Amyloid beta proteins inhibit Cl(-)-ATPase activity in cultured rat hippocampal neurons

[Amyloid β hypothesis in Alzheimer's disease and Cl--ATPase-Neuronal cell death via PI4KIIα inhibition and recovery agents]

In the brains of patients with Alzheimer's disease, a decrease in phosphatidylinositol phosphate (PIP) requiring Cl^--ATPase activity was found. In cultured rat hippocampal neurons, pathophysiological concentrations of amyloid β proteins (Aβs≤10 nM) lowered PIP levels and Cl^--ATPase activity with an increase in intracellular Cl^- concentrations, resulting in Cl^--dependent enhancements in glutamate neurotoxicity and, ultimately, neuronal cell death. Pathophysiological concentrations of Aβs(0.1-10 nM) directly lowered phosphatidylinositol-4-kinase. Non-toxic peptide fragments of Aβ, such as Ile-Gly-Leu, recovered Aβ-induced inhibition of recombinant human phosphatidylinositol-4-kinase IIα (PI4KIIα) and the intrahippocampally administered Aβ-induced degeneration of hippocampal neurons and impairment of spatial memory in mice. Agents with the potential to block these neurotoxic mechanisms of Aβ were summarized herein as (1) Aβ antagonists, (2) substrates of PI4K, (3) PI4K product, (4) PI4K activators, and (5) GABAc receptor stimulants.

Distinction between mild cognitive impairment and Alzheimer's disease by CSF amyloid β40 and β42, and protein-conjugated acrolein

BACKGROUND

We found previously that the amyloid β40/42 (Aβ40/42) ratio and the level of protein-conjugated acrolein (PC-Acro) in plasma were increased in mild cognitive impairment (MCI) and Alzheimer's disease (AD) subjects. We determined whether MCI and AD subjects can be differentiated based on the levels of Aβ40, Aβ42, and PC-Acro in cerebrospinal fluid (CSF).

METHODS

Aβ40, Aβ42, PC-Acro, Tau and phosphorylated Tau in CSF were measured by ELISA.

RESULTS

Median values of Aβ40, Aβ40/PC-Acro and Aβ40/42 in CSF were significantly lower in 54 AD subjects than those in 40 MCI subjects. Severity of VOI (volume of interest) atrophy was most intensely correlated with the decrease in Aβ40/PC-Acro and then that in Aβ40 and Aβ42/PC-Acro. MMSE was most intensely correlated with the decrease in Aβ42 and Aβ40, and then that in Aβ42/PC-Acro and Aβ40/PC-Acro.

CONCLUSION

A decrease in Aβ40/PC-Acro in CSF is well correlated with brain damage, and a decrease in Aβ42 and Aβ40 is well correlated with cognitive ability. Measurement of PC-Acro together with Aβ40 and Aβ42 provides a more precise evaluation of severity of AD subjects.

Comparable attenuation of Abeta(25-35)-induced neurotoxicity by quercitrin and 17beta-estradiol in cultured rat hippocampal neurons

In the present work, potential protective effects of quercitrin (a phytoestrogen) on Abeta-induced neurotoxicity in cultured rat hippocampal neurons were investigated in comparison with 17beta-estradiol. Cell viability, oxidative status, and antioxidative potentials were used as comparative parameters. Co-exposure of cultured neurons to Abeta(25-35) with either quercitrin or 17beta-estradiol (50-100 microM) for 72 h attenuated Abeta(25-35)-induced neurotoxicity and lipid peroxidation, but not Abeta(25-35)-induced ROS accumulation. However, only 17beta-estradiol counteracted a reduction in glutathione content and only quercitrin counteracted a reduction in glutathione peroxidase activity. Both compounds displayed no effects on superoxide dismutase activity. A specific estrogen receptor antagonist, ICI 182780, did not abolish neuroprotective effects of quercitrin and 17beta-estradiol. These findings suggested that quercitrin and 17beta-estradiol attenuated Abeta(25-35)-induced neurotoxicity in a comparable manner. Underlying neuroprotective mechanisms of both compounds were probably not related to estrogen receptor-mediated genomic mechanisms but might involve with their antioxidant and free radical scavenging properties.

N type rapid inactivation in human Kv1.4 channels: functional role of a putative C-terminal helix

Voltage gated potassium channels are tetrameric membrane proteins, which have a central role in cellular excitability. Human Kv1.4 channels open on membrane depolarization and inactivate rapidly by a 'ball and chain' mechanism whose molecular determinants have been mapped to the cytoplasmic N terminus of the channel. Here we show that the other terminal end of the channel also plays a role in channel inactivation. Swapping the C-terminal residues of hKv1.4 with those from two non-inactivating channels (hKv1.1 and hKv1.2) affects the rates of inactivation, as well as the recovery of the channel from the inactivated state. Secondary structure predictions of the hKv1.4 sequence reveal a helical structure at its distal C-terminal. Complete removal or partial disruption of this helical region results in channels with remarkably slowed inactivation kinetics. The ionic selectivity and voltage-dependence of channel opening were similar to hKv1.4, indicative of an unperturbed channel pore. These results demonstrate that fast inactivation is modulated by structural elements in the C-terminus, suggesting that the process involves the concerted action of the N- and C-termini.

Depolarization recruits DCC to the plasma membrane of embryonic cortical neurons and enhances axon extension in response to netrin-1

The netrin-1 receptor Deleted in Colorectal Cancer (DCC) is required for the formation of major axonal projections by embryonic cortical neurons, including the corpus callosum, hippocampal commissure, and cortico-thalamic tracts. The presentation of DCC by axonal growth cones is tightly regulated, but the mechanisms regulating DCC trafficking within neurons are not well understood. Here, we investigated the mechanisms regulating DCC recruitment to the plasma membrane of embryonic cortical neurons. In embryonic spinal commissural neurons, protein kinase A (PKA) activation recruits DCC to the plasma membrane and enhances axon chemoattraction to netrin-1. We demonstrate that PKA activation similarly recruits DCC and increases embryonic cortical neuron axon extension, which, like spinal commissural neurons, respond to netrin-1 as a chemoattractant. We then determined if depolarization might recruit DCC to the plasma membrane. Neither netrin-1 induced axon extension, nor levels of plasma membrane DCC, were altered by depolarizing embryonic spinal commissural neurons with elevated levels of KCl. In contrast, depolarizing embryonic cortical neurons increased the amount of plasma membrane DCC, including at the growth cone, and increased axon outgrowth evoked by netrin-1. Inhibition of PKA, phosphatidylinositol-3-kinase, protein kinase C, or exocytosis blocked the depolarization-induced recruitment of DCC and suppressed axon outgrowth. Inhibiting protein synthesis did not affect DCC recruitment, nor were the distributions of trkB or neural cell adhesion molecule (NCAM) influenced by depolarization, consistent with selective mobilization of DCC. These findings identify a role for membrane depolarization modulating the response of axons to netrin-1 by regulating DCC recruitment to the plasma membrane.

Protective effects of Aβ-derived tripeptide, Aβ32–34, on Aβ1–42-induced phosphatidylinositol 4-kinase inhibition and neurotoxicity

We previously reported that the neurotoxicity of pathophysiological concentrations of amyloid beta proteins (Abetas, 0.1-10nM) as assessed by the inhibition of type II phosphatidylinositol 4-kinase (PI4KII) activity and the enhancement of glutamate toxicity was blocked by a short fragment of Abeta, Abeta(31-35). Such protective effects of shorter fragments derived from Abeta(31-35) were examined in this study to reach the shortest effective peptide, using recombinant human PI4KII and primary cultured rat hippocampal neurons. Among the peptides tested (Abeta(31-34), Abeta(31-33), Abeta(31-32), Abeta(32-35), Abeta(33-35), Abeta(34-35), Abeta(32-34), Abeta(33-34) and Abeta(32-33)), Abeta(31-34), Abeta(32-35) and Abeta(32-34) blocked both the Abeta(1-42)-induced inhibition of PI4KII activity and enhancement of glutamate toxicity on cell viability. The shortest peptide among them, Abeta(32-34), showed a dose-dependent protective effect with 50% effective concentration near 1nM, while Abeta(34-32), with a reverse amino acid sequence for Abeta(32-34), showed no protective effects. Thus, a tripeptide, Abeta(32-34) i.e. Ile-Gly-Leu, may be available as a lead compound for designing effective Abeta antagonists.

Soybean-derived phosphatidylinositol inhibits in vivo low concentrations of amyloid beta protein-induced degeneration of hippocampal neurons in V337M human tau-expressing mice

In our previous reports using primary cultured rat hippocampal neurons, pathophysiological concentrations (< or =10 nM) of amyloid beta proteins (Abetas) showed neurotoxicity via a phosphatidylinositol metabolism disorder, and soybean-derived phosphatidylinositol protected the neurons against the Abeta's neurotoxicity. In the present study, such a neurotoxic effect of Abeta and a neuroprotective effect of phosphatidylinositol were examined in vivo using transgenic mice expressing V337 M human tau. Intrahippocampal CA1 injection of 1.5 mul of 100 nM or 1 microM Abeta25-35 increased the number of degenerating neurons with an apoptotic feature in bilateral hippocampal CA1, CA2, CA3 and dentate gyrus regions in 1 month, demonstrating an in vivo neurotoxic effect of Abeta at lower concentrations after diffusion. Intrahippocampal co-injection or intracerebroventricular administration of 1.5 microl of 500 nM phosphatidylinositol prevented the Abeta25-35-induced neuronal degeneration in all the hippocampal regions, while co-injection of another acidic phospholipid, phosphatidylserine (1.5 microl, 500 nM) with Abeta25-35 showed no protective effects. Thus, exogenously applied phosphatidylinositol appeared to minimize the toxic effects of Abeta in vivo. These results suggest that soybean-derived phosphatidylinositol may be effective in the treatment of Alzheimer's disease.

Down-regulation of Cl- pump ClP55 subunit induced enhancement of glutamate neurotoxicity in cultured rat hippocampal neurons

To test whether the increased intracellular Cl- concentration ([Cl-]i) is responsible for the enhanced glutamate toxicity, antisense oligonucleotide of ClP55, a Cl- -ATPase/pump associated protein, was transfected in cultured rat hippocampal neurons. Neuronal [Cl-]i in the antisense oligonucleotide-transfected culture increased to a level 3- to 4-fold higher than that in control. Glutamate exposure (10 microM, 10 min) increased neuronal apoptosis and decreased Akt-pS473 level in the antisense oligonucleotide-transfected neurons, but not in control or sense oligonucleotide-transfected ones, suggesting the responsibility of elevated [Cl-]i in the enhancement of glutamate neurotoxicity.

Chloride-dependency of amyloid β protein-induced enhancement of glutamate neurotoxicity in cultured rat hippocampal neurons

In our previous studies, pathophysiological concentrations of amyloid-beta (Abeta) proteins increased intracellular Cl(-) concentration ([Cl(-)]i) and enhanced glutamate neurotoxicity in primary cultured neurons, suggesting Cl(-)-dependent changes in glutamate signaling. To test this possibility, we examined the effects of isethionate-replaced low Cl(-) medium on the Abeta-induced enhancement of glutamate neurotoxicity in the primary cultured rat hippocampal neurons. In a normal Cl(-) (135 mM) medium, treatment with 10 nM Abeta25-35 for 2 days increased neuronal [Cl(-)]i to a level three times higher than that of control as assayed using a Cl(-)-sensitive fluorescent dye, while in a low Cl(-) (16 mM) medium such an Abeta25-35-induced increase in [Cl(-)]i was not observed. The Abeta treatment aggravated glutamate neurotoxicity in a normal Cl(-) medium as measured by mitochondrial reducing activity and lactate dehydrogenase (LDH) release, while in a low Cl(-) medium the Abeta treatment did not enhance glutamate toxicity. Upon such Abeta plus glutamate treatment under a normal Cl(-) condition, activated anti-apoptotic molecule Akt (Akt-pS473) level monitored by Western blot significantly decreased to 74% of control. Under a low Cl(-) condition, a resting Akt-pS473 level was higher than that under a normal Cl(-) condition and did not significantly change upon Abeta plus glutamate treatment. Tyrosine phosphorylation levels of 110 and 60 kDa proteins (pp110 and pp60) increased upon Abeta plus glutamate treatment under a normal Cl(-), but not low Cl(-), condition. These findings indicated that Abeta-induced enhancement of glutamate neurotoxicity is Cl(-)-dependent. Chloride-sensitive Akt pathway and tyrosine phosphorylation of proteins (pp110 and pp60) may be involved in this process.

Attenuation of amyloid β (Aβ)-induced inhibition of phosphatidylinositol 4-kinase activity by Aβ fragments, Aβ20–29 and Aβ31–35

We previously reported that pathophysiological concentrations of amyloid beta protein (Abeta25-35, 0.1-10 nM) directly inhibited type II phosphatidylinositol 4-kinase (PI4KII) activity in neuronal plasma membranes, which resulted in the enhanced glutamate neurotoxicity. In the present study, we examined the effects of Abeta fragments, Abeta20-29 and Abeta31-35, on the 10 nM Abeta25-35- or Abeta1-42-induced inhibition of PI4KII activity. Both of the peptide fragments recovered the inhibition of rat brain plasma membrane PI4KII activity over the concentration range of 0.1-5 nM. Such protection by the Abeta fragments was observed in the 10 nM Abeta25-35-induced inhibition of recombinant human PI4KII, suggesting that these Abeta fragments blocked the inhibition on PI4KII molecule. The Abeta25-35-induced enhancement of glutamate neurotoxicity was also completely inhibited in the presence of these fragments. Thus, Abeta20-29 and Abeta31-35 ameliorated the Abeta-enhanced glutamate neurotoxicity probably through attenuation of Abeta-induced inhibition of PI4KII activity.

Anxiolytic agent, dihydrohonokiol-B, recovers amyloid β protein-induced neurotoxicity in cultured rat hippocampal neurons

The effects of anxiolytic honokiol derivative, dihydrohonokiol-B (DHH-B), on amyloid beta protein (Abeta(25-35), 10 nM)-induced changes in Cl(-)-ATPase activity, intracellular Cl- concentration ([Cl-]i) and glutamate neurotoxicity were examined in cultured rat hippocampal neurons. DHH-B (10 ng/ml) recovered Abeta-induced decrease in neuronal Cl(-)-ATPase activity without any changes in the activities of Na+/K+-ATPase and anion-insensitive Mg2+-ATPase. A GABA(C) receptor antagonist (1,2,5,6,-tetrahydropyridin-4-yl) methyl-phosphinic acid (TPMPA, 15 microM), inhibited the protective effects of DHH-B on Cl(-)-ATPase activity. DHH-B reduced Abeta-induced elevation of [Cl-]i as assayed using a Cl(-)-sensitive fluorescent dye, and prevented Abeta-induced aggravation of glutamate neurotoxicity. These data suggest that DHH-B exerts the neuroprotective action against Abeta through GABA(C) receptor stimulation.

Pathophysiological concentrations of amyloid beta proteins directly inhibit rat brain and recombinant human type II phosphatidylinositol 4-kinase activity

We previously found that pathophysiological concentrations (< or = 10 nm) of an amyloid beta protein (Abeta25-35) reduced the plasma membrane phosphatidylinositol monophosphate level in cultured rat hippocampal neurons with a decrease in phosphatidylinositol 4-monophosphate-dependent Cl- -ATPase activity. As this suggested an inhibitory effect of Abeta25-35 on plasma membrane phosphatidylinositol 4-kinase (PI4K) activity, in vitro effects of Abetas on PI4K activity was examined using rat brain subcellular fractions and recombinant human type II PI4K (PI4KII). Abeta25-35 (10 nm) inhibited PI4KII activity, but neither PI 3-kinase (PI3K) nor type III PI4K (PI4KIII) activity, in microsomal fractions, while 100 nm Abeta25-35 inhibited PI3K activity in mitochondrial fractions. In plasma membrane-rich fractions, Abetas (> 0.5 nm) dose-dependently inhibited PI4KII activity, the maximal inhibition to 77-87% of control being reached around 10 nm of Abetas without significant changes in apparent Km values for ATP and PI, suggesting non-competitive inhibition by Abetas. The inhibition by 10 nm Abeta25-35 was reversible. In recombinant human PI4KIIalpha, inhibition profiles of Abetas were similar to those in rat brain plasma membranes. Therefore, pathophysiological concentrations of Abetas directly and reversibly inhibited plasma membrane PI4KII activity, suggesting that plasma membrane PI4KII is a target of Abetas in the pathogenesis of Alzheimer's disease.

Non-steroidal anti-inflammatory drugs protect amyloid beta protein-induced increase in the intracellular Cl- concentration in cultured rat hippocampal neurons

Long-term use of non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen reportedly decrease a risk for the progression of Alzheimer's disease (AD), whose mechanisms are still controversial. We previously reported that pathophysiological concentrations (1-10 nM) of amyloid beta proteins (Abetas) increased intracellular Cl- concentration ([Cl-]i) and aggravated glutamate neurotoxicity in the rat brain neuronal culture. In this study, we examined the effects of therapeutic concentrations of ibuprofen and other drugs with cyclo-oxygenase (COX)-1 and/or COX-2 inhibiting activities on 10 nM Abeta25-35-induced changes in cultured rat hippocampal neurons. Ibuprofen (10-100 microM) dose-dependently inhibited the Abeta25-35-induced increase in [Cl-]i in pyramidal cell-like neurons. Not only ibuprofen, aspirin (100 microM), indomethacin (50 microM), and selective COX-1 or COX-2 inhibitor (10 nM ketrolac or 2 microM NS398) also blocked the Abeta-induced increase in neuronal [Cl-]i, though such effects of COX-2 preferring drugs were limited in aggregated Abeta-induced changes. Further, ibuprofen as well as selective COX-1 or COX-2 inhibitor reduced Abeta-induced aggravation of glutamate toxicity as assessed by cell viability. These findings suggest that NSAIDs protect neurons from Abeta-induced degeneration via inhibition of neuronal COX-1 as well as COX-2.

Amyloid β(1–42) and its β(25–35) fragment induce activation and membrane translocation of cytosolic phospholipase A2 in bovine retina capillary pericytes

We investigated changes in cytosolic phospholipase A(2) (cPLA(2)) and calcium-independent PLA(2) (iPLA(2)) activities in bovine retina capillary pericytes after stimulation with 50 microM amyloid-beta (Abeta) (1-42) and its (25-35) fragment, over 24 h (mild, sublethal model of cell damage). In the presence of Abeta peptides, we found that cPLA(2) activity was increased and translocated from the cytosolic fraction to the membrane system, particularly in the nuclear region. Reversed-sequence Abeta(35-25) peptide did not stimulate or induce cPLA(2) translocation. Exposure to both Abeta peptides had no significant effect on cPLA(2) protein content as tested by Western immunoblot analysis. The addition of Abetas to quiescent pericytes was followed by phosphorylation of cPLA(2) and arachidonic acid release. Treatment with inhibitors (AACOCF(3), staurosporine and cycloheximide) resulted in a sharp decrease in basal and stimulated cPLA(2) activity. Inactivating effects of bromoenol lactone (BEL), inhibitor of iPLA(2), demonstrated that the stimulation of total PLA(2) activity by Abetas was mediated by both PLA(2) enzymes. Taken together with our previous observations that both Abeta peptides may induce hydrolysis of phosphatidylcholine, the present results provide evidence that this process is cooperatively mediated by cPLA(2) activation/translocation and iPLA(2) activation. The effect is very likely triggered by a mild prooxidant mechanism which was not able to divert the cell to degeneration. The data confirm the hypothesis that pericytes could be a target of potential vascular damage and reactivity during processes involving amyloid accumulation.

Assemblages of prion fragments: novel model systems for understanding amyloid toxicity

We report the conformational and toxic properties of two novel fibril-forming prion amyloid sequences, GAVVGGLG (PrP(119-126)) and VVGGLGG (PrP(121-127)). The conformational preferences of these fragments were studied in differing microenvironments of TFE/water mixtures and SDS solution. Interestingly, with an increase in TFE concentration, PrP(119-126) showed a helical conformational propensity, whereas PrP(121-127) adopted a more random coil structure. In 5% SDS, PrP(119-126) showed more alpha-helical content than in TFE solution, and PrP(121-127) exhibited a predominantly random coil conformation. However, both peptides took a random coil conformation in water, and over time the random coil transformed into a beta-sheet structure with a significant percentage of helical conformation and beta-turn structure in PrP(119-126) and PrP(121-127), respectively, as observed with CD spectroscopy. The aged fibrils of PrP(119-126) were insoluble in SDS, and PrP(121-127) was extractable with SDS solution. These fibrils were characterized by transmission electron microscopy. Both PrP(119-126) and PrP(121-127) formed stable monolayer's consisting of multimeric assemblages at the air-water interface. Monomeric PrP(119-126) was more toxic to astrocytes than the control Abeta peptide; however, the fibrillar form of PrP(119-126) was less toxic to astrocytes. PrP(121-127) elicited moderate toxicity in both soluble and fibrillar forms on astrocytes. Furthermore, quenching experiments using acroyl-labeled PrP(119-126) and PrP(121-127) with eosin-labeled synaptosomal membrane revealed that these prion fragments bind to anion-exchange protein. The binding of PrP(119-126) and PrP(121-127) with a membrane microdomain (lipid raft) was also analyzed using pyrenated derivatives. We conclude that the formation of PrP(119-126) and PrP(121-127) fibrils is a concentration-dependent process that involves coil to sheet conversion with aging. PrP(119-126), the sequence with intrinsic helical propensity, is more toxic in monomer form, and the fibril formation in this case seems to be protective to cells. For PrP(121-127), the SDS-soluble fibrils are more cytotoxic, indicating that a higher order assemblage structure is required for cytotoxic activity of this peptide.

Single cell RT-PCR demonstrates differential expression of GABAC receptor rho subunits in rat hippocampal pyramidal and granule cells

Although gamma-aminobutyric acid (GABA)C receptor rho1, rho2 and rho3 subunits are reportedly expressed in pyramidal and granule cells in the hippocampus at various developmental stages, it is not clear whether these three rho subunits are coexpressed in a single neuron. To attempt to answer this question, we performed single-cell RT-PCR for rho subunits from neurons of rat brain hippocampus. In hippocampal cultures, pyramidal cells were positive for rho1 mRNA expression in 89%, rho2 in 94% and rho3 in 94%, while granule cells were positive for rho1 mRNA in only 6%, rho2 in 36% and rho3 in 91%. Intensive amplification of the RT-PCR products by the second PCR revealed that all the three rho subunits were coexpressed in a single pyramidal and granule cells from both of the cultures and the slices. These results suggest that all the three GABAC receptor rho1, rho2 and rho3 subunits are present probably in different compositions in pyramidal and granule cells in the rat hippocampus.

Soybean-derived phosphatidylinositol recovers amyloid beta protein-induced neurotoxicity in cultured rat hippocampal neurons

Effects of soybean-derived phosphatidylinositol (PI) on amyloid beta protein (10 nM Abeta(25-35))-induced changes in Cl(-)-ATPase activity, intracellular Cl- concentration ([Cl-]i) and glutamate neurotoxicity were examined using cultured rat hippocampal neurons. Soybean-derived PI (> or =5 nM) dose-dependently recovered Abeta-induced decrease in neuronal Cl(-)-ATPase activity without any changes in the activities of Na+,K(+)-ATPase and anion-insensitive Mg(2+)-ATPase. Soybean-derived PI reduced Abeta-induced elevation of [Cl-](i) as assayed using a Cl(-)-sensitive fluorescent dye, and prevented Abeta-induced aggravation of glutamate neurotoxicity assayed by mitochondrial 2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, monosodium salt reducing activity and plasma membrane lactate dehydrogenase release. These data suggest that soybean-derived PI may be useful as a therapeutic and/or preventive strategy for Alzheimer's disease.

[Ionic mechanisms underlying the regulation of cell proliferation, differentiation and death]

Ion channels and transporters act as major components that regulate membrane excitability in neurons, muscles, and some secretory glands, but may also contribute to the regulation of proliferation, differentiation, and death in a greater variety of cells including non-excitable ones. The molecular basis of ionic mechanisms underlying the later regulation has been partly identified in the last several years and is a hot issue now. In this short review, some of the molecular mechanisms underlying these regulations and novel compounds acting on the mechanisms were introduced as exciting topics in this area. Several types of transient receptor potential (TRP), identified as Ca(2+)-permeable, non-selective cation channels, may play obligatory roles in functional complexes, which regulate multiple signal transduction pathways triggering proliferation, differentiation, or death of many cell types. In addition, the relation between Cl(-) pump activity and the induction of beta-amyloid protein toxicity for neuronal cell death in Alzheimer disease was described. Unique functions of H(+) channel and pump in osteoclasts in bone mineral homeostasis and remodeling were also discussed. Finally, topics about activation of specific types of Cl(-) channels and K(+) channels, which are responsible for the induction of apoptosis or proliferation in several types of cells, were introduced.

Disulfonic stilbenes prevent beta-amyloid (25-35) neuronal toxicity in rat cortical cultures

Anion exchange proteins were recently identified among some of the proteins found clustered together in the hallmark plaques and tangles of Alzheimer's patient's brains. Anion exchange proteins underlie chloride/bicarbonate exchange, cell shape regulation and participate in removal of aged cells by the immune system. In this study we compared the neuroprotective efficacy of an anion exchanger inhibitor, 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), against beta-amyloid((25-35)) neurotoxicity, staurosporine-induced apoptosis and glutamate-induced necrosis in primary cortical cultures. We demonstrate potent neuroprotective efficacy with DIDS against beta-amyloid((25-35)) and staurosporine, but not against glutamate. Our results suggest that anion exchange proteins may play an important role in beta-amyloid toxicity and that DIDS may represent a viable therapeutic agent for Alzheimer's disease.

Phosphatidylinositol and PI-4-monophosphate recover amyloid beta protein-induced inhibition of Cl- -ATPase activity

The neuronal Cl- -ATPase/pump is a candidate for an outwardly directed active Cl- transport system, which requires phosphatidylinositol-4-monophosphate (PI4P) for its optimal activity. We previously reported that low concentrations (1-10 nM) of amyloid beta proteins (Abetas, Abeta1-42, Abeta25-35), the neurotoxic peptides in Alzheimer's disease, reduced Cl- -ATPase activity in cultured rat hippocampal neurons without any changes in the activities of Na+/K+-ATPase or anion-insensitive Mg(2+)-ATPase, and decreased PI, PIP, and PIP2 levels in neuronal plasma membranes (Journal of Neurochemistry 2001, 78, 569-579). In this study, we examined the effects of exogenously applied PI and PI4P on the Abeta25-35-induced changes in Cl- -ATPase activity, the intracellular concentration of Cl- ([Cl- ]i), and glutamate neurotoxicity using primary cultured rat hippocampal neurons. The Abeta decreased Cl- -ATPase activity to 47% of control and increased [Cl- ]i in hippocampal pyramidal cell-like neurons to a level 3 times higher than the control. The addition of PI (50-750 nM) or PI4P (50-150 nM) dose-dependently blocked the inhibitory effects of Abeta on Cl- -ATPase activity. High doses of PI (750 nM) and PI4P (100-150 nM) reduced Na+/K+-ATPase activity to 41% and 35% of control, respectively, but this inhibition was attenuated by the co-application of phosphatidylserine (PS, 1 micro M). PI or PI4P (75 nM each) reversed the Abeta-induced increase in [Cl-]i. In the Abeta-exposed culture, stimulation by glutamate (10 micro M, 10 min) resulted in an increase in DNA fragmentation and decreases in cell viability. Addition of PI or PI4P prevented the Abeta-induced aggravation of glutamate neurotoxicity. Thus, PI and PI4P were demonstrated to prevent Abeta-induced decreases in Cl- -ATPase activity and increases in neuronal [Cl- ]i in parallel with the attenuation of Abeta-induced aggravation of glutamate neurotoxicity.

Protective effects of estradiol against amyloid beta protein-induced inhibition of neuronal Cl(-)-ATPase activity

Low concentrations of amyloid beta proteins (Abetas, 1-10 nM) were recently demonstrated to reduce Cl(-)-ATPase activity in parallel with an increase in the intracellular Cl(-) concentration ([Cl(-)]i) and decreases in plasma membrane phosphorylated phosphatidylinositol (PIP and PIP2) levels in cultured rat hippocampal neurons. In this study, 17 beta-estradiol (estradiol) at a therapeutic concentration (1.8 nM) for Alzheimer's disease was found to block these Abeta (Abeta25-35)-induced changes. This protective effect of estradiol on Cl(-)-ATPase activity was antagonized by a pure estrogen receptor antagonist, ICI182780 and inhibitors for cyclic GMP-dependent protein kinase (PKG) (KT5823), Ca(2+)-calmodulin-dependent protein kinase II (CaMKII) (KN62) and phosphatidylinositol (PI) 4-kinase (wortmannin and quercetin). Estradiol recovered Abeta-induced decreases in plasma membrane phosphoinositide (PIP and PIP2) levels, this effect being inhibited by KT5823 and KN62. Glutamate toxicity was augmented in neurons with elevated [Cl(-)]i either by Abeta-treatment or carbachol+KCl+LiCl-treatment. The increased glutamate toxicity in the Abeta-treated neurons was attenuated by estradiol. Thus, a therapeutic concentration of estradiol protected Abeta-treated neurons against inhibition of Cl(-)-ATPase activity and an increase in [Cl(-)]i through its receptor, probably via PKG- and CaMKII(-)mediated recovery of PI4P formation. Elevated [Cl(-)]i may be related to enhancement of glutamate toxicity.

Presenilin-1 mutations alter K+ currents in the human neuroblastoma cell line, SH-SY5Y

Mutations in presenilin 1 (PS1) are the major cause of autosomal dominant Alzheimer's disease. We have measured the voltage-gated K+ current in the human neuroblastoma cell line SH-SY5Y using whole-cell patch-clamp. When cells were stably transfected to over-express PS1, no change in K+ current was observed. However, over-expression of a deletion mutation (deltaE9) in PS1 led to a decreased K+ current. These changes were channel specific since no change in the Na+ current could be observed in the same cells. Confocal microscopy revealed that the K(V)3.1 K+ channel subunit had a diminished plasma membrane distribution when the deltaE9 over-expressing cells were compared to control cells. Intracellular retention of Kv3.1 is consistent with the notion that PS1 can modulate the activity and trafficking of ion channels in central neurones and implicates a compromise in electrical signalling as an underlying factor in the pathogenesis of familial Alzheimer's disease.