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

Elucidation of the time-dependent degradation process in insoluble hyaluronic acid formulations with a controlled degradation rate

Degradation rate of hyaluronic acid to prolong its stability in vivo would be beneficial. We investigated a potential solution for prolonging the stability of hyaluronic acid within the body. We focused on decreasing the swelling ratio to slow the degradation rate of hyaluronic acid by insolubilizing sodium hyaluronate without using potentially harmful substances such as crosslinkers or modifiers. Hyaluronic acid formulations were created with three different swelling ratios and time-dependent morphological changes in hyaluronic acid formulations and were scored based on each swelling ratio. In vivo degradation was modeled in simulated body fluid and the extent of decay of test membranes were monitored over time. Results showed that, by adjusting the swelling ratio, the degradation rate of hyaluronic acid formulation could be controlled. Our research could lead to improvements in many products, not only preventive materials for postoperative adhesions, but also pharmaceutical products such as osteoarthritis treatments and cosmetic medicines.

Distinct response to heparin by two chicken brain type creatine kinase subunits

In the chicken, two creatine kinase-type B (B-CK) isoproteins, Ba- and Bb-CK, both of which are derived from a single copy gene by alternative splicing, dimerize in neural tissues. The two isoproteins contain distinct N-terminal portions, but their functional difference remains unknown. We investigated the binding affinities of Ba- and Bb-CK to heparin, hyaluronan and chondroitin sulfates, and examined the influence of these glycosaminoglycans on enzyme activity. Chicken retinal samples analyzed by Western blotting and amino acid sequence study after two-dimensional gel electrophoresis showed that heparin binds Bb-CK, but not Ba-CK, while hyaluronan and chondroitin sulfates showed no interaction with either isoprotein. Using fusion proteins covering the distinct N-terminal portions, we also showed that heparin did not react with the N-terminus of Ba-CK, but did react with that of Bb-CK. Site-directed mutagenesis of basic amino acids found in the N-terminal portion of Bb-CK identified three basic amino acids critical for this binding. Furthermore, heparin dose-dependently inhibited the enzymatic activities of Ba-CK; Bb-CK activities were less intensely inhibited. Hyaluronan and chondroitin sulfates had no effects on the activities of these enzymes. Thus, the N-terminal portion of B-CK is critical to mediate its affinity to heparin and control enzyme activity, which may be important for regulating energy metabolism in neural tissues such as brain and retina, unique organs abundant in heparan sulfates.

Competitive binding of heparin with hyaluronan to a specific motif in SPACR

The critical hyaluronan binding motif (HABM) in sialoprotein associated with cones and rods (SPACR) has already been determined. As sialoproteoglycan associated with cones and rods, another interphotoreceptor matrix molecule, binds to chondroitin sulfate and heparin with or without the employment of HABMs, respectively, we evaluated and compared the binding of these glycosaminoglycans to SPACR. A western blotting study in combination with inhibition assays showed that heparin bound specifically to SPACR. A series of GST fusion proteins covering the whole SPACR molecule narrowed down the region responsible for the binding. Finally, a site-directed mutagenesis assay demonstrated that the critical HABM also acts as a specific binding site for heparin. These results were supported with mutual inhibitions by hyaluronan and heparin in analyses using GST fusion proteins and native SPACR derived from retina. Thus, these glycosaminoglycans bind to SPACR in a different manner than to sialoproteoglycan associated with cones and rods. The competitive binding between hyaluronan and heparin to SPACR, mediated through the identical HABM, may dominate the functions of SPACR, in turn involving physiological and pathological processes involved in retinal development, aging and other related disorders.

Extracellular matrix of the central nervous system: from neglect to challenge

The basic concept, that specialized extracellular matrices rich in hyaluronan, chondroitin sulfate proteoglycans (aggrecan, versican, neurocan, brevican, phosphacan), link proteins and tenascins (Tn-R, Tn-C) can regulate cellular migration and axonal growth and thus, actively participate in the development and maturation of the nervous system, has in recent years gained rapidly expanding experimental support. The swift assembly and remodeling of these matrices have been associated with axonal guidance functions in the periphery and with the structural stabilization of myelinated fiber tracts and synaptic contacts in the maturating central nervous system. Particular interest has been focused on the putative role of chondroitin sulfate proteoglycans in suppressing central nervous system regeneration after lesions. The axon growth inhibitory properties of several of these chondroitin sulfate proteoglycans in vitro, and the partial recovery of structural plasticity in lesioned animals treated with chondroitin sulfate degrading enzymes in vivo have significantly contributed to the increased awareness of this long time neglected structure.

Molecular cloning and characterization of the expression pattern of the zebrafish alpha2, 8-sialyltransferases (ST8Sia) in the developing nervous system

Sialyltransferases are Golgi type II transmembrane glycoproteins involved in the biosynthesis of sialylated glycolipids and glycoproteins. These sialylated compounds play fundamental roles in the development of a variety of tissues including the nervous system. In this study, we have molecularly cloned from zebrafish sources, the orthologues of the six human alpha2,8-sialyltransferases (ST8Sia), a family of sialyltransferases implicated in the alpha2-8-mono-, oligo-, and poly-sialylation of glycoproteins and gangliosides and we have analysed their expression pattern in the embryonic zebrafish nervous system, using in situ hybridization. Our results show that all six ST8Sia exhibit distinct and overlapping patterns of expression in the developing zebrafish central nervous system with spatial and temporal regulation of the expression of these genes, which suggests a role for the alpha2-8-sialylated compounds in the developing nervous system.

Versican, a major hyaluronan-binding component in the dermis, loses its hyaluronan-binding ability in solar elastosis

Versican interacts with hyaluronan (HA) at its N-terminus and with fibrillin-1 at its C terminus. As versican in the dermis connects microfibrils to the HA-rich matrix for viscoelasticity, dermal diseases may involve destruction of these complexes. A recombinant versican protein, rVN, covering the HA binding region (HABR) of human versican and a polyclonal antibody, 6084, against rVN were prepared and characterized. Blotting analyses of skin extracts with 6084 and biotin-conjugated HA revealed that versican was a major HA-binding component in the dermis. Matrix metalloprotease-12, which is expressed in areas of solar elastosis, degraded versican and abrogated its HA-binding ability. Immunohistochemical analyses revealed that the elastic materials in solar elastosis lesions were negative for 6084, but positive for 2B1, an antibody recognizing the C-terminus of versican, indicating loss of the HABR in the aggregated elastic fibers. This loss of the HA-binding ability of versican followed by HA exclusion may be responsible for the pathological and phenotypical changes observed in solar elastosis.

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.

Versican in the developing brain: lamina-specific expression in interneuronal subsets and role in presynaptic maturation

Chondroitin sulfate proteoglycans (CSPGs) of the extracellular matrix help stabilize synaptic connections in the postnatal brain and impede regeneration after injury. Here, we show that a CSPG of the lectican family, versican, also promotes presynaptic maturation in the developing brain. In the embryonic chick optic tectum, versican is expressed selectively by subsets of interneurons confined to the retinorecipient laminae, in which retinal axons arborize and form synapses. It is a major receptor for the Vicia villosa B4 lectin (VVA), shown previously to inhibit invasion of the retinorecipient lamina by retinal axons (Inoue and Sanes, 1997). In vitro, versican promotes enlargement of presynaptic varicosities in retinal axons. Depletion of versican in ovo, by RNA interference, results in retinal arbors with smaller than normal varicosities. We propose that versican provides a lamina-specific cue for presynaptic maturation and discuss the related but distinct effects of versican depletion and VVA blockade.

Distinctive Expression Patterns of Heparan Sulfate O-Sulfotransferases and Regional Differences in Heparan Sulfate Structure in Chick Limb Buds

The skeletal tissue development and patterning in chick limb buds are known to be under the spacio-temporal control of various heparin-binding cell growth factors such as fibroblast growth factors and bone morphogenetic proteins. Different structural regions on heparan sulfate (HS) chains of proteoglycans could be implicated in regional differences in the binding capacities of these cell growth factors, by which they could selectively interact with targeted cells and regulate their signaling in those processes. In this study we first demonstrated by cDNA cloning that one heparan sulfate 2-O-sulfotransferase (HS2ST) and two isoforms of heparan sulfate 6-O-sulfotransferase (HS6ST-1 and -2) occurred in chick embryos and had different substrate specificities each other. We next showed by whole mount in situ hybridization that the HS6ST-1 and HS6ST-2 transcripts were preferentially localized to the anterior proximal region and at the posterior proximal region of the limb bud, respectively, whereas the HS2ST transcript was distributed rather uniformly throughout the bud. Analyses of the structures of HS from different regions of the wing buds have shown variation in that 6-O-sulfated residues are more abundant in the proximal than distal region, whereas iduronosyl 6-O-sulfated residues are abundant in the anterior proximal region and glucuronosyl 6-O-sulfated residues in the posterior proximal region. These results suggest that HS with different sulfation patterns created with multiple sulfotransferase activities provides an appropriate extracellular environment for morphogenetic signal transduction.

Expression of glycosaminoglycans during development of the rat retina

PURPOSE

To investigate the spatiotemporal expression of glycosaminoglycans during development of the rat retina.

METHODS

Hyaluronan and sulfated glycosaminoglycans, including chondroitin sulfate, heparan sulfate and keratan sulfate were detected using biotinylated hyaluronan binding protein, immunohistochemical analysis, respectively, in the rat retina at various stages of development.

RESULTS

Hyaluronan was expressed in the nerve fiber layer, inner plexiform layer and outer plexiform layer during early postnatal stages (postnatal day 1-14; P1-P14) and was undetectable after P21. In contrast, hyaluronan was faintly observed in the photoreceptor layer on P7, and gradually increased up to P49. The spatiotemporal expression pattern of chondroitin sulfate was similar to that of hyaluronan. Heparan sulfate was also detected in the nerve fiber layer, inner plexiform layer and outer plexiform layer during early postnatal stages (P1-P14). In addition, heparan sulfate was expressed in the inner limiting membrane during all stages of development. Keratan sulfate was not detected in the retina at any stage of development.

CONCLUSIONS

Hyaluronan, chondroitin sulfate and heparan sulfate are expressed in nerve fiber-rich layers during early postnatal stages and may regulate neurite outgrowth. In adulthood, both hyaluronan and chondroitin sulfate are expressed in the photoreceptor layer and may consist of the interphotoreceptor matrix. In addition, heparan sulfate is expressed in the inner limiting membrane throughout the various stages of development and may be associated with the structure of the inner limiting membrane.