Etude de l'effet des oestrogènes sur la fonction plaquettaire : rôle des récepteurs alpha et béta des oestrogènes

Chez la femme, une augmentation du risque thrombotique a été rapportée lors de la prise d'un traitement hormonal substitutif de la ménopause ainsi que dans la seconde moitié de la grossesse, période caractérisée par une élévation majeure des taux d'œstrogènes. Alors que de nombreuses études ont fait la lumière sur les modifications de l'hémostase associées à la prise d'un traitement hormonal substitutif ou à la grossesse, nous disposons de peu de données concernant les effets des œstrogènes sur la fonction des plaquettes sanguines, éléments clés des processus d'hémostase et de thrombose. Au cours de notre travail de thèse, nous avons donc eu pour objectif de déterminer les effets d'une administration chronique de 17 béta-œstradiol à des doses élevées, mais physiologiques, sur la fonction plaquettaire de souris C57BL/6J. Pour ce faire, des études ex vivo nous ont permis de caractériser l'agrégation de plaquettes issues de souris traitées ou non en réponse à des agonistes forts. Nous avons ensuite utilisé un modèle de thromboembolisme afin de comparer in vivo les effets d'une administration de doses élevées d'œstradiol à des doses endogènes. Enfin, l'utilisation de chimères hématopoïétiques nous a amené à définir le rôle des récepteurs des œstrogènes alpha et béta et de la fonction transactivatrice AF-1 du récepteur des œstrogènes alpha dans les effets observés. Mieux comprendre les implications des œstrogènes dans l'augmentation du risque thrombotique pourrait aider au développement de SERMs (Selective Estrogen Receptor Modulators), modulateurs capables de se lier aux récepteurs des œstrogènes et d'induire, selon le tissu considéré, des effets agonistes ou antagonistes.Although estrogens are recognized to favour a deleterious effect on the venous thrombosis risk and a preventive action on the development of arterial atheroma, their effect on platelet functions in vivo remains unclear. The main aim of this work was to evaluate the impact of a chronic treatment of oestradiol (E2) on platelet functions in mouse. Platelets from E2-treated mice showed a marked decrease in their responsiveness ex-vivo compared to non-treated mice. Accordingly, E2 treatment increased tail bleeding time and elicited an impressive resistance to thromboembolism following injection of an epinephrin-collagen mix. Haematopoietic transgenic chimera mice demonstrated that E2 action on bleeding time and thromboembolism resistance was mediated by the haematopoietic ER alpha but not ER béta and that ER alpha activation function-1 was dispensable. Altogether, we demonstrate that E2 can elicit an antiaggregant action in an ER alpha-dependent, activation function-1-independent manner, opening the way for new potential strategies for antithrombotic and vasculoprotective therapies

Nuclear imaging of thrombosis in small animal

Thromboembolic disorders are a major cause of morbidity and mortality worldwide. The progress in noninvasive imaging techniques has led to the development of radionuclide imaging based on SPECT and PET approaches to observe molecular and cellular processes that may underlie the onset and progression of disease. The advantages of using normal and genetically modified small animal research have spurred the development of dedicated small animal imaging systems. Animal models of venous and arterial thrombosis are largely used and have improved our understanding of the etiology and pathogenesis of thrombosis. Here, we review the literature regarding nuclear imaging of thrombosis in mice and rats

Vers une optimisation de la modulation du récepteur des œstrogènes dans le traitement hormonal de la ménopause

Les femmes vivent désormais plus d’un tiers de leur vie après la survenue de la ménopause. Le déclin de la production d’œstrogènes endogènes au cours de cette période s’accompagne fréquemment de troubles fonctionnels qui affectent la qualité de vie. Ces symptômes peuvent être soulagés par un traitement hormonal (THM) initialement fondé sur l’administration d’œstrogènes conjugués équins (principalement aux États-Unis, par voie orale) ou d’un œstrogène naturel, le 17β-estradiol (en Europe, notamment par voie transdermique). Le récepteur des œstrogènes α (REα) relaye la majorité des effets physiologiques des œstrogènes. REα appartient à la superfamille des récepteurs nucléaires. Il régule la transcription de gènes via ses fonctions activatrices (AF1 et AF2). Outre ces actions génomiques classiques, les œstrogènes peuvent aussi activer une sous-population de récepteurs REα présents à la membrane des cellules et ainsi induire des signaux rapides. Dans cette revue, nous résumerons l’évolution des THM depuis les débuts de la substitution hormonale jusqu’aux nouvelles molécules émergentes fondées sur une modulation sélective du REα. Nous décrirons également les progrès récents sur la compréhension des mécanismes d’action des œstrogènes, en détaillant les rôles respectifs des REα nucléaire et membranaire et les développements thérapeutiques possibles qui pourraient en découler

Chronic estradiol treatment reduces platelet responses and protects mice from thromboembolism through the hematopoietic estrogen receptor α.

International audienceAlthough estrogens are known to have a deleterious effect on the venous thrombosis risk and a preventive action on the development of arterial atheroma, their effect on platelet function in vivo remains unclear. Here, we demonstrate that a chronic high physiologic level of estradiol (E2) in mice leads to a marked decrease in platelet responsiveness ex vivo and in vivo compared with ovariectomized controls. E2 treatment led to increased bleeding time and a resistance to thromboembolism. Hematopoietic chimera mice harboring a selective deletion of estrogen receptors (ERs) α or β were used to demonstrate that the effects of E2 were exclusively because of hematopoietic ERα. Within ERα the activation function-1 domain was not required for resistance to thromboembolism, as was previously shown for atheroprotection. This domain is mandatory for E2-mediated reproductive function and suggests that this role is controlled independently. Differential proteomics indicated that E2 treatment modulated the expression of platelet proteins including β1 tubulin and a few other proteins that may impact platelet production and activation. Overall, these data demonstrate a previously unrecognized role for E2 in regulating the platelet proteome and platelet function, and point to new potential antithrombotic and vasculoprotective therapeutic strategies

Selective Liver Estrogen Receptor Modulation Prevents Steatosis, Diabetes, and Obesity Through the Anorectic Growth Differentiation Factor 15 Hepatokine in Mice

International audienceHepatocyte estrogen receptor α (ERα) was recently recognized as a relevant molecular target for nonalcoholic fatty liver disease (NAFLD) prevention. The present study defined to what extent hepatocyte ERα could be involved in preserving metabolic homeostasis in response to a full (17β-estradiol [E2]) or selective (selective estrogen receptor modulator [SERM]) activation. Ovariectomized mice harboring a hepatocyte-specific deletion ( mice) and their wild-type (WT) littermates were fed a high-fat diet (HFD) and concomitantly treated with E2, tamoxifen (TAM; the most used SERM), or vehicle. As expected, both E2 and TAM prevented all HFD-induced metabolic disorders in WT mice, and their protective effects against steatosis were abolished in mice. However, while E2 still prevented obesity and glucose intolerance in mice, hepatocyte deletion also abrogated TAM-mediated control of food intake as well as its beneficial actions on adiposity, insulin sensitivity, and glucose homeostasis, suggesting a whole-body protective role for liver-derived circulating factors. Moreover, unlike E2, TAM induced a rise in plasma concentration of the anorectic hepatokine growth differentiation factor 15 (Gdf15) through a transcriptional mechanism dependent on hepatocyte ERα activation. Accordingly, ERα was associated with specific binding sites in the regulatory region in hepatocytes from TAM-treated mice but not under E2 treatment due to specific epigenetic modifications. Finally, all the protective effects of TAM were abolished in HFD-fed knockout mice. We identified the selective modulation of hepatocyte ERα as a pharmacologic strategy to induce sufficient anorectic hepatokine Gdf15 to prevent experimental obesity, type 2 diabetes, and NAFLD

Effect of chronic estradiol plus progesterone treatment on experimental arterial and venous thrombosis in mouse

<div><p>Postmenopausal hormone replacement therapy (HRT) with estrogen plus progestogens is the first line therapy to treat menopausal symptoms. The progestogen is added to estrogen to reduce or eliminate the excess risk of endometrial cancer due to the unopposed effect of estrogen. Whereas progestin clearly opposes the proliferative and deleterious long-term actions of estrogen on the endometrium, the interference of progestin on the other estrogen action remains unclear. We previously reported that chronic subcutaneous 17α-estradiol (E2) in mice decreases platelet responsiveness, prolongs the tail-bleeding time and protects against acute thromboembolism. Here, we report the tissue-specific interference of progesterone (P4) on the action of E2 in ovariectomized mice. We first confirm that, in our experimental conditions, P4 attenuates the proliferative action of E2 on the uterus and the effects of E2 on vagina weight and lubrication. We then studied the effect of E2 combined with P4 on hemostasis and thrombosis <i>in vivo</i> in mice and found that P4 did not interfere with the main actions of E2 on platelets, bleeding time and arterial and venous thrombosis. Thus, whereas activation of progesterone receptor interferes with the action of E2 on its classic sex targets, P4 appears to have minimal effect on the hemostasis and thrombosis actions of E2, supporting the prominent role of estrogens and the accessory role of natural progestin on the extra-reproductive cells and tissues involved in thrombosis.</p></div

Effects of a chronic administration of E2, P4 and combined treatment on the uteri and vagina of mice.

<p><b>(A)</b> Uterine weights, epithelial proliferation and luminal epithelial height after the different treatments. Representative sections from uterus stained with Ki-67 antigen. <b>(B)</b> Vagina weights, epithelial proliferation and luminal epithelial height after the different treatments. Representative sections from vagina stained with Ki-67 antigen are shown. <b>(C)</b> Vaginal lubrication (mg). Data are presented as mean ± SD. To test the respective roles of each treatment, a one-way ANOVA was performed and a Bonferroni’s multiple comparison test. * t test vs OVX. $ t test vs E2.</p

Inferior vena cava stasis in OVX and E2-, P4- and E2+P4- treated mice.

<p><b>(A)</b> 24 hours after the induction of the stasis in the inferior vena cava by ligation, mice were killed and thrombi were harvested. The mean weight of the thrombi is presented ± SD. * t test vs OVX, $ t test vs E2. <b>(B)</b> Following ferric chloride injury of the carotid artery, the thrombus formed was visualized by high-frequency ultrasound after. Longitudinal views of a mouse without thrombus and with a stable thrombus are shown.</p

Hematologic parameters.

<p><b>(A)</b> Blood cells counts in ovariectomized (OVX), E2, P4- and E2+P4-treated mice. OVX (n = 5), +E2 (n = 5), P4 (n = 5), E2+P4 (n = 5). <b>(B)</b> Platelet count recovery after immune thrombocytopenia. Thrombocytopenia was induced after 3 weeks of treatment by intraperitoneal injection of anti-mouse GPIbα antibody. Blood samples were collected before injection (D = 0) and 2, 4, 7, 9, 12 and 15 days after. OVX (n = 5), E2 (n = 5), E2+P4 (n = 5). <b>(C)</b> Total bone marrow cell numbers between OVX, E2-, P4- and E2+P4- treated mice. Bone marrow was flushed from 2 femurs and total bone marrow cell numbers was obtained using a Beckman Coulter Counter. OVX (n = 8), E2 (n = 5), P4 (n = 5), E2+P4 (n = 6). Mean ± SD. To test the respective roles of each treatment, a one-way ANOVA was performed and a Bonferroni’s multiple comparison test. * t test vs OVX. $ t test vs P4.</p