Cholesteryl ester transfer protein (CETP) polymorphism modifies the Alzheimer's disease risk associated with APOE ε4 allele

Dynamic functional network connectivity and its association with lipid metabolism in Alzheimer's disease

AIMS

The study aims to examine the changing trajectory characteristics of dynamic functional network connectivity (dFNC) and its correlation with lipid metabolism-related factors across the Alzheimer's disease (AD) spectrum populations.

METHODS

Data from 242 AD spectrum subjects, including biological, neuroimaging, and general cognition, were obtained from the Alzheimer's Disease Neuroimaging Initiative for this cross-sectional study. The study utilized a sliding-window approach to assess whole-brain dFNC, investigating group differences and associations with biological and cognitive factors. Abnormal dFNC was used in the classification of AD spectrum populations by support vector machine. Mediation analysis was performed to explore the relationships between lipid-related indicators, dFNC, cerebrospinal fluid (CSF) biomarkers, and cognitive performance.

RESULTS

Significant group difference concerning were observed in relation to APOE-ε4 status, CSF biomarkers, and cognitive scores. Two reoccurring connectivity states were identified: state-1 characterized by frequent but weak connections, and state-II characterized by less frequent but strong connections. Pre-AD subjects exhibited a preference for spending more time in state-I, whereas AD patients tended remain in state-II for longer periods. Group difference in dFNC was primarily found between AD and non-AD participants within each state. The dFNC of state-I yielded strong power to distinguish AD from other groups compared with state-II. APOE-ε4+, high polygenic score, and high serum lipid group were strongly associated with network disruption between association cortex system and sensory cortex system that characterized elevation of cognitive function, which may suggest a compensatory mechanism of dFNC in state-I, whereas differential connections of state-II mediated the relationships between APOE-ε4 genotype and CSF biomarkers, and cognitive indicators.

CONCLUSION

The dysfunction of dFNC temporal-spatial patterns and increased cognition in individuals with APOE-ε4, high polygenic score, and higher serum lipid levels shed light on the lipid-related mechanisms of dynamic network reorganization in AD.

Roles of peripheral lipoproteins and cholesteryl ester transfer protein in the vascular contributions to cognitive impairment and dementia

This narrative review focuses on the role of cholesteryl ester transfer protein (CETP) and peripheral lipoproteins in the vascular contributions to cognitive impairment and dementia (VCID). Humans have a peripheral lipoprotein profile where low-density lipoproteins (LDL) represent the dominant lipoprotein fraction and high-density lipoproteins (HDL) represent a minor lipoprotein fraction. Elevated LDL-cholesterol (LDL-C) levels are well-established to cause cardiovascular disease and several LDL-C-lowering therapies are clinically available to manage this vascular risk factor. The efficacy of LDL-C-lowering therapies to reduce risk of all-cause dementia and AD is now important to address as recent studies demonstrate a role for LDL in Alzheimer's Disease (AD) as well as in all-cause dementia. The LDL:HDL ratio in humans is set mainly by CETP activity, which exchanges cholesteryl esters for triglycerides across lipoprotein fractions to raise LDL and lower HDL as CETP activity increases. Genetic and pharmacological studies support the hypothesis that CETP inhibition reduces cardiovascular risk by lowering LDL, which, by extension, may also lower VCID. Unlike humans, wild-type mice do not express catalytically active CETP and have HDL as their major lipoprotein fraction. As HDL has potent beneficial effects on endothelial cells, the naturally high HDL levels in mice protect them from vascular disorders, likely including VCID. Genetic restoration of CETP expression in mice to generate a more human-like lipid profile may increase the relevance of murine models for VCID studies. The therapeutic potential of existing and emerging LDL-lowering therapies for VCID will be discussed. Figure Legend. Cholesteryl Ester Transfer Protein in Alzheimer's Disease. CETP is mainly produced by the liver, and exchanges cholesteryl esters for triglycerides across lipoprotein fractions to raise circulating LDL and lower HDL as CETP activity increases. Low CETP activity is associated with better cardiovascular health, due to decreased LDL and increased HDL, which may also improve brain health. Although most peripheral lipoproteins cannot enter the brain parenchyma due to the BBB, it is increasingly appreciated that direct access to the vascular endothelium may enable peripheral lipoproteins to have indirect effects on brain health. Thus, lipoproteins may affect the cerebrovasculature from both sides of the BBB. Recent studies show an association between elevated plasma LDL, a well-known cardiovascular risk factor, and a higher risk of AD, and considerable evidence suggests that high HDL levels are associated with reduced CAA and lower neuroinflammation. Considering the potential detrimental role of LDL in AD and the importance of HDL's beneficial effects on endothelial cells, high CETP activity may lead to compromised BBB integrity, increased CAA deposits and greater neuroinflammation. Abbreviations: CETP - cholesteryl transfer ester protein; LDL - low-density lipoproteins; HDL - high-density lipoproteins; BBB - blood-brain barrier; CAA - cerebral amyloid angiopathy, SMC - smooth muscle cells, PVM - perivascular macrophages, RBC - red blood cells.

The evolving role of cholesteryl ester transfer protein inhibition beyond cardiovascular disease

The main role of cholesteryl ester transfer protein (CETP) is the transfer of cholesteryl esters and triglycerides between high-density lipoprotein (HDL) particles and triglyceride-rich lipoprotein and low-density lipoprotein (LDL) particles. There is a long history of investigations regarding the inhibition of CETP as a target for reducing major adverse cardiovascular events. Initially, the potential effect on cardiovascular events of CETP inhibitors was hypothesized to be mediated by their ability to increase HDL cholesterol, but, based on evidence from anacetrapib and the newest CETP inhibitor, obicetrapib, it is now understood to be primarily due to reducing LDL cholesterol and apolipoprotein B. Nevertheless, evidence is also mounting that other roles of HDL, including its promotion of cholesterol efflux, as well as its apolipoprotein composition and anti-inflammatory, anti-oxidative, and anti-diabetic properties, may play important roles in several diseases beyond cardiovascular disease, including, but not limited to, Alzheimer's disease, diabetes, and sepsis. Furthermore, although Mendelian randomization analyses suggested that higher HDL cholesterol is associated with increased risk of age-related macular degeneration (AMD), excess risk of AMD was absent in all CETP inhibitor randomized controlled trial data comprising over 70,000 patients. In fact, certain HDL subclasses may, in contrast, be beneficial for treating the retinal cholesterol accumulation that occurs with AMD. This review describes the latest biological evidence regarding the relationship between HDL and CETP inhibition for Alzheimer's disease, type 2 diabetes mellitus, sepsis, and AMD.

CETP inhibitor evacetrapib enters mouse brain tissue

High levels of plasma cholesterol, especially high levels of low-density lipoprotein cholesterol (LDL-C), have been associated with an increased risk of Alzheimer's disease. The cholesteryl ester transfer protein (CETP) in plasma distributes cholesteryl esters between lipoproteins and increases LDL-C in plasma. Epidemiologically, decreased CETP activity has been associated with sustained cognitive performance during aging, longevity, and a lower risk of Alzheimer's disease. Thus, pharmacological CETP inhibitors could be repurposed for the treatment of Alzheimer's disease as they are safe and effective at lowering CETP activity and LDL-C. Although CETP is mostly expressed by the liver and secreted into the bloodstream, it is also expressed by astrocytes in the brain. Therefore, it is important to determine whether CETP inhibitors can enter the brain. Here, we describe the pharmacokinetic parameters of the CETP inhibitor evacetrapib in the plasma, liver, and brain tissues of CETP transgenic mice. We show that evacetrapib crosses the blood-brain barrier and is detectable in brain tissue 0.5 h after a 40 mg/kg i.v. injection in a non-linear function. We conclude that evacetrapib may prove to be a good candidate to treat CETP-mediated cholesterol dysregulation in Alzheimer's disease.

The Cholesteryl Ester Transfer Protein (CETP) raises Cholesterol Levels in the Brain

The cholesteryl ester transfer protein (CETP) is a lipid transfer protein responsible for the exchange of cholesteryl esters and triglycerides between lipoproteins. Decreased CETP activity is associated with longevity, cardiovascular health, and maintenance of good cognitive performance. Interestingly, mice lack the CETP-encoding gene and have very low levels of LDL particles compared with humans. Currently, the molecular mechanisms induced because of CETP activity are not clear. To understand how CETP activity affects the brain, we utilized CETP transgenic (CETPtg) mice that show elevated LDL levels upon induction of CETP expression through a high-cholesterol diet. CETPtg mice on a high-cholesterol diet showed up to 22% higher cholesterol levels in the brain. Using a microarray on mostly astrocyte-derived mRNA, we found that this cholesterol increase is likely not because of elevated de novo synthesis of cholesterol. However, cholesterol efflux is decreased in CETPtg mice along with an upregulation of the complement factor C1Q, which plays a role in neuronal cholesterol clearance. Our data suggest that CETP activity affects brain health through modulating cholesterol distribution and clearance. Therefore, we propose that CETPtg mice constitute a valuable research tool to investigate the impact of cholesterol metabolism on brain function.

Western Diet Induces Impairment of Liver-Brain Axis Accelerating Neuroinflammation and Amyloid Pathology in Alzheimer's Disease

Alzheimer's disease (AD) is an aging-dependent, irreversible neurodegenerative disorder and the most common cause of dementia. The prevailing AD hypothesis points to the central role of altered cleavage of amyloid precursor protein (APP) and formation of toxic amyloid-β (Aβ) deposits in the brain. The lack of efficient AD treatments stems from incomplete knowledge on AD causes and environmental risk factors. The role of lifestyle factors, including diet, in neurological diseases is now beginning to attract considerable attention. One of them is western diet (WD), which can lead to many serious diseases that develop with age. The aim of the study was to investigate whether WD-derived systemic disturbances may accelerate the brain neuroinflammation and amyloidogenesis at the early stages of AD development. To verify this hypothesis, transgenic mice expressing human APP with AD-causing mutations (APPswe) were fed with WD from the 3rd month of age. These mice were compared to APPswe mice, in which short-term high-grade inflammation was induced by injection of lipopolysaccharide (LPS) and to untreated APPswe mice. All experimental subgroups of animals were subsequently analyzed at 4-, 8-, and 12-months of age. APPswe mice at 4- and 8-months-old represent earlier pre-plaque stages of AD, while 12-month-old animals represent later stages of AD, with visible amyloid pathology. Already short time of WD feeding induced in 4-month-old animals such brain neuroinflammation events as enhanced astrogliosis, to a level comparable to that induced by the administration of pro-inflammatory LPS, and microglia activation in 8-month-old mice. Also, WD feeding accelerated increased Aβ production, observed already in 8-month-old animals. These brain changes corresponded to diet-induced metabolic disorders, including increased cholesterol level in 4-months of age, and advanced hypercholesterolemia and fatty liver disease in 8-month-old mice. These results indicate that the westernized pattern of nourishment is an important modifiable risk factor of AD development, and that a healthy, balanced, diet may be one of the most efficient AD prevention methods.

Defective Lysosomal Lipid Catabolism as a Common Pathogenic Mechanism for Dementia

Dementia poses an ever-growing burden to health care and social services as life expectancies have grown across the world and populations age. The most common forms of dementia are Alzheimer's disease (AD), vascular dementia, frontotemporal dementia (FTD), and Lewy body dementia, which includes Parkinson's disease (PD) dementia and dementia with Lewy bodies (DLB). Genomic studies over the past 3 decades have identified variants in genes regulating lipid transporters and endosomal processes as major risk determinants for AD, with the most significant being inheritance of the ε4 allele of the APOE gene, encoding apolipoprotein E. A recent surge in research on lipid handling and metabolism in glia and neurons has established defective lipid clearance from endolysosomes as a central driver of AD pathogenesis. The most prevalent genetic risk factors for DLB are the APOE ε4 allele, and heterozygous loss of function mutations in the GBA gene, encoding the lysosomal catabolic enzyme glucocerebrosidase; whilst heterozygous mutations in the GRN gene, required for lysosomal catabolism of sphingolipids, are responsible for a significant proportion of FTD cases. Homozygous mutations in the GBA or GRN genes produce the lysosomal storage diseases Gaucher disease and neuronal ceroid lipofuscinosis. Research from mouse and cell culture models, and neuropathological evidence from lysosomal storage diseases, has established that impaired cholesterol or sphingolipid catabolism is sufficient to produce the pathological hallmarks of dementia, indicating that defective lipid catabolism is a common mechanism in the etiology of dementia.

Adipose-Derived Molecules-Untouched Horizons in Alzheimer's Disease Biology

The global incidence of Alzheimer's disease (AD) is on the rise with the increase in obesity and metabolic disease epidemic. Obesity is co-morbid with the increase in mass of adipose tissue, which secretes numerous molecules that are biologically important. Obesity and its associated conditions are perhaps involved in the causative pathway of AD. Immunologically important cytokines such as IL-1β, IL-10, and IL-18, which are released by adipose tissue, are also found to be associated with AD. Besides, the expression of IL-6, IFNγ, and TNF alpha are also associated with AD. Ang-I and Ang-II are found to mediate the progression of AD. Complement factors B, C4b, and H are differentially expressed in AD. Overall, several adipocyte-derived cytokines are found to be dysregulated in AD, and their role in AD remains to be studied. The induction of autophagy is a very promising strategy in the treatment of AD. A variety of adipose-derived molecules have been shown to modulate autophagy. However, very little literature is available on the role of adipose-derived molecules in inducing autophagy in microglial cells of AD. Understanding the role of adipose-derived molecules in the development of AD, especially in the induction of autophagy, would open up new avenues in devising strategies for the treatment of AD.

Associations of cholesteryl ester transfer protein (CETP) gene variants with pituitary adenoma

AIM

The aim was to evaluate the association of CETP (rs5882 and rs708272) single nucleotide polymorphisms with the presence, invasiveness, hormonal activity and recurrence of pituitary adenoma (PA).

METHODS

The study group included 142 patients with PA and the control group, 753 healthy subjects. The genotyping of CETP (rs5882 and rs708272) was performed using a real-time PCR method.

RESULTS

After statistical analysis we found that CETP rs708272 genotype G/A under the over-dominant model was associated with the decreased odds of PA (OR=0.637; 95%CI: 0.443-0.917; P=0.015), active PA (OR=0.538; 95%CI: 0.335-0.865; P =0.01) and non-recurrent PA (OR=0.602; 95% CI: 0.402 - 0.902; P =0.014). When compared to controls, the rs708272 genotype G/A was less frequent in the active PA subgroup (37.5% vs 52.7%, P =0.009) and the non-recurrent PA subgroup (40.2% vs 52.7%, P=0.013), while the rs5882 genotype A/A was less frequent in the non-recurrent PA subgroup (37.5% vs 46.2%, P=0.015).

CONCLUSION

Our study showed that CETP rs708272 genotype G/A may be associated with a decreased risk of PA.

Candidate SNP Markers of Familial and Sporadic Alzheimer's Diseases Are Predicted by a Significant Change in the Affinity of TATA-Binding Protein for Human Gene Promoters

While year after year, conditions, quality, and duration of human lives have been improving due to the progress in science, technology, education, and medicine, only eight diseases have been increasing in prevalence and shortening human lives because of premature deaths according to the retrospective official review on the state of US health, 1990-2010. These diseases are kidney cancer, chronic kidney diseases, liver cancer, diabetes, drug addiction, poisoning cases, consequences of falls, and Alzheimer's disease (AD) as one of the leading pathologies. There are familial AD of hereditary nature (~4% of cases) and sporadic AD of unclear etiology (remaining ~96% of cases; i.e., non-familial AD). Therefore, sporadic AD is no longer a purely medical problem, but rather a social challenge when someone asks oneself: “What can I do in my own adulthood to reduce the risk of sporadic AD at my old age to save the years of my lifespan from the destruction caused by it?” Here, we combine two computational approaches for regulatory SNPs: Web service SNP_TATA_Comparator for sequence analysis and a PubMed-based keyword search for articles on the biochemical markers of diseases. Our purpose was to try to find answers to the question: “What can be done in adulthood to reduce the risk of sporadic AD in old age to prevent the lifespan reduction caused by it?” As a result, we found 89 candidate SNP markers of familial and sporadic AD (e.g., rs562962093 is associated with sporadic AD in the elderly as a complication of stroke in adulthood, where natural marine diets can reduce risks of both diseases in case of the minor allele of this SNP). In addition, rs768454929, and rs761695685 correlate with sporadic AD as a comorbidity of short stature, where maximizing stature in childhood and adolescence as an integral indicator of health can minimize (or even eliminate) the risk of sporadic AD in the elderly. After validation by clinical protocols, these candidate SNP markers may become interesting to the general population [may help to choose a lifestyle (in childhood, adolescence, and adulthood) that can reduce the risks of sporadic AD, its comorbidities, and complications in the elderly].

Longitudinal lipid profile variations and clinical change in Alzheimer's disease dementia

Hypercholesterolemia and statin use have been unevenly associated with clinical change in Alzheimer's disease dementia. In this longitudinal study, 192 consecutive outpatients with late-onset Alzheimer's disease dementia were stratified according to APOE haplotypes, and followed for one year to investigate associations of lipid profile variations and lipophilic statin therapy with changes in cognition, caregiver burden, basic and instrumental functionality. Overall, 102 patients (53.1%) carried APOE4+ haplotypes and 90 (46.9%) carried APOE4- haplotypes; 189 patients (98.4%) used either a cholinesterase inhibitor, or Memantine, or both; 144 patients had dyslipidemias and 143 of them received statin therapy. Total cholesterol, LDL-cholesterol, Mini-Mental State Examination scores, and functional independence scores were significantly lower at the end of the follow-up, while Clinical Dementia Rating sum-of-boxes scores were higher. Exclusively for APOE4- carriers, rising LDL-cholesterol levels were associated with a trend toward improvements in the Index of Independence in Activities of Daily Living (β=0.010; ρ=0.16), whereas rising HDL-cholesterol levels were associated with lowered scores (β=-0.051; ρ=0.04). Lipophilic statin therapy had non-significant protective effects over Clinical Dementia Rating sum-of-boxes score variations only for APOE4- carriers. APOE4- haplotypes might enhance lipid availability to protect neuronal membranes, thus overcoming their supposed dysfunction in cholesterol metabolism, while APOE4+ carriers have inefficient neural repair mechanisms. In conclusion, APOE haplotypes seem to influence the protective effects of lipid profile variations for patients with Alzheimer's disease dementia, but current evidence is insufficient to propose lipid-lowering drugs as specific anti-dementia therapy.

Cholesteryl Ester Transfer Protein Intimately Involved in Dyslipidemia-Related Susceptibility to Cognitive Deficits in Type 2 Diabetic Patients

BACKGROUND

Cholesteryl ester transfer protein (CETP) is involved in diabetic dyslipidemia.

OBJECTIVE

We aim to test the hypothesis that CETP might be of importance in mediating dyslipidemia-related susceptibility to cognitive deficits in diabetic patients.

METHODS

We recruited 190 type 2 diabetic patients and divided them into two groups according to the Montreal Cognitive Assessment (MoCA) score. The association between CETP and cognitive decline was analyzed with logistic regression and stratification.

RESULTS

There were 110 diabetic patients with mild cognition impairment (MCI) and 80 healthy cognition subjects as controls. Dyslipidemia is more common among diabetic patients with MCI; they had a significant increase of serum CETP concentrations, which was negatively correlated with MoCA (r = -0.638; p < 0.001). Negative correlations were also found between the serum CETP concentration with the Auditory Verbal Learning Test (r = -0.266; p = 0.008), indicating memory deficit. Logistic regression analysis revealed that CETP concentration was an independent factor of diabetic MCI (p < 0.001). Further stratification study showed that high serum levels of CETP was an independent risk factor of MCI in diabetic patients with a low density lipoproteins level ≥2.59 mmol/L, or high density lipoproteins level ≤1.0 mmol/L for men and ≤1.3 mmol/L for women, or TG level ≥1.7 mmol/L, after adjusting for age, sex, education, and glucose control (all ps < 0.05).

CONCLUSIONS

CETP was intimately involved in dyslipidemia-related susceptibility to cognitive decline, especially memory function in type 2 diabetic patients.

Cholesteryl ester transfer protein genotype modifies the effect of apolipoprotein ε4 on memory decline in older adults

Apolipoprotein ε4 (ApoE4) is a strong genetic risk factor for sporadic Alzheimer's disease and memory decline in older adults. A single-nucleotide polymorphism in the cholesteryl ester transfer protein (CETP) gene (isoleucine to valine; V405) is associated with slower memory decline and a lower risk of Alzheimer's disease. As both genes regulate cholesterol, we hypothesized that the favorable CETPV405 allele may buffer the effect of ApoE4 on memory decline in older adults. Using linear regression, we examined the interactive effect of ApoE4 by CETPV405 on memory decline among 909 community-dwelling, nondemented, older adults (≥70 years) from the Einstein Aging Study. Episodic memory was measured using the picture version of the Free and Cued Selective Reminding Test with immediate recall (pFCSRT+IR). There was a significant ApoE × CETP interaction on decline in pFCSRT+IR scores (p = 0.01). ApoE4 carriers experienced faster decline than noncarriers among CETPI405I homozygotes (p = 0.007) and in CETPI405V heterozygotes (p = 0.015) but not in CETPV405V homozygotes (p = 0.614). Results suggest that the CETPV405 allele buffers ApoE4-associated memory decline in a gene dose-dependent manner.

Genetic markers of cholesterol transport and gray matter diffusion: a preliminary study of the CETP I405V polymorphism

Variations of the cholesteryl ester transfer protein polymorphism (CETP I405V/rs5882) have been associated with an increased risk for neurodegeneration, particularly when examined in conjunction with the epsilon 4 isoform of apolipoprotein E (ApoE4). Despite these identified relationships, the impact of I405V on gray matter microstructure remains unknown. The present study examined the impact of the CETP I405V polymorphism on gray matter integrity among 52 healthy adults between ages 51 and 85. Gray matter was measured bilaterally using diffusion tensor imaging (DTI) metrics of fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD). Participants were grouped according to a dominant statistical model (II genotype vs. IV/VV genotypes) and secondary analyses were completed to examine the interactive effects of CETP and ApoE4 on DTI metrics. Compared to individuals with the IV/VV genotypes, II homozygotes demonstrated significantly higher MD in bilateral temporal, parietal, and occipital gray matter. Secondary analyses revealed higher FA and AD in the left temporal lobe of IV/VV genotypes with an ApoE4 allele. Our results provide preliminary evidence that CETP II homozygosity is a predisposing risk factor for gray matter abnormalities in posterior brain regions in healthy older adults, independent of an ApoE4 allele.

The potential of cholesteryl ester transfer protein as a therapeutic target

INTRODUCTION

Over recent decades, attempts to ascertain the pro-atherogenic nature of plasma cholesteryl ester transfer protein (CETP) and to establish the relevance of its pharmacological blockade as a promising high density lipoproteins-raising and anti-atherogenic therapy have been disappointing.

AREAS COVERED

The current review focuses on CETP as a multifaceted protein, on genetic variations at the CETP gene and on their possible consequences for cardiovascular risk in human populations. Specific attention is given to physiological modulation of endogenous CETP activity by the apoC1 inhibitor. Finally, the rationale behind the need for selection of patients to treat is discussed in the light of recent studies.

EXPERT OPINION

At this stage one can only speculate on the clinical outcome of pharmacological CETP inhibitors in high-risk populations, but recent advances give cause to adjust the expectations from now on. The CETP effect is probably largely influenced by the overall metabolic state, and whether CETP blockade may be relevant or not in promoting cholesterol disposal is still questioned. The possible need for a careful stratification of patients to treat with CETP inhibitors is outlined. Finally, manipulation of CETP activity should be considered with caution in the context of sepsis and infectious diseases.

Epistasis in the risk of human neuropsychiatric disease

Neuropsychiatric disease represents the ideal class of disease to assess the role of epistasis, as more genes are expressed in the brain than in any other tissue. In this chapter, two well-studied neuropsychiatric diseases are examined, Alzheimer's disease (AD) and schizophrenia, which have been shown to have multiple and, often, replicated interactions that associate with clinical endpoints or related phenotypes. In each case, a single gene is represented in a plurality of epistatic interactions, apolipoprotein E (APOE) for AD and catechol-O-methyltransferase for schizophrenia. Interestingly, of the two, only APOE has clear-cut and consistent evidence for a marginal association. Unraveling the underlying reasons is important in understanding both genetic etiology and architecture as well as how to use genetics to provide better personalized treatments.

Recombinant adenovirus-mediated overexpression of 3β-hydroxysteroid-Δ24 reductase

3β-Hydroxysteroid-Δ24 reductase (DHCR24) is a multifunctional enzyme that localizes to the endoplasmic reticulum and has neuroprotective and cholesterol-synthesizing activities. DHCR24 overexpression confers neuroprotection against apoptosis caused by amyloid β deposition. The present study aimed to construct two recombinant adenoviruses driving DHCR24 expression specifically in neurons. Two SYN1 promoter DNA fragments were obtained from human (h) and rat (r). Recombinant Ad-r(h)SYN1-DHCR24 was transfected into AD-293, N2A (mouse neuroblastoma), and MIN6 (mouse pancreatic carcinoma) cells. Western blot analysis showed DHCR24 was specially expressed in 293 and N2A cells, but no specific band was found in MIN6 cells. This demonstrates that the recombinant adenoviruses successfully express DHCR24, and no expression is observed in non-neuronal cells. TUNEL assay results showed apoptosis was inhibited in adenovirus-transfected neurons. Detecting reactive oxygen species by immunofluorescence, we found that adenovirus transfection inhibits apoptosis through scavenging excess reactive oxygen species. Our findings show that the recombinant DHCR24 adenoviruses induce neuron-specific DHCR24 expression, and thereby lay the foundation for further studies on DHCR24 gene therapy for Alzheimer's disease.

Population-based analysis of cholesteryl ester transfer protein identifies association between I405V and cognitive decline: the Cache County Study

Cholesterol has been implicated in the pathogenesis of late-onset Alzheimer's disease (LOAD) and the cholesteryl ester transfer protein (CETP) is critical to cholesterol regulation within the cell, making CETP an Alzheimer's disease candidate gene. Several studies have suggested that CETP I405V (rs5882) is associated with cognitive function and LOAD risk, but findings vary and most studies have been conducted using relatively small numbers of samples. To test whether this variant is involved in cognitive function and LOAD progression, we genotyped 4486 subjects with up to 12 years of longitudinal cognitive assessment. Analyses revealed an average 0.6-point decrease per year in the rate of cognitive decline for each additional valine (p < 0.011). We failed to detect the association between CETP I405V and LOAD status (p < 0.28). We conclude that CETP I405V is associated with preserved cognition over time but is not associated with LOAD status.

Retinoids as potential targets for Alzheimer's disease

Vitamin A and its derivatives, the retinoids, modulate several physiological and pathological processes through their interactions with nuclear retinoid receptor proteins termed as retinoic acid receptors (RARs) and retinoid X receptors (RXRs). An increasing body of evidence signifies the existence of retinoid signaling in diverse brain areas including cortex, amygdala, hypothalamus, hippocampus, and striatum suggesting its involvement in adult brain functions. Defective retinoid signaling has been evidenced in the pathology of Alzheimer's disease. Reports demonstrate that vitamin A deprived mice exhibit serious defects in spatial learning and memory signifying its importance in the maintenance of memory functions. Retinoid signaling impacts the development of AD pathology through multiple pathways. Ligand activation of RAR and RXR in APP/PS1 transgenic mice ameliorated the symptoms of AD and reduced amyloid accumulation and tau hyperphosphorylation. Retinoids also reduce the production of pro-inflammatory cytokines and chemokines by astrocytes and the microglia. Studies also suggest that neuronal cell lines treated with retinoid agonists exhibit an up-regulation in the expression and activity of choline acetyltransferase (ChAT). Reports depict that retinoic acid isomers enhance, the expression of genes linked with cholesterol efflux e.g. apoe, abca-1 and abcg-1 proteins in astrocytes. Furthermore numerous studies also indicate antioxidant potential of retinoids. Through this review we concisely summarize the biology of retinoids, emphasizing on their probable neuroprotective mechanisms that will help to elucidate the pivotal role of these receptors in AD pathology.

The PSEN1, p.E318G variant increases the risk of Alzheimer's disease in APOE-ε4 carriers

The primary constituents of plaques (Aβ42/Aβ40) and neurofibrillary tangles (tau and phosphorylated forms of tau [ptau]) are the current leading diagnostic and prognostic cerebrospinal fluid (CSF) biomarkers for AD. In this study, we performed deep sequencing of APP, PSEN1, PSEN2, GRN, APOE and MAPT genes in individuals with extreme CSF Aβ42, tau, or ptau levels. One known pathogenic mutation (PSEN1 p.A426P), four high-risk variants for AD (APOE p.L46P, MAPT p.A152T, PSEN2 p.R62H and p.R71W) and nine novel variants were identified. Surprisingly, a coding variant in PSEN1, p.E318G (rs17125721-G) exhibited a significant association with high CSF tau (p = 9.2 × 10(-4)) and ptau (p = 1.8 × 10(-3)) levels. The association of the p.E318G variant with Aβ deposition was observed in APOE-ε4 allele carriers. Furthermore, we found that in a large case-control series (n = 5,161) individuals who are APOE-ε4 carriers and carry the p.E318G variant are at a risk of developing AD (OR = 10.7, 95% CI = 4.7-24.6) that is similar to APOE-ε4 homozygous (OR = 9.9, 95% CI = 7.2.9-13.6), and double the risk for APOE-ε4 carriers that do not carry p.E318G (OR = 3.9, 95% CI = 3.4-4.4). The p.E318G variant is present in 5.3% (n = 30) of the families from a large clinical series of LOAD families (n = 565) and exhibited a higher frequency in familial LOAD (MAF = 2.5%) than in sporadic LOAD (MAF = 1.6%) (p = 0.02). Additionally, we found that in the presence of at least one APOE-ε4 allele, p.E318G is associated with more Aβ plaques and faster cognitive decline. We demonstrate that the effect of PSEN1, p.E318G on AD susceptibility is largely dependent on an interaction with APOE-ε4 and mediated by an increased burden of Aβ deposition.

Liver X receptors: emerging therapeutic targets for Alzheimer's disease

Alzheimer's disease (AD) is a complex neurodegenerative disorder, typified by the pathological accumulation of ß-amyloid peptides (Aß) and neurofibrillary tangles within the brain, culminating to cognitive impairment. Epidemiological and biochemical data have suggested a link between cholesterol content, APP (amyloid precursor protein) processing, Aß, inflammation and AD. The intricacy of the disease presents considerable challenges for the development of newer therapeutic agents. Liver X receptors (LXRa and LXRß) are oxysterol activated nuclear receptors that play essential role in lipid and glucose homeostasis, steroidogenesis and inflammatory responses. LXR signalling impacts the development of AD pathology through multiple pathways. Reports indicate that genetic loss of either lxra or lxrß in APP/PS1 transgenic mice results in increased amyloid plaque load. Studies also suggest that ligand activation of LXRs in Tg2576 mice enhanced, the expression of genes linked with cholesterol efflux e.g. apoe, abca-1, down regulated APP processing and Aß production with significant improvement in memory functions. LXR agonists have also depicted to inhibit neuroinflammation through modulation of microglial phagocytosis and by repressing the expression of cox2, mcp1 and iNos in glial cells. This review summarizes in brief the biology of LXRs, with an emphasis on their probable pathophysiological mechanisms that may elicit the defending role of these receptors in brains of AD patients.

Dyslipidemia and dementia: current epidemiology, genetic evidence, and mechanisms behind the associations

The role of cholesterol in the etiology of Alzheimer's disease (AD) is still controversial. Some studies exploring the association between lipids and/or lipid lowering treatment and AD indicate a harmful effect of dyslipidemia and a beneficial effect of statin therapy on AD risk. The findings are supported by genetic linkage and association studies that have clearly identified several genes involved in cholesterol metabolism or transport as AD susceptibility genes, including apolipoprotein E, apolipoprotein J, and the sortilin-related receptor. Functional cell biology studies support a critical involvement of lipid raft cholesterol in the modulation of amyloid-β protein precursor (AβPP) processing by β- and γ-secretase resulting in altered amyloid-β production. Contradictory evidence comes from epidemiological studies showing no or controversial association between dyslipidemia and AD risk. Additionally, cell biology studies suggest that there is little exchange between circulating and brain cholesterol, that increased membrane cholesterol is protective by inhibiting loss of membrane integrity through amyloid cytotoxicity, and that cellular cholesterol inhibits co-localization of BACE1 and AβPP in non-raft membrane domains, thereby increasing generation of plasmin, an amyloid-β-degrading enzyme. The aim of this review is to summarize the findings of epidemiological and cell biological studies to elucidate the role of cholesterol in AD etiology.

The CETP I405V polymorphism is associated with an increased risk of Alzheimer's disease

The cholesteryl ester transfer protein (CETP) gene plays an essential role in regulating cholesterol homeostasis and is a candidate susceptibility gene for late-onset Alzheimer's disease (AD). Recent finding suggests that the CETP I405V polymorphism (rs5882) is associated with a slower rate of memory decline and a lower risk of incident dementia. Using data from two ongoing epidemiologic clinical-pathologic cohort studies of aging and dementia in the United States, the Religious Order Study and the Memory and Aging Project, we evaluated the association of the CETP I405V polymorphism (rs5882) with cognitive decline and risk of incident AD in more than 1300 participants of European ancestry. Our results suggest that the CETP I405V polymorphism was associated with a faster rather than a slower rate of decline in cognition over time, and an increased risk of incident AD. This finding is consistent with data showing that the CETP I405V is associated with increased neuritic plaque density at autopsy.

Cholesteryl Ester Transfer Protein (CETP) genotype and cognitive function in persons aged 35 years or older

Common polymorphisms of the Cholestryl Ester Transfer Protein (CETP) gene may predict lower risk of cognitive decline. We investigated the association of cognitive function with CETP genotype in a population-based cohort of 4135 persons aged 35-82 years. Cognitive function was measured with the Ruff Figural Fluency Test (RFFT; worst score, 0 points; best score, 175 points) and CETP I405V and Taq1B genotypes were determined by polymerase chain reaction. RFFT score was not associated with I405V genotype in persons aged 35-64 years. Remarkably, beyond age 65, homozygous valine carriers had higher RFFT scores than heterozygous carriers and noncarriers: RFFT (SD), 52 (21), 49 (18), and 47 (17) points, respectively (p = 0.005). There also was a statistically significant interaction between I405V genotype and age. Beyond age 65, the difference between homozygous valine carriers and noncarriers increased by 0.11 point per year (p = 0.005). RFFT score was not associated with Taq1B genotype. In conclusion, CETP I405V valine homozygosity was associated with better cognitive function in persons aged 65 years or older.

CETP polymorphisms associate with brain structure, atrophy rate, and Alzheimer's disease risk in an APOE-dependent manner

Two alleles in cholesteryl ester transfer protein (CETP) gene polymorphisms have been disputably linked to enhanced cognition and decreased risk of Alzheimer's disease (AD): the V and A alleles of I405V and C-629A. This study investigates whether these polymorphisms affect brain structure in 188 elderly controls and 318 AD or mild cognitive impairment (MCI) subjects from the Alzheimer's Disease Neuroimaging Initiative cohort. Nominally signficant associations were dependent on APOE ε4 carrier status. In APOE ε4 carriers, the V and A alleles, both of which decrease CETP and increase HDL, associated with greater baseline cortical thickness and less 12-month atrophy in the medial temporal lobe. Conversely, in APOE ε4 non-carriers, the I allele, which increases CETP and decreases HDL, associated with greater baseline thickness, less atrophy and lower risk of dementia. These results suggest CETP may contribute to the genetic variability of brain structure and dementia susceptibility in an APOE-dependent manner.

Association of a functional polymorphism in the cholesteryl ester transfer protein (CETP) gene with memory decline and incidence of dementia

CONTEXT

Polymorphisms in the cholesteryl ester transfer protein (CETP) gene have been associated with exceptional longevity and lower cardiovascular risk, but associations with memory decline and dementia risk are unclear.

OBJECTIVE

To test the hypothesis that a single-nucleotide polymorphism (SNP) at CETP codon 405 (isoleucine to valine V405; SNP rs5882) is associated with a lower rate of memory decline and lower risk of incident dementia, including Alzheimer disease (AD).

DESIGN, SETTING, AND PARTICIPANTS

Prospective cohort study comprising 608 community-dwelling adults without dementia aged 70 years or older from the Einstein Aging Study with CETP genotype available. Fifteen participants with prevalent dementia were excluded, and 70 without follow-up--63 lost to follow-up and 7 new to the study--were excluded from the Cox proportional hazards model, which included 523 participants in the analysis. Standardized neuropsychological and neurological measures were administered annually from 1994-2009. Linear mixed-effects models adjusted for sex, education, race, medical comorbidities, and apolipoprotein (APOE) epsilon4 examined associations of V405 genotype with longitudinal performance on cognitive tests of episodic memory (Free and Cued Selective Reminding Test [FCSRT], possible scores of 0-48), attention (Digit Span), and psychomotor speed (Digit Symbol Substitution). The V405 genotype was the main predictor of incident dementia or AD in similarly adjusted Cox proportional hazards models with age as the time scale.

MAIN OUTCOME MEASURES

Memory decline and incident dementia.

RESULTS

Valine allele frequency was 43.5%. A total of 40 cases of incident dementia occurred during follow-up (mean [(SD], 4.3 [3.1] years). Compared with isoleucine homozygotes, valine homozygotes had significantly slower memory decline on the FCSRT (0.43 points per year of age for isoleucine; 95% confidence interval [CI], -0.58 to -0.29 vs 0.21 points per year of age for valine; 95% CI, -0.39 to -0.04; difference in linear age slope, 0.22; 95% CI, 0.02 to 0.41; P = .03) and no significant differences on the Digit Span or Digit Symbol Substitution tests. Valine homozygotes also had lower risk of dementia (hazard ratio, 0.28; 95% CI, 0.10-0.85; P = .02) and AD (hazard ratio, 0.31; 95% CI, 0.10-0.95; P = .04).

CONCLUSION

This preliminary report suggests that CETP V405 valine homozygosity is associated with slower memory decline and lower incident dementia and AD risk.

Cholesterol metabolism and transport in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder, affecting millions of people worldwide. Apart from age, the major risk factor identified so far for the sporadic form of AD is possession of the epsilon4 allele of apolipoprotein E (APOE), which is also a risk factor for coronary artery disease (CAD). Other apolipoproteins known to play an important role in CAD such as apolipoprotein B are now gaining attention for their role in AD as well. AD and CAD share other risk factors, such as altered cholesterol levels, particularly high levels of low density lipoproteins together with low levels of high density lipoproteins. Statins--drugs that have been used to lower cholesterol levels in CAD, have been shown to protect against AD, although the protective mechanism(s) involved are still under debate. Enzymatic production of the beta amyloid peptide, the peptide thought to play a major role in AD pathogenesis, is affected by membrane cholesterol levels. In addition, polymorphisms in several proteins and enzymes involved in cholesterol and lipoprotein transport and metabolism have been linked to risk of AD. Taken together, these findings provide strong evidence that changes in cholesterol metabolism are intimately involved in AD pathogenic processes. This paper reviews cholesterol metabolism and transport, as well as those aspects of cholesterol metabolism that have been linked with AD.

Association of CETP polymorphisms with the risk of vascular dementia and white matter lesions

Cholesteryl ester transfer protein (CETP), a component of the high density lipoprotein (HDL), plays a central role in reverse cholesterol transport. We investigated the association of two putative functional CETP polymorphisms (C-629A and I405V) with the risk of vascular dementia (VD) and tested if this association is influenced by the presence of APOE4 allele. Our study included 163 VD patients (mean age: 74.25 +/- 7.9 years) and 452 cognitively healthy probands (mean age: 70.81 +/- 7.9 years). As a biological correlate, the association of CETP gene variants with white matter lesion (WML) load was investigated. Neither the C-629A (P = 0.169) nor the I405V (P = 0.840) polymorphism was associated with VD risk in the whole sample. However, in non-carriers of the APOE4 allele, homozygote carriers of the CETP C-629A A allele presented with an increased risk of VD (P = 0.01). Whereas in APOE4 carriers, no association of CETP polymorphisms with VD risk was detected. In addition, carriers of the CETP C-629A AA genotype presented with decreased WML load in the frontal brain (P = 0.009). Our results suggest that CETP gene polymorphisms might influence WML load and the risk of VD, the latter in non-carriers of the APOE4 allele.

Genetic epidemiology in aging research

Over the last two decades, aging research has expanded to include not only age-related disease models, and conversely, longevity and disease-free models, but also focuses on biological mechanisms related to the aging process. By viewing aging on multiple research frontiers, we are rapidly expanding knowledge as a whole and mapping connections between biological processes and particular age-related diseases that emerge. This is perhaps most true in the field of genetics, where variation across individuals has improved our understanding of aging mechanisms, etiology of age-related disease, and prediction of therapeutic responses. A close partnership between gerontologists, epidemiologists, and geneticists is needed to take full advantage of emerging genome information and technology and bring about a new age for biological aging research. Here we review current genetic findings for aging across both disease-specific and aging process domains. We then highlight the limitations of most work to date in terms of study design, genomic information, and trait modeling and focus on emerging technology and future directions that can partner genetic epidemiology and aging research fields to best take advantage of the rapid discoveries in each.

Genetic determinants of human health span and life span: progress and new opportunities

We review three approaches to the genetic analysis of the biology and pathobiology of human aging. The first and so far the best-developed is the search for the biochemical genetic basis of varying susceptibilities to major geriatric disorders. These include a range of progeroid syndromes. Collectively, they tell us much about the genetics of health span. Given that the major risk factor for virtually all geriatric disorders is biological aging, they may also serve as markers for the study of intrinsic biological aging. The second approach seeks to identify allelic contributions to exceptionally long life spans. While linkage to a locus on Chromosome 4 has not been confirmed, association studies have revealed a number of significant polymorphisms that impact upon late-life diseases and life span. The third approach remains theoretical. It would require longitudinal studies of large numbers of middle-aged sib-pairs who are extremely discordant or concordant for their rates of decline in various physiological functions. We can conclude that there are great opportunities for research on the genetics of human aging, particularly given the huge fund of information on human biology and pathobiology, and the rapidly developing knowledge of the human genome.

The cholesteryl ester transfer protein (CETP) gene and the risk of Alzheimer's disease

Like the apolipoprotein E (APOE) gene, the most common genetic determinant for Alzheimer's disease (AD), the cholesteryl ester transfer protein (CETP) is involved in lipid metabolism. We studied the I405V polymorphism of the CETP gene in relation to AD. We genotyped 544 AD cases and 5,404 controls from the Rotterdam study, using a TaqMan allelic discrimination assay. Odds ratios (ORs) for AD were estimated using logistic regression analysis. CETP VV carriers showed significantly increased high-density lipoprotein levels compared to the IV and II carriers. In the overall analysis of AD, the risk of disease for the VV carriers of the CETP polymorphism was non-significantly increased compared to II carriers OR(VV) = 1.33, 95% confidence interval (CI) 0.96-1.90 p = 0.08). In those without the APOE*4 allele, the risk of AD for VV carriers was increased 1.67-fold (95% CI 1.11-2.52, p = 0.01). The difference in the relationship between CETP and AD between APOE*4 carriers and APOE*4 non-carriers was statistically significant (p for interaction = 0.04). Our results suggest that the VV genotype of the I405V polymorphism of the CETP gene increases the risk of AD in the absence of the APOE*4 allele, probably through a cholesterol metabolism pathway in the brain.

Genetic factors affecting HDL levels, structure, metabolism and function

PURPOSE OF REVIEW

HDL is a recognized negative risk factor for the cardiovascular diseases. Establishing the genetic determinants of HDL concentration and functions would add to the prediction of cardiovascular risk and point to the biochemical mechanisms underlying this risk. The present review focuses on various approaches to establish genetic determinants of the HDL concentration, structure and function.

RECENT FINDINGS

While many genes contribute to the HDL concentration and collectively account for half of the variability, polymorphism of individual candidate genes contributes little. There are strong interactions between environmental and genetic influences. Recent findings have confirmed that APOA1 and ABCA1 exert the strongest influence on HDL concentrations and risk of atherosclerosis. CETP and lipases also affect the HDL concentration and functionality, but their connection to the atherosclerosis risk is conditional on the interaction between environmental and genetic factors.

SUMMARY

Analysis of genetic determinants of HDL-cholesterol in patients with specific disease states or in response to the environmental condition may be a more accurate way to assess variations in HDL concentration. This may result in defining the rules of interaction between genetic and environmental factors and lead to understanding the mechanisms responsible for the variations in HDL concentration and functionality.