Inhibition of MMP-9 expression by PPARγ activators in human bronchial epithelial cells

Background: The release of matrix degrading enzymes such as matrix metalloproteinase 9 (MMP-9) from bronchial epithelial cells is critically involved in airway wall remodelling in chronic inflammatory processes of the respiratory system. MMP-9 expression is induced by inflammatory mediators such as tumour necrosis factor (TNF)-alpha, but to date nothing is known about the mechanisms of inhibition of MMP-9 expression in these cells. Methods: A study was undertaken to examine whether activators of the nuclear transcription factor peroxisome proliferator activated receptor gamma (PPARgamma) might modulate MMP-9 expression in two different bronchial epithelial cell lines. Results: PPARgamma was expressed and was functionally active in NL20 and BEAS cells. Activation of PPARgamma by rosiglitazone or pioglitazone significantly reduced TNF-alpha and PMA induced MMP-9 gelatinolytic activity in a concentration dependent manner in both cell lines, but did not alter the expression of tissue inhibitor of MMPs type 1 (TIMP-1), the local inhibitor of MMP-9. Northern blot analysis revealed a decrease in MMP-9 mRNA expression following treatment with PPARgamma which resulted from the inhibition of NF-kappaB activation in these cells, as determined by transient transfection assays and electromobility shift assays. Conclusion: Activation of PPARgamma in human bronchial epithelial cells limits the expression of matrix degrading MMP-9. This might have therapeutic applications in chronic inflammatory processes of the respiratory system.