Loss of hypothalamic Furin affects POMC to proACTH cleavage and feeding behavior in high-fat diet-fed mice.

OBJECTIVE: The hypothalamus regulates feeding and glucose homeostasis through the balanced action of different neuropeptides, which are cleaved and activated by the proprotein convertases PC1/3 and PC2. However, the recent association of polymorphisms in the proprotein convertase FURIN with type 2 diabetes, metabolic syndrome, and obesity, prompted us to investigate the role of FURIN in hypothalamic neurons controlling glucose and feeding. METHODS: POMC-Cre+/- mice were bred with Furinfl/fl mice to generate conditional knockout mice with Furin-deletion in neurons expressing proopiomelanocortin (POMCFurKO), and Furinfl/fl mice were used as controls. POMCFurKO and controls were periodically monitored on both normal chow diet and high fat diet (HFD) for body weight and glucose tolerance by established in-vivo procedures. Food intake was measured in HFD-fed FurKO and controls. Hypothalamic Pomc mRNA was measured by RT-qPCR. ELISAs quantified POMC protein and resulting peptides in the hypothalamic extracts of POMCFurKO mice and controls. The in-vitro processing of POMC was studied by biochemical techniques in HEK293T and CHO cell lines lacking FURIN. RESULTS: In control mice, Furin mRNA levels were significantly upregulated on HFD feeding, suggesting an increased demand for FURIN activity in obesogenic conditions. Under these conditions, the POMCFurKO mice were hyperphagic and had increased body weight compared to Furinfl/fl mice. Moreover, protein levels of POMC were elevated and ACTH concentrations markedly reduced. Also, the ratio of α-MSH/POMC was decreased in POMCFurKO mice compared to controls. This indicates that POMC processing was significantly reduced in the hypothalami of POMCFurKO mice, highlighting for the first time the involvement of FURIN in the cleavage of POMC. Importantly, we found that in vitro, the first stage in processing where POMC is cleaved into proACTH was achieved by FURIN but not by PC1/3 or the other proprotein convertases in cell lines lacking a regulated secretory pathway. CONCLUSIONS: These results suggest that FURIN processes POMC into proACTH before sorting into the regulated secretory pathway, challenging the dogma that PC1/3 and PC2 are the only convertases responsible for POMC cleavage. Furthermore, its deletion affects feeding behaviors under obesogenic conditions.

Hypothalamic AgRP neurons exert top-down control on systemic TNF-α release during endotoxemia.

Loss of appetite and negative energy balance are common features of endotoxemia in all animals and are thought to have protective roles by reducing nutrient availability to host and pathogen metabolism. Accordingly, fasting and caloric restriction have well-established anti-inflammatory properties. However, in response to reduced nutrient availability at the cellular and organ levels, negative energy balance also recruits distinct energy-sensing brain circuits, but it is not known whether these neuronal systems have a role in its anti-inflammatory effects. Here, we report that hypothalamic AgRP neurons-a critical neuronal population for the central representation of negative energy balance-have parallel immunoregulatory functions. We found that when endotoxemia occurs in fasted mice, the activity of AgRP neurons remains sustained, but this activity does not influence feeding behavior and endotoxemic anorexia. Furthermore, we found that endotoxemia acutely desensitizes AgRP neurons, which also become refractory to inhibitory signals. Mimicking this sustained AgRP neuron activity in fed mice by chemogenetic activation-a manipulation known to recapitulate core behavioral features of fasting-results in reduced acute tumor necrosis factor alpha (TNF-α) release during endotoxemia. Mechanistically, we found that endogenous glucocorticoids play an important role: glucocorticoid receptor deletion from AgRP neurons prevents their endotoxemia-induced desensitization, and importantly, it counteracts the fasting-induced suppression of TNF-α release, resulting in prolonged sickness. Together, these findings provide evidence directly linking AgRP neuron activity to the acute response during endotoxemia, suggesting that these neurons are a functional component of the immunoregulatory effects associated with negative energy balance and catabolic metabolism.

Chronic glucocorticoid treatment induces hepatic lipid accumulation and hyperinsulinaemia in part through actions on AgRP neurons.

Glucocorticoids (GCs) are widely prescribed anti-inflammatory medicines, but their use can lead to metabolic side-effects. These may occur through direct actions of GCs on peripheral organs, but could also be mediated by the hypothalamic AgRP neurons, which can increase food intake and modify peripheral metabolism. Therefore, the aim of this study was to examine the metabolic effects of chronic treatment with the GC corticosterone (Cort, 75 µg/ml in drinking water) in mice lacking the glucocorticoid receptor (GR) on AgRP neurons. Female AgRP-GR KO mice had delayed onset of Cort-induced hyperphagia. However, AgRP-GR KO had little impact on the increased body weight or adiposity seen with 3 weeks Cort treatment. Cort caused hepatic steatosis in control mice, but in Cort treated female AgRP-GR KO mice there was a 25% reduction in liver lipid content and lower plasma triglycerides. Additionally, Cort treatment led to hyperinsulinaemia, but compared to controls, Cort-treated AgRP-GR KO mice had both lower fasting insulin levels and lower insulin levels during a glucose tolerance test. In conclusion, these data indicate that GCs do act through AgRP neurons to contribute, at least in part, to the adverse metabolic consequences of chronic GC treatment.

Reduced Stability and pH-Dependent Activity of a Common Obesity-Linked PCSK1 Polymorphism, N221D.

Common mutations in the human prohormone convertase (PC)1/3 gene (PCKSI) are linked to increased risk of obesity. Previous work has shown that the rs6232 single-nucleotide polymorphism (N221D) results in slightly decreased activity, although whether this decrease underlies obesity risk is not clear. We observed significantly decreased activity of the N221D PC1/3 enzyme at the pH of the trans-Golgi network; at this pH, the mutant enzyme was less stable than wild-type enzyme. Recombinant N221D PC1/3 also showed enhanced susceptibility to heat stress. Enhanced susceptibility to tunicamycin-induced endoplasmic reticulum stress was observed in AtT-20/PC2 cell clones in which murine PC1/3 was replaced by human N221D PC1/3, as compared with wild-type human PC1/3. However, N221D PC1/3-expressing AtT-20/PC2 clones processed proopiomelanocortin to α-MSH similarly to wild-type PC1/3. We also generated a CRISPR-edited mouse line expressing the N221D mutation in the PCKSI gene. When homozygous N221D mice were fed either a standard or a high-fat diet, we found no increase in body weight compared with their wild-type sibling controls. Sexual dimorphism was observed in pituitary ACTH for both genotypes, with females exhibiting lower levels of pituitary ACTH. In contrast, hypothalamic α-MSH content for both genotypes was higher in females compared with males. Hypothalamic corticotropin-like intermediate peptide content was higher in wild-type females compared with wild-type, but not N221D, males. Taken together, these data suggest that the increased obesity risk linked to the N221D allele in humans may be due in part to PC1/3-induced loss of resilience to stressors rather than strictly to decreased enzymatic activity on peptide precursors.

Metabolic Abnormalities of Chronic High-Dose Glucocorticoids Are Not Mediated by Hypothalamic AgRP in Male Mice.

Glucocorticoids are potent and widely used medicines but often cause metabolic side effects. A murine model of corticosterone treatment resulted in increased hypothalamic expression of the melanocortin antagonist AgRP in parallel with obesity and hyperglycemia. We investigated how these adverse effects develop over time, with particular emphasis on hypothalamic involvement. Wild-type and Agrp-/- male mice were treated with corticosterone for 3 weeks. Phenotypic, biochemical, protein, and mRNA analyses were undertaken on central and peripheral tissues, including white and brown adipose tissue, liver, and muscle, to determine the metabolic consequences. Corticosterone treatment induced hyperphagia within 1 day in wild-type mice, which persisted for 3 weeks. Despite this early increase in food intake, the body weight only started to increase after 10 days. Hyperinsulinemia occurred at day 1. Also, although after 2 days, alterations were present in the genes often associated with insulin resistance in several peripheral tissues, hyperglycemia only developed at 3 weeks. Throughout, sustained elevation in hypothalamic Agrp expression was present. Mice with Agrp deleted [using clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9, Agrp-/-] were partially protected against corticosterone-induced hyperphagia. However, Agrp-/- mice still had corticosterone-induced increases in body weight and adiposity similar to those of the Agrp+/+ mice. Loss of Agrp did not diminish corticosterone-induced hyperinsulinemia or correct changes in hepatic gluconeogenic genes. Chronic glucocorticoid treatment in mice mimics many of the metabolic side effects seen in patients and leads to a robust increase in Agrp. However, AgRP does not appear to be responsible for most of the glucocorticoid-induced adverse metabolic effects.

Quantitative mass spectrometry for human melanocortin peptides in vitro and in vivo suggests prominent roles for ß-MSH and desacetyl α-MSH in energy homeostasis.

OBJECTIVE: The lack of pro-opiomelanocortin (POMC)-derived melanocortin peptides results in hypoadrenalism and severe obesity in both humans and rodents that is treatable with synthetic melanocortins. However, there are significant differences in POMC processing between humans and rodents, and little is known about the relative physiological importance of POMC products in the human brain. The aim of this study was to determine which POMC-derived peptides are present in the human brain, to establish their relative concentrations, and to test if their production is dynamically regulated. METHODS: We analysed both fresh post-mortem human hypothalamic tissue and hypothalamic neurons derived from human pluripotent stem cells (hPSCs) using liquid chromatography tandem mass spectrometry (LC-MS/MS) to determine the sequence and quantify the production of hypothalamic neuropeptides, including those derived from POMC. RESULTS: In both in vitro and in vivo hypothalamic cells, LC-MS/MS revealed the sequence of hundreds of neuropeptides as a resource for the field. Although the existence of ß-melanocyte stimulating hormone (MSH) is controversial, we found that both this peptide and desacetyl α-MSH (d-α-MSH) were produced in considerable excess of acetylated α-MSH. In hPSC-derived hypothalamic neurons, these POMC derivatives were appropriately trafficked, secreted, and their production was significantly (P < 0.0001) increased in response to the hormone leptin. CONCLUSIONS: Our findings challenge the assumed pre-eminence of α-MSH and suggest that in humans, d-α-MSH and ß-MSH are likely to be the predominant physiological products acting on melanocortin receptors.

Maternal overnutrition programs epigenetic changes in the regulatory regions of hypothalamic Pomc in the offspring of rats.

BACKGROUND AND OBJECTIVE: Maternal overnutrition has been implicated in affecting the offspring by programming metabolic disorders such as obesity and diabetes, by mechanisms that are not clearly understood. This study aimed to determine the long-term impact of maternal high-fat (HF) diet feeding on epigenetic changes in the offspring's hypothalamic Pomc gene, coding a key factor in the control of energy balance. Further, it aimed to study the additional effects of postnatal overnutrition on epigenetic programming by maternal nutrition. METHODS: Eight-week-old female Sprague-Dawley rats were fed HF diet or low-fat (LF) diet for 6 weeks before mating, and throughout gestation and lactation. At postnatal day 21, samples were collected from a third offspring and the remainder were weaned onto LF diet for 5 weeks, after which they were either fed LF or HF diet for 12 weeks, resulting in four groups of offspring differing by their maternal and postweaning diet. RESULTS: With maternal HF diet, offspring at weaning had rapid early weight gain, increased adiposity, and hyperleptinemia. The programmed adult offspring, subsequently fed LF diet, retained the increased body weight. Maternal HF diet combined with offspring HF diet caused more pronounced hyperphagia, fat mass, and insulin resistance. The ARC Pomc gene from programmed offspring at weaning showed hypermethylation in the enhancer (nPE1 and nPE2) regions and in the promoter sequence mediating leptin effects. Interestingly, hypermethylation at the Pomc promoter but not at the enhancer region persisted long term into adulthood in the programmed offspring. However, there were no additive effects on methylation levels in the regulatory regions of Pomc in programmed offspring fed a HF diet. CONCLUSION: Maternal overnutrition programs long-term epigenetic alterations in the offspring's hypothalamic Pomc promoter. This predisposes the offspring to metabolic disorders later in life.

International survey on high- and low-dose synacthen test and assessment of accuracy in preparing low-dose synacthen.

OBJECTIVE: The short synacthen test (SST) is widely used to assess patients for adrenal insufficiency, but the frequency and protocols used across different centres for the low-dose test (LDT) are unknown. This study aimed to survey centres and test the accuracy of ten different synacthen preparation strategies used for the LDT. METHODS: Members of 6 international endocrine societies were surveyed regarding diagnostic tests used for adrenal insufficiency, and in particular the SST. Synacthen was diluted for the LDT and concentrations measured using a synacthen ELISA. RESULTS: Survey responses were received from 766 individuals across 60 countries (52% adult, 45% paediatric endocrinologists). The SST is used by 98% of centres: 92% using high-dose (250 µg), 43% low-dose and 37% both. Ten low-dose dilution methods were assessed and variation in synacthen concentration was demonstrated with intramethod coefficients of variation (CV) ranging from 2.1% to 109%. The method using 5% dextrose as a diluent was the least variable (CV of 2.1%). The variation in dilution methods means that the dose of synacthen administered in a LDT may vary between 0.16 and 0.81 µg. CONCLUSIONS: The high-dose SST is the most popular diagnostic test of adrenal insufficiency, but up to 72% of paediatric endocrinologists use a LDT. There is considerable variation observed both within and between low-dose synacthen dilution methods creating considerable risk of inaccurate dosing and thereby invalid results.

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 11ß-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.

Maternal undernutrition programs tissue-specific epigenetic changes in the glucocorticoid receptor in adult offspring.

Epidemiological data indicate that an adverse maternal environment during pregnancy predisposes offspring to metabolic syndrome with increased obesity, and type 2 diabetes. The mechanisms are still unclear although epigenetic modifications are implicated and the hypothalamus is a likely target. We hypothesized that maternal undernutrition (UN) around conception in sheep would lead to epigenetic changes in hypothalamic neurons regulating energy balance in the offspring, up to 5 years after the maternal insult. We found striking evidence of decreased glucocorticoid receptor (GR) promoter methylation, decreased histone lysine 27 trimethylation, and increased histone H3 lysine 9 acetylation in hypothalami from male and female adult offspring of UN mothers. These findings are entirely compatible with the increased GR mRNA and protein observed in the hypothalami. The increased GR predicted the decreased hypothalamic proopiomelanocortin expression and increased obesity that we observed in the 5-year-old adult males. The epigenetic and expression changes in GR were specific to the hypothalamus. Hippocampal GR mRNA and protein were decreased in UN offspring, whereas pituitary GR was altered in a sex-specific manner. In peripheral polymorphonuclear leukocytes there were no changes in GR methylation or protein, indicating that this epigenetic analysis did not predict changes in the brain. Overall, these results suggest that moderate changes in maternal nutrition, around the time of conception, signal life-long and tissue-specific epigenetic alterations in a key gene regulating energy balance in the hypothalamus.

Atorvastatin administration is associated with dose-related changes in IGF bioavailability.

OBJECTIVE: IGF levels, their binding proteins (IGFBPs) and high-dose statin therapy have been linked to the development of diabetes. We aimed to identify whether atorvastatin caused dose-related changes in IGF proteins. DESIGN AND METHODS: We measured IGF1, IGF2, IGFBP1 and IGFBP3 concentrations at baseline, 6 and 12 months in Protection Against Nephropathy in Diabetes with Atorvastatin trial participants with type 2 diabetes randomised to 10 mg (n=59) vs 80 mg (n=60) of atorvastatin (n=119; mean (S.D.): age 64 (10) years; 83% male; HbA1c 61 (10) mmol/mol; blood pressure 131/73 mmHg). RESULTS: Atorvastatin was associated with overall reductions in circulating IGF1, IGF2 and IGFBP3 concentrations (P<0.05 for all changes). The adjusted mean (95% CI) between-group differences that indicate dose-related changes in IGF proteins were not significant for IGF1: -3 (-21 to 14) ng/ml; IGF2: -23 (-65 to 18) ng/ml and IGFBP3: -0.34 (-0.71 to 0.03) µg/ml, negative values indicating numerically greater lowering with high dose. The IGFBP1 concentration did not change with atorvastatin therapy overall but the adjusted mean (95% CI) between-group difference indicating a dose-related change in log IGFBP1 was highly significant -0.41 (-0.69 to 0.13, P=0.004). CONCLUSION: IGF1, IGF2 and IGFBP3 concentrations decreased following atorvastatin therapy. A differential effect of low- vs high-dose atorvastatin on IGFBP1 concentrations was observed with likely implications for IGF bioavailability. The dose-related differential impact of atorvastatin treatment on concentration of IGF proteins merits investigation as a mechanism to explain the worsening of glucose tolerance with statin therapy.

Epigenetic changes in fetal hypothalamic energy regulating pathways are associated with maternal undernutrition and twinning.

Undernutrition during pregnancy is implicated in the programming of offspring for the development of obesity and diabetes. We hypothesized that maternal programming causes epigenetic changes in fetal hypothalamic pathways regulating metabolism. This study used sheep to examine the effect of moderate maternal undernutrition (60 d before to 30 d after mating) and twinning to investigate changes in the key metabolic regulators proopiomelanocortin (POMC) and the glucocorticoid receptor (GR) in fetal hypothalami. Methylation of the fetal hypothalamic POMC promoter was reduced in underfed singleton, fed twin, and underfed twin groups (60, 73, and 63% decrease, respectively). This was associated with reduced DNA methyltransferase activity and altered histone methylation and acetylation. Methylation of the hypothalamic GR promoter was decreased in both twin groups and in maternally underfed singleton fetuses (52, 65, and 55% decrease, respectively). This correlated with changes in histone methylation and acetylation and increased GR mRNA expression in the maternally underfed singleton group. Alterations in GR were hypothalamic specific, with no changes in hippocampi. Unaltered levels of OCT4 promoter methylation indicated gene-specific effects. In conclusion, twinning and periconceptional undernutrition are associated with epigenetic changes in fetal hypothalamic POMC and GR genes, potentially resulting in altered energy balance regulation in the offspring.

Deletion of Lkb1 in pro-opiomelanocortin neurons impairs peripheral glucose homeostasis in mice.

OBJECTIVE: AMP-activated protein kinase (AMPK) signaling acts as a sensor of nutrients and hormones in the hypothalamus, thereby regulating whole-body energy homeostasis. Deletion of Ampkα2 in pro-opiomelanocortin (POMC) neurons causes obesity and defective neuronal glucose sensing. LKB1, the Peutz-Jeghers syndrome gene product, and Ca(2+)-calmodulin-dependent protein kinase kinase ß (CaMKKß) are key upstream activators of AMPK. This study aimed to determine their role in POMC neurons upon energy and glucose homeostasis regulation. RESEARCH DESIGN AND METHODS: Mice lacking either Camkkß or Lkb1 in POMC neurons were generated, and physiological, electrophysiological, and molecular biology studies were performed. RESULTS: Deletion of Camkkß in POMC neurons does not alter energy homeostasis or glucose metabolism. In contrast, female mice lacking Lkb1 in POMC neurons (PomcLkb1KO) display glucose intolerance, insulin resistance, impaired suppression of hepatic glucose production, and altered expression of hepatic metabolic genes. The underlying cellular defect in PomcLkb1KO mice involves a reduction in melanocortin tone caused by decreased α-melanocyte-stimulating hormone secretion. However, Lkb1-deficient POMC neurons showed normal glucose sensing, and body weight was unchanged in PomcLkb1KO mice. CONCLUSIONS: Our findings demonstrate that LKB1 in hypothalamic POMC neurons plays a key role in the central regulation of peripheral glucose metabolism but not body-weight control. This phenotype contrasts with that seen in mice lacking AMPK in POMC neurons with defects in body-weight regulation but not glucose homeostasis, which suggests that LKB1 plays additional functions distinct from activating AMPK in POMC neurons.

Epigenetic changes in the hypothalamic pro-opiomelanocortin gene: a mechanism linking maternal undernutrition to obesity in the offspring?

Maternal undernutrition is associated with programming of obesity in offspring. While previous evidence has linked programming to the hypothalamic, pituitary, and adrenal (HPA) axis it could also affect the hypothalamic neuropeptides which regulate food intake and energy balance. Alpha melanocyte stimulating hormone (αMSH), a key regulator of these neuronal pathways, is derived from pro-opiomelanocortin (POMC) which is therefore a prime target for the programming of obesity. Several models of maternal undernutrition have identified changes in POMC in hypothalami from foetuses or offspring at various ages. These models have also shown that the offspring go on to develop obesity and/or glucose intolerance. It is our hypothesis that programming leads to epigenetic changes in hypothalamic neuropeptide genes. Therefore when there is subsequent increased food availability, the epigenetic changes could cause dysfunctional transcriptional regulation of energy balance. We present evidence of epigenetic changes in the POMC gene promoter in foetal hypothalami after peri-conceptional undernutrition. In this model there are also epigenetic changes in the hypothalamic glucocorticoid receptor with consequent up-regulation of the receptor which could lead to alterations in the regulation of POMC and neuropeptide Y (NPY) in the hypothalamus. Thus maternal undernutrition could cause epigenetic changes in the POMC and glucocorticoid receptor genes, in the foetal hypothalamus, which may predispose the offspring to altered regulation of food intake, energy expenditure and glucose homeostasis, later in life.

Epigenetic changes in the hypothalamic proopiomelanocortin and glucocorticoid receptor genes in the ovine fetus after periconceptional undernutrition.

Maternal food restriction is associated with the development of obesity in offspring. This study examined how maternal undernutrition in sheep affects the fetal hypothalamic glucocorticoid receptor (GR) and the appetite-regulating neuropeptides, proopiomelanocortin (POMC) and neuropeptide Y, which it regulates. In fetuses from ewes undernourished from -60 to +30 d around conception, there was increased histone H3K9 acetylation (1.63-fold) and marked hypomethylation (62% decrease) of the POMC gene promoter but no change in POMC expression. In the same group, acetylation of histone H3K9 associated with the hypothalamic GR gene was increased 1.60-fold and the GR promoter region was hypomethylated (53% decrease). In addition, there was a 4.7-fold increase in hypothalamic GR expression but no change in methylation of GR gene expression in the anterior pituitary or hippocampus. Interestingly, hypomethylation of both POMC and GR promoter markers in fetal hypothalami was also identified after maternal undernutrition from -60 to 0 d and -2 to +30 d. In comparison, the Oct4 gene, was hypermethylated in both control and underfed groups. Periconceptional undernutrition is therefore associated with marked epigenetic changes in hypothalamic genes. Increase in GR expression in the undernourished group may contribute to fetal programming of a predisposition to obesity, via altered GR regulation of POMC and neuropeptide Y. These epigenetic changes in GR and POMC in the hypothalamus may also predispose the offspring to altered regulation of food intake, energy expenditure, and glucose homeostasis later in life.

ACTH: cellular peptide hormone synthesis and secretory pathways.

Adrenocorticotrophic hormone (ACTH) is derived from the prohormone, pro-opiomelanocortin (POMC). This precursor undergoes proteolytic cleavage to yield a number of different peptides which vary depending on the tissue. In the anterior pituitary, POMC is processed to ACTH by the prohormone convertase, PC1 and packaged in secretory granules ready for stimulated secretion. In response to stress, corticotrophin releasing hormone (CRH), stimulates release of ACTH from the pituitary cell which in turn causes release of glucocorticoids from the adrenal gland. In tissues, such as the hypothalamus and skin, ACTH is further processed intracellularly to alpha melanocyte stimulating hormone (alphaMSH) which has distinct roles in these tissues. The prohormone, POMC, is itself released from cells and found in the human circulation at concentrations greater than ACTH. While much is known about the tightly regulated synthesis of POMC, there is still a lot to learn about the mechanisms for differentiating secretion of POMC, and the POMC-derived peptides. Understanding what happens to the POMC released from cells will provide new insights into its function.

Discovery and optimization of novel, non-steroidal glucocorticoid receptor modulators.

A virtual screening approach comprising a 3-D similarity search based on known GR modulators was used to identify a novel series of non-steroidal glucocorticoid receptor (GR) antagonists. Optimization of the initial hit to provide potent compounds which exhibit good selectivity against other steroidal nuclear hormone receptors is described.

Identification and optimisation of a series of substituted 5-(1H-pyrazol-3-yl)-thiophene-2-hydroxamic acids as potent histone deacetylase (HDAC) inhibitors.

Optimisation of ADS100380, a sub-micromolar HDAC inhibitor identified using a virtual screening approach, led to a series of substituted 5-(1H-pyrazol-3-yl)-thiophene-2-hydroxamic acids (6a-i), that possessed significant HDAC inhibitory activity. Subsequent functionalisation of the pendent phenyl group of compounds 6f and 6g provided analogues 6j-w with further enhanced enzyme and anti-proliferative activity. Compound 6j demonstrated efficacy in a mouse xenograft experiment.

Agouti-related protein is posttranslationally cleaved by proprotein convertase 1 to generate agouti-related protein (AGRP)83-132: interaction between AGRP83-132 and melanocortin receptors cannot be influenced by syndecan-3.

Agouti-related protein (AGRP) plays a key role in energy homeostasis. The carboxyl-terminal domain of AGRP acts as an endogenous antagonist of the melanocortin-4 receptor (MC4-R). It has been suggested that the amino-terminal domain of AGRP binds to syndecan-3, thereby modulating the effects of carboxyl-terminal AGRP at the MC4-R. This model assumes that AGRP is secreted as a full-length peptide. In this study we found that AGRP is processed intracellularly after Arg(79)-Glu(80)-Pro(81)-Arg(82). The processing site suggests cleavage by proprotein convertases (PCs). RNA interference and overexpression experiments showed that PC1/3 is primarily responsible for cleavage in vitro, although both PC2 and PC5/6A can also process AGRP. Dual in situ hybridization demonstrated that PC1/3 is expressed in AGRP neurons in the rat hypothalamus. Moreover, hypothalamic extracts from PC1-null mice contained 3.3-fold more unprocessed full-length AGRP, compared with wild-type mice, based on combined HPLC and RIA analysis, demonstrating that PC1/3 plays a role in AGRP cleavage in vivo. We also found that AGRP(83-132) is more potent an antagonist than full-length AGRP, based on cAMP reporter assays, suggesting that posttranslational cleavage is required to potentiate the effect of AGRP at the MC4-R. Because AGRP is cleaved into distinct amino-terminal and carboxyl-terminal peptides, we tested whether amino-terminal peptides modulate food intake. However, intracerebroventricular injection of rat AGRP(25-47) and AGRP(50-80) had no effect on body weight, food intake, or core body temperature. Because AGRP is cleaved before secretion, syndecan-3 must influence food intake independently of the MC4-R.

Proopiomelanocortin-derived peptides in rat cerebrospinal fluid and hypothalamic extracts: evidence that secretion is regulated with respect to energy balance.

Regulation of proopiomelanocortin (POMC) is an important means of controlling the central melanocortin system. It has never been established whether the spectrum of POMC-derived peptides synthesized and secreted from the hypothalamus is altered in response to changes in energy homeostasis in vivo. To monitor secretion, we analyzed peptide content of rat cerebrospinal fluid. Strikingly, both the POMC precursor and ACTH were readily detected. Moreover, levels of both were lower in samples from obese Zucker rats (fa/fa) vs. lean Zucker rats (+/+, fa/+) and from fasted vs. fed rats, whereas alpha MSH could not be detected. POMC levels were also decreased in hypothalamic extracts from obese and fasted animals. In contrast, despite being the most predominant peptide in extracts, alpha MSH levels were not significantly changed in any of the rat models. The ratio of precursor to derived peptides in cerebrospinal fluid was significantly higher in obese vs. lean and fed vs. fasted rats, indicating that secretion of POMC-derived peptides is differentially down-regulated during negative energy balance. In contrast to peptide analysis, we found that POMC gene expression was not significantly decreased in fasted rat hypothalami. We conclude that regulation of peptide secretion is an important mechanism by which the POMC system is controlled.