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Regulated cleavage of the amyloid precursor protein (APP): Molecular and cellular basis
FOURTH INTERNATIONAL CONFERENCE ON ALZHEIMER’S DISEASE
homolog of dynactin. The 74 kD polypeptide appeared as a triplet of closely resolved bands as previously described for dynein intermediate chains. DAP 124 kD immunoreactivity increased three-fold over a seven day incubation, while immunoreactivity of the 74 kD polypeptide increased seven-fold. Similar results were obtained when differentiated PC 12 cells were cultured in the presence of Alzheimer’s disease (AD) brain extracts. Examination of DAPs from AD temporal cortex homogenates by immunobloting revealed that twofold more 74 kD polypeptide was free in supernatants aher centrifugation as opposed to bound dynein complexes in the pellet, when compared to control brain homogenates. These data suggest that the NGF-sensitive 74 kD DAP is altered in AD cortex, and as such may be a component of defective axonal transport in AD neurons.
PLENARY LECTURES II
s39
is found in the circulation normally. The possible importance of SAP as a precursor to AP is further corroborated by recent work showing that AP
homologous peptides can cross the blood-brain barrier. Hence s key questionin AD research currently is what factors alter SAP in the disease state, promoting conformational changes, aggregation, amyloid formation and cell death. Numerous mutations have been found in the AP precursor (PPP) gene, associated with early onset familial AD. However, AP deposition typically occurs in the absence of PPP mutations. Therefore other factors are more important in the majority of AD patients. Recently biochemical and immunohistochemical studies have shown the importance of two apolipoproteins in fibrillogenesis: apolipoprotein (apo) J, which forms a complex with SAP, and apo E. We proposed in 1991 that apo E is s “pathological chaperone,”acting to promote and/or stabilize a P-pleated sheet structure. This hypothesis is supported by the finding that a specific isotype of apo e, ~4, is associated with late-onset familial and sporadic AD. in addition, in vrtro studies with AP peptides have identified aggregation inhibitors or “desaggrins” in normal biological fluids. We hypothesize that a balance exists between factors which promote fibril formation, suchas apo E and dessggrins.These interactions as well as brain specific factors may be critical lo determining why SAP is initially deposited as preamyloid and why in some locations preamyloid progresses on lo neuritic plaque formation.
159 THE EPIDEMIOLOGY OF ALZHEIMER’S DISEASE: BEYOND RISK FACTORS. J.A. Mortimer. Geriatr. Res. Educ. Clin. Ctr., V.A. Medical
Center, and Depts. of Neurology and Epidemiology, University of Minnesota, Minneapolis, MN 55417 USA. Case-control and cohort studies have identified several putative risk factors for Alrheimer’s disease. Some of these risk factors appear nom modifiable, e.g., age, or to account for so few cases of the disease as to have little public health impact, e.g., severe head injury. Others may lend themselves to programs aimed at modifying the risk of AD. An important contribution of epidemiology is the identification of risk factors that may help explain the pathogenesis of the disease. Although we have known for decades that family history of dementia is an important risk factor for AD, it is only recently that the association of the apolipoprotein e4 allele with increased risk of the disease has become evident. This important discovery raises new questions that are being explored in epidemiological studies: How much disease is explained by the allelic distribution of the gene for apolipoprotein e? Are differences in AD prevalence between populations explained by relative frequencies of different alleles? How does age modify the expression of this gene in increasing the risk of AD? Recent data from population based samples provide strong support for its effect in modifying the risk of AD, for perhaps explaining cross-cultural differences in AD prevalence, and show important differences in age-specific expression. The interplay of epidemiology and neurobiology also is evident in other areas. An explanation for the association between head trauma and increased risk of AD, seen in case-control studies, is provided by the observation of increased beta amyloid production following severe head injury. Furthermore, new epidemiologic data suggest that the association between low education and increased risk of dementia in late life may be a reflection of deficient brain development early in life, indexed by lower intelligence and smaller head (brain) size. Ongoing epidemiologic studies continue to have an important impact on understanding the pathogenetic mechanisms of AD, including those showing associations with estrogen replacement and the use of antiinflammatory drugs. The partnership between epidemiology and neurobiology is likely to increase in importance as our knowledge of the pathogenesis of AD grows.
160 AMYLOIDS, GENES AND CHAPERONES IN ALZHEIMER’S DISEASE Bias Frangione, NYU Medical Center, New York, 10016 The defining neuropathological lesions of Alzbeimer’s disease (AD) are the deposition of amyloid p (AP) in the form of congophilic angiopathy and tile plaques, as well as the aggregation of abnormally phosphorylated r into neurofibrillary tangles. Our working hypothesis is that the key issues in AD are the inherent fibrillogenicity of AD and factors which influence fibril formation. Work on the Dutch variant of familial AD has led 10 the conclusion that a vascular source of AP contributes significantly to both
congophilic angiopathy and early plaques. As predicted, it has recently been found that peptides with the same amino acid sequence as AD exist as a normal soluble protein (SAP) in biological fluids. This links AD more closely to some of the systemic amyloidoses, where the amyloid precursor
161 REGULATED CLEAVAGE OF THE AMYLOID PRECURSOR PROTEIN WP): MOLECULAR AND CELLULAR BASIS. P. Greengard’, J. D. Buxbaum’ and S. E. Gandfl. ‘Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, NY, Department of Neurology and Neuroscience, Cornell University Medical College, New York, NY. The relative utilization of alternative processing pathways for APP can be regulated by various signal transduction pathways which involve protein phosphorylation. For example, activation of protein kinase C, or inactivation of protein phosphatases 1 and 2A, leads to a relative increase in the utilization of the nonamyloidogenic, “a-secretase” cleavage pathway for APP processing and a decrease in AP production. Acetylcholine and various other phospholipase C/protein kinase C-linked first messengers have similar effects. Calcium stimulates APP secretion and decreases AP peptide formation in a protein kinase C-independent manner. The molecular and cellular basis for the regulation of APP processing by protein phosphorylation is the current focus APP is a of investigation in numerous laboratories. phosphoprotein; however, recent evidence from studies of the metabolism of mutant APP molecules suggests that the state of phosphorylation of the APP cytoplasmic tail is not suflicient to account for the effects of protein kinase C on APP processing. Other possible targets for protein kinase C which might account for its ability to alter APP processing include the APP ectodomain, various components of the APP trafficking pathway, e.g., those involved in the transport of APP from the trans-golgi network to the cell surface, as well as the secretase enzymes themselves.
162 FOR ALZHEIMER’S DISEASE. L.J. Thai. Depts. University of California San Diego, and San Diego VA Center, San Diego, CA USA. Strategies for treating Alzheimer’s Disease (ADI are a direct outgrowth of knowledge derived from understanding the neurobiological basis of the disorder. Strategies pursued during the 1970’s and 1990’s were largely neurotransminer replacement approaches designed to produce short term ameliorization of symptoms. Deficiencies of the cholinergic system have been best characterized, remain closely correlated to the cognitive disorder. and are a target for treatment, especially with respect to cholinesterase inhibitors. During 1993, the first cholinesterase inhibitor was approved for use in patients with AD based on the demonstration that a proportion of treated patients demonstrated modest cwnitive and global improvement when exposed to the cholinesterasa inhibitor, tetrahydroaminoacridine. Work continues with numerous other cholinestarase inhibitors. However, replacement therapy is unlikely to significantly alter the course of the illness.
TREATMENT
STRATEGIES
Neurolopyand Neurosciences,
homolog of dynactin. The 74 kD polypeptide appeared as a triplet of closely resolved bands as previously described for dynein intermediate chains. DAP 124 kD immunoreactivity increased three-fold over a seven day incubation, while immunoreactivity of the 74 kD polypeptide increased seven-fold. Similar results were obtained when differentiated PC 12 cells were cultured in the presence of Alzheimer’s disease (AD) brain extracts. Examination of DAPs from AD temporal cortex homogenates by immunobloting revealed that twofold more 74 kD polypeptide was free in supernatants aher centrifugation as opposed to bound dynein complexes in the pellet, when compared to control brain homogenates. These data suggest that the NGF-sensitive 74 kD DAP is altered in AD cortex, and as such may be a component of defective axonal transport in AD neurons.
PLENARY LECTURES II
s39
is found in the circulation normally. The possible importance of SAP as a precursor to AP is further corroborated by recent work showing that AP
homologous peptides can cross the blood-brain barrier. Hence s key questionin AD research currently is what factors alter SAP in the disease state, promoting conformational changes, aggregation, amyloid formation and cell death. Numerous mutations have been found in the AP precursor (PPP) gene, associated with early onset familial AD. However, AP deposition typically occurs in the absence of PPP mutations. Therefore other factors are more important in the majority of AD patients. Recently biochemical and immunohistochemical studies have shown the importance of two apolipoproteins in fibrillogenesis: apolipoprotein (apo) J, which forms a complex with SAP, and apo E. We proposed in 1991 that apo E is s “pathological chaperone,”acting to promote and/or stabilize a P-pleated sheet structure. This hypothesis is supported by the finding that a specific isotype of apo e, ~4, is associated with late-onset familial and sporadic AD. in addition, in vrtro studies with AP peptides have identified aggregation inhibitors or “desaggrins” in normal biological fluids. We hypothesize that a balance exists between factors which promote fibril formation, suchas apo E and dessggrins.These interactions as well as brain specific factors may be critical lo determining why SAP is initially deposited as preamyloid and why in some locations preamyloid progresses on lo neuritic plaque formation.
159 THE EPIDEMIOLOGY OF ALZHEIMER’S DISEASE: BEYOND RISK FACTORS. J.A. Mortimer. Geriatr. Res. Educ. Clin. Ctr., V.A. Medical
Center, and Depts. of Neurology and Epidemiology, University of Minnesota, Minneapolis, MN 55417 USA. Case-control and cohort studies have identified several putative risk factors for Alrheimer’s disease. Some of these risk factors appear nom modifiable, e.g., age, or to account for so few cases of the disease as to have little public health impact, e.g., severe head injury. Others may lend themselves to programs aimed at modifying the risk of AD. An important contribution of epidemiology is the identification of risk factors that may help explain the pathogenesis of the disease. Although we have known for decades that family history of dementia is an important risk factor for AD, it is only recently that the association of the apolipoprotein e4 allele with increased risk of the disease has become evident. This important discovery raises new questions that are being explored in epidemiological studies: How much disease is explained by the allelic distribution of the gene for apolipoprotein e? Are differences in AD prevalence between populations explained by relative frequencies of different alleles? How does age modify the expression of this gene in increasing the risk of AD? Recent data from population based samples provide strong support for its effect in modifying the risk of AD, for perhaps explaining cross-cultural differences in AD prevalence, and show important differences in age-specific expression. The interplay of epidemiology and neurobiology also is evident in other areas. An explanation for the association between head trauma and increased risk of AD, seen in case-control studies, is provided by the observation of increased beta amyloid production following severe head injury. Furthermore, new epidemiologic data suggest that the association between low education and increased risk of dementia in late life may be a reflection of deficient brain development early in life, indexed by lower intelligence and smaller head (brain) size. Ongoing epidemiologic studies continue to have an important impact on understanding the pathogenetic mechanisms of AD, including those showing associations with estrogen replacement and the use of antiinflammatory drugs. The partnership between epidemiology and neurobiology is likely to increase in importance as our knowledge of the pathogenesis of AD grows.
160 AMYLOIDS, GENES AND CHAPERONES IN ALZHEIMER’S DISEASE Bias Frangione, NYU Medical Center, New York, 10016 The defining neuropathological lesions of Alzbeimer’s disease (AD) are the deposition of amyloid p (AP) in the form of congophilic angiopathy and tile plaques, as well as the aggregation of abnormally phosphorylated r into neurofibrillary tangles. Our working hypothesis is that the key issues in AD are the inherent fibrillogenicity of AD and factors which influence fibril formation. Work on the Dutch variant of familial AD has led 10 the conclusion that a vascular source of AP contributes significantly to both
congophilic angiopathy and early plaques. As predicted, it has recently been found that peptides with the same amino acid sequence as AD exist as a normal soluble protein (SAP) in biological fluids. This links AD more closely to some of the systemic amyloidoses, where the amyloid precursor
161 REGULATED CLEAVAGE OF THE AMYLOID PRECURSOR PROTEIN WP): MOLECULAR AND CELLULAR BASIS. P. Greengard’, J. D. Buxbaum’ and S. E. Gandfl. ‘Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, NY, Department of Neurology and Neuroscience, Cornell University Medical College, New York, NY. The relative utilization of alternative processing pathways for APP can be regulated by various signal transduction pathways which involve protein phosphorylation. For example, activation of protein kinase C, or inactivation of protein phosphatases 1 and 2A, leads to a relative increase in the utilization of the nonamyloidogenic, “a-secretase” cleavage pathway for APP processing and a decrease in AP production. Acetylcholine and various other phospholipase C/protein kinase C-linked first messengers have similar effects. Calcium stimulates APP secretion and decreases AP peptide formation in a protein kinase C-independent manner. The molecular and cellular basis for the regulation of APP processing by protein phosphorylation is the current focus APP is a of investigation in numerous laboratories. phosphoprotein; however, recent evidence from studies of the metabolism of mutant APP molecules suggests that the state of phosphorylation of the APP cytoplasmic tail is not suflicient to account for the effects of protein kinase C on APP processing. Other possible targets for protein kinase C which might account for its ability to alter APP processing include the APP ectodomain, various components of the APP trafficking pathway, e.g., those involved in the transport of APP from the trans-golgi network to the cell surface, as well as the secretase enzymes themselves.
162 FOR ALZHEIMER’S DISEASE. L.J. Thai. Depts. University of California San Diego, and San Diego VA Center, San Diego, CA USA. Strategies for treating Alzheimer’s Disease (ADI are a direct outgrowth of knowledge derived from understanding the neurobiological basis of the disorder. Strategies pursued during the 1970’s and 1990’s were largely neurotransminer replacement approaches designed to produce short term ameliorization of symptoms. Deficiencies of the cholinergic system have been best characterized, remain closely correlated to the cognitive disorder. and are a target for treatment, especially with respect to cholinesterase inhibitors. During 1993, the first cholinesterase inhibitor was approved for use in patients with AD based on the demonstration that a proportion of treated patients demonstrated modest cwnitive and global improvement when exposed to the cholinesterasa inhibitor, tetrahydroaminoacridine. Work continues with numerous other cholinestarase inhibitors. However, replacement therapy is unlikely to significantly alter the course of the illness.
TREATMENT
STRATEGIES
Neurolopyand Neurosciences,