The high molecular weight Cat-301 chondroitin sulfate proteoglycan from brain is related to the large aggregating proteoglycan from cartilage, aggrecan

Expression of versican isoforms V0/V1 by pancreatic cancer associated fibroblasts increases fibroblast proliferation

BACKGROUND

Versican is a large extracellular matrix (ECM) proteoglycan with four isoforms V0-3. Elevated V0/V1 levels in breast cancer and glioma regulate cell migration and proliferation, but the role of versican in pancreatic ductal adenocarcinoma (PDAC) remains unclear.

METHODS

In this study, we evaluated the expression levels of versican isoforms, as well as their cellular source and interacting partners, in vivo, in human and mouse primary and metastatic PDAC tumours and in vitro, in pancreatic tumour cells and fibroblasts using immunostaining, confocal microscopy and qPCR techniques. We also investigated the effect of versican expression on fibroblast proliferation and migration using genetic and pharmacological approaches.

RESULTS

We found that versican V0/V1 is highly expressed by cancer-associated fibroblasts (CAFs) in mouse and human primary and metastatic PDAC tumours. Our data also show that exposing fibroblasts to tumour-conditioned media upregulates V0 and V1 expressions, while Verbascoside (a CD44 inhibitor) downregulates V0/V1 expression. Importantly, V0/V1 knockdown significantly inhibits fibroblast proliferation. Mechanistically, we found that inhibiting hyaluronan synthesis does not affect versican co-localisation with CD44 in fibroblasts.

CONCLUSION

CAFs express high levels of versican V0/V1 in primary and liver metastatic PDAC tumours and versican V0/V1 supports fibroblast proliferation.

Keratan sulfate, an electrosensory neurosentient bioresponsive cell instructive glycosaminoglycan

The roles of keratan sulfate (KS) as a proton detection glycosaminoglycan in neurosensory processes in the central and peripheral nervous systems is reviewed. The functional properties of the KS-proteoglycans aggrecan, phosphacan, podocalyxcin as components of perineuronal nets in neurosensory processes in neuronal plasticity, cognitive learning and memory are also discussed. KS-glycoconjugate neurosensory gels used in electrolocation in elasmobranch fish species and KS substituted mucin like conjugates in some tissue contexts in mammals need to be considered in sensory signalling. Parallels are drawn between KS's roles in elasmobranch fish neurosensory processes and its roles in mammalian electro mechanical transduction of acoustic liquid displacement signals in the cochlea by the tectorial membrane and stereocilia of sensory inner and outer hair cells into neural signals for sound interpretation. The sophisticated structural and functional proteins which maintain the unique high precision physical properties of stereocilia in the detection, transmittance and interpretation of acoustic signals in the hearing process are important. The maintenance of the material properties of stereocilia are essential in sound transmission processes. Specific, emerging roles for low sulfation KS in sensory bioregulation are contrasted with the properties of high charge density KS isoforms. Some speculations are made on how the molecular and electrical properties of KS may be of potential application in futuristic nanoelectronic, memristor technology in advanced ultrafast computing devices with low energy requirements in nanomachines, nanobots or molecular switches which could be potentially useful in artificial synapse development. Application of KS in such innovative areas in bioregulation are eagerly awaited.

Sexually dimorphic perineuronal nets in the rodent and primate reproductive circuit

Perineuronal nets are extracellular glycoprotein structures that have been found on some neurons in the central nervous system and that have been shown to regulate their structural plasticity. Until now work on perineuronal nets has been focused on their role in cortical structures where they are selectively expressed on parvalbumin-positive neurons and are reported to restrict the experience-dependent plasticity of inhibitory afferents. Here, we examined the expression of perineuronal nets subcortically, showing that they are expressed in several discrete structures, including nuclei that comprise the brain network controlling reproductive behaviors (e.g., mounting, lordosis, aggression, and social defense). In particular, perineuronal nets were found in the posterior dorsal division of the medial amygdala, the medial preoptic nucleus, the posterior medial bed nucleus of the stria terminalis, the ventrolateral ventromedial hypothalamus and adjacent tuberal nucleus, and the ventral premammillary nucleus in both the mouse and primate brain. Comparison of perineuronal nets in male and female mice revealed a significant sexually dimorphic expression, with expression found prominently on estrogen receptor expressing neurons in the medial amygdala. These findings suggest that perineuronal nets may be involved in regulating neural plasticity in the mammalian reproductive system.

Keratan sulfate, a complex glycosaminoglycan with unique functional capability

From an evolutionary perspective keratan sulfate (KS) is the newest glycosaminoglycan (GAG) but the least understood. KS is a sophisticated molecule with a diverse structure, and unique functional roles continue to be uncovered for this GAG. The cornea is the richest tissue source of KS in the human body but the central and peripheral nervous systems also contain significant levels of KS and a diverse range of KS-proteoglycans with essential functional roles. KS also displays important cell regulatory properties in epithelial and mesenchymal tissues and in bone and in tumor development of diagnostic and prognostic utility. Corneal KS-I displays variable degrees of sulfation along the KS chain ranging from non-sulfated polylactosamine, mono-sulfated and disulfated disaccharide regions. Skeletal KS-II is almost completely sulfated consisting of disulfated disaccharides interrupted by occasional mono-sulfated N-acetyllactosamine residues. KS-III also contains highly sulfated KS disaccharides but differs from KS-I and KS-II through 2-O-mannose linkage to serine or threonine core protein residues on proteoglycans such as phosphacan and abakan in brain tissue. Historically, the major emphasis on the biology of KS has focused on its sulfated regions for good reason. The sulfation motifs on KS convey important molecular recognition information and direct cell behavior through a number of interactive proteins. Emerging evidence also suggest functional roles for the poly-N-acetyllactosamine regions of KS requiring further investigation. Thus further research is warranted to better understand the complexities of KS.

Formation and remodeling of the brain extracellular matrix in neural plasticity: Roles of chondroitin sulfate and hyaluronan

BACKGROUND

The extracellular matrix (ECM) of the brain is rich in glycosaminoglycans such as chondroitin sulfate (CS) and hyaluronan. These glycosaminoglycans are organized into either diffuse or condensed ECM. Diffuse ECM is distributed throughout the brain and fills perisynaptic spaces, whereas condensed ECM selectively surrounds parvalbumin-expressing inhibitory neurons (PV cells) in mesh-like structures called perineuronal nets (PNNs). The brain ECM acts as a non-specific physical barrier that modulates neural plasticity and axon regeneration.

SCOPE OF REVIEW

Here, we review recent progress in understanding of the molecular basis of organization and remodeling of the brain ECM, and the involvement of several types of experience-dependent neural plasticity, with a particular focus on the mechanism that regulates PV cell function through specific interactions between CS chains and their binding partners. We also discuss how the barrier function of the brain ECM restricts dendritic spine dynamics and limits axon regeneration after injury.

MAJOR CONCLUSIONS

The brain ECM not only forms physical barriers that modulate neural plasticity and axon regeneration, but also forms molecular brakes that actively controls maturation of PV cells and synapse plasticity in which sulfation patterns of CS chains play a key role. Structural remodeling of the brain ECM modulates neural function during development and pathogenesis.

GENERAL SIGNIFICANCE

Genetic or enzymatic manipulation of the brain ECM may restore neural plasticity and enhance recovery from nerve injury. This article is part of a Special Issue entitled Neuro-glycoscience, edited by Kenji Kadomatsu and Hiroshi Kitagawa.

Review : Glial Boundaries and Scars: Programs for Normal Development and Wound Healing in the Brain

Early studies of glial boundaries, which are composed of immature astrocytes and extracellular matrix mol ecules (which they express), initially offered insight into the partitioning that occurs in the developing nervous system. More recently, however, it has been suggested that similar "boundaries" may have important roles in other processes occurring in the brain, including repair after traumatic brain injury. As more is understood about the expression and function of boundary molecules and glia, their potential importance is becoming apparent in numerous neuropathological conditions, including neurodegeneration and neuroregeneration in Alzheimer's and Huntington's diseases as well as in brain neoplasms. Furthermore, before we can hope to fully understand and facilitate regeneration in the compromised brain, our knowledge of the glial boundary, both during development and in the adult, must be more complete. The Neuroscientist 1:142-154, 1995

Aggrecan and chondroitin-6-sulfate abnormalities in schizophrenia and bipolar disorder: a postmortem study on the amygdala

Perineuronal nets (PNNs) are specialized extracellular matrix aggregates surrounding distinct neuronal populations and regulating synaptic functions and plasticity. Previous findings showed robust PNN decreases in amygdala, entorhinal cortex and prefrontal cortex of subjects with schizophrenia (SZ), but not bipolar disorder (BD). These studies were carried out using a chondroitin sulfate proteoglycan (CSPG) lectin marker. Here, we tested the hypothesis that the CSPG aggrecan, and 6-sulfated chondroitin sulfate (CS-6) chains highly represented in aggrecan, may contribute to these abnormalities. Antibodies against aggrecan and CS-6 (3B3 and CS56) were used in the amygdala of healthy control, SZ and BD subjects. In controls, aggrecan immunoreactivity (IR) was observed in PNNs and glial cells. Antibody 3B3, but not CS56, also labeled PNNs in the amygdala. In addition, dense clusters of CS56 and 3B3 IR encompassed CS56- and 3B3-IR glia, respectively. In SZ, numbers of aggrecan- and 3B3-IR PNNs were decreased, together with marked reductions of aggrecan-IR glial cells and CS-6 (3B3 and CS56)-IR 'clusters'. In BD, numbers of 3B3-IR PNNs and CS56-IR clusters were reduced. Our findings show disruption of multiple PNN populations in the amygdala of SZ and, more modestly, BD. Decreases of aggrecan-IR glia and CS-6-IR glial 'clusters', in sharp contrast to increases of CSPG/lectin-positive glia previously observed, indicate that CSPG abnormalities may affect distinct glial cell populations and suggest a potential mechanism for PNN decreases. Together, these abnormalities may contribute to a destabilization of synaptic connectivity and regulation of neuronal functions in the amygdala of subjects with major psychoses.

Choindroitinase ABC I-mediated enhancement of oncolytic virus spread and anti tumor efficacy: a mathematical model

Oncolytic viruses are genetically engineered viruses that are designed to kill cancer cells while doing minimal damage to normal healthy tissue. After being injected into a tumor, they infect cancer cells, multiply inside them, and when a cancer cell is killed they move on to spread and infect other cancer cells. Chondroitinase ABC (Chase-ABC) is a bacterial enzyme that can remove a major glioma ECM component, chondroitin sulfate glycosoamino glycans from proteoglycans without any deleterious effects in vivo. It has been shown that Chase-ABC treatment is able to promote the spread of the viruses, increasing the efficacy of the viral treatment. In this paper we develop a mathematical model to investigate the effect of the Chase-ABC on the treatment of glioma by oncolytic viruses (OV). We show that the model's predictions agree with experimental results for a spherical glioma. We then use the model to test various treatment options in the heterogeneous microenvironment of the brain. The model predicts that separate injections of OV, one into the center of the tumor and another outside the tumor will result in better outcome than if the total injection is outside the tumor. In particular, the injection of the ECM-degrading enzyme (Chase-ABC) on the periphery of the main tumor core need to be administered in an optimal strategy in order to infect and eradicate the infiltrating glioma cells outside the tumor core in addition to proliferative cells in the bulk of tumor core. The model also predicts that the size of tumor satellites and distance between the primary tumor and multifocal/satellite lesions may be an important factor for the efficacy of the viral therapy with Chase treatment.

Chondroitinase and growth factors enhance activation and oligodendrocyte differentiation of endogenous neural precursor cells after spinal cord injury

The adult spinal cord harbours a population of multipotent neural precursor cells (NPCs) with the ability to replace oligodendrocytes. However, despite this capacity, proliferation and endogenous remyelination is severely limited after spinal cord injury (SCI). In the post-traumatic microenvironment following SCI, endogenous spinal NPCs mainly differentiate into astrocytes which could contribute to astrogliosis that exacerbate the outcomes of SCI. These findings emphasize a key role for the post-SCI niche in modulating the behaviour of spinal NPCs after SCI. We recently reported that chondroitin sulphate proteoglycans (CSPGs) in the glial scar restrict the outcomes of NPC transplantation in SCI by reducing the survival, migration and integration of engrafted NPCs within the injured spinal cord. These inhibitory effects were attenuated by administration of chondroitinase (ChABC) prior to NPC transplantation. Here, in a rat model of compressive SCI, we show that perturbing CSPGs by ChABC in combination with sustained infusion of growth factors (EGF, bFGF and PDGF-AA) optimize the activation and oligodendroglial differentiation of spinal NPCs after injury. Four days following SCI, we intrathecally delivered ChABC and/or GFs for seven days. We performed BrdU incorporation to label proliferating cells during the treatment period after SCI. This strategy increased the proliferation of spinal NPCs, reduced the generation of new astrocytes and promoted their differentiation along an oligodendroglial lineage, a prerequisite for remyelination. Furthermore, ChABC and GF treatments enhanced the response of non-neural cells by increasing the generation of new vascular endothelial cells and decreasing the number of proliferating macrophages/microglia after SCI. In conclusions, our data strongly suggest that optimization of the behaviour of endogenous spinal NPCs after SCI is critical not only to promote endogenous oligodendrocyte replacement, but also to reverse the otherwise detrimental effects of their activation into astrocytes which could negatively influence the repair process after SCI.

Lectican proteoglycans, their cleaving metalloproteinases, and plasticity in the central nervous system extracellular microenvironment

The extracellular matrix (ECM) in the central nervous system actively orchestrates and modulates changes in neural structure and function in response to experience, after injury, during disease, and with changes in neuronal activity. A component of the multi-protein, ECM aggregate in brain, the chondroitin sulfate (CS)-bearing proteoglycans (PGs) known as lecticans, inhibit neurite outgrowth, alter dendritic spine shape, elicit closure of critical period plasticity, and block target reinnervation and functional recovery after injury as the major component of a glial scar. While removal of the CS chains from lecticans with chondroitinase ABC improves plasticity, proteolytic cleavage of the lectican core protein may change the conformation of the matrix aggregate and also modulate neural plasticity. This review centers on the roles of the lecticans and the endogenous metalloproteinase families that proteolytically cleave lectican core proteins, the matrix metalloproteinases (MMPs) and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs), in neural plasticity. These extracellular metalloproteinases modulate structural neural plasticity-including changes in neurite outgrowth and dendritic spine remodeling-and synaptic plasticity. Some of these actions have been demonstrated to occur via cleavage of the PG core protein. Other actions of the proteases include cleavage of non-matrix substrate proteins, whereas still other actions may occur directly at the cell surface without proteolytic cleavage. The data convincingly demonstrate that metalloproteinases modulate physiological and pathophysiological neural plasticity.

Models of CNS injury in the nonhuman primate: A new era for treatment strategies

Central nervous system (CNS) injuries affect all levels of society indiscriminately, resulting in functional and behavioral deficits with devastating impacts on life expectancies, physical and emotional wellbeing. Considerable literature exists describing the pathophysiology of CNS injuries as well as the cellular and molecular factors that inhibit regrowth and regeneration of damaged connections. Based on these data, numerous therapeutic strategies targeting the various factors of repair inhibition have been proposed and on-going assessment has demonstrated some promising results in the laboratory environ. However, several of these treatment strategies have subsequently been taken into clinical trials but demonstrated little to no improvement in patient outcomes. As a result, options for clinical interventions following CNS injuries remain limited and effective restorative treatment strategies do not as yet exist. This review discusses some of the current animal models, with focus on nonhuman primates, which are currently being modeled in the laboratory for the study of CNS injuries. Last, we review the current understanding of the mechanisms underlying repair/regrowth inhibition and the current trends in experimental treatment strategies that are being assessed for potential translation to clinical applications.

Immunohistochemical parcellation of the ferret (Mustela putorius) visual cortex reveals substantial homology with the cat (Felis catus)

Electrophysiological mapping of the adult ferret visual cortex has until now determined the existence of 12 retinotopically distinct areas; however, in the cat, another member of the Carnivora, 20 distinct visual areas have been identified by using retinotopic mapping and immunolabeling. In the present study, the immunohistochemical approach to demarcate the areal boundaries of the adult ferret visual cortex was applied in order to overcome the difficulties in accessing the sulcal surfaces of a small, gyrencephalic brain. Nonphosphorylated neurofilament (NNF) expression profiles were compared with another classical immunostain of cortical nuclei, Cat-301 chondroitin sulfate proteoglycan (CSPG). Together, these two markers reliably demarcated the borders of the 12 previously defined areas and revealed further arealization beyond those borders to a total of 19 areas: 21a and 21b; the anterolateral, posterolateral, dorsal, and ventral lateral suprasylvian areas (ALLS, PLLS, DLS, and VLS, respectively); and the splenial and cingulate visual areas (SVA and CVA). NNF expression profile and location of the newly defined areas correlate with previously defined areas in the cat. Moreover, NNF and Cat-301 together revealed discrete expression domains in the posteroparietal (PP) cortex, demarcating four subdivisions in the caudal lateral and medial domains (PPcL and PPcM) and rostral lateral and medial domains (PPrL and PPrM), where only two retinotopic maps have been previously identified (PPc and PPr). Taken together, these studies suggest that NNF and Cat-301 can illustrate the homology between cortical areas in different species and draw out the principles that have driven evolution of the visual cortex.

Differential distribution of aggrecan isoforms in perineuronal nets of the human cerebral cortex

Aggrecan is a component of the CNS extracellular matrix (ECM) and we show here that the three primary alternative spliced transcripts of the aggrecan gene found in cartilage are also present in the adult CNS. Using a unique panel of core protein-directed antibodies against human aggrecan we further show that different aggrecan isoforms are deposited in perineuronal nets (PNNs) and neuropil ECM of Brodmann’s area 6 of the human adult cerebral cortex. According to their distribution pattern, the identified cortical aggrecan isoforms were subdivided into five clusters spanning from cluster 1, comprised isoforms that appeared widespread throughout the cortex, to cluster 5, which was an aggrecan-free subset. Comparison of brain and cartilage tissues showed a different relative abundance of aggrecan isoforms, with cartilage-specific isoforms characterizing cluster 5, and PNN-associated isoforms lacking keratan sulphate chains. In the brain, isoforms of cluster 1 were disclosed in PNNs surrounding small-medium interneurons of layers II–V, small-medium pyramidal neurons of layers III and V and large interneurons of layer VI. Aggrecan PNNs enveloped both neuron bodies and neuronal processes, encompassing pre-terminal nerve fibres, synaptic boutons and terminal processes of glial cells and aggrecan was also observed in continuous ‘coats’ associated with satellite, neuron-associated cells of a putative glial nature. Immunolabelling for calcium-binding proteins and glutamate demonstrated that aggrecan PNNs were linked to defined subsets of cortical interneurons and pyramidal cells. We suggest that in the human cerebral cortex, discrete, layer-specific PNNs are assembled through the participation of selected aggrecan isoforms that characterize defined subsets of cortical neurons.

Effects of covalently attached chondroitin sulfate on aggrecan cleavage by ADAMTS-4 and MMP-13

Aggrecan is degraded by several aggrecanase-1 (ADAMTS-4) isoforms differing in the number of sulfated glycosaminoglycan (sGAG)-binding motifs. ADAMTS-4 and MMPs cleave aggrecan more efficiently within the chondroitin sulfate (CS)-rich region than the interglobular domain (IGD). We investigated the influence of CS on aggrecan core protein cleavage by ADAMTS-4 (p68) and (p40) as well as MMP-13, which has no recognizable GAG-binding sites. Chondroitinase ABC-treated cartilage aggrecan was cleaved with ADAMTS-4 (p68) less efficiently than CS-substituted aggrecan within the CS-2 domain. Keratanase-treated aggrecan exhibited reduced IGD cleavage, but when both CS and KS were removed, the IGD cleavage was restored. This result suggests that KS in the IGD may compete with CS for ADAMTS-4 (p68) binding. In the absence of KS, however, p68 binding was shifted to the CS-2 domain. CS-deficient full-length recombinant aggrecan (rbAgg) was produced by chondroitinase ABC treatment, or by expression in the xylosyltransferase-deficient CHO-pgsA745 cell line. When digested with the ADAMTS-4 (p68), each of these preparations exhibited reduced CS-2 domain cleavage compared to CS-substituted CHO-K1 cell-derived aggrecan. Additionally, CS-deficient rbAgg showed increased IGD scission prior to cleavage within the CS-2 domain. ADAMTS-4 (p40) readily cleaved both rbAggs within the IGD, but cleaved poorly within the CS-2 domain, indicating little CS dependence. MMP-13, in contrast, cleaved the CS region and the IGD of both CS-substituted and CS-deficient rbAgg equally well. These data indicate that covalently bound CS enhances ADAMTS-4-mediated cleavage within the CS-rich region. MMP-13 also cleaves preferentially within the CS-region, but by an apparently CS-independent mechanism.

Distribution of hyaluronan in the central nervous system of the frog

The qualitative and quantitative distribution pattern of hyaluronan (HA), a component of the extracellular matrix (ECM), was studied in the frog central nervous system by using a highly specific HA probe and digital image analysis. HA reaction was observed in both the white and the gray matter, showing a very intense staining around the perikarya and dendrites in the perineuronal net (PN). In the telencephalon, strong reaction was found in different parts of the olfactory system, in the pallium, and in the amygdala. In the diencephalon, intensive staining was found in the nucleus of Bellonci, the dorsal habenula, the lateral and central thalamic nuclei, and the subependymal zone of the third ventricle. In the mesencephalon, layers of optic tectum displayed different intensities, with the strongest reaction in layers B, D, F, 3, and 5. Other structures of the mesencephalon showed regional differences. The PN was especially intensively stained around the perikarya of the toral nuclei, the oculomotor and trochlear nuclei, and the basal optic nucleus. In the rhombencephalon, the granular layer of cerebellum, the vestibulocochlear nuclei, the superior olive, the spinal tract of the trigeminal nerve, and parts of the reticular formation showed the most intense reaction in the PN. In the spinal cord, considerable HA staining was found in the white matter and around the perikarya of motoneurons. The present study is the first description of the HA-positive areas of frog brain and spinal cord demonstrating the heterogeneity of HA distribution in the frog central nervous system.

Ontogeny of rat chondrocyte proliferation: studies in embryo, adult and osteoarthritic (OA) cartilage

The aim of this work was to study the ontogeny of chondrocyte cell division using embryo, adult and osteoarthritic (OA) cartilage. We searched for mitosis phases and performed a comparative evaluation of mitotic index, basic fibroblast growth factor b (FGFb), transforming growth factor beta1 (TGF-beta1) receptors, cyclin dependent kinase (CDK1) and Cyclin-B expression in fetal, neonate, 3, 5, 8 weeks old rats and experimental OA. Our results showed that mitosis phases were observed in all normal cartilage studied, although, we found a decrease in mitotic index in relation to tissue development. No mitosis was detected in OA cartilage. We also found a statistical significant reduction in cell number in OA cartilage, compared with the normal tissue. Furthermore, FGFb and TGF-beta1 receptors diminished in relation to tissue development, and were very scarce in experimental OA. Western blot assays showed CDK-1 expression in all cases, including human-OA cartilage. Similar results were observed for Cyclin-B, except for 8 weeks, when it was not expressed. Our results suggest that cell division seems to be scarce, if not absent within the OA cartilage studied. Nevertheless, the existence of factors essential for cell division leaves open the question concerning chondrocyte proliferation in OA cartilage, which is likely to be present in the early stages of the disease.

Destruction of extracellular matrix proteoglycans is pervasive in simian retroviral neuroinfection

Disruption of the perineuronal matrix has been reported in human immunodeficiency virus (HIV) encephalitis. To better understand the extent of matrix disruption during lentiviral encephalitis, we characterized the extracellular matrix (ECM) damage in brains of 12 macaques infected with simian immunodeficiency virus (SIV). Matrix integrity was assessed by Wisteria floribunda lectin histochemistry. Confocal microscopy was used to quantify matrix loss, macrophage infiltration, and synaptic damage. Disruption of brain ECM was present shortly after retroviral infection, preceding parenchymal macrophage infiltration. In agreement with previous observations, reduced staining of presynaptic and postsynaptic proteins in SIV encephalitis occurred concurrently with matrix abnormalities. Lentiviral infection induced microglial and macrophage expression of two disintegrins and metalloproteinases with thrombospondin motifs (ADAMTS-1 and ADAMTS-4), with high substrate specificity for matrix proteoglycans. Matrix damage is pervasive during SIV neuroinfection, which suggests interventions to conserve brain matrix proteoglycans might avert or delay retroviral-induced neurodegeneration.

Molecular cloning of Bral2, a novel brain-specific link protein, and immunohistochemical colocalization with brevican in perineuronal nets☆

The hyaluronan binding chondroitin sulphate proteoglycans, called lecticans, are the abundant extracellular matrix molecules in the developing and/or adult brain. The link proteins (LPs) are also known to be coordinately present in brain. We report here the molecular cloning and expression analysis of a novel member of LPs: Bral2, predominantly expressed in brain. The Bral2 mRNA expression is first detected at P20 and continued through adulthood, suggesting its functional importance and association with adult-type lecticans. The substantial immunoreactivity of Bral2 is found in several nuclei throughout the midbrain and hindbrain in a perineuronal net pattern. In situ hybridization revealed that Bral2 is synthesized by these neurons themselves, especially by the GABAergic neurons in the cerebellar cortex. Interestingly, the colocalization and synergic importance of Bral2 and brevican in the perineuronal nets is indicated by the comparative immunohistochemical analysis using wild-type and brevican-deficient mouse brain. Our results suggest that Bral2 is involved in the formation of extracellular matrix contributing to perineuronal nets and facilitate the understanding of a functional role of these extracellular matrices.

Molecular mechanisms of glioma invasiveness: the role of proteases

The invasive nature of brain-tumour cells makes an important contribution to the ineffectiveness of current treatment modalities, as the remaining tumour cells inevitably infiltrate the surrounding normal brain tissue, which leads to tumour recurrence. Such local invasion remains an important cause of mortality and underscores the need to understand in more detail the mechanisms of tumour invasiveness. Several proteases influence the malignant characteristics of gliomas--could their inhibition prove to be a useful therapeutic strategy?

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.

Versican V2 is a major extracellular matrix component of the mature bovine brain

We have isolated and characterized the proteoglycan isoforms of versican from bovine brain extracts. Our approach included (i) cDNA cloning and sequencing of the entire open reading frame encoding the bovine versican splice variants; (ii) preparation of antibodies against bovine versican using recombinant core protein fragments and synthetic peptides; (iii) isolation of versican isoforms by ammonium sulfate precipitation followed by anion exchange and hyaluronan affinity chromatography; and (iv) characterization by SDS-polyacrylamide gel electrophoresis and Coomassie Blue staining or immunoblotting. Our results demonstrate that versican V2 is, together with brevican, a major component of the mature brain extracellular matrix. Versicans V0 and V1 are only present in relatively small amounts. Versican V2 migrates after chondroitinase ABC digestion with an apparent molecular mass of about 400 kDa, whereas it barely enters a 4-15% polyacrylamide gel without the enzyme treatment. The 400-kDa product is recognized by antibodies against the glycosaminoglycan-alpha domain and against synthetic NH2- and COOH-terminal peptides. Our preparations contain no major proteolytic products of versican, e.g. hyaluronectin or glial hyaluronate-binding protein. Having biochemical quantities of versican V2 available will allow us to test its putative modulatory role in neuronal cell adhesion and axonal growth.

Transcripts for secreted and GPI-anchored brevican are differentially distributed in rat brain

Brevican is a member of the aggrecan/versican family of proteoglycans. In contrast to the other family members, brevican occurs both as soluble isoforms secreted into the extracellular space and membrane-bound isoforms which are anchored to the cell surface via a glycosylphosphatidylinositol (GPI) moiety. Expression of both variants, which are encoded by two differentially processed transcripts from the same gene, is confined to the nervous system. In the current study, we have used in situ hybridization to examine the cellular sites of synthesis for both mRNAs during postnatal development of the rat brain. Whereas the 3.6-kb transcript encoding secreted brevican displays a widespread distribution in grey matter structures, including cerebellar and cerebral cortex, hippocampus and thalamic nuclei with silver grains accumulating over neuronal cell bodies, the smaller transcript (3.3 kb) encoding GPI-anchored isoforms appears to be largely confined to white matter tracts and diffusely distributed glial cells. This expression pattern is further confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR) experiments with RNA from different glial cell cultures, and by biochemical data demonstrating that the crude membrane fraction from isolated optic nerve contains high amounts of phosphatidylinositol-specific phospholipase C (PI-PLC)-sensitive brevican immunoreactivity. During ontogenetic development, both brevican transcripts are generally up-regulated. However, the expression of glypiated brevican is delayed by about 1 week, compared with the expression of the secreted isoform. This late appearance of GPI-linked brevican, its predominant expression in glial cells and its tight association with brain myelin fractions suggest a functional role in neuroglia.

Regulatory activities of the 5'- and 3'-untranslated regions and promoter of the human aggrecan gene

Identification and characterization of the regulatory elements of the human aggrecan gene are necessary first steps in addressing the molecular mechanisms through which the gene is regulated. Using luciferase reporter constructs driven by the human aggrecan promoter or the cytomegalovirus promoter, the 5'- and 3'-untranslated regions of the human aggrecan gene were found to regulate gene expression transcriptionally in a promoter- and/or cell type-specific manner. Independent of cell type, the 5'-untranslated region was inhibitory with respect to the cytomegalovirus promoter, but it was stimulatory to the human aggrecan promoter. The 5'-untranslated region inhibited the cytomegalovirus promoter by approximately 60% in both chondrocytes and NIH 3T3 cells, but it stimulated the activity of the human aggrecan promoter about 8-fold in chondrocytes and 40-fold in NIH 3T3 cells. In contrast, the 3'-untranslated region inhibited the activities of the human aggrecan promoter by 40-70% in both cell types, but it stimulated the cytomegalovirus promoter activities by 50-60% in NIH 3T3 cells and inhibited its activity by 70% in chondrocytes. The differential effects of the untranslated regions on the two types of promoters may be a reflection of differences in regulation of TATA-less promoters, such as the human aggrecan promoter, and TATA-containing promoters, such as the cytomegalovirus promoter.

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.

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.

Growth cone behavior in the presence of soluble chondroitin sulfate proteoglycan (CSPG), compared to behavior on CSPG bound to laminin or fibronectin

Proteoglycans (PGs) are complex macromolecules of the extracellular matrix (ECM) that have a wide variety of effects on developing and regenerating neurons in vivo and in vitro. One hypothesis regarding the mechanisms of PG regulation of neuronal behavior states that the conformation of PGs may be critical, and thus that ECM- or cell surface-bound PGs may operate differently than secreted (soluble) PGs. Therefore, this study examined differences between the effects of soluble chondroitin sulfate proteoglycan (CSPG) and substratum-bound CSPG on neuronal growth cone behavior. Dissociated chicken dorsal root ganglion (DRG) neurons were cultured on either laminin (LN) or fibronectin (FN), both sensory neurite outgrowth-promotin glycoproteins. CSPG (or chondroitin sulfate alone) was either bound to FN or LN, or was added to the culture media. Subsequently, using time lapse video microscopy and image analysis, this study measured: (1) neuronal attachment, (2) neurite outgrowth, (3) rate of neurite elongation, and (4) filopodial length and lifespan. To determine the site of CSPG action, DRG neurons were grown on either: CS-1, a FN peptide [Humphries M. J. et al. (1987) J. biol. Chem. 262, 6886-6892], or a recombinant FN protein, RFNIIIcs (Maejne, submitted), both of which permit DRG attachment and outgrowth but do not have recognized CSPG binding sites, and the resulting neuronal behavior was compared to that of DRG neurons grown on intact FN. The results of these studies confirm that the effect of CSPG on DRG neurons is concentration-, conformation- and substratum-dependent. On I.N, soluble CSPG had little to no effect on neurite initiation or outgrowth, while substratum-bound CSPG inhibited neurite outgrowth. In contrast, on FN, soluble CSPG inhibited neurite outgrowth and decreased the rate of neurite elongation. Soluble CSPG did not affect the length of sensory growth cone filopodia or filopodial lifespan on either LN or FN. From the FN fragment experiments, we found that: (1) soluble CSPG reduces neurite outgrowth on FN or FN fragments, but not on LN, up to 80%, and reduces elongation rate on FN up to 50%, and (2) soluble CSPG regulates neuronal behavior by binding directly to growth cones elongating on FN. Given that substratum-bound CSPG from a variety of sources is inhibitory to neurite outgrowth and to the rate of neurite elongation, while soluble CSPG often has different effects on growth cone behavior, the regulation of growth cone behavior by CSPGs may be dependent upon CSPG conformation. Further, CSPG may affect growth cone behavior by either binding to the substratum or by binding directly to growth cones.

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.

Molecular cloning of human fibroblast hyaluronic acid-binding protein confirms its identity with P-32, a protein co-purified with splicing factor SF2. Hyaluronic acid-binding protein as P-32 protein, co-purified with splicing factor SF2

The purification of a 68-kDa hyaluronic acid-binding protein (HA-binding protein), a homodimer of 34 kDa that binds specifically to hyaluronic acid, has been reported earlier by us (Gupta, S., Batchu, R.B., and Datta, K. (1991) Eur. J. Cell Biol. 56, 58-67). Here, we report the isolation of a partial cDNA clone from a lambda gt11 cDNA expression library of human skin fibroblast by immuno-screening with HA-binding protein antiserum. The internal polypeptide sequence (83 residues) of the purified hyaluronic acid-binding protein is identical to the predicted protein sequence derived from hyaluronic acid-binding protein cDNA, suggesting the authenticity of the clone. Interestingly, this hyaluronic acid-binding protein cDNA sequence has complete homology with the cDNA sequence of a protein P-32, co-purified with the human pre-mRNA splicing factor SF2 (Krainer, A.R., Mayeda, A., Kozak, D., and Binns, G. (1991) Cell 66, 383-394). Furthermore, the data on the N-terminal sequence of hyaluronic acid-binding protein and the predicted polypeptide of P-32 revealed the identical coding sequence of 209 amino acids for both the proteins. As the identity and functional characterization of P-32 have not yet been reported, P-32 cDNA was expressed in Escherichia coli, and the recombinant P-32 protein was purified by hyaluronic acid-Sepharose affinity chromatography. The recombinant P-32 protein showed immunocross-reactivity with the polyclonal antibodies raised against HA-binding protein. The predicted amino acid sequence of the protein fulfilled the minimal criteria for binding to hyaluronic acid, i.e. two basic amino acids flanking a seven-amino acid stretch, as reported for other hyaluronic acid affinity of the recombinant P-32 protein was confirmed by biotinylated hyaluronic acid binding assay. The binding of recombinant P-32 protein to biotinylated hyaluronic acid binding assay. The binding of recombinant P-32 protein to biotinylated hyaluronic acid can be competed only with excess unlabeled hyaluronic acid, confirming its specificity toward hyaluronic acid. All these results suggest that both P-32, co-purified with the human pre-mRNA splicing factor SF2, and 34-kDa hyaluronic acid-binding protein reported by us are the same protein and that it is a new member of the hyaluronic acid-binding protein family, the "hyaladherins."

Receptor-mediated adhesive and anti-adhesive functions of chondroitin sulfate proteoglycan preparations from embryonic chicken brain

Chondroitin sulfate proteoglycans inhibit the adhesion of cells to extracellular matrix proteins that otherwise permit adhesion. Although proteoglycans are widely assumed to act by masking the other protein in a mixed substrate, recent studies suggest that proteoglycans inhibit adhesion through mechanisms initiated by their binding to specific cell surface receptors. To explore this issue, we developed a purification scheme to isolate proteoglycan aggregates, monomers, and core proteins. Two distinct adhesion assays were used to study the interaction of these proteoglycan preparations with human foreskin fibroblasts: the gravity assay in which cell attachment is stabilized by cell spreading, and the centrifugation assay in which spreading does not play a role. All proteoglycan preparations mediate adhesion in the centrifugation assay but not in the gravity assay. In the centrifugation assay, proteoglycan aggregates and monomers are considerably more active than other extracellular matrix proteins while proteoglycan core proteins are at least as active as other extracellular matrix proteins. Proteoglycan core proteins bind to cell-associated hyaluronic acid, but not to integrins. Using mixed substrates in the gravity assay, all proteoglycan preparations inhibited cell attachment to fibronectin and vitronectin but not to collagen I and laminin. Although proteoglycan aggregates and monomers are more active than core proteins in inhibiting adhesion in the gravity assay, core proteins are still clearly active. A variety of control experiments suggest that the inhibition of cell attachment by proteoglycans is mediated through the specific interactions of proteoglycans with cell surface receptors, resulting in the inhibition of cell spreading. These results suggest at least two molecular mechanisms for proteoglycan-fibroblast interactions, one involving the chondroitin sulfate on the proteoglycan and an as yet unidentified receptor, the other involving the proteoglycan core protein and cell-associated hyaluronic acid.

Brevican, a chondroitin sulfate proteoglycan of rat brain, occurs as secreted and cell surface glycosylphosphatidylinositol-anchored isoforms

cDNA clones encoding proteins related to the aggrecan/versican family of proteoglycan core proteins have been isolated with antisera against rat brain synaptic junctions. Two sets of overlapping cDNAs have been characterized that differ in their 3'-terminal regions. Northern analyses with probes derived from unique regions of each set were found to hybridize with two brain-specific transcripts of 3.3 and 3.6 kilobases (kb). The 3.6-kb transcript encodes a polypeptide that exhibits 82% sequence identity with bovine brevican and is thought to be the rat ortholog of brevican. Interestingly, the polypeptide deduced from the open reading frame of the 3.3-kb transcript is truncated just carboxyl-terminal of the central domain of brevican and instead contains a putative glypiation signal. Antibodies raised against a bacterially expressed glutathione S-transferase-brevican fusion protein have been used to show that both soluble and membrane-bound brevican isoforms exist. Treatment of the crude membrane fraction and purified synaptic plasma membranes with phosphatidylinositol-specific phospholipase C revealed that isoforms of brevican are indeed glycosylphosphatidylinositol-anchored to the plasma membrane. Moreover, digestions with chondroitinase ABC have indicated that rat brevican, like its bovine ortholog, is a conditional chondroitin sulfate proteoglycan. Immunohistochemical studies have shown that brevican is widely distributed in the brain and is localized extracellularly. During postnatal development, amounts of both soluble and phosphatidylinositol-specific phospholipase C-sensitive isoforms increase, suggesting a role for brevican in the terminally differentiating and the adult nervous system.

On the existence of a cartilage-like proteoglycan and link proteins in the central nervous system

Monoclonal antibodies (mAbs) against the major constituents of cartilage extracellular matrix, aggrecan and link protein, were screened by indirect immunofluorescence on frozen sections of bovine spinal cord. Antibodies against aggrecan and link protein gave rise to very similar perineuronal labeling in spinal cord gray matter. Aggrecan and link protein reactivities were seen in other regions of the central nervous system (CNS), although their distributions were not always coincident. Pretreatment of the tissue section with Streptomyces hyaluronidase, which is hyaluronate-specific, led to the loss of both reactivities. On Western blots, anti-aggrecan mAbs reacted with a large chondroitin sulfate proteoglycan. The chondroitinase-treated CNS proteoglycan co-migrated with the chondroitinase- and keratanase-treated cartilage proteoglycan. In CNS tissue homogenates, the addition of Streptomyces hyaluronidase brought about the release of the proteoglycan from the tissue. Anti-link protein mAbs were reactive with two species in the bovine CNS, the mobilities of which were very similar to those of the cartilage link proteins. The release of these species from the tissue required hyaluronidase. A rabbit antiserum against aggrecan was used to identify a similar proteoglycan in the rat CNS. In spinal cord-derived cell cultures, the labeled material was associated with astrocytes. An aggrecan cDNA hybridized to a 9.5 kb mRNA in the rat CNS. We conclude that the perineuronal matrix consists, in part, of a hyaluronate-bound aggrecan-like proteoglycan and link proteins, and that the former is produced by astrocytes.

Up-regulation of a chondroitin sulphate epitope during regeneration of mouse sciatic nerve: evidence that the immunoreactive molecules are related to the chondroitin sulphate proteoglycans decorin and versican

After transection of adult mouse sciatic nerve, the expression of a chondroitin sulphate epitope recognized by the monoclonal antibody 473-HD (mAb 473-HD) was found to be up-regulated. The epitope was localized immunocytochemically mainly in Schwann cell basal laminae and, more weakly, also in the endoneurium. In cultures of mouse dorsal root ganglion cells, Schwann cells expressed high levels but fibroblasts only low levels of the epitope. To identify the molecule(s) carrying this chondroitin sulphate epitope, human sciatic nerves were extracted with phosphate-buffered saline and shown to contain two chondroitin sulphate proteoglycans of apparent molecular weights of 130 and 900 kDa. The 900 kDa and, more weakly, the 130 kDa proteoglycan were reactive with mAb 473-HD, which was found to recognize chondroitin-6-sulphate as epitope. Following chondroitinase ABC treatment of the 130 kDa proteoglycan, a core protein of approximately 45 kDa was seen and shown to react with polyclonal antibodies against the chondroitin-dermatan sulphate proteoglycan decorin from human fibroblasts. Chondroitinase ABC treatment of the 900 kDa proteoglycan yielded a core protein with a molecular weight of approximately 400 kDa that was recognized by polyclonal antibodies against recombinantly expressed fusion proteins from human versican. After transection of adult mouse sciatic nerves, the distal nerve stumps showed up-regulation of the chondroitin-6-sulphate epitope of the 900 kDa proteoglycan, whereas the core protein of this proteoglycan did not show any detectable change in the level of expression. In contrast, the core protein of the 130 kDa proteoglycan was up-regulated in expression. These observations suggest that versican- and decorin-like molecules may contribute to successful regeneration in the peripheral nervous system of mammals.

Further characterization of axonally transported proteoglycans

We report further analysis of axonally transported proteoglycans in soluble and membranous subfractions of goldfish optic tectum. Distribution of transported 35SO4 radioactivity was 35.2% soluble, 63.4% Triton-NaCl extractable and 1.4% unextracted. Proteoglycans isolated on DEAE cellulose were treated with chondroitinase AC or nitrous acid and remaining heparan sulfate proteoglycans (HSPGs) and chondroitin sulfate proteoglycans (CSPGs) were sized on Sepharose CL-6B. Kav values and estimated molecular weights were: Soluble CSPG-0.36 (160 kDa), Triton-NaCl extracted CSPG-.031 (200 kDa), Soluble HSPG-0.37 (150 kDa), Triton-NaCl extracted HSPG-0.37 (150 kDa). For constituent CS and HS chains the Kav values and estimated molecular weights on CL-6B were: Soluble CS-0.55 (15 kDa), Triton-NaCl extracted CS-0.55 (15 kDa), Soluble HS-0.59 (13 kDa) and Triton-NaCl extracted HS-0.65 (9 kDa). CS was shown to be sulfated exclusively at carbon 4 for both soluble and Triton NaCl extracted fractions.

Analysis of aggrecan and tenascin gene expression in mouse skeletal tissues by northern and in situ hybridization using species specific cDNA probes

Cartilage matrix is an interacting multicomponent system of collagen fibrils, fibril-associated small proteoglycans, and large proteoglycans and glycoproteins entrapped within the fibrillar network. In order to better understand the relationships between these different components we have constructed short cDNA clones for detection of mRNAs for two major noncollagenous macromolecules of cartilage matrix, aggrecan and tenascin. We subsequently determined their corresponding mRNA levels by Northern analysis in a panel of total RNAs isolated from several newborn mouse tissues. The expression of aggrecan was strictly restricted to cartilages while tenascin mRNA was present at variable levels in most of the tissues studied. The cDNA clones were also used to identify the cells responsible for aggrecan and tenascin production in newborn mouse tissues by in situ hybridization. With this technique aggrecan mRNA was detected in chondrocytes throughout the developing skeleton in a pattern very similar but not identical to those of type II and IX collagen mRNAs. In the newborn mouse skeleton tenascin and aggrecan mRNAs were expressed essentially in a mutually exclusive manner, tenascin transcripts being present in osteoblasts, periosteal and perichondrial cells, and in cells at articular surfaces. None of these cells expressed the cartilage specific collagen or aggrecan genes. The results further suggest different patterns of gene expression in chondrocytes based on their location in the different cartilages.

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.

Characterization of proteoglycans synthesized by murine embryonal carcinoma cells (P19) reveals increased expression of perlecan (heparan sulfate proteoglycan) during neuronal differentiation

Proteoglycans (PGs) incorporated into cell layer and secreted into media were characterized during retinoic acid-induced neuronal differentiation of cultured P19 murine embryonal carcinoma cells. Heparan sulfate significantly increased (P < 0.01) in cell layer following neuronal differentiation of P19 cells by 3.9-fold. CL-4B gel chromatography revealed the major PGs present in cell layer of stem cells eluted as a broad peak with a Kav = 0.65, and was susceptible to chondroitin ABC lyase. The chondroitin ABC lyase resistant material eluted as a broad peak between Kav = 0.40 and Kav = 0.60, and was only partially digested with heparitinase/heparinase (with resistant material eluting at Kav = 0.70). Therefore, the cell layer of stem cells contained primarily chondroitin sulfate/dermatan sulfate (CS/DS) PGs, with lesser amounts of heparan sulfate proteoglycans (HSPGs). This was confirmed by SDS-PAGE. The CS/DS PGs in the cell layer of stem cells had an apparent M(r) of approximately > 200 kDa, and the HSPGs had an apparent M(r) of approximately 140-230 kDa. In contrast, the major PGs in the cell layer of neurons consisted primarily of HSPGs, with only a minor proportion of CS/DS PGs. Furthermore, both gel filtration chromatography and SDS-PAGE analysis revealed a larger HSPG in the cell layer of neurons (Kav = 0.3-0.6 on CL-4B following chondroitin ABC lyase digestion; M(r) 170 kDa- > 400 kDa on SDS-PAGE) in comparison to stem cells (Kav = 0.4-0.6 on CL-4B following chondroitin ABC lyase digestion; M(r) 140-230 kDa on SDS-PAGE). Likewise, the major PGs secreted into media of stem cells consisted almost exclusively of CS/DS PGs, with lesser amounts of HSPGs, whereas an increase in HSPGs in the media of neurons was apparent. Western, Northern, and immunocytochemical analysis demonstrated that mRNA transcript and protein levels for a specific HSPG (i.e., perlecan) markedly increased in cell layer following P19 neuronal differentiation. Perlecan core protein was identified by Western blot analysis using specific monoclonal and polyclonal antibodies, as a large HSPG with a core protein of apparent M(r) approximately 370-400 kDa, and was observed primarily in extracts from neurons. Northern blot analysis with a cDNA to perlecan revealed a significant (P < 0.01) 12.7-fold increase in expression of perlecan in neurons (day 9) in comparison to stem cells. The increase in perlecan message during P19 neuronal differentiation was concomitant with a significant (P < 0.01) 26.3-fold increase in message for beta-amyloid precursor protein (beta PP).(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Identification of the proteoglycan versican in aorta and smooth muscle cells by DNA sequence analysis, in situ hybridization and immunohistochemistry

Versican is a large chondroitin sulfate proteoglycan (CSPG) initially identified in cultured human fibroblasts. Previous studies have shown that there is a versican-like molecule in cultured monkey smooth muscle cells. In this study, we have cloned and sequenced the large CSPG from cultured monkey smooth muscle cells, fetal and juvenile monkey aorta, and human fetal aorta. The cDNA sequence from human fetal aorta is completely homologous to the human fibroblast versican. We obtained 2.5 kb of cDNA sequence from monkey aortic RNA and cultured monkey smooth muscle cell RNA. This sequence covers three distinct domains of versican (hyaluronic acid binding domain, glycosaminoglycan attachment domain and protein binding domain) and demonstrates over 90% homology to the human versican sequence. In situ hybridization histochemistry indicates that the versican RNA transcript is located in the epithelium throughout the tunica media of the aorta. Western blot analysis and immunohistochemistry also confirm the presence of versican in human and monkey aorta.

Immunohistochemical localization of glycosaminoglycans in experimental rat glioma models

Changes of glycosaminoglycan distribution in and around C6 glioma and ethylnitrosourea(ENU)-induced glioma in rats were investigated using monoclonal antibodies that specifically recognize epitopes on chondroitin-0-sulfate proteoglycan (C-0-S), chondroitin-4-sulfate proteoglycan (C-4-S), dermatan sulfate proteoglycan (DS), chondroitin-6-sulfate proteoglycan (C-6-S) and keratan sulfate proteoglycan (KS) after chondroitinase ABC digestion. In the normal brain tissues, C-0-S was located on the surface of the neurons. In addition, extracellular staining in the cerebral cortex and axoplasmic staining in the brain stem and the reticular thalamic nucleus were seen. C-0-S was negative, however, both in the C6 and ENU-induced gliomas. C-4-S or DS was detected only in some of the neurons in the normal brain tissues. They were detected in the peripheral part of the ENU-induced gliomas, but not in the C6 gliomas. C-6-S was located on the surface of some neurons and in the white matter of the normal brain, but it was not detected in C6 gliomas. In all ENU-induced gliomas, C-6-S was identified in the adventitia of the vascular structures within the tumor. In some of them, C-6-S appeared in the peripheral part of the tumor. KS was immunostained in the glial cells in the hippocampus, corpus callosum, brain stem, and the floor of the third ventricle. It was also detected in the peritumoral brain tissues both in the C6 and ENU-induced rat gliomas. The significance of glycosaminoglycans in these glioma models was discussed.

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.

Perineuronal nets--a specialized form of extracellular matrix in the adult nervous system

One century ago, Camillo Golgi described 'perineuronal nets' enwrapping the cell bodies and proximal dendrites of certain neurons in the adult mammalian central nervous system and suggested that they represent a supportive and protective scaffolding. Although other neuroanatomists validated the existence of these nets on selected neurons in the adult brain, there was a lack of agreement on their origins, composition and function. The application of modern molecular and ultrastructural methods has brought new insights and a renewed interest in these classic observations. Recent data suggest that perineuronal nets result from the visualization of extracellular matrix molecules that are confined to the space interposed between glial processes and the nerve cells that they outline. The material confined to these spaces can be visualized selectively by antibodies directed to glycoproteins (e.g., tenascin and restrictin/janusin), proteoglycans (e.g., chondroitin sulfates), markers for hyaluronan as well as by lectins recognizing N-acetylgalactosamine and by monoclonal antibodies directed to epitopes on unknown molecules (e.g., HNK-1, VC1.1 and Cat 301). This review examines the emerging clarification of classical observations of perineuronal nets and the functional implications suggested by their molecular composition. Also discussed are studies that further extend observations on the time of development and of the specificity in the occurrence of perineuronal nets. In the adult brain the molecules constituting the 'perineuronal nets of matrix' could serve as recognition molecules between certain neurons and their surrounding cells and participate in the selection and consolidation of their relationship.

Claustrin, an antiadhesive neural keratan sulfate proteoglycan, is structurally related to MAP1B

Our laboratory has recently identified a keratan sulfate proteoglycan (KSPG), named claustrin, that inhibits neural cell adhesion and neurite outgrowth in the chick nervous system. Antisera prepared against claustrin were used to screen a cDNA expression library from embryonic day 9 chick brain. Initial characterization of positive cDNAs revealed a high degree of homology to the mouse MAP1B gene, although these cDNAs represent a 5' truncated fragment of MAP1B. Protein sequencing of three peptides derived from a tryptic digest of purified, keratanase-treated claustrin also revealed strong homology to MAP1B, and confirmed the authenticity of the 3.4 kb claustrin cDNA. To further determine the relationship between these two proteins, we used antibodies against MAP1B and KSPGs in immunoblotting and immunohistochemical studies. These studies demonstrated cross-reactivity between MAP1B and claustrin antibodies, and that monoclonal antibodies to cartilage keratan sulfate react with MAP1B in rat nervous tissue, and with claustrin in the chick nervous system. In addition, keratanase treatment of a taxol microtubule fraction from chick or rat brain eliminated MAP1B, as detected by immunoblotting with the MAP5 monoclonal antibody. These results suggest that MAP1B and claustrin are highly related, if not identical, proteins.