Abstract A-kinase anchoring proteins (AKAPs) form large macromolecular signaling complexes that specifically target cAMP-dependent protein kinase (PKA) to unique subcellular compartments and thus, ...provide high specificity to PKA signaling. For example, the AKAP79/150 family tethers PKA, PKC and PP2B to neuronal membranes and postsynaptic densities and plays an important role in synaptic function. Several studies suggested that AKAP79/150 anchored PKA contributes to mechanisms associated with synaptic plasticity and memory processes, but the precise role of AKAPs in these processes is still unknown. In this study we established the mouse brain distribution of AKAP150 using two well-characterized AKAP150 antibodies. Using Western blotting and immunohistochemistry we showed that AKAP150 is widely distributed throughout the mouse brain. The highest AKAP150 expression levels were observed in striatum, cerebral cortex and several other forebrain regions (e.g. olfactory tubercle), relatively high expression was found in hippocampus and olfactory bulb and low/no expression in cerebellum, hypothalamus, thalamus and brain stem. Although there were some minor differences in mouse AKAP150 brain distribution compared to the distribution in rat brain, our data suggested that rodents have a characteristic AKAP150 brain distribution pattern. In general we observed that AKAP150 is strongly expressed in mouse brain regions involved in learning and memory. These data support its suggested role in synaptic plasticity and memory processes.
The majority of people with Down syndrome (DS) develop dementia due to Alzheimer's disease (AD). Neuropathological features are characterized by an accumulation of amyloid-β (Aβ) deposits and the ...presence of an activated immune response. Neutrophil Gelatinase-Associated Lipocalin (NGAL) is a newly identified (neuro)inflammatory constituent in AD.
This study examines NGAL as an inflammatory marker in DS and its associations with plasma Aβ peptides according to the follow-up clinical diagnosis of dementia.
Baseline serum NGAL and plasma Aβ40, Aβ42, Aβ(n40), and Aβ(n42) were quantified in 204 people with DS. The diagnosis of dementia in DS was established by follow-up clinical assessments. The following study groups were characterized: DS with AD at baseline (n = 67), DS without AD (n = 53), and non-demented DS individuals that converted to AD (n = 84). Serum NGAL was analyzed in 55 elderly non-DS, non-demented people.
Serum NGAL levels were significantly increased in DS subjects compared to non-DS people. Serum NGAL levels were not associated with clinical dementia symptoms in DS. However, NGAL was positively associated with Aβ42 and Aβ(n42) in demented DS individuals and with Aβ40 and Aβ(n40) in the non-demented DS group. NGAL was negatively associated with Aβ42/Aβ40 and Aβ(n42)/Aβ(n40) ratios in converted DS subjects. These associations persisted for Aβ(n40), Aβ42/Aβ40, and Aβ(n42)/Aβ(n40) after adjusting for demographics measures, apolipoprotein E ε4 allele, platelets, and anti-inflammatory medication.
Serum NGAL levels are increased in DS and associated with distinct species of Aβ depending on the progression of dementia as diagnosed by baseline and follow-up clinical assessments.
Both genetic and pharmacological studies demonstrated that contextual fear conditioning is critically regulated by cyclic AMP-dependent protein kinase (PKA). Since PKA is a broad range protein ...kinase, a mechanism for confining its activity is required. It has been shown that intracellular spatial compartmentalization of PKA signaling is mediated by A-kinase anchoring proteins (AKAPs). Here, we investigated the role of PKA anchoring to AKAPs in different stages of the memory process (acquisition, consolidation, retrieval and extinction) using contextual fear conditioning, a hippocampus-dependent learning task. Mice were injected intracerebroventricularly or intrahippocampally with the membrane permeable PKA anchoring disrupting peptides St-Ht31 or St-superAKAP-IS at different time points during the memory process. Blocking PKA anchoring to AKAPs resulted in an impairment of fear memory consolidation. Moreover, disrupted PKA anchoring promoted contextual fear extinction in the mouse hippocampus. We conclude that the temporal and spatial compartmentalization of hippocampal PKA signaling pathways, as achieved by anchoring of PKA to AKAPs, is specifically instrumental in long-term contextual fear memory consolidation and extinction, but not in acquisition and retrieval.
It is unclear whether protein phosphatases, which counteract the actions of protein kinases, play a beneficial role in the formation and extinction of previously acquired fear memories. In this ...study, we investigated the role of the calcium/calmodulin dependent phosphatase 2B, also known as calcineurin (CaN) in the formation of contextual fear memory and extinction of previously acquired contextual fear. We used a temporally regulated transgenic approach, that allowed us to selectively inhibit neuronal CaN activity in the forebrain either during conditioning or only during extinction training leaving the conditioning undisturbed. Reducing CaN activity through the expression of a CaN inhibitor facilitated contextual fear conditioning, while it impaired the extinction of previously formed contextual fear memory. These findings give the first genetic evidence that neuronal CaN plays an opposite role in the formation of contextual fear memories and the extinction of previously formed contextual fear memories.
Numerous studies have revealed the pleiotropic functions of tumor necrosis factor alpha (TNF-α), and have linked it with several neurodegenerative disorders. This review describes the signaling ...pathways induced by TNF-α via its two receptors (TNFR1 and TNFR2), and their functions in neurodegenerative processes as in Alzheimer’s disease (AD), Parkinson’s disease (PD), multiple sclerosis (MS), and ischemic stroke. It has become clear that TNF-α may exert divergent actions in neurodegenerative disorders, including neurodegenerative and neuroprotective effects, which appear to depend on its signaling via either TNFR1 or TNFR2. Specific targeting of these receptors is a promising therapeutic strategy for many disorders.
•C57Bl6 PKU mice have a mild phenotype for enhanced hippocampal microglia activation.•Hippocampal microglia activation does not differ between BTBR PKU and BTBR WT mice.•Hippocampal microglia ...activation is higher in WT BTBR than in WT C57Bl6 mice.•Hippocampal microglia activation seems unrelated to sleep disturbances in PKU mice.
Toxic levels of phenylalanine in blood and brain is a characteristic of (untreated) phenylketonuria (PKU), leading to cognitive deficits in PKU mice. In addition, our recent findings showed that PKU mice (as well as PKU patients) have a disturbed sleep/wake cycle. As a consequence, sleep loss may contribute to cognitive deficits in PKU. Sleep loss has been linked to increased activation of microglia in the hippocampus. In this study, we set out to examine morphological features of the microglia population in the hippocampus of the mouse PKU model, using both the C57Bl/6 and the BTBR strain and their wild-type controls (age 5.3 ± 0.5 months; n = 16 per group, both males and females; n = 8 each). Microglial activation is reflected by retraction and thickening of the dendritic branches and an increase in cell body size of a microglial cell. Such morphological changes of microglia were studied by way of immunohistochemical staining for Iba-1, a microglia-specific calcium binding protein. We measured the number of microglia in seven subregions of the dorsal hippocampus. The level of microglial activation was determined, based on the ratio between the soma size and total cell size (soma size plus the area covered by the dendritic branches). Results showed subtle but statistical significant activation of hippocampal microglia in the C57Bl6, but not in the BTBR, PKU mice when compared with their wild-type controls. Also the total number of microglia was higher in the C57Bl/6 PKU (compared to the wild-type) mouse, but not in the BTBR PKU mouse. It is concluded that the C57Bl/6 PKU mouse has mildly higher microglia activity, which may support rather than hamper hippocampal homeostasis. The results further indicate that high levels of phenylalanine or disturbed sleep patterns do not consequently cause hippocampal microglial activation in the PKU mouse. It is currently unknown why the two PKU mouse strains show these differences in number and activation level of their hippocampal microglia, and to what extent it influences hippocampal functioning. Further scrutinizing the role of microglia functioning in the context of PKU is therefore warranted.
Previous studies have shown that tumor necrosis factor-alpha (TNF-α) induces neuroprotection against excitotoxic damage in primary cortical neurons via sustained nuclear factor-kappa B (NF-κB) ...activation. The transcription factor NF-κB can regulate the expression of small conductance calcium-activated potassium (KCa) channels. These channels reduce neuronal excitability and as such may yield neuroprotection against neuronal overstimulation. In the present study we investigated whether TNF-α-mediated neuroprotective signaling is inducing changes in the expression of small conductance KCa channels. Interestingly, the expression of KCa2.2 channel was up-regulated by TNF-α treatment in a time-dependent manner whereas the expression of KCa2.1 and KCa2.3 channels was not altered. The increase in KCa2.2 channel expression after TNF-α treatment was shown to be dependent on TNF-R2 and NF-κB activation. Furthermore, activation of small conductance KCa channels by 6,7-dichloro-1H-indole-2,3-dione 3-oxime or cyclohexyl-2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl-amine-induced neuroprotection against a glutamate challenge. Treatment with the small conductance KCa channel blocker apamin or KCa2.2 channel siRNA reverted the neuroprotective effect elicited by TNF-α. We conclude that treatment of primary cortical neurons with TNF-α leads to increased KCa2.2 channel expression which renders neurons more resistant to excitotoxic cell death.
Soluble oligomeric (misfolded) species of amyloid-β (Aβ) are the main mediators of toxicity in Alzheimer's disease (AD). These oligomers subsequently form aggregates of insoluble fibrils that ...precipitate as extracellular and perivascular plaques in the brain. Active immunization against Aβ is a promising disease modifying strategy. However, eliciting an immune response against Aβ in general may interfere with its biological function and was shown to cause unwanted side-effects. Therefore, we have developed a novel experimental vaccine based on conformational neo-epitopes that are exposed in the misfolded oligomeric Aβ, inducing a specific antibody response.
Here we investigate the protective effects of the experimental vaccine against oligomeric Aβ1-42-induced neuronal fiber loss in vivo.
C57BL/6 mice were immunized or mock-immunized. Antibody responses were measured by enzyme-linked immunosorbent assay. Next, mice received a stereotactic injection of oligomeric Aβ1-42 into the nucleus basalis of Meynert (NBM) on one side of the brain (lesion side), and scrambled Aβ1-42 peptide in the contralateral NBM (control side). The densities of choline acetyltransferase-stained cholinergic fibers origination from the NBM were measured in the parietal neocortex postmortem. The percentage of fiber loss in the lesion side was determined relative to the control side of the brain.
Immunized responders (79%) showed 23% less cholinergic fiber loss (p = 0.01) relative to mock-immunized mice. Moreover, fiber loss in immunized responders correlated negatively with the measured antibody responses (R2 = 0.29, p = 0.02).
These results may provide a lead towards a (prophylactic) vaccine to prevent or at least attenuate (early onset) AD symptoms.
Amyloid-β (Aβ) is toxic to neurons and such toxicity is – at least in part – mediated via the NMDA receptor. Calpain, a calcium dependent cystein protease, is part of the NMDA receptor-induced ...neurodegeneration pathway, and we previously reported that inhibition of calpain prevents excitotoxic lesions of the cholinergic nucleus basalis magnocellularis of Meynert. The present study reveals that inhibition of calpain is also neuroprotective in an
in vivo model of Aβ oligomer-induced neurodegeneration in rats. Aβ-induced lesions of the nucleus basalis induced a significant decrease in the number of cholinergic neurons and their projecting fibers, as determined by analysis of choline-acetyltransferase in the nucleus basalis magnocellularis and cortical mantle of the lesioned animals. Treatment with the calpain inhibitor A-705253 significantly attenuated cholinergic neurodegeneration in a dose-dependent manner. Calpain inhibition also significantly diminished the accompanying neuroinflammatory response, as determined by immunohistochemical analysis of microglia activation. Administration of β-amyloid markedly impaired performance in the novel object recognition test. Treatment with the calpain inhibitor, A-705253, dose-dependently prevented this behavioral deficit.
In order to determine whether pre-treatment with the calpain inhibitor is necessary to exhibit its full protective effect on neurons we induced Aβ toxicity in primary neuronal cultures and administered A-705253 at various time points before and after Aβ oligomer application. Although the protective effect was higher when A-705253 was applied before induction of Aβ toxicity, calpain inhibition was still beneficial when applied up to 1
h post-treatment.
We conclude that inhibition of calpains may represent a valuable strategy for the prevention of Aβ oligomer-induced neuronal decline and associated cognitive deterioration.
In the present paper by David E. Hurtado and colleagues report on a new mouse model for AD bearing Aβ and MAPT pathology by crossing PS19 and PDAPP Tg mice. Here, we tried to highlight the importance ...and necessity of the critical and systematic analysis of models such as the Braak like staging in AD mouse models.
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