Abstract:

Objective To investigate the effect of type 2 taste receptor （T2R）38 activation on ferroptosis of human airway epithelium NuLi-1 cells induced by cigarette smoke exposure， and to clarify its possible mechanism. Methods The human airway epithelial NuLi-1 cells were divided into control group （without any treatment）， cigarette smoke extract （CSE） group （treated with 5% CSE for 24 h） and CSE+T2R38 specific agonist phenylthiocarbamide （PTC） group（CSE+PTC group） （treated with 5% CSE and 1 mmol·L^-1 PTC for 24 h）. The expression levels of T2R38 mRNA and protein in NuLi-1 cells in various groups were determined by real-time fluorescence quantitative PCR （RT-qPCR） and Western blotting methods. The cell viabilities in various groups were determined by cell counting kit-8 （CCK-8） assay. The activities of inducible nitric oxide synthase （iNOS）， endothelial nitric oxide synthase （eNOS）， and superoxide dismutase （SOD） in the cells in various groups were measured by kits. DAX-J2 red fluorescence probe was used to determine the levels of nitric oxide（NO） in the cells in various groups. The reactive oxygen species（ROS） levels in the cells in various groups were detected by fluorescent probe kit. The levels of malondialdehyde （MDA）， Fe²⁺， and reduced glutathione （GSH） in the cells in various groups were determined by enzyme-linked immunosorbent assay （ELISA） method. Western blotting method was used to determine the expression levels of nuclear factor erythroid 2-related factor 2 （Nrf2） and glutathione peroxidases 4 （GPx4） proteins in the cells in various groups. Results Compared with control group， the expression levels of T2R38 mRNA and protein in NuLi-1 cells in CSE group were increased （P<0.05）. Compared with control group， the viability of NuLi-1 cells in CSE group was decreased （P<0.05）， the activities of iNOS and SOD in cells in CSE group were increased （P<0.05）， the levels of NO and ROS were increased （P<0.05）， the levels of MDA and Fe²⁺ were increased（P<0.05）， and the GSH level and the expression levels of Nrf2 and GPx4 proteins were decreased. Compared with CSE group， the viability of NuLi-1 cells in CSE+PTC group was increased（P<0.05）， the activity of SOD and the GSH level in the cells were increased（P<0.05）， the activity of iNOS in cells was decreased （P<0.05）， the levels of NO and ROS in cells were decreased （P<0.05）， the levels of MDA and Fe²⁺ were decreased （P<0.05）， and the expression levels of Nrf2 and GPx4 proteins were increased （P<0.05）. There was no significant difference in eNOS activity among control group， CSE group， and CSE+PTC group （P>0.05）. Conclusion Activation of bitter taste receptor T2R38 can inhibit ferroptosis in human airway epithelium NuLi-1 cells induced by cigarette smoke exposure， and its mechanism may be related to the reduction of iNOS activity in the cells.

Key words: Chronic obstructive pulmonary disease, Human airway epithelium cell, Bitter taste receptor, Type 2 taste receptor 38, Inducible nitric oxide synthase, Ferroptosis