Concanavalin A: a tool to investigate neuronal plasticity

Anti-inflammatory and anti-necrotic effects of lectins from Canavalia ensiformis and Canavalia brasiliensis in experimental acute pancreatitis

Lectins isolated from Canavalia ensiformis (ConA) and Canavalia brasiliensis (ConBr) are promising molecules to prevent cell death. Acute pancreatitis, characterized by acinar cell necrosis and inflammation, presents significant morbidity and mortality. This study has investigated the effects of ConA and ConBr in experimental acute pancreatitis and pancreatic acinar cell death induced by bile acid. Pancreatitis was induced by retrograde pancreatic ductal injection of 3% sodium taurocholate (Na-TC) in male Swiss mice. ConA or ConBr (0.1, 1 or 10 mg/kg) were intravenously applied to mice 1 h and 12 h after induction. After 24 h, the severity of pancreatitis was evaluated by serum amylase and lipase, histopathological changes and myeloperoxidase assay. Pancreatic acinar cells were incubated with ConA (200 µg/ml) or ConBr (200 µg/ml) and taurolithocholic acid 3-sulfate (TLCS; 500 µM). Necrosis and changes in mitochondrial membrane potential (ΔѰm) were detected by fluorescence confocal microscopy. Treatment (post-insult) with ConA and ConBr decreased pancreatic damage caused by retrograde injection of Na-TC in mice, reducing pancreatic neutrophil infiltration, edema and necrosis. In addition, ConA and ConBr decreased pancreatic acinar cell necrosis and depolarization of ΔѰm caused by TLCS. The inhibition of necrosis was prevented by the lectin domain blockade. In conclusion, ConA and ConBr markedly inhibited in vitro and in vivo damage, effects partly dependent on the interaction with mannose residues on acinar cells. These data support the potential application of these proteins for treatment of acute pancreatitis.

Concanavalin A: coordination diversity to xenobiotic metal ions and biological consequences

The binding ability of lectins has gained attention owing to the carbohydrate-specific interactions of these proteins. Such interactions can be applied to diverse fields of biotechnology, including the detection, isolation, and concentration of biological target molecules. The physiological aspects of the lectin concanavalin A (ConA) have been intensively studied through structural and functional investigations. X-ray crystallography studies have proven that ConA has two β-sheets and a short α-helix and that it exists in the form of a metalloprotein containing Mn²⁺ and Ca²⁺. These heterometals are coordinated with side chains located in a metal-coordinated domain (MCD), and they affect the structural environment in the carbohydrate-binding domain (CBD), which interacts with carbohydrates through hydrogen bonds. Recent studies have shown that ConA can regulate biophysical interactions with glycoproteins in virus envelopes because it specifically interacts with diverse polysaccharides through its CBD (Tyr, Asn, Asp, and Arg residues positioned next to the MCD). Owing to their protein-protein interaction abilities, ConA can form diverse self-assembled complexes including monomers, dimers, trimers, and tetramers, thus affording unique results in different applications. In this regard, herein, we present a review of the structural modifications in ConA through metal-ion coordination and their effect on complex formation. In recent approaches, ConA has been applied for viral protein detection, on the basis of the interactions of ConA. These aspects indicate that lectins should be thoroughly investigated with respect to their biophysical interactions, for avoiding unexpected changes in their interaction abilities.

Animal Galectins and Plant Lectins as Tools for Studies in Neurosciences

Lectins are proteins or glycoproteins of non-immunological origin capable of reversibly and specifically binding to glycoconjugates. They exist in free form or associated with cells and are widely distributed in nature, being found in plants, microorganisms, and animals. Due to their characteristics and mainly due to the possibility of reversible binding to glycoconjugates, lectins have stood out as important tools in research involving Neurobiology. These proteins have the ability to modulate molecular targets in the central nervous system (CNS) which may be involved with neuroplasticity, neurobehavioral effects, and neuroprotection. The present report integrates existing information on the activity of animal and plant lectins in different areas of Neuroscience, presenting perspectives to direct new research on lectin function in the CNS, providing alternatives for understanding neurological diseases such as mental disorders, neurodegenerative, and neuro-oncological diseases, and for the development of new drugs, diagnoses and therapies in the field of Neuroscience.

ConA-Like Lectins: High Similarity Proteins as Models to Study Structure/Biological Activities Relationships

Lectins are a widely studied group of proteins capable of specific and reversible binding to carbohydrates. Undoubtedly, the best characterized are those extracted from plants of the Leguminosae family. Inside this group of proteins, those from the Diocleinae subtribe have attracted attention, in particular Concanavalin A (ConA), the best-studied lectin of the group. Diocleinae lectins, also called ConA-like lectins, present a high similarity of sequence and three-dimensional structure and are known to present inflammatory, vasoactive, antibiotic, immunomodulatory and antitumor activities, among others. This high similarity of lectins inside the ConA-like group makes it possible to use them to study structure/biological activity relationships by the variability of both carbohydrate specificity and biological activities results. It is in this context the following review aims to summarize the most recent data on the biochemical and structural properties, as well as biological activities, of ConA-like lectins and the use of these lectins as models to study structure/biological activity relationships.

Neuropharmacological characterization of frutalin in mice: Evidence of an antidepressant-like effect mediated by the NMDA receptor/NO/cGMP pathway

In this study we evaluated the effect of frutalin (FTL) on mouse behavior. Mice (n=6/group) were treated (i.p.) with FTL (0.25; 0.5 or 1mg/kg) or vehicle and submitted to several tests (hole-board/HBT, elevated plus maze/PMT, open field/OFT, tail suspension/TST, or forced swimming/FST). Yohimbine, ketamine, l-NAME, aminoguanidine, 7-NI, methylene blue, l-arginine or dl-serine was administered 30min before FTL (0.5mg/kg). To evaluate the subchronic effect, animals were injected with FTL or vehicle for 7days and submitted to the FST. Molecular docking was simulated using FTL against NOS and the NMDA receptor. No changes were observed in the HBT or the OFT. FTL (0.25mg/kg) increased the number of entries into enclosed arms in the PMT. FTL reduced immobility in the TST (0.25 and 0.5mg/kg) and the FST (0.25mg/kg; 0.5mg/kg). The effect of FTL was dependent on carbohydrate interaction and protein structure integrity and was reduced by ketamine, l-NAME, aminoguanidine, 7-NI and methylene blue, but not by l-arginine, yohimbine or dl-serine. The antidepressant-like effect remained after subchronic treatment. The molecular docking study revealed a strong interaction between FTL and NOS and NMDA. FTL was found to have an antidepressant-like effect mediated by the NMDA receptor/NO/cGMP pathway.

Surface Modification of Polydivinylbenzene Microspheres with a Fluorinated Glycopolymer Using Thiol-Halogen Click Chemistry

Distillation-precipitation polymerization of divinylbenzene was applied to obtain uniform-sized polymeric microspheres. The microspheres were then modified with polypentafluorostyrene chains utilizing surface-initiated atom transfer radical polymerization techniques. The hydrophobic fluoropolymer-coated microsphere was then converted to a hydrophilic biopolymer by performing thiol-halogen click chemistry between polypentafluorostyrene and 1-thio-β-D-glucose sodium salt. The semi-fluorinated glycopolymer showed good binding ability with Concanavalin A as determined by confocal microscopy and turbidity experiments.

Brain effects of the lectin from Canavalia ensiformis in adult rats previously suckled in favorable and unfavorable conditions: A spreading depression and microglia immunolabeling study

OBJECTIVE

To evaluate in adult rats, previously suckled under favorable and unfavorable conditions, the brain electrophysiological and microglial effects of the treatment early in life with the lectin (ConA) from Canavalia ensiformis.

METHODS

Male Wistar newborn rats (n = 89) were suckled under favorable or unfavorable conditions, represented by litters with 6-7 pups or 12-14 pups (groups N6 and N12, respectively). From postnatal days 5-24, they were treated intraperitoneally with 1 or 10 mg/kg ConA (groups L1 and L10, respectively), or with saline solution (group Sal), or no treatment (group Naïve). At 90-120 days of age, cortical spreading depression (CSD) was recorded at two parietal points for 4 hours, and CSD parameters (velocity of propagation and amplitude and duration of the DC slow potential change) were measured. Fixative-perfused brain sections were reacted with anti-Iba1 antibodies to quantify immunolabeled microglia.

RESULTS

Compared with the control groups, ConA-treated animals dose-dependently presented with reduced CSD propagation velocities and increased amplitude and duration of the CSD slow potential change. Microglia Iba-1 immunoreactivity was lower in both nutritional groups treated with ConA, in comparison with the control groups. The CSD hemisphere presented with higher immunoreactivity compared with the CSD-free hemisphere.

DISCUSSION

Attenuation in CSD propagation and microglia reaction was associated in adulthood with ConA treatment during brain development, indicating that the lectin can affect the electrophysiological and microglial development, and suggesting long-lasting protective action of the lectin on the rat brain, which is not impeded by the unfavorable suckling condition.

Vatairea macrocarpa lectin (VML) induces depressive-like behavior and expression of neuroinflammatory markers in mice

Lectins are proteins capable of reversible binding to the carbohydrates in glycoconjugates that can regulate many physiological and pathological events. Galectin-1, a β-galactoside-binding lectin, is expressed in the central nervous system (CNS) and exhibits neuroprotective functions. Additionally, lectins isolated from plants have demonstrated beneficial action in the CNS. One example is a lectin with mannose-glucose affinity purified from Canavalia brasiliensis seeds, ConBr, which displays neuroprotective and antidepressant activity. On the other hand, the effects of the galactose-binding lectin isolated from Vatairea macrocarpa seeds (VML) on the CNS are largely unknown. The aim of this study was to verify if VML is able to alter neural function by evaluating signaling enzymes, glial and inflammatory proteins in adult mice hippocampus, as well as behavioral parameters. VML administered by intracerebroventricular (i.c.v) route increased the immobility time in the forced swimming test (FST) 60 min after its injection through a carbohydrate recognition domain-dependent mechanism. Furthermore, under the same conditions, VML caused an enhancement of COX-2, GFAP and S100B levels in mouse hippocampus. However, phosphorylation of Akt, GSK-3β and mitogen-activated protein kinases named ERK1/2, JNK1/2/3 and p38(MAPK), was not changed by VML. The results reported here suggest that VML may trigger neuroinflammatory response in mouse hippocampus and exhibit a depressive-like activity. Taken together, our findings indicate a dual role for galactose binding lectins in the modulation of CNS function.

Concanavalin-A-induced autophagy biomarkers requires membrane type-1 matrix metalloproteinase intracellular signaling in glioblastoma cells

Pre-clinical trials for cancer therapeutics support the anti-neoplastic properties of the lectin from Canavalia ensiformis (Concanavalin-A, ConA) in targeting apoptosis and autophagy in a variety of cancer cells. Given that membrane type-1 matrix metalloproteinase (MT1-MMP), a plasma membrane-anchored matrix metalloproteinase, is a glycoprotein strongly expressed in radioresistant and chemoresistant glioblastoma that mediates pro-apoptotic signalling in brain cancer cells, we investigated whether MT1-MMP could also signal autophagy. Among the four lectins tested, we found that the mannopyranoside/glucopyranoside-binding ConA, which is also well documented to trigger MT1-MMP expression, increases autophagic acidic vacuoles formation as demonstrated by Acridine Orange cell staining. Although siRNA-mediated MT1-MMP gene silencing effectively reversed ConA-induced autophagy, inhibition of the MT1-MMP extracellular catalytic function with Actinonin or Ilomastat did not. Conversely, direct overexpression of the recombinant Wt-MT1-MMP protein triggered proMMP-2 activation and green fluorescent protein-microtubule-associated protein light chain 3 puncta indicative of autophagosomes formation, while deletion of MT1-MMP's cytoplasmic domain disabled such autophagy induction. ConA-treated U87 cells also showed an upregulation of BNIP3 and of autophagy-related gene members autophagy-related protein 3, autophagy-related protein 12 and autophagy-related protein 16-like 1, where respective inductions were reversed when MT1-MMP gene expression was silenced. Altogether, we provide molecular evidence supporting the pro-autophagic mechanism of action of ConA in glioblastoma cells. We also highlight new signal transduction functions of MT1-MMP within apoptotic and autophagic pathways that often characterize cancer cell responses to chemotherapeutic drugs.

The lectin concanavalin-A signals MT1-MMP catalytic independent induction of COX-2 through an IKKgamma/NF-kappaB-dependent pathway

The lectin from Canavalia ensiformis (Concanavalin-A, ConA), one of the most abundant lectins known, enables one to mimic biological lectin/carbohydrate interactions that regulate extracellular matrix protein recognition. As such, ConA is known to induce membrane type-1 matrix metalloproteinase (MT1-MMP) which expression is increased in brain cancer. Given that MT1-MMP correlated to high expression of cyclooxygenase (COX)-2 in gliomas with increasing histological grade, we specifically assessed the early proinflammatory cellular signaling processes triggered by ConA in the regulation of COX-2. We found that treatment with ConA or direct overexpression of a recombinant MT1-MMP resulted in the induction of COX-2 expression. This increase in COX-2 was correlated with a concomitant decrease in phosphorylated AKT suggestive of cell death induction, and was independent of MT1-MMP's catalytic function. ConA- and MT1-MMP-mediated intracellular signaling of COX-2 was also confirmed in wild-type and in Nuclear Factor-kappaB (NF-kappaB) p65(-/-) mutant mouse embryonic fibroblasts (MEF), but was abrogated in NF-kappaB1 (p50)(-/-) and in I kappaB kinase (IKK) gamma(-/-) mutant MEF cells. Collectively, our results highlight an IKK/NF-kappaB-dependent pathway linking MT1-MMP-mediated intracellular signaling to the induction of COX-2. That signaling pathway could account for the inflammatory balance responsible for the therapy resistance phenotype of glioblastoma cells, and prompts for the design of new therapeutic strategies that target cell surface carbohydrate structures and MT1-MMP-mediated signaling. Concise summary Concanavalin-A (ConA) mimics biological lectin/carbohydrate interactions that regulate the proinflammatory phenotype of cancer cells through yet undefined signaling. Here we highlight an IKK/NF-kappaB-dependent pathway linking MT1-MMP-mediated intracellular signaling to the induction of cyclooxygenase-2, and that could be responsible for the therapy resistance phenotype of glioblastoma cells.

The function of activity-regulated genes in the nervous system

The mammalian brain is plastic in the sense that it shows a remarkable capacity for change throughout life. The contribution of neuronal activity to brain plasticity was first recognized in relation to critical periods of development, when manipulating the sensory environment was found to profoundly affect neuronal morphology and receptive field properties. Since then, a growing body of evidence has established that brain plasticity extends beyond development and is an inherent feature of adult brain function, spanning multiple domains, from learning and memory to adaptability of primary sensory maps. Here we discuss evolution of the current view that plasticity of the adult brain derives from dynamic tuning of transcriptional control mechanisms at the neuronal level, in response to external and internal stimuli. We then review the identification of "plasticity genes" regulated by changes in the levels of electrical activity, and how elucidating their cellular functions has revealed the intimate role transcriptional regulation plays in fundamental aspects of synaptic transmission and circuit plasticity that occur in the brain on an every day basis.

The simultaneous treatment of MMP-2 stimulants in retinal transplantation enhances grafted cell migration into the host retina

The success of functional retinal cell transplantation has been limited by the low efficiency of the transplanted cell integration into the host retina. Given that the extracellular matrix (ECM) is thought to inhibit entry and axonal outgrowth of grafted neural cells into the host retina, modulation of the ECMs in the host environment may overcome this limitation. Here, we demonstrate that matrix metalloprotease-2 (MMP-2) expression is associated with the high migratory potential of adult rat hippocampus-derived neural stem cells compared with retinal progenitor cells. In addition, MMP-2, as well as its reported inducers concanavalin A and 17beta-estradiol, can trigger the migration of retinal progenitor cells into explanted retinas. Inhibitors of MMP-2 suppressed these effects. Intense cell migration is not required for photoreceptor transplantation; however, the environment that allows the transplanted cells to integrate is most important. Migration of the transplanted cells is a good index of the acceptance of grafted cell of the host tissue. Strategies modulating the environment by MMP-2 stimulation may provide an advance in the development of retinal transplantation.

Modulatory effects of dextran sulfate and fucoidan on binding and channel properties of AMPA receptors isolated from rat brain

Previous work showed that the glycosaminoglycan (GAG) dextran sulfate (500 kDa) altered the binding and channel properties of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors. The current study compared the effects of dextran sulfate with another GAG, fucoidan (100-180 kDa), to determine whether GAG-mediated changes in high-affinity binding of AMPA receptors have a concomitant influence on specific channel properties. Dextran sulfate was more potent in inhibiting high-affinity AMPA binding to solubilized receptors (EC(50) of 7 nM) compared to fucoidan (EC(50) of 124 nM). Similarly, dextran sulfate was more potent in modulating the channel properties of purified and reconstituted AMPA receptors. Dextran sulfate, at 1 mug/ml (2 nM), produced a three to fourfold increase in open channel probability and a threefold increase in mean burst duration of channel activity elicited by 283 nM AMPA. The mean open time was increased by two to threefold and closed times were decreased by two to eightfold. Fucoidan produced similar effects at a concentration many times higher than that of dextran sulfate. Dextran sulfate and fucoidan had no effect on the single channel conductance or the ability of a specific antagonist to block AMPA channels. The effects of GAGs on multichannel patches showed an interactive channel gating behavior resulting in macroscopic currents with long lived open channel life times. These findings suggest that GAG components of proteoglycans can interact with and alter the binding affinity of AMPA receptors and modulate their functional properties.

Sulfate- and size-dependent polysaccharide modulation of AMPA receptor properties

Previous work found evidence that alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-type glutamate receptors interact with and are functionally regulated by the glycosaminoglycan heparin. The present study tested whether dextran species affect ligand binding, channel kinetics, and calcium permeability of AMPA receptors. Dextran sulfate of 500 kDa markedly reduced high affinity [3H]AMPA binding in solubilized hippocampal membranes. In isolated receptors reconstituted in a lipid bilayer, the same dextran sulfate prolonged the lifetime of open states exhibited by AMPA-induced channel fluctuations. The large polysaccharide further changed the single channel kinetics by increasing the open channel probability five- to sixfold. Such modulation of channel activity corresponded with enhanced levels of calcium influx as shown in hippocampal neurons loaded with Fluo3AM dye. With an exposure time of <1 min, AMPA produced a dose-dependent increase in intracellular calcium that was blocked by 6-cyano-7-nitroquinoxaline-2,3-dione disodium (CNQX). Dextran sulfate, at the same concentration range that modified ligand binding (EC50 of 5-10 nM), enhanced the AMPA-induced calcium influx by as much as 60%. The enhanced influx was blocked by CNQX, although unchanged by the N-methyl-D-aspartate (NMDA) receptor antagonist AP5. Confocal microscopy showed that the increase in calcium occurred in neuronal cell bodies and their processes. Interestingly, smaller 5-8-kDa dextran sulfate and a non-sulfated dextran of 500 kDa had little or no effect on the binding, channel, and calcium permeability properties. Together, these findings suggest that synaptic polysaccharide species modulate hippocampal AMPA receptors in a sulfate- and size-dependent manner.

Cell surface glycoprotein PZR is a major mediator of concanavalin A-induced cell signaling

PZR is an immunoglobulin superfamily cell surface protein containing a pair of immunoreceptor tyrosine-based inhibitory motifs. As a glycoprotein, PZR displays a strong association with concanavalin A (ConA), a member of the plant lectin family. Treatment of several cell lines with ConA caused tyrosine phosphorylation of a major cellular protein. Immunoblotting and immunoprecipitation studies indicated that this protein corresponded to PZR. Tyrosine phosphorylation of PZR was accompanied by recruitment of SHP-2 and was inhibited by PP1, a selective inhibitor of the Src family tyrosine kinases. Furthermore, c-Src was constitutively associated with PZR and was activated upon treatment of cells with ConA. Moreover, tyrosine phosphorylation of PZR was markedly enhanced in v-Src-transformed NIH-3T3 cells and was predominant in Escherichia coli cells co-expressing c-Src. Expression of an intracellular domain-truncated form of PZR in HT-1080 cells affected cell morphology and had a dominant negative effect on ConA-induced tyrosine phosphorylation of PZR, activation of c-Src, and agglutination of the cells. Together, the data indicate that PZR is a major receptor of ConA and has an important role in cell signaling via c-Src. Considering the various biological activities of ConA, the study of PZR may have major therapeutic implications.

Role of neurotrophins and lectins in prevention of ototoxicity

Degeneration of hair cells (HC) and/or spiral ganglion neurons (SGN) is a major cause of hearing loss. Postnatal rat cochlear explant cultures are used to study the toxic actions of different classes of ototoxins and to identify molecules that can protect SGN and HC from ototoxic damage. Various ototoxins induce differential damage to HC and/or SGN. While gentamicin preferentially causes HC death, sodium salicylate selectively induces degeneration of SGN. In contrast, cisplatin results in destruction of both SGN and HC. Specific neurotrophins, including NT-4/5, BDNF, and NT-3, greatly protect SGN from all three types of ototoxins. In contrast, NGF and other growth factors have no effect. Of the 51 compounds examined, only concanavalin A (Con A), a lectin molecule, significantly protects HC from gentamicin. A dose-dependent study of Con A shows that maximal protection occurred at 100 nM. Further experiments indicates that preincubation of Con A with gentamicin does not form a complex, and coaddition of Con A and gentamicin to bacterial cultures, such as E. Coli cultures, does not interfere with the antibiotic activity of gentamicin. When the other 21 lectins are examined, Erythrina cristagalli lectin and Detura stramonium lectin also show activity similar to Con A. These findings may help elucidate the mechanisms of ototoxins and suggest that specific neurotrophins and lectins may be of therapeutic value in the prevention of ototoxin-induced hearing loss.

MLCK-A, an unconventional myosin light chain kinase from Dictyostelium, is activated by a cGMP-dependent pathway

Dictyostelium myosin II is activated by phosphorylation of its regulatory light chain by myosin light chain kinase A (MLCK-A), an unconventional MLCK that is not regulated by Ca2+/calmodulin. MLCK-A is activated by autophosphorylation of threonine-289 outside of the catalytic domain and by phosphorylation of threonine-166 in the activation loop by an unidentified kinase, but the signals controlling these phosphorylations are unknown. Treatment of cells with Con A results in quantitative phosphorylation of the regulatory light chain by MLCK-A, providing an opportunity to study MLCK-A's activation mechanism. MLCK-A does not alter its cellular location upon treatment of cells with Con A, nor does it localize to the myosin-rich caps that form after treatment. However, MLCK-A activity rapidly increases 2- to 13-fold when Dictyostelium cells are exposed to Con A. This activation can occur in the absence of MLCK-A autophosphorylation. cGMP is a promising candidate for an intracellular messenger mediating Con A-triggered MLCK-A activation, as addition of cGMP to fresh Dictyostelium lysates increases MLCK-A activity 3- to 12-fold. The specific activity of MLCK-A in cGMP-treated lysates is 210-fold higher than that of recombinant MLCK-A, which is fully autophosphorylated, but lacks threonine-166 phosphorylation. Purified MLCK-A is not directly activated by cGMP, indicating that additional cellular factors, perhaps a kinase that phosphorylates threonine-166, are involved.

Cross-linking of NCAM receptors on neurons induces programmed cell death

Programmed cell death has been implicated in the loss of neurons that occurs in many neurodegenerative diseases. This has led to an increased interest in the types of stimuli that can initiate neurons to undergo programmed cell death. Previously, we have shown that cross-linking of membrane receptors with the lectin concanavalin A can trigger programmed cell death in neurons [D.H. Cribbs, V.M. Kreng, A.J. Anderson, C.W. Cotman, Cross-linking of Concanavalin A receptors on cortical neurons induces programmed cell death, Neuroscience 75 (1996) 173-185]. Concanavalin A, however, binds to many surface glycoproteins and therefore, it is important to determine whether certain specific receptors can initiate the program. We found that surface immobilized anti-neural cell adhesion molecules (NCAM) monoclonal antibodies provide a good substrate for adhesion and neurite outgrowth for cortical neurons. However, neurons treated directly with soluble anti-NCAM monoclonal antibodies show significant cell death after 24 h and exhibit the morphological and biochemical features indicative of apoptosis, including membrane blebbing, cell shrinkage, condensation of nuclear chromatin and internucleosomal DNA cleavage.

Lectin-binding properties of oligodendrocyte lineage cells aid in defining functionally important surface proteins

Oligodendrocytes are the myelin-forming cells of the central nervous system. They develop from migratory and proliferative precursor cells, which differentiate to mature myelinating cells. As a first step toward investigating the expression of cell surface glycoproteins by oligodendrocyte lineage cells, we tested 14 different lectins for their binding to oligodendrocyte lineage cells. Peanut agglutinin (PNA) was the only lectin used that showed a differentiation stage-dependent binding to oligodendrocytes. PNA-binding molecules are specifically expressed by oligodendrocyte precursor cells, downregulated with differentiation, and reexpressed by mature oligodendrocytes. It was additionally observed that PNA stimulates the proliferation of oligodendrocyte precursor cells. PNA may therefore be a useful tool for isolating and characterizing important cell surface glycoproteins expressed by oligodendrocyte lineage cells.

Effects of L-trans-pyrrolidine-2,4-dicarboxylate, a glutamate uptake inhibitor, on NMDA receptor-mediated calcium influx and extracellular glutamate accumulation in cultured cerebellar granule neurons

Glutamate uptake inhibitor, L-trans-pyrrolidine-2,4-dicarboxylate (PDC, 20 muM) elevated basal and N-methyl-D-aspartate (NMDA, 100 muM)-induced extracellular glutamate accumulation, while it did not augment kainate (100 muM)-induced glutamate accumulation in cultured cerebellar granule neurons. However, pretreatment with PDC for 1 h significantly reduced NMDA-induced glutamate accumulation, but did not affect kainate-induced response. Pretreatment with glutamate (5 muM) for 1 h also reduced NMDA-induced glutamate accumulation, but did not kainate-induced response. Upon a brief application (3-10 min), PDC did neither induce elevation of intracellular calcium concentration ([Ca(2+)](i)) nor modulate NMDA-induced [Ca(2+)](i) elevation. Pretreatment with PDC for 1 h reduced NMDA-induced [Ca(2+)](i) elevation, but it did not reduce kainate-induced [Ca(2+)](i) elevation. These results suggest that glutamate concentration in synaptic clefts of neuronal cells is increased by prolonged exposure (1 h) of the cells to PDC, and the accumulated glutamate subsequently induces selective desensitization of NMDA receptor.

Cross-linking of concanavalin A receptors on cortical neurons induces programmed cell death

The loss of neurons by programmed cell death is a normal feature of the nervous system during development and has recently been implicated as a major mechanism of cell death in neurodegenerative diseases. In some cases, programmed cell death is induced by the activation of membrane receptors and is referred to as activation-induced programmed cell death. Activation-induced programmed cell death has been previously described in cells from the immune system, in which the activation of receptors by receptor clustering leads to programmed cell death. To determine whether activation-induced programmed cell death occurs in neurons, Concanavalin A was used to cross-link membrane receptors on cortical neurons. Concanavalin A-induced neuronal death was dose dependent and effective at concentrations previously shown to induce activation-induced programmed cell death in lymphocytes. Programmed cell death was attenuated when Concanavalin A-specific binding to neurons was blocked with methyl alpha-D-mannopyranoside. Succinyl Concanavalin A, which bound to Concanavalin A receptors but was ineffective at cross-linking them, did not induce programmed cell death. Concanavalin A-induced neuronal death exhibited many of the hallmarks associated with programmed cell death, such as membrane blebbing, nuclear condensation and margination, and internucleosomal DNA cleavage. In addition, neurons exposed to Concanavalin A displayed a rapid, robust, and persistent increase in the immediate early gene protein c-Jun. A similar increase in c-Jun precedes programmed cell death induced by beta-amyloid in neurons, and under some conditions an increase in c-Jun has been shown to be required for programmed cell death to occur in neurons. Increased expression of c-jun and other immediate early genes has also been correlated with activation-induced programmed cell death in lymphocytes. These observations suggest that Concanavalin A induces activation-induced programmed cell death in neurons via signals produced from the cross-linking of receptors on neuronal membranes. These results also raise the possibility that beta-amyloid induces programmed cell death in a similar manner, by causing the cross-linking of receptors on neuronal membranes. This mechanism may be relevant to neuronal programmed cell death that occurs during development and neurodegeneration.

Myosin light chain kinase (MLCK) gene disruption in Dictyostelium: a role for MLCK-A in cytokinesis and evidence for multiple MLCKs

We have created a strain of Dictyostelium that is deficient for the Ca2+/calmodulin-independent MLCK-A. This strain undergoes cytokinesis less efficiently than wild type, which results in an increased frequency of multinucleate cells when grown in suspension. The MLCK-A-cells are able, however, to undergo development and to cap crosslinked surface receptors, processes that require myosin heavy chain. Phosphorylated regulatory light chain (RLC) is still present in MLCK-A-cells, indicating that Dictyostelium has one or more additional protein kinases capable of phosphorylating RLC. Concanavalin A treatment was found to induce phosphorylation of essentially all of the RLC in wild-type cells, but RLC phosphorylation levels in MLCK-A-cells are unaffected by concanavalin A. Thus MLCK-A is regulated separately from the other MLCK(s) in the cell.

Ag, a novel protein secreted from Aplysia glia

We have isolated a cDNA (ag for Aplysia glial) corresponding to an mRNA specific to the nervous system of Aplysia californica. In this study, we characterized the ag cDNA sequence and the distribution of ag mRNA and protein in the Aplysia nervous system. The ag cDNA contains an open reading frame that encodes a novel 29 kD protein. In situ hybridizations demonstrate that ag mRNA is conspicuously absent from the cell bodies of the large neurons constituting the external layer of the ganglia. Instead, it is largely confined to a subset of small, apparently non-neuronal cells surrounding the neurons at the border of the neuropil, is sparsely scattered within the neuropil, and is widespread within the connective nerves, a pattern consistent with glial localization. Polyclonal anti-ag antiserum recognizes a protein between 27 and 29 kD that is more broadly distributed, especially within the neuropil. The distributions of ag mRNA and protein, together with the presence of a putative signal peptide, suggest that ag protein is secreted. Two findings support this hypothesis: first, ag protein is detectable by western blot in Aplysia hemolymph. Second, full length ag protein expressed in COS cells is secreted, but ag lacking the putative signal peptide is not. Secretion from glia raises the possibility that this abundant protein may affect neighboring neurons.

Loss of cortical serotonin2A signal transduction in senescent rats: reversal following inhibition of protein kinase C

Using grease gap recordings, age-related changes in serotonin2A receptors were assessed in sensorimotor regions of the cortex by examining serotonin-induced facilitation of the N-methyl-D-aspartate depolarization in cortical wedges prepared from young adult (3-6 months) and senescent (22-34 months) Fisher 344 rats. Serotonin (10-100 microM) facilitated the N-methyl-D-aspartate depolarization in wedges from young adult rats in a concentration-dependent manner, whereas no facilitation was observed in wedges from senescent rats. Similar results were obtained when +/- 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane, a mixed serotonin2A and serotonin2C receptor agonist, was substituted for serotonin. In contrast, agonists at alpha 1A-adrenoceptors, metabotropic glutamate receptors and muscarinic cholinoceptors facilitated the N-methyl-D-aspartate depolarization in wedges from both young adult and senescent rats. Chelerythrine and staurosporine, inhibitors of protein kinase C, but not concanavalin A, myo-inositol or calmodulin antagonists, restored the serotonin facilitation in wedges from senescent animals. In situ hybridization histochemistry revealed that serotonin2A receptor messenger RNA was present in layers II-VI of the cortex, with the highest density of silver grains located in layers III and V of both young adult and senescent rats. Detailed examination of layer V showed that silver grains were significantly higher than background only over pyramidal cells. We conclude that serotonin2A receptors are expressed by pyramidal cells in both young adult and senescent rats and that serotonin acts directly on these receptors to facilitate the N-methyl-D-aspartate depolarization. Moreover, in senescent rats, signal transduction at cortical serotonin2A receptors involved with facilitation of the N-methyl-D-aspartate response is compromised as a result of protein kinase C activation.

Concanavalin A reduces habituation in the tectum of the frog

In the tectum of Rana pipiens, responses to repeated flashes of light to the ipsilateral eye display considerable habituation. We have employed the plant lectin concanavalin A (Con A), which can diminish desensitization of glutamate receptors in vitro, in order to examine whether desensitization of glutamate receptors contributes to this habituation. The ipsilateral eye's projection reaches each tectal lobe indirectly, being relayed from the opposite tectal lobe via the tecto-isthmo-tectal projection. One of the sites along this pathway at which habituation may take place is the retinotectal synapse, where glutamate is a putative transmitter. Pretreatment of one lobe of the tectum with Con A significantly diminished the habituation of responses recorded in the other tectal lobe to light offset, with less of an effect on responses to light onset. These data suggest that OFF habituation may reflect glutamate receptor desensitization at the retinotectal synapse. In contrast, recordings from retinotectal terminals indicate that a primary site of habituation of ON responses is within the retina.

Regulation of bradykinin sensitivity in peripheral sensory fibres of the neonatal rat by nitric oxide and cyclic GMP

Bradykinin-induced activation of peripheral sensory fibres was studied using an in vitro preparation of the neonatal rat spinal cord with attached tail. Noxious heat stimulation, as well as the applications of bradykinin and capsaicin, to the tail evoked reproducible responses recorded as a depolarization of a lumbar ventral root. Prolonged administration of a supramaximal concentration of bradykinin invariably induced a complete but selective desensitization to a subsequent bradykinin challenge. Bradykinin-induced desensitization was significantly attenuated by concanavalin-A and the effect of concanavalin-A was prevented by alpha-methyl mannoside. Both cyclic GMP and sodium nitroprusside induced a long lasting reduction of bradykinin responsiveness in peripheral fibres. The effect of nitroprusside was prevented by concanavalin-A, and by methylene blue, an inhibitor of guanylyl cyclase. Methylene blue also reduced bradykinin-induced desensitization. L-arginine, but not D-arginine, induced a desensitization to bradykinin. On the other hand, 7-nitroindazole (7-NI, 200-500 nM), an inhibitor of NOS, reduced the desensitization of bradykinin responses but higher concentrations of 7-NI (IC50 = 6.7 +/- 0.9 microM) selectively attenuated responses to bradykinin. The effects of 7-NI were attenuated by L-arginine pretreatment. These data suggest that bradykinin-induced desensitization of peripheral sensory fibres is mediated in part via NO and cyclic GMP dependent mechanisms: possibly NO production is required for guanylate cyclase activation.

Studies on the dopamine-dependent modulation of amino acid-gated currents in cone horizontal cells of the perch (Perca fluviatilis)

The whole-cell patch-clamp technique was employed to record membrane currents from isolated horizontal cells in culture. Concentration-response relationships for currents induced by L-glutamate, kainate and quisqualate were measured. Preincubation with dopamine changed the parameters of the concentration-response curves in a particular way for each agonist. The maximum currents induced by glutamate increased by 50-100% and the EC50-values were slightly shifted to higher values. The increase of kainate-induced maximum currents after dopamine incubation did not exceed 30% but the EC50-values were clearly shifted to lower concentrations. Quisqualate-induced maximum currents were not enhanced by dopamine preincubation but the EC50-values were shifted to lower concentrations. The dopamine-dependent modulation was affected by removal of magnesium and preincubation with concanavalin A and aniracetam. The concentration-response relation and the time-course of the dopamine effect on glutamate-induced currents is described.

Multiple mechanisms of serotonin 5-HT2 receptor desensitization

Desensitization of serotonin 5-HT2 receptor-mediated enhancement of the N-methyl-D-aspartate (NMDA) depolarization was studied in rat cortical neurons. Serotonin and (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) induced long term desensitization. Staurosporine, a nonspecific protein kinase C inhibitor, potentiated the serotonin and DOI facilitation, suggesting acute desensitization was operative. In the case of DOI, long term desensitization was prevented by staurosporine. Activators of protein kinase C abolished the serotonin facilitation, an action prevented by staurosporine. Concanavalin A potentiated the facilitation at 100 microM, but not 30 microM serotonin, suggesting these receptors undergo dose dependent internalization. Calmodulin antagonists prevent long term desensitization induced by serotonin. The depolarization induced by NMDA alone was not altered by staurosporine, protein kinase C activators, concanavalin A or calmodulin antagonists. Serotonin at 100 microM, but not 30 microM, induced heterologous desensitization of phenylephrine and carbachol induced facilitation of the NMDA depolarization. We conclude that serotonin 5-HT2 receptors both induce and undergo several forms of desensitization.

Up-regulation of polysialic acid in peripheral myelinated axons of rat chronically exposed to 2,5-hexanedione

Myelinated nerve fibres isolated from Wistar rats chronically exposed to 2,5-hexanedione (0.8 ml/kg/day, intraperitoneally) over a period of 20 days, were stained with lectin-horseradish peroxidase conjugates. The lectins with high affinity for terminal D-galactopyranosyl residues, Bandeiraea simplicifolia-B4 (BSA I-B4) and peanut agglutinin (PNA), showed glycoconjugates in the control nodes of Ranvier. In the treated animals, application of PNA-HRP caused weak reactivity to the node of Ranvier; digestion with sialidase prior to the application of PNA-HRP conjugate enhanced reactivity, thus revealing the presence of a sialoglycoprotein. The results indicate that glycoconjugates of the Ranvier node undergo a rearrangement during exposure to 2,5-hexanedione. In particular, neutral glycoproteins with terminal galactose are replaced by sialoglycoproteins. These findings are consistent with the proposed role of polysialic acid as a regulator of axonal behaviour during regeneration.

Phosphorylation and modulation of a kainate receptor (GluR6) by cAMP-dependent protein kinase

Ligand-gated ion channels gated by glutamate constitute the major excitatory neurotransmitter system in the mammalian brain. The functional modulation of GluR6, a kainate-activated glutamate receptor, by adenosine 3',5'-monophosphate-dependent protein kinase A (PKA) was examined with receptors expressed in human embryonic kidney cells. Kainate-evoked currents underwent a rapid desensitization that was blocked by lectins. Kainate currents were potentiated by intracellular perfusion of PKA, and this potentiation was blocked by co-application of an inhibitory peptide. Site-directed mutagenesis was used to identify the site or sites of phosphorylation on GluR6. Although mutagenesis of two serine residues, Ser684 and Ser666, was required for complete abolition of the PKA-induced potentiation, Ser684 may be the preferred site of phosphorylation in native GluR6 receptor complexes. These results indicate that glutamate receptor function can be directly modulated by protein phosphorylation and suggest that a dynamic regulation of excitatory receptors could be associated with some forms of learning and memory in the mammalian brain.

Expression of naked plasmids by cultured myotubes and entry of plasmids into T tubules and caveolae of mammalian skeletal muscle

Plasmid DNA or artificial mRNA injected intramuscularly into skeletal muscle via a 27 g needle expressed transgenes at relatively efficient levels in skeletal myofibers and cardiac cells. In the present study, several approaches were used to determine the mechanism of cellular uptake. After exposure of naked plasmid DNA, primary rat muscle cells in vitro expressed transgenes to a much greater extent than other types of immortalized or primary cells. In vivo light microscope studies showed that intramuscularly injected plasmid DNA was distributed throughout the muscle and was able to diffuse through the extracellular matrix, cross the external lamina, and enter myofibers. Electron microscope studies showed that colloidal gold conjugated to plasmid DNA traversed the external lamina and entered T tubules and caveolae, while gold complexed with polylysine, polyethylene glycol or polyglutamate primarily remained outside of the myofibers. The results indicate that it is highly unlikely that the plasmid DNA enters the myofiber simply by the needle grossly disrupting the sarcolemma. In addition, transient membrane disruptions do not appear to be responsible for the uptake of DNA. Furthermore, no evidence for endocytosis could be found. The possible uptake of plasmid DNA by some type of cell membrane transporter, in particular via potocytosis, is discussed.

Directional control of neurite outgrowth from cultured hippocampal neurons is modulated by the lectin concanavalin A

Cell surface carbohydrates play an important role in the regulation of neurite outgrowth during neuronal development. We have investigated the actions of the plant lectin concanavalin A (Con A), a carbohydrate-binding protein, on neurite outgrowth from hippocampal pyramidal neurons in primary cell culture. Neurons plated in culture medium containing nanomolar concentrations of Con A have a larger number of primary neurites arising directly from the cell soma than do neurons plated in culture medium alone. Furthermore, Con A causes counterclockwise turning of neurites in over 70% of the cultured neurons. Both of these effects of Con A are blocked by the hapten sugar alpha-methyl-D-mannopyranoside, suggesting that they result from the interaction of Con A with a cell surface carbohydrate. Another lectin with a different sugar specificity, wheat germ agglutinin, does not modulate neurite outgrowth. Analysis of neurite outgrowth using video-enhanced microscopy reveals that the counterclockwise turning is accompanied by directionally biased extension of filopodia from the growth cones of growing neurites. Treatment of the neurons with cytochalasin, which disrupts actin polymerization, eliminates the neurite turning induced by Con A, suggesting that actin microfilaments are involved in directional control of neurite outgrowth.