Meta-analysis on association between the ATP-binding cassette transporter A1 gene (ABCA1) and Alzheimer's disease

Association Between ABCA1 R219K Variant and Alzheimer's Disease: An Updated Meta-Analysis and Systematic Review

BACKGROUND

Over a dozen studies have investigated the effect of the R219K variant in the ATP-binding cassette transporter A1 (ABCA1) gene on the risk of Alzheimer's disease (AD), but the results are conflicting.

OBJECTIVE

We performed a systematic review and meta-analysis to comprehensively assess the association between the ABCA1 R219K variant and the risk of AD.

METHODS

Studies included in the meta-analysis were obtained by searching PubMed, Web of Science and AlzGene. Review Manager 5.4 was used for meta-analysis. Both the odds ratio (OR) and its 95% confidence interval (CI) were used to evaluate the effect of ABCA1 R219K polymorphism on AD susceptibility. Heterogeneity between the included studies was assessed using I2 statistics and Cochran Qtest. Funnel plots were used to assess publication bias.

RESULTS

A total of 14 eligible studies involving 10084 subjects were retrieved from PubMed, Web of Science and AlzGene. Meta-analysis results showed that R219K polymorphism was significantly associated with a decreased risk of AD in Chinese under a recessive model (OR = 0.67; 95% CI = 0.51- 0.88; P = 0.004).

CONCLUSION

The present meta-analysis indicated that the KK genotype of R219K polymorphism may act as a protective factor for AD in the Chinese population. Additional studies with larger sample sizes are needed to further confirm this association.

Association between the ABCA1 (R219K) polymorphism and lipid profiles: a meta-analysis

Conflicting evidence was found about the relationship between lipid profiles and R219K polymorphism in adenosine triphosphate-binding cassette exporter A1 (ABCA1) gene. In this study, four meta-analyses were conducted to assess the effect of R219K on lipid levels, including high-density lipoprotein cholesterol (HDLC), low-density lipoprotein cholesterol, total cholesterol, and triglycerides (TG). A total of 125 samples of 87 studies (about 60,262 subjects) were included. The effect of each study was expressed using the standard mean difference (SMD) and 95% confidence interval (95% CI) and pooled by meta-analysis in the random-effects model. Subgroup and meta-regression analyses were conducted to explore potential heterogeneity sources. The overall pooled effect showed the following results. (1) The R219K was significantly associated with HDLC level (SMD = - 0.25 mmol/L, 95%CI - 0.32 to - 0.18, z = - 6.96, P < 0.01, recessive genetic model). People with different genotypes had significantly different HDLC levels under the recessive, codominant and dominant genetic models (all Ps < 0.01). (2) A weak and indeterminate relationship between R219K and TG level was observed (SMD = 0.18 mmol/L, 95%CI 0.06-0.30, z = 3.01, P < 0.01, recessive genetic model). These findings suggested that R219K was associated with HDLC and TG levels, which might implicate a promising clinical application for lipid-related disorders, though the influences of race, health status, BMI, and other heterogeneity sources should be considered when interpreting current findings. The protocol was registered at PROSPERO (registration number: CRD42021231178).

The Role of the ATP-Binding Cassette A1 (ABCA1) in Human Disease

Cholesterol homeostasis is essential in normal physiology of all cells. One of several proteins involved in cholesterol homeostasis is the ATP-binding cassette transporter A1 (ABCA1), a transmembrane protein widely expressed in many tissues. One of its main functions is the efflux of intracellular free cholesterol and phospholipids across the plasma membrane to combine with apolipoproteins, mainly apolipoprotein A-I (Apo A-I), forming nascent high-density lipoprotein-cholesterol (HDL-C) particles, the first step of reverse cholesterol transport (RCT). In addition, ABCA1 regulates cholesterol and phospholipid content in the plasma membrane affecting lipid rafts, microparticle (MP) formation and cell signaling. Thus, it is not surprising that impaired ABCA1 function and altered cholesterol homeostasis may affect many different organs and is involved in the pathophysiology of a broad array of diseases. This review describes evidence obtained from animal models, human studies and genetic variation explaining how ABCA1 is involved in dyslipidemia, coronary heart disease (CHD), type 2 diabetes (T2D), thrombosis, neurological disorders, age-related macular degeneration (AMD), glaucoma, viral infections and in cancer progression.

Proprotein Convertase Subtilisin/Kexin Type 9, Brain Cholesterol Homeostasis and Potential Implication for Alzheimer's Disease

Alzheimer’s disease (AD) has been associated with dysregulation of brain cholesterol homeostasis. Proprotein convertase subtilisin/kexin type 9 (PCSK9), beyond the known role in the regulation of plasma low-density lipoprotein cholesterol, was first identified in the brain with a potential involvement in brain development and apoptosis. However, its role in the central nervous system (CNS) and in AD pathogenesis is still far from being understood. While in vitro and in vivo evidence led to controversial results, genetic studies apparently did not find an association between PCSK9 loss of function mutations and AD risk or prevalence. In addition, a potential impairment of cognitive performances by the treatment with the PCSK9 inhibitors, alirocumab and evolocumab, have been excluded, although ongoing studies with longer follow-up will provide further insights. PCSK9 is able to affect the expression of neuronal receptors involved in cholesterol homeostasis and neuroinflammation, and higher PCSK9 concentrations have been found in the cerebrospinal fluid (CSF) of AD patients. In this review article, we critically examined the science of PCSK9 with respect to its modulatory role of the mechanisms underlying the pathogenesis of AD. In addition, based on literature data, we made the hypothesis to consider brain PCSK9 as a negative modulator of brain cholesterol homeostasis and neuroinflammation and a potential pharmacological target for treatment.

Differences in ABCA1 R219K Polymorphisms and Serum Indexes in Alzheimer and Parkinson Diseases in Northern China

BACKGROUND ABCA1 R219K single-nucleotide polymorphisms (SNPs) was related to Alzheimer disease (AD) but not Parkinson disease (PD). Here, we analyzed the associations among ABCA1 R219K distribution, serum biomarkers, AD, and PD in a population in northern China. MATERIAL AND METHODS We used the Mini-Mental State Examination (MMSE) and the Hoehn and Yahr scale (H-Y) to evaluate AD and PD progression, separately. ABCA1 R219K was analyzed by matrix-assisted laser desorption ionization time of flight time mass spectrometry (MALDI-TOF-MS). Serum indexes were determined by enzyme-linked immunosorbent assay (ELISA). RESULTS ABCA1 R219K RR+RK genotype frequency in AD and PD patients was lower than that in normal controls (NC), while ABCA1 R219K KK genotype frequency was significantly higher. ABCA1 R219K RR genotype frequency in AD patients and NC was lower than that in PD patients, while ABCA1 R219K RK+KK genotype frequency was significantly higher. ABCA1 R219K RR genotype was positively correlated to MMSE value in AD patients, while ABCA1 R219K KK genotype was negatively correlated to H-Y value in PD patients. Serum factors were significantly different among AD and PD patients and NC. Serum ABCA1, ApoA1, ApoA2, ApoB, HDL, TC, IL-1β, IL-6, and TNF-α were significantly different between AD and PD patients. CONCLUSIONS ABCA1 R219K R allele was the risk factor inducing abnormal serum levels of ApoA2, LDL, and TG in AD patients, and abnormal levels of serum ABCA1, HDL, IL-1b, IL-6, and TNF-α in PD patients, while ABCA1 R219K K allele was the risk factor inducing lower ABCA1 in AD patients. IL-1β, IL-6, and TNF-α were negatively correlated to MMSE in AD patients but positively correlated to H-Y in PD patients, while HDL was positively related to H-Y in PD patients.

Influence of four polymorphisms in ABCA1 and PTGS2 genes on risk of Alzheimer's disease: a meta-analysis

We preformed this meta-analysis to investigate the influence of ABCA1 (ATP-binding cassette sub-family A member 1) rs2422493 (C-477T), rs1800977 (C-14T), rs2066718 (V771M), and PTGS2 (Prostaglandin-endoperoxide synthase 2) rs20417 (G-765C) polymorphisms on the risk of Alzheimer's disease (AD). Seventeen eligible case-control studies were acquired from PubMed, Embase, Alzgene, Chinese National Knowledge Infrastructure and Wanfang databases. The pooled odds ratios (ORs) with 95 % confidence intervals (95 % CI) were calculated to evaluate the association under five genetic models. Combined data indicated that ABCA1 rs2422493 polymorphism was statistically significant associated with increasing AD risk in three genetic models (allelic T vs C: OR = 1.12, 95 % CI: 1.01-1.24; homozygous TT vs CC: OR = 1.26, 95 % CI: 1.03-1.55; and recessive TT vs TC + CC: OR = 1.33, 95 % CI: 1.12-1.58) while no association was found between two other ABCA1 polymorphisms and AD susceptibility. Nevertheless, a further risk-stratification analysis showed that ApoE-ε4 carriers with any ABCA1 polymorphism suffered a much higher probability to be AD patients. Meanwhile, PTGS2 rs20417 polymorphism was linked to decreasing AD risk with a P < 0.0001 in five genetic models (e.g., allelic C vs G: OR = 0.59, 95 % CI: 0.50-0.70; homozygous CC vs GG: OR = 0.31, 95 % CI: 0.18-0.52; and heterozygous CG vs GG: OR = 0.64, 95 % CI: 0.52-0.78). In summary, our meta-analysis results showed that ABCA1 rs2422493 polymorphism was a risk factor for AD while PTGS2 rs20417 variant showed a protective effect on AD risk. In addition, ABCA1 rs2066718 and rs1800977 polymorphisms might not contribute to AD susceptibility in general population, but they should play a role on AD development when interacted with ApoE-ε4.

Loss-of-function mutation in ABCA1 and risk of Alzheimer's disease and cerebrovascular disease

INTRODUCTION

The adenosine triphosphate-binding cassette transporter A1 (ABCA1) is a major cholesterol transporter highly expressed in the liver and brain. In the brain, ABCA1 lipidates apolipoprotein E (apoE), facilitates clearance of amyloid-β, and may be involved in maintenance of the blood-brain barrier via apoE-mediated pathways.

METHODS

We tested whether a loss-of-function mutation in ABCA1, N1800H, is associated with plasma levels of apoE and with risk of Alzheimer's disease (AD) in 92,726 individuals and with risk of cerebrovascular disease in 64,181 individuals.

RESULTS

N1800H AC (0.2%) versus AA (99.8%) was associated with a 13% lower plasma level of apoE (P = 1 × 10(-11)). Multifactorially adjusted hazard ratios for N1800H AC versus AA were 4.13 (95% confidence interval, 1.32-12.9) for AD, 2.46 (1.10-5.50) for cerebrovascular disease, and 8.28 (2.03-33.7) for the hemorrhagic stroke subtype.

DISCUSSION

A loss-of-function mutation in ABCA1, present in 1:500 individuals, was associated with low plasma levels of apoE and with high risk of AD and cerebrovascular disease in the general population.

ATP-binding cassette transporter A1: from metabolism to neurodegeneration

ATP-binding cassette transporter A1 (ABCA1) mediates cholesterol efflux to lipid-free apolipoprotein A-I (apoA-I) and apolipoprotein E (apoE). ABCA1 is an essential regulator of high density lipoproteins (HDL) and reverse cholesterol transport - a role that determines its importance for atherosclerosis. Over the last 10 years studies have provided convincing evidence that ABCA1, via its control of apoE lipidation, also has a role in Alzheimer's disease (AD). A series of reports have revealed a significant impact of ABCA1 on Aβ deposition and clearance in AD model mice, as well as an association of common and rare ABCA1 gene variants with the risk for AD. Since APOE is the major genetic risk factor for late onset AD, the regulation of apoE level or its functionality by ABCA1 may prove significant for AD pathogenesis. ABCA1 is transcriptionally regulated by Liver X Receptors (LXR) and Retinoic X Receptors (RXR) which provides a starting point for drug discovery and development of synthetic LXR and RXR agonists for treatment of metabolic and neurodegenerative disorders. This review summarizes the recent results of research on ABCA1, particularly relevant to atherosclerosis and AD.