AbstractAlzheimer’s Disease Risk Research Articles

FUNGAL INFECTIONS, USE OF ANTIFUNGAL AGENTS, AND THE RISK OF ALZHEIMER’S DISEASE

Abstract Alzheimer’s Disease (AD) is a complex neurodegenerative disorder leading to progressive cognitive decline and death. Accumulating evidence suggests that common adult infections, such as recurrent fungal infections, may play a major role in AD development. In this study we used administrative claims data, 1991-2017, from a 5% sample of U.S. Medicare beneficiaries age 65+ to study the potential relationship between fungal infections, use of antifungal drugs and AD onset. In unweighted analysis using the Cox model, we found that after accounting for demographic and health-related differences, the presence of fungal infections, independent of treatment increased the risk of AD [Hazard Ratio(HR):1.98; 95% Confidence Interval(CI):1.89-1.92]. The strength of the effect did not change when the population was restricted to Medicare beneficiaries with Medicare Part D (prescription drug) coverage in 2006+ (HR:1.99; CI:1.97-2.01). We then split the latter group into yearly split-episode data and calculated the medication possession ratios (MPR) of three major groups of antifungal agents: imidazole, triazole and polyenes and re-estimated our models. Although the effect associated with fungal infection did not change, higher MPRs of imidazole (HR:0.61; CI:0.48-0.76) and especially triazole (HR:0.37; CI:0.24-0.58) were found to be protective. In contrast, higher MPRs of polyenes were associated with increased risk (HR:1.32; CI:1.08-1.63). In summary, fungal infections were found to be strongly associated with AD risk with the effect being strongly modified by use of common antifungal treatments. More research is required to better define the biological mechanisms engendering these associations.

SHIP-1 Inhibitors improve human microglial-like cell function

Abstract Alzheimer’s disease (AD) is associated with progressive formation of Aβ plaques and neuronal cell death in the brain. Microglia maintain brain homeostasis and their dysfunction is implicated in AD pathology. Triggering receptor expressed on myeloid cells #2 (TREM2) promotes phagocytosis, migration, and metabolic fitness of microglia. TREM2 signaling is inhibited by src-homology 2(SH2) domain containing inositol phosphatase 1 (SHIP-1), encoded by INPP5D, in macrophages and osteoclasts, and the rs669 SNP is associated with increased brain SHIP-1 expression and confers AD risk. We hypothesize that overexpression of SHIP-1 leads to reduced TREM2 signaling and subsequent microglial dysfunction. To test this hypothesis, we treated human microglial like (HMC3) cells, expressing endogenous TREM2, SHIP-1, Iba-1, and CD68, with small molecule inhibitors of SHIP-1 (SHIPi) (3AC) and its paralog SHIP-2 (K161). Treatment with SHIPi significantly increases the surface expression of TREM2 and CD68 as detected by flow cytometry, while not changing Iba-1 expression. Additionally, we demonstrate that treatment of HMC3 cells with SHIPi significantly improves their ability to phagocytose fluorescently tagged Aβ. At concentrations that promote phagocytosis, SHIPi were non-toxic at 72 hours. Together, these data have given us early evidence that SHIPi can promote human microglia-like cell phagocytosis. Further studies are underway to determine the effect of SHIPi on metabolic fitness. SHIPi are safe and effective in mouse models of metabolic dysfunction and obesity and could be an ideal treatment for AD alone or in combination with stimulating TREM2 antibodies.

Human and mouse single-nucleus transcriptomics reveal TREM2-dependent and -independent cellular responses in Alzheimer’s disease

Abstract Alzheimer’s disease (AD) is the most common form of dementia that is initiated by extracellular plaque deposition and intraneuronal hyperphosphorylated tau aggregates. Reactive astrocytosis and microgliosis are secondary cellular responses to pathology that have gained increasing attention. Variants of the microglia receptor TREM2 increase AD risk and activation of “disease-associated microglia” (DAM) is dependent on TREM2 in mouse models of AD. To investigate global transcriptomic changes during AD pathology, we surveyed gene expression changes associated with AD pathology and TREM2 in Ab-driven 5XFAD mouse model and human AD by single nucleus RNA sequencing. We confirmed the presence of Trem2-dependent DAM and identified a novel Serpina3n+C4b+ reactive oligodendrocyte population in mice. Interestingly, remarkably different glial phenotypes were evident in human AD. Microglia signature was reminiscent of IRF8-driven reactive microglia in peripheral nerve injury. Oligodendrocyte signatures suggested impaired axonal myelination and metabolic adaptation to neuronal degeneration. Astrocyte profiles indicated weakened metabolic coordination with neurons. Notably, the reactive phenotype of microglia was less palpable in TREM2 R47H and R62H carriers than in non-carriers, demonstrating a TREM2 requirement in both mouse and human AD, despite the marked species-specific differences.

THE ROLE OF FOXO3 TRANSCRIPTION FACTOR IN ALZHEIMER’S DISEASE PATHOLOGY

Alzheimer’s disease (AD) is a progressive and degenerative brain disease and age is one of its strongest risk factors. Aging is a complex process but it is reasonable that a delayed aging process may lower the risk of AD or postpone its pathogenesis. Studies in C. elegans revealed that the activity of DAF-16 is required for the life span extension in many long-lived strains. The mammalian homologs for DAF-16 are the Forkhead box O (FOXO) transcription factors. FOXO3, one of the members in the FOXO family, has been identified in several studies as a susceptibility gene for human longevity. I found that the expression level of Foxo3 in the mouse brain decreases with age or in an AD mouse model. To further study the role of Foxo3 in AD, I generated Foxo3 conditional knockout mice which depletes Foxo3 in neural cells. These mice have reactive astrogliosis in the cortex and also upregulation of some astrocytes specific markers like Gfap and Aqp4. In vitro culture of primary astrocytes from the knockout mice shows impaired respiratory capacity in the Seahorse mito stress test, which corresponds to the expression level change of metabolic genes like Acot1. When we bred the knockout mice with 5xFAD, a mouse model for amyloid pathology. I found increased plaque load and core plaque size in the cortex of the mice with Foxo3 deficiency. This study shows the critical function of FOXO3 in maintaining brain homeostasis and provide new insights into AD pathogenesis and drug discovery.

Decoding Alzheimer's in the Age of Genome-Wide Analyses

Alzheimer’s disease (AD) is strongly influenced by genetic factors as evidenced by numerous family and twin studies. Over the past two decades, others and we have co-discovered three early-onset familial AD genes, APP, PSEN1, and PSEN2, which can carry any of >200 fully penetrant mutations characterized by mendelian inheritance. For late-onset AD, the most prevalent and highest impact risk factor is the epsilon 4 variant of APOE, which increases risk by 3.7-fold in the heterozygous state and >10-fold when two copies are inherited. As part of our Alzheimer’s Genome Project funded by the Cure Alzheimer’s Fund and the NIMH, we have been identifying novel AD candidate genes. In Bertram et al. (2008), we reported genome-wide association of AD with several loci including the spinocerebellar ataxia 1 gene, ATXN1, and the SIGLEC3 gene, CD33. Functional studies of the ATXN1 gene carried out both in vitro and in vivo in ATXN1 knockout mice show that ATXN1 can regulate Aβ levels via modulation of β-secretase. CD33 is just one of several genes (TREM2, CR1, etc) involved in the innate immune system of the brain that have been associated with AD risk. In addition, we discovered association of AD with ADAM10, which encodes the major α-secretase in the brain. Re-sequencing of this gene in the best associated AD families led to two rare mutations that tightly co-segregated with AD in seven (of 1000) AD families screened, all with average age of onset ~70 years. We have shown both mutations to impair ADAM10 non-amyloidogenic cleavage of APP in vitro and in transgenic mice, including double trangenics with AD (tg2576) mice. Thus, these are the first rare, highly penetrant mutations reported for late-onset AD. We have also carried out genome-wide association studies on >800 well-characterized late-onset AD families (NIMH and NIA-LOAD samples) using Affymetrix genotyping arrays containing either one million (6.0) or 20,000 coding SNPs. More recently, we have performed whole genome sequencing (Illumina, Hiseq) on over 1500 samples from AD families/sibships. The elucidation of the genes and functional variants influencing risk for AD should continue to enhance our understanding of AD etiology and pathogenesis. Ultimately, these genes will be used to predict risk for AD and guide novel the development of therapies for the effective treatment and prevention of this terrible disease.

The therapeutic potential of glucagon-like peptide-1 analogs in the treatment of Alzheimer’s disease

Alzheimer’s disease (AD) affects more than 25% of individuals over 80 years of age and its prevalence is expected to rise with the increase of life expectancy. Existing drugs only provide symptomatic benefits but there are no currently available diseasemodifying therapies. However, evidence from preclinical studies indicates that several drugs approved for other indications could have beneficial effects on Alzheimer’s pathology, and some of them are currently being evaluated in clinical trials [1]. In the last decades an increase in the incidence of both type 2 diabetes (T2D) and neurodegenerative disorders has been observed, posing a significant health and social challenge due to increased morbidity and mortality. T2D increases the risk of AD and there is an increased incidence of T2D in AD patients [2], probably due to common pathophysiological mechanisms shared between these diseases, and one that can be identified is insulin desensitization. Indeed, in AD brain, insulin signaling is desensitized, showing a molecular profile similar to that found in peripheral tissues of diabetic subjects [3]. Glucagon-like peptide-1 (GLP-1) is an incretin hormone with several effects on glycemic homeostasis, stimulating insulin and decreasing glucagon secretion. Currently, the GLP-1 receptor agonists exendin-4, liraglutide and lixisenatide are approved for treatment of T2D [4]. Besides its metabolic effects, GLP-1 has also been shown to act as a growth factor in the brain, inducing neurite growth and protecting against oxidative injury; GLP-1 receptor knock-out mice present with impaired hippocampal long-term potentiation of synaptic transmission [5]. The GLP-1 receptor is found in neurons throughout the nervous system, is maintained during aging and disease, and GLP-1 and its analogs effectively cross the blood–brain barrier. In the context of AD-related brain amyloid pathology, the preclinical results of GLP-1 analogs have shown promising potential. Exendin-4 has been shown to reduce endogenous levels of β-amyloid in the mouse brain [6]. Liraglutide has also been shown to protect synapses from the detrimental effects of amyloid [7,8] and it was able to significantly reduce the β-amyloid plaque load and the total amount of β-amyloid in the brain of a transgenic mouse model of AD. Importantly, in a late-stage animal model of AD, liraglutide demonstrated restorative effects in both brain structure and function, reducing both β-amyloid plaques and soluble amyloid oligomers [9], suggesting that liraglutide could potentially influence the amyloid production. Moreover, GLP-1 analogs have been demonstrated to promote cell proliferation in the rat hippocampus and increase the number of neuronal progenitor cells in mouse models of diabetes. GLP-1R activators induce the differentiation of neuronal stem cell and stimulate neurite outgrowth in a manner similar to nerve “…preclinical evidence strongly supports the hypothesis that GLP-1 analogs can represent promising candidates for Alzheimer’s disease treatment.”

Decoding Alzheimer’s in the age of genome-wide analyses

Alzheimer’s disease (AD) is strongly influenced by genetic factors as evidenced by numerous family and twin studies. Over the past two decades, others and we have co-discovered three early-onset familial AD genes, APP, PSEN1, and PSEN2, which can carry any of >200 fully penetrant mutations characterized by mendelian inheritance. For late-onset AD, the most prevalent and highest impact risk factor is the epsilon 4 variant of APOE, which increases risk by 3.7-fold in the heterozygous state and >10-fold when two copies are inherited. As part of our Alzheimer’s Genome Project funded by the Cure Alzheimer’s Fund and the NIMH, we have been identifying novel AD candidate genes. In Bertram et al. (2008), we reported genome-wide association of AD with several loci including the spinocerebellar ataxia 1 gene, ATXN1, and the SIGLEC3 gene, CD33. Functional studies of the ATXN1 gene carried out both in vitro and in vivo in ATXN1 knockout mice show that ATXN1 can regulate Aβ levels via modulation of β-secretase. CD33 is just one of several genes (TREM2, CR1, etc) involved in the innate immune system of the brain that have been associated with AD risk. In addition, we discovered association of AD with ADAM10, which encodes the major α-secretase in the brain. Re-sequencing of this gene in the best associated AD families led to two rare mutations that tightly co-segregated with AD in seven (of 1000) AD families screened, all with average age of onset ~70 years. We have shown both mutations to impair ADAM10 non-amyloidogenic cleavage of APP in vitro and in transgenic mice, including double trangenics with AD (tg2576) mice. Thus, these are the first rare, highly penetrant mutations reported for late-onset AD. We have also carried out genome-wide association studies on >800 well-characterized late-onset AD families (NIMH and NIA-LOAD samples) using Affymetrix genotyping arrays containing either one million (6.0) or 20,000 coding SNPs. More recently, we have performed whole genome sequencing (Illumina, Hiseq) on over 1500 samples from AD families/sibships. The elucidation of the genes and functional variants influencing risk for AD should continue to enhance our understanding of AD etiology and pathogenesis. Ultimately, these genes will be used to predict risk for AD and guide novel the development of therapies for the effective treatment and prevention of this terrible disease.

Possible APOE Genotype and Sex Dependent Effects of 17-α- estradiol on Alzheimers Disease Pathology

Alzheimer’s disease (AD) remains the most prevalent cause of elderly dementia, posing an increasingly important health problem as the population ages [1]. AD is a neurodegenerative disorder defined by the presence of extracellular deposits of β-amyloid (Aβ), intraneuronal accumulations of neurofibrillary tangles containing hyperphosporylated tau protein, and the progressive loss of synapses and neurons that correlate with atrophy of brain regions [2]. Specific areas of the brain that show particularly severe neuronal loss include the entorhinal cortex, pyramidal neurons in the CA1 subregion of the hippocampus, and the noradrenergic neurons of the locus coeruleus [3-5]. The neuronal populations within these areas mediate attention, learning, memory and other neural processes associated with higher cognitive function. The specific mechanism(s) that underlie neuronal loss are not clearly understood, and there are no approved methods to slow this neurodegeneration. Of the risk factors identified that facilitate AD progression, the strongest are aging, the inheritance of the e4 allele of the Apolipoprotein E (APOE) gene, and sex - women have a higher incidence of AD than men [6]. The APOE gene encodes a 34 kDa protein that is the major protein component of CNS lipoproteins, involved in lipid transport and redistribution [7]. Even though there is no clear understanding of the role of APOE in AD pathology, the role of APOE4 isoform has been shown to affect synaptic structure, Aβ clearance and transport across blood brain barrier as well as energy metabolism [8]. In mice, APOE4 decrease dendritic spine density and neuronal complexity in various cortical brain regions [9]. In addition, APOE4 mice show impaired learning and memory in the Barnes maze tests [10]. These effects were observed in absence of significant Aβ accumulation suggesting Aβ independent mechanisms contributing to functional impairments in APOE4 carriers. There is a stronger association of APOE with AD in women than men that correlates well with greater hippocampal atrophy, plaque pathology and cognitive decline [11]. The gradual loss of sex steroid hormones in women may contribute to age associated cognitive decline [12]. A neuroprotective role of natural and synthetic estrogens in the mammalian brain has been established during the past decade. In particular, 17-β-estradiol (β-E2), has commonly been known to play a pivotal role in female reproductive physiology, enhances synaptic plasticity, neurite growth, hippocampal neurogliosis and long-term potentiation [13,14]. β-E2 is also effective in several neural injury and toxicity models. In animal models of AD, β-E2 reduces Aβ pathology and improves cognition [15], although the effectiveness of β-E2 is reduced in the presence of APOE4 [16]. This latter observation is consistent with a role for APOE in modulating the biological effects of estrogen-based therapy. Early estrogen replacement therapy prior to menopause has been shown to reduce the AD risk in postmenopausal women [17]. However the effects of β-E2 on peripheral targets in both men and women limit its usefulness as a potential therapy for AD. In the past decade concerns have been raised over the safety of long-term 17-β-E2 treatment as

Epidemiological findings of vascular risk factors in Alzheimer’s disease: implications for therapeutic and preventive intervention

Alzheimer’s disease (AD) is a multifactorial disorder, in which the detrimental effects of vascular risk factors and related disorders (e.g., smoking, obesity, hypertension, diabetes, dyslipidemia and inflammation) have been frequently suggested in numerous observational studies of the general population. In recent years, systematic reviews and meta-analyses of population-based prospective studies have concluded from the life-course perspective, an age-dependent association with the risk of AD for several vascular factors, such as high blood pressure, obesity and high total cholesterol, such that possessing these factors in midlife is associated with an increased risk of late-life AD, whereas having a low level in late life or a decline after middle age in these factors may anticipate clinical onset of AD. The biological plausibility for these vascular factors and related disorders being involved in the pathogenesis and clinical manifestation of AD is also supported by population-based neuroimaging and neuropathological studies. However, randomized placebo-controlled trials that target those major cardiovascular risk factors (e.g., antihypertensive, hormone replacement and anti-inflammatory therapies) have generally failed to prove to be efficacious preventive or therapeutic approaches for AD. The multifactorial nature of AD and the age-dependent relationship between vascular risk factors and the risk of AD should be taken into consideration in the future when designing preventive or therapeutic intervention against the dementing disorder.

Advanced magnetic resonance imaging techniques in the diagnostics of Alzheimer's disease: how much imaging is enough?

Alzheimer’s disease (AD) is the most common progressive neurodegenerative disorder characterized by gradual deterioration in cognition, function, and behavior. The number of patients with dementia is increasing in the Western world. Neuroimaging plays an important role in the study and clinical diagnosis of AD. It is of utmost importance to exclude potentially treatable conditions such as brain tumors, hematomas, and hydrocephalus. According to a meta-analysis potentially reversible causes were seen in 9% and actually reversed in only 0.6% of dementia cases (0.29% partially, 0.31% fully) (1). Techniques that are widely used in clinical practice are still largely based on structural magnetic resonance (MR) imaging and volumetry. Recently Wattjes et al. (2) concluded that although MR imaging should be the preferred imaging modality due its lack of ionizing radiation and higher contrast resolution, 64-detector row computed tomography (CT) is a suitable and accurate imaging method with which to evaluate global cortical atrophy, medial temporal lobe atrophy, and white matter changes in a memory clinic setting, and it can be considered a nearly equivalent alternative to MR imaging in patients who cannot undergo MR examination. However, it should be noted that measures of brain atrophy typically reflect the relatively late stages of neuronal loss and may not be ideal for identifying early neuropathological changes. There is increasing evidence showing that the pathological process associated with AD may begin years or decades before diagnosis. But: do the advanced techniques help in assessing therapeutic effects or improve patient outcome? Early detection of AD risk would enable preventive or more effective treatment of the patients, resulting in a time delay in symptom onset that may decrease the prevalence of the disease (3). Therefore, in addition to the structural MR imaging procedures a spectrum of novel MR imaging tools is being adopted for the scientific study of pathological processes underlying the development of AD, including blood oxygenation level-dependent (BOLD) functional MRI studies of brain activation and functional connectivity, perfusion measurements with arterial spin labeling (ASL), MR spectroscopy (MRS), and diffusion tensor imaging (DTI). Functional MRI on BOLD contrast allows noninvasive in vivo assessment of hemodynamic responses to external stimuli. ASL is a non-invasive MR imaging technique for the measurement of regional cerebral blood flow by labeling of the arterial water and using it as an endogenous tracer. Although challenging (4), hippocampal MRS combined with quantitative measurements of hippocampal atrophy may improve the early diagnosis of AD. DTI can be used to determine the orientation of fiber tracts and the neural network connections between different brain regions. Fractional anisotropy has become an imaging marker commonly used to study microstructural white matter abnormalities in various pathological states. There is growing interest in using DTI for AD studies (5, 6). In this issue of Acta Radiologica a comprehensive state of the art review by Dr Li Tie-Qiang (3) discusses the use of these advanced imaging techniques mainly in research. The review allows you to get an excellent overview of the advanced MR imaging techniques and the article is highly recommended reading.

PKR and PP1C Polymorphisms in Alzheimer’s Disease Risk

Alzheimer’s disease (AD) is a neurodegenerative disease characterized by senile plaques and neurofibrillary tangles. Senile plaques are deposits of amyloid s-peptide (As) produced by the cleavage of a transmembrane protein termed Amyloid Precursor Protein (APP). The amyloidogenic cleavage of APP is performed by γ-secretase complex and s-site APP cleaving enzyme 1 (BACE1), a key enzyme in AD that can be activated by different noxious stimuli. Interestingly, some viruses could activate double-stranded RNA-activated protein kinase (PKR), which phosphorylates Eukaryotic Initiation Factor 2 alpha (eIF2α). This phosphorylation stops global translation to avoid any synthesis of viral infective proteins, but paradoxically up-regulates BACE1 translation. One of the viral mechanisms to circumvent eIF2α phosphorylation is the recruitment of protein phosphatase 1 (PP1), to fully dephosphorylate eIF2α and allow viral protein synthesis. Due to the functional relationship between BACE1, PKR, PP1 and AD we have performed a large (1122 cases and 1191 control individuals) case-control genetic analysis using two biallelic polymorphisms rs2254958 and rs7480390, located within the genes coding for PKR and the catalytic unit A of PP1, respectively. Although a trend to association of the rs2254958 TT genotype with AD risk was found, our results show that neither rs7480390 nor rs2254958 are associated with AD susceptibility.

Prevention of Alzheimer's Disease and Other Dementias

Alzheimer's disease (AD) affects 150 000 Australians and prevention is a high priority. Approaches to reduce the risk of AD and other dementias can be based on the risk factors that have been suggested from case‐control and longitudinal studies. There is some evidence of benefit from vitamin E supplements (and possibly also vitamin C), a well'balanced diet including adequate folate and vitamin B12, keeping physically and mentally alert, avoiding head injury, continuing moderate alcohol intake, avoiding excess aluminium exposure, avoiding smoking, and keeping elevated blood pressure, diabetes and other vascular risk factors under control. There are currently insufficient data to support the use of cholesterol'lowering agents, anti'inflammatory agents, oestrogen, caffeine, or ginkgo biloba to prevent dementia, but large prospective randomised placebo'controlled prevention trials are in progress for some of these agents and may alter these recommendations. Approaches in the future which look very promising are anti'amyloid vaccination and gene therapy. Targeting high risk groups, such as those with mild cognitive impairment, may increase the benefit of preventative approaches.