Thyroid hormone receptor {beta} (TR{beta}) and liver X receptor (LXR) regulate carbohydrate response element binding protein (ChREBP) expression in a tissue selective manner.

Thyroid hormone- (TR) and Liver X- (LXR)receptors are transcription factors involved in lipogenesis. Both receptors recognize the same consensus DNA response element in vitro. It was previously shown that their signalling pathways interact in the control of cholesterol elimination in the liver. In the present study ChREBP, a major transcription factor controlling the activation of glucose-induced lipogenesis in liver, is characterized as a direct target of thyroid hormones(TH) in liver and white adipose tissue(WAT), the two main lipogenic tissues in mice. Using genetic and molecular approaches ChREBP is shown to be specifically regulated by TRbeta, but not by TRalpha in vivo even in WAT where both TR isoforms are expressed. However this isotype specificity is not found in vitro. This TRbeta specific regulation correlates with the loss of TH-induced lipogenesis in TRbeta-/- mice. Fasting/refeeding experiments show that TRbeta is not required for the activation of ChREBP expression particularly marked in WAT following refeeding. However TH can stimulate ChREBP expression in WAT even under fasting conditions suggesting completely independent pathways. Since ChREBP has been described as an LXR target, the interaction of LXR and TRbeta in ChREBP regulation was assayed both in vitro and in vivo. Each receptor recognizes a different response element on the ChREBP promoter, located only eight base pairs apart.There is a crosstalk between LXR and TRbeta signalling on the ChREBP promoter in liver but not in WAT where LXR does not regulate ChREBP expression. The molecular basis for this crosstalk has been determined in in vitro systems

Thyroid hormones and metabolic disorders

Les hormones thyroïdiennes jouent un rôle dans de nombreux processus métabolique tels que le développement, la croissance et le contrôle du métabolisme. Les HT se fixent sur leurs récepteurs nucléaires, les TR (TRalpha et beta). Ces TR sont des facteurs de transcription dont l’activité est contrôlée par la fixation de leur ligand, ils appartiennent à la super famille des récepteurs nucléaires d’hormone. Au cours de ma thèse je me suis intéressée aux rôles des TR dans deux contextes particuliers. Dans un premier temps, j’ai pu mettre en évidence le rôle de TRbeta dans la régulation du métabolisme hépatique via l’activation d’un gène clé ChREBP permettant la détection du glucose. Par l’utilisation d’animaux transgéniques et des systèmes in vitro, j’ai pu montrer que TRbeta régule positivement l’expression de ChREBP via le fixation sur son élément de réponse présent de le promoteur. Nous avons pu montrer que cette activation est isoforme spécifique, indépendante d’un autre récepteur nucléaire LXR. Dans un deuxième temps, j’ai montré que l’autre isoforme de TR, TRalpha est impliqué dans le développement de l’athérosclérose, une maladie cardiovasculaire. Par l’utilisation d’un modèle de souris transgénique, j’ai pu mettre en évidence que TRalpha possède à la fois un rôle anti-inflammatoire et également il est capable de stimuler l’élimination du cholestérol par les macrophages. L’absence de ce récepteur induit une augmentation du développement de la maladie ainsi que des cytokines circulantes chez la souris. Par l’utilisation d’un système in vitro, j’ai pu mettre en évidence que l’absence de TRalpha diminue l’efflux de cholestérol dans les macrophages de souris. Ces données suggèrent un nouveau rôle des HT/TR dans le développement de pathologies humaines, notamment un effet anti-inflammatoire longtemps supposer mais mis en évidence que très récemment.Thyroid hormones (TH) play a role in many processes such as development, growth and metabolic control. HT bind to their nuclear receptors, the TR (TRalpha and beta). TRs belong to the superfamily of nuclear hormone receptors. These TRs are transcription factors whose activity is controlled by the binding of their ligand. During my PhD thesis I focused on the roles of TR in two contexts. Initially, I highlighted the role of TRbeta in the regulation of the hepatic metabolism via the activation of the key gene ChREBP, a glucose-responsive transcription factor. Using transgenic animal models and in vitro systems, I showed that TRbeta up regulates the expression of ChREBP via binding to its response element present in the promoter. I have shown that this activation is isoform specific and independent of another nuclear receptor LXR. In a second part, I demonstrated that the TRalpha isoform is involved in the development of atherosclerosis, a cardiovascular disease. Using a transgenic mice model, I observed that TRalpha has an anti-inflammatory effect and it is also able to stimulate the reverse cholesterol transport by macrophages. The absence of this receptor induces an increase in the development of the disease as well as in the level of circulating cytokines in mice. The deletion of TRalpha decreases the cholesterol efflux in bone marrow derived macrophages in vitro and it is correlated with a decrease of ABCA1 expression. All these data suggest a novel role of HT / TR in the development of human pathologies, including an anti-inflammatory role assumed, but recently demonstrated

Hormones thyroïdiennes et désordres métaboliques

Les hormones thyroïdiennes jouent un rôle dans de nombreux processus métabolique tels que le développement, la croissance et le contrôle du métabolisme. Les HT se fixent sur leurs récepteurs nucléaires, les TR (TRalpha et beta). Ces TR sont des facteurs de transcription dont l activité est contrôlée par la fixation de leur ligand, ils appartiennent à la super famille des récepteurs nucléaires d hormone. Au cours de ma thèse je me suis intéressée aux rôles des TR dans deux contextes particuliers. Dans un premier temps, j ai pu mettre en évidence le rôle de TRbeta dans la régulation du métabolisme hépatique via l activation d un gène clé ChREBP permettant la détection du glucose. Par l utilisation d animaux transgéniques et des systèmes in vitro, j ai pu montrer que TRbeta régule positivement l expression de ChREBP via le fixation sur son élément de réponse présent de le promoteur. Nous avons pu montrer que cette activation est isoforme spécifique, indépendante d un autre récepteur nucléaire LXR. Dans un deuxième temps, j ai montré que l autre isoforme de TR, TRalpha est impliqué dans le développement de l athérosclérose, une maladie cardiovasculaire. Par l utilisation d un modèle de souris transgénique, j ai pu mettre en évidence que TRalpha possède à la fois un rôle anti-inflammatoire et également il est capable de stimuler l élimination du cholestérol par les macrophages. L absence de ce récepteur induit une augmentation du développement de la maladie ainsi que des cytokines circulantes chez la souris. Par l utilisation d un système in vitro, j ai pu mettre en évidence que l absence de TRalpha diminue l efflux de cholestérol dans les macrophages de souris. Ces données suggèrent un nouveau rôle des HT/TR dans le développement de pathologies humaines, notamment un effet anti-inflammatoire longtemps supposer mais mis en évidence que très récemment.Thyroid hormones (TH) play a role in many processes such as development, growth and metabolic control. HT bind to their nuclear receptors, the TR (TRalpha and beta). TRs belong to the superfamily of nuclear hormone receptors. These TRs are transcription factors whose activity is controlled by the binding of their ligand. During my PhD thesis I focused on the roles of TR in two contexts. Initially, I highlighted the role of TRbeta in the regulation of the hepatic metabolism via the activation of the key gene ChREBP, a glucose-responsive transcription factor. Using transgenic animal models and in vitro systems, I showed that TRbeta up regulates the expression of ChREBP via binding to its response element present in the promoter. I have shown that this activation is isoform specific and independent of another nuclear receptor LXR. In a second part, I demonstrated that the TRalpha isoform is involved in the development of atherosclerosis, a cardiovascular disease. Using a transgenic mice model, I observed that TRalpha has an anti-inflammatory effect and it is also able to stimulate the reverse cholesterol transport by macrophages. The absence of this receptor induces an increase in the development of the disease as well as in the level of circulating cytokines in mice. The deletion of TRalpha decreases the cholesterol efflux in bone marrow derived macrophages in vitro and it is correlated with a decrease of ABCA1 expression. All these data suggest a novel role of HT / TR in the development of human pathologies, including an anti-inflammatory role assumed, but recently demonstrated.LYON-ENS Sciences (693872304) / SudocSudocFranceF

Inhibition of RORα/γ suppresses atherosclerosis via inhibition of both cholesterol absorption and inflammation

Objective: Cardiovascular diseases (CVDs) are the leading cause of mortality in Western countries. Atherosclerosis is a multi-step inflammatory disease characterized at early stages by accumulation of cholesterol in the arterial wall followed by recruitment of immune cells. We sought to determine if pharmacological suppression of RORα/γ activity is beneficial in treatment of atherosclerosis. Methods: To identify the role of RORα and RORγ in atherosclerosis, we used the LDL-R−/− mouse model of atherosclerosis placed on a high cholesterol diet treated with SR1001, a RORα/γ inverse agonist, for four weeks. Results: Our results demonstrate that treatment with the ROR inverse agonist substantially decreases plaque formation in vivo. The mechanism of the anti-atherogenic activity of the inhibition of RORα/γ activity appeared to be due to targeting two distinct pathways. SR1001 treatment reduced plasma low density lipoprotein (LDL) level without affecting high density lipoprotein (HDL) via increasing intestinal cholesterol excretion. Treatment with SR1001 also induced an anti-atherogenic immune profile that was characterized by a reduction in Th17 cells and an increase in Treg and Th2 cells. Our data suggest that RORα and RORγ play a critical role in atherosclerosis development by regulating at least two major pathways important in the pathology of this disease: cholesterol flux and inflammation. Conclusion: Our data suggest that pharmacological targeting of RORα/γ may be an effective method for treatment of atherosclerosis offering a distinct mechanism of action relative to statins. Keywords: Drug discovery, Nuclear receptor, Atherosclerosis, Cholesterol, Heart disease, RO

Metabolic Characterization of a Novel RORα Knockout Mouse Model without Ataxia

The retinoic acid receptor-related receptor α (RORα) is a nuclear receptor that plays an important role in regulation of metabolism and the immune system. Genetic deletion of the receptor yields mice with significant cerebellar developmental issues associated with severe ataxia. Although many metabolic studies have been performed in these models, the impaired locomotor activity of these mice is known to affect their normal mobility and feeding behaviors. This creates some difficulty in interpretation of the role of RORα in models of metabolic disease where feeding and muscle function is a critical component of the pathophysiology. We generated a mouse with a floxed Rora allele that we crossed with a mouse line expressing Cre recombinase under the control of the EIIa promoter to obtain a full body deletion of Rora. This cross led to a partial deletion of the Rora locus likely due to mosaic expression of the EIIa-Cre transgene. These mice lack any signs of ataxia but display an improved metabolic profile relative to normal WT mice. The mice were resistant to diet- and age-induced metabolic syndrome and exhibited improved glucose tolerance and increased insulin sensitivity. Decreased RORα expression in the mice was also associated with reduced inflammation in models of metabolic syndrome. These data indicate that suppression of RORα activity improves metabolic function and reduces inflammation

Role of thyroid hormone receptor TRalpha in atherosclerosis development

International audienceCardiovascular (CV) diseases including atherosclerosis are the leading cause of death in western countries. High level blood cholesterol is sufficient to drive atherosclerosis development in both human and mouse experimental models. Thyroid hormone (T3) modulates cholesterolemia and blood pressure: high T3 level delays atherosclerosis progression in humans. T3 action is mediated by transcription factors the Thyroid Hormone Receptors encoded by two different genes TRalpha and TRbeta. TRalpha is clearly the key player for T3 regulation of cholesterol level. In the present study our goal was to assess whether T3 and TR are involved in the development of atherosclerosis independently of their role in modifying the lipid profile. We took the genetic approach and introduced the TRalpha 0/0 mutation, abrogating TRalpha expression, in the classic ApoE KO model. TRalpha is highly expressed in the aorta and TRalpha mice have normal serum cholesterol levels. TRalpha ApoE mice have been fed either a western style (HFD) or a chow diet and were analyzed for atherosclerosis development over a 30 weeks period. Lipid profiles have been established and plaque formation was followed using high-resolution ultrasound echography. TRalpha ApoE mice exhibit a much more rapid development of plaques despite a better lipid profile than ApoE mice and a clear resistance to HFD induced obesity. Bone graft experiments showed that the TRalpha bone marrow compartment is largely responsible for atherosclerosis. In conclusion TRalpha participates to the T3 protective effect against CVD and deregulation of TRalpha expression predisposes mice to atherosclerosis without negatively modifying their lipid profile

Investigating the Environmental Survival of Marteilia refringens, a Marine Protozoan Parasite of the Flat Oyster Ostrea edulis, Through an Environmental DNA and Microscopy-Based Approach

Outside-host parasite survival is a key parameter to better understand disease mechanisms, especially for marine pathogens transmitted from one host to another through an environmental stage. For non-cultivable micro-parasites like Marteilia refringens, a protozoan parasite infecting the flat oyster Ostrea edulis, investigating this parameter requires innovative approaches. In the present study, we have developed an Environmental DNA (eDNA)-based method allowing detecting and quantifying up to 25 and 10 parasites DNA in seawater and sediment, respectively. This method was used in combination with light and transmission electron microscopy (TEM) to study experimentally parasite survival in seawater and flat oyster faeces after its release from naturally infected oysters. M. refringens DNA could be detected up to 20 days, in both seawater and oyster faeces with a more stable detection over time in the latter. Light and transmission microscopy confirm that parasites leaving flat oysters are sporangia. We also observed a membrane dissolution of the sporangia over time that could indicate the release of parasite spore. This study not only improves our understanding of M. refringens ecology but also highlights the interest to combine molecular and microscopical analysis to study non-cultivable micro-parasites life cycle outside their host

Novel pH-sensitive probes with a ratiometric detection for intracellular pH

International audienceThe development of new pH-sensitive fluorescent probes based on a push-pull architecture is presented with a 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofurane as strong electron acceptor group. With a small structural change, it is possible to obtain a large range of phenolic pKa from 4.8 to 8.6 with some close to neutrality, underlining the role of the electron density modulation on the acidic properties. Remarkable changes in the optical properties (both absorption and fluorescence) were observed as a function of the pH. Ratiometric imaging of intracellular pH was carried out with the most promising probes and highlighted the possibility to distinguish near-neutral minor pH fluctuations in cells