High-fat diet increases gliosis and immediate early gene expression in APOE3 mice, but not APOE4 mice

High-fat diet and neuroinflammation: The role of mitochondria

In recent years, increasing evidence has supported that high-fat diet (HFD) can induce the chronic, low-grade neuroinflammation in the brain, which is closely associated with the impairment of cognitive function. As the key organelles responsible for energy metabolism in the cell, mitochondria are believed to involved in the pathogenesis of a variety of neurological disorders. This review summarizes the current progress in the field of the relationship between HFD exposure and neurodegenerative diseases, and outline the major routines of HFD induced neuroinflammation and its pathological significance in the pathogenesis of neurodegenerative diseases. Furthermore, the article highlights the pivotal role of mitochondrial dysfunction in driving the neuroinflammation in the setting of HFD. Danger-associated molecular patterns (DAMPs) from damaged mitochondria can activate innate immune signaling pathways, while mitochondrial dysfunction itself can lead to metabolic remodeling of inflammatory cells, thus inducing neuroinflammation. More importantly, mitochondrial damage, neuroinflammation, and insulin resistance caused by HFD form a mutually reinforcing vicious cycle, ultimately leading to the death of neurons and promoting the progression of neurodegenerative diseases. Thus, in-depth elucidation of the role and underlying mechanisms of mitochondrial dysfunction in HFD-induced metabolic disorders may not only expand our understanding of the mechanistic linkages between HFD and etiology of neurodegenerative diseases, but also help develop the specific strategies for the prevention and treatment of neurodegenerative diseases.

APOE4 rat model of Alzheimer's disease: sex differences, genetic risk and diet

The strongest genetic risk factor for Alzheimer's disease (AD) is the ε4 allele of apolipoprotein E (ApoE ε4). A high fat diet also adds to the risk of dementia and AD. In addition, there are sex differences as women carriers have a higher risk of an earlier onset and rapid decline in memory than men. The present study looked at the effect of the genetic risk of ApoE ε4 together with a high fat/high sucrose diet (HFD/HSD) on brain function in male and female rats using magnetic resonance imaging. We hypothesized female carriers would present with deficits in cognitive behavior together with changes in functional connectivity as compared to male carriers. Four-month-old wildtype and human ApoE ε4 knock-in (TGRA8960), male and female Sprague Dawley rats were put on a HFD/HSD for four months. Afterwards they were imaged for changes in function using resting state BOLD functional connectivity. Images were registered to, and analyzed, using a 3D MRI rat atlas providing site-specific data on 173 different brain areas. Resting state functional connectivity showed male wildtype had greater connectivity between areas involved in feeding and metabolism while there were no differences between female and male carriers and wildtype females. The data were unexpected. The genetic risk was overshadowed by the diet. Male wildtype rats were most sensitive to the HFD/HSD presenting with a deficit in cognitive performance with enhanced functional connectivity in neural circuitry associated with food consumption and metabolism.

Physiopathological Roles of White Adiposity and Gut Functions in Neuroinflammation

White adipose tissue (WAT) and the gut are involved in the development of neuroinflammation when an organism detects any kind of injury, thereby triggering metainflammation. In fact, the autonomous nervous system innervates both tissues, although the complex role played by the integrated sympathetic, parasympathetic, and enteric nervous system functions have not been fully elucidated. Our aims were to investigate the participation of inflamed WAT and the gut in neuroinflammation. Firstly, we conducted an analysis into how inflamed peripheral WAT plays a key role in the triggering of metainflammation. Indeed, this included the impact of the development of local insulin resistance and its metabolic consequences, a serious hypothalamic dysfunction that promotes neurodegeneration. Then, we analyzed the gut-brain axis dysfunction involved in neuroinflammation by examining cell interactions, soluble factors, the sensing of microbes, and the role of dysbiosis-related mechanisms (intestinal microbiota and mucosal barriers) affecting brain functions. Finally, we targeted the physiological crosstalk between cells of the brain-WAT-gut axis that restores normal tissue homeostasis after injury. We concluded the following: because any injury can result not only in overall insulin resistance and dysbiosis, which in turn can impact upon the brain, but that a high-risk of the development of neuroinflammation-induced neurodegenerative disorder can also be triggered. Thus, it is imperative to avoid early metainflammation by applying appropriate preventive (e.g., lifestyle and diet) or pharmacological treatments to cope with allostasis and thus promote health homeostasis.

Effects of obesogenic diet and 17β-estradiol in female mice with APOE 3/3, 3/4, and 4/4 genotypes

The main genetic risk factor for Alzheimer's disease (AD) is the apolipoprotein E ε4 allele (APOE4). AD risk associated with APOE4 disproportionately affects women. Furthermore, human and rodent studies indicate that the cognitive deficits associated with APOE4 are greater in females. One modifiable AD risk factor is obesity during middle age. Given that approximately two-thirds of US adults are overweight, it is important to understand how obesity affects AD risk, how it interacts with APOE4, and the extent to which its detrimental effects can be mitigated with therapeutics. One intervention study for women is estrogen-based hormone therapy, which can exert numerous health benefits when administered in early middle age. No experimental studies have examined the interactions among APOE4, obesity, and hormone therapy in aging females. To begin to explore these issues, we considered how obesity outcomes are affected by treatment with estradiol at the onset of middle age in female mice with human APOE3 and APOE4. Furthermore, to explore how gene dosage affects outcomes, we compared mice homozygous for APOE3 (3/3) and homozygous (4/4) or hemizygous (3/4) for APOE4. Mice were examined over a 4-month period that spans the transition into reproductive senescence, a normal age-related change that models many aspects of human perimenopause. Beginning at 5 months of age, mice were maintained on a control diet (10% fat) or high-fat diet (HFD; 60% fat). After 8 weeks, by which time obesity was present in all HFD groups, mice were implanted with an estradiol or vehicle capsule that was maintained for the final 8 weeks. Animals were assessed on a range of metabolic and neural measures. Overall, APOE4 was associated with poorer metabolic function and cognitive performance. However, an obesogenic diet induced relatively greater impairments in metabolic function and cognitive performance in APOE3/3 mice. Estradiol treatment improved metabolic and cognitive outcomes across all HFD groups, with APOE4/4 generally exhibiting the greatest benefit. APOE3/4 mice were intermediate to the homozygous genotypes on many measures but also exhibited unique profiles. Together, these findings highlight the importance of the APOE genotype as a modulator of the risks associated with obesity and the beneficial outcomes of estradiol.

Sex-dependent effects of carbohydrate source and quantity on caspase-1 activity in the mouse central nervous system

BACKGROUND

Mounting evidence links glucose intolerance and diabetes as aspects of metabolic dysregulation that are associated with an increased risk of developing dementia. Inflammation and inflammasome activation have emerged as a potential link between these disparate pathologies. As diet is a key factor in both the development of metabolic disorders and inflammation, we hypothesize that long term changes in dietary factors can influence nervous system function by regulating inflammasome activity and that this phenotype would be sex-dependent, as sex hormones are known to regulate metabolism and immune processes.

METHODS

5-week-old male and female transgenic mice expressing a caspase-1 bioluminescent reporter underwent cranial window surgeries and were fed control (65% complex carbohydrates, 15% fat), high glycemic index (65% carbohydrates from sucrose, 15% fat), or ketogenic (1% complex carbohydrates, 79% fat) diet from 6 to 26 weeks of age. Glucose regulation was assessed with a glucose tolerance test following a 4-h morning fast. Bioluminescence in the brain was quantified using IVIS in vivo imaging. Blood cytokine levels were measured using cytokine bead array. 16S ribosomal RNA gene amplicon sequencing of mouse feces was performed to assess alterations in the gut microbiome. Behavior associated with these dietary changes was also evaluated.

RESULTS

The ketogenic diet caused weight gain and glucose intolerance in both male and female mice. In male mice, the high glycemic diet led to increased caspase-1 biosensor activation over the course of the study, while in females the ketogenic diet drove an increase in biosensor activation compared to their respective controls. These changes correlated with an increase in inflammatory cytokines present in the serum of test mice and the emergence of anxiety-like behavior. The microbiome composition differed significantly between diets; however no significant link between diet, glucose tolerance, or caspase-1 signal was established.

CONCLUSIONS

Our findings suggest that diet composition, specifically the source and quantity of carbohydrates, has sex-specific effects on inflammasome activation in the central nervous system and behavior. This phenotype manifested as increased anxiety in male mice, and future studies are needed to determine if this phenotype is linked to alterations in microbiome composition.

Obesity affects brain cortex gene expression in an APOE genotype and sex dependent manner

OBJECTIVE

Obesity is the top modifiable risk factor for Alzheimer's disease. We hypothesized that high fat diet (HFD)-induced obesity alters brain transcriptomics in APOE-genotype and sex dependent manners. Here, we investigated interactions between HFD, APOE, and sex, using a knock-in mouse model of the human APOE3 and APOE4 alleles.

METHODS

Six-month-old APOE3-TR and APOE4-TR mice were treated with either HFD or control chow. After 4 months, total RNA was extracted from the cerebral cortices and analyzed by poly-A enriched RNA sequencing on the Illumina platform.

RESULTS

Female mice demonstrated profound HFD-induced transcriptomic changes while there was little to no effect in males. In females, APOE3 brains demonstrated about five times more HFD-induced transcriptomic changes (399 up-regulated and 107 down-regulated genes) compared to APOE4 brains (30 up-regulated and 60 down-regulated). Unsupervised clustering analysis revealed two gene sets that responded to HFD in APOE3 mice but not in APOE4 mice. Pathway analysis demonstrated that HFD in APOE3 mice affected cortical pathways related to feeding behavior, blood circulation, circadian rhythms, extracellular matrix, and cell adhesion.

CONCLUSIONS

Female mice and APOE3 mice have the strongest cortical transcriptomic responses to HFD related to feeding behavior and extracellular matrix remodeling. The relative lack of response of the APOE4 brain to stress associated with obesity may leave it more susceptible to additional stresses that occur with aging and in AD.

Identification of lncRNA-miRNA-mRNA Networks in the Lenticular Nucleus Region of the Brain Contributes to Hepatolenticular Degeneration Pathogenesis and Therapy

Long non-coding RNAs (lncRNAs) are a recently discovered group of non-coding RNAs that play a crucial role in the regulation of various human diseases, especially in the study of nervous system diseases which has garnered significant attention. However, there is limited knowledge on the identification and function of lncRNAs in hepatolenticular degeneration (HLD). The objective of this study was to identify novel lncRNAs and determine their involvement in the networks associated with HLD. We conducted a comprehensive analysis of RNA sequencing (RNA-seq) data, reverse transcription-quantitative polymerase chain reaction (RT-qPCR), and computational biology to identify novel lncRNAs and explore their potential mechanisms in HLD. We identified 212 differently expressed lncRNAs, with 98 upregulated and 114 downregulated. Additionally, 32 differently expressed mRNAs were found, with 15 upregulated and 17 downregulated. We obtained a total of 1131 pairs of co-expressed lncRNAs and mRNAs by Pearson correlation test and prediction and annotation of the lncRNA-targeted miRNA-mRNA network. The differential lncRNAs identified in this study were found to be involved in various biological functions and signaling pathways. These include translational initiation, motor learning, locomotors behavior, dioxygenase activity, integral component of postsynaptic membrane, neuroactive ligand-receptor interaction, nuclear factor-kappa B (NF-κB) signaling pathway, cholinergic synapse, sphingolipid signaling pathway, and Parkinson's disease signaling pathway, as revealed by the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses. Six lncRNAs, including XR_001782921.1 (P < 0.01), XR_ 001780581.1 (P < 0.01), ENSMUST_00000207119 (P < 0.01), XR_865512.2 (P < 0.01), TCONS_00005916 (P < 0.01), and TCONS_00020683 (P < 0.01), showed significant differences in expression levels between the model group and normal group by RT-qPCR. Among these, four lncRNAs (TCONS_00020683, XR_865512.2, XR_001780581.1, and ENSMUST00000207119) displayed a high degree of conservation. This study provides a unique perspective for the pathogenesis and therapy of HLD by constructing the lncRNA-miRNA-mRNA network. This insight provides a foundation for future exploration in this field.

Circadian Regulation of Apolipoproteins in the Brain: Implications in Lipid Metabolism and Disease

The circadian rhythm is a 24 h internal clock within the body that regulates various factors, including sleep, body temperature, and hormone secretion. Circadian rhythm disruption is an important risk factor for many diseases including neurodegenerative illnesses. The central and peripheral oscillators' circadian clock network controls the circadian rhythm in mammals. The clock genes govern the central clock in the suprachiasmatic nucleus (SCN) of the brain. One function of the circadian clock is regulating lipid metabolism. However, investigations of the circadian regulation of lipid metabolism-associated apolipoprotein genes in the brain are lacking. This review summarizes the rhythmic expression of clock genes and lipid metabolism-associated apolipoprotein genes within the SCN in Mus musculus. Nine of the twenty apolipoprotein genes identified from searching the published database (SCNseq and CircaDB) are highly expressed in the SCN. Most apolipoprotein genes (ApoE, ApoC1, apoA1, ApoH, ApoM, and Cln) show rhythmic expression in the brain in mice and thus might be regulated by the master clock. Therefore, this review summarizes studies on lipid-associated apolipoprotein genes in the SCN and other brain locations, to understand how apolipoproteins associated with perturbed cerebral lipid metabolism cause multiple brain diseases and disorders. This review describes recent advancements in research, explores current questions, and identifies directions for future research.

Hippocampal neurogenesis and Arc expression are enhanced in high-fat fed prepubertal female pigs by a diet including omega-3 fatty acids and Bifidobacterium breve CECT8242

PURPOSE

Obesity during childhood has become a pandemic disease, mainly caused by a diet rich in sugars and fatty acids. Among other negative effects, these diets can induce cognitive impairment and reduce neuroplasticity. It is well known that omega-3 and probiotics have a beneficial impact on health and cognition, and we have hypothesized that a diet enriched with Bifidobacterium breve and omega-3 could potentiate neuroplasticity in prepubertal pigs on a high-fat diet.

METHODS

Young female piglets were fed during 10 weeks with: standard diet (T1), high-fat (HF) diet (T2), HF diet including B. breve CECT8242 (T3) and HF diet including the probiotic and omega-3 fatty acids (T4). Using hippocampal sections, we analyzed by immunocytochemistry the levels of doublecortin (DCX) to study neurogenesis, and activity-regulated cytoskeleton-associated protein (Arc) as a synaptic plasticity related protein.

RESULTS

No effect of T2 or T3 was observed, whereas T4 increased both DCX+ cells and Arc expression. Therefore, a diet enriched with supplements of B. breve and omega-3 increases neurogenesis and synaptic plasticity in prepubertal females on a HF diet from nine weeks of age to sexual maturity. Furthermore, the analysis of serum cholesterol and HDL indicate that neurogenesis was related to lipidic demand in piglets fed with control or HF diets, but the neurogenic effect induced by the T4 diet was exerted by mechanisms independent of this lipidic demand.

CONCLUSION

Our results show that the T4 dietary treatment is effective in potentiating neural plasticity in the dorsal hippocampus of prepubertal females on a HF diet.

Age, sex, and apolipoprotein E isoform alter contextual fear learning, neuronal activation, and baseline DNA damage in the hippocampus

Age, female sex, and apolipoprotein E4 (E4) are risk factors to develop Alzheimer's disease (AD). There are three major human apoE isoforms: E2, E3, and E4. Compared to E3, E4 increases while E2 decreases AD risk. However, E2 is associated with increased risk and severity of post-traumatic stress disorder (PTSD). In cognitively healthy adults, E4 carriers have greater brain activation during learning and memory tasks in the absence of behavioral differences. Human apoE targeted replacement (TR) mice display differences in fear extinction that parallel human data: E2 mice show impaired extinction, mirroring heightened PTSD symptoms in E2 combat veterans. Recently, an adaptive role of DNA double strand breaks (DSBs) in immediate early gene expression (IEG) has been described. Age and disease synergistically increase DNA damage and decrease DNA repair. As the mechanisms underlying the relative risks of apoE, sex, and their interactions in aging are unclear, we used young (3 months) and middle-aged (12 months) male and female TR mice to investigate the influence of these factors on DSBs and IEGs at baseline and following contextual fear conditioning. We assessed brain-wide changes in neural activation following fear conditioning using whole-brain cFos imaging in young female TR mice. E4 mice froze more during fear conditioning and had lower cFos immunoreactivity across regions important for somatosensation and contextual encoding compared to E2 mice. E4 mice also showed altered co-activation compared to E3 mice, corresponding to human MRI and cognitive data, and indicating that there are differences in brain activity and connectivity at young ages independent of fear learning. There were increased DSB markers in middle-aged animals and alterations to cFos levels dependent on sex and isoform, as well. The increase in hippocampal DSB markers in middle-aged animals and female E4 mice may play a role in the risk for developing AD.

Apolipoprotein E in lipid metabolism and neurodegenerative disease

Dysregulation of lipid metabolism has emerged as a central component of many neurodegenerative diseases. Variants of the lipid transport protein, apolipoprotein E (APOE), modulate risk and resilience in several neurodegenerative diseases including late-onset Alzheimer's disease (LOAD). Allelic variants of the gene, APOE, alter the lipid metabolism of cells and tissues and have been broadly associated with several other cellular and systemic phenotypes. Targeting APOE-associated metabolic pathways may offer opportunities to alter disease-related phenotypes and consequently, attenuate disease risk and impart resilience to multiple neurodegenerative diseases. We review the molecular, cellular, and tissue-level alterations to lipid metabolism that arise from different APOE isoforms. These changes in lipid metabolism could help to elucidate disease mechanisms and tune neurodegenerative disease risk and resilience.

Effects of APOE Genotype and Western Diet on Metabolic Phenotypes in Female Mice

Western diets high in sugars and saturated fats have been reported to induce metabolic and inflammatory impairments that are associated with several age-related disorders, including Alzheimer's disease (AD) and type 2 diabetes (T2D). The apolipoprotein E (APOE) genotype is associated with metabolic and inflammatory outcomes that contribute to risks for AD and T2D, with the APOE4 genotype increasing risks relative to the more common APOE3 allele. In this study, we investigated the impacts of the APOE genotype on systemic and neural effects of the Western diet. Female mice with knock-in of human APOE3 or APOE4 were exposed to control or Western diet for 13 weeks. In the control diet, we observed that APOE4 mice presented with impaired metabolic phenotypes, exhibiting greater adiposity, higher plasma leptin and insulin levels, and poorer glucose clearance than APOE3 mice. Behaviorally, APOE4 mice exhibited worse performance in a hippocampal-dependent learning task. In visceral adipose tissue, APOE4 mice exhibited generally higher expression levels of macrophage- and inflammation-related genes. The cerebral cortex showed a similar pattern, with higher expression of macrophage- and inflammation-related genes in APOE4 than APOE3 mice. Exposure to the Western diet yielded modest, statistically non-significant effects on most metabolic, behavioral, and gene expression measures in both APOE genotypes. Interestingly, the Western diet resulted in reduced gene expression of a few macrophage markers, specifically in APOE4 mice. The observed relative resistance to the Western diet suggests protective roles of both female sex and young adult age. Further, the data demonstrate that APOE4 is associated with deleterious systemic and neural phenotypes and an altered response to a metabolic stressor, findings relevant to the understanding of interactions between the APOE genotype and risks for metabolic disorders.

Sex and diet-dependent gene alterations in human and rat brains with a history of nicotine exposure

Introduction

Chronic nicotine exposure induces changes in the expression of key regulatory genes associated with metabolic function and neuronal alterations in the brain. Many bioregulatory genes have been associated with exposure to nicotine, but the modulating effects of sex and diet on gene expression in nicotine-exposed brains have been largely unexplored. Both humans and rodents display motivation for nicotine use and the emergence of withdrawal symptoms during abstinence. Research comparing pre-clinical models with human subjects provides an important opportunity to understand common biomarkers of the harmful effects of nicotine as well as information that may help guide the development of more effective interventions for nicotine cessation.

Methods

Human postmortem dorsolateral prefrontal cortex (dLPFC) tissue BA9 was collected from female and male subjects, smokers and non-smokers (N = 12 per group). Rat frontal lobes were collected from female and male rats that received a regular diet (RD) or a high-fat diet (HFD) (N = 12 per group) for 14 days following implantation of a osmotic mini-pump (Alzet) that delivered nicotine continuously. Controls (control-s) received a sham surgical procedure. RNA was extracted from tissue from human and rat samples and reversed-transcribed to cDNA. Gene expression of CHRNA10 (Cholinergic receptor nicotinic alpha 10), CERKL (Ceramide Kinase-Like), SMYD1 (SET and MYD Domin Containing 1), and FA2H (Fatty Acid 2-Hydrolase) in humans was compared to rats in each subset of groups and quantified by qPCR methods. Additionally, protein expression of FA2H was analyzed by immunohistochemistry (IHC) in human dLPFC.

Results

Humans with a history of smoking displayed decreased CHRNA10 (p = 0.0005), CERKL (p ≤ 0.0001), and SMYD1 (p = 0.0005) expression and increased FA2H (p = 0.0097) expression compared to non-smokers (p < 0.05). Similar patterns of results were observed in nicotine exposed vs. control rats. Interestingly, sex-related differences in gene expression for CERKL and FA2H were observed. In addition, ANCOVA analysis showed a significant effect of nicotine in a sex-different manner, including an increase in CERKL in male and female rats with RD or HFD. In rats exposed to an HFD, FA2H gene expression was lower in nicotine-treated rats compared to RD rats treated with nicotine. Protein expression of FA2H (p = 0.001) by IHC was significantly higher in smokers compared to non-smokers.

Conclusion

These results suggest that a history of long-term nicotine exposure in humans alters the expression of sphingolipid metabolism-related (CERKL, SMYD1, and FA2H) and neuronal (CHRNA10) marker genes similarly as compared to rats. Sex- and diet-dependent differences appear in nicotine-exposed rats, critical in regulating sphingolipid metabolism and nicotinic acetylcholine receptors. This research enhances the construct validity of rat models of nicotine usage by showing a similar pattern of changes in gene expression in human subjects with a smoking history.

Obesogenic Diet-Induced Neuroinflammation: A Pathological Link between Hedonic and Homeostatic Control of Food Intake

Obesity-induced neuroinflammation is a chronic aseptic central nervous system inflammation that presents systemic characteristics associated with increased pro-inflammatory cytokines such as interleukin 1 beta (IL-1β) and interleukin 18 (IL-18) and the presence of microglia and reactive astrogliosis as well as the activation of the NLRP3 inflammasome. The obesity pandemic is associated with lifestyle changes, including an excessive intake of obesogenic foods and decreased physical activity. Brain areas such as the lateral hypothalamus (LH), lateral septum (LS), ventral tegmental area (VTA), and nucleus accumbens (NAcc) have been implicated in the homeostatic and hedonic control of feeding in experimental models of diet-induced obesity. In this context, a chronic lipid intake triggers neuroinflammation in several brain regions such as the hypothalamus, hippocampus, and amygdala. This review aims to present the background defining the significant impact of neuroinflammation and how this, when induced by an obesogenic diet, can affect feeding control, triggering metabolic and neurological alterations.

Obesity-Induced Brain Neuroinflammatory and Mitochondrial Changes

Obesity is defined as abnormal and excessive fat accumulation, and it is a risk factor for developing metabolic and neurodegenerative diseases and cognitive deficits. Obesity is caused by an imbalance in energy homeostasis resulting from increased caloric intake associated with a sedentary lifestyle. However, the entire physiopathology linking obesity with neurodegeneration and cognitive decline has not yet been elucidated. During the progression of obesity, adipose tissue undergoes immune, metabolic, and functional changes that induce chronic low-grade inflammation. It has been proposed that inflammatory processes may participate in both the peripheral disorders and brain disorders associated with obesity, including the development of cognitive deficits. In addition, mitochondrial dysfunction is related to inflammation and oxidative stress, causing cellular oxidative damage. Preclinical and clinical studies of obesity and metabolic disorders have demonstrated mitochondrial brain dysfunction. Since neuronal cells have a high energy demand and mitochondria play an important role in maintaining a constant energy supply, impairments in mitochondrial activity lead to neuronal damage and dysfunction and, consequently, to neurotoxicity. In this review, we highlight the effect of obesity and high-fat diet consumption on brain neuroinflammation and mitochondrial changes as a link between metabolic dysfunction and cognitive decline.

Body Mass Index Decrease Has a Distinct Association with Alzheimer's Disease Pathophysiology in APOE ɛ4 Carriers and Non-Carriers

BACKGROUND

Body mass index (BMI) changes may be related to Alzheimer's disease (AD) alterations, but it is unclear how the apolipoprotein E ɛ4 (APOE ɛ4) allele affects their association.

OBJECTIVE

To explore the association of BMI changes with AD pathologies in APOE ɛ4 carriers and non-carriers.

METHODS

In 862 non-demented ADNI participants with≥2 BMI measurements, we investigated the relationships between BMI slopes and longitudinal changes in amyloid-β (Aβ) accumulation, neurodegeneration and cognition, and follow-up tau deposition in different Aβ and APOE ɛ4 statuses.

RESULTS

In Aβ+ APOE ɛ4 non-carriers, faster BMI declines were associated with faster rates of Aβ accumulation (standardized β (βstd) = -0.29, p = 0.001), AD meta regions of interest (metaROI) hypometabolism (βstd = 0.23, p = 0.026), memory declines (βstd = 0.17, p = 0.029), executive function declines (βstd = 0.19, p = 0.011), and marginally faster Temporal-metaROI cortical thinning (βstd = 0.15, p = 0.067) and higher follow-up Temporal-metaROI tau deposition (βstd = -0.17, p = 0.059). Among Aβ- individuals, faster BMI decreases were related to faster Aβ accumulation (βstd = -0.25, p = 0.023) in APOE ɛ4 carriers, whereas predicted faster declines in memory and executive function in both APOE ɛ4 carriers (βstd = 0.25, p = 0.008; βstd = 0.32, p = 0.001) and APOE ɛ4 non-carriers (βstd = 0.11, p = 0.030; βstd = 0.12, p = 0.026).

CONCLUSIONS

This study highlights the significance of tracking BMI data in older adults by providing novel insights into how body weight fluctuations and APOE ɛ4 interact with AD pathology and cognitive decline.

A multi-hit hypothesis for an APOE4-dependent pathophysiological state

The APOE gene encoding the Apolipoprotein E protein is the single most significant genetic risk factor for late-onset Alzheimer's disease. The APOE4 genotype confers a significantly increased risk relative to the other two common genotypes APOE3 and APOE2. Intriguingly, APOE4 has been associated with neuropathological and cognitive deficits in the absence of Alzheimer's disease-related amyloid or tau pathology. Here, we review the extensive literature surrounding the impact of APOE genotype on central nervous system dysfunction, focussing on preclinical model systems and comparison of APOE3 and APOE4, given the low global prevalence of APOE2. A multi-hit hypothesis is proposed to explain how APOE4 shifts cerebral physiology towards pathophysiology through interconnected hits. These hits include the following: neurodegeneration, neurovascular dysfunction, neuroinflammation, oxidative stress, endosomal trafficking impairments, lipid and cellular metabolism disruption, impaired calcium homeostasis and altered transcriptional regulation. The hits, individually and in combination, leave the APOE4 brain in a vulnerable state where further cumulative insults will exacerbate degeneration and lead to cognitive deficits in the absence of Alzheimer's disease pathology and also a state in which such pathology may more easily take hold. We conclude that current evidence supports an APOE4 multi-hit hypothesis, which contributes to an APOE4 pathophysiological state. We highlight key areas where further study is required to elucidate the complex interplay between these individual mechanisms and downstream consequences, helping to frame the current landscape of existing APOE-centric literature.

APOE in the bullseye of neurodegenerative diseases: impact of the APOE genotype in Alzheimer's disease pathology and brain diseases

ApoE is the major lipid and cholesterol carrier in the CNS. There are three major human polymorphisms, apoE2, apoE3, and apoE4, and the genetic expression of APOE4 is one of the most influential risk factors for the development of late-onset Alzheimer's disease (AD). Neuroinflammation has become the third hallmark of AD, together with Amyloid-β plaques and neurofibrillary tangles of hyperphosphorylated aggregated tau protein. This review aims to broadly and extensively describe the differential aspects concerning apoE. Starting from the evolution of apoE to how APOE's single-nucleotide polymorphisms affect its structure, function, and involvement during health and disease. This review reflects on how APOE's polymorphisms impact critical aspects of AD pathology, such as the neuroinflammatory response, particularly the effect of APOE on astrocytic and microglial function and microglial dynamics, synaptic function, amyloid-β load, tau pathology, autophagy, and cell-cell communication. We discuss influential factors affecting AD pathology combined with the APOE genotype, such as sex, age, diet, physical exercise, current therapies and clinical trials in the AD field. The impact of the APOE genotype in other neurodegenerative diseases characterized by overt inflammation, e.g., alpha- synucleinopathies and Parkinson's disease, traumatic brain injury, stroke, amyotrophic lateral sclerosis, and multiple sclerosis, is also addressed. Therefore, this review gathers the most relevant findings related to the APOE genotype up to date and its implications on AD and CNS pathologies to provide a deeper understanding of the knowledge in the APOE field.

Plcg2M28L Interacts With High Fat/High Sugar Diet to Accelerate Alzheimer's Disease-Relevant Phenotypes in Mice

Obesity is recognized as a significant risk factor for Alzheimer's disease (AD). Studies have supported the notion that obesity accelerates AD-related pathophysiology in mouse models of AD. The majority of studies, to date, have focused on the use of early-onset AD models. Here, we evaluate the impact of genetic risk factors on late-onset AD (LOAD) in mice fed with a high fat/high sugar diet (HFD). We focused on three mouse models created through the IU/JAX/PITT MODEL-AD Center. These included a combined risk model with APOE4 and a variant in triggering receptor expressed on myeloid cells 2 (Trem2R47H ). We have termed this model, LOAD1. Additional variants including the M28L variant in phospholipase C Gamma 2 (Plcg2M28L ) and the 677C > T variant in methylenetetrahydrofolate reductase (Mthfr 677C > T ) were engineered by CRISPR onto LOAD1 to generate LOAD1.Plcg2M28L and LOAD1.Mthfr 677C > T . At 2 months of age, animals were placed on an HFD that induces obesity or a control diet (CD), until 12 months of age. Throughout the study, blood was collected to assess the levels of cholesterol and glucose. Positron emission tomography/computed tomography (PET/CT) was completed prior to sacrifice to image for glucose utilization and brain perfusion. After the completion of the study, blood and brains were collected for analysis. As expected, animals fed a HFD, showed a significant increase in body weight compared to those fed a CD. Glucose increased as a function of HFD in females only with cholesterol increasing in both sexes. Interestingly, LOAD1.Plcg2M28L demonstrated an increase in microglia density and alterations in regional brain glucose and perfusion on HFD. These changes were not observed in LOAD1 or LOAD1.Mthfr 677C > T animals fed with HFD. Furthermore, LOAD1.Plcg2M28L but not LOAD1.Mthfr 677C > T or LOAD1 animals showed transcriptomics correlations with human AD modules. Our results show that HFD affects the brain in a genotype-specific manner. Further insight into this process may have significant implications for the development of lifestyle interventions for the treatment of AD.

Apolipoprotein ε4 modifies obesity-related atrophy in the hippocampal formation of cognitively healthy adults

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Age-related inverted U-shaped curve of hippocampal myelin/neurite packing.

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Reduced hippocampal myelin/neurite packing and size/complexity in obesity.

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APOE modifies the effects of obesity on hippocampal size/complexity.

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Age-related slowing of spatial navigation but no risk effects on cognition.

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CA/DG predict episodic memory and subiculum predicts spatial navigation performance.

Characterizing age- and risk-related hippocampal vulnerabilities may inform about the neural underpinnings of cognitive decline. We studied the impact of three risk-factors, Apolipoprotein (APOE)-ε4, a family history of dementia, and central obesity, on the CA1, CA2/3, dentate gyrus and subiculum of 158 cognitively healthy adults (38-71 years). Subfields were labelled with the Automatic Segmentation of Hippocampal Subfields and FreeSurfer (version 6) protocols. Volumetric and microstructural measurements from quantitative magnetization transfer and Neurite Orientation Density and Dispersion Imaging were extracted for each subfield and reduced to three principal components capturing apparent myelin/neurite packing, size/complexity, and metabolism. Aging was associated with an inverse U-shaped curve on myelin/neurite packing and affected all subfields. Obesity led to reductions in myelin/neurite packing and size/complexity regardless of APOE and family history of dementia status. However, amongst individuals with a healthy Waist-Hip-Ratio, APOE ε4 carriers showed lower size/complexity than non-carriers. Segmentation protocol type did not affect this risk pattern. These findings reveal interactive effects between APOE and central obesity on the hippocampal formation of cognitively healthy adults.