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M. J. Kelley, M. Aga, J. M. Bradley, K. E. Keller, T. S. Acott; Podosome- or Invadopodia-Like Structures (PILS) and Focal Extracellular Matrix Turnover by Trabecular Meshwork Cells. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1608.
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© ARVO (1962-2015); The Authors (2016-present)
Matrix metalloproteinases (MMPs)-2 and -14 colocalize at structures on trabecular meshwork (TM) cells. These structures resemble podosomes or invadopodia, specialized adhesion and degradation structures seen on some types of cells. Studies were conducted to determine whether TM cells exhibit podosomes or invadopodia and whether they function in focal extracellular matrix (ECM) turnover.
Cultured porcine and human TM cells and perfused anterior segments were studied, with and without perturbation by mechanical stretching, elevated pressure, TNFα, IL-1α, or TGFβ2. Cellular localization of proteins was investigated by immunohistochemistry. TM cells, labeled with CellTracker Red, were cultured on fluorescein isothiocyanate (FITC)-labeled collagen type I and confocal time lapse images of ECM degradation and associated cell movements were collected.
MMP-2, MMP-14, and tissue inhibitor of MMPs (TIMP-2) colocalized at PILS with cortactin, caldesmon, α-actinin, and phosphotyrosine. Tubulin, vimentin, and actin colocalized or intersected with PILS. Syndecan-2, integrins αV and β1, and a versican neo-epitope, which is created by ADAMTS 4 cleavage, also colocalized with PILS. Fibronectin fibrils intersected the PILS. Mechanical stretching, TNFα, and TGFβ2 treatment increased the number and size of PILS, while IL-1α had only modest effects. TM cells grown on FITC-conjugated collagen type I exhibited focal degradation craters and on longer exposure, large regions of extensive degradation. Time-lapse imaging showed dramatic movement of TM cell processes during this ECM degradation and movement and internalization of degraded FITC-labeled fragments. MMP-2, MMP-14 and cortactin colocalized in the juxtacanalicular and other regions of perfused human anterior segment organ cultures.
TM cells exhibited numerous PILS, in which a number of typical markers are colocalized with MMP-2 and MMP-14. These structures were also found within the juxtacanalicular region of human anterior segments, suggesting that they are not simply a cell culture phenomenon. Collagen degradation, with active TM cell process movement and apparent fragment uptake, suggests that PILS serve as focal sites for targeted ECM turnover, an event that has been linked to modifications of aqueous humor outflow resistance.
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