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

Differential responses of hypothalamus-pituitary-adrenal axis immediate early genes to corticosterone and circadian drive

The hypothalamus-pituitary-adrenal (HPA) axis diurnal cycle of activity is manifest in circadian rhythms of ACTH and corticosterone secretion, which in the rat peak around the onset of the dark period. This cycle is thought to be driven by daily fluctuations in activity of CRH neurons within the paraventricular nucleus of the hypothalamus (PVN), controlled by suprachiasmatic nucleus inputs. In this study we examined whether the circadian drive that regulates ACTH and corticosterone basal secretion in the rat is reflected in PVN immediate early gene expression and, if so, whether different genes respond uniformly or uniquely to circadian stimulatory input. In addition, we examined how circadian drive and acute stress, two categories of stimuli that induce HPA axis activation, comparatively affect gene expression within different components of the HPA axis (c-fos mRNA, CRH heteronuclear RNA, and zif268 mRNA in PVN; c-fos mRNA, proopiomelanocortin heteronuclear RNA, and zinc finger 268 mRNA in anterior pituitary; c-fos mRNA and nerve growth factor I-B mRNA in adrenal cortex). Finally, we examined whether circadian differences in gene expression depend on endogenous glucocorticoids and, if so, whether the dependence is on an acute or permissive influence of the hormone. We found that a circadian drive that regulates HPA axis basal hormone secretion is also manifest on basal c-fos gene expression in the PVN. Moreover, we show that different immediate early genes within the HPA axis anatomical components display different diurnal patterns of gene expression. These differential patterns result, in part, from gene-specific responses to circadian signals and acute and/or permissive glucocorticoid actions.

Circadian expression of genes regulating food intake

OBJECTIVE

The Agouti-related protein (AgRP), neuropeptide Y (NPY), proopiomelanocortin (POMC), cocaine and amphetamine-regulated transcript (CART), Orexin, melanin concentrating hormone (MCH), leptin, and its hypothalamic receptor (LR) are key regulators of food intake and energy homeostasis. In the present study, we examined the circadian expression profiles of these genes.

RESEARCH METHODS AND PROCEDURES

We used quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) to measure mRNA levels, spectral analysis to evaluate periodicity, and correlation analysis to examine for associations with diurnal food intake.

RESULTS

No gene in particular stood out as a strong candidate, but the overall circadian expression profiles of leptin and its hypothalamic receptor came close to statistically and graphically resembling the diurnal feeding behavior of mice. In mathematical terms, adrenal AgRP exhibited strong circadian expression and had the highest correlation with food intake, followed by leptin. Yet its highest point of expression occurred 8 hours after nocturnal food intake had peaked, suggesting that adrenal AgRP could not play a direct role in the initiation of nocturnal feeding; neither did hypothalamic AgRP, NPY, POMC, CART, Orexin, or MCH.

DISCUSSION

These data show that ad libitum feeding in mice is influenced by complex central and peripheral circuits involving orexigenic and anorectic agents of which leptin and its hypothalamic receptor could play more prevalent roles.

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.

The acute and chronic effects of adrenocorticotropin on the levels of messenger ribonucleic acid and protein of steroidogenic enzymes in rat adrenal in vivo

The purpose of this study was to evaluate the effects of acute (a single injection) and chronic stimulation (twice daily injection for 9 days) by ACTH on changes occurring in the temporal expression of steroidogenic enzymes in the rat adrenal in vivo. Under acute ACTH stimulation, the level of steroidogenic acute regulatory protein (StAR) messenger RNA (mRNA) was increased within 0.5 h in both zona glomerulosa (ZG) and zona fasciculata-reticularis (ZFR), with maximal increases of 220-370% and 300-350% in the ZG and ZFR, respectively. Increases in the levels of StAR protein in homogenates were also found in the ZG (700%) and the ZFR (300%), but were delayed compared with those of their mRNA. Furthermore, the increase in mitochondrial StAR protein was concomitant with that in the homogenate, indicating that the entry of StAR into mitochondria might not be necessary to increase steroidogenesis during the early stimulatory phase. The levels of c-jun, c-fos, junB, and fosB mRNA in ZG and ZFR were also rapidly maximally elevated within 0.5-1 h after ACTH administration and fell to near control levels 5 h posttreatment. The levels of c-jun protein were already increased in both zones at 1 h, reached 200% at 3 h, and remained elevated 5 h post-ACTH treatment. The levels of c-Fos protein were maximally increased by 240% in both zones after 1 h and decreased thereafter to control values at 5 h. Few changes were observed in the adrenal protein contents of cholesterol side-chain cleavage cytochrome P450 (P450scc), cytochrome P450 11beta-hydroxylase (P450C11), cytochrome P450 21-hydroxylase (P450C21), and 3beta-hydroxysteroid dehydrogenase (3betaHSD). Under chronic stimulation by ACTH, we observed elevations in the levels of plasma corticosteroids and changes in the mRNA and protein levels of many adrenal steroidogenic enzymes in both zones. In the ZG, administration of ACTH for 9 days provoked an increase in the level of StAR mRNA (210-270%) and a decrease in the levels of 3betaHSD, cytochrome P450 aldosterone synthase (P450aldo), and AT1 receptor mRNA (by 40%, 70%, and 90%, respectively), whereas the levels of P450scc and P450C21 mRNA did not differ significantly from the control values. Western blotting analysis showed that the adrenal ZG protein levels of StAR and P450scc were increased (150%), 3betaHSD was not changed, and P450C21 was decreased by 70%. In the ZFR, the levels of P450scc and StAR mRNAs were increased (260% and 570-870%, respectively). The levels of 3betaHSD, P450C21, and P450C11 mRNA did not differ from control values in that zone. Western blotting analysis showed that the ZFR protein level of 3betaHSD was not changed, P450scc and P450C21 were decreased by 40% and 60%, respectively, and StAR was increased by 160%. Although c-fos and fosB mRNAs were undetectable after 9 days of chronic ACTH treatment, c-jun mRNA and its protein were still detectable, suggesting a basic role for this protooncogene in maintaining the integrity and function of the adrenal cortex. When dexamethasone was administered to rats for 5 days to inhibit their ACTH secretion, the mRNA levels of many steroidogenic enzymes were decreased, with the exception of StAR, 3betaHSD, and P450aldo. These results confirm the importance of physiological concentrations of ACTH in maintaining normal levels of adrenocortical enzymes and also indicate that in addition to ACTH, other factors are involved in controlling the expression of StAR, 3betaHSD, and P450aldo. In conclusion, we showed that ACTH acutely increases StAR mRNA followed, after a delay, by an increase in the level of StAR protein; this suggests that posttranslational modifications of the StAR precursor occurred during the early stimulatory phase and before the apparent translation of the newly formed mRNA. The rapid induction of protooncogenes suggests their participation in the action of ACTH to stimulate steroidogenesis. (ABSTRACT TRUNCATED)

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.

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.

Diurnal expression of c-fos in the mouse retina

The diurnal levels of c-fos mRNA were studied in the mouse retinas by means of RNA blot analysis. Mice were kept on a 12/12 h dark/light cycle and gene expression was studied at various time points during the day and night periods. The highest levels of c-fos mRNA were measured during the first half of the night period. The high levels persisted for about 4-5 h. The c-fos mRNA levels declined during the second half of the night period and remained low during the day period. Continuous illumination of mice during the first hours of the night period prevented the increase in c-fos mRNA. If mice were kept in the dark during the day period, they failed to show an increase in c-fos mRNA levels in the subsequent night period. Hence, following activation of c-fos during the night period, a refractory period exists at which illumination is required before c-fos can be induced again by dark. Although light appears to suppress the activation of c-fos in the night period, a short lived burst in c-fos expression of 30-60 min in duration was observed when dark-adapted animals were illuminated, either at the transition between the dark and light period or during the dark period. Thus, it appears that c-fos is activated in at least two different cell types in the retina which respond differently to light and dark stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)

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.