Background: The eosinophil is a prominent cell in allergic lung inflammation and is exposed to a range of cytokines, including TNF-alpha, at the site of allergen challenge. Matrix metalloproteinases (MMPs) and tissue inhibitors of matrix metalloproteinases (TIMPs) produced by inflammatory cells are thought to play a crucial role in interstitial matrix turnover and tissue remodeling in acute and chronic lung diseases. In addition, protein kinase C is known to be important in MMP-9 expression and secretion.
Objective: We investigated the regulation of eosinophil-derived MMP-9 and TIMP proteins by TNF-alpha.
Methods: Using RT-PCR and gelatin zymography, we investigated the ability of human eosinophils to produce and secrete active MMP-9 on stimulation with TNF-alpha. We also studied the production of TIMP-1 and TIMP-2 in eosinophils by using Western blotting.
Results: The gelatinolytic activity of MMP-9 in unstimulated eosinophils was low, but it increased by 95% after TNF-alpha stimulation. This increase was regulated at both the transcriptional and translational levels. The transcription inhibitor actinomycin D, the nuclear factor kappaB (NFkappaB) inhibitor N-CBZ-Leu-Leu-Leu-AL, the protein synthesis inhibitor cycloheximide, and the protein kinase C inhibitor H7 significantly decreased MMP-9 activity in TNF-alpha-treated cells. TIMP-1 and TIMP-2 gene expression and protein production varied significantly among different cell donors.
Conclusion: Eosinophils, on stimulation with TNF-alpha, may play a major role in asthmatic airway remodeling through increased MMP-9 production at the inflammatory site.