Metformin inhibits nuclear receptor TR4-mediated hepatic stearoyl-CoA desaturase 1 gene expression with altered insulin sensitivity

Comparative Evaluation and Profiling of Chemical Tools for the Nuclear Hormone Receptor Family 2

Nuclear receptors regulate transcription in response to ligand signals and enable the pharmacological control of gene expression. However, many nuclear receptors are still poorly explored and are not accessible to ligand-based target identification studies. In particular, most members of the NR2 family are among the least studied proteins of the class, and apart from the retinoid X receptors (RXR), validated NR2 ligands are very rare. Here, we gathered the NR2 modulators reported in literature for comparative profiling in uniform test systems. Most candidate compounds displayed insufficient on-target activity or selectivity to be used as chemical tools for NR2 receptors underscoring the urgent need for further NR2 ligand development. Nevertheless, a small NR2 modulator set could be assembled for application in a chemogenomic fashion. There are 48 ligand-activated transcription factors in humans forming the superfamily of nuclear receptors (NRs, Figure 1a),1,2 which translate (endogenous) ligand signals into changes in gene expression patterns.3 The multifaceted roles of NRs span pivotal physiological processes, encompassing metabolism, inflammation, and cellular differentiation.4 Over decades, the NR1 and NR3 receptor families, including (steroid) hormone receptors and lipid sensors, have emerged as well-explored therapeutic targets of essential drugs like, for example, glucocorticoids as anti-inflammatory drugs, estrogen receptor modulators as contraceptives and anticancer agents, and PPAR agonists as oral antidiabetics.5-7 Despite this progress, a significant portion of the NR superfamily remains understudied, particularly within the NR2 family which comprises the hepatocyte nuclear factor-4 receptors (HNF4α/γ; NR2A1/2), the retinoid X receptors (RXRα/β/γ; NR2B1-3), the testicular receptors (TR2/4; NR2C1/2), the tailless-like receptors (TLX and PNR; NR2E1/3), and the COUP-TF-like receptors (COUP-TF1/2, V-erBA-related gene; NR2F1/2/6).8,9 Apart from RXR, all NR2 receptors are considered as orphan, and their ligands remain widely elusive. Therefore, chemical tools for most NR2 receptors are rare and poorly annotated posing an obstacle to target identification and validation studies. To enable chemogenomics on NR2 receptors and improve annotation, of the few available ligands, we gathered a scarce collection of NR2 modulators (agonists, antagonists, inverse agonists) for comparative evaluation and profiling. While the NR2B family (RXR) is well covered with high-quality ligands and a few early tools are available for NR2E1, we found the available ligands of the NR2A and NR2C families of insufficient quality to be used as chemical tools.

Roles of Nuclear Orphan Receptors TR2 and TR4 during Hematopoiesis

TR2 and TR4 (NR2C1 and NR2C2, respectively) are evolutionarily conserved nuclear orphan receptors capable of binding direct repeat sequences in a stage-specific manner. Like other nuclear receptors, TR2 and TR4 possess important roles in transcriptional activation or repression with developmental stage and tissue specificity. TR2 and TR4 bind DNA and possess the ability to complex with available cofactors mediating developmental stage-specific actions in primitive and definitive erythrocytes. In erythropoiesis, TR2 and TR4 are required for erythroid development, maturation, and key erythroid transcription factor regulation. TR2 and TR4 recruit and interact with transcriptional corepressors or coactivators to elicit developmental stage-specific gene regulation during hematopoiesis.

Metformin and the Liver: Unlocking the Full Therapeutic Potential

Metformin is a highly effective medication for managing type 2 diabetes mellitus. Recent studies have shown that it has significant therapeutic benefits in various organ systems, particularly the liver. Although the effects of metformin on metabolic dysfunction-associated steatotic liver disease and metabolic dysfunction-associated steatohepatitis are still being debated, it has positive effects on cirrhosis and anti-tumoral properties, which can help prevent the development of hepatocellular carcinoma. Furthermore, it has been proven to improve insulin resistance and dyslipidaemia, commonly associated with liver diseases. While more studies are needed to fully determine the safety and effectiveness of metformin use in liver diseases, the results are highly promising. Indeed, metformin has a terrific potential for extending its full therapeutic properties beyond its traditional use in managing diabetes.

TR4 worsen urosepsis by regulating GSDMD

BACKGROUND

Urosepsis is a life-threatening organ disease in which pathogenic microorganisms in the urine enter the blood through the vessels, causing an imbalance in the immune response to infection. The aim of this study was to elucidate the role of testicular orphan receptor 4 (TR4) in urosepsis.

METHODS

The role of TR4 in the progression and prognosis of urosepsis was confirmed by analyzing data from online databases and clinical human samples. To mimic urosepsis, we injected E. coli bacteria into the renal pelvis of mice to create a urosepsis model. Hematoxylin and eosin staining was used to observe histopathological changes in urosepsis. The effects of the upregulation or downregulation of TR4 on macrophage pyroptosis were verified in vitro. Chromatin immunoprecipitation assay was used to verify the effect of TR4 on Gasdermin D (GSDMD) transcription.

RESULTS

TR4 was more highly expressed in the nonsurviving group than in the surviving group. Furthermore, overexpressing TR4 promoted inflammatory cytokine expression, and knocking down TR4 attenuated inflammatory cytokine expression. Mechanistically, TR4 promoted pyroptosis by regulating the expression of GSDMD in urosepsis. Furthermore, we also found that TR4 knockdown protected mice from urosepsis induced by the E. coli.

CONCLUSIONS

TR4 functions as a key regulator of urosepsis by mediating pyroptosis, which regulates GSDMD expression. Targeting TR4 may be a potential strategy for urosepsis treatment.

Biguanides and glucagon like peptide 1 receptor agonists in the amelioration of post liver transplant weight gain; a scoping review of the mechanism of action, safety and efficacy

Weight gain post-liver transplant can lead to adverse patient outcomes in the post-transplant period. Pharmacotherapy and other measures can be utilised to reduce the burden and occurrence of weight gain in this population. We explored the mechanism of action, safety, and efficacy of these medications, specifically GLP-1 receptor agonists and metformin, focusing on liver transplant patients. This scoping review was conducted in line with the scoping review structure as outlined by the PRISMA guidelines. Metformin and GLP-1 receptor agonists have been observed to be safe and effective in liver transplant patients. Experimental models have found liver-centric weight loss mechanisms in this drug cohort. There is a paucity of evidence about the use of antihyperglycemics in a post-transplant population for weight loss purposes. However, some small studies have shown strong safety and efficacy data. The evidence in relation to using these medications in patients with metabolic syndrome for weight loss warrants further study in a transplant population.

Metformin: update on mechanisms of action on liver diseases

Substantial attention has been paid to the various effects of metformin on liver diseases; the liver is the targeted organ where metformin exerts its antihyperglycemic properties. In non-alcoholic fatty liver disease (NAFLD), studies have shown that metformin affects the ATP/AMP ratio to activate AMPK, subsequently governing lipid metabolism. The latest research showed that low-dose metformin targets the lysosomal AMPK pathway to decrease hepatic triglyceride levels through the PEN2-ATP6AP1 axis in an AMP-independent manner. Metformin regulates caspase-3, eukaryotic initiation factor-2a (eIF2a), and insulin receptor substrate-1 (IRS-1) in palmitate-exposed HepG2 cells, alleviating endoplasmic reticulum (ER) stress. Recent observations highlighted the critical association with intestinal flora, as confirmed by the finding that metformin decreased the relative abundance of Bacteroides fragilis while increasing Akkermansia muciniphila and Bifidobacterium bifidum. The suppression of intestinal farnesoid X receptor (FXR) and the elevation of short-chain fatty acids resulted in the upregulation of tight junction protein and the alleviation of hepatic inflammation induced by lipopolysaccharide (LPS). Additionally, metformin delayed the progression of cirrhosis by regulating the activation and proliferation of hepatic stellate cells (HSCs) via the TGF-β1/Smad3 and succinate-GPR91 pathways. In hepatocellular carcinoma (HCC), metformin impeded the cell cycle and enhanced the curative effect of antitumor medications. Moreover, metformin protects against chemical-induced and drug-induced liver injury (DILI) against hepatotoxic drugs. These findings suggest that metformin may have pharmacological efficacy against liver diseases.

Stearoyl coenzyme A desaturase-1: multitasker in cancer, metabolism, and ferroptosis

Cancer progression is a highly balanced process and is maintained by a sequence of finely tuned metabolic pathways. Stearoyl coenzyme A desaturase-1 (SCD1), the fatty enzyme that converts saturated fatty acids into monounsaturated fatty acids, is a critical modulator of the fatty acid metabolic pathway. SCD1 expression is associated with poor prognosis in several cancer types. SCD1 triggers an iron-dependent cell death called ferroptosis and elevated levels of SCD1 protect cancer cells against ferroptosis. Pharmacological inhibition of SCD1 as monotherapy and in combination with chemotherapeutic agents shows promising antitumor potential in preclinical models. In this review, we summarize the role of SCD in cancer cell progression, survival, and ferroptosis and discuss potential strategies to exploit SCD1 inhibition in future clinical trials.

Efficacy Confirmation Test of Black Cumin (Nigella sativa L.) Seeds Extract Using a High-Fat Diet Mouse Model

To deal with the adverse effects associated with the use of currently available treatments for metabolic disorders, such as type 2 diabetes, there is a need to find an alternative drug compound. In the present study, we investigated the therapeutic potential of black cumin (Nigella sativa L.) seeds extract (BCS extract) for type 2 diabetes using a 45% Kcal-fed obese mouse model. The BCS extract at different doses (400–100 mg/kg) showed a dose-dependent improvement tendency in high-fat diet (HFD)-induced obesity, non-alcoholic fatty liver disease (NAFLD), hyperlipidemia, and diabetic nephropathy compared to the metformin (250 mg/kg). In particular, BCS extract at a dose of 200 mg/kg significantly inhibited the HFD-induced metabolic conditions. The oral administration of BCS extract (200 mg/kg) significantly inhibited the oxidative stress through lipid peroxidation, normalized the activity of sugar metabolism-related enzymes and the expression of genes involved in fat metabolism, and inhibited insulin resistance through glucose and fat metabolism by regulating the 5’-AMP-activated protein kinase (AMPK) expression. Furthermore, BCS extract (200 mg/kg) showed renal damage improvement effects compared to the metformin (250 mg/kg). The results clearly show that BCS aqueous extract at an appropriate concentration could help in the treatment of metabolic disorders, and BCS aqueous extract can be used as a functional food for various diabetic complications, such as obesity, diabetes, and NAFLD.

Structures of human TR4LBD-JAZF1 and TR4DBD-DNA complexes reveal the molecular basis of transcriptional regulation

Testicular nuclear receptor 4 (TR4) modulates the transcriptional activation of genes and plays important roles in many diseases. The regulation of TR4 on target genes involves direct interactions with DNA molecules via the DNA-binding domain (DBD) and recruitment of coregulators by the ligand-binding domain (LBD). However, their regulatory mechanisms are unclear. Here, we report high-resolution crystal structures of TR4DBD, TR4DBD-DNA complexes and the TR4LBD-JAZF1 complex. For DNA recognition, multiple factors come into play, and a specific mutual selectivity between TR4 and target genes is found. The coactivators SRC-1 and CREBBP can bind at the interface of TR4 originally occupied by the TR4 activation function region 2 (AF-2); however, JAZF1 suppresses the binding through a novel mechanism. JAZF1 binds to an unidentified surface of TR4 and stabilizes an α13 helix never reported in the nuclear receptor family. Moreover, the cancer-associated mutations affect the interactions and the transcriptional activation of TR4 in vitro and in vivo, respectively. Overall, our results highlight the crucial role of DNA recognition and a novel mechanism of how JAZF1 reinforces the autorepressed conformation and influences the transcriptional activation of TR4, laying out important structural bases for drug design for a variety of diseases, including diabetes and cancers.

Metabolomic profiles of metformin in breast cancer survivors: a pooled analysis of plasmas from two randomized placebo-controlled trials

BACKGROUND

Obesity is a major health concern for breast cancer survivors, being associated with high recurrence and reduced efficacy during cancer treatment. Metformin treatment is associated with reduced breast cancer incidence, recurrence and mortality. To better understand the underlying mechanisms through which metformin may reduce recurrence, we aimed to conduct metabolic profiling of overweight/obese breast cancer survivors before and after metformin treatment.

METHODS

Fasting plasma samples from 373 overweight or obese breast cancer survivors randomly assigned to metformin (n = 194) or placebo (n = 179) administration were collected at baseline, after 6 months (Reach For Health trial), and after 12 months (MetBreCS trial). Archival samples were concurrently analyzed using three complementary methods: untargeted LC-QTOF-MS metabolomics, targeted LC-MS metabolomics (AbsoluteIDQ p180, Biocrates), and gas chromatography phospholipid fatty acid assay. Multivariable linear regression models and family-wise error correction were used to identify metabolites that significantly changed after metformin treatment.

RESULTS

Participants (n = 352) with both baseline and study end point samples available were included in the analysis. After adjusting for confounders such as study center, age, body mass index and false discovery rate, we found that metformin treatment was significantly associated with decreased levels of citrulline, arginine, tyrosine, caffeine, paraxanthine, and theophylline, and increased levels of leucine, isoleucine, proline, 3-methyl-2-oxovalerate, 4-methyl-2-oxovalerate, alanine and indoxyl-sulphate. Long-chain unsaturated phosphatidylcholines (PC ae C36:4, PC ae C38:5, PC ae C36:5 and PC ae C38:6) were significantly decreased with the metformin treatment, as were phospholipid-derived long-chain n-6 fatty acids. The metabolomic profiles of metformin treatment suggest change in specific biochemical pathways known to impair cancer cell growth including activation of CYP1A2, alterations in fatty acid desaturase activity, and altered metabolism of specific amino acids, including impaired branched chain amino acid catabolism.

CONCLUSIONS

Our results in overweight breast cancer survivors identify new metabolic effects of metformin treatment that may mechanistically contribute to reduced risk of recurrence in this population and reduced obesity-related cancer risk reported in observational studies.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT01302379 and EudraCT Protocol #: 2015-001001-14.

Targeting Energy Expenditure-Drugs for Obesity Treatment

Obesity and overweight are associated with lethal diseases. In this context, obese and overweight individuals infected by COVID-19 are at greater risk of dying. Obesity is treated by three main pharmaceutical approaches, namely suppressing appetite, reducing energy intake by impairing absorption, and increasing energy expenditure. Most compounds used for the latter were first envisaged for other medical uses. However, several candidates are now being developed explicitly for targeting obesity by increasing energy expenditure. This review analyzes the compounds that show anti-obesity activity exerted through the energy expenditure pathway. They are classified on the basis of their development status: FDA-approved, Withdrawn, Clinical Trials, and Under Development. The chemical nature, target, mechanisms of action, and description of the current stage of development are described for each one.

Testicular orphan receptor 4 (TR4) promotes papillary thyroid cancer invasion via activating circ-FNLA/miR-149-5p/MMP9 signaling

The incidence and mortality of papillary thyroid cancer (PTC) have steadily increased. Although conventional therapies are very effective toward differentiated PTC patients, very limited therapeutic options are applicable to those patients with distant metastases. Therefore, better understanding of the molecular biology of metastatic PTC helps identify novel targets and facilitates the development of new therapies. In this study, we first found that testicular orphan receptor 4 (TR4) was significantly increased in PTC tumors spreading to lymph nodes compared to the paired primary tumors. Experimental evidence suggested that TR4 drove PTC progression via promoting its cell invasion and cell migration. Mechanistically, TR4 transcriptionally regulated the expression level of circ-filamin A (FLNA), which competed with matrix metalloproteinase 9 (MMP9) for microRNA (miR)-149-5p binding and led to an increased protein level of MMP9. Interruption assays with various gene manipulations verified that the TR4/circ-FLNA/miR-149-5p/MMP9 signaling axis played a central role in cell invasion and cell migration of PTC cells. Moreover, a xenografted mouse model also confirmed that the TR4/circ-FLNA signal promoted PTC tumor growth. Overall, our study pinpoints the oncogenic role of TR4 in PTC development, and the targeting of TR4/circ-FLNA/miR-149-5p/MMP9 signaling may be an alternative option for metastatic PTC patients.

An 'omics approach to investigate the growth effects of environmentally relevant concentrations of guanylurea exposure on Japanese medaka (Oryzias latipes)

Metformin is a widely prescribed pharmaceutical used in the treatment of numerous human health disorders, including Type 2 Diabetes, and as a results of its widespread use, metformin is thought to be the most prevalent pharmaceutical in the aquatic environment by weight. The removal of metformin during the water treatment process is directly related to the formation of its primary degradation product, guanylurea, generally present at higher concentrations in surface waters relative to metformin. Growth effects observed in 28-day early life stage (ELS) Japanese medaka exposed to guanylurea were found to be similar to growth effects in 28-day ELS medaka exposed to metformin; however, effect concentrations were orders of magnitude below those of metformin. The present study uses a multi-omics approach to investigate potential mechanisms by which low-level, 1 ng · L-1 nominal, guanylurea exposure may lead to altered growth in 28-day post hatch medaka via shotgun metabolomics and proteomics and qPCR. Specifically, analyses show 6 altered metabolites, 66 altered proteins and 2 altered genes. Collectively, metabolomics, proteomics, and gene expression data (using qPCR) indicate that developmental exposure to guanylurea exposure alters a number of important pathways related to the overall health of ELS fish, including biomolecule metabolism, cellular energetics, nervous system function/development, cellular communication and structure, and detoxification of reactive oxygen species, among others. To our knowledge, this is the first study to both report the molecular level effects of guanylurea on non-target aquatic organisms, and to relate molecular-level changes to whole organism effects.

The role of FATP1 in lipid accumulation: a review

Lipid accumulation in mammals has been widely studied for decades due to its significant association with obesity in humans and meat quality in livestock animals. Fatty acid transport 1 (FATP1) is an evolutionarily conserved protein that localizes to the plasma membrane to enhance the transportation of fatty acids (FAs). In line with this function, FATP1 is involved in the metabolism of FAs, including their esterification and oxidation. In addition, the expression of FATP1 can be regulated by several energy-related factors, such as insulin and PPAR activators and transcription factors. These events connect FATP1 with cellular lipid accumulation. Recently, several studies have suggested that FATP1 acts as a facilitator in cellular lipid accumulation, whereas others hold a contrary view. Here, we will review these data and probe the possibility that FATP1 acts as a regulator in lipid accumulation, which will provide effective information for studies on the relationship between FATP1 and obesity in humans and meat quality in livestock animals.

Targeting the TR4 nuclear receptor with antagonist bexarotene can suppress the proopiomelanocortin signalling in AtT-20 cells

Drug options for the life‐threatening Cushing's disease are limited, and surgical resection or radiation therapy is not invariably effective. Testicular receptor 4 (TR4) has been identified as a novel drug target to treat Cushing's disease. We built the structure model of TR4 and searched the TR4 antagonist candidate via in silico virtual screening. Bexarotene was identified as an antagonist of TR4 that can directly interact with TR4 ligand binding domain (TR4‐LBD) and induces a conformational change in the secondary structure of TR4‐LBD. Bexarotene suppressed AtT‐20 cell growth, proopiomelanocortin (POMC) expression and adrenocorticotropin (ACTH) secretion. Mechanism dissection revealed that bexarotene could suppress TR4‐increased POMC expression via promoting the TR4 translocation from the nucleus to the cytoplasm. This TR4 translocation might then result in reducing the TR4 binding to the TR4 response element (TR4RE) on the 5’ promoter region of POMC. Results from in vivo mouse model also revealed that oral bexarotene administration markedly suppressed ACTH‐secreting tumour growth, adrenal enlargement and the secretion of ACTH and corticosterone in mice with already established tumours. Together, these results suggest that bexarotene may be developed as a potential novel therapeutic drug to better suppress Cushing's disease.

Identification of Small-Molecule Regulators of Testicular Receptor 4 via a Drug Repurposing Screening

The testicular receptor 4 (TR4) is a nuclear receptor implicated in multiple pathological processes, including cancer development, chemotherapy, and radiotherapy resistance. However, no effective TR4 small-molecule regulator is available to date. Here, we assessed a physical-interaction-based surface plasmon resonance imaging assay for discovery of TR4 regulators. We screened 1018 FDA-approved drugs and obtained 126 drugs with K _D values below 10^-6 M. The dual-luciferase-based biological assay verified four activatory compounds and two inhibitory compounds against TR4. Among them, nilotinib exhibited the most potent inhibitor, with an EC₅₀ of 1.05 μM, while genistein represented the most potent activator, with an EC₅₀ of 2.42 μM. Both drugs were predicted to bind in the ligand binding pocket of TR4. The circular dichroism spectroscopic assay revealed differed conformation changes upon nilotinib or genistein binding. These results established our combined physical and biological approaches as a highly effective way to identify and develop new TR4 regulators.

Metformin: Metabolic Rewiring Faces Tumor Heterogeneity

Tumor heterogeneity impinges on all the aspects of tumor history, from onset to metastasis and relapse. It is growingly recognized as a propelling force for tumor adaptation to environmental and micro-environmental cues. Metabolic heterogeneity perfectly falls into this process. It strongly contributes to the metabolic plasticity which characterizes cancer cell subpopulations-capable of adaptive switching under stress conditions, between aerobic glycolysis and oxidative phosphorylation-in both a convergent and divergent modality. The mitochondria appear at center-stage in this adaptive process and thus, targeting mitochondria in cancer may prove of therapeutic value. Metformin is the oldest and most used anti-diabetic medication and its relationship with cancer has witnessed rises and falls in the last 30 years. We believe it is useful to revisit the main mechanisms of action of metformin in light of the emerging views on tumor heterogeneity. We first analyze the most consolidated view of its mitochondrial mechanism of action and then we frame the latter in the context of tumor adaptive strategies, cancer stem cell selection, metabolic zonation of tumors and the tumor microenvironment. This may provide a more critical point of view and, to some extent, may help to shed light on some of the controversial evidence for metformin's anticancer action.

Beta-catenin inhibits TR4-mediated lipid accumulation in 3T3-L1 adipocytes via induction of Slug

Background

TR4, an orphan nuclear receptor plays a key role in glucose and lipid metabolism by regulating the expression of genes involved in energy metabolism. We previously reported that overexpression of TR4 in 3T3-L1 adipocytes promotes lipid accumulation in part by facilitating fatty acid uptake and synthesis, indicating that TR4 tightly regulates lipid homeostasis during adipogenesis. Here, we report that β-catenin suppresses TR4 transcriptional activity and that this inhibition is achieved through induction of Slug gene, a well-known transcription repressor in a variety of cells

Methods

To generate the stable cell line, 3T3-L1 cells were transfected with plasmids then cultured in presence of geneticin and/or blasticidin for 2 weeks. The lipid accumulation was measured by Oil Red O. The TR4-Slug and TR4-β-catenin interactions were checked by GST pull-down and mammalian two-hybrid assay. The TR4 transcriptional activities on various promoters were measured by luciferase activity. To check the binding affinity of TR4, we performed the gel shift and chromatin immunoprecipitation (ChIP) assay. Gene expression was detected by RT-qPCR at the mRNA level and western blotting at the protein level.

Results

Stable overexpression of Slug gene in 3T3-L1 preadipocytes strongly inhibited differentiation of 3T3-L1 preadipocytes. Using GST pull-down, gel shift and ChIP assays, we found that Slug abolished the formation of TR4 homodimers through direct interaction with TR4 and reduced the binding affinity of TR4 for its response elements located in TR4 target gene promoters such as fatty acid transport protein 1 and pyruvate carboxylase. Consistently, Slug inhibited TR4 target gene expression and was accompanied by repression of TR4-induced lipid accumulation in 3T3-L1 adipocytes.

Conclusions

Our results demonstrated that Slug inhibits 3T3-L1 adipogenesis through suppression of TR4 transcriptional activity.

Targeting the radiation-induced TR4 nuclear receptor-mediated QKI/circZEB1/miR-141-3p/ZEB1 signaling increases prostate cancer radiosensitivity

Early studies indicated that the testicular nuclear receptor 4 (TR4) might play key roles in altering prostate cancer (PCa) progression; however, its ability to alter PCa radiosensitivity remains unclear. Here, we found that suppressing TR4 expression promoted radiosensitivity and better suppressed PCa by modulating the protein quaking (QKI)/circZEB1/miR-141-3p/ZEB1 signaling pathway. Mechanism dissection studies revealed that TR4 could transcriptionally increase the RNA-binding protein QKI to increase circZEB1 levels, which then sponges the miR-141-3p to increase the expression of its host gene ZEB1. Preclinical studies with an in vivo mouse model further proved that combining radiation therapy (RT) with metformin promoted radiosensitivity to suppress PCa progression. Together, these results suggest that TR4 may play key roles in altering PCa radiosensitivity and show that targeting this newly identified TR4-mediated QKI/circZEB1/miR-141-3p/ZEB1 signaling pathway may help in the development of a novel RT to better suppress the progression of PCa.

Fortifying diet with rapeseed oil instead of butterfat attenuates the progression of diet-induced non-alcoholic fatty liver disease (NAFLD) and impairment of glucose tolerance

BACKGROUND

Absolute dietary fat intake but even more so fatty acid pattern is discussed to be critical in the development of non-alcoholic fatty liver disease (NAFLD). Here, we determined if switching a butterfat enriched diet to a rapeseed oil (RO) enriched diet affects progression of an existing NAFLD and glucose intolerance in mice.

METHODS

For eight weeks, female C57Bl/6J mice were either fed a liquid control (C) or a butterfat-, fructose- and cholesterol-rich diet (BFC, 25E% butterfat) to induce early signs of steatohepatitis and glucose intolerance in mice. For additional five weeks mice received either BFC or C or a fat-, fructose- and cholesterol-rich and control diet, in which butterfat was replaced with RO (ROFC and CRO). Markers of glucose metabolism, liver damage and intestinal barrier were assessed.

RESULTS

Exchanging butterfat with RO attenuated the progression of BFC diet-induced NAFLD and glucose intolerance. Beneficial effects of RO were associated with lower portal endotoxin levels and an attenuation of the induction of the toll-like receptor-4-dependent signaling cascades in liver. Peroxisome proliferator-activated receptor γ activity was induced in small intestine of ROFC-fed mice.

CONCLUSION

Taken together, exchanging butterfat with RO attenuated the progression of diet-induced steatohepatitis and glucose intolerance in mice.

Identification of MicroRNA-Target Gene-Transcription Factor Regulatory Networks in Colorectal Adenoma Using Microarray Expression Data

Objective

The aim of the study was to find the key genes, microRNAs (miRNAs) and transcription factors (TFs) and construct miRNA-target gene-TF regulatory networks to investigate the underlying molecular mechanism in colorectal adenoma (CRA).

Methods

Four mRNA expression datasets and one miRNA expression dataset were downloaded from Gene Expression Omnibus (GEO) database. Differentially expressed miRNAs (DEMs) and differentially expressed genes (DEGs) were identified between CRA and normal samples. Moreover, functional enrichment analysis for DEGs was carried out utilizing the Cytoscape-plugin, known as ClueGO. These DEGs were mapped to STRING database to construct a protein-protein interaction (PPI) network. Then, a miRNA-target gene regulatory network was established to screen key DEMs. In addition, similar workflow of the analyses were also performed comparing the CRC samples with CRA ones to screen key DEMs. Finally, miRNA-target gene-TF regulatory networks were constructed for these key DEMs using iRegulon plug-in in Cytoscape.

Results

We identified 514 DEGs and 167 DEMs in CRA samples compared to healthy samples. Functional enrichment analysis revealed that these DEGs were significantly enriched in several terms and pathways, such as regulation of cell migration and bile secretion pathway. A PPI network was constructed including 325 nodes as well as 890 edges. A total of 59 DEGs and 65 DEMs were identified in CRC samples compared to CRA ones. In addition, Two key DEMs in CRA samples compared to healthy samples were identified, such as hsa-miR-34a and hsa-miR-96. One key DEM, hsa-miR-29c, which was identified when we compared the differentially expressed molecules found in the comparison CRA versus normal samples to the ones obtained in the comparison CRC versus CRA, was also identified in CRC samples compared to CRA ones. The miRNA-target gene-TF regulatory networks for these key miRNAs included two TFs, one TF and five TFs, respectively.

Conclusion

These identified key genes, miRNA, TFs and miRNA-target gene-TF regulatory networks associated with CRA, to a certain degree, may provide some hints to enable us to better understand the underlying pathogenesis of CRA.

Targeting the TR4 nuclear receptor-mediated lncTASR/AXL signaling with tretinoin increases the sunitinib sensitivity to better suppress the RCC progression

Renal cell carcinoma (RCC) is one of the most lethal urological tumors. Using sunitinib to improve the survival has become the first-line therapy for metastatic RCC patients. However, the occurrence of sunitinib resistance in the clinical application has curtailed its efficacy. Here we found TR4 nuclear receptor might alter the sunitinib resistance to RCC via altering the TR4/lncTASR/AXL signaling. Mechanism dissection revealed that TR4 could modulate lncTASR (ENST00000600671.1) expression via transcriptional regulation, which might then increase AXL protein expression via enhancing the stability of AXL mRNA to increase the sunitinib resistance in RCC. Human clinical surveys also linked the expression of TR4, lncTASR, and AXL to the RCC survival, and results from multiple RCC cell lines revealed that targeting this newly identified TR4-mediated signaling with small molecules, including tretinoin, metformin, or TR4-shRNAs, all led to increase the sunitinib sensitivity to better suppress the RCC progression, and our preclinical study using the in vivo mouse model further proved tretinoin had a better synergistic effect to increase sunitinib sensitivity to suppress RCC progression. Future successful clinical trials may help in the development of a novel therapy to better suppress the RCC progression.

SCD1 regulates the AMPK/SIRT1 pathway and histone acetylation through changes in adenine nucleotide metabolism in skeletal muscle

Stearoyl-CoA desaturase (SCD) is a rate-limiting enzyme that catalyzes the synthesis of monounsaturated fatty acids. It plays an important role in regulating skeletal muscle metabolism. Lack of the SCD1 gene increases the rate of fatty acid β-oxidation through activation of the AMP-activated protein kinase (AMPK) pathway and the upregulation of genes that are related to fatty acid oxidation. The mechanism of AMPK activation under conditions of SCD1 deficiency has been unclear. In the present study, we found that the ablation/inhibition of SCD1 led to AMPK activation in skeletal muscle through an increase in AMP levels whereas muscle-specific SCD1 overexpression decreased both AMPK phosphorylation and the adenosine monophosphate/adenosine triphosphate (AMP/ATP) ratio. Changes in AMPK phosphorylation that were caused by SCD1 down- and upregulation affected NAD⁺ levels following changes in NAD⁺ -dependent deacetylase sirtuin-1 (SIRT1) activity and histone 3 (H3K9) acetylation and methylation status. Moreover, mice with muscle-targeted overexpression of SCD1 were more susceptible to high-fat diet-induced lipid accumulation and the development of insulin resistance compared with wild-type mice. These data show that SCD1 is involved in nucleotide (ATP and NAD⁺ ) metabolism and suggest that the SCD1-dependent regulation of muscle steatosis and insulin sensitivity are mediated by cooperation between AMPK- and SIRT1-regulated pathways. Altogether, the present study reveals a novel mechanism that links SCD1 with the maintenance of metabolic homeostasis and insulin sensitivity in skeletal muscle.

Anti-obesity and fatty liver-preventing activities of Lonicera caerulea in high-fat diet-fed mice

Blue honeysuckle (BH, Lonicera caerulea) is used as a traditional medicine in Russia, Japan and China, but is not commonly considered as an edible berry in Europe, USA or Korea. BH has been revealed to decrease serum cholesterol and triacylglycerol (triglyceride or TG) levels through the activation of AMP-activated protein kinase (AMPK), thus it is expected to be a health functional food and pharmaceutical agent for the prevention of non-alcoholic liver damage, in addition to effects as a suppressor of hyperlipidemia and as an anti-obesity agent. In the present study, the pharmacological activity of BH extract (BHe) was observed in high-fat diet (HFD)-fed mice. Significant increases in fat pad weight, body weight, fat accumulation (body and abdominal fat density, and thickness of the periovarian and abdominal wall) and serum biochemical levels (aspartate transaminase, alanine amino-transferase, alkaline phosphatase, lactate dehydrogenase, γ-glutamyltransferase, total cholesterol, low-density lipoprotein and TG, with the exception of high-density lipoprotein) were observed in HFD-fed mice. In addition, increases in adipocyte hypertrophy, the area of steatohepatitis and hepatocyte hypertrophy were observed, whereas decreased zymogen content was identified upon histopathological observation. Increased deterioration of the endogenous antioxidant defense system (liver catalase, glutathione and superoxide dismutase) and hepatic lipid peroxidation was observed. In addition, there were decreases in hepatic glucokinase activity, AMPKα1 and AMPKα2 mRNA expression, adipose tissue uncoupling protein 2 expression, and adiponectin mRNA expression, increases in phosphoenolpyruvate carboxykinase and glucose-6-phosphatase activity, hepatic acetyl-CoA carboxylase 1 mRNA expression, and the expression of leptin, CCAAT/enhancer-binding protein (C/EBP) α, C/EBPβ and sterol-regulatory-element-binding protein 1c mRNA in the periovarian tissue. Furthermore, non-alcoholic fatty liver disease (NAFLD) and obesity were significantly inhibited by the continuous administration of BHe for 84 days. These results revealed that BHe may be a promising novel drug or functional food candidate for the treatment of obesity and NAFLD.

Metformin attenuates triglyceride accumulation in HepG2 cells through decreasing stearyl-coenzyme A desaturase 1 expression

BACKGROUND

The prevalence of nonalcoholic fatty liver disease (NAFLD) has increased worldwide. Metformin decreases triglyceride (TG) accumulation in hepatocytes in vivo and in vitro. Stearyl-coenzyme A desaturase 1 (SCD1) knockout mice also show decreased liver TG accumulation; however, whether SCD1 plays a role in the effect of metformin on TG accumulation is unknown. Therefore, the aim of this study was to investigate whether SCD1 mediated the effect of metformin on TG accumulation.

METHODS

HepG2 and AML12 cells were exposed to high glucose and high insulin with or without metformin. An adenovirus was used for the SCD1 knockdown and overexpression. The triglyceride level in cells was detected. The expression of related genes was detected by Western blot and quantitative real-time PCR. A dual-luciferase reporter assay was used to determine the effect of metformin on the transcriptional activity of the SCD1 promoter.

RESULTS

Metformin decreased TG accumulation to normal level in HepG2 cells exposed to high glucose and high insulin. The expression of SCD1 and fatty acid synthetase (FAS) was also decreased to normal level by metformin. Knockdown of SCD1 mimicked the effect of metformin on decreasing TG levels in AML12 cells, and the overexpression of SCD1 attenuated the effect of metformin on decreasing TG accumulation in HepG2 cells. The dual-luciferase reporter assay showed that the transcriptional activity of the SCD1 promoter (- 550/+ 199) after metformin treatment was 2-fold lower compared to control group in HepG2 cells. Additionally, the phosphorylation of AMPK after metformin treatment was 2-fold higher, and the expression of sterol regulatory element-binding protein-1c (SREBP-1c) after metformin treatment was about 2-fold lower compared to high glucose and high insulin group in HepG2 cells.

CONCLUSIONS

Together, these results reveal that metformin reduces TG accumulation in HepG2 cells via inhibiting the expression of SCD1.

Preclinical studies using miR-32-5p to suppress clear cell renal cell carcinoma metastasis via altering the miR-32-5p/TR4/HGF/Met signaling

While testicular nuclear receptor 4 (TR4) may promote prostate cancer (PCa) metastasis, its role in the clear cell renal cell carcinoma (ccRCC) remains unclear. Here we found a higher expression of TR4 in ccRCC tumors from patients with distant metastases than those from metastasis-free patients, suggesting TR4 may play positive roles in the ccRCC metastasis. Results from multiple in vitro ccRCC cell lines also confirmed TR4's positive roles in promoting ccRCC cell invasion/migration via altering the microRNA (miR-32-5p)/TR4/HGF/Met/MMP2-MMP9 signaling. Mechanism dissection revealed that miR-32-5p could suppress TR4 protein expression levels via direct binding to the 3'UTR of TR4 mRNA, and TR4 might then alter the HGF/Met signaling at the transcriptional level via direct binding to the TR4-response-elements (TR4RE) on the HGF promoter. Then the in vitro data also demonstrated the efficacy of Sunitinib, a currently used drug to treat ccRCC, could be increased after targeting this newly identified miR-32-5p/TR4/HGF/Met signaling. The preclinical study using the in vivo mouse model with xenografted ccRCC cells confirmed the in vitro cell lines data. Together, these findings suggest that TR4 is a key player to promote ccRCC metastasis and targeting this miR-32-5p/TR4/HGF/Met signaling with small molecules including TR4-shRNA or miR-32-5p may help to develop a new therapy to better suppress the ccRCC metastasis.

TR4 nuclear receptor enhances the cisplatin chemo-sensitivity via altering the ATF3 expression to better suppress HCC cell growth

Early studies indicated that TR4 nuclear receptor (TR4) may play a key role to modulate the prostate cancer progression, its potential linkage to liver cancer progression, however, remains unclear. Here we found that higher TR4 expression in hepatocellular carcinoma (HCC) cells might enhance the efficacy of cisplatin chemotherapy to better suppress the HCC progression. Knocking down TR4 with TR4-siRNA in HCC Huh7 and Hep3B cells increased cisplatin chemotherapy resistance and overexpression of TR4 with TR4-cDNA in HCC LM3 and SNU387 cells increased cisplatin chemotherapy sensitivity. Mechanism dissection found that TR4 might function through altering the ATF3 expression at the transcriptional level to enhance the cisplatin chemotherapy sensitivity, and interrupting ATF3 expression via ATF3-siRNA reversed TR4-enhanced cisplatin chemotherapy sensitivity in HCC cells. The in vivo HCC mouse model using xenografted HCC LM3 cells also confirmed in vitro cell lines data showing TR4 enhanced the cisplatin chemotherapy sensitivity. Together, these results provided a new potential therapeutic approach via altering the TR4-ATF3 signals to increase the efficacy of cisplatin to better suppress the HCC progression.

TR2 and TR4 Orphan Nuclear Receptors: An Overview

Testicular nuclear receptors 2 and 4 (TR2, TR4), also known as NR2C1 and NR2C2, belong to the nuclear receptor superfamily and were first cloned in 1989 and 1994, respectively. Although classified as orphan receptors, several natural molecules, their metabolites, and synthetic compounds including polyunsaturated fatty acids (PUFAs), PUFA metabolites 13-hydroxyoctadecadienoic acid, 15-hydroxyeicosatetraenoic acid, and the antidiabetic drug thiazolidinediones can transactivate TR4. Importantly, many of these ligands/activators can also transactivate peroxisome proliferator-activated receptor gamma (PPARγ), also known as NR1C3 nuclear receptor. Both TR4 and PPARγ can bind to similar hormone response elements (HREs) located in the promoter of their common downstream target genes. However, these two nuclear receptors, even with shared ligands/activators and shared binding ability for similar HREs, have some distinct functions in many diseases they influence. In cancer, PPARγ inhibits thyroid, lung, colon, and prostate cancers but enhances bladder cancer. In contrast, TR4 inhibits liver and prostate cancer initiation but enhances pituitary corticotroph, liver, and prostate cancer progression. In type 2 diabetes, PPARγ increases insulin sensitivity but TR4 decreases insulin sensitivity. In cardiovascular disease, PPARγ inhibits atherosclerosis but TR4 enhances atherosclerosis through increasing foam cell formation. In bone physiology, PPARγ inhibits bone formation but TR4 increases bone formation. Together, the contrasting impact of TR4 and PPARγ on different diseases may raise a critical issue about drug used to target any one of these nuclear receptors.

17β-Estradiol suppresses visceral adipogenesis and activates brown adipose tissue-specific gene expression

Both functional ovaries and estrogen replacement therapy (ERT) reduce the risk of type 2 diabetes (T2D). Understanding the mechanisms underlying the antidiabetic effects of 17β-estradiol (E2) may permit the development of a molecular targeting strategy for the treatment of metabolic disease. This study examines how the promotion of insulin sensitivity and weight loss by E2 treatment in high-fat-diet (HFD)-fed mice involve several anti-adipogenic processes in the visceral adipose tissue. Magnetic resonance imaging (MRI) revealed specific reductions in visceral adipose tissue volume in HFD+E2 mice, compared with HFD mice. This loss of adiposity was associated with diminished visceral adipocyte size and reductions in expression of lipogenic genes, adipokines and of the nuclear receptor nr2c2/tr4. Meanwhile, expression levels of adipose triglyceride lipase/pnpla2 and leptin receptor were increased. As mRNA levels of stat3, a transcription factor involved in brown adipose tissue differentiation, were also increased in visceral adipose, the expression of other brown adipose-specific markers was assessed. Both expression and immunohistochemical staining of ucp-1 were increased, and mRNA levels of dio-2, and of adrβ3, a regulator of ucp-1 expression during the thermogenic response, were increased. Furthermore, expression of cpt-1b, a brown adipose-specific gene involved in fatty acid utilization, was also increased. Methylation studies demonstrated that the methylation status of both dio-2 and adrβ3 was significantly reduced. These results show that improved glycemic control and weight loss due to E2 involve anti-adipogenic mechanisms which include suppressed lipogenesis and augmented fatty acid utilization, and in addition, the activation of brown adipose tissue-specific gene expression in association with E2-dependent epigenetic modifications in these genes.

Metformin, beyond an insulin sensitizer, targeting heart and pancreatic β cells

Metformin, a biguanide derivate, is known as the first-line antidiabetic agent for type 2 diabetes mellitus (T2DM) treatment. It reduces insulin resistance and decreases blood glucose concentration by inhibiting gluconeogenesis and suppressing hepatic glucose production with improved peripheral tissue insulin sensitivity. As an insulin sensitizer, metformin takes pleiotropic actions and exerts protective effects on multiple organs mainly in insulin-targeted tissues such as liver, muscle, and adipose tissues. Recent studies discover that metformin also plays essential roles in heart and pancreatic β cells - two important organs in metabolic regulation. Metformin not only protects T2DM patients from cardiovascular diseases and heart failure, but also restores insulin secretion activities and protects pancreatic β cells from lipotoxicity or glucotoxicity. Although accumulated evidence shed light on the metformin action, the precise mechanism of metformin is still under investigation. Further laboratory investigations and clinical trials are needed to pinpoint a map of metformin action. Based on recent findings, this review characterizes the beneficial role of metformin in cardiovascular diseases and pancreatic β cells.

CREB/GSK-3β signaling pathway regulates the expression of TR4 orphan nuclear receptor gene

In this study, we show that reduction of glucose concentration increases TR4 expression in 3T3-L1 cells via stimulation of the GSK-3β-CREB pathway. While GSK-3β and CREB increased TR4 expression in 3T3-L1 cells, inhibition of CREB expression or activity resulted in loss of GSK-3β-mediated enhancement of TR4 expression. In addition, CREB enhanced murine TR4 promoter activity via direct binding to a cAMP response element located in the promoter, and this CREB effect was further strengthened by GSK-3β. Moreover, silencing of TR4 expression by a gene-specific microRNA inhibited CREB-induced lipid accumulation in 3T3-L1 adipocytes, suggesting that TR4 could be a key mediator of CREB-induced lipogenesis.

Fermentation of Green Tea with 2% Aquilariae lignum Increases the Anti-Diabetic Activity of Green Tea Aqueous Extracts in the High Fat-Fed Mouse

Anti-diabetic effects on the metabolomic differences between green tea (GT) and Aquilariae lignum-fermented green tea (fGT) were investigated in the high fat-fed mouse. To prove the differences, hypoglycemic (blood glucose, insulin and glycated hemoglobin levels, pancreas weights and histopathological-immunohistochemistrical analysis of pancreas–insulin/glucagon cells), hepato- and nephron-protective (the changes in liver and kidney weight, histopathology of liver and kidney, serum aminotransferases (AST and ALT) levels, blood urea nitrogen, and serum creatinine levels), and hypolipidemic (the changes of serum total cholesterol, triglyceride, low- and high-density lipoprotein levels with fecal TC and TG contents) effects were evaluated. In addition, liver lipid peroxidation, the glutathione contents, and catalase and superoxide dismutase activities were measured according to the hepatic glucose-regulating enzyme activities of glucokinase (GK), glucose-6-phosphatase (G6pase) and phosphoenolpyruvate carboxykinase (PEPCK) for action mechanisms. As a result, fGT showed a stronger hypoglycemic, hepato- and nephron-protective, hypolipidemic, and anti-oxidant effect than GT in high fat-fed mice. In addition, fGT-treated mice exerted more favorable inhibitory activities against GK, G6pase, PERCK activities as compared to GT-treated mice. Taken together, fGT fermented with Aquilariae lignum, 1:49 (2%; g/g) has a stronger effect compared with GT. Therefore, fGT has the potential to increase bioactivity against type 2 diabetics.

RGC-32 Deficiency Protects against Hepatic Steatosis by Reducing Lipogenesis

Hepatic steatosis is associated with insulin resistance and metabolic syndrome because of increased hepatic triglyceride content. We have reported previously that deficiency of response gene to complement 32 (RGC-32) prevents high-fat diet (HFD)-induced obesity and insulin resistance in mice. This study was conducted to determine the role of RGC-32 in the regulation of hepatic steatosis. We observed that hepatic RGC-32 was induced dramatically by both HFD challenge and ethanol administration. RGC-32 knockout (RGC32(-/-)) mice were resistant to HFD- and ethanol-induced hepatic steatosis. The hepatic triglyceride content of RGC32(-/-) mice was decreased significantly compared with WT controls even under normal chow conditions. Moreover, RGC-32 deficiency decreased the expression of lipogenesis-related genes, sterol regulatory element binding protein 1c (SREBP-1c), fatty acid synthase, and stearoyl-CoA desaturase 1 (SCD1). RGC-32 deficiency also decreased SCD1 activity, as indicated by decreased desaturase indices of the liver and serum. Mechanistically, insulin and ethanol induced RGC-32 expression through the NF-κB signaling pathway, which, in turn, increased SCD1 expression in a SREBP-1c-dependent manner. RGC-32 also promoted SREBP-1c expression through activating liver X receptor. These results demonstrate that RGC-32 contributes to the development of hepatic steatosis by facilitating de novo lipogenesis through activating liver X receptor, leading to the induction of SREBP-1c and its target genes. Therefore, RGC-32 may be a potential novel drug target for the treatment of hepatic steatosis and its related diseases.

Combining metformin therapy with caloric restriction for the management of type 2 diabetes and nonalcoholic fatty liver disease in obese rats

Weight loss is recommended for patients with nonalcoholic fatty liver disease (NAFLD), while metformin may lower liver enzymes in type 2 diabetics. Yet, the efficacy of the combination of weight loss and metformin in the treatment of NAFLD is unclear. We assessed the effects of metformin, caloric restriction, and their combination on NAFLD in diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. Male OLETF rats (age 20 weeks; n = 6-8 per group) were fed ad libitum (AL), given metformin (300 mg·kg(-1)·day(-1); Met), calorically restricted (70% of AL; CR), or calorically restricted and given metformin (CR+Met) for 12 weeks. Met lowered adiposity compared with AL but not to the same magnitude as CR or CR+Met (p < 0.05). Although only CR improved fasting insulin and glucose, the combination of CR+Met was needed to improve post-challenge glucose tolerance. All treatments lowered hepatic triglycerides, but further improvements were observed in the CR groups (p < 0.05, Met vs. CR or CR+Met) and a further reduction in serum alanine aminotransferases was observed in CR+Met rats. CR lowered markers of hepatic de novo lipogenesis (fatty acid synthase, acetyl-CoA carboxylase (ACC), and stearoyl-CoA desaturase-1 (SCD-1)) and increased hepatic mitochondrial activity (palmitate oxidation and β-hydroxyacyl CoA dehydrogenase (β-HAD) activity). Changes were enhanced in the CR+Met group for ACC, SCD-1, β-HAD, and the mitophagy marker BNIP3. Met decreased total hepatic mTOR content and inhibited mTOR complex 1, which may have contributed to Met-induced reductions in de novo lipogenesis. These findings in the OLETF rat suggest that the combination of caloric restriction and metformin may provide a more optimal approach than either treatment alone in the management of type 2 diabetes and NAFLD.

TR4 Nuclear Receptor Alters the Prostate Cancer CD133+ Stem/Progenitor Cell Invasion via Modulating the EZH2-Related Metastasis Gene Expression

The testicular nuclear receptor 4 (TR4) is a member of the nuclear receptor superfamily that mediates various biologic functions with key impacts on metabolic disorders and tumor progression. Here, we demonstrate that TR4 may play a positive role in prostate cancer CD133(+) stem/progenitor (S/P) cell invasion. Targeting TR4 with lentiviral silencing RNA significantly suppressed prostate cancer CD133(+) S/P cell invasion both in vitro and in vivo. Mechanism dissection found that TR4 transcriptionally regulates the oncogene EZH2 via binding to its 5' promoter region. The consequences of targeting TR4 to suppress EZH2 expression may then suppress the expression of its downstream key metastasis-related genes, including NOTCH1, TGFβ1, SLUG, and MMP9. Rescue approaches via adding the EZH2 reversed the TR4-mediated prostate cancer S/P cell invasion. Together, these results suggest that the TR4→EZH2 signaling may play a critical role in the prostate cancer S/P cell invasion and may allow us to develop a better therapy to battle the prostate cancer metastasis.

AMPK as a potential anticancer target - friend or foe?

Adenosine monophosphate-activated protein kinase (AMPK) is a key player in maintaining energy homeostasis in response to metabolic stress. Beyond diabetes and metabolic syndrome, there is a growing interest in the therapeutic exploitation of the AMPK pathway in cancer treatment in light of its unique ability to regulate cancer cell proliferation through the reprogramming of cell metabolism. Although many studies support the tumor-suppressive role of AMPK, emerging evidence suggests that the metabolic checkpoint function of AMPK might be overridden by stress or oncogenic signals so that tumor cells use AMPK activation as a survival strategy to gain growth advantage. These findings underscore the complexity in the cellular function of AMPK in maintaining energy homeostasis under physiological versus pathological conditions. Thus, this review aims to provide an overview of recent findings on the functional interplay of AMPK with different cell metabolic and signaling effectors, particularly histone deacetylases, in mediating downstream tumor suppressive or promoting mechanisms in different cell systems. Although AMPK activation inhibits tumor growth by targeting multiple signaling pathways relevant to tumorigenesis, under certain cellular contexts or certain stages of tumor development, AMPK might act as a protective response to metabolic stresses, such as nutrient deprivation, low oxygen, and low pH, or as downstream effectors of oncogenic proteins, including androgen receptor, hypoxia-inducible factor-1α, c-Src, and MYC. Thus, investigations to define at which stage(s) of tumorigenesis and cancer progression or for which genetic aberrations AMPK inhibition might represent a more relevant strategy than AMPK activation for cancer treatment are clearly warranted.

TR4 nuclear receptor enhances prostate cancer initiation via altering the stem cell population and EMT signals in the PPARG-deleted prostate cells

A recent report indicated that the TR4 nuclear receptor might suppress the prostate cancer (PCa) initiation via modulating the DNA damage/repair system. Knocking-out peroxisome proliferator-activated receptor gamma (PPARG), a nuclear receptor that shares similar ligands/activators with TR4, promoted PCa initiation. Here we found 9% of PCa patients have one allele of PPARG deletion. Results from in vitro cell lines and in vivo mouse model indicated that during PCa initiation TR4 roles might switch from suppressor to enhancer in prostate cells when PPARG was deleted or suppressed (by antagonist GW9662). Mechanism dissection found targeting TR4 in the absence of PPARG might alter the stem cell population and epithelial-mesenchymal transition (EMT) signals. Together, these results suggest that whether TR4 can enhance or suppress PCa initiation may depend on the availability of PPARG and future potential therapy via targeting PPARG to battle PPARG-related diseases may need to consider the potential side effects of TR4 switched roles during the PCa initiation.

TR4 Nuclear Receptor Different Roles in Prostate Cancer Progression

Nuclear receptors are important to maintain the tissue homeostasis. Each receptor is tightly controlled and under a very complicated balance. In this review, we summarize the current findings regarding the nuclear receptor TR4 and its role in prostate cancer (PCa) progression. In general, TR4 can inhibit the PCa carcinogenesis. However, when PPARγ is knocked out, activation of TR4 can have an opposite effect to promote the PCa carcinogenesis. Clinical data also indicates that higher TR4 expression is found in PCa tissues with high Gleason scores compared to those tissues with low Gleason scores. In vitro and in vivo studies show that TR4 can promote PCa progression. Mechanism dissection indicates that TR4 inhibits PCa carcinogenesis through regulating the tumor suppressor ATM to reduce DNA damages. On the other hand, in the absence of PPARγ, TR4 tends to increase the stem cell population and epithelial-mesenchymal transition (EMT) via regulating CCL2, Oct4, EZH2, and miRNA-373-3p expression that results in increased PCa carcinogenesis. In opposition to PCa initiation, TR4 can increase PCa metastasis via modulating the CCL2 signals. Finally, targeting TR4 enhances the chemotherapy and radiation therapy sensitivity in PCa. Together, these data suggest TR4 is a key player to control PCa progression, and targeting TR4 with small molecules may provide us a new and better therapy to suppress PCa progression.

Effects of metformin on weight loss: potential mechanisms

PURPOSE OF REVIEW

Despite the known glucose-lowering effects of metformin, more recent clinical interest lies in its potential as a weight loss drug. Herein, we discuss the potential mechanisms by which metformin decreases appetite and opposes unfavorable fat storage in peripheral tissues.

RECENT FINDINGS

Many individuals struggle to maintain clinically relevant weight loss from lifestyle and bariatric surgery interventions. Long-term follow-up from the Diabetes Prevention Program demonstrates that metformin produces durable weight loss, and decreased food intake by metformin is the primary weight loss mechanism. Although the effect of metformin on appetite is likely to be multifactorial, changes in hypothalamic physiology, including leptin and insulin sensitivity, have been documented. In addition, novel work in obesity highlights the gastrointestinal physiology and circadian rhythm changes by metformin as not only affecting food intake, but also the regulation of fat oxidation and storage in liver, skeletal muscle, and adipose tissue.

SUMMARY

Metformin induces modest weight loss in overweight and obese individuals at risk for diabetes. A more detailed understanding of how metformin induces weight loss will likely lead to optimal co-prescription of lifestyle modification with pharmacology for the treatment of obesity independent of diabetes.

The role of testicular nuclear receptor 4 in chemo-resistance of docetaxel in castration-resistant prostate cancer

Docetaxel-based therapy is one of the first-line options for castration-resistant prostate cancer (CRPC). However, a large proportion of CRPC patients show different extents of docetaxel resistance. The current study aims to investigate the role of testicular nuclear receptor 4 (TR4) in docetaxel resistance in CRPC. TR4 expression level in prostate biopsy samples from CRPC patients treated with docetaxel was measured by immunohistochemistry (IHC). Alternation of TR4 expression in prostate cancer (PCa) cell line PC3 was applied to find out the influence of TR4 on half-maximal inhibitory concentration (IC50), cell viability and cell apoptosis. Patients who failed to achieve prostate-specific antigen (PSA) response (<50% PSA reduction from baseline) after docetaxel-based chemotherapy had a comparatively higher TR4 expression than those who achieved PSA response (⩾50% PSA reduction from baseline). Knocking down TR4 in PC3 cells led to a lower IC50 dose, poorer cell viability and more cell apoptosis when treated with docetaxel, whereas overexpression of TR4 in PC3 led to a higher IC50 dose, better cell viability and less cell apoptosis. TR4 enhances the chemo-resistance of docetaxel in CRPC. It may serve as a biomarker to determine the prognosis of docetaxel-based therapy and as a potential therapy target to combine with docetaxel to better suppress CRPC.

TR4 nuclear receptor promotes prostate cancer metastasis via upregulation of CCL2/CCR2 signaling

Testicular nuclear receptor 4 (TR4) plays protective roles against oxidative stress and DNA damage and might contribute to aging. Our recent clinical tumor tissue staining results showed higher expression of TR4 in prostate cancer (PCa) patients with high Gleason scores compared to the tissues with the low Gleason scores. In vitro migration/invasion assays after manipulation of the TR4 expression in PCa cells showed that TR4 promoted PCa cells migration/invasion. Mechanism dissection found that the CCL2/CCR2 signal plays the key role in the mediation of TR4-promoted PCa cells migration/invasion. Chromatin immunoprecipitation and Luciferase assays further confirmed TR4 modulation of CCL2 at the transcriptional level and addition of the CCR2 antagonist led to interruption of the TR4-enhanced PCa cells migration/invasion. Finally, the orthotopic xenografted mice studies using the luciferase expressing CWR22Rv1 cells found that TR4 enhanced PCa metastasis and this increased metastasis was reversed when the CCR2 antagonist was injected into the mice. Together, these in vitro and in vivo results revealed a positive role of TR4 in PCa metastasis and demonstrated CCL2/CCR2 signaling as an important mediator in exerting TR4 action. This finding suggests that TR4 may represent a biomarker related to PCa metastasis and targeting the TR4-CCL2/CCR2 axis may become a new therapeutic approach to battle PCa metastasis.

Overexpression of juxtaposed with another zinc finger gene 1 reduces proinflammatory cytokine release via inhibition of stress-activated protein kinases and nuclear factor-κB

As an inhibitor of the nuclear receptor subfamily 2, group C, member 2 signaling pathway, juxtaposed with another zinc finger gene 1 (JAZF1) has been shown to be involved in gluconeogenesis, lipid metabolism, and insulin sensitivity. However, its role in hepatic lipogenesis and chronic low-grade inflammation leading to nonalcoholic fatty liver disease remains unknown. The aim of this study was to examine whether JAZF1 overexpression in vivo or in vitro can protect against palmitic acid (PA)-induced and high-fat diet (HFD)-induced systemic inflammatory responses, and the potential mechanism of this process. JAZF1 overexpression vector was transfected into PA-treated IAR-20 hepatocytes. The mRNA expression levels of proinflammatory cytokines were measured by real-time quantitative PCR, and stress-activated protein kinase activities were measured by immunoblotting. For in vivo studies, JAZF1 transgenic mice were fed an HFD for 12 weeks. Liver tissue was obtained for histological examination, real-time RT-PCR, and western blot analysis. PA significantly increased the expression levels of tumor necrosis factor-α, monocyte chemotactic protein-1 and interleukin-8 mRNA in IAR-20 hepatocytes in a dose-dependent and time-dependent manner. Treatment with JAZF1 or stress-activated protein kinase inhibitors inhibited PA-induced tumor necrosis factor-α, monocyte chemotactic protein-1 and interleukin-8 expression in these cells. In JAZF1-treated cells, the decreased expression of proinflammatory cytokines was accompanied by decreased p38 mitogen-activated protein kinase and c-Jun N-terminal kinase phosphorylation and increased nuclear factor-κB inhibitor-α protein levels, similarly to the role of signaling inhibitors. In vivo, HFD-induced expression of proinflammatory cytokines was markedly attenuated in JAZF1-Tg mice as compared with controls. This attenuation was accompanied by decreased activation of c-Jun N-terminal kinase, p38 mitogen-activated protein kinase, and nuclear factor-κB. These data provide evidence for the important role of JAZF1 in preventing lipogenesis and systemic inflammation-related disease.

Differential roles of PPARγ vs TR4 in prostate cancer and metabolic diseases

Peroxisome proliferator-activated receptor γ (PPARγ, NR1C3) and testicular receptor 4 nuclear receptor (TR4, NR2C2) are two members of the nuclear receptor (NR) superfamily that can be activated by several similar ligands/activators including polyunsaturated fatty acid metabolites, such as 13-hydroxyoctadecadienoic acid and 15-hydroxyeicosatetraenoic acid, as well as some anti-diabetic drugs such as thiazolidinediones (TZDs). However, the consequences of the transactivation of these ligands/activators via these two NRs are different, with at least three distinct phenotypes. First, activation of PPARγ increases insulin sensitivity yet activation of TR4 decreases insulin sensitivity. Second, PPARγ attenuates atherosclerosis but TR4 might increase the risk of atherosclerosis. Third, PPARγ suppresses prostate cancer (PCa) development and TR4 suppresses prostate carcinogenesis yet promotes PCa metastasis. Importantly, the deregulation of either PPARγ or TR4 in PCa alone might then alter the other receptor's influences on PCa progression. Knocking out PPARγ altered the ability of TR4 to promote prostate carcinogenesis and knocking down TR4 also resulted in TZD treatment promoting PCa development, indicating that both PPARγ and TR4 might coordinate with each other to regulate PCa initiation, and the loss of either one of them might switch the other one from a tumor suppressor to a tumor promoter. These results indicate that further and detailed studies of both receptors at the same time in the same cells/organs may help us to better dissect their distinct physiological roles and develop better drug(s) with fewer side effects to battle PPARγ- and TR4-related diseases including tumor and cardiovascular diseases as well as metabolic disorders.

High oleic/stearic fatty-acid desaturation index in cord plasma from infants of mothers with gestational diabetes

OBJECTIVE

Enhanced fatty-acid desaturation by stearoyl-CoA desaturase enzyme-1 (SCD1) is associated with obesity. This study determined desaturation in the cord plasma of newborns of mothers with and without gestational diabetes (GDM).

STUDY DESIGN

Newborns of mothers with GDM (n=21) and without (control, n=22) were recruited. Cord plasma fatty-acid desaturation indices (palmitoleic/palmitic, oleic/stearic ratios) were compared, and correlated with anthropometrics and biochemical measures. A subset of very low-density lipoprotein (VLDL) desaturation indices were determined to approximate the liver SCD1 activity.

RESULT

The total oleic/stearic index was higher in GDM, despite adjustment for cord glucose concentrations. Among GDM and controls, the oleic/stearic index correlated with cord glucose concentrations (rs=0.36, P=0.02). Both palmitoleic/palmitic and oleic/stearic indices correlated with waist circumference (r=0.47, P=0.001; r=0.37, P=0.01). The VLDL oleic/stearic index was higher in GDM.

CONCLUSION

The elevated total oleic/stearic index suggests increased lipogenesis in GDM newborns. Factors in addition to glucose supply may influence fetal SCD1 activity.

Minireview: Pathophysiological roles of the TR4 nuclear receptor: lessons learned from mice lacking TR4

Testicular nuclear receptor 4 (TR4), also known as NR2C2, belongs to the nuclear receptor superfamily and shares high homology with the testicular nuclear receptor 2. The natural ligands of TR4 remained unclear until the recent discoveries of several energy/lipid sensors including the polyunsaturated fatty acid metabolites, 13-hydroxyoctadecadienoic acid and 15-hydroxyeicosatetraenoic acid, and their synthetic ligands, thiazolidinediones, used for treatment of diabetes. TR4 is widely expressed throughout the body and particularly concentrated in the testis, prostate, cerebellum, and hippocampus. It has been shown to play important roles in cerebellar development, forebrain myelination, folliculogenesis, gluconeogenesis, lipogenesis, muscle development, bone development, and prostate cancer progression. Here we provide a comprehensive summary of TR4 signaling including its upstream ligands/activators/suppressors, transcriptional coactivators/repressors, downstream targets, and their in vivo functions with potential impacts on TR4-related diseases. Importantly, TR4 shares similar ligands/activators with another key nuclear receptor, peroxisome proliferator-activated receptor γ, which raised several interesting questions about how these 2 nuclear receptors may collaborate with or counteract each other's function in their related diseases. Clear dissection of such molecular mechanisms and their differential roles in various diseases may help researchers to design new potential drugs with better efficacy and fewer side effects to battle TR4 and peroxisome proliferator-activated receptor γ involved diseases.

JAZF1 can regulate the expression of lipid metabolic genes and inhibit lipid accumulation in adipocytes

JAZF1 is a newly identified gene with unknown functions. A recent genome-wide association study showed that JAZF1 is associated with type 2 diabetes and is highly expressed in liver and adipose tissue. Studies have demonstrated that JAZF1 is the co-repressor for nuclear orphan receptor TAK1, whereas most nuclear orphan receptor family members are involved in the regulation of lipid metabolism. Therefore, JAZF1 could be closely related to glycolipid metabolism. In this study, JAZF1 was significantly upregulated during the induced differentiation process of 3T3-L1 preadipocytes. The overexpression of JAZF1 inhibited lipid accumulation in differentiated mature 3T3-L1 adipocytes and significantly inhibited the expression of SREBPl, ACC, and FAS, which were important in lipid synthesis, while upregulating the expression of key enzyme hormone-sensitive lipase in lipoclasis. Moreover, SREBPl exhibited an inhibitory function on the expression of JAZF1. SREBP1 reversed the inhibitory action on lipid accumulation of JAZF1. SREBP1 and JAZF1 were observed to regulate each other in adipocytes. Therefore, JAZF1 could regulate the expression of particular genes related to lipid metabolism and inhibit lipid accumulation in adipocytes. This result suggests that JAZF1 may be a potential target for the treatment of diseases, such as obesity and lipid metabolism disorders.

Combining metformin and aerobic exercise training in the treatment of type 2 diabetes and NAFLD in OLETF rats

Here, we sought to compare the efficacy of combining exercise and metformin for the treatment of type 2 diabetes and nonalcoholic fatty liver disease (NAFLD) in hyperphagic, obese, type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. OLETF rats (age: 20 wk, hyperglycemic and hyperinsulinemic; n = 10/group) were randomly assigned to sedentary (O-SED), SED plus metformin (O-SED + M; 300 mg·kg(-1)·day(-1)), moderate-intensity exercise training (O-EndEx; 20 m/min, 60 min/day, 5 days/wk treadmill running), or O-EndEx + M groups for 12 wk. Long-Evans Tokushima Otsuka (L-SED) rats served as nonhyperphagic controls. O-SED + M, O-EndEx, and O-EndEx + M were effective in the management of type 2 diabetes, and all three treatments lowered hepatic steatosis and serum markers of liver injury; however, O-EndEx lowered liver triglyceride content and fasting hyperglycemia more than O-SED + M. In addition, exercise elicited greater improvements compared with metformin alone on postchallenge glycemic control, liver diacylglycerol content, hepatic mitochondrial palmitate oxidation, citrate synthase, and β-HAD activities and in the attenuation of markers of hepatic fatty acid uptake and de novo fatty acid synthesis. Surprisingly, combining metformin and aerobic exercise training offered little added benefit to these outcomes, and in fact, metformin actually blunted exercise-induced increases in complete mitochondrial palmitate oxidation and β-HAD activity. In conclusion, aerobic exercise training was more effective than metformin administration in the management of type 2 diabetes and NAFLD outcomes in obese hyperphagic OLETF rats. Combining therapies offered little additional benefit beyond exercise alone, and findings suggest that metformin potentially impairs exercise-induced hepatic mitochondrial adaptations.