Glucocorticoids are required for meal-induced changes in the expression of hypothalamic neuropeptides

Glucocorticoids contribute to metabolic and liver impairments induced by lactation overnutrition in male adult rats

Introduction: Lactation overnutrition is a programming agent of energy metabolism, and litter size reduction leads to the early development of obesity, which persists until adulthood. Liver metabolism is disrupted by obesity, and increased levels of circulating glucocorticoids are pointed as a possible mediator for the obesity development, since bilateral adrenalectomy (ADX) can reduce obesity in different models of obesity. Methods: This study aimed to evaluate the effects of glucocorticoids on metabolic changes and liver lipogenesis and insulin pathway induced by lactation overnutrition. For this, on the postnatal day 3 (PND), 3 pups (small litter-SL) or 10 pups (normal litter-NL) were kept with each dam. On PND 60, male Wistar rats underwent bilateral adrenalectomy (ADX) or fictitious surgery (sham), and half of ADX animals received corticosterone (CORT- 25 mg/L) diluted in the drinking fluid. On PND 74, the animals were euthanized by decapitation for trunk blood collection, and liver dissection and storage. Results and Discussion: SL rats presented increased corticosterone, free fatty acids, total and LDL-cholesterol plasma levels, without changes in triglycerides (TG) and HDL-cholesterol. The SL group also showed increased content of liver TG, and expression of fatty acid synthase (FASN), but decreased expression of PI3K_p110 in the liver, compared to NL rats. In the SL group, the ADX decreased plasma levels of corticosterone, FFA, TG and HDL cholesterol, liver TG, and liver expression of FASN, and IRS2, compared to sham animals. In SL animals, CORT treatment increased plasma levels of TG and HDL cholesterol, liver TG, and expression of FASN, IRS1, and IRS2, compared with the ADX group. In summary, the ADX attenuated plasma and liver changes observed after lactation overnutrition, and CORT treatment could reverse most ADX-induced effects. Thus, increased circulating glucocorticoids are likely to play a pivotal role in liver and plasma impairments induced by lactation overnutrition in male rats.

Identification and characterization of hypothalamic circular RNAs associated with bovine residual feed intake

Residual feed intake (RFI) is crucial economic indicator used for calculating the feed efficiency of growing beef cattle. circRNA plays an important biological role in gene transcriptional regulation, but little is known about its potential functional regulation underlying RFI phenotypic variation. As the core center of regulation of animal feeding, the hypothalamus is closely associated with RFI. Therefore, the present study aimed to identify the key genes and functional pathways contributing to variance in cattle RFI phenotypes using RNA sequencing from hypothalamic tissue samples, in order to gain insight into the potential regulatory role of circRNAs in bovine RFI phenotypic variation. Differentially expressed genes were detected by RNA sequencing for beef cattle in the high and low RFI groups, followed by GO, KEGG enrichment, and circRNA-miRNA co-expression network analysis. A total of 257 circRNAs were differentially expressed between the two groups, with 128 significantly upregulated and 129 significantly downregulated genes in H group compared to L group. Among them, 9 unique circRNAs were present in group L and 4 unique circRNAs were present in group H. GO and KEGG enrichment analysis of the source genes of the differentially expressed circRNAs revealed that they were mainly involved in metabolic processes, such as cellular metabolic processes, cellular macromolecular metabolic processes, and regulatory pathways related to nutrient metabolism, including protein and amino acid metabolism, as well as vitamin metabolism and pancreatic secretion associated with the animal feeding behavior. The circRNAs detected in this study were mostly novel, and have not been investigated directly to be associated with the RFI phenotype. Interestingly, most miRNAs of differentially expressed circRNAs predicted based on the circRNA-miRNA co-expression network analysis by using top 50 differentially expressed circRNAs and 13 unique circRNAs, have been reported to be related to animal RFIs, implying that circRNAs in bovine hypothalamic tissue may regulate phenotypic variation in RFI through miRNAs. The study results illustrate the complex biological functions of the hypothalamus in regulating feed efficiency and showing the potential role of circRNAs in the feeding behavior regulation of livestock, which would contributing to expanding the understanding of circRNA.

Adrenalectomy impairs vasoactive intestinal peptide-induced changes in food intake and plasma parameters

PURPOSE

The aim of this study is to evaluate the effects of adrenalectomy (ADX) and glucocorticoid in the changes induced by intracerebroventricular (ICV) administration of vasoactive intestinal peptide (VIP) on food intake and plasma parameters, as well as VIP receptor subtype 2 (VPAC2) mRNA expression in different hypothalamic nuclei of male rats.

METHODS

Male Wistar rats (260-280 g) were subjected to ADX or sham surgery, 7 days before the experiments. Half of ADX animals received corticosterone (ADX + CORT) in the drinking water. Animals with 16 h of fasting received ICV microinjection of VIP or saline (0.9% NaCl). After 15 min: (1) animals were fed, and the amount of food ingested was quantified for 120 min; or (2) animals were euthanized and blood was collected for biochemical measurements. Determination of VPAC2 mRNA levels in LHA, ARC, and PVN was performed from animals with microinjection of saline.

RESULTS

VIP treatment promoted the anorexigenic effect, which was not observed in ADX animals. Microinjection of VIP also induced an increase in blood plasma glucose and corticosterone levels, and a reduction in free fatty acid plasma levels, but adrenalectomy abolished these effects. In addition, adrenalectomy reduced mRNA expression of VPAC2 in the lateral hypothalamic area and arcuate nucleus, but not in the paraventricular nucleus.

CONCLUSIONS

These results suggest that adrenal glands are required for VIP-induced changes in food intake and plasma parameters, and these responses are associated with reduction in the expression of VPAC2 in the hypothalamus after adrenalectomy.

Extra-adrenal glucocorticoids contribute to the postprandial increase of circulating leptin in mice

Leptin, an adipokine secreted by white adipocytes, is known for its function in regulating food intake and energy expenditure, but the mechanisms regulating its circulating levels is not fully understood. Our previous findings suggest that as yet unidentified humoral factors released from enterocytes are involved. The present study tested glucocorticoids (GCs) as candidate factors. Supplementation of corticosterone and cortisol promoted leptin production in murine adipocytes from the 3T3-L1 cell strain and human adipocytes from the Simpson Golabi-Behmel syndrome (SGBS) cell strain, respectively. These changes were observed in the absence but not presence of the GC-receptor antagonist mifepristone. The cortisol concentration in conditioned medium (CM) of human enterocyte-like Caco-2 cells was increased by phorbol-12-myristate 13-acetate and decreased by metyrapone. When SGBS adipocytes were cultured in these CMs, leptin production was positively associated with cortisol concentrations. During a 2-h refeeding after fasting, plasma leptin levels continued to increase in sham-operated mice, transiently increased at 60 min in adrenalectomized mice, and were unchanged in mifepristone-administered mice. These results suggest that extra-adrenal GCs contribute to the GC-receptor signaling-dependent increase of postprandial circulating leptin, whereas further studies will be required to determine whether enterocytes participate in the GCs-mediated increase of postprandial circulating leptin.

The Functional and Clinical Significance of the 24-Hour Rhythm of Circulating Glucocorticoids

Adrenal glucocorticoids are major modulators of multiple functions, including energy metabolism, stress responses, immunity, and cognition. The endogenous secretion of glucocorticoids is normally characterized by a prominent and robust circadian (around 24 hours) oscillation, with a daily peak around the time of the habitual sleep-wake transition and minimal levels in the evening and early part of the night. It has long been recognized that this 24-hour rhythm partly reflects the activity of a master circadian pacemaker located in the suprachiasmatic nucleus of the hypothalamus. In the past decade, secondary circadian clocks based on the same molecular machinery as the central master pacemaker were found in other brain areas as well as in most peripheral tissues, including the adrenal glands. Evidence is rapidly accumulating to indicate that misalignment between central and peripheral clocks has a host of adverse effects. The robust rhythm in circulating glucocorticoid levels has been recognized as a major internal synchronizer of the circadian system. The present review examines the scientific foundation of these novel advances and their implications for health and disease prevention and treatment.

Restricted Feeding Schedules Modulate in a Different Manner the Expression of Clock Genes in Rat Hypothalamic Nuclei

Food access restriction is associated to changes in gene expression of the circadian clock system. However, there are only a few studies investigating the effects of non-photic synchronizers, such as food entrainment, on the expression of clock genes in the central oscillators. We hypothesized that different feeding restriction patterns could modulate the expression of clock genes in the suprachiasmatic nucleus (SCN) “master” clock and in extra-SCN oscillators such as the paraventricular (PVN) and arcuate (ARC) hypothalamic nuclei. Wistar rats were divided into four groups: Control group (CG; food available ad libitum), Restricted night-fed (RF-n; food access during 2 h at night), Restricted day-fed (RF-d; food access during 2 h at daytime), Day-fed (DF; food access during 12 h at daytime). After 21 days, rats were decapitated between ZT2-ZT3 (0800–0900 h); ZT11-ZT12 (1700–1800 h), or ZT17-18 (2300–2400 h). Plasma corticosterone was measured by radioimmunoassay (RIA). The expression of Clock, Bmal1, Per1, Per2, Per3, Cry1, Cry2, Rev-erbα, and Rorα were assessed in SCN, PVN, and ARC hypothalamic nuclei by RT-PCR and calculated by the 2^{[−DeltaDeltaCT(Cyclethreshold)]}(2^−ΔΔCT) method. Restricted food availability during few h led to decreased body weight in RF-n and RF-d groups compared to controls and DF group. We also observed an anticipatory corticosterone peak before food availability in RF-n and RF-d groups. Furthermore, the pattern of clock gene expression in response to RF-n, RF-d, and DF schedules was affected differently in the SCN, PVN, and ARC hypothalamic nuclei. In conclusion, the master oscillator in SCN as well as the oscillator in PVN and ARC, all brain areas involved in food intake, responds in a tissue-specific manner to feeding restriction.

Elevated Hypothalamic Glucocorticoid Levels Are Associated With Obesity and Hyperphagia in Male Mice

Glucocorticoid (Gc) excess, from endogenous overproduction in disorders of the hypothalamic-pituitary-adrenal axis or exogenous medical therapy, is recognized to cause adverse metabolic side effects. The Gc receptor (GR) is widely expressed throughout the body, including brain regions such as the hypothalamus. However, the extent to which chronic Gcs affect Gc concentrations in the hypothalamus and impact on GR and target genes is unknown. To investigate this, we used a murine model of corticosterone (Cort)-induced obesity and analyzed Cort levels in the hypothalamus and expression of genes relevant to Gc action. Mice were administered Cort (75 μg/mL) or ethanol (1%, vehicle) in drinking water for 4 weeks. Cort-treated mice had increased body weight, food intake, and adiposity. As expected, Cort increased plasma Cort levels at both zeitgeber time 1 and zeitgeber time 13, ablating the diurnal rhythm. Liquid chromatography dual tandem mass spectrometry revealed a 4-fold increase in hypothalamic Cort, which correlated with circulating levels and concentrations of Cort in other brain regions. This occurred despite decreased 11β-hydroxysteroid dehydrogenase (Hsd11b1) expression, the gene encoding the enzyme that regenerates active Gcs, whereas efflux transporter Abcb1 mRNA was unaltered. In addition, although Cort decreased hypothalamic GR (Nr3c1) expression 2-fold, the Gc-induced leucine zipper (Tsc22d3) mRNA increased, which indicated elevated GR activation. In keeping with the development of hyperphagia and obesity, Cort increased Agrp, but there were no changes in Pomc, Npy, or Cart mRNA in the hypothalamus. In summary, chronic Cort treatment causes chronic increases in hypothalamic Cort levels and a persistent elevation in Agrp, a mediator in the development of metabolic disturbances.

Glucocorticoids and non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the global obesity and metabolic disease epidemic and is rapidly becoming the leading cause of liver cirrhosis and indication for liver transplantation worldwide. The hallmark pathological finding in NAFLD is excess lipid accumulation within hepatocytes, but it is a spectrum of disease ranging from benign hepatic steatosis to steatohepatitis through to fibrosis, cirrhosis and risk of hepatocellular carcinoma. The exact pathophysiology remains unclear with a multi-hit hypothesis generally accepted as being required for inflammation and fibrosis to develop after initial steatosis. Glucocorticoids have been implicated in the pathogenesis of NAFLD across all stages. They have a diverse array of metabolic functions that have the potential to drive NAFLD acting on both liver and adipose tissue. In the fasting state, they are able to mobilize lipid, increasing fatty acid delivery and in the fed state can promote lipid accumulation. Their action is controlled at multiple levels and in this review will outline the evidence base for the role of GCs in the pathogenesis of NAFLD from cell systems, rodent models and clinical studies and describe interventional strategies that have been employed to modulate glucocorticoid action as a potential therapeutic strategy.

Developmental programming of hypothalamic neuronal circuits: impact on energy balance control

The prevalence of obesity in adults and children has increased globally at an alarming rate. Mounting evidence from both epidemiological studies and animal models indicates that adult obesity and associated metabolic disorders can be programmed by intrauterine and early postnatal environment- a phenomenon known as "fetal programming of adult disease." Data from nutritional intervention studies in animals including maternal under- and over-nutrition support the developmental origins of obesity and metabolic syndrome. The hypothalamic neuronal circuits located in the arcuate nucleus controlling appetite and energy expenditure are set early in life and are perturbed by maternal nutritional insults. In this review, we focus on the effects of maternal nutrition in programming permanent changes in these hypothalamic circuits, with experimental evidence from animal models of maternal under- and over-nutrition. We discuss the epigenetic modifications which regulate hypothalamic gene expression as potential molecular mechanisms linking maternal diet during pregnancy to the offspring's risk of obesity at a later age. Understanding these mechanisms in key metabolic genes may provide insights into the development of preventative intervention strategies.

Involvement of oxidative stress in the regulation of NPY/CART-mediated appetite control in amphetamine-treated rats

Amphetamine (AMPH) treatment can suppress appetite and increase oxidative stress in the brain. AMPH-induced appetite suppression is associated with the regulation of neuropeptide Y (NPY) and cocaine- and amphetamine-regulated transcript (CART) in the hypothalamus. The present study explored whether antioxidants, including glutathione S-transferase (GST) and glutathione peroxidase (GP), were involved in this NPY/CART-mediated appetite control. Rats were treated daily with AMPH for four days. Changes in food intake and expression levels of hypothalamic NPY, CART, GST, and GP were examined and compared. Results showed that, in AMPH-treated rats, (1) food intake and NPY expression decreased, while CART, GST, and GP expression increased; (2) NPY knockdown in the brain enhanced the decrease in NPY and the increases in CART, GST, and GP expression; and (3) central inhibition of reactive oxygen species production decreased GST and GP and modulated AMPH anorexia and the expression levels of NPY and CART. The present results suggest that oxidative stress in the brain participates in regulating NPY/CART-mediated appetite control in AMPH-treated rats. These results may advance the knowledge regarding the molecular mechanism of AMPH-evoked or NPY/CART-mediated appetite suppression.

Novel aspects of glucocorticoid actions

Normal hypothalamic-pituitary-adrenal (HPA) axis activity leading to the rhythmic and episodic release of adrenal glucocorticoids (GCs) is essential for body homeostasis and survival during stress. Acting through specific intracellular receptors in the brain and periphery, GCs regulate behaviour, as well as metabolic, cardiovascular, immune and neuroendocrine activities. By contrast to chronic elevated levels, circadian and acute stress-induced increases in GCs are necessary for hippocampal neuronal survival and memory acquisition and consolidation, as a result of the inhibition of apoptosis, the facilitation of glutamatergic neurotransmission and the formation of excitatory synapses, and the induction of immediate early genes and dendritic spine formation. In addition to metabolic actions leading to increased energy availability, GCs have profound effects on feeding behaviour, mainly via the modulation of orexigenic and anorixegenic neuropeptides. Evidence is also emerging that, in addition to the recognised immune suppressive actions of GCs by counteracting adrenergic pro-inflammatory actions, circadian elevations have priming effects in the immune system, potentiating acute defensive responses. In addition, negative-feedback by GCs involves multiple mechanisms leading to limited HPA axis activation and prevention of the deleterious effects of excessive GC production. Adequate GC secretion to meet body demands is tightly regulated by a complex neural circuitry controlling hypothalamic corticotrophin-releasing hormone (CRH) and vasopressin secretion, which are the main regulators of pituitary adrenocorticotrophic hormone (ACTH). Rapid feedback mechanisms, likely involving nongenomic actions of GCs, mediate the immediate inhibition of hypothalamic CRH and ACTH secretion, whereas intermediate and delayed mechanisms mediated by genomic actions involve the modulation of limbic circuitry and peripheral metabolic messengers. Consistent with their key adaptive roles, HPA axis components are evolutionarily conserved, being present in the earliest vertebrates. An understanding of these basic mechanisms may lead to novel approaches for the development of diagnostic and therapeutic tools for disorders related to stress and alterations of GC secretion.

Glucocorticoids increase NPY gene expression via hypothalamic AMPK signaling in broiler chicks

Glucocorticoids (GCs) induce profound hyperphagia in birds. However, the neuronal regulatory network underlying GC-provoked hyperphagia is unclear. To determine whether any cross talk occurs among hypothalamic GC receptors (GRs), AMP-activated protein kinase (AMPK), and GCs in the regulation of appetite, we performed an intracerebroventricular injection of mifepristone (a GR inhibitor) and compound C (an AMPK inhibitor) on GC-treated male chicks. The results indicate that central GC administration increased the expression of GR and neuropeptide Y mRNA, as well as phosphorylated AMPKα(Thr172) and acetyl-coenzyme A carboxylase(Ser79). Blocking AMPK significantly attenuated GC-induced hyperphagia. Blocking GR significantly attenuated part of the AMPK signaling pathway and GC-induced hyperphagia. Thus, the results suggest that GCs cause hyperphagia via the AMPK-neuropeptide Y signaling pathway.

Oxytocin projections to the nucleus of the solitary tract contribute to the increased meal-related satiety responses in primary adrenal insufficiency

Anorexia is a common clinical manifestation of primary adrenal gland failure. Adrenalectomy (ADX)-induced hypophagia is reversed by oxytocin (OT) receptor antagonist and is associated with increased activation of satiety-related responses in the nucleus of the solitary tract (NTS). This study evaluated OT projections from the paraventricular nucleus of the hypothalamus (PVN) to the NTS after ADX and the effect of pretreatment with intracerebroventricular injection of an OT receptor antagonist ([d(CH2)5,Tyr(Me)(2),Orn(8)]-vasotocin; OVT) on the activation of NTS neurons induced by feeding in adrenalectomized rats. Adrenalectomized animals showed higher OT labelling in the NTS than the sham and the ADX with corticosterone replacement (ADX + B) groups. Adrenalectomized animals exhibited co-localization of the anterograde tracer Phaseolus vulgaris leucoagglutinin and OT in axons in the NTS as well as OT fibres apposing NTS neurons activated by refeeding. After vehicle pretreatment, compared with fasting, refeeding increased the numbers of Fos- and Fos + TH-immunoreactive neurons in the NTS in sham, ADX and ADX + B groups, with a higher number of these immunolabelled neurons in adrenalectomized animals. Compared with fasting conditions, refeeding also increased the activation of NTS neurons in OVT-pretreated sham, ADX and ADX + B groups, but there was no difference among the three experimental groups. These data demonstrate that OT is upregulated in projections to the NTS following ADX and that OT receptor antagonist reverses the greater activation of NTS neurons induced by feeding after ADX. The data indicate that OT pathways to the NTS contribute to higher satiety-related responses and, thus, to reduce meal size in primary adrenal insufficiency.

Characterization, tissue distribution and regulation of agouti-related protein (AgRP) in a cyprinid fish (Schizothorax prenanti)

Agouti-related protein (AgRP) is an important neuropeptide involved in the regulation of feeding in both mammals and fish. In this study, we have cloned the full-length cDNA sequence for AgRP in a cyprinid fish (Schizothorax prenanti). The AgRP gene, encoding 126-amino acids, was strongly expressed in the brain. The AgRP gene was detected in embryos at developmental stages. Further, its mRNA was detectable in unfertilized eggs. An experiment was conducted to determine the expression profile of AgRP during short-term and long-term fasting of the hypothalamus. The expression level of AgRP in unfed fish was significantly increased at 3 and 4h post-fasting than in fed fish but did not affect AgRP mRNA expression after 14 days fasting. Overall, our results suggest that AgRP is a conserved peptide that might be involved in the regulation of short-term feeding and other physiological function in Schizothorax prenanti.