A mutation in the amyloid precursor protein associated with hereditary Alzheimer's disease

Alzheimer's disease is a form of localized amyloidosis characterized by cerebral cortical amyloid plaques, neurofibrillary tangles, and amyloid deposits within the walls of leptomeningeal vessels. Although most cases of Alzheimer's disease are sporadic, kindreds with autosomal-dominant inheritance of the syndrome suggest that a single mutation may be important in pathogenesis. Direct sequencing of DNA from a family with autopsy-proven Alzheimer's disease revealed a single amino acid substitution (Phe for Val) in the transmembrane domain of the amyloid precursor protein. This mutation correlates with the presence of Alzheimer's disease in all patients in this study, and may be the inherited factor causing both amyloid fibril formation and dementia.     

Amyloid beta protein precursor gene and hereditary cerebral hemorrhage with amyloidosis (Dutch)

Human hereditary cerebral hemorrhage with amyloidosis of the Dutch type (HCHWA-D), an autosomal dominant form of cerebral amyloid angiopathy (CAA), is characterized by extensive amyloid deposition in the small leptomeningeal arteries and cortical arterioles, which lead to an early death of those afflicted in their fifth or sixth decade. Immunohistochemical and biochemical studies have indicated that the amyloid subunit in HCHWA-D is antigenically related to and homologous in sequence with the amyloid beta protein isolated from brains of patients with Alzheimer's disease and Down syndrome. The amyloid beta protein is encoded by the amyloid beta protein precursor (APP) gene located on chromosome 21. Restriction fragment length polymorphisms detected by the APP gene were used to examine whether this gene is a candidate for the genetic defect in HCHWA-D. The data indicate that the APP gene is tightly linked to HCHWA-D and therefore, in contrast to familial Alzheimer's disease, cannot be excluded as the site of mutation in HCHWA-D.     

Prevention of transthyretin amyloid disease by changing protein misfolding energetics

Genetic evidence suggests that inhibition of amyloid fibril formation by small molecules should be effective against amyloid diseases. Known amyloid inhibitors appear to function by shifting the aggregation equilibrium away from the amyloid state. Here, we describe a series of transthyretin amyloidosis inhibitors that functioned by increasing the kinetic barrier associated with misfolding, preventing amyloidogenesis by stabilizing the native state. The trans-suppressor mutation, threonine 119 --> methionine 119, which is known to ameliorate familial amyloid disease, also functioned through kinetic stabilization, implying that this small-molecule strategy should be effective in treating amyloid diseases.     

Diverse gene expression for isotypes of murine serum amyloid A protein during acute phase reaction

Serum amyloid A protein (SAA) is a precursor for a major component of amyloid fibrils, which, upon deposition, cause secondary amyloidosis in diseases such as rheumatoid arthritis. In mice, SAA is encoded by at least three genes, which show diverse expression during inflammation. Furthermore, in amyloidosis-resistant SJL mice, the gene expression for one SAA isotype, SAA2, is defective, although SAA2 gene expression is normal in amyloidosis-susceptible BALB/c mice. Because only SAA2-derived products deposit in mouse amyloid tissues, the resistance of SJL mice to amyloidosis seems to be due to defective SAA2 gene expression. Thus, the study emphasizes the importance of SAA gene structure in determining susceptibility to amyloidosis.     

Trans-suppression of misfolding in an amyloid disease

The transthyretin (TTR) amyloid diseases, representative of numerous misfolding disorders, are of considerable interest because there are mutations that cause or suppress disease. The Val30 --> Met30 (V30M) TTR mutation is the most prevalent cause of familial amyloid polyneuropathy in heterozygotes, whereas a Thr119 --> Met119 (T119M) mutation on the second TTR allele protects V30M carriers from disease. Here, we show that the incorporation of one or more T119M TTR subunits into a predominantly V30M tetramer strongly stabilized the mixed tetramer against dissociation. Dissociation is required for amyloid formation, so these findings provide a molecular explanation for intragenic trans-suppression of amyloidosis. The data also suggest a potential therapeutic strategy, provide insight into tissue-specific deposition and amyloid composition, and support the validity of the amyloid hypothesis in human disease.     

A portrait of Alzheimer secretases--new features and familiar faces

The amyloid beta-peptide (Abeta) is a principal component of the cerebral plaques found in the brains of patients with Alzeheimer's disease (AD). This insoluble 40- to 42-amino acid peptide is formed by the cleavage of the Abeta precursor protein (APP). The three proteases that cleave APP, alpha-, beta-, and gamma-secretases, have been implicated in the etiology of AD. beta-Secretase is a membrane-anchored protein with clear homology to soluble aspartyl proteases, and alpha-secretase displays characteristics of certain membrane-tethered metalloproteases. gamma-Secretase is apparently an oligomeric complex that includes the presenilins, which may be the catalytic component of this protease. Identification of the alpha-, beta-, and gamma-secretases provides potential targets for designing new drugs to treat AD.     

Amyloidosis induced in mice by Escherichia coli endotoxin

Amyloidosis was produced in mice by repeated subcutaneous injections of 0.5-or 0.005-milligram amounts of Escherichia coli endotoxin. Of the two strains of mice examined, amyloidosis was induced more readily in one than in the other. The ability of endotoxin to induce amyloidosis lends support to the view that stimulation of reticuloendothelial cells leads to amyloid formation.     

Deposits of amyloid beta protein in the central nervous system of transgenic mice.

Alzheimer's disease is characterized by widespread deposition of amyloid in the central nervous system. The 4-kilodalton amyloid beta protein is derived from a larger amyloid precursor protein and forms amyloid deposits in the brain by an unknown pathological mechanism. Except for aged nonhuman primates, there is no animal model for Alzheimer's disease. Transgenic mice expressing amyloid beta protein in the brain could provide such a model. To investigate this possibility, the 4-kilodalton human amyloid beta protein was expressed under the control of the promoter of the human amyloid precursor protein in two lines of transgenic mice. Amyloid beta protein accumulated in the dendrites of some but not all hippocampal neurons in 1-year-old transgenic mice. Aggregates of the amyloid beta protein formed amyloid-like fibrils that are similar in appearance to those in the brains of patients with Alzheimer's disease.     

Conservation of brain amyloid proteins in aged mammals and humans with Alzheimer's disease

The formation of clusters of altered axons and dendrites surrounding extracellular deposits of amyloid filaments (neuritic plaques) is a major feature of the human brain in both aging and Alzheimer's disease. A panel of antibodies against amyloid filaments and their constituent proteins from humans with Alzheimer's disease cross-reacted with neuritic plaque and cerebrovascular amyloid deposits in five other species of aged mammals, including monkey, orangutan, polar bear, and dog. Antibodies to a 28-amino acid peptide representing the partial protein sequence of the human amyloid filaments recognized the cortical and microvascular amyloid of all of the aged mammals examined. Plaque amyloid, plaque neurites, and neuronal cell bodies in the aged animals showed no reaction with antibodies to human paired helical filaments. Thus, with age, the amyloid proteins associated with progressive cortical degeneration in Alzheimer's disease are also deposited in the brains of other mammals. Aged primates can provide biochemically relevant models for principal features of Alzheimer's disease: cerebrovascular amyloidosis and neuritic plaque formation.     

Gene dosage of the amyloid beta precursor protein in Alzheimer's disease

The progressive deposition in the human brain of amyloid filaments composed of the amyloid beta protein is a principal feature of Alzheimer's disease (AD). Densitometric analysis of Southern blots probed with a complementary DNA for the amyloid protein has been carried out to determine the relative dosage of this gene in genomic DNA of 14 patients with AD, 12 aged normal subjects, and 10 patients with trisomy 21 (Down syndrome). Whereas patients in the last group showed the expected 1.5-fold increase in dosage of this gene, none of the patients with AD had a gene dosage higher than that of the normal controls. These results do not support the hypothesis that the genetic defect in AD involves duplication of a segment of chromosome 21 containing the amyloid gene. Alternative mechanisms for the brain-specific increase in amyloid protein deposition in AD should be considered.     

Amyloid beta protein precursor is possibly a heparan sulfate proteoglycan core protein

The amyloid beta protein peptide is a major constituent of amyloid plaque cores in Alzheimer's disease and is apparently derived from a higher molecular weight precursor. It is now shown that the core protein of a heparan sulfate proteoglycan secreted from a nerve cell line (PC12) has an amino acid sequence and a size very similar to those of the amyloid beta protein precursor and that these molecules are antigenically related. This amyloid beta protein precursor-related protein is not found in the conditioned medium of a variant cell line (F3 PC12) that does not secrete heparan sulfate proteoglycan. The synaptic localization and metabolism of this class of proteoglycans are consistent with its potential involvement in central nervous system dysfunction.     

Neurotoxicity of a fragment of the amyloid precursor associated with Alzheimer's disease

Amyloid deposition in senile plaques and the cerebral vasculature is a marker of Alzheimer's disease. Whether amyloid itself contributes to the neurodegenerative process or is simply a by-product of that process is unknown. Pheochromocytoma (PC12) and fibroblast (NIH 3T3) cell lines were transfected with portions of the gene for the human amyloid precursor protein. Stable PC12 cell transfectants expressing a specific amyloid-containing fragment of the precursor protein gradually degenerated when induced to differentiate into neuronal cells with nerve growth factor. Conditioned medium from these cells was toxic to neurons in primary hippocampal cultures, and the toxic agent could be removed by immunoabsorption with an antibody directed against the amyloid polypeptide. Thus, a peptide derived from the amyloid precursor may be neurotoxic.     

Beta amyloid gene duplication in Alzheimer's disease and karyotypically normal Down syndrome

With the recently cloned complementary DNA probe, lambda Am4 for the chromosome 21 gene encoding brain amyloid polypeptide (beta amyloid protein) of Alzheimer's disease, leukocyte DNA from three patients with sporadic Alzheimer's disease and two patients with karyotypically normal Down syndrome was found to contain three copies of this gene. Because a small region of chromosome 21 containing the ets-2 gene is duplicated in patients with Alzheimer's disease, as well as in karyotypically normal Down syndrome, duplication of a subsection of the critical segment of chromosome 21 that is duplicated in Down syndrome may be the genetic defect in Alzheimer's disease.     

Creation of "amyloid" fibrils from Bence Jones proteins in vitro

"Amyloid" fibrils have been created from some human Bence Jones proteins by proteolytic digestion under physiologic conditions. These fibrils with an antiparallel, beta-pleated sheet conformation consist of only a portion of the variable region of the immunoglobulin light polypeptide chain and share the physical properties of amyloid fibrils. The relation between amyloidosis and immunoglobulins is thus more firmly established and a pathogenetic mechanism for amyloid fibril formation is suggested.     

Localization of amyloid beta protein messenger RNA in brains from patients with Alzheimer's disease

The distribution of cells containing messenger RNA that encodes amyloid beta protein was determined in hippocampi and in various cortical regions from cynomolgus monkeys, normal humans, and patients with Alzheimer's disease by in situ hybridization. Both 35S-labeled RNA antisense and sense probes to amyloid beta protein messenger RNA were used to ensure specific hybridization. Messenger RNA for amyloid beta protein was expressed in a subset of neurons in the prefrontal cortex from monkeys, normal humans, and patients with Alzheimer's disease. This messenger RNA was also present in the neurons of all the hippocampal fields from monkeys, normal humans and, although to a lesser extent in cornu ammonis 1, patients with Alzheimer's disease. The distribution of amyloid beta protein messenger RNA was similar to that of the neurofibrillary tangles of Alzheimer's disease in some regions, but the messenger RNA was also expressed in other neurons that are not usually involved in the pathology of Alzheimer's disease.     

Uroporphyrinogen decarboxylase structural mutant (Gly281----Glu) in a case of porphyria

Uroporphyrinogen decarboxylase deficiency in man is responsible for familial porphyria cutanea tarda and hepatoerythropoietic porphyria. A recent study of a family with hepatoerythropoietic porphyria showed that the enzyme defect resulted from rapid degradation of the protein in vivo. Cloning and sequencing of a complementary DNA for the mutated gene revealed that the mutation was due to the replacement of a glycine residue by a glutamic acid residue at position 281. This base change leads to a protein that is very rapidly degraded in the presence of cell lysate. Characterization of the mutation will allow comparison of this defect in a homozygous patient with defects in other patients with familial porphyria cutanea tarda.     

Exogenous induction of cerebral beta-amyloidogenesis is governed by agent and host

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.     

Neurotrophic and neurotoxic effects of amyloid beta protein: reversal by tachykinin neuropeptides

The amyloid beta protein is deposited in the brains of patients with Alzheimer's disease but its pathogenic role is unknown. In culture, the amyloid beta protein was neurotrophic to undifferentiated hippocampal neurons at low concentrations and neurotoxic to mature neurons at higher concentrations. In differentiated neurons, amyloid beta protein caused dendritic and axonal retraction followed by neuronal death. A portion of the amyloid beta protein (amino acids 25 to 35) mediated both the trophic and toxic effects and was homologous to the tachykinin neuropeptide family. The effects of the amyloid beta protein were mimicked by tachykinin antagonists and completely reversed by specific tachykinin agonists. Thus, the amyloid beta protein could function as a neurotrophic factor for differentiating neurons, but at high concentrations in mature neurons, as in Alzheimer's disease, could cause neuronal degeneration.     

Cleavage of amyloid beta peptide during constitutive processing of its precursor

The amyloid beta peptide (A beta P) is a small fragment of the much larger, broadly distributed amyloid precursor protein (APP). Abundant A beta P deposition in the brains of patients with Alzheimer's disease suggests that altered APP processing may represent a key pathogenic event. Direct protein structural analyses showed that constitutive processing in human embryonic kidney 293 cells cleaves APP in the interior of the A beta P, thus preventing A beta P deposition. A deficiency of this processing event may ultimately prove to be the etiological event in Alzheimer's disease that gives rise to senile plaque formation.     

Platelet coagulation factor XIa-inhibitor, a form of Alzheimer amyloid precursor protein

An inhibitor of coagulation factor XIa was purified from serum-free conditioned medium of HepG2 liver cells. Platelets stimulated with thrombin or calcium ionophore (A23187) secrete a protein functionally and immunologically identical to the inhibitor, implying a role for this inhibitor in hemostasis. Analysis of the amino-terminal amino acid sequence and immunologic reactivity showed the inhibitor to be a truncated form of the Alzheimer's amyloid precursor protein that contains a Kunitz-type serine protease inhibitor domain and at least a portion of the amyloid beta protein. It inhibits factor XIa and trypsin with a Ki of 450 +/- 50 pM and 20 +/- 10 pM, respectively. Heparin (1 unit/ml) did not significantly effect inhibition of trypsin, but inhibition of XIa was 15 times greater (Ki = 25 +/- 15 pM) in the presence of heparin.