Altered fine structures of corneal and skeletal keratan sulfate and chondroitin/dermatan sulfate in macular corneal dystrophy

The role of corneal endothelium in macular corneal dystrophy development and recurrence

Macular corneal dystrophy (MCD) is a progressive, bilateral stromal dystrophic disease that arises from mutations in carbohydrate sulfotransferase 6 (CHST6). Corneal transplantation is the ultimate therapeutic solution for MCD patients. Unfortunately, postoperative recurrence remains a significant challenge. We conducted a retrospective review of a clinical cohort comprising 102 MCD patients with 124 eyes that underwent either penetrating keratoplasty (PKP) or deep anterior lamellar keratoplasty (DALK). Our results revealed that the recurrence rate was nearly three times higher in the DALK group (39.13%, 9/23 eyes) compared with the PKP group (10.89%, 11/101 eyes), suggesting that surgical replacement of the corneal endothelium for treating MCD is advisable to prevent postoperative recurrence. Our experimental data confirmed the robust mRNA and protein expression of CHST6 in human corneal endothelium and the rodent homolog CHST5 in mouse endothelium. Selective knockdown of wild-type Chst5 in mouse corneal endothelium (ACsiChst5), but not in the corneal stroma, induced experimental MCD with similar extracellular matrix synthesis impairments and corneal thinning as observed in MCD patients. Mice carrying Chst5 point mutation also recapitulated clinical phenotypes of MCD, along with corneal endothelial abnormalities. Intracameral injection of wild-type Chst5 rescued the corneal impairments in ACsiChst5 mice and retarded the disease progression in Chst5 mutant mice. Overall, our study provides new mechanistic insights and therapeutic approaches for MCD treatment by high-lighting the role of corneal endothelium in MCD development.

Tissue-specific expression of carbohydrate sulfotransferases drives keratan sulfate biosynthesis in the notochord and otic vesicles of Xenopus embryos

Keratan sulfate (KS) is a glycosaminoglycan that is enriched in vertebrate cornea, cartilage, and brain. During embryonic development, highly sulfated KS (HSKS) is first detected in the developing notochord and then in otic vesicles; therefore, HSKS has been used as a molecular marker of the notochord. However, its biosynthetic pathways and functional roles in organogenesis are little known. Here, I surveyed developmental expression patterns of genes related to HSKS biosynthesis in Xenopus embryos. Of these genes, the KS chain-synthesizing glycosyltransferase genes, beta-1,3-N-acetylglucosaminyltransferase (b3gnt7) and beta-1,4-galactosyltransferase (b4galt4), are strongly expressed in the notochord and otic vesicles, but also in other tissues. In addition, their notochord expression is gradually restricted to the posterior end at the tailbud stage. In contrast, carbohydrate sulfotransferase (Chst) genes, chst2, chst3, and chst5.1, are expressed in both notochord and otic vesicles, whereas chst1, chst4/5-like, and chst7 are confined to otic vesicles. Because the substrate for Chst1 and Chst3 is galactose, while that for others is N-acetylglucosamine, combinatorial, tissue-specific expression patterns of Chst genes should be responsible for tissue-specific HSKS enrichment in embryos. As expected, loss of function of chst1 led to loss of HSKS in otic vesicles and reduction of their size. Loss of chst3 and chst5.1 resulted in HSKS loss in the notochord. These results reveal that Chst genes are critical for HSKS biosynthesis during organogenesis. Being hygroscopic, HSKS forms “water bags” in embryos to physically maintain organ structures. In terms of evolution, in ascidian embryos, b4galt and chst-like genes are also expressed in the notochord and regulate notochord morphogenesis. Furthermore, I found that a chst-like gene is also strongly expressed in the notochord of amphioxus embryos. These conserved expression patterns of Chst genes in the notochord of chordate embryos suggest that Chst is an ancestral component of the chordate notochord.

Human theca arises from ovarian stroma and is comprised of three discrete subtypes

Theca cells serve multiple essential functions during the growth and maturation of ovarian follicles, providing structural, metabolic, and steroidogenic support. While the function of theca during folliculogenesis is well established, their cellular origins and the differentiation hierarchy that generates distinct theca sub-types, remain unknown. Here, we performed single cell multi-omics analysis of primary cell populations purified from human antral stage follicles (1-3 mm) to define the differentiation trajectory of theca/stroma cells. We then corroborated the temporal emergence and growth kinetics of defined theca/stroma subpopulations using human ovarian tissue samples and xenografts of cryopreserved/thawed ovarian cortex, respectively. We identified three lineage specific derivatives termed structural, androgenic, and perifollicular theca cells, as well as their putative lineage-negative progenitor. These findings provide a framework for understanding the differentiation process that occurs in each primordial follicle and identifies specific cellular/molecular phenotypes that may be relevant to either diagnosis or treatment of ovarian pathologies.

Potential of Biofermentative Unsulfated Chondroitin and Hyaluronic Acid in Dermal Repair

Chondroitin obtained through biotechnological processes (BC) shares similarities with both chondroitin sulfate (CS), due to the dimeric repetitive unit, and hyaluronic acid (HA), as it is unsulfated. In the framework of this experimental research, formulations containing BC with an average molecular size of about 35 KDa and high molecular weight HA (HHA) were characterized with respect to their rheological behavior, stability to enzymatic hydrolysis and they were evaluated in different skin damage models. The rheological characterization of the HHA/BC formulation revealed a G’ of 92 ± 3 Pa and a G″ of 116 ± 5 Pa and supported an easy injectability even at a concentration of 40 mg/mL. HA/BC preserved the HHA fraction better than HHA alone. BTH was active on BC alone only at high concentration. Assays on scratched keratinocytes (HaCaT) monolayers showed that all the glycosaminoglycan formulations accelerated cell migration, with HA/BC fastening healing 2-fold compared to the control. In addition, in 2D HaCaT cultures, as well as in a 3D skin tissue model HHA/BC efficiently modulated mRNA and protein levels of different types of collagens and elastin remarking a functional tissue physiology. Finally, immortalized human fibroblasts were challenged with TNF-α to obtain an in vitro model of inflammation. Upon HHA/BC addition, secreted IL-6 level was lower and efficient ECM biosynthesis was re-established. Finally, co-cultures of HaCaT and melanocytes were established, showing the ability of HHA/BC to modulate melanin release, suggesting a possible effect of this specific formulation on the reduction of stretch marks. Overall, besides demonstrating the safety of BC, the present study highlights the potential beneficial effect of HHA/BC formulation in different damage dermal models.

Medium-Term Clinical Outcomes of Deep Anterior Lamellar Keratoplasty versus Penetrating Keratoplasty for Macular Corneal Dystrophy

Purpose

To compare the postoperative outcomes of deep anterior lamellar keratoplasty (DALK) and penetrating keratoplasty (PKP) for macular corneal dystrophy (MCD).

Design

Single-center, retrospective, interventional case series.

Methods

A chart review was performed of 100 patients (157 eyes) who underwent primary DALK (DALK group) and PKP (PKP group) for histopathologically confirmed MCD for whom at least 12 months of follow-up were available. Between-group comparisons were performed of visual acuity (VA), graft survival, and postoperative complications.

Results

There were 22 eyes in the DALK group and 135 in the PKP group. Postoperative best-corrected visual acuity (BCVA) of 20/40 or better was achieved in 90.9% of the DALK group and 76.3% of the PKP group (P=0.12). At last visit, graft survival was 95.5% (21 eyes) and 91.1% (123 eyes) in DALK and PKP groups, respectively (P=0.69, Log rank test). Corneal graft rejection episodes occurred in 1 (4.5%) DALK graft and 19 (14.1%) PKP grafts. Five of the 19 graft rejections in the PKP group were irreversible. Microbial keratitis and cataract occurred in 6 (4.5%) and 15 (11.1%) PKP eyes. One (4.5%) eye in the DALK group had cataract and none of the DALK cases developed microbial keratitis. Clinically significant recurrence was observed in 4 (2.9%) PKP eyes and 1 (4.5%) DALK eye (P=0.69), respectively.

Conclusion

DALK is a viable option for MCD without Descemet membrane involvement. DALK had comparable medium-term visual and survival outcomes to PKP. DALK has the advantage of lower open sky intraoperative complications and lower graft rejection episodes.

Mendelian randomization analysis identified genes pleiotropically associated with central corneal thickness

OBJECTIVE

To prioritize genes that were pleiotropically or potentially causally associated with central corneal thickness (CCT).

METHODS

We applied the summary data-based Mendelian randomization (SMR) method integrating summarized data of genome-wide association study (GWAS) on CCT and expression quantitative trait loci (eQTL) data to identify genes that were pleiotropically associated with CCT. We performed separate SMR analysis using CAGE eQTL data and GTEx eQTL data. SMR analyses were done for participants of European and East Asian ancestries, separately.

RESULTS

We identified multiple genes showing pleiotropic association with CCT in the participants of European ancestry. CLIC3 (ILMN_1796423; PSMR = 4.15 × 10- 12), PTGDS (ILMN_1664464; PSMR = 6.88 × 10- 9) and C9orf142 (ILMN_1761138; PSMR = 8.09 × 10- 9) were the top three genes using the CAGE eQTL data, and RP11-458F8.4 (ENSG00000273142.1; PSMR = 5.89 × 10- 9), LCNL1 (ENSG00000214402.6; PSMR = 5.67 × 10- 8), and PTGDS (ENSG00000107317.7; PSMR = 1.92 × 10- 7) were the top three genes using the GTEx eQTL data. No genes showed significantly pleiotropic association with CCT in the participants of East Asian ancestry after correction for multiple testing.

CONCLUSION

We identified several genes pleiotropically associated with CCT, some of which represented novel genes influencing CCT. Our findings provided important leads to a better understanding of the genetic factors influencing CCT, and revealed potential therapeutic targets for the treatment of primary open-angle glaucoma and keratoconus.

Extracellular Matrix Deposition and Remodeling after Corneal Alkali Burn in Mice

Corneal transparency relies on the precise arrangement and orientation of collagen fibrils, made of mostly Type I and V collagen fibrils and proteoglycans (PGs). PGs are essential for correct collagen fibrillogenesis and maintaining corneal homeostasis. We investigated the spatial and temporal distribution of glycosaminoglycans (GAGs) and PGs after a chemical injury. The chemical composition of chondroitin sulfate (CS)/dermatan sulfate (DS) and heparan sulfate (HS) were characterized in mouse corneas 5 and 14 days after alkali burn (AB), and compared to uninjured corneas. The expression profile and corneal distribution of CS/DSPGs and keratan sulfate (KS) PGs were also analyzed. We found a significant overall increase in CS after AB, with an increase in sulfated forms of CS and a decrease in lesser sulfated forms of CS. Expression of the CSPGs biglycan and versican was increased after AB, while decorin expression was decreased. We also found an increase in KS expression 14 days after AB, with an increase in lumican and mimecan expression, and a decrease in keratocan expression. No significant changes in HS composition were noted after AB. Taken together, our study reveals significant changes in the composition of the extracellular matrix following a corneal chemical injury.

Distribution and Function of Glycosaminoglycans and Proteoglycans in the Development, Homeostasis and Pathology of the Ocular Surface

The ocular surface, which forms the interface between the eye and the external environment, includes the cornea, corneoscleral limbus, the conjunctiva and the accessory glands that produce the tear film. Glycosaminoglycans (GAGs) and proteoglycans (PGs) have been shown to play important roles in the development, hemostasis and pathology of the ocular surface. Herein we review the current literature related to the distribution and function of GAGs and PGs within the ocular surface, with focus on the cornea. The unique organization of ECM components within the cornea is essential for the maintenance of corneal transparency and function. Many studies have described the importance of GAGs within the epithelial and stromal compartment, while very few studies have analyzed the ECM of the endothelial layer. Importantly, GAGs have been shown to be essential for maintaining corneal homeostasis, epithelial cell differentiation and wound healing, and, more recently, a role has been suggested for the ECM in regulating limbal stem cells, corneal innervation, corneal inflammation, corneal angiogenesis and lymphangiogenesis. Reports have also associated genetic defects of the ECM to corneal pathologies. Thus, we also highlight the role of different GAGs and PGs in ocular surface homeostasis, as well as in pathology.

Progress in Corneal Stromal Repair: From Tissue Grafts and Biomaterials to Modular Supramolecular Tissue-Like Assemblies

Corneal injuries and degenerative conditions have major socioeconomic consequences, given that in most cases, they result in blindness. In the quest of the ideal therapy, tissue grafts, biomaterials, and modular engineering approaches are under intense investigation. Herein, advancements and shortfalls are reviewed and future perspectives for these therapeutic strategies discussed.

A structural model for the in vivo human cornea including collagen-swelling interaction

A structural model of the in vivo cornea, which accounts for tissue swelling behaviour, for the three-dimensional organization of stromal fibres and for collagen-swelling interaction, is proposed. Modelled as a binary electrolyte gel in thermodynamic equilibrium, the stromal electrostatic free energy is based on the mean-field approximation. To account for active endothelial ionic transport in the in vivo cornea, which modulates osmotic pressure and hydration, stromal mobile ions are shown to satisfy a modified Boltzmann distribution. The elasticity of the stromal collagen network is modelled based on three-dimensional collagen orientation probability distributions for every point in the stroma obtained by synthesizing X-ray diffraction data for azimuthal angle distributions and second harmonic-generated image processing for inclination angle distributions. The model is implemented in a finite-element framework and employed to predict free and confined swelling of stroma in an ionic bath. For the in vivo cornea, the model is used to predict corneal swelling due to increasing intraocular pressure (IOP) and is adapted to model swelling in Fuchs' corneal dystrophy. The biomechanical response of the in vivo cornea to a typical LASIK surgery for myopia is analysed, including tissue fluid pressure and swelling responses. The model provides a new interpretation of the corneal active hydration control (pump-leak) mechanism based on osmotic pressure modulation. The results also illustrate the structural necessity of fibre inclination in stabilizing the corneal refractive surface with respect to changes in tissue hydration and IOP.

Biosynthesis of glycosaminoglycans: associated disorders and biochemical tests

Glycosaminoglycans (GAG) are long, unbranched heteropolymers with repeating disaccharide units that make up the carbohydrate moiety of proteoglycans. Six distinct classes of GAGs are recognized. Their synthesis follows one of three biosynthetic pathways, depending on the type of oligosaccharide linker they contain. Chondroitin sulfate, dermatan sulfate, heparan sulfate, and heparin sulfate contain a common tetrasaccharide linker that is O-linked to specific serine residues in core proteins. Keratan sulfate can contain three different linkers, either N-linked to asparagine or O-linked to serine/threonine residues in core proteins. Finally, hyaluronic acid does not contain a linker and is not covalently attached to a core protein. Most inborn errors of GAG biosynthesis are reported in small numbers of patients. To date, in 20 diseases, convincing evidence for pathogenicity has been presented for mutations in a total of 16 genes encoding glycosyltransferases, sulfotransferases, epimerases or transporters. GAG synthesis defects should be suspected in patients with a combination of characteristic clinical features in more than one connective tissue compartment: bone and cartilage (short long bones with or without scoliosis), ligaments (joint laxity/dislocations), and subepithelial (skin, sclerae). Some produce distinct clinical syndromes. The commonest laboratory tests used for this group of diseases are analysis of GAGs, enzyme assays, and molecular testing. In principle, GAG analysis has potential as a general first-line diagnostic test for GAG biosynthesis disorders.

Glycosaminoglycans in the human cornea: age-related changes

AIM

To investigate possible age-related changes in glycosaminoglycans (GAGs) in the human cornea. The substances today called GAGs were previously referred to as mucopolysaccharides.

METHODS

Samples of human cornea were taken from 12 younger (age 21 ± 1.2) and 12 older (age 72 ± 1.6) male subjects. Samples were weighed, homogenized, and used for biochemical and molecular analyses. All the quantitative results were statistically analyzed.

RESULTS

The human cornea appears to undergo age-related changes, as evidenced by our biochemical and molecular results. The total GAG and hyaluronic acid counts were significantly higher in the younger subjects than in the older subjects. The sulfated heavy GAGs, such as chondroitin, dermatan, keratan, and heparan sulfate, were lower in the younger subjects than in the older subjects.

DISCUSSION

GAGs of the human cornea undergo numerous age-related changes. Their quantity is significantly altered in the elderly in comparison with younger subjects. GAGs play an important role in age-related diseases of the human cornea.

Differentiating chondroitin sulfate glycosaminoglycans using collision-induced dissociation; uronic acid cross-ring diagnostic fragments in a single stage of tandem mass spectrometry

The stereochemistry of the hexuronic acid residues of the structure of glycosaminoglycans (GAGs) is a key feature that affects their interactions with proteins and other biological functions. Electron based tandem mass spectrometry methods, in particular electron detachment dissociation (EDD), have been able to distinguish glucuronic acid (GlcA) from iduronic acid (IdoA) residues in some heparan sulfate tetrasaccharides by producing epimer-specific fragments. Similarly, the relative abundance of glycosidic fragment ions produced by collision-induced dissociation (CID) or EDD has been shown to correlate with the type of hexuronic acid present in chondroitin sulfate GAGs. The present work examines the effect of charge state and degree of sodium cationization on the CID fragmentation products that can be used to distinguish GlcA and IdoA containing chondroitin sulfate A and dermatan sulfate chains. The cross-ring fragments (2,4)A(n) and (0,2)X(n) formed within the hexuronic acid residues are highly preferential for chains containing GlcA, distinguishing it from IdoA. The diagnostic capability of the fragments requires the selection of a molecular ion and fragment ions with specific ionization characteristics, namely charge state and number of ionizable protons. The ions with the appropriate characteristics display diagnostic properties for all the chondroitin sulfate and dermatan sulfate chains (degree of polymerization of 4-10) studied.

Mechanisms of self-organization for the collagen fibril lattice in the human cornea

The transparency of the human cornea depends on the regular lattice arrangement of the collagen fibrils and on the maintenance of an optimal hydration--the achievement of both depends on the presence of stromal proteoglycans (PGs) and their linear sidechains of negatively charged glycosaminoglycans (GAGs). Although the GAGs produce osmotic pressure by the Donnan effect, the means by which they exert positional control of the lattice is less clear. In this study, a theoretical model based on equilibrium thermodynamics is used to describe restoring force mechanisms that may control and maintain the fibril lattice and underlie corneal transparency. Electrostatic-based restoring forces that result from local charge density changes induced by fibril motion, and entropic elastic restoring forces that arise from duplexed GAG structures that bridge neighbouring fibrils, are described. The model allows for the possibility that fibrils have a GAG-dense coating that adds an additional fibril force mechanism preventing fibril aggregation. Swelling pressure predictions are used to validate the model with results showing excellent agreement with experimental data over a range of hydration from 30 to 200% of normal. The model suggests that the electrostatic restoring force is dominant, with the entropic forces from GAG duplexes being an order or more smaller. The effect of a random GAG organization, as observed in recent imaging, is considered in a dynamic model of the lattice that incorporates randomness in both the spatial distribution of GAG charge and the topology of the GAG duplexes. A striking result is that the electrostatic restoring forces alone are able to reproduce the image-based lattice distribution function for the human cornea, and thus dynamically maintain the short-range order of the lattice.

Simultaneous analysis of heparan sulfate, chondroitin/dermatan sulfates, and hyaluronan disaccharides by glycoblotting-assisted sample preparation followed by single-step zwitter-ionic-hydrophilic interaction chromatography

Glycosaminoglycans (GAGs) play important roles in cell adhesion and growth, maintenance of extracellular matrix (ECM) integrity, and signal transduction. To fully understand the biological functions of GAGs, there is a growing need for sensitive, rapid, and quantitative analysis of GAGs. The present work describes a novel analytical technique that enables high throughput cellular/tissue glycosaminoglycomics for all three families of uronic acid-containing GAGs, hyaluronan (HA), chondroitin sulfate (CS)/dermatan sulfate (DS), and heparan sulfate (HS). A one-pot purification and labeling procedure for GAG Δ-disaccharides was established by chemo-selective ligation of disaccharides onto high density hydrazide beads (glycoblotting) and subsequent labeling by fluorescence. The 17 most common disaccharides (eight comprising HS, eight CS/DS, and one comprising HA) could be separated with a single chromatography for the first time by employing a zwitter-ionic type of hydrophilic-interaction chromatography column. These novel analytical techniques were able to precisely characterize the glycosaminoglycome in various cell types including embryonal carcinoma cells and ocular epithelial tissues (cornea, conjunctiva, and limbus).

Electron tomography reveals multiple self-association of chondroitin sulphate/dermatan sulphate proteoglycans in Chst5-null mouse corneas

The spatial distribution of collagen fibrils in the corneal stroma is essential for corneal transparency and is primarily regulated by extrafibrillar proteoglycans, which are multi-functional polymers that interact with hybrid type I/V collagen fibrils. In order to understand more about proteoglycan organisation and collagen associations in the cornea, three-dimensional electron microscopy reconstructions of collagen-proteoglycan interactions in the anterior, mid and posterior stroma from a Chst5 knockout mouse, which lacks a keratan sulphate sulphotransferase, were obtained. Both longitudinal and transverse section show sinuous, oversized proteoglycans with near-periodic, orthogonal off-shoots. In many cases, these proteoglycans traverse over 400nm of interfibrillar space interconnecting over 10 collagen fibrils. The reconstructions suggest that multiple chondroitin sulphate/dermatan sulphate proteoglycans have aggregated laterally and, possibly, end-to-end, with orthogonal extensions protruding from the main electron-dense stained filament. We suggest possible mechanisms as to how sulphation differences may lead to this increase in aggregation of proteoglycans in the Chst5-null mouse corneal stroma and how this relates to proteoglycan packing in healthy corneas.

Knockout of ADAMTS5 does not eliminate cartilage aggrecanase activity but abrogates joint fibrosis and promotes cartilage aggrecan deposition in murine osteoarthritis models

To investigate the role of ADAMTS5 in murine osteoarthritis (OA), resulting from destabilization of the medial meniscus (DMM model) or from TGFb1 injection and enforced uphill treadmill running (TTR model). Wild-type (WT) and ADAMTS5-/- mice were subjected to either DMM or TTR and joints were evaluated for meniscal damage, cartilage changes, and fibrotic ingrowths from the joint margins. Cartilage lesions were quantified on an 8-point scoring system. Cartilage chondroitin sulfate (CS) content was evaluated by SafraninO staining and by quantitative electrophoresis (FACE). The abundance of aggrecan, versican, and specific aggrecanase-generated products was determined by Western analysis. Joint changes were similar for WT mice taken through either the DMM or the TTR model. ADAMTS5 ablation essentially eliminated cartilage erosion and fibrous overgrowth in both models. In the TTR model, ADAMTS5 ablation did not eliminate aggrecanase activity from the articular cartilage but blocked fibrosis and resulted in the accumulation of aggrecan in the articular cartilage. The cartilage protection provided by ADAMTS5 ablation in the mouse does not result from prevention of aggrecanase activity per se, but it appears to be due to a blockade of joint tissue fibrosis and a concomitant increase in cartilage aggrecan content.

Structural collagen alterations in macular corneal dystrophy occur mainly in the posterior stroma

PURPOSE

Collagen fibrils in the corneal stroma in macular corneal dystrophy, on average, are more closely spaced than in the normal cornea. This study was conducted to investigate if this occurs uniformly across the stroma or is more prevalent at certain stromal depths.

METHODS

Microbeam synchrotron X-ray fiber diffraction patterns were obtained in 25 microm steps across the whole thickness of a thin strip of a macular corneal dystrophy cornea obtained at keratoplasty. Data were analyzed for mean collagen interfibrillar spacing at all positions. Serum was analyzed immunochemically to determine immunophenotype, and transmission electron microscopy was carried out to visualize stromal ultrastructure.

RESULTS

Keratan sulphate was not detectable in blood serum, classifying the disease as macular corneal dystrophy type I. Collagen interfibrillar spacing dropped linearly with stromal depth from the anterior to posterior cornea, measuring 5-10% less in the posterior 100 microm of the MCD stroma compared to the anterior 100 microm (p < 0.001). Isolated pockets of collagen fibrils with unusually large diameters were identified in the deep stroma.

CONCLUSIONS

Collagen fibril spacing is reduced and large-diameter collagen fibrils are seen in macular corneal dystrophy type I, with the deep stroma affected more. We speculate that the ultrastructural abnormalities are more prevalent in the posterior stroma because the structural influence of sulphated keratan sulphate glycosaminoglycans/proteoglycans is high in this region of the cornea.

Localization and expression of CHST6 and keratan sulfate proteoglycans in the human cornea

Macular corneal dystrophy (MCD; OMIM 217800) is a rare autosomal recessive inherited disorder caused by mutations in the carbohydrate sulfotransferase 6 (CHST6) and characterised by the presence of unsulfated keratan sulfate proteoglycans (KSPGs) forming abnormal deposits that eventually lead to visual impairment. The aim of this study is to understand in which corneal cells CHST6 and KSPGs are expressed and exert their activity. Expression and localization of CHST6, keratan sulfate (KS) and proteins of the KSPGs, such as mimecan and lumican, were assessed both in human cornea sections and in cultured primary keratinocytes (n = 3) and keratocytes (n = 4). Immunohistochemistry, semiquantitative RT-PCR, in situ RNA hybridization and HPLC analysis of glycosaminoglycans were used as read-outs. In human corneas KS was predominantly found in the stroma, but absent, or barely detectable, in the corneal epithelium. A similar pattern of distribution was found in the epidermis, with KS mainly localised in the derma. As expected, in the cornea CHST6 (the gene encoding the enzyme which transfers sulfate residues onto KSPGs) was found expressed in the suprabasal, but not basal, layers of the epithelium, in the stroma and in the endothelium. Analyses of KS by means of HPLC showed that in vitro cultured stromal keratocytes express and secrete more KS than keratinocytes, thus mirroring results observed in vivo. Similarly expression of the CHST6 gene and of KS proteoglycans such as mimecan, lumican is limited to stromal keratocytes. Unlike keratocytes, corneal keratinocytes do not synthesize mimecan or lumican, and express very little, if none, CHST6. Any drug/gene therapy or surgical intervention aimed at curing this rare genetic disorder must therefore involve and target stromal keratocytes. If coupled to the accuracy of HPLC-based assay that we developed to determine the amount of KS in serum, our findings could lead to more targeted therapeutic treatments of the ocular features in MCD patients.

Proteomic analysis of potential keratan sulfate, chondroitin sulfate A, and hyaluronic acid molecular interactions

PURPOSE

Corneal stroma extracellular matrix (ECM) glycosaminoglycans (GAGs) include keratan sulfate (KS), chondroitin sulfate A (CSA), and hyaluronic acid (HA). Embryonic corneal keratocytes and sensory nerve fibers grow and differentiate according to chemical cues they receive from the ECM. This study asked which of the proteins that may regulate keratocytes or corneal nerve growth cone immigration interact with corneal GAGs.

METHODS

Biotinylated KS (bKS), CSA (bCSA), and HA (bHA) were prepared and used in microarray protocols to assess their interactions with 8268 proteins and a custom microarray of 85 extracellular epitopes of nerve growth-related proteins. Surface plasmon resonance (SPR) was performed with bKS and SLIT2, and their ka, kd, and KD were determined.

RESULTS

Highly sulfated KS interacted with 217 microarray proteins, including 75 kinases, several membrane or secreted proteins, many cytoskeletal proteins, and many nerve function proteins. CSA interacted with 24 proteins, including 10 kinases and 2 cell surface proteins. HA interacted with 6 proteins, including several ECM-related structural proteins. Of 85 ECM nerve-related epitopes, KS bound 40 proteins, including SLIT, 2 ROBOs, 9 EPHs, 8 Ephrins (EFNs), 8 semaphorins (SEMAs), and 2 nerve growth factor receptors. CSA bound nine proteins, including ROBO2, 2 EPHs, 1 EFN, two SEMAs, and netrin 4. HA bound no ECM nerve-related epitopes. SPR confirmed that KS binds SLIT2 strongly. The KS core protein mimecan/osteoglycin bound 15 proteins.

CONCLUSIONS

Corneal stromal GAGs bind, and thus could alter the availability or conformation of, many proteins that may influence keratocyte and nerve growth cone behavior in the cornea.

Structural and biochemical aspects of keratan sulphate in the cornea

Keratan sulphate (KS) is the predominant glycosaminoglycan (GAG) in the cornea of the eye, where it exists in proteoglycan (PG) form. KS-PGs have long been thought to play a pivotal role in the establishment and maintenance of the array of regularly-spaced and uniformly- thin collagen fibrils which make up the corneal stroma. This characteristic arrangement of fibrils allows light to pass through the cornea. Indeed, perturbations to the synthesis of KS-PG core proteins in genetically altered mice lead to structural matrix alterations and corneal opacification. Similarly, mutations in enzymes responsible for the sulphation of KS-GAG chains are causative for the inherited human disease, macular corneal dystrophy, which is manifested clinically by progressive corneal cloudiness starting in young adulthood.

High expression of osteoglycin decreases gelatinase activity of murine hepatocarcinoma Hca-F cells

AIM: To investigate the possible correlation between osteoglycin expression and gelatinase activity of mouse hepatocarcinoma Hca-F cells.

METHODS: A eukaryotic expression plasmid pIRESpuro3 osteoglycin(+) was constructed and transfected into Hca-F cells to investigate the possible correlation between osteoglycin expression and gelatinase activity of Hca-F cells cultured with extract of lymph node, liver, spleen or in DMEM medium. The activity of gelatinases was examined through zymographic analysis.

RESULTS: High expression of osteoglycin attenuated the gelatinase activity of Hca-F cells cultured with extract of lymph node, and at the same time, decreased the metastatic potential of Hca-F cells to peripheral lymph nodes in vivo.

CONCLUSION: High expression of osteoglycin decreases the gelatinase activity of Hca-F cells cultured with extract of lymph node; regulation of gelatinase activity might be one of mechanisms that osteoglycin contributes to lymphatic metastasis suppression.

Changes in the biochemical constituents and morphologic appearance of the human cervical stroma during pregnancy

OBJECTIVE

The cervix is the lower portion of the uterus. It is composed of fibrous tissue and its mechanical integrity is crucial for maintaining a healthy gestation. During normal pregnancy, the cervical extracellular matrix (ECM) remodels in preparation for labor. The objective of this study was to investigate the biochemical and morphological changes in cervical stroma associated with physiological remodeling during normal pregnancy.

STUDY DESIGN

Using human cervical tissue obtained from pregnant and non-pregnant patients, the ECM was analyzed for its biochemical constituents and histologic morphology. The ECM was assayed for hydration, collagen concentration, collagen solubility, total sulfated glycosaminoglycan concentration, and individual disaccharide concentration. The ECM morphology was visualized using conventional histological techniques (Masson's trichrome stain, polarized light microscopy) as well as second harmonic generation (SHG) imaging.

RESULTS

When comparing pregnant to non-pregnant tissue, significant increases were measured for total sulfated glycosaminoglycans, hyaluronic acid, and collagen solubility. The microscopy studies confirmed that the collagenous network of the cervical stroma was anisotropic and pregnancy was associated with a discernable decrease in collagen organization.

CONCLUSION

Significant changes were seen in the concentration and organization of cervical ECM constituents during normal pregnancy.

Decorin and its galactosaminoglycan chain: extracellular regulator of cellular function?

A molecular network of extracellular matrix molecules determines the tissue architecture and accounts for mechanical properties like compressibility or stretch resistance. It is widely accepted that the elements of the cellular microenvironment are important regulators of the cellular behavior in vitro and in vivo. One large group comprising these molecules is the family of proteoglycans. Both, the core proteins and, in particular, the attached galactosaminoglycans, contribute to the regulation network as they bind a variety of signaling molecules, e.g. cytokines, chemokines, growth, and differentiation factors. We would like to emphasize specific patterns of epimerization and sulfation within the galactosaminoglycans chains, because these result in "motifs" that are responsible for the modulation of signal factor binding, release and activity. This property is crucial in physiological and pathological conditions, for example development and wound healing.

Determination of beta4-galactosyltransferase-7 activity using high-performance liquid chromatography-electrospray ionization tandem mass spectrometry

OBJECTIVES

Patients with Ehlers-Danlos syndrome were described to contain reduced activities of beta4-galactosyltransferase-7 (beta4Gal-T7). Therefore, measurement of beta4Gal-T7 activity can help to characterize defects in proteoglycan biosynthesis in patients with connective tissue diseases.

DESIGN AND METHODS

We developed a sensitive and specific method to assay beta4Gal-T7 which is based on the transfer of galactose from UDP-galactose to the synthetic peptide Bio-BIK-F-Xyl.

RESULTS

Calibration curves exhibited consistent linearity in the range of 10-2000 microg/L Bio-BIK-F-Xyl-Gal, corresponding to a beta4Gal-T7 activity of 3.5-659 microU/L. The limit of detection and the lower limit of quantification were 3.70 microg/L (1.22 microU/L) and 4.50 microg/L Bio-BIK-F-Xyl-Gal (1.48 microU/L beta4Gal-T7 activity), respectively. Interassay imprecision (CV) was 8.1-13.1% in the range from 15.9 to 659 microU/L, and mean recovery was 85.3% (range 61.7-106.3%).

CONCLUSIONS

This sensitive, robust and interference-free LC-MS/MS assay allows an accurate determination of beta4Gal-T7 activity in human body fluids.

High expression of osteoglycin decreases the metastatic capability of mouse hepatocarcinoma Hca-F cells to lymph nodes

Osteoglycin, one of the matrix molecules, belongs to the small leucine-rich proteoglycan gene family and might play important roles in cell growth and differentiation and in pathological processes such as fibrosis and cancer growth. In this study, a eukaryotic expression plasmid pIRESpuro3 osteoglycin(+) was constructed and transfected into mouse hepatocarcinoma Hca-F cells to evaluate the contribution of osteoglycin to the malignant behavior of Hca-F. It was found that Hca-F cells transfected with pIRESpuro3 osteoglycin(+) showed significantly decreased potential for both migration and invasion. Furthermore, Hca-F cells transfected with osteoglycin showed decreased metastatic potential to peripheral lymph nodes. However, proliferation potential and adhesive capacity of Hca-F cells to different protein substrates were not influenced by osteoglycin transfection. In summary, high expression of osteoglycin decreases the metastatic capability of Hca-F to lymph nodes.

Mechanical and biochemical properties of human cervical tissue

The mechanical integrity of cervical tissue is crucial for maintaining a healthy gestation. Altered tissue biochemistry can cause drastic changes in the mechanical properties of the cervix and contribute to premature cervical dilation and delivery. We present an investigation of the mechanical and biochemical properties of cervical samples from human hysterectomy specimens. Three clinical cases were investigated: nonpregnant hysterectomy patients with previous vaginal deliveries; nonpregnant hysterectomy patients with no previous vaginal deliveries; and pregnant hysterectomy patients at time of cesarean section. Tissue samples were tested in confined compression, unconfined compression and tension. Cervical tissue samples for the three clinical cases were also subjected to biochemical analysis. Biochemical assays measured cervical tissue hydration, collagen content, collagen extractability and sulfated glycosaminoglycan (GAG) content. Results from the mechanical tests indicate that cervical stroma has a nonlinear, time-dependent stress response with varying degrees of conditioning and hysteresis depending on its obstetric background. It was found that the nonpregnant tissue was significantly stiffer than the pregnant tissue in both tension and compression. Further, collagen extractability, sulfated GAG content and hydration were substantially higher in the pregnant tissue. This study is the first important step towards the attainment of an improved understanding of the complex interplay between the molecular structure of cervical tissue and its macroscopic mechanical properties.

Autosomal recessive CHED associated with novel compound heterozygous mutations in SLC4A11

PURPOSE

To determine the genetic basis of autosomal recessive congenital hereditary endothelial dystrophy (CHED2) in an American patient of Chinese ancestry.

METHODS

Slit-lamp examination of the proband and his parents, as well as histopathologic examination of excised corneal specimens from the proband, were performed to confirm the diagnosis of autosomal recessive CHED. DNA was collected from the proband and his parents, and all 19 exons of the SLC4A11 gene were amplified and screened.

RESULTS

The proband showed diffuse bilateral corneal edema, which was not present in either of his parents. After the performance of bilateral penetrating keratoplasties, histopathologic examination of the excised corneal specimens showed marked corneal stromal edema and an absence of corneal endothelial cells. Screening of SLC4A11 showed 2 heterozygous mutations: c.743G>A (Ser232Asn) and c.1033A>T (Arg329X). The proband's mother was found to be heterozygous for the Ser232Asn missense mutation, and his father was heterozygous for the Arg329X nonsense mutation. No other coding region sequence variants were identified in the proband or his parents, and neither of the identified mutations was identified in 100 control individuals.

CONCLUSIONS

CHED2 is associated with mutations in SLC4A11, a member of the SLC4 family of base transporters. Although the majority of affected individuals reported to date have shown homozygous mutations, associated with consanguinity in the Burmese, Indian, and Pakistani populations, we report 2 novel, independently sorting SLC4A11 mutations in an affected individual of Chinese ancestry.

Effect of body temperature on chondroitinase ABC's ability to cleave chondroitin sulfate glycosaminoglycans

Chondroitinase ABC (Ch'ase ABC) is a bacterial lyase that degrades chondroitin sulfate (CS), dermatan sulfate, and hyaluronan glycosaminoglycans (GAGs). This enzyme has received significant attention as a potential therapy for promoting central nervous system and peripheral nervous system repair based on its degradation of CS GAGs. Determination of the stability of Ch'ase ABC activity at temperatures equivalent to normal (37 degrees C) and elevated (39 degrees C) body temperatures is important for optimizing its clinical usage. We report here data obtained from examining enzymatic activity at these temperatures across nine lots of commercially available protease-free Ch'ase ABC. CS GAG degrading activity was assayed by using 1) immunohistochemical detection of unsaturated disaccharide stubs generated by digestion of proteoglycans in tissue sections and 2) fluorophore-assisted carbohydrate electrophoresis (FACE) and/or high-performance liquid chromatography (HPLC) to separate and quantify unsaturated disaccharide digestion products. Our results indicate that there is a significant effect of lot and time on enzymatic thermostability. Average enzymatic activity is significantly decreased at 1 and 3 days at 39 degrees C and 37 degrees C, respectively. Furthermore, the average activity seen after 1 day was significantly different between the two temperatures. Addition of bovine serum albumin as a stabilizer significantly preserved enzymatic activity at 1 day, but not 3 days, at 39 degrees C. These results show that the CS GAG degrading activity of Ch'ase ABC is significantly decreased with incubation at body temperature over time and that all lots do not show equal thermostability. These findings are important for the design and interpretation of experimental and potential clinical studies involving Ch'ase ABC.

Multistage mass spectrometric sequencing of keratan sulfate-related oligosaccharides

To establish a universal protocol for sequencing keratan sulfate (KS) using mass spectrometry (MS), systematic electrospray ionization-MSn fragmentation experiments were carried out for 10 KS-related oligosaccharides of defined structure. Under the experimental conditions employed, fully charged molecular-related ions were observed as dominant peaks in all MS(1) spectra, which clearly reflected the number of sulfates and sialic acids in the oligosaccharide structures. In the subsequent MS2, almost all of the oligosaccharides gave fragment ions corresponding to their dehydrated molecular-related ions as well as (0,2)A(r) scission ions (according to the nomenclature developed by Domon and Costello, where "r" represents the reducing end in this study). Further fragmentation of the (0,2)A(r) ions in MS3 predominantly yielded the corresponding (2,4)A(r) ions. Finally, in MS(4), these (2,4)A(r) ions were subjected to extensive glycosidic cleavage. Hence, the MS4 data of KS oligosaccharides provided sufficient information for their sequence determination. In addition, some important features of MSn fragmentation became evident. These findings should lead to the establishment of consensus rules applied for KS oligosaccharides, including those previously unidentified, and also accelerate functional studies on KS, i.e., KS-related glycosaminoglycomics.

Carbohydrate post-glycosylational modifications

Carbohydrate modification is a common phenomenon in nature. Many carbohydrate modifications such as some epimerization, O-acetylation, O-sulfation, O-methylation, N-deacetylation, and N-sulfation, take place after the formation of oligosaccharide or polysaccharide backbones. These modifications can be categorized as carbohydrate post-glycosylational modifications (PGMs). Carbohydrate PGMs further extend the complexity of the structures and the synthesis of carbohydrates and glycoconjugates. They also increase the capacity of the biological regulation that is achieved by finely tuning the structures of carbohydrates. Developing efficient methods to obtain structurally defined naturally occurring oligosaccharides, polysaccharides, and glycoconjugates with carbohydrate PGMs is essential for understanding the biological significance of carbohydrate PGMs. Combined with high-throughput screening methods, synthetic carbohydrates with PGMs are invaluable probes in structure-activity relationship studies. We illustrate here several classes of carbohydrates with PGMs and their applications. Recent progress in chemical, enzymatic, and chemoenzymatic syntheses of these carbohydrates and their derivatives are also presented.

Matrix morphogenesis in cornea is mediated by the modification of keratan sulfate by GlcNAc 6-O-sulfotransferase

Matrix assembly and homeostasis in collagen-rich tissues are mediated by interactions with proteoglycans (PGs) substituted with sulfated glycosaminoglycans (GAGs). The major GAG in cornea is keratan sulfate (KS), which is N-linked to one of three PG core proteins. To ascertain the importance of the carbohydrate chain sulfation step in KS functionality, we generated a strain of mice with a targeted gene deletion in Chst5, which encodes an N-acetylglucosamine-6-O-sulfotransferase that is integral to the sulfation of KS chains. Corneas of homozygous mutants were significantly thinner than those of WT or heterozygous mice. They lacked high-sulfated KS, but contained the core protein of the major corneal KSPG, lumican. Histochemically stained KSPGs coassociated with fibrillar collagen in WT corneas, but were not identified in the Chst5-null tissue. Conversely, abnormally large chondroitin sulfate/dermatan sulfate PG complexes were abundant throughout the Chst5-deficient cornea, indicating an alteration of controlled PG production in the mutant cornea. The corneal stroma of the Chst5-null mouse exhibited widespread structural alterations in collagen fibrillar architecture, including decreased interfibrillar spacing and a more spatially disorganized collagen array. The enzymatic sulfation of KS GAG chains is thus identified as a key requirement for PG biosynthesis and collagen matrix organization.

Differential immunogold localisation of sulphated and unsulphated keratan sulphate proteoglycans in normal and macular dystrophy cornea using sulphation motif-specific antibodies

Keratan sulphate (KS) proteoglycans (PGs) are key molecules in the corneal stroma for tissue organisation and transparency. Macular corneal dystrophy (MCD) is a rare, autosomal recessive disease characterised by disturbances in KS expression. MCD is caused by mutations in CHST6, a gene encoding the enzyme responsible for KS sulphation. Sulphated KS is absent in type I disease causing corneal opacity and loss of vision. Genetic studies have highlighted the mutational heterogeneity in MCD, but supportive immunohistochemical studies on corneal KS have previously been limited by the availability of antibodies mostly reactive only with highly sulphated KS epitopes. In this study, we employed four antibodies against specific KS sulphation patterns, including one against unsulphated KS, to investigate their reactivity in a case of MCD compared with normal cornea using high-resolution immunogold electron microscopy. Mutation analysis indicated type I MCD with deletion of the entire open reading frame of CHST6. Contrast enhanced fixation revealed larger PG structures in MCD than normal. Unlike normal cornea, MCD cornea showed positive labelling with antibody to unsulphated KSPG, but was negative with antibodies to sulphated KSPG. These antibodies will thus facilitate high-resolution investigations of phenotypic heterogeneity in support of genetic studies in this disease.

The glycosaminoglycan attachment regions of human aggrecan

Aggrecan possesses both chondroitin sulfate (CS) and keratan sulfate (KS) chains attached to its core protein, which reside mainly in the central region of the molecule termed the glycosaminoglycan-attachment region. This region is further subdivided into the KS-rich domain and two adjacent CS-rich domains (CS1 and CS2). The CS1 domain of the human is unique in exhibiting length polymorphism due to a variable number of tandem amino acid repeats. The focus of this work was to determine how length polymorphism affects the structure of the CS1 domain and whether CS and KS chains can coexist in the different glycosaminoglycan-attachment domains. The CS1 domain possesses several amino acid repeat sequences that divide it into three subdomains. Variation in repeat number may occur in any of these domains, with the consequence that CS1 domains of the same length may possess different amino acid sequences. There was no evidence to support the presence of KS in either the CS1 or the CS2 domains nor the presence of CS in the KS-rich domain. The structure of the CS chains was shown to vary between the CS1 and CS2 domains, particularly in the adult, with variation occurring in chain length and the sulfation of the non-reducing terminal N-acetyl galactosamine residue. CS chains in the adult CS2 domain were shorter than those in the CS1 domain and possessed disulfated terminal residues in addition to monosulfated residues. There was, however, no change in the sulfation pattern of the disaccharide repeats in the CS chains from the two domains.

Identification of glycosaminoglycans in human airway secretions

Glycosaminoglycans (GAGs), known to be present in airway mucus, are macromolecules with a variety of structural and biological functions. In the present work, we used fluorophore-assisted carbohydrate electrophoresis (FACE) to identify and relatively quantify GAGs in human tracheal aspirates (HTA) obtained from healthy volunteers. Primary cultures of normal human bronchial epithelial (NHBE) and submucosal gland (SMG) cells were used to assess their differential contribution to GAGs in mucus. Distribution was further assessed by immunofluorescence in human trachea tissue sections and in cell cultures. HTA samples contained keratan sulfate (KS), chondroitin/dermatan sulfate (CS/DS), and hyaluronan (HA), whereas heparan sulfate (HS) was not detected. SMG cultures secreted CS/DS and HA, CS/DS being the most abundant GAGs in these cultures. NHBE cells synthesized KS, HA, and CS/DS. Confocal microscopy showed that KS was exclusively found at the apical border of NHBE cells and on the apical surface of ciliated epithelial cells in tracheal tissues. CS/DS and HA were present in both NHBE and SMG cells. HS was only found in the extracellular matrix in trachea tissue sections. In summary, HTA samples contain KS, CS/DS, and HA, mirroring a mixture of secretions originated in surface epithelial cells and SMGs. We conclude that surface epithelium is responsible for most HA and all KS present in secretions, whereas glands secrete most of CS/DS. These data suggest that, in diseases where the contribution to secretions of glands versus epithelial cells is altered, the relative concentration of individual GAGs, and therefore their biological activities, will also be affected.

Inherited corneal disease: the evolving molecular, genetic and imaging revolution

Advances in molecular genetics and in vivo ocular imaging modalities have enhanced our understanding of the corneal dystrophies. To date at least 11 genes have been identified, in which mutations manifest in corneal disease. In addition there are at least eight other loci identified to which corneal dystrophies have been linked. The information gained from the knowledge of gene function, aberrant protein production, or altered enzyme activity in the cornea, has resulted in greater knowledge of the pathophysiological mechanisms in these disorders. In vivo confocal microscopy has recently enabled microstructural study of dystrophic corneas throughout the disease course, rather than being limited to histopathological analysis of tissue removed at corneal transplantation. This perspective article summarizes the current knowledge, with emphasis on the genes, mutant proteins and resultant mechanisms that lead to manifestations of disease, along with characteristic findings with in vivo confocal microscopy.

Separation of keratan-sulfate-derived disaccharides by high-performance liquid chromatography and postcolumn derivatization with 2-cyanoacetamide and fluorimetric detection

In this paper, we report a rapid, sensitive, and quantitative procedure to conduct disaccharide compositional analyses of keratan sulfates (KS) by means of high-performance liquid chromatography (HPLC) separation and postcolumn derivatization with 2-cyanoacetamide and fluorimetric detection of products generated by hydrolysis of this glycosaminoglycan with Bacillus sp. keratanase II or Escherichia freundii endo-beta-galactosidase. Following E. freundii endo-beta-galactosidase digestion of bovine corneal KS, the monosulfated disaccharide glcNAc6sbeta(1-->3)gal, accounting for approximately equals 95% nmol and 50% yield products, is produced. On the contrary, bovine corneal KS treated with endo-beta-N-acetylglucosaminidase (keratanase II) from Bacillus sp. generates two major products, the monosulfated disaccharide galbeta(1-->4)glcNAc6s ( approximately equals 50% nmol product) and the disulfated disaccharide gal6sbeta(1-->4)glcNAc6s ( approximately equals 40% nmol product) for over 90% nmol products. These disaccharides are separated and readily determined within 30 min by using a linear-gradient strong anion-exchange separation. A linear relationship was found for the two purified disaccharides over a wide range of concentrations, from approximately equals 108 pmol, 50 ng, to 2,160 pmol, 1,000 ng, for the disaccharide galbeta(1-->4)glcNAc6s, and from 92 pmol, 50 ng, to 1,840 pmol, 1,000 ng, for the disaccharide gal6sbeta(1-->4)glcNAc6s. HPLC analysis was applied to the quantitative and qualitative determination of KS produced by 3T3-J2 murine fibroblasts in the cell medium. The amount of KS was found to be 2.80+/-0.34 microg/ml/10(6) cells and composed of approximately equals 71% nmol of disaccharide galbeta(1-->4)glcNAc6s and 18% nmol of the disulfated disaccharide gal6sbeta(1-->4)glcNAc6s having approximately equals 1.20 sulfate groups/disaccharide. Our data illustrate that the HPLC procedure reported represents an improved approach for the quantitative and compositional microanalyses of KS, especially applicable to experimentation involving small amounts ( approximately 50 ng) of this glycosaminoglycan and in relation to its biological function and pathological importance.

Penetrating keratoplasty for macular corneal dystrophy

PURPOSE

To determine the prognosis of penetrating keratoplasty (PK) for macular corneal dystrophy (MCD).

DESIGN

Single-center, retrospective, interventional, noncomparative case series.

PARTICIPANTS

One hundred forty-one patients (229 eyes) with MCD.

INTERVENTION

Retrospective review of the medical record of every patient who underwent primary PK for histopathologically confirmed MCD at the King Khaled Eye Specialist Hospital between January 1, 1983 and December 31, 2002 and for whom at least 12 months of follow-up is available.

MAIN OUTCOME MEASURES

Visual acuity (VA), graft survival, and postoperative complications.

RESULTS

After a mean follow-up period of 5.9+/-3.8 years (range, 1-17), the mean best-corrected VA was 20/50. At the most recent visit, 206 (90.0%) grafts were clear, and 23 (10.0%) had failed. Probabilities of graft survival were 98.1% at 1 year, 89.8% at 5 years, 82.1% at 10 years, and 74.1% at 15 years. There was a statistically significant increased likelihood of graft failure if the patient was older than 40 years at the time of surgery (P<0.00003). The differences in graft failure between patients older than 40 and those younger were not attributable to statistically significant differences in duration of follow-up, donor age, or donor endothelial cell counts. Corneal endothelial rejection episodes occurred in 47 (20.0%) grafts, but resulted in irreversible graft failure in only 8 (3.5%) eyes. Eighteen (27.3%) of 66 eyes with a recipient size of > or =7.5 mm developed a graft rejection episode, compared with 27 (16.6%) of 163 eyes with a recipient size of <7.5 mm (P = 0.04). Microbial keratitis occurred in 14 (6.1%) grafts and was more likely to occur in patients over 40 (14.0% vs. 3.0%, P = 0.01). Clinically significant recurrence was observed in 12 (5.2%) grafts, after a mean interval of 84+/-48.2 months, and was directly related to patient age (P = 0.04) and inversely related to donor graft size (P = 0.04).

CONCLUSIONS

Good visual results and excellent graft survival can be achieved after PK for MCD. The risk of graft failure is higher in patients older than 40 years.

A glycomic approach to proteoglycan with a two-dimensional polysaccharide chain map

Glycosaminoglycan chains were liberated from proteoglycans (bovine lung, tracheal cartilage, and cerebrum) by successive digestion with actinase and with cellulase from Aspergillus niger, which has endo-beta-xylosidase activity. The glycosaminoglycan chains were fluorescence-labeled with 2-aminopyridine after digestion with Streptomyces hyaluronidase. The resulting pyridylamino-glycosaminoglycans, including heparan sulfate, chondroitin sulfate/dermatan sulfate, and heparin, were separated by high-performance liquid chromatography. Each separated fraction was analyzed by two types of high-performance liquid chromatography: gel-filtration chromatography and anion-exchange chromatography. The correlation between molecular weight and degree of sulfation could be shown on the two-dimensional polysaccharide chain map. Use of a commonly available cellulase with endo-beta-xylosidase activity together with the two-dimensional polysaccharide chain map allows easy analysis of various glycosaminoglycan chains and comprehensive comparison among the structures. These techniques will become useful tools in the further development of glycotechnology and glycome analysis.

Keratocyte phenotype mediates proteoglycan structure: a role for fibroblasts in corneal fibrosis

In pathological corneas, accumulation of fibrotic extracellular matrix is characterized by proteoglycans with altered glycosaminoglycans that contribute to the reduced transparency of scarred tissue. During wound healing, keratocytes in the corneal stroma transdifferentiate into fibroblasts and myofibroblasts. In this study, molecular markers were developed to identify keratocyte, fibroblast, and myofibroblast phenotypes in primary cultures of corneal stromal cells and the structure of glycosaminoglycans secreted by these cells was characterized. Quiescent primary keratocytes expressed abundant protein and mRNA for keratocan and aldehyde dehydrogenase class 3 and secreted proteoglycans containing macromolecular keratan sulfate. Expression of these marker compounds was reduced in fibroblasts and also in transforming growth factor-beta-induced myofibroblasts, which expressed high levels of alpha-smooth muscle actin, biglycan, and the extra domain A (EDA or EIIIA) form of cellular fibronectin. Collagen types I and III mRNAs were elevated in both fibroblasts and in myofibroblasts. Expression of these molecular markers clearly distinguishes the phenotypic states of stromal cells in vitro. Glycosaminoglycans secreted by fibroblasts and myofibroblasts were qualitatively similar to and differed from those of keratocytes. Chondroitin/dermatan sulfate abundance, chain length, and sulfation were increased as keratocytes became fibroblasts and myofibroblasts. Fluorophore-assisted carbohydrate electrophoresis analysis demonstrated increased N-acetylgalactosamine sulfation at both 4- and 6-carbons. Hyaluronan, absent in keratocytes, was secreted by fibroblasts and myofibroblasts. Keratan sulfate biosynthesis, chain length, and sulfation were significantly reduced in both fibroblasts and myofibroblasts. The qualitatively similar expression of glycosaminoglycans shared by fibroblasts and myofibroblasts suggests a role for fibroblasts in deposition of non-transparent fibrotic tissue in pathological corneas.

Tandem mass spectrometric strategies for determination of sulfation positions and uronic acid epimerization in chondroitin sulfate oligosaccharides

Chondroitin sulfate (CS) is a glycosaminoglycan consisting of repeating (HexA-GalNAc sulfate) disaccharides, the functions of which depend on patterns of sulfation and uronic acid epimerization. The correlation of biological activities with structure requires a strategy to determine the sequences of CS oligosaccharides without the need for total isolation. Tandem mass spectrometry has enabled the development of proteomics, based on CID fragmentation of ions produced from complex mixtures of proteolytic peptides, and has the potential for rapid sequencing of CS and other glycosaminoglycan classes. The most challenging aspects of CS sequencing are to distinguish GalNAc residues sulfated at the 4- versus the 6-position and uronic acid epimers. This work describes the utility of (1) reducing terminal derivatives and (2) control of precursor ion charge state for tandem mass spectrometric strategies for determining GalNAc sulfation positional isomers of CS. The capability of tandem MS to differentiate uronic acid epimers is also shown, providing evidence that complete or nearly complete information on CS covalent structure may be obtained using tandem MS.

Proteoglycan alterations and collagen reorganisation in the secondary avian cornea during development

PURPOSE

It is thought that proteoglycan (PG) alterations, collagen matrix reorganisation and the onset of corneal transparency in the developing avian cornea might be related events. The current histochemical study was designed to establish the character and distribution of corneal PG filaments in relation to collagen organisation during tissue morphogenesis.

METHODS

Corneas from days 13-18 developing chicken embryos were treated with cuprolinic blue (CuB) to examine sulphated PGs by transmission electron microscopy and quantitative image analysis.

RESULTS

On developmental day 13, corneas contained poorly defined lamellae and a large number of both small and large CuB-stained PG filaments, randomly distributed and often in collagen-free regions. By day 14 and after, the large CuB-stained PG filaments were much less abundant. At this time, too, collagen fibrils displayed an axial alignment and an occasional periodic arrangement of small CuB-stained PG filaments along their axes. By developmental day 15, lamellae were well formed and continued to increase in number and size thereafter. Between developmental days 16 and 17, there was a significant increase (p < 0.001) in the number of small, collagen-associated PG filaments. This increase persisted into day 18.

CONCLUSIONS

The size, number and distribution of sulphated, CuB-stained PG filaments in the developing avian cornea change over time. This is particularly true between developmental days 13 and 14 and between days 16 and 17, concurrent with previously documented structural changes.

Chronic pulsatile shear stress impacts synthesis of proteoglycans by endothelial cells: effect on platelet aggregation and coagulation

Endothelial-derived proteoglycans are important regulators of the coagulation-pathway in vivo and our primary objective of this study was to determine whether chronic shear stress affected the synthesis, release, and activity of proteoglycans from bovine aortic endothelial cells (BAEC). BAEC were cultured under shear and proteoglycans were purified from BAEC conditioned media and analyzed using both anionic exchange and size exclusion chromatography. The overall amount of proteoglycans produced per cell was significantly greater for the high shear-treated samples compared to the low shear-treated samples indicating that the shear magnitude did impact cell responsiveness. While overall size and composition of the proteoglycans and glycosaminoglycan (GAG) side chains were not altered by shear, the relative proportion of the high and low molecular weight species was inversely related to shear and differed significantly from that found under static tissue culture conditions. Moreover, a unique proteoglycan peak was identified from low shear stress (5 +/- 2 dynes/cm(2)) conditioned media when compared to high shear conditions (23 +/- 8 dynes/cm(2)) via anionic exchange chromatography, suggesting that subtle changes in the GAG structures may impact activity of these molecules. In order to characterize whether these changes impacted proteoglycan function, we studied the effects of shear specific proteoglycans on the inhibition of thrombin-induced human platelet aggregation as well as on platelet-fibrin clot dynamics. Proteoglycans from high shear-treated samples were less effective inhibitors of both platelet aggregation and blood coagulation inhibition than proteoglycans from low shear-treated samples and both were less effective than proteoglycans isolated from static tissue culture samples. However, due to changes in the overall proteoglycan synthesis and release rate, the high and low shear-treated sample had essentially identical effects on these activities, suggesting that the cells were able to compensate for stress-induced proteoglycan changes. Our data suggests that shear stress, by altering proteoglycan synthesis and fine structure, may play a role in maintaining vascular hemodynamics and hemostasis.