Extracellular matrix regulates the amount of the beta-amyloid precursor protein and its amyloidogenic fragments

Integrated Systems Analysis Deciphers Transcriptome and Glycoproteome Links in Alzheimer's Disease

Glycosylation is increasingly recognized as a potential therapeutic target in Alzheimer's disease. In recent years, evidence of Alzheimer's disease-specific glycoproteins has been established. However, the mechanisms underlying their dysregulation, including tissue- and cell-type specificity, are not fully understood. We aimed to explore the upstream regulators of aberrant glycosylation by integrating multiple data sources using a glycogenomics approach. We identified dysregulation of the glycosyltransferase PLOD3 in oligodendrocytes as an upstream regulator of cerebral vessels and found that it is involved in COL4A5 synthesis, which is strongly correlated with amyloid fiber formation. Furthermore, COL4A5 has been suggested to interact with astrocytes via extracellular matrix receptors as a ligand. This study suggests directions for new therapeutic strategies for Alzheimer's disease targeting glycosyltransferases.

Role of Vitronectin and Its Receptors in Neuronal Function and Neurodegenerative Diseases

Vitronectin (VTN), a multifunctional glycoprotein with various physiological functions, exists in plasma and the extracellular matrix. It is known to be involved in the cell attachment, spreading and migration through binding to the integrin receptor, mainly via the RGD sequence. VTN is also widely used in the maintenance and expansion of pluripotent stem cells, but its effects go beyond that. Recent evidence shows more functions of VTN in the nervous system as it participates in neural differentiation, neuronutrition and neurogenesis, as well as in regulating axon size, supporting and guiding neurite extension. Furthermore, VTN was proved to play a key role in protecting the brain as it can reduce the permeability of the blood-brain barrier by interacting with integrin receptors in vascular endothelial cells. Moreover, evidence suggests that VTN is associated with neurodegenerative diseases, such as Alzheimer's disease, but its function has not been fully understood. This review summarizes the functions of VTN and its receptors in neurons and describes the role of VTN in the blood-brain barrier and neurodegenerative diseases.

Multi-omic analyses in Abyssinian cats with primary renal amyloid deposits

The amyloidoses constitute a group of diseases occurring in humans and animals that are characterized by abnormal deposits of aggregated proteins in organs, affecting their structure and function. In the Abyssinian cat breed, a familial form of renal amyloidosis has been described. In this study, multi-omics analyses were applied and integrated to explore some aspects of the unknown pathogenetic processes in cats. Whole-genome sequences of two affected Abyssinians and 195 controls of other breeds (part of the 99 Lives initiative) were screened to prioritize potential disease-associated variants. Proteome and miRNAome from formalin-fixed paraffin-embedded kidney specimens of fully necropsied Abyssinian cats, three affected and three non-amyloidosis-affected were characterized. While the trigger of the disorder remains unclear, overall, (i) 35,960 genomic variants were detected; (ii) 215 and 56 proteins were identified as exclusive or overexpressed in the affected and control kidneys, respectively; (iii) 60 miRNAs were differentially expressed, 20 of which are newly described. With omics data integration, the general conclusions are: (i) the familial amyloid renal form in Abyssinians is not a simple monogenic trait; (ii) amyloid deposition is not triggered by mutated amyloidogenic proteins but is a mix of proteins codified by wild-type genes; (iii) the form is biochemically classifiable as AA amyloidosis.

Seeding and Growth of β-Amyloid Aggregates upon Interaction with Neuronal Cell Membranes

In recent years, the prevalence of amyloid neurodegenerative diseases such as Alzheimer's disease (AD) has significantly increased in developed countries due to increased life expectancy. This amyloid disease is characterized by the presence of accumulations and deposits of β-amyloid peptide (Aβ) in neuronal tissue, leading to the formation of oligomers, fibers, and plaques. First, oligomeric intermediates that arise during the aggregation process are currently thought to be primarily responsible for cytotoxicity in cells. This work aims to provide further insights into the mechanisms of cytotoxicity by studying the interaction of Aβ aggregates with Neuro-2a (N2a) neuronal cells and the effects caused by this interaction. For this purpose, we have exploited the advantages of advanced, multidimensional fluorescence microscopy techniques to determine whether different types of Aβ are involved in higher rates of cellular toxicity, and we measured the cellular stress caused by such aggregates by using a fluorogenic intracellular biothiol sensor. Stress provoked by the peptide is evident by N2a cells generating high levels of biothiols as a defense mechanism. In our study, we demonstrate that Aβ aggregates act as seeds for aggregate growth upon interacting with the cellular membrane, which results in cell permeability and damage and induces lysis. In parallel, these damaged cells undergo a significant increase in intracellular biothiol levels.

Low Density Receptor-Related Protein 1 Interactions With the Extracellular Matrix: More Than Meets the Eye

The extracellular matrix (ECM) is a biological substrate composed of collagens, proteoglycans and glycoproteins that ensures proper cell migration and adhesion and keeps the cell architecture intact. The regulation of the ECM composition is a vital process strictly controlled by, among others, proteases, growth factors and adhesion receptors. As it appears, ECM remodeling is also essential for proper neuronal and glial development and the establishment of adequate synaptic signaling. Hence, disturbances in ECM functioning are often present in neurodegenerative diseases like Alzheimer’s disease. Moreover, mutations in ECM molecules are found in some forms of epilepsy and malfunctioning of ECM-related genes and pathways can be seen in, for example, cancer or ischemic injury. Low density lipoprotein receptor-related protein 1 (Lrp1) is a member of the low density lipoprotein receptor family. Lrp1 is involved not only in ligand uptake, receptor mediated endocytosis and lipoprotein transport—functions shared by low density lipoprotein receptor family members—but also regulates cell surface protease activity, controls cellular entry and binding of toxins and viruses, protects against atherosclerosis and acts on many cell signaling pathways. Given the plethora of functions, it is not surprising that Lrp1 also impacts the ECM and is involved in its remodeling. This review focuses on the role of Lrp1 and some of its major ligands on ECM function. Specifically, interactions with two Lrp1 ligands, integrins and tissue plasminogen activator are described in more detail.

Amyloid Beta Influences Vascular Smooth Muscle Contractility and Mechanoadaptation

Amyloid beta accumulation in neuronal and cerebrovascular tissue is a key precursor to development of Alzheimer's disease and can result in neurodegeneration. While its persistence in Alzheimer's cases is well-studied, amyloid beta's direct effect on vascular function is unclear. Here, we measured the effect of amyloid beta treatment on vascular smooth muscle cell functional contractility and modeled the mechanoadaptive growth and remodeling response to these functional perturbations. We found that the amyloid beta 1-42 isoform induced a reduction in vascular smooth muscle cell mechanical output and reduced response to vasocontractile cues. These data were used to develop a thin-walled constrained mixture arterial model that suggests vessel growth, and remodeling in response to amyloid betamediated alteration of smooth muscle function leads to decreased ability of cerebrovascular vessels to vasodilate. These findings provide a possible explanation for the vascular injury and malfunction often associated with the development of neurodegeneration in Alzheimer's disease.

MALDI-mass spectrometry imaging identifies vitronectin as a common constituent of amyloid deposits

Amyloids are pathological intra- and extracellular fibrillar aggregates of polypeptides with a cross-β-sheet structure and characteristic tinctorial properties. The amyloid deposits commonly enclose several non-fibrillar components of the extracellular matrix. Their potential to regulate the formation and aggregation process of amyloid fibrils is still poorly understood. For a better understanding of the role of the extracellular matrix in amyloidosis, it is essential to gain deeper insights into the composition of amyloid deposits. Here, we utilized matrix-assisted laser desorption and ionization mass spectrometry imaging to identify extracellular matrix compounds in amyloid deposits. Using this technique, we identified and determined the spatial distribution of vitronectin within AApoAI-, ALλ-, ATTR- and AIns amyloid deposits and, using immunohistochemistry, validated the spatial overlap of vitronectin with amyloids in 175 cases with diverse types of amyloid in several different tissues.

APP mRNA splicing is upregulated in the brain of biglycan transgenic mice

Many of the risk factors for cerebrovascular disease and atherosclerosis also increase the risk of Alzheimer's disease, characterized by the cerebral deposition of beta-amyloid plaques resulting from the abnormal processing of the transmembrane amyloid precursor protein (APP). The initiating event of cholesterol-induced atherosclerosis is the retention and accumulation of atherogenic apolipoprotein B (apoB) together with low-density lipoproteins in the vascular intima. Biglycan, a member of the small leucine-rich protein family, was suspected of contributing to this process. The individual and combined overexpressions of biglycan and apoB-100 were therefore examined on the cortical APP mRNA levels of transgenic mice by means of semiquantitative PCR. As compared with the control littermates, transgenic biglycan mice had significantly increased cortical APP695 (122%) and APP770 (157%) mRNA levels, while the double transgenic (apoB(+/-)xbiglycan(+/-)) mice did not exhibit any changes. These results provide the first experimental evidence that the atherogenic risk factor biglycan alters APP splicing and may participate in the pathogenesis of both Alzheimer and vascular dementias.

Acetylcholinesterase induces the expression of the β-amyloid precursor protein in glia and activates glial cells in culture

Acetylcholinesterase (AChE) activities in CNS physiopathology are increasingly diverse and range from neuritogenesis, through synaptogenesis, to enhancement of amyloid fiber assembly. In Alzheimer's disease, senile plaques and neurodegeneration specially affect regions enriched for cholinergic synapses. In this study we show an effect of AChE that could contribute to the increased deposition of Abeta in certain regions. Affinity-purified AChE induced the expression of amyloid-beta-precursor protein (beta-APP) in glial cells in a concentration-dependent manner up to 5 nM. In glia, AChE also increased inducible nitric oxide synthase (iNOS) assessed by immunocytochemistry and decreased reductive metabolism as evidence of cell activation. AChE could increase the expression of beta-APP in astrocytes and microglia as result of the activation of glial cells. As a whole, we found that AChE has additional effects that could result in an increased synthesis of Abeta, both by increasing beta-APP expression of astrocytes and by further activating glial cells.

Measurement of laminins in the cerebrospinal fluid obtained from patients with Alzheimer's disease and vascular dementia using a modified enzyme-linked immunosorbent assay

We developed a new enzyme-linked immunosorbent assay (ELISA) system using antibodies against intact human laminin, laminin alpha(5)-chain, laminin beta(1)-chain, laminin gamma(1)-chain and laminin alpha(1)-chain peptide (YFQRYLI). Using this ELISA, we measured the anti-laminin immunoreactivity levels in the cerebrospinal fluid (CSF) obtained from patients with Alzheimer's disease (AD), vascular dementia (VaD), and other disorders. The present study showed the levels of certain laminins in CSF to demonstrate significant differences in the chain levels in different dementias. The AD group showed a significantly lower level of anti-laminin gamma(1) immunoreactivity. The late-onset AD group showed significantly elevated anti-laminin alpha(1)-peptide (YFQRYLI) immunoreactivity levels in comparison with the early-onset AD group and controls. On the other hand, the VaD group showed significantly higher levels of anti-intact human laminin and anti-laminin beta(1) immunoreactivity. The assays of anti-laminin immunoreactivity levels in CSF provided an efficient sensitivity (85.0%) and specificity (93.7%) for the diagnosis of AD by using the ratio of tau to anti-intact human laminin immunoreactivity levels. These results suggest that CSF laminin or its derivatives may correlate with the pathogenesis of AD and VaD, and the prevention of the proteolytic activity may be an effective therapeutic method for either preventing or slowing down the progression of AD. Furthermore, it was shown that performing ELISA for CSF laminins may prove to be useful for detecting the biological markers of AD and VaD.

Neuroplasticity in Alzheimer's disease

Ramon y Cajal proclaimed in 1928 that "once development was ended, the founts of growth and regeneration of the axons and dendrites dried up irrevocably. In the adult centers the nerve paths are something fixed, ended and immutable. Everything must die, nothing may be regenerated. It is for the science of the future to change, if possible, this harsh decree." (Ramon y Cajal, 1928). In large part, despite the extensive knowledge gained since then, the latter directive has not yet been achieved by 'modern' science. Although we know now that Ramon y Cajal's observation on CNS plasticity is largely true (for lower brain and primary cortical structures), there are mechanisms for recovery from CNS injury. These mechanisms, however, may contribute to the vulnerability to neurodegenerative disease. They may also be exploited therapeutically to help alleviate the suffering from neurodegenerative conditions.

Transcriptional activation and increase in expression of Alzheimer's beta-amyloid precursor protein gene is mediated by TGF-beta in normal human astrocytes

The overexpression of the Alzheimer amyloid precursor protein (APP) and its subsequent proteolytic processing may be one of several factors contributing to amyloid beta-peptide (Abeta) deposition in plaques and microvasculature in Alzheimer's disease (AD) brain. Cytokines and growth factors can influence the expression of APP in response to brain injury, but the underlying mechanisms are largely unknown. We examined the mechanisms by which transforming growth factor-beta (TGF-beta) affects the expression of APP in normal human astrocytes. We report that, TGF-beta up-regulated the expression of APP at the transcription level as determined by nuclear run-on experiments. Transient transfection of astrocytes with APP gene promoter (-2832 bp) chloramphenicol acetyltransferase (CAT) reporter constructs led to increased reporter activity upon TGF-beta stimulation. This reporter activity was mainly attributed to the APP proximal domain (-488 bp). The increase in APP gene transcription was associated with significant accumulation of intracellular APP, APP carboxyl terminal derived fragments, and total secreted Abeta. In addition, we observed a significant increase in levels of TGF-beta in Abeta plaques and its immediate vicinity in AD-affected brain relative to controls. These results indicate that high levels of TGF-beta in the cortex, may serve to up-regulate APP synthesis in reactive astrocytes and indirectly contributes to Abeta deposition. Closely related processes may induce cerebrovascular pathology in AD brain.

Differential distribution of laminins in Alzheimer disease and normal human brain tissue

Immunocytochemistry, Western blotting, and RT-PCR were used to identify the isoforms of laminin expressed in the Alzheimer disease, but not in normal human brain tissue. We found that alpha 1 laminin was heavily over-expressed in Alzheimer disease frontal cortex, and localized in reactive astrocytes of the grey and white matter, and as punctate deposits in the senile placques of the Alzheimer brain tissue. Antibodies against the C-terminal neurite outgrowth domain of the gamma 1 laminin demonstrated expression of the gamma 1 laminin in GFAP-immunoreactive reactive astrocytes of the Alzheimer disease frontal cortex. The gamma 1 laminin was also heavily over-expressed in reactive astrocytes of both grey and white matter. Although antibodies against the C-terminal neurite outgrowth domain failed to localize gamma 1 laminin in senile plaques, antibodies against the N-terminal domains of the gamma 1 laminin demonstrated gamma 1 laminin as punctate deposits in the senile plaques. The present results indicate that enhanced and specialized expression patterns of alpha 1 and gamma 1 laminins distinctly associate these two laminins with the Alzheimer disease. The fact that domain specific antibodies localize both alpha1 and gamma 1 laminins in the senile plaques as punctate deposits and in astrocytes of both the gray and white matter indicate that these laminins and their specific domains may have distinct functions in the pathophysiology of the Alzheimer disease.

Interactions of laminin with the amyloid beta peptide. Implications for Alzheimer's disease

Extensive neuronal cell loss is observed in Alzheimer's disease. Laminin immunoreactivity colocalizes with senile plaques, the characteristic extracellular histopathological lesions of Alzheimer brain, which consist of the amyloid beta (A(beta)) peptide polymerized into amyloid fibrils. These lesions have neurotoxic effects and have been proposed to be a main cause of neurodegeneration. In order to understand the pathological significance of the interaction between laminin and amyloid, we investigated the effect of laminin on amyloid structure and toxicity. We found that laminin interacts with the A(beta)1-40 peptide, blocking fibril formation and even inducing depolymerization of preformed fibrils. Protofilaments known to be intermediate species of A(beta) fibril formation were also detected as intermediate species of laminin-induced A(beta) fibril depolymerization. Moreover, laminin-amyloid interactions inhibited the toxic effects on rat primary hippocampal neurons. As a whole, our results indicate a putative anti-amyloidogenic role of laminin which may be of biological and therapeutic interest for controlling amyloidosis, such as those observed in cerebral angiopathy and Alzheimer's disease.

A unifying hypothesis of Alzheimer's disease. IV. Causation and sequence of events

Contrary to common concepts, the brain in Alzheimer's disease (AD) does not follow a suicide but a rescue program. Widely shared features of metabolism in starvation, hibernation and various conditions of energy deprivation, e.g. ischemia, allow the definition of a deprivation syndrome which is a phylogenetically conserved adaptive response to energetic stress. It is characterized by hypometabolism, oxidative stress and adjustments of the glucose-fatty acid cycle. Cumulative evidence suggests that the brain in aging and AD actively adapts to the progressive fuel deprivation. The counterregulatory mechanisms aim to preserve glucose for anabolic needs and promote the oxidative utilization of ketone bodies. The agent mediating the metabolic switch is soluble Abeta which inhibits glucose utilization and stimulates ketone body utilization at various levels. These processes, which are initiated during normal aging, include inhibition of pro-glycolytic neurohormones, cholinergic transmission, and pyruvate dehydrogenase, the key transmitter and effector systems regulating glucose metabolism. Hormonal and effector systems which promote ketone body utilization, such as glucocorticosteroid and galanin activity, GABAergic transmission, nitric oxide, lipid transport, Ca2+ elevation, and ketone body metabolizing enzymes, are enhanced. A multitude of risk factors feed into this pathophysiological cascade at a variety of levels. Taking into account its pleiotropic regulatory actions in the deprivation response, a new name for Abeta is suggested: deprivin. On the other hand, cumulative evidence, taken together compelling, suggests that senile plaques are the dump rather than the driving force of AD. Moreover, the neurotoxic action of fibrillar Abeta is a likely in vitro artifact but does not contribute significantly to the in vivo pathophysiological events. This archaic program, conserved from bacteria to man, aims to ensure the survival of a deprived organism and controls such divergent processes as sporulation, hibernation, aging and aging-related diseases. In contrast to the immature brain, ketone body utilization of the aged brain is no longer sufficient to meet the energetic demands and is later supplemented by lactate, thus recapitulating in reverse order the sequential fuel utilization of the immature brain. The transduction pathways which operate to switch metabolism also convey the programming and balancing of the de-/redifferentiation/apoptosis cell cycle decisions. This encompasses the reiteration of developmental processes such as transcription factor activation, tau hyperphosphorylation, and establishment of growth factor independence by means of Ca2+ set point shift. Thus, the increasing energetic insufficiency results in the progressive centralization of metabolic activity to the neuronal soma, leading to pruning of the axonal/dendritic trees, loss of neuronal polarity, downregulation of neuronal plasticity and, eventually, depending on the Ca2+ -energy-redox homeostasis, degeneration of vulnerable neurons. Finally, it is outlined that genetic (e.g. Down's syndrome, APP and presenilin mutations and apoE4) and environmental risk factors represent progeroid factors which accelerate the aging process and precipitate the manifestation of AD as a progeroid systemic disease. Aging and AD are related to each other by threshold phenomena, corresponding to stage 2, the stage of resistance, and stage 3, exhaustion, of a metabolic stress response.

Laminins and human disease

The laminin protein family has diverse tissue expression patterns and is involved in the pathology of a number of organs, including skin, muscle, and nerve. In the skin, laminins 5 and 6 contribute to dermal-epidermal cohesion, and mutations in the constituent chains result in the blistering phenotype observed in patients with junctional epidermolysis bullosa (JEB). Allelic heterogeneity is observed in patients with JEB: mutations that results in premature stop codons produce a more severe phenotype than do missense mutations. Gene therapy approaches are currently being studied in the treatment of this disease. A blistering phenotype is also observed in patients with acquired cicatricial pemphigoid (CP). Autoantibodies targeted against laminins 5 and 6 destabilize epithelial adhesion and are pathogenic. In muscle cells, laminin alpha 2 is a component of the bridge that links the actin cytoskeleton to the extracellular matrix. In patients with laminin alpha 2 mutations, the bridge is disrupted and mature muscle cells apoptose. Congenital muscular dystrophy (CMD) results. The role of laminin in diseases of the nervous system is less well defined, but the extracellular protein has been shown to serve an important role in peripheral nerve regeneration. The adhesive molecule influences neurite outgrowth, neural differentiation, and synapse formation. The broad spatial distribution of laminin gene products suggests that laminin may be involved in a number of diseases for which pathogenic mechanisms are still being unraveled.

Wnt signaling function in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease with progressive dementia accompanied by three main structural changes in the brain: diffuse loss of neurons; intracellular protein deposits termed neurofibrillary tangles (NFT) and extracellular protein deposits termed amyloid or senile plaques, surrounded by dystrophic neurites. Two major hypotheses have been proposed in order to explain the molecular hallmarks of the disease: The 'amyloid cascade' hypothesis and the 'neuronal cytoskeletal degeneration' hypothesis. While the former is supported by genetic studies of the early-onset familial forms of AD (FAD), the latter revolves around the observation in vivo that cytoskeletal changes - including the abnormal phosphorylation state of the microtubule associated protein tau - may precede the deposition of senile plaques. Recent studies have suggested that the trafficking process of membrane associated proteins is modulated by the FAD-linked presenilin (PS) proteins, and that amyloid beta-peptide deposition may be initiated intracellularly, through the secretory pathway. Current hypotheses concerning presenilin function are based upon its cellular localization and its putative interaction as macromolecular complexes with the cell-adhesion/signaling beta-catenin molecule and the glycogen synthase kinase 3beta (GSK-3beta) enzyme. Developmental studies have shown that PS proteins function as components in the Notch signal transduction cascade and that beta-catenin and GSK-3beta are transducers of the Wnt signaling pathway. Both pathways are thought to have an important role in brain development, and they have been connected through Dishevelled (Dvl) protein, a known transducer of the Wnt pathway. In addition to a review of the current state of research on the subject, we present a cell signaling model in which a sustained loss of function of Wnt signaling components would trigger a series of misrecognition events, determining the onset and development of AD.

Cysteine 144 is a key residue in the copper reduction by the beta-amyloid precursor protein

The beta-amyloid precursor protein (beta-APP) contains a copper-binding site localized between amino acids 135 and 156 (beta-APP(135-156)). We have employed synthetic beta-APP peptides to characterize their capacities to reduce Cu(II) to Cu(I). Analogues of the wild-type beta-APP(135-156) peptide, containing specific amino acid substitutions, were used to establish which residues are specifically involved in the reduction of copper by beta-APP(135-156). We report here that beta-APP's copper-binding domain reduced Cu(II) to Cu(I). The single-mutant beta-APP(His147-->Ala) and the double-mutant beta-APP(His147-->Ala/His149-->Ala) showed a small decrease in copper reduction in relation to the wild-type peptide and the beta-APP(Cys144-->Ser) mutation abolished it, suggesting that Cys144 is the key amino acid in the oxidoreduction reaction. Our results confirm that soluble beta-APP is involved in the reduction of Cu(II) to Cu(I).

Laminin 1 attenuates beta-amyloid peptide Abeta(1-40) neurotoxicity of cultured fetal rat cortical neurons

A growing amount of evidence indicates the involvement of extracellular matrix components, especially laminins, in the development of Alzheimer's disease, although their role remains unclear. In this study, we clearly demonstrate that laminin 1 inhibits beta-amyloid peptide (Abeta)-induced neuronal cell death by preventing the fibril formation and interaction of the Abeta peptide with cell membranes. The presence of laminin at a laminin/Abeta peptide molar ratio of 1:800 significantly inhibits the Abeta-induced apoptotic events, together with inhibition of amyloid fibril formation. The inhibitory effects of laminin 1 were time- and dose-dependent, whereas laminin 2 had less effect on Abeta neurotoxicity. A preincubation of laminin and Abeta was not required to observe the protective effect of laminin, suggesting a direct interaction between laminin 1 and Abeta. Moreover, laminin had no effect on the toxicity of the fibrillar Abeta peptide, suggesting an interaction of laminin with nonfibrillar species of the Abeta peptide, sequestering the peptide in a soluble form. These data extend our understanding of laminin-dependent binding of Abeta and highlight the possible modulation role of laminin regarding Abeta aggregation and neurotoxicity in vivo.

PC12 and neuro 2a cells have different susceptibilities to acetylcholinesterase-amyloid complexes, amyloid25-35 fragment, glutamate, and hydrogen peroxide

This work addresses the differential effects of several oxidative insults on two neuronal cell lines, PC12 and Neuro 2a cells, extensively used as neuronal models in vitro. We measured cellular damage using the cytotoxic assays for MTT reduction and LDH release and found that acetylcholinesterase (AChE)-amyloid-beta-peptide (Abeta) complexes, Abeta25-35 fragment, glutamate and H2O2 were over 200-fold more toxic to PC12 than to Neuro 2a cells. 17alpha and 17beta estradiol were able to protect both cell types from damage caused by H2O2 or glutamate. By contrast, other insults not related to oxidative stress, such as those caused by the nonionic detergent Triton X-100 and serum deprivation, induced a similar level of damage in both PC12 and Neuro 2a cells. Considering that the Abeta peptide, H2O2 and glutamate are cellular insults that cause an increase in reactive oxygen species (ROS), the intracellular levels of the antioxidant compound, glutathione were verified. Neuro 2a cells were found to have 4- to 5-fold more glutathione than PC12 cells. Our results suggest that Neuro 2a cells are less susceptible to exposure to AChE-Abeta complexes, Abeta25-35 fragment, glutamate and H2O2 than PC12 cells, due to higher intracellular levels of antioxidant defense factors.

Laminin inhibits both Abeta40 and Abeta42 fibril formation but does not affect Abeta40 or Abeta42-induced cytotoxicity in PC12 cells

Laminin has recently been reported to inhibit both Abeta40 and Abeta42 fibril formation in vitro. Laminin was thus suggested to be an effective therapeutic agent for Alzheimer's disease. However, some recent reports have shown that Abeta fibril formation may not necessarily be linked to the development of Abeta neurotoxicity. In the present study, we thus investigated whether or not laminin affects Abeta40 and Abeta42-induced neurotoxicity. The findings of the present study by using the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) dye reduction test showed laminin not to have an inhibitory effect on Abeta40 or Abeta42-induced cytotoxicity in PC12 cells while Abeta fibril formation was inhibited under the conditions used in the present study. The findings of the present study therefore do not support the hypothesis that Abeta fibril formation is absolutely required for the development of Abeta cytotoxicity.

The inhibitory effect of laminin 1 and synthetic peptides deduced from the sequence in the laminin alpha1 chain on Abeta40 fibril formation in vitro

We investigated whether or not laminin 1 and the two different synthetic peptides deduced from the sequence in the laminin alphal chain, both of which mediate cell attachment and neurite outgrowth in PC12 cells, have an effect on Abeta40 fibril formation in vitro. A thioflavine-T fluorometric assay showed a synthetic peptide containing the YFQRYLI sequence from the laminin alpha1 chain to inhibit Abeta40 fibril formation while the inhibitory effect of this peptide was found to be somewhat less than that of intact laminin 1. These results were confirmed by electron microscopic observations using negative staining. The findings of the present study suggested that the synthetic peptide derived from the laminin alpha1 chain may thus be an effective therapeutic agent for either preventing or slowing down the progression of amyloidogenesis in Alzheimer's disease.

Laminin inhibits Abeta42 fibril formation in vitro

In the present study, we investigated whether or not laminin inhibits Abeta42 fibril formation in the same manner as Abeta40. Both a thioflavine-T fluorometric assay and electron microscopy by negative staining demonstrated laminin to have a concentration-dependent inhibitory effect on Abeta42 fibril formation. The amyloid fibril formation was inhibited approximately by 70% due to the presence of 1.0 mg/ml laminin co-incubated with 1. 0 mg/ml Abeta42 peptide (molar ratio; Abeta42 peptide:laminin=200:1). These results thus suggested that laminin or its derivatives may be effective as therapeutic agents to either prevent or slow down the progression of amyloidogenesis in Alzheimer's disease.

Cellular and molecular basis of estrogen's neuroprotection. Potential relevance for Alzheimer's disease

Alzheimer's disease (AD) is one of the most common types of dementia among the aged population, with a higher prevalence in women. The reason for this latter observation remained unsolved for years, but recent studies have provided evidence that a lack of circulating estrogen in postmenopausal women could be a relevant factor. Moreover, follow-up studies among postmenopausal women who had received estrogen-replacement therapy (ERT), suggested that they had a markedly reduced risk of developing AD. In addition, studies among older women who already had AD indeed confirmed that a decrease in estrogen levels was likely to be an important factor in triggering the pathogenesis of the disease. In this review article, we will discuss the evidence suggesting that estrogen may have a protective role against AD, mainly through its action as: a trophic factor for cholinergic neurons, a modulator for the expression of apolipoprotein E (ApoE) in the brain, an antioxidant compound decreasing the neuronal damage caused by oxidative stress, and a promoter of the physiological nonamyloidogenic processing of the amyloid precursor protein (APP), decreasing the production of the amyloid-beta-peptide (A beta), a key factor in the pathogenesis of AD.

Enhanced aggregation of beta-amyloid-containing peptides by extracellular matrix and their degradation by the 68 kDa serine protease prepared from human brain

To explore whether extracellular matrix components in human brain affect the deposition and aggregation of beta-amyloid containing peptides, human brain samples from patients with sporadic Alzheimer's disease and normal aged were analyzed by Western blot analysis. All major beta-amyloid-containing peptides contained epitope(s) which is recognized by anti heparan sulfate antibody. Incubation of brain beta-amyloid-containing peptides with human collagen type IV in neutral pH efficiently generated a high molecular weight aggregated band, approximately 5-fold that of the control sample. We have previously found a serine protease which is capable of cleaving an oligopeptide at the N-terminus of beta-amyloid. In this study, the protease, which also contains heparan sulfate glycoconjugates, degraded the above brain peptides as natural substrates, although with different efficiency. These findings suggest that extra-cellular matrix components affect the processing and aggregation of beta-amyloid-containing peptides in human brain.

Laminin inhibits amyloid-beta-peptide fibrillation

Laminin, an important extracellular matrix component is induced by brain injury and colocalizes with amyloid-beta-peptide (A beta) deposits in Alzheimer brains. We report here that laminin inhibits amyloid fibril formation as determined by thioflavin T fluorescence spectroscopy and electron microscopic examination. The inhibition of amyloid formation by laminin was concentration dependent and was observed at a laminin concentration of 300 nM, corresponding to a laminin/A beta protein molar ratio of 1:800. The potential effect of laminin, may prove important to inhibit A beta fibrillogenesis in vivo, specifically at the level of cerebral blood vessels.