A specific structural interaction of Alzheimer's peptide A beta 1-42 with alpha 1-antichymotrypsin

Extracellular protein components of amyloid plaques and their roles in Alzheimer's disease pathology

Alzheimer's disease (AD) is pathologically defined by the presence of fibrillar amyloid β (Aβ) peptide in extracellular senile plaques and tau filaments in intracellular neurofibrillary tangles. Extensive research has focused on understanding the assembly mechanisms and neurotoxic effects of Aβ during the last decades but still we only have a brief understanding of the disease associated biological processes. This review highlights the many other constituents that, beside Aβ, are accumulated in the plaques, with the focus on extracellular proteins. All living organisms rely on a delicate network of protein functionality. Deposition of significant amounts of certain proteins in insoluble inclusions will unquestionably lead to disturbances in the network, which may contribute to AD and copathology. This paper provide a comprehensive overview of extracellular proteins that have been shown to interact with Aβ and a discussion of their potential roles in AD pathology. Methods that can expand the knowledge about how the proteins are incorporated in plaques are described. Top-down methods to analyze post-mortem tissue and bottom-up approaches with the potential to provide molecular insights on the organization of plaque-like particles are compared. Finally, a network analysis of Aβ-interacting partners with enriched functional and structural key words is presented.

Polymorphic SERPINA3 prolongs oligomeric state of amyloid beta

Molecular chaperon SERPINA3 colocalizes with accumulated amyloid peptide in Alzheimer’s disease (AD) patient’s brain. From the QTL analysis, we narrowed down Serpina3 with two SNPs in senescence-accelerated mouse prone (SAMP) 8 strain. Our study showed SAMP8 type Serpina3 prolonged retention of oligomeric Aβ 42 for longer duration (72 hr) while observing under transmission electron microscope (TEM). From Western blot results, we confirmed presence of Aβ 42 oligomeric forms (trimers, tetramers) were maintained for longer duration only in the presences of SAMP8 type Serpina3. Using SH-SY5Y neuroblastoma cell line, we observed until 36 hr preincubated Aβ 42 with SAMP8 type Serpina3 caused neuronal cell death compared to 12 hr preincubated Aβ 42 with SAMR1 or JF1 type Serpina3 proteins. Similar results were found by extending this study to analyze the effect of polymorphism of SERPINA3 gene of the Japanese SNP database for geriatric research (JG-SNP). We observed that polymorphic SERPINA3 I308T (rs142398813) prolonged toxic oligomeric Aβ 42 forms till 48 hr in comparison to the presence wild type SERPINA3 protein, resulting neuronal cell death. From this study, we first clarified pathogenic regulatory role of polymorphic SERPINA3 in neurodegeneration.

Two β-strands of RAGE participate in the recognition and transport of amyloid-β peptide across the blood brain barrier

Amyloid-β (Aβ) peptide is central to the development of brain pathology in Alzheimer disease (AD) patients. Association with receptors for advanced glycation end-products (RAGE) enables the transport of Aβ peptide from circulating blood to human brain, and also causes the activation of the NF-κB signaling pathway. Here we show that two β-strands of RAGE participate in the interaction with Aβ peptide. Serial deletion analysis of the RAGE V domain indicates that the third and eighth β-strands are required for interaction with Aβ peptide. Site-directed mutagenesis of amino acids located in the third and eighth β-strands abolish the interaction of RAGE with Aβ peptide. Wild-type RAGE activates the NF-κB signaling pathway in response to Aβ peptide treatment, while a RAGE mutant defective in Aβ binding does not. Furthermore, use of peptide for the third β-strand or a RAGE monoclonal antibody that targets the RAGE-Aβ interaction interface inhibited transport of the Aβ peptide across the blood brain barrier in a mice model. These results provide information crucial to the development of RAGE-derived therapeutic reagents for Alzheimer disease.

Inhibition of heat- and chemical-induced aggregation of various proteins reveals chaperone-like activity of the acute-phase component and serine protease inhibitor human alpha(1)-antitrypsin

In vitro chaperone-like activity of the serpin family member and plasma acute-phase component human alpha(1)-antitrypsin (AAT) has been shown for the first time. Results of light-scattering experiments demonstrated that AAT efficiently inhibits both heat- and chemical-induced aggregation of various test proteins including alcohol dehydrogenase, aldolase, carbonic anhydrase, catalase, citrate synthase, enolase, glutathione S-transferase, l-lactate dehydrogenase, and beta(L)-crystallin. The results suggest that the unique metastable serpin architecture enables dual function, protease inhibiton as well as chaperone activity and highlight the serpin superfamily as a possible source of additional intra- and extracellular chaperones (e.g. alpha(1)-antichymotrypsin). The present finding is surprising in the light of the well-known role of mutated forms of AAT and other serpins in the pathogenesis of diseases called serpinopathies that featured with aberrant conformational transitions and consequent self-aggregation of serpin proteins.

A SNP in the ACT gene associated with astrocytosis and rapid cognitive decline in AD

There is biochemical and animal model evidence supporting a pathological role of the ACT gene in AD. However, direct genetic evidence remains controversial and has been mostly limited to individual single nucleotide polymorphism (SNP) analysis. To resolve this apparent conflict we have used a high-density ACT SNP map, constructed haplotypes and explored correlations with phenotype. SNPs were identified by sequencing and used to construct haplotypes in 668 AD patients and 419 controls and a case-control association study was performed. Five SNPs, comprising five common haplotypes, represented 93% of ACT gene variation. Although no single SNP or haplotype was associated with AD status, a SNP in intron 2 was associated with later onset and more rapid cognitive decline (P=0.04). This SNP was both individually associated with severe astrocytosis (P=0.004) in AD patients and when combined with the signal sequence SNP (P=0.002). This suggests that astrocytosis may have a protective function for a limited period in some patients. These SNP associations either support a direct role for the ACT gene, in AD pathology or alternatively reflect linkage with polymorphisms in other genes nearby.

Plasma and CSF serpins in Alzheimer disease and dementia with Lewy bodies

OBJECTIVE

Serine protease inhibitors (serpins), the acute phase reactants and regulators of the proteolytic processing of proteins, have been recognized as potential contributors to the pathogenesis of Alzheimer disease (AD). We measured plasma and CSF levels of serpins in controls and patients with dementia.

METHODS

Using rocket immunoelectrophoresis, ELISA, and Luminex xMAP technology, we analyzed plasma levels of alpha(1)-antichymotrypsin and alpha(1)-antitrypsin, and CSF levels of alpha(1)-antichymotrypsin, alpha(1)-antitrypsin, and neuroserpin along with three standard biomarkers (total tau, tau phosphorylated at threonine-181, and the A beta(1-42)) in patients with AD (n = 258), patients with dementia with Lewy bodies (DLB; n = 38), and age-matched controls (n = 37).

RESULTS

The level of CSF neuroserpin was significantly higher in AD compared with controls and DLB, whereas CSF alpha(1)-antichymotrypsin and alpha(1)-antitrypsin were significantly higher in both AD and DLB groups than in controls. Results from logistic regression analyses demonstrate a relationship between higher CSF levels of alpha(1)-antichymotrypsin and neuroserpin and increased predicted probability and odds ratios (ORs) of AD (OR 5.3, 95% CI 1.3 to 20.8 and OR 3.3, CI 1.3 to 8.8). Furthermore, a logistic regression model based on CSF alpha(1)-antichymotrypsin, neuroserpin, and A beta(1-42) enabled us to discriminate between AD patients and controls with a sensitivity of 94.7% and a specificity of 77.8%.

CONCLUSIONS

Higher CSF levels of neuroserpin and alpha(1)-antichymotrypsin were associated with the clinical diagnosis of Alzheimer disease (AD) and facilitated the diagnostic classification of AD vs controls. CSF serpin levels did not improve the diagnostic classification of AD vs dementia with Lewy bodies.

Serpin Acceleration of Amyloid Fibril Formation: A Role for Accessory Proteins

Protein aggregation underlies an increasing number of human diseases. Recent experiments have shown that the aggregation reaction is exquisitely specific involving particular interactions between non-native proteins. However, aggregation of certain proteins, for example beta-amyloid, in vivo leads to the recruitment of other proteins into the aggregate. Antichymotrypsin, a non-fibril forming protein, is always observed to be associated with beta-amyloid plaques in Alzheimer's sufferers. The role of antichymotrypsin is controversial with studies showing it can either accelerate or inhibit the aggregation reaction. To investigate the role of antichymotrypsin in fibrillogenesis we have studied its interaction with apolipoprotein C-II, a well characterized model system for the study of fibrillogenesis. Our data demonstrate that sub-stoichiometric amounts of antichymotrypsin and its alternate structural forms can dramatically accelerate the aggregation of apolipoprotein C-II, whereas the presence of alpha(1)-antitrypsin, a structural homologue of antichymotrypsin, cannot. Sedimentation velocity experiments show more apolipoprotein C-II fibrils were formed in the presence of antichymotrypsin. Using pull-down assays and immuno-gold labeling we demonstrate an interaction between antichymotrypsin and apolipoprotein C-II fibrils that specifically occurs during fibrillogenesis. Taken together these data demonstrate an interaction between antichymotrypsin and apolipoprotein C-II that accelerates fibrillogenesis and indicates a specific role for accessory proteins in protein aggregation.

Molecular chaperons, amyloid and preamyloid lesions in the BRI2 gene-related dementias: a morphological study

Molecular chaperons or amyloid-associated proteins (AAPs) are deposited in vascular and parenchymal amyloid lesions in Alzheimer's disease (AD) and other amyloidoses. AAPs, such as apolipoprotein E (ApoE) or apolipoprotein J (ApoJ) have been strongly implicated in the pathogenesis of AD in vitro and in vivo. Furthermore the possession of the ApoE in4 allele is a well-studied risk factor for AD. In view of the similarities between AD and both familial British dementia (FBD) and familial Danish dementia (FDD), we investigated the presence of AAPs in these two diseases to understand better their role in the general process of amyloidogenesis. Immunohistochemistry for ApoE, ApoJ, serum amyloid P (SAP), alpha-1-antichymotrypsin, cystatin C, heparan sulphate proteoglycans, such as agrin, perlecan, syndecans, glypican-1 and for heparan sulphate glycosaminoglycan (HS GAG) side chains was carried out together with immunohistochemical preparations specific to the amyloid subunits. Significant or extensive staining for ApoE, ApoJ, agrin, glypican-1 and HS GAG side chains was found in both amyloid (fibrillar) and preamyloid (nonfibrillar) deposits in FBD and FDD. The remaining AAPs, including SAP, were predominantly found in amyloid lesions. Only very weak staining was present in a small proportion of the amyloid lesions using perlecan immunohistochemistry. These findings suggest that the deposition patterns of AAPs in FBD and FDD are mostly similar to those in AD. The presence of AAPs in the preamyloid lesions supports the notion that chaperon molecules may play a role in the early steps of fibrillogenesis.

Modification of estrone at the 6, 16, and 17 positions: novel potent inhibitors of 17beta-hydroxysteroid dehydrogenase type 1

The 17beta-hydroxysteroid dehydrogenases (17beta-HSDs) catalyze the interconversion between the oxidized and reduced forms of androgens and estrogens at the 17 position. The 17beta-HSD type 1 enzyme (17beta-HSD1) catalyzes the reduction of estrone to estradiol and is expressed in malignant breast cells. Inhibitors of this enzyme thus have potential as treatments for hormone dependent breast cancer. Here we report the syntheses and biological evaluation of novel inhibitors based on the estrone or estradiol template. These have been investigated by modification at the 6, 16 or 17 positions or combinations of these in order to gain information about structure-activity relationships by probing different areas in the enzyme active site. Activity data have been incorporated into a QSAR with predictive power, and the X-ray crystal structures of compounds 15 and 16c have been determined. Compound 15 has an IC50 of 320 nM for 17beta-HSD1 and is selective for 17beta-HSD1 over 17beta-HSD2. Three libraries of amides are also reported that led to the identification of inhibitors 19e and 20a, which have IC50 values of 510 and 380 nM respectively, and 20 h which, having an IC50 value of 37 nM, is the most potent inhibitor of 17beta-HSD1 reported to date. These amides are also selective for 17beta-HSD1 over 17beta-HSD2.

Effects of Alzheimer's peptide and alpha1-antichymotrypsin on astrocyte gene expression

We employed gene array technology to investigate the effects of alpha1-antichymotrypsin (ACT), soluble or fibrillar Alzheimer's peptide (Abeta(1-42)) alone and the combination of ACT/Abeta(1-42) on human astrocytes. Using a 1.2-fold change as significance threshold, 398 astrocyte genes showed altered expression in response to these treatments compared to controls. Of the 276 genes affected by the ACT/soluble Abeta(1-42) combination, 195 (70.6%) were suppressed. The ACT/fibrillar Abeta(1-42) combination affected expression of 64 genes of which 58 (90.5%) were up-regulated. The most prominent gene expression changes in response to the ACT/soluble Abeta(1-42), were the down-regulation of at least 60 genes involved in transcription, signal transduction, apoptosis and neurogenesis. The ACT/fibril Abeta(1-42) increased the expression of genes involved in transcription regulation and signal transduction. Surprisingly, gene expression of astrocytes exposed to soluble or fibrillar Abeta(1-42) alone was largely unaffected. Thus, the molecular forms generated by the combination of ACT/Abeta(1-42) alter expression of astrocyte genes more profoundly in breadth and magnitude than soluble or fibrillar Abeta(1-42) alone, suggesting that pathogenic effects of Abeta(1-42) may occur as a consequence of its association with other proteins.

Estradiol−Adenosine Hybrid Compounds Designed to Inhibit Type 1 17β-Hydroxysteroid Dehydrogenase

The steroidogenic enzyme type 1 17beta-hydroxysteroid dehydrogenase (17beta-HSD) is involved in the synthesis of estradiol (E(2)), a hormone well-known to stimulate the growth of estrogen-sensitive tumors. To obtain compounds able to control E(2) formation, two moieties were linked with a methylene side chain: an adenosine moiety for interacting with the cofactor-binding site and an E(2) moiety for interacting with the substrate-binding site. When tested as inhibitors of type 1 17beta-HSD, the hybrid compounds inhibited the reductive activity (E(1) into E(2)) with IC(50) values ranging from 52 to 1,000 nM. The optimal side-chain length was determined to be eight methylene groups for a 16 beta-orientation. The presence of two components (E(2) and adenosine) is essential for good inhibition, since 16 beta-nonyl-E(2) and 5-nonanoyl-O-adenosine, two compounds having only one of the components, did not inhibit the enzyme. Moreover, the 3D-structure analysis of EM-1,745 complexed with type 1 17beta-HSD showed key interactions with both substrate- and cofactor-binding sites.

Novel and potent 17beta-hydroxysteroid dehydrogenase type 1 inhibitors

Structure-based drug design using the crystal structure of human 17beta-hydroxysteroid dehydrogenase type 1 (17beta-HSD1) led to the discovery of novel, selective, and the most potent inhibitors of 17beta-HSD1 reported to date. Compounds 1 and 2 contain a side chain with an m-pyridylmethyl-amide functionality extended from the 16beta position of a steroid scaffold. A mode of binding is proposed for these inhibitors, and 2 is a steroid-based 17beta-HSD1 inhibitor with the potential for further development.

Synthesis of Simplified Hybrid Inhibitors of Type 1 17β-Hydroxysteroid Dehydrogenase via Cross-Metathesis and Sonogashira Coupling Reactions

[structure: see text] The inhibitor of type 1 17beta-hydroxysteroid dehydrogenase EM-1745 (1) exhibits affinity for both the substrate (estrone or estradiol) and the cofactor (NAD(P)H) binding domains. However, to increase its bioavailability, this compound needs to be simplified. The efficient and convergent synthesis of simplified substrate/cofactor hybrid inhibitors (compounds 2) involving a cross-metathesis and a Sonogashira coupling reaction as key steps is described. Compounds 2a-c were also tested as enzyme inhibitors and compared to EM-1745.

[BIG-H3 protein: mutation of codon 124 and corneal amyloidosis]

In 1997, a group of hereditary corneal dystrophies was related to mutations in the TGFBI (BIGH3) gene. Within this group, some corneal dystrophies present particular biochemical features in that they are characterized by corneal amyloid deposition. Contrary to clinical and genetic knowledge, the biochemical characteristics of the encoded protein (Big-h3) and the mechanisms of its amyloid conversion remain unclear. We review the current knowledge on the Big-h3 protein and focus on the behavior of the codon 124 region. We discuss this protein's mechanisms of amyloid conversion from our results and previous reports as well as from other types of amyloidosis. These data provide a better understanding of the putative processes leading to the phenotypic variations linked with their respective codon 124 mutation.

Amyloid precursor protein (APP) and the biology of proteolytic processing: relevance to Alzheimer's disease

The processing of amyloid precursor protein (APP) generates amyloid-beta (Abeta) peptides 1-40 and 1-42. The latter is neurotoxic and its accumulation results in amyloid fibril formation and the generation of senile plaques, the hallmark of Alzheimer's disease (AD). Whilst there has been considerable progress made in understanding the generation of Abeta by alpha-, beta- and gamma-secretase activity on APP, recently enzymes involved in the degradation of Abeta have been identified including neprilysin and insulin-degrading enzyme (IDE). We review the pathways involved in proteolytic processing of APP and discuss the potential implications of aberrant proteolysis on neurodegeneration. It is conceivable that single nucleotide polymorphisms (SNPs) in the regulatory regions of genes in these proteolytic cascades, which alter their expression, could contribute to some of the age-related changes seen in AD.

Alzheimer's peptide and serine proteinase inhibitors in glaucoma and exfoliation syndrome

The occurrence of inflammation with accompanying amyloid formation in pseudoexfoliation syndrome (PEX) resembles other inflammation-associated amyloidoses such as Alzheimer's disease (AD). To test whether the same proteins can be identified in PEX as in AD, we qualitatively analysed for Alzheimer's peptide (Abeta1-42) and the proteinase inhibitors alpha1-antichymotrypsin (ACT) and alpha-antitrypsin (AAT) in the aqueous humor of patients with and without PEX material. Ninety aqueous humor samples were collected from patients in the age group between 46 and 95 during cataract surgery. Protein profiles in samples were analysed by electrophoresis followed by Western blotting. Blots were developed using specific antibodies against Abeta1-42, AAT and ACT and peroxidase-conjugated IgG as a second antibody. At least one of the analysed proteins was found in 68.8% of 90 cases studied. Abeta1-42 peptide was found in 22.2% of all cases, among them in seven cases with PEX (total n =16) and in four with glaucoma (total n = 10). ACT and AAT were detected in 17.8 and 28.9% of all cases, respectively. In addition, female patients had significantly higher frequencies of detected ACT and AAT, compared to males. Abeta1-42, ACT and AAT were also found in 17.6, 14.7 and 23.5% of the control (non-XF and non-glaucoma) samples (n = 68). Alzheimer's peptide is present in the aqueous humor of patients with PEX and glaucoma suggesting that these diseases may share common features in the biochemistry and etiologies with AD. The presence of Abeta and inflammation-associated proteins in aqueous from cataract cases without detectable PEX raises the possibility that these proteins may reflect early amyloid-related changes in the eye.

Physiopathological modulators of amyloid aggregation and novel pharmacological approaches in Alzheimer's disease

The biological mechanisms underlying the neuropathology of Alzheimer's disease (AD) are complex, as several factors likely contribute to the development of the disease. Therefore, it is not surprising that a number of different possible therapeutic approaches addressing distinct aspects of this disease are currently being investigated. Among these are ways to prevent amyloid aggregation and/or deposition, to prevent neuronal degeneration, and to increase brain neurotransmitter levels. Here, we discuss possible roles of endogenous modulators of Abeta aggregation in the physiopathology of AD and some of the strategies currently under consideration to interfere with brain levels of beta-amyloid, its aggregation and neurotoxicity.

Alpha1-antichymotrypsin/Alzheimer's peptide Abeta(1-42) complex perturbs lipid metabolism and activates transcription factors PPARgamma and NFkappaB in human neuroblastoma (Kelly) cells

Amyloid-beta peptide (Abeta) and the serpin proteinase inhibitor alpha1-antichymotrypsin (ACT) are components of the amyloid plaques associated with Alzheimer's disease (AD). Abeta exists in soluble monomeric and oligomeric forms and in an insoluble polymerised fibrillar form, but it is not clear which of these plays the most important role in the etiology of AD. In vitro, Abeta(1-42) interacts with ACT, and as a result of this, ACT loses its proteinase inhibitor activity and polymerisation of Abeta(1-42) is promoted. Here we provide evidence that new molecular forms resulting from incubation of ACT with Abeta(1-42) have multiple cellular level effects on neuronal cells. The mixture of soluble Abeta and an ACT/Abeta complex formed by 2 hr incubation at a 10:1 molar ratio of Abeta:ACT strongly induce cellular proliferation and expression of transcription factors peroxisome proliferator-activated receptor-gamma (PPARgamma) and NFkappaB, and also increase uptake and depress degradation of native and oxidised low-density lipoprotein (LDL) by cells. Similar but less pronounced effects are seen when cells are exposed to the Abeta peptide alone preincubated for 2 hr. Abeta(1-42) and to a lesser extent ACT/Abeta(1-42) complex mixture prepared by 2 hr incubation both inhibit association of native LDL with cells. Neither ACT alone nor the Abeta(1-42) and ACT/Abeta(1-42) forms prepared by 24-hr incubation show any significant effects in these assays. We propose that specific molecular forms of Abeta(1-42) and ACT/Abeta(1-42) complex mixture, both dependent on the abundances of Abeta(1-42) and ACT/Abeta(1-42) in vivo and on their time of exposure to each other, have cellular effects which are important for the initiation and progression of the pathologies associated with AD.

Effect of cytokines, dexamethasone and the A/T-signal peptide polymorphism on the expression of alpha(1)-antichymotrypsin in astrocytes: significance for Alzheimer's disease

Proinflammatory cytokines and acute phase proteins, such as alpha(1)-antichymotrypsin, are over expressed in microglia and astrocytes in brain regions with abundant mature amyloid plaques, suggesting a glial cell-led brain acute phase response in the Alzheimer neuropathology. In this paper, we show that alpha(1)-antichymotrypsin gene expression in human astrocytes is elevated by interleukin-1 and interleukin-6, and further enhanced by glucocorticoid, while the homologous contrapsin gene in rat astrocytes is unaffected by these cytokines. These distinct gene regulation mechanisms might help to explain the differential susceptibility of humans and rodents to amyloid formation of the Alzheimer's type. In addition, we demonstrate that the alpha(1)-antichymotrypsin A-allele that encodes a different signal peptide and is a suggested risk factor for Alzheimer's disease gives rise to a reduced level of immature alpha(1)-antichymotrypsin in transfected cells. The physiological result would be an enhanced ability of the A-encoded alpha(1)-antichymotrypsin protein to become secreted and promote extracellular amyloid formation. We discuss our findings in terms of a model in which cytokine-induced alpha(1)-antichymotrypsin synthesis in astrocytes constitutes a specific inflammatory pathway that accelerates the development of Alzheimer's disease and could at least partly underlie the regional specificity and species restriction of the neuropathology.

A novel approach for studying endogenous abeta processing using cultured primary neurons isolated from APP transgenic mice

The central component of senile amyloid plaques in Alzheimer's disease (AD) is the beta-amyloid peptide (Abeta), derived from proteolytic processing of the amyloid precursor protein (APP). In this study, we developed an in vitro model to measure and identify soluble Abeta from primary cortical neurons. Neurons were isolated from mice transgenic for human APP695 containing the K670N, M671L double mutation. We characterized soluble Abeta using Western blot and ELISA assays. We found that the Abeta levels in conditioned media from these neurons were readily detectable and almost five times higher than in CSF. The majority of Abeta in the media was Abeta1-40; however, Abeta1-42 was also detectable. When the neurons were exposed to Phorbol 12-myristate 13-acetate (PMA), alpha1-antichymotrypsin, or alpha1-antitrypsin, the alterations of soluble Abeta levels were consistent with other models reported. Most importantly, the soluble Abeta in our model was remarkably stable, and aliquots were unchanged after prolonged incubations or repeated freeze/thaw cycles. The Abeta appeared to be monomeric by Western blot analysis. Soluble Abeta coimmunoprecipitated with endogenous mouse apolipoprotein E from the primary cultures. Taken together, our data demonstrated that using a Western blot assay to detect soluble Abeta from transgenic mouse overexpressing APP695 is sensitive, specific, and reliable and provides an accessible model for examining the neuronal metabolism of APP and Abeta.

Alpha-1-antichymotrypsin promotes beta-sheet amyloid plaque deposition in a transgenic mouse model of Alzheimer's disease

Alpha(1)-antichymotrypsin (ACT), an acute-phase inflammatory protein, is an integral component of the amyloid deposits in Alzheimer's disease (AD) and has been shown to catalyze amyloid beta-peptide polymerization in vitro. We have investigated the impact of ACT on amyloid deposition in vivo by generating transgenic GFAP-ACT-expressing mice and crossing them with the PDGF-hAPP/V717F mice, which deposit amyloid in an age-dependent manner. The number of amyloid deposits measured by Congo Red birefringence was increased in the double ACT/amyloid precursor protein (APP) transgenic mice compared with transgenic mice that only expressed APP, particularly in the hippocampus where ACT expression was highest, and the increase was preceded by elevated total amyloid beta-peptide levels at an early age. Our data demonstrate that ACT promotes amyloid deposition and provide a specific mechanism by which inflammation and the subsequent upregulation of astrocytic ACT expression in AD brain contributes to AD pathogenesis.

Astroglial expression of human alpha(1)-antichymotrypsin enhances alzheimer-like pathology in amyloid protein precursor transgenic mice

Proteases and their inhibitors play key roles in physiological and pathological processes. Cerebral amyloid plaques are a pathological hallmark of Alzheimer's disease (AD). They contain amyloid-ss (Ass) peptides in tight association with the serine protease inhibitor alpha(1)-antichymotrypsin.(1,2) However, it is unknown whether the increased expression of alpha(1)-antichymotrypsin found in AD brains counteracts or contributes to the disease. We used regulatory sequences of the glial fibrillary acidic protein gene(3) to express human alpha(1)-antichymotrypsin (hACT) in astrocytes of transgenic mice. These mice were crossed with transgenic mice that produce human amyloid protein precursors (hAPP) and Ass in neurons.(4,5) No amyloid plaques were found in transgenic mice expressing hACT alone, whereas hAPP transgenic mice and hAPP/hACT doubly transgenic mice developed typical AD-like amyloid plaques in the hippocampus and neocortex around 6 to 8 months of age. Co-expression of hAPP and hACT significantly increased the plaque burden at 7 to 8, 14, and 20 months. Both hAPP and hAPP/hACT mice showed significant decreases in synaptophysin-immunoreactive presynaptic terminals in the dentate gyrus, compared with nontransgenic littermates. Our results demonstrate that hACT acts as an amyloidogenic co-factor in vivo and suggest that the role of hACT in AD is pathogenic.

Review: modulating factors in amyloid-beta fibril formation

Amyloid formation is a key pathological feature of Alzheimer's disease and is considered to be a major contributing factor to neurodegeneration and clinical dementia. Amyloid is found as both diffuse and senile plaques in the parenchyma of the brain and is composed primarily of the 40- to 42-residue amyloid-beta (Abeta) peptides. The characteristic amyloid fiber exhibits a high beta-sheet content and may be generated in vitro by the nucleation-dependent self-association of the Abeta peptide and an associated conformational transition from random to beta-conformation. Growth of the fibrils occurs by assembly of the Abeta seeds into intermediate protofibrils, which in turn self-associate to form mature fibers. This multistep process may be influenced at various stages by factors that either promote or inhibit Abeta fiber formation and aggregation. Identification of these factors and understanding the driving forces behind these interactions as well as the structural motifs necessary for these interactions will help to elucidate potential sites that may be targeted to prevent amyloid formation and its associated toxicity. This review will discuss some of the modulating factors that have been identified to date and their role in fibrillogenesis.

Glial-derived proteins activate cultured astrocytes and enhance beta amyloid-induced glial activation

A prominent feature of Alzheimer's disease (AD) pathology is an abundance of activated glia (astrocytes and microglia) in close proximity to the amyloid plaques. These activated glia overexpress a number of proteins that may participate in the progression of the disease, possibly by propagation of inflammatory and oxidative stress responses. The beta-amyloid peptide 1-42 (Abeta), a major constituent of neuritic plaques, can itself induce glial activation. However, little is known about whether other plaque components, especially the upregulated glial proteins, can induce glial activation or modulate the effects of Abeta on glia. In this study, we focused on four glial proteins that are abundant in amyloid plaques and/or that are known to interact with Abeta: alpha1-antichymotrypsin (ACT), interleukin-1beta (IL-1beta), S100beta, and butyrylcholinesterase (BChE). We examined the ability of these proteins to activate rat cortical astrocyte cultures and to influence the ability of Abeta to activate astrocytes. Treatment of astrocytes with ACT, IL-1beta, or S100beta resulted in glial activation, as assessed by reactive morphology, upregulation of IL-1beta, and production of inducible nitric oxide synthase and nitric oxide. The ability of Abeta to induce astrocyte activation was also enhanced in the presence of each of these three proteins. In contrast, BChE alone did not activate astrocytes and had no effect on Abeta-induced activation. These results suggest that certain proteins produced by activated glia may contribute to the chronic glial activation seen in AD through their ability to stimulate astrocytes directly or through their ability to modulate Abeta-induced activation.

Translation of the alzheimer amyloid precursor protein mRNA is up-regulated by interleukin-1 through 5'-untranslated region sequences

The amyloid precursor protein (APP) has been associated with Alzheimer's disease (AD) because APP is processed into the beta-peptide that accumulates in amyloid plaques, and APP gene mutations can cause early onset AD. Inflammation is also associated with AD as exemplified by increased expression of interleukin-1 (IL-1) in microglia in affected areas of the AD brain. Here we demonstrate that IL-1alpha and IL-1beta increase APP synthesis by up to 6-fold in primary human astrocytes and by 15-fold in human astrocytoma cells without changing the steady-state levels of APP mRNA. A 90-nucleotide sequence in the APP gene 5'-untranslated region (5'-UTR) conferred translational regulation by IL-1alpha and IL-1beta to a chloramphenicol acetyltransferase (CAT) reporter gene. Steady-state levels of transfected APP(5'-UTR)/CAT mRNAs were unchanged, whereas both base-line and IL-1-dependent CAT protein synthesis were increased. This APP mRNA translational enhancer maps from +55 to +144 nucleotides from the 5'-cap site and is homologous to related translational control elements in the 5'-UTR of the light and and heavy ferritin genes. Enhanced translation of APP mRNA provides a mechanism by which IL-1 influences the pathogenesis of AD.

Inflammation, antichymotrypsin, and lipid metabolism: autogenic etiology of Alzheimer's disease

Alzheimer's disease is a multifactor pathology, some of whose causes have been inferred from genetic studies, primarily of associated early-onset cases. Much evidence implicates the A beta amyloid peptide as a neurotoxic agent, with chronic inflammation as an accompanying physiological contributor to the disease. The two central questions of how A beta kills neurons and of the autogenic basis of disease remain unanswered. We hypothesize that specific interactions of A beta with the inflammatory serpin, alpha 1-antichymotrypsin, abolish the serpin proteinase inhibitor activity and stimulate formation of the neurotoxic fibrillar form of A beta. Further, the fibrillar A beta interacts with specific cell surface receptors, prompting its own biosynthesis and disrupting cellular cholesterol metabolism. These molecular and cellular interactions autogenically sustain the processes of A beta formation, fibrillization, and receptor interaction, the last of which culminates in neuronal death through disruption of cholesterol metabolism.

Different sensitivity to the cytotoxic action of IAPP fibrils in two insulin-producing cell lines, HIT-T15 and RINm5F cells

We studied whether fibrils spontaneously formed by islet amyloid polypeptide (IAPP, also designated amylin) are cytotoxic to insulin producing cells by examining two different insulin producing cell lines, HIT-T15 and RINm5F. IAPP fibrils (</=10microM) added to HIT-T15 cells for one week did not diminish cell viability (tetrazolium bioreduction) or DNA synthesis (3H-thymidine incorporation) nor did it increase cell death (trypan blue staining) or degree of apoptosis (TUNEL assay), and glucose-stimulated insulin secretion and the cytosolic concentration of Ca2+ were unaffected. Similarly, control fibrils (Alzheimer's peptide, Abeta1-42, fibrils) did not reduce cellular function. In contrast, IAPP fibrils decreased cell viability (tetrazolium bioreduction) and increased number of apoptotic cells in RINm5F cells. Furthermore, hydrogen peroxide markedly impaired tetrazolium bioreduction in RINm5F cells but not in HIT-T15 cells. Glutathione reductase activity was increased by IAPP fibrils in RINm5F cells but not in HIT-T15 cells. Our data suggest a different sensitivity for the cytotoxic action of IAPP fibrils between RINm5F and HIT-T15 cells, which may be ascribed to different sensitivity to formation and action of oxygen intermediates.

Alzheimer's peptide Abeta1-42 binds to two beta-sheets of alpha1-antichymotrypsin and transforms it from inhibitor to substrate

The serpin alpha1-antichymotrypsin is a major component of brain amyloid plaques in Alzheimer's disease. In vitro alpha1-antichymotrypsin interacts with the Alzheimer's amyloid peptide Abeta1-42 and stimulates both formation and disruption of neurotoxic Abeta1-42 fibrils in a concentration-dependent manner. We have constructed a new hybrid model of the complex between Abeta1-42 and alpha1-antichymotrypsin in which both amino and carboxyl sequences of Abeta1-42 insert into two different beta-sheets of alpha1-antichymotrypsin. We have tested this model and shown experimentally that full-length and amino-terminal segments of Abeta1-42 bind to alpha1-antichymotrypsin as predicted. We also show that Abeta1-42 forms both intra- and intermolecular SDS-stable complexes with alpha1-antichymotrypsin and that the binding of Abeta1-42 to alpha1-antichymotrypsin abolishes the inhibitory activity of the latter and its ability to form stable complex with chymotrypsin. The existence of both inter- as well as intramolecular complexes of Abeta1-42 explains the nonlinear concentration-dependent effects of alpha1-antichymotrypsin on Abeta1-42 fibril formation, which we have reinvestigated here over a broad range of Abeta1-42:alpha1-antichymotrypsin ratios. These data suggest a molecular basis for the distinction between amorphous and fibrillar Abeta1-42 in vivo. The reciprocal effects of Abeta1-42 and alpha1-antichymotrypsin could play a role in the etiology of Alzheimer's disease.

Prostaglandin E2 induced polymerization of human alpha-1-antichymotrypsin and suppressed its protease inhibitory activity: implications for Alzheimer's disease

Different molecular forms of alpha-1-antichymotrypsin (ACT) in sera and cerebrospinal fluids from patients with Alzheimer's disease (AD) were detected. Monomeric and polymeric ACT were observed by polyacrylamide gel electrophoresis of both sera and cerebrospinal fluids. ACT polymers were increased in AD patients with the apolipoprotein E (APOE) 4 allele. Increased levels of inactive ACT molecules were also detected in brain homogenates of patients with the APOE 4 allele. Experimental conditions promoting in vitro polymerization of ACT and the effect of polymerization on the biological activity of this serpin were also explored. Incubation of this serpin with prostaglandins of E series (PGE 2) induced ACT polymerization and decreased its activity. Amyloid beta-peptide1-42 did not significantly affected the biological activity of ACT. Inactivation of protease inhibitors by inflammatory molecules such as PGE 2 released from activated microglia in AD brains may promote amyloid deposition and neurodegeneration.

Inhibitory conformation of the reactive loop of alpha 1-antitrypsin

The reactive site loop of the serpin family of serine proteinase inhibitors is flexible and can adopt a number of diverse conformations. A 2.9 A resolution structure of alpha 1-antitrypsin-the principal proteinase inhibitor in human plasma-shows the loop in a stable canonical conformation matching that found in all other families of serine proteinase inhibitors. This unexpected finding in the absence of loop insertion into the body of the molecule favours a two-stage mechanism of inhibition and provides a model for the heparin activation of antithrombin. The beta-pleated strand conformation of the loop also accounts for the polymerization of the serpins in disease and for their association with other beta-sheet structures, most notably the beta-amyloid of Alzheimer's disease.