ABSTRACT
The G protein-coupled receptor Gpr30 (Gper) was recently claimed to bind to estradiol and to activate cytoplasmic signal transduction pathways in response to estradiol. However, there are conflicting data regarding the role of Gpr30 as an estrogen receptor (ER): several laboratories were unable to demonstrate estradiol binding to GPR30 or estradiol-activated signal transduction in Gpr30-expressing cells. To clarify the potential role of Gpr30 as an ER, we generated Gpr30-deficient mice. Although Gpr30 was expressed in all reproductive organs, histopathological analysis did not reveal any abnormalities in these organs in Gpr30-deficient mice. Mutant male and female mice were as fertile as their wild-type littermates, indicating normal function of the hypothalamic-pituitary-gonadal axis. Moreover, we analyzed estrogenic responses in two major estradiol target organs, the uterus and the mammary gland. For that purpose, we examined different readout paradigms such as morphological measures, cellular proliferation, and target gene expression. Our data demonstrate that in vivo Gpr30 is dispensable for the mediation of estradiol effects in reproductive organs. These results are in clear contrast to the phenotype of mice lacking the classic ER alpha (Esr1) or aromatase (Cyp19a1). We conclude that the perception of Gpr30 (based on homology related to peptide receptors) as an ER might be premature and has to be reconsidered.
Subject(s)
Estradiol/pharmacology , Mammary Glands, Animal/physiology , Receptors, G-Protein-Coupled/physiology , Uterus/physiology , Animals , Animals, Newborn , ErbB Receptors/genetics , Female , Gene Expression Profiling , Histocytochemistry , Litter Size/physiology , Male , Mammary Glands, Animal/drug effects , Mammary Glands, Animal/pathology , Mice , Mice, Inbred C57BL , Mice, Knockout , RNA/chemistry , RNA/genetics , Receptors, Estrogen , Receptors, G-Protein-Coupled/deficiency , Receptors, G-Protein-Coupled/genetics , Reverse Transcriptase Polymerase Chain Reaction , Transcriptional Activation , Uterus/drug effects , Uterus/pathologyABSTRACT
Estrogen receptor (ER) ligands that are able to prevent postmenopausal bone loss, but have reduced activity in the uterus and the mammary gland might be of great value for hormone therapy. It is well established that the classical ER can activate genomic as well as nongenomic signal transduction pathways. In this study, we analyse the in vivo behaviour of ER ligands that stimulate nongenomic ER effects to the same extent as estradiol, but show clearly reduced activation of genomic ER effects in vitro. Using different readout parameters such as morphological changes, cellular proliferation, and target gene induction, we are able to demonstrate that ER ligands with reduced genomic activity in vitro show a better dissociation of bone versus uterine and mammary gland effects than estradiol that stimulates genomic and nongenomic effects to the same extent. We conclude that pathway-selective ER ligands may represent an interesting option for hormone therapy.
Subject(s)
Estrogen Receptor Modulators/metabolism , Genome/drug effects , Receptors, Estrogen/metabolism , Selective Estrogen Receptor Modulators/pharmacology , Uterus/growth & development , Animals , Cell Proliferation , Cohort Studies , Dose-Response Relationship, Drug , Epithelial Cells/physiology , Estradiol/pharmacology , Estrenes/pharmacology , Estrogens/pharmacology , Female , In Vitro Techniques , Ligands , Mammary Glands, Animal/cytology , Mammary Glands, Animal/metabolism , Mice , Mice, Inbred C57BL , Mice, Inbred Strains , Organ Size , Ovariectomy , Time Factors , Uterus/cytology , Uterus/metabolismABSTRACT
The role of progestins in combined hormone therapy is the inhibition of uterine epithelial cell proliferation. The Women's Health Initiative study provided evidence for an increased risk of breast cancer in women treated with conjugated equine estrogens plus the synthetic progestin medroxyprogesterone acetate (MPA), compared with conjugated equine estrogens-only treatment. These findings continue to be discussed, and it remains to be clarified whether the results obtained for MPA in the Women's Health Initiative study are directly applicable to other progestins used in hormone therapy. In this study we compared in a mouse model the effects of the synthetic progestins, MPA, and drospirenone in two major target organs: the uterus and mammary gland. As quantitative measures of progestin activity, we analyzed maintenance of pregnancy, ductal side branching in the mammary gland, and proliferation of mammary and uterine epithelial cells as well as target gene induction in both organs. The outcome of this study is that not all synthetic progestins exhibit the same effects. MPA demonstrated uterine activity and mitogenic activity in the mammary gland at the same doses. In contrast, drospirenone behaved similarly to the natural hormone, progesterone, and exhibited uterine activity at doses lower than those leading to considerable proliferative effects in the mammary gland. We hypothesize that the safety of combined hormone therapy in postmenopausal women may be associated with a dissociation between the uterine and mammary gland activities of the progestin component.
