Intracellular Cholesterol Efflux Research Articles

Exposure to lipid mixture induces intracellular lipid droplet formation and impairs mitochondrial functions in astrocytes

Astrocytes, the predominant glial cells in the central nervous system (CNS), play diverse roles including metabolic support for neurons, provision of neurotrophic factors, facilitation of synaptic neurotransmitter uptake, regulation of ion balance, and involvement in synaptic formation. The accumulation of lipids has been noted in various neurological conditions, yet the response of astrocytes to lipid-rich environments remains unclear. In this study, primary astrocytes isolated from the neonatal rat cortex were exposed to a lipid mixture (LM) comprising cholesterol and various fatty acids to explore their reaction. Our results showed that astrocyte viability remained unchanged following 24 h of 5% or 10% LM treatment. However, exposure to LM for 96 h resulted in reduced cell viability. In addition, LM treatment led to the accumulation of lipid droplets (LDs) in astrocytes, with LD size increasing over prolonged exposure periods. Following 24 h of LM treatment and then 48 h in fresh medium, a significant reduction in intracellular LD size was observed in cultures treated with 5% LM, while no change occurred in cultures exposed to 10% LM. Yet, exposure to 10% LM for 24 h significantly increased the expression of the cholesterol efflux regulatory protein/ATP-binding cassette transporter (ABCA1) gene, responsible for intracellular cholesterol efflux, resulting in reduced cholesterol content within astrocytes. Moreover, LM exposure led to decreased mitochondrial membrane potential (MMP) and increased levels of mature apoptosis-inducing factor (AIF). The smaller LDs were observed to co-localize with microtubule-associated protein 1A/1 B light chain 3 B (LC3) and lysosomal-associated membrane protein-1 (LAMP-1) in LM-treated astrocytes, coinciding with lysosomal acidification. These results indicate that the continuous buildup of LDs in astrocytes residing in lipid-enriched environments may be attributed to disruptions caused by LM in mitochondrial and lysosomal functions. Such disruptions could potentially impede the supportive role of astrocytes in neuronal function.

The role of ATP-binding cassette subfamily G member 1 in tumor progression.

ATP-binding cassette subfamily G member 1 is mostly known as a transporter for intracellular cholesterol efflux, and a number of studies indicate that ABCG1 also functions actively in tumor initiation and progression. This review aimed to provide an overall review of how ABCG1 acts in tumor progression. A comprehensive searching about ABCG1 and tumor was conducted up to November 2023 using proper keywords through databases including PubMed and Web of Science. Overall, ABCG1 plays a crucial role in the development of multiple tumorigenesis. ABCG1 enhances tumor-promoting ability through conferring stem-like properties to cancer cells and mediates chemoresistance in multiple cancers. Additionally, ABCG1 may act as a kinase to phosphorylate downstream molecules and induces tumor growth. In tumor microenvironment, ABCG1 plays a substantial role in immunity response through macrophages to create a tumor-favoring circumstance. High expression of ABCG1 is usually associated with poor prognosis, which means ABCG1 may be a potential biomarker for early diagnosis and prognosis of various cancers. ABCG1-targeted therapy may provide a novel treatment for cancer patients.

Inflammatory corpuscle AIM2 facilitates macrophage foam cell formation by inhibiting cholesterol efflux protein ABCA1

The inflammatory corpuscle recombinant absents in melanoma 2 (AIM2) and cholesterol efflux protein ATP binding cassette transporter A1(ABCA1) have been reported to play opposing roles in atherosclerosis (AS) plaques. However, the relationship between AIM2 and ABCA1 remains unclear. In this study, we explored the potential connection between AIM2 and ABCA1 in the modulation of AS by bioinformatic analysis combined with in vitro experiments. The GEO database was used to obtain AS transcriptional profiling data; screen differentially expressed genes (DEGs) and construct a weighted gene co-expression network analysis (WGCNA) to obtain AS-related modules. Phorbol myristate acetate (PMA) was used to induce macrophage modelling in THP-1 cells, and ox-LDL was used to induce macrophage foam cell formation. The experiment was divided into Negative Control (NC) group, Model Control (MC) group, AIM2 overexpression + ox-LDL (OE AIM2 + ox-LDL) group, and AIM2 short hairpin RNA + ox-LDL (sh AIM2 + ox-LDL) group. The intracellular cholesterol efflux rate was detected by scintillation counting; high-performance liquid chromatography (HPLC) was used to detect intracellular cholesterol levels; apoptosis levels were detected by TUNEL kit; levels of inflammatory markers (IL-1β, IL-18, ROS, and GSH) were detected by ELISA kits; and levels of AIM2 and ABCA1 proteins were detected by Western blot. Bioinformatic analysis revealed that the turquoise module correlated most strongly with AS, and AIM2 and ABCA1 were co-expressed in the turquoise module with a trend towards negative correlation. In vitro experiments demonstrated that AIM2 inhibited macrophage cholesterol efflux, resulting in increased intracellular cholesterol levels and foam cell formation. Moreover, AIM2 had a synergistic effect with ox-LDL, exacerbating macrophage oxidative stress and inflammatory response. Silencing AIM2 ameliorated the above conditions. Furthermore, the protein expression levels of AIM2 and ABCA1 were consistent with the bioinformatic analysis, showing a negative correlation. AIM2 inhibits ABCA1 expression, causing abnormal cholesterol metabolism in macrophages and ultimately leading to foam cell formation. Inhibiting AIM2 may reverse this process. Overall, our study suggests that AIM2 is a reliable anti-inflammatory therapeutic target for AS. Inhibiting AIM2 expression may reduce foam cell formation and, consequently, inhibit the progression of AS plaques.

Role of ABCA1 in Atherosclerosis: Novel Mutations and Potential Plant-derived Therapies.

ATP-binding cassette transporter A1 (ABCA1) is one of the key proteins regulating cholesterol homeostasis and playing a crucial role in atherosclerosis development. ABCA1 regulates the rate-limiting step of reverse cholesterol transport, facilitates the efflux of surplus intracellular cholesterol and phospholipids, and suppresses inflammation through several signalling pathways. At the same time, many mutations and Single Nucleotide Polymorphisms (SNPs) have been identified in the ABCA1 gene, which affects its biological function and is associated with several hereditary diseases (such as familial hypo-alpha-lipoproteinaemia and Tangier disease) and increased risk of cardiovascular diseases (CVDs). This review summarises recently identified mutations and SNPs in their connection to atherosclerosis and associated CVDs. Also, we discuss the recently described application of various plant-derived compounds to modulate ABCA1 expression in different in vitro and in vivo models. Herein, we present a comprehensive overview of the association of ABCA1 mutations and SNPs with CVDs and as a pharmacological target for different natural-derived compounds and highlight the potential application of these phytochemicals for treating atherosclerosis through modulation of ABCA1 expression.

Effect of Moringa oleifera on semen quality profiles in endangered Teressa goat under tropical humid island ecosystem

Objective: To investigate the effect of Moringa oleifera leaf extract on semen quality parameters in Teressa goat buck. Methods: A total of 25 semen samples from six bucks were selected for the study. Spermatozoa of 150× 106 were incubated in 0, 300, 500 and 700 μg of leaf extract as group I, II, III and IV, respectively. Liquid stored semen samples were analysed for motility, viability, total sperm abnormalities, plasma membrane, acrosomal and nuclear integrities, seminal plasma intracellular enzymes [aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH)] and total antioxidant capacity (TAC) and spermatozoa malondialdehyde (MDA) and cholesterol efflux in comparison with the control group (group I) for up to 72 h. Results: Moringa oleifera leaf extract (500 μg/150× 106 spermatozoa)-treated semen had significantly higher motility, viability, plasma membrane, acrosomal and nuclear integrities, and TAC (P<0.05), and had significantly lower total sperm abnormalities, AST, ALT, LDH, MDA production and cholesterol efflux compared to those in other Moringa oleifera leaf extract treated (300 or 700 μg/150×106 spermatozoa) and control groups at different hours of liquid storage (P<0.05). Semen quality parameters and TAC showed an increasing trend and total sperm abnormalities, MDA production, leakage of intra-cellular enzymes and cholesterol efflux showed a decreasing trend from group I to group III and then an opposite trend from group II to group IV at different hours of liquid storage. Conclusions: Moringa oleifera leaf extract 500 μg/150×106 spermatozoa can be used for liquid semen preservation in Teressa goat at Andaman and Nicobar Islands.

Retinoid X receptor gamma dictates the activation threshold of group 2 innate lymphoid cells and limits type 2 inflammation in the small intestine

Group 2 innate lymphoid cells (ILC2s) are crucial in promoting type 2 inflammation that contributes to both anti-parasite immunity and allergic diseases. However, the molecular checkpoints in ILC2s that determine whether to immediately launch a proinflammatory response are unknown. Here, we found that retinoid X receptor gamma (Rxrg) was highly expressed in small intestinal ILC2s and rapidly suppressed by alarmin cytokines. Genetic deletion of Rxrg did not impact ILC2 development but facilitated ILC2 responses and the tissue inflammation induced by alarmins. Mechanistically, RXRγ maintained the expression of its target genes that support intracellular cholesterol efflux, which in turn reduce ILC2 proliferation. Furthermore, RXRγ expression prevented ILC2 response to mild stimulations, including low doses of alarmin cytokine and mechanical skin injury. Together, we propose that RXRγ expression and its mediated lipid metabolic states function as a cell-intrinsic checkpoint that confers the threshold of ILC2 activation in the small intestine.

Saikosaponins ameliorate hyperlipidemia in rats by enhancing hepatic lipid and cholesterol metabolism

Ethnopharmacological relevanceHyperlipidemia is the systemic manifestation of abnormal lipid metabolism, characterized by elevated circulating levels of cholesterol and triglyceride and a high risk of cardiovascular events. Radix Bupleuri (RB) is a traditional Chinese herbal product used to treat liver diseases. Our previous study demonstrated that Saikosaponins (SSs), the most potent bioactive ingredients in RB, ameliorate hepatic steatosis. However, whether SSs have anti-hyperlipidemia effects and plausible underlying mechanisms remain elusive. Aim of the studyTo comprehensively evaluate the lipid-lowering potential of SSs against hyperlipidemia in rats. Materials and methodsRNA sequencing and untargeted metabolomics approaches were applied to analyze the changes in the liver transcriptome and serum lipid profile in long-term high-fat diet feeding-induced hyperlipidemia rats in response to SSs or positive drug simvastatin (SIM) intervention. ResultsOur data revealed that SSs significantly alleviated HFD-induced hypertriglyceridemia and hypercholesterolemia. Combined with the analysis of gene ontology enrichment analysis and gene set enrichment analysis, we found that SSs remarkably repaired the unbalanced blood lipid metabolic spectrum in a dose-dependent manner by increasing the hepatic uptake of circulating fatty acids and facilitating mitochondrial respiration in fatty acid oxidation, comparable to SIM group. In addition, SSs markedly modulated cholesterol clearance by promoting intracellular cholesterol efflux, HDL remodeling, LDL particle clearance, and bile acid synthesis. SSs also efficiently protected the liver from lipid overload-related oxidative stress and lipid peroxidation, as well as substantially exaggerated inflammatory response. ConclusionOur research not only unraveled the intricate mechanisms underlying the lipid-lowering functions of SSs but also provided novel perspectives on developing an SSs-based therapeutic strategy for the treatment of hyperlipidemia. ClassificationMetabolism.

Transcriptome Analysis of PC12 Cells Reveals That <i>trans</i>-Banglene Upregulates <i>RT1-CE1</i> and Downregulates <i>abca1</i> in the Neurotrophic Pathway

trans-Banglene and cis(c)-banglene possess neurotrophin-like activity in rat neurons. However, the molecular mechanisms underlying t-banglene-induced neurotrophic activity in rat and human neurons remain unclear. Here, we performed transcriptome analysis in PC12 cells, a rat adrenal gland pheochromocytoma cell line treated with t-banglene, using comprehensive RNA sequencing. The differentially expressed gene analysis of the sequencing data revealed that the expression of RT1 class I, locus CE1 (RT1-CE1) was upregulated, and that of ATP binding cassette subfamily A member 1 (abca1), myosin light chain 6, and hippocampus abundant transcript 1 was downregulated in t-banglene-treated PC12 cells, with statistically significant differences. We also confirmed the RT1-CE1 upregulation and abca1 downregulation in t-banglene-treated PC12 cells by real-time reverse transcription quantitative PCR. RT1-CEl is a major histocompatibility complex class I (MHCI) protein. ABCAl is a major cholesterol transporter that regulates efflux of intracellular cholesterol and phospholipids. Thus, our results suggest an exciting link between MHCI, cholesterol regulation, and neural development.

Tetramethylpyrazine and Paeoniflorin Synergistically Attenuate Cholesterol Efflux in Macrophage Cells via Enhancing ABCA1 and ABCG1 Expression.

The formation of foam cells is a characteristic of the occurrence and development of atherosclerosis. ATP-binding cassette subfamily A1 and G1 (ABCA1 and ABCG1) and scavenger receptor B1 (SR-B1) play critical roles in promoting intracellular cholesterol efflux to high-density lipoprotein (HDL) or apolipoprotein A1 (apoA1). We attempted to test the effect of the tetramethylpyrazine-paeoniflorin pair (TP) on cholesterol outflow in foam cells derived from macrophages. In this study, RAW264.7 macrophages were treated with 80 mg/L oxidized low-density lipoprotein (ox-LDL) for 24 h to obtain foam cells. Then they were intervened with TP (tetramethylpyrazine 40 ug/ml plus paeoniflorin 80 ug/ml) for additional 24 h. The distribution of cholesterol in foam cells was evaluated by oil red O staining. The contents of total cholesterol (TC) and free cholesterol (FC) were assessed with commercial kits. Fluorescent imaging was observed with a fluorescent inverted microscope. The capacity of cholesterol efflux was measured with a fluorescent plate reader, and the transcript and protein levels of ABCA1, ABCG1, and SR-B1 were detected by Western blot and quantitative polymerase chain reactions (Q-PCRs). Cytokines in the medium were detected by ELISA and adjusted by total cellular proteins. The results showed that TP decreased ox-LDL-induced cholesterol deposition and foam cell formation by promoting cholesterol efflux to apoA1, which was related to the upregulation of ABCA1 and ABCG1. Moreover, TP decreased the secretion of ox-LDL-induced tumor necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1β), and monocyte chemotactic protein-1 (MCP-1), an important profoam cell cytokine in atherosclerosis.

Role of ABCA1 in Cardiovascular Disease.

Cholesterol homeostasis plays a significant role in cardiovascular disease. Previous studies have indicated that ATP-binding cassette transporter A1 (ABCA1) is one of the most important proteins that maintains cholesterol homeostasis. ABCA1 mediates nascent high-density lipoprotein biogenesis. Upon binding with apolipoprotein A-I, ABCA1 facilitates the efflux of excess intracellular cholesterol and phospholipids and controls the rate-limiting step of reverse cholesterol transport. In addition, ABCA1 interacts with the apolipoprotein receptor and suppresses inflammation through a series of signaling pathways. Thus, ABCA1 may prevent cardiovascular disease by inhibiting inflammation and maintaining lipid homeostasis. Several studies have indicated that post-transcriptional modifications play a critical role in the regulation of ABCA1 transportation and plasma membrane localization, which affects its biological function. Meanwhile, carriers of the loss-of-function ABCA1 gene are often accompanied by decreased expression of ABCA1 and an increased risk of cardiovascular diseases. We summarized the ABCA1 transcription regulation mechanism, mutations, post-translational modifications, and their roles in the development of dyslipidemia, atherosclerosis, ischemia/reperfusion, myocardial infarction, and coronary heart disease.

Expression of SR-BI and LXRα in Macrophage Origin Foam Cells of Mouse RAW264.7 Up-regulated by Astragalus Polysaccharide.

Objective To investigate the influences of Astragalus polysaccharides (APS) on the expressions of SR-BI(Scavenger receptor-BI) and LXR α in RAW264.7 macrophage origin foam cells. Methods Mouse RAW264.7 cells were induced in foam cells and identification of the foamed by oil-red O staining. The RAW264.7 macrophage origin foam cells were dealt with APS with distinct contents (0, 10, 20, 50, or 100 mg/L). The mRNA and protein expressions of SR-BI and LXRα were measured by RT-PCR as well as ELISA, respectively. Results Macrophages were differentiated into foam cells 48 h after ox-LDL induction. In contrast to the control part, the mRNA and protein expressions of SR-BI and LXRα in RAW264.7 macrophage origin foam cells were up-regulated dosage-dependently after being treated with different concentrations of APS (P < 0.05). Conclusion APS could promote intracellular cholesterol efflux by up-regulating the expressions of SR-BI and LXR α of RAW264.7 cells.

AICAR upregulates ABCA1/ABCG1 expression in the retinal pigment epithelium and reduces Bruch's membrane lipid deposit in ApoE deficient mice

The etiology of age-related macular degeneration (AMD) is diverse; however, recent evidence suggests that the lipid metabolism-cholesterol pathway might be associated with the pathophysiology of AMD. The ATP-binding cassette (ABC) transporters, ABCA1 and ABCG1, are essential for the formation of high-density lipoprotein (HDL) and the regulation of macrophage cholesterol efflux. The failure of retinal or retinal pigment epithelium (RPE) cholesterol efflux to remove excess intracellular lipids causes morphological and functional damage to the retina. In this study, we investigated whether treatment with 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR), an AMP-activated protein kinase (AMPK) activator, improves RPE cholesterol efflux and Bruch's membrane (BM) lipid deposits. The protein and mRNA levels of ABCA1 and ABCG1 in ARPE-19 cells and retinal and RPE/choroid tissue from apolipoprotein E-deficient (ApoE-/-) mice were evaluated after 24 weeks of AICAR treatment. The cholesterol efflux capacity of ARPE-19 cells and the cholesterol-accepting capacity of apoB-depleted serum from mice were measured. The thickness of the BM and the degree of lipid deposition were evaluated using electron microscopy. AICAR treatment increased the phosphorylation of AMPK and the protein and mRNA expression of ABCA1 and ABCG1 in vitro. It promoted cholesterol efflux from ARPE-19 cells and upregulated the protein and mRNA levels of ABCA1 and ABCG1 in the retina and RPE in vivo. ApoB-depleted serum from the AICAR-treated group showed enhanced cholesterol-accepting capacity. Long-term treatment with AICAR reduced BM thickening and lipid deposition in ApoE-/- mice. In conclusion, AICAR treatment increased the expression of lipid transporters in the retina and RPE in vivo, facilitated intracellular cholesterol efflux from the RPE in vitro, and improved the functionality of HDL to accept cholesterol effluxed from the cell, possibly via AMPK activation. Collectively, these effects might contribute to the improvement of early age-related pathologic changes in the BM. Pharmacological improvement of RPE cholesterol efflux via AMPK activation may be a potential treatment strategy for AMD.

Berberine attenuates atherosclerotic lesions and hepatic steatosis in ApoE-/- mice by down-regulating PCSK9 via ERK1/2 pathway.

BackgroundIt has been demonstrated that berberine (BBR), a kind of alkaloid derived from Chinese herbal medicine, has multiple pharmacological effects on human’s diseases including anti-atherosclerosis action. However, although the previous studies showed that the beneficial impact of BBR on atherosclerosis might be associated with proprotein convertase subtilisin/kexin type 9 (PCSK9), the exact underlying mechanism are not fully determined. The present study aimed to investigate potential mechanisms of anti-atherosclerosis by BBR using ApoE-/- mice.MethodsThe eight-week mice were divided into five groups: group 1 (wild type C57BL/6J mice with normal diet), group 2 (ApoE-/- mice with normal diet), group 3 [ApoE-/- mice with high-fat diet (HFD)], group 4 (ApoE-/- mice with HFD, and treatment with low dose BBR of 50 mg/kg/d), and group 5 (ApoE-/- mice with HFD, and treatment with high dose BBR of 100 mg/kg/d). After a 16-week treatment, the blood sample, aorta and liver were collected for lipid analysis, hematoxylin-eosin (HE) or oil red O staining, and Western blotting respectively. Besides, HepG2 Cells were cultured and treated with different concentrations of BBR (0, 5, 25 and 50 µg/mL) for 24 hours. Subsequently, cells were collected for real-time PCR or western blotting assays. Finally, the expression levels of PCSK9, LDL receptor (LDLR), ATP-binding cassette transporter A1 (ABCA1), ATP-binding cassette transporter G1 (ABCG1), and scavenger receptor class B type I (SR-BI) were examined.ResultsFifty mg/kg/d and 100 mg/kg/d of BBR decreased total cholesterol (TC), triglyceride (TG), low-density lipoprotein (LDL) cholesterol (LDL-C), and increased high-density lipoprotein cholesterol (HDL-C) level. Moreover, BBR reduced aorta atherosclerotic plaque, and ameliorated lipid deposition in ApoE-/- mice fed with HFD. Finally, in vitro study showed that BBR promoted intracellular cholesterol efflux, up-regulated LDLR and down-regulated PCSK9 expression via the ERK1/2 pathway in cultured HepG2 cells.ConclusionsData indicated that BBR significantly attenuated lipid disorder, reduced aortic plaque formation, and alleviated hepatic lipid accumulation in ApoE-/- mice fed with HFD, which was associated with down-regulation of PCSK9 through ERK1/2 pathway.

Morroniside Promotes PGC-1α-Mediated Cholesterol Efflux in Sodium Palmitate or High Glucose-Induced Mouse Renal Tubular Epithelial Cells.

Lipid deposition is an etiology of renal damage caused by lipid metabolism disorder in diabetic nephropathy (DN). Thus, reducing lipid deposition is a feasible strategy for the treatment of DN. Morroniside (MOR), an iridoid glycoside isolated from the Chinese herb Cornus officinalis Sieb. et Zucc., is considered to be an effective drug in inhibiting oxidative stress, reducing inflammatory response, and countering apoptosis. To explore the protective mechanism of MOR in attenuating renal lipotoxicity in DN, we investigated the effect of MOR on an in vitro model of lipid metabolism disorder of DN established by stimulating mouse renal tubular epithelial cells (mRTECs) with sodium palmitate (PA) or high glucose (HG). Oil Red O and filipin cholesterol staining assays were used to determine intracellular lipid accumulation status. Results revealed that PA or HG stimulation inhibited the expressions of peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), liver X receptors (LXR), ATP-binding cassette subfamily A member 1 (ABCA1), ABCG1, and apolipoprotein E (ApoE) in mRTECs as evidenced by western blot and quantitative real-time PCR, resulting in increased intracellular lipid deposition. Interestingly, MOR upregulated expressions of PGC-1α, LXR, ABCA1, ABCG1, and ApoE, thus reducing cholesterol accumulation in mRTECs, suggesting that MOR might promote cholesterol efflux from mRTECs via the PGC-1α/LXR pathway. Of note, silencing PGC-1α reversed the promotive effect of MOR on PA- or HG-induced cellular cholesterol accumulation. In conclusion, our results suggest that MOR has a protective effect on mRTECs under high lipid or high glucose conditions, which may be related to the promotion of intracellular cholesterol efflux mediated by PGC-1α.

Targeting HDL in tumor microenvironment: New hope for cancer therapy.

Epidemiological studies have shown that plasma HDL-C levels are closely related to the risk of prostate cancer, breast cancer, and other malignancies. As one of the key carriers of cholesterol regulation, high-density lipoprotein (HDL) plays an important role in tumorigenesis and cancer development through anti-inflammation, antioxidation, immune-modulation, and mediating cholesterol transportation in cancer cells and noncancer cells. In addition, the occurrence and progression of cancer are closely related to the alteration of the tumor microenvironment (TME). Cancer cells synthesize and secrete a variety of cytokines and other factors to promote the reprogramming of surrounding cells and shape the microenvironment suitable for cancer survival. By analyzing the effect of HDL on the infiltrating immune cells in the TME, as well as the relationship between HDL and tumor-associated angiogenesis, it is suggested that a moderate increase in the level of HDL in vivo with consequent improvement of the function of HDL in the TME and induction of intracellular cholesterol efflux may be a promising strategy for cancer therapy.

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.

Melatonin activates ABCA1 via the BiP/NRF1 pathway to suppress high-cholesterol-induced apoptosis of mesenchymal stem cells

BackgroundRetarded wound healing in patients with obesity contributes to a risk of complications associated with vascular insufficiency and oxidative stress. The high cholesterol levels of patients with obesity are associated with apoptosis of engrafted umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs). Melatonin contributes to the prevention of cholesterol accumulation in patients with obesity via a mechanism that is poorly understood. We therefore investigated the regulatory mechanism of melatonin in cholesterol-induced apoptosis.MethodsThe protective effects of melatonin on cholesterol-induced apoptosis were investigated in UCB-MSCs. We used a mouse model of induced obesity to show that melatonin treatment restored the survival rate of transplanted UCB-MSCs and their wound-healing capacity. The mean values of the treatment groups were compared with those of the control group using Student’s t test, and differences among three or more groups were analyzed using one-way analysis of variance with Dunnett’s multiple comparison test.ResultsMelatonin treatment increased the expression of ATP-binding cassette subfamily A member 1 (ABCA1), which reduced cholesterol accumulation and cholesterol-induced apoptosis. The mouse skin wound healing model showed that melatonin treatment restored the survival rate of transplanted UCB-MSCs and the wound-healing capacity of obese mice. Melatonin inhibited the expression of binding immunoglobulin protein (BiP) through the regulation of MT2/Sp1-dependent microRNA-597-5p. Melatonin decreased the co-localization of BiP with nuclear factor erythroid 2-related factor 1 (NRF1), which resulted in increased ABCA1 expression.ConclusionMelatonin induced the efflux of intracellular cholesterol through ABCA1 to decrease apoptosis of UCB-MSCs via an MT2-dependent BiP/NRF1 pathway.

ABCG1 Attenuates Oxidative Stress Induced by H2O2 through the Inhibition of NADPH Oxidase and the Upregulation of Nrf2-Mediated Antioxidant Defense in Endothelial Cells

Summary. Oxidative stress is an important factor that is related to endothelial dysfunction. ATP-binding cassette transporter G1 (ABCG1), a regulator of intracellular cholesterol efflux, has been found to prevent endothelial activation in vessel walls. To explore the role of ABCG1 in oxidative stress production in endothelial cells, HUAECs were exposed to H2O2 and transfected with the specific ABCG1 siRNA or ABCG1 overexpression plasmid. The results showed that overexpression of ABCG1 by ABCG1 plasmid or liver X receptor (LXR) agonist T0901317 treatment inhibited ROS production and MDA content induced by H2O2 in HUAECs. Furthermore, ABCG1 upregulation blunted the activity of prooxidant NADPH oxidase and the expression of Nox4, one of the NADPH oxidase subunits. Moreover, the increased migration of Nrf2 from the cytoplasm to the nucleus and antioxidant HO-1 expression were detected in HUAECs with upregulation of ABCG1. Conversely, ABCG1 downregulation by ABCG1 siRNA increased NADPH oxidase activity and Nox4 expression and abrogated the increase at Nrf2 nuclear protein levels. In addition, intracellular cholesterol load interfered with the balance between NADPH oxidase activity and HO-1 expression. It was suggested that ABCG1 attenuated oxidative stress induced by H2O2 in endothelial cells, which might be involved in the balance between decreased NADPH oxidase activity and increased Nrf2/OH-1 antioxidant defense signaling via its regulation for intracellular cholesterol accumulation.

Over-activation of NMDA receptors promotes ABCA1 degradation and foam cell formation

ATP-binding cassette transporter A1 (ABCA1) is an essential regulator of intracellular cholesterol efflux. Secreted cholesterol binds to lipid-free apolipoprotein A-I (apoA-I) in peripheral blood to constitute high-density lipoprotein cholesterol (HDL) complexes. ABCA1 protein on the surface of macrophages acts as a crucial controller in preventing cholesterol accumulation. Importantly, ABCA1 is unstable and easily degraded via a series of biochemical activities, including but not limited to calpain-mediated and ubiquitin-proteasome system-mediated processes. How accelerated ABCA1 degradation impacts disordered lipid metabolism in macrophages and foam cell formation is unclear. N-methyl d-aspartate receptors (NMDARs) are ionotropic glutamate receptors with high calcium permeability. Calcium influx via NMDARs activates downstream signaling pathways. Over-activation of NMDARs stimulated by NMDA contributes to dysfunctional lipid metabolism in macrophages and foam cell formation via promotion of calpain-mediated ABCA1 proteolysis. However, increased NMDAR activity does not affect liver X receptor expression or ABCA1 mRNA levels. Following NMDA receptor silencing or calpain inhibition, NMDA treatment did not reduce ABCA1 protein levels, nor caused lipid accumulation in macrophages. In addition, NMDAR over-activation activates NF-κB signaling to promote IL-1β and IL-6 macrophage marker expression. However, NMDAR silencing and calpain inhibition reduce inflammatory macrophage responses. In summary, our study suggests that NMDAR activation reduces surface ABCA1 protein, promotes lipid accumulation, and induces the production and secretion of many inflammatory mediators in macrophages, possibly through enhanced calpain-mediated ABCA1 protein degradation. Thus, the NMDAR receptor may be a novel pharmacologic target for atherosclerosis therapy.

Correlates and Predictors of Cerebrospinal Fluid Cholesterol Efflux Capacity from Neural Cells, a Family of Biomarkers for Cholesterol Epidemiology in Alzheimer's Disease.

Basic research has implicated intracellular cholesterol in neurons, microglia, and astrocytes in the pathogenesis of Alzheimer's disease (AD), but there is presently no assay to access intracellular cholesterol in neural cells in living people in the context of AD. To devise and characterize an assay that can access intracellular cholesterol and cholesterol efflux in neural cells in living subjects. We modified the protocol for high-density lipoprotein cholesterol efflux capacity (CEC) from macrophages, a biomarker that accesses cholesterol in macrophages in atherosclerosis. To measure cerebrospinal fluid (CSF) CECs from neurons, microglia, and astrocytes, CSF was exposed to, correspondingly, neuronal, microglial, and astrocytic cholesterol source cells. Human neuroblastoma SH-SY5Y, mouse microglial N9, and human astroglial A172 cells were used as the cholesterol source cells. CSF samples were screened for contamination with blood. CSF CECs were measured in a small cohort of 22 individuals. CSF CECs from neurons, microglia, and astrocytes were moderately to moderately strongly correlated with CSF concentrations of cholesterol, apolipoprotein A-I, apolipoprotein E, and clusterin (Pearson's r = 0.53-0.86), were in poor agreement with one another regarding CEC of the CSF samples (Lin's concordance coefficient rc = 0.71-0.76), and were best predicted by models consisting of, correspondingly, CSF phospholipid (R2 = 0.87, p < 0.0001), CSF apolipoprotein A-I and clusterin (R2 = 0.90, p < 0.0001), and CSF clusterin (R2 = 0.62, p = 0.0005). Characteristics of the CSF CEC metrics suggest a potential for independent association with AD and provision of fresh insight into the role of cholesterol in AD pathogenesis.