New integrative approaches to discovery of pathophysiological mechanisms triggered by night shift work.

Synchronization to periodic cues such as food/water availability and light/dark cycles is crucial for living organisms' homeostasis. Both factors have been heavily influenced by human activity, with artificial light at night (ALAN) being an evolutionary challenge imposed over roughly the last century. Evidence from studies in humans and animal models shows that overt circadian misalignment, such as that imposed to about 20% of the workforce by night shift work (NSW), negatively impinges on the internal temporal order of endocrinology, physiology, metabolism, and behavior. Moreover, NSW is often associated to mistimed feeding, with both unnatural behaviors being known to increase the risk of chronic diseases, such as eating disorders, overweight, obesity, cardiovascular, metabolic (particularly type 2 diabetes mellitus) and gastrointestinal disorders, some types of cancer, as well as mental disease including sleep disturbances, cognitive disorders, and depression. Regarding deleterious effects of ALAN on reproduction, increased risk of miscarriage, preterm delivery and low birth weight have been reported in shift-worker women. These mounting lines of evidence prompt further efforts to advance our understanding of the effects of long-term NSW on health. Emerging data suggest that NSW with or without mistimed feeding modify gene expression and functional readouts in different tissues/organs, which seem to translate into persistent cardiometabolic and endocrine dysfunction. However, this research avenue still faces multiple challenges, such as functional characterization of new experimental models more closely resembling human long-term NSW and mistimed feeding in males versus females; studying further target organs; identifying molecular changes by means of deep multi-omics analyses; and exploring biomarkers of NSW with translational medicine potential. Using high-throughput and systems biology is a relatively new approach to study NSW, aimed to generate experiments addressing new biological factors, pathways, and mechanisms, going beyond the boundaries of the circadian clock molecular machinery.

Gestational chronodisruption impairs hippocampal expression of NMDA receptor subunits Grin1b/Grin3a and spatial memory in the adult offspring.

Epidemiological and experimental evidence correlates adverse intrauterine conditions with the onset of disease later in life. For a fetus to achieve a successful transition to extrauterine life, a myriad of temporally integrated humoral/biophysical signals must be accurately provided by the mother. We and others have shown the existence of daily rhythms in the fetus, with peripheral clocks being entrained by maternal cues, such as transplacental melatonin signaling. Among developing tissues, the fetal hippocampus is a key structure for learning and memory processing that may be anticipated as a sensitive target of gestational chronodisruption. Here, we used pregnant rats exposed to constant light treated with or without melatonin as a model of gestational chronodisruption, to investigate effects on the putative fetal hippocampus clock, as well as on adult offspring's rhythms, endocrine and spatial memory outcomes. The hippocampus of fetuses gestated under light:dark photoperiod (12:12 LD) displayed daily oscillatory expression of the clock genes Bmal1 and Per2, clock-controlled genes Mtnr1b, Slc2a4, Nr3c1 and NMDA receptor subunits 1B-3A-3B. In contrast, in the hippocampus of fetuses gestated under constant light (LL), these oscillations were suppressed. In the adult LL offspring (reared in LD during postpartum), we observed complete lack of day/night differences in plasma melatonin and decreased day/night differences in plasma corticosterone. In the adult LL offspring, overall hippocampal day/night difference of gene expression was decreased, which was accompanied by a significant deficit of spatial memory. Notably, maternal melatonin replacement to dams subjected to gestational chronodisruption prevented the effects observed in both, LL fetuses and adult LL offspring. Collectively, the present data point to adverse effects of gestational chronodisruption on long-term cognitive function; raising challenging questions about the consequences of shift work during pregnancy. The present study also supports that developmental plasticity in response to photoperiodic cues may be modulated by maternal melatonin.

Impact of gestational chronodisruption on fetal cardiac genomics.

We recently reported that gestational chronodisruption induces fetal growth restriction and marked effects on fetal adrenal physiology. Here, whole-transcriptome profiling was used to test whether gestational chronodisruption modifies gene expression in the fetal heart, potentially altering cardiac development. At day 10 of gestation (E10), pregnant rats were randomized in two groups: constant light (LL) and control 12 h light/12 h dark photoperiod (LD). RNA isolated from E18 heart was subjected to microarray analysis (Affymetrix platform for 28,000 genes). Integrated transcriptional changes were assessed by gene ontology and pathway analysis. Significant differential expression was found for 383 transcripts in LL relative to LD fetal heart (280 up-regulated and 103 down-regulated); with 42 of them displaying a 1.5-fold or greater change in gene expression. Deregulated markers of cardiovascular disease accounted for alteration of diverse gene networks in LL fetal heart, including local steroidogenesis and vascular calcification, as well as cardiac hypertrophy, stenosis and necrosis/cell death. DNA integrity was also overrepresented, including a 2.1-fold increase of Hmga1 mRNA, which encodes for a profuse architectural transcription factor. microRNA analysis revealed up-regulation of miRNAs 218-1 and 501 and concurrent down-regulation of their validated target genes. In addition, persistent down-regulation of Kcnip2 mRNA and hypertrophy of the left ventricle were found in the heart from 90 days-old offspring from LL mothers. The dysregulation of a relevant fraction of the fetal cardiac transcriptome, together with the diversity and complexity of the gene networks altered by gestational chronodisruption, suggest enduring molecular changes which may shape the hypertrophy observed in the left ventricle of adult LL offspring.

Melatonina inhibe la respuesta de cortisol a ACTH: posible mediación a través del gen reloj Per1 / Melatonin inhibition of the cortisol response to ACTH may be exerted through period circadian protein homolog 1 (Per1)

Background: Circadian cortisol production results from the interaction of the circadian production of ACTH, the autonomic nervous system and intrinsic factors within the gland. An additional regulator is the neuro-hormone melatonin. In human adrenal gland cultures, melatonin inhibited ACTH stimulated cortisol production and Per1 mRNA expression. ACTH actions on the adrenal involve early and late responses. Aim: To investigate the effects of melatonin on the time course of ACTH stimulated cortisol production and of Per1 expression in the lamb adrenal gland. Material and Methods: Adrenal glands and plasma of five newborn lambs were obtained. Adrenal glands were cut in 15 mg explants. Three of these explants were stored for RNA extraction. The rest of explants were using in different culture protocols with ACTH and melatonin. Results: Lambs had an in vivo a circadian variation in plasma cortisol and in adrenal Per1 expression. In vitro, ACTH stimulated an early and late increase in cortisol production and an early increase in Per1 expression reaching a maximum at 3 hours of treatment. Melatonin inhibited the early Per1 response to ACTH without affecting the early ACTH stimulated cortisol production. However, melatonin inhibited the late response of cortisol production to ACTH. Conclusions: The inhibitory actions of melatonin on Per1 response to ACTH may contribute to the inhibitory effects of melatonin on adrenal steroidogenic response to ACTH.

La melatonina reduce la respuesta de cortisol al ACTH en humanos / Melatonin reduces cortisol response to ACTH in humans

Background: Melatonin receptors are widely distributed in human tissues but they have not been reported in human adrenal gland. Aim: To assess if the human adrenal gland expresses melatonin receptors and if melatonin affeets cortisol response to ACTH in dexamethasone suppressed volunteers. Material and methods: Adrenal glands were obtained from 4 patients undergoing unilateral nephrectomy-adrenalectomy for renal cáncer. Expression of mRNA MT1 and MT2 melatonin receptors was measured by Reverse Transcriptase Polymerase Chain Reaction (RT-PCR). The effect of melatonin on the response to intravenous (i.v.) ACTH was tested (randomized cross-over, double-blind, placebo-controlled tríal) in eight young healthy males pretreated with dexamethasone (1 mg) at 23:00 h. On the next day at 08:00 h, an i.v. Une was inserted, at 08:30 h, and after a blood sample, subjeets ingested 6 mg melatonin or placebo. At 09:00 h, 1-24 ACTH (Cortrosyn, 1µg/1.73 m² body surface área) was injected, drawing samples at 0, 15, 30, 45 and 60 minutes after. Melatonin, cortisol, cortisone, progesterone, aldosterone, DHEA-S, testosterone and prolactin were measured by immunoassay. Results: The four adrenal glands expressed only MT1 receptor mRNA. Melatonin ingestión reduced the cortisol response to ACTH from 14.6+1.45µg/dl at 60 min in the placebo group to 10.8+1.2µg/dl in the melatonin group (p <0.01 mixed model test). It did not affect other steroid hormone levels and abolished the morningphysiological decline of prolactin. Conclusions: The expression ofMTl melatonin receptor in the human adrenal, and the melatonin reduction of ACTH-stimulated cortisol production suggest a direct melatonin action on the adrenal gland .

[Melatonin reduces cortisol response to ACTH in humans]. / La melatonina reduce la respuesta de cortisol al ACTH en humanos.

BACKGROUND: Melatonin receptors are widely distributed in human tissues but they have not been reported in human adrenal gland. AIM: To assess if the human adrenal gland expresses melatonin receptors and if melatonin affects cortisol response to ACTH in dexamethasone suppressed volunteers. MATERIAL AND METHODS: Adrenal glands were obtained from 4 patients undergoing unilateral nephrectomy-adrenalectomy for renal cancer. Expression of mRNA MT1 and MT2 melatonin receptors was measured by Reverse TranscriPtase Polymerase Chain Reaction (RT-PCR). The effect of melatonin on the response to intravenous (i.v.) ACTH was tested (randomized cross-over, double-blind, placebo-controlled trial) in eight young healthy males pretreated with dexamethasone (1 mg) at 23:00 h. On the next day, at 08:00 h, an i.v. line was inserted, at 08:30 h, and after a blood sample, subjects ingested 6 mg melatonin or placebo. At 09:00 h, 1-24 ACTH (Cortrosyn, 1 microg/1.73 m2 body surface area) was injected, drawing samples at 0, 15, 30, 45 and 60 minutes after. Melatonin, cortisol, cortisone, progesterone, aldosterone, DHEA-S, testosterone and prolactin were measured by immunoassay. RESULTS: The four adrenal glands expressed only MT1 receptor mRNA. Melatonin ingestion reduced the cortisol response to ACTH from 14.6 +/- 1.45 microg/dl at 60 min in the placebo group to 10.8 +/- 1.2 microg/dl in the melatonin group (p < 0.01 mixed model test). It did not affect other steroid hormone levels and abolished the morning physiological decline of prolactin. CONCLUSIONS: The expression of MT1 melatonin receptor in the human adrenal, and the melatonin reduction of ACTH-stimulated cortisol production suggest a direct melatonin action on the adrenal gland.

Rhythmic expression of functional MT1 melatonin receptors in the rat adrenal gland.

We previously demonstrated that melatonin is involved in the regulation of adrenal glucocorticoid production in diurnal primates through activation of MT1 membrane-bound melatonin receptors. However, whether melatonin has a similar role in nocturnal rodents remains unclear. Using an integrative approach, here we show that the adult rat adrenal gland expresses a functional MT1 melatonin receptor in a rhythmic fashion. We found that: 1) expression of the cognate mRNA encoding for the MT1 membrane-bound melatonin receptor, displaying higher levels in the day/night transition (1800-2200 h); 2) expression of the predicted 37-kDa MT1 polypeptide in immunoblots from adrenals collected at 2200 h but not 1000 h; 3) no expression of the MT2 melatonin receptor mRNA and protein; 4) specific high-affinity 2-[(125)I]iodomelatonin binding in membrane fractions and frozen sections from adrenals collected at 2200 h but not 0800 h (dissociation constant = 14.22 +/- 1.23 pm; maximal binding capacity = 0.88 +/- 0.02 fmol/mg protein); and 5) in vitro clock time-dependent inhibition of ACTH-stimulated corticosterone production by 1-100 nm melatonin, which was reversed by 1 microm luzindole (a melatonin membrane receptor antagonist). Our findings indicate not only expression but also high amplitude diurnal variation of functional MT1 melatonin receptors in the rat adrenal gland. It is conceivable that plasma melatonin may play a role to fine-tune corticosterone production in nocturnal rodents, probably contributing to the down slope of the corticosterone rhythm.

Maternal melatonin stimulates growth and prevents maturation of the capuchin monkey fetal adrenal gland.

The primate fetal adrenal reaches a large size relative to body weight followed by a rapid decrease in size in the postnatal period. We tested the hypothesis that maternal melatonin stimulates growth and prevents maturation of the primate fetal adrenal gland. We suppressed maternal melatonin by exposing eight pregnant capuchin monkeys to constant light (LL) from 63% to 90% gestation (term 155 days). Three of these received daily oral melatonin replacement (LL + Mel). Five mothers remaining in light:dark cycle were used as controls. Fetuses were delivered at 90% gestation. The absence of maternal melatonin selectively decreased fetal adrenal weight (Control: 488.8 +/- 51.5; LL: 363.2 +/- 27.7 and LL + Mel 519 +/- 46 mg; P < 0.05 ANOVA) without effecting fetal weight, placental weight or the weight of other fetal tissues. Changes in fetal adrenal size were accompanied by an increase in the levels of Delta5-3beta-hydroxysteroid dehydrogenase (3beta-HSD) mRNA (Control: 0.8 +/- 0.2; LL: 5.2 +/- 0.6 and LL + Mel 0.8 +/- 0.1; 3beta-HSD/18S-rRNA; P < 0.05 ANOVA). In vitro we found that maternal melatonin suppression increased basal progesterone production to levels similar to those of the adult adrenal gland (Control: 0.36 +/- 0.09; LL 0.99 +/- 0.13; LL + Mel 0.18 +/- 0.06 and adult: 0.88 +/- 0.10 ng/mg of tissue; P < 0.05 ANOVA) but no change in cortisol production. We found an increased production of cortisone (Control: 1.65 +/- 0.60; LL: 5.44 +/- 0.63; LL + Mel: 2.90 +/- 0.38 and adult: 1.70 +/- 0.45 ng/mg of tissue; P < 0.05 ANOVA). Collectively, the effects of maternal melatonin suppression and their reversion by maternal melatonin replacement suggest that maternal melatonin stimulates growth and prevents maturation of the capuchin monkey fetal adrenal gland.

Maternal melatonin selectively inhibits cortisol production in the primate fetal adrenal gland.

We tested the hypothesis that in primates, maternal melatonin restrains fetal and newborn adrenal cortisol production. A functional G-protein-coupled MT1 membrane-bound melatonin receptor was detected in 90% gestation capuchin monkey fetal adrenals by (a) 2-[(125)I] iodomelatonin binding (K(d), 75.7 +/- 6.9 pm; B(max), 2.6 +/- 0.4 fmol (mg protein)(-1)), (b) cDNA identification, and (c) melatonin inhibition of adrenocorticotrophic hormone (ACTH)- and corticotrophin-releasing hormone (CRH)-stimulated cortisol but not of dehydroepiandrosterone sulphate (DHAS) production in vitro. Melatonin also inhibited ACTH-induced 3beta-hydroxysteroid dehydrogenase mRNA expression. To assess the physiological relevance of these findings, we next studied the effect of chronic maternal melatonin suppression (induced by exposure to constant light during the last third of gestation) on maternal plasma oestradiol during gestation and on plasma cortisol concentration in the 4- to 6-day-old newborn. Constant light suppressed maternal melatonin without affecting maternal plasma oestradiol concentration, consistent with no effect on fetal DHAS, the precursor of maternal oestradiol. However, newborns from mothers under constant light condition had twice as much plasma cortisol as newborns from mothers maintained under a normal light-dark schedule. Newborns from mothers exposed to chronic constant light and daily melatonin replacement had normal plasma cortisol concentration. Our results support a role of maternal melatonin in fetal and neonatal primate cortisol regulation.

The Circadian Timing system: Making Sense of day/night gene expression

The circadian time-keeping system ensures predictive adaptation of individuals to the reproducible 24-h day/night alternations of our planet by generating the 24-h (circadian) rhythms found in hormone release and cardiovascular, biophysical and behavioral functions, and others. In mammals, the master clock resides in the suprachiasmatic nucleus (SCN) of the hypothalamus. The molecular events determining the functional oscillation of the SCN neurons with a period of 24-h involve recurrent expression of several clock proteins that interact in complex transcription/translation feedback loops. In mammals, a glutamatergic monosynaptic pathway originating from the retina regulaltes the clock gene expression pattern in the SCN neurons, synchronizing them to the light:dark cycle. The emerging concept is that neural/humoral output signals from the SCN impinge upon peripheral clocks located in other areas of the brain, heart, lung, gastrointestinal tract, liver, kidney, fibroblasts, and most of the cell phenotypes, resulting in overt circadian rhythms in integrated physiological functions. Here we review the impact of day/night alternation on integrated physiology; the molecular mechanisms and input/output signaling pathways involved in SCN circadian function; the current concept of peripheral clocks; and the potential role of melatonin as a circadian neuroendocrine transducer.