The role of glycosaminoglycan motifs in regulating neuronal growth, guidance and inhibition

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178 plausible that astrocyte-mediated neuronal inhibition is attributed in part to hitherto unknown secretion of endosulfatases at the injury site. The final part of the dissertation explores how modulation of GAG biosynthetic machinery in the reactive astrocytes can reduce their inhibitory effects. Upon characterizing GAGs present in the astrocyte CM, it was observed that CM mostly contains CSPGs. Hence, mono click-xylosides molecules were exploited to modulate the synthesis of CSPGs in reactive astrocytes. Neuronal inhibition in the presence of click xylosides-treated astrocyte CM was directly correlated to the glycosylation density of PGs present in the CM. The use of mono-xylosides suggested that glycosylation is critical to mediate the functionality of CSPGs. Using b-xyloside or conjugating monovalent CS chains using a PEG linker the importance of multivalency in CS-mediated neuronal inhibition was confirmed. While monovalent CS chains did not affect neurite outgrowth or viability, when the glycosylation density was increased in the form of PGs, either by cluster xyloside priming or by chemical conjugation, the CS chains became inhibitory towards neurons. This suggests that the basic role of the protein part of PGs, with respect to their inhibitory functions, is to present CS chains in high density. Therefore, reducing the density of CS chains can effectively reverse neuronal inhibition by astrocyte-CSPGs. In summary, the final part of the dissertation work has established the efficacy of click-xylosides in reducing the glial scar inhibition and proposes it as an attractive therapeutic approach to enhance neuronal recovery following the CNS injury.