed in parallel both in male and female mice.
To evaluate the activity of sialidases (enzymes that modify glycocalyx), we used a previously built fluorescent metabolic labelling model to investigate sialidase activity in live brain tissue slices. We were not able to identify any metabolic sialidase activity neither in post-natal nor in adult brains.
To evaluate the activity of sialidases (enzymes that modify glycocalyx), we used a previously built fluorescent metabolic labelling model to investigate sialidase activity in live brain tissue slices. We were not able to identify any metabolic sialidase activity neither in post-natal nor in adult brains.
Operating this grant equipped the fellow with new knowledge and technical skills as well as the scientific and administrative aspects of grant management. This expertise of handling the projects related to the fundamental socioeconomic challenges related to neurodevelopmental-neuropsychiatric disorders will foster future development of the researcher. Also, we hope that innovative ideas, knowledge and skills in this project may accelerate the investigation of synaptic pruning in neurodevelopment.