Immunopurification and characterization of a neuronal heparan sulfate proteoglycan

Association of tailed acetylcholinesterase to lipidic membranes in mammalian skeletal muscle

Tailed acetylcholinesterase (AChE) was studied in three subcellular membrane fractions of mouse skeletal muscle: a fraction enriched in isolated motor endplates (C), an extrasynaptic membrane fraction (A) and a microsomal fraction (S). In the (C) fraction, tailed asymmetric 16S AChE required high salt conditions to be extracted, while in (A) and (S) microsomal membranes, a collagenase sensitive 16S form, was extracted by detergent alone. This apparent "hydrophobic" property suggests that there is a pool of 16S AChE which is probably bound to lipidic membranes. The detergent extractable (DE) 16S AChE was not concentrated in motor endplate-rich regions and differential inhibition of external and internal AChE demonstrated that it could have both intra- and extracellular locations in the adult differentiated muscle fibres.

An antibody to the tetraspan membrane protein CD9 promotes neurite formation in a partially alpha3beta1 integrin-dependent manner

The tetraspan cell surface glycoprotein, CD9, has been implicated in cellular signaling during growth and differentiation in the hematopoietic and nervous systems. Because CD9 expression is induced early in development in sensory and sympathetic neuroblasts, we investigated the role of CD9 in neurite outgrowth. We plated dissociated cells from neonatal sympathetic ganglia on immobilized anti-CD9 antibodies or antibodies against other cell surface molecules. We show here that B2C11, an anti-CD9 antibody that has been shown previously to activate Schwann cells in vitro, promotes robust neurite outgrowth from sympathetic neurons that is greater than that on other antibody surfaces and is comparable to neurite outgrowth on a collagen substratum. In addition, B2C11 causes dramatic morphological changes in neurons and glia from dissociated ganglia, including a flattening of these cells. Because CD9 interacts with integrins in many cell types including Schwann cells, and specifically with the alpha3beta1 integrin in some cells, we tested whether the effect of B2C11 on neurite outgrowth is mediated by this integrin. An anti-alpha3beta1 antibody, Ralph 3-1, attenuates the extent of neurite outgrowth on B2C11 and collagen, but not on laminin. Because the alpha3beta1 integrin has been shown to mediate neurite outgrowth on different substrates, these results provide a functional significance for the CD9-alpha3beta1 interaction; downstream signaling may be activated by this cis interaction on the cell surface in response to external cues that promote neurite outgrowth.

The interaction of vascular endothelial cells and dorsal root ganglion neurites is mediated by vitronectin and heparan sulfate proteoglycans

The interaction of peripheral nerve and blood vessels during development was studied by using DRG explant culture plated on confluent monolayer of vascular endothelial cells (VEC). The comparison of neurite length on various substrates showed a preference of DRG neurites in the following order; thrombospondin > laminin, vitronectin > fibronectin, VEC monolayer > collagen I, rat astrocyte monolayer. On layers of fibroblasts (3T3) or gliomas (C6), neurite extension was not observed. To identify the neurite outgrowth promoting adhesion molecules on VEC surface, several antibodies and synthetic peptides were added to the culture medium of DRG. With vitronectin antibody or with peptides containing the Arg-Gly-Asp (RGD) sequence, 30-40% of neurite outgrowth was inhibited and these two effects were not additive. Therefore, a part of neurite outgrowth in this system is mediated by vitronectin in RGD dependent manner. Another molecule which promotes neurite outgrowth on VEC was identified by a new monoclonal antibody (MAb) EC1. In the Western blot analysis, the immunoreactive band which was over 400 kDa was intensified by guanidine HCl extraction. EC1 immunoreactive band disappeared after the treatment of heparitinase but not with other glycolyases, indicating that EC1 antigen is heparan sulfate proteoglycan(s). The DRG neurite outgrowth was inhibited by MAb EC1 by about 30-40%. By the combination of MAb EC1 and RGD peptide, the neurite outgrowth in explant culture was inhibited by about 50%, and in DRG dissociated culture nearly 100% inhibition was observed. Thus, for the DRG neurite elongation on VEC, vitronectin and heparan sulfate proteoglycan(s) are playing crucial roles.

The glycophosphatidylinositol anchor affects the conformation of Thy-1 protein

Thy-1 has the structure of a single variable-type immunoglobulin domain anchored to the external face of the plasma membrane via a glycophosphatidylinositol moiety. When the lipid is removed from this anchor by either phospholipase C or D, the reactivity of the delipidated Thy-1 for a range of antibodies, including those known to be determined by amino acid residues, is impaired. We have investigated in detail the effect of delipidation on the reaction with the OX7 monoclonal antibody, determined by the allelic variant residue Arg 89. Analysis of the kinetics of OX7 binding shows that delipidation affects primarily the dissociation of antibody, increasing the dissociation rate constant kdiss from 0.27 × 10(−3) s-1 to 2.39 × 10(−3) s-1. Addition of phospholipase to preformed antibody-antigen complex causes an immediate change from the slow to the faster dissociation rate, implying that delipidation induces a conformational change in the Thy-1 protein that is sufficiently strong to dissociate bound antibody. This conformational change can be demonstrated directly by the circular dichroism spectrum of human Thy-1 that detects changes in the environment of Tyr residues located near the antigenic epitopes. Molecular dynamics studies suggest that, on delipidation, a conformational change occurs in the glycan chain that affects the protein in the region of the antigenic epitopes. This study thus demonstrates that the glycophosphatidylinositol anchor strongly influences the conformation of Thy-1 protein by a mechanism that could occur generally with membrane proteins of this class.

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.

Distribution of heparan sulfate proteoglycans in embryonic chicken neural retina and isolated inner limiting membrane

Quantitative distribution of proteoglycans was studied in retinal neural epithelium and its basement membrane (inner limiting membrane). Heparan sulfate proteoglycans (HSPGs) were primarily associated with both inner and outer plexiform (synaptic) layers, and inner limiting membrane (ILM), as determined by autoradiographs of lyase-digested cryosections. Based on distribution of 35S-sulfate-labeled proteoglycans, the isolated ILM contained on average approximately three fourths of its proteoglycans as HSPGs and one fourth as chondroitin sulfate/dermatan sulfate proteoglycans (CS/DSPGs), whereas the remaining retina contained approximately equal amounts of the two proteoglycans (PGs). Immunohistochemical staining indicates that the core proteins of the HSPGs in the ILM are distinct from those of the plexiform layers. The photoreceptor layer, which other studies have shown to contain much of the extracellular CS/DSPGs, was not examined. Enrichment of distinct HSPGs in the ILM and plexiform layers support the conclusion that the HSPGs may be intimately involved in the different developmental events characterizing the two regions: development and extension of ganglion cell axons in the former, synaptogenesis and neuronal function in the latter.

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)

Modulation of neurite promoting proteoglycans by neuronal differentiation

A human cell line committed to neuronal lineage was used to examine the influence of differentiation on proteoglycan synthesis and function. Where the LA-N-2 cells were stimulated to differentiate towards a phenotype of cholinergic neurons, proteoglycans of the heparan sulphate class increased relative to chondroitin sulphate proteoglycans and displayed more homogeneously shorter glycosaminoglycan chains with increasing degrees of sulphation. The changes were accompanied by increasing potency of the heparan sulphate proteoglycans in neurite growth-promoting activity when immobilized on a laminin substrate. These studies begin to address the role of activity-independent growth and differentiation on the synthesis and release by neurons of neurite growth-promoting proteoglycans. The observations have implications for understanding the role of proteoglycan overexpression and the production of dystrophic neurites in Alzheimer disease.

Isolation and partial characterization of a cell-surface heparan sulfate proteoglycan from embryonic rat spinal cord

Cell-surface heparan sulfate proteoglycans (HSPGs) are potential mediators of neuronal cell adhesion, spreading, and neurite outgrowth on various extra-cellular matrix molecules. One possible site of HSPG attachment is a heparin binding domain of fibronectin, which is present in the synthetic peptide FN-C/H II. In this study, HSPGs extracted from embryonic rat spinal cord by detergent were purified by ion-exchange chromatography, gel filtration, and affinity chromatography on an agarose column coupled with FN-C/H II conjugated to ovalbumin (OA). Heparitinase treatment of the iodinated HSPG fraction led to the appearance of a major protein core with a molecular size of 72 kDa, as determined by reducing SDS-PAGE. The intact proteoglycan has a molecular size of approximately 150-165 kDa, containing heparan sulfate glycosaminoglycan chains of about 10-15 kDa. Anti-HSPG antibodies recognized the 72 kDa core protein by immunoblotting, and stained the surface of spinal cord neurons, oligodendrocytes, and a subset of astrocytes. These results identify a cell-surface HSPG that may mediate neuron-substratum or neuron-glia interactions in embryonic central nervous system.

Decorin and a large dermatan sulfate proteoglycan in bovine striated muscle

Proteoglycans were extracted and isolated from adult bovine muscle tissue by dissociative extraction followed by density gradient centrifugation, gel chromatography and ion-exchange chromatography. Two proteoglycans were characterized; one of large molecular size (PG-L) and one of small molecular size (PG-S). The recovery of PG-L and PG-S was 33% and 67%, respectively. By cellulose acetate electrophoresis before and after treatment with chondroitinase AC and ABC both samples were shown to carry predominantly dermatan sulfate chains. The large proteoglycan was recognized with an antibody against a large dermatan sulfate proteoglycan from bovine sclera, whereas the small was recognized by an antibody against decorin from bovine sclera. Chondroitinase ABC treatment of PG-S followed by SDS-PAGE showed a core protein with a molecular weight of 45 kDa, which also reacted with the decorin antibody. Amino-acid analysis of both PG-L and PG-S revealed an amino-acid composition closely similar, although not identical, to the large dermatan sulfate proteoglycan from bovine sclera and decorin, respectively. Immunohistochemical analyses of muscle tissue sections showed that decorin and the large dermatan sulfate proteoglycan are present in the perimysium layers of muscle tissue, although although with a somewhat different pattern of distribution. Decorin was, in addition, found in the endomysium.

Developmental regulation of neural response to FGF-1 and FGF-2 by heparan sulfate proteoglycan

Murine neural precursor cells and cell lines derived from them are stimulated by members of the heparin-binding fibroblast growth factor (FGF) family. The activity of FGF is regulated by heparan sulfate proteoglycans (HSPGs), and this interaction is an essential prerequisite for the binding of growth factor to the signal transducing receptors. Messenger RNA for FGF-2 was detectable in the neuroepithelium at embryonic day 9, and the HSPGs produced by these cells at this time preferentially bound FGF-2. However, at embryonic day 11, when messenger RNA for FGF-1 was first detectable, there was a switch in the binding specificity of the HSPG to FGF-1. Thus, a single species of HSPG undergoes a rapid, tightly controlled change in growth factor-binding specificity concomitant with the temporal expression of the FGFs.

Binding of secreted human neuroblastoma proteoglycans to the Alzheimer's amyloid A4 peptide

Proteoglycans (PGs) may play a fundamental role in all forms of amyloidosis. In Alzheimer's disease, proteoglycans are found deposited in senile plaques and in neurofibrillary tangles. However, the cellular source of these deposited PGs and their role in amyloidosis in Alzheimer's disease is unknown. Proteoglycans were purified from conditioned medium of human neuroblastoma cells (SKNSH-SY 5Y). Two species of proteoglycans were identified by enzyme susceptibility including a heparan sulfate proteoglycan and a dermatan sulfate proteoglycan. A monoclonal antibody to the protein core of a vascular basement membrane heparan sulfate proteoglycan found in senile plaques in Alzheimer's disease cross-reacted with the proteoglycans secreted by human neuroblastoma cells. Binding between 35SO4-labelled neuroblastoma proteoglycans and the Alzheimer amyloid (A4) peptide was demonstrated by affinity chromatography. Specificity studies demonstrated that binding of human neuroblastoma proteoglycans to the amyloid peptide was specific for a heparan sulfate glycosaminoglycan, with some binding to a dermatan sulfate proteoglycan. Binding to A4 was also demonstrated by a chemically deglycosylated protein core preparation. No significant binding of neuroblastoma proteoglycans was found to two other basic peptides derived from the extracellular domain of the beta-amyloid precursor, demonstrating the specificity of proteoglycan binding to the A4 peptide. Human neuroblastoma proteoglycans may bind to the-Alzheimer amyloid A4 peptide in a region with a heparin binding consensus sequence [VHHQKL] which also contains the cleavage site of the beta-amyloid precursor protein. Neuronal proteoglycans may either regulate the secretion of the amyloid protein precursor or modify the binding of the amyloid protein precursor to other cellular adhesion molecules. Alterations in this binding may be related to the pathogenesis of amyloid deposition in Alzheimer's disease.

Effects of 4-deoxy-L-threo-pentose, a novel carbohydrate, on neural cell proteoglycan synthesis and function

A novel carbohydrate, 4-deoxy-L-threo-pentose (4-deoxyxylose), was synthesized by way of reductive dechlorination of a chlorodeoxy sugar. This carbohydrate, an analogue of xylose which is required for the initiation of glycosaminoglycan (GAG) synthesis, was used to explore the function of GAG side chains in neurite outgrowth on a laminin substrate. 4-Deoxyxylose inhibited the incorporation of 35SO4 into the GAGs of neuronal and astrocytic proteoglycans, with no effect being seen on the incorporation of [3H]glucosamine into proteoglycan. Direct analysis of the heparan sulphate fraction from such cells using nitrous acid digestion confirmed that the GAGs were undersulphated. No inhibition of either 35SO4 or [3H]glucosamine incorporation was observed in primary mouse hepatocytes exposed to 4-deoxyxylose. 4-Deoxyxylose produced a direct dose-dependent inhibition of neurite outgrowth by sensory neurons, and medium conditioned by neurons or astrocytes in the presence of 4-deoxyxylose displayed less laminin-complexed neurite-promoting activity than medium conditioned in its absence. These data suggest that 4-deoxyxylose inhibits neurite outgrowth by altering the sulphation of the GAGs of heparan sulphate proteoglycans.

Thy-1 involvement in neurite outgrowth: Perturbation by antibodies, phospholipase C, and mutation

Thy-1 is a major cell surface protein anchored in the plasma membrane of neurons and lymphocytes by a covalent glyco-phosphatidyl-inositide linkage. Despite thorough characterization of the molecule's physicochemical properties, its biological function remains elusive. In this study we demonstrate that (i) monoclonal antibodies directed against Thy-1 are capable of enhancing neurite outgrowth from sympathetic neurons in culture, as well as stimulating the initiation of neurite sprouting from cultured adrenal chromaffin cells and PC12 cells. This effect is not observed with monovalent, Fab antibody fragments. Treatment with intact antibodies also results in the shedding of Thy-1 into the culture medium. (ii) Treatment of chromaffin cells with phosphatidyl-inositol-specific phospholipase C also results in an induction of neurite sprouting. The lipase effect can be blocked by preincubating the cells with monovalent anti-Thy-1 Fab fragments, indicating that the outgrowth stimulation is specifically due to removal of Thy-1. (iii) An entirely different approach to elucidating the function of Thy-1 involves mutagenesis of PC12 cells. Selection for Thy-1-deficient mutants revealed that cells lacking Thy-1 sprout neurites spontaneously at a very high frequency. A novel role for Thy-1 is proposed wherein the results of the mutant cell studies are compatible with the antibody and lipase data. Each of the perturbations can be viewed as releasing an inhibition that Thy-1 normally exerts on neurite outgrowth. We suggest that Thy-1 normally acts to stabilize neuronal membranes and processes, possibly through homophilic interactions.

Neurite growth modulation associated with astrocyte proteoglycans: influence of activators of inflammation

Of the three classes of sulphated proteoglycans produced by type 1 astrocytes in vitro and released into conditioned medium, only heparan sulphate (HS) was associated with enhanced neurite growth by sensory neurons following pretreatment of a laminin substratum. Astrocyte-conditioned medium (ACM) produced in the presence of certain inflammatory mediators had reduced titers of neurite-promoting activity. The low activity ACM contained inhibitors of neurite growth. Heparan sulphate proteoglycans may modulate neurite growth when complexed to constituents of the extracellular milieu either directly or by interacting with other growth-promoting or growth-inhibitory factors.

Domains of neuronal heparan sulphate proteoglycans involved in neurite growth on laminin

A single neuronal cell assay of neurite growth was utilized to determine types and domains of neuronal proteoglycans involved in neurite growth on laminin. Perturbations of biosynthesis and processing, enzymatic digestion with specific lyases, and competition with glycosaminoglycan side chains produced complementary data consistent with a molecular model implicating glycosaminoglycan (GAG) residues of heparan sulphate proteoglycans (HSPGs) in neurite growth. The observations suggest that HSPGs promote neurite growth on laminin by bridging between binding domains for HSPGs on laminin and on the neuronal cell surface, and that the bridge is tethered at both ends by non-covalent interactions between the binding domains and GAG side chains. Sulphation of the GAGs of HSPGs appears to be critical to the tethering and/or neurite growth-promoting activity of neuronal HSPGs.

Neurite formation on laminin: effects of a galactosyltransferase on primary sensory neurons

Avian embryonic sensory neurons from ED8 chick possess a trypsin-labile cell surface galactosyltransferase (GalTase) activity that glycosylates laminin in the presence of uridine 5' galactose (UDPgal). In a 4 h biological assay concentration dependent partial inhibition of neurite growth on laminin was observed in the presence of (i) alpha-lactalbumin, a specific inhibitor of the enzyme, (ii) N-acetylglucosamine (GlcNac), the appropriate acceptor substrate, or its polymer chitotriose, and (iii) UDPgal, the catalytic substrate. Prior exposure of substrate-immobilized laminin to glycosidase partially inhibited neurite growth. Alpha-lactalbumin did not influence cell adhesion at saturating concentrations for inhibition of neurite formation. Neurite growth on fibronectin was not inhibited by prior exposure to glycosidase or by alpha-lactalbumin, and fibronectin was not an appropriate substrate for glycosylation by the sensory neurons. These observations extend the catalogue of domains of laminin that subserve neurite growth, and define in functional terms a class of neuronal receptors that interact with lactosaminoglycan-type oligosaccharides of laminin.

Core protein of chondroitin sulfate proteoglycan promotes neurite outgrowth from cultured neocortical neurons

Chondroitin sulfate proteoglycan (CS-PG) was purified from rat brain and examined for its effect on neurite outgrowth in primary cultures of embryonic rat neocortical neurons. Neurite outgrowth was increased in culture wells coated with CS-PG. The core protein and glycosaminoglycan (GAG) prepared from the CS-PG were also examined for neurite-promoting activity. The activity was observed in culture wells coated with the core protein but not with GAG. These results suggest that CS-PG stimulates neurite outgrowth from the cultured neurons via its core protein.

Characterization of glycosaminoglycans produced by primary astrocytes in vitro

Quantitative biosynthetic studies with cultures highly enriched for glial fibrillary acidic protein (GFAP+) cells of neonatal mammalian brain demonstrated production of four proteoglycans: hyaluronate (HA), heparan sulphate (HS), chondroitin sulphate (CS), and dermatan sulphate (DS). The glycosaminoglycans were present in cell conditioned medium and in the cellular compartment. There were qualitative differences in the subcellular disposition of the various proteoglycans. The ratio of HS to CS/DS in cell extracts was 1:1, while in medium this ratio was 1:6. All of the glycosaminoglycans were associated with core proteins that were integral to the cell membrane and associated with the cell surface by non-covalent interactions involving glycosaminoglycans. Less than 20% of the HS was non-covalently associated with the astrocyte cell surface reflecting in part the proportionately smaller amounts of this proteoglycan released to astrocyte conditioned medium. HS released to medium was undersulphated relative to that associated with cells. The astrocyte can contribute proteoglycans to the extracellular milieu and displays cell surface proteoglycans that have the potential to provide appropriate substrates for neuron adhesion, process extension, and other cell-cell interactions.

Beta amyloid precursor protein mediates neuronal cell-cell and cell-surface adhesion

The beta-amyloid precursor protein (APP) is a membrane-bound glycoprotein which has been proposed to play a role both as a growth factor and a mediator of cell adhesion. Using the Neuro-2A neuroblastoma cell line, we have investigated the capacity of APP to mediate neural cell adhesion. The cells express the protein at a high level, the immunohistochemical staining pattern at the level of the membrane having a punctate pattern. Fab' fragments of antibodies to the extracellular portion of the molecule were found to inhibit cell binding to a collagen substrate, but not to laminin, fibronectin, or poly-l-lysine. Fab' fragments of antibodies to the nerve cell adhesion molecule N-CAM also inhibited binding of Neuro-2A cells specifically to collagen. This inhibition of cell-surface binding was accompanied by a repression of neurite outgrowth in differentiating cells in the presence of antibodies. APP antibodies also inhibited neuron-neuron and neuron-glial binding, but not glial-glial cell adhesion. These data suggest that the APP, which is expressed primarily on differentiated neuronal cells, may play a role in the mediation of both cell-cell and cell-substrate adhesion.

Changes in glycosaminoglycans during the neuritogenesis in PC12 pheochromocytoma cells induced by nerve growth factor

Previously, we had suggested that heparan sulfate (HS) makes some contribution to a flat-shaped morphology of PC12D cells. Therefore, we carried out quantitative and qualitative analyses of glycosaminoglycans (GAGs), the polysaccharide moiety of proteoglycans, during neuritogenesis in PC12 cells that is induced by nerve growth factor (NGF). (a) In PC12 cells, NGF induced a flat-shaped morphology with a few short processes after 3 days of culture, and then it elicited short and long neurites after 6 (in approximately 30% of cells) and 9 (in 60-70%) days of culture, respectively. (b) HS and chondroitin sulfate (CS) were detected in the cell layer at all times. Only CS was found in the medium at 3 and 6 days, whereas a low level of HS, in addition to CS, was detectable on day 9. (c) In the NGF-treated cultures, the amounts of cell-associated HS per cell were two to three times as high as those in the respective nontreated cultures at all times, whereas the amount based on phospholipid was about twofold higher after 3 days of culture. (d) The levels of HS labeled with [35S]sulfate during the last 48 h of the culture were 1.5- to twofold higher in the NGF-treated cultures than in the respective controls at any time. (e) The amount of cell-associated CS per cell (or per unit of phospholipid), but not of labeled CS per cell, was transiently enhanced at 3 days in culture with or without NGF.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and biochemical characterization of a neural proteoglycan expressing the L5 carbohydrate epitope

The monoclonal L5 antibody reacts with an N-glycosidically linked carbohydrate structure which is present on the neural cell adhesion molecule L1, neural chondroitin sulfate proteoglycans, and other not yet identified glycosylated proteins. Using this antibody, we isolated and characterized proteoglycans from adult mouse brain and cultured astrocytes biosynthetically labeled with Na2 35SO4 and a 3H-amino acid mixture. Our data suggest that the L5 proteoglycans of both sources are identical in their biochemical properties. The apparent molecular mass of the L5 proteoglycan is approximately 500 kDa. Digestion of the iodinated L5 proteoglycan from mouse brain and of the [35S]methionine-labeled L5 proteoglycan from cultured astrocytes with proteinase-free chondroitinases ABC and AC revealed three major core proteins with apparent molecular masses of approximately 380, 360, and 260 kDa. These represent molecularly distinct protein cores.

A retinal ganglion cell neurotrophic factor purified from the superior colliculus

Dissociated neonatal rat retinal ganglion cells can be maintained by the addition of an extract from the neonatal superior colliculus. This extract can support 95% of ganglion cells over 24 h in culture; in addition it promotes the expression of neurites from these cells. This report describes the purification of a neurotrophic factor from the superior colliculus which supports the survival of 80% of retinal ganglion cells over 24 h in vitro. The purification procedure involves a combination of dye-ligand, anion-exchange, and molecular sieve chromatography. The purified neurotrophic factor has a Stokes radius of approximately 200 A using molecular sieve chromatography in the presence of a chaotropic agent. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified factor indicates that it is a glycoprotein that migrates with a molecular mass greater than 400 kDa. Further characterization of this high-molecular-mass glycoprotein by enzymatic digestion demonstrated that it is a chondroitin sulfate proteoglycan. This factor is clearly distinguishable from other neurotrophic factors that have an effect on retinal ganglion cells such as brain-derived neurotrophic factor and fibroblast growth factor. The chondroitin sulfate proteoglycan from the neonatal superior colliculus is the first proteoglycan to be identified as a neurotrophic factor.

Functional interactions of neuronal heparan sulphate proteoglycans with laminin

Quantitative biosynthetic studies using cellular extracts and neuron conditioned medium demonstrated that heparan sulphate proteoglycans (HSPGs) comprised 20-25% of the sulphated proteoglycans produced by neurons while the remainder consisted of chondroitin sulphate proteoglycans (CSPGs). When chromatographic fractions containing guanidine extracted and partially purified proteoglycans from culture medium conditioned by neurons (NCM) were used to pretreat a laminin substrate, neurite formation by sensory neurons was enhanced. Enhanced neurite promoting activity was not apparent if, during the pretreatment of the laminin substrate with NCM, heparan sulphate glycosaminoglycans (HS) were present. To determine the molecular basis of cell surface HSPG interactions with immobilized laminin, adhesion and neurite growth by dissociated sensory neurons were quantified at 4 h in vitro--a time at which there was no apparent contribution of released proteoglycans to neurite growth. Whereas adhesion was not influenced, neurite growth was partially inhibited in a dose-dependent manner if the sensory neurons were coincubated with HS, and if the cells were pretreated, prior to seeding, with heparitinase. The inhibitory effect produced by coincubation with saturating concentrations of HS was no longer apparent if the cells had been pretreated with heparitinase. These findings distinguish quantitatively between neurite growth on laminin and on laminin-HSPG complexes, and suggest that some neuronal cell surface and released HSPGs are involved in neurite growth by virtue of non-covalent interactions with glycosaminoglycan binding domains of laminin.

Mast cells, nerves and fibrosis in the appendix: a morphological assessment

Mast cells are closely associated with nerves in the mucosa of the appendix vermiformis, and obliteration of the appendiceal lumen by fibrous tissue is accompanied by neurogenous hyperplasia. However, changes in the density of mast cells in this process have not been reported. Accordingly, fibrosis was graded in haematoxylin and eosin sections from 46 samples of human appendix. This was compared with mast cell number in toluidine blue-stained slides and nerve density in PGP9.5-immunoreactive sections. In the mucosa, the mast cell number in the samples with minimal fibrosis was three times greater than in those classified as normal (P less than 0.0001), and this declined in the more fibrotic samples. The mucosal nerve scores paralleled the mucosal mast cell changes, and stereological analysis revealed a correlation of mast cell number and nerve density within the lamina propria of the same specimens (r = 0.49-0.90). In the submucosa, mast cell numbers and nerve scores were not significantly different in the different histological grades and obliterated samples resembled normal submucosa, except that a dense axial block of nerve staining was often present. The progressive fibrotic changes in appendices provide a human model for studying the relationships of nerves, mast cells, and fibrosis in the gastrointestinal tract.

A diverse set of developmentally regulated proteoglycans is expressed in the rat central nervous system

Cellular interactions in neural development are influenced by various extracellular proteins, many of which bind glycosaminoglycans or proteoglycans. Precise functions of nervous system proteoglycans remain unknown, in part because neural proteoglycan composition is poorly understood. In this study, 25 putative proteoglycan core proteins were identified in subcellular fractions of rat brain. Levels of many of these varied considerably during development. Membrane-associated proteoglycans included two heparan sulfate proteoglycans (cores of 50 and 59 kd) that are covalently linked to glycosyl-phosphatidylinositol lipid, as well as several that appear to aggregate either with themselves or with copurifying proteins. These data indicate that brain proteoglycans exhibit the abundance, structural diversity, and developmental regulation that would be anticipated for molecules with diverse developmental functions.

Immunolocalization and quantitation of a novel nerve terminal protein in spinal cord development

In the adult spinal cord, the neuron-specific protein NT75 is located in nerve terminals synapsing in the superficial laminae of the dorsal horn. The present study examines the occurrence of NT75 in the developing rat spinal cord. NT75 immunoreactivity is detectable in primary afferent axons at the dorsal root entry zone on embryonic day 15. Subsequently, staining of presumptive nerve terminals appears in the deeper laminae of the dorsal horn, expanding into the superficial laminae during the first postnatal week. NT75 staining also appears in developing corticospinal tract axons in the brainstem at birth, and at lumbosacral levels by postnatal day 5. As NT75-positive nerve terminals approach the adult distribution, staining of primary afferent and corticospinal axons decreases, becoming undetectable by postnatal day 30. Dense transient staining of presumed nerve terminals in the ventral horn is also apparent during early postnatal development. Quantitative analysis of developing spinal cord shows a low level of NT75 immunoreactivity at birth. NT75 activity then increases substantially, reaching values by the third and fourth postnatal weeks up to 2.5 times that seen in adults. The occurrence of NT75 immunoreactivity correlates with the reported time course of synaptic development in the spinal cord. In addition, the results suggest that NT75 immunoreactivity is maintained at high levels in the nerve terminals of certain neural pathways into adulthood, whereas in other systems NT75 immunoreactivity may be detectable only during development.

Characterization of cell-associated proteoglycans synthesized by embryonic neural retinal cells

To begin to understand the properties of the neuronal heparan sulfate proteoglycan (HSPG) that interacts with the neural cell adhesion molecule (NCAM), we have analyzed proteoglycans synthesized by dissociated embryonic retinal cells in culture. Because NCAM plays an integral role in cell-cell interactions, we have focused on cell-associated HSPGs. Proteoglycans were isolated from embryonic Day 10 retinal cell cultures labeled with 35SO4 and separated into fractions that either flowed through or were retained on phenyl-Sepharose. Molecules binding phenyl-Sepharose have been proposed to be capable of insertion into the plasma membrane, and thus may be involved in binding to NCAM. Proteoglycans binding to phenyl-Sepharose had an estimated molecular mass of 400-500 kDa, and contained 60% HSPG and 40% chondroitin sulfate proteoglycan (CSPG). The putative membrane-associated HSPGs, with an average molecular weight of 360 kDa, were shown to contain heparan sulfate chains of 40 and 20 kDa, and multiple core proteins with the major core protein having a molecular weight of approximately 130 kDa. The membrane-associated CSPGs also exhibited multiple core proteins, with sizes ranging from 120 to 220 kDa. These data suggest that multiple membrane-associated HSPGs and CSPGs are synthesized by embryonic neural retina cells, which may explain the diversity in function of this class of proteoglycans.

Specific effects of ethanol on neurite-promoting proteoglycans of neuronal origin

Quantitative analysis of proteoglycan synthesis and release by neurons indicated that of the total incorporation of 35SO4 and [3H]glucosamine into proteoglycan, approximately 75% was chondroitin sulphate while approximately 25% was heparan sulphate. Using a biological assay it has been shown that heparan sulphate proteoglycans (HSPGs) in conditioned medium promote neurite outgrowth from sensory neurons when complexed to a laminin substrate. Culture media conditioned in the presence of ethanol did not enhance neurite formation over control levels. Co-incubation of neurons with beta-D-xyloside, an inhibitor of proteoglycan synthesis, reduced neurite outgrowth after 20 h in culture and the combination of ethanol and beta-D-xyloside produced no further inhibition than with either ethanol or beta-D-xyloside used alone. If the laminin substrate was coated with medium conditioned by neurons, the direct inhibitory effects on process formation seen when ethanol was co-incubated with neurons were no longer observed. Ethanol inhibited the incorporation of 35SO4 and [3H]glucosamine into HSPG by neurons while having little or no effect on incorporation into chondroitin sulphate. These results suggest that inhibition of neuronal synthesis of HSPGs by ethanol is responsible for the decrease in neurite promoting activity of medium conditioned in the presence of ethanol.

Expression and cellular localization of amyloid beta-protein precursor transcripts in normal human brain and in Alzheimer's disease

Two classes of amyloid beta-protein precursors which differ by the presence of a serine protease inhibitor domain have been described. We have used synthetic oligonucleotide probes to investigate the tissue distribution and cellular localization of mRNAs encoding the two classes of amyloid beta-protein precursors. RNA blot analysis showed that transcripts encoding the protease inhibitor sequence are ubiquitously expressed in peripheral and central tissues. By contrast, transcripts lacking the protease inhibitor domain were only found in the central nervous system. By in situ hybridization on cerebral cortex and hippocampal formation both types of transcripts were present exclusively in nerve cells and they appeared to be produced by the same cells. A reduction in the transcript lacking the protease inhibitor domain was observed in frontal cortex from Alzheimer's disease patients. The present results indicate that there exists no correlation between the distribution of amyloid amyloid beta-protein precursor mRNAs and the tissue and cellular pathology of Alzheimer's disease; they also suggest that an overproduction of amyloid beta-protein precursor mRNA is unlikely to be responsible for amyloid beta-protein deposition in Alzheimer's disease.

Glycosaminoglycan-related epitopes surrounding different subsets of mammalian central neurons

Among a panel of monoclonal antibodies generated against monkey brain tissue, a class of antibodies was found to produce perineuronal staining of small subsets of mammalian central neurons. Three antibodies (MAbs 473, 376, 528) we report here define two different, though partially overlapping, neuronal subsets in the monkey neocortex. All 3 antibodies stain in addition certain chondrocytes. The neural immunoreactivities were lost, and the chondral immunoreactivities either lost or enhanced, after treatment of the sections with chondroitinase ABC. Independently, 3 other antibodies (MAbs 1B5, 9A2, 3B3) with established specificity to glycosaminoglycan epitopes also produced perineuronal staining of a related subset of central neurons. Immunoblot experiments with two of the antibodies revealed bands of high molecular weight. These findings indicate that certain glycosaminoglycans occur surrounding mammalian central neurons, and suggest that different neuronal subsets are associated with different combinations of proteoglycan epitopes.

Properties of nervous tissue proteoglycans relevant to studies on Alzheimer's disease

Our comments concern certain properties of nervous tissue proteoglycans which were not emphasized in the review by Snow and Wight, with particular attention to the proposed relation of the amyloid beta protein precursor to a heparan sulfate proteoglycan core protein.

Characterization of a heparan sulfate proteoglycan that copurifies with the neural cell adhesion molecule

We have demonstrated previously that the neural cell adhesion molecule (NCAM) interacts with a neuronal heparan sulfate proteoglycan. The binding of this proteoglycan(s) by NCAM appears to be required for NCAM-mediated cell adhesion, although the mechanism is unclear. In the present study we show that a heparan sulfate proteoglycan copurifies with NCAM, and provide an initial biochemical characterization of the proteoglycan. The copurification of a heparan sulfate proteoglycan with NCAM was demonstrated following immunopurification of NCAM from a detergent extract of cell membranes derived from Na2(35)SO4-labeled neural retinal cells. A large-molecular-weight, 35SO4-labeled molecule copurified with NCAM isolated from these neural cell cultures, and was resistant to chondroitinase ABC treatment, but degraded completely by nitrous acid treatment. These results indicate that the molecule is a heparan sulfate proteoglycan. Although this proteoglycan copurifies with NCAM, it is not detected when the neuron-glia cell adhesion molecule (NgCAM) is immunopurified using the 8D9 monoclonal antibody. The heparan sulfate proteoglycan may also be a membrane-associated proteoglycan since it interacts with phenyl-Sepharose. Molecular weight characterization of the proteoglycan by gel filtration chromatography indicates a molecular weight of 400-520 kDa. The heparan sulfate glycosaminoglycan chains were shown to have an average molecular weight of approximately 40 kDa, and the polypeptide backbone was estimated to be 120 kDa by polyacrylamide gel electrophoresis. These data therefore demonstrate that a neuronal heparan sulfate proteoglycan copurifies with NCAM.

Glycosaminoglycan composition of PC12 pheochromocytoma cells: a comparison with PC12D cells, a new subline of PC12 cells

PC12D cells, a new subline of conventional PC12 cells, respond not only to nerve growth factor but also to cyclic AMP by extending their neurites. These cells are flat in shape and are similar in appearance to PC12 cells that have been treated with nerve growth factor for a few days. In both cell lines, we have characterized the glycosaminoglycans, the polysaccharide moieties of proteoglycans, which are believed to play an important role in cell adhesion and in cell morphology. Under the present culture conditions, only chondroitin sulfate was detected in the media from PC12 and PC12D cells, whereas both chondroitin sulfate and heparan sulfate were found in the cell layers. The levels of cell-associated heparan sulfate and chondroitin sulfate were about twofold and fourfold higher in PC12D cells than in PC12 cells, respectively. Compared to PC12 cells, the amounts of [35S]sulfate incorporated for 48 h into chondroitin sulfate were twofold lower but those into heparan sulfate were 35% higher in PC12D cells. The amount of chondroitin sulfate released by PC12D cells into the medium was about a half of that released by PC12 cells. The ratio of [35S]sulfate-labeled heparan sulfate to chondroitin sulfate was 6.2 in PC12D cells and 2.2 in PC12 cells. These results suggest that there may be some correlation between the increase in content of glycosaminoglycans and the change in cell morphology, which is followed by neurite outgrowth.

The ultrastructural localization of sulfated proteoglycans is identical in the amyloids of Alzheimer's disease and AA, AL, senile cardiac and medullary carcinoma-associated amyloidosis

The cationic dyes cuprolinic blue and ruthenium red were used to ultrastructurally localize proteoglycans (PGs) within the neuritic plaque and neurofibrillary tangle of Alzheimer's disease. Highly sulfated PGs were specifically localized to the amyloid fibril of the neuritic plaque and the paired filaments of the neurofibrillary tangle. This demonstrates that highly sulfated PGs either comprise part of the Alzheimer's amyloid fibril and paired filament or are intimately associated with them. Four unrelated types of amyloid--AA (inflammation-associated), AL (immunoglobulin light chain), senile cardiac (prealbumin) and medullary carcinoma-associated amyloid (procalcitonin)--showed an identical pattern of localization of highly sulfated PG to the different amyloid fibrils. This constant close spatial relationship between PGs and diverse amyloid proteins suggests that PGs may play a role in amyloidogenesis.

Genetic evidence for the role of Thy-1 in neurite outgrowth in the mouse

Non-neuronal accessory cells of mouse dorsal root ganglion cultures secrete a complex that stimulates neurite outgrowth in neonatal sympathetic ganglion neurons. A monoclonal antibody that binds to these two cell types also immunoprecipitates neurite outgrowth complex from mouse conditioned medium and binds to mouse brain tissue. Genetic analysis of the component recognized by the antibody revealed that it maps to the Thy-1 locus on mouse chromosome 9. Further studies of cell-type specificity, sedimentation analysis and antibody competition, confirmed that it is indistinguishable from the product of the Thy-1 locus. The finding of an association between Thy-1 and neurite outgrowth complex in the mouse argues for a role of the Thy-1 locus in the interactions of neurons with their surroundings.

Is astrocyte laminin involved in axon guidance in the mammalian CNS?

This paper provides evidence for the expression of laminin on glia in correlation with axon elongation and nerve pathway formation during embryonic development of the mouse optic nerve and other parts of the central nervous system (CNS). We show that punctate deposits of laminin on immature glial cells precede the entrance of the first optic axons into the nerve, and remain in close association with growing axons. Furthermore, we show that in one particular region of the optic pathway that the retinal ganglion cell axons avoid in normal animals (i.e., the pigmented area of the distal nerve) the punctate laminin matrix is missing. As the optic nerve matures punctate laminin deposits disappear, and laminin is reduced in the astroglial cytoplasm. The close correlation of the punctate form of laminin with early axonal growth is true not only in the optic nerve but also in some other parts of the CNS. We demonstrate such punctate laminin deposits in a model of astrocyte-induced regeneration of the corpus callosum in acallosal mice (G. Smith, R. Miller, and J. Silver, 1986, J. Comp. Neurol. 251, 23-43), and in glia associated with several normal developing axon trajectories, such as the corpus callosum, fornix, and pathways in the embryonic hindbrain. In all of these regions punctate laminin deposits are found on astroglia that are associated with early growing axons. Our results indicate that the punctate form of laminin, produced by astrocytes, may be an important factor involved in axon elongation and nerve pathway formation in the mammalian CNS.

Adhesion of neural cells to extracellular matrix constituents. Involvement of glycosaminoglycans and cell adhesion molecules

Single cell suspensions of early postnatal mouse cerebellum adhere to substrate-bound culture supernatants of the teratocarcinoma cell line PF-HR9 and can be inhibited to adhere by antibodies to the neural cell adhesion molecules L1 and N-CAM. Adhesion can also be inhibited by the glycosaminoglycans heparin and heparan sulfate, and less by chondroitin sulfate or hyaluronic acid. Heparinase treatment of cells, but not of HR9 substrate, reduces adhesion. Adhesion does not appear to be mediated by laminin, a constituent of HR9 extracellular matrix, since L1 and N-CAM antibodies do not interfere with cell adhesion on EHS sarcoma laminin as substrate and since antibodies to EHS sarcoma laminin partially inhibit adhesion to HR9 extracellular matrix which contains laminin. Of the other extracellular matrix constituents analysed in HR9 culture supernatants (collagen type IV, a heparan sulfate proteoglycan and fibronectin) none could be shown to promote adhesion, when coated as substrate, suggesting that yet unidentified compounds are responsible for L1- or N-CAM-mediated cell adhesion. These experiments show for the first time that extracellular matrix constituents can act as binding partners for the neural cell adhesion molecules L1 and N-CAM.

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.

Proteoglycan synthesis in flat cell-free cultures of chick embryo retinal neurons and photoreceptors

Extracellular matrix and cell surface proteoglycans are thought to play important roles in neural development and regeneration. Central nervous system proteoglycans have been isolated and characterized from rat and sheep brain and from chick neural retina. An experimental advantage offered by the latter tissue is that it is avascular and can be isolated free of connective tissue and pigment epithelium. Therefore, proteoglycans synthesized by this tissue are derived exclusively from neural cells. However, it has not yet been determined whether neurons and photoreceptors contribute to proteoglycan synthesis or whether these molecules are largely glial in origin. In the present study we have addressed this question using cultures of chick neural retinal cells free of flat, glial-like cells. Proteoglycans synthesized by cultures of retinal neurons, photoreceptors, and undifferentiated, process-free round cells from 8-day embryonic chick neural retina were metabolically labeled in vitro using [35S]sulfate and [3H]glucosamine as precursors. Radiolabeled proteoglycans accumulated in the medium, and could also be extracted from the cell layer by sequential treatments with Triton X-100 and with guanidine HCl. The proteoglycans were isolated by ion-exchange chromatography, and characterized by gel filtration chromatography and by susceptibility to degradation by enzymatic and chemical treatments. Overall, heparan sulfate proteoglycans were the predominant type of proteoglycan synthesized in vitro by the cultured neural retinal cells at this developmental stage. The medium and the Triton extract contained different proportions of both chondroitin sulfate and heparan sulfate proteoglycans, while heparan sulfate was the only proteoglycan recovered from the guanidine extract. These studies demonstrate that heparan sulfate and chondroitin sulfate proteoglycans are actively synthesized by cultures of neural retinal cells free of flat, glial-like cells.

Proteoglycans synthesized by embryonic chicken retina in culture: composition and compartmentalization

Characteristics of the chondroitin sulfate/dermatan sulfate proteoglycans (CS/DSPGs) and heparan sulfate proteoglycans (HSPGs) from retinas of 14-day chicken embryos were examined following specific lyase digestion of the HSPG and CS/DSPG glycosaminoglycans, respectively. On the basis of gel exclusion chromatography the prevalent CS/DSPGs in the tissue were above Mr 400 X 10(3) with two or three glycosaminoglycan chains of Mr 60-70 X 10(3). The HSPGs existed in two distinct populations in the tissue. Those in the dominant population appeared to be in the range of Mr 250-300 X 10(3) with 9 to 12 glycosaminoglycan chains of Mr 15-25 X 10(3). The other population consisted of free heparan sulfate chains of Mr 15-25 X 10(3). The HSPGs in the medium tended to be intermediate in size. To examine the distribution of proteoglycans, tissues were sequentially homogenized and extracted in saline and reextracted with 4 M guanidine HCl (GdnHCl) and Triton X-100 (TX), or they were washed in heparin solution and dissociated to single cells with trypsin before sequential extraction in saline and GdnHCl with TX. Through comparison of the results of these two extraction methods, CS/DSPGs were found to be almost entirely within the medium or matrix or loosely associated with the cell surface, and most HSPGs were associated with either the basal lamina or the plasma membrane. The single heparan sulfate glycosaminoglycan chains appeared to be intracellular degradation products. These results support reports that CS/DSPGs may be present in the retina interphotoreceptor matrix and that HSPGs may be present in regions of synaptogenesis, associated with cell membranes.

Lead-dependent deposits in diverse synaptic vesicles: suggestive evidence for the presence of anionic binding sites

We have observed electron dense deposits dependent on incubation of aldehyde-fixed tissues with lead ions within synaptic vesicles of several types of neurons that differ in the neurotransmitters utilized and in the secretory granules of the adrenal medulla. Evidently, vesicle components that can interact with lead ions are widespread. A plausible explanation for the occurrence of the deposits is the presence of anionic binding sites within the vesicles. This would agree well with other biochemical, cytochemical, and immunocytochemical evidence, such as that indicating the presence of sulfated macromolecules in certain synaptic vesicles. Anionic binding sites could play significant roles by participating in processes such as Ca2+ storage, stabilization of pH gradients, or the control of osmotic phenomena.

Effects of nerve growth factor-induced differentiation on the heparan sulfate of PC12 pheochromocytoma cells and comparison with developing brain

We have examined the size, charge, and sulfation pattern of heparan sulfate in the cell-soluble fraction, membranes, and culture medium of PC12 pheochromocytoma cells cultured in the presence and absence of nerve growth factor (NGF) and compared the structural features of PC12 cell heparan sulfate to that of rat brain at several stages of early postnatal development. Nitrous acid degradation studies revealed significant differences in the distribution of N-sulfate and N-acetyl groups in heparan sulfate present in the PC12 cell-soluble fraction, membranes, and medium and demonstrated that NGF treatment led to an increased proportion of N-sulfated segments in the cell-associated heparan sulfate, although no such change was seen in that released into the culture medium. There was very little change in the N-sulfation of brain heparan sulfate during the first 30 days after birth. In brain, most of the heparan sulfate glucosamine residues are N-sulfated and yield predominantly di- and tetrasaccharide nitrous acid degradation products, whereas PC12 cell heparan sulfate contains large blocks of N-acetylglucosamine residues. There was very little difference in the overall charge or size (approximately 15,000 Da) of heparan sulfate chains between the different PC12 cell fractions or brain, although NGF treatment led to a decrease in the proportion of less-charged chains in the PC12 cell membranes and a small increase in molecular size. Our studies therefore demonstrate the presence in PC12 cells of several pools of heparan sulfate having different structural properties, and that significant alterations in the charge, size, and sulfation pattern of PC12 cell heparan sulfate accompany NGF-induced differentiation and neurite outgrowth.

Comparison of the Schwann cell surface and Schwann cell extracellular matrix as promoters of neurite growth

The ability of Schwann cells to influence the direction and rate of neurite growth was investigated in a tissue culture model of the bands of Büngner of injured peripheral nerve. The arrangement of this culture system allowed testing of the growth-promoting properties of the Schwann cell surface and extracellular matrix (ECM) assembled by Schwann cells rather than soluble substances secreted into conditioned medium. Various components of peripheral nerve were examined separately as substrata for regenerating neurites: (i) Schwann cells and their ECM; (ii) Schwann cells alone; (iii) Schwann cell ECM alone; (iv) Schwann cells, fibroblasts, and their assembled ECM; (v) Schwann cells, their ECM and neurites; and (vi) purified laminin. Regenerating peripheral neurites were from explants of foetal rat dorsal root ganglia, which had been cultured for several weeks to rid them of accompanying non-neuronal cells, or from explants of foetal rat superior cervical ganglia, which contained non-neuronal cells. CNS neurites from the somatosensory cortex of embryonic rats were also studied; these neurites may be either first growing or regenerating. Neurites from all types of explants studied grew longer and were guided on a substratum of Schwann cells or Schwann cell ECM compared with a collagen substratum. The presence of fibroblasts during ECM assembly did not enhance the neurite growth-promoting activity. The design of the experiments suggested that the factors by which the Schwann cells or their ECM promoted and guided neurite outgrowth were surface-bound rather than medium-borne. Electron microscopic examination showed that neurites grew on either Schwann cell surfaces or basal lamina material. Attempts to define the chemical nature of the neurite growth-promoting effect of ECM by partial enzymatic digestion did not identify any single component as essential. Purified laminin was a more effective promoter of outgrowth of peripheral neurites than were Schwann cells or Schwann cell ECM. Cortical explants also grew on laminin, but neurites were accompanied on this substratum by a massive migration of non-neuronal cells; the neurites appeared to extend primarily on the non-neuronal cells rather than by direct attachment to the laminin substratum. This characteristic outgrowth of cortical non-neuronal cells on laminin was not consistently seen on Schwann cell ECM. In conclusion, either the Schwann cell surface or the ECM produced and assembled by Schwann cells promotes neurite outgrowth and guides that outgrowth from the several types of peripheral and CNS neurons studied in this report.

Extracellular mammalian polysaccharides: glycosaminoglycans and proteoglycans

This review of the mammalian extracellular matrix polysaccharides covered the glycosaminoglycans (GAGs) and their association into proteoglycans. As they necessarily pertain to the chromatographic and electrophoretic separations of these molecules, the structural features of the five principal GAGs were briefly reviewed. Much of the current structural work as well as the separation technology has been concerned with the sulfation state and copolymeric sequences of the individual classes of GAGs. The separation methods discussed included electrophoresis by agarose, acrylamide and cellulose acetate, high-performance liquid chromatography (HPLC), ion-exchange, gel permeation and biospecific affinity methods. Since detection systems are an integral part of chemical separation technology, current thoughts about the best methods to assay GAGs or detect column fractions were discussed. These included polysaccharide-specific detection systems such as Alcian blue dye, 1,9-dimethylmethylene blue, bovine serum albumin-Coomassie blue, as well as non-specific carbohydrate detection systems such as the carbazole or indole hydrochloride methods. Instrumentation used in the detection of chromatography fractions for these molecules was discussed, since the usual ultraviolet detector, standard with HPLC equipment, is often unsatisfactory. The most sensitive specific detection method for GAGs is the use of monoclonal antibodies, which are only now becoming commercially available. The use of these antibodies, combined with HPLC separation, appears to be the best available biochemical technology for studying the extracellular matrix polysaccharides. Finally, the association between proteoglycans, GAGs and mammalian disease processes was reviewed, emphasizing mucopolysaccharidoses and arthritis. The early detection of both of these diseases is desired for effective counselling and treatment. Many of the methods discussed here have been applied, but others are yet to be tried in efforts to further that goal.

Cyclophosphamide treatment used to manipulate the immune response for the production of monoclonal antibodies

After immunization with a complex mixture of antigens, a considerable bias toward obtaining monoclonal antibodies to immunodominant determinants exists. By selectively killing antigen-stimulated lymphocytes, the cytotoxic drug cyclophosphamide can be used to manipulate the bias of the normal immune response. Cyclophosphamide has been used to tolerize mice to one set of antigens followed by immunization with a similar but slightly different set of antigens. This approach yields an enhanced frequency of antibodies that distinguish the two sets of antigens. Cyclophosphamide treatment has also allowed us to produce monoclonal antibodies to weakly immunogenic glycosaminoglycans and to obtain a high frequency of apparently anti-idiotypic antibodies.

Isolation of the heparan sulfate proteoglycans from the extracellular matrix of rat skeletal muscle

We have previously shown that asymmetric collagen-tailed acetylcholinesterase (AChE) is anchored to the extracellular matrix (ECM) by heparan sulfate proteoglycans (HSPGs). Here we present our studies on the characterization of such PGs from the ECM of rat skeletal muscles. After radiolabeling with 35SO4 for 24h, PGs were extracted from the muscle ECM with 4.0 M guanidine-HCl containing protease inhibitors. PGs were subsequently isolated using sequential DEAE-Sephacel chromatography, digestion with chondroitinase ABC, and Sepharose CL-4B. Two different hydrodynamic size species of HSPGs were found. One type had a Mr of 4-6 X 10(5) (Kav = 0.25) as estimated by gel chromatography in the presence of 1% SDS and accounted for 75% of the total HSPGs. The other HSPG had a Mr 1.5-2.5 X 10(5) (Kav = 0.41). The glycosaminoglycan (GAG) side chains (Mr 20,000 and 12,000) were found composed only of heparan sulfate as determined by nitrous acid oxidation and heparitinase treatment. The large-sized HSPG, which is concentrated in synaptic regions, contains only GAG chains of Mr 20,000, suggesting that each HSPG contains only one kind of heparan sulfate chain in its structure. Our results definitively establish by biochemical criteria that the basement membrane of mammalian skeletal muscle contains HSPGs, the likely matrix receptor for the immobilization of the asymmetric collagen-tailed AChE at the neuromuscular junction.