Ganglioside inhibition of glutamate-mediated protein kinase C translocation in primary cultures of cerebellar neurons

Serotonin Signaling through Lipid Membranes

Serotonin (5-HT) is a vital modulatory neurotransmitter responsible for regulating most behaviors in the brain. An inefficient 5-HT synaptic function is often linked to various mental disorders. Primarily, membrane proteins controlling the expression and activity of 5-HT synthesis, storage, release, receptor activation, and inactivation are critical to 5-HT signaling in synaptic and extra-synaptic sites. Moreover, these signals represent information transmission across membranes. Although the lipid membrane environment is often viewed as fairly stable, emerging research suggests significant functional lipid-protein interactions with many synaptic 5-HT proteins. These protein-lipid interactions extend to almost all the primary lipid classes that form the plasma membrane. Collectively, these lipid classes and lipid-protein interactions affect 5-HT synaptic efficacy at the synapse. The highly dynamic lipid composition of synaptic membranes suggests that these lipids and their interactions with proteins may contribute to the plasticity of the 5-HT synapse. Therefore, this broader protein-lipid model of the 5-HT synapse necessitates a reconsideration of 5-HT's role in various associated mental disorders.

Protein kinase C gamma interneurons in the rat medullary dorsal horn: distribution and synaptic inputs to these neurons, and subcellular localization of the enzyme

The γ isoform of protein kinase C (PKCγ), which is concentrated in interneurons in the inner part of lamina II (IIi ) of the dorsal horn, has been implicated in the expression of tactile allodynia. Lamina IIi PKCγ interneurons were shown to be activated by tactile inputs and to participate in local circuits through which these inputs can reach lamina I, nociceptive output neurons. That such local circuits are gated by glycinergic inhibition and that A- and C-fibers low threshold mechanoreceptors (LTMRs) terminate in lamina IIi raise the general issue of synaptic inputs to lamina IIi PKCγ interneurons. Combining light and electron microscopic immunochemistry in the rat spinal trigeminal nucleus, we show that PKCγ-immunoreactivity is mostly restricted to interneurons in lamina IIi of the medullary dorsal horn, where they constitute 1/3 of total neurons. The majority of synapses on PKCγ-immunoreactive interneurons are asymmetric (likely excitatory). PKCγ-immunoreactive interneurons appear to receive exclusively myelinated primary afferents in type II synaptic glomeruli. Neither large dense core vesicle terminals nor type I synaptic glomeruli, assumed to be the endings of unmyelinated nociceptive terminals, were found on these interneurons. Moreover, there is no vesicular glutamate transporter 3-immunoreactive bouton, specific to C-LTMRs, on PKCγ-immunoreactive interneurons. PKCγ-immunoreactive interneurons contain GABAA ergic and glycinergic receptors. At the subcellular level, PKCγ-immunoreactivity is mostly concentrated on plasma membranes, close to, but not within, postsynaptic densities. That only myelinated primary afferents were found to contact PKCγ-immunoreactive interneurons suggests that myelinated, but not unmyelinated, LTMRs play a critical role in the expression of mechanical allodynia.

Protein kinase C-β mediates neuronal activation of Na(+)/H(+) exchanger-1 during glutamate excitotoxicity

Na(+)/H(+) exchanger-1 (NHE-1) activity is known to play a critical role in the neuronal injury caused by glutamate. However, the underlying mechanism is not clear. This study shows that NHE-1 activation and its phosphorylation during glutamate exposure were attenuated by the inhibition of protein kinase C (PKC)-βI and -βII, leading to reduced neuronal death. In addition, activations of PKC-βI and -βII by PKC-βI and -βII CAT plasmid or by PMA, PKC-β pharmacological activator have stimulated the activity and phosphorylation of NHE-1, which were abolished by inhibition of PKC-β in neuronal cells. Furthermore, the inhibition of PKC-β has mediated neuroprotective effect on glutamate-induced cells, which is similar to neuroprotective efficacy of siRNA NHE-1 transfection. Taken together, these results suggest that activation of the PKC-βI and -βII pathway by glutamate increases the activity and phosphorylation of NHE-1, and that these increases contribute to neuronal cell death. In this study, we demonstrate that PKC-βI and -βII are involved in the regulation of NHE-1 activation following glutamate exposure in neuron.

Retracted Article: A highly concise and practical route to clavaminols, sphinganine and (+)-spisulosine via indium mediated allylation of α-hydrazino aldehyde and a theoretical insight into the stereochemical aspects of the reaction

The stereoselective synthesis of 1,2-amino alcohols is reported by proline-catalyzed α-amination of aldehyde and one-pot indium mediated allylation of the crude α-hydrazino aldehydes.

Regulation of hippocampus-dependent memory by the zinc finger protein Zbtb20 in mature CA1 neurons

The mammalian hippocampus harbours neural circuitry that is crucial for associative learning and memory. The mechanisms that underlie the development and regulation of this complex circuitry are not fully understood. Our previous study established an essential role for the zinc finger protein Zbtb20 in the specification of CA1 field identity in the developing hippocampus. Here, we show that conditionally deleting Zbtb20 specifically in mature CA1 pyramidal neurons impaired hippocampus-dependent memory formation, without affecting hippocampal architecture or the survival, identity and basal excitatory synaptic activity of CA1 pyramidal neurons. We demonstrate that mature CA1-specific Zbtb20 knockout mice exhibited reductions in long-term potentiation (LTP) and NMDA receptor (NMDAR)-mediated excitatory post-synaptic currents. Furthermore, we show that activity-induced phosphorylation of ERK and CREB is impaired in the hippocampal CA1 of Zbtb20 mutant mice. Collectively, these results indicate that Zbtb20 in mature CA1 plays an important role in LTP and memory by regulating NMDAR activity, and activation of ERK and CREB.

β-N-oxalyl-L-α,β-diaminopropionic acid regulates mitogen-activated protein kinase signaling by down-regulation of phosphatidylethanolamine-binding protein 1

β-N-Oxalyl-L-α,β-diaminopropionic acid (l-ODAP) an α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor agonist activates protein kinase C in white leghorn chick brain. The current study focuses on the protein kinase C downstream signaling targets associated with L-ODAP excitotoxicity in SK-N-MC human neuroblastoma cells and white leghorn male chick (Gallus domesticus) brain extracts. L-ODAP treatment in SK-N-MC cells (1.5 mM) and chicks (0.5 mg/g body weight) results in a decreased expression and increased phosphorylation of phosphatidylehthanolamine-binding protein 1 (PEBP1) up to 4 h which however, returns to normal by 8 h. D-ODAP, the non-toxic enantiomer however, did not affect PEBP1 levels in either chick brain or SK-N-MC cells. Decreased PEBP1 expression correlated with subsequent activation of Raf-1, MEK and ERK signaling components of the mitogen-activated protein kinase cascade and nuclear translocation of hypoxia inducible factor-1α (HIF-1α) in chick brain nuclear extracts and SK-N-MC cells. SK-N-MC cells over-expressing PEBP1 inhibited nuclear translocation of HIF-1α when treated with l-ODAP, indicating that down-regulation of PEBP1 is responsible for HIF-1α stabilization and nuclear localization. Excitotoxicity of L-ODAP may thus be the result of phosphorylation and down-regulation of PEBP1, a crucial signaling protein regulating diverse signaling cascades. L-ODAP induced convulsions and seizures in chicks could be the result of a hypoxic insult to brain.

Cerebral protection of salvianolic acid A by the inhibition of granulocyte adherence

Ischemic stroke is one of the most common causes of death and disability that is induced by ischemia reperfusion (IR). Granulocyte adherence has been proven to be a principal cause of IR. Salvianolic acid A (Sal A) is one of the major active components of Danshen, a Chinese herbal medicine used for the treatment of cardiovascular and cerebrovascular diseases, such as ischemic stroke. Some experimental studies have shown the strong cerebral protection effect of Sal A. However, little information is available about the effect of Sal A on granulocyte adherence to brain micro-vascular endothelial cells (BMEC). Therefore, the aim of the present study was to investigate the effect of Sal A on the leukocyte adhesion rate and the intercellular cell adhesion molecule-1 (ICAM-1) expression in BMEC injured by hypoxia/reoxygenation (H/R), using a rheometer, qRT-PCR, and flow cytometry (FCM). The results of the adhesion rate gathered by the rheometer showed that Sal A could remarkably inhibit the adherence of granulocytes on BMEC in the case of H/R injury. Moreover, PCR and FCM results showed that Sal A could decrease the expression of ICAM-1 on BMEC on the gene and protein levels. In conclusion, the study demonstrated that the inhibition of granulocyte adherence is one of the targets of Sal A in the treatment of ischemic stroke. Meanwhile, Sal A inhibits of granulocyte adherence by decreasing the expression of ICAM-1 in BMEC.

High-yielding synthesis of sphingoid-type bases

An efficient methodology for the synthesis of sphingoid-type bases is reported. It involves the stereoselective addition of a racemic 3-alkoxy allenylzinc to enantiopure N-tert-butylsulfinyl imines and a cross-metathesis reaction as the key steps. It has been successfully applied to the syntheses of sphinganine and naturally occurring bioactive related compounds, among which the hydrolysis product of clavaminol H and two spisulosines. All of these compounds have been prepared in six steps from N-tert-butylsulfinyl imines in high overall yields (>56%).

Ceramide signaling in cancer and stem cells

Most of the previous work on the sphingolipid ceramide has been devoted to its function as an apoptosis inducer. Recent studies, however, have shown that in stem cells, ceramide has additional nonapoptotic functions. In this article, ceramide signaling will be reviewed in light of 'systems interface biology': as an interconnection of sphingolipid metabolism, membrane biophysics and cell signaling. The focus will be on the metabolic interconversion of ceramide and sphingomyelin or sphingosine-1-phosphate. Lipid rafts and sphingolipid-induced protein scaffolds will be discussed as a membrane interface for lipid-controlled cell signaling. Ceramide/sphingomyelin and ceramide/sphingosine-1-phosphate-interdependent cell-signaling pathways are significant for the regulation of cell polarity, apoptosis and/or proliferation, and as novel pharmacologic targets in cancer and stem cells.

TPO-independent megakaryocytopoiesis

Megakaryocytopoiesis is a continuous developmental process of platelet production. In this process, a complex network of hemopoietic growth factors are involved, among which TPO (thrombopoietin) is the most thoroughly investigated regulator of MKs (megakaryocytes). In addition to TPO, other regulators also have non-negligible effects on megakaryocytopoiesis. The majority of their effects are independent of TPO signaling. To date, TPO-independent megakaryocytopoiesis forms a regulatory system that includes four signals and (an) unknown signaling pathway(s). These four pathways are the gp 130 (glycoprotein 130)-dependent signaling pathway, the Notch pathway, NMDA (N-methyl-d-aspartate) receptor-mediated signaling, and the SDF-1 (stromal cell-derived factor-1)/FGF-4 (fibroblast growth factor-4) paradigm. Understanding of the TPO-independent regulatory system is important because the system may offer additional opportunities to understand the developmental process and the mechanisms of disorders characterized by abnormal MK and platelet production, such as thrombocytopenia and thrombocythemia, and to advance the development of therapeutics.

TCDD alters PKC signaling pathways in developing neuronal cells in culture

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is known to induce neurodevelopmental deficits such as poor cognitive development and motor dysfunction. However, the mechanism of TCDD-mediated neurotoxicity remains unclear. Since PKC signaling is one of the most pivotal events involved in neuronal function and development, we analyzed the effects of TCDD on the PKC signaling pathway in cerebellar granule cells derived from PND-7 rat brain. Immunoblot analysis revealed the presence of PKC-alpha, betaII, delta, epsilon, lambda and iota in both cytosol and membrane fractions of cerebellar granule cells, but PKC-gamma was below the detectable level. TCDD induced a significant translocation of PKC-alpha, -betaII and -epsilon from cytosol to membrane fraction (p<0.05) and a marginal translocation of PKC-delta at high dose only (p<0.1). It also increased RACK-1, an adaptor protein for PKC, in a dose-dependent manner. Exposure to TCDD induced a dose-dependent increase of both [3H] PDBu binding and the intracellular calcium level. The results suggest that the selective PKC isozymes and RACK-1 are involved in TCDD-mediated signaling pathway and these proteins may be possible molecular targets in neuronal cells for TCDD exposure. Our study provides basic data to understand mechanism of TCDD-induced neurotoxicity with respect to PKC signaling pathway and a scientific basis for improving the health risk assessment of neurotoxicants by identifying intracellular target molecules in neuronal cells.

Changes in the composition of detergent-resistant membrane domains of cultured neurons following protein kinase C activation

Changes in the composition of cell fractions, and in particular of detergent-resistant membranes (DRM) isolated from cultured rat cerebellar granule cells, were taken as possible changes in lipid raft composition during a signal transduction event. After activation of protein kinase C (PKC) with phorbol esters (PMA) or glutamate, the content of PKC and of proteins highly enriched (GAP43, Fyn, and PrP(c)) or not (MARCKS) in DRM was followed. PKC activation strongly increased its association with membranes (from 2% to 75%), causing its enrichment within DRM; the substrate GAP43, enriched in DRM, remained membrane associated, but its proportion in DRM dramatically decreased (from about 40% to 2.5%), suggesting its shift from raft to nonraft membranes, possibly as a consequence of phosphorylation by PKC. The distribution of Fyn and PrP(c) (DRM-enriched) and of MARCKS (present mainly outside DRM) did not change. PKC activation was followed by an increase of GAP43 and MARCKS phosphorylation (about 7- and 8-fold, respectively). Noteworthy was that, after cell treatment with the lipid raft-disrupting drug methyl-beta-cyclodextrin, PKC activation occurred normally, followed by MARCKS phosphorylation, but GAP43 phosphorylation did not occur. Taken altogether, these data suggest that the integrity of lipid rafts is necessary for PKC to affect GAP43 and catalyze its phosphorylation.

Interaction of endogenous ligands mediating antinociception

It is well known that a multitude of transmitters and receptors are involved in the nociceptive system, some of them increasing and others inhibiting the pain sensation both peripherally and centrally. These substances, which include neurotransmitters, hormones, etc., can modify the activity of nerves involved in the pain pathways. Furthermore, the organism itself can express very effective antinociception under different circumstances (e.g. stress), and, during such situations, the levels of various endogenous ligands change. A very exciting field of pain research relates to the roles of endogenous ligands. Most of them have been suggested to influence pain transmission, but only a few studies have been performed on the interactions of different endogenous ligands. This review focuses on the results of antinociceptive interactions after the co-administration of endogenous ligands. The data based on 55 situations reveal that the interactions between the endogenous ligands are very different, depending on the substances, the pain tests, the species of animals and the route of administrations. It is also revealed that only a few of the possible interactions between endogenous ligands have been investigated to date, in spite of the fact that the type of antinociceptive interaction between different endogenous ligands could hardly be predicted. The results indicate that the combination of endogenous ligands should not be omitted from the pain therapy arsenal. Attention will hopefully be drawn to the complex interdependence of endogenous ligands and their potential use in clinical practice.

Semisynthetic sphingoglycolipid LIGA20 is neuroprotective against human immunodeficiency virus-gp120-mediated apoptosis

Apoptosis and neuronal atrophy are commonly seen in patients infected with the human immunodeficiency virus type 1 (HIV-1) in the late phase of infection. The HIV-1 envelope glycoprotein gp120 has been suggested to be a causal agent of neuronal loss. Therefore, blocking gp120 neurotoxicity may be an effective way to reduce the neuronal degeneration seen in HIV patients. Brain-derived neurotrophic factor (BDNF) prevents gp120-mediated apoptosis in cerebellar granule cells. However, BDNF poorly crosses the blood-brain barrier and therefore may not be a suitable therapy for HIV patients. LIGA20 is a semisynthetic sphingoglycolipid that may be a valid alternative to BDNF. In fact, it has been shown that LIGA20 mimics the neuroprotective properties of BDNF. The present study was undertaken to characterize the relative potency of LIGA20 to antagonize gp120-mediated apoptosis. Cerebellar granule cells were exposed to gp120IIIB (5 nM) or stromal-cell derived factor-1 (SDF), the natural ligand for the CXCR4 receptor to which gp120 binds, alone or in combination with LIGA20 (5 microM), and cell death/survival was determined 12 and 24 hr later by various markers of apoptosis. LIGA20 blocked the neurotoxic effect of gp120 and SDF. The neurotrophic effect of LIGA20 was reversed by K252a, a tyrosine kinase inhibitor used to block TrkB signaling, suggesting the involvement of TrkB activation. These findings provide the rationale for exploring the ability of compounds that mimic BDNF activity to reduce neuronal cell death in HIV-1-positive patients.

Enhanced susceptibility to kainate-induced seizures, neuronal apoptosis, and death in mice lacking gangliotetraose gangliosides: protection with LIGA 20, a membrane-permeant analog of GM1

Knock-out (KO) mice lacking gangliotetraose gangliosides attributable to disruption of the gene for GM2/GD2 synthase [GalNAcT (UDP-N-acetylgalactosamine:GM3/GD3 beta-1,4-N-acetylgalactosaminyltransferase; EC 2.4.1.92 [EC])] are revealing key neural functions for the complex gangliosides of brain. This study has found such animals to be highly susceptible to kainic acid (KA)-induced seizures in terms of both seizure severity and duration. Intraperitoneal injection of 25 mg/kg KA produced status epilepticus for approximately 200 min in normal mice or heterozygotes and more than four times longer in the KO mice. The latter group suffered approximately 30% mortality, which increased to approximately 75% at dosage of 30 mg/kg KA, compared with 10-14% for the other two genotypes at the latter dosage. Nissl staining and terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling assay revealed substantial deterioration of pyramidal neurons attributable to apoptosis in the KO hippocampus, especially the CA3 region. Seizure activity in the KO mouse was only moderately diminished by intraperitoneal injection of GM1 ganglioside, whereas LIGA 20, a semisynthetic analog of GM1, substantially reduced both seizure severity and cell damage. The potency of LIGA 20 was correlated with its enhanced membrane permeability (compared with GM1), as seen in the increased uptake of [3H]LIGA 20 into the subcellular fractions of brain including cell nuclei. The latter finding is consonant with LIGA 20-induced restoration of the Na+/Ca2+ exchanger located at the inner membrane of the nuclear envelope in KO mice, an exchanger dependent on tight association with GM1 or its analog for optimal activity. These results point to a neuroprotective role for GM1 and its associated exchanger in the nucleus, based on regulation of Ca2+ flux between nucleoplasm and nuclear envelope.

D-amino acids in the central nervous system in health and disease

Recent evidence has shown that d-amino acids are present in animals and humans in high concentrations and fulfill specific biological functions. In the central nervous system, two d-amino acids, d-serine and d-aspartate, occur in considerable concentrations. d-Serine is synthesized and metabolized endogenously and the same might account for d-aspartate. d-Serine has been studied most extensively and was shown to play a role in excitatory amino acid metabolism, being a co-agonist of the N-methyl-d-aspartate (NMDA) receptor. Insight into d-serine metabolism is relevant for physiological NMDA receptor (NMDAr) activation and for all the disorders associated with an altered function of the NMDAr, such as schizophrenia, ischemia, epilepsy, and neurodegenerative disorders. d-Aspartate appears to play a role in development and endocrine function, but the precise function of d-aspartate and other d-amino acids in animals and humans requires further investigation. As d-amino acids play biological roles, alterations in the concentrations of d-amino acids might occur in some disorders and relate to the pathogenesis of these disorders. d-Amino acid concentrations may then not only help in the diagnostic process, but also provide novel therapeutic targets. Consequently, the presence and important roles of d-amino acids in higher organisms do not only challenge former theories on mammalian physiology, but also contribute to exciting new insights in human disease.

In vitro activation of protein kinase C by beta-N-oxalyl-L-alpha,beta-diaminopropionic acid, the Lathyrus sativus neurotoxin

Beta-N-oxalyl-L-alpha,beta-diaminopropionic acid (L-ODAP) toxicity has been associated with lathyrism; a spastic paraparesis caused by excessive dietary intake of the pulse Lathyrus sativus. We investigated the effect of Lathyrus neurotoxin L-ODAP on protein kinase C (PKC) activity under in vitro conditions. L-ODAP activated phosphorylation activity of purified chick brain PKC. Both lysine-rich (histone III-S) and arginine-rich (protamine sulfate) substrate phosphorylation was enhanced in the presence of L-ODAP. The activation is concentration dependent, and maximal activation is observed at 100 microM concentration. Protamine sulfate phosphorylation was enhanced by 47%, whereas histone III-S phosphorylation was enhanced by 50% over PS/PDBu/Ca2+ dependent activity. The nontoxic D-isomer (D-ODAP) did not affect both histone III-S and protamine sulfate phosphorylation activity. These results indicate that L-ODAP taken up by neuronal cells could also contribute to PKC activation and so be associated with toxicity.

Ganglioside GT1B and melatonin inhibit brain mitochondrial DNA damage and seizures induced by kainic acid in mice

The effects of ganglioside GT1b or melatonin on damage to brain mitochondrial DNA (mtDNA) and seizures induced by kainic acid were investigated both in vivo and in vitro. An intraperitoneal (i.p.) injection of kainic acid (45 mg/kg) produced broad-spectrum limbic and severe sustained seizures in all of the treated mice. These seizures were completely abolished by an intracerebroventricular (i.c.v.) injection of ganglioside GT1b (90 nmol/brain), a potent inhibitor of glutamate receptor mediated activation and translocation of protein kinase C and lipid peroxidation, or an i.p. injection of melatonin (20 mg/kg), a potent scavenger of hydroxyl radicals (*OH). The administration of kainic acid caused damage to mtDNA in brain frontal and central portion of cortex in mice. The damage to mtDNA was abolished by pre-injection of ganglioside GT1b (90 nmol/brain, i.c.v.) or melatonin (20 mg/kg, i.p.). In vitro exposure of kainic acid (0.25, 0.5 or 1.0 mM) inflicted damage to mtDNA in a concentration-dependent manner. The damage to mtDNA induced by 1.0 mM kainic acid was attenuated by the co-treatment with 60 microM ganglioside GT1b or 1.5 mM melatonin. Furthermore, kainic acid (0.5 or 1.0 mM) increased lipid peroxidation in a concentration-dependent manner when incubated with a homogenate prepared from mice brain at 37 degrees C for 20 or 60 min. However, the increased lipid peroxidation was completely abolished by the co-treatment with ganglioside GT1b (60 microM) or melatonin (1.5 mM). These results suggest that reactive oxygen species including hydroxyl radical (*OH) may play a role in the damage to brain mtDNA and seizures induced by kainic acid. We conclude that the preventive effect of melatonin or ganglioside GT1b against kainic acid-induced mtDNA damage or seizures may be due to its scavenging of reactive oxygen species including the *OH.

D-2-amino-5-phosphonopentanoic acid inhibits intrathecal pertussis toxin-induced thermal hyperalgesia and protein kinase Cgamma up-regulation

The aim of the present study was to examine the effect of intrathecal (i.t.) injection of pertussis toxin (PTX) on the nociceptive threshold and protein kinase C (PKC) expression in the rat spinal cord. The role of N-methyl-D-aspartic acid (NMDA) receptors in these changes was also examined. Male Wistar rats were implanted with two i.t. catheters, one of which was connected to a mini-osmotic pump and used to infuse saline or D-2-amino-5-phosphonopentanoic acid (D-AP5) (2 microg/h) starting on day 3 after i.t. catheter insertion. Two days later, a single injection of saline or PTX (2 microg) was given via the other catheter, followed by a flush with 10 microl of saline. On day 4 after PTX or saline injection, the thermal paw withdrawal latency was measured, then the rats were sacrificed by decapitation, and the dorsal part of the lumbosacral spinal segments was removed for PKC Western blotting assays. In PTX-treated rats, thermal hyperalgesia was observed, and the PKCgamma content of both the synaptosomal membrane and cytosolic fractions was significantly increased. The levels of alpha-, betaI-, or betaII-PKC isozymes in these fractions were unaffected by PTX treatment. Infusion of the NMDA antagonist, D-AP5, prevented both the thermal hyperalgesia and the increase in PKCgamma isoform expression in PTX-treated rats, and had no effect on these values in nai;ve rats. Intrathecal injection of the PKC inhibitor, chelerythrine (10 microg), significantly inhibited the thermal hyperalgesia observed in PTX-treated rats. These results show that i.t. injection of PTX induced thermal hyperalgesia accompanied by a selective increase in PKCgamma expression in both the synaptosomal membrane and cytosolic fractions of the dorsal horn of the rat lumbar spinal cord, and both effects were inhibited by the NMDA receptor antagonist, D-AP5.

Gangliosides activate Trk receptors by inducing the release of neurotrophins

We used NIH-3T3 fibroblasts expressing the different Trk receptors to examine whether GM1 ganglioside and its semisynthetic derivative LIGA20 activate various neurotrophin receptors. GM1 induced autophosphorylation of TrkC more potently than TrkA or TrkB receptors. In contrast, LIGA20 activated TrkB tyrosine phosphorylation only. Therefore, Scatchard analysis was performed to determine whether GM1 binds to TrkC. GM1 failed to displace neurotrophin-3 binding, suggesting that this ganglioside does not act as a ligand for Trk receptors. In addition, GM1 failed to induce autophosphorylation of a chimeric receptor consisting of the extracellular domain of the tumor necrosis factor receptor and the intracellular domain of TrkA, suggesting that GM1 does not affect the tyrosine kinase domain. We next determined whether GM1 induces the release of neurotrophins from fibroblast cells. GM1 induced a rapid and significant increase in the amount of neurotrophin-3, but not other neurotrophins. This effect was independent of the presence of Trk because K252a did not prevent GM1-mediated release of neurotrophin-3. Moreover, GM1-mediated TrkC autophosphorylation was blocked by TrkC-IgG (but not TrkB-IgG) receptor bodies, further suggesting that GM1 activates TrkC by inducing the release of neurotrophin-3. This hypothesis was also tested in cultured cerebellar granule cells. GM1 induced neurotrophin-3 (but not brain-derived neurotrophic factor or nerve growth factor) release. In contrast, LIGA20 increased the secretion of brain-derived neurotrophic factor. Our data show that gangliosides may activate different Trk receptors by differentially affecting the release of neurotrophins.

Modulation of VIP-Stimulated cAMP Formation by Excitatory Amino Acids in Mouse Cerebral Cortex

We have investigated the modulatory action of excitatory amino acids (EAA) on vasoactive intestinal polypeptide (VIP)-stimulated cAMP formation in mouse cerebral cortical slices. Glutamate and aspartate potentiate in a concentration-dependent manner the effect of VIP. In order to characterize the type of receptor involved, we have used three prototypical EAA receptor agonists, that is, kainate, N-methyl-d-aspartate (NMDA) and quisqualate. Kainate mimicked the effect of glutamate, NMDA was inactive and quisqualate displayed an inhibitory action. Furthermore, ibotenate also potentiated the effect of VIP on cAMP formation, while l-homocysteate exhibited an inhibitory action. Ibotenate was 4-fold more potent and 2.5 times more effective than glutamate. However, the effects of kainate and ibotenate were not additive, suggesting the activation of a common receptor. Thus, based on this metabotropic action, EAA can be categorized into the following classes: (i) those that potentiate the effect of VIP, such as glutamate, aspartate, kainate and ibotenate; (ii) those that inhibit the effect of VIP, such as l-homocysteate and quisqualate; and (iii) those that are ineffective, such as NMDA and d-homocysteate. The effects of glutamate or ibotenate on VIP-stimulated cAMP formation were completely inhibited by l-phosphoserine and only partially by kynurenate. In a low chloride medium, or in the presence of 8-(N,N-diethylamino) octyl-3,4,5-trimethoxybenzoate-hydrochloride (TMB-8), an inhibitor of calcium release from internal stores, EAA did not potentiate the effect of VIP, thus stressing the importance of these ions for the transduction of the glutamatergic signal. Our results indicate the existence of marked interactions between EAA and VIP on cAMP formation; the pharmacology of these interactions is, however, clearly distinct from the classical pharmacology of EAA which is mainly based on electrophysiological and binding studies.

A Nitric Oxide Synthase Activity Selectively Stimulated by NMDA Receptors Depends on Protein Kinase C Activation in Mouse Striatal Neurons

In mouse striatal neurons in primary culture, the maximal increase in intracellular cyclic guanosine monophosphate level evoked by N-methyl-d-aspartic acid (NMDA) receptor activation was twice that induced by kainate, KCl and ionomycin. Quisqualate was almost inactive. All responses were mediated by nitric oxide (NO) production since they were blocked by haemoglobin (a NO scavenger) and by l-NG-monomethylarginine and l-NG-nitroarginine, the effects of both arginine analogues being reversed by an excess of l-arginine. Several results indicate that NMDA receptors stimulate a specific NO synthase activity. This specifically NMDA-activated NO synthase was blocked by nanomolar concentrations of l-NG-nitroarginine, whereas the responses evoked by other agents, including kainate, KCl and ionomycin, were only blocked by micromolar concentrations of this NO synthase inhibitor. The NMDA response could not be totally reproduced by an increase in cytosolic calcium (Ca2+) alone. In contrast, in the presence of staurosporine, an inhibitor of protein kinases C (PKC), as well as after desensitization of PKC induced by long-term treatment with the phorbol ester, phorbol-12, 13-dibutyrate, NMDA-stimulated NO production was selectively reduced, reaching the level evoked by kainate or Ca2+ increase. In conclusion, our results suggest that in striatal neurons, NMDA selectively stimulates a NO synthase activity which is inhibited by low concentrations of l-NG-nitro-arginine, through a mechanism involving PKC.

Developmental changes in the protein composition of sphingolipid- and cholesterol-enriched membrane domains of rat cerebellar granule cells

The biological role of cell membrane domains has been investigated in a number of eukariotic cells, but less attention has been paid to the neuron. In the present investigation, we assessed the changes in lipid and protein composition of detergent-resistant membrane fractions prepared from cultured rat cerebellar granule cells, during differentiation and maturation in vitro. At any stage of the cell life, low-density, detergent-resistant fractions, characterised by the specific presence of prion protein, were enriched in glycolipids, cholesterol, and sphingomyelin. The enrichment in sphingomyelin was developmentally regulated, increasing continuously during cell differentiation and maturation. Concerning proteins, domains were enriched in Fyn and TAG-1, which present exclusively within this fraction at any stage of cell culture, and in GAP-43, mainly during the differentiation stage. On the other side, proteins affecting signal transduction and cytoskeleton-related proteins (heterotrimeric G-proteins, protein kinase C, MARCKS, tubulin), were not enriched within detergent-resistant fractions during cell differentiation, but were recovered within this fraction in mature neurons. These results indicate that during different cellular life stages, specific proteins are recruited within detergent-resistant membrane domains of the neuron and suggest their involvement in specific physiological phenomena (differentiation, maturation and/or aging).

Parathyroid hormone effects on signaling pathways in endothelial cells vary with peptide concentration

We have previously reported that parathyroid hormone (PTH) has specific effects on a human umbilical vein endothelial cell line. Further studies were performed to characterize the signaling cascades initiated by PTH. We report that PTH induced the appearance of voltage sensitive calcium channels. Furthermore, PTH increased ceramide but not diacylglycerol content. Since elevations in [Ca(2+)](i) and phospholipid turnover are signals for the activation of protein kinase C (PKC), the cells were screened for PKC isoforms. PTH induced a redistribution of the PKCepsilon to the particulate fractions of cell homogenates. In summary, PTH induced PKC translocation through a calcium-phospholipid pathway in an endothelial cell line.

Reduced hyperalgesia induced by nerve injury, but not by inflammation in mice lacking protein kinase C gamma isoform

Protein kinase C is one of protein kinases which might be involved in the nerve injury- or inflammation-induced hyperalgesia. The present study was designed to investigate the hyperalgesia with thermal paw-withdrawal test induced by sciatic nerve ligation or by intraplantar injection of a complete Freund's adjuvant solution in protein kinase C gamma knockout and its wild-type mice. Either sciatic nerve ligation or intraplantar injection of a complete Freund's adjuvant caused a marked decrease of the paw-withdrawal latency only on the ipsilateral, but not on the contralateral side of the paw in wild-type mice. This ipsilateral hyperalgesia induced by sciatic nerve ligation was significantly attenuated in protein kinase C gamma knockout mice. On the other hand, the ipsilateral hyperalgesia induced by complete Freund's adjuvant remained about the same in protein kinase C gamma knockout mice as in wild-type mice. The results indicate that protein kinase C gamma is involved in the development of the thermal hyperalgesia induced by nerve ligation, but not by complete Freund's adjuvant-induced inflammation.

Differential effects of NMDA and group I mGluR antagonists on both nociception and spinal cord protein kinase C translocation in the formalin test and a model of neuropathic pain in rats

Coincident with nociception, both noxious chemical stimulation of the hind paw and chronic constriction injury (CCI) of the sciatic nerve produce an increase in protein kinase C (PKC) translocation in the spinal cord of rats. Noxious stimulus-induced PKC translocation likely depends on glutamate activity at either N-methyl-D-aspartate (NMDA) receptors or group I metabotropic glutamate receptors (mGluR1/5) in the spinal cord dorsal horn. This study compares nociceptive responses to, and the alterations in membrane-associated PKC, induced by noxious chemical stimulation of the hindpaw and CCI of the sciatic nerve, as well as their modulation by both NMDA and mGluR1/5 receptor antagonists. Three groups of rats were given a single intrathecal (i.t.) injection of either vehicle, dizocilpine maleate (MK-801, 60 nmol), an NMDA receptor antagonist, or (S)-4-carboxyphenylglycine (S)-4CPG, (150 nmol), an mGluR1/5 antagonist, 10 min prior to a 50 microl of 2.5% formalin injection into the ventral surface of one hind paw. Another three groups of rats were given twice daily injections of either vehicle, MK-801 (30 nmol) or (S)-4CPG (90 nmol) i.t. for 5 days starting 30 min before CCI or sham injury of the sciatic nerve. Nociceptive responses were assessed for a 60 min period after the formalin injection in the first three groups, and tests of mechanical and cold allodynia were performed on days 4, 8, 12 and 16 after CCI for the latter three groups. Furthermore, changes in the levels of membrane-associated PKC, as assayed by quantitative autoradiography of the specific binding of [3H]-phorbol 12,13-dibutyrate ([3H]-PDBu) in the dorsal horn of the lumbar spinal cord sections, were assessed in formalin-injected rats (at 5, 25 and 60 min) and in neuropathic rats 5 days after CCI, treated (as above) with vehicle, MK-801 or (S)-4CPG. The results indicate that i.t. treatment with MK-801 significantly reduced nociceptive scores in the formalin test and also produced a significant suppression of formalin-induced increases in [3H]-PDBu binding in laminae I-II, III-VI and X of the lumbar spinal cord. In contrast, i.t. treatment with (S)-4CPG failed to significantly affect either nociceptive behaviours in the formalin test or formalin-induced increases in [3H]-PDBu binding in laminae I-II and III-VI of the lumbar spinal cord. On the other hand, i.t. treatment with either MK-801 or (S)-4CPG produced a significant reduction in mechanical and cold hypersensitivity, as well as [3H]-PDBu binding in laminae I-II and III-VI of the lumbar spinal cord, after CCI. These results suggest that while NMDA, but not mGluR1/5, receptors are involved in translocation of PKC and nociception in a model of persistent acute pain, both types of receptors influence the translocation of PKC in dorsal horn and mechanical and cold allodynia in a model of chronic neuropathic pain.

Therapeutic potential of PKC inhibitors in painful diabetic neuropathy

Diabetic neuropathy accompanied by anomalies in pain perception is one of the most frequent complications in insulin-dependent diabetes in humans. Many clinical and experimental studies have suggested that diabetes or hyperglycaemia alters pain sensitivity. In humans, diabetic neuropathy can be associated with burning, tactile hypersensitivity. Behavioural reactions of hyperalgesia in animal models of diabetes have been described. However, the aetiology of these disturbances is still unknown, although metabolic factors such as hyperglycaemia or neurotransmitter alteration may be involved. Activation of protein kinase C (PKC) has been implicated in changes in pain perception. Phorbol esters, which activate PKC, enhance the thermal hyperalgesia in diabetic mice and enhance nociceptive responses after tissue injury induced by formalin. Electrophysiological experiments have shown that activation of PKC leads to long-lasting enhancement of excitatory amino acid-mediated currents in dorsal horn neurones and trigeminal neurones. Thus, activation of PKC may underlie the neuronal sensitisation that produces hyperalgesia in diabetic neuropathy.

Hyperalgesia induced by peripheral inflammation is mediated by protein kinase C betaII isozyme in the rat spinal cord

We have addressed the molecular mechanism(s) of hyperalgesia, which depends on increased excitability of dorsal horn neurons and on sensitization of primary afferent nociceptors, during peripheral inflammation. Following unilateral adjuvant-induced inflammation in the rat hind paw, time-course changes in behavioral hyperalgesia and functional activities of Ca2+/phospholipid-dependent protein kinase C isozymes were examined. Inflammation was characterized by increase in paw diameter, and behavioral hyperalgesia was quantified as paw withdrawal latency from a radiant heat source. Behavioral hyperalgesia on the injected paw was significantly increased. This was accompanied by a significant increase in total functional membrane-associated protein kinase C activity, whereas total cytosolic protein kinase C activity was unchanged on the sides of the lumbar spinal cord both contralateral and ipsilateral to the inflammation. Importantly, on the side of lumbar cord ipsilateral to the inflamed paw, the activity of membrane-associated protein kinase CbetaII was increased following the same time-course as the paw withdrawal latency decrease, suggesting an increased translocation of protein kinase Cbetall to the membrane related to behavioral hyperalgesia. A defined mixture of purified gangliosides, which inhibits intracellular protein kinase C translocation and activation, decreased inflammation-induced paw withdrawal latency, and specifically decreased the activity of membrane-associated protein kinase Cbetall on the side of the spinal cord ipsilateral to the inflammation. Quantitative immunohistochemical analyses demonstrated intensified protein kinase CbetaII-like immunoreactivity on the side of the spinal cord ipsilateral to the inflammation. Time-course for increases in the activity of membrane-associated protein kinase CbetaII, and in intensity of protein kinase CbetaII-immunoreactivity, paralleled inflammation-mediated changes in paw withdrawal latency and paw diameter. Our findings indicate an apparent involvement of protein kinase CbetaII isozyme specifically in the molecular mechanism(s) of thermal hyperalgesia.

The role of spinal cholecystokinin B receptors in thermal allodynia and hyperalgesia in diabetic mice

We examined the tail-flick response to various heat intensities in diabetic and non-diabetic mice. Heat intensities were set to one of six values by adjusting the source of voltage for a 50-W projection bulb to 20, 25, 35, 50, 65 and 80 V. Tail-flick latencies at source voltages of 35 and 50 V in diabetic mice were significantly shorter than those in non-diabetic mice. However, tail-flick latencies at 25, 65 and 80 V in diabetic mice were not significantly altered. Although tail-flick latencies in non-diabetic mice were not affected by i.t. pre-treatment with CI-988, a selective cholecystokinin B (CCK(B)) receptor antagonist, those at 35 and 50 V in diabetic mice were significantly increased. In non-diabetic mice, i.t. pre-treatment with cholecystokinin octapeptide (CCK-8), at a dose of 0.3 ng, decreased tail-flick latencies at 35 and 50 V. Furthermore, the attenuation of tail-flick latencies induced by i.t. pre-treatment with CCK-8 in non-diabetic mice was reversed by i.t. pre-treatment with CI-988. Protein kinase C (PKC) activator phorbol-12, 13-dibutyrate (PDBu)-induced reduction in the tail-flick latencies at heat intensities of 35 and 50 V in non-diabetic mice was dose-dependently and significantly reversed by i.t. pre-treatment with CI-988. On the other hand, the CCK-8-induced thermal hyperalgesia and allodynia at heat intensities of 35 and 50 V in non-diabetic mice were inhibited when PKC activity was inhibited by i.t. pre-treatment with calphostin C. These results indicate that the thermal allodynia and hyperalgesia in diabetic mice may be due, at least in part, to the activation of CCK(B) receptors followed by the activation of PKC in the spinal cord.

Possible molecular targets of halogenated aromatic hydrocarbons in neuronal cells

Halogenated aromatic hydrocarbon including polychlorinated biphenyls (PCBs) are persistent and bioaccumulative environmental toxicants. Although health effects associated with exposure to these chemicals, including motor dysfunction and impairment in memory and learning, have been identified, their molecular site of action is unknown. Previous study from this laboratory demonstrated that, while ortho PCBs perturbed intracellular signaling mechanisms including Ca2+ homeostasis, receptor-mediated inositol phosphate production and translocation of PKC, non-ortho PCBs did not. Since PKC signaling pathway is implicated in the modulation of motor behavior, as well as learning and memory, and the roles of PKC are isoform-specific, we have now studied the effects of two structurally distinct PCBs on isoforms of PKC in cerebellar granule cell culture model. Cells were exposed to 2,2'-dichlorobiphenyl (ortho PCB; 2,2'-DCB) or 4,4'-dichlorobiphenyl (non-ortho PCB; 4,4'-DCB) for 15 min, respectively, and subsequently fractionated and immunoblotted against the selected PKC monoclonal antibodies (alpha, gamma, delta, epsilon, lambda, iota). While 2,2'-DCB induced a translocation of PKC-alpha [cytosol (% control): 54 +/- 12 at 25 microM and 66 +/- 10 at 50 microM; membrane (% control): 186 +/- 37 at 25 microM and 200 +/- 48 at 50 microM] and -epsilon [cytosol (% control): 92 +/- 12 at 25 microM and 97 +/- 15 at 50 microM; membrane (% control): 143 +/- 23 at 25 microM and 192 +/- 24 at 50 microM] from cytosol to membrane fraction in a concentration-dependent manner, 4,4'-DCB had no effects. 2,2'-DCB induced translocation of PKC-alpha was blocked by pretreatment with sphingosine, suggesting a possible role of sphingolipid pathway. Although reports on implication of PKC-gamma with learning and memory are relatively extensive, the expression of this particular isoform in the primary cerebellar granule cells was below the detectable level. PKC-delta, -lambda and -iota were present in these cells, but were not altered by PCB exposure. These results suggest that the effects of 2,2'-DCB on PKC is isoform-dependent and PKC-alpha as well as PKC-epsilon may be target molecules for ortho-PCBs in neuronal cells.

Differential regulation of primary protein kinase C substrate (MARCKS, MLP, GAP-43, RC3) mRNAs in the hippocampus during kainic acid-induced seizures and synaptic reorganization

In the mature hippocampus, kainic acid seizures lead to excitotoxic cell death and synaptic reorganization in which granule cell axons (mossy fibers) form ectopic synapses on granule cell dendrites. In the present study, we examined the expression of four major, developmentally regulated protein kinase C (PKC) substrates (MARCKS, MLP, GAP-43, RC3), which have different subcellular and regional localizations in the hippocampus at several time points (6 hr, 12 hr, 18 hr, 24 hr, 48 hr, 5 days, or 15 days) following kainic acid seizures using in situ hybridization. Consistent with previous reports, following kainate seizures, GAP-43 mRNA expression exhibited a delayed and protracted elevation in the granule cell layer, which peaked at 24 hr, whereas expression in fields CA1 and CA3 remained relatively unchanged. Conversely, RC3 mRNA expression exhibited a delayed reduction in the granule cell layer that was maximal at 18 hr, as well as a reduction CA1 at 48 hr, whereas CA3 levels did not change. MARCKS mRNA expression in the granule cell layer and CA1 remained stable following kainate, although an elevation was observed in subfield CA3c at 12 hr. Similarly, MLP mRNA expression did not change in the granule cell layer or CA1 following kainate but exhibited a protracted elevation in subfields CA3b,c beginning at 6 hr post-kainate. Collectively these data demonstrate that different PKC substrate mRNAs exhibit unique expression profiles and regulation in the different cell fields of the mature hippocampus following kainic acid seizures and during subsequent synaptic reorganization. The expression profiles following kainate seizures bear resemblance to those observed during postnatal hippocampal development, which may indicate the recruitment of common regulatory mechanisms.

Involvement of spinal protein kinase C in thermal hyperalgesia evoked by partial sciatic nerve ligation, but not by inflammation in the mouse

Activation of several protein kinases contributes to the development of hyperalgesia evoked by injuries. The present study was designed to investigate the role of protein kinase C in the spinal cord in thermal hyperalgesia evoked by sciatic nerve ligation or by intraplantar injection of complete Freund's adjuvant. The paw withdrawal latency on the ipsilateral side, but not on the contralateral side, was markedly decreased after sciatic nerve ligation. Intraplantar injection of complete Freund's adjuvant also caused markedly decreases of the paw withdrawal latency. Intrathecal pretreatment with protein kinase C inhibitor calphostin C (100 and 250 ng) attenuated the decrease of the paw withdrawal latency evoked by sciatic nerve ligation. In contrast, the decrease of the paw withdrawal latency evoked by inflammation was only slightly attenuated by intrathecal pretreatment with calphostin C. The results indicate that protein kinase C in the spinal cord is involved in the development of the thermal hyperalgesia evoked by nerve ligation and is much less involved in the thermal hyperalgesia by complete Freund's adjuvant's-induced inflammation.

Extracellular guanosine 5' triphosphate enhances nerve growth factor-induced neurite outgrowth via increases in intracellular calcium

Extracellular guanosine 5' triphosphate (GTP) enhances nerve growth factor-dependent neurite outgrowth from rat pheochromocytoma (PC12) cells; cultures of PC12 cells exposed to GTP and nerve growth factor together contain significantly more neurite-bearing cells than do those exposed to either nerve growth factor or GTP alone [Gysbers J. W. and Rathbone M. P. (1996) Int. J. devl Neurosci. 14, 19-34]. PC12 cells contain specific cell surface binding sites for extracellular GTP, which do not bind ATP or uridine 5' triphosphate. Exposure of PC12 cells to extracellular GTP (300microM) produced a robust and sustained increase in intracellular Ca(2+) ([Ca(2+)](i)), different from the transient response to the addition of ATP. The GTP-induced [Ca(2+)](i) increase was blocked by the L-type calcium channel inhibitor, nifedipine. The L-type Ca(2+) channel inhibitors, nifedipine or verapamil, also inhibited the enhancement of neurite outgrowth by GTP, but did not affect neurite outgrowth stimulated by nerve growth factor alone. Pre-treatment of PC12 cells with ryanodine (0.5-50microM) depleted calcium from internal stores and prevented the further release of calcium by GTP. Similarly, pre-treatment of PC12 cells with thapsigargin (an inhibitor of internal store Ca(2+)/ATPase) or dantrolene (which blocks Ca(2+) release from some of these stores) also reduced the enhancement of neurite outgrowth by GTP. Therefore, Ca(2+)-induced Ca(2+) release from specific stores, present in PC12 cells, is involved in the enhancement of nerve growth factor-induced neurite outgrowth by GTP, possibly acting at specific binding sites on the cell surface. GTP is proving to be an important extracellular trophic modulator in the central nervous system. These studies show that the neuritogenic actions of GTP involve moderate but sustained increases in intracellular Ca(2+) which are likely due to activation of L-type Ca(2+) channels and Ca(2+)-induced Ca(2+) release from intracellular stores. These effects of extracellular GTP are likely mediated at the cell surface and may be related to specific GTP binding sites which are distinct from G-proteins and from hitherto described purine nucleotide (P2) receptors. These data indicate a mechanism whereby the neuritogenic effects of GTP are mediated and emphasize the importance of considering GTP as a neurotrophic mediator.

Tubulin anchoring to glycolipid-enriched, detergent-resistant domains of the neuronal plasma membrane

After incubation of intact living cultured rat cerebellar granule cells at 37 degrees C with a new GM1 ganglioside analog, carrying a diazirine group and labeled with (125)I in the ceramide moiety, followed by photoactivation, a relatively small number of radiolabeled proteins were detected in a membrane-enriched fraction. A protein of about 55 kDa with a pI of about 5 carried a large portion of the radioactivity even if incubation and cross-linking were performed at 4 degrees C and in the presence of inhibitors of endocytosis, suggesting that it is cross-linked at the plasma membrane. Immunoprecipitation and Western blotting experiments showed the positivity of this protein for tubulin. Trypsin treatment of intact cells ruled out the involvement of a plasma membrane surface tubulin. Release of radioactivity from cross-linked tubulin after KOH treatment (but not hydroxylamine treatment) suggested that the photoactivated ganglioside reacts with an ester-linked fatty acid anchor of tubulin. Low buoyancy, detergent-resistant membrane fractions, isolated from cells after incubation with the GM1 analogue and photoactivation, proved their enrichment in endogenous and radioactive GM1 ganglioside, sphingomyelin, cholesterol, signal transduction proteins, and tubulin. It is noteworthy that radioactive tubulin was also detected in this fraction, indicating the presence of tubulin molecules carrying a fatty acid anchor in detergent-resistant, ganglioside-enriched domains of the plasma membrane. Parallel experiments carried out with a phosphatidylcholine analogue, also carrying a diazirine group and labeled with (125)I in the fatty acid moiety, showed the specificity of tubulin interaction with GM1. Taken together, these results indicate that some tubulin molecules are associated with a lipid anchor to detergent-resistant glycolipid-enriched domains of the plasma membrane. This novel feature of membrane domains can provide a key for a better understanding of their biological role.

GM1 ganglioside restores abnormal responses to acute thermal and mechanical stimuli in aged rats

We investigated the effect of aging on the responses to thermal and mechanical stimuli in rats. Young (3-5 months old) and aged (22-24 months old) male Sprague-Dawley rats were tested in the hot plate, high- and low-intensity radiant heat tail flick, and von Frey hair assays. Compared to young rats, aged rats displayed longer latencies in the hot plate and the high-intensity tail flick assays (hypoalgesia), but there was no difference in the low-intensity tail flick assay. In addition, aged rats had decreased thresholds to mechanical stimuli produced by von Frey hairs compared with young rats (mechanical allodynia). Administration of GM1 ganglioside, 30 mg/kg, i.p., once daily for 30 days, to aged rats partially restored the responses in the hot plate and von Frey hair assays. GM1 had no effect on the altered responses in the tail flick test in aged rats, and in general, had no effect on any sensory modality tested in young rats.

Dynamics of glycolipid domains in the plasma membrane of living cultured neurons, following protein kinase C activation: a study performed by excimer-formation imaging

Dynamic changes of glycolipid domains within the plasma membranes of cultured rat cerebellar granule cells have been investigated. For this purpose, a pyrene-labelled derivative of G(M1) ganglioside has been incorporated in the cell plasma membrane, and the rate of excimer formation, directly related to the formation of domains, has been studied by a fluorescence imaging technique (excimer-formation imaging). Fluorescence imaging showed that upon addition of 100 microM glutamate, indirectly inducing the activation of protein kinase C (PKC), glycolipid concentration within domains increases in cell bodies. Comparable effects were exerted by the addition of PMA, directly inducing the activation of PKC. On the contrary, the phorbol ester was not effective in the presence of the specific PKC inhibitor, bisindolylmaleimide. These results suggest that glycolipid-enriched domains are dynamic supramolecular structures affected by membrane-associated events, such as PKC activation. Dynamic changes of domains could be important in modulating their postulated participation in a series of functions, including signal transduction and lipid/protein sorting.

Ganglioside GM1 protection from apoptosis of rat heart fibroblasts

Ceramide is involved as a mediator of apoptosis induced by a variety of signaling molecules or stressful events. Ceramide-derived sphingosine 1-phosphate behaves as an antiapoptotic agent. The ganglioside GM1 is known to protect neuronal cell lines from apoptosis induced by serum/growth factor withdrawal and its effect is mediated in part by the direct activation of the trkA NGF receptor [G. Ferrari et al. (1995) J. Biol. Chem. 270, 3074-3080]. We show that GM1, similarly to sphingosine 1-phosphate, protects rat heart fibroblasts from apoptosis induced by the protein kinase C inhibitor staurosporine and by C2-ceramide. Furthermore, we show that GM1 induces the synthesis of sphingosine 1-phosphate and that this effect is partially prevented by the sphingosine kinase inhibitor N,N-dimethylsphingosine. We conclude that the antiapoptotic action of GM1 is largely to be ascribed to an increased sphingosine kinase activity.

Ganglioside GD1b supresses immunoglobulin production by human peripheral blood mononuclear cells

Gangliosides are sialic acid-containing glycolipids, that have various immunomodulatory effects. We previously reported that various gangliosides in vitro either inhibited or enhanced spontaneous immunoglobulin (Ig) production by human peripheral blood mononuclear cells (PBMC). GD1b was one of the inhibitory gangliosides. In this study, we further examined the mechanism for the inhibitory effect of GD1b. The inhibitory effect of GD1b was revealed at 0.1 microM, increased dose dependently, and was maximized at 10 microM, which reduced spontaneous IgG, IgM, and IgA production of human PBMC by 50.5%, 52.0%, and 48.3% compared with controls, respectively. GD1b did not affect the proliferation and viability of PBMC. GD1b did not alter Ig production of B cells alone. Interleukin 6 (IL-6) and IL-10 each partially reversed the GD1b-induced inhibition of Ig production by PBMC, and the addition of both cytokines completely reversed the inhibition. When endogenous IL-6 and IL-10 were neutralized by specific antibodies, GD1b did not reveal inhibitory effects on the Ig production. GD1b inhibited IL-6 and IL-10 production of CD4+ T cells, without affecting those of CD8+ T cells, monocytes, or B cells. When CD4+ T cells were preincubated with GD1b and washed and cultured with B cells and monocytes, Ig production was also suppressed. These results suggest that GD1b may indirectly suppress Ig production of B cells in whole PBMC by reducing IL-6 and IL-10 production of CD4+ T cells. GD1b may act as an important inhibitor of human humoral immune responses.

Gangliosides attenuate ethanol-induced apoptosis in rat cerebellar granule neurons

Ethanol significantly enhances cell death of differentiated rat cerebellar granule neurons on culture in a serum-free medium containing a depolarizing concentration of KCl (25 mM), 5 microM MK-801 (an NMDA receptor antagonist), and 20-200 mM ethanol for 1-4 days. Cell death augmented by ethanol was concentration- and time-dependent with neurons displaying hallmark apoptotic morphology and DNA fragmentation that correlated with the activation of cytosolic caspase-3. Inclusion of 5 microM MK-801 or 100 microM glycine in culture media did not alter rates of cell death indicating ethanol toxicity is mediated via an NMDA receptor-independent pathway. Preincubation with 50 microM gangliosides GM1, GD1a, GD1b or GT1b for 2 h, or preincubation with 10 microM LIGA20 (a semisynthetic GM1 with N-dichloroacetylsphingosine) for 10 min, attenuated caspase-3 activity and ethanol-induced cell death. Data show native gangliosides and a synthetic derivative are potently neuroprotective in this model of ethanol toxicity, and potentially serve as useful probes to further unravel the mechanisms relevant to neuronal apoptosis.

Possible involvement of spinal protein kinase C in thermal allodynia and hyperalgesia in diabetic mice

We examined the tail-flick response to various heat intensities in diabetic and non-diabetic mice. Heat intensities were set to one of five values by adjusting the source voltage of a 50-W projection bulb to 25, 35, 50, 65 and 80 V. These heat intensities produced surface skin heating rates of 0.1, 0.4, 0.9, 3.0 and 7.3 degrees C/s, respectively. Tail-flick latencies at source voltages of 35 and 50 V in diabetic mice were significantly shorter than those in non-diabetic mice. However, there were no significant differences in tail-flick latencies at 25, 65 and 80 V. In non-diabetic mice, tail-flick latencies were not affected by intrathecal (i.t.) pretreatment with capsaicin 24 h before testing. Tail-flick latencies at 35 and 50 V in diabetic mice were increased by pretreatment with capsaicin. Moreover, although tail-flick latencies in non-diabetic mice were not affected by i.t. pretreatment with calphostin C, a selective protein kinase C inhibitor, those at 35 and 50 V in diabetic mice were increased. However, i.t. pretreatment with (8R, 9S, 11S)-(-)-9-hydroxy-9-n-hexyloxy-carbonyl-8-methyl-2, 3, 9, 10-tetrahydro-8, 11-epoxy-1H, 8H, 11H-2, 7b, 11a-triazadibenzo [a, g]cycloocta[cde]-trinden-1-one (KT5720), a selective protein kinase A inhibitor, did not affect tail-flick latencies in either diabetic or non-diabetic mice. In non-diabetic mice, i.t. pretreatment with phorbol 12,13-dibutyrate (PDB), a protein kinase C activator, decreased tail-flick latencies at 35 and 50 V. Tail-flick latencies in diabetic mice were not affected by i.t. pretreatment with PDB 60 min before testing. Furthermore, the attenuation of tail-flick latencies induced by i.t. pretreatment with PDB in non-diabetic mice was reversed by i.t. pretreatment with capsaicin 24 h before testing. These results indicate that diabetic mice exhibit thermal allodynia and hyperalgesia. Furthermore, this thermal allodynia and hyperalgesia in diabetic mice may be due to the enhanced release of substance P followed by activation of protein kinase C in the spinal cord.

Differential subcellular redistribution of protein kinase C isozymes in the rat hippocampus induced by kainic acid

Protein kinase C (PKC) consists of a family of Ca2+/phospholipid-dependent isozymes that has been implicated in the delayed neurotoxic effects of glutamate in vitro. In the present study, we assessed the effect of the glutamate analogue kainic acid (KA) on the subcellular expression of PKC isozymes in the hippocampus (HPC) in the period preceding (0.5, 1.5, 12, and 24 h) and during (120 h) hippocampal necrosis using western blot analysis and PKC isozyme-specific antibodies. Before subcellular fractionation (cytosol + membrane), hippocampi were microdissected into "HPC" (fields CA1-CA3) and "dentate gyrus" (DG; granule cells + hilus) regions. Four general patterns of alterations in PKC isozyme expression/distribution were observed following KA treatment. The first pattern was a relative stability in expression following KA treatment and was most apparent for cytosol PKCalpha (HPC + DG) and membrane (HPC) and cytosol (DG) PKCbetaII. The second pattern, observed with PKCgamma and PKCepsilon, was characterized by an initial increase in expression in both membrane and cytosolic fractions before seizure activity (0.5 h) followed by a gradual decrease until significant reductions are observed by 120 h. The third pattern, exhibited by PKCdelta, involved an apparent translocation, increasing in the membrane and decreasing in the cytosol, followed by down-regulation in both fractions and subsequent recovery. The fourth pattern was observed with PKCzeta only and entailed a significant reduction in expression before and during limbic motor seizures followed by a dramatic fivefold increase in the membrane fraction during the period of hippocampal necrosis (120 h). Although these patterns did not segregate according to conventional PKC isozyme classifications, they do indicate dynamic isozyme-specific regulation by KA. The subcellular redistribution of PKC isozymes may contribute to the histopathological sequelae produced by KA in the hippocampus and may model the pathogenesis associated with diseases involving glutamate-induced neurotoxicity.

Molecular pathways mediating activation by kainate of mitogen-activated protein kinase in oligodendrocyte progenitors

Oligodendroglial cells express ionotropic glutamate receptors of alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid hydrobromide (AMPA) and kainate (KA) subtypes. Recently, we reported that AMPA receptor agonists increased 45Ca2+ uptake and phospholipase C (PLC) activity. To further elucidate the intracellular signaling mechanisms, we examined the effects of AMPA and KA on mitogen-activated protein kinase (MAPK). KA caused a time- and concentration-dependent increase in MAPK activity (predominantly the p42mapk or ERK2) and the effect was blocked by 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX), a competitive AMPA/KA receptor antagonist. Furthermore, the noncompetitive antagonists of AMPA receptor GYKI 52466 and LY 303070 prevented the actions of the agonists, indicating that the effect of KA on MAPK activation is mediated through AMPA receptors in oligodendrocyte progenitors. Chelation of extracellular Ca2+ by EDTA or inhibition of PLC with U73122 abolished MAPK activation by KA. In addition, KA-stimulated MAPK activation was reduced by the protein kinase C (PKC) inhibitors, H7 and bisindolylmaleimide, as well as downregulation of PKC by prolonged exposure to phorbol esters. The involvement of PKC in the signal transduction pathways was further supported by the ability of KA to induce translocation of PKC measured by [3H]PDBu binding. Interestingly, a wortmannin-sensitive phosphatidylinositol 3-kinase and a pertussis toxin (PTX)-sensitive G protein form part of the molecular pathways mediating MAPK activation by AMPA receptor. A specific inhibitor of MAPK kinase, PD 098059, blocked MAPK activation and reduced KA-induced c-fos gene expression. All together, these results indicate that MAPK is implicated in the transmission of AMPA signaling to the nucleus and requires extracellular Ca2+, and PLC/PKC activation.

Isoform-specific translocation of protein kinase C following glutamate administration in primary hippocampal neurons

High concentrations of glutamate, the major excitatory neurotransmitter in the mammalian brain, lead to intracellular calcium overload resulting in excitotoxic damage and death of neurons. Since protein kinase C (PKC) is involved in neuronal degeneration resulting from cerebral ischemia and from glutamate excitotoxicity, we investigated the effect of glutamate on changes in the cellular distribution of various PKC isoforms in cultured hippocampal neurons in comparison with the effects elicited by the PKC activator phorbol ester. Out of the expressed PKC isoforms alpha, gamma, epsilon, zeta and lambda only the conventional isoforms PKC alpha and gamma responded to glutamate. Using subcellular fractionation and Western blotting with isoform-specific antibodies and immunocytochemical localization with confocal laser scanning microscopy, we observed that phorbol ester and glutamate have different effects on PKC isoform redistribution: Whereas phorbol ester resulted in translocation of PKC alpha and PKC gamma toward a membrane fraction, the glutamate-mediated rise in intracellular calcium concentration induced a translocation mainly toward a detergent-insoluble, cytoskeletal fraction. Immunocytochemical analysis revealed an isoform-specific translocation following glutamate treatment: PKC gamma was translocated mainly to cytoplasmic, organelle-like structures, whereas PKC alpha redistributed to the plasma membrane and into the cell nucleus. The latter result is of special interest, as it indicates that nuclear PKC may play a role in processes of excitotoxic cell damage.

The induction of pain: an integrative review

The highly disagreeable sensation of pain results from an extraordinarily complex and interactive series of mechanisms integrated at all levels of the neuroaxis, from the periphery, via the dorsal horn to higher cerebral structures. Pain is usually elicited by the activation of specific nociceptors ('nociceptive pain'). However, it may also result from injury to sensory fibres, or from damage to the CNS itself ('neuropathic pain'). Although acute and subchronic, nociceptive pain fulfils a warning role, chronic and/or severe nociceptive and neuropathic pain is maladaptive. Recent years have seen a progressive unravelling of the neuroanatomical circuits and cellular mechanisms underlying the induction of pain. In addition to familiar inflammatory mediators, such as prostaglandins and bradykinin, potentially-important, pronociceptive roles have been proposed for a variety of 'exotic' species, including protons, ATP, cytokines, neurotrophins (growth factors) and nitric oxide. Further, both in the periphery and in the CNS, non-neuronal glial and immunecompetent cells have been shown to play a modulatory role in the response to inflammation and injury, and in processes modifying nociception. In the dorsal horn of the spinal cord, wherein the primary processing of nociceptive information occurs, N-methyl-D-aspartate receptors are activated by glutamate released from nocisponsive afferent fibres. Their activation plays a key role in the induction of neuronal sensitization, a process underlying prolonged painful states. In addition, upon peripheral nerve injury, a reduction of inhibitory interneurone tone in the dorsal horn exacerbates sensitized states and further enhance nociception. As concerns the transfer of nociceptive information to the brain, several pathways other than the classical spinothalamic tract are of importance: for example, the postsynaptic dorsal column pathway. In discussing the roles of supraspinal structures in pain sensation, differences between its 'discriminative-sensory' and 'affective-cognitive' dimensions should be emphasized. The purpose of the present article is to provide a global account of mechanisms involved in the induction of pain. Particular attention is focused on cellular aspects and on the consequences of peripheral nerve injury. In the first part of the review, neuronal pathways for the transmission of nociceptive information from peripheral nerve terminals to the dorsal horn, and therefrom to higher centres, are outlined. This neuronal framework is then exploited for a consideration of peripheral, spinal and supraspinal mechanisms involved in the induction of pain by stimulation of peripheral nociceptors, by peripheral nerve injury and by damage to the CNS itself. Finally, a hypothesis is forwarded that neurotrophins may play an important role in central, adaptive mechanisms modulating nociception. An improved understanding of the origins of pain should facilitate the development of novel strategies for its more effective treatment.