Transthyretin accelerates vascular Abeta deposition in a mouse model of Alzheimer's disease

Q-Rich Yeast Prion [PSI+] Accelerates Aggregation of Transthyretin, a Non-Q-Rich Human Protein

Interactions amongst different amyloid proteins have been proposed as a probable mechanism of aggregation and thus an important risk factor for the onset as well as progression of various neurodegenerative disorders including Alzheimer's, Parkinson's, Huntington's, and Amyotrophic Lateral Sclerosis. Evidences suggest that transthyretin (TTR), a plasma protein associated with transthyretin amyloidosis or familial polyneuropathy (FAP) interacts with heterologous amyloid proteins including amyloid beta and islet amyloid polypeptide. In addition, recent clinical studies have revealed the presence of systemic polyneuropathy associated with FAP mutations in patients with spinocerebral ataxia, amyotrophic lateral sclerosis, and new familial systematic prion disease. Hence, it is important to investigate the interactions amongst different amyloid proteins to gain better insight into the pathology of amyloid disorders. Yeast has been an excellent model system to study interaction/ cross-seeding between heterologous amyloid proteins, more because of presence of endogenous yeast prions. Here, we examined interactions of non-glutamine (non-Q)-rich transthyretin, with glutamine (Q)-rich yeast prion protein Sup35. We established aggregation of an engineered double (F87M/L110M) mutant M-TTR-GFP in yeast. This mutant is monomeric and readily formed aggregates compared to WT-TTR-GFP in yeast at acidic pH. Interestingly, aggregation of M-TTR-GFP was significantly enhanced in presence of [PSI⁺], an endogenous prion form of Sup35. Different variants of [PSI⁺] seeded M-TTR-GFP with different efficiencies and curing of [PSI⁺] (losing the prion form) in these strains reduced aggregation. Moreover, overexpression of prion domain of Sup35 fused to RFP (NM-RFP) also increased M-TTR-GFP aggregation. M-TTR-GFP and NM-RFP aggregates co-localized in perivacuolar and juxtranuclear region. Sup35 protein was even immunocaptured in M-TTR-GFP aggregates. However, M-TTR-GFP overexpression did not induce Sup35 aggregation. Thus, it appears to be a unidirectional interaction between these two amyloid proteins. However, no affect on M-TTR-GFP aggregation was observed due to another yeast prion, [PIN⁺]. Our findings thus show the molecular interaction of transthyretin with yeast prion and support that sequence similarity is not the prime requirement for heterologous amyloid interactions.

Transthyretin Suppresses Amyloid-β Secretion by Interfering with Processing of the Amyloid-β Protein Precursor

In Alzheimer's disease (AD), most hippocampal and cortical neurons show increased staining with anti-transthyretin (TTR) antibodies. Genetically programmed overexpression of wild type human TTR suppressed the neuropathologic and behavioral abnormalities in APP23 AD model mice and TTR-Aβ complexes have been isolated from some human AD brains and those of APP23 transgenic mice. In the present study, in vitro NMR analysis showed interaction between the hydrophobic thyroxine binding pocket of TTR and the cytoplasmic loop of the C99 fragment released by β-secretase cleavage of AβPP, with Kd = 86±9 μM. In cultured cells expressing both proteins, the interaction reduced phosphorylation of C99 (at T668) and suppressed its cleavage by γ-secretase, significantly decreasing Aβ secretion. Coupled with its previously demonstrated capacity to inhibit Aβ aggregation (with the resultant cytotoxicity in tissue culture) and its regulation by HSF1, these findings indicate that TTR can behave as a stress responsive multimodal suppressor of AD pathogenesis.

Influence of Coding Variability in APP-Aβ Metabolism Genes in Sporadic Alzheimer's Disease

The cerebral deposition of Aβ42, a neurotoxic proteolytic derivate of amyloid precursor protein (APP), is a central event in Alzheimer's disease (AD)(Amyloid hypothesis). Given the key role of APP-Aβ metabolism in AD pathogenesis, we selected 29 genes involved in APP processing, Aβ degradation and clearance. We then used exome and genome sequencing to investigate the single independent (single-variant association test) and cumulative (gene-based association test) effect of coding variants in these genes as potential susceptibility factors for AD, in a cohort composed of 332 sporadic and mainly late-onset AD cases and 676 elderly controls from North America and the UK. Our study shows that common coding variability in these genes does not play a major role for the disease development. In the single-variant association analysis, the main hits, none of which statistically significant after multiple testing correction (1.9e-4 Collapse

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MESH Headings

• Alzheimer Disease/genetics
• Alzheimer Disease/metabolism
• Amyloid beta-Peptides/genetics
• Amyloid beta-Peptides/metabolism
• Amyloid beta-Protein Precursor/genetics
• Amyloid beta-Protein Precursor/metabolism
• Computational Biology
• Exome
• Humans

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Grants

• U24 AG021886 NIA NIH HHS
• P50 AG016574 NIA NIH HHS
• U01 AG052411 NIA NIH HHS
• MR/L016397/1 Medical Research Council
• P01 AG026276 NIA NIH HHS
• Z01 AG000950 Intramural NIH HHS
• G1100695 Medical Research Council
• RF1 AG044546 NIA NIH HHS
• Wellcome Trust
• R01 AG018023 NIA NIH HHS
• U01 AG006786 NIA NIH HHS
• P01 AG003991 NIA NIH HHS
• P50 AG005681 NIA NIH HHS
• Alzheimer’s Research UK
• Wellcome Trust/MRC Joint Call in Neurodegeneration Award
• National Institute for Health Research Biomedical Research Unit in Dementia at University College London Hospitals
• the Big Lottery
• Alzheimer's Research UK
• Intramural Research Programs of the National Institute on Aging and the National Institute of Neurological Disease and Stroke

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Affiliation(s)

Celeste Sassi Reta Lila, Weston Research Laboratories, Department of Molecular Neuroscience, UCL Institute of Neurology, London, United Kingdom Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, MD, United States of America Department of Experimental Neurology, Center for Stroke Research Berlin (CSB), Charite’ Universitätmedizin, Berlin, Germany German Center for Neurodegenerative Diseases (DZNE), Berlin site, Germany
Perry G. Ridge Departments of Biology, Neuroscience, Brigham Young University, Provo, UT, United States of America
Michael A. Nalls Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, MD, United States of America
Raphael Gibbs Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, MD, United States of America
Jinhui Ding Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, MD, United States of America
Michelle K. Lupton King's College London Institute of Psychiatry, London, United Kingdom QIMR Berghofer Medical Research Institute, Brisbane, Queensland, Australia
Claire Troakes King's College London Institute of Psychiatry, London, United Kingdom
Katie Lunnon King's College London Institute of Psychiatry, London, United Kingdom
Safa Al-Sarraj King's College London Institute of Psychiatry, London, United Kingdom
Kristelle S. Brown Translation Cell Sciences-Human Genetics, School of Life Sciences, Queens Medical Centre, University of Nottingham, Nottingham, United Kingdom
Christopher Medway Translation Cell Sciences-Human Genetics, School of Life Sciences, Queens Medical Centre, University of Nottingham, Nottingham, United Kingdom
Jenny Lord Translation Cell Sciences-Human Genetics, School of Life Sciences, Queens Medical Centre, University of Nottingham, Nottingham, United Kingdom
James Turton Translation Cell Sciences-Human Genetics, School of Life Sciences, Queens Medical Centre, University of Nottingham, Nottingham, United Kingdom
ARUK Consortium
Kevin Morgan Translation Cell Sciences-Human Genetics, School of Life Sciences, Queens Medical Centre, University of Nottingham, Nottingham, United Kingdom
John F. Powell King's College London Institute of Psychiatry, London, United Kingdom
John S. Kauwe Departments of Biology, Neuroscience, Brigham Young University, Provo, UT, United States of America
Carlos Cruchaga Washington University, Division of Biology and Biomedical Sciences St. Louis, MO, United States of America
Jose Bras Reta Lila, Weston Research Laboratories, Department of Molecular Neuroscience, UCL Institute of Neurology, London, United Kingdom
Alison M. Goate Icahn School of Medicine at Mount Sinai, Icahn Medical Institute, New York, NY, United States of America
Andrew B. Singleton Laboratory of Neurogenetics, National Institute on Aging, National Institutes of Health, Bethesda, MD, United States of America
Rita Guerreiro Reta Lila, Weston Research Laboratories, Department of Molecular Neuroscience, UCL Institute of Neurology, London, United Kingdom
John Hardy Reta Lila, Weston Research Laboratories, Department of Molecular Neuroscience, UCL Institute of Neurology, London, United Kingdom

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Identifying aging-related genes in mouse hippocampus using gateway nodes

Background

High-throughput studies continue to produce volumes of metadata representing valuable sources of information to better guide biological research. With a stronger focus on data generation, analysis models that can readily identify actual signals have not received the same level of attention. This is due in part to high levels of noise and data heterogeneity, along with a lack of sophisticated algorithms for mining useful information. Networks have emerged as a powerful tool for modeling high-throughput data because they are capable of representing not only individual biological elements but also different types of relationships en masse. Moreover, well-established graph theoretic methodology can be applied to network models to increase efficiency and speed of analysis. In this project, we propose a network model that examines temporal data from mouse hippocampus at the transcriptional level via correlation of gene expression. Using this model, we formally define the concept of “gateway” nodes, loosely defined as nodes representing genes co-expressed in multiple states. We show that the proposed network model allows us to identify target genes implicated in hippocampal aging-related processes.

Results

By mining gateway genes related to hippocampal aging from networks made from gene expression in young and middle-aged mice, we provide a proof-of-concept of existence and importance of gateway nodes. Additionally, these results highlight how network analysis can act as a supplement to traditional statistical analysis of differentially expressed genes. Finally, we use the gateway nodes identified by our method as well as functional databases and literature to propose new targets for study of aging in the mouse hippocampus.

Conclusions

This research highlights the need for methods of temporal comparison using network models and provides a systems biology approach to extract information from correlation networks of gene expression. Our results identify a number of genes previously implicated in the aging mouse hippocampus related to synaptic plasticity and apoptosis. Additionally, this model identifies a novel set of aging genes previously uncharacterized in the hippocampus. This research can be viewed as a first-step for identifying the processes behind comparative experiments in aging that is applicable to any type of temporal multi-state network.

Blood-brain-barriers in aging and in Alzheimer's disease

The aging process correlates with a progressive failure in the normal cellular and organ functioning; these alterations are aggravated in Alzheimer's disease (AD). In both aging and AD there is a general decrease in the capacity of the body to eliminate toxic compounds and, simultaneously, to supply the brain with relevant growth and nutritional factors. The barriers of the brain are targets of this age related dysfunction; both the endothelial cells of the blood-brain barrier and the choroid plexus epithelial cells of the blood-cerebrospinal fluid barrier decrease their secretory capacity towards the brain and their ability to remove toxic compounds from the brain. Additionally, during normal aging and in AD, the permeability of the brain barriers increase. As such, a greater contact of the brain parenchyma with the blood content alters the highly controlled neural environment, which impacts on neural function. Of interest, the brain barriers are more than mere obstacles to the passage of molecules and cells, and therefore active players in brain homeostasis, which is still to be further recognized and investigated in the context of health and disease. Herein, we provide a review on how the brain barriers change during aging and in AD and how these processes impact on brain function.

Neurotoxicity and memory deficits induced by soluble low-molecular-weight amyloid-β1-42 oligomers are revealed in vivo by using a novel animal model

Neuronal and synaptic degeneration are the best pathological correlates for memory decline in Alzheimer's disease (AD). Although the accumulation of soluble low-molecular-weight amyloid-β (Aβ) oligomers has been suggested to trigger neurodegeneration in AD, animal models overexpressing or infused with Aβ lack neuronal loss at the onset of memory deficits. Using a novel in vivo approach, we found that repeated hippocampal injections of small soluble Aβ(1-42) oligomers in awake, freely moving mice were able to induce marked neuronal loss, tau hyperphosphorylation, and deficits in hippocampus-dependent memory. The neurotoxicity of small Aβ(1-42) species was observed in vivo as well as in vitro in association with increased caspase-3 activity and reduced levels of the NMDA receptor subunit NR2B. We found that the sequestering agent transthyretin is able to bind the toxic Aβ(1-42) species and attenuated the loss of neurons and memory deficits. Our novel mouse model provides evidence that small, soluble Aβ(1-42) oligomers are able to induce extensive neuronal loss in vivo and initiate a cascade of events that mimic the key neuropathological hallmarks of AD.

Modulation of iron metabolism in aging and in Alzheimer's disease: relevance of the choroid plexus

Iron is essential for mammalian cellular homeostasis. However, in excess, it promotes free radical formation and is associated with aging-related progressive deterioration and with neurodegenerative disorders such as Alzheimer's disease (AD). There are no mechanisms to excrete iron, which makes iron homeostasis a very tightly regulated process at the level of the intestinal absorption. Iron is believed to reach the brain through receptor-mediated endocytosis of iron-bound transferrin by the brain barriers, the blood-cerebrospinal fluid (CSF) barrier, formed by the choroid plexus (CP) epithelial cells and the blood-brain barrier (BBB) formed by the endothelial cells of the brain capillaries. Importantly, the CP epithelial cells are responsible for producing most of the CSF, the fluid that fills the brain ventricles and the subarachnoid space. Recently, the finding that the CP epithelial cells display all the machinery to locally control iron delivery into the CSF may suggest that the general and progressive senescence of the CP may be at the basis of the impairment of regional iron metabolism, iron-mediated toxicity, and the increase in inflammation and oxidative stress that occurs with aging and, particularly, in AD.

Transthyretin: roles in the nervous system beyond thyroxine and retinol transport

Transthyretin (TTR) is a plasma- and cerebrospinal fluid-circulating protein. Besides the primordially attributed systemic role as a transporter molecule of thyroxine (T₄) and retinol (through the binding to retinol-binding protein [RBP]), TTR has been recognized as a protein with important functions in several aspects of the nervous system physiology. TTR has been shown to play an important role in behavior, cognition, amidated neuropeptide processing and nerve regeneration. Furthermore, it has been proposed that TTR is neuroprotective in Alzheimer's disease and cerebral ischemia. Mutations in TTR are a well-known cause of familial amyloidotic polyneuropathy, an autosomal dominant neurodegenerative disorder characterized by systemic deposition of TTR amyloid fibrils, particularly in the peripheral nervous system. The purpose of this review is to highlight the roles of TTR in the nervous system, beyond its systemic role as a transporter molecule of T₄ and RBP-retinol.

Transthyretin and the brain re-visited: is neuronal synthesis of transthyretin protective in Alzheimer's disease?

Since the mid-1990's a trickle of publications from scattered independent laboratories have presented data suggesting that the systemic amyloid precursor transthyretin (TTR) could interact with the amyloidogenic β-amyloid (Aβ) peptide of Alzheimer's disease (AD). The notion that one amyloid precursor could actually inhibit amyloid fibril formation by another seemed quite far-fetched. Further it seemed clear that within the CNS, TTR was only produced in choroid plexus epithelial cells, not in neurons. The most enthusiastic of the authors proclaimed that TTR sequestered Aβ in vivo resulting in a lowered TTR level in the cerebrospinal fluid (CSF) of AD patients and that the relationship was salutary. More circumspect investigators merely showed in vitro interaction between the two molecules. A single in vivo study in Caenorhabditis elegans suggested that wild type human TTR could suppress the abnormalities seen when Aβ was expressed in the muscle cells of the worm. Subsequent studies in human Aβ transgenic mice, including those from our laboratory, also suggested that the interaction reduced the Aβ deposition phenotype. We have reviewed the literature analyzing the relationship including recent data examining potential mechanisms that could explain the effect. We have proposed a model which is consistent with most of the published data and current notions of AD pathogenesis and can serve as a hypothesis which can be tested.

Neuronal production of transthyretin in human and murine Alzheimer's disease: is it protective?

Transthyretin (TTR), a systemic amyloid precursor in the human TTR amyloidoses, interacts with β-amyloid (Aβ) in vitro, inhibits Aβ fibril formation, and suppresses the Alzheimer's disease (AD) phenotype in APP23 mice bearing a human APP gene containing the Swedish autosomal dominant AD mutation. In the present study, we show that TTR is a neuronal product upregulated in AD. Immunohistochemical analysis reveals that, in contrast to brains from non-demented age-matched individuals and control mice, the majority of hippocampal neurons from human AD and all those from the APP23 mouse brains contain TTR. Quantitative PCR for TTR mRNA and Western blot analysis show that primary neurons from APP23 mice transcribe TTR mRNA, and the cells synthesize and secrete TTR protein. TTR mRNA abundance is greatly increased in cultured cortical and hippocampal embryonic neurons and cortical lysates from adult APP23 mice. Antibodies specific for TTR and Aβ pulled down TTR/Aβ complexes from cerebral cortical extracts of APP23 mice and some human AD patients but not from control brains. In complementary tissue culture experiments, recombinant human TTR suppressed the cytotoxicity of soluble Aβ aggregates added to mouse neurons and differentiated human SH-SY5Y neuroblastoma cells. The findings that production of Aβ, its precursor, or its related peptides induces neuronal TTR transcription and synthesis and the presence of Aβ/TTR complexes in vivo suggest that increased TTR production coupled with interaction between TTR and Aβ and/or its related peptides may play a role in natural resistance to human AD.

Molecular basis for certain neuroprotective effects of thyroid hormone

The pathophysiology of brain damage that is common to ischemia-reperfusion injury and brain trauma include disodered neuronal and glial cell energetics, intracellular acidosis, calcium toxicity, extracellular excitotoxic glutamate accumulation, and dysfunction of the cytoskeleton and endoplasmic reticulum. The principal thyroid hormones, 3,5,3'-triiodo-l-thyronine (T(3)) and l-thyroxine (T(4)), have non-genomic and genomic actions that are relevant to repair of certain features of the pathophysiology of brain damage. The hormone can non-genomically repair intracellular H(+) accumulation by stimulation of the Na(+)/H(+) exchanger and can support desirably low [Ca(2+)](i.c.) by activation of plasma membrane Ca(2+)-ATPase. Thyroid hormone non-genomically stimulates astrocyte glutamate uptake, an action that protects both glial cells and neurons. The hormone supports the integrity of the microfilament cytoskeleton by its effect on actin. Several proteins linked to thyroid hormone action are also neuroprotective. For example, the hormone stimulates expression of the seladin-1 gene whose gene product is anti-apoptotic and is potentially protective in the setting of neurodegeneration. Transthyretin (TTR) is a serum transport protein for T(4) that is important to blood-brain barrier transfer of the hormone and TTR also has been found to be neuroprotective in the setting of ischemia. Finally, the interesting thyronamine derivatives of T(4) have been shown to protect against ischemic brain damage through their ability to induce hypothermia in the intact organism. Thus, thyroid hormone or hormone derivatives have experimental promise as neuroprotective agents.

Identification and validation of novel cerebrospinal fluid biomarkers for staging early Alzheimer's disease

BACKGROUND

Ideally, disease modifying therapies for Alzheimer disease (AD) will be applied during the 'preclinical' stage (pathology present with cognition intact) before severe neuronal damage occurs, or upon recognizing very mild cognitive impairment. Developing and judiciously administering such therapies will require biomarker panels to identify early AD pathology, classify disease stage, monitor pathological progression, and predict cognitive decline. To discover such biomarkers, we measured AD-associated changes in the cerebrospinal fluid (CSF) proteome.

METHODS AND FINDINGS

CSF samples from individuals with mild AD (Clinical Dementia Rating [CDR] 1) (n = 24) and cognitively normal controls (CDR 0) (n = 24) were subjected to two-dimensional difference-in-gel electrophoresis. Within 119 differentially-abundant gel features, mass spectrometry (LC-MS/MS) identified 47 proteins. For validation, eleven proteins were re-evaluated by enzyme-linked immunosorbent assays (ELISA). Six of these assays (NrCAM, YKL-40, chromogranin A, carnosinase I, transthyretin, cystatin C) distinguished CDR 1 and CDR 0 groups and were subsequently applied (with tau, p-tau181 and Aβ42 ELISAs) to a larger independent cohort (n = 292) that included individuals with very mild dementia (CDR 0.5). Receiver-operating characteristic curve analyses using stepwise logistic regression yielded optimal biomarker combinations to distinguish CDR 0 from CDR>0 (tau, YKL-40, NrCAM) and CDR 1 from CDR<1 (tau, chromogranin A, carnosinase I) with areas under the curve of 0.90 (0.85-0.94 95% confidence interval [CI]) and 0.88 (0.81-0.94 CI), respectively.

CONCLUSIONS

Four novel CSF biomarkers for AD (NrCAM, YKL-40, chromogranin A, carnosinase I) can improve the diagnostic accuracy of Aβ42 and tau. Together, these six markers describe six clinicopathological stages from cognitive normalcy to mild dementia, including stages defined by increased risk of cognitive decline. Such a panel might improve clinical trial efficiency by guiding subject enrollment and monitoring disease progression. Further studies will be required to validate this panel and evaluate its potential for distinguishing AD from other dementing conditions.

Characterization of the interaction of β-amyloid with transthyretin monomers and tetramers

β-Amyloid (Aβ) is the main protein component of the amyloid plaques associated with Alzheimer's disease. Transthyretin (TTR) is a homotetramer that circulates in both blood and cerebrospinal fluid. Wild-type (wt) TTR amyloid deposits are linked to senile systemic amyloidosis, a common disease of aging, while several TTR mutants are linked to familial amyloid polyneuropathy. Several recent studies provide support for the hypothesis that these two amyloidogenic proteins interact, and that this interaction is biologically relevant. For example, upregulation of TTR expression in Tg2576 mice was linked to protection from the toxic effects of Aβ deposition [Stein, T. D., and Johnson, J. A. (2002) J. Neurosci. 22, 7380-7388]. We examined the interaction of Aβ with wt TTR as well as two mutants: F87M/L110M, engineered to be a stable monomer, and T119M, a naturally occurring mutant with a tetrameric stability higher than that of the wild type. On the basis of enzyme-linked immunoassays as well as cross-linking experiments, we conclude that Aβ monomers bind more to TTR monomers than to TTR tetramers. The data further suggest that TTR tetramers interact preferably with Aβ aggregates rather than Aβ monomers. Through tandem mass spectrometry analysis of cross-linked TTR-Aβ fragments, we identified the A strand, in the inner β-sheet of TTR, as well as the EF helix, as regions of TTR that are involved with Aβ association. Light scattering and electron microscopy studies demonstrate that the outcome of the TTR-Aβ interaction strongly depends on TTR quaternary structure. While TTR tetramers may modestly enhance aggregation, TTR monomers decidedly arrest Aβ aggregate growth. These data provide important new insights into the nature of TTR-Aβ interactions. Such interactions may regulate TTR-mediated protection against Aβ toxicity.

Transthyretin as a potential CSF biomarker for Alzheimer's disease and dementia with Lewy bodies: effects of treatment with cholinesterase inhibitors

BACKGROUND

Previous studies have indicated that transthyretin (TTR) levels in cerebrospinal fluid (CSF) are altered in depression and dementia. The present study aimed to investigate whether CSF TTR can be used to discriminate between patients with Alzheimer's disease (AD) and patients with dementia with Lewy bodies (DLB) with or without medication, as well as to reveal whether CSF TTR correlates with depression in dementia.

METHODS

CSF samples from 59 patients with AD, 13 patients with DLB and 13 healthy controls were collected, and biochemical analysis was performed. Subjects were assessed for the presence of depression.

RESULTS

No significant differences in CSF TTR were found between AD, DLB, and control subjects or between depressed and non-depressed dementia patients. Interestingly, we found a significant reduction in CSF TTR (14%) in AD patients who were medicated with cholinesterase inhibitors compared to those AD patients who were not.

CONCLUSIONS

Significant reductions in CSF TTR were found after cholinesterase inhibitor treatment in patients with AD compared to untreated individuals. CSF TTR was unaltered in patients with DLB and had no relationship to depression in the present cohort with dementias.

Differential modification of Cys10 alters transthyretin's effect on beta-amyloid aggregation and toxicity

Tg2576 mice produce high levels of beta-amyloid (Abeta) and develop amyloid deposits, but lack neurofibrillary tangles and do not suffer the extensive neuronal cell loss characteristic of Alzheimer's disease. Protection from Abeta toxicity has been attributed to up-regulation of transthyretin (TTR), a normal component of plasma and cerebrospinal fluid. We compared the effect of TTR purified from human plasma (pTTR) with that produced recombinantly (rTTR) on Abeta aggregation and toxicity. pTTR slowed Abeta aggregation but failed to protect primary cortical neurons from Abeta toxicity. In contrast, rTTR accelerated aggregation, while effectively protecting neurons. This inverse correlation between Abeta aggregation kinetics and toxicity is consistent with the hypothesis that soluble intermediates rather than insoluble fibrils are the most toxic Abeta species. We carried out a detailed comparison of pTTR with rTTR to ascertain the probable cause of these different effects. No differences in secondary, tertiary or quaternary structure were detected. However, pTTR differed from rTTR in the extent and nature of modification at Cys10. We hypothesize that differential modification at Cys10 regulates TTR's effect on Abeta aggregation and toxicity.

Mobile and cordless telephones, serum transthyretin and the blood-cerebrospinal fluid barrier: a cross-sectional study

BACKGROUND

Whether low-intensity radiofrequency radiation damages the blood-brain barrier has long been debated, but little or no consideration has been given to the blood-cerebrospinal fluid barrier. In this cross-sectional study we tested whether long-term and/or short-term use of wireless telephones was associated with changes in the serum transthyretin level, indicating altered transthyretin concentration in the cerebrospinal fluid, possibly reflecting an effect of radiation.

METHODS

One thousand subjects, 500 of each sex aged 18-65 years, were randomly recruited using the population registry. Data on wireless telephone use were assessed by a postal questionnaire and blood samples were analyzed for serum transthyretin concentrations determined by standard immunonephelometric techniques on a BN Prospec instrument.

RESULTS

The response rate was 31.4%. Logistic regression of dichotomized TTR serum levels with a cut-point of 0.31 g/l on wireless telephone use yielded increased odds ratios that were statistically not significant. Linear regression of time since first use overall and on the day that blood was withdrawn gave different results for males and females: for men significantly higher serum concentrations of TTR were seen the longer an analogue telephone or a mobile and cordless desktop telephone combined had been used, and in contrast, significantly lower serum levels were seen the longer an UMTS telephone had been used. Adjustment for fractions of use of the different telephone types did not modify the effect for cumulative use or years since first use for mobile telephone and DECT, combined. For women, linear regression gave a significant association for short-term use of mobile and cordless telephones combined, indicating that the sooner blood was withdrawn after the most recent telephone call, the higher the expected transthyretin concentration.

CONCLUSION

In this hypothesis-generating descriptive study time since first use of mobile telephones and DECT combined was significantly associated with higher TTR levels regardless of how much each telephone type had been used. Regarding short-term use, significantly higher TTR concentrations were seen in women the sooner blood was withdrawn after the most recent telephone call on that day.

Association of TTR polymorphisms with hippocampal atrophy in Alzheimer disease families

In vitro and animal model studies suggest that transthyretin (TTR) inhibits the production of the amyloid β protein, a major contributor to Alzheimer disease (AD) pathogenesis. We evaluated the association of 16 TTR single nucleotide polymorphisms (SNPs) with AD risk in 158 African American and 469 Caucasian discordant sibships from the MIRAGE Study. There was no evidence for association of TTR with AD in either population sample. To examine the possibility that TTR SNPs affect specific components of the AD process, we tested association of these SNPs with four measures of neurodegeneration and cerebrovascular disease defined by magnetic resonance imaging (MRI) in a subset of 48 African American and 265 Caucasian sibships. Five of seven common SNPs and several haplotypes were significantly associated with hippocampal atrophy in the Caucasian sample. Two of these SNPs also showed marginal evidence for association in the African American sample. Results for the other MRI traits were unremarkable. This study highlights the potential value of neuroimaging endophenotypes as a tool for finding genes influencing AD pathogenesis.

Clearance of amyloid-beta peptide across the blood-brain barrier: implication for therapies in Alzheimer's disease

The main receptors for amyloid-beta peptide (Abeta) transport across the blood-brain barrier (BBB) from brain to blood and blood to brain are low-density lipoprotein receptor related protein-1 (LRP1) and receptor for advanced glycation end products (RAGE), respectively. In normal human plasma a soluble form of LRP1 (sLRP1) is a major endogenous brain Abeta 'sinker' that sequesters some 70 to 90 % of plasma Abeta peptides. In Alzheimer's disease (AD), the levels of sLRP1 and its capacity to bind Abeta are reduced which increases free Abeta fraction in plasma. This in turn may increase brain Abeta burden through decreased Abeta efflux and/or increased Abeta influx across the BBB. In Abeta immunotherapy, anti-Abeta antibody sequestration of plasma Abeta enhances the peripheral Abeta 'sink action'. However, in contrast to endogenous sLRP1 which does not penetrate the BBB, some anti-Abeta antibodies may slowly enter the brain which reduces the effectiveness of their sink action and may contribute to neuroinflammation and intracerebral hemorrhage. Anti-Abeta antibody/Abeta immune complexes are rapidly cleared from brain to blood via FcRn (neonatal Fc receptor) across the BBB. In a mouse model of AD, restoring plasma sLRP1 with recombinant LRP-IV cluster reduces brain Abeta burden and improves functional changes in cerebral blood flow (CBF) and behavioral responses, without causing neuroinflammation and/or hemorrhage. The C-terminal sequence of Abeta is required for its direct interaction with sLRP and LRP-IV cluster which is completely blocked by the receptor-associated protein (RAP) that does not directly bind Abeta. Therapies to increase LRP1 expression or reduce RAGE activity at the BBB and/or restore the peripheral Abeta 'sink' action, hold potential to reduce brain Abeta and inflammation, and improve CBF and functional recovery in AD models, and by extension in AD patients.