Complex regulation of acute and chronic neuroinflammatory responses in mouse models deficient for nuclear factor kappa B p50 subunit.

Inflammation is a major mechanism of acute brain injury and chronic neurodegeneration. This neuroinflammation is known to be substantially regulated by the transcription factor NF-κB, which is predominantly found in the form of heterodimer of p65 (RelA) and p50 subunit, with p50/p50 homodimers being also common. The p65 subunit has a transactivation domain, whereas p50 is chiefly involved in DNA binding. Binding of the p65/p50 heterodimers is thought to induce expression of numerous proinflammatory genes in microglia. Here we show that cultured microglia deficient for the gene (Nfkb1) encoding p50 subunit show reduced induction of proinflammatory mediators, increased expression of anti-inflammatory genes, and increased expression of CD45, an immunoregulatory molecule, in response to lipopolysaccharide (LPS) exposure, but increased capacity to take up ß-amyloid (Aß) which is associated with enhanced release of tumor necrosis factor alpha (TNFα). However, Nfkb1 deficiency strongly increases leukocyte infiltration and the expression of proinflammatory genes in response to intrahippocampal administration of LPS. Also, when crossing Nfkb1 deficient mice with APdE9 transgenic mice the expression of proinflammatory genes was strongly enhanced, whereas Aß burden was slightly but significantly reduced. These alterations in expression of inflammatory mediators in Nfkb1 deficient mice were associated with reduced expression of CD45. Our data demonstrates a crucial and complex role p50 subunit of NF-κB in brain inflammation, especially in regulating the phenotype of microglia after acute and chronic inflammatory insults relevant to clinical conditions, contributing to both pro-inflammatory and anti-inflammatory responses of microglia, infiltration of leukocytes, and clearance of Aß in Alzheimer's disease.

Effects of human intravenous immunoglobulin on amyloid pathology and neuroinflammation in a mouse model of Alzheimer's disease.

BACKGROUND: Human intravenous immunoglobulin (hIVIG) preparation is indicated for treating primary immunodeficiency disorders associated with impaired humoral immunity. hIVIG is known for its anti-inflammatory properties and a decent safety profile. Therefore, by virtue of its constituent natural anti-amyloid beta antibodies and anti-inflammatory effects, hIVIG is deemed to mediate beneficial effects to patients of Alzheimer's disease (AD). Here, we set out to explore the effects of hIVIG in a mouse model of AD. METHODS: We treated APP/PS1dE9 transgenic and wild-type mice with weekly injections of a high hIVIG dose (1 g/kg) or saline for 3 or 8 months. Treatment effect on brain amyloid pathology and microglial reactivity was assessed by ELISA, immunohistochemistry, RT-PCR, and confocal microscopy. RESULTS: We found no evidence for reduction in Aß pathology; instead 8 months of hIVIG treatment significantly increased soluble levels of Aß40 and Aß42. In addition, we noticed a significant reduction in CD45 and elevation of Iba-1 markers in specific sub-populations of microglial cells. Long-term hIVIG treatment also resulted in significant suppression of TNF-α and increase in doublecortin positive adult-born neurons in the dentate gyrus. CONCLUSIONS: Our data indicate limited ability of hIVIG to impact amyloid burden but shows changes in microglia, pro-inflammatory gene expression, and neurogenic effects. Immunomodulation by hIVIG may account for its beneficial effect in AD patients.

WNT signaling in activated microglia is proinflammatory.

Microglia activation is central to the neuroinflammation associated with neurological and neurodegenerative diseases, particularly because activated microglia are often a source of proinflammatory cytokines. Despite decade-long research, the molecular cascade of proinflammatory transformation of microglia in vivo remains largely elusive. Here, we report increased ß-catenin expression, a central intracellular component of WNT signaling, in microglia undergoing a proinflammatory morphogenic transformation under pathogenic conditions associated with neuroinflammation such as Alzheimer's disease. We substantiate disease-associated ß-catenin signaling in microglia in vivo by showing age-dependent ß-catenin accumulation in mice with Alzheimer's-like pathology (APdE9). In cultured mouse microglia expressing the WNT receptors Frizzled FZD(4,5,7,8) and LDL receptor-related protein 5/6 (LRP5/6), we find that WNT-3A can stabilize ß-catenin. WNT-3A dose dependently induces LRP6 phosphorylation with downstream activation of disheveled, ß-catenin stabilization, and nuclear import. Gene-expression profiling reveals that WNT-3A stimulation specifically increases the expression of proinflammatory immune response genes in microglia and exacerbates the release of de novo IL-6, IL-12, and tumor necrosis factor α. In summary, our data suggest that the WNT family of lipoglycoproteins can instruct proinflammatory microglia transformation and emphasize the pathogenic significance of ß-catenin-signaling networks in this cell type.

Role of reactive oxygen species in the progression of Alzheimer's disease.

The pathogenesis of Alzheimer's disease (AD) involves neurodegeneration following the deposition of ß-amyloid (Aß) plaques and neurofibrillary tangles in vulnerable brain regions. The vulnerability of the brain to reactive oxygen species (ROS) is now emerging as a key detrimental factor driving AD pathogenesis. Oxidative stress (OS) irreversibly damages cellular biomolecules and perturbs neuronal functions. Scientific evidence is emerging that supports the therapeutic effects of antioxidants in preventing the onset and delaying the progression of AD pathology. In this review, we highlight the role of the OS in AD and the importance of antioxidants in its treatment.

Human intravenous immunoglobulin provides protection against Aß toxicity by multiple mechanisms in a mouse model of Alzheimer's disease.

BACKGROUND: Purified intravenous immunoglobulin (IVIG) obtained from the plasma of healthy humans is indicated for the treatment of primary immunodeficiency disorders associated with defects in humoral immunity. IVIG contains naturally occurring auto-antibodies, including antibodies (Abs) against ß-amyloid (Aß) peptides accumulating in the brains of Alzheimer's disease (AD) patients. IVIG has been shown to alleviate AD pathology when studied with mildly affected AD patients. Although its mechanisms-of-action have been broadly studied, it remains unresolved how IVIG affects the removal of natively formed brain Aß deposits by primary astrocytes and microglia, two major cell types involved in the neuroinflammatory responses. METHODS: We first determined the effect of IVIG on Aß toxicity in primary neuronal cell culture. The mechanisms-of-action of IVIG in reduction of Aß burden was analyzed with ex vivo assay. We studied whether IVIG solubilizes natively formed Aß deposits from brain sections of APP/PS1 mice or promotes Aß removal by primary glial cells. We determined the role of lysosomal degradation pathway and Aß Abs in the IVIG-promoted reduction of Aß. Finally, we studied the penetration of IVIG into the brain parenchyma and interaction with brain deposits of human Aß in a mouse model of AD in vivo. RESULTS: IVIG was protective against Aß toxicity in a primary mouse hippocampal neuron culture. IVIG modestly inhibited the fibrillization of synthetic Aß1-42 but did not solubilize natively formed brain Aß deposits ex vivo. IVIG enhanced microglia-mediated Aß clearance ex vivo, with a mechanism linked to Aß Abs and lysosomal degradation. The IVIG-enhanced Aß clearance appears specific for microglia since IVIG did not affect Aß clearance by astrocytes. The cellular mechanisms of Aß clearance we observed have potential relevance in vivo since after peripheral administration IVIG penetrated to mouse brain tissue reaching highest concentrations in the hippocampus and bound selectively to Aß deposits in co-localization with microglia. CONCLUSIONS: Our results demonstrate that IVIG promotes recognition and removal of natively formed brain Aß deposits by primary microglia involving natural Aß Abs in IVIG. These findings may have therapeutic relevance in vivo as IVIG penetrates through the blood-brain barrier and specifically binds to Aß deposits in brain parenchyma.

Memantine lowers amyloid-beta peptide levels in neuronal cultures and in APP/PS1 transgenic mice.

Memantine is a moderate-affinity, uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist that stabilizes cognitive, functional, and behavioral decline in patients with moderate to severe Alzheimer's disease (AD). In AD, the extracellular deposition of fibrillogenic amyloid-beta peptides (Abeta) occurs as a result of aberrant processing of the full-length Abeta precursor protein (APP). Memantine protects neurons from the neurotoxic effects of Abeta and improves cognition in transgenic mice with high brain levels of Abeta. However, it is unknown how memantine protects cells against neurodegeneration and affects APP processing and Abeta production. We report the effects of memantine in three different systems. In human neuroblastoma cells, memantine, at therapeutically relevant concentrations (1-4 muM), decreased levels of secreted APP and Abeta(1-40). Levels of the potentially amylodogenic Abeta(1-42) were undetectable in these cells. In primary rat cortical neuronal cultures, memantine treatment lowered Abeta(1-42) secretion. At the concentrations used, memantine treatment was not toxic to neuroblastoma or primary cultures and increased cell viability and/or metabolic activity under certain conditions. In APP/presenilin-1 (PS1) transgenic mice exhibiting high brain levels of Abeta(1-42), oral dosing of memantine (20 mg/kg/day for 8 days) produced a plasma drug concentration of 0.96 microM and significantly reduced the cortical levels of soluble Abeta(1-42). The ratio of Abeta(1-40)/Abeta(1-42) increased in treated mice, suggesting effects on the gamma-secretase complex. Thus, memantine reduces the levels of Abeta peptides at therapeutic concentrations and may inhibit the accumulation of fibrillogenic Abeta in mammalian brains. Memantine's ability to preserve neuronal cells against neurodegeneration, to increase metabolic activity, and to lower Abeta level has therapeutic implications for neurodegenerative disorders.

Amyloid-ß and Tau Dynamics in Human Brain Interstitial Fluid in Patients with Suspected Normal Pressure Hydrocephalus.

BACKGROUND: Amyloid-ß (Aß1 - 42), total tau (T-tau), and phosphorylated tau (P-tau181) in the cerebrospinal fluid (CSF) are the most promising biomarkers of Alzheimer's disease (AD). Still, little is known about the dynamics of these molecules in the living brain. In a transgenic mouse brain, soluble Aß decreases with increasing age and advanced Aß pathology as seen similarly in CSF. OBJECTIVE: To assess the relationship between AD-related pathological changes in human brain tissue, ventricular and lumbar CSF, and brain interstitial fluid (ISF). METHODS: Altogether 11 patients with suspected idiopathic normal pressure hydrocephalus underwent frontal cortical brain biopsy, 24-h intraventricular pressure monitoring, and a microdialysis procedure. AD-related biomarkers were analyzed from brain tissue, CSF, and ISF. RESULTS: ISF T-tau levels decreased strongly within the first 12 h, then plateauing until the end of the experiment. Aß1 - 42 and P-tau181 remained stable during the experiment (n = 3). T-tau and P-tau were higher in the ISF than in ventricular or lumbar CSF, while Aß1 - 42 levels were within similar range in both CSF and ISF samples. ISF P-tau correlated with the ventricular CSF T-tau (r = 0.70, p = 0.017) and P-tau181 (r = 0.64, p = 0.034). Five patients with amyloid pathology in the brain biopsy tended to reveal lower ISF Aß1 - 42 levels than those six without amyloid pathology. CONCLUSIONS: This is the first study to report ISF Aß and tau levels in the human brain without significant brain injury. The set-up used enables sampling from the brain ISF for at least 24 h without causing adverse effects due to the microdialysis procedure to follow the dynamics of the key molecules in AD pathogenesis in the living brain at various stages of the disease.

Intravenous immunoglobulins for Alzheimer's disease.

Alzheimer's disease (AD) is a chronic neurodegenerative disease associated with intracerebral accumulation of aggregated amyloid-beta (Aß) and tau proteins, as well as neuroinflammation. Human intravenous immunoglobulin (IVIG) is a mixture of polyclonal IgG antibodies isolated and pooled from thousands of healthy human donors. The scientific rationale for testing IVIG as a potential AD treatment include its natural anti-Aß antibody activity, its favorable safety profile and inherent anti-inflammatory/immunomodulatory properties. Over the past decade, several clinical and pre-clinical experimental findings, advanced our knowledge about biological and therapeutic properties of IVIG that are relevant to AD therapy. Anti-amyloid antibodies in IVIG show significantly higher binding avidity for amyloid oligomers and fibrils than for Aß monomers. In a double transgenic murine model of AD, intracerebral injection of IVIG causes suppression of Aß fibril pathology whereas long term peripheral IVIG treatments causes elevation of total brain Aß levels with no measurable impact on Aß deposits or tendency for inducing cerebral microhemmorhage. Furthermore, chronic IVIG treatment suppressed neuroinflammation and fostered adult hippocampal neurogenesis. In clinical studies with AD patients, IVIG showed an acceptable safety profile and has not been reported to increase the incidence of amyloid related imaging abnormalities. Preliminary studies on small number of patients reported clinical benefits in mild to moderate stage AD patients. However, double blind, placebo controlled studies later did not replicate those initial findings. Interestingly though, in APOE4 carriers and in moderate disease stage subgroups, positive cognitive signals were reported. Nevertheless, both clinical and experimental (mouse) studies show that antibodies in IVIG can accumulate in CNS and its biological activities include neutralization of Aß oligomers, suppression of neuroinflammation and immunomodulation. Identifying mediators of IVIG's effects at the cellular and molecular level is warranted. In light of its favourable safety profile and aforementioned biological properties, IVIG is still an enigmatic experimental candidate with enormous potential for being an AD therapeutic.

Increased γ-secretase activity in idiopathic normal pressure hydrocephalus patients with ß-amyloid pathology.

The potential similarity between the brain pathology of idiopathic normal pressure hydrocephalus (iNPH) and Alzheimer disease (AD) is intriguing and thus further studies focusing on the underlying molecular mechanisms may offer valuable information for differential diagnostics and the development of treatments for iNPH. Here, we investigated ß- and γ-secretase activities in relation to amyloid-ß (Aß) pathology in the brain tissue samples collected from iNPH and AD patients. ß- and γ-secretase activities were measured from the frontal cortical biopsies of 26 patients with suspected iNPH as well as post-mortem tissue samples from the inferior temporal cortex of 74 AD patients and eight subjects without neurofibrillary pathology. In iNPH samples with detectable Aß plaques, γ-secretase activity was significantly increased (∼ 1.6-fold) when compared to iNPH samples without Aß plaques (p = 0.009). In the AD samples, statistically significant differences in the γ-secretase activity were not observed with respect to disease severity (mild, moderate and severe AD according to neurofibrillary pathology). Conversely, ß-secretase activity was unaltered in iNPH samples with or without Aß plaques, while it was significantly increased in relation to disease severity in the AD patients. These results show for the first time increased γ-secretase but not ß-secretase activity in the biopsy samples from the frontal cortex of iNPH patients with AD-like Aß pathology. Conversely, the opposite was observed in these secretase activities in AD patients with respect to neurofibrillary pathology. Despite the resemblances in the Aß pathology, iNPH and AD patients appear to have marked differences in the cellular mechanisms responsible for the production of Aß.

Cerebrospinal fluid biomarker and brain biopsy findings in idiopathic normal pressure hydrocephalus.

BACKGROUND: The significance of amyloid precursor protein (APP) and neuroinflammation in idiopathic normal pressure hydrocephalus (iNPH) and Alzheimer's disease (AD) is unknown. OBJECTIVE: To investigate the role of soluble APP (sAPP) and amyloid beta (Aß) isoforms, proinflammatory cytokines, and biomarkers of neuronal damage in the cerebrospinal fluid (CSF) in relation to brain biopsy Aß and hyperphosphorylated tau (HPτ) findings. METHODS: The study population comprised 102 patients with possible NPH with cortical brain biopsies, ventricular and lumbar CSF samples, and DNA available. The final clinical diagnoses were: 53 iNPH (91% shunt-responders), 26 AD (10 mixed iNPH+AD), and 23 others. Biopsy samples were immunostained against Aß and HPτ. CSF levels of AD-related biomarkers (Aß42, p-tau, total tau), non-AD-related Aß isoforms (Aß38, Aß40), sAPP isoforms (sAPPα, sAPPß), proinflammatory cytokines (several interleukins (IL), interferon-gamma, monocyte chemoattractant protein-1, tumor necrosis factor-alpha) and biomarkers of neuronal damage (neurofilament light and myelin basic protein) were measured. All patients were genotyped for APOE. RESULTS: Lumbar CSF levels of sAPPα were lower (p<0.05) in patients with shunt-responsive iNPH compared to non-iNPH patients. sAPPß showed a similar trend (p = 0.06). CSF sAPP isoform levels showed no association to Aß or HPτ in the brain biopsy. Quantified Aß load in the brain biopsy showed a negative correlation with CSF levels of Aß42 in ventricular (r = -0.295, p = 0.003) and lumbar (r = -0.356, p = 0.01) samples, while the levels of Aß38 and Aß40 showed no correlation. CSF levels of proinflammatory cytokines and biomarkers of neuronal damage did not associate to the brain biopsy findings, diagnosis, or shunt response. Higher lumbar/ventricular CSF IL-8 ratios (p<0.001) were seen in lumbar samples collected after ventriculostomy compared to the samples collected before the procedure. CONCLUSIONS: The role of sAPP isoforms in iNPH seems to be independent from the amyloid cascade. No neuroinflammatory background was observed in iNPH or AD.