TR4 nuclear receptor functions as a fatty acid sensor to modulate CD36 expression and foam cell formation

Nuclear Receptors and the Hidden Language of the Metabolome

Nuclear hormone receptors (NHRs) are a family of ligand-regulated transcription factors that control key aspects of development and physiology. The regulation of NHRs by ligands derived from metabolism or diet makes them excellent pharmacological targets, and the mechanistic understanding of how NHRs interact with their ligands to regulate downstream gene networks, along with the identification of ligands for orphan NHRs, could enable innovative approaches for cellular engineering, disease modeling and regenerative medicine. We review recent discoveries in the identification of physiologic ligands for NHRs. We propose new models of ligand-receptor co-evolution, the emergence of hormonal function and models of regulation of NHR specificity and activity via one-ligand and two-ligand models as well as feedback loops. Lastly, we discuss limitations on the processes for the identification of physiologic NHR ligands and emerging new methodologies that could be used to identify the natural ligands for the remaining 17 orphan NHRs in the human genome.

Lipid-Laden Macrophages in Pulmonary Diseases

Pulmonary surfactants play a crucial role in managing lung lipid metabolism, and dysregulation of this process is evident in various lung diseases. Alternations in lipid metabolism lead to pulmonary surfactant damage, resulting in hyperlipidemia in response to lung injury. Lung macrophages are responsible for recycling damaged lipid droplets to maintain lipid homeostasis. The inflammatory response triggered by external stimuli such as cigarette smoke, bleomycin, and bacteria can interfere with this process, resulting in the formation of lipid-laden macrophages (LLMs), also known as foamy macrophages. Recent studies have highlighted the potential significance of LLM formation in a range of pulmonary diseases. Furthermore, growing evidence suggests that LLMs are present in patients suffering from various pulmonary conditions. In this review, we summarize the essential metabolic and signaling pathways driving the LLM formation in chronic obstructive pulmonary disease, pulmonary fibrosis, tuberculosis, and acute lung injury.

Role of carboxylesterase and arylacetamide deacetylase in drug metabolism, physiology, and pathology

Carboxylesterases (CES1 and CES2) and arylacetamide deacetylase (AADAC), which are expressed primarily in the liver and/or gastrointestinal tract, hydrolyze drugs containing ester and amide bonds in their chemical structure. These enzymes often catalyze the conversion of prodrugs, including the COVID-19 drugs remdesivir and molnupiravir, to their pharmacologically active forms. Information on the substrate specificity and inhibitory properties of these enzymes, which would be useful for drug development and toxicity avoidance, has accumulated. Recently,in vitroandin vivostudies have shown that these enzymes are involved not only in drug hydrolysis but also in lipid metabolism. CES1 and CES2 are capable of hydrolyzing triacylglycerol, and the deletion of their orthologous genes in mice has been associated with impaired lipid metabolism and hepatic steatosis. Adeno-associated virus-mediated human CES overexpression decreases hepatic triacylglycerol levels and increases fatty acid oxidation in mice. It has also been shown that overexpression of CES enzymes or AADAC in cultured cells suppresses the intracellular accumulation of triacylglycerol. Recent reports indicate that AADAC can be up- or downregulated in tumors of various organs, and its varied expression is associated with poor prognosis in patients with cancer. Thus, CES and AADAC not only determine drug efficacy and toxicity but are also involved in pathophysiology. This review summarizes recent findings on the roles of CES and AADAC in drug metabolism, physiology, and pathology.

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.

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.

Senescence-associated 13-HODE production promotes age-related liver steatosis by directly inhibiting catalase activity

Aging is a major risk factor for metabolic disorders. Polyunsaturated fatty acid-derived bioactive lipids play critical roles as signaling molecules in metabolic processes. Nonetheless, their effects on age-related liver steatosis remain unknown. Here we show that senescent liver cells induce liver steatosis in a paracrine manner. Linoleic acid-derived 9-hydroxy-octadecadienoic acid (9-HODE) and 13-HODE increase in middle-aged (12-month-old) and aged (20-month-old) male mouse livers and conditioned medium from senescent hepatocytes and macrophages. Arachidonate 15-lipoxygenase, an enzyme for 13-HODE and 9-HODE production, is upregulated in senescent cells. A 9-HODE and 13-HODE mixture induces liver steatosis and activates SREBP1. Furthermore, catalase (CAT) is a direct target of 13-HODE, and its activity is decreased by 13-HODE. CAT overexpression reduces 13-HODE-induced liver steatosis and protects male mice against age-related liver steatosis. Therefore, 13-HODE produced by senescent hepatocytes and macrophages activates SREBP1 by directly inhibiting CAT activity and promotes liver steatosis.

New insights into the suppression of inflammation and lipid accumulation by JAZF1

Atherosclerosis is one of the leading causes of disease and death worldwide. The identification of new therapeutic targets and agents is critical. JAZF1 is expressed in many tissues and is found at particularly high levels in adipose tissue (AT). JAZF1 suppresses inflammation (including IL-1β, IL-4, IL-6, IL-8, IL-10, TNFα, IFN-γ, IAR-20, COL3A1, laminin, and MCP-1) by reducing NF-κB pathway activation and AT immune cell infiltration. JAZF1 reduces lipid accumulation by regulating the liver X receptor response element (LXRE) of the SREBP-1c promoter, the cAMP-response element (CRE) of HMGCR, and the TR4 axis. LXRE and CRE sites are present in many cytokine and lipid metabolism gene promoters, which suggests that JAZF1 regulates these genes through these sites. NF-κB is the center of the JAZF1-mediated inhibition of the inflammatory response. JAZF1 suppresses NF-κB expression by suppressing TAK1 expression. Interestingly, TAK1 inhibition also decreases lipid accumulation. A dual-targeting strategy of NF-κB and TAK1 could inhibit both inflammation and lipid accumulation. Dual-target compounds (including prodrugs) 1-5 exhibit nanomolar inhibition by targeting NF-κB and TAK1, EGFR, or COX-2. However, the NF-κB suppressing activity of these compounds is relatively low (IC50 > 300 nM). Compounds 6-14 suppress NF-κB expression with IC50 values ranging from 1.8 nM to 38.6 nM. HS-276 is a highly selective, orally bioavailable TAK1 inhibitor. Combined structural modifications of compounds using a prodrug strategy may enhance NF-κB inhibition. This review focused on the role and mechanism of JAZF1 in inflammation and lipid accumulation for the identification of new anti-atherosclerotic targets.

Molecular Markers of Early Immune Response in Tuberculosis: Prospects of Application in Predictive Medicine

Tuberculosis (TB) remains an important public health problem and one of the leading causes of death. Individuals with latent tuberculosis infection (LTBI) have an increased risk of developing active TB. The problem of the diagnosis of the various stages of TB and the identification of infected patients in the early stages has not yet been solved. The existing tests (the tuberculin skin test and the interferon-gamma release assay) are useful to distinguish between active and latent infections. But these tests cannot be used to predict the development of active TB in individuals with LTBI. The purpose of this review was to analyze the extant data of the interaction of M. tuberculosis with immune cells and identify molecular predictive markers and markers of the early stages of TB. An analysis of more than 90 sources from the literature allowed us to determine various subpopulations of immune cells involved in the pathogenesis of TB, namely, macrophages, dendritic cells, B lymphocytes, T helper cells, cytotoxic T lymphocytes, and NK cells. The key molecular markers of the immune response to M. tuberculosis are cytokines (IL-1β, IL-6, IL-8, IL-10, IL-12, IL-17, IL-22b, IFNɣ, TNFa, and TGFß), matrix metalloproteinases (MMP-1, MMP-3, and MMP-9), and their inhibitors (TIMP-1, TIMP-2, TIMP-3, and TIMP-4). It is supposed that these molecules could be used as biomarkers to characterize different stages of TB infection, to evaluate the effectiveness of its treatment, and as targets of pharmacotherapy.

Propionate regulates tight junction barrier by increasing endothelial-cell selective adhesion molecule in human intestinal Caco-2 cells

Regulation of the intestinal barrier is closely associated with intestinal microbial metabolism. This study investigated the role of propionate, a major short-chain fatty acid produced by intestinal microorganisms, in the regulation of the tight junction (TJ) barrier in human intestinal Caco-2 cells. Propionate strengthened TJ barrier integrity, as indicated by decreased permeability to macromolecules and increased transepithelial electrical resistance in Caco-2 cells. DNA microarray analysis revealed that propionate upregulated endothelial cell-selective adhesion molecule (ESAM), a TJ-associated protein, without any increase in other TJ proteins. The upregulation of ESAM was confirmed using quantitative reverse transcription-PCR, immunoblotting, and immunofluorescence analyses. Luciferase promoter analysis demonstrated that propionate induced the transcriptional activation of ESAM. The effects of propionate were sensitive to nilotinib inhibition of NR2C2. Overexpression of human ESAM (hESAM) in canine kidney epithelial MDCK-II cells lowered the permeability to macromolecules in a manner similar to that of propionate-treated Caco-2 cells. hESAM overexpression facilitated calcium-induced assembly of the TJ complex in MDCK-II cells. Taken together, propionate strengthened the intestinal TJ barrier by increasing ESAM levels in Caco-2 cells.

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.

Leukocyte inflammatory phenotype and function in migraine patients compared with matched non-migraine volunteers: a pilot study

Background

Migraine is a neurological condition characterized by chronic inflammation. However, not much is known about the potential role of peripheral blood immune cells in the pathophysiology of migraine.

Methods

We investigated the status of peripheral blood immune cells of 15 adults with frequent episodic or chronic migraine recruited chronologically from a randomized clinical trial (RCT) on Nutrition for Migraine (NCCIH 5R01AT007813-05) and 15 non-migraine, healthy volunteers (control) matched by age, gender, and Body Mass Index (BMI).

Continuous variables were presented as means ± standard deviationas well as medians, and comparisons between patients and healthy volunteers were performed with non-parametric Wilcoxon signed rank tests. Statistical analysis was performed using Stata (StataCorp. 2019. Stata Statistical Software). Fluorescence-Activated Cell Sorting (FACS) data were processed using FlowJo software (Ashland, OR: Becton, Dickenson and Company; 2019).

Results

We observed that migraineurs had a significantly lower percentage of non-classical monocytes (CD14⁺CD16⁺⁺) in blood circulation, compared to the control group. In addition, Migraineurs also showed a significantly lower percentage of blood CD3⁺CD4⁺ helper T cells and CD4⁺CD25⁺ regulatory T cells, compared to controls. Differences in leukocyte surface markers between chronic migraine patients and their matched controls were more prominent than those between episodic migraine patients and their matched controls.

Conclusions

Our results suggest that migraine is associated with dysregulated peripheral immune homeostasis and that inflammation and autoimmunity may play a role in its pathophysiology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-022-02781-4.

CD36 Senses Dietary Lipids and Regulates Lipids Homeostasis in the Intestine

Dietary lipids absorbed in the intestine are closely related to the development of metabolic syndrome. CD36 is a multi-functional scavenger receptor with multiple ligands, which plays important roles in developing hyperlipidemia, insulin resistance, and metabolic syndrome. In the intestine, CD36 is abundant on the brush border membrane of the enterocytes mainly localized in proximal intestine. This review recapitulates the update and current advances on the importance of intestinal CD36 in sensing dietary lipids and regulating intestinal lipids uptake, synthesis and transport, and regulating intestinal hormones secretion. However, further studies are still needed to demonstrate the complex interactions between intestinal CD36 and dietary lipids, as well as its importance in diet associated metabolic syndrome.

Correlation analysis of epicardial adipose tissue thickness, C-reactive protein, interleukin-6, visfatin, juxtaposed with another zinc finger protein 1, and type 2 diabetic macroangiopathy

Background

To investigate the correlation between the thickness of epicardial adipose tissue (EAT), C-reactive protein (CRP), interleukin (IL) -6, visfatin, juxtaposed with another zinc finger protein 1 (JAZF1) and type 2 diabetic mellitus (T2DM) macroangiopathy.

Methods

The study enrolled 82 patients with T2DM with macroangiopathy (the Complication Group), and 85 patients with T2DM (the Diabetes Group) who were admitted to Shandong Provincial Third Hospital from February 2018 to February 2020. In addition, 90 healthy people who underwent physical examination at the same hospital during the same period were enrolled (the Healthy Control Group). Age, gender, height, weight, waist circumference (WC), hip circumference (HC), diabetic course and therapeutic drugs, waist hip ratio (WHR), and body mass index (BMI) were recorded and calculated.

Results

The baseline characteristics of the three groups were comparable, and the diabetic course of the Complication Group and the Diabetes Group was not significantly different (P > 0.05). The WHR of the Complication Group was higher than that of the Diabetes Group and the Healthy Control Group, with statistical significance (P < 0.05). The FPG, 2hPG, HbA1C, CRP, IL-6, Visfatin, JAZF1, HOMA-IR, EAT thickness, and baPWV of the Complication Group were all higher than those of the Diabetes Group and the Healthy Control Group (P < 0.05, respectively). The JAZF1 and FIns of the Complication Group and Diabetes Group were lower than those of the Healthy Control Group, and JAZF1 of the Complication Group was lower than the Diabetes Group with statistical significance (P<0.05, respectively). Pearson correlation analysis showed that the EAT thickness was positively correlated with CRP, IL-6, visfatin, and JAZF1 (r = 0.387, 0.451, 0.283, 0.301, respectively, all P<0.001). Pearson correlation analysis showed that baPWV was positively correlated with EAT thickness, CRP, IL-6, visfatin, and JAZF1 (r = 0.293, 0.382, 0.473, 0.286, respectively, all P < 0.001). Multivariate stepwise regression analysis showed that FPG, 2hPG, HbA1C, CRP, IL-6, visfatin, JAZF1, and EAT thickness were independent risk factors that affected T2DM macroangiopathy.

Conclusions

Clinical monitoring and treatment of T2DM macroangiopathy can use CRP, IL-6, Visfatin, JAZF1, and EAT thickness as new targets to delay the progression of the disease. Further research on the relationship between the above factors and the pathogenesis of T2DM macroangiopathy may be helpful provide new treatment strategies.

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.

CD36 in Atherosclerosis: Pathophysiological Mechanisms and Therapeutic Implications

PURPOSE OF REVIEW

Atherosclerosis is a chronic disease characterized by lipid retention and inflammation in the artery wall. The retention and oxidation of low-density lipoprotein (LDL) in sub-endothelial space play a critical role in atherosclerotic plaque formation and destabilization. Oxidized LDL (ox-LDL) and other modified LDL particles are avidly taken up by endothelial cells, smooth muscle cells, and macrophages mainly through several scavenger receptors, including CD36 which is a class B scavenger receptor and membrane glycoprotein.

RECENT FINDINGS

Animal studies performed on CD36-deficient mice suggest that deficiency of CD36 prevents the development of atherosclerosis, though with some debate. CD36 serves as a signaling hub protein at the crossroad of inflammation, lipid metabolism, and fatty acid metabolism. In addition, the level of soluble CD36 (unattached to cells) in the circulating blood was elevated in patients with atherosclerosis and other metabolic disorders. We performed a state-of-the-art review on the structure, ligands, functions, and regulation of CD36 in the context of atherosclerosis by focusing on the pathological role of CD36 in the dysfunction of endothelial cells, smooth muscle cells, monocytes/macrophages, and platelets. Finally, we highlight therapeutic possibilities to target CD36 expression/activity in atherosclerosis.

Mycobacterium tuberculosis and macrophage nuclear receptors: What we do and don't know

Nuclear receptors (NRs) are ligand-activated transcription factors that are expressed in a wide variety of cells and play a major role in lipid signaling. NRs are key regulators of immune and metabolic functions in macrophages and are linked to macrophage responses to microbial pathogens. Pathogens are also known to induce the expression of specific NRs to promote their own survival. In this review, we focus on the NRs recently shown to influence macrophage responses to Mycobacterium tuberculosis (M.tb), a significant cause of morbidity and mortality worldwide. We provide an overview of NR-controlled transcriptional activity and regulation of macrophage activation. We also discuss in detail the contribution of specific NRs to macrophage responses to M.tb, including influence on macrophage phenotype, cell signaling, and cellular metabolism. We pay particular attention to PPARγ since it is required for differentiation of alveolar macrophages, an important niche for M.tb, and its role during M.tb infection is becoming increasingly appreciated. Research into NRs and M.tb is still in its early stages, therefore continuing to advance our understanding of the complex interactions between M.tb and macrophage NRs may reveal the potential of NRs as pharmacological targets for the treatment of tuberculosis.

Cooperative cobinding of synthetic and natural ligands to the nuclear receptor PPARγ

Crystal structures of peroxisome proliferator-activated receptor gamma (PPARγ) have revealed overlapping binding modes for synthetic and natural/endogenous ligands, indicating competition for the orthosteric pocket. Here we show that cobinding of a synthetic ligand to the orthosteric pocket can push natural and endogenous PPARγ ligands (fatty acids) out of the orthosteric pocket towards an alternate ligand-binding site near the functionally important omega (Ω)-loop. X-ray crystallography, NMR spectroscopy, all-atom molecular dynamics simulations, and mutagenesis coupled to quantitative biochemical functional and cellular assays reveal that synthetic ligand and fatty acid cobinding can form a 'ligand link' to the Ω-loop and synergistically affect the structure and function of PPARγ. These findings contribute to a growing body of evidence indicating ligand binding to nuclear receptors can be more complex than the classical one-for-one orthosteric exchange of a natural or endogenous ligand with a synthetic ligand.

The role of NR2C2 in the prolactinomas

Prolactinomas are the most frequently observed pituitary adenomas. Prolactinomas invasion is a key risk factor associated with operation results, and it is highly correlated with clinical prognosis. Nuclear receptor subfamily 2 group C member 2 (NR2C2) first cloned from testis is involved in the invasion and metastasis of several human tumors. In 46 patients with prolactinamas, the expression levels of CCNB1, Notch2, and NR2C2 was determined with tissue micro-array (TMA). The association between NR2C2 levels and clinical parameters was established with univariate analysis. The levels of Notch2 and CCNB1 were analyzed by RT-PCR and western blot techniques.The average methylation levels of the NR2C2 promoter were 0.505 and 0.825 in invasive prolactinomas (IPA) and non-IPA groups, respectively (p = 0.013). Univariate analysis also showed that there is a significant relationship between high NR2C2 expression and invasion (x2 = 7.043, p = 0.008), prolactin granules (x2 = 8.712, p = 0.003), and tumor size (x2 = 4.261, p = 0.039.) With the knockdown of NR2C2, cell proliferation was inhibited. Genes related to epithelial-mesenchymal transition (EMT) induced the apoptosis in MMQ cells. In addition, the level of Notch2 and CCNB1 were down-regulated with the knockdown of NR2C2. Moreover, miR-129-5p reduced mRNA levels of NR2C2, and they inhibited cell proliferation by inducing apoptosis levels of MMQ cells. Our findings proved NR2C2 played the important role in tumorigenesis tumor invasion of prolactinomas; moreover, NR2C2 is identified as a potential target.

CD36 and lipid metabolism in the evolution of atherosclerosis

BACKGROUND

CD36 is a multi-functional class B scavenger receptor, which acts as an important modulator of lipid homeostasis and immune responses.

SOURCES OF DATA

This review uses academic articles.

AREAS OF AGREEMENT

CD36 is closely related to the development and progression of atherosclerosis.

AREAS OF CONTROVERSY

Both persistent up-regulation of CD36 and deficiency of CD36 increase the risk for atherosclerosis. Abnormally up-regulated CD36 promotes inflammation, foam cell formation, endothelial apoptosis, macrophage trapping and thrombosis. However, CD36 deficiency also causes dyslipidemia, subclinical inflammation and metabolic disorders, which are established risk factors for atherosclerosis.

GROWING POINTS

There may be an 'optimal protective window' of CD36 expression.

AREAS TIMELY FOR DEVELOPING RESEARCH

In addition to traditionally modulating protein functions using gene overexpression or deficiency, the modulation of CD36 function at post-translational levels has recently been suggested to be a potential therapeutic strategy.

9- and 13-HODE regulate fatty acid binding protein-4 in human macrophages, but does not involve HODE/GPR132 axis in PPAR-γ regulation of FABP4

BACKGROUND

Both activation of monocytes and increased serum fatty acid binding protein-4 (FABP4) occur in diabetes and are associated with increased atherosclerosis. The oxidized lipid, 9-hydroxyoctadecadienoic acid (9-HODE) increases FABP4 in macrophages, and is a ligand for G protein-coupled receptor 132 (GPR132). We investigated the involvement of GPR132 in mediating the 9-, 13-HODE stimulation of FABP4 secretion, and whether GPR132 expression is increased in monocytes from patients with type 2 diabetes.

METHODS

The effects of siRNA silencing of GPR132 gene and of the PPAR-γ antagonist T0070907 were studied in THP-1 cells. Serum levels of FABP4 and other adipokines were measured in patients with diabetes, and monocyte subpopulations were analyzed using flow cytometry. GPR132 mRNA was quantified in isolated CD14⁺ cells.

RESULTS

9-HODE and 13-HODE increased FABP4 expression in THP-1 monocytes and macrophages, and also increased GPR132 expression. Silencing of GPR132 did not influence the increase in FABP4 with 9-HODE, 13-HODE, or rosiglitazone (ROSI). By contrast, T0070907 inhibited the effect of all three ligands on FABP4 expression. Diabetic subjects had increased serum FABP4, and activated monocytes. They also expressed higher levels of GPR132 mRNA in CD14⁺ cells.

CONCLUSIONS

We conclude that GPR132 is an independent monocyte activation marker in diabetes, but does not contribute to PPAR-γ-mediated induction of FABP4 by HODEs.

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.

Testicular orphan receptor 4 promotes tumor progression and implies poor survival through AKT3 regulation in seminoma

Seminoma is the most common testicular germ cell tumor worldwide and mainly occurs in 15-35-year-old young men. Early studies have indicated that testicular nuclear receptor 4 (TR4) first cloned from testis is involved in the invasion and metastasis of several human tumors; however, little attention is paid to the function of TR4 in seminoma. Our immunohistochemical (IHC) staining results showed that patients with advanced stage tumors tended to have higher expression of TR4. Importantly, there was a significant association between elevated TR4 expression and reduced overall survival in seminoma patients. In vitro MTS, western blot and transwell assays, after manipulating TR4 expression in Tcam-2 cells, revealed that TR4 induced epithelial-to-mesenchymal transition (EMT) and promoted Tcam-2 cell proliferation and invasion. Mechanism dissection demonstrated that AKT3, a critical component in the signaling pathway, played a crucial role in mediating TR4-promoted Tcam-2 cell proliferation and invasion. We further revealed that TR4 modulated AKT3 at the transcriptional level via chromatin immunoprecipitation and luciferase assays. Meanwhile, addition of the AKT3 siRNA blocked the function of TR4. Overall, these findings first elucidate that TR4 is a novel prognostic marker and plays a critical role in the metastatic capacity of Tcam-2 cells by EMT regulation and, consequently, targeting TR4-AKT3 pathway may serve as a potential therapeutic approach for seminoma.

Silencing carboxylesterase 1 in human THP-1 macrophages perturbs genes regulated by PPARγ/RXR and RAR/RXR: down-regulation of CYP27A1-LXRα signaling

Macrophage foam cells store excess cholesterol as cholesteryl esters, which need to be hydrolyzed for cholesterol efflux. We recently reported that silencing expression of carboxylesterase 1 (CES1) in human THP-1 macrophages [CES1KD (THP-1 cells with CES1 expression knocked down) macrophages] reduced cholesterol uptake and decreased expression of CD36 and scavenger receptor-A in cells loaded with acetylated low-density lipoprotein (acLDL). Here, we report that CES1KD macrophages exhibit reduced transcription of cytochrome P45027A1 (CYP27A1) in nonloaded and acLDL-loaded cells. Moreover, levels of CYP27A1 protein and its enzymatic product, 27-hydroxycholesterol, were markedly reduced in CES1KD macrophages. Transcription of LXRα (liver X receptor α) and ABCA1 (ATP-binding cassette transporter A1) was also decreased in acLDL-loaded CES1KD macrophages, suggesting reduced signaling through PPARγ-CYP27A1-LXRα. Consistent with this, treatment of CES1KD macrophages with agonists for PPARγ, RAR, and/or RAR/RXR partially restored transcription of CYP27A1 and LXRα, and repaired cholesterol influx. Conversely, treatment of control macrophages with antagonists for PPARγ and/or RXR decreased transcription of CYP27A1 and LXRα Pharmacologic inhibition of CES1 in both wild-type THP-1 cells and primary human macrophages also decreased CYP27A1 transcription. CES1 silencing did not affect transcript levels of PPARγ and RXR in acLDL-loaded macrophages, whereas it did reduce the catabolism of the endocannabinoid 2-arachidonoylglycerol. Finally, the gene expression profile of CES1KD macrophages was similar to that of PPARγ knockdown cells following acLDL exposures, further suggesting a mechanistic link between CES1 and PPARγ. These results are consistent with a model in which abrogation of CES1 function attenuates the CYP27A1-LXRα-ABCA1 signaling axis by depleting endogenous ligands for the nuclear receptors PPARγ, RAR, and/or RXR that regulate cholesterol homeostasis.

Core hydrophobicity tuning of a self-assembled particle results in efficient lipid reduction and favorable organ distribution

Atherosclerosis, the deadliest disease in the United States, arises due to the build up of plaques in the arteries as a result of excessive cholesterol deposition and an impaired cholesterol removal process. High density lipoproteins (HDL), popularly known as "good cholesterol", are naturally occurring nano-sized particles that, along with apolipoproteins, are deployed to maintain cholesterol homeostasis in the body. Both cholesterol efflux, from the fat-laden macrophages in the arteries, and intracellular lipid transport, to deliver cholesterol to the mitochondria of liver cells for metabolism, hold key responsibilities to maintain healthy lipid levels inside the body. We designed a library of nine mitochondria targeted polymer-lipid hybrid nanoparticles (NPs), comprised of completely synthetic yet biodegradable components, that are capable of performing HDL-like functions. Using this library, we optimized a superior mitochondria targeted NP candidate, which can show favourable organ distribution, therapeutic potential, and non-toxic properties. Two targeted NP formulations with optimum NP size, zeta potential, and cholesterol binding and release properties were identified. Lipid reduction and anti-oxidative properties of these two NPs demonstrated cholesterol removal ability. In vivo therapeutic evaluation of the targeted-NP formulations in apolipoprotein E knockout (apoE^-/^-) mice indicated lipid reduction and anti-inflammatory properties compared to non-targeted NPs. This synthetic targeted NP with potential abilities to participate in both extra- and intracellular cholesterol transport might potentiate therapeutic interventions for heart diseases.

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.

Recent advances in understanding Cushing disease: resistance to glucocorticoid negative feedback and somatic USP8 mutations

Cushing’s disease is a rare disease with a characteristic phenotype due to significant hypercortisolism driven by over-secretion of adrenocorticotropic hormone and to high morbidity and mortality if untreated. It is caused by a corticotroph adenoma of the pituitary, but the exact mechanisms leading to tumorigenesis are not clear. Recent advances in molecular biology such as the discovery of somatic mutations of the ubiquitin-specific peptidase 8 ( USP8) gene allow new insights into the pathogenesis, which could be translated into exciting and much-needed therapeutic applications.

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.

miRNA-133a attenuates lipid accumulation via TR4-CD36 pathway in macrophages

lipid metabolism is the major causes of atherosclerosis. There is increasing evidence that miR-133a plays an important role in atherosclerosis. However, the regulatory mechanism of miR-133a in macrophages is still unclear. Several lines of evidence indicate that loss of TR4 leads to reduce lipid accumulation in liver and adipose tissues, etc, and lesional macrophages-derived TR4 can greatly increase the foam cell formation through increasing the CD36-mediated the uptake of ox-LDL. Interestingly, computational analysis suggests that TR4 may be a target gene of miR-133a. Here, we examined whether miR-133a regulates TR4 expression in ox-LDL-induced mouse RAW 264.7 macrophages, thereby affecting lipid accumulation. Using ox-LDL-treatment RAW 264.7 macrophages transfected with miR-133a mimics or inhibitors, we have showed that miR-133a can directly regulate the expression of TR4 in RAW 264.7 cells, thereby attenuates CD36-medide lipid accumulation. Furthermore, our studies suggest an additional explanation for the regulatory mechanism of miR-133a regulation to its functional target, TR4 in RAW 264.7 macrophages. Thus, our findings suggest that miR-133a may regulate lipid accumulation in ox-LDL-stimulated RAW 264.7 macrophages via TR4-CD36 pathway.

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.

Structures and regulation of non-X orphan nuclear receptors: A retinoid hypothesis

Nuclear receptors are defined as a family of ligand regulated transcription factors [1-6]. While this definition reflects that ligand binding is a key property of nuclear receptors, it is still a heated subject of debate if all the nuclear receptors (48 human members) can bind ligands (ligands referred here to both physiological and synthetic ligands). Recent studies in nuclear receptor structure biology and pharmacology have undoubtedly increased our knowledge of nuclear receptor functions and their regulation. As a result, they point to new avenues for the discovery and development of nuclear receptor regulators, including nuclear receptor ligands. Here we review the recent literature on orphan nuclear receptor structural analysis and ligand identification, particularly on the orphan nuclear receptors that do not heterodimerize with retinoid X receptors, which we term as non-X orphan receptors. We also propose a speculative "retinoid hypothesis" for a subset of non-X orphan nuclear receptors, which we hope to help shed light on orphan nuclear receptor biology and drug discovery. This article is part of a Special Issue entitled 'Orphan Nuclear Receptors'.

The Differential Effects of Anti-Diabetic Thiazolidinedione on Prostate Cancer Progression Are Linked to the TR4 Nuclear Receptor Expression Status

The insulin sensitizers, thiazolidinediones (TZDs), have been used as anti-diabetic drugs since the discovery of their ability to alter insulin resistance through transactivation of peroxisome proliferator-activated receptors (PPARs). However, their side effects in hepatitis, cardiovascular diseases, and bladder cancer resulted in some selling restrictions in the USA and Europe. Here, we found that the potential impact of TZDs on the prostate cancer (PCa) progression might be linked to the TR4 nuclear receptor expression. Clinical surveys found that 9% of PCa patients had one allele TR4 deletion in their tumors. TZD increased cell growth and invasion in PCa cells when TR4 was knocked down. In contrast, TZD decreased PCa progression in PCa cells with wild type TR4. Mechanism dissection found that the Harvey Rat Sarcoma (HRAS) oncogene increased on TZD treatment of the TR4 knocked-down CWR22Rv1 and C4-2 cells, and interruption with HRAS inhibitor resulted in reversal of TZD-induced PCa progression. Together, these results suggest that TZD treatment may promote PCa progression depending on the TR4 expression status that may be clinically relevant since extra caution may be needed for those diabetic PCa patients receiving TZD treatment who have one allele TR4 deletion.

Testicular orphan nuclear receptor 4 is associated with the radio-sensitivity of prostate cancer

BACKGROUND

It is well known that a significant number of prostate cancers (PCa) showed different extents of radio-resistance and the tumor may recur after treatment. Recent studies demonstrated that Testicular orphan nuclear receptor 4 (TR4) could play a critical role in anti-oxidative stress responses and might modulate the DNA damage repair. The objective of this study is to investigate the role of TR4 in the radiotherapy for PCa.

METHODS

The TR4 expression in tissue samples from PCa patients treated with brachytherapy was measured by immunohistochemistry (IHC). Cell survival test and colony formation assay were applied to test the radio-sensitivity of PCa cells with modulated TR4 gene expression upon irradiation.

RESULTS

PCa patients with biochemical recurrence (BCR) after brachytherapy tend to have higher TR4 expression (80%, n = 30) as compared to those without BCR (36.67%, n = 30). Survival analysis demonstrated a significant higher BCR occurrence in patients with high level of TR4 expression (HR = 3.474, 95%CI 1.678-7.192, P = 0.0008). Multivariate analysis showed that the TR4 staining score on IHC was the only significant variable for predicting the PCa patients' clinical outcomes after radiotherapy (OR = 9.919, 95% CI 2.516-39.101, P = 0.001). Using cell survival test and colony forming assay, we found that the addition of functional TR4 in PC3 cells lead to elevated radio-resistance. In contrast, knocking-down TR4 in LNCaP cells resulted in increased radio-sensitivity. The γH2AX foci kinetic analysis suggested that knocking down TR4 might delay the PCa cell's DNA damage repair which would enhance the radio-sensitivity.

CONCLUSION

TR4 could mediate the PCa cells' radio-sensitivity and might become a prognostic indicator for PCa patients received radiotherapy. This study provides a novel approach to manipulate radio-sensitivity of PCa cells, and may bring a promoted therapeutic outcome of radiotherapy to battle PCa in future.

TR4 nuclear receptor increases prostate cancer invasion via decreasing the miR-373-3p expression to alter TGFβR2/p-Smad3 signals

Testicular nuclear receptor 4 (TR4), a member of the nuclear receptor superfamily, may play important roles to modulate the metabolic diseases and prostate tumorigenesis. Here we found TR4 could increase prostate cancer (PCa) cell invasion. Mechanism dissection revealed that TR4 might increase PCa cell invasion via decreasing the miR-373-3p expression that resulted in the activation of the TGFβR2/p-Smad3 signals. The in vivo mouse model using orthotopically xenografted CWR22Rv1 cell line transfected with luciferase-reporter confirmed in vitro cell line studies showing TR4 increased PCa metastasis via decreasing the miR-373-3p expression. Together, these data suggest that TR4 may increase PCa metastasis via a newly identified signal and targeting these TR4/miR-473-3p/TGFβR2/p-Smad3 signals using TR4 antagonist or TR4-siRNA or miR-373-3p may allow us to develop a new potential therapeutic approach to better suppress PCa metastasis.

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.

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.

Oxidized high-density lipoprotein impairs endothelial progenitor cells' function by activation of CD36-MAPK-TSP-1 pathways

AIMS

High-density lipoprotein (HDL) levels inversely correlate with cardiovascular events due to the protective effects on vascular wall and stem cells, which are susceptible to oxidative modifications and then lead to potential pro-atherosclerotic effects. We proposed that oxidized HDL (ox-HDL) might lead to endothelial progenitor cells (EPCs) dysfunction and investigated underlying mechanisms.

RESULTS

ox-HDL was shown to increase apoptosis and intracellular reactive oxygen species levels, but to reduce migration, angiogenesis, and cholesterol efflux of EPCs in a dose-dependent manner. p38 mitogen-activated protein kinase (MAPK) and NF-κB were activated after ox-HDL stimulation, which also upregulated thrombospondin-1 (TSP-1) expression without affecting vascular endothelial growth factor. Effects caused by ox-HDL could be significantly attenuated by pretreatment with short hairpin RNA-mediated CD36 knockdown or probucol. Data of in vivo experiments and the inverse correlation of ox-HDL and circulating EPC numbers among patients with coronary artery diseases (CAD) or CAD and type 2 diabetes also supported it. Meanwhile, HDL separated from such patients could significantly increase cultured EPC's caspase 3 activity, further supporting our proposal.

INNOVATION

This is the most complete study to date of how ox-HDL would impair EPCs function, which was involved with activation of CD36-p38 MAPK-TSP-1 pathways and proved by not only the inverse relationship between ox-HDL and circulating EPCs in clinic but also pro-apoptotic effects of HDL separated from patients' serum.

CONCLUSION

Activation of CD36-p38 MAPK-TSP-1 pathways contributes to the pathological effects of ox-HDL on EPCs' dysfunction, which might be one of the potential etiological factors responsible for the disturbed neovascularization in chronic ischemic disease.

Targeting TR4 nuclear receptor suppresses prostate cancer invasion via reduction of infiltrating macrophages with alteration of the TIMP-1/MMP2/MMP9 signals

Background

TR4 nuclear receptor 4 (TR4) plays an important role in macrophages-associated foam cell formation of cardiovascular diseases and infiltrating macrophages are critical for prostate cancer (PCa) progression. However, the linkage of macrophages and TR4 and their impacts on PCa metastasis remains unclear.

Results

Knocking-down TR4 in human PCa cells (C4-2, CWR22Rv1), but not in human macrophages cells (THP-1), led to suppress the macrophages infiltration to PCa cells. The consequences of such suppression of the recruitment of macrophages toward PCa then resulted in suppressing the PCa cell invasion. Mechanism dissection found that knocking-down TR4 in PCa cells suppressed metastasis-related genes including MMP2, with induction of TIMP-1. Interruption assays using TIMP-1 neutralizing antibody could then reverse TR4-macrophage-mediated PCa invasion. IHC staining showed higher TR4 level, more macrophage infiltration, lower TIMP-1 and stronger MMP2/MMP9 in tumor tissues of the Gleason score 5 + 4 patients compared with the Gleason score 3 + 3 patients.

Conclusion

Targeting TR4 in prostate tumor microenvironment might represent a potential new therapeutic approach to better battle PCa metastasis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-014-0281-1) contains supplementary material, which is available to authorized users.

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.

Macrophage immunoregulatory pathways in tuberculosis

Macrophages, the major host cells harboring Mycobacterium tuberculosis (M.tb), are a heterogeneous cell type depending on their tissue of origin and host they are derived from. Significant discord in macrophage responses to M.tb exists due to differences in M.tb strains and the various types of macrophages used to study tuberculosis (TB). This review will summarize current concepts regarding macrophage responses to M.tb infection, while pointing out relevant differences in experimental outcomes due to the use of divergent model systems. A brief description of the lung environment is included since there is increasing evidence that the alveolar macrophage (AM) has immunoregulatory properties that can delay optimal protective host immune responses. In this context, this review focuses on selected macrophage immunoregulatory pattern recognition receptors (PRRs), cytokines, negative regulators of inflammation, lipid mediators and microRNAs (miRNAs).

Oxidized lipids and lysophosphatidylcholine induce the chemotaxis, up-regulate the expression of CCR9 and CXCR4 and abrogate the release of IL-6 in human monocytes

Lipids through regulation of chronic inflammation play key roles in the development of various diseases. Here, we report that a mixed population of human primary monocytes migrated towards LPC, as well as oxidized linoleic acid isoforms 9-S-HODE, 9-R-HODE and 13-R-HODE. Incubation with 9-R-HODE, 13-R-HODE and LPC resulted in increased expression of CXCR4, the receptor for SDF-1α/CXCL12, correlated with increased monocyte migration towards SDF-1α/CXCL12. Further, we report increased expression of CCR9, the receptor for TECK/CCL25, after stimulation with these lipids. Upon examining the migratory response towards TECK/CCL25, it was observed that an increase in CCR9 expression upon pre-treatment with 9-S-HODE, 9-R-HODE, 13-R-HODE and LPC resulted in increased migration of monocytes expressing CCR9. Only LPC but not any other lipid examined increased the influx of intracellular Ca²⁺ in monocytes. Finally, 9-S-HODE, 9-R-HODE, 13-R-HODE, or LPC inhibited the release of IL-6 from monocytes suggesting that these lipids may play important role in controlling inflammatory responses.

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.

Prostate Cancer Related JAZF1 Gene is Associated with Schizophrenia

BACKGROUND

Epidemiological studies have shown that there is a reduced risk of prostate cancer among persons diagnosed with schizophrenia (SCZ). However, the mechanism of such relationship is not clear. The reduced incidence of cancer observed in SCZ patients may be related to differences in genetic background. Recently, the JAZF1 gene is found to be associated with prostate cancer and type 2 diabetes. However, no study has focused on the association of JAZF1 with the risk of SCZ.

METHODS

We examined genetic associations of 118 single-nucleotide polymorphisms (SNPs) within the JAZF1 gene with SCZ using one European American (EA) sample of 1,149 cases and 1,347 controls. Logistic regression analysis of SCZ as a binary trait was performed using PLINK software.

RESULTS

The most significant association with SCZ was observed with rs10258132 (p = 0.0011); while the next best signal was rs17156259 (p = 0.0031). The third best associated SNP was rs7791865 (p = 0.00889). In addition, haplotype analyses revealed that the A-C haplotype from rs10244184 and rs10258132 was associated with SCZ (p = 0.00093); and the G-G haplotype from rs17156238 and rs17156259 was associated with SCZ (p = 0.00455).

CONCLUSION

These findings provide evidence of several genetic variants in JAZF1 gene influencing the risk of SCZ and will serve as a resource for replication in other populations.

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.

Fetal globin gene repressors as drug targets for molecular therapies to treat the β-globinopathies

The human β-globin locus is comprised of embryonic, fetal, and adult globin genes that are expressed in a developmental stage-specific manner. Mutations in the globin locus give rise to the β-globinopathies, β-thalassemia and sickle cell disease, which begin to manifest symptoms around the time of birth. Although the fetal globin genes are autonomously silenced in adult-stage erythroid cells, mutations lying both within and outside the locus lead to natural variations in the level of fetal globin gene expression, and some of these significantly ameliorate the clinical symptoms of the β-globinopathies. Multiple reports have now identified several transcription factors that are involved in fetal globin gene repression in definitive (adult)-stage erythroid cells (the TR2/TR4 heterodimer, MYB, KLFs, BCL11A, and SOX6). To carry out their repression functions, chromatin-modifying enzymes (such as DNA methyltransferase, histone deacetylases, and lysine-specific histone demethylase 1) are additionally involved as a consequence of forming large macromolecular complexes with the DNA-binding subunits of these cellular machines. This review focuses on the molecular mechanisms underlying fetal globin gene silencing and possible near-future molecularly targeted therapies for treating the β-globinopathies.