Cellular cofactors for amyloid beta-peptide-induced cell stress. Moving from cell culture to in vivo

Aging is not a disease: distinguishing age-related macular degeneration from aging

Age-related macular degeneration (AMD) is a disease of the outer retina, characterized most significantly by atrophy of photoreceptors and retinal pigment epithelium accompanied with or without choroidal neovascularization. Development of AMD has been recognized as contingent on environmental and genetic risk factors, the strongest being advanced age. In this review, we highlight pathogenic changes that destabilize ocular homeostasis and promote AMD development. With normal aging, photoreceptors are steadily lost, Bruch's membrane thickens, the choroid thins, and hard drusen may form in the periphery. In AMD, many of these changes are exacerbated in addition to the development of disease-specific factors such as soft macular drusen. Para-inflammation, which can be thought of as an intermediate between basal and robust levels of inflammation, develops within the retina in an attempt to maintain ocular homeostasis, reflected by increased expression of the anti-inflammatory cytokine IL-10 coupled with shifts in macrophage plasticity from the pro-inflammatory M1 to the anti-inflammatory M2 polarization. In AMD, imbalances in the M1 and M2 populations together with activation of retinal microglia are observed and potentially contribute to tissue degeneration. Nonetheless, the retina persists in a state of chronic inflammation and increased expression of certain cytokines and inflammasomes is observed. Since not everyone develops AMD, the vital question to ask is how the body establishes a balance between normal age-related changes and the pathological phenotypes in AMD.

Neurotoxicity of amyloid β-protein: synaptic and network dysfunction

Evidence for an ever-expanding variety of molecular mediators of amyloid β-protein neurotoxicity (membrane lipids, receptor proteins, channel proteins, second messengers and related signaling cascades, cytoskeletal proteins, inflammatory mediators, etc.) has led to the notion that the binding of hydrophobic Aβ assemblies to cellular membranes triggers multiple effects affecting diverse pathways. It appears unlikely that there are only one or two cognate receptors for neurotoxic forms of Aβ and also that there are just one or two assembly forms of the peptide that induce neuronal dysfunction. Rather, various soluble (diffusible) oligomers of Aβ that may be in dynamic equilibrium with insoluble, fibrillar deposits (amyloid plaques) and that can bind to different components of neuronal and non-neuronal plasma membranes appear to induce complex patterns of synaptic dysfunction and network disorganization that underlie the intermittent but gradually progressive cognitive manifestations of the clinical disorder. Modern analyses of this problem utilize electrophysiology coupled with synaptic biochemistry and behavioral phenotyping of animal models to elucidate the affected circuits and assess the effects of potential therapeutic interventions.

PPAR alpha: a novel radiation target in locally exposed Mus musculus heart revealed by quantitative proteomics

Radiation exposure of the thorax is associated with a markedly increased risk of cardiac morbidity and mortality with a latency period of decades. Although many studies have confirmed the damaging effect of ionizing radiation on the myocardium and cardiac endothelial structure and function, the molecular mechanism behind this damage is not yet elucidated. Peroxisome proliferator-activated receptor alpha (PPAR alpha), a transcriptional regulator of lipid metabolism in heart tissue, has recently received great attention in the development of cardiovascular disease. The goal of this study was to investigate radiation-induced cardiac damage in general and the role of PPAR alpha in this process in particular. C57BL/6 mice received local heart irradiation with X-ray doses of 8 and 16 gray (Gy) at the age of 8 weeks. The mice were sacrificed 16 weeks later. Radiation-induced changes in the cardiac proteome were quantified using the Isotope Coded Protein Label (ICPL) method followed by mass spectrometry and software analysis. Significant alterations were observed in proteins involved in lipid metabolism and oxidative phosphorylation. Ionizing radiation markedly changed the phosphorylation and ubiquitination status of PPAR alpha. This was reflected as decreased expression of its target genes involved in energy metabolism and mitochondrial respiratory chain confirming the proteomics data. This study suggests that persistent alteration of cardiac metabolism due to impaired PPAR alpha activity contributes to the heart pathology after radiation.

Increased CSF-BACE 1 activity is associated with ApoE-epsilon 4 genotype in subjects with mild cognitive impairment and Alzheimer's disease

The Apolipoprotein (ApoE) epsilon 4 allele is a major genetic risk factor of Alzheimer's disease, and may affect the production of amyloid beta (A beta(1-42)). Recently, we have shown that beta-secretase (BACE 1) activity can be reliably detected within the brain and human CSF. Here, we have examined an association between the ApoE genotype and CSF-levels of BACE 1 activity in Alzheimer's disease and mild cognitive impairment (MCI). A total of 148 subjects were included: 60 Alzheimer's disease patients, 51 MCI subjects and 37 elderly healthy controls. The CSF-levels of A beta(1-42), BACE 1 activity and BACE protein were measured in all of these subjects. The differences between ApoE-epsilon 4 carriers and ApoE-epsilon 4 non-carriers in these CSF-based measures were determined controlling for gender, age and MMSE score. The ApoE-epsilon 4 genotype was associated with increased BACE 1 activity in both Alzheimer's disease (P = 0.03) and MCI (P = 0.04) subjects. Levels of A beta(1-42) were decreased in ApoE-epsilon 4 carriers in MCI (P = 0.004) but not Alzheimer's disease subjects. This study is the first to demonstrate the association between ApoE-epsilon 4 and CSF-BACE 1 activity in MCI and Alzheimer's disease subjects. The assessment of BACE 1 in CSF may provide a sensitive measure to detect in vivo alterations in the amyloidogenic processing potentially modified by the ApoE genotype.

Inhibiting protein–amyloid interactions with small molecules: A surface chemistry approach

This paper presents a surface-based approach to inhibit the binding of proteins to Alzheimer's-related beta-amyloid (Abeta) fibrils with small molecules. It reports the idea of using an intracellular, disease-related fibril as a material whose surface can be coated with small molecules. Using an ELISA-based assay, molecular surface coatings with thioflavin T are shown to inhibit 65+/-10% of the binding of two different anti-Abeta IgGs to Abeta fibrils. A molecular surface coating with 3,6-diamino acridine was able to inhibit 76+/-10% of the binding of an anti-Abeta IgG to Abeta fibrils. Maximal inhibition of these protein-amyloid interactions appears in the low to mid-micromolar range of small molecule. This demonstration that molecular surface coatings can be used to attenuate the interaction of proteins with these fibrils suggests a potentially new strategy for therapeutics in neurodegenerative amyloid diseases.

Investigations with cultured human microglia on pathogenic mechanisms of Alzheimer's disease and other neurodegenerative diseases

Inflammation-mediated mechanisms for human neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD) have evolved from being on the fringe of medical hypotheses to mainstream thinking. Pioneering immunopathology studies with human brain tissues identified microglia associated with neuropathologic hallmarks of these diseases. As activated macrophages were known to produce many potential toxic products, this gave rise to the hypothesis that activated microglia (brain resident macrophages) could be contributing to the degeneration of key target neurons in these diseases, as well as potential vascular dysfunction. Studies with microglia derived from different sources, including human brains, have confirmed that activated microglia can mediate neuronal cell death. Based on these theories, a number of human clinical trials with antiinflammatory agents have been carried out on AD patients. Results to date have indicated a lack of effectiveness at slowing disease progression and have begun to cast doubt on the significance of inflammation in AD. It has been shown recently that activating microglia through immunization of amyloid plaque-developing mice with amyloid beta peptide (Abeta) has promise as a therapeutic strategy and despite some setbacks, has potential as a treatment for AD patients. This article will consider experimental data with microglia to determine whether the additional targets need to be investigated. The use of human microglia cultures, in particular those derived from elderly diseased human brains, offers an experimental system that can closely model the cell type activated in human neurodegenerative diseases. Experimental data produced by our laboratory and others is reviewed to determine the contribution of this unique experimental model to understanding disease mechanisms and possibly discovering new therapeutic targets.

Stimulation of G-proteins in human control and Alzheimer's disease brain by FAD mutants of APP(714-723): implication of oxidative mechanisms

We report the effects of amyloid precursor protein (APP) fragment 714-723 (APP(714-723); peptide P1) and its V717F and V717G mutants (peptides P2 and P3, respectively) on G-protein activity ([35S]GTPgammaS binding) in membranes from postmortem human control and Alzheimer's disease (AD) brains. The peptides P1, P2, and P3 revealed a significant stimulatory effect on [35S]GTPgammaS binding in control temporal cortex. The most potent stimulator, P3, at 10 microM concentration enhanced [35S]GTPgammaS binding by 500%. The effect was threefold stronger than that for wild-type P1 and twofold stronger than that for P2. In sporadic AD, the stimulatory effect of P1, P2, and P3 on G-proteins was reduced significantly whereas in Swedish familial AD (SFAD), only P1 elicited marked stimulation (at 10 microM by 50%). In control sensory postcentral cortex, the stimulation of G-proteins by P3 was 1.5-fold lower than that in control temporal cortex, whereas in AD and SFAD the effect showed no remarkable regional difference. Treatment of membranes with H2O2 produced 1.5-fold higher stimulation in [35S]GTPgammaS binding to temporal cortex than that in binding to sensory postcentral cortex. In AD and SFAD, the stimulation by H2O2 revealed no significant regional difference. Glutathione, desferrioxamine (DFO), and 17beta-estradiol markedly decreased the strong stimulatory effect by P3 on [35S]GTPgammaS binding to control temporal cortex, with the protective effect by DFO being most potent. The G(alphaO)-protein levels were not changed in AD or SFAD brain membranes as compared to levels in control membranes. We suggest that strong G-protein stimulation by P3 in the human brain implies the specific (per)oxidation mechanism that might be affected by regional content of peroxidizing substrates and antioxidants.

ABAD enhances Abeta-induced cell stress via mitochondrial dysfunction

Amyloid-beta peptide (Abeta) binding alcohol dehydrogenase (ABAD), an enzyme present in neuronal mitochondria, is a cofactor facilitating Abeta-induced cell stress. We hypothesized that ABAD provides a direct link between Abeta and cytotoxicity via mitochondrial oxidant stress. Neurons cultured from transgenic (Tg) mice with targeted overexpression of a mutant form of amyloid precursor protein and ABAD (Tg mAPP/ABAD) displayed spontaneous generation of hydrogen peroxide and superoxide anion, and decreased ATP, as well as subsequent release of cytochrome c from mitochondria and induction of caspase-3-like activity followed by DNA fragmentation and loss of cell viability. Generation of reactive oxygen species (ROS) was associated with dysfunction at the level of mitochondrial complex IV (cytochrome c oxidase, or COX). In neurons cultured from Tg mAPP/ABAD mice, COX activity was selectively decreased, and cyanide, an inhibitor of complex IV, exacerbated leakage of ROS, induction of caspase-3-like activity, and DNA fragmentation. In vivo, Tg mAPP/ABAD mice displayed reduced levels of brain ATP and COX activity, diminished glucose utilization, as well as electrophysiological abnormalities in hippocampal slices compared with Tg mAPP mice. In contrast, neither Tg ABAD mice nor nontransgenic (non-TG) littermates showed similar changes in ATP, COX activity, glucose utilization or electrophysiological properties. Each of the genotypes (Tg ABAD, Tg mAPP and Tg mAPP/ABAD mice, and non-TG littermates) displayed normal reproductive fitness, development and lifespan (1) These findings link ABAD-induced oxidant stress to critical aspects of Alzheimer's disease (AD)-associated cellular dysfunction, suggesting a pivotal role for this enzyme in the pathogenesis of AD.

Familial amyloidotic polyneuropathy: protein aggregation in the peripheral nervous system

The molecular pathology underlying transthyretin (TTR)-related amyloidosis is largely unknown. It is possible that a common factor in the amyloidogenesis process exists among the different forms; this common factor can involve changes produced by mutations in the three-dimensional structure of TTR, rendering it prone to deposition as amyloid. This amyloidogenic potential, together with other yet unidentified factors, contribute to amyloid deposition. The factors that trigger fibril formation and/or neurodegeneration in TTR-related amyloidosis present central questions for which there are still no available clues. We recently showed in vitro that TTR fibrils trigger NF-kappaB activation, and subsequent studies identified some inflammatory and apoptotic pathways opening perspectives to understand the neurodegeneration process in familial amyloidotic polyneuropathy (FAP). It is current opinion that the modified TTR represents an amyloidogenic intermediate, which integrates the fibril structure; analyses of FAP fibrils have proved that TTR in the fibrils maintains a beta-conformation and have suggested that the TTR monomer is the building block in fibrils. This concept has been questioned recently by investigators, and only future studies on native and synthetic TTR fibrils using high-resolution structural techniques will further elucidate fibril structure and the aggregation pathway. Modulators responsible for phenotypic diversity can be addressed by mice transgenic for different human TTR mutations. Different lines are now available; incomplete penetrance and environmental influence on the deposition of mutant TTR has been observed. Therefore, these animals constitute important tools to address modulators of phenotypic expression and pathophysiological consequences of amyloid deposition at cellular/molecular levels. They are pivotal for testing potential drugs for TTR amyloidosis as well.

Molecular and functional dissection of TGF-beta1-induced cerebrovascular abnormalities in transgenic mice

Cerebrovascular abnormalities, such as reduced blood flow, microvascular fibrosis, and cerebrovascular amyloid angiopathy, are prominent in Alzheimer's disease (AD). However, their etiology is poorly understood and it is unclear whether cerebrovascular changes contribute to functional impairments in the absence of neurodegeneration. In humans with AD, transforming growth factor-beta1 (TGF-beta1) mRNA levels in the midfrontal gyrus correlate positively with the relative degree of cerebrovascular amyloid deposition in that brain region, suggesting a possible role for TGF-beta1 in human cerebrovascular abnormalities. Transgenic mice overexpressing TGF-beta1 in astrocytes develop AD-like cerebrovascular abnormalities, including perivascular astrocytosis, microvascular basement membrane thickening, and accumulation of thioflavin S-positive amyloid in the absence of parenchymal degeneration. Mice overexpressing TGF-beta1 alone or in addition to human amyloid precursor protein (hAPP) show selective accumulation of human beta-amyloid (Abeta) in blood vessels and develop cerebral hemorrhages in old age. In 9-month-old TGF-beta1 transgenic mice, cerebral blood flow (CBF) in the limbic system was significantly less than in nontransgenic littermate controls. Aged TGF-beta1 mice also showed overall reduced cerebral glucose uptake (CGU) as a measure of brain activity. Thus, chronic overproduction of TGF-beta1 in the brain results in structural and functional impairments reminiscent of those in AD cases with amyloid angiopathy.

Inflammation in neurodegenerative disease--a double-edged sword

Inflammation is a defense reaction against diverse insults, designed to remove noxious agents and to inhibit their detrimental effects. It consists of a dazzling array of molecular and cellular mechanisms and an intricate network of controls to keep them in check. In neurodegenerative diseases, inflammation may be triggered by the accumulation of proteins with abnormal conformations or by signals emanating from injured neurons. Given the multiple functions of many inflammatory factors, it has been difficult to pinpoint their roles in specific (patho)physiological situations. Studies of genetically modified mice and of molecular pathways in activated glia are beginning to shed light on this issue. Altered expression of different inflammatory factors can either promote or counteract neurodegenerative processes. Since many inflammatory responses are beneficial, directing and instructing the inflammatory machinery may be a better therapeutic objective than suppressing it.

The AGE-receptor in the pathogenesis of diabetic complications

Native glucose-derived glycation derivatives (advanced glycation end products, AGE) in vascular, renal and neuronal tissues contribute to organ damage. Glycation derivatives include a number of chemically and cell-reactive substances, also termed glycoxidation products or glycotoxins (GT). Cell-associated AGE-specific receptors (AGE-Rs), AGE-R1-3, RAGE, as well as the scavenger receptors ScR-II and CD-36 that are present on vascular, renal, hemopoietic, and neuronal/glial cells, serve in the regulation of AGE uptake and removal. AGE-Rs also modulate cell activation, growth-related mediators, and cell proliferation, consequently influencing organ structure/function. This occurs via oxidant stress triggered via receptor-dependent or -independent pathways, and leads to signal activation pathways, resulting in pro-inflammatory responses. In susceptible individuals, the AGE-R expression/function may be subject to environmental or gene-related modulation, which in turn may influence tissue-specific gene functions. In this context, altered expression and activity of AGE-R components has recently been found in both mouse diabetes models and humans with diabetic complications. Although several gene polymorphisms are detected in most AGE-R components, no significant correlation to diabetic complications has as yet been found. Further investigation is underway to define whether primary or secondary genetic links of pathogenic significance exist in this system. Various AGE-binding peptides or soluble receptors have emerged as potential sequestering agents for toxic AGEs as potential therapies for diabetic complications.

Familial amyloid polyneuropathy: receptor for advanced glycation end products-dependent triggering of neuronal inflammatory and apoptotic pathways

Familial amyloid polyneuropathy (FAP) is a neurodegenerative disorder associated with extracellular deposition of mutant transthyretin (TTR) amyloid fibrils, particularly in the peripheral nervous system. We have hypothesized that binding of TTR fibrils to the receptor for advanced glycation end products (RAGE) on critical cellular targets is associated with a destructive stress response underlying peripheral nerve dysfunction. Analysis of nerve biopsy samples from patients with FAP (n = 16) at different stages of disease (0-3), compared with age-matched controls (n = 4), by semiquantitative immunohistology and in situ hybridization showed increased levels of RAGE, beginning at the earliest stages of the disease (FAP 0; p < 0.02) and especially localized in axons. Upregulation of proinflammatory cytokines (tumor necrosis factor-alpha and interleukin-1beta) (approximately threefold; p < 0.02) and the inducible form of nitric oxide synthase (iNOS) ( approximately 2.5-fold; p < 0.04) was also observed in a distribution overlapping RAGE expression. Tyrosine nitration and increased activated caspase-3 in axons from FAP patients (p < 0.03) were apparent. Although these data suggest the presence of ongoing neuronal stress, there was no upregulation of neurotrophins (nerve growth factor and neurotrophin-3) in FAP nerves. Studies on cultured neuronal-like, Schwann, and endothelial cells incubated with TTR fibrils displayed RAGE-dependent expression of cytokines and iNOS at early times (6 and 12 hr, respectively), followed by later (24 hr) activation of caspase-3 and DNA fragmentation. We propose that the interaction of TTR fibrils with RAGE may contribute to cellular stress and toxicity in FAP. Furthermore, there is an apparent lack of responsiveness of Schwann cells in FAP nerve to provide neurotrophic factors.

Familial amyloid polyneuropathy: receptor for advanced glycation end products-dependent triggering of neuronal inflammatory and apoptotic pathways

Familial amyloid polyneuropathy (FAP) is a neurodegenerative disorder associated with extracellular deposition of mutant transthyretin (TTR) amyloid fibrils, particularly in the peripheral nervous system. We have hypothesized that binding of TTR fibrils to the receptor for advanced glycation end products (RAGE) on critical cellular targets is associated with a destructive stress response underlying peripheral nerve dysfunction. Analysis of nerve biopsy samples from patients with FAP (n = 16) at different stages of disease (0-3), compared with age-matched controls (n = 4), by semiquantitative immunohistology and in situ hybridization showed increased levels of RAGE, beginning at the earliest stages of the disease (FAP 0; p < 0.02) and especially localized in axons. Upregulation of proinflammatory cytokines (tumor necrosis factor-alpha and interleukin-1beta) (approximately threefold; p < 0.02) and the inducible form of nitric oxide synthase (iNOS) ( approximately 2.5-fold; p < 0.04) was also observed in a distribution overlapping RAGE expression. Tyrosine nitration and increased activated caspase-3 in axons from FAP patients (p < 0.03) were apparent. Although these data suggest the presence of ongoing neuronal stress, there was no upregulation of neurotrophins (nerve growth factor and neurotrophin-3) in FAP nerves. Studies on cultured neuronal-like, Schwann, and endothelial cells incubated with TTR fibrils displayed RAGE-dependent expression of cytokines and iNOS at early times (6 and 12 hr, respectively), followed by later (24 hr) activation of caspase-3 and DNA fragmentation. We propose that the interaction of TTR fibrils with RAGE may contribute to cellular stress and toxicity in FAP. Furthermore, there is an apparent lack of responsiveness of Schwann cells in FAP nerve to provide neurotrophic factors.

Secreted forms of the amyloid-beta precursor protein are ligands for the class A scavenger receptor

Upon activation, platelets secrete a 120-kDa protein that competes for the binding and internalization of acetyl low density lipoproteins (AcLDL) by macrophages. From the amino-terminal amino acid sequence, amino acid composition, and immunoblot analysis, we identified the active factor in platelet secretion products as sAPP, an alpha-secretase cleavage product of the beta-amyloid precursor protein (APP), that contains a Kunitz-type protease inhibitor (KPI) domain. We showed that both sAPP751 (also called Nexin II) and sAPP695, which does not contain a KPI domain, are ligands for the class A scavenger receptor (SR-A). Chinese hamster ovary cells stably transfected to express the SR-A bound and internalized 4-fold more human platelet-derived sAPP than control cells. The binding and internalization of sAPP were inhibited by the SR-A antagonist fucoidin. In addition, sAPP competed as effectively as fucoidin for SR-A-mediated cell association and degradation of (125)I-AcLDL. To determine if the KPI domain is required for the binding of sAPP to the SR-A, APP751 and APP695 were expressed in Chinese hamster ovary cells, and sAPP751 and sAPP695 purified from the medium were tested for their binding to the SR-A. sAPP751 and sAPP695 were equally effective in competing for the cell association of (125)I-AcLDL by SR-A-expressing cells, demonstrating that the KPI domain is not essential for binding. We also found that sAPP751 is present in extracts of atherosclerotic lesions and that sAPP competes for the SR-A-mediated cell association of oxidized low density lipoprotein. Deletion mutagenesis indicated that a negatively charged region of APP (residues 191-264) contributes to binding to the SR-A. These results suggest that the SR-A contributes to the clearance of sAPP and that sAPP competes for the cell association of other SR-A ligands.

beta-Amyloid protein induces the formation of purine dimers in cellular DNA

Experimental evidence implicates oxidative free radical reactions as central in the processes of neurodegenerative diseases. In particular, cellular interactions with the beta-amyloid protein have been linked to neuron cell death in Alzheimer's disease. Also, uncharacterized dimeric purine moieties have been detected in oxidized DNAs. It has been suggested that inadequate excision-repair of such products plays a functional role in the neurological degeneration observed in familial Alzheimer's disease, Down's syndrome, and xeroderma pigmentosum. Therefore, in order to obtain a reagent to monitor the presence of such products, the purine dimer 8-8-(2'-deoxyguanosyl)-2'-deoxyguanosine-5'-monophosphate was used as a hapten for elicitation of rabbit anti-purine dimer antiserum. This antiserum specifically recognizes various purified 8-8-bideoxyribonucleosides and 8-8-bideoxyribonucleotides. We found that DNA oxidized by the Fenton reaction is specifically recognized by this antiserum. This reagent can therefore be used to demonstrate formation and excision of DNA purine dimers. Moreover, incubation of cultured rat pheochromocytoma PC-12 cells with the beta-amyloid protein resulted in formation of these purine dimers in cellular DNA. These dimers were subsequently removed from cellular DNA. From these results we conclude that the free radicals generated by A beta cause oxidative DNA alterations including purine dimers. Deficient repair of this type of DNA damage might result in neural cell loss via apoptosis. Our findings suggest mechanisms for the roles of beta-amyloid and oxidative free radicals in neurodegenerative diseases and the role of DNA excision-repair in the prevention of lethal neurotoxicity.

TGF-beta1 promotes microglial amyloid-beta clearance and reduces plaque burden in transgenic mice

Abnormal accumulation of the amyloid-beta peptide (Abeta) in the brain appears crucial to pathogenesis in all forms of Alzheimer disease (AD), but the underlying mechanisms in the sporadic forms of AD remain unknown. Transforming growth factor beta1 (TGF-beta1), a key regulator of the brain's responses to injury and inflammation, has been implicated in Abeta deposition in vivo. Here we demonstrate that a modest increase in astroglial TGF-beta1 production in aged transgenic mice expressing the human beta-amyloid precursor protein (hAPP) results in a three-fold reduction in the number of parenchymal amyloid plaques, a 50% reduction in the overall Abeta load in the hippocampus and neocortex, and a decrease in the number of dystrophic neurites. In mice expressing hAPP and TGF-beta1, Abeta accumulated substantially in cerebral blood vessels, but not in parenchymal plaques. In human cases of AD, Abeta immunoreactivity associated with parenchymal plaques was inversely correlated with Abeta in blood vessels and cortical TGF-beta1 mRNA levels. The reduction of parenchymal plaques in hAPP/TGF-beta1 mice was associated with a strong activation of microglia and an increase in inflammatory mediators. Recombinant TGF-beta1 stimulated Abeta clearance in microglial cell cultures. These results demonstrate that TGF-beta1 is an important modifier of amyloid deposition in vivo and indicate that TGF-beta1 might promote microglial processes that inhibit the accumulation of Abeta in the brain parenchyma.

Stress and molecular chaperones in disease

Stress, a common phenomenon in today's society, is suspected of playing a role in the development of disease. Stressors of various types, psychological, physical, and biological, abound. They occur in the working and social environments, in air, soil, water, food, and medicines. Stressors impact on cells directly or indirectly, cause protein denaturation, and elicit a stress response. This is mediated by stress (heat-shock) genes and proteins, among which are those named molecular chaperones because they assist other proteins to achieve and maintain a functional shape (the native configuration), and to recover it when partially lost due to stress. Denatured proteins tend to aggregate and precipitate. The same occurs with abnormal proteins due to mutations, or to failure of post-transcriptional or post-translational mechanisms. These abnormal proteins need the help of molecular chaperones as much as denatured molecules do, especially during stress. A cell with normal antistress mechanisms, including a complete and functional set of chaperones, may be able to withstand stress if its intensity is not beyond that which will cause irreversible protein damage. There is a certain threshold that normal cells have above which they cannot cope with stress. A cell with an abnormal protein that has an intrinsic tendency to misfold and aggregate is more vulnerable to stress than normal counterparts. Furthermore, these abnormal proteins may precipitate even in the absence of stress and cause diseases named proteinopathies. It is possible that stress contributes to the pathogenesis of proteinopathies by promoting protein aggregation, even in cells that possess a normal chaperoning system. Examples of proteinopathies are age-related degenerative disorders with protein deposits in various tissues, most importantly in the brain where the deposits are associated with neuronal degeneration. It is conceivable that stress enhances the progression of these diseases by facilitating protein unfolding and misfolding, which lead to aggregation and deposition. A number of reports in the last few years have described research aimed at elucidating the role of heatshock proteins, molecular chaperones in particular, in the pathogenesis of neurodegenerative disorders. The findings begin to shed light on the molecular mechanism of protein aggregation and deposition, and of the ensuing cell death. The results also begin to elucidate the role of molecular chaperones in pathogenesis. This is a fascinating area of research with great clinical implications. Although there are already several experimental models for the study of proteinopathies, others should be developed using organisms that are better known now than only a few years ago and that offer unique advantages. Use of these systems and of information available in databases from genome sequencing efforts should boost research in this field. It should be possible in the not-too-distant future to develop therapeutic and preventive means for proteinopathies based on the use of heat-shock protein and molecular chaperone genes and proteins.

Receptor-dependent cell stress and amyloid accumulation in systemic amyloidosis

Accumulation of fibrils composed of amyloid A in tissues resulting in displacement of normal structures and cellular dysfunction is the characteristic feature of systemic amyloidoses. Here we show that RAGE, a multiligand immunoglobulin superfamily cell surface molecule, is a receptor for the amyloidogenic form of serum amyloid A. Interactions between RAGE and amyloid A induced cellular perturbation. In a mouse model, amyloid A accumulation, evidence of cell stress and expression of RAGE were closely linked. Antagonizing RAGE suppressed cell stress and amyloid deposition in mouse spleens. These data indicate that RAGE is a potential target for inhibiting accumulation of amyloid A and for limiting cellular dysfunction induced by amyloid A.