Modulation of O-GlcNAc cycling influences α-synuclein amplification, degradation, and associated neuroinflammatory pathology

Background: The accumulation and propagation of α-synuclein (α-syn) are hallmark features of Parkinson's disease (PD) and related neurodegenerative disorders. O-GlcNAcylation, an abundant post-translational modification throughout the brain, is regulated by the enzymatic activity of the cycling Enzymes O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) and has been implicated in altering α-syn toxicity. Nevertheless, the interplay between modulating O-GlcNAc cycling and α-syn aggregation and the propagation of amyloid pathology is not well elucidated.

Methods: To this end, we delivered conformational strains of α-syn in the striatum of mice or neuronal and microglial co-cultured cells following pharmacologically or genetically inhibited OGT and OGA. The substantia nigra was injected with an adeno-associated viral vector coding for α-syn combined with α-syn preformed fibrils to examine α-syn-induced dopaminergic cytotoxicity. The α-syn pathology and spreading, protein O-GlcNAcylation, OGT and OGA levels, microglial inflammation, and behavioral impairments were evaluated. Furthermore, the O-GlcNAc modification and proteolysis status of α-syn under O-GlcNAc cycling modification were also assessed using a combination of approaches, including Click-iT™ O-GlcNAc enzyme labeling, sWGA pulldown, HPLC-MS/MS, and immunohistochemical analysis following Proteasome and autophagy-lysosome inhibition.

Results: We found that modulation of O-GlcNAc cycling, governed by the two Enzymes OGT and OGA, significantly affected α-syn aggregation, propagation, dopaminergic neuronal degeneration, and microglial inflammation. Pathological α-syn transmission to adjacent cells and anatomically connected brain regions was found to suppress recipient cellular O-GlcNAc levels, concomitant with reduced OGT expression. Pharmacological inhibition or genetic knockdown of OGT exacerbated α-syn aggregation, enhanced its intercellular transmission, and intensified NOD-, LRR-, and pyrin domain-containing 3 (NLRP3)-mediated microglial inflammation. Conversely, increasing O-GlcNAcylation via OGA inhibition ameliorated these pathological processes. Furthermore, we demonstrate that enzymatic O-GlcNAcylation significantly regulates the aggregation of fibril-induced initial dimer formation and facilitates the clearance of α-syn aggregates through autophagosome-lysosome flux.

Conclusions: These findings highlight the critical regulatory role of O-GlcNAc modification in α-syn pathology and conformational strain formation, and provide mechanical evidence that enhancing O-GlcNAc modifications alleviates pathological α-syn proteolysis by restoring autophagosome-lysosome flux.

Neuroinflammation; O-GlcNAcylation; Proteolysis; α-synuclein.