Tissue-Specific Expression of GLP1R in Mice: Is the Problem of Antibody Nonspecificity Solved?

Abstract

Accurate localization of receptors is of importance in the assignment of role for ligand-receptor signaling in the tissue of interest and conceivably derives functional meaning to receptor signaling in that tissue. For example, expression of glucagon-like peptide 1 receptor (GLP1R) on the β-cells of the pancreas indicates that GLP-1 via binding to GLP1R on these cells helps with secretion of insulin from the pancreas. Similarly, GLP1R expression in the liver takes on a different meaning due to the change in organ and organ function. Hence, it is imperative that tissue- and cell-specific expression profile is known for accuracy of conclusions drawn about role of GLP-1/GLP1R signaling in modulation of the function of an organ. So far, this has been elusive due to the paucity of “good” antibodies against GLP1R that produce accurate, reliable, and reproducible data (1,2). The commercially available antibodies as of today are thought to be either nonspecific (i.e., bind to other proteins in addition to GLP1R) or inaccurate (i.e., do not bind to GLP1R at all or are not sensitive enough to detect GLP1R in quantifiable amounts). The reasons for this are many. First, G-protein–coupled receptors (GPCRs) are in general expressed in low numbers in vivo, making it difficult to generate sufficient material for immunization and can take many months to years to produce sufficient amounts. Second, the epitopes are made up of small discontinuous segments, making them inaccessible to standard peptide or recombinant protein technology as these small segments in isolation cannot fold or assemble together. Third, the epitopes are largely dependent on the membrane for structure and purification, and thus removal of the membrane typically results in …