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

A Gain-of-function Mutation in the Gating Domain of ITPR1 Impairs Motor Movement and Increases Thermal and Mechanical Sensitivity

Inositol 1,4,5-trisphosphate receptor type 1 (ITPR1) is an intracellular Ca²⁺ release channel important for a number of fundamental cellular functions. Consistent with its critical physiological significance, mutations in ITPR1 are associated with disease. Surprisingly, nearly all the disease-associated ITPR1 mutations characterized to date are loss of function. Despite the paucity of ITPR1 gain-of-function (GOF) mutations, enhanced ITPR1 function as a result of dysregulation by ITPR1 interacting proteins is thought to be associated with ataxia, learning and memory impairments, Alzheimer's disease (AD) progression, and chronic pain. However, direct evidence for the role of ITPR1 GOF in disease is lacking. To determine whether GOF in ITPR1 itself has pathological ramifications, we employed a newly developed mouse model expressing an ITPR1 mutation in the gating domain of the channel, D2594K, that markedly increased the channel's sensitivity to activation by IP₃. Behavioral studies showed that the ITPR1-D2594K^+/- mutant mice displayed motor deficits and reduced muscle strength. However, the ITPR1-D2594K^+/- mutation did not significantly alter hippocampal learning and memory and did not change learning and memory impairments when crossed with the 5xFAD AD model mice. On the other hand, ITPR1-D2594K^+/- mice exhibited increased sensitivity to thermal and mechanical stimulation compared to WT. Interestingly, R-carvedilol treatment attenuated the enhanced thermal and mechanical nociception in ITPR1-D2594K^+/- mice. Thus, the ITPR1-D2594K^+/- mutation in the channel's gating domain has a marked impact on motor movements and pain perception, but little effect on hippocampal learning and memory.

N-Acetyl-Cysteine: Modulating the Cysteine Redox Proteome in Neurodegenerative Diseases

In the last twenty years, significant progress in understanding the pathophysiology of age-associated neurodegenerative diseases has been made. However, the prevention and treatment of these diseases remain without clinically significant therapeutic advancement. While we still hope for some potential genetic therapeutic approaches, the current reality is far from substantial progress. With this state of the issue, emphasis should be placed on early diagnosis and prompt intervention in patients with increased risk of neurodegenerative diseases to slow down their progression, poor prognosis, and decreasing quality of life. Accordingly, it is urgent to implement interventions addressing the psychosocial and biochemical disturbances we know are central in managing the evolution of these disorders. Genomic and proteomic studies have shown the high molecular intricacy in neurodegenerative diseases, involving a broad spectrum of cellular pathways underlying disease progression. Recent investigations indicate that the dysregulation of the sensitive-cysteine proteome may be a concurrent pathogenic mechanism contributing to the pathophysiology of major neurodegenerative diseases, opening new therapeutic opportunities. Considering the incidence and prevalence of these disorders and their already significant burden in Western societies, they will become a real pandemic in the following decades. Therefore, we propose large-scale investigations, in selected groups of people over 40 years of age with decreased blood glutathione levels, comorbidities, and/or mild cognitive impairment, to evaluate supplementation of the diet with low doses of N-acetyl-cysteine, a promising and well-tolerated therapeutic agent suitable for long-term use.

BCAT-induced autophagy regulates Aβ load through an interdependence of redox state and PKC phosphorylation-implications in Alzheimer's disease

Leucine, nutrient signal and substrate for the branched chain aminotransferase (BCAT) activates the mechanistic target of rapamycin (mTORC1) and regulates autophagic flux, mechanisms implicated in the pathogenesis of neurodegenerative conditions such as Alzheimer's disease (AD). BCAT is upregulated in AD, where a moonlighting role, imparted through its redox-active CXXC motif, has been suggested. Here we demonstrate that the redox state of BCAT signals differential phosphorylation by protein kinase C (PKC) regulating the trafficking of cellular pools of BCAT. We show inter-dependence of BCAT expression and proteins associated with the P13K/Akt/mTORC1 and autophagy signalling pathways. In response to insulin or an increase in ROS, BCATc is trafficked to the membrane and docks via palmitoylation, which is associated with BCATc-induced autophagy through PKC phosphorylation. In response to increased levels of BCATc, as observed in AD, amyloid β (Aβ) levels accumulate due to a shift in autophagic flux. This effect was diminished when incubated with leucine, indicating that dietary levels of amino acids show promise in regulating Aβ load. Together these findings show that increased BCATc expression, reported in human AD brain, will affect autophagy and Aβ load through the interdependence of its redox-regulated phosphorylation offering a novel target to address AD pathology.

Differential Levels and Phosphorylation of Type 1 Inositol 1,4,5-Trisphosphate Receptor in Four Different Murine Models of Huntington Disease

BACKGROUND

The intracellular ion channel type 1 inositol 1,4,5-trisphosphate receptor (IP3R1) releases Ca2+ from the endoplasmic reticulum upon stimulation with IP3. Perturbation of IP3R1 has been implicated in the development of several neurodegenerative disorders, including Huntington disease (HD).

OBJECTIVE

To elucidate the putative role of IP3R1 phosphorylation in HD, we investigated IP3R1 levels and protein phosphorylation state in the striatum, hippocampus and cerebellum of four murine HD models.

METHODS

Quantitative immunoblotting with antibodies to IP3R1 protein and its phosphorylated serines 1589 and 1755 was applied to brain homogenates from R6/1 mice to study early-onset aggressive HD. To determine if IP3R1 changes precede overt pathology, we immunostained tissues from the regions of interest and several control regions for IP3R1 in tgHDCAG51n rats and BACHD and zQ175DNKI mice, all recognized models for late-onset HD.

RESULTS

R6/1 mice had reduced total IP3R1 immunoreactivity, variably reduced serine1755-phosphorylation in all regions investigated, and reduced serine1589-phosphorylation in cerebellum. IP3R1 levels were decreased relative to cell-specific marker proteins. In tgHDCAG51n rats we found reduced IP3R1 levels in the cerebellum, but otherwise unchanged IP3R1 phosphorylation and protein levels. In BACHD and zQ175DNKI mice only age-dependent decline of IP3R1 was observed.

CONCLUSION

The level and phosphorylation of IP3R1 is reduced to a variable degree in the different HD models relative to control, indicating that earlier findings in more aggressive exon 1-truncated HD models may not be replicated in models with higher construct validity. Further analysis of possible coupling of reduced IP3R1 levels with development of neuropathological responses and cell-specific degeneration is warranted.

Astroglial Calcium Signaling in Aging and Alzheimer's Disease

Astrocytes are the homeostatic and protective cells of the central nervous system (CNS). In neurological diseases, astrocytes undergo complex changes, which are subclassified into (1) reactive astrogliosis, an evolutionary conserved defensive rearrangement of cellular phenotype aimed at neuroprotection; (2) pathological remodeling, when astrocytes acquire new features driving pathology; and (3) astrodegeneration, which is manifested by astroglial atrophy and loss of homeostatic functions. In aging brains as well as in the brains affected by Alzheimer's disease (AD), astrocytes acquire both atrophic and reactive phenotypes in a region- and disease-stage-dependent manner. Prevalence of atrophy overreactivity, observed in certain brain regions and in terminal stages of the disease, arguably facilitates the development of neurological deficits. Astrocytes exhibit ionic excitability mediated by changes in intracellular concentration of ions, most importantly of Ca²⁺ and Na⁺, with intracellular ion dynamics triggered by the activity of neural networks. AD astrocytes associated with senile plaques demonstrate Ca²⁺ hyperactivity in the form of aberrant Ca²⁺ oscillations and pathological long-range Ca²⁺ waves. Astroglial Ca²⁺ signaling originating from Ca²⁺ release from the endoplasmic reticulum is a key factor in initiating astrogliotic response; deficient Ca²⁺ signaling toolkits observed in entorhinal and prefrontal cortices of AD model animals may account for vulnerability of these regions to the pathology.

Plasma metabolomics in early Alzheimer's disease patients diagnosed with amyloid biomarker

An untargeted metabolomics study has been carried out using plasma samples from patients with Mild Cognitive Impairment due to Alzheimer's disease patients (MCI-AD, n = 29) and healthy people (n = 29)). They have been classified following the National Institute on Aging and Alzheimer's Association (NIA-AA) recommendations and cerebrospinal fluid biomarkers. The analytical method was based on liquid chromatography coupled to high resolution mass spectrometry. The data process from the corresponding metabolic profiles retained 1158 molecular features in positive and 424 in negative ionization mode. Differences between metabolomic profiles from MCI-AD patients and healthy participants were investigated using a penalized logistic regression analysis (ElasticNet), and being able to select automatically the most informative variables (53 molecular features). From the molecular features selected for the elastic net models, 16 variables were preliminarily identified by The Human Metabolome Database (amino acids, lipids…). However, only 4 of these variables were tentatively identified by MS/MS and all ions fragmentation modes, being choline the only confirmed metabolite. Regarding their metabolic pathways, they could be involved in cholinergic system, energy metabolism, amino acids and lipids pathways. To conclude, this is a reliable approach to early AD mechanisms, and choline has been identified as a promising AD diagnosis metabolite. SIGNIFICANCE: The untargeted analysis carried out in human plasma samples from early Alzheimer's disease patients and healthy individuals, and the use of sophisticated statistical tools, identified some metabolic pathways and plasma biomarkers. Preliminarily, cholinergic system, energy metabolism, and aminoacids and lipids pathways may be involved in early Alzheimer's disease development.

Astroglia in Alzheimer's Disease

Alzheimer's disease is the most common cause of dementia. Cellular changes in the brains of the patients suffering from Alzheimer's disease occur well in advance of the clinical symptoms. At the cellular level, the most dramatic is a demise of neurones. As astroglial cells carry out homeostatic functions of the brain, it is certain that these cells are at least in part a cause of Alzheimer's disease. Historically, Alois Alzheimer himself has recognised this at the dawn of the disease description. However, the role of astroglia in this disease has been understudied. In this chapter, we summarise the various aspects of glial contribution to this disease and outline the potential of using these cells in prevention (exercise and environmental enrichment) and intervention of this devastating disease.

Astroglial calcium signalling in Alzheimer's disease

Neuroglial contribution to Alzheimer's disease (AD) is pathologically relevant and highly heterogeneous. Reactive astrogliosis and activation of microglia contribute to neuroinflammation, whereas astroglial and oligodendroglial atrophy affect synaptic transmission and underlie the overall disruption of the central nervous system (CNS) connectome. Astroglial function is tightly integrated with the intracellular ionic signalling mediated by complex dynamics of cytosolic concentrations of free Ca²⁺ and Na⁺. Astroglial ionic signalling is mediated by plasmalemmal ion channels, mainly associated with ionotropic receptors, pumps and solute carrier transporters, and by intracellular organelles comprised of the endoplasmic reticulum and mitochondria. The relative contribution of these molecular cascades/organelles can be plastically remodelled in development and under environmental stress. In AD astroglial Ca²⁺ signalling undergoes substantial reorganisation due to an abnormal regulation of expression of Ca²⁺ handling molecular cascades.

Acute Effects of Muscarinic M1 Receptor Modulation on AβPP Metabolism and Amyloid-β Levels in vivo: A Microdialysis Study

Indirect modulation of cholinergic activity by cholinesterase inhibition is currently a widely established symptomatic treatment for Alzheimer's disease (AD). Selective activation of certain muscarinic receptor subtypes has emerged as an alternative cholinergic-based amyloid-lowering strategy for AD, as selective muscarinic M1 receptor agonists can reduce amyloid-β (Aβ) production by shifting endoproteolytic amyloid-β protein precursor (AβPP) processing toward non-amyloidogenic pathways. In this study, we addressed the hypothesis that acute stimulation of muscarinic M1 receptors can inhibit Aβ production in awake and freely moving AβPP transgenic mice. By combining intracerebral microdialysis with retrodialysis, we determined hippocampal Aβ concentrations during simultaneous pharmacological modulation of brain M1 receptor function. Infusion with a M1 receptor agonist AF102B resulted in a rapid reduction of interstitial fluid (ISF) Aβ levels while treatment with the M1 antagonist dicyclomine increased ISF Aβ levels reaching significance within 120 minutes of treatment. The reduction in Aβ levels was associated with PKCα and ERK activation resulting in increased levels of the α-secretase ADAM17 and a shift in AβPP processing toward the non-amyloidogenic processing pathway. In contrast, treatment with the M1 receptor antagonist dicyclomine caused a decrease in levels of phosphorylated ERK that was independent of PKCα, and led to an elevation of β-secretase levels associated with increased amyloidogenic AβPP processing. The results of this study demonstrate rapid effects of in vivo M1 receptor modulation on the ISF pool of Aβ and suggest that intracerebral microdialysis with retrodialysis is a useful technical approach for monitoring acute treatment effects of muscarinic receptor modulators on AβPP/Aβ metabolism.

Cholinergic Mechanisms in the Cerebral Cortex: Beyond Synaptic Transmission

Functional overviews of cholinergic mechanisms in the cerebral cortex have traditionally focused on the release of acetylcholine with modulator and transmitter effects. Recently, however, data have emerged that extend the role of acetylcholine and cholinergic innervations to a range of housekeeping and metabolic functions. These include regulation of amyloid precursor protein (APP) processing with production of amyloid β (Aβ) and other APP fragments and control of the phosphorylation of microtubule-associated protein (MAP) tau. Evidence has been also presented for receptor-ligand like interactions of cholinergic receptors with soluble Aβ peptide and MAP tau, with modulator and signaling effects. Moreover, high-affinity binding of Aβ to the neurotrophin receptor p75 (p75NTR) enriched in basalo-cortical cholinergic projections has been implicated in clearance of Aβ and nucleation of amyloid plaques. Here, we critically evaluate these unorthodox cholinergic mechanisms and discuss their role in neuronal physiology and the biology of Alzheimer's disease.

Ca2+ dysregulation in the endoplasmic reticulum related to Alzheimer's disease: A review on experimental progress and computational modeling

Alzheimer's disease (AD) is a devastating, incurable neurodegenerative disease affecting millions of people worldwide. Dysregulation of intracellular Ca(2+) signaling has been observed as an early event prior to the presence of clinical symptoms of AD and is believed to be a crucial factor contributing to its pathogenesis. The progressive and sustaining increase in the resting level of cytosolic Ca(2+) will affect downstream activities and neural functions. This review focuses on the issues relating to the increasing Ca(2+) release from the endoplasmic reticulum (ER) observed in AD neurons. Numerous research papers have suggested that the dysregulation of ER Ca(2+) homeostasis is associated with mutations in the presenilin genes and amyloid-β oligomers. These disturbances could happen at many different points in the signaling process, directly affecting ER Ca(2+) channels or interfering with related pathways, which makes it harder to reveal the underlying mechanisms. This review paper also shows that computational modeling is a powerful tool in Ca(2+) signaling studies and discusses the progress in modeling related to Ca(2+) dysregulation in AD research.

Contribution of Ca2+ release channels to hippocampal synaptic plasticity and spatial memory: potential redox modulation

SIGNIFICANCE

Memory is an essential human cognitive function. Consequently, to unravel the cellular and molecular mechanisms responsible for the synaptic plasticity events underlying memory formation, storage and loss represents a major challenge of present-day neuroscience.

RECENT ADVANCES

This review article first describes the wide-ranging functions played by intracellular Ca2+ signals in the activity-dependent synaptic plasticity processes underlying hippocampal spatial memory, and next, it focuses on how the endoplasmic reticulum Ca2+ release channels, the ryanodine receptors, and the inositol 1,4,5-trisphosphate receptors contribute to these processes. We present a detailed examination of recent evidence supporting the key role played by Ca2+ release channels in synaptic plasticity, including structural plasticity, and the formation/consolidation of spatial memory in the hippocampus.

CRITICAL ISSUES

Changes in cellular oxidative state particularly affect the function of Ca2+ release channels and alter hippocampal synaptic plasticity and the associated memory processes. Emphasis is placed in this review on how defective Ca2+ release, presumably due to increased levels of reactive oxygen species, may cause the hippocampal functional defects that are associated to aging and Alzheimer's disease (AD).

FUTURE DIRECTIONS

Additional studies should examine the precise molecular mechanisms by which Ca2+ release channels contribute to hippocampal synaptic plasticity and spatial memory formation/consolidation. Future studies should test whether redox-modified Ca2+ release channels contribute toward generating the intracellular Ca2+ signals required for sustained synaptic plasticity and hippocampal spatial memory, and whether loss of redox balance and oxidative stress, by altering Ca2+ release channel function, presumably contribute to the abnormal memory processes that occur during aging and AD.

Uncoupling of M1 muscarinic receptor/G-protein interaction by amyloid β(1-42)

The overproduction of β-amyloid (Aβ) fragments in transgenic APPswe/PS1dE9 mice results in formation of amyloid deposits in the cerebral cortex and hippocampus starting around four months of age and leading to cognitive impairment much later. We have previously found an age and transgene-dependent weakening of muscarinic receptor-mediated transmission that was not present in young (6-10-week-old) animals but preceded both amyloid deposits and cognitive deficits. Now we investigated immediate and prolonged in vitro effects of non-aggregated Aβ(1-42) on coupling of individual muscarinic receptor subtypes expressed in CHO (Chinese hamster ovary) cells and their underlying mechanisms. Immediate application of 1 μM Aβ(1-42) had no effect on the binding of the muscarinic antagonist N-methylscopolamine or the agonist carbachol. In contrast, 4-day treatment of CHO cells expressing the M1 muscarinic receptor with 100 nM Aβ(1-42) significantly changed the binding characteristics of the muscarinic agonist carbachol and reduced the extent of the M1 receptor-stimulated breakdown of phosphatidylinositol while it did not demonstrate overt toxic effects. The treatment had no influence on the expression of either G-proteins or muscarinic receptors. In concert, we found no change in the gene expression of muscarinic receptor subtypes and gene or protein expression of the G(s), G(q/11), and G(i/o) G-proteins in the cerebral cortex of young adult APPswe/PS1dE9 mice that demonstrate high concentrations of soluble Aβ(1-42) and impaired muscarinic receptor-mediated G-protein activation. Our results provide strong evidence that the initial injurious effects of Aβ(1-42) on M1 muscarinic receptor-mediated transmissionis is due to compromised coupling of the receptor with G(q/11) G-protein.

Effect of Huannao Yicong prescription [See Text] extract on β-amyloid precursor protein metabolic signal transduction-related protein in brain tissue of dementia model transgenic mouse

OBJECTIVE

To observe the effect of Huannao Yicong Prescription (, HNYC, a Chinese medical compound) extract on β-amyloid precursor protein (APP) metabolic signal transduction related protein kinase C (PKC), tyrosine amyloid protein kinase (TrKA), and glycogen synthase kinase-3 (GSK-3) in brain tissue of transgenic mouse dementia model induced by APP.

METHODS

Sixty dementia model transgenic 3-month-old mice induced by APP695V717I were randomly allocated in four groups: the model group (A), the Donepezil (0.65×10(-3) g·kg(-1)·(-1))-treated group (B), and the two HNYC-treated groups (C and D) with high dosage (2.8 g·kg(-1)·(-1)) and low dosage (1.4 g·kg(-1)·(-1)) of HNYC extract, respectively, 15 mice in each group. Besides, a normal control group was set up with 15 C57BL/6J mice with the same age and genetic background as the model mice. The drugs for treatment were administered once a day by dissolving in equal-volume distilled water through gastric infusion, continued for 6 months, to mice in group A and to normal control group equal-volume distilled water was administered instead. Spatial learning and memory capacity of mice were observed by Morris water maze; their one-time escape response memory capacity was tested by diving platform; and changes of PKC, TrkA, and GSK-3 levels in hippocampus and cortex of brain were detected by Western blotting.

RESULTS

HNYC extract showed significant effects on increasing the time of model mice for swimming through the flat roof and the swimming time and path in the fourth quadrant P<0.05 or P<0.01). Diving platform test showed that the latent times in Groups B and C were longer than that in Group A significantly (P <0.05 and P<0.01). Compared with the normal control group, PKC and TrkA protein expression levels in hippocampus and cortex of model mice's brain lowered significantly (P<0.01), while GSK-3 protein expression increased significantly (P<0.01); compared with Group A (the model group), hippocampal and cortical levels of PKC protein expression in the intervened groups (B-D) as well as those of TrkA in Group C were higher (P<0.01 or P<0.05), while hippocampal levels of GSK-3 in intervened groups were lower (P<0.01).

CONCLUSION

HNYC extract could obviously increase the protein expressions of PKC and TrkA and decrease the expression of GSK-3 protein in brain tissue of transgenetic mice model of dementia, and regulate APP metabolic signal transduction path, and thus to suppress the production of Aβ, which is one of the dominant mechanisms for improving learning/memory capacity of dementia model animals.

Intermolecular association between caspase-mediated cleavage fragments of phospholipase D1 protects against apoptosis

Phospholipase D plays an anti-apoptotic role but little is known about dynamics of phospholipase D turnover during apoptosis. We have recently identified phospholipase D1 as a new substrate of caspases which generates the N-terminal and C-terminal fragment of phospholipase D1. In the present study, we tried to investigate whether association of the caspase cleavage fragments may be involved in regulation of apoptosis. Ectopically expressed C-terminal fragment, but not N-terminal fragment of phospholipase D1, is exclusively imported into the nucleus via a nuclear localization sequence; however, endogenous C-terminal fragment of phospholipase D1 from etoposide-induced apoptotic cells and Alzheimer's disease brain tissues with active caspase-3, was localized in the cytosolic fraction as well as the nuclear fraction. Intermolecular association between the two fragments of phospholipase D1 through hydrophobic residues within the catalytic motif inhibited nuclear localization of C-terminal fragment of phospholipase D1, and two catalytic motif and nuclear localization sequence regulated nuclocytoplasmic shuttling of phospholipase D1. Moreover, hydrophobic residues involved in the intermolecular association are also required for both its enzymatic activity and anti-apoptotic function. Taken together, we demonstrate that interdomain association and dissociation of phospholipase D1 might provide new insights into modulation of apoptosis.

Novel mechanism of increased Ca2+ release following oxidative stress in neuronal cells involves type 2 inositol-1,4,5-trisphosphate receptors

Dysregulation of Ca(2+) signaling following oxidative stress is an important pathophysiological mechanism of many chronic neurodegenerative disorders, including Alzheimer's disease, age-related macular degeneration, glaucomatous and diabetic retinopathies. However, the underlying mechanisms of disturbed intracellular Ca(2+) signaling remain largely unknown. We here describe a novel mechanism for increased intracellular Ca(2+) release following oxidative stress in a neuronal cell line. Using an experimental approach that included quantitative polymerase chain reaction, quantitative immunoblotting, microfluorimetry and the optical imaging of intracellular Ca(2+) release, we show that sub-lethal tert-butyl hydroperoxide-mediated oxidative stress result in a selective up-regulation of type-2 inositol-1,4,5,-trisphophate receptors. This oxidative stress mediated change was detected both at the transcriptional and translational level and functionally resulted in increased Ca(2+) release into the nucleoplasm from the membranes of the nuclear envelope at a given receptor-specific stimulus. Our data describe a novel source of Ca(2+) dysregulation induced by oxidative stress with potential relevance for differential subcellular Ca(2+) signaling specifically within the nucleus and the development of novel neuroprotective strategies in neurodegenerative disorders.

Diverse roles of extracellular calcium-sensing receptor in the central nervous system

The G-protein-coupled calcium-sensing receptor (CaSR), upon activation by Ca(2+) or other physiologically relevant polycationic molecules, performs diverse functions in the brain. The CaSR is widely expressed in the central nervous system (CNS) and is characterized by a robust increase in its expression during postnatal brain development over adult levels throughout the CNS. Developmental increases in CaSR levels in brain correlate with myelinogenesis. Indeed, neural stem cells differentiating to the oligodendrocyte lineage exhibit the highest CaSR expression compared with those differentiating to astrocytic or neuronal lineages. In adult CNS, CaSR has broad relevance in maintaining local ionic homeostasis. CaSR shares an evolutionary relationship with the metabotropic glutamate receptor and forms heteromeric complexes with the type B-aminobutyric acid receptor subunits that affects its cell surface expression, activation, signaling, and functions. In normal physiology as well as in pathologic conditions, CaSR is activated by signals arising from mineral ions, amino acids, polyamines, glutathione, and amyloid-beta in conjunction with Ca(2+) and other divalent cationic ligands. CaSR activation regulates membrane excitability of neurons and glia and affects myelination, olfactory and gustatory signal integration, axonal and dendritic growth, and gonadotrophin-releasing hormonal-neuronal migration. Insofar as the CaSR is a clinically important therapeutic target for parathyroid disorders, development of its agonists or antagonists as therapeutics for CNS disorder could be a major breakthrough.

Calcium induces expression of cytoplasmic gelsolin in SH-SY5Y and HEK-293 cells

Gelsolin plays an important role in the regulation of amyloid beta-protein fibrillogenesis. We report here that calcium ionophore A23187 induces the expression of cytoplasmic gelsolin (c-gelsolin), and that protein kinase C (PKC) is involved in the up-regulation of c-gelsolin. In the presence of calcium, both SH-SY5Y and HEK-293 cells upon treatment with A23187 showed an increase in c-gelsolin expression in a concentration-dependent manner. Calcium-mediated up-regulation of c-gelsolin was inhibited by cycloheximide (a general inhibitor of protein synthesis). When cells were pretreated with staurosporine (an inhibitor of a variety of protein kinases including PKC), the up-regulation of c-gelsolin induced by A23187 was inhibited. Calphostin C, an inhibitor of PKC, blocked the up-regulation of c-gelsolin induced by A23187, while inhibitors of mitogen-activated protein kinases had no effect on c-gelsolin expression. In addition, phorbol-12-myristate-13-acetate, an activator of PKC, up-regulated c-gelsolin expression. These results suggest that calcium mediates up-regulation of c-gelsolin in a PKC-dependent manner.

Control of intracellular calcium signaling as a neuroprotective strategy

Both acute and chronic degenerative diseases of the nervous system reduce the viability and function of neurons through changes in intracellular calcium signaling. In particular, pathological increases in the intracellular calcium concentration promote such pathogenesis. Disease involvement of numerous regulators of intracellular calcium signaling located on the plasma membrane and intracellular organelles has been documented. Diverse groups of chemical compounds targeting ion channels, G-protein coupled receptors, pumps and enzymes have been identified as potential neuroprotectants. The present review summarizes the discovery, mechanisms and biological activity of neuroprotective molecules targeting proteins that control intracellular calcium signaling to preserve or restore structure and function of the nervous system. Disease relevance, clinical applications and new technologies for the identification of such molecules are being discussed.

Protein kinase C activators as synaptogenic and memory therapeutics

The last decade has witnessed a rapid progress in understanding of the molecular cascades that may underlie memory and memory disorders. Among the critical players, activity of protein kinase C (PKC) isoforms is essential for many types of learning and memory and their dysfunction, and is critical in memory disorders. PKC inhibition and functional deficits lead to an impairment of various types of learning and memory, consistent with the observations that neurotoxic amyloid inhibits PKC activity and that transgenic animal models with PKCbeta deficit exhibit impaired capacity in cognition. In addition, PKC isozymes play a regulatory role in amyloid production and accumulation. Restoration of the impaired PKC signal pathway pharmacologically results in an enhanced memory capacity and synaptic remodeling / repair and synaptogenesis, and, therefore, represents a potentially important strategy for the treatment of memory disorders, including Alzheimer's dementia. The PKC activators, especially those that are isozyme-specific, are a new class of drug candidates that may be developed as future memory therapeutics.

Calcium in the initiation, progression and as an effector of Alzheimer's disease pathology

The cause(s) of sporadic Alzheimer’s disease (sAD) are complex and currently poorly understood. They likely result from a combination of genetic, environmental, proteomic and lipidomic factors that crucially occur only in the aged brain. Age-related changes in calcium levels and dynamics have the potential to increase the production and accumulation of both amyloid-β peptide (Aβ) and τ pathologies in the AD brain, although these two pathologies themselves can induce calcium dyshomeostasis, particularly at synaptic membranes. This review discuses the evidence for a role for calcium dyshomeostasis in the initiation of pathology, as well as the evidence for these pathologies themselves disrupting normal calcium homeostasis, which lead to synaptic and neuronal dysfunction, synaptotoxicity and neuronal loss, underlying the dementia associated with the disease.

Evidence supporting a role for the calcium-sensing receptor in Alzheimer disease

The calcium-sensing receptor (CASR) is a G-protein coupled, transmembrane receptor that responds to changes in Ca(2+) levels. We hypothesized that the CASR could have a role in Alzheimer disease (AD) given expression of the CASR in brain, knowledge that calcium dysregulation promotes susceptibility to neuronal cell damage, the important role that the CASR plays in calcium regulation, and the fact that systemic calcium homeostasis and G-protein signal transduction are altered in AD patients. To investigate the association of CASR variation in AD susceptibility, we genotyped a polymorphic dinucleotide repeat marker within intron 4, one SNP within the promoter region and three non-synonymous SNPs within exon 7 of the CASR gene and tested for association analysis, using a well-characterized cohort of AD cases (n = 692) and controls (n = 435). The dinucleotide repeat polymorphism was significantly associated with AD status (OR = 1.62; 95% CI: 1.27-2.07, P = 0.00037, Bonferroni corrected P = 0.0011) and the three non-synonymous SNP haplotype was boarderline associated with AD status (P = 0.032, Bonferroni corrected P = 0.096). Stratifying by APOE4 allele carrier status revealed that the significant association was only in non-APOE4 carriers (OR of 1.90; 95% CI: 1.37-2.62, P = 0.0001). We also investigated whether apoE or beta amyloid could activate the calcium-sensing receptor. The receptor activation assays revealed that apoE as well as beta amyloid activated the CASR and that the level of activation appeared to be isoform dependent for apoE. These data support our hypothesis that the CASR has a role in AD susceptibility, particularly in individuals without an APOE4 allele.

Activation of glycogen synthase kinase-3 induces Alzheimer-like tau hyperphosphorylation in rat hippocampus slices in culture

Formation of neurofibrillary tangle from hyperphosphorylated tau is one of the hallmark lesions seen in Alzheimer's disease (AD) brain, and neuronal deregulation of glycogen synthase kinase-3 (GSK-3) activity plays key role in tau hyperphosphorylation. In the present study, the role of GSK-3 on tau phosphorylation in hippocampus slice culture was examined by incubating the slice with wortmannin (WT), an inhibitor of phosphatidylinositol 3-kinase (PI3K) and GF-109203X (GFX), an inhibitor of protein kinase C (PKC). It was found that treatment of the slices with GFX or WT separately induced tau hyperphosphorylation both at Ser396/Ser404 (PHF-1) and Ser199/Ser202 (Tau-1) sites. The phosphorylation rate of tau at PHF-1 and Tau-1 epitopes was further increased when GFX and WT were used in combination, and at this condition, AD-like tau accumulation was observed. GSK-3 activity was significantly increased with a concurrently decreased level of inactivated form of GSK-3. Lithium chloride (LiCl), a GSK-3 inhibitor, prevented tau from WT- and GFX-induced hyperphosphorylation. It suggests that GSK-3 is regulated through PI3K and PKC pathway, and activation of GSK-3 not only induces hyperphosphorylation of tau but also leads to accumulation of tau in cultured rat brain slice.

Prolonged Alzheimer-like tau hyperphosphorylation induced by simultaneous inhibition of phosphoinositol-3 kinase and protein kinase C in N2a cells

Co-injection of wortmannin (inhibitor of phosphatidylinositol-3 kinase, PI3K) and GF109203X (inhibitor of protein kinase C, PKC) into the rat brain was found to induce spatial memory deficiency and enhance tau hyperphosphorylation in the hippocampus of rat brain. To establish a cell model with durative Alzheimer-like tau hyperphosphorylation in this study, we treated N2a neuroblastoma cells with wortmannin and GF109203X separately and simultaneously, and measured the glycogen synthase kinase 3 (GSK-3) activity by gamma-32P-labeling and the level of tau phosphorylation by Western blotting. It was found that the application of wortmannin alone only transitorily increased the activity of GSK-3 (about 1 h) and the level of tau hyperphosphorylation at Ser396/Ser404 and Ser199/Ser202 sites (no longer than 3 h); however, a prolonged and intense activation of GSK-3 (over 12 h) and enhanced tau hyperphosphorylation (about 24 h) were observed when these two selective kinase inhibitors were applied together. We conclude that the simultaneous inhibition of PI3K and PKC can induce GSK-3 overactivation, and further strengthen and prolong the Alzheimer-like tau hyperphosphorylation in N2a cells, suggesting the establishment of a cell model with early pathological events of Alzheimer's disease.

Overactivation of glycogen synthase kinase-3 by inhibition of phosphoinositol-3 kinase and protein kinase C leads to hyperphosphorylation of tau and impairment of spatial memory

Neurofibrillary tangles (NFTs) consisting of the hyperphosphorylated microtubule-associated protein tau are a defining pathological characteristic of Alzheimer's disease (AD). Hyperphosphorylation of tau is hypothesized to impair the microtubule stabilizing function of tau, leading to the formation of paired helical filaments and neuronal death. Glycogen synthase kinase-3 (GSK-3) has been shown to be one of several kinases that mediate tau hyperphosphorylation in vitro. However, molecular mechanisms underlying overactivation of GSK-3 and its potential linkage to AD-like pathologies in vivo remain unclear. Here, we demonstrate that injection of wortmannin (a specific inhibitor of phosphoinositol-3 kinase) or GF-109203X (a specific inhibitor of protein kinase C) into the left ventricle of rat brains leads to overactivation of GSK-3, hyperphosphorylation of tau at Ser 396/404/199/202 and, most significantly, impaired spatial memory. The effects of wortmannin and GF-109203X are additive. Significantly, specific inhibition of GSK-3 activity by LiCl prevents hyperphosphorylation of tau, and spatial memory impairment resulting from PI3K and PKC inhibition. These results indicate that in vivo inhibition of phosphoinositol-3 kinase and protein kinase C results in overactivation of GSK-3 and tau hyperphosphorylation and support a direct role of GSK-3 in the formation of AD-like cognitive deficits.

Neurons and plaques of Alzheimer's disease patients highly express the neuronal membrane docking protein p42IP4/centaurin alpha

The protein p42(IP4) (also called centaurin alpha), identified as a brain-specific InsP4/PtdInsP3 (PIP3)-binding protein, has been shown to be localized in human brain, specifically expressed in neurons. Several casein kinases have been found to be involved in Alzheimer's disease (AD) pathology. Since casein kinase I was reported to possess a binding domain for p42(IP4), we here investigated the expression and localization of p42(IP4) in AD brains. In cortical neurons of AD brains intracellular immunostaining for p42(IP4) exceeded the level seen in these neurons of normal brain. Statistically, significantly more p42(IP4)-immunoreactive neurons were found in temporal and angular cortex of AD patients as compared to control brain. Mostly impressively, neuritic plaques displayed a very prominent signal. Thus, we suggest that the up-regulated p42(IP4) in AD neurons may serve as a docking protein to recruit signaling molecules such as different subtypes of casein kinase I to the plasma membrane. This is the first indication for a functional interaction of these protein in possible neuronal damage. Therefore proteins such as p42(IP4), central players in signaling, may be appropriate targets for preventing neurodegenerative processes.

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.

A gene expression profile of Alzheimer's disease

Postmortem analysis of brains of patients with Alzheimer's disease (AD) has led to diverse theories about the causes of the pathology, suggesting that this complex disease involves multiple physiological changes. In an effort to better understand the variety and integration of these changes, we generated a gene expression profile for AD brain. Comparing affected and unaffected brain regions in nine controls and six AD cases, we showed that 118 of the 7050 sequences on a broadly representative cDNA microarray were differentially expressed in the amygdala and cingulate cortex, two regions affected early in the disease. The identity of these genes suggests the most prominent upregulated physiological correlates of pathology involve chronic inflammation, cell adhesion, cell proliferation, and protein synthesis (31 upregulated genes). Conversely, downregulated correlates of pathology involve signal transduction, energy metabolism, stress response, synaptic vesicle synthesis and function, calcium binding, and cytoskeleton (87 downregulated genes). The results support several separate theories of the causes of AD pathology, as well as add to the list of genes associated with AD. In addition, approximately 10 genes of unknown function were found to correlate with the pathology.

Protein kinase C isoforms as therapeutic targets in nervous system disease states

Neuronal tissues display high levels of protein kinase C (PKC) activity and isoform expression. The activation of this enzymatic system is important in the control of short and long term brain functions (ion channel regulation, receptor modulation, neurotransmitter release, synaptic potentiation/depression, neuronal survival) that are related to diverse brain pathologies. This review will describe recent developments in PKC regulation and changes in levels, isoforms and activation in acute and chronic neurodegenerative pathologies as well as in affective and psychic disorders. The recent availability of isoform selective inhibitors and activators may help to understand better the relevance of PKC in central nervous system (CNS) physiology and pathology and to identify new and safer pharmacologic strategies to be tested in different disease states.

Decreased expression of nitric oxide synthase in the colonic myenteric plexus of aged rats

Nitric oxide (NO) is a major non-adrenergic, non-cholinergic (NANC) inhibitory neurotransmitter in the gastrointestinal tract. NO released from the myenteric plexus enhances colonic transit and facilitates propulsion of the colonic contents by mediating descending relaxation. Although it has been suggested that colonic transit delays with aging, the mechanism of delayed colonic transit in aging remains unclear. We hypothesized that advanced age is associated with decreased expression of neuronal NO synthase (nNOS) and concomitant reduction in synthesis of NO in the rat colon. We studied nNOS mRNA expression, nNOS-immunohistochemistry, nNOS-immunoblotting and NOS catalytic activity in the mid-colon obtained from young (age 4-8 months) and aged (age 22-28 months) Fisher (F344xBN)F1 rats. Western blot analysis of PGP 9.5, a generic neuronal marker, of the colonic tissues were employed to study whether the total number of neurons of the myenteric plexus is reduced with aging. The number of nNOS-immunoreactive cells and nNOS synthesis in the colonic myenteric plexus were significantly reduced in aged rats. In contrast, expression of PGP 9.5 in colonic tissues was not affected in aged rats. Northern blot analysis demonstrated that the expression of neuronal nNOS mRNA was significantly reduced in the colonic tissues in aged rats. Basal and veratridine-induced release of L-[(3)H]citrulline were significantly decreased in colonic tissues from aged rats, compared to young rats. It is suggested that advanced age is associated with diminished gene expression of nNOS, nNOS synthesis and catalytic activity of NOS. This may explain the mechanism of delayed colonic transit observed in advanced age.

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.

Protein kinase C anchoring deficit in postmortem brains of Alzheimer's disease patients

Protein kinase C (PKC) has been implicated in the pathophysiology of Alzheimer's disease (AD). The levels of particular isoforms and the activation of PKC are reduced in postmortem brain cortex of AD subjects. Receptors for activated C kinase (RACK) are a family of proteins involved in anchoring activated PKCs to relevant subcellular compartments. Recent evidence has indicated that the impaired activation (translocation) of PKC in the aging brain is associated with a deficit in RACK1, the most well-characterized member of this family. The present study was conducted to determine whether alterations in RACK1 occurred in cortical areas where an impaired translocation of PKC has been demonstrated in AD. Here we report the presence of RACK1 immunoreactivity in human brain frontal cortex for the first time and demonstrate a decrease in RACK1 content in cytosol and membrane extracts in AD when compared with non-AD controls. By comparison, the levels of the RACK1-related PKCbetaII were not modified in the same membrane extracts. These observations add a new perspective in understanding the disease-associated defective PKC signal transduction and indicate that a decrease in an anchoring protein for PKC is an additional determinant of this deficit.

Rationalizing a pharmacological intervention on the amyloid precursor protein metabolism

The treatment of Alzheimer's disease remains a major challenge because of our incomplete understanding of the triggering events that lead to the selective neurodegeneration characteristic of Alzheimer's brains. The rational design of a pharmacological intervention is therefore a great theoretical challenge. One approach involves the study of the pharmacological modulation of the amyloid precursor protein metabolism, in which the goal is to reduce the formation of beta-amyloid in the hope of reducing the formation of a potentially neurotoxic peptide. Such an approach has led to the identification of a complex intracellular mechanism that can be regulated by neurotransmitters and other ligands.

Systemic treatment with GPI 1046 improves spatial memory and reverses cholinergic neuron atrophy in the medial septal nucleus of aged mice

Systemic treatment with GPI 1046, a non-immunosuppressive ligand of the immunophilin FKBP12 (FK-506-binding protein 12 kDa), has previously been shown to promote morphological recovery of the nigrostriatal dopaminergic projection after MPTP lesion in mice, and of lesioned sciatic nerve fibres after nerve crush in rats. In the present study, we investigated whether chronic systemic treatment with GPI 1046 could affect the decline of spatial learning and memory, and the atrophy of medial septal cholinergic neurons, associated with late senescence in C57 black mice. Three-month old (young) and 18-19-month old (aged) male C57BL/6N-Nia mice were first trained in a place learning task in the Morris water maze. Based on their performance relative to young controls, aged animals were then allocated to treatment groups (10 mg/kg GPI 1046, or vehicle). Retention of the spatial platform location was assessed after 3 weeks of dosing. We found that aged animals that had been dosed with GPI 1046 now performed at a significantly better level than their vehicle control group. Aged animals that had shown the greatest degree of impairment during training in the place learning task showed the greatest relative degree of improvement under treatment and were statistically indistinguishable from young, or aged unimpaired control animals. Cell volumes of cholinergic cells in the medial septal nucleus were assessed after an additional 10 months of dosing at 30 months of age, using stereological methods. We found that aged animals displayed a significant 34% decrease in volume of these cells relative to young controls. This atrophy was significantly reversed in aged GPI 1046-treated animals (13% shrinkage). We conclude that chronic systemic treatment with GPI 1046 positively affects memory mechanisms in the aged mouse, possibly by acting on the septohippocampal cholinergic system.

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.

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.