Parkinson’s disease (PD) is a degressive, neurodegenerative disease that affects approximately four million people worldwide. The disease is characterized by the progressive loss of midbrain dopaminergic (DAergic) neurons, which are highly related with the motor control. As the disease progresses, movement disorders appear such as tremor, rigidity, and bradykinesia, but also disorders in speech and neuropsychiatric disturbances occur.Current therapies for PD focus on symptomatic treatment, while pharmacological methods to prevent or delay the degeneration of neurons have not been discovered yet. The Nurr1 nuclear receptor, which is expressed predominantly in the substantia nigra of the midbrain, has emerged as a target for the treatment of Parkinson’s disease due to its neuroprotective action and contribution in DAergic neuron development. It has been shown that partial loss of Nurr1 function in people due to mutations leads to neuronal death. Thus, the reinforcement of Nurr1 operation via the discovery of novel potent agonists is imperative. Unfortunately, the accomplishment of this task is complicated as Nurr1 ligand binding domain (LBD) lacks a cavity for ligand binding due to the tight packing chains from several hydrophobic amino-acids in the region normally occupied by ligands in other nuclear receptors. However, the activation of Nurr1 can be feasible through heterodimer formation with Retinoid X Receptors (RXR) and especially with RXRα, which are all capable of binding ligands and therefore, mediate Nurr1 expression in midbrain. Therefore, we seek here to identify potent binders of RXRα as a means to increase Nurr1 levels. Based on the fact that multiple RXRα receptor conformations exist depending on binding of RXRα to different heterodimerization partners, we aim to increase the specificity of identified binders for the heterodimer Nurr1/RXRα. For this purpose, we describe here a new computational protocol for the selection of RXRα receptor structures that is used to perform Structure-Based Virtual Screening (SBVS) calculations for the discovery of NURR1 activators. In our study, we developed a computational protocol, where the choice of RXRα conformations for performing the SBVS is based on four criteria: (a) Pairwise comparison of the receptor conformations according to RMSD calculations, (b) analysis and clustering of RXRα structures comparing the binding-site shape and volume using SiteMap, (c) docking of a small-database of known actives for a specific heterodimer partner to the resulting shape-diverse subset of binding sites from (a) and (b) using Glide 5.8 SP and XP, and (d) retrieving representative protein conformations for the structure of interest from MD simulations using GROMACS. Virtual Screening was performed on three different subsets of RXRα receptor conformations, based on their binding to different heterodimerization partners. The final RXRα receptors to be used in SBVS were selected as mentioned above aiming to enhance the success rate and the selectivity of the hits. The Maybridge Hitfinder and Zinc databases were used in this SBVS exercise by first applying the SP filter on the full database and then the XP filter on the top 10,000 compounds of the Maybridge database and the top 40,000 compounds of the ZINC database. Compounds were selected as follows: Molecules that scored high when docked in the RXRα protein ensemble that bind to the heterodimer partner of interest and at the same time scored low for RXRα structures that bind to heterodimer partners of no interest, were selected in order to achieve selectivity. The efficiect selection was also based on their different orientation at the binding site of the various RXRα structures and different interactions with specific surrounding residues in order to maximize their selectivity potential. Finally, a post-processing step was imposed to the top-scoring compounds by using Chembioserver and FAF-Drugs2 filtering tools as well as pharmacological property prediction with the QikProp software. In vitro agonism of these compounds is still pending experimental testing. The workflow of this protocol is shown in Fig. 1. Figure 1: SBVS protocol developed for the discovery of novel selective Nurr1/RXRα agonists. / --

The secretory phospholipase A2 (sPLA2) family is a group of enzymes that catalyze the hydrolysis of glycerophospholipids at the sn-2 position, generating free fatty acids and lysophospholipids. The sPLA2 family has been implicated in various physiological and pathological activities. Eleven sPLA2’s have been identified in mammals, and the function of each isoform likely reflects its tissue distribution and substrate specificity. Studies in vitro indicate that Group X (GX) sPLA2 potently releases arachidonic acid (AA) and lysophosphatidylcholine from mammalian cell membranes. Interestingly, some of the biological effects mediated by GX sPLA2 in vitro are independent of its catalytic activity. Despite a wealth of in vitro data, the in vivo function of GX sPLA2 still remains to be elucidated. In order to define the function of GX sPLA2 in vivo, our laboratory recently generated C57BL/6 mice with targeted deletion of GX sPLA2 (GX-/- mice). When fed a normal rodent diet, GX-/- mice gained significantly more weight and had increased adiposity compared to GX+/+ mice, which was not attributable to alterations in food consumption or energy expenditure. When treated with adipogenic stimuli ex vivo, stromal vascular cells isolated from adipose tissue of GX-/- mice accumulated significantly more (20%) triglyceride compared to cells from GX+/+ mice. Conversely, overexpression of GX sPLA2, but not catalytically inactive GX sPLA2, resulted in a significant 50% reduction in triglyceride accumulation in OP9 adipocytes. The induction of adipogenic genes, including PPAR-γ, SREBP-1c, SCD-1 and FAS was also significantly blunted by 50-80% in OP9 cells overexpressing GX sPLA2. Activation of the liver X receptor (LXR), a nuclear receptor known to upregulate adipogenic gene expression, was suppressed in 3T3-L1 and OP9 cells when GX sPLA2 was overexpressed. Thus, hydrolytic products generated by GX sPLA2 negatively regulate adipogenesis, possibly by suppressing LXR activation.

Group X secretory phospholipase A2 (GX sPLA2) hydrolyzes membrane phospholipids producing free fatty acids and lysophospholipids. Previous studies from our lab suggest that mice with targeted deletion of GX sPLA2 (GX KO) have increased age-related weight gain due to an increase in overall adiposity. Paradoxically, this increased adiposity is associated with improved age-related glucose intolerance. GX KO mice also demonstrate a reduced inflammatory response to lipopolysaccharide injection. In vitro studies indicate this phenotype may be attributable to blunted macrophage mediated inflammatory responses. Given the role of macrophages in promoting adipose tissue (AT) inflammation and metabolic dysfunction in response to diet-induced obesity, we hypothesized that GX KO mice would be protected from the obesity related metabolic derangements associated with overfeeding. Unexpectedly, GX KO mice were only partially protected from high fat (HFD) diet-induced glucose intolerance and showed no improvement in HFD-induced insulin resistance. Moreover, GX KO mice were not protected against HFD-induced AT inflammation. GX sPLA2 is produced as a proenzyme (pro-GX sPLA2), and propeptide cleavage is required for enzymatic activity. Furin-like proprotein convertases (PCs) have recently been implicated in the proteolytic activation of pro-GX sPLA2; however the identity of individual PCs involved is unclear. Previous findings from our lab have shown that GX sPLA2 is expressed in the adrenals where it regulates glucocorticoid production. GX KO mice have increased plasma corticosterone levels under both basal and ACTH-induced stress conditions. However, how GX sPLA2 is regulated in the adrenals is still uncertain. We hypothesized that PCs may be involved in the proteolytic activation of pro-GX sPLA2 in the adrenals. Here we report the novel findings that the PCs, furin and PCSK6, proteolytically activate pro-GX sPLA2 in Y1 adrenal cells. Furthermore, we demonstrate that PC dependent processing of pro-GX sPLA2 is necessary for GX sPLA2 dependent suppression of steroidogenesis. Finally, we provide evidence that pro-GX sPLA2 processing by PCs is enhanced in response to adrenocorticotropic hormone (ACTH), suggesting a novel mechanism for negatively regulating adrenal steroidogenesis. Cumulatively, these studies provide valuable insight into the function and regulation of GX sPLA2.

Pluripotent stem cells have the capacity to develop into different cell lineages and can be manipulated into certain cell types through the use of small molecule inducers. Retinoic acid (RA) signaling through retinoic acid receptors (RAR) and retinoid X receptors (RXR) has the ability to direct lineage determination but has yielded disappointing results in promoting skeletal myogenesis in embryonic stem (ES) cells. RXR is crucial in embryonic development although it is generally considered to act as a silent partner for other nuclear receptors such as RAR. Our findings demonstrate that rexinoid specific signaling enhances skeletal myogenesis and requires β-catenin but not RAR. Moreover, RXR signalling in mouse ES cells can efficiently enhance skeletal myogenesis and closely recapitulates sequential events observed in vivo. Since ES cells closely represent the properties of the developing embryo, efficiently generating skeletal muscle provides a means to further scrutinize signaling pathways in myogenic development in view of developing therapies for muscle related diseases.

The orphan nuclear receptor EAR-2 (NR2F6) is a gene that I previously found to be expressed at a higher level in clonogenic leukemia single cells than in leukemia cells that can not divide. For this thesis I undertook to perform the first investigations of the roles EAR-2 may play in normal haematopoiesis and in the pathogenesis of acute myelogenous leukaemia. Here, I show that EAR-2 is overexpressed in the bone marrow of patients with MDS, AML and CMML compared to healthy controls and that EAR-2 is a gatekeeper to hematopoietic differentiation. Over-expression of EAR-2 prevents the differentiation of cell lines, while knock down induces their spontaneous differentiation. In vitro, primary bone marrow cells that over-express EAR-2 do not differentiate into granulocytes in suspension culture, but have greatly extended replating capacity in colony assays. In vivo, overexpression of EAR-2 in a chimeric mouse model leads to a condition that resembles myelodysplastic syndrome characterised by hypercellular bone marrow, an increase in blasts, abnormal localization of immature progenitors, morphological dysplasia of the erythroid lineage and a competitive advantage over wild-type cells, that eventually leads to AML in a subset of the mice. Furthermore, animals that are transplanted with grafts of sorted bone marrow develop a rapidly fatal leukemia that is characterized by pancytopenia, enlargement of the spleen, infiltration of blasts into the spleen, liver and peripheral blood. Interestingly, development of leukemia is preceded by expansion of the stem cell compartment. Overexpression of EAR-2 increases the maintenance of KSL primitive bone marrow cells in ex vivo suspension culture, while knockdown of EAR-2 induces rapid differentiation of KSL cells into granulocytes. These data establish that EAR-2 is a novel oncogene that regulates hematopoietic cell differentiation. Furthermore, I show that EAR-2 is also a novel negative regulator of T-cell lymphopoiesis, and demonstrate that down-regulation of EAR-2 is important for the survival, proliferation and differentiation of T-cell progenitors. Overall, this work establishes that expression of EAR-2 is an important determinant of cell fate decisions in the hematopoietic system.

Nuclear Hormone Receptors (NRs) are hormone dependent DNA binding proteins that translate physiological signals into gene expression. Gene products have been identified that belong to the NR superfamily on the basis of homology. However, the endogenous and /or synthetic ligands that regulate their activity remain unknown, consequently, this subgroup of proteins are designated as orphans). Retinoic acid receptor related orphan receptors alpha and gamma(RORα and γ) are orphan NRs, and are preferentially expressed in skeletal muscle a major metabolic tissue and other tissues including pancreas, thymus, prostate, liver, adipose and testis. Surprisingly, the specific roles of ROR α and γ in skeletal muscle, a peripheral tissue, have not been examined. Muscle is one of the most energy demanding tissues which accounts for ~40% of the total body mass and energy expenditure, ~75% of glucose disposal and relies heavily on β-oxidation of fatty acids. We hypothesize that ROR α and γ regulates metabolism in this major mass lean tissue. Initially, this hypothesis was examined by “gain and loss” of function studies in an in-vitro mouse skeletal muscle cell culture model. Previous in vitro studies analyzed the role of RORα in the regulation of lipid homeostasis in skeletal muscle cells. We similarly conducted in vitro RORγ gain and loss of function studies in skeletal muscle cells to understand the role of this isoform in metabolism. We utilized stable ectopic over-expression of VP16-RORγ (gain of function), native RORγ and RORγΔH12 (loss of function) vectors to modulate RORγ mRNA expression and function. Candidate driven expression profiling of lines that ectopically express the native and variant forms of RORγ suggested that this orphan NR has a function in regulating the expression of genes that control lipid homeostasis (fatty acid-binding protein 4), CD36 (fatty acid translocase), lipoprotein lipase and uncoupling protein 3), carbohydrate metabolism (GLUT5 (fructose transporter), adiponectin receptor 2 and interleukin 15 (IL-15)) and muscle mass (including myostatin and IL-15). Interestingly, our study revealed a function for RORγ in the pathway that regulates production of reactive oxygen species which was also correlated with increased expression of UCP3 mRNA. Subsequently, we conducted in vivo studies with mouse models displaying global and muscle specific perturbation in RORα expression and function to elucidate the physiological role of this orphan NR in the context of metabolism.Along these lines, we characterized homozygous staggerer mice (sg/sg) in the context of lipid, carbohydrate and energy homeostasis. Staggerer mice were characterized by decreased and dysfunctional retinoic acid receptor-related orphan receptor alpha (RORα) expression. We observed decreases in serum (and liver) triglycerides and total and high density lipoprotein serum cholesterol in staggerer mice. Moreover, the staggerer mice were associated with reduced adiposity, decreased fat pad mass and adipocyte size. Candidate-based expression profiling demonstrated that the dyslipidemia in staggerer mice was associated with decreased hepatic expression of SREBP-1c, and the reverse cholesterol transporters, ABCA1 and ABCG1. This was consistent with the reduced serum lipids. Furthermore, the lean phenotype in staggerer mice was also characterized by significantly increased expression of PGC-1α, PGC-1β, and lipin1mRNAin liver and white and brown adipose tissue from staggerer mice. In addition, we observed a significant 4-fold increase in β2-adrenergic receptor mRNA in brown adipose tissue. Finally, dysfunctional RORα expression protects against diet-induced obesity. Following a 10-week high fat diet, wild-type (but not sg/sg) mice exhibited a ~20% weight gain, increased hepatic triglycerides, and notable white and brown adipose tissue accumulation. In summary, these changes in gene expression (that modulate lipid homeostasis) in metabolic tissues were involved in decreased adiposity and resistance to diet induced obesity in the sg/sg mice, despite hyperphagia. Finally, we specifically modulated RORα signaling in skeletal muscle by the targeted over-expression of truncated RORαΔDE (lacking the ligand binding domain) driven by a myogenic specific promoter, to investigate the contribution of this peripheral tissue to the RORα phenotype. Interestingly, transgenic heterozygous animals exhibit increased fasting blood glucose levels and mild glucose intolerance. Expression profiling (and western analysis) identified perturbations in the insulin signaling cascade. For example, we observed attenuation of p85alpha (PI3K) and Akt2 (mRNA and protein) expression; and insulin dependent induction of phospho-Akt2. In concordance, significantly increased levels of active phospho-AMPK were detected in the muscle of transgenic mice (relative to wt littermates). The increase in phospho-AMPK correlated with: (i) the suppression of lipogenic gene expression; and (ii) increased phospho-ACC and activation of genes involved in fatty acid oxidation in the skeletal muscle of transgenic animals. In conclusion, we suggest these orphan nuclear receptors (RORα and γ) are key modulators of fat and carbohydrate homeostasis in skeletal muscle tissue. Specifically, we propose that, RORα plays vital role in fat accumulation in adipose tissue and insulin mediated glucose homeostasis in skeletal muscle. Therefore we suggest that selective muscle specific RORα modulators may have utility in the treatment of type2 diabetes and obesity.

Os PPARs são fatores de transcrição ativados por ligantes, pertencentes à superfamília dos receptores nucleares, que são considerados sensores de lipídeos capazes de transformar alterações nos padrões de lipídeos/ácidos graxos dos organismos em atividade metabólica. Com isto, os 3 isotipos (α, δ e γ) estão associados a diferentes desordens metabólicas como doenças vasculares, diabetes, obesidade, câncer e certas doenças mentais que constituem um grave problema de saúde pública mundial, o que torna esta classe de proteínas, um valioso alvo para a indústria farmacêutica. Embora a importância do hPPARδ na regulação da transcrição de genes relacionados a uma série de processos metabólicos seja conhecida, não há ainda nenhum fármaco no mercado cujo alvo seja este receptor. O maior conhecimento a respeito da estrutura deste receptor pode trazer esclarecimentos capazes de auxiliar o desenvolvimento racional de fármacos. Desta forma, no presente trabalho, buscou-se encontrar características estruturais importantes para a seletividade e especificidade dos ligantes pelo isotipo δ. Para tal, determinou-se as condições de expressão e purificação da proteína hPPARδ LBD, bem como as condições apropriadas de manutenção da mesma por meio da técnica de dicroísmo circular. O estado oligomérico deste receptor foi determinado em solução através das técnicas de cromatografia por exclusão de tamanho e por espalhamento dinâmico de luz, onde se concluiu que a proteína é monomérica nas condições testadas. Além disto, através de uma estrutura de alta resolução da proteína hPPARδ LBD com o ligante GW 0742, propôs-se a construção de dois mutantes, V312M e I328M, através dos quais concluiu-se que estes dois resíduos são potencialmente importantes para interação de ligantes estruturalmente relacionados com GW 0742, ao isotipo δ, indicando dois determinantes relacionados à seletividade de ligantes por este isotipo. Como existem poucos relatos sobre a estrutura completa deste receptor, e consequentemente da influência que os domínios N-terminal e DBD apresentam sobre o domínio LBD, um breve estudo da interação diferencial entre o receptor nuclear hPPARδ Full e três diferentes cofatores, em presença de ligante agonista e antagonista foi realizado. Para isto, determinou-se as condições de expressão e purificação da proteína hPPARδ Full, e prosseguiu-se com ensaios de anisotropia de fluorescência, através dos quais ficou claro que cada cofator apresenta um padrão diferente de interação com a proteína que pode ser dependente de outras regiões da proteína além daquelas já classicamente descritas. Isto é um forte indicativo de que diferentes regiões do hPPARδ podem ser chave no processo de regulação por intermédio de cofatores. / PPARs are transcription factors activated by ligands, belonging to the superfamily of nuclear receptors, which are considered to be lipid sensors capable of making changes in patterns of lipid/fatty acid metabolic activity of organisms. The three isotypes (α, δ and γ) are associated with different metabolic disorders and vascular diseases as diabetes, obesity, cancer and certain mental illnesses which comprise a serious worldwide public health problem, making this class of proteins a valuable target for the pharmaceutical industry. Although it is known the importance of hPPARδ in regulating transcription of genes related to a series of metabolic processes, there is still no drug on the market directed to this receptor. Knowledge about the structure of this receptor can bring clarification able to assist the rational development of drugs. Therefore, in the present study, we sought to find structural features important for selectivity and specificity of ligand binding by the isotype δ. To this end, we determined the conditions of expression and purification of the protein hPPARδ LBD, as well as the appropriate conditions for maintaining it through the technique of circular dichroism. The oligomeric state of this receptor in solution was determined through the techniques of size exclusion chromatography and dynamic light scattering, which concluded that the protein is monomeric under the conditions tested. In addition, through a high-resolution structure of the protein hPPARδ LBD with the ligand GW 0742, we proposed the construction of two mutants, V312M and I328M, through which it was concluded that these two residues are potentially important for interaction of ligands structurally related to GW 0742 with the δ isotype. As there are few reports based on the complete structure of this receptor, and consequently about the influence of the N-terminal and DBD domains with the LBD domain, a brief study of the interaction between the nuclear receptor differential hPPARδ Full and three different cofactors in the presence of agonist and antagonist ligands were performed. For this, we determined the conditions of expression and purification of the protein hPPARδ Full, and using fluorescence anisotropy, it became clear that each cofactor has a different pattern of interaction with the protein which may be dependent on other regions of the protein in addition to those already described classically. This is a strong indication that different regions of hPPARδ can be key points in the regulatory process through cofactors.

Chez les patients diabétiques, le flux hépatique du glucose est perturbé affectant les voies qui lui sont associées telle que la voie de biosynthèse des hexosamines (HBP). Cette voie permet la production d’UDP-GlcNAc à partir du glucose. Ce substrat est engagé dans une modification post-traductionnelle (PTM) réversible des protéines appelée O-GlcNAcylation. Elle consiste à transférer du GlcNAc à partir d’UDP-GlcNAc sur un résidu serine ou thréonine. Une O-GlcNAcylation anormale des protéines contribue à la glucotoxicité hépatique et au diabète de type 2. FXR (Farnesoid X Receptor), un récepteur nucléaire fortement exprimé dans le foie, contrôle le métabolisme des acides biliaires ainsi que l'homéostasie glucidique et lipidique. Après son activation par un ligand et son hétérodimérisaton avec RXR (Retinoid X Receptor), FXR régule la transcription de gènes cibles en se fixant sur ses éléments de réponse. L’expression génique de FXR est augmentée dans des modèles animaux de diabète et ses activités transcriptionnelles en font une cible thérapeutique potentielle dans le contrôle des troubles métaboliques. Considérant ces informations, nous avons émis l’hypothèse que FXR est un substrat de la HBP et que les variations des flux hépatiques de glucose affectent son activité transcriptionnelle. Nous avons démontré, par différentes techniques, que FXR est O-GlcNAcylé in vitro et in vivo et que le glucose augmente sa fixation sur ces éléments de réponse et son activité transcriptionnelle. En outre, nous avons montré que l’inhibition de la voie HBP diminue l’expression génique et protéique de FXR mais également que la sérine 62 joue un rôle important dans la MPT de ce récepteur nucléaire. En conclusion, nos résultats montrent que le récepteur nucléaire FXR est sensible aux variations hépatiques des flux de glucose et que la O-GlcNAcylation de FXR augmente son activité transcriptionnelle ainsi que son expression génique et protéique dans différents modèles hépatiques humains et murins. / In diabetic patients, hepatic glucose flux is disrupted affecting associated pathways such as the hexosamine biosynthesis pathway (HBP). This pathway allows the production of UDP-GlcNAc from glucose. This substrate is engaged in a reversible post-translational modification (PTM) of proteins called O-GlcNAcylation. This PTM involves the transfer of GlcNAc from UDP-GlcNAc to serine or threonine residue of proteins. Abnormal O-GlcNAcylation of proteins contributes to liver glucotoxicity and type 2 diabetes. FXR (Farnesoid X Receptor), a nuclear receptor highly expressed in the liver controls the bile acids metabolism, glucose and lipid homeostasis. After its activation by ligand and its hétérodimérisaton with RXR (Retinoid X Receptor), FXR regulates the transcription of target genes by binding to its response elements. The FXR gene expression is increased in diabetes animal models and its transcriptional activities are a potential therapeutic target in the control of metabolic disorders. Considering this information, we hypothesized that FXR is a substrate of HBP and variations of hepatic glucose flux affect its transcriptional activity. We have demonstrated by many experiments that FXR is O-GlcNAcylated both in vitro and in vivo and glucose increases its binding to its response elements and its transcriptional activity. In addition, we have shown that the inhibition of HBP decreases FXR gene and protein expression. We demonstrated also that the serine 62 plays an important role in the PTM of this nuclear receptor. In conclusion, our results show that FXR is sensitive to variations of hepatic glucose flux and that the O-GlcNAcylation of FXR increases its transcriptional activity and its gene and protein expression in different human and mouse liver models.

Pluripotent stem cells have the capacity to develop into different cell lineages and can be manipulated into certain cell types through the use of small molecule inducers. Retinoic acid (RA) signaling through retinoic acid receptors (RAR) and retinoid X receptors (RXR) has the ability to direct lineage determination but has yielded disappointing results in promoting skeletal myogenesis in embryonic stem (ES) cells. RXR is crucial in embryonic development although it is generally considered to act as a silent partner for other nuclear receptors such as RAR. Our findings demonstrate that rexinoid specific signaling enhances skeletal myogenesis and requires β-catenin but not RAR. Moreover, RXR signalling in mouse ES cells can efficiently enhance skeletal myogenesis and closely recapitulates sequential events observed in vivo. Since ES cells closely represent the properties of the developing embryo, efficiently generating skeletal muscle provides a means to further scrutinize signaling pathways in myogenic development in view of developing therapies for muscle related diseases.

No description available.