Hormonal regulation of osteoclast function.

Hormones and cytokines indirectly control the formation of osteoclasts from hemopoietic precursors by acting upon osteoblastic stromal cells and, in some cases, also upon cells of the immune system. These intermediate cells produce factors that act in a paracrine manner to influence precursor proliferation or differentiation. Successful osteoclast formation in vitro requires contact between stromal and hemopoietic cells, leading to the concept of a membrane-associated stromal cell molecule that specifically programs osteoclast differentiation. Attention has been focused further on this by the recent discovery of a soluble member of the tumor necrosis factor (TNF) receptor family which is both a product of and a ligand for osteoblastic stromal cells. Once they are formed in the presence of osteoblasts, osteoclasts are active, and hormones or cytokines do not promote the activity of mature osteoclasts, but more likely influence their survival. Of the two best known hormonal inhibitors of bone resorption in vivo, calcitonin acts directly upon osteoclasts to inhibit their activity, whereas estrogen acts indirectly, via the regulation of several cytokines.     

Hormonal regulation of cytoplasmic estrogen and progesterone receptors in the beagle uterus and oviduct

The hormonal regulation of uterine and oviductal cytoplasmic estrogen and progesterone receptors was studied in immature beagles that were untreated, treated with estradiol-17β, or treated sequentially with estradiol and progesterone. Estradiol treatment increased the concentration of estrogen receptors in both tissues. Progesterone receptors were not detectable in the reproductive tract of untreated animals, but increased dramatically under the influence of estradiol. Estrogen withdrawal following estrogen stimulation, concomitant estrogen plus progesterone administration, and estrogen withdrawal plus progesterone administration all caused significant reductions in both estrogen and progesterone receptors in uterine and oviductal cytosols when compared to estrogen treatment alone. Estrogen withdrawal resembled estrogen plus progesterone administration in reducing both estrogen and progesterone receptor levels, although estrogen withdrawal plus progesterone administration resulted in a further reduction in both receptor concentrations. The same positive and negative relationships between estrogen and progesterone receptor content were observed in uterine cytosols from cycling and ovariectomized adults. These data suggest that estrogen and progesterone regulate their respective receptors and that tissue sensitivity to both steroids may be controlled by mechanisms involving fluctuations in receptor concentration in the reproductive tract of the beagle.     

Hormonal regulation of B-cell function and systemic lupus erythematosus

The prevalence of systemic lupus erythematosus (SLE) is far higher in females than in males and numerous investigations to understand this gender bias have been performed, which propose as casual actors genetic predispositions and sex hormones effects. We will describe in this review how the sex hormones estrogen and prolactin influence B cell maturation and selection, permitting B cells to mature to immunocompetence in a mouse model of lupus. Finally, we will discuss the relevance and implications of these results for human disease.     

Hormonal regulation of RNA synthesis and specific gene expression in Xenopus oviduct cells in primary culture

The studies described in this report were carried out as a first step towards the elucidation of mechanisms underlying the tissue specificity of regulation of gene expression by estrogen. Using a procedure established earlier in our laboratory for primary culture of Xenopus hepatocytes, we have characterized how estradiol-17 beta and progesterone affect the rate of synthesis of total RNA and that of accumulation of two oviduct-specific mRNAs in Xenopus oviduct cells in primary culture. In cells that had recovered from 'culture shock' 3 days after they were plated out, both hormones had only a slight or no effect on the overall rate of labelling of newly synthesized RNA over 24 h. Cloned cDNA probes for two mRNAs, termed 7F and 6G and specifying as yet unknown proteins expressed in the oviduct and not in the liver, were used to quantify the two mRNAs. The levels of both mRNAs declined for the first 2 days in culture after which they were stabilized. When added to the oviduct cell cultures 3 days after they were plated out, estradiol increased the steady-state concentration (relative to total RNA) of 7F and 6G mRNAs by 3- to 7-fold after 60-80 h, but with different time-course and dose-response kinetics for the two messages. The antiestrogen tamoxifen also exerted different degrees of antagonist effect on the estrogen-induced accumulation of 7F and 6G mRNAs. Although the protein products of these two oviduct-specific mRNAs have not yet been characterized, these studies set the stage for comparing the regulation by estrogen of their genes with that of vitellogenin genes in primary cultures of Xenopus oviduct cells and hepatocytes.     

Hormonal regulation of the growth and steroidogenic function of human granulosa cells.

The aim of this study was to assess development-related interactions between gonadotropins and insulin-like growth factor (IGF-I) on DNA synthesis and steroidogenesis in human granulosa cells. "Immature" granulosa cells were obtained from follicles during the late luteal phase or first half of the follicular phase; "mature" granulosa cells came from follicles during the second half of the follicular phase but before the midcycle LH surge; and granulosa-lutein cells were obtained as a by-product of in vitro fertilization. Granulosa cells were cultured for 96 h in serum-free medium 199 with and without LH or FSH, and in the presence and absence of IGF-I. The cell monolayers were then incubated with [3H]methyl thymidine to assess DNA synthesis. Spent culture medium was assayed for progesterone and estradiol content. Immature granulosa cells: Tritiated thymidine uptake in granulosa cell cultures from immature follicles were significantly increased by IGF-I. FSH was able to maintain or increase basal and IGF-I stimulated growth whereas LH had no effect. Basal progesterone production was low and not increased by either FSH or LH. However, treatment with FSH, but not LH, increased aromatase activity. Mature granulosa cells: IGF-I also stimulated thymidine uptake. However, whereas FSH either maintained or increased thymidine uptake by these cells, LH dose dependently suppressed thymidine uptake. This inhibitory action of LH was accentuated by the presence of IGF-I. Despite the inhibitory effect of LH on thymidine uptake, the gonadotropin markedly stimulated steroid production and the maximal steroidogenic response to LH was equivalent to 3-fold greater than that to FSH. Granulosa-lutein cells: Patterns of basal and IGF-I- and gonadotropin-stimulated steroid synthesis were similar to those observed for mature granulosa cells but steroid production rates were higher. Suppression of basal and IGF-I-stimulated thymidine uptake by LH was even more pronounced. These results suggest that the granulosa cell LH receptor, once expressed, negatively regulates cell growth and, simultaneously, positively regulates steroid synthesis. This development related event could be crucial to the mechanism whereby granulosa cells cease to divide and commence maximal rates of steroid synthesis in response to the LH surge.     

Hormonal regulation of energy partitioning

A loop system exists between hypothalamic neuropeptide Y (NPY) and peripheral adipose tissue leptin to maintain normal body homeostasis. When hypothalamic NPY levels are increased by fasting or by intracerebroventricular (i.c.v.) infusion, food intake and body weight increase. NPY has genuine hormono-metabolic effects. It increases insulin and corticosterone secretion relative to controls. These hormonal changes, acting singly or combined, favor adipose tissue lipogenic activity, while producing muscle insulin resistance. They also promote leptin release from adipose tissue. When infused i.c.v. to normal rats to mimic its central effects, leptin decreases NPY levels, thus food intake and body weight. Leptin i.c.v. has also genuine hormono-metabolic effects. It decreases insulinemia and adipose tissue storage ability, enhancing glucose disposal. Leptin increases the expression of uncoupling proteins (UCP-1, -2, -3) and thus energy dissipation. Leptin-induced changes favor oxidation at the expense of storage. Circadian fluctuations of NPY and leptin levels maintain normal body homeostasis. In animal obesity, defective hypothalamic leptin receptor activation prevent leptin from acting, with resulting obesity, insulin and leptin resistance.     

Hormonal regulation of vascular calcification

Recent evidence suggests that vascular calcification is a controlled process and involves the altered differentiation of mesenchymal cells. For example, vitamin D(3) was reported to enhance vascular calcification by suppressing PTHrP action that is an inhibitor of calcification. Quite recently, leptin has been shown to enhance the osteoblastic differentiation of stromal cells and calcification of vascular cells. These results suggest the intimate relationship between bone and lipid or adipose tissue.     

Hormonal regulation of the NF-kappaB signaling pathway

Studies with mammalian vascular cells have suggested growth inhibitory effects of estrogen on the vascular wall. To investigate the involvement of estrogen receptor-alpha (ER) in the control of endothelial cell proliferation, we have stably transfected human estrogen receptor-alpha cDNA into the endothelial cell line ECV304. The clone ECV-ER, thus obtained, over-expresses estrogen receptor to a level approximately 10-fold higher than the parent cell line. Effects of this over-expression were studied on the cell growth rate, and on the levels of secreted endothelin-1 and vascular endothelial growth factor (VEGF). Similar to the previously reported data in other cell types, we found the transfection of ER in ECV304 cells to be inhibitory to their growth. Our ER-over-expressing clone of ECV304 also showed an inhibition of secreted endothelin-1 and VEGF levels. Moreover, the growth inhibition of this ER-over-expressing clone was reversed by the addition of endothelin-1 or VEGF to the medium. In view of the growth-stimulatory effect of endothelin-1 and VEGF on vascular cells, our results indicate that estrogen receptor-alpha may bring about its growth inhibition partly by suppressing endothelin-1 and/or VEGF production in ECV304 cells.     

Hormonal regulation of thecal cell function during antral follicle development in bovine ovaries

The hormonal regulation of thecal cell function was investigated with cells isolated at various stages of antral follicle development. Bovine thecal cells were isolated from small antral, medium antral, and large Graffian follicles (small, medium, and large ovarian follicles). Serum-free cultures of thecal cells were established and viable for a minimum of 6-8 days of culture. The purity of the thecal cell population was characterized cytochemically and was found to contain less than 5% endothelial cell and/or granulosa cell contamination. The steroidogenic capacity of this purified population of thecal cells in serum-free culture was examined through an analysis of androgen and progesterone production. Androgen production was high during the first 3 days of culture, then declined to undetectable levels. Production of androstenedione was approximately 10-fold higher than production of testosterone. Progesterone production remained relatively constant throughout the 8-day culture period. hCG was found to stimulate androgen production during days 1-3 of culture, but had a negligible effect on progesterone production. In contrast, hCG stimulated progesterone production during days 3-6 of culture, but had a negligible effect on androgen production. Insulin stimulated progesterone production during days 3-6 of culture, but had no effect on androgen or progesterone production during days 1-3 of culture. The minimum effective concentrations of hCG and insulin required to stimulate steroidogenesis of the thecal cells ranged from approximately 1-10 ng/ml. Addition of serum to the cultures decreased androgen production and suppressed the hormone responsiveness of the cells. Thecal cells in culture appear to alter their steroidogenic capacity from an androgen-producing cell to a progesterone-producing cell. Analysis of the developmental regulation of thecal cell function revealed that androgen production and hormone responsiveness were relatively constant in small, medium, and large follicles. In contrast, progesterone production and hormone responsiveness were highest in small follicles, intermediate in medium follicles, and lowest in large follicles. A more general analysis of the developmental regulation of thecal cell function examined the secretion of radiolabeled proteins. A large number of radiolabeled proteins were secreted by thecal cells, ranging in molecular mass from 5-500 kDa. Interestingly, insulin and hCG had no major effect on secretion of proteins by cells isolated from any of the stages of development examined.(ABSTRACT TRUNCATED AT 400 WORDS)