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 b-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 b-catenin signaling in microglia in vivo by showing age-dependent b-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 b-catenin. WNT-3A dose dependently induces LRP6 phosphorylation with downstream activation of disheveled, b-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 a. In summary, our data suggest that the WNT family of lipoglycoproteins can instruct proinflammatory microglia transformation and emphasize the pathogenic significance of b-catenin-signaling networks in this cell type. V V C

Amyloid plaques and hyperphosphorylated tau in cortical brain biopsies are reflected by low CSF Aβ42 and high CSF tau and p-tau levels, respectively.

BackgroundThe significance of amyloid precursor protein (APP) and neuroinflammation in idiopathic normal pressure hydrocephalus (iNPH) and Alzheimer's disease (AD) is unknown.ObjectiveTo investigate the role of soluble APP (sAPP) and amyloid beta (Aβ) isoforms, proinflammatory cytokines, and biomarkers of neuronal damage in the cerebrospinal fluid (CSF) in relation to brain biopsy Aβ and hyperphosphorylated tau (HPτ) findings.MethodsThe 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 Aβ and HPτ. CSF levels of AD-related biomarkers (Aβ42, p-tau, total tau), non-AD-related Aβ isoforms (Aβ38, Aβ40), sAPP isoforms (sAPPα, sAPPβ), 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.ResultsLumbar CSF levels of sAPPα were lower (p<0.05) in patients with shunt-responsive iNPH compared to non-iNPH patients. sAPPβ showed a similar trend (p = 0.06). CSF sAPP isoform levels showed no association to Aβ or HPτ in the brain biopsy. Quantified Aβ load in the brain biopsy showed a negative correlation with CSF levels of Aβ42 in ventricular (r = −0.295, p = 0.003) and lumbar (r = −0.356, p = 0.01) samples, while the levels of Aβ38 and Aβ40 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.ConclusionsThe role of sAPP isoforms in iNPH seems to be independent from the amyloid cascade. No neuroinflammatory background was observed in iNPH or AD.

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 (Aβ) occurs due to aberrant processing of the full-length Aβ precursor protein (APP). Memantine protects neurons from the neurotoxic effects of Aβ and improves cognition in transgenic mice with high brain levels of Aβ. However, it is unknown how memantine protects cells against neurodegeneration and affects APP processing and Aβ production. We report the effects of memantine in three different systems. In human neuroblastoma cells, memantine, at therapeutically relevant concentrations (1-4 μM), decreased levels of secreted APP and Aβ . Levels of the potentially amylodogenic Aβ 1-42 were undetectable in these cells. In primary rat cortical neuronal cultures, memantine treatment lowered Aβ 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 Aβ 1-42 , oral dosing of memantine (20 mg/kg/day for 8 days) produced plasma drug concentration of 0.96 μM and significantly reduced the cortical levels of soluble Aβ . The ratio of Aβ 1-40 /Aβ 1-42 increased in treated mice, suggesting effects on the γ-secretase complex. Thus, memantine reduces the levels of Aβ peptides at therapeutic concentrations and may inhibit the accumulation of fibrillogenic Aβ in mammalian brains. Memantine's ability to preserve neuronal cells against neurodegeneration, increase metabolic activity, and lower Aβ level has therapeutic implications for neurodegenerative disorders. KeywordsAging; cortex; dementia; lysosome; membrane; tissue culture; memory In Alzheimer's disease (AD), a gradual impairment in short-term memory and cognition results from the dysfunction and death of neurons in the hippocampus, limbic system, and cerebral cortex (Goedert and Spillantini, 2006;Tanzi and Bertram, 2008). AD is characterized by brain * Contributed equally ** Corresponding author: Debomoy K. Lahiri, PhD, Department of Psychiatry, Indiana University School of Medicine, 791 Union Drive, Indianapolis, USA, Tel: (317) 274-2706; Fax: (317) NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript depositions of amyloid plaques and neurofibrillary tangles, loss of the synaptophysin protein, and deficits in cholinergic neurotransmission (Giacobini, 2003;Lahiri et al., 2003;Reinhard et al., 2005;Selkoe, 2005). These aberrations are believed to result, in part, from oxidative stress, membrane damage, and the over-production and accumulation of amyloid-β peptide (Aβ), a 39-43 amino acid polypeptide that is a core constituent of amyloid plaques (Dumery et al., 2001;Sambamurti et al., 2006). Two Aβ peptides predominate in brain tissue, one i...

BackgroundPurified 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 β-amyloid (Aβ) 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 Aβ deposits by primary astrocytes and microglia, two major cell types involved in the neuroinflammatory responses.MethodsWe first determined the effect of IVIG on Aβ toxicity in primary neuronal cell culture. The mechanisms-of-action of IVIG in reduction of Aβ burden was analyzed with ex vivo assay. We studied whether IVIG solubilizes natively formed Aβ deposits from brain sections of APP/PS1 mice or promotes Aβ removal by primary glial cells. We determined the role of lysosomal degradation pathway and Aβ Abs in the IVIG-promoted reduction of Aβ. Finally, we studied the penetration of IVIG into the brain parenchyma and interaction with brain deposits of human Aβ in a mouse model of AD in vivo.ResultsIVIG was protective against Aβ toxicity in a primary mouse hippocampal neuron culture. IVIG modestly inhibited the fibrillization of synthetic Aβ1-42 but did not solubilize natively formed brain Aβ deposits ex vivo. IVIG enhanced microglia-mediated Aβ clearance ex vivo, with a mechanism linked to Aβ Abs and lysosomal degradation. The IVIG-enhanced Aβ clearance appears specific for microglia since IVIG did not affect Aβ clearance by astrocytes. The cellular mechanisms of Aβ 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 Aβ deposits in co-localization with microglia.ConclusionsOur results demonstrate that IVIG promotes recognition and removal of natively formed brain Aβ deposits by primary microglia involving natural Aβ Abs in IVIG. These findings may have therapeutic relevance in vivo as IVIG penetrates through the blood-brain barrier and specifically binds to Aβ deposits in brain parenchyma.