Abstract
Bitter-taste receptors (T2Rs) have emerged as key players in host–pathogen interactions and important modulators of oral innate immunity. Previously, we reported that T2R14 is expressed in gingival epithelial cells (GECs) and interacts with competence stimulating peptides (CSPs) secreted by the cariogenic Streptococcus mutans. The underlying mechanisms of the innate immune responses and physiological effects of T2R14 on Gram-positive bacteria are not well characterized. In this study, we examined the role of T2R14 in internalization and growth inhibitory effects on Gram-positive bacteria, namely Staphylococcus aureus and S. mutans. We utilized CRISPR-Cas9 T2R14 knockdown (KD) GECs as the study model to address these key physiological mechanisms. Our data reveal that the internalization of S. aureus is significantly decreased, while the internalization of S. mutans remains unaffected upon knockdown of T2R14 in GECs. Surprisingly, GECs primed with S. mutans CSP-1 resulted in an inhibition of growth for S. aureus, but not for S. mutans. The GECs infected with S. aureus induced T2R14-dependent human β-defensin-2 (hBD-2) secretion; however, S. mutans–infected GECs did not induce hBD-2 secretion, but induced T2R14 dependent IL-8 secretion. Interestingly, our results show that T2R14 KD affects the cytoskeletal reorganization in GECs, thereby inhibiting S. aureus internalization. Our study highlights the distinct mechanisms and a direct role of T2R14 in influencing physiological responses to Gram-positive bacteria in the oral cavity.
Highlights
Oral epithelial cells are in constant communication with several diverse microbes under both normal and pathological conditions
T2Rs have been identified as important modulators of innate immune responses in several cell types, including sinonasal epithelial cells; upper airway epithelial cells; immune cells, such as macrophages; and gingival epithelial cells (GECs) [2,9,10,11]
To characterize the role of T2R14 in bacterial internalization, the OKF6 WT, MOCK and T2R14 KD cells were infected by using S. aureus and S. mutans
Summary
Oral epithelial cells are in constant communication with several diverse microbes under both normal and pathological conditions. Host cells express toll-like receptors (TLRs), which can recognize pathogen-associated molecular patterns (PAMPs). Gram-positive organisms and lipopolysaccharide in Gram-negative organisms [1]. Apart from these above-mentioned molecules, bacteria secrete quorum-sensing molecules (QSMs) that are recognized by bitter taste receptors (T2Rs) [2,3,4]. T2Rs have been identified as important modulators of innate immune responses in several cell types, including sinonasal epithelial cells; upper airway epithelial cells; immune cells, such as macrophages; and gingival epithelial cells (GECs) [2,9,10,11]. The stimulation of bronchial airway epithelial cells by bitter compounds resulted in an increase in intracellular Ca2+ , resulting in increased ciliary beat frequency [12], nitric oxide (NO) production and increased bactericidal effects in sinonasal epithelial cells [10] and regulation of type-2 immunity against gut pathogens [13,14]
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