Abstract
Purpose:
Fibulin 5 is an extracellular matrix protein which promotes adhesion of endothelial cells through interaction of integrins. Missense variations in the gene which encodes Fibulin 5 (FBLN5) have been associated with age-related macular degeneration (AMD) and the characteristic formation of cuticular drusen (1). A patient presented to Southampton Eye Unit with AMD. Due to the presence of distinct small circular drusen the patient was screened for single nucleotide polymorphisms (SNPs) in FBLN5 by single-strand conformation polymorphism. 2 SNPs were identified in exon 4 of FBLN5, one of which was non-synonymous (Gln-124-Pro). The patient was followed for 10 years until death. Whereupon the patient’s eyes were donated for research.
Methods:
Optical coherence tomography and fundus imaging were carried out to monitor AMD progression. Immunohistochemistry and western blotting were performed for Fibulin 5 (Santa Cruz Biotechnology, Inc.) and Elastin (Elastin Products Company, Inc.), to determine if there were differences in expression between the central and peripheral regions of the RPE/choroid and retina.
Results:
Retinal imaging demonstrated soft and cuticular drusen which did not progress significantly over time. As quantified by western blot analysis there was significantly more Fibulin 5 expression in the central versus peripheral RPE/choroid (p=0.019) and also in the RPE/choroid compared to the retina (p=0.034). This is consistent with immunocytochemical staining intensity and with previously published results (2). Elastin expression was reduced in the retina compared to the RPE/choroid however this did not reach significance. An increase in elastin expression was observed in the peripheral RPE/choroid when compared to the macula region. This was in agreement with immunocytochemical staining.
Conclusions:
Fibulin 5 has a diverse range of interactions, including integrin binding and elastinogenesis. The Gln-124-Pro missense mutation has been significantly associated with decreased Fibulin 5 secretion, with a possible corresponding reduction in elastinogenesis (3). Disruption of the elastic tissue of Bruch’s membrane observed in this patient may have contributed to the phenotype of discrete sub-RPE deposits observed clinically. 1) Stone EM et al. N Engl J Med. 2004 351(4):346 2) Mullins RF et al. Exp Eye Res. 2007 84(2):378 3) Lotery AJ et al. Hum Mutat. 2006 27(6):568
Keywords: 412 age-related macular degeneration •
519 extracellular matrix •
659 protein structure/function