How tight are your genes? Transcriptional and posttranscriptional regulation of the leptin receptor, NPY, and POMC genes

β2 adrenergic receptors and leptin interplay to decrease food intake in chicken

1. The present study was designed to examine the effects of intracerebroventricular (ICV) injection of different α and [Formula: see text] adrenergic receptor antagonists on leptin-induced hypophagia in broiler chickens.2. The study consisted of six experiments. In all experiments, chickens were deprived of feed for 3 h prior to the ICV injections and thereafter were returned immediately to the individual cages and cumulative feed intake, based on the percentage of body weight, was measured at 30, 60 and 120 min post-injection.3. In experiment 1, leptin (2.5, 5 or 10 µg) were injected in birds. In experiment 2, groups received either control solution, prazosin (10 nmol), leptin (10 µg) or a co-injection of prazosin (10 nmol) and leptin (10 µg). The other experiments were conducted as experiment 2, but instead of prazosine (10 nmol), yohimbine (13 nmol) was used in experiment 3, metoprolol (24 nmol) in experiment 4, ICI 118,551 (5 nmol) in experiment 5 and SR 59230R (5 nmol) in experiment 6 were injected either in a group or in combination with leptin (10 µg).4. The results of this study revealed a dose-dependent hypophagic effect of leptin and, in experiment 5, ICV co-injection of ICI118, 551 (5 nmol) and leptin (10 µg) significantly attenuated this effect (P˂0.5). These results suggest that the hypophagic effect of leptin is probably mediated by β2 adrenergic receptors in chickens.

Maternal obesity influences expression and DNA methylation of the adiponectin and leptin systems in human third-trimester placenta

BACKGROUND

It is well established that obesity is associated with dysregulation of the ratio between the two major adipokines leptin and adiponectin. Furthermore, it was recently reported that maternal obesity has a significant impact on placental development. Leptin and adiponectin are present at the fetal-maternal interface and are involved in the development of a functional placenta. However, less is known about leptin and adiponectin's involvement in the placental alterations described in obese women. Hence, the objective of the present study was to characterize the placental expression and DNA methylation of these two adipokine systems (ligands and receptors) in obese women.

RESULTS

Biopsies were collected from the fetal and maternal sides of third-trimester placenta in obese and non-obese (control) women. In both groups, leptin levels were higher on the fetal side than the maternal side, suggesting that this cytokine has a pivotal role in fetal growth. Secondly, maternal obesity (in the absence of gestational diabetes) was associated with (i) elevated DNA methylation of the leptin promoter on fetal side only, (ii) hypomethylation of the adiponectin promoter on the maternal side only, (iii) significantly low levels of leptin receptor protein (albeit in the absence of differences in mRNA levels and promoter DNA methylation), (iv) significantly low levels of adiponectin receptor 1 mRNA expression on the maternal side only, and (v) elevated DNA methylation of the adiponectin receptor 2 promoter on the maternal side only.

CONCLUSION

Our present results showed that maternal obesity is associated with the downregulation of both leptin/adiponectin systems in term placenta, and thus a loss of the beneficial effects of these two adipokines on placental development. Maternal obesity was also associated with epigenetic changes in leptin and adiponectin systems; this highlighted the molecular mechanisms involved in the placenta's adaptation to a harmful maternal environment.

Sex Steroid Hormones Regulate Leptin Transcript Accumulation and Protein Secretion in 3T3-L1 Cells

Leptin is an adipokine produced by fat cells that regulates food consumption and metabolic activity. Sexual dimorphism in leptin and fat stores have been observed in humans and rodents with females having more leptin and greater levels of subcutaneous fat than males. One potential mechanism leading to this dimorphism is steroid hormone regulated synthesis of transcripts encoding leptin. Identification of direct regulatory mechanisms is difficult in animals or primary adipocytes due to these intertwined dimorphisms. We used well-characterized 3T3-L1 murine adipocytes to demonstrate that dihydrotestosterone (DHT) reduced Leptin (Lep) transcript abundance and cytosolic and secreted leptin protein. The magnitude of this effect was greatest on secreted leptin, which was decreased by DHT to 30% of the control. In contrast, 17β-estradiol significantly increased the abundance of transcripts encoding leptin and increased secreted leptin to 230% of the control. Treatment with estrogen and androgen receptor antagonists had opposite effects on Lep transcript abundance to steroid treatments, indicating that these transcriptional effects are mediated through the canonical steroid hormone signaling pathways. These results indicate that short-term treatments with steroid hormones are sufficient to alter both Lep transcript accumulation and leptin protein secretion, and may play a role in the sexual dimorphism of this adipokine.

Effects of trans-10,cis-12 conjugated linoleic acid on body composition in genetically obese mice

Conjugated linoleic acid (CLA) has shown a number of biologically beneficial effects, including prevention of obesity. The purpose of this study was to test effects of dietary supplementation of 0.5% trans-10,cis-12 CLA in a high fat diet in neuronal basic helix-loop-helix 2 knock-out animals (N2KO), which is a unique animal model representing adult-onset inactivity-related obesity. Eight wild-type (WT) and eight N2KO female mice were fed either 0.5% trans-10,cis-12 CLA-containing diet or control diet (with 20% soybean oil diet) for 12 weeks. Body weights, food intake, adipose tissue weights, body compositions, and blood parameters were analyzed. Overall, N2KO animals had greater body weights, food intake, adipose tissue weights, and body fat compared to WT animals. CLA supplementation decreased overall body weights and total fat, and the effect of dietary CLA on adipose tissue reduction was greater in N2KO than in WT mice. Serum leptin and triglyceride levels were reduced by CLA in both N2KO and WT animals compared to control animals, while there was no effect by CLA on serum cholesterol. The effect of CLA to lower fat mass, increase lean body mass, and lower serum leptin and triglycerides in sedentary mice supports the possibility of using CLA to prevent or alleviate ailments associated with obesity.

Adrenalectomy enhances endotoxemia-induced hypophagia: higher activation of corticotrophin-releasing-factor and proopiomelanocortin hypothalamic neurons

Inflammatory and infectious processes evoke neuroendocrine and behavioral changes known as acute-phase response that includes activation of the hypothalamo-pituitary-adrenal (HPA) axis and reduction of food intake. Besides its action as the most important ACTH secretagogue, corticotrophin-releasing factor (CRF), synthesized in the paraventricular nucleus (PVN), is also involved in the control of food intake. Alpha-melanocyte stimulating hormone (alpha-MSH) in the arcuate nucleus also plays a role in the energy homeostasis, possessing anorexigenic effects. To investigate the participation of neuropeptides involved in the regulation of food intake during endotoxemia, we administrated lipopolysaccharide (LPS) in sham-operated and adrenalectomized (ADX) male Wistar rats to evaluate food intake, hormone responses and Fos-CRF and Fos-alpha-MSH immunoreactivity in the PVN and arcuate nucleus, as well as CRF and POMC mRNA expression in these hypothalamic nuclei. In sham-operated rats, treatment with LPS (100 microg/kg) showed lower food intake, higher plasma ACTH and corticosterone levels, as well as an increase in Fos-CRF double labeled neurons and CRF mRNA expression in the PVN, with no changes in Fos-alpha-MSH immunoreactivity and POMC mRNA expression in the arcuate nucleus, compared to saline treated rats. After LPS treatment, ADX rats showed further increase in plasma ACTH levels, marked decrease of food intake, higher Fos-CRF immunoreactive neurons in the PVN and CRF mRNA expression, as well as an increase in Fos-alpha-MSH immunoreactivity and POMC mRNA expression in the arcuate nucleus, compared to sham-operated rats treated with LPS. In conclusion, the present data indicate that the marked hypophagia during endotoxemia following ADX is associated with an increased activation of CRF and POMC neurons in the hypothalamus and an increased mRNA expression of these neuropeptides.

Expression of the hypothalamic transcription factor Nhlh2 is dependent on energy availability

Mice with a deletion of the hypothalamic basic helix-loop-helix transcription factor Nhlh2 display adult onset obesity, implicating Nhlh2 in the neuronal circuits regulating energy availability. Nhlh2 colocalises with the hypothalamic thyrotrophin-releasing hormone (TRH) neurones in the paraventricular nucleus (PVN) and pro-opiomelanocortin (POMC) neurones in the arcuate nucleus. We show that Nhlh2 expression is significantly reduced in response to 24-h food deprivation in the arcuate nucleus, PVN, lateral hypothalamus, ventromedial hypothalamus (VMH) and dorsomedial hypothalamus (DMH). Food intake for 2 h following deprivation stimulates Nhlh2 expression in the arcuate nucleus and the PVN, and leptin injection following deprivation results in increased Nhlh2 expression in the arcuate nucleus, PVN, lateral hypothalamus, VMH, and DMH. Hypothalamic Nhlh2 expression in response to leptin injection is maximal by 2 h. Following leptin injection, Nhlh2 mRNA colocalises in POMC neurones in the arcuate nucleus and TRH neurones in the PVN. Nhlh2 mRNA expression in POMC neurones in the arcuate nucleus and TRH neurones in the PVN is reduced with energy deprivation and is stimulated with food intake and leptin injection. Modulation of POMC expression in response to changes in energy availability is not affected in mice with a targeted deletion of Nhlh2. However, deletion of Nhlh2 does result in loss of normal TRH mRNA expression in mice exposed to food deprivation and leptin stimulation. These data implicate Nhlh2 as a regulatory target of the leptin-mediated energy availability network of the hypothalamus, and TRH as a putative downstream target of Nhlh2.

Distinct impaired regulation of SOCS3 and long and short isoforms of the leptin receptor in visceral and subcutaneous fat of lean and obese women

Animal studies have illustrated the importance of the expression in adipose tissue of the leptin receptor (OB-R), and of SOCS3 an inhibitor of the leptin signaling pathway, in body weight regulation. The aim of the present study was to investigate in human adipose tissues of the same patients the OB-R isoforms and SOCS3 expression. Subcutaneous and omental adipose tissues were obtained from 6 lean and 18 morbidly obese women. The long isoform OB-Rb mRNA mediating leptin signaling, and SOCS3 mRNA are abundantly present in the subcutaneous fat of lean women, but are 90% and 70% decreased (P<0.0001) in obese women. In visceral fat from lean and obese women, both OB-Rb and SOCS3 mRNA are detected at very low levels. Subcutaneous/visceral ratios for OB-Ra the short OB-R isoform, OB-Rb, and SOCS3 mRNA abundance strongly correlate with the insulin sensitivity index, HOMA-% S, (r=0.49, P<0.0001, r=0.42, P=0.0002 and r=0.38, P=0.0002, respectively) in both lean and obese patients without type 2 diabetes. The near absence of OB-Rb mRNA and the similarly decreased SOCS3 expression in obese adipose tissue may reflect a defective leptin signaling pathway that could play a role in the impairment of insulin sensitivity associated with excess adiposity.

Towards a pro-inflammatory and immunomodulatory emerging role of leptin

Leptin is a 16 kDa adipocyte-secreted hormone that regulates weight centrally and links nutritional status with neuroendocrine and immune function. Since its cloning in 1994, leptin's role in regulating immune and inflammatory response has become increasingly evident. Actually, the increase of leptin production that occurs during infection and inflammation strongly suggests that leptin is a part of the cytokines loop which governs the inflammatory-immune response and the host defence mechanism. Indeed, leptin stimulates the production of pro-inflammatory cytokines from cultured monocytes and enhances the production of Th1 type cytokines from stimulated lymphocytes. Several studies have implicated leptin in the pathogenesis of autoimmune inflammatory conditions such as type 1 diabetes, rheumatoid arthritis and chronic bowel disease. Obesity is characterized by elevated circulating leptin levels which might contribute significantly to the so called low-grade systemic inflammation, making obese individuals more susceptible to the increased risk of developing cardiovascular diseases, type II diabetes or inflammatory articular degenerative disease such as osteorathritis (OA). As a matter of fact, a key role for leptin in OA has been recently demonstrated since leptin exhibits, in synergy with other pro-inflammatory cytokines, a detrimental effect on articular cartilage cells by promoting nitric oxide synthesis. This review will focus prevalently on the complex relationships existing among leptin, inflammatory response and immunity, trying to provide surprising insights into leptin's role and to discuss challenges and prospects for the future.

Neuropeptide Y in the medial basal hypothalamus and medial preoptic area during the induction of LH surge may be controlled by locus coeruleus

The multiple control of gonadotropin releasing hormone (GnRH)/luteinizing hormone (LH) secretion involves locus coeruleus (LC) and neuropeptide Y (NPY). The objective of the present study was to analyze the possible contribution of the LC to the control of NPY activity in the medial basal hypothalamus (MBH) and medial preoptic area (MPOA) during the LH surge induced by estrogen (E(2)) and progesterone (P(4)). Ovariectomized adult Wistar rats were submitted to the hormone replacement and to the LC bilateral lesion (lesioned groups) or sham surgery (control groups). On the day of the experiment the rats were decapitated at 11:00, 13:00, 15:00 and 17:00 h for plasma and brain collection. Plasma LH was determined by radioimmunoassay. MBH and MPOA were microdissected for the measurement of NPY by enzyme immunoassay. NPY mRNA levels in MBH were assessed by the ribonuclease protection assay. The results showed that LC lesion: decreased the plasma LH; increased the content of NPY in the MBH and reduced the increase of NPY content in the MPOA during afternoon in which LH surge was induced. The increased NPY content in MBH was not associated with an increase of the respective mRNA content, suggesting the action of postranscriptional and/or postranslational mechanisms. In conclusion, the NPY activity in the MPOA on LH surge induced by estrogen and progesterone could be controlled by LC through two ways, at least: one direct way, by the release of NPY from LC neurons terminals that innervate the MPOA and they release NA and NPY; one indirect way, by the control of release but not synthesis of NPY from neurons in the MBH which innervate the MPOA.

Regulation of body weight and thermogenesis in seasonally acclimatized Brandt's voles (Microtus brandti)

Seasonal changes in an animal's morphology, physiology, and behavior are considered to be an adaptive strategy for survival and reproductive success. In the present study, we examined body weight and several behavioral, physiological, hormonal, and biochemical markers in seasonally acclimatized Brandt's voles (Microtus brandti) to test our hypothesis that Brandt's voles can decrease energy intake associated with decrease in body weight, body fat content, serum leptin level, and increasing thermogenesis in winter conditions. We found that the body weight of Brandt's voles was lowest in winter (December to February) and highest in spring and early summer (May to June). This seasonal variation in body weight was associated with changes in other markers examined. For example, the winter decrease in body weight was accompanied by increased energy intake and enhanced nonshivering thermogenesis (NST) as well as by decreased body fat mass and reduced levels of circulating leptin. Further, circulating levels of leptin were positively correlated with body weight and body fat mass, and negatively correlated with energy intake and uncoupling protein 1 contents. Together, these data do not support our hypothesis and suggest that leptin may be involved in this process and serve as a starvation signal in Brandt's voles.

Leptin effects on food and water intake in lines of chickens selected for high or low body weight

There is an association between autonomic nervous system output and obesity. The sympathetic nervous system stimulates lipid metabolism and regulates food intake and, hence, body weight. Leptin, produced by adipocytes in proportion to their size, has been shown to directly stimulate the satiety center. In the experiment reported here, food and water intake were compared after intracerebroventricular administration of human recombinant leptin to lines of chickens that had undergone divergent selection for over 45 generations from a common White Rock base population for high (HWS) or low (LWS) body weight at 8 weeks-of-age. Leptin caused a linear decrease in food intake in chickens from the LWS line whereas no effect was observed in those from the HWS line. The HWS chickens tended to have reduced water intake post leptin administration. Others reported that leptin decreased food intake in both broiler and Leghorn chickens. Leptin concentration in the central nervous system may not contribute directly to the difference of body weight between HWS and LWS chickens.

The Nhlh2 transcription factor is required for female sexual behavior and reproductive longevity

Nhlh2 is a member of the basic helix-loop-helix (bHLH) transcription factor family and is expressed in developing and adult neuroendocrine tissues such as the pituitary and hypothalamus. Targeted deletion of Nhlh2 (N2KO) in mice results in hypogonadism and obesity. While gonadally intact male N2KO mice are infertile and lack male sexual behavior, female N2KO mice can become pregnant and carry litters to full term. Unlike normal females in which fertility averages 8-12 months with approximately one pregnancy per month, N2KO females have a shorter reproductive span with most females supporting only three to four pregnancies in a 9-month period. In addition, N2KO females exhibit abnormal estrous cycles characterized by a truncated estrus and a prolonged proestrus. We have found that while young female N2KO mice ovulate the same number of oocytes as normal females in response to exogenous hormones, the number of oocytes released by aged N2KO females is reduced over 50%. Interestingly, oocytes from N2KO females are equally competent for in vitro fertilization assays when compared to oocytes from similarly aged normal and heterozygous mice. We have further demonstrated that both young and old N2KO females show at least a 50% reduction in hormone-stimulated sexual behavior as measured by their lordosis quotient. This suggests that N2KO females show a lifelong behavioral hyporesponsiveness to exogenous steroid hormones accompanied by a reduction in reproductive longevity via reduced ovulation with aging. Potential gene regulatory mechanisms that involve the action of the Nhlh2 transcription factor on female fertility and sexual behavior are discussed.

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.

Decreased hypothalamic concentration of neuropeptide Y correlates with onset of hyperphagia in fa/fa rats on postnatal day 12

An increased action of hypothalamic neuropeptide Y (NPY) has been proposed as a major factor in the pathophysiology of the obesity syndrome in Zucker (fa/fa) rats. Using a developmental strategy to test this hypothesis, we showed previously that significantly more arcuate NPY was expressed in fa/fa pups than in lean littermates on postnatal day (P) 2 and throughout the preweaning period [Physiol. Behav. 67 (1999) 521], and that hyperphagia first appeared on P12 [Am. J. Physiol. 275 (1998) R1106]. To test the hypothesis further, we used a specific radioimmunoassay to measure the concentration of hypothalamic NPY peptide in lean (+/+ and +/fa) and obese fa/fa Zucker rat pups on P9, P10, and P12. The concentration of NPY in fa/fa pups was not significantly different from that of the other genotypes. There was, however, a significant decrease in NPY concentration from P9 to P12 in fa/fa pups, but not in lean pups. The combination of increased NPY message and decreasing concentration of NPY peptide in fa/fa pups with age is consistent with, but does not prove, increased release of hypothalamic NPY in fa/fa pups just before and on P12 when hyperphagia emerges. These results provide further support for the importance of hypothalamic NPY in the phenotypic expression of hyperphagia in the fa/fa pups during the second postnatal week.

Reduced voluntary activity precedes adult-onset obesity in Nhlh2 knockout mice

Targeted deletion of the neuronal basic helix-loop-helix transcription factor Nhlh2 results in adult-onset obesity in mice. Measurement of body weight and body composition in animals aged 3-25 weeks indicates that while male and female Nhlh2 knockout (N2KO) animals both show adult-onset obesity, the time frame for development of obesity is different, with females becoming obese by 7 weeks of age and males becoming obese by 10 weeks of age. Heterozygous (HET) animals also become obese but with a slower onset, indicating a dosage effect for the activity of the Nhlh2 transcription factor. Food intake, body temperature, and voluntary activity were measured in both preobese and obese N2KO, HET, and wild-type (WT) animals to determine which factors contributed to weight gain. While increased food intake and decreased body temperature were found in older obese N2KO animals, only reduced physical activity preceded the onset of obesity in N2KO mice. N2KO animals had no deficit in either circadian rhythm or balance and motor control, indicating that reduced voluntary activity is the result of a behavioral change. These data demonstrate a role for the Nhlh2 transcription factor in controlling genes important to energy expenditure, and more specifically voluntary physical activity of animals.

Metabolic diseases: the environment determines the odds, even for genes

The odds for well-being or illness are determined by the interplay of genetic and environmental impacts. In this review, normal and disturbed body weight regulation are used to demonstrate the role of integrative bioresearch in bridging the gap between identified genotypes and an understanding of the functions of redundant and plastic control systems underlying phenotypes.

Hypothalamic bHLH transcription factors are novel candidates in the regulation of energy balance

The basic helix-loop-helix transcription factors, neurological basic-helix-loop-helix-2 (Nhlh-2), neurogenic differentiation-1 (NeuroD-1) and single minded-1 (Sim-1) could have roles in energy balance regulation, although supporting evidence is inconclusive. This study in mice provides further evidence that Nhlh-2 and NeuroD-1 are involved in energy balance regulation. In situ hybridization was used to study the expression of the genes in relation to physiological status and genetic background within hypothalamic nuclei that are involved in energy balance regulation. These studies show reduced expression of Nhlh-2 mRNA in the arcuate (ARC) nucleus and NeuroD-1 mRNA in the paraventricular (PVN) nucleus in obese ob/ob and 24 h food-deprived mice relative to respective controls, suggesting regulation by leptin. Interestingly, Nhlh-2 mRNA expression is reduced in obese db/db mice, whereas NeuroD-1 remains unchanged, suggesting different mechanisms of regulation by leptin of these two genes. To study the role of leptin in the regulation of these genes, leptin was injected intraperitoneally in obese ob/ob mice and mRNA expression evaluated after 1 h or 4 h, or after twice-daily injection for 7 days. None of these regimes restored Nhlh-2 or NeuroD-1 to wild-type mRNA levels. These latter data suggest either that the regulation of the Nhlh-2 and NeuroD-1 genes by leptin is indirect or that the apparent leptin insensitivity of the gene expression reflects a developmental deficit that is a consequence of the phenotype of the obese ob/ob mice. The relationship between Nhlh-2 and candidate energy balance-related genes was studied by dual in situ hybridization. Nhlh-2 mRNA was coexpressed in a subpopulation (30%) of ARC neurons expressing pro-opiomelanocortin (POMC) mRNA, suggesting a potential functional relationship.

KO's and organisation of peptidergic feeding behavior mechanisms

Feeding behavior results from complex interactions arising between numerous neuromediators, including classical neurotransmitters and neuropeptides present in hypothalamic networks. One way to unravel these complex mechanisms is to examine animal models with a deletion of genes coding for the different neuropeptides involved in the regulation of feeding. The aim of this review is to focus on feeding and body weight regulation in mice lacking neuropeptide Y (NPY), melanocortins (POMC), corticotropin-releasing hormone, melanin-concentrating hormone, or bombesin-like peptides respectively. The phenotypes, which relate to the deletion of gene coding for the peptides, rarely include changes in body weight and food intake, indicating therefore the existence of redundant mechanisms to compensate for the loss of the peptide. The phenotype is much more marked when the gene deletion is targeted towards the functioning of the peptidergic machinery, e.g. the receptors and especially the POMC and NPY receptors, as well as one subtype of bombesin receptor (BRS-3). These knockout models are also interesting when examining the role of environmental and social factors in the determination of feeding behavior. They have granted us better knowledge of all these integrated and complex mechanisms. Moreover, they are also valuable tools for pharmacological studies when specific antagonists are lacking. From the information obtained by the study of knockouts, it is possible to determine certain targets for selective drugs that could be efficient for the pharmacological treatment of obesity. However, at the present state of our knowledge, it seems necessary to target several peptides in order to get good results with weight loss. It will also be imperative to associate these multitherapies with changes in eating and behavioral habits, in order to obtain complete effectiveness and long-lasting results.