Regulation of prohormone convertase 1 (PC1) by gp130-related cytokines

Mineralocorticoid Receptor May Regulate Glucose Homeostasis through the Induction of Interleukin-6 and Glucagon-Like peptide-1 in Pancreatic Islets

Because the renin-angiotensin-aldosterone system influences glucose homeostasis, the mineralocorticoid receptor (MR) signal in pancreatic islets may regulate insulin response upon glucose load. Glucagon-like peptide-1 (GLP-1) production is stimulated by interleukin-6 (IL-6) in pancreatic α-cells. To determine how glucose homeostasis is regulated by interactions of MR, IL-6 and GLP-1 in islets, we performed glucose tolerance and histological analysis of islets in primary aldosteronism (PA) model rodents and conducted in vitro experiments using α-cell lines. We measured active GLP-1 concentration in primary aldosteronism (PA) patients before and after the administration of MR antagonist eplerenone. In PA model rodents, aldosterone decreased insulin-secretion and the islet/pancreas area ratio and eplerenone added on aldosterone (E+A) restored those with induction of IL-6 in α-cells. In α-cells treated with E+A, IL-6 and GLP-1 concentrations were increased, and anti-apoptotic signals were enhanced. The E+A-treatment also significantly increased MR and IL-6 mRNA and these upregulations were blunted by MR silencing using small interfering RNA (siRNA). Transcriptional activation of the IL-6 gene promoter by E+A-treatment required an intact MR binding element in the promoter. Active GLP-1 concentration was significantly increased in PA patients after eplerenone treatment. MR signal in α-cells may stimulate IL-6 production and increase GLP-1 secretion, thus protecting pancreatic β-cells and improving glucose homeostasis.

Ketamine and Etomidate Down-regulate the Hypothalamic-Pituitary-Adrenal Axis in an Endotoxemic Mouse Model

BACKGROUND

We compared the effects of etomidate and ketamine on the hypothalamic-pituitary-adrenal axis during sepsis.

METHODS

Mice (n = 5/group) were injected intraperitoneally with lipopolysaccharide (10 mg/kg) and 6 h later randomized to receive ketamine (100 mg/kg), etomidate (30 mg/kg), or saline. At two time points (12 and 48 h), messenger RNA levels of hypothalamic corticotropin-releasing hormone, pituitary proopiomelanocortin, and four adrenal enzymes (P450 side-chain cleavage, 3β-hydroxysteroid deshydrogenase, 21-hydroxylase, and 11β-hydroxylase) were measured by in situ hybridization (results are presented as optical density), and plasma levels of corticosterone and adrenocorticotropin hormones were measured by enzyme-linked immunosorbent assay (mean ± SD).

RESULTS

At 12 h, lipopolysaccharide induced an overexpression of corticotropin-releasing hormone (32 ± 5 vs. 18 ± 6, P < 0.01), proopiomelanocortin (21 ± 3 vs. 8 ± 0.9, P < 0.0001), P450 side-chain cleavage (32 ± 4 vs. 23 ± 10, P < 0.05), 21-hydroxylase (17 ± 5 vs. 12 ± 2, P < 0.05), and 11β-hydroxylase (11 ± 4 vs. 6 ± 0.5, P = 0.001), and an elevation of corticosterone (642 ± 165 vs. 98.3 ± 63 ng/ml, P < 0.0001). Etomidate and ketamine reduced P450 side-chain cleavage (19 ± 7 and 19 ± 3 vs. 32 ± 4, P < 0.01), 21-hydroxylase (8 ± 0.8 and 8 ± 1 vs. 17 ± 5, P < 0.001), 11β-hydroxylase (4 ± 0.5 and 7 ± 1 vs. 11 ± 4, P < 0.001 and P < 0.05), and corticosterone (413 ± 189 and 260 ± 161 vs. 642 ± 165 ng/ml, P < 0.05 and P < 0.01). Ketamine also inhibited adrenocorticotropin hormone production (2.5 ± 3.6 vs. 36 ± 15 pg/ml, P < 0.05). At 48 h, all four adrenal enzymes were down-regulated by lipopolysaccharide administration with corticosterone levels similar to the control group. Ketamine and etomidate did not modify corticosterone plasma levels.

CONCLUSIONS

Our endotoxemic model induces an initial activation of the hypothalamic-pituitary-adrenal axis, followed by a secondary inhibition of adrenal steroidogenesis processes. Ketamine and etomidate inhibit the enzyme expression and activity of the adrenal gland at the early stage.

The suppression of maternal-fetal leukemia inhibitory factor signal relay pathway by maternal immune activation impairs brain development in mice

Recent studies in rodents suggest that maternal immune activation (MIA) by viral infection is associated with schizophrenia and autism in offspring. Although maternal IL-6 is though t to be a possible mediator relating MIA induced these neuropsychiatric disorders, the mechanism remains to be elucidated. Previously, we reported that the maternal leukemia inhibitory factor (LIF)–placental ACTH–fetal LIF signaling relay pathway (maternal–fetal LIF signal relay) promotes neurogenesis of fetal cerebrum in rats. Here we report that the maternal–fetal LIF signal relay in mice is suppressed by injection of polyriboinosinic-polyribocytidylic acid into dams, which induces MIA at 12.5 days post-coitum. Maternal IL-6 levels and gene expression of placental suppressor of cytokine signaling 3 (Socs3) increased according to the severity of MIA and gene expression of placental Socs3 correlated with maternal IL-6 levels. Furthermore, we show that MIA causes reduction of LIF level in the fetal cerebrospinal fluid, resulting in the decreased neurogenesis in the cerebrum. These findings suggest that maternal IL-6 interferes the maternal–fetal LIF signal relay by inducing SOCS3 in the placenta and leads to decreased neurogenesis.

Morphine treatment selectively regulates expression of rat pituitary POMC and the prohormone convertases PC1/3 and PC2

The prohormone convertases, PC1/3 and PC2 are thought to be responsible for the activation of many prohormones through processing including the endogenous opioid peptides. We propose that maintenance of hormonal homeostasis can be achieved, in part, via alterations in levels of these enzymes that control the ratio of active hormone to prohormone. In order to test the hypothesis that exogenous opioids regulate the endogenous opioid system and the enzymes responsible for their biosynthesis, we studied the effect of short-term morphine or naltrexone treatment on pituitary PC1/3 and PC2 as well as on the level of pro-opiomelanocortin (POMC), the precursor gene for the biosynthesis of the endogenous opioid peptide, β-endorphin. Using ribonuclease protection assays, we observed that morphine down-regulated and naltrexone up-regulated rat pituitary PC1/3 and PC2 mRNA. Immunofluorescence and Western blot analysis confirmed that the protein levels changed in parallel with the changes in mRNA levels and were accompanied by changes in the levels of phosphorylated cyclic-AMP response element binding protein. We propose that the alterations of the prohormone processing system may be a compensatory mechanism in response to an exogenous opioid ligand whereby the organism tries to restore its homeostatic hormonal milieu following exposure to the opioid, possibly by regulating the levels of multiple endogenous opioid peptides and other neuropeptides in concert.

Influence of hypothalamic IL-6/gp130 receptor signaling on the HPA axis response to chronic stress

Abnormal basal activity and stress-evoked reactivity of the hypothalamic-pituitary-adrenal (HPA) axis are often seen in depression, implicating HPA axis dysfunction as a potentially causative or exacerbating factor. Chronic stress is also a factor in depression, but it is not known what may underlie the shift from adaptive to maladaptive HPA activity over the course of chronic stress. Interleukin 6 (IL-6), a stress-inducible cytokine that signals through gp130 and IL-6Rα receptors to activate the JAK/STAT3 signaling cascade, is elevated in some subtypes of depression, and may have a modulatory effect on HPA activation, raising the possibility that IL-6 contributes to depression through effects on the HPA axis. In this study, we examined the effects of three different stress modalities, acute footshock, chronic intermittent cold (CIC) stress and chronic unpredictable stress (CUS) on IL-6 signaling in the hypothalamus. We also investigated whether IL-6 modulates the HPA response to chronic stress, by blocking IL-6 signaling in the brain during CIC stress using either a neutralizing antibody or an inhibitor of STAT3 phosphorylation. We show that IL-6 and STAT3 in the hypothalamus are activated in response to footshock and CUS. We also found that basal IL-6 signaling through the JAK/STAT3 pathway is required for the sustained CORT response to chronic, but not acute, cold stress and therefore is a potential determinant of plasticity in the HPA axis specifically during chronic stress exposure.

Hypothalamic opioid-melanocortin appetitive balance and addictive craving

Whilst the parallels between drug and food craving are receiving increasing attention, the recently elucidated complex physiology of the hypothalamic appetite regulatory centres has been largely overlooked in the efforts to understand drug craving which is one of the most refractory and problematic aspects of drug and behavioural addictions. Important conceptual gains could be made by researchers from both appetite and addiction neuroscience if they were to have an improved understanding of each others' disciplines. It is well known in addiction medicine that the use of many substances is elevated in opiate dependency. There is voluminous evidence of very high rates of drug use in opiate agonist maintained patients, and the real possibility exists that opiate agonist therapy therefore increases drug craving. Conversely, opiate antagonist therapy with naloxone or naltrexone has been shown to reduce most chemical and behavioural addictions, and naltrexone is now being developed together with bupropion as the anti-obesity drug "Contrave". Hypothalamic melanocortins, particularly α-MSH, are known to constitute the main brake to consumptive behaviour of food. There is a well described antagonism between melanocortins and opioids at many loci including the hypothalamus. Administration of exogenous opiates is known to both suppress α-MSH and to stimulate hedonic food consumption. Opiate maintenance programs are associated with weight gain. As monoamines, opioids and cannabinoids are known to be involved in appetite regulation, and as endorphin opioids are known to be perturbed in other addictions, further exploration of the hypothalamic appetite regulatory centre would appear to be an obvious, albeit presently largely overlooked, locus in which to study drug and other craving mechanisms.

The suppressor of cytokine signalling 2 (SOCS2) is a key repressor of insulin secretion

AIMS/HYPOTHESIS

Suppressor of cytokine signalling (SOCS) proteins are powerful inhibitors of pathways involved in survival and function of pancreatic beta cells. Whereas SOCS1 and SOCS3 have been involved in immune and inflammatory processes, respectively, in beta cells, nothing is known about SOCS2 implication in the pancreas.

METHODS

Transgenic (tg) mice were generated that constitutively produced SOCS2 in beta cells (betaSOCS2) to define whether this protein is implicated in beta cell functioning and/or survival.

RESULTS

Constitutive production of SOCS2 in beta cells leads to hyperglycaemia and glucose intolerance. This phenotype is not a consequence of decreased beta cell mass or inhibition of insulin synthesis. However, insulin secretion to various secretagogues is profoundly altered in intact animals and isolated islets. Interestingly, constitutive SOCS2 production dampens the rise in cytosolic free calcium concentration induced by glucose, while glucose metabolism is unchanged. Moreover, tg islets have a depletion in endoplasmic reticulum Ca(2+) stores, suggesting that SOCS2 interferes with calcium fluxes. Finally, in betaSOCS2 mice proinsulin maturation is impaired, leading to an altered structure of insulin secretory granules and augmented levels of proinsulin. The latter is likely to be due to decreased production of prohormone convertase 1 (PC1/3), which plays a key role in proinsulin cleavage.

CONCLUSIONS/INTERPRETATIONS

SOCS2 was shown to be a potent regulator of proinsulin processing and insulin secretion in beta cells. While its constitutive production is insufficient to induce overt diabetes in this mouse model, it causes glucose intolerance. Thus, increased SOCS2 production could be an important event predisposing to beta cell failure.

Regulation of the hypothalamic thyrotropin releasing hormone (TRH) neuron by neuronal and peripheral inputs

The hypothalamic-pituitary-thyroid (HPT) axis plays a critical role in mediating changes in metabolism and thermogenesis. Thus, the central regulation of the thyroid axis by Thyrotropin Releasing Hormone (TRH) neurons in the paraventricular nucleus of the hypothalamus (PVN) is of key importance for the normal function of the axis under different physiological conditions including cold stress and changes in nutritional status. Before the TRH peptide becomes biologically active, a series of tightly regulated processes occur including the proper folding of the prohormone for targeting to the secretory pathway, its post-translational processing, and targeting of the processed peptides to the secretory granules near the plasma membrane of the cell ready for secretion. Multiple inputs coming from the periphery or from neurons present in different areas of the brain including the hypothalamus are responsible for the activation or inhibition of the TRH neuron and in turn affect the output of TRH and the set point of the axis.

Differential regulation of prohormone convertase 1/3, prohormone convertase 2 and phosphorylated cyclic-AMP-response element binding protein by short-term and long-term morphine treatment: implications for understanding the "switch" to opiate addiction

Drug addiction is a state of altered brain reward and self-regulation mediated by both neurotransmitter and hormonal systems. Although an organism's internal system attempts to maintain homeostasis when challenged by exogenous opiates and other drugs of abuse, it eventually fails, resulting in the transition from drug use to drug abuse. We propose that the attempted maintenance of hormonal homeostasis is achieved, in part, through alterations in levels of processing enzymes that control the ratio of active hormone to pro-hormone. Two pro-hormone convertases, PC1/3 and PC2 are believed to be responsible for the activation of many neurohormones and expression of these enzymes is dependent on the presence of a cyclic-AMP response element (CRE) in their promoters. Therefore, we studied the effects of short-term (24-h) and long-term (7-day) morphine treatment on the expression of hypothalamic PC1/3 and PC2 and levels of phosphorylated cyclic-AMP-response element binding protein (P-CREB). While short-term morphine exposure down-regulated, long-term morphine exposure up-regulated P-CREB, PC1/3 and PC2 protein levels in the rat hypothalamus as determined by Western blot analysis. Quantitative immunofluorescence studies confirmed these regulatory actions of morphine in the paraventricular and dorsomedial nucleus of the hypothalamus. Specific radioimmunoassays demonstrated that the increase in PC1/3 and PC2 levels following long-term morphine led to increased TRH biosynthesis as evidence by increased TRH/5.4 kDa C-terminal proTRH-derived peptide ratios in the median eminence. Promoter activity experiments in rat somatomammotrope GH3 cells containing the mu-opioid receptor demonstrated that the CRE(s) in the promoter of PC1/3 and PC2 is required for morphine-induced regulation of PC1/3 and PC2. Our data suggest that the regulation of the prohormone processing system by morphine may lead to alterations in the levels of multiple bioactive hormones and may be a compensatory mechanism whereby the organism tries to restore its homeostatic hormonal milieu. The down-regulation of PC1/3, PC2 and P-CREB by short-term morphine and up-regulation by long-term morphine treatment may be a signal mediating the switch from drug use to drug abuse.

Nescient helix-loop-helix 2 interacts with signal transducer and activator of transcription 3 to regulate transcription of prohormone convertase 1/3

Mechanisms controlling body weight involve gene regulation through the activation of signal transduction pathways. The Janus kinase/signal transducer and activator of transcription (STAT) signal transduction pathway is the mechanism primarily used by leptin in the hypothalamus. The transcription factor nescient helix-loop-helix 2 (Nhlh2) is a downstream target of leptin signaling and is expressed in proopiomelanocortin arcuate neurons. Proopiomelanocortin is cleaved by prohormone convertase 1/3 (PC1/3) to produce peptides that regulate the body's response to energy availability. Previous studies show that the PC1/3 promoter contains STAT3 sites mediating leptin-induced PC1/3 expression, and that Nhlh2 is required for hypothalamic PC1/3 expression because Nhlh2 knockout mice have reduced PC1/3 mRNA levels. Studies herein reveal that leptin-induced PC1/3 gene expression is abrogated in N2KO mice, and that in a hypothalamic cell line both STAT3 and Nhlh2 are required for the full transcriptional response of a PC1/3 reporter gene after leptin stimulation. Furthermore, it is shown that Nhlh2 binds to E-box motifs found adjacent to STAT3 sites in the PC1/3 promoter both in vitro and in chromatin immunoprecipitation assays. Finally, two different protein-protein interaction assays confirm the presence of a STAT3:Nhlh2 heterodimer on the PC1/3 promoter. The Nhlh2:STAT3 heterodimer may be an important transcriptional regulator of other hypothalamic genes in the leptin signaling pathway. These data confirm Nhlh2 as an integral element of the Janus kinase/STAT signaling pathway and are the first to demonstrate coordinated control of PC1/3 transcription by Nhlh2 and STAT3 after leptin stimulation.

Regulation of prohormone convertases in hypothalamic neurons: implications for prothyrotropin-releasing hormone and proopiomelanocortin

Recent evidence demonstrated that posttranslational processing of neuropeptides is critical in the pathogenesis of obesity. Leptin or other physiological changes affects the biosynthesis and processing of many peptides hormones as well as the regulation of the family of prohormone convertases responsible for the maturation of these hormones. Regulation of energy balance by leptin involves regulation of several proneuropeptides such as proTRH and proopiomelanocortin. These proneuropeptide precursors require for their maturation proteolytic cleavage by the prohormone convertases 1 and 2 (PC1/3 and PC2). Because biosynthesis of mature peptides in response to leptin requires prohormone processing, it is hypothesized that leptin might regulate hypothalamic PC1/3 and PC2 expression, ultimately leading to coordinated processing of prohormones into mature peptides. Leptin has been shown to increase PC1/3 and PC2 promoter activities, and starvation of rats, leading to low serum leptin levels, resulted in a decrease in PC1/3 and PC2 gene and protein expression in the paraventricular and arcuate nucleus of the hypothalamus. Changes in nutritional status also changes proopiomelanocortin processing in the nucleus of the solitary tract, but this is not reversed by leptin. The PCs are also physiologically regulated by states of hyperthyroidism, hyperglycemia, inflammation, and suckling, and a recently discovered nescient helix-loop-helix-2 transcription factor is the first one to show an ability to regulate the transcription of PC1/3 and PC2. Therefore, the coupled regulation of proneuropeptide/processing enzymes may be a common process, by which cells generate more effective processing of prohormones into mature peptides.

Cellular colocalization and coregulation between hypothalamic pro-TRH and prohormone convertases in hypothyroidism

The prohormone convertases (PCs), PC1/3 and PC2, are involved in the tissue-specific endoproteolytic posttranslational processing of many hormonal precursors within the secretory pathway. One important prohormone, pro-thyrotropin-releasing hormone (TRH), is expressed in both hypophysiotropic (where it regulates the secretion of thyroid-stimulating hormone) and nonhypophysiotropic regions of the brain. Pro-TRH is processed at specific sites in the secretory pathway, primarily by PC1/3 followed by PC2. We hypothesized that thyroid hormone status in specific nuclei of the brain would alter pro-TRH processing by inducing changes in PC1/3 and PC2 expression. Therefore, we examined pro-TRH, PC1/3, and PC2 coexpression and coregulation in the paraventricular nucleus (PVN), lateral hypothalamus (LH), and ventromedial nucleus (VMN) of hypothyroid and euthyroid rats. Our results show that 6-n-propyl-2-thiouracil (PTU) treatment producing hypothyroidism induced a significant increase in the expression of PC1/3, PC2, and pro-TRH in the PVN and LH, but not VMN. When confocal studies were performed, an increase in colocalization of PC1/3 or PC2 in pro-TRH was observed only in PVN, a response that was especially prominent in the ventral and medial areas of the PVN. PTU did not regulate colocalization in the VMH or LH. Regulation of colocalization of processing enzyme and prohormone expression is a novel mechanism to alter hormonal biosynthesis.

Leukemia inhibitory factor signaling is implicated in embrionic development of the HPA axis

Leukemia inhibitory factor (LIF) is expressed in the hypothalamic-pituitary adrenal (HPA) axis and stimulates pituitary POMC transcription. The role of LIF receptor signaling in HPA axis development was examined. Lifr -/- and Lifr +/+ fetuses were obtained by Cesarean section on E18.5. Despite a 3-fold induction of hypothalamic CRH mRNA, pituitary POMC mRNA and RU486-induced ACTH levels were decreased in Lifr -/- mice. High CRH may be caused by increased central TNFalpha and IL-6 expression. Lifr -/- mice demonstrate elevated pituitary glucocorticoid (GR) and mineralocorticoid (MR) receptor mRNA and protein levels, indicating the importance of LIF signaling for HPA axis development.

Regulation of regional expression in rat brain PC2 by thyroid hormone/characterization of novel negative thyroid hormone response elements in the PC2 promoter

The prohormone convertases (PCs) PC1 and PC2 are involved in the tissue-specific endoproteolytic processing of neuropeptide precursors within the secretory pathway. We previously showed that changes in thyroid status altered pituitary PC2 mRNA and that this regulation was due to triiodothyronine-dependent interaction of the thyroid hormone receptor (TR) with negative thyroid hormone response elements (nTREs) contained in a large proximal region of the human PC2 promoter. In the current study, we examined the in vivo regulation of brain PC2 mRNA by thyroid status and found that 6-n-propyl-2-thiouracil-induced hypothyroidism stimulated, whereas thyroxine-induced hyperthyroidism suppressed, PC2 mRNA levels in the rat hypothalamus and cerebral cortex. To address the mechanism of T3 regulation of the PC2 gene, we used human PC2 (hPC2) promoter constructs transiently transfected into GH3 cells and found that triiodothyronine negatively and 9-cis-retinoic acid positively regulated hPC2 promoter activity. EMSAs, using purified TRalpha1 and retinoid X receptor-beta (RXRbeta) proteins demonstrated that TRalpha bound the distal putative nTRE-containing oligonucleotide in the PC2 promoter, and RXR bound to both nTRE-containing oligonucleotides. EMSAs with oligonucleotides containing deletion mutations of the nTREs demonstrated that the binding to TR and RXR separately is reduced, but specific binding to TR and RXR together persists even with deletion of each putative nTRE. We conclude that there are two novel TRE-like sequences in the hPC2 promoter and that these regions act in concert in a unique manner to facilitate the effects of thyroid hormone and 9-cis-retinoic acid on PC2.

Pituitary cell lines and their endocrine applications

The pituitary gland is an important component of the endocrine system, and together with the hypothalamus, exerts considerable influence over the functions of other endocrine glands. The hypothalamus either positively or negatively regulates hormonal productions in the pituitary through its release of various trophic hormones which act on specific cell types in the pituitary to secrete a variety of pituitary hormones that are important for growth and development, metabolism, reproductive and nervous system functions. The pituitary is divided into three sections-the anterior lobe which constitute the majority of the pituitary mass and is composed primarily of five hormone-producing cell types (thyrotropes, lactotropes, corticotropes, somatotropes and gonadotropes) each secreting thyrotropin, prolactin, ACTH, growth hormone and gonadotropins (FSH and LH) respectively. There is also a sixth cell type in the anterior lobe-the non-endocrine, agranular, folliculostellate cells. The intermediate lobe produces melanocyte-stimulating hormone and endorphins, whereas the posterior lobe secretes anti-diuretic hormone (vasopressin) and oxytocin. Representative cell lines of all the six cell types of the anterior pituitary have been established and have provided valuable information on genealogy of the various cell lineages, endocrine feedback control of hormone synthesis and secretions, intrapituitary interactions between the various cell types, as well as the role of specific transcription factors that determine each differentiated cell phenotype. In this review, we will discuss the morphology and function of the cell types that make up the anterior pituitary, and the characteristics of the various functional anterior pituitary cell systems that have been established to be representative of each anterior pituitary cell lineage.

Comparative study of gp130 cytokine effects on corticotroph AtT-20 cells--redundancy or specificity of neuroimmunoendocrine modulators?

OBJECTIVE

This comparative in vitro study examined the effects of all known gp130 cytokines on murine corticotroph AtT-20 cell function.

METHODS

Cytokines were tested at equimolar concentrations from 0.078 to 10 nM. Tyrosine phosphorylation of the signal transducer and activator of transcription (STAT)3 and STAT1, the STAT-dependent suppressor of cytokine signaling (SOCS)-3 promoter activity, SOCS-3 gene expression, STAT-dependent POMC promoter activity and adrenocorticotropic hormone (ACTH) secretion were determined.

RESULTS

Leukemia inhibitory factor (LIF), human oncostatin M (OSM) and cardiotrophin (CT)-1 (LIFR/gp130 ligands), as well as ciliary neurotrophic factor (CNTF) and novel neurotrophin-1/B-cell stimulating factor-3 (CNTFR alpha/LIFR/gp130 ligands) are potent stimuli of corticotroph cells in vitro. In comparison, interleukin (IL)-6 (IL-6R/gp130 ligand) and IL-11 (IL-11R/gp130 ligand) exhibited only modest direct effects on corticotrophs, while murine OSM (OSMR/gp130 ligand) showed no effect.

CONCLUSION

(i) CNTFR complex ligands are potent stimuli of corticotroph function, comparable to LIFR complex ligands; (ii) IL-6 and IL-11 are relatively weak direct stimuli of corticotroph function; (iii) differential effects of human and murine OSM suggest that LIFR/gp130 (OSMR type I) but not OSMR/gp130 (OSMR type II) are involved in corticotroph signaling. (iv) CT-1 has the hitherto unknown ability to stimulate corticotroph function, and (v) despite redundant immuno-neuroendocrine effects of different gp130 cytokines, corticotroph cells are preferably activated through the LIFR and CNTFR complexes.

Late gestation modulation of fetal glucocorticoid effects requires the receptor for leukemia inhibitory factor: an observational study

BACKGROUND

Ablation of the low-affinity receptor subunit for leukemia inhibitory factor (LIFR) causes multi-systemic defects in the late gestation fetus. Because corticosterone is known to have a broad range of effects and LIF function has been associated with the hypothalamo-pituitary-adrenal axis, this study was designed to determine the role for LIFR in the fetus when exposed to the elevated maternal glucocorticoid levels of late gestation. Uncovering a requirement for LIFR in appropriate glucocorticoid response will further understanding of control of glucocorticoid function.

METHODS

Maternal adrenalectomy or RU486 administration were used to determine the impact of the maternal glucocorticoid surge on fetal development in the absence of LIFR. The mice were analyzed by a variety of histological techniques including immunolabeling and staining techniques (hematoxylin and eosin, Alizarin red S and alcian blue). Plasma corticosterone was assayed using radioimmunoassay.

RESULTS

Maternal adrenalectomy does not improve the prognosis for LIFR null pups and exacerbates the effects of LIFR loss. RU486 noticeably improves many of the tissues affected by LIFR loss: bone density, skeletal muscle integrity and glial cell formation. LIFR null pups exposed during late gestation to RU486 in utero survive natural delivery, unlike LIFR null pups from untreated litters. But RU486 treated LIFR null pups succumb within the first day after birth, presumably due to neural deficit resulting in an inability to suckle.

CONCLUSION

LIFR plays an integral role in modulating the fetal response to elevated maternal glucocorticoids during late gestation. This role is likely to be mediated through the glucocorticoid receptor and has implications for adult homeostasis as a direct tie between immune, neural and hormone function.

Prohormone convertase 2 enzymatic activity and its regulation in neuro-endocrine cells and tissues

We used the fluorometric substrate, pGlu-Arg-Thr-Lys-Arg-MCA and the C-terminal peptide of human 7B2(155-185), a specific inhibitor of prohormone convertase 2 (PC2), to specifically measure the enzymatic activity of the prohormone convertases, PC2. Using lysates from the pancreatic alpha cell line, alphaTC1-6 cells, which contain moderate levels of PC2 enzymatic activity, we determined that the PC2 assay was linear with respect to time of incubation and protein added and had a pH optimum of 5.5 and a calcium optimum of 2.5 mM. Rat pituitary contained high levels of PC2 enzymatic activity, while the hypothalamus and other brain regions contained moderate levels. This enzyme assay was used to document that both mice null for PC2 as well as mice null for the PC2 cofactor, 7B2, had only trace levels of PC2 activity in various brain regions, while mice heterozygous for these alleles had approximately half of the PC2 activity in most brain regions. PC2 enzymatic activity and PC2 mRNA levels were somewhat discordant suggesting that PC2 mRNA levels do not always reflect PC2 enzymatic activity.

In vivo activation of the interleukin-6 receptor/gp130 signaling pathway in pituitary corticotropes of lipopolysaccharide-treated rats

Adrenocorticotropic hormone (ACTH) release from anterior pituitary corticotropes is greatly increased during peripheral inflammation induced by lipopolysaccharide (LPS) administration. Interleukin-6 (IL-6) is thought to participate in LPS-induced ACTH release, but whether or not corticotropes are directly targeted by this cytokine is unclear. Therefore, we investigated the expression and activation of IL-6 signaling components in the pituitary of rats 2 and 4 h after administration of LPS (250 microg/kg). Intraperitoneal LPS treatment provoked the nuclear translocation of signal transducer and activator of transcription 3 (STAT-3) and Fos expression in the anterior pituitary lobe, as demonstrated by immunohistochemistry. By using in situ hybridization, we demonstrated that suppressor of cytokine signaling 3 (SOCS-3) and c-fos mRNAs were significantly induced by the LPS treatment in the anterior lobe of the pituitary. Dual in situ hybridization revealed that most corticotropes expressed IL-6 receptor and gp130 mRNAs, and that 2 h after LPS treatment, SOCS-3 and c-fos mRNAs were induced in corticotropes. Our results suggest that LPS-induced IL-6 could regulate the hypothalamo-pituitary-adrenal axis by directly targeting corticotropes during peripheral inflammation.

Bacterial lipopolysaccharide-induced coordinate downregulation of arginine vasopressin receptor V3 and corticotropin-releasing factor receptor 1 messenger ribonucleic acids in the anterior pituitary of endotoxemic steers

AVP and CRF are potent stimulators of pituitary ACTH secretion in cattle. Actions of AVP and CRF at the anterior pituitary are mediated by AVP receptor V3 (V3) and CRF receptor 1 (CRFR1). The primary objective of these studies was to determine the effect of systemic inflammatory stress on V3 and CRFR1 mRNAs in the bovine anterior pituitary. Holstein steers (n = 20) were injected with 200 ng/kg bacterial lipopolysaccharide (LPS) and tissues collected 0, 2, 4, 12, and 24 h later. All animals responded to LPS administration with an increase in body temperature, plasma ACTH, and cortisol (p < 0.05). Abundance of anterior pituitary V3 mRNA was decreased at 2, 4, and 12 h following LPS administration (p < 0.05) and returned to basal by 24 h. A similar temporal regulation of pituitary CRFR1 mRNA (p < 0.05), but not pituitary pro-opiomelanocortin (POMC) mRNA, was observed following LPS administration. Similar downregulation of CRFR1 mRNA was not observed in other brain regions following LPS administration (cerebellum, hypothalamus). Our results indicate that V3 and CRFR1 mRNAs are coordinately downregulated in the anterior pituitary during systemic inflammatory stress. Decreased AVP and CRF receptor expression may help regulate the pituitary-adrenal response to stress.

Up-regulation of splenic prohormone convertases PC1 and PC2 in diabetic rats

Organisms respond to infection in a complex manner involving bidirectional interactions between the neuroendocrine and immune systems. Many of the bioactive endocrine/immune factors are synthesized in a precursor form and are expected to be activated by prohormone convertases (PCs). Since patients with both type 1 and type 2 diabetes have an increased incidence and severity of infections, we hypothesized that in a condition of hyperglycemia, these processing enzymes would be activated in an immune tissue, the spleen. To test this hypothesis, we treated rats with intraperitoneal streptozotocin (STZ) (50 mg/kg/day) daily for 5 days and measured splenic PC1 and PC2 mRNA by ribonuclease protection assay. We found that PC1 mRNA was increased 6.0+/-0.02-fold (P<0.05) and PC2 mRNA was increased 1.80+/-0.01-fold (P<0.005) in the spleen of rats that received STZ compared to rats that received vehicle. Western blot indicated that the 75-kDa form of PC1 was the only form of PC1 present in the spleen and that this form increased with STZ treatment. Immunohistochemistry revealed that PC1 was found in both the white pulp (T-lymphocytes) and red pulp (monocytes and macrophages) and that its increase in immunoreactivity occurred primarily in the white pulp. PC2 and pro-opiomelanocortin (POMC, a possible splenic substrate for PC1/PC2) immunoreactivity was found predominantly in the red pulp. STZ induced an increase in splenic PC1 and POMC, but not PC2 protein levels. We conclude that in the STZ model of diabetes, splenic PCs are induced, which could lead to an increased activation of many immune-derived hormones. We speculate that this up-regulation of prohormone converting enzymes may be related to the increased infections seen in patients with both type 1 and type 2 diabetes.

Regulation of prohormone convertase 1 (PC1) by thyroid hormone

The prohormone convertases (PCs) PC1 and PC2 are key enzymes capable of processing a variety of prohormones to their bioactive forms. In this study, we demonstrated that 6-n-propyl-2-thiouracil (PTU)-induced hypothyroidism stimulated, whereas triido-L-thyronine (T(3))-induced hyperthyroidism suppressed, PC1 mRNA levels in the rat anterior pituitary. Using 5' deletions of the human PC1 (hPC1) promoter transiently transfected into GH3 (a somatotroph cell line) cells, we found that T(3) negatively regulated hPC1 promoter activity and that this regulation required the region from -82 to +19 bp relative to the transcription start site. Electrophoretic mobility shift assays (EMSAs) using purified thyroid hormone receptor-alpha1 (TR alpha 1) and retinoid X receptor-beta (RXRbeta) proteins and GH3 nuclear extracts demonstrated that the region from -10 to +19 bp of the hPC1 promoter bound TR alpha 1 as both a monomer and a homodimer and bound TR alpha 1/RXR beta as a heterodimer and multimer. EMSAs with oligonucleotides containing point mutations of the putative negative thyroid response elements (TREs) exhibited diminished homodimer and loss of multimer binding. We conclude that there are multiple novel TRE-like sequences in the hPC1 promoter located from -10 to +19 bp.

Interactions between the prohormone convertase 2 promoter and the thyroid hormone receptor

The majority of prohormones are cleaved at paired basic residues to generate bioactive hormones by prohormone convertases (PCs). As PC1 and PC2, two neuroendocrine-specific PCs, appear to be the key enzymes capable of processing a variety of prohormones, alterations of PC2 and/or PC1 levels will probably have a profound effect on hormonal homeostasis. We investigated the regulation of PC2 messenger RNA (mRNA) by thyroid hormone using GH3 cells to demonstrate that T3 negatively regulated PC2 mRNA levels in a dose- and time-dependent fashion. Functional analysis of progressive 5'-deletions of the human (h) PC2 promoter luciferase constructs in GH3 cells demonstrated that the regulation probably occurs at the transcriptional level, and that putative negative thyroid hormone response elements were located within the region from -44 to + 137 bp relative to the transcriptional start site. Transient transfections in JEG-3 cells and COS-1 cells showed that the suppressive effect of T3 was equally mediated by the thyroid hormone receptor (TR) isoforms TRalpha1 and TRbeta1. Electrophoretic mobility shift assays using purified TRal and retinoid X receptor-beta protein as well as GH3 nuclear extracts showed that regions from +51 to +71 bp and from +118 to +137 bp of the hPC2 promoter bind to TRalpha1 as both a monomer and a homodimer and with TRalpha1/retinoid X receptor-beta as a heterodimer. Finally, the in vivo regulation of pituitary PC2 mRNA by thyroid status was demonstrated in rats. These results demonstrate that T3 negatively regulates PC2 expression at the transcriptional level and that functional negative thyroid hormone response elements exist in the hPC2 promoter. We postulate that the alterations of PC2 activity may mediate some of the pathophysiological consequences of hypo- or hyperthyroidism.

Regulation of pancreatic PC1 and PC2 associated with increased glucagon-like peptide 1 in diabetic rats

The pancreatic processing enzymes, PC1 and PC2, convert proinsulin to insulin and convert proglucagon to glucagon and glucagon-like peptide 1 (GLP-1). We examined the effect of streptozotocin (STZ) treatment on the regulation of these enzymes and the production of insulin, glucagon, and GLP-1 in the rat. Pancreatic PC1 and PC2 mRNA increased >2-fold and >4-fold, respectively, in rats receiving intraperitoneal STZ (50 mg/kg) daily for 5 days. Immunocytochemistry revealed that, although pancreatic islet cells in the STZ-treated rats were sparse and atrophic PC1, PC2, glucagon, and GLP-1 immunoreactivity increased dramatically in the remaining islet cells. Heightened PC1 and PC2 expression was seen in cells expressing glucagon but not in insulin-expressing cells. Furthermore, in STZ-treated rats, bioactive GLP-1(7-36 amide) accumulated in pancreatic extracts and serum 3- and 2.5-fold, respectively, over control animals. This treatment also caused a 2-fold increase in the ratio of amidated forms of GLP-1 immunoreactivity to total glucagon immunoreactivity in the pancreas but did not affect the ratio of proinsulin to insulin. We conclude that hyperglycemic rats have an increased expression of prohormone converting enzymes in islet alpha cells, leading to an increase in amidated GLP-1, which can then exert an insulinotropic effect on the remaining beta cells.