The role of sialylation in glia-neuron communications and stress responses

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The project focuses on the molecular, cellular, and genetic mechanisms underlying the neural functions of glycoprotein sialylation. Although the brain is the organ with the most prominent sialylation in human body, and recent studies implicated sialylation defects in several neurological diseases, the functions of this important type of glycosylation in the nervous system are still poorly understood. The intricacies of glycosylation, increased pleiotropy and redundancy, and limitations of available genetic approaches significantly hinder the research on sialylation in the overwhelmingly complex vertebrate nervous system. A suitable model system would be an important tool for more efficient mechanistic studies in this area. The proposal focuses on Drosophila as a model organism to investigate the neural functions of N-linked sialylation. Several key evolutionarily conserved enzymes were previously characterized in the Drosophila sialylation pathway, including DSiaT, a sole sialyltransferase in Drosophila, and CSAS, CMP-Sialic Acid Synthetase producing sugar donor for DSiaT. Using a combination of in vitro and in vivo approaches, previous studies revealed that Drosophila sialylation is highly regulated process limited to the nervous system and involved in control of neural excitability, development of neuromuscular junctions (NMJs), and the regulation of voltage-gated channels. Novel functions of N-linked sialylation in the nervous system regulation suggested by previous research are expected to be conserved in humans and be relevant for pathologic mechanisms of neurological diseases. Preliminary research revealed that sialylation is involved in glia-neuron interactions, and that defects of sialylation result in neurodegeneration and increased sensitivity to oxidative stress. CSAS was found to be responsible for rate-limiting effect on Drosophila sialylation, playing a key role in neural regulation. The proposed project will capitalize on previous and preliminary data to extend research towards (i) revealing sialylation-mediated mechanisms of glia-neuron coupling, (ii) elucidating the role of sialylation in promoting neuronal viability and resistance to oxidative stress, (iii) characterizing functional and molecular targets of sialylation using advanced chemical biology and glycoproteomics approaches. The research plan is based on interdisciplinary strategy that combines the advantages of Drosophila model, including amenability to genetic manipulations, exhaustively characterized nervous system, low redundancy of glycosylation pathways, and well-established neurobiological methods, with advanced biochemical and glycoproteomic approaches. The results will shed light on conserved principles of neural regulation and homeostasis, which will be valuable for biomedical feilds. Moreover, the project will establish Drosophila as a versatile model for future research on glycosylation in the nervous system to uncover pathological mechanisms of neurological diseases.