- Email: [email protected]
S2-01-03
Symposia S2-01: Progress in Genetic Research 3) Frank R, Hargreaves, Nat Rev Drug Discov. 2003,7; 2(7):566-80 4) Smith D, Proc Natl Acad Sci U S A. 2002,4,2; 99(7): 4135-4137 5) Ashburner J et al., Lancet Neurol. 2003, 2;2(2):79-88 PL-02-02
BETA-SECRETASE AS A THERAPEUTIC TARGET
Martin O. Citron, Amgen, Thousand Oaks, CA, USA. Contact e-mail: [email protected] Finding inhibitors of A42 generation is a major goal of Alzheimer’s disease drug development. Two target protease activities, -and ␥-secretase, were operationally defined in the early 90s, but progress in this area was slow, because the actual enzymes were not understood at the molecular level. Some years ago we identified a novel membrane bound aspartic protease, BACE1, as -secretase. This finding has been confirmed and BACE1 and its homolog BACE2 have been characterized in detail by many groups. Major progress has been made in two areas: First, the x-ray crystal structure, which is critical for rational inhibitor design, has been solved and shown to be similar to that of other pepsin family members. Second, knockout studies show that BACE1 is critical for A generation, but the knockout mice show an otherwise normal phenotype, raising the possibility that therapeutic BACE1 inhibition could be accomplished without major mechanism based toxicity. However, target-mediated toxicity of -secretase inhibition cannot be ruled out based on the currently available data alone. While various peptidic -secretase inhibitors have been published, the key challenge now is the generation of more drug-like compounds that could be developed for therapeutic purposes. Other current areas of investigation, including identification of additional BACE1 substrates, the potential role of BACE1 overexpression in AD and the phenotype of BACE2 knockout mice will be discussed. PL-02-03
TAU AND TAUOPATHIES
Jesus Avila, Universidad Autonoma de Madrid, Madrid, Spain. Contact e-mail: [email protected] Background: Tau, a microtubule associated protein, can aberrantly polymerize, in phosphorylated form, yielding the paired helical filaments found in the brain of Alzheimer’s disease patients. Objective(s): Our purpose is to know tau pathology related with its phosphorylation and its assembly. Methods: In vitro analysis and the use of mouse models. Conclusions: Tau assembly can be reproduced in vitro by mixing tau protein with polymerization inducers like heparin or Coenzyme Q0, being the assembly of phosphotau facilitated in the presence of Co.Q0. Polymerization of tau has been also mimified by using transgenic mouse models. In these models, human tau, bearing some of the mutations found in patients with FTDP-17, was expressed. Mutations on APP and/or PS-1 will facilitate tau phosphorylation by kinases like GSK3. Thus, a transgenic mouse model overexpressing GSK3 was also characterized. In some of these mouse models, a link between tau phosphorylation and tau assembly has been established. Finally, the possible toxic effect of phosphotau or tau aggregates will be discussed. MONDAY, JULY 17, 2006 SYMPOSIA S2-01 PROGRESS IN GENETIC RESEARCH S2-01-01
SYSTEMATIC META-ANALYSIS OF ALZHEIMER’S DISEASE GENETIC ASSOCIATION STUDIES - THE ALZGENE DATABASE
S23
suggest that the common late-onset form of AD is caused by a variety of independent genetic (and non-genetic) risk factors. In the past decade, literally hundreds of reports have been published claiming or refuting genetic association with putative AD genes, and currently nearly 10 association studies are published each month. For the research community as well as the public this wealth of information has become increasingly difficult to follow, evaluate and—most importantly—to interpret. To better understand these findings, we have created a comprehensive and publicly available database (“AlzGene”; hosted by the Alzheimer Research Forum, available at www.alzgene.org) which systematically collects and summarizes all genetic association studies in the field of AD. In addition to displaying essential details for each study (e.g., sample sizes, onset age, genotype numbers), the database provides up-to-date summary effect size estimates and assessments of publication bias for each polymorphism across all studies. The results of these meta-analyses should help to better distinguish the relevant AD risk genes from false-positive reports as well as those with negligible effects. Currently, the AlzGene database includes nearly 1,000 individual studies of over 300 different candidate genes. At the meeting we will present a comprehensive summary of these metaanalyses with a particular focus on genes which significantly increase or decrease the risk for AD. S2-01-02
IDENTIFICATION OF NOVEL GENES AND MUTATIONS IN ALZHEIMER DISEASE
Christine Van Broeckhoven, VIB8 - Department of Molecular Genetics, Neurodegenerative Brain Diseases Group, University of Antwerp, Antwerpen, Belgium. Contact e-mail: [email protected] Background: Alzheimer disease (AD) is genetically heterogeneous with both causal and susceptibility genes contributing to its genetic etiology. The current genes and mutations explain approximately 80%, indicating that several other genetic factors remain to be identified. Objectives: To identify novel genes and mutation mechanisms underlying the risk for both early- and late-onset AD. Methods: We systematically sample patients with AD using a standardized protocol for phenotyping including an extensive clinical examination, memory tests and brain imaging. Also biochemical data is collected of biomarkers analyzed in cerebrospinal fluid and serum, and in autopsied brain. In all patients we determine the APOE genotype. In patients with onset age ⬍70 years mutation analysis is performed of 5 dementia genes: APP, PSEN1, PSEN2, MAPT and PRNP. Of each index patient we sample the spouse and children, and in case of a positive family history all cooperative family members are sampled for genome-wide segregation and association studies using STR and/or SNP markers. Results: In a series of 180 early-onset AD patients we identified 1 APP mutation (Val717Ile, 0.5%), 3 APP promoter mutations that increase APP transcription (1.7%) but no APP genomic duplication mutations. Of some milder APP promoter mutations the frequency increased with onset age. We also identified 6 mutations in PSEN1 and PSEN2 (3.3%). In 1 AD patient, with an onset age of 69 years, we detected a PRNP octapeptide insertion and in MAPT we found the intron 10 (IVS10⫹29G⬎A) variant of which the pathogenic nature is still controversial. Conclusions: Together, our data suggest that the frequency of mutations in the five dementia genes is around 6%. Of interest is the observation of several mutations in patients with onset ⬎65 years and duration of disease in old age, suggesting that some mutations have a milder pathogenic effect. S2-01-03
SYSTEMATIC SCREENS IDENTIFY NOVEL GENES FOR LOAD SUSCEPTIBILITY ON CHROMOSOMES 9 AND 10
Lars Bertram1, Matthew B. McQueen2, Kristina Mullin1, Deborah Blacker1,2, Rudolph E. Tanzi1, 1Massachusetts General Hospital, Charlestown, MA, USA; 2Harvard School of Public Health, Boston, MA, USA. Contact e-mail: [email protected]
Alison M. Goate, Washington University School of Medicine, St. Louis, MO, USA. Contact e-mail: [email protected]
Alzheimer’s disease (AD) is a genetically complex and heterogeneous disorder showing an age-dependent dichotomy. Several lines of evidence
Background: Late-onset AD (LOAD) probably results from the combined effects of variation in a number of genes as well as environmental factors.
S24
Symposia S2-02: D&CC (Molecular Pathology/Histopathological)
Early genetic studies of LOAD demonstrated that the 4 variant of APOE is associated with increased risk of LOAD. Genome-wide linkage screens in LOAD families have identified several other chromosomal regions, implying that other genetic risk factors besides APOE must exist. We identified putative LOAD susceptibility loci on chromosomes 9, 10 and 12. Objective: To use a systematic approach to screen single nucleotide polymorphisms (SNPs) across these chromosomal regions to identify evidence of association between LOAD and specific genes. Methods: We performed a SNP scan across the entire linkage region on chromosome 9 and 10 using DNA samples collected from LOAD patients and matched non-demented individuals. Allele frequencies of tested SNPs were compared using chi square statistics to identify disease-associated variants. To reduce the likelihood of identifying spurious associations, we employed three independent LOAD case-control series, and have carried out genotyping and analysis in two phases. Results: Of the 1,397 chromosome 10 markers tested in the exploratory sample, one marker, rs498055, was significantly associated with AD in all three case-control series, with an allelic p-value of 0.00004. Linkage disequilbrium (LD) analyses indicate that rs498055 is located in a block containing 6 candidate genes. Functional analysis of these candidate genes is ongoing. A similar analysis of 674 SNPs on chromosome 9 resulted in the identification of several SNPs in three genes that are significantly associated with AD. The most significant marker has a P-value of 0.0006 and OR of 0.79 (CI 0.69-0.9) in the meta-analysis of all three sample sets combined. This SNP is located within an LD block wholly contained within a biological candidate gene that is located under a previously identified linkage peak. Functional studies suggest that the SNP is associated with variable levels of gene expression and a differential response to apoptosis. Conclusions: We provided replicated evidence for LOAD susceptibility genes on both chromosomes 9 and 10. S2-01-04
THE ROLE OF THE TAU GENE IN AD
John Hardy, National Institute of Aging (NIA), Bethesda, MD, USA. Contact e-mail: [email protected] Abstract not available. S2-01-05
FUTURE OF ASSOCIATION STUDIES IN COMMON AD
Ulrich Finckh, Laboratoriumsmedizin Dortmund, Dortmund, Germany. Contact e-mail: [email protected] Background: Only approximately 0.5% of all Alzheimer dementias (AD) are caused by heterozygous mutations in one of several single major genes for autosomal dominant familial AD. Multifactorial etiologies are assumed to underlie all other AD (common AD), including sporadic cases as well as those with positive family history. Twin studies suggest heritabilities between 50 and 80% of common AD. Of the genetic components of common AD, a significant, yet variable and not exactly known fraction (50%?) is attributable to the E4 risk allele of APOE. Meanwhile, genotypes or allele frequencies of over 200 positional or functional candidate genes have been investigated for associations with common AD. However, besides APOE, none of the numerous positive findings in the candidate genes survived replication consistently. Objective(s): To propose criteria for an optimized strategy to investigate candidate genes for common AD. Methods: The PubMed database was searched for genetic association studies on common AD. Conclusions: None of the candidates tested up to now seems to fulfill the three major criteria that are known to be fulfilled by APOE: 1. Evidence of linkage; 2. evidence of functional biochemical involvement; 3. presence of haplotypes with proven functional differences (“isoforms”). Presumably only candidates fulfilling simultaneously these three major criteria are most suitable for future genetic association studies on common AD.
S2-01-06
GENETICS & EPIGENETIC STUDIES IN AD
Debomoy K. Lahiri1, Yuan-Wen Ge1, Md Riyaz Basha2, Bryan Maloney1, De-Mao Chen1, Nasser Zawia2, 1Indiana University School of Medicine, Indianapolis, IN, USA; 2University of Rhode Island, Kingston, RI, USA. Contact e-mail: [email protected] Background: The amyloid beta-peptide (A), cleaved from the A-precursor protein (APP) is a leading candidate for the cause of Alzheimer’s disease (AD). Both APP and A appear in healthy individuals. What triggers normal APP and A to be over-expressed and potentially neurotoxic in sporadic cases of AD? Moreover, when and how does this trigger mechanism apply? We have recently characterized two APP gene promoter polymorphisms, which appear to influence the risk of late-onset. Work in the field suggests that the APP gene can be triggered by different agents, including metals, hormones and cytokines. We have recently discovered that developmental exposure of rats to xenobiotic Pb resulted in a delayed (20 months later) over-expression of APP mRNA and an elevation in levels of APP and its amyloidogenic A product. By contrast, APP expression, and APP and A levels, were unaffected when the rats were exposed to Pb in old age. Early developmental Pb exposure induces latent differences in repair of oxidative DNA damage in rat brain. Objective(s): Our hypothesis is that triggering agents (environmental or dietary) operating at a very early stage of development could perturb APP gene regulation via its transcriptional machinery, leading to latent overexpression and subsequent A production. Early studies also suggest APP overexpression in specific areas of the brain in AD patients. Methods: We have utilized cell culture and animal models to study genetic and epigenetic mechanisms at levels of DNA (cloning and transfecion), RNA (Northern, RT/PCR), and protein/ peptides (Western blotting and ELISA). Conclusions: Expression of the APP and BACE genes can be modulated by different chemicals, factors, and free radicals. Characterization of regulatory regions delineates the role of transcriptional factors and response elements in amyloidogenesis. Developmental exposure to Pb elevates A levels in old age via reprogramming of the de novo synthesis of APP, through disturbances of epigenetic pathways such as DNA methylation. Exposure to Pb inhibits the activity of DNA methylases both in vitro and in vivo. These studies are important as they provide a biological mechanism for environmental and other risk factors on the etiology of AD. Supported by NIH grants. MONDAY, JULY 17, 2006 SYMPOSIA S2-02 D&CC (MOLECULAR PATHOLOGY/HISTOPATHOLOGICAL) S2-02-01
A-RELATED CEREBRAL AMYLOID ANGIOPATHY
Orso Bugiani, Istituto Nazionale Neurologico Carlo Besta, Milan, Italy. Contact e-mail: [email protected] Deposition of A in the neuropil and the cerebral vessel walls is a hallmark of both brain aging and Alzheimer’s disease (AD). At the vascular level, A deposition increases the width of the vessel wall and destroys the muscular lamina, while the lumen is reduced. Leptomeningeal and perforating arteries of the cerebral and cerebellar hemispheres are selectively involved. Whether CAA is symptomatic depends on the amount of related lesions, such as multiple cortical and subcortical infarcts, periventricular edema (leukoaraiosis by MRI) due to chronic hypoxia, multiple hematomas in the cerebral cortex, spontaneous relapsing bleeding in the white matter of frontal or temporal lobes, and subarachnoid haemorrhage. Previous bleeding can be recognized by hemosiderin deposits revealed by round shadows in T2*-weighted MRI images. Parenchimal lesions may be responsible for a sudden worsening of cognitive deterioration in AD patients, which occurs after severe headache, fits, and stroke. Such symptoms may affect both patients with the sporadic form of AD and patients with the familial form. Several mutations in the APP gene (A692G, E693G, D694N, A713T) are associated with familial AD and symptomatic CAA.
BETA-SECRETASE AS A THERAPEUTIC TARGET
Martin O. Citron, Amgen, Thousand Oaks, CA, USA. Contact e-mail: [email protected] Finding inhibitors of A42 generation is a major goal of Alzheimer’s disease drug development. Two target protease activities, -and ␥-secretase, were operationally defined in the early 90s, but progress in this area was slow, because the actual enzymes were not understood at the molecular level. Some years ago we identified a novel membrane bound aspartic protease, BACE1, as -secretase. This finding has been confirmed and BACE1 and its homolog BACE2 have been characterized in detail by many groups. Major progress has been made in two areas: First, the x-ray crystal structure, which is critical for rational inhibitor design, has been solved and shown to be similar to that of other pepsin family members. Second, knockout studies show that BACE1 is critical for A generation, but the knockout mice show an otherwise normal phenotype, raising the possibility that therapeutic BACE1 inhibition could be accomplished without major mechanism based toxicity. However, target-mediated toxicity of -secretase inhibition cannot be ruled out based on the currently available data alone. While various peptidic -secretase inhibitors have been published, the key challenge now is the generation of more drug-like compounds that could be developed for therapeutic purposes. Other current areas of investigation, including identification of additional BACE1 substrates, the potential role of BACE1 overexpression in AD and the phenotype of BACE2 knockout mice will be discussed. PL-02-03
TAU AND TAUOPATHIES
Jesus Avila, Universidad Autonoma de Madrid, Madrid, Spain. Contact e-mail: [email protected] Background: Tau, a microtubule associated protein, can aberrantly polymerize, in phosphorylated form, yielding the paired helical filaments found in the brain of Alzheimer’s disease patients. Objective(s): Our purpose is to know tau pathology related with its phosphorylation and its assembly. Methods: In vitro analysis and the use of mouse models. Conclusions: Tau assembly can be reproduced in vitro by mixing tau protein with polymerization inducers like heparin or Coenzyme Q0, being the assembly of phosphotau facilitated in the presence of Co.Q0. Polymerization of tau has been also mimified by using transgenic mouse models. In these models, human tau, bearing some of the mutations found in patients with FTDP-17, was expressed. Mutations on APP and/or PS-1 will facilitate tau phosphorylation by kinases like GSK3. Thus, a transgenic mouse model overexpressing GSK3 was also characterized. In some of these mouse models, a link between tau phosphorylation and tau assembly has been established. Finally, the possible toxic effect of phosphotau or tau aggregates will be discussed. MONDAY, JULY 17, 2006 SYMPOSIA S2-01 PROGRESS IN GENETIC RESEARCH S2-01-01
SYSTEMATIC META-ANALYSIS OF ALZHEIMER’S DISEASE GENETIC ASSOCIATION STUDIES - THE ALZGENE DATABASE
S23
suggest that the common late-onset form of AD is caused by a variety of independent genetic (and non-genetic) risk factors. In the past decade, literally hundreds of reports have been published claiming or refuting genetic association with putative AD genes, and currently nearly 10 association studies are published each month. For the research community as well as the public this wealth of information has become increasingly difficult to follow, evaluate and—most importantly—to interpret. To better understand these findings, we have created a comprehensive and publicly available database (“AlzGene”; hosted by the Alzheimer Research Forum, available at www.alzgene.org) which systematically collects and summarizes all genetic association studies in the field of AD. In addition to displaying essential details for each study (e.g., sample sizes, onset age, genotype numbers), the database provides up-to-date summary effect size estimates and assessments of publication bias for each polymorphism across all studies. The results of these meta-analyses should help to better distinguish the relevant AD risk genes from false-positive reports as well as those with negligible effects. Currently, the AlzGene database includes nearly 1,000 individual studies of over 300 different candidate genes. At the meeting we will present a comprehensive summary of these metaanalyses with a particular focus on genes which significantly increase or decrease the risk for AD. S2-01-02
IDENTIFICATION OF NOVEL GENES AND MUTATIONS IN ALZHEIMER DISEASE
Christine Van Broeckhoven, VIB8 - Department of Molecular Genetics, Neurodegenerative Brain Diseases Group, University of Antwerp, Antwerpen, Belgium. Contact e-mail: [email protected] Background: Alzheimer disease (AD) is genetically heterogeneous with both causal and susceptibility genes contributing to its genetic etiology. The current genes and mutations explain approximately 80%, indicating that several other genetic factors remain to be identified. Objectives: To identify novel genes and mutation mechanisms underlying the risk for both early- and late-onset AD. Methods: We systematically sample patients with AD using a standardized protocol for phenotyping including an extensive clinical examination, memory tests and brain imaging. Also biochemical data is collected of biomarkers analyzed in cerebrospinal fluid and serum, and in autopsied brain. In all patients we determine the APOE genotype. In patients with onset age ⬍70 years mutation analysis is performed of 5 dementia genes: APP, PSEN1, PSEN2, MAPT and PRNP. Of each index patient we sample the spouse and children, and in case of a positive family history all cooperative family members are sampled for genome-wide segregation and association studies using STR and/or SNP markers. Results: In a series of 180 early-onset AD patients we identified 1 APP mutation (Val717Ile, 0.5%), 3 APP promoter mutations that increase APP transcription (1.7%) but no APP genomic duplication mutations. Of some milder APP promoter mutations the frequency increased with onset age. We also identified 6 mutations in PSEN1 and PSEN2 (3.3%). In 1 AD patient, with an onset age of 69 years, we detected a PRNP octapeptide insertion and in MAPT we found the intron 10 (IVS10⫹29G⬎A) variant of which the pathogenic nature is still controversial. Conclusions: Together, our data suggest that the frequency of mutations in the five dementia genes is around 6%. Of interest is the observation of several mutations in patients with onset ⬎65 years and duration of disease in old age, suggesting that some mutations have a milder pathogenic effect. S2-01-03
SYSTEMATIC SCREENS IDENTIFY NOVEL GENES FOR LOAD SUSCEPTIBILITY ON CHROMOSOMES 9 AND 10
Lars Bertram1, Matthew B. McQueen2, Kristina Mullin1, Deborah Blacker1,2, Rudolph E. Tanzi1, 1Massachusetts General Hospital, Charlestown, MA, USA; 2Harvard School of Public Health, Boston, MA, USA. Contact e-mail: [email protected]
Alison M. Goate, Washington University School of Medicine, St. Louis, MO, USA. Contact e-mail: [email protected]
Alzheimer’s disease (AD) is a genetically complex and heterogeneous disorder showing an age-dependent dichotomy. Several lines of evidence
Background: Late-onset AD (LOAD) probably results from the combined effects of variation in a number of genes as well as environmental factors.
S24
Symposia S2-02: D&CC (Molecular Pathology/Histopathological)
Early genetic studies of LOAD demonstrated that the 4 variant of APOE is associated with increased risk of LOAD. Genome-wide linkage screens in LOAD families have identified several other chromosomal regions, implying that other genetic risk factors besides APOE must exist. We identified putative LOAD susceptibility loci on chromosomes 9, 10 and 12. Objective: To use a systematic approach to screen single nucleotide polymorphisms (SNPs) across these chromosomal regions to identify evidence of association between LOAD and specific genes. Methods: We performed a SNP scan across the entire linkage region on chromosome 9 and 10 using DNA samples collected from LOAD patients and matched non-demented individuals. Allele frequencies of tested SNPs were compared using chi square statistics to identify disease-associated variants. To reduce the likelihood of identifying spurious associations, we employed three independent LOAD case-control series, and have carried out genotyping and analysis in two phases. Results: Of the 1,397 chromosome 10 markers tested in the exploratory sample, one marker, rs498055, was significantly associated with AD in all three case-control series, with an allelic p-value of 0.00004. Linkage disequilbrium (LD) analyses indicate that rs498055 is located in a block containing 6 candidate genes. Functional analysis of these candidate genes is ongoing. A similar analysis of 674 SNPs on chromosome 9 resulted in the identification of several SNPs in three genes that are significantly associated with AD. The most significant marker has a P-value of 0.0006 and OR of 0.79 (CI 0.69-0.9) in the meta-analysis of all three sample sets combined. This SNP is located within an LD block wholly contained within a biological candidate gene that is located under a previously identified linkage peak. Functional studies suggest that the SNP is associated with variable levels of gene expression and a differential response to apoptosis. Conclusions: We provided replicated evidence for LOAD susceptibility genes on both chromosomes 9 and 10. S2-01-04
THE ROLE OF THE TAU GENE IN AD
John Hardy, National Institute of Aging (NIA), Bethesda, MD, USA. Contact e-mail: [email protected] Abstract not available. S2-01-05
FUTURE OF ASSOCIATION STUDIES IN COMMON AD
Ulrich Finckh, Laboratoriumsmedizin Dortmund, Dortmund, Germany. Contact e-mail: [email protected] Background: Only approximately 0.5% of all Alzheimer dementias (AD) are caused by heterozygous mutations in one of several single major genes for autosomal dominant familial AD. Multifactorial etiologies are assumed to underlie all other AD (common AD), including sporadic cases as well as those with positive family history. Twin studies suggest heritabilities between 50 and 80% of common AD. Of the genetic components of common AD, a significant, yet variable and not exactly known fraction (50%?) is attributable to the E4 risk allele of APOE. Meanwhile, genotypes or allele frequencies of over 200 positional or functional candidate genes have been investigated for associations with common AD. However, besides APOE, none of the numerous positive findings in the candidate genes survived replication consistently. Objective(s): To propose criteria for an optimized strategy to investigate candidate genes for common AD. Methods: The PubMed database was searched for genetic association studies on common AD. Conclusions: None of the candidates tested up to now seems to fulfill the three major criteria that are known to be fulfilled by APOE: 1. Evidence of linkage; 2. evidence of functional biochemical involvement; 3. presence of haplotypes with proven functional differences (“isoforms”). Presumably only candidates fulfilling simultaneously these three major criteria are most suitable for future genetic association studies on common AD.
S2-01-06
GENETICS & EPIGENETIC STUDIES IN AD
Debomoy K. Lahiri1, Yuan-Wen Ge1, Md Riyaz Basha2, Bryan Maloney1, De-Mao Chen1, Nasser Zawia2, 1Indiana University School of Medicine, Indianapolis, IN, USA; 2University of Rhode Island, Kingston, RI, USA. Contact e-mail: [email protected] Background: The amyloid beta-peptide (A), cleaved from the A-precursor protein (APP) is a leading candidate for the cause of Alzheimer’s disease (AD). Both APP and A appear in healthy individuals. What triggers normal APP and A to be over-expressed and potentially neurotoxic in sporadic cases of AD? Moreover, when and how does this trigger mechanism apply? We have recently characterized two APP gene promoter polymorphisms, which appear to influence the risk of late-onset. Work in the field suggests that the APP gene can be triggered by different agents, including metals, hormones and cytokines. We have recently discovered that developmental exposure of rats to xenobiotic Pb resulted in a delayed (20 months later) over-expression of APP mRNA and an elevation in levels of APP and its amyloidogenic A product. By contrast, APP expression, and APP and A levels, were unaffected when the rats were exposed to Pb in old age. Early developmental Pb exposure induces latent differences in repair of oxidative DNA damage in rat brain. Objective(s): Our hypothesis is that triggering agents (environmental or dietary) operating at a very early stage of development could perturb APP gene regulation via its transcriptional machinery, leading to latent overexpression and subsequent A production. Early studies also suggest APP overexpression in specific areas of the brain in AD patients. Methods: We have utilized cell culture and animal models to study genetic and epigenetic mechanisms at levels of DNA (cloning and transfecion), RNA (Northern, RT/PCR), and protein/ peptides (Western blotting and ELISA). Conclusions: Expression of the APP and BACE genes can be modulated by different chemicals, factors, and free radicals. Characterization of regulatory regions delineates the role of transcriptional factors and response elements in amyloidogenesis. Developmental exposure to Pb elevates A levels in old age via reprogramming of the de novo synthesis of APP, through disturbances of epigenetic pathways such as DNA methylation. Exposure to Pb inhibits the activity of DNA methylases both in vitro and in vivo. These studies are important as they provide a biological mechanism for environmental and other risk factors on the etiology of AD. Supported by NIH grants. MONDAY, JULY 17, 2006 SYMPOSIA S2-02 D&CC (MOLECULAR PATHOLOGY/HISTOPATHOLOGICAL) S2-02-01
A-RELATED CEREBRAL AMYLOID ANGIOPATHY
Orso Bugiani, Istituto Nazionale Neurologico Carlo Besta, Milan, Italy. Contact e-mail: [email protected] Deposition of A in the neuropil and the cerebral vessel walls is a hallmark of both brain aging and Alzheimer’s disease (AD). At the vascular level, A deposition increases the width of the vessel wall and destroys the muscular lamina, while the lumen is reduced. Leptomeningeal and perforating arteries of the cerebral and cerebellar hemispheres are selectively involved. Whether CAA is symptomatic depends on the amount of related lesions, such as multiple cortical and subcortical infarcts, periventricular edema (leukoaraiosis by MRI) due to chronic hypoxia, multiple hematomas in the cerebral cortex, spontaneous relapsing bleeding in the white matter of frontal or temporal lobes, and subarachnoid haemorrhage. Previous bleeding can be recognized by hemosiderin deposits revealed by round shadows in T2*-weighted MRI images. Parenchimal lesions may be responsible for a sudden worsening of cognitive deterioration in AD patients, which occurs after severe headache, fits, and stroke. Such symptoms may affect both patients with the sporadic form of AD and patients with the familial form. Several mutations in the APP gene (A692G, E693G, D694N, A713T) are associated with familial AD and symptomatic CAA.