Ca2+ Permeable AMPA Receptor Induced Long-Term Potentiation Requires PI3/MAP Kinases but Not Ca/CaM-Dependent Kinase II

Ca²⁺ influx via GluR2-lacking Ca²⁺-permeable AMPA glutamate receptors (CP-AMPARs) can trigger changes in synaptic efficacy in both interneurons and principle neurons, but the underlying mechanisms remain unknown. We took advantage of genetically altered mice with no or reduced GluR2, thus allowing the expression of synaptic CP-AMPARs, to investigate the molecular signaling process during CP-AMPAR-induced synaptic plasticity at CA1 synapses in the hippocampus. Utilizing electrophysiological techniques, we demonstrated that these receptors were capable of inducing numerous forms of long-term potentiation (referred to as CP-AMPAR dependent LTP) through a number of different induction protocols, including high-frequency stimulation (HFS) and theta-burst stimulation (TBS). This included a previously undemonstrated form of protein-synthesis dependent late-LTP (L-LTP) at CA1 synapses that is NMDA-receptor independent. This form of plasticity was completely blocked by the selective CP-AMPAR inhibitor IEM-1460, and found to be dependent on postsynaptic Ca²⁺ ions through calcium chelator (BAPTA) studies. Surprisingly, Ca/CaM-dependent kinase II (CaMKII), the key protein kinase that is indispensable for NMDA-receptor dependent LTP at CA1 synapses appeared to be not required for the induction of CP-AMPAR dependent LTP due to the lack of effect of two separate pharmacological inhibitors (KN-62 and staurosporine) on this form of potentiation. Both KN-62 and staurosporine strongly inhibited NMDA-receptor dependent LTP in control studies. In contrast, inhibitors for PI3-kinase ({"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002 and wortmannin) or the MAPK cascade (PD98059 and U0126) significantly attenuated this CP-AMPAR-dependent LTP. Similarly, postsynaptic infusion of tetanus toxin (TeTx) light chain, an inhibitor of exocytosis, also had a significant inhibitory effect on this form of LTP. These results suggest that distinct synaptic signaling underlies GluR2-lacking CP-AMPAR-dependent LTP, and reinforces the recent notions that CP-AMPARs are important facilitators of synaptic plasticity in the brain.     

Reduced calcium/calmodulin-dependent protein kinase II activity in the hippocampus is associated with impaired cognitive function in MPTP-treated mice

Parkinson's disease (PD) patients frequently reveal deficit in cognitive functions during the early stage in PD. The dopaminergic neurotoxin, MPTP-induced neurodegeneration causes an injury of the basal ganglia and is associated with PD-like behaviors. In this study, we demonstrated that deficits in cognitive functions in MPTP-treated mice were associated with reduced calcium/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation and impaired long-term potentiation (LTP) induction in the hippocampal CA1 region. Mice were injected once a day for 5days with MPTP (25mg/kg i.p.). The impaired motor coordination was observed 1 or 2week after MPTP treatment as assessed by rota-rod and beam-walking tasks. In immunoblotting analyses, the levels of tyrosine hydroxylase protein and CaMKII autophosphorylation in the striatum were significantly decreased 1week after MPTP treatment. By contrast, deficits of cognitive functions were observed 3-4weeks after MPTP treatment as assessed by novel object recognition and passive avoidance tasks but not Y-maze task. Impaired LTP in the hippocampal CA1 region was also observed in MPTP-treated mice. Concomitant with impaired LTP induction, CaMKII autophosphorylation was significantly decreased 3weeks after MPTP treatment in the hippocampal CA1 region. Finally, the reduced CaMKII autophosphorylation was closely associated with reduced AMPA-type glutamate receptor subunit 1 (GluR1; Ser-831) phosphorylation in the hippocampal CA1 region of MPTP-treated mice. Taken together, decreased CaMKII activity with concomitant impaired LTP induction in the hippocampus likely account for the learning disability observed in MPTP-treated mice.     

Domain Contributions to Signaling Specificity Differences Between Ras-Guanine Nucleotide Releasing Factor (Ras-GRF) 1 and Ras-GRF2

Ras-GRF1 (GRF1) and Ras-GRF2 (GRF2) constitute a family of similar calcium sensors that regulate synaptic plasticity. They are both guanine exchange factors that contain a very similar set of functional domains, including N-terminal pleckstrin homology, coiled-coil, and calmodulin-binding IQ domains and C-terminal Dbl homology Rac-activating domains, Ras-exchange motifs, and CDC25 Ras-activating domains. Nevertheless, they regulate different forms of synaptic plasticity. Although both GRF proteins transduce calcium signals emanating from NMDA-type glutamate receptors in the CA1 region of the hippocampus, GRF1 promotes LTD, whereas GRF2 promotes θ-burst stimulation-induced LTP (TBS-LTP). GRF1 can also mediate high frequency stimulation-induced LTP (HFS-LTP) in mice over 2-months of age, which involves calcium-permeable AMPA-type glutamate receptors. To add to our understanding of how proteins with similar domains can have different functions, WT and various chimeras between GRF1 and GRF2 proteins were tested for their abilities to reconstitute defective LTP and/or LTD in the CA1 hippocampus of Grf1/Grf2 double knock-out mice. These studies revealed a critical role for the GRF2 CDC25 domain in the induction of TBS-LTP by GRF proteins. In contrast, the N-terminal pleckstrin homology and/or coiled-coil domains of GRF1 are key to the induction of HFS-LTP by GRF proteins. Finally, the IQ motif of GRF1 determines whether a GRF protein can induce LTD. Overall, these findings show that for the three forms of synaptic plasticity that are regulated by GRF proteins in the CA1 hippocampus, specificity is encoded in only one or two domains, and a different set of domains for each form of synaptic plasticity.     

The anti-inflammatory cytokine, interleukin (IL)-10, blocks the inhibitory effect of IL-1 beta on long term potentiation. A role for JNK

Several effects of the proinflammatory cytokine, interleukin-1 beta (IL-1 beta), have been described in the central nervous system, and one area of the brain where marked changes have been reported is the hippocampus. Among these changes are an IL-1 beta-induced inhibition of long term potentiation (LTP) in perforant path-granule cell synapses and an attenuation of glutamate release in synaptosomes prepared from the hippocampus. Evidence suggests that, at least in circulating cells, the anti-inflammatory cytokine, IL-10, antagonizes certain effects of IL-1. We investigated the effect of IL-10 on IL-1 beta-induced inhibition of LTP and glutamate release. The evidence presented indicates that IL-1 beta stimulates the stress-activated protein kinase, c-Jun-activated protein kinase (JNK), and IL-1 receptor-associated kinase, which may explain its inhibitory effect on release and LTP, and that IL-10 reversed the IL-1 beta-induced stimulation of JNK activity and inhibition of release and LTP. We observed that IL-10 abrogated the stimulatory effect of IL-1 beta on superoxide dismutase activity and reactive oxygen species production, whereas the H(2)O(2)-induced inhibition of LTP was also blocked by IL-10. We present evidence that suggests that the action of IL-10 may be mediated by its ability to induce shedding of the IL-1 type I receptor.     

Ventral Tegmental Area Inactivation Suppresses the Expression of CA1 Long Term Potentiation in Anesthetized Rat

The hippocampus receives dopaminergic projections from the ventral tegmental area (VTA). Modulatory effect of dopamine on hippocampal long term potentiation (LTP) has been studied before, but there are conflicting results and some limitations in previous reports. Most of these studies show a significant effect of dopamine on the late phase of LTP in CA1 area of the hippocampus, while few reports show an effect on the early phase. Moreover, they generally manipulated dopamine receptors in the hippocampus and there are few studies investigating influence of the VTA neural activity on hippocampal LTP in the intact brain. Besides, VTA neurons contain other neurotransmitters such as glutamate and GABA that may modify the net effect of dopamine. In this study we examined the effect of VTA reversible inactivation on the induction and maintenance of early LTP in the CA1 area of anesthetized rats, and also on different phases of learning of a passive avoidance (PA) task. We found that inactivation of the VTA by lidocaine had no effect on CA1 LTP induction and paired-pulse facilitation, but its inactivation immediately after tetanic stimulation transiently suppressed the expression of LTP. Blockade of the VTA 20 min after tetanic stimulation had no effect on the magnitude of LTP. Moreover, VTA inactivation immediately after training impaired memory in the passive avoidance task, while its blockade before or 20 min after training produced no memory deficit. It can be concluded that VTA activity has no effect on CA1 LTP induction and acquisition of PA task, but involves in the expression of LTP and PA memory consolidation.     

Pituitary adenylate cyclase-activating polypeptide (PACAP) prevents hippocampal neurons from apoptosis by inhibiting JNK/SAPK and p38 signal transduction pathways

We have demonstrated that ischemic neuronal death (apoptosis) of rat CA1 region of the hippocampus was prevented by infusing pituitary adenylate cyclase-activating polypeptide (PACAP) either intracerebroventricularly or intravenously. We have also demonstrated that the activity of mitogen-activated protein (MAP) kinase family members, including ERK (extracellular signal-regulated kinase), Jun N-terminal kinase (JNK)/stress-activated protein kinase (SAPK) and p38, was increased in the hippocampus within 1-6 h after brain ischemia. The molecular mechanisms underlying the PACAP anti-apoptotic effect were demonstrated in this study. Ischemic stress had a strong influence on MAP kinase family, especially on JNK/SAPK and p38. PACAP inhibited the activation of JNK/SAPK and p38 after ischemic stress, while ERK is not suppressed. These findings suggest that PACAP inhibits the JNK/SAPK and p38 signaling pathways, thereby protecting neurons against apoptosis.     

Mechanism of prostaglandin D(2)-stimulated heat shock protein 27 induction in osteoblasts

We previously showed that prostaglandin D(2) (PGD(2)) stimulates activation of protein kinase C (PKC). We investigated whether PGD(2) stimulates the induction of heat shock protein (HSP) 27 and HSP70 in osteoblast-like MC3T3-E1 cells and the mechanism underlying the induction. PGD(2) increased the levels of HSP27 while having little effect on HSP70 levels. PGD(2) stimulated the accumulation of HSP27 dose dependently in the range between 10 nM and 10 microM. PGD(2) induced an increase in the levels of mRNA for HSP27. The PGD(2)-stimulated accumulation of HSP27 was reduced by staurosporine or calphostin C, inhibitors of PKC. PGD(2) induced the phosphorylation of p44/p42 mitogen-activated protein (MAP) kinase and p38 MAP kinase. The HSP27 accumulation induced by PGD(2) was significantly suppressed by PD98059, an inhibitor of the upstream kinase of p44/p42 MAP kinase, or SB203580, an inhibitor of p38 MAP kinase. Calphostin C suppressed the PGD(2)-induced phosphorylation of p44/p42 MAP kinase and p38 MAP kinase. PD98059 or SB203580 suppressed the PGD(2)-increased levels of mRNA for HSP27. These results strongly suggest that PGD(2) stimulates HSP27 induction through p44/p42 MAP kinase activation and p38 MAP kinase activation in osteoblasts and that PKC acts at a point upstream from both the MAP kinases.     

Rap1-induced p38 mitogen-activated protein kinase activation facilitates AMPA receptor trafficking via the GDI.Rab5 complex. Potential role in (S)-3,5-dihydroxyphenylglycene-induced long term depression

Recent evidence has emphasized the importance of p38 mitogen-activated protein kinase (MAPK) in the induction of metabotropic glutamate receptor (mGluR)-dependent long term depression (LTD) at hippocampal CA3-CA1 synapses. However, the cascade responsible of mGluR to activate p38 MAPK and the signaling pathway immediately downstream from it to induce synaptic depression is poorly understood. Here, we show that transient activation of group I mGluR with the selective agonist (S)-3,5-dihydroxyphenylglycine (DHPG) activates p38 MAPK through G protein betagamma-subunit, small GTPase Rap1, and MAPK kinase 3/6 (MKK3/6), thus resulting in mGluR5-dependent LTD. Furthermore, our data clearly show that an accelerating AMPA receptor endocytosis by stimulating the formation of guanyl nucleotide dissociation inhibitor-Rab5 complex is a potential downstream processing of p38 MAPK activation to mediate DHPG-LTD. These results suggest an important role for Rap1-MKK3/6-p38 MAPK pathway in the induction of mGluR-dependent LTD by directly coupling to receptor trafficking machineries to facilitate the loss of synaptic AMPA receptors.     

P2X7 receptor mediated phosphorylation of p38MAP kinase in the hippocampus

This study was designed to explore the effect of P2X7 receptor (P2X7R) activation on the expression of p38 MAP kinase (p38 MAPK) enzyme in hippocampal slices of wild-type (WT) and P2X7R^−/− mice using the Western blot technique and to clarify its role in P2X7 receptor mediated [³H]glutamate release. ATP (1 mM) and the P2X7R agonist BzATP (100 μM) significantly increased p38 MAPK phosphorylation in WT mice, and these effects were absent in the hippocampal slices of P2X7R^−/− mice. Both ATP- and BzATP-induced p38 MAPK phosphorylations were sensitive to the p38 MAP kinase inhibitor, SB203580 (1 μM). ATP elicited [³H]glutamate release from hippocampal slices, which was significantly attenuated by SB203580 (1 μM) but not by the extracellular signal-regulated kinase (ERK1/2) inhibitor, PD098095 (10 μM). Consequently, we suggest that P2X7Rs and p38 MAPK are involved in the stimulatory effect of ATP on glutamate release in the hippocampal slices of WT mice.     

G protein-coupled receptors control NMDARs and metaplasticity in the hippocampus

Long-term potentiation (LTP) and long-term depression (LTD) are the major forms of functional synaptic plasticity observed at CA1 synapses of the hippocampus. The balance between LTP and LTD or "metaplasticity" is controlled by G-protein coupled receptors (GPCRs) whose signal pathways target the N-methyl-D-asparate (NMDA) subtype of excitatory glutamate receptor. We discuss the protein kinase signal cascades stimulated by Galphaq and Galphas coupled GPCRs and describe how control of NMDAR activity shifts the threshold for the induction of LTP.     

Disruption of MET Receptor Tyrosine Kinase,an Autism Risk Factor,Impairs Developmental Synaptic Plasticity in the Hippocampus

As more genes conferring risks to neurodevelopmental disorders are identified, translating these genetic risk factors into biological mechanisms that impact the trajectory of the developing brain is a critical next step. Here, we report that disrupted signaling mediated MET receptor tyrosine kinase (RTK), an established risk factor for autism spectrum disorders, in the developing hippocampus glutamatergic circuit leads to profound deficits in neural development, synaptic transmission, and plasticity. In cultured hippocampus slices prepared from neonatal mice, pharmacological inhibition of MET kinase activity suppresses dendritic arborization and disrupts normal dendritic spine development. In addition, single‐neuron knockdown (RNAi) or overexpression of Met in the developing hippocampal CA1 neurons leads to alterations, opposite in nature, in basal synaptic transmission and long‐term plasticity. In forebrain‐specific Met conditional knockout mice (Met^fx/fx;emx1^cre), an enhanced long‐term potentiation (LTP) and long‐term depression (LTD) were observed at early developmental stages (P12–14) at the Schaffer collateral to CA1 synapses compared with wild‐type littermates. In contrast, LTP and LTD were markedly reduced at young adult stage (P56–70) during which wild‐type mice show robust LTP and LTD. The altered trajectory of synaptic plasticity revealed by this study indicate that temporally regulated MET signaling as an intrinsic, cell autonomous, and pleiotropic mechanism not only critical for neuronal growth and functional maturation, but also for the timing of synaptic plasticity during forebrain glutamatergic circuits development.     

Improved spatial learning is associated with increased hippocampal but not prefrontal long‐term potentiation in mGluR4 knockout mice

Although much information about metabotropic glutamate receptors (mGluRs) and their role in normal and pathologic brain function has been accumulated during the last decades, the role of group III mGluRs is still scarcely documented. Here, we examined mGluR4 knockout mice for types of behavior and synaptic plasticity that depend on either the hippocampus or the prefrontal cortex (PFC). We found improved spatial short‐ and long‐term memory in the radial arm maze, which was accompanied by enhanced long‐term potentiation (LTP) in hippocampal CA1 region. In contrast, LTP in the PFC was unchanged when compared with wild‐type controls. Changes in paired‐pulse facilitation that became overt in the presence of the GABA_A antagonist picrotoxin indicated a function of mGluR4 in maintaining the excitation/inhibition balance, which is of crucial importance for information processing in the brain and the deterioration of these processes in neuropsychological disorders such as autism, epilepsy and schizophrenia .     

Increased Phosphorylation of a 17-kDa Protein Kinase C Substrate (P17) in Long-Term Potentiation

Hippocampal long-term potentiation (LTP) is a persistent increase in the efficacy of synaptic transmission, which is widely thought to be a cellular mechanism that could contribute to learning and memory. Studies on the biochemical mechanisms underlying LTP suggest the involvement of protein kinases in both LTP induction and maintenance. In this report we describe an LTP-associated increase in the phosphorylation in vitro of a 17-kDa protein kinase C (PKC) substrate protein, which we have termed P17, in homogenates from the CA1 region of rat hippocampal slices. This LTP-associated increase in phosphorylation was expressed independent of significant levels of free Ca2+, as phosphorylation reactions were performed in the presence of 500 microM EGTA. The increased phosphorylation of P17 was substantially inhibited by PKC(19-36), a selective inhibitor of PKC. These data support the model that persistent PKC activation contributes to the maintenance of LTP and implicate P17 as a potential target for PKC in the CA1 region of the hippocampus.     

NMDA Receptor-Dependent Long-Term Potentiation and Long-Term Depression (LTP/LTD)

Long-term potentiation and long-term depression (LTP/LTD) can be elicited by activating N-methyl-d-aspartate (NMDA)-type glutamate receptors, typically by the coincident activity of pre- and postsynaptic neurons. The early phases of expression are mediated by a redistribution of AMPA-type glutamate receptors: More receptors are added to potentiate the synapse or receptors are removed to weaken synapses. With time, structural changes become apparent, which in general require the synthesis of new proteins. The investigation of the molecular and cellular mechanisms underlying these forms of synaptic plasticity has received much attention, because NMDA receptor–dependent LTP and LTD may constitute cellular substrates of learning and memory.Long-term synaptic plasticity is a generic term that applies to a long-lasting experience-dependent change in the efficacy of synaptic transmission. Here we will focus on N-methyl-d-aspartate (NMDA) receptor–dependent synaptic potentiation (LTP) and depression (LTD), two forms of activity-dependent long-term changes in synaptic efficacy that have been extensively studied. Because both LTP and LTD are believed to represent cellular correlates of learning and memory, they have attracted considerable interest. In this article we will focus on the molecular and cellular mechanisms associated with LTP and LTD. As for other forms of long-term synaptic plasticity, a characterization of LTP and LTD involves describing the molecular mechanisms that are required to elicit the change (induction), followed by an investigation of the mechanism of expression (hours) and maintenance (days). The best-characterized form of NMDA receptor (NMDAR)-dependent LTP occurs between CA3 and CA1 pyramidal neurons of the hippocampus (Fig. 1). Throughout the chapter we will mostly refer to this specific form of LTP. At these CA3-CA1 Schaffer collateral synapses, the loci of both induction and expression are situated in the postsynaptic neuron.Open in a separate windowFigure 1.NMDAR-dependent LTD and LTP in the hippocampus. (A) Historical drawing by Ramon y Cajal (1909) of the trisynaptic pathway in the hippocampus. LTP and LTD are induced by activation of NMDARs at synapses between CA3 and CA1 pyramidal neurons (blue and red). In contrast, LTP at mossy fiber synapses onto CA3 neurons (green on blue) is NMDAR-independent. (B) This electron microscopy image shows the densely packed neuropil in the CA1 region of the hippocampus and highlights two asymmetric CA3-CA1 synapses. Note the typical “bouton en passant” configuration of synapse 1 and the prominent spine in synapse 2. The postsynaptic densities (PSDs) are visible. Scale bar, 200 nm. (Image kindly provided by Rafael Luján, Universitad de Castilla-La Mancha.) (C) Bidirectional change in CA3-CA1 synaptic efficacy by LTD and LTP in the same synapses monitored by extracellular field recordings in an acute slice preparation of the hippocampus. Note the contrasting induction protocols (Data from C Lüscher, unpubl.).     

G protein-coupled receptors control NMDARs and metaplasticity in the hippocampus

Long-term potentiation (LTP) and long-term depression (LTD) are the major forms of functional synaptic plasticity observed at CA1 synapses of the hippocampus. The balance between LTP and LTD or “metaplasticity” is controlled by G-protein coupled receptors (GPCRs) whose signal pathways target the N-methyl-D-asparate (NMDA) subtype of excitatory glutamate receptor. We discuss the protein kinase signal cascades stimulated by Gαq and Gαs coupled GPCRs and describe how control of NMDAR activity shifts the threshold for the induction of LTP.     

GABA and Endocannabinoids Mediate Depotentiation of Schaffer Collateral Synapses Induced by Stimulation of Temperoammonic Inputs

Long-term potentiation (LTP) of Schaffer collateral (SC) synapses in the hippocampus is thought to play a key role in episodic memory formation. Because the hippocampus is a shorter-term, limited capacity storage system, repeated bouts of learning and synaptic plasticity require that SC synapses reset to baseline at some point following LTP. We previously showed that repeated low frequency activation of temperoammonic (TA) inputs to the CA1 region depotentiates SC LTP without persistently altering basal transmission. This heterosynaptic depotentiation involves adenosine A1 receptors but not N-methyl-D-aspartate receptors, metabotropic glutamate receptors or L-type calcium channels. In the present study, we used rat hippocampal slices to explore other messengers contributing to TA-induced SC depotentiation, and provide evidence for the involvement of cannabinoid-1 and γ-aminobutyric acid (GABA) type-A receptors as more proximal signaling events leading to synaptic resetting, with A1 receptor activation serving as a downstream event. Surprisingly, we found that TA-induced SC depotentiation is independent of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate glutamate receptors. We also examined the involvement of mitogen-activated protein kinases (MAPKs), and found a role for extracellular-signal related kinase 1/2 and p38 MAPK, but not c-Jun-N-terminal kinase. These results indicate that low frequency stimulation of TA inputs to CA1 activates a complex signaling network that instructs SC synaptic resetting. The involvement of GABA and endocannabinoids suggest mechanisms that could contribute to cognitive dysfunction associated with substance abuse and neuropsychiatric disorders.     

p21(Cip-1/SDI-1/WAF-1) expression via the mitogen-activated protein kinase signaling pathway in insulin-induced chondrogenic differentiation of ATDC5 cells

The embryonal carcinoma-derived cell line, ATDC5, differentiates into chondrocytes in response to insulin or insulin-like growth factor-I stimulation. In this study, we investigated the roles of mitogen-activated protein (MAP) kinases in insulin-induced chondrogenic differentiation of ATDC5 cells. Insulin-induced accumulation of glycosaminoglycan and expression of chondrogenic differentiation markers, type II collagen, type X collagen, and aggrecan mRNA were inhibited by the MEK1/2 inhibitor (U0126) and the p38 MAP kinase inhibitor (SB203580). Conversely, the JNK inhibitor (SP600125) enhanced the synthesis of glycosaminoglycan and expression of chondrogenic differentiation markers. Insulin-induced phosphorylation of ERK1/2 and JNK but not that of p38 MAP kinase. We have previously clarified that the induction of the cyclin-dependent kinase inhibitor, p21(Cip-1/SDI-1/WAF-1), is essential for chondrogenic differentiation of ATDC5 cells. To assess the relationship between the induction of p21 and MAP kinase activity, we investigated the effect of these inhibitors on insulin-induced p21 expression in ATDC5 cells. Insulin-induced accumulation of p21 mRNA and protein was inhibited by the addition of U0126 and SB203580. In contrast, SP600125 enhanced it. Inhibitory effects of U0126 or stimulatory effects of SP600125 on insulin-induced chondrogenic differentiation were observed when these inhibitors exist in the early phase of differentiation, suggesting that MEK/ERK and JNK act on early phase differentiation. SB202580, however, is necessary not only for early phase but also for late phase differentiation, indicating that p38 MAP kinase stimulates differentiation by acting during the entire period of cultivation. These results for the first time demonstrate that up-regulation of p21 expression by ERK1/2 and p38 MAP kinase is required for chondrogenesis, and that JNK acts as a suppressor of chondrogenesis by down-regulating p21 expression.     

Sphingosine 1-Phosphate Regulates Heat Shock Protein 27 Induction by a p38 MAP Kinase-Dependent Mechanism in Aortic Smooth Muscle Cells

In an aortic smooth muscle cell line, A10 cells, we investigated the effect of sphingosine 1-phosphate on the induction of heat shock protein 27 (HSP27), a low-molecular-weight heat shock protein. Sphingosine 1-phosphate significantly induced the accumulation of HSP27 in a pertussis toxin-sensitive manner. The effect was dose-dependent in the range between 0.1 and 30 microM. Sphingosine 1-phosphate stimulated an increase in the levels of mRNA for HSP27. Sphingosine 1-phosphate stimulated both p42/p44 mitogen-activated protein (MAP) kinase and p38 MAP kinase activation. PD98059, an inhibitor of the upstream kinase that activates p42/p44 MAP kinase, did not affect sphingosine 1-phosphate-stimulated HSP27 induction. In contrast, SB203580, an inhibitor of p38 MAP kinase, reduced sphingosine 1-phosphate-induced HSP27 induction. SB203580 reduced the levels of mRNA for HSP27 induced by sphingosine 1-phosphate. These results indicate that sphingosine 1-phosphate stimulates the induction of HSP27 via p38 MAP kinase activation in aortic smooth muscle cells.     

p38 MAPK Participates in the Mediation of GLT-1 Up-regulation During the Induction of Brain Ischemic Tolerance by Cerebral Ischemic Preconditioning

Our previous study has proved that the up-regulation of glial glutamate transporter 1 (GLT-1) played an important role in the acquisition of brain ischemic tolerance after cerebral ischemic preconditioning (CIP) in rats. However, little is known about the mechanism involved in the up-regulation of GLT-1 in the process. The present study investigates whether p38 MAPK, ERK1/2, and/or JNK participates in the up-regulation of GLT-1 during the induction of brain ischemic tolerance by CIP. It was found that CIP significantly enhanced the expression of p-p38 MAPK without altering p-ERK1/2 and p-JNK expression in the CA1 hippocampus. Inhibition of p38 MAPK function by its selective inhibitor SB203580 or knockdown p38 MAPK expression by its antisense oligodeoxynucleotides (AS-ODNs) suppressed the induction of brain ischemic tolerance. Furthermore, p38 MAPK was activated earlier than the up-regulation of GLT-1 in the CA1 hippocampus after CIP. Meanwhile, the expression of p-p38 MAPK by astrocytes was increased, and p38 MAPK AS-ODNs dose-dependently inhibited the up-regulation of GLT-1 after CIP. Taken together, it could be concluded that p38 MAPK participates in the mediation of GLT-1 up-regulation during the induction of brain ischemic tolerance after CIP.