Axonopathy, Tau Abnormalities, and Dyskinesia, but No Neurofibrillary Tangles in P25-transgenic Mice

The Journal of Comparative Neurology. May, 2002  |  Pubmed ID: 11932941

Neurofibrillary tangles, one of the pathologic hallmarks of Alzheimer's disease (AD), are composed of abnormally polymerized tau protein. The hyperphosphorylation of tau alters its normal cellular function and is thought to promote the formation of neurofibrillary tangles. Growing evidence suggests that cyclin-dependent kinase 5 (cdk5) plays a role in tau phosphorylation, but the function of the enzyme in tangle formation remains uncertain. In AD, cdk5 is constitutively activated by p25, a highly stable, 25kD protein thought to be increased in the AD brain. To test the hypothesis that p25/cdk5 interactions promote neurofibrillary pathology, we created transgenic mouse lines that overexpress the human p25 protein specifically in neurons. Mice with high transgenic p25 expression have augmented cdk5 activity and develop severe hindlimb semiparalysis and mild forelimb dyskinesia beginning at approximately 3 months of age. Immunohistochemical and ultrastructural analyses showed widespread axonal degeneration with focal accumulation of tau in various regions of the brain and, to a lesser extent, the spinal cord. However, there was no evidence of neurofibrillary tangles in neuronal somata or axons, nor were paired helical filaments evident ultrastructurally. These studies confirm that p25 overexpression can lead to tau abnormalities and axonal degeneration in vivo but do not support the hypothesis that p25-related induction of cdk5 is a primary event in the genesis of neurofibrillary tangles.

Proteopathy: the Next Therapeutic Frontier?

Current Opinion in Investigational Drugs (London, England : 2000). May, 2002  |  Pubmed ID: 12090553

The abnormal conformation and assembly of proteins is a probable cause of many degenerative diseases of old age. These proteopathies include such clinically disparate neurological disorders as Alzheimer's disease. Parkinson's disease and Creutzfeldt-Jakob disease, as well as a variety of non-neurological maladies. The involvement of protein pathology in these diseases is well established and we are beginning to understand the process whereby proteins self-assemble and injure tissues; however, we remain largely in the dark regarding the fundamental origins of the proteopathies. Our present knowledge suggests three broad therapeutic approaches to abrogating the proteopathic cascade: reduce the production of the offending proteins, prevent their self-assembly, or promote their removal.

Exogenous Induction of Cerebral Beta-amyloidosis in BetaAPP-transgenic Mice

Peptides. Jul, 2002  |  Pubmed ID: 12128081

A key commonality of most age-related neurodegenerative diseases is the accumulation of aggregation-prone proteins in the brain. Except for the prionoses, the initiation and propagation of these proteopathies in vivo remains poorly understood. In a previous study, we found that the deposition of the amyloidogenic peptide Abeta can be induced by injection of dilute extracts of Alzheimeric neocortex into the brains of Tg2576 transgenic mice overexpressing the human beta-amyloid precursor protein. The present study was undertaken to assess the pathology after long-term (12 months) incubation, and to clarify the distinctive anatomical distribution of seeded Abeta-immunoreactivity. All mice were injected at 3 months of age; 5 months later, as expected, Abeta deposits were concentrated mostly in the injected hemisphere. After 12 months, abundant, transgene-derived Abeta deposits were present bilaterally in the forebrain, but plaque load was still clearly greater in the extract-injected hemisphere. There was also evidence of tau hyperphosphorylation in axons of the corpus callosum that had been injured by the injection, most prominently in transgenic mice, but also, to a lesser degree, in non-transgenic mice. Five months following injection of AD-extract, an isolated cluster of Abeta-immunoreactive microglia was sometimes evident in the ipsilateral entorhinal cortex; the strong innervation of the hippocampus by entorhinal cortical neurons suggests the possible spread of seeded pathology from the injection site via neuronal transport mechanisms. Finally, using India Ink to map the local dispersion of injectate, we found that Abeta induction is especially potent in places where the injectate is sequestered. The AD-seeding model can illuminate the emergence and spread of cerebral beta-amyloidosis and tau hyperphosphorylation, and thus could enhance our understanding of AD and its pathogenic commonalties with other cerebral proteopathies.

Deposition of Alzheimer's Beta-amyloid is Inversely Correlated with P-glycoprotein Expression in the Brains of Elderly Non-demented Humans

Pharmacogenetics. Oct, 2002  |  Pubmed ID: 12360104

Deposition of the beta-amyloid peptide (Abeta) in the brain occurs during normal ageing and is substantially accelerated in patients with Alzheimer's disease. Since Abeta is continuously produced in the brain, it has been suggested that a clearance mechanism should exist to prevent its accumulation and subsequent aggregation. Until now, little attention has been paid to the possible role of P-glycoprotein (P-gp), a member of the ATP binding cassette superfamily of transporter proteins, in the pathogenesis of Alzheimer's disease. A recent study demonstrated that Abeta40 and Abeta42 interact directly with P-gp. We therefore hypothesized that Abeta accumulation in the brain would correlate inversely with the degree of vascular P-gp expression. To study early pathogenetic factors that influence the deposition of Abeta, at routine autopsies, brain tissue samples were taken from 243 non-demented subjects who died between the ages of 50 and 91 years. Vascular P-gp expression and the number of Abeta40- and Abeta42-positive senile plaques were assessed immunohistochemically in the medial temporal lobe. In addition, the apolipoprotein E (apoE) genotypes, as well as multiple drug resistance gene 1 ( ) polymorphisms (exon 2, G-1A; exon 21, G2677T/A; exon 26, C3436T), were also determined for each case. P-gp expression was not correlated with genotypes, but we found a significant inverse correlation between P-gp expression and the deposition of both Abeta40 and Abeta42 in the medial temporal lobe. Our results provide the first evidence in human brain tissue that the accumulation of Abeta may be influenced by the expression of P-gp in blood vessels, and suggest that P-gp may influence the elimination of Abeta from brain.

Xanthomatosis

Journal of Neurosurgery. Oct, 2002  |  Pubmed ID: 12405396

Alzheimer's Abeta Vaccination of Rhesus Monkeys (Macaca Mulatta)

Mechanisms of Ageing and Development. Feb, 2004  |  Pubmed ID: 15037022

Recent preliminary data suggest that vaccination with Alzheimer's Abeta might reduce senile plaque load and stabilize cognitive decline in human Alzheimer's disease. To examine the mechanisms and consequences of anti-Abeta-antibody formation in a species more closely related to humans, rhesus monkeys (Macaca mulatta) were vaccinated with aggregated Abeta(1-42). Immunized monkeys developed anti-Abeta titers exceeding 1:1000, and their plasma Abeta levels were 5-10-fold higher than the plasma Abeta levels observed in monkeys vaccinated with aggregated amylin. These data support the use of non-human primates to model certain phenomena associated with vaccination of humans with aggregated Alzheimer's Abeta.

Alzheimer A Beta Vaccination of Rhesus Monkeys (Macaca Mulatta)

Alzheimer Disease and Associated Disorders. Jan-Mar, 2004  |  Pubmed ID: 15195463

Recent preliminary data suggest that vaccination with Alzheimer A beta might reduce senile plaque load and stabilize cognitive decline in human Alzheimer disease. To examine the mechanisms and consequences of anti-A beta-antibody formation in a species more closely related to humans, rhesus monkeys (Macaca mulatta) were vaccinated with aggregated A beta 1-42. Immunized monkeys developed anti-A beta titers exceeding 1:1000, and their plasma A beta levels were 5- to 10-fold higher than the plasma A beta levels observed in monkeys vaccinated with aggregated amylin. These data support the use of nonhuman primates to model certain phenomena associated with vaccination of humans with aggregated Alzheimer A beta.

Aging, Gender and APOE Isotype Modulate Metabolism of Alzheimer's Abeta Peptides and F-isoprostanes in the Absence of Detectable Amyloid Deposits

Journal of Neurochemistry. Aug, 2004  |  Pubmed ID: 15287908

Aging and apolipoprotein E (APOE) isoform are among the most consistent risks for the development of Alzheimer's disease (AD). Metabolic factors that modulate risk have been elusive, though oxidative reactions and their by-products have been implicated in human AD and in transgenic mice with overt histological amyloidosis. We investigated the relationship between the levels of endogenous murine amyloid beta (Abeta) peptides and the levels of a marker of oxidation in mice that never develop histological amyloidosis [i.e. APOE knockout (KO) mice with or without transgenic human APOEepsilon3 or human APOEepsilon4 alleles]. Aging-, gender-, and APOE-genotype-dependent changes were observed for endogenous mouse brain Abeta40 and Abeta42 peptides. Levels of the oxidized lipid F2-isoprostane (F2-isoPs) in the brains of the same animals as those used for the Abeta analyses revealed aging- and gender-dependent changes in APOE KO and in human APOEepsilon4 transgenic KO mice. Human APOEepsilon3 transgenic KO mice did not exhibit aging- or gender-dependent increases in F2-isoPs. In general, the changes in the levels of brain F2-isoPs in mice according to age, gender, and APOE genotype mirrored the changes in brain Abeta levels, which, in turn, paralleled known trends in the risk for human AD. These data indicate that there exists an aging-dependent, APOE-genotype-sensitive rise in murine brain Abeta levels despite the apparent inability of the peptide to form histologically detectable amyloid. Human APOEepsilon3, but not human APOEepsilon4, can apparently prevent the aging-dependent rise in murine brain Abeta levels, consistent with the relative risk for AD associated with these genotypes. The fidelity of the brain Abeta/F2-isoP relationship across multiple relevant variables supports the hypothesis that oxidized lipids play a role in AD pathogenesis, as has been suggested by recent evidence that F2-isoPs can stimulate Abeta generation and aggregation.

The Role of P-glycoprotein in Cerebral Amyloid Angiopathy; Implications for the Early Pathogenesis of Alzheimer's Disease

Current Alzheimer Research. May, 2004  |  Pubmed ID: 15975076

It has been shown in vitro that beta-amyloid (Abeta) is transported by P-glycoprotein (P-gp). Previously, we demonstrated that Abeta immunoreactivity is significantly elevated in brain tissue of individuals with low expression of P-gp in vascular endothelial cells. These findings led us to hypothesize that P-gp might be involved in the clearance of Abeta in normal aging and particularly in Alzheimer's disease (AD). As we were interested in the early pathogenesis of Abeta deposition, we studied the correlation between cerebral amyloid angiopathy (CAA) and P-gp expression in brain tissue samples from 243 non-demented elderly cases (aged 50 to 91 years). We found that endothelial P-gp and vascular Abeta were never colocalized, i.e., vessels with high P-gp expression showed no Abeta deposition in their walls, and vice versa. Abeta deposition occurred first in arterioles where P-gp expression was primarily low, and disappeared completely with the accumulation of Abeta. At this early stage, P-gp was upregulated in capillaries, suggesting a compensatory mechanism to increase Abeta clearance from the brain. Capillaries were usually affected only at later stages of CAA, at which point P-gp was lost even in these vessels. We hypothesize that Abeta clearance may be altered in individuals with diminished P-gp expression due, e.g., to genetic or environmental effects (such as drug administration). The impairment of Abeta clearance could lead to the accumulation and earlier deposition of Abeta, both in the walls of blood vessels and in the brain parenchyma, thus elevating the risk of CAA and AD.

Proteomic Identification of the Involvement of the Mitochondrial Rieske Protein in Epilepsy

Epilepsia. Mar, 2005  |  Pubmed ID: 15730530

Kindled seizures are widely used to model epileptogenesis, but the molecular mechanisms underlying the attainment of kindling status are largely unknown. Recently we showed that achievement of kindling status in the Sprague-Dawley rat is associated with a critical developmental interval of 25 +/- 1 days; the identification of this long, well-defined developmental interval for inducing kindling status makes possible a dissection of the cellular and genetic events underlying this phenomenon and its relation to normal and pathologic brain function.

Emerging Prospects for the Disease-modifying Treatment of Alzheimer's Disease

Biochemical Pharmacology. Apr, 2005  |  Pubmed ID: 15763538

The currently approved therapies for Alzheimer's disease (AD) in the US are designed to modify the function of specific neurotransmitter systems in the brain. While these palliative treatments can benefit some patients for a period of time, they do not halt the relentless cognitive and behavioral deterioration that characterize this neurodegenerative disorder. Consequently, much current research on AD is directed toward illuminating the disease process itself, particularly the abnormal accumulation of certain proteins in brain: the amyloid-beta protein (Abeta) in senile plaques and cerebral blood vessels, and the tau protein in neurofibrillary tangles. Genetic, biochemical and pathologic evidence now favors a primary role of Abeta aggregation in the Alzheimer proteopathic cascade, and studies in mice indicate that lowering the amount of this protein in brain can be beneficial. Recently, Abeta-immunization therapy has emerged as a particularly promising therapeutic option for treating Alzheimer's disease, but unexpected treatment-related side-effects are an overriding issue. These adverse events were not anticipated from preclinical studies with rodents; hence, more biologically relevant models, such as nonhuman primates, are needed to test the safety and efficacy of novel therapies for Alzheimer's disease.

Calcium Channel Alpha2-delta Type 1 Subunit is the Major Binding Protein for Pregabalin in Neocortex, Hippocampus, Amygdala, and Spinal Cord: an Ex Vivo Autoradiographic Study in Alpha2-delta Type 1 Genetically Modified Mice

Brain Research. Feb, 2006  |  Pubmed ID: 16460711

Pregabalin is a synthetic amino acid compound effective in clinical trials for the treatment of post-herpetic neuralgia, diabetic peripheral neuropathy, generalized anxiety disorder and adjunctive therapy for partial seizures of epilepsy. However, the mechanisms by which pregabalin exerts its therapeutic effects are not yet completely understood. In vitro studies have shown that pregabalin binds with high affinity to the alpha(2)-delta (alpha(2)-delta) subunits (Type 1 and 2) of voltage-gated calcium channels. To assess whether alpha(2)-delta Type 1 is the major central nervous system (CNS) binding protein for pregabalin in vivo, a mutant mouse with an arginine-to-alanine mutation at amino acid 217 of the alpha(2)-delta Type 1 protein (R217A mutation) was generated. Previous site-directed mutagenesis studies revealed that the R217A mutation dramatically reduces alpha(2)-delta 1 binding to pregabalin in vitro. In this autoradiographic analysis of R217A mice, we show that the mutation to alpha(2)-delta Type 1 substantially reduces specific pregabalin binding in CNS regions that are known to preferentially express the alpha(2)-delta Type 1 protein, notably the neocortex, hippocampus, basolateral amygdala and spinal cord. In mutant mice, pregabalin binding was robust throughout regions where the alpha(2)-delta Type 2 subunit mRNA is abundant, such as cerebellum. These findings, in conjunction with prior in vitro binding data, provide evidence that the alpha(2)-delta Type 1 subunit of voltage-gated calcium channels is the major binding protein for pregabalin in CNS. Moreover, the distinct localization of alpha(2)-delta Type 1 and mutation-resistant binding (assumed to be alpha(2)-delta Type 2) in brain areas subserving different functions suggests that identification of subunit-specific ligands could further enhance pharmacologic specificity.

Cerebrovascular P-glycoprotein Expression is Decreased in Creutzfeldt-Jakob Disease

Acta Neuropathologica. May, 2006  |  Pubmed ID: 16523342

The abnormal conformation and assembly of proteins in the central nervous system is increasingly thought to be a critical pathogenic mechanism in neurodegenerative disorders such as Creutzfeldt-Jakob disease (CJD) and Alzheimer's disease (AD). CJD is marked primarily by the buildup of misfolded prion protein (PrP(Sc)) in brain, whereas the accrual of beta-amyloid protein (Abeta) and tau protein are characteristic for AD. Prior studies have shown that the ATP-binding cassette transporter P-glycoprotein (P-gp) is a cellular efflux pump for Abeta, and that age-associated deficits in P-gp may be involved in the pathogenesis of Alzheimer's disease. In the present study, we investigated the relationship between P-gp and idiopathic CJD, and found that CJD, like AD, is associated with a decrease in the expression of cerebrovascular P-gp. In some instances, Abeta and PrP deposits coexist in cases of CJD, suggesting the possibility of pathogenic interactions. Since there is, to date, no evidence that PrP itself is a substrate for P-gp, we hypothesize that the age-related deficits in P-gp could promote the accumulation of PrP(Sc) either by promoting the buildup of Abeta (which could act as a seed for the aggregation of PrP(Sc)), or by overloading the ubiquitin-proteasomal catabolic system, and thereby facilitating the accumulation of PrP. Alternatively, the loss of P-gp could be a non-specific response to neurodegenerative changes in the central nervous system. In either case, dysfunction of this critical toxin-elimination pathway in CJD and AD suggests that selectively increasing cerebrovascular P-gp function could open new therapeutic pathways for the prevention and/or treatment of a number of proteopathic disorders of the central nervous system.

Alzheimer Therapeutics-what After the Cholinesterase Inhibitors?

Age and Ageing. Jul, 2006  |  Pubmed ID: 16644763

Inducible Proteopathies

Trends in Neurosciences. Aug, 2006  |  Pubmed ID: 16806508

Numerous degenerative diseases are characterized by the aberrant polymerization and accumulation of specific proteins. These proteopathies include neurological disorders such as Alzheimer's disease, Parkinson's disease, Huntington's disease and the prion diseases, in addition to diverse systemic disorders, particularly the amyloidoses. The prion diseases have been shown to be transmissible by an alternative conformation of the normal cellular prion protein. Other proteopathies have been thought to be non-transmissible, but there is growing evidence that some systemic and cerebral amyloidoses can be induced by exposure of susceptible hosts to cognate molecular templates. As we review here, the mechanistic similarities among these diseases provide unprecedented opportunities for elucidating the induction of protein misfolding and assembly in vivo, and for developing an integrated therapeutic approach to degenerative proteopathies.

Exogenous Induction of Cerebral Beta-amyloidogenesis is Governed by Agent and Host

Science (New York, N.Y.). Sep, 2006  |  Pubmed ID: 16990547

Protein aggregation is an established pathogenic mechanism in Alzheimer's disease, but little is known about the initiation of this process in vivo. Intracerebral injection of dilute, amyloid-beta (Abeta)-containing brain extracts from humans with Alzheimer's disease or beta-amyloid precursor protein (APP) transgenic mice induced cerebral beta-amyloidosis and associated pathology in APP transgenic mice in a time- and concentration-dependent manner. The seeding activity of brain extracts was reduced or abolished by Abeta immunodepletion, protein denaturation, or by Abeta immunization of the host. The phenotype of the exogenously induced amyloidosis depended on both the host and the source of the agent, suggesting the existence of polymorphic Abeta strains with varying biological activities reminiscent of prion strains.

MDR1-P-Glycoprotein (ABCB1) Mediates Transport of Alzheimer's Amyloid-beta Peptides--implications for the Mechanisms of Abeta Clearance at the Blood-brain Barrier

Brain Pathology (Zurich, Switzerland). Oct, 2007  |  Pubmed ID: 17610523

Amyloid-beta (Abeta) is the major component of the insoluble amyloid plaques that accumulate intracerebrally in patients with Alzheimer's disease (AD). It has been suggested that MDR1-P-glycoprotein (ABCB1, P-gp) plays a substantial role in the elimination of Abeta from the brain. In the present study, MDR1-transfected LLC cells growing in a polarized cell layer were used to characterize the interaction of Abeta1-40/1-42 with P-gp. In this system, P-gp-mediated transport can be followed by the efflux of the fluorescent dye rhodamine-123, or of Abeta itself from the cells into the apical extracellular space. Abeta significantly decreased the apical efflux of rhodamine-123, and the transcellular transport of Abeta1-40 and Abeta1-42 into the apical chamber could be demonstrated using both ELISA and fluorescence (FITC)-labeled peptides. This transport was inhibited by a P-gp modulator. Furthermore, ATP-dependent, P-gp-mediated transport of the fluorescence-labeled peptides could be demonstrated in isolated, inside-out membrane vesicles. Our data support the concept that P-gp is important for the clearance of Abeta from brain, and thus may represent a target protein for the prevention and/or treatment of neurodegenerative disorders such as AD.

The Response of the Aged Brain to Stroke: Too Much, Too Soon?

Current Neurovascular Research. Aug, 2007  |  Pubmed ID: 17691975

Old age is associated with an enhanced susceptibility to stroke and poor recovery from brain injury, but the cellular processes underlying these phenomena are only recently coming to light. Potential mechanisms include changes in brain plasticity-promoting factors, unregulated expression of neurotoxic factors, or differences in the generation of scar tissue that impedes the formation of new axons and blood vessels in the infarcted region. Behaviorally, aged rats are more severely impaired by stroke than are young rats, and they also show diminished functional recovery. Infarct volume does not differ significantly in young and aged animals, but critical differences are apparent in the cytological response to stroke, most notably an age-related acceleration of the establishment of the glial scar. The early infarct in older rats is associated with a premature accumulation of BrdU-positive microglia and astrocytes, persistence of activated oligodendrocytes, a high incidence of neuronal degeneration, and accelerated apoptosis. Regeneration-associated mechanisms in the rat brain are active throughout life, albeit at lower levels in the aged animals. However; after stroke in aged rats, neuroepithelial marker-positive cells emanating largely from capillaries did not make a significant contribution to neurogenesis in the infarcted cortex of aged animals. Furthermore, the expression of plasticity-associated proteins, such as MAP1B, was delayed in aged rats. Tissue recovery was further delayed by the upregulation of Nogo, ephrin-A5 and MAG, which exert a powerful negative effect on axonal sprouting in the aged peri-infarct cortex, and by an age-related increase in the amount of the neurotoxic C-terminal fragment of the beta-amyloid precursor protein (betaAPP) at 2 wks post-stroke. Our findings indicate that the aged brain has the capability to mount a cytoproliferative response to injury, but the timing of the cellular and genetic response to cerebral insult is dysregulated in aged animals, thereby further compromising functional recovery. Elucidating the molecular basis of this phenomenon in the aging brain could yield novel approaches to neurorestoration following stroke or head injury in the elderly.

Development of Transgenic Rats Producing Human Beta-amyloid Precursor Protein As a Model for Alzheimer's Disease: Transgene and Endogenous APP Genes Are Regulated Tissue-specifically

BMC Neuroscience. 2008  |  Pubmed ID: 18302776

Alzheimer's disease (AD) is a devastating neurodegenerative disorder that affects a large and growing number of elderly individuals. In addition to idiopathic disease, AD is also associated with autosomal dominant inheritance, which causes a familial form of AD (FAD). Some instances of FAD have been linked to mutations in the beta-amyloid protein precursor (APP). Although there are numerous mouse AD models available, few rat AD models, which have several advantages over mice, have been generated.

Long-term Hypothermia Reduces Infarct Volume in Aged Rats After Focal Ischemia

Neuroscience Letters. Jun, 2008  |  Pubmed ID: 18456407

In aged humans, stroke is a major cause of disability for which no neuroprotective measures are available. A viable alternative to conventional drug-based neuroprotective therapies is brain/body cooling, or hypothermia. In animal studies of focal ischemia, short-term hypothermia consistently reduces infarct size. Nevertheless, efficient neuroprotection requires long-term, regulated lowering of whole body temperature. Focal cerebral ischemia was produced by reversible occlusion of the right middle cerebral artery in 17-month-old male Sprague-Dawley rats. After stroke, the aged rats were exposed for 2 days to a mixture of air and a mild inhibitor of oxidative phosphorylation, hydrogen sulfide (H(2)S), which resulted in sustained, deep hypothermia (30.8+/-0.7 degrees C). Long-term hypothermia led to a 50% reduction in infarct size with a concomitant reduction in the number of phagocytic cells. At the transcription level, hypothermia caused a reduction in the mRNA coding for caspase 12, NF-kappa B and grp78 in the peri-infarcted region, suggesting an overall decrease in the transcriptional activity related to inflammation and apoptosis. Behaviorally, hypothermia was associated with better performance on tests that require complex sensorimotor skills, in the absence of obvious neurological deficits or physiological side effects, in aged rats. Conclusions: Prolonged, H(2)S-induced hypothermia is a simple and efficacious method to limit the damage inflicted by stroke in aged rats.

Tauopathy with Paired Helical Filaments in an Aged Chimpanzee

The Journal of Comparative Neurology. Jul, 2008  |  Pubmed ID: 18481275

An enigmatic feature of age-related neurodegenerative diseases is that they seldom, if ever, are fully manifested in nonhuman species under natural conditions. The neurodegenerative tauopathies are typified by the intracellular aggregation of hyperphosphorylated microtubule-associated protein tau (MAPT) and the dysfunction and death of affected neurons. We document the first case of tauopathy with paired helical filaments in an aged chimpanzee (Pan troglodytes). Pathologic forms of tau in neuronal somata, neuropil threads, and plaque-like clusters of neurites were histologically identified throughout the neocortex and, to a lesser degree, in allocortical and subcortical structures. Ultrastructurally, the neurofibrillary tangles consisted of tau-immunoreactive paired helical filaments with a diameter and helical periodicity indistinguishable from those seen in Alzheimer's disease. A moderate degree of Abeta deposition was present in the cerebral vasculature and, less frequently, in senile plaques. Sequencing of the exons and flanking intronic regions in the genomic MAPT locus disclosed no mutations that are associated with the known human hereditary tauopathies, nor any polymorphisms of obvious functional significance. Although the lesion profile in this chimpanzee differed somewhat from that in Alzheimer's disease, the copresence of paired helical filaments and Abeta-amyloidosis indicates that the molecular mechanisms for the pathogenesis of the two canonical Alzheimer lesions--neurofibrillary tangles and senile plaques--are present in aged chimpanzees.

Clinico-pathologic Function of Cerebral ABC Transporters - Implications for the Pathogenesis of Alzheimer's Disease

Current Alzheimer Research. Aug, 2008  |  Pubmed ID: 18690837

In recent years it has become evident that ABC transporters fulfill important barrier functions in normal organs and during disease processes. Most importantly, resistance to drugs in cancer cells led to intense oncological and pharmacological investigations in which researchers were able to highlight important pharmacological interactions of chemotherapeuticals with ABC transporter function. Recently, the development of neurodegenerative diseases and the maintenance of neuronal stem cells have been linked to the activity of ABC transporters. Here, we summarize findings from cell culture experiments, animal models and studies of patients with Alzheimer's disease. Furthermore, we discuss pharmacological interactions and computational methods for risk assessment.

The Synthesis and Structure-activity Relationship of Substituted N-phenyl Anthranilic Acid Analogs As Amyloid Aggregation Inhibitors

Bioorganic & Medicinal Chemistry Letters. Feb, 2009  |  Pubmed ID: 19121939

It is believed that beta-amyloid aggregation is an important event in the development of Alzheimer's disease. In the course of our studies to identify beta-amyloid aggregation inhibitors, a series of N-phenyl anthranilic acid analogs were synthesized and studied for beta-amyloid inhibition activity. The synthesis, structure-activity relationship, and in vivo activity of these analogs are discussed.

Alzheimer's Disease and Blood-brain Barrier Function-Why Have Anti-beta-amyloid Therapies Failed to Prevent Dementia Progression?

Neuroscience and Biobehavioral Reviews. Jul, 2009  |  Pubmed ID: 19481107

Proteopathies of the brain are defined by abnormal, disease-inducing protein deposition that leads to functional abrogation and death of neurons. Immunization trials targeting the removal of amyloid-beta plaques in Alzheimer's disease have so far failed to stop the progression of dementia, despite autopsy findings of reduced plaque load. Here, we summarize current knowledge of the relationship between AD pathology and blood-brain barrier function, and propose that the activation of the excretion function of the blood-brain barrier might help to achieve better results in trials targeting the dissolution of cerebral amyloid-beta aggregates. We further discuss a possible role of oligomers in limiting the efficacy of immunotherapy.

Induction of Cerebral Beta-amyloidosis: Intracerebral Versus Systemic Abeta Inoculation

Proceedings of the National Academy of Sciences of the United States of America. Aug, 2009  |  Pubmed ID: 19622727

Despite the importance of the aberrant polymerization of Abeta in the early pathogenic cascade of Alzheimer's disease, little is known about the induction of Abeta aggregation in vivo. Here we show that induction of cerebral beta-amyloidosis can be achieved in many different brain areas of APP23 transgenic mice through the injection of dilute Abeta-containing brain extracts. Once the amyloidogenic process has been exogenously induced, the nature of the induced Abeta-deposition is determined by the brain region of the host. Because these observations are reminiscent of a prion-like mechanism, we then investigated whether cerebral beta-amyloidosis also can be induced by peripheral and systemic inoculations or by the intracerebral implantation of stainless steel wires previously coated with minute amounts of Abeta-containing brain extract. Results reveal that oral, intravenous, intraocular, and intranasal inoculations yielded no detectable induction of cerebral beta-amyloidosis in APP23 transgenic mice. In contrast, transmission of cerebral beta-amyloidosis through the Abeta-contaminated steel wires was demonstrated. Notably, plasma sterilization, but not boiling of the wires before implantation, prevented the induction of beta-amyloidosis. Our results suggest that minute amounts of Abeta-containing brain material in direct contact with the CNS can induce cerebral beta-amyloidosis, but that systemic cellular mechanisms of prion uptake and transport to the CNS may not apply to Abeta.

Ovarian Aging in Squirrel Monkeys (Saimiri Sciureus)

Reproduction (Cambridge, England). Nov, 2009  |  Pubmed ID: 19656956

In female squirrel monkeys (Saimiri sciureus), the reproductive period normally extends from approximately 2.5 years to the mid-teens. In the present study, we examined the age-associated cytological changes in the ovaries of 24 squirrel monkeys ranging in age from newborn to approximately 20 years. We found a significant, age-related decline in the number of primordial follicles, with the most pronounced loss occurring between birth and 5 years. After approximately 8 years of age, relatively few primordial follicles were evident in the ovarian sections examined. An unusual feature of the aging squirrel monkey ovary is the emergence of highly differentiated, encapsulated clusters of granulosa cells that increase in size and number, particularly after the age of 8 years. Many of these cells express anti-Müllerian hormone, and, histologically, the clusters resemble granulosa cell tumors in humans. However, granulosa cell clusters (GCCs) are present in both ovaries of all older squirrel monkeys, and they display no obvious signs of malignancy, suggesting that they are a normal feature of ovarian aging in this species. Our findings indicate that reproductive senescence in female squirrel monkeys, as in other primates, involves the inexorable depletion of ovarian follicles. In addition, the consistent appearance of abundant, well-differentiated clusters of granulosa cells in older squirrel monkeys, prior to the cessation of reproduction, suggests that these structures may influence the later stages of reproductive potential in this species. Analysis of GCCs in older squirrel monkeys also could yield insights into the pathophysiology of granulosa cell tumors in humans.

Deficient High-affinity Binding of Pittsburgh Compound B in a Case of Alzheimer's Disease

Acta Neuropathologica. Feb, 2010  |  Pubmed ID: 19690877

Radiolabeled Pittsburgh compound B (PIB) is a benzothiazole imaging agent that usually binds with high affinity, specificity, and stoichiometry to cerebral beta-amyloid (Abeta) in patients with Alzheimer's disease. Among a cohort of ten AD subjects examined postmortem, we describe a case of idiopathic, end-stage Alzheimer's disease with heavy Abeta deposition yet substantially diminished high-affinity binding of (3)H-PIB to cortical homogenates and unfixed cryosections. Cortical tissue samples were analyzed by immunohistochemistry, electron microscopy, ELISA, immunoblotting, MALDI-TOF mass spectrometry, in vitro (3)H-PIB binding and (3)H-PIB autoradiography. The PIB-refractory subject met the histopathological criteria for AD. However, cortical tissue from this case contained more vascular beta-amyloidosis, higher levels of insoluble Abeta40 and Abeta42, and a higher ratio of Abeta40:Abeta42 than did tissue from the nine comparison AD cases. Furthermore, cerebral Abeta from the PIB-refractory subject displayed an unusual distribution of low- and high-molecular weight Abeta oligomers, as well as a distinct pattern of N- and C-terminally truncated Abeta peptides in both the soluble and insoluble cortical extracts. Genetically, the patient was apolipoprotein-E3/4 heterozygous, and exhibited no known AD-associated mutations in the genes for the beta-amyloid precursor protein, presenilin1 or presenilin2. Our findings suggest that PIB may differentially recognize polymorphic forms of multimeric Abeta in humans with Alzheimer's disease. In addition, while the prevalence of PIB-refractory cases in the general AD population remains to be determined, the paucity of high-affinity binding sites in this AD case cautions that minimal PIB retention in positron-emission tomography scans of demented patients may not always rule out the presence of Alzheimer-type Abeta pathology.

The Grandmother Effect and the Uniqueness of the Human Aging Phenotype

Gerontology. 2010  |  Pubmed ID: 19864883

This issue of Gerontology includes a response by van Bodegom et al. to Herndon's recent article on the implications of the grandmother hypothesis for studies of aging and cognition. Although this hypothesis will doubtlessly continue to stimulate discussion, we focus here on our contention that human and non-human primate life histories have evolved essential differences and that these should be addressed in studies comparing aging in humans and chimpanzees.

Mosaic Aging

Medical Hypotheses. Jun, 2010  |  Pubmed ID: 20110150

Although all multicellular organisms undergo structural and functional deterioration with age, senescence is not a uniform process. Rather, each organism experiences a constellation of changes that reflect the heterogeneous effects of age on molecules, cells, organs and systems, an idiosyncratic pattern that we refer to as mosaic aging. Varying genetic, epigenetic and environmental factors (local and extrinsic) contribute to the aging phenotype in a given individual, and these agents influence the type and rate of functional decline, as well as the likelihood of developing age-associated afflictions such as cardiovascular disease, arthritis, cancer, and neurodegenerative disorders. Identifying key factors that drive aging, clarifying their activities in different systems, and in particular understanding how they interact will enhance our comprehension of the aging process, and could yield insights into the permissive role that senescence plays in the emergence of acute and chronic diseases of the elderly.

Days to Criterion As an Indicator of Toxicity Associated with Human Alzheimer Amyloid-beta Oligomers

Annals of Neurology. Aug, 2010  |  Pubmed ID: 20641005

Recent evidence suggests that high molecular weight soluble oligomeric Abeta (oAbeta) assemblies (also known as Abeta-derived diffusible ligands, or ADDLs) may represent a primary neurotoxic basis for cognitive failure in Alzheimer disease (AD). To date, most in vivo studies of oAbeta/ADDLs have involved injection of assemblies purified from the cerebrospinal fluid of human subjects with AD or from the conditioned media of Abeta-secreting cells into experimental animals. We sought to study the bioactivities of endogenously formed oAbeta/ADDLs generated in situ from the physiological processing of human amyloid precursor protein (APP) and presenitin1 (PS1) transgenes.

Peripherally Applied Abeta-containing Inoculates Induce Cerebral Beta-amyloidosis

Science (New York, N.Y.). Nov, 2010  |  Pubmed ID: 20966215

The intracerebral injection of β-amyloid-containing brain extracts can induce cerebral β-amyloidosis and associated pathologies in susceptible hosts. We found that intraperitoneal inoculation with β-amyloid-rich extracts induced β-amyloidosis in the brains of β-amyloid precursor protein transgenic mice after prolonged incubation times.

Molecular Polymorphism of Abeta in Alzheimer's Disease

Neurobiology of Aging. Apr, 2010  |  Pubmed ID: 18619711

Alzheimer's disease is defined pathologically by the presence of senile plaques, which consist primarily of extracellular aggregates of fibrillar Abeta peptide, and neurofibrillary tangles, which are abnormal, intracellular bundles of fibrillar tau protein. The advent of amyloid binding agents as diagnostic imaging probes for Alzheimer's disease (AD) has made it imperative to understand at a molecular and disease level what these ligands are reporting. In addition to improving the accuracy of diagnosis, we argue that these selective ligands can serve as probes for molecular polymorphisms that may govern the pathogenicity of abnormal protein aggregates.

Automated Detection of Amyloid-β-related Cortical and Subcortical Signal Changes in a Transgenic Model of Alzheimer's Disease Using High-field MRI

Journal of Alzheimer's Disease : JAD. 2011  |  Pubmed ID: 20966552

In vivo imaging of amyloid-β (Aβ) load as a biomarker of Alzheimer's disease (AD) would be of considerable clinical relevance for the early diagnosis and monitoring of treatment effects. Here, we investigated automated quantification of in vivo T2 relaxation time as a surrogate measure of plaque load in the brains of ten AβPP/PS1 transgenic mice (age 20 weeks) using in vivo MRI acquisitions on a 7T Bruker ClinScan magnet. AβPP/PS1 mice present with rapid-onset cerebral β-amyloidosis, and were compared with eight age-matched, wild-type control mice (C57Bl/6J) that do not develop Aβ-deposition in brain. Data were analyzed with a novel automated voxel-based analysis that allowed mapping the entire brain for significant signal changes. In AβPP/PS1 mice, we found a significant decrease in T2 relaxation times in the deeper neocortical layers, caudate-putamen, thalamus, hippocampus, and cerebellum compared to wildtype controls. These changes were in line with the histological distribution of cerebral Aβ plaques and activated microglia. Grey matter density did not differ between wild-type mice and AβPP/PS1 mice, consistent with a lack of neuronal loss in histological investigations. High-field MRI with automated mapping of T2 time changes may be a useful tool for the detection of plaque load in living transgenic animals, which may become relevant for the evaluation of amyloid lowering intervention effects in future studies.

Amyloid by Default

Nature Neuroscience. Jun, 2011  |  Pubmed ID: 21613991

The Role of the ATP-binding Cassette Transporter P-glycoprotein in the Transport of β-amyloid Across the Blood-brain Barrier

Current Pharmaceutical Design. 2011  |  Pubmed ID: 21827406

The blood-brain barrier (BBB) protects the brain against endogenous and exogenous compounds and plays an important part in the maintenance of the microenvironment of the brain. In particular, the importance of brain-to-blood transport of brain-derived metabolites across the BBB has gained increasing attention as a potential mechanism in the pathogenesis of neurodegenerative disorders such as Alzheimer's disease, which is characterized by the aberrant polymerization and accumulation of specific misfolded proteins, particularly β-amyloid (Aβ). There is growing evidence that the ABC transport protein P-glycoprotein (P-gp), a major component of the BBB, mediates the efflux of Aβ from the brain. In this review, we discuss the possible role of P-gp in Alzheimer's disease and other neurodegenerative disorders, and consider how a fuller understanding of this function might promote the development of more effective treatment strategies.

Cerebral Amyloid-β Proteostasis is Regulated by the Membrane Transport Protein ABCC1 in Mice

The Journal of Clinical Investigation. Oct, 2011  |  Pubmed ID: 21881209

In Alzheimer disease (AD), the intracerebral accumulation of amyloid-β (Aβ) peptides is a critical yet poorly understood process. Aβ clearance via the blood-brain barrier is reduced by approximately 30% in AD patients, but the underlying mechanisms remain elusive. ABC transporters have been implicated in the regulation of Aβ levels in the brain. Using a mouse model of AD in which the animals were further genetically modified to lack specific ABC transporters, here we have shown that the transporter ABCC1 has an important role in cerebral Aβ clearance and accumulation. Deficiency of ABCC1 substantially increased cerebral Aβ levels without altering the expression of most enzymes that would favor the production of Aβ from the Aβ precursor protein. In contrast, activation of ABCC1 using thiethylperazine (a drug approved by the FDA to relieve nausea and vomiting) markedly reduced Aβ load in a mouse model of AD expressing ABCC1 but not in such mice lacking ABCC1. Thus, by altering the temporal aggregation profile of Aβ, pharmacological activation of ABC transporters could impede the neurodegenerative cascade that culminates in the dementia of AD.

Soluble Aβ Seeds Are Potent Inducers of Cerebral β-amyloid Deposition

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience. Oct, 2011  |  Pubmed ID: 21994365

Cerebral β-amyloidosis and associated pathologies can be exogenously induced by the intracerebral injection of small amounts of pathogenic Aβ-containing brain extract into young β-amyloid precursor protein (APP) transgenic mice. The probable β-amyloid-inducing factor in the brain extract has been identified as a species of aggregated Aβ that is generated in its most effective conformation or composition in vivo. Here we report that Aβ in the brain extract is more proteinase K (PK) resistant than is synthetic fibrillar Aβ, and that this PK-resistant fraction of the brain extract retains the capacity to induce β-amyloid deposition upon intracerebral injection in young, pre-depositing APP23 transgenic mice. After ultracentrifugation of the brain extract, <0.05% of the Aβ remained in the supernatant fraction, and these soluble Aβ species were largely PK sensitive. However, upon intracerebral injection, this soluble fraction accounted for up to 30% of the β-amyloid induction observed with the unfractionated extract. Fragmentation of the Aβ seeds by extended sonication increased the seeding capacity of the brain extract. In summary, these results suggest that multiple Aβ assemblies, with various PK sensitivities, are capable of inducing β-amyloid aggregation in vivo. The finding that small and soluble Aβ seeds are potent inducers of cerebral β-amyloidosis raises the possibility that such seeds may mediate the spread of β-amyloidosis in the brain. If they can be identified in vivo, soluble Aβ seeds in bodily fluids also could serve as early biomarkers for cerebral β-amyloidogenesis and eventually Alzheimer's disease.

PIB Binding in Aged Primate Brain: Enrichment of High-affinity Sites in Humans with Alzheimer's Disease

Neurobiology of Aging. Feb, 2011  |  Pubmed ID: 19329226

Aged nonhuman primates accumulate large amounts of human-sequence amyloid β (Aβ) in the brain, yet they do not manifest the full phenotype of Alzheimer's disease (AD). To assess the biophysical properties of Aβ that might govern its pathogenic potential in humans and nonhuman primates, we incubated the benzothiazole imaging agent Pittsburgh Compound B (PIB) with cortical tissue homogenates from normal aged humans, humans with AD, and from aged squirrel monkeys, rhesus monkeys, and chimpanzees with cerebral Aβ-amyloidosis. Relative to humans with AD, high-affinity PIB binding is markedly reduced in cortical extracts from aged nonhuman primates containing levels of insoluble Aβ similar to those in AD. The high-affinity binding of PIB may be selective for a pathologic, human-specific conformation of multimeric Aβ, and thus could be a useful experimental tool for clarifying the unique predisposition of humans to Alzheimer's disease.

Pathogenic Protein Seeding in Alzheimer Disease and Other Neurodegenerative Disorders

Annals of Neurology. Oct, 2011  |  Pubmed ID: 22028219

The misfolding and aggregation of specific proteins is a seminal occurrence in a remarkable variety of neurodegenerative disorders. In Alzheimer disease (the most prevalent cerebral proteopathy), the two principal aggregating proteins are β-amyloid (Aβ) and tau. The abnormal assemblies formed by conformational variants of these proteins range in size from small oligomers to the characteristic lesions that are visible by optical microscopy, such as senile plaques and neurofibrillary tangles. Pathologic similarities with prion disease suggest that the formation and spread of these proteinaceous lesions might involve a common molecular mechanism-corruptive protein templating. Experimentally, cerebral β-amyloidosis can be exogenously induced by exposure to dilute brain extracts containing aggregated Aβ seeds. The amyloid-inducing agent probably is Aβ itself, in a conformation generated most effectively in the living brain. Once initiated, Aβ lesions proliferate within and among brain regions. The induction process is governed by the structural and biochemical nature of the Aβ seed, as well as the attributes of the host, reminiscent of pathogenically variant prion strains. The concept of prionlike induction and spreading of pathogenic proteins recently has been expanded to include aggregates of tau, α-synuclein, huntingtin, superoxide dismutase-1, and TDP-43, which characterize such human neurodegenerative disorders as frontotemporal lobar degeneration, Parkinson/Lewy body disease, Huntington disease, and amyotrophic lateral sclerosis. Our recent finding that the most effective Aβ seeds are small and soluble intensifies the search in bodily fluids for misfolded protein seeds that are upstream in the proteopathic cascade, and thus could serve as predictive diagnostics and the targets of early, mechanism-based interventions. Establishing the clinical implications of corruptive protein templating will require further mechanistic and epidemiologic investigations. However, the theory that many chronic neurodegenerative diseases can originate and progress via the seeded corruption of misfolded proteins has the potential to unify experimental and translational approaches to these increasingly prevalent disorders.

The Presence of Aβ Seeds, and Not Age Per Se, is Critical to the Initiation of Aβ Deposition in the Brain

Acta Neuropathologica. Jan, 2012  |  Pubmed ID: 22101366

The deposition of the β-amyloid (Aβ) peptide in senile plaques and cerebral Aβ-amyloid angiopathy can be seeded in β-amyloid precursor protein (APP)-transgenic mice by the intracerebral infusion of brain extracts containing aggregated Aβ. Previous studies of seeded β-amyloid induction have used relatively short incubation periods to dissociate seeded β-amyloid induction from endogenous β-amyloid deposition of the host, thus precluding the analysis of the impact of age and extended incubation periods on the instigation and spread of Aβ lesions in brain. In the present study using R1.40 APP-transgenic mice (which do not develop endogenous Aβ deposition up to 15 months of age) we show that: (1) seeding at 9 months of age does not induce more Aβ deposition than seeding at 3 months of age, provided that the incubation period (6 months) is the same; and (2) very long-term (12 months) incubation after a focal application of the seed results in the emergence of Aβ deposits throughout the forebrain. These findings indicate that the presence of Aβ seeds, and not the age of the host per se, is critical to the initiation of Aβ aggregation in the brain, and that Aβ deposition, actuated in one brain area, eventually spreads throughout the brain.

Nonhuman Primate Models of Alzheimer-Like Cerebral Proteopathy

Current Pharmaceutical Design. Jan, 2012  |  Pubmed ID: 22288403

Nonhuman primates are useful for the study of age-associated changes in the brain and behavior in a model that is biologically proximal to humans. The Aβ and tau proteins, two key players in the pathogenesis of Alzheimer's disease (AD), are highly homologous among primates.With age, all nonhuman primates analyzed to date develop senile (Aβ) plaques and cerebral β-amyloid angiopathy. In contrast, significant tauopathy is unusual in simians, and only humans manifest the profound tauopathy, neuronal degeneration and cognitive impairment that characterize Alzheimer's disease. Primates thus are somewhat paradoxical models of AD-like pathology;on the one hand, they are excellent models of normal aging and naturally occurring Aβ lesions, and they can be useful for testing diagnostic and therapeutic agents targeting aggregated forms of Aβ. On the other hand, the resistance of monkeys and apes to tauopathy and AD-related neurodegeneration, in the presence of substantial cerebral Aβ deposition, suggests that a comparative analysis of human and nonhuman primates could yield informative clues to the uniquely human predisposition to Alzheimer's disease.

Exogenous Seeding of Cerebral β-amyloid Deposition in βAPP-transgenic Rats

Journal of Neurochemistry. Mar, 2012  |  Pubmed ID: 22017494

J. Neurochem. (2012) 120, 660-666. ABSTRACT: Deposition of the amyloid-β (Aβ) peptide in senile plaques and cerebral Aβ angiopathy (CAA) can be stimulated in Aβ-precursor protein (APP)-transgenic mice by the intracerebral injection of dilute brain extracts containing aggregated Aβ seeds. Growing evidence implicates a prion-like mechanism of corruptive protein templating in this phenomenon, in which aggregated Aβ itself is the seed. Unlike prion disease, which can be induced de novo in animals that are unlikely to spontaneously develop the disease, previous experiments with Aβ seeding have employed animal models that, as they age, eventually will generate Aβ lesions in the absence of seeding. In the present study, we first established that a transgenic rat model expressing human APP (APP21 line) does not manifest endogenous deposits of Aβ within the course of its median lifespan (30 months). Next, we injected 3-month-old APP21 rats intrahippocampally with dilute Alzheimer brain extracts containing aggregated Aβ. After a 9-month incubation period, these rats had developed senile plaques and CAA in the injected hippocampus, whereas control rats remained free of such lesions. These findings underscore the co-dependence of agent and host in governing seeded protein aggregation, and show that cerebral Aβ-amyloidosis can be induced even in animals that are relatively refractory to the spontaneous origination of parenchymal and vascular deposits of Aβ.