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Karen Duff

Publications and source records attributed to Karen Duff.

At least 37 records · Page 2Linked to original sources
PubMed2004

Links between the pathology of Alzheimer's disease and vascular dementia.

The major neuropathological lesions defining Alzheimer's disease (AD) include neurofibrillary tangles and amyloid plaques, which are mainly composed of abnormally phosphorylated tau and amyloid-beta (A beta), respectively. Numerous neuropathological and neuroimaging studies indicate that at least one-third of AD cases are complicated by some degree of vascular pathology, whereas in a similar proportion of patients clinically diagnosed with vascular dementia, AD pathology is also present. Many classical vascular risk factors such as hypertension, diabetes mellitus, and hypercholesterolemia have recently been shown also to increase the risk of AD. Growing evidence suggests that vascular pathology lowers the threshold for the clinical presentation of dementia at a given level of AD-related pathology and potentially directly promotes AD lesions such as A beta plaques. Cerebral ischemia, chronically up-regulates expression of the amyloid precursor protein (APP), which is the precursor to the amyloid beta peptide and damages the blood-brain barrier (BBB), affecting A beta peptide clearance from the brain. Recognition of the importance of these vascular risk factors for AD-related dementia and their treatment will be beneficial not only for preventing cardiac, cerebral, and peripheral complications of vascular disease, but also will likely have a direct impact on the occurrence of sporadic AD in older subjects. In this paper, we review some of the links between vascular risk factors and AD pathology and present data on the direct effect of ischemia on cognitive function and A beta deposition in a mouse model of AD.

Alzheimer Disease↗
PubMed2004

Transgenic mouse models of Alzheimer's disease: how useful have they been for therapeutic development?

Transgenic mice have been created in an attempt to generate models of human Alzheimer's disease, but success has been partial and unpredictable. The overall aim of this paper is to illustrate how genomics can be used in translational research, turning genetic information in the form of pathogenic mutations into clinically useful drugs against a major human disease. This paper will illustrate how genetic information allows researchers to dissect the aetiology of a disease and then replicate the disease in vivo through the process of transgenesis. The limitations of recreating a condition like Alzheimer's disease in a transgenic mouse, how far the mice have advanced understanding of the disease and how useful they have been for the development of therapeutics will then be discussed.

Alzheimer Disease↗
PubMed2004

Amyloid-beta deposition is associated with decreased hippocampal glucose metabolism and spatial memory impairment in APP/PS1 mice.

In Alzheimer disease (AD) patients, early memory dysfunction is associated with glucose hypometabolism and neuronal loss in the hippocampus. Double transgenic (Tg) mice co-expressing the M146L presenilin 1 (PS1) and K670N/M671L, the double "Swedish" amyloid precursor protein (APP) mutations, are a model of AD amyloid-beta deposition (Abeta) that exhibits earlier and more profound impairments of working memory and learning than single APP mutant mice. In this study we compared performance on spatial memory tests, regional glucose metabolism, Abeta deposition, and neuronal loss in APP/PS1, PS1, and non-Tg (nTg) mice. At the age of 2 months no significant morphological and metabolic differences were detected between 3 studied genotypes. By 8 months, however, APP/PS1 mice developed selective impairment of spatial memory, which was significantly worse at 22 months and was accompanied by reduced glucose utilization in the hippocampus and a 35.8% dropout of neurons in the CA1 region. PS1 mice exhibited a similar degree of neuronal loss in CA1 but minimal memory deficit and no impairment of glucose utilization compared to nTg mice. Deficits in 22 month APP/PS1 mice were accompanied by a substantially elevated Abeta load, which rose from 2.5% +/- 0.4% at 8 months to 17.4% +/- 4.6%. These findings implicate Abeta or APP in the behavioral and metabolic impairments in APP/PS1 mice and the failure to compensate functionally for PS1-related hippocampal cell loss.

Alzheimer Disease↗
PubMed2004

Presenilin mutations in familial Alzheimer disease and transgenic mouse models accelerate neuronal lysosomal pathology.

The neuronal lysosomal system is a major degradative pathway, induced by cell stress and closely linked to Alzheimer disease (AD) and other neurodegenerative diseases. Here, we show that mutations of presenilin (PS) 1 and 2, which cause familial early-onset AD (FAD), induce more severe lysosomal system neuropathology in humans than does sporadic AD (SAD). Cathepsin D and B levels were higher in PS-FAD neocortex than in SAD and, unlike neurons in SAD, expressed higher levels of the cation-independent mannose-6-phosphate receptor. Lysosomal pathology was also evident in more populations of neurons in PS-FAD brains, including the less vulnerable neurons in laminae II and IV and affected neurons contained high numbers of hydrolase-positive vesicular compartments with a broader range of abnormal morphology. In transgenic mice expressing mutant amyloid precursor protein (APPswe), introducing mutant PSI significantly upregulated the lysosomal system in neocortical and hippocampal neurons. This upregulation, though milder in severity, resembled that seen in human PS-FAD. Accumulation of hydrolases in dystrophic neurites in senile plaques was particularly strong, suggesting that amyloid deposition may be a stimulus for local mobilization of the lysosomal system. PS1 mice lacking the APPswe transgene also had a mild lysosomal response in some neuronal populations, which was not seen in the APPswe mice. Our findings suggest that presenilin mutations have amyloid-independent effects on the lysosomal system, which are synergistic with the lysosomal system pathology that is associated with beta-amyloid.

Aged↗
PubMed2004

Rat transgenic models with a phenotype of intracellular Abeta accumulation in hippocampus and cortex.

In this communication we report the characterization of several transgenic rat lines expressing human AbetaPP carrying the Swedish and Indiana mutations (coded UKUR28), the human presenilin 1 transgene with the 'Finn' mutation (coded UKUR19) and double transgenic rats expressing both transgenes (coded UKUR25). In these Tg rats, the AbetaPP and PS1 transgene expression was largely restricted to the hippocampus and neocortex. The PS1 transgenic rats did not produce visible changes in Abeta immunoreactivity. The AbetaPP transgenic rats (both the single Tg UKUR28, and double Tg UKUR25) generated a phenotype of intra-neuronalbeta accumulation without plaque formation and with no increased immunoreactivity for AbetaPP amino and carboxyl-terminal epitopes. This phenotype was apparent as early as 6 months of age in the transgenic rat lines carrying the human AbetaPP transgene. No senile plaques of aggregated Abeta were observed in any of the transgenic lines generated, up to 24 months of age. The hAbetaPP single homozygous Tg line (UKUR28) showed an increase in ERK2, without changes in glycogen synthase kinase 3 (GSK3) activity. A preliminary protein analysis of the hippocampus of the double transgenic rat (UKUR25) by mass spectrometry showed differences in the protein profile between this transgenic line and controls.

Alzheimer Disease↗
PubMed2003

Presenilin redistribution associated with aberrant cholesterol transport enhances beta-amyloid production in vivo.

Epidemiology, in vitro, and in vivo studies strongly implicate a role for cholesterol in the pathogenesis of Alzheimer's disease (AD). We have examined the impact of aberrant intracellular cholesterol transport on the processing of the amyloid precursor protein (APP) in a mouse model of Niemann-Pick type C (NPC) disease. In the NPC mouse brain, cholesterol accumulates in late endosomes/lysosomes. This was associated with the accumulation of beta-C-terminal fragments (CTFs) of APP, but the level of beta-secretase and its activity were not affected. Alpha-secretase activity and secreted APPalpha generation were also not affected, suggesting CTFs increased because of decreased clearance. The level of presenilin-1 (PS-1) was unchanged, but gamma-secretase activity was greatly enhanced, which correlated with an increase in Abeta40 and Abeta42 levels. These events were associated with abnormal distribution of PS-1 in the endosomal system. Our results show that aberrant cholesterol trafficking is associated with the potentiation of APP processing components in vivo, leading to an overall increase in Abeta levels.

Amyloid Precursor Protein Secretases↗
PubMed2003

Cdk5 is a key factor in tau aggregation and tangle formation in vivo.

Tau aggregation is a common feature of neurodegenerative diseases such as Alzheimer's disease, and hyperphosphorylation of tau has been implicated as a fundamental pathogenic mechanism in this process. To examine the impact of cdk5 in tau aggregation and tangle formation, we crossed transgenic mice overexpressing the cdk5 activator p25, with transgenic mice overexpressing mutant (P301L) human tau. Tau was hyperphosphorylated at several sites in the double transgenics, and there was a highly significant accumulation of aggregated tau in brainstem and cortex. This was accompanied by increased numbers of silver-stained neurofibrillary tangles (NFTs). Insoluble tau was also associated with active GSK. Thus, cdk5 can initiate a major impact on tau pathology progression that probably involves several kinases. Kinase inhibitors may thus be beneficial therapeutically.

Animals↗
PubMed2003

Co-localization of cholesterol, apolipoprotein E and fibrillar Abeta in amyloid plaques.

Recent evidence strongly suggests a role for cholesterol and apolipoprotein E in the etiology of Alzheimer's disease. We have demonstrated the co-localization of cholesterol and apolipoprotein E with beta-amyloid immunoreactivity and thioflavin S immunofluorescence in AD type plaques of a transgenic mouse model. Cholesterol and apolipoprotein E co-localized to the core of thioflavin S-positive (fibrillar) plaques, but not thioflavin S-negative (diffuse) plaques from an early age. By 18 months of age, there was extensive coverage of fibrillar plaques immunopositive for apolipoprotein E and cholesterol oxidase. These findings support evidence that cholesterol and apolipoprotein E are involved in fibrillar plaque formation or maintenance, and suggest that cholesterol may impact amyloid formation extracellularly, as well as through an intracellular effect.

Alzheimer Disease↗
PubMed2003

Novel therapeutic approach for the treatment of Alzheimer's disease by peripheral administration of agents with an affinity to beta-amyloid.

Plaques containing beta-amyloid (Abeta) peptides are one of the pathological features of Alzheimer's disease, and the reduction of Abeta is considered a primary therapeutic target. Amyloid clearance by anti-Abeta antibodies has been reported after immunization, and recent data have shown that the antibodies may act as a peripheral sink for Abeta, thus altering the periphery/brain dynamics. Here we show that peripheral treatment with an agent that has high affinity for Abeta (gelsolin or GM1) but that is unrelated to an antibody or immune modulator reduced the level of Abeta in the brain, most likely because of a peripherally acting effect. We propose that in general, compounds that sequester plasma Abeta could reduce or prevent brain amyloidosis, which would enable the development of new therapeutic agents that are not limited by the need to penetrate the brain or evoke an immune response.

Alzheimer Disease↗
PubMed2003

Detection of Alzheimer's amyloid in transgenic mice using magnetic resonance microimaging.

The presence of amyloid-beta (Abeta) plaques in the brain is a hallmark pathological feature of Alzheimer's disease (AD). Transgenic mice overexpressing mutant amyloid precursor protein (APP), or both mutant APP and presenilin-1 (APP/PS1), develop Abeta plaques similar to those in AD patients, and have been proposed as animal models in which to test experimental therapeutic approaches for the clearance of Abeta. However, at present there is no in vivo whole-brain imaging method to detect Abeta plaques in mice or men. A novel method is presented to detect Abeta plaques in the brains of transgenic mice by magnetic resonance microimaging (muMRI). This method uses Abeta1-40 peptide, known for its high binding affinity to Abeta, magnetically labeled with either gadolinium (Gd) or monocrystalline iron oxide nanoparticles (MION). Intraarterial injection of magnetically labeled Abeta1-40, with mannitol to transiently open the blood-brain barrier (BBB), enabled the detection of many Abeta plaques. Furthermore, the numerical density of Abeta plaques detected by muMRI and by immunohistochemistry showed excellent correlation. This approach provides an in vivo method to detect Abeta in AD transgenic mice, and suggests that diagnostic MRI methods to detect Abeta in AD patients may ultimately be feasible.

Alzheimer Disease↗
PubMed2003

Use of in vivo models to study the role of cholesterol in the etiology of Alzheimer's disease.

Cholesterol has been implicated in the pathogenesis of Alzheimer's disease, both through intracellular effects, and through an extracellular effect due to its physical interaction with plaque associated amyloid. Epidemiology studies have implicated high cholesterol as a risk factor for AD, and have shown that the use of cholesterol reducing agents (statins) can be protective against the disease. We, and others have shown that cholesterol levels modulate the processing of the amyloid precursor protein (APP) both in vivo and in vitro, affecting the accumulation of Abeta (Abeta) peptides which may directly impact the risk of AD. This review describes the biology of sterols, and identifies how cholesterol may exacerbate the pathogenesis of AD. Data from in vivo and in vitro studies will then be presented to describe how treatments aimed at modulating lipid levels may be efficacious in treating AD.

Alzheimer Disease↗
PubMed2003

Hyperphosphorylation and aggregation of tau in mice expressing normal human tau isoforms.

Neurofibrillary tangles are composed of insoluble aggregates of the microtubule-associated protein tau. In Alzheimer's disease the accumulation of neurofibrillary tangles occurs in the absence of tau mutations. Here we present mice that develop pathology from non-mutant human tau, in the absence of other exogenous factors, including beta-amyloid. The pathology in these mice is Alzheimer-like, with hyperphosphorylated tau accumulating as aggregated paired helical filaments. This pathologic tau accumulates in the cell bodies and dendrites of neurons in a spatiotemporally relevant distribution.

Age Factors↗
PubMed2003

Changes in apolipoprotein E expression in response to dietary and pharmacological modulation of cholesterol.

Apolipoprotein E (ApoE) influences the risk of late onset Alzheimer's disease (AD) in an isoform-dependent manner, such that the presence of the apoE epsilon4 allele increases the risk of AD while the presence of the apoE epsilon2 allele appears to be protective. Although a number of ApoE functions are isoform dependent and may underlie the "risk factor" activity of AD, its ability to bind amyloid beta peptides and influence their clearance and/or deposition has gained strong experimental support. Evidence suggests that in addition to genotype, increased ApoE transcription can contribute to AD risk. There is growing evidence in support of the hypothesis that disrupted cholesterol metabolism is an early risk factor for AD. Studies in animal models have shown that chronic changes in cholesterol metabolism associate with changes in brain Abeta accumulation, a process instrumental for establishing AD pathology. ApoE mediates cholesterol homeostasis in the body and is a major lipid carrier in brain. As such, its expression in the periphery and in brain changes in response to changes in cholesterol metabolism. Here, we used a transgenic mouse model of Alzheimer's amyloidosis to examine whether the diet-induced or pharmacologically induced changes in plasma cholesterol that result in altered brain amyloidosis also affect ApoE content in liver and in brain. We found that chronic changes in total cholesterol in plasma lead to changes in ApoE mRNA levels in brain. We also found that cholesterol loading of primary glial cells increases cellular and secreted ApoE levels and that long-term treatment of astrocytes and microglia with statins leads to a decrease in the cellular and/or secreted ApoE. These observations suggest that disrupted cholesterol metabolism may increase the risk of developing AD in part due to the effect of cholesterol on brain ApoE expression.

Alzheimer Disease↗
PubMed2003

Brain damage results in down-regulation of N-acetylaspartate as a neuronal osmolyte.

N-acetyl-L-aspartate (NAA) is present in the vertebrate brain, where its concentration is one of the highest of all free amino acids. Although NAA is synthesized and stored primarily in neurons, it is not hydrolyzed in these cells. However, after its regulated release into extracellular fluid, neuronal NAA is hydrolyzed by amidohydrolase II that is present in oligodendrocytes. About 30% of neurons do not contain appreciable amounts of NAA, but its prominence in 1H nuclear magnetic resonance spectroscopic (MRS) studies has led to its wide use as a neuronal marker in diagnostic human medicine as both an indicator of brain pathology, and of disease progression in a variety of central nervous system (CNS) diseases. Loss of NAA has been interpreted as indicating either loss of neurons, or loss of neuron viability. In this investigation, the upregulation of NAA in early stages of construction of the CNS, and its downregulation in experimentally induced damage models of the CNS is reported. The results of this study indicate that the buildup of NAA is not required for viability of neurons in monocellular cultures, and that NAA is lost from multicellular cultured brain slice explants that contain viable neurons. Thus, loss of NAA does not necessarily indicate either loss of neurons or their function. The NAA system, when present in the brain, appears to reflect a high degree of cellular integration, and therefore may be a unique metabolic construct of the intact vertebrate brain.

Alzheimer Disease↗
PubMed2002

Imaging brain amyloid of Alzheimer disease in vivo in transgenic mice with an Abeta peptide radiopharmaceutical.

Abeta 1-40 is a potential peptide radiopharmaceutical that could be used to image the brain Abeta amyloid of Alzheimer disease in vivo, should this peptide be made transportable through the blood-brain barrier in vivo. The blood-brain barrier transport of [ 125 I]-Abeta 1-40 in a transgenic mouse model was enabled by conjugation to the rat 8D3 monoclonal antibody to the mouse transferrin receptor. The Abeta 1-40 -8D3 conjugate is a bifunctional molecule that binds the blood-brain barrier TfR and undergoes transport into brain and binds the Abeta amyloid plaques of Alzheimer disease. App SW /Psen1 double-transgenic and littermate control mice were administered either unconjugated Abeta 1-40 or the Abeta 1-40 -8D3 conjugate intravenously, and brain scans were obtained 6 hours later. Immunocytochemical analysis showed abundant Abeta immunoreactive plaques in the brains of the App SW /Psen1 transgenic mice and there was a selective retention of radioactivity in the brains of these mice at 6 hours after intravenous administration of the conjugate. In contrast, there was no selective sequestration either of the conjugate in control littermate mouse brain or of unconjugated Abeta 1-40 in transgenic mouse brain. In conclusion, the results show that it is possible to image the Abeta amyloid burden in the brain in vivo with an amyloid imaging agent, provided the molecule is conjugated to a blood-brain barrier drug-targeting system.

Alzheimer Disease↗
PubMed2002

Cholesterol in Alzheimer's disease and tauopathy.

Cholesterol has been implicated in the pathogenesis of amyloid plaques in Alzheimer's disease (AD) and in the formation of neurofibrillary pathology in Niemann-Pick disease. Several epidemiology studies have implicated high cholesterol as a risk factor for AD and have shown that the use of cholesterol-reducing agents (statins) can be protective against the disease. We and others have shown that cholesterol levels modulate the processing of the amyloid precursor protein (APP) both in vivo and in vitro, affecting the accumulation of A-beta (Abeta) peptides that may directly impact the risk of AD. Mutations in the Niemann-Pick C gene (NPC) result in deficient cholesterol transport/storage. Clinically, Niemann-Pick disease causes a severe childhood lipidosis, with neurodegeneration characterized by the presence of AD-type neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau. Studies of mouse models of NPC show that defects in cellular cholesterol trafficking are associated with enhanced generation of Abeta and the hyperphosphorylation of tau, further implicating the cholesterol homeostasis pathway as a risk factor for amyloidosis.

Alzheimer Disease↗
PubMed2002

Organotypic slice cultures from transgenic mice as disease model systems.

Organotypic slice cultures have been prepared from the brains of transgenic mice with Alzheimer's disease-type pathology. Cell types within the slice undergo differentiation and slices can be maintained in culture for up to 6 mo when prepared from young neonates. Slices have been prepared from mice overexpressing genes of relevance to Alzheimer's disease, including mutant or wild-type tau. Neurons in these slices develop neurons that are immunoreactive for a number of markers of abnormal tau. Organotypic slice models are currently being used to test the impact of tangle enhancers or inhibitors as a prescreen for efficacy before testing drugs in vivo.

Alzheimer Disease↗