Live Imaging of Nitric Oxide Dynamics Reveals Cell Type–Specific NO Signaling in Air–Liquid Interface Cultures of Human Sinonasal Epithelial Cells

Background/Objectives: Chronic rhinosinusitis with nasal polyps (CRSwNP) is charac-terized by epithelial remodeling, impaired mucociliary clearance, and altered nitric oxide (NO) metabolism. However, the cell type–specific mechanisms of NO production and the functional roles of nitric oxide synthase (NOS) isoforms in sinonasal epithelial cells remain unclear. This study investigated NO production dynamics in air–liquid in-terface (ALI) cultures of human sinonasal epithelial cells. Methods: Human sinonasal epithelial cells were differentiated under ALI conditions. Expression of inducible NOS (iNOS) and endothelial NOS (eNOS) was analyzed by quantitative RT-PCR. Intracellular NO production was evaluated using the NO-sensitive fluorescent probe DAF-FM com-bined with laser scanning confocal microscopy. Cell type–specific NO production was examined in ciliated and non-ciliated epithelial cells using the NOS inhibitors L-NAME and 1400W. Results: CRSwNP tissues demonstrated significantly increased iNOS ex-pression and elevated iNOS/eNOS ratios compared with controls, whereas eNOS ex-pression showed no significant difference. ALI cultures successfully reproduced dif-ferentiated sinonasal epithelium containing ciliated and basal cells. DAF-FM fluores-cence revealed significantly greater NO production in ciliated epithelial cells than in non-ciliated cells. Non-selective NOS inhibition by L-NAME markedly suppressed NO production in both cell types, whereas selective iNOS inhibition by 1400W reduced but did not abolish NO production in ciliated cells. Conclusions: NO production mecha-nisms differ according to sinonasal epithelial cell subtype. Ciliated epithelial cells maintain both eNOS- and iNOS-dependent NO production, whereas non-ciliated cells predominantly rely on iNOS-derived NO. Dysregulated spatial NO signaling associated with ciliated cell loss may contribute to epithelial dysfunction and chronic inflammation in CRSwNP.