Genetics of Alzheimer's disease

Frequency of variants in Mendelian Alzheimer's disease genes within the Alzheimer's Disease Sequencing Project

BackgroundPrior studies examined variants within presenilin-2 (PSEN2), presenilin-1 (PSEN1), and amyloid precursor protein (APP) genes. However, previously-reported clinically-relevant variants and other predicted damaging missense (DM) variants have not been characterized in a newer release of the Alzheimer's Disease Sequencing Project (ADSP).ObjectiveTo characterize previously-reported clinically-relevant variants and DM variants in PSEN2, PSEN1, APP within the participants from the ADSP.MethodsWe identified rare variants (MAF < 1%) in PSEN2, PSEN1, and APP in 14,641 individuals with whole genome sequencing and 16,849 individuals with whole exome sequencing available (Ntotal = 31,490). We additionally curated variants from ClinVar, OMIM, and Alzforum and report carriers of variants in clinical databases as well as predicted DM variants in these genes.ResultsWe detected 31 previously-reported clinically-relevant variants with alternate alleles observed within the ADSP: 4 variants in PSEN2, 25 in PSEN1, and 2 in APP. The overall variant carrier rate for the 31 clinically-relevant variants in the ADSP was 0.3%. We observed that 79.5% of the variant carriers were cases compared to 3.9% were controls. In those with AD, the mean age of onset of AD among carriers of these clinically-relevant variants was 19.6 ± 1.4 years earlier compared with noncarriers (p = 7.8 × 10-57). Additionally, we identified 197 rare variants (MAF < 1%) within ADSP participants not reported in known clinical databases.ConclusionsA small proportion of individuals in the ADSP are carriers of a previously-reported clinically-relevant variant allele for AD and these participants have significantly earlier age of AD onset compared to noncarriers.

Frequency of Variants in Mendelian Alzheimer's Disease Genes within the Alzheimer's Disease Sequencing Project (ADSP)

BACKGROUND

Prior studies using the ADSP data examined variants within presenilin-2 (PSEN2), presenilin-1 (PSEN1), and amyloid precursor protein (APP) genes. However, previously-reported clinically-relevant variants and other predicted damaging missense (DM) variants have not been characterized in a newer release of the Alzheimer's Disease Sequencing Project (ADSP).

OBJECTIVE

To characterize previously-reported clinically-relevant variants and DM variants in PSEN2, PSEN1, APP within the participants from the ADSP.

METHODS

We identified rare variants (MAF <1%) previously-reported in PSEN2, PSEN1, and APP in the available ADSP sample of 14,641 individuals with whole genome sequencing and 16,849 individuals with whole exome sequencing available for research-use (Ntotal = 31,490). We additionally curated variants in these three genes from ClinVar, OMIM, and Alzforum and report carriers of variants in clinical databases as well as predicted DM variants in these genes.

RESULTS

We detected 31 previously-reported clinically-relevant variants with alternate alleles observed within the ADSP: 4 variants in PSEN2, 25 in PSEN1, and 2 in APP. The overall variant carrier rate for the 31 clinically-relevant variants in the ADSP was 0.3%. We observed that 79.5% of the variant carriers were cases compared to 3.9% were controls. In those with AD, the mean age of onset of AD among carriers of these clinically-relevant variants was 19.6 ± 1.4 years earlier compared with noncarriers (p-value=7.8×10-57).

CONCLUSION

A small proportion of individuals in the ADSP are carriers of a previously-reported clinically-relevant variant allele for AD and these participants have significantly earlier age of AD onset compared to noncarriers.

Impaired cellular copper regulation in the presence of ApoE4

The strongest genetic risk factor for late-onset Alzheimer's disease (AD) is allelic variation of the APOE gene, with the following risk structure: ε4 > ε3 > ε2. The biochemical basis for this risk profile is unclear. Here, we reveal a new role for the APOE gene product, apolipoprotein E (ApoE) in regulating cellular copper homeostasis, which is perturbed in the AD brain. Exposure of ApoE target replacement (TR) astrocytes (immortalised astrocytes from APOE knock-in mice) to elevated copper concentrations resulted in exacerbated copper accumulation in ApoE4- compared to ApoE2- and ApoE3-TR astrocytes. This effect was also observed in SH-SY5Y neuroblastoma cells treated with conditioned medium from ApoE4-TR astrocytes. Increased intracellular copper levels in the presence of ApoE4 may be explained by reduced levels and delayed trafficking of the copper transport protein, copper-transporting ATPase 1 (ATP7A/Atp7a), potentially leading to impaired cellular copper export. This new role for ApoE in copper regulation lends further biochemical insight into how APOE genotype confers risk for AD and reveals a potential contribution of ApoE4 to the copper dysregulation that is a characteristic pathological feature of the AD brain.

Essential New Complexity-Based Themes for Patient-Centered Diagnosis and Treatment of Dementia and Predementia in Older People: Multimorbidity and Multilevel Phenomenology

Dementia is a highly prevalent condition with devastating clinical and socioeconomic sequela. It is expected to triple in prevalence by 2050. No treatment is currently known to be effective. Symptomatic late-onset dementia and predementia (SLODP) affects 95% of patients with the syndrome. In contrast to trials of pharmacological prevention, no treatment is suggested to remediate or cure these symptomatic patients. SLODP but not young onset dementia is intensely associated with multimorbidity (MUM), including brain-perturbating conditions (BPCs). Recent studies showed that MUM/BPCs have a major role in the pathogenesis of SLODP. Fortunately, most MUM/BPCs are medically treatable, and thus, their treatment may modify and improve SLODP, relieving suffering and reducing its clinical and socioeconomic threats. Regrettably, the complex system features of SLODP impede the diagnosis and treatment of the potentially remediable conditions (PRCs) associated with them, mainly due to failure of pattern recognition and a flawed diagnostic workup. We suggest incorporating two SLODP-specific conceptual themes into the diagnostic workup: MUM/BPC and multilevel phenomenological themes. By doing so, we were able to improve the diagnostic accuracy of SLODP components and optimize detecting and favorably treating PRCs. These revolutionary concepts and their implications for remediability and other parameters are discussed in the paper.

A systems biology-based identification and in vivo functional screening of Alzheimer's disease risk genes reveal modulators of memory function

Genome-wide association studies (GWASs) have uncovered over 75 genomic loci associated with risk for late-onset Alzheimer's disease (LOAD), but identification of the underlying causal genes remains challenging. Studies of induced pluripotent stem cell (iPSC)-derived neurons from LOAD patients have demonstrated the existence of neuronal cell-intrinsic functional defects. Here, we searched for genetic contributions to neuronal dysfunction in LOAD using an integrative systems approach that incorporated multi-evidence-based gene mapping and network-analysis-based prioritization. A systematic perturbation screening of candidate risk genes in Caenorhabditis elegans (C. elegans) revealed that neuronal knockdown of the LOAD risk gene orthologs vha-10 (ATP6V1G2), cmd-1 (CALM3), amph-1 (BIN1), ephx-1 (NGEF), and pho-5 (ACP2) alters short-/intermediate-term memory function, the cognitive domain affected earliest during LOAD progression. These results highlight the impact of LOAD risk genes on evolutionarily conserved memory function, as mediated through neuronal endosomal dysfunction, and identify new targets for further mechanistic interrogation.

Epigenetic Regulation of Neural Stem Cells in Developmental and Adult Stages

The development of the nervous system is regulated by numerous intracellular molecules and cellular signals that interact temporally and spatially with the extracellular microenvironment. The three major cell types in the brain, i.e., neurons and two types of glial cells (astrocytes and oligodendrocytes), are generated from common multipotent neural stem cells (NSCs) throughout life. However, NSCs do not have this multipotentiality from the beginning. During cortical development, NSCs sequentially obtain abilities to differentiate into neurons and glial cells in response to combinations of spatiotemporally modulated cell-intrinsic epigenetic alterations and extrinsic factors. After the completion of brain development, a limited population of NSCs remains in the adult brain and continues to produce neurons (adult neurogenesis), thus contributing to learning and memory. Many biological aspects of brain development and adult neurogenesis are regulated by epigenetic changes via behavioral control of NSCs. Epigenetic dysregulation has also been implicated in the pathogenesis of various brain diseases. Here, we present recent advances in the epigenetic regulation of NSC behavior and its dysregulation in brain disorders.

Genome-wide association study and expression of candidate genes for Fe and Zn concentration in sorghum grains

Sorghum germplasm showed grain Fe and Zn genetic variability, but a few varieties were biofortified with these minerals. This work contributes to narrowing this gap. Fe and Zn concentrations along with 55,068 high-quality GBS SNP data from 140 sorghum accessions were used in this study. Both micronutrients exhibited good variability with respective ranges of 22.09-52.55 ppm and 17.92-43.16 ppm. Significant marker-trait associations were identified on chromosomes 1, 3, and 5. Two major effect SNPs (S01_72265728 and S05_58213541) explained 35% and 32% of Fe and Zn phenotypic variance, respectively. The SNP S01_72265728 was identified in the cytochrome P450 gene and showed a positive effect on Fe accumulation in the kernel, while S05_58213541 was intergenic near Sobic.005G134800 (zinc-binding ribosomal protein) and showed negative effect on Zn. Tissue-specific in silico expression analysis resulted in higher levels of Sobic.003G350800 gene product in several tissues such as leaf, root, flower, panicle, and stem. Sobic.005G188300 and Sobic.001G463800 were expressed moderately at grain maturity and anthesis in leaf, root, panicle, and seed tissues. The candidate genes expressed in leaves, stems, and grains will be targeted to improve grain and stover quality. The haplotypes identified will be useful in forward genetics breeding.

Ginkgo biloba extract mitigates the neurotoxicity of AlCl3 in alzheimer rat's model: role of apolipoprotein E4 and clusterin genes in stimulating ROS generation and apoptosis

PURPOSE

Alzheimer's disease (AD) appears as a result of an increase in the accumulation of amyloid beta peptide (Aβ) and a decrease in neurotransmitters (acetylcholine) within the brain cells which may be due to increase in acetylcholinesterase (AchE) activity and change in expression of Apolipoprotein E4 (ApoE4) and Clusterin (Clu) genes. The aim of the present study was using natural products such as Ginkgo biloba (G. biloba) extract that has the potential to reduce Aβ formation and increase AchE inhibition with its ability to save neuronal DNA from damage.

METHODS

Sixty male aged rats were divided into six experimental groups exposed to AlCl3 to induce AD model and were treated with G. biloba extract. Collected brain tissues were used to assess the apoptosis rate, reactive oxygen species (ROS) generation, AchE inhibitory activity, expression alteration in ApoE4 and Clu genes, DNA fragmentations and gutathione peroxidase (GPx) activity.Results: The results exhibited that rats exposed to AlCl3 increased significantly rate of apoptosis, ROS formation, DNA fragmentation, up-regulation of ApoE4 and Clu genes as well as decrease of AchE inhibitory activity and GPx activity compared with those in control rats. However, treatment of AlCl3-rats with G. biloba extract improved the above neurotoxicity results induced by AlCl3 exposure.

CONCLUSIONS

It is therefore likely that G. biloba extract's protective properties against AD are due to its ability to activate the response against oxidative stress.

Mesenchymal Stem Cells from Familial Alzheimer's Patients Express MicroRNA Differently

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the predominant form of dementia globally. No reliable diagnostic, predictive techniques, or curative interventions are available. MicroRNAs (miRNAs) are vital to controlling gene expression, making them valuable biomarkers for diagnosis and prognosis. This study examines the transcriptome of olfactory ecto-mesenchymal stem cells (MSCs) derived from individuals with the PSEN1(A431E) mutation (Jalisco mutation). The aim is to determine whether this mutation affects the transcriptome and expression profile of miRNAs and their target genes at different stages of asymptomatic, presymptomatic, and symptomatic conditions. Expression microarrays compare the MSCs from mutation carriers with those from healthy donors. The results indicate a distinct variation in the expression of miRNAs and mRNAs among different symptomatologic groups and between individuals with the mutation. Using bioinformatics tools allows us to identify target genes for miRNAs, which in turn affect various biological processes and pathways. These include the cell cycle, senescence, transcription, and pathways involved in regulating the pluripotency of stem cells. These processes are closely linked to inter- and intracellular communication, vital for cellular functioning. These findings can enhance our comprehension and monitoring of the disease's physiological processes, identify new disorder indicators, and develop innovative treatments and diagnostic tools for preventing or treating AD.

Multi-Omic Blood Biomarkers as Dynamic Risk Predictors in Late-Onset Alzheimer's Disease

Late-onset Alzheimer's disease is the leading cause of dementia worldwide, accounting for a growing burden of morbidity and mortality. Diagnosing Alzheimer's disease before symptoms are established is clinically challenging, but would provide therapeutic windows for disease-modifying interventions. Blood biomarkers, including genetics, proteins and metabolites, are emerging as powerful predictors of Alzheimer's disease at various timepoints within the disease course, including at the preclinical stage. In this review, we discuss recent advances in such blood biomarkers for determining disease risk. We highlight how leveraging polygenic risk scores, based on genome-wide association studies, can help stratify individuals along their risk profile. We summarize studies analyzing protein biomarkers, as well as report on recent proteomic- and metabolomic-based prediction models. Finally, we discuss how a combination of multi-omic blood biomarkers can potentially be used in memory clinics for diagnosis and to assess the dynamic risk an individual has for developing Alzheimer's disease dementia.

Biomarkers in Alzheimer's Disease: Are Olfactory Neuronal Precursors Useful for Antemortem Biomarker Research?

Alzheimer's disease (AD), as the main cause of dementia, affects millions of people around the world, whose diagnosis is based mainly on clinical criteria. Unfortunately, the diagnosis is obtained very late, when the neurodegenerative damage is significant for most patients. Therefore, the exhaustive study of biomarkers is indispensable for diagnostic, prognostic, and even follow-up support. AD is a multifactorial disease, and knowing its underlying pathological mechanisms is crucial to propose new and valuable biomarkers. In this review, we summarize some of the main biomarkers described in AD, which have been evaluated mainly by imaging studies in cerebrospinal fluid and blood samples. Furthermore, we describe and propose neuronal precursors derived from the olfactory neuroepithelium as a potential resource to evaluate some of the widely known biomarkers of AD and to gear toward searching for new biomarkers. These neuronal lineage cells, which can be obtained directly from patients through a non-invasive and outpatient procedure, display several characteristics that validate them as a surrogate model to study the central nervous system, allowing the analysis of AD pathophysiological processes. Moreover, the ease of obtaining and harvesting endows them as an accessible and powerful resource to evaluate biomarkers in clinical practice.

miRNA-211-5p inhibition enhances the protective effect of hucMSC-derived exosome in Aβ1-40 -induced SH-SY5Y cells by increasing NEP expression

Exosomes derived from human umbilical cord mesenchymal stem cells (hucMSCs) could alleviate Alzheimer's disease (AD) defects. Additionally, engineered exosomes are more effective in treating diseases. In this study, we established an in vitro model of AD by treating SH-SY5Y cells with Aβ1-40 . We observed that incubation with hucMSC-derived exosomes effectively protected SH-S5Y5 cells from Aβ1-40 -induced damage. Since NEP plays a central role in suppressing AD development, we screened NEP-targeting miRNAs that are differentially expressed in control and AD patients. We identified miR-211-5p as a potent repressor of NEP expression. Exosomes purified from hucMSCs overexpressing miR-211-5p inhibitor exhibited significantly greater efficiency than control exosomes in mitigating the injury caused by Aβ1-40 treatment. However, this enhanced protective effect was nullified by the knockdown of NEP. These observations demonstrate that inhibition of miR-211-5p has the potential to improve the efficacy of hucMSC-derived exosomes in AD treatment by increasing NEP expression.

Deep Brain Stimulation beyond the Clinic: Navigating the Future of Parkinson's and Alzheimer's Disease Therapy

Deep brain stimulation (DBS) is a surgical procedure that uses electrical neuromodulation to target specific regions of the brain, showing potential in the treatment of neurodegenerative disorders such as Parkinson's disease (PD) and Alzheimer's disease (AD). Despite similarities in disease pathology, DBS is currently only approved for use in PD patients, with limited literature on its effectiveness in AD. While DBS has shown promise in ameliorating brain circuits in PD, further research is needed to determine the optimal parameters for DBS and address any potential side effects. This review emphasizes the need for foundational and clinical research on DBS in different brain regions to treat AD and recommends the development of a classification system for adverse effects. Furthermore, this review suggests the use of either a low-frequency system (LFS) or high-frequency system (HFS) depending on the specific symptoms of the patient for both PD and AD.

Baseline grey matter volumes and white matter hyperintensities predict decline in functional activities in older adults over a 5-year follow-up period

INTRODUCTION

Functional independence is an essential predictor of quality of life in aging, yet few accessible predictors of functional decline have been identified. This study examined associations between baseline structural neuroimaging markers and longitudinal functional status.

METHODS

Linear mixed effects models with follow-up time interaction terms related baseline grey matter volume and white matter hyperintensities (WMHs) to functional trajectory, adjusting for demographic and medical covariates. Subsequent models assessed interactions with cognitive status and apolipoprotein E (APOE) ε4 status.

RESULTS

Smaller baseline grey matter volumes, particularly in regions commonly affected by Alzheimer's disease (AD), and greater baseline WMHs were associated with faster functional decline over a mean 5-year follow-up. Effects were stronger in APOE-ε4 carriers on grey matter variables. Cognitive status interacted with most MRI variables.

DISCUSSION

Greater atrophy in AD-related regions and higher WMH burden at study entry were associated with faster functional decline, particularly among participants at increased risk of AD.

The neuroprotective effects of oxygen therapy in Alzheimer’s disease: a narrative review

Alzheimer’s disease (AD) is a degenerative neurological disease that primarily affects the elderly. Drug therapy is the main strategy for AD treatment, but current treatments suffer from poor efficacy and a number of side effects. Non-drug therapy is attracting more attention and may be a better strategy for treatment of AD. Hypoxia is one of the important factors that contribute to the pathogenesis of AD. Multiple cellular processes synergistically promote hypoxia, including aging, hypertension, diabetes, hypoxia/obstructive sleep apnea, obesity, and traumatic brain injury. Increasing evidence has shown that hypoxia may affect multiple pathological aspects of AD, such as amyloid-beta metabolism, tau phosphorylation, autophagy, neuroinflammation, oxidative stress, endoplasmic reticulum stress, and mitochondrial and synaptic dysfunction. Treatments targeting hypoxia may delay or mitigate the progression of AD. Numerous studies have shown that oxygen therapy could improve the risk factors and clinical symptoms of AD. Increasing evidence also suggests that oxygen therapy may improve many pathological aspects of AD including amyloid-beta metabolism, tau phosphorylation, neuroinflammation, neuronal apoptosis, oxidative stress, neurotrophic factors, mitochondrial function, cerebral blood volume, and protein synthesis. In this review, we summarized the effects of oxygen therapy on AD pathogenesis and the mechanisms underlying these alterations. We expect that this review can benefit future clinical applications and therapy strategies on oxygen therapy for AD.

Epigenetic Modifications by Estrogen and Androgen in Alzheimer's Disease

For the development and maintenance of neuron networks in the brain, epigenetic mechanisms are necessary, as indicated by recent findings. This includes some of the high-order brain processes, such as behavior and cognitive functions. Epigenetic mechanisms could influence the pathophysiology or etiology of some neuronal diseases, altering disease susceptibility and therapy responses. Recent studies support epigenetic dysfunctions in neurodegenerative and psychiatric conditions, such as Alzheimer's disease (AD). These dysfunctions in epigenetic mechanisms also play crucial roles in the transgenerational effects of the environment on the brain and subsequently in the inheritance of pathologies. The possible role of gonadal steroids in the etiology and progression of neurodegenerative diseases, including Alzheimer's disease, has become the subject of a growing body of research over the last 20 years. Recent scientific findings suggest that epigenetic changes, driven by estrogen and androgens, play a vital role in brain functioning. Therefore, exploring the role of estrogen and androgen-based epigenetic changes in the brain is critical for the deeper understanding of AD. This review highlights the epigenetic modifications caused by these two gonadal steroids and the possible therapeutic strategies for AD.

Genome-wide association of polygenic risk extremes for Alzheimer's disease in the UK Biobank

In just over a decade, advances in genome-wide association studies (GWAS) have offered an approach to stratify individuals based on genetic risk for disease. Using recent Alzheimer's disease (AD) GWAS results as the base data, we determined each individual's polygenic risk score (PRS) in the UK Biobank dataset. Using individuals within the extreme risk distribution, we performed a GWAS that is agnostic of AD phenotype and is instead based on known genetic risk for disease. To interpret the functions of the new risk factors, we conducted phenotype analyses, including a phenome-wide association study. We identified 246 loci surpassing the significance threshold of which 229 were not reported in the base AD GWAS. These include loci that showed suggestive levels of association in the base GWAS and loci not previously suspected to be associated with AD. Among these, there are loci, such as IL34 and KANSL1, that have since been shown to be associated with AD in recent studies. We also show highly significant genetic correlations with multiple health-related outcomes that provide insights into prodromal symptoms and comorbidities. This is the first study to utilize PRS as a phenotype-agnostic group classification in AD genetic studies. We identify potential new loci for AD and detail phenotypic analysis of these PRS extremes.

Associations between Certain Polymorphisms in Proinflammatory Cytokines and Predisposition of Alzheimer's Disease: A Meta-Analysis

BACKGROUND

Functional gene polymorphisms of proinflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-8 (IL-8), and interleukin-18 (IL-18) may contribute to the onset and development of Alzheimer's disease (AD), but the relationships between these polymorphisms and predisposition of AD remain controversial.

OBJECTIVES

This meta-analysis was conducted to more robustly assess relationships between TNF-α/IL-6/IL-8/IL-18 polymorphisms and predisposition of AD by pooling the findings of relevant studies.

METHODS

A comprehensive literature searching was performed in PubMed, Embase, Web of Science, Wanfang, and CNKI databases, and 63 studies were found to be eligible for quantitative analyses.

RESULTS

The pooled meta-analysis results showed that genotypic frequencies of TNF-α rs1800629, IL-6 rs1800795, IL-8 rs4073, and IL-18 rs187238 polymorphisms among AD cases and controls of Asian ethnicity differed significantly. But, we did not observe such genotypic frequencies differences in Caucasians.

CONCLUSIONS

This meta-analysis suggests that TNF-α rs1800629, IL-6 rs1800795, IL-8 rs4073, and IL-18 rs187238 polymorphisms may affect predisposition of AD in Asians, but not in Caucasians.

IL-6, IL-8 and IL-10 polymorphisms may impact predisposition of Alzheimer's disease: a meta-analysis

Gene polymorphisms in interleukin-6 (IL-6), interleukin-8 (IL-8), and interleukin-10 (IL-10) may affect the predisposition of Alzheimer's disease (AD), but the results of the so far published studies remain controversial. The authors conducted this meta-analysis to assess relationships between IL-6/IL-8/IL-10 polymorphisms and predisposition of AD by pooling the findings of so far published studies. A comprehensive search of Pubmed, Embase, Web of Science, and CNKI was endorsed by the authors to identify the already published studies. Forty-five studies were found to be eligible for meta-analyses. The pooled meta-analyses results showed that genotypic frequencies of IL-6 - 174 G/C, IL-6 - 572 G/C and IL-10 - 1082 A/G polymorphisms among patients with AD and controls differed significantly. Moreover, genotypic frequencies of IL-6 - 174 G/C, IL-6 - 572 G/C, and IL-8 - 251 A/T polymorphisms among patients with AD and controls in Asians also differed significantly. But no such genotypic frequencies' differences were observed for IL-10 - 819 C/T and 592 C/A polymorphisms. This meta-analysis suggests that IL-6 - 174 G/C, IL-6 - 572 G/C, and IL-10 - 1082 A/G polymorphisms may affect the predisposition of AD in overall population. Moreover, IL-6 - 174 G/C, IL-6 - 572 G/C, and IL-8 - 251 A/T polymorphisms may affect the predisposition of AD in Asians.

Revelation of Pivotal Genes Pertinent to Alzheimer's Pathogenesis: A Methodical Evaluation of 32 GEO Datasets

Alzheimer’s disease (AD), a dreadful neurodegenerative disorder that affects cognitive and behavioral function in geriatric populations, is characterized by the presence of amyloid deposits and neurofibrillary tangles in brain regions. The International D World Alzheimer Report2018 noted a global prevalence of 50 million AD cases and forecasted a threefold rise to 139 million by 2050. Although there exist numerous genetic association studies pertinent to AD in different ethnicities, critical genetic factors and signaling pathways underlying its pathogenesis remain ambiguous. This study was aimed to analyze the genetic data retrieved from 32 Gene Expression Omnibus datasets belonging to diverse ethnic cohorts in order to identify overlapping differentially expressed genes (DEGs). Stringent selection criteria were framed to shortlist appropriate datasets based on false discovery rate (FDR) p-value and log FC, and relevant details of upregulated and downregulated DEGs were retrieved. Among the 32 datasets, only six satisfied the selection criteria. The GEO2R tool was employed to retrieve significant DEGs. Nine common DEGs, i.e., SLC5A3, BDNF, SST, SERPINA3, RTN3, RGS4, NPTX, ENC1 and CRYM were found in more than 60% of the selected datasets. These DEGs were later subjected to protein–protein interaction analysis with 18 AD-specific literature-derived genes. Among the nine common DEGs, BDNF, SST, SERPINA3, RTN3 and RGS4 exhibited significant interactions with crucial proteins including BACE1, GRIN2B, APP, APOE, COMT, PSEN1, INS, NEP and MAPT. Functional enrichment analysis revealed involvement of these genes in trans-synaptic signaling, chemical transmission, PI3K pathway signaling, receptor–ligand activity and G protein signaling. These processes are interlinked with AD pathways.

Alzheimer's disease: a tale of two diseases?

Sporadic late-onset Alzheimer's disease (SLOAD) and familial early-onset Alzheimer's disease (FEOAD) associated with dominant mutations in APP, PSEN1 and PSEN2, are thought to represent a spectrum of the same disorder based on near identical behavioral and histopathological features. Hence, FEOAD transgenic mouse models have been used in past decades as a surrogate to study SLOAD pathogenic mechanisms and as the gold standard to validate drugs used in clinical trials. Unfortunately, such research has yielded little output in terms of therapeutics targeting the disease's development and progression. In this short review, we interrogate the widely accepted view of one, dimorphic disease through the prism of the Bmi1+/- mouse model and the distinct chromatin signatures observed between SLOAD and FEOAD brains.

Relationship Between Chronic Noise Exposure, Cognitive Impairment, and Degenerative Dementia: Update on the Experimental and Epidemiological Evidence and Prospects for Further Research

Degenerative dementia, of which Alzheimer's disease is the most common form, is characterized by the gradual deterioration of cognitive function. The events that trigger and promote degenerative dementia are not clear, and treatment options are limited. Experimental and epidemiological studies have revealed chronic noise exposure (CNE) as a potential risk factor for cognitive impairment and degenerative dementia. Experimental studies have indicated that long-term exposure to noise might accelerate cognitive dysfunction, amyloid-β deposition, and tau hyperphosphorylation in different brain regions such as the hippocampus and cortex. Epidemiological studies are increasingly examining the possible association between external noise exposure and dementia. In this review, we sought to construct a comprehensive summary of the relationship between CNE, cognitive dysfunction, and degenerative dementia. We also present the limitations of existing evidence as a guide regarding important prospects for future research.

X-factors in human disease: Impact of gene content and dosage regulation

The gene content of the X and Y chromosomes has dramatically diverged during evolution. The ensuing dosage imbalance within the genome of males and females has led to unique chromosome-wide regulatory mechanisms with significant and sex-specific impacts on X-linked gene expression. X inactivation or silencing of most genes on one X chromosome chosen at random in females profoundly affects the manifestation of X-linked diseases, as males inherit a single maternal allele, while females express maternal and paternal alleles in a mosaic manner. An additional complication is the existence of genes that escape X inactivation and thus are ubiquitously expressed from both alleles in females. The mosaic nature of X-linked gene expression and the potential for escape can vary between individuals, tissues, cell types, and stages of life. Our understanding of the specialized nature of X-linked genes and of the multilayer epigenetic regulation that influence their expression throughout the organism has been helped by molecular studies conducted by tissue-specific and single-cell-specific approaches. In turn, the definition of molecular events that control X silencing has helped develop new approaches for the treatment of some X-linked disorders. This review focuses on the peculiarities of the X chromosome genetic content and epigenetic regulation in shaping the manifestation of congenital and acquired X-linked disorders in a sex-specific manner.

Discovery and Validation of Key Biomarkers Based on Immune Infiltrates in Alzheimer's Disease

BACKGROUND

As the most common neurodegenerative disease, Alzheimer's disease (AD) leads to progressive loss of cognition and memory. Presently, the underlying pathogenic genes of AD patients remain elusive, and effective disease-modifying therapy is not available. This study explored novel biomarkers that can affect diagnosis and treatment in AD based on immune infiltration.

METHODS

The gene expression profiles of 139 AD cases and 134 normal controls were obtained from the NCBI GEO public database. We applied the computational method CIBERSORT to bulk gene expression profiles of AD to quantify 22 subsets of immune cells. Besides, based on the use of the Least Absolute Shrinkage Selection Operator (LASSO), this study also applied SVM-RFE analysis to screen key genes. GO-based semantic similarity and logistic regression model analyses were applied to explore hub genes further.

RESULTS

There was a remarkable significance in the infiltration of immune cells between the subgroups. The proportions for monocytes, M0 macrophages, and dendritic cells in the AD group were significantly higher than those in the normal group, while the proportion of some cells was lower than that of the normal group, such as NK cell resting, T-cell CD4 naive, T-cell CD4 memory activation, and eosinophils. Additionally, seven genes (ABCA2, CREBRF, CD72, CETN2, KCNG1, NDUFA2, and RPL36AL) were identified as hub genes. Then we performed the analysis of immune factor correlation, gene set enrichment analysis (GSEA), and GO based on seven hub genes. The AUC of ROC prediction model in test and validation sets were 0.845 and 0.839, respectively. Eventually, the mRNA expression analysis of ABCA2, NDUFA2, CREBRF, and CD72 revealed significant differences among the seven hub genes and then was confirmed by RT-PCR.

CONCLUSION

A model based on immune cell infiltration might be used to forecast AD patients' diagnosis, and it provided a new perspective for AD treatment targets.

Diagnostic and Prognostic Laboratory Testing for Alzheimer Disease

This article focuses on current clinical laboratory testing to diagnose Alzheimer disease and monitor its progression throughout its disease course. Several clinically available tests focus on analysis of amyloid and tau levels in cerebrospinal fluid as well as autosomal dominant and risk factor genes. Although the current armament of clinical laboratory testing is limited by invasiveness of cerebrospinal fluid collection, rarity of autosomal dominant genetic mutations, and uncertainties of risk inherent in nonpenetrant genes, the field is poised to advance the clinical repertoire of laboratory diagnostic testing.

Verification of CRISPR editing and finding transgenic inserts by Xdrop indirect sequence capture followed by short- and long-read sequencing

Validation of CRISPR-Cas9 editing typically explores the immediate vicinity of the gene editing site and distal off-target sequences, which has led to the conclusion that CRISPR-Cas9 editing is very specific. However, an increasing number of studies suggest that on-target unintended editing events like deletions and insertions are relatively frequent but unfortunately often missed in the validation of CRISPR-Cas9 editing. The deletions may be several kilobases-long and only affect one allele. The gold standard in molecular validation of gene editing is direct sequencing of relatively short PCR amplicons. This approach allows the detection of small editing events but fails in detecting large rearrangements, in particular when only one allele is affected. Detection of large rearrangements requires that an extended region is analyzed and the characterization of events may benefit from long-read sequencing. Here we implemented Xdrop™, a new microfluidic technology that allows targeted enrichment of long regions (~100 kb) using just a single standard PCR primer set. Sequencing of the enriched CRISPR-Cas9 gene-edited region in four cell lines on long- and short-read sequencing platforms unravelled unknown and unintended genome editing events. The analysis revealed accidental kilobases-large insertions in three of the cell lines, which remained undetected using standard procedures. We also applied the targeted enrichment approach to identify the integration site of a transgene in a mouse line. The results demonstrate the potential of this technology in gene editing validation as well as in more classic transgenics.

The biological pathways of Alzheimer disease: a review

Alzheimer disease is a progressive neurodegenerative disorder, mainly affecting older people, which severely impairs patients' quality of life. In the recent years, the number of affected individuals has seen a rapid increase. It is estimated that up to 107 million subjects will be affected by 2050 worldwide. Research in this area has revealed a lot about the biological and environmental underpinnings of Alzheimer, especially its correlation with β-Amyloid and Tau related mechanics; however, the precise molecular events and biological pathways behind the disease are yet to be discovered. In this review, we focus our attention on the biological mechanics that may lie behind Alzheimer development. In particular, we briefly describe the genetic elements and discuss about specific biological processes potentially associated with the disease.

The Differential Influence of Immune, Endocytotic, and Lipid Metabolism Genes on Amyloid Deposition and Neurodegeneration in Subjects at Risk of Alzheimer's Disease

BACKGROUND

Over 20 single-nucleotide polymorphisms (SNPs) are associated with increased risk of Alzheimer's disease (AD). We categorized these loci into immunity, lipid metabolism, and endocytosis pathways, and associated the polygenic risk scores (PRS) calculated, with AD biomarkers in mild cognitive impairment (MCI) subjects.

OBJECTIVE

The aim of this study was to identify associations between pathway-specific PRS and AD biomarkers in patients with MCI and healthy controls.

METHODS

AD biomarkers ([18F]Florbetapir-PET SUVR, FDG-PET SUVR, hippocampal volume, CSF tau and amyloid-β levels) and neurocognitive tests scores were obtained in 258 healthy controls and 451 MCI subjects from the ADNI dataset at baseline and at 24-month follow up. Pathway-related (immunity, lipid metabolism, and endocytosis) and total polygenic risk scores were calculated from 20 SNPs. Multiple linear regression analysis was used to test predictive value of the polygenic risk scores over longitudinal biomarker and cognitive changes.

RESULTS

Higher immune risk score was associated with worse cognitive measures and reduced glucose metabolism. Higher lipid risk score was associated with increased amyloid deposition and cortical hypometabolism. Total, immune, and lipid scores were associated with significant changes in cognitive measures, amyloid deposition, and brain metabolism.

CONCLUSION

Polygenic risk scores highlights the influence of specific genes on amyloid-dependent and independent pathways; and these pathways could be differentially influenced by lipid and immune scores respectively.

Genetic associations of in vivo pathology influence Alzheimer's disease susceptibility

INTRODUCTION

Although the heritability of sporadic Alzheimer's disease (AD) is estimated to be 60-80%, addressing the genetic contribution to AD risk still remains elusive. More specifically, it remains unclear whether genetic variants are able to affect neurodegenerative brain features that can be addressed by in vivo imaging techniques.

METHODS

Targeted sequencing analysis of the coding and UTR regions of 132 AD susceptibility genes was performed. Neuroimaging data using 11C-Pittsburgh Compound B positron emission tomography (PET), 18F-fluorodeoxyglucose PET, and MRI that are available from the KBASE (Korean Brain Aging Study for Early Diagnosis and Prediction of Alzheimer's disease) cohort were acquired. A total of 557 participants consisted of 336 cognitively normal (CN) adults, 137 mild cognitive impairment (MCI), and 84 AD dementia (ADD) groups.

RESULTS

We called 5391 high-quality single nucleotide variants (SNVs) on AD susceptibility genes and selected significant associations between variants and five in vivo AD pathologies: (1) amyloid β (Aβ) deposition, (2) AD-signature region cerebral glucose metabolism (AD-Cm), (3) posterior cingulate cortex (PCC) cerebral glucose metabolism (PCC-Cm), (4) AD-signature region cortical thickness (AD-Ct), and (5) hippocampal volume (Hv). The association analysis for common variants (allele frequency (AF) > 0.05) yielded several novel loci associated with Aβ deposition (PIWIL1-rs10848087), AD-Cm (NME8-rs2722372 and PSEN2-rs75733498), AD-Ct (PSEN1-rs7523) and, Hv (CASS4-rs3746625). Meanwhile, in a gene-based analysis for rare variants (AF < 0.05), cases carrying rare variants in LPL, FERMT2, NFAT5, DSG2, and ITPR1 displayed associations with the neuroimaging features. Exploratory voxel-based brain morphometry between the variant carriers and non-carriers was performed subsequently. Finally, we document a strong association of previously reported APOE variants with the in vivo AD pathologies and demonstrate that the variants exert a causal effect on AD susceptibility via neuroimaging features.

CONCLUSIONS

This study provides novel associations of genetic factors to Aβ accumulation and AD-related neurodegeneration to influence AD susceptibility.

Anti-Alzheimer's Materials Isolated from Marine Bio-resources: A Review

The most common type of dementia found in the elderly population is Alzheimer's disease. The disease not only impacts the patients and their families but also the society therefore, the main focus of researchers is to search new bioactive materials for treating AD. The marine environment is a rich source of functional ingredients and to date, we can find sufficient research relating to anti- Alzheimer's compounds isolated from marine environment. Therefore, this review focuses on the anti- Alzheimer's material from marine bio-resources and then expounds on the anti-Alzheimer's compounds from marine seaweed, marine animal and marine microorganisms. Moreover, because of the complexity of the disease, different hypothesizes have been elaborated and active compounds have been isolated to inhibit different stages of pathophysiological mechanisms. Sulfated polysaccharides, glycoprotein, and enzymatic hydrolysates from marine seaweeds, peptides, dietary omega-3 polyunsaturated fatty acids and skeletal polysaccharide from marine animals and secondary metabolites from marine microorganism are summarized in this review under the anti-Alzheimer's compounds from the marine.

Dance for People with Alzheimer's Disease: A Systematic Review

BACKGROUND

In recent years, several reviews have addressed the effectiveness of dance therapy in dementia, healthy older adults, or the elderly in general. However, reviews regarding the effect of this therapy exclusively on patients diagnosed with Alzheimer's disease have not been found.

OBJECTIVE

The purpose of this study is to review the available literature describing clinical trials which explore the effects of dancing on psychological and physical outcomes, functionality, cognitive function, and quality of life in patients diagnosed with Alzheimer's disease. In addition, this review aims to assess the quality of studies that perform dance therapy interventions in these patients.

METHODS

This study is a systematic review of randomized and non-randomized clinical trials regarding the effect of intervention including a dancing activity in people diagnosed with Alzheimer's disease.

RESULTS

In total, the evidence for this review rests on 12 studies with a total of 349 participants. The findings of this mini-review confirm the positive effect of dance therapy on physical and cognitive function, functionality, psychological outcomes, and quality of life in people with Alzheimer's disease.

CONCLUSION

Most of the studies implementing dance as part of the therapeutic treatment has shown to improve or slow the worsening in the quality of life of patients with Alzheimer's disease and their caregivers. Future research focused on these patients should use a more exhaustive methodology and make a more detailed description of these kind of interventions.

Overdosing on iron: Elevated iron and degenerative brain disorders

IMPACT STATEMENT

Brain degenerative disorders, which include some neurodevelopmental disorders and age-associated diseases, cause debilitating neurological deficits and are generally fatal. A large body of emerging evidence indicates that iron accumulation in neurons within specific regions of the brain plays an important role in the pathogenesis of many of these disorders. Iron homeostasis is a highly complex and incompletely understood process involving a large number of regulatory molecules. Our review provides a description of what is known about how iron is obtained by the body and brain and how defects in the homeostatic processes could contribute to the development of brain diseases, focusing on Alzheimer's disease and Parkinson's disease as well as four other disorders belonging to a class of inherited conditions referred to as neurodegeneration based on iron accumulation (NBIA) disorders. A description of potential therapeutic approaches being tested for each of these different disorders is provided.

A novel variant c.3706C>T p.(Avg 1236Cys) in the ABCA7 gene in a Saudi patient with susceptibility to Alzheimer's disease 9

Alzheimer's disease (AD) is the most common cause of dementia with around 50 million people suffering from this disease worldwide. Mutations in the ATP-binding cassette sub-family A member 7 (ABCA7) have been reported to cause susceptibility to AD 9 (OMIM #608907). In this study, we report a novel variant in ABCA7 in a Saudi patient with susceptibility to AD 9 and a strong family history of neurodegenerative disorders, which may be explained by the same variant. We studied a single 57-year-old female patient with typical symptoms of AD supported by MRI findings from a Saudi family with a positive history of a similar disease in multiple individuals. The case study was conducted in King Abdulaziz Medical City in Jeddah, Saudi Arabia. Whole-exome sequencing identified the novel heterozygous variant c.3706C>T p.(Avg 1236Cys) in the ABCA7 gene, which leads to an amino acid exchange. Furthermore, bioinformatics in silico programs predict a pathogenic effect for this variant. To the best of our knowledge, the variant has not been described in the literature so far as evidenced by a thorough literature review using multiple databases such as Ovid, Medline, EMBASE, ProQuest, Science Direct, Google Scholar, and PubMed. In this article, we reported a middle-aged Saudi woman with a novel variant in ABCA7 who had clinical features of both AD and Parkinson's disease. Given the reported function of this gene, it is most likely that it is etiological and pathological because of the presenting complex neurological disease due to decreased clearance of β-amyloid and α-Synuclein. We illustrate the importance of this interesting gene that could be implicated in several neurodegenerative disorders.

Integrated individually electrochemical array for simultaneously detecting multiple Alzheimer's biomarkers

Simultaneous detection of multiple biomarkers is benefit for reducing the detection cycles, avoiding the false-positive signals, and providing the cross validation, which provide the opportunity to understand the pathogenic mechanisms and achieve precise early diagnosis. Here, we demonstrate the mini-pillar-based individual electrochemical array for simultaneous detection of multiple biomarkers. On such platform, the mini-pillar could confine the microdroplet as individual and open-channel microreactor, which is extremely helpful for reducing reagent consumption and extracting internal information, and the electrodes array embedded in mini-pillar are integrated on one side to achieve multiple and simultaneous electrochemical sensing. The introduction of gold nanodendrites by electrodeposition has greatly enhanced sensitivity via improving probe-binding capacity and response signals. Sensitive and selective detection of multiple Alzheimer's biomarkers including Tau, ApoE4, Amyloid-β and miRNA-101 on such mini-pillar-based biosensor is also achieved. Such biosensor platform with the advantages of high-yield, high sensitivity, low-waste and multiple signals output shows great promise in sensing multiple biomolecules for disease diagnosis and health monitoring.

"Amyloid-beta accumulation cycle" as a prevention and/or therapy target for Alzheimer's disease

The cell cycle and its regulators are validated targets for cancer drugs. Reagents that target cells in a specific cell cycle phase (e.g., antimitotics or DNA synthesis inhibitors/replication stress inducers) have demonstrated success as broad-spectrum anticancer drugs. Cyclin-dependent kinases (CDKs) are drivers of cell cycle transitions. A CDK inhibitor, flavopiridol/alvocidib, is an FDA-approved drug for acute myeloid leukemia. Alzheimer's disease (AD) is another serious issue in contemporary medicine. The cause of AD remains elusive, although a critical role of latent amyloid-beta accumulation has emerged. Existing AD drug research and development targets include amyloid, amyloid metabolism/catabolism, tau, inflammation, cholesterol, the cholinergic system, and other neurotransmitters. However, none have been validated as therapeutically effective targets. Recent reports from AD-omics and preclinical animal models provided data supporting the long-standing notion that cell cycle progression and/or mitosis may be a valid target for AD prevention and/or therapy. This review will summarize the recent developments in AD research: (a) Mitotic re-entry, leading to the "amyloid-beta accumulation cycle," may be a prerequisite for amyloid-beta accumulation and AD pathology development; (b) AD-associated pathogens can cause cell cycle errors; (c) thirteen among 37 human AD genetic risk genes may be functionally involved in the cell cycle and/or mitosis; and (d) preclinical AD mouse models treated with CDK inhibitor showed improvements in cognitive/behavioral symptoms. If the "amyloid-beta accumulation cycle is an AD drug target" concept is proven, repurposing of cancer drugs may emerge as a new, fast-track approach for AD management in the clinic setting.

APOE region molecular signatures of Alzheimer's disease across races/ethnicities

The role of even the strongest genetic risk factor for Alzheimer's disease (AD), the apolipoprotein E (APOE) ε4 allele, in its etiology remains poorly understood. We examined molecular signatures of AD defined as differences in linkage disequilibrium patterns between AD-affected and -unaffected whites (2673/16,246), Hispanics (392/867), and African Americans (285/1789), separately. We focused on 29 polymorphisms from 5 genes in the APOE region emphasizing beneficial and adverse effects of the APOE ε2- and ε4-coding single-nucleotide polymorphisms, respectively, and the differences in the linkage disequilibrium structures involving these alleles between AD-affected and -unaffected subjects. Susceptibility to AD is likely the result of complex interactions of the ε2 and ε4 alleles with other polymorphisms in the APOE region, and these interactions differ across races/ethnicities corroborating differences in the adverse and beneficial effects of the ε4 and ε2 alleles. Our findings support complex race/ethnicity-specific haplotypes promoting and protecting against AD in this region. They contribute to better understanding of polygenic and resilient mechanisms, which can explain why even homozygous ε4 carriers may not develop AD.

Association of Polygenic Risk Score with Age at Onset and Cerebrospinal Fluid Biomarkers of Alzheimer's Disease in a Chinese Cohort

To evaluate whether the polygenic profile modifies the development of sporadic Alzheimer's disease (sAD) and pathological biomarkers in cerebrospinal fluid (CSF), 462 sAD patients and 463 age-matched cognitively normal (CN) controls were genotyped for 35 single-nucleotide polymorphisms (SNPs) that are significantly associated with sAD. Then, the alleles found to be associated with sAD were used to build polygenic risk score (PRS) models to represent the genetic risk. Receiver operating characteristic (ROC) analyses and the Cox proportional hazards model were used to evaluate the predictive value of PRS for the sAD risk and age at onset. We measured the CSF levels of Aβ42, Aβ42/Aβ40, total tau (T-tau), and phosphorylated tau (P-tau) in a subgroup (60 sAD and 200 CN participants), and analyzed their relationships with the PRSs. We found that 14 SNPs, including SNPs in the APOE, BIN1, CD33, EPHA1, SORL1, and TOMM40 genes, were associated with sAD risk in our cohort. The PRS models built with these SNPs showed potential for discriminating sAD patients from CN controls, and were able to predict the incidence rate of sAD and age at onset. Furthermore, the PRSs were correlated with the CSF levels of Aβ42, Aβ42/Aβ40, T-tau, and P-tau. Our study suggests that PRS models hold promise for assessing the genetic risk and development of AD. As genetic risk profiles vary among populations, large-scale genome-wide sequencing studies are urgently needed to identify the genetic risk loci of sAD in Chinese populations to build accurate PRS models for clinical practice.

Central and Peripheral Mechanisms in ApoE4-Driven Diabetic Pathology

Apolipoprotein E (APOE) ε4 gene allele and type 2 diabetes mellitus (T2DM) are prime risk factors for Alzheimer's disease (AD). Despite evidence linking T2DM and apoE4, the mechanism underlying their interaction is yet to be determined. In the present study, we employed a model of APOE-targeted replacement mice and high-fat diet (HFD)-induced insulin resistance to investigate diabetic mechanisms associated with apoE4 pathology and the extent to which they are driven by peripheral and central processes. Results obtained revealed an intriguing pattern, in which under basal conditions, apoE4 mice display impaired glucose and insulin tolerance and decreased insulin secretion, as well as cognitive and sensorimotor characteristics relative to apoE3 mice, while the HFD impairs apoE3 mice without significantly affecting apoE4 mice. Measurements of weight and fasting blood glucose levels increased in a time-dependent manner following the HFD, though no effect of genotype was observed. Interestingly, sciatic electrophysiological and skin intra-epidermal nerve fiber density (IENFD) peripheral measurements were not affected by the APOE genotype or HFD, suggesting that the observed sensorimotor and cognitive phenotypes are related to central nervous system processes. Indeed, measurements of hippocampal insulin receptor and glycogen synthase kinase-3β (GSK-3β) activation revealed a pattern similar to that obtained in the behavioral measurements while Akt activation presented a dominant effect of diet. HFD manipulation induced genotype-independent hyperlipidation of apoE, and reduced levels of brain apoE in apoE3 mice, rendering them similar to apoE4 mice, whose brain apoE levels were not affected by the diet. No such effect was observed in the peripheral plasma levels of apoE, suggesting that the pathological effects of apoE4 under the control diet and apoE3 under HFD conditions are related to the decreased levels of brain apoE. Taken together, our data suggests that diabetic mechanisms play an important role in mediating the pathological effects of apoE4 and that consequently, diabetic-related therapy may be useful in treating apoE4 pathology in AD.

Neuroinflammation and Neurogenesis in Alzheimer's Disease and Potential Therapeutic Approaches

In adult brain, new neurons are generated throughout adulthood in the subventricular zone and the dentate gyrus; this process is commonly known as adult neurogenesis. The regulation or modulation of adult neurogenesis includes various intrinsic pathways (signal transduction pathway and epigenetic or genetic modulation pathways) or extrinsic pathways (metabolic growth factor modulation, vascular, and immune system pathways). Altered neurogenesis has been identified in Alzheimer's disease (AD), in both human AD brains and AD rodent models. The exact mechanism of the dysregulation of adult neurogenesis in AD has not been completely elucidated. However, neuroinflammation has been demonstrated to alter adult neurogenesis. The presence of various inflammatory components, such as immune cells, cytokines, or chemokines, plays a role in regulating the survival, proliferation, and maturation of neural stem cells. Neuroinflammation has also been considered as a hallmark neuropathological feature of AD. In this review, we summarize current, state-of-the art perspectives on adult neurogenesis, neuroinflammation, and the relationship between these two phenomena in AD. Furthermore, we discuss the potential therapeutic approaches, focusing on the anti-inflammatory and proneurogenic interventions that have been reported in this field.

Stem Cell Therapy for Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disease caused by eventually aggregated amyloid β (Aβ) plaques in degenerating neurons of the aging brain. These aggregated protein plaques mainly consist of Aβ fibrils and neurofibrillary tangles (NFTs) of phosphorylated tau protein. Even though some cholinesterase inhibitors, NMDA receptor antagonist, and monoclonal antibodies were developed to inhibit neurodegeneration or activate neural regeneration or clear off the Aβ deposits, none of the treatment is effective in improving the cognitive and memory dysfunctions of the AD patients. Thus, stem cell therapy represents a powerful tool for the treatment of AD. In addition to discussing the advents in molecular pathogenesis and animal models of this disease and the treatment approaches using small molecules and immunoglobulins against AD, we will focus on the stem cell sources for AD using neural stem cells (NSCs); embryonic stem cells (ESCs); and mesenchymal stem cells (MSCs) from bone marrow, umbilical cord, and umbilical cord blood. In particular, patient-specific-induced pluripotent stem cells (iPS cells) are proposed as a future prospective and the challenges for the treatment of AD.

Redox proteomics and amyloid β-peptide: insights into Alzheimer disease

Alzheimer disease (AD) is a progressive neurodegenerative disorder associated with aging and characterized pathologically by the presence of senile plaques, neurofibrillary tangles, and neurite and synapse loss. Amyloid beta-peptide (1-42) [Aβ(1-42)], a major component of senile plaques, is neurotoxic and induces oxidative stress in vitro and in vivo. Redox proteomics has been used to identify proteins oxidatively modified by Aβ(1-42) in vitro and in vivo. In this review, we discuss these proteins in the context of those identified to be oxidatively modified in animal models of AD, and human studies including familial AD, pre-clinical AD (PCAD), mild cognitive impairment (MCI), early AD, late AD, Down syndrome (DS), and DS with AD (DS/AD). These redox proteomics studies indicate that Aβ(1-42)-mediated oxidative stress occurs early in AD pathogenesis and results in altered antioxidant and cellular detoxification defenses, decreased energy yielding metabolism and mitochondrial dysfunction, excitotoxicity, loss of synaptic plasticity and cell structure, neuroinflammation, impaired protein folding and degradation, and altered signal transduction. Improved access to biomarker imaging and the identification of lifestyle interventions or treatments to reduce Aβ production could be beneficial in preventing or delaying the progression of AD. This article is part of the special issue "Proteomics".

The p.R47H Variant of TREM2 Gene is Associated With Late-onset Alzheimer Disease in Colombian Population

OBJECTIVE

We evaluated the association of several single-nucleotide polymorphisms in the triggering receptor expressed on myeloid cells 2 (TREM2) gene in a Colombian sample of late-onset Alzheimer disease (LOAD).

METHODS

The p.Q33* (rs104894002), p.R47H (rs75932628), p.R62H (rs143332484), and p.D87N (rs142232675) variants of TREM2 gene were directly genotyped using KASPar technology in 358 cases and 329 healthy controls. Sanger sequencing was used to validate >10% of KASPar's results. The Fisher exact test was used to compare the distribution of allelic and genotype frequency between cases and controls, and the Bonferroni correction was set at P<0.05.

RESULTS

The minor allele frequency of rs75932628-T was 0.009 in cases and was not found in any healthy controls which suggests a significant association between rs75932628-T and LOAD risk in our sample (P=0.010). The rs143332484-T variant did not exhibit a significant association (P=0.160), whereas rs104894002 and rs142232675 were not found.

CONCLUSIONS

Our findings suggest that the rs75932628-T variant of TREM2 is an important risk factor for LOAD in the Colombian population.

Modelling mitochondrial dysfunction in Alzheimer’s disease using human induced pluripotent stem cells

Alzheimer’s disease (AD) is the most common form of dementia. To date, only five pharmacological agents have been approved by the Food and Drug Administration for clinical use in AD, all of which target the symptoms of the disease rather than the cause. Increasing our understanding of the underlying pathophysiology of AD will facilitate the development of new therapeutic strategies. Over the years, the major hypotheses of AD etiology have focused on deposition of amyloid beta and mitochondrial dysfunction. In this review we highlight the potential of experimental model systems based on human induced pluripotent stem cells (iPSCs) to provide novel insights into the cellular pathophysiology underlying neurodegeneration in AD. Whilst Down syndrome and familial AD iPSC models faithfully reproduce features of AD such as accumulation of Aβ and tau, oxidative stress and mitochondrial dysfunction, sporadic AD is much more difficult to model in this way due to its complex etiology. Nevertheless, iPSC-based modelling of AD has provided invaluable insights into the underlying pathophysiology of the disease, and has a huge potential for use as a platform for drug discovery.

Association of MS4A6A, CD33, and TREM2 gene polymorphisms with the late-onset Alzheimer's disease

Introduction: Alzheimer’s disease (AD), which is a progressive neurodegenerative disorder, causes structural and functional brain disruption. MS4A6A, TREM2, and CD33 gene polymorphisms loci have been found to be associated with the pathobiology of late-onset AD (LOAD). In the present study, we tested the hypothesis of association of LOAD with rs983392, rs75932628, and rs3865444 polymorphisms in MS4A6A, TREM2, CD33 genes, respectively.

Methods: In the present study, 113 LOAD patients and 100 healthy unrelated age- and gender-matched controls were selected. DNA was extracted from blood samples by the salting-out method and the genotyping was performed by RFLP-PCR. Electrophoresis was carried out on agarose gel. Sequencing was thereafter utilized for the confirmation of the results.

Results: Only CD33 rs3865444 polymorphism revealed a significant difference in the genotypic frequencies of GG (P = 0.001) and GT (P = 0.001), and allelic frequencies of G (P = 0.033) and T (P = 0.03) between LOAD patients and controls.

Conclusion: The evidence from the present study suggests that T allele of CD33 rs3865444 polymorphism is associated with LOAD in the studied Iranian population.

Binding between Prion Protein and Aβ Oligomers Contributes to the Pathogenesis of Alzheimer's Disease

A plethora of evidence suggests that protein misfolding and aggregation are underlying mechanisms of various neurodegenerative diseases, such as prion diseases and Alzheimer's disease (AD). Like prion diseases, AD has been considered as an infectious disease in the past decades as it shows strain specificity and transmission potential. Although it remains elusive how protein aggregation leads to AD, it is becoming clear that cellular prion protein (PrP^C) plays an important role in AD pathogenesis. Here, we briefly reviewed AD pathogenesis and focused on recent progresses how PrP^C contributed to AD development. In addition, we proposed a potential mechanism to explain why infectious agents, such as viruses, conduce AD pathogenesis. Microbe infections cause Aβ deposition and upregulation of PrP^C, which lead to high affinity binding between Aβ oligomers and PrP^C. The interaction between PrP^C and Aβ oligomers in turn activates the Fyn signaling cascade, resulting in neuron death in the central nervous system (CNS). Thus, silencing PrP^C expression may turn out be an effective treatment for PrP^C dependent AD.

Type II Diabetes Mellitus Accelerates Age-Dependent Aβ Pathology in Cynomolgus Monkey Brain

Accumulating evidence suggests that diabetes mellitus (DM) is one of the strongest risk factors for developing Alzheimer's disease (AD). However, it remains unclear how DM accelerates AD pathology in the brain. Cynomolgus monkey (Macaca fascicularis) is one of the nonhuman primates used for biomedical research, and we can observe spontaneous formation of AD pathology, such as senile plaques (SPs) and neurofibrillary tangles (NFTs), with the advance of aging. Furthermore, obesity is occasionally observed and frequently leads to development of type II DM (T2DM) in laboratory-housed cynomolgus monkeys. These findings suggest that cynomolgus monkey is a useful species to study the relationship between T2DM and AD pathology. In T2DM-affected monkey brains, SPs were observed in frontal and temporal lobe cortices almost 5 years earlier than healthy control monkeys. Moreover, age-related endocytic pathology, such as intraneuronal accumulation of enlarged endosomes, was exacerbated in T2DM-affected monkey brains. Since accumulating evidences suggest that endocytic dysfunction is involved in Aβ pathology, T2DM may aggravate age-related endocytic dysfunction, leading to the acceleration of Aβ pathology.

A candidate gene study of risk for dementia in older, postmenopausal women: Results from the Women's Health Initiative Memory Study

OBJECTIVE

While a number of single nucleotide polymorphisms (SNPs) associated with Alzheimer's disease (AD) or cognitive impairment have been identified, independent replications remain the only way to validate proposed signals. We investigated SNPs in candidate genes associated with either cognitive impairment or AD pathogenesis and their relationships with probable dementia (PD) in the Women's Health Initiative Memory Study (WHIMS).

METHODS

We analyzed 96 SNPs across five genes (APOE/TOMM40, BDNF, COMT, SORL1, and KIBRA) in 2857 women (ages ≥65) from the WHIMS randomized trials of hormone therapy using a custom Illumina GoldenGate assay; 19% of the sample were MCI (N = 165) or PD (N = 387), and the remaining 81% were free of cognitive impairment. SNP associations were evaluated for PD in non-Hispanic whites adjusting for age and HT using logistic regression under an additive genetic model.

RESULTS

One SNP (rs157582), located in the TOMM40 gene nearby APOE, was associated with the PD phenotype based on a P value accounting for multiple comparisons. An additional 12 SNPs were associated with the PD phenotype at P ≤ 0.05 (APOE: rs405509, rs439401; TOMM40: rs8106922, and KIBRA: rs4320284, rs11740112, rs10040267, rs13171394, rs6555802, rs2241368, rs244904, rs6555805, and rs10475878). Results of the sensitivity analyes excluding MCI were similar, with addition of COMT rs737865 and BDNF rs1491850 (P ≤ 0.05).

CONCLUSIONS

Our results in older women provide supporting evidence that the APOE/TOMM40 genes confer dementia risk and extend these findings to COMT, BDNF, and KIBRA. Our findings may lead to a better understanding of the role these genes play in cognition and cognitive impairment.

Plasma amyloid beta levels and platelet mitochondrial respiration in patients with Alzheimer's disease

OBJECTIVES

Altered amyloid metabolism and mitochondrial dysfunction play key roles in the development of Alzheimer's disease (AD). We asked whether an association exists between disturbed platelet mitochondrial respiration and the plasma concentrations of Aβ₄₀ and Aβ₄₂ in patients with AD.

DESIGN AND METHODS

Plasma Aβ₄₀ and Aβ₄₂ concentrations and mitochondrial respiration in intact and permeabilized platelets were measured in 50 patients with AD, 15 patients with vascular dementia and 25 control subjects. A pilot longitudinal study was performed to monitor the progression of AD in a subgroup 11 patients with AD.

RESULTS

The mean Aβ₄₀, Aβ₄₂ and Aβ₄₂/Aβ₄₀ levels were not significantly altered in patients with AD compared with controls. The mitochondrial respiratory rate in intact platelets was significantly reduced in patients with AD compared to controls, particularly the basal respiratory rate, maximum respiratory capacity, and respiratory reserve; however, the flux control ratio for basal respiration was increased. A correlation between the plasma Aβ₄₂ concentration and mitochondrial respiration in both intact and permeabilized platelets differs in controls and patients with AD.

CONCLUSIONS

Based on our data, (1) mitochondrial respiration in intact platelets, but not the Aβ level itself, may be included in a panel of biomarkers for AD; (2) dysfunctional mitochondrial respiration in platelets is not explained by changes in plasma Aβ concentrations; and (3) the association between mitochondrial respiration in platelets and plasma Aβ levels differs in patients with AD and controls. The results supported the hypothesis that mitochondrial dysfunction is the primary factor contributing to the development of AD.