Loss of complex O-glycosylation impairs exocrine pancreatic function and induces MODY8-like diabetes in mice

Gerrit Wolters-Eisfeld,Kai Bachmann,Pascal Steffen,Jakob R Izbicki,Baris Mercanoglu,Bianca T Hofmann,Jörg Schrader,Nicola Gagliani,Maximilian Bockhorn,Thomas Wolpers,Claudia Schnabel,Christoph Wagener,Sönke Harder,Cenap Güngör,Babett Steglich,Hartmut Schlüter

doi:10.1038/s12276-018-0157-3

Abstract

Cosmc is ubiquitously expressed and acts as a specific molecular chaperone assisting the folding and stability of core 1 synthase. Thus, it plays a crucial role in the biosynthesis of O-linked glycosylation of proteins. Here, we show that ablation of Cosmc in the exocrine pancreas of mice causes expression of truncated O-glycans (Tn antigen), resulting in exocrine pancreatic insufficiency with decreased activities of digestive enzymes and diabetes. To understand the molecular causes of the pleiotropic phenotype, we used Vicia villosa agglutinin to enrich Tn antigen-modified proteins from Cosmc-KO pancreatic lysates and performed a proteomic analysis. Interestingly, a variety of proteins were identified, of which bile salt-activated lipase (also denoted carboxyl-ester lipase, Cel) was the most abundant. In humans, frameshift mutations in CEL cause maturity-onset diabetes of the young type 8 (MODY8), a monogenic syndrome of diabetes and pancreatic exocrine dysfunction. Here, we provide data suggesting that differentially O-glycosylated Cel could negatively affect beta cell function. Taken together, our findings demonstrate the importance of correct O-glycan formation for normal exocrine and endocrine pancreatic function, implying that aberrant O-glycans might be relevant for pathogenic mechanisms of the pancreas.

Highlights

Among the multifarious spectrum of post-translational modifications, glycosylation is the most common and most diverse one
To investigate the role of O-glycosylation in the function of the pancreas in vivo, we generated a conditional Cosmc flox mouse line that was interbred with a pancreas specific transcription factor 1a (Ptf1a)-Cre line to induce Tn antigen expression in pancreatic acinar cells
The results clearly indicate dysfunctional Tsynthase in Cosmc-KO mice compared to WT (Fig. 1c)

Summary

Introduction

Among the multifarious spectrum of post-translational modifications, glycosylation is the most common and most diverse one. For some forms of glycosylation, there is substantial knowledge of their synthesis and biological functions. Our knowledge of O-linked glycosylation is severely limited and represents an emerging field in research[1]. O-glycans are covalently α-linked via an Nacetylgalactosamine (GalNAc) moiety to Ser and Thr residues[2,3] by the enzyme family of polypeptide N-. The mammalian pancreas is a glandular organ with endocrine and exocrine functions. While endocrine cells are located in the islets of Langerhans and secrete insulin, glucagon, somatostatin and pancreatic polypeptide, the exocrine acinar cells produce inactive precursors of digestive enzymes that are stored in zymogen granules. Zymogen granules migrate to the apical plasma membrane and release their contents into

Methods

Results

Conclusion