Nouveaux modèles pour le criblage de modulateurs / perturbateurs des voies de signalisation régulées par les Liver X receptors

Liver X Receptors (LXRs) are transcription factors among the nuclear receptors superfamily present in humans under two isoforms: LXRα and LXRβ. These isoforms have redundant and specific roles in cholesterol homeostasis, steroids, and immunity. Like other nuclear receptors, LXRs are targets of exogenous ligands that can impact their activity. This phenomenon is double-edged. On the one hand, precise and specific modulation of LXRs would lead to the development of therapeutic molecules. On the other hand, inappropriate disturbances of LXRs signaling pathways would lead to the identification of new Endocrine Disruptor Chemicals (EDCs). As part of this thesis, I analyzed the binding way and the activities of flavonoid ligands on LXRs. This led to the discovery of specific binding pattern depending on agonist/antagonist behavior. I have also been able to develop an in vivo screening system for LXRs ligands in the Drosophila melanogaster model. This tool allows the discrimination of agonist ligands by optical quantification of fluorescence in larvae. In order to discover LXRs isoforms- specific ligands, I started the construction of a double screening system allowing the simultaneous analysis of molecule activity on LXRα and LXRβ. All these results are promising in synthesis or discovery of therapeutic molecules as well as in the ECDs identification.Les Liver X Receptors (LXRs) sont des facteurs de transcription appartenant à la superfamille des récepteurs nucléaires présents chez l’homme sous deux isoformes : LXRα et LXRβ. Ces isoformes ont des rôles redondants et spécifiques dans l’homéostasie du cholestérol, des stéroïdes et dans l’immunité. Comme d’autres récepteurs nucléaires, les LXRs sont la cible de ligands exogènes pouvant impacter leur activité. Ce phénomène est à double tranchant. D’une part, une modulation précise et spécifique des LXRs conduirait au développement de molécules thérapeutiques. D’autre part, des perturbations inappropriées des voies de signalisation LXRs mèneraient à l’identification de nouveaux Endocrine Disruptor Chemicals (EDCs). Dans le cadre de cette thèse, j’ai analysé les modalités de fixation et les activités de ligands flavonoïdes sur les LXRs. Ceci a conduit à la découverte de profils de liaison spécifiques en fonction des activités agonistes/antagonistes. J’ai également pu mettre au point un système de criblage in vivo de ligands des LXRs chez le modèle Drosophila melanogaster. Cet outil permet la discrimination de ligands agonistes par quantification optique de la fluorescence chez les larves. Dans le but de découvrir des ligands des LXRs spécifique de l’isoforme, j’ai entrepris la construction d’un double système de criblage autorisant l’analyse simultanée de l’action d’une molécule sur LXRα et LXRβ. L’ensemble de ces résultats se montrent prometteurs dans la synthèse ou la découverte de molécules thérapeutique ainsi que dans l’identification d’EDCs

New models for the screening of modulators / disturbers of signal channels regulated by Liver X receptors

Les Liver X Receptors (LXRs) sont des facteurs de transcription appartenant à la superfamille des récepteurs nucléaires présents chez l’homme sous deux isoformes : LXRα et LXRβ. Ces isoformes ont des rôles redondants et spécifiques dans l’homéostasie du cholestérol, des stéroïdes et dans l’immunité. Comme d’autres récepteurs nucléaires, les LXRs sont la cible de ligands exogènes pouvant impacter leur activité. Ce phénomène est à double tranchant. D’une part, une modulation précise et spécifique des LXRs conduirait au développement de molécules thérapeutiques. D’autre part, des perturbations inappropriées des voies de signalisation LXRs mèneraient à l’identification de nouveaux Endocrine Disruptor Chemicals (EDCs). Dans le cadre de cette thèse, j’ai analysé les modalités de fixation et les activités de ligands flavonoïdes sur les LXRs. Ceci a conduit à la découverte de profils de liaison spécifiques en fonction des activités agonistes/antagonistes. J’ai également pu mettre au point un système de criblage in vivo de ligands des LXRs chez le modèle Drosophila melanogaster. Cet outil permet la discrimination de ligands agonistes par quantification optique de la fluorescence chez les larves. Dans le but de découvrir des ligands des LXRs spécifique de l’isoforme, j’ai entrepris la construction d’un double système de criblage autorisant l’analyse simultanée de l’action d’une molécule sur LXRα et LXRβ. L’ensemble de ces résultats se montrent prometteurs dans la synthèse ou la découverte de molécules thérapeutique ainsi que dans l’identification d’EDCs.Liver X Receptors (LXRs) are transcription factors among the nuclear receptors superfamily present in humans under two isoforms: LXRα and LXRβ. These isoforms have redundant and specific roles in cholesterol homeostasis, steroids, and immunity. Like other nuclear receptors, LXRs are targets of exogenous ligands that can impact their activity. This phenomenon is double-edged. On the one hand, precise and specific modulation of LXRs would lead to the development of therapeutic molecules. On the other hand, inappropriate disturbances of LXRs signaling pathways would lead to the identification of new Endocrine Disruptor Chemicals (EDCs). As part of this thesis, I analyzed the binding way and the activities of flavonoid ligands on LXRs. This led to the discovery of specific binding pattern depending on agonist/antagonist behavior. I have also been able to develop an in vivo screening system for LXRs ligands in the Drosophila melanogaster model. This tool allows the discrimination of agonist ligands by optical quantification of fluorescence in larvae. In order to discover LXRs isoforms- specific ligands, I started the construction of a double screening system allowing the simultaneous analysis of molecule activity on LXRα and LXRβ. All these results are promising in synthesis or discovery of therapeutic molecules as well as in the ECDs identification

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

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

Stress as an immunomodulator: liver X receptors maybe the answer.

International audienceStress is a reflex response, both psychological and physiological, of the body to a difficult situation that requires adaptation. Stress is at the intersection of the objective event and the subjective event. The physiological mechanisms involved in chronic stress are numerous and can contribute to a wide variety of disorders, in all systems including the immune system. Stress modifies the Th1/Th2 balance via the HPA axis and a set of immune mediators. This will make the body more vulnerable to external infections in a scientific way while others claim the opposite, stress could be considered immune stimulatory. The development of synthetic LXR ligands such as T0901317 and GW3965 as well as an understanding of the direct involvement of these receptors in the regulation of proopiomelanocortin (POMC) gene expression and indirectly by producing a variety of cytokines in a stressor response, will open in the near future new therapeutic methods against the undesirable effects of stress on the behavior of the immune system

Biological properties of propolis extracts: Something new from an ancient product.

International audienceNatural products are an interesting source of new therapeutics, especially for cancer therapy as 70% of them have botany origin. Propolis, a resinous mixture that honey bees collect and transform from tree buds, sap flows, or other botanical sources, has been used by ethnobotany and traditional practitioners as early in Egypt as 3000 BCE. Enriched in flavonoids, phenol acids and terpene derivatives, propolis has been widely used for its antibacterial, antifungal and anti-inflammatory properties. Even though it is a challenge to standardize propolis composition, chemical analyses have pointed out interesting molecules that also present anti-oxidant and anti-proliferative properties that are of interest in the field of anti-cancer therapy. This review describes the various geographical origins and compositions of propolis, and analyzes how the main compounds of propolis could modulate cell signaling. A focus is made on the putative use of propolis in prostate cancer

Ethanolic extract of Algerian propolis decreases androgen receptor transcriptional activity in cultured LNCaP cells.

Antiandrogens have a peculiar place in the treatment of metastatic prostate cancer by blocking the androgen receptor (AR). Unfortunately, aggressive tumors could rapidly develop into a castration resistant state. It is therefore essential to look for new molecules that are more effective, affecting not only the androgen signaling and with minimum undesirable effects. Natural products are an interesting source of new therapeutics, especially for cancer therapy as 70% of them have botanical origin. Based on an ethnobotany screening, we evaluated the effects of ethanolic extract of propolis (EEP) from Algeria on LNCaP cells. Results pointed out that EEP reduces the survival of LNCaP cells with an IC50 of 0.04 mg/ml, induces the apoptosis and blocks the cell cycle at G0/G1 phase. Interestingly, EEP decreased the accumulation of AR suggesting some anti-androgen activity. Indeed, secreted amount of the androgen target protein PSA was decreased when LNCaP cells were incubated with EEP, starting after 4 h of treatment. This anti-androgen activity was also shown on the androgen target genes Fkbp5 and Sgk1. Finally, the capacity of EEP to block AR functioning was demonstrated in transient transfections with human AR and the reporter gene ARE-tk-Luc. Propolis antagonizes the induction of the luciferase activity induced by the natural androgen DHT (10(-8)M) or the synthetic AR agonist R1881 (10(-7)M). Altogether, these results highlight the potential pharmacological effects of EEP in future treatments of prostate cancer

Screening for liver X receptor modulators: Where are we and for what use?

Chronic inflammation is now a well-known precursor for cancer development. Infectious prostatitis are the most common causes of prostate inflammation, but emerging evidence points the role of metabolic disorders as a potential source of cancer-related inflammation. Although the widely used treatment for prostate cancer based on androgen deprivation therapy (ADT) effectively decreases tumor size, it also causes profound alterations in immune tumor microenvironment within the prostate. Here, we demonstrate that prostates of a mouse model invalidated for nuclear receptors liver X receptors (LXRs), crucial lipid metabolism and inflammation integrators, respond in an unexpected way to androgen deprivation. Indeed, we observed profound alterations in immune cells composition, which was associated with chronic inflammation of the prostate. This was explained by the recruitment of phagocytosis-deficient macrophages leading to aberrant hyporesponse to castration. This phenotypic alteration was sufficient to allow prostatic neoplasia. Altogether, these data suggest that ADT and inflammation resulting from metabolic alterations interact to promote aberrant proliferation of epithelial prostate cells and development of neoplasia. This raises the question of the benefit of ADT for patients with metabolic disorders

New Insights in Prostate Cancer Development and Tumor Therapy: Modulation of Nuclear Receptors and the Specific Role of Liver X Receptors

Prostate cancer (PCa) incidence has been dramatically increasing these last years in westernized countries. Though localized PCa is usually treated by radical prostatectomy, androgen deprivation therapy is preferred in locally advanced disease in combination with chemotherapy. Unfortunately, PCa goes into a castration-resistant state in the vast majority of the cases, leading to questions about the molecular mechanisms involving the steroids and their respective nuclear receptors in this relapse. Interestingly, liver X receptors (LXRα/NR1H3 and LXRβ/NR1H2) have emerged as new actors in prostate physiology, beyond their historical roles of cholesterol sensors. More importantly LXRs have been proposed to be good pharmacological targets in PCa. This rational has been based on numerous experiments performed in PCa cell lines and genetic animal models pointing out that using selective liver X receptor modulators (SLiMs) could actually be a good complementary therapy in patients with a castration resistant PCa. Hence, this review is focused on the interaction among the androgen receptors (AR/NR3C4), estrogen receptors (ERα/NR3A1 and ERβ/NR3A2), and LXRs in prostate homeostasis and their putative pharmacological modulations in parallel to the patients’ support

Flavonoids differentially modulate liver X receptors activity—Structure-function relationship analysis

International audienceLiver X receptors (LXRs) α (NR1H3) and β (NR1H2) are nuclear receptors that have been involved in the regulation of many physiological processes, principally in the control of cholesterol homeostasis, as well as in the control of the cell death and proliferation balance. These receptors are thus promising therapeutic targets in various pathologies such as dyslipidemia, atherosclerosis, diabetes and/or cancers. These receptors are known to be activated by specific oxysterol compounds. The screening for LXR-specific ligands is a challenging process: indeed, these molecules should present a specificity towards each LXR-isoform. Because some natural products have significant effects in the regulation of the LXR-regulated homeostasis and are enriched in flavonoids, we have decided to test in cell culture the effects of 4 selected flavonoids (galangin, quercetin, apigenin and naringenin) on the modulation of LXR activity using double-hybrid experiments. In silico, molecular docking suggests specific binding pattern between agonistic and antagonistic molecules. Altogether, these results allow a better understanding of the ligand binding pocket of LXRα/β. They also improve our knowledge about flavonoid mechanism of action, allowing the selection and development of better LXR selective ligands

Reduction in gut‐derived MUFAs via intestinal stearoyl‐CoA desaturase 1 deletion drives susceptibility to NAFLD and hepatocarcinoma

International audienceNonalcoholic fatty liver disease (NAFLD) is defined by a set of hepatic conditions ranging from steatosis to steatohepatitis (NASH), characterized by inflammation and fibrosis, eventually predisposing to hepatocellular carcinoma (HCC). Together with fatty acids (FAs) originated from adipose lipolysis and hepatic lipogenesis, intestinal-derived FAs are major contributors of steatosis. However, the role of mono-unsaturated FAs (MUFAs) in NAFLD development is still debated. We previously established the intestinal capacity to produce MUFAs, but its consequences in hepatic functions are still unknown. Here, we aimed to determine the role of the intestinal MUFA-synthetizing enzyme stearoyl-CoA desaturase 1 (SCD1) in NAFLD. We used intestinal-specific Scd1-KO (iScd1-/- ) mice and studied hepatic dysfunction in different models of steatosis, NASH, and HCC. Intestinal-specific Scd1 deletion decreased hepatic MUFA proportion. Compared with controls, iScd1-/- mice displayed increased hepatic triglyceride accumulation and derangement in cholesterol homeostasis when fed a MUFA-deprived diet. Then, on Western diet feeding, iScd1-/- mice triggered inflammation and fibrosis compared with their wild-type littermates. Finally, intestinal-Scd1 deletion predisposed mice to liver cancer. Conclusions: Collectively, these results highlight the major importance of intestinal MUFA metabolism in maintaining hepatic functions and show that gut-derived MUFAs are protective from NASH and HCC