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Modulation of Sub-RPE Deposits In Vitro: A Potential Model for Age-Related Macular Degeneration

¹From the Divisions of Pathology and ²Cell Biology, Institute of Ophthalmology, University College, London, United Kingdom; and the ³Biological Structure and Function Section, Biomedical Sciences Division, Imperial College, London, United Kingdom.

PURPOSE. Sub-RPE deposits form in a variety of conditions most notably in age-related macular degeneration. The purpose of this study was to generate sub-RPE deposits in vitro and to test the hypotheses that high protein concentrations or retinal homogenate increase deposit formation and that a challenge with tumor necrosis factor (TNF)- or metalloproteinase (MMP)-2 decreases such deposits.

METHODS. ARPE-19 cells were grown on plastic and on collagen type I–coated membrane inserts in media containing various concentrations of fetal calf serum (FCS), bovine serum albumin, or porcine retinal homogenate. In addition, cells grown on membrane inserts were treated with TNF- or MMP-2. Sub-RPE deposits were assessed by electron microscopy and classified into fibrillar, condensed, banded, and membranous subtypes. The area of the micrograph occupied by each type was estimated with a point-counting technique. MMP-2 activity was assessed in tissue culture supernatants by zymography.

RESULTS. With increasing time in culture, total deposit formation did not change, but the amount of condensed material deposited by ARPE-19 cells increased while the fibrillar component decreased. Albumin challenge resulted in an increased amount of deposit, predominantly of the membranous type. Challenge with retinal homogenate led to a greater net deposit formation with significant increases in the condensed and banded forms. Cells treated with TNF- or MMP-2 showed a dramatic reduction in all types of sub-RPE deposit. Zymography demonstrated that unchallenged cells produced predominantly MMP-2. Retinal homogenate challenge reduced the total amount of active MMP-2 produced, and TNF- stimulated MMP-9 production.

CONCLUSIONS. Sub-RPE deposits formed in vitro share ultrastructural features with those seen in vivo. Deposit formation can be modulated by challenge with retinal homogenate, TNF-, or MMP-2. Significantly, the results provide proof of the principle that sub-RPE deposits can be formed and modified in vitro.

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