Olle Korsgren’s projects – Islet imaging

Antibody-based proteomics for discovery and exploration of proteins expressed in pancreatic islets

In collaboration with Lars Johansson, Dept. of Radiology, Oncology and Radiation Sciences; Olof Eriksson, Dept. of Medicinal Chemistry, and Fredrik Pontén, IGP

While there have been significant advances in the fields of genomics and proteomics to support our understanding of differential gene and protein expression in disease, this has not had a significant impact on our understanding of beta cell loss in TID. Likewise, advances in imaging hardware and software have revolutionized medical diagnosis and therapy but have so far not been applied to the study of beta cell mass. The successful completion of this project will establish beta cell imaging in humans to gain further understanding of the pathophysiology of the disease and to allow stringent evaluation of any treatment aiming for beta cell preservation, proliferation and replacement.

Identification of the transmembrane protein tetraspandin-7

The HPA database currently includes over 6,800 unique proteins together with information relating to their expression within normal and human tumour tissues (www.proteinatlas.org). An in silico discovery strategy (search engine) is developed based on the advanced search tool for proteins highly expressed in pancreatic islets, but not expressed in the exocrine parenchyma. A preliminary search yielded 110 proteins.

In parallel, we have initiated a detailed proteomic characterization of human pancreatic islets with focus on membrane protein profiling. Beta cell specific genes encoding a transmembrane protein will be identified by a proteomics and bioinformatics approach. For uncharacterized genes signal sequence prediction and hydrophobicity plots will be used to predict transmembrane regions.

Utilizing this approach we have already identified several novel islet specific proteins highly interesting as potential targets for PET imaging. Among those is tetraspandin-7 (TSPAN7), a transmembrane protein that may be involved in cell proliferation and cell motility. In islet cells the staining distribution was similar to insulin, showing distinct positivity in pancreatic islets (see image on the right). Importantly, TSPAN7 antibodies are able to specifically detect beta cells in FACS analysis of islet single cells, demonstrating exposure of extracellular domains of the protein.

Quantitative RT-PCR, PAGE and Western blotting are applied to determine relative expression levels and molecular mass, offering a gold standard for the validation process of identified proteins.