Probes for INS

Glucagon-like peptide-1 (GLP-1) is an incretin hormone which stimulates insulin release and inhibits glucagon secretion from the pancreas in a glucose-dependent manner. Incretin-based therapies, consisting of GLP-1 receptor (GLP-1R) agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors, are used for the treatment of T2D. Immunohistochemical studies for GLP-1R expression have previously been hampered by the use of unspecific polyclonal antibodies. This study used a new monoclonal antibody to assess GLP-1R expression in pancreatic tissue from 23 patients with T2D, including 7 with a DPP-4 inhibitor and 1 with a GLP-1R agonist treatment history. A software-based automated image analysis algorithm was used for quantitating intensities and area fractions of GLP-1R positive compartments. The highest intensity GLP-1R immunostaining was seen in beta-cells in islets (average signal intensity 76,1 (± 8, 1)). GLP-1R/insulin double-labelled single cells or small clusters of cells were also frequently located within or in close vicinity of ductal epithelium in all samples and with the same GLP-1R immunostaining intensity as found in beta-cells in islets. In the exocrine pancreas a large proportion of acinar cells expressed GLP-1R with a 3-fold lower intensity of immunoreactivity as compared to beta-cells (average signal intensity 25,5 (± 3,3)). Our studies did not unequivocally demonstrate GLP-1R immunoreactivity on normal-appearing ductal epithelium. Pancreatic intraepithelial neoplasia (PanINs; a form of non-invasive pancreatic ductular neoplasia) were seen in most samples, and a minority of these expressed low levels of GLP-1R. These data confirm the ubiquity of early stage PanIN lesions in patients with T2D and do not support the hypothesis that incretin-based therapies are associated with progression towards the more advanced stage PanIN lesions.

Glucagon-like peptide-1 (GLP-1) is a physiological regulator of appetite and long-acting GLP-1 receptor agonists (GLP-1RA) lower food intake and bodyweight in both human and animal studies. The effects are mediated through brain GLP-1Rs, and several brain nuclei expressing the GLP-1R may be involved. To date, mapping the complete location of GLP-1R protein in the brain has been challenged by lack of good antibodies and the discrepancy between mRNA and protein especially relevant in neuronal axonal processes. Here, we present a novel and specific monoclonal GLP-1R antibody for immunohistochemistry with murine tissue and show detailed distribution of GLP-1R expression as well as mapping of GLP-1R mRNA by non-radioactive in situ hybridization. Semi-automated image analysis was performed to map the GLP-1R distribution to atlas plates from the Allen Institute of Brain Science (AIBS). The GLP-1R was abundantly expressed in numerous regions including the septal nucleus, the hypothalamus and the brain stem. GLP-1R protein expression was also observed on neuronal projections in brain regions devoid of any mRNA which has not been observed in earlier reports. Taken together, these findings provide new knowledge on GLP-1R expression in neuronal cell bodies and neuronal projections.