25-Hydroxycholesterol-3-sulfate regulates macrophage lipid metabolism via the LXR/SREBP-1 signaling pathway

Larsucosterol: endogenous epigenetic regulator for treating chronic and acute liver diseases

Larsucosterol, a potent endogenous epigenetic regulator, has been reported to play a significant role in lipid metabolism, inflammatory responses, and cell survival. The administration of larsucosterol has demonstrated a reduction in lipid accumulation within hepatocytes and the attenuation of inflammatory responses induced by lipopolysaccharide (LPS) and TNFα in macrophages, alleviating LPS- and acetaminophen (ATMP)-induced multiple organ injury, and decreasing mortalities in animal models. Results from phase 1 and 2 clinical trials have shown that larsucosterol has potential as a biomedicine for the treatment of acute and chronic liver diseases. Recent evidence suggests that larsucosterol is a promising candidate for treating alcohol-associated hepatitis with positive results from a phase 2a clinical trial, and for metabolic dysfunction-associated steatohepatitis (MASH) from a phase 1b clinical trial. In this review, we present a culmination of our recent research efforts spanning two decades. We summarize the discovery, physiological and pharmacological mechanisms, and clinical applications of larsucosterol. Furthermore, we elucidate the pathophysiological pathways of metabolic dysfunction-associated steatotic liver diseases (MASLD), metabolic dysfunction-associated steatohepatitis (MASH), and acute liver injuries. A central focus of the review is the exploration of the therapeutic potential of larsucosterol in treating life-threatening conditions, including acetaminophen overdose, endotoxin shock, MASLD, MASH, hepatectomy, and alcoholic hepatitis.

Cholestenoic acid as endogenous epigenetic regulator decreases hepatocyte lipid accumulation in vitro and in vivo

Cholestenoic acid (CA) has been reported as an important biomarker of many severe diseases, but its physiological and pathological roles remain unclear. This study aimed to investigate the potential role of CA in hepatic lipid homeostasis. Enzyme kinetic studies revealed that CA specifically activates DNA methyltransferases 1 (DNMT1) at low concentration with EC50 = 1.99 × 10-6 M and inhibits the activity at higher concentration with IC50 = 9.13 × 10-6 M, and specifically inhibits DNMT3a, and DNMT3b activities with IC50= 8.41 × 10-6 M and IC50= 4.89 × 10-6 M, respectively. In a human hepatocyte in vitro model of high glucose (HG)-induced lipid accumulation, CA significantly increased demethylation of 5mCpG in the promoter regions of over 7,000 genes, particularly those involved in master signaling pathways such as calcium-AMPK and 0.0027 at 6 h. RNA sequencing analysis showed that the downregulated genes are affected by CA encoding key enzymes, such as PCSK9, MVK, and HMGCR, which are involved in cholesterol metabolism and steroid biosynthesis pathways. In addition, untargeted lipidomic analysis showed that CA significantly reduced neutral lipid levels by 60% in the cells cultured in high-glucose media. Administration of CA in mouse metabolic dysfunction-associated steatotic liver disease (MASLD) models significantly decreases lipid accumulation, suppresses the gene expression involved in lipid biosynthesis in liver tissues, and alleviates liver function. This study shows that CA as an endogenous epigenetic regulator decreases lipid accumulation via epigenetic regulation. The results indicate that CA can be considered a potential therapeutic target for the treatment of metabolic disorders.NEW & NOTEWORTHY To our knowledge, this study is the first to identify the mitochondrial monohydroxy bile acid cholestenoic acid (CA) as an endogenous epigenetic regulator that regulates lipid metabolism through epigenome modification in human hepatocytes. The methods used in this study are all big data analysis, and the results of each part show the global regulation of CA on human hepatocytes rather than narrow point effects.

Targeting Liver X Receptors for the Treatment of Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) refers to a range of conditions in which excess lipids accumulate in the liver, possibly leading to serious hepatic manifestations such as steatohepatitis, fibrosis/cirrhosis and cancer. Despite its increasing prevalence and significant impact on liver disease-associated mortality worldwide, no medication has been approved for the treatment of NAFLD yet. Liver X receptors α/β (LXRα and LXRβ) are lipid-activated nuclear receptors that serve as master regulators of lipid homeostasis and play pivotal roles in controlling various metabolic processes, including lipid metabolism, inflammation and immune response. Of note, NAFLD progression is characterized by increased accumulation of triglycerides and cholesterol, hepatic de novo lipogenesis, mitochondrial dysfunction and augmented inflammation, all of which are highly attributed to dysregulated LXR signaling. Thus, targeting LXRs may provide promising strategies for the treatment of NAFLD. However, emerging evidence has revealed that modulating the activity of LXRs has various metabolic consequences, as the main functions of LXRs can distinctively vary in a cell type-dependent manner. Therefore, understanding how LXRs in the liver integrate various signaling pathways and regulate metabolic homeostasis from a cellular perspective using recent advances in research may provide new insights into therapeutic strategies for NAFLD and associated metabolic diseases.

A concerted mechanism involving ACAT and SREBPs by which oxysterols deplete accessible cholesterol to restrict microbial infection

Most of the cholesterol in the plasma membranes (PMs) of animal cells is sequestered through interactions with phospholipids and transmembrane domains of proteins. However, as cholesterol concentration rises above the PM's sequestration capacity, a new pool of cholesterol, called accessible cholesterol, emerges. The transport of accessible cholesterol between the PM and the endoplasmic reticulum (ER) is critical to maintain cholesterol homeostasis. This pathway has also been implicated in the suppression of both bacterial and viral pathogens by immunomodulatory oxysterols. Here, we describe a mechanism of depletion of accessible cholesterol from PMs by the oxysterol 25-hydroxycholesterol (25HC). We show that 25HC-mediated activation of acyl coenzyme A: cholesterol acyltransferase (ACAT) in the ER creates an imbalance in the equilibrium distribution of accessible cholesterol between the ER and PM. This imbalance triggers the rapid internalization of accessible cholesterol from the PM, and this depletion is sustained for long periods of time through 25HC-mediated suppression of SREBPs and continued activation of ACAT. In support of a physiological role for this mechanism, 25HC failed to suppress Zika virus and human coronavirus infection in ACAT-deficient cells, and Listeria monocytogenes infection in ACAT-deficient cells and mice. We propose that selective depletion of accessible PM cholesterol triggered by ACAT activation and sustained through SREBP suppression underpins the immunological activities of 25HC and a functionally related class of oxysterols.

Pathogenic role of 25-hydroxycholesterol in cancer development and progression

Cholesterol is an essential lipid that serves several important functions, including maintaining the homeostasis of cells, acting as a precursor to bile acid and steroid hormones and preserving the stability of membrane lipid rafts. 25-hydroxycholesterol (25-HC) is a cholesterol derivative that may be formed from cholesterol. 25-HC is a crucial component in various biological activities, including cholesterol metabolism. In recent years, growing evidence has shown that 25-HC performs a critical function in the etiology of cancer, infectious diseases and autoimmune disorders. This review will summarize the latest findings regarding 25-HC, including its biogenesis, immunomodulatory properties and role in innate/adaptive immunity, inflammation and the development of various types of cancer.

Deciphering the role of aberrant DNA methylation in NAFLD and NASH

The global incidence of nonalcoholic fatty liver disease (NAFLD) is mounting incessantly, and it is emerging as the most frequent cause of chronic and end stage liver disorders. It is the starting point for a range of conditions from simple steatosis to more progressive nonalcoholic steatohepatitis (NASH) and associated hepatocellular carcinoma (HCC). Dysregulation of insulin secretion and dyslipidemia due to obesity and other lifestyle variables are the primary contributors to establishment of NAFLD. Onset and progression of NAFLD is orchestrated by an interplay of metabolic environment with genetic and epigenetic factors. An incompletely understood mechanism of NAFLD progression has greatly hampered the progress in identification of novel prognostic and therapeutic strategies. Emerging evidence suggests altered DNA methylation pattern as a key determinant of NAFLD pathogenesis. Environmental and lifestyle factors can manipulate DNA methylation patterns in a reversible manner, which manifests as changes in gene expression. In this review we attempt to highlight the importance of DNA methylation in establishment and progression of NAFLD. Development of novel diagnostic, prognostic and therapeutic strategies centered around DNA methylation signatures and modifiers has also been explored.

Studies in the antiviral molecular mechanisms of 25-hydroxycholesterol: Disturbing cholesterol homeostasis and post-translational modification of proteins

Efficient antiviral drug discovery has been a pressing issue of global public health concern since the outbreak of coronavirus disease 2019. In recent years, numerous in vitro and in vivo studies have shown that 25-hydroxycholesterol (25HC), a reactive oxysterol catalyzed by cholesterol-25-hydroxylase, exerts broad-spectrum antiviral activity with high efficiency and low toxicity. 25HC restricts viral internalization and disturbs the maturity of viral proteins using multiple mechanisms. First, 25HC reduces lipid rafts and cholesterol in the cytomembrane by inhibiting sterol-regulatory element binding proteins-2, stimulating liver X receptor, and activating Acyl-coenzyme A: cholesterol acyl-transferase. Second, 25HC impairs endosomal pathways by restricting the function of oxysterol-binding protein or Niemann-pick protein C1, causing the virus to fail to release nucleic acid. Third, 25HC disturbs the prenylation of viral proteins by suppressing the sterol-regulatory element binding protein pathway and glycosylation by increasing the sensitivity of glycans to endoglycosidase. This paper reviews previous studies on the antiviral activity of 25HC in order to fully understand its role in innate immunity and how it may contribute to the development of urgently needed broad-spectrum antiviral drugs.

Different functions of vitamin E homologues in the various types of cell death induced by oxysterols

24(S)-Hydroxycholesterol (24S-OHC) and 25-hydroxycholesterol (25-OHC) are produced by cholesterol 24-hydroxylase and cholesterol 25-hydroxylase, respectively. The purpose of the present study was to determine the type of cell death induced by these oxysterols in neuronal cells, hepatic cells, and keratinocytes, and to elucidate the inhibitory effect of vitamin E homologues on various types of cell death. In human neuronal cells (SH-SY5Y cells), 24S-OHC and 25-OHC caused a cell death that was independent of caspase activation. We reported previously that the esterification of 24S-OHC by acyl-CoA:cholesterol acyltransferase 1 (ACAT1) and the resulting formation of a lipid droplet (LD)-like structure are responsible for the 24S-OHC-induced neuronal cell death. Here, we found that 25-OHC also induced ACAT1-mediated 25-OHC esterification and LD formation in neuronal cells. 25-OHC-induced cell death was inhibited by α-tocopherol (α-Toc) but not by α-tocotrienol (α-Toc3), as observed for 24S-OHC-induced cell death in SH-SY5Y cells. In human hepatic cells (HepG2 cells), these oxysterols caused a cell death that was caspase- and oxysterol-esterification-independent. This cell death was suppressed by both α-Toc and α-Toc3, suggesting the involvement of free-radical-mediated lipid peroxidation in the cell death induced by these oxysterols in hepatic cells. In human keratinocytes (HaCaT cells), these oxysterols caused a caspase-dependent but oxysterol-esterification-independent cell death that was inhibited by α-Toc but not by α-Toc3. These results suggest that α-Toc and α-Toc3 act as radical-scavenging antioxidants against oxysterol-induced cell death in the same way in hepatic cells, whereas their behavior is different in inhibition of cell death in neuronal cells and keratinocytes. Collectively, these results demonstrated that 24S-OHC and 25-OHC induced the same type of cell death in each of the cell types examined, and that α-Toc and α-Toc3 exerted different effects, depending on the type of cell death.

25-Hydroxycholesterol 3-Sulfate Recovers Acetaminophen Induced Acute Liver Injury via Stabilizing Mitochondria in Mouse Models

Acetaminophen (APAP) overdose is one of the most frequent causes of acute liver failure (ALF). N-acetylcysteine (NAC) is currently being used as part of the standard care in the clinic but its usage has been limited in severe cases, in which liver transplantation becomes the only treatment option. Therefore, there still is a need for a specific and effective therapy for APAP induced ALF. In the current study, we have demonstrated that treatment with 25-Hydroxycholesterol 3-Sulfate (25HC3S) not only significantly reduced mortality but also decreased the plasma levels of liver injury markers, including LDH, AST, and ALT, in APAP overdosed mouse models. 25HC3S also decreased the expression of those genes involved in cell apoptosis, stabilized mitochondrial polarization, and significantly decreased the levels of oxidants, malondialdehyde (MDA), and reactive oxygen species (ROS). Whole genome bisulfite sequencing analysis showed that 25HC3S increased demethylation of 5mCpG in key promoter regions and thereby increased the expression of those genes involved in MAPK-ERK and PI3K-Akt signaling pathways. We concluded that 25HC3S may alleviate APAP induced liver injury via up-regulating the master signaling pathways and maintaining mitochondrial membrane polarization. The results suggest that 25HC3S treatment facilitates the recovery and significantly decreases the mortality of APAP induced acute liver injury and has a synergistic effect with NAC in propylene glycol (PG) for the injury.

The oxysterome and its receptors as pharmacological targets in inflammatory diseases

Oxysterols have gained attention over the last decades and are now considered as fully fledged bioactive lipids. The study of their levels in several conditions, including atherosclerosis, obesity and neurodegenerative diseases, led to a better understanding of their involvement in (patho)physiological processes such as inflammation and immunity. For instance, the characterization of the cholesterol-7α,25-dihydroxycholesterol/GPR183 axis and its implication in immunity represents an important step in the oxysterome study. Besides this axis, others were identified as important in several inflammatory pathologies (such as colitis, lung inflammation and atherosclerosis). However, the oxysterome is a complex system notably due to a redundancy of metabolic enzymes and a wide range of receptors. Indeed, deciphering oxysterol roles and identifying the potential receptor(s) involved in a given pathology remain challenging. Oxysterol properties are very diverse, but most of them could be connected by a common component: inflammation. Here, we review the implication of oxysterol receptors in inflammatory diseases.

25-Hydroxycholesterol 3-sulfate is an endogenous ligand of DNA methyltransferases in hepatocytes

The oxysterol sulfate, 25-hydroxycholesterol 3-sulfate (25HC3S), has been shown to play an important role in lipid metabolism, inflammatory response, and cell survival. However, the mechanism(s) of its function in global regulation is unknown. The current study investigates the molecular mechanism by which 25HC3S functions as an endogenous epigenetic regulator. To study the effects of oxysterols/sterol sulfates on epigenetic modulators, 12 recombinant epigenetic enzymes were used to determine whether 25HC3S acts as their endogenous ligand. The enzyme kinetic study demonstrated that 25HC3S specifically inhibited DNA methyltransferases (DNMTs), DNMT1, DNMT3a, and DNMT3b with IC50 of 4.04, 3.03, and 9.05 × 10-6 M, respectively. In human hepatocytes, high glucose induces lipid accumulation by increasing promoter CpG methylation of key genes involved in development of nonalcoholic fatty liver diseases. Using this model, whole genome bisulfate sequencing analysis demonstrated that 25HC3S converts the 5mCpG to CpG in the promoter regions of 1,074 genes. In addition, we observed increased expression of the demethylated genes, which are involved in the master signaling pathways, including MAPK-ERK, calcium-AMP-activated protein kinase, and type II diabetes mellitus pathways. mRNA array analysis showed that the upregulated genes encoded for key elements of cell survival; conversely, downregulated genes encoded for key enzymes that decrease lipid biosynthesis. Taken together, our results indicate that the expression of these key elements and enzymes are regulated by the demethylated signaling pathways. We summarized that 25HC3S DNA demethylation of 5mCpG in promoter regions is a potent regulatory mechanism.

Cholesterol Metabolites 25-Hydroxycholesterol and 25-Hydroxycholesterol 3-Sulfate Are Potent Paired Regulators: From Discovery to Clinical Usage

Oxysterols have long been believed to be ligands of nuclear receptors such as liver × receptor (LXR), and they play an important role in lipid homeostasis and in the immune system, where they are involved in both transcriptional and posttranscriptional mechanisms. However, they are increasingly associated with a wide variety of other, sometimes surprising, cell functions. Oxysterols have also been implicated in several diseases such as metabolic syndrome. Oxysterols can be sulfated, and the sulfated oxysterols act in different directions: they decrease lipid biosynthesis, suppress inflammatory responses, and promote cell survival. Our recent reports have shown that oxysterol and oxysterol sulfates are paired epigenetic regulators, agonists, and antagonists of DNA methyltransferases, indicating that their function of global regulation is through epigenetic modification. In this review, we explore our latest research of 25-hydroxycholesterol and 25-hydroxycholesterol 3-sulfate in a novel regulatory mechanism and evaluate the current evidence for these roles.

DNA Methylation in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a widespread hepatic disorder in the United States and other Westernized countries. Nonalcoholic steatohepatitis (NASH), an advanced stage of NAFLD, can progress to end-stage liver disease, including cirrhosis and liver cancer. Poor understanding of mechanisms underlying NAFLD progression from simple steatosis to NASH has limited the development of effective therapies and biomarkers. An accumulating body of studies has suggested the importance of DNA methylation, which plays pivotal roles in NAFLD pathogenesis. DNA methylation signatures that can affect gene expression are influenced by environmental and lifestyle experiences such as diet, obesity, and physical activity and are reversible. Hence, DNA methylation signatures and modifiers in NAFLD may provide the basis for developing biomarkers indicating the onset and progression of NAFLD and therapeutics for NAFLD. Herein, we review an update on the recent findings in DNA methylation signatures and their roles in the pathogenesis of NAFLD and broaden people’s perspectives on potential DNA methylation-related treatments and biomarkers for NAFLD.

Cholesterol and oxysterol sulfates: Pathophysiological roles and analytical challenges

Cholesterol and oxysterol sulfates are important regulators of lipid metabolism, inflammation, cell apoptosis, and cell survival. Among the sulfate-based lipids, cholesterol sulfate (CS) is the most studied lipid both quantitatively and functionally. Despite the importance, very few studies have analysed and linked the actions of oxysterol sulfates to their physiological and pathophysiological roles. Overexpression of sulfotransferases confirmed the formation of a range of oxysterol sulfates and their antagonistic effects on liver X receptors (LXRs) prompting further investigations how are the changes to oxysterol/oxysterol sulfate homeostasis can contribute to LXR activity in the physiological milieu. Here, we aim to bring together for novel roles of oxysterol sulfates, the available techniques and the challenges associated with their analysis. Understanding the oxysterol/oxysterol sulfate levels and their pathophysiological mechanisms could lead to new therapeutic targets for metabolic diseases. LINKED ARTICLES: This article is part of a themed issue on Oxysterols, Lifelong Health and Therapeutics. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.16/issuetoc.

A chalcone derivative, 1m-6, exhibits atheroprotective effects by increasing cholesterol efflux and reducing inflammation-induced endothelial dysfunction

BACKGROUND AND PURPOSE

Atherosclerosis, resulting from lipid dysregulation and vascular inflammation, causes atherosclerotic cardiovascular disease (ASCVD), which contributes to morbidity and mortality worldwide. Chalcone and its derivatives possess beneficial properties, including anti-inflammatory, antioxidant and antitumour activity with unknown cardioprotective effects. We aimed to develop an effective chalcone derivative with antiatherogenic potential.

EXPERIMENTAL APPROACH

Human THP-1 cells and HUVECs were used as in vitro models. Western blots and real-time PCRs were performed to quantify protein, mRNA and miRNA expressions. The cholesterol efflux capacity was assayed by ³ H labelling of cholesterol. LDL receptor knockout (Ldlr^-/- ) mice fed a high-fat diet were used as an in vivo atherogenesis model. Haematoxylin and eosin and oil red O staining were used to analyse plaque formation.

KEY RESULTS

Using ATP-binding cassette transporter A1 (ABCA1) expression we identified the chalcone derivative, 1m-6, which enhances ABCA1 expression and promotes cholesterol efflux in THP-1 macrophages. Moreover, 1m-6 stabilizes ABCA1 mRNA and suppresses the expression of potential ABCA1-regulating miRNAs through nuclear factor erythroid 2-related factor 2 (Nrf2)/haem oxygenase-1 (HO-1) signalling. Additionally, 1m-6 significantly inhibits TNF-α-induced expression of adhesion molecules, vascular cell adhesion molecule 1 (VCAM-1) and intercellular adhesion molecule 1 (ICAM-1), plus production of proinflammatory cytokines via inhibition of JAK/STAT3 activation and the modulation of Nrf2/HO-1 signalling in HUVECs. In atherosclerosis-prone mice, 1m-6 significantly reduces lipid accumulation and atherosclerotic plaque formation.

CONCLUSION AND IMPLICATIONS

Our study demonstrates that 1m-6 produces promising atheroprotective effects by enhancing cholesterol efflux and suppressing inflammation-induced endothelial dysfunction, which opens a new avenue for treating ASCVD.

LINKED ARTICLES

This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.23/issuetoc.

Inhibition of LXR signaling by SULT2B1b promotes liver regeneration after partial hepatectomy in mouse models of nonalcoholic fatty liver disease

Hydroxysteroid sulfotransferase 2B1b (SULT2B1b) plays a critical role in hepatic energy homeostasis. Liver X receptors (LXRs) are implicated in multiple physiological functions, including the inhibition of hepatocyte proliferation and regulation of fatty acid and cholesterol metabolism. We have previously reported that SULT2B1b promotes hepatocyte proliferation by inactivating LXR signaling in vivo and in vitro, leading to our hypothesis that SULT2B1b promotes fatty liver regeneration. In the present study, female C57BL/6 and S129 mice were fed a high-fat diet for 8 wk to establish a nonalcoholic fatty liver disease (NAFLD) mouse model. 70% partial hepatectomy (PH) was performed to induce liver regeneration. Our experiments revealed that the SULT2B1b overexpression significantly promotes the regeneration of hepatocytes in NAFLD C57BL/6 mice after PH, increasing liver regrowth by 11% within 1 day, and then by 21%, 33%, and 24% by 2, 3, and 5 days post-PH, respectively. Compared with the wild-type NAFLD S129 mice, SULT2B1 deletion NAFLD S129 mice presented reduced hepatocyte regeneration at postoperative day 2, as verified by decreased liver regrowth (37.4% vs. 46.1%, P < 0.05) and the results of immunohistochemical staining, quantitative real-time polymerase chain reaction, and Western blot analysis. Moreover, LXRα signaling and SULT2B1b expression are highly correlated in the regeneration of NAFLD mouse liver; SULT2B1b overexpression suppresses LXRα signaling, while the LXRα-signaling agonist T0901317 blocks SULT2B1b-induced hepatocyte regeneration in NAFLD mouse liver. Thus, the upregulation of SULT2B1b may promote hepatocyte regeneration via the suppression of LXRα activation in NAFLD mice, providing a potential strategy for improving hepatic-steatosis-related liver regeneration disorders.NEW & NOTEWORTHY This study demonstrates for the first time that hydroxysteroid sulfotransferase 2B1b (SULT2B1b) overexpression promotes the regeneration of fatty liver after partial hepatectomy in mice with nonalcoholic fatty liver disease, while reducing triglyceride accumulation in the regenerative fatty liver. Liver X receptor signaling may be crucial in the SULT2B1b-mediated regeneration of fatty liver. Thus, SULT2B1b may be a potential target for treating hepatic steatosis-related liver regeneration disorders.

High Glucose Induces Lipid Accumulation via 25-Hydroxycholesterol DNA-CpG Methylation

This work investigates the relationship between high-glucose (HG) culture, CpG methylation of genes involved in cell signaling pathways, and the regulation of carbohydrate and lipid metabolism in hepatocytes. The results indicate that HG leads to an increase in nuclear 25-hydroxycholesterol (25HC), which specifically activates DNA methyltransferase-1 (DNMT1), and regulates gene expression involved in intracellular lipid metabolism. The results show significant increases in ^5mCpG levels in at least 2,225 genes involved in 57 signaling pathways. The hypermethylated genes directly involved in carbohydrate and lipid metabolism are of PI3K, cAMP, insulin, insulin secretion, diabetic, and NAFLD signaling pathways. The studies indicate a close relationship between the increase in nuclear 25HC levels and activation of DNMT1, which may regulate lipid metabolism via DNA CpG methylation. Our results indicate an epigenetic regulation of hepatic cell metabolism that has relevance to some common diseases such as non-alcoholic fatty liver disease and metabolic syndrome.

Cholesterol metabolism regulation mediated by SREBP-2, LXRα and miR-33a in rainbow trout (Oncorhynchus mykiss) both in vivo and in vitro

Cholesterol metabolism is greatly affected in fish fed plant-based diet. The regulation of cholesterol metabolism is mediated by both transcriptional factors such as sterol regulatory element-binding proteins (SREBPs) and liver X receptors (LXRs), and posttranscriptional factors including miRNAs. In mammals, SREBP-2 and LXRα are involved in the transcriptional regulation of cholesterol synthesis and elimination, respectively. In mammals, miR-33a is reported to directly target genes involved in cholesterol catabolism. The present study aims to investigate the regulation of cholesterol metabolism by SREBP-2 and LXRα and miR-33a in rainbow trout using in vivo and in vitro approaches. In vivo, juvenile rainbow trout of ~72 g initial body weight were fed a total plant-based diet (V) or a marine diet (M) containing fishmeal and fish oil. In vitro, primary cell culture hepatocytes were stimulated by graded concentrations of 25-hydroxycholesterol (25-HC). The hepatic expression of cholesterol synthetic genes, srebp-2 and miR-33a as well as miR-33a level in plasma were increased in fish fed the plant-based diet, reversely, their expression in hepatocytes were inhibited with the increasing 25-HC in vitro. However, lxrα was not affected neither in vivo nor in vitro. Our results suggest that SREBP-2 and miR-33a synergistically enhance the expression of cholesterol synthetic genes but do not support the involvement of LXRα in the regulation of cholesterol elimination. As plasma level of miR-33a appears as potential indicator of cholesterol synthetic capacities, this study also highlights circulating miRNAs as promising noninvasive biomarker in aquaculture.

The marine-derived furanone reduces intracellular lipid accumulation in vitro by targeting LXRα and PPARα

Recent studies have demonstrated that commercially available lipid‐lowering drugs cause various side effects; therefore, searching for anti‐hyperlipidaemic compounds with lower toxicity is a research hotspot. This study was designed to investigate whether the marine‐derived compound, 5‐hydroxy‐3‐methoxy‐5‐methyl‐4‐butylfuran‐2(5H)‐one, has an anti‐hyperlipidaemic activity, and the potential underlying mechanism in vitro. Results showed that the furanone had weaker cytotoxicity compared to positive control drugs. In RAW 264.7 cells, the furanone significantly lowered ox‐LDL‐induced lipid accumulation (~50%), and its triglyceride (TG)‐lowering effect was greater than that of liver X receptor (LXR) agonist T0901317. In addition, it significantly elevated the protein levels of peroxisome proliferator‐activated receptors (PPARα) and ATP‐binding cassette (ABC) transporters, which could be partially inhibited by LXR antagonists, GSK2033 and SR9243. In HepG2 cells, it significantly decreased oleic acid‐induced lipid accumulation, enhanced the protein levels of low‐density lipoprotein receptor (LDLR), ABCG5, ABCG8 and PPARα, and reduced the expression of sterol regulatory element‐binding protein 2 (~32%). PPARα antagonists, GW6471 and MK886, could significantly inhibit the furanone‐induced lipid‐lowering effect. Furthermore, the furanone showed a significantly lower activity on the activation of the expression of lipogenic genes compared to T0901317. Taken together, the furanone exhibited a weak cytotoxicity but had powerful TC‐ and TG‐lowering effects most likely through targeting LXRα and PPARα, respectively. These findings indicate that the furanone has a potential application for the treatment of dyslipidaemia.

6-Ketocholestanol suppresses lipid accumulation by decreasing FASN gene expression through SREBP-dependent regulation in HepG2 cells

Nuclear receptors, such as liver X receptors (LXRs) and sterol regulatory element-binding proteins (SREBPs), are key regulators of lipogenic genes, including fatty acid synthase (FASN). It has been reported that several oxycholesterols (OCs) act as LXR ligands; however, it is unclear whether all OC molecular species act as ligands. We previously demonstrated that the absorption rate of dietary 6-ketocholestanol (6-keto), an oxycholesterol, is the highest of all the OCs using thoracic lymph duct-cannulated rats. However, limited information is available about the physiological significance of 6-keto. In this study, we investigated whether treatment with 6-keto increases intracellular triacylglycerol (TAG) levels through up-regulation of lipogenic gene expression in HepG2 cells. 6-Keto treatment significantly reduced intracellular TAG levels through down-regulation of lipogenic genes including FASN. Although 6-keto significantly suppressed FASN gene promoter activities, the action was completely diminished when mutations were present in the SREBP promoter site. TO901317 (TO) significantly increased FASN gene promoter activities, whereas simultaneous treatment with TO and 6-keto significantly reduced this activity. We also compared the effects of several OCs that are oxidized at the carbon-6 and -7 in the B-ring of cholesterol on FASN gene promoter activities. Similar to 6-keto, 6α-OH and 6β-OH significantly reduced the activity of the FASN gene promoter, which suggests that oxidation of carbon-6 in the B-ring may play an important role in the reduction of FASN expression. Our results indicate that 6-keto suppresses lipid accumulation by decreasing FASN gene expression through SREBP-dependent regulation in HepG2 cells.

Fast liquid chromatography-mass spectrometry reveals side chain oxysterol heterogeneity in breast cancer tumour samples

Oxysterols can contribute to proliferation of breast cancer through activation of the Estrogen Receptors, and to metastasis through activation of the Liver X Receptors. Endogenous levels of both esterified and free sidechain-hydroxylated oxysterols were examined in breast cancer tumours from Estrogen Receptor positive and negative breast tumours, using a novel fast liquid chromatography tandem mass spectrometry method. Multiple aliquots of five milligram samples of 22 tumours were analysed for oxysterol content to assess intra- and inter-tumour variation. Derivatization was performed with Girard T reagent (with and without alkaline hydrolysis) and sample clean-up was performed using a robust automatic on-line column switching system ("AFFL"). Oxysterols were separated isocratically on a 2.1 mm inner diameter column packed with ACE SuperPhenylHexyl core shell particles using a mobile phase consisting of 0.1% formic acid in H₂O/methanol/acetonitrile (57/10/33, v/v/v) followed by a wash out step (0.1% formic acid in methanol/acetonitrile, 50/50, v/v). The total analysis time, including sample clean-up and column reconditioning, was 8 min (80% time reduction compared to other on-line systems). Analysis revealed large intra-tumour variations of sidechain oxysterols, resulting in no significant differences in endogenous oxysterols levels between Estrogen Receptor positive and Estrogen Receptor negative breast cancers. However, a correlation between esterified and free 27-hydroxycholesterol was observed. The same correlation was not observed for 24S-hydroxycholesterol or 25-hydroxycholesterol. The oxysterol heterogeneity of tumour tissue is a critical factor when assessing the role of these lipids in cancer.

25-hydroxycholesterol impairs neuronal and muscular development in zebrafish

Oxysterols have essential effects on brain homeostasis and their levels are often altered in neurodegenerative and neuroinflammatory diseases. Several studies have demonstrated the cytotoxic effects of 25-HC on different cell lines, however, not much is known about its effects on neurons in vivo. In this study, we examined the effects of 25-HC exposure on the nervous system development in the zebrafish. We showed that survival rate of zebrafish embryos/larvae is significantly decreased at doses of 25-HC above 40 μM. 25-HC was found to affect the motility of zebrafish larvae, primary motor axon and muscle morphology. Furthermore, larvae treated with 25-HC showed a reduced neuronal network and number of HuC-positive cells in the brain. An increased cell death was also observed in both the brain and spinal cord of zebrafish treated with 25-HC. Interestingly, administration of 25-HC at later stages of development (24 and 48 h post fertilization) had no detrimental effects on motor axons. Altogether, our findings show that elevated levels of 25-HC may have important consequences on neuronal development and cell survival.

Metabolism in Immune Cell Differentiation and Function

The immune system is a central determinant of organismal health. Functional immune responses require quiescent immune cells to rapidly grow, proliferate, and acquire effector functions when they sense infectious agents or other insults. Specialized metabolic programs are critical regulators of immune responses, and alterations in immune metabolism can cause immunological disorders. There has thus been growing interest in understanding how metabolic processes control immune cell functions under normal and pathophysiological conditions. In this chapter, we summarize how metabolic programs are tuned and what the physiological consequences of metabolic reprogramming are as they relate to immune cell homeostasis, differentiation, and function.

Decreased All- trans Retinoic Acid-Induced Expression of Sodium-Iodide Transporter in Mammary Epithelial Cells Caused by Conjugated Linoleic Acid Isomers

Expression of sodium-iodide symporter (NIS) is stimulated by sterol-regulatory-element-binding transcription factors (SREBFs) in mammary epithelial MCF-7 cells. Because conjugated linoleic acid (CLA) isomers have been shown to inhibit transcriptional activity of SREBFs in the mammary gland, the hypothesis was tested that CLA isomers inhibit NIS expression induced by all- trans retinoic acid (ATRA) in MCF-7 cells through inhibiting SREBF activity. c9t11-CLA and t10c12-CLA decreased ATRA-induced NIS-mRNA expression from 1.00 (ATRA alone) to 0.80 ± 0.12 (200 μM c9t11-CLA, P < 0.05) and 0.62 ± 0.10 (200 μM t10c12-CLA, P < 0.05), NIS-protein expression from 1.00 (ATRA alone) to 0.77 ± 0.08 (200 μM c9t11-CLA, P < 0.05) and 0.63 ± 0.05 (200 μM t10c12-CLA, P < 0.05), and NIS-promoter activity from 1.00 (ATRA alone) to 0.74 ± 0.13 (200 μM c9t11-CLA, P < 0.05) and 0.76 ± 0.13 (200 μM t10c12-CLA, P < 0.05); however, c9t11-CLA and t10c12-CLA increased the mRNA levels of SREBF isoforms and their target genes. In contrast, the mRNA expression of peroxisome-proliferator-activated receptor γ (PPARG) was strongly induced by ATRA alone but decreased by CLA isomers from 1.00 (ATRA alone) to 0.80 ± 0.06 (200 μM c9t11-CLA, P < 0.05) and 0.86 ± 0.06 (200 μM t10c12-CLA, P < 0.05). Overexpression of PPARγ in MCF-7 cells increased basal NIS-promoter activity, and treatment with the PPARγ ligand troglitazone stimulated ATRA-induced NIS-promoter activity. In conclusion, the results suggest that CLA isomers exert their effect on the expression of NIS by decreasing PPARG expression in MCF-7 cells.

Orally administration of Neolentinus lepideus extracts attenuated ethanol induced accumulation of hepatic lipid in mice

In this study, we examined the effects of the water extract of Neolentinus lepideus (WENL), an edible mushroom, on ethanol-induced hepatic lipid accumulation. Ethanol-induced oil red O-positive spots on AML-12 hepatocytes were attenuated by WENL treatment. Furthermore, the oral administration of WENL in acute and chronic ethanol-fed mouse models resulted in the decrease in blood triglyceride and the accumulation of lipid droplets in the liver. Interestingly, the transcriptional expression related to lipid metabolisms, such as sterol regulatory element-binding protein 1, and cytochrome P450 2E1, was decreased by WENL treatment in both ethanol-induced AML-12 hepatocytes and our chronic ethanol-fed mouse models. In addition, WENL effectively attenuated the ethanol induced activation of MAP kinases and NF-κB in AML-12 hepatocytes. Taken together, our results suggested that WENL can be effective in alleviating alcohol-induced hepatic lipid accumulation and may be used as potential candidate for the prevention of alcoholic fatty liver disease.

Collaborative effects of chlorogenic acid and caffeine on lipid metabolismviathe AMPKα-LXRα/SREBP-1c pathway in high-fat diet-induced obese mice

The combination of CGA and caffeine exhibits anti-obesity effects and regulates lipid metabolismviathe AMPKα-LXRα/SREBP-1c signaling pathway in mice with high-fat diet-induced obesity.

Activation of liver X receptor plays a central role in antiviral actions of 25-hydroxycholesterol

Production of 25-hydroxycholesterol (25HC), a potent inhibitor of viral infection, is catalyzed by cholesterol 25-hydroxylase (CH25H). We previously reported that 25HC induced CH25H expression in a liver X receptor (LXR)-dependent manner, implying that LXR can play an important role in antiviral infection. In this study, we determined that activation of LXR by 25HC or synthetic ligands [T0901317 (T317) or GW3965] inhibited infection of herpes simplex virus type 1 (HSV-1) or MLV-(VSV)-GFP in HepG2 cells or RAW 264.7 macrophages. Genetic deletion of LXRα, LXRβ, or CH25H expression in HepG2 cells by CRISPR/Cas9 method increased cell susceptibility to HSV-1 infection and attenuated the inhibition of LXR on viral infection. Lack of interferon (IFN)-γ expression also increased cell susceptibility to viral infection. However, it attenuated, but did not block, the inhibition of LXR on HSV-1 infection. In addition, expression of CH25H, but not IFN-γ, was inversely correlated to cell susceptibility to viral infection and the antiviral actions of LXR. Metabolism of 25HC into 25HC-3-sulfate (25HC3S) by cholesterol sulfotransferase-2B1b moderately reduced the antiviral actions of 25HC because 25HC3S is a weaker inhibitor of HSV-1 infection than 25HC. Furthermore, administration of T317 to BALB/c mice reduced HSV-1 growth in mouse tissues. Taken together, we demonstrate an antiviral system of 25HC with involvement of LXR activation, interaction between CH25H and IFN-γ, and 25HC metabolism.

The challenges and promise of targeting the Liver X Receptors for treatment of inflammatory disease

The Liver X Receptors (LXRs) are oxysterol-activated transcription factors that upregulate a suite of genes that together promote coordinated mobilization of excess cholesterol from cells and from the body. The LXRs, like other nuclear receptors, are anti-inflammatory, inhibiting signal-dependent induction of pro-inflammatory genes by nuclear factor-κB, activating protein-1, and other transcription factors. Synthetic LXR agonists have been shown to ameliorate atherosclerosis and a wide range of inflammatory disorders in preclinical animal models. Although this has suggested potential for application to human disease, systemic LXR activation is complicated by hepatic steatosis and hypertriglyceridemia, consequences of lipogenic gene induction in the liver by LXRα. The past several years have seen the development of multiple advanced LXR therapeutics aiming to avoid hepatic lipogenesis, including LXRβ-selective agonists, tissue-selective agonists, and transrepression-selective agonists. Although several synthetic LXR agonists have made it to phase I clinical trials, none have progressed due to unforeseen adverse reactions or undisclosed reasons. Nonetheless, several sophisticated pharmacologic strategies, including structure-guided drug design, cell-specific drug targeting, as well as non-systemic drug routes have been initiated and remain to be comprehensively explored. In addition, recent studies have identified potential utility for targeting the LXRs during therapy with other agents, such as glucocorticoids and rexinoids. Despite the pitfalls encountered to date in translation of LXR agonists to human disease, it appears likely that this accelerating field will ultimately yield effective and safe applications for LXR targeting in humans.

Cholesterol metabolites alleviate injured liver function and decrease mortality in an LPS-induced mouse model

BACKGROUND

Oxysterol sulfation plays a fundamental role in the regulation of many biological events. Its products, 25-hydroxycholesterol 3-sulfate (25HC3S) and 25-hydroxycholesterol 3, 25-disulfate (25HCDS), have been demonstrated to be potent regulators of lipid metabolism, inflammatory response, cell apoptosis, and cell survival. In the present study, we tested these products' potential to treat LPS-induced acute liver failure in a mouse model.

METHODS

Acute liver failure mouse model was established by intravenous injection with LPS. The injured liver function was treated with intraperitoneal administration of 25HC, 25HC3S or 25HCDS. Serum enzymatic activities were determined in our clinic laboratory. ELISA assays were used to detect pro-inflammatory factor levels in sera. Western blot, Real-time Quantitative PCR and RT² Profiler PCR Array analysis were used to determine levels of gene expression.

RESULTS

Administration of 25HC3S/25HCDS decreased serum liver-impaired markers; suppressed secretion of pro-inflammatory factors; alleviated liver, lung, and kidney injury; and subsequently increased the survival rate in the LPS-induced mouse model. These effects resulted from the inhibition of the expression of genes involved in the pro-inflammatory response and apoptosis and the simultaneous induction of the expression of genes involved in cell survival. Compared to 25HC, 25HC3S and 25HCDS exhibited significantly stronger effects in these activities, indicating that the cholesterol metabolites play an important role in the inflammatory response, cell apoptosis, and cell survival in vivo.

CONCLUSIONS

25HC3S/25HCDS has potential to serve as novel biomedicines in the therapy of acute liver failure and acute multiple organ failure.

Transgenic Overexpression of Steroid Sulfatase Alleviates Cholestasis

BACKGROUND AND AIM

Sulfotransferase (SULT)-mediated sulfation and steroid sulfatase (STS)-mediated desulfation represent two critical mechanisms that regulate the chemical and functional homeostasis of endogenous and exogenous molecules. STS catalyzes the hydrolysis of steroid sulfates to form hydroxysteroids. Oxygenated cholesterol derivative oxysterols are known to be endogenous ligands of the liver X receptor (LXR), a nuclear receptor with anti-cholestasis activity, whereas the sulfated oxysterols antagonize LXR signaling. The conversion of sulfated oxysterols to their non-sulfated counterparts is catalyzed by STS. The aim of this study is to determine whether STS can alleviate cholestasis by increasing the activity of LXR.

METHODS

Liver-specific STS transgenic mice were created and subject to the lithocholic acid (LCA)-induced model of cholestasis.

RESULTS

Transgenic overexpression of STS in the liver promoted bile acid elimination and alleviated LCA-induced cholestasis. The protective effect of the STS transgene was associated with the activation of LXR and induction of LXR target genes, likely because of the increased conversion of the antagonistic oxysterol sulfates to the agonistic oxysterols.

CONCLUSIONS

STS has a novel function in controlling the homeostasis of bile acids by regulating endogenous LXR ligands.

Polyphenol-rich apple extract inhibits dexamethasone-induced sebaceous lipids production by regulating SREBP1 expression

Sebum production and excretion is a primary function of the sebaceous glands, but abnormally increased sebum production is a major cause of acne vulgaris. To identify a new candidate that regulates sebum production, we investigated the possible inhibitory effects of apple polyphenols (APP) purified from unripe apples on primary cultured human sebocytes and in patients with acne vulgaris. Dexamethasone (Dex) increased lipid synthesis and expression of the sterol response element-binding protein 1 (SREBP 1) and its target enzymes, acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS), in the sebocytes. However, APP inhibited Dex-induced lipid production and expression of SREBP-1, ACC and FAS. APP also inhibited the increase in the expression and activation of glucocorticoid receptor in the sebocytes. Taken together, these results suggest that APP may be useful to regulate sebum production and may alleviate sebum-involved skin disease, such as acne vulgaris.

A novel transgenic mouse model of lysosomal storage disorder

Knockout technology has proven useful for delineating functional roles of specific genes. Here we describe and provide an explanation for striking pathology that occurs in a subset of genetically engineered mice expressing a rat Ca_Vβ2a transgene under control of the cardiac α-myosin heavy chain promoter. Lesions were limited to mice homozygous for transgene and independent of native Cacnb2 genomic copy number. Gross findings included an atrophied pancreas; decreased adipose tissue; thickened, orange intestines; and enlarged liver, spleen, and abdominal lymph nodes. Immune cell infiltration and cell engulfment by macrophages were associated with loss of pancreatic acinar cells. Foamy macrophages diffusely infiltrated the small intestine's lamina propria, while similar macrophage aggregates packed liver and splenic red pulp sinusoids. Periodic acid-Schiff-positive, diastase-resistant, iron-negative, Oil Red O-positive, and autofluorescent cytoplasm was indicative of a lipid storage disorder. Electron microscopic analysis revealed liver sinusoids distended by clusters of macrophages containing intracellular myelin "swirls" and hepatocytes with enlarged lysosomes. Additionally, build up of cholesterol, cholesterol esters, and triglycerides, along with changes in liver metabolic enzyme levels, were consistent with a lipid processing defect. Because of this complex pathology, we examined the transgene insertion site. Multiple transgene copies inserted into chromosome 19; at this same site, an approximate 180,000 base pair deletion occurred, ablating cholesterol 25-hydroxylase and partially deleting lysosomal acid lipase and CD95 Loss of gene function can account for the altered lipid processing, along with hypertrophy of the immune system, which define this phenotype, and serendipitously provides a novel mouse model of lysosomal storage disorder.

Oxysterols: From cholesterol metabolites to key mediators

Oxysterols are cholesterol metabolites that can be produced through enzymatic or radical processes. They constitute a large family of lipids (i.e. the oxysterome) involved in a plethora of physiological processes. They can act through GPCR (e.g. EBI2, SMO, CXCR2), nuclear receptors (LXR, ROR, ERα) and through transporters or regulatory proteins. Their physiological effects encompass cholesterol, lipid and glucose homeostasis. Additionally, they were shown to be involved in other processes such as immune regulatory functions and brain homeostasis. First studied as precursors of bile acids, they quickly emerged as interesting lipid mediators. Their levels are greatly altered in several pathologies and some oxysterols (e.g. 4β-hydroxycholesterol or 7α-hydroxycholestenone) are used as biomarkers of specific pathologies. In this review, we discuss the complex metabolism and molecular targets (including binding properties) of these bioactive lipids in human and mice. We also discuss the genetic mouse models currently available to interrogate their effects in pathophysiological settings. We also summarize the levels of oxysterols reported in two key organs in oxysterol metabolism (liver and brain), plasma and cerebrospinal fluid. Finally, we consider future opportunities and directions in the oxysterol field in order to gain a better insight and understanding of the complex oxysterol system.

Sterol regulatory element-binding proteins are regulators of the sodium/iodide symporter in mammary epithelial cells

The sodium/iodide symporter (NIS), which is essential for iodide concentration in the thyroid, is reported to be transcriptionally regulated by sterol regulatory element-binding proteins (SREBP) in rat FRTL-5 thyrocytes. The SREBP are strongly activated after parturition and throughout lactation in the mammary gland of cattle and are important for mammary epithelial cell synthesis of milk lipids. In this study, we tested the hypothesis that the NIS gene is regulated also by SREBP in mammary epithelial cells, in which NIS is functionally expressed during lactation. Regulation of NIS expression and iodide uptake was investigated by means of inhibition, silencing, and overexpression of SREBP and by reporter gene and DNA-binding assays. As a mammary epithelial cell model, the human MCF-7 cell line, a breast adenocarcinoma cell line, which shows inducible expression of NIS by all-trans retinoic acid (ATRA), and unlike bovine mammary epithelial cells, is widely used to investigate the regulation of mammary gland NIS and NIS-specific iodide uptake, was used. Inhibition of SREBP maturation by treatment with 25-hydroxycholesterol (5 µM) for 48h reduced ATRA (1 µM)-induced mRNA concentration of NIS and iodide uptake in MCF-7 cells by approximately 20%. Knockdown of SREBP-1c and SREBP-2 by RNA interference decreased the mRNA and protein concentration of NIS by 30 to 50% 48h after initiating knockdown, whereas overexpression of nuclear SREBP (nSREBP)-1c and nSREBP-2 increased the expression of NIS in MCF-7 cells by 45 to 60%, respectively, 48h after initiating overexpression. Reporter gene experiments with varying length of NIS promoter reporter constructs revealed that the NIS 5'-flanking region is activated by nSREBP-1c and nSREBP-2 approximately 1.5- and 4.5-fold, respectively, and activation involves a SREBP-binding motif (SRE) at -38 relative to the transcription start site of the NIS gene. Gel shift assays using oligonucleotides spanning either the wild-type or the mutated SRE at -38 of the NIS 5'-flanking region showed that in vitro-translated nSREBP-1c and nSREBP-2 bind only the wild-type but not the mutated SRE at -38 of NIS. Collectively, the present results from cell culture experiments with human mammary epithelial MCF-7 cells and from genetic studies show for the first time that the NIS gene and iodide uptake are regulated by SREBP in cultured human mammary epithelial cells. Future studies are necessary to clarify if the regulation of NIS expression and iodide uptake by SREBP also applies to the lactating bovine mammary epithelium.

A novel hypothesis for atherosclerosis as a cholesterol sulfate deficiency syndrome

BACKGROUND

Despite a vast literature, atherosclerosis and the associated ischemia/reperfusion injuries remain today in many ways a mystery. Why do atheromatous plaques make and store a supply of cholesterol and sulfate within the major arteries supplying the heart? Why are treatment programs aimed to suppress certain myocardial infarction risk factors, such as elevated serum homocysteine and inflammation, generally counterproductive?

METHODS

Our methods are based on an extensive search of the literature in atherosclerotic cardiovascular disease as well as in the area of the unique properties of water, the role of biosulfates in the vascular wall, and the role of electromagnetic fields in vascular flow. Our investigation reveals a novel pathology linked to atherosclerosis that better explains the observed facts than the currently held popular view.

RESULTS

We propose a novel theory that atherosclerosis can best be explained as being due to cholesterol sulfate deficiency. Furthermore, atheromatous plaques replenish the supply of cholesterol and sulfate to the microvasculature, by exploiting the inflammatory agent superoxide to derive sulfate from homocysteine and other sulfur sources. We argue that the sulfate anions attached to the glycosaminoglycans in the glycocalyx are essential in maintaining the structured water that is crucial for vascular endothelial health and erythrocyte mobility through capillaries. Sulfate depletion leads to cholesterol accumulation in atheromas, because its transport through water-based media depends on sulfurylation. We show that streaming potential induces nitric oxide (NO) release, and NO derivatives break down the extracellular matrix, redistributing sulfate to the microvasculature. We argue that low (less negative) zeta potential due to insufficient sulfate anions leads to hypertension and thrombosis, because these responses can increase streaming potential and induce nitric-oxide mediated vascular relaxation, promoting oxygen delivery. Our hypothesis is a parsimonious explanation of multiple features of atherosclerotic cardiovascular disease.

CONCLUSIONS

If our interpretation is correct, then it would have a significant impact on how atherosclerosis is treated. We recommend a high intake of sulfur-containing foods as well as an avoidance of exposure to toxicants that may impair sulfate synthesis.

Nanoparticles containing a liver X receptor agonist inhibit inflammation and atherosclerosis

Liver X receptor (LXR) signaling pathways regulate lipid metabolism and inflammation, which has generated widespread interest in developing synthetic LXR agonists as potential therapeutics for the management of atherosclerosis. In this study, it is demonstrated that nanoparticles (NPs) containing the synthetic LXR agonist GW3965 (NP-LXR) exert anti-inflammatory effects and inhibit the development of atherosclerosis without causing hepatic steatosis. These NPs are engineered through self-assembly of a biodegradable diblock poly(lactide-co-glycolide)-b-poly(ethylene glycol) (PLGA-b-PEG) copolymer. NP-LXR is significantly more effective than free GW3965 at inducing LXR-target gene expression and suppressing inflammatory factors in macrophages in vitro and in vivo. Additionally, the NPs elicit negligible lipogenic gene stimulation in the liver. Using the Ldlr (-/-) mouse model of atherosclerosis, abundant colocalization of fluorescently labeled NPs within plaque macrophages following systemic administration is seen. Notably, six intravenous injections of NP-LXR over 2 weeks markedly reduce the CD68-positive cell (macrophage) content of plaques (by 50%) without increasing total cholesterol or triglycerides in the liver and plasma. Together, these findings identify GW3965-encapsulated PLGA-b-PEG NPs as a promising nanotherapeutic approach to combat atherosclerosis, providing the benefits of LXR agonists without their adverse effects on hepatic and plasma lipid metabolism.

Sterol metabolism controls T(H)17 differentiation by generating endogenous RORγ agonists

Retinoic acid receptor-related orphan receptor γ (RORγt) controls the differentiation of naive CD4(+) T cells into the TH17 lineage, which are critical cells in the pathogenesis of autoimmune diseases. Here we report that during TH17 differentiation, cholesterol biosynthesis and uptake programs are induced, whereas their metabolism and efflux programs are suppressed. These changes result in the accumulation of the cholesterol precursor, desmosterol, which functions as a potent endogenous RORγ agonist. Generation of cholesterol precursors is essential for TH17 differentiation as blocking cholesterol synthesis with chemical inhibitors at steps before the formation of active precursors reduces differentiation. Upon activation, metabolic changes also lead to production of specific sterol-sulfate conjugates that favor activation of RORγ over the TH17-inhibiting sterol receptor LXR. Thus, TH17 differentiation is orchestrated by coordinated sterol synthesis, mobilization and metabolism to selectively activate RORγ.

Deciphering the roles of the constitutive androstane receptor in energy metabolism

The constitutive androstane receptor (CAR) is initially defined as a xenobiotic nuclear receptor that protects the liver from injury. Detoxification of damaging chemicals is achieved by CAR-mediated induction of drug-metabolizing enzymes and transporters. More recent research has implicated CAR in energy metabolism, suggesting a therapeutic potential for CAR in metabolic diseases, such as type 2 diabetes and obesity. A better understanding of the mechanisms by which CAR regulates energy metabolism will allow us to take advantage of its effectiveness while avoiding its side effects. This review summarizes the current progress on the regulation of CAR nuclear translocation, upstream modulators of CAR activity, and the crosstalk between CAR and other transcriptional factors, with the aim of elucidating how CAR regulates glucose and lipid metabolism.

Effect of sex hormones on levels of mRNAs coding for proteins involved in lipid metabolism in macrophages

The effects of sex hormones estradiol (E2), testosterone (Te), and 5α-dihydrotestosterone (DT) on cholesterol accumulation induced by modified low density lipoproteins (LDL) in macrophages differentiated from human peripheral blood monocytes and on the levels of mRNAs coding for proteins involved in lipid metabolism have been studied. All three hormones at physiological concentrations (1 nM) are capable of reducing cholesterol accumulation in cells. The treatment of cells with modified and native (not inducing cholesterol accumulation) LDL results in similar alterations in the expression of several mRNAs aimed primarily at homeostatic regulation of lipid metabolism. These alterations depend on the sex of macrophage donors and in some cases are even reversed in cells obtained from male and female donors. The cells not treated with modified LDL have no significant gender differences in the expression of the examined mRNAs. Hormones, either independently or in combination with the modified LDL, influence the levels of some mRNAs, and each hormone shows an individual range of effects. Correlation analysis of changes in mRNA content in the cells showed that the hormones may interfere with coordination of gene expression. Hormone action leads to: (1) reduced coupling of the content of individual mRNAs with their initial levels in the control cells; (2) reduced coupling of different mRNA levels; (3) regrouping of mRNAs between the clusters; and (4) changes in the number of factors that determine the correlation links between mRNAs. The data show that sex hormones may have impact on the level of expression of certain genes and, in particular, on the coordination of gene expression in macrophages.

Identification of novel regulatory cholesterol metabolite, 5-cholesten, 3β,25-diol, disulfate

Oxysterol sulfation plays an important role in regulation of lipid metabolism and inflammatory responses. In the present study, we report the discovery of a novel regulatory sulfated oxysterol in nuclei of primary rat hepatocytes after overexpression of the gene encoding mitochondrial cholesterol delivery protein (StarD1). Forty-eight hours after infection of the hepatocytes with recombinant StarD1 adenovirus, a water-soluble oxysterol product was isolated and purified by chemical extraction and reverse-phase HPLC. Tandem mass spectrometry analysis identified the oxysterol as 5-cholesten-3β, 25-diol, disulfate (25HCDS), and confirmed the structure by comparing with a chemically synthesized compound. Administration of 25HCDS to human THP-1-derived macrophages or HepG2 cells significantly inhibited cholesterol synthesis and markedly decreased lipid levels in vivo in NAFLD mouse models. RT-PCR showed that 25HCDS significantly decreased SREBP-1/2 activities by suppressing expression of their responding genes, including ACC, FAS, and HMG-CoA reductase. Analysis of lipid profiles in the liver tissues showed that administration of 25HCDS significantly decreased cholesterol, free fatty acids, and triglycerides by 30, 25, and 20%, respectively. The results suggest that 25HCDS inhibits lipid biosynthesis via blocking SREBP signaling. We conclude that 25HCDS is a potent regulator of lipid metabolism and propose its biosynthetic pathway.

Semi-interpenetrating network (sIPN) co-electrospun gelatin/insulin fiber formulation for transbuccal insulin delivery

PURPOSE

This work was aimed at developing a semi-interpenetrating network (sIPN) co-electrospun gelatin/insulin fiber scaffold (GIF) formulation for transbuccal insulin delivery.

METHODS

Gelatin was electrospun into fibers and converted into an sIPN following eosin Y-initiated polymerization of polyethylene glycol diacrylate (PEG-DA). The cytocompatibility, degradation rate and mechanical properties were examined in the resulting sIPNs with various ratios of PEG-DA to eosin Y to find a suitable formulation for transbuccal drug delivery. Insulin was co-electrospun with gelatin into fibers and converted into an sIPN-GIF using this suitable formulation. The in vitro release kinetics of insulin was evaluated using ELISA. The bioactivity of released insulin was analyzed in 3T3-L1 preadipocytes using Western blotting and Oil Red O staining. The transbuccal permeability of released insulin was determined using an in vitro porcine oral mucosa model.

RESULTS

The sIPN-GF formulation of GF cross-linked by PEG-DA (1% w/v) with eosin Y (5% v/v) possessed no cytotoxic effect, a moderate degradation rate with degradation half-life of 49 min, and a significant enhancement in mechanical properties. This formulation was used to fabricate sIPN-GIF. Insulin release was extended up to 4 h by sIPN-GIF. The released insulin successfully triggered intracellular AKT phosphorylation and induced adipocyte differentiation in 3T3-L1 preadipocytes. The transbuccal permeability of released insulin was determined on the order of 10(-7) cm/s.

CONCLUSIONS

Insulin can be fabricated into an sIPN-GIF formulation following co-electrospinning and cross-linking without losing bioactivity. It proved the potential of this new formulation for transbuccal insulin delivery.

25-Hydroxycholesterol acts as an amplifier of inflammatory signaling

Cross-talk between sterol regulatory pathways and inflammatory pathways has been demonstrated to significantly impact the development of both atherosclerosis and infectious disease. The oxysterol 25-hydroxycholesterol (25HC) plays multiple roles in lipid biosynthesis and immunity. We recently used a systems biology approach to identify 25HC as an innate immune mediator that had a predicted role in atherosclerosis and we demonstrated a role for 25HC in foam cell formation. Here, we show that this mediator also has several complex roles in the antiviral response. The host response to viruses involves gene regulatory circuits with multiple feedback loops and we show here that 25HC acts as an amplifier of inflammatory signaling in macrophages. We determined that 25HC amplifies inflammatory signaling, at least in part, by mediating the recruitment of the AP-1 components FBJ osteosarcoma oncogene (FOS) and jun proto-oncogene (JUN) to the promoters of a subset of Toll-like receptor-responsive genes. Consistent with previous reports, we found that 25HC inhibits in vitro infection of airway epithelial cells by influenza. Surprisingly, we found that deletion of Ch25h, the gene encoding the enzyme responsible for 25HC production, is protective in a mouse model of influenza infection as a result of decreased inflammatory-induced pathology. Thus, our study demonstrates, for the first time to our knowledge, that in addition to its direct antiviral role, 25HC also regulates transcriptional responses and acts as an amplifier of inflammation via AP-1 and that the resulting alteration in inflammatory response leads to increased tissue damage in mice following infection with influenza.

Sulfation of 25-hydroxycholesterol regulates lipid metabolism, inflammatory responses, and cell proliferation

Intracellular lipid accumulation, inflammatory responses, and subsequent apoptosis are the major pathogenic events of metabolic disorders, including atherosclerosis and nonalcoholic fatty liver diseases. Recently, a novel regulatory oxysterol, 5-cholesten-3b, 25-diol 3-sulfate (25HC3S), has been identified, and hydroxysterol sulfotransferase 2B1b (SULT2B1b) has been elucidated as the key enzyme for its biosynthesis from 25-hydroxycholesterol (25HC) via oxysterol sulfation. The product 25HC3S and the substrate 25HC have been shown to coordinately regulate lipid metabolism, inflammatory responses, and cell proliferation in vitro and in vivo. 25HC3S decreases levels of the nuclear liver oxysterol receptor (LXR) and sterol regulatory element-binding proteins (SREBPs), inhibits SREBP processing, subsequently downregulates key enzymes in lipid biosynthesis, decreases intracellular lipid levels in hepatocytes and THP-1-derived macrophages, prevents apoptosis, and promotes cell proliferation in liver tissues. Furthermore, 25HC3S increases nuclear PPARγ and cytosolic IκBα and decreases nuclear NF-κB levels and proinflammatory cytokine expression and secretion when cells are challenged with LPS and TNFα. In contrast to 25HC3S, 25HC, a known LXR ligand, increases nuclear LXR and decreases nuclear PPARs and cytosol IκBα levels. In this review, we summarize our recent findings, including the discovery of the regulatory oxysterol sulfate, its biosynthetic pathway, and its functional mechanism. We also propose that oxysterol sulfation functions as a regulatory signaling pathway.

The impact of exposure to serum lipids during in vitro culture on the transcriptome of bovine blastocysts

In vitro culture has a detrimental impact on early embryonic development, and serum addition to IVC is recognized to compromise blastocyst quality. Particularly, serum fatty acids affect embryonic lipid composition and reduce cryopreservation survival. To understand the molecular pathways of serum-induced embryonic stress, this study examined the early development of bovine embryos produced in different protein- or lipid-supplemented culture media: BSA alone (control), BSA + serum lipid fraction (SELF), delipidated serum and total serum. These protein-lipid treatments were applied from the eight to 16 cell stages to the blastocyst stage. As planned, SELF treatment increased the fatty acid concentration in the medium compared with control medium but did not induce embryo toxicity. However, microarray comparison between blastocysts cultured in BSA without or with SELF revealed differential transcriptomic profile associated with ceramide-induced oxidative stress and inflammation. Moreover, the SELF treatment had a significant impact on genes involved in cholesterol metabolism (LDLR, HMGCS1), with the potential upstream control of the transcription factors SREBP and PPARA, two major regulators of cholesterol metabolism. In addition, the expression of pluripotence-related genes (APEX, CLDN6) was downregulated in blastocysts subjected to either SELF or total serum. Taken together, these results illustrate how the early embryonic transcriptome responds to increased lipid exposure through an inflammatory and metabolic signature.

Role of the constitutive androstane receptor in obesity and type 2 diabetes: a case study of the endobiotic function of a xenobiotic receptor

The constitutive androstane receptor (CAR, NR1I3) is a member of the nuclear receptor superfamily. Initially recognized as a xenobiotic receptor, CAR has been increasingly appreciated for its endobiotic functions in influencing glucose and lipid metabolism, whose dysregulations are implicated in the most prevalent metabolic disorders, such as obesity and type 2 diabetes. Given the metabolic benefits of CAR activation, CAR may represent an attractive therapeutic target to manage obesity and type 2 diabetes. Further studies are necessary to understand the mechanisms of action of CAR in metabolic diseases and to determine the human relevance of the antidiabetic effect of CAR.

Sterol-izing innate immunity

In this issue of Immunity, studies by Blanc et al. (2013) and Liu et al. (2013) reveal how interferon induction of cholesterol-25-hydroxylase mediates innate immunity against multiple diverse viruses.

5-cholesten-3β,25-diol 3-sulfate decreases lipid accumulation in diet-induced nonalcoholic fatty liver disease mouse model

Sterol regulatory element-binding protein-1c (SREBP-1c) increases lipogenesis at the transcriptional level, and its expression is upregulated by liver X receptor α (LXRα). The LXRα/SREBP-1c signaling may play a crucial role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). We previously reported that a cholesterol metabolite, 5-cholesten-3β,25-diol 3-sulfate (25HC3S), inhibits the LXRα signaling and reduces lipogenesis by decreasing SREBP-1c expression in primary hepatocytes. The present study aims to investigate the effects of 25HC3S on lipid homeostasis in diet-induced NAFLD mouse models. NAFLD was induced by feeding a high-fat diet (HFD) in C57BL/6J mice. The effects of 25HC3S on lipid homeostasis, inflammatory responses, and insulin sensitivity were evaluated after acute treatments or long-term treatments. Acute treatments with 25HC3S decreased serum lipid levels, and long-term treatments decreased hepatic lipid accumulation in the NAFLD mice. Gene expression analysis showed that 25HC3S significantly suppressed the SREBP-1c signaling pathway that was associated with the suppression of the key enzymes involved in lipogenesis: fatty acid synthase, acetyl-CoA carboxylase 1, and glycerol-3-phosphate acyltransferase. In addition, 25HC3S significantly reduced HFD-induced hepatic inflammation as evidenced by decreasing tumor necrosis factor and interleukin 1 α/β mRNA levels. A glucose tolerance test and insulin tolerance test showed that 25HC3S administration improved HFD-induced insulin resistance. The present results indicate that 25HC3S as a potent endogenous regulator decreases lipogenesis, and oxysterol sulfation can be a key protective regulatory pathway against lipid accumulation and lipid-induced inflammation in vivo.

Cholesterol metabolite, 5-cholesten-3β-25-diol-3-sulfate, promotes hepatic proliferation in mice

Oxysterols are well known as physiological ligands of liver X receptors (LXRs). Oxysterols, 25-hydroxycholesterol (25HC) and 27-hydroxycholesterol as endogenous ligands of LXRs, suppress cell proliferation via LXRs signaling pathway. Recent reports have shown that sulfated oxysterol, 5-cholesten-3β-25-diol-3-sulfate (25HC3S) as LXRs antagonist, plays an opposite direction to oxysterols in lipid biosynthesis. The present report was to explore the effect and mechanism of 25HC3S on hepatic proliferation in vivo. Following administration, 25HC3S had a 48 h half life in the circulation and widely distributed in mouse tissues. Profiler™ PCR array and RTqPCR analysis showed that either exogenous or endogenous 25HC3S generated by overexpression of oxysterol sulfotransferase (SULT2B1b) plus administration of 25HC significantly up-regulated the proliferation gene expression of Wt1, Pcna, cMyc, cyclin A, FoxM1b, and CDC25b in a dose-dependent manner in liver while substantially down-regulating the expression of cell cycle arrest gene Chek2 and apoptotic gene Apaf1. Either exogenous or endogenous administration of 25HC3S significantly induced hepatic DNA replication as measured by immunostaining of the PCNA labeling index and was associated with reduction in expression of LXR response genes, such as ABCA1 and SREBP-1c. Synthetic LXR agonist T0901317 effectively blocked 25HC3S-induced hepatic proliferation.

CONCLUSIONS

25HC3S may be a potent regulator of hepatocyte proliferation and oxysterol sulfation may represent a novel regulatory pathway in liver proliferation via inactivating LXR signaling.