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LY Marmorstein, FL Munier, Y Arsenijevic, DF Schorderet, PJ McLaughlin, AD Marmorstein; Abnormal Accumulation of EFEMP1 Protein Within and Beneath the RPE Underlies the Retinal Pathology in Malattia Leventinese . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4563.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Malattia Leventinese/Doyne honeycomb retinal dystrophy (ML/DHRD) is an inherited macular disorder characterized by drusen beneath the retinal pigment epithelium (RPE) and caused by a mutation (R345W) in EFEMP1, a gene of unknown function. The purpose of this study is to elucidate how the mutation in EFEMP1 causes the pathogenesis of ML/DHRD. Methods: Polyclonal (Pab) and monoclonal (3-5) antibodies recognizing EFEMP1 were raised in rabbits and mice respectively. They were used for western blotting, immunoprecipitation, and immunohistochemistry. In situ hybridization was used to determine which cells in the eye produce EFEMP1 mRNA. Pulse chase experiments were conducted to follow the biogenesis of wild type and mutated EFEMP1 in transfected RPE-J cells. Results: Both wild type and mutated EFEMP1 are 55-kDa secreted proteins. However, the mutant accumulates within the cell and is secreted ≷5 fold less efficiently than the wild type protein. Under non-reduced conditions, the mutant migrates faster than wild type EFEMP1, indicating improperly formed disulfide bonds in the mutant which alter the protein conformation. Based on in situ hybridization, RPE, photoreceptors, and numerous other retinal and choroidal cell types produce EFEMP1 mRNA. When examined by immunohistochemistry, EFEMP1 protein was found predominantly in the interphotoreceptor matrix and the nerve fiber layer but not in the choroid or Bruch's membrane of normal human, pig, and rat eyes. In a donor eye from a ML patient homozygous for the R345W mutation, EFEMP1 was found to accumulate within and beneath the RPE cells but not through the complete thickness of sub-RPE deposits. Conclusion: EFEMP1 is a secreted protein not present at the site of drusen formation in healthy retina and is not a major component of drusen associated with ML. The R345W mutation promotes the aberrant accumulation of EFEMP1 within and beneath the RPE cell, suggesting that mutated EFEMP1 is involved in drusen formation through the impairment of trafficking between Bruch's membrane and RPE cells and/or within RPE cells.
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