GPR21 (G protein-coupled receptor 21) is an orphan receptor belonging to the class A rhodopsin-like family of G protein-coupled receptors (GPCRs). Characterized by seven transmembrane domains, GPCRs play crucial roles in cellular signaling and are implicated in various physiological processes. Despite its identification over two decades ago, the endogenous ligand of GPR21 remains unidentified, limiting a comprehensive understanding of its biological function.
GPR21 is expressed in multiple tissues, including the central nervous system, liver, adipose tissue, and pancreas, suggesting potential roles in metabolic regulation and neurophysiology. Preclinical studies link GPR21 to insulin resistance, obesity, and type 2 diabetes. For example, GPR21-knockout mice exhibit improved glucose tolerance and reduced adiposity, while overexpression correlates with metabolic dysregulation. However, conflicting data and the absence of selective agonists/antagonists complicate mechanistic insights.
GPR21 antibodies are essential tools for detecting receptor expression, localization, and interaction partners. They enable applications like Western blotting, immunohistochemistry, and flow cytometry to map tissue distribution or quantify expression changes in disease models. Commercial antibodies typically target extracellular or intracellular epitopes, with validation relying on knockout controls. Challenges include specificity concerns due to GPCR structural homology and limited functional validation. Nonetheless, GPR21 antibodies remain critical for unraveling its pathophysiological roles and advancing drug discovery efforts targeting metabolic or neurological disorders.