PTEN, Akt, and GSK3beta signalling in rat primary cortical neuronal cultures following tumor necrosis factor-alpha and trans-4-hydroxy-2-nonenal treatments

PTEN is a dual phosphatase that negatively regulates the phosphatidylinositol 3-kinase (PI3K)/Akt signalling pathway important for cell survival. We determined effects of the inflammation and oxidative stresses of tumor necrosis factor-alpha (TNFalpha) and trans-4-hydroxy-2-nonenal (HNE), respectively, on PTEN, Akt, and GSK3beta signalling in rat primary cortical neurons. The inhibitors bisperoxovanadium [bpV(Pic)] and LY294002 were also used to determine PTEN and PI3K involvement in TNFalpha and HNE modulation of neuronal cell death. PTEN inhibition with bpV(Pic) alone did not affect Ser(473)Akt or Ser(9)GSK3beta phosphorylation. Instead, effects of this inhibitor were manifest when it was used together with TNFalpha and to a lesser extent with HNE. TNFalpha together with PTEN inhibition increased phosphorylation of Ser(473)Akt and Ser(9)GSK3beta. TNFalpha and HNE both gave decreased numbers of viable and increased numbers of early apoptotic neurons. PTEN inhibition partially reversed the toxic effect of TNFalpha as shown by an increased number of viable and a decreased number of early apoptotic neurons. All effects were reversed by PI3K inhibition. HNE together with inhibition of PTEN gave increased Ser(473)Akt but not Ser(9)GSK3beta phosphorylation and no effects on the number of viable or early apoptotic cells. In conclusion, PTEN inhibition gives a mild reversal of TNFalpha- but not HNE-induced cell death via the PI3K pathway.

Involvement of glutaredoxin-1 and thioredoxin-1 in beta-amyloid toxicity and Alzheimer's disease

Strong evidence indicates oxidative stress in the pathogenesis of Alzheimer's disease (AD). Amyloid beta (Abeta) has been implicated in both oxidative stress mechanisms and in neuronal apoptosis. Glutaredoxin-1 (GRX1) and thioredoxin-1 (TRX1) are antioxidants that can inhibit apoptosis signal-regulating kinase (ASK1). We examined levels of GRX1 and TRX1 in AD brain as well as their effects on Abeta neurotoxicity. We show an increase in GRX1 and a decrease in neuronal TRX1 in AD brains. Using SH-SY5Y cells, we demonstrate that Abeta causes an oxidation of both GRX1 and TRX1, and nuclear export of Daxx, a protein downstream of ASK1. Abeta toxicity was inhibited by insulin-like growth factor-I (IGF-I) and by overexpressing GRX1 or TRX1. Thus, Abeta neurotoxicity might be mediated by oxidation of GRX1 or TRX1 and subsequent activation of the ASK1 cascade. Deregulation of GRX1 and TRX1 antioxidant systems could be important events in AD pathogenesis.

Flow cytometry as a method for studying effects of stressors on primary rat neurons

The mechanisms associated with cell death have been an important focus for neurobiology research. In the present study, the methodology of flow cytometry was used to optimize quantification of the toxic effects of tumor necrosis factor-alpha (TNF-alpha), trans-4-hydroxy-2-nonenal (4-HNE), and aged amyloid-beta (Abeta1-42) on rat primary cortical neurons. The fluorescent dyes annexin V-FITC and propidium iodide (PI) were used to identify populations of viable, early apoptotic, necrotic and late apoptotic cells by flow cytometry. Prior to exposure, the primary cultures showed 83% cell viability. Flow cytometry following labeling of cells with a specific neuronal marker, TUJ-1, revealed 82% pure neuronal populations, whereas approximately 7% were astrocytic as shown by glial fibrillary acidic protein positivity. Exposure of primary cultures to TNF-alpha, 4-HNE, and aged Abeta1-42 gave an increased number of early apoptotic cells. We show that flow cytometry is a suitable method for quantifying effects of different stressors on neurons in primary cultures. This technique could be useful for screening and testing of pharmacological compounds relevant to neurodegenerative disorders.

Distribution of presenilin 1 and 2 and their relation to Notch receptors and ligands in human embryonic/foetal central nervous system

Notch signaling in vertebrates is mediated by four Notch receptors (Notch-1, -2, -3, and -4) that are activated by interacting with at least five different Notch ligands, Jagged-1, Jagged-2, Delta-1, -2, and -3. Recent studies have shown that the gamma-secretase-like intramembranous cleavage of Notch receptors to release their cytoplasmic signaling domains requires the presenilin (PS) proteins 1 and 2 (PS1 and PS2). Here, we used immunohistochemistry to compare the distribution of all four Notch receptor proteins and three ligands in the context of co-localization with PS1 and PS2 in first trimester human central nervous system (CNS). In addition, we investigated Notch receptors and ligands expression by Western blotting. The study was performed on the forebrain and spinal cord of human embryonic/foetal CNS (5-11 gestational weeks). Results showed a divergent distribution of the different Notch receptor proteins with only Notch-1 being co-localized with PS1 and PS2. Notch-2 was only seen occasionally within the developing cortex and spinal cord. Notch-3 expression was restricted to neuroepithelial cells of the spinal cord and endothelial cells in blood vessels of both developing cerebral cortex and spinal cord. The weak, punctate staining of Notch-4 in the neuroepithelium of the spinal cord could not be confirmed with Western blotting. Neither Notch-2, nor -3 showed overlap with either PS1 or PS2 immunoreactivity. The ligand Jagged-1 was found sporadically in the neuroepithelial cell layer in cerebral cortex of the earlier stages of development and of the spinal cord during the first trimester while Jagged-2 was not detected. Jagged-1 and Jagged-2 immunoreactivities were not found in the 9-11-week cortex. No co-distribution of Jagged-1 and PS1 or PS2 was found. Delta-1 ligand expression was detected in neuroepithelial cells of the ventricular zone of the cerebral cortex, and also in maturating neurons in the cortical plate and ventral horns of the developing spinal cord. The presence of Notch-1, Delta-1 and Jagged-1 in the neuroepithelium of developing CNS indicates that Notch signaling in proliferating human progenitor cells only involves these two receptor ligands and that cleavage of Notch-1 is mediated both by PS1 and PS2. The strong immunoreactivity of Notch-1, Delta-1 and PS1 in the cortical plate and in maturating neurons of the spinal cord also suggests that these proteins may regulate the maturation processes of post-mitotic neurons. The pronounced PS1 immunoreactivity in neurites in the hindbrain and spinal cord without detectable expression of any Notch receptor or ligand suggests that a possible role for PS1 in neurite growth involves either gamma-secretase-mediated cleavage of other substrates or gamma-secretase-independent mechanisms.

Apolipoprotein E and β-amyloid (1-42) regulation of glycogen synthase kinase-3β

Glycogen synthase kinase-3beta (GSK-3beta) is implicated in regulating apoptosis and tau protein hyperphosphorylation in Alzheimer's disease (AD). We investigated the effects of two key AD molecules, namely apoE (E3 and E4 isoforms) and beta-amyloid (Abeta) 1-42 on GSK-3beta and its major upstream regulators, intracellular calcium and protein kinases C and B (PKC and PKB) in human SH-SY5Y neuroblastoma cells. ApoE3 induced a mild, transient, Ca2+-independent and early activation of GSK-3beta. ApoE4 effects were biphasic, with an early strong GSK-3beta activation that was partially dependent on extracellular Ca2+, followed by a GSK-3beta inactivation. ApoE4 also activated PKC-alpha and PKB possibly giving the subsequent GSK-3beta inhibition. Abeta(1-42) effects were also biphasic with a strong activation dependent partially on extracellular Ca2+ followed by an inactivation. Abeta(1-42) induced an early and potent activation of PKC-alpha and a late decrease of PKB activity. ApoE4 and Abeta(1-42) were more toxic than apoE3 as shown by MTT reduction assays and generation of activated caspase-3. ApoE4 and Abeta(1-42)-induced early activation of GSK-3beta could lead to apoptosis and tau hyperphosphorylation. A late inhibition of GSK-3beta through activation of upstream kinases likely compensates the effects of apoE4 and Abeta(1-42) on GSK-3beta, the unbalanced regulation of which may contribute to AD pathology.

Ca(2+) stores and capacitative Ca(2+) entry in human neuroblastoma (SH-SY5Y) cells expressing a familial Alzheimer's disease presenilin-1 mutation

Presenilins are involved in the proteolytic production of Alzheimer's amyloid peptides, but are also known to regulate Ca(2+) homeostasis in various cells types. In the present study, we examined intracellular Ca(2+) stores coupled to muscarinic receptors and capacitative Ca(2+) entry (CCE) in the human neuroblastoma SH-SY5Y cell line, and how these were modulated by over-expression of either wild-type presenilin 1 (PS1wt) or a mutant form of presenilin 1 (PS1 deltaE9) which predisposes to early-onset Alzheimer's disease. Ca(2+) stores discharged by application of 100 microM muscarine (in Ca(2+)-free perfusate) in PS1wt and PS1 DeltaE9 cells were significantly larger than those in control cells, as determined using Fura-2 microfluorimetry. Subsequent CCE, observed in the absence of muscarine when Ca(2+) was re-admitted to the perfusate, was unaffected in PS1wt cells, but significantly suppressed in PS1 deltaE9 cells. However, when Ca(2+) stores were fully depleted with thapsigargin, CCE was similar in all three cell groups. Western blots confirmed increased levels of PS1 in the transfected cells, but also demonstrated that the proportion of intact PS1 in the PS1 deltaE9 cells was far greater than in the other two cell groups. This study represents the first report of modulation of both Ca(2+) stores and CCE in a human, neurone-derived cell line, and indicates a distinct effect of the PS1 mutation deltaE9 over wild-type PS1.

Loss of stimulatory effect of guanosine triphosphate on [(35)S]GTPgammaS binding correlates with Alzheimer's disease neurofibrillary pathology in entorhinal cortex and CA1 hippocampal subfield

Heterotrimeric guanosine triphosphate (GTP)-binding proteins (G-proteins) couple many different cell surface receptor types to intracellular effector mechanisms. Uncoupling between receptors and G-proteins and between G-proteins and adenylyl cyclase (AC) and phospholipase C (PLC) has been described for Alzheimer's disease (AD) brain. However, there is little information on whether altered G-protein signaling in AD is just an end-stage phenomenon or is important for the progression of disease pathology. Here we used [(35)S]GTPgammaS autoradiography to study G-protein distribution in sections of entorhinal cortex and hippocampus from 23 cases staged for neurofibrillary changes and amyloid deposits according to Braak and Braak (Acta Neuropathol. [1991] 82:239-259). We also studied the effects of GTP, which has been found to increase [(35)S]GTPgammaS binding in an Mg(2+)-dependent manner. Results show that the ability of GTP (3 microM) to stimulate [(35)S]GTPgammaS binding declined significantly with staging for neurofibrillary changes in the entorhinal cortex (P < 0.05, ANOVA) and CA1 subfield of the hippocampus (P < 0.05, ANOVA). No significant changes were seen for [(35)S]GTPgammaS binding in the absence of GTP. Our results suggest a decrease in G-protein GTP hydrolysis, which correlates with the progression of AD neurofibrillary changes, in the regions most affected by this pathology. These alterations appear to occur prior to stages corresponding to clinical disease and could lead to an impaired regulation of several signaling systems in AD brain.

Receptor-G-protein signalling in Alzheimer's disease

Based on radioligand binding studies, it has long been assumed that the neurochemical pathology of Alzheimer's disease (AD) does not involve widespread changes in post-synaptic neurotransmitter function. However, more recent studies suggest that receptor function in AD may be compromised due to disrupted post-receptor signal transduction, in particular that mediated by the G-protein regulated phosphoinositide hydrolysis and adenylate cyclase (AC) pathways. The phosphoinositide hydrolysis pathway has been shown to be altered at a number of levels in AD post-mortem brains, including impaired agonist and G-protein regulation of phospholipase C, decreased protein kinase C (PKC) levels and activity, and a reduced number of receptor sites for the second messenger, Ins(1,4,5)P3. Of these, loss of Ins(1,4,5)P3 receptors and PKC in the entorhinal cortex and hippocampus correlates with AD-related neurofibrillary changes, as staged according to Braak's protocol. Disregulation of the phosphoinositide hydrolysis pathway may therefore have consequences for the progression of AD pathology. In contrast to the extensive pattern of disruption seen with the phosphoinositide hydrolysis pathway, changes to AC signalling in AD appear more circumscribed. Disruptions include a lesion at the level of Gs-protein stimulation of AC and, at least in the hippocampus, reduced enzyme activities in response to forskolin stimulation. Of these, the latter change has been shown to precede neurofibrillary changes. Apart from a loss of calcium/calmodulin sensitive AC isoforms, other components of this signalling pathway, including G-protein levels, Gi-protein mediated inhibition and protein kinase A levels and activity, remain relatively preserved in the disorder.

Dysfunctional intracellular calcium homoeostasis: a central cause of neurodegeneration in Alzheimer's disease

The clinical symptoms of all forms of Alzheimer's disease (AD) result from a slowly progressive neurodegeneration that is associated with the excessive deposition of beta-amyloid (A beta) in plaques and in the cerebrovasculature, and the formation of intraneuronal neurofibrillary tangles, which are composed primarily of abnormally hyperphosphorylated tau protein. The sequence of cellular events that cause this pathology and neurodegeneration is unknown. It is, however, most probably linked to neuronal signal transduction systems that become misregulated in the brains of certain individuals, causing excessive A beta to be formed and/or deposited, tau to become aggregated and hyperphosphorylated and neurons to degenerate. We hypothesize that a progressive alteration in the ability of neurons to regulate intracellular calcium, particularly at the level of the endoplasmic reticulum, is a crucial signal transduction event that is linked strongly to the initiation and development of AD pathology. In this chapter we will discuss the key findings that lend support to this hypothesis.

Regulation of apolipoprotein E secretion in rat primary hippocampal astrocyte cultures

Apolipoprotein E isoforms may have differential effects on a number of pathological processes underlying Alzheimer's disease. Recent studies suggest that the amount, rather than the type, of apolipoprotein E may also be an important determinant for Alzheimer's disease. Therefore, understanding the regulated synthesis of apolipoprotein E is important for determining its role in Alzheimer's disease. We show here that in rat primary hippocampal astrocyte cultures, dibutyryl-cAMP increased apolipoprotein E secretion with time in a dose-dependent manner (to 177% at 48 h) and that retinoic acid potentiated this effect (to 298% at 48 h). Dibutyryl-cAMP also gave a rapid, albeit transient, increase of apolipoprotein E mRNA expression (to 200% at 1 h). In contrast, the protein kinase C activator phorbol 12-myristate 13-acetate decreased both apolipoprotein E secretion (to 59% at 48 h) and mRNA expression (to 22% at 1 h). Phorbol 12-myristate 13-acetate also reversed the effects of dibutyryl-cAMP. Apolipoprotein E secretion was also modulated by receptor agonists for the adenylyl cyclase/cAMP pathway. Isoproterenol (50 nM, a beta-adrenoceptor agonist) enhanced, while clonidine (250 nM, an alpha2-adrenoceptor agonist) decreased, secreted apolipoprotein E. We also analysed the effects of agonists for the phospholipase C/protein kinase C pathway. Arterenol (1 microM, an alpha1-adrenoceptor agonist) and serotonin (2.5 microM) enhanced, whereas carbachol (10 microM, an acetylcholine muscarinic receptor agonist) decreased secreted apolipoprotein E. The effects of these non-selective receptor agonists were modest, probably due to effects on different signalling pathways. Arterenol also potentiated the isoproterenol-mediated increase. We also show that phorbol 12-myristate 13-acetate and dibutyryl-cAMP have opposite effects on nerve growth factor, as compared to apolipoprotein E, secretion, suggesting that the results obtained were unlikely to be due to a general effect on protein synthesis. We conclude that astrocyte apolipoprotein E production can be regulated by factors that affect cAMP intracellular concentration or activate protein kinase C. Alterations in these signalling pathways in Alzheimer's disease brain may have consequences for apolipoprotein E secretion in this disorder.

Akt activity in presenilin 1 wild-type and mutation transfected human SH-SY5Y neuroblastoma cells after serum deprivation and high glucose stress

The majority of early-onset familial Alzheimer disease cases are caused by mutations in the genes encoding presenilin 1 (PS1) and presenilin 2 (PS2). Presenilin mutations have been hypothesised to cause Alzheimer disease either by altering amyloid precursor protein metabolism or by increasing the vulnerability of neurons to undergo death by apoptosis. We showed previously that PS1 exon 9 deletion (PS1 DeltaE9) and L250S mutations predispose SH-SY5Y neuroblastoma cells to high glucose stress-induced apoptosis and that the anti-apoptotic effect of insulin-like growth factor I (IGF-I) is compromised by these mutations. The present study investigates whether the susceptibility of PS1 mutation transfected SH-SY5Y cells to undergo apoptosis is likely due to a downregulation of Akt/protein kinase B (Akt), a key intermediate in the phosphatidylinositol 3 (PI3)-kinase arm of the IGF-I signaling pathway. We used two methods to determine the regulation of Akt in response to the pro-apoptotic stimuli of serum deprivation and high glucose stress, as well as treatment with IGF-I. We also looked at the phosphorylatiom state of GSK-3beta at Ser9. Using a kinase assay with immunoprecipitated Akt, we detected an increased Akt activity in PS1 L250S cells at 1 hr after the combination of 20 mM glucose plus 10 nM IGF-I, when compared to the other cell types. This effect, however, was transient in that no mutation related differences were seen at either 6- or 24-hr post-treatment. Immunoblotting for Phospho-Akt as a ratio of total Akt, as well as for GSK-3beta phosphorylated at Ser9 revealed no apparent between cell type and treatment differences. This data strongly indicates that PS1 wt and mutant cells show no major differences in the pattern of Akt regulation after exposure to the pro-apoptotic stimuli of either serum deprivation or high glucose stress, or treatment with IGF-I. It is suggested that another component of IGF-I signaling is likely disrupted in these cells to increase their vulnerability to undergo death by apoptosis.

Caspase cleavage of exon 9 deleted presenilin-1 is an early event in apoptosis induced by calcium ionophore A 23187 in SH-SY5Y neuroblastoma cells

Presenilins (PSs) are mutated in a majority of familial Alzheimer disease (FAD) cases. Mutated PSs may cause FAD by a number of pro-apoptotic mechanisms, or by regulating gamma-secretase activity, a protease involved in beta-amyloid precursor protein processing to the neurotoxic beta-amyloid peptide. Besides their normal endoproteolytic processing, PSs are substrates for caspases, being cleaved to alternative N-terminal and C-terminal fragments. So far little is known about the role of PSs cleavage in the apoptotic machinery. Here, we used SH-SY5Y neuroblastoma cells stably transfected with wild-type or exon 9 deleted presenilin 1 (PS1) in a time-course study after the exposure to the calcium ionophore A23187. During and after exposure to A 23187, intracellular calcium levels were higher in exon 9 deleted PS1 cells as compared with non-transfected and wild-type PS1 transfected cells. Cell death and the enrichment of apoptotic cells after A23187 exposure were increased by overexpression of exon 9 deleted PS1 as compared with the control cell lines. Wild-type PS1 cells were compared with exon 9 deleted PS1 cells and the temporal relationship between PS1 and other caspase substrates cleavages was analyzed. Exon 9 deleted PS1 cells exhibited a higher caspase-3 activation and a greater cleavage of PS1 and poly(ADP-ribose) polymerase (PARP) compared with wild-type PS1 cells. Exon 9 deleted PS1 cleavage occurred earlier than other caspase substrate cleavages (i.e., PARP and gelsolin), simultaneous with minimum detectable caspase-3 activation. Therefore, alternative cleavage of PS1 may play an important role for the regulation of the proteolytic cascade activated during apoptosis.

Apolipoprotein E isoform-specific disruption of phosphoinositide hydrolysis: protection by estrogen and glutathione

The mechanism(s) by which the E4 isoform of apolipoprotein E (apoE4) influences Alzheimer's disease (AD) are not fully known. We report that apoE4, but not apoE3, disrupts carbachol-stimulated phosphoinositide (PI) hydrolysis in SH-SY5Y neuroblastoma cells. Carbachol responses were also disrupted by beta-amyloid (Abeta) (1-42) and apoE4/Abeta(1-42) complexes, but not by apoE3/Abeta(1-42). Glutathione and estrogen protected against apoE4 and Abeta(1-42) effects, as well as those of H(2)O(2). Estrogen protection was partially blocked by wortmannin, suggesting the involvement of phosphatidylinositol 3-kinase. An apoE4-induced disruption of acetylcholine muscarinic receptor-mediated signalling may explain the lower effectiveness of cholinergic replacement treatments in apoE4 AD patients. Also, the beneficial effect of estrogen in AD may be partially due to its ability to protect against apoE4- and Abeta(1-42)-mediated disruption of PI hydrolysis.

Apolipoprotein E: a major piece in the Alzheimer's disease puzzle

Alzheimer's disease (AD) is a complex neurodegenerative disorder with multiple etiologies. The presence of the E4 isoform of apolipoprotein E (apoE) has been shown to increase the risk and to decrease the age of onset for AD and is the major susceptibility factor known for the disease. ApoE4 has been shown to intensify all the biochemical disturbances characteristic of AD, including beta amyloid (Abeta) deposition, tangle formation, neuronal cell death, oxidative stress, synaptic plasticity and dysfunctions of lipid homeostasis and cholinergic signalling. In contrast, other apoE isoforms are protective. Here we review and discuss these major hypotheses of the apoE4-AD association.

Expression of presenilin-1 and Notch-1 receptor in human embryonic CNS

In vitro studies have shown that the Alzheimer's disease-related presenilin-1 protein can mediate Notch-1 receptor cleavage during signalling. In the present study, we compared the distribution of presenilin-1 and Notch-1 receptor immunoreactivities in human embryonic CNS tissue during the first trimester of development. Our aim was to gain insight into whether these proteins are likely to interact functionally during human fetal brain development. CNS material was obtained from routine abortions, cryosectioned and studied by means of immunohistochemistry with antibodies to presenilin-1 and Notch-1. At very early stages of embryonic development (four to five gestational weeks) intensive presenilin-1 immunoreactivity could be seen predominantly in neurites in the ventral horn of the spinal cord, where it overlapped with 200-kDa neurofilament immunoreactivity. Presenilin-1 immunoreactivity was also seen in neuroblasts of the ventricular zone of the tel- and mesencephalon, as well as of the brainstem. Notch-1 receptor appeared in neuronal and ependymal cells throughout the CNS. Seven- to eight-week CNS tissue showed similar patterns of presenilin-1 and Notch-1 receptor expression in the spinal cord and cerebral cortex as was seen at five weeks. Both proteins were localised in the neuroepithelial cell layer lining the ventricles, as well as in the cortical plate layer, where immunoreactivity was seen in the cell bodies. In addition, presenilin-1 immunoreactivity was seen in thin neurites in the subplate of the developing cortex. At 10 weeks, presenilin-1 immunoreactivity was reduced in the spinal cord. These results show that, although presenilin-1 and Notch-1 receptor are localised to the same differentiating cell populations in the human cerebral cortex, making a direct interaction possible, these proteins are otherwise confined to different neurons or neuronal compartments, suggesting a role for presenilin-1 during early CNS differentiation that does not involve Notch-1 receptor processing. Double staining for presenilin-1 in the endoplasmic reticulum and presenilin-1 in the Golgi showed overlap to some extent in investigated CNS regions, but not in neurites. This suggests that presenilin-1 function during neurogenesis is not exclusively correlated to protein processing within the endoplasmic reticulum and Golgi, but that presenilin-1 may also be involved in other processes, such as axonal and dendritic outgrowth or synaptic formation. In summary, our findings provide supportive evidence that the presenilin-1 protein is involved in the development and maturation of the human fetal CNS. The presence of presenilin-1 immunoreactivity in both the cell bodies and neurites of developing neurons strongly suggests divergent mechanisms of function for presenilin-1 during human brain development. These may include interactions with any of the Notch receptor proteins, as well as Notch-independent mechanisms.

Effects of apolipoprotein E (apoE) isoforms, beta-amyloid (Abeta) and apoE/Abeta complexes on protein kinase C-alpha (PKC-alpha) translocation and amyloid precursor protein (APP) processing in human SH-SY5Y neuroblastoma cells and fibroblasts

We investigated the effects of different apolipoprotein E (apoE) isoforms, Abeta (1-42), and apoE/Abeta complexes on PKC-alpha translocation and APP processing in human SH-SY5Y neuroblastoma cells and fibroblasts. Treatment of cells with either 10 nM apoE3 or apoE4, 10 microM Abeta (1-42), or apoE/Abeta complexes induced significant translocation of PKC-alpha in both cell types. Effects were seen using both human recombinant apoE and apoE loaded into beta-very low density lipoprotein (beta-VLDL) particles. Time course (5-24 h) studies of APP processing revealed that some conditions induced transient or moderate increases in the secretion of proteins detected by 22C11. In contrast, the secretion of alpha-secretase cleaved APP was either not modified or transiently decreased, as determined by immunoblotting with the antibody 6E10. These results suggest that apoE, Abeta (1-42) and apoE/Abeta complexes can modulate PKC activity but do not have major consequences for APP processing. These effects could contribute to the reported PKC alterations seen in AD. However, it is unlikely that the contribution of different apoE isoforms to AD pathology occurs via effects on APP processing.

Beta-VLDL protects against A beta(1-42) and apoE toxicity in human SH-SY5Y neuroblastoma cells

The toxic effects of beta-amyloid (A beta) (1-42), apolipoprotein E (apoE) isoforms, and apoE/A beta complexes were studied in human SH-SY5Y neuroblastoma cells and fibroblasts using MTT reduction. In SH-SY5Y cells, A beta(1-42) gave time-dependent toxicity over 2-48 h, which was reduced by co-incubation with rabbit beta-very low density lipoproteins (beta-VLDL). Human recombinant apoE3 and E4 isoforms were also toxic by themselves and also potentiated A beta effects when used alone, but not when associated with beta-VLDL. None of the treatments were toxic to human fibroblasts. These results suggest that beta-VLDL has a protective role on A beta-induced neurotoxicity and that the status of apoE or the conformation of lipoprotein containing apoE particles may be important for determining the contribution of apoE to neurodegeneration.

Alzheimer's disease presenilin-1 exon 9 deletion and L250S mutations sensitize SH-SY5Y neuroblastoma cells to hyperosmotic stress-induced apoptosis

Mutations in the presenilin-1 (PS1) and presenilin-2 (PS2) genes account for the majority of early-onset familial Alzheimer's disease cases. Recent studies suggest that presenilin gene mutations predispose cells to apoptosis by mechanisms involving altered calcium homeostasis and oxidative damage. In the present study, we determined whether PS1 mutations also sensitize cells to hyperosmotic stress-induced apoptosis. For this, we established SH-SY5Y neuroblastoma cell lines stably transfected with wild-type PS1 or either the PS1 exon 9 deletion (deltaE9) or PS1 L250S mutants. Cultured cells were exposed to an overnight (17 h) serum deprivation, followed by a 30 min treatment with either 20 mM glucose, 10 nM insulin-like growth factor-1 or 20 mM glucose + 10 nM insulin-like growth factor-1. Cells were then cultured for a further 3, 6 or 24 h and stained for apoptotic condensed nuclei using propidium iodide. Confirmation that cells were undergoing an active apoptotic process was achieved by labelling of DNA strand breaks using the terminal dUTP nick end labelling (TUNEL) technique. We also determined cell viability using 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction. Propidium iodide staining revealed that all cell lines and controls showed an increased number of apoptotic cells appearing with condensed nuclei at 24 h compared with 6 h and 3 h. High glucose-induced hyperosmotic stress resulted in significantly more apoptotic cells in the PS1 deltaE9 and PS1 L250S mutation cell lines at 24 h, compared with the wild-type PS1 lines (P < 0.001, ANOVA for both comparisons). Mean values (+/-S.D.) for the percentage number of apoptotic cells at 24 h following high glucose treatment were 16.1 +/- 3.5%, 26.7 +/- 5.5% and 31.0 +/- 5.7% for the wild-type PS1, PS1 deltaE9 and PS1 L250S lines, respectively. The pro-apoptotic effects of high glucose treatment were reversed by 10 nM insulin-like growth factor-1, although to a lesser extent in the mutation cell lines (5.8 +/- 2.4%, 15.2 +/- 7.3% and 13.2 +/- 2.0% for the wild-type PS1, PS1 deltaE9 (P < 0.01 for comparison with wild-type PS1) and PS1 L250S (P < 0.01 for comparison with wild-type PS1) transfected lines, respectively. TUNEL labelling of cells at 24 h following treatment gave essentially the same results pattern as obtained using propidium iodide. The percentage number of apoptotic cells with DNA strand breaks (means +/- S.D.) following high glucose treatment was 15.4 +/- 2.6% for the wild-type PS1, 26.8 +/- 3.2% for the PS1 deltaE9 (P < 0.001 for comparison with wild-type PS1) and 29.7 +/- 6.1% for the PS1 L250S transfected lines (P < 0.001 for comparison with wild-type PS1). The PS1 deltaE9 and PS1 L250S transfected lines also showed a higher number of apoptotic cells with DNA strand breaks at 24 h following high glucose plus insulin-like growth factor-1 treatment (11.4 +/- 2.0% and 14.3 +/- 2.8%, respectively), compared with values for the wild-type PS1 lines (8.5 +/- 2.4%). These differences were significant (P < 0.01) for the comparison of wild-type PS1 and PS1 L250S, but not PS1 deltaE9 lines. The mutation-related increases in number of apoptotic cells at 24 h following high glucose treatment were not accompanied by significant differences in cell viability at this time-point. Our results indicate that PS1 mutations predispose to hyperosmotic stress-induced apoptosis and that the anti-apoptotic effects of insulin-like growth factor-1 are compromised by these mutations. Perturbations of insulin-like growth factor-1 signalling may be involved in PS1 mutation-related apoptotic neuronal cell death in Alzheimer's disease.

Quantitative autoradiography of [3H]forskolin binding sites in post-mortem brain staged for Alzheimer's disease neurofibrillary changes and amyloid deposits

Adenylyl cyclase (AC) signal transduction has been shown to be affected in Alzheimer's disease (AD). Deficits have been described in different components of the system, from the receptor to the effector level. [3H]forskolin is a diterpene that binds with high affinity to AC. In the present report, we used autoradiography to study [3H]forskolin binding to sections of entorhinal cortex and hippocampus from 23 cases staged for AD pathology according to Braak and Braak [Acta Neuropathol. 82 (1991) 239-259]. This protocol defines six stages according to neurofibrillary changes, which start in the entorhinal region (stages I-II), spread to the hippocampus (stages III-IV) and finally to the isocortical areas (stages V-VI). The amyloid classification includes three stages in which the basal isocortex is first affected (stage A), followed by other isocortical association areas (stage B) and finally the primary isocortical areas (stage C). We also studied the effects of the GTP-analogue Gpp[NH]p on binding, in order to detect changes in G-protein-AC coupling. We used two different concentrations of Gpp[NH]p, that were previously reported to inhibit and stimulate [3H]forskolin binding via Gi and Gs, respectively. Results showed that [3H]forskolin binding declined significantly with staging for neurofibrillary changes only in the entorhinal region (P < 0.05, ANOVA). In addition, the decrease in [3H]forskolin binding observed in the presence of 1 microM Gpp[NH]p diminished significantly with staging in the entorhinal region (P < 0.05, ANOVA). No significant changes were seen with amyloid staging, with the exception of the CA1 subfield of the hippocampus, where [3H]forskolin binding in the absence of Gpp[NH]p was significantly decreased at stage B compared with all other stages (P < 0.05, ANOVA). In conclusion, our results showed a very limited decrease in [3H]forskolin binding with the progression of AD pathology, suggesting that the AC levels may be largely preserved in the disease. The specific change in the effect of a low concentration of Gpp[NH]p on the binding could indicate the loss of Ca2+/calmodulin-sensitive AC isoforms in AD.

Nicergoline stimulates protein kinase C mediated alpha-secretase processing of the amyloid precursor protein in cultured human neuroblastoma SH-SY5Y cells

We investigated the ability of the antidementia agents, nicergoline, aniracetam and hydergine to stimulate PKC mediated alpha-secretase amyloid precursor protein (APP) processing in cultured human neuroblastoma SH-SY5Y cells. Western immunoblotting of cell conditioned media using the Mabs 22C11 and 6E10 revealed the presence of 2 bands with molecular mass of 90 and 120 kDa, corresponding to possible alternatively glycosylated forms of secreted APP (APPs). Short-term (30 min and 2 h) treatment of cells with nicergoline gave an increased intensity of both bands, compared to non-treated cells. Maximal nicergoline effects, of the order of 150-200% over basal APPs release, were seen at concentrations between 1 and 10 microM. Under the same condition, 1 microM PdBu, used as a positive control, gave 500-1000% increases of basal APPs release. In contrast, aniracetam and hydergine, did not show any effect on APPs secretion. 2 h treatment with nicergoline had no effect on cellular full-length APP levels, as determined by immunoblotting of cell extracts with 22C11 and CT15 antibodies. Immunoblotting with PKC isoform specific antibodies of soluble and membrane fractions prepared from 2 h treated cells, showed that nicergoline (50 microM) and PdBu (1 microM) both induced translocation of PKC alpha, gamma and epsilon, but not PKC beta. The involvement of PKC in mediating nicergoline stimulated APPs release was also studied using specific inhibitors. 1 microM calphostin C, a broad range PKC inhibitor, significantly reduced both PdBu (1 microM) and nicergoline (10 microM) induced APPs release. In contrast, Go6976 (1 microM), a selective PKC alpha and beta1 inhibitor, as well as the cAMP-dependent protein kinase inhibitor, H89 (1 microM) were without effect. These results indicate that nicergoline can modulate alpha-secretase APP processing by a PKC dependent mechanism that is likely to involve the gamma and epsilon isoforms of this enzyme.

Distribution of active glycogen synthase kinase 3beta (GSK-3beta) in brains staged for Alzheimer disease neurofibrillary changes

Accumulation of paired helical filaments (PHFs) in neurofibrillary tangles, neuropil threads, and dystrophic neurites is one of the major neuropathological hallmarks of Alzheimer disease (AD). The principal protein subunit of PHFs is the abnormally hyperphosphorylated tau. Glycogen synthase kinase 3beta (GSK-3beta) is one of the candidate kinases involved in PHF-tau formation. To play a role in PHF-tau formation, it would be expected that GSK-3beta is active in tangle bearing neurons. In the present study, we investigated the regional and intracellular distributions of active and inactive forms of GSK-3beta in brains staged for neurofibrillary changes. We found that neurons with tangle-like inclusions positive for active, but not inactive, GSK-3beta appear initially in the Pre-alpha layer of the entorhinal cortex and extend to other brain regions, coincident with the sequence of the development of neurofibrillary changes. Active, but not inactive, GSK-3beta was found to initially accumulate in the cytoplasm of pretangle neurons. These data provide direct in situ evidence that is consistent with the involvement of GSK-3beta in PHF-tau formation.

Inhibition of [3H]forskolin binding by Gpp[NH]p may reflect adenylate cyclase coupling to Gi

The effect of the GTP analogue guanylyl-5'-imidodiphosphate (Gpp[NH]p) on [3H]forskolin binding was studied in rat brain using autoradiography. In the striatum the presence of 100 microM Gpp[NH]p produced a 40% increase in binding, whereas a decrease of about 30% was observed with low Gpp[NH]p concentrations (0.1 microM). In the molecular layer of the cerebellum all concentrations of Gpp[NH]p decreased [3H]forskolin binding. The decrease in binding disappeared in both striatum and the molecular layer of cerebellum in sections pretreated with 100 microM N-ethylmaleimide (NEM) for 10 min. NEM pretreatment did not significantly affect the stimulation of [3H]forskolin binding by micromolar concentrations of Gpp[NH]p in the striatum, but reversed the decrease observed in the molecular layer of the cerebellum, to an increase. Based on these data we suggest that the effects of Gpp[NH]p on [3H]forskolin binding may involve both Gs and Gi, where stimulation produces an increase and decrease in binding, respectively. The regional effects of Gpp[NH]p may reflect differences in the responsiveness of adenylate cyclase to Gs- and Gi-mediated effects.

Alterations in the ryanodine receptor calcium release channel correlate with Alzheimer's disease neurofibrillary and beta-amyloid pathologies

Investigation of the integrity of the ryanodine receptor in Alzheimer's disease is important because it plays a critical role in the regulation of calcium release from the endoplasmic reticulum in brain, impairment of which is believed to contribute to the pathogenesis of Alzheimer's disease. The present study compared ryanodine receptor levels and their functional modulation in particulate fractions from control and Alzheimer's disease temporal cortex, occipital cortex and putamen. Relationships between ryanodine receptor changes and the progression of Alzheimer's disease pathology were determined by examining autoradiographic [3H]ryanodine binding in entorhinal cortex/anterior hippocampus sections from 22 cases that had been staged for neurofibrillary changes and beta-amyloid deposition. A significant (P < 0.02) 40% decrease in the Bmax for [3H]ryanodine binding and significantly higher IC50 values for both magnesium and Ruthenium Red inhibition of [3H]ryanodine binding were detected in Alzheimer's disease temporal cortex particulate fractions compared to controls. Immunoblot analyses showed Type 2 ryanodine receptor holoprotein levels to be decreased by 20% (P < 0.05) in these Alzheimer's disease cases compared to controls. No significant differences were detected in [3H]ryanodine binding comparing control and Alzheimer's disease occipital cortex or putamen samples. The autoradiography study detected increased [3H]ryanodine binding in the subiculum, CA2 and CA1 regions in cases with early (stage I-II) neurofibrillary pathology when compared to Stage 0 cases. Analysis of variance of data with respect to the different stages of neurofibrillary pathology revealed significant stage-related declines of [3H]ryanodine binding in the subiculum (P < 0.02) with trends towards significant decreases in CA1, CA2 and CA4. Post-hoc testing with Fisher's PLSD showed significant reductions (74-94%) of [3H]ryanodine binding in the subiculum, and CA1-CA4 regions of the late isocortical stage (V-VI) cases compared to the early entorhinal stage I-II cases. [3H]Ryanodine binding also showed significant declines with staging for beta-amyloid deposition in the entorhinal cortex (P < 0.01) and CA4 (P < 0.05) with trends towards a significant decrease in the dentate gyrus. We conclude that alterations in ryanodine receptor binding and function are very early events in the pathogenesis of Alzheimer's disease, and may be fundamental to the progression of both neurofibrillary and beta-amyloid pathologies.

Protein kinase C and amyloid precursor protein processing in skin fibroblasts from sporadic and familial Alzheimer's disease cases

Non-amyloidogenic alpha-secretase processing of amyloid precursor protein (APP) is stimulated by protein kinase C (PKC). Levels and activity of PKC are decreased in sporadic Alzheimer's disease skin fibroblasts. We investigated whether alterations in PKC and PKC-mediated APP processing occur also in fibroblasts established from individuals with familial Alzheimer's disease APP KM670/671NL, PS1 M146V and H163Y mutations. These pathogenic mutations are known to alter APP metabolism to increase Abeta. PKC activities, but not levels, were decreased by 50% in soluble fractions from sporadic Alzheimer's disease cases. In contrast, familial Alzheimer's disease fibroblasts showed no significant changes in PKC enzyme activity. Fibroblasts bearing the APP KM670/671NL mutation showed no significant differences in either PKC levels or PKC-mediated soluble APP (APPs) secretion, compared to controls. Fibroblasts bearing PS1 M146V and H163Y mutations showed a 30% increase in soluble PKC levels and a 40% decrease in PKC-mediated APPs secretion. These results indicate that PKC deficits are unlikely to contribute to increased Abeta seen with APP and PS1 mutations, and also that PS1 mutations decrease alpha-secretase derived APPs production independently of altered PKC activity.

Amyloid precursor protein metabolism in fibroblasts from individuals with one, two or three copies of the amyloid precursor protein (APP) gene

Protein kinase C (PKC)-activated modulation of amyloid precursor protein (APP) metabolism has been investigated in natural models of altered APP expression due to the presence of one, two or three copies of the APP gene. We show that levels of APP present in human skin fibroblasts strongly influence the effect of PKC activation of soluble APP (sAPP) release. Thus fibroblasts derived from a patient with a deletion in chromosome 21 including the APP locus (Delta21) had lower levels of both APP mRNA and cell-associated APP, and showed an exaggerated phorbol-ester-induced sAPP release, when compared with fibroblasts from control individuals. In contrast, fibroblasts from chromosome 21 trisomic Down's syndrome patients failed to show a concentration-dependent response to phorbol ester treatment. These results suggest that the levels of APP expression can affect the degree of response to PKC-mediated modulation of the metabolism of this protein.

A quantitative autoradiographic study of [3H]cAMP binding to cytosolic and particulate protein kinase A in post-mortem brain staged for Alzheimer's disease neurofibrillary changes and amyloid deposits

The cAMP-dependent protein kinase (PKA) has been implicated in the Alzheimer's disease pathology of abnormal tau phosphorylation leading to neurofibrillary tangle (NFT) formation, as well as in amyloid precursor protein alpha-secretase processing. In the present study, we determined whether [3H]cAMP binding to cytosolic and particulate PKA showed any relationship to the extent of Alzheimer's disease pathology at post-mortem. Autoradiographic [3H]cAMP binding to cytosolic and particulate PKA was measured in sections of entorhinal cortex/hippocampal formation from 23 cases that had been staged for Alzheimer's disease-related neurofibrillary changes and amyloid deposits according to Braak and Braak [H. Braak, E. Braak, Neuropathological staging of Alzheimer's-related changes, Acta Neuropathol. 82 (1991) 239-259]. [3H]cAMP binding to cytosolic PKA showed statistically significant reductions in the entorhinal cortex (P<0.01, ANOVA) with respect to neurofibrillary changes. Post-hoc analysis with Fisher's PLSD test showed significant reductions of [3H]cAMP binding to cytosolic PKA at the isocortical stages (V and VI), compared to the non-pathological (O) (by 55%, P<0.01), transentorhinal (I and II) (by 58%, P<0.001) and limbic (III and IV) (by 45%, P<0.05) stages. A significant reduction (by 25%, P<0.05) was also seen in the transentorhinal compared to the limbic stages. [3H]cAMP binding to cytosolic PKA showed no significant alterations with respect to neurofibrillary changes in either the subiculum, CA1-CA4 subfields of the hippocampus or the dentate gyrus. [3H]cAMP binding to cytosolic PKA also showed significant declines in the entorhinal cortex (P<0.01) and subiculum (P<0.05) with respect to staging for amyloid deposits. Post-hoc analysis with Fisher's PLSD test showed significant reductions of [3H]cAMP binding to cytosolic PKA in the entorhinal cortex at amyloid stage C compared to stages O (by 41%, P<0.01) and A (by 38%, P<0.01). In the subiculum, there were significant reductions of [3H]cAMP binding at stages C (by 41%, P<0.01) and B (by 40%, P<0.05), respectively, compared to stage O. [3H]cAMP binding to particulate PKA did not show significant relationships to staging for either neurofibrillary changes or amyloid deposits in either the entorhinal cortex or any of the hippocampal subregions. These findings suggest that whereas [3H]cAMP binding to cytosolic PKA in the entorhinal cortex is reduced with progression of neurofibrillary and amyloid pathology, other hippocampal regions show a preservation of cytosolic and particulate PKA even in late stage pathologies.

Inhibition of [3H]forskolin binding by Gpp[NH]p may reflect adenylyl cyclase coupling to Gi

The effect of the GTP-analogue guanylyl 5'-imidodiphosphate (Gpp[NH]p) on [3H]forskolin binding was studied in rat brain using autoradiography. In the striatum, 100 microM Gpp[NH]p produced a 40% increase in binding, whereas a decrease of about 30% was observed with low Gpp[NH]p concentrations (0.1-1 microM). In the molecular layer of the cerebellum all concentrations of Gpp[NH]p decreased [3H]forskolin binding. The decrease in binding disappeared in both striatum and the molecular layer of cerebellum in sections pretreated with 100 microM N-ethylmaleimide (NEM) for 10 min. NEM pretreatment did not significantly affect the stimulation of [3H]forskolin binding by micromolar concentrations of Gpp[NH]p in the striatum, but reversed the decrease observed in the molecular layer of the cerebellum, to an increase. Based on these data we suggest that the effects of the GTP-analogue Gpp[NH]p on [3H]forskolin binding may involve both Gs and Gi, where a stimulation produces an increase and decrease in binding respectively. The regional effects of Gpp[NH]p may reflect differences in the responsiveness of adenylyl cyclase to Gs and Gi-mediated effects.

Alpha-ketoglutarate dehydrogenase in Alzheimer brains bearing the APP670/671 mutation

Alzheimer's disease (AD) is associated with a striking reduction in the activity of the alpha-ketoglutarate dehydrogenase complex (KGDHC). The deficiency occurs in brains from AD patients of undefined etiology, and in fibroblasts from both sporadic and familial AD cases. To further assess the nature of the abnormality of KGDHC in AD, KGDHC activities and immunoreactivities were analyzed in brains from AD patients bearing the Swedish APP670/671 mutation. This gene defect causes overproduction of the amyloid beta peptide. KGDHC activities were reduced by 55 to 57% compared with control values in the mutation-bearing AD cases in the medial temporal and superior frontal cortices. The immunochemical levels of KGDHC subunits Elk (-51%) and E2k (-76%) declined, whereas E3 concentrations were unchanged. The results suggest that mitochondrial dysfunction is a part of the pathophysiological process in AD even when the primary pathogenic cause is nonmitochondrial.

Accumulation of cyclin-dependent kinase 5 (cdk5) in neurons with early stages of Alzheimer's disease neurofibrillary degeneration

Cyclin-dependent kinase 5 (cdk5) is one of the candidate kinases involved in the abnormal hyperphosphorylation of tau. To have a direct effect on tau hyperphosphorylation, cdk5 protein levels and enzyme activity should be upregulated in especially those neurons that develop neurofibrillary tangles (NFTs). We studied the distribution of cdk5 immunoreactivity in neurons with or without early- and late-stage NFTs in hippocampal, entorhinal, transentorhinal, temporal and frontal cortices, and cerebellum of Alzheimer's disease (AD) and control brain. The immunocytochemical localisation of cdk5 was compared with that obtained using antibodies to PHF-tau (tau in paired helical filaments of NFTs, mAb AT8) and ubiquitin as markers of early and late stage NFTs, respectively. Immunoreactivities of cdk5 and PHF-tau were found in neuronal perikarya and processes of hippocampal, entorhinal, transentorhinal, temporal and frontal, and cerebellar cortices. An apparent increase of cdk5 immunoreactivity was seen in pretangle neurons and in neurons bearing early stage NFTs. These findings suggest that this kinase might be involved in the formation of NFTs at a relatively early stage in the neocortex.

Loss of inositol 1,4,5-trisphosphate receptor sites and decreased PKC levels correlate with staging of Alzheimer's disease neurofibrillary pathology

Inositol 1,4,5-trisphosphate (IP3), inositol 1,3,4,5-tetrakisphosphate (IP4) and protein kinase C (PKC) play important roles in the phosphoinositide hydrolysis signal transducing pathway. Several studies have shown severe deficits in both IP3 receptor levels and PKC levels and activity in Alzheimer's disease brain, although the relationship of these changes to disease pathology is poorly understood. In the present study, we determined the autoradiographic localization of [3H]IP3 and [3H]IP4 binding to their calcium mobilizing receptor sites and [3H]phorbol 12,13-dibutyrate ([3H]PDBu) binding to PKC in sections of entorhinal cortex/hippocampal formation and cerebellum from 24 cases that had been staged for Alzheimer's disease-related neurofibrillary changes and amyloid deposition according to Braak and Braak [Acta Neuropathol. Berl., 82 (1991) 239-259]. Results indicated that [3H]IP3 binding showed a trend towards a decline with staging for neurofibrillary changes in the entorhinal region (0.05 < P < 0.10, ANOVA) and subiculum (0.05 < P < 0.10). In the former region, [3H]IP3 binding showed a significant decline with staging for amyloid deposition (P < 0.05). [3H]IP3 binding in the CA1 region showed statistically significant declines with respect to both neurofibrillary changes and amyloid staging (P < 0.05). [3H]IP3 binding levels in the other hippocampal subregions were too low to quantify accurately. The binding of [3H]IP4 showed no significant changes with either neurofibrillary changes or amyloid staging in any of the regions investigated. In contrast, [3H]PDBu binding showed significant declines with neurofibrillary staging in the entorhinal region (P < 0.01), subiculum (P < 0.001), CA1 (P < 0.001), CA2 (P < 0.001), CA3 (P < 0.001) and CA4 (P < 0.0001) regions and the dentate gyrus (P < 0.0001). Of these regions, only the subiculum showed a significant decline of [3H]PDBu binding with amyloid staging. There were no significant neurofibrillary or amyloid stage-related changes in either [3H]IP3, [3H]IP4 or [3H]PDBu binding in the molecular layer of the cerebellum. These findings suggest that reduced IP3 receptor and PKC levels in the entorhinal cortex/hippocampal formation reflect and may be important for the progression of Alzheimer's disease neurofibrillary pathology. The data also suggests that hippocampal IP3 receptor loss is related to the extent of amyloid deposition.

Subcellular distribution of protein phosphatases and abnormally phosphorylated tau in the temporal cortex from Alzheimer's disease and control brains

Microtubule-associated protein tau is abnormally hyperphosphorylated in the brain of patients with Alzheimer's disease (AD). In vitro studies have shown that protein phosphatases PP-2A and PP-2B can convert Alzheimer like tau to its normal state and that the activities of PP-1, PP-2A, and phosphotyrosyl-protein phosphatase (PTP) are reduced in AD brain. However, to have a direct effect on the regulation of phosphorylation on tau, these enzymes have to exist in neurons. Using specific polyclonal antibodies the levels of protein phosphatases PP-1, PP-2A, and PP-2B were determined by indirect ELISA in superior temporal cortical gray matter of AD and control brains. The protein levels of PP-2A and PP-2B were significantly increased in postsynaptosomal supernatant 2 (S2) of the AD group, and this alteration showed a significant linear correlation with levels of hyperphosphorylated tau. PP-1 and PTP-1B levels were not significantly changed in any of the AD fractions. Because of the large variation from case to case, the activity levels of none of the phosphatases investigated were significantly different between the AD and control groups. However, the PP-2B specific activity (activity/protein) showed a significant linear inverse correlation with hyperphosphorylated tau. These studies suggest that any attempt by the AD brain to compensate for the decreased tau phosphatase activity remains unsuccessful and that the decrease in phosphatase activity might contribute to increased levels of abnormally phosphorylated tau.

Elevated protein levels of protein phosphatases PP-2A and PP-2B in astrocytes of Alzheimer's disease temporal cortex

Previous studies have shown that activities of the protein phosphatases PP-2A and PP-2B towards the microtubule associated protein tau are reduced in Alzheimer's disease (AD) frontal cortex (Gong et al., 1993, 1995), suggesting that PP-2A and PP-2B are involved in the hyperphosphorylation of tau in AD. Most recently, we found that protein levels of PP-2A and PP-2B are elevated in postsynaptic supernatant (S2) fractions prepared from AD temporal cortex, and that the activities of these enzymes were not significantly different between AD and control cases (Pei et al., in press). In the present study, we found that astroglia positive for PP-2A and PP-2B immunoreactivities were greater in numbers in AD medial temporal cortex, compared to controls. GFAP levels, as determined by indirect ELISA, were approximately 1.5 times greater in the P1 (500 x g) fraction from AD temporal cortex, compared to controls. GFAP levels in the P1 fraction showed significant correlations with PP-2A and PP-2B levels in the postsynaptic S2 (20,000 x g) fraction from the same brains. These results suggest that astrogliosis probably accounts for the increased levels of PP-2A and PP-2B in the S2 fraction in AD brain and that the levels of these enzymes per neuron are likely to be decreased.

Amyloid precursor protein heat shock response in lymphoblastoid cell lines bearing presenilin-1 mutations

The amyloid precursor protein (APP) gene promoter contains a heat shock element. An abnormal APP heat shock response could increase accumulation of A beta, the APP metabolite found in Alzheimer's disease amyloid plaques. Since A beta production is affected by presenilin-1 (PS-1) mutations, we investigated whether basal APP levels or response to heat shock were altered in lymphoblastoid cell lines from 8 PS-1 mutation-bearers and 9 control members of Alzheimer's disease families. Lymphoblastoid cell lines were incubated at 42 degrees C for 35 min and allowed to recover at 37 degrees C for 1, 3, 8, 24 and 48 h. APP mRNA levels, quantified using RNA-RNA solution hybridisation, increased significantly at 1 and 3 h post-heat shock to between 123% and 163% of pre-heat shock (0 h) levels and returned to normal by 8 h. Semi-quantitative Western immunoblotting of cell lysates using the 22C11 antibody detected two major bands, migrating at approximately 145 and approximately 120 kDa. Band optical densities increased significantly at 3 h to approximately 155% of 0 h levels, following the increase in APP mRNA levels and showing a similar reversibility. APP mRNA and protein responses were comparable in the PS-1 mutation-bearing and control cell lines. This study shows that both APP mRNA and protein are induced in lymphoblastoid cell lines following heat shock and that this response is not affected by PS-1 mutations which are pathogenic for Alzheimer's disease.

Effects of beta-amyloid-(25-35) peptides on radioligand binding to excitatory amino acid receptors and voltage-dependent calcium channels: evidence for a selective affinity for the glutamate and glycine recognition sites of the NMDA receptor

The neurotoxic fragment corresponding to residues 25-35 of the beta-amyloid (A beta) peptide [A beta-(25-35)] has been shown to exert effects on (+)-[3H]5-methyl-10, 11-dihydro-5H-dibenzo[a,d]-cyclohepten-5,10-imine maleate ([3H]MK-801) binding to the cation channel of the N-methyl-D-aspartate (NMDA) receptor. In the present study, we investigated whether the amidated and carboxylic acid C-terminated forms of A beta-(25-35) [A beta-(25-35-NH2) and A beta-(25-35-COOH), respectively] exert effects on other excitatory amino acid receptor and cation channel types in rat cortical membranes. Both A beta-(25-35-NH2) and A beta-(25-35-COOH) gave statistically significant dose-dependent inhibitions of [3H]glutamate and [3H]glycine binding to the agonist recognition sites of the NMDA receptor. Ten microM A beta-(25-35-NH2) and A beta-(25-35-COOH) gave 25% and 20% inhibitions of [3H]glutamate binding and 75% and 70% inhibitions of [3H]glycine binding, respectively. A beta-(25-35-NH2), but not A beta-(25-35-COOH), gave a small (ca. 17% at 10 microM) statistically significant increase of [3H]amino-3-hydroxy-5-methylisoxazole-4-propionate ([3H]AMPA) binding. [3H]kainate binding was not significantly affected by either peptide. Similarly, neither peptide affected either the maximal level or EC50 value for calcium stimulation of [3H]nitrendipine binding. It is concluded that A beta-(25-35) shows slight affinity for the agonist recognition sites of the NMDA receptor, but not for other excitatory amino acid receptor types or for L-type voltage-dependent calcium channels.

Abnormalities in Alzheimer's disease fibroblasts bearing the APP670/671 mutation

Abnormalities in cultured fibroblasts from familial Alzheimer's Disease (FAD) cases uniquely enable the determination of how gene defects alter cell biology in living tissue from affected individuals. The current study focused on measures of calcium regulation and oxidative metabolism in fibroblast lines from controls and FAD individuals with the Swedish APP670/671 mutation. Bombesin-induced elevations in calcium in APP670/671 mutation-bearing lines were reduced by 40% (p < 0.05), a striking contrast to the 100% increase seen in sporadic AD and presenilin-1 (PS1) mutation-bearing cells in previously published studies. The APP670/671 mutation-bearing lines did not exhibit the exaggerated 4-bromo-A23187 releasable pool of calcium following 10 nM bradykinin, the enhanced sensitivity of calcium stores to low concentrations of bradykinin, nor the reduced activity of alpha-ketoglutarate dehydrogenase previously reported in cells from sporadic AD and mutant PS1 FAD. Thus, an altered regulation of internal calcium stores is common to all AD lines, but the calcium pool affected and the polarity of the alteration varies, apparently in association with particular gene mutations. Comparison of signal transduction in cell lines from multiple, genetically characterized AD families will allow testing of the hypothesis that these various pathogenic FAD abnormalities that lead to AD converge at the level of abnormal signal transduction.

Presenilin-1, amyloid precursor protein and amyloid precursor-like protein 2 mRNA levels in human superior frontal cortex during aging

The presenilin-1 (PS-1) and amyloid precursor protein (APP) genes carry mutations which co-segregate with early-onset familial Alzheimer's disease. The APP and PS-1 gene products may be involved in the aetiology of the more common late onset form of Alzheimer's disease, where increasing age is a major risk factor. To investigate whether age affected mRNA expression of these genes, we quantified PS-1, total APP, APP containing the kunitz-type protease inhibitor (KPI) domain and amyloid precursor-like protein 2 (APLP2) mRNAs in post-mortem superior frontal cortices from 23 control subjects aged 38 to 89 years using solution hybridisation-RNase protection assays. PS-1, total APP, APP KPI and APLP2 mRNA levels were unchanged over this age range. PS-1 was the least abundant mRNA, at approximately 7% of total APP, the most highly expressed mRNA studied (10.8 copies/pg total RNA). The proportion of total APP encoding the KPI domain (approximately 52%) was unaffected by age. APLP2 mRNA was present at approximately 29% of the total APP mRNA level. Significant positive correlations were present between total APP, APP KPI and APLP2 mRNA levels. These results indicate that the increased prevalence of Alzheimer's disease cannot be attributed to alterations in cortical PS-1, APP and APLP2 mRNA levels or APP KPI splicing during aging.

A novel pathogenic mutation (Leu262Phe) found in the presenilin 1 gene in early-onset Alzheimer's disease

Several mutations causing early-onset familial Alzheimer's disease (AD) have been detected in the presenilin 1 (PS-1) gene. Pathogenic mutations have also been described in an homologous gene, presenilin 2 (PS-2). In order to screen for mutations in these genes, cDNA samples from early-onset AD cases were analysed, using single strand conformation polymorphism (SSCP) and direct cDNA sequencing. Two missense mutations in the PS-1 gene were detected, a previously unidentified amino acid substitution Leu262Phe and an earlier reported amino acid substitution Glu318Gly. No disease-related mutations were found in the PS-2 gene.

G protein subunit levels in fibroblasts from familial Alzheimer's disease patients: lower levels of high molecular weight Gs alpha isoform in patients with decreased beta-adrenergic receptor stimulated cAMP formation

Abnormalities in G protein linked signal transduction pathways have been detected in fibroblasts from individuals with familial and sporadic Alzheimer's disease. The present study used Gs alpha, Gi alpha, Gq alpha and Go alpha G protein subunit antisera, immunoblotting and densitometry to quantify levels of these proteins in control fibroblasts and in fibroblasts from individuals with familial Alzheimer's disease (FAD). The FAD fibroblasts were from individuals with the APPK670N,M671L mutation, different presenilin 1 (PS1) mutations and one fibroblast cell line from an individual with FAD of unknown genetic aetiology. Results revealed a significant reduction in the large Gs alpha subunit in fibroblasts with the PS1 mutations and in the fibroblast cell line of unknown genetic aetiology, when compared to control levels. This decrease was not apparent in the APPK670N,M671L FAD fibroblasts. Immunoreactivity for Go alpha was not detected in any of the fibroblast cell lines. No differences were observed in Gi alpha or Gq alpha levels when comparing any of the control and Alzheimer's disease fibroblast groups. WE conclude that with the exception of decreased levels of the large Gs alpha subunit, gross alterations in the levels of the Gi alpha, Gq alpha and Go alpha are not associated with the G protein-coupled signal transduction disturbances described previously for some of these FAD fibroblasts.

Autoradiographic characterisation of [35S]GTP gamma S binding sites in rat brain

The binding of [35S]GTP gamma S was characterised with autoradiography in rat brain. The binding was saturable, but the rate of dissociation was very slow. Analysis of binding isotherms revealed one class of binding sites with a Kd of 0.8 microM. The specific binding was 98%. Different guanine nucleotides were all able to compete with [35S]GTP gamma S binding. However, no displacement was seen by the ATP-analogue App[NH]p, indicating that [35S]GTP gamma S does not bind to ATP-sites. Autoradiograms showed a highly homogenous distribution of [35S]GTP gamma S binding, in grey as well as in white matter. However, the pattern changed dramatically in the presence of GTP, which, unlike the non-hydrolysable GTP-analogues Gpp[NH]p and GTP gamma S, did not displace [35S]GTP gamma S binding throughout the brain. In white matter areas the binding was potently displaced, while in many grey matter areas, e.g., the striatum, the binding was seen to increase. This GTP-induced increase in [35S]GTP gamma S binding was strongly Mg(2+)-dependent, with an optimum at 10 mM. This, together with the finding that the regional effects of GTP correspond well to previously reported distribution of low Km GTPase, suggest that the levels of binding of [35S]GTP gamma S in the presence of GTP may reflect functional G-protein activity.

Autoradiographic characterization of [3H]cGMP binding sites in the rat brain

Quantitative autoradiography was used to characterize and localize [3H]cGMP binding sites in the rat brain. [3H]cGMP binding was found to be pH-sensitive (with two optima at 7.4 and 5.0) and Mg2+-dependent. At pH 7.4, the binding was dependent on inclusion of the phosphodiesterase inhibitor IBMX. In contrast, at pH 5.0, IBMX had little effect on binding. The binding of [3H]cGMP was reversible and saturable with a Kd of 22 nM at pH 7.4 and 36 nM at pH 5.0. Bmax values were 172 fmol/mg at pH 7.4 and 462 fmol/mg at pH 5.0. [3H]cGMP binding was inhibited by cGMP and its analogues, with cGMP and cAMP being the most potent at pH 7.4 and cGMP and 8-Br-cGMP being the most potent at pH 5.0. Using an extracellular pH 7.4 buffer, the selective cGMP-dependent protein kinase (PKG) inhibitor Rp-8pCPT-cGMPS had very little effect on [3H]cGMP binding. In contrast, with a cytosolic pH 5.0 buffer, Rp-8pCPT-cGMPS displaced binding in the cerebellum. This indicates that PKG is localized in the cerebellum, and that the binding to PKG is favored under cytosolic conditions. Autoradiographic localization of [3H]cGMP binding sites revealed a heterogeneous distribution with the highest densities in the substantia nigra and interpeduncular nucleus. High densities were also observed in the basal ganglia, the medial habenular nucleus, the frontoparietal cortex, the lateral amygdaloid nucleus and the subiculum. It is concluded that the nature of [3H]cGMP binding is complex, with one site probably being related to cytosolic PKG mainly found in the cerebellum, and one site probably representing cGMP-stimulated phosphodiesterase mainly located in the forebrain.

Cerebrospinal fluid apolipoprotein E (apoE) levels in Alzheimer's disease patients are increased at follow up and show a correlation with levels of tau protein

Apolipoprotein E (apoE) levels were compared in cerebrospinal fluid (CSF) taken on two occasions, with an average 15 months follow up, from groups of patients with Alzheimer's disease (AD: n = 18), mild cognitive impairment (MCI; n = 9) and other dementia disorders (ODD; n = 9). In these groups, CSF apoE levels were between 2-3-fold higher than values for a group of 27 healthy age-matched controls. CSF apoE levels in the AD group were significantly increased at follow up, compared to levels obtained on the first sampling occasion. For the same cases it had been shown previously that CSF tau protein levels were increased at follow up [Blomberg, M., Jensen, M., Basun, H., Lannfelt, L. and Wahlund, L-O., Neurosci. Lett., 214 (1996) 163-166]. The AD, but not MCI, ODD or control groups, also showed statistically significant correlations between CSF apoE and tau protein levels at both the first (r = 0.585, P < 0.01) and follow up (r = 0.695, P > 0.001 ) samplings. It is concluded that CSF measures of both apoE and tau may reflect an intimate relationship between these two proteins in AD and could prove useful in monitoring the progression of this condition.

Differential regulation of adenylyl cyclase in fibroblasts from sporadic and familial Alzheimer's disease cases with PS1 and APP mutations

beta-Adrenoceptor- and forskolin-stimulated adenylyl cyclase activities were determined in primary skin fibroblasts established from patients with sporadic Alzheimer's disease (AD) and from individuals with familial APP KM670/671NL, PS1 M146V and PS1 H163Y mutations. Our data showed a significantly decreased beta-adrenoceptor-stimulated adenylyl cyclase activity in fibroblasts from sporadic AD compared with age-matched controls (p < 0.001, Student's unpaired t-test). In contrast, both beta-adrenoceptor- and forskolin-stimulated adenylyl cyclase activities were significantly increased in fibroblasts bearing PS1 M146V and PS1 H163Y mutations compared with controls (p < 0.01 and p < 0.05, respectively). No differences were seen between cell lines with and without the Swedish APP KM670/671NL double mutation. We suggest that various gene mutations associated with AD have different consequences for the regulation of adenylyl cyclase signal transduction in this disorder.

Decreased beta-adrenoceptor-stimulated adenylyl cyclase activity in lymphocytes from Alzheimer's disease patients

Previous studies have shown that in Alzheimer's disease post-mortem brain there are disruptions of both beta1-adrenoceptor-G-protein coupling and G-protein stimulation of adenylyl cyclase activity. Decreased beta-adrenoceptor stimulated adenylyl cyclase activity has also been shown in Alzheimer's disease primary skin fibroblasts. In the present study, we determined the regulation of adenylyl cyclase in Alzheimer's disease patients using an easily accessible tissue source, namely peripheral blood lymphocytes. beta-Adrenoceptor- and forskolin-stimulated adenylyl cyclase activities were investigated in lymphocytes from 12 Alzheimer's disease and 12 carefully matched and selected control subjects. No significant differences were found in basal or forskolin-stimulated enzyme activities between Alzheimer's disease and control lymphocytes. In contrast, isoprenaline-stimulated adenylyl cyclase activities were significantly lower in the Alzheimer's disease groups, as compared to controls. These results indicate that there is a widespread disruption of beta-adrenoceptor-G-protein-enzyme coupling in different tissues from Alzheimer's disease patients, and that adenylyl cyclase disturbances previously reported in Alzheimer's disease brain do not occur as a consequence of disease pathology or of terminal illness.

Alzheimer's, ageing and amyloid: an absurd allegory?

Recent research into the pathogenesis of Alzheimer's disease (AD) has focused upon the proposed neurotoxic role played by the beta-amyloid peptide. Other important neurochemical disturbances, such as the dramatic breakdown of intracellular signalling, should however not be overlooked. In the present article, the authors attempt to investigate the relationship between signalling disturbances and beta-amyloid and ask the question 'which came first?' The available evidence is discussed, and it is concluded that the need for a wide, rather than restricted, focus on biochemical events associated with AD is required if progress is to be made in the understanding and eventual treatment of this disease.

Autoradiographic characterization of [3H]inositol (1,4,5) trisphosphate and [3H]inositol (1,3,4,5) tetrakisphosphate binding sites in human brain

Autoradiographic techniques were used to investigate the characteristics of tritiated inositol(1,4,5)trisphosphate ([3H]IP3) and inositol (1,3,4,5) tetrakisphosphate ([3H]IP4) binding to human brain. In brain sections [3H]IP3 exhibited a two-site binding with KD values of 87 nM and 9.3 microM respectively for the higher and lower affinity sites. [3H]IP4 also bound to two sites with KD values of 43 nM and 1.4 microM, respectively. With the conditions fixed in this study, [3H]IP3 and [3H]IP4 autoradiography in the cortex, caudate, hippocampus and cerebellum were performed. The most prominent [3H]IP3 binding among these regions was found in the cerebellum, particularly in the molecular layer. Within the hippocampus, the subiculum and the CA1 region showed much more prominent binding than the other subfields. [3H]IP4, binding was fairly homogeneous in the regions studied, with the exception of a slightly higher binding in the molecular layer of the cerebellum.

A new quantitative solution hybridisation-RNase protection assay for APP and APLP2 mRNA

Amyloid precursor protein (APP) and amyloid precursor-like protein 2 (APLP2) are members of a multigene family of proteins implicated in the pathogenesis of Alzheimer's disease. We describe the development of an RNA-RNA solution hybridisation-RNase protection assay to quantify APP mRNA. APP mRNA splice forms containing the Kunitz-type protease inhibitor (KPI) insert, and APLP2 mRNA in total nucleic acid extracts from a range of tissue types. Solution hybridisation-RNase protection assay enables absolute quantification of target mRNA, by conversion of the hybridisation signal to pg mRNA using a standard curve. The assay is sensitive, capable of detecting 1 pg target mRNA, and reproducible, with an inter-assay variability of less than 10% and an intra-assay variability of 3-4%. We quantified APP and APLP2 mRNA in cell lines and post-mortem human brain tissue samples. To test whether we could detect physiological differences in APP mRNA levels, a fibroblast cell line with a paternal chromosome 21 deletion of the region including the APP gene was analysed and found to express half as much APP mRNA as control fibroblasts. In addition, a reversible, approx. 30% increase in APP mRNA levels was detected in human lymphoblastoid cell lines following heat shock, a physical stimulus previously shown to increase APP expression. Regional differences in the expression of APP and APLP2 were seen in human post-mortem cerebral cortex and cerebellum. Levels of APP and APLP2 mRNA were highest in the temporal cortex, slightly lower in frontal and occipital cortices, and lowest in the cerebellum. The highest proportion of KPI-containing APP was seen in the frontal and temporal cortices. The ratio of APP:APLP2 mRNA was 1:0.3 in the cortical tissue and 1:0.8 in the cerebellum. In conclusion, quantitative solution hybridisation-RNase protection assay of total APP. APP KPI and APLP2 mRNA provides a new tool to improve the resolution of studies of potentially subtle alterations in the expression of these genes in both cell culture model systems and Alzheimer's disease post-mortem human brain tissue.

Quantification of APP and APLP2 mRNA in APOE genotyped Alzheimer's disease brains

Amyloid precursor protein (APP) is metabolised to produce A beta, a peptide found aggregated in Alzheimer's disease neuritic plaques. APP is a member of a multigene protein family which includes amyloid precursor-like protein 2 (APLP2). Since A beta accumulation can be triggered by factors acting up- or downstream of APP processing, we investigated whether APP mRNA expression was altered in Alzheimer's disease post-mortem cerebral cortex. In addition, we characterised cortical APLP2 mRNA levels. Quantitative RNA-RNA solution hybridisation-RNase protection was used to assay total APP. APP containing the Kunitz-type protease inhibitor (KPI) insert and APLP2 mRNA in mid-temporal and superior frontal cortices from apolipoprotein E-genotyped subjects with Alzheimer's disease, other neurological diseases and non-demented controls. Approximately 3 times more APP than APLP2 mRNA was detected and about 70% of total APP mRNA contained the KPI insert in the control subjects. Total APP and APLP2 mRNA levels were significantly reduced in Alzheimer's disease mid-temporal, but not superior frontal cortex, suggesting that regional reductions in these mRNA correlate with severity of disease pathology. A small significant increase in the proportion of APP KPI mRNA was seen in both cortical regions in Alzheimer's disease. Apolipoprotein E genotype did not influence cortical levels of total APP, APP KPI or APLP2 mRNA. Alzheimer's disease-related increases in tissue DNA content were seen in both regions studied, while tissue RNA levels were reduced in the positive disease controls. In summary, these results indicate that Alzheimer's disease is not associated with over-expression of either APP or APLP2 mRNA. Our findings reveal a disease-associated increase in the proportion of APP KPI-containing isoforms, and further investigation should clarify whether this predisposes affected individuals to A beta production and aggregation, or reflects later events such as gliosis and neuronal cell death.

The neurochemistry of Alzheimer's disease

The last 15-20 years have seen a wealth of studies to characterize the neurochemical abnormalities of Alzheimer's disease, in particular those involving the beta-amyloid and tau proteins, as well as more recently, apolipoprotein E4. This article provides a summary of the evidence for the involvement of these proteins in Alzheimer's disease pathogenesis based on postmortem brain and CSF studies.

Neurotransmitter receptor/G-protein mediated signal transduction in Alzheimer's disease brain

Recent evidence suggests that the neurochemical pathology of Alzheimer's disease includes severe disruptions of the neurotransmitter receptor/G-protein mediated phosphatidylinositol hydrolysis and adenylyl cyclase signal transduction pathways. The present article briefly reviews evidence from postmortem studies describing disruptions to these systems and speculates as to the importance of these changes in terms of contributing to disease pathology and limiting the success of neurotransmitter replacement strategies.

Impaired G-protein-stimulated adenylyl cyclase activity in Alzheimer's disease brain is not accompanied by reduced cyclic-AMP-dependent protein kinase A activity

Previous studies have shown that the regulation of adenylyl cyclase activity is disrupted in Alzheimer's disease postmortem brain. In the present study, we determined whether disrupted adenylyl cyclase is accompanied by altered cAMP-dependent protein kinase activity in Alzheimer's disease superior temporal cortex and cerebellum. GTP gamma S-stimulated adenylyl cyclase activity was significantly lower in Alzheimer's disease superior temporal cortex, but not cerebellum, compared to values from a series of matched control cases. Neither basal or forskolin-stimulated adenylyl cyclase activities were significantly different between the Alzheimer's disease and control brain regions. No significant differences were seen in either particulate or soluble fraction cAMP-dependent protein kinase activities between the Alzheimer's disease and control brain regions. It is concluded that disrupted adenylyl cyclase signalling in Alzheimer's disease brain occurs specifically at the level of Gs-protein-enzyme interactions and is not accompanied by an altered cAMP-dependent protein kinase activity.