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A. Kumar, A. El-Osta, A. A. Hussain, J. Marshall; Levels and Binding of Active Matrix Metalloproteinase (MMP) Enzymes in Human Bruch’s Membrane. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5996.
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Coupled processes of synthesis and degradation are required to maintain the functional and structural competence of Bruch’s membrane. A deficiency in the degradation process (mediated by the MMP system) is thought to underlie the observed age-related deterioration of the membrane. The present investigation has quantified the age-related variation in levels of ACTIVE MMPs 2&9 and assessed the possibility of sequestration by binding as a mechanism for inactivity of the MMP system in ageing Bruch’s membrane.
Freshly isolated Bruch’s-choroid preparations (13 eyes, age range 21-84 years) were mounted in Ussing chambers and MMPs eluted with PBS at a hydrostatic pressure of 14-16mmHg. Membrane and eluted fractions were subjected to gelatin zymography for quantification of active and inactive (Pro) MMPs 2&9.
The donors were divided into a young-middle aged group (21-55yrs) and an elderly group (56-84yrs). In intact Bruch’s (membrane plus eluant fractions), active levels of MMP-2 (expressed as percentage of total MMP-2) were low in the younger group but rose markedly in the elderly (3.7%+/- 2.9 vs. 12.8%+/-6.5 respectively, p<0.05). After elution, the amount remaining bound in the young was 4.4% +/- 6.2 NS but was significantly elevated in the elderly (24.1% +/- 8.7 p<0.01). Active MMP-9 levels in intact Bruch’s were very low and did not show an age-dependency. Elution resulted in lower bound levels in both sets of donors (p<0.05).
Although high levels of ACTIVATED MMP-2 were present in ageing human Bruch’s, their increased binding to the matrix may explain the reduction in degradation capacity of ageing Bruch’s membrane. The relevance of this finding to functional deterioration of Bruch’s in normal ageing and age-related diseases will be discussed.
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