Impaired N‐linked glycosylation of uptake and efflux transporters in human non‐alcoholic fatty liver disease

• Published in: Liver international Vol. 37; no. 7; pp. 1074 - 1081
• Main Authors: Clarke, John D., Novak, Petr, Lake, April D., Hardwick, Rhiannon N., Cherrington, Nathan J.
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.07.2017
• Subjects: Biological Transport; Biomarkers; Biosynthesis; Blotting, Western; Case-Control Studies; Degradation; drug transporters; Efflux; Endoplasmic Reticulum - metabolism; Fatty liver; Gene expression; Gene Expression Profiling; Genes; Glycan; Glycosylation; hepatobiliary drug disposition; Humans; Liver; Liver - metabolism; Liver diseases; Membrane trafficking; Membrane Transport Proteins - genetics; Membrane Transport Proteins - metabolism; Multidrug resistance; N-glycans; Non-alcoholic Fatty Liver Disease - diagnosis; Non-alcoholic Fatty Liver Disease - genetics; Non-alcoholic Fatty Liver Disease - metabolism; Non‐alcoholic steatohepatitis; N‐linked glycosylation; Oligosaccharyltransferase; Organic anion transporting polypeptide; Plasma proteins; Polypeptides; Polysaccharides; Protein folding; Protein Processing, Post-Translational; Protein transport; Proteins; Quality control; Sodium; Steatosis; Transcriptome; drug transporters; hepatobiliary drug disposition; N-linked glycosylation; Non-alcoholic steatohepatitis
• ISSN: 1478-3223; 1478-3231; 1478-3231
• DOI: 10.1111/liv.13362

Background & Aims N‐linked glycosylation of proteins is critical for proper protein folding and trafficking to the plasma membrane. Drug transporters are one class of proteins that have reduced function when glycosylation is impaired. N‐linked glycosylation of plasma proteins has also been investigated as a biomarker for several liver diseases, including non‐alcoholic fatty liver disease (NAFLD). The purpose of this study was to assess the transcriptomic expression of genes involved in protein processing and glycosylation, and to determine the glycosylation status of key drug transporters during human NAFLD progression. Methods Human liver samples diagnosed as healthy, steatosis, and non‐alcoholic steatohepatitis (NASH) were analysed for gene expression of glycosylation‐related genes and for protein glycosylation using immunoblot. Results Genes involved in protein processing in the ER and biosynthesis of N‐glycans were significantly enriched for down‐regulation in NAFLD progression. Included in the down regulated N‐glycan biosynthesis category were genes involved in the oligosaccharyltransferase complex, N‐glycan quality control, N‐glycan precursor biosynthesis, N‐glycan trimming to the core, and N‐glycan extension from the core. N‐glycan degradation genes were unaltered in the progression to NASH. Immunoblot analysis of the uptake transporters organic anion transporting polypeptide‐1B1 (OATP1B1), OATP1B3, OATP2B1, and Sodium/Taurocholate Co‐transporting Polypeptide (NTCP) and the efflux transporter multidrug resistance‐associated protein 2 (MRP2) demonstrated a significant loss of glycosylation following the progression to NASH. Conclusions These data suggest that the loss of glycosylation of key uptake and efflux transporters in humans NASH may influence transporter function and contribute to altered drug disposition observed in NASH.