Hyaluronan synthase immunoreactivity in the anterior segment of the primate eye

Relationship of choroidal thickness and axial length with posterior vitreous detachment in patients with high myopia

Although accumulating evidence suggests a higher prevalence of posterior vitreous detachment (PVD) in highly myopic eyes, the relation between ocular biometric features and PVD stages in such eyes remains unclear. Therefore, we enrolled 170 patients with high myopia (axial length ≥ 26.0 mm) to investigate the status of PVD regarding subfoveal choroidal thickness and axial length. Utilising swept-source optical coherence tomography, we classified the PVD status into five stages. The distribution of PVD grades increased as the choroidal thickness decreased and axial length increased (P < 0.01). On adjusting for age and sex, decreased choroidal thickness and increased axial length were associated with more advanced PVD stages: odds ratios with the highest vs. lowest groups were 0.31 (95% confidence interval [CI] 0.09-1.01; P_trend = 0.009) for choroidal thickness and 5.16 (95% CI 1.34-19.80; P_trend = 0.002) for axial length. The inverse association between choroidal thickness and PVD status seemed stronger in women than in men (P_interaction = 0.05). In conclusion, we firstly observed a significant trend of decreased choroidal thickness, along with increased axial length, with increased grade of PVD, particularly among women with highly myopic eyes, suggesting that advanced morphological myopic changes contribute to PVD in middle-aged adults.

Stem Cell Therapy for Corneal Regeneration Medicine and Contemporary Nanomedicine for Corneal Disorders

The ocular surface is the outermost part of the visual system that faces many extrinsic or intrinsic threats, such as chemical burn, infectious pathogens, thermal injury, Stevens-Johnson syndrome, ocular pemphegoid, and other autoimmune diseases. The cornea plays an important role in conducting light into the eyes and protecting intraocular structures. Several ocular surface diseases will lead to the neovascularization or conjunctivalization of corneal epithelium, leaving opacified optical media. It is believed that some corneal limbal cells may present stem cell-like properties and are capable of regenerating corneal epithelium. Therefore, cultivation of limbal cells and reconstruction of the ocular surface with these limbal cell grafts have attracted tremendous interest in the past few years. Currently, stem cells are found to potentiate regenerative medicine by their capability of differentiation into multiple lineage cells. Among these, the most common cell sources for clinical use are embryonic, adult, and induced stem cells. Different stem cells have varied specific advantages and limitations for in vivo and in vitro expansion. Other than ocular surface diseases, culture and transplantation of corneal endothelial cells is another major issue for corneal decompensation and awaits further studies to find out comprehensive solutions dealing with nonregenerative corneal endothelium. Recently, studies of in vitro endothelium culture and ρ-associated kinase (ROCK) inhibitor have gained encouraging results. Some clinical trials have already been finished and achieved remarkable vision recovery. Finally, nanotechnology has shown great improvement in ocular drug delivery systems during the past two decades. Strategies to reconstruct the ocular surface could combine with nanoparticles to facilitate wound healing, drug delivery, and even neovascularization inhibition. In this review article, we summarized the major advances of corneal limbal stem cells, limbal stem cell deficiency, corneal endothelial cell culture/transplantation, and application of nanotechnology on ocular surface reconstruction. We also illustrated potential applications of current knowledge for the future treatment of ocular surface diseases.

Hyaluronic acid secretion by synoviocytes alters under cyclic compressive load in contracted collagen gels

Knee osteoarthritis is a degenerative disease of diarthrodial joints. Biomechanical factors are considered as risk factors for the disease, the knee joint being normally subject to pressure. Some studies have examined the biomechanical environment of the knee joint in vitro. The aim of this study was to establish a culture model to mimic the knee joint environment. As a first step, synoviocytes induced contraction of three-dimensional collagen gels. Next, contracted collagen gels containing synoviocytes underwent cyclical compression ranging from 0 to 40 kPa at a frequency of 1.0 Hz for 1.5, 3, 6 and 12 h using the FX-4000C™ Flexercell(®) Compression Plus™ System. RNA in collagen gels was extracted immediately after compression and mRNA expression levels of HAS genes were analyzed by quantitative RT-PCR. Culture medium was collected 48 h after compression and analyzed by agarose gel electrophoresis and cellulose acetate electrophoresis. Synoviocytes in contracted collagen gels were stimulated by cyclic compressive load. Long-term compressive stimulation led to the production of higher molecular weight hyaluronic acid, whereas, short-term, compressive stimulation increased the total amount of hyaluronic acid. Furthermore, mRNA expression levels of both HAS-1 and HAS-2 were significantly higher than without compression. Taken together, using this gel culture system, synoviocytes synthesized higher molecular weight hyaluronic acid and produced large quantities of hyaluronic acid through up-regulation of HAS gene expression. Therefore, the contracted collagen gel model will be a useful in vitro three-dimensional model of the knee joint.

Perturbation of hyaluronan synthesis in the trabecular meshwork and the effects on outflow facility

PURPOSE

Hyaluronan (HA) is a major component of the aqueous outflow pathway. However, the contribution of HA to human outflow resistance remains unclear. Three HA synthase genes (HAS1-3) have been identified. Here, we evaluate the contribution of each of the HAS proteins to outflow facility in anterior segment perfusion culture.

METHODS

Two methods were used to reduce HA synthesis: 1 mM 4-methylumbelliferone (4MU) was used to inhibit all HAS synthases and shRNA silencing lentivirus was generated to knock down expression of each HAS individually. Quantitative RT-PCR, Western immunoblotting and an HA ELISA assay were used to assess HAS mRNA and protein levels and HA concentration, respectively. The effects of 4MU treatment and HAS gene silencing on outflow facility were assessed in human and porcine perfusion culture.

RESULTS

Quantitative RT-PCR and Western immunoblotting showed a reduction of each HAS in response to their respective silencing and 4MU treatment. HA concentration was concomitantly reduced. Treatment with 4MU decreased outflow facility in human anterior segments but increased outflow facility in porcine eyes. Lentiviral delivery of HAS1 and HAS2 silencing vectors caused similar opposite effects on outflow facility. Silencing of HAS3 did not significantly affect outflow resistance in either species.

CONCLUSIONS

This is the first conclusive evidence for a significant role of HA in the human outflow pathway. HA chains synthesized by HAS1 and HAS2 contribute to outflow resistance, while hyaluronan produced by HAS3 does not appear to play a significant role.

Progenitors for the corneal endothelium and trabecular meshwork: a potential source for personalized stem cell therapy in corneal endothelial diseases and glaucoma

Several adult stem cell types have been found in different parts of the eye, including the corneal epithelium, conjunctiva, and retina. In addition to these, there have been accumulating evidence that some stem-like cells reside in the transition area between the peripheral corneal endothelium (CE) and the anterior nonfiltering portion of the trabecular meshwork (TM), which is known as the Schwalbe's Ring region. These stem/progenitor cells may supply new cells for the CE and TM. In fact, the CE and TM share certain similarities in terms of their embryonic origin and proliferative capacity in vivo. In this paper, we discuss the putative stem cell source which has the potential for replacement of lost and nonfunctional cells in CE diseases and glaucoma. The future development of personalized stem cell therapies for the CE and TM may reduce the requirement of corneal grafts and surgical treatments in glaucoma.

Hyalocytes: essential cells of the vitreous cavity in vitreoretinal pathophysiology?

PURPOSE

To review the present understanding of hyalocytes.

METHODS

A review of recent studies that investigated the roles of hyalocytes in the pathophysiology of the vitreous cavity.

RESULTS

Studies on immunocytochemistry and chimeric mice with green fluorescent protein transgenic mice show that hyalocytes belong to the monocyte/macrophage lineage and derive from bone marrow. The effects of hyalocytes on the vitreous cavity environment can be divided into three categories: synthesis of extracellular matrix, regulation of the vitreous cavity immunology, and modulation of inflammation. In noninflamed eyes, vitreous cavity is an immune-privileged site that is maintained by a system called vitreous cavity-associated immune deviation, in which hyalocytes play the role of antigen-presenting cells. However, cultured hyalocytes proliferate in response to inflammatory molecules and secrete vascular endothelial growth factor and urokinase-type plasminogen activator. A collagen gel embedded with hyalocytes contracts over time, which is enhanced by transforming growth factor-β but is inhibited by Rho kinase inhibitor. These results suggest that hyalocytes can be an exacerbating factor in inflamed eyes. Clinically, hyalocytes are frequently found in the surgically removed specimens of epiretinal membrane or proliferative vitreoretinopathy.

CONCLUSION

Elucidating the properties of hyalocytes is important to understand the biology of vitreous cavity and to develop novel treatments for vitreoretinal diseases.

Hyaluronan Synthases, Hyaluronan and Its CD44 Receptors in the Posterior Segment of Rabbit Eye

To understand the possible roles of the hyaluronan synthetase (HAS)/hyaluronan (HA)/CD44 signaling system in the posterior eye segment, we investigated the expression of rabbit HAS isoforms and CD44 mRNA by RT-PCR and the level of HA by using HA assay and immunohistochemistry. HA was detectable in vitreous, retina and choroid. The expression of three HAS isoforms was clearly detected in both retina and choroids. Rabbit choroid showed a significant increase of the HAS2 and HAS3 expression compared with rabbit retina (HAS2 p = 0.0014 < 0.05; HAS3 p = 0.0006 < 0.05). Similarly, mRNA expression of CD44 was detected in both retina and choroids. This evidence may suggest that the HAS/HA/CD44 signaling system is important in maintaining the functional structure of retina and choroid.

Hyaluronan synthase in trabecular meshwork cells

BACKGROUND/AIMS

Hyaluronan is present in the trabecular meshwork where it is involved in the pathophysiology of aqueous outflow environment. In this study, the expression and regulation of hyaluronan synthase (HAS), which is the enzyme synthesising hyaluronan, in trabecular meshwork cells were investigated.

METHODS

Cultured bovine trabecular meshwork cells (BTMCs) were used. HAS expression in BTMCs was examined by RT-PCR. The effects of transforming growth factor beta (TGF-beta) and platelet derived growth factor BB (PDGF-BB) on HAS expression in BTMCs were examined by quantitative RT-PCR. The HAS2 expression by TGF-beta and PDGF-BB at the protein level was also confirmed immunohistochemically. The production of hyaluronan from BTMCs was detected by high performance liquid chromatography (HPLC).

RESULTS

Three HAS isoforms were expressed in BTMCs at the mRNA level. Among HAS isoforms, only the expression of HAS2 mRNA was increased by the administration of TGF-beta or PDGF-BB. HAS2 upregulation by these growth factors was also confirmed at the protein level. Further, hyaluronan production from BTMCs was stimulated by TGF-beta or PDGF-BB.

CONCLUSION

Expression of HAS in trabecular meshwork may maintain the hyaluronan content in the aqueous outflow pathway. Its production is regulated by TGF-beta and PDGF-BB. The regulation of the expression of HAS in trabecular meshwork might be useful for modulating the aqueous outflow environment.

Vascular remnants in the rabbit vitreous body. II. Enzyme digestion and immunohistochemical studies

The purpose of this study was to evaluate the composition of ghost vessels and the newly identified intravitreal structures type 1 and 2 (IVS-1 and 2) observed in the rabbit vitreous body. Rabbit eyes (n = 10, 0.5- approximately 36 months of age) were fixed and embedded in plastic. Post-embedding immuno transmission electron microscopy and enzyme digestion methods specifically directed at vascular extracellular matrix components (collagen IV, elastin and hyaluronan) were used in order to confirm the postulated vascular origin of IVS-1 and 2. In addition, markers of vitreous extracellular matrix components (collagen II, hyaluronan) were used. The postulated vascular nature of ghost vessels and IVS-1 was confirmed by a positive labelling with anti-collagen IV, whereas the demonstration of elastin (by anti-elastin antibodies and elastase digestion) in IVS-1 and 2 confirms their arterial origin. These vascular remnants were also labelled with a hyaluronan marker and with anti-collagen II. The presence of remnants of the hyaloid artery system throughout the vitreous matrix is in conflict with a strict spatial separation between the primary and secondary vitreous during embryonic development as proposed in the literature. It strongly supports an alternative theory which suggests an interactive remodelling of this matrix. The presence of hyaluronan in remnants of the hyaloid system is inconclusive, since hyaluronan is a component both of the adult vitreous matrix and of the vascular extracellular matrix. The presence of collagen II in vascular structures is highly interesting, since it supports another challenging theory, which suggests that lamellae develop alongside tracts formerly occupied by the larger hyaloid vessels.

Structural macromolecules and supramolecular organisation of the vitreous gel

The vitreous gel is a transparent extracellular matrix that fills the cavity behind the lens of the eye and is surrounded by and attached to the retina. This gel liquefies during ageing and in 25-30% of the oppulation the residual gel structure eventually collapses away from the posterior retina in a process called posterior retina in a process called posterior vitreous detachment. This process plays a pivotal role in a number of common blinding conditions including rhegmatogenous retinal detachment, proliferative diabetic retinopathy and macular hole formation. In order to understand the molecular events underlying vitreous liquefaction and posterior vitreous detachment and to develop new therapies it is important to understand the molecular basis of normal vitreous gel structure and how this is altered during ageing. It has previously been established that a dilute dispersion of thin (heterotypic) collagen fibrils is essential to the gel structure and that age-related vitreous liquefaction is intimately related to a process whereby these collagen fibrils aggregate. Collagen fibrils have a natural tendency to aggregate so a key question that has to be addressed is: what normally maintains the spacing of the collagen fibrils? In mammalian vitreous a network of hyaluronan normally fills the spaces between these collagen fibrils. This hyaluronan network can be removed without destroying the gel structure, so the hyaluronan is not essential for maintaining the spacing of the collagen fibrils although it probably does increase the mechanical resilience of the gel. The thin heterotypic collagen fibrils have a coating of non-covalently bound macromolecules which, along with the surface features of the collagen fibrils themselves, probably play a fundamental role in maintaining gel stability. They are likely to both maintain the short-range spacing of vitreous collagen fibrils and to link the fibrils together to form a contiguous network. A collagen fibril-associated macromolecule that may contribute to the maintenance of short-range spacing is opticin, a newly discovered extracellular matrix leucine-rich repeat protein. In addition, surface features of the collagen fibrils such as the chondroitin sulphate glycosaminoglycan chains of type IX collagen proteoglycan may also play an important role in maintaining fibril spacing. Furthering our knowledge of these and other components related to the surface of the heterotypic collagen fibrils will allow us to make important strides in understanding the macromolecular organisation of this unique and fascinating tissue. In addition, it will open up new therapeutic opportunities as it will allow the development of therapeutic reagents that can be used to modulate vitreous gel structure and thus treat a number of common, potentially blinding, ocular conditions.

Functional morphology of the trabecular meshwork in primate eyes

The trabecular meshwork forms most of the resistance to aqueous humor outflow needed for maintenance of a pressure gradient between intraocular pressure of approximately 17 mmHg and venous pressure of approximately 10 mmHg. The composition of the extracellular material in the subendothelial or cribriform layer seems to be mainly responsible for outflow resistance. The aqueous humor pathways through the subendothelial layer can be influenced by ciliary muscle contraction and presumably also by contractile elements recently found both in trabecular meshwork and scleral spur. Pharmacologically induced disconnection of inner wall and cribriform cells leads to wash out of extracellular material through breaks of the endothelial lining of Schlemm's canal and to increase of outflow facility. In glaucomatous eyes the resistance to aqueous humor outflow is increased due to an increase in different forms of extracellular material deposited within the cribriform layer. The amount of this newly developed extracellular material is correlated with loss of axons in the optic nerve, indicating that a common factor is responsible for both changes. To investigate the effect of various factors on the biology of trabecular cells monolayer cultures derived from cribriform and corneoscleral trabecular meshwork have been established. The two cell lines can be differentiated because cribriform cells in vivo as in vitro stain for alphabeta-crystallin whereas the corneoscleral cells remain unstained. The effect of TGFbeta, a growth factor increased in aqueous humor of glaucomatous eyes and glycocorticoids on trabecular meshwork cells show typical changes in formation of extracellular matrix components and of stress proteins. Dexamethasone and oxidative damage also lead to increase of trabecular meshwork inducible glucocorticoid response (TIGR) protein. A mutation of the TIGR-gene family has recently been found in families with juvenile and chronic simple glaucoma. Future research has to clarify the significance of these genetic factors for the pathophysiology of glaucoma and the role of trabecular cell activity in this respect.

Molecular cloning, expression, and characterization of the authentic hyaluronan synthase from group C Streptococcus equisimilis

We previously reported the first cloning of a functional glycosaminoglycan synthase, the hyaluronan synthase (HAS) from Group A Streptococcus pyogenes (spHAS) (DeAngelis, P. L., Papaconstantinou, J., and Weigel, P. H. (1993) J. Biol. Chem. 268, 19181-19184). Group A spHAS was unrelated to a putative Group C HA synthase reported by others (Lansing, M., Lellig, S., Mausolf, A., Martini, I. , Crescenzi, F., Oregon, M., and Prehm, P. (1993) Biochem. J. 289, 179-184). Here we report the isolation of a bona fide HA synthase gene from a highly encapsulated strain of Group C Streptococcus equisimilis. The encoded protein, designated seHAS, is 417 amino acids long (calculated molecular weight, 47,778; calculated pI, 9.1) and is the smallest member of the HAS family identified thus far. The enzyme migrates anomalously fast in SDS-polyacrylamide gel electrophoresis (approximately 42,000 Da). The seHAS protein shows no similarity (<2% identity) to the previously reported Group C gene, which is not an HA synthase. The seHAS and spHAS protein and coding sequences are 72 and 70% identical, respectively. seHAS is also similar to eukaryotic HAS1 (approximately 31% identical), HAS2 (approximately 28% identical), and HAS3 (28% identical). The deduced protein sequence of seHAS was confirmed by reactivity with a synthetic peptide antibody. Recombinant seHAS expressed in Escherichia coli was recovered in membranes as a major protein (approximately 10% of the total protein) and synthesized very large HA (Mr >7 x 10(6)) in the presence of UDP-GlcNAc and UDP-GlcA. The product contained equimolar amounts of both sugars and was degraded by the specific Streptomyces hyaluronidase. Comparison of the two recombinant streptococcal enzymes in isolated membranes showed that seHAS and spHAS are essentially identical in the steady-state size distribution of HA chains they synthesize, but seHAS has an intrinsic 2-fold faster rate of chain elongation (Vmax) than spHAS. seHAS is the most active HA synthase identified thus far; it polymerizes HA at an average rate of 160 monosaccharides/s. The two bacterial HA synthase genes may have arisen from a common ancient gene shared with the early evolving vertebrates.

Hyaluronan in the exfoliation syndrome

PURPOSE

To histochemically analyze if the glycoseaminoglycan component of pseudoexfoliation material consists of hyaluronan.

METHODS

The hyaluronan binding region of cartilage proteoglycans was utilized in a staining specific for hyaluronan. The technique has been described and employed previously. Human donor eyes with and without the presence of visible pseudoexfoliations were analyzed.

RESULTS

Hyaluronan was found to coat the fibrillar exfoliation material on the lens, the zonules, the iris epithelium and the ciliary body. It was also found on a capsular bag following cataract surgery.

CONCLUSION

In the anterior chamber hyaluronan constitutes one part of the exfoliation material. Abnormal findings of hyaluronan could be found in the cornea.

Proteoglycan expression by human trabecular meshworks

PURPOSE

Proteoglycans may serve important roles in trabecular meshwork structure or function. Detailed molecular characterization and identification of specific trabecular proteoglycan core proteins has been limited.

METHODS

Radiolabeled proteoglycans were extracted from cultured human trabecular meshworks and subjected to ion exchange and molecular sieve chromatography. Peaks were subjected to glycosaminoglycan content analysis. Reverse transcription with polymerase chain reaction was used to identify trabecular mRNAs of several common proteoglycan core proteins. Western immunoblots of trabecular extracts were also utilized to identify these proteoglycan core proteins.

RESULTS

The proteoglycans elute from ion exchange columns at high salt and molecular sieve column profiles, and they exhibit broad peaks typical of the proteoglycan microheterogeneity seen in other tissues. The four common glycosaminoglycan side-chains were identified on these proteoglycans. Trabecular cells in organ or cell culture contain mRNAs coding for decorin, biglycan, versican, perlecan and a basement membrane glycoprotein, SPARC. Syndecan-1 transcripts were present at very low levels, while aggrecan transcripts were not detectable. Decorin, biglycan, versican and perlecan core proteins were also identified by immunoblots of trabecular cell extracts.

CONCLUSIONS

Several common proteoglycans are expressed by trabecular cells in organ explant or cell culture. Their general characteristics are not unlike those found in other tissues. These proteoglycans may serve important functions in the trabecular outflow pathway.