The nasal respiratory epithelium contains thousands of specialized chemoreceptor cells (solitary chemosensory cells) that form functional contacts with the trigeminal nerve. Activation of the trigeminal nerve either directly by irritants or through the agency of these cells evokes protective airway reflexes such as sneezing, coughing or apnea. The proposed experiments investigate the role of these solitary chemosensory cells in the detection of quorum sensing molecules secreted by pathogenic bacteria as they transition from being benign to the virulent state. Our preliminary data show that the cells and the trigeminal system at large can respond to bacterial signaling molecules. The experiments in this proposal will examine the chemical specificity of the response, test the transduction cascade and possible role of T2R (bitter taste) receptor molecules, and finally examine the effects on the surrounding epithelium and the trigeminal sensory nerve fibers of activation of the chemosensory cells. In order to assess the effectiveness of various bacterial signaling molecules, we will use two bioassay systems: i) respiratory reflexes evoked by application of the compound to the nasal epithelium in a semi-intact preparation, and ii) Ca ++ -imaging of chemosensory cells isolated from the epithelium of transgenic mice in which GFP marks the relevant cell population. We will use the same preparations to assess the potential role of T2R receptors and the associated PLC-signal cascade. Specific blockers of PLC- signalling should disrupt transduction and eliminate the Ca ++ signal if the T2R/PLC pathway is necessary. Similarly, respiratory depression should be lessened in both TRPM5 and gustducin-knockout animals if these elements are crucial for the transduction of bacterial signals. Finally, we will assess whether activation of the chemosensory cells secondarily causes changes in the surrounding epithelium - either via release of paracrine mediators (e.g. ATP, acetyl choline) or through the agency of activation of the peptidergic nerve fibers that innervate the epithelium. Taken together, these experiments will determine the mechanisms used by solitary chemosensory cell to detect the bacterial signaling molecules and whether the cells are instrumental in provoking a local tissue and/or immune response to the potential pathogens.
The proposed research will investigate a newly discovered nasal chemosensory system that detects molecules that regulate the virulence of pathogenic bacteria. This research is designed to test the possible role of these sensors in a first line of tissue defense against bacterial nasal and upper respiratory infections.
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