1 Department of Internal Medicine, Division of Endocrinology, Diabetology, Vascular Disease, Nephrology and Clinical Chemistry, University Hospital Tübingen, Tübingen, Germany.
2 Institute of Diabetes Research and Metabolic Diseases (IDM) of the Helmholtz Center Munich at the University Tübingen, Tübingen, Germany.
3 German Center for Diabetes Research (DZD) at the University, Tübingen, Germany.
4 Institute of Basic Medical Sciences, University of Oslo, Oslo, Norway.
5 Institute of Anatomy, University of Regensburg, Regensburg, Germany.
6 Institute of Cellular and Molecular Physiology, Friedrich-Alexander University Erlangen-Nürnberg (FAU), Erlangen, Germany.