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Peroxisome proliferator-activated receptors (PPARs) activity has significant implications for the development of novel therapeutic modalities against neurodegenerative diseases. Although PPAR-α, PPAR-β/δ, and PPAR-γ nuclear receptor expressions are significantly reported in the brain, their implications in brain physiology and other neurodegenerative diseases still require extensive studies. PPAR signaling can modulate various cell signaling mechanisms involved in the cells contributing to on- and off-target actions selectively to promote therapeutic effects as well as the adverse effects of PPAR ligands. Both natural and synthetic ligands for the PPARα, PPARγ, and PPARβ/δ have been reported. PPARα (WY 14.643) and PPARγ agonists can confer neuroprotection by modulating mitochondrial dynamics through the redox system. The pharmacological effect of these agonists may deliver effective clinical responses by protecting vulnerable neurons from Aβ toxicity in Alzheimer’s disease (AD) patients. Therefore, the current review delineated the ligands’ interaction with 3D-PPARs to modulate neuroprotection, and also deciphered the efficacy of numerous drugs, viz. Aβ aggregation inhibitors, vaccines, and γ -secretase inhibitors against AD; this review elucidated the role of PPAR and their receptor isoforms in neural systems, and neurodegeneration in human beings. Further, we have substantially discussed the efficacy of PPREs as potent transcription factors in the brain, and the role of PPAR agonists in neurotransmission, PPAR gamma coactivator-1α (PGC-1α) and mitochondrial dynamics in neuroprotection during AD conditions. This review concludes with the statement that the development of novel PPARs agonists may benefit patients with neurodegeneration, mainly AD patients, which may help mitigate the pathophysiology of dementia, subsequently improving overall the patient’s quality of life.

Focal cerebral ischemia is a major cardiovascular disease that seriously threatens human health. Its neuromodulator is sodium butyrate, whose underlying mechanisms remain unclear. This study aimed to clarify the neuronal anti-inflammatory mechanisms of sodium butyrate against focal cerebral ischemia. A rat model of focal cerebral ischemia was established by administering sodium butyrate before middle cerebral artery occlusion (MCAO) was conducted. The neuroprotective effects of sodium butyrate were evaluated 24 h after MCAO in terms of neurological score, infarction volume, and inflammatory biomarkers. The expression levels of nuclear receptor subfamily 4 group A1 (Nur77), nod-like receptor protein 3 (NLRP3), caspase-1, and interleukin-1β (IL-1β) in brain tissues were also analyzed. HT22 cells stimulated with oxygen and glucose deprivation (OGD) were treated with sodium butyrate and siNur77 to explore the role of sodium butyrate in the Nur77/NLRP3-mediated inflammatory response. Sodium butyrate treatment significantly attenuated the neurological impairment and neuroinflammation induced by cerebral ischemia. In cerebral ischemia, Nur77 expression was dysregulated as mediated by sodium butyrate, and NLRP3-related inflammatory factors were produced in vivo and in vitro. Nur77 was identified as a negative regulator of NLRP3 in HT22 cells under OGD conditions. The anti-inflammatory effect of sodium butyrate was achieved by upregulating the expression of Nur77, which subsequently suppressed the neuronal NLRP3-mediated inflammatory response. Overall, sodium butyrate elicited a neuroprotective effect against focal cerebral ischemia by modulating Nur77/NLRP3-mediated inflammatory responses.

Peroxisome proliferator activated receptors (PPARs) are a group of nuclear receptors and the ligand-activated intracellular transcription factors that are known to play a key role in physiological processes such as cell metabolism, proliferation, differentiation, tissue remodeling, inflammation, and atherosclerosis. However, in the past two decades, many reports claim that PPARs also play an imperious role as a tumor suppressor. PPAR- gamma (PPARγ), one of the best-known from the family of PPARs, is known to express in colon, breast, bladder, lung, and prostate cancer cells. Its function in tumour cells includes the modulation of several pathways involved in multiplication and apoptosis. The ligands of PPARγ act by PPARγ dependent as well as independent pathways and are also found to regulate different inflammatory mediators and transcription factors in systemic inflammation and in tumor microenvironment. Both synthetic and natural ligands that are known to activate PPARγ, suppress the tumor cell growth and multiplication through the regulation of inflammatory pathways, as found out from different functional assays and animal studies. Cancer and inflammation are interconnected processes that are now being targeted to achieve tumor suppression by decreasing the risks and burden posed by cancer cells. Therefore, PPARγ can serve as a promising target for development of clinical drug molecule attenuating the proliferation of cancer cells. In this perspective, this mini review highlights the PPARγ as a potential target for drug development aiming for anti-inflammatory and thereby suppressing tumors.

Heme is an essential biomolecule and cofactor involved in a myriad of biological processes. In this review, we focus on how heme binding to heme regulatory motifs (HRMs), catalytic sites, and gas signaling molecules as well as how changes in the heme redox state regulate protein structure, function, and degradation. We also relate these heme-dependent changes to the affected metabolic processes. We center our discussion on two HRM-containing proteins: human heme oxygenase-2, a protein that binds and degrades heme (releasing Fe(2+) and CO) in its catalytic core and binds Fe(3+)-heme at HRMs located within an unstructured region of the enzyme, and the transcriptional regulator Rev-erbβ, a protein that binds Fe(3+)-heme at an HRM and is involved in CO sensing. We will discuss these and other proteins as they relate to cellular heme composition, homeostasis, and trafficking. In addition, we will discuss the HRM-containing family of proteins and how the stability and activity of these proteins are regulated in a dependent manner through the HRMs. Then, after reviewing CO-mediated protein regulation of heme proteins, we turn our attention to the involvement of heme, HRMs, and CO in circadian rhythms. In sum, we stress the importance of understanding the various roles of heme and the distribution of the different heme pools as they relate to the heme redox state, CO, and heme binding affinities.

BACKGROUND AND AIMS: Peroxisome proliferator–activated receptor α (PPARα, NR1C1) is a ligand-activated nuclear receptor involved in the regulation of lipid catabolism and energy homeostasis. PPARα activation induces hepatomegaly and plays an important role in liver regeneration, but the underlying mechanisms remain unclear. APPROACH AND RESULTS: In this study, the effect of PPARα activation on liver enlargement and regeneration was investigated in several strains of genetically modified mice. PPARα activation by the specific agonist WY-14643 significantly induced hepatomegaly and accelerated liver regeneration after 70% partial hepatectomy (PHx) in wild-type mice and Ppara(fl/fl) mice, while these effects were abolished in hepatocyte-specific Ppara-deficient (Ppara(ΔHep)) mice. Moreover, PPARα activation promoted hepatocyte hypertrophy around the central vein area and hepatocyte proliferation around the portal vein area. Mechanistically, PPARα activation regulated expression of yes-associated protein (YAP) and its downstream targets (connective tissue growth factor, cysteine-rich angiogenic inducer 61, and ankyrin repeat domain 1) as well as proliferation-related proteins (cyclins A1, D1, and E1). Binding of YAP with the PPARα E domain was critical for the interaction between YAP and PPARα. PPARα activation further induced nuclear translocation of YAP. Disruption of the YAP–transcriptional enhancer factor domain family member (TEAD) association significantly suppressed PPARα-induced hepatomegaly and hepatocyte enlargement and proliferation. In addition, PPARα failed to induce hepatomegaly in adeno-associated virus–Yap short hairpin RNA–treated mice and liver-specific Yap-deficient mice. Blockade of YAP signaling abolished PPARα-induced hepatocyte hypertrophy around the central vein area and hepatocyte proliferation around the portal vein area. CONCLUSIONS: This study revealed a function of PPARα in regulating liver size and liver regeneration through activation of the YAP–TEAD signaling pathway. These findings have implications for understanding the physiological functions of PPARα and suggest its potential for manipulation of liver size and liver regeneration.

It is well-known that the pregnane X receptor (PXR)/Nr1i2 is a critical xenobiotic-sensing nuclear receptor enriched in liver and intestine and is responsible for drug-drug interactions, due to its versatile ligand binding domain (LBD) and target genes involved in xenobiotic biotransformation. PXR can be modulated by various xenobiotics including pharmaceuticals, nutraceuticals, dietary factors, and environmental chemicals. Microbial metabolites such as certain secondary bile acids (BAs) and the tryptophan metabolite indole-3-propionic acid (IPA) are endogenous PXR activators. Gut microbiome is increasingly recognized as an important regulator for host xenobiotic biotransformation and intermediary metabolism. PXR regulates and is regulated by the gut-liver axis. This review summarizes recent research advancements leveraging pharmaco- and toxico-metagenomic approaches that have redefined the previous understanding of PXR. Key topics covered in this review include: (1) genome-wide investigations on novel PXR-target genes, novel PXR-DNA interaction patterns, and novel PXR-targeted intestinal bacteria; (2) key PXR-modulating activators and suppressors of exogenous and endogenous sources; (3) novel bidirectional interactions between PXR and gut microbiome under physiologic, pathophysiological, pharmacological, and toxicological conditions; and (4) modifying factors of PXR-signaling including species and sex differences and time (age, critical windows of exposure, and circadian rhythm). The review also discusses critical knowledge gaps and important future research topics centering around PXR. SIGNIFICANCE STATEMENT: This review summarizes recent research advancements leveraging O'mics approaches that have redefined the previous understanding of the xenobiotic-sensing nuclear receptor pregnane X receptor (PXR). Key topics include: (1) genome-wide investigations on novel PXR-targeted host genes and intestinal bacteria as well as novel PXR-DNA interaction patterns; (2) key PXR modulators including microbial metabolites under physiological, pathophysiological, pharmacological, and toxicological conditions; and (3) modifying factors including species, sex, and time.

Steroids are critical for various physiological processes and used to treat inflammatory conditions. Steroids act by two distinct pathways. The genomic pathway is initiated by the steroid binding to nuclear receptors while the non-genomic pathway involves plasma membrane receptors. It has been proposed that steroids might also act in a more indirect mechanism by altering biophysical properties of membranes. Yet, little is known about the effect of steroids on membranes, and steroid-membrane interactions are complex and challenging to characterise. The focus of this review is to outline what is currently known about the interactions of steroids with phospholipid bilayers and illustrate the complexity of these systems using cortisone and progesterone as the main examples. The combined findings from current work demonstrate that the hydrophobicity and planarity of the steroid core does not provide a consensus for steroid-membrane interactions. Even small differences in the substituents on the steroid core can result in significant changes in steroid-membrane interactions. Furthermore, steroid-induced changes in phospholipid bilayer properties are often dependent on steroid concentration and lipid composition. This complexity means that currently there is insufficient information to establish a reliable structure–activity relationship to describe the effect of steroids on membrane properties. Future work should address the challenge of connecting the findings from studying the effect of steroids on phospholipid bilayers to cell membranes. Insights from steroid-membrane interactions will benefit our understanding of normal physiology and assist drug development.

Perfluorinated carboxylic acids (PFCAs) are environmental pollutants for which human exposure has been documented. PFCAs at high doses were known regulate xenobiotic transporters partly through PPARα and CAR in rodents. Less is known regarding how various PFCAs at a lower concentration modulate transporters for endogenous substrates such as amino acids in human hepatocytes. Such studies are of particular importance because amino acids are involved in chemical detoxification and their transport system may serve as promising therapeutic targets for structurally similar xenobiotics. The focus of this study was to further elucidate how PFCAs modulate transporters involved in intermediary metabolism and xenobiotic biotransformation. We tested the hepatic transcriptomic response of HepaRG cells exposed to 45 mM PFOA, PFNA, or PFDA in triplicates for 24 h (vehicle: 0.1% DMSO), as well as the prototypical ligands for PPARα (WY-14643, 45 µM) and CAR (CITCO, 2 µM). PFCAs with increasing carbon chain lengths (C8-C10) regulated more liver genes, with amino acid metabolism and transport ranked among the top enriched pathways and PFDA ranked as the most potent PFCA tested. Genes encoding amino acid transporters, which are essential for protein synthesis, were novel inducible targets by all 3 PFCAs, suggesting a potentially protective mechanism to reduce further toxic insults. None of the transporter regulations appeared to be through PPARα or CAR but potential involvement of Nrf2 is noted for all 3 PFCAs. In conclusion, PFCAs with increasing carbon chain lengths up-regulate amino acid transporters and modulate xenobiotic transporters to limit further toxic exposures in HepaRG cells. Significance Statement Little is known regarding how various PFCAs modulate the transporters for endogenous substrates in human liver cells. Using HepaRG cells, this study is among the first to show that PFCAs with increasing carbon chain lengths up-regulate amino acid transporters, which are essential for protein synthesis, and modulate xenobiotic transporters to limit further toxic exposures at concentrations lower than what was used in literature.

Like other members of the superfamily of nuclear receptors, the peroxisome proliferator-activated receptor γ (PPARγ), is a ligand-activated transcription factor known for its insulin-sensitizing actions in the periphery. Despite only sparse evidence for PPARγ in the CNS, many reports suggest direct PPARγ-mediated actions in the brain. This study aimed to (i) map PPARγ expression in rodent brain areas, involved in the regulation of cognitive, motivational, and emotional functions, (ii) examine the regulation of central PPARγ by physiological variables (age, sex, obesity); (iii) chemotypically identify PPARγ-expressing cells in the frontal cortex (FC) and hippocampus (HP); (iv) study whether activation of PPARγ by pioglitazone (Pio) in FC and HP cells can induce target gene expression; and (v) demonstrate the impact of activated PPARγ on learning behavior and motivation. Immunoreactive PPARγ was detectable in specific sub-nuclei/subfields of the FC, HP, nucleus accumbens, amygdala, hypothalamus, thalamus, and granular layers of the cerebellum. PPARγ protein levels were upregulated during aging and in high fat diet-induced obesity. PPARγ mRNA expression was upregulated in the amygdala of females (but not males) that were made obese. Neural precursor cells, mature neurons, and astrocytes in primary FC and HP cultures were shown to express PPARγ. Pioglitazone dose-dependently upregulated PPARγ target genes in manner that was specific to the origin (FC or HP) of the cultures. Lastly, administration of Pio impaired motivation and associative learning. Collectively, we provide evidence for the presence of regulatable PPARγ in the brain and demonstrate their participation the regulation of key behaviors.

Bile acids (BAs) are amphipathic molecules important for metabolism of cholesterol, absorption of lipids and lipid soluble vitamins, bile flow, and regulation of gut microbiome. There are over 30 different BA species known to exist in humans and mice, which are endogenous modulators of at least 6 different membrane or nuclear receptors. This diversity of ligands and receptors play important roles in health and disease; however, the full functions of each individual BA in vivo remain unclear. We generated a mouse model lacking the initiating enzymes, CYP7A1 and CYP27A1, in the two main pathways of BA synthesis. Because females are more susceptible to BA related diseases, such as intrahepatic cholestasis of pregnancy, we expanded this model into female mice. The null mice of Cyp7a1 and Cyp27a1 were crossbred to create double knockout (DKO) mice. BA concentrations in female DKO mice had reductions in serum (63%), liver (83%), gallbladder (94%), and small intestine (85%), as compared to WT mice. Despite low BA levels, DKO mice had a similar expression pattern to that of WT mice for genes involved in BA regulation, synthesis, conjugation, and transport. Additionally, through treatment with a synthetic FXR agonist, GW4064, female DKO mice responded to FXR activation similarly to WT mice., Graphical abstract A mouse model lacking the initiating enzymes, CYP7A1 and CYP27A1, in the two main pathways of BA synthesis was generated.Image 1

G protein-coupled estrogen receptor (GPER), which is different from traditional estrogen nuclear receptors (ERs), mediates the rapid transduction of nongenomic signals in cells, and works by regulating transcription and intracellular second messengers. Studies have shown that GPER may regulate oocyte maturation, but the relevant mechanism is not entirely clear. Here, goat cumulus-oocyte complexes (COCs) were used as a model to explore the regulation and mechanism of GPER on oocyte maturation. Our study showed that 17β-estradiol (E2) significantly reduced cyclic guanosine monophosphate (cGMP) synthesis in COCs and accelerated the meiotic resumption of goat oocytes via GPER. Further investigation found that GPER mediated the downregulation of natriuretic peptide receptor 2 (NPR2) protein expression in goat cumulus cells by E2. In addition, we found that E2 significantly upregulated the mRNA levels of epidermal growth (EGF)-like factors in goat cumulus cells through GPER, and activated the downstream EGF receptor (EGFR) and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathways. Both AG1478 (EGFR inhibitor) and U0126 (ERK1/2 inhibitor) abolished the inhibitory effect of E2 on the protein expression of NPR2. These results indicate that, through GPER, E2 upregulates the mRNA levels of EGF-like factors in goat cumulus cells and activates the downstream EGF signaling network to suppress the expression of NPR2 protein, which results in a decrease in cGMP synthesis and acceleration of meiotic resumption in goat oocytes.

Endocrine disruptors are hormone analog compounds responsible for interfering in the normal hypothalamo-hypophyseal-gonadal axis signaling mechanism through the nuclear receptors acting either as steroid agonist or antagonists. A number of endocrine disruptor of plant origin named as phytoestrogens have been reported for their adverse effects on neuroendocrine system. However, several phytoestrogens have been reported to have shown beneficial functions in contrary to other endocrine disrupting agent. The phytoestrogens have the ability to bind the estrogen receptors and progesterone receptors to show the antagonist or agonist function of ovarian steroid. The present literature overview illustrates the beneficial effects of the phytocompounds present in Scoparia dulcis, Cynoglossum zeylanicum, Dysoxylum alliarum that has been used by indigenous communities for various female reproductive diseases treatments. The in vivo studies on animal model system, fractionation of compounds from crude extract and in silico studies of selected compounds of Scoparia dulcis, Cynoglossum zeylanicum has shown the estrogen agonist properties. The effects on female reproductive organ were exerted modulating the endocrine axis showing the proliferation of the luminal and stromal epithelium of the uterus. However, the extract of Dysoxylum alliarum has shown degeneration of the implanted embryo during early gestation in albino rat. All of these plants have reported the presence of phytoestrogens and their mechanism of signaling through the steroid receptors needs to be elucidated. The finding gives a comprehensive report on the beneficial use of these plants acting as functional modulator of ovarian steroid receptors. Further studies on the compounds can project them as alternative to the Estrogens for various hormone replacement therapies.

[Image: see text] The orphan nuclear receptor tailless homologue (TLX) is expressed almost exclusively in neural stem cells acting as an essential factor for their survival and is hence considered as a promising drug target in neurodegeneration. However, few studies have characterized the roles of TLX due to the lack of ligands and limited functional understanding. Here, we identify xanthines including caffeine and istradefylline as TLX modulators that counteract the receptor’s intrinsic repressor activity. Mutagenesis of residues lining a cavity within the TLX ligand binding domain altered the activity of these ligands, suggesting direct interactions with helix 5. Using xanthines as tool compounds, we observed a ligand-sensitive recruitment of the co-repressor silencing mediator for retinoid or thyroid-hormone receptors, TLX homodimerization, and heterodimerization with the retinoid X receptor. These protein–protein interactions evolve as factors that modulate the TLX function and suggest an unprecedented role of TLX in directly repressing other nuclear receptors.

Within the EuroMix project, we have previously developed an adverse outcome pathway (AOP)-based in vitro assay toolbox to investigate the combined effects of liver steatosis-inducing compounds in human HepaRG hepatocarcinoma cells. In this study, we applied the toolbox to further investigate mixture effects of combinations, featuring either similarly acting or dissimilarly acting substances. The valproic acid structural analogs 2-propylheptanoic acid (PHP) and 2-propylhexanoic acid (PHX) were chosen for establishing mixtures of similarly acting substances, while a combination with the pesticidal active substance clothianidin (CTD) was chosen for establishing mixtures of dissimilarly acting compounds. We first determined relative potency factors (RPFs) for each compound based on triglyceride accumulation results. Thereafter, equipotent mixtures were tested for nuclear receptor activation in transfected HepG2 cells, while gene expression and triglyceride accumulation were investigated in HepaRG cells, following the proposed AOP for liver steatosis. Dose addition was observed for all combinations and endpoints tested, indicating the validity of the additivity assumption also in the case of the tested mixtures of dissimilarly acting substances. Gene expression results indicate that the existing steatosis AOP can still be refined with respect to the early key event (KE) of gene expression, in order to reflect the diversity of molecular mechanisms underlying the adverse outcome. Supplementary Information The online version contains supplementary material available at 10.1007/s00204-021-03182-1.

BACKGROUND Berberine (BBR) is always used in combination with florfenicol for treating avian in China. OBJECTIVE This study aims to investigate the effects of BBR on the pharmacokinetics of florfenicol in broilers. METHODS Male broilers were randomly divided into the control group and the BBR group (BG). Note that 50 mg/kg BBR or sterile water was orally administrated to broilers. On the 8th day, florfenicol [30 mg/kg body weight (BW)] was orally administered to broilers in both groups. The plasma concentrations of florfenicol were determined by ultra-high-performance liquid chromatography (UHPLC). The levels of cytochrome P450 (CYP) 3A37, multidrug resistance 1 (MDR1), and chicken xenobiotic-sensing orphan nuclear receptor (CXR) mRNA expression in the liver and jejunum were determined by the real-time PCR. RESULTS The results showed that the Cmax , t1/2z , MRT(0-∞) , and AUC(0-∞) of florfenicol in BG were significantly increased (by 55.71%, 28.32%, 35.19%, and 55.62%, respectively), while the Tmax and CLz/F of florfenicol were significantly decreased (by 52.13% and 35.82%, respectively). In BG, the levels of CYP3A37, MDR1, and CXR mRNA expression in the liver were significantly decreased to 0.72-fold, 0.67-fold, and 0.59-fold, respectively, and the corresponding mRNA expression in the jejunum were significantly decreased to 0.66-fold, 0.55-fold, and 0.64-fold levels, respectively, relative to their levels in the control group. CONCLUSIONS BBR altered the pharmacokinetics of florfenicol, probably related to its inhibition of CYP3A37, MDR1, and CXR mRNA expression in the jejunum and liver.

Background: Berberine (BBR) is an isoquinoline alkaloid extracted from the Chinese medicine, exerting a variety of pharmacological effects. BBR is partially metabolized by cytochrome 3A4 (CYP3A4) in vivo. Some reports indicated that BBR could inhibit the activity of CYP3A4. However, the underlying mechanisms are not completely understood. CYP3A4 is reported to be transcriptionally regulated by two nuclear receptors, nuclear transcription X receptor (PXR) and constitutive androstane receptor (CAR), and degraded via the ubiquitin-proteasome system. Hence, we tried to explore the mechanisms of CYP3A4 inhibition on both transcriptive and protein levels. Methods: Western Blot, RT-PCR and Co-immunoprecipitation were used to perform the experiments. Results: Our results showed that BBR inhibited the transcription of CYP3A4 gene by downregulating PXR. In addition, BBR accelerated the degradation of CYP3A4 protein via polyubiquitination pathway. Conclusion: These findings may lead to the determination of novel drug-drug interactions with BBR, and contribute to future clinical application of BBR.

Steroid receptors activate gene transcription through recruitment of a number of coregulators to facilitate histone modification, chromatin remodeling, and general transcription machinery stabilization. Understanding the structures of full-length steroid receptor and coregulatory complexes has been difficult due to their large molecular sizes and dynamic structural conformations. Recent developments in cryo-electron microscopy (cryoEM) technology and proteomics have advanced the structural studies of steroid receptor complexes. Here, we will review the insights we learned from cryoEM studies of the estrogen and androgen receptor transcriptional complexes. Despite similar domain organizations, the two receptors have different coregulator interaction modes. The cryoEM structures now have revealed the fundamental differences between the two receptors and their functional mechanisms.

Extracellular vesicles (EVs) transfer functional molecules between cells. CD63 is a widely recognized EV marker that contributes to EV secretion from cells. However, the regulation of its expression remains largely unknown. Ferritin is a cellular iron storage protein that can also be secreted by the exosome pathway, and serum ferritin levels classically reflect body iron stores. Iron metabolism–associated proteins such as ferritin are intricately regulated by cellular iron levels via the iron responsive element-iron regulatory protein (IRE-IRP) system. Herein, we present a novel mechanism demonstrating that the expression of the EV-associated protein CD63 is under the regulation of the IRE-IRP system. We discovered a canonical IRE in the 5′ untranslated region of CD63 messenger RNA that is responsible for regulating its expression in response to increased iron. Cellular iron loading caused a marked increase in CD63 expression and the secretion of CD63+ EVs from cells, which were shown to contain ferritin-H and ferritin-L. Our results demonstrate that under iron loading, intracellular ferritin is transferred via nuclear receptor coactivator 4 (NCOA4) to CD63+ EVs that are then secreted. Such iron-regulated secretion of the major iron storage protein ferritin via CD63+ EVs, is significant for understanding the local cell-to-cell exchange of ferritin and iron.

Aryl hydrocarbon receptors (AHRs), a class of ligand-dependent nuclear receptors that regulate cellular responses by inducing the expression of various target genes in response to external signals, are implicated in maintaining retinal tissue homeostasis. Previous studies have shown that the regulation of AHR-induced gene expression requires transcriptional co-regulators. However, it is not yet clear how chromatin remodelers, histone methyltransferases and coactivators interact during AHR-mediated gene expression in human retinal cells. In this study, we reveal that the histone methyltransferase MLL1 and the coactivator FLII are involved in AHR-mediated gene expression in retinal pigment epithelial cells. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) significantly increased the expression of CYP1A1, CYP1B1 and AHRR in ARPE-19 cells, whereas FLII or MLL1 depletion significantly reduced the expression of these genes induced by TCDD. Mechanistically, FLII binds to AHR in a ligand-dependent manner in ARPE-19 cells. In particular, the binding of FLII to MLL1 occurs through the GelB domain of FLII. In addition, MLL1 binds to AHR in a ligand-independent manner. FLII is involved in the recruitment of the BRG1 chromatin remodeler and MLL1 histone methyltransferase to the AHR-regulated CYP1A1 gene region in ARPE-19 cells and consequently, plays an important role in RNA polymerase II binding and transcriptional activity by modulating chromatin accessibility. Our results identify the functions and mechanisms of action of FLII and MLL1 in AHR-induced gene expression in human retinal pigment epithelial cells.

Liver receptor homolog-1 (LRH-1) has emerged as a regulator of hepatic glucose, bile acid, and mitochondrial metabolism. However, the functional mechanism underlying the effect of LRH-1 on lipid mobilization has not been addressed. This study investigated the regulatory function of LRH-1 in lipid metabolism in maintaining a normal liver physiological state during fasting. The Lrh-1f/f and LRH-1 liver-specific knockout (Lrh-1LKO) mice were either fed or fasted for 24 h, and the liver and serum were isolated. The livers were used for qPCR, western blot, and histological analysis. Primary hepatocytes were isolated for immunocytochemistry assessments of lipids. During fasting, the Lrh-1LKO mice showed increased accumulation of triglycerides in the liver compared to that in Lrh-1f/f mice. Interestingly, in the Lrh-1LKO liver, decreases in perilipin 5 (PLIN5) expression and genes involved in β-oxidation were observed. In addition, the LRH-1 agonist dialauroylphosphatidylcholine also enhanced PLIN5 expression in human cultured HepG2 cells. To identify new target genes of LRH-1, these findings directed us to analyze the Plin5 promoter sequence, which revealed -1620/-1614 to be a putative binding site for LRH-1. This was confirmed by promoter activity and chromatin immunoprecipitation assays. Additionally, fasted Lrh-1f/f primary hepatocytes showed increased co-localization of PLIN5 in lipid droplets (LDs) compared to that in fasted Lrh-1LKO primary hepatocytes. Overall, these findings suggest that PLIN5 might be a novel target of LRH-1 to mobilize LDs, protect the liver from lipid overload, and manage the cellular needs during fasting. [BMB Reports 2021; 54(9): 476-481].

Graphical abstract, Highlights • Susceptibility of 12 nuclear receptors to binding by PCDFs was investigated in silico. • Androgen receptor was found to be susceptible to binding by PCDFs. • Male reproductive dysfunctions from PCDF exposure may be due to inappropriate binding of PCDFs to androgen receptor., Polychlorinated dibenzofurans (PCDFs) are known to cause endocrine disruption in humans and wildlife but the mechanisms underlying this disruption have not been adequately investigated. In this paper, the susceptibility of the endocrine system to disruption by PCDF congeners via nuclear receptor binding was studied using molecular docking simulation. Findings revealed that some PCDF congeners exhibit high probabilities of binding to androgen receptor in its agonistic and antagonistic conformations. In depth molecular docking analysis of the receptor-ligand complexes formed by PCDFs with androgen receptor in its agonistic and antagonistic conformations showed that, these complexes were stabilized by electrostatic, van der Waals, pi-effect and hydrophobic interactions. It was also observed that PCDF molecules mimic the modes of interaction observed in androgen-testosterone and androgen-bicalutamide complexes, utilizing between 65 and 83% of the amino acid residues used by the co-crystallized ligands for binding. This computational study suggests that some PCDF congeners may act as agonists and antagonists of androgen receptor in humans and wildlife via inapproprate binding to the receptor.

The farnesoid X receptor (FXR) is a nuclear receptor and transcriptional regulator activated by bile acids or synthetic FXR agonists. FXR is expressed highly in the liver and intestine where modulation of FXR critically regulates the expression of genes involved in cholesterol and bile acid homeostasis, hepatic gluconeogenesis/lipogenesis, and inflammation. We review the roles of FXR and one of its intestinal target genes, fibroblast growth factor (FGF) 15 in mice/FGF19 in humans, play in regulating these important pathways in health and diseases. The main purpose of this review is to review therapeutics that target bile acid signaling to treat non-alcoholic steatohepatitis (NASH), a stage of disease within the spectrum of non-alcoholic fatty liver disease (NAFLD) with a focus on current preclinical studies in mice and clinical research. NASH is a huge medical burden and characterized by hepatic steatosis, inflammation, and progressive development of liver fibrosis. However, there is currently no Food and Drug Administration approved treatment option for NASH. While there are multiple factors contributing to NASH pathophysiology, bile acid regulation is proposed to have a major role in NASH pathogenesis. Synthetic FXR agonists and FGF19 protein may be promising agents to treat NASH, with obeticholic acid (OCA), cilofexor, tropifexor, nidufexor, EDP-305, and NGM282 currently in phase II or III clinical trials of NASH. FXR antagonism has also emerged, and antagonists like ursodeoxycholic acid (UDCA) and glycine-beta-muricholic acid (Gly-MCA) are in pre-clinical stage development for NASH treatment. This mini review seeks to evaluate and organize the literature available on FXR ligands and pathways for the treatment of NASH.

Peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear receptor and the molecular target of thiazolidinedione-class antidiabetic drugs. It has been reported that the loss of function R288H mutation in the human PPARγ ligand-binding domain (LBD) may be associated with the onset of colon cancer. A previous in vitro study showed that this mutation dampens 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2, a natural PPARγ agonist)-dependent transcriptional activation; however, it is poorly understood why the function of the R288H mutant is impaired and what role this arginine (Arg) residue plays. In this study, we found that the apo-form of R288H PPARγ mutant displays several altered conformational arrangements of the amino acid side chains in LBD: 1) the loss of a salt bridge between Arg288 and Glu295 leads to increased helix 3 movement; 2) closer proximity of Gln286 and His449 via a hydrogen bond, and closer proximity of Cys285 and Phe363 via hydrophobic interaction, stabilize the helix 3-helix 11 interaction; and 3) there is steric hindrance between Cys285/Gln286/Ser289/His449 and the flexible ligands 15d-PGJ2, 6-oxotetracosahexaenoic acid (6-oxoTHA), and 17-oxodocosahexaenoic acid (17-oxoDHA). These results suggest why Arg288 plays an important role in ligand binding and why the R288H mutation is disadvantageous for flexible ligand binding.

Background and Aims: Prochloraz (PCZ) is an imidazole fungicide which is used in agriculture and gardening. PCZ, with endo crine disrupting effect, disrupts reproductive and developmental functions. Previously, the effects of PCZ on the estrogen and androgen receptors have been shown in vitro and in vivo. Because of endocrine disrupting effects, PCZ could influence nuclear receptors which acted as ER and AR antagonists. Besides, PCZ has been thought to have no genotoxic effects. Therefore, we aimed to investigate possible effects of PCZ on nuclear receptor genes and epigenetic mechanisms in human prostate carci noma (PC-3) cells. Methods: In the present study, MTT and LDH tests were applied to evaluate the cell viability. Expression levels of nuclear receptor genes such as AhR, PXR, PPARα, PPARγ were studied on real-time quantitative PCR. For global DNA methylation analysis, the levels of 5-methylcytosine (5-mC%) were measured by elisa kit. Results: According to MTT and LDH test results, IC50 value of PCZ has been determined as 144.19 and 116.65 μM, respectively. There were significant changes for the expression levels of AhR, PPARα and PPARγ genes after 5-50 μM of PCZ treat ments. 5 and 50 μM of PCZ decreased the levels of 5-mC% in the rates of 22.6% and 26.9%, respectively. Conclusion: It has been suggested that PCZ may cause alterations on the expressions of nuclear receptor genes which could be related to endocrine disrupting effects and may have implications on global DNA methylation.

BACKGROUND AND AIMS: Chronically administered parenteral nutrition (PN) in patients with intestinal failure carries the risk for developing PN-associated cholestasis (PNAC). We have demonstrated that farnesoid X receptor (FXR) and liver X receptor (LXR), proinflammatory interleukin-1 beta (IL-1β), and infused phytosterols are important in murine PNAC pathogenesis. In this study we examined the role of nuclear receptor liver receptor homolog 1 (LRH-1) and phytosterols in PNAC. APPROACH AND RESULTS: In a C57BL/6 PNAC mouse model (dextran sulfate sodium [DSS] pretreatment followed by 14 days of PN; DSS-PN), hepatic nuclear receptor subfamily 5, group A, member 2/LRH-1 mRNA, LRH-1 protein expression, and binding of LRH-1 at the Abcg5/8 and Cyp7a1 promoter was reduced. Interleukin-1 receptor–deficient mice (Il-1r(−/−)/DSS-PN) were protected from PNAC and had significantly increased hepatic mRNA and protein expression of LRH-1. NF-κB activation and binding to the LRH-1 promoter were increased in DSS-PN PNAC mice and normalized in Il-1r(−/−)/DSS-PN mice. Knockdown of NF-κB in IL-1β–exposed HepG2 cells increased expression of LRH-1 and ABCG5. Treatment of HepG2 cells and primary mouse hepatocytes with an LRH-1 inverse agonist, ML179, significantly reduced mRNA expression of FXR targets ATP binding cassette sub-family C member 2/multidrug resistance associated protein 2 (ABCC2/MRP2), nuclear receptor subfamily 0, groupB, member 2/small heterodimer partner (NR0B2/SHP), and ATP binding cassette subfamily B member 11/bile salt export pump (ABCB11/BSEP). Co-incubation with phytosterols further reduced expression of these genes. Similar results were obtained by suppressing the LRH-1 targets ABCG5/8 by treatment with small interfering RNA, IL-1β, or LXR antagonist GSK2033. Liquid chromatography–mass spectrometry and chromatin immunoprecipitation experiments in HepG2 cells showed that ATP binding cassette subfamily G member 5/8 (ABCG5/8) suppression by GSK2033 increased the accumulation of phytosterols and reduced binding of FXR to the SHP promoter. Finally, treatment with LRH-1 agonist, dilauroyl phosphatidylcholine (DLPC) protected DSS-PN mice from PNAC. CONCLUSIONS: This study suggests that NF-κB regulation of LRH-1 and downstream genes may affect phytosterol-mediated antagonism of FXR signaling in the pathogenesis of PNAC. LRH-1 could be a potential therapeutic target for PNAC. (Hepatology 2021;0:1–17).

Glucocorticoids (GCs) are widely used to treat a variety of autoimmune and inflammatory diseases; however, systemic delivery of GCs is associated with side effects that affect essentially every organ system, reflecting the nearly ubiquitous expression of the glucocorticoid receptor (GR). Targeted delivery of GCs to diseased tissues using antibody-glucocorticoid conjugates (GC-ADCs) offers a therapeutic alternative to overcome these adverse effects. Herein, we describe novel classes of GCs that exhibited greater potency than dexamethasone and budesonide, a 100-fold selectivity toward the GR over other nuclear receptors, and no in vitro safety liability in pharmacology assays (hERG, AMES) and that demonstrated a substantial reduction in tumor necrosis factor-α (TNF-α) release in mice challenged with lipopolysaccharide (LPS). The site-specific conjugated GC-ADCs via cathepsin-cleavable linkers were highly stable in plasma and specifically released GCs in antigen-positive cells, suggesting that these novel GCs can serve as ADC payloads to treat autoimmune and inflammatory diseases.

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