Autoradiography in mice reveals receptor expression in sub-epithelial myofibroblasts.
Having confirmed the binding of [125I]-hGLP-2(1-33,M10Y) to rodent GLP-2Rs, we did autoradiography studies in mice with this radioligand. In all mice examined (n=6), we observed strong labeling in the SEMFs of the gastrointestinal (GI) tract (figure 5c,e and supplementary figure 2) and in the islet cells of the endocrine pancreas (figure 5d,f and supplementary figure 2). These data are consistent with previous data (El-Jamal et al. 2014; De Heer et al. 2007; Ørskov et al. 2005), and thereby confirming at the protein level what was shown at the level of GLP-2R mRNA transcript. Injection of unlabeled GLP-2(1-33) prior to the radioligand abrogated labeling in both tissues (figure 5e,f), supporting the specific binding of [125I]-hGLP-2(1-33,M10Y).‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬
Since the pancreas is known for high expression levels of the GLP-1R and given the observed binding of both hGLP-2-based radioligands to the hGLP-1R (figure 4), we tested the binding of the radioligands to the mouse and rat GLP-1R. Here, we were surprised by a very high specific binding of both radioligands to the mouse GLP-1R (mGLP-1R), while no binding was observed for the rat GLP-1R (rGLP-1R) (supplementary figure 3). The binding of both radioligands to mGLP-1R reached the same Emax as for the mouse GLP-2R (mGLP-2R), but have a 32-fold lower affinity (table 2).