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Efficient mucociliary clearance is necessary to protect the respiratory tract from infection. Mucociliary dysfunction is common in respiratory diseases including asthma, chronic obstructive pulmonary disease, and cystic fibrosis. Rescuing mucociliary clearance by stimulating the metabolism of respiratory ciliated epithelia could offer new treatments for respiratory diseases. However, the coupling between cellular metabolism and mechanical output in respiratory ciliated epithelia is poorly understood. We propose to study this coupling with autofluorescence microscopy and optical coherence tomography (OCT), to measure cellular metabolism and ciliary motility, respectively. The autofluorescent metabolic co-enzymes NAD(P)H and FAD provide non-invasive measures of metabolism through the optical redox ratio (NAD(P)H intensity divided by FAD intensity), while OCT measures both the frequency of ciliary beating and cilia-driven fluid flow. Preliminary experiments were performed in ex vivo mouse trachea using an epifluorescence microscope and a spectral-domain OCT system. Cilia-driven fluid flow was quantified using 2D particle tracking velocimetry (PTV-OCT) and TrackMate, a particle-tracking tool. PTV-OCT was validated by manual particle tracking (within 4% agreement) and a calibrated flow phantom (r=0.998, p<0.001). Treatment of the trachea with cyanide, a complex IV inhibitor that reduces intracellular ATP levels, demonstrated that an increase in optical redox ratio (p<0.001) reflects a decrease in cilia-driven flow (p<0.05). Additional studies using human samples are underway to explore how pathologically altered metabolism affects ciliary motility. This optical imaging approach could provide a better understanding of respiratory disease pathogenesis, and new therapeutic targets. In the future, these technologies could also monitor intensive care patients through an endoscope.
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