Characterisation and modulation of the gelatinase system of human Bruch's membrane

    Student thesis: Doctoral ThesisDoctor of Philosophy

    Abstract

    Ageing of Bruch’s membrane is associated with structural and functional deterioration. Accumulation of normal and abnormal collagen in ageing Bruch’s has led to the hypothesis of diminished matrix degradation mediated normally by a family of protease enzymes called the matrix metalloproteinases (MMPs). Underlying mechanisms leading to diminished MMP activity in ageing Bruch’s remain unknown but functional changes of diminished transport are well documented. Ageing remains the biggest risk factor in AMD with nearly 30% of all individuals reaching the age of 85 years showing some loss of central vision. In the present thesis, the gelatinase system (constituting MMPs 2&9) has been examined resulting in the identification and characterisation of three additional high molecular weight species termed HMW 1&2 and a large macromolecular weight MMP complex (LMMC). HMW1&2 were shown to be covalently bonded homo-and/or hetero- polymers of pro-MMPs 2&9. HMW species in effect sequester pro-MMPs 2&9 reducing the pool available for activation and the age-related increase in HMW species is expected to augment this reduction. In Bruch’s membrane from donors with AMD, levels of HMW1&2 were considerably elevated (p<0.05) with a concomitant reduction in the amount of active MMPs 2&9 (p<0.05). The reduction in activated MMP species therefore underlies the reduced degradative capacity of Bruch’s in these patients. Elution studies demonstrated the existence of a free-bound equilibrium for the gelatinases with the bound forms being retained by hydrophobic, ionic or metal mediated interactions. Since divalent metal ions are deposited in Bruch’s of AMD donors, metal chelation was assessed as a possible means of inducing MMP release. Metal chelation with EGTA resulted in the release of active forms of MMP2 and significantly improved the fluid transport properties of the membrane (p<0.005).
    Date of Award1 May 2012
    Original languageEnglish
    Awarding Institution
    • King's College London
    SupervisorJohn Marshall (Supervisor)

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