Mammalian brain glycoproteins exhibit diminished glycan complexity compared to other tissues

Sarah E Williams,Sylvain Lehoux,Murat Cetinbas,Ramnik J Xavier,Ruslan I Sadreyev,Maxence Noel,Richard D Cummings,Edward M Scolnick,Robert G Mealer,Jordan W Smoller

doi:10.1038/s41467-021-27781-9

Abstract

Glycosylation is essential to brain development and function, but prior studies have often been limited to a single analytical technique and excluded region- and sex-specific analyses. Here, using several methodologies, we analyze Asn-linked and Ser/Thr/Tyr-linked protein glycosylation between brain regions and sexes in mice. Brain N-glycans are less complex in sequence and variety compared to other tissues, consisting predominantly of high-mannose and fucosylated/bisected structures. Most brain O-glycans are unbranched, sialylated O-GalNAc and O-mannose structures. A consistent pattern is observed between regions, and sex differences are minimal compared to those in plasma. Brain glycans correlate with RNA expression of their synthetic enzymes, and analysis of glycosylation genes in humans show a global downregulation in the brain compared to other tissues. We hypothesize that this restricted repertoire of protein glycans arises from their tight regulation in the brain. These results provide a roadmap for future studies of glycosylation in neurodevelopment and disease.

Highlights

Glycosylation is essential to brain development and function, but prior studies have often been limited to a single analytical technique and excluded region- and sex-specific analyses
Less attention has been paid to N- and O-linked protein glycosylation, with a few studies showing the importance of particular modifications such as the Lewis X antigen (LeX)[3,27,28,29], human natural killer antigen (HNK-1)[30,31], polysialic acid[32,33], bisecting GlcNAc34,35, and O-mannosylation[36,37,38]
Utilizing MALDI-TOF glycomics, mass spectrometry (MS)/MS, lectin blotting, and RNA sequencing, we have generated a comprehensive map of the predominant N- and O-linked protein glycans across multiple brain regions and both sexes of mice

Summary

Introduction

Glycosylation is essential to brain development and function, but prior studies have often been limited to a single analytical technique and excluded region- and sex-specific analyses. Brain glycans correlate with RNA expression of their synthetic enzymes, and analysis of glycosylation genes in humans show a global downregulation in the brain compared to other tissues. We hypothesize that this restricted repertoire of protein glycans arises from their tight regulation in the brain. Glycans may consist of a single monosaccharide or can be extended into elaborate sugar oligo/polysaccharides[12] These structures are covalently attached to lipids or certain amino acids of proteins, which designates protein glycans as either N-glycans or O-glycans. For a more complete picture of brain protein glycosylation, we analyzed the frontal cortex, hippocampus, striatum, and cerebellum of male and female C57BL/6 mice using multiple validated techniques, and present a comprehensive portrait of Nand O-glycosylation in the brain characterized by a surprisingly restricted set of glycans and overall downregulation of the pathway

Methods

Results

Conclusion