Regulation of glucocorticoid receptors in the kidney of immature and mature male rats

Age-Dependent Decrease in Renal Glucocorticoid Receptor Function Is Reversed by Dietary Restriction in Mice

The effects of age and dietary restriction (alternate days of feeding for 3 months) on the concentration, activation, and DNase I digestion of nuclear-bound glucocorticoid receptors (GRs) in the kidney of male mice at two different ages (5 months as adult and 20 months as old) were investigated. A significant decrease (30%) in the concentration of renal GRs was observed in older ad libitum (AL)-fed mice as compared to the adult mice. Dietary restriction (DR) of older mice significantly increased (28%) the level of GRs as compared to the AL-fed control animals. The affinity of the receptor for the hormone remained the same for both AL- and DR-fed animals at both ages. Scatchard and slot blot analyses of the data confirmed the decreased level of renal GRs in older mice compared to the adult mice as well as an increased level of receptor in older DR mice. Activation studies of GRs by both salt and heat indicated a decreased (15-20%) activation of renal GRs in older animals compared to the adult mice in the AL-fed group. It was further observed that DR significantly enhanced (30%) the degree of both salt- and heat-dependent activation of GRs in older animals compared to the AL-fed animals of the age-matched group. DNase I digestion and extraction of nuclear-bound GR complexes showed a lower degree (26%) of extraction in older AL-fed animals compared to the adult animals. However, DR did not alter the pattern of digestibility of bound GR complexes. These above findings indicate that DR could reverse the decrease of GR function in older animals and may provide better adaptability of kidney in water and electrolyte balance.

Streptozotocin-induced diabetes and glucocorticoid receptor regulation: tissue- and age-specific variation

Streptozotocin (STZ) -induced diabetic effects were analyzed for glucocorticoid receptor (GR) level and for in vitro activation of GR by specific binding analysis, using [3H]dexamethasone, a synthetic glucocorticoid, and by DNA cellulose and nuclear binding assay, in the liver and kidney of 15- (immature) and 120-day-old (mature) male mice. Comparison of GR level (fmol/mg protein) among the control mice reveals decreased (22-33%) specific binding in the liver and kidney of mature mice compared with immature ones. Scatchard analyses, however, reveal no change in the affinity (K(d)) of receptor at these two ages of mice. STZ-induced diabetes did not alter the level of GR in either of the tissues at both the ages studied. The GR from both the tissues underwent thermal activation, albeit the extent of activation was more pronounced in mature liver compared to immature, with no such difference of activation in the kidney. In diabetic mice, the activation of hepatic GR exhibits reduced DNA cellulose ( approximately 20-23%) and nuclear (24-30%) binding compared to control mice. In contrast, thermal activation of kidney GR does not show marked differences in diabetic mice at either of the ages studied. Cross-mixing experiments (i.e. binding of activated GR from diabetic mice to nuclei of control and vice-versa) performed on the mature liver, indicate receptor specificity. These findings reveal tissue- and age- specific variations in the level of GR that is not influenced under diabetic conditions. However, the activation of hepatic GR is reduced during STZ-induced diabetes that might play a role in controlling glucose homeostasis in diabetic animals.

Estrogens influence growth, maturation, and amyloid beta-peptide production in neuroblastoma cells and in a beta-APP transfected kidney 293 cell line

During development in vivo and in vitro, estrogens: a) increase brain excitability, particularly in limbic structures; b) are responsible for the maturation and cyclicity of limbic-hypothalamic interrelations; c) enhance myelinogenesis; and d) may act with NGF to stimulate neurite formation. In senescence, estrogen administration would improve memory in postmenopausal women. The absence or low levels of estrogens after menopause would increase prevalence of Alzheimer's dementia (AD) more in women than men, irrespective of age or ethnicity. In the present study, addition of 17-beta estradiol to cultured human neuroblastoma cells affected growth slightly, but stimulated cell maturation as shown by increased tyrosine hydroxylase activity. The extracellular deposition in brain tissue and around blood vessels of the amyloid beta-peptide (A beta), a 4.3 kD fragment of the larger integral membrane protein, beta-amyloid precursor protein (beta-APP), is considered an important characteristic of AD. We investigated whether 17-beta estradiol may influence the formation of the A beta (thus the abnormal accumulation of amyloid proteins) in neuroblastoma cells and in a beta-APP transfected human kidney 293 cell line. Two doses of 17 beta-estradiol were added to the cultures of both cell lines. Cells were grown until confluence, metabolically labeled with 35S-methionine, immunoprecipitated with the rabbit antiserum R1282, gel electrophoresed and autoradiographed in order to compare levels of A beta under the different estradiol concentrations. While in neuroblastoma cells, levels of A beta were only slightly reduced after estradiol and a dose-effect relationship with the hormone could not be demonstrated, in the 293 cells, A beta band intensity decreased as concentration of estradiol increased. These data support the role of estrogen in normal and abnormal brain metabolism and suggest potential hormonal interventions which may reduce or prevent the formation of amyloid deposits occur in AD.

Renal handling of drugs and amino acids after impairment of kidney or liver function--influences of maturity and protective treatment

Renal tubular cells are involved both in secretion and in reabsorption processes within the kidney. Normally, most xenobiotics are secreted into the urine at the basolateral membrane of the tubular cell, whereas amino acids are reabsorbed quantitatively at the luminal side. Under different pathological or experimental circumstances, these transport steps may be changed, e.g., they may be reduced by renal impairment (reduction of kidney mass, renal ischemia, administration of nephrotoxins) or they may be enhanced after stimulation of transport carriers. Furthermore, a distinct interrelationship exists between excretory functions of the kidney and the liver. That means liver injury can influence renal transport systems also (hepato-renal syndrome). In this review, the following aspects were included: based upon general information concerning different transport pathways for xenobiotics and amino acids within kidney cells and upon a brief characterization of methods for testing impairment of kidney function, the maturation of renal transport and its stimulation are described. Similarities and differences between the postnatal development of kidney function and the increase of renal transport capacity after suitable stimulatory treatment by, for example, various hormones or xenobiotics are reviewed. Especially, renal transport in acute renal failure is described for individuals of different ages. Depending upon the maturity of kidney function, age differences in susceptibility to kidney injury occur: if energy-requiring processes are involved in the transport of the respective substance, then adults, in general, are more susceptible to renal failure than young individuals, because in immature organisms, anaerobic energy production predominates within the kidney. On the other hand, adult animals can better compensate for the loss of renal tissue (partial nephrectomy). With respect to stimulation of renal transport capacity after repeated pretreatment with suitable substances, age differences also exist: most stimulatory schedules are more effective in young, developing individuals than in mature animals. Therefore, the consequences of the stimulation of renal transport can be different in animals of different ages and are discussed in detail. Furthermore, the extent of stimulation is different for the transporters located at the basolateral and at the luminal membranes: obviously the tubular secretion at the contraluminal membrane can be stimulated more effectively than reabsorption processes at the luminal side.

Developmental and hormonal regulation of glucocorticoid receptor messenger RNA in the rat

The biological action of glucocorticoids is dependent upon tissue-specific levels of the glucocorticoid receptor (GR). During stress, the hypothalamic-pituitary-adrenal axis is stimulated, and high levels of glucocorticoids circulate. This axis is modulated by negative feedback by glucocorticoids, which inhibit hypothalamic and pituitary hormone secretion and downregulate GR gene expression. To study the developmental tissue-specific regulation of the GR, we measured the relative concentration of GR mRNA in fetal, neonatal, adult, and aged rats and examined the effects of dexamethasone on GR gene expression. Three different tissue-specific developmental patterns of GR mRNA accumulation were found. In addition, there was an age-dependent tissue-specific pattern in the feedback regulation of GR mRNA by glucocorticoids. In the fetus and neonate, GR mRNA abundance was not regulated by circulating glucocorticoids. The adult pattern of glucocorticoid feedback inhibition of GR mRNA expression appeared between 2 and 7 d of life in liver, and after 7 but before 14 d of age in brain. The GR was biologically active in the 2-d-old neonate, however, since dexamethasone enhanced gene expression of angiotensinogen, which is another glucocorticoid responsive gene. These data demonstrate that the GR gene is regulated by both developmental and tissue-specific factors, and provide another molecular basis for ontogenic variations in the hypothalamic-pituitary-adrenal response to stress.