Matrix metalloproteinase-2 from bronchial epithelial cells induces the proliferation of subepithelial fibroblasts

Background: In bronchial asthma, subepithelial fibrosis in the conducting airways is associated with increased numbers of subepithelial fibroblasts. Objective: This study examined the hypothesis that MMP-2 from airway epithelial cells induces the proliferation of subepithelial fibroblasts. Methods: Using primary bronchial epithelial cells MMP-2, MT1-MMP and TIMP-2 mRNA expression were assessed by Northern blotting and RT-PCR. Primary bronchial epithelial cells transfected with constructs encoding pro-MMP-2 and MT1-MMP (MMP-14). Results: Transfected cells showed enhanced expression of the appropriate mRNA species by RT-PCR and enhanced MMP-2 or MT1-MMP activity by zymography. Active MMP-2 levels in epithelial supernatants were increased most by cotransfection with pro-MMP-2 and MT1-MMP encoding constructs. By measuring tritiated thymidine incorporation, supernatants from transfected cells were found to enhance DNA synthesis of primary airway fibroblast cultures compared with controls. There was a strong correlation (r = 0.9, P < 0.01) between MMP-2 levels in epithelial cell conditioned media and fibroblast proliferation as indicated by DNA synthesis. The MMP inhibitor 1,10-phenanthroline attenuated the increased proliferation, while the addition of exogenous purified MMP-2 alone also increased fibroblast proliferation. Conclusions: Our results support a role for MMP-2 in mediating cross-talk between epithelial cells and myofibroblasts.