Complement C1q and C3 mRNA expression in the frontal cortex of Alzheimer's patients

Stem Cell Therapies for Intracerebral Hemorrhage: Review of Preclinical and Clinical Studies

Despite recent developments in the treatments for ischemic stroke, such as tissue plasminogen activator (t-PA) and thrombectomy, effective therapies for intracerebral hemorrhage (ICH) remain scarce. Stem cell therapies have attracted considerable attention owing to their potential neuro-regenerative ability; preclinical and clinical studies have been conducted to explore strategies for achieving functional recovery following ICH. In this review, we summarize the findings of preclinical studies on stem cell therapies of ICH, with a focus on different animal models, stem cell sources, transplantation methods, and their potential mechanisms of action. We also provide an overview of data from clinical trials to discuss the current status and future perspectives. Understanding the effectiveness and limitations of stem cell therapy and the future prospects could expand the applications of this novel therapeutic approach for ICH.

Neuroprotective Action of Coumarin Derivatives through Activation of TRKB-CREB-BDNF Pathway and Reduction of Caspase Activity in Neuronal Cells Expressing Pro-Aggregated Tau Protein

Hyperphosphorylation and aggregation of the microtubule binding protein tau is a neuropathological hallmark of Alzheimer’s disease/tauopathies. Tau neurotoxicity provokes alterations in brain-derived neurotrophic factor (BDNF)/tropomycin receptor kinase B (TRKB)/cAMP-response-element binding protein (CREB) signaling to contribute to neurodegeneration. Compounds activating TRKB may therefore provide beneficial effects in tauopathies. LM-031, a coumarin derivative, has demonstrated the potential to improve BDNF signaling in neuronal cells expressing pro-aggregated ΔK280 tau mutant. In this study, we investigated if LM-031 analogous compounds provide neuroprotection effects through interaction with TRKB in SH-SY5Y cells expressing ΔK280 tau_RD-DsRed folding reporter. All four LMDS compounds reduced tau aggregation and reactive oxygen species. Among them, LMDS-1 and -2 reduced caspase-1, caspase-6 and caspase-3 activities and promoted neurite outgrowth, and the effect was significantly reversed by knockdown of TRKB. Treatment of ERK inhibitor U0126 or PI3K inhibitor wortmannin decreased p-CREB, BDNF and BCL2 in these cells, implying that the neuroprotective effects of LMDS-1/2 are via activating TRKB downstream ERK, PI3K-AKT and CREB signaling. Furthermore, LMDS-1/2 demonstrated their ability to quench the intrinsic fluorescence of tryptophan residues within the extracellular domain of TRKB, thereby consolidating their interaction with TRKB. Our results suggest that LMDS-1/2 exert neuroprotection through activating TRKB signaling, and shed light on their potential application in therapeutics of Alzheimer’s disease/tauopathies.

Identification of the function and mechanism of m6A reader IGF2BP2 in Alzheimer's disease

Alzheimer’s disease, the most common form of dementia in the elderly, is a kind of neurodegenerative disease. However, its pathogenesis and diagnosis remain unclear. M6A is related to nervous system development and neurodegenerative diseases. Here in this study, using multiple RNA-seq datasets of Alzheimer’s brain tissues, along with bioinformatic analysis, we innovatively found that m6A reader protein IGF2BP2 was abnormally highly expressed in Alzheimer’s patients. After compared between Alzheimer’s and normal brain samples, and between IGF2BP2- high and IGF2BP2- low subgroups of Alzheimer’s patients, we took the shared differentially expressed genes as the relevant gene sets of IGF2PB2 affecting Alzheimer’s disease occurrence for subsequent analysis. Then, weight gene correlation analysis was conducted and 17 functional modules were identified. The module that most positively correlated with Alzheimer’s disease and IGF2PB2-high subgroups were mainly participated in ECM receptor interaction, focal adhesion, cytokine-cytokine receptor interaction, and TGF-beta signaling pathway. Afterwards, a hub gene-based model including 20 genes was constructed by LASSO regression and validated by ROC curve for Alzheimer diagnosis. Finally, we preliminarily elucidated that IGF2BP2 could bind with mRNAs in a m6A-dependent manner. This study first elucidates the pathogenic role of IGF2BP2 in Alzheimer’s disease. IGF2BP2 and its relevant m6A modifications are potential to be new diagnostic and therapeutic targets for Alzheimer’s patients.

The complement cascade in Alzheimer's disease: a systematic review and meta-analysis

Genetic evidence implicates a causal role for the complement pathway in Alzheimer's disease (AD). Since studies have shown inconsistent differences in cerebrospinal fluid (CSF) and peripheral blood complement protein concentrations between AD patients and healthy elderly, this study sought to summarize the clinical data. Original peer-reviewed articles measuring CSF and/or blood concentrations of complement or complement regulator protein concentrations in AD and healthy elderly control (HC) groups were included. Of 2966 records identified, means and standard deviations from 86 studies were summarized as standardized mean differences (SMD) by random effects meta-analyses. In CSF, concentrations of clusterin (N_AD/N_HC = 625/577, SMD = 0.53, Z₈ = 8.81, p < 0.005; I² < 0.005%) and complement component 3 (C3; N_AD/N_HC = 299/522, SMD = 0.45, Z₃ = 3.21, p < 0.005; I² = 68.40%) were significantly higher in AD, but differences in C1q, C-reactive protein (CRP), serum amyloid protein (SAP), and factor H concentrations were not significant. In peripheral blood, concentrations of CRP were elevated in AD (N_AD/N_HC = 3404/3332, SMD = 0.44, Z₄₃ = 3.43, p < 0.005; I² = 93.81%), but differences between groups in C3, C4, C1-inhibitor, SAP, factor H and clusterin concentrations were not significant, and inconsistent between studies. Of 64 complement pathway proteins or regulators in the quantitative synthesis, trends in C1q, factor B, C4a, and late-stage complement pathway components (e.g. C9) in blood, C4 in CSF, and the membrane attack complex in blood and CSF, might be investigated further. The results collectively support elevated complement pathway activity in AD, which was best characterized by increased CSF clusterin concentrations and less consistently by CSF C3 concentrations. Complement activity related to an AD diagnosis was not reflected consistently by the peripheral blood proteins investigated.

Association Between Adenosine A2A Receptors and Connexin 43 Regulates Hemichannels Activity and ATP Release in Astrocytes Exposed to Amyloid-β Peptides

Increasing evidence implicates astrocytes and the associated purinergic modulation in Alzheimer's disease (AD), characterized by cognitive deficits involving the extracellular amyloid-β peptides (Aβ) accumulation. Aβ can affect astrocytic gliotransmitters release, namely ATP, which is rapidly metabolized into adenosine by ecto-5'-nucleotidase, CD73, resulting in adenosine A_2A receptors (A_2AR) activation that bolsters neurodegeneration. AD's brains exhibit an upregulation of A_2AR and of connexin 43 (Cx43), which in astrocytes forms hemichannels that can mediate ATP release. However, a coupling between astrocytic A_2AR and Cx43 remains to be established. This was now investigated using astrocytic primary cultures exposed to Aβ_1-42 peptides. Aβ triggered ATP release through Cx43 hemichannels, a process blocked by A_2AR antagonists and mimicked by selective A_2AR activation. A_2AR directly regulated hemichannels activity and prevented Cx43 upregulation and phosphorylation observed in Aβ_1-42-exposed astrocytes. Moreover, a proximity ligand assay revealed a physical association between astrocytic A_2AR and Cx43. Finally, the blockade of CD73-mediated extracellular formation of ATP-derived adenosine prevented the Aβ-induced increase of Cx43 hemichannel activity and of ATP release. Overall, the data identify a feed-forward loop involving astrocytic A_2AR and Cx43 hemichannels, whereby A_2AR increase Cx43 hemichannel activity leading to increased ATP release, which is converted into adenosine by CD73, sustaining the increased astrocytic A_2AR activity in AD-like conditions.

Complement Component C3 Loss leads to Locomotor Deficits and Altered Cerebellar Internal Granule Cell In Vitro Synaptic Protein Expression in C57BL/6 Mice

Complement component 3 (C3) expression is increased in the cerebellum of aging mice that demonstrate locomotor impairments and increased excitatory synapse density. However, C3 regulation of locomotion, as well as C3 roles in excitatory synapse function, remains poorly understood. Here, we demonstrate that constitutive loss of C3 function in mice evokes a locomotor phenotype characterized by decreased speed, increased active state locomotor probability, and gait ataxia. C3 loss does not alter metabolism or body mass composition. No evidence of significant muscle weakness or degenerative arthritis was found in C3 knockout mice to explain decreased gait speeds. In an enriched primary cerebellar granule cell culture model, loss of C3 protein results in increased excitatory synaptic density and increased response to KCl depolarization. Our analysis of excitatory synaptic density in the cerebellar internal granule cell and molecular layers did not demonstrate increased synaptic density in vivo, suggesting the presence of compensatory mechanisms regulating synaptic development. Functional deficits in C3 knockout mice are therefore more likely to result from altered synaptic function and/or connectivity than gross synaptic deficits. Our data demonstrate a novel role for complement proteins in cerebellar regulation of locomotor output and control.

lncRNA-Associated Competitive Endogenous RNA Regulatory Network in an Aβ25-35-Induced AD Mouse Model Treated with Tripterygium Glycoside

BACKGROUND

Tripterygium glycoside (TG) has been suggested to have protective effects on the diseases of the central nervous system including Alzheimer's disease (AD). The mechanisms involving lncRNA-associated competing endogenous RNAs (ceRNAs) were shown to play important roles in the development of AD. However, the ceRNA mechanism of TG in treating AD is still unknown. Thus, we aimed to explore the ceRNA mechanism in the treatment of AD with TG.

METHODS

A total of 32 C57BL/6J mice were administered 3 µL of Aβ25-35 (dual side, 1 mg/mL) by a single stereotactic injection in the brain to conduct AD mouse model. AD mouse models were randomly selected and divided into the AD+normal saline (NS) group (n=16) and the AD+TG group (n=16). The expression data of lncRNAs, mRNAs, and miRNAs in the hippocampus of mice from AD+NS group (n=3) and the AD+TG group (n=3) were obtained by microarray analysis. The MuTaME method was used to predict the ceRNA regulatory network. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed using the DAVID database. A protein-protein interaction (PPI) network was constructed by using STRING software.

RESULTS

TG can significantly improve spatial memory and inhibit the production of p-tau in an Aβ25-35-induced AD mouse model. A total of 661 differentially expressed lncRNAs, 503 mRNAs, and 13 miRNAs were identified. A ceRNA network involving the top 200 mRNA-miRNA-lncRNA pairs with 16 lncRNAs, 11 miRNAs, and 52 mRNAs was visualized. And a PPI network complex filtered 26 gene nodes in DEGs was predicted.

CONCLUSION

We have identified 503 DEGs, 661 DElncRNAs, and 13 DEmiRNAs during treatment with TG in Aβ25-35-induced AD mouse model. A ceRNA network based on the DElncRNAs, DEmRNAs, and DEmiRNAs was conducted, which provided new insight into the lncRNA-mediated ceRNA regulatory mechanisms underlying the effects of TG in the treatment of AD.

Methylxanthines and Neurodegenerative Diseases: An Update

Methylxanthines (MTX) are purine derived xanthine derivatives. Whereas naturally occurring methylxanthines like caffeine, theophylline or theobromine are widely consumed in food, several synthetic but also non-synthetic methylxanthines are used as pharmaceuticals, in particular in treating airway constrictions. Besides the well-established bronchoprotective effects, methylxanthines are also known to have anti-inflammatory and anti-oxidative properties, mediate changes in lipid homeostasis and have neuroprotective effects. Known molecular mechanisms include adenosine receptor antagonism, phosphodiesterase inhibition, effects on the cholinergic system, wnt signaling, histone deacetylase activation and gene regulation. By affecting several pathways associated with neurodegenerative diseases via different pleiotropic mechanisms and due to its moderate side effects, intake of methylxanthines have been suggested to be an interesting approach in dealing with neurodegeneration. Especially in the past years, the impact of methylxanthines in neurodegenerative diseases has been extensively studied and several new aspects have been elucidated. In this review we summarize the findings of methylxanthines linked to Alzheimer´s disease, Parkinson's disease and Multiple Sclerosis since 2017, focusing on epidemiological and clinical studies and addressing the underlying molecular mechanisms in cell culture experiments and animal studies in order to assess the neuroprotective potential of methylxanthines in these diseases.

Pharmacogenetic and Association Studies on the Influence of HLA Alleles and Rivastigmine on the Iranian Patients with Late-Onset Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder affecting cognitive function. A number of allelic genes from HLA complex have shown variable associations with AD in different populations. In this study, we investigated the association of DQB1*06:00/x, DRB1*04:00/x, DRB1*15:00/x, and B*07:00/x genotypes with AD and their relevance to the efficacy of rivastigmine treatment in the Iranian population. Our findings suggest that DQB1*06:00/x genotype offers strong protection against AD (P = 0.0074), while B*07:00/x genotype imposes a significant susceptibility for sporadic Alzheimer's disease (SAD) (P = 0.009). Interestingly, B*07:00/x genotype does not show any apparent associations with familial Alzheimer's disease (FAD). Our studies also suggest a pharmacogenetic relationship between drug treatment and presence of a particular genotype in the Iranian LOAD patient population. The Clinical Dementia Rating analysis showed that LOAD patients carrying DRB1*04:00/x genotype tend to display a downward trend in the disease severity and symptoms after 2-year follow-up with rivastigmine treatment. Moreover, in our total patient population, the carriers of DQB1*06:00/x and B*07:00/x alleles have better and worse responses to rivastigmine respectively. We also measured the clinical relevance of the testing for these genotypes employing prevalence-corrected positive predictive value (PcPPV) formula. The PcPPV of testing for DQB1*06:00/x in the Iranian LOAD patients was 1.17% which means that people carrying this genotype have half of the probability of the absolute risk for developing LOAD, whereas the PcPPV of testing for B*07:00/x was 4.45% for SAD, which can be interpreted as a doubling chance for developing LOAD among the Iranian population carrying this genotype. These results also suggest that DQβ1 peptide containing positively charged AAs histidine³⁰ and arginine⁵⁵ and HLA class I β chain containing negatively charges aspartic acid¹¹⁴ and glutamic acid^45,152 in their binding groove plays important roles in protection against and susceptibility for LOAD respectively.

Trajectory of change in brain complement factors from neonatal to young adult humans

Immune system components also regulate synapse formation and refinement in neurodevelopment. The complement pathway, associated with cell lysis and phagocytosis, is implicated in synaptic elimination. Aberrant adolescent synaptic pruning may underpin schizophrenia onset; thus, changes in cortical complement activity during human development are of major interest. Complement is genetically linked to schizophrenia via increased C4 copy number variants, but the developmental trajectory of complement expression in the human brain is undetermined. As complement increases during periods of active synaptic engulfment in rodents, we hypothesized that complement expression would increase during postnatal development in humans, particularly during adolescence. Using human postmortem prefrontal cortex, we observed that complement activator (C1QB and C3) transcripts peaked in early neurodevelopment, and were highest in toddlers, declining in teenagers (all ANCOVAs between F = 2.41 -3.325, p = .01-0.05). We found that C4 protein was higher at 1-5 years (H = 16.378, p = .012), whereas C3 protein levels were unchanged with age. The microglial complement receptor subunit CD11b increased in mRNA early in life and peaked in the toddler brain (ANCOVA: pH, F = 4.186, p = .003). Complement inhibitors (CD46 and CD55) increased at school age, but failed to decrease like complement activators (both ANCOVAs, F > 4.4, p < .01). These data suggest the activation of complement in the human prefrontal cortex occurs between 1 and 5 years. We did not find evidence of induction of complement factors during adolescence and instead found increased or sustained levels of complement inhibitor mRNA at maturation. Dysregulation of these typical patterns of complement may predispose the brain to neurodevelopmental disorders such as autism or schizophrenia.

Locus Coeruleus Modulates Neuroinflammation in Parkinsonism and Dementia

Locus Coeruleus (LC) is the main noradrenergic nucleus of the central nervous system, and its neurons widely innervate the whole brain. LC is severely degenerated both in Alzheimer’s disease (AD) and in Parkinson’s disease (PD), years before the onset of clinical symptoms, through mechanisms that differ among the two disorders. Several experimental studies have shown that noradrenaline modulates neuroinflammation, mainly by acting on microglia/astrocytes function. In the present review, after a brief introduction on the anatomy and physiology of LC, we provide an overview of experimental data supporting a pathogenetic role of LC degeneration in AD and PD. Then, we describe in detail experimental data, obtained in vitro and in vivo in animal models, which support a potential role of neuroinflammation in such a link, and the specific molecules (i.e., released cytokines, glial receptors, including pattern recognition receptors and others) whose expression is altered by LC degeneration and might play a key role in AD/PD pathogenesis. New imaging and biochemical tools have recently been developed in humans to estimate in vivo the integrity of LC, the degree of neuroinflammation, and pathology AD/PD biomarkers; it is auspicable that these will allow in the near future to test the existence of a link between LC-neuroinflammation and neurodegeneration directly in patients.

Molecular identification of protein kinase C beta in Alzheimer's disease

The purpose of this study was to investigate the potential roles of protein kinase C beta (PRKCB) in the pathogenesis of Alzheimer’s disease (AD). We identified 2,254 differentially expressed genes from 19,245 background genes in AD versus control as well as PRKCB-low versus high group. Five co-expression modules were constructed by weight gene correlation network analysis. Among them, the 1,222 genes of the turquoise module had the strongest relation to AD and those with low PRKCB expression, which were enriched in apoptosis, axon guidance, gap junction, Fc gamma receptor (FcγR)-mediated phagocytosis, mitogen-activated protein kinase (MAPK) and vascular endothelial growth factor (VEGF) signaling pathways. The intersection pathways of PRKCB in AD were determined, including gap junction, FcγR-mediated phagocytosis, MAPK and VEGF signaling pathways. Based on the performance evaluation of the area under the curve of 75.3%, PRKCB could accurately predict the onset of AD. Therefore, low expressions of PRKCB was a potential causative factor of AD, which might be involved in gap junction, FcγR-mediated phagocytosis, MAPK and VEGF signaling pathways.

Exploring the Potential of Therapeutic Agents Targeted towards Mitigating the Events Associated with Amyloid-β Cascade in Alzheimer's Disease

One of the most commonly occurring neurodegenerative disorders, Alzheimer's disease (AD), encompasses the loss of cognitive and memory potential, impaired learning, dementia and behavioral defects, and has been prevalent since the 1900s. The accelerating occurrence of AD is expected to reach 65.7 million by 2030. The disease results in neural atrophy and disrupted inter-neuronal connections. Amongst multiple AD pathogenesis hypotheses, the amyloid beta (Aβ) cascade is the most relevant and accepted form of the hypothesis, which suggests that Aβ monomers are formed as a result of the cleavage of amyloid precursor protein (APP), followed by the conversion of these monomers to toxic oligomers, which in turn develop β-sheets, fibrils and plaques. The review targets the events in the amyloid hypothesis and elaborates suitable therapeutic agents that function by hindering the steps of plaque formation and lowering Aβ levels in the brain. The authors discuss treatment possibilities, including the inhibition of β- and γ-secretase-mediated enzymatic cleavage of APP, the immune response generating active immunotherapy and passive immunotherapeutic approaches targeting monoclonal antibodies towards Aβ aggregates, the removal of amyloid aggregates by the activation of enzymatic pathways or the regulation of Aβ circulation, glucagon-like peptide-1 (GLP-1)-mediated curbed accumulation and the neurotoxic potential of Aβ aggregates, bapineuzumab-mediated vascular permeability alterations, statin-mediated Aβ peptide degradation, the potential role of ibuprofen and the significance of natural drugs and dyes in hindering the amyloid cascade events. Thus, the authors aim to highlight the treatment perspective, targeting the amyloid hypothesis, while simultaneously emphasizing the need to conduct further investigations, in order to provide an opportunity to neurologists to develop novel and reliable treatment therapies for the retardation of AD progression.

Soluble Prion Peptide 107-120 Protects Neuroblastoma SH-SY5Y Cells against Oligomers Associated with Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent form of dementia and soluble amyloid β (Aβ) oligomers are thought to play a critical role in AD pathogenesis. Cellular prion protein (PrPC) is a high-affinity receptor for Aβ oligomers and mediates some of their toxic effects. The N-terminal region of PrPC can interact with Aβ, particularly the region encompassing residues 95-110. In this study, we identified a soluble and unstructured prion-derived peptide (PrP107-120) that is external to this region of the sequence and was found to successfully reduce the mitochondrial impairment, intracellular ROS generation and cytosolic Ca2+ uptake induced by oligomeric Aβ42 ADDLs in neuroblastoma SH-SY5Y cells. PrP107-120 was also found to rescue SH-SY5Y cells from Aβ42 ADDL internalization. The peptide did not change the structure and aggregation pathway of Aβ42 ADDLs, did not show co-localization with Aβ42 ADDLs in the cells and showed a partial colocalization with the endogenous cellular PrPC. As a sequence region that is not involved in Aβ binding but in PrP self-recognition, the peptide was suggested to protect against the toxicity of Aβ42 oligomers by interfering with cellular PrPC and/or activating a signaling that protected the cells. These results strongly suggest that PrP107-120 has therapeutic potential for AD.

Potential Bidirectional Relationship Between Periodontitis and Alzheimer's Disease

Alzheimer’s disease (AD) is the most prevalent form of dementia in the elderly population, representing a global public health priority. Despite a large improvement in understanding the pathogenesis of AD, the etiology of this disorder remains still unclear, and no current treatment is able to prevent, slow, or stop its progression. Thus, there is a keen interest in the identification and modification of the risk factors and novel molecular mechanisms associated with the development and progression of AD. In this context, it is worth noting that several findings support the existence of a direct link between neuronal and non-neuronal inflammation/infection and AD progression. Importantly, recent studies are now supporting the existence of a direct relationship between periodontitis, a chronic inflammatory oral disease, and AD. The mechanisms underlying the association remain to be fully elucidated, however, it is generally accepted, although not confirmed, that oral pathogens can penetrate the bloodstream, inducing a low-grade systemic inflammation that negatively affects brain function. Indeed, a recent report demonstrated that oral pathogens and their toxic proteins infect the brain of AD patients. For instance, when AD progresses from the early to the more advanced stages, patients could no longer be able to adequately adhere to proper oral hygiene practices, thus leading to oral dysbiosis that, in turn, fuels infection, such as periodontitis. Therefore, in this review, we will provide an update on the emerging (preclinical and clinical) evidence that supports the relationship existing between periodontitis and AD. More in detail, we will discuss data attesting that periodontitis and AD share common risk factors and a similar hyper-inflammatory phenotype.

SPON1 Can Reduce Amyloid Beta and Reverse Cognitive Impairment and Memory Dysfunction in Alzheimer's Disease Mouse Model

Alzheimer’s disease (AD) is a complex, age-related neurodegenerative disease that is the most common form of dementia. However, the cure for AD has not yet been founded. The accumulation of amyloid beta (Aβ) is considered to be a hallmark of AD. Beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), also known as beta secretase is the initiating enzyme in the amyloidogenic pathway. Blocking BACE1 could reduce the amount of Aβ, but this would also prohibit the other functions of BACE1 in brain physiological activity. SPONDIN1 (SPON1) is known to bind to the BACE1 binding site of the amyloid precursor protein (APP) and blocks the initiating amyloidogenesis. Here, we show the effect of SPON1 in Aβ reduction in vitro in neural cells and in an in vivo AD mouse model. We engineered mouse induced neural stem cells (iNSCs) to express Spon1. iNSCs harboring mouse Spon1 secreted SPON1 protein and reduced the quantity of Aβ when co-cultured with Aβ-secreting Neuro 2a cells. The human SPON1 gene itself also reduced Aβ in HEK 293T cells expressing the human APP transgene with AD-linked mutations through lentiviral-mediated delivery. We also demonstrated that injecting SPON1 reduced the amount of Aβ and ameliorated cognitive dysfunction and memory impairment in 5xFAD mice expressing human APP and PSEN1 transgenes with five AD-linked mutations.

Activation of mGluR1 Mediates C1q-Dependent Microglial Phagocytosis of Glutamatergic Synapses in Alzheimer's Rodent Models

Microglia and complements appear to be involved in the synaptic and cognitive deficits in Alzheimer's disease (AD), though the mechanisms remain elusive. In this study, utilizing two types of rodent model of AD, we reported increased complement C1q-mediated microglial phagocytosis of hippocampal glutamatergic synapses, which led to synaptic and cognitive deficits. We also found increased activity of the metabotropic glutamate receptor 1 (mGluR1) in hippocampal CA1 in the modeled rodents. Artificial activation of mGluR1 signaling promoted dephosphorylation of fragile X mental retardation protein (FMRP) and facilitated the local translation machinery of synaptic C1q mRNA, thus mimicking the C1q-mediated microglial phagocytosis of hippocampal glutamatergic synapses and synaptic and cognitive deficiency in the modeled rodents. However, suppression of mGluR1 signaling inhibited the dephosphorylation of FMRP and repressed the local translation of synaptic C1q mRNA, which consequently alleviated microglial phagocytosis of synapses and restored the synaptic and cognitive function in the rodent models. These findings illustrate a novel molecular mechanism underlying C1q-mediated microglial phagocytosis of hippocampal glutamatergic synapses in AD.

Bipolar disorder patients display reduced serum complement levels and elevated peripheral blood complement expression levels

OBJECTIVE

Bipolar disorder (BD) patients have recently been shown to exhibit increased proinflammatory cytokine levels indicating the role of inflammation in this disease. As inflammatory responses often include complement level alterations and complement production is influenced by cytokines, we aimed to find out whether complement system is activated in BD in a time-dependent manner and complement factors are involved in BD pathogenesis.

METHODS

Serum C4, factor B, sC5b-9 and neuron-specific enolase levels were measured by enzyme-linked immunosorbent assay, whereas peripheral blood mononuclear cell messenger RNA (mRNA) expression levels of C1q, C4, factor B and CD55 were measured by real-time polymerase chain reaction in chronic BD patients (n=22), first episode BD patients (n=24) and healthy controls (n=19).

RESULTS

Serum complement levels were significantly reduced in chronic BD patients as compared with first episode BD patients and healthy controls. Serum levels of complement factors showed significant inverse correlation with disease duration, severity of manic symptoms and serum neuron-specific enolase levels. In chronic BD patients, peripheral blood mononuclear cell mRNA expression levels of C1q, C4 and factor B were significantly elevated, whereas the mRNA expression level of the complement inhibitor CD55 was significantly reduced.

CONCLUSIONS

Our results suggest that complement factor levels are reduced in BD presumably due to overconsumption of the complement system and complement production is increased at mRNA level possibly as a compensation measure. Complement factors might potentially be used as indicators of disease severity, neuronal loss and cognitive dysfunction.

Periodontitis and Alzheimer's Disease: A Possible Comorbidity between Oral Chronic Inflammatory Condition and Neuroinflammation

Periodontitis is an oral chronic infection/inflammatory condition, identified as a source of mediators of inflammation into the blood circulation, which may contribute to exacerbate several diseases. There is increasing evidence that inflammation plays a key role in the pathophysiology of Alzheimer’s disease (AD). Although inflammation is present in both diseases, the exact mechanisms and crosslinks between periodontitis and AD are poorly understood. Therefore, this article aims to review possible comorbidity between periodontitis and AD. Here, the authors discuss the inflammatory aspects of periodontitis, how this oral condition produces a systemic inflammation and, finally, the contribution of this systemic inflammation for worsening neuroinflammation in the progression of AD.

Complement component 3 (C3) expression in the hippocampus after excitotoxic injury: role of C/EBPβ

Background

The CCAAT/enhancer-binding protein β (C/EBPβ) is a transcription factor implicated in the control of proliferation, differentiation, and inflammatory processes mainly in adipose tissue and liver; although more recent results have revealed an important role for this transcription factor in the brain. Previous studies from our laboratory indicated that CCAAT/enhancer-binding protein β is implicated in inflammatory process and brain injury, since mice lacking this gene were less susceptible to kainic acid-induced injury. More recently, we have shown that the complement component 3 gene (C3) is a downstream target of CCAAT/enhancer-binding protein β and it could be a mediator of the proinflammatory effects of this transcription factor in neural cells.

Methods

Adult male Wistar rats (8–12 weeks old) were used throughout the study. C/EBPβ^+/+ and C/EBPβ^–/– mice were generated from heterozygous breeding pairs. Animals were injected or not with kainic acid, brains removed, and brain slices containing the hippocampus analyzed for the expression of both CCAAT/enhancer-binding protein β and C3.

Results

In the present work, we have further extended these studies and show that CCAAT/enhancer-binding protein β and C3 co-express in the CA1 and CA3 regions of the hippocampus after an excitotoxic injury. Studies using CCAAT/enhancer-binding protein β knockout mice demonstrate a marked reduction in C3 expression after kainic acid injection in these animals, suggesting that indeed this protein is regulated by C/EBPβ in the hippocampus in vivo.

Conclusions

Altogether these results suggest that CCAAT/enhancer-binding protein β could regulate brain disorders, in which excitotoxic and inflammatory processes are involved, at least in part through the direct regulation of C3.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0742-0) contains supplementary material, which is available to authorized users.

Brain omega-3 polyunsaturated fatty acids modulate microglia cell number and morphology in response to intracerebroventricular amyloid-β 1-40 in mice

BACKGROUND

Neuroinflammation is a proposed mechanism by which Alzheimer's disease (AD) pathology potentiates neuronal death and cognitive decline. Consumption of omega-3 polyunsaturated fatty acids (PUFA) is associated with a decreased risk of AD in human observational studies and exerts protective effects on cognition and pathology in animal models. These fatty acids and molecules derived from them are known to have anti-inflammatory and pro-resolving properties, presenting a potential mechanism for these protective effects.

METHODS

Here, we explore this mechanism using fat-1 transgenic mice and their wild type littermates weaned onto either a fish oil diet (high in n-3 PUFA) or a safflower oil diet (negligible n-3 PUFA). The fat-1 mouse carries a transgene that enables it to convert omega-6 to omega-3 PUFA. At 12 weeks of age, mice underwent intracerebroventricular (icv) infusion of amyloid-β 1-40. Brains were collected between 1 and 28 days post-icv, and hippocampal microglia, astrocytes, and degenerating neurons were quantified by immunohistochemistry with epifluorescence microscopy, while microglia morphology was assessed with confocal microscopy and skeleton analysis.

RESULTS

Fat-1 mice fed with the safflower oil diet and wild type mice fed with the fish oil diet had higher brain DHA in comparison with the wild type mice fed with the safflower oil diet. Relative to the wild type mice fed with the safflower oil diet, fat-1 mice exhibited a lower peak in the number of labelled microglia, wild type mice fed with fish oil had fewer degenerating neurons, and both exhibited alterations in microglia morphology at 10 days post-surgery. There were no differences in astrocyte number at any time point and no differences in the time course of microglia or astrocyte activation following infusion of amyloid-β 1-40.

CONCLUSIONS

Increasing brain DHA, through either dietary or transgenic means, decreases some elements of the inflammatory response to amyloid-β in a mouse model of AD. This supports the hypothesis that omega-3 PUFA may be protective against AD by modulating the immune response to amyloid-β.

Astrocyte-Microglia Cross Talk through Complement Activation Modulates Amyloid Pathology in Mouse Models of Alzheimer's Disease

Increasing evidence supports a role of neuroinflammation in the pathogenesis of Alzheimer's disease (AD). Previously, we identified a neuron-glia signaling pathway whereby Aβ acts as an upstream activator of astroglial nuclear factor kappa B (NF-κB), leading to the release of complement C3, which acts on the neuronal C3a receptor (C3aR) to influence dendritic morphology and cognitive function. Here we report that astrocytic complement activation also regulates Aβ dynamics in vitro and amyloid pathology in AD mouse models through microglial C3aR. We show that in primary microglial cultures, acute C3 or C3a activation promotes, whereas chronic C3/C3a treatment attenuates, microglial phagocytosis and that the effect of chronic C3 exposure can be blocked by cotreatment with a C3aR antagonist and by genetic deletion of C3aR. We further demonstrate that Aβ pathology and neuroinflammation in amyloid precursor protein (APP) transgenic mice are worsened by astroglial NF-κB hyperactivation and resulting C3 elevation, whereas treatment with the C3aR antagonist (C3aRA) ameliorates plaque load and microgliosis. Our studies define a complement-dependent intercellular cross talk in which neuronal overproduction of Aβ activates astroglial NF-κB to elicit extracellular release of C3. This promotes a pathogenic cycle by which C3 in turn interacts with neuronal and microglial C3aR to alter cognitive function and impair Aβ phagocytosis. This feedforward loop can be effectively blocked by C3aR inhibition, supporting the therapeutic potential of C3aR antagonists under chronic neuroinflammation conditions.

SIGNIFICANCE STATEMENT

The complement pathway is activated in Alzheimer's disease. Here we show that the central complement factor C3 secreted from astrocytes interacts with microglial C3a receptor (C3aR) to mediate β-amyloid pathology and neuroinflammation in AD mouse models. Our study provides support for targeting C3aR as a potential therapy for Alzheimer's disease.

Signaling pathways regulating neuron-glia interaction and their implications in Alzheimer's disease

Astrocytes are the most abundant cells in the central nervous system. They play critical roles in neuronal homeostasis through their physical properties and neuron-glia signaling pathways. Astrocytes become reactive in response to neuronal injury and this process, referred to as reactive astrogliosis, is a common feature accompanying neurodegenerative conditions, particularly Alzheimer's disease. Reactive astrogliosis represents a continuum of pathobiological processes and is associated with morphological, functional, and gene expression changes of varying degrees. There has been a substantial growth of knowledge regarding the signaling pathways regulating glial biology and pathophysiology in recent years. Here, we attempt to provide an unbiased review of some of the well-known players, namely calcium, proteoglycan, transforming growth factor β, NFκB, and complement, in mediating neuron-glia interaction under physiological conditions as well as in Alzheimer's disease. This review discusses the role of astrocytic NFκB and calcium as well as astroglial secreted factors, including proteoglycans, TGFβ, and complement in mediating neuronal function and AD pathogenesis through direct interaction with neurons and through cooperation with microglia.

Microglia: a new frontier for synaptic plasticity, learning and memory, and neurodegenerative disease research

We focus on emerging roles for microglia in synaptic plasticity, cognition and disease. We outline evidence that ramified microglia, traditionally thought to be functionally "resting" (i.e. quiescent) in the normal brain, in fact are highly dynamic and plastic. Ramified microglia continually and rapidly extend processes, contact synapses in an activity and experience dependent manner, and play a functionally dynamic role in synaptic plasticity, possibly through release of cytokines and growth factors. Ramified microglial also contribute to structural plasticity through the elimination of synapses via phagocytic mechanisms, which is necessary for normal cognition. Microglia have numerous mechanisms to monitor neuronal activity and numerous mechanisms also exist to prevent them transitioning to an activated state, which involves retraction of their surveying processes. Based on the evidence, we suggest that maintaining the ramified state of microglia is essential for normal synaptic and structural plasticity that supports cognition. Further, we propose that change of their ramified morphology and function, as occurs in inflammation associated with numerous neurological disorders such as Alzheimer's and Parkinson's disease, disrupts their intricate and essential synaptic functions. In turn altered microglia function could cause synaptic dysfunction and excess synapse loss early in disease, initiating a range of pathologies that follow. We conclude that the future of learning and memory research depends on an understanding of the role of non-neuronal cells and that this should include using sophisticated molecular, cellular, physiological and behavioural approaches combined with imaging to causally link the role of microglia to brain function and disease including Alzheimer's and Parkinson's disease and other neuropsychiatric disorders.

Complement receptor 1 (CR1) and Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disease and it poses an ever-increasing burden to an aging population. Several loci responsible for the rare, autosomal dominant form of AD have been identified (APP, PS1 and PS2), and these have facilitated the development of the amyloid cascade hypothesis of AD aetiology. The late onset form of the disease (LOAD) is poorly defined genetically, and up until recently the only known risk factor was the ε4 allele of APOE. Recent genome-wide association studies (GWAS) have identified common genetic variants that increase risk of LOAD. Two of the genes highlighted in these studies, CLU and CR1, suggest a role for the complement system in the aetiology of AD. In this review we analyse the evidence for an involvement of complement in AD. In particular we focus on one gene, CR1, and its role in the complement cascade. CR1 is a receptor for the complement fragments C3b and C4b and is expressed on many different cell types, particularly in the circulatory system. We look at the evidence for genetic polymorphisms in the gene and the possible physiological effects of these well-documented changes. Finally, we discuss the possible impact of CR1 genetic polymorphisms in relation to the amyloid cascade hypothesis of AD and the way in which CR1 may lead to AD pathogenesis.

Complement component C1q inhibits beta-amyloid- and serum amyloid P-induced neurotoxicity via caspase- and calpain-independent mechanisms

Alzheimer's disease is a neurodegenerative disorder characterized by neuronal loss, beta-amyloid (Abeta) plaques, and neurofibrillary tangles. Complement protein C1q has been found associated with fibrillar Abeta deposits, however the exact contributions of C1q to Alzheimer's disease is still unknown. There is evidence that C1q, as an initiator of the inflammatory complement cascade, may accelerate disease progression. However, neuronal C1q synthesis is induced after injury/infection suggesting that it may be a beneficial response to injury. In this study, we report that C1q enhances the viability of neurons in culture and protects neurons against Abeta- and serum amyloid P (SAP)-induced neurotoxicity. Investigation of potential signaling pathways indicates that caspase and calpain are activated by Abeta, but C1q had no effect on either of these pathways. Interestingly, SAP did not induce caspase and calpain activation, suggesting that C1q neuroprotection is in distinct from caspase and calpain pathways. In contrast to Abeta- and SAP-induced neurotoxicity, neurotoxicity induced by etoposide or FCCP was unaffected by the addition of C1q, indicating pathway selectivity for C1q neuroprotection. These data support a neuroprotective role for C1q which should be further investigated to uncover mechanisms which may be therapeutically targeted to slow neurodegeneration via direct inhibition of neuronal loss.

Differential regulation of Abeta42-induced neuronal C1q synthesis and microglial activation

Expression of C1q, an early component of the classical complement pathway, has been shown to be induced in neurons in hippocampal slices, following accumulation of exogenous Aβ42. Microglial activation was also detected by surface marker expression and cytokine production. To determine whether C1q induction was correlated with intraneuronal Aβ and/or microglial activation, D-(-)-2-amino-5-phosphonovaleric acid (APV, an NMDA receptor antagonist) and glycine-arginine-glycine-aspartic acid-serine-proline peptide (RGD, an integrin receptor antagonist), which blocks and enhances Aβ42 uptake, respectively, were assessed for their effect on neuronal C1q synthesis and microglial activation. APV inhibited, and RGD enhanced, microglial activation and neuronal C1q expression. However, addition of Aβ10–20 to slice cultures significantly reduced Aβ42 uptake and microglial activation, but did not alter the Aβ42-induced neuronal C1q expression. Furthermore, Aβ10–20 alone triggered C1q production in neurons, demonstrating that neither neuronal Aβ42 accumulation, nor microglial activation is required for neuronal C1q upregulation. These data are compatible with the hypothesis that multiple receptors are involved in Aβ injury and signaling in neurons. Some lead to neuronal C1q induction, whereas other(s) lead to intraneuronal accumulation of Aβ and/or stimulation of microglia.

Complement C3 and C5 play critical roles in traumatic brain cryoinjury: blocking effects on neutrophil extravasation by C5a receptor antagonist

The role of complement components in traumatic brain injury is poorly understood. Here we show that secondary damage after acute cryoinjury is significantly reduced in C3-/- or C5-/- mice or in mice treated with C5a receptor antagonist peptides. Injury sizes and neutrophil extravasation were compared. While neutrophil density increased following traumatic brain injury in wild type (C57BL/6) mice, C3-deficient mice demonstrated lower neutrophil extravasation and injury sizes in the brain. RNase protection assay indicated that C3 contributes to the induction of brain inflammatory mediators, MIF, RANTES (CCL5) and MCP-1 (CCL2). Intracranial C3 injection induced neutrophil extravasation in injured brains of C3-/- mice suggesting locally produced C3 is important in brain inflammation. We show that neutrophil extravasation is significantly reduced in both C5-/- mice and C5a receptor antagonist treated cryoinjured mice suggesting that one of the possible mechanisms of C3 effect on neutrophil extravasation is mediated via downstream complement activation products such as C5a. Our data indicates that complement inhibitors may ameliorate traumatic brain injury.

Neuronal localization of C1q in preclinical Alzheimer's disease

Complement has been postulated to contribute to inflammatory reactions associated with the neuropathology of Alzheimer's disease (AD). C1q, an initial component of the complement cascade, is associated with neuritic plaques and with neurons in the hippocampus of AD brain. Here, we report the presence of C1q in a cognitively intact subject, previously identified as preclinical AD. We compared in detail brain tissue of this preclinical case with a genetically related late-onset AD case. In the AD brain, C1q was typically associated with fibrillar Abeta plaques in frontal cortex and with plaques and neurons in the hippocampus. In the preclinical subject, C1q was abundantly present but it was cell-associated only, being primarily colocalized with neurons in both frontal cortex and hippocampus. However, no predominant cortical neuronal C1q localization was found in other preclinical cases or in Down's cases of different ages. Thus, it is possible that this neuronal-associated C1q reflects an early, but transient, response to injury that may modulate the progression of neurological dysfunction in AD.

Activation of complement in the central nervous system: roles in neurodegeneration and neuroprotection

The complement system is an essential effector of the humoral and cellular immunity involved in cytolysis and immune/inflammatory responses. Complement participates in host defense against pathogens by triggering the formation of the membrane attack complex. Complement opsonins (C1q, C3b, and iC3b) interact with surface complement receptors to promote phagocytosis, whereas complement anaphylatoxins C3a and C5a initiate local inflammatory responses that ultimately contribute to the protection and healing of the host. However, activation of complement to an inappropriate extent has been proposed to promote tissue injury. There is now compelling evidence that complement activation in the brain is a double-edged sword in that it can exert beneficial or detrimental effects depending on the pathophysiological context. This review focuses on the roles of the complement system in the pathogenesis of acute brain injury (cerebral ischemia and trauma) and chronic neurodegeneration (Alzheimer's disease). Because many effects of the complement appear to promote neuronal survival and tissue remodeling, directing activation of the complement system in the brain may provide a better therapeutic rationale than inhibiting it.

Endogenous brain cytokine mRNA and inflammatory responses to lipopolysaccharide are elevated in the Tg2576 transgenic mouse model of Alzheimer's disease

Beta-amyloid (Abeta) plaques have been shown to induce inflammatory changes in Alzheimer's disease brains. Cortical, but not cerebellar tissue from 16-month-old Tg2576 (Tg+) mice showed significant increases in interleukin (IL)-1alpha (2.2-fold), IL-1beta (3.4-fold), tumor necrosis factor-alpha (3.9-fold), and monocyte chemoattractant protein-1 (2.5-fold) mRNA levels compared to controls (Tg-). These changes were not apparent in 6-month-old Tg+ mice except for TNF-alpha. mRNA levels of glial fibrillary acidic protein and complement components, C1qA and C3 were also elevated in aged mice. Lipopolysaccharide (LPS) (25 microg/mouse, i.v.) induced a significantly greater production of IL-1beta protein in the cortices and hippocampi of Tg+ vs. Tg- mice at 1, 2, 4, and 6 h. Experiments in 6-month-old mice showed that not only was there less cytokine produced compared to 16-month-old mice, but the exacerbated cytokine response to LPS in Tg+ mice was not apparent. Higher levels of Abeta1-40 were measured in the cortices of 6- and 16-month-old Tg+ mice at 4-6 h after LPS, which returned to baseline after 18 h. We demonstrate that Abeta plaques elicit inflammatory responses in Tg2576 mice that are further exacerbated when challenged by an exogenous inflammatory insult, which may serve to amplify degenerative processes.

Two-dimensional gel analysis of secreted proteins induced by interleukin-1 beta in rat astrocytes

Interleukin-1 beta (IL-1 beta) is a pro-inflammatory cytokine produced in the brain by endogenous microglial cells responding to injury. Levels of IL-1 beta are elevated in several neurodegenerative disorders, including Alzheimer's disease. IL-1 beta, which can act as a mitogen for astrocytes, also elicits the expression and secretion of multiple factors and paracrine 'second messengers' such as other cytokines, nerve growth factor, prostaglandins and nitric oxide that may in turn modulate neuronal and glial responses to injury. Utilizing giant, high-resolution two-dimensional gel electrophoresis, we have sought to more fully define the potential range of protein mediators that are secreted by astrocytes treated with IL-1 beta. In cultured rat astrocytes, we observe dramatic increases in the secretion of eight different protein species after 24 h of treatment with human recombinant IL-1 beta (1 U/ml). Seven of the proteins are also induced by tumor necrosis factor-alpha or basic fibroblast growth factor. Based on immunoprecipitation with specific antisera, we have identified three of these proteins as plasminogen activator inhibitor type-1, ceruloplasmin, and complement component C3. The identities of the other proteins, including the IL-1 beta-specific induction, are currently unknown. Characterization of these downstream modulators of IL-1 beta action complements gene-based approaches and will provide a better understanding of astrocyte responses to injury as well as markers for astrocyte activation in neurodegenerative diseases.

Detection of complement alternative pathway mRNA and proteins in the Alzheimer's disease brain

Previous research on complement activation in the Alzheimer's disease (AD) brain has focused almost exclusively on the classical complement pathway. The alternative pathway represents another important arm for complement activation, converging with the classical cascade at the C5 cleavage step. Here, we show that mRNA for a critical alternative pathway component, factor B, is present in AD frontal cortex and that the factor D cleaved split products of factor B, Bb and Ba, are significantly increased, indicating alternative pathway activation. By contrast, the two major inhibitors of alternative pathway activation, factor H and factor I, are present at the level of mRNA and protein but are not significantly upregulated. Immunohistochemical analysis reveals significant positive staining in AD sections for all three components. Taken together with previous reports demonstrating alternative pathway activation by amyloid beta peptide, these findings suggest that conditions conducive to chronic alternative pathway activation may exist in the AD brain.

Complement components of the innate immune system in health and disease in the CNS

The innate immune system and notably the complement (C) system play important roles in host defense to recognise and kill deleterious invaders or toxic entities, but activation at inappropriate sites or to an excessive degree can cause severe tissue damage. C has been implicated as a factor in the exacerbation and propagation of tissue injury in numerous diseases including neurodegenerative disorders. In this article, we review the evidence indicating that brain cells can synthesise a full lytic C system and also express specific C inhibitors (to protect from C activation and C lysis) and C receptors (involved in cell activation, chemotaxis and phagocytosis). We also summarise the mechanisms involved in the antibody-independent activation of the classical pathway of C in Alzheimer's disease, Huntington's disease and Pick's disease. Although the primary role of C activation on a target cell is to induce cell lysis (particularly of neurons), we present evidence indicating that C (C3a, C5a, sublytic level of C5b-9) may also be involved in pro- as well as anti-inflammatory activities. Moreover, we discuss evidence suggesting that local C activation may contribute to tissue remodelling activities during repair in the CNS.

Research on ageing in Germany

The present review on ageing research in Germany is biased towards experimental biogerontology, because this is the field which will define the future of ageing research as a whole. In absolute numbers of publications between 1995 and 1999, Germany is comparable to other large European countries. However, Germany ranks definitively last among 10 major developed countries if the numbers of scientific papers per year are seen in relation to the economic capability. This is true for the whole of biomedical research, but it is even more exaggerated for ageing research. There are potent groups in German ageing research capable of producing a good fraction of high-impact papers, however. There are many more researchers in areas highly relevant to gerontology which recently became attracted by gerontological problems. However, the importance of modern biogerontology has not made clear to decision-makers in Germany, so that structural and financial limitations will probably prevent any significant rise in the near future, which would be necessary to keep Germany along with other developed countries.

Intravascular infusions of soluble beta-amyloid compromise the blood-brain barrier, activate CNS glial cells and induce peripheral hemorrhage

Vascular wall levels of soluble beta-amyloid1-40 (Abeta1-40) are elevated in Alzheimer's disease (AD). Moreover, plasma Abeta levels are increased in familial AD, as well as in some cases of sporadic AD. To determine the histopathologic and behavioral consequences of elevated vascular Abeta levels, Abeta1-40 (50 micrograms in distilled water) or vehicle was intravenously infused twice daily into 3-month old male Sprague-Dawley rats for 2 weeks. Intravenous Abeta infusions impaired blood-brain barrier integrity, as indicated by substantial perivascular and parenchyma IgG immunostaining within the brain. Also evident in Abeta-infused animals was an increase in GFAP immunostaining around cerebral blood vessels, and an enhancement of OX-42 microglial immunostaining in brain white matter. Gross pulmonary hemorrhage was noted in most Abeta-infused animals. All the observed changes occurred in the absence of Congo red birefringence. No significant cognitive deficits were present in Abeta-infused animals during water maze acquisition and retention testing, which was conducted during the second week of treatment. These results indicate that circulating Abeta can: (1) induce vessel dysfunction/damage in both the brain and the periphery without complex Abeta fibril formation/deposition, and (2) induce an activation of brain astrocytes and microglia. Taken together, our results suggest that if circulating Abeta is elevated in AD, it is likely to have a pathophysiologic role.

Expression of complement C4 and C9 genes by human astrocytes

Evidence exists that complement activation is involved in the pathogenesis of Alzheimer's disease (AD). It has been previously demonstrated that central nervous system (CNS) resident cells can synthesize complement proteins. Two key proteins in the complement pathway are the complement C4 and C9 proteins. Using reverse transcription-polymerase chain reaction, ELISA, immunocytochemical and immunoblot techniques, we showed that primary human astrocytes constitutively expressed complement C4 mRNA and protein, and that this was increased when cells were treated with interferon-gamma, but inhibited when cells were treated with interleukin-1beta (IL-1beta). C4 immunoreactivity could be localized to GFAP-positive astrocytes when protein secretion was inhibited. These results indicated that astrocytes could be a source of complement C4 in the human CNS. In addition it was shown that stimulated astrocytes could also express complement C9 mRNA, though C9 protein was not detectable in culture supernatants.

Characterization of the AD7C-NTP cDNA expression in Alzheimer's disease and measurement of a 41-kD protein in cerebrospinal fluid

We have isolated a novel Alu sequence-containing cDNA, designated AD7c-NTP, that is expressed in neurons, and overexpressed in brains with Alzheimer's disease (AD). The 1,442-nucleotide AD7c-NTP cDNA encodes an approximately 41-kD protein. Expression of AD7c-NTP was confirmed by nucleic acid sequencing of reverse transcriptase PCR products isolated from brain. AD7c-NTP cDNA probes hybridized with 1. 4 kB mRNA transcripts by Northern blot analysis, and monoclonal antibodies generated with the recombinant protein were immunoreactive with approximately 41-45-kD and approximately 18-21-kD molecules by Western blot analysis. In situ hybridization and immunostaining studies localized AD7c-NTP gene expression in neurons. Using a quantitative enzyme-linked sandwich immunoassay (Ghanbari, K., I. Beheshti, and H. Ghanbari, manuscript submitted for publication) constructed with antibodies to the recombinant protein, AD7c-NTP levels were measured under code in 323 clinical and postmortem cerebrospinal fluid (CSF) samples from AD, age-matched control, Parkinson's disease, and neurological disease control patients. The molecular mass of the AD7c-NTP detected in CSF was approximately 41 kD. In postmortem CSF, the mean concentration of AD7c-NTP in cases of definite AD (9.2+/-8.2 ng/ml) was higher than in the aged control group (1.6+/-0.9; P < 0.0001). In CSF samples from individuals with early possible or probable AD, the mean concentration of AD7c-NTP (4.6+/-3.4) was also elevated relative to the levels in CSF from age-matched (1.2+/-0.7) and neurological disease (1.0+/-0.9) controls, and ambulatory patients with Parkinson's disease (1.8+/-1.1) (all P < 0.001). CSF levels of AD7c-NTP were correlated with Blessed dementia scale scores (r = 0. 66; P = 0.0001) rather than age (r = -0.06; P > 0.1). In vitro studies demonstrated that overexpression of AD7c-NTP in transfected neuronal cells promotes neuritic sprouting and cell death, the two principal neuroanatomical lesions correlated with dementia in AD. The results suggest that abnormal AD7c-NTP expression is associated with AD neurodegeneration, and during the early stages of disease, CSF levels correlate with the severity of dementia.

Interleukin-6-associated inflammatory processes in Alzheimer's disease: new therapeutic options

The cytokine interleukin-6 is consistently detected in the brains of Alzheimer's disease patients but not in the brains of nondemented elderly persons. Until recently it was unclear whether an interleukin-6-associated inflammatory mechanism is an early or late event in the pathological cascade of Alzheimer's disease. We investigated whether interleukin-6 could be detected in plaques of Alzheimer's disease patients prior to the onset of neuritic degeneration. We found interleukin-6 mostly in plaques where neuritic pathology has not yet developed. This indicates that the appearance of interleukin-6 may precede neuritic changes and is not just a consequence of neuritic degeneration. Therefore, one may hypothesize that activation of inflammatory mechanisms may cause neuritic degeneration in plaques. A suppression of interleukin-6 synthesis could, therefore, be of therapeutic value. Upon screening a number of substances, we found that a small number of nonsteroidal antiinflammatory drugs, including tenidap, were able to inhibit interleukin-6 synthesis in cultured human astrocytoma cells. These substances may be therapeutically useful in Alzheimer's disease and should be evaluated in clinical studies.

The participation of interleukin-6, a stress-inducible cytokine, in the pathogenesis of Alzheimer's disease

A loss of synapses in the cortices of demented persons appears to be the primary correlate of Alzheimer's disease (AD). However, it is still unclear how synaptic pathology is connected to other pathological findings such as neurofibrillary and neuritic degeneration or inflammatory markers in AD. Interleukin-6 (IL-6) immunoreactivity has previously been detected in plaques in the brains of AD patients. In addition, elevated IL-6 concentrations have been measured biochemically in the brains of AD patients. Since transgenic mice bearing additional copies of the IL-6 gene under the control of a brain-specific promoter develop a marked cortical pathology including severe alterations of the dendritic arborization of cortical neurons, an IL-6 related inflammatory event could well be connected to the synaptic pathology in AD. In this study, we investigated whether IL-6 immunoreactivity in plaques could already be found prior to the onset of neuritic changes, or whether the presence of this cytokine is restricted to the later stages of plaque formation. While diffuse plaques represent an early stage of plaque formation, primitive and classic plaques (displaying neuritic pathology) are thought to reflect later stages of plaque pathology. Using a silver-staining method, we classified plaque stages in serial sections of paraffin-embedded cortices of clinically diagnosed and histopathologically confirmed AD patients and of control persons with no clinical history of dementia. Adjacent sections were stained with an antibody directed against IL-6. IL-6 was detectable in a significant proportion of plaques, but only in the brains of demented patients. In the AD cases, IL-6 was found in diffuse plaques in a significantly higher ratio as would have been expected from a random distribution of IL-6 among all plaque types. This observation suggests that IL-6 expression may precede neuritic changes and that in AD an immunological mechanism may be involved both in the transformation from diffuse to primitive plaques and in the development of dementia. The reasons for the increased expression of IL-6 in the brains of AD patients are still unknown. Basal IL-6 levels were found to be slightly elevated along normal aging. Based on several studies indicating that IL-6 expression is inducible also by psychological stress, one could speculate whether long-lasting stressful experiences may contribute to the pathological process underlying Alzheimer's disease.