Bitter taste receptors (T2Rs) role in oral innate immunity and their characterization in extracellular vesicles (EVs)
Medapati, Manoj Reddy
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Bitter taste receptors (T2Rs) belong to the G protein-coupled receptor family. There are 25 T2Rs, which are primarily expressed in oral tissues and mediate bitter taste perception. Recent studies identified bacterial quorum-sensing molecules (QSMs) as ligands for T2Rs expressed in airways. Most of the known QSM ligands of T2Rs were derived from Pseudomonas aeruginosa. These QSM ligands are mainly acyl homoserine lactone (AHL) such as C12-AHL, C8-AHL and quinolones such as HHQ and NHQ. However, till now there are no studies on T2R’s interaction with Gram-positive bacterial QSMs in gingival epithelial cells (GECs). The cariogenic bacterium, Streptococcus mutans, secretes competence stimulating peptides (CSPs) as QSMs. The first part of my thesis elucidates the role of T2R and S. mutans CSPs interaction in mediating GEC innate immune responses. The second part of my study, characterizes the physiological role of T2R14 in Gram-positive bacterial internalization and survival. The final chapter, reports the characterization of T2Rs expressed in extracellular vesicles (EVs) isolated from cultured cells and saliva. Transcriptomic and western blot analyses identify T2R14 to be highly expressed in GECs. My results suggest that only S. mutans CSP-1 induces robust intracellular calcium mobilization in GECs, compared to CSP-2 and CSP-3. The knock down of T2R14 by CRISPR-Cas9 revealed CSP-1 mediated cytokine regulation (IL-6, IL-8 and TNF-α) and modulation of dHL-60 migration. Interestingly, CSP-1 and bitter agonist mediated T2R14 activation in GECs inhibits growth of Staphylococcus aureus but not for S. mutans. Further, immuno transmission electron microscopy (immuno-TEM) and ELISA show presence of T2R4 and T2R38 in EVs. In conclusion, this work provides novel insights into the roles of T2Rs in oral tissues and in host-microbe interactions.
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