A chondroitin sulphate proteoglycan from human cultured glial and glioma cells. Structural and functional properties

Activated macrophages and the blood-brain barrier: inflammation after CNS injury leads to increases in putative inhibitory molecules

The cellular responses to spinal cord or brain injury include the production of molecules that modulate wound healing. This study examined the upregulation of chondroitin sulfate proteoglycans, a family of molecules present in the wound healing matrix that may inhibit axon regeneration in the central nervous system (CNS) after trauma. We have demonstrated increases in these putative inhibitory molecules in brain and spinal cord injury models, and we observed a close correlation between the tissue distribution of their upregulation and the presence of inflammation and a compromised blood-brain barrier. We determined that the presence of degenerating and dying axons injured by direct trauma does not provide a sufficient signal to induce the increases in proteoglycans observed after injury. Activated macrophages, their products, or other serum components that cross a compromised blood-brain barrier may provide a stimulus for changes in extracellular matrix molecules after CNS injury. While gliosis is associated with increased levels of proteoglycans, not all reactive astrocytes are associated with augmented amounts of these extracellular matrix molecules, which suggests a heterogeneity among glial cells that exhibit a reactive phenotype. Chondroitin sulfate also demarcates developing cavities of secondary necrosis, implicating these types of boundary molecules in the protective response of the CNS to trauma.

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.

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.

Neurological cholinesterases in the normal brain and in Alzheimer's disease: relationship to plaques, tangles, and patterns of selective vulnerability

Butyrylcholinesterase (BChE) and an altered form of acetylcholinesterase (AChE) accumulate in the plaques and tangles of Alzheimer's disease (AD). The sources for these plaque- and tangle-bound cholinesterases have not been identified. We now report that AChE and BChE activities with pH preferences and inhibitor selectivities identical to those of plaque- and tangle-bound cholinesterases are found in the astrocytes and oligodendrocytes of control and AD brains. These glial-type cholinesterases are selectively inhibited by indolamines and protease inhibitors. In control brains glial-type cholinesterases appear confined to the intracellular space, whereas in patients with AD they decorate plaques and tangles as well. In control and AD brains AChE-positive glia are distributed throughout the cortical layers and subcortical white matter, whereas BChE-positive glia reach high densities only in the deep cortical layers and white matter. In non-AD control brains, the ratio of BChE to AChE glia was higher in entorhinal and inferotemporal cortex, two regions with a high susceptibility to the pathology of AD, than in primary somatosensory and visual cortex, two areas with a relatively lower susceptibility to the disease process. There was no age-related differences in the density or distribution of cholinesterase-positive glia. In comparison with age-matched control specimens, AD brains had a significantly higher density of BChE glia and a lower density of AChE glia in entorhinal and inferotemporal regions but not in the primary somatosensory or visual areas. These results suggest that glia constitute a likely source for the cholinesterase activity of plaques and tangles and that a high ratio of BChE- to AChE-positive glia may play a permissive or causative role in the neuropathology of AD.

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.

Proteoglycans in the pathogenesis of Alzheimer's disease and other amyloidoses

Proteoglycans and the amyloid P component are two constituents of amyloid that appear to be present regardless of the type of amyloid protein deposited, the extent of amyloid deposition and the tissue or organ involved. This article reviews the literature concerning proteoglycans and/or glycosaminoglycans in amyloidosis and describes recent studies which demonstrate their localization to the characteristic lesions of Alzheimer's disease and the amyloid plaques containing PrP protein in the prion diseases. Additionally, the possible interaction of proteoglycans with various amyloidogenic proteins, including the beta-amyloid protein in Alzheimer's disease is discussed. It is postulated that proteoglycans localized to a number of different amyloids play a common role in the pathogenesis of amyloidosis. Some of these hypothesized roles include 1) inducing amyloidogenic precursor proteins to form amyloid fibrils containing a predominant beta-pleated sheet structure, 2) influencing amyloid deposition to occur at specific anatomical sites within tissues and/or 3) aiding in prevention of amyloid degradation once amyloid has formed.

Immunoelectron microscopic localization of hyaluronic acid-binding region and link protein epitopes in brain

The 1C6 monoclonal antibody to the hyaluronic acid-binding region weakly stained a 65-kD component in immunoblots of the chondroitin sulfate proteoglycans of brain, and the 8A4 monoclonal antibody, which recognizes two epitopes in the polypeptide portion of link protein, produced strong staining of a 45-kD component present in the brain proteoglycans. These antibodies were utilized to examine the localization of hyaluronic acid-binding region and link protein epitopes in rat cerebellum. Like the chondroitin sulfate proteoglycans themselves and hyaluronic acid, hyaluronic acid-binding region and link protein immunoreactivity changed from a predominantly extracellular to an intracellular (cytoplasmic and intra-axonal) location during the first postnatal month of brain development. The cell types which showed staining of hyaluronic acid-binding region and link protein, such as granule cells and their axons (the parallel fibers), astrocytes, and certain myelinated fibers, were generally the same as those previously found to contain chondroitin sulfate proteoglycans and hyaluronic acid. Prominent staining of some cell nuclei was also observed. In agreement with earlier conclusions concerning the localization of hyaluronic acid and chondroitin sulfate proteoglycans, there was no intracellular staining of Purkinje cells or nerve endings or staining of certain other structures, such as oligodendroglia and synaptic vesicles. The similar localizations and coordinate developmental changes of chondroitin sulfate proteoglycans, hyaluronic acid, hyaluronic acid-binding region, and link protein add further support to previous evidence for the unusual cytoplasmic localization of these proteoglycans in mature brain. Our results also suggest that much of the chondroitin sulfate proteoglycan of brain may exist in the form of aggregates with hyaluronic acid.

Formation of chondroitin sulphate proteoglycan in cartilage regenerated from free perichondrial graft

Perichondrium from rabbit auricular or rib cartilage was used as a free autogenous graft and transplanted either to the subcutaneous tissue of the back of the rabbit or to an experimental defect in the femur condyles. Outgrowth of new tissue, morphologically indistinguishable from cartilage, was observed after six weeks. Inorganic 35SO4, administered in vivo, was incorporated into the newly formed tissue. The labelled products were isolated, identified, and compared with those obtained from authentic cartilage of auricular, rib or joint surfaces. The products of newly formed cartilage were similar to those of authentic cartilage. The results support earlier morphological findings, indicating that perichondrium from rib cartilage has a better ability to regenerate than auricular perichondrium. The synovial environment seems to have a positive effect on the generation of cartilage.

Isolation and immunohistochemical localization of a chondroitin sulfate proteoglycan from adult rat brain

A chondroitin sulfate proteoglycan called PGM1 has been isolated from the particulate fraction of adult rat forebrain. Delipidation of the material, solubilization of proteoglycans in guanidinium chloride, precipitation at low ionic strength, and final extraction at pH 5.0 were used for its isolation. Proteoglycans were subjected to further purification by diethylaminoethyl-cellulose chromatography. Individual components were separated by gel filtration. PGM1 appeared to be a high-molecular-weight chondroitin sulfate proteoglycan, capable of strong interaction with hyaluronic acid. It was finally isolated by gel filtration on Ultrogel AcA 22 in the presence of 4 M guanidinium chloride. Monospecific antibodies obtained in rabbits against the purified molecule did not cross-react with other brain proteoglycans. Immunocytochemical techniques revealed an almost unique association of this compound with axons, particularly those known to contain neurofilaments. However, not all these axons and all parts of these axons contained PGM1. This component was not detectable in liver, intestine, spleen, kidney, lung, heart, skin, hair, lens, and muscle, a finding suggesting a specificity for the nervous tissue. This component is expressed in neural cell cultures. Despite the preservation of the neuronal specificity, it seems to lose its specific axonal localization in vitro.

Immunohistochemical identification of heparan sulphate proteoglycan in secondary systemic amyloidosis

The distribution of proteoglycans in kidneys from patients with secondary (AA) systemic amyloidosis was investigated. Antisera reacting with the protein cores of chondroitin sulphate proteoglycan (CSPG), dermatan sulphate proteoglycan (DSPG) and heparan sulphate proteoglycan (HSPG) were used in conjunction with the peroxidase-antiperoxidase (PAP) method. HSPG was the only proteoglycan found to be specifically localized to the amyloid deposits. The staining was most intense on the endothelial side of the deposits in both the glomeruli and in the vessel walls. No staining was observed after absorption of the HSPG antiserum with a fraction of the amyloid preparations, corresponding in size to that reported for glomerular HSPG. The possible role of HSPG and endothelial cells in the pathogenesis of the amyloid deposits is discussed.

Extracellular matrices in multicellular spheroids of human glioma origin: increased incorporation of proteoglycans and fibronectin as compared to monolayer cultures

Tumor spheroids were cultured from five human glioma cell lines which differed considerably in their relative amount and composition of glycosaminoglycans (GAG), fibronectin and other extracellular matrix (ECM) components when grown as monolayer cultures. These differences were also evident when the cells were grown as spheroids. Under the 3-dimensional geometry of the spheroid system, there was, however, generally a more extensive ECM. Especially noteworthy was the presence of a small proteoglycan, probably a dermatan sulphate proteoglycan, in the ECM of the spheroids, but not in the monolayers. Noteworthy was also the appearance of fibronectin in spheroids which did not show any staining for fibronectin when grown as monolayer. The two spheroid types (U-87MG, U-105MG) with the most extensive matrix, and with the lowest proportion of hyaluronic acid (HA), had a low proliferation rate, whereas the three other spheroid types (U-118MG, U-138MG, U-251MG) with a less extensive ECM, and a relatively high production of HA had a much higher proliferation rate. These data provide further evidence for the usefulness of culturing cell lines as spheroids in the process of understanding important cell biological phenomena.

Axonal transport of proteoglycans to the goldfish optic tectum

The study addressed the question of whether 35SO4 labeled molecules that have been delivered to the goldfish optic nerve terminals by rapid axonal transport include soluble proteoglycans. For analysis, tectal homogenates were subfractionated into a soluble fraction (soluble after centrifugation at 105,000 g), a lysis fraction (soluble after treatment with hypotonic buffer followed by centrifugation at 105,000 g) and a final 105,000 g pellet fraction. The soluble fraction contained 25.7% of incorporated radioactivity and upon DEAE chromatography was resolved into a fraction of sulfated glycoproteins eluting at 0-0.32 M NaCl and containing 39.5% of total soluble label and a fraction eluting at 0.32-0.60 M NaCl containing 53.9% of soluble label. This latter fraction was included on columns of Sepharose CL-6B with or without 4 M guanidine and after pronase digestion was found to have 51% of its radioactivity contained in the glycosaminoglycans (GAGs) heparan sulfate and chondroitin (4 or 6) sulfate in the ratio of 70% to 30%. Mobility of both intact proteoglycans and constituent GAGs on Sepharose CL-6B indicated a size distribution that is smaller than has been observed for proteoglycans and GAGs from cultured neuronal cell lines. Similar analysis of lysis fraction, containing 11.5% of incorporated 35SO4, showed a mixture of heparan sulfate and chondroitin sulfate containing proteoglycans, apparent free heparan sulfate and few, if any, sulfated glycoproteins. Overall, the results support the hypothesis that soluble proteoglycans are among the molecules axonally transported in the visual system.

Distribution in cesium chloride gradients of proteoglycans of chick embryo brain and characterization of a large aggregating proteoglycan

Proteoglycans were extracted from 14-day chick embryo brains, which had been labelled in vitro with [35S]sulfate or 3H-labelled amino acids. 4.0 M guanidinium chloride (containing proteinase inhibitors) extracted 94% of the 35S-labelled glycoconjugates. Following cesium chloride equilibrium centrifugation, the proteoglycans in each fraction were characterized by chromatography on Sepharose CL-2B. The most dense fraction (D1), which contained no detectable non-proteoglycan proteins, contained a large, aggregating chondroitin sulfate proteoglycan in addition to small chondroitin sulfate and heparan sulfate proteoglycans. The less dense fractions (D2-D6) contained both small chondroitin sulfate and heparan sulfate proteoglycans. Removal of hyaluronate from the D1 sample by digestion with Streptomyces hyaluronidase in the presence of proteinase inhibitors showed that aggregation of the large chondroitin sulfate proteoglycan is hyaluronate-dependent. Aggregation was restored by re-addition of hyaluronate. Reduction and alkylation, which blocked aggregation of a cartilage A1 proteoglycan, did not interfere with aggregation of the large brain proteoglycan.

Immunohistochemical study of chondroitin sulfate in human gliomas

A polyclonal rabbit antiserum was utilized to localize chondroitin sulfate in human gliomas. Tissue sections were digested with chondroitinase ABC to create the antigenic determinant on the chondroitin sulfate proteoglycan molecule. Normal CNS tissue showed a positive immunohistochemical staining both in white and gray matter, sparing the cytoplasm of glial and neuronal cells. Differentiated astrocytomas presented the same pattern as the normal CNS. Anaplastic astrocytomas and glioblastomas showed progressive reduction of parenchymal positivity as anaplasia increased. These data suggest that chondroitin sulfate is a character expressed by differentiated CNS cells and that it is lost with dedifferentiation. Vascular structures presented positive material in the adventitia in all the oncotypes. A discontinuous positivity was observed in the basal membrane zone of the vessels.