Olfactory receptors affect inflammatory processes of lung epithelial cells

Background Lung epithelial cells are centrally involved in the development of non-type 2 inflammation, e.g. in COPD and cystic fibrosis, for which therapeutic options are needed. Olfactory receptors (ORs) belong to the group of pharmacologically used G-protein coupled receptors and are expressed in almost every cell type where they influence numerous cellular processes.

Hypothesis Olfactory receptors expressed in lung epithelial cells regulate cellular pathological processes associated with non-type 2 inflammation and therefore might be considered as therapeutic targets.

Methods Experiments were conducted in the lung epithelial cell line A549 and primary human air-liquid interface (ALI) cultured lung epithelial cells. Calcium imaging screening of 100 OR ligands was used to identify ORs in A549. OR expression was validated by RT-PCR and Western blot in A549 and ALI cells. Immunocytochemical staining revealed localization of the ORs in A549 cells. Effects of OR activation were investigated in A549 by measuring 1) intracellular cAMP concentrations by luminescence, 2) cellular vitality by annexin/PI staining, 3) wound healing by scratch assay, 4) proliferation by an MTT-based assay, and 5) the secretion of the non-type 2 key cytokine IL-8 in the absence and presence of bacterial PAMPs by ELISA.

Results The screening revealed a dose-dependent increase of intracellular calcium in A549 cells after stimulation with Brahmanol or Cinnamaldehyde. The expression of the corresponding OR2AT4 and OR2J3 was verified in A549 and ALI cells. Stimulation of OR2J3 by Cinnamaldehyde caused a decrease in the secretion of IL-8 in the absence and presence of bacterial PAMPs, proliferation, and wound healing but increased cAMP. In contrast, stimulation of OR2AT4 by Brahmanol caused increased wound healing and the secretion of IL-8 in the absence and presence of bacterial PAMPs but did not affect cAMP and proliferation. Both ORs did not affect vitality.

Conclusion Our experiments showed the expression of OR2AT4 and OR2J3 in A549 and ALI cells. Stimulation of ORs influenced pathophysiological processes. These are the first indications of a potential use of ORs as therapeutic targets, either by reducing inflammation or protecting against infections by increasing wound healing and production of proinflammatory cytokines.

Publication History

Article published online:
09 March 2023