Hyaluronan localization in tissues of the mouse posterior eye wall: absence in the interphotoreceptor matrix

Role of FGF and Hyaluronan in Choroidal Neovascularization in Sorsby Fundus Dystrophy

Sorsby's fundus dystrophy (SFD) is an inherited blinding disorder caused by mutations in the tissue inhibitor of metalloproteinase-3 (TIMP3) gene. The SFD pathology of macular degeneration with subretinal deposits and choroidal neovascularization (CNV) closely resembles that of the more common age-related macular degeneration (AMD). The objective of this study was to gain further insight into the molecular mechanism(s) by which mutant TIMP3 induces CNV. In this study we demonstrate that hyaluronan (HA), a large glycosaminoglycan, is elevated in the plasma and retinal pigment epithelium (RPE)/choroid of patients with AMD. Mice carrying the S179C-TIMP3 mutation also showed increased plasma levels of HA as well as accumulation of HA around the RPE in the retina. Human RPE cells expressing the S179C-TIMP3 mutation accumulated HA apically, intracellularly and basally when cultured long-term compared with cells expressing wildtype TIMP3. We recently reported that RPE cells carrying the S179C-TIMP3 mutation have the propensity to induce angiogenesis via basic fibroblast growth factor (FGF-2). We now demonstrate that FGF-2 induces accumulation of HA in RPE cells. These results suggest that the TIMP3-MMP-FGF-2-HA axis may have an important role in the pathogenesis of CNV in SFD and possibly AMD.

Structure and barrier properties of human embryonic stem cell-derived retinal pigment epithelial cells are affected by extracellular matrix protein coating

Extracellular matrix (ECM) interactions play a vital role in cell morphology, migration, proliferation, and differentiation of cells. We investigated the role of ECM proteins on the structure and function of human embryonic stem cell-derived retinal pigment epithelial (hESC-RPE) cells during their differentiation and maturation from hESCs into RPE cells in adherent differentiation cultures on several human ECM proteins found in native human Bruch's membrane, namely, collagen I, collagen IV, laminin, fibronectin, and vitronectin, as well as on commercial substrates of xeno-free CELLstart™ and Matrigel™. Cell pigmentation, expression of RPE-specific proteins, fine structure, as well as the production of basal lamina by hESC-RPE on different protein coatings were evaluated after 140 days of differentiation. The integrity of hESC-RPE epithelium and barrier properties on different coatings were investigated by measuring transepithelial resistance. All coatings supported the differentiation of hESC-RPE cells as demonstrated by early onset of cell pigmentation and further maturation to RPE monolayers after enrichment. Mature RPE phenotype was verified by RPE-specific gene and protein expression, correct epithelial polarization, and phagocytic activity. Significant differences were found in the degree of RPE cell pigmentation and tightness of epithelial barrier between different coatings. Further, the thickness of self-assembled basal lamina and secretion of the key ECM proteins found in the basement membrane of the native RPE varied between hESC-RPE cultured on compared protein coatings. In conclusion, this study shows that the cell culture substrate has a major effect on the structure and basal lamina production during the differentiation and maturation of hESC-RPE potentially influencing the success of cell integrations and survival after cell transplantation.

Cloning and characterization of cell strains derived from human corneal stroma and sclera

PURPOSE

To establish human corneal stroma- and sclera-derived cells as models for studying diseases of the anterior segment of the eye.

METHODS

Using a recombinant retrovirus system, we transfected human papilloma virus 16 E6 and E7 (HPV16 E6/E7) into human corneal stroma- and sclera-derived cells. The primary cells and established cell strains were characterized by assessing the mRNA expression of collagen, matrix metalloproteinase, and tissue inhibitor of metalloproteinase by reverse transcription-polymerase chain reaction. We also examined the effects of inflammatory cytokines on hyaluronan synthase expression and hyaluronan products.

RESULTS

Both a corneal stroma-derived cell strain, Cs3, and a sclera-derived cell strain, Sc1, were obtained, and both cell strains could be passaged up to 25 times. The mRNA expression pattern observed in the primary cells was identical to that observed in the cell strains. Hyaluronan synthase 1 and 2 mRNAs were increased by transforming growth factor beta and platelet-derived growth factor BB. Significant differences were observed between the hyaluronan products with and without cytokine treatment.

CONCLUSION

Cell strains derived from corneal stroma and sclera fibroblast cells can be established using HPV16 E6/E7 immortalized genes of the same origin. The phenotypic cell characteristics did not change after transfection, immortalization, or successive passages in culture.

Age-related macular degeneration: activation of innate immunity system via pattern recognition receptors

Age-related macular degeneration (AMD) is the most common cause of irreversible loss of central vision. Histopathological studies have demonstrated that inflammation is the key player in the pathogenesis of AMD. Genetic studies have revealed that complement factor H is a strong risk factor for the development of AMD. However, innate immunity defence involves several other pattern recognition receptors (PRRs) which can trigger inflammatory responses. Retinal pigment epithelial (RPE) cells have the main role in the immune defence in macula. In this study, we examine in detail the endogenous danger signals which can activate different PRRs in RPE cells, such as Toll-like, NOD-like and scavenger receptors along with complement system. We also characterise the signalling pathways triggered by PRRs in evoking inflammatory responses. In addition, we will discuss whether AMD pathology could represent the outcome of chronic activation of the innate immunity defence in human macula.

Pigment epithelium-derived factor binds to hyaluronan. Mapping of a hyaluronan binding site

Pigment epithelium-derived factor (PEDF) is a multifunctional serpin with antitumorigenic, antimetastatic, and differentiating activities. PEDF is found within tissues rich in the glycosaminoglycan hyaluronan (HA), and its amino acid sequence contains putative HA-binding motifs. We show that PEDF coprecipitation with glycosaminoglycans in media conditioned by human retinoblastoma Y-79 cells decreased after pretreatments with hyaluronidase, implying an association between HA and PEDF. Direct binding of human recombinant PEDF to highly purified HA was demonstrated by coprecipitation in the presence of cetylpyridinium chloride. Binding of PEDF to HA was concentration-dependent and saturable. The PEDF-HA interactions were sensitive to increasing NaCl concentrations, indicating an ionic nature of these interactions and having affinity higher than PEDF-heparin. Competition assays showed that PEDF can bind heparin and HA simultaneously. PEDF chemically modified with fluorescein retained the capacity for interacting with HA but lacked heparin affinity, suggesting one or more distinct HA-binding regions on PEDF. The HA-binding region was examined by site-directed mutagenesis. Single-point and cumulative alterations at basic residues within the putative HA-binding motif K189A/K191A/R194A/K197A drastically reduced the HA-binding activity without affecting heparin- or collagen I binding of PEDF. Cumulative alterations at sites critical for heparin binding (K146A/K147A/R149A) decreased HA affinity but not collagen I binding. Thus these clusters of basic residues (BXBXXBXXB and BX3AB2XB motifs) in PEDF are functional regions for binding HA. In the spatial PEDF structure they are located in distinct areas away from the collagen-binding site. The HA-binding activity of PEDF may contribute to deposition in the extracellular matrix and to its reported antitumor/antimetastatic effects.

The effect of recombinant human hyaluronidase on dexamethasone penetration into the posterior segment of the eye after sub-Tenon's injection

PURPOSE

The aim of this study was to investigate the extent if recombinant human hyaluronidase (rhuPH20) can enhance trans-scleral penetration of sub-Tenon's dexamethasone (DM) into the posterior segment of the eye.

METHODS

rhuPH20 was purified from conditioned media through a series of ion exchange, hydrophobic interaction, aminophenylboronate, and hydroxyapatite chromatography to greater than 90% purity based upon specific activity. Only the right eye of each rabbit was injected. The first group (n = 16) received an injection of DM and rhuPH20, whereas the second group (n = 16) received DM only. The eyes were enucleated 1, 2, 3, and 6 h after the injection, and the choroid, retina, vitreous, aqueous, and serum were harvested. DM concentration was assessed by mass spectrometry. Histology (n = 2) and immunohistochemistry (n = 2) was performed to detect toxicity and the presence of the rHuPH20, respectively.

RESULTS

We observed no histopathologic damage to ocular tissues after sub-Tenon's injection. This enzyme significantly increased DM level in the choroid and the retina 3 h after administration. The rise in levels was transient returning to normal levels by 6 h.

CONCLUSIONS

Sub-Tenon's coinjection of rHuPH20 with DM resulted in a general increase in DM levels in ocular tissues and the serum, with significant increase in the choroid and the retina, 3 h after administration.

Molecular Cloning and Characterization of Chick SPACRCAN

MY-174, a monoclonal antibody that reacts with specific sialylated O-linked glycoconjugates of chick SPACR (sialoprotein associated with cones and rods), also recognizes another molecule of 300 kDa. Here, we verified that this 300-kDa molecule is chick SPACRCAN (sialoproteoglycan associated with cones and rods), another member of a novel interphotoreceptor matrix molecule family. Screening for chick SPACRCAN was carried out by plaque hybridization using a probe for chick SPACR. Specific polyclonal antibodies raised against chick SPACRCAN were used for the following experiments. To determine whether the 300-kDa molecule detected by MY-174 was identical to 300-kDa chick SPACRCAN, the migrations of these bands were examined after various glycosidase digestions. Furthermore, the expression levels were measured during retinal development and compared with those of chick SPACR. The results demonstrated that the 300-kDa molecule recognized by MY-174 was chick SPACRCAN, and we further identified it as a proteoglycan with chondroitin sulfate chains. SPACRCAN had heavily sialylated N- and O-linked glycoconjugates, and its MY-174 antigenicity was abolished by O-glycanase treatment after neuraminidase treatment, as observed for chick SPACR. During retinal development, the mRNA and core protein expression levels, MY-174 antigenicity, and hyaluronan binding ability of SPACRCAN peaked around embryonic day 17 and then gradually decreased, whereas the corresponding expression levels of SPACR simply increased, but not its hyaluronan binding ability. The MY-174 reactivity of SPACRCAN in the adult retina was decreased compared with that in the newborn retina, whereas that of SPACR was increased. The decreased hyaluronan binding of SPACR was induced by an inhibitory effect of the excess of sialic acids in the adult stage. Thus, with similar core protein structures and specific sialylated glycoconjugates but distinct chondroitin sulfate chains, SPACRCAN and SPACR may have separate roles in the retina due to their differing expression profiles during development.

A mouse model for Stickler's syndrome: ocular phenotype of mice carrying a targeted heterozygous inactivation of type II (pro)collagen gene (Col2a1)

The influences of targeted heterozygous inactivation of type II (pro)collagen gene (Col2a1) on eye structures in the 15-month-old C57BL/6JOlaHsd mouse was studied. The eyes were collected from C57BL mice heterozygous for a targeted inactivation of one allele of the Col2a1 gene (Col2a1(+/-) mice). The eyes of C57BL mice with normal gene alleles were used as controls (Col2a1(+/+) mice). Ocular histology was analyzed from tissue sections, stained with hematoxylin and eosin, toluidine blue and alcian blue. Type II collagen was localized by immunohistochemistry. Hyaluronan (HA) was stained utilizing the biotinylated complex of the hyaluronan-binding region of aggrecan and link protein (bHABC). The anterior segment of the eye was well-formed in both genotypes, but typical folding of ciliary processes was decreased, while increased stromal extracellular matrix vacuolization was seen in the Col2a1(+/-) mice. In the lens of these mice, subcapsular extracellular matrix changes were observed. Differences in retinal structures or the number of the eyes with retinal detachment were not detected between the genotypes. In Col2a1(+/-) mice, staining for type II collagen was weaker in cornea, ciliary body, iris, lens, vitreous, retina, choroid and sclera than in the control mice. HA staining was detected in the extraocular tissues, ciliary body, iris and the choroid of both genotypes. HA staining was observed only in the vitreous body of the control animals. Heterozygous inactivation of Col2a1 gene causes structural defects in the murine eye. The observed structural changes in the ciliary body, lens and vitreous of the Col2a1(+/-) mice may represent ocular features found in the human Stickler syndrome, where the abnormalities result from COL2A1 gene mutations which lead to functional haploinsufficiency.

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.

Neurocan-GFP fusion protein: a new approach to detect hyaluronan on tissue sections and living cells

Hyaluronan is an unsulfated glycosaminoglycan (GAG) that is ubiquitously expressed in the extracellular matrix (ECM) of all vertebrates, where hyaluronan rich matrices constitute a particular permissive environment for the development of complex biological structures and also for tumor progression. Because of its conserved structure and ubiquitous expression, antibodies for its histochemical detection cannot be produced. We have engineered a fusion protein, neurocan-GFP, and expressed it as a secreted molecule in mammalian cells. Neurocan-GFP fusion protein specifically binds to hyaluronan and directly visualizes hyaluronan on tissue sections, revealing a very detailed picture of hyaluronan distribution. The fluorescent fusion protein can be used in combination with antibodies and nuclear markers for double or triple staining. In addition, it is suitable to visualize hyaluronan on living cells by time-lapse video microscopy. The successful production and application of the neurocan-GFP fusion protein opens up new perspectives for using GFP fusion proteins as detection tools in histological and cytological studies complementing conventional antibody and biotin/avidin techniques.

Molecular cloning and characterization of chick sialoprotein associated with cones and rods, a developmentally regulated glycoprotein of interphotoreceptor matrix

MY-174 is an IgM class monoclonal antibody originally established against chick PG-M/versican. The antibody specifically stains the photoreceptor layer, where we recently reported an absence of PG-M/versican. In this study, we re-characterized the antibody and identified the molecule that reacts to MY-174 at the photoreceptor layer. Immunohistochemistry localized the antigen to the matrix surrounding photoreceptors. A variety of glycosidase digestions showed that the antigen is the 150-kDa glycoprotein that has sialylated N- and O-linked glycoconjugates having a molecular mass of more than 30-kDa. The peptide sequences obtained from purified MY-174 antigen showed we had sequenced a full-length cDNA with an open reading frame of 2787 base pairs, encoding a polypeptide of 928 amino acids, with 56 and 54% identities to human and mouse sialoprotein associated with cones and rods (SPACRs), respectively, and with the structural features observed in SPACRs. The specific sialylated O-glycoconjugates here are involved in the epitope structure for MY-174. SPACR first appeared by embryonic days 15-16, and expression increased with developmental age, paralleling the adhesion between neural retina and retinal pigment epithelium. Thus, we concluded that the MY-174 antigen at the photoreceptor layer, a developmentally regulated glycoprotein, is identical to chick SPACR and may be involved in a novel system mediating adhesion between neural retina and retinal pigment epithelium.

Choroidal vascular permeability in visually regulated eye growth

The choroidal thickness fluctuates both diurnally and in response to changes in visual input. The fluctuations may represent a physiologic means of aligning the retinal photoreceptors with the focal position of distant images during the emmetropization process. To evaluate the basis for choroidal thickness changes, we studied the sources of the extravascular fluid in the chick choroid in two visually-regulated ocular growth conditions: accelerated ocular growth in goggle-induced form-deprivation myopia and ocular growth retardation in the recovery from myopia after goggle removal. Two week old chicks, controls, myopic and those recovering from myopia, received fluorescein dextran (MW = 140,000) as a tracer. It was given by intravenous injection to identify a potential vascular pathway and by intracameral injection to identify a potential pathway from the anterior chamber to the suprachoroidal space. Using a microscopically positioned needle, clear fluid was aspirated from the suprachoroidal space of the enucleated chick eye; this fluid presumably corresponds to the contents of the lacunae, prominent lymphatic-like structures of the chick choroid. Plasma, aqueous humor and suprachoroidal fluid were sampled 1 hr after injection and assayed for both protein content and the tracer dye. Sulfated glycosaminoglycans were assayed in the suprachoroidal fluid, choroid and sclera under each experimental condition. In control chicks, aqueous humor and suprachoroidal fluid protein concentrations were about 0.8 and 9% of plasma levels respectively. Aqueous humor protein concentration was unaltered in myopic or recovering eyes. Suprachoroidal fluid protein concentration in myopic eyes fell dramatically to 1.5% of plasma levels (P < 0.001). In contrast, recovery from myopia led to a marked increase in suprachoroidal fluid protein level to 30% of that in plasma (P < 0.001). None of the procedures affected suprachoroidal fluid protein in the contralateral control eyes. In all three groups of chicks, fluorescein dextran distribution in the suprachoroidal fluid at 1 hr after intravenous injection tracked protein levels, with reduced levels in myopic eyes and elevated levels in recovering eyes. After intracameral injection, suprachoroidal fluid dextran levels were higher in injected eyes of control chicks (P < 0.01) and in recovering eyes (P < 0.001) but lower in myopic eyes (P < 0.01), compared to the levels in the respective contralateral non-injected eyes in each group. Sulfated glycosaminoglycan levels were at the limits of detection in the suprachoroidal fluid under all conditions and, on a whole choroid basis, were unaltered in the choroid in either myopia or recovery. Suprachoroidal fluid is lymph-like in nature and largely derives from plasma. Sulfated glycosaminoglycan levels do not seem to regulate the fluid content of the choroid in either myopia or recovery. Instead, the changes in protein and marker dye levels in myopic and recovering eyes suggest markedly altered choroidal circulatory dynamics and capillary permeability in both conditions.

Hyaluronan in the interphotoreceptor matrix of the eye: species differences in content, distribution, ligand binding and degradation

Hyaluronan (HA) distribution in the posterior eye wall from the vitreous through the sclera, with special consideration to localization in the retina and interphotoreceptor matrix (IPM), was evaluated in human, bovine, guinea pig, dog, rat and mouse tissues using a specific probe for HA (bHABC, biotinylated hyaluronan binding complex). The sclera, some regions of the choroid and vitreous body was positive for HA, as was the basal lamina of the retina (inner limiting membrane). bHABC binding was detected in the IPM of all species studied except the mouse. Predigestion with Streptomyces hyaluronidase for 3 hr before bHABC application eliminated binding in the vitreous, choroid, sclera and basal lamina of the retina, but did not eliminate bHABC binding in the IPM. In tissues from all species studied, incubation for 6 hr with hyaluronidase eliminated bHABC binding in the IPM, except for two human samples. In these two human samples, HA specific binding in the IPM persisted even after 24 hr enzyme treatment. bHABC failed to bind to any tissue layer when bHABC was preincubated with hyaluronan oligosaccharides before application. The resistance of the IPM HA to hyaluronidase digestion may reflect extensive coverage of HA binding sites by ligands present in this compartment which hinder enzyme access. The absence of bHABC binding to the IPM when the probe is preincubated with HA oligosaccharides indicates that the binding reflects specific interaction with HA. We conclude that, with the exception of the mouse, HA is a prominent constituent of the IPM, where it may serve to organize the matrix by functioning as a basic scaffold to which other macromolecules in the insoluble IPM are attached.