Inhibition of O-GlcNAcase leads to elevation of O-GlcNAc tau and reduction of tauopathy and cerebrospinal fluid tau in rTg4510 mice

Abstract

BackgroundHyperphosphorylation of microtubule-associated protein tau is a distinct feature of neurofibrillary tangles (NFTs) that are the hallmark of neurodegenerative tauopathies. O-GlcNAcylation is a lesser known post-translational modification of tau that involves the addition of N-acetylglucosamine onto serine and threonine residues. Inhibition of O-GlcNAcase (OGA), the enzyme responsible for the removal of O-GlcNAc modification, has been shown to reduce tau pathology in several transgenic models. Clarifying the underlying mechanism by which OGA inhibition leads to the reduction of pathological tau and identifying translatable measures to guide human dosing and efficacy determination would significantly facilitate the clinical development of OGA inhibitors for the treatment of tauopathies.MethodsGenetic and pharmacological approaches are used to evaluate the pharmacodynamic response of OGA inhibition. A panel of quantitative biochemical assays is established to assess the effect of OGA inhibition on pathological tau reduction. A “click” chemistry labeling method is developed for the detection of O-GlcNAcylated tau.ResultsSubstantial (>80%) OGA inhibition is required to observe a measurable increase in O-GlcNAcylated proteins in the brain. Sustained and substantial OGA inhibition via chronic treatment with Thiamet G leads to a significant reduction of aggregated tau and several phosphorylated tau species in the insoluble fraction of rTg4510 mouse brain and total tau in cerebrospinal fluid (CSF). O-GlcNAcylated tau is elevated by Thiamet G treatment and is found primarily in the soluble 55 kD tau species, but not in the insoluble 64 kD tau species thought as the pathological entity.ConclusionThe present study demonstrates that chronic inhibition of OGA reduces pathological tau in the brain and total tau in the CSF of rTg4510 mice, most likely by directly increasing O-GlcNAcylation of tau and thereby maintaining tau in the soluble, non-toxic form by reducing tau aggregation and the accompanying panoply of deleterious post-translational modifications. These results clarify some conflicting observations regarding the effects and mechanism of OGA inhibition on tau pathology, provide pharmacodynamic tools to guide human dosing and identify CSF total tau as a potential translational biomarker. Therefore, this study provides additional support to develop OGA inhibitors as a treatment for Alzheimer’s disease and other neurodegenerative tauopathies.Electronic supplementary materialThe online version of this article (doi:10.1186/s13024-017-0181-0) contains supplementary material, which is available to authorized users.

Systems biology identifies preserved integrity but impaired metabolism of mitochondria due to a glycolytic defect in Alzheimer's disease neurons

“…Glycosylation‐related enzymes are particularly abundant in neurons, and reduced glycolytic flux could impair glycosylation precursor biosynthetic pathways. Indeed, decreased O‐glycosylation has been observed in AD patients, its induction is protective in cell and animal models of AD (Zhu, Shan, Yuzwa, & Vocadlo, ), and inhibition of a glycoside hydrolase prevented cognitive decline, plaque formation and tau aggregates in transgenic mouse models of neurodegeneration (Hastings et al, ; Yuzwa et al, ). On this aspect, however, studies in appropriate neuronal models are lacking.…”

O-GlcNAc homeostasis contributes to cell fate decisions during hematopoiesis

“…We treated GATA-1-ER cells for 30 h with both E 2 and TMG, a highly selective inhibitor of OGA that blocks removal of the O-GlcNAc moiety by the enzyme, to determine whether the reduction in total cellular O-GlcNAcylation is required for proper erythroid differentiation (45)(46)(47). Cells treated with TMG maintain the O-GlcNAc moiety on target proteins, leading to increased global levels of O-GlcNAcylation and altered O-GlcNAc cycling.…”

O-GlcNAc Homeostasis Controls Cell Fate Decisions During Hematopoiesis

“…To determine if reduction in total cellular O-GlcNAcylation is required for proper erythroid differentiation, we treated GATA-1-ER cells with both E2 and Thiamet G (TMG), a highly selective inhibitor of OGA that blocks the enzymes ability to remove the O-GlcNAc moiety (Yuzwa et al 2008;Yuzwa et al 2012;Hastings et al 2017). Cells treated with TMG lose the ability to remove the O-GlcNAc moiety leading to increased cellular O-GlcNAc levels, and ultimately alters O-GlcNAc cycling.…”