2-Pyrrolidinone induces a long-lasting facilitation of hippocampal synaptic transmission by enhancing α7 ACh receptor responses via a PKC pathway

Cognitive dysfunction in diabetic rats is prevented by pyridoxamine treatment. A multidisciplinary investigation

OBJECTIVE

The impact of diabetes mellitus on the central nervous system is less widely studied than in the peripheral nervous system, but there is increasing evidence that it elevates the risk of developing cognitive deficits. The aim of this study was to characterize the impact of experimental diabetes on the proteome and metabolome of the hippocampus. We tested the hypothesis that the vitamin B6 isoform pyridoxamine is protective against functional and molecular changes in diabetes.

METHODS

We tested recognition memory using the novel object recognition (NOR) test in streptozotocin (STZ)-induced diabetic, age-matched control, and pyridoxamine- or insulin-treated diabetic male Wistar rats. Comprehensive untargeted metabolomic and proteomic analyses, using gas chromatography-mass spectrometry and iTRAQ-enabled protein quantitation respectively, were utilized to characterize the molecular changes in the hippocampus in diabetes.

RESULTS

We demonstrated diabetes-specific, long-term (but not short-term) recognition memory impairment and that this deficit was prevented by insulin or pyridoxamine treatment. Metabolomic analysis showed diabetes-associated changes in 13/82 identified metabolites including polyol pathway intermediates glucose (9.2-fold), fructose (4.9-fold) and sorbitol (5.2-fold). We identified and quantified 4807 hippocampal proteins; 806 were significantly altered in diabetes. Pathway analysis revealed significant alterations in cytoskeletal components associated with synaptic plasticity, glutamatergic signaling, oxidative stress, DNA damage and FXR/RXR activation pathways in the diabetic rat hippocampus.

CONCLUSIONS

Our data indicate a protective effect of pyridoxamine against diabetes-induced cognitive deficits, and our comprehensive 'omics datasets provide insight into the pathogenesis of cognitive dysfunction enabling development of further mechanistic and therapeutic studies.

Simvastatin Enhances Activity and Trafficking of α7 Nicotinic Acetylcholine Receptor in Hippocampal Neurons Through PKC and CaMKII Signaling Pathways

Simvastatin (SV) enhances glutamate release and synaptic plasticity in hippocampal CA1 region upon activation of α7 nicotinic acetylcholine receptor (α7nAChR). In this study, we examined the effects of SV on the functional activity of α7nAChR on CA1 pyramidal cells using patch-clamp recording and explored the underlying mechanisms. We found that the treatment of hippocampal slices with SV for 2 h induced a dose-dependent increase in the amplitude of ACh-evoked inward currents (I_ACh) and the level of α7nAChR protein on the cell membrane without change in the level of α7nAChR phosphorylation. These SV-induced phenotypes were suppressed by addition of farnesol (FOH) that converts farnesyl pyrophosphate, but not geranylgeraniol. Similarly, the farnesyl transferase inhibitor FTI277 was able to increase the amplitude of I_ACh and enhance the trafficking of α7nAChR. The treatment with SV enhanced phosphorylation of CaMKII and PKC. The SV-enhanced phosphorylation of CaMKII rather than PKC was blocked by FOH, Src inhibitor PP2 or NMDA receptor antagonist MK801 and mimicked by FTI. The SV-enhanced phosphorylation of PKC was sensitive to the IP3R antagonist 2-APB. The SV-increased amplitude of I_ACh was suppressed by PKC inhibitor GF109203X and Go6983, or CaMKII inhibitor KN93. The SV- and FTI-enhanced trafficking of α7nAChR was sensitive to KN93, but not GF109203X or Go6983. The PKC activator PMA increased α7nAChR activity, but had no effect on trafficking of α7nAChR. Collectively, these results indicate that acute treatment with SV enhances the activity and trafficking of α7nAChR by increasing PKC phosphorylation and reducing farnesyl-pyrophosphate to trigger NMDA receptor-mediated CaMKII activation.

Dilinoleoylphosphatidylcholine ameliorates scopolamine-induced impairment of spatial learning and memory by targeting alpha7 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.

Hormone effects on specific and global brain functions

The first demonstration of how biochemical changes in neurons in specific parts of the brain direct a complete mammalian behavior derived from the effects of estrogens in hypothalamic neurons that facilitate lordosis behavior, the primary reproductive behavior of female quadrupeds (Pfaff. Estrogens and Brain Function. 1980; Pfaff. Drive: Neurobiological and Molecular Mechanisms of Sexual Motivation. 1999). Sex behaviors depend on sexual arousal that in turn depends on a primitive function: generalized CNS arousal (Pfaff. Brain Arousal and Information Theory. 2006). Here we summarize one of the ways in which a generalized arousal transmitter, norepinephrine, can influence the electrical excitability of ventromedial hypothalamic cells in a way that will foster female sex behavior.

PROBLEMS OF POSITIVE LIST SYSTEM REVEALED BY SURVEY OF PESTICIDE RESIDUE IN FOOD

The positive list system became effective from May 29, 2006 to improve the regulation of residual agricultural chemicals (pesticides, feed additives and veterinary drugs) in foods. In accordance with the system, we investigated pesticide residues in 50 agricultural products purchased in Morioka city from March to November 2006. Analyses were performed according to the "Multiresidue Method for Agricultural Chemicals by GC/MS", the Notice of the Ministry of Health, Labour and Welfare. Five pesticides and two non-agricultural chemicals were detected from 16 samples. Ortho-phenylphenol (OPP) was detected from 8 samples: immature pea, snap bean, kiwi, plain-boiled bamboo shoot, mango, white asparagus, lemon and domestic shiitake mushroom. Maximum residue limits (MRLs) have not been established for these products, and they exceeded the uniform level of 0.01 ppm. DDT was detected from Philippines banana (0.30 ppm) and Korean paprika (0.45 ppm). The residual level in Philippines banana was lower than the MRL, but Korean paprika exceeded its MRL. Chlorpyrifos, Thiabendazole and Imazaril were detected from citrus imported from the U.S.A., but their residue levels were lower than the respective MRLs. Aniline and 2-pyrrolidone were detected from several imported products. These two may not be regulated by the positive list system because they are not agricultural chemicals, although their derivatives are used as pesticides or veterinary drugs. Three problems have been revealed from this survey: 1) application of the uniform level to minor agricultural products, 2) residues of non-agricultural chemicals whose toxicity is uncertain, 3) metabolites of agricultural chemicals, which are also regulated by the positive list system, have not been clearly defined.

Beneficial effect of intracellular free high-mannose oligosaccharides on cryopreservation of mammalian cells and proteins

The cryoprotective effect of intracellular free high-mannose oligosaccharides (HMOS) on mammalian cells and proteins was examined by monitoring PC-12 cell viability and assaying protein kinase C (PKC)-epsilon activity. 1-Deoxymannojirimycin, an inhibitor of alpha-mannosidase, to cause an increase in intracellular free HMOS, significantly rescued PC-12 cells with 2-h freezing insult at -15 degrees C in a concentration (1-50mM)- and pretreatment time (48-72h)-dependent manner, as compared with unpretreated cells; full rescue from freezing injury was obtained with 1-deoxymannojirimycin at more than 25mM for 48-h pretreatment and more than 3mM for 72- and 96-h pretreatment. For PC-12 cells pretreated with 1-deoxymannojirimycin at 1mM for 72h, thawed cell viability after more than 8-w cryopreservation at -80 degrees C in 10% (v/v) dimethyl sulfoxide was much higher than that for cells without pretreatment. PKC-epsilon activity was well preserved after 16-h cryopreservation at -20 degrees C in the presence of mannose 9-N-acetylglucosamine 2 (Man9-GlcNAc2) (1 mM), an HMOS, while the activity was reduced to 15% without Man9-GlcNAc2. Collectively, the results of the present study suggest that intracellular free HMOS is a key molecule to protect mammalian cells and proteins from freezing injury; in other words, HMOS could be a new target for cryopreservation of mammalian cells and proteins.

The linoleic acid derivative DCP-LA selectively activates PKC-ɛ, 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 microM) 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-epsilon. Furthermore, DCP-LA activated PKC in HEK-293 cells that was inhibited by the small, interfering RNA against PKC-epsilon. In the cell-free PKC assay, of the nine isozymes examined here, DCP-LA most strongly activated PKC-epsilon, 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-gamma, a conventional PKC, but to a much lesser extent compared with that for PKC-epsilon, by a mechanism distinct from PKC-epsilon activation. Thus, DCP-LA serves as a selective activator of PKC-epsilon, possibly by binding to the phosphatidylserine binding site on PKC-epsilon. These results may provide fresh insight into lipid signaling in PKC activation.

Dilinoleoyl-phosphatidylethanolamine from Hericium erinaceum protects against ER stress-dependent Neuro2a cell death via protein kinase C pathway

In many types of neurodegeneration, neuronal cell death is induced by endoplasmic reticulum (ER) stress. Hence, natural products able to reduce ER stress are candidates for use in the attenuation of neuronal cell death and, hence, in the reduction of the damage, which occurs in neurodegenerative disease. In this study, we investigated ER stress-reducing natural products from an edible mushroom, Hericium erinaceum. As a result of screening by cell viability assay on the protein glycosylation inhibitor tunicamycin-induced (i.e., ER stress-dependent) cell death, we found that dilinoleoyl-phosphatidylethanolamine (DLPE) was one of the molecules effective at reducing ER stress-dependent cell death in the mouse neuroblastoma cell line Neuro2a cells. A purified DLPE, commercially available, also exhibited a reducing effect on this ER stress-dependent cell death. Therefore, we concluded that DLPE has potential as a protective molecule in ER stress-induced cell death. From the structure of DLPE, it was hypothesized that it might activate protein kinase C (PKC). The activity of PKC-epsilon, a novel-type PKC, was increased by adding DLPE, and PKC-gamma, a conventional-type PKC, was activated on the coaddition of diolein and DLPE, as shown by in vitro enzyme activity analysis. The protecting activity of DLPE was attenuated in the presence of a PKC inhibitor GF109203X but not completely diminished. Therefore, DLPE can protect neuronal cells from ER stress-induced cell death, at least in part by the PKC pathway.

Effects of cis-unsaturated free fatty acids on PKC-ε activation and nicotinic ACh receptor responses

Linoleic acid (C18:2omega6) (10 microM) depressed ACh-evoked whole-cell membrane currents followed by potentiation of the currents in Xenopus oocytes expressing Torpedo ACh receptors. The potentiation was never obtained with linoleoylamide (10 microM), which contains CONH2 instead of COOH on linoleic acid. In the assay of protein kinase C (PKC) using a reversed phase high-performance liquid chromatography, linoleic acid activated PKC-epsilon but linoleoylamide otherwise had no effect on it. Of a variety of cis-unsaturated free fatty acids with 20 hydrocarbon chains (C20), 8-eicosenoic acid (C20:1omega12) potentiated ACh receptor channel currents without depression. 11,14-Eicosadienoic acid (C20:2omega6), 5,8,11-eicosatrienoic acid (C20:3omega9), 5,8,11,14-eicosatetraenoic acid (arachidonic acid) (C20:4omega6), and 5,8,11,14,17-eicosapentaenoic acid (C20:5omega3) depressed and potentiated the currents. In contrast, only a depression was obtained with 5-eicosenoic acid (C20:1omega15), 11-eicosenoic acid (C20:1omega9), and 8,11,14-eicosatrienoic acid (C20:3omega6). All the free fatty acids (C20) involved PKC-epsilon activation, with no significant difference in the potency among them. Taken together, it appears that carboxyl on cis-unsaturated free fatty acids plays a significant role in PKC-epsilon activation and potentiation of nicotinic ACh receptor responses. The role of the number and position of the cis-double bonds in the receptor responses, however, remains an open question.