The absence of myelin basic protein promotes neuroinflammation and reduces amyloid β-protein accumulation in Tg-5xFAD mice

Identification of Novel Biomarkers for Alzheimer's Disease and Related Dementias Using Unbiased Plasma Proteomics

Alzheimer's disease (AD) and related dementias (ADRD) is a complex disease with multiple pathophysiological drivers that determine clinical symptomology and disease progression. These diseases develop insidiously over time, through many pathways and disease mechanisms and continue to have a huge societal impact for affected individuals and their families. While emerging blood-based biomarkers, such as plasma p-tau181 and p-tau217, accurately detect Alzheimer neuropthology and are associated with faster cognitive decline, the full extension of plasma proteomic changes in ADRD remains unknown. Earlier detection and better classification of the different subtypes may provide opportunities for earlier, more targeted interventions, and perhaps a higher likelihood of successful therapeutic development. In this study, we aim to leverage unbiased mass spectrometry proteomics to identify novel, blood-based biomarkers associated with cognitive decline. 1,786 plasma samples from 1,005 patients were collected over 12 years from partcipants in the Massachusetts Alzheimer's Disease Research Center Longitudinal Cohort Study. Patient metadata includes demographics, final diagnoses, and clinical dementia rating (CDR) scores taken concurrently. The Proteograph™ Product Suite (Seer, Inc.) and liquid-chromatography mass-spectrometry (LC-MS) analysis were used to process the plasma samples in this cohort and generate unbiased proteomics data. Data-independent acquisition (DIA) mass spectrometry results yielded 36,259 peptides and 4,007 protein groups. Linear mixed effects models revealed 138 differentially abundant proteins between AD and healthy controls. Machine learning classification models for AD diagnosis identified potential candidate biomarkers including MBP, BGLAP, and APoD. Cox regression models were created to determine the association of proteins with disease progression and suggest CLNS1A, CRISPLD2, and GOLPH3 as targets of further investigation as potential biomarkers. The Proteograph workflow provided deep, unbiased coverage of the plasma proteome at a speed that enabled a cohort study of almost 1,800 samples, which is the largest, deep, unbiased proteomics study of ADRD conducted to date.

Proteomic characterization of aging-driven changes in the mouse brain by co-expression network analysis

Brain aging causes a progressive decline in functional capacity and is a strong risk factor for dementias such as Alzheimer's disease. To characterize age-related proteomic changes in the brain, we used quantitative proteomics to examine brain tissues, cortex and hippocampus, of mice at three age points (3, 15, and 24 months old), and quantified more than 7000 proteins in total with high reproducibility. We found that many of the proteins upregulated with age were extracellular proteins, such as extracellular matrix proteins and secreted proteins, associated with glial cells. On the other hand, many of the significantly downregulated proteins were associated with synapses, particularly postsynaptic density, specifically in the cortex but not in the hippocampus. Our datasets will be helpful as resources for understanding the molecular basis of brain aging.

White matter injury, cholesterol dysmetabolism, and APP/Abeta dysmetabolism interact to produce Alzheimer's disease (AD) neuropathology: A hypothesis and review

We postulate that myelin injury contributes to cholesterol release from myelin and cholesterol dysmetabolism which contributes to Abeta dysmetabolism, and combined with genetic and AD risk factors, leads to increased Abeta and amyloid plaques. Increased Abeta damages myelin to form a vicious injury cycle. Thus, white matter injury, cholesterol dysmetabolism and Abeta dysmetabolism interact to produce or worsen AD neuropathology. The amyloid cascade is the leading hypothesis for the cause of Alzheimer's disease (AD). The failure of clinical trials based on this hypothesis has raised other possibilities. Even with a possible new success (Lecanemab), it is not clear whether this is a cause or a result of the disease. With the discovery in 1993 that the apolipoprotein E type 4 allele (APOE4) was the major risk factor for sporadic, late-onset AD (LOAD), there has been increasing interest in cholesterol in AD since APOE is a major cholesterol transporter. Recent studies show that cholesterol metabolism is intricately involved with Abeta (Aβ)/amyloid transport and metabolism, with cholesterol down-regulating the Aβ LRP1 transporter and upregulating the Aβ RAGE receptor, both of which would increase brain Aβ. Moreover, manipulating cholesterol transport and metabolism in rodent AD models can ameliorate pathology and cognitive deficits, or worsen them depending upon the manipulation. Though white matter (WM) injury has been noted in AD brain since Alzheimer's initial observations, recent studies have shown abnormal white matter in every AD brain. Moreover, there is age-related WM injury in normal individuals that occurs earlier and is worse with the APOE4 genotype. Moreover, WM injury precedes formation of plaques and tangles in human Familial Alzheimer's disease (FAD) and precedes plaque formation in rodent AD models. Restoring WM in rodent AD models improves cognition without affecting AD pathology. Thus, we postulate that the amyloid cascade, cholesterol dysmetabolism and white matter injury interact to produce and/or worsen AD pathology. We further postulate that the primary initiating event could be related to any of the three, with age a major factor for WM injury, diet and APOE4 and other genes a factor for cholesterol dysmetabolism, and FAD and other genes for Abeta dysmetabolism.

Chlamydia pneumoniae can infect the central nervous system via the olfactory and trigeminal nerves and contributes to Alzheimer's disease risk

Chlamydia pneumoniae is a respiratory tract pathogen but can also infect the central nervous system (CNS). Recently, the link between C. pneumoniae CNS infection and late-onset dementia has become increasingly evident. In mice, CNS infection has been shown to occur weeks to months after intranasal inoculation. By isolating live C. pneumoniae from tissues and using immunohistochemistry, we show that C. pneumoniae can infect the olfactory and trigeminal nerves, olfactory bulb and brain within 72 h in mice. C. pneumoniae infection also resulted in dysregulation of key pathways involved in Alzheimer’s disease pathogenesis at 7 and 28 days after inoculation. Interestingly, amyloid beta accumulations were also detected adjacent to the C. pneumoniae inclusions in the olfactory system. Furthermore, injury to the nasal epithelium resulted in increased peripheral nerve and olfactory bulb infection, but did not alter general CNS infection. In vitro, C. pneumoniae was able to infect peripheral nerve and CNS glia. In summary, the nerves extending between the nasal cavity and the brain constitute invasion paths by which C. pneumoniae can rapidly invade the CNS likely by surviving in glia and leading to Aβ deposition.

The Therapeutic and Diagnostic Potential of Amyloid β Oligomers Selective Antibodies to Treat Alzheimer's Disease

Improvements have been made in the diagnosis of Alzheimer’s disease (AD), manifesting mostly in the development of in vivo imaging methods that allow for the detection of pathological changes in AD by magnetic resonance imaging (MRI) and positron emission tomography (PET) scans. Many of these imaging methods, however, use agents that probe amyloid fibrils and plaques–species that do not correlate well with disease progression and are not present at the earliest stages of the disease. Amyloid β oligomers (AβOs), rather, are now widely accepted as the Aβ species most germane to AD onset and progression. Here we report evidence further supporting the role of AβOs as pathological instigators of AD and introduce promising anti-AβO diagnostic probes capable of distinguishing the 5xFAD mouse model from wild type mice by PET and MRI. In a developmental study, Aβ oligomers in 5xFAD mice were found to appear at 3 months of age, just prior to the onset of memory dysfunction, and spread as memory worsened. The increase of AβOs is prominent in the subiculum and correlates with concomitant development of reactive astrocytosis. The impact of these AβOs on memory is in harmony with findings that intraventricular injection of synthetic AβOs into wild type mice induced hippocampal dependent memory dysfunction within 24 h. Compelling support for the conclusion that endogenous AβOs cause memory loss was found in experiments showing that intranasal inoculation of AβO-selective antibodies into 5xFAD mice completely restored memory function, measured 30–40 days post-inoculation. These antibodies, which were modified to give MRI and PET imaging probes, were able to distinguish 5xFAD mice from wild type littermates. These results provide strong support for the role of AβOs in instigating memory loss and salient AD neuropathology, and they demonstrate that AβO selective antibodies have potential both for therapeutics and for diagnostics.

Dunalialla salina microalgea and its isolated zeaxanthin mitigate age-related dementia in rats: Modulation of neurotransmission and amyloid-β protein

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D. salina as well as its isolated zeaxanthin showed marked recovery of the D-gal-induced effect on the escape latency time.

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D. salina exerted an amelioration in the brain Aβ contents and an increase in the brain 5-HT, NE and DOP levels.

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These effects were confirmed by histopathological increase in number of viable neurons in both cerebral cortex and hippocampus.

Age-related deterioration of sensorimotor and cognitive abilities suggests that the brain undergoes regressive alterations with aging that compromise its function. Thus, the present study was designed to assess the efficacy of Dunaliella salina in counteracting D-galactose (D-gal)-induced dementia brain aging and its modulatory role in attenuating amyloid β (Aβ) protein and neurotransmitters. Aging associated dementia was generated by injection of D-gal (200 mg/kg; i.p) of rats for 8 weeks. D. salina biomass (250 mg/kg), polar (30 mg/kg), its carotenoid (30 mg/kg) fractions as well as the isolated zeaxanthin (250 μg/kg) were given orally simultaneously with D-gal for additional two weeks. Twenty-four hours after the last treatment dose; behavioral, biochemical and histopathological assessment were performed. Results showed that oral treatment of motor deficit rats with D. salina biomass and its isolated polar and carotenoid fractions showed amelioration in the motor coordination assessed by the rotarod test and in the memory and learning capabilities evaluated by Morris water maze test. D. salina also showed a reduction in brain levels of inflammatory indicators viz. interlekin-1β and inducible nitric oxide synthetase as well as brain contents of Aβ protein and myelin base protein. Likewise, oral treatment with D. salina biomass and its isolated polar and carotenoid fractions exhibited an increase in the rats’ brain neurotransmitters and their metabolites. Furthermore, histopathological investigations have confirmed all of these results. Our findings suggest that D. salina overcomes brain aging and thereby repairs age-related dementia, both for its modulating function in attenuating the Aβ protein and neurotransmitters.

ADeditome provides the genomic landscape of A-to-I RNA editing in Alzheimer's disease

A-to-I RNA editing, contributing to nearly 90% of all editing events in human, has been reported to involve in the pathogenesis of Alzheimer's disease (AD) due to its roles in brain development and immune regulation, such as the deficient editing of GluA2 Q/R related to cell death and memory loss. Currently, there are urgent needs for the systematic annotations of A-to-I RNA editing events in AD. Here, we built ADeditome, the annotation database of A-to-I RNA editing in AD available at https://ccsm.uth.edu/ADeditome, aiming to provide a resource and reference for functional annotation of A-to-I RNA editing in AD to identify therapeutically targetable genes in an individual. We detected 1676 363 editing sites in 1524 samples across nine brain regions from ROSMAP, MayoRNAseq and MSBB. For these editing events, we performed multiple functional annotations including identification of specific and disease stage associated editing events and the influence of editing events on gene expression, protein recoding, alternative splicing and miRNA regulation for all the genes, especially for AD-related genes in order to explore the pathology of AD. Combing all the analysis results, we found 108 010 and 26 168 editing events which may promote or inhibit AD progression, respectively. We also found 5582 brain region-specific editing events with potentially dual roles in AD across different brain regions. ADeditome will be a unique resource for AD and drug research communities to identify therapeutically targetable editing events. Significance: ADeditome is the first comprehensive resource of the functional genomics of individual A-to-I RNA editing events in AD, which will be useful for many researchers in the fields of AD pathology, precision medicine, and therapeutic researches.

Proteomic Profiling of Cerebrum Mitochondria, Myelin Sheath, and Synaptosome Revealed Mitochondrial Damage and Synaptic Impairments in Association with 3 × Tg-AD Mice Model

Alzheimer's disease (AD) is the most common age-associated dementia with complex pathological hallmarks. Mitochondrion, synaptosome, and myelin sheath appear to be vulnerable and play a key role in the pathogenesis of AD. To clarify the early mechanism associated with AD, followed by subcellular components separation, we performed iTRAQ (isobaric tags for relative and absolute quantification)-based proteomics analysis to simultaneously investigate the differentially expressed proteins (DEPs) within the mitochondria, synaptosome, and myelin sheath in the cerebrum of the 6-month-old triple transgenic AD (3 × Tg-AD) and 6-month-old wild-type (WT) mice. A large number of DEPs between the AD and WT mice were identified. Most of them are related to mitochondria and synaptic dysfunction and cytoskeletal protein change. Differential expressions of Lrpprc, Nefl, and Sirpa were verified by Western blot analysis. The results suggest that decreased energy metabolism, impaired amino acid metabolism and neurotransmitter synthesis, increase compensatory fatty acid metabolism, up-regulated cytoskeletal protein expression, and oxidative stress are the early events of AD. Among these, mitochondrial damage, synaptic dysfunction, decreased energy metabolism, and abnormal amino acid metabolism are the most significant events. The results indicate that it is feasible to separate and simultaneously perform proteomics analysis on the three subcellular components.

Inhibition of matrix metalloproteinase-9 secretion by dimethyl sulfoxide and cyclic adenosine monophosphate in human monocytes

BACKGROUND

Matrix metalloproteinases (MMPs), including MMP-9, are an integral part of the immune response and are upregulated in response to a variety of stimuli. New details continue to emerge concerning the mechanistic and regulatory pathways that mediate MMP-9 secretion. There is significant evidence for regulation of inflammation by dimethyl sulfoxide (DMSO) and 3',5'-cyclic adenosine monophosphate (cAMP), thus investigation of how these two molecules may regulate both MMP-9 and tumor necrosis factor α (TNFα) secretion by human monocytes was of high interest. The hypothesis tested in this study was that DMSO and cAMP regulate MMP-9 and TNFα secretion by distinct mechanisms.

AIM

To investigate the regulation of lipopolysaccharide (LPS)-stimulated MMP-9 and tumor necrosis factor α secretion in THP-1 human monocytes by dimethyl sulfoxide and cAMP.

METHODS

The paper describes a basic research study using THP-1 human monocyte cells. All experiments were conducted at the University of Missouri-St. Louis in the Department of Chemistry and Biochemistry. Human monocyte cells were grown, cultured, and prepared for experiments in the University of Missouri-St. Louis Cell Culture Facility as per accepted guidelines. Cells were treated with LPS for selected exposure times and the conditioned medium was collected for analysis of MMP-9 and TNFα production. Inhibitors including DMSO, cAMP regulators, and anti-TNFα antibody were added to the cells prior to LPS treatment. MMP-9 secretion was analyzed by gel electrophoresis/western blot and quantitated by ImageJ software. TNFα secretion was analyzed by enzyme-linked immuno sorbent assay. All data is presented as the average and standard error for at least 3 trials. Statistical analysis was done using a two-tailed paired Student t-test. P values less than 0.05 were considered significant and designated as such in the Figures. LPS and cAMP regulators were from Sigma-Aldrich, MMP-9 standard and antibody and TNFα antibodies were from R&D Systems, and amyloid-β peptide was from rPeptide.

RESULTS

In our investigation of MMP-9 secretion from THP-1 human monocytes, we made the following findings. Inclusion of DMSO in the cell treatment inhibited LPS-induced MMP-9, but not TNFα, secretion. Inclusion of DMSO in the cell treatment at different concentrations inhibited LPS-induced MMP-9 secretion in a dose-dependent fashion. A cell-permeable cAMP analog, dibutyryl cAMP, inhibited both LPS-induced MMP-9 and TNFα secretion. Pretreatment of the cells with the adenylyl cyclase activator forskolin inhibited LPS-induced MMP-9 and TNFα secretion. Pretreatment of the cells with the general cAMP phosphodiesterase inhibitor IBMX reduced LPS-induced MMP-9 and TNFα in a dose-dependent fashion. Pre-treatment of monocytes with an anti-TNFα antibody blocked LPS-induced MMP-9 and TNFα secretion. Amyloid-β peptide induced MMP-9 secretion, which occurred much later than TNFα secretion. The latter two findings strongly suggested an upstream role for TNFα in mediating LPS-stimulate MMP-9 secretion.

CONCLUSION

The cumulative data indicated that MMP-9 secretion was a distinct process from TNFα secretion and occurred downstream. First, DMSO inhibited MMP-9, but not TNFα, suggesting that the MMP-9 secretion process was selectively altered. Second, cAMP inhibited both MMP-9 and TNFα with a similar potency, but at different monocyte cell exposure time points. The pattern of cAMP inhibition for these two molecules suggested that MMP-9 secretion lies downstream of TNFα and that TNFα may a key component of the pathway leading to MMP-9 secretion. This temporal relationship fit a model whereby early TNFα secretion directly led to later MMP-9 secretion. Lastly, antibody-blocking of TNFα diminished MMP-9 secretion, suggesting a direct link between TNFα secretion and MMP-9 secretion.

Cellular senescence and Alzheimer disease: the egg and the chicken scenario

Globally, 50 million people live with dementia, with Alzheimer disease (AD) being responsible for two-thirds of the total cases. As ageing is the main risk factor for dementia-related neurodegeneration, changes in the timing or nature of the cellular hallmarks of normal ageing might be key to understanding the events that convert normal ageing into neurodegeneration. Cellular senescence is a candidate mechanism that might be important for this conversion. Under persistent stress, as occurs in ageing, both postmitotic cells - including neurons - and proliferative cells - such as astrocytes and microglia, among others - can engender a state of chronic cellular senescence that is characterized by the secretion of pro-inflammatory molecules that promote the functional decline of tissues and organs. Ablation of senescent cells has been postulated as a promising therapeutic venue to target the ageing phenotype and, thus, prevent or mitigate ageing-related diseases. However, owing to a lack of evidence, it is not possible to label cellular senescence as a cause or a consequence of neurodegeneration. This Review examines cellular senescence in the context of ageing and AD, and discusses which of the processes - cellular senescence or AD - might come first.

MALDI imaging directed laser ablation tissue microsampling for data independent acquisition proteomics

A multimodal workflow for mass spectrometry imaging was developed that combines MALDI imaging with protein identification and quantification by liquid chromatography tandem mass spectrometry (LC-MS/MS). Thin tissue sections were analyzed by MALDI imaging, and the regions of interest (ROI) were identified using a smoothing and edge detection procedure. A midinfrared laser at 3-μm wavelength was used to remove the ROI from the brain tissue section after MALDI mass spectrometry imaging (MALDI MSI). The captured material was processed using a single-pot solid-phase-enhanced sample preparation (SP3) method and analyzed by LC-MS/MS using ion mobility (IM) enhanced data independent acquisition (DIA) to identify and quantify proteins; more than 600 proteins were identified. Using a modified database that included isoform and the post-translational modifications chain, loss of the initial methionine, and acetylation, 14 MALDI MSI peaks were identified. Comparison of the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways of the identified proteins was achieved through an evolutionary relationships classification system.

Antifibrotic Effects of Amyloid-Beta and Its Loss in Cirrhotic Liver

The function and regulation of amyloid-beta (Aβ) in healthy and diseased liver remains unexplored. Because Aβ reduces the integrity of the blood-brain barrier we have examined its potential role in regulating the sinusoidal permeability of normal and cirrhotic liver. Aβ and key proteins that generate (beta-secretase 1 and presenilin-1) and degrade it (neprilysin and myelin basic protein) were decreased in human cirrhotic liver. In culture, activated hepatic stellate cells (HSC) internalized Aβ more efficiently than astrocytes and HSC degraded Aβ leading to suppressed expression of α-smooth muscle actin (α-SMA), collagen 1 and transforming growth factor β (TGFβ). Aβ also upregulated sinusoidal permeability marker endothelial NO synthase (eNOS) and decreased TGFβ in cultured human liver sinusoidal endothelial cells (hLSEC). Liver Aβ levels also correlate with the expression of eNOS in transgenic Alzheimer’s disease mice and in human and rodent cirrhosis/fibrosis. These findings suggest a previously unexplored role of Aβ in the maintenance of liver sinusoidal permeability and in protection against cirrhosis/fibrosis via attenuation of HSC activation.

Nitric oxide might be an inducing factor in cognitive impairment in Alzheimer's disease via downregulating the monocarboxylate transporter 1

Alzheimer's disease (AD) is a typical neurodegenerative disease in central nervous system (CNS). Generally speaking, patients with severe AD are often accompanied with cognitive impairment. Oligodendrocytes (OLs) are myelin-forming cells in CNS, and myelin injury potentially has something to do with the cognitive impairment in AD. Based on the previous experimental studies, it has been recognized that nitric oxide (NO), as a signaling molecule, might have an influence on the axon and myelin by affecting the energy transport mechanism of OLs through monocarboxylate transporter 1 (MCT1). Interestingly, a novel model of cell signaling----axo-myelinic synapse (AMS) has been put forward. In the context of this model, chances are that a new way is established in which NO can influence the pathogenesis of AD by down-regulating the expression of MCT1. As a consequence, it may provide attractive prospective and underlying drug targeting effects for the treatment of AD.

Large-scale proteomic analysis of human brain identifies proteins associated with cognitive trajectory in advanced age

In advanced age, some individuals maintain a stable cognitive trajectory while others experience a rapid decline. Such variation in cognitive trajectory is only partially explained by traditional neurodegenerative pathologies. Hence, to identify new processes underlying variation in cognitive trajectory, we perform an unbiased proteome-wide association study of cognitive trajectory in a discovery (n = 104) and replication cohort (n = 39) of initially cognitively unimpaired, longitudinally assessed older-adult brain donors. We find 579 proteins associated with cognitive trajectory after meta-analysis. Notably, we present evidence for increased neuronal mitochondrial activities in cognitive stability regardless of the burden of traditional neuropathologies. Furthermore, we provide additional evidence for increased synaptic abundance and decreased inflammation and apoptosis in cognitive stability. Importantly, we nominate proteins associated with cognitive trajectory, particularly the 38 proteins that act independently of neuropathologies and are also hub proteins of protein co-expression networks, as promising targets for future mechanistic studies of cognitive trajectory.

Reduction of the expression of the late-onset Alzheimer's disease (AD) risk-factor BIN1 does not affect amyloid pathology in an AD mouse model

Alzheimer's disease (AD) is pathologically characterized by the deposition of the β-amyloid (Aβ) peptide in senile plaques in the brain, leading to neuronal dysfunction and eventual decline in cognitive function. Genome-wide association studies have identified the bridging integrator 1 (BIN1) gene within the second most significant susceptibility locus for late-onset AD. BIN1 is a member of the amphiphysin family of proteins and has reported roles in the generation of membrane curvature and endocytosis. Endocytic dysfunction is a pathological feature of AD, and endocytosis of the amyloid precursor protein is an important step in its subsequent cleavage by β-secretase (BACE1). In vitro evidence implicates BIN1 in endosomal sorting of BACE1 and Aβ generation in neurons, but a role for BIN1 in this process in vivo is yet to be described. Here, using biochemical and immunohistochemistry analyses we report that a 50% global reduction of BIN1 protein levels resulting from a single Bin1 allele deletion in mice does not change BACE1 levels or localization in vivo, nor does this reduction alter the production of endogenous murine Aβ in nontransgenic mice. Furthermore, we found that reduction of BIN1 levels in the 5XFAD mouse model of amyloidosis does not alter Aβ deposition nor behavioral deficits associated with cerebral amyloid burden. Finally, a conditional BIN1 knockout in excitatory neurons did not alter BACE1, APP, C-terminal fragments derived from BACE1 cleavage of APP, or endogenous Aβ levels. These results indicate that BIN1 function does not regulate Aβ generation in vivo.

Proteomic Analysis of Mouse Brain Subjected to Spaceflight

There is evidence that spaceflight poses acute and late risks to the central nervous system. To explore possible mechanisms, the proteomic changes following spaceflight in mouse brain were characterized. Space Shuttle Atlantis (STS-135) was launched from the Kennedy Space Center (KSC) on a 13-day mission. Within 3–5 h after landing, brain tissue was collected to evaluate protein expression profiles using quantitative proteomic analysis. Our results showed that there were 26 proteins that were significantly altered after spaceflight in the gray and/or white matter. While there was no overlap between the white and gray matter in terms of individual proteins, there was overlap in terms of function, synaptic plasticity, vesical activity, protein/organelle transport, and metabolism. Our data demonstrate that exposure to the spaceflight environment induces significant changes in protein expression related to neuronal structure and metabolic function. This might lead to a significant impact on brain structural and functional integrity that could affect the outcome of space missions.

Lipopolysaccharide Associates with Amyloid Plaques, Neurons and Oligodendrocytes in Alzheimer's Disease Brain: A Review

This review proposes that lipopolysaccharide (LPS, found in the wall of all Gram-negative bacteria) could play a role in causing sporadic Alzheimer’s disease (AD). This is based in part upon recent studies showing that: Gram-negative E. coli bacteria can form extracellular amyloid; bacterial-encoded 16S rRNA is present in all human brains with over 70% being Gram-negative bacteria; ultrastructural analyses have shown microbes in erythrocytes of AD patients; blood LPS levels in AD patients are 3-fold the levels in control; LPS combined with focal cerebral ischemia and hypoxia produced amyloid-like plaques and myelin injury in adult rat cortex. Moreover, Gram-negative bacterial LPS was found in aging control and AD brains, though LPS levels were much higher in AD brains. In addition, LPS co-localized with amyloid plaques, peri-vascular amyloid, neurons, and oligodendrocytes in AD brains. Based upon the postulate LPS caused oligodendrocyte injury, degraded Myelin Basic Protein (dMBP) levels were found to be much higher in AD compared to control brains. Immunofluorescence showed that the dMBP co-localized with β amyloid (Aβ) and LPS in amyloid plaques in AD brain, and dMBP and other myelin molecules were found in the walls of vesicles in periventricular White Matter (WM). These data led to the hypothesis that LPS acts on leukocyte and microglial TLR4-CD14/TLR2 receptors to produce NFkB mediated increases of cytokines which increase Aβ levels, damage oligodendrocytes and produce myelin injury found in AD brain. Since Aβ_1–42 is also an agonist for TLR4 receptors, this could produce a vicious cycle that accounts for the relentless progression of AD. Thus, LPS, the TLR4 receptor complex, and Gram-negative bacteria might be treatment or prevention targets for sporadic AD.

Amyloid Proteins and Their Role in Multiple Sclerosis. Considerations in the Use of Amyloid-PET Imaging

Thioflavin T derivatives are used in positron-emission tomography (PET) studies to detect amyloid protein deposits in patients with Alzheimer disease. These tracers bind extensively to white matter, which suggests that they may be useful in studies of multiple sclerosis (MS), and that proteins resulting from proteolytic processing of the amyloid precursor protein (APP) may contribute to MS. This article reviews data from both clinical and preclinical studies addressing the role of these proteins, whether they are detected in CSF studies or using PET imaging. APP is widely expressed in demyelinated axons and may have a protective effect in MS and in experimental allergic encephalomyelitis in animals. Several mechanisms associated with this increased expression may affect the degree of remyelination in MS. Amyloid-PET imaging may help determine the degree of demyelination and provide information on the molecular changes linked to APP proteolytic processing experienced by patients with MS.

In-vivo imaging of grey and white matter neuroinflammation in Alzheimer's disease: a positron emission tomography study with a novel radioligand, [18F]-FEPPA

Our primary aim was to compare neuroinflammation in cognitively intact control subjects and patients with Alzheimer's disease (AD) by using positron emission tomography (PET) with translocator protein 18 kDa (TSPO)-specific radioligand [(18)F]-FEPPA. [(18)F]-FEPPA PET scans were acquired on a high-resolution research tomograph in 21 patients with AD (47- 81 years) and 21 control subjects (49-82 years). They were analyzed by using a 2-tissue compartment model with arterial plasma input function. Differences in neuroinflammation, indexed as [(18)F]-FEPPA binding were compared, adjusting for differences in binding affinity class as determined by a single polymorphism in the TSPO gene (rs6971). In grey matter areas, [(18)F]-FEPPA was significantly higher in AD compared with healthy control subjects. Large increases were seen in the hippocampus, prefrontal, temporal, parietal and occipital cortex (average Cohen's d= 0.89). Voxel-based analyses confirmed significant clusters of neuroinflammation in the frontal, temporal and parietal cortex in patients with AD. In white matter, [(18)F]-FEPPA binding was elevated in the posterior limb of the internal capsule, and the cingulum bundle. Higher neuroinflammation in the parietal cortex (r= -0.7, P= 0.005), and posterior limb of the internal capsule (r= -0.8, P=0.001) was associated with poorer visuospatial function. In addition, a higher [(18)F]-FEPPA binding in the posterior limb of the internal capsule was associated with a greater impairment in language ability (r= -0.7, P=0.004). Elevated neuroinflammation can be detected in AD patients throughout the brain grey and white matter by using [(18)F]-FEPPA PET. Our results also suggest that neuroinflammation is associated with some cognitive deficits.

Myelin basic protein associates with AβPP, Aβ1-42, and amyloid plaques in cortex of Alzheimer's disease brain

The goal of this study was to show that myelin and axons in cortical gray matter are damaged in Alzheimer's disease (AD) brain. Superior temporal gyrus gray matter of AD patients (9 male, 14 female) was compared to cognitively normal controls (8 male, 7 female). Myelin basic protein (MBP) and a degraded myelin basic protein complex (dMBP) were quantified by Western blot. Brain sections were immunostained for MBP, dMBP, axonal neurofilament protein (NF), autophagy marker microtubule-associated proteins 1A/B light chain 3B precursor (LC3B), amyloid-β protein precursor (AβPP), and amyloid markers amyloid β1-42 (Aβ1-42) and FSB. Co-immunoprecipitation and mass spectroscopy evaluated interaction of AβPP/Aβ1-42 with MBP/dMBP. Evidence of axonal injury in AD cortex included appearance of AβPP in NF stained axons, and NF at margins of amyloid plaques. Evidence of myelin injury in AD cortex included (1) increased dMBP in AD gray matter compared to control (p < 0.001); (2) dMBP in AD neurons; and (3) increased LC3B that co-localized with MBP. Evidence of interaction of AβPP/Aβ1-42 with myelin or axonal components included (1) greater binding of dMBP with AβPP in AD brain; (2) MBP at the margins of amyloid plaques; (3) dMBP co-localized with Aβ1-42 in the core of amyloid plaques in AD brains; and (4) interactions between Aβ1-42 and MBP/dMBP by co-immunoprecipitation and mass spectrometry. We conclude that damaged axons may be a source of AβPP. dMBP, MBP, and NF associate with amyloid plaques and dMBP associates with AβPP and Aβ1-42. These molecules could be involved in formation of amyloid plaques.

Region-Specific Alterations of Matrix Metalloproteinase Activity in Multiple System Atrophy

BACKGROUND

MSA is a sporadic progressive neurodegenerative disorder characterized by a variable combination of parkinsonism, cerebellar ataxia, and autonomic dysfunction. The pathological hallmark of MSA is the accumulation of alpha-synuclein aggregates in the cytoplasm of oligodendrocytes along with neuronal loss and neuroinflammation, as well as blood-brain barrier dysfunction and myelin deterioration. Matrix metalloproteinases are zinc-dependent endopeptidases involved in the remodeling of the extracellular matrix, demyelination, and blood-brain barrier permeability. Several lines of evidence indicate a role for these enzymes in various pathological processes, including stroke, multiple sclerosis, Parkinson's, and Alzheimer's disease.

METHODS

This study aimed to assess potential alterations of matrix metalloproteinase-1, -2, -3, and -9 expression or activity in MSA postmortem brain tissue.

RESULTS

Gelatin zymography revealed increased matrix metalloproteinase-2 activity in the putamen, but not in the frontal cortex, of MSA patients relative to controls. Immunohistochemistry revealed increased number of glial cells positive for matrix metalloproteinase-1, -2, and -3 in the putamen and frontal cortex of MSA patients. Double immunofluorescence revealed that matrix metalloproteinase-2 and -3 were expressed in astrocytes and microglia. Only matrix metalloproteinase-2 colocalized with alpha-synuclein in oligodendroglial cytoplasmic inclusions.

CONCLUSION

These results demonstrate widespread alterations of matrix metalloproteinase expression in MSA and a pattern of increased matrix metalloproteinase-2 expression and activity affecting preferentially a brain region severely affected (putamen) over a relatively spared region (frontal cortex). Elevated matrix metalloproteinase expression may thus contribute to the disease process in MSA by promoting blood-brain barrier dysfunction and/or myelin degradation.

Activation of the factor XII-driven contact system in Alzheimer's disease patient and mouse model plasma

Alzheimer's disease (AD) is characterized by accumulation of the β-amyloid peptide (Aβ), which likely contributes to disease via multiple mechanisms. Increasing evidence implicates inflammation in AD, the origins of which are not completely understood. We investigated whether circulating Aβ could initiate inflammation in AD via the plasma contact activation system. This proteolytic cascade is triggered by the activation of the plasma protein factor XII (FXII) and leads to kallikrein-mediated cleavage of high molecular-weight kininogen (HK) and release of proinflammatory bradykinin. Aβ has been shown to promote FXII-dependent cleavage of HK in vitro. In addition, increased cleavage of HK has been found in the cerebrospinal fluid of patients with AD. Here, we show increased activation of FXII, kallikrein activity, and HK cleavage in AD patient plasma. Increased contact system activation is also observed in AD mouse model plasma and in plasma from wild-type mice i.v. injected with Aβ42. Our results demonstrate that Aβ42-mediated contact system activation can occur in the AD circulation and suggest new pathogenic mechanisms, diagnostic tests, and therapies for AD.

N-terminal region of myelin basic protein reduces fibrillar amyloid-β deposition in Tg-5xFAD mice

Alzheimer's disease is a progressive neurodegenerative disorder that is characterized by extensive deposition of fibrillar amyloid-β (Aβ) in the brain. Previously, myelin basic protein (MBP) was identified to be a potent inhibitor to Aβ fibril formation, and this inhibitory activity was localized to the N-terminal residues 1-64, a fragment designated MBP1. Here, we show that the modest neuronal expression of a fusion protein of the biologically active MBP1 fragment and the enhanced green fluorescent protein (MBP1-EGFP) significantly improved the performance of spatial learning memory in Tg-5xFAD mice, a model of pathologic Aβ accumulation in brain. The levels of insoluble Aβ and fibrillar amyloid were significantly reduced in bigenic Tg-5xFAD/Tg-MBP1-EGFP mice. Quantitative stereological analysis revealed that the reduction in amyloid was because of a reduction in the size of fibrillar plaques rather than a decrease in plaque numbers. The current findings support previous studies showing that MBP1 inhibits Aβ fibril formation in vitro and demonstrate the ability of MBP1 to reduce Aβ pathology and improve behavioral performance.

Behavioral and EEG changes in male 5xFAD mice

Transgenic animal models of Alzheimer's disease (AD) are widely used to investigate mechanisms of pathophysiology and cognitive dysfunctions. A model with a very early development of parenchymal plaque load at the age of 2months is the 5xFAD mouse (Tg6799, Oakley et al. 2006). These 5xFAD mice over-express both human amyloid precursor protein (APP) and human presenilin 1 (PS1). Mice from this line have a high APP expression correlating with a high burden and an accelerated accumulation of the 42 amino acid species of amyloid-β (Aβ). The aim of this study was the behavioral and functional investigations of 5xFAD males because in most studies females of this strain were characterized. In comparison to literature of transgenic 5xFAD females, transgenic 5xFAD males showed decreased anxiety in the elevated plus maze, reduced locomotion and exploration in the open field and disturbances in learning performance in the Morris water maze starting at 9months of age. Electroencephalogram (EEG) recordings on 6month old transgenic mice revealed a decrease of delta, theta, alpha, beta and gamma frequency bands whereas the subdelta frequency was increased. EEG recordings during sleep showed a reduction of rapid eye movement sleep in relation to the amount of total sleep. Thus, 5xFAD males develop early functional disturbances and subsequently behavioral deficits and therefore they are a good mouse model for studying Alzheimer's disease.