Altered cellular localisation and expression, together with unconventional protein trafficking, of prion protein, PrP C , in type 1 diabetes

Aims/hypothesis Normal cellular prion protein (PrP C ) is a conserved mammalian glycoprotein found on the outer plasma membrane leaflet through a glycophosphatidylinositol anchor. Although PrP C is expressed by a wide range of tissues throughout the body, the complete repertoire of its functions has not been fully determined. The misfolded pathogenic isoform PrP Sc (the scrapie form of PrP) is a causative agent of neurodegenerative prion diseases. The aim of this study is to evaluate PrP C localisation, expression and trafficking in pancreases from organ donors with and without type 1 diabetes and to infer PrP C function through studies on interacting protein partners. Methods In order to evaluate localisation and trafficking of PrP C in the human pancreas, 12 non-diabetic, 12 type 1 diabetic and 12 autoantibody-positive organ donor tissue samples were analysed using immunofluorescence analysis. Furthermore, total RNA was isolated from 29 non-diabetic, 29 type 1 diabetic and 24 autoantibody-positive donors to estimate PrP C expression in the human pancreas. Additionally, we performed PrP C -specific immunoblot analysis on total pancreatic protein from non-diabetic and type 1 diabetic organ donors to test whether changes in PrP C mRNA levels leads to a concomitant increase in PrP C protein levels in human pancreases. Results In non-diabetic and type 1 diabetic pancreases (the latter displaying both insulin-positive [INS(+)] and -negative [INS(−)] islets), we found PrP C in islets co-registering with beta cells in all INS(+) islets and, strikingly, unexpected activation of PrP C in alpha cells within diabetic INS(−) islets. We found PrP C localised to the plasma membrane and endoplasmic reticulum (ER) but not the Golgi, defining two cellular pools and an unconventional protein trafficking mechanism bypassing the Golgi. We demonstrate PrP C co-registration with established protein partners, neural cell adhesion molecule 1 (NCAM1) and stress-inducible phosphoprotein 1 (STI1; encoded by STIP1 ) on the plasma membrane and ER, respectively, linking PrP C function with cyto-protection, signalling, differentiation and morphogenesis. We demonstrate that both PRNP (encoding PrP C ) and STIP1 gene expression are dramatically altered in type 1 diabetic and autoantibody-positive pancreases. Conclusions/interpretation As the first study to address PrP C expression in non-diabetic and type 1 diabetic human pancreas, we provide new insights for PrP C in the pathogenesis of type 1 diabetes. We evaluated the cell-type specific expression of PrP C in the human pancreas and discovered possible connections with potential interacting proteins that we speculate might address mechanisms relevant to the role of PrP C in the human pancreas. Graphical abstract