Journal of Endocrinology current issue

Plasticity of the zona reticularis in the adult marmoset adrenal cortex: voyages of discovery in the New World

Pattison, J C., Abbott, D. H, Saltzman, W., Conley, A. J, Bird, I. M — Fri, 13 Nov 2009 09:14:33 PST

Adrenarche in humans occurs at the age of 5–7 years, yet the process by which dehydroepiandrosterone (DHEA) biosynthesis in the adrenal zona reticularis (ZR) increases so dramatically remains as a matter of debate. One suggestion is that increased DHEA production by P450c17 (CYP17A1 as listed in HUGO Database) in the ZR results from a coincident fall in the expression of HSD3B, which would otherwise compete for pregnenolone substrate. Nonetheless, studies of human and rhesus adrenal show that cytochrome b5 (CYTB5) expression increases in the ZR with DHEA biosynthesis, and cloned human and rhesus P450c17 show selective increases in 17,20-lyase activity in the presence of CYTB5. The marmoset, a New World primate, expresses a fetal zone during development which regresses after birth. Adult males, however, do not develop an obvious functional ZR, while females develop a ZR in a manner that depends on their social/gonadal status. In all social and physiologic states, changes in marmoset ZR function relate directly to changes in the expression of CYTB5. Recent cloning and expression of marmoset P450c17 also show that while amino acid sequence homology is in the order of ~85% of that found in human and rhesus sequences, and basal lyase activity is low compared with rhesus, all previously described amino acids critical to human 17,20-lyase activity are completely conserved. Furthermore, the 17,20-lyase activity of the marmoset P450c17 clone is dramatically increased by addition of CYTB5. We propose that these combined data from the marmoset model provide further compelling evidence that the control of ZR CYTB5 expression is a key determinant of ZR function.

Can faulty antennae increase adiposity? The link between cilia proteins and obesity

Sen Gupta, P., Prodromou, N. V, Chapple, J P. — Fri, 13 Nov 2009 09:14:33 PST

Primary cilia are sensory organelles that protrude from the surface of most mammalian cell types. In humans and mice, mutations in proteins required for normal cilia function have been identified as causing a class of disorders with overlapping phenotypes known as ciliopathies. Recent evidence has linked obesity in ciliopathies to both the regulation of energy homeostasis in the hypothalamus and to adipogenesis. This article considers the role of cilia in these processes and whether cilia dysfunction may be relevant to more common forms of obesity.

Improved insulin sensitivity by calorie restriction is associated with reduction of ERK and p70S6K activities in the liver of obese Zucker rats

Zheng, Y., Zhang, W., Pendleton, E., Leng, S., Wu, J., Chen, R., Sun, X. J. — Fri, 13 Nov 2009 09:14:33 PST

Calorie restriction (CR) improves obesity-related insulin resistance through undefined molecular mechanisms. Insulin receptor substrate (IRS)-1 serine/threonine kinases have been proposed to modulate insulin sensitivity through phosphorylation of IRS proteins. The aim of this study is to test the hypothesis that changes in the activity of IRS1 serine/threonine kinases may underlie the molecular mechanism of CR in improving insulin sensitivity. Obese and lean Zucker rats were subjected to 40% CR or allowed to feed ad libitum (AL) for 20 weeks; body weight and insulin sensitivity were monitored throughout this period. The activity of IRS1 serine/threonine kinases – including JNK, ERK, MTOR/p70^S6K (RPS6KB1 as listed in the MGI Database), glycogen synthase kinase 3β (GSK3B), AMPK (PRKAA1 as listed in the MGI Database), and protein kinase C (PRKCQ) in liver tissue extracts was measured by an in vitro kinase assay using various glutathione-S-transferase (GST)–IRS1 fragments as substrates, while phosphorylation of IRS1 and serine kinases was determined by western blotting using phosphospecific antibodies. CR in obese rats significantly reduced body weight and increased insulin sensitivity compared to AL controls. Serine kinase activity toward IRS1^S612 (corresponding to S616 in human IRS1) and IRS1^S632/635 (corresponding to S636/639 in human IRS1) was increased in obese rats compared to lean littermates, and was markedly decreased following CR. Concomitantly, obesity increased and CR decreased the activity of hepatic ERK and p70^S6K against IRS1. The close association between the activity of hepatic ERK and p70^S6K with insulin resistance suggests an important role for ERK and p70^S6K in the development of insulin resistance, presumably via phosphorylation of IRS proteins.

In vivo activation of gene transcription via oestrogen response elements by a raloxifene analogue

Fri, 13 Nov 2009 09:14:33 PST

Raloxifene is a selective oestrogen receptor modulator with tissue-specific effects. The mechanisms behind the effects of raloxifene are partly unclear, and the aim of the present study was to investigate whether raloxifene can activate the classical oestrogen-signalling pathway in vivo in three known oestrogen-responsive organs, uterus (reproductive organ), bone (non-reproductive organ) and thymus (immune organ). For this purpose, we have used reporter mice with a luciferase gene under control of oestrogen-responsive elements (EREs), enabling detection of in vivo activation of gene transcription via the classical oestrogen pathway. Three-month-old ovariectomized ERE-luciferase mice were treated with the raloxifene analogue (LY117018), oestradiol (OE₂) or vehicle for 3 weeks. Luciferase activation was measured in bone, uterus and thymus, and compared to bone parameters, and uterus and thymus weights. The raloxifene analogue affected bone mineral density (BMD) to the same extent as OE₂, and both treatments resulted in increased luciferase activity in bone. As expected, OE₂ treatment resulted in increased uterus weight and increased uterine luciferase activity, while the effect of LY117018 on uterus weight and luciferase activity was modest and significantly lower than the effect of OE₂. LY117018 and OE₂ treatment resulted in similar luciferase activation in thymus. However, only OE₂ treatment resulted in thymic atrophy, while no effect on thymus weight was seen after LY117018 treatment. In summary, the raloxifene analogue LY117018 can activate the classical oestrogen pathway in bone, uterus and thymus in vivo, and this activation is associated with BMD and uterus weight, but not thymus weight.

Comparable effects of moderate intensity exercise on changes in anorectic gut hormone levels and energy intake to high intensity exercise

Ueda, S.-y., Yoshikawa, T., Katsura, Y., Usui, T., Fujimoto, S. — Fri, 13 Nov 2009 09:14:33 PST

There is growing interest in the effects of exercise on plasma gut hormone levels and subsequent energy intake (EI) but the effects of mode and exercise intensity on anorectic hormone profiles on subsequent EI remain to be elucidated. We aimed to investigate whether circulating peptide YY_3–36 (PYY_3–36) and glucagon-like peptide-1 (GLP-1 or GCG as listed in the HUGO Database) levels depend on exercise intensity, which could affect subsequent EI. Ten young male subjects (mean±s.d., age: 23.4±4.3 years, body mass index: 22.5±1.0 kg/m², and maximum oxygen uptake (VO_{2 max}): 45.9±8.5 ml/kg per min) received a standardized breakfast, which was followed by constant cycling exercise at 75% VO_{2 max} (high intensity session), 50% VO_{2 max} (moderate intensity session), or rest (resting session) for 30 min. At lunch, a test meal was presented, and EI was calculated. Blood samples were obtained during three sessions for measurements of glucose, insulin, PYY_3–36, and GLP-1, which includes GLP-1 (7–36) amide and GLP-1 (9–36) amide. Increases in blood PYY_3–36 levels were dependent on the exercise intensity (effect of session: P<0.001 by two-way ANOVA), whereas those in GLP-1 levels were similar between two different exercise sessions. Of note, increase in area under the curve values for GLP-1 levels was negatively correlated with decrease in the EI in each exercise session (high: P<0.001, moderate: P=0.002). The present findings raise the possibility that each gut hormone exhibits its specific blood kinetics in response to two different intensities of exercise stimuli and might play differential roles in regulation of EI after exercise.

Age and tissue specific differences in the development of acute insulin resistance following injury

Zhai, L., Messina, J. L — Fri, 13 Nov 2009 09:14:33 PST

Injuries, hemorrhage, sepsis, burn, and critical illnesses all induce insulin resistance, and insulin resistance is strongly associated with advancing age. However, the effect of age on injury induced insulin resistance is not well studied. We performed surgical trauma in male rats of three different ages (3-, 6-, and 10-weeks old). Rats were either hemorrhaged to a mean arterial pressure of 35–40 mmHg and subsequently maintained at that pressure for up to 90 min, or maintained without hemorrhage as controls. Results indicate that insulin-induced intracellular signaling was diminished in liver and skeletal muscle of 6- and 10-week old rats following trauma and hemorrhage. In even younger rats, immediately post-weaning (~3 weeks of age), insulin signaling was lost in liver, but not in skeletal muscle. Glucocorticoids can play a role in the chronic development of insulin resistance. Our results demonstrate that corticosterone levels were increased in 6- and 10-week old animals following hemorrhage, but little change was measured in 3-week old animals. Blockade of glucocorticoid synthesis prevented the development of insulin resistance in skeletal muscle, but not in liver of 6- and 10-week old rats. Moreover, skeletal muscle glucocorticoid receptor levels increased dramatically between 3 and 6 weeks of age. These results indicate that trauma and hemorrhage-induced hepatic insulin resistance occurs at all ages tested. However, there is no development of insulin resistance following trauma and hemorrhage in skeletal muscle of post-weaning rats. In skeletal muscle of 6- and 10-week old rats, inhibition of glucocorticoid levels prevents the development of insulin resistance.

Improving the pharmacokinetics/pharmacodynamics of prolactin, GH, and their antagonists by fusion to a synthetic albumin-binding peptide

Langenheim, J. F, Chen, W. Y — Fri, 13 Nov 2009 09:14:33 PST

To prolong the circulation half-life of human prolactin (hPRL), human GH (hGH), and their competitive antagonists, hPRL-G129R and hGH-G120R, we examined the effects of fusing a serum albumin-binding peptide (SA20) to their amino- or carboxyl-terminus. Fusion of the SA20 peptide to the amino-terminus of the ligands was less detrimental upon their ability to induce or inhibit signal transduction and cell proliferation in vitro than fusion to the carboxyl-terminus. Pharmacokinetic (PK) studies in mice revealed that the half-life of SA20-hPRL and SA20-hGH was prolonged and their clearance was reduced in comparison with hPRL and hGH. Pharmacodynamic (PD) studies in 8-week-old female mice revealed that lobuloalveolar development in mammary glands was greater in all three groups (daily, every 2 days, or every third day over a 12-day period) of mice treated with SA20-hPRL (4 mg/kg) compared with hPRL (3.59 mg/kg). Similarly, daily administration (i.p.) of SA20-hGH (8 mg/kg) or hGH (7.15 mg/kg) to 23-day-old female mice over a 40-day period revealed the superiority of SA20-hGH over hGH as measured by weight gain, body length, and lobuloalveolar development in the mammary glands. These findings indicate that SA20 modification of hPRL, hGH, and their respective antagonists improves their PK/PD properties.

Melanin-concentrating hormone reduces somatolactin release from cultured goldfish pituitary cells

Fri, 13 Nov 2009 09:14:33 PST

Melanin-concentrating hormone (MCH)-containing neurons directly innervate the adenohypophysis in the teleost pituitary. We examined immunohistochemically the relationship between MCH-containing nerve fibres or endings and somatolactin (SL)-producing cells in the goldfish pituitary. Nerve fibres or endings with MCH-like immunoreactivity were identified in the neurohypophysis in close proximity to the adenohypophysial cells showing SL-like immunoreactivity. We also examined the effect of MCH on SL release from cultured goldfish pituitary cells and SL synthesis using a cell immunoblot and a real-time PCR method. Treatment of individually dispersed pituitary cells with MCH 10^–7 M for 3 h decreased the area of SL-like immunoreactivity on immunoblots, and MCH-induced reductions in SL release were blocked by treatment with the mammalian MCH receptor (MCHR) antagonist, compound-30, at a concentration of 10^–5 M. Treatment with 10^–7 M MCH for 3 h did not affect sl- and -β (smtla and -b as given in the Zfin Database) mRNA expression levels. These led us to explore the signal transduction mechanism leading to the inhibition of SL release, for which we examined whether MCH-induced reductions in SL release are mediated by the G_i or G_q protein-coupled signalling pathway. The MCH-induced reductions in SL release were abolished by treatment with the G_i/o protein inhibitors, NF023 (10^–5 M) or pertussis toxin (260 ng/ml), but not by the phospholipase C inhibitor, U-73122 (3x10^–6 M). These results indicate that MCH can potentially function as a hypothalamic factor suppressing SL release via the MCHR, and subsequently through the G_i protein to inhibit the adenylate cyclase/cAMP/protein kinase A-signalling pathway in goldfish pituitary cells.

TRI3 is implicated in glucotoxicity- and endoplasmic reticulum-stress-induced {beta}-cell apoptosis

Fri, 13 Nov 2009 09:14:33 PST