Scavenger Receptor B1 Expression Research Articles

Cav3.1 T-type calcium channel blocker NNC 55-0396 reduces atherosclerosis by increasing cholesterol efflux

Calcium channel blockers (CCBs) are commonly used as antihypertensive agents. While certain L-type CCBs exhibit antiatherogenic effects, the impact of Cav3.1 T-type CCBs on antiatherogenesis and lipid metabolism remains unexplored. NNC 55–0396 (NNC) is a highly selective blocker of T-type calcium channels (Cav3.1 channels). We investigated the effects of NNC on relevant molecules and molecular mechanisms in human THP-1 macrophages. Cholesterol efflux, an indicator of reverse cholesterol transport (RCT) efficiency, was assessed using [3H]-labeled cholesterol. In vivo, high cholesterol diet (HCD)-fed LDL receptor knockout (Ldlr-/-) mice, an atherosclerosis-prone model, underwent histochemical staining to analyze plaque burden. Treatment of THP-1 macrophages with NNC facilitated cholesterol efflux and reduced intracellular cholesterol accumulation. Pharmacological and genetic interventions demonstrated that NNC treatment or Cav3.1 knockdown significantly enhanced the protein expression of scavenger receptor B1 (SR-B1), ATP-binding cassette transporter A1 (ABCA1), ATP-binding cassette transporter G1 (ABCG1), and liver X receptor alpha (LXRα) transcription factor. Mechanistic analysis revealed that NNC activates p38 and c-Jun N-terminal kinase (JNK) phosphorylation, leading to increased expression of ABCA1, ABCG1, and LXRα-without involving the microRNA pathway. LXRα isrequired for NNC–induced ABCA1 and ABCG1 expression. Administering NNC diminished atherosclerotic lesion area and lipid deposition in HCD-fed Ldlr-/- mice. NNC's anti-atherosclerotic effects, achieved through enhanced cholesterol efflux and inhibition of lipid accumulation, suggest a promising therapeutic approach for hypertensive patients with atherosclerosis. This research highlights the potential of Cav3.1 T-type CCBs in addressing cardiovascular complications associated with hypertension.

Abstract IA020: Exploiting cholesterol metabolism for treatment resistant ccRCC patients

Abstract Clear cell renal cell carcinoma (ccRCC) is characterized by large intracellular lipid droplets (LDs) comprised primarily of free and esterified cholesterol molecules; however, the functional significance of cholesterol accumulation in ccRCC cells was unknown. We demonstrated that, surprisingly, genes encoding cholesterol biosynthetic pathway enzymes are strongly repressed in ccRCC cells, making them auxotrophic for exogenous cholesterol. Intriguingly, Mendelian randomization analyses of over 31,000 human genomes indicate a causal link between elevated serum levels of high-density lipoprotein (HDL) cholesterol and ccRCC risk. Depriving ccRCC cells of either cholesterol or HDL compromises proliferation and survival in vitro and ccRCC tumor growth in vivo; in contrast, elevated dietary cholesterol promotes tumor growth. We showed that Scavenger Receptor B1 (SCARB1) is uniquely required for cholesterol import by ccRCC cells, and inhibiting SCARB1 expression or activity is sufficient to cause ccRCC cell cycle arrest and apoptosis accompanied by elevated intracellular reactive oxygen species (ROS) levels and decreased PI3K/AKT signaling. Collectively, our data reveal a previously unrecognized cholesterol dependency in ccRCC and implicate SCARB1 as a therapeutic target that may contribute to novel strategies for treating kidney cancer. Citation Format: M. Celeste Simon. Exploiting cholesterol metabolism for treatment resistant ccRCC patients [abstract]. In: Proceedings of the AACR Special Conference: Advances in Kidney Cancer Research; 2023 Jun 24-27; Austin, Texas. Philadelphia (PA): AACR; Cancer Res 2023;83(16 Suppl):Abstract nr IA020.

Synthetic Lipid Nanoparticles Actively Target Acute Myeloid Leukemia (AML) Cells and Induce Ferroptosis through Decreased Expression of Glutathione Peroxidase 4

Introduction: Relapsed and refractory AML patients have a 30% 5-year overall survival (SEER 2012-2018). We found that certain cancer cells that are highly dependent on cholesterol uptake and express the high-affinity receptor for cholesterol-rich high-density lipoproteins (HDL), scavenger receptor type B-1 (SR-B1), also highly express the redox enzyme, glutathione peroxidase 4 (GPX4) (Rink et al 2020). GPX4 has been shown to detoxify lipid peroxides in cancer cells and prevent cell death through ferroptosis, an iron-dependent redox form of cell death. Using a synthetic lipid nanoparticle (Au-LNP) that actively targets SR-B1, we showed modulation of cancer cell cholesterol uptake and metabolism is accompanied by a reduction in GPX4 expression. As a result, Au-LNP therapy kills these cells via ferroptosis. In AML, high GPX4 expression is associated with worse overall survival (Akiyama et al. Blood 2021). Therefore, we hypothesized that high SR-B1 expression would enable Au-LNP to target AML cells, modulate cell cholesterol, and reduce GPX4 resulting in AML cell death by ferroptosis. Methods: GEPIA is an interactive web server that houses the RNA sequencing expression data from the TCGA and the GTEx projects. We selected the LAML database and interrogated the survival data using the top 25% and bottom 25% SR-B1 expression as cutoffs. The cell lines MV4-11 (biphenotypic B-myelomonocytic AML with translocation t(4;11) and FLT3-ITD mutation), HEL (erythroblast AML), and U937 (promonocytic AML) were used for these studies. Au-LNPs were synthesized by surface-functionalizing 5nm gold (Au) nanoparticles with apolipoprotein A-I and phospholipids. SR-B1 and GPX4 levels were measured by western blot and flow cytometry. Cell viability was measured using the MTS assay, annexin V/propidium iodide staining, and a colony forming assay. Colonies were counted by an automated microscope and analyzed with Fiji. Lipid oxidation levels were measured by a C11 BODIPY flow cytometry assay. Surface biomarker changes were measured by flow cytometry. Primary AML samples were obtained by collecting the buffy coat from peripheral blood samples from 2 patients with AML and isolating CD34 positive blasts (IRB# STU00208941). Results: In the LAML database in GEPIA, we found a significant survival detriment with high SR-B1 expression (75th percentile) when compared with low SR-B1 expression (25th percentile; p = 0.023; hazard ratio = 2.5) (Figure 1). SR-B1 expression was observed in all three AML cell lines tested (MV4-11, HEL, U937). Au-LNPs potently induced cell death in each cell line, with IC50s for MV4-11 (4.7 nM), HEL (0.8 nM), and U937 (4.6 nM) that were much lower than with cytarabine (535 nM, 259 nM, and 96 nM, respectively). In the colony forming assays, Au-LNPs significantly decreased MV4-11 colony counts compared with PBS control. By contrast, β-Hydroxy β-methylglutaryl-CoA (HMG-CoA) inhibitors, such as atorvastatin and rosuvastatin, had no effect on cell viability, with concentrations up to 50 µM. Au-LNPs reduced GPX4 expression in MV4-11 and HEL cells, leading to the accumulation of lipid peroxides by C11 BODIPY assay. Au-LNPs-induced cell death was prevented by the addition of the lipophilic antioxidant ferrostatin-1 and the iron chelator deferoxamine (DFO), supporting the hypothesis that Au-LNP-induced cell death occurred by ferroptosis. Low dose Au-LNPs increased expression of CD11c (dendritic cell marker), CD16 (monocyte marker), and CD24 (neutrophil marker) on MV4-11 cells, suggesting an increase in myeloid differentiation. Finally, we isolated CD34+ blasts from peripheral blood samples of two AML patients. Both patients’ blasts expressed SR-B1 as detected by flow cytometry, and Au-LNPs showed significant cell killing in both patient samples. Conclusion: We have demonstrated that Au-LNP target SR-B1, expressed by both AML cell lines and in primary AML samples, and induce cell death by ferroptosis resulting from depletion of GPX4. Future studies targeting the cholesterol scavenger receptor SR-B1 and investigating relevant resistance pathways and opportunities for synergy with available agents are indicated. Figure 1. Overall survival of AML patients in the LAML database stratified by scavenger receptor B1 expression. (Tang, Z. et al. (2017) GEPIA: a web server for cancer and normal gene expression profiling and interactive analyses. Nucleic Acids Res, 10.1093/nar/gkx247) Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Low High-Density Lipoprotein Cholesterol (HDL) Is a Significant Poor Prognostic Factor in Malignant Lymphoma

Objective: HDL is reportedly an independent prognostic factor in some malignant lymphoma (ML). We retrospectively analyzed the correlation between the prognosis of ML, including both Hodgkin's lymphoma (HL) and non-Hodgkin's lymphoma (NHL) and dyslipidemia in patient cases from our experience.Methods: Analyzed patients were; ML patients admitted to our hospital between April, 2009 and March, 2015. We excluded the patients who did not receive any treatments or were observed for less than two years after starting treatment. Dyslipidemia was defined as blood serum HDL, low-density lipoprotein cholesterol (LDL), and Triglyceride (TG) levels <40 mg/dL, >140 mg/dL, and >150 mg/dL, respectively. We performed statistically univariate and multivariate analyses.Results: Analyzed patients were: total 221 patients, median age of 68 (20-89), male 130 and female 91, B cell NHL 183, T/NK cell NHL 29, HL 8, and others 1, age under 60 62 and above 60 159, Performance Status (PS) 0-1 172 and 2-4 49, Ann Arbor classification I-II 48 and III-IV 173. 57 patients were deceased and 164 were alive at the analysis. The low HDL group (97 cases) showed a significantly shorter survival than high HDL group (124 cases; p = 0.0001), while there were no correlations between either high TG (38 cases) or high LDL (22 cases) and survival. In multivariate analysis, PS 2 or more, and low HDL were extracted as significant adverse prognostic factors.Discussion: The mechanisms of this correlation between survival of ML and low HDL level are still unclear. It is reported that inflammatory cytokines produced by ML cells may induce dyslipidemia. Because scavenger receptor-B1 with high affinity for HDL is highly expressed on ML cell-surface, it is possible that low HDL is correlated to the ML tumor-volume or fast tumor turnover. Since expression of scavenger receptor-B1 is low on normal lymphocytes, consumption of HDL may occur in ML. In this point there have been several attempts for treatment using HDL, such as an administration of HDL nanoparticle as a drug delivery vehicle in animal lymphoma-models. Thus, we will further investigate this correlation between HDL and ML with more patients and also study the mechanism. DisclosuresNo relevant conflicts of interest to declare.

Desmodium gyrans dc modulates lipid trafficking in cultured macrophages and improves functional high-density lipoprotein in male wistar rats.

OBJECTIVE:High-density lipoprotein (HDL) cholesterol-mediated atherosclerotic plaque regression has gained wide therapeutic attention. The whole plant methanolic extract of the medicinal plant Desmodium gyrans Methanolic Extract (DGM) has shown to mitigate hyperlipidemia in high fat- and-cholesterol fed rats and rabbits with significant HDL enhancing property. The study aimed to assess the functionality and mechanistic basis of HDL promoting effect of DGM.MATERIALS AND METHODS:Macrophage cholesterol efflux and foam cell formation assays were performed in THP-1 macrophages. Male Wistar rats were given DGM extract over 1 month and assessed the serum HDL, Apolipoprotein A1 (Apo-A1), and paraoxonase activity. Quantitative Polymerase chain reaction was carried out to assess the expression level of Apo-A1, SR-B1 (Scavenger receptor B1), and Cholesteryl ester transfer protein (CETP) on cDNA of HepG2 cells exposed to DGM.RESULTS:Pretreatment of DGM inhibited uptake of oxidized lipids and enhanced the lipid efflux by THP-1-derived macrophages. Oral administration of DGM (100 and 250 mg/kg) progressively enhanced the serum HDL, Apo-A1 level, and associated paraoxonase activity in normal male Wistar rats. In support to this, DGM exposed HepG2 cells documented dose-dependent increase in the expression of SR-B1 and Apo-A1 mRNA, while reduced the CETP expression.CONCLUSION:Overall the results indicated that DGM modulates lipid trafficking and possesses functional HDL enhancing potential through increased Apo-A1 levels and paraoxonase activity. Further, reduced CETP expression and increased expression of SR-B1 suggest the reverse cholesterol transport promoting role of DGM.

HDL (High-Density Lipoprotein) Remodeling and Magnetic Resonance Imaging-Assessed Atherosclerotic Plaque Burden: Study in a Preclinical Experimental Model.

HDL (high-density lipoprotein) role in atherosclerosis is controversial. Clinical trials with CETP (cholesterylester transfer protein)-inhibitors have not provided benefit. We have shown that HDL remodeling in hypercholesterolemia reduces HDL cardioprotective potential. We aimed to assess whether hypercholesterolemia affects HDL-induced atherosclerotic plaque regression. Approach and Results: Atherosclerosis was induced in New Zealand White rabbits for 3-months by combining a high-fat-diet and double-balloon aortic denudation. Then, animals underwent magnetic resonance imaging (basal plaque) and randomized to receive 4 IV infusions (1 infusion/wk) of HDL isolated from normocholesterolemic (NC-HDL; 75 mg/kg; n=10), hypercholesterolemic (HC-HDL; 75 mg/Kg; n=10), or vehicle (n=10) rabbits. Then, animals underwent a second magnetic resonance imaging (end plaque). Blood, aorta, and liver samples were obtained for analyses. Follow-up magnetic resonance imaging revealed that NC-HDL administration regressed atherosclerotic lesions by 4.3%, whereas, conversely, the administration of HC-HDLs induced a further 6.5% progression (P<0.05 versus basal). Plaque characterization showed that HC-HDL administered animals had a 2-fold higher lipid and cholesterol content versus those infused NC-HDL and vehicle (P<0.05). No differences were observed among groups in CD31 levels, nor in infiltrated macrophages or smooth muscle cells. Plaques from HC-HDL administered animals exhibited higher Casp3 (caspase 3) content (P<0.05 versus vehicle and NC-HDL) whereas plaques from NC-HDL infused animals showed lower expression of Casp3, Cox1 (cyclooxygenase 1), inducible nitric oxide synthase, and MMP (metalloproteinase) activity (P<0.05 versus HC-HDL and vehicle). HDLs isolated from animals administered HC-HDL displayed lower antioxidant potential and cholesterol efflux capacity as compared with HDLs isolated from NC-HDL-infused animal and vehicle or donor HDL (P<0.05). There were no differences in HDL-ApoA1 content, ABCA1 (ATP-binding cassette transporter A1) vascular expression, and SRB1 (scavenger receptor B1) and ABCA1 liver expression. HDL particles isolated from a hypercholesterolemic milieu lose their ability to regress and stabilize atherosclerotic lesions. Our data suggest that HDL remodeling in patients with co-morbidities may lead to the loss of HDL atheroprotective functions.

Transport of LDLs into the arterial wall: impact in atherosclerosis.

Atherosclerosis is a complicated cardiovascular disease characterized by unbalanced lipid metabolism and unresolved inflammation that occurred inside of arteries. The transcytosis of LDL across the endothelium and its accumulation in the arterial wall is the initial step of atherosclerosis. Here, we summarize recent research into the understanding of the regulatory mechanisms of endothelial LDL transcytosis and its relevance in the development of atherosclerosis. A number of recent studies have revealed the contribution of caveolae, activin-like kinase 1 (ALK1) or scavenger receptor B1 (SR-B1) in endothelial LDL transcytosis and the progression of atherosclerosis. Caveolin-1 (Cav-1), the major protein component in caveolae, is required for the formation of caveolae and caveolae-mediated LDL uptake and transcytosis across the endothelium. SR-B1 and ALK1 directly bind LDL and facilitate the transport of LDL through the endothelial cells. The change in expression of caveolae-associated proteins and SR-B1 regulates endothelial LDL transcytosis and the pathogenesis of atherosclerosis. Caveolae, ALK1 and SR-B1 are identified as key regulators in the LDL transcytosis across the endothelium. Endothelial LDL transcytosis might be a potential therapeutic approach to limit the initiation of early atherosclerosis and treat the atherosclerotic vascular diseases.

Mimetic sHDL nanoparticles: A novel drug-delivery strategy to target triple-negative breast cancer

BackgroundWithanolides are naturally derived heat shock protein 90 inhibitors that are potent in preclinical models of triple negative breast cancers. Conjugation to synthetic high-density lipoprotein nanoparticles improves solubility and targets delivery to the scavenger receptor B1. Triple negative breast cancers highly overexpress the scavenger receptor B1, and we hypothesize that encapsulation of the novel withalongolide A 4,19,27-triacetate by synthetic high-density lipoprotein will have enhanced efficacy against triple negative breast cancers in vivo. MethodsValidated human triple negative breast cancer cell lines were evaluated for the scavenger receptor B1 expression by quantitative polymerase chain reaction and Western blot. Withalongolide A 4,19,27-triacetate inhibitory concentration50 values were obtained using CellTiter-Glo assays (Promega, Madison, WI, USA). The scavenger receptor B1–mediated drug uptake was evaluated in vitro under fluorescence microscopy and in vivo with IVIS imaging of mouse xenografts (MD-MBA-468LN). To evaluate drug efficacy, mice were treated with synthetic high-density lipoprotein alone, withalongolide A 4,19,27-triacetate alone, withalongolide A 4,19,27-triacetate synthetic high-density lipoprotein, and chemotherapy or Prussian blue stain (control). ResultsTriple negative breast cancer cell lines had greater scavenger receptor B1 expression by quantitative polymerase chain reaction and Western blot versus controls. Fluorescent-labeled synthetic high-density lipoprotein uptake was scavenger receptor B1–mediated in vitro, and in vivo tumor uptake using IVIS imaging demonstrated significantly increased tumor radiant efficiency versus control. Inhibitory concentration50 for withalongolide A 4,19,27-triacetate–treated cells with or without synthetic high-density lipoprotein encapsulation were 70-fold to 200-fold more potent than synthetic high-density lipoprotein alone. In triple negative breast cancer mouse xenografts, treatment with synthetic high-density lipoprotein withalongolide A 4,19,27-triacetate resulted in a 54% decrease in tumor volume compared with the control or with synthetic high-density lipoprotein alone. ConclusionThe synthetic high-density lipoprotein withalongolide A 4,19,27-triacetate nanoconjugates are potent against triple negative breast cancers and show improved scavenger receptor B1–mediated targeting. Treatment with synthetic high-density lipoprotein–encapsulated withalongolide A 4,19,27-triacetate is able to significantly decrease the growth of tumor in mice compared with the control and has better efficacy than the current standard of care, warranting further evaluation as a novel therapeutic agent.

Upregulation of Scavenger Receptor B1 Is Required for Steroidogenic and Nonsteroidogenic Cholesterol Metabolism in Prostate Cancer.

Aberrant cholesterol metabolism is increasingly appreciated to be essential for prostate cancer initiation and progression. Transcript expression of the high-density lipoprotein-cholesterol receptor scavenger receptor B1 (SR-B1) is elevated in primary prostate cancer. Hypothesizing that SR-B1 expression may help facilitate malignant transformation, we document increased SR-B1 protein and transcript expression in prostate cancer relative to normal prostate epithelium that persists in lethal castration-resistant prostate cancer (CRPC) metastasis. As intratumoral steroid synthesis from the precursor cholesterol can drive androgen receptor (AR) pathway activity in CRPC, we screened androgenic benign and cancer cell lines for sensitivity to SR-B1 antagonism. Benign cells were insensitive to SR-B1 antagonism, and cancer line sensitivity inversely correlated with expression levels of full-length and splice variant AR. In androgen-responsive CRPC cell model C4-2, SR-B1 antagonism suppressed cholesterol uptake, de novo steroidogenesis, and AR activity. SR-B1 antagonism also suppressed growth and viability and induced endoplasmic reticulum stress and autophagy. The inability of exogenous steroids to reverse these effects indicates that AR pathway activation is insufficient to overcome cytotoxic stress caused by a decrease in the availability of cholesterol. Furthermore, SR-B1 antagonism decreased cholesterol uptake, growth, and viability of the AR-null CRPC cell model PC-3, and the small-molecule SR-B1 antagonist block lipid transport-1 decreased xenograft growth rate despite poor pharmacologic properties. Overall, our findings show that SR-B1 is upregulated in primary and castration-resistant disease and is essential for cholesterol uptake needed to drive both steroidogenic and nonsteroidogenic biogenic pathways, thus implicating SR-B1 as a novel and potentially actionable target in CRPC. SIGNIFICANCE: These findings highlight SR-B1 as a potential target in primary and castration-resistant prostate cancer that is essential for cholesterol uptake needed to drive steroidogenic and nonsteroidogenic biogenic pathways.

Intestinal absorption of astaxanthin and fucoxanthin: Role peroxisome proliferator-activated receptor gamma and scavenger receptor B1 and modulation by selected peroxisome proliferator-activated receptor gamma ligands

Background: Non-provitamin A carotenoids astaxanthin (AX) and fucoxanthin (FX) are bioactive molecules that are abundant in seafood. Although their dietary intake is beneficial, only around 10% of ingested carotenoids are absorbed. Recent studies have speculated the role of redundant lipid transporters such as scavenger receptor B1 (SRB1), in carotenoids transport, and this SRB1 transporter is under the control of nuclear transcription factor peroxisome proliferator-activated receptor gamma (PPARγ). Aims and Objectives: This study aims at investigating the role of SRB1 and its transcriptional regulation by PPARγ, under the influence of selected PPARγ agonists (conjugated linoleic acid [CLA] and pioglitazone [PGZ]) in intestinal uptake of AX and FX. Materials and Methods: AX and FX were extracted from shrimp carapace and the seaweed Padina tetrastomatica, purified, and purity were assessed. The carotenoids are then gavaged for 14 days, and along with CLA or PGZ. On the 15th day, the animals were sacrificed and tissues were analyzed for carotenoid uptake (liver and serum), protein expression (PPARγ and SRB1) in enterocytes by western blotting and gene expression (PPARα, PPARγ, peroxisome proliferator-activated gamma coactivator 1α, SRB1, and sterol regulatory element-binding protein 1) by quantitative polymerase chain reaction. Results: The results of the study indicate an increase in intestinal uptake, when coadministered with PPARγ agonists (AXCLA>AXPGZ>AX and FXCLA>FXPGZ>FX), signifying a role of PPARγ in the process. Protein expression of PPARγ in comparison with the control in AXCLA increased (1.4 folds); AX and AXPGZ groups had no change. FX and FXPGZ treatments exhibited half the expression, which was restored in FXCLA (1.1 folds). The SRB1 was decreased in AX and did not change in FX group (0.3 and 1.0 folds, respectively). Although AXCLA group exhibited a decrease in SRB1 expression, when compared to control (0.57 folds), there was an increase in comparison with the AX group. There was a similar increase in FXCLA group (1.3 folds). PGZ treatment did not show any significant change in SRB1 expression either with AX or FX (AXPGZ-1.2 and FX PGZ 1.0 folds). Similarly, gene expression of PPARγ and SRB1 increased in AX (2.0 and 1.57), CLA (2.4 and 3.9), and AXCLA groups (4.9 and 3.0 folds), respectively, with an additive effect in AXCLA. Conclusion: These results indicate that the absorption of carotenoids is modulated by the PPARγ agonists CLA and PGZ, by altering the protein and gene expression of PPARγ and SRB1, also the carotenoids themselves influence these markers.

Influencing factors, underlying mechanism and interactions affecting hypercholesterolemia in adult offspring with caffeine exposure during pregnancy

Epidemiological surveys suggest that adult hypercholesterolemia has an intrauterine origin and exhibits gender differences. Our previous study demonstrated that adult rats with intrauterine growth retardation (IUGR) offspring rats induced by prenatal caffeine exposure (PCE) had a higher serum total cholesterol (TCH) level. In this study, we aimed to analyze the influencing factors, underlying mechanism and interactions affecting hypercholesterolemia in adult offspring with caffeine exposure during pregnancy. Pregnant rats were administered caffeine (120 mg/kg d) from gestational day 11 until delivery. Offspring rats fed a normal diet or a high-fat diet (HFD) were euthanized at postnatal week 24, and blood and liver samples were collected. The results showed that PCE could increase the serum levels of TCH and low-density lipoprotein-cholesterol (LDL-C), and the hepatic expression of HMG CoA reductase (HMGCR) and apolipoprotein B (ApoB), but decreased the high-density lipoprotein-cholesterol (HDL-C) level and the hepatic expression of scavenger receptor B1 (SR-B1) and LDL receptor (LDLR). Furthermore, PCE, HFD and gender interact with each other to influence the serum cholesterol phenotype and expression of hepatic cholesterol metabolic genes. These results suggest that the hypercholesterolemia in adult offspring rats induced by PCE mainly resulted from enhanced synthesis and the weakened reverse transport of cholesterol in the liver, furthermore HFD could aggravate this effect, which is caused by hepatic cholesterol metabolic disorders. Moreover, cholesterol metabolism in female rats was more sensitive to neuroendocrine changes and HFD than that in males. This study confirmed the influencing factors (such as a HFD and female gender) of hypercholesterolemia in IUGR offspring providing theoretical and experimental bases for the effective prevention of fetal-originated hypercholesterolemia.

Obesity-induced overexpression of miRNA-24 regulates cholesterol uptake and lipid metabolism by targeting SR-B1

Scavenger Receptor B1 (SR-B1) is an 82 kDa integral membrane glycoprotein that mediates selective uptake of high-density lipoprotein cholesteryl ester (CE) in vitro and in vivo. Previously, we defined several kinds of regulatory mechanisms of SR-B1 expression and function. Here, we have dissected the function of a novel miR-24 on SR-B1 expression, HDL uptake and lipid metabolism. We showed that miR-24 was upregulated in HepG2 cells cultured in the mimicked hyperlipidemic condition and in the livers of dietary induced and genetic obesity mice. Overexpression of miR-24 inhibited SR-B1 expression by directly targeting SR-B1 3′ UTR and repressed HDL uptake and steroidogenesis in steroidogenic cells. HepG2 cells with miR-24 showed attenuation of TG levels and lipid accumulation. Moreover, we validated that overexpression of miR-24 downregulated the expression of certain genes involved in lipogenesis, FASN, ACLY and SCD1, and increased the expression of genes of cholesterol synthesis, HMGCR, DHCR24 and SREBP2. Taken together, we demonstrated that obesity induced miR-24 repressed HDL uptake, steroid hormone synthesis and lipid metabolism by targeting SR-B1.

New insights into the role of glycosylation in lipoprotein metabolism.

Human genetics has provided new insights into the role of protein glycosylation in regulating lipoprotein metabolism. Here we review these new developments and discuss the biological insights they provide. Case descriptions of patients with congenital defects in N-glycosylation (CDG-I) frequently describe a distinct hypocholesterolemia in these rare multisystem clinical syndromes. Two novel CDGs with disturbed Golgi homeostasis and trafficking defects result in mixed glycosylation disorders, hepatic steatosis and hypercholesterolemia. In addition, the presence of particular N-glycans is essential for physiological membrane expression of scavenger receptor B1 and for adequate lipolytic activity of endothelial lipase. GalNAc-T2, a specific O-glycosyl transferase, was found to be a direct modulator of HDL metabolism across mammals, validating its relationship with HDL-c found in genome-wide association studies. Furthermore, genetic variation in ASGR1, the major subunit of the asialoglycoprotein receptor (ASGPR), was found to be associated with a reduction in LDL-c and risk of coronary artery disease. Protein glycosylation plays an important regulatory role in lipoprotein metabolism. Greater insight into how protein glycosylation regulates lipoprotein metabolism could provide novel approaches for the treatment of dyslipidemia.

Modulation of cutaneous scavenger receptor B1 levels by exogenous stressors impairs “in vitro” wound closure

Scavenger receptor B1 (SR-B1) is a trans-membrane protein, involved in tissue reverse cholesterol transport. Several studies have demonstrated that SR-B1 is also implicated in other physiological processes, such as bacteria and apoptotic cells recognition and regulation of intracellular tocopherol and carotenoids levels. Among the tissues where it is localized, SR-B1 has been shown to be significantly expressed in human epidermis. Our group has demonstrated that SR-B1 levels are down-regulated in human cultured keratinocytes by environmental stressors, such as cigarette smoke, via cellular redox imbalance. Our present study aimed to investigate whether such down-regulation was confirmed in a 3D skin model and under other environmental challengers such as particulate matter and ozone. We also investigated the association between oxidation-induced SR-B1 modulation and impaired wound closure. The data obtained showed that not only cigarette, but also the other environmental stressors reduced SR-B1 expression in epidermal cutaneous tissues and that this effect might be involved in impaired wound healing.

Toll-like receptor 2 downregulates the cholesterol efflux by activating the nuclear factor-κB pathway in macrophages and may be a potential therapeutic target for the prevention of atherosclerosis.

Atherosclerosis is a chronic inflammatory disease, which is triggered by lipid retention. Toll-like receptor 2 (TLR2) is a novel target for therapeutic intervention in atherosclerosis. In addition, nuclear factor-κB (NF-κB) serves important roles in stress response and inflammation. The present study investigated whether TLR2 is involved in the activation of cholesterol efflux in macrophages by regulating the NF-κB pathway. The human monocytic THP-1 cell line and murine macrophage RAW264.7 cell line were treated with 50 µg/ml oxidized low-density lipoprotein (ox-LDL) for 48 h in order to obtain macrophage foam cells. The cholesterol efflux of the cell lines under exogenous TLR2 treatment was assessed by liquid scintillation counting. Furthermore, the protein and mRNA expression levels of ATP binding cassette transporter A1 (ABCA1), ABCG1 and scavenger receptor B1 (SR-B1) were examined by western blot and quantitative polymerase chain reaction assays, respectively. To detect the effect of NF-κB on cholesterol efflux, the cells were divided into three groups, including the control, 10 ng/ml lipopolysaccharides (LPS; 24 h) and 10 ng/ml LPS + 50 µM pyrrolidinedithiocarbamate (PDTC; 24 h) groups. The results indicated that ox-LDL induced foam cell formation in the THP-1 and RAW264.7 cells, while TLR2 significantly decreased the cholesterol efflux in dose- and time-dependent manners. Accordingly, TLR2 reduced ABCA1, ABCG1 and SR-B1 expression at the transcriptional and translational levels in a dose-dependent manner. In addition, application of PDTC (an NF-κB specific inhibitor) markedly suppressed the LPS-induced downregulation of cholesterol efflux. These data revealed that TLR2 may be involved in the activation of cholesterol efflux in macrophages by regulating the NF-κB signaling pathway.

Effects and Interactions of Prenatal Ethanol Exposure, a Post-Weaning High-Fat Diet and Gender on Adult Hypercholesterolemia Occurrence in Offspring Rats

Background/Aims: Prenatal ethanol exposure (PEE) could induce intrauterine programming of hypothalamic-pituitary-adrenal axis-associated neuroendocrine metabolism, resulting in intrauterine growth retardation and susceptibility to adult hypercholesterolemia in offspring. This study aimed to analyse the effects and interactions of PEE, a post-weaning high-fat diet (HFD) and gender on the occurrence of adult hypercholesterolemia in offspring rats. Methods: Wistar female rats were treated with ethanol (4 g/kg.d) at gestational days 11-20. The offspring were given a normal diet or HFD after weaning, and the blood cholesterol metabolism phenotype and expression of hepatic cholesterol metabolism related genes were detected in 24-week-old offspring. Furthermore, the interactions among PEE, HFD, and gender on hypercholesterolemia occurrence were analysed. Results: PEE increased the serum total cholesterol (TCH) and low-density lipoprotein-cholesterol (LDL-C) levels and decreased the serum high-density lipoprotein-cholesterol (HDL-C) level in adult offspring rats; the changes in female offspring were greater than those in males. At the same time, the mRNA expression levels of hepatic cholesterol metabolic enzymes (apolipoprotein B (ApoB) and 7α-hydroxylase (CYP7A1))—were increased, while the mRNA expression levels of the scavenger receptor B1 (SR-B1) and LDL receptor (LDLR) were decreased. Furthermore, a three-way ANOVA showed there were interactions among PEE, post-weaning HFD and gender. For PEE offspring, a post-weaning HFD aggravated the elevated hepatic ApoB and CYP7A1 expression and reduced SR-B1 and LDLR expression; the changes in hepatic SR-B1 and CYP7A1 expression were greater in female HFD rats than in males. Conclusion: Our findings suggest that a post-weaning HFD could aggravate offspring hypercholesterolemia caused by PEE and that this mechanism might be associated with hepatic cholesterol metabolic disorders that are aggravated by a post-weaning HFD; hepatic cholesterol metabolism was more sensitive to neuroendocrine metabolic alterations by PEE and a post-weaning HFD in the female offspring than in the male offspring.

Astrocytes from old Alzheimer's disease mice are impaired in Aβ uptake and in neuroprotection

In Alzheimer's disease (AD), astrocytes undergo morphological changes ranging from atrophy to hypertrophy, but the effect of such changes at the functional level is still largely unknown. Here, we aimed to investigate whether alterations in astrocyte activity in AD are transient and depend on their microenvironment, or whether they are irreversible. We established and characterized a new protocol for the isolation of adult astrocytes and discovered that astrocytes isolated from old 5xFAD mice have higher GFAP expression than astrocytes derived from WT mice, as observed in vivo. We found high C1q levels in brain sections from old 5xFAD mice in close vicinity to amyloid plaques and astrocyte processes. Interestingly, while old 5xFAD astrocytes are impaired in uptake of soluble Aβ42, this effect was reversed upon an addition of exogenous C1q, suggesting a potential role for C1q in astrocyte-mediated Aβ clearance. Our results suggest that scavenger receptor B1 plays a role in C1q-facilitated Aβ uptake by astrocytes and that expression of scavenger receptor B1 is reduced in adult old 5xFAD astrocytes. Furthermore, old 5xFAD astrocytes show impairment in support of neuronal growth in co-culture and neurotoxicity concomitant with an elevation in IL-6 expression. Further understanding of the impact of astrocyte impairment on AD pathology may provide insights into the etiology of AD.

Abstract 3672: Expression patterns of scavenger receptor B-1 (SR-B1) to guide biomimetic HDL gold nanoparticle therapy

Abstract Introduction: Treatment options for many advanced cancers are fairly limited. New therapies that can open new paradigm are urgently needed. We have recently developed a novel synthetic biomimetic HDL gold nanoparticle (HDL NP) that demonstrated anti-tumor activity in cancer cells via apoptosis (Yang et al. PNAS, 2013) Its activity correlated with the expression of scavenger receptor-B1 (SR-B1) that binds to natural HDLs and HDL NPs. SR-B1 is a high-affinity HDL receptor that facilitates the bidirectional flux of free cholesterol and the transport of esterified cholesterol to cells. The mechanism of action of HDL NPs involved alterations in cholesterol flux and metabolism as well as cholesterol-based cell-signaling pathways. Understanding the expression patterns of SR-B1 in various human cancers can assist in developing HDL NP therapy to broader indications. Methods: We used Oncomine Research Edition public database to assess the gene expression levels of SR-B1 in various human cell lines, cancer tissues, and normal tissues. T test was use to compare cell line with the highest SR-B1 expression with the rest of cell lines of various tumor types. Also comparison was made between resected human cancer tissues and their counterpart normal tissues across various histologies. Each significant t test results from all publicly available array datasets within Oncomine were counted and compared among different tumor types. Results: First, we compared the mRNA levels of SR-B1 in human cancer tissues with those of normal tissues. Twenty different tumor types were included. Among 20 different datasets of renal cell carcinoma, 12 (60%) revealed statistically significant increase in SR-B1 expression in cancer compared with normal renal tissue samples. Other tumor types that showed ≥10% of databsets demonstrating the same pattern of expression were esophageal (44%, 4/9), melanoma (43%, 3/7), gastric (26%, 6/23), leukemia (21%, 6/29), lymphoma (20%, 6/30), colorectal (19%, 7/36), liver (15%, 2/13), and prostate cancer (15%, 3/20). Second, we compared the mRNA levels of SR-B1 across various human cancer cell lines. Among 17 different datasets that contain cancer cell lines including melanoma cell lines, melanoma was found to have the highest level of SR-B1 expression compared with the rest of the cell lines of various cancer types in 11 (65%) datasets. Other tumor types associated with ≥10% of datasets demonstrating the same highest level of SR-B1 expression were liver (33%, 4/12), kidney (12%, 2/17), and leukemia (11%, 2/19). Discussion: We found that renal cell carcinoma, melanoma, and hepatocellular carcinoma were among the cancers that expressed higher levels of SR-B1 compared with other cancers as well as with their normal tissues. These tumors merit further investigation as targets for HDL NP therapy either in the form of mono-therapy or in combination. Citation Format: Young Kwang Chae, Alan Pan, Denise Scholtens, Shuo Yang, Jonathan Rink, Colby S. Thaxton, Leo Gordon. Expression patterns of scavenger receptor B-1 (SR-B1) to guide biomimetic HDL gold nanoparticle therapy. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3672. doi:10.1158/1538-7445.AM2015-3672

Exploring the link between scavenger receptor B1 expression and chronic obstructive pulmonary disease pathogenesis.

Chronic obstructive pulmonary disease (COPD) has been recognized as one of the major causes of morbidity and mortality in the United States; it is the third leading cause of deaths in the United States, with approximately 15 million Americans affected with COPD. Although exposure to cigarette smoke has been shown to be the main, if not the only, risk factor for COPD, the mechanisms underlying this association remain unclear. Most smokers do not develop COPD, suggesting that a combination of exposure and susceptibility (genetic background) is required. Several mechanisms contribute to the pathogenesis of COPD, such as influx of inflammatory cells into the lung, imbalance between proteolytic and antiproteolytic molecules, disruption of the balance between apoptosis and replenishment of structural cells in the lung, and disruption of oxidant/antioxidant balance. The scavenger receptor BI (SRB1) plays an important role in mediating the uptake of high-density lipoprotein (HDL)-derived cholesterol and cholesteryl ester in tissues. In addition to its role as the HDL receptor, SRB1 is also involved in pathogen recognition, identification of apoptotic cells, tissue antioxidant uptake (tocopherol and carotenoids), and lung surfactant composition, all factors involved in COPD pathogenesis. Therefore, it is possible that lung SRB1 levels are involved in the development of COPD.

Impact of Silver and Iron Nanoparticle Exposure on Cholesterol Uptake by Macrophages.

Macrophages are central to the development of atherosclerosis by absorbing lipids, promoting inflammation, and increasing plaque deposition. Nanoparticles (NPs) are becoming increasingly common in biomedical applications thereby increasing exposure to the immune and vascular systems. This project investigated the influence of NPs on macrophage function and specifically cholesterol uptake. Macrophages were exposed to 20 nm silver NPs (AgNPs), 110 nm AgNPs, or 20 nm Fe3O4NPs for 2 h and NP uptake, cytotoxicity, and subsequent uptake of fluorescently labeled cholesterol were assessed. Macrophage uptake of NPs did not induce cytotoxicity at concentrations utilized (25 μg/mL); however, macrophage exposure to 20 nm AgNPs reduced subsequent uptake of cholesterol. Further, we assessed the impact of a cholesterol-rich environment on macrophage function following NP exposure. In these sets of experiments, macrophages internalized NPs, exhibited no cytotoxicity, and altered cholesterol uptake. Alterations in the expression of scavenger receptor-B1 following NP exposure, which likely influences cholesterol uptake, were observed. Overall, NPs alter cholesterol uptake, which may have implications in the progression of vascular or immune mediated diseases. Therefore, for the safe development of NPs for biomedical applications, it is necessary to understand their impact on cellular function and biological interactions in underlying disease environments.