Protease nexin-II, a potent antichymotrypsin, shows identity to amyloid beta-protein precursor

Neurofibrillary tangles of Guamanian amyotrophic lateral sclerosis, parkinsonism-dementia and neurologically normal Guamanians contain a 4- to 4.5-kilodalton protein which is immunoreactive to anti-amyloid beta/A4-protein antibodies

Neurofibrillary tangles (NFT), one of the neurodegenerative features of Alzheimer's disease, Down's syndrome and normal aging, is a constant, widespread neuropathological finding in Guamanian amyotrophic lateral sclerosis (ALS), parkinsonism-dementia (PD) and in neurologically normal Guamanians, dying of causes other than ALS and PD. NFT in brain tissue sections of patients with Guamanian ALS and PD were immunoreactive to antibodies directed against a 43-amino acid synthetic peptide homologous to amyloid beta/A4-protein (anti-SP43) associated with Alzheimer's disease. NFT extracted from frozen brain tissues of Guamanian patients with ALS and PD and from tissues of neurologically normal Guamanians were congophilic and birefringent. By negative-stain electron microscopy, NFT preparations contained bundles and/or isolated single, straight, unpaired filaments in Guamanian ALS and occasionally pairing of filaments in neurologically normal Guamanians, measuring 5-20 nm in diameter. Formic acid digestion of NFT preparations, followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and size-exclusion high-pressure liquid chromatography, showed a protein with an apparent molecular mass of 4- to 4.5-kDa, which by Western blot analysis was immunoreactive to anti-SP43. Immunoabsorption of purified NFT or SP43 with anti-SP43 abolished immunostaining. Our study corroborate previous data that amyloid beta/A4-protein is present in NFT in Guamanian PD. Furthermore, our data indicate that amyloid beta/A4-protein is present in NFT in brain tissues of patients with Guamanian ALS and in neurologically normal Guamanians, suggesting a common mechanism of amyloidogenesis with NFT formation in Alzheimer's disease and normal brain aging.

Alpha 1-antichymotrypsin binding to Alzheimer A beta peptides is sequence specific and induces fibril disaggregation in vitro

The serine protease inhibitor alpha 1-antichymotrypsin (ACT) consistently colocalizes with amyloid deposits of Alzheimer's disease (AD) and may contribute to the generation of amyloid proteins and/or physically affect fibril assembly. AD amyloid fibrils are composed primarily of A beta, which is a proteolytic fragment of the larger beta-amyloid precursor protein. Using negative-stain and immunochemical electron microscopy, we have investigated the binding of ACT to the fibrils formed by four synthetic A beta analogues corresponding to the wild-type human 1-40 sequence [Hwt(1-40)], a 1-40 peptide [HDu(1-40)] containing the Glu22-->Gln mutation found in hereditary cerebral hemorrhage with amyloidosis of the Dutch type, the N-terminal 1-28 residues [beta(1-28)], and an internal fragment of A beta containing residues 11-28 [beta(11-28)]. Each of these peptide analogues assembled into 70-90-A-diameter fibrils resembling native amyloid and, except for beta(11-28), bound ACT, as indicated by the appearance of 80-100-A globular particles that adhered to preformed fibrils and that could be decorated with anti-ACT antibodies. Under the conditions used, ACT binding destabilized the in vitro fibrils and produced a gradual dissolution of the macromolecular assemblies into constituent filaments and shorter fragments. The internal fragment (11-28) did not exhibit ACT binding or any structural changes. These results suggest that a specific sequence likely contained within the N-terminal 10 residues of A beta is responsible for the formation of the ACT-amyloid complex.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular cloning of the cDNA for a human amyloid precursor protein homolog: evidence for a multigene family

Alzheimer's disease is a degenerative neurological disorder characterized by neural loss and brain lesions associated with plaques containing large amounts of the beta/A4 amyloid peptide. Molecular cloning of the cDNA for this peptide from human brain has shown it to be derived by proteolysis from a much larger precursor called the amyloid precursor protein (APP). The biological role of the precursor is unknown, but it has been shown to be transcribed in many human tissues in addition to brain. In the present report, we describe the molecular cloning from a human placental library of a full-length cDNA for a molecule closely related to APP. This novel molecule, which we have called amyloid precursor protein homolog (APPH), shares overall domain organization with APP. It is 763 amino acids in length and appears to encode a signal peptide, a large apparent extracellular domain including a Kunitz inhibitor domain, a transmembrane region, and a short cytoplasmic domain. Northern analysis indicates that it occurs in at least two molecular forms and is transcribed in human brain, heart, lung, liver, and kidney, in addition to placenta. On the basis of its extensive sequence similarity and conservation of domain structure, APPH is the nearest relative of APP yet identified in an emerging multigene family.

Amino acid sequence RERMS represents the active domain of amyloid beta/A4 protein precursor that promotes fibroblast growth

The growth of A-1 fibroblasts depends on exogenous amyloid beta/A4 protein precursor (APP), providing a simple bioassay to study the function of APP. Our preliminary study, testing the activity of a series of fragments derived from the secreted form of APP-695 (sAPP-695) on this bioassay, has shown that at least one of the active sites of sAPP-695 was localized within a 40-mer sequence (APP296-335, Kang sequence; Roch, J.-M., I. P. Shapiro, M. P. Sundsmo, D. A. C. Otero, L. M. Refolo, N. K. Robakis, and T. Saitoh. 1992. J. Biol. Chem. 267:2214-2221). In the present study, to further characterize the growth-promoting activity of sAPP-695 on fibroblasts, we applied a battery of synthetic peptides on this bioassay and found that: (a) the sequence of five amino acids, RERMS (APP328-332), was uniquely required for the growth-promoting activity of sAPP-695; (b) the activity was sequence-specific because the reverse-sequence peptide of the active domain had no activity; and (c) the four-amino-acid peptide RMSQ (APP330-333), which partially overlaps the COOH-terminal side of the active sequence RERMS, could antagonize the activity of sAPP-695. Furthermore, a recombinant protein which lacks this active domain (APP20-591 without 306-335) did not promote fibroblast cell growth, suggesting that this domain is the only site of sAPP-695 involved in the growth stimulation. The availability of these biologically active, short peptides and their antagonists should prove to be an essential step for the elucidation of APP involvement in regulation of cellular homeostasis.

Molecular profile of reactive astrocytes--implications for their role in neurologic disease

The central nervous system responds to diverse neurologic injuries with a vigorous activation of astrocytes. While this phenomenon is found in many different species, its function is obscure. Understanding the molecular profile characteristic of reactive astrocytes should help define their function. The purpose of this review is to provide a summary of molecules whose levels of expression differentiate activated from resting astrocytes and to use the molecular profile of reactive astrocytes as the basis for speculations on the functions of these cells. At present, reactive astrocytosis is defined primarily as an increase in the number and size of cells expressing glial fibrillary acidic protein. In vivo, this increase in glial fibrillary acidic protein-positive cells reflects predominantly phenotypic changes of resident astroglia rather than migration or proliferation of such cells. Upon activation, astrocytes upmodulate the expression of a large number of molecules. From this molecular profile it becomes apparent that reactive astrocytes may benefit the injured nervous system by participating in diverse biological processes. For example, upregulation of proteases and protease inhibitors could help remodel the extracellular matrix, regulate the concentration of different proteins in the neuropil and clear up debris from degenerating cells. Cytokines are key mediators of immunity and inflammation and could play a critical role in the regulation of the blood-central nervous system interface. Neurotrophic factors, transporter molecules and enzymes involved in the metabolism of excitotoxic amino acids or in the antioxidant pathway may help protect neurons and other brain cells by controlling neurotoxin levels and contributing to homeostasis within the central nervous system. Therefore, an impairment of astroglial performance has the potential to exacerbate neuronal dysfunction. Based on the synopsis of studies presented, a number of issues become apparent that deserve a more extensive analysis. Among them are the relative contribution of microglia and astrocytes to early wound repair, the characterization of astroglial subpopulations, the specificity of the astroglial response in different diseases as well as the analysis of reactive astrocytes with techniques that can resolve fast physiologic processes. Differences between reactive astrocytes in vivo and primary astrocytes in culture are discussed and underline the need for the development and exploitation of models that will allow the analysis of reactive astrocytes in the intact organism.

Cellular specificity and regional distribution of amyloid beta protein precursor alternative transcripts are unaltered in Alzheimer hippocampal formation

Studies comparing the expression of the amyloid beta protein precursor (APP) gene in brains of patients with Alzheimer's disease (AD) and control individuals have resulted in contradictory findings indicative of selective reductions and relative increases of APP alternative transcripts in AD brain. It has been suggested that changes in APP expression in relation to AD neuropathology may represent highly specific and localized events involving only select populations of cells in particular brain regions. For example, reported AD-related alterations in ratios of APP alternative transcripts could be attributed to changes in expression of APP in specific neuronal subpopulations, and/or reactive astrocytes and/or microglia. To address this question, we have employed in situ hybridization using biotinylated oligonucleotide probes designed to localize specific APP mRNA transcripts in the hippocampal formation of AD patients and age-matched controls since this method allows a clear distinction of the classes of neurons and glia containing a particular message.(ABSTRACT TRUNCATED AT 250 WORDS)

A metalloproteinase inhibitor domain in Alzheimer amyloid protein precursor

Extracellular deposition of amyloid beta-protein (beta-AP), or A4 protein (M(r) 4,000), is associated with Alzheimer's disease and with Down's syndrome (trisomy for chromosome 21). The large membrane-bound precursor protein (APP) of beta-AP is normally cleaved within the beta-AP region by a putative proteinase (APP secretase) to release its extracellular portion; beta-AP is produced by an alternative proteolytic processing. Here we demonstrate that APP contains a proteinase inhibitor domain for the matrix metalloproteinase gelatinase A, which is located in the C-terminal glycosylated region of the secretory forms of APP. In addition, we show that the gelatinase has an APP secretase-like activity, which hydrolyses the Lys16-Leu17 bond in the beta-AP sequence. Our results indicate that the proteinase inhibitor domain of APP and gelatinase A may be involved in the formation of beta-AP.

NGF deprivation and neuronal degeneration trigger altered beta-amyloid precursor protein gene expression in the rat superior cervical ganglia in vivo and in vitro

In order to study the expression of beta-amyloid precursor protein (APP) isoforms during neuronal degeneration we have used the rat superior cervical ganglia (SCG) as an experimental model. In the neonate these sympathetic ganglia are nerve growth factor (NGF) dependent and in vivo administration of anti-NGF antiserum results in exaggerated neuronal degeneration. Analysis of APP mRNA transcripts in the SCG, following NGF deprivation, revealed a coincident decrease in APP695 and augmentation of APP751/770. These changes were specific to the SCG and were not seen in sensory ganglia. Subsequent in vitro studies, using primary dissociated cultures of sympathetic or cortical neurones, confirmed these changes in APP gene expression during neuronal degeneration. These observations may have important implications for the generation of beta-amyloid in Alzheimer's disease.

Plasminogen activator inhibitor 1, the primary regulator of fibrinolysis, in normal human cerebrospinal fluid

The occurrence of type-1 plasminogen activator inhibitor (PAI-1) in human cerebrospinal fluid (CSF) has not previously been reported. As a member of the serpin superfamily of serine protease inhibitors and an acute phase response component, PAI-1 has powerful potential roles in nervous system homeostasis. We have detected this serpin antigen using a polyclonal anti-PAI-1 antibody in normal human CSF. In Western blotting, PAI-1 in several CSF samples appears as a two-band antigen of Mr = 54 and 35 kDa, presumably the intact and proteolytic fragment, respectively. In vitro complex formation studies confirm that the 54 kDa form of PAI-1 interacts with 125I-urokinase after activation with SDS, but the 35 kDa form does not. Quantification of total PAI-1 antigen in 18 normal human CSF samples by ELISA reveals a mean value of 1.0 +/- 0.07 (SEM) micrograms/dL, indicating that a relatively low concentration of the inhibitor occurs in normal human CSF. This information should now allow comparison of PAI-1 levels and activity in various neurologic disorders.

Evidence for excitoprotective and intraneuronal calcium-regulating roles for secreted forms of the beta-amyloid precursor protein

The beta-amyloid precursor protein (beta APP) is a membrane-spanning glycoprotein that is the source of the beta-amyloid peptide (beta AP) which accumulates as senile plaques in the brains of patients with Alzheimer's disease. beta APP is normally processed such that a cleavage occurs within the beta AP, liberating secreted forms of beta APP (APPss) from the cell. The neuronal functions of these forms are unknown. We now report that APPss have a potent neuroprotective action in cultured rat hippocampal and septal neurons and in human cortical neurons. APPs695 and APPs751 protected neurons against hypoglycemic damage, and the neuroprotection was abolished by antibodies to a specific region common to both APPs695 and APPs751. APPss caused a rapid and prolonged reduction in [Ca2+]i and prevented the rise in [Ca2+]i that normally mediated hypoglycemic damage. APPss also protected neurons against glutamate neurotoxicity, effectively raising the excitotoxic threshold. APPss may normally play excitoprotective and neuromodulatory roles. Alternative processing of APPss in Alzheimer's disease may contribute to neuronal degeneration by compromising the normal function of APPss and by promoting the deposition of beta AP.

Inhibitory spectra of purified protease nexin-II and related proteins towards cellular proteinases

Amyloid beta protein (beta/A4) is deposited in senile plaques of patients with Alzheimer's disease. This protein is derived from a larger membrane-associated protein, termed amyloid precursor protein (APP). The constitutive processing of APP occurs at the central portion of beta/A4, resulting in the release of large N-terminal peptides. We have purified these peptides from the culture medium of cDNA-transfected COS-1 cells. Some of the isoforms contain the Kunitz-type protease inhibitor (KPI) domain and strongly inhibit trypsin, chymotrypsin and plasmin, but do not inhibit kallikrein, prolyl endopeptidase or granzyme A. The peptides also do not inhibit cysteine proteases such as cathepsin B or calpain. Soluble APPs lacking the KPI domain fail to inhibit any of these proteases. The results indicate that the KPI domain in soluble APPs has protease inhibitory activity against certain serine proteases.

Potential role of protease nexin-2/amyloid beta-protein precursor as a cerebral anticoagulant

The amyloid beta-protein precursor (APP) is the parent molecule to the amyloid beta-protein which is a major constituent of neuritic plaques and cerebrovascular deposits in Alzheimer's disease (AD). The protease inhibitor, protease nexin-2 (PN-2), is the secreted form of APP that contains the Kunitz protease inhibitor (KPI) domain. We reported that the predominant isoform of APP in human brain contains the KPI domain and is thus PN-2. Quantitation of PN-2/APP in various tissues revealed that it is primarily found in brain. Circulating blood platelets are another rich source of PN-2/APP. Platelet PN-2/APP is contained in platelet alpha granules and is secreted upon activation of platelets by physiological agonists. Protease inhibition measurements demonstrated that PN-2/APP is a potent inhibitor of intrinsic blood coagulation factor XIa. These findings suggest that PN-2/APP may play a role in the regulation of blood coagulation and platelets may serve as a systemic vehicle to deliver large amounts of this protein to sites of vascular injury. In addition, we propose that the rich, and relatively exclusive, investment of PN-2/APP in brain suggests that it may function locally as an intracerebral anticoagulant.

N-linked glycosylation of beta-amyloid precursor protein

The beta-amyloid peptide that accumulates in the brain of patients with Alzheimer's disease is derived by proteolytic processing of a family of membrane bound beta-amyloid precursor proteins (beta APPs). The three major isoforms of beta APP, derived by alternative splicing, contain 695, 751, and 770 amino acids. They are heavily O-glycosylated and contain two N-linked glycosylation sites. The pathways leading to beta-amyloid deposition in brain are not clear. It is possible that defects in metabolic and processing pathways of beta APP lead to the increased production and deposition of beta-amyloid. In many cases post-translational modifications, such as glycosylation, are important in regulating such pathways. We studied N-linked glycosylation of the 695 amino acid form of beta APP in detail by deleting the two potential glycosylation sites at Asn467 and Asn496. The mutants were examined both in a cell-free transcription/translation/glycosylation system and in transfected Chinese hamster ovary (CHO) cells. In both systems, only Asn467 was glycosylated. In CHO cells the N-linked oligosaccharide on beta APP was completely resistant to Endoglycosidase H, suggesting that it is of complex type. These mutants will be useful for studying the role of glycosylation in the metabolism of beta APP.

A 109-amino-acid C-terminal fragment of Alzheimer's-disease amyloid precursor protein contains a sequence, -RHDS-, that promotes cell adhesion

Amyloid beta (A beta), the major constituent of the fibrils composing senile plaques and vascular amyloid deposits in Alzheimer's disease (AD) and related disorders, is a 39-42-residue self-aggregating degradation peptide of a larger multidomain membrane glycoprotein designated amyloid precursor protein (APP). An array of biological functions has been assigned to different APP domains, including growth regulation, neurotoxicity, inhibitory activity of serine proteinases and promotion of cell-cell and cell-matrix interactions. A beta is generated through an as-yet-unknown catabolic pathway that by-passes or inhibits the cleavage of APP within the A beta sequence. We have identified a 16 kDa intermediate APP C-terminal fragment containing A beta in leptomeningeal vessels of aged normal individuals and AD patients by means of its immunoreactivity with a panel of four different anti-(APP C-terminal) antibodies, indicating a different pathway of APP processing. Previous studies have indicated that the APP C-terminal domain is the most likely to be involved in cell-matrix interactions. A 109-amino-acid construct C109 with a sequence analogous to the C-terminal of APP (positions 587-695 of APP695), similar in length and immunoreactivity to the 16 kDa fragment, was found to promote cell adhesion. By use of synthetic peptides, this activity was initially located to the extracellular 28 residues of A beta. Inhibition studies demonstrated that the sequence RHDS (amino acids 5-8 of A beta, corresponding to residues 601-604 of APP695 was responsible for the adhesion-promoting activity. The interaction is dependent on bivalent cations and can be blocked either by the tetrapeptides RHDS and RGDS or by an anti-(beta 1 integrin) antibody. Thus, through integrin-like surface receptors, APP or its derivative proteolytic fragments containing the sequence RHDS may modulate cell-cell or cell-matrix interactions.

Amyloid precursor protein mRNA encoding the Kunitz protease inhibitor domain is increased by kainic acid-induced seizures in rat hippocampus

A 168-nucleotide exon, found in alternatively spliced amyloid precursor protein (APP) mRNAs, encodes a Kunitz protease inhibitor (KPI) domain. Kainic acid (ip) caused a selective increase of KPI mRNA in rat hippocampus. By in situ hybridization, KPI mRNA was induced in the neuronal layers of the hippocampus 11-12 h after the onset of kainate-induced seizures. The kainate-induced elevation of the KPI-containing APP-770 mRNA was blocked by pretreatment with the anticonvulsant pentobarbital. These data suggest that kainate-induced seizures cause alterations in APP RNA stability and/or processing in rat hippocampal neurons.

Fibril formation by primate, rodent, and Dutch-hemorrhagic analogues of Alzheimer amyloid beta-protein

Deposition of extraneuronal fibrils that assemble from the 39-43 residue beta/A4 amyloid protein is one of the earliest histopathological features of Alzheimer's disease. We have used negative-stain electron microscopy, Fourier-transform infrared (FT-IR) spectroscopy, and fiber X-ray diffraction to examine the structure and properties of synthetic peptides corresponding to residues 1-40 of the beta/A4 protein of primate [Pm(1-40); human and monkey], rodent [Ro(1-40); with Arg5-->Gly, Tyr10-->Phe, and His13-->Arg], and hereditary cerebral hemorrhage with amyloidosis of the Dutch type (HCHWA-D) [Du(1-40); with Glu22-->Gln]. As controls, we examined a reverse primate sequence [Pm*(40-1)] and an extensively substituted primate peptide [C(1-40); with Glu3-->Arg, Arg5-->Glu, Asp7-->Val, His13-->Lys, Lys16-->His, Val18-->Asp, Phe19-->Ser, Phe20-->Tyr, Ser26-->Pro, Ala30-->Val, Ile31-->Ala, Met35-->norLeu, Gly38-->Ile, Val39-->Ala, and Val40-->Gly]. The assembly of these peptides was studied to understand the relationship between species-dependent amyloid formation and beta/A4 sequence and the effect of a naturally occurring point mutation of fibrillogenesis. The three N-terminal amino acid differences between Pm(1-40) and Ro(1-40) had virtually no effect on the morphology or organization of the fibrils formed by these peptides, indicating that the lack of amyloid deposits in rodent brain is not due directly to specific changes in its beta/A4 sequence. beta-Sheet and fibril formation, judged by FT-IR, was maximal within the pH range 5-8 for Pm(1-40), pH 5-10.5 for Du(1-40), and pH 2.5-8 for Ro(1-40).(ABSTRACT TRUNCATED AT 250 WORDS)

Alzheimer's disease untangled

The last year has seen major advances in the study of Alzheimer's disease (AD). Four mutations involving amino acid substitutions in exons 16 and 17 of the amyloid precursor protein (APP) gene, have been identified which co-segregate with the disease in some families multiply affected by early onset Alzheimer's disease. These mutations are strongly suggestive of a causative role for the amyloid precursor protein in Alzheimer's disease. Despite their rarity, these mutations are important because they represent the first known cause of Alzheimer's disease. Processing of APP must be central to the pathogenesis of the disease although the precise effects of these amino acid substitutions are not understood. Work is now being undertaken to characterise the processing pathways of APP and to identify other causes of AD. The development of models of AD using the APP mutations offers the possibility of identifying drug targets and developing more effective treatments than are presently available.

Amyloid precursor protein is localized in growing neurites of neonatal rat brain

Previous studies have indicated that amyloid precursor protein (APP) might be a trophic agent in the nervous system, possibly through the regulation of cell adhesion and the protease/protease inhibitor activity. Additionally, APP is upregulated during the development of the nervous system. In order to further study the role of APP in neuritic outgrowth, we examined the patterns of distribution of APP in the immature neonatal rat brain (P1). Laser-scanning confocal imaging of double-immunolabeled sections showed that a subpopulation of the anti-GAP43-immunoreactive outgrowing neurites contained APP immunoreactivity in the neocortex and hippocampus. These fine, long neuritic processes were also positive with antibodies against phosphorylated neurofilaments and were glial fibrillary acidic protein (GFAP) negative. In addition, anti-APP strongly immunolabeled neurons in the inner cortical layers, while GAP43 strongly immunolabeled the neuropil surrounding them. These observations are consistent with a previous study where APP was localized to aberrant sprouting neurites and suggest a possible role for APP in neuritic outgrowth in plaques of patients with Alzheimer's disease (AD), which might explain the abnormal neuritic response found in AD.

Evidence for intracellular cleavage of the Alzheimer's amyloid precursor in PC12 cells

The Alzheimer's amyloid precursor (APP) is cleaved by an unidentified enzyme (APP secretase) to produce soluble APP. Fractionation of PC12 cell homogenates in a detergent-free buffer showed the presence of the Kunitz protease inhibitor (KPI)-containing soluble APP (nexin II) in the particulate fraction. Digitonin or sodium carbonate treatment of this fraction solubilized nexin II suggesting that it is contained in the lumen of vesicles. Nexin II production was not affected by lysosomotropic agents, suggesting that APP secretase is not a lysosomal enzyme. Labelling of cell surface proteins by iodination failed to detect full-length APP on the surface of PC12 cells, suggesting that most of this protein is located intracellularly. Furthermore, pulse-chase experiments showed that nexin II is detected in cell extracts before it appears in the culture medium. Cellular nexin II was detected at zero time of chase after only 5 min of pulse labelling with 35S-sulfate, indicated that APP secretase cleavage takes place immediately after APP is sulfated. Temperature block, pulse-chase, and 35S-sulfate-labelling experiments suggested that APP is cleaved by APP secretase intracellularly in the trans-Golgi network (TGN) or in a post-Golgi compartment.

Human amyloid precursor protein ameliorates behavioral deficit of flies deleted for Appl gene

Drosophila amyloid precursor protein-like (Appl) gene encodes a protein product (APPL) similar to beta-amyloid precursor protein (APP) associated with Alzheimer's disease. To understand the in vivo function of APPL protein, we have generated flies deleted for the Appl gene. These flies are viable, fertile, and morphologically normal, yet they exhibit subtle behavioral deficits. We show that a fast phototaxis defect in Appl- flies is partially rescued by transgenes expressing the wild-type, but not a mutant, APPL protein. We further demonstrate a functional homology between APPL and APP, since transgenes expressing human APP show a similar level of rescue as transgenes expressing fly APPL.

Beta-amyloid precursor protein isoforms in various rat brain regions and during brain development

To address the question of the possible functions of different Alzheimer's disease beta-amyloid precursor protein (beta-APP) isoforms in the brain, we studied their expression at different times during postnatal rat brain development and in various regions of the adult rat brain. Polyclonal antibodies directed to two peptide antigens were used. The majority of all beta-APP forms was found to be soluble as revealed by western blot analysis. The highest level of most beta-APP forms was reached in the second postnatal week, which is the time of brain maturation and completion of synaptic connections. Strikingly high concentrations of the Kunitz protease inhibitor-containing beta-APP were present in the adult olfactory bulb, where continuous synaptogenesis occurs in the adult animal. These findings support the idea of an involvement of beta-APPs in the processes of cell differentiation and, probably, in the establishment of synaptic contacts.

Changes in acetylcholinesterase and butyrylcholinesterase in Alzheimer's disease resemble embryonic development--a study of molecular forms

The pattern of molecular forms of acetylcholinesterase (AChE, EC 3.1.1.7) and butyrylcholinesterase (BChE, EC 3.1.1.8) separated by density gradient centrifugation was investigated in the brain and cerebrospinal fluid in Alzheimer's disease (AD), in human embryonic brain and in rat brain after experimental cholinergic deafferentation of the cerebral cortex. While a selective loss of the AChE G4 form was a rather constant finding in AD, a small but significant increase of G1 for both AChE and BChE was found in the most severely affected cases. Both in normal human brain and in AD a significant relationship could be established between the AChE G4/G1 ratio in different brain regions and the activity of choline acetyltransferase (ChAT). A similar decrease of the AChE G4 form as observed in AD can be induced in rat by experimental cholinergic deafferentation of the cerebral cortex. The increase in G1 of both AChE and BChE in different brain regions in AD is quantitatively related to the local density of neuritic plaques which are histochemically reactive for both enzymes. In human embryonic brain, a high abundance of G1 and a low G4/G1 ratio for both AChE and BChE was found resembling the pattern observed in AD. Furthermore, both in embryonic brain and in AD AChE shows no substrate inhibition which is a constant feature of the enzyme in the adult human brain. It is, therefore, concluded that the degeneration of the cholinergic cortical afferentation in AD as reflected by a decrease of AChE G4 is accompanied by the process of a neuritic sprouting response involved in plaque formation which is probably associated with the expression of a developmental form of the enzyme.

Human brain beta A4 amyloid protein precursor of Alzheimer's disease: purification and partial characterization

The major component of the amyloid deposition that characterizes Alzheimer's disease is the 4-kDa beta A4 protein, which is derived from a much larger amyloid protein precursor (APP). A procedure for the complete purification of APP from human brain is described. The same amino terminal sequence of APP was found in two patients with Alzheimer's disease and one control subject. Two major forms of APP were identified in human brain with apparent molecular masses of 100-110 kDa and 120-130 kDa. Soluble and membrane fractions of brain contained nearly equal amounts of APP in both humans and rats. Immunoprecipitation with carboxyl terminus-directed antibodies indicates that the soluble forms of APP are truncated. Carboxyl terminus truncation of membrane-associated forms of human brain APP was also found to occur during postmortem autolysis. The availability of purified human brain APP will facilitate the investigation of its normal function and the events that lead to its abnormal cleavage in patients with Alzheimer's disease.

Axonal sprouting induced in the sciatic nerve by the amyloid precursor protein (APP) and other antiproteases

Protease inhibition is the mechanism by which some trophic factors promote the extension of neurites. In the rat sciatic nerve, we assessed the ability to induce sprouts of the APP isoform that embodies the Kunitz antiprotease domain and other antiproteases. With the electron microscope, axonal sprouts were found when antiproteases were supplied but not after administration of inactive substances. We conclude that axons have a drive to sprout which can be released by the unbalance of an extracellular protease-antiprotease system. We propose that this system is involved in the pathogenesis of Alzheimer's disease.

A calcium-stimulated serine protease from monkey brain degrades the beta-amyloid precursor protein

Amyloid deposition, a histopathological feature of Alzheimer's disease brain, may be the underlying cause of this disease. The isolation of enzymes involved in both the normal and aberrant or alternative processing of the beta-amyloid precursor protein may lead to an understanding of how beta-protein, the major component of amyloid deposits, is formed in the brain parenchyma and vasculature of Alzheimer's disease patients and aged humans. As the same kind of deposits is also found in aged primates, the use of primates will undoubtedly help to understand the mechanisms of amyloid deposition, both spatially and temporally. Here we report the partial purification from adult monkey brain of a calcium-activated serine protease that is immunoreactive with antibodies against cathepsin G and is potentially involved in the abnormal degradation of the beta-amyloid precursor protein. Moreover, immunoreactivity with cathepsin G antibodies was localised to astrocytes in both adult and aged monkey cortex, suggesting that our protease may be expressed in astrocytes.

Molecular and cellular biology of Alzheimer amyloid

Alzheimer's Disease (AD), a disorder of unknown etiology, is the most common form of adult-onset dementia and is characterized by severe intellectual deterioration. The definitive diagnosis of AD is made by postmortem examination of the brain, which reveals large quantities of neurofibrillary tangles (NFT) and senile plaques within the parenchyma. The NFT are composed of paired helical filaments associated with several cytoskeletal proteins. The primary protein component of senile plaques is beta/A4 amyloid, a 42-43 amino acid peptide derived from a much larger molecule, the amyloid precursor protein (APP). Vascular beta/A4 amyloidosis is also prevalent in the disease. The mechanism by which beta/A4 amyloid accumulates in the AD brain is unknown. Recent research has demonstrated that the precursor molecule, APP, is a transmembrane protein with a large extracytoplasmic domain, a membrane spanning region that includes the portion that gives rise to beta/A4 amyloid, and a short intracytoplasmic domain. The precursor has multiple forms among which are those that differ by a variable length insert within the extracytoplasmic domain. The insert has sequence homology to the family of Kunitz protease inhibitor proteins. Cellular and animal models have been developed to study the nature of APP processing and the biological and behavioral consequences of beta/A4 amyloidosis. The results of such studies indicate that the normal processing of APP involves enzymatic cleavage of the molecule within the beta/A4 amyloid region, thus preventing the accumulation of beta/A4 in the normal brain. The factors leading to abnormal processing of APP, and consequent beta/A4 amyloid accumulation within the AD brain, have yet to be identified. In cell culture, the biological effects associated with beta/A4 amyloid include neurotrophic and neurotoxic activities, while the peptide has also been shown to have dramatic behavioral effects in animal models.

A novel correlation between the levels of beta-amyloid protein precursor and tau transcripts in the aged human brain

beta-Amyloid protein precursor (APP) and tau are implicated in the pathogenesis of Alzheimer's disease. We quantified the levels of APP and tau transcripts in the three cortical regions of 38 aged human brains obtained from consecutive autopsied patients. The level of APP mRNA was directly proportional to that of tau mRNA to a remarkable extent, suggesting coordinate expression of the APP and tau genes, whereas much weaker correlations were noted among mRNAs encoding other neuronal proteins. From the previous data on the differential expression of APP and tau mRNAs, the levels of APP-751 and -695 mRNAs were calculated and found to be proportional to those of four-repeat and three-repeat tau mRNAs, respectively, whereas that of APP-770 mRNA was rather constant. These results suggest that the mRNA concentrations of APP isoforms are linked to those of tau isoforms in the aged human brain.

Alzheimer's disease and hereditary cerebral hemorrhage with amyloidosis-Dutch type share a decrease in cerebrospinal fluid levels of amyloid beta-protein precursor

The amyloid beta-protein is a 39-42 amino acid peptide that is deposited in senile plaques and in cerebral vessel walls in individuals with Alzheimer's disease, Down's syndrome, hereditary cerebral hemorrhage with amyloidosis-Dutch type (HCHWA-D), and, to a much lesser extent, normal aging. It is derived from abnormal proteolytic processing of its parent protein, the amyloid beta-protein precursor. Here we show that individuals with the HCHWA-D mutation and clinically manifesting the disease have markedly decreased cerebrospinal fluid levels of soluble amyloid beta-protein precursor (0.7 +/- 0.4 micrograms/ml) compared with age-matched normal subjects (3.0 +/- 0.2 micrograms/ml) as determined by quantitative immunoblotting and enzyme-linked immunosorbent assays. Similarly, age-matched patients diagnosed with probable Alzheimer's disease also have decreased cerebrospinal fluid levels of soluble amyloid beta-protein precursor (1.0 +/- 0.3 micrograms/ml). These parallel findings suggest a common biochemical marker for these two diseases and further establish the pathogenic relatedness of HCHWA-D and Alzheimer's disease.

High level expression, purification, and characterization of the Kunitz-type protease inhibitor domain of protease nexin-2/amyloid beta-protein precursor

The protease inhibitor, protease nexin-2 (PN-2), is the secreted isoform of the Alzheimer's amyloid beta-protein precursor (A beta PP) that contains the Kunitz-type protease inhibitor (KPI) domain. Here we describe the use of the methylotrophic industrial yeast Pichia pastoris as a host system for the large scale production of the KPI domain of PN-2/A beta PP. In addition to the 57 amino acid KPI domain, the expression product contained an additional four amino acid residues at its amino terminus that correspond to amino acids 285-288 of A beta PP (Ponte et al. 1988 Nature 311:525-527). This expression system generated yields of greater than 1.0 gram of KPI domain per liter of fermentation media. The secreted 61 amino acid product was purified to homogeneity and biochemically characterized. Amino acid analysis and sequencing of the entire expressed KPI domain verified its integrity. Similar to native PN-2/A beta PP, the purified KPI domain potently inhibited trypsin, chymotrypsin, and coagulation factor XIa. Although heparin augments the inhibition of factor XIa by native PN-2/A beta PP it had no effect on the inhibition of factor XIa by expressed KPI domain suggesting that heparin binds to regions on native PN-2/A beta PP outside of the protease inhibitory domain. This KPI domain expression product should be useful in studying the physiologic and pathophysiologic functions of PN-2/A beta PP.

Beta-amyloid precursor protein cleavage by a membrane-bound protease

The principal component of amyloid plaques in Alzheimer disease is beta-amyloid protein, an approximately 4-kDa peptide derived from amyloid precursor proteins. Previous studies have established that amyloid precursor proteins are secreted after proteolytic cleavage within the beta-amyloid peptide. The present investigation documents that, in cultured cells, amyloid precursor protein is cleaved on the plasma membrane by a membrane-bound endoprotease and that the specificity of peptide bond hydrolysis is largely independent of the primary sequence of the precursor. The principal determinants of cleavage appear to be an alpha-helical conformation and the distance (12-13 residues) of the hydrolyzed bond from membrane.

The amyloid protein precursor of Alzheimer's disease is a mediator of the effects of nerve growth factor on neurite outgrowth

The beta A4 protein, the major component of the amyloid deposition characterizing Alzheimer's disease, derives from the amyloid protein precursor (APP), an integral membrane protein with soluble derivatives. The function of APP is unknown. Both soluble and membrane-associated human brain APP (10(-10) M) significantly increased (P less than 0.025) neurite length and branching in pheochromocytoma PC12 cells, but did not affect the number of neurites per cell. At higher concentrations, APP was cytotoxic, with a half-maximal concentration of 5 x 10(-9) M. Nerve growth factor (NGF) is known to affect APP expression in vivo and in vitro. Antibodies to APP specifically diminished the effects of NGF on neurite length and branching. Thus APP may act to mediate neurite outgrowth promotion by NGF.

Expression of protease nexin-II in human dorsal root ganglia. A correlative immunocytochemical and in situ hybridization study

Protease nexin-II (PN-II) is a potent chymotrypsin inhibitor that forms SDS-stable inhibitory complexes with epidermal growth factor binding protein, the gamma-subunit of nerve growth factor, and trypsin, and represents the secreted form of the amyloid beta-protein precursor (APP) that contains the Kunitz-type protease inhibitor domain. To determine the expression of PN-II within the peripheral nervous system, human dorsal root ganglia were processed for immunocytochemistry using well-characterized monoclonal antibodies against PN-II and for in situ hybridization studies using 35S-RNA PN-II probes for both APP751 and APP770. Highly specific immunoperoxidase staining of PN-II was demonstrated within the cytoplasm of dorsal root ganglia neurons and their processes in cryostat (fresh frozen) and vibratome (paraformaldehyde-fixed) sections. In situ hybridization using an anti-sense 35S-RNA PN-II probe demonstrated the presence of intense neuronal labeling. Labeling was not observed when the corresponding sense 35S-RNA PN-II probe was used. Although the precise functional role of PN-II/APP is not clear, the accumulation of amyloid beta-protein within the neuropil appears to be one of the earliest events in the pathogenesis of Alzheimer's disease (AD). Thus knowledge of the cell populations expressing the PN-II/APP gene would certainly be helpful for studies of the molecular mechanisms leading to the morphological and functional changes of AD. The results of this study clearly establish the expression of PN-II and its mRNA within the dorsal root ganglia neurons and their processes, and provide another point of departure for studies of the molecular mechanisms underlying the deposition of amyloid beta-protein and its relationships to the formation of neuritic plaques and neurofibrillary tangles.

Aggregation of the amyloid precursor protein within degenerating neurons and dystrophic neurites in Alzheimer's disease

Using a monoclonal antibody raised against purified, native, human protease nexin-2/amyloid precursor protein, which recognizes an amino terminal epitope on the amyloid precursor protein and detects all major isoforms of amyloid precursor protein, we examined the localization of the amyloid precursor protein within Alzheimer's and aged control brains. Very light cytoplasmic neuronal amyloid precursor protein staining but no neuritic staining was visible in control brains. In the Alzheimer's brain, we detected numerous amyloid precursor protein-immunopositive neurons with moderate to strong staining in select regions. Many neurons also contained varying levels of discrete granular, intracellular accumulations of amyloid precursor protein, and a few pyramidal neurons in particular appeared completely filled with amyloid precursor protein granules. "Ghost"-like deposits of amyloid precursor protein granules arranged in pyramidal, plaque-like shapes were identified. We detected long, amyloid precursor protein-immunopositive neurites surrounding and entering plaques. Many contained swollen varicosities along their length or ended in bulbous tips. Amyloid precursor protein immunoreactivity in the Alzheimer's brain was primarily present as granular deposits (plaques). The amyloid precursor protein granules do not appear to co-localize within either astrocytes or microglia, as evidenced by double-labeling immunohistochemistry with anti-glial fibrillary acidic protein and anti-leukocyte common antigen antibodies or Rinucus cummunicus agglutin lectin. Amyloid precursor protein could occasionally be detected in blood vessels in Alzheimer's brains. The predominantly neuronal and neuritic localization of amyloid precursor protein immunoreactivity indicates a neuronal source for much of the amyloid precursor protein observed in Alzheimer's disease pathology, and suggests a time-course of plaque development beginning with neuronal amyloid precursor protein accumulation, then deposition into the extracellular space, subsequent processing by astrocytes or microglia, and resulting in beta-amyloid peptide accumulation in plaques.

Detection of distinct isoform patterns of the beta-amyloid precursor protein in human platelets and lymphocytes

Cerebral deposition of the amyloid beta-protein (A beta P), approximately 40 residue fragment of the integral membrane protein, beta-amyloid precursor protein (beta APP), has been implicated as the probable cause of some cases of familial Alzheimer's disease (AD). The parallels between A beta P deposition in AD and the deposition of certain plasma proteins in systemic amyloid diseases has heightened interest in the analysis of beta APP in circulating cells and plasma. Here, we describe distinct isoform patterns of beta APP in peripheral platelets and lymphocytes. PCR-mediated amplification of mRNA from purified platelets demonstrated the expression of all three major beta APP transcripts (beta APP770,751,695). The full-length, approximately 140 kDa form of beta APP751,770 was detected in membranes of resting and activated platelets but very little immature, approximately 122 kDa beta APP751,770 was found, suggesting a different processing of beta APP in platelets than that described in a variety of cultured cells and tissues. Platelets stimulated with thrombin, calcium ionophore, or collagen released the soluble, carboxyl-truncated form of beta APP (protease nexin-II), but no evidence for the shedding of full-length beta APP associated with platelet microparticles was found, in contrast to previous reports. As a positive control marker for microparticles, the fibrinogen receptor subunit, GPIIIa, was readily detected in platelet releasates. Resting and activated platelets contained similar amounts of the approximately 10 kDa carboxyl terminal beta APP fragment that is retained in platelet membranes following the constitutive cleavage of protease nexin-II. Nonstimulated peripheral B and T lymphocytes contained small amounts of membrane-associated mature and immature beta APP751,770. The potentially amyloidogenic full-length beta APP molecules present in circulating platelets and lymphocytes but not in microparticles could serve as a source of the microvascular A beta P deposited during aging and particularly in AD.

Epitope map of two polyclonal antibodies that recognize amyloid lesions in patients with Alzheimer's disease

Two synthetic peptides with sequences identical with those of fragments of the extracellular domain of the Alzheimer's-disease amyloid precursor protein (APP) were used to raise antibodies. SP28 comprises positions 597-624 of the APP695 isoform, whereas SP41 extends towards the N-terminus (amino acids 584-624) and contains the entire SP28 peptide. Using e.l.i.s.a. and inhibition experiments we identified the two beta-turn-containing segments 602-607 and 617-624 as the epitopes recognized by anti-SP41 and anti-SP28 respectively. Both antibodies immunolabelled amyloid lesions in brains from Alzheimer's-disease patients and patients with related disorders, whereas they were unreactive in control brains. However, when probed on immunoblots, anti-SP28 failed to detect full-length APP from baculovirus-infected Sf9 cells, and anti-SP41 reacted weakly compared with other anti-APP antisera. The data suggest that these antibodies are directed to conformational epitopes not existent in the native molecules but present after alternative APP processing.

Protein phosphorylation regulates secretion of Alzheimer beta/A4 amyloid precursor protein

Extracellular deposition of the beta/A4 amyloid peptide is a characteristic feature of the brain in patients with Alzheimer disease. beta/A4 amyloid is derived from the amyloid precursor protein (APP), an integral membrane protein that exists as three major isoforms (APP695, APP751, and APP770). Secreted forms of APP found in blood plasma and cerebrospinal fluid arise by proteolytic cleavage of APP within the beta/A4 amyloid domain, precluding the possibility of amyloidogenesis for that population of molecules. In the present study, we have demonstrated that treatment of PC12 cells with phorbol ester produces a severalfold increase in secretion of APP695, APP751, and APP770. This increase is augmented by simultaneous treatment with the protein phosphatase inhibitor okadaic acid. These data indicate that protein phosphorylation regulates intra-beta/A4 amyloid cleavage and APP secretion. These and other results suggest that APP molecules can normally follow either of two processing pathways: regulated secretion or proteolytic degradation unassociated with secretion.

Arginine specific endopeptidases modify the aggregation properties of a synthetic peptide derived from Alzheimer beta/A4 amyloid

A synthetic peptide corresponding to the first 28 amino acids of the Alzheimer disease amyloid beta/A4 peptide (3.2 kDa) aggregated to a high molecular weight (15 kDa) on SDS/urea polyacrylamide gels. Proteinase K, V8 protease, trypsin, and endopeptidase Lys-C readily degraded the aggregate. By contrast, when digested by endopeptidase Arg-C, a new polypeptide aggregate of higher molecular weight (16 kDa) was observed on denaturing gels without degraded smaller products. The new aggregate was comprised of three peptides: an intact beta/A4(1-28) and partially degraded peptides beta/A4(1-5) plus beta/A4(6-28). The results were confirmed by treatment of beta/A4 with other arginine-specific proteases: the gamma subunit of nerve growth factor and clostripain. The results indicate that arginine-specific proteases, including a growth factor processing enzyme, can nick aggregated beta/A4(1-28) amyloid and alter the configuration to produce a more complex aggregated form. If similar highly specific proteolytic mechanisms occur in the Alzheimer disease brain, the processing may promote the formation of high molecular weight aggregates that contribute to the development of relatively insoluble senile plaque core protein.

Role of amyloid precursor protein (APP): study with antisense transfection of human neuroblastoma cells

The function of amyloid precursor protein (APP) was investigated in human neuroblastoma La-N-1 cells by stable transfection with a DNA construct encoding antisense APP mRNA. Levels of APP mRNA, as well as proteins, were reduced by 80-90% in antisense APP transfected (ASAT) cells. ASAT cells exhibited three main features as a result of APP gene expression deprivation: (1) a 30% reduction in cell proliferation, (2) reduced cell adhesion that could be reversed by the addition of La-N-1 conditioned media as a source of secreted APP, and (3) a two- and four-fold increase in neurite-bearing cells suggesting that cellular APP may be involved in neurite extension. The first two features confirm previously reported functions for APP in proliferation and adhesion of non-neuronal cell types but the use of neuroblastoma cells in this study disclose a novel role for cellular APP in neurite extension.

Decreased levels of soluble amyloid beta-protein precursor in cerebrospinal fluid of live Alzheimer disease patients

The amyloid beta-protein is deposited in senile plaques and the cerebrovasculature in Alzheimer disease (AD). Since it is derived from proteolytic processing of its parent protein, the amyloid beta-protein precursor (APP), we investigated whether levels of the secreted forms of APP are altered in cerebrospinal fluid (CSF) of AD patients. Quantitative immunoblotting studies with the anti-APP monoclonal antibody P2-1 revealed that probable AD patients had markedly lower CSF APP levels than did demented non-Alzheimer-type patients and healthy control subjects. Using antibody P2-1 in an enzyme-linked immunosorbent assay, we measured CSF levels of APP in a larger population consisting of 13 patients diagnosed with probable AD, 18 patients diagnosed with dementia (non-Alzheimer type), and 16 nondemented, healthy controls. Mean CSF levels of APP were approximately 3.5-fold lower in the live patients diagnosed with probable AD compared to the demented non-Alzheimer-type controls or the nondemented, healthy individuals. These findings suggest that abnormal metabolism of APP is reflected in the extracellular fluids of the central nervous system and that CSF levels of soluble APP provide a useful biochemical marker to assist in the clinical diagnosis of AD.

Regulated splicing of the amyloid precursor protein gene during postnatal development of the rat basal forebrain

The expression of the amyloid precursor protein (APP) gene has been examined in the basal forebrain of rats from birth to adulthood. Levels of total APP mRNA are highest at birth and at postnatal day 15 (P15). The most abundant transcript in rat brain is APP-695, whose expression has previously been found to be largely restricted to the central nervous system. Comparison of the developmental profiles of APP-695 mRNA with that of Kunitz-protease inhibitor (KPI)-containing APP mRNA shows that the greatest difference in expression occurs at P15, when APP-695 message levels are over 6-fold higher than KPI-containing APP mRNA (APP-751, APP-770). This is the largest difference in the APP-695/KPI-APP ratio observed during postnatal development and coincides with the period of maximal neurotrophic responsiveness in the basal forebrain. These results suggest that the APP gene is alternatively spliced during postnatal development and that regulated expression of APP-695 may be influenced by neurotrophic factors in vivo.

Localization of amyloid precursor protein in GAP43-immunoreactive aberrant sprouting neurites in Alzheimer's disease

Previous in vitro studies have suggested that amyloid precursor protein (APP) could be involved in cell surface adhesion, neuritic growth and survival of hippocampal neurons. In the present study, involvement of APP in aberrant sprouting in Alzheimer's disease (AD) was studied by comparing immunolabeling patterns of anti-APP and anti-growth-associated protein 43 (anti-GAP43). Confocal laser imaging of frontal cortex sections double-immunolabeled for APP and GAP43 showed an increase, in AD, of presynaptic boutons immunostained with anti-GAP43 that contained anti-APP immunoreactivity. The neuritic plaques in AD cases presented intense anti-GAP43 immunoreactive abnormal neurites colocalized with anti-APP. Three-dimensional reconstruction of the plaques showed that anti-APP was colocalized with anti-GAP43 in 57.5% of the aberrant sprouting neurites. We conclude that co-expression of APP with GAP43 in the plaque might be involved in the aberrant sprouting response observed in AD.