Interaction of lumican with aggrecan in the aging human sclera.
OBJECTIVE
Lumican is a keratan sulfate proteoglycan originally identified in cornea, but present in a variety of connective tissues where it presumably regulates collagen fibril formation and organization. The present study was designed to describe the chemical nature of lumican core protein in the aging human sclera.


METHODS
Western blot analyses, immunohistochemistry, and immunoaffinity chromatography were used to detect and purify the lumican core protein from tissue extracts from human donors 6 to 89 years of age. Treatment of lumican with chondroitinase ABC, keratanase-I and -II, and/or endo-beta-galactosidase was used to determine the degree of glycosylation of the lumican core protein.


RESULTS
Lumican was present in the human sclera as a 70- to 80-kDa core protein with short unsulfated lactosaminoglycan side chains. In addition, on Western blots, a larger >200-kDa species was apparent that was immunologically related to lumican. This high-molecular-weight material increased in scleral extracts with increasing age. The complex was most abundant in unreduced samples, and approximately two thirds of the 70- to 80-kDa lumican core protein was released from the complex on reduction of the scleral extract. Further characterization of the >200-kDa lumican-immunopurified complex indicated that aggrecan (the cartilage proteoglycan) was covalently associated with lumican.


CONCLUSIONS
Reducible and nonreducible lumican-aggrecan interactions occur in the scleral extracellular matrix and result in the formation of high-molecular-weight complexes that increase with age. These results represent the first report demonstrating lumican-aggrecan interactions and suggest they may play a role in age-related scleral extracellular matrix changes.
Dunlevy
Jane R
JR
Department of Anatomy and Cell Biology, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58203, USA. jdunlevy@medicine.nodak.edu
Rada
Jody A Summers
JA
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D053674:Aggrecans; D000375:Aging / Q000502:physiology*; D015153:Blotting, Western; D002648:Child; D011508:Chondroitin Sulfate Proteoglycans / Q000302:isolation & purification / Q000378:metabolism*; D002846:Chromatography, Affinity; D005109:Extracellular Matrix / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000302:isolation & purification / Q000378:metabolism*; D006031:Glycosylation; D006801:Humans; D007124:Immunoenzyme Techniques; D007632:Keratan Sulfate / Q000302:isolation & purification / Q000378:metabolism*; D037181:Lectins, C-Type; D000071234:Lumican; D008875:Middle Aged; D008970:Molecular Weight; D011509:Proteoglycans / Q000302:isolation & purification / Q000378:metabolism*; D012590:Sclera / Q000378:metabolism*
D053674:Aggrecans; D011508:Chondroitin Sulfate Proteoglycans; D016326:Extracellular Matrix Proteins; C000604306:LUM protein, human; D037181:Lectins, C-Type; D000071234:Lumican; D011509:Proteoglycans; D007632:Keratan Sulfate