CysLT1 receptor upregulation by TGF-β and IL-13 is associated with bronchial smooth muscle cell proliferation in response to LTD4

Background: Airway remodeling is a feature of chronic asthma. It involves a number of structural changes, including bronchi-at smooth muscle cell (BSMC) hyperplasia and hypertrophy. Cysteinyl leukotrienes (cysLTs) have been suggested to play a role in airway remodeling in addition to their numerous other physiopathologic effects. Objectives: This work was aimed at characterizing the potential modulation of CysLT1 receptor expression by cytokines and the eventual functional relevance of this modulation. Methods: Expression of CysLT1 receptor was measured by flow cytometry and immunofluoreseence microscopy. Transcripts were measured by RT-PCR and BSMC proliferation by crystal violet staining. Results: When human BSMC were exposed to transforming growth factor (TGF)-beta, IL-13, or IFN-gamma, their expression of CysLT1 receptor was significantly augmented in a time- and concentration-dependent manner. Interestingly, IL-4 had no significant effect on CysLT1 receptor expression in BSMC. Moreover, IL-13 and IFN-gamma but not TGF-beta were able to increase CysLT1 mRNA levels. Finally, when BSMC were pre-treated with TGF-beta or IL-13 but not IFN-gamma, their responsiveness to LTD4 was markedly enhanced in terms of BSMC proliferation. Whereas TGF-beta, IL-13, or LTD4 alone had little effect on BSMC proliferation, preexposure of the cells to TGF-beta or IL-13 for 24 hours resulted in a significant increase in proliferation in response to LTD4. The enhanced proliferation was totally prevented by pretreating the cytokine-primed BSMC with the selective CysLT1 receptor antagonist Montelukast. Conclusions: Taken together, our findings indicate a synergy between certain cytokines and cysITs, mediated by the augmented expression of the CysLT1 receptor and subsequent LTD4-triggered BSMC proliferation. These findings support a role for cysLTs in the airway remodeling observed in asthmatic patients and may provide a rationale for preventive and therapeutic intervention.