RFUVA catalyzes cross-linking reactions that require production of singlet oxygen ((1)O(2)), whose half-life is extended by D(2)O. Carbonyl-based cross-linking reactions dominate in the corneal stroma, but other possible reaction schemes are proposed. The use of D(2)O as solution media for RF would enable concentration decreases or significant strength enhancement in treated corneas.

Left ventricular mass (LVM) and cardiac gene expression are complex traits regulated by factors both intrinsic and extrinsic to the heart. To dissect the major determinants of LVM, we combined expression quantitative trait locus1 and quantitative trait transcript2 (QTT) analyses of the cardiac transcriptome in the rat. Using these methods and in vitro functional assays, we identified osteoglycin (Ogn) as a major candidate regulator of rat LVM, with increased Ogn protein expression associated with elevated LVM. We also applied genome-wide QTT analysis to the human heart and observed that, out of ~22,000 transcripts, OGN transcript abundance had the © 2008 Nature Publishing Group Correspondence should be addressed to T.J.A. (t.aitman@csc.mrc.ac.uk) or S.A.C. (stuart.cook@imperial.ac.uk).. 11 These authors contributed equally to this work. AUTHOR CONTRIBUTIONS The study was designed by S.A.C., E.P. and T.J.A.; S.A.C. obtained funding, supervised the study and coordinated the collaborations; R.S. performed PCR-based experiments and genotyping; H.L. and M.K.K. generated rat microarray data; B.S. and Y.M.P. generated human microarray data; M.B. generated immunofluorescence confocal micrographs; R.S. and H.L. performed cell culture and cloning experiments; R.S., B.S. and M.B. performed immunoblotting; P.J.M. and R.S. performed in vivo analyses in Ogn knockout mice; E.S.T., L.M.C., M.D.W. and G.W.C. provided and genotyped the Ogn knockout mice; N.H. and J.F. carried out sequence analysis of Ogn; T.W.K., V.K. and M.P. provided telemetric blood pressure data; P.P.P. provided human tissues for protein studies; S.K.P., D.J.P. and C.K. provided the human cardiac MRI data; E.P. designed, interpreted and supervised all statistical analyses; E.P., I.G. and R.S. performed statistical and bioinformatic analyses and were aided by J.M.; and E.P. and S.A.C. wrote the manuscript.Note: Supplementary information is available on the Nature Genetics website.Reprints and permissions information is available online at http://npg.nature.com/reprintsandpermissions Europe PMC Funders GroupAuthor Manuscript Nat Genet. Author manuscript; available in PMC 2009 September 11. Elevated indexed LVM is a major cause of morbidity and mortality and is regulated, in part, by hemodynamic indices3. However, only a small proportion of LVM variation is determined by hemodynamic effects4, and it has been proposed that genetic influences may also be important5,6. Many studies have shown that gene expression is heritable and that the genetic control of transcription affects physiological traits and disease phenotypes1,7. We have shown that gene transcription is highly heritable in the rat heart8, which led us to hypothesize that the genetic control of cardiac gene expression may be important in regulating LVM. Here, we used an integrated approach combining correlation of expression quantitative trait loci (eQTL)1 and genome-wide expression profiles with physiological traits, previously designated as quantitative trait transcript (QTT) analysis2, to ide...

Bovine cornea contains three unique keratan sulfate proteoglycans (KSPGs), of which two (lumican and keratocan) have been characterized using molecular cloning. The gene for the third protein (KSPG25) has not been identified. This study examined the relationship between the KSPG25 protein and the gene for osteoglycin, a 12-kDa bone glycoprotein. The N-terminal amino acid sequence of KSPG25 occurs in osteoglycin cDNA cloned from bovine cornea. The osteoglycin amino acid sequence makes up the C-terminal 47% of the deduced sequence of the KSPG25 protein. Antibodies to osteoglycin reacted with intact corneal KSPG, with KSPG25 protein, and with a 36-kDa protein, distinct from lumican and keratocan. KSPG25-related proteins, not modified with keratan sulfate, were also detected in several connective tissues. Northern blot analysis showed mRNA transcripts of 2.4, 2.5, and 2.6 kilobases in numerous tissues with the 2.4-kilobase transcript enriched in ocular tissues. Ribonuclease protection analysis detected several protected KSPG25 mRNA fragments, suggesting alternate splicing of KSPG25 transcripts. We conclude that the full-length translation product of the gene producing osteoglycin is a corneal keratan sulfate proteoglycan, also present in many non-corneal tissues without keratan sulfate chains. The multiple size protein products of this gene appear to result from in situ proteolytic processing and/or alternative splicing of mRNA. The name mimecan is proposed for this gene and its products.The corneal stroma of vertebrate organisms contains a unique class of molecules, corneal keratan sulfate proteoglycans (KSPGs), 1 consisting of several related proteins each bearing keratan sulfate. The specialized nature of corneal proteoglycans was recognized almost 60 years ago with the initial description of keratan sulfate, the most abundant glycosaminoglycan in cornea (1). Corneal keratan sulfate is a highly sulfated, linear polymer of N-acetyllactosamine, linked to asparagine residues in the KSPG core proteins (2). The unusual abundance of keratan sulfate in the cornea and studies of heritable metabolic diseases suggest that the KSPG molecules are essential in maintenance of corneal transparency (3, 4). Understanding the role of the KSPGs in corneal transparency, their interactions with cells and other matrix molecules, and the tissue-specific nature of their biosynthesis requires complete knowledge of their structure. Although we have excellent information regarding the carbohydrate components of the KSPGs, the core proteins as representatives of the primary KSPG gene products are still not fully understood.Research from our laboratory has shown that keratan sulfate is attached to three unique proteins in bovine cornea (5, 6). The cDNAs for two of these proteins, keratocan and lumican (originally designated 37A and 37B), have been cloned and sequenced (7,8). A third 25-kDa KSPG core protein, KSPG25, was recognized as unique from lumican and keratocan, but its primary sequence is not yet known. The deduced amino acid sequence...

Corneal cross-linking using riboflavin and ultraviolet-A (RFUVA) is a clinical treatment targeting the stroma in progressive keratoconus. The stroma contains keratocan, lumican, mimecan, and decorin, core proteins of major proteoglycans (PGs) that bind collagen fibrils, playing important roles in stromal transparency. Here, a model reaction system using purified, non-glycosylated PG core proteins in solution in vitro has been compared with reactions inside an intact cornea, ex vivo, revealing effects of RFUVA on interactions between PGs and collagen cross-linking. Irradiation with UVA and riboflavin cross-links collagen ␣ and ␤ chains into larger polymers. In addition, RFUVA cross-links PG core proteins, forming higher molecular weight polymers. When collagen type I is mixed with individual purified, non-glycosylated PG core proteins in solution in vitro and subjected to RFUVA, both keratocan and lumican strongly inhibit collagen cross-linking. However, mimecan and decorin do not inhibit but instead form cross-links with collagen, forming new high molecular weight polymers. In contrast, corneal glycosaminoglycans, keratan sulfate and chondroitin sulfate, in isolation from their core proteins, are not cross-linked by RFUVA and do not form cross-links with collagen. Significantly, when RFUVA is conducted on intact corneas ex vivo, both keratocan and lumican, in their natively glycosylated form, do form cross-links with collagen. Thus, RFUVA causes cross-linking of collagen molecules among themselves and PG core proteins among themselves, together with limited linkages between collagen and keratocan, lumican, mimecan, and decorin. RFUVA as a diagnostic tool reveals that keratocan and lumican core proteins interact with collagen very differently than do mimecan and decorin.The cornea is the transparent, dome-shaped tissue covering the front of the eye. It is a powerful refracting surface, providing 65-75% of the eye's focusing power, and is made up of three distinct layers: epithelium, stroma, and endothelium. The stroma comprises about 90% of cornea thickness in humans (1).Although it is very highly innervated, it does not contain any blood vessels (2-4). Collagen gives the cornea its strength, elasticity, and form (5). The unique molecular shape, paracrystalline arrangement, and very regular fine diameter of the evenly spaced collagen fibrils are essential in producing a transparent cornea (6, 7).In the corneal stromal extracellular matrix, glycosaminoglycan (GAG) 2 polysaccharides are the most abundant negatively charged macromolecules and are classified on the basis of their repeating disaccharide structures into four main groups: keratan sulfate (KS), chondroitin sulfate/dermatan sulfate (CS/DS), heparan sulfate and heparin, and hyaluronan. Glycosaminoglycans, normally covalently attached to proteoglycan (PG) core proteins, play important roles in corneal transparency, nerve growth cone guidance, and cell adhesion, largely dependent on their patterns of sulfation or lack of it (8, 9). The corneal stroma is comp...

Lumican is one of the major keratan sulfate proteoglycans (KSPG) in vertebrate corneas. We previously cloned the murine lumican cDNA. This study determines the structure of murine lumican gene (Lum) and its expression during mouse embryonic developments. The mouse lumican gene was isolated from a bacterial artificial chromosome mouse genomic DNA library and characterized by polymerase chain reaction and Southern hybridization. The lumican gene spans 6.9 kilobase pairs of mouse genome. The gene consists of three exons and two introns. Exon 1 constitutes 88 bases (b) of untranslated sequence. Exon 2 is 883 b and contains most of the coding sequence of lumican mRNA, and exon 3 has 152 b of coding sequence and 659 b of 3 noncoding sequence. The mouse lumican gene has a TATCA element, a presumptive TATA box, which locates 27 b 5-upstream from the transcription initiation site. Northern hybridization and in situ hybridization indicate that in early stages of embryonic development, day 7 post coitus the embryo expresses little or no lumican. Thereafter, different levels of lumican mRNA can be detected in various organ systems, such as cornea stroma, dermis, cartilage, heart, lung, and kidney. The cornea and heart are the two tissues that have the highest expression in adult. Immunoblotting studies found that KSPG core proteins became abundant in the cornea and sclera by postnatal day 10 but that sulfated KSPG could not be detected until after the eyes open. These results indicate that lumican is widely distributed in most interstitial connective tissues. The modification of lumican with keratan sulfates in cornea is concurrent with eye opening and may contribute to corneal transparency.Corneal strength and transparency depend upon the development and maintenance of an organized extracellular matrix, including uniformly small diameter collagen fibrils with lamellae of consistent interfibrillar spacing. The collagen fibrils of adjacent lamella sheets are perpendicular to one another (1, 2).The mechanism that governs the formation of collagen lamellae in cornea stroma is not well understood. It has been suggested, however, that the ratios of different collagen types in making up the fibrillar corneal collagen and other extracellular specialized matrix components, e.g. proteoglycans and glycoprotein are essential for the development of a transparent cornea (1,(3)(4)(5)(6)(7)(8). In addition to interaction with collagen fibrils, proteoglycans in stroma also play a role in corneal hydration due to their high negative charge of sulfated carbohydrate moieties (9 -11).The hydrophilic properties of the stroma result from stromal proteoglycans that constitute the second most abundant biological materials in stroma, after collagen (12, 13). The keratan sulfate proteoglycans (KSPGs) 1 are uniquely abundant in the cornea, constituting the major proteoglycans of the corneal stroma. Currently, three corneal KSPG core proteins have been identified, i.e. keratocan, lumican, and mimican (osteoglycin), which were previously designated 3...