Identification of LOXL1 protein and Apolipoprotein E as components of surgically isolated pseudoexfoliation material by direct mass spectrometry.
Pseudoexfoliation (PEX) syndrome is the commonest cause of secondary glaucoma. Many extracellular matrix proteins and elastic fibre structure components are present in the pathological PEX deposits in the anterior segment of the eye including the anterior lens capsule. Common coding variants in the lysyl oxidase-like 1 (LOXL1) gene, involved in cross-linking elastin, have been reported to be strongly associated with PEX syndrome in various human populations. The mechanism by which the LOXL1 protein contributes to the formation of PEX material is unknown. A comprehensive map of the component proteins of PEX deposits can aid the understanding of disease pathogenesis. The purpose of this study was to identify additional protein constituents of pathological PEX deposits. We employed a novel proteomics approach by performing mass spectrometry on "isolated" PEX material surgically removed from the anterior lens capsule of affected eyes. This approach led to the identification of LOXL1 protein and Apolipoprotein E (ApoE) in PEX material. Previously identified protein constituents, latent-transforming growth factor beta-binding protein-2, complement 3 and clusterin were also detected. Immunohistochemical analysis of lens capsules from affected eyes confirmed the presence of both LOXL1 and ApoE in pathological PEX deposits. ApoE is a novel component of these deposits. This is the first report where a direct analytical approach has led to the identification of LOXL1 in PEX deposits and is consistent with its detection in these deposits by immunolabelling in another recent report. LOXL1 is both genetically associated with PEX syndrome and present in pathological PEX deposits. Hence it clearly has an important and direct role in pathophysiology of the disease. In conclusion, additional as yet unknown components are present in pathological PEX deposits and mass spectrometry of "isolated" PEX material is an effective strategy for their identification.
Sharma
Shiwani
S
Department of Ophthalmology, Flinders University, Bedford Park, South Australia 5042, Australia. shiwani.sharma@flinders.edu.au
Chataway
Tim
T
Burdon
Kathryn P
KP
Jonavicius
Lisa
L
Klebe
Sonja
S
Hewitt
Alex W
AW
Mills
Richard A
RA
Craig
Jamie E
JE
D000368:Aged; D000369:Aged, 80 and over; D000594:Amino Acid Oxidoreductases / Q000737:chemistry / Q000378:metabolism*; D000595:Amino Acid Sequence; D001057:Apolipoproteins E / Q000737:chemistry / Q000378:metabolism*; D017889:Exfoliation Syndrome / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000378:metabolism*; D005136:Eye Proteins / Q000378:metabolism*; D005260:Female; D006801:Humans; D007124:Immunoenzyme Techniques; D007903:Lens Capsule, Crystalline / Q000378:metabolism; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D053719:Tandem Mass Spectrometry
D001057:Apolipoproteins E; D016326:Extracellular Matrix Proteins; D005136:Eye Proteins; D010446:Peptide Fragments; D000594:Amino Acid Oxidoreductases; C445313:LOXL1 protein, human