The differential regulation of CART gene expression in a pituitary cell line and primary cell cultures of ovine pars tuberalis cells

The role of CART in islet biology

Cocaine- and amphetamine-regulated transcript (CART) is mostly known for its appetite regulating effects in the central nervous system. However, CART is also highly expressed in the peripheral nervous system as well as in certain endocrine cells. Our group has dedicated more than 20 years to understand the role of CART in the pancreatic islets and in this review we summarize what is known to date about CART expression and function in the islets. CART is expressed in both islet cells and nerve fibers innervating the islets. Large species differences are at hand and CART expression is highly dynamic and increased during development, as well as in Type 2 Diabetes and certain endocrine tumors. In the human islets CART is expressed in alpha cells and beta cells and the expression is increased in T2D patients. CART increases insulin secretion, reduces glucagon secretion, and protects against beta cell death by reducing apoptosis and increasing proliferation. It is still not fully understood how CART mediates its effects or which receptors that are involved. Nevertheless, CART is endowed with several properties that are beneficial in a T2D perspective. Many of the described effects of CART resemble those of GLP-1, and interestingly CART has been found to potentiate some of the effects of GLP-1, paving the way for CART-based treatments in combination with GLP-1-based drugs.

Differential Regulation of the Expression of the Two Thyrotropin Beta Subunit Paralogs by Salmon Pituitary Cells In Vitro

We recently characterized two paralogs of the thyrotropin (TSH) beta subunit in Atlantic salmon, tshβa and tshβb, issued from teleost-specific whole genome duplication. The transcript expression of tshβb, but not of tshβa, peaks at the time of smoltification, which revealed a specific involvement of tshβb paralog in this metamorphic event. Tshβa and tshβb are expressed by distinct pituitary cells in salmon, likely related to TSH cells from the pars distalis and pars tuberalis, respectively, in mammals and birds. The present study aimed at investigating the neuroendocrine and endocrine factors potentially involved in the differential regulation of tshβa and tshβb paralogs, using primary cultures of Atlantic salmon pituitary cells. The effects of various neurohormones and endocrine factors potentially involved in the control of development, growth, and metabolism were tested. Transcript levels of tshβa and tshβb were measured by qPCR, as well as those of growth hormone (gh), for comparison and validation. Corticotropin-releasing hormone (CRH) stimulated tshβa transcript levels in agreement with its potential role in the thyrotropic axis in teleosts, but had no effect on tshβb paralog, while it also stimulated gh transcript levels. Thyrotropin-releasing hormone (TRH) had no effect on neither tshβ paralogs nor gh. Somatostatin (SRIH) had no effects on both tshβ paralogs, while it exerted a canonical inhibitory effect on gh transcript levels. Thyroid hormones [triiodothyronine (T3) and thyroxine (T4)] inhibited transcript levels of both tshβ paralogs, as well as gh, but with a much stronger effect on tshβa than on tshβb and gh. Conversely, cortisol had a stronger inhibitory effect on tshβb than tshβa, while no effect on gh. Remarkably, insulin-like growth factor 1 (IGF1) dose-dependently stimulated tshβb transcript levels, while it had no effect on tshβa, and a classical inhibitory effect on gh. This study provides the first data on the neuroendocrine factors involved in the differential regulation of the expression of the two tshβ paralogs. It suggests that IGF1 may be involved in triggering the expression peak of the tshβb paralog at smoltification, thus representing a potential internal signal in the link between body growth and smoltification metamorphosis.

Cocaine- and amphetamine-regulated transcript promoter regulated by nicotine in nerve growth factor-treated PC12 cells

Nicotine and cocaine- and amphetamine-regulated transcripts (CART) have several overlapping functions, such as the regulation of reward, feeding behavior, stress response, and anxiety. Previous studies showed that nicotine regulates CART expression in various brain regions. However, the molecular mechanisms underlying this regulation are not known. This study investigated the regulatory effect of nicotine on promoter activity of the CART gene in PC12 cells, which were differentiated into a neuronal phenotype by nerve growth factor (NGF) treatment. Two vectors containing reporter genes (Gaussia luciferase or mCherry) and the 1,140-bp upstream of the transcriptional start site of the mouse CART gene are used to analyze the CART promoter activity. Transient transfection of PC12 cells with either vector displayed strong promoter activity in both undifferentiated and differentiated PC12 cells. CART promoter activity in the PC12 cell line is increased by forskolin or NGF treatment. In differentiated PC12 cells, exposure to 50 nM nicotine for 6 h increased CART promoter activity. However, treatment with higher nicotine doses for 6 h and treatment with all nicotine doses for 24 h showed no effect. A nicotine concentration of 50 nM is comparable to brain nicotine levels experienced by chronic smokers over long periods of time. Taken together, these data indicate that nicotine may exert some of its actions through the regulation of CART transcription in the brain.

Regulation of Pituitary Cocaine- and Amphetamine-Regulated Transcript Expression and Secretion by Hypothalamic Gonadotropin-Releasing Hormone in Chickens

There is increasing evidence that cocaine- and amphetamine-regulated transcript (CART) peptide is abundantly expressed in the anterior pituitary of birds and mammals, suggesting that CART peptide may be a novel pituitary hormone and its expression and secretion is likely controlled by the hypothalamic factor(s). To substantiate this hypothesis, using chicken as an animal model, we examined the effects of gonadotropin-releasing hormone (GnRH) on pituitary CART secretion and expression and investigated whether GnRH could modulate plasma CART levels. The results showed that: (1) chicken GnRH (GnRH1 and GnRH2) could potently stimulate CART peptide secretion in intact pituitaries incubated in vitro, as detected by Western blot; (2) GnRH could also stimulate CART mRNA expression in cultured pituitary cells, as revealed by quantitative real-time polymerase chain reaction (qPCR) assay; (3) GnRH actions on pituitary CART expression and secretion are likely mediated by GnRH receptor coupled to the intracellular Ca²⁺, MEK/ERK, and cAMP/PKA signaling pathways; and (4) plasma CART levels are high in chickens at various developmental stages (1.2–3.5 ng/ml) and show an increasing trend towards sexual maturity, as detected by enzyme-linked immunosorbent assay (ELISA). Moreover, plasma CART levels could be significantly induced by intraperitoneal administration of GnRH in chicks. Taken together, our data provide the first collective evidence that CART peptide is a novel pituitary hormone and its expression and secretion are tightly controlled by hypothalamic GnRH, thus likely being an active player in the hypothalamic-pituitary-gonadal (HPG) axis.

Study on the relationship between expression patterns of cocaine-and amphetamine regulated transcript and hormones secretion in porcine ovarian follicles

Background

Cocaine-and amphetamine regulated transcript (CART) is an endogenous neuropeptide, which is widespread in animals, plays a key role in regulation of follicular atresia in cattle and sheep. Among animal ovaries, CART mRNA was firstly found in the cattle ovaries. CART was localized in the antral follicles oocytes, granulosa and cumulus cells by immunohistochemistry and in situ hybridization. Further research found that secretion of E₂ was inhibited in granulosa cells with a certain dose of CART, the effect depends on the stage of cell differentiation, suggesting that CART could play a crucial role in regulating follicle atresia. The objective of this study was to characterize the CART expression model and hormones secretion in vivo and vitro in pig follicle granulosa cells, preliminarily studied whether CART have an effect on granulosa cells proliferation and hormones secretion in multiparous animals such as pigs.

Methods

The expression levels of CART mRNA in granulosa cells of different follicles were analyzed using qRT-PCR technology. Immunohistochemistry technology was used to localize CART peptide. Granulosa cells were cultured in medium supplemented with different concentrations of CART and FSH for 168 h using Long-term culture system, and observed using a microscope. The concentration of Estradiol (E₂) and progesterone (P) in follicular fluids of different test groups were detected by enzyme linked immunosorbent assay (ELISA).

Results

Results showed that expression level of CART mRNA was highest in medium follicles, and significantly higher than that in large and small follicles (P < 0.05). Immunohistochemical results showed that CART were expressed both in granulosa cells and theca cells of large follicles, while CART were detected only in theca cells of medium and small follicles. After the granulosa cells were cultured for 168 h, and found that concentrations of E₂ increase with concentrations of follicle-stimulating hormone (FSH) increase when the CART concentration was 0 μM. And the concentration of FSH reached 25 ng/mL, the concentration of E₂ is greatest. It shows that the production of E₂ needs induction of FSH in granulosa cells of pig ovarian follicles. With the increasing of CART concentrations (0.01, 0.1, 1 μM), E₂ concentration has a declining trend, when the FSH concentrations were 25 and 50 ng/mL in the medium, respectively.

Conclusions

These results suggested that CART plays a role to inhibit granulosa cells proliferation and E₂ production, which induced by FSH in porcine ovarian follicular granulosa cells in vitro, but the inhibition effect is not significant. So we hypothesis CART maybe not a main local negative regulatory factor during porcine follicular development, which is different from the single fetal animals.

Corticotropin-releasing hormone (CRH) stimulates cocaine- and amphetamine-regulated transcript gene (CART1) expression through CRH type 1 receptor (CRHR1) in chicken anterior pituitary

Cocaine- and amphetamine-regulated transcript (CART) peptide(s) is generally viewed as neuropeptide(s) and can control food intake in vertebrates, however, our recent study revealed that CART1 peptide is predominantly expressed in chicken anterior pituitary, suggesting that cCART1 peptide is a novel pituitary hormone in chickens and its expression is likely controlled by hypothalamic factor(s). To test this hypothesis, in this study, we examined the spatial expression of CART1 in chicken anterior pituitary and investigated the effect of hypothalamic corticotropin-releasing hormone (CRH) on pituitary cCART1 expression. The results showed that: 1) CART1 is expressed in both caudal and cephalic lobes of chicken anterior pituitary, revealed by quantitative real-time PCR (qPCR), western blot and immuno-histochemical staining; 2) CRH potently stimulates cCART1 mRNA expression in cultured chick pituitary cells, as examined by qPCR, and this effect is blocked by CP154526 (and not K41498), an antagonist specific for chicken CRH type I receptor (cCRHR1), suggesting that cCRHR1 expressed on corticotrophs mediates this action; 3) the stimulatory effect of CRH on pituitary cCART1 expression is inhibited by pharmacological drugs targeting the intracellular AC/cAMP/PKA, PLC/IP3/Ca(2+), and MEK/ERK signaling pathways. This finding, together with the functional coupling of these signaling pathways to cCRHR1 expressed in CHO cells demonstrated by luciferase reporter assay systems, indicates that these intracellular signaling pathways coupled to cCRHR1 can mediate CRH action. Collectively, our present study offers the first substantial evidence that hypothalamic CRH can stimulate pituitary CART1 expression via activation of CRHR1 in a vertebrate species.

Orexigenic Gene Expression in Late Gestation Ovine Foetal Hypothalamus is Sensitive to Maternal Undernutrition and Realimentation

Adverse nutritional effects on developing foetal hypothalamic appetitive pathways may contribute to programmed hyperphagia and obesity in intra-uterine growth-restricted, low birth weight offspring. In the present study, for the first time, hypothalamic gene expression for primary orexigenic and anorexigenic genes was examined in late gestation ovine foetuses (130 days; term=145 days) whose mothers were undernourished (UN) or well-nourished (C) throughout pregnancy, or transferred from UN to C on day 90 (UN-C). Pregnancies resulted from singleton embryo transfer into adolescent growing ewes. Body weight, carcass fat content and perirenal adipose tissue (PAT) mass were all lower for UN (n=9) than C (n=7) and intermediate for UN-C foetuses (n=6), with no effect of sex. PAT leptin gene expression (by the reverse transcriptase-polymerase chain reaction) was lower in UN than C and UN-C groups, and lower in males than females. Gene expression (by in situ hybridisation with radiolabelled riboprobes) in the arcuate nucleus was greater in UN than C foetuses for neuropeptide Y (NPY), agouti-related peptide (AGRP) and leptin receptor (OBRb) but not different for pro-opiomelanocortin and cocaine- and amphetamine-regulated transcript. Gene expression in UN-C foetuses was intermediate for NPY and AGRP and not different from C foetuses for OBRb. Gene expression for NPY, AGRP and OBRb correlated negatively with foetal carcass fat content and with PAT leptin gene expression across all groups. Males had greater mRNA expression for AGRP than females, with NPY and OBRb showing similar trends. Therefore, maternal undernutrition throughout pregnancy increased orexigenic gene expression in the late gestation foetal hypothalamus, and expression levels were largely normalised by improved maternal nutrition in the last third of pregnancy. These findings may have implications for avoiding or correcting prenatal programming of postnatal hyperphagia and obesity.

Chromatin immunoprecipitation assays revealed CREB and serine 133 phospho-CREB binding to the CART gene proximal promoter

Both over expression of cyclic AMP response element binding protein (CREB) in the nucleus accumbens (NAc), and intra-accumbal injection of cocaine- and amphetamine-regulated transcript (CART) peptides, have been shown to decrease cocaine reward. Also, over expression of CREB in the rat NAc increased CART mRNA and peptide levels, but it is not known if this was due to a direct action of P-CREB on the CART gene promoter. The goal of this study was to test if CREB and P-CREB bound directly to the CRE site in the CART promoter, using chromatin immunoprecipitation (ChIP) assays. ChIP assay with anti-CREB antibodies showed an enrichment of the CART promoter fragment containing the CRE region over IgG precipitated material, a non-specific control. Forskolin, which was known to increase CART mRNA levels in GH3 cells, was utilized to show that the drug increased levels of P-CREB protein and P-CREB binding to the CART promoter CRE-containing region. A region of the c-Fos promoter containing a CRE cis-regulatory element was previously shown to bind P-CREB, and it was used here as a positive control. These data suggest that the effects of CREB over expression on blunting cocaine reward could be, at least in part, attributed to the increased expression of the CART gene by direct interaction of P-CREB with the CART promoter CRE site, rather than by some indirect action.

Regulation of cocaine- and amphetamine-regulated transcript mRNA expression by calcium-mediated signaling in GH3 cells

Cocaine- and amphetamine-regulated-transcript (CART) peptides are associated with multiple physiological processes, including, feeding, body weight, and the response to drugs of abuse. CART mRNA and peptide levels and the expression of the CART gene appears to be under the control of a number of extra- and intra-cellular factors including the transcription factor, cAMP response element binding protein (CREB). Similar to the effects of CART, Ca(2+) signaling leads to the phosphorylation of CREB and has been associated with both feeding and the actions of psychostimulants; therefore, we hypothesized that Ca(2+) may play a role in CART gene regulation. We used real-time PCR (rtPCR) and GH3 cells to examine the effect of ionomycin, which increases intracellular Ca(2+), on CART mRNA levels. Ionomycin increased CART mRNA in a dose- and time-dependent manner. The effect of ionomycin appeared transient as CART mRNA had returned to control levels 3 h following treatment. Calmidazolium and KN93, inhibitors of calmodulin and Ca(2+)-modulated protein (CaM) kinases respectively, attenuated the effect of ionomycin (10 microM) on CART mRNA levels suggesting a calmodulin-dependent mechanism. Western immunoblotting indicated that ionomycin increased phosphorylated cAMP response element binding protein (pCREB) levels and electrophoretic mobility shift assay/supershift assay using antibodies against pCREB demonstrated increased levels of a CART oligo/pCREB protein complex. Finally, we showed that injection of ionomycin into the rat nucleus accumbens increases CART mRNA levels. To our knowledge, this is the first study providing evidence that the CART gene is, in part, regulated by Ca(2+)/CaM/CREB-dependent cell signaling.

CART peptides: regulators of body weight, reward and other functions

Over the past decade or so, CART (cocaine- and amphetamine-regulated transcript) peptides have emerged as major neurotransmitters and hormones. CART peptides are widely distributed in the CNS and are involved in regulating many processes, including food intake and the maintenance of body weight, reward and endocrine functions. Recent studies have produced a wealth of information about the location, regulation, processing and functions of CART peptides, but additional studies aimed at elucidating the physiological effects of the peptides and at characterizing the CART receptor(s) are needed to take advantage of possible therapeutic applications.

Expression of energy balance regulatory genes in the developing ovine fetal hypothalamus at midgestation and the influence of hyperglycemia

Evidence suggests that the prenatal nutritional environment influences the risk of developing obesity, a major health problem worldwide. It is hypothesized that fetal nutrition influences the developing neuroendocrine hypothalamus, the integrative control center for postnatal energy balance regulation. The present aim was to determine whether relevant hypothalamic genes are expressed in midgestation and whether they are nutritionally (glucose) sensitive at this time. Hypothalami from a cohort of 81-day singleton sheep fetuses, with varying glycemia by virtue of maternal dietary and/or growth hormone treatment, were subject to in situ hybridization analysis for primary orexigenic, anorexigenic, and related receptor genes (term = 147 days, n = 24). Neuropeptide Y, agouti-related peptide, proopiomelanocortin (POMC), cocaine- and amphetamine-regulated transcript (CART), and insulin receptor mRNAs were all localized in the hypothalamic arcuate nucleus (ARC) of all fetuses, whereas leptin receptor mRNA was expressed more abundantly in the ventromedial hypothalamic nucleus. ARC expression levels of POMC and CART genes, but none of the other genes, were positively correlated with fetal plasma glucose concentrations. Therefore, key central components of adult energy balance regulation were already present as early as midgestation (equivalent to 22 wk in humans), and two anorexigenic components were upregulated by elevated glycemia. Such changes provide a potential mechanism for the prenatal origins of postnatal energy balance dysregulation and obesity.

Nutritional influences on reproductive neuroendocrine output: insulin, leptin, and orexigenic neuropeptide signaling in the ovine hypothalamus

This study investigated how changing nutritional status may alter reproductive neuroendocrine (LH) output via circulating leptin and insulin signaling through orexigenic hypothalamic pathways. Thin sheep were given an increasing nutritional plane (INP), sheep with intermediate adiposity a static nutritional plane (SNP), and fat sheep a decreasing nutritional plane (DNP) for 6 wk. Mean group adiposities converged by wk 6, LH output increased in INP, remained unchanged in SNP, and decreased in DNP sheep. Plasma and cerebrospinal fluid (CSF) insulin and plasma leptin concentrations increased in INP but did not change in the SNP and DNP groups. In INP sheep, LH output correlated positively with adiposity and plasma and CSF insulin concentrations and negatively with orexigenic neuropeptide Y gene expression in the hypothalamic arcuate nucleus (ARC). In DNP sheep, LH output correlated positively with adiposity, CSF leptin concentrations, and ARC proopiomelanocortin gene expression and negatively with leptin receptor (OB-Rb) and agouti-related peptide gene expression in the ARC. These data are consistent with the feedback response to an increasing nutritional plane being mediated by increasing circulating insulin entering the brain and stimulating LH via inhibition of hypothalamic neuropeptide Y and the response to a decreasing nutritional plane being mediated by altered hypothalamic leptin signaling brought about by increased OB-Rb expression and decreased melanocortin signaling. Because end point adiposity was similar yet LH output was different, the hypothalamus apparently retains a nutritional memory, based on changes in orexigenic neuropeptide expression, that influences contemporary neuroendocrine responses.

The CART gene: structure and regulation

CART peptides are important neuropeptides that are involved in a variety of physiologic processes. The regulation of the CART gene is critical since peptides are regulated and secreted in response to specific stimuli. CART mRNA must also be controlled in order to respond to specific stimuli such as psychostimulant drugs and leptin. The regulation of the CART gene is central to maintaining homeostasis of peptide production. The 5' upstream region of the CART gene contains powerful regulatory elements that must be involved in transcriptional regulation via different signaling pathways. This review touches on several aspects related to CART gene regulation such as: (i) CART genomic structure, (ii) stimuli that alter CART mRNA levels, (iii) promoter characterization, (iv) role of the cAMP/PKA/CREB signal transduction pathway, and (v) role of the CART 5' and 3' ends in CART mRNA regulation. The goal of this review is to present current data so as to encourage further work in the field of CART gene regulation.

Regulation of CART mRNA in the rat nucleus accumbens via D3 dopamine receptors

A variety of studies indicate that CART in the nucleus accumbens (NAcc) is involved in the action of psychostimulants. In order to understand in more detail if and how dopamine is involved in the regulation of CART mRNA in the NAcc, the present studies of individual receptors were performed. The D1 agonist, dihydrexidine, and the D1 antagonist, SCH23,390, were administered separately and in combination to adult male rats; however, no changes were found in CART mRNA as measured by in situ hybridization. The D2/3 agonist, quinpirole, was administered either separately or in combination with the D2 selective antagonist, L741,626, or the D3 selective antagonist, GR103,691. Quinpirole produced a decrease in CART mRNA of up to 43%. This effect was blocked by pretreatment with the D3 antagonist GR103, 691, but not by the D2 antagonist, L741,626. CART peptide levels showed a similar decrement after acute quinpirole. CART mRNA levels in the NAcc of D3 mutant mice were found to be higher than that in wild-type animals, but treating the mutants with quinpirole failed to produce a decrease in CART expression like that observed in wild-type rodents. These findings demonstrate that CART is regulated by dopamine in the NAcc, at least partly by D3 dopamine receptors.

Pituitary cocaine- and amphetamine-regulated transcript expression depends on the strain, sex and oestrous cycle in the rat

Cocaine- and amphetamine-regulated transcript (CART) mRNA and peptides are abundant in the adenohypophysis, but their role in pituitary function has not yet been elucidated. CART peptides were recently shown to colocalise with luteinising hormone (LH) or prolactin in rat anterior pituitary, and contradictory results concerning the peptide effects on pituitary hormonal secretions were obtained in vitro from pituitary cell cultures. Thus, we reinvestigated the expression of CART mRNA within the pituitary. Immunohistochemistry for pituitary hormones was performed on sections from adult male Wistar rats followed by in situ hybridisation using CART mRNA antisense 35S-labelled probes. The most represented CART-expressing cells were lactotrophs (42 +/- 1% of CART cells) and gonadotrophs (32 +/- 3%), followed by thyrotrophs (10 +/- 2%), corticotrophs (7 +/- 2%) and somatotrophs (6 +/- 1%). In the pars tuberalis, CART mRNA was easily detectable in gonadotrophs and lactotrophs and, to a lesser extent, in corticotrophs and thyrotrophs. CART peptide was quickly and potently released from perifused pituitary by depolarisation (K+ 30 mM for 15 min; 465 +/- 37% over basal release, n = 5). Gonadotrophin-releasing hormone and thyrotrophin-releasing hormone (0.1 microM) were also active to a lesser extent (138 +/- 11% and 71 +/- 17, n = 7, respectively). CART (0.1 microM) did not modify basal LH or prolactin release but selectively inhibited K+-induced LH release without affecting K+-induced prolactin secretion. Pituitary CART mRNA and content were sex dependent and varied during the oestrous cycle, being lower in dioestrous 2. Pituitary CART content also varied widely amongst rat strains being five to six-fold higher in Wistar and Fischer rats compared to Brown Norway and Lou C rats. Ageing differentially affected pituitary CART mRNA and content, resulting in a marked decrease in Lou C and an increase in Wistar and Sprague-Dawley rats. Taken together, these results suggest that pituitary CART expression is dependent of the sex steroid environment and may be physiologically involved in LH secretion.

Increased maternal nutrition alters development of the appetite‐regulating network in the brain

Individuals exposed to an increased nutrient supply before birth have a high risk of becoming obese children and adults. It has been proposed that exposure of the fetus to high maternal nutrient intake results in permanent changes within the central appetite regulatory network. No studies, however, have investigated the impact of increased maternal nutrition on the appetite regulatory network in species in which this network develops before birth, as in the human. In the present study, pregnant ewes were fed a diet which provided 100% (control, n = 8) or approximately 160% (well-fed, n = 8) of metabolizable energy requirements. Ewes were allowed to lamb spontaneously, and lambs were sacrificed at 30 days of postnatal age. All fat depots were dissected and weighed, and expression of the appetite-regulating neuropeptides and the leptin receptor (OBRb) were determined by in situ hybridization. Lambs of well-fed ewes had higher glucose (Glc) concentrations during early postnatal life (F = 5.93, P<0.01) and a higher relative subcutaneous (s.c.) fat mass at 30 days of age (34.9+/-4.7 g/kg vs. 22.8+/-3.3 g/kg; P<0.05). The hypothalamic expression of pro-opiomelanocortin was higher in lambs of well-fed ewes (0.48+/-0.09 vs. 0.28+/-0.04, P<0.05). In lambs of overnourished mothers, but not in controls, the expression of OBRb was inversely related to total relative fat mass (r2 = 0.50, P = 0.05, n = 8), and the direct relationship between the expression of the central appetite inhibitor CART and fat mass was lost. The expression of neuropeptide Y and AGRP was inversely related to total relative fat mass (NPY, r2 = 0.28, P<0.05; agouti-related peptide, r2 = 0.39, P<0.01). These findings suggest that exposure to increased nutrition before birth alters the responses of the central appetite regulatory system to signals of increased adiposity after birth.

Cocaine- and amphetamine-regulated transcript is localized in pituitary lactotropes and is regulated during lactation

Cocaine- and amphetamine-regulated transcript (CART) is a highly expressed peptide implicated in the regulation of feeding, reward and reinforcement, and stress-related behaviors. CART has been localized to discrete cell populations in the brain, gut, adrenal gland, and pancreas. In contrast, CART-producing cell types in the pituitary gland remain ill defined. In the present study, double-label immunohistochemistry, employing a high-affinity antiserum we generated against CART-(62-102), was used to identify CART-producing cells in the pituitary gland. In the anterior pituitary, the majority of CART immunoreactivity (-ir) was localized in lactotropes; minor populations of CART-ir cells were identified as somatotropes and corticotropes. In the posterior pituitary, CART-ir extensively colocalized with oxytocin-containing fibers; in contrast, only a few vasopressin fibers contained CART-ir. As expected, CART colocalized with oxytocin in magnocellular neurons of the supraoptic nucleus. The effects of bromocriptine, a potent dopamine receptor agonist, were examined to determine whether CART mRNA expression and protein release are regulated in a similar fashion as prolactin. Similar to prolactin, CART mRNA expression and protein release were significantly decreased after bromocriptine treatment of dispersed rat anterior pituitary cells in culture. To explore the putative physiological role of pituitary CART, we compared levels of CART mRNA expression in lactating and nonlactating female rats. CART mRNA levels were significantly increased in the anterior pituitary and supraoptic nucleus of lactating rats. Furthermore, levels of CART in the systemic circulation were significantly elevated at the onset of lactation, peaked on d 10 of lactation and returned to baseline values 10 d after pups were weaned. The current study describes the cellular localization and regulation of CART expression and protein release from the rat pituitary gland. These findings suggest a putative role for CART in lactation.

Cocaine- and amphetamine-regulated transcript peptides play a role in drug abuse and are potential therapeutic targets

Cocaine- and amphetamine-regulated transcript (CART) peptides (55 to 102 and 62 to 102) are neurotransmitters with important roles in a number of physiologic processes. They have a role in drug abuse by virtue of the fact that they are modulators of mesolimbic function. Key findings supporting a role in drug abuse are as follows. First, high densities of CART-containing nerve terminals are localized in mesolimbic areas. Second, CART 55 to 102 blunts some of the behavioral effects of cocaine and dopamine (DA). This functional antagonism suggests that CART peptides be considered as targets for medications development. Third, CREB in the nucleus accumbens has been shown to have an opposing effect on cocaine self-administration. CREB may activate CART expression in that region, and, if so, CART may mediate at least some of the effects of CREB. Fourth, in addition to the effects of CART on DA, DA can influence CART in the accumbens. Thus a complex interacting circuitry likely exists. Fifth, in humans, CART is altered in the ventral tegmental area of cocaine overdose victims, and a mutation in the CART gene associates with alcoholism. Overall, it is clear that there are functional interactions among CART, DA, and cocaine and that plausible cellular mechanisms exist to explain some of these actions. Future studies will clarify and extend these findings.

Impact of glucose infusion on the structural and functional characteristics of adipose tissue and on hypothalamic gene expression for appetite regulatory neuropeptides in the sheep fetus during late gestation

In the present study, our aim was to determine whether intrafetal glucose infusion increases fetal adiposity, synthesis and secretion of leptin and regulates gene expression of the 'appetite regulatory' neuropeptides neuropepetide Y (NPY), agouti-related peptide (AGRP), pro-opiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) and receptors (leptin receptor (OB-Rb) and melancortin 3 receptor (MC3R)) within the fetal hypothalamus. Glucose (50% dextrose in saline) or saline was infused (7.5 ml h(-1)) into fetal sheep between 130 and 140 days gestation (term = 150 +/- 3 days gestation). Glucose infusion increased circulating glucose and insulin concentrations, mean lipid locule size (532.8 +/- 3.3 microm2 versus 456.7 +/- 14.8 microm2) and total unilocular fat mass (11.7 +/- 0.6 g versus 8.9 +/- 0.6 g) of the perirenal fat depot. The expression of OB-Rb mRNA was higher in the ventromedial nucleus compared to the arcuate nucleus of the hypothalamus in both glucose and saline infused fetuses (F= 8.04; P < 0.01) and there was a positive correlation between expression of OB-Rb and MC3R mRNA in the arcuate nucleus (r= 0.81; P < 0.005). Glucose infusion increased mRNA expression for POMC, but not for the anorectic neuropeptide CART, or the orexigenic neuropeptides NPY and AGRP, in the arcuate nucleus of the fetal hypothalamus. These findings demonstrate that increased circulating glucose and insulin regulate gene expression of the neuropeptides within the fetal hypothalamus that are part of the neural network regulating energy balance in adult life.

Evidence that cocaine- and amphetamine-regulated transcript is a novel intraovarian regulator of follicular atresia

We recently obtained evidence that cocaine- and amphetamine-regulated transcript (CART), a potent anorectic neuropeptide, is expressed in the bovine ovary. The objectives of this study were to characterize bovine ovarian CART and determine its localization, regulation, and regulatory role during follicular development. CART mRNA was detected in stroma of adult ovaries and in large follicles, but was undetectable in several peripheral tissues, fetal ovaries, and corpora lutea. Within the ovary, CART mRNA and peptide were localized to the granulosal layer of some, but not all, antral follicles, with low, but detectable, expression in oocytes and cumulus cells. CART mRNA was undetectable in granulosal cells of dominant ovulatory follicles collected before and after the preovulatory gonadotropin surge, but was detected in the granulosal layer of adjacent subordinate follicles. In addition, amounts of CART mRNA and follicular fluid concentrations of CART peptide were greater in subordinate follicles vs. dominant follicles of the first follicular wave. Furthermore, CART treatment inhibited basal estradiol production, but not progesterone production, by granulosal cells in a dose-dependent fashion, and the effect was dependent on stage of cell differentiation. We conclude that granulosal cell CART expression is temporally regulated and potentially associated with follicle health status, and CART can inhibit granulosal cell estradiol production. Thus, CART may be a novel local regulator of follicular atresia in the bovine ovary.

Transcriptional regulation of the CART promoter in CATH.a cells

Changes in Cocaine- and Amphetamine-Regulated Transcript (CART) mRNA levels have been observed in brain as a result of various physiologic stimuli including feeding, drugs of abuse, stress and glucocorticoids, and activators of the cyclic AMP (cAMP) and protein kinase A (PKA) pathway. Accordingly, we are interested in identifying factors involved in CART gene regulation. CATH.a cells, derived from the locus coeruleus (LC), express a 213-bp CART mRNA species that is translated and processed. The promoter activity of three CART-LUC constructs containing 3451, 641, and 102 bp of 5' upstream sequence, respectively, were tested in CATH.a cells. cAMP regulation was detected in the construct containing 641 bp of CART promoter sequence which contains a consensus CRE site. Mutation of the CRE site within -641CART-LUC significantly reduced basal and forskolin-induced promoter activity. Additionally, forskolin-induced transcription was inhibited by a dominant-negative mutant of CRE-binding protein (CREB) in CATH.a cells. Finally, tropin-releasing factor (CRF), an endogenously occurring activator of the cAMP/PKA pathway in CATH.a cells, was shown to increase transcriptional activity that was inhibited by a CRF receptor antagonist and a PKA inhibitor. This study provides evidence that the CRE site in the CART proximal promoter is involved in cAMP/PKA/CREB regulation in cells having a neuronal phenotype. Also, given the evidence for involvement of CREB in reward and reinforcement, these results are compatible with a role for CART in these processes as well.

Regulation of rat pituitary cocaine- and amphetamine-regulated transcript (CART) by CRH and glucocorticoids

Cocaine- and amphetamine-regulated transcript (CART) was originally isolated from rat brain, but CART is also synthesized and stored in the anterior pituitary. The localization of pituitary CART and factors regulating its synthesis are largely unknown. The regulation of pituitary CART synthesis and release in response to CRH and glucocorticoids was examined in vitro and in vivo. CART immunoreactivity (CART-IR) was released from anterior pituitary segments. This release was increased 15-fold in response to corticotropin-releasing hormone (CRH). Intraperitoneal administration of CRH to rats significantly increased plasma CART-IR. Furthermore, CART-IR content and plasma CART-IR were significantly increased in adrenalectomized rats, and anterior pituitary CART mRNA expression, CART-IR content, and plasma CART-IR were significantly decreased in corticosterone-treated rats. Plasma CART-IR showed a pattern of diurnal variation similar to that of ACTH and corticosterone, and plasma CART-IR was positively correlated with corticosterone. CART-IR was detectable in the medium of the corticotroph cell line AtT-20. Dual in situ hybridization for prepro-CART (ppCART) mRNA expression and immunocytochemistry for ACTH showed localization of ppCART mRNA to a subpopulation of ACTH-immunoreactive cells. These findings demonstrate that pituitary CART expression and release are regulated by CRH and the glucocorticoid environment and that pituitary CART is partly localized to corticotrophs.

Cocaine- and amphetamine-regulated transcript co-contained in thyrotropin-releasing hormone (TRH) neurons of the hypothalamic paraventricular nucleus modulates TRH-induced prolactin secretion

TRH synthesized in hypophysiotropic neurons of the hypothalamic paraventricular nucleus (PVN) stimulates the release of TSH and prolactin from the anterior pituitary gland. Recent data from our laboratories have demonstrated that TRH and cocaine- and amphetamine-regulated transcript (CART) are co-contained only in hypophysiotropic neurons in the PVN. To determine whether CART and TRH interact in the regulation of anterior pituitary function, we have studied the effects of CART on TRH-induced release of TSH and prolactin in anterior pituitary cell cultures, and the effects of hypo- and hyperthyroidism on CART mRNA in the PVN. Dispersed anterior lobe cells from male rats were treated with CART (10(-6), 10(-8), 10(-10), and 10(-12) m) or TRH (10(-7) m) alone and TRH (10(-7) m) combined with various concentrations of CART for 4 h at 37 C. The medium was assayed for prolactin and TSH by RIA. TRH resulted in a marked increase of both prolactin and TSH release, whereas CART had no effect on prolactin or TSH secretion. When the two peptides were used in combination, CART dose-dependently inhibited TRH-induced prolactin release but had no significant effect on TRH-induced TSH release. By semiquantitative analysis of in situ hybridization autoradiographs, CART mRNA was significantly elevated in hypothyroid animals, whereas a reduction in CART mRNA was observed in hyperthyroid animals compared with euthyroid controls. These data raise the possibility that CART expressed in hypophysiotropic TRH neurons has an important role in the modulation of TRH-induced prolactin secretion. Increased secretion of CART may be responsible for the reduced TRH-induced prolactin response during hypothyroidism.

Cocaine- and amphetamine-regulated transcript is present in hypothalamic neuroendocrine neurones and is released to the hypothalamic-pituitary portal circuit

Cocaine- and amphetamine-regulated transcript (CART) is present in a number of hypothalamic nuclei. Besides actions in circuits regulating feeding behaviour and stress responses, the hypothalamic functions of CART are largely unknown. We report that CART immunoreactivity is present in hypothalamic neuroendocrine neurones. Adult male rats received a systemic injection of the neuronal tracer Fluorogold (FG) 2 days before fixation, and subsequent double- and triple-labelling immunoflourescence analysis demonstrated that neuroendocrine CART-containing neurones were present in the anteroventral periventricular, supraoptic, paraventricular (PVN) and periventricular nuclei of the hypothalamus. In the PVN, CART-positive neuroendocrine neurones were found in all of cytoarchitectonically identified nuclei. In the periventricular nucleus, approximately one-third of somatostatin cells were also CART-immunoreactive. In the medial parvicellular subnucleus of the PVN, CART and FG coexisted with thyrotrophin-releasing hormone, whereas very few of the corticotrophin-releasing hormone containing cells were CART-immunoreactive. In the arcuate nucleus, CART was extensively colocalized with pro-opiomelanocortin in the ventrolateral part, but completely absent from neuroendocrine neurones of the dorsomedial part. To assess the possible role of CART as a hypothalamic-releasing factor, immunoreactive CART was measured in blood samples from the long portal vessels connecting the median eminence with the anterior pituitary gland. Adult male rats were anaesthetized and the infundibular stalk exposed via a transpharyngeal approach. The long portal vessels were transected and blood collected in 30-min periods (one prestimulatory and three poststimulatory periods). Compared to systemic venous plasma samples, baseline concentrations of immunoreactive CART were elevated in portal plasma. Exposure to sodium nitroprusside hypotension triggered a two-fold elevation of portal CART42-89 immunoreactivity throughout the 90-min stimulation period. In contrast, the concentration of portal plasma CART immunoreactivity dropped in the vehicle infused rats. The current study provides further evidence that CART is a neuroendocrine-releasing factor with a possible impact on anterior pituitary function during states of haemodynamic stress.

CART gene promoter transcription is regulated by a cyclic adenosine monophosphate response element

OBJECTIVE

To define the regulatory DNA sequence controlling the expression of the cocaine-amphetamine-regulated transcript (CART) gene expression.

RESEARCH METHODS AND PROCEDURES

A rat genomic library was screened for genomic clones containing the CART gene and upstream DNA sequence. A clone containing exons 1 and 2 of the rat CART gene plus 1.2 kb of upstream sequence was isolated. The 1.2-kb upstream sequence and truncated segments of this sequence were cloned into a luciferase reporter vector for analysis of transcriptional activity in the CART expressing pituitary GH3 cell line. Luciferase reporter assays, gel shift assays, and site-directed mutagenesis were used to analyze potential regulatory regions in the 1.2-kb 5' DNA sequence.

RESULTS

Sequence analysis of the 1.2-kb upstream sequence reveals several potential regulatory elements. Luciferase reporter assays demonstrate that within the first 162 bp of the start codon is a functional cyclic adenosine monophosphate (cAMP) response element that can induce cAMP-regulated gene expression of the CART promoter in GH3 cells. Mutation of this cAMP response element abolishes cAMP-stimulated transcription [corrected]. Furthermore, the promoter is active in a neuronal cell line where it also demonstrates cAMP responsiveness.

DISCUSSION

cAMP-mediated transcription of the CART promoter may be an important aspect of the regulation of the CART gene. However, the cellular context of expression is also important because the CART promoter is not responsive to cAMP stimulation in all cell types. Other transcription factor binding sequences are likely to play a key role in CART promoter regulation.

Cocaine and amphetamine-regulated transcript mRNA regulation in the hypothalamus in lean and obese rodents

Cocaine and amphetamine-regulated transcript (CART) mRNA and immunoreactivity are expressed abundantly in the hypothalamus. Central administration of various fragments of this neuropeptide decreases food intake in rodents. To find out whether CART might play a role in the physiological regulation of energy balance, we used in situ hybridization to investigate whether CART mRNA abundance changed in two chronic obese/fat versus lean states and after acute dietary restriction. In the first study, mice were treated with goldthioglucose to destroy glucose-responsive neurones in the ventromedial hypothalamus. This produced hyperphagia and obesity: 7 weeks after treatment, those receiving goldthioglucose weighed 70% more than the controls. CART mRNA abundance in the arcuate nucleus of goldthioglucose-treated mice was decreased by 71% compared to levels in the control mice, but CART expression was unaffected in the dorsolateral hypothalamus. In the second study, male Siberian hamsters were exposed to short days to induce a physiological winter response in which body weight decreases as fat reserves are catabolized, and food intake correspondingly declines. After 8 weeks in short days, body weight had declined by 18% relative to controls maintained in long days in a summer fat state. CART mRNA levels did not differ significantly between the two groups in any hypothalamic areas. In the third study, male Siberian hamsters, either in long days or after 12 weeks exposure to short days to induce weight loss, were subject to a 48-h period of fasting. Although photoperiod per se did not affect CART expression, fasting produced a significant decrease in CART mRNA in the arcuate nucleus of hamsters in both the long- and short-day state. We conclude that CART-producing cells are involved in energy homeostasis: the marked decrease in CART expression in the arcuate nucleus in goldthioglucose-lesioned mice may contribute to the development of obesity, and the decrease following acute dietary restriction in hamsters may reflect a compensatory mechanism to reduce caloric expenditure, but our results do not indicate that CART is involved in long-term seasonal regulation of body weight.

CART promoter CRE site binds phosphorylated CREB

It has been shown previously that: CART (cocaine- and amphetamine-regulated transcript) mRNA is tightly regulated in brain; protein kinase A (PKA) is involved in CART expression in GH3 cells; and a cyclic AMP-responsive element (CRE) site is present in the proximal promoter region of the CART gene. Thus, the goal of this study was to test if CRE binding protein (CREB) can bind to the consensus CRE site and if phosphorylation of CREB occurs in GH3 cells under conditions of enhanced CART gene expression. Electromobility shift assays showed that a 27-bp oligonucleotide containing the CART CRE site was indeed bound by nuclear factors. Western blotting showed that incubation of GH3 cells with forskolin, which enhances CART mRNA expression, caused an increase in phosphorylated CREB (P-CREB) levels. Supershift analyses indicated that the CART CRE oligo/protein complex interacted with a P-CREB antibody. Taken together, these data indicate that P-CREB is a likely regulator of CART expression in GH3 cells.

Modeling the pathways of energy balance using the N1E-115 murine neuroblastoma cell line

A good in vitro model within which to investigate molecular interactions between feeding relevant neuropeptide systems has been lacking. Consequently, we began using reverse transcriptase-polymerase chain reaction (RT-PCR) to screen various neuronal cell lines for the presence of feeding relevant neuropeptides and receptors. N1E-115 murine neuroblastoma cells have emerged as an attractive candidate for further analysis because they contain mRNA for a variety of key systems implicated in the regulation of energy homeostasis.

Leptin secretion and hypothalamic neuropeptide and receptor gene expression in sheep

Peripheral and hypothalamic mechanisms underlying the hyperphagia of lactation have been investigated in sheep. Sheep were fed ad libitum and killed at 6 and 18 days of lactation; ad libitum-fed nonlactating sheep were killed as controls. Despite increased food intake, lactating ewes were in negative energy balance. Lactation decreased plasma leptin and adipose tissue leptin mRNA concentrations. OB-Rb gene expression, determined by in situ hybridization, was increased in the hypothalamic arcuate nucleus (ARC) and ventromedial hypothalamic nucleus (VMH) at both stages of lactation. Neuropeptide Y (NPY) was increased by lactation in both the ARC and dorsomedial hypothalamus (DMH), although increased gene expression in the DMH was only apparent at day 18 of lactation. Gene expression was decreased for cocaine- and amphetamine-regulated transcript (CART) in the ARC and VMH and for proopiomelanocortin in ARC during lactation. Agouti-related peptide gene expression was increased in the ARC, and melanocortin receptor expression was unchanged in both the ARC and VMH with lactation. Thus the hypoleptinemia of lactation may activate NPY orexigenic pathways and attenuate anorexigenic melanocortin and CART pathways in the hypothalamus to promote the hyperphagia of lactation.