Preliminary Evaluation of OR51E2-Mediated cAMP Signaling After Propionic Acid Stimulation in A549 Cells

Olfactory receptor 51E2 (OR51E2) is a G protein-coupled receptor traditionally associated with odor detection in the olfactory epithelium. However, recent studies have shown that olfactory receptors can also be expressed in non-olfactory tissues, where they may contribute to cellular signaling and physiological responses. OR51E2 is of particular interest because it has been described as a receptor responsive to short-chain fatty acids, including propionic acid. Understanding how this receptor responds to specific ligands may help clarify the functional role of olfactory receptors outside the olfactory system. This study aimed to evaluate the activation of OR51E2 by propionic acid using an in vitro cellular model. A549 cells were used as the experimental cell line and were transfected to overexpress OR51E2 together with the cAMP GloSensor system. After transfection, cells were stimulated with propionic acid in order to assess whether receptor activation could induce changes in intracellular cyclic AMP (cAMP) levels. Forskolin was used as a receptor-independent positive control to confirm the functionality of the cAMP signaling pathway and the responsiveness of the assay system. The experimental approach was based on the measurement of ligand-induced cAMP production through a luminescence-based assay. By comparing OR51E2-overexpressing cells with appropriate control conditions, this study aimed to determine whether propionic acid produces a detectable receptor-mediated response in A549 cells. The use of forskolin allowed validation of the assay performance and provided a reference for maximal cAMP pathway activation. Overall, this thesis provides a preliminary functional evaluation of OR51E2 signaling in A549 cells after stimulation with propionic acid. The results may contribute to a better understanding of ectopically expressed olfactory receptors and support the use of cell-based assays for studying receptor activation by small chemical molecules.