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

The Role of Extracellular Matrix Components in the Spreading of Pathological Protein Aggregates

Several neurodegenerative diseases are characterized by the accumulation of aggregated misfolded proteins. These pathological agents have been suggested to propagate in the brain via mechanisms similar to that observed for the prion protein, where a misfolded variant is transferred from an affected brain region to a healthy one, thereby inducing the misfolding and/or aggregation of correctly folded copies. This process has been characterized for several proteins, such as α-synuclein, tau, amyloid beta (Aβ) and less extensively for huntingtin and TDP-43. α-synuclein, tau, TDP-43 and huntingtin are intracellular proteins, and their aggregates are located in the cytosol or nucleus of neurons. They have been shown to spread between cells and this event occurs, at least partially, via secretion of these protein aggregates in the extracellular space followed by re-uptake. Conversely, Aβ aggregates are found mainly extracellularly, and their spreading occurs in the extracellular space between brain regions. Due to the inherent nature of their spreading modalities, these proteins are exposed to components of the extracellular matrix (ECM), including glycans, proteases and core matrix proteins. These ECM components can interact with or process pathological misfolded proteins, potentially changing their properties and thus regulating their spreading capabilities. Here, we present an overview of the documented roles of ECM components in the spreading of pathological protein aggregates in neurodegenerative diseases with the objective of identifying the current gaps in knowledge and stimulating further research in the field. This could potentially lead to the identification of druggable targets to slow down the spreading and/or progression of these pathologies.

Bioinformatic analysis of the human brain extracellular matrix proteome in neurodegenerative disorders

Alzheimer's, Parkinson's, and Huntington's diseases are characterized by selective degeneration of specific brain areas. Although increasing number of studies report alteration of the extracellular matrix on these diseases, an exhaustive characterization at the brain's matrix level might contribute to the development of more efficient cell restoration therapies. In that regard, proteomics-based studies are a powerful approach to uncover matrix changes. However, to date, the majority of proteomics studies report no or only a few brain matrix proteins with altered expression. This study aims to reveal the changes in the brain extracellular matrix by integrating several proteomics-based studies performed with postmortem tissue. In total, 67 matrix proteins with altered expression were collected. By applying a bioinformatic approach, we were able to reveal the dysregulated biological processes. Among them are processes related to the organization of the extracellular matrix, glycosaminoglycans and proteoglycans' metabolism, blood coagulation, and response to injury and oxidative stress. In addition, a protein was found altered in all three diseases-collagen type I alpha 2-and its binding partners further identified. A ClueGO network was created, depicting the GO groups associated with these binding partners, uncovering the processes that may consequently be affected. These include cellular adhesion, cell signaling through membrane receptors, inflammatory processes, and apoptotic cell death in response to oxidative stress. Overall, we were able to associate the contribution of the modification of extracellular matrix components to essential biological processes, highlighting the investment needed on proteomics studies with specific focus on the extracellular matrix in neurodegeneration.

Synthesis and biological evaluation of modified laminin peptide (N2S2-KDP) with enhanced affinity for neuronal growth and targeted molecular imaging (SPECT)

An analog of γ1 laminin (RDIAEIIKDI) decapeptide has been used to augment neuronal survival and regeneration after injuries, during aging and other CNS disorder. As a prime synthetic peptide, KDI, is responsible for the neurite outgrowth of human embryonic neurons. In this study, we have designed, modified a KDI derivative and synthesized by replacing isoleucine (I) with Pro (P) amino acid at C-terminal to enhance its potency towards neurite growth. -Cys-Gly-Cys (-CGC) N2S2 motif was also incorporated in the present design for peptide radiolabeling. The modified peptide showed a better binding with the desired 3T1M receptor for neurite growth. The peptide was synthesized using solid phase peptide synthesis and Fmoc-strategy with more than 80% yield. The receptor binding studies of 99mTc-N2S2-KDP in Neuro2A cell lines showed Kd value in 31 nM range and the complex showed appreciable brain uptake in mice. The results on human SH-SY5Y indicate that the unlabeled N2S2-KDP may perhaps be useful for neurite growth in neurodegenerative disorder.

Extracellular Matrix Proteins Involved in Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases and characterized by cognitive and memory impairments. Emerging evidence suggests that the extracellular matrix (ECM) in the brain plays an important role in the etiology of AD. It has been detected that the levels of ECM proteins have changed in the brains of AD patients and animal models. Some ECM components, for example, elastin and heparan sulfate proteoglycans, are considered to promote the upregulation of extracellular amyloid-beta (Aβ) proteins. In addition, collagen VI and laminin are shown to have interactions with Aβ peptides, which might lead to the clearance of those peptides. Thus, ECM proteins are involved in both amyloidosis and neuroprotection in the AD process. However, the molecular mechanism of neuronal ECM proteins on the pathophysiology of AD remains elusive. More investigation of ECM proteins with AD pathogenesis is needed, and this may lead to novel therapeutic strategies and biomarkers for AD.

Aberrant interactions between amyloid-beta and alpha5 laminins as possible driver of neuronal disfunction in Alzheimer's disease

It has been widely accepted that laminins are involved in pathogenesis of Alzheimer's disease (AD). Amyloid plaques in AD patients are associated with immunostaining using antibodies raised against laminin-111, and laminin-111 has been shown to prevent aggregation of amyloid peptides. Although numerous articles describe small peptides from laminin-111 that are capable to disaggregate amyloid buildups and reduce neurotoxicity in in vitro and in vivo models, there is no approved laminin-111-based therapeutic approaches for treatment of AD. Also, it has been shown that immunoreactivity to laminin-111 appears late in development of cerebral amyloidosis. Based on the published data, we hypothesize that aberrant interaction between amyloid-beta and α5-laminins such as laminin-511 prevents the necessary laminin signaling into neurons leading to neurodegeneration and contributing to the early development of AD. Laminin-511 is the key extracellular protein that protects neurons from anoikis, inhibits excitoxicity and provides signaling that stabilizes dendritic spines and synapses in the developed brain. Absence of the signaling from laminin-511 leads to behavioral defects in mice. Laminin-511 and hippocampal neurons are in direct contact and accumulation of amyloid-beta that has been shown to avidly bind laminin-511 may physically decouple the interaction between α5-laminins and the neuronal membrane receptors inhibiting the signaling. Under this hypothesis, protein domains and peptides from laminin α5 chain may have a therapeutic potential in treatment of AD and the appearance of laminin-111 in the amyloid plaques is simply a consequence of the disease.

Complexing Aβ prevents the cellular anomalies induced by the Peptide alone

Retention of intracellular secreted APP (isAPP) can be provoked by the neurotoxic peptide Aβ. The latter decreases in the cerebrospinal fluid of Alzheimer’s disease (AD) patients, as a consequence of its cerebral accumulation and deposition into senile plaques. Of similar relevance, secreted APP (sAPP) levels can be associated with AD. The studies here presented, reinforce the link between sAPP and Aβ and address putative therapeutic strategies. Laminin and gelsolin are potential candidates; both prevent Aβ fibril formation by complexing with Aβ, thus attenuating its neurotoxicity. We show that preincubation of Aβ with laminin and gelsolin has the effect of rendering it less potent to isAPP accumulation in cortical neurons. This appears to be related to a decrease in F-actin polymerization, whereas Aβ alone induces the polymerization. Further, Aβ decreases gelsolin levels, and the latter is involved in Aβ removal. Our data indicates that Aβ-laminin and Aβ-gelsolin complexes are less neurotoxic and also less potent than fibrillar Aβ at inducing isAPP retention. These results validate the potential of these proteins as therapeutic strategies that prevent the Aβ-induced effects. In hence, given that Aβ decreases the levels of proteins involved in its own clearance, this may contribute to the mechanisms underlying AD pathology.

Misfolding of amyloidogenic proteins and their interactions with membranes

In this paper, we discuss amyloidogenic proteins, their misfolding, resulting structures, and interactions with membranes, which lead to membrane damage and subsequent cell death. Many of these proteins are implicated in serious illnesses such as Alzheimer’s disease and Parkinson’s disease. Misfolding of amyloidogenic proteins leads to the formation of polymorphic oligomers and fibrils. Oligomeric aggregates are widely thought to be the toxic species, however, fibrils also play a role in membrane damage. We focus on the structure of these aggregates and their interactions with model membranes. Study of interactions of amlyoidogenic proteins with model and natural membranes has shown the importance of the lipid bilayer in protein misfolding and aggregation and has led to the development of several models for membrane permeabilization by the resulting amyloid aggregates. We discuss several of these models: formation of structured pores by misfolded amyloidogenic proteins, extraction of lipids, interactions with receptors in biological membranes, and membrane destabilization by amyloid aggregates perhaps analogous to that caused by antimicrobial peptides.

Surface-bound basement membrane components accelerate amyloid-β peptide nucleation in air-free wells: an in vitro model of cerebral amyloid angiopathy

Cerebral amyloid angiopathy is caused by deposition of the amyloid β-peptide which consists of mainly 39-40 residues to the cortical and leptomeningeal vessel walls. There are no definite in vitro systems to support the hypothesis that the vascular basement membrane may act as a scaffold of amyloid β-peptide carried by perivascular drainage flow and accelerate its amyloid fibril formation in vivo. We previously reported the critical roles of interfaces and agitation on the nucleation of amyloid fibrils at low concentrations of amyloid β-peptide monomers. Here, we reproduced the perivascular drainage flow in vitro by using N-hydroxysuccinimide-Sepharose 4 Fast flow beads as an inert stirrer in air-free wells rotated at 1rpm. We then reproduced the basement membranes in the media of cerebral arteries in vitro by conjugating Matrigel and other proteins on the surface of Sepharose beads. These beads were incubated with 5μM amyloid β(1-40) at 37°C without air, where amyloid β(1-40) alone does not form amyloid fibrils. Using the initiation time of fibril growth kinetics (i.e., the lag time of fibril growth during which nuclei, on-pathway oligomers and protofibrils are successively formed) as a parameter of the efficiency of biological molecules to induce amyloid fibril formation, we found that basement membrane components including Matrigel, laminin, fibronectin, collagen type IV and fibrinogen accelerate the initiation of amyloid β-peptide fibril growth in vitro. These data support the essential role of vascular basement membranes in the development of cerebral amyloid angiopathy.

Kallikrein-related peptidase 6 in Alzheimer's disease and vascular dementia

Human kallikrein-related peptidase 6 (KLK6) is highly expressed in the central nervous system. Although the physiological roles of this serine protease are unknown, in vitro substrates include amyloid precursor protein and components of the extracellular matrix, which are altered in neurological disease, particularly Alzheimer's disease (AD). We have compared KLK6 expression in post-mortem brain tissue in AD, vascular dementia (VaD) and controls. We studied the distribution of KLK6 in the temporal cortex and white matter by immunohistochemistry, and measured KLK6 mRNA and protein levels in the frontal and temporal cortex from 15 AD, 15 VaD and 15 control brains. Immunohistochemistry showed KLK6 to be restricted to endothelial cells. After adjustment for variations in vessel density by measurement of factor VIII-related antigen, we found KLK6 protein and mRNA levels to be significantly decreased in the frontal but not the temporal cortex in AD. In VaD, KLK6 protein level was significantly increased in the frontal cortex. Our findings suggest that an altered KLK6 expression may contribute to vascular abnormalities in AD and VaD.

Abnormal post-translational and extracellular processing of brevican in plaque-bearing mice over-expressing APPsw

Aggregation of amyloid-beta (Abeta) in the forebrain of Alzheimer's disease (AD) subjects may disturb the molecular organization of the extracellular microenvironment that modulates neural and synaptic plasticity. Proteoglycans are major components of this extracellular environment. To test the hypothesis that Abeta, or another amyloid precursor protein (APP) dependent mechanism modifies the accumulation and/or turnover of extracellular proteoglycans, we examined whether the expression and processing of brevican, an abundant extracellular, chondroitin sulfate (CS)-bearing proteoglycan, were altered in brains of Abeta-depositing transgenic mice (APPsw - APP gene bearing the Swedish mutation) as a model of AD. The molecular size of CS chains attached to brevican was smaller in hippocampal tissue from APPsw mice bearing Abeta deposits compared to non-transgenic mice, likely because of changes in the CS chains. Also, the abundance of the major proteolytic fragment of brevican was markedly diminished in extracts from several telencephalic regions of APPsw mice compared to non-transgenic mice, yet these immunoreactive fragments appeared to accumulate adjacent to the plaque edge. These results suggest that Abeta or APP exert inhibitory effects on proteolytic cleavage mechanisms responsible for synthesis and turnover of proteoglycans. As proteoglycans stabilize synaptic structure and inhibit molecular plasticity, defective brevican processing observed in Abeta-bearing mice and potentially end-stage human AD, may contribute to deficient neural plasticity.

Attenuation of beta-amyloid-induced toxicity by sialic-acid-conjugated dendrimers: role of sialic acid attachment

beta-Amyloid (Abeta) is the primary protein component of senile plaques in Alzheimer's disease and is believed to be associated with neurotoxicity in the disease. We and others have shown that Abeta binds with relatively high affinity to clustered sialic acid residues on cell surfaces and that removal of cell surface sialic acids attenuates Abeta toxicity. We have also shown that sialic acid functionalized dendrimeric polymers can act as mimics of cell surface sialic acid clusters and attenuate Abeta-induced neurotoxicity. In the current study, we prepared sialic-acid-conjugated dendrimers using a physiologically relevant attachment of the sialic acid to the dendrimeric termini, and evaluated the Abeta toxicity attenuation properties of the dendrimers. We compared performance of sialic-acid-conjugated dendrimeric polymers in which the sialic acid moieties were attached to dendrimeric termini via the anomeric hydroxyl group of the sialic acid, a physiological attachment, to polymers in which the attachment was made via the carboxylic acid group on the sialic acid, a non-physiological attachment. This work enhances our understanding of Abeta-cell surface binding and is a step towards the development of new classes of sequestering agents as therapeutics for the prevention of Abeta toxicity in AD.

Membrane disordering effects of beta-amyloid peptides

The interaction of Abeta with synaptosomal plasma membranes decreases membrane fluidity. Using model membrane/liposome systems the interaction of Abeta with specific lipids (e.g. phospholipids, gangliosides, cholesterol) has been defined. The formation of the beta-sheet structure of Abeta when undergoing peptide aggregation is important for Abeta's membrane perturbing properties. This effect can be correlated with the peptide length of Abeta, the longer Abeta1-42 having the greatest effect on membrane fluidity and on neurotoxicity.

Alpha2beta1 and alphaVbeta1 integrin signaling pathways mediate amyloid-beta-induced neurotoxicity

Pathological hallmarks of Alzheimer's disease are the presence of extracellular amyloid plaques, intracellular neurofibrillary tangles, and neurodegeneration. The principal component of amyloid plaques is the amyloid-beta peptide (Abeta). Accumulating evidence indicates that Abeta may play a causal role in Alzheimer's disease. In this report, we demonstrate that Abeta deposition and neurotoxicity in human cortical primary neurons are mediated through alpha2beta1 and alphaVbeta1 integrins using specific integrin-blocking antibodies. An aberrant integrin signaling pathway causing the neurotoxicity is mediated through Pyk2. The role of alpha2beta1 and alphaVbeta1 integrins can be extended to another amyloidosis using an amylin in vitro neurotoxicity model. These results indicate that the alpha2beta1 and alphaVbeta1 integrin signaling pathway may be critical components of neurodegeneration in Alzheimer's disease and that integrins may recognize and be activated by a shared structural motif of polymerizing amyloidogenic proteins.

The beta-amyloid peptide of Alzheimer's disease decreases adhesion of vascular smooth muscle cells to the basement membrane

Cerebral amyloid angiopathy (CAA) is a major feature of Alzheimer's disease pathology. In CAA, degeneration of vascular smooth muscle cells (VSMCs) occurs close to regions of the basement membrane where the amyloid protein (Abeta) builds up. In this study, the possibility that Abeta disrupts adhesive interactions between VSMCs and the basement membrane was examined. VSMCs were cultured on a commercial basement membrane substrate (Matrigel). The presence of Abeta in the Matrigel decreased cell-substrate adhesion and cell viability. Full-length oligomeric Abeta was required for the effect, as N- and C-terminally truncated peptide analogues did not inhibit adhesion. Abeta that was fluorescently labelled at the N-terminus (fluo-Abeta) bound to Matrigel as well as to the basement membrane heparan sulfate proteoglycan (HSPG) perlecan and laminin. Adhesion of VSMCs to perlecan or laminin was decreased by Abeta. As perlecan influences VSMC viability through the extracellular signal-regulated kinase (ERK)1/2 signalling pathway, the effect of Abeta1-40 on ERK1/2 phosphorylation was examined. The level of phospho-ERK1/2 was decreased in cells following Abeta treatment. An inhibitor of ERK1/2 phosphorylation enhanced the effect of Abeta on cell adhesion. The studies suggest that Abeta can decrease VSMC viability by disrupting VSMC-extracellular matrix (ECM) adhesion.

Docosahexaenoic acid prevents neuronal apoptosis induced by soluble amyloid-β oligomers

A growing body of evidence supports the notion that soluble oligomers of amyloid-beta (Abeta) peptide interact with the neuronal plasma membrane, leading to cell injury and inducing death-signalling pathways that could account for the increased neurodegeneration occurring in Alzheimer's disease (AD). Docosahexaenoic acid (DHA, C22:6, n-3) is an essential polyunsaturated fatty acid in the CNS and has been shown in several epidemiological and in vivo studies to have protective effects against AD and cognitive alterations. However, the molecular mechanisms involved remain unknown. We hypothesized that DHA enrichment of plasma membranes could protect neurones from apoptosis induced by soluble Abeta oligomers. DHA pre-treatment was observed to significantly increase neuronal survival upon Abeta treatment by preventing cytoskeleton perturbations, caspase activation and apoptosis, as well as by promoting extracellular signal-related kinase (ERK)-related survival pathways. These data suggest that DHA enrichment probably induces changes in neuronal membrane properties with functional outcomes, thereby increasing protection from soluble Abeta oligomers. Such neuroprotective effects could be of major interest in the prevention of AD and other neurodegenerative diseases.

Differential gene expression in human brain pericytes induced by amyloid-beta protein

Cerebral amyloid angiopathy is one of the characteristics of Alzheimer's disease (AD) and this accumulation of fibrillar amyloid-beta (Alphabeta) in the vascular wall is accompanied by marked vascular damage. In vitro, Abeta1-40 carrying the 'Dutch' mutation (DAbeta1-40) induces degeneration of cultured human brain pericytes (HBP). To identify possible intracellular mediators of Abeta-induced cell death, a comparative cDNA expression array was performed to detect differential gene expression of Abeta-treated vs. untreated HBP. Messenger RNA expression of cyclin D1, integrin beta4, defender against cell death-1, neuroleukin, thymosin beta10, and integrin alpha5 were increased in DAbeta1-40-treated HBP, whereas insulin-like growth factor binding protein-2 mRNA expression was decreased. Corresponding protein expression was investigated in AD and control brains to explore a potential role for these proteins in pathological lesions of the AD brain. Cyclin D1 expression was increased in cerebral amyloid angiopathy and cells in a perivascular position, suggesting that the cell cycle may be disturbed during Abeta-mediated degeneration of cerebrovascular cells. Moreover, cyclin D1 expression, but also that of integrin beta4, defender against cell death-1, neuroleukin and thymosin beta10 was found in a subset of senile plaques, suggesting a role for these proteins in the pathogenesis of senile plaques.

Clinical and molecular study in congenital muscular dystrophy with partial laminin alpha 2 (LAMA2) deficiency

Complete laminin alpha2 (LAMA2) deficiency causes approximately half of congenital muscular dystrophy (CMD) cases. Many loss-of-function mutations have been reported in these severe, neonatal-onset patients, but only single missense mutations have been found in milder CMD with partial laminin alpha2 deficiency. Here, we studied nine patients diagnosed with CMD who showed abnormal white-matter signal at brain MRI and partial deficiency of laminin alpha2 on immunofluorescence of muscle biopsy. We screened the entire 9.5 kb laminin alpha2 mRNA from patient muscle biopsy by direct capillary automated sequencing, single strand conformational polymorphism (SSCP), or denaturing high performance liquid chromatography (DHPLC) of overlapping RT-PCR products followed by direct sequencing of heteroduplexes. We identified laminin alpha2 sequence changes in six of nine CMD patients. Each of the gene changes identified, except one, was novel, including three missense changes and two splice-site mutations. The finding of partial laminin alpha2 deficiency by immunostaining is not specific for laminin alpha2 gene mutation carriers, with only two patients (22%) showing clear causative mutations, and an additional three patients (33%) showing possible mutations. The clinical presentation and disease progression was homogeneous in the laminin alpha2-mutation positive and negative CMD patients.

Medicinal chemistry approaches for the treatment and prevention of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia, which is characterised by progressive deterioration of memory and higher cortical functions that ultimately result in total degradation of intellectual and mental activities. Modern strategies in the search of new therapeutic approaches are based on the morphological and biochemical characteristics of AD, and focused on following directions: agents that compensate the hypofunction of cholinergic system, agents that interfere with the metabolism of beta-amyloid peptide, agents that protect nerve cells from toxic metabolites formed in neurodegenerative processes, agents that activate other neurotransmitter systems that indirectly compensate for the deficit of cholinergic functions, agents that affect the process of the formation of neurofibrillary tangles, anti-inflammatory agents that prevent the negative response of nerve cells to the pathological process. The goal of the present review is the validation and an analysis from the point of view of medicinal chemistry of the principles of the directed search of drugs for the treatment and prevention of AD and related neurodegenerative disorders. It is based on systematization of the data on biochemical and structural similarities in the interaction between physiologically active compounds and their biological targets related to the development of such pathologies. The main emphasis is on cholinomimetic, anti-amyloid and anti-metabolic agents, using the data that were published during the last 3 to 4 years, as well as the results of clinical trials presented on corresponding websites.

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.

Passive immunization against beta-amyloid peptide protects central nervous system (CNS) neurons from increased vulnerability associated with an Alzheimer's disease-causing mutation

To characterize the effects of the familial Alzheimer's disease-causing Swedish mutations of amyloid precursor protein (SwAPP) on the vulnerability of central nervous system neurons, we induced epileptic seizures in transgenic mice expressing SwAPP. The transgene expression did not change the seizure threshold, but consistently more neurons degenerated in brains of SwAPP mice as compared with wild-type littermates. The degenerating neurons were stained both by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling and by Gallyas silver impregnation. A susceptible population of neurons accumulated intracellular Abeta and immunoreacted with antibodies against activated caspase-3. To demonstrate that increased Abeta levels mediated the increased vulnerability, we infused antibodies against Abeta and found a significant reduction in neuronal loss that was paralleled by decreased brain levels of Abeta. Because the SwAPP mice exhibited no amyloid plaques at the age of these experiments, transgenic overproduction of Abeta in brain rendered neurons susceptible to damage much earlier than the onset of amyloid plaque formation. Our data underscore the possibility that Abeta is toxic, that it increases the vulnerability of neurons to excitotoxic events produced by seizures, and that lowering Abeta by passive immunization can protect neurons from Abeta-related toxicity.

Per-6-substituted beta-cyclodextrin libraries inhibit formation of beta-amyloid-peptide (A beta)-derived, soluble oligomers

Alzheimer's disease is the most common cause of dementia in older individuals with compelling evidence favoring neuron dysfunction and death triggered by assembled forms of A beta(1-42). While large neurotoxic amyloid fibrils have been known for years, recent studies show that soluble protofibril and A beta(1-42)-derived diffusible ligands (ADDLs) may also be involved in neurotoxicity. In the present work, dot-blot immunoassays discriminating ADDLs from monomers were used to screen libraries of per-substituted beta-cyclodextrin (beta-CD) derivatives for inhibition of ADDLs formation. Libraries were prepared from per-6-iodo-beta-CD by treatment with various amine nucleophiles. The most active library tested (containing >2000 derivatives) was derived from imidazole, N, N-dimethylethylenediamine and furfurylamine, which at 10 microM total library, inhibited ADDLs formation (10 nM A beta(1-42)) over a period of 4 hours. The latter was confirmed by a western blot assay showing decreased amounts of the initially formed A beta(1-42) tetramer. These preliminary experiments suggest that derivatized forms of beta-CD can interfere with the oligomerization process of A beta(1-42).

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.

Laminin affects polymerization, depolymerization and neurotoxicity of Abeta peptide

Amyloid deposition in Alzheimer fibrils forms neurotoxic senile plaques in a process that may be modulated by associated proteins. In this work we demonstrate the ability of laminin-1 and laminin-2 to inhibit fibril formation and toxicity on cultured rat hippocampal neurons. We confirm that the laminin-1-derived peptide YFQRYLI inhibits efficiently both fibril formation and neurotoxicity and show that the IKVAV peptide inhibits amyloid neurotoxicity despite its slight inhibition of fibril formation. On other hand, laminin-1 induces disaggregation of preformed fibrils in vitro, characterized as a progressive disassembly of fibrils into protofibrils and further clearance of these latter species, leading to a continual inhibition of amyloid neurotoxicity.

Biologically active sequence (KDI) mediates the neurite outgrowth function of the gamma-1 chain of laminin-1

A neurite outgrowth domain of the gamma1-chain of laminin-1 (RDIAEIIKDI) promotes axon guidance of rat hippocampal neurons, regulates the nuclear movement phase of neuronal migration, and binds to the cellular prion protein (Liesi et al. [1995] J. Neurosci. Res. 134:447-486; Matsuzawa et al. [1998] J. Neurosci. Res. 53:114-124; Graner et al. [2000] Brain Res. Mol. Brain Res. 76:85-92). Using electrophysiology and neuronal culture experiments, we show that this 10 amino acid peptide or its smaller domains induces potassium currents in primary central neurons. Both these currents and the neurotoxicity of high concentrations of the 10 amino acid peptide antigen are prevented by pertussis toxin. The smallest peptide domain capable of inducing both potassium currents and promoting neurite outgrowth of human spinal cord neurons is a tri-peptide KDI. Our results indicate that KDI may be the biologically active domain of the gamma1 laminin, capable of modulating electrical activity and survival of central neurons via a G-protein coupled mechanism. These results expand the wide variety of functions already reported for the members of the laminin-gene family. They suggest that biologically active peptide domains of the gamma1 laminin may provide tools to promote neuronal regeneration after injuries and to enhance neuronal survival during aging and neuronal degeneration.

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 nonfibrillar form of the fusogenic prion protein fragment [118-135] induces apoptotic cell death in rat cortical neurons

Neuronal loss is a salient feature of prion diseases. However, its cause and mechanism, particularly its relationship with the accumulation and precipitation of the pathogenic, protease-resistant isoform PrP(Sc) of the cellular prion protein PrP(C), are still an enigma. Several studies suggest that neuronal loss could occur through a process of programmed cell death, which is consistent with the lack of inflammation in these conditions. By analogy with the pathological events occurring during the development of Alzheimer's disease, controversies still exist regarding the relationship between amyloidogenesis, prion aggregation, and neuronal loss. We recently demonstrated that a prion protein fragment (118-135) displayed membrane-destabilizing properties and was able to induce, in a nonfibrillar form, the fusion of unilamellar liposomes. To unravel the mechanism of prion protein neurotoxicity, we characterize the effects of the human Pr[118-135] peptide on rat cortical neurons. We demonstrate that low concentrations of the Pr[118-135] peptide, in a nonfibrillar form, induce a time- and dose- dependent apoptotic cell death, including caspase activation, DNA condensation, and fragmentation. This toxicity might involve oxidative stress, because antioxidant molecules, such as probucol and propyl gallate, protect neurons against prion peptide toxicity. By contrast, a nonfusogenic variant Pr[118-135, 0 degrees ] peptide, which displays the same amino acid composition but several amino acid permutations, is not toxic to cortical neurons, which emphasizes the critical role of the fusogenic properties of the prion peptide in its neurotoxicity. Taken together, our results suggest that the interaction between the Pr[118-135] peptide and the plasma membrane of neurons might represent an early event in a cascade leading to neurodegeneration.

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.