Tetsu Nagata

A New Amyloid β Variant Favoring Oligomerization in Alzheimer's-Type Dementia

Soluble oligomers of amyloid β (Aβ), rather than amyloid fibrils, have been proposed to initiate synaptic and cognitive dysfunction in Alzheimers disease (AD). However, there is no direct evidence in humans that this mechanism can cause AD. Here, we report a novel amyloid precursor protein (APP) mutation that may provide evidence to address this question.

The linoleic acid derivative DCP-LA selectively activates PKC-ϵ, possibly binding to the phosphatidylserine binding site

This study examined the effect of 8-[2-(2-pentyl-cyclopropylmethyl)-cyclopropyl]-octanoic acid (DCP-LA), a newly synthesized linoleic acid derivative with cyclopropane rings instead of cis-double bonds, on protein kinase C (PKC) activity. In the in situ PKC assay with reverse-phase high-performance liquid chromatography, DCP-LA significantly activated PKC in PC-12 cells in a concentration-dependent (10 nM–100 μM) manner, with the maximal effect at 100 nM, and the DCP-LA effect was blocked by GF109203X, a PKC inhibitor, or a selective inhibitor peptide of the novel PKC isozyme PKC-ϵ. Furthermore, DCP-LA activated PKC in HEK-293 cells that was inhibited by the small, interfering RNA against PKC-ϵ. In the cell-free PKC assay, of the nine isozymes examined here, DCP-LA most strongly activated PKC-ϵ, with >7-fold potency over other PKC isozymes, in the absence of dioleoyl-phosphatidylserine and 1,2-dioleoyl-sn-glycerol; instead, the DCP-LA action was inhibited by dioleoyl-phosphatidylserine. DCP-LA also activated PKC-γ, a conventional PKC, but to a much lesser extent compared with that for PKC-ϵ, by a mechanism distinct from PKC-ϵ activation. Thus, DCP-LA serves as a selective activator of PKC-ϵ, possibly by binding to the phosphatidylserine binding site on PKC-ϵ. These results may provide fresh insight into lipid signaling in PKC activation.

(-)-Epigallocatechin gallate protects against NO stress-induced neuronal damage after ischemia by acting as an anti-oxidant.

The present study investigated the effects of (-)-epigallocatechin gallate (EGCG), which is the major component of polyphenol in green tea, on nitric oxide (NO) stress-induced neuronal damage, by monitoring NO mobilizations in the intact rat hippocampus and assaying the viability of cultured rat hippocampal neurons. A 10-min ischemia increased NO (NO(3)(-)/NO(2)(-)) concentrations in the intact rat hippocampus, while EGCG (50 mg/kg i.p.) inhibited the increase by 77% without affecting hippocampal blood flow. The NO donor, sodium nitroprusside (SNP; 50 microM), produced NO (NO(3)(-)/NO(2)(-)), while EGCG inhibited it in a dose-dependent manner at concentrations ranging from 50 to 200 microM. Treatment with SNP (100 microM) reduced the viability of cultured rat hippocampal neurons to 22% of control levels, while EGCG caused it to recover to 51% for 10 microM, 73% for 20 microM, and 70% for 50 microM. Taken together, it appears that EGCG could protect against ischemic neuronal damage by deoxidizing peroxynitrate/peroxynitrite, which is converted to NO radical or hydroxy radical.

The linoleic acid derivative FR236924 facilitates hippocampal synaptic transmission by enhancing activity of presynaptic α7 acetylcholine receptors on the glutamatergic terminals

The present study aimed at understanding the effect of FR236924, a newly synthesized linoleic acid derivative with cyclopropane rings instead of cis-double bonds, on hippocampal synaptic transmission in both the in vitro and in vivo systems. FR236924 increased the rate of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor-mediated miniature excitatory postsynaptic currents, without affecting the amplitude, triggered by nicotine in CA1 pyramidal neurons of rat hippocampal slices, that is inhibited by GF109203X, a selective protein kinase C (PKC) inhibitor or alpha-bungarotoxin, an inhibitor of alpha7 acetylcholine (ACh) receptors. FR236924 stimulated glutamate release from rat hippocampal slices and in the hippocampus of freely behaving rats, and the effect was also inhibited by GF109203X or alpha-bungarotoxin. FR236924 induced a transient huge potentiation followed by a long-lasting potentiation in the slope of field excitatory postsynaptic potentials recorded from the CA1 region of rat hippocampal slices, and the latter effect was blocked by GF109203X or alpha-bungarotoxin. Likewise, the compound persistently facilitated hippocampal synaptic transmission in the CA1 region of the intact rat hippocampus. It is concluded from these results that FR236924 stimulates glutamate release by functionally targeting presynaptic alpha7 ACh receptors on the glutamatergic terminals under the influence of PKC, responsible for the facilitatory action on hippocampal synaptic transmission. This may provide evidence for a link between cis-unsaturated free fatty acids and presynaptic alpha7 ACh receptors in hippocampal synaptic plasticity.

Modulation of P2X receptors via adrenergic pathways in rat dorsal root ganglion neurons after sciatic nerve injury

Abstract The present study examined noradrenaline‐induced modulation of ATP‐evoked currents in dorsal root ganglion (DRG) neurons after sciatic nerve injury (transection). ATP (10 μM) generated fast/mixed type of whole‐cell membrane currents, possibly as mediated via P2X3/P2X3‐like receptors, and slow type of the currents, possibly as mediated via P2X2/3 receptors, in acutely dissociated L4/5 DRG neurons, without significant difference between sham and injury group. For sham group, noradrenaline (10 μM) enhanced fast/mixed type of ATP‐evoked currents in ipsilateral DRG neurons, that is not inhibited by H‐7, a broad inhibitor of protein kinases, but otherwise it had no effect on slow type of the currents. For injury group, noradrenaline (10 μM) significantly potentiated slow type of ATP‐evoked currents in ipsilateral DRG neurons, that is abolished by H‐7 or GF109203X, a selective inhibitor of protein kinase C (PKC), while it depressed fast/mixed type of the currents. In the analysis of real‐time reverse transcription‐polymerase chain reaction, an increase in the mRNAs for α1b, α2a, α2d, and β2 adrenergic receptors was found with the ipsilateral DRGs after sciatic nerve injury. Collectively, the results of the present study suggest that noradrenaline potentiates P2X2/3 receptor currents by activating PKC via α1 adrenergic receptors linked to Gq protein, perhaps dominantly α1b adrenergic receptors, in DRG neurons after sciatic nerve injury. This may account for a nociceptive pathway in response to noradrenergic sprouting after peripheral nerve injury.

The inhibitory and facilitatory actions of amyloid-β peptides on nicotinic ACh receptors and AMPA receptors

The present study investigated the effects of amyloid-beta peptides on nicotinic ACh receptors (Torpedo, alpha 4 beta 2, and alpha 7 receptors) and AMPA receptors expressed in Xenopus oocytes by monitoring whole-cell membrane currents. Ten-minutes treatment with amyloid-beta(1-42) (1 microM) inhibited Torpedo ACh receptor currents, reaching 53% of original levels 30 min after treatment. Amyloid-beta(1-40) inhibited the currents in a dose-dependent manner (0.1-10 microM) during treatment, gradually reversing after treatment. Amyloid-beta(1-40) and amyloid-beta(1-42) (0.1 microM) depressed alpha 4 beta 2 receptor currents to each 69% and 62% of original levels at 10-min treatment and lesser depression was obtained with alpha 7 receptors. Amyloid-beta(1-42) (0.1 microM) did not significantly inhibit AMPA receptor currents, but amyloid-beta(1-40) (0.1 microM) potentiated the currents to 145-191% of original levels. Amyloid-beta peptides, thus, exert their diverse actions on nicotinic ACh receptors and AMPA receptors, and the inhibitory actions on nicotinic ACh receptors may account for the deterioration of learning and memory in Alzheimers disease.

Interleukin-18 stimulates synaptically released glutamate and enhances postsynaptic AMPA receptor responses in the CA1 region of mouse hippocampal slices.

The present study examined the effects of the proinflammatory cytokine interleukin-18 (IL-18) on mouse hippocampal synaptic transmission. IL-18 (100 ng/ml) significantly increased amplitude and frequency of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor-mediated miniature excitatory postsynaptic currents (AMPA-mEPSCs), that are monitored from CA1 pyramidal neurons of mouse hippocampal slices. IL-18 (100 ng/ml) enhanced slope of basal field excitatory postsynaptic potentials (fEPSPs) that are recorded from the CA1 region of mouse hippocampal slices. There was no significant difference in the expression of Schaffer collateral/CA1 long-term potentiation (LTP) between in the presence and absence of IL-18, although IL-18 tended to inhibit saturation levels of the potentiation induced by tetanic stimulation in a dose-dependent manner at concentrations ranged from 10 ng/ml to 1 microg/ml. Paired-pulse facilitation in the presence of IL-18 (100 ng/ml) was not influenced after tetanic stimulation, while that in the absence of IL-18 was depressed. The results of the present study, thus, suggest that IL-18 stimulates synaptically released glutamate and enhances postsynaptic AMPA receptor responses in CA1 pyramidal neurons of mouse hippocampal slices, thereby facilitating basal hippocampal synaptic transmission without affecting the LTP.

Interleukin-18 regulates motor activity, anxiety and spatial learning without affecting synaptic plasticity.

Expression of Schaffer collateral-CA1 long-term potentiation (LTP) and long-term depression (LTD) was not affected in hippocampal slices from wild-type mice pretreated with lipopolysaccharide (0.25mg/kg, i.p.), to increase interleukin-18 (IL-18) concentrations in the brain. For IL-18 knock-out (IL-18 KO) mice, the LTP was still expressed, the extent being similar to that for wild-type mice. In the open-field test to assess motor activity, rearing activity for IL-18 KO mice was significantly suppressed as compared with that for wild-type mice, without significant difference in the locomotion activity between two groups. In the passive avoidance test to assess fear memory, the retention latency for IL-18 KO mice was much shorter than for wild-type mice, without significant difference in the acquisition latency between two groups. In the water maze test, the acquisition latency for IL-18 KO mice significantly prolonged as compared with that for wild-type mice, without significant difference in the retention latency between two groups. For IL-18 KO mice, intraventricular injection with IL-18 for 4 days (total, 240 fg) prior to water maze task shortened the prolonged acquisition latency, reaching a level similar to that for wild-type mice. The results of the present study, thus, suggest that IL-18 is a critical regulator for exploratory activity, fear memory, and spatial learning.

Dilinoleoylphosphatidylcholine ameliorates scopolamine-induced impairment of spatial learning and memory by targeting α7 nicotinic ACh receptors

AIMS The present study was conducted to understand the role of 1,2-dilynoleoyl-sn-glycero-3-phosphocholine (DLPhtCho) in cognitive functions. MAIN METHODS Two-electrode voltage-clamp was made to Xenopus oocytes expressing rat alpha7 acetylcholine (ACh) receptors. Field excitatory postsynaptic potentials (fEPSPs) were monitored from the CA1 region of rat hippocampal slices. Water maze test was carried out to assess spatial learning and memory for rats. KEY FINDINGS In the oocyte expression system, DLPhtCho at a concentration of 10 microM potentiated ACh-evoked currents to approximately 190% of basal amplitudes 70 min after 10-min treatment. In contrast, 1-stearoyl-2-lynoleoyl-sn-glycero-3-phosphocholine (SLPhtCho), 1-palmitoyl-2-linoleoyl-sn-glycero-3-phosphocholine (PLPhtCho), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPhtCho) had no effect on the currents. DLPhtCho (10 microM) enhanced slope of fEPSPs to about 150% of basal levels at 70-min treatment, that is inhibited by alpha-bungarotoxin, an inhibitor of alpha7 ACh receptors, while no enhancement was obtained with SLPhtCho, PLPhtCho, or POPhtCho. In the water maze test, oral administration with DLPhtCho (5 mg/kg) significantly shortened the prolonged acquisition latency for rats intraperitoneally injected with scopolamine (1 mg/kg). SIGNIFICANCE The results of the present study show that DLPhtCho improves scopolamine-induced learning and memory deficits, possibly by facilitating hippocampal synaptic transmission under the control of alpha7 ACh receptors. DLPhtCho, therefore, could be developed as a beneficial anti-dementia drug.

DCP-LA Stimulates AMPA Receptor Exocytosis Through CaMKII Activation due to PP-1 Inhibition

The linoleic acid derivative 8‐[2‐(2‐pentyl‐cyclopropylmethyl)‐cyclopropyl]‐octanoic acid (DCP‐LA) activated Ca2+/calmodulin‐dependent protein kinase II (CaMKII) by inhibiting protein phosphatase‐1 (PP‐1). DCP‐LA induced a transient huge facilitation of synaptic transmission monitored from the CA1 region of rat hippocampal slices, which was largely inhibited by the CaMKII inhibitor KN‐93. DCP‐LA potentiated kainate‐evoked whole‐cell membrane currents for Xenopus oocytes expressing α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazole propionic acid (AMPA) receptors composed of the GluR1, GluR3, GluR1/GluR2, GluR1/GluR3, and GluR1/GluR2/GluR3 subunits, and the potentiation was significantly inhibited by KN‐93. A similar potentiation was still found with mutant GluR1 (S831A) receptor lacking CaMKII phosphorylation site. The GluR1 and GluR2 subunits formed AMPA receptors in the rat hippocampus, and DCP‐LA increased expression of both the subunits on the plasma membrane. The DCP‐LA action was blocked by KN‐93 and the exocytosis inhibitor botulinum toxin type A, but not by the endocytosis inhibitor phenylarsine oxide. DCP‐LA, thus, appears to activate CaMKII through PP‐1 inhibition, that stimulates AMPA receptor exocytosis to increase expression of the receptors on the plasma membrane, responsible for potentiate AMPA receptor responses and facilitation of hippocampal synaptic transmission. J. Cell. Physiol. 221: 183–188, 2009.