Background: Toluene diisocyanate (TDI) is the most important cause of occupational asthma (OA), and various pathogenic mechanisms have been suggested; of which, neurogenic inflammation is an important pathway to induce airway inflammation. Transient Receptor Potential Melastatin 8 (TRPM8) is a well-established cold sensing cation channel and expressed in neuronal cells as well as bronchial epithelial cells. A recent genome-wide association study (GWAS) from TDI-exposed workers showed a significant association for the rs10803666 SNP mapping to the TRPM8 gene.
Objective: We hypothesized TRPM8, located in airway epithelial cells may involve in the pathogenic mechanisms of TDI-induced OA and investigated its role.
Methods: Bronchial epithelial cells (BEAS-2B) were treated with TDI in dose- and time- dependent manners. The expression levels of mRNA and protein of TRPM8 were determined by quantitative RT-PCR and Western blotting. Its morphological change by TDI was evaluated immunocytochemisty. The alteration of inflammatory cytokines’ transcripts was examined in accordance with TRPM8 activation by TDI. ELISA of TRPM8 was performed using the induced sputum of asthmatics and normal controls.
Results: TRPM8 expression at both mRNA and protein levels were noted in airway epithelial cells, which were enhanced by TDI. TRPM8 activation by TDI led to significant increases in mRNA for interleukin (IL)-4, IL-13, IL-25, and IL-33. Increased expressions of the cytokine genes by TDI were partly attenuated after the treatment with a TRPM8 antagonist. In sputum samples, the expression of IL-25, 33, and TSLP mRNA as well as TRPM8 increased in the sputum of asthmatics compared than normal controls. There was a significant association between TRPM8 and IL-25 mRNA expression in asthmatics.
Conclusion: TDI exposure induces increased expression of TRPM8 mRNA in airway epithelial cells coupled with the enhanced expression of inflammatory cytokines. In addition, the expression of TRPM8 was increased in the sputum samples in asthmatics as severity increase. These results suggest that TRPM8 may be involved in the epithelial inflammation and subsequent airway remodeling of TDI-OA.
