Microbes and Alzheimer's Disease

A Bacterial Component to Alzheimer's-Type Dementia Seen via a Systems Biology Approach that Links Iron Dysregulation and Inflammagen Shedding to Disease

The progression of Alzheimer's disease (AD) is accompanied by a great many observable changes, both molecular and physiological. These include oxidative stress, neuroinflammation, and (more proximal to cognitive decline) the death of neuronal and other cells. A systems biology approach seeks to organize these observed variables into pathways that discriminate those that are highly involved (i.e., causative) from those that are more usefully recognized as bystander effects. We review the evidence that iron dysregulation is one of the central causative pathway elements here, as this can cause each of the above effects. In addition, we review the evidence that dormant, non-growing bacteria are a crucial feature of AD, that their growth in vivo is normally limited by a lack of free iron, and that it is this iron dysregulation that is an important factor in their resuscitation. Indeed, bacterial cells can be observed by ultrastructural microscopy in the blood of AD patients. A consequence of this is that the growing cells can shed highly inflammatory components such as lipopolysaccharides (LPS). These too are known to be able to induce (apoptotic and pyroptotic) neuronal cell death. There is also evidence that these systems interact with elements of vitamin D metabolism. This integrative systems approach has strong predictive power, indicating (as has indeed been shown) that both natural and pharmaceutical iron chelators might have useful protective roles in arresting cognitive decline, and that a further assessment of the role of microbes in AD development is more than highly warranted.

Inflammasome Involvement in Alzheimer's Disease

Inflammasomes are responsible for the maturation of pro-inflammatory cytokines such as interleukin (IL)-1β, IL-18, and IL-33 and activation of inflammatory cell death, pyroptosis. They assemble in response to cellular infection and stress or to tissue damage, promote inflammatory reactions, and are important in regulating innate immunity particularly by acting as platforms for activation of caspase proteases. They appear to be involved in several pathological processes activated by microbes including Alzheimer's disease (AD). Best characterized in microbial pathogenesis is the nucleotide-binding domain and leucine-rich repeat (NLR)-protein 3 (NLRP3) inflammasome. AD is a neurodegenerative condition in which the neuropathological hallmarks are the deposition of amyloid-β (Aβ) and hyperphosphorylated tau protein coated neurofibrillary tangles. For decades, the role of the innate immune system in the etiology of AD was considered less important, but the recently discovered inflammatory genes by genome-wide association studies driving inflammation in this disease has changed this view. Innate immune inflammatory activity in the AD brain can result from the pathological hallmark protein Aβ as well as from specific bacterial infections that tend to possess weak immunostimulatory responses for peripheral blood myeloid cell recruitment to the brain. The weak immunostimulatory activity is a consequence of their immune evasion strategies and survival. In this review we discuss the possibility that inflammasomes, particularly via the NLR family of proteins NLRP3 are involved in the pathogenesis of AD. In addition, we discuss the plausible contribution of specific bacteria playing a role in influencing the activity of the NLRP3 inflammasome to AD progression.

Homocysteine, Infections, Polyamines, Oxidative Metabolism, and the Pathogenesis of Dementia and Atherosclerosis

Hyperhomocysteinemia is a risk factor for development of dementia and Alzheimer's disease (AD), and low blood levels of folate and cobalamin are associated with hyperhomocysteinemia and AD. In elderly subjects with cognitive decline, supplementation with folate, cobalamin, and pyridoxal demonstrated reduction of cerebral atrophy in gray matter regions vulnerable to the AD process. Multiple pathogenic microbes are implicated as pathogenic factors in AD and atherosclerosis, and the deposition of amyloid-β (Aβ), phosphorylation of tau protein, neuronal injury, and apoptosis in AD are secondary to microbial infection. Glucose utilization and blood flow are reduced in AD, and these changes are accompanied by downregulation of glucose transport, Na, K-ATPase, oxidative phosphorylation, and energy consumption. Thioretinaco ozonide, the complex formed from thioretinamide, cobalamin, ozone, and oxygen is proposed to constitute the active site of oxidative phosphorylation, catalyzing synthesis of adenosine triphosphate (ATP) from nicotinamide adenine dinucleotide (NAD+) and phosphate. Pathogenic microbes cause synthesis of polyamines in host cells by increasing the transfer of aminopropyl groups from adenosyl methionine to putrescine, resulting in depletion of intracellular adenosyl methionine concentrations in host cells. Depletion of adenosyl methionine causes dysregulation of methionine metabolism, hyperhomocysteinemia, reduced biosynthesis of thioretinamide and thioretinaco ozonide, decreased oxidative phosphorylation, decreased production of nitric oxide and peroxynitrite, and impaired host response to infectious microbes, contributing to the pathogenesis of dementia and atherosclerosis.

Inhibition of cyclin-dependent kinase 5 affects early neuroinflammatory signalling in murine model of amyloid beta toxicity

BACKGROUND

Cyclin-dependent kinase 5 (Cdk5) belongs to the family of proline-directed serine/threonine kinases and plays a critical role in neuronal differentiation, migration, synaptogenesis, plasticity, neurotransmission and apoptosis. The deregulation of Cdk5 activity was observed in post mortem analysis of brain tissue of Alzheimer's disease (AD) patients, suggesting the involvement of Cdk5 in the pathomechanism of this neurodegenerative disease. However, our recent study demonstrated the important function of Cdk5 in regulating inflammatory reaction.

METHODS

Since the role of Cdk5 in regulation of inflammatory signalling in AD is unknown, we investigated the involvement of Cdk5 in neuroinflammation induced by single intracerebroventricular (icv) injection of amyloid beta protein (Aβ) oligomers in mouse. The brain tissue was analysed up to 35 days post injection. Roscovitine (intraperitoneal administration) was used as a potent Cdk5 inhibitor. The experiments were also performed on human neuroblastoma SH-SY5Y as well as mouse BV2 cell lines treated with exogenous oligomeric Aβ.

RESULTS

Our results demonstrated that single injection of Aβ oligomers induces long-lasting activation of microglia and astrocytes in the hippocampus. We observed also profound, early inflammatory response in the mice hippocampus, leading to the significant elevation of pro-inflammatory cytokines expression (e.g. TNF-α, IL-1β, IL-6). Moreover, Aβ oligomers elevated the formation of truncated protein p25 in mouse hippocampus and induced overactivation of Cdk5 in neuronal cells. Importantly, administration of roscovitine reduced the inflammatory processes evoked by Aβ in the hippocampus, leading to the significant decrease of cytokines level.

CONCLUSIONS

These studies clearly show the involvement of Cdk5 in modulation of brain inflammatory response induced by Aβ and may indicate this kinase as a novel target for pharmacological intervention in AD.

Development, Application, and Results from a Precision-medicine Platform that Personalizes Multi-modal Treatment Plans for Mild Alzheimer's Disease and At-risk Individuals

INTRODUCTION

Alzheimer's Disease (AD) is a progressive neurodegenerative condition in which individuals exhibit memory loss, dementia, and impaired metabolism. Nearly all previous single-treatment studies to treat AD have failed, likely because it is a complex disease with multiple underlying drivers contributing to risk, onset, and progression. Here, we explored the efficacy of a multi-therapy approach based on the disease risk factor status specific to individuals with AD diagnosis or concern.

METHODS

Novel software from uMETHOD Health was designed to execute a precision-medicinebased approach to develop personalized treatment recommendations with the goal of slowing or reversing biologic drivers of AD. AD-associated inputs encompassed genomic data, bio-specimen measurements, imaging data (such as MRIs or PET scans), medical histories, medications, allergies, co-morbidities, relevant lifestyle factors, and results of neuropsychological testing. Algorithms were then employed to prioritize physiologic and lifestyle states with the highest probability of contributing to disease status, and these priorities were incorporated into a personalized care plan, which was delivered to physicians and supported by health coaches to increase adherence. The sample included 40 subjects with Subjective Cognitive Decline patients (SCD), and Mild Cognitive Impairment Patients (MCI).

RESULTS

Software analysis was completed for 40 individuals. They remained on their treatment plan for an average of 8.4 months, equal to 2.8 iterations of care plans. 80% of individuals overall showed improved memory function scores or held steady, as measured by standardized cognitive evaluations. Cognitive assessments showed significant improvement in the SCD group (Composite P value .002, Executive P value .01), and the CNS-VS Executive domain showed significant results in the combined group as well (P value .01). There was also biomarker improvement over time observed from the blood panels. 8 out of 12 selected biomarkers showed slight, though statistically non-significant, improvement overall for symptomatic individuals, and 6 out of 12 for the overall population. Only one biomarker, homocysteine, showed significant improvement, though (P values .03, .04, .002).

CONCLUSIONS

Our analysis of these individuals lead to several interesting observations together suggesting that AD risk factors comprise a network of interlocking feedback loops that may be modifiable. Our findings indicate previously unidentified connectivity between AD risk factors, suggesting that treatment regimens should be tailored to the individual and multi-modal to simultaneously return several risk factors to a normative state. If successfully performed, the possibility to slow progression of AD and possibly reverse aspects of cognitive decline may become achievable.

Positive Feedback Loops in Alzheimer's Disease: The Alzheimer's Feedback Hypothesis

The dominant model for Alzheimer's disease (AD) is the amyloid cascade hypothesis, in which the accumulation of excess amyloid-β (Aβ) leads to inflammation, excess glutamate and intracellular calcium, oxidative stress, tau hyperphosphorylation and tangle formation, neuronal loss, and ultimately dementia. In a cascade, AD proceeds in a unidirectional fashion, with events only affecting downstream processes. Compelling evidence now exists for the presence of positive feedback loops in AD, however, involving oxidative stress, inflammation, glutamate, calcium, and tau. The pathological state of AD is thus a system of positive feedback loops, leading to amplification of the initial perturbation, rather than a linear cascade. Drugs may therefore be effective by targeting numerous points within the loops, rather than concentrating on upstream processes. Anti-inflammatories and anti-oxidants may be especially valuable, since these processes are involved in many loops and hence would affect numerous processes in AD.

Ivan Illich's Medical Nemesis and the 'age of the show': On the Expropriation of Death

What Ivan Illich regarded in his Medical Nemesis as the 'expropriation of health' takes place on the surfaces and in the spaces of the screens all around us, including our cell phones but also the patient monitors and (increasingly) the iPads that intervene between nurse and patient. To explore what Illich called the 'age of the show', this essay uses film examples, like Creed and the controversial documentary Vaxxed, and the television series Nurse Jackie. Rocky's cancer in his last film (submitting to chemo to 'fight' cancer) highlights what Illich along with Petr Skrabanek called the 'expropriation of death'. In contrast to what Illich denotes as 'Umsonstigkeit' - grace or gift, given undeservedly, i.e., gratuitously - medical science tends to be tempted by what Illich terms scientistic 'black magic', taking over (expropriating) the life and the death of the patient in increasingly technological ways, a point underscored in the concluding section on the commercial prospects of xenotransplants using factory farm or mass-produced human-pig mosaics or chimeras.

Enhanced expressions of neurodegeneration-associated factors, UPS impairment, and excess Aβ accumulation in the hippocampus of mice with persistent cerebral toxocariasis

BACKGROUND

Toxocariasis is a worldwide zoonotic parasitic disease mainly caused by Toxocara canis. Humans can be infected by accidental ingestion of T. canis embryonated ovum-contaminated food, water, or encapsulated larvae in paratenic hosts' viscera or meat. Since humans and mice are paratenic hosts of T. canis, the wandering larvae might cause mechanical tissue damage and excretory-secretory antigens may trigger inflammatory injuries to local organs. Long-term residence of T. canis larvae in a paratenic host's brain may cause cerebral toxocariasis (CT) that contributes to cerebral damage, neuroinflammation and neuropsychiatric disorders in mice and clinical patients. Since the hippocampus has been long recognized as being responsible for learning and memory functions, parasitic invasion of this site may cause neuroinflammatory and neurodegenerative disorders. The present study intended to assess pathological changes, expressions of neurodegeneration-associated factors (NDAFs), including transforming growth factor (TGF)-β1, S100B, glial fibrillary acidic protein (GFAP), transglutaminase type 2 (TG2), claudin-5, substance P (SP) and interleukin (IL)-1β, and the ubiquitin-proteasome system (UPS) function in the hippocampus and associated cognitive behavior in ICR mice orally inoculated with a high, medium or low-dose of T. canis embryonated ova during a 20-week investigation.

RESULTS

Results indicated although there were insignificant differences in learning and memory function between the experimental mice and uninfected control mice, possibly because the site where T. canis larvae invaded was the surrounding area but not the hippocampus per se. Nevertheless, enhanced expressions of NDAF, persistent UPS impairment and excess amyloid β (Aβ) accumulation concomitantly emerged in the experimental mice hippocampus at 8, 16 and 20 weeks post-infection.

CONCLUSIONS

We thus postulate that progressive CT may still progress to neurodegeneration due to enhanced NDAF expressions, persistent UPS impairment and excess Aβ accumulation in the hippocampus.

Role of the peripheral innate immune system in the development of Alzheimer's disease

Alzheimer's disease is one of the most devastating neurodegenerative diseases. The exact cause of the disease is still not known although many scientists believe in the beta amyloid hypothesis which states that the accumulation of the amyloid peptide beta (Aβ) in brain is the initial cause which consequently leads to pathological neuroinflammation. However, it was recently shown that Aβ may have an important role in defending the brain against infections. Thus, the balance between positive and negative impact of Aβ may determine disease progression. Microglia in the brain are innate immune cells, and brain-initiated inflammatory responses reflected in the periphery suggests that Alzheimer's disease is to some extent also a systemic inflammatory disease. Greater permeability of the blood brain barrier facilitates the transport of peripheral immune cells to the brain and vice versa so that a vicious circle originating on the periphery may contribute to the development of overt clinical AD. Persistent inflammatory challenges by pathogens in the periphery, increasing with age, may also contribute to the central propagation of the pathological changes seen clinically. Therefore, the activation status of peripheral innate immune cells may represent an early biomarker of the upcoming impact on the brain. The modulation of these cells may thus become a useful mechanism for modifying disease progression.

Prion Protein PRNP: A New Player in Innate Immunity? The Aβ Connection

The prion protein PRNP has been centrally implicated in the transmissible spongiform encephalopathies (TSEs), but its normal physiological role remains obscure. We highlight emerging evidence that PRNP displays antimicrobial activity, inhibiting the replication of multiple viruses, and also interacts directly with Alzheimer's disease (AD) amyloid-β (Aβ) peptide whose own antimicrobial role is now increasingly secure. PRNP and Aβ share share membrane-penetrating, nucleic acid binding, and antiviral properties with classical antimicrobial peptides such as LL-37. We discuss findings that binding of abnormal nucleic acids to PRNP leads to oligomerization of the protein, and suggest that this may be an entrapment and sequestration process that contributes to its antimicrobial activity. Some antimicrobial peptides are known to be exploited by infectious agents, and we cover evidence that PRNP is usurped by herpes simplex virus (HSV-1) that has evolved a virus-encoded 'anti-PRNP'.unction. These findings suggest that PRNP, like LL-37 and Aβ, is likely to be a component of the innate immune system, with implications for the pathoetiology of both AD and TSE.

The Porphyromonas gingivalis/Host Interactome Shows Enrichment in GWASdb Genes Related to Alzheimer's Disease, Diabetes and Cardiovascular Diseases

Periodontal disease is of established etiology in which polymicrobial synergistic ecology has become dysbiotic under the influence of Porphyromonas gingivalis. Following breakdown of the host's protective oral tissue barriers, P. gingivalis migrates to developing inflammatory pathologies that associate with Alzheimer's disease (AD). Periodontal disease is a risk factor for cardiovascular disorders (CVD), type II diabetes mellitus (T2DM), AD and other chronic diseases, whilst T2DM exacerbates periodontitis. This study analyzed the relationship between the P. gingivalis/host interactome and the genes identified in genome-wide association studies (GWAS) for the aforementioned conditions using data from GWASdb (P < 1E-03) and, in some cases, from the NCBI/EBI GWAS database (P < 1E-05). Gene expression data from periodontitis or P. gingivalis microarray was compared to microarray datasets from the AD hippocampus and/or from carotid artery plaques. The results demonstrated that the host genes of the P. gingivalis interactome were significantly enriched in genes deposited in GWASdb genes related to cognitive disorders, AD and dementia, and its co-morbid conditions T2DM, obesity, and CVD. The P. gingivalis/host interactome was also enriched in GWAS genes from the more stringent NCBI-EBI database for AD, atherosclerosis and T2DM. The misregulated genes in periodontitis tissue or P. gingivalis infected macrophages also matched those in the AD hippocampus or atherosclerotic plaques. Together, these data suggest important gene/environment interactions between P. gingivalis and susceptibility genes or gene expression changes in conditions where periodontal disease is a contributory factor.

Alzheimer's disease and gut microbiota modifications: The long way between preclinical studies and clinical evidence

Recent studies have suggested the role of an infectious component in the pathogenesis of Alzheimer's disease (AD). In light of this, research has focused on some bacteria constituting the intestinal microbial flora which can produce amyloid. Once generated, the latter hypothetically triggers a systemic inflammatory response which compromises complex brain functions, such as learning and memory. Clinical studies have shown that, in cognitively impaired elderly patients with brain amyloidosis, there is lower abundance in the gut of E. rectale and B. fragilis, two bacterial species which have an anti-inflammatory activity, versus a greater amount of pro-inflammatory genera such as Escherichia/Shigella. According to these findings, some clinical studies have demonstrated that supplementation with Lactobacilli- and Bifidobacteria- based probiotics has improved cognitive, sensory and emotional functions in subjects with AD. Moreover, certain herbal products, in particular dietetic polyphenols, have proved capable of restoring dysbiosis and, therefore, their prebiotic role could be effective in counteracting the onset of AD regardless of their activity of free radical scavenging or enhancement of the cell stress response. One of the recent greatest novelties in the field of neurodegenerative diseases is the chance to prevent or slow down AD progression with agents, such as probiotics and prebiotics, acting outside the central nervous system.

Immune and Imaging Correlates of Mild Cognitive Impairment Conversion to Alzheimer's Disease

Amnestic mild cognitive impairment (aMCI) conversion to Alzheimer’s disease (AD) is seen in a sizable portion of aMCI patients; correlates predicting such conversion are poorly defined but neuroinflammation and the reactivation of chronic viral infections are suspected to play a role in this phenomenon. We analyzed these aspects in two homogeneous groups of aMCI who did or did not convert to AD over a 24-months period. Results showed that at baseline in those aMCI individuals who did not convert to AD: 1) Aβ_1-42 stimulated production of the pro-inflammatory cytokines IL6 and IL1β by CD14⁺ cells was significantly reduced (p = 0.01), 2) CD14⁺/IL-33⁺ cells were increased (p = 0.0004); 3) MFI of TLR8 and TLR9 was significantly increased, and 4) better preserved hippocampus volumes were observed and correlated with IL33⁺/CD14⁺ cells. Notably, Aβ_1-42 stimulated production of the antiviral cytokine IFN-λ was increased as well in non-AD converters, although with a borderline statistical significance (p = 0.05). Data herein indicating that proinflammatory cytokines are reduced, whereas IFN-λ production and TLR8 and 9 MFI are augmented in those aMCI in whom AD conversion is not observed suggest that the ability to mount stronger antiviral response within an antiiflammatory milieu associates with lack of AD conversion.

Hypothesis for the cause and therapy of neurodegenerative diseases

The cause and therapy of neurodegenerative diseases remain unsolved puzzles. These diseases are correlated with presence of beta sheet-rich amyloid assemblies. Here, I derive and assemble puzzle pieces to obtain a loose end-tying hypothesis for cause with direct implications for therapy. I use the following extrapolations to find connectable puzzle pieces: (a) the traditional extrapolation that amyloid/amyloid precursors cause disease, (b) a recent extrapolation that amyloid-forming proteins, some of which are virus protein homologs, are components of an empirically obscure innate immune system that counters insults, including those by both viruses and bacteria, (c) a new extrapolation that various insults produce assemblies with structural features in common and that amyloid-forming, innate immune system proteins recognize these features and, then, counter insults by co-assembly, (d, 1) a second new extrapolation that beta sheet is a common structural feature and is extended during insult-neutralizing co-assembly and (d, 2) an appendix, derived from studies of phages T3 and T4, that most insult-produced assemblies are obscure to current biochemical analysis. The hypothesis is the following. One function of amyloid-forming proteins is non-classical innate immunity to biological insults. This immunity works via beta sheet-extending co-assembly of amyloid-forming proteins with beta sheet-containing insult products. For example, co-assembly with beta sheet-containing viral assembly intermediates inhibits virus production. Amyloid-forming proteins cause neurodegenerative disease when errant, typically overproduced. Other innate immunity systems sometimes exacerbate symptoms. This hypothesis suggests the following therapy, based on manipulating Nature's chemistry. First, conduct directed evolution to obtain low-pathogenicity, chronic symptom-producing viruses with assembly intermediates that co-assemble with and destabilize both amyloid and amyloid sub-assemblies. Then, infect patients with these viruses.

Substantial fibrin amyloidogenesis in type 2 diabetes assessed using amyloid-selective fluorescent stains

BACKGROUND

We have previously shown that many chronic, inflammatory diseases are accompanied, and possibly partly caused or exacerbated, by various coagulopathies, manifested as anomalous clots in the form of 'dense matted deposits'. More recently, we have shown that these clots can be amyloid in nature, and that the plasma of healthy controls can be induced to form such clots by the addition of tiny amounts of bacterial lipopolysaccharide or lipoteichoic acid. Type 2 diabetes (T2D) is also accompanied by raised levels of LPS.

METHODS

We use superresolution and confocal microscopies to investigate the amyloid nature of clots from healthy and T2D individuals.

RESULTS

We show here, with the established stain thioflavin T and the novel stains Amytracker™ 480 and 680, that the clotting of plasma from type 2 diabetics is also amyloid in nature, and that this may be prevented by the addition of suitable concentrations of LPS-binding protein.

CONCLUSION

This implies strongly that there is indeed a microbial component to the development of type 2 diabetes, and suggests that LBP might be used as treatment for it and its sequelae.

Laser-captured microglia in the Alzheimer's and Parkinson's brain reveal unique regional expression profiles and suggest a potential role for hepatitis B in the Alzheimer's brain

Expression array data from dozens of laboratories, including our own, show significant changes in expression of many genes in Alzheimer's disease (AD) patients compared with normal controls. These data typically rely on brain homogenates, and information about transcripts specific to microglia and other central nervous system (CNS) cell types, which far outnumber microglia-specific transcripts, is lost. We therefore used single-cell laser capture methods to assess the full range of microglia-specific expression changes that occur in different brain regions (substantia nigra and hippocampus CA1) and disease states (AD, Parkinson's disease, and normal controls). Two novel pathways, neuronal repair and viral processing were identified. Based on KEGG analysis (Kyoto Encyclopedia of Genes and Genomes, a collection of biological pathways), one of the most significant viruses was hepatitis B virus (HBV) (false discovery rate < 0.00000001). Immunohistochemical analysis using HBV-core antibody in HBV-positive control, amnestic mild cognitive impairment, and HBV-positive AD cases show increased HBV immunoreactivity as disease pathology increases. These results are the first, to our knowledge, to show regional differences in human microglia. In addition, these data reveal new functions for microglia and suggest a novel risk factor for AD.

Periodontitis, Microbiomes and their Role in Alzheimer's Disease

As far back as the eighteenth and early nineteenth centuries, microbial infections were responsible for vast numbers of deaths. The trend reversed with the introduction of antibiotics coinciding with longer life. Increased life expectancy however, accompanied the emergence of age related chronic inflammatory states including the sporadic form of Alzheimer's disease (AD). Taken together, the true challenge of retaining health into later years of life now appears to lie in delaying and/or preventing the progression of chronic inflammatory diseases, through identifying and influencing modifiable risk factors. Diverse pathogens, including periodontal bacteria have been associated with AD brains. Amyloid-beta (Aβ) hallmark protein of AD may be a consequence of infection, called upon due to its antimicrobial properties. Up to this moment in time, a lack of understanding and knowledge of a microbiome associated with AD brain has ensured that the role pathogens may play in this neurodegenerative disease remains unresolved. The oral microbiome embraces a range of diverse bacterial phylotypes, which especially in vulnerable individuals, will excite and perpetuate a range of inflammatory conditions, to a wide range of extra-oral body tissues and organs specific to their developing pathophysiology, including the brain. This offers the tantalizing opportunity that by controlling the oral-specific microbiome; clinicians may treat or prevent a range of chronic inflammatory diseases orally. Evolution has equipped the human host to combat infection/disease by providing an immune system, but Porphyromonas gingivalis and selective spirochetes, have developed immune avoidance strategies threatening the host-microbe homeostasis. It is clear from longitudinal monitoring of patients that chronic periodontitis contributes to declining cognition. The aim here is to discuss the contribution from opportunistic pathogens of the periodontal microbiome, and highlight the challenges, the host faces, when dealing with unresolvable oral infections that may lead to clinical manifestations that are characteristic for AD.

Microbiota-Brain-Gut Axis and Neurodegenerative Diseases

PURPOSE OF REVIEW

The purposes of this review were as follows: first, to provide an overview of the gut microbiota and its interactions with the gut and the central nervous system (the microbiota-gut-brain axis) in health, second, to review the relevance of this axis to the pathogenesis of neurodegenerative diseases, such as Parkinson's disease, and, finally, to assess the potential for microbiota-targeted therapies.

RECENT FINDINGS

Work on animal models has established the microbiota-gut-brain axis as a real phenomenon; to date, the evidence for its operation in man has been limited and has been confronted by considerable logistical challenges. Animal and translational models have incriminated a disturbed gut microbiota in a number of CNS disorders, including Parkinson's disease; data from human studies is scanty. While a theoretical basis can be developed for the use of microbiota-directed therapies in neurodegenerative disorders, support is yet to come from high-quality clinical trials. In theory, a role for the microbiota-gut-brain axis is highly plausible; clinical confirmation is awaited.

Cholesterol Changes the Mechanisms of Aβ Peptide Binding to the DMPC Bilayer

Using isobaric-isothermal all-atom replica-exchange molecular dynamics (REMD) simulations, we investigated the equilibrium binding of Aβ10-40 monomers to the zwitterionic dimyristoylphosphatidylcholine (DMPC) bilayer containing cholesterol. Our previous REMD simulations, which studied binding of the same peptide to the cholesterol-free DMPC bilayer, served as a control, against which we measured the impact of cholesterol. Our findings are as follows. First, addition of cholesterol to the DMPC bilayer partially expels the Aβ peptide from the hydrophobic core and promotes its binding to bilayer polar headgroups. Using thermodynamic and energetics analyses, we argued that Aβ partial expulsion is not related to cholesterol-induced changes in lateral pressure within the bilayer but is caused by binding energetics, which favors Aβ binding to the surface of the densely packed cholesterol-rich bilayer. Second, cholesterol has a protective effect on the DMPC bilayer structure against perturbations caused by Aβ binding. More specifically, cholesterol reduces bilayer thinning and overall depletion of bilayer density beneath the Aβ binding footprint. Third, we found that the Aβ peptide contains a single cholesterol binding site, which involves hydrophobic C-terminal amino acids (Ile31-Val36), Phe19, and Phe20 from the central hydrophobic cluster, and cationic Lys28 from the turn region. This binding site accounts for about 76% of all Aβ-cholesterol interactions. Because cholesterol binding site in the Aβ10-40 peptide does not contain the GXXXG motif featured in cholesterol interactions with the transmembrane domain C99 of the β-amyloid precursor protein, we argued that the binding mechanisms for Aβ and C99 are distinct reflecting their different conformations and positions in the lipid bilayer. Fourth, cholesterol sharply reduces the helical propensity in the bound Aβ peptide. As a result, cholesterol largely eliminates the emergence of helical structure observed upon Aβ transition from a water environment to the cholesterol-free DMPC bilayer. We explain this effect by the formation of hydrogen bonds between cholesterol and the Aβ backbone, which prevent helix formation. Taken together, we expect that our simulations will advance understanding of a molecular-level mechanism behind the role of cholesterol in Alzheimer's disease.

Cathepsin B plays a critical role in inducing Alzheimer's disease-like phenotypes following chronic systemic exposure to lipopolysaccharide from Porphyromonas gingivalis in mice

A number of clinical and experimental studies have revealed a strong association between periodontitis and accelerated cognitive decline in Alzheimer's disease (AD); however, the mechanism of the association is unknown. In the present study, we tested the hypothesis that cathepsin (Cat) B plays a critical role in the initiation of neuroinflammation and neural dysfunction following chronic systemic exposure to lipopolysaccharide from Porphyromonas gingivalis (PgLPS) in mice (1mg/kg, daily, intraperitoneally). Young (2months old) and middle-aged (12months old) wild-type (WT; C57BL/6N) or CatB-deficient (CatB^-/-) mice were exposed to PgLPS daily for 5 consecutive weeks. The learning and memory function were assessed using the passive avoidance test, and the expression of amyloid precursor protein (APP), CatB, TLR2 and IL-1β was analyzed in brain tissues by immunohistochemistry and Western blotting. We found that chronic systemic exposure to PgLPS for five consecutive weeks induced learning and memory deficits with the intracellular accumulation of Aβ in neurons in the middle-aged WT mice, but not in young WT or middle-aged CatB^-/- mice. PgLPS significantly increased the expression of CatB in both microglia and neurons in middle-aged WT mice, while increased expression of mature IL-1β and TLR2 was restricted to microglia in the hippocampus of middle-aged WT mice, but not in that of the middle-aged CatB^-/- ones. In in vitro studies, PgLPS (1µg/ml) stimulation upregulated the mean mRNA expression of IL-1β, TLR2 and downregulated the protein levels of IκBα in the cultured MG6 microglia as well as in the primary microglia from WT mice, which were significantly inhibited by the CatB-specific inhibitor CA-074Me as well as by the primary microglia from CatB^-/- mice. Furthermore, the mean mRNA expression of APP and CatB were significantly increased in the primary cultured hippocampal neurons after treatment with conditioned medium from PgLPS-treated WT primary microglia, but not after treatment with conditioned medium neutralized with anti-IL-1beta, and not after treatment with conditioned medium from PgLPS-treated CatB^-/- primary microglia or with PgLPS directly. Taken together, these findings indicate that chronic systemic exposure to PgLPS induces AD-like phenotypes, including microglia-mediated neuroinflammation, intracellular Aβ accumulation in neurons and impairment of the learning and memory functions in the middle-aged mice in a CatB-dependent manner. We propose that CatB may be a therapeutic target for preventing periodontitis-associated cognitive decline in AD.

Genetic, Transcriptome, Proteomic, and Epidemiological Evidence for Blood-Brain Barrier Disruption and Polymicrobial Brain Invasion as Determinant Factors in Alzheimer's Disease

Diverse pathogens are detected in Alzheimer's disease (AD) brains. A bioinformatics survey showed that AD genome-wide association study (GWAS) genes (localized in bone marrow, immune locations and microglia) relate to multiple host/pathogen interactomes (Candida albicans, Cryptococcus neoformans, Bornavirus, Borrelia burgdorferri, cytomegalovirus, Ebola virus, HSV-1, HERV-W, HIV-1, Epstein-Barr, hepatitis C, influenza, Chlamydia pneumoniae, Porphyrymonas gingivalis, Helicobacter pylori, Toxoplasma gondii, Trypanosoma cruzi). These interactomes also relate to the AD hippocampal transcriptome and to plaque or tangle proteins. Upregulated AD hippocampal genes match those upregulated by multiple bacteria, viruses, fungi, or protozoa in immunocompetent cells. AD genes are enriched in GWAS datasets reflecting pathogen diversity, suggesting selection for pathogen resistance, as supported by the old age of AD patients, implying resistance to earlier infections. APOE4 is concentrated in regions of high parasitic burden and protects against childhood tropical infections and hepatitis C. Immune/inflammatory gain of function applies to APOE4, CR1, and TREM2 variants. AD genes are also expressed in the blood-brain barrier (BBB), which is disrupted by AD risk factors (age, alcohol, aluminum, concussion, cerebral hypoperfusion, diabetes, homocysteine, hypercholesterolemia, hypertension, obesity, pesticides, pollution, physical inactivity, sleep disruption, smoking) and by pathogens, directly or via olfactory routes to basal-forebrain BBB control centers. The BBB benefits from statins, NSAIDs, estrogen, melatonin, memantine, and the Mediterranean diet. Polymicrobial involvement is supported by upregulation of bacterial, viral, and fungal sensors/defenders in the AD brain, blood, or cerebrospinal fluid. AD serum amyloid-β autoantibodies may attenuate its antimicrobial effects favoring microbial survival and cerebral invasion leading to activation of neurodestructive immune/inflammatory processes, which may also be augmented by age-related immunosenescence. AD may thus respond to antibiotic, antifungal, or antiviral therapy.

Infection of microglia with Porphyromonas gingivalis promotes cell migration and an inflammatory response through the gingipain-mediated activation of protease-activated receptor-2 in mice

Despite a clear correlation between periodontitis and cognitive decline in Alzheimer's disease, the precise mechanism underlying the relationship remains unclear. The periodontal pathogen Porphyromonas gingivalis produces a unique class of cysteine proteinases termed gingipains that comprises Arg-gingipain (Rgp) and Lys-gingipain (Kgp). Rgp and Kgp are important in the bacterial mediated host cell responses and the subsequent intracellular signaling in infected cells. In the present study, we attempted to clarify the potential effects of Rgp and Kgp on the cellular activation of brain-resident microglia. We provide the first evidence that Rgp and Kgp cooperatively contribute to the P. gingivalis-induced cell migration and expression of proinflammatory mediators through the activation of protease-activated receptor 2. The subsequent activation of phosphoinositide 3-kinase/Akt and mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase/ERK pathways contributes to cell migration and inflammatory response of microglia.

Lipopolysaccharide-binding protein (LBP) reverses the amyloid state of fibrin seen in plasma of type 2 diabetics with cardiovascular co-morbidities

Type 2 diabetes (T2D) has many cardiovascular complications, including a thrombotic propensity. Many such chronic, inflammatory diseases are accompanied (and may be exacerbated, and possibly even largely caused) by amyloid fibril formation. Recognising that there are few strong genetic associations underpinning T2D, but that amyloidogenesis of amylin is closely involved, we have been seeking to understand what might trigger the disease. Serum levels of bacterial lipopolysaccharide are raised in T2D, and we recently showed that fibrin(ogen) polymerisation during blood clotting can be affected strongly by LPS. The selectivity was indicated by the regularisation of clotting by lipopolysaccharide-binding protein (LBP). Since coagulopathies are a hallmark of T2D, we wondered whether they might too be caused by LPS (and reversed by LBP). We show here, using SEM and confocal microscopy, that platelet-poor-plasma from subjects with T2D had a much greater propensity for hypercoagulability and for amyloidogenesis, and that these could both be reversed by LBP. These data imply that coagulopathies are an important feature of T2D, and may be driven by ‘hidden’ LPS. Given the prevalence of amyloid formation in the sequelae of diabetes, this opens up novel strategies for both the prevention and treatment of T2D.

Herpes Simplex Virus Type 1 Neuronal Infection Perturbs Golgi Apparatus Integrity through Activation of Src Tyrosine Kinase and Dyn-2 GTPase

Herpes simplex virus type 1 (HSV-1) is a ubiquitous pathogen that establishes a latent persistent neuronal infection in humans. The pathogenic effects of repeated viral reactivation in infected neurons are still unknown. Several studies have reported that during HSV-1 epithelial infection, the virus could modulate diverse cell signaling pathways remodeling the Golgi apparatus (GA) membranes, but the molecular mechanisms implicated, and the functional consequences to neurons is currently unknown. Here we report that infection of primary neuronal cultures with HSV-1 triggers Src tyrosine kinase activation and subsequent phosphorylation of Dynamin 2 GTPase, two players with a role in GA integrity maintenance. Immunofluorescence analyses showed that HSV-1 productive neuronal infection caused a scattered and fragmented distribution of the GA through the cytoplasm, contrasting with the uniform perinuclear distribution pattern observed in control cells. In addition, transmission electron microscopy revealed swollen cisternae and disorganized stacks in HSV-1 infected neurons compared to control cells. Interestingly, PP2, a selective inhibitor for Src-family kinases markedly reduced these morphological alterations of the GA induced by HSV-1 infection strongly supporting the possible involvement of Src tyrosine kinase. Finally, we showed that HSV-1 tegument protein VP11/12 is necessary but not sufficient to induce Dyn2 phosphorylation. Altogether, these results show that HSV-1 neuronal infection triggers activation of Src tyrosine kinase, phosphorylation of Dynamin 2 GTPase, and perturbation of GA integrity. These findings suggest a possible neuropathogenic mechanism triggered by HSV-1 infection, which could involve dysfunction of the secretory system in neurons and central nervous system.

To What Extent Are the Terminal Stages of Sepsis, Septic Shock, Systemic Inflammatory Response Syndrome, and Multiple Organ Dysfunction Syndrome Actually Driven by a Prion/Amyloid Form of Fibrin?

A well-established development of increasing disease severity leads from sepsis through systemic inflammatory response syndrome, septic shock, multiple organ dysfunction syndrome, and cellular and organismal death. Less commonly discussed are the equally well-established coagulopathies that accompany this. We argue that a lipopolysaccharide-initiated (often disseminated intravascular) coagulation is accompanied by a proteolysis of fibrinogen such that formed fibrin is both inflammatory and resistant to fibrinolysis. In particular, we argue that the form of fibrin generated is amyloid in nature because much of its normal α-helical content is transformed to β-sheets, as occurs with other proteins in established amyloidogenic and prion diseases. We hypothesize that these processes of amyloidogenic clotting and the attendant coagulopathies play a role in the passage along the aforementioned pathways to organismal death, and that their inhibition would be of significant therapeutic value, a claim for which there is considerable emerging evidence.

Brain Under Stress and Alzheimer's Disease

Modern society is characterized by the ubiquity of stressors that affect every individual to different extents. Furthermore, experimental, clinical, and epidemiological data have shown that chronic activation of the stress response may participate in the development of various somatic as well as neuropsychiatric diseases. Surprisingly, the role that stress plays in the etiopathogenesis of Alzheimer's disease (AD) has not yet been studied in detail and is therefore not well understood. However, accumulated data have shown that neuroendocrine and behavioral changes accompanying the stress response affect neuronal homeostasis and compromise several key neuronal processes. Mediators of the neuroendocrine stress response, if elevated repeatedly or chronically, exert direct detrimental effects on the brain by impairing neuronal metabolism, plasticity, and survival. Stress-induced hormonal and behavioral reactions may also participate in the development of hypertension, atherosclerosis, insulin resistance, and other peripheral disturbances that may indirectly induce neuropathological processes participating in the development and progression of AD. Importantly, stress-induced detrimental effects as etiological factors of AD are attractive because they can be reduced by several approaches including behavioral and pharmacological interventions. These interventions may therefore represent an important strategy for prevention or attenuation of the progression of AD.

Differential Phenotypes of Myeloid-Derived Suppressor and T Regulatory Cells and Cytokine Levels in Amnestic Mild Cognitive Impairment Subjects Compared to Mild Alzheimer Diseased Patients

Alzheimer disease (AD) is the most prevalent form of dementia although the underlying cause(s) remains unknown at this time. However, neuroinflammation is believed to play an important role and suspected contributing immune parameters can be revealed in studies comparing patients at the stage of amnestic mild cognitive impairment (aMCI) to healthy age-matched individuals. A network of immune regulatory cells including regulatory T cells (Tregs) and myeloid-derived suppressor cells (MDSCs) maintains immune homeostasis but there are very few data on the role of these cells in AD. Here, we investigated the presence of these cells in the blood of subjects with aMCI and mild AD (mAD) in comparison with healthy age-matched controls. We also quantitated several pro- and anti-inflammatory cytokines in sera which can influence the development and activation of these cells. We found significantly higher levels of MDSCs and Tregs in aMCI but not in mAD patients, as well as higher serum IL-1β levels. Stratifying the subjects based on CMV serostatus that is known to influence multiple immune parameters showed an absence of differences between aMCI subjects compared to mAD patients and healthy controls. We suggest that the increase in MDSCs and Tregs number in aMCI subjects may have a beneficial role in modulating inflammatory processes. However, this protective mechanism may have failed in mAD patients, allowing progression of the disease. This working hypothesis obviously requires testing in future studies.

Association between human herpesvirus infections and dementia or mild cognitive impairment: a systematic review protocol

INTRODUCTION

Persisting neurotropic viruses are proposed to increase the risk of dementia, but evidence of association from robust, adequately powered population studies is lacking. This is essential to inform clinical trials of targeted preventive interventions.

METHODS AND ANALYSIS

We will carry out a comprehensive systematic review of published and grey literature of the association between infection with, reactivation of, vaccination against or treatment of any of the eight human herpesviruses and dementia or mild cognitive impairment. We will search the Cochrane Library, Embase, Global Health, Medline, PsycINFO, Scopus, Web of Science, clinical trials registers, the New York Academy of Medicine Grey Literature Report, Electronic Theses Online Service through the British Library and the ISI Conference Proceedings Citation Index for randomised controlled trials, cohort, caseâ€"control, case crossover or self-controlled case series studies reported in any language up to January 2017. Titles, abstracts and full-text screening will be conducted by two researchers independently. Data will be extracted systematically from eligible studies using a piloted template. We will assess risk of bias of individual studies in line with the Cochrane Collaboration tool. We will conduct a narrative synthesis, grouping studies by exposure and outcome definitions, and will describe any differences by population subgroups and dementia subtypes. We will consider performing meta-analyses if there are adequate numbers of sufficiently homogeneous studies. The overall quality of cumulative evidence will be assessed using selected Grading of Recommendations, Assessment, Development and Evaluations criteria.

ETHICS AND DISSEMINATION

As this is a review of existing studies, no ethical approval is required. Results will be disseminated through a peer-reviewed publication and at national and international conferences. We anticipate the review will clarify the current extent and quality of evidence for a link between herpesviruses and dementia, identify gaps and inform the direction of future research.

PROSPERO REGISTRATION NUMBER

CRD42017054684.

16S rRNA Next Generation Sequencing Analysis Shows Bacteria in Alzheimer's Post-Mortem Brain

The neurological deterioration associated with Alzheimer's disease (AD), involving accumulation of amyloid-beta peptides and neurofibrillary tangles, is associated with evident neuroinflammation. This is now seen to be a significant contributor to pathology. Recently the tenet of the privileged status of the brain, regarding microbial compromise, has been questioned, particularly in terms of neurodegenerative diseases. It is now being considered that microbiological incursion into the central nervous system could be either an initiator or significant contributor to these. This is a novel study using 16S ribosomal gene-specific Next generation sequencing (NGS) of extracted brain tissue. A comparison was made of the bacterial species content of both frozen and formaldehyde fixed sections of a small cohort of Alzheimer-affected cases with those of cognitively unimpaired (normal). Our findings suggest an increase in bacterial populations in Alzheimer brain tissue compared with normal.

Herpes virus seroepidemiology in the adult Swedish population

Background

Herpes viruses establish a life-long latency and can cause symptoms during both first-time infection and later reactivation. The aim of the present study was to describe the seroepidemiology of Herpes simplex type 1 (HSV1), Herpes simplex type 2 (HSV2), Cytomegalovirus (CMV), Varicella Zoster virus (VZV) and Human herpes virus type 6 (HHV6) in an adult Swedish population (35–95 years of age).

Methods

Presence of antibodies against the respective viruses in serum from individuals in the Betula study was determined with an enzyme-linked immunosorbent assay (ELISA). Singular samples from 535 persons (53.9% women, mean age at inclusion 62.7 ± 14.4 years) collected 2003-2005 were analyzed for the five HHVs mentioned above. In addition, samples including follow-up samples collected 1988–2010 from 3,444 persons were analyzed for HSV.

Results

Prevalence of HSV1 was 79.4%, HSV2 12.9%, CMV 83.2%, VZV 97.9%, and HHV6 97.5%. Herpes virus infections were more common among women (p = 0.010) and a lower age-adjusted HSV seroprevalence was found in later birth cohorts (p < 0.001). The yearly incidence of HSV infection was estimated at 14.0/1000.

Conclusion

Women are more often seropositive for HHV, especially HSV2. Age-adjusted seroprevalence for HSV was lower in later birth cohorts indicating a decreasing childhood and adolescent risk of infection.

Holocranohistochemistry enables the visualization of α-synuclein expression in the murine olfactory system and discovery of its systemic anti-microbial effects

Braak and Del Tredici have proposed that typical Parkinson disease (PD) has its origins in the olfactory bulb and gastrointestinal tract. However, the role of the olfactory system has insufficiently been explored in the pathogeneses of PD and Alzheimer disease (AD) in laboratory models. Here, we demonstrate applications of a new method to process mouse heads for microscopy by sectioning, mounting, and staining whole skulls (‘holocranohistochemistry’). This technique permits the visualization of the olfactory system from the nasal cavity to mitral cells and dopamine-producing interneurons of glomeruli in the olfactory bulb. We applied this method to two specific goals: first, to visualize PD- and AD-linked gene expression in the olfactory system, where we detected abundant, endogenous α-synuclein and tau expression in the olfactory epithelium. Furthermore, we observed amyloid-β plaques and proteinase-K-resistant α-synuclein species, respectively, in cranial nerve-I of APP- and human SNCA-over-expressing mice. The second application of the technique was to the modeling of gene–environment interactions in the nasal cavity of mice. We tracked the infection of a neurotropic respiratory-enteric-orphan virus from the nose pad into cranial nerves-I (and -V) and monitored the ensuing brain infection. Given its abundance in the olfactory epithelia, we questioned whether α-synuclein played a role in innate host defenses to modify the outcome of infections. Indeed, Snca-null mice were more likely to succumb to viral encephalitis versus their wild-type littermates. Moreover, using a bacterial sepsis model, Snca-null mice were less able to control infection after intravenous inoculation with Salmonella typhimurium. Together, holocranohistochemistry enabled new discoveries related to α-synuclein expression and its function in mice. Future studies will address: the role of Mapt and mutant SNCA alleles in infection paradigms; the contribution of xenobiotics in the initiation of idiopathic PD; and the safety to the host when systemically targeting α-synuclein by immunotherapy.

Is heart disease a risk factor for low dementia test battery scores in older persons with Down syndrome? Exploratory, pilot study, and commentary

OBJECTIVES

Certain heart conditions and diseases are common in Down syndrome (DS; trisomy 21), but their role in early onset dementia that is prevalent in older adults with DS has not been evaluated. To address this knowledge gap, we conducted a study of risk factors for low neurocognitive/behavioral scores obtained with a published dementia test battery (DTB). Participants were adults with DS living in New York (N = 29; average age 46 years). We asked three questions. 1. Does having any type of heart disease affect the association between DTB scores and chronological age? 2. Does thyroid status affect the association between heart disease and DTB scores? 3. Are the E4 or E2 alleles of apolipoprotein E (APOE) associated with DTB scores or with heart disease?

METHOD

The study was retrospective, pilot, and exploratory. It involved analysis of information in a database previously established for the study of aging in DS. Participants had moderate intellectual disability on average. Information for each person included: gender, age, a single DTB score obtained by combining results from individual subscales of the DTB, the presence or absence of heart disease, thyroid status (treated hypothyroidism or normal), and APOE genotype. Trends were visualized by inspection of graphs and contingency tables. Statistical methods used to evaluate associations included Pearson correlation analysis, Fisher's exact tests (2-tailed), and odds ratio analysis. P values were interpreted at the 95% confidence level without Bonferroni correction. P values >.05<.1 were considered trends.

RESULTS

The negative correlation between DTB scores and age was significant in those with heart disease but not in those without. Heart disease was significantly associated with DTB scores >1 SD below the sample mean; there was a strong association between heart disease and low DTB scores in those with treated hypothyroidism but not in those with normal thyroid status. The APOE genotype was weakly associated with heart disease (E4, predisposing; E2, protective) in males.

CONCLUSIONS

On the basis of the potentially important findings from the present study, large prospective studies are warranted to confirm and extend the observations. In these, particular heart conditions or diseases and other medical comorbidities in individuals should be documented.

The Alu neurodegeneration hypothesis: A primate-specific mechanism for neuronal transcription noise, mitochondrial dysfunction, and manifestation of neurodegenerative disease

It is hypothesized that retrotransposons have played a fundamental role in primate evolution and that enhanced neurologic retrotransposon activity in humans may underlie the origin of higher cognitive function. As a potential consequence of this enhanced activity, it is likely that neurons are susceptible to deleterious retrotransposon pathways that can disrupt mitochondrial function. An example is observed in the TOMM40 gene, encoding a β-barrel protein critical for mitochondrial preprotein transport. Primate-specific Alu retrotransposons have repeatedly inserted into TOMM40 introns, and at least one variant associated with late-onset Alzheimer’s disease originated from an Alu insertion event. We provide evidence of enriched Alu content in mitochondrial genes and postulate that Alus can disrupt mitochondrial populations in neurons, thereby setting the stage for progressive neurologic dysfunction. This Alu neurodegeneration hypothesis is compatible with decades of research and offers a plausible mechanism for the disruption of neuronal mitochondrial homeostasis, ultimately cascading into neurodegenerative disease.

Homeostasis-altering molecular processes as mechanisms of inflammasome activation

The innate immune system uses a distinct set of germline-encoded pattern recognition receptors (PRRs) to initiate downstream inflammatory cascades. This recognition system is in stark contrast to the adaptive immune system, which relies on highly variable, randomly generated antigen receptors. A key limitation of the innate immune system's reliance on fixed PRRs is its inflexibility in responding to rapidly evolving pathogens. Recent advances in our understanding of inflammasome activation suggest that the innate immune system also has sophisticated mechanisms for responding to pathogens for which there is no fixed PRR. This includes the recognition of debris from dying cells, known as danger-associated molecular patterns (DAMPs), which can directly activate PRRs in a similar manner to pathogen-associated molecular patterns (PAMPs). Distinct from this, emerging data for the inflammasome components NLRP3 (NOD-, LRR- and pyrin domain-containing 3) and pyrin suggest that they do not directly detect molecular patterns, but instead act as signal integrators that are capable of detecting perturbations in cytoplasmic homeostasis, for example, as initiated by infection. Monitoring these perturbations, which we term 'homeostasis-altering molecular processes' (HAMPs), provides potent flexibility in the capacity of the innate immune system to detect evolutionarily novel infections; however, HAMP sensing may also underlie the sterile inflammation that drives chronic inflammatory diseases.

The Infectious Etiology of Alzheimer's Disease

BACKGROUND

Inflammation is a part of the first line of defense of the body against invasive pathogens, and plays a crucial role in tissue regeneration and repair. A proper inflammatory response ensures the suitable resolution of inflammation and elimination of harmful stimuli, but when the inflammatory reactions are inappropriate it can lead to damage of the surrounding normal cells. The relationship between infections and Alzheimer's Disease (AD) etiology, especially lateonset AD (LOAD) has been continuously debated over the past three decades.

METHODS

This review discusses whether infections could be a causative factor that promotes the progression of AD and summarizes recent investigations associating infectious agents and chronic inflammation with AD. Preventive and therapeutic approaches to AD in the context of an infectious etiology of the disease are also discussed.

RESULTS

Emerging evidence supports the hypothesis of the role of neurotropic viruses from the Herpesviridae family, especially Human herpesvirus 1 (HHV-1), Cytomegalovirus (CMV), and Human herpesvirus 2 (HHV-2), in AD neuropathology. Recent investigations also indicate the association between Hepatitis C virus (HCV) infection and dementia. Among bacteria special attention is focused on spirochetes family and on periodontal pathogens such as Porphyromonas gingivalis or Treponema denticola that could cause chronic periodontitis and possibly contribute to the clinical onset of AD.

CONCLUSION

Chronic viral, bacterial and fungal infections might be causative factors for the inflammatory pathway in AD.

Modulation of Immune Responses to Herpes Simplex Virus Type 1 by IFNL3 and IRF7 Polymorphisms: A Study in Alzheimer's Disease

Herpes simplex virus type 1 (HSV-1) has long been suspected to play a role in Alzheimer's disease (AD), the most common form of dementia. IFN-lambda (IFN-λ) is one of the key cytokine in innate antiviral defenses and, in particular, has an appreciable antiviral activity against HSV-1 infection. IFN-λ expression is regulated by the interaction between two different proteins: Mediator Complex 23 (MED23) and Interferon-Responsive Transcription Factor 7 (IRF7); single nucleotide polymorphisms (SNPs) in these genes as well as in IFNL3 were shown to be differently distributed in AD patients. In this study, allelic discrimination analysis for IFNL3 rs12979860, MED23 rs3756784, and IRF7 rs6598008, as well as IFN-λ serum concentration and anti-HSV-1 antibody (Ab) titers were performed in 79 AD patients, 57 mild cognitive impairment (MCI) individuals, and 81 healthy controls (HC) who were HSV-1-seropositive. Results showed that INF-λ serum concentration was increased in AD and MCI carrying the IFNL3 T allele compared to HC (AD versus HC: p = 0.014; MCI versus HC: p = 0.029), with the highest anti-HSV-1 Ab titers seen in AD patients carrying the IFNL3 CC genotype (p = 0.012 versus HC). Notably, anti-HSV-1 Ab titers were higher in AD and MCI individuals carrying the IRF7 AA genotype compared to HC (p = 0.018 for both). MED23 polymorphisms did not show any statistical association either with serum IFN-λ or with anti-HSV-1 Ab. Data herein suggest that the IFNL3 rs12979860 and IRF7 rs6598008 polymorphisms modulate immune responses against HSV-1 via their effect on the IFN-λ pathway. These results help to clarify the possible role of HSV-1 infection in AD pathogenesis.

Antibodies from multiple sclerosis patients preferentially recognize hyperglucosylated adhesin of non-typeable Haemophilus influenzae

In autoimmune diseases, there have been proposals that exogenous “molecular triggers”, i.e., specific ‘non-self antigens’ accompanying infectious agents, might disrupt control of the adaptive immune system resulting in serious pathologies. The etiology of multiple sclerosis (MS) remains unclear. However, epidemiologic data suggest that exposure to infectious agents may be associated with increased MS risk and progression may be linked to exogenous, bacterially-derived, antigenic molecules, mimicking mammalian cell surface glycoconjugates triggering autoimmune responses. Previously, antibodies specific to a gluco-asparagine (N-Glc) glycopeptide, CSF114(N-Glc), were identified in sera of an MS patient subpopulation. Since the human glycoproteome repertoire lacks this uniquely modified amino acid, we turned our attention to bacteria, i.e., Haemophilus influenzae, expressing cell-surface adhesins including N-Glc, to establish a connection between H. influenzae infection and MS. We exploited the biosynthetic machinery from the opportunistic pathogen H. influenzae (and the homologous enzymes from A. pleuropneumoniae) to produce a unique set of defined glucosylated adhesin proteins. Interestingly we revealed that a hyperglucosylated protein domain, based on the cell-surface adhesin HMW1A, is preferentially recognized by antibodies from sera of an MS patient subpopulation. In conclusion the hyperglucosylated adhesin is the first example of an N-glucosylated native antigen that can be considered a relevant candidate for triggering pathogenic antibodies in MS.

High avidity HSV-1 antibodies correlate with absence of amnestic Mild Cognitive Impairment conversion to Alzheimer's disease

Amnestic Mild Cognitive Impairment (aMCI) is an alteration in cognitive abilities that can progress to Alzheimer's disease (AD), a condition in which herpes simplex type 1 (HSV-1) infection might play a pathogenetic role. Prognostic indexes capable of predicting aMCI conversion to AD are only partially understood. The objective of the present work is to verify whether HSV-1 immune responses is involved in conversion of aMCI to AD and correlate with grey matter brain morphometry. Two homogeneous groups of individuals who did or did not convert to AD over a 24-months period were selected after retrospective analysis of a cohort of patients with a diagnosis of aMCI. The selection of subjects was based on: a) clinical follow-up; b) neurocognitive evaluation at baseline and after 24months; c) availability of serum and DNA samples at baseline. 36 aMCI individuals, 21 of whom did (aMCI-converters) and 15 of whom did not (aMCI-non-converters) convert to AD, were included in the study. HSV-1 antibody (Ab) titers, avidity index and APOE genotyping were performed in all the enrolled individuals at baseline. Brain magnetic resonance imaging (MRI) by 1.5T scanner results at baseline were available as well in most (29/36) of these individuals. HSV-1-specific Ab titers were increased at baseline in aMCI-non-converters, and the avidity of these Ab was significantly higher in aMCI-non-converter compared to aMCI-converter (p=0.0018). Receiver operating characteristics analysis showed that HSV-1 avidity had a predictive value in distinguishing between aMCI-non-converters and aMCI-converters (p<0.0001). Notably, a positive correlation was detected as well between HSV-1 antibody titers and MRI-evaluated cortical volumes in the left hippocampus and amigdala (p_corr<0.05). In conclusion, stronger HSV-1-specific humoral responses associate with protection against AD conversion and better-preserved cortical volumes. These results reinforce the hypothesis for a role for HSV-1 in the pathogenesis of AD.