Biomedical subjects

Douglas G Walker

Publications and source records attributed to Douglas G Walker.

16 recordsLinked to original sources

PubMed2006

Alterations in immunological and neurological gene expression patterns in Alzheimer's disease tissues.

Microarray technology was utilized to isolate disease-specific changes in gene expression by sampling across inferior parietal lobes of patients suffering from late onset AD or non-AD-associated dementia and non-demented controls. Primary focus was placed on understanding how inflammation plays a role in AD pathogenesis. Gene ontology analysis revealed that the most differentially expressed genes related to nervous system development and function and neurological disease followed by genes involved in inflammation and immunological signaling. Pathway analysis also implicated a role for chemokines and their receptors, specifically CXCR4 and CCR3, in AD. Immunohistological analysis revealed that these chemokine receptors are upregulated in AD patients. Western analysis demonstrated an increased activation of PKC, a downstream mediator of chemokine receptor signaling, in the majority of AD patients. A very specific cohort of genes related to amyloid beta accumulation and clearance were found to be significantly altered in AD. The most significantly downregulated gene in this data set was the endothelin converting enzyme 2 (ECE2), implicated in amyloid beta clearance. These data were subsequently confirmed by real-time PCR and Western blot analysis. Together, these findings open up new avenues of investigation and possible therapeutic strategies targeting inflammation and amyloid clearance in AD patients.

Aged↗

PubMed2006

Gene expression profiles in anatomically and functionally distinct regions of the normal aged human brain.

In this article, we have characterized and compared gene expression profiles from laser capture microdissected neurons in six functionally and anatomically distinct regions from clinically and histopathologically normal aged human brains. These regions, which are also known to be differentially vulnerable to the histopathological and metabolic features of Alzheimer's disease (AD), include the entorhinal cortex and hippocampus (limbic and paralimbic areas vulnerable to early neurofibrillary tangle pathology in AD), posterior cingulate cortex (a paralimbic area vulnerable to early metabolic abnormalities in AD), temporal and prefrontal cortex (unimodal and heteromodal sensory association areas vulnerable to early neuritic plaque pathology in AD), and primary visual cortex (a primary sensory area relatively spared in early AD). These neuronal profiles will provide valuable reference information for future studies of the brain, in normal aging, AD and other neurological and psychiatric disorders.

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PubMed2006

Impaired platelet mitochondrial activity in Alzheimer's disease and mild cognitive impairment.

Mitochondrial abnormalities are found in Alzheimer's disease (AD), but previous reports have not examined at-risk groups. In subjects with AD, mild cognitive impairment (MCI), and non-demented aged controls, platelet and lymphocyte mitochondria were isolated and analyzed for Complexes I, III, and IV of the electron transport chain. Western blots were used to control for differential enrichment of samples. Results demonstrated significant declines in Complexes III and IV in AD, and a significant decline in Complex IV in MCI. This report confirms mitochondrial deficiencies in AD, extends them to MCI, and suggests they are present at the earliest symptomatic stages of disease.

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PubMed2006

Secretory PLA2-IIA: a new inflammatory factor for Alzheimer's disease.

Secretory phospholipase A2-IIA (sPLA2-IIA) is an inflammatory protein known to play a role in the pathogenesis of many inflammatory diseases. Although this enzyme has also been implicated in the pathogenesis of neurodegenerative diseases, there has not been a direct demonstration of its expression in diseased human brain. In this study, we show that sPLA2-IIA mRNA is up-regulated in Alzheimer's disease (AD) brains as compared to non-demented elderly brains (ND). We also report a higher percentage of sPLA2-IIA-immunoreactive astrocytes present in AD hippocampus and inferior temporal gyrus (ITG). In ITG, the majority of sPLA2-IIA-positive astrocytes were associated with amyloid beta (Abeta)-containing plaques. Studies with human astrocytes in culture demonstrated the ability of oligomeric Abeta1-42 and interleukin-1beta (IL-1beta) to induce sPLA2-IIA mRNA expression, indicating that this gene is among those induced by inflammatory cytokines. Since exogenous sPLA2-IIA has been shown to cause neuronal injury, understanding the mechanism(s) and physiological consequences of sPLA2-IIA upregulation in AD brain may facilitate the development of novel therapeutic strategies to inhibit the inflammatory responses and to retard the progression of the disease.

Journal Article↗

PubMed2006

Circle of Willis atherosclerosis: association with Alzheimer's disease, neuritic plaques and neurofibrillary tangles.

The role of intracranial atherosclerosis in Alzheimer's disease (AD) has been a subject of debate since the first decade of the last century. The initial "vascular hypothesis" of AD was rejected after a series of mid-twentieth century gross anatomical postmortem studies that showed an inconstant relationship between intracranial atherosclerosis and senile dementia. These early studies did not utilize statistical methods, however, and the investigators did not appear to consider the possibility that intracranial atherosclerosis might have a probabilistic, rather than an absolute, effect on AD risk. Recent studies by three independent groups have found a significant statistical association between postmortem measures of circle of Willis atherosclerosis and AD. The present study was undertaken to further address the validity of this association in a large autopsy series, including cases diagnosed neuropathologically with vascular dementia (VaD) and non-AD dementias. Postmortem gross anatomical grading of circle of Willis atherosclerosis was performed in 397 subjects classified by neuropathological diagnosis, including 92 non-demented elderly controls, 215 with AD, 30 with VaD and 60 with non-AD dementias. Circle of Willis atherosclerosis was more severe in subjects with AD and VaD than in control subjects, while it was equivalent between control subjects and subjects with non-AD dementias. Increasing atherosclerotic grade increased the odds ratios (OR) for the diagnoses of both AD and VaD and also increased the ORs for both increased neuritic plaque density and higher Braak neurofibrillary tangle stage. The significance of these associations was retained after consideration of the effects of age, gender and the apolipoprotein E-epsilon4 allele. The results suggest that the statistical association between intracranial atherosclerosis and AD is not an artifact of diagnostic misclassification or of unequal distribution of the apolipoprotein E-epsilon4 allele.

Aged↗

PubMed2006

Upregulated expression of purinergic P2X(7) receptor in Alzheimer disease and amyloid-beta peptide-treated microglia and in peptide-injected rat hippocampus.

The expression of the purinergic receptor subtype P2X(7)R, a nonselective cationic channel activated by high levels of adenosine triphosphate (ATP), has been studied in adult microglia obtained from Alzheimer disease (AD) and nondemented (ND) brains, in fetal human microglia exposed to Abeta(1-42) peptide and in vivo in Abeta(1-42)-injected rat hippocampus. Semiquantitative reverse transcriptase-polymerase chain reaction showed enhanced expression (increase of 70%) of P2X(7)R in AD microglia compared with ND cells (analysis of 6 AD and 8 ND cases). Immunohistochemical analysis showed prominent P2X(7)R expression in association with Abeta plaques and localized to HLA-DR-immunoreactive microglia. In cultured fetal human microglia, cells exposed to Abeta(1-42) (5 microM for 18 hours) had significantly elevated levels of P2X(7)R (by 106%) compared with untreated cells. Amplitudes of Ca(2+) responses in these cells, induced by the selective P2X(7)R agonist BzATP, were increased by 145% with Abeta(1-42) pretreatment relative to control (no peptide pretreatment) and were largely blocked if the P2X(7)R inhibitor-oxidized ATP (oxATP) was added with peptide in pretreatment solution. In vivo, double immunostaining analysis showed considerable P2X(7)R colocalized with microglia after injection of Abeta(1-42) (1 nmol) into rat hippocampus. The overall results suggest roles of P2X(7)R in mediating microglial purinergic inflammatory responses in AD brain.

Adenosine Triphosphate↗

PubMed2005

Gene expression changes by amyloid beta peptide-stimulated human postmortem brain microglia identify activation of multiple inflammatory processes.

A central feature of the inflammatory pathology in Alzheimer's disease is activated microglia clustered around aggregated amyloid beta (Abeta) peptide-containing plaques. In vitro-cultured microglia can be activated to an inflammatory state by aggregated Abeta with the induction of a range of different neurotoxic factors and provide a model system for studying microglia Abeta interactions. Gene expression responses of human postmortem brain-derived microglia to aggregated Abeta were measured using whole genome microarrays to address the hypothesis that Abeta interactions with human microglia primarily induce proinflammatory genes and not activation of genes involved in Abeta phagocytosis and removal. The results demonstrated that Abeta activation of microglia induced a large alteration in gene transcription including activation of many proinflammatory cytokines and chemokines, most notably, interleukin (IL)-1beta, IL-8, and matrix metalloproteinases (MMP), including MMP1, MMP3, MMP9, MMP10, and MMP12. All of these genes could amplify ongoing inflammation, resulting in further neuronal loss. Changes in expression of receptors associated with Abeta phagocytosis did not match the changes in proinflammatory gene expression. Time-course gene expression profiling, along with real-time polymerase chain reaction validation of expression changes, demonstrated an acute phase of gene induction for many proinflammatory genes but also chronic activation for many other potentially toxic products. These chronically activated genes included indoleamine 2,3-dioxygenase and kynureninase, which are involved in formation of the neurotoxin quinolinic acid, and S100A8, a potential proinflammatory chemokine. These studies show that activation of microglia by Abeta induces multiple genes that could be involved in inflammatory responses contributing to neurodegenerative processes.

Aged↗

PubMed2005

Gene expression correlates of neurofibrillary tangles in Alzheimer's disease.

Neurofibrillary tangles (NFT) constitute one of the cardinal histopathological features of Alzheimer's disease (AD). To explore in vivo molecular processes involved in the development of NFTs, we compared gene expression profiles of NFT-bearing entorhinal cortex neurons from 19 AD patients, adjacent non-NFT-bearing entorhinal cortex neurons from the same patients, and non-NFT-bearing entorhinal cortex neurons from 14 non-demented, histopathologically normal controls (ND). Of the differentially expressed genes, 225 showed progressively increased expression (AD NFT neurons > AD non-NFT neurons > ND non-NFT neurons) or progressively decreased expression (AD NFT neurons < AD non-NFT neurons < ND non-NFT neurons), raising the possibility that they may be related to the early stages of NFT formation. Immunohistochemical studies confirmed that many of the implicated proteins are dysregulated and preferentially localized to NFTs, including apolipoprotein J, interleukin-1 receptor-associated kinase 1, tissue inhibitor of metalloproteinase 3, and casein kinase 2, beta. Functional validation studies are underway to determine which candidate genes may be causally related to NFT neuropathology, thus providing therapeutic targets for the treatment of AD.

Aged, 80 and over↗

PubMed2005

Perturbations in calcium-mediated signal transduction in microglia from Alzheimer's disease patients.

Calcium-sensitive fluorescence microscopy has been used to study Ca2+-dependent signal transduction pathways in microglia obtained from Alzheimer's disease (AD) patients and non-demented (ND) individuals. Data were obtained from nine AD cases and seven ND individuals and included basal levels of intracellular Ca2+ [Ca2+]i, peak amplitudes (Delta[Ca2+]i) and time courses of adenosine triphosphate (ATP) responses and amplitudes of an initial transient response and a subsequent second component of Ca2+ influx through store-operated channels (SOC) induced by platelet-activating factor (PAF). Overall, AD microglia were characterized by significantly higher (20%) basal Ca2+ [Ca2+]i relative to ND cells. The Delta[Ca2+]i of ATP and initial phase of PAF responses, which reflect rapid depletion of Ca2+ from endoplasmic reticulum stores, were reduced by respective values of 63% and 59% in AD cells relative to amplitudes recorded from ND microglia. Additionally, AD microglia showed diminished amplitudes (reduction of 61%) of SOC-mediated Ca2+ entry induced by PAF and prolonged time courses (increase of 60%) of ATP responses with respect to ND microglia. We have generally replicated these results with exposure of human fetal microglia to beta amyloid (5 microM Abeta1-42 applied for 24 hr). Overall, these data indicate significant abnormalities are present in Ca2+-mediated signal transduction in microglia isolated from AD patients.

Adenosine Triphosphate↗

PubMed2004

RAGE potentiates Abeta-induced perturbation of neuronal function in transgenic mice.

Receptor for Advanced Glycation Endproducts (RAGE), a multiligand receptor in the immunoglobulin superfamily, functions as a signal-transducing cell surface acceptor for amyloid-beta peptide (Abeta). In view of increased neuronal expression of RAGE in Alzheimer's disease, a murine model was developed to assess the impact of RAGE in an Abeta-rich environment, employing transgenics (Tgs) with targeted neuronal overexpression of RAGE and mutant amyloid precursor protein (APP). Double Tgs (mutant APP (mAPP)/RAGE) displayed early abnormalities in spatial learning/memory, accompanied by altered activation of markers of synaptic plasticity and exaggerated neuropathologic findings, before such changes were found in mAPP mice. In contrast, Tg mice bearing a dominant-negative RAGE construct targeted to neurons crossed with mAPP animals displayed preservation of spatial learning/memory and diminished neuropathologic changes. These data indicate that RAGE is a cofactor for Abeta-induced neuronal perturbation in a model of Alzheimer's-type pathology, and suggest its potential as a therapeutic target to ameliorate cellular dysfunction.

Alzheimer Disease↗

PubMed2004

ABAD directly links Abeta to mitochondrial toxicity in Alzheimer's disease.

Mitochondrial dysfunction is a hallmark of beta-amyloid (Abeta)-induced neuronal toxicity in Alzheimer's disease (AD). Here, we demonstrate that Abeta-binding alcohol dehydrogenase (ABAD) is a direct molecular link from Abeta to mitochondrial toxicity. Abeta interacts with ABAD in the mitochondria of AD patients and transgenic mice. The crystal structure of Abeta-bound ABAD shows substantial deformation of the active site that prevents nicotinamide adenine dinucleotide (NAD) binding. An ABAD peptide specifically inhibits ABAD-Abeta interaction and suppresses Abeta-induced apoptosis and free-radical generation in neurons. Transgenic mice overexpressing ABAD in an Abeta-rich environment manifest exaggerated neuronal oxidative stress and impaired memory. These data suggest that the ABAD-Abeta interaction may be a therapeutic target in AD.

3-Hydroxyacyl CoA Dehydrogenases↗

PubMed2004

Substantia nigra Marinesco bodies are associated with decreased striatal expression of dopaminergic markers.

Marinesco bodies are nuclear inclusions found in pigmented neurons of the substantia nigra and locus ceruleus of humans and monkeys. It has long been known that the frequency of these inclusions increases with advancing age, but no pathologic associations have ever been established. We quantified Marinesco body frequency in human autopsy subjects, classified as young normal controls, elderly controls, dementia with Lewy bodies (DLB), Alzheimer disease (AD), and Parkinson disease (PD). Elderly controls, AD cases, and DLB cases had significantly increased Marinesco body frequencies relative to young controls and DLB cases had significantly increased frequencies relative to elderly controls, while PD cases did not differ from young controls; cases with AD did not differ from elderly controls. Lewy body-containing neurons had significantly higher Marinesco body frequencies than non-Lewy body-containing neurons. Marinesco body frequency in elderly control cases correlated significantly, in inverse fashion, with striatal concentrations of the dopaminergic neuron markers dopamine transporter and tyrosine hydroxylase. These statistical associations suggest that Marinesco bodies constitute or mark a pathologic process that may be related to, or contribute to, age-related motor dysfunction and/or Lewy body disorders. Further studies are needed to ascertain the molecular basis of Marinesco body formation; preliminary studies indicate that proteasome dysfunction can lead to similar abnormalities in cultured cells.

Adult↗

PubMed2004

Atherosclerosis, vascular amyloidosis and brain hypoperfusion in the pathogenesis of sporadic Alzheimer's disease.

We postulate that severe atherosclerotic occlusion of the circle of Willis and leptomeningeal arteries is an important factor in the pathogenesis of some sporadic Alzheimer's disease (AD) cases. These arterial stenoses are complicated by an overwhelming amyloid accumulation in the walls of leptomeningeal and cortical arteries resulting in a significant decrease in perfusion pressure and consequent ischemia/hypoxia of the brain tissue. We also propose that the distal areas of the white matter (WM) will be the first affected by a lack of oxygen and nutrients. Our hypotheses are supported by the following observations: (1) the number of stenoses is more frequent in AD than in the control population (p = 0.008); (2) the average index of occlusion is greater in AD than in the control group (p < 0.00001); (3) the index of stenosis and the total number of stenoses per case are positively correlated (R = 0.67); (4) the index of stenosis correlates with the neuropathological lesions of AD and with the MMSE psychometric test; (5) the number and degree of atherosclerosis of the anterior, middle and posterior cerebral arteries is more severe in cases of AD than in the control population; (6) atherosclerosis severity is apparently associated with the severity of the vascular amyloidosis; (7) the WM rarefaction correlates with the severity of the atherosclerosis and vascular amyloidosis; (8) the total cell count and microvessel count in the areas of WM rarefaction correlate with the neuropathological lesions of AD and with the MMSE score. Our data strongly suggest that severe hemodynamic disturbances contribute to sporadic AD and support the numerous observations indicating cardiovascular system participation in the pathogenesis of these dementias.

Alzheimer Disease↗

PubMed2003

Thiorphan-induced neprilysin inhibition raises amyloid beta levels in rabbit cortex and cerebrospinal fluid.

Studies on the pathogenesis of Alzheimer's disease (AD) suggest overproduction of amyloid beta (Abeta) may not be the only pathogenic route to AD. Decreased degradation of Abeta is another possible disease mechanism. Neprilysin is a neutral endopeptidase that has been proposed to be the major enzyme responsible for Abeta degradation. Studies have reported correlations between Abeta deposition and neprilysin activity in the human brain. This study shows that intracerebroventricular infusion of thiorphan, a neprilysin inhibitor, raises cortical and cerebrospinal fluid (CSF) Abeta concentrations in rabbits. Rabbits treated with thiorphan for 5 days had levels of CSF and cortical Abeta40 that were 147 and 142% of the control group, respectively. Results for Abeta42 showed a similar trend. The results indicate that age-related decreases of neprilysin could lead to increased brain concentrations of Abeta, plaque formation, and AD.

Alzheimer Disease↗

PubMed2002

Modeling Alzheimer's disease immune therapy mechanisms: interactions of human postmortem microglia with antibody-opsonized amyloid beta peptide.

The induction of an antibody response to amyloid beta (Abeta) peptide has become a strategy for the treatment of Alzheimer's disease (AD). This has proven effective in reducing the plaque burden in transgenic mice that develop Abeta plaques similar to human AD patients. The mechanism for enhanced clearance of Abeta is partly due to the interaction of immunoglobulin Fcgamma receptor-expressing microglia and specific antibody-opsonized Abeta deposits. This interaction can stimulate Fcgamma receptor-mediated phagocytosis, but also results in inflammatory activation of these cells. Consequently, interaction of microglia with antibody-antigen complexes could exacerbate the existing inflammation in the brains of AD patients. In this study, we used substrate-bound Abeta and cultured human microglia from AD and non-demented cases to model interaction of microglia and antibody-opsonized plaques in AD brains. Enhanced production of tumor necrosis factor-alpha, macrophage colony stimulating factor, interleukin-10, and superoxide ions was detected. We also demonstrated enhanced uptake of opsonized Abeta by microglia, which was reduced significantly in the presence of excess IgG, indicative of the involvement of Fcgamma receptor-mediated mechanisms. Human microglia were shown in this study to express mRNA for Fcgamma receptors I, IIa, IIb, and III. The expression of Fcgamma receptor II was augmented by proinflammatory stimulation. These results suggest that initial interactions of human microglia with antibody-opsonized amyloid could result in increased inflammation. The consequence of this on inflammatory pathology in AD brains needs to be considered before immunization is used as a strategy for treating AD.

Alzheimer Disease↗

PubMed2002

Increased expression of the urokinase plasminogen-activator receptor in amyloid beta peptide-treated human brain microglia and in AD brains.

The urokinase plasminogen-activator receptor (uPAR) is involved in many processes in inflammation including the migration of inflammatory-associated cells to sites of tissue damage. This receptor, also designated as CD87, is induced in response to a range of stimuli and is a marker of macrophage activation. Its role in inflammatory responses of microglia in Alzheimer's disease (AD) has not been previously investigated. In this study we demonstrate that uPAR mRNA and protein expression is induced following incubation of human post-mortem brain-derived microglia with fibrillar amyloid beta (Abeta) peptide. This response was stronger with Abeta peptide than with other tested pro-inflammatory agents. Induction of uPAR surface expression by microglia was inhibited by the antioxidant N-acetyl-cysteine, indicating that this gene may be induced as a result of oxidative stress-related mechanisms. The significance of these findings to AD was investigated. UPAR protein levels were significantly increased in human brain tissues from the hippocampus, superior frontal gyrus and inferior temporal gyrus of AD cases compared with similar tissues from non-demented cases. Increased uPAR expression was not demonstrated in AD cerebellum. Finally, increased uPAR immunoreactivity was demonstrated in activated microglia in AD brain samples using two different antibodies to uPAR. These results provide a connection between the induction of oxidative stress in AD and microglial activation, and establish a possible involvement of uPAR in AD pathogenesis.

Aged↗