Rescue of ApoE4-related lysosomal autophagic failure in Alzheimer's disease by targeted small molecules

Homozygosity for the ε4 allele of APOE increases the odds of developing Alzheimer's by 12 to 15 times relative to the most common ε3;ε3 genotype, and its association with higher plaque loads comports with evidence that APOEε4 compromises autophagy. The ApoE4 protein specifically binds a cis element ("CLEAR") in the promoters of several autophagy genes to block their transcription. We used a multifaceted approach to identify a druggable site in ApoE4, and virtual screening of lead-like compounds identified small molecules that specifically bind to this site to impede ApoE4::DNA binding. We validated these molecules both in vitro and in vivo with models expressing ApoE4, including ApoE4 targeted-replacement mice. One compound was able to significantly restore transcription of several autophagy genes and protected against amyloid-like aggregation in a C. elegans AD model. Together, these findings provide proof-of-principle evidence for pharmacological remediation of lysosomal autophagy by ApoE4 via ApoE4-targeted lead molecules that represent a novel tack on neurodegenerative disorders.

Glial Fibrillary Acidic Protein: A Biomarker and Drug Target for Alzheimer’s Disease

Glial fibrillary acidic protein (GFAP) is an intermediate filament structural protein involved in cytoskeleton assembly and integrity, expressed in high abundance in activated glial cells. GFAP is neuroprotective, as knockout mice are hypersensitive to traumatic brain injury. GFAP in cerebrospinal fluid is a biomarker of Alzheimer’s disease (AD), dementia with Lewy bodies, and frontotemporal dementia (FTD). Here, we present novel evidence that GFAP is markedly overexpressed and differentially phosphorylated in AD hippocampus, especially in AD with the apolipoprotein E [ε4, ε4] genotype, relative to age-matched controls (AMCs). Kinases that phosphorylate GFAP are upregulated in AD relative to AMC. A knockdown of these kinases in SH-SY5Y-APP_Sw human neuroblastoma cells reduced amyloid accrual and lowered protein aggregation and associated behavioral traits in C. elegans models of polyglutamine aggregation (as observed in Huntington’s disease) and of Alzheimer’s-like amyloid formation. In silico screening of the ChemBridge structural library identified a small molecule, MSR1, with stable and specific binding to GFAP. Both MSR1 exposure and GF AP-specific RNAi knockdown reduce aggregation with remarkably high concordance of aggregate proteins depleted. These data imply that GFAP and its phosphorylation play key roles in neuropathic aggregate accrual and provide valuable new biomarkers, as well as novel therapeutic targets to alleviate, delay, or prevent AD.

Porphyromonas gingivalis Outer Membrane Vesicles as the Major Driver of and Explanation for Neuropathogenesis, the Cholinergic Hypothesis, Iron Dyshomeostasis, and Salivary Lactoferrin in Alzheimer's Disease

Porphyromonas gingivalis (Pg) is a primary oral pathogen in the widespread biofilm-induced "chronic" multi-systems inflammatory disease(s) including Alzheimer's disease (AD). It is possibly the only second identified unique example of a biological extremophile in the human body. Having a better understanding of the key microbiological and genetic mechanisms of its pathogenesis and disease induction are central to its future diagnosis, treatment, and possible prevention. The published literature around the role of Pg in AD highlights the bacteria's direct role within the brain to cause disease. The available evidence, although somewhat adopted, does not fully support this as the major process. There are alternative pathogenic/virulence features associated with Pg that have been overlooked and may better explain the pathogenic processes found in the "infection hypothesis" of AD. A better explanation is offered here for the discrepancy in the relatively low amounts of "Pg bacteria" residing in the brain compared to the rather florid amounts and broad distribution of one or more of its major bacterial protein toxins. Related to this, the "Gingipains Hypothesis", AD-related iron dyshomeostasis, and the early reduced salivary lactoferrin, along with the resurrection of the Cholinergic Hypothesis may now be integrated into one working model. The current paper suggests the highly evolved and developed Type IX secretory cargo system of Pg producing outer membrane vesicles may better explain the observed diseases. Thus it is hoped this paper can provide a unifying model for the sporadic form of AD and guide the direction of research, treatment, and possible prevention.

A Novel Microtubule-Binding Drug Attenuates and Reverses Protein Aggregation in Animal Models of Alzheimer's Disease

Age-progressive neurodegenerative pathologies, including Alzheimer’s disease (AD), are distinguished and diagnosed by disease-specific components of intra- or extra-cellular aggregates. Increasing evidence suggests that neuroinflammation promotes protein aggregation, and is involved in the etiology of neurological diseases. We synthesized and tested analogs of the naturally occurring tubulin-binding compound, combretastatin A-4. One such analog, PNR502, markedly reduced the quantity of Alzheimer-associated amyloid aggregates in the BRI-Aβ_1–42 mouse model of AD, while blunting the ability of the pro-inflammatory cytokine IL-1β to raise levels of amyloid plaque and its protein precursors in a neuronal cell-culture model. In transgenic Caenorhabditis elegans (C. elegans) strains that express human Aβ_1–42 in muscle or neurons, PNR502 rescued Aβ-induced disruption of motility (3.8-fold, P < 0.0001) or chemotaxis (1.8-fold, P < 0.05), respectively. Moreover, in C. elegans with neuronal expression of Aβ_1–42, a single day of PNR502 exposure reverses the chemotaxis deficit by 54% (P < 0.01), actually exceeding the protection from longer exposure. Moreover, continuous PNR502 treatment extends nematode lifespan 23% (P ≤ 0.001). Given that PNR502 can slow, prevent, or reverse Alzheimer-like protein aggregation in human-cell-culture and animal models, and that its principal predicted and observed binding targets are proteins previously implicated in Alzheimer’s, we propose that PNR502 has therapeutic potential to inhibit cerebral Aβ_1–42 aggregation and prevent or reverse neurodegeneration.

Interleukin-1β drives NEDD8 nuclear-to-cytoplasmic translocation, fostering parkin activation via NEDD8 binding to the P-ubiquitin activating site

Background

Neuroinflammation, typified by elevated levels of interleukin-1 (IL-1) α and β, and deficits in proteostasis, characterized by accumulation of polyubiquitinated proteins and other aggregates, are associated with neurodegenerative disease independently and through interactions of the two phenomena. We investigated the influence of IL-1β on ubiquitination via its impact on activation of the E3 ligase parkin by either phosphorylated ubiquitin (P-Ub) or NEDD8.

Methods

Immunohistochemistry and Proximity Ligation Assay were used to assess colocalization of parkin with P-tau or NEDD8 in hippocampus from Alzheimer patients (AD) and controls. IL-1β effects on PINK1, P-Ub, parkin, P-parkin, and GSK3β—as well as phosphorylation of parkin by GSK3β—were assessed in cell cultures by western immunoblot, using two inhibitors and siRNA knockdown to suppress GSK3β. Computer modeling characterized the binding and the effects of P-Ub and NEDD8 on parkin. IL-1α, IL-1β, and parkin gene expression was assessed by RT-PCR in brains of 2- and 17-month-old PD-APP mice and wild-type littermates.

Results

IL-1α, IL-1β, and parkin mRNA levels were higher in PD-APP mice compared with wild-type littermates, and IL-1α-laden glia surrounded parkin- and P-tau-laden neurons in human AD. Such neurons showed a nuclear-to-cytoplasmic translocation of NEDD8 that was mimicked in IL-1β-treated primary neuronal cultures. These cultures also showed higher parkin levels and GSK3β-induced parkin phosphorylation; PINK1 levels were suppressed. In silico simulation predicted that binding of either P-Ub or NEDD8 at a singular position on parkin opens the UBL domain, exposing Ser₆₅ for parkin activation.

Conclusions

The promotion of parkin- and NEDD8-mediated ubiquitination by IL-1β is consistent with an acute neuroprotective role. However, accumulations of P-tau and P-Ub and other elements of proteostasis, such as translocated NEDD8, in AD and in response to IL-1β suggest either over-stimulation or a proteostatic failure that may result from chronic IL-1β elevation, easily envisioned considering its early induction in Down’s syndrome and mild cognitive impairment. The findings further link autophagy and neuroinflammation, two important aspects of AD pathogenesis, which have previously been only loosely related.

A probe in the connection between inflammation, cognition and suicide

BACKGROUND

Increased inflammation is linked to suicide risk. However, it is unclear whether increased inflammation drives suicidal crises or is a trait associated with lifetime suicidal behavior. Limited data exist on the sources of increased inflammation observed in suicidal patients and on its downstream effects.

AIMS

To examine factors associated with inflammation and with suicidal ideation severity in acutely suicidal depressed patients.

METHODS

Fifty-two adult depressed patients of both sexes hospitalized for severe suicidal ideation were characterized for suicidality, depression, anxiety, medical comorbidity, psychological and physical pain, impulsivity, verbal fluency, C-reactive protein (CRP) and interleukin (IL) 6. Two generalized linear models were performed with either CRP or suicidal ideation severity as dependent variables.

RESULTS

CRP levels were positively associated with age, body mass index (BMI), IL6, current physical pain and number of lifetime suicide attempts. Suicidal ideation severity was not significantly correlated with either CRP or IL6. Suicidal ideation severity was positively associated with female sex, presence of an anxiety disorder, current physical pain, number of lifetime suicide attempts and with delay discounting for medium and large losses.

CONCLUSIONS

Increased inflammation is not associated with acute suicidal risk, but seems to represent a trait associated with lifetime suicidal behavior.

Apolipoprotein E4 inhibits autophagy gene products through direct, specific binding to CLEAR motifs

Introduction:

Alzheimer apolipoprotein E (APOE) ε4/ε4 carriers have earlier disease onset and more protein aggregates than patients with other APOE genotypes. Autophagy opposes aggregation, and important autophagy genes are coordinately regulated by transcription factor EB (TFEB) binding to “coordinated lysosomal expression and regulation” (CLEAR) DNA motifs.

Methods:

Autophagic gene expression was assessed in brains of controls and Alzheimer’s disease (AD) patients parsed by APOE genotype and in a glioblastoma cell line expressing either apoE3 or apoE4. Computational modeling assessed interactions between apoE and mutated apoE with CLEAR or modified DNA.

Results:

Three TFEB-regulated mRNA transcripts—SQSTM, MAP1LC3B, and LAMP2—were lower in AD ε4/ε4 than in AD ε3/ε3 brains. Computational modeling predicted avid specific binding of apoE4 to CLEAR motifs. ApoE was found in cellular nuclei, and in vitro binding assays suggest competition between apoE4 and TFEB at CLEAR sites.

Conclusion:

ApoE4-CLEAR interactions may account for suppressed autophagy in APOE ε4/ε4 carriers and, in this way, contribute to earlier AD onset.

Proteins that mediate protein aggregation and cytotoxicity distinguish Alzheimer's hippocampus from normal controls

Neurodegenerative diseases are distinguished by characteristic protein aggregates initiated by disease‐specific ‘seed’ proteins; however, roles of other co‐aggregated proteins remain largely unexplored. Compact hippocampal aggregates were purified from Alzheimer's and control‐subject pools using magnetic‐bead immunoaffinity pulldowns. Their components were fractionated by electrophoretic mobility and analyzed by high‐resolution proteomics. Although total detergent‐insoluble aggregates from Alzheimer's and controls had similar protein content, within the fractions isolated by tau or Aβ_1–42 pulldown, the protein constituents of Alzheimer‐derived aggregates were more abundant, diverse, and post‐translationally modified than those from controls. Tau‐ and Aβ‐containing aggregates were distinguished by multiple components, and yet shared >90% of their protein constituents, implying similar accretion mechanisms. Alzheimer‐specific protein enrichment in tau‐containing aggregates was corroborated for individuals by three analyses. Five proteins inferred to co‐aggregate with tau were confirmed by precise in situ methods, including proximity ligation amplification that requires co‐localization within 40 nm. Nematode orthologs of 21 proteins, which showed Alzheimer‐specific enrichment in tau‐containing aggregates, were assessed for aggregation‐promoting roles in C. elegans by RNA‐interference ‘knockdown’. Fifteen knockdowns (71%) rescued paralysis of worms expressing muscle Aβ, and 12 (57%) rescued chemotaxis disrupted by neuronal Aβ expression. Proteins identified in compact human aggregates, bound by antibody to total tau, were thus shown to play causal roles in aggregation based on nematode models triggered by Aβ_1–42. These observations imply shared mechanisms driving both types of aggregation, and/or aggregate‐mediated cross‐talk between tau and Aβ. Knowledge of protein components that promote protein accrual in diverse aggregate types implicates common mechanisms and identifies novel targets for drug intervention.

Aging, Alzheimer's, and APOE genotype influence the expression and neuronal distribution patterns of microtubule motor protein dynactin-P50

Reports from neural cell cultures and experimental animal studies provide evidence of age- and disease-related changes in retrograde transport of spent or misfolded proteins destined for degradation or recycling. However, few studies address these issues in human brain from those who either age without dementia and overt neuropathology, or succumb to Alzheimer's; especially as such propensity may be influenced by APOE genotype. We studied the expression and distribution of the dynein subunit dynactin-P50, the β amyloid precursor protein (βAPP), and hyperphosphorylated tau (P-tau) in tissues and tissue sections of brains from non-demented, neuropathology-free patients and from Alzheimer patients, with either APOE ε3,3 or APOE ε4,4. We found that advanced age in patients without dementia or neuropathological change was associated with coordinated increases in dynactin-P50 and βAPP in neurons in pyramidal layers of the hippocampus. In contrast, in Alzheimer's, βAPP and dynactin were significantly reduced. Furthermore, the dynactin-P50 and βAPP that was present was located primarily in dystrophic neurites in Aβ plaques. Tissues from Alzheimer patients with APOE ε3,3 had less P-tau, more βAPP, dynactin-P50, and synaptophysin than did tissues from Alzheimer patients carrying APOE ε4,4. It is logical to conclude, then, that as neurons age successfully, there is coordination between retrograde delivery and maintenance and repair, as well as between retrograde delivery and degradation and/or recycling of spent proteins. The buildup of proteins slated for repair, synaptic viability, transport, and re-cycling in neuron soma and dystrophic neurites suggest a loss of this coordination in Alzheimer neurons. Inheritance of APOE ε3,3 rather than APOE ε4,4, is associated with neuronal resilience, suggestive of better repair capabilities, more synapses, more efficient transport, and less hyperphosphorylation of tau. We conclude that even in disease the ε3 allele is neuroprotective.

Loss of angiotensin II receptor expression in dopamine neurons in Parkinson's disease correlates with pathological progression and is accompanied by increases in Nox4- and 8-OH guanosine-related nucleic acid oxidation and caspase-3 activation

Background

In rodent models of Parkinson’s disease (PD), dopamine neuron loss is accompanied by increased expression of angiotensin II (AngII), its type 1 receptor (AT1), and NADPH oxidase (Nox) in the nigral dopamine neurons and microglia. AT1 blockers (ARBs) stymie such oxidative damage and neuron loss. Whether changes in the AngII/AT1/Nox4 axis contribute to Parkinson neuropathogenesis is unknown. Here, we studied the distribution of AT1 and Nox4 in dopamine neurons in two nigral subregions: the less affected calbindin-rich matrix and the first-affected calbindin-poor nigrosome 1 of three patients, who were clinically asymptomatic, but had nigral dopamine cell loss and Braak stages consistent with a neuropathological diagnosis of PD (prePD). For comparison, five clinically- and neuropathologically-confirmed PD patients and seven age-matched control patients (AMC) were examined.

Results

AT1 and Nox4 immunoreactivity was noted in dopamine neurons in both the matrix and the nigrosome 1. The total cellular levels of AT1 in surviving dopamine neurons in the matrix and nigrosome 1 declined from AMC>prePD>PD, suggesting that an AngII/AT1/Nox4 axis orders neurodegenerative progression. In this vein, the loss of dopamine neurons was paralleled by a decline in total AT1 per surviving dopamine neuron. Similarly, AT1 in the nuclei of surviving neurons in the nigral matrix declined with disease progression, i.e., AMC>prePD>PD. In contrast, in nigrosome 1, the expression of nuclear AT1 was unaffected and similar in all groups. The ratio of nuclear AT1 to total AT1 (nuclear + cytoplasmic + membrane) in dopamine neurons increased stepwise from AMC to prePD to PD. The proportional increase in nuclear AT1 in dopamine neurons in nigrosome 1 of prePD and PD patients was accompanied by elevated nuclear expression of Nox4, oxidative damage to DNA, and caspase-3-mediated cell loss.

Conclusions

Our observations are consistent with the idea that AngII/AT1/Nox4 axis-mediated oxidative stress gives rise to the dopamine neuron dysfunction and loss characteristic of the neuropathological and clinical manifestations of PD and suggest that the chance for a neuron to survive increases in association with lower total as well as nuclear AT1 expression. Our results support the need for further evaluation of ARBs as disease-modifying agents in PD.

Phenotypic profile of alternative activation marker CD163 is different in Alzheimer's and Parkinson's disease

Background

Microglial activation is a pathological feature common to both Alzheimer’s and Parkinson’s diseases (AD and PD). The classical activation involves release of pro-inflammatory cytokines and reactive oxygen species. This is necessary for maintenance of tissue homeostasis and host defense, but can cause bystander damage when the activation is sustained and uncontrolled. In recent years the heterogeneous nature of microglial activation states in neurodegenerative diseases has become clear and the focus has shifted to alternative activation states that promote tissue maintenance and repair. We studied the distribution of CD163, a membrane-bound scavenger receptor found on perivascular macrophages. CD163 has an immunoregulatory function, and has been found in the parenchyma in other inflammatory diseases e.g. HIV-encephalitis and multiple sclerosis. In this study, we used immunohistochemistry to compare CD163 immunoreactivity in 31 AD cases, 27 PD cases, and 16 control cases. Associations of microglia with pathological hallmarks of AD and PD were investigated using double immunofluorescence.

Results

Parenchymal microglia were found to be immunoreactive for CD163 in all of the AD cases, and to a lesser extent in PD cases. There was prominent staining of CD163 immunoreactive microglia in the frontal and occipital cortices of AD cases, and in the brainstem of PD cases. Many of them were associated with Aß plaques in both diseases, and double staining with CD68 demonstrates their phagocytic capability. Leakage of fibrinogen was observed around compromised blood vessels, raising the possibility these microglia might have originated from the periphery.

Conclusions

Increase in microglia’s CD163 immunoreactivity was more significant in AD than PD, and association of CD163 immunoreactive microglia with Aβ plaques indicate microglia’s attraction towards extracellular protein pathology, i.e. extracellular aggregates of Aβ as compared to intracellular Lewy Bodies in PD. Double staining with CD163 and CD68 might point towards their natural inclination to phagocytose plaques. Fibrinogen leakage and compromise of the blood brain barrier raise the possibility that these are not resident microglia, but systemic macrophages infiltrating the brain.

The neuroinflammatory response in humans after traumatic brain injury

AIMS

Traumatic brain injury is a significant cause of morbidity and mortality worldwide. An epidemiological association between head injury and long-term cognitive decline has been described for many years and recent clinical studies have highlighted functional impairment within 12 months of a mild head injury. In addition chronic traumatic encephalopathy is a recently described condition in cases of repetitive head injury. There are shared mechanisms between traumatic brain injury and Alzheimer's disease, and it has been hypothesized that neuroinflammation, in the form of microglial activation, may be a mechanism underlying chronic neurodegenerative processes after traumatic brain injury.

METHODS

This study assessed the microglial reaction after head injury in a range of ages and survival periods, from <24-h survival through to 47-year survival. Immunohistochemistry for reactive microglia (CD68 and CR3/43) was performed on human autopsy brain tissue and assessed 'blind' by quantitative image analysis. Head injury cases were compared with age matched controls, and within the traumatic brain injury group cases with diffuse traumatic axonal injury were compared with cases without diffuse traumatic axonal injury.

RESULTS

A major finding was a neuroinflammatory response that develops within the first week and persists for several months after traumatic brain injury, but has returned to control levels after several years. In cases with diffuse traumatic axonal injury the microglial reaction is particularly pronounced in the white matter.

CONCLUSIONS

These results demonstrate that prolonged microglial activation is a feature of traumatic brain injury, but that the neuroinflammatory response returns to control levels after several years.

Epilepsy: neuroinflammation, neurodegeneration, and APOE genotype

Background

Precocious development of Alzheimer-type neuropathological changes in epilepsy patients, especially in APOE ϵ4,4 carriers is well known, but not the ways in which other APOE allelic combinations influence this outcome. Frozen and paraffin-embedded tissue samples resected from superior temporal lobes of 92 patients undergoing temporal lobectomies as a treatment for medication-resistant temporal lobe epilepsy were used in this study. To determine if epilepsy-related changes reflect those in another neurological condition, analogous tissue samples harvested from 10 autopsy-verified Alzheimer brains, and from 10 neurologically and neuropathologically normal control patients were analyzed using immunofluorescence histochemistry, western immunoblot, and real-time PCR to determine genotype effects on neuronal number and size, neuronal and glial expressions of amyloid β (Aβ) precursor protein (βAPP), Aβ, apolipoprotein E (ApoE), S100B, interleukin-1α and β, and α and β secretases; and on markers of neuronal stress, including DNA/RNA damage and caspase 3 expression.

Results

Allelic combinations of APOE influenced each epilepsy-related neuronal and glial response measured as well as neuropathological change. APOE ϵ3,3 conferred greatest neuronal resilience denoted as greatest production of the acute phase proteins and low neuronal stress as assessed by DNA/RNA damage and caspase-3 expression. Among patients having an APOE ϵ2 allele, none had Aβ plaques; their neuronal sizes, like those with APOE ϵ3,3 genotype were larger than those with other genotypes. APOE ϵ4,4 conferred the weakest neuronal resilience in epilepsy as well as in Alzheimer patients, but there were no APOE genotype-dependent differences in these parameters in neurologically normal patients.

Conclusions

Our findings provide evidence that the strength of the neuronal stress response is more related to patient APOE genotype than to either the etiology of the stress or to the age of the patient, suggesting that APOE genotyping may be a useful tool in treatment decisions.

Down's syndrome, neuroinflammation, and Alzheimer neuropathogenesis

Down syndrome (DS) is the result of triplication of chromosome 21 (trisomy 21) and is the prevailing cause of mental retardation. In addition to the mental deficiencies and physical anomalies noted at birth, triplication of chromosome 21 gene products results in the neuropathological and cognitive changes of Alzheimer's disease (AD). Mapping of the gene that encodes the precursor protein (APP) of the β-amyloid (Aβ) present in the Aβ plaques in both AD and DS to chromosome 21 was strong evidence that this chromosome 21 gene product was a principal neuropathogenic culprit in AD as well as DS. The discovery of neuroinflammatory changes, including dramatic proliferation of activated glia overexpressing a chromosome 2 gene product--the pluripotent immune cytokine interleukin-1 (IL-1)--and a chromosome 21 gene product--S100B--in the brains of fetuses, neonates, and children with DS opened the possibility that early events in Alzheimer pathogenesis were driven by cytokines. The specific chromosome 21 gene products and the complexity of the mechanisms they engender that give rise to the neuroinflammatory responses noted in fetal development of the DS brain and their potential as accelerators of Alzheimer neuropathogenesis in DS are topics of this review, particularly as they relate to development and propagation of neuroinflammation, the consequences of which are recognized clinically and neuropathologically as Alzheimer's disease.

Nox4-generated superoxide drives angiotensin II-induced neural stem cell proliferation

Reactive oxygen species (ROS) have been reported to affect neural stem cell self-renewal and therefore may be important for normal development and may influence neurodegenerative processes when ROS activity is elevated. To determine if increasing production of superoxide, via activation of NADPH oxidase (Nox), increases neural stem cell proliferation, 100 nM angiotensin II (Ang II) - a strong stimulator of Nox - was applied to cultures of a murine neural stem cell line, C17.2. Twelve hours following a single treatment with Ang II, there was a doubling of the number of neural stem cells. This increase in neural stem cell numbers was preceded by a gradual elevation of superoxide levels (detected by dihydroethidium fluorescence) from the steady state at 0, 5, and 30 min and gradually increasing from 1 h to the maximum at 12 h, and returning to baseline at 24 h. Ang II-dependent proliferation was blocked by the antioxidant N-acetyl-L-cysteine. Confocal microscopy revealed the presence of two sources of intracellular ROS in C17.2 cells: (i) mitochondrial and (ii) extramitochondrial; the latter indicative of the involvement of one or more specific isoforms of Nox. Of the Nox family, mRNA expression for one member, Nox4, is abundant in neural stem cell cultures, and Ang II treatment resulted in elevation of the relative levels of Nox4 protein. SiRNA targeting of Nox4 mRNA reduced both the constitutive and Ang II-induced Nox4 protein levels and attenuated Ang II-driven increases in superoxide levels and stem cell proliferation. Our findings are consistent with our hypothesis that Ang II-induced proliferation of neural stem cells occurs via Nox4-generated superoxide, suggesting that an Ang II/Nox4 axis is an important regulator of neural stem cell self-renewal and as such may fine-tune normal, stress- or disease-modifying neurogenesis.

Apolipoprotein E expression is elevated by interleukin 1 and other interleukin 1-induced factors

Background

We have previously outlined functional interactions, including feedback cycles, between several of the gene products implicated in the pathogenesis of Alzheimer's disease. A number of Alzheimer-related stressors induce neuronal expression of apolipoprotein E (ApoE), β-amyloid precursor protein (βAPP), and fragments of the latter such as amyloid β-peptide (Aβ) and secreted APP (sAPP). These stressors include interleukin-1 (IL-1)-mediated neuroinflammation and glutamate-mediated excitotoxicity. Such circumstances are especially powerful when they transpire in the context of an APOE ε4 allele.

Methods

Semi-quantitative immunofluorescence imaging was used to analyze rat brains implanted with IL-1β slow-release pellets, sham pellets, or no pellets. Primary neuronal or NT2 cell cultures were treated with IL-1β, glutamate, Aβ, or sAPP; relative levels of ApoE mRNA and protein were measured by RT-PCR, qRT-PCR, and western immunoblot analysis. Cultures were also treated with inhibitors of multi-lineage kinases--in particular MAPK-p38 (SB203580), ERK (U0126), or JNK (SP600125)--prior to exposure of cultures to IL-1β, Aβ, sAPP, or glutamate.

Results

Immunofluorescence of tissue sections from pellet-implanted rats showed that IL-1β induces expression of βAPP, IL-1α, and ApoE; the latter was confirmed by western blot analysis. These protein changes were mirrored by increases in their mRNAs, as well as in those encoding IL-1β, IL-1β-converting enzyme (ICE), and tumor necrosis factor (TNF). IL-1β also increased ApoE expression in neuronal cultures. It stimulated release of sAPP and glutamate in these cultures too, and both of these agents--as well as Aβ--stimulated ApoE expression themselves, suggesting that they may contribute to the effect of IL-1β on ApoE levels. Inhibitors of MAPK-p38, ERK, and JNK inhibited ApoE induction by all these agents except glutamate, which was sensitive only to inhibitors of ERK and JNK.

Conclusion

Conditions of glial activation and hyperexcitation can elevate proinflammatory cytokines, ApoE, glutamate, βAPP, and its secreted fragments. Because each of these factors promotes glial activation and neuronal hyperexcitation, these relationships have the potential to sustain self-propagating neurodegenerative cycles that could culminate in a progressive neurodegenerative disorder such as Alzheimer's disease.

Alzheimer's - Looking beyond plaques

Mounting evidence shows that inflammation plays a critical role in causing Alzheimer’s disease. Over the last few decades we have gone from a situation where inflammation was generally believed to have no role in the disease to the current picture where chronic activation of IL-1 inflammation has been shown to account for many of the hallmarks of the disease. This review is a personal account of the quest to prove that inflammation plays a critical role in causing Alzheimer’s disease.

Generation of reactive oxygen species in 1-methyl-4-phenylpyridinium (MPP+) treated dopaminergic neurons occurs as an NADPH oxidase-dependent two-wave cascade

BACKGROUND

Reactive oxygen species (ROS), superoxide and hydrogen peroxide (H2O2), are necessary for appropriate responses to immune challenges. In the brain, excess superoxide production predicts neuronal cell loss, suggesting that Parkinson's disease (PD) with its wholesale death of dopaminergic neurons in substantia nigra pars compacta (nigra) may be a case in point. Although microglial NADPH oxidase-produced superoxide contributes to dopaminergic neuron death in an MPTP mouse model of PD, this is secondary to an initial die off of such neurons, suggesting that the initial MPTP-induced death of neurons may be via activation of NADPH oxidase in neurons themselves, thus providing an early therapeutic target.

METHODS

NADPH oxidase subunits were visualized in adult mouse nigra neurons and in N27 rat dopaminergic cells by immunofluorescence. NADPH oxidase subunits in N27 cell cultures were detected by immunoblots and RT-PCR. Superoxide was measured by flow cytometric detection of H2O2-induced carboxy-H2-DCFDA fluorescence. Cells were treated with MPP+ (MPTP metabolite) following siRNA silencing of the Nox2-stabilizing subunit p22phox, or simultaneously with NADPH oxidase pharmacological inhibitors or with losartan to antagonize angiotensin II type 1 receptor-induced NADPH oxidase activation.

RESULTS

Nigral dopaminergic neurons in situ expressed three subunits necessary for NADPH oxidase activation, and these as well as several other NADPH oxidase subunits and their encoding mRNAs were detected in unstimulated N27 cells. Overnight MPP+ treatment of N27 cells induced Nox2 protein and superoxide generation, which was counteracted by NADPH oxidase inhibitors, by siRNA silencing of p22phox, or losartan. A two-wave ROS cascade was identified: 1) as a first wave, mitochondrial H2O2 production was first noted at three hours of MPP+ treatment; and 2) as a second wave, H2O2 levels were further increased by 24 hours. This second wave was eliminated by pharmacological inhibitors and a blocker of protein synthesis.

CONCLUSIONS

A two-wave cascade of ROS production is active in nigral dopaminergic neurons in response to neurotoxicity-induced superoxide. Our findings allow us to conclude that superoxide generated by NADPH oxidase present in nigral neurons contributes to the loss of such neurons in PD. Losartan suppression of nigral-cell superoxide production suggests that angiotensin receptor blockers have potential as PD preventatives.

Capillary cerebral amyloid angiopathy identifies a distinct APOE epsilon4-associated subtype of sporadic Alzheimer's disease

The deposition of amyloid beta-protein (Abeta) in the vessel wall, i.e., cerebral amyloid angiopathy (CAA), is associated with Alzheimer's disease (AD). Two types of CAA can be differentiated by the presence or absence of capillary Abeta-deposits. In addition, as in Alzheimer's disease, risk for capillary CAA is associated with the apolipoprotein E (APOE) epsilon4-allele. Because these morphological and genetic differences between the two types of AD-related CAA exist, the question arises as to whether there exist further differences between AD cases with and without capillary CAA and, if so, whether capillary CAA can be employed to distinguish and define specific subtypes of AD. To address this question, we studied AD and control cases both with and without capillary CAA to identify the following: (1) distinguishing neuropathological features; (2) alterations in perivascular protein expression; and (3) genotype-specific associations. More widespread Abeta-plaque pathology was observed in AD cases with capillary CAA than in those without. Expression of perivascular excitatory amino acid transporter 2 (EAAT-2/GLT-1) was reduced in cortical astrocytes of AD cases with capillary CAA in contrast to those lacking capillary Abeta-deposition and controls. Genetically, AD cases with capillary CAA were strongly associated with the APOE epsilon4 allele compared to those lacking capillary CAA and to controls. To further validate the existence of distinct types of AD we analyzed polymorphisms in additional apoE- and cholesterol-related candidate genes. Our results revealed an association between AD cases without capillary CAA (i.e., AD cases with CAA but lacking capillary CAA and AD cases without CAA) and the T-allele of the alpha(2)macroglobulin receptor/low-density lipoprotein receptor-related protein-1 (LRP-1) C766T polymorphism as opposed to AD cases with capillary CAA and non-AD controls. Taken together, these results indicate that AD cases with capillary CAA differ significantly from other AD cases both genetically and morphologically, thereby pointing to a specific capillary CAA-related and APOE epsilon4-associated subtype of AD.

Neuroinflammatory Cytokines-The Common Thread in Alzheimer's Pathogenesis

This article discusses the potential role of the cytokine cycle and its corollary as drivers of the relentless progression of Alzheimer's neuropathologies, whether they are the result of gene mutations, gene polymorphisms, and/or environmental and comorbid conditions. Based on the discovery of cytokine overexpression as an accompaniment to the dementia-related glial activation, the cytokine hypothesis was proposed. This states that in response to the negative impact on neurons of known and unknown risk factors-which include genetic inheritance, comorbid and environmental factors-microglia and astrocytes become activated and produce excess amounts of the immune-modulating cytokine interleukin-1 (IL-1) and the neuritogenic cytokine S100B, respectively. Finding that these glial events occur in fetuses and neonates with Down syndrome provided the first evidence that productive immune responses by activated glia precede rather than follow overt AD-related pathology. This finding can be added to the demonstration of IL-1 induction of amyloid β (Aβ) precursor protein and astrocyte activation with excess production of neuritogenic factor S100B. This combination suggests that IL-1 and S100B overexpression would favor the Aβ production and dystrophic neurite growth necessary for laying down neuritic Aβ plaques. This, together with demonstration of IL-1 induction of excessive production of the precursors of other features common in AD prompted a corollary to the cytokine hypothesis. The corollary states that regardless of the primary cause of the neuronal insult, the result will be chronic glial activation, which in turn will result in further neuronal injury, still more glial activation with excess cytokine expression and so on. This article discusses known causes, genetic and environmental risk factors, and comorbid conditions, and the potential contribution of glial activation with excessive cytokine expression to each.

Parenchymal and vascular Abeta-deposition and its effects on the degeneration of neurons and cognition in Alzheimer's disease

The deposition of the amyloid beta-protein (Abeta) is one of the pathological hallmarks of Alzheimer's disease (AD). Abeta-deposits show the morphology of senile plaques and cerebral amyloid angiopathy (CAA). Senile plaques and vascular Abeta-deposits occur first in neocorti-cal areas. Then, they expand hierarchically into further brain regions. The distribution of Abeta plaques throughout the entire brain, thereby correlates with the clinical status of the patients. Imaging techniques for Abeta make use of the hierarchical distribution of Abeta to distinguish AD patients from non-AD patients. However, pathology seen in AD patients represents a late stage of a pathological process starting 10-30 years earlier in cognitively normal individuals. In addition to the fibrillar amyloid of senile plaques, oligomeric and monomeric Abeta is found in the brain. Recent studies revealed that oligomeric Abeta is presumably the most toxic Abeta-aggregate, which interacts with glutamatergic synapses. In doing so, dendrites are presumed to be the primary target for Abeta-toxicity. In addition, vascular Abeta-deposits can lead to capillary occlusion and blood flow disturbances presumably contributing to the alteration of neurons in addition to the direct neurotoxic effects of Abeta. All these findings point to an important role of Abeta and its aggregates in the neurodegenerative process of AD. Since there is already significant neuron loss in AD patients, treatment strategies aimed at reducing the amyloid load will presumably not cure the symptoms of dementia but they may stop disease progression. Therefore, it seems to be necessary to protect the brain from Abeta-toxicity already in stages of the disease with minor neuron loss before the onset of cognitive symptoms.

Cerebral amyloid angiopathy and its relationship to Alzheimer's disease

Cerebral amyloid angiopathy (CAA) is characterized by the deposition of the amyloid beta-protein (A beta) within cerebral vessels. The involvement of different brain areas in CAA follows a hierarchical sequence similar to that of Alzheimer-related senile plaques. Alzheimer's disease patients frequently exhibit CAA. The expansion of CAA in AD often shows the pattern of full-blown CAA. The deposition of A beta within capillaries distinguishes two types of CAA. One with capillary A beta-deposition is characterized by a strong association with the apolipoprotein E (APOE) epsilon 4 allele and by its frequent occurrence in Alzheimer's disease cases whereas the other one lacking capillary A beta-deposits is not associated with APOE epsilon 4. Capillary CAA can be seen in every stage of CAA or AD-related A beta-deposition. AD cases with capillary CAA show more widespread capillary A beta-deposition than non-demented cases as well as capillary occlusion. In a mouse model of CAA, capillary CAA was associated with capillary occlusion and cerebral blood flow disturbances. Thus, blood flow alterations with subsequent hypoperfusion induced by CAA-related capillary occlusion presumably point to a second mechanism in which A beta adversely affects the brain in AD in addition to its direct neurotoxic effects.

The role of interleukin-1 in neuroinflammation and Alzheimer disease: an evolving perspective

Elevation of the proinflammatory cytokine Interleukin-1 (IL-1) is an integral part of the local tissue reaction to central nervous system (CNS) insult. The discovery of increased IL-1 levels in patients following acute injury and in chronic neurodegenerative disease laid the foundation for two decades of research that has provided important details regarding IL-1's biology and function in the CNS. IL-1 elevation is now recognized as a critical component of the brain's patterned response to insults, termed neuroinflammation, and of leukocyte recruitment to the CNS. These processes are believed to underlie IL-1's function in the setting of acute brain injury, where it has been ascribed potential roles in repair as well as in exacerbation of damage. Explorations of IL-1's role in chronic neurodegenerative disease have mainly focused on Alzheimer disease (AD), where indirect evidence has implicated it in disease pathogenesis. However, recent observations in animal models challenge earlier assumptions that IL-1 elevation and resulting neuroinflammatory processes play a purely detrimental role in AD, and prompt a need for new characterizations of IL-1 function. Potentially adaptive functions of IL-1 elevation in AD warrant further mechanistic studies, and provide evidence that enhancement of these effects may help to alleviate the pathologic burden of disease.

Perispinal etanercept: potential as an Alzheimer therapeutic

Tumor necrosis factor-alpha (TNF) is one of a number of systemic and immunomodulating cytokines that generally act to promote acute-phase reactions but can drive degenerative changes when chronically elevated. Traditional focus on TNF has been directed at these inflammation-related functions. Of particular relevance to intersections between neuroinflammation and neurodegeneration is the ability of TNF to increase expression of interleukin-1 (IL-1), which in turn increases production of the precursors necessary for formation of amyloid plaques, neurofibrillary tangles, and Lewy bodies. More recent data have revealed that TNF, one of the few gliotransmitters, has strikingly acute effects on synaptic physiology. These complex influences on neural health suggest that manipulation of this cytokine might have important impacts on diseases characterized by glial activation, cytokine-mediated neuroinflammation, and synaptic dysfunction. Toward such manipulation in Alzheimer's disease, a six-month study was conducted with 15 probable-Alzheimer patients who were treated weekly with perispinal injection of Etanercept, an FDA-approved TNF inhibitor that is now widely used for treatment of rheumatoid arthritis and other systemic diseases associated with inflammation. The results demonstrated that perispinal administration of etanercept could provide sustained improvement in cognitive function for Alzheimer patients. Additionally, the authors were impressed by the striking rapidity with which these improvements occurred in the study patients. An example of this rapid improvement is presented in this issue as a case report by Tobinick and Gross. Such rapid gain of function inspires speculation about the role of gliotransmission or other equally rapid synaptic events in the relationship of TNF to Alzheimer-impacted neurophysiology. Because of the inability of large molecules such as etanercept to cross the blood brain barrier following conventional systemic administration, it is likely that the more direct drug delivery system pioneered by Tobinick also contributed to the effectiveness of the treatment. If so, this system could be useful in drug delivery to the brain in other neural disorders, as well as in animal research studies, many of which currently employ delivery strategies that inflict damage to neural cells and thus engender neuroinflammatory responses.

Glial expression of cannabinoid CB(2) receptors and fatty acid amide hydrolase are beta amyloid-linked events in Down's syndrome

Recent data suggest that the endocannabinoid system (ECS) may be involved in the glial response in different types of brain injury. Both acute and chronic insults seem to trigger a shift in the pattern of expression of some elements of this system from neuronal to glial. Specifically, data obtained in human brain tissue sections from Alzheimer's disease patients showed that the expression of cannabinoid receptors of the CB(2) type is induced in activated microglial cells while fatty acid amide hydrolase (FAAH) expression is increased in reactive astrocytes. The present study was designed to determine the time-course of the shift from neuronal to glial induction in the expression of these proteins in Down's syndrome, sometimes referred to as a human model of Alzheimer-like beta-amyloid (Abeta) deposition. Here we present immunohistochemical evidence that both CB(2) receptors and FAAH enzyme are induced in Abeta plaque-associated microglia and astroglia, respectively, in Down's syndrome. These results suggest that the induction of these elements of the ECS contributes to, or is a result of, amyloid deposition and subsequent plaque formation. In addition, they confirm a striking differential pattern of distribution of FAAH and CB(2) receptors.

Common inflammatory mechanisms in Lewy body disease and Alzheimer disease

Cortical Lewy body disease as a cause of dementia has been recognized for more than 40 years. Only in the past 15 to 20 years, however, has the true frequency of this entity come to be appreciated, primarily because of the advent of sensitive and specific immunohistochemical diagnostic techniques. We now know that there is frequent and extensive overlap, both clinically and pathologically, between Lewy body and Alzheimer diseases. Although some of this overlap may be attributable to common genetic and environmental risk factors, it is also now apparent that the 2 diseases share common neuroinflammatory mechanisms involving activation of microglia, overexpression of interleukin-1 and other inflammatory mediators, and inflammatory toxicity to neurons. Activated microglia are found in association with alpha-synuclein-containing neurons and glia in Parkinson disease, in dementia with Lewy bodies, and in multiple system atrophy, and these associations are reminiscent of microglial associations with neurofibrillary tangle-containing neurons in Alzheimer disease. In vitro and in vivo experimental work has shown reciprocal induction between alpha-synuclein and injured neurons on one hand and activated microglia and cytokine overexpression on the other. These neuroinflammatory processes may be a common link driving progression in both diseases and explaining the frequent overlap between the 2 diseases.

Association of the glutathione S-transferase omega-1 Ala140Asp polymorphism with cerebrovascular atherosclerosis and plaque-associated interleukin-1 alpha expression

BACKGROUND AND PURPOSE

Glutathione S-transferase omega-1 is a multifunctional enzyme. The Asp/Asp genotype of the Ala140Asp polymorphism of the GSTO1 gene has been alleged to increase the risk of vascular dementia. The objective of this study is to address the question of whether common vessel disorders known to cause vascular dementia are modified in their severity by this polymorphism.

METHODS

The severity and expansion of atherosclerosis in the circle of Willis vessels, cerebral small vessel disease, and cerebral amyloid angiopathy were studied in a sample of 79 autopsy cases. Genotyping of the GSTO1 Ala140Asp polymorphism as well as immunohistochemistry for glutathione S-transferase omega-1 was performed.

RESULTS

Carriers of the GSTO1 Asp/Asp genotype presented with more severe and widespread atherosclerosis than noncarriers. However, there was no effect on small vessel disease expansion and cerebral amyloid angiopathy severity. Immunohistochemically, we detected interleukin-1 alpha expressing macrophages in the lipid core of atherosclerosis plaques exhibiting glutathione S-transferase omega-1-positive material. GSTO1 Asp/Asp carriers showed larger areas of atherosclerosis plaques containing interleukin-1 alpha-positive material than carriers of the GSTO1 Ala-allele.

CONCLUSIONS

The GSTO1 Asp/Asp genotype presumably modulates the severity and expansion of atherosclerosis in the circle of Willis. The cellular colocalization of glutathione S-transferase omega-1 and interleukin-1 alpha suggests a functional interaction between both proteins which in part might explain the function of glutathione S-transferase omega-1 in the pathogenesis of cerebral atherosclerosis.

APP-BP1 inhibits Abeta42 levels by interacting with Presenilin-1

Background

The β-amyloid precursor protein (APP) is sequentially cleaved by the β- and then γ-secretase to generate the amyloid β-peptides Aβ40 and Aβ42. Increased Aβ42/Aβ40 ratios trigger amyloid plaque formations in Alzheimer's disease (AD). APP binds to APP-BP1, but the biological consequence is not well understood.

Results

We report that when the endogenous APP-BP1 was suppressed by small interfering RNAs (siRNAs), cell-associated Aβ42 was dramatically increased in APP₆₉₅ expressing primary neurons. The accumulation of Aβ42 was accompanied by significant increases in APP and APP-CTF in APP-BP1 siRNA expressing neurons. In contrast, APP-BP1 overexpression in primary neurons significantly decreased the levels of Aβ and endogenous APP but not APLPs. We also investigated the potential mechanism of APP-BP1-mediated APP processing. APP-BP1 co-precipitated with Presenilin-1 (PS1) in native rat brain extracts, co-migrated with the γ-secretase components in brain membrane extracts in glycerol gradient centrifugation, and colocalized in primary neurons. Further, the endogenous PS1-CTF was significantly downregulated by APP-BP1 expression.

Conclusion

Our data suggest that APP-BP1 may inhibit Aβ42 production by interacting with PS1 under physiological conditions.

Dementia with Lewy bodies: Definition, diagnosis, and pathogenic relationship to Alzheimer's disease

Clinical dementia associated with the appearance of Lewy bodies in the cerebral cortex has been recognized for over 40 years. Until the 1990s, however, cortical Lewy body disease was thought to be a rare cause of dementia. At that time, the advent of sensitive and specific immunohistochemical techniques for highlighting these elusive structures led to the recognition of cortical Lewy body disease as a common substrate for clinical dementia. Current diagnostic criteria recognize dementia with Lewy bodies as a clinicopathological entity. Also recognized is the closely related (and perhaps biologically identical) entity of Parkinson's disease dementia, which differs from dementia with Lewy bodies only in the temporal sequence of appearance of clinical symptoms. The generic term "Lewy body disease" encompasses both entities. There is frequent and extensive overlap, both clinically and pathologically, between dementia with Lewy bodies and Alzheimer's disease. The two diseases share several genetic and environmental risk factors that have in common increased inflammatory states associated with increased disease risk. Moreover, pathological and experimental work has implicated the involvement of activated microglia and of microglia-derived interleukin-1 in the pathogenesis of the pathognomonic lesions of both diseases. Such neuroinflammatory processes may be the common link driving progression in both diseases and explaining the frequent overlap between the two diseases.

Interleukin-1 mediates Alzheimer and Lewy body pathologies

Background

Clinical and neuropathological overlap between Alzheimer's (AD) and Parkinson's disease (PD) is now well recognized. Such cases of concurrent AD and Lewy body disease (AD/LBD) show neuropathological changes that include Lewy bodies (α-synuclein aggregates), neuritic amyloid plaques, and neurofibrillary tangles (hyperphosphorylated tau aggregates). The co-occurrence of these clinical and neuropathological changes suggests shared pathogenic mechanisms in these diseases, previously assumed to be distinct. Glial activation, with overexpression of interleukin-1 (IL-1) and other proinflammatory cytokines, has been increasingly implicated in the pathogenesis of both AD and PD.

Methods

Rat primary cultures of microglia and cortical neurons were cultured either separately or as mixed cultures. Microglia or cocultures were treated with a secreted fragment (sAPPα) of the β-amyloid precursor protein (βAPP). Neurons were treated with IL-1β or conditioned medium from sAPPα-activated microglia, with or without IL-1 receptor antagonist. Slow-release pellets containing either IL-1β or bovine serum albumin (control) were implanted in cortex of rats, and mRNA for various neuropathological markers was analyzed by RT-PCR. Many of the same markers were assessed in tissue sections from human cases of AD/LBD.

Results

Activation of microglia with sAPPα resulted in a dose-dependent increase in secreted IL-1β. Cortical neurons treated with IL-1β showed a dose-dependent increase in sAPPα release, an effect that was enhanced in the presence of microglia. IL-1β also elevated the levels of α-synuclein, activated MAPK-p38, and phosphorylated tau; a concomitant decrease in levels of synaptophysin occurred. Delivery of IL-1β by slow-release pellets elevated mRNAs encoding α-synuclein, βAPP, tau, and MAPK-p38 compared to controls. Finally, human cases of AD/LBD showed colocalization of IL-1-expressing microglia with neurons that simultaneously overexpressed βAPP and contained both Lewy bodies and neurofibrillary tangles.

Conclusion

Our findings suggest that IL-1 drives production of substrates necessary for formation of the major neuropathological changes characteristic of AD/LBD.

Potential Inflammatory biomarkers in Alzheimer's disease

The role of the brain's innate immune system in Alzheimer pathogenesis is now well established. Proinflammatory cytokines elaborated by this system, in particular activated microglia-derived interleukin-1 (IL-1), drive a cascade of neurotoxic changes that are important for the development and progression of both the neuritic plaques and neurofibrillary tangles characteristic of Alzheimer's disease. Cytokine expression may also be modulated by variants of genes. For instance, inheritance of certain IL-1 gene variants is associated with Alzheimer's disease. The potential for using blood levels of proinflammatory cytokines as biomarkers of disease progression, however, remains unrealized. The interpretation of cytokine levels in the blood is complicated by the fact, for example, that the overexpression of IL-1 in Alzheimer brain may act to increase adrenal cortisol production through the hypothalamic-pituitary-adrenal axis, which acts to limit macrophage activation and peripheral cytokine production.

Neuropsychiatric associations of apolipoprotein E alleles in subjects with combat-related posttraumatic stress disorder

Previous studies have reported associations between apolipoprotein E (APOE) genotype, cognitive function, and psychopathology in psychiatric populations. The authors investigated the associations between APOE allele status, memory function, and posttraumatic stress disorder (PTSD) symptom severity in PTSD subjects. Presence of the APOE 2 allele was associated with significantly worse reexperiencing symptoms and impaired memory function in this population.

Inflammation and neurodegenerative diseases

The decline in mental fitness associated with Alzheimer disease is accompanied by physical changes in the brain, including the development of characteristic plaques and neurofibrillary tangles, but the pathogenesis of those changes is not clear. Recent work suggests that the activation of microglia in response to injury, illness, aging, or other causes begins a cascade of events that can best be characterized as an inflammatory process. This cascade is mediated at first by the proinflammatory cytokine interleukin 1, which is overexpressed by the activated microglia. Through various pathways, interleukin 1 causes neuronal death, which activates more microglia, which in turn release more interleukin 1 in a self-sustaining and self-amplifying fashion. Over a period of years, this slow, smoldering inflammation in the brain destroys sufficient neurons to cause the clinical signs of Alzheimer disease.

Apolipoprotein E co-localizes with newly formed amyloid beta-protein (Abeta) deposits lacking immunoreactivity against N-terminal epitopes of Abeta in a genotype-dependent manner

Different types of amyloid beta-protein (Abeta)-containing plaques occur in brains of Alzheimer's disease (AD) patients. Diffuse plaques seen during early stages of AD differ from neuritic plaques in later stages both with respect to the length of the Abeta peptides and the presence of other proteins, e.g., apolipoprotein-E (apoE). Since apoE is involved in Abeta transport and clearance, and the epsilon4-allele of the apolipoprotein-E gene (APOE) is a major risk factor for sporadic AD, it is plausible to speculate that apoE plays a pathophysiological role in the initiation of Abeta deposition. To address the issue of whether binding of apoE to Abeta is involved in initial Abeta deposition, we studied the human medial temporal lobe of 60 autopsy cases encompassing the full spectrum of AD-related pathology. In temporal lobe regions, which become involved for the first time at a given stage of beta-amyloidosis, all plaques represent newly formed plaques, and these were studied with immunohistochemical methods. ApoE was present in 36 cases, and was frequently co-localized with newly formed Abeta deposits detectable with anti-Abeta(42) but not with antibodies raised against N-terminal epitopes of Abeta. In 10 additional cases, immunoreactivity against apoE was completely lacking in newly formed plaques, which, at the same time, displayed immunoreactivity against N-terminal epitopes of Abeta. The failure of N-terminal epitopes of Abeta to co-localize with apoE in newly formed plaques indicates that these deposits presumably contain apoE-Abeta complexes, in which the N-terminal epitopes of Abeta are often concealed after complexing with apoE, thus preventing subsequent binding of antibodies. Moreover, apoE-positive newly formed plaques were seen more frequently in APOE epsilon4/4 cases than in non-APOE epsilon4/4 individuals, thereby underlining the potentially crucial role of apoE for the development of Abeta deposits.

The impact of argyrophilic grain disease on the development of dementia and its relationship to concurrent Alzheimer's disease-related pathology

Argyrophilic grain disease (AGD) constitutes a neurodegenerative disorder that occurs in the brains of the elderly and affects 5% of all patients with dementia. Tau protein-containing lesions known as argyrophilic grains and located predominantly in limbic regions of the brain characterize this disease. Dementia is encountered in only a subset of cases that display the morphological pattern of AGD. The aim of this study is to determine the role of concurrent Alzheimer's disease (AD)-related pathology for the development of dementia in AGD patients. A total of 204 post-mortem brains from 30 demented and 49 nondemented AGD patients, 39 AD patients, and from 86 nondemented controls without AGD were staged for AD-related neurofibrillary tangles (NFTs) as well as amyloid beta-protein (Abeta) deposition. To identify differences in AD-related pathology between demented and nondemented AGD cases, and to differentiate the pattern of AD-related changes in demented and nondemented AGD cases from that seen in AD and nondemented controls, we statistically compared the stages of Abeta and NFT distribution among these groups. Using a logistic regression model, we showed that AGD has a significant effect on the development of dementia beyond that attributable to AD-related pathology (P < 0.005). Demented AGD cases showed lower stages of AD-related pathology than did pure AD cases but higher stages than nondemented AGD patients. AGD associated dementia was seen in the presence of NFT (Braak)-stages II-IV and Abeta-phases 2-3, whereas those stages were not associated with dementia in the absence of AGD. In conclusion, AGD is a clinically relevant neurodegenerative entity that significantly contributes to the development of dementia by lowering the threshold for cognitive deficits in the presence of moderate amounts of AD-related pathology.

S100B-induced microglial and neuronal IL-1 expression is mediated by cell type-specific transcription factors

Both the astrocytic cytokine S100B and the pro-inflammatory interleukin-1 (IL-1) are elevated in Alzheimer's disease, and each has been implicated in Alzheimer-related neuropathology. We examined the gene-regulatory events through which S100B induces IL-1beta expression. In primary microglia, S100B activated the transcription factors Sp1 and NFkappaB, followed by an increase in IL-1beta mRNA levels. The latter was blocked by a peptide inhibitor of NFkappaB or by a double-stranded oligonucleotide containing a NFkappaB-binding site to serve as "decoy" DNA and reduce available NFkappaB. But in primary cortical neurons, decoy and siRNA experiments indicated that the IL-1beta induction by S100B was mediated by Sp1 without evidence of a role for NFkappaB. Our results suggest that the elevation of S100B and IL-1 in Alzheimer brain and consequent neurodegenerative events are mediated through cell-type specific gene-regulatory events, providing mechanistic insight into connections between glial activation and neuronal dysfunction.

Glia and their cytokines in progression of neurodegeneration

A glia-mediated, inflammatory immune response is an important component of the neuropathophysiology of Alzheimer's disease, of the midlife neurodegeneration of Down's syndrome, and of other age-related neurodegenerative conditions. All of these conditions are associated with early and often dramatic activation of, and cytokine overexpression in, microglia and astrocytes, sometimes decades before pathological changes consistent with a diagnosis of Alzheimer's disease are apparent, as in patients with Down's syndrome or head injury. Brains of normal elderly individuals also often show Alzheimer-type neuropathological changes, although to a lesser degree than those seen in Alzheimer's disease itself. These normal age-related glial changes, likely a response to the normal wear and tear of the aging process, raise the threshold of glial activation and thus may explain the fact that even genetically determined Alzheimer's disease, resulting from genetic mutations such as those in beta-amyloid precursor protein and presenilins or from genetic duplication such as of chromosome 21, only shows the full manifestation of the disease decades after birth. In the more common sporadic form of Alzheimer's disease, age-related increases in glial activation and expression of cytokines may act in synergy with other genetic and acquired environmental risks to culminate in the development of disease.

Funding free and universal access to Journal of Neuroinflammation

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[Relationship between apoptosis of neurons and microglia activation in Alzheimer's disease]

OBJECTIVE

To assess the relationship between microglia activation and apoptosis of neurons, and the significance of activated microglias in the formation and progression of senile plaques in Alzheimer's disease.

METHODS

IL-1alpha and beta-amyloid immunohistochemistry, combined with TUNEL assay were used to assess brain tissue samples from 10 patients with Alzheimer's disease and 4 negative control cases without neurological disease.

RESULTS

The number of resting microglias in the brains of Alzheimer's disease patients was similar to that of the control group (P > 0.05), but the number of activated microglias was significant greater in the Alzheimer's disease patients than that of the controls (P < 0.01). The activated microglias displayed altered size and morphology, and was therefore, categorized into three subtypes as primed, enlarged and phagocytic microglias. The numbers of primed, enlarged and phagocytic microglias were 5.4 +/- 0.87, 11.5 +/- 1.25, and 3.4 +/- 0.32 microglia/mm2 and represented 26.6%, 56.65%, and 16.75% of all activated microglias respectively. The number of TUNEL positive apoptotic neurons was significantly greater in Alzheimer patients than that in the control group (P < 0.05). There was a close relationship between the apoptosis of neurons and the activation of microglias (P < 0.01). The activated microglias were differentially distributed among four different plaque types in Alzheimer patients. Many primed (42.3%) and most of the enlarged and phagocytic microglias (56.2% and 70.6%) were present in the diffuse neuritic plaques.

CONCLUSIONS

Hyperplasia and activation of microglias are a common phenomena in AD and may play an important role in its pathogenesis. There is a close relationship between the apoptosis of neurons and activation of microglias. The activation of microglias may play a key pathogenic role in senile plaque formation and progression of Alzheimer disease.

Microglia and neuroinflammation: a pathological perspective

Microglia make up the innate immune system of the central nervous system and are key cellular mediators of neuroinflammatory processes. Their role in central nervous system diseases, including infections, is discussed in terms of a participation in both acute and chronic neuroinflammatory responses. Specific reference is made also to their involvement in Alzheimer's disease where microglial cell activation is thought to be critically important in the neurodegenerative process.

Trisomy 21 and the brain

In fetuses with Down syndrome, neurons fail to show normal dendritic development, yielding a "tree in winter" appearance. This developmental failure is thought to result in mental retardation. In adults with Down syndrome, neuronal loss is dramatic and neurofibrillary and neuritic Abeta plaque pathologies are consistent with Alzheimer disease. These pathological changes are thought to underlie the neuropsychological and physiological changes in older individuals with Down syndrome. Two chromosome 21-based gene products, beta-amyloid precursor protein (betaAPP) and S100B, have been implicated in these neuronal and interstitial changes. Although not necessary for mental retardation and other features, betaAPP gene triplication is necessary, although perhaps not sufficient, for development of Alzheimer pathology. S100B is overexpressed throughout life in Down patients, and mice with extra copies of the S100B gene have dendritic abnormalities. S100B overexpression correlates with Alzheimer pathology in post-adolescent Down syndrome patients and has been implicated in Abeta plaque pathogenesis. Interleukin-1 (IL-1) is a non-chromosome-21-based cytokine that is also overexpressed throughout life in Down syndrome. IL-1 upregulates betaAPP and S100B expression and drives numerous neurodegenerative and self-amplifying cascades that support a neuroinflammatory component in the pathogenesis of sporadic and Down syndrome-related Alzheimer disease.

Welcome to the Journal of Neuroinflammation!

Welcome to the Journal of Neuroinflammation, an open-access, peer-reviewed, online journal that focuses on innate immunological responses of the central nervous system, involving microglia, astrocytes, cytokines, chemokines, and related molecular processes. 'Neuroinflammation' is an encapsulization of the idea that microglial and astrocytic responses and actions in the central nervous system have a fundamentally inflammation-like character, and that these responses are central to the pathogenesis and progression of a wide variety of neurological disorders. This concept has its roots in the discoveries of inflammatory cytokines and proteins in the plaques of Alzheimer disease, and these ideas have been extended to other neurodegenerative diseases, to ischemic/toxic diseases, to tumor biology and even to normal brain development. The Journal of Neuroinflammation, published by BioMed Central, will bring together work focusing on microglia, astrocytes, cytokines, chemokines, and related molecular processes in the central nervous system. All articles published in the Journal of Neuroinflammation will be immediately listed in PubMed, and access to published articles will be universal and free through the internet.

Induction of serine racemase expression and D-serine release from microglia by amyloid beta-peptide

Background

Roles for excitotoxicity and inflammation in Alzheimer's disease have been hypothesized. Proinflammatory stimuli, including amyloid β-peptide (Aβ), elicit a release of glutamate from microglia. We tested the possibility that a coagonist at the NMDA class of glutamate receptors, D-serine, could respond similarly.

Methods

Cultured microglial cells were exposed to Aβ. The culture medium was assayed for levels of D-serine by HPLC and for effects on calcium and survival on primary cultures of rat hippocampal neurons. Microglial cell lysates were examined for the levels of mRNA and protein for serine racemase, the enzyme that forms D-serine from L-serine. The racemase mRNA was also assayed in Alzheimer hippocampus and age-matched controls. A microglial cell line was transfected with a luciferase reporter construct driven by the putative regulatory region of human serine racemase.

Results

Conditioned medium from Aβ-treated microglia contained elevated levels of D-serine. Bioassays of hippocampal neurons with the microglia-conditioned medium indicated that Aβ elevated a NMDA receptor agonist that was sensitive to an antagonist of the D-serine/glycine site (5,7-dicholorokynurenic acid; DCKA) and to enzymatic degradation of D-amino acids by D-amino acid oxidase (DAAOx). In the microglia, Aβ elevated steady-state levels of dimeric serine racemase, the apparent active form of the enzyme. Promoter-reporter and mRNA analyses suggest that serine racemase is transcriptionally induced by Aβ. Finally, the levels of serine racemase mRNA were elevated in Alzheimer's disease hippocampus, relative to age-matched controls.

Conclusions

These data suggest that Aβ could contribute to neurodegeneration through stimulating microglia to release cooperative excitatory amino acids, including D-serine.

Microglial activation by uptake of fDNA via a scavenger receptor

The fate of the fragmented DNA (fDNA) observed in neuronal nuclei in Alzheimer brain is unknown. However, its fate is suggested as fDNA is found in the cytoplasm of adjacent activated microglia. After a brief incubation with fDNA, approximately 70% of microglia had fDNA in their cytoplasm, were activated, and overexpressed interleukin-1beta. Microglial activation enhanced uptake whereas blocking scavenger receptors suppressed this uptake. These results suggest that the brain rids itself of fDNA from dying neurons through microglial uptake, activation, and overexpression of IL-1. Such overexpression of IL-1 in Alzheimer brain has been linked to Alzheimer pathogenesis.

Increased susceptibility of S100B transgenic mice to perinatal hypoxia-ischemia

S100B is a glial-derived protein that is a well-established biomarker for severity of neurological injury and prognosis for recovery. Cell-based and clinical studies have implicated S100B in the initiation and maintenance of a pathological, glial-mediated proinflammatory state in the central nervous system. However, the relationship between S100B levels and susceptibility to neurological injury in vivo has not been determined. We used S100B transgenic (Tg) and knockout (KO) mice to test the hypothesis that overexpression of S100B increases vulnerability to cerebral hypoxic-ischemic injury and that this response correlates with an increase in neuroinflammation from activated glia. Postnatal day 8 Tg mice subjected to hypoxia-ischemia showed a significant increase in mortality compared with KO and wild-type mice. Tg mice also exhibited greater cerebral injury and volume loss in the ischemic hemisphere after an 8-day recovery, as assessed by histopathology and magnetic resonance imaging. Measurement of glial fibrillary acidic protein and S100B levels showed a significant increase in the Tg mice, consistent with heightened glial activation and neuroinflammation in response to injury. This is the first demonstration to our knowledge that overexpression of S100B in vivo enhances pathological response to injury.

Interleukin-1 mediates pathological effects of microglia on tau phosphorylation and on synaptophysin synthesis in cortical neurons through a p38-MAPK pathway

The presence of tangles of abnormally phosphorylated tau is a characteristic of Alzheimer's disease (AD), and the loss of synapses correlates with the degree of dementia. In addition, the overexpression of interleukin-1 (IL-1) has been implicated in tangle formation in AD. As a direct test of the requirement for IL-1 in tau phosphorylation and synaptophysin expression, IL-1 actions in neuron-microglia cocultures were manipulated. Activation of microglia with secreted beta-amyloid precursor protein or lipopolysaccharide elevated their expression of IL-1alpha, IL-1beta, and tumor necrosis factor alpha (TNFalpha) mRNA. When such activated microglia were placed in coculture with primary neocortical neurons, a significant increase in the phosphorylation of neuronal tau was accompanied by a decline in synaptophysin levels. Similar effects were evoked by treatment of neurons with recombinant IL-1beta. IL-1 receptor antagonist (IL-1ra) as well as anti-IL-1beta antibody attenuated the influence of activated microglia on neuronal tau and synaptophysin, but anti-TNFalpha antibody was ineffective. Some effects of microglial activation on neurons appear to be mediated by activation of p38 mitogen-activated protein kinase (p38-MAPK), because activated microglia stimulated p38-MAPK phosphorylation in neurons, and an inhibitor of p38-MAPK reversed the influence of IL-1beta on tau phosphorylation and synaptophysin levels. Our results, together with previous observations, suggest that activated microglia may contribute to neurofibrillary pathology in AD through their production of IL-1, activation of neuronal p38-MAPK, and resultant changes in neuronal cytoskeletal and synaptic elements.