Bitter and sweet taste receptor physiology in airway ciliated cells

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We recently discovered that human nasal ciliated cells express the T2R bitter taste receptors. When activated by secreted bacterial products, T2Rs in cilia stimulates an innate immune signaling cascade involving calcium-driven nitric oxide production that increases ciliary beating as well as directly kills bacteria. Genetic polymorphisms in the TAS2R38 gene, one of the T2Rs in cilia, may underlie susceptibility to infection in patients with chronic rhinosinusitis. We hypothesize that activation of T2R bitter receptor responses in airway ciliated cells will activate innate immune to help eradicate infections without the use of conventional antibiotics. Understanding how to develop topical therapeutics targeting these pathways requires further knowledge of the identity of other cilia-localized chemosensory receptors in cilia as well as their signaling pathways and downstream effects. There remains a critical need for knowledge of the cell biology and physiology of extraoral taste receptors in general. We hypothesize that sinonasal and bronchial motile cilia express multiple chemosensory receptors, as we have identified multiple T2Rs (4,14,16, and 38) and T1Rs 2 and 3 (components of the sweet taste receptor) localized to sinonasal cilia. Interestingly, T2Rs and T1Rs activate different pathways, in contrast to the tongue where their intracellular signaling is similar. Cilia T2Rs activate Ca2+-dependent NO production, possibly also involving the kinase AKT. Activation of cilia T1R2/3 activates a distinct signaling pathway that regulates airway epithelial glucose transporters. Understanding cilia chemosensation and the unique signaling pathways involved will shed light on how to leverage these receptors for therapeutic benefit as well as elucidate mechanisms of non-canonical taste receptor signaling that may be highly relevant to the tongue and/or the many extraoral tissues where they are expressed. In Aim 1, we will further elucidate the signaling of cilia T2Rs using a combination of live cell imaging, biochemical, and molecular approaches in differentiated primary human cells and cell lines cultured at air-liquid interface. In Aim 2, we will use similar techniques to elucidate the signaling mechanism by which T1R receptors regulate glucose transport in the airway as well as its regulation by T1R receptors in primary human and mouse cells. In Aim 3, we will examine the localization and interactions of T1Rs and T2Rs using a combination of live-cell imaging and biochemistry, as well as identify the cilia chemosensory repertoire by biochemical cilia purification and proteomics. Together, the independent yet inter-related aims will examine important chemosensory functions of airway cilia, revealing new ways to leverage chemosensory receptors as therapeutic targets for airway diseases. Equally importantly, we will reveal new insights into the cell biology of extraoral taste receptor function that will likely translate to T1Rs and T2Rs in other tissues. While much of T2R and T1R cell biology has been inferred from heterologous systems, our unique model system will allow us to study the function and interactions of endogenous T1R and T2R function in differentiated primary human cells.