Fig 2: Localization of DPP6 expression in human pancreas. (A–E) A representative human pancreas stained for DPP6 (A, red), insulin (B, white), somatostatin (C, green); overlay of DPP6 (red), insulin (white) and somatostatin (green) (D); overlay of DPP6 (red) and somatostatin (green) (E); the data indicate co-staining of insulin and DPP6, but not somatostatin and DPP6; (F–J) A representative human pancreas stained for glucagon (F, green), DPP6 (G, red), insulin (H, white); DPP6 (red) and glucagon (green) overlay (I); overlay of DPP6 (red), insulin (white) and glucagon (green) (J), the data indicate co-staining of both insulin and glucagon with DPP6; (K) Morphometric quantification of DPP6 area in pancreata from T1D patients as compared to control, non-diabetic individuals (n = 3). (L–P) A representative human pancreas from a subject with long-term type 1 diabetes (16 years of disease) stained for glucagon (L, green), DPP6 (M, red), insulin (N, white); Hoechst (O, blue); (P) overlay of DPP6 (green), glucagon (red), insulin (white) and Hoechst (blue), indicating that in the absence of insulin positive cells, the remaining glucagon positive cells co-stain for DPP6. In total, 3 pancreata from normoglycemic individuals and 3 from type 1 diabetes subjects were analysed. White scale bar represents 20 µm.

Fig 3: Expression of DPP6 in human islets and EndoC-ßH1 cells and other tissues evaluated by qPCR and histology. (A) Quantitative RT-PCR (qPCR) of DPP6 mRNA expression (detecting a shared sequence among all DPP6 splice variants) in EndoC-ßH1 cells (n = 5) and human pancreatic islets (n = 4) that were exposed or not to cytokines (IL-1ß + IFN-?) for 48 h, as compared to pancreatic exocrine tissue (n = 6), two exocrine cell lines (Capan-2 (n = 3) and PANC (n = 3)), and 14 other non-pathological human tissues (n = 1). (B) Immunoblot of EndoC-ßH1 cells under control conditions or following a 48h exposure to cytokines (IL-1ß and IFN-?), with alpha-tubulin as a reference protein. A representative figure is shown at the top and densitometric analysis at the bottom (n = 5), this figure displays a cropped blot, the full-length version is included in supplementary figure 8; (C–F) Immunocytochemistry of EndoC-ßH1 cells. (C) An overlay with cells stained with an anti-DPP6 monoclonal antibody (mAb, red), co-stained for insulin (green) and Hoechst in blue. The separate channels are displayed in (D) insulin (green) and (E) DPP6 (red) (n = 3). The mostly surface localization of DPP6 (red) can be observed in (F) (n = 4), with blue signals indicating Hoechst staining. The negative staining control of EndoC-ßH1 cells (without the DPP6 antibody) is placed in the top right corner of panel F. White scale bar represents 1 µm. RT-qPCR and the western blot data are presented as means ± SEM. Paired and unpaired two-way ANOVA (indicated with * and $, respectively), and unpaired one-way ANOVA (indicated with #) with Šídák correction for multiple comparisons; *, $ and # p = 0.05 as indicated by bars.

Fig 4: DPP6 expression in different human tissues as determined by RNA sequencing. (A) Expression of DPP6 mRNA based on the RNA-sequencing of human pancreatic islets; (n = 5) treated or not with IL-1ß + IFN-? (cyto) for 48 h12; and compared to 16 other human tissues under basal condition (Illumina Body Map 2.0; GSE30611). (B) Expression pattern of DPP6 splice variants in human pancreatic islets exposed or not to IL-1ß + IFN-? (cyto); human pancreatic islets express mainly the DPP6-001 variant, (n = 5); (C) Expression of the isoform DPP6-001 in human pancreatic islets exposed or not to IL-1ß + IFN-? (cyto), (n = 5) as compared to other human tissues; the highest extra-pancreatic expression is seen in brain, colon and thyroid.