Knock-down of the oxysterol receptor LXRα impairs cholesterol efflux in human primary macrophages: Lack of compensation by LXRβ activation

Inhibition of LXR Signaling in Human Foam Cells Impairs Macrophage-to-Endothelial Cell Cross Talk and Promotes Endothelial Cell Inflammation

BACKGROUND

During atherogenesis, macrophages turn into foam cells by engulfing lipids present within the atheroma plaques. The shift of foam cells toward proinflammatory or anti-inflammatory phenotypes, a critical step in disease progression, is still poorly understood. LXRs (liver X receptors) play a pivotal role in the macrophage response to lipid, promoting the expression of key genes of cholesterol efflux, mitigating intracellular cholesterol accumulation. LXRs also exert balanced actions on inflammation in human macrophages, displaying both proinflammatory and anti-inflammatory effects.

METHODS

Our study explored the role of LXRs in the functional response of human macrophage to lipid-rich plaque environment. We used primary human macrophages treated with atheroma plaque extracts and assessed the impact of pharmacological LXR inhibition by GSK2033 on cholesterol homeostasis and inflammatory response. Ultimately, we evaluated macrophage and endothelial cell cross talk by assessing the impact of macrophage-conditioned supernatants on the human endothelial cell.

RESULTS

LXR inhibition by GSK2033 resulted in increased levels of cholesterol and oxysterols in human macrophages, alongside notable changes in the cholesterol ester profile. This was accompanied by heightened secretion of proinflammatory cytokines such as IL (interleukin)-6 and TNFα (tumor necrosis factor-α), despite a transcriptional repression of IL-1β. Conditioned media from GSK2033-treated macrophages more effectively activated ICAM-1 (intercellular adhesion molecule-1) and CCL2 (C-C motif ligand 2) expression in endothelial cells.

CONCLUSIONS

Our findings illustrate the intricate relationship between LXR function, cholesterol metabolism, and inflammation in human macrophages. While LXR is required for the proper handling of plaque lipids by macrophages, the differential regulation of IL-1β versus IL-6/TNFα secretion by LXRs could be challenging for potential pharmacological interventions.

The powerful potential of amino acid menthyl esters for anti-inflammatory and anti-obesity therapies

Our newly developed menthyl esters of valine and isoleucine exhibit anti-inflammatory properties beyond those of the well-known menthol in macrophages stimulated by lipopolysaccharide (LPS) and in a mouse model of colitis induced by sodium dextran sulfate. Unlike menthol, which acts primarily through the cold-sensitive TRPM8 channel, these menthyl esters displayed unique mechanisms that operate independently of this receptor. They readily penetrated target cells and efficiently suppressed LPS-stimulated tumour necrosis factor-alpha (Tnf) expression mediated by liver X receptor (LXR), a key nuclear receptor that regulates intracellular cholesterol and lipid balance. The menthyl esters showed affinity for LXR and enhanced the transcriptional activity through their non-competitive and potentially synergistic agonistic effect. This effect can be attributed to the crucial involvement of SCD1, an enzyme regulated by LXR, which is central to lipid metabolism and plays a key role in the anti-inflammatory response. In addition, we discovered that the menthyl esters showed remarkable efficacy in suppressing adipogenesis in 3T3-L1 adipocytes at the mitotic clonal expansion stage in an LXR-independent manner as well as in mice subjected to diet-induced obesity. These multiple capabilities of our compounds establish them as formidable allies in the fight against inflammation and obesity, paving the way for a range of potential therapeutic applications.

Lipid droplet-associated hydrolase mobilizes stores of liver X receptor sterol ligands and protects against atherosclerosis

Foam cells in atheroma are engorged with lipid droplets (LDs) that contain esters of regulatory lipids whose metabolism remains poorly understood. LD-associated hydrolase (LDAH) has a lipase structure and high affinity for LDs of foam cells. Using knockout and transgenic mice of both sexes, here we show that LDAH inhibits atherosclerosis development and promotes stable lesion architectures. Broad and targeted lipidomic analyzes of primary macrophages and comparative lipid profiling of atheroma identified a broad impact of LDAH on esterified sterols, including natural liver X receptor (LXR) sterol ligands. Transcriptomic analyzes coupled with rescue experiments show that LDAH modulates the expression of prototypical LXR targets and leads macrophages to a less inflammatory phenotype with a profibrotic gene signature. These studies underscore the role of LDs as reservoirs and metabolic hubs of bioactive lipids, and suggest that LDAH favorably modulates macrophage activation and protects against atherosclerosis via lipolytic mobilization of regulatory sterols.

Inhibition of DHCR24 activates LXRα to ameliorate hepatic steatosis and inflammation

Liver X receptor (LXR) agonism has theoretical potential for treating NAFLD/NASH, but synthetic agonists induce hyperlipidemia in preclinical models. Desmosterol, which is converted by Δ24-dehydrocholesterol reductase (DHCR24) into cholesterol, is a potent endogenous LXR agonist with anti-inflammatory properties. We aimed to investigate the effects of DHCR24 inhibition on NAFLD/NASH development. Here, by using APOE*3-Leiden. CETP mice, a well-established translational model that develops diet-induced human-like NAFLD/NASH characteristics, we report that SH42, a published DHCR24 inhibitor, markedly increases desmosterol levels in liver and plasma, reduces hepatic lipid content and the steatosis score, and decreases plasma fatty acid and cholesteryl ester concentrations. Flow cytometry showed that SH42 decreases liver inflammation by preventing Kupffer cell activation and monocyte infiltration. LXRα deficiency completely abolishes these beneficial effects of SH42. Together, the inhibition of DHCR24 by SH42 prevents diet-induced hepatic steatosis and inflammation in a strictly LXRα-dependent manner without causing hyperlipidemia. Finally, we also showed that SH42 treatment decreased liver collagen content and plasma alanine transaminase levels in an established NAFLD model. In conclusion, we anticipate that pharmacological DHCR24 inhibition may represent a novel therapeutic strategy for treatment of NAFLD/NASH.

Emerging Insights into Liver X Receptor α in the Tumorigenesis and Therapeutics of Human Cancers

Liver X receptor α (LXRα), a member of the nuclear receptor superfamily, is identified as a protein activated by ligands that interacts with the promoters of specific genes. It regulates cholesterol, bile acid, and lipid metabolism in normal physiological processes, and it participates in the development of some related diseases. However, many studies have demonstrated that LXRα is also involved in regulating numerous human malignancies. Aberrant LXRα expression is emerging as a fundamental and pivotal factor in cancer cell proliferation, invasion, apoptosis, and metastasis. Herein, we outline the expression levels of LXRα between tumor tissues and normal tissues via the Oncomine and Tumor Immune Estimation Resource (TIMER) 2.0 databases; summarize emerging insights into the roles of LXRα in the development, progression, and treatment of different human cancers and their diversified mechanisms; and highlight that LXRα can be a biomarker and therapeutic target in diverse cancers.

The LXRB-SREBP1 network regulates lipogenic homeostasis by controlling the synthesis of polyunsaturated fatty acids in goat mammary epithelial cells

Background

In rodents, research has revealed a role of liver X receptors (LXR) in controlling lipid homeostasis and regulating the synthesis of polyunsaturated fatty acids (PUFA). Recent data suggest that LXRB is the predominant LXR subtype in ruminant mammary cells, but its role in lipid metabolism is unknown. It was hypothesized that LXRB plays a role in lipid homeostasis via altering the synthesis of PUFA in the ruminant mammary gland. We used overexpression and knockdown of LXRB in goat primary mammary epithelial cells (GMEC) to evaluate abundance of lipogenic enzymes, fatty acid profiles, content of lipid stores and activity of the stearoyl-CoA desaturase (SCD1) promoter.

Results

Overexpression of LXRB markedly upregulated the protein abundance of LXRB while incubation with siRNA targeting LXRB markedly decreased abundance of LXRB protein. Overexpression of LXRB plus T0901317 (T09, a ligand for LXR) dramatically upregulated SCD1 and elongation of very long chain fatty acid-like fatty acid elongases 5–7 (ELOVL 5–7), which are related to PUFA synthesis. Compared with the control, cells overexpressing LXRB and stimulated with T09 had greater concentrations of C16:0, 16:1, 18:1n7,18:1n9 and C18:2 as well as desaturation and elongation indices of C16:0. Furthermore, LXRB-overexpressing cells incubated with T09 had greater levels of triacylglycerol and cholesterol. Knockdown of LXRB in cells incubated with T09 led to downregulation of genes encoding elongases and desaturases. Knockdown of LXRB attenuated the increase in triacylglycerol and cholesterol that was induced by T09. In cells treated with dimethylsulfoxide, knockdown of LXRB increased the concentration of C16:0 at the expense of C18:0, while a significant decrease in C18:2 was observed in cells incubated with both siLXRB and T09. The abundance of sterol regulatory element binding transcription factor 1 precursor (pSREBP1) and its mature fragment (nSREBP1) was upregulated by T09, but not LXRB overexpression. In the cells cultured with T09, knockdown of LXRB downregulated the abundance for pSREBP1 and nSREBP1. Luciferase reporter assays revealed that the activities of wild type SCD1 promoter or fragment with SREBP1 response element (SRE) mutation were decreased markedly when LXRB was knocked down. Activity of the SCD1 promoter that was induced by T09 was blocked when the SRE mutation was introduced.

Conclusion

The current study provides evidence of a physiological link between the LXRB and SREBP1 in the ruminant mammary cell. An important role was revealed for the LXRB-SREBP1 network in the synthesis of PUFA via the regulation of genes encoding elongases and desaturases. Thus, targeting this network might elicit broad effects on lipid homeostasis in ruminant mammary gland.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00774-4.

Natural Products Targeting Liver X Receptors or Farnesoid X Receptor

Nuclear receptors (NRs) are a superfamily of transcription factors induced by ligands and also function as integrators of hormonal and nutritional signals. Among NRs, the liver X receptors (LXRs) and farnesoid X receptor (FXR) have been of significance as targets for the treatment of metabolic syndrome-related diseases. In recent years, natural products targeting LXRs and FXR have received remarkable interests as a valuable source of novel ligands encompassing diverse chemical structures and bioactive properties. This review aims to survey natural products, originating from terrestrial plants and microorganisms, marine organisms, and marine-derived microorganisms, which could influence LXRs and FXR. In the recent two decades (2000-2020), 261 natural products were discovered from natural resources such as LXRs/FXR modulators, 109 agonists and 38 antagonists targeting LXRs, and 72 agonists and 55 antagonists targeting FXR. The docking evaluation of desired natural products targeted LXRs/FXR is finally discussed. This comprehensive overview will provide a reference for future study of novel LXRs and FXR agonists and antagonists to target human diseases, and attract an increasing number of professional scholars majoring in pharmacy and biology with more in-depth discussion.

Effects of allyl isothiocyanate on the expression, function, and its mechanism of ABCA1 and ABCG1 in pulmonary of COPD rats

BACKGROUND AND AIMS

Allyl isothiocyanate(AITC) has been shown to play an important role in the improved symptoms of chronic obstructive pulmonary disease(COPD) and the inhibition of inflammation, but the role in COPD lipid metabolism disorder and the molecular mechanism remains unclear. We aimed to explore whether and how AITC affects COPD by regulating lipid metabolism and inflammatory response.

METHODS

The COPD rat model was established by cigarette smoke exposure. Cigarette smoke extract stimulated 16HBE cells to induce a cell model. The effect of AITC treatment was detected by lung function test, H&E staining, Oil red O staining, immunohistochemistry, ELISA, CCK-8, HPLC, fluorescence efflux test, siRNA, RT-PCR, and Western blotting. Biological analysis was performed to analyze the results. Graphpad Prism 8.0 software was used for statistical analysis.

RESULTS

AITC can improve lung function and pathological injury in COPD rats. The levels of IL-1 β and TNF- α in the AITC treatment group were significantly lower than those in the model group(P < 0.05), and the lipid metabolism was also improved (P < 0.05). AITC reverses CSE-induced down-regulation of LXR α, ABCA1, and ABCG1 expression and function in a time-and concentration-dependent manner (P < 0.05). AITC regulates the cholesterol metabolism disorder induced by CSE in NR8383 cells and attenuates macrophage inflammation (P < 0.05). In addition, after silencing LXR α with siRNA, the effect of AITC was also inhibited.

CONCLUSION

These results suggest that AITC improves COPD by promoting RCT process and reducing inflammatory response via activating LXR pathways.

Atrial Natriuretic Peptide Inhibited ABCA1/G1-dependent Cholesterol Efflux Related to Low HDL-C in Hypertensive Pregnant Patients

Objective: It has been reported that atrial natriuretic peptide (ANP) regulates lipid metabolism by stimulating adipocyte browning, lipolysis, and lipid oxidation, and by impacting the secretion of adipokines. In our previous study, we found that the plasma ANP concentration of hypertensive disorders of pregnancy (HDP) was significantly increased in comparison to that of normotensive pregnancy patients. Thus, this study’s objective was to investigate the lipid profile in patients with HDP and determine the effects of ANP on the cholesterol efflux in THP-1 macrophages.

Methods: A total of 265 HDP patients and 178 normotensive women as the control group were recruited. Clinical demographic characteristics and laboratory profile data were collected. Plasma total triglycerides (TGs), total cholesterol (TC), low-density cholesterol (LDL-C), and high-density cholesterol (HDL-C) were compared between the two groups. THP-1 monocytes were incubated with different concentrations of ANP. ATP-binding cassette transporter A1 (ABCA1) and ATP-binding cassette transporter G1 (ABCG1) mRNA and protein were evaluated. ABCA1- and ABCG1-mediated cholesterol efflux to apolipoprotein A-Ⅰ (apoA-Ⅰ) and HDL, respectively, were measured by green fluorescent labeled NBD cholesterol. Natriuretic peptide receptor A (NPR-A) siRNA and specific agonists of the peroxisome proliferator–activated receptor-γ (PPAR-γ) and liver X receptor α (LXRα) were studied to investigate the mechanism involved.

Results: Plasma TG, TC, LDL-C, and LDL-C/HDL-C were significantly increased, and HDL-C was significantly decreased in the HDP group in comparison to the control (all p < 0.001). ANP inhibited the expression of ABCA1 and ABCG1 at both the mRNA and protein levels in a dose-dependent manner. The functions of ABCA1- and ABCG1-mediated cholesterol efflux to apoA-I and HDL were significantly decreased. NPR-A siRNA further confirmed that ANP binding to its receptor inhibited ABCA1/G1 expression through the PPAR-γ/LXRα pathway.

Conclusions: ABCA1/G1 was inhibited by the stimulation of ANP when combined with NPR-A through the PPAR-γ/LXRα pathway in THP-1 macrophages. The ABCA1/G1-mediated cholesterol efflux was also impaired by the stimulation of ANP. This may provide a new explanation for the decreased level of HDL-C in HDP patients.

Alisol B 23-acetate, a new promoter for cholesterol efflux from dendritic cells, alleviates dyslipidemia and inflammation in advanced atherosclerotic mice

Atherosclerosis (AS) is characterized by dyslipidemia and chronic inflammation. In the high-fat environment, the lipid metabolism of dendritic cells (DCs) is abnormal, which leads to abnormal immune function, promotes the occurrence of immune inflammatory reactions, and promotes the development of AS. Alisol B 23-acetate (23B) is a triterpenoid in the rhizomes of Alisma, which is a traditional Chinese medicine. Here, we identified cholesterol metabolism-related targets of 23B through a virtual screen, and further transcriptome analysis revealed that 23B can change antigen presentation and cholesterol metabolism pathways in cholesterol-loaded DCs. In vitro experiments confirmed that 23B promoted cholesterol efflux from ApoE^-/- DCs, reduced the expression of MHC II, CD80, and CD86, and inhibited the activation of CD4⁺ T cells and the production of inflammatory cytokines IL-12 and IFN-γ. In advanced AS mice, 23B can decrease triacylglycerol (TG) levels and increase high-density lipoprotein-cholesterol (HDL-C) levels in plasma and the expression of cholesterol efflux genes in the aorta. Neither helper T cells 1 (Th1) nor regulatory T cells (Tregs) in peripheral blood changed significantly in the presence of 23B, but 23B reduced the levels of IL-12 and IFN-γ in serum. However, 23B did not change the total cholesterol (TC) and low-density lipoprotein-cholesterol (LDL-C) levels in serum or lipid accumulation in the aorta. Moreover, 23B did not increase the production of IL-10 and TGF-β1 in vivo or in vitro. These results indicate that 23B promotes cholesterol efflux from DCs, which can improve the immune inflammatory response and contribute to controlling the inflammatory status of AS.

Liver X receptors and liver physiology

The liver x receptors LXRα (NR1H3) and LXRβ (NR1H2) are members of the nuclear hormone receptor superfamily of ligand dependent transcription factors that regulate transcription in response to the direct binding of cholesterol derivatives. Studies using genetic knockouts and synthetic ligands have defined the LXRs as important modulators of lipid homeostasis throughout the body. This review focuses on the control of cholesterol and fatty acid metabolism by LXRs in the liver and how modifying LXR activity can influence the pathology of liver diseases.

CTRP9 alleviates foam cells apoptosis by enhancing cholesterol efflux

The apoptosis of foam cells leads to instability of atherosclerotic plaques. This study was designed to explore the protective role of CTRP9 in foam cell apoptosis. In our experiment, CTRP9 alleviated foam cell apoptosis. Meanwhile, CTRP9 upregulated the expression of proteins important for cholesterol efflux, such as LXRα, CYP27A1, ABCG1 and ABCA1, and improved cholesterol efflux in foam cells. Moreover, CTRP9 inhibited Wnt3a and β-catenin expression and β-catenin nuclear translocation in foam cells. In addition, adenovirus overexpression of Wnt3a abolished the effect of CTRP9 on macrophage apoptosis. Mechanistically, the AMPK inhibitor abolished the effect of CTRP9 on foam cell apoptosis, and downregulation of AdipoR1 by siRNA abrogated the activation of AMPK and the effect of CTRP9 on foam cell apoptosis. We concluded that CTRP9 achieved these protective effects on foam cells through the AdipoR1/AMPK pathway.

The roles of liver X receptor α in inflammation and inflammation-associated diseases

Liver X receptor α (LXRα; also known as NR1H3), an isoform of LXRs, is a member of the nuclear receptor family of transcription factors and plays essential roles in the transcriptional control of cholesterol homeostasis. Previous in-depth phenotypic analyses of mouse models with deficient LXRα have also demonstrated various physiological functions of this receptor within inflammatory responses. LXRα activation exerts a combination of metabolic and anti-inflammatory actions resulting in the modulation and the amelioration of inflammatory disorders. The tight "repercussions" between LXRα and inflammation, as well as cholesterol homeostasis, have suggested that LXRα could be pharmacologically targeted in pathologies such as atherosclerosis, acute lung injury, and Alzheimer's disease. This review gives an overview of the recent advances in understanding the roles of LXRα in inflammation and inflammation-associated diseases, which will help in the design of future experimental researches on the potential of LXRα and advance the investigation of LXRα as pharmacological inflammatory targets.

Selective LXR agonist DMHCA corrects retinal and bone marrow dysfunction in type 2 diabetes

In diabetic dyslipidemia, cholesterol accumulates in the plasma membrane, decreasing fluidity and thereby suppressing the ability of cells to transduce ligand-activated signaling pathways. Liver X receptors (LXRs) make up the main cellular mechanism by which intracellular cholesterol is regulated and play important roles in inflammation and disease pathogenesis. N, N-dimethyl-3β-hydroxy-cholenamide (DMHCA), a selective LXR agonist, specifically activates the cholesterol efflux arm of the LXR pathway without stimulating triglyceride synthesis. In this study, we use a multisystem approach to understand the effects and molecular mechanisms of DMHCA treatment in type 2 diabetic (db/db) mice and human circulating angiogenic cells (CACs), which are hematopoietic progenitor cells with vascular reparative capacity. We found that DMHCA is sufficient to correct retinal and BM dysfunction in diabetes, thereby restoring retinal structure, function, and cholesterol homeostasis; rejuvenating membrane fluidity in CACs; hampering systemic inflammation; and correcting BM pathology. Using single-cell RNA sequencing on lineage-sca1+c-Kit+ (LSK) hematopoietic stem cells (HSCs) from untreated and DMHCA-treated diabetic mice, we provide potentially novel insights into hematopoiesis and reveal DMHCA's mechanism of action in correcting diabetic HSCs by reducing myeloidosis and increasing CACs and erythrocyte progenitors. Taken together, these findings demonstrate the beneficial effects of DMHCA treatment on diabetes-induced retinal and BM pathology.

Regulation mechanism of silkworm pupa oil PUFAs on cholesterol metabolism in hepatic cell L-02

BACKGROUND

Silkworm pupa oil polyunsaturated fatty acid (SPO PUFA) has been confirmed to have a cholesterol-lowering function.

METHODS AND RESULTS

The effect of SPO PUFA and its main component, α-linolenic acid (ALA), on the metabolism of cholesterol and its regulation was investigated. The model of lipid denatured cells were constructed to carry out lipid accumulation, cholesterol metabolism and transformation. Real-time PCR and western blots were also used to analyze the expression levels of related genes and proteins to investigate the cholesterol efflux regulation mechanism. The data indicated that SPO PUFA and ALA dose-dependently decreased intracellular total cholesterol (TC) and enhanced total bile acid (TBA). They could also promote cholesterol removal by enhancing bile acid secretion and by upregulating genes LXRα, PPARγ, ABCA1, ABCG1, and CYP7A1, which were regulated by LXRα/PPARγ-ABCA1/ABCG1-CYP7A1 nuclear receptor signal pathways.

CONCLUSIONS

This study is of great significance in maintaining the balance of cholesterol and lipid metabolism, and in reducing the risk of steatohepatitis. © 2019 Society of Chemical Industry.

Saikosaponin A protects chickens against pullorum disease via modulation of cholesterol

The worsening problem of antibiotic resistance prompts the need for alternative strategies that do not directly target bacteria. Virulent Salmonella pullorum strains can invade macrophages and lead to a systemic infection. Saikosaponin A (SSa), a bioactive saponin isolated from Radix bupleuri, has been demonstrated to exhibit anti-inflammatory, hepatoprotective, and cholesterol regulatory activity. The aim of this study was to investigate the effects of SSa on Salmonella-induced pullorum disease in chickens and clarify the possible mechanism. A S. pullorum-induced pullorum disease chicken model was used to confirm the protective effect of SSa in vivo. The model of HD11 cells infected with S. pullorum was used to investigate the molecular mechanism of SSa in vitro. In vivo, SSa prolonged the survival time and decreased the liver bacterial burdens in the pullorum disease model. In vitro, SSa dose-dependently suppressed the invasion of HD11 cells by S. pullorum. SSa depleted cholesterol in the lipid rafts, disrupted the formation of lipid rafts, and promoted the transcription of LXRα, ABCA1, and ABCG1. Moreover, the addition of water-soluble cholesterol and inhibition of LXRα with the LXRα antagonist geranylgeranyl pyrophosphate reversed the inhibitory effects of SSa on the invasion of HD11 cells by S. pullorum. In conclusion, the protective effect of SSa against S. pullorum infection is associated with the upregulation of the LXRα-ABCG1/ABCA1 pathway, which results in a decrease in cholesterol in the lipid rafts of HD11 cells, thereby suppressing the invasion of HD11 cells by S. pullorum. These results validate SSa as a host-target drug for the prevention of bacterial diseases, including those caused by S. pullorum.

Targeting Foam Cell Formation in Atherosclerosis: Therapeutic Potential of Natural Products

Foam cell formation and further accumulation in the subendothelial space of the vascular wall is a hallmark of atherosclerotic lesions. Targeting foam cell formation in the atherosclerotic lesions can be a promising approach to treat and prevent atherosclerosis. The formation of foam cells is determined by the balanced effects of three major interrelated biologic processes, including lipid uptake, cholesterol esterification, and cholesterol efflux. Natural products are a promising source for new lead structures. Multiple natural products and pharmaceutical agents can inhibit foam cell formation and thus exhibit antiatherosclerotic capacity by suppressing lipid uptake, cholesterol esterification, and/or promoting cholesterol ester hydrolysis and cholesterol efflux. This review summarizes recent findings on these three biologic processes and natural products with demonstrated potential to target such processes. Discussed also are potential future directions for studying the mechanisms of foam cell formation and the development of foam cell-targeted therapeutic strategies.

Liver X Receptor Alpha Is Important in Maintaining Blood-Brain Barrier Function

Dysfunction of the blood-brain barrier (BBB) contributes significantly to the pathogenesis of several neuroinflammatory diseases, including multiple sclerosis (MS). Potential players that regulate BBB function are the liver X receptors (LXRs), which are ligand activated transcription factors comprising two isoforms, LXRα, and LXRβ. However, the role of LXRα and LXRβ in regulating BBB (dys)function during neuroinflammation remains unclear, as well as their individual involvement. Therefore, the goal of the present study is to unravel whether LXR isoforms have different roles in regulating BBB function under neuroinflammatory conditions. We demonstrate that LXRα, and not LXRβ, is essential to maintain barrier integrity in vitro. Specific knockout of LXRα in brain endothelial cells resulted in a more permeable barrier with reduced expression of tight junctions. Additionally, the observed dysfunction was accompanied by increased endothelial inflammation, as detected by enhanced expression of vascular cell adhesion molecule (VCAM-1) and increased transendothelial migration of monocytes toward inflammatory stimuli. To unravel the importance of LXRα in BBB function in vivo, we made use of the experimental autoimmune encephalomyelitis (EAE) MS mouse model. Induction of EAE in a constitutive LXRα knockout mouse and in an endothelial specific LXRα knockout mouse resulted in a more severe disease score in these animals. This was accompanied by higher numbers of infiltrating leukocytes, increased endothelial VCAM-1 expression, and decreased expression of the tight junction molecule claudin-5. Together, this study reveals that LXRα is indispensable for maintaining BBB integrity and its immune quiescence. Targeting the LXRα isoform may help in the development of novel therapeutic strategies to prevent BBB dysfunction, and thereby neuroinflammatory disorders.

HSP70 induces liver X receptor pathway activation and cholesterol reduction in vitro and in vivo

Objective

Heat Shock Proteins (HSPs) maintain cellular homeostasis under stress. HSP70 represents a major stress-inducible family member and has been identified as a druggable target in inherited cholesterol-sphingolipid storage diseases. We investigated if HSP70 modulates cholesterol accumulation in more common conditions related to atherogenesis.

Methods

We studied the effects of recombinant HSP70 in cholesterol-laden primary macrophages from human blood donors and pharmacological HSP70 upregulation in high-cholesterol diet fed zebrafish.

Results

Recombinant HSP70 facilitated cholesterol removal from primary human macrophage foam cells. RNA sequencing revealed that HSP70 induced a robust transcriptional re-programming, including upregulation of key targets of liver X receptors (LXR), master regulators of whole-body cholesterol removal. Mechanistically, HSP70 interacted with the macrophage LXRalpha promoter, increased LXRalpha and its target mRNAs, and led to elevated levels of key proteins facilitating cholesterol efflux, including ATP-binding cassette transporters A1 and G1. Pharmacological augmentation of endogenous HSP70 in high-cholesterol diet fed zebrafish activated LXR and its target mRNAs and reduced cholesterol storage at the whole organism level.

Conclusion

These data demonstrate that HSP70 exerts a cholesterol lowering effect in primary human cells and animals and uncover a nuclear action of HSP70 in mediating cross-talk between HSP and LXR transcriptional regulation.

6-Gingerol Regulates Hepatic Cholesterol Metabolism by Up-regulation of LDLR and Cholesterol Efflux-Related Genes in HepG2 Cells

Gingerols, the pungent ingredients in ginger, are reported to possess a cholesterol-lowering activity. However, the underlying mechanism remains unclear. The present study was to investigate how 6-gingerol (6-GN), the most abundant gingerol in fresh ginger, regulates hepatic cholesterol metabolism. HepG2 cells were incubated with various concentrations of 6-GN ranging from 50 to 200 μM for 24 h. Results showed that both cellular total cholesterol and free cholesterol decreased in a dose-dependent manner. Besides, 6-GN ranging from 100 to 200 μM increased the LDLR protein and uptake of fluorescent-labeled LDL. Moreover, the mRNA and protein expressions of cholesterol metabolism-related genes were also examined. It was found that 6-GN regulated cholesterol metabolism via up-regulation of LDLR through activation of SREBP2 as well as up-regulation of cholesterol efflux-related genes LXRα and ABCA1.

Critical Role of the Human ATP-Binding Cassette G1 Transporter in Cardiometabolic Diseases

ATP-binding cassette G1 (ABCG1) is a member of the large family of ABC transporters which are involved in the active transport of many amphiphilic and lipophilic molecules including lipids, drugs or endogenous metabolites. It is now well established that ABCG1 promotes the export of lipids, including cholesterol, phospholipids, sphingomyelin and oxysterols, and plays a key role in the maintenance of tissue lipid homeostasis. Although ABCG1 was initially proposed to mediate cholesterol efflux from macrophages and then to protect against atherosclerosis and cardiovascular diseases (CVD), it becomes now clear that ABCG1 exerts a larger spectrum of actions which are of major importance in cardiometabolic diseases (CMD). Beyond a role in cellular lipid homeostasis, ABCG1 equally participates to glucose and lipid metabolism by controlling the secretion and activity of insulin and lipoprotein lipase. Moreover, there is now a growing body of evidence suggesting that modulation of ABCG1 expression might contribute to the development of diabetes and obesity, which are major risk factors of CVD. In order to provide the current understanding of the action of ABCG1 in CMD, we here reviewed major findings obtained from studies in mice together with data from the genetic and epigenetic analysis of ABCG1 in the context of CMD.

LXR agonist treatment of blastic plasmacytoid dendritic cell neoplasm restores cholesterol efflux and triggers apoptosis

Blastic plasmacytoid dendritic cell (PDC) neoplasm (BPDCN) is an aggressive hematological malignancy with a poor prognosis that derives from PDCs. No consensus for optimal treatment modalities is available today and the full characterization of this leukemia is still emerging. We identified here a BPDCN-specific transcriptomic profile when compared with those of acute myeloid leukemia and T-acute lymphoblastic leukemia, as well as the transcriptomic signature of primary PDCs. This BPDCN gene signature identified a dysregulation of genes involved in cholesterol homeostasis, some of them being liver X receptor (LXR) target genes. LXR agonist treatment of primary BPDCN cells and BPDCN cell lines restored LXR target gene expression and increased cholesterol efflux via the upregulation of adenosine triphosphate-binding cassette (ABC) transporters, ABCA1 and ABCG1. LXR agonist treatment was responsible for limiting BPDCN cell proliferation and inducing intrinsic apoptotic cell death. LXR activation in BPDCN cells was shown to interfere with 3 signaling pathways associated with leukemic cell survival, namely: NF-κB activation, as well as Akt and STAT5 phosphorylation in response to the BPDCN growth/survival factor interleukin-3. These effects were increased by the stimulation of cholesterol efflux through a lipid acceptor, the apolipoprotein A1. In vivo experiments using a mouse model of BPDCN cell xenograft revealed a decrease of leukemic cell infiltration and BPDCN-induced cytopenia associated with increased survival after LXR agonist treatment. This demonstrates that cholesterol homeostasis is modified in BPDCN and can be normalized by treatment with LXR agonists which can be proposed as a new therapeutic approach.

LXR agonist T0901317 upregulates thrombomodulin expression in glomerular endothelial cells by inhibition of nuclear factor‑κB

Dysfunction of glomerular endothelial cells (GECs) induces a variety of symptoms, including proteinuria, inflammation, vascular diseases, fibrosis and thrombosis. Thrombomodulin (TM) acts as a vasoprotective molecule on the surface of the vascular endothelial cells to maintain the homeostasis of the endothelial microenvironment by suppressing cellular proliferation, adhesion and inflammatory responses. Liver X receptor (LXR), a nuclear receptor (NR) and a bile acid‑activated transcription factor, regulates metabolism and cholesterol transport, vascular tension and inflammation. Previous studies indicated that TM expression is upregulated by various NRs; however, it is unclear whether pharmacological modulation of LXR may affect TM expression and GEC function. The current study revealed that LXR activation by its agonist, T0901317, upregulates the expression and activity of TM. This effect was mediated specifically through LXR‑α, and not through LXR‑β. Additionally, T0901317 treatment inhibited nuclear factor‑κB (NF‑κB) signaling and the secretion of high glucose‑induced proinflammatory mediators, including tumor necrosis factor‑α and interleukin‑1β in GECs. Co‑immunoprecipitation experiments determined that treatment with T0901317 enhances the interaction between LXR‑α and the transcriptional coactivator, p300, in GEC extracts. The present findings suggest that NF‑κB may be a negative regulator of TM expression, and its removal may contribute to TM gene expression, particularly when in competition with the T0901317‑enhanced formation of the LXR/p300 complex. Therefore, LXR may be a novel molecular target for manipulating TM in GECs, which may advance the treatment of endothelial cell‑associated diseases.

Effects of pomegranate peel polyphenols on lipid accumulation and cholesterol metabolic transformation in L-02 human hepatic cells via the PPARγ-ABCA1/CYP7A1 pathway

PPPs, PC and PEA in different concentrations were found to decrease the total cholesterol (TC) content and increase the total bile acid (TBA) content of a human hepatic cell model, and so possess a lipid-lowering effect.

Liver X receptor-α and miR-130a-3p regulate expression of sphingosine 1-phosphate receptor 2 in human umbilical vein endothelial cells

Recent studies have shown that activation of liver X receptors (LXRs) attenuates the development of atherosclerosis, not only by regulating lipid metabolism but also by suppressing inflammatory signaling. Sphingosine 1-phosphate receptor 2 (S1PR2), an important inflammatory gene product, plays a role in the development of various inflammatory diseases. It was proposed that S1PR2 might be regulated by LXR-α. In the present study, the effect of LXR-α on tumor necrosis factor-α (TNF-α)-induced S1PR2 expression in human umbilical vein endothelial cells (HUVECs) was investigated and the underlying mechanism was explored. The results demonstrated that TNF-α led to an increase in S1PR2 expression and triggered a downregulation of LXR-α expression in HUVECs as well. Downregulation of LXR-α with specific small interfering RNA (siRNA) remarkably enhanced the primary as well as TNF-α-induced expression of S1PR2 in HUVECs. Activation of LXR-α by agonist GW3965 inhibited both primary and TNF-α-induced S1PR2 expression. GW3965 also attenuated S1PR2-induced endothelial barrier dysfunction. The data further showed that TNF-α induced a significant decrease in miR-130a-3p expression. Overexpression of miR-130a-3p with mimic product reduced S1PR2 protein expression, and inhibition of miR-130a-3p by specific inhibitor resulted in an increase in S1PR2 protein expression. Furthermore, activation of LXRs with agonist enhanced the expression of miR-130a-3p, and knockdown of LXR-α by siRNA suppressed miR-130a-3p expression. These results suggest that LXR-α might downregulate S1PR2 expression via miR-130a-3p in quiescent HUVECs. Stimulation of TNF-α attenuates the activity of LXR-α and results in enhanced S1PR2 expression.

Acanthoic acid ameliorates lipopolysaccharide-induced acute lung injury

Acanthoic acid, a pimaradiene diterpene isolated from Acanthopanax koreanum, has been reported to have anti-inflammatory activities. However, the effects of acanthoic acid on LPS-induced acute lung injury have not been reported. The purpose of this study was to investigate the protective effect of acanthoic acid on LPS-induced ALI and to clarify the possible anti-inflammatory mechanisms. In vivo, an LPS-induced ALI model in mice was used to assess the protective effects of acanthoic acid on ALI. Meanwhile, mouse alveolar macrophages MH-S were stimulated with LPS in the presence or absence of acanthoic acid. The expressions of TNF-α, IL-6 and IL-1β were measured by ELISA. LXRα and NF-κB expression were detected by Western blot analysis. The results showed that acanthoic acid downregulated LPS-induced TNF-α, IL-6 and IL-1β production in BALF. MPO activity and lung wet-to-dry ratio were also inhibited by acanthoic acid. In addition, acanthoic acid attenuated lung histopathologic changes. In vitro, acanthoic acid inhibited inflammatory cytokines TNF-α, IL-6 and IL-1β production and NF-κB activation in LPS-stimulated alveolar macrophages. Acanthoic acid was found to up-regulated the expression of LXRα. The inhibition of acanthoic acid on LPS-induced cytokines and NF-κB activation can be abolished by LXRα siRNA. In conclusion, our results suggested that the protective effect of acanthoic acid on LPS-induced ALI was due to its ability to activate LXRα, thereby inhibiting LPS-induced inflammatory response.

Regulation of HDL genes: transcriptional, posttranscriptional, and posttranslational

HDL regulation is exerted at multiple levels including regulation at the level of transcription initiation by transcription factors and signal transduction cascades; regulation at the posttranscriptional level by microRNAs and other noncoding RNAs which bind to the coding or noncoding regions of HDL genes regulating mRNA stability and translation; as well as regulation at the posttranslational level by protein modifications, intracellular trafficking, and degradation. The above mechanisms have drastic effects on several HDL-mediated processes including HDL biogenesis, remodeling, cholesterol efflux and uptake, as well as atheroprotective functions on the cells of the arterial wall. The emphasis is on mechanisms that operate in physiologically relevant tissues such as the liver (which accounts for 80% of the total HDL-C levels in the plasma), the macrophages, the adrenals, and the endothelium. Transcription factors that have a significant impact on HDL regulation such as hormone nuclear receptors and hepatocyte nuclear factors are extensively discussed both in terms of gene promoter recognition and regulation but also in terms of their impact on plasma HDL levels as was revealed by knockout studies. Understanding the different modes of regulation of this complex lipoprotein may provide useful insights for the development of novel HDL-raising therapies that could be used to fight against atherosclerosis which is the underlying cause of coronary heart disease.

Tormentic acid reduces inflammation in BV-2 microglia by activating the liver X receptor alpha

Tormentic acid (TA) has been reported to have anticancer, anti-inflammatory and anti-atherogenic properties. However, the effects of TA on neuroinflammation have not been reported. In this study, we investigated whether TA inhibited lipopolysaccharide (LPS)-induced inflammatory response in BV2 microglia cells. BV2 microglia cells were treated with TA for 1h before exposure to LPS. The expression of inducible nitric oxide synthase (iNOS), Cyclooxygenase-2 (COX-2), Nuclear factor κB (NF-κB) and liver X receptor alpha (LXRα) was detected by western blotting. The expression of cytokines Tumor necrosis factor-alpha (TNF-α) and interleukin 1beta (IL-1β) was detected by enzyme-linked immunosorbent assays (ELISA). Results showed that TA inhibited nitric oxide (NO), prostaglandin E2 (PGE2) production by inhibiting iNOS and COX-2 expression. TA also inhibited LPS-induced inflammatory cytokines TNF-α and IL-1β expression. Furthermore, TA could activate LXRα and inhibit LPS-induced NF-κB activation. Knowdown of LXRα reversed the anti-inflammatory effects of TA. In conclusion, our results indicate that TA exerts an anti-inflammatory effect on LPS-stimulated BV2 microglia cells by activating LXRα.

Activation of liver-X-receptor α but not liver-X-receptor β protects against myocardial ischemia/reperfusion injury

BACKGROUND

Liver-X-receptors, LXRα (NR1H3) and LXRβ (NR1H2), encode 2 different but highly homologous isoforms of transcription factors belonging to the nuclear receptor superfamily. Whether LXRα and LXRβ subtypes have discrete roles in the regulation of cardiac physiology/pathology is unknown. We determine the role of each LXR subtype in myocardial ischemia/reperfusion (MI/R) injury.

METHODS AND RESULTS

Mice (wild type; those genetically depleted of LXRα, LXRβ, or both; and those overexpressing LXRα or LXRβ by in vivo intramyocardial adenoviral vector) were subjected to MI/R injury. Both LXRα and LXRβ were detected in wild-type mouse heart. LXRα, but not LXRβ, was significantly upregulated after MI/R. Dual activation of LXRα and LXRβ by natural and synthetic agonists reduced myocardial infarction and improved contractile function after MI/R. Mechanistically, LXR activation inhibited MI/R-induced oxidative stress and nitrative stress, attenuated endoplasmic reticulum stress and mitochondrial dysfunction, and reduced cardiomyocyte apoptosis in ischemic/reperfused myocardium. The aforementioned cardioprotective effects of LXR agonists were impaired in the setting of cardiac-specific gene silencing of LXRα, but not LXRβ subtype. Moreover, LXRα/β double-knockout and LXRα-knockout mice, but not LXRβ-knockout mice, increased MI/R injury, exacerbated MI/R-induced oxidative/nitrative stress, and aggravated endoplasmic reticulum stress and mitochondrial dysfunction. Furthermore, cardiac LXRα, not LXRβ, overexpression via adenoviral transfection suppressed MI/R injury.

CONCLUSIONS

Our study provides the first direct evidence that the LXRα, but not LXRβ, subtype is a novel endogenous cardiac protective receptor against MI/R injury. Drug development strategies specifically targeting LXRα may be beneficial in treating ischemic heart disease.

Liver X receptor agonist prevents LPS-induced mastitis in mice

Liver X receptor-α (LXR-α) which belongs to the nuclear receptor superfamily, is a ligand-activated transcription factor. Best known for its ability to regulate lipid metabolism and transport, LXRs have recently also been implicated in regulation of inflammatory response. The aim of this study was to investigate the preventive effects of synthetic LXR-α agonist T0901317 on LPS-induced mastitis in mice. The mouse model of mastitis was induced by injection of LPS through the duct of mammary gland. T0901317 was injected 1h before and 12h after induction of LPS intraperitoneally. The results showed that T0901317 significantly attenuated the infiltration of neutrophilic granulocytes, and the activation of myeloperoxidase (MPO); down-regulated the level of pro-inflammatory mediators including TNF-α, IL-1β, IL-6, COX-2 and PEG2; inhibited the phosphorylation of IκB-α and NF-κB p65, caused by LPS. Moreover, we report for the first time that LXR-α activation impaired LPS-induced mastitis. Taken together, these data indicated that T0901317 had protective effect on mastitis and the anti-inflammatory mechanism of T0901317 on LPS induced mastitis in mice may be due to its ability to inhibit NF-κB signaling pathway. LXR-α activation can be used as a therapeutic approach to treat mastitis.

Cholesterol efflux is LXRα isoform-dependent in human macrophages

BACKGROUND

The nuclear receptor liver X receptor (LXR) has two isoforms: LXRα and LXRβ. LXR activation promotes cholesterol efflux in macrophages, but the relative importance of each LXR isoform in mediating cholesterol efflux remains elusive.

METHODS

We evaluated the ability of different doses of LXRs agonist T0901317 to affect cholesterol efflux in human macrophages and its relationship with mRNA and protein levels of several well-characterized proteins involved in cholesterol efflux, including ABCA1, ABCG1, SR-BI, LXRβ and LXRα, using quantitative real-time PCR, Western blotting, and siRNA techniques.

RESULTS

Here we show that LXRα rather than LXRβ sustains baseline cholesterol efflux in human blood-derived macrophages. Treatment of human macrophages with a non-isoform-specific LXR agonist T0901317 substantially increased HDL- and apoA-I-mediated cholesterol efflux, which was associated with increased mRNA and protein expression levels of ABCA1, ABCG1, SR-BI, LXRα and LXRβ. The siRNA- mediated silencing of LXRα, but not LXRβ significantly reduced the protein levels of ABCA1,ABCG1, and SR-BI as wellas HDL- and ApoA1-mediated cholesterol in human macrophages.

CONCLUSIONS

These findings imply that LXRα- rather than LXRβ- specific agonists may promote reverse cholesterol transport in humans.

22(R)-hydroxycholesterol and pioglitazone synergistically decrease cholesterol ester via the PPARγ-LXRα-ABCA1 pathway in cholesterosis of the gallbladder

Cholesterosis is a disease of cholesterol metabolism characterized by the presence of excessive lipid droplets in the cytoplasm. These lipid droplets are mainly composed of cholesterol esters derived from free cholesterol. The removal of excess cholesterol from gallbladder epithelial cells (GBECs) is very important for the maintenance of intracellular cholesterol homeostasis and the preservation of gallbladder function. Several lines of evidence have indicated that the activation of either peroxisome proliferator-activated receptor gamma (PPARγ) or liver X receptor α (LXRα) relates to cholesterol efflux. While pioglitazone can regulate the activation of PPARγ, 22(R)-hydroxycholesterol can activate LXRα and is a metabolic intermediate in the biosynthesis of steroid hormones. However, the effect of 22(R)-hydroxycholesterol in combination with pioglitazone on cholesterosis of the gallbladder is unclear. GBECs were treated with pioglitazone, 22(R)-hydroxycholesterol or PPARγ siRNA followed by Western blot analysis for ATP-binding cassette transporter A1 (ABCA1), PPARγ and LXRα. Cholesterol efflux to apoA-I was determined, and Oil Red O staining was performed to monitor variations in lipid levels in treated GBECs. Our data showed that 22(R)-hydroxycholesterol can modestly up-regulate LXRα while simultaneously increasing ABCA1 by 56%. The combination of 22(R)-hydroxycholesterol and pioglitazone resulted in a 3.64-fold increase in ABCA1 expression and a high rate of cholesterol efflux. Oil Red O staining showed an obvious reduction in the lipid droplets associated with cholesterosis in GBECs. In conclusion, the present findings indicate that the anti-lipid deposition action of 22(R)-hydroxycholesterol combined with pioglitazone involves the activation of the PPARγ-LXRα-ABCA1 pathway, increased ABCA1 expression and the efflux of cholesterol from GBECs. Thus, 22(R)-hydroxycholesterol synergistically combined with pioglitazone to produce a remarkable effect on lipid deposition in cholesterosis GBECs.

Liver X receptor activation stimulates iron export in human alternative macrophages

RATIONALE

In atherosclerotic plaques, iron preferentially accumulates in macrophages where it can exert pro-oxidant activities.

OBJECTIVE

The objective of this study was, first, to better characterize the iron distribution and metabolism in macrophage subpopulations in human atherosclerotic plaques and, second, to determine whether iron homeostasis is under the control of nuclear receptors, such as the liver X receptors (LXRs).

METHODS AND RESULTS

Here we report that iron depots accumulate in human atherosclerotic plaque areas enriched in CD68 and mannose receptor (MR)-positive (CD68(+)MR(+)) alternative M2 macrophages. In vitro IL-4 polarization of human monocytes into M2 macrophages also resulted in a gene expression profile and phenotype favoring iron accumulation. However, M2 macrophages on iron exposure acquire a phenotype favoring iron release, through a strong increase in ferroportin expression, illustrated by a more avid oxidation of extracellular low-density lipoprotein by iron-loaded M2 macrophages. In line, in human atherosclerotic plaques, CD68(+)MR(+) macrophages accumulate oxidized lipids, which activate LXRα and LXRβ, resulting in the induction of ABCA1, ABCG1, and apolipoprotein E expression. Moreover, in iron-loaded M2 macrophages, LXR activation induces nuclear factor erythroid 2-like 2 expression, thereby increasing ferroportin expression, which, together with a decrease of hepcidin mRNA levels, promotes iron export.

CONCLUSIONS

These data identify a role for M2 macrophages in iron handling, a process regulated by LXR activation.

Differential regulation of gene expression by LXRs in response to macrophage cholesterol loading

The ability of cells to precisely control gene expression in response to intracellular and extracellular signals plays an important role in both normal physiology and in pathological settings. For instance, the accumulation of excess cholesterol by macrophages initiates a genetic response mediated by the liver X receptors (LXRs)-α (NR1H3) and LXRβ (NR1H2), which facilitates the transport of cholesterol out of cells to high-density lipoprotein particles. Studies using synthetic LXR agonists have also demonstrated that macrophage LXR activation simultaneously induces a second network of genes that promotes fatty acid and triglyceride synthesis that may support the detoxification of excess free cholesterol by storage in the ester form. We now show that treatment of human THP-1 macrophages with endogenous or synthetic LXR ligands stimulates both transcriptional and posttranscriptional pathways that result in the selective recruitment of the LXRα subtype to LXR-regulated promoters. Interestingly, when human or mouse macrophages are loaded with cholesterol under conditions that mimic the development of atherogenic macrophage foam cells, a selective LXR response is generated that induces genes mediating cholesterol transport but does not coordinately regulate genes involved in fatty acid synthesis. The gene-selective response to cholesterol loading occurs, even in the presence of LXRα binding to the promoter of the gene encoding the sterol regulatory element-binding protein-1c, the master transcriptional regulator of fatty acid synthesis. The ability of promoter bound LXRα to recruit RNA polymerase to the sterol regulatory element-binding protein-1c promoter, however, appears to be ligand selective.

LXR activation by GW3965 alters fat tissue distribution and adipose tissue inflammation in ob/ob female mice

To investigate the role of liver X receptor (LXR) in adipose tissue metabolism during obesity, ob/ob mice were treated for 5 weeks with the synthetic LXR agonist GW3965. MRI analysis revealed that pharmacological activation of LXR modified fat distribution by decreasing visceral (VS) fat and inversely increasing subcutaneous (SC) fat storage without affecting whole body fat content. This was concordant with opposite regulation by GW3965 of the lipolytic markers hormone-sensitive lipase (HSL) and adipose triglyceride lipase (ATGL) in the two fat depots; moreover, the expression of genes involved in lipogenesis was significantly induced in SC fat. Lipidomic analysis suggested that changes in lipid composition in response to GW3965 also varied between VS and SC fat. In both depots, the observed alteration in lipid composition indicated an overall change toward less lipotoxic lipids. Flow cytometry analysis showed decreased immune cell infiltration in adipose tissue of ob/ob mice in response to GW3965 treatment, which in VS fat mainly affected the macrophage population and in SC fat the lymphocyte population. In line with this, the expression and secretion of proinflammatory markers was decreased in both fat deposits with GW3965 treatment.