Decreased O-Linked GlcNAcylation Protects from Cytotoxicity Mediated by Huntingtin Exon1 Protein Fragment

Background: Earlier reports indicate that O-GlcNAcylation might be protective in neurodegenerative disorders. Results: Suppressing O-GlcNAcylation modulates autophagy to enhance the viability of neuronal cells expressing cytotoxic mutant huntingtin exon 1 protein (mHtt). Conclusion:O-GlcNAcylation regulates the clearance of mHtt by modulating the fusion of autophagosomes with lysosomes. Significance: This regulatory mechanism emerges as a novel therapeutic strategy for Huntington disease. O-GlcNAcylation is an important post-translational modification of proteins and is known to regulate a number of pathways involved in cellular homeostasis. This involves dynamic and reversible modification of serine/threonine residues of different cellular proteins catalyzed by O-linked N-acetylglucosaminyltransferase and O-linked N-acetylglucosaminidase in an antagonistic manner. We report here that decreasing O-GlcNAcylation enhances the viability of neuronal cells expressing polyglutamine-expanded huntingtin exon 1 protein fragment (mHtt). We further show that O-GlcNAcylation regulates the basal autophagic process and that suppression of O-GlcNAcylation significantly increases autophagic flux by enhancing the fusion of autophagosome with lysosome. This regulation considerably reduces toxic mHtt aggregates in eye imaginal discs and partially restores rhabdomere morphology and vision in a fly model for Huntington disease. This study is significant in unraveling O-GlcNAcylation-dependent regulation of an autophagic process in mediating mHtt toxicity. Therefore, targeting the autophagic process through the suppression of O-GlcNAcylation may prove to be an important therapeutic approach in Huntington disease.