Team 1 : Nuclear receptors in the metabolic syndrome Team 2 : Molecular control of monocyte/ macrophage functions in cardiometabolic syndrome Team 3 : Immunoinflammation and cardiovascular diseases Team 4 : Molecular analysis of gene regulation in cardiometabolic diseases
*********** Intensive investigations in our laboratory led to position nuclear receptors as key players in the control of metabolic and inflammatory pathways implicated in atherosclerosis and cardiovascular diseases (CVDs). Indeed, over the past 4 years, we have contributed significantly to 1) demonstrate the implication of nuclear receptors in metabolic perturbations of lipid and glucose metabolism and energy homeostasis, 2) demonstrate the role of nuclear receptors in macrophage functions, in the vascular wall and 3) better understand the molecular mechanisms by which nuclear receptors modulate atherosclerosis progression, analyzing particularly their ability to regulate gene expression and integrated biological responses. Together, these studies identified nuclear receptors as potential therapeutic targets in the field of metabolic diseases and atherosclerosis, and allowed a better understanding of side effects of synthetic nuclear receptor ligands currently used in therapeutics or still in development. In spite of the progress in the knowledge of the role of nuclear receptors in atherosclerosis and CVDs, our understanding of their mode of action at the molecular level as well as their pathophysiological role in the metabolic syndrome and type 2 diabetes, two pathologies predisposing to CVDs, remains incomplete. Our research project is entitled âNuclear receptors, cardiovascular diseases and diabetesâ. It will focus on two shared and related objectives aiming at, first, understanding the contribution of nuclear receptors as regulators of the expression of key genes involved in atherosclerosis pathophysiology and, second, evaluating the therapeutic potential of potent and selective ligands for these receptors for prevention, or at least attenuation of atherosclerosis development and subsequent CVDs. In this specific context, our research objectives are as follows: - to better understand the metabolic functions of the nuclear receptors FXR, ReverbÎ± and RORÎ±, and to study other receptors which are emerging as important metabolic regulators, - to better define the molecular regulation of monocyte differentiation and macrophage functions by the nuclear receptors PPARÎł and LXRs, and the cyclin-CDK inhibitor CDKN2A p16INK4a (p16) (which we found to be expressed in macrophages), and to assess potential cross-talk mechanisms and their consequences on cardiometabolic diseases, - to extend our knowledge on the contribution of other immune cell types, besides macrophages, to atherosclerosis pathophysiology, with a particular attention on the modulation by PPARÎł of mast cell and B lymphocyte functions, - to better control nuclear receptors transcriptional cell-specific activities and use molecular approaches to validate the interest of nuclear receptors and associated cofactors as therapeutic targets.
In order to answer these questions in a coherent and integrated manner with a considerable degree of transversality, we organized the Research Unit into four interacting teams:
The research project of team 1, headed by Bart Staels (âNuclear receptors in the metabolic syndromeâ), will study the metabolic perturbations predisposing to atherosclerosis and will in particular focus on two programs. First, this team will unravel the functions of FXR in the main organs involved in lipid and glucose metabolism, namely the liver, adipose tissue, intestine and pancreas by using rodent models, human tissues, and molecular and pharmacological approaches. In parallel, it will study the role of Rev-erbÎ± and RORÎ± as regulators of energy homeostasis and transducers of circadian signals into metabolic responses. For that, it will elucidate the physiological functions of Rev-erbÎ± and RORÎ± in whole-body glucose homeostasis and in the development of insulin resistance and type 2 diabetes, it will determine the role of Rev-erbÎ± and RORÎ± in adipose tissue physiology, it will further explore the role of Rev-erbÎ± in bile acid metabolism and lipid absorption, and a potential crosstalk with FXR at the hepatic and/or intestinal levels. The team will assess the role of Rev-erbÎ± and RORÎ± in atherogenesis, and it will investigate whether Rev-erbÎ± and RORÎ± play a role in the intricate link between the circadian molecular clock and metabolic pathways. By considering atherosclerosis as an inflammatory disease, team 2 (âMolecular control of monocyte/ macrophage functions in cardiometabolic syndromeâ), headed by Giulia Chinetti, will focus its activities to increase our understanding on the role of macrophages in the development of atherosclerosis, and will be studying the implication of macrophages in metabolic disorders when infiltrating adipose tissue or the vascular wall. The specific aims of this team are, first, to unravel the influence of obesity and metabolic syndrome on monocyte function, as well as its modulation by PPARÎł. To this aim, this team will assess the influence of obesity, its associated co-morbidities and weight loss on peripheral blood mononuclear cell (PBMC) functions and, in particular, on the ability of monocytes to differentiate into alternative anti-inflammatory macrophages, and will study the influence of PPARÎł ligands (TZDs) on the promotion of alternative differentiation of monocytes from obese and/or diabetic patients and the molecular basis of inter-individual variation in response to TZD treatment. This last aspect of the study will employ a wide range of genomic and post-genomic techniques that will be developed together with team 4. The second aim is to characterize cholesterol metabolism in alternative macrophages and its regulation by PPARÎł in vitro in human macrophages, and ex-vivo in macrophages infiltrated into human atherosclerotic lesions. The third program is to study the role of LXRs and PPARÎł in the control of adipose tissue macrophage functions and the cross-talk with adipocytes. Finally, in a fourth part of the project, team 2 will study the pathophysiological functions of the PPAR-target gene p16 in macrophages with respect to atherosclerosis and metabolic diseases as well as its potential cross-talk with other nuclear receptors such as PPARs, for which we previously reported their implication in the regulation of metabolic disorders and atherosclerosis development. In vitro and in vivo approaches will be used in the project : differentiation of both human and murine monocytes into alternative or classical macrophages followed by p16 expression analysis; in close collaboration with team 4, studies on the molecular interaction of p16 with other nuclear receptors, and, thanks to the technical expertise of team 1 in the use of animal models and in vivo experimentations, performing bone marrow transplantation from p16-deficient or wild-type mice into atherosclerosis-prone or ob/ob mice, followed by treatment with specific ligands of different nuclear receptors. Besides macrophages, most of the immune cell types have been shown or are suspected to contribute to the pathophysiological process of atherosclerosis. Therefore, and building on an experience in the field of immuno-inflammation and allergic diseases and a longstanding and successful collaboration with our Unit, David Dombrowicz joined our Unit as an emerging team (Team 3) which entitled âImmunoinflammation and cardiovascular diseasesâ. His research project will relate to the contribution of the immune system to cardiometabolic diseases, and within the framework of an immunophenotyping platform, that will be developed, he will study the impact of metabolic alterations on the immune system. Particularly, the implication of mast cells and B lymphocytes in atherosclerosis development and the regulation of these cell types by PPARÎł will be analysed, using adoptive transfer of PPARÎł-deficient target cells to target cell-deficient animals, and, in order to corroborate the results obtained on animal models, in close collaboration with team 2, in blood, aortic lesions and adipose tissue from obese and diabetic patients treated or not with PPARÎł-agonists. Team 4 (âMolecular analysis of gene regulation in cardiometabolic diseasesâ), managed by Philippe Lefebvre, aims at understanding the roles and the mechanism of action of nuclear receptors and their coregulators in the metabolic disorders or the normalization of pathologic conditions related to cardiometabolic diseases. The project will be organized into four key research themes. The first one will study the mechanisms underlying the transactivating and transrepressive activities of the nuclear receptor PPARÎł, activities conditioning the normolipemic and anti-inflammatory effects, respectively, of PPARÎł ligands. In a second theme, and in coordination with team 1, the identification of the yet poorly understood molecular mechanisms of action of FXR will be studied. The identification of FXR cofactors and the definition of their specific functions, the characterization of the primary FXR transcriptional program in hepatocytes (identification of genomic FXR DNA binding sites), and the characterization of the regulation of the expression of FXR and of its coregulators in normal and pathological conditions will be carried out. In the third theme, the role of the 132-kDa Transcriptional Regulating Protein (TreP-132) in the regulation of the cell cycle by nuclear receptors, and the underlying molecular mechanisms, will be characterized, with a particular interest into its role in the development of restenosis and atherosclerosis. The objective of the fourth theme comes from previous unanticipated new roles for the nuclear orphan receptor NR4A subclass and potential novel functions in pancreatic beta-cell adaptation in response to a metabolic challenge. The identification of the molecular mechanisms controlled by NR4As in pancreas biology will be studied in vitro using rat and mouse beta-insulinoma cells and in vivo using diabetic animal models in a concerted action with team 1.
We will study the biological and molecular mechanisms controlling the development of atherosclerosis in order to develop preventive and therapeutic strategies against its cardiovascular complications, and study metabolic risk factors, such as dyslipidemia and type 2 diabetes. We will focus on the regulation of genes involved in these pathologies and on the consequences of their dysregulation, studying the molecular basis and the pathophysiological involvement of nuclear receptors, transcription factors which our Unit has been studying for several years. Four different teams will be organized around a Unit project entitled âNuclear receptors, cardiovascular diseases and diabetesâ. Team 1 (Nuclear receptors in the metabolic syndrome) will study the metabolic functions of nuclear receptors (FXR, Rev-erbÎ±, RORÎ±) and their interest as potential therapeutic targets in humans. Team 2 (Molecular control of monocyte/macrophage functions in the cardiometabolic syndrome) will focus its activities on the role of PPARÎł in peripheral blood mononuclear cells from obese subjects, and will study the role of PPARs, LXRs and the cyclin-dependent kinase inhibitor CDKN2Ap16INK4a in the molecular regulation of monocyte differentiation and macrophage functions in the vascular wall and adipose tissues during obesity. The mechanisms by which nuclear receptors control the contribution of other cells from the immune system to atherosclerosis will be studied by team 3 (Immunoinflammation and cardiovascular diseases) with a particular interest for the control by PPARÎł of mast cell and B lymphocyte functions. Team 4 (Molecular analysis of gene regulation in cardiometabolic diseases) will investigate how nuclear receptors control gene expression and affect metabolic functions, allowing the unraveling of novel regulatory pathways and the validation of nuclear receptors as pharmacological targets. Our Unit possesses all required expertise in cellular and molecular biological techniques, and benefits from comprehensive technical platforms in biochemistry and histology. The Unit has also a longstanding experience in the development and study of new animals models in particular genetically-modified mice.