Two immunologically and developmentally distinct chondroitin sulfate proteolglycans in embryonic chick brain

Lamprey lecticans link new vertebrate genes to the origin and elaboration of vertebrate tissues

The evolution of vertebrates from an invertebrate chordate ancestor involved the evolution of new organs, tissues, and cell types. It was also marked by the origin and duplication of new gene families. If, and how, these morphological and genetic innovations are related is an unresolved question in vertebrate evolution. Hyaluronan is an extracellular matrix (ECM) polysaccharide important for water homeostasis and tissue structure. Vertebrates possess a novel family of hyaluronan binding proteins called Lecticans, and studies in jawed vertebrates (gnathostomes) have shown they function in many of the cells and tissues that are unique to vertebrates. This raises the possibility that the origin and/or expansion of this gene family helped drive the evolution of these vertebrate novelties. In order to better understand the evolution of the lectican gene family, and its role in the evolution of vertebrate morphological novelties, we investigated the phylogeny, genomic arrangement, and expression patterns of all lecticans in the sea lamprey (Petromyzon marinus), a jawless vertebrate. Though both P. marinus and gnathostomes each have four lecticans, our phylogenetic and syntenic analyses are most consistent with the independent duplication of one of more lecticans in the lamprey lineage. Despite the likely independent expansion of the lamprey and gnathostome lectican families, we find highly conserved expression of lecticans in vertebrate-specific and mesenchyme-derived tissues. We also find that, unlike gnathostomes, lamprey expresses its lectican paralogs in distinct subpopulations of head skeleton precursors, potentially reflecting an ancestral diversity of skeletal tissue types. Together, these observations suggest that the ancestral pre-duplication lectican had a complex expression pattern, functioned to support mesenchymal histology, and likely played a role in the evolution of vertebrate-specific cell and tissue types.

Aggrecan, the Primary Weight-Bearing Cartilage Proteoglycan, Has Context-Dependent, Cell-Directive Properties in Embryonic Development and Neurogenesis: Aggrecan Glycan Side Chain Modifications Convey Interactive Biodiversity

This review examines aggrecan's roles in developmental embryonic tissues, in tissues undergoing morphogenetic transition and in mature weight-bearing tissues. Aggrecan is a remarkably versatile and capable proteoglycan (PG) with diverse tissue context-dependent functional attributes beyond its established role as a weight-bearing PG. The aggrecan core protein provides a template which can be variably decorated with a number of glycosaminoglycan (GAG) side chains including keratan sulphate (KS), human natural killer trisaccharide (HNK-1) and chondroitin sulphate (CS). These convey unique tissue-specific functional properties in water imbibition, space-filling, matrix stabilisation or embryonic cellular regulation. Aggrecan also interacts with morphogens and growth factors directing tissue morphogenesis, remodelling and metaplasia. HNK-1 aggrecan glycoforms direct neural crest cell migration in embryonic development and is neuroprotective in perineuronal nets in the brain. The ability of the aggrecan core protein to assemble CS and KS chains at high density equips cartilage aggrecan with its well-known water-imbibing and weight-bearing properties. The importance of specific arrangements of GAG chains on aggrecan in all its forms is also a primary morphogenetic functional determinant providing aggrecan with unique tissue context dependent regulatory properties. The versatility displayed by aggrecan in biodiverse contexts is a function of its GAG side chains.

Putative Inhibitory Extracellular Matrix Molecules Do Not Prevent Dorsal Root Regeneration into Fetal Spinal Cord Transplants

We examined the distribution of several extracellular matrix molecules (ECM) and their relationship to regenerating axons in embryonic day 14 spinal cord transplants 1 to 12 weeks after transplantation into adult rats. We used immunocytochemical tech niques to label chondroitin sulfate proteoglycans (CSPGs) and tenascin-C in adjacent sections. Synthesis of these molecules by astrocytes is thought to be one mechanism by which astrocytes inhibit regeneration in the central nervous system (CNS); glial fibrillary acidic protein antibody was used to label astrocytes and examine their rela tionship to both the ECM molecules and regenerating calcitonin gene-related pep tide (CORP)-contammg dorsal roots. We also compared the expression and distribu tion of these five markers in transplants with normal spinal cord development.

Aggrecan is expressed by embryonic brain glia and regulates astrocyte development

Determination of the molecules that regulate astrocyte development has been hindered by the paucity of markers that identify astrocytic precursors in vivo. Here we report that the chondroitin sulfate proteoglycan aggrecan both regulates astrocyte development and is expressed by embryonic glial precursors. During chick brain development, the onset of aggrecan expression precedes that of the astrocytic marker GFAP and is concomitant with detection of the early glial markers GLAST and glutamine synthetase. In co-expression studies, we established that aggrecan-rich cells contain the radial glial markers nestin, BLBP and GLAST and later in embryogenesis, the astroglial marker GFAP. Parallel in vitro studies showed that ventricular zone cultures, enriched in aggrecan-expressing cells, could be directed to a GFAP-positive fate in G5-supplemented differentiation media. Analysis of the chick aggrecan mutant nanomelia revealed marked increases in the expression of the astrocyte differentiation genes GFAP, GLAST and GS in the absence of extracellular aggrecan. These increases in astrocytic marker gene expression could not be accounted for by changes in precursor proliferation or cell death, suggesting that aggrecan regulates the rate of astrocyte differentiation. Taken together, these results indicate a major role for aggrecan in the control of glial cell maturation during brain development.

Extracellular regulators of axonal growth in the adult central nervous system

Robust axonal growth is required during development to establish neuronal connectivity. However, stable fibre patterns are necessary to maintain adult mammalian central nervous system (CNS) function. After adult CNS injury, factors that maintain axonal stability limit the recovery of function. Extracellular molecules play an important role in preserving the stability of the adult CNS axons and in restricting recovery from pathological damage. Adult axonal growth inhibitors include a group of proteins on the oligodendrocyte, Nogo-A, myelin-associated glycoprotein, oligodendrocyte-myelin glycoprotein and ephrin-B3, which interact with axonal receptors, such as NgR1 and EphA4. Extracellular proteoglycans containing chondroitin sulphates also inhibit axonal sprouting in the adult CNS, particularly at the sites of astroglial scar formation. Therapeutic perturbations of these extracellular axonal growth inhibitors and their receptors or signalling mechanisms provide a degree of axonal sprouting and regeneration in the adult CNS. After CNS injury, such interventions support a partial return of neurological function.

Neural progenitors populate the cerebrospinal fluid of preterm patients with hydrocephalus

OBJECTIVES

To evaluate cerebrospinal fluid (CSF) of preterm patients with hydrocephalus for neural progenitors.

STUDY DESIGN

This report describes a prospective study of CSF obtained from preterm infants, either with progressive posthemorrhagic hydrocephalus (PPHH) or without known intercranial pathology. Cells recovered by centrifugation were analyzed by reverse transcriptase-polymerase chain reaction or by immunocytometry. Alternatively, cells were cultured by using methods permissive to neural progenitor growth and analyzed by immunocytochemistry and Western blotting.

RESULTS

Human CSF cells were obtained from 20 preterm infants at approximately 27 weeks estimated gestational age (15 infants with PPHH, 5 control infants). The number of these cells removed over time from patients with PPHH were substantial, based on our calculations. Cells recovered from patients with PPHH transcribe markers for neural progenitors, all the mature cells types of the central nervous system, and a large battery of chondroitin sulfate proteoglycan genes, including the entire aggrecan/lectican family. These cells proliferated in culture, and precursor markers were detected by Western blotting, immunocytochemistry, and cytometry. Cells could not be cultured from control patients.

CONCLUSIONS

Neural progenitor accumulation in CSF could confound the clinical interpretation of CSF cell counts in hydrocephalus and may play as yet undetermined roles in the biology of injury after hydrocephalus. These findings suggest the potential for neural stem cell propagation from CSF.

Sulfated HNK-1 Epitope in Developing and Mature Kidney: A New Marker for Thin Ascending Loop of Henle and Tubular Injury in Acute Tubular Necrosis

The HNK-1 carbohydrate epitope is a 3-sulfo-glucuronyl residue attached to lactosamine structures on glycoproteins, proteoglycans, or glycolipids mostly expressed in the nervous system. Here, using monoclonal antibodies against the sulfated HNK-1 carbohydrate epitope, we first examined its distribution in developing and adult kidneys, then its expression in kidneys with tubular necrosis and renal neoplasms. This HNK-1 epitope was expressed in the human, rabbit, and rat, but not mouse kidney. It was detected within a subset of epithelial cells in the renal vesicle and in comma- and S-shaped bodies during early stages of nephrogenesis. In ureteral bud derivatives, the epitope was present transiently in the area where the collecting duct fused with the nephron. In the adult kidney, expression of the HNK-1 epitope became mainly restricted to the thin ascending loop of Henle where this epitope was carried by heparan- and chondro-proteoglycan. In pathological conditions, HNK-1 epitope expression increased dramatically in proximal epithelial tubule cells in kidneys with acute tubular necrosis. In tumors, the HNK-1 epitope was expressed in the epithelial component of nephroblastomas and in a subgroup of papillary renal cell carcinomas. These data suggest that molecules carrying the sulfated HNK-1 carbohydrate epitope may play an important role in critical stages of renal development and in the physiology of thin ascending loop of Henle. (J Histochem Cytochem 54:575-584, 2006)

Accumulation of Transforming Growth Factor-β2 and Nitrated Chondroitin Sulfate Proteoglycans in Cerebrospinal Fluid Correlates with Poor Neurologic Outcome in Preterm Hydrocephalus

BACKGROUND

Progressive post-hemorrhagic hydrocephalus in preterm infants strongly predicts abnormal neurologic development, and often accompanies cystic periventricular leukomalacia (cPVL). Transforming growth factor-beta1 (TGF-beta1), associated with hydrocephalus, can upregulate the chondroitin sulfate proteoglycan (CSPG) synthesis. To date, CSPG and their nitrated metabolites (NT-CSPG) have not been evaluated in hydrocephalus.

OBJECTIVES

We hypothesized that TGF-beta1, TGF-beta2, CSPG, and NT-CSPG would accumulate in cerebrospinal fluid (CSF) in preterm hydrocephalus, and their concentrations would correlate with poor long-term outcomes.

METHODS

TGF-beta1, TGF-beta2, CSPG, and NT-CSPG concentrations in CSF were measured prospectively by ELISA in 29 preterm newborns with (n=22) or without (n=34) progressive post-hemorrhagic hydrocephalus, and correlated with progressive neonatal hydrocephalus and neurologic outcome. Only concentrations from each patient's initial CSF sample were used for statistical analysis.

RESULTS

Compared to neonates without hydrocephalus, CSF [TGF-beta1], [TGF-beta2], [CSPG] and [NT-CSPG] were significantly greater by >3-, >35-, >8-, and >3-fold, respectively. Unlike CSF [TGF-beta2] and [CSPG], [TGF-beta1] correlated with CSF [total protein]. Only CSF [NT-CSPG] correlated with cPVL. Unlike [TGF-beta2] or [CSPG], [NT-CSPG] correlation with preterm progressive post-hemorrhagic hydrocephalus (PPHH) was explained entirely by the presence of cPVL among these patients. [TGF-beta2] was >20-fold greater in preterm survivors who required a ventriculoperitoneal shunt for PPHH (n=9), as compared to survivors who did not require a shunt (n=2), or those without hydrocephalus (n=12). [TGF-beta2] and [NT-CSPG] correlated inversely with Bayley Index Scores (15.0 months median adjusted age).

CONCLUSIONS

This is the first report that [TGF-beta2], [CSPG], and [NT-CSPG], measured well before term, accumulate abnormally in preterm progressive post-hemorrhagic hydrocephalus CSF, and correlate with adverse neurologic outcome.

Neural precursors express multiple chondroitin sulfate proteoglycans, including the lectican family

Chondroitin sulfate proteoglycans (CSPGs) abnormally accumulate in cerebrospinal fluid (CSF) of both human neonates with preterm hydrocephalus, and P8 hydrocephalic mice. We hypothesized CSF CSPGs are synthesized by neural precursors, separated from ventricular CSF by ependyma, which is often disrupted in hydrocephalus. Western blotting demonstrates that neural precursors cultured as neurospheres secrete CSPGs (> 30 microg/ml) into their media which appear to be very similar to these CSF CSPGs. Some CSPGs bear the stage-specific embryonic antigen-1 (ssea-1), associated with embryonic/neural stem cells. Neurospheres transcribe many CSPG genes, including the entire aggrecan/lectican family, phosphacan, and tenascin. Phosphacan can be detected in media by Western blotting. Aggrecan can be detected in media after purification using hyaluronic acid affinity chromatography. During differentiation, neurospheres downregulate CSPGs. This is the first report to show that proliferating neural precursors synthesize lecticans, including aggrecan, which are downregulated with differentiation. These observations suggest novel links between CSPGs and CNS precursor biology.

Use of a novel double-sandwich enzyme-linked immunosorbent assay method for assaying chondroitin sulfate proteoglycans that bear 3-nitrotyrosine core protein modifications, a previously unrecognized proteoglycan modification in hydrocephalus

3-Nitrotyrosine is a useful marker for nitric oxide-mediated tissue injury. However, which proteins are preferred peroxynitrite modification targets is unclear. Chondroitin sulfate proteoglycans (CSPGs) abnormally accumulate in cerebrospinal fluid of human neonates with hydrocephalus and may be a target for peroxynitrite modification. We examined (1). whether CSPG core protein can be modified by peroxynitrite in vitro; (2). to what degree in comparison to bovine serum albumin (BSA), the most commonly used nitrated protein standard; (3). whether nitrated CSPGs can be measured directly in biological samples; and (4). whether nitrated proteoglycan concentrations in cerebrospinal fluid correlate with disease. In vitro nitration of bovine aggrecan was performed by exposure to different peroxynitrite concentrations, and 3-nitrotyrosine products were measured. Bovine serum albumin (BSA) nitration was also performed in comparison. A larger percentage of tyrosine residues were nitrated in aggrecan than in BSA under all conditions tested. An enzyme-linked immunosorbent assay (ELISA) for 3-nitrotyrosine consistently overestimated aggrecan nitration when nitrated BSA was used as the standard. This is important as most current assays of nitration in biological samples use nitrated BSA as the standard. Therefore, if nitrated CPSGs were a substantial portion of the nitrated proteins in a sample, total nitrated protein content would be overestimated. Aggrecan retained its function of binding hyaluronic acid despite substantial nitration. A double-sandwich ELISA was developed for nitrated CSPGs in biological samples, using nitrated aggrecan as standard. [Nitrated CSPG] was found to be significantly elevated in preterm hydrocephalus cerebrospinal fluid (P<0.02), but correlated poorly with cerebrospinal fluid [nitric oxide] (P>0.069), suggesting that nitrated CSPG and NO levels may be independant markers of tissue injury. Peroxynitrite-mediated protein tyrosine nitration is a previously unrecognized modification of CSPGs, and may reflect level of brain injury in hydrocephalus.

Aggrecan regulates telencephalic neuronal aggregation in culture

Proteoglycans have been suggested to play roles in pattern formation in the developing central nervous system. In the chick embryo, aggrecan, a chondroitin sulfate proteoglycan, has a regionally-specific and developmentally-regulated expression profile. Telencephalic neuronal cultures, when aggregated, exhibit aggrecan expression patterns comparable to those observed in vivo. The chicken mutation nanomelia produces a truncated aggrecan species that cannot be processed further and is not secreted. Neurons from normal and nanomelic chick embryo telencephalon were scored for aggregate formation and analyzed for distribution of aggrecan protein and expression of aggrecan mRNA. Distinctly different pattern formation, with respect to aggregate size (smaller) and number (fewer) were observed in poly-L-lysine plated neuronal cultures derived from nanomelic embryos when compared to those derived from normal embryos. Significantly, the nanomelic phenotype was subsequently rescued upon addition of the brain-specific form of aggrecan. Modulation of neuronal aggregate formation was mimicked by treatment with chondroitinase ABC but not other glycanases, and was rescued by addition of chondroitin 6-sulfate to the culture media. Lastly, although broad and diffuse distribution of aggrecan among the cell aggregates in the culture paradigm was observed by immunocytochemistry, mRNA in situ hybridization revealed that only a small population of cells in the center of the aggregates was responsible for the production of the secreted aggrecan found associated with neuronal aggregates. These studies suggest a function for aggrecan as a diffusible signal in CNS histomorphogenesis.

Neurocan in the embryonic avian heart and vasculature

The chondroitin sulfate proteoglycan (CSPG) neurocan was previously considered to be nervous-system specific. However, we have found neurocan in the embryonic heart and vasculature. In stage 11 quail embryos, neurocan was prominently expressed in the myocardium, dorsal mesocardium, heart-forming fields, splanchnic mesoderm, and vicinity of the extraembryonic vaculature, and at lower levels in the endocardium. A comparison of neurocan staining with QH1 staining of vascular endothelial cells demonstrates that neurocan is frequently expressed by cells adjacent to endothelial cells, rather than by endothelial cells themselves. In some cases, a dispersed subset of cells are neurocan-positive in a field of cells that otherwise appear uniform in morphology. Later in development, neurocan expression becomes relatively limited to the nervous system. However, even in 10-day embryos, neurocan is expressed in the chorio-allantoic membrane in the tissue that separates closely packed, small-diameter blood vessels. In summary, our results suggest that neurocan may function as a barrier that regulates vascular patterning during development.

Developmental expression of the HNK-1 carbohydrate epitope on aggrecan during chondrogenesis

Previously, we showed that the HNK-1 carbohydrate epitope is expressed on aggrecan synthesized in the notochord but not in mature cartilage. In the present study, we demonstrate that in immature cartilage (embryonic day 6) the HNK-1 epitope is also expressed predominantly on aggrecan proteoglycan molecules. This finding was verified by using an aggrecan-deficient mutant, the nanomelic chick, which lacks HNK-1 immunostaining in the extracellular matrix of dividing and hypertrophic chondrocytes as late as embryonic day 12. By using both biochemical and immunologic approaches, the initially prominent expression of the HNK-1 epitope is down-regulated as development of limb and vertebral cartilage proceeds, so that by embryonic day 14 no HNK-1 is detectable. Localization changes with development and the HNK-1-aggrecan matrix becomes restricted to dividing and hypertrophic chondrocytes and is particularly concentrated in the intraterritorial matrix. Concomitant with the temporal and spatial decreases in HNK-1, there is a significant increase in keratan-sulfate content and the aggrecan-borne HNK-1 epitope is closely associated with proteolytic peptides that contain keratan sulfate chains, rather than chondroitin sulfate chains or carbohydrate-free domains. Lastly, the diminution in HNK-1 expression is consistent with a reduction in mRNA transcripts specific for at least one of the key enzymes in HNK-1 oligosaccharide biosynthesis, the HNK-1 sulfotransferase. These findings indicate that the HNK-1 carbohydrate may be a common modifier of several proteoglycans (such as aggrecan) that are usually expressed early in development, and that HNK-1 addition to these molecules may be regulated by tissue- and temporal-specific expression of requisite sulfotransferases and glycosyltransferases.

The extracellular matrix in axon regeneration

This review of ECM molecules shows quite clearly the function of the ECM in development but more importantly in the mature CNS after injury. Most of the proteoglycans, especially the large CS-PGs, are able to inhibit neurite outgrowth and in vivo experiments are now in progress to specifically inhibit these important molecules. The nature of growth promoter ECM molecules in the CNS after injury, either within or distant from the injury is now becoming better appreciated and we suggest that the laminin family should be important targets for exploration. Indeed, a better understanding of the interaction of laminin with those ECM components that are inhibitory is a clear goal for the future. Our ultimate aim must be to change the balance of factors at lesion sites to allow the more permissive environment after CNS injury to predominate.

Chondrodysplasias due to proteoglycan defects

The proteoglycans, especially the large chondroitin sulfate proteoglycan aggrecan, have long been viewed as important components of the extracellular matrix of cartilage. The drastic change in expression during differentiation from mesenchyme to cartilage, the loss of tissue integrity associated with proteoglycan degradation in several disease processes and, most important, the demonstration of abnormalities in proteoglycan production concomitant with the aberrant growth patterns exhibited by the brachymorphic mouse, the cartilage matrix deficient mouse, and the nanomelic chick provide the strongest evidence that the proteoglycan aggrecan is essential during differentiation and for maintenance of the skeletal elements. More recently, mutations associated with proteoglycans other than aggrecan, especially the heparan sulfate proteoglycans, glypican and perlecan, suggest an important role for these molecules in skeletal development as well. This review focuses on the molecular bases of the hereditary proteoglycan defects in animal models, as well as of some human chondrodysplasias, that collectively are providing a better understanding of the role of proteoglycans in the development and maintenance of the skeletal elements.

Domain organization, genomic structure, evolution, and regulation of expression of the aggrecan gene family

Proteoglycans are complex macromolecules, consisting of a polypeptide backbone to which are covalently attached one or more glycosaminoglycan chains. Molecular cloning has allowed identification of the genes encoding the core proteins of various proteoglycans, leading to a better understanding of the diversity of proteoglycan structure and function, as well as to the evolution of a classification of proteoglycans on the basis of emerging gene families that encode the different core proteins. One such family includes several proteoglycans that have been grouped with aggrecan, the large aggregating chondroitin sulfate proteoglycan of cartilage, based on a high number of sequence similarities within the N- and C-terminal domains. Thus far these proteoglycans include versican, neurocan, and brevican. It is now apparent that these proteins, as a group, are truly a gene family with shared structural motifs on the protein and nucleotide (mRNA) levels, and with nearly identical genomic organizations. Clearly a common ancestral origin is indicated for the members of the aggrecan family of proteoglycans. However, differing patterns of amplification and divergence have also occurred within certain exons across species and family members, leading to the class-characteristic protein motifs in the central carbohydrate-rich region exclusively. Thus the overall domain organization strongly suggests that sequence conservation in the terminal globular domains underlies common functions, whereas differences in the central portions of the genes account for functional specialization among the members of this gene family.

The HNK-1 carbohydrate epitope in the eye: basic science and functional implications

The HNK-1 carbohydrate epitope is part of many cell membrane and extracellular matrix molecules. It has been implicated in cell to cell and cell to extracellular matrix adhesion, and antibodies to the HNK-1 epitope are emerging as a versatile tool in eye research. They have been used to identify a novel cell type in the human eye, the subepithelial matrix cells that reside in the inner connective tissue layer (ICTL) of the ciliary body. Although these cells resemble fibroblasts in ultrastructure, they form a distinct cell population that differs in its antigenic profile from fibroblasts of other tissues. These cells are associated with the elastic fiber system of the ICTL. Other structures in the human eye that harbor the HNK-1 epitope in a nonrandom pattern are the ciliary and iris epithelia, the zonular lamella, the lens capsule, the retina, glial cells of the optic and ciliary nerves, and scleral fibroblasts. The HNK-1 epitope in the eye appears early during embryonic development and is phylogenetically conserved, but many interspecies differences exist in its distribution. The role of the HNK-1 epitope may be to structurally stabilize the ciliary body and the retina, and to participate in zonular attachments. The HNK-1 epitope has been linked with many common eye diseases. The subepithelial matrix cells seem to be susceptible to undergo irreversible damage as a result of glaucoma, thermal injury, and tissue compression. This epitope has proved to be useful in identifying intraocular deposits of exfoliation syndrome. It can explain the adhesiveness of exfoliation material. Intraocular exfoliation material differs in HNK-1 immunoreactivity from the extraocular fibrillopathy of exfoliation syndrome and its presence in fellow eyes also argues against the concept of unilateral exfoliation syndrome. The HNK-1 epitope is found in the extracellular matrix of secondary cataract and anterior subcapsular cataract, and it may contribute to their pathogenesis. Finally, the HNK-1 epitope can be used to trace neuroepithelial derivatives of the optic vesicle in developmental anomalies and in tumors of the eye. Eventual identification of molecules that bear the HNK-1 epitope in the eye will likely shed light on many aspects of ocular physiology and pathobiology

Role of the C-terminal G3 domain in sorting and secretion of aggrecan core protein and ubiquitin-mediated degradation of accumulated mutant precursors

Aggrecan is a complex multidomain macromolecule that undergoes extensive processing and post-translational modification. A thorough understanding of the events and signals that promote translocation of aggrecan through the secretory pathway is lacking. To investigate which features of the C-terminal G3 region are necessary for successful translocation of the core protein, a number of deletion constructs based on the chick aggrecan cDNA sequence were prepared and transiently expressed in COS-1 cells and the natural host, embryonic chick chondrocytes; stable cell lines were established as well. The present results clearly establish a precise requirement for that portion of the G3 C-lectin domain encoded by exon 15 for: (i) translocation from the endoplasmic reticulum (ER) to the Golgi, (ii) secretion from the cell, (iii) galactosylation of chondroitin sulfate (CS) chains, (iv) generation of Ca(+2)-dependent galactose binding ability. Furthermore, in the absence of this subdomain there is excess accumulation in the ER of expression products leading to a stress-related response involving the chaperones Grp78 and protein disulfide isomerase, followed by degradation via a ubiquitin-proteosome pathway. All of these events in the model system faithfully mimic the naturally occurring nanomelic mutant, which also elicits a ubiquitin-mediated degradation response due to the accumulation of the truncated core protein precursor. This study represents the first report of the mode of degradation of overexpressed or misfolded proteoglycans and suggests that, although proteoglycans follow different glycosylation pathways from other glycoproteins, they are monitored by an ER surveillance system similar to that which detects other misfolded proteins.

Cell specific-chondroitin sulfate proteoglycan expression during CNS morphogenesis in the chick embryo

There is increasing evidence that proteoglycans, particularly chondroitin sulfate proteoglycans (CSPGs), are integral components in the assembly of the extracellular matrix during early stages of histogenesis. The differential expression of several CSPGs in the developing CNS has raised questions on their origin, phenotype (chemical and structural characteristics), regulation of expression and function. The S103L monoclonal antibody has been an invaluable specific reagent to identify and study a large and abundant CSPG in embryonic chick brain. In the present study we demonstrate that during embryogenesis of the chick CNS, the S103L CSPG (B-aggrecan) is synthesized by neurons of all major neuronal cell types but not by astrocytes, is developmentally regulated, and is associated predominantly with neuronal somata, suggesting that neuronal-specific regulatory mechanisms control the expression of the S103L CSPG in culture. Neurons also exhibit differential expression of glycosaminoglycan type (i.e., KS) and sulfation patterns on different CSPGs when compared to astrocytes, meningial cells or chondrocytes, implying the existence of additional, cell type-specific modes of regulation of the final CSPG phenotype (chemical and structural posttranslational characteristics). A specific temporal pattern of expression of the S103L-CSPG was observed which may contribute to conditions that induce or stabilize specific cell phenotypes during CNS development. In contrast, the other major CSPG in the CNS recognized by the HNK-1 antibody, is synthesized by all cell types of different cell lineages over the entire embryonic period, suggesting a more global cell maintenance function for this CSPG.

Proteoglycans in the developing brain: new conceptual insights for old proteins

Proteoglycans are a heterogeneous class of proteins bearing sulfated glycosaminoglycans. Some of the proteoglycans have distinct core protein structures, and others display similarities and thus may be grouped into families such as the syndecans, the glypicans, or the hyalectans (or lecticans). Proteoglycans can be found in almost all tissues being present in the extracellular matrix, on cellular surfaces, or in intracellular granules. In recent years, brain proteoglycans have attracted growing interest due to their highly regulated spatiotemporal expression during nervous system development and maturation. There is increasing evidence that different proteoglycans act as regulators of cell migration, axonal pathfinding, synaptogenesis, and structural plasticity. This review summarizes the most recent data on structures and functions of brain proteoglycans and focuses on new physiological concepts for their potential roles in the developing central nervous system.

Transcriptional and posttranscriptional regulation of proteoglycan gene expression

Proteoglycans are among the most complex and sophisticated molecules of mammalian systems in terms of their protein and carbohydrate moieties. These macromolecules are in a continuous interplay with each other and the cell surface signal-transducing pathways, some of which are beginning to be elucidated. Because of their domain structure, catalytic potential, and diversity, these molecules appear to be designed for integrating numerous signaling events. For example, some proteoglycans interact with hyaluronan and lectins, thereby linking cell surfaces and distant matrix molecules. Some interact with collagen during the complex process of fibrillogenesis and regulate this biological process fundamental to animal life. Others interact with growth factors and serve as depot available during growth or tissue remodeling. In this review, we center on the most recent developments of proteoglycan biology, focusing primarily on genomic organization and transcriptional and posttranscriptional control. We discuss only those proteoglycans whose gene and promoter elements have been characterized and proved to be functional. When possible, we correlate the effects of growth factors and cytokines on proteoglycan gene expression with the topology of cis-acting elements in their genomic control regions. The analysis leads to a comprehensive critical appraisal of the principles that underlie the regulation of proteoglycan gene expression and to the delineation of common regulatory mechanisms.

Molecular cloning and expression of a second glucuronyltransferase involved in the biosynthesis of the HNK-1 carbohydrate epitope

A cDNA encoding a novel glucuronyltransferase was cloned from a rat brain cDNA library. The cDNA sequence contained an open reading frame encoding 324 amino acids, with type II transmembrane topology. The amino acid sequence revealed 49% homology to rat GlcAT-P, a glucuronyltransferase involved in the biosynthesis of the HNK-1 carbohydrate epitope of glycoproteins, [Terayama et al. (1997) Proc. Natl. Acad. Sci. USA 94, 6093-6098] and the highest sequence homology was found in the catalytic region. Northern blot analysis indicated that this newly cloned glucuronyltransferase is expressed in the nervous system, consistent with the selective localization of the HNK-1 carbohydrate epitope in the nervous system. Transfection of this cDNA into COS-1 cells induced the expression of the HNK-1 carbohydrate epitope on cell surfaces, and induced the morphological changes in these cells. These results indicated that this newly cloned cDNA is a second glucuronyltransferase involved in the biosynthesis of the HNK-1 carbohydrate epitope.

Immunodetection and partial cDNA sequence of the proteoglycan, superficial zone protein, synthesized by cells lining synovial joints

We have previously described a large proteoglycan named superficial zone protein that was isolated and purified from culture medium of superficial slices of bovine articular cartilage. Monoclonal antibodies were raised against superficial zone protein and used as probes in Western blot analyses for immunohistochemical studies both to determine precisely which cells within the joint synthesize the proteoglycan and to isolate a cDNA fragment from a bovine chondrocyte lambdagt11 library that encodes part of the proteoglycan. The cDNA fragment that was obtained with use of monoclonal antibody 6-A-1 encodes the 3' end of the sequence for superficial zone protein. On Western blots, monoclonal antibody 3-A-4 recognized an epitope on native, but not reduced, superficial zone protein, whereas monoclonal antibody 6-A-1 reacted with both native and denatured antigen. The proteoglycan was immunolocalized with monoclonal antibody 3-A-4 in chondrocytes predominantly within the superficial zone of fetal and adult articular cartilage and in some cells of the synovial lining. However, the proteoglycan was not detected in chondrocytes deep in articular cartilage, in nasal septal cartilage, or in synovial stromal cells. The only matrix staining positively for superficial zone protein was at the articular surface bordering the synovial cavity in adult, but not fetal, joints. Isolated chondrocytes and synovial cells showed intracellular binding of monoclonal antibody 3-A-4, and flow-cytometric analysis with the antibody gave the following percentages of immunopositive cells: 37.4, 52.5, 3.4, and 7.5 from chondrocytes from the full-thickness, superficial, and deep zones and from synovial cells, respectively. Thus, both chondrocytes and synovial cells bordering the joint cavity synthesize superficial zone protein and substantiate its usefulness as a phenotypic marker of particular cellular species lining the articular cavity.

Purification and characterization of a glucuronyltransferase involved in the biosynthesis of the HNK-1 epitope on glycoproteins from rat brain

The glucuronyltransferase involved in the biosynthesis of the HNK-1 epitope on glycoproteins was purified to an apparent homogeneity from the Nonidet P-40 extract of 2-week postnatal rat forebrain by sequential chromatographies on CM-Sepharose CL-6B, UDP-GlcA-Sepharose 4B, asialo-orosomucoid-Sepharose 4B, Matrex gel Blue A, Mono Q, HiTrap chelating, and HiTrap heparin columns. The purified enzyme migrated as a 45-kDa protein upon SDS-polyacrylamide gel electrophoresis under reducing conditions, but eluted as a 90-kDa protein upon Superose gel filtration in the presence of Nonidet P-40, suggesting that the enzyme forms homodimers under non-denatured conditions. The enzyme transferred glucuronic acid to various glycoprotein acceptors bearing terminal N-acetyllactosamine structure such as asialo-orosomucoid, asialo-fetuin, and asialo-neural cell adhesion molecule, whereas little activity was detected to paragloboside, a precursor glycolipid of the HNK-1 epitope on glycolipids. These results suggested that the enzyme is specifically associated with the biosynthesis of the HNK-1 epitope on glycoproteins. Sphingomyelin was specifically required for expression of the enzyme activity. Stearoyl-sphingomyelin (18:0) was the most effective, followed by palmitoyl-sphingomyelin (16:0) and lignoceroyl-sphingomyelin (24:0). Interestingly, activity was demonstrated only for sphingomyelin with a saturated fatty acid, i.e. not for that with an unsaturated fatty acid, regardless of the length of the acyl group.

Expression of HNK-1 carbohydrate and its binding protein, SBP-1, in apposing cell surfaces in cerebral cortex and cerebellum

Sulfoglucuronyl carbohydrate is the terminal moiety of neolacto-oligosaccharides, expressed on several glycoproteins of the immunoglobulin superfamily involved in cell-cell recognition and on two glycolipids. Sulfoglucuronyl carbohydrate is temporally and spatially regulated in the developing nervous system. It appears to be involved in neural cell recognition and in cell adhesion processes through its interaction with specific proteins on cell surfaces. Previously we have characterized a specific sulfoglucuronyl carbohydrate-binding protein in rat brain. Sulfoglucuronyl carbohydrate binding protein-1 is structurally similar to a 30,000 mol. wt adhesive and neurite outgrowth promoting protein amphoterin [Rauvala and Pihlaskari (1987) J. biol. Chem. 262, p. 16,625]. The pattern of expression of sulfoglucuronyl carbohydrate binding protein-1 in developing rat nervous system was studied to understand the significance of its interaction with sulfoglucuronyl carbohydrate-bearing molecules. Biochemical analyses showed that the expression of sulfoglucuronyl carbohydrate binding protein-1 was developmentally regulated similarly to sulfoglucuronyl carbohydrate. Immunocytochemical localization of sulfoglucuronyl carbohydrate binding protein-1 and sulfoglucuronyl carbohydrate was performed by bright-field and fluorescent confocal laser scanning microscopy. In postnatal day 7 rat cerebellum, sulfoglucuronyl carbohydrate binding protein-1 was primarily associated with neurons of the external and internal granule cell layers. The sulfoglucuronyl carbohydrate binding protein-1 immunoreactivity was absent in Purkinje cell bodies and their dendrites in the molecular layer, as well as in Bergmann glial fibres and in white matter. In contrast, sulfoglucuronyl carbohydrate (reactive with HNK-1 antibody) was localized in processes surrounding granule neurons in the internal granule cell layer. Sulfoglucuronyl carbohydrate was also expressed in Purkinje neurons and their dendrites in the molecular layer and their axonal processes in the white matter. To a lesser extent Bergmann glial fibres were also positive for sulfoglucuronyl carbohydrate. In the cerebral cortex, at embryonic day 21, sulfoglucuronyl carbohydrate binding protein-1 was mainly observed in immature neurons of the cortical plate and subplate and dividing cells near the ventricular zone. Whereas, sulfoglucuronyl carbohydrate was strongly expressed in the fibres of the subplate and marginal zone. Sulfoglucuronyl carbohydrate was also found in the processes surrounding the sulfoglucuronyl carbohydrate binding protein-1-expressing neuronal cell bodies in the cortical plate and in ventricular zone. The specific localization of sulfoglucuronyl carbohydrate binding protein- in cerebellar granule neurons and neurons of the cerebral cortex was also confirmed by immunocytochemistry of the dissociated tissue cell cultures. The complementary localization of sulfoglucuronyl carbohydrate and sulfoglucuronyl carbohydrate binding protein-1, both in cerebral cortex and cerebellum, in apposing cellular structures indicate possible interaction between the two and signalling during the process of cell migration and arrest of migration.

Chondroitin sulfate proteoglycan specific to retinal horizontal neurons

ABSTRACT Proteoglycans (PGs) are a diverse group of highly glycosylated macromolecules that are implicated in the development and maintenance of neuronal circuitry. With its highly ordered, layered structure, the retina ideally serves to define the synthesis, processing, and distribution of these molecules within a specific cellular subpopulation. In retinal sections, monoclonal antibody (MAb) 6A2 immunostained a horizontal cell-specific antigen. Antigen 6A2 was expressed within abundant processes in the outer plexiform layer and in rare neurites that extend across the inner nuclear layer to the inner plexiform layer. Ultrastructurally, the antigen was localized to cisternae within horizontal cell somata, along tubulovesicular structures in dendrites, and in the perisynaptic space encircling presynaptic terminals of the cone photoreceptor triad. These findings suggest that this PG is synthesized within the horizontal cells, transported to the terminals, and released into the extracellular spaces just proximal to the synapse. Based on the focal stain in the adjacent photoreceptor cell, it is possible that antigen is pinocytosed by this cell and is concentrated at the ribbon synapse. In Western immunoblots of retinal homogenates, MAb 6A2 recognized a heterogeneous chondroitin sulfate (CS) PG (CSPG) of approximately 400-500 kDa. After sequential enzymatic removal of CS glycosaminoglycans, a major broad band of 300-500 kDa was identified by MAb 1B5, which detects CSPGs that bear uronic acid linked to unsulfated N-acetylgalactosamine as the initial disaccharide in the CS chain. Localization of this PG around presynaptic terminals of the horizontal neuron and at the ribbon synapse suggests that it may play a modulatory and sustaining role at the synapse.

Double staining of proteoglycans and the HNK-1 carbohydrate epitope in pseudoexfoliation material

PURPOSE

We combined the techniques of both immunogold and cupromeronic-blue staining with electron microscopy to investigate the possible relationship between proteoglycans and the HNK-1 carbohydrate epitope in pseudoexfoliation material.

METHODS

The anterior segment was obtained from an enucleated eye with pseudoexfoliation syndrome. After cupromeronic-blue staining, following the method of Scott, specimens were embedded in L. R. White resin. Ultrathin sections were incubated successively in primary monoclonal antibodies, and 10 nm gold-conjugated secondary antibody.

RESULTS

The present study showed simultaneous presence of the HNK-1 epitope and proteoglycans associated with zonular fibrils and pseudoexfoliation material on the posterior surface of the iris. The HNK-1 epitope was immunolocalized to the periphery of the pseudoexfoliation fibers, while cupromeronic blue-positive filaments bridged adjacent pseudoexfoliation fibers.

CONCLUSIONS

Proteoglycans and the HNK-1 epitope might play a substantial role in the formation of pseudoexfoliation material via their adhesive function. Proteoglycans probably do not directly bear the HNK-1 epitope in pseudoexfoliation material.

Isolation and characterization of chondroitin sulfate proteoglycans from embryonic quail that influence neural crest cell behavior

The movement of neural crest cells is controlled in part by extracellular matrix. Aggrecan, the chondroitin sulfate proteoglycan from adult cartilage, curtails the ability of neural crest cells to adhere, spread, and move across otherwise favorable matrix substrates in vitro. Our aim was to isolate, characterize, and compare the structure and effect on neural crest cells of aggrecan and proteoglycans purified from the tissues through which neural crest cells migrate. We metabolically radiolabeled proteoglycans in E2.5 quail embryos and isolated and characterized proteoglycans from E3.3 quail trunk and limb bud. The major labeled proteoglycan was highly negatively charged, similar in hydrodynamic size to chick limb bud versican/PG-M, smaller than adult cartilage aggrecan but larger than reported for embryonic sternal cartilage aggrecan. The molecular weight of the iodinated core protein was about 400 kDa, which is more than reported for aggrecan but less than that of chick versican/PG-M. The proteoglycan bore chondroitin sulfate glycosaminoglycan chains of 45 kDa, which is larger than those of aggrecan. It lacked dermatan sulfate, heparan sulfate, or keratan sulfate chains. It bound to collagen type I, like aggrecan, but not to fibronectin (unlike versican/PG-M), collagen type IV, or laminin-1 in solid-phase assays and it bound to hyaluronate in gel-shift assays. When added at concentrations between 10 and 30 microg/ml to substrates of fibronectin, trunk proteoglycan inhibited neural crest cell spreading and migration. Attenuation of cell spreading was shown to be the most sensitive and titratable measure of the effect on neural crest cells. This effect was sensitive to digestion with chondroitinase ABC. Similar cell behavior was also produced by aggrecan and the small dermatan sulfate proteoglycan decorin; however, 30-fold more aggrecan was required to produce an effect of similar magnitude. When added in solution to neural crest cells which were already spread and migrating on fibronectin, the embryonic proteoglycan rapidly and reversibly caused complete rounding of the cells, being at least 30-fold more potent than aggrecan in this activity.

Spatially and temporally regulated modification of the receptor-like protein tyrosine phosphatase zeta/beta isoforms with keratan sulphate in the developing chick brain

Protein tyrosine phosphatase zeta (PTPzeta/RPTPbeta) is a proteoglycan-type receptor-like protein tyrosine phosphatase specifically expressed in the brain. In addition to the transmembrane form (PTPzeta-A), the extracellular splice variant (PTPzeta-S) occurs as a major soluble chondroitin sulphate proteoglycan in the brain. We prepared antibodies which specifically recognize PTPzeta-A and -S, and analysed the carbohydrate structures on the two PTPzeta isoforms in the developing chick brain. Immunoprecipitation experiments using these antibodies revealed that almost all of the keratan sulphate recognized by a monoclonal antibody (5D4) was exclusively bound to PTPzeta-A and PTPzeta-S. Addition of keratan sulphate to these proteoglycans markedly increased from embryonic day (E) 11, in contrast to the addition of Le(x) and HNK-1 carbohydrates, which gradually increased during development in accordance with expression of the core proteins, suggesting that keratan sulphate modification plays some specific roles. Moreover, at the early embryonic stage keratan sulphate was observed only in several restricted regions, especially at boundary regions such as the roof plate of the tectum, the zona limitans intrathalamica in the diencephalon, and the mesencephalon-metencephalon boundary. At the mesencephalon-metencephalon boundary, keratan sulphate modification of PTPzeta isoforms was specifically observed from E3 to E6 on a ring of cells encircling the neural tube and their radially oriented processes, which were identified as radial glial fibres. This expression pattern of keratan sulphate spatiotemporally corresponded well to the formation of the fovea isthmi, a groove separating the mesencephalon from the metencephalon. These results suggest that carbohydrates including keratan sulphate on PTPzeta isoforms play important roles in brain development by modulating the cell-cell and/or cell-substrate interactions mediated by these molecules.

Immunoelectron microscopic localization of the HNK-1 carbohydrate epitope in the anterior segment of pseudoexfoliation and normal eyes

PURPOSE

To study the presence of the cell-adhesion related HNK-1 carbohydrate epitope in the anterior segment of pseudoexfoliation and normal eyes by immunoelectron microscopy.

METHODS

Anterior segment tissue of 6 autopsy eyes with pseudoexfoliation (PEX) syndrome (5 eyes without glaucoma and 1 with glaucoma), and 6 normal autopsy eyes without PEX syndrome were studied by an electron microscopic immunogold technique using a monoclonal antibody to the HNK-1 epitope.

RESULTS

In both normal and PEX eyes, the HNK-1 epitope could be immunolocalized to the basement membranes of both ciliary epithelia and posterior iris pigmented epithelium, to the lens capsule and zonular lamella, and to the pigmented epithelial cells of iris and ciliary body. Within the inner connective tissue layer of the ciliary body, the gold label was mainly associated with the periphery of elastic fibers and microfibrillar bundles. PEX material on the surfaces of posterior iris, ciliary body, anterior lens capsule, zonular fibers, and uveal part of the trabecular meshwork reacted strongly with the HNK-1 antibody. In contrast, PEX material accumulations within the iris stroma or the juxtacanalicular tissue of the trabecular meshwork showed only weak immunoreactivity, while PEX material in the conjunctiva was totally negative.

CONCLUSIONS

The wide distribution of the HNK-1 epitope in anterior segment tissues and its association with a variety of extracellular and cellular structures was ultrastructurally demonstrated. In PEX syndrome, the varying labelling density of PEX fibers indicates a deviating carbohydrate composition in different locations of the eye. The HNK-1 epitope might be involved in the adhesiveness of PEX deposits on intraocular surfaces.

N-Acetylglucosaminyl transferase regulates the expression of the sulfoglucuronyl glycolipids in specific cell types in cerebellum during development

In the adult cerebellum, sulfoglucuronyl glycolipids (SGGLs) are specifically localized in Purkinje cells and their dendrites in the molecular layer. Other major cell types such as granule neurons and glial cells lack SGGLs. To explain the cell specific localization and the known biphasic expression of SGGLs, enzymic activities of four glycosyltransferases involved in the biosynthesis of SGGLs were studied in murine cerebellar mutants, in distinct cellular layers of rat cerebellum, and in isolated granule neurons during development. The enzymes studied were lactosylceramide: N-acetylglucosaminyl transferase (GlcNAc-Tr), lactotriaosylceramide:galactosyltransferase, neolactotetraosylceramide:glucuronyltransferase, and glucuronylglycolipid:sulfotransferase. In the cerebellum of Purkinje cell-deficient mutants, such as (pcd/pcd) and lurcher (Lc/+) where Purkinje cells are lost, GlcNAc-Tr was absent, but the other three glycosyltransferase were not severely affected. This indicated that the latter three enzymes were localized in other cell types, such as in mature granule neurons and glial cells, in addition to that in Purkinje cells, and the lack of SGGLs in these mutants was due to absence of GlcNAc-Tr. Analyses of the enzymes in the specific micro-dissected cellular layers also showed that Purkinje cell layer and molecular layer (where Purkinje cell dendrites are localized) contained all four enzymes. However, granule neurons and glial cells in the white matter lacked GlcNAc-Tr, but expressed the other three enzymes. It was concluded that the absence of SGGLs in adult granule neurons and glial cells was due to specific deficiency of the GlcNAc-Tr. Although adult granule neurons lacked GlcNAc-Tr and therefore SGGLs, isolated granule neurons from the neonatal cerebellum contained all four enzymes necessary for the synthesis of SGGLs. With development, the activity of GlcNAc-Tr in the isolated granule neurons declined but the other enzymes were not as affected, indicating that immature granule neurons were capable of synthesizing SGGLs and with maturation the synthesis was down-regulated. This also explains the biphasic expression of SGGLs in the developing cerebellum.

The nanomelic mutation in the aggrecan gene is expressed in chick chondrocytes and neurons

We have established the presence of at least two large chondroitin sulfate proteoglycans in the developing chick brain, one that reacts exclusively with HNK-1, a carbohydrate epitope found on several neural specific molecules, and one that reacts with S103L, a defined peptide epitope in the CS-2 domain of the cartilage-specific chondroitin sulfate proteoglycan (CSPG), aggrecan. In order to determine the relationships between the two distinct S103L-reactive CSPGs from cartilage (chondrocytes) and brain (neurons), as well as among the three large CSPGs expressed in brain, S103L, HNK-1 and versican, we studied the expression of these multiple proteoglycan species in the brain of nanomelic chicks. We have previously shown that homozygous embryos expressing the nanomelic phenotype exhibit a single point mutation in the aggrecan gene. In the present study, the S103L CSPG is not accumulated or synthesized by embryonic chick CNS tissue or E8CH neuronal cultures derived from nanomelic chick embryo cerebral hemispheres. In contrast, expression of both versican and the HNK-1 CSPG was normal in the mutant embryo CNS. Pulse chase experiments demonstrated the presence of the 380 kDa precursor in normal neurons and the 300 kDa truncated precursor in nanomelic neurons. Northern blot analysis revealed normal-sized mRNA but reduced levels of expression of the S103L CSPG message in nanomelic neurons, while expression of the versican message was comparable in normal and nanomelic neurons. Most conclusively, the point mutation previously identified in nanomelic cartilage mRNA was also identified in nanomelic brain mRNA. Together these results provide evidence that a single aggrecan gene is expressed in both cartilage and CNS tissue leading to the production of identical core proteins which then undergo differential and tissue-specific post-translation processing, resulting in the characteristic tissue-specific proteoglycans. Furthermore, versican and the HNK-1 CSPG, although structurally and chemically similar to the S103L CSPG, are the products of separate genes.

Up-regulation of a keratan sulfate proteoglycan following cortical injury in neonatal rats

The up-regulation of the keratan sulfate proteoglycan (ABAKAN) was examined using indirect immunohistochemical methods. Previous studies indicate that the keratan sulfate proteoglycan is associated with astrocytes in the optic nerve and in the developing rat brain. In model culture systems, this proteoglycan is capable of inhibiting the growth of neurites over laminin. To determine whether the proteoglycan is up-regulated specifically during reactive gliosis, stab wounds were made in the cerebral cortex of early postnatal rats, and the up-regulation of the proteoglycan was related to the developmentally regulated gliotic response to injury. Following a stab wound in the cortex of the late postnatal rat, reactive gliosis was consistently observed along with an up-regulation of ABAKAN. When the cortex was injured on postnatal day 2, there was a variable gliotic response and considerable variation in the regulation of proteoglycan expression. Biochemical analysis revealed that ABAKAN is a large proteoglycan with multiple keratan sulfate side-chains, at least one chondroitin sulfate side-chain and at least one additional carbohydrate chain with a terminal 3-sulfoglucuronic acid. Taken together, these data demonstrate that the boundary proteoglycan ABAKAN is also associated with reactive gliosis during early postnatal development.

S103L reactive chondroitin sulfate proteoglycan (aggrecan) mRNA expressed in developing chick brain and cartilage is encoded by a single gene

A large chondroitin sulfate proteoglycan (CSPG) identified in embryonic chick brain, and synthesized exclusively by neurons in a developmentally expressed pattern that coincides with migration and establishment of neuronal nuclei, reacts with a monoclonal antibody (S103L) developed against the cartilage-specific CSPG, aggrecan. The relationship of the brain and cartilage S103L CSPGs was established by chemical, biosynthetic and molecular analyses. Significant posttranslational differences (absence of keratan sulfate (KS), less CS, and different sulfation patterns) distinguish the brain S103L species from the cartilage S103L species. However, quantitative and qualitative Northern analysis, cassette RT-PCR and direct cloning and sequencing of the entire brain-specific S103L CSPG coding sequence, all indicate that the brain and cartilage core proteins are identical. Thus, although the S103L CSPG synthesized by chick brain and cartilage are the product of a single gene, they are clearly biochemically distinct and differentially expressed proteoglycan products, suggesting tissue specific roles for these proteoglycan homologs.

Structure and cellular distribution of mouse brain testican. Association with the postsynaptic area of hippocampus pyramidal cells

The complete deduced primary structure of mouse brain testican has been established from cDNA cloning. The cDNA encodes a polypeptide of 442 amino acids belonging to the proteoglycan family. The mouse brain testican core protein is 95% identical to its human testicular counterpart. In situ hybridization investigations revealed that mouse testican mRNA is mainly present in a subpopulation of pyramidal neurons localized in the CA3 area of the hippocampus. An immunocytochemical approach, with antibodies directed against an overexpressed chimeric antigen, produced in bacterial systems, showed that testican is associated with the postsynaptic region of these pyramidal neurons. Testican includes several putative functional domains related to extracellular or pericellular proteins associated with binding and/or regulatory functions. On the basis of its structural organization and its occurrence in postsynaptic areas, this proteoglycan might contribute to various neuronal mechanisms in the central nervous system.

Purification, characterization and developmental expression of a brain-specific chondroitin sulfate proteoglycan, 6B4 proteoglycan/phosphacan

A large brain-specific chondroitin sulfate proteoglycan, identified with monoclonal antibody 6B4 (6B4 proteoglycan/phosphacan), was isolated from rat brain. Soluble proteoglycans in the phosphate-buffered saline extract from 20-day-old rat whole brain were fractionated by anion exchange chromatography and CsCl density gradient centrifugation. 6B4 proteoglycan was further purified by gel filtration and additional ion exchange chromatography. The molecular mass of 6B4 proteoglycan shifted from 800 to 300 x 10(3) mol. wt after chondroitinase ABC digestion. The core protein was substituted with chondroitin sulfate chains with an average molecular weight of 21,000, keratan sulfate and HNK-1 carbohydrates. Glycosidase digestion of 6B4 proteoglycan with O-glycanase, N-glycanase, endo-beta-galactosidase, or keratanase did not remove the HNK-1 epitopes. The expression of 6B4 proteoglycan was developmentally regulated in the rat cerebral cortex; appearing first at embryonic day 14, peaking at postnatal day 0, and persisting throughout adulthood at a lower level. Immunohistochemical analysis indicated that 6B4 proteoglycan was distributed along the radial glial fibers and on the migrating neurons in the embryonal rar cerebrum. The radial glial fibers were stained intensely all along their length, but the neurons in the cortical plate were not stained in contrast to the moderate staining of the migrating neurons in the intermediate zone and the subplate. From postnatal day 5 to postnatal day 20, 6B4 proteoglycan was present throughout the cortex. After postnatal day 30, staining of the neuropil was weakened, and the expression of 6B4 proteoglycan was restricted around subsets of neurons. The positive neurons were mostly non-pyramidal cells (> 95%) and were relatively concentrated in layers IV and VI of the primary somatosensory cortex. Immunohistochemical analysis of the dissociated cortical neurons indicated that 6B4 proteoglycan was distributed on the cell bodies and neurites. 6B4 proteoglycan strikingly promoted neurite extension of cortical neurons from embryonic day-16 rat embryos when coated on coverslips as a substrate. 6B4 proteoglycan is a brain-specific chondroitin sulfate proteoglycan which carries keratan sulfate and HNK-1 carbohydrates. The spatiotemporal expression profile and effects on the dissociated cerebral neurons suggest that 6B4 proteoglycan plays important roles in the migration and differentiation of neurons in the immature cortex, and also in the maintenance of subsets of neurons in the mature cortex.

Analysis of proteoglycan expression in developing chicken brain: characterization of a heparan sulfate proteoglycan that interacts with the neural cell adhesion molecule

In the present study we have characterized the major proteoglycans of chick brain, focusing on their pattern of expression in development and on identifying the heparan sulfate proteoglycan (HSPG) that binds to the neural cell adhesion molecule (NCAM). The major chondroitin sulfate proteoglycans (CSPG) are a heterogeneous group of molecules with an average MW of 450 kDa. Protein core analysis reveals multiple protein cores between 100 and 350 kDa. The HSPGs are somewhat smaller, with an average MW of 350 kDa, and the major brain HSPG possesses a 250 kDa protein core. During development the relative percentage of HSPG decreases from approximately 50% of total sulfate-labeled PG at E6 to 25% by E10. In order to begin to characterize the HSPG that interacts with NCAM, we initially used an antiserum produced against a HSPG which was previously shown to copurify with NCAM (Cole and Burg: Exp Cell Res 182:44-60, 1989). This antiserum immunoprecipitated a HSPG core protein of 250 kDa, corresponding to the major HSPG of chick brain. We also show that the major brain HSPG binds to a synthetic peptide that encodes the heparan sulfate-binding domain of NCAM, and that monoclonal antibodies to a recently identified chick retinal HSPG recognize this NCAM-binding HSPG. This HSPG was immunopurified from E10 chick brain using the 6D2 monoclonal antibody, and has been shown to bind an affinity column containing the heparan sulfate-binding peptide of NCAM. Consistent with its ability to bind NCAM, we show that the intact 6D2 HSPG inhibits cell adhesion to a HBD peptide substratum, and also binds chick brain cells when employed as a substratum.

Glycans and the modulation of neural-recognition molecule function

Neural-recognition molecules are carbohydrate-bearing glycoproteins, glycolipids or proteoglycans that are found at the cell surface or in the extracellular matrix that regulate cell interactions during development, modification of synaptic activity and regeneration of nerve connections after damage in the adult. The expression of the carbohydrates appears to be fine tuned to these functions. Among the identified carbohydrates are polysialic acid, a 3'-sulfated glucuronic acid, and oligomannosidic residues. They act not only between apposing partner cell surfaces (trans-interaction) but also between recognition molecules within the surface membrane of one cell (cis-interaction), thereby forming complexes that influence transduction of signals to the cell interior.

Structural analysis of glycosaminoglycans derived from axonally transported proteoglycans in regenerating goldfish optic nerve

Structural characteristics of glycosaminoglycans (GAGs) derived from axonally transported proteoglycans (PGs) were compared in 21 days regenerating and intact goldfish optic tracts. Twenty one days following unilateral optic nerve crushes, fish received intraocular injections of 35SO4. Eight hours post injection, tracts were removed and the 35SO4-labeled GAGs, chondroitin sulfate (CS) and heparan sulfate (HS), isolated. The HS from regenerating optic tracts had a DEAE elution profile indicative of decreased charge density, while heparitinase treatment of HS followed by Sephadex G50 analysis of the resulting fragments showed a change in the elution pattern, suggesting reduced overall sulfation. HPLC analysis of HS disaccharides revealed a difference in the sulfation pattern of regenerating tract HS, characterized by the reduced presence of tri-sulfated disaccharides. Other structural features, such as the sizes of CS and HS, and the sulfation of CS, showed no changes during regeneration. These results indicate that changes in the structure of axonally transported HS accompany regeneration of goldfish optic axons.

Brain development and multiple molecular species of proteoglycan

The occurrence of multiple proteoglycan species is a characteristic of the brain. The structural features of individually characterized proteoglycans in the brain are first introduced in brief, then some examples are shown that suggest a relationship between multiple proteoglycans and the many distinct cell types and neural circuits in the brain. Typical experiments demonstrated the neuronal-activity-dependent expression of neural proteoglycans during the critical developmental period of some functional systems such as the visual and vibrissal barrel systems. In addition, the binding properties of neural proteoglycans to other cell surface molecules are discussed in conjunction with their involvement in cell-cell and cell-substratum interactions. This review also covers other potential functions of proteoglycans not only in the development and maintenance of the brain but also in the pathogenesis of Alzheimer's disease. Proteoglycans are really coming of age in neuroscience.

Expression and biological functions of sulfoglucuronyl glycolipids (SGGLs) in the nervous system--a review

Sulfoglucuronyl carbohydrate linked to neolactotetraose reacts with HNK-1 antibody. The HNK-1 carbohydrate epitope is found in two major glycolipids, several glycoproteins and in some proteoglycans of the nervous system. Most of the HNK-1 reactive glycoproteins so far identified are neural cell adhesion molecules and/or are involved in cell-cell interactions. HNK-1 carbohydrate is highly immunogenic. Several HNK-1-like antibodies, including IgM of some patients with plasma cell abnormalities and having peripheral neuropathy, have been described. This article summarizes published work mainly on sulfoglucuronyl glycolipids, SGGLs and covers: structural requirements of the carbohydrate epitope for binding to HNK-1 and human antibodies, expression of the lipids in various neural areas, stage and region specific developmental expression in CNS and PNS, immunocytochemical localization, loss of expression in Purkinje cell abnormality murine mutations, biosynthetic regulation of expression by a single enzyme N-acetylglucosaminyl transferase, identification of receptor-like carbohydrate binding neural proteins (lectins), and perceived role of the carbohydrate in physiological functions. The latter includes role in: pathogenesis of certain peripheral neuropathies, in migration of neural crest cells, as a ligand in cell-cell adhesion/interaction and as a promoter of neurite outgrowth for motor neurons. Multiple expression of HNK-1 carbohydrate in several molecules and in various neural cell types at specific stages of nervous system development has puzzled investigators as to its specific biological function, but this may also suggest its importance in multiple systems during cell differentiation and migration processes.

Proteoglycans and the acute-phase response in Alzheimer's disease brain

Alzheimer's disease is a dementing disorder affecting increasingly large numbers of individuals in the aging population. The characteristic neuropathologic changes of Alzheimer's disease are the deposition of extracellular amyloid plaques, neurons containing neurofibrillary tangles, and neuronal cell loss. The A4 amyloid peptide is the major constituent of senile plaques. In addition to the A4 peptide, senile plaques contain a variety of molecular species, including proteoglycans and inflammatory components. The presence of proteoglycans in the amyloid deposits of Alzheimer's disease and of systemic amyloidoses suggests that these molecules play an active role in the pathogenesis of amyloidosis. However, the molecular mechanisms that lead to the codeposition of amyloid peptide with proteoglycans is still unknown. Recent evidence suggests that the metabolism of proteoglycans is altered in Alzheimer's disease patients. The acute-phase response observed in the brain of patients affected by Alzheimer's disease may be responsible for this effect. In this article, we discuss the role of proteoglycans in Alzheimer's disease, and the possible interactions between factors involved in brain inflammatory mechanisms and proteoglycans in the pathogenesis of Alzheimer's disease.

Developmentally regulated expression of a brain specific species of chondroitin sulfate proteoglycan, neurocan, identified with a monoclonal antibody IG2 in the rat cerebrum

The mammalian brain contains many species of proteoglycan. To identify each proteoglycan species, we have raised monoclonal antibodies against soluble chondroitin sulfate proteoglycans purified from 10-day-old rat brains. One monoclonal antibody, named monoclonal antibody 1G2, recognized two proteoglycan species with 220,000 and 150,000 mol. wt core glycoproteins (chondroitin sulfate proteoglycan-220 and chondroitin sulfate proteoglycan-150). Partial amino acid sequences of N-termini of their core proteins coincided with those of neurocan, a brain-unique chondroitin sulfate proteoglycan species, whose complete coding sequence was recently reported [Rauch et al. (1992) J. biol. Chem. 269, 19,536-19,547]. Western blots revealed that chondroitin sulfate proteoglycan-220 became detectable in the rat cerebrum on embryonic day 14, and that it disappeared from the brain around postnatal day 30. In contrast, a fairly large amount of chondroitin sulfate proteoglycan-150 remained in the mature brain. Immunohistochemical studies revealed that 1G2 antigen was first localized in the preplate zone, then both in the marginal zone and in the subplate of the rat cerebrum on embryonic day 16, prior to arrival of the first thalamic afferents at the cortex. On embryonic day 20, immunolabeling with monoclonal antibody 1G2 began to spread from the subplate into the developing cortical plate. On postnatal day 10, the neuropil of the cerebrum, except for the barrel field, was diffusely stained with the antibody, intensely in the hippocampus and superficial layers (I-III) of the cerebral cortex and weakly elsewhere. The barrel hollows were stained very weakly compared with the barrel walls at this stage. The immunoreactivity in the hippocampus and superficial cortical layers was weakened in the mature brain, so that no particular staining pattern, but weak and diffuse staining was observed in the adult rat cerebrum. The 1G2 antigen was immunohistochemically associated largely with glial fibrillary acidic protein-positive cells in primary cultures of the neonatal rat cerebrum. Both chondroitin sulfate proteoglycan-220 and chondroitin sulfate proteoglycan-150 were detected in the conditioned media not only of highly enriched cultures of fetal rat cortical neurons but also of pure cultures of mature astrocytes; more (12- to 20-fold) in the astrocyte conditioned media. Astrocytes, in addition to neurons, may be a cellular source of neurocan in brain at least under certain physiological conditions. The spaciotemporal expression pattern of 1G2 epitope-bearing proteoglycan, or neurocan, suggests that this proteoglycan species plays some roles at least in forming the elongation pathway for early cortical afferent fibers as well as the functional barrel structure in the somatosensory cortex.

Nervous tissue proteoglycans

The structure, biosynthesis, localization, and possible functional roles of nervous tissue glycosaminoglycans and proteoglycans were last reviewed several years ago. Since that time, there has been an exponential increase in publications on the neurobiology of proteoglycans. This review will therefore focus on reports which have appeared in the period after 1988, and especially on those concerning the properties of individual characterized nervous tissue proteoglycans. Related areas such as the regulation of glycosaminoglycan biosynthesis and the roles of cell surface proteoglycans in adhesion and growth control are covered in other contributions to this special topic issue.

Expression of versican mRNA is developmentally regulated in the brain of the embryonic chick and the developing rat

RNA prepared from the brains of chick embryos at 12 days of incubation contained a 12-kb transcript that hybridized with a cDNA probe for the aggregating proteoglycan versican. No transcripts were detected in the brains of newborn rats while, at 3 days of postnatal development, three sizes of transcripts were present. None were detected in the 6-day old brain and, at later stages, the smallest transcript predominated.