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A. Kumar, A. A. Hussain, J. Marshall; Mobility of Matrix Metalloproteinases (MMPs) in the Ageing Human Bruch's Membrane. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5639.
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Ageing of Bruch's membrane is associated with a drastic reduction in its capacity for nutritional and waste transport. Underlying mechanisms for reduced porosity include deposition of debris, oxidative damage, and greater fibrillar cross-linking. MMP's have been identified within Bruch's and constitute the degradative arm of a remodelling process for maintaining the structural integrity of the membrane. Having demonstrated release of these enzymes by the retinal pigment epithelium (RPE), the present investigation was designed to to evaluate the dynamics of the MMP mobility process through Bruch's membrane.
MMP dynamics were determined by quantifying the rate of release of endogenous MMP's 2&9 following application of a hydrostatic pressure head to Bruch's surface whilst the preparation was held in an open modified Ussing chamber. The ensuing fluid transport across the preparation was collected at timed intervals onto pre-weighed filter paper discs and following elution with Tris-HCl buffer, the amount of released MMP's was quantified by gelatin zymography.
The elution profile for MMP's 2&9 when plotted as amount against elution volume showed sigmoidal characteristics with 98% removal of the endogenous pool of these enzymes. X-50, representing the elution volume required to remove 50% of endogenous MMP's was determined to be 15 ±0.5 µl per 4mm disc of membrane (n=7, donar age range 55 - 73 years ).
The elution profiles showed that these MMP's were not bound to components of Bruch's membrane but after release from the RPE performed a surveillance function with a turnover in the endogenous pool every 22 hours. The relevance of this MMP-surveillance system in maintaining structural and functional competence of ageing Bruch's will be discussed.
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