LXR, a nuclear receptor that defines a distinct retinoid response pathway

Structure-based virtual screening for identification of potential non-steroidal LXR modulators against neurodegenerative conditions

Liver X Receptors (LXRs) are members of the nuclear receptor superfamily that regulate cholesterol metabolism. LXRs have been suggested as promising targets against many neurodegenerative diseases (NDDs). The present study was aimed to identify novel non-steroidal molecules that may potentially modulate LXR activity. The structure-based virtual screening (SBVS) was used to search for suitable compounds from the Asinex library. The top hits were selected and filtered based on their binding affinity for LXR α and β isoforms. Based on molecular docking and scoring results, 24 compounds were selected that had binding energy in the range of - 13.9 to - 12 for LXRα and - 12.5 to - 11 for LXRβ, which were higher than the reference ligands (GW3965 and TO901317). Further, the five hits referred to as model 29, 64, 202, 250, 313 were selected by virtue of their binding interactions with amino acid residues at the active site of LXRs. The selected hits were then subjected to absorption, distribution, metabolism, excretion, and toxicity (ADMET) analysis and blood-brain permeability prediction. It was observed that the selected hits had better pharmacokinetic properties with no toxicity and could cross blood-brain barrier. Further, the selected hits were analysed for dynamic evolution of the system with LXRs by molecular dynamics (MD) simulation at 100 ns using GROMACS. The MD simulation results validated that selected hits possess a remarkable amount of flexibility, stability, compactness, binding energy and exhibited limited conformational modification. The root mean square deviation (RMSD) values of the top-scoring hits complexed with LXRα and LXRβ were 0.05-0.6 nm and 0.05-0.45 nm respectively, which is greater than the protein itself. Altogether the study identified potential non-steroidal LXR modulators that appear to be effective against various neurodegenerative conditions involving perturbed cholesterol and lipid homeostasis.

Lactic acid bacteria-derived γ-linolenic acid metabolites are PPARδ ligands that reduce lipid accumulation in human intestinal organoids

Gut microbiota regulate physiological functions in various hosts, such as energy metabolism and immunity. Lactic acid bacteria, including Lactobacillus plantarum, have a specific polyunsaturated fatty acid saturation metabolism that generates multiple fatty acid species, such as hydroxy fatty acids, oxo fatty acids, conjugated fatty acids, and trans-fatty acids. How these bacterial metabolites impact host physiology is not fully understood. Here, we investigated the ligand activity of lactic acid bacteria–produced fatty acids in relation to nuclear hormone receptors expressed in the small intestine. Our reporter assays revealed two bacterial metabolites of γ-linolenic acid (GLA), 13-hydroxy-cis-6,cis-9-octadecadienoic acid (γHYD), and 13-oxo-cis-6,cis-9-octadecadienoic acid (γKetoD) activated peroxisome proliferator-activated receptor delta (PPARδ) more potently than GLA. We demonstrate that both γHYD and γKetoD bound directly to the ligand-binding domain of human PPARδ. A docking simulation indicated that four polar residues (T289, H323, H449, and Y473) of PPARδ donate hydrogen bonds to these fatty acids. Interestingly, T289 does not donate a hydrogen bond to GLA, suggesting that bacterial modification of GLA introducing hydroxy and oxo group determines ligand selectivity. In human intestinal organoids, we determined γHYD and γKetoD increased the expression of PPARδ target genes, enhanced fatty acid β-oxidation, and reduced intracellular triglyceride accumulation. These findings suggest that γHYD and γKetoD, which gut lactic acid bacteria could generate, are naturally occurring PPARδ ligands in the intestinal tract and may improve lipid metabolism in the human intestine.

Therapeutic Drug-Induced Metabolic Reprogramming in Glioblastoma

Glioblastoma WHO IV (GBM), the most common primary brain tumor in adults, is a heterogenous malignancy that displays a reprogrammed metabolism with various fuel sources at its disposal. Tumor cells primarily appear to consume glucose to entertain their anabolic and catabolic metabolism. While less effective for energy production, aerobic glycolysis (Warburg effect) is an effective means to drive biosynthesis of critical molecules required for relentless growth and resistance to cell death. Targeting the Warburg effect may be an effective venue for cancer treatment. However, past and recent evidence highlight that this approach may be limited in scope because GBM cells possess metabolic plasticity that allows them to harness other substrates, which include but are not limited to, fatty acids, amino acids, lactate, and acetate. Here, we review recent key findings in the literature that highlight that GBM cells substantially reprogram their metabolism upon therapy. These studies suggest that blocking glycolysis will yield a concomitant reactivation of oxidative energy pathways and most dominantly beta-oxidation of fatty acids.

Liver X Receptor Regulation of Glial Cell Functions in the CNS

In this review, we discuss the role of liver X receptors (LXRs) in glial cells (microglia, oligodendrocytes and astrocytes) in the central nervous system (CNS). LXRs are oxysterol-activated nuclear receptors that, in adults, regulate genes involved in cholesterol homeostasis, the modulation of inflammatory responses and glutamate homeostasis. The study of LXR knockout mice has revealed that LXRβ plays a key role in maintaining the health of dopaminergic neurons in the substantia nigra, large motor neurons in the spinal cord and retinal ganglion cells in the eye. In the peripheral nervous system (PNS), LXRβ is responsible for the health of the spiral ganglion neurons (SGNs) in the cochlea. In addition, LXRs are essential for the homeostasis of the cerebrospinal fluid (CSF), and in LXRαβ^−/− mice, the lateral ventricles are empty and lined with lipid-laden cells. As LXRαβ^−/− mice age, lipid vacuoles accumulate in astrocytes surrounding blood vessels. By seven months of age, motor coordination becomes impaired, and there is a loss of motor neurons in the spinal cord of LXRβ^−/− mice. During development, migration of neurons in the cortex and cerebellum is retarded in LXRβ^−/− mice. Since LXRs are not expressed in dopaminergic or motor neurons in adult mice, the neuroprotective effects of LXRs appear to come from LXRs in glial cells where they are expressed. However, despite the numerous neurological deficits in LXR^−/− rodents, multiple sclerosis has the clear distinction of being the only human neurodegenerative disease in which defective LXR signaling has been identified. In this review, we summarize the regulation and functions of LXRs in glial cells and analyze how targeting LXRs in glial cells might, in the future, be used to treat neurodegenerative diseases and, perhaps, disorders caused by aberrant neuronal migration during development.

Current Options and Future Perspectives in the Treatment of Dyslipidemia

Low-density lipoprotein cholesterol (LDL-C) plays a crucial role in the development of atherosclerosis. Statin therapy is the standard treatment for lowering LDL-C in primary and secondary prevention. However, some patients do not reach optimal LDL-C target levels or do not tolerate statins, especially when taking high doses long-term. Combining statins with different therapeutic approaches and testing other new drugs is the future key to reducing the burden of cardiovascular disease (CVD). Recently, several new cholesterol-lowering drugs have been developed and approved; others are promising results, enriching the pharmacological armamentarium beyond statins. Triglycerides also play an important role in the development of CVD; new therapeutic approaches are also very promising for their treatment. Familial hypercholesterolemia (FH) can lead to CVD early in life. These patients respond poorly to conventional therapies. Recently, however, new and promising pharmacological strategies have become available. This narrative review provides an overview of the new drugs for the treatment of dyslipidemia, their current status, ongoing clinical or preclinical trials, and their prospects. We also discuss the new alternative therapies for the treatment of dyslipidemia and their relevance to practice.

Human adaptation to high altitude: a review of convergence between genomic and proteomic signatures

Both genomics- and proteomics-based investigations have identified several essential genes, proteins, and pathways that may facilitate human adaptive genotype/phenotype in a population-specific manner. This comprehensive review provides an up-to-date list of genes and proteins identified for human adaptive responses to high altitudes. Genomics studies for indigenous high-altitude populations like Tibetans, Andeans, Ethiopians, and Sherpas have identified 169 genes under positive natural selection. Similarly, global proteomics studies have identified 258 proteins (± 1.2-fold or more) for Tibetan, Sherpa, and Ladakhi highlanders. The primary biological processes identified for genetic signatures include hypoxia-inducible factor (HIF)-mediated oxygen sensing, angiogenesis, and erythropoiesis. In contrast, major biological processes identified for proteomics signatures include 14–3-3 mediated sirtuin signaling, integrin-linked kinase (ILK), phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT), and integrin signaling. Comparing genetic and protein signatures, we identified 7 common genes/proteins (HBB/hemoglobin subunit beta, TF/serotransferrin, ANGPTL4/angiopoietin-related protein 4, CDC42/cell division control protein 42 homolog, GC/vitamin D-binding protein, IGFBP1/insulin-like growth factor-binding protein 1, and IGFBP2/insulin-like growth factor-binding protein 2) involved in crucial molecular functions like IGF-1 signaling, LXR/RXR activation, ferroptosis signaling, iron homeostasis signaling and regulation of cell cycle. Our combined multi-omics analysis identifies common molecular targets and pathways for human adaptation to high altitude. These observations further corroborate convergent positive selection of hypoxia-responsive molecular pathways in humans and advocate using multi-omics techniques for deciphering human adaptive responses to high altitude.

Nuclear hormone receptors in demyelinating diseases

Demyelination results from the pathological loss of myelin and is a hallmark of many neurodegenerative diseases. Despite the prevalence of demyelinating diseases, there are no disease modifying therapies that prevent the loss of myelin or promote remyelination. This review aims to summarize studies in the field that highlight the importance of nuclear hormone receptors in the promotion and maintenance of myelination and the relevance of nuclear hormone receptors as potential therapeutic targets for demyelinating diseases. These nuclear hormone receptors include the estrogen receptor, progesterone receptor, androgen receptor, vitamin D receptor, thyroid hormone receptor, peroxisome proliferator-activated receptor, liver X receptor, and retinoid X receptor. Pre-clinical studies in well-established animal models of demyelination have shown a prominent role of these nuclear hormone receptors in myelination through their promotion of oligodendrocyte maturation and development. The activation of the nuclear hormone receptors by their ligands also promotes the synthesis of myelin proteins and lipids in mouse models of demyelination. There are limited clinical studies that focus on how the activation of these nuclear hormone receptors could alleviate demyelination in patients with diseases such as multiple sclerosis (MS). However, the completed clinical trials have reported improved clinical outcome in MS patients treated with the ligands of some of these nuclear hormone receptors. Together, the positive results from both clinical and pre-clinical studies point to nuclear hormone receptors as promising therapeutic targets to counter demyelination.

Impact of Inflammatory Bowel Disease (IBD) and IBD Medications on Risk of Hyperlipidemia and in vitro Hepatic Lipogenic-Related Gene Expression: A Population-Based Cohort Study

Patients with inflammatory bowel disease (IBD) present a higher risk of developing cardiovascular diseases (CVDs) due to chronic inflammation, which plays an essential role in atherogenesis. Hyperlipidemia is another risk factor for CVDs; however, the association between IBD, IBD medications, and hyperlipidemia remains controversial. We conducted a nationwide, population-based, retrospective, cohort study to examine the effect of IBD and IBD medications on the risk of developing hyperlipidemia. The effects of IBD medications on the expression of lipogenesis-related hepatic genes were also evaluated. We obtained data from the Longitudinal Health Insurance Database of Taiwan from patients with new-onset IBD and a comparison cohort of patients without IBD. A Cox proportional hazards regression model was used to analyze the difference in the risk of developing hyperlipidemia between the two cohorts. We also examined the influence of IBD medications on the expression of lipogenesis-related hepatic genes. After adjusting for comorbidities and confounding factors, the case group (N = 14,524) had a higher risk for hyperlipidemia than the control group (N = 14,524) [adjusted hazards ratio (aHR), 2.18]. Patients with IBD that did not receive IBD medications exhibited a significantly higher risk of hyperlipidemia (aHR, 2.20). In those treated with IBD medications, the risk of developing hyperlipidemia was significantly lowered than those without such medications (all aHR ≤ 0.45). Gene expression analysis indicated that IBD medications downregulated the expression of lipogenesis-related genes. Screening blood lipids in IBD patients is needed to explore the specific role and impact of IBD medications in the development of CVD.

Targeting Nuclear Receptors in Lung Cancer—Novel Therapeutic Prospects

Lung cancer, the second most commonly diagnosed cancer, is the major cause of fatalities worldwide for both men and women, with an estimated 2.2 million new incidences and 1.8 million deaths, according to GLOBOCAN 2020. Although various risk factors for lung cancer pathogenesis have been reported, controlling smoking alone has a significant value as a preventive measure. In spite of decades of extensive research, mechanistic cues and targets need to be profoundly explored to develop potential diagnostics, treatments, and reliable therapies for this disease. Nuclear receptors (NRs) function as transcription factors that control diverse biological processes such as cell growth, differentiation, development, and metabolism. The aberrant expression of NRs has been involved in a variety of disorders, including cancer. Deregulation of distinct NRs in lung cancer has been associated with numerous events, including mutations, epigenetic modifications, and different signaling cascades. Substantial efforts have been made to develop several small molecules as agonists or antagonists directed to target specific NRs for inhibiting tumor cell growth, migration, and invasion and inducing apoptosis in lung cancer, which makes NRs promising candidates for reliable lung cancer therapeutics. The current work focuses on the importance of various NRs in the development and progression of lung cancer and highlights the different small molecules (e.g., agonist or antagonist) that influence NR expression, with the goal of establishing them as viable therapeutics to combat lung cancer.

A cholestatic pattern predicts major liver-related outcomes in patients with non-alcoholic fatty liver disease

BACKGROUND & AIMS

NAFLD patients usually have an increase in AST/ALT levels, but cholestasis can also be observed. We aimed to assess in subjects with NAFLD the impact of the (cholestatic) C pattern on the likelihood of developing major liver-related outcomes (MALO).

METHODS

Five hundred and eighty-two consecutive patients with biopsy-proven NAFLD or a clinical diagnosis of NAFLD-related compensated cirrhosis were classified as hepatocellular (H), C and mixed (M) patterns, by using the formula (ALT/ALT Upper Limit of Normal-ULN)/(ALP/ALP ULN). MALO were recorded during follow-up. An external cohort of 1281 biopsy-proven NAFLD patients was enrolled as validation set.

RESULTS

H, M and C patterns were found in 153 (26.3%), 272 (46.7%) and 157 (27%) patients respectively. During a median follow-up of 78 months, only 1 (0.6%) patient with H pattern experienced MALO, whilst 15 (5.5%) and 38 (24.2%) patients in M and C groups had MALO. At multivariate Cox regression analysis, age >55 years (HR 2.55, 95% CI 1.17-5.54; p = .01), platelets <150 000/mmc (HR 0.14, 95% CI 0.06-0.32; p < .001), albumin <4 g/L(HR 0.62, 95% CI 0.35-1.08; p = .09), C versus M pattern (HR 7.86, 95% CI 1.03-60.1; p = .04), C versus H pattern(HR 12.1, 95% CI 1.61-90.9; p = .01) and fibrosis F3-F4(HR 35.8, 95% CI 4.65-275.2; p < .001) were independent risk factors for MALO occurrence. C versus M pattern(HR 14.3, 95% CI 1.90-105.6; p = .008) and C versus H pattern (HR 15.6, 95% CI 2.10-115.1; p = .0068) were confirmed independently associated with MALO occurrence in the validation set. The immunohistochemical analysis found a significantly higher prevalence of moderate-high-grade ductular metaplasia combined with low-grade ductular proliferation in C pattern when compared with the biochemical H pattern. Gene expression analysis showed a lower expression of NR1H3, RXRα and VCAM1 in patients with the C pattern.

CONCLUSIONS

The presence of a cholestatic pattern in patients with NAFLD predicts a higher risk of MALO independently from other features of liver disease.

Dietary soya saponin improves the lipid metabolism and intestinal health of laying hens

Soya saponin (SS) is a natural active substance of leguminous plant, which could improve lipid metabolism and regulate immune function. Intestinal flora might play a key role in the biological functions of SS. The objective of this study was to measure the effects of dietary SS on immune function, lipid metabolism, and intestinal flora of laying hens with or without antibiotic treated. The experiment was designed as a factorial arrangement of 3 dietary SS treatments × 2 antibiotic treatments. Birds were fed a basal diet (CON) or a low-SS diet (50 SS) containing 50 mg/kg SS, or a high-SS diet (500 SS) containing 500 mg/kg SS. Birds were cofed with or without antibiotics. The growth experiment lasted for 10 wk. Results showed that birds fed the 50 mg/kg SS diet tended to have lower abdominal fat rate. The gene expression of liver X receptor-α (LxR-α) in liver and serum total cholesterol (TC) were dropped, and the gene expression of acyl-CoA thioesterase 8 (ACOT8) in liver were upregulated. Compared with CON group, the levels of lysozyme, IL-10, and transforming growth factor (TGF-β) in the serum were elevated as along with gene expression of IL-10, TGF-β, and LYZ in ileum of both 50 and 500 SS group. However, the level of secretory immunoglobulin A (sIgA) and Mucin-2 in the ileum were downregulated in the 500 SS group. Additionally, Lactobacillus and Lactobacillus gasseri were the dominant bacteria in the 50 SS group, whereas the relative abundance of Lactobacillus was dropped in the 500 SS group. With combined antibiotics treatment, the α-diversity of bacteria was reduced, and the biological effects of SS were eliminated. In conclusion, the lipid metabolism, immune function, and intestinal flora of the laying hens were improved with the dietary supplementation of 50 mg/kg SS. But dietary 500 mg/kg SS had negative effects on laying hens.

Integrative analysis reveals multiple modes of LXR transcriptional regulation in liver

The nuclear receptors liver X receptor (LXR) α and β play crucial roles in hepatic metabolism. Many genes induced in response to pharmacologic LXR agonism have been defined; however, the transcriptional consequences of loss of LXR binding to its genomic targets are less well characterized. Here, we addressed how deletion of both LXRα and LXRβ from mouse liver (LXR double knockout [DKO]) affects the transcriptional regulatory landscape by integrating changes in LXR binding, chromatin accessibility, and gene expression. Many genes involved in fatty acid metabolism showed reduced expression and chromatin accessibility at their intergenic and intronic regions in LXRDKO livers. Genes that were up-regulated with LXR deletion had increased chromatin accessibility at their promoter regions and were enriched for functions not linked to lipid metabolism. Loss of LXR binding in liver reduced the activity of a broad set of hepatic transcription factors, inferred through changes in motif accessibility. By contrast, accessibility at promoter nuclear factor Y (NF-Y) motifs was increased in the absence of LXR. Unexpectedly, we also defined a small set of LXR targets for direct ligand-dependent repression. These genes have LXR-binding sites but showed increased expression in LXRDKO liver and reduced expression in response to the LXR agonist. In summary, the binding of LXRs to the hepatic genome has broad effects on the transcriptional landscape that extend beyond its canonical function as an activator of lipid metabolic genes.

Transcriptional Regulation of Hepatic Autophagy by Nuclear Receptors

Autophagy is an adaptive self-eating process involved in degradation of various cellular components such as carbohydrates, lipids, proteins, and organelles. Its activity plays an essential role in tissue homeostasis and systemic metabolism in response to diverse challenges, including nutrient depletion, pathogen invasion, and accumulations of toxic materials. Therefore, autophagy dysfunctions are intimately associated with many human diseases such as cancer, neurodegeneration, obesity, diabetes, infection, and aging. Although its acute post-translational regulation is well described, recent studies have also shown that autophagy can be controlled at the transcriptional and post-transcriptional levels. Nuclear receptors (NRs) are in general ligand-dependent transcription factors consisting of 48 members in humans. These receptors extensively control transcription of a variety of genes involved in development, metabolism, and inflammation. In this review, we discuss the roles and mechanisms of NRs in an aspect of transcriptional regulation of hepatic autophagy, and how the NR-driven autophagy pathway can be harnessed to treat various liver diseases.

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.

Recognition of fold- and function-specific sites in the ligand-binding domain of the thyroid hormone receptor-like family

BACKGROUND

The thyroid hormone receptor-like (THR-like) family is the largest transcription factors family belonging to the nuclear receptor superfamily, which directly binds to DNA and regulates the gene expression and thereby controls various metabolic processes in a ligand-dependent manner. The THR-like family contains receptors THRs, RARs, VDR, PPARs, RORs, Rev-erbs, CAR, PXR, LXRs, and others. THR-like receptors are involved in many aspects of human health, including development, metabolism and homeostasis. Therefore, it is considered an important therapeutic target for various diseases such as osteoporosis, rickets, diabetes, etc.

METHODS

In this study, we have performed an extensive sequence and structure analysis of the ligand-binding domain (LBD) of the THR-like family spanning multiple taxa. We have use different computational tools (information-theoretic measures; relative entropy) to predict the key residues responsible for fold and functional specificity in the LBD of the THR-like family. The MSA of THR-like LBDs was further used as input in conservation studies and phylogenetic clustering studies.

RESULTS

Phylogenetic analysis of the LBD domain of THR-like proteins resulted in the clustering of eight subfamilies based on their sequence homology. The conservation analysis by relative entropy (RE) revealed that structurally important residues are conserved throughout the LBDs in the THR-like family. The multi-harmony conservation analysis further predicted specificity in determining residues in LBDs of THR-like subfamilies. Finally, fold and functional specificity determining residues (residues critical for ligand, DBD and coregulators binding) were mapped on the three-dimensional structure of thyroid hormone receptor protein. We then compiled a list of natural mutations in THR-like LBDs and mapped them along with fold and function-specific mutations. Some of the mutations were found to have a link with severe diseases like hypothyroidism, rickets, obesity, lipodystrophy, epilepsy, etc.

CONCLUSION

Our study identifies fold and function-specific residues in THR-like LBDs. We believe that this study will be useful in exploring the role of these residues in the binding of different drugs, ligands, and protein-protein interaction among partner proteins. So this study might be helpful in the rational design of either ligands or receptors.

Synthesis and structure activity relationship of the first class of LXR inverse agonists

Liver X Receptors (LXRs) are members of the nuclear receptor family, and they play significant role in lipid and cholesterol metabolism. Moreover, they are key regulators of several inflammatory pathways. Pharmacological modulation of LXRs holds great potential in treatment of metabolic diseases, neurodegenerative diseases, and cancer. We were the first group to identify LXR inverse agonists SR9238 (6) and SR9243 (7) and demonstrate their potential utility in treating liver diseases and cancer. Here, we present the results of structure-activity relationship (SAR) studies, based around SR9238 (6) and SR9243 (7). This study led to identification of 16, 17, 19, and 38, which were more potent inverse agonists than SR9238 (6) and SR9243 (7) and inhibited expression of the fatty acid synthase gene in DU145 cells. We previously demonstrated that inhibition of FASN is correlated to the anticancer activity of SR9243 (7) and this suggests that new inverse agonists have great potential as anticancer agents. We identified compounds with distinct selectivity toward both LXR isoforms, which can be excellent tools to study the pharmacology of both isoforms. We employed molecular dynamic (MD) simulations to better understand the molecular mechanism underlying inverse agonist activity and to guide our future design.

Genomic Variants and Multilevel Regulation of ABCA1, ABCG1, and SCARB1 Expression in Atherogenesis

Atheroprotective properties of human plasma high-density lipoproteins (HDLs) are determined by their involvement in reverse cholesterol transport (RCT) from the macrophage to the liver. ABCA1, ABCG1, and SR-BI cholesterol transporters are involved in cholesterol efflux from macrophages to lipid-free ApoA-I and HDL as a first RCT step. Molecular determinants of RCT efficiency that may possess diagnostic and therapeutic meaning remain largely unknown. This review summarizes the progress in studying the genomic variants of ABCA1, ABCG1, and SCARB1, and the regulation of their function at transcriptional and post-transcriptional levels in atherosclerosis. Defects in the structure and function of ABCA1, ABCG1, and SR-BI are caused by changes in the gene sequence, such as single nucleotide polymorphism or various mutations. In the transcription initiation of transporter genes, in addition to transcription factors, long noncoding RNA (lncRNA), transcription activators, and repressors are also involved. Furthermore, transcription is substantially influenced by the methylation of gene promoter regions. Post-transcriptional regulation involves microRNAs and lncRNAs, including circular RNAs. The potential biomarkers and targets for atheroprotection, based on molecular mechanisms of expression regulation for three transporter genes, are also discussed in this review.

Influences of antidepressant medications on the risk of developing hyperlipidemia in patients with depression by a population-based cohort study and on in vitro hepatic lipogenic-related gene expression

BACKGROUND

Depression increases the risk of cardiovascular disease (CVD). The association between antidepressant medications (ADMs) and CVD remains controversial. Hyperlipidemia is a risk factor for CVD. We conducted a nationwide population-based retrospective cohort study to examine depression and ADM use on the risk of developing hyperlipidemia. The effects of ADMs on the expression of lipogenesis-related hepatic genes were also evaluated.

METHODS

We obtained data from the Longitudinal Health Insurance Database of Taiwan on patients with new-onset depression and a comparison cohort without depression. A Cox proportional hazards regression model was used to analyze the differences in the risk of developing hyperlipidemia between these two cohorts. We also examined the influence of ADMs on the expression of lipogenesis-related hepatic genes.

RESULTS

After adjustment for comorbidities and confounding factors, the case group (N = 38,322) had a higher risk for hyperlipidemia than that of the control cohort (N = 38,322) [adjusted hazards ratio (aHR) =1.16]. Patients with depression who did not receive ADM therapy exhibited a significantly higher risk of hyperlipidemia (aHR = 1.61). However, in patients with depression treated with ADMs, the risk of developing hyperlipidemia was significantly lowered compared to the patients without ADMs (all aHR < 0.81). Gene expression analysis indicated that ADMs downregulated the expression of lipogenesis-related hepatic genes.

LIMITATIONS

Unmeasured confounding risk factors for hyperlipidemia might not have been included in the study.

CONCLUSIONS

ADMs reduced hyperlipidemia risk in patients with depression, partly by downregulating the expression of lipogenesis-related genes and improving the patients' lipid profiles. Early diagnosis and management of hyperlipidemia would further facilitate the prevention of CVD.

Aberrant Cholesterol Metabolism in Ovarian Cancer: Identification of Novel Therapeutic Targets

Cholesterol is an essential substance in mammalian cells, and cholesterol metabolism plays crucial roles in multiple biological functions. Dysregulated cholesterol metabolism is a metabolic hallmark in several cancers, beyond the Warburg effect. Reprogrammed cholesterol metabolism has been reported to enhance tumorigenesis, metastasis and chemoresistance in multiple cancer types, including ovarian cancer. Ovarian cancer is one of the most aggressive malignancies worldwide. Alterations in metabolic pathways are characteristic features of ovarian cancer; however, the specific role of cholesterol metabolism remains to be established. In this report, we provide an overview of the key proteins involved in cholesterol metabolism in ovarian cancer, including the rate-limiting enzymes in cholesterol biosynthesis, and the proteins involved in cholesterol uptake, storage and trafficking. Also, we review the roles of cholesterol and its derivatives in ovarian cancer and the tumor microenvironment, and discuss promising related therapeutic targets for ovarian cancer.

Characterization and prognostic value of LXR splice variants in triple-negative breast cancer

Activity of liver x receptor (LXR), the homeostatic regulator of cholesterol metabolism, is elevated in triple-negative breast cancer (BCa) relative to other BCa subtypes, driving drug resistance and metastatic gene signatures. The loci encoding LXRα and LXRβ produce multiple alternatively spliced proteins, but the true range of variants and their relevance to cancer remain poorly defined. Here, we report seven LXR splice variants, three of which have not previously been reported and five that were prognostic for disease-free survival. Expression of full-length LXRα splice variants was associated with poor prognosis, consistent with a role as an oncogenic driver of triple-negative tumor pathophysiology. Contrary to this was the observation that high expression of truncated LXRα splice variants or any LXRβ splice variant was associated with longer survival. These findings indicate that LXR isoform abundance is an important aspect of understanding the link between dysregulated cholesterol metabolism and cancer pathophysiology.

The wHole Story About Fenestrations in LSEC

The porosity of liver sinusoidal endothelial cells (LSEC) ensures bidirectional passive transport of lipoproteins, drugs and solutes between the liver capillaries and the liver parenchyma. This porosity is realized via fenestrations - transcellular pores with diameters in the range of 50-300 nm - typically grouped together in sieve plates. Aging and several liver disorders severely reduce LSEC porosity, decreasing their filtration properties. Over the years, a variety of drugs, stimulants, and toxins have been investigated in the context of altered diameter or frequency of fenestrations. In fact, any change in the porosity, connected with the change in number and/or size of fenestrations is reflected in the overall liver-vascular system crosstalk. Recently, several commonly used medicines have been proposed to have a beneficial effect on LSEC re-fenestration in aging. These findings may be important for the aging populations of the world. In this review we collate the literature on medicines, recreational drugs, hormones and laboratory tools (including toxins) where the effect LSEC morphology was quantitatively analyzed. Moreover, different experimental models of liver pathology are discussed in the context of fenestrations. The second part of this review covers the cellular mechanisms of action to enable physicians and researchers to predict the effect of newly developed drugs on LSEC porosity. To achieve this, we discuss four existing hypotheses of regulation of fenestrations. Finally, we provide a summary of the cellular mechanisms which are demonstrated to tune the porosity of LSEC.

Cinnamic Acid Ameliorates Nonalcoholic Fatty Liver Disease by Suppressing Hepatic Lipogenesis and Promoting Fatty Acid Oxidation

BACKGROUND

Cinnamic acid (CA) has been shown to have many beneficial effects including regulating lipid metabolism and reducing obesity. However, its effect on nonalcoholic fatty liver disease (NAFDL) has not been investigated in detail. Thus, we performed this study in order to explore CA's effect on hepatic lipid metabolism and the underlying mechanisms.

METHOD

Oleic acid (OA) was used to induce lipid accumulation in HepG2 cells. After coincubation with CA, the cells were stained with oil red O and the triglyceride (TG) content was assessed. Key genes in lipogenesis and fatty acid oxidation pathways were tested. Additionally, db/db and wt/wt mice were divided into three groups, with the wt/wt mice representing the normal group and the db/db mice being divided into the NAFLD and CA groups. After 4 weeks of oral treatment, all mice were sacrificed and the blood lipid profile and liver tissues were assessed.

RESULTS

CA treatment reduced the lipid accumulation in HepG2 cells and in db/db mouse livers. ACLY, ACC, FAS, SCD1, PPARγ, and CD36 were significantly downregulated, while CPT1A, PGC1α, and PPARα were significantly upregulated.

CONCLUSION

CA's therapeutic effect on NAFLD may be attributed to its ability to lower hepatic lipid accumulation, which is mediated by suppression of hepatic lipogenesis and fatty acid intake, as well as increased fatty acid oxidation.

Regulation of cholesterol biosynthesis and lipid metabolism: A microRNA management perspective

Cellular disruption of lipid and cholesterol metabolism results in pathological processes linked to metabolic and cardiovascular diseases. Classically, at the transcription stages, the Cholesterol levels are controlled by two cellular pathways. First, the SREBP transcription factor family controls Cholesterol biosynthesis via transcriptional regulation of critical rate-limiting cholesterogenic and lipogenic proteins. Secondly, The LXR/RXR transcription factor family controls cholesterol shuttling via transcriptional regulation of cholesterol transport proteins. In addition, the posttranscriptional control of gene expression of various enzymes and proteins of cholesterol biosynthesis pathways is mediated by small non-coding microRNAs. Regulatory noncoding miRNAs are critical regulators of biological processes, including developmental and metabolic functions. miRNAs function to fine-tune lipid and cholesterol metabolism pathways by controlling the mRNA levels and translation of critical molecules in each pathway. This review discusses the regulatory roles of miRNAs in cholesterol and lipid metabolism via direct and indirect effects on their target genes, including SREBP, LXR, HDL, LDL, and ABCA transporters. We also discuss the therapeutic implications of miRNA functions and their purported role in the potentiation of small molecule therapies.

Regulation of zebrafish fin regeneration by vitamin D signaling

BACKGROUND

Vitamin D is an essential nutrient that has long been known to regulate skeletal growth and integrity. In models of major appendage regeneration, treatment with vitamin D analogs has been reported to improve aspects of zebrafish fin regeneration in specific disease or gene misexpression contexts, but also to disrupt pattern in regenerating salamander limbs. Recently, we reported strong mitogenic roles for vitamin D signaling in several zebrafish tissues throughout life stages, including epidermal cells and osteoblasts of adult fins. To our knowledge, molecular genetic approaches to dissect vitamin D function in appendage regeneration have not been described.

RESULTS

Using a knock-in GFP reporter for the expression of the vitamin D target gene and negative regulator cyp24a1, we identified active vitamin D signaling in adult zebrafish fins during tissue homeostasis and regeneration. Transgenic expression of cyp24a1 or a dominant-negative vitamin D receptor (VDR) inhibited regeneration of amputated fins, whereas global vitamin D treatment accelerated regeneration. Using tissue regeneration enhancer elements, we found that local enhancement of VDR expression could improve regeneration with low doses of a vitamin D analog.

CONCLUSIONS

Vitamin D signaling enhances the efficacy of fin regeneration in zebrafish.

Saringosterol from Sargassum fusiforme Modulates Cholesterol Metabolism and Alleviates Atherosclerosis in ApoE-Deficient Mice

Dysregulation of cholesterol homeostasis is a major risk factor of atherosclerosis, which can lead to serious health problems, including heart attack and stroke. Liver X receptor (LXR) α and β are transcription factors belonging to the nuclear receptor superfamily, which play important roles in cholesterol homeostasis. Selectively activating LXRβ provides a promising strategy for the treatment of atherosclerosis. Here, we employed atherosclerotic apoE-knockout mice to evaluate the effects of saringosterol, a phytosterol with potent and selective action for LXRβ, which we identified previously in edible marine seaweed Sargassum fusiforme. We found that saringosterol treatment reduced the atherosclerotic plaque burden without having undesirable adverse hepatic effects in apoE-deficient mice fed an atherogenic diet. Meanwhile, reduced serum levels of cholesterol, accompanied by altered expression of LXR-regulated genes involved in cholesterol absorption, transport, efflux, excretion, and elimination, were observed in apoE-knockout mice after saringosterol treatment. Together, our study not only establishes saringosterol as an effective cholesterol-lowering and anti-atherogenic phytosterol but also provides insights into the underlying mechanism.

Untangling the Cooperative Role of Nuclear Receptors in Cardiovascular Physiology and Disease

The heart is the first organ to acquire its physiological function during development, enabling it to supply the organism with oxygen and nutrients. Given this early commitment, cardiomyocytes were traditionally considered transcriptionally stable cells fully committed to contractile function. However, growing evidence suggests that the maintenance of cardiac function in health and disease depends on transcriptional and epigenetic regulation. Several studies have revealed that the complex transcriptional alterations underlying cardiovascular disease (CVD) manifestations such as myocardial infarction and hypertrophy is mediated by cardiac retinoid X receptors (RXR) and their partners. RXRs are members of the nuclear receptor (NR) superfamily of ligand-activated transcription factors and drive essential biological processes such as ion handling, mitochondrial biogenesis, and glucose and lipid metabolism. RXRs are thus attractive molecular targets for the development of effective pharmacological strategies for CVD treatment and prevention. In this review, we summarize current knowledge of RXR partnership biology in cardiac homeostasis and disease, providing an up-to-date view of the molecular mechanisms and cellular pathways that sustain cardiomyocyte physiology.

MIG12 is involved in the LXR activation-mediated induction of the polymerization of mammalian acetyl-CoA carboxylase

Liver X receptors (LXR) α and β are a family of nuclear receptors that regulate lipogenesis by controlling the expression of the genes involved in the synthesis of fatty acids. MID1IP1, which encodes MIG12, is a target gene of LXR. MIG12 induces fatty acid synthesis by stimulating the polymerization-mediated activation of acetyl-CoA carboxylase (ACC). Here, we show that LXR's activation stimulates ACC polymerization in HepG2 cells by increasing the expression of MIG12. A knockdown of MID1IP1 abrogated the stimulation completely. The mutations of MIG12's leucine-zipper domain reduced the interaction between MIG12 and ACC, thus decreasing the MIG12's capacity to stimulate ACC polymerization. These results indicate that LXR's activation stimulates lipogenesis not only through the induction of the genes encoding lipogenic enzymes but also through MIG12's stimulation of ACC polymerization.

Berteroin ameliorates lipid accumulation through AMPK-mediated regulation of hepatic lipid metabolism and inhibition of adipocyte differentiation

AIMS

Berteroin (5-methylthiopentyl isothiocyanate) is a naturally occurring sulforaphane analog containing a non-oxidized sulfur atom in cruciferous vegetables. The objectives of the present study were to determine the effects of berteroin on lipid metabolism in hepatocytes and adipocytes and to elucidate the mechanisms involved.

MAIN METHODS

The effect of berteroin on lipid metabolism were evaluated in liver X receptor α agonist-stimulated HepG2 cells and adipocyte differentiation-induced 3T3-L1 cells using MTT assay, western blot, real time polymerase chain reaction, oil red O staining, and triglyceride assay.

KEY FINDINGS

T0901317 treatment increased the expression of sterol regulatory element binding protein (SREBP)-1c, a major transcription factor that mediates lipogenesis, and berteroin pretreatment significantly inhibited the expressions of T0901317-induced SREBP-1c and lipogenic genes. Especially, berteroin had a greater inhibitory effect on T0901317-induced SREBP-1c activation than sulforaphane, AICAR, or metformin. Berteroin also markedly suppressed lipid droplet formations and triglyceride accumulations caused by both T0901317 stimulation in HepG2 hepatocytes and differentiation induction in 3T3-L1 preadipocytes. However, berteroin significantly increased the expression of mitochondrial fatty acid oxidation-related genes (carnitine palmitoyltransferase 1 (CPT-1) and peroxisome proliferator-activated receptor gamma coactivator-1α) and the phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) in HepG2 cells. Interestingly, effects of berteroin on the expressions of SREBP-1c protein and CPT-1 mRNA were remarkably prevented by compound C (an AMPK inhibitor).

SIGNIFICANCE

Our results suggest berteroin-inhibited hepatic lipid accumulation and adipocyte differentiation might be mediated by AMPK activation and that berteroin might be useful for the prevention, amelioration, and treatment of metabolic diseases, including hepatic steatosis.

Mechanistic aspects of carotenoid health benefits - where are we now?

Dietary intake and tissue levels of carotenoids have been associated with a reduced risk of several chronic diseases, including cardiovascular diseases, type 2 diabetes, obesity, brain-related diseases and some types of cancer. However, intervention trials with isolated carotenoid supplements have mostly failed to confirm the postulated health benefits. It has thereby been speculated that dosing, matrix and synergistic effects, as well as underlying health and the individual nutritional status plus genetic background do play a role. It appears that our knowledge on carotenoid-mediated health benefits may still be incomplete, as the underlying mechanisms of action are poorly understood in relation to human relevance. Antioxidant mechanisms - direct or via transcription factors such as NRF2 and NF-κB - and activation of nuclear hormone receptor pathways such as of RAR, RXR or also PPARs, via carotenoid metabolites, are the basic principles which we try to connect with carotenoid-transmitted health benefits as exemplified with described common diseases including obesity/diabetes and cancer. Depending on the targeted diseases, single or multiple mechanisms of actions may play a role. In this review and position paper, we try to highlight our present knowledge on carotenoid metabolism and mechanisms translatable into health benefits related to several chronic diseases.

Expanding Roles of De Novo Lipogenesis in Breast Cancer

In recent years, lipid metabolism has gained greater attention in several diseases including cancer. Dysregulation of fatty acid metabolism is a key component in breast cancer malignant transformation. In particular, de novo lipogenesis provides the substrate required by the proliferating tumor cells to maintain their membrane composition and energetic functions during enhanced growth. However, it appears that not all breast cancer subtypes depend on de novo lipogenesis for fatty acid replenishment. Indeed, while breast cancer luminal subtypes rely on de novo lipogenesis, the basal-like receptor-negative subtype overexpresses genes involved in the utilization of exogenous-derived fatty acids, in the synthesis of triacylglycerols and lipid droplets, and fatty acid oxidation. These metabolic differences are specifically associated with genomic and proteomic changes that can perturb lipogenic enzymes and related pathways. This behavior is further supported by the observation that breast cancer patients can be stratified according to their molecular profiles. Moreover, the discovery that extracellular vesicles act as a vehicle of metabolic enzymes and oncometabolites may provide the opportunity to noninvasively define tumor metabolic signature. Here, we focus on de novo lipogenesis and the specific differences exhibited by breast cancer subtypes and examine the functional contribution of lipogenic enzymes and associated transcription factors in the regulation of tumorigenic processes.

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.

Oxysterols and mesenchymal stem cell biology

Mesenchymal stem cells have the ability to differentiate into several cell types when exposed to determined substances, including oxysterols. Oxysterols are cholesterol products derived from its auto-oxidation by reactive species or from enzymatic action. They are present in the body in low quantities under physiological conditions and exhibit several physiological and pharmacological actions according to both the types of oxysterol and tissue. Some of them are cytotoxic while others have been shown to promote cell differentiation through the action on several different receptors, such as nuclear LXR receptors and Smoothened receptor ligands. Here, we review the main pathways by which oxysterols have been associated with cell differentiation and death of mesenchymal stem cells.

Progression from Monoclonal gammopathy of undetermined significance of the immunoglobulin M class (IgM-MGUS) to Waldenstrom Macroglobulinemia is associated with an alteration in lipid metabolism

The molecular events that modulate the progression of monoclonal gammopathy of undetermined significance of the immunoglobulin M class (IgM-MGUS) to Waldenstrom Macroglobulinemia (WM) are mostly unknown. We implemented comparative proteomics and metabolomics analyses on patient serum samples to identify differentially expressed molecules crucial to the progression from IgM-MGUS to WM. Our data identified altered lipid metabolism as a discriminating factor between MGUS, WM, and matched normal controls. Levels of many fatty acids, including polyunsaturated fatty acids and dicarboxylic acids, were significantly downregulated in WM sera when compared to MGUS. These reductions were associated with diminished 15-LOX and PPAR protein expression and increased 5-LOX and GPX4 expression in WM versus MGUS patients’ samples. Furthermore, WM serum samples showed increased lipid peroxidation compared to MGUS. Treatment with IL-6 or TNFα, upstream regulators of differentially expressed proteins between MGUS and WM, increased lipid absorption and lipid peroxidation in WM cell lines. Knock-down of 15-LOX expression increased WM cell survival, an effect accompanied by increased 5-LOX and GPX4 expression. In summary, our data show that reduced fatty acid and lipid metabolite levels in the serum of the WM patients are associated with increased lipid peroxidation and that downregulation of 15-LOX increases the survival of WM cells. These data are highly significant in identifying the biomarkers of disease progression and designing targeted therapeutic intervention.

27-Hydroxycholesterol induces macrophage gene expression via LXR-dependent and -independent mechanisms

27-Hydroxycholesterol (27OHChol) exhibits agonistic activity for liver X receptors (LXRs). To determine roles of the LXR agonistic activity in macrophage gene expression, we investigated the effects of LXR inhibition on the 27OHChol-induced genes. Treatment of human THP-1 cells with GSK 2033, a potent cell-active LXR antagonist, results in complete inhibition in the transcription of LXR target genes (such as LXRα and ABCA1) induced by 27OHChol or a synthetic LXR ligand TO 901317. Whereas expression of CCL2 and CCL4 remains unaffected by GSK 2033, TNF-α expression is further induced and 27OHChol-induced CCL3 and CXCL8 genes are suppressed at both the transcriptional and protein translation levels in the presence of GSK 2033. This LXR antagonist downregulates transcript levels and surface expression of CD163 and CD206 and suppresses the transcription of CD14, CD80, and CD86 genes without downregulating their surface levels. GSK 2033 alone had no effect on the basal expression levels of the aforementioned genes. Collectively, these results indicate that LXR inhibition leads to differential regulation of 27-hydroxycholesterol-induced genes in macrophages. We propose that 27OHChol induces gene expression and modulates macrophage functions via LXR-dependent and -independent mechanisms.

Liver X receptors and skeleton: Current state-of-knowledge

The liver X receptors (LXR) is a nuclear receptor that acts as a prominent regulator of lipid homeostasis and inflammatory response. Its therapeutic effectiveness against various diseases like Alzheimer's disease and atherosclerosis has been investigated in detail. Emerging pieces of evidence now reveal that LXR is also a crucial modulator of bone remodeling. However, the molecular mechanisms underlying the pharmacological actions of LXR on the skeleton and its role in osteoporosis are poorly understood. Therefore, in the current review, we highlight LXR and its actions through different molecular pathways modulating skeletal homeostasis. The studies described in this review propound that LXR in association with estrogen, PTH, PPARγ, RXR hedgehog, and canonical Wnt signaling regulates osteoclastogenesis and bone resorption. It regulates RANKL-induced expression of c-Fos, NFATc1, and NF-κB involved in osteoclast differentiation. Additionally, several studies suggest suppression of RANKL-induced osteoclast differentiation by synthetic LXR ligands. Given the significance of modulation of LXR in various physiological and pathological settings, our findings indicate that therapeutic targeting of LXR might potentially prevent or treat osteoporosis and improve bone quality.

Danthron ameliorates obesity and MAFLD through activating the interplay between PPARα/RXRα heterodimer and adiponectin receptor 2

Obesity and associated metabolic associated fatty liver diseases (MAFLD) are strongly associated with dysfunction of glucose and lipid metabolism. AMPKα and PPARα are key regulators in the lipid and glucose homeostasis, indicating that novel agents to activate them are promising therapeutic approaches for metabolic syndrome. Noticeably, as a natural anthraquinone derivative extracted from rhubarb, danthron can activate AMPKα in vitro. However, the protective effect of danthron on obesity and associated MAFLD in vivo, as well as the underlying mechanism remains unknown. In this study, obesity and associated MAFLD was induced in C57BL/6J mice by high fat diet (HFD), which were subjected to evaluations on the parameters of systematic metabolism. Simultaneously, the molecular mechanism of danthron on lipid metabolism was investigated in 3T3-L1-derived adipocytes and HepG2 cells in vitro. In vivo, danthron significantly attenuated the obesity and MAFLD by enhancing hepatic fatty acid oxidation, decreasing lipid synthesis, and promoting mitochondrial homeostasis. Mechanistically, danthron significantly promoted combination of RXRα and PPARα, enhanced the binding of RXRα/PPARα heterodimer to the promoter of adiponectin receptor 2 (AdipoR2), by which activating the AMPKα and PPARα pathway. Moreover, PPARα and AdipoR2 can interplay in a loop style. Collectively, this study demonstrates that danthron can substantially ameliorate obesity and associated hepatic steatosis via AdipoR2-mediated dual PPARα/AMPKα activation, which suggests that danthron might be a novel therapeutic approach for inhibition of obesity and hepatic steatosis.

Epigenetic Regulation of Kupffer Cell Function in Health and Disease

Kupffer cells, the resident macrophages of the liver, comprise the largest pool of tissue macrophages in the body. Within the liver sinusoids Kupffer cells perform functions common across many tissue macrophages including response to tissue damage and antigen presentation. They also engage in specialized activities including iron scavenging and the uptake of opsonized particles from the portal blood. Here, we review recent studies of the epigenetic pathways that establish Kupffer cell identity and function. We describe a model by which liver-environment specific signals induce lineage determining transcription factors necessary for differentiation of Kupffer cells from bone-marrow derived monocytes. We conclude by discussing how these lineage determining transcription factors (LDTFs) drive Kupffer cell behavior during both homeostasis and disease, with particular focus on the relevance of Kupffer cell LDTF pathways in the setting of non-alcoholic fatty liver disease and non-alcoholic steatohepatitis.

Liver X Receptor Expression and Pentraxin 3 Production in Chronic Rhinosinusitis and Sinonasal Mucosal Fibroblast Cells

The long pentraxin 3 (PTX3) is a prototypic molecule for recognizing pathogens. Liver X receptors (LXRs), belonging to nuclear receptors (NRs) for cholesterol metabolism through heterodimerizing with other NRs, were recently reported to participate in inflammation. However, their roles in chronic rhinosinusitis without nasal polyps (CRSsNP) are unclear. Therefore, this study was sought to explore roles of LXRs in chronic rhinosinusitis (CRS) sinonasal tissues and derived fibroblasts. Immunohistochemistry indicated that LXRα and β expression and lipid/fat deposition were differentially expressed in the control and CRSsNP nasal mucosa. GW7647 (a peroxisome proliferator activated receptor α (PPARα) agonist) and GW3965 (a dual agonist for LXRα and β) significantly caused PTX3 induction in the fibroblast cells. GW3965 induced PTX3 mRNA and protein expression, and the induction substantially led to PTX3 secretion. Meanwhile, an endogenous agonist-cholesterol had a similar enhancing effect on the induction of PTX3 protein. LXR siRNA knockdown to lower LXRα or β expression significantly compromised PTX3 induction. Interestingly, GW3965 also induced phosphoinositide 3-kinase/protein kinase B (PI3K/Akt) activation and its inhibition reduced PTX3 expression. Collectively, we demonstrated here for the first time that CRSsNP nasal mucosa differentially expresses LXRα and β and deposits lipids/fats that may contain cholesterol metabolites to activate LXRs. Activation of LXRs leads to PTX3 production in sinonasal mucosa-derived fibroblasts. Our previous study showed PTX3 overexpression in the nasal cavity of CRSsNP, whereas this study highlights that cholesterol metabolites and LXR activation regulate PTX3 production and may contribute to antimicrobial activity and tissue repair during CRSsNP progression.

Reverse Cholesterol Transport Pathway and Cholesterol Efflux in Diabetic Retinopathy

Cholesterol esters, synthesized from cholesterol with long-chain fatty acids, are essential components of plasma lipoproteins and cell membranes that participate in various metabolic processes in the body. Cholesterol can be excreted through the cholesterol reverse transport (RCT) pathway when excessive cholesterol is produced in the extrahepatic cells, which is regulated by the liver X receptor (LXR) and its downstream regulators ATP-binding cassette subfamily A member 1 (ABCA1) and ATP-binding cassette subfamily G member 1 (ABCG1) genes. Abnormal cholesterol metabolism is closely associated with the development of diabetic retinopathy (DR). However, the precise underlying mechanism of the RCT pathway in the pathogenesis of DR is still not fully understood. This review focused on cholesterol metabolism, with a particular emphasis on the RCT pathway and its correlation with the development of DR. Particular attention has been paid to the key regulators of the RCT pathway: LXR, ABCA1, and ABCG1 genes and their potential therapeutic targets in the management of DR.

Hepatic Mediators of Lipid Metabolism and Ketogenesis: Focus on Fatty Liver and Diabetes

BACKGROUND

Diabetes mellitus (DM) is a chronic disorder that it is caused by the absence of insulin secretion due to the inability of the pancreas to produce it (type 1 diabetes; T1DM), or due to defects of insulin signaling in the peripheral tissues, resulting in insulin resistance (type 2 diabetes; T2DM). Commonly, the occurrence of insulin resistance in T2DM patients reflects the high prevalence of obesity and non-alcoholic fatty liver disease (NAFLD) in these individuals. In fact, approximately 60% of T2DM patients are also diagnosed to have NAFLD, and this condition is strongly linked with insulin resistance and obesity. NAFLD is the hepatic manifestation of obesity and metabolic syndrome and includes a spectrum of pathological conditions, which range from simple steatosis (NAFL), non-alcoholic steatohepatitis (NASH), cirrhosis and hepatocellular carcinoma. NAFLD manifestation is followed by a series of hepatic lipid deregulations and the main abnormalities are increased triglyceride levels, increased hepatic production of VLDL and a reduction in VLDL catabolism. During the progression of NAFLD, the production of ketone bodies progressively reduces while hepatic glucose synthesis and output increases. In fact, most of the fat that enters the liver can be disposed of through ketogenesis, preventing the development of NAFLD and hyperglycemia.

OBJECTIVE

This review will focus on the pathophysiological aspect of hepatic lipid metabolism deregulation, ketogenesis, and its relevance in the progression of NAFLD and T2DM.

CONCLUSION

A better understanding of the molecular mediators involved in lipid synthesis and ketogenesis can lead to new treatments for metabolic disorders in the liver, such as NAFLD.

Remodeling of whole-body lipid metabolism and a diabetic-like phenotype caused by loss of CDK1 and hepatocyte division

Cell cycle progression and lipid metabolism are well-coordinated processes required for proper cell proliferation. In liver diseases that arise from dysregulated lipid metabolism, hepatocyte proliferation is diminished. To study the outcome of CDK1 loss and blocked hepatocyte proliferation on lipid metabolism and the consequent impact on whole-body physiology, we performed lipidomics, metabolomics, and RNA-seq analyses on a mouse model. We observed reduced triacylglycerides in liver of young mice, caused by oxidative stress that activated FOXO1 to promote the expression of Pnpla2/ATGL. Additionally, we discovered that hepatocytes displayed malfunctioning β-oxidation, reflected by increased acylcarnitines (ACs) and reduced β-hydroxybutyrate. This led to elevated plasma free fatty acids (FFAs), which were transported to the adipose tissue for storage and triggered greater insulin secretion. Upon aging, chronic hyperinsulinemia resulted in insulin resistance and hepatic steatosis through activation of LXR. Here, we demonstrate that loss of hepatocyte proliferation is not only an outcome but also possibly a causative factor for liver pathology.

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.

Effects of Urate-Lowering Therapy on Risk of Hyperlipidemia in Gout by a Population-Based Cohort Study and on In Vitro Hepatic Lipogenesis-Related Gene Expression

Patients with gout are at a higher risk of cardiovascular disease, which is associated with hyperlipidemia. Management of gout in Taiwan is poor, and the association between urate-lowering therapy (ULT) among gout patients and hyperlipidemia is unclear. We conducted a retrospective cohort study using data from the Longitudinal Health Insurance Database (LHID) of Taiwan on new-onset gout patients and a comparison cohort without gout. A Cox proportional hazards model was used to analyze differences in the risk of hyperlipidemia between patients with and without gout after considering related comorbidities. We also examined the ULT medications on the hepatic expression of lipogenesis-related genes. After adjusting for potential confounders, the case group (44,413 patients) was found to have a higher risk of hyperlipidemia than the control cohort (177,652 patients) [adjusted hazards ratio (aHR) = 2.55]. Gout patients without antigout treatment had significantly higher risk of hyperlipidemia than the control cohort (aHR = 3.10). Among gout patients receiving ULT, except those receiving probenecid (aHR = 0.80), all had significantly lower risk of hyperlipidemia than gout patients without ULT (all aHR < 0.90). Using real-time polymerase chain reaction, we found that most of the antigout drugs decreased the expression of hepatic genes related to lipogenesis in differentiated HepaRG cells. These data indicate that these antigout drugs reduce hyperlipidemia in gout patients, partly via the reduction in expression of lipogenesis-related genes, leading to improved blood lipid profiles. We provide evidence of the strong association between gout and hyperlipidemia and highlight the need for appropriate treatment guidelines.

In vitro anti-inflammatory and anti-lipid accumulation properties of taxifolin-rich extract from the Japanese larch, Larix kaempferi

The Japanese larch, (Larix kaempferi) is known to contain abundant taxifolin (dihydroquercetin) in its xylem. In this study, to assess the bioactivities of taxifolin rich methanol extract of L. kaempferi (LK-ME), anti-inflammatory effect, and the anti-lipid accumulation effect of LK-ME were investigated. The results showed that nitric oxide (NO) and reactive oxygen species (ROS) were reduced after treatment with LK-ME, and that lipid accumulation in adipocyte differentiated 3T3-L1 cells was inhibited after the cells were grown in medium containing LK-ME. Taxifolin, the major compound contained in LK-ME, and its related compounds, quercetin and luteolin also exhibited similar effects with LK-ME. The LK-ME exhibits relatively strong anti-inflammatory and anti-lipid accumulation activities compared with that of similar amounts of taxifolin contained in LK-ME, suggesting that other minor compounds contained in LK-ME is involved in the effects. These results indicate the potential of taxifolin-rich L. kaempferi extract for use as a supplement to prevent excess inflammation and obesity.

The secretome of liver X receptor agonist-treated early outgrowth cells decreases atherosclerosis in Ldlr-/- mice

Endothelial progenitor cells (EPCs) promote the maintenance of the endothelium by secreting vasoreparative factors. A population of EPCs known as early outgrowth cells (EOCs) is being investigated as novel cell‐based therapies for the treatment of cardiovascular disease. We previously demonstrated that the absence of liver X receptors (LXRs) is detrimental to the formation and function of EOCs under hypercholesterolemic conditions. Here, we investigate whether LXR activation in EOCs is beneficial for the treatment of atherosclerosis. EOCs were differentiated from the bone marrow of wild‐type (WT) and LXR‐knockout (Lxrαβ−/−) mice in the presence of vehicle or LXR agonist (GW3965). WT EOCs treated with GW3965 throughout differentiation showed reduced mRNA expression of endothelial lineage markers (Cd144, Vegfr2) compared with WT vehicle and Lxrαβ−/− EOCs. GW3965‐treated EOCs produced secreted factors that reduced monocyte adhesion to activated endothelial cells in culture. When injected into atherosclerosis‐prone Ldlr−/− mice, GW3965‐treated EOCs, or their corresponding conditioned media (CM) were both able to reduce aortic sinus plaque burden compared with controls. Furthermore, when human EOCs (obtained from patients with established CAD) were treated with GW3965 and the CM applied to endothelial cells, monocyte adhesion was decreased, indicating that our results in mice could be translated to patients. Ex vivo LXR agonist treatment of EOCs therefore produces a secretome that decreases early atherosclerosis in Ldlr−/− mice, and additionally, CM from human EOCs significantly inhibits monocyte to endothelial adhesion. Thus, active factor(s) within the GW3965‐treated EOC secretome may have the potential to be useful for the treatment of atherosclerosis.

Nuclear receptors and transcriptional regulation in non-alcoholic fatty liver disease

BACKGROUND

As a result of a sedentary lifestyle and excess food consumption in modern society, non-alcoholic fatty liver disease (NAFLD) characterized by fat accumulation in the liver is becoming a major disease burden. Non-alcoholic steatohepatitis (NASH) is an advanced form of NAFLD characterized by inflammation and fibrosis that can lead to hepatocellular carcinoma and liver failure. Nuclear receptors (NRs) are a family of ligand-regulated transcription factors that closely control multiple aspects of metabolism. Their transcriptional activity is modulated by various ligands, including hormones and lipids. NRs serve as potential pharmacological targets for NAFLD/NASH and other metabolic diseases.

SCOPE OF REVIEW

In this review, we provide a comprehensive overview of NRs that have been studied in the context of NAFLD/NASH with a focus on their transcriptional regulation, function in preclinical models, and studies of their clinical utility.

MAJOR CONCLUSIONS

The transcriptional regulation of NRs is context-dependent. During the dynamic progression of NAFLD/NASH, NRs play diverse roles in multiple organs and different cell types in the liver, which highlights the necessity of targeting NRs in a stage-specific and cell-type-specific manner to enhance the efficacy and safety of treatment methods.

Liver X Receptors: Regulators of Cholesterol Metabolism, Inflammation, Autoimmunity, and Cancer

The interplay between cellular stress and immune response can be variable and sometimes contradictory. The mechanisms by which stress-activated pathways regulate the inflammatory response to a pathogen, in autoimmunity or during cancer progression remain unclear in many aspects, despite our recent knowledge of the signalling and transcriptional pathways involved in these diseases. In this context, over the last decade many studies demonstrated that cholesterol metabolism is an important checkpoint for immune homeostasis and cancer progression. Indeed, cholesterol is actively metabolized and can regulate, through its mobilization and/or production of active derivatives, many aspects of immunity and inflammation. Moreover, accumulation of cholesterol has been described in cancer cells, indicating metabolic addiction. The nuclear receptors liver-X-receptors (LXRs) are important regulators of intracellular cholesterol and lipids homeostasis. They have also key regulatory roles in immune response, as they can regulate inflammation, innate and adaptive immunity. Moreover, activation of LXRs has been reported to affect the proliferation and survival of different cancer cell types that show altered metabolic pathways and accumulation of cholesterol. In this minireview we will give an overview of the recent understandings about the mechanisms through which LXRs regulate inflammation, autoimmunity, and cancer, and the therapeutic potential for future treatment of these diseases through modulation of cholesterol metabolism.