Novel model of secreted human tau protein reveals the impact of the abnormal N-glycosylation of tau on its aggregation propensity

Moran Frenkel-Pinter,Ashim Paul,Malak Abu-Hussein,Ehud Gazit,Yelena Losev,Daniel Segal,Isam Khalaila

doi:10.1038/s41598-019-39218-x

Moran Frenkel-Pinter, Ashim Paul + Show 5 more

Open Access

https://doi.org/10.1038/s41598-019-39218-x

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Abstract

Alzheimer’s disease (AD) is the most common neurodegenerative disorder and has no disease-modifying treatment yet. The hallmarks of AD are two amyloidogenic proteins: tau and amyloid β (Aβ). Tau undergoes several posttranslational modifications, including N-glycosylation. Tau was reported to be N-glycosylated in AD brains, but not in healthy counterparts, which may affect AD etiology. Here, we aimed to examine the effect of N-glycosylation on aggregation propensity of tau. To that end, a novel SH-SY5Y cell-based model was generated in which recombinant human tau (htau) is forced to be secreted from the cells. Secreted htau was found to localize in the secretory pathway compartments and to undergo N-glycosylation. Following N-glycan cleavage of the secreted htau, various biophysical results collectively indicated that the untreated N-glycosylated secreted htau is markedly less aggregative, contains thinner and shorter fibrils, as compared to treated de-glycosylated secreted htau. This finding shows that N-glycans attached to htau may affect its aggregation. This could help to better understand the effect of N-glycosylated htau on AD progression.

Highlights

Alzheimer disease (AD) is a severe progressive neurodegenerative disorder and a major cause of dementia for which no disease-modifying treatment is currently available[1,2,3]
While most of the research on N-glycosylation of tau has focused on identification of the sugars involved and the interplay between N-glycosylation and phosphorylation on tau from Alzheimer’s disease (AD) brains, to the best of our knowledge, no studies directly examined the effect of N-glycosylation of tau on its aggregation propensity
Calnexin signal was evident in both cell types (Fig. 1b,f and Supplementary Fig. S1) and colocalization of senile plaques (SPs)-htau and calnexin signals was clearly observed in SP-htau expressing cells (Fig. 1h and Supplementary Fig. S1) but not in non-transfected cells (Fig. 1d and Supplementary Fig. S1), suggesting that SP-htau is associated with the endoplasmic reticulum (ER)

Summary

Introduction

Alzheimer disease (AD) is a severe progressive neurodegenerative disorder and a major cause of dementia for which no disease-modifying treatment is currently available[1,2,3]. Few studies have examined the abnormal N-glycosylation of the tau protein and its involvement in AD Both composition and structure of the N-glycans on tau were found to be partially different between hyperphosphorylated tau (p-tau) and PHF-tau in the AD brain[20]. Comparison of the aggregation propensity of media containing secreted htau before and after enzymatic removal of N-glycans using peptide-N4-(N-acetyl-beta-glucosaminyl) asparagine amidase (PNGase-F), revealed that the former is less aggregative than the latter and comprises less dense fibrillary aggregates. This result suggests that N-glycosylation reduces the aggregation propensity of secreted htau. This cell-based model provides novel means for studying tau engendered AD pathology

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