Early events in the action of glucocorticoids in developing tissues

Influence of short-term glucocorticoid therapy on regulatory T cells in vivo

BACKGROUND

Pre- and early clinical studies on patients with autoimmune diseases suggested that induction of regulatory T(T(reg)) cells may contribute to the immunosuppressive effects of glucocorticoids (GCs).

OBJECTIVE

We readdressed the influence of GC therapy on T(reg) cells in immunocompetent human subjects and naïve mice.

METHODS

Mice were treated with increasing doses of intravenous dexamethasone followed by oral taper, and T(reg) cells in spleen and blood were analyzed by FACS. Sixteen patients with sudden hearing loss but without an inflammatory disease received high-dose intravenous prednisolone followed by stepwise dose reduction to low oral prednisolone. Peripheral blood T(reg) cells were analyzed prior and after a 14 day GC therapy based on different markers.

RESULTS

Repeated GC administration to mice for three days dose-dependently decreased the absolute numbers of T(reg) cells in blood (100 mg dexamethasone/kg body weight: 2.8±1.8×10(4) cells/ml vs. 33±11×10(4) in control mice) and spleen (dexamethasone: 2.8±1.9×10(5)/spleen vs. 95±22×10(5)/spleen in control mice), which slowly recovered after 14 days taper in spleen but not in blood. The relative frequency of FOXP3(+) T(reg) cells amongst the CD4(+) T cells also decreased in a dose dependent manner with the effect being more pronounced in blood than in spleen. The suppressive capacity of T(reg) cells was unaltered by GC treatment in vitro. In immunocompetent humans, GCs induced mild T cell lymphocytosis. However, it did not change the relative frequency of circulating T(reg) cells in a relevant manner, although there was some variation depending on the definition of the T(reg) cells (FOXP3(+): 4.0±1.5% vs 3.4±1.5%*; AITR(+): 0.6±0.4 vs 0.5±0.3%, CD127(low): 4.0±1.3 vs 5.0±3.0%* and CTLA4+: 13.8±11.5 vs 15.6±12.5%; * p<0.05).

CONCLUSION

Short-term GC therapy does not induce the hitherto supposed increase in circulating T(reg) cell frequency, neither in immunocompetent humans nor in mice. Thus, it is questionable that the clinical efficacy of GCs is achieved by modulating T(reg) cell numbers.

Fetal lung maturation in estrogen-deprived baboons

We have previously shown that estrogen plays a central integrative role in regulating key aspects of fetal-placental development and that inhibition of estrogen production during the second half of baboon pregnancy suppressed fetal adrenal function. Because maturation of the fetal lung is dependent on cortisol of fetal adrenal origin, the current study determined whether lung development and expression of surfactant proteins (SPs) A and B were altered at term in estrogen-deprived baboons. Fetal lungs were obtained on d 100, 165, and 175 of gestation (term = d 184) from untreated baboons and on d 165 from animals treated daily during the second half of pregnancy either with the aromatase inhibitor CGS 20267 alone or with CGS 20267 and estradiol benzoate. Umbilical venous estradiol levels were suppressed by more than 95% by CGS 20267 and elevated by CGS 20267 and estrogen. Although umbilical serum cortisol levels were also suppressed by 35% by CGS 20267, cortisol levels in the fetal lung of estrogen-suppressed baboons were similar to values in untreated animals. Immunocytochemistry demonstrated that CGS 20267 treatment did not alter fetal lung expression of the 11 beta-hydroxysteroid dehydrogenase enzyme-1 enzyme catalyzing reduction of cortisone to cortisol. However, immunocytochemical expression of the 11 beta-hydroxysteroid dehydrogenase enzyme-2 catalyzing oxidation of cortisol to cortisone appeared lower in lungs of estrogen-deprived fetuses and restored to normal by CGS 20267 and estrogen. SP-A levels in fetal lungs of untreated baboons were increased 16- to 20-fold between d 100 and d 165-175 of gestation in untreated baboons and baboons treated with CGS 20267 or CGS 20267 and estrogen. Similarly, SP-B levels in fetal lungs of untreated baboons were increased 10-fold between d 100 and d 165-175 of gestation in untreated baboons and baboons treated with CGS 20267 or CGS 20267 and estrogen. Moreover, in estrogen-suppressed baboons, as in untreated animals, the fetal lung continued to grow and exhibited normal alveolarization on histology. We conclude that development of the primate fetal lung can occur in utero in baboons in which fetal serum cortisol levels have been suppressed by the relative absence of estrogen perhaps because of the ability of the lung to coordinate local production of cortisol.

Angiotensin II receptors on human fetal adrenal cells

OBJECTIVE

Our objective was to determine if angiotensin II receptors are present on adrenal cells isolated from the human fetal zone and neocortex and to investigate if angiotensin II affects steroid production by these cells.

STUDY DESIGN

Primary cultures of both fetal zone and neocortex cells were prepared from fetal adrenal glands. Experiments were conducted to examine the binding of radiolabeled angiotensin II, angiotensin II activation of phospholipase C, and angiotensin II effects on steroidogenesis.

RESULTS

The majority of angiotensin II binding sites were of the type 1 subtype, as determined by displacement of radiolabeled angiotensin with specific receptor antagonists. Angiotensin II caused an increase in tritiated inositol phosphate accumulation in both neocortex and fetal zone cells. This increase could be blocked by type 1 angiotensin II receptor antagonists. Angiotensin II stimulated the production of cortisol, dehydroepiandrosterone, and dehydroepiandrosterone sulfate production during treatment for 2 days. The stimulation by angiotensin II, however, was substantially less than that seen in response to corticotropin treatment.

CONCLUSIONS

The human fetal adrenal gland contains type 1 angiotensin II receptors early in gestation. The number of these receptors, albeit low, is sufficient to activate inositol phosphate production and steroidogenesis.

Nucleotides alter glucocorticoid receptor properties in an age-dependent manner

The effects of various nucleotides on the binding of [3H] dexamethasone to rat liver cytosolic glucocorticoid receptors of various age groups were examined. In all the age groups studied (neonatal 4-10 days; adult, 45-60 days; and aged, 18-22 months), maximum receptor binding was obtained at 6 mM ATP concentration. At 6 mM ATP, binding was enhanced 20-100% (depending on the age groups) above controls. ADP was found to be as effective as ATP, whereas the effectiveness of other nucleotides was UTP greater than GTP greater than CTP. Interestingly, addition of any nucleotide to neonatal cytosol resulted in a higher binding of the hormone to receptor as compared to cytosols from the adult and aged animals. Although ATP or ADP added with 5 mM dithiothreitol gave optimum receptor binding for all of the 3 age groups tested, significantly higher hormone receptor binding was obtained upon addition of nucleotides plus dithiothreitol to cytosols from neonatal and aged rats as compared to adult rats. The time and temperature dependent inactivation of unbound glucocorticoid receptors was more effectively inhibited by addition of nucleotide plus dithiothreitol in aged animals than in neonatal and adult animals. This observation was used in the partial purification and characterization of hepatic glucocorticoid receptors from aged rats.

Glucocorticoid receptors: from development to aging. A review

Glucocorticoid responses are known to be altered during development and aging in many tissues. Therefore, in the past several years considerable attention has been given to determining if glucocorticoid receptors are altered with age. In this review, studies concerning glucocorticoid receptor ontogenic and age-dependent changes in number, affinity and physicochemical properties are summarized. In addition, possible mechanisms of age-related changes in the receptor are discussed along with future goals and approaches which may be of great importance in this area of research.

Glutamine synthetase activity in the developing secondary palate and induction by dexamethasone

Glutamine synthetase (EC 6.3.1.2) (GS) and glutamyltransferase (EC 2.3.2.1) (GT) specific activity were examined in developing A/Jax and C57BL/6J (C57) mouse fetal secondary palates. In addition, the induction of palatal GS was also examined after maternal injection of dexamethasone. Palatal GT activity was uniformly higher in A/J than C57 palates with both strains showing highest activity late on day 13 of gestation and a drop in activity by early day 14. In contrast, A/J palatal GS activity peaked transiently late on day 13, dropped by early day 14 and remained lower throughout the remaining period of palatal development. Palatal GS activity in C57 mouse fetuses, although failing to show a discrete transient peak of activity, remained at a constant elevated level from early day 13 to late day 14 and did not decrease until day 15 of gestation. These elevated levels of palatal GS and GT activity correspond to the gestation period of maximal palatal glycoconjugate biosynthesis. Thus, palatal GS activity may play an important regulatory role in the synthesis of these macromolecules. A/J and C57BL/6J mice exhibit different susceptibilities to glucocorticoid-induced cleft palate. However, maternal administration of a non-teratogenic dose of dexamethasone on either late day 12 or late day 13 resulted in a dramatic stimulation of both A/J and C57 fetal palatal GS but not GT activity when assay 18 h later. A/J palatal tissue responded to dexamethasone with greater induction of palatal GS activity than enzyme activity in C57 palates. Palatal GS, sensitive to glucocorticoid stimulation, may thus be an important link in expressing hormonal control of normal palatal differentiation.

Glucocorticoid receptors and inhibition of neonatal mouse dermal fibroblast growth in primary culture

Primary cultures of dermal fibroblasts from neonatal mice were used to investigate some of the anti-inflammatory effects of glucocorticoids in vitro as influenced by the genetic background of two different strains of mice (A/J and C47 Bl/6J). Fibroblasts were cultured in the absence or presence of various glucocorticoids for 2-7 days. After 4-7 days in the presence of steroid, DNA synthesis was reduced by 50-85% while protein synthesis was inhibited by 50-60%. Corticosterone produced a dose-dependent inhibition of DNA synthesis in these cells with a 50% reduction occurring at 10 nM. Specific, high affinity, low capacity binding proteins for [3H]dexamethasone or [3H]triamcinolone acetonide were identified in the cytoplasm of neonatal dermal fibroblasts which had an apparent Kd of 9 nM and approximately 5,200-6,400 binding sites/cell. Sedimentation analysis of the [3H]triamcinolone acetonide-receptor complexes on low salt glycerol gradients exhibited binding in the 7 to 8 S region of the gradients. These studies demonstrate that inhibition of growth of primary cultures of mouse neonatal dermal fibroblasts by glucocorticoids is probably mediated by a receptor-mediated pathway, and that this primary culture system might be useful in delineating other anti-inflammatory effects of glucocorticoids in vitro.

Lung development and the pulmonary surfactant system: hormonal ifluences

The effect of hormones on developmental events is not a new area of scientific investigation. However, in the last decade, the developing lung has been the focus of an increasing amount of basic and applied research. Inadequate development of the newborn's respiratory system precludes extra-uterine existence; indeed, such respiratory inadequacy has been a leading cause of death in premature infants. Tremendous strides have been made in understanding the basic cell biology of the developing lung. Much has been learned about the source, composition, and function of pulmonary surfactant, a surface-active material produced by the lung and essential to alveolar stability. Deficient stores of this material is a major etiologic factor in the respiratory distress syndrome of the newborn (RDS). This fact, coupled with observations that certain hormones can accelerate lung development and the consequent availability of adequate stores of pulmonary surfactant, has led to a large body of literaturae dealing with the effects of hormones (and other agents) on lung development. It is the purpose of this literature review (1) to discuss the various kinds of investigations which have linked surfactant synthesis to the type II pulmonary epithelial cell; and (2) to review the current status of research dealing with the effects of glucocorticoids and thyroid hormones on lung maturation.

Involvement of glucocorticoids in the development of the secondary palate

Genetic differences between various inbred strains of mice in the levels of glucocorticoid receptors embryonic in maxillary mesenchyme cells appear to be reflected in the magnitude of the responses to steroids in these cells. High levels of glucocorticoids cause significant growth inhibition in maxillary mesenchyme cells with subsequent alterations in the production of extracellular matrix components. The presence of higher levels of cytoplasmic glucocorticoid receptor proteins may be one factor which could predispose those strains such as A/J to a greater inhibition of craniofacial growth in vivo by glucocorticoids and therefore increase the frequency of cleft palate production. Furthermore, women with infertility treated with glucocorticoids to support pregnancy give birth to infants with a marked decrease in birth weight [98]. Pharmacologic doses of glucocorticoids can also cause a dramatic reduction in the growth of a number of fetal tissues in mice and humans. In fact, there is evidence that glucocorticoids may be a causative factor in the production of cleft palate in primates [52]. The nature of the molecular elements which determine the biochemical and physiologic responses to glucocorticoids in the palate still remains largely unknown. Although in the mouse there is some evidence to suggest that the major histocompatibility locus (H-2) might be involved, the level(s) at which this control is exerted is unknown. It is possible that this locus may regulate in some manner the level of glucocorticoid receptors and the response to glucocorticoids in the secondary palate. Moreover, there is evidence to suggest that other genes distinct from, but closely linked to the H-2 locus may be important in determining both the strain-dependent differences in susceptibility to glucocorticoid-induced cleft palate and the intracellular levels of cyclic AMP in the secondary palate. It is also apparent that glucocorticoids in conjunction with other hormones or growth factors such as epidermal growth factor and agents which regulate cyclic nucleotide metabolism are essential for the normal development of the secondary palate. Excesses or deficiencies in either the level of these growth regulators and/or in their receptors in specific fetal tissues at defined periods in development are likely to lead to certain fetal malformations. Definition and integration of the genetic, biochemical, and endocrine factors which are involved in the control of cellular growth as influenced by alterations in the composition of cell surface and extracellular matrix components should provide some insights into the events associated with normal palatogenesis.

Kinetics of the glucocorticoid hormone-receptor interaction. False association constants determined in slowly equilibrating systems

The usual way of in vitro determination of association constants for hormone-receptor complexes is criticized. It is shown that if incubation time is short, relative to the half-life of the hormone-receptor complex, the value of the apparent Ka is proportional to the time of incubation. No sign of lack of equilibrium is apparent from the Scatchard plots. The case of rapidly denaturing receptor molecule is also discussed, with similar conclusions. Although terminology and examples are taken from the field of the glucocorticoid receptor research, all deductions are valid for other systems with similar association (and denaturation or monomolecular transformation) mechanisms and kinetic parameters.

Responses of the immature fowl to a single injection of adrenocorticotrophic hormone

Chicks, aged 1 or 21 d, were injected with long-acting ACTH (6, 12, 30 or 60 IU/kg) and changes in plasma glucose and cholesterol and in adrenal weight and cholesterol measured. 2. No consistent response was observed in the 1-d-old chicks. 3. Hyperglycaemia and adrenal cholesterol depletion could be demonstrated in the 3-week-old bird at all doses. 4. The duration of the hyperglycaemic response was dose-dependent but there was only limited evidence that adrenal cholesterol depletion was similarly dependent. 5. Starving the 3-week-old bird overnight led to a significant hypercholesteraemia which was reduced after ACTH. In contrast no change in plasma cholesterol concentration was noted in fully fed birds.

Binding of glucocorticoids to liver nuclei and chromatin of fetal, immature and adult rats

The interaction of dexamethasone with nuclei and chromatin was investigated following incubation of liver slices from fetal, immature (6-day-old) and adult rats with the labeled steroid at 37 degrees. The number of specific binding sites for dexamethasone in purified liver nuclei increases with the age of the animal in a manner similar to that previously reported for the cytoplasmic receptor. The high affinity nuclear binding approaches saturation at 40 and 500 nM dexamethasone in fetal and adult liver, respectively. In comparison with dexamethasone, the relative efficiency of corticosterone to accumulate in the nucleus is 9 percent in fetal liver and only 1 percent in adult liver. Specifically bound dexamethasone in adult nuclei exists in at least three forms; a Tris-soluble, a KC1-soluble, and a residual (non-extractable with KC1 or DNase) form. Part of the Tris-soluble steroid is associated with macromolecules sedimenting at about 4 S both in the presence and absence of 0.4 M KC1. This form of the receptor was not detected in fetal liver nuclei. In liver chromatin, bound dexamethasone exists in a KC1-soluble and a residual form, the latter comprising the major fraction of steroid associated with chromatin from both fetal and adult tissue (60 and 75 percent, respectively). Treatment with Triton X-100 releases about 20 percent of the radioactivity in adult liver nuclei, but has no effect on fetal liver nuclei. In contrast with the above observations in the intact tissue, the major fraction of steroid bound to chromatin in cell-free systems is KC1- and DNase-soluble, only 30 percent remaining in the residual pellet.