Repression of the nuclear receptor small heterodimer partner by steatotic drugs and in advanced nonalcoholic fatty liver disease

Drug-Induced Fatty Liver Disease (DIFLD): A Comprehensive Analysis of Clinical, Biochemical, and Histopathological Data for Mechanisms Identification and Consistency with Current Adverse Outcome Pathways

Drug induced fatty liver disease (DIFLD) is a form of drug-induced liver injury (DILI), which can also be included in the more general metabolic dysfunction-associated steatotic liver disease (MASLD), which specifically refers to the accumulation of fat in the liver unrelated to alcohol intake. A bi-directional relationship between DILI and MASLD is likely to exist: while certain drugs can cause MASLD by acting as pro-steatogenic factors, MASLD may make hepatocytes more vulnerable to drugs. Having a pre-existing MASLD significantly heightens the likelihood of experiencing DILI from certain medications. Thus, the prevalence of steatosis within DILI may be biased by pre-existing MASLD, and it can be concluded that the genuine true incidence of DIFLD in the general population remains unknown. In certain individuals, drug-induced steatosis is often accompanied by concomitant injury mechanisms such as oxidative stress, cell death, and inflammation, which leads to the development of drug-induced steatohepatitis (DISH). DISH is much more severe from the clinical point of view, has worse prognosis and outcome, and resembles MASH (metabolic-associated steatohepatitis), as it is associated with inflammation and sometimes with fibrosis. A literature review of clinical case reports allowed us to examine and evaluate the clinical features of DIFLD and their association with specific drugs, enabling us to propose a classification of DIFLD drugs based on clinical outcomes and pathological severity: Group 1, drugs with low intrinsic toxicity (e.g., ibuprofen, naproxen, acetaminophen, irinotecan, methotrexate, and tamoxifen), but expected to promote/aggravate steatosis in patients with pre-existing MASLD; Group 2, drugs associated with steatosis and only occasionally with steatohepatitis (e.g., amiodarone, valproic acid, and tetracycline); and Group 3, drugs with a great tendency to transit to steatohepatitis and further to fibrosis. Different mechanisms may be in play when identifying drug mode of action: (1) inhibition of mitochondrial fatty acid β-oxidation; (2) inhibition of fatty acid transport across mitochondrial membranes; (3) increased de novo lipid synthesis; (4) reduction in lipid export by the inhibition of microsomal triglyceride transfer protein; (5) induction of mitochondrial permeability transition pore opening; (6) dissipation of the mitochondrial transmembrane potential; (7) impairment of the mitochondrial respiratory chain/oxidative phosphorylation; (8) mitochondrial DNA damage, degradation and depletion; and (9) nuclear receptors (NRs)/transcriptomic alterations. Currently, the majority of, if not all, adverse outcome pathways (AOPs) for steatosis in AOP-Wiki highlight the interaction with NRs or transcription factors as the key molecular initiating event (MIE). This perspective suggests that chemical-induced steatosis typically results from the interplay between a chemical and a NR or transcription factors, implying that this interaction represents the primary and pivotal MIE. However, upon conducting this exhaustive literature review, it became evident that the current AOPs tend to overly emphasize this interaction as the sole MIE. Some studies indeed support the involvement of NRs in steatosis, but others demonstrate that such NR interactions alone do not necessarily lead to steatosis. This view, ignoring other mitochondrial-related injury mechanisms, falls short in encapsulating the intricate biological mechanisms involved in chemically induced liver steatosis, necessitating their consideration as part of the AOP's map road as well.

Targeting nuclear receptors for NASH/MASH: From bench to bedside

The onset of metabolic dysfunction-associated steatohepatitis (MASH) or non-alcoholic steatohepatitis (NASH) represents a tipping point leading to liver injury and subsequent hepatic complications in the natural progression of what is now termed metabolic dysfunction-associated steatotic liver diseases (MASLD), formerly known as non-alcoholic fatty liver disease (NAFLD). With no pharmacological treatment currently available for MASH/NASH, the race is on to develop drugs targeting multiple facets of hepatic metabolism, inflammation, and pro-fibrotic events, which are major drivers of MASH. Nuclear receptors (NRs) regulate genomic transcription upon binding to lipophilic ligands and govern multiple aspects of liver metabolism and inflammation. Ligands of NRs may include hormones, lipids, bile acids, and synthetic ligands, which upon binding to NRs regulate the transcriptional activities of target genes. NR ligands are presently the most promising drug candidates expected to receive approval from the United States Food and Drug Administration as a pharmacological treatment for MASH. This review aims to cover the current understanding of NRs, including nuclear hormone receptors, non-steroid hormone receptors, circadian NRs, and orphan NRs, which are currently undergoing clinical trials for MASH treatment, along with NRs that have shown promising results in preclinical studies.

Therapeutic Role of Polyphenol Extract from Prunus cerasifera Ehrhart on Non-Alcoholic Fatty Liver

Prunus cerasifera Ehrhart (P. cerasifera) flourishes uniquely in the arid landscapes of Xinjiang, China. Preliminary studies have revealed the therapeutic potential of its polyphenol extract (PPE) in mitigating liver lipid accumulation in mice fed a high-fat diet. We established a mouse model that was subjected to a continuous high-fat diet for 24 weeks and administered PPE to investigate the effects of PPE on cholesterol and BA metabolism in NAFLD mice. The results showed that PPE administration (200 and 400 mg/kg/day, BW) led to a reduction in liver TC, an increase in liver T-BAs, and normalization of the disrupted fecal BA profile. Concurrently, it decreased levels of lipotoxic BAs and inhibited hepatic cholesterol synthesis (evidenced by reduced HMGCR activity) and intestinal cholesterol absorption (indicated by lower ACAT2 levels) while enhancing intestinal cholesterol efflux (via LXRα, ABCA1, ABCG5, and ABCG8) and stimulating hepatic BA synthesis (CYP7A1, CYP27A1) and secretion (BSEP). PPE thus led to a significant reduction in lipotoxic BAs metabolized by gut microbiota and a downregulation of the BA secretion pathway under its influence. Our findings reveal the therapeutic effect of PPE on NAFLD mice via regulating cholesterol and BA metabolism, providing a theoretical basis for exploring the potential functions of P. cerasifera.

Weight-independent effects of Roux-en-Y gastric bypass surgery on remission of nonalcoholic fatty liver disease in mice

OBJECTIVE

Obesity is a driver of non-alcoholic fatty liver disease (NAFLD), and interventions that decrease body weight, such as bariatric surgery and/or calorie restriction (CR), may serve as effective therapies. This study compared the effects of Roux-en-Y gastric bypass surgery (RYGB) and CR on hepatic function in mice with obesity and NAFLD.

METHODS

C57BL/6J mice were fed a high-fat diet to promote obesity. At 16 weeks of age, mice were randomized to sham surgery (sham), RYGB, or CR weight matched to RYGB (WM). Body weight/composition, food intake, and energy expenditure (EE) were measured throughout treatment. Liver histopathology was evaluated from H&E-stained sections. Hepatic enzymes and glycogen content were determined by ELISA. Transcriptional signatures were revealed via RNA sequencing.

RESULTS

RYGB reduced hepatic lipid content and adiposity while increasing EE and lean body mass relative to WM. Hepatic glycogen and bile acid content were increased after RYGB relative to sham and WM. RYGB activated enterohepatic signaling and genes regulating hepatic lipid homeostasis.

CONCLUSIONS

RYGB improved whole-body composition and hepatic lipid homeostasis to a greater extent than CR in mice. RYGB was associated with discrete remodeling of the hepatic transcriptome, suggesting that surgery may be mechanistically additive to CR.

Targeting super enhancers for liver disease: a review

Background

Super enhancers (SEs) refer to the ultralong regions of a gene accompanied by multiple transcription factors and cofactors and strongly drive the expression of cell-type-related genes. Recent studies have demonstrated that SEs play crucial roles in regulating gene expression related to cell cycle progression and transcription. Aberrant activation of SEs is closely related to the occurrence and development of liver disease. Liver disease, especially liver failure and hepatocellular carcinoma (HCC), constitutes a major class of diseases that seriously endanger human health. Currently, therapeutic strategies targeting SEs can dramatically prevent disease progression and improve the prognosis of animal models. The associated new approaches to the treatment of related liver disease are relatively new and need systematic elaboration.

Objectives

In this review, we elaborate on the features of SEs and discuss their function in liver disease. Additionally, we review their application prospects in clinical practice in the future. The article would be of interest to hepatologists, molecular biologists, clinicians, and all those concerned with targeted therapy and prognosis of liver disease.

Methodology

We searched three bibliographic databases (Web of Science Core Collection, Embase, PubMed) from 01/1981 to 06/2022 for peer-reviewed scientific publications focused on (1) gene treatment of liver disease; (2) current status of SE research; and (3) targeting SEs for liver disease. We included English language original studies only.

Results

The number of published studies considering the role of enhancers in liver disease is considerable. Since SEs were just defined in 2013, the corresponding data on SEs are scarce: approximately 50 papers found in bibliographic databases on the correlation between enhancers (or SEs) and liver disease. Remarkably, half of these papers were published in the past three years, indicating the growing interest of the scientific community in this issue. Studies have shown that treatments targeting components of SEs can improve outcomes in liver disease in animal and clinical trials.

Conclusions

The treatment of liver disease is facing a bottleneck, and new treatments are needed. Therapeutic regimens targeting SEs have an important role in the treatment of liver disease. However, given the off-target effect of gene therapy and the lack of clinical trials, the available experimental data are still fragmented and controversial.

Methionine cycle in nonalcoholic fatty liver disease and its potential applications

As a chronic metabolic disease affecting epidemic proportions worldwide, the pathogenesis of Nonalcoholic Fatty Liver Disease (NAFLD) is not clear yet. There is also a lack of precise biomarkers and specific medicine for the diagnosis and treatment of NAFLD. Methionine metabolic cycle, which is critical for the maintaining of cellular methylation and redox state, is involved in the pathophysiology of NAFLD. However, the molecular basis and mechanism of methionine metabolism in NAFLD are not completely understood. Here, we mainly focus on specific enzymes that participates in methionine cycle, to reveal their interconnections with NAFLD, in order to recognize the pathogenesis of NAFLD from a new angle and at the same time, explore the clinical characteristics and therapeutic strategies.

The Synbiotic Combination of Akkermansia muciniphila and Quercetin Ameliorates Early Obesity and NAFLD through Gut Microbiota Reshaping and Bile Acid Metabolism Modulation

Gut microbiota plays a key role in obesity and non-alcoholic fatty liver disease (NAFLD), so synbiotics could be a therapeutic alternative. We aim to evaluate a nutritional intervention together with the administration of the bacteria Akkermansia muciniphila and the antioxidant quercetin in an in vivo model of early obesity and NAFLD. 21-day-old rats were fed with control or high-fat diet for six weeks. Then, all animals received control diet supplemented with/without quercetin and/or A. muciniphila for three weeks. Gut microbiota, NAFLD-related parameters, circulating bile acids (BAs) and liver gene expression were analyzed. The colonization with A. muciniphila was associated with less body fat, while synbiotic treatment caused a steatosis remission, linked to hepatic lipogenesis modulation. The synbiotic promoted higher abundance of Cyanobacteria and Oscillospira, and lower levels of Actinobacteria, Lactococcus, Lactobacillus and Roseburia. Moreover, it favored elevated unconjugated hydrophilic BAs plasma levels and enhanced hepatic expression of BA synthesis and transport genes. A. muciniphila correlated with circulating BAs and liver lipid and BA metabolism genes, suggesting a role of this bacterium in BA signaling. Beneficial effects of A. muciniphila and quercetin combination are driven by gut microbiota modulation, the shift in BAs and the gut-liver bile flow enhancement.

Polygoni Multiflori Radix Praeparata Ethanol Extract Exerts a Protective Effect Against High-Fat Diet Induced Non-Alcoholic Fatty Liver Disease in Mice by Remodeling Intestinal Microbial Structure and Maintaining Metabolic Homeostasis of Bile Acids

In the prescription of Traditional Chinese Medicine for lipid metabolism, Polygoni Multiflori Radix Preparata (ZhiHeShouWu, RPMP) was widely used. In recent years, RPMP ethanol extract has been reported for the treatment of non-alcoholic fatty liver disease (NAFLD). However, the role of RPMP ethanol extract in the treatment of NAFLD has not been fully elucidated. Therefore, we examined the optimal therapeutic dose of RPMP ethanol extracts. Afterward, a mouse model of non-alcoholic fatty liver induced by a high-fat diet (HFD) was treated with RPMP ethanol extract to further evaluate the mechanism of action of RPMP ethanol extract treatment. And the serum lipid metabolism indexes and liver function indexes showed that the RPMP ethanol extract in the 1.35 g/kg dose group exhibited better therapeutic effects than the 2.70 g/kg dose group. Meanwhile, RPMP ethanol extract can regulate the biochemical indicators of serum and liver to normal levels, and effectively reduce liver steatosis and lipid deposition. RPMP ethanol extract treatment restored HFD-induced disruption of the compositional structure of the intestinal microbial (IM) and bile acids (BAs) pools. And restore the reduced expression of intestinal barrier-related genes caused by HFD administration, which also effectively regulates the expression of genes related to the metabolism of BAs in mice. Thus, RPMP ethanol extract can effectively improve the abnormal lipid metabolism and hepatic lipid accumulation caused by HFD, which may be related to the regulation of IM composition, maintenance of intestinal barrier function, and normal cholesterol metabolism in the body.

Molecular mechanisms of hepatotoxic cholestasis by clavulanic acid: Role of NRF2 and FXR pathways

Treatment of β-lactamase positive bacterial infections with a combination of amoxicillin (AMOX) and clavulanic acid (CLAV) causes idiosyncratic drug-induced liver injury (iDILI) in a relevant number of patients, often with features of intrahepatic cholestasis. This study aims to determine serum bile acid (BA) levels in amoxicillin/clavulanate (A+C)-iDILI patients and to investigate the mechanism of cholestasis by A+C in human in vitro hepatic models. In six A+C-iDILI patients, significant elevations of serum primary conjugated BA definitely demonstrated A+C-induced cholestasis. In cultured human Upcyte hepatocytes and HepG2 cells, CLAV was more cytotoxic than AMOX, and, at subcytotoxic concentrations, it altered the expression of more than 1,300 genes. CLAV, but not AMOX, downregulated the expression of key genes for BA transport (BSEP, NTCP, OSTα and MDR2) and synthesis (CYP7A1 and CYP8B1). CLAV also caused early oxidative stress, with reduced GSH/GSSG ratio, along with induction of antioxidant nuclear factor erythroid 2-related factor 2 (NRF2) target genes. Activation of NRF2 by sulforaphane also resulted in downregulation of NTCP, OSTα, ABCG5, CYP7A1 and CYP8B1. CLAV also inhibited the BA-sensor farnesoid X receptor (FXR), in agreement with the downregulation of FXR targets BSEP, OSTα and ABCG5. We conclude that CLAV, the culprit molecule in A+C, downregulates several key biliary transporters by modulating NRF2 and FXR signaling, thus likely promoting intrahepatic cholestasis. On top of that, increased ROS production and GSH depletion may aggravate the cholestatic injury by A+C.

Small heterodimer partner (SHP) aggravates ER stress in Parkinson's disease-linked LRRK2 mutant astrocyte by regulating XBP1 SUMOylation

Background

Endoplasmic reticulum (ER) stress is a common feature of Parkinson’s disease (PD), and several PD-related genes are responsible for ER dysfunction. Recent studies suggested LRRK2-G2019S, a pathogenic mutation in the PD-associated gene LRRK2, cause ER dysfunction, and could thereby contribute to the development of PD. It remains unclear, however, how mutant LRRK2 influence ER stress to control cellular outcome. In this study, we identified the mechanism by which LRRK2-G2019S accelerates ER stress and cell death in astrocytes.

Methods

To investigate changes in ER stress response genes, we treated LRRK2-wild type and LRRK2-G2019S astrocytes with tunicamycin, an ER stress-inducing agent, and performed gene expression profiling with microarrays. The XBP1 SUMOylation and PIAS1 ubiquitination were performed using immunoprecipitation assay. The effect of astrocyte to neuronal survival were assessed by astrocytes-neuron coculture and slice culture systems. To provide in vivo proof-of-concept of our approach, we measured ER stress response in mouse brain.

Results

Microarray gene expression profiling revealed that LRRK2-G2019S decreased signaling through XBP1, a key transcription factor of the ER stress response, while increasing the apoptotic ER stress response typified by PERK signaling. In LRRK2-G2019S astrocytes, the transcriptional activity of XBP1 was decreased by PIAS1-mediated SUMOylation. Intriguingly, LRRK2-GS stabilized PIAS1 by increasing the level of small heterodimer partner (SHP), a negative regulator of PIAS1 degradation, thereby promoting XBP1 SUMOylation. When SHP was depleted, XBP1 SUMOylation and cell death were reduced. In addition, we identified agents that can disrupt SHP-mediated XBP1 SUMOylation and may therefore have therapeutic activity in PD caused by the LRRK2-G2019S mutation.

Conclusion

Our findings reveal a novel regulatory mechanism involving XBP1 in LRRK2-G2019S mutant astrocytes, and highlight the importance of the SHP/PIAS1/XBP1 axis in PD models. These findings provide important insight into the basis of the correlation between mutant LRRK2 and pathophysiological ER stress in PD, and suggest a plausible model that explains this connection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-021-00747-1.

Typhae pollen polysaccharides protect hypoxia-induced PC12 cell injury via regulation of miR-34a/SIRT1

This current research was performed to investigate the role of typhae pollen polysaccharides (TPP) in hypoxia-treated PC12 cell which was an in vitro cell model of cerebral ischemia. Hypoxia-treated cells were treated with TPP for 12 h. Cell viability and apoptosis were detected by 3-(4,5-dimethylthiazol-2-yl)-2 5-diphenyl-2H-tetrazolium bromide (MTT) assay and flow cytometry, respectively. Cell apoptotic proteins and PI3K/AKT and Ras/Raf/MEK/ERK signal pathway–associated proteins were also examined by western blot. Furthermore, abnormal expression of miR-34a and silent information regulator 1 (SIRT1) was achieved by transfection. Besides, the expression of miR-34a and SIRT1 was examined by quantitative real-time polymerase chain reaction (qRT-PCR). The expression of SIRT1 was detected by qRT-PCR and western blot. The relationship between miR-34a and SIRT1 was verified by luciferase assay. We found that TPP enhanced cell viability and inhibited apoptosis in hypoxia-treated PC12 cells. Moreover, TPP increased the accumulated levels of Bcl-2 while decreased expression of Bax, cleaved Caspase-3, and cleaved PARP. TPP downregulated miR-34a expression while induced by hypoxia. Further results showed that miR-34a overexpression reversed the results led by TPP in cell viability, apoptosis, and its related proteins. In addition, SIRT1 was upregulated by TPP and was verified to be a target of miR-34a. Silence of SIRT1 led to the opposite results led by TPP. In the end, TPP activated PI3K/AKT and Ras/Raf/MEK/ERK signal pathways. In conclusion, TPP plays important roles in regulating cell viability and apoptosis in hypoxia-treated PC12 cells via modulating miR-34a/SIRT1, as well as activating PI3K/AKT and Ras/Raf/MEK/ERK signal pathways.

Interplay of lamin A and lamin B LADs on the radial positioning of chromatin

Immunosuppressive drugs such as cyclosporin A (CsA) can elicit hepatotoxicity by affecting gene expression. Here, we address the link between CsA and large-scale chromatin organization in HepG2 hepatocarcinoma cells. We show the existence of lamina-associated domains (LADs) interacting with lamin A, lamin B, or both. These ‘A-B’, ‘A-only’ and ‘B-only’ LADs display distinct fates after CsA treatment: A-B LADs remain constitutive or lose A, A-only LADs mainly lose A or switch to B, and B-only LADs remain B-only or acquire A. LAD rearrangement is overall uncoupled from changes in gene expression. Three-dimensional (3D) genome modeling predicts changes in radial positioning of LADs as LADs switch identities, which are corroborated by fluorescence in situ hybridization. Our results reveal interplay between A- and B-type lamins on radial locus positioning, suggesting complementary contributions to large-scale genome architecture. The data also unveil a hitherto unsuspected impact of cytotoxic drugs on genome conformation.Abbreviations: ChIP-seq: chromatin immunoprecipitation sequencing; CsA: cyclosporin A; FISH; fluorescence in situ hybridization; ICMT: isoprenylcysteine methyltransferase; LAD: lamina-associated domain; TAD: topologically-associated domain

Disruption of hepatic small heterodimer partner induces dissociation of steatosis and inflammation in experimental nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a leading cause of chronic liver disease worldwide and is characterized by steatosis, inflammation, and fibrosis. The molecular mechanisms underlying NASH development remain obscure. The nuclear receptor small heterodimer partner (Shp) plays a complex role in lipid metabolism and inflammation. Here, we sought to determine SHP's role in regulating steatosis and inflammation in NASH. Shp deletion in murine hepatocytes (Shp ^Hep-/-) resulted in massive infiltration of macrophages and CD4⁺ T cells in the liver. Shp ^Hep-/- mice developed reduced steatosis, but surprisingly increased hepatic inflammation and fibrosis after being fed a high-fat, -cholesterol, and -fructose (HFCF) diet. RNA-Seq analysis revealed that pathways involved in inflammation and fibrosis are significantly activated in the liver of Shp ^Hep-/- mice fed a chow diet. After having been fed the HFCF diet, WT mice displayed up-regulated peroxisome proliferator-activated receptor γ (Pparg) signaling in the liver; however, this response was completely abolished in the Shp ^Hep-/- mice. In contrast, livers of Shp ^Hep-/- mice had consistent NF-κB activation. To further characterize the role of Shp specifically in the transition of steatosis to NASH, mice were fed the HFCF diet for 4 weeks, followed by Shp deletion. Surprisingly, Shp deletion after steatosis development exacerbated hepatic inflammation and fibrosis without affecting liver steatosis. Together, our results indicate that, depending on NASH stage, hepatic Shp plays an opposing role in steatosis and inflammation. Mechanistically, Shp deletion in hepatocytes activated NF-κB and impaired Pparg activation, leading to the dissociation of steatosis, inflammation, and fibrosis in NASH development.

A Network Involving Gut Microbiota, Circulating Bile Acids, and Hepatic Metabolism Genes That Protects Against Non-Alcoholic Fatty Liver Disease

SCOPE

Gut microbiota contributes to non-alcoholic fatty liver disease (NAFLD) pathogenesis by multiple mechanisms not yet completely understood. Novel differential features between germ-free mice (GFm) transplanted with protective or non-protective cecal microbiota against NAFLD are investigated.

METHODS AND RESULTS

Gut microbiota composition, plasma, and fecal bile acids (BAs) and liver mRNAs are quantified in GFm recipients from four donor mice differing in NAFLD severity (control diet, high-fat diet [HFD]-responder, HFD-non-responder, and quercetin-supplemented HFD). Transplanted GFm are on control or HFD for 16-weeks. Multivariate analysis shows that GFm colonized with microbiota from HFD-non-responder and quercetin supplemented-HFD donors (protected against NAFLD) clusters together, whereas GFm colonized with microbiota from control and HFD-responder mice (non-protected against NAFLD) establishes another cluster. Protected phenotype is associated with increased gut Desulfovibrio and Oscillospira, reduced gut Bacteroides and Oribacterium, lower primary and higher secondary BAs in plasma and feces, induction of hepatic BA transporters, and repression of hepatic lipogenic and BA synthesis genes.

CONCLUSION

Protective gut microbiota associates with increased specific secondary BAs, which likely inhibit lipogenic pathways and enhance bile flow in the liver. This novel cross-talk between gut and liver, via plasma BAs, that promotes protection against NAFLD may have clinical and nutritional relevance.

Functional assessment of genetic variants located in the promoter of SHP1 (NR0B2)

Small heterodimer partner 1 (SHP1, NR0B2) is a member of the superfamily of nuclear receptors (NRs). Even if this orphan receptor, unlike other NRs, lacks the DNA-binding domain, it is capable of regulating transcription by repressing the activity of other NRs by direct protein-protein interaction. Accordingly, SHP1 is part of negative feedback loops of the transcriptional regulation of genes involved in drug metabolism and various metabolic pathways including bile acid and glucose homeostasis. Although it is known that several interacting partners of SHP1 also modulate its expression, there is little information about genetic variability of this regulatory mechanism. Our study aimed to identify genetic variants in the NR0B2 promoter region and to determine their impact on NR0B2 transcription. For this, DNA samples originating from 119 participants of the population-based cohort Study of Health in Pomerania were analyzed by Sanger sequencing revealing four genetic variants: NR0B2:c.-594T>C (rs71636795), NR0B2:c.-414G>C (newly identified), NR0B2:c.-423C>T (rs78182695), and NR0B2:c.-224delCTGA (rs145613139) localized in the 5' untranslated region of NR0B2. The impact of these variants on transactivation of the NR0B2 promoter by NRs known to be regulators of SHP1 expression (hepatocyte nuclear factor 4α, liver receptor homolog-1, and farnesoid X receptor) was assessed in a cell-based reporter gene assay, showing that transactivation by hepatocyte nuclear factor 4α and liver receptor homolog-1 was significantly decreased in the presence of the genetic variant NR0B2:c.-594T>C, even though this effect was cell specific. However, SHP1 mRNA expression in a small collection of human kidney samples was not affected by these genetic variants.

Hepatocyte nuclear receptor SHP suppresses inflammation and fibrosis in a mouse model of nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is a burgeoning health problem worldwide, ranging from nonalcoholic fatty liver (NAFL, steatosis without hepatocellular injury) to the more aggressive nonalcoholic steatohepatitis (NASH, steatosis with ballooning, inflammation, or fibrosis). Although many studies have greatly contributed to the elucidation of NAFLD pathogenesis, the disease progression from NAFL to NASH remains incompletely understood. Nuclear receptor small heterodimer partner (Nr0b2, SHP) is a transcriptional regulator critical for the regulation of bile acid, glucose, and lipid metabolism. Here, we show that SHP levels are decreased in the livers of patients with NASH and in diet-induced mouse NASH. Exposing primary mouse hepatocytes to palmitic acid and lipopolysaccharide in vitro, we demonstrated that the suppression of Shp expression in hepatocytes is due to c-Jun N-terminal kinase (JNK) activation, which stimulates c-Jun-mediated transcriptional repression of Shp Interestingly, in vivo induction of hepatocyte-specific SHP in steatotic mouse liver ameliorated NASH progression by attenuating liver inflammation and fibrosis, but not steatosis. Moreover, a key mechanism linking the anti-inflammatory role of hepatocyte-specific SHP expression to inflammation involved SHP-induced suppression of NF-κB p65-mediated induction of chemokine (C-C motif) ligand 2 (CCL2), which activates macrophage proinflammatory polarization and migration. In summary, our results indicate that a JNK/SHP/NF-κB/CCL2 regulatory network controls communications between hepatocytes and macrophages and contributes to the disease progression from NAFL to NASH. Our findings may benefit the development of new management or prevention strategies for NASH.

Identification of an Oleanane-Type Triterpene Hedragonic Acid as a Novel Farnesoid X Receptor Ligand with Liver Protective Effects and Anti-inflammatory Activity

Farnesoid X receptor (FXR) and G-protein-coupled bile acid receptor 1 (GPBAR1) are two important bile acid (BA) receptors. As non-BAs drug template for GPBAR1, none of the natural oleanane-type triterpenes have been reported as FXR ligands, despite FXR and GPBAR1 having similar binding pockets for BAs. Here, we report the natural triterpene hedragonic acid that has been isolated from the stem and root of Celastrus orbiculatus Thunb. (COT) as an effective agonist for FXR. Both biochemical amplified luminescent proximity homogeneous assay and cell-based reporter assays showed that hedragonic acid regulated the transcriptional activity of FXR. Circular dichroism spectroscopy further suggested the conformational changes of FXR upon the binding of hedragonic acid. Interestingly, the crystal structure of hedragonic acid-bound FXR revealed a unique binding mode with hedragonic acid occupying a novel binding pocket different from the classic binding position. The structural comparison between hedragonic acid-bound FXR and oleanolic acid-bound GPBAR1 explained the molecular basis for the selectivity of oleanane-type triterpenes for FXR. Moreover, hedragonic acid treatment protected mice from liver injury induced by acetaminophen overdose and decreased hepatic inflammatory responses in an FXR-dependent manner, suggesting that hedragonic acid might be one of the major components of COT for its multifunctional pharmaceutical uses. In conclusion, our results provide novel structure templates for drug design based on natural triterpenes by targeting FXR and/or GPBAR1 with pharmaceutical values.

Circadian rhythmicity: A functional connection between differentiated embryonic chondrocyte-1 (DEC1) and small heterodimer partner (SHP)

Circadian rhythm misalignment has been increasingly recognized to pose health risk for a wide range of diseases, particularly metabolic disorders. The liver maintains metabolic homeostasis and expresses many circadian genes, such as differentiated embryo chondrocyte-1 (DEC1) and small heterodimer partner (SHP). DEC1 is established to repress transcription through E-box elements, and SHP belongs to the superfamily of nuclear receptors and has multiple E-box elements in its promoter. Importantly, DEC1 and SHP are inversely oscillated. This study was performed to test the hypothesis that the SHP gene is a target gene of DEC1. Cotransfection demonstrated that DEC1 repressed the SHP promoter and attenuated the transactivation of the classic circadian activator complex of Clock/Bmal1. Site-directed mutagenesis, electrophoretic mobility shift assay and chromatin immunoprecipitation established that the repression was achieved through the E-box in the proximal promoter. Transfection of DEC1 suppressed the expression of SHP. In circadian-inducing cells, the epileptic agent valproate inversely altered the expression of DEC1 and SHP. Both DEC1 and SHP are involved in energy balance and valproate is known to induce hepatic steatosis. Our findings collectively establish that DEC1 participates in the negative loop of SHP oscillating expression with potential implications in metabolic homeostasis.

Cholic Acid Feeding Leads to Increased CYP2D6 Expression in CYP2D6-Humanized Mice

Cytochrome P450 2D6 (CYP2D6) is a major drug-metabolizing enzyme, but the factors governing transcriptional regulation of its expression remain poorly understood. Based on previous reports of small heterodimer partner (SHP) playing an important role as a transcriptional repressor of CYP2D6 expression, here we investigated how a known upstream regulator of SHP expression, namely cholestasis triggered by cholic acid (CA) feeding in mice, can lead to altered CYP2D6 expression. To this end, CYP2D6-humanized (Tg-CYP2D6) mice were fed with a CA-supplemented or control diet for 14 days, and hepatic expression of multiple genes was examined. Unexpectedly, CA feeding led to insignificant changes in SHP mRNA but also to significant (2.8-fold) decreases in SHP protein levels. In silico analysis of the SHP gene regulatory region revealed a putative binding site for a microRNA, miR-142-3p. Results from luciferase reporter assays suggest that miR-142-3p targets the SHP gene. Hepatic expression of miR-142-3p was significantly increased in CA-fed mice (∼5-fold), suggesting a potential role of miR-142-3p in the regulation of SHP expression in cholestasis. The decreased SHP protein levels were accompanied by increased expression and activity of CYP2D6 in the liver of CA-fed mice. These results suggest potential roles of differential hepatic levels of bile acids in the transcriptional regulation of CYP2D6 expression.

Nuclear Receptors as Therapeutic Targets in Liver Disease: Are We There Yet?

Nuclear receptors (NR) are ligand-modulated transcription factors that play diverse roles in cell differentiation, development, proliferation, and metabolism and are associated with numerous liver pathologies such as cancer, steatosis, inflammation, fibrosis, cholestasis, and xenobiotic/drug-induced liver injury. The network of target proteins associated with NRs is extremely complex, comprising coregulators, small noncoding microRNAs, and long noncoding RNAs. The importance of NRs as targets of liver disease is exemplified by the number of NR ligands that are currently used in the clinics or in clinical trials with promising results. Understanding the regulation by NR during pathophysiological conditions, and identifying ligands for orphan NR, points to a potential therapeutic approach for patients with liver diseases. An overview of complex NR metabolic networks and their pharmacological implications in liver disease is presented here.

New Insights into Orphan Nuclear Receptor SHP in Liver Cancer

Small heterodimer partner (SHP; NR0B2) is a unique orphan nuclear receptor (NR) that contains a putative ligand-binding domain but lacks a DNA-binding domain. SHP is a transcriptional corepressor affecting diverse metabolic processes including bile acid synthesis, cholesterol and lipid metabolism, glucose and energy homeostasis, and reproductive biology via interaction with multiple NRs and transcriptional factors (TFs). Hepatocellular carcinoma (HCC) is one of the most deadly human cancers worldwide with few therapeutic options and poor prognosis. Recently, it is becoming clear that SHP plays an antitumor role in the development of liver cancer. In this review, we summarize the most recent findings regarding the new SHP interaction partners, new structural insights into SHP’s gene repressing activity, and SHP protein posttranslational modifications by bile acids. We also discuss the pleiotropic role of SHP in regulating cell proliferation, apoptosis, DNA methylation, and inflammation that are related to antitumor role of SHP in HCC. Improving our understanding of SHP’s antitumor role in the development of liver cancer will provide new insights into developing novel treatments or prevention strategies. Future research will focus on developing more efficacious and specific synthetic SHP ligands for pharmaceutical applications in liver cancer and several metabolic diseases such as hypercholesterolemia, obesity, diabetes, and fatty liver disease.