Induction of c-fos-like protein in the rat adrenal cortex by acute stress--immunocytochemical evidence

Effect of Dietary Sodium Modulation on Pig Adrenal Steroidogenesis and Transcriptome Profiles

Primary aldosteronism is a frequent form of endocrine hypertension caused by aldosterone overproduction from the adrenal cortex. Regulation of aldosterone biosynthesis has been studied in rodents despite differences in adrenal physiology with humans. We, therefore, investigated pig adrenal steroidogenesis, morphology, and transcriptome profiles of the zona glomerulosa (zG) and zona fasciculata in response to activation of the renin-angiotensin-aldosterone system by dietary sodium restriction. Six-week-old pigs were fed a low- or high-sodium diet for 14 days (3 pigs per group, 0.4 g sodium/kg feed versus 6.8 g sodium/kg). Plasma aldosterone concentrations displayed a 43-fold increase (P=0.011) after 14 days of sodium restriction (day 14 versus day 0). Low dietary sodium caused a 2-fold increase in thickness of the zG (P<0.001) and an almost 3-fold upregulation of CYP11B (P<0.05) compared with high dietary sodium. Strong immunostaining of the KCNJ5 (G protein-activated inward rectifier potassium channel 4), which is frequently mutated in primary aldosteronism, was demonstrated in the zG. mRNA sequencing transcriptome analysis identified significantly altered expression of genes modulated by the renin-angiotensin-aldosterone system in the zG (n=1172) and zona fasciculata (n=280). These genes included many with a known role in the regulation of aldosterone synthesis and adrenal function. The most highly enriched biological pathways in the zG were related to cholesterol biosynthesis, steroid metabolism, cell cycle, and potassium channels. This study provides mechanistic insights into the physiology and pathophysiology of aldosterone production in a species closely related to humans and shows the suitability of pigs as a translational animal model for human adrenal steroidogenesis.

Differential expression of c-fos and tyrosine hydroxylase mRNA in the adrenal gland of the infant rat: evidence for an adrenal hyporesponsive period

Rats exhibit a stress hyporesponsive period from postnatal day (PND) 4-14 in which the neonate displays a minimal corticosterone response to stress. We used the maternal deprivation model to test whether this adrenocortical hyporesponsiveness to stress results from a decrease in adrenal sensitivity to ACTH. Neonates (PND 6, 9, and 12) were injected ip with dexamethasone to block endogenous ACTH release, and 4 h later injected with graded doses of ACTH and killed. In another experiment, neonates were injected with isotonic saline and adrenal glands were collected at 30, 60, and 120 min post injection to examine c-fos and tyrosine hydroxylase mRNA levels using in situ hybridization. Maternally deprived pups demonstrated elevated corticosterone levels at the two highest ACTH doses and showed a greater magnitude in glucocorticoid secretion compared with the nondeprived pups. Maternally deprived pups given a saline injection exhibited elevated basal and stress-induced levels of corticosterone, in contrast to the nondeprived pups that showed a minimal response. Strikingly, maternally deprived pups exhibited elevated levels of adrenocortical c-fos mRNA, whereas the nondeprived pups did not. In contrast, the pattern of c-fos gene expression in the adrenal medulla in both groups did not display any correlation with glucocorticoid secretion. Tyrosine hydroxylase gene expression in the adrenal medulla was observed in both nondeprived and maternally deprived pups, with the latter exhibiting an earlier response of greater magnitude. These results demonstrate that the suppression of steroidogenesis occurs directly in the adrenal cortex and provide further evidence for an adrenal hyporesponsive period in the rat.

Regulation of primary response and specific genes in adrenal cells by peptide hormones and growth factors

Using cultured bovine adrenal fasciculata cells (BAC), we investigated the effects of two hormones, corticotropin (ACTH) and angiotensin II (Ang-II) and two growth factors, insulin-like growth factors I (IGF-I) and transforming growth factor beta 1 (TGF beta 1), on the mRNA levels of nuclear proto-oncogenes of the Fos and Jun families and on the mRNA levels of genes expressed in BAC coding for ACTH and AT1 receptors, cytochrome P450scc and P450 17 alpha and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD). ACTH and IGF-1 increased c-fos and jun-B mRNA levels early with later increases in the levels of mRNA for the ACTH receptor and the three steroidogenic enzymes, and enhanced steroidogenic responses to both ACTH and Ang-II. In contrast, Ang-II increased mRNA coding for the three proto-oncogenes (cfos, c-jun, and jun-B), decreased those for P450 17 alpha and 3 beta-HSD, and caused marked homologous and heterologous steroidogenic desensitization. TGF beta 1 increased only jun-B mRNA and markedly reduced BAC-differentiated functions and steroidogenic responsiveness to both ACTH and Ang-II. The long-term effects of ACTH on human adrenal fasciculata cells were comparable with those observed in BAC, whereas the long term effects of Ang-II and TGF beta 1 were different from those observed in BAC. Whether these species-specific differences are related to a different effect of these factors on proto-oncogene expression is not yet known.

In vivo effects of adrenocorticotropin on c-jun, jun-B, c-fos and fos-B in rat adrenal

We have studied the in vivo effects of adrenocorticotropin (ACTH) on mRNA levels of c-jun, jun-B, c-fos and fos-B, in rat adrenals. In control rats, c-jun mRNA was abundant in both zona glomerulosa (ZG) and zona fasciculatareticularis (ZF-R). Although less abundant than c-jun, the mRNA of jun-B could be detected in both zones, whereas that of c-fos could barely be detected and that of fos-B could not. After an injection with short acting ACTH, mRNA levels of c-jun, c-fos, jun-B and fos-B were maximally increased in both zones within 30 min. Within 5h, the mRNA levels decreased towards control levels for c-jun, to below control levels for jun-B, and to undetectable levels for c-fos and fos-B. After a sustained stimulation by two daily administrations of long acting ACTH, the mRNA of c-jun was still abundant in both zones, although its level decreased by 50% and 80% after 36h and 9 days, respectively, after the first injection. Under such conditions, the mRNA level of jun-B was increased, that of fos-B could barely be detected, and that of c-fos could not be detected. To conclude, these results suggest that jun-B, fos-B, and also c-fos play a role in triggering early events leading to an increased steroidogenesis, as well as a basic role in maintaining the integrity of the adrenal cortex in the case of c-jun and jun-B.

Peptide hormone and growth factor regulation of nuclear proto-oncogenes and specific functions in adrenal cells

Among the large number of immediate early genes, nuclear proto-oncogenes of the Fos and Jun families, have been postulated to be involved in the long-term effects of several growth factors on cell differentiation and/or multiplication. Since adrenal cell differentiated functions appear to be regulated by specific hormones and growth factors, the effects of these factors on proto-oncogene mRNA levels were analysed in bovine adrenal fasciculata cells (BAC) in culture. Corticotropin (ACTH) and insulin-like growth factor I increased c-fos and jun-B mRNA, but had no effect on c-jun mRNA and these early changes were associated with a later increase in BAC specific function [ACTH receptors, cytochrome P450 17 alpha) and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD)] and an enhanced steroidogenic responsiveness to both ACTH and angiotensin-II (A-II). On the other hand, A-II increased the three proto-oncogene (c-fos, c-jun and jun-B) mRNAs, induced a decrease of P450 17 alpha and 3 beta-HSD and caused a marked homologous and heterologous (ACTH) densitization. Transforming growth factor beta 1 which only increased jun-B mRNA, markedly reduced BAC differentiated functions and the steroidogenic responsiveness to both ACTH and A-II. Thus, it is postulated that the proto-oncoproteins encoded by the immediate early genes may play a role in the long-term effects of peptide hormones and growth factors on BAC differentiated functions.

Differential expression of fos family and jun family mRNAs in the rat hypothalamo-pituitary-adrenal axis after immobilization stress

We aimed to clarify the regulatory mechanism of the hypothalamo-pituitary-adrenal axis that plays key roles in initiating stress responses, as well as the roles of immediate early genes in this process. We investigated the stress-induced activation of fos and jun family proto-oncogenes by means of in situ hybridization histochemistry. Immobilization stress induced c-fos and jun B mRNAs in the parvocellular region of the hypothalamic paraventricular nucleus, the anterior and intermediate lobes of pituitary, and in the adrenal gland after 7 min of immobilization, although no c-fos or jun B mRNAs were detected in these and other organs in control rats. The levels of these mRNAs peaked after 30-60 min of immobilization, then declined. A low level of fos B mRNA appeared at 15-30 min and peaked after 60-90 min. On the contrary, c-jun and jun D mRNAs were constitutively expressed in the paraventricular nucleus and adrenal cortex. These findings indicate that the members of the fos and jun family proto-oncogenes play different roles in the transcriptional regulation of genes involved in the hypothalamo-pituitary-adrenal axis, and that monitoring immediate early genes is a useful method for following stress-induced cellular responses in the neuro-endocrine system.

fos-lacZ transgenic mice: mapping sites of gene induction in the central nervous system

A transgenic mouse line containing a fos-lacZ fusion gene was derived in which beta-galactosidase activity identified cell populations expressing fos either constitutively or after stimulation. Seizures and light pulses induced nuclear lacZ activity in defined populations of neurons in vivo, and an array of neurotransmitters, including glutamate, induced the transgene in primary brain cultures. In unstimulated mice, the major sites of fos-lacZ expression were skin, hair follicle, and bone. fos-lacZ mice provide a new avenue for activity mapping studies based on gene expression.

Attenuation of Fos-like immunoreactivity induced by a single electroconvulsive shock in brains of aging mice

c-fos is a proto-oncogene that encodes for a nuclear phosphoprotein with DNA binding properties and is presumed to have an important role in the long-term regulation of neuronal function. It is thought to act as a 'third messenger' molecule in signal transduction systems and its expression has been shown to be induced by a variety of exogenous and endogenous stimuli. This study examines the differential expression of the Fos protein in various brain regions after a single electroconvulsive shock (ECS) in 6-, 13-, and 28-month-old B6C3 mice. The animals received an acute electroconvulsive shock (90 V for 0.3 s), without prior anesthesia, through earclip electrodes and exhibited generalized tonic-clonic seizures lasting 20-36 s. Animals were anesthetized and perfused intracardially with 2.5% acrolein, 4% paraformaldehyde at 0.5, 1.0, 2.0 and 4.0 h postshock. The brains were Vibratome-sectioned (30 microns) and examined using a Fos antibody, directed against a conserved region of both mouse and human Fos by standard immunocytochemical methods. Systematic sampling of the total number of Fos immunostained neurons in amygdala, hippocampus and the cerebral cortex showed peak values at the 1-h time point followed by a steady decline thereafter in all age groups. In a second experiment, Fos-like immunoreactivity was compared 1 h after ECS in the hippocampus, amygdala and the cortex in all 3 age groups. There was increased expression of Fos-like immunoreactivity after ECS- compared to non-ECS-treated controls in all age groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Fos-like immunoreactivity in cultured rat pinealocytes

The expression of Fos-like proteins in cultured rat pinealocytes was investigated immunocytochemically. Pineal glands of 2-day-old rats were dissociated and maintained in culture for 13 days, the last 24 h deprived of animal sera. The pinealocytes were identified morphologically and by serotonin-immunostaining. Incubations with phorbol dibutyrate (PDBu), 8-bromo-cAMP and isoprenaline were carried out for 2 h to test whether Fos-like protein synthesis is activated via serum response element (SRE), calcium/cyclic AMP response element (Ca/CRE) and beta-receptors, respectively. In untreated serum-deprived control cultures, one third of pinealocytes were Fos-immunoreactive suggesting that Fos protein may have a homeostatic role. In cultures incubated with PDBu, more than 70% of the pinealocytes had Fos-like immunoreactive material in their nuclei. Similarly, in cultures incubated with 8-bromo-cAMP or isoprenaline, more than 70% of the pinealocytes were Fos positive. The c-fos gene could be involved in the regulation of pineal melatonin synthesis and SRE and Ca/CRE probably participate in its activation process in pinealocytes.

The immediate-early genes c-fos and c-jun are differentially expressed in the rat adrenal gland after capsaicin treatment

In situ hybridization histochemistry was used to study the expression of c-fos and c-jun mRNA in the rat adrenal gland of untreated and capsaicin treated rats. In untreated animals, very low levels of c-fos mRNA were present both in zona fasciculata and reticulata of the adrenal cortex, with no detectable labelling in the zona glomerulosa or adrenal medulla. In contrast, the levels of c-jun mRNA were high in the cortical layers fasciculata and reticulata, again without labelling in the zona glomerulosa or adrenal medulla. After capsaicin (25 mg/kg, s.c.), a rapid increase in both c-fos and c-jun mRNA levels was observed in adrenal medulla. Capsaicin also induced an increase in c-fos mRNA levels in all 3 cortical layers, especially in the zona glomerulosa, whereas only small changes in c-jun mRNA levels were seen in zona fasciculata and reticulata. The present results indicate that c-fos and c-jun mRNA levels are both increased in the adrenal gland after capsaicin treatment, although the time course, magnitude and regional distribution of these increases differed for the two mRNAs.

Circadian rhythm in c-fos-like immunoreactivity in the rat brain

The circadian variation in the expression of Fos protein(s) in the rat brain was studied immunohistochemically. The number of Fos-immunoreactive nuclei was statistically increased in the hippocampus and caudate putamen after the onset of darkness. Unlike the cells of the hippocampus and putamen the cells in the suprachiasmatic nucleus displayed a circadian variation with the lowest values during the nighttime and the highest in the morning. As the circadian rhythm of Fos expression in the normal rat brain may correlate with that reported for ACTH and corticosteroids, the results suggest that the fos gene is involved in mediating physiological activation of specific neuron populations of intact rats.

Administration of adrenocorticotropic hormone (ACTH) enhances Fos expression in the rat adrenal cortex

The effect of ACTH on the expression of Fos in rat adrenal glands was investigated immunocytochemically at both light and electron microscopic levels. An approximately 4-fold increase in the number of Fos-positive cortical cells per unit area of the adrenal cortex was found 45 min following a single injection of ACTH (i.v., 2 IU/kg b.w.), as compared with the control animals. The number of immunoreactive cells reached a maximum 90 min after ACTH injection and remained high 150 min after the injection. However, 5 h following the injection it declined significantly. At the ultrastructural level, the ACTH-induced Fos-like immunoreactivity was localized in the nuclei of cortical cells, exclusively confined to the nuclear regions associated with the euchromatin. The result that ACTH enhances Fos-like immunoreactivity suggests that ACTH is involved in c-fos induction in adrenal cortical cells. The characteristic intracellular localization of Fos-like immunoreactivity implies that Fos, once synthesized, may be rapidly translocated into the nuclei of the cells, where it participates in transcriptional regulation of genetic events.

Circadian rhythm in c-fos protein expression in the rat adrenal cortex

The circadian variation in the expression of c-fos protein(s) in the adrenal cortex of adult rats was investigated immunocytochemically. The animals were maintained in standard laboratory facilities with a 12:12 h light:dark schedule (07.00-19.00 h) until sacrificed. The number of c-fos immunoreactive (c-fos IR) cells was statistically constant in the zona fasciculata and zona reticulata at 20.00 h and 24.00 h, and 04.00 h, but was decreased to 52% at 08.00 h and to 18% at 12.00 h, respectively, when compared to the 24.00 h value. At 16.00 h, the number of c-fos IR cells was increased again to 63% of the 24.00 h value. In the zona granulosa c-fos IR was observed only at 20.00 h and 24.00 h. Administration of dexamethasone, a potent inhibitor of ACTH release, significantly reduced the number of c-fos IR cells. As the circadian rhythm of c-fos expression in the adrenal cortex correlates to that reported for ACTH secretion from the pituitary, the results suggest that c-fos gene is involved in mediating physiological ACTH-induced responses in the adrenal cortical cells.