Deciphering the molecular function of the estrogen receptor a in fat metabolism

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Reproduction is an energetically costly process with profound effects on fat metabolism, the major form of energy source in wild and domestic animals. In mammals, the ovarian sex hormone 17b-estradiol (E2) has major roles in both the control of reproductive functions and in the regulation of lipid and glucose homeostasis. For example, ovariectomy in mice causes a significant redistribution of lipid storage and an increase in fat mass. Conversely, E2 treatment restores normal fat metabolism in mice with reproductive deficiency. These effects of E2 in fat tissues are mediated by the oestrogen receptor a (ERa), a ligand-dependent transcription factor expressed in both adipose and reproductive tissues. Interestingly, many environnemental contaminants (called endocrine disrupting chemicals (EDCs)) have the potential to act as ERa agonists or antagonists, potentially affecting fat metabolism. On the other hand, adipose tissues also play an important role in the regulation of the reproductive axis by secreting bioactive peptides such as adipokines. Thus, the redundancy in E2 signalling pathways between reproductive functions and fat metabolism are of major interest for the understanding of the interplay between energy regulation and reproductive fitness. The main objective of this research program is to establish the role of ERa in fat metabolism and explore the mechanisms by which E2 and estrogenic and antiestrogenic EDCs regulates gene expression in adipose tissues. We will test the hypothesis that ERa is an essential regulator in directing adipose cell-type-specific gene expression program and a modulator of fat cell function during the reproductive cycle. The two specific objectives are: (1) to explore the role of ERa in the establishment of specific transcriptional programs in adipose tissue during estrous cycle, and (2) to examine the impact of EDCs with estrogenic and anti-estrogenic activity on ERa signalling in fat tissues. We will first explore the morphology and determine the key physiological features of the adipose tissue in ERa depleted female mice as compared to their wild-type (WT) counterpart. We will undertake genome-wide transcriptomic analysis of the effects of ERa deletion in the adipose tissue during the estrous cycle in mice using RNA-seq technology. This will be followed by ChIP-seq analysis to identify the ERa binding sites in WT adipose tissue. For the second objective, we will determine whether specifics EDCs interfere with ERa signalling in fat tissues and how this affect adipose tissues phenotype. We will first evaluate the impact of different EDCs on ERa activity in adipose tissue using a mouse model that endogenously express the luciferase reporter gene under the control of a promoter containing an estrogen responsive element (ERE). EDCs found to modulate ERa function will be further investigated with a more in-depth physiological and molecular analysis of fat tissue. These experiments will include stereological examination of the adipocytes and specific measurements of endocrine parameters. Moreover, we will also investigate the molecular effects of EDCs on the regulation of ERa target genes identified in the objective 1, using RT-qPCR and ChIP assays in adipocytes. Overall, we propose a novel and comprehensive investigation, using multiple models and techniques to determine the molecular mechanisms by which a reproductive hormone such as E2 regulates fat metabolism in animals and how EDCs may interfere in this physiological pathway to affect reproductive fitness.