Matrix Metalloproteinases Contribute to Retinal Degeneration in a Murine Model of Glaucoma

Abstract

Abstract: : Purpose: Irreversible loss of ganglion cells constitutes the major retinal pathology in glaucoma. Although intraocular pressure, in part, is recognized as a risk factor, the mechanisms that lead to ganglion cell (RGC) loss in glaucoma are less clear. The purpose of this investigation is to determine the role of extracellular matrix modulating proteases (MMPs) in ganglion cell loss and retinal damage.We used DBA/2NNia mice that spontaneously develop a pigmentary glaucoma with increase in intraocular pressure and loss of RGC over the age range 6–13 months. Methods: Activities of MMPs in retinal proteins extracted from glaucomatous DBA/2NNia mice at 3,6,9,12–13 months and age–matched non–glaucomatous C57BL/6 mice were determined by gelatin–zymography assays. Expression of MMP–9, MMP–2, TIMP–1, and TIMP–2 (tissue inhibitors of metalloproteinases) proteins in retinal protein extracts was determined by Western blot analysis. Localization of MMP–2, MMP–9, and glial fibrillary acidic protein (GFAP) was determined by immunolocalization studies. Changes in the extracellular matrix protein laminin were determined by immunolocalization studies and Western blot analysis. Results: Age–related up–regulation in MMP–9 and MMP–2 gelatinolytic activity and proteins was observed in DBA2/NNia mice but not in age–matched C57BL/6 mice. Immunolocalization studies indicated an association between an increase in MMP–9 and –2 in the ganglion cell layer and degradation of laminin from the ganglion cell layer. These changes were associated with the GFAP upregulation stress–response and the time–course for loss of RGCs in the retina. No significant change in TIMPs was observed either in DBA2/NNia or age–matched C57BL/6 retinas. Conclusions: These results indicate that increased levels of MMP–9 and –2 are associated with retinal stress and ganglion cell loss in a murine model of glaucoma.

Keywords: ganglion cells • extracellular matrix