Inflammation in Alzheimer disease-a brief review of the basic science and clinical literature

Extracts from Dendropanax morbifera Leaves Have Modulatory Effects on Neuroinflammation in Microglia

Dendropanax morbifera (D. morbifera), a species endemic to Korea, is largely distributed throughout the southern part of the country. Its leaves, stems, roots, and seeds have been used as a form of alternative medicine for various diseases and neurological disorders including paralysis, stroke, and migraine. However, the molecular mechanisms that underlie the remedial effects of D. morbifera remain largely unknown. In this paper, extracts from D. morbifera leaves were prepared using ethyl acetate as a solvent (abbreviated as DMLE). The modulatory effects of DMLE on neuroinflammation were studied in a lipopolysaccharide (LPS)-stimulated BV2 murine microglial cell line. Production of pro-inflammatory cytokines, activation of mitogen-activated protein kinases (MAPKs) and nuclear factor-kappa B (NF-[Formula: see text]B), and different M1/M2 activation states of microglia were examined. DMLE treatment suppressed the production of pro-inflammatory cytokines including tumor necrosis factor-[Formula: see text] (TNF-[Formula: see text]), interleukin-6 (IL-6), and nitric oxide (NO) in LPS-stimulated BV2 cells. DMLE treatment also attenuated the activation of MAPKs and NF-[Formula: see text]B. In a novel discovery, we found that DMLE up-regulated the marker genes representing an alternative, anti-inflammatory M2 polarization, while suppressing the expression of the classical, pro-inflammatory M1 activation state genes. Here, we uncovered the cellular mechanisms underlying the beneficial effects of D. morbifera against neuroinflammation using BV2 microglia cells. These results strongly suggest that DMLE was able to counter the effects of LPS on BV2 cells via control of microglia polarization states. Additionally, study results indicated that DMLE may have therapeutic potential as a neuroinflammation-suppressing treatment for neurodegenerative diseases.

The endocytic pathway in microglia during health, aging and Alzheimer's disease

Microglia, the main phagocytes of the central nervous system (CNS), are involved in the surveillance and maintenance of nervous tissue. During normal tissue homeostasis, microglia migrates within the CNS, phagocytose dead cells and tissue debris, and modulate synapse pruning and spine formation via controlled phagocytosis. In the event of an invasion by a foreign body, microglia are able to phagocytose the invading pathogen and process it proteolytically for antigen presentation. Internalized substrates are incorporated and sorted within the endocytic pathway and thereafter transported via complex vesicular routes. When targeted for degradation, substrates are delivered to acidic late endosomes and lysosomes. In these, the enzymatic degradation relies on pH and enzyme content. Endocytosis, sorting, transport, compartment acidification and degradation are regulated by complex signaling mechanisms, and these may be altered during aging and pathology. In this review, we discuss the endocytic pathway in microglia, with insight into the mechanisms controlling lysosomal biogenesis and pH regulation. We also discuss microglial lysosome function associated with Alzheimer's disease (AD) and the mechanisms of amyloid-beta (Aβ) internalization and degradation. Finally, we explore some therapies currently being investigated to treat AD and their effects on microglial response to Aβ, with insight in those involving enhancement of lysosomal function.

PRECISION MEDICINE - The Golden Gate for Detection, Treatment and Prevention of Alzheimer's Disease

During this decade, breakthrough conceptual shifts have commenced to emerge in the field of Alzheimer's disease (AD) recognizing risk factors and the non-linear dynamic continuum of complex pathophysiologies amongst a wide dimensional spectrum of multi-factorial brain proteinopathies/neurodegenerative diseases. As is the case in most fields of medicine, substantial advancements in detecting, treating and preventing AD will likely evolve from the generation and implementation of a systematic precision medicine strategy. This approach will likely be based on the success found from more advanced research fields, such as oncology. Precision medicine will require integration and transfertilization across fragmented specialities of medicine and direct reintegration of Neuroscience, Neurology and Psychiatry into a continuum of medical sciences away from the silo approach. Precision medicine is biomarker-guided medicine on systems-levels that takes into account methodological advancements and discoveries of the comprehensive pathophysiological profiles of complex multi-factorial neurodegenerative diseases, such as late-onset sporadic AD. This will allow identifying and characterizing the disease processes at the asymptomatic preclinical stage, where pathophysiological and topographical abnormalities precede overt clinical symptoms by many years to decades. In this respect, the uncharted territory of the AD preclinical stage has become a major research challenge as the field postulates that early biomarker guided customized interventions may offer the best chance of therapeutic success. Clarification and practical operationalization is needed for comprehensive dissection and classification of interacting and converging disease mechanisms, description of genomic and epigenetic drivers, natural history trajectories through space and time, surrogate biomarkers and indicators of risk and progression, as well as considerations about the regulatory, ethical, political and societal consequences of early detection at asymptomatic stages. In this scenario, the integrated roles of genome sequencing, investigations of comprehensive fluid-based biomarkers and multimodal neuroimaging will be of key importance for the identification of distinct molecular mechanisms and signaling pathways in subsets of asymptomatic people at greatest risk for progression to clinical milestones due to those specific pathways. The precision medicine strategy facilitates a paradigm shift in Neuroscience and AD research and development away from the classical "one-size-fits-all" approach in drug discovery towards biomarker guided "molecularly" tailored therapy for truly effective treatment and prevention options. After the long and winding decade of failed therapy trials progress towards the holistic systems-based strategy of precision medicine may finally turn into the new age of scientific and medical success curbing the global AD epidemic.

Inflammatory Response in the CNS: Friend or Foe?

Inflammatory reactions could be both beneficial and detrimental to the brain, depending on strengths of their activation in various stages of neurodegeneration. Mild activation of microglia and astrocytes usually reveals neuroprotective effects and ameliorates early symptoms of neurodegeneration; for instance, released cytokines help maintain synaptic plasticity and modulate neuronal excitability, and stimulated toll-like receptors (TLRs) promote neurogenesis and neurite outgrowth. However, strong activation of glial cells gives rise to cytokine overexpression/dysregulation, which accelerates neurodegeneration. Altered mutual regulation of p53 protein, a major tumor suppressor, and NF-κB, the major regulator of inflammation, seems to be crucial for the shift from beneficial to detrimental effects of neuroinflammatory reactions in neurodegeneration. Therapeutic intervention in the p53-NF-κB axis and modulation of TLR activity are future challenges to cope with neurodegeneration.

One protein, multiple pathologies: multifaceted involvement of amyloid β in neurodegenerative disorders of the brain and retina

Accumulation of amyloid β (Aβ) and its aggregates in the ageing central nervous system is regarded synonymous to Alzheimer's disease (AD) pathology. Despite unquestionable advances in mechanistic and diagnostic aspects of the disease understanding, the primary cause of Aβ accumulation as well as its in vivo roles remains elusive; nonetheless, the majority of the efforts to address pathological mechanisms for therapeutic development are focused towards moderating Aβ accumulation in the brain. More recently, Aβ deposition has been identified in the eye and is linked with distinct age-related diseases including age-related macular degeneration, glaucoma as well as AD. Awareness of the Aβ accumulation in these markedly different degenerative disorders has led to an increasing body of work exploring overlapping mechanisms, a prospective biomarker role for Aβ and the potential to use retina as a model for brain related neurodegenerative disorders. Here, we present an integrated view of current understanding of the retinal Aβ deposition discussing the accumulation mechanisms, anticipated impacts and outlining ameliorative approaches that can be extrapolated to the retina for potential therapeutic benefits. Further longitudinal investigations in humans and animal models will determine retinal Aβ association as a potential pathognomonic, diagnostic or prognostic biomarker.

Prospective Study of Oral Health and Risk of Primary Open-Angle Glaucoma in Men: Data from the Health Professionals Follow-up Study

PURPOSE

Tooth loss or periodontal disease is associated with systemic endothelial dysfunction, which has been implicated in primary open-angle glaucoma (POAG). The relationship between oral health and POAG has received limited attention. Thus, we evaluated the association between oral health history and risk of POAG and POAG subtypes.

DESIGN

Prospective cohort study.

PARTICIPANTS

Health Professionals Follow-up Study participants (40 536 men) followed biennially from 1986 to 2012. At each 2-year risk period, eligible participants were aged 40+ years, were free of POAG, and reported eye examinations.

METHODS

By using validated questions, we updated participants' status on number of natural teeth, teeth lost, periodontal disease with bone loss, and root canal treatments.

MAIN OUTCOME MEASURES

During follow-up, 485 incident cases of POAG were confirmed with medical records and classified into subtypes defined by intraocular pressure (IOP; ≥ or <22 mmHg) or visual field (VF) loss pattern at diagnosis (peripheral loss only or early paracentral loss). Multivariable relative risks (MVRRs) and 95% confidence intervals (CIs) were estimated.

RESULTS

Number of natural teeth, periodontal disease, and root canal treatment were not associated with POAG. However, compared with no report of tooth loss, a report of losing teeth within the past 2 years was associated with a 1.45-fold increased risk of POAG (95% CI, 1.06-1.97); in particular, a report within the past 2 years of both losing teeth and having a prevalent diagnosis of periodontal disease was associated with a 1.85-fold increased risk of POAG (95% CI, 1.07-3.18). The associations with recent tooth loss were not significantly different for the POAG subtypes (P for heterogeneity ≥0.36), although associations were strongest in relation to the POAG subtypes with IOP <22 mmHg (MVRR, 1.93; 95% CI, 1.09-3.43) and early paracentral VF loss (MVRR, 2.27; 95% CI, 1.32-3.88).

CONCLUSIONS

Although the number of natural teeth was not associated with risk of POAG, recent tooth loss was associated with an increased risk of POAG. Because these findings may be due to chance, they need confirmation in larger studies.

Interferon Gamma: Influence on Neural Stem Cell Function in Neurodegenerative and Neuroinflammatory Disease

Interferon-gamma (IFNγ), a pleiotropic cytokine, is expressed in diverse neurodegenerative and neuroinflammatory conditions. Its protective mechanisms are well documented during viral infections in the brain, where IFNγ mediates non-cytolytic viral control in infected neurons. However, IFNγ also plays both protective and pathological roles in other central nervous system (CNS) diseases. Of the many neural cells that respond to IFNγ, neural stem/progenitor cells (NSPCs), the only pluripotent cells in the developing and adult brain, are often altered during CNS insults. Recent studies highlight the complex effects of IFNγ on NSPC activity in neurodegenerative diseases. However, the mechanisms that mediate these effects, and the eventual outcomes for the host, are still being explored. Here, we review the effects of IFNγ on NSPC activity during different pathological insults. An improved understanding of the role of IFNγ would provide insight into the impact of immune responses on the progression and resolution of neurodegenerative diseases.

Amyloid-β 1-24 C-terminal truncated fragment promotes amyloid-β 1-42 aggregate formation in the healthy brain

Substantial data indicate that amyloid-β (Aβ), the major component of senile plaques, plays a central role in Alzheimer’s Disease and indeed the assembly of naturally occurring amyloid peptides into cytotoxic aggregates is linked to the disease pathogenesis. Although Aβ42 is a highly aggregating form of Aβ, the co-occurrence of shorter Aβ peptides might affect the aggregation potential of the Aβ pool. In this study we aimed to assess whether the structural behavior of human Aβ42 peptide inside the brain is influenced by the concomitant presence of N-terminal fragments produced by the proteolytic activity of glial cells. We show that the occurrence of the human C-terminal truncated 1–24 Aβ fragment impairs Aβ42 clearance through blood brain barrier and promotes the formation of Aβ42 aggregates even in the healthy brain. By showing that Aβ1-24 has seeding properties for aggregate formation in intracranially injected wild type mice, our study provide the proof-of-concept that peptides produced upon Aβ42 cleavage by activated glial cells may cause phenotypic defects even in the absence of genetic mutations associated with Alzheimer’s Disease, possibly contributing to the development of the sporadic form of the pathology.

Overexpression of serum amyloid a 1 induces depressive-like behavior in mice

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by loss of memory and cognitive abilities. In AD, amyloid β (Aβ) protein aggregates in the brain of patients, forming amyloid plaques. Aβ plaques are known to be surrounded by activated microglial cells. Serum amyloid A (SAA) is elevated from several hundred to 1000-fold as part of the immune response against various injuries, including trauma, infection, and inflammation. Additionally, continuous elevation of SAA is related to the development of amyloidosis. This study was designed to identify the relationship between SAA1 and AD using liver specific SAA1 overexpressing mice (TG), because SAA1 is expressed in the liver during the acute phase. We detected exogenous SAA1 expression in the brain of TG mice. This result implies that liver-derived SAA1 migrates to the brain tissues. Thus, we confirmed that the blood brain barrier (BBB) functioned normally using Evans-blue staining and CARS. Furthermore, our results show an increase in the accumulation of the 87kDa form of Aβ in TG mice compared to wild type mice (WT). Additionally, the number of microglial cells and levels of pro-inflammatory cytokines were increased. Next, we investigated the relationship between SAA1 and depression by performing social interaction tests. The results showed that TG mice have a tendency to avoid stranger mice and an impaired social recognition. In conclusion, the SAA1 TG mouse model is a valuable model to study depression.

Tenascin-C Is Associated with Cored Amyloid-β Plaques in Alzheimer Disease and Pathology Burdened Cognitively Normal Elderly

Tenascin-C (TN-C) is an extracellular matrix glycoprotein linked to inflammatory processes in pathological conditions including Alzheimer disease (AD). We examined the distribution of TN-C immunoreactivity (ir) in relation to amyloid-β (Aβ) plaques and vascular Aβ deposits in autopsy brain tissues from 14 patients with clinical and neuropathological AD and 10 aged-matched controls with no cognitive impairment; 5 of the controls had Aβ plaques and 5 did not. TN-C ir was abundant in cortical white matter and subpial cerebral gray matter in all cases, whereas TN-C ir was weak in blood vessels. In all cases with Aβ plaques but not in plaque-free controls, TN-C ir was detected as large (>100 µm in diameter) diffuse extracellular deposits in cortical grey matter. TN-C plaques completely overlapped and surrounded cored Aβ plaques labeled with X-34, a fluorescent derivative of Congo red, and they were associated with reactive astrocytes astrocytes, microglia and phosphorylated tau-containing dystrophic neurites. Diffuse Aβ plaques lacking amyloid cores, reactive glia or dystrophic neurites showed no TN-C ir. In cases with cerebral amyloid angiopathy, TN-C ir in vessel walls did not spread into the surrounding neuropil. These results suggest a role for TN-C in Aβ plaque pathogenesis and its potential as a biomarker and therapy target.

Exposure to air pollution as a potential contributor to cognitive function, cognitive decline, brain imaging, and dementia: A systematic review of epidemiologic research

BACKGROUND

Dementia is a devastating condition typically preceded by a long prodromal phase characterized by accumulation of neuropathology and accelerated cognitive decline. A growing number of epidemiologic studies have explored the relation between air pollution exposure and dementia-related outcomes.

METHODS

We undertook a systematic review, including quality assessment, to interpret the collective findings and describe methodological challenges that may limit study validity. Articles, which were identified according to a registered protocol, had to quantify the association of an air pollution exposure with cognitive function, cognitive decline, a dementia-related neuroimaging feature, or dementia.

RESULTS

We identified 18 eligible published articles. The quality of most studies was adequate to exemplary. Almost all reported an adverse association between at least one pollutant and one dementia-related outcome. However, relatively few studies considered outcomes that provide the strongest evidence for a causal effect, such as within-person cognitive or pathologic changes. Reassuringly, differential selection would likely bias toward a protective association in most studies, making it unlikely to account for observed adverse associations. Likewise, using a formal sensitivity analysis, we found that unmeasured confounding is also unlikely to explain reported adverse associations.

DISCUSSION

We also identified several common challenges. First, most studies of incident dementia identified cases from health system records. As dementia in the community is underdiagnosed, this could generate either non-differential or differential misclassification bias. Second, almost all studies used recent air pollution exposures as surrogate measures of long-term exposure. Although this approach may be reasonable if the measured and etiologic exposure windows are separated by a few years, its validity is unknown over longer intervals. Third, comparing the magnitude of associations may not clearly pinpoint which, if any, pollutants are the probable causal agents, because the degree of exposure misclassification differs across pollutants. The epidemiologic evidence, alongside evidence from other lines of research, provides support for a relation of air pollution exposure to dementia. Future studies with improved design, analysis and reporting would fill key evidentiary gaps and provide a solid foundation for recommendations and possible interventions.

DNA-PK Deficiency in Alzheimer's Disease

Alzheimer's disease (AD) is characterized by neuronal death with an accumulaton of intra-cellular neurofibrillary tangles (NFT) and extracellular amyloid plaques. Reduced DNA repair ability has been reported in AD brains. In neurons, the predominant mechanism to repair double-strand DNA breaks (DSB) is non-homologous end joining (NHEJ) that requires DNA-dependent protein kinase (DNA-PK) activity. DNA-PK is a holoenzyme comprising the p460 kD DNA-PK catalytic subunit (DNA-PKcs) and its activator Ku, a heterodimer of p86 (Ku80) and p70 (Ku70) subunits. Upon binding to double-stranded DNA ends, Ku recruits DNA-PKcs to process NHEJ. In AD brains, reduced NHEJ activity as well as DNA-PKcs and Ku protein levels have been shown. Normal aging brains also show a reduction in both DNA-PKcs and Ku levels questioning a direct link between NHEJ ability and AD, and suggesting additional players/events in AD pathogenesis. Deficiency of Ku80, a somatostatin receptor, can disrupt somatostatin signaling thus inducing amyloid beta (Aβ) generation, which in turn can potentiate DNA-PKcs degradation and consequently loss of NHEJ activity, an additional step negatively affecting DSB repair. Trigger of these two different pathways culminating in genome instability may differentiate the outcomes between AD and normal aging.

Associations Between Serum Inflammatory Markers and Hippocampal Volume in a Community Sample

OBJECTIVES

To quantify associations between inflammatory biomarkers and hippocampal volume (HV) and to examine effect modification according to sex, race, and age.

DESIGN

Cross-sectional analyses using generalized estimating equations to account for familial clustering; standardized β-coefficients adjusted for age, sex, race, and education.

SETTING

Community cohorts in Jackson, Mississippi and Rochester, Minnesota.

PARTICIPANTS

The Genetic Epidemiology Network of Arteriopathy study.

MEASUREMENTS

C-reactive protein (CRP), interleukin-6 (IL-6), and soluble tumor necrosis factor receptors 1 (sTNFR-1) and 2 (sTNFR-2) from peripheral blood were measured in a sample of 773 non-Hispanic whites (61% women, aged 60.2 ± 9.8) and 514 African Americans (70% women, aged 63.9 ± 8.1) who also underwent brain magnetic resonance imaging. Biomarkers were standardized and compared according to sex, race and age with HV.

RESULTS

In the full sample, higher sTNFR-1 and sTNFR-2 were associated with smaller HV. Each standard deviation (SD) increase in sTNFR-1 was associated with 59.1 mm(3) (95% confidence interval (CI) = -101.4 to -16.7 mm(3) ) smaller HV and each SD increase in sTNFR-2 associated with 48.8 mm(3) (95% CI = -92.2 to -5.3 mm(3) ) smaller HV. Relationships were stronger for sTNFR-2 in men (HV = -116.6 mm(3) for each SD increase, 95% CI = -201.0 to -32.1) than women (HV = -26.0 per SD increase, 95% CI = -72.4-20.5) and sTNFR-1 in non-Hispanic whites (HV = -84.7 mm(3) per SD increase, 95% CI = -142.2 to -27.1) than African Americans (HV = -14.1 mm(3) per SD increase, 95% CI = -78.3-50.1). Associations between IL-6 or CRP and HV were not supported.

CONCLUSION

Higher levels of sTNFRs were associated cross-sectionally with smaller hippocampi. Longitudinal data are needed to determine whether these biomarkers may help to identify risk of late-life cognitive impairment.

The human-specific CASP4 gene product contributes to Alzheimer-related synaptic and behavioural deficits

Recent studies have indicated that innate immune signalling molecules are involved in late-onset Alzheimer's disease (LOAD) risk. Amyloid beta (Aβ) accumulates in AD brain, and has been proposed to act as a trigger of innate immune responses. Caspase-4 is an important part of the innate immune response. We recently characterized transgenic mice carrying human CASP4, and observed that the mice manifested profound innate immune responses to lipopolysaccharide (LPS). Since these inflammatory processes are important in the aetiology of AD, we have now analysed the correlation of expression of caspase-4 in human brain with AD risk genes, and studied caspase-4 effects on AD-related phenotypes in APPswe/PS1deltaE9 (APP/PS1) mice. We observed that the expression of caspase-4 was strongly correlated with AD risk genes including TYROBP, TREM2, CR1, PSEN1, MS4A4A and MS4A6A in LOAD brains. Caspase-4 expression was upregulated in CASP4/APP/PS1 mice in a region-specific manner, including hippocampus and prefrontal cortex. In APP/PS1 mice, caspase-4 expression led to impairments in the reversal phase of a Barnes maze task and in hippocampal synaptic plasticity, without affecting soluble or aggregated Aβ levels. Caspase-4 was expressed predominantly in microglial cells, and in the presence of CASP4, more microglia were clustered around amyloid plaques. Furthermore, our data indicated that caspase-4 modulates microglial cells in a manner that increases proinflammatory processes. We propose that microglial caspase-4 expression contributes to the cognitive impairments in AD, and that further study of caspase-4 will enhance our understanding of AD pathogenesis and may lead to novel therapeutic targets in AD.

siRNA-mediated silencing of phosphodiesterase 4B expression affects the production of cytokines in endotoxin-stimulated primary cultured microglia

Phosphodiesterase 4 (PDE4) has four subtypes: PDE4A, PDE4B, PDE4C and PDE4D. The expression of PDE4 subtypes in microglial cells and the specific contribution of each subtype to inflammation remain unclear. In this study, the expression of PDE4 subtypes in primary microglial cells was assayed. Primary microglial cells were then transfected with specific small interfering RNA (siRNA) against each PDE4 subtype. PDE4 subtype A-D knockdown was confirmed by quantitative polymerase chain reaction. Secreted cytokines in the supernatant and intracellular cyclic adenosine monophosphate (cAMP) levels of transfected cells were measured. The effect of PDE4B siRNA on the activation of extracellular regulated protein kinase (ERK) induced by lipopolysaccharide (LPS) in microglia was further tested by western blotting. Results showed that the primary microglial cells expressed all four types of PDE4s at the protein level. Transfection with the four siRNAs inhibited PDE4 subtype A-D mRNA expression, respectively. In primary microglial cells, treatment with PDE4B siRNA significantly inhibited the expression of tumor necrosis factor-α and interleukin (IL)-1β, and enhanced the expression of cAMP, while siRNAs to other subtypes had no significant effects. However, none of the four siRNAs had any significant effect on the expression of IL-10. Furthermore, in the PDE4B group, the level of phosphorylated ERK was reduced. Among the four PDE4 subtypes, PDE4B plays an important role in regulating inflammatory responses in microglia, potentially through initially regulating the intracellular cAMP concentration.

Cytokines and Cytokine Receptors Involved in the Pathogenesis of Alzheimer's Disease

Inflammatory mechanisms are implicated in the pathology of Alzheimer's disease (AD). However, it is unclear whether inflammatory alterations are a cause or consequence of neurodegeneration leading to dementia. Clarifying this issue would provide valuable insight into the early diagnosis and therapeutic management of AD. To address this, we compared the mRNA expression profiles of cytokines in the brains of AD patients with "non-demented individuals with AD pathology" and non-demented healthy control (ND) individuals. "Non-demented individuals with AD pathology" are referred to as high pathology control (HPC) individuals that are considered an intermediate subset between AD and ND. HPC represents a transition between normal aging and early stage of AD, and therefore, is useful for determining whether neuroinflammation is a cause or consequence of AD pathology. We observed that immunological conditions that produce cytokines in the HPC brain were more representative of ND than AD. To validate these result, we investigated the expression of inflammatory mediators at the protein level in postmortem brain tissues. We examined the protein expression of tumor necrosis factor (TNF)α and its receptors (TNFRs) in the brains of AD, HPC, and ND individuals. We found differences in soluble TNFα and TNFRs expression between AD and ND groups and between AD and HPC groups. Expression in the temporal cortex was lower in the AD brains than HPC and ND. Our findings indicate that alterations in immunological conditions involving TNFR-mediated signaling are not the primary events initiating AD pathology, such as amyloid plaques and tangle formation. These may be early events occurring along with synaptic and neuronal changes or later events caused by these changes. In this review, we emphasize that elucidating the temporal expression of TNFα signaling molecules during AD is important to understand the selective tuning of these pathways required to develop effective therapeutic strategies for AD.

Salidroside suppresses inflammation in a D-galactose-induced rat model of Alzheimer's disease via SIRT1/NF-κB pathway

Age-related inflammation is the predominant factor for neurodegenerative diseases like Alzheimer's disease (AD). In the present study, we examined memory performance and neuroinflammation in D-galactose (D-gal)-induced sub-acute aging model of rats. Our results demonstrated that chronic administration of D-gal (120 mg/kg) produced cognitive impairment as determined by Morris water maze (MWM) test and step-down passive avoidance test. D-gal also activated nuclear factor kappa B (NF-κB) p65/RelA by down-regulating the expression level of sirtuins 1 (SIRT1) in the hippocampus. Treatment with Salidroside (Sal, 20, 40 mg/kg) for 28 days ameliorated D-gal-induced memory deficits and inflammatory mediators including tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). Moreover, D-gal-induced activation of NF-κB signaling pathway in the brain was also inhibited by Sal via up-regulating SIRT1. These results suggest that D-gal-triggered memory impairment and inflammatory response may be associated with SIRT1/NF-κB signaling pathway, whereas treatment with Sal could positively affect these changes in hippocampus.

Relation of Poor Memory to Soluble Tumor Necrosis Factor Receptor Type Two (sTNF-RII)

The association of soluble tumor necrosis factor receptor type two with poor memory in patients with breast cancer and controls found by Patel et al (2015) may confirm the finding of Holmes et al in 2009 that tumor necrosis factor α is linked to cognitive decline.

Antibody-Mediated Targeting of Tau In Vivo Does Not Require Effector Function and Microglial Engagement

The spread of tau pathology correlates with cognitive decline in Alzheimer's disease. In vitro, tau antibodies can block cell-to-cell tau spreading. Although mechanisms of anti-tau function in vivo are unknown, effector function might promote microglia-mediated clearance. In this study, we investigated whether antibody effector function is required for targeting tau. We compared efficacy in vivo and in vitro of two versions of the same tau antibody, with and without effector function, measuring tau pathology, neuron health, and microglial function. Both antibodies reduced accumulation of tau pathology in Tau-P301L transgenic mice and protected cultured neurons against extracellular tau-induced toxicity. Only the full-effector antibody enhanced tau uptake in cultured microglia, which promoted release of proinflammatory cytokines. In neuron-microglia co-cultures, only effectorless anti-tau protected neurons, suggesting full-effector tau antibodies can induce indirect toxicity via microglia. We conclude that effector function is not required for efficacy, and effectorless tau antibodies may represent a safer approach to targeting tau.

Serum- and glucocorticoid-inducible kinases in microglia

Microglia are derived from myelogenous cells and contribute to immunological and inflammatory responses in central nervous system. They play important roles not only in infectious diseases and inflammation after stroke, but also in psychiatric diseases such as schizophrenia. While recent studies suggest the significances of serum- and glucocorticoid-inducible kinases (SGKs) in other immune cells such as macrophages, T cells and dendritic cells, their role in microglia remains unknown. Here we, for the first time, report that SGK1 and SGK3 are expressed in multiple microglial cell lines. An SGK inhibitor, gsk650394, inhibits cell viability. In addition, lipopolysaccharide-induced expression of inflammatory regulators iNOS and TNFα was enhanced by gsk650394. Furthermore, translocation of NF-κB was enhanced by gsk650394. Taken together, these findings suggest that SGKs may play an important role in regulating microglial viability and inflammatory responses.

Hippocampal Aβ expression, but not phosphorylated tau, predicts cognitive deficits following repeated peripheral poly I:C administration

Alzheimer's disease is marked by the accumulation of the amyloid-beta (Aβ) peptide, and increases in phosphorylation of the microtubule associated protein, tau. Changes in these proteins are considered responsible, in part, for the progressive neuronal degeneration and cognitive deficits seen in AD. We examined the effect of repeated consecutive peripheral poly I:C injections on cognitive deficits, central Aβ, and phosphorylated tau accumulation, following three treatment durations: 7, 14, and 21 days. Forty-eight hours after the final injection, animals were trained in a contextual fear-conditioning paradigm, and tested 24h later. Immediately after testing, the hippocampus was collected to quantify Aβ and phosphorylated tau accumulation. Results showed that, although poly I:C-induced Aβ was significantly elevated at all time points examined, poly I:C only disrupted cognition after 14 and 21 days of administration. Moreover, elevations in phosphorylated tau were not seen until the 14-day time point. Interestingly, phosphorylated tau expression then declined at the 21-day time point. Finally, we demonstrated that Aβ levels are a stronger predictor of cognitive dysfunction, explaining 37% of the variance, whereas phosphorylated tau levels only accounted for 0.2%. Taken together, these results support the hypothesis that inflammation-induced elevation in Aβ disrupts cognition, independently of phosphorylated tau, and suggest that long-term administration of poly I:C may provide a model to investigate the contribution of long-term inflammation toward the development of Alzheimer's-like pathology.

Arabidopsis thaliana extracts optimized for polyphenols production as potential therapeutics for the APOE-modulated neuroinflammation characteristic of Alzheimer's disease in vitro

Although the cause of Alzheimer's disease (AD) is unknown, glial-induced neuroinflammation is an early symptom. Familial AD is caused by increases in amyloid-beta (Aβ) peptide, particularly soluble oligomeric (oAβ), considered a proximal neurotoxin and neuroinflammatory stimuli. APOE4, a naturally occurring genotype of APOE, is the greatest genetic risk factor for AD; increasing risk up to 12-fold compared to APOE3 and APOE2. oAβ-induced neuroinflammation is greater with APOE4 compared to APOE3 and APOE2. As sinapates and flavonoids have anti-inflammatory properties, a protocol was developed for optimizing polyphenol production in seedlings of Arabidopsis thaliana (A. thaliana). Three mutants (cop1, prn1, xpf3) were identified, and the extracts treated with liver microsomes to mimic physiological metabolism, with HPLC and MS performed on the resulting metabolites for peak identification. These extracts were used to treat primary glial cells isolated from human APOE-targeted-replacement (APOE-TR) and APOE-knock-out (KO) mice, with neuroinflammation induced by lipopolysaccharide (LPS) or oAβ. The dose-response data for TNFα secretion demonstrate the followed the order: APOE-KO > APOE4 > APOE3 > APOE2, with xpf3 the most effective anti-neuroinflammatory across APOE genotypes. Thus, the plant-based approach described herein may be particularly valuable in treating the APOE4-induced neuroinflammatory component of AD risk.

Polygenic risk of Alzheimer disease is associated with early- and late-life processes

OBJECTIVE

To examine associations between aggregate genetic risk and Alzheimer disease (AD) markers in stages preceding the clinical symptoms of dementia using data from 2 large observational cohort studies.

METHODS

We computed polygenic risk scores (PGRS) using summary statistics from the International Genomics of Alzheimer's Project genome-wide association study of AD. Associations between PGRS and AD markers (cognitive decline, clinical progression, hippocampus volume, and β-amyloid) were assessed within older participants with dementia. Associations between PGRS and hippocampus volume were additionally examined within healthy younger participants (age 18-35 years).

RESULTS

Within participants without dementia, elevated PGRS was associated with worse memory (p = 0.002) and smaller hippocampus (p = 0.002) at baseline, as well as greater longitudinal cognitive decline (memory: p = 0.0005, executive function: p = 0.01) and clinical progression (p < 0.00001). High PGRS was associated with AD-like levels of β-amyloid burden as measured with florbetapir PET (p = 0.03) but did not reach statistical significance for CSF β-amyloid (p = 0.11). Within the younger group, higher PGRS was associated with smaller hippocampus volume (p = 0.05). This pattern was evident when examining a PGRS that included many loci below the genome-wide association study (GWAS)-level significance threshold (16,123 single nucleotide polymorphisms), but not when PGRS was restricted to GWAS-level significant loci (18 single nucleotide polymorphisms).

CONCLUSIONS

Effects related to common genetic risk loci distributed throughout the genome are detectable among individuals without dementia. The influence of this genetic risk may begin in early life and make an individual more susceptible to cognitive impairment in late life. Future refinement of polygenic risk scores may help identify individuals at risk for AD dementia.

A Translational Pharmacology Approach to Predicting Outcomes of Preexposure Prophylaxis Against HIV in Men and Women Using Tenofovir Disoproxil Fumarate With or Without Emtricitabine

BACKGROUND

A novel translational pharmacology investigation was conducted by combining an in vitro efficacy target with mucosal tissue pharmacokinetic (PK) data and mathematical modeling to determine the number of doses required for effective human immunodeficiency virus (HIV) preexposure prophylaxis (PrEP).

METHODS

A PK/pharmacodynamic (PD) model was developed by measuring mucosal tissue concentrations of tenofovir, emtricitabine, their active metabolites (tenofovir diphosphate [TFVdp] and emtricitabine triphosphate [FTCtp], respectively), and competing endogenous nucleotides (dATP and dCTP) in 47 healthy women. TZM-bl and CD4(+) T cells were used to identify 90% effective concentration (EC90) ratios of TFVdp to dATP and FTCtp to dCTP (alone and in combination) for protection against HIV. Monte-Carlo simulations were then performed to identify minimally effective dosing strategies to protect lower female genital tract and colorectal tissues.

RESULTS

The colorectal TFVdp concentration was 10 times higher than that in the lower female genital tract, whereas concentrations of endogenous nucleotides were 7-11 times lower. Our model predicted that ≥98% of the population achieved protective mucosal tissue exposure by the third daily dose of tenofovir disoproxil fumarate plus emtricitabine. However, a minimum adherence to 6 of 7 doses/week (85%) was required to protect lower female genital tract tissue from HIV, while adherence to 2 of 7 doses/week (28%) was required to protect colorectal tissue.

CONCLUSIONS

This model is predictive of recent PrEP trial results in which 2-3 doses/week was 75%-90% effective in men but ineffective in women. These data provide a novel approach for future PrEP investigations that can optimize clinical trial dosing strategies.

Neurobiology of Alzheimer's Disease: Integrated Molecular, Physiological, Anatomical, Biomarker, and Cognitive Dimensions

Background: Alzheimer’s disease (AD), the most common form of dementia, is a progressive neurodegenerative disorder with interrelated molecular, physiological, anatomical, biomarker, and cognitive dimensions. Methods: This article reviews the biological changes (genetic, molecular, and cellular) underlying AD and their correlation with the clinical syndrome. Results: Dementia associated with AD is related to the aberrant production, processing, and clearance of beta-amyloid and tau. Beta-amyloid deposition in brain follows a distinct spatial progression starting in the basal neocortex, spreading throughout the hippocampus, and eventually spreading to the rest of the cortex. The spread of tau pathology through neural networks leads to a distinct and consistent spatial progression of neurofibrillary tangles, beginning in the transentorhinal and hippocampal region and spreading superolaterally to the primary areas of the neocortex. Synaptic dysfunction and cell death is shown by progressive loss of cerebral metabolic rate for glucose and progressive brain atrophy. Decreases in synapse number in the dentate gyrus of the hippocampus correlate with declining cognitive function. Amyloid changes are detectable in cerebrospinal fluid and with amyloid imaging up to 20 years prior to the onset of symptoms. Structural atrophy may be detectable via magnetic resonance imaging up to 10 years before clinical signs appear. Conclusion: This review highlights the progression of biological changes underlying AD and their association with the clinical syndrome. Many changes occur before overt symptoms are evident and biomarkers provide a means to detect AD pathology even in patients without symptoms.

Herpes Simplex Virus Type 1 and Other Pathogens are Key Causative Factors in Sporadic Alzheimer's Disease

This review focuses on research in epidemiology, neuropathology, molecular biology, and genetics regarding the hypothesis that pathogens interact with susceptibility genes and are causative in sporadic Alzheimer's disease (AD). Sporadic AD is a complex multifactorial neurodegenerative disease with evidence indicating coexisting multi-pathogen and inflammatory etiologies. There are significant associations between AD and various pathogens, including Herpes simplex virus type 1 (HSV-1), Cytomegalovirus, and other Herpesviridae, Chlamydophila pneumoniae, spirochetes, Helicobacter pylori, and various periodontal pathogens. These pathogens are able to evade destruction by the host immune system, leading to persistent infection. Bacterial and viral DNA and RNA and bacterial ligands increase the expression of pro-inflammatory molecules and activate the innate and adaptive immune systems. Evidence demonstrates that pathogens directly and indirectly induce AD pathology, including amyloid-β (Aβ) accumulation, phosphorylation of tau protein, neuronal injury, and apoptosis. Chronic brain infection with HSV-1, Chlamydophila pneumoniae, and spirochetes results in complex processes that interact to cause a vicious cycle of uncontrolled neuroinflammation and neurodegeneration. Infections such as Cytomegalovirus, Helicobacter pylori, and periodontal pathogens induce production of systemic pro-inflammatory cytokines that may cross the blood-brain barrier to promote neurodegeneration. Pathogen-induced inflammation and central nervous system accumulation of Aβ damages the blood-brain barrier, which contributes to the pathophysiology of AD. Apolipoprotein E4 (ApoE4) enhances brain infiltration by pathogens including HSV-1 and Chlamydophila pneumoniae. ApoE4 is also associated with an increased pro-inflammatory response by the immune system. Potential antimicrobial treatments for AD are discussed, including the rationale for antiviral and antibiotic clinical trials.

Influence of Allergy on Immunoglobulins and Amyloid-β in the Cerebrospinal Fluid of Patients with Alzheimer's Disease

BACKGROUND

Peripheral inflammation has been suggested to influence the development of Alzheimer's disease (AD). Elevated levels of pro-inflammatory markers in the plasma of patients with AD indicate that a systemic pro-inflammatory status occurs concomitantly with inflammatory changes in the brain.

OBJECTIVE

To investigate whether allergy influences the levels of immunoglobulins (Ig) and of pro- and anti-inflammatory cytokines in the serum and cerebrospinal fluid (CSF) from patients with AD, mild cognitive impairment (MCI), and subjective cognitive impairment (SCI).

METHODS

IgA, IgG, and its subclasses, IgM, and cytokines were analyzed in CSF and serum from patients with SCI, MCI, and AD, with or without allergy. The relation between allergy and Mini-Mental State Examination (MMSE) scores, and between allergy and CSF biomarkers for AD (phosphorylated (p)-tau, total (t)-tau, amyloid-β 42 (Aβ₄₂), were analyzed.

RESULTS

In MCI, the CSF levels of IgG2 were lower in allergic patients, and in AD, the levels of IgA and the IgG1/total IgG ratio were lower in allergic patients, compared to patients without allergy. MCI subjects with allergy had higher serum IgM levels compared to those without allergy. CSF levels of Aβ₄₂ were lower and MMSE scores were higher in AD patients with allergy than in those without allergy.

CONCLUSIONS

The presence of allergy was associated with seemingly beneficial effects on AD as suggested by higher Aβ₄₂ levels in CSF, and higher MMSE scores. Higher IgM levels and lower other Ig classes suggest that allergy may influence senescence of the immune response.

Pelargonidin improves memory deficit in amyloid β25-35 rat model of Alzheimer's disease by inhibition of glial activation, cholinesterase, and oxidative stress

Alzheimer's disease (AD) is a multifactorial disorder with devastating outcomes and few mostly palliative available therapeutic strategies. Pelargonidin (Pel), an anthocyanin compound, is an estrogen receptor agonist with lower side effects versus estrogen. This study examined neuroprotective effect of Pel on intrahippocampal amyloid β25-35 (Aβ) rat model of AD. Rats were divided into groups of sham, Aβ, and Pel-pretreated Aβ (10mg/kg; p.o.). Animals underwent Morris water maze (MWM) test in addition to measurement of hippocampal oxidative stress, acetylcholinesterase (AChE) activity, glial fibrillary acidic protein (GFAP) and inducible nitric oxide synthase (iNOS). Pel pretreatment of Aβ group significantly improved escape latency and distance swum in MWM versus Aβ group and attenuated hippocampal malondialdehyde (MDA) and increased catalase activity with no significant change of nitrite. Meanwhile, Pel improved hippocampal AChE activity and lowered GFAP level with no significant change of iNOS. Our results suggest that Pel could improve Aβ25-35-induced memory deficit through mitigation of oxidative stress, cholinergic dysfunction, and astrocyte reaction.

Changes in the Chemical Barrier Composition of Tears in Alzheimer's Disease Reveal Potential Tear Diagnostic Biomarkers

Alzheimer’s disease (AD) is one of the most common neurodegenerative diseases, with increasing prevalence affecting millions of people worldwide. Currently, only autopsy is able to confirm the diagnosis with a 100% certainty, therefore, biomarkers from body fluids obtained by non-invasive means provide an attractive alternative for the diagnosis of Alzheimer`s disease. Global changes of the protein profile were examined by quantitative proteomics; firstly, electrophoresis and LC-MS/MS were used, thereafter, SRM-based targeted proteomics method was developed and applied to examine quantitative changes of tear proteins. Alterations in the tear flow rate, total tear protein concentration and composition of the chemical barrier specific to AD were demonstrated, and the combination of lipocalin-1, dermcidin, lysozyme-C and lacritin was shown to be a potential biomarker, with an 81% sensitivity and 77% specificity.

A long-acting formulation of the integrase inhibitor raltegravir protects humanized BLT mice from repeated high-dose vaginal HIV challenges

OBJECTIVES

Pre-exposure prophylaxis (PrEP) using antiretroviral drugs (ARVs) has been shown to reduce HIV transmission in people at high risk of HIV infection. Adherence to PrEP strongly correlates with the level of HIV protection. Long-acting injectable ARVs provide sustained systemic drug exposures over many weeks and can improve adherence due to infrequent parenteral administration. Here, we evaluated a new long-acting formulation of raltegravir for prevention of vaginal HIV transmission.

METHODS

Long-acting raltegravir was administered subcutaneously to BALB/c, NSG (NOD-scid-gamma) and humanized BLT (bone marrow-liver-thymus) mice and rhesus macaques. Raltegravir concentration in peripheral blood and tissue was analysed. Suppression of HIV replication was assessed in infected BLT mice. Two high-dose HIV vaginal challenges were used to evaluate protection from HIV transmission in BLT mice.

RESULTS

Two weeks after a single subcutaneous injection of long-acting raltegravir in BLT mice (7.5 mg) and rhesus macaques (160 mg), the plasma concentration of raltegravir was comparable to 400 mg orally, twice daily in humans. Serum collected from mice 3 weeks post-administration of long-acting raltegravir efficiently blocked HIV infection of TZM-bl indicator cells in vitro. Administration of long-acting raltegravir suppressed viral RNA in plasma and cervico-vaginal fluids of infected BLT mice, demonstrating penetration of active raltegravir into the female reproductive tract. Using transmitted/founder HIV we observed that BLT mice administered a single subcutaneous dose of long-acting raltegravir were protected from two high-dose HIV vaginal challenges 1 week and 4 weeks after drug administration.

CONCLUSIONS

These preclinical results demonstrated the efficacy of long-acting raltegravir in preventing vaginal HIV transmission.

Complement and microglia mediate early synapse loss in Alzheimer mouse models

Synapse loss in Alzheimer's disease (AD) correlates with cognitive decline. Involvement of microglia and complement in AD has been attributed to neuroinflammation, prominent late in disease. Here we show in mouse models that complement and microglia mediate synaptic loss early in AD. C1q, the initiating protein of the classical complement cascade, is increased and associated with synapses before overt plaque deposition. Inhibition of C1q, C3, or the microglial complement receptor CR3 reduces the number of phagocytic microglia, as well as the extent of early synapse loss. C1q is necessary for the toxic effects of soluble β-amyloid (Aβ) oligomers on synapses and hippocampal long-term potentiation. Finally, microglia in adult brains engulf synaptic material in a CR3-dependent process when exposed to soluble Aβ oligomers. Together, these findings suggest that the complement-dependent pathway and microglia that prune excess synapses in development are inappropriately activated and mediate synapse loss in AD.

T-cell brain infiltration and immature antigen-presenting cells in transgenic models of Alzheimer's disease-like cerebral amyloidosis

Cerebral beta-amyloidosis, one of the pathological hallmarks of Alzheimer's disease (AD), elicits a well-characterised, microglia-mediated local innate immune response. In contrast, it is not clear whether cells of the adaptive immune system, in particular T-cells, react to cerebral amyloidosis in AD. Even though parenchymal T-cells have been described in post-mortem brains of AD patients, it is not known whether infiltrating T-cells are specifically recruited to the extracellular deposits of beta-amyloid, and whether they are locally activated into proliferating, effector cells upon interaction with antigen-presenting cells (APCs). To address these issues we have analysed by confocal microscopy and flow-cytometry the localisation and activation status of both T-cells and APCs in transgenic (tg) mice models of AD-like cerebral amyloidosis. Increased numbers of infiltrating T-cells were found in amyloid-burdened brain regions of tg mice, with concomitant up-regulation of endothelial adhesion molecules ICAM-1 and VCAM-1, compared to non-tg littermates. The infiltrating T-cells in tg brains did not co-localise with amyloid plaques, produced less interferon-gamma than those in controls and did not proliferate locally. Bona-fide dendritic cells were virtually absent from the brain parenchyma of both non-tg and tg mice, and APCs from tg brains showed an immature phenotype, with accumulation of MHC-II in intracellular compartments. These results indicate that cerebral amyloidosis promotes T-cell infiltration but interferes with local antigen presentation and T-cell activation. The inability of the brain immune surveillance to orchestrate a protective immune response to amyloid-beta peptide might contribute to the accumulation of amyloid in the progression of the disease.

High-resolution analytical imaging and electron holography of magnetite particles in amyloid cores of Alzheimer's disease

Abnormal accumulation of brain metals is a key feature of Alzheimer’s disease (AD). Formation of amyloid-β plaque cores (APC) is related to interactions with biometals, especially Fe, Cu and Zn, but their particular structural associations and roles remain unclear. Using an integrative set of advanced transmission electron microscopy (TEM) techniques, including spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM), nano-beam electron diffraction, electron holography and analytical spectroscopy techniques (EDX and EELS), we demonstrate that Fe in APC is present as iron oxide (Fe₃O₄) magnetite nanoparticles. Here we show that Fe was accumulated primarily as nanostructured particles within APC, whereas Cu and Zn were distributed through the amyloid fibers. Remarkably, these highly organized crystalline magnetite nanostructures directly bound into fibrillar Aβ showed characteristic superparamagnetic responses with saturated magnetization with circular contours, as observed for the first time by off-axis electron holography of nanometer scale particles.

Long-term association between the dietary inflammatory index and cognitive functioning: findings from the SU.VI.MAX study

PURPOSE

Inflammation is a ubiquitous underlying mechanism of the links between diet and cognitive functioning. No study has yet evaluated the overall inflammatory potential of the diet, using the dietary inflammatory index (DII), in relation to cognitive functioning. In a French cohort of middle-aged adults, we evaluated the association between the DII, assessed in midlife, and cognitive performance evaluated 13 years later.

METHODS

The DII is a literature-derived dietary index developed to determine the inflammatory potential of diet. The DII was estimated at baseline (1994-1996) among 3080 subjects of the SU.VI.MAX (supplementation with antioxidant vitamins and minerals) cohort. Cognitive performance was assessed in 2007-2009 via a battery of standardized neuropsychological tests. Principal component analysis was performed to extract a summary score of cognitive performance. Multivariable-adjusted linear regression analyses were performed to provide regression coefficients and 95 % confidence intervals (95 % CI).

RESULTS

In a multivariate model, a strong inverse association was observed between a higher DII (reflecting a more inflammatory diet) and overall cognitive functioning (mean difference Q4 vs. Q1 = -1.76; 95 % CI = -2.81, -0.72, P for trend =0.002). With regard to specific cognitive domains, similar associations were observed with scores reflecting verbal memory, but not executive functioning.

CONCLUSION

This study suggests that a pro-inflammatory diet at midlife might be associated with subsequent lower cognitive functioning. A diet exhibiting anti-inflammatory properties may help to maintain cognitive health during aging.

CLINICAL TRIAL REGISTRATION

Clinicaltrials.gov (number NCT00272428).

Sex hormones and adult hippocampal neurogenesis: Regulation, implications, and potential mechanisms

Neurogenesis within the adult hippocampus is modulated by endogenous and exogenous factors. Here, we review the role of sex hormones in the regulation of adult hippocampal neurogenesis in males and females. The review is framed around the potential functional implications of sex hormone regulation of adult hippocampal neurogenesis, with a focus on cognitive function and mood regulation, which may be related to sex differences in incidence and severity of dementia and depression. We present findings from preclinical studies of endogenous fluctuations in sex hormones relating to reproductive function and ageing, and from studies of exogenous hormone manipulations. In addition, we discuss the modulating roles of sex, age, and reproductive history on the relationship between sex hormones and neurogenesis. Because sex hormones have diverse targets in the central nervous system, we overview potential mechanisms through which sex hormones may influence hippocampal neurogenesis. Lastly, we advocate for a more systematic consideration of sex and sex hormones in studying the functional implications of adult hippocampal neurogenesis.

Immunotherapies in Alzheimer's disease: Too much, too little, too late or off-target?

Years of research have highlighted the importance of the immune system in Alzheimer's disease (AD), a system that, if manipulated during strategic time windows, could potentially be tackled to treat this disorder. However, to minimize adverse effects, it is essential to first grasp which exact aspect of it may be targeted. Several clues have been collected over the years regarding specific immune players strongly modulated during different stages of AD progression. However, the inherent complexity of the immune system as well as conflicting data make it quite challenging to pinpoint a specific immune target in AD. In this review, we discuss immune-related abnormalities observed in the periphery as well as in the brain of AD patients, in relation to known risk factors of AD such as genetics, type-2 diabetes or obesity, aging, physical inactivity and hypertension. Although not investigated yet in clinical trials, C5 complement system component, CD40/CD40L interactions and the CXCR2 pathway are altered in AD patients and may represent potential therapeutic targets. Immunotherapies tested in a clinical context, those aiming to attenuate the innate immune response and those used to facilitate the removal of pathological proteins, are further discussed to try and understand the causes of the limited success reached. The prevailing eagerness to move basic research data to clinic should not overshadow the fact that a careful preclinical characterization of a drug is still required to ultimately improve the chance of clinical success. Finally, specific elements to consider prior to initiate large-scale trials are highlighted and include the replication of preclinical data, the use of small-scale human studies, the sub-typing of AD patients and the determination of pharmacokinetic and pharmacodynamics parameters such as brain bioavailability and target engagement.

Analysis of the Putative Role of CR1 in Alzheimer's Disease: Genetic Association, Expression and Function

Chronic activation of the complement system and induced inflammation are associated with neuropathology in Alzheimer’s disease (AD). Recent large genome wide association studies (GWAS) have identified single nucleotide polymorphisms (SNPs) in the C3b/C4b receptor (CR1 or CD35) that are associated with late onset AD. Here, anti-CR1 antibodies (Abs) directed against different epitopes of the receptor, were used to localize CR1 in brain, and relative binding affinities of the CR1 ligands, C1q and C3b, were assessed by ELISA. Most Abs tested stained red blood cells in blood vessels but showed no staining in brain parenchyma. However, two monoclonal anti-CR1 Abs labeled astrocytes in all of the cases tested, and this reactivity was preabsorbed by purified recombinant human CR1. Human brain-derived astrocyte cultures were also reactive with both mAbs. The amount of astrocyte staining varied among the samples, but no consistent difference was conferred by diagnosis or the GWAS-identified SNPs rs4844609 or rs6656401. Plasma levels of soluble CR1 did not correlate with diagnosis but a slight increase was observed with rs4844609 and rs6656401 SNP. There was also a modest but statistically significant increase in relative binding activity of C1q to CR1 with the rs4844609 SNP compared to CR1 without the SNP, and of C3b to CR1 in the CR1 genotypes containing the rs6656401 SNP (also associated with the larger isoform of CR1) regardless of clinical diagnosis. These results suggest that it is unlikely that astrocyte CR1 expression levels or C1q or C3b binding activity are the cause of the GWAS identified association of CR1 variants with AD. Further careful functional studies are needed to determine if the variant-dictated number of CR1 expressed on red blood cells contributes to the role of this receptor in the progression of AD, or if another mechanism is involved.

The adaptive immune system restrains Alzheimer's disease pathogenesis by modulating microglial function

The innate immune system is strongly implicated in the pathogenesis of Alzheimer's disease (AD). In contrast, the role of adaptive immunity in AD remains largely unknown. However, numerous clinical trials are testing vaccination strategies for AD, suggesting that T and B cells play a pivotal role in this disease. To test the hypothesis that adaptive immunity influences AD pathogenesis, we generated an immune-deficient AD mouse model that lacks T, B, and natural killer (NK) cells. The resulting "Rag-5xfAD" mice exhibit a greater than twofold increase in β-amyloid (Aβ) pathology. Gene expression analysis of the brain implicates altered innate and adaptive immune pathways, including changes in cytokine/chemokine signaling and decreased Ig-mediated processes. Neuroinflammation is also greatly exacerbated in Rag-5xfAD mice as indicated by a shift in microglial phenotype, increased cytokine production, and reduced phagocytic capacity. In contrast, immune-intact 5xfAD mice exhibit elevated levels of nonamyloid reactive IgGs in association with microglia, and treatment of Rag-5xfAD mice or microglial cells with preimmune IgG enhances Aβ clearance. Last, we performed bone marrow transplantation studies in Rag-5xfAD mice, revealing that replacement of these missing adaptive immune populations can dramatically reduce AD pathology. Taken together, these data strongly suggest that adaptive immune cell populations play an important role in restraining AD pathology. In contrast, depletion of B cells and their appropriate activation by T cells leads to a loss of adaptive-innate immunity cross talk and accelerated disease progression.

Signaling pathways regulating neuron-glia interaction and their implications in Alzheimer's disease

Astrocytes are the most abundant cells in the central nervous system. They play critical roles in neuronal homeostasis through their physical properties and neuron-glia signaling pathways. Astrocytes become reactive in response to neuronal injury and this process, referred to as reactive astrogliosis, is a common feature accompanying neurodegenerative conditions, particularly Alzheimer's disease. Reactive astrogliosis represents a continuum of pathobiological processes and is associated with morphological, functional, and gene expression changes of varying degrees. There has been a substantial growth of knowledge regarding the signaling pathways regulating glial biology and pathophysiology in recent years. Here, we attempt to provide an unbiased review of some of the well-known players, namely calcium, proteoglycan, transforming growth factor β, NFκB, and complement, in mediating neuron-glia interaction under physiological conditions as well as in Alzheimer's disease. This review discusses the role of astrocytic NFκB and calcium as well as astroglial secreted factors, including proteoglycans, TGFβ, and complement in mediating neuronal function and AD pathogenesis through direct interaction with neurons and through cooperation with microglia.

Identification of Vulnerable Cell Types in Major Brain Disorders Using Single Cell Transcriptomes and Expression Weighted Cell Type Enrichment

The cell types that trigger the primary pathology in many brain diseases remain largely unknown. One route to understanding the primary pathological cell type for a particular disease is to identify the cells expressing susceptibility genes. Although this is straightforward for monogenic conditions where the causative mutation may alter expression of a cell type specific marker, methods are required for the common polygenic disorders. We developed the Expression Weighted Cell Type Enrichment (EWCE) method that uses single cell transcriptomes to generate the probability distribution associated with a gene list having an average level of expression within a cell type. Following validation, we applied EWCE to human genetic data from cases of epilepsy, Schizophrenia, Autism, Intellectual Disability, Alzheimer's disease, Multiple Sclerosis and anxiety disorders. Genetic susceptibility primarily affected microglia in Alzheimer's and Multiple Sclerosis; was shared between interneurons and pyramidal neurons in Autism and Schizophrenia; while intellectual disabilities and epilepsy were attributable to a range of cell-types, with the strongest enrichment in interneurons. We hypothesized that the primary cell type pathology could trigger secondary changes in other cell types and these could be detected by applying EWCE to transcriptome data from diseased tissue. In Autism, Schizophrenia and Alzheimer's disease we find evidence of pathological changes in all of the major brain cell types. These findings give novel insight into the cellular origins and progression in common brain disorders. The methods can be applied to any tissue and disorder and have applications in validating mouse models.

Identification of Vulnerable Cell Types in Major Brain Disorders Using Single Cell Transcriptomes and Expression Weighted Cell Type Enrichment

The cell types that trigger the primary pathology in many brain diseases remain largely unknown. One route to understanding the primary pathological cell type for a particular disease is to identify the cells expressing susceptibility genes. Although this is straightforward for monogenic conditions where the causative mutation may alter expression of a cell type specific marker, methods are required for the common polygenic disorders. We developed the Expression Weighted Cell Type Enrichment (EWCE) method that uses single cell transcriptomes to generate the probability distribution associated with a gene list having an average level of expression within a cell type. Following validation, we applied EWCE to human genetic data from cases of epilepsy, Schizophrenia, Autism, Intellectual Disability, Alzheimer's disease, Multiple Sclerosis and anxiety disorders. Genetic susceptibility primarily affected microglia in Alzheimer's and Multiple Sclerosis; was shared between interneurons and pyramidal neurons in Autism and Schizophrenia; while intellectual disabilities and epilepsy were attributable to a range of cell-types, with the strongest enrichment in interneurons. We hypothesized that the primary cell type pathology could trigger secondary changes in other cell types and these could be detected by applying EWCE to transcriptome data from diseased tissue. In Autism, Schizophrenia and Alzheimer's disease we find evidence of pathological changes in all of the major brain cell types. These findings give novel insight into the cellular origins and progression in common brain disorders. The methods can be applied to any tissue and disorder and have applications in validating mouse models.

Magnetic Resonance Spectroscopy discriminates the response to microglial stimulation of wild type and Alzheimer's disease models

Microglia activation has emerged as a potential key factor in the pathogenesis of Alzheimer’s disease. Metabolite levels assessed by magnetic resonance spectroscopy (MRS) are used as markers of neuroinflammation in neurodegenerative diseases, but how they relate to microglial activation in health and chronic disease is incompletely understood. Using MRS, we monitored the brain metabolic response to lipopolysaccharides (LPS)-induced microglia activation in vivo in a transgenic mouse model of Alzheimer’s disease (APP/PS1) and healthy controls (wild-type (WT) littermates) over 4 hours. We assessed reactive gliosis by immunohistochemistry and correlated metabolic and histological measures. In WT mice, LPS induced a microglial phenotype consistent with activation, associated with a sustained increase in macromolecule and lipid levels (ML9). This effect was not seen in APP/PS1 mice, where LPS did not lead to a microglial response measured by histology, but induced a late increase in the putative inflammation marker myoinositol (mI) and metabolic changes in total creatine and taurine previously reported to be associated with amyloid load. We argue that ML9 and mI distinguish the response of WT and APP/PS1 mice to immune mediators. Lipid and macromolecule levels may represent a biomarker of activation of healthy microglia, while mI may not be a glial marker.