In studies of human endometrium and separated endometrial stromal cells, considerable evidence has been assembled for the existence of an endometrial stromal cell vasoactive peptide system. The primary components of this system are (i) parathyroid hormone-related protein (PTH-rP, a vasorelaxant), (ii) endothelin-1 (ET-1, a vasocontractant), (iii) enkephalinase (a plasma membrane ectoenzyme that degrades ET-1), and (iv) transforming growth factors-beta (TGF-beta1, -2, and -3). Each of these components is synthesized in the endometrial stromal cells (which are contiguous with the spiral arteries/arterioles) in a manner that is regulated by sex steroid hormones (endocrine control) and modulated by locally-produced factors (autocrine/paracrine control). PTH- rP and ET-1 are known to be effective in modulating vascular tone/blood flow when acting via the adventitial surface of vessels. PTH-rP synthesis in stromal cells is stimulated by estradiol-17beta (E2). ET-1 synthesis is not affected by E2, but is inhibited by progestin. Moreover, the specific activity (SA) of enkephalinase is increased by progestin. Thus, progestin acts in a dualistic manner to maintain low levels of the vasoconstrictor, ET-1. TGF-beta1 is produced in endometrial stromal cells commencing during the luteal phase of the cycle; and, TGF-beta1 acts in concert with progesterone to promote decidualization. But in addition, TGF-beta acts in a highly selective, gene-specific manner to overcome selected actions of progesterone, viz., TGF-beta1 acts to overcome the progestin attenuation of ET-1 and PTH-rP synthesis; and, TGF-beta1 acts to overcome the progestin-induced increase in enkephalinase SA. Therefore, TGFs-beta plus progesterone promotes decidualization; but, TGFs-beta also complement progesterone withdrawal to prepare the endometrium for menstruation. We hypothesize that synthetic progestins act to modify the synthesis/degradation of stromal cell vasoactive peptides such that endometrial growth/development is adversely affected, giving rise to disturbed angiogenesis, atypical vascular endothelial cell function/integrity, aberrant endometrial development, and, thereby, erratic endometrial bleeding. The effects of synthetic progestins can be promulgated by the development of cellular estrogen unresponsiveness promoted by the actions of these steroids, via the progesterone receptor per se (or other steroid receptors), and by inducing alterations in the rate of stromal cell synthesis/activation of TGFs-beta. Therefore, the objectives of the research proposed are to define: (i) the regulation of expression of PTH-rP, ET-1, and enkephalinase in human endometrial stromal cells, (ii) the role and mechanism(s) of action of TGF-beta to complement or to oppose selected actions of progesterone, and (iii) the role of synthetic progestins in the synthesis/activation of TGFs-beta in endometrium. In selected studies, the action of progesterone will be compared and contrasted with those of synthetic progestins. To accomplish these objectives, we propose 3 specific aims: (i) to define the biomolecular processes by which the tissue levels and actions of PTH-rP and ET-1 in human endometrium are regulated; (ii) to identify the mechanism by which TGFs-beta act as highly-selective gene-specific antiprogestins in human endometrium; and (iii) to evaluate the potential for the regulation of latent TGF-beta synthesis and activation in human endometrium.
