Proteomics-Based Characterization of the Effects of MMP14 on the Protein Content of Exosomes from Corneal Fibroblasts

Background: Exosomes secreted by corneal fibroblasts contain matrix metalloproteinase (MMP) 14, which is known to influence pro-MMP2 accumulation on exosomes. Accordingly, we hypothesized that the enzymatic activity of MMP14 may alter the protein content of corneal fibroblast- secreted exosomes. Objective: The aim of this study was to investigate the effects of MMP14 on the composition and biological activity of corneal fibroblast-derived exosomes. Methods: Knock out of the catalytic domain (ΔExon4) of MMP14 in corneal fibroblasts was used to determine the effect of MMP14 expression on the characteristics of fibroblast-secreted exosomes. The amount of secreted proteins and their size distribution were measured using Nano Tracking Analysis. Proteins within exosomes from wild-type (WT) and ΔExon4-deficient fibroblasts were identified by liquid chromatography-tandem mass spectrometry (MS/MS) proteomics analysis. The proteolytic effects of MMP14 were evaluated in vitro via MS identification of eliminated proteins. The biological functions of MMP14-carrying exosomes were investigated via fusion to endothelial cells and flow cytometric assays. Results: Exosomes isolated from WT and ΔExon4-deficient fibroblasts exhibited similar size distributions and morphologies, although WT fibroblasts secreted a greater amount of exosomes. The protein content, however, was higher in ΔExon4-deficient fibroblast-derived exosomes than in WT fibroblast-derived exosomes. Proteomics analysis revealed that WT-derived exosomes included proteins that regulated cell migration, and ΔExon4 fibroblast-derived exosomes contained additional proteins that were cleaved by MMP14. Conclusion: Our findings suggest that MMP14 expression influences the protein composition of exosomes secreted by corneal fibroblasts, and through those biological components, MMP14 in corneal fibroblasts derived-exosomes may regulate corneal angiogenesis.