OR2AT4 and OR1A2 counterregulate molecular pathophysiological processes of steroid-resistant inflammatory lung diseases in human alveolar macrophages.

BACKGROUND: Therapeutic options for steroid-resistant non-type 2 inflammation in obstructive lung diseases are lacking. Alveolar macrophages are central in the progression of these diseases by releasing proinflammatory cytokines, making them promising targets for new therapeutic approaches. Extra nasal expressed olfactory receptors (ORs) mediate various cellular processes, but clinical data are lacking. This work investigates whether ORs in human primary alveolar macrophages could impact pathophysiological processes and could be considered as therapeutic targets. METHODS: Human primary alveolar macrophages were isolated from bronchoalveolar lavages of 50 patients with pulmonary diseases. The expression of ORs was validated using RT-PCR, immunocytochemical staining, and Western blot. Changes in intracellular calcium levels were analyzed in real-time by calcium imaging. A luminescent assay was used to measure the cAMP concentration after OR stimulation. Cytokine secretion was measured in cell supernatants 24 h after stimulation by ELISA. Phagocytic ability was measured by the uptake of fluorescent-labeled beads by flow cytometry. RESULTS: We demonstrated the expression of functional OR2AT4 and OR1A2 on mRNA and protein levels. Both ORs were primarily located in the plasma membrane. Stimulation with Sandalore, the ligand of OR2AT4, and Citronellal, the ligand of OR1A2, triggered a transient increase of intracellular calcium and cAMP. In the case of Sandalore, this calcium increase was based on a cAMP-dependent signaling pathway. Stimulation of alveolar macrophages with Sandalore and Citronellal reduced phagocytic capacity and release of proinflammatory cytokines. CONCLUSION: These are the first indications for utilizing olfactory receptors as therapeutic target molecules in treating steroid-resistant lung diseases with non-type 2 inflammation.

The monocyte-dependent immune response to bacteria is suppressed in smoking-induced COPD.

COPD patients have an increased susceptibility to bacterial airway infections that can induce exacerbations. In response to infections, circulating monocytes become recruited to the infected tissue and secrete cytokines. We hypothesized that this cytokine response is reduced in COPD. Cultured peripheral blood monocytes of never smokers (NS) and smokers without (S) and with COPD (3 study populations, n = 36-37) were stimulated with extracts of Haemophilus influenzae, Staphylococcus aureus, or Streptococcus pneumoniae or with four different pathogen-associated molecular patterns (PAMPs). Four cytokines and 9 PAMP-related signaling molecules were measured and compared between the groups. Granulocyte-macrophage-colony-stimulating-factor responses to all stimulants were reduced in S and COPD compared to NS. Tumor-necrosis-factor-α responses to all bacterial extracts, peptidoglycan, and lipopolysaccharide were reduced in S and/or COPD. Interleukin-10 responses to S. aureus and lipoteichoic acid were increased in COPD. Correlations to pack-years and lung function were found. The peptidoglycan-receptor NOD2 and the mRNA of the lipopolysaccharide-receptor TLR4 were reduced in S and COPD. Cytokine responses of monocytes to bacteria are suppressed by smoking and in COPD possibly due to NOD2 and TLR4 reduction and/or interleukin-10 increase. This might help to explain the increased susceptibility to bacterial infections. These systemic molecular pathologies might be targets for therapeutic strategies to prevent infection-induced exacerbations. KEY MESSAGES: COPD subjects have an increased susceptibility to bacterial infections. This implies defects in the immune response to bacteria and is critical for disease progression. The cytokine response of monocytes to bacteria is reduced in COPD. This might be due to a reduced NOD2 and TLR4 and an increased IL-10 expression. This can explain the increased susceptibility to infections and help to identify drug targets.