Multi‐omics Studies Reveal Altered Hippocampal N‐Glycosylation in High Fat Diet‐Induced Obese Mice

Abstract

BackgroundObesity is a major public health issue afflicting over 93 million people in the US and is projected to continue increasing. Impairments of cognitive abilities such as memory loss and mood disorders such as depression and anxiety are debilitating conditions associated with obesity. N‐glycosylation, an essential posttranslational modification of proteins is required for hippocampal long‐term potentiation and memory consolidation. However, whether altered N‐glycosylation is a potential mechanism involved in impaired hippocampal functioning in obesity remains unknown.AimOur goal was to develop a multi‐omics platform including glycomics, proteomics, and transcriptomics to determine the impact of high‐fat‐diet (HFD) consumption on hippocampal N‐glycosylation and expression of cell surface receptors in the context of diet‐induced obesity.HypothesisWe hypothesize that in HFD‐induced obese mice abnormal hippocampal N‐glycosylation occurs, affecting cell surface expression and signaling of key receptors.MethodsC57BL/6J male mice were fed a HFD (45% fat) for 8 weeks to induce obesity or a low‐fat diet (LFD, 10% fat) as the lean control group. Mice were euthanized, and brain tissues collected. Hippocampi were surgically dissected and processed for glycomics, proteomics, glycoproteomics, and RT‐qPCR analysis. Hippocampal cell membrane fractions (MF) were obtained, and N‐glycans released and analyzed by nano‐Liquid Chromatography‐Mass Spectrometry (nanoLC‐MS). Peptides and glycopeptides derived from MF were analyzed by nano‐LC‐FusionOrbitrap MS. Expression level of glycosyltransferase genes were obtained by qPCR.ResultsThe N‐glycome of LFD‐fed mice was dominated by highly branched fucosylated and sialylated N‐glycans (61%) while in HFD‐fed obese mice these N‐glycans were significantly decreased (51%). Correspondingly, transcript analysis of the glycosyltransferases showed that MGAT2 gene, which encodes the enzyme responsible for initiating the synthesis of complex branched N‐glycans, was significantly decreased by 50% in hippocampi of HFD‐fed obese mice compared to lean controls. Our findings show a decrease in complex branched glycans on the hippocampal cell surface of HFD‐obese mice that may be due to the downregulation of the MGAT2 gene. Proteomics and glycoproteomic analysis revealed site‐specific occupancy of over hundreds of hippocampal cell surface receptors.ConclusionsOur results suggest that chronic consumption of HFD and induced obesity results in abnormal hippocampal cell surface N‐glycosylation, and a possible enzyme associated with the altered glycosylation phenotype was identified. Aberrant N‐glycosylation may contribute to altered neuronal or glial cell function. This approach may be useful to identify novel targets for the development of new treatments for obesity‐associated mood and cognitive deficits.Support or Funding InformationFunding from National Institutes of Health, NIDDK (award 5R21DK118379) to M.B.