Title : Matrix metalloproteinase-7 restricts RSV infection through cleavage of viral and host entry factors
Abstract:
Introduction & Aim: The airway epithelium constitutes the primary barrier against respiratory viral pathogens and actively shapes innate immune responses through the secretion of bioactive mediators. Among these, MMP-7 (matrilysin), a zinc-dependent endopeptidase constitutively produced by airway epithelial cells, has established roles in extracellular matrix remodeling and chemokine processing, yet its contribution to antiviral defense remains undefined. Here, we investigated whether airway epithelial-derived MMP-7 exerts direct antiviral activity against RSV and sought to elucidate its underlying molecular mechanisms.
Methods: The study used both in vitro and in vivo methods. Molecular docking analysis was conducted to examine the interactions between MMP-7 and RSV G glycoprotein. Human airway epithelial cells (A549 and Hep-2) were pre-treated with recombinant MMP-7 to determine viral infectivity (plaque assay and GFP based imaging) during and after RSV infection. The ability of MMP-7 to interact specifically with CCR3 over CCR1, CCR5, and CX3CR1 was assessed by determining the effect on eosinophils binding to CCL11/eotaxin-1 and eosinophil chemotaxis. The direct proteolytic activity of MMP-7 on the RSV G glycoprotein was assessed by SDS-PAGE following incubation with various concentrations of MMP-7. Mice (wild type and MMP-7 deficient) were intranasally infected with RSV (106 pfu) and assessed on day 5 post-infection for pulmonary viral load, number of inflammatory cells in lungs, and mucus production.
Results & Discussion: Since matrix metalloproteinases (MMPs) degrade a broad range of substrates, chemokine receptors may represent previously unrecognized targets within the MMP degradome. Here, we identify MMP-7 as the principal enzyme mediating CCR3 processing, a chemokine receptor that regulates eosinophil and Th2 cell trafficking, while showing no activity toward CCR1, CCR5, or CX3CR1. Flow cytometry analyses further demonstrate that MMP-7 treatment of chemokine receptor–transfected cells reduce eotaxin
binding to CCR3? cells, whereas MIP-1β binding to CCR5? cells remain unaffected. Consistently, MMP-7–mediated CCR3 cleavage results in a loss of eosinophil chemoattractant activity. Moreover, pre-treatment of airway epithelial cells with recombinant human MMP-7 inhibits respiratory syncytial virus (RSV) infection in a dose-dependent manner. Structural modelling of MMP-7 and the RSV G protein identified stable interaction interfaces, while in vitro MMP-7–mediated proteolytic cleavage of RSV-G inhibited RSV infection of airway epithelial cells. The role of MMP-7 as a protective factor in RSV infection was confirmed by in vivo studies showing that MMP-7 deficient mice had a higher pulmonary viral burden than wild-type. MMP-7 deficient mice also showed greater inflammatory infiltrate as well as increased mucus hypersecretion and elevated PAS-positive goblet cells, further supporting the critical protective function of epithelial-derived MMP-7.
Conclusion: MMP-7 is a key regulator of airway inflammation and antiviral immunity. It decreases eosinophil chemotaxis by cleaving the CCR3 receptor, thereby reducing eosinophil driven inflammation. In parallel MMP-7 also acts directly on RSV-G attachment proteins, altering its binding to host receptors and consequently reducing viral infectious capacity. The combination of those functions results in a marked reduction in pulmonary inflammation and viral pathogenesis in mouse models of respiratory infection. Therefore, MMP-7 is a dual-action mediator of both immune regulation and antiviral defense and highlights its potential as a therapeutic target for respiratory viral diseases.
