Ursodeoxycholic acid inhibits liver X receptor α-mediated hepatic lipogenesis via induction of the nuclear corepressor SMILE

Androgen synthesis cell-specific CREBZF deficiency alters adrenal cortex steroid secretion and develops behavioral abnormalities in adult male mice

The global challenge of male infertility is escalating, notably due to the decreased testosterone (T) synthesis in testicular Leydig cells under stress, underscoring the critical need for a more profound understanding of its regulatory mechanisms. CREBZF, a novel basic region-leucine zipper transcription factor, regulates testosterone synthesis in mouse Leydig cells in vitro; however, further validation through in vivo experiments is essential. Our study utilized Cyp17a1-Cre to knock out CREBZF in androgen-synthesis cells and explored the physiological roles of CREBZF in fertility, steroid hormone synthesis, and behaviors in adult male mice. Conditional knockout (cKO) CREBZF did not affect fertility and serum testosterone level in male mice. Primary Leydig cells isolated from CREBZF-cKO mice showed impaired testosterone secretion and decreased mRNA levels of Star, Cyp17a1, and Hsd3b1. Loss of CREBZF resulted in thickening of the adrenal cortex, especially X-zone, with elevated serum corticosterone and dehydroepiandrosterone levels and decreased serum dehydroepiandrosterone sulfate levels. Immunohistochemical staining revealed increased expression of StAR, Cyp11a1, and 17β-Hsd3 in the adrenal cortex of CREBZF-cKO mice, while the expression of AR was significantly reduced. Along with the histological changes and abnormal steroid levels in the adrenal gland, CREBZF-cKO mice showed higher anxiety-like behavior and impaired memory in the elevated plus maze and Barnes maze, respectively. In summary, CREBZF is dispensable for fertility, and CREBZF deficiency in Leydig cells promotes adrenal function in adult male mice. These results shed light on the requirement of CREBZF for fertility, adrenal steroid synthesis, and stress response in adult male mice, and contribute to understanding the crosstalk between testes and adrenal glands.

Activation of CTU2 expression by LXR promotes the development of hepatocellular carcinoma

Cytosolic thiouridylase 2 (CTU2) is an enzyme modifying transfer RNAs post-transcriptionally, which has been implicated in breast cancer and melanoma development. And we found CTU2 participated in hepatocellular carcinoma (HCC) progression here. HepG2 cells as well as xenograft nude mice model were employed to investigate the role of CTU2 in HCC development in vitro and in vivo respectively. Further, we defined CTU2 as a Liver X receptor (LXR) targeted gene, with a typical LXR element in the CTU2 promoter. CTU2 expression was activated by LXR agonist and depressed by LXR knockout. Interestingly, we also found CTU2 took part in lipogenesis by directly enhancing the synthesis of lipogenic proteins, which provided a novel mechanism for LXR regulating lipid synthesis. Meanwhile, lipogenesis was active during cell proliferation, particularly in tumor cells. Reduction of CTU2 expression was related to reduced tumor burden and synergized anti-tumor effect of LXR ligands by inducing tumor cell apoptosis and inhibiting cell proliferation. Taken together, our study identified CTU2 as an LXR target gene. Inhibition of CTU2 expression could enhance the anti-tumor effect of LXR ligand in HCC, identifying CTU2 as a promising target for HCC treatment and providing a novel strategy for the application of LXR agonists in anti-tumor effect.

Emerging Role of SMILE in Liver Metabolism

Small heterodimer partner-interacting leucine zipper (SMILE) is a member of the CREB/ATF family of basic leucine zipper (bZIP) transcription factors. SMILE has two isoforms, a small and long isoform, resulting from alternative usage of the initiation codon. Interestingly, although SMILE can homodimerize similar to other bZIP proteins, it cannot bind to DNA. As a result, SMILE acts as a co-repressor in nuclear receptor signaling and other transcription factors through its DNA binding inhibition, coactivator competition, and direct repression, thereby regulating the expression of target genes. Therefore, the knockdown of SMILE increases the transactivation of transcription factors. Recent findings suggest that SMILE is an important regulator of metabolic signals and pathways by causing changes in glucose, lipid, and iron metabolism in the liver. The regulation of SMILE plays an important role in pathological conditions such as hepatitis, diabetes, fatty liver disease, and controlling the energy metabolism in the liver. This review focuses on the role of SMILE and its repressive actions on the transcriptional activity of nuclear receptors and bZIP transcription factors and its effects on liver metabolism. Understanding the importance of SMILE in liver metabolism and signaling pathways paves the way to utilize SMILE as a target in treating liver diseases.

Emerging Role of SMILE in Liver Metabolism

Small heterodimer partner-interacting leucine zipper (SMILE) is a member of the CREB/ATF family of basic leucine zipper (bZIP) transcription factors. SMILE has two isoforms, a small and long isoform, resulting from alternative usage of the initiation codon. Interestingly, although SMILE can homodimerize similar to other bZIP proteins, it cannot bind to DNA. As a result, SMILE acts as a co-repressor in nuclear receptor signaling and other transcription factors through its DNA binding inhibition, coactivator competition, and direct repression, thereby regulating the expression of target genes. Therefore, the knockdown of SMILE increases the transactivation of transcription factors. Recent findings suggest that SMILE is an important regulator of metabolic signals and pathways by causing changes in glucose, lipid, and iron metabolism in the liver. The regulation of SMILE plays an important role in pathological conditions such as hepatitis, diabetes, fatty liver disease, and controlling the energy metabolism in the liver. This review focuses on the role of SMILE and its repressive actions on the transcriptional activity of nuclear receptors and bZIP transcription factors and its effects on liver metabolism. Understanding the importance of SMILE in liver metabolism and signaling pathways paves the way to utilize SMILE as a target in treating liver diseases.

SMILE Downregulation during Melanogenesis Induces MITF Transcription in B16F10 Cells

SMILE (small heterodimer partner-interacting leucine zipper protein) is a transcriptional corepressor that potently regulates various cellular processes such as metabolism and growth in numerous tissues. However, its regulatory role in skin tissue remains uncharacterized. Here, we demonstrated that SMILE expression markedly decreased in human melanoma biopsy specimens and was inversely correlated with that of microphthalmia-associated transcription factor (MITF). During melanogenesis, α-melanocyte-stimulating hormone (α-MSH) induction of MITF was mediated by a decrease in SMILE expression in B16F10 mouse melanoma cells. Mechanistically, SMILE was regulated by α-MSH/cAMP/protein kinase A signaling and suppressed MITF promoter activity via corepressing transcriptional activity of the cAMP response element-binding protein. Moreover, SMILE overexpression significantly reduced α-MSH-induced MITF and melanogenic genes, thereby inhibiting melanin production in melanocytes. Conversely, SMILE inhibition increased the transcription of melanogenic genes and melanin contents. These results indicate that SMILE is a downstream effector of cAMP-mediated signaling and is a critical factor in the regulation of melanogenic transcription; in addition, they suggest a potential role of SMILE as a corepressor in skin pigmentation.

Ursodeoxycholic acid reduces antitumor immunosuppression by inducing CHIP-mediated TGF-β degradation

TGF-β is essential for inducing systemic tumor immunosuppression; thus, blocking TGF-β can greatly enhance antitumor immunity. However, there are still no effective TGF-β inhibitors in clinical use. Here, we show that the clinically approved compound ursodeoxycholic acid (UDCA), by degrading TGF-β, enhances antitumor immunity through restraining Treg cell differentiation and activation in tumor-bearing mice. Furthermore, UDCA synergizes with anti-PD-1 to enhance antitumor immunity and tumor-specific immune memory in tumor-bearing mice. UDCA phosphorylates TGF-β at T282 site via TGR5-cAMP-PKA axis, causing increased binding of TGF-β to carboxyl terminus of Hsc70-interacting protein (CHIP). Then, CHIP ubiquitinates TGF-β at the K315 site, initiating p62-dependent autophagic sorting and subsequent degradation of TGF-β. Notably, results of retrospective analysis shows that combination therapy with anti-PD-1 or anti-PD-L1 and UDCA has better efficacy in tumor patients than anti-PD-1 or anti-PD-L1 alone. Thus, our results show a mechanism for TGF-β regulation and implicate UDCA as a potential TGF-β inhibitor to enhance antitumor immunity.

Oxidative Stress, Genomic Integrity, and Liver Diseases

Excess reactive oxygen species production and free radical formation can lead to oxidative stress that can damage cells, tissues, and organs. Cellular oxidative stress is defined as the imbalance between ROS production and antioxidants. This imbalance can lead to malfunction or structure modification of major cellular molecules such as lipids, proteins, and DNAs. During oxidative stress conditions, DNA and protein structure modifications can lead to various diseases. Various antioxidant-specific gene expression and signal transduction pathways are activated during oxidative stress to maintain homeostasis and to protect organs from oxidative injury and damage. The liver is more vulnerable to oxidative conditions than other organs. Antioxidants, antioxidant-specific enzymes, and the regulation of the antioxidant responsive element (ARE) genes can act against chronic oxidative stress in the liver. ARE-mediated genes can act as the target site for averting/preventing liver diseases caused by oxidative stress. Identification of these ARE genes as markers will enable the early detection of liver diseases caused by oxidative conditions and help develop new therapeutic interventions. This literature review is focused on antioxidant-specific gene expression upon oxidative stress, the factors responsible for hepatic oxidative stress, liver response to redox signaling, oxidative stress and redox signaling in various liver diseases, and future aspects.

Mogrol suppresses lung cancer cell growth by activating AMPK-dependent autophagic death and inducing p53-dependent cell cycle arrest and apoptosis

Lung carcinoma is the leading cause of cancer-related death worldwide. Chemotherapy remains the cornerstone of lung cancer treatment. Unfortunately, most types of cancer will develop resistance to chemotherapies over the time. One of the efforts to prevent the chemotherapy resistance is to find alternative chemotherapy drugs. Mogrol has been found to have antitumor activity. However, little is known about the pharmacological mechanisms underlying the suppression of mogrol on lung cancers. In this study, we observed that mogrol exposure significantly reduced the tumor volume and weight in tumor-bearing nude mice without obvious effect on body weight and cardiac function. Mogrol also significantly inhibited the proliferation and migration of lung cancer cells, including non-small-cell lung carcinoma cells, A549, H1299, H1975 and SK-MES-1 cells, with no obvious effect on control human bronchial epithelial cells (HBE). Further studies revealed that mogrol stirred excessive autophagy and autophagic flux, and finally, autophagic cell death, in lung cancer cells, which could be attenuated by autophagy inhibitors, 3-MA and chloroquine. Furthermore, mogrol significantly activated AMPK to induce autophagy and autophagic cell death, which could be abrogated by Compound C, an AMPK inhibitor. In addition, mogrol induced a significant increase in p53 activity in lung cancer cells, accompanied with cell cycle arrest and apoptosis, which could be weakened by p53 silence. Our results indicated that mogrol effectively suppressed lung cancer cells in vivo and in vitro by inducing the excessive autophagy and autophagic cell death via activating AMPK signaling pathway, as well as cell cycle arrest and apoptosis via activating p53 pathway.

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.

Epigallocatechin-3-Gallate Suppresses BMP-6-Mediated SMAD1/5/8 Transactivation of Hepcidin Gene by Inducing SMILE in Hepatocytes

Hepcidin, a major regulator of systemic iron homeostasis, is mainly induced in hepatocytes by activating bone morphogenetic protein 6 (BMP-6) signaling in response to changes in the iron status. Small heterodimer partner-interacting leucine zipper protein (SMILE), a polyphenol-inducible transcriptional co-repressor, regulates hepatic gluconeogenesis and lipogenesis. Here, we examine the epigallocatechin-3-gallate (EGCG) effect on BMP-6-mediated SMAD1/5/8 transactivation of the hepcidin gene. EGCG treatment significantly decreased BMP-6-induced hepcidin gene expression and secretion in hepatocytes, which, in turn, abated ferroportin degradation. SMILE overexpression significantly decreased BMP receptor-induced hepcidin promoter activity. SMILE overexpression also significantly suppressed BMP-6-mediated induction of hepcidin mRNA and its secretion in HepG2 and AML12 cells. EGCG treatment inhibited BMP-6-mediated hepcidin gene expression and secretion, which were significantly reversed by SMILE knockdown in hepatocytes. Interestingly, SMILE physically interacted with SMAD1 in the nucleus and significantly blocked DNA binding of the SMAD complex to the BMP-response element on the hepcidin gene promoter. Taken together, these findings suggest that SMILE is a novel transcriptional repressor of BMP-6-mediated hepcidin gene expression, thus contributing to the control of iron homeostasis.

Lyophilized Maqui (Aristotelia chilensis) Berry Administration Suppresses High-Fat Diet-Induced Liver Lipogenesis through the Induction of the Nuclear Corepressor SMILE

The liver is one of the first organs affected by accumulated ectopic lipids. Increased de novo lipogenesis and excessive triglyceride accumulation in the liver are hallmarks of nonalcoholic fatty liver disease (NAFLD) and are strongly associated with obesity, insulin resistance, and type 2 diabetes. Maqui dietary supplemented diet-induced obese mice showed better insulin response and decreased weight gain. We previously described that these positive effects of maqui are partially due to an induction of a brown-like phenotype in subcutaneous white adipose tissue that correlated with a differential expression of Chrebp target genes. In this work, we aimed to deepen the molecular mechanisms underlying the impact of maqui on the onset and development of the obese phenotype and insulin resistance focusing on liver metabolism. Our results showed that maqui supplementation decreased hepatic steatosis caused by a high-fat diet. Changes in the metabolic profile include a downregulation of the lipogenic liver X receptor (LXR) target genes and of fatty acid oxidation gene expression together with an increase in the expression of small heterodimer partner interacting leucine zipper protein (Smile), a corepressor of the nuclear receptor family. Our data suggest that maqui supplementation regulates lipid handling in liver to counteract the metabolic impact of a high-fat diet.

Oral Administration of Germinated, Pigmented, Giant Embryo Rice (Oryza sativa L. cv. Keunnunjami) Extract Improves the Lipid and Glucose Metabolisms in High-Fat Diet-Fed Mice

Obesity is a significant risk factor for chronic diseases. The effect of ethanol extract from germinated Keunnunjami, blackish-purple rice with a giant embryo, compare to ordinary brown rice, on the body weight and lipid and glucose metabolism in high-fat diet-fed mice was analyzed. Mice were fed with a high-fat diet-fed for 3 weeks and then orally administered with either distilled water (HF) or extract (0.25%, w/w) from brown, germinated brown, Keunnunjami, and germinated Keunnunjami rice for 4 weeks. Control mice were fed with a normal diet and orally administered with distilled water. The HF group showed markedly higher body weight and triglyceride, cholesterol, fatty acid, glucose, and insulin levels than the control group. However, the oral administration of rice extracts ameliorated this high-fat diet-induced obesity, hyperlipidemia, and hypoglycemia through the modulation of adipokine production, lipogenic and glucose-regulating enzyme activities, and mRNA expression of genes associated with lipid and glucose metabolism. The germinated Keunnunjami extract exhibited greater hypolipidemic, hypoglycemic, and body weight-lowering effects than the other rice extracts. The results demonstrated that germination could further enhance the physiological properties of rice and that germinated Keunnunjami extract has a strong therapeutic potential against high-fat diet-induced obesity, hyperlipidemia, and hyperglycemia.

Epigallocatechin-3-Gallate (EGCG)-Inducible SMILE Inhibits STAT3-Mediated Hepcidin Gene Expression

Hepatic peptide hormone hepcidin, a key regulator of iron metabolism, is induced by inflammatory cytokine interleukin-6 (IL-6) in the pathogenesis of anemia of inflammation or microbial infections. Small heterodimer partner-interacting leucine zipper protein (SMILE)/CREBZF is a transcriptional corepressor of nuclear receptors that control hepatic glucose and lipid metabolism. Here, we examined the role of SMILE in regulating iron metabolism by inflammatory signals. Overexpression of SMILE significantly decreased activation of the Janus kinase 2-signal transducer and activator of transcription 3 (STAT3)-mediated hepcidin production and secretion that is triggered by the IL-6 signal in human and mouse hepatocytes. Moreover, SMILE co-localized and physically interacted with STAT3 in the nucleus in the presence of IL-6, which significantly suppressed binding of STAT3 to the hepcidin gene promoter. Interestingly, epigallocatechin-3-gallate (EGCG), a major component of green tea, induced SMILE expression through forkhead box protein O1 (FoxO1), as demonstrated in FoxO1 knockout primary hepatocytes. In addition, EGCG inhibited IL-6-induced hepcidin expression, which was reversed by SMILE knockdown. Finally, EGCG significantly suppressed lipopolysaccharide-induced hepcidin secretion and hypoferremia through induction of SMILE expression in mice. These results reveal a previously unrecognized role of EGCG-inducible SMILE in the IL-6-dependent transcriptional regulation of iron metabolism.

Neddylation of sterol regulatory element-binding protein 1c is a potential therapeutic target for nonalcoholic fatty liver treatment

Nonalcoholic fatty liver disease (NAFLD) is a risk factor for progression of steatohepatitis, liver cirrhosis, and liver cancer. Although pathological condition of NAFLD, which arises from an excessive accumulation of triglyceride in the liver, is accompanied by elevated sterol regulatory element-binding protein 1c (SREBP1c) level, it is largely unknown which factors are involved in the modification of SREBP1c. In this study, we discovered that neddylation of SREBP1c competes with its ubiquitination and stabilizes SREBP1c protein level, and eventually promotes hepatic steatosis. We also demonstrated that human homolog of mouse double minute 2 (HDM2) acts as an E3 neddylation ligase of SREBP1c. Further, treatment with the neddylation inhibitor, MLN4924, attenuates high-fat diet-induced hepatic steatosis by reducing the levels of SREBP1c protein and hepatic triglyceride. Our results indicate that the blockade of SREBP1c neddylation could be a novel approach in the defense against NAFLD.

Sesamin, a Naturally Occurring Lignan, Inhibits Ligand-Induced Lipogenesis through Interaction with Liver X Receptor Alpha (LXRα) and Pregnane X Receptor (PXR)

Liver X receptor (LXR) is a nuclear receptor that regulates various biological processes, including de novo lipogenesis, cholesterol metabolism, and inflammation. Selective inhibition of LXR may aid the treatment of nonalcoholic fatty liver disease (NAFLD). Sesamin is a naturally occurring lignan in many dietary plants and has a wide range of beneficial effects on metabolism. The mechanism underlying sesamin action especially on the regulation of LXR remains elusive. Reporter assays, mRNA and protein expression, and in silico modeling were used to identify sesamin as an antagonist of LXRα. Sesamin was applied to the hepatic HepaRG and intestinal LS174T cells and showed that it markedly ameliorated lipid accumulation in the HepaRG cells, by reducing LXRα transactivation, inhibiting the expression of downstream target genes. This effect was associated with the stimulation of AMP-activated protein kinase (AMPK) signaling pathway, followed by decreased T0901317-LXRα-induced expression of SREBP-1c and its downstream target genes. Mechanistically, sesamin reduced the recruitment of SRC-1 but enhanced that of SMILE to the SREBP-1c promoter region under T0901317 treatment. It regulated the transcriptional control exerted by LXRα by influencing its interaction with coregulators and thus decreased mRNA and protein levels of genes downstream of LXRα and reduced lipid accumulation in hepatic cells. Additionally, sesamin reduced valproate- and rifampin-induced LXRα and pregnane X receptor (PXR) transactivation. This was associated with reduced expression of target genes and decreased lipid accumulation. Thus, sesamin is an antagonist of LXRα and PXR and suggests that it may alleviate drug-induced lipogenesis via the suppression of LXRα and PXR signaling.

CREBZF regulates testosterone production in mouse Leydig cells

CREBZF, including the two isoforms SMILE (long isoform of CREBZF) and Zhangfei (short isoform of CREBZF), has been identified as a novel transcriptional coregulator of a variety of nuclear receptors. Our previous studies found that SMILE is expressed in the mouse uterine luminal and glandular epithelium and is upregulated by estrogen. In the present study, CREBZF was age-dependently and -specifically expressed in mouse interstitial Leydig cells during sexual maturation. The expression pattern of CREBZF exhibited an age-related increase, and SMILE was the dominant isoform in the mouse testis. Although hCG did not affect CREBZF expression, CREBZF silencing significantly inhibited hCG-stimulated testosterone production in primary Leydig cells and MLTC-1 cells. Meanwhile, the serum concentration of testosterone was significantly decreased after microinjection of lentiviral-mediated shRNA-CREBZF into the mature mouse testis. In addition, CREBZF silencing markedly decreased P450c17, 17β-HSD, and 3β-HSD expression following hCG stimulation in primary Leydig cells, and this inhibitory effect was obviously reversed by overexpression of CREBZF. Furthermore, CREBZF significantly upregulated the mRNA levels of Nr4a1 and Nr5a1, which are the essential orphan nuclear receptors for steroidogenic gene expression. Together our data indicate that CREBZF promotes hCG-induced testosterone production in mouse Leydig cells by affecting Nr4a1 and Nr5a1 expression levels and subsequently increasing the expression of steroidogenic genes such as 3β-HSD, 17β-HSD, and P450c17, suggesting a potential important role of CREBZF in testicular testosterone synthesis.

Ursodeoxycholic acid ameliorates hepatic lipid metabolism in LO2 cells by regulating the AKT/mTOR/SREBP-1 signaling pathway

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD), the most common chronic liver disease, can progress into nonalcoholic steatohepatitis (NASH), cirrhosis, and even hepatocellular carcinoma. Bile acids such as ursodeoxycholic acid (UDCA) play an essential role in the pathogenesis of NAFLD by regulating the level of sterol regulatory element-binding protein (SREBP) 1c, but the underlying regulatory mechanism remains elusive. Increased evidence indicates that the AKT/mTOR/SREBP-1 signaling pathway is a key pathway to regulate hepatic cellular lipid metabolism. UDCA may regulate the AKT/mTOR/SREBP-1 signaling pathway to ameliorate hepatic lipid metabolism.

AIM

To investigate the functional mechanism of UDCA in an oleic acid (OA)-induced cellular model of NAFLD.

METHODS

The cellular model of NAFLD was established using OA and treated with UDCA. First, the best concentration of UDCA was selected. For the best time-dependent assay, cells were stimulated with OA only or co-treated with OA and 2 mmol/L UDCA for 24 h, 48 h, and 72 h. Oil red O staining was used to observe the accumulation of intracellular lipids, while the intracellular contents of triglyceride, alanine aminotransferase (ALT), gamma-glutamyl transpeptidase (GGT), and aspartate aminotransferase (AST) were detected by enzymatic methods. Meanwhile, the expression levels of AKT/mTOR/SREBP-1 signaling pathway-related proteins were detected by real-time PCR and Western blot.

RESULTS

In the NAFLD cell model established with LO2 cells induced using OA, lipid accumulation was obvious. UDCA significantly inhibited lipid accumulation at different concentrations (especially 2 mmol/L) and decreased cell growth ability at different time points. The biochemical parameters like ALT, AST, and GGT were significant improved by UDCA. UDCA treatment vividly repressed the activation of AKT, mTOR, and CRTC2 and the expression of nSREBP-1 in LO2 cells induced with OA.

CONCLUSION

Our findings demonstrate the effect of UDCA in improving NAFLD. UDCA attenuates OA-induced hepatic steatosis mainly by regulation of AKT/mTOR/SREBP-1 signal transduction.

Ursolic Acid, a Novel Liver X Receptor α (LXRα) Antagonist Inhibiting Ligand-Induced Nonalcoholic Fatty Liver and Drug-Induced Lipogenesis

Nonalcoholic fatty liver disease (NAFLD) is a very common liver disease, and its incidence has significantly increased worldwide. The liver X receptor α (LXRα) is a multifunctional nuclear receptor that controls lipid homeostasis. Inhibition of LXRα transactivation may be beneficial for NAFLD and hyperlipidemia treatment. Ursolic acid (UA) is a plant triterpenoid with many beneficial effects; however, the mechanism of its action on LXRα remains elusive. We evaluated the effects of UA on T0901317 (T090)-induced LXRα activation and steatosis. UA significantly decreased the LXR response element and sterol regulatory element-binding protein-1c ( SREBP-1c) gene promoter activities, mRNA, protein expression of LXRα target genes, and hepatic cellular lipid content in a T090-induced mouse model. A molecular docking study indicated that UA bound competitively with T090 at the LXRα ligand binding domain. UA stimulated AMP-activated protein kinase (AMPK) phosphorylation in hepatic cells and increased corepressor, small heterodimer partner-interacting leucine zipper protein (SMILE) but decreased coactivator, steroid receptor coactivator-1 (SRC-1) recruitment to the SREBP-1c promoter region. In contrast, UA induced SRC-1 binding but decreased SMILE binding to reverse cholesterol transport-related gene promoters in intestinal cells, increasing lipid excretion from intestinal cells. Additionally, UA reduced valproate-induced LXRα mediated and rifampin-induced pregnane X receptor mediated lipogenesis, offering potential treatments for drug-induced hepatic steatosis. Thus, UA displays liver specificity and can be selectively repressed while RCT stimulation by LXRα is preserved and enhanced. This is a novel therapeutic option to treat NAFLD and may be helpful in developing LXR agonists to prevent atherosclerosis.

Oleanolic Acid Inhibits Liver X Receptor Alpha and Pregnane X Receptor to Attenuate Ligand-Induced Lipogenesis

Liver X receptor α (LXRα) controls important biological and pathophysiological processes such as lipid homeostasis. Inhibiting LXRα transactivation may beneficial in the treatment of nonalcoholic fatty liver disease (NAFLD), which is one of the main causes of liver diseases and hyperlipidemia. Oleanolic acid (OA) is a naturally occurring triterpenoid found in many plants. It has several beneficial effects on biological pathways; however, the mechanisms underlying its effects on LXRα are unclear. Therefore, we evaluated the effects of OA on T0901317-induced LXRα activation and explored whether OA can attenuate hepatic lipogenesis. The results showed that OA significantly decreased the promoter activities of LXR response element and sterol regulatory element binding protein-1c (SREBP-1c). It also decreased the mRNA and protein expression of LXRα target genes. These resulted in reduced hepatocellular lipid content. Our results also revealed that the overall binding pose of OA is similar to the X-ray pose of T0901317. Furthermore, OA stimulated AMP-activated protein kinase phosphorylation in hepatic cells. Additionally, it increased small heterodimer partner-interacting leucine zipper protein (SMILE) but decreased steroid receptor coactivator-1 (SRC-1) recruitment to the SREBP-1c promoter region. OA also enhanced LXRα-mediated induction of reverse cholesterol transport (RCT)-related gene, ATP-binding cassette transporter (ABC) A1, and ABCG1 expression in intestinal cells. It was found that OA increased the binding of SRC-1 but decreased SMILE recruitment to the ABCG1 gene promoter region. Furthermore, it reduced valproate- and rifampin-induced LXRα- and pregnane X receptor-mediated lipogenesis, respectively, which indicates its potential benefit in treating drug-induced hepatic steatosis. The results also show that OA is liver-specific and can be selectively repressed of lipogenesis. Moreover, it preserves and enhances LXRα-induced RCT stimulation. The results show that OA may be a promising treatment for NAFLD. Additionally, it can be used in the development of LXRα agonists to prevent atherosclerosis.

Hepatic CREBZF couples insulin to lipogenesis by inhibiting insig activity and contributes to hepatic steatosis in diet-induced insulin-resistant mice

Insulin is critical for the regulation of de novo fatty acid synthesis, which converts glucose to lipid in the liver. However, how insulin signals are transduced into the cell and then regulate lipogenesis remains to be fully understood. Here, we identified CREB/ATF bZIP transcription factor (CREBZF) of the activating transcription factor/cAMP response element-binding protein (ATF/CREB) gene family as a key regulator for lipogenesis through insulin-Akt signaling. Insulin-induced gene 2a (Insig-2a) decreases during refeeding, allowing sterol regulatory element binding protein 1c to be processed to promote lipogenesis; but the mechanism of reduction is unknown. We show that Insig-2a inhibition is mediated by insulin-induced CREBZF. CREBZF directly inhibits transcription of Insig-2a through association with activating transcription factor 4. Liver-specific knockout of CREBZF causes an induction of Insig-2a and Insig-1 and resulted in repressed lipogenic program in the liver of mice during refeeding or upon treatment with streptozotocin and insulin. Moreover, hepatic CREBZF deficiency attenuates hepatic steatosis in high-fat, high-sucrose diet-fed mice. Importantly, expression levels of CREBZF are increased in livers of diet-induced insulin resistance or genetically obese ob/ob mice and humans with hepatic steatosis, which may underscore the potential role of CREBZF in the development of sustained lipogenesis in the liver under selective insulin resistance conditions.

CONCLUSION

These findings uncover an unexpected mechanism that couples changes in extracellular hormonal signals to hepatic lipid homeostasis; disrupting CREBZF function may have the therapeutic potential for treating fatty liver disease and insulin resistance. (Hepatology 2018).

Therapeutic pro-fibrogenic signaling pathways in fibroblasts

Myofibroblasts (MFs) play a critical role in the progression of chronic inflammatory and fibroproliferative diseases in different tissues/organs, whatever the etiology. Fibrosis is preceded and sustained by persistent injury and inflammatory response in a profibrogenic scenario involving mutual interactions, operated by several mediators and pathways, of MFs and related precursor cells with innate immunity cells and virtually any cell type in a defined tissue. These interactions, mediators and related signaling pathways are critical in initiating and perpetuating the differentiation of precursor cells into MFs that in different tissues share peculiar traits and phenotypic responses, including the ability to proliferate, produce ECM components, migrate and contribute to the modulation of inflammatory response and tissue angiogenesis. Literature studies related to liver, lung and kidney fibrosis have outlined a number of MF-related core regulatory fibrogenic signaling pathways conserved across these different organs and potentially targetable in order to develop effective antifibrotic therapeutic strategies.

Endocrine-disrupting chemicals and fatty liver disease

A growing epidemic of nonalcoholic fatty liver disease (NAFLD) is paralleling the increase in the incidence of obesity and diabetes mellitus in countries that consume a Western diet. As NAFLD can lead to life-threatening conditions such as cirrhosis and hepatocellular carcinoma, an understanding of the factors that trigger its development and pathological progression is needed. Although by definition this disease is not associated with alcohol consumption, exposure to environmental agents that have been linked to other diseases might have a role in the development of NAFLD. Here, we focus on one class of these agents, endocrine-disrupting chemicals (EDCs), and their potential to influence the initiation and progression of a cascade of pathological conditions associated with hepatic steatosis (fatty liver). Experimental studies have revealed several potential mechanisms by which EDC exposure might contribute to disease pathogenesis, including the modulation of nuclear hormone receptor function and the alteration of the epigenome. However, many questions remain to be addressed about the causal link between acute and chronic EDC exposure and the development of NAFLD in humans. Future studies that address these questions hold promise not only for understanding the linkage between EDC exposure and liver disease but also for elucidating the molecular mechanisms that underpin NAFLD, which in turn could facilitate the development of new prevention and treatment opportunities.

Ursodeoxycholic acid attenuates experimental autoimmune arthritis by targeting Th17 and inducing pAMPK and transcriptional corepressor SMILE

BACKGROUND

Ursodeoxycholic acid (UDCA) has been known that UDCA has prominent effects on liver, however, there is little known about its influence on autoimmune disease. Here, the benefit of UDCA on arthritis rheumatoid (RA) in vivo was tested.

METHODS

RA mouse were induced using collagen II (CIA, collagen induced arthritis) where the disease severity or UDCA-related signaling pathway such as AMP-activated protein kinase (AMPK) or small heterodimer partner interacting leucine zipper protein (SMILE) was evaluated by westerblot and immunohistochemical staining. Gene expression was measured by realtime-polymerase chain reaction (PCR).

RESULTS

The administration of UDCA effectively alleviated the arthritic score and incidence with decreased cartilage damage and lipid metabolic parameters. UDCA also suppressed the secretion of pro-inflammatory cytokines. It was confirmed that UDCA upregulated the expression of SMILE and transcriptional activity of PPARγ via controlling AMPK or p38 activity.

CONCLUSIONS

In the present study, the therapeutic effect of UDCA inducing SMILE through AMPK activation in rheumatoid arthritis mouse as well as other autoimmune disease was proposed.

Ursodeoxycholic Acid Suppresses Lipogenesis in Mouse Liver: Possible Role of the Decrease in β-Muricholic Acid, a Farnesoid X Receptor Antagonist

The farnesoid X receptor (FXR) is a major nuclear receptor of bile acids; its activation suppresses sterol regulatory element-binding protein 1c (SREBP1c)-mediated lipogenesis and decreases the lipid contents in the liver. There are many reports showing that the administration of ursodeoxycholic acid (UDCA) suppresses lipogenesis and reduces the lipid contents in the liver of experimental animals. Since UDCA is not recognized as an FXR agonist, these effects of UDCA cannot be readily explained by its direct activation of FXR. We observed that the dietary administration of UDCA in mice decreased the expression levels of SREBP1c and its target lipogenic genes. Alpha- and β-muricholic acids (MCA) and cholic acid (CA) were the major bile acids in the mouse liver but their contents decreased upon UDCA administration. The hepatic contents of chenodeoxycholic acid and deoxycholic acid (DCA) were relatively low but were not changed by UDCA. UDCA did not show FXR agonistic or antagonistic potency in in vitro FXR transactivation assay. Taking these together, we deduced that the above-mentioned change in hepatic bile acid composition induced upon UDCA administration might cause the relative increase in the FXR activity in the liver, mainly by the reduction in the content of β-MCA, a farnesoid X receptor antagonist, which suggests a mechanism by which UDCA suppresses lipogenesis and decreases the lipid contents in the mouse liver.

Role of the liver X receptors in skin physiology: Putative pharmacological targets in human diseases

Liver X receptors (LXRs) are members of the nuclear receptor superfamily that have been shown to regulate various physiological functions such as lipid metabolism and cholesterol homeostasis. Concordant reports have elicited the possibility to target them to cure many human diseases including arteriosclerosis, cancer, arthritis, and diabetes. The high relevance of modulating LXR activities to treat numerous skin diseases, mainly those with exacerbated inflammation processes, contrasts with the lack of approved therapeutic use. This review makes an assessment to sum up the findings regarding the physiological roles of LXRs in skin and help progress towards the therapeutic and safe management of their activities. It focuses on the possible pharmacological targeting of LXRs to cure or prevent selected skin diseases.

Ligands of Therapeutic Utility for the Liver X Receptors

Liver X receptors (LXRs) have been increasingly recognized as a potential therapeutic target to treat pathological conditions ranging from vascular and metabolic diseases, neurological degeneration, to cancers that are driven by lipid metabolism. Amidst intensifying efforts to discover ligands that act through LXRs to achieve the sought-after pharmacological outcomes, several lead compounds are already being tested in clinical trials for a variety of disease interventions. While more potent and selective LXR ligands continue to emerge from screening of small molecule libraries, rational design, and empirical medicinal chemistry approaches, challenges remain in minimizing undesirable effects of LXR activation on lipid metabolism. This review provides a summary of known endogenous, naturally occurring, and synthetic ligands. The review also offers considerations from a molecular modeling perspective with which to design more specific LXRβ ligands based on the interaction energies of ligands and the important amino acid residues in the LXRβ ligand binding domain.

Ursodeoxycholic acid decreases age-related adiposity and inflammation in mice

Ursodeoxycholic acid (UDCA), a natural, hydrophilic nontoxic bile acid, is clinically effective for treating cholestatic and chronic liver diseases. We investigated the chronic effects of UDCA on age-related lipid homeostasis and underlying molecular mechanisms. Twenty-week-old C57BL/6 male and female mice were fed a diet with or without 0.3% UDCA supplementation for 25 weeks. UDCA significantly reduced weight gain, adiposity, hepatic triglyceride, and hepatic cholesterol without incidental hepatic injury. UDCA-mediated hepatic triglyceride reduction was associated with downregulated hepatic expression of peroxisome proliferator-activated receptor-γ, and of other genes involved in lipogenesis (Chrebp, Acaca, Fasn, Scd1, and Me1) and fatty acid uptake (Ldlr, Cd36). The inflammatory cytokines Tnfa, Ccl2, and Il6 were significantly decreased in liver and/or white adipose tissues of UDCA-fed mice. These data suggest that UDCA exerts beneficial effects on age-related metabolic disorders by lowering the hepatic lipid accumulation, while concurrently reducing hepatocyte and adipocyte susceptibility to inflammatory stimuli. [BMB Reports 2016; 49(2): 105-110]

Miltefosine Suppresses Hepatic Steatosis by Activating AMPK Signal Pathway

BACKGROUND AND PURPOSE

It has been accepted that AMPK (Adenosine monophosphate-activated protein kinase) activation exhibits many beneficial effects on glucolipid metabolism. Lysophosphatidylcholine (LPC) is an important lysophospholipid which can improve blood glucose levels in diabetic mice and attenuate inflammation by activating AMPK signal pathway in macrophages. Synthetic alkylphospholipids (ALPs), such as miltefosine, is used as an alternate of LPC for the clinical application. Here, we investigated whether miltefosine could have an impact on hepatic steatosis and related metabolic disorders.

EXPERIMENTAL APPROACH

Mice were fed with high fat diet (HFD) for 16 weeks to generate an obese model. Next, the obese mice were randomly divided into three groups: saline-treated and miltefosine-treated (2.5 or 5 mg/kg/d) groups. Miltefosine was intraperitoneally administrated into mice for additional 4 weeks plus HFD treatment.

KEY RESULTS

It was shown that miltefosine treatment could substantially improve glucose metabolism, prevented hepatic lipid accumulation, and inhibited liver inflammation in HFD-fed mice by activating AMPK signal pathway. In vitro, miltefosine stimulated AMPKα phosphorylation both in time and dose dependent manner and decreased lipid accumulation in liver cells. When a specific AMPK inhibitor compound C was used to treat mice, the antagonistic effects of miltefosine on HFD-induced mouse hyperlipidaemia and liver steatosis were abolished. Treatment with miltefosine also dramatically inhibited the HFD-induced liver inflammation in mice.

CONCLUSIONS AND IMPLICATIONS

Here we demonstrated that miltefosine might be a new activator of AMPK signal pathway in vivo and in vitro and be useful for treatment of hepatic steatosis and related metabolic disorders.

Activation of liver X receptor/retinoid X receptor pathway ameliorates liver disease in Atp7B(-/-) (Wilson disease) mice

Wilson disease (WD) is a hepatoneurological disorder caused by mutations in the copper-transporter, ATP7B. Copper accumulation in the liver is a hallmark of WD. Current therapy is based on copper chelation, which decreases the manifestations of liver disease, but often worsens neurological symptoms. We demonstrate that in Atp7b(-/-) mice, an animal model of WD, liver function can be significantly improved without copper chelation. Analysis of transcriptional and metabolic changes in samples from WD patients and Atp7b(-/-) mice identified dysregulation of nuclear receptors (NRs), especially the liver X receptor (LXR)/retinoid X receptor heterodimer, as an important event in WD pathogenesis. Treating Atp7b(-/-) mice with the LXR agonist, T0901317, ameliorated disease manifestations despite significant copper overload. Genetic markers of liver fibrosis and inflammatory cytokines were significantly decreased, lipid profiles normalized, and liver function and histology were improved.

CONCLUSIONS

The results demonstrate the major role of an altered NR function in the pathogenesis of WD and suggest that modulation of NR activity should be explored as a supplementary approach to improving liver function in WD. (Hepatology 2016;63:1828-1841).

Ursodeoxycholic Acid Ameliorated Diabetic Nephropathy by Attenuating Hyperglycemia-Mediated Oxidative Stress

Oxidative stress has a great role in diabetes and diabetes induced organ damage. Endoplasmic reticulum (ER) stress is involved in the onset of diabetic nephropathy. We hypothesize that ER stress inhibition could protect against kidney injury through anti-oxidative effects. To test whether block ER stress could attenuate oxidative stress and improve diabetic nephropathy in vivo and in vitro, the effect of ursodeoxycholic acid (UDCA), an ER stress inhibitor, on spontaneous diabetic nephropathy db/db mice, ER stress inducer or high glucose-triggered podocytes were studied. Mice were assigned to 3 groups (n=6 per group): control group (treated with vehicle), db/db group (treated with vehicle), and UDCA group (db/db mice treated with 40 mg/kg/d UDCA). After 8 weeks treatment, mice were sacrificed. Blood and kidneys were collected for the assessment of albumin/creatinine ratio, blood urea nitrogen (BUN), serum creatinine (SCr), insulin, total cholesterol, triglyceride, low density lipoprotein cholesterol (LDL-C), oxidized LDL-C, high density lipoprotein cholesterol (HDL-C), non-esterified fatty acid (NEFA), superoxide dismutase (SOD), catalase (CAT), methane dicarboxylic aldehyde (MDA), the expressions of SOD isoforms and glutathione peroxidase 1, as well as histopathological examination. In addition, generation of reactive oxygen species (ROS) was detected by 2'7'-dichlorodihydrofluorescein diacetate (DCFH-DA) fluorescence. The results showed that UDCA alleviated renal ER stress-evoked cell death, oxidative stress, renal dysfunction, ROS production, upregulated the expression of Bcl-2 and suppressed Bax in vivo and in vitro. Hence, inhibition ER stress diminishes oxidative stress and exerts renoprotective effects.

The Role of Nuclear Receptors in the Pathophysiology, Natural Course, and Drug Treatment of NAFLD in Humans

Nonalcoholic fatty liver disease (NAFLD) describes steatosis, nonalcoholic steatohepatitis with or without fibrosis, and hepatocellular carcinoma, namely the entire alcohol-like spectrum of liver disease though observed in the nonalcoholic, dysmetabolic, individual free of competing causes of liver disease. NAFLD, which is a major public health issue, exhibits intrahepatic triglyceride storage giving rise to lipotoxicity. Nuclear receptors (NRs) are transcriptional factors which, activated by ligands, are master regulators of metabolism and also have intricate connections with circadian control accounting for cyclical patterns in the metabolic fate of nutrients. Several transcription factors, such as peroxisome proliferator-activated receptors, liver X receptors, farnesoid X receptors, and their molecular cascades, finely regulate energetic fluxes and metabolic pathways. Dysregulation of such pathways is heavily implicated in those metabolic derangements characterizing insulin resistance and metabolic syndrome and in the histogenesis of progressive NAFLD forms. We review the role of selected NRs in NAFLD pathogenesis. Secondly, we analyze the role of NRs in the natural history of human NAFLD. Next, we discuss the results observed in humans following administration of drug agonists or antagonists of the NRs pathogenically involved in NAFLD. Finally, general principles of treatment and lines of research in human NAFLD are briefly examined.

Ajuba Preferentially Binds LXRα/RXRγ Heterodimer to Enhance LXR Target Gene Expression in Liver Cells

The liver X receptors (LXRs) are important regulators of lipid, cholesterol, and glucose homeostasis by transcriptional regulation of many key genes in these processes, and the transcriptional activities of LXRs are finely controlled by cooperating with retinoid X receptors and many other coregulators. Here, we report that the LIM protein Ajuba binds to the hinge and the ligand binding domains of LXRα via its C-terminal tandem LIM motifs and enhances LXR target gene expression in liver cells. Depletion of Ajuba in HepG2 cells and in mouse primary hepatocytes decreases LXR target gene expression, whereas stable expression of Ajuba in HepG2 cells results in increased expression of these genes. Mechanistic investigations found that Ajuba selectively interacts with LXRα/retinoid X receptor-γ heterodimer to form a ternary complex, which displays a higher transactivation activity to LXR target genes. Moreover, Ajuba and LXR mutually affect their DNA binding activity at endogenous target chromatins and the cooperation between Ajuba and LXRα is dependent on the functional LXR response elements located in the target promoters. Together, our studies demonstrate that Ajuba is a novel coactivator for LXRs and may play important role in lipid and glucose metabolism.

Orphan nuclear receptor oestrogen-related receptor γ (ERRγ) plays a key role in hepatic cannabinoid receptor type 1-mediated induction of CYP7A1 gene expression

Bile acids are primarily synthesized from cholesterol in the liver and have important roles in dietary lipid absorption and cholesterol homoeostasis. Detailed roles of the orphan nuclear receptors regulating cholesterol 7α-hydroxylase (CYP7A1), the rate-limiting enzyme in bile acid synthesis, have not yet been fully elucidated. In the present study, we report that oestrogen-related receptor γ (ERRγ) is a novel transcriptional regulator of CYP7A1 expression. Activation of cannabinoid receptor type 1 (CB1 receptor) signalling induced ERRγ-mediated transcription of the CYP7A1 gene. Overexpression of ERRγ increased CYP7A1 expression in vitro and in vivo, whereas knockdown of ERRγ attenuated CYP7A1 expression. Deletion analysis of the CYP7A1 gene promoter and a ChIP assay revealed an ERRγ-binding site on the CYP7A1 gene promoter. Small heterodimer partner (SHP) inhibited the transcriptional activity of ERRγ and thus regulated CYP7A1 expression. Overexpression of ERRγ led to increased bile acid levels, whereas an inverse agonist of ERRγ, GSK5182, reduced CYP7A1 expression and bile acid synthesis. Finally, GSK5182 significantly reduced hepatic CB1 receptor-mediated induction of CYP7A1 expression and bile acid synthesis in alcohol-treated mice. These results provide the molecular mechanism linking ERRγ and bile acid metabolism.

Clinically Relevant Mechanisms of Lipid Synthesis, Transport, and Storage

Lipids not only are fundamental nutrients but also serve as basic structural components of cells and as multifunctional signaling molecules. Lipid metabolism pathways underlie basic processes in health and disease and are the targets of novel therapeutics. In this review, we explore the molecular control of lipid synthesis, trafficking, and storage, with a focus on clinically relevant pathways. To illustrate the clinical relevance of molecular lipid regulation, we highlight how these biochemical processes contribute to the pathogenesis of nonalcoholic fatty liver disease, a component of the metabolic syndrome and a paradigmatic example of lipid dysregulation.

Omega-3 polyunsaturated fatty acid and ursodeoxycholic acid have an additive effect in attenuating diet-induced nonalcoholic steatohepatitis in mice

Nonalcoholic steatohepatitis (NASH) can progress into liver cirrhosis; however, no definite treatment is available. Omega-3 polyunsaturated fatty acid (omega-3) has been reported to alleviate experimental NASH, although its beneficial effect was not evident when tested clinically. Thus, this study aimed to investigate the additive effect of omega-3 and ursodeoxycholic acid (UDCA) on diet-induced NASH in mice. C57BL/6 mice were given a high-fat diet (HFD) for 24 weeks, at which point the mice were divided into three groups and fed HFD alone, HFD with omega-3 or HFD with omega-3 in combination with UDCA for another 24 weeks. Feeding mice an HFD and administering omega-3 improved histologically assessed liver fibrosis, and UDCA in combination with omega-3 further attenuated this disease. The assessment of collagen α1(I) expression agreed with the histological evaluation. Omega-3 in combination with UDCA resulted in a significant attenuation of inflammation whereas administering omega-3 alone failed to improve histologically assessed liver inflammation. Quantitative analysis of tumor necrosis factor α showed an additive effect of omega-3 and UDCA on liver inflammation. HFD-induced hepatic triglyceride accumulation was attenuated by omega-3 and adding UDCA accentuated this effect. In accordance with this result, the expression of sterol regulatory binding protein-1c decreased after omega-3 administration and adding UDCA further diminished SREBP-1c expression. The expression of inducible nitric oxide synthase (iNOS), which may reflect oxidative stress-induced tissue damage, was suppressed by omega-3 administration and adding UDCA further attenuated iNOS expression. These results demonstrated an additive effect of omega-3 and UDCA for alleviating fibrosis, inflammation and steatosis in diet-induced NASH.