Apolipoprotein E epsilon 4 allele distributions in late-onset Alzheimer's disease and in other amyloid-forming diseases

Do microbes play a role in Alzheimer's disease?

Alzheimer's disease is a complex and progressive condition that affects essential neurological functions such as memory and reasoning. In the brain, neuronal loss, synaptic dysfunction, proteinopathy, neurofibrillary tangles, and neuroinflammation are the hallmarks of Alzheimer's disease pathophysiology. In addition, recent evidence has highlighted that microbes, whether commensal or pathogenic, also have the ability to interact with their host and to regulate its immune system, therefore participating in the exchanges that lead to peripheral inflammation and neuropathology. Because of this intimate relationship, bacteria, viruses, fungi, and protozoa have been implicated in the development of Alzheimer's disease. Here, we bring together current and most recent evidence of the role of microbes in Alzheimer's disease, raising burning questions that need to be addressed to guide therapeutic approaches and potential prophylactic strategies.

Inflammasome signaling is dispensable for ß-amyloid-induced neuropathology in preclinical models of Alzheimer's disease

Background

Alzheimer's disease (AD) is the most common neurodegenerative disorder affecting memory and cognition. The disease is accompanied by an abnormal deposition of ß-amyloid plaques in the brain that contributes to neurodegeneration and is known to induce glial inflammation. Studies in the APP/PS1 mouse model of ß-amyloid-induced neuropathology have suggested a role for inflammasome activation in ß-amyloid-induced neuroinflammation and neuropathology.

Methods

Here, we evaluated the in vivo role of microglia-selective and full body inflammasome signalling in several mouse models of ß-amyloid-induced AD neuropathology.

Results

Microglia-specific deletion of the inflammasome regulator A20 and inflammasome effector protease caspase-1 in the AppNL-G-F and APP/PS1 models failed to identify a prominent role for microglial inflammasome signalling in ß-amyloid-induced neuropathology. Moreover, global inflammasome inactivation through respectively full body deletion of caspases 1 and 11 in AppNL-G-F mice and Nlrp3 deletion in APP/PS1 mice also failed to modulate amyloid pathology and disease progression. In agreement, single-cell RNA sequencing did not reveal an important role for Nlrp3 signalling in driving microglial activation and the transition into disease-associated states, both during homeostasis and upon amyloid pathology.

Conclusion

Collectively, these results question a generalizable role for inflammasome activation in preclinical amyloid-only models of neuroinflammation.

APOE4-promoted gliosis and degeneration in tauopathy are ameliorated by pharmacological inhibition of HMGB1 release

Apolipoprotein E4 (APOE4) is an important driver of Tau pathology, gliosis, and degeneration in Alzheimer's disease (AD). Still, the mechanisms underlying these APOE4-driven pathological effects remain elusive. Here, we report in a tauopathy mouse model that APOE4 promoted the nucleocytoplasmic translocation and release of high-mobility group box 1 (HMGB1) from hippocampal neurons, which correlated with the severity of hippocampal microgliosis and degeneration. Injection of HMGB1 into the hippocampus of young APOE4-tauopathy mice induced considerable and persistent gliosis. Selective removal of neuronal APOE4 reduced HMGB1 translocation and release. Treatment of APOE4-tauopathy mice with HMGB1 inhibitors effectively blocked the intraneuronal translocation and release of HMGB1 and ameliorated the development of APOE4-driven gliosis, Tau pathology, neurodegeneration, and myelin deficits. Single-nucleus RNA sequencing revealed that treatment with HMGB1 inhibitors diminished disease-associated and enriched disease-protective subpopulations of neurons, microglia, and astrocytes in APOE4-tauopathy mice. Thus, HMGB1 inhibitors represent a promising approach for treating APOE4-related AD.

Neuronal apoE4 induces early hyperexcitability in select populations of hippocampal neurons by altering Nell2 expression

The impact of apolipoprotein E4 (apoE4), the strongest genetic risk factor for Alzheimer's disease (AD), on neuronal function remains unclear. We investigated this by examining excitatory neurons in the hippocampus of young and aged human apoE4 knock-in (apoE4-KI) and apoE3-KI mice using electrophysiology and single-nucleus RNA-sequencing (snRNA-seq). In young apoE4-KI mice, we identified region-specific subpopulations of excitatory neurons with hyperexcitability underlain by reduced cell size, which were eliminated by selective removal of neuronal apoE4. Aged apoE4-KI mice showed an increased fraction of hyperexcitable granule cells, a pronounced inhibitory deficit, and E/I imbalance in the dentate gyrus, contributing to network dysfunction. snRNA-seq analysis revealed neuron type-specific and age-dependent transcriptomic changes, identifying Nell2 overexpression in apoE4-KI mice. Reducing Nell2 expression in specific neuronal types of apoE4-KI mice with CRISPRi rescued their morphological and excitability phenotypes, supporting Nell2 overexpression as a cause for apoE4-induced neuronal dysfunction. Our findings highlight the early transcriptomic and morpho-electric alterations behind the apoE4-induced neuronal dysfunction in AD.

HIGHLIGHTS

ApoE4 causes hyperexcitability of select hippocampal neurons in young apoE4 mice.ApoE4 causes dentate hyperexcitability and inhibitory deficit in aged apoE4 mice.snRNA-seq reveals apoE genotype-, cell type-, and age-dependent transcriptomic changes.Nell2 overexpression identified as a cause of apoE4-induced neuronal hyperexcitability.

Complement receptor 1 is expressed on brain cells and in the human brain

Genome wide association studies (GWAS) have highlighted the importance of the complement cascade in pathogenesis of Alzheimer's disease (AD). Complement receptor 1 (CR1; CD35) is among the top GWAS hits. The long variant of CR1 is associated with increased risk for AD; however, roles of CR1 in brain health and disease are poorly understood. A critical confounder is that brain expression of CR1 is controversial; failure to demonstrate brain expression has provoked the suggestion that peripherally expressed CR1 influences AD risk. We took a multi-pronged approach to establish whether CR1 is expressed in brain. Expression of CR1 at the protein and mRNA level was assessed in human microglial lines, induced pluripotent stem cell (iPSC)-derived microglia from two sources and brain tissue from AD and control donors. CR1 protein was detected in microglial lines and iPSC-derived microglia expressing different CR1 variants when immunostained with a validated panel of CR1-specific antibodies; cell extracts were positive for CR1 protein and mRNA. CR1 protein was detected in control and AD brains, co-localizing with astrocytes and microglia, and expression was significantly increased in AD compared to controls. CR1 mRNA expression was detected in all AD and control brain samples tested; expression was significantly increased in AD. The data unequivocally demonstrate that the CR1 transcript and protein are expressed in human microglia ex vivo and on microglia and astrocytes in situ in the human brain; the findings support the hypothesis that CR1 variants affect AD risk by directly impacting glial functions.

Analysis of the time-dependent changes of phospholipids in the brain regions of a mouse model of Alzheimer's disease

Phospholipid levels are reported to be decreased in Alzheimer's disease (AD). For a better understanding, we investigated the time-dependent changes of phospholipids species in a mouse model of AD. The levels of phospholipids in the hippocampus and prefrontal cortex of wild-type and APP-Tg (J20) mice were measured by LC-ESI-MS/MS. Compared to wild-type, total phosphatidylcholine (PC), phosphatidylethanolamine (PE), and lysophosphatidylcholine (LPC) were Increased at 3 months but decreased at 6 months in the cortex of J20 mice. Total lysophosphatidylethanolamine (LPE) was decreased both at 3 and 6 months. PC was decreased and LPC was increased at 6 months, resulting in an increased LPC/PC ratio in the hippocampus of J20 mice. At species levels, PCA analysis could discriminate wild-type and J20 based on PC and LPC distribution at 6 months. At 6 months, several highly abundant PC including PC (16:0/16:0), PC (16:0/18:0), PC (16:0/18:1), and PC (18:0/18:1) were decreased in the cortex and hippocampus of J20. Conversely, LPC species including LPC 16:0, LPC 18:1, and LPC 20:4 were increased especially in the hippocampal area. Increased activation of phospholipid-metabolizing enzyme cPLA2 was seen in the hippocampus and cortex of J20 mice at 9 months. On the other hand, ROS levels started to increase as early as 3 months. Compared to 3 months, ROS levels were higher at 6 months in J20 mice. Thus, we demonstrated here a time- and area-dependent alteration of phospholipid composition during the early stage of AD, which could be important in understanding the pathological process.

The neuroimmune axis of Alzheimer's disease

Alzheimer's disease (AD) is a genetically complex and heterogeneous disorder with multifaceted neuropathological features, including β-amyloid plaques, neurofibrillary tangles, and neuroinflammation. Over the past decade, emerging evidence has implicated both beneficial and pathological roles for innate immune genes and immune cells, including peripheral immune cells such as T cells, which can infiltrate the brain and either ameliorate or exacerbate AD neuropathogenesis. These findings support a neuroimmune axis of AD, in which the interplay of adaptive and innate immune systems inside and outside the brain critically impacts the etiology and pathogenesis of AD. In this review, we discuss the complexities of AD neuropathology at the levels of genetics and cellular physiology, highlighting immune signaling pathways and genes associated with AD risk and interactions among both innate and adaptive immune cells in the AD brain. We emphasize the role of peripheral immune cells in AD and the mechanisms by which immune cells, such as T cells and monocytes, influence AD neuropathology, including microglial clearance of amyloid-β peptide, the key component of β-amyloid plaque cores, pro-inflammatory and cytotoxic activity of microglia, astrogliosis, and their interactions with the brain vasculature. Finally, we review the challenges and outlook for establishing immune-based therapies for treating and preventing AD.

Disclosure of Genetic Risk Factors for Alzheimer's Disease to Cognitively Healthy Individuals-From Current Practice towards a Personalised Medicine Scenario

Alzheimer's disease (AD) is a genetically complex disorder. In addition to the relatively small number of pathogenic variants causing autosomal dominant AD, many others have been associated with the much more common sporadic form. The E4 allele of the Apolipoprotein E (APOE) is the first discovered genetic risk factor for AD. In addition, more than 70 genetic risk loci contributing to AD have been identified. Current guidelines do not recommend AD susceptibility genetic testing in cognitively healthy adults because the implications for clinical care are limited. However, secondary prevention clinical trials of disease-modifying therapies enrol individuals based on genetic criteria, and participants are often informed of APOE testing results. Moreover, the availability of direct-to-consumer genetic testing allows individuals to learn their own AD genetic risk profile without medical supervision. A number of research protocols for AD susceptibility genetic testing have been proposed. In Italy, disclosure processes and protocols beyond those developed for inherited dementia have not been established yet. We reviewed the literature on the current practice and clinical issues related to disclosing AD genetic risk to cognitively healthy individuals and provide suggestions that may help to develop specific guidelines at the national level.

Differential Neuropathology, Genetics, and Transcriptomics in Two Kindred Cases with Alzheimer’s Disease and Lewy Body Dementia

Alzheimer’s disease (AD) and Lewy body dementia (LBD) are two different forms of dementia, but their pathology may involve the same cortical areas with overlapping cognitive manifestations. Nonetheless, the clinical phenotype is different due to the topography of the lesions driven by the different underlying molecular processes that arise apart from genetics, causing diverse neurodegeneration. Here, we define the commonalities and differences in the pathological processes of dementia in two kindred cases, a mother and a son, who developed classical AD and an aggressive form of AD/LBD, respectively, through a neuropathological, genetic (next-generation sequencing), and transcriptomic (RNA-seq) comparison of four different brain areas. A genetic analysis did not reveal any pathogenic variants in the principal AD/LBD-causative genes. RNA sequencing highlighted high transcriptional dysregulation within the substantia nigra in the AD/LBD case, while the AD case showed lower transcriptional dysregulation, with the parietal lobe being the most involved brain area. The hippocampus (the most degenerated area) and basal ganglia (lacking specific lesions) expressed the lowest level of dysregulation. Our data suggest that there is a link between transcriptional dysregulation and the amount of tissue damage accumulated across time, assessed through neuropathology. Moreover, we highlight that the molecular bases of AD and LBD follow very different pathways, which underlie their neuropathological signatures. Indeed, the transcriptome profiling through RNA sequencing may be an important tool in flanking the neuropathological analysis for a deeper understanding of AD and LBD pathogenesis.

Alzheimer’s disease – the journey of a healthy brain into organ failure

As the most common dementia, Alzheimer’s disease (AD) exacts an immense personal, societal, and economic toll. AD was first described at the neuropathological level in the early 1900s. Today, we have mechanistic insight into select aspects of AD pathogenesis and have the ability to clinically detect and diagnose AD and underlying AD pathologies in living patients. These insights demonstrate that AD is a complex, insidious, degenerative proteinopathy triggered by Aβ aggregate formation. Over time Aβ pathology drives neurofibrillary tangle (NFT) pathology, dysfunction of virtually all cell types in the brain, and ultimately, overt neurodegeneration. Yet, large gaps in our knowledge of AD pathophysiology and huge unmet medical need remain. Though we largely conceptualize AD as a disease of aging, heritable and non-heritable factors impact brain physiology, either continuously or at specific time points during the lifespan, and thereby alter risk for devolvement of AD. Herein, I describe the lifelong journey of a healthy brain from birth to death with AD, while acknowledging the many knowledge gaps that remain regarding our understanding of AD pathogenesis. To ensure the current lexicon surrounding AD changes from inevitable, incurable, and poorly manageable to a lexicon of preventable, curable, and manageable we must address these knowledge gaps, develop therapies that have a bigger impact on clinical symptoms or progression of disease and use these interventions at the appropriate stage of disease.

The interaction and pathogenesis between cognitive impairment and common cardiovascular diseases in the elderly

Both cognitive impairment and cardiovascular diseases have a high incidence in the elderly population, increasing the burden of care and reducing the quality of life. Studies have suggested that cognitive impairment interacts with cardiovascular diseases such as coronary heart disease, abnormal blood pressure, heart failure, and arrhythmia. On one hand, cognitive impairment in the elderly influences the progression and self-management of cardiovascular diseases and increases the risk of cardiovascular-related adverse events. On the other hand, coronary heart disease, heart failure, higher blood pressure variability, orthostatic hypotension, and atrial fibrillation may aggravate cognitive impairment. The role of blood pressure levels on cognition remains controversial. Several shared biological pathways have been proposed as the underlying mechanism for the association. Cardiovascular diseases may lead to cognitive decline even dementia through cerebral perfusion damage, brain structural changes, inflammation, β-amyloid deposition, and neuroendocrine disorders. It is of great significance to study the interaction and put forward effective interventions in an overall perspective to reduce care burden and improve the quality of life of the elderly patients.

Drosophila as a model to study autophagy in neurodegenerative diseases and digestive tract

Autophagy regulates cellular homeostasis by degrading and recycling cytosolic components and damaged organelles. Disruption of autophagic flux has been shown to induce or facilitate neurodegeneration and accumulation of autophagic vesicles is overt in neurodegenerative diseases. The fruit fly Drosophila has been used as a model system to identify new factors that regulate physiology and disease. Here we provide a historical perspective of how the fly models have offered mechanistic evidence to understand the role of autophagy in neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Charcot-Marie-Tooth neuropathy, and polyglutamine disorders. Autophagy also plays a pivotal role in maintaining tissue homeostasis and protecting organism health. The gastrointestinal tract regulates organism health by modulating food intake, energy balance, and immunity. Growing evidence is strengthening the link between autophagy and digestive tract health in recent years. Here, we also discuss how the fly models have advanced the understanding of digestive physiology regulated by autophagy.

Brain transcriptomes of zebrafish and mouse Alzheimer's disease knock-in models imply early disrupted energy metabolism

Energy production is the most fundamentally important cellular activity supporting all other functions, particularly in highly active organs, such as brains. Here, we summarise transcriptome analyses of young adult (pre-disease) brains from a collection of 11 early-onset familial Alzheimer's disease (EOFAD)-like and non-EOFAD-like mutations in three zebrafish genes. The one cellular activity consistently predicted as affected by only the EOFAD-like mutations is oxidative phosphorylation, which produces most of the energy of the brain. All the mutations were predicted to affect protein synthesis. We extended our analysis to knock-in mouse models of APOE alleles and found the same effect for the late onset Alzheimer's disease risk allele ε4. Our results support a common molecular basis for the initiation of the pathological processes leading to both early and late onset forms of Alzheimer's disease, and illustrate the utility of zebrafish and knock-in single EOFAD mutation models for understanding the causes of this disease.

Summary: Young adult zebrafish mutants and a mouse model of a genetic variant promoting early- and late-onset Alzheimer's disease, respectively, share changes in brain gene expression, indicating disturbance of oxidative phosphorylation.

The Alzheimer's disease drug development landscape

Background

Alzheimer’s disease (AD) is a devastating neurodegenerative disease leading to dementia. The field has made significant progress over the last 15 years. AD diagnosis has shifted from syndromal, based on signs and symptoms, to a biomarker construct based on the pathological hallmarks of the disease: amyloid β deposition, pathologic tau, and neurodegeneration. Numerous genetic risk factors for sporadic AD have been identified, providing further insight into the molecular underpinnings of the disease. For the last two decades, however, drug development for AD has been proven to be particularly challenging. Here, we provide a unique overview of the drug development landscape for AD. By comparing preclinical and clinical drug development pipelines, we aim to describe trends and differences regarding target classes and therapeutic modalities in preclinical and clinical development.

Methods

We analyzed proprietary and public databases and company websites for drugs in preclinical development for AD by the pharmaceutical industry and major clinical trial registries for drugs in clinical development for AD. Drugs were categorized by target class and treatment modality.

Results

We found a higher proportion of preclinical interventions targeting molecular pathways associated with sporadic AD genetic risk variants, compared to clinical stage interventions. These include apolipoprotein E (ApoE) and lipids, lysosomal/endosomal targets, and proteostasis. Further, we observed a trend suggesting that more traditional therapeutic modalities are developed for these novel targets, while more novel treatment modalities such as gene therapies and enzyme treatments are in development for more traditional targets such as amyloid β and tau. Interestingly, the percentage of amyloid β targeting therapies in preclinical development (19.2%) is even higher than the percentage in clinical development (10.7%), indicating that diversification away from interventions targeting amyloid-beta has not materialized. Inflammation is the second most popular target class in both preclinical and clinical development.

Conclusions

Our observations show that the AD drug development pipeline is diversifying in terms of targets and treatment modalities, while amyloid-targeting therapies remain a prominent avenue of development as well. To further advance AD drug development, novel companion diagnostics are needed that are directed at disease mechanisms related to genetic risk factors of AD, both for patient stratification and assessment of therapeutic efficacy in clinical trials.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-021-00927-z.

The Amyloid-β Pathway in Alzheimer's Disease

Breakthroughs in molecular medicine have positioned the amyloid-β (Aβ) pathway at the center of Alzheimer's disease (AD) pathophysiology. While the detailed molecular mechanisms of the pathway and the spatial-temporal dynamics leading to synaptic failure, neurodegeneration, and clinical onset are still under intense investigation, the established biochemical alterations of the Aβ cycle remain the core biological hallmark of AD and are promising targets for the development of disease-modifying therapies. Here, we systematically review and update the vast state-of-the-art literature of Aβ science with evidence from basic research studies to human genetic and multi-modal biomarker investigations, which supports a crucial role of Aβ pathway dyshomeostasis in AD pathophysiological dynamics. We discuss the evidence highlighting a differentiated interaction of distinct Aβ species with other AD-related biological mechanisms, such as tau-mediated, neuroimmune and inflammatory changes, as well as a neurochemical imbalance. Through the lens of the latest development of multimodal in vivo biomarkers of AD, this cross-disciplinary review examines the compelling hypothesis- and data-driven rationale for Aβ-targeting therapeutic strategies in development for the early treatment of AD.

A Review of Oxidative Stress Products and Related Genes in Early Alzheimer's Disease

Oxidative stress is associated with the progression of Alzheimer’s disease (AD). Reactive oxygen species can modify lipids, DNA, RNA, and proteins in the brain. The products of their peroxidation and oxidation are readily detectable at incipient stages of disease. Based on these oxidation products, various biomarker-based strategies have been developed to identify oxidative stress levels in AD. Known oxidative stress-related biomarkers include lipid peroxidation products F2-isoprostanes, as well as malondialdehyde and 4-hydroxynonenal which both conjugate to specific amino acids to modify proteins, and DNA or RNA oxidation products 8-hydroxy-2’-deoxyguanosine (8-OHdG) and 8-hydroxyguanosine (8-OHG), respectively. The inducible enzyme heme oxygenase type 1 (HO-1) is found to be upregulated in response to oxidative stress-related events in the AD brain. While these global biomarkers for oxidative stress are associated with early-stage AD, they generally poorly differentiate from other neurodegenerative disorders that also coincide with oxidative stress. Redox proteomics approaches provided specificity of oxidative stress-associated biomarkers to AD pathology by the identification of oxidatively damaged pathology-specific proteins. In this review, we discuss the potential combined diagnostic value of these reported biomarkers in the context of AD and discuss eight oxidative stress-related mRNA biomarkers in AD that we newly identified using a transcriptomics approach. We review these genes in the context of their reported involvement in oxidative stress regulation and specificity for AD. Further research is warranted to establish the protein levels and their functionalities as well as the molecular mechanisms by which these potential biomarkers are involved in regulation of oxidative stress levels and their potential for determination of oxidative stress and disease status of AD patients.

Forgot to Exercise? Exercise Derived Circulating Myokines in Alzheimer's Disease: A Perspective

Regular exercise plays an essential role in maintaining healthy neurocognitive function and central nervous system (CNS) immuno-metabolism in the aging CNS. Physical activity decreases the risk of developing Alzheimer's Disease (AD), is associated with better AD prognosis, and positively affects cognitive function in AD patients. Skeletal muscle is an important secretory organ, communicating proteotoxic and metabolic stress to distant tissues, including the CNS, through the secretion of bioactive molecules collectively known as myokines. Skeletal muscle undergoes significant physical and metabolic remodeling during exercise, including alterations in myokine expression profiles. This suggests that changes in myokine and myometabolite secretion may underlie the well-documented benefits of exercise in AD. However, to date, very few studies have focused on specific alterations in skeletal muscle-originating secreted factors and their potential neuroprotective effects in AD. In this review, we discuss exercise therapy for AD prevention and intervention, and propose the use of circulating myokines as novel therapeutic tools for modifying AD progression.

Pathway-Specific Genetic Risk for Alzheimer's Disease Differentiates Regional Patterns of Cortical Atrophy in Older Adults

Brain aging is highly variable and represents a challenge to delimit aging from disease processes. Moreover, genetic factors may influence both aging and disease. Here we focused on this issue and investigated effects of multiple genetic loci previously identified to be associated with late-onset Alzheimer's disease (AD) on brain structure of older adults from a population sample. We calculated a genetic risk score (GRS) using genome-wide significant single-nucleotide polymorphisms from genome-wide association studies of AD and tested its effect on cortical thickness (CT). We observed a common pattern of cortical thinning (right inferior frontal, left posterior temporal, medial occipital cortex). To identify CT changes by specific biological processes, we subdivided the GRS effect according to AD-associated pathways and performed follow-up analyses. The common pattern from the main analysis was further differentiated by pathway-specific effects yielding a more bilateral pattern. Further findings were located in the superior parietal and mid/anterior cingulate regions representing 2 unique pathway-specific patterns. All patterns, except the superior parietal pattern, were influenced by apolipoprotein E. Our step-wise approach revealed atrophy patterns that partially resembled imaging findings in early stages of AD. Our study provides evidence that genetic burden for AD contributes to structural brain variability in normal aging.

The Impact of Complement Genes on the Risk of Late-Onset Alzheimer's Disease

Late-onset Alzheimer's disease (LOAD), the most common cause of dementia, and a huge global health challenge, is a neurodegenerative disease of uncertain aetiology. To deliver effective diagnostics and therapeutics, understanding the molecular basis of the disease is essential. Contemporary large genome-wide association studies (GWAS) have identified over seventy novel genetic susceptibility loci for LOAD. Most are implicated in microglial or inflammatory pathways, bringing inflammation to the fore as a candidate pathological pathway. Among the most significant GWAS hits are three complement genes: CLU, encoding the fluid-phase complement inhibitor clusterin; CR1 encoding complement receptor 1 (CR1); and recently, C1S encoding the complement enzyme C1s. Complement activation is a critical driver of inflammation; changes in complement genes may impact risk by altering the inflammatory status in the brain. To assess complement gene association with LOAD risk, we manually created a comprehensive complement gene list and tested these in gene-set analysis with LOAD summary statistics. We confirmed associations of CLU and CR1 genes with LOAD but showed no significant associations for the complement gene-set when excluding CLU and CR1. No significant association with other complement genes, including C1S, was seen in the IGAP dataset; however, these may emerge from larger datasets.

Therapeutic considerations for APOE and TOMM40 in Alzheimers disease: A tribute to Allen Roses MD

Introduction: Four years ago this Autumn, pioneering neurologist Prof. Allen. D. Roses passed away. Hence, we have taken time to reflect on his work and legacy in Alzheimer's disease (AD) research. Prof. Roses rejected the widely accepted amyloid hypothesis, which identifies amyloid beta (Aβ) protein accumulation within the brain as the cause of AD. Instead, he proposed that the epsilon type 4 allele of apolipoprotein (APOE- Ɛ4) and translocase of outer mitochondrial membrane 40 homolog (TOMM40) were preeminent factors in the pathogenesis and progression of AD, particularly in late-onset AD (LOAD). This rejection of the amyloid hypothesis has generated new investigations into APOE and TOMM40 as risk factors for AD. Areas covered: We discuss the contributions of Prof. Roses to AD research, describe how APOE-Ɛ4 and TOMM40 have been posited to trigger neuropathological changes leading to AD, and explore paths to future clinical applications built on the foundations of his research. Expert opinion: The unconventional methodology of targeting APOE and TOMM40 offers great potential for the development of effective preventive and disease-modifying AD interventions. Future preclinical and clinical investigations will greatly benefit from the groundbreaking scientific discoveries of Prof. Roses.

A prospective cohort study of prodromal Alzheimer's disease: Prospective Imaging Study of Ageing: Genes, Brain and Behaviour (PISA)

This prospective cohort study, "Prospective Imaging Study of Ageing: Genes, Brain and Behaviour" (PISA) seeks to characterise the phenotype and natural history of healthy adult Australians at high future risk of Alzheimer's disease (AD). In particular, we are recruiting midlife and older Australians with high and low genetic risk of dementia to discover biological markers of early neuropathology, identify modifiable risk factors, and establish the very earliest phenotypic and neuronal signs of disease onset. PISA utilises genetic prediction to recruit and enrich a prospective cohort and follow them longitudinally. Online surveys and cognitive testing are used to characterise an Australia-wide sample currently totalling over 3800 participants. Participants from a defined at-risk cohort and positive controls (clinical cohort of patients with mild cognitive impairment or early AD) are invited for onsite visits for detailed functional, structural and molecular neuroimaging, lifestyle monitoring, detailed neurocognitive testing, plus blood sample donation. This paper describes recruitment of the PISA cohort, study methodology and baseline demographics.

Can Healthy Diets, Regular Exercise, and Better Lifestyle Delay the Progression of Dementia in Elderly Individuals?

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by memory loss and multiple cognitive impairments. Current healthcare costs for over 50 million people afflicted with AD are about $818 million and are projected to be $2 billion by 2050. Unfortunately, there are no drugs currently available that can delay and/or prevent the progression of disease in elderly individuals and in AD patients. Loss of synapses and synaptic damage are largely correlated with cognitive decline in AD patients. Women are at a higher lifetime risk of developing AD encompassing two-thirds of the total AD afflicted population. Only about 1-2% of total AD patients can be explained by genetic mutations in APP, PS1, and PS2 genes. Several risk factors have been identified, such as Apolipoprotein E4 genotype, type 2 diabetes, traumatic brain injury, depression, and hormonal imbalance, are reported to be associated with late-onset AD. Strong evidence reveals that antioxidant enriched diets and regular exercise reduces toxic radicals, enhances mitochondrial function and synaptic activity, and improves cognitive function in elderly populations. Current available data on the use of antioxidants in mouse models of AD and antioxidant(s) supplements in diets of elderly individuals were investigated. The use of antioxidants in randomized clinical trials in AD patients was also critically assessed. Based on our survey of current literature and findings, we cautiously conclude that healthy diets, regular exercise, and improved lifestyle can delay dementia progression and reduce the risk of AD in elderly individuals and reverse subjects with mild cognitive impairment to a non-demented state.

Apolipoprotein E Triggers Complement Activation in Joint Synovial Fluid of Rheumatoid Arthritis Patients by Binding C1q

We identified apolipoprotein E (ApoE) as one of the proteins that are found in complex with complement component C4d in pooled synovial fluid of rheumatoid arthritis (RA) patients. Immobilized human ApoE activated both the classical and the alternative complement pathways. In contrast, ApoE in solution demonstrated an isoform-dependent inhibition of hemolysis and complement deposition at the level of sC5b-9. Using electron microscopy imaging, we confirmed that ApoE interacts differently with C1q depending on its context; surface-bound ApoE predominantly bound C1q globular heads, whereas ApoE in a solution favored the hinge/stalk region of C1q. As a model for the lipidated state of ApoE in lipoprotein particles, we incorporated ApoE into phosphatidylcholine/phosphatidylethanolamine liposomes and found that the presence of ApoE on liposomes increased deposition of C1q and C4b from serum when analyzed using flow cytometry. In addition, posttranslational modifications associated with RA, such as citrullination and oxidation, reduced C4b deposition, whereas carbamylation enhanced C4b deposition on immobilized ApoE. Posttranslational modification of ApoE did not alter C1q interaction but affected binding of complement inhibitors factor H and C4b-binding protein. This suggests that changed ability of C4b to deposit on modified ApoE may play an important role. Our data show that posttranslational modifications of ApoE alter its interactions with complement. Moreover, ApoE may play different roles in the body depending on its solubility, and in diseased states such as RA, deposited ApoE may induce local complement activation rather than exert its typical role of inhibition.

Genetic Study of Alzheimer's Disease in Saudi Population

BACKGROUND

Alzheimer's disease (AD) is a chronic neurological disorder associated with mental decline and dementia. Several studies focused on investigating the molecular basis of the disease that led to the identification of several causative genes and risk associated alleles. Replication of these studies and findings from different populations is very important.

OBJECTIVE

Molecular assessment of a cohort of 117 familial and sporadic AD cases from Saudi Arabia.

METHODS

Comprehensive screening for point mutations was carried out by direct sequencing of coding regions in the three known AD causative genes: PSEN1, PSEN2, APP, as well as the AD associated gene SORL1. All patients were also genotyped for APOE alleles. In silico 3D protein structure analysis was performed for two novel SORL1 variants.

RESULTS

We identified a total of eight potential pathogenic missense variants in all studied genes. Five of these variants were not previously reported including four in SORL1 (p.Val297Met, p.Arg1084Cys, p.Asp1100Asn, and p.Pro1213Ser) and one in APP (p.Glu380Lys). The frequency of APOE-ɛ4 allele was 21.37% of total investigated cases. In silico 3D protein structure analysis of two SORL1 novel missense variants (p.Pro1213Ser and p.Arg1084Cys) suggested that these variants may affect the folding of the proteins and disturb their structure.

CONCLUSIONS

Our comprehensive analysis of the open reading frame of the known genes have identified potential pathogenic rare variants in 18/117 cases. We found that point mutations in AD main genes (PSEN1, PSEN2, and APP) were underrepresented in our cohort of patients. Our results confirm involvement of SORL1 in familial and sporadic AD cases.

The multiplex model of the genetics of Alzheimer's disease

Genes play a strong role in Alzheimer's disease (AD), with late-onset AD showing heritability of 58-79% and early-onset AD showing over 90%. Genetic association provides a robust platform to build our understanding of the etiology of this complex disease. Over 50 loci are now implicated for AD, suggesting that AD is a disease of multiple components, as supported by pathway analyses (immunity, endocytosis, cholesterol transport, ubiquitination, amyloid-β and tau processing). Over 50% of late-onset AD heritability has been captured, allowing researchers to calculate the accumulation of AD genetic risk through polygenic risk scores. A polygenic risk score predicts disease with up to 90% accuracy and is an exciting tool in our research armory that could allow selection of those with high polygenic risk scores for clinical trials and precision medicine. It could also allow cellular modelling of the combined risk. Here we propose the multiplex model as a new perspective from which to understand AD. The multiplex model reflects the combination of some, or all, of these model components (genetic and environmental), in a tissue-specific manner, to trigger or sustain a disease cascade, which ultimately results in the cell and synaptic loss observed in AD.

Intracerebral Expression of AAV-APOE4 Is Not Sufficient to Alter Tau Burden in Two Distinct Models of Tauopathy

Apolipoprotein E4 (APOE4) is the major genetic risk factor for sporadic Alzheimer's disease (AD), which is characterized by amyloid β (Aβ) plaques and tau tangles. Though the role of APOE4 in Aβ pathogenesis has been mechanistically defined in rodent models, much less is known regarding the relationship of APOE4 to tau pathogenesis. Recent studies have indicated a possible correlation between APOE isoform-dependent alterations in tau pathology and neurodegeneration. To explore whether neuronal expression of APOE4 triggers tauopathy, here we delivered adeno-associated viruses (AAV) expressing human APOE4 in two different models of tauopathy-rTg4510 and PS19 lines. Intracerebroventricular delivery of AAV-APOE4 in neonatal rTg4510 and PS19 mice resulted in increased APOE4 protein in neurons but did not result in altered phosphorylated tau burden, pretangle tau pathology, or silver-positive tangle pathology. Biochemical analysis of synaptic proteins did not reveal substantial alterations. Our results indicate that over-expression of APOE4 in neurons, using an AAV-mediated approache, is not sufficient to accelerate or otherwise alter the inherent tau pathology that occurs in mice overexpressing mutant human tau.

Sex modulates the ApoE ε4 effect on brain tau deposition measured by 18F-AV-1451 PET in individuals with mild cognitive impairment

The strongest genetic risk factor for Alzheimer's disease (AD) is the Apolipoprotein E type 4 allele (ApoE ε4). The interaction between sex and ApoE ε4 carrier status on AD risk remains an area of intense investigation. We hypothesized that sex modulates the relationship between ApoE ε4 carrier status and brain tau deposition (a quantitative endophenotype in AD) in individuals with mild cognitive impairment (MCI).

Methods: Preprocessed ¹⁸F-AV-1451 tau and ¹⁸F-AV-45 amyloid PET images, T1-weighted structural magnetic resonance imaging (MRI) scans, demographic information, and cerebrospinal fluid (CSF) total tau (t-tau) and phosphorylated tau (p-tau) measurements from 108 MCI subjects in the Alzheimer's Disease Neuroimaging Initiative (ADNI) database were included. After downloading pre-processed images from ADNI, an iterative reblurred Van Cittertiteration partial volume correction (PVC) method was applied to all PET images. MRIs were used for PET spatial normalization. Regions of interest (ROIs) were defined in standard space, and standardized uptake value ratio (SUVR) images relative to cerebellum were computed. ApoE ε4 by sex interaction analyses on ¹⁸F-AV-1451 and CSF tau (t-tau, p-tau) were assessed using generalized linear models. The association between ¹⁸F-AV-1451 SUVR and CSF tau (t-tau, p-tau) was assessed.

Results: After applying PVC and controlling for age, education level and global cortical ¹⁸F-AV-45 SUVR, we found that the entorhinal cortex, amygdala, parahippocampal gyrus, posterior cingulate, and occipital ROIs exhibited a significant ApoE ε4 by sex interaction effect (false discovery rate P < 0.1) among MCI individuals. We also found a significant ApoE ε4 by sex interaction effect on CSF t-tau and p-tau. ¹⁸F-AV-1451 SUVR in the 5 ROIs with ApoE ε4 by sex interaction was significantly correlated with CSF p-tau and t-tau.

Conclusions: Our findings suggest that women are more susceptible to ApoE ε4-associated accumulation of neurofibrillary tangles in MCI compared to males. Both CSF tau (p-tau, t-tau) and brain tau PET are robust quantitative biomarkers for studying ApoE ε4 by sex effects on brain tau deposition in MCI participants.

KLOTHO heterozygosity attenuates APOE4-related amyloid burden in preclinical AD

OBJECTIVE

To examine whether the KLOTHO gene variant KL-VS attenuates APOE4-associated β-amyloid (Aβ) accumulation in a late-middle-aged cohort enriched with Alzheimer disease (AD) risk factors.

METHODS

Three hundred nine late-middle-aged adults from the Wisconsin Registry for Alzheimer's Prevention and the Wisconsin Alzheimer's Disease Research Center were genotyped to determine KL-VS and APOE4 status and underwent CSF sampling (n = 238) and/or 11C-Pittsburgh compound B (PiB)-PET imaging (n = 183). Covariate-adjusted regression analyses were used to investigate whether APOE4 exerted expected effects on Aβ burden. Follow-up regression analyses stratified by KL-VS genotype (i.e., noncarrier vs heterozygous; there were no homozygous individuals) evaluated whether the influence of APOE4 on Aβ was different among KL-VS heterozygotes compared to noncarriers.

RESULTS

APOE4 carriers exhibited greater Aβ burden than APOE4-negative participants. This effect was stronger in CSF (t = -5.12, p < 0.001) compared with PiB-PET (t = 3.93, p < 0.001). In the stratified analyses, this APOE4 effect on Aβ load was recapitulated among KL-VS noncarriers (CSF: t = -5.09, p < 0.001; PiB-PET: t = 3.77, p < 0 .001). In contrast, among KL-VS heterozygotes, APOE4-positive individuals did not exhibit higher Aβ burden than APOE4-negative individuals (CSF: t = -1.03, p = 0.308; PiB-PET: t = 0.92, p = 0.363). These differential APOE4 effects remained after KL-VS heterozygotes and noncarriers were matched on age and sex.

CONCLUSION

In a cohort of at-risk late-middle-aged adults, KL-VS heterozygosity was associated with an abatement of APOE4-associated Aβ aggregation, suggesting KL-VS heterozygosity confers protections against APOE4-linked pathways to disease onset in AD.

Brain ApoA-I, ApoJ and ApoE Immunodetection in Cerebral Amyloid Angiopathy

Cerebral amyloid angiopathy (CAA) is a common cause of lobar intracerebral hemorrhage (ICH) in elderly individuals and it is the result of the cerebrovascular deposition of beta-amyloid (Aβ) protein. CAA is frequently found in patients with Alzheimer's disease (AD), although it has an independent contribution to the cognitive deterioration associated with age. Specific apolipoproteins (Apo) have been associated with Aβ fibrillization and clearance from the brain. In this regard, in the present study, we analyzed the brain levels of ApoE, ApoA-I, and ApoJ/clusterin in autopsy brains from 20 post-mortem cases with CAA type I, CAA type II, with parenchymal Aβ deposits or without Aβ deposits. Our objective was to find a possible differential pattern of apolipoproteins distribution in the brain depending on the CAA pathological presentation. The protein expression levels were adjusted by the APOE genotype of the patients included in the study. We found that ApoE and ApoJ were abundantly present in meningeal, cortical, and capillary vessels of the brains with vascular Aβ accumulation. ApoE and ApoJ also deposited extracellularly in the parenchyma, especially in cases presenting Aβ diffuse and neuritic parenchymal deposits. In contrast, ApoA-I staining was only relevant in capillary walls in CAA type I cases. On the other hand, ICH was the principal cause of death among CAA patients in our cohort. We found that CAA patients with ICH more commonly had APOEε2 compared with CAA patients without ICH. In addition, patients who suffered an ICH presented higher vascular ApoE levels in brain. However, higher ApoE presence in cortical arteries was the only independent predictor of suffering an ICH in our cohort after adjusting by age and APOE genotype. In conclusion, while ApoE and ApoJ appear to be involved in both vascular and parenchymal Aβ pathology, ApoA-I seems to be mainly associated with CAA, especially in CAA type I pathology. We consider that our study helps to molecularly characterize the distribution subtypes of Aβ deposition within the brain.

Related biomarkers of neurocognitive impairment in children with obstructive sleep apnea

OBJECTIVES

Different experiment approaches have demonstrated that children with obstructive sleep apnea (OSA) exhibit neurocognitive and behavioral deficits. This review summarized the potential biomarkers of OSA-associated neurocognitive impairment in children.

METHODS

A scoping review of studies on children with OSA that evaluated the potential value of different markers in identifying neurocognitive impairment was undertaken. Additionally, the biomarkers were categorized according to the different research methods, including brain imaging studies, serological indicators and urine markers.

RESULTS

Majority of the studies that evaluated blood biomarkers, plasma insulin growth factor-1 (IGF-1) and Alzheimer's disease (AD)-related biomarkers appeared to exhibit a favorable profile, and could discriminate between OSA children with or without neurocognitive impairments. Brain imaging studies and urinary neurotransmitters could also be helpful for screening OSA cognitive morbidity in children.

CONCLUSION

Due to limited research methods available in children, the cognitive susceptibility of children with OSA has been rarely studied. The main reason for this may be the limited research methods in children. Numerous study populations of children and complex psychological tests are required, which involve major labor and costs.Multi-center prospective studies are needed to identify suitable biomarkers for the timely prediction and effective intervention to prevent neurocognitive impairment in children with OSA and to explore further opportunities in this arena.

Exploiting Drug-Apolipoprotein E Gene Interactions in Hypertension to Preserve Cognitive Function: The 3-City Cohort Study

OBJECTIVES

The objective was to test the hypothesis that antihypertensive drugs have a differential effect on cognition in carriers and noncarriers of the apolipoprotein ε4 (APOE4) polymorphism.

DESIGN

Prospective population-based cohort, France.

SETTING AND PARTICIPANTS

A total of 3359 persons using antihypertensive drugs (median age 74 years, 62% women) were serially assessed up to 10 years follow-up.

MEASURES

Exposure to antihypertensive drug use was established in the first 2 years. Cognitive function was assessed at baseline, 2, 4, 7, and 10 years with a validated test battery covering global cognition, verbal fluency, immediate visual recognition memory, processing speed, and executive function. Clinically significant change in cognitive function was determined using reliable change indices represented as z scores and analyzed with linear mixed-models.

RESULTS

From 3359 persons exposed to antihypertensive drugs, 653 were APOE4 carriers (5.1% homozygous, 94.9% heterozygous) and median follow-up was 5.2 years (interquartile range 3.7-8.0). In APOE4 carriers, improved general cognitive function over time was associated with exposure to angiotensin converting enzyme inhibitors [β = .14; 95% confidence interval (CI) .06-.23, P = .001] and angiotensin receptor blockers (β = .11; 95% CI .02-.21, P = .019). Improved verbal fluency was associated with angiotensin converting enzyme inhibitors (β = .11; 95% CI .03-.20, P = .012).

CONCLUSIONS

Renin-angiotensin-system blockade was associated with improved general cognitive function in APOE4 carriers. Findings did not support renin-angiotensin-system drugs' lipophilicity or ability to cross the blood-brain barrier as potential mechanisms. The findings have implications for selecting the optimal antihypertensive drug in older populations at risk of cognitive decline and dementia.

The Biology of Glial Cells and Their Complex Roles in Alzheimer's Disease: New Opportunities in Therapy

Even though Alzheimer's disease (AD) is of significant interest to the scientific community, its pathogenesis is very complicated and not well-understood. A great deal of progress has been made in AD research recently and with the advent of these new insights more therapeutic benefits may be identified that could help patients around the world. Much of the research in AD thus far has been very neuron-oriented; however, recent studies suggest that glial cells, i.e., microglia, astrocytes, oligodendrocytes, and oligodendrocyte progenitor cells (NG2 glia), are linked to the pathogenesis of AD and may offer several potential therapeutic targets against AD. In addition to a number of other functions, glial cells are responsible for maintaining homeostasis (i.e., concentration of ions, neurotransmitters, etc.) within the central nervous system (CNS) and are crucial to the structural integrity of neurons. This review explores the: (i) role of glial cells in AD pathogenesis; (ii) complex functionalities of the components involved; and (iii) potential therapeutic targets that could eventually lead to a better quality of life for AD patients.

Convergent molecular defects underpin diverse neurodegenerative diseases

In our ageing population, neurodegenerative disorders carry an enormous personal, societal and economic burden. Although neurodegenerative diseases are often thought of as clinicopathological entities, increasing evidence suggests a considerable overlap in the molecular underpinnings of their pathogenesis. Such overlapping biological processes include the handling of misfolded proteins, defective organelle trafficking, RNA processing, synaptic health and neuroinflammation. Collectively but in different proportions, these biological processes in neurons or non-neuronal cells lead to regionally distinct patterns of neuronal vulnerability and progression of pathology that could explain the disease symptomology. With the advent of patient-derived cellular models and novel genetic manipulation tools, we are now able to interrogate this commonality despite the cellular complexity of the brain in order to develop novel therapeutic strategies to prevent or arrest neurodegeneration. Here, we describe broadly these concepts and their relevance across neurodegenerative diseases.

Herpes Simplex Virus Vectors for Gene Transfer to the Central Nervous System

Neurodegenerative diseases (NDs) have a profound impact on human health worldwide and their incidence is predicted to increase as the population ages. ND severely limits the quality of life and leads to early death. Aside from treatments that may reduce symptoms, NDs are almost completely without means of therapeutic intervention. The genetic and biochemical basis of many NDs is beginning to emerge although most have complex etiologies for which common themes remain poorly resolved. Largely relying on progress in vector design, gene therapy is gaining increasing support as a strategy for genetic treatment of diseases. Here we describe recent developments in the engineering of highly defective herpes simplex virus (HSV) vectors suitable for transfer and long-term expression of large and/or multiple therapeutic genes in brain neurons in the complete absence of viral gene expression. These advanced vector platforms are safe, non-inflammatory, and persist in the nerve cell nucleus for life. In the near term, it is likely that HSV can be used to treat certain NDs that have a well-defined genetic cause. As further information on disease etiology becomes available, these vectors may take on an expanded role in ND therapies, including gene editing and repair.

The age of onset and evolution of Braak tangle stage and Thal amyloid pathology of Alzheimer's disease in individuals with Down syndrome

While post mortem studies have identified the major cell types and functional systems affected in Alzheimer’s disease (AD) the initial sites and molecular characteristics of pathology are still unclear. Because individuals with Down syndrome (DS) (trisomy 21) develop the full pathological changes of AD in a predictable way by the time they reach middle to late age, a study of the brains of such persons at different ages makes an ideal ‘model system’ in which the sites of earliest onset of pathology can be detected and the subsequent progression of changes be monitored. In the present study we have examined the brains of 56 individuals with DS ranging from new-born to 76 years for the presence of amyloid and tau pathology in key cortical and subcortical regions. Amyloid pathology was found to commence in the late teens to twenties as a deposition of diffuse plaques initially within the temporal neocortex, quickly involving other neocortical regions but only reaching subcortical regions and cerebellum by the late forties. Cerebral amyloid angiopathy did not regularly commence until after 45–50 years of age. Tau pathology usually commenced after 35 years of age, initially involving not only entorhinal areas and hippocampus but also subcortical regions such as locus caeruleus (LC) and dorsal raphe nucleus (DRN). Later, tau pathology spread throughout the neocortex reaching occipital lobes in most instances by mid-50 years of age. Such a pattern of spread is consistent with that seen in typical AD. We found no evidence that tau pathology might commence within the brain in DS before amyloid deposition had occurred, but there was limited data that suggests tau pathology in LC or DRN might predate that in entorhinal areas and hippocampus or at least be coincident.

Integrated analysis of human genetic association study and mouse transcriptome suggests LBH and SHF genes as novel susceptible genes for amyloid-β accumulation in Alzheimer's disease

Alzheimer's disease (AD) is a common neurological disease that causes dementia in humans. Although the reports of associated pathological genes have been increasing, the molecular mechanism leading to the accumulation of amyloid-β (Aβ) in human brain is still not well understood. To identify novel genes that cause accumulation of Aβ in AD patients, we conducted an integrative analysis by combining a human genetic association study and transcriptome analysis in mouse brain. First, we examined genome-wide gene expression levels in the hippocampus, comparing them to amyloid Aβ level in mice with mixed genetic backgrounds. Next, based on a GWAS statistics obtained by a previous study with human AD subjects, we obtained gene-based statistics from the SNP-based statistics. We combined p values from the two types of analysis across orthologous gene pairs in human and mouse into one p value for each gene to evaluate AD susceptibility. As a result, we found five genes with significant p values in this integrated analysis among the 373 genes analyzed. We also examined the gene expression level of these five genes in the hippocampus of independent human AD cases and control subjects. Two genes, LBH and SHF, showed lower expression levels in AD cases than control subjects. This is consistent with the gene expression levels of both the genes in mouse which were negatively correlated with Aβ accumulation. These results, obtained from the integrative approach, suggest that LBH and SHF are associated with the AD pathogenesis.

A Novel Association of Polymorphism in the ITGA4 Gene Encoding the VLA-4 α4 Subunit with Increased Risk of Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent cause of dementia in elderly people worldwide. Many studies support the hypothesis that the inflammation of the CNS contributes to the neurodegeneration and disease progression. The integrin molecule α4β1, also known as very late antigen 4 (VLA-4), belongs to adhesion molecules that activate the inflammatory process through the migration of immune cells into the CNS. Therefore, the objective of our study was to analyze the association between two polymorphisms located in the ITGA4 gene encoding the α4 subunit of VLA-4 and the risk of AD. 104 late-onset AD patients and 206 control subjects from Slovakia were genotyped for ITGA4 gene SNP polymorphism rs113276800 (-269C/A) and rs1143676 (+3061A/G). The same study cohorts were also genotyped for the APOE-ε4, which is a known genetic factor associated with increased risk of AD developing. ITGA4 polymorphism analysis revealed significantly higher frequency of the +3061AG carriers in AD group compared to the controls (P ≤ 0.05). Following the APOE-ε4 stratification of study groups, the association remained significant only in APOE-ε4 noncarriers. Our study suggests a novel association of ITGA4 +3061A/G polymorphism with AD and its possible contribution to the disease pathology.

Warning SINEs: Alu elements, evolution of the human brain, and the spectrum of neurological disease

Alu elements are a highly successful family of primate-specific retrotransposons that have fundamentally shaped primate evolution, including the evolution of our own species. Alus play critical roles in the formation of neurological networks and the epigenetic regulation of biochemical processes throughout the central nervous system (CNS), and thus are hypothesized to have contributed to the origin of human cognition. Despite the benefits that Alus provide, deleterious Alu activity is associated with a number of neurological and neurodegenerative disorders. In particular, neurological networks are potentially vulnerable to the epigenetic dysregulation of Alu elements operating across the suite of nuclear-encoded mitochondrial genes that are critical for both mitochondrial and CNS function. Here, we highlight the beneficial neurological aspects of Alu elements as well as their potential to cause disease by disrupting key cellular processes across the CNS. We identify at least 37 neurological and neurodegenerative disorders wherein deleterious Alu activity has been implicated as a contributing factor for the manifestation of disease, and for many of these disorders, this activity is operating on genes that are essential for proper mitochondrial function. We conclude that the epigenetic dysregulation of Alu elements can ultimately disrupt mitochondrial homeostasis within the CNS. This mechanism is a plausible source for the incipient neuronal stress that is consistently observed across a spectrum of sporadic neurological and neurodegenerative disorders.

ABCA1 Deficiency Affects Basal Cognitive Deficits and Dendritic Density in Mice

ATP-binding cassette transporter A1 (ABCA1) mediates cholesterol efflux to lipid-free apolipoproteins and regulates the generation of high density lipoproteins. Previously, we have shown that lack of Abca1 significantly increases amyloid deposition and cognitive deficits in Alzheimer’s disease model mice expressing human amyloid-β protein precursor (APP). The goal of this study was to determine if ABCA1 plays a role in memory deficits caused by amyloid-β (Aβ) oligomers and examine neurite architecture of pyramidal hippocampal neurons. Our results confirm previous findings that Abca1 deficiency significantly impairs spatial memory acquisition and retention in the Morris water maze and long-term memory in novel object recognition of APP transgenic mice at a stage of early amyloid pathology. Neither test demonstrated a significant difference between Abca1^ko and wild-type (WT) mice. We also examined the effect of intra-hippocampal infused Aβ oligomers on cognitive performance of Abca1^ko mice, compared to control infusion of scrambled Aβ peptide. Age-matched WT mice undergoing the same infusions were also used as controls. In this model system, we found a statistically significant difference between WT and Abca1^ko mice infused with scrambled Aβ, suggesting that Abca1^ko mice are vulnerable to the effect of mild stresses. Moreover, examination of neurite architecture in the hippocampi revealed a significant decrease in neurite length, number of neurite segments, and branches in Abca1^ko mice when compared to WT mice. We conclude that mice lacking ABCA1 have basal cognitive deficits that prevent them from coping with additional stressors, which is in part due to impairment of neurite morphology in the hippocampus.

Mitochondrial Regulatory Pathways in the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is an age-associated neurodegenerative brain disorder with progressive cognitive decline that leads to terminal dementia and death. For decades, amyloid-beta (Aβ) and neurofibrillary tangle (NFT) aggregation hypotheses have dominated studies on the pathogenesis and identification of potential therapeutic targets in AD. Little attention has been paid to the mitochondrial molecular/biochemical pathways leading to AD. Mitochondria play a critical role in cell viability and death including neurons and neuroglia, not only because they regulate energy and oxygen metabolism but also because they regulate cell death pathways. Mitochondrial impairment and oxidative stress are implicated in the pathogenesis of AD. Interestingly, current therapeutics provide symptomatic benefits to AD patients resulting in the use of preventive trials on presymptomatic subjects. This review article elucidates the pathophysiology of AD and emphasizes the need to explore the mitochondrial pathways to provide solutions to unanswered questions in the prevention and treatment of AD.

Pharmacogenetics

Pharmacogenetics is the study of how genetics influences drug treatment outcomes. Much research has been conducted to identify and characterize gene variants that impact the pharmacokinetic and pharmacodynamic aspects of medications used to treat neurologic and psychiatric disorders. This chapter reviews the current state of pharmacogenetic aspects of these treatments. Medications with supporting pharmacogenetic information in product labeling, clinical guidelines, or important mechanistic implications are discussed. At this time, clinically relevant genetic variation in drug metabolizing enzymes may inform drug dosing for a number of medications metabolized in the liver. Additionally, genetic variation in immunological genes may be tested to assess risk for severe hypersensitivity reactions to some anticonvulsant drugs. Finally, a growing body of research highlights that genetic polymorphisms in drug targets may influence symptom response or tolerability to some treatments.

Apo E4 Alleles and Impaired Olfaction as Predictors of Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia that affects more than 5 million Americans. It is the only disease among the 10 causes of death that cannot be slowed or cured, thus raising the need for identification of early preclinical markers that could be the focus of preventative efforts. Although evidence is escalating that abnormalities in olfactory structure and function precede AD development and early cognitive impairments by one or more decades, the importance of olfaction is largely overlooked in AD, and such testing is not routinely performed in neurology clinics. Nevertheless, research using the olfactory model, has begun to advance our understanding of the preclinical pathophysiology of AD. Notably, an interesting series of studies is beginning to illuminate the relationship between Apolipoprotein E (ApoE) ε4 polymorphism and olfactory dysfunction and late-onset Alzheimer's disease. In this article, we reviewed present research on the significance of ApoE and olfaction to AD, summarized current studies on the associations and mechanisms of ApoE and olfactory dysfunction, and highlighted important gaps for future work to further advance the translational application of the olfactory paradigm to early, preclinical diagnosis and treatment of AD.

Hippocampal synaptic and neural network deficits in young mice carrying the human APOE4 gene

INTRODUCTION

Apolipoprotein E4 (APOE4) is a major genetic risk factor for late-onset sporadic Alzheimer disease. Emerging evidence demonstrates a hippocampus-associated learning and memory deficit in aged APOE4 human carriers and also in aged mice carrying human APOE4 gene. This suggests that either exogenous APOE4 or endogenous APOE4 alters the cognitive profile and hippocampal structure and function. However, little is known regarding how Apoe4 modulates hippocampal dendritic morphology, synaptic function, and neural network activity in young mice.

AIM

In this study, we compared hippocampal dendritic and spine morphology and synaptic function of young (4 months) mice with transgenic expression of the human APOE4 and APOE3 genes.

METHODS

Hippocampal dendritic and spine morphology and synaptic function were assessed by neuronal imaging and electrophysiological approaches.

RESULTS

Morphology results showed that shortened dendritic length and reduced spine density occurred at hippocampal CA1 neurons in Apoe4 mice compared to Apoe3 mice. Electrophysiological results demonstrated that in the hippocampal CA3-CA1 synapses of young Apoe4 mice, basic synaptic transmission, and paired-pulse facilitation were enhanced but long-term potentiation and carbachol-induced hippocampal theta oscillations were impaired compared to young Apoe3 mice. However, both Apoe genotypes responded similarly to persistent stimulations (4, 10, and 40 Hz for 4 seconds).

CONCLUSION

Our results suggest significant alterations in hippocampal dendritic structure and synaptic function in Apoe4 mice, even at an early age.

Role of BACE1 in Alzheimer's synaptic function

Alzheimer's disease (AD) is the most common age-dependent disease of dementia, and there is currently no cure available. This hallmark pathologies of AD are the presence of amyloid plaques and neurofibrillary tangles. Although the exact etiology of AD remains a mystery, studies over the past 30 have shown that abnormal generation or accumulation of β-amyloid peptides (Aβ) is likely to be a predominant early event in AD pathological development. Aβ is generated from amyloid precursor protein (APP) via proteolytic cleavage by β-site APP cleaving enzyme 1 (BACE1). Chemical inhibition of BACE1 has been shown to reduce Aβ in animal studies and in human trials. While BACE1 inhibitors are currently being tested in clinical trials to treat AD patients, it is highly important to understand whether BACE1 inhibition will significantly impact cognitive functions in AD patients. This review summarizes the recent studies on BACE1 synaptic functions. This knowledge will help to guide the proper use of BACE1 inhibitors in AD therapy.

Hippocampal thinning linked to longer TOMM40 poly-T variant lengths in the absence of the APOE ε4 variant

INTRODUCTION

The translocase of outer mitochondrial membrane 40 (TOMM40), which lies in linkage disequilibrium with apolipoprotein E (APOE), has received attention more recently as a promising gene in Alzheimer's disease (AD) risk. TOMM40 influences AD pathology through mitochondrial neurotoxicity, and the medial temporal lobe (MTL) is the most likely brain region for identifying early manifestations of AD-related morphology changes.

METHODS

In this study, we examined the effects of TOMM40 using high-resolution magnetic resonance imaging in 65 healthy, older subjects with and without the APOE ε4 AD-risk variant.

RESULTS

Examining individual subregions within the MTL, we found a significant relationship between increasing poly-T lengths of the TOMM40 variant and thickness of the entorhinal cortex only in subjects who did not carry the APOE ε4 allele.

DISCUSSION

Our data provide support for TOMM40 variant repeat length as an important contributor to AD-like MTL pathology in the absence of APOE ε4.