The tissue-specific effects of different 17β-estradiol doses reveal the key sensitizing role of AF1 domain in ERα activity

Membrane estrogen receptor α signaling modulates the sensitivity to estradiol treatment in a dose- and tissue- dependent manner

Estradiol (E2) affects both reproductive and non-reproductive tissues, and the sensitivity to different doses of E2 varies between tissues. Membrane estrogen receptor α (mERα)-initiated signaling plays a tissue-specific role in mediating E2 effects, however, it is unclear if mERα signaling modulates E2 sensitivity. To determine this, we treated ovariectomized C451A females, lacking mERα signaling, and wildtype (WT) littermates with physiological (0.05 μg/mouse/day (low); 0.6 μg/mouse/day (medium)) or supraphysiological (6 μg/mouse/day (high)) doses of E2 (17β-estradiol-3-benzoate) for three weeks. Low-dose treatment increased uterus weight in WT, but not C451A mice, while non-reproductive tissues (gonadal fat, thymus, trabecular and cortical bone) were unaffected in both genotypes. Medium-dose treatment increased uterus weight and bone mass and decreased thymus and gonadal fat weights in WT mice. Uterus weight was also increased in C451A mice, but the response was significantly attenuated (- 85%) compared to WT mice, and no effects were triggered in non-reproductive tissues. High-dose treatment effects in thymus and trabecular bone were significantly blunted (- 34% and - 64%, respectively) in C451A compared to WT mice, and responses in cortical bone and gonadal fat were similar between genotypes. Interestingly, the high dose effect in uterus was enhanced (+ 26%) in C451A compared to WT mice. In conclusion, loss of mERα signaling reduces the sensitivity to physiological E2 treatment in both non-reproductive tissues and uterus. Furthermore, the E2 effect after high-dose treatment in uterus is enhanced in the absence of mERα, suggesting a protective effect of mERα signaling in this tissue against supraphysiological E2 levels.

The different natural estrogens promote endothelial healing through distinct cell targets

The main estrogen, 17β-estradiol (E2), exerts several beneficial vascular actions through estrogen receptor α (ERα) in endothelial cells. However, the impact of other natural estrogens such as estriol (E3) and estetrol (E4) on arteries remains poorly described. In the present study, we report the effects of E3 and E4 on endothelial healing after carotid artery injuries in vivo. After endovascular injury, which preserves smooth muscle cells (SMCs), E2, E3, and E4 equally stimulated reendothelialization. By contrast, only E2 and E3 accelerated endothelial healing after perivascular injury that destroys both endothelial cells and SMCs, suggesting an important role of this latter cell type in E4's action, which was confirmed using Cre/lox mice inactivating ERα in SMCs. In addition, E4 mediated its effects independently of ERα membrane-initiated signaling, in contrast with E2. Consistently, RNA sequencing analysis revealed that transcriptomic and cellular signatures in response to E4 profoundly differed from those of E2. Thus, whereas acceleration of endothelial healing by estrogens had been viewed as entirely dependent on endothelial ERα, these results highlight the very specific pharmacological profile of the natural estrogen E4, revealing the importance of dialogue between SMCs and endothelial cells in its arterial protection.

Targeting androgen signaling in ILC2s protects from IL-33-driven lung inflammation, independently of KLRG1

BACKGROUND

Allergic asthma is more severe and frequent in women than in men. In male mice, androgens negatively control group 2 innate lymphoid cell (ILC2) development and function by yet unknown mechanisms.

OBJECTIVES

We sought to investigate the impact of androgen on ILC2 homeostasis and IL-33-mediated inflammation in female lungs. We evaluated the role of androgen receptor (AR) signaling and the contribution of the putative inhibitory receptor killer cell lectin-like receptor G1 (KLRG1).

METHODS

Subcutaneous pellets mimicking physiological levels of androgen were used to treat female mice together with mice expressing a reporter enzyme under the control of androgen response elements and mixed bone marrow chimeras to assess the cell-intrinsic role of AR activation within ILC2s. We generated KLRG1-deficient mice.

RESULTS

We established that lung ILC2s express a functionally active AR that can be in vivo targeted with exogenous androgens to negatively control ILC2 homeostasis, proliferation, and function. Androgen signaling upregulated KLRG1 on ILC2s, which inhibited their proliferation on E-cadherin interaction. Despite evidence that KLRG1 impaired the competitive fitness of lung ILC2s during inflammation, KLRG1 deficiency neither alters in vivo ILC2 numbers and functions, nor did it lead to hyperactive ILC2s in either sexes.

CONCLUSIONS

AR agonists can be used in vivo to inhibit ILC2 homeostatic numbers and ILC2-dependent lung inflammation through cell-intrinsic AR activation. Although androgen signals in ILC2s to upregulate KLRG1, we demonstrate that KLRG1 is dispensable for androgen-mediated inhibition of pulmonary ILC2s.

Segregation of nuclear and membrane-initiated actions of estrogen receptor using genetically modified animals and pharmacological tools

Estrogen receptor alpha (ERα) and beta (ERβ) are members of the nuclear receptor superfamily, playing widespread functions in reproductive and non-reproductive tissues. Beside the canonical function of ERs as nuclear receptors, in this review, we summarize our current understanding of extra-nuclear, membrane-initiated functions of ERs with a specific focus on ERα. Over the last decade, in vivo evidence has accumulated to demonstrate the physiological relevance of this ERα membrane-initiated-signaling from mouse models to selective pharmacological tools. Finally, we discuss the perspectives and future challenges opened by the integration of extra-nuclear ERα signaling in physiology and pathology of estrogens.

The extra-nuclear interactome of the estrogen receptors: implications for physiological functions

Over the last decades, a great body of evidence has defined a novel view of the cellular mechanism of action of the steroid hormone 17β-estradiol (E2) through its estrogen receptors (i.e., ERα and ERβ). It is now clear that the E2-activated ERs work both as transcription factors and extra-nuclear plasma membrane-localized receptors. The activation of a plethora of signal transduction cascades follows the E2-dependent engagement of plasma membrane-localized ERs and is required for the coordination of gene expression, which ultimately controls the occurrence of the pleiotropic effects of E2. The definition of the molecular mechanisms by which the ERs locate at the cell surface (i.e., palmitoylation and protein association) determined the quest for understanding the specificity of the extra-nuclear E2 signaling. The use of mice models lacking the plasma membrane ERα localization unveiled that the extra-nuclear E2 signaling is operational in vivo but tissue-specific. However, the underlying molecular details for such ERs signaling diversity in the perspective of the E2 physiological functions in the different cellular contexts are still not understood. Therefore, to gain insights into the tissue specificity of the extra-nuclear E2 signaling to physiological functions, here we reviewed the known ERs extra-nuclear interactors and tried to extrapolate from available databases the ERα and ERβ extra-nuclear interactomes. Based on literature data, it is possible to conclude that by specifically binding to extra-nuclear localized proteins in different sub-cellular compartments, the ERs fine-tune their molecular activities. Moreover, we report that the context-dependent diversity of the ERs-mediated extra-nuclear E2 actions can be ascribed to the great flexibility of the physical structures of ERs and the spatial-temporal organization of the logistics of the cells (i.e., the endocytic compartments). Finally, we provide lists of proteins belonging to the potential ERα and ERβ extra-nuclear interactomes and propose that the systematic experimental definition of the ERs extra-nuclear interactomes in different tissues represents the next step for the research in the ERs field. Such characterization will be fundamental for the identification of novel druggable targets for the innovative treatment of ERs-related diseases.

Estrogen receptor-α signaling in post-natal mammary development and breast cancers

17β-estradiol controls post-natal mammary gland development and exerts its effects through Estrogen Receptor ERα, a member of the nuclear receptor family. ERα is also critical for breast cancer progression and remains a central therapeutic target for hormone-dependent breast cancers. In this review, we summarize the current understanding of the complex ERα signaling pathways that involve either classical nuclear “genomic” or membrane “non-genomic” actions and regulate in concert with other hormones the different stages of mammary development. We describe the cellular and molecular features of the luminal cell lineage expressing ERα and provide an overview of the transgenic mouse models impacting ERα signaling, highlighting the pivotal role of ERα in mammary gland morphogenesis and function and its implication in the tumorigenic processes. Finally, we describe the main features of the ERα-positive luminal breast cancers and their modeling in mice.

A Tale of Ice and Fire: The Dual Role for 17β-Estradiol in Balancing DNA Damage and Genome Integrity

17β-estradiol (E2) regulates human physiology both in females and in males. At the same time, E2 acts as a genotoxic substance as it could induce DNA damages, causing the initiation of cellular transformation. Indeed, increased E2 plasma levels are a risk factor for the development of several types of cancers including breast cancer. This paradoxical identity of E2 undermines the foundations of the physiological definition of "hormone" as E2 works both as a homeostatic regulator of body functions and as a genotoxic compound. Here, (i) the molecular circuitries underlying this double face of E2 are reviewed, and (ii) a possible framework to reconcile the intrinsic discrepancies of the E2 function is reported. Indeed, E2 is a regulator of the DNA damage response, which this hormone exploits to calibrate its genotoxicity with its physiological effects. Accordingly, the genes required to maintain genome integrity belong to the E2-controlled cellular signaling network and are essential for the appearance of the E2-induced cellular effects. This concept requires an "upgrade" to the vision of E2 as a "genotoxic hormone", which balances physiological and detrimental pathways to guarantee human body homeostasis. Deregulation of this equilibrium between cellular pathways would determine the E2 pathological effects.

Critical Role of Estrogens on Bone Homeostasis in Both Male and Female: From Physiology to Medical Implications

Bone is a multi-skilled tissue, protecting major organs, regulating calcium phosphate balance and producing hormones. Its development during childhood determines height and stature as well as resistance against fracture in advanced age. Estrogens are key regulators of bone turnover in both females and males. These hormones play a major role in longitudinal and width growth throughout puberty as well as in the regulation of bone turnover. In women, estrogen deficiency is one of the major causes of postmenopausal osteoporosis. In this review, we will summarize the main clinical and experimental studies reporting the effects of estrogens not only in females but also in males, during different life stages. Effects of estrogens on bone involve either Estrogen Receptor (ER)α or ERβ depending on the type of bone (femur, vertebrae, tibia, mandible), the compartment (trabecular or cortical), cell types involved (osteoclasts, osteoblasts and osteocytes) and sex. Finally, we will discuss new ongoing strategies to increase the benefit/risk ratio of the hormonal treatment of menopause.

Estetrol prevents Western diet-induced obesity and atheroma independently of hepatic estrogen receptor α

Estetrol (E4), a natural estrogen synthesized by the human fetal liver, is currently evaluated in phase III clinical studies as a new menopause hormone therapy. Indeed, E4 significantly improves vasomotor and genito-urinary menopausal symptoms and prevents bone demineralization. Compared with other estrogens, E4 was found to have limited effects on coagulation factors in the liver of women allowing to expect less thrombotic events. To fully delineate its clinical potential, the aim of this study was to assess the effect of E4 on metabolic disorders. Here, we studied the pathophysiological consequences of a Western diet (42% kcal fat, 0.2% cholesterol) in ovariectomized female mice under chronic E4 treatment. We showed that E4 reduces body weight gain and improves glucose tolerance in both C57Bl/6 and LDLR^-/- mice. To evaluate the role of hepatic estrogen receptor (ER) α in the preventive effect of E4 against obesity and associated disorders such as atherosclerosis and steatosis, mice harboring a hepatocyte-specific ERα deletion (LERKO) were crossed with LDLR^-/- mice. Our results demonstrated that, whereas liver ERα is dispensable for the E4 beneficial actions on obesity and atheroma, it is necessary to prevent steatosis in mice. Overall, these findings suggest that E4 could prevent metabolic, hepatic, and vascular disorders occurring at menopause, extending the potential medical interest of this natural estrogen as a new hormonal treatment.NEW & NOTEWORTHY Estetrol prevents obesity, steatosis, and atherosclerosis in mice fed a Western diet. Hepatic ERα is necessary for the prevention of steatosis, but not of obesity and atherosclerosis.