ABCA1 and ABCG1 or ABCG4 act sequentially to remove cellular cholesterol and generate cholesterol-rich HDL

Enhancing of cerebral Abeta clearance by modulation of ABC transporter expression: a review of experimental approaches

Clearance of amyloid-beta (Aβ) from the brain is impaired in both early-onset and late-onset Alzheimer's disease (AD). Mechanisms for clearing cerebral Aβ include proteolytic degradation, antibody-mediated clearance, blood brain barrier and blood cerebrospinal fluid barrier efflux, glymphatic drainage, and perivascular drainage. ATP-binding cassette (ABC) transporters are membrane efflux pumps driven by ATP hydrolysis. Their functions include maintenance of brain homeostasis by removing toxic peptides and compounds, and transport of bioactive molecules including cholesterol. Some ABC transporters contribute to lowering of cerebral Aβ. Mechanisms suggested for ABC transporter-mediated lowering of brain Aβ, in addition to exporting of Aβ across the blood brain and blood cerebrospinal fluid barriers, include apolipoprotein E lipidation, microglial activation, decreased amyloidogenic processing of amyloid precursor protein, and restricting the entrance of Aβ into the brain. The ABC transporter superfamily in humans includes 49 proteins, eight of which have been suggested to reduce cerebral Aβ levels. This review discusses experimental approaches for increasing the expression of these ABC transporters, clinical applications of these approaches, changes in the expression and/or activity of these transporters in AD and transgenic mouse models of AD, and findings in the few clinical trials which have examined the effects of these approaches in patients with AD or mild cognitive impairment. The possibility that therapeutic upregulation of ABC transporters which promote clearance of cerebral Aβ may slow the clinical progression of AD merits further consideration.

Effect of Naoxintong Capsule on Microglia and Proteomics of Cortex After Myocardial Infarction in Rats

Neuroinflammation caused by microglia in the central nervous system (CNS) is observed after myocardial infarction (MI). However, the inflammatory response mechanism remains unclear. BuChang Naoxintong capsule (NXT) is a Chinese medicine for treating ischemic cardio-cerebrovascular diseases, requiring more studies to understand the pharmacodynamic mechanism. Permanent ligation of the left anterior descending coronary artery (LAD) was performed in rats. Additionally, histopathological staining in the left ventricular (LV) and immunofluorescence within the brain cortex after 1 d and 7 d of MI were performed to determine the NXT pharmacodynamic action and best administration dosage. Proteomics helped obtain the essential proteins related to neuroinflammation and MI in the heart and brain tissue after 7 d of MI. Based on TTC, HE, Masson, and immunofluorescence staining results of CD206 and IBA-1, NXT demonstrated a better pharmacodynamic action towards myocardial injury and neuroinflammation after 7 d of MI. Moreover, the human equivalent dosage of NXT (220 mg/kg) became the best administration dose. The proteome bioinformatics analysis in the LV and brain cortex was performed. Thus, the elongation of very long-chain fatty acids protein 5 (ELOVL5) and ATP-binding cassette subfamily G member 4 (ABCG4) became critical proteins related to MI and neuroinflammation. The western blotting results indicated that ABCG4 expression possessed the same trend as the proteomics results. The auto-dock results revealed that ABCG4 had a good binding ability with Ferulic acid, Paeoniflorin, and Tanshinone II A, the key ingredients of NXT. The cellular thermal shift assay results demonstrated that ABCG4 showed better thermal stability post-NXT treatment. NXT can improve myocardial injury, such as heart infarct size, pathological injury, myocardial fibrosis, and inflammatory cell infiltration. Additionally, brain neuroinflammation induced by microglia after MI affects the expression and structure of ABCG4. Thus, ABCG4 could be the key protein associated with MI and neuroinflammation.

Behavioral and Metabolic Effects of ABCG4 KO in the APPswe,Ind (J9) Mouse Model of Alzheimer's Disease

The pathogenesis of Alzheimer's disease (AD) is complex and involves an imbalance between production and clearance of amyloid-ß peptides (Aß), resulting in accumulation of Aß in senile plaques. Hypercholesterolemia is a major risk factor for developing AD, with cholesterol shown to accumulate in senile plaques and increase production of Aß. ABCG4 is a member of the ATP-binding cassette transporters predominantly expressed in the CNS and has been suggested to play a role in cholesterol and Aß efflux from the brain. In this study, we bred Abcg4 knockout (KO) with the APPSwe,Ind (J9) mouse model of AD to test the hypothesis that loss of Abcg4 would exacerbate the AD phenotype. Unexpectedly, no differences were observed in novel object recognition (NOR) and novel object placement (NOP) behavioral tests, or on histologic examinations of brain tissues for senile plaque numbers. Furthermore, clearance of radiolabeled Aß from the brains did not differ between Abcg4 KO and control mice. Metabolic testing by indirect calorimetry, glucose tolerance test (GTT), and insulin tolerance test (ITT) were also mostly similar between groups with only a few mild metabolic differences noted. Overall, these data suggest that the loss of ABCG4 did not exacerbate the AD phenotype.

Upstream lipid and metabolic systems are potential causes of Alzheimer's disease, Parkinson's disease and dementias

Brain health requires circuits, cells and molecular pathways to adapt when challenged and to promptly reset once the challenge has resolved. Neurodegeneration occurs when adaptability becomes confined, causing challenges to overwhelm neural circuitry. Studies of rare and common neurodegenerative diseases suggest that the accumulation of lipids can compromise circuit adaptability. Using microglia as an example, we review data that suggest increased lipid concentrations cause dysfunctional inflammatory responses to immune challenges, leading to Alzheimer's disease, Parkinson's disease and dementia. We highlight current approaches to treat lipid metabolic and clearance pathways and identify knowledge gaps towards restoring adaptive homeostasis in individuals who are at-risk of losing cognition.

Hypomethylation of ABCG1 in peripheral blood as a potential marker for the detection of coronary heart disease

BACKGROUND

Novel molecular biomarkers for the risk assessment and early detection of coronary heart disease (CHD) are urgently needed for disease prevention. Altered methylation of ATP-binding cassette subfamily G member 1 (ABCG1) has been implicated in CHD but was mostly studied in Caucasians. Exploring the potential relationship between ABCG1 methylation in blood and CHD among the Chinese population would yield valuable insights.

METHODS

Peripheral blood samples were obtained from a case-control study (287 CHD patients vs. 277 controls) and a prospective nested case-control study (171 CHD patients and 197 matched controls). DNA extraction and bisulfite-specific PCR amplification techniques were employed for sample processing. Quantitative assessment of methylation levels was conducted using mass spectrometry. Statistical analyses involved the utilization of logistic regression and nonparametric tests.

RESULTS

We found hypomethylation of ABCG1 in whole blood was associated with the risk of CHD in both studies, which was enhanced in heart failure (HF) patients, female and younger subjects. When combined with baseline characteristics, altered ABCG1 methylation showed improved predictive effect for differentiating CHD cases, ischemic cardiomyopathy (ICM) cases, younger than 60 years CHD cases, and female CHD cases from healthy controls (area under the curve (AUC) = 0.68, 0.71, 0.74, and 0.73, respectively).

CONCLUSIONS

We demonstrated a robust link between ABCG1 hypomethylation in whole blood and CHD risk in the Chinese population and provided novel evidence indicating that aberrant ABCG1 methylation in peripheral blood can serve as an early detection biomarker for CHD patients.

The interplay between microbial metabolites and macrophages in cardiovascular diseases: A comprehensive review

The gut microbiome has emerged as a crucial player in developing and progressing cardiovascular diseases (CVDs). Recent studies have highlighted the role of microbial metabolites in modulating immune cell function and their impact on CVD. Macrophages, which have a significant function in the pathogenesis of CVD, are very vulnerable to the effects of microbial metabolites. Microbial metabolites, such as short-chain fatty acids (SCFAs) and trimethylamine-N-oxide (TMAO), have been linked to atherosclerosis and the regulation of immune functions. Butyrate has been demonstrated to reduce monocyte migration and inhibit monocyte attachment to injured endothelial cells, potentially contributing to the attenuation of the inflammatory response and the progression of atherosclerosis. On the other hand, TMAO, another compound generated by gut bacteria, has been linked to atherosclerosis due to its impact on lipid metabolism and the accumulation of cholesterol in macrophages. Indole-3-propionic acid, a tryptophan metabolite produced solely by microbes, has been found to promote the development of atherosclerosis by stimulating macrophage reverse cholesterol transport (RCT) and raising the expression of ABCA1. This review comprehensively discusses how various microbiota-produced metabolites affect macrophage polarization, inflammation, and foam cell formation in CVD. We also highlight the mechanisms underlying these effects and the potential therapeutic applications of targeting microbial metabolites in treating CVD.

Behavioral and metabolic and effects of ABCG4 KO in the APPswe,Ind (J9) mouse model of Alzheimer's disease

The pathogenesis of Alzheimer's disease (AD) is complex and involves an imbalance between production and clearance of amyloid-ß peptides (Aß), resulting in accumulation of Aß in senile plaques. Hypercholesterolemia is a major risk factor for developing AD, with cholesterol shown to accumulate in senile plaques and increase production of Aß. ABCG4 is a member of the ATP-binding cassette transporters predominantly expressed in the CNS, and has been suggested to play a role in cholesterol and Aß efflux from the brain. In this study, we bred Abcg4 knockout (KO) with the APPSwe,Ind (J9) mouse model of AD to test the hypothesis that loss of Abcg4 would exacerbate the AD phenotype. Unexpectedly, no differences were observed in Novel object recognition (NOR) and Novel object placement (NOP) behavioral tests, or on histologic examinations of brain tissues for senile plaque numbers. Furthermore, clearance of radiolabeled Aß from the brains did not differ between Abcg4 KO and control mice. Metabolic testing by indirect calorimetry, glucose tolerance test (GTT) and insulin tolerance test (ITT), were also mostly similar between groups with only a few mild metabolic differences noted. Overall these data suggest that the loss of ABCG4 did not exacerbate the AD phenotype.

Is reverse cholesterol transport regulated by active cholesterol?

This review considers the hypothesis that a small portion of plasma membrane cholesterol regulates reverse cholesterol transport in coordination with overall cellular homeostasis. It appears that almost all of the plasma membrane cholesterol is held in stoichiometric complexes with bilayer phospholipids. The minor fraction of cholesterol that exceeds the complexation capacity of the phospholipids is called active cholesterol. It has an elevated chemical activity and circulates among the organelles. It also moves down its chemical activity gradient to plasma HDL, facilitated by the activity of ABCA1, ABCG1, and SR-BI. ABCA1 initiates this process by perturbing the organization of the plasma membrane bilayer, thereby priming its phospholipids for translocation to apoA-I to form nascent HDL. The active excess sterol and that activated by ABCA1 itself follow the phospholipids to the nascent HDL. ABCG1 similarly rearranges the bilayer and sends additional active cholesterol to nascent HDL, while SR-BI simply facilitates the equilibration of the active sterol between plasma membranes and plasma proteins. Active cholesterol also flows downhill to cytoplasmic membranes where it serves both as a feedback signal to homeostatic ER proteins and as the substrate for the synthesis of mitochondrial 27-hydroxycholesterol (27HC). 27HC binds the LXR and promotes the expression of the aforementioned transport proteins. 27HC-LXR also activates ABCA1 by competitively displacing its inhibitor, unliganded LXR. § Considerable indirect evidence suggests that active cholesterol serves as both a substrate and a feedback signal for reverse cholesterol transport. Direct tests of this novel hypothesis are proposed.

Identification of key upregulated genes involved in foam cell formation and the modulatory role of statin therapy

BACKGROUND

We aimed to investigate the possible effect of statins on important genes/proteins involved in foam cell formation.

METHODS

The gene expression profile of the GSE9874, GSE54666, and GSE7138from the Omnibus database were usedto identify genes involved in foam cell formation. The protein-protein interaction (PPI) network and MCODE analysis of the intersection of three databases were analyzed. We used molecular docking analysis to investigate the possible interaction of different statins with the overexpressed hub genes obtained from PPI analysis.

RESULTS

The intersection among the three datasets showed 54 upregulated and 26 down-regulated genes. The most critical overexpressed genes/proteins obtained as hub genes included: G6PD, NPC1, ABCA1, ABCG1, PGD, PLIN2, PPAP2B, and TXNRD1 based on PPI analysis. Functional enrichment analysis of 81 intersection DEGs at the biological process level focusing on the cholesterol metabolic process, secondary alcohol biosynthetic process and the cholesterol biosynthetic process. Under cellular components, the analysis confirmed that these 81 intersection DEGs were mainly applied in endoplasmic reticulum membrane, lysosome and lytic vacuole. The molecular functions were identified as sterol binding, oxidoreductase activity and NADP binding. The molecular docking showed that all statins appear to affect important protein targets overexpressed in foam cell formation. However, lipophilic statins, especially pitavastatin and lovastatin, had a greater effect than hydrophilic statins. The most significant protein target of all the overexpressed genes interacting with all statin types was ABCA1.

CONCLUSION

The effect of lipophilic statins was shown for several critical proteins in foam cell formation.

The small HDL particle hypothesis of Alzheimer's disease

We propose the hypothesis that small high-density lipoprotein (HDL) particles reduce the risk of Alzheimer's disease (AD) by virtue of their capacity to exchange lipids, affecting neuronal membrane composition and vascular and synaptic functions. Concentrations of small HDLs in cerebrospinal fluid (CSF) and plasma were measured in 180 individuals ≥60 years of age using ion mobility methodology. Small HDL concentrations in CSF were positively associated with performance in three domains of cognitive function independent of apolipoprotein E (APOE) ε4 status, age, sex, and years of education. Moreover, there was a significant correlation between levels of small HDLs in CSF and plasma. Further studies will be aimed at determining whether specific components of small HDL exchange across the blood, brain, and CSF barriers, and developing approaches to exploit small HDLs for therapeutic purposes.

The Reentry Helix Is Potentially Involved in Cholesterol Sensing of the ABCG1 Transporter Protein

ABCG1 has been proposed to play a role in HDL-dependent cellular sterol regulation; however, details of the interaction between the transporter and its potential sterol substrates have not been revealed. In the present work, we explored the effect of numerous sterol compounds on the two isoforms of ABCG1 and ABCG4 and made efforts to identify the molecular motifs in ABCG1 that are involved in the interaction with cholesterol. The functional readouts used include ABCG1-mediated ATPase activity and ABCG1-induced apoptosis. We found that both ABCG1 isoforms and ABCG4 interact with several sterol compounds; however, they have selective sensitivities to sterols. Mutational analysis of potential cholesterol-interacting motifs in ABCG1 revealed altered ABCG1 functions when F571, L626, or Y586 were mutated. L430A and Y660A substitutions had no functional consequence, whereas Y655A completely abolished the ABCG1-mediated functions. Detailed structural analysis of ABCG1 demonstrated that the mutations modulating ABCG1 functions are positioned either in the so-called reentry helix (G-loop/TM5b,c) (Y586) or in its close proximity (F571 and L626). Cholesterol molecules resolved in the structure of ABCG1 are also located close to Y586. Based on the experimental observations and structural considerations, we propose an essential role for the reentry helix in cholesterol sensing in ABCG1.

Clinical Significance of Lipid Transport Function of ABC Transporters in the Innate Immune System

ABC transporters are a large family of proteins that transport a variety of substrates across cell plasma membranes. Because of this, they are involved in many physiological processes. It is of interest to note that many ABC transporters are involved in the transport of various lipids. In addition, this function may be related to the innate immune system. The evidence that ABC transporters are involved in the regulation of the innate immune system through the transport of various substances greatly enhances the understanding of their clinical significance. ABC transporters are involved in the cellular homeostasis of cholesterol as well as in the regulation of its content in lipid rafts. Through these mechanisms, they can regulate the function of membrane proteins, including receptors of the innate immune system. By regulating lipid transport, some members of ABC transporters are involved in phagocytosis. In addition, ABC transporters are involved in the transport of lipopolysaccharide, lipid mediators of inflammation, and perform other functions in the innate immune system.

Brain-specific loss of Abcg1 disturbs cholesterol metabolism and aggravates pyroptosis and neurological deficits after traumatic brain injury

Based on accumulating evidence, cholesterol metabolism dysfunction has been suggested to contribute to the pathophysiological process of traumatic brain injury (TBI) and lead to neurological deficits. As a key transporter of cholesterol that efflux from cells, the ATP-binding cassette (ABC) transporter family exerts many beneficial effects on central nervous system (CNS) diseases. However, there is no study regarding the effects and mechanisms of ABCG1 on TBI. As expected, TBI resulted in the different time-course changes of cholesterol metabolism-related molecules in the injured cortex. Considering ABCG1 is expressed in neuron and glia post-TBI, we generated nestin-specific Abcg1 knockout (Abcg1-KO) mice using the Cre/loxP recombination system. These Abcg1-KO mice showed reduced plasma high-density lipoprotein cholesterol levels and increased plasma lower-density lipoprotein cholesterol levels under the base condition. After TBI, these Abcg1-KO mice were susceptible to cholesterol metabolism turbulence. Moreover, Abcg1-KO exacerbated TBI-induced pyroptosis, apoptosis, neuronal cell insult, brain edema, neurological deficits, and brain lesion volume. Importantly, we found that treating with retinoid X receptor (RXR, the upstream molecule of ABCG1) agonist, bexarotene, in Abcg1-KO mice partly rescued TBI-induced neuronal damages mentioned above and improved functional deficits versus vehicle-treated group. These data show that, in addition to regulating brain cholesterol metabolism, Abcg1 improves neurological deficits through inhibiting pyroptosis, apoptosis, neuronal cell insult, and brain edema. Moreover, our findings demonstrate that the cerebroprotection of Abcg1 on TBI partly relies on the activation of the RXRalpha/PPARgamma pathway, which provides a potential therapeutic target for treating TBI.

Amyloid β, Lipid Metabolism, Basal Cholinergic System, and Therapeutics in Alzheimer’s Disease

The presence of insoluble aggregates of amyloid β (Aβ) in the form of neuritic plaques (NPs) is one of the main features that define Alzheimer’s disease. Studies have suggested that the accumulation of these peptides in the brain significantly contributes to extensive neuronal loss. Furthermore, the content and distribution of cholesterol in the membrane have been shown to have an important effect on the production and subsequent accumulation of Aβ peptides in the plasma membrane, contributing to dysfunction and neuronal death. The monomeric forms of these membrane-bound peptides undergo several conformational changes, ranging from oligomeric forms to beta-sheet structures, each presenting different levels of toxicity. Aβ peptides can be internalized by particular receptors and trigger changes from Tau phosphorylation to alterations in cognitive function, through dysfunction of the cholinergic system. The goal of this review is to summarize the current knowledge on the role of lipids in Alzheimer’s disease and their relationship with the basal cholinergic system, as well as potential disease-modifying therapies.

HDL-like-Mediated Cell Cholesterol Trafficking in the Central Nervous System and Alzheimer's Disease Pathogenesis

The main aim of this work is to review the mechanisms via which high-density lipoprotein (HDL)-mediated cholesterol trafficking through the central nervous system (CNS) occurs in the context of Alzheimer’s disease (AD). Alzheimer’s disease is characterized by the accumulation of extracellular amyloid beta (Aβ) and abnormally hyperphosphorylated intracellular tau filaments in neurons. Cholesterol metabolism has been extensively implicated in the pathogenesis of AD through biological, epidemiological, and genetic studies, with the APOE gene being the most reproducible genetic risk factor for the development of AD. This manuscript explores how HDL-mediated cholesterol is transported in the CNS, with a special emphasis on its relationship to Aβ peptide accumulation and apolipoprotein E (ApoE)-mediated cholesterol transport. Indeed, we reviewed all existing works exploring HDL-like-mediated cholesterol efflux and cholesterol uptake in the context of AD pathogenesis. Existing data seem to point in the direction of decreased cholesterol efflux and the impaired entry of cholesterol into neurons among patients with AD, which could be related to impaired Aβ clearance and tau protein accumulation. However, most of the reviewed studies have been performed in cells that are not physiologically relevant for CNS pathology, representing a major flaw in this field. The ApoE4 genotype seems to be a disruptive element in HDL-like-mediated cholesterol transport through the brain. Overall, further investigations are needed to clarify the role of cholesterol trafficking in AD pathogenesis.

High-Density Lipoproteins: A Role in Inflammation in COPD

Chronic obstructive pulmonary disease (COPD) is a widespread disease associated with high rates of disability and mortality. COPD is characterized by chronic inflammation in the bronchi as well as systemic inflammation, which contributes significantly to the clinically heterogeneous course of the disease. Lipid metabolism disorders are common in COPD, being a part of its pathogenesis. High-density lipoproteins (HDLs) are not only involved in lipid metabolism, but are also part of the organism's immune and antioxidant defense. In addition, HDL is a versatile transport system for endogenous regulatory agents and is also involved in the removal of exogenous substances such as lipopolysaccharide. These functions, as well as information about lipoprotein metabolism disorders in COPD, allow a broader assessment of their role in the pathogenesis of heterogeneous and comorbid course of the disease.

Baicalein inhibits macrophage lipid accumulation and inflammatory response by activating the PPARγ/LXRα pathway

Lipid accumulation and inflammatory response are two major risk factors for atherosclerosis. Baicalein, a phenolic flavonoid widely used in East Asian countries, possesses a potential atheroprotective activity. However, the underlying mechanisms remain elusive. This study was performed to explore the impact of baicalein on lipid accumulation and inflammatory response in THP-1 macrophage-derived foam cells. Our results showed that baicalein up-regulated the expression of ATP binding cassette transporter A1 (ABCA1), ABCG1, liver X receptor α (LXRα), and peroxisome proliferator-activated receptor γ (PPARγ), promoted cholesterol efflux, and inhibited lipid accumulation. Administration of baicalein also reduced the expression and secretion of TNF-α, IL-1β, and IL-6. Knockdown of LXRα or PPARγ with siRNAs abrogated the effects of baicalein on ABCA1 and ABCG1 expression, cholesterol efflux, lipid accumulation as well as pro-inflammatory cytokine release. In summary, these findings suggest that baicalein exerts a beneficial effect on macrophage lipid accumulation and inflammatory response by activating the PPARγ/LXRα signaling pathway.

Evolutionary origin and sequence signatures of the heterodimeric ABCG5/ABCG8 transporter

ATP-binding cassette (ABC) systems, characterized by ABC-type nucleotide-binding domains (NBDs), play crucial roles in various aspects of human physiology. Human ABCG5 and ABCG8 form a heterodimeric transporter that functions in the efflux of sterols. We used sequence similarity search, multiple sequence alignment, phylogenetic analysis, and structure comparison to study the evolutionary origin and sequence signatures of ABCG5 and ABCG8. Orthologs of ABCG5 and ABCG8, supported by phylogenetic analysis and signature residues, were identified in bilaterian animals, Filasterea, Fungi, and Amoebozoa. Such a phylogenetic distribution suggests that ABCG5 and ABCG8 could have originated in the last common ancestor of Amorphea (the unikonts), the eukaryotic group including Amoebozoa and Opisthokonta. ABCG5 and ABCG8 were missing in genomes of various lineages such as snakes, jawless vertebrates, non-vertebrate chordates, echinoderms, and basal metazoan groups. Amino-acid changes in key positions in ABCG8 Walker A motif and/or ABCG5 C-loop were observed in most tetrapod organisms, likely resulted in the loss of ATPase activity at one nucleotide-binding site. ABCG5 and ABCG8 in Ecdysozoa (such as insects) exhibit elevated evolutionary rates and accumulate various changes in their NBD functional motifs. Alignment inspection revealed several residue positions that show different amino-acid usages in ABCG5/ABCG8 compared to other ABCG subfamily proteins. These residues were mapped to the structural cores of transmembrane domains (TMDs), the NBD-TMD interface, and the interface between TMDs. They serve as sequence signatures to differentiate ABCG5/ABCG8 from other ABCG subfamily proteins, and some of them may contribute to substrate specificity of the ABCG5/ABCG8 transporter.

Pathways and Mechanisms of Cellular Cholesterol Efflux-Insight From Imaging

Cholesterol is an essential molecule in cellular membranes, but too much cholesterol can be toxic. Therefore, mammalian cells have developed complex mechanisms to remove excess cholesterol. In this review article, we discuss what is known about such efflux pathways including a discussion of reverse cholesterol transport and formation of high-density lipoprotein, the function of ABC transporters and other sterol efflux proteins, and we highlight their role in human diseases. Attention is paid to the biophysical principles governing efflux of sterols from cells. We also discuss recent evidence for cholesterol efflux by the release of exosomes, microvesicles, and migrasomes. The role of the endo-lysosomal network, lipophagy, and selected lysosomal transporters, such as Niemann Pick type C proteins in cholesterol export from cells is elucidated. Since oxysterols are important regulators of cellular cholesterol efflux, their formation, trafficking, and secretion are described briefly. In addition to discussing results obtained with traditional biochemical methods, focus is on studies that use established and novel bioimaging approaches to obtain insight into cholesterol efflux pathways, including fluorescence and electron microscopy, atomic force microscopy, X-ray tomography as well as mass spectrometry imaging.

Structure and transport mechanism of the human cholesterol transporter ABCG1

The reverse cholesterol transport pathway is responsible for the maintenance of human cholesterol homeostasis, an imbalance of which usually leads to atherosclerosis. As a key component of this pathway, the ATP-binding cassette transporter ABCG1 forwards cellular cholesterol to the extracellular acceptor nascent high-density lipoprotein (HDL). Here, we report a 3.26-Å cryo-electron microscopy structure of cholesterol-bound ABCG1 in an inward-facing conformation, which represents a turnover condition upon ATP binding. Structural analyses combined with functional assays reveals that a cluster of conserved hydrophobic residues, in addition to two sphingomyelins, constitute a well-defined cholesterol-binding cavity. The exit of this cavity is closed by three pairs of conserved Phe residues, which constitute a hydrophobic path for the release of cholesterol in an acceptor concentration-dependent manner. Overall, we propose an ABCG1-driven cholesterol transport cycle initiated by sphingomyelin-assisted cholesterol recruitment and accomplished by the release of cholesterol to HDL.

Diagnostic and prognostic value of ABC transporter family member ABCG1 gene in clear cell renal cell carcinoma

As the most common histologic subtype of renal cancer, clear cell renal cell carcinoma (ccRCC) poses a serious threat to public health. However, there are no specific molecular-targeted drugs for ccRCC at present. Human ATP-binding cassette (ABC) transporter family plays an important role in homeostasis maintenance. This study aimed to evaluate the potential diagnostic value of ABC genes in ccRCC. A total of 952 samples of ccRCC patients (707) and controls (245) from three different datasets were included for analysis. Receiver operating characteristic analysis and t-test were used to analyze the differential expression of ABC genes in ccRCC patients and control samples at mRNA level during screening and validations. The Cancer Genome Atlas (TCGA-ccRCC) dataset was utilized to investigate the correlation between ABC genes expression and prognostic value in ccRCC. We then investigated the interactions between ABCG1 and proteins in the Comparative Toxicogenomics Database (CTD). Finally, we found that ATP-binding cassette transporter G member 1 (ABCG1) was over-expressed in ccRCC patients compared with healthy samples at mRNA level. Cox regression analysis and Kaplan-Meier analysis showed that ccRCC patients with high ABCG1 expression had better overall survival (OS) than those patients with low expression (hazard ratio (HR) = 0.662, p = 0.007). This study demonstrated that ABCG1 is a potential diagnostic and prognostic biomarker in ccRCC and discussed the molecular mechanisms underlying the relationship between ccRCC and ABCG1, which might provide guidance for better management and treatment of ccRCC in the future.

1H-NMR Plasma Lipoproteins Profile Analysis Reveals Lipid Metabolism Alterations in HER2-Positive Breast Cancer Patients

The lipid tumour demand may shape the host metabolism adapting the circulating lipids composition to its growth and progression needs. This study aims to exploit the straightforward 1H-NMR lipoproteins analysis to investigate the alterations of the circulating lipoproteins' fractions in HER2-positive breast cancer and their modulations induced by treatments. The baseline 1H-NMR plasma lipoproteins profiles were measured in 43 HER2-positive breast cancer patients and compared with those of 28 healthy women. In a subset of 32 patients, longitudinal measurements were also performed along neoadjuvant chemotherapy, after surgery, adjuvant treatment, and during the two-year follow-up. Differences between groups were assessed by multivariate PLS-DA and by univariate analyses. The diagnostic power of lipoproteins subfractions was assessed by ROC curve, while lipoproteins time changes along interventions were investigated by ANOVA analysis. The PLS-DA model distinguished HER2-positive breast cancer patients from the control group with a sensitivity of 96.4% and specificity of 90.7%, mainly due to the differential levels of VLDLs subfractions that were significantly higher in the patients' group. Neoadjuvant chemotherapy-induced a significant drop in the HDLs after the first three months of treatment and a specific decrease in the HDL-3 and HDL-4 subfractions were found significantly associated with the pathological complete response achievement. These results indicate that HER2-positive breast cancer is characterized by a significant host lipid mobilization that could be useful for diagnostic purposes. Moreover, the lipoproteins profiles alterations induced by the therapeutic interventions could predict the clinical outcome supporting the application of 1H-NMR lipoproteins profiles analysis for longitudinal monitoring of HER2-positive breast cancer in large clinical studies.

ABCG1 and ABCG4 as key transporters in the development of pulmonary alveolar proteinosis by nanoparticles

Pulmonary alveolar proteinosis (PAP) has been reported in rodents treated with nanoparticles (NPs). However, little is known about the type of NPs producing PAP and their toxicity mechanisms. Here, we assembled seven PAP-inducing NPs and TiO₂ NPs as a negative control. At 1 and 6 months after a single intratracheal instillation in rats, pulmonary inflammation and the gene expression of ATP-binding cassette (ABC) transporters and related genes were evaluated in separated alveolar macrophages (AMs). One month after intratracheal instillation, seven NPs (Eu₂O₃, In₂O₃, Pr₆O₁₁, Sm₂O₃, Tb₄O₇, and NiO) caused PAP, but only In₂O₃ NPs caused persistent PAP at 6 months after treatment. The levels of phospholipids, indicators of PAP, showed good correlations with the gene expression profile of five transporters (ABCA1, ABCB4, ABCB8, ABCG1, and ABCG4), which effluxing phospholipids in AMs. Among them, ABCG1 and ABCG4 might be key transporters involved in PAP development because both showed a negative correlation with the magnitude of PAP, while others might be compensatory transporters for PAP recovery, as they showed a positive correlation. In conclusion, the identification of seven PAP-producing NPs implies that PAP may be an emerging occupational disease and that ABCG1 and ABCG4 may be therapeutic targets for PAP.

Structure of the Human Cholesterol Transporter ABCG1

ABCG1 is an ATP binding cassette (ABC) transporter that removes excess cholesterol from peripheral tissues. Despite its role in preventing lipid accumulation and the development of cardiovascular and metabolic disease, the mechanism underpinning ABCG1-mediated cholesterol transport is unknown. Here we report a cryo-EM structure of human ABCG1 at 4 Å resolution in an inward-open state, featuring sterol-like density in the binding cavity. Structural comparison with the multidrug transporter ABCG2 and the sterol transporter ABCG5/G8 reveals the basis of mechanistic differences and distinct substrate specificity. Benzamil and taurocholate inhibited the ATPase activity of liposome-reconstituted ABCG1, whereas the ABCG2 inhibitor Ko143 did not. Based on the structural insights into ABCG1, we propose a mechanism for ABCG1-mediated cholesterol transport.

Lipid accumulation and novel insight into vascular smooth muscle cells in atherosclerosis

Atherosclerosis is a chronic and progressive process. It is the most important pathological basis of cardiovascular disease and stroke. Vascular smooth muscle cells (VSMCs) are an essential cell type in atherosclerosis. Previous studies have revealed that VSMCs undergo phenotypic transformation in atherosclerosis to participate in the retention of atherogenic lipoproteins as well as the formation of the fibrous cap and the underlying necrotic core in plaques. The emergence of lineage-tracing studies indicates that the function and number of VSMCs in plaques have been greatly underestimated. In addition, recent studies have revealed that VSMCs make up at least 50% of the foam cell population in human and mouse atherosclerotic lesions. Therefore, understanding the formation of lipid-loaded VSMCs and their regulatory mechanisms is critical to elucidate the pathogenesis of atherosclerosis and to explore potential therapeutic targets. Moreover, combination of many complementary technologies such as lineage tracing, single-cell RNA sequencing (scRNA-seq), flow cytometry, and mass cytometry (CyTOF) with immunostaining has been performed to further understand the complex VSMC function. Correct identification of detrimental and beneficial processes may reveal successful therapeutic treatments targeting VSMCs and their derivatives during atherosclerosis. The purpose of this review is to summarize the process of lipid-loaded VSMC formation in atherosclerosis and to describe novel insight into VSMCs gained by using multiple advanced methods.

Lipid Transporters Beam Signals from Cell Membranes

Lipid composition in cellular membranes plays an important role in maintaining the structural integrity of cells and in regulating cellular signaling that controls functions of both membrane-anchored and cytoplasmic proteins. ATP-dependent ABC and P4-ATPase lipid transporters, two integral membrane proteins, are known to contribute to lipid translocation across the lipid bilayers on the cellular membranes. In this review, we will highlight current knowledge about the role of cholesterol and phospholipids of cellular membranes in regulating cell signaling and how lipid transporters participate this process.

The Role of ABC Transporters in Lipid Metabolism and the Comorbid Course of Chronic Obstructive Pulmonary Disease and Atherosclerosis

Chronic obstructive pulmonary disease (COPD) ranks among the leading causes of morbidity and mortality worldwide. COPD rarely occurs in isolation and is often combined with various diseases. It is considered that systemic inflammation underlies the comorbid course of COPD. The data obtained in recent years have shown the importance of violations of the cross-links of lipid metabolism and the immune response, which are links in the pathogenesis of both COPD and atherosclerosis. The role of lipid metabolism disorders in the pathogenesis of the comorbid course of COPD and atherosclerosis and the participation of ATP-binding cassette (ABC) transporters in these processes is discussed in this article. It is known that about 20 representatives of a large family of ABC transporters provide lipid homeostasis of cells by moving lipids inside the cell and in its plasma membrane, as well as removing lipids from the cell. It was shown that some representatives of the ABC-transporter family are involved in various links of the pathogenesis of COPD and atherosclerosis, which can determine their comorbid course.

Multidrug Resistance in Mammals and Fungi-From MDR to PDR: A Rocky Road from Atomic Structures to Transport Mechanisms

Multidrug resistance (MDR) can be a serious complication for the treatment of cancer as well as for microbial and parasitic infections. Dysregulated overexpression of several members of the ATP-binding cassette transporter families have been intimately linked to MDR phenomena. Three paradigm ABC transporter members, ABCB1 (P-gp), ABCC1 (MRP1) and ABCG2 (BCRP) appear to act as brothers in arms in promoting or causing MDR in a variety of therapeutic cancer settings. However, their molecular mechanisms of action, the basis for their broad and overlapping substrate selectivity, remains ill-posed. The rapidly increasing numbers of high-resolution atomic structures from X-ray crystallography or cryo-EM of mammalian ABC multidrug transporters initiated a new era towards a better understanding of structure-function relationships, and for the dynamics and mechanisms driving their transport cycles. In addition, the atomic structures offered new evolutionary perspectives in cases where transport systems have been structurally conserved from bacteria to humans, including the pleiotropic drug resistance (PDR) family in fungal pathogens for which high resolution structures are as yet unavailable. In this review, we will focus the discussion on comparative mechanisms of mammalian ABCG and fungal PDR transporters, owing to their close evolutionary relationships. In fact, the atomic structures of ABCG2 offer excellent models for a better understanding of fungal PDR transporters. Based on comparative structural models of ABCG transporters and fungal PDRs, we propose closely related or even conserved catalytic cycles, thus offering new therapeutic perspectives for preventing MDR in infectious disease settings.

Analysis of Sequence Divergence in Mammalian ABCGs Predicts a Structural Network of Residues That Underlies Functional Divergence

The five members of the mammalian G subfamily of ATP-binding cassette transporters differ greatly in their substrate specificity. Four members of the subfamily are important in lipid transport and the wide substrate specificity of one of the members, ABCG2, is of significance due to its role in multidrug resistance. To explore the origin of substrate selectivity in members 1, 2, 4, 5 and 8 of this subfamily, we have analysed the differences in conservation between members in a multiple sequence alignment of ABCG sequences from mammals. Mapping sets of residues with similar patterns of conservation onto the resolved 3D structure of ABCG2 reveals possible explanations for differences in function, via a connected network of residues from the cytoplasmic to transmembrane domains. In ABCG2, this network of residues may confer extra conformational flexibility, enabling it to transport a wider array of substrates.

Materno-fetal cholesterol transport during pregnancy

Cholesterol is a major nutrient required for fetal growth. It is also a precursor for the synthesis of steroid hormones and essential for the development and maturation of fetal organs. During pregnancy, the placenta controls the transport of cholesterol from the mother to the fetus and vice versa. Cholesterol originating from the maternal circulation has to cross two main membrane barriers to reach the fetal circulation: Firstly, cholesterol is acquired by the apical side of the syncytiotrophoblast (STB) from the maternal circulation as high-density lipoprotein (HDL)-, low-density lipoprotein (LDL)- or very-low-density lipoprotein (VLDL)-cholesterol and secreted at the basal side facing the villous stroma. Secondly, from the villous stroma cholesterol is taken up by the endothelium of the fetal vasculature and transported to the fetal vessels. The proteins involved in the uptake of HDL-, LDL-, VLDL- or unesterified-cholesterol are scavenger receptor type B class 1 (SR-B1), cubulin, megalin, LDL receptor (LDLR) or Niemann-Pick-C1 (NPC1) which are localized at the apical and/or basal side of the STB or at the fetal endothelium. Through interaction with apolipoproteins (e.g. apoA1) cholesterol is effluxed either to the maternal or fetal circulation via the ATP-binding-cassette (ABC)-transporter A1 and ABCG1 localized at the apical/basal side of the STB or the endothelium. In this mini-review, we summarize the transport mechanisms of cholesterol across the human placenta, the expression and localization of proteins involved in the uptake and efflux of cholesterol, and the expression pattern of cholesterol transport proteins in pregnancy pathologies such as pre-eclampsia, gestational diabetes mellitus and intrauterine growth retardation.

Polydatin inhibits LPS-induced inflammatory response in BV2 microglia by disrupting the formation of lipid rafts

OBJECTIVE

Polydatin has been used in the treatment of various inflammatory diseases. However, its role in the regulation of neuroinflammation has not been reported. In this study, we designed to investigate the anti-inflammatory effects of polydatin in LPS-stimulated BV2 microglia cells.

METHODS

Inflammatory mediators TNF-α, IL-1β, NO, and PGE2 production were measured by ELISA. The protein of signaling pathways were detected by western blot analysis.

RESULTS

The results showed that polydatin significantly ameliorated the production of TNF-α, IL-1β, NO, and PGE2 up-regulated by LPS. Polydatin also blocked LPS-induced NF-κB activation. In addition, PI3K and AKT, the up-stream molecules of NF-κB signaling pathway, were inhibited by the treatment of polydatin. Also, we found the formation of lipid rafts was inhibited by polydatin through attenuating the cholesterol content. Finally, polydatin was found to increase the expression of ABCA1 and ABCG1.

CONCLUSION

In conclusion, the results of the present study suggested that polydatin exhibited its anti-inflammatory effects in BV2 cells through disrupting lipid rafts, which subsequently inhibiting PI3K/AKT signaling pathway.

Mammalian ABCG-transporters, sterols and lipids: To bind perchance to transport?

Members of the ATP binding cassette (ABC) transporter family perform a critical function in maintaining lipid homeostasis in cells as well as the transport of drugs. In this review, we provide an update on the ABCG-transporter subfamily member proteins, which include the homodimers ABCG1, ABCG2 and ABCG4 as well as the heterodimeric complex formed between ABCG5 and ABCG8. This review focusses on progress made in this field of research with respect to their function in health and disease and the recognised transporter substrates. We also provide an update on post-translational regulation, including by transporter substrates, and well as the involvement of microRNA as regulators of transporter expression and activity. In addition, we describe progress made in identifying structural elements that have been recognised as important for transport activity. We furthermore discuss the role of lipids such as cholesterol on the transport function of ABCG2, traditionally thought of as a drug transporter, and provide a model of potential cholesterol binding sites for ABCG2.

Adiponectin's mechanisms in high-density lipoprotein biogenesis and cholesterol efflux

AIM

Among adiponectin's beneficial properties is its ability to promote cellular cholesterol efflux, thereby generating high-density lipoprotein (HDL) particles. However, adiponectin's role in the regulation of macrophage lipid metabolism, a crucial process in atherogenesis, remains poorly investigated. The aim of this study was to characterize the adiponectin's role in HDL biogenesis.

METHODS AND RESULTS

We perform kinetics studies in baby hamster kidney (BHK) and Tamm-Horsfall protein 1 (THP-1) cell lines to elucidate adiponectin's role in HDL biogenesis. In cholesterol-enriched cells, specific molar doses of adiponectin stimulated cholesterol efflux with high efficiency to apoA-I. In the presence of adiponectin, BHK cells expressing ATP binding cassette transporter A1 (ABCA1) or ABCG1 generated lipidated particles having α electrophoretic mobility (α-HDL) and a molecular size of 7.5-20 nm. Interestingly, in THP-1 macrophages, cholesterol efflux was associated with more lipidated preβ1-HDL particles. Direct molecular interaction of adiponectin with apoA-I enhanced the affinity of apoA-I to free cholesterol and resulted in an increase in preβ1-HDL particles from plasma ex vivo. Adiponectin increased ABCA1 and ABCG1 protein expression and activated the formation of ABCA1-linked cholesterol oxidase sensitive plasma membrane domains.

CONCLUSION

Adiponectin upregulated ABCA1 and ABCG1 protein expression, reduced lipid accumulation, and efficiently promoted nascent HDL formation. These results highlight that these cellular processes are interconnected through adiponectin and ABCA1- and ABCG1-dependent. In this pathway, adiponectin increased the affinity of apoA-I to cholesterol and effectively accelerated cholesterol removal from the plasma membrane to HDL particles. Thus, by accelerating HDL biogenesis, adiponectin may have therapeutic potential for atherosclerotic cardiovascular disease prevention and management.

DNA methylation microarrays identify epigenetically regulated lipid related genes in obese patients with hypercholesterolemia

BACKGROUND

Epigenetics can contribute to lipid disorders in obesity. The DNA methylation pattern can be the cause or consequence of high blood lipids. The aim of the study was to investigate the DNA methylation profile in peripheral leukocytes associated with elevated LDL-cholesterol level in overweight and obese individuals.

METHODS

To identify the differentially methylated genes, genome-wide DNA methylation microarray analysis was performed in leukocytes of obese individuals with high LDL-cholesterol (LDL-CH, ≥ 3.4 mmol/L) versus control obese individuals with LDL-CH, < 3.4 mmol/L. Biochemical tests such as serum glucose, total cholesterol, HDL cholesterol, triglycerides, insulin, leptin, adiponectin, FGF19, FGF21, GIP and total plasma fatty acids content have been determined. Oral glucose and lipid tolerance tests were also performed. Human DNA Methylation Microarray (from Agilent Technologies) containing 27,627 probes for CpG islands was used for screening of DNA methylation status in 10 selected samples. Unpaired t-test and Mann-Whitney U-test were used for biochemical and anthropometric parameters statistics. For microarrays analysis, fold of change was calculated comparing hypercholesterolemic vs control group. The q-value threshold was calculated using moderated Student's t-test followed by Benjamini-Hochberg multiple test correction FDR.

RESULTS

In this preliminary study we identified 190 lipid related CpG loci differentially methylated in hypercholesterolemic versus control individuals. Analysis of DNA methylation profiles revealed several loci engaged in plasma lipoprotein formation and metabolism, cholesterol efflux and reverse transport, triglycerides degradation and fatty acids transport and β-oxidation. Hypermethylation of CpG loci located in promoters of genes regulating cholesterol metabolism: PCSK9, LRP1, ABCG1, ANGPTL4, SREBF1 and NR1H2 in hypercholesterolemic patients has been found. Novel epigenetically regulated CpG sites include ABCG4, ANGPTL4, AP2A2, AP2M1, AP2S1, CLTC, FGF19, FGF1R, HDLBP, LIPA, LMF1, LRP5, LSR, NR1H2 and ZDHHC8 genes.

CONCLUSIONS

Our results indicate that obese individuals with hypercholesterolemia present specific DNA methylation profile in genes related to lipids transport and metabolism. Detailed knowledge of epigenetic regulation of genes, important for lipid disorders in obesity, underlies the possibility to influence target genes by changing diet and lifestyle, as DNA methylation is reversible and depends on environmental factors. These findings give rise for further studies on factors that targets methylation of revealed genes.

Participation of ABC-transporters in lipid metabolism and pathogenesis of atherosclerosis

Atherosclerosis is one of the key causes of morbidity and mortality worldwide. It is known that a leading role in the development and progression of atherosclerosis is played by a violation of lipid metabolism. ABC transporters provide lipid cell homeostasis, performing a number of transport functions - moving lipids inside the cell, in the plasma membrane, and also removing lipids from the cell. In a large group of ABC transporters, about 20 take part in lipid homeostasis, playing, among other things, an important role in the pathogenesis of atherosclerosis. It was shown that cholesterol is not only a substrate for a number of ABC transporters, but also able to modulate their activity. Regulation of activity is carried out due to specific lipid-protein interactions.

Do ABC transporters regulate plasma membrane organization?

The plasma membrane (PM) spatiotemporal organization is one of the major factors controlling cell signaling and whole-cell homeostasis. The PM lipids, including cholesterol, determine the physicochemical properties of the membrane bilayer and thus play a crucial role in all membrane-dependent cellular processes. It is known that lipid content and distribution in the PM are not random, and their transversal and lateral organization is highly controlled. Mainly sphingolipid- and cholesterol-rich lipid nanodomains, historically referred to as rafts, are extremely dynamic “hot spots” of the PM controlling the function of many cell surface proteins and receptors. In the first part of this review, we will focus on the recent advances of PM investigation and the current PM concept. In the second part, we will discuss the importance of several classes of ABC transporters whose substrates are lipids for the PM organization and dynamics. Finally, we will briefly present the significance of lipid ABC transporters for immune responses.

Lipid efflux mechanisms, relation to disease and potential therapeutic aspects

Lipids are hydrophobic and amphiphilic molecules involved in diverse functions such as membrane structure, energy metabolism, immunity, and signaling. However, altered intra-cellular lipid levels or composition can lead to metabolic and inflammatory dysfunction, as well as lipotoxicity. Thus, intra-cellular lipid homeostasis is tightly regulated by multiple mechanisms. Since most peripheral cells do not catabolize cholesterol, efflux (extra-cellular transport) of cholesterol is vital for lipid homeostasis. Defective efflux contributes to atherosclerotic plaque development, impaired β-cell insulin secretion, and neuropathology. Of these, defective lipid efflux in macrophages in the arterial walls leading to foam cell and atherosclerotic plaque formation has been the most well studied, likely because a leading global cause of death is cardiovascular disease. Circulating high density lipoprotein particles play critical roles as acceptors of effluxed cellular lipids, suggesting their importance in disease etiology. We review here mechanisms and pathways that modulate lipid efflux, the role of lipid efflux in disease etiology, and therapeutic options aimed at modulating this critical process.

Circulating microRNA Associated to Different Stages of Liver Steatosis in Prader-Willi Syndrome and Non-Syndromic Obesity

BACKGROUND

Prader-Willi syndrome (PWS) is a rare and poorly characterized disease. Recent genomic and transcriptomic studies contributed to elucidate the molecular bases of the syndrome. In this study, we characterized the expression of circulating miRNAs in patients with PWS compared to those with non-syndromic obesity in association with liver steatosis.

METHODS

MiRNAs were studied by qRT-PCR in serum samples from 30 PWS and 30 non-syndromic obese subjects.

RESULTS

MiRNA expression was associated with the presence of the syndrome and to the grade of liver steatosis. MiR-122-5p, miR-151a, miR-92a-3p were up-regulated in obese (4.38-fold, p < 0.01; 2.72-fold, p < 0.05; 1.34-fold p < 0.05, respectively) and were able to differentiate obese from PWS (AUC = 0.81, sens/spec 78/71%). When stratifying groups according to the presence of steatosis, the expression of miR-151a-5p, miR-92a-3p, miR-106b-5p, and miR-93-5p were lower in PWS with steatosis grade 1. Within the group with steatosis grade 1, miR-151a-5p was significantly distinguished PWS from obese (AUC = 0.85, sens/spec 80/85%) and the combination of miR-106b-5p and miR-93-5p showed higher performances in discriminating different grades of steatosis in PWS (AUC = 0.84, sens/spec 93/74%).

CONCLUSIONS

MiRNAs represent a tool to better classify and characterize PWS, providing new information about the clinical picture and the extent of steatosis.

Epigenetic Link Between Statin Therapy and Type 2 Diabetes

OBJECTIVE

To investigate the role of epigenetics in statins' diabetogenic effect comparing DNA methylation (DNAm) between statin users and nonusers in an epigenome-wide association study in blood.

RESEARCH DESIGN AND METHODS

Five cohort studies' participants (n = 8,270) were classified as statin users when they were on statin therapy at the time of DNAm assessment with Illumina 450K or EPIC array or noncurrent users otherwise. Associations of DNAm with various outcomes like incident type 2 diabetes, plasma glucose, insulin, and insulin resistance (HOMA of insulin resistance [HOMA-IR]) as well as with gene expression were investigated.

RESULTS

Discovery (n = 6,820) and replication (n = 1,450) phases associated five DNAm sites with statin use: cg17901584 (1.12 × 10-25 [DHCR24]), cg10177197 (3.94 × 10-08 [DHCR24]), cg06500161 (2.67 × 10-23 [ABCG1]), cg27243685 (6.01 × 10-09 [ABCG1]), and cg05119988 (7.26 × 10-12 [SC4MOL]). Two sites were associated with at least one glycemic trait or type 2 diabetes. Higher cg06500161 methylation was associated with higher fasting glucose, insulin, HOMA-IR, and type 2 diabetes (odds ratio 1.34 [95% CI 1.22, 1.47]). Mediation analyses suggested that ABCG1 methylation partially mediates the effect of statins on high insulin and HOMA-IR. Gene expression analyses showed that statin exposure and ABCG1 methylation were associated with ABCG1 downregulation, suggesting epigenetic regulation of ABCG1 expression. Further, outcomes insulin and HOMA-IR were significantly associated with ABCG1 expression.

CONCLUSIONS

This study sheds light on potential mechanisms linking statins with type 2 diabetes risk, providing evidence on DNAm partially mediating statins' effects on insulin traits. Further efforts shall disentangle the molecular mechanisms through which statins may induce DNAm changes, potentially leading to ABCG1 epigenetic regulation.

High Concentration of Medium-Sized HDL Particles and Enrichment in HDL Paraoxonase 1 Associate With Protection From Vascular Complications in People With Long-standing Type 1 Diabetes

OBJECTIVE

A subset of people with long-standing type 1 diabetes (T1D) appears to be protected from microvascular and macrovascular complications. Previous studies have focused on improved abilities to respond to glucose and its downstream effects as protective mechanisms. It is unclear whether lipoproteins play a role in the vascular health of these people. We therefore determined whether HDL particle concentration, size, function, and/or protein composition associate with protection from vascular complications.

RESEARCH DESIGN AND METHODS

We studied two independent cross-sectional cohorts with T1D: the T1D Exchange Living Biobank (n = 47) and the Joslin Medalist Study (n = 100). Some of the subjects had vascular complications, whereas others never exhibited vascular complications, despite an average duration of diabetes in the cohorts of 45 years. We assessed HDL particle size and concentration by calibrated ion mobility analysis, the HDL proteome by targeted mass spectrometry, and HDL function ex vivo by quantifying cholesterol efflux capacity and inhibition of monocyte adhesion to endothelial cells.

RESULTS

In both cohorts, people without vascular complications exhibited significantly higher concentrations of medium-sized HDL particles (M-HDL) independently of total and HDL cholesterol levels. While no consistent differences in HDL functions were observed ex vivo, people without vascular complications had higher levels of HDL-associated paraoxonase 1 (PON1), an enzyme that inhibits atherosclerosis in animal models.

CONCLUSIONS

Elevated concentrations of M-HDL particles and elevated levels of HDL-associated PON1 may contribute to long-term protection from the vascular complications of diabetes by pathways that are independent of total cholesterol and HDL cholesterol.

Hyperalphalipoproteinemic scavenger receptor BI knockout mice exhibit a disrupted epidermal lipid barrier

Scavenger receptor class B type I (SR-BI) mediates the selective uptake of cholesteryl esters (CE) from high-density lipoproteins (HDL). An impaired SR-BI function leads to hyperalphalipoproteinemia with elevated levels of cholesterol transported in the HDL fraction. Accumulation of cholesterol in apolipoprotein B (apoB)-containing lipoproteins has been shown to alter skin lipid composition and barrier function in mice. To investigate whether these hypercholesterolemic effects on the skin also occur in hyperalphalipoproteinemia, we compared skins of wild-type and SR-BI knockout (SR-BI^-/-) mice. SR-BI deficiency did not affect the epidermal cholesterol content and induced only minor changes in the ceramide subclasses. The epidermal free fatty acid (FFA) pool was, however, enriched in short and unsaturated chains. Plasma CE levels strongly correlated with epidermal FFA C18:1 content. The increase in epidermal FFA coincided with downregulation of cholesterol and FFA synthesis genes, suggesting a compensatory response to increased flux of plasma cholesterol and FFAs into the skin. Importantly, the SR-BI^-/- epidermal lipid barrier showed increased permeability to ethyl-paraminobenzoic acid, indicating an impairment of the barrier function. In conclusion, increased HDL-cholesterol levels in SR-BI^-/- mice can alter the epidermal lipid composition and lipid barrier function similarly as observed in hypercholesterolemia due to elevated levels of apoB-containing lipoproteins.

Identification of candidate ATP-binding cassette transporter gene family members in Diaphorina citri (Hemiptera: Psyllidae) via adult tissues transcriptome analysis

The ATP-binding cassette (ABC) transporters exist in all living organisms and play major roles in various biological functions by transporting a wide variety of substrates across membranes. The functions of ABC transporters in drug resistance have been extensively studied in vertebrates; however, they are rarely characterized in agricultural pests. The Asian citrus psyllid, Diaphorina citri, is one of the most damaging pests of the Citrus genus because of its transmission of Huanglongbing, also known as Yellow Dragon disease. In this study, the next-generation sequencing technique was applied to research the ABC transporters of D. citri. Fifty-three ABC transporter genes were found in the RNA-Seq data, and among these ABC transporters, 4, 4, 5, 2, 1, 4, 18 and 15 ABC proteins belonged to the ABCA-ABCH subfamilies, respectively. Different expression profiles of 52 genes between imidacloprid-resistant and imidacloprid-susceptible strains were studied by qRT-PCR; 5 ABCGs and 4 ABCHs were significantly upregulated in the imidacloprid-resistant strain. In addition, five of the nine upregulated genes were widely expressed in adult tissues in spatial expression analysis. The results suggest that these genes may play key roles in this phenotype. In general, this study contributed to our current understanding of D. citri resistance to insecticides.

Effect of Saccharomyces cerevisiae fermentation product on feed intake parameters, lactation performance, and metabolism of transition dairy cattle

The transition period in dairy cattle is characterized by many stressors, including an abrupt diet change, but yeast product supplementation can alter the rumen environment to increase dairy cattle productivity. Saccharomyces cerevisiae fermentation product (SCFP) was fed from -29 ± 5 to 42 d relative to calving (RTC) to evaluate the effects on feed intake, milk production, and metabolism. Treatments were control (n = 30) or SCFP (n = 34) incorporated into a total mixed ration. Cows were individually fed 3×/d prepartum and 2×/d postpartum. Blood samples were collected once during each of the following time points RTC: d -28 to -24 (wk -4), d -14 to -10 (wk -2), d 3 to 7 (wk 1), d 12 to 16 (wk 2), and d 31 to 35 (wk 5). Liver biopsies were taken once between d -19 and d -12 (wk -3) and at 14 d in milk. Cows were milked 2×/d, and samples were taken 2 d/wk for composition analysis. Dry matter intake did not differ by treatment, but SCFP increased meals per day and decreased time between meals. Body weight (measured at enrollment, d 0, and d 42 RTC) and body condition score (scored weekly) were not affected by treatment. Milk, energy-corrected milk, and fat-corrected milk yields did not differ by treatment. Milk fat concentration was greater for SCFP, with significant differences in wk 4 and 5. Milk lactose concentration tended to be greater for the control and milk urea nitrogen tended to be lesser for the control, but there were no treatment effects on milk protein concentration or somatic cell count. Assuming equal digestibility, energy balance deficit was greater for SCFP than for the control (-6.15 vs. -4.34 ± 0.74 Mcal/d), with significant differences in wk 4 and 5. Plasma concentrations of free fatty acids, β-hydroxybutyrate, glucose, and insulin did not differ with treatment, but cholesterol was greater for SCFP. Liver triglyceride increased and liver cholesterol decreased with time. Liver triglyceride did not differ by treatment, but liver cholesterol tended to be lesser in SCFP. Relative mRNA abundance of cholesterol-related genes (SREBF2, HMGCS1, HMGCR, MTTP, SPOB100, APOA1), FGF21, and CPT1A did not differ by treatment, but PCK1 tended to be greater for SCFP. The ketogenic transcript HMGCS2 was greater for SCFP, which aligns with SCFP increasing incidence of subclinical ketosis; however, BDH did not differ between treatments. In conclusion, SCFP supplementation increased meals per day with less time between meals, increased milk fat concentration, altered cholesterol metabolism, and increased incidence of subclinical ketosis, but early-lactation milk yield and metabolism were generally unaffected.

The Adaptor Protein Alix is Involved in the Interaction Between the Ubiquitin Ligase NEDD4-1 and its Targets, ABCG1 and ABCG4

Several ATP-Binding Cassette (ABC) transporters, including ABCG1 and the related ABCG4, are essential regulators of cellular lipid homeostasis. ABCG1 is expressed ubiquitously and is functional in the context of atherosclerosis. However, ABCG4 is expressed almost exclusively in brain and has been linked to Alzheimer's disease (AD). These transporters are highly regulated post-translationally by E3 ubiquitin ligases, with the ligase NEDD4-1 (Neural precursor cell-expressed developmentally downregulated gene 4) implicated in their protein stability. In this study, we investigated interacting partners of ABCG1 using peptide-mass spectrometry and identified the potential adaptor protein, Alix (apoptosis-linked gene 2-interacting protein X). In this paper, we hypothesized and investigated whether Alix could facilitate the interaction between NEDD4-1 and the ABC transporters. We showed that Alix and NEDD4-1 proteins were co-expressed in several commonly used cell lines. Knockdown of Alix in cells overexpressing ABCG1 or ABCG4 increased transporter protein expression while co-immunoprecipitation experiments showed interaction between NEDD4-1, Alix, and ABC transporters. In summary, we provide evidence that Alix serves as a co-factor for the interaction between the E3-ubiquitin ligase NEDD4-1 and the ABC transporter targets, ABCG1 and ABCG4.

Coffee prevents fatty liver disease induced by a high-fat diet by modulating pathways of the gut-liver axis

Coffee consumption is inversely associated with the risk of non-alcoholic fatty liver disease (NAFLD). A gap in the literature still exists concerning the intestinal mechanisms that are involved in the protective effect of coffee consumption towards NAFLD. In this study, twenty-four C57BL/6J mice were divided into three groups each receiving a standard diet, a high-fat diet (HFD) or an HFD plus decaffeinated coffee (HFD+COFFEE) for 12 weeks. Coffee supplementation reduced HFD-induced liver macrovesicular steatosis (P < 0·01) and serum cholesterol (P < 0·001), alanine aminotransferase and glucose (P < 0·05). Accordingly, liver PPAR- α (P < 0·05) and acyl-CoA oxidase-1 (P < 0·05) as well as duodenal ATP-binding cassette (ABC) subfamily A1 (ABCA1) and subfamily G1 (ABCG1) (P < 0·05) mRNA expressions increased with coffee consumption. Compared with HFD animals, HFD+COFFEE mice had more undigested lipids in the caecal content and higher free fatty acid receptor-1 mRNA expression in the duodenum and colon. Furthermore, they showed an up-regulation of duodenal and colonic zonulin-1 (P < 0·05), duodenal claudin (P < 0·05) and duodenal peptide YY (P < 0·05) mRNA as well as a higher abundance of Alcaligenaceae in the faeces (P < 0·05). HFD+COFFEE mice had an energy intake comparable with HFD-fed mice but starting from the eighth intervention week they gained significantly less weight over time. Data altogether showed that coffee supplementation prevented HFD-induced NAFLD in mice by reducing hepatic fat deposition and metabolic derangement through modification of pathways underpinning liver fat oxidation, intestinal cholesterol efflux, energy metabolism and gut permeability. The hepatic and metabolic benefits induced by coffee were accompanied by changes in the gut microbiota.

ABCA1 Agonist Mimetic Peptide CS-6253 Induces Microparticles Release From Different Cell Types by ABCA1-Efflux-Dependent Mechanism

BACKGROUND

Small peptides based on the C-terminal domain of apo E have recently been proposed as ATP-binding cassette transporter A1 (ABCA1) agonist with therapeutic potential. Previous work has shown that a novel synthetic peptide, CS-6253, acts synergistically with apolipoprotein A-I or alone to generate high-density lipoprotein (HDL) particles; we have also shown that cells can release microparticles (50-350 nm in apparent diameter) in an ABCA1- and apolipoprotein A-I-dependent manner. The purpose of this study was to explore the ability of a novel synthetic peptide CS-6253 to induce microparticle release from various cell lines in the process of HDL biogenesis.

METHODS

The effects of CS-6253 on microparticle formation through the ABCA1 transporter were examined in vitro using cell-based systems and pharmacologic manipulations.

RESULTS

In cell-based systems combined with fast performance liquid chromatography and nano-sight-tracking analysis, we show that ABCA1 and CS-6253 mediate and increase the production of microparticles containing cholesterol. CS-6253 in baby hamster kidney cells not expressing ABCA1 (baby hamster kidney mock cells) did not alter cholesterol removal across the plasma membrane in the absence of ABCA1 expression even at high concentrations. We report that CS-6253 is not cytotoxic.

CONCLUSIONS

The present study shows that CS-6253 generates cholesterol containing microparticles with size heterogeneity (100-350 nm) in an ABCA1-dependent manner. We show that microparticles contribute to cell cholesterol efflux from monocyte-macrophage cells. At high doses, CS-6253 is not able to extract cholesterol from cells not expressing ABCA1, indicating that CS-6253 requires ABCA1 cooperation for cholesterol mobilization. We conclude that CS-6253 is an ABCA1 agonist peptide that promotes cellular cholesterol efflux through HDL biogenesis and microparticle formation.

Cholesterol transport system: An integrated cholesterol transport model involved in atherosclerosis

Atherosclerosis, the pathological basis of most cardiovascular disease (CVD), is closely associated with cholesterol accumulation in the arterial intima. Excessive cholesterol is removed by the reverse cholesterol transport (RCT) pathway, representing a major antiatherogenic mechanism. In addition to the RCT, other pathways are required for maintaining the whole-body cholesterol homeostasis. Thus, we propose a working model of integrated cholesterol transport, termed the cholesterol transport system (CTS), to describe body cholesterol metabolism. The novel model not only involves the classical view of RCT but also contains other steps, such as cholesterol absorption in the small intestine, low-density lipoprotein uptake by the liver, and transintestinal cholesterol excretion. Extensive studies have shown that dysfunctional CTS is one of the major causes for hypercholesterolemia and atherosclerosis. Currently, several drugs are available to improve the CTS efficiently. There are also several therapeutic approaches that have entered into clinical trials and shown considerable promise for decreasing the risk of CVD. In recent years, a variety of novel findings reveal the molecular mechanisms for the CTS and its role in the development of atherosclerosis, thereby providing novel insights into the understanding of whole-body cholesterol transport and metabolism. In this review, we summarize the latest advances in this area with an emphasis on the therapeutic potential of targeting the CTS in CVD patients.

Epigenome-wide association study of adiposity and future risk of obesity-related diseases

BACKGROUND

Obesity is an established risk factor for several common chronic diseases such as breast and colorectal cancer, metabolic and cardiovascular diseases; however, the biological basis for these relationships is not fully understood. To explore the association of obesity with these conditions, we investigated peripheral blood leucocyte (PBL) DNA methylation markers for adiposity and their contribution to risk of incident breast and colorectal cancer and myocardial infarction.

METHODS

DNA methylation profiles (Illumina Infinium® HumanMethylation450 BeadChip) from 1941 individuals from four population-based European cohorts were analysed in relation to body mass index, waist circumference, waist-hip and waist-height ratio within a meta-analytical framework. In a subset of these individuals, data on genome-wide gene expression level, biomarkers of glucose and lipid metabolism were also available. Validation of methylation markers associated with all adiposity measures was performed in 358 individuals. Finally, we investigated the association of obesity-related methylation marks with breast, colorectal cancer and myocardial infarction within relevant subsets of the discovery population.

RESULTS

We identified 40 CpG loci with methylation levels associated with at least one adiposity measure. Of these, one CpG locus (cg06500161) in ABCG1 was associated with all four adiposity measures (P = 9.07×10-8 to 3.27×10-18) and lower transcriptional activity of the full-length isoform of ABCG1 (P = 6.00×10-7), higher triglyceride levels (P = 5.37×10-9) and higher triglycerides-to-HDL cholesterol ratio (P = 1.03×10-10). Of the 40 informative and obesity-related CpG loci, two (in IL2RB and FGF18) were significantly associated with colorectal cancer (inversely, P < 1.6×10-3) and one intergenic locus on chromosome 1 was inversely associated with myocardial infarction (P < 1.25×10-3), independently of obesity and established risk factors.

CONCLUSION

Our results suggest that epigenetic changes, in particular altered DNA methylation patterns, may be an intermediate biomarker at the intersection of obesity and obesity-related diseases, and could offer clues as to underlying biological mechanisms.