The consequences of reducing expression of the alpha7 nicotinic receptor by RNA interference and of stimulating its activity with an alpha7 agonist in SH-SY5Y cells indicate that this receptor plays a neuroprotective role in connection with the pathogenesis of Alzheimer's disease

In order to examine the neuroprotective effects of the alpha7 nicotinic receptor (nAChR) in relationship to the pathogenesis of Alzheimer's disease (AD), neuroblastoma (SH-SY5Y) cells were transfected with small interference RNAs (siRNAs) that targets specifically towards alpha7 nAChR or exposed to 20microM 3-[2,4-dimethoxybenzylidene] anabaseine (DMXB), a selective agonist of this same receptor. The levels of alpha7 nAChR mRNA and protein were measured by RT-PCR and Western blotting, respectively. The levels of the alpha-form of secreted amyloid precursor protein (alphaAPPs), total APP and the extracellular signal-regulated kinase 1/2 (ERK1/2) were also determined by Western blotting. SH-SY5Y cells transfected with siRNA or exposed to DMXB were then treated with 1microM Abeta(25-35), following which the levels of lipid peroxidation and rate of reduction of MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] were characterized by utilizing spectrophotometric procedures. Compared to controls, SH-SY5Y cells transfected with siRNA expressed the decreases in the levels of alpha7 nAChR mRNA and protein by 81% and 69% lower levels, respectively; exhibited reduced levels of the alphaAPPs and ERK1/2 proteins; and demonstrated enhanced lipid peroxidation and a decreased rate of MTT reduction. In cells exposed to DMXB, the level of alpha7 nAChR protein was elevated by 23%, with no alteration in the content of the corresponding mRNA; the levels of the alphaAPPs and ERK1/2 proteins were increased. Inhibition of the expression of the alpha7 nAChR gene enhanced the toxicity exerted by Abeta, whereas stimulation of this receptor attenuated this toxicity exerted. These findings indicate that alpha7 nAChR may play a significant neuroprotective role by enhancing cleavage of APP by alpha-secretase, regulating signal transduction, improving antioxidant defenses and inhibiting the toxicity of Abeta, which is connected with the pathogenesis of AD.     

The role of cholesterol in Alzheimer's neuro-pathogenesis]

Alzheimer's Disease (AD) is the most common neurodegenerative disorder in western societies affecting up to 15 million individuals worldwide.It leads to death after a progressive memory deficit and cognitive impairment accompanied by the appearance of two pathological hallmarks in specific brain areas: neurofibrillary tangles and amyloid plaques. Cholesterol homeostasis may play a key role in AD pathogenesis and this is supported by the demonstration that cholesterol-rich membrane domain, so-called Rafts,are disorganized in affected brains. Retrospective clinical studies indicate that individuals chronically treated with cholesterol synthesis inhibitors,statins, are at lower risk of developing AD but current literature is conflicting with regard to the neuroprotective effects of statins on cognitive impairment.Before recommending statins for prevention and/or treatment of AD it is important to investigate more the role of cholesterol levels in neurodegenerative disorders.     

Inhibiting gene expression of alpha3 nicotinic receptor in SH-SY5Y cells with the effects on APP metabolism and antioxidation in Alzheimer's disease

In order to examine the effects of alpha3 nicotinic acetylcholine receptor (nAChR) in connection with the pathogenesis of Alzheimer's disease (AD), neuroblastoma (SH-SY5Y) cells were transfected with small interference RNAs (siRNAs) that target specifically towards alpha3 nAChR. The expressions of alpha3 nAChR mRNA and protein were measured by real-time PCR and Western blotting, respectively. The levels of the alpha-form of secreted amyloid precursor protein (alphaAPPs) and total-APP were determined by Western blotting. SH-SY5Y cells transfected with siRNA were then treated with 1muM beta-amyloid peptide (Abeta)(1-42), following which the levels of lipid peroxidation, the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), and the reduction rate of MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] were characterized by utilizing spectrophotometric procedures. As compared to controls, SH-SY5Y cells transfected with siRNA expressed the decreases in the levels of alpha3 nAChR mRNA and protein by 98% and 66% lower levels, respectively; exhibited reduced level of the alphaAPPs; and demonstrated enhanced lipid peroxidation, decreased rate of MTT reduction, and declined activities of SOD and GSH-Px. Inhibited gene expression of the alpha3 nAChR enhanced the toxicity exerted by Abeta. These results indicate that alpha3 nAChR may improve cleavage of APP by alpha-secretase, enhance antioxidation and inhibit the toxicity of Abeta, suggesting that the receptor might play an important role in AD.     

Influence of cholesterol and lovastatin on alpha-form of secreted amyloid precursor protein and expression of alpha7 nicotinic receptor on astrocytes

The influence of cholesterol and the lovastatin (cholesterol-lowering drug) on secretion of alpha-secretase cleavage product of amyloid precursor protein (APP) and expression of nicotinic acetylcholine receptors (nAChRs) was investigated in human HTB-15 astrocytes. The results showed that exposure of cholesterol to astrocytes inhibited the secretion of alpha-form of secreted APP (alphaAPPs) and reduced cell viability, while lovastatin enhanced the alpha-secretase processing on astrocytes; cholesterol treatment decreased expression of alpha7 nAChR, whereas lovastatin induced an up-regulation of the receptor; the increase in alphaAPPs resulted from lovastatin was partially inhibited by the alpha7 nAChR antagonists, alpha-bungarotoxin or methyllycaconitine; cholesterol or lovastatin did not influence either whole APP level or expression of alpha4 nAChR. We suggest that high dose of cholesterol may inhibit both the activity of alpha-secretase in APP metabolic processing and the expression of alpha7 nAChR, while lovastatin may stimulate alpha-secretase cleavage processing that might be regulated by alpha7 nAChR.     

Expression and localization of mitochondrial ferritin mRNA in Alzheimer's disease cerebral cortex

Mitochondrial ferritin (MtF) has been identified as a novel ferritin encoded by an intron-lacking gene with specific mitochondrial localization located on chromosome 5q23.1. MtF has been associated with neurodegenerative disorders such as Friedreich ataxia and restless leg syndrome. However, little information is available about MtF in Alzheimer's disease (AD). In this study, therefore, we investigated the expression and localization of MtF messenger RNA (mRNA) in the cerebral cortex of AD and control cases using real-time polymerase chain reaction (PCR) as well as in situ hybridization histochemistry. We also examined protein expression using western-blot assay. In addition, we used in vitro methods to further explore the effect of oxidative stress and β-amyloid peptide (Aβ) on MtF expression. To do this we examined MtF mRNA and protein expression changes in the human neuroblastoma cell line, IMR-32, after treatment with Aβ, H2O2, or both. The neuroprotective effect of MtF on oxidative stress induced by H(2)O(2) was measured by MTT assay. The in situ hybridization studies revealed that MtF mRNA was detected mainly in neurons to a lesser degree in glial cells in the cerebral cortex. The staining intensity and the number of positive cells were increased in the cerebral cortex of AD patients. Real-time PCR and western-blot confirmed that MtF expression levels in the cerebral cortex were significantly higher in AD cases than that in control cases at both the mRNA and the protein level. Cell culture experiments demonstrated that the expression of both MtF mRNA and protein were increased by treatment with H2O2 or a combination of Aβ and H2O2, but not with Aβ alone. Finally, MtF expression showed a significant neuroprotective effect against H2O2-induced oxidative stress (p<0.05). The present study suggests that MtF is involved in the pathology of AD and may play a neuroprotective role against oxidative stress.     

Statins prevent cholinesterase inhibitor blockade of sympathetic alpha7-nAChR-mediated currents in rat superior cervical ganglion neurons

Statins are reported to be beneficial in treating a multitude of disorders including dementia due to Alzheimer disease (AD) and vascular dementia (VaD) with varying, yet-to-be determined mechanisms of actions. Although cholinesterase inhibitors (ChEIs) are still recommended as the primary drug of choice for AD and related diseases, their efficacy is frequently questioned. We recently reported that alpha7-neuronal acetylcholine nicotinic receptor (alpha7-nAChR)-mediated neurogenic vasodilation of porcine cerebral arteries was blocked by ChEIs, and this blockade was prevented by statin pretreatment. The exact mechanism of interaction between ChEIs and statins remains unclear. Activation of alpha7-nAChRs located on perivascular postganglionic sympathetic nerve terminals releases norepinephrine, which then acts on presynaptic beta(2)-adrenoceptors located on neighboring nitrergic nerve terminals, resulting in nitric oxide release and vasodilation. The present study, therefore, was designed to determine whether interaction of ChEIs and statins occurs at the alpha7-nAChR level. We examined effects of concurrent application of ChEIs and statins on alpha7-nAChR-mediated inward currents in primary neuronal cultures of rat superior cervical ganglion cells, the origin of the perivascular sympathetic innervation to the cerebral arteries. The results indicated that physostigmine, neostigmine, and galantamine inhibited choline- and nicotine-induced whole cell currents in a concentration-dependent manner. This inhibition, which was noncompetitive in nature, was prevented by concurrent application of mevastatin and lovastatin in a concentration-dependent manner. These results suggest that statins protect alpha7-nAChR function directly at the receptor level. Since alpha7-nAChR is neuroprotective, having beneficial effects on memory and cerebral vascular function, its functional inhibition by ChEIs may explain in part the limitation of its effectiveness in AD and VaD therapy. Protection of alpha7-nAChR function from ChEI inhibition by concurrent administration of statins may provide an alternative strategy in improving the efficacy of AD and VaD therapy.     

Statins reduce amyloid-beta production through inhibition of protein isoprenylation

Epidemiological evidence suggests that long term treatment with hydroxymethylglutaryl-CoA reductase inhibitors, or statins, decreases the risk for developing Alzheimer disease (AD). However, statin-mediated AD protection cannot be fully explained by reduction of cholesterol levels. In addition to their cholesterol lowering effects, statins have pleiotropic actions and act to lower the concentrations of isoprenoid intermediates, such as geranylgeranyl pyrophosphate and farnesyl pyrophosphate. The Rho and Rab family small G-proteins require addition of these isoprenyl moieties at their C termini for normal GTPase function. In neuroblastoma cell lines, treatment with statins inhibits the membrane localization of Rho and Rab proteins at statin doses as low as 200 nm, without affecting cellular cholesterol levels. In addition, we show for the first time that at low, physiologically relevant, doses statins preferentially inhibit the isoprenylation of a subset of GTPases. The amyloid precursor protein (APP) is proteolytically cleaved to generate beta-amyloid (Abeta), which is the major component of senile plaques found in AD. We show that inhibition of protein isoprenylation by statins causes the accumulation of APP within the cell through inhibition of Rab family proteins involved in vesicular trafficking. Moreover, inhibition of Rho family protein function reduces levels of APP C-terminal fragments due to enhanced lysosomal dependent degradation. Statin inhibition of protein isoprenylation results in decreased Abeta secretion. In summary, we show that statins selectively inhibit GTPase isoprenylation at clinically relevant doses, leading to reduced Abeta production in an isoprenoid-dependent manner. These studies provide insight into the mechanisms by which statins may reduce AD pathogenesis.     

Macrophage colony stimulating factor prevents NMDA-induced neuronal death in hippocampal organotypic cultures

Macrophage colony stimulating factor (M-CSF) and its receptor are up-regulated in the brain in Alzheimer's disease (AD), in transgenic mouse models for AD, and experimental models for traumatic and ischemic brain injury. M-CSF induces activation and proliferation of microglial cells and expression of proinflammatory cytokines. We examined the role of M-CSF in excitotoxic neuronal cell death in organotypic hippocampal cultures. NMDA treatment induced neuronal apoptosis and caspase-3 activation in organotypic hippocampal cultures, whereas treatment with M-CSF protected hippocampal neurons from NMDA-induced apoptosis. Caspase-3 activation was inhibited by M-CSF treatment to the same degree as with the caspase inhibitor Z-VAD-FMK. These results suggest that M-CSF has neuroprotective properties through inhibition of caspase-3 that could promote neuronal survival after excitotoxic insult. The role of M-CSF in neurological disease should be reevaluated as a microglial activator with potentially neuroprotective effects.     

Inhibition of geranylgeranylation mediates the effects of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors on microglia

Inflammatory responses involving microglia, the resident macrophages of the brain, are thought to contribute importantly to the progression of Alzheimer's disease (AD) and possibly other neurodegenerative disorders. The present study tested whether the mevalonate-isoprenoid biosynthesis pathway, which affects inflammation in many types of tissues, tonically regulates microglial activation. This question takes on added significance given the potential use of statins, drugs that block the rate-limiting step (3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase)) in mevalonate and cholesterol synthesis, in AD treatment. Both mevastatin and simvastatin caused a concentration- and time-dependent activation of microglia in cultured rat hippocampal slices. This response consisted of a transformation of the cells from a typical resting configuration to an amoeboid, macrophage-like morphology, increased expression of a macrophage antigen, and up-regulation of the cytokine tumor necrosis factor-alpha. Evidence for proliferation was also obtained. Statin-induced microglial changes were blocked by mevalonate but not by cholesterol, indicating that they were probably due to suppression of isoprenoid synthesis. In accord with this, the statin effects were absent in slices co-incubated with geranylgeranyl pyrophosphate, a mevalonate product that provides for the prenylation of Rho GTPases. Finally, PD98089, a compound that blocks activation of extracellularly regulated kinases1/2, suppressed statin-induced up-regulation of tumor necrosis factor-alpha but had little effect on microglial transformation. These results suggest that 1) the mevalonate-isoprenoid pathway is involved in regulating microglial morphology and in controlling expression of certain cytokines and 2) statins have the potential for enhancing a component of AD with uncertain relationships to other features of the disease.     

Galanin in Alzheimer disease

Galanin (GAL) and GAL receptors (GALR) are overexpressed in limbic brain regions associated with cognition in Alzheimer disease (AD). The functional consequences of this overexpression are unclear. Because GAL inhibits cholinergic transmission and restricts long-term potentiation in the hippocampus, GAL overexpression may exacerbate clinical features of AD. In contrast, GAL expression increases in response to neuronal injury, and galaninergic hyperinnervation prevents the decreased production of protein phosphatase 1 subtype mRNAs in cholinergic basal forebrain neurons in AD. Thus, GAL may also be neuroprotective for AD. Further elucidation of GAL activity in selectively vulnerable brain regions will help gauge the therapeutic potential of GALR ligands for the treatment of AD.     

Inhibition of PTEN Attenuates Endoplasmic Reticulum Stress and Apoptosis via Activation of PI3K/AKT Pathway in Alzheimer’s Disease

Amyloid plaques and neurofibrillary tangles are pathologic hallmarks of Alzheimer’s disease (AD). Endoplasmic reticulum (ER) stress has been implicated in the loss of neurons in AD. The phosphatase and tensin homolog deleted on chromosome ten (PTEN) plays an important role in regulating neuronal survival processes. However, the direct effects of the PTEN on ER stress and apoptosis in AD have not been elucidated. In this study, we demonstrate that the expression of PTEN and ER stress related proteins, GRP78 and CHOP, increased in APP/PS1 transgenic AD mice compared with WT mice. A PTEN inhibitor, dipotassium bisperoxo-(5-hydroxypyridine-2-carboxyl)-oxovanadate (bpv) could decrease apoptosis, induce AKT phosphorylation and inhibit the ER stress response proteins in hippocampus in APP/PS1 transgenic AD model mice. Furthermore, treatment with the specific PI3K inhibitor, LY294002, significantly blocked the anti-apoptotic effects of bpv in AD mice. The expression in GRP78, CHOP and apoptosis levels by bpv was reversed after PI3K inhibitor treatment. Taken together, our results indicate that the neuroprotective role of bpv involves the suppression of ER stress via the activation of the PI3K/AKT signalling pathways in APP/PS1 transgenic AD model mice.     

Effects of Lovastatin and Pravastatin on Amyloid Processing and Inflammatory Response in TgCRND8 Brain

Previous studies suggest that treatment with statins reduce beta amyloid (Abeta) deposition in brains of mouse models of Alzheimer's disease (AD) and may reduce the prevalence of AD in humans. Since lipophilicity influences the biological efficacy of statins, we compared the effects of lovastatin, a lipophilic statin, to effects of the hydrophilic pravastatin on amyloid processing and inflammatory responses in brain. Three-month old TgCRND8 mice expressing mutant human amyloid precursor protein (mHuAPP) were treated daily with various doses of either statin. After 1 month, levels of cerebral soluble and fibrillar Abeta peptides, soluble sAPPalpha, and inflammatory cytokines were measured. Both statins caused dose-dependent reductions in total Abeta peptides with parallel increases in total sAPPalpha. At all doses, slightly greater effects were observed with lovastatin than with pravastatin. In contrast, only lovastatin significantly increased levels of IL-1beta and of TNFalpha in a dose-dependent manner. Lovastatin, but not pravastatin, decreased succinic dehydrogenase and increased lactate dehydrogenase activities in skeletal muscle and increased TUNEL staining in liver. Our data demonstrate that both statins shift the balance of APP processing from excessive beta-toward the normal alpha-cleavage while reducing the total amyloid burden in TgCRND8 brain and that lovastatin, but not pravastatin, potentiates cerebral inflammation and is associated with liver and muscle histotoxicity in these animals. These data show that pravastatin can reduce amyloid burden without potentiating inflammatory responses in brain and, therefore, may have a wider dose-range of safety than have lipophilic statins in the treatment or prevention of AD.     

Amyloid beta-protein interactions with membranes and cholesterol: causes or casualties of Alzheimer's disease

Amyloid beta-protein (Abeta) is thought to be one of the primary factors causing neurodegeneration in Alzheimer's disease (AD). This protein is an amphipathic molecule that perturbs membranes, binds lipids and alters cell function. Several studies have reported that Abeta alters membrane fluidity but the direction of this effect has not been consistently observed and explanations for this lack of consistency are proposed. Cholesterol is a key component of membranes and cholesterol interacts with Abeta in a reciprocal manner. Abeta impacts on cholesterol homeostasis and modification of cholesterol levels alters Abeta expression. In addition, certain cholesterol lowering drugs (statins) appear to reduce the risk of AD in human subjects. However, the role of changes in the total amount of brain cholesterol in AD and the mechanisms of action of statins in lowering the risk of AD are unclear. Here we discuss data on membranes, cholesterol, Abeta and AD, and propose that modification of the transbilayer distribution of cholesterol in contrast to a change in the total amount of cholesterol provides a cooperative environment for Abeta synthesis and accumulation in membranes leading to cell dysfunction including disruption in cholesterol homeostasis.     

Activation of α-secretase cleavage

Alpha-secretase-mediated cleavage of the amyloid precursor protein (APP) releases the neuroprotective APP fragment sαAPP and prevents amyloid β peptide (Aβ) generation. Moreover, α-secretase-like cleavage of the Aβ transporter 'receptor for advanced glycation end products' counteracts the import of blood Aβ into the brain. Assuming that Aβ is responsible for the development of Alzheimer's disease (AD), activation of α-secretase should be preventive. α-Secretase-mediated APP cleavage can be activated via several G protein-coupled receptors and receptor tyrosine kinases. Protein kinase C, mitogen-activated protein kinases, phosphatidylinositol 3-kinase, cAMP and calcium are activators of receptor-induced α-secretase cleavage. Selective targeting of receptor subtypes expressed in brain regions affected by AD appears reasonable. Therefore, the PACAP receptor PAC1 and possibly the serotonin 5-HT(6) receptor subtype are promising targets. Activation of APP α-secretase cleavage also occurs upon blockade of cholesterol synthesis by statins or zaragozic acid A. Under physiological statin concentrations, the brain cholesterol content is not influenced. Statins likely inhibit Aβ production in the blood by α-secretase activation which is possibly sufficient to inhibit AD development. A disintegrin and metalloproteinase 10 (ADAM10) acts as α-secretase on APP. By targeting the nuclear retinoic acid receptor β, the expression of ADAM10 and non-amyloidogenic APP processing can be enhanced. Excessive activation of ADAM10 should be avoided because ADAM10 and also ADAM17 are not APP-specific. Both ADAM proteins cleave various substrates, and therefore have been associated with tumorigenesis and tumor progression.     

Amyloid beta-protein interactions with membranes and cholesterol: causes or casualties of Alzheimer's disease

Amyloid beta-protein (Aβ) is thought to be one of the primary factors causing neurodegeneration in Alzheimer's disease (AD). This protein is an amphipathic molecule that perturbs membranes, binds lipids and alters cell function. Several studies have reported that Aβ alters membrane fluidity but the direction of this effect has not been consistently observed and explanations for this lack of consistency are proposed. Cholesterol is a key component of membranes and cholesterol interacts with Aβ in a reciprocal manner. Aβ impacts on cholesterol homeostasis and modification of cholesterol levels alters Aβ expression. In addition, certain cholesterol lowering drugs (statins) appear to reduce the risk of AD in human subjects. However, the role of changes in the total amount of brain cholesterol in AD and the mechanisms of action of statins in lowering the risk of AD are unclear. Here we discuss data on membranes, cholesterol, Aβ and AD, and propose that modification of the transbilayer distribution of cholesterol in contrast to a change in the total amount of cholesterol provides a cooperative environment for Aβ synthesis and accumulation in membranes leading to cell dysfunction including disruption in cholesterol homeostasis.     

Diammonium glycyrrhizinate upregulates PGC-1α and protects against Aβ1-42-induced neurotoxicity

Mitochondrial dysfunction is a hallmark of beta-amyloid (Aβ)-induced neurotoxicity in Alzheimer's disease (AD), and is considered an early event in AD pathology. Diammonium glycyrrhizinate (DG), the salt form of Glycyrrhizin, is known for its anti-inflammatory effects, resistance to biologic oxidation and membranous protection. In the present study, the neuroprotective effects of DG on Aβ(1-42)-induced toxicity and its potential mechanisms in primary cortical neurons were investigated. Exposure of neurons to 2 μM Aβ(1-42) resulted in significant viability loss and cell apoptosis. Accumulation of reactive oxygen species (ROS), decreased mitochondrial membrane potential, and activation of caspase-9 and caspase-3 were also observed after Aβ(1-42) exposure. All these effects induced by Aβ(1-42) were markedly reversed by DG treatment. In addition, DG could alleviate lipid peroxidation and partially restore the mitochondrial function in Aβ(1-42)-induced AD mice. DG also significantly increased the PGC-1α expression in vivo and in vitro, while knocking down PGC-1α partially blocked the protective effects, which indicated that PGC-1α contributed to the neuroprotective effects of DG. Furthermore, DG significantly decreased the escape latency and search distance and increased the target crossing times of Aβ(1-42)-induced AD mice in the Morris water maze test. Therefore, these results demonstrated that DG could attenuate Aβ(1-42)-induced neuronal injury by preventing mitochondrial dysfunction and oxidative stress and improved cognitive impairment in Aβ(1-42)-induced AD mice, indicating that DG exerted potential beneficial effects on AD.     

Nicotine increases the expression of high affinity nerve growth factor receptors in both in vitro and in vivo

Impairment in nerve growth factor (NGF)-mediated support to basal forebrain cholinergic neurons may represent an initial insult to certain neural cells in Alzheimer's disease (AD). High affinity NGF receptor (TrkA) levels are decreased in AD brains as compared to age-matched control brains. One of the approaches suggested for the treatment of AD exploits the ability of small molecular substances to enhance the expression of endogenous growth factors and/or their receptors. The purpose of this study was to determine whether treatment with nicotine in both in vitro and in vivo settings would increase the neural expression of TrkA receptors. Using a differentiated PC12 neuronal-like system, chronic nicotine treatment increased cell surface TrkA receptor expression. Nicotine's action was blocked by co-treatment with either the non-competitive nicotinic acetylcholine receptor (nAChR) antagonist mecamylamine or with the alpha7 nAChR-selective antagonist methyllycaconitine. Surprisingly, certain low doses of mecamylamine alone also increased TrkA receptor levels. Rats prepared with chronic indwelling intravenous catheters were continuously infused with nicotine to deliver a total dose of 12 mg/kg over 24 hr. This treatment resulted in a significant 44% increase in TrkA receptor expression in the hippocampus. As in the cell experiments, mecamylamine also increased hippocampal TrkA receptor expression. In fact, the ratio of the maximal mecamylamine response to the maximal nicotine response that was measured in vitro, i.e., 0.43 was remarkably similar to that for the in vivo experiment, i.e., 0.47. Since in our previous studies the increase in TrkA expression produced by nicotine was shown to be related to its cytoprotective actions, these results suggest that nicotine's neuroprotective actions might also be mediated through the drug's interaction with central alpha7 nAChRs and subsequent increase in TrkA receptor expression.     

Preservation of Noradrenergic Neurons in the Locus Ceruleus that Coexpress Galanin mRNA in Alzheimer's Disease

Galanin (GAL) innervation is hypertrophied in the basal forebrain and cortex of patients with Alzheimer's disease (AD). Increased GAL could exacerbate the cognitive and behavioral deficits of AD because GAL acts as an inhibitory modulator of cholinergic and noradren-ergic neurotransmission. The locus ceruleus (LC) may be a source of increased GAL in AD because (a) GAL is coexpressed in a subset of LC neurons, (b) GAL expression is up-regulated with neuronal injury, and (c) the LC undergoes extensive degeneration in AD. Therefore, we have used in situ hybridization histochemistry to measure GAL gene expression in the LC of AD patients and sex- and age-matched nondemented controls. Despite the extensive loss of norepinephrine neurons with AD, GAL mRNA-expressing neurons in the LC did not differ between groups. This resulted in a significant increase in the percentage of neuromelanin-pigmented cells that coexpressed GAL in AD patients compared with controls. These findings raise the possibility that the increased incidence of GAL expression among remaining LC neurons contributes to the hyperinnervation of GAL fibers in AD. Furthermore, GAL may be neuroprotective in the LC.     

Alzheimer's disease: cholesterol, membrane rafts, isoprenoids and statins

Alzheimer''s disease (AD) is a heterogeneous neurodegenerative disorder and the most prevalent form of dementia worldwide. AD is characterized pathologically by amyloid-β plaques, neurofibrillary tangles and neuronal loss, and clinically by a progressive loss of cognitive abilities. At present, the fundamental molecular mechanisms underlying the disease are unclear and no treatment for AD is known. Epidemiological evidence continues to mount linking vascular diseases, such as hypertension and diabetes, and hypercholesterolaemia with an increased risk for developing AD. A growing amount of evidence suggests a mechanistic link between cholesterol metabolism in the brain and the formation of amyloid plaques in AD development. Cholesterol and statins clearly modulate β-amyloid precursor protein (βAPP) processing in cell culture and animal models. Statins not only reduce endogenous cholesterol synthesis but also exert other various pleiotrophic effects, such as the reduction in protein isoprenylation. Through these effects statins modulate a variety of cellular functions involving both cholesterol (and membrane rafts) and isoprenylation. Although clearly other factors, such as vascular inflammation, oxidative stress and genetic factors, are intimately linked with the progression of AD, this review focuses on the present research findings describing the effect of cholesterol, membrane rafts and isoprenylation in regulating βAPP processing and in particular γ-secretase complex assembly and function and AD progression, along with consideration for the potential role statins may play in modulating these events.