Showing papers in "Endocrinology in 2004"
TL;DR: The purpose of this study was to examine the source of adipokines released by the visceral and sc adipose tissues of obese humans and found that most of the adipokine release by the nonfat cells of adipose tissue was due to cells retained in the tissue matrix after collagenase digestion.
Abstract: The purpose of this study was to examine the source of adipokines released by the visceral and sc adipose tissues of obese humans. Human adipose tissue incubated in primary culture for 48 h released more prostaglandin E(2), IL-8, and IL-6 than adiponectin, whereas the release of plasminogen activator inhibitor 1 and hepatocyte growth factor was less than that of adiponectin but greater than that of leptin. IL-10 and TNFalpha were released in amounts less than those of leptin, whereas vascular endothelial growth factor and IL1-beta were released in much lower amounts. The accumulation of adipokines was also examined in the three fractions (adipose tissue matrix, isolated stromovascular cells, and adipocytes) obtained by collagenase digestion of adipose tissue. Over 90% of the adipokine release by adipose tissue, except for adiponectin and leptin, could be attributed to nonfat cells. Visceral adipose tissue released greater amounts of vascular endothelial growth factor, IL-6, and plasminogen activator inhibitor 1 compared with abdominal sc tissue. The greatly enhanced total release of TNFalpha, IL-8, and IL-10 by adipose tissue from individuals with a body mass index of 45 compared with 32 was due to nonfat cells. Furthermore, most of the adipokine release by the nonfat cells of adipose tissue was due to cells retained in the tissue matrix after collagenase digestion.
1,564 citations
TL;DR: Kisspeptins are products of the KiSS-1 gene, which bind to a G protein-coupled receptor known as GPR54, and it is concluded that kisspeptin-GPR54 signaling may be part of the hypothalamus circuitry that governs the hypothalamic secretion of GnRH.
Abstract: Kisspeptins are products of the KiSS-1 gene, which bind to a G protein-coupled receptor known as GPR54. Mutations or targeted disruptions in the GPR54 gene cause hypogonadotropic hypogonadism in humans and mice, suggesting that kisspeptin signaling may be important for the regulation of gonadotropin secretion. To examine the effects of kisspeptin-54 (metastin) and kisspeptin-10 (the biologically active C-terminal decapeptide) on gonadotropin secretion in the mouse, we administered the kisspeptins directly into the lateral cerebral ventricle of the brain and demonstrated that both peptides stimulate LH secretion. Further characterization of kisspeptin-54 demonstrated that it stimulated both LH and FSH secretion, at doses as low as 1 fmol; moreover, this effect was shown to be blocked by pretreatment with acyline, a potent GnRH antagonist. To learn more about the functional anatomy of kisspeptins, we mapped the distribution of KiSS-1 mRNA in the hypothalamus. We observed that KiSS-1 mRNA is expressed in areas of the hypothalamus implicated in the neuroendocrine regulation of gonadotropin secretion, including the anteroventral periventricular nucleus, the periventricular nucleus, and the arcuate nucleus. We conclude that kisspeptin-GPR54 signaling may be part of the hypothalamic circuitry that governs the hypothalamic secretion of GnRH.
1,090 citations
TL;DR: Accumulating evidence suggests that in addition to its original description as a CDK-dependent regulator of the cell cycle, cyclin D1 also conveys cell cycle orCDK-independent functions.
Abstract: Cyclin D1 encodes the regulatory subunit of a holoenzyme that phosphorylates and inactivates the retinoblastoma protein and promotes progression through the G1-S phase of the cell cycle. Amplification or overexpression of cyclin D1 plays pivotal roles in the development of a subset of human cancers including parathyroid adenoma, breast cancer, colon cancer, lymphoma, melanoma, and prostate cancer. Of the three D-type cyclins, each of which binds cyclin-dependent kinase (CDK), it is cyclin D1 overexpression that is predominantly associated with human tumorigenesis and cellular metastases. In recent years accumulating evidence suggests that in addition to its original description as a CDK-dependent regulator of the cell cycle, cyclin D1 also conveys cell cycle or CDK-independent functions. Cyclin D1 associates with, and regulates activity of, transcription factors, coactivators and corepressors that govern histone acetylation and chromatin remodeling proteins. The recent findings that cyclin D1 regulates cellular metabolism, fat cell differentiation and cellular migration have refocused attention on novel functions of cyclin D1 and their possible role in tumorigenesis. In this review, both the classic and novel functions of cyclin D1 are discussed with emphasis on the CDK-independent functions of cyclin D1.
940 citations
TL;DR: The results suggest that glucocorticoid-induced loss of bone strength results in part from increased death of osteocytes, independent of bone loss, and demonstrate for the first time that excess glucOCorticoids directly affect bone forming cells in vivo.
Abstract: Whether the negative impact of excess glucocorticoids on the skeleton is due to direct effects on bone cells, indirect effects on extraskeletal tissues, or both is unknown. To determine the contribution of direct effects of glucocorticoids on osteoblastic/osteocytic cells in vivo, we blocked glucocorticoid action on these cells via transgenic expression of 11beta-hydroxysteroid dehydrogenase type 2, an enzyme that inactivates glucocorticoids. Osteoblast/osteocyte-specific expression was achieved by insertion of the 11beta-hydroxysteroid dehydrogenase type 2 cDNA downstream from the osteoblast-specific osteocalcin promoter. The transgene did not affect normal bone development or turnover as demonstrated by identical bone density, strength, and histomorphometry in adult transgenic and wild-type animals. Administration of excess glucocorticoids induced equivalent bone loss in wild-type and transgenic mice. As expected, cancellous osteoclasts were unaffected by the transgene. However, the increase in osteoblast apoptosis that occurred in wild-type mice was prevented in transgenic mice. Consistent with this, osteoblasts, osteoid area, and bone formation rate were significantly higher in glucocorticoid-treated transgenic mice compared with glucocorticoid-treated wild-type mice. Glucocorticoid-induced osteocyte apoptosis was also prevented in transgenic mice. Strikingly, the loss of vertebral compression strength observed in glucocorticoid-treated wild-type mice was prevented in the transgenic mice, despite equivalent bone loss. These results demonstrate for the first time that excess glucocorticoids directly affect bone forming cells in vivo. Furthermore, our results suggest that glucocorticoid-induced loss of bone strength results in part from increased death of osteocytes, independent of bone loss.
708 citations
TL;DR: The study suggests that the ARC is selectively leptin resistant in DIO mice and that this may be caused by elevated suppressor of cytokine signaling 3 in this hypothalamic nucleus.
Abstract: Leptin resistance in diet-induced obese (DIO) mice is characterized by elevated serum leptin and a decreased response to exogenous leptin and is caused by unknown defects in the central nervous system. Leptin normally acts on several brain nuclei, but a detailed description of leptin resistance within individual brain regions has not been reported. We first mapped leptin-responsive cells in brains from DIO mice using phospho-signal transducer and activator of transcription (P-STAT3) immunohistochemistry. After 16 wk of high-fat-diet feeding, leptin-activated P-STAT3 staining within the arcuate nucleus (ARC) was dramatically decreased. In contrast, other hypothalamic and extrahypothalamic nuclei remained leptin sensitive. Reduced leptin-induced P-STAT3 in the ARC could also be detected after 4 wk and as early as 6 d of a high-fat diet. To examine potential mechanisms for leptin-resistant STAT3 activation in the ARC of DIO mice, we measured mRNA levels of candidate signaling molecules in the leptin receptor-STAT3 pathway. We found that the level of suppressor of cytokine signaling 3 (SOCS-3), an inhibitor of leptin signaling, is specifically increased in the ARC of DIO mice. The study suggests that the ARC is selectively leptin resistant in DIO mice and that this may be caused by elevated suppressor of cytokine signaling 3 in this hypothalamic nucleus. Defects in leptin action in the ARC may play a role in the pathogenesis of leptin-resistant obesity.
703 citations
TL;DR: The current data support the contention that the hypothalamic KiSS-1/GPR54 system is a pivotal factor in central regulation of the gonadotropic axis at puberty and in adulthood.
Abstract: The gonadotropic axis is centrally controlled by a complex regulatory network of excitatory and inhibitory signals that is activated at puberty. Recently, loss of function mutations of the gene encoding G protein-coupled receptor 54 (GPR54), the putative receptor for the KiSS-1-derived peptide metastin, have been associated with lack of puberty onset and hypogonadotropic hypogonadism. Yet the pattern of expression and functional role of the KiSS-1/GPR54 system in the rat hypothalamus remain unexplored to date. In the present work, expression analyses of KiSS-1 and GPR54 genes were conducted in different physiological and experimental settings, and the effects of central administration of KiSS-1 peptide on LH release were assessed in vivo. Persistent expression of KiSS-1 and GPR54 mRNAs was detected in rat hypothalamus throughout postnatal development, with maximum expression levels at puberty in both male and female rats. Hypothalamic expression of KiSS-1 and GPR54 genes changed throughout the estrous cycle and was significantly increased after gonadectomy, a rise that was prevented by sex steroid replacement both in males and females. Moreover, hypothalamic expression of the KiSS-1 gene was sensitive to neonatal imprinting by estrogen. From a functional standpoint, intracerebroventricular administration of KiSS-1 peptide induced a dramatic increase in serum LH levels in prepubertal male and female rats as well as in adult animals. In conclusion, we provide novel evidence of the developmental and hormonally regulated expression of KiSS-1 and GPR54 mRNAs in rat hypothalamus and the ability of KiSS-1 peptide to potently stimulate LH secretion in vivo. Our current data support the contention that the hypothalamic KiSS-1/GPR54 system is a pivotal factor in central regulation of the gonadotropic axis at puberty and in adulthood.
695 citations
TL;DR: The results establish an in vivo orexigenic function for NPY and AgRP, mediating the effect of ghrelin, as well as the involvement of the melanocortin pathway inghrelin signaling.
Abstract: Ghrelin, a stomach-derived orexigenic hormone, has stimulated great interest as a potential target for obesity control. Pharmacological evidence indicates that ghrelin's effects on food intake are mediated by neuropeptide Y (NPY) and agouti-related protein (AgRP) in the central nervous system. These include intracerebroventricular application of antibodies to neutralize NPY and AgRP, and the application of an NPY Y1 receptor antagonist, which blocks some of the orexigenic effects of ghrelin. Here we describe treatment of Agrp(-/-);Npy(-/-) and Mc3r(-/-);Mc4r(-/-) double knockout mice as well as Npy(-/-) and Agrp(-/-) single knockout mice with either ghrelin or an orally active nonpeptide ghrelin agonist. The data demonstrate that NPY and AgRP are required for the orexigenic effects of ghrelin, as well as the involvement of the melanocortin pathway in ghrelin signaling. Our results outline a functional interaction between the NPY and AgRP pathways. Although deletion of either NPY or AgRP caused only a modest or nondetectable effect, ablation of both ligands completely abolished the orexigenic action of ghrelin. Our results establish an in vivo orexigenic function for NPY and AgRP, mediating the effect of ghrelin.
668 citations
TL;DR: It is concluded that apoptosis is the main mode of FFA- and cytokine-induced beta-cell death but the mechanisms involved are different, suggesting that FFAs trigger an endoplasmic reticulum (ER) stress response through an NF-kappaB- and nitric oxide-independent mechanism.
Abstract: Apoptosis is probably the main form of beta-cell death in both type 1 diabetes mellitus (T1DM) and T2DM. In T1DM, cytokines contribute to beta-cell destruction through nuclear factor-kappaB (NF-kappaB) activation. Previous studies suggested that in T2DM high glucose and free fatty acids (FFAs) are beta-cell toxic also via NF-kappaB activation. The aims of this study were to clarify whether common mechanisms are involved in FFA- and cytokine-induced beta-cell apoptosis and determine whether TNFalpha, an adipocyte-derived cytokine, potentiates FFA toxicity through enhanced NF-kappaB activation. Apoptosis was induced in insulinoma (INS)-1E cells, rat islets, and fluorescence-activated cell sorting-purified beta-cells by oleate, palmitate, and/or cytokines (IL-1beta, interferon-gamma, TNFalpha). Palmitate and IL-1beta induced a similar percentage of apoptosis in INS-1E cells, whereas oleate was less toxic. TNFalpha did not potentiate FFA toxicity in primary beta-cells. The NF-kappaB-dependent genes inducible nitric oxide synthase and monocyte chemoattractant protein-1 were induced by IL-1beta but not by FFAs. Cytokines activated NF-kappaB in INS-1E and beta-cells, but FFAs did not. Moreover, FFAs did not enhance NF-kappaB activation by TNFalpha. Palmitate and oleate induced C/EBP homologous protein, activating transcription factor-4, and immunoglobulin heavy chain binding protein mRNAs, X-box binding protein-1 alternative splicing, and activation of the activating transcription factor-6 promoter in INS-1E cells, suggesting that FFAs trigger an endoplasmic reticulum (ER) stress response. We conclude that apoptosis is the main mode of FFA- and cytokine-induced beta-cell death but the mechanisms involved are different. Whereas cytokines induce NF-kappaB activation and ER stress (secondary to nitric oxide formation), FFAs activate an ER stress response via an NF-kappaB- and nitric oxide-independent mechanism. Our results argue against a unifying hypothesis for the mechanisms of beta-cell death in T1DM and T2DM.
554 citations
TL;DR: The model of chronic effects of stress and GCs, showing a stressor-induced preference for comfort food, and a comfort-food reduction in activity of the HPA axis, tends to support this study.
Abstract: We suggested a new model of the effects of glucocorticoids (GCs) exerted during chronic stress, in which GCs directly stimulate activities in the brain while indirectly inhibiting activity in the hypothalamo-pituitary-adrenal (HPA) axis through their metabolic shifts in energy stores in the periphery. This study is an initial test of our model. In a 2 x 2 design, we provided ad lib access to calorically dense lard and sucrose (comfort food) + chow or chow alone, and repeatedly restrained half of the rats in each group for 5 d (3 h/d). We measured caloric intake, body weight, caloric efficiency, ACTH, corticosterone (B), and testosterone during the period of restraint and leptin, insulin, and fat depot weights, as well as hypothalamic corticotropin-releasing factor mRNA at the end of the period. We hypothesized that chronically restrained rats would exhibit a relative increase in comfort food ingestion and that these rats would have reduced HPA responses to repeated restraint. Although total caloric intake was reduced in both groups of restrained rats, compared with controls, the proportion of comfort food ingested increased in the restrained rats compared with their nonrestrained controls. Moreover, caloric efficiency was rescued in the stressed, comfort food group. Furthermore, ACTH and B responses to the repeated restraint bouts were reduced in the rats with access to comfort food. Corticotropin-releasing factor mRNA was reduced in control rats eating comfort food compared with those eating chow, but there were no differences between the stressed groups. The results of this experiment tend to support our model of chronic effects of stress and GCs, showing a stressor-induced preference for comfort food, and a comfort-food reduction in activity of the HPA axis.
551 citations
TL;DR: Stable differentiated INS-1E cells represent a stable and valuable beta-cell model and retained the amplifying pathway, as judged by glucose-evoked augmentation of insulin release in a depolarized state.
Abstract: Rat insulinoma-derived INS-1 cells constitute a widely used beta-cell surrogate. However, due to their nonclonal nature, INS-1 cells are heterogeneous and are not stable over extended culture periods. We have isolated clonal INS-1E cells from parental INS-1 based on both their insulin content and their secretory responses to glucose. Here we describe the stable differentiated INS-1E beta-cell phenotype over 116 passages (no. 27-142) representing a 2.2-yr continuous follow-up. INS-1E cells can be safely cultured and used within passages 40-100 with average insulin contents of 2.30 +/- 0.11 microg/million cells. Glucose-induced insulin secretion was dose-related and similar to rat islet responses. Secretion saturated with a 6.2-fold increase at 15 mm glucose, showing a 50% effective concentration of 10.4 mm. Secretory responses to amino acids and sulfonylurea were similar to those of islets. Moreover, INS-1E cells retained the amplifying pathway, as judged by glucose-evoked augmentation of insulin release in a depolarized state. Regarding metabolic parameters, INS-1E cells exhibited glucose dose-dependent elevations of NAD(P)H, cytosolic Ca(2+), and mitochondrial Ca(2+) levels. In contrast, mitochondrial membrane potential, ATP levels, and cell membrane potential were all fully activated by 7.5 mm glucose. Using the perforated patch clamp technique, 7.5 and 15 mm glucose elicited electrical activity to a similar degree. A K(ATP) current was identified in whole cell voltage clamp using diazoxide and tolbutamide. As in native beta-cells, tolbutamide induced electrical activity, indicating that the K(ATP)conductance is important in setting the resting potential. Therefore, INS-1E cells represent a stable and valuable beta-cell model.
549 citations
TL;DR: This article showed that glucagon-like peptides (GLP-1 and GLP-2) directly regulate signaling pathways coupled to cell proliferation and apoptosis, which may be mediated by direct or indirect effects on target cells.
Abstract: Gut peptides exert diverse effects regulating satiety, gastrointestinal motility and acid secretion, epithelial integrity, and both nutrient absorption and disposal. These actions are initiated by activation of specific G protein-coupled receptors and may be mediated by direct or indirect effects on target cells. More recent evidence demonstrates that gut peptides, exemplified by glucagon-like peptides-1 and 2 (GLP-1 and GLP-2), directly regulate signaling pathways coupled to cell proliferation and apoptosis. GLP-1 receptor activation enhances beta-cell proliferation and promotes islet neogenesis via activation of pdx-1 expression. The proliferative effects of GLP-1 appear to involve multiple intracellular pathways, including stimulation of Akt, activation of protein kinase Czeta, and transactivation of the epidermal growth factor receptor through the c-src kinase. GLP-1 receptor activation also promotes cell survival in beta-cells and neurons via increased levels of cAMP leading to cAMP response element binding protein activation, enhanced insulin receptor substrate-2 activity and, ultimately, activation of Akt. These actions of GLP-1 are reflected by expansion of beta-cell mass and enhanced resistance to beta-cell injury in experimental models of diabetes in vivo. GLP-2 also promotes intestinal cell proliferation and confers resistance to cellular injury in a variety of cell types. Administration of GLP-2 to animals with experimental intestinal injury promotes regeneration of the gastrointestinal epithelial mucosa and confers resistance to apoptosis in an indirect manner via yet-to-be identified GLP-2 receptor-dependent regulators of mucosal growth and cell survival. These proliferative and antiapoptotic actions of GLP-1 and GLP-2 may contribute to protective and regenerative actions of these peptides in human subjects with diabetes and intestinal disorders, respectively.
TL;DR: It is suggested that increasing endogenous adiponectin levels has direct effects on insulin sensitivity and may induce similar physiological responses as prolonged treatment with peroxisomal proliferator-activated receptor gamma agonists.
Abstract: Adiponectin is a plasma protein expressed exclusively in adipose tissue. Adiponectin levels are linked to insulin sensitivity, but a direct effect of chronically elevated adiponectin on improved insulin sensitivity has not yet been demonstrated. We identified a dominant mutation in the collagenous domain of adiponectin that elevated circulating adiponectin values in mice by 3-fold. Adiponectinemia raised lipid clearance and lipoprotein lipase activity, and suppressed insulin-mediated endogenous glucose production. The induction of adiponectin during puberty and the sexual dimorphism in adult adiponectin values were preserved in these transgenic animals. As a result of elevated adiponectin, serum PRL values and brown adipose mass both increased. The effects on carbohydrate and lipid metabolism were associated with elevated phosphorylation of 5′-AMP-activated protein kinase in liver and elevated expression of peroxisomal proliferator-activated receptor γ2, caveolin-1, and mitochondrial markers in white adip...
TL;DR: Treatment with FGF19 prevented or reversed the diabetes that develops in mice made obese by genetic ablation of brown adipose tissue or genetic absence of leptin, and profiled the F GF19-induced gene expression changes in the liver and brown fat.
Abstract: Hormonal control of metabolic rate can be important in regulating the imbalance between energy intake and expenditure that underlies the development of obesity. In mice fed a high-fat diet, human fibroblast growth factor 19 (FGF19) increased metabolic rate [1.53 +/- 0.06 liters O(2)/h.kg(0.75) (vehicle) vs. 1.93 +/- 0.05 liters O(2)/h.kg(0.75) (FGF19); P < 0.001] and decreased respiratory quotient [0.82 +/- 0.01 (vehicle) vs. 0.80 +/- 0.01 (FGF19); P < 0.05]. In contrast to the vehicle-treated mice that gained weight (0.14 +/- 0.05 g/mouse.d), FGF19-treated mice lost weight (-0.13 +/- 0.03 g/mouse.d; P < 0.001) without a significant change in food intake. Furthermore, in addition to a reduction in weight gain, treatment with FGF19 prevented or reversed the diabetes that develops in mice made obese by genetic ablation of brown adipose tissue or genetic absence of leptin. To explore the mechanisms underlying the FGF19-mediated increase in metabolic rate, we profiled the FGF19-induced gene expression changes in the liver and brown fat. In brown adipose tissue, chronic exposure to FGF19 led to a gene expression profile that is consistent with activation of this tissue. We also found that FGF19 acutely increased liver expression of the leptin receptor (1.8-fold; P < 0.05) and decreased the expression of acetyl coenzyme A carboxylase 2 (0.6-fold; P < 0.05). The gene expression changes were consistent with the experimentally determined increase in fat oxidation and decrease in liver triglycerides. Thus, FGF19 is able to increase metabolic rate concurrently with an increase in fatty acid oxidation.
TL;DR: The data indicate that FGF-23 induces phenotypic changes in mice resembling those of patients with ADHR, OOM, and XLH and that F GF-23 is an important determinant of Pi homeostasis and bone mineralization.
Abstract: Mutations in the fibroblast growth factor 23 gene, FGF23, cause autosomal dominant hypophosphatemic rickets (ADHR). The gene product, FGF-23, is produced by tumors from patients with oncogenic osteomalacia (OOM), circulates at increased levels in most patients with X-linked hypophosphatemia (XLH) and is phosphaturic when injected into rats or mice, suggesting involvement in the regulation of phosphate (Pi) homeostasis. To better define the precise role of FGF-23 in maintaining Pi balance and bone mineralization, we generated transgenic mice that express wild-type human FGF-23, under the control of the alpha1(I) collagen promoter, in cells of the osteoblastic lineage. At 8 wk of age, transgenic mice were smaller (body weight = 17.5 +/- 0.57 vs. 24.3 +/- 0.37 g), exhibited decreased serum Pi concentrations (1.91 +/- 0.27 vs. 2.75 +/- 0.22 mmol/liter) and increased urinary Pi excretion when compared with wild-type littermates. The serum concentrations of human FGF-23 (undetectable in wild-type mice) was markedly elevated in transgenic mice (>7800 reference units/ml). Serum PTH levels were increased in transgenic mice (231 +/- 62 vs. 139 +/- 44 pg/ml), whereas differences in calcium and 1,25-dihydroxyvitamin D were not apparent. Expression of Npt2a, the major renal Na(+)/Pi cotransporter, as well as Npt1 and Npt2c mRNAs, was significantly decreased in the kidneys of transgenic mice. Histology of tibiae displayed a disorganized and widened growth plate and peripheral quantitative computerized tomography analysis revealed reduced bone mineral density in transgenic mice. The data indicate that FGF-23 induces phenotypic changes in mice resembling those of patients with ADHR, OOM, and XLH and that FGF-23 is an important determinant of Pi homeostasis and bone mineralization.
TL;DR: Exposure of humans to bisphenol A (BPA), a monomer in polycarbonate plastics and a constituent of resins used in food packaging and dentistry, is significant and further studies are warranted to assess the effects of BPA on male fertility.
Abstract: Exposure of humans to bisphenol A (BPA), a monomer in polycarbonate plastics and a constituent of resins used in food packaging and dentistry, is significant. In this report exposure of rats to 2.4 microg/kg.d (a dose that approximates BPA levels in the environment) from postnatal d 21-35 suppressed serum LH (0.21 +/- 0.05 ng/ml; vs. control, 0.52 +/- 0.04; P < 0.01) and testosterone (T) levels (1.62 +/- 0.16 ng/ml; vs. control, 2.52 +/- 0.21; P < 0.05), in association with decreased LHbeta and increased estrogen receptor beta pituitary mRNA levels as measured by RT-PCR. Treatment of adult Leydig cells with 0.01 nm BPA decreased T biosynthesis by 25% as a result of decreased expression of the steroidogenic enzyme 17alpha-hydroxylase/17-20 lyase. BPA decreased serum 17beta-estradiol levels from 0.31 +/- 0.02 ng/ml (control) to 0.22 +/- 0.02, 0.19 +/- 0.02, and 0.23 +/- 0.03 ng/ml in rats exposed to 2.4 microg, 10 microg, or 100 mg/kg.d BPA, respectively, from 21-35 d of age (P < 0.05) due to its ability to inhibit Leydig cell aromatase activity. Exposures of pregnant and nursing dams, i.e. from gestation d 12 to postnatal d 21, decreased T levels in the testicular interstitial fluid from 420 +/- 34 (control) to 261 +/- 22 (P < 0.05) ng/ml in adulthood, implying that the perinatal period is a sensitive window of exposure to BPA. As BPA has been measured in several human populations, further studies are warranted to assess the effects of BPA on male fertility.
TL;DR: In vivo data suggest that rosiglitazone therapy may pose a significant risk of adverse skeletal effects in humans.
Abstract: Rosiglitazone is an FDA-approved oral antidiabetic agent for the treatment of type 2 diabetes. This compound improves insulin sensitivity through the activation of the nuclear receptor, peroxisome proliferator-activated receptor- (PPAR-). In addition to sensitizing cells to insulin, the PPAR-2 isoform appears to be critical for the regulation of osteoblast and adipocyte differentiation from common mesenchymal bone marrow progenitors. We have demonstrated previously that PPAR-2 activated with rosiglitazone acts as a dominant inhibitor of osteoblastogenesis in murine bone marrow in vitro. Here, we show that in vivo, rosiglitazone administration results in significant bone loss. When rosiglitazone (20g/g body weight/d) was given to 6-month-old, nondiabetic C57BL/6 mice for 7 wk, a significant decrease in total body bone mineral density was observed. Analysis of bone microarchitecture, using micro-computed tomography, demonstrated a decrease in bone volume, trabecular width, and trabecular number and an increase in trabecular spacing. Histomorphometric analysis showed a decrease in bone formation rate, with a simultaneous increase in fat content in the bone marrow. Changes in bone morphology and structure were accompanied by changes in the expression of osteoblast- and adipocytespecific marker genes; the expression of the osteoblastspecific genes Runx2/Cbfa1, Dlx5, and 1(I)collagen were decreased, whereas the expression of the adipocyte-specific fatty acid binding protein aP2, was increased. These in vivo data suggest that rosiglitazone therapy may pose a significant risk of adverse skeletal effects in humans. (Endocrinology 145: 401– 406, 2004)
TL;DR: Data indicate that e CB signaling negatively modulates HPA axis function in a context-dependent manner and suggest that pharmacological augmentation of eCB signaling could serve as a novel approach to the treatment of anxiety-related disorders.
Abstract: Activation of the hypothalamic-pituitary-adrenal (HPA) axis is critical for the adaptation and survival of animals upon exposure to stressful stimuli, and data suggest that endocannabinoid (eCB) signaling modulates neuroendocrine function. We have explored the role of eCB signaling in the modulation of stress-induced HPA axis activation. Administration of the CB1receptor antagonist/inverse agonist SR141716 (0.01, 0.1, 1, and 5 mg/kg, ip) to male mice produced a small, dosedependent increase in the serum corticosterone (CORT) concentration. Despite this effect, the highest dose of SR141716 did not significantly increase neuronal activity within the paraventricularnucleusofthehypothalamus,asmeasuredby the induction of Fos protein. Similarly, exposure of mice to 30 min of restraint increased serum CORT concentrations, but did not produce a consistent, statistically significant increase in Fos expression within the PVN. However, pretreatment of mice with SR141716 before restraint stress robustly potentiated restraint-induced CORT release and Fos expression within the PVN. Pretreatment of mice with either the CB1 receptor agonist CP55940, the eCB transport inhibitor AM404, or the fatty acid amide hydrolase inhibitor URB597 significantly decreased or eliminated restraint-induced CORT release. Upon exposure to acute restraint, hypothalamic 2-arachidonylglycerol content was reduced compared with the control value; however, afte r5do frestraint exposure (which resulted in an attenuated CORT response), the hypothalamic 2-arachidonylglycerol content was increased compared with the control value. These data indicate that eCB signaling negatively modulates HPA axis function in a context-dependent manner and suggest that pharmacological augmentation of eCB signaling could serve as a novel approach to the treatment of anxiety-related disorders. (Endocrinology 145: 5431–5438, 2004)
TL;DR: Using a novel unilateral local infusion strategy, it is demonstrated that ghrelin promotes bone marrow adipogenesis in vivo by a direct peripheral action, the first in vivo demonstration of a direct adipogenic effect of des-octanoyl gh Relin, a major circulating form of ghrel in that lacks GH-releasing activity.
Abstract: Ghrelin promotes fat accumulation, despite potent stimulation of the lipolytic hormone, GH. The function of the major circulating isoform of ghrelin, des-octanoyl ghrelin, is unclear, because it does not activate the GH secretagogue receptor (GHS-R1a) and lacks the endocrine activities of ghrelin. We have now addressed these issues by infusing ghrelin, des-octanoyl ghrelin, or synthetic GHS-R1a agonists into three rat models with moderate, severe, or total GH deficiency. We show that in the context of significant GH secretion, the adipogenic effect of systemic ghrelin infusion is pattern dependent. However, this adipogenic action is not mediated by the pituitary hormones. Using a novel unilateral local infusion strategy, we demonstrate that ghrelin promotes bone marrow adipogenesis in vivo by a direct peripheral action. Surprisingly, this effect was also observed with des-octanoyl ghrelin, whereas a potent synthetic GHS-R1a agonist was ineffective. Thus, these adipogenic effects are mediated by a receptor other than GHS-R1a. This is the first in vivo demonstration of a direct adipogenic effect of des-octanoyl ghrelin, a major circulating form of ghrelin that lacks GH-releasing activity. We suggest that the ratio of ghrelin and des-octanoyl ghrelin production could help regulate the balance between adipogenesis and lipolysis in response to nutritional status.
TL;DR: In this article, the authors consider the possibility that transient differences in gene expression in developing brains may cause permanent differences in brain structure but prevent them as well, by compensating for potentially differentiating effects of sex differences in gonadal hormone levels and sex chromosomal gene expression.
Abstract: Despite decades of research, we do not know the functional significance of most sex differences in the brain. We are heavily invested in the idea that sex differences in brain structure cause sex differences in behavior. We rarely consider the possibility that sex differences in brain structure may also prevent sex differences in overt functions and behavior, by compensating for sex differences in physiological conditions, e.g. gonadal hormone levels that may generate undesirable sex differences if left unchecked. Such a dual function for sex differences is unlikely to be restricted to adult brains. This review will entertain the possibility that transient sex differences in gene expression in developing brains may cause permanent differences in brain structure but prevent them as well, by compensating for potentially differentiating effects of sex differences in gonadal hormone levels and sex chromosomal gene expression. Consistent application of this dual-function hypothesis will make the search for the functional significance of sex differences more productive.
TL;DR: The experimental approach was designed to result in a mild and transient period of maternal hypothyroxinemia at the beginning of corticogenesis, and when extrapolated to man, these results stress the need for prevention of hypothyruinemia before midpregnancy, however moderate, and whichever the underlying cause.
Abstract: Epidemiological studies and case reports show that even a relatively minor degree of maternal hypothyroxinemia during the first half of gestation is potentially dangerous for optimal fetal neurodevelopment. Our experimental approach was designed to result in a mild and transient period of maternal hypothyroxinemia at the beginning of corticogenesis. Normal rat dams received the goitrogen 2-mercapto-1-methylimidazole for only 3 d, from embryonic d 12 (E12) to E15. Maternal thyroid hormones decreased transiently to 70% of normal serum values, without clinical signs of hypothyroidism. Dams were injected daily with 5-bromo-2-deoxyuridine (BrdU) during 3 d, from E14 –E16 or E17–E19. Their pups were tested for audiogenic seizure susceptibility 39 d after birth (P39) and killed at P40. Cells that had incorporated BrdU were identified by immunocytochemistry, and quantified: numerous heterotopic cells were found, whether labeled at E14 –E16 or E17–E19, that were identified as neurons. The cytoarchitecture and the radial distribution of BrdU-labeled neurons was significantly affected in the somatosensory cortex and hippocampus of 83% of the pups. The radial distribution of -aminobutyric acidergic neurons was, however, normal. The infusion of dams with T4 between E13 and E15 avoided these alterations, which were not prevented when the T4 infusion was delayed to E15–E18. In total, 52% of the pups born to the goitrogen-treated dams responded to an acoustic stimulus with wild runs, followed in some by seizures. When extrapolated to man, these results stress the need for prevention of hypothyroxinemia before midpregnancy, however moderate, and whichever the underlying cause. (Endocrinology 145: 4037– 4047, 2004)
TL;DR: Strong evidence that glucocorticoids modify feeding is provided and the role of insulin on the choice of ingested calories is discussed, as well as suggesting some central neural pathways that may be involved in these actions of glucocORTicoids and insulin.
Abstract: Glucocorticoids have a major effect on food intake that is underappreciated, although the effects of glucocorticoids on metabolism and abdominal obesity are quite well understood. Physiologically appropriate concentrations of naturally secreted corticosteroids (cortisol in humans, corticosterone in rats) have major stimulatory effects on caloric intake and, in the presence of insulin, preference. We first address the close relationship between glucocorticoids and energy balance under both normal and abnormal conditions. Because excess caloric intake is stored in different fat depots, we also address the systemic effects of glucocorticoids on redistribution of stored energy preponderantly into intraabdominal fat depots. We provide strong evidence that glucocorticoids modify feeding and then discuss the role of insulin on the choice of ingested calories, as well as suggesting some central neural pathways that may be involved in these actions of glucocorticoids and insulin. Finally, we discuss the evolutionary utility of these actions of the stress hormones, and how dysregulatory effects of chronically elevated glucocorticoids may occur in our modern, rich societies.
TL;DR: It is reported that peripheral (ip) administration of OXM dose-dependently inhibited both fast-induced and dark-phase food intake without delaying gastric emptying and there was a significant increase in c-fos immunoreactivity in the arcuate nucleus (ARC).
Abstract: Oxyntomodulin (OXM) is a circulating gut hormone released post prandially from cells of the gastrointestinal mucosa. Given intracerebroventricularly to rats, it inhibits food intake and promotes weight loss. Here we report that peripheral (ip) administration of OXM dose-dependently inhibited both fast-induced and dark-phase food intake without delaying gastric emptying. Peripheral OXM administration also inhibited fasting plasma ghrelin. In addition, there was a significant increase in c-fos immunoreactivity, a marker of neuronal activation, in the arcuate nucleus (ARC). OXM injected directly into the ARC caused a potent and sustained reduction in refeeding after a fast. The anorectic actions of ip OXM were blocked by prior intra-ARC administration of the glucagonlike peptide-1 (GLP-1) receptor antagonist, exendin9 –39, suggesting that the ARC, lacking a complete blood-brain barrier, could be a potential site of action for circulating OXM. The actions of ip GLP-1, however, were not blocked by prior intraARC administration of exendin9 –39, indicating the potential existence of different OXM and GLP-1 pathways. Seven-day ip administration of OXM caused a reduction in the rate of body weight gain and adiposity. Circulating OXM may have a role in the regulation of food intake and body weight. (Endocrinology 145: 2687–2695, 2004)
TL;DR: Procyanidins have insulin-like effects in insulin-sensitive cells that could help to explain their antihyperglycemic effect in vivo, which was significantly increased if PE administration was accompanied by a low insulin dose.
Abstract: Flavonoids are functional constituents of many fruits and vegetables. Some flavonoids have antidiabetic properties because they improve altered glucose and oxidative metabolisms of diabetic states. Procyanidins are flavonoids with an oligomeric structure, and it has been shown that they can improve the pathological oxidative state of a diabetic situation. To evaluate their effects on glucose metabolism, we administered an extract of grape seed procyanidins (PE) orally to streptozotocin-induced diabetic rats. This had an antihyperglycemic effect, which was significantly increased if PE administration was accompanied by a low insulin dose. The antihyperglycemic effect of PE may be partially due to the insulinomimetic activity of procyanidins on insulin-sensitive cell lines. PE stimulated glucose uptake in L6E9 myotubes and 3T3-L1 adipocytes in a dose-dependent manner. Like insulin action, the effect of PE on glucose uptake was sensitive to wortmannin, an inhibitor of phosphoinositol 3-kinase and to SB203580, an inhibitor of p38 MAPK. PE action also stimulated glucose transporter-4 translocation to the plasma membrane. In summary, procyanidins have insulin-like effects in insulin-sensitive cells that could help to explain their antihyperglycemic effect in vivo. These effects must be added to their antioxidant activity to explain why they can improve diabetic situations.
TL;DR: Enteroendocrine cells in the mouse are remarkably similar to those in humans, making it likely that insights learned from the mouse may contribute to both the authors' understanding and treatment of a variety of human disorders.
Abstract: For over 30 yr, it has been known that enteroendocrine cells derive from common precursor cells in the intestinal crypts. Until recently, relatively little was understood about the events that result in commitment to endocrine differentiation or the segregation of over 10 different hormone-expressing cell types in the gastrointestinal tract. The earliest cell fate decisions appear to be regulated by the Notch signaling pathway. Notch is inactive in endocrine precursor cells, allowing for expression of the proendocrine basic helix-loop-helix proteins Math1 and neurogenin3. Differentiating precursor cells activate Notch in neighboring cells to switch off expression of proendocrine factors and inhibit endocrine differentiation. Math1 is the first factor involved in endocrine specification, committing cells to become one of three secretory lineages-goblet, Paneth, and enteroendocrine. Neurogenin3 appears to be a downstream target that is essential for endocrine cell differentiation. Events that control the segregation of each mature lineage from progenitor cells have not been characterized in detail. The transcription factors Pax4, Pax6, BETA2/NeuroD, and pancreatic-duodenal homeobox 1 have all been implicated in enteroendocrine differentiation. BETA2/NeuroD appears to coordinate secretin gene expression in S-type enteroendocrine cells with cell cycle arrest as cells terminally differentiate. Powerful genetic approaches have established the murine intestine as the most important model for studying enteroendocrine differentiation. Enteroendocrine cells in the mouse are remarkably similar to those in humans, making it likely that insights learned from the mouse may contribute to both our understanding and treatment of a variety of human disorders.
TL;DR: It is demonstrated, for the first time, that androgens positively regulate PDE5, thus providing a possible explanation about the highest abundance of this enzyme in male genital tract.
Abstract: By real-time RT-PCR and Western blot analysis, we found that phosphodiesterase type 5 (PDE5) mRNA and protein abundance was several fold higher in human male than in female reproductive tracts. The highest mRNA level (>1 × 107 molecules/μg total RNA) was detected in human corpora cavernosa (CC), where PDE5 protein was immunolocalized in both muscular and endothelial compartment. The possible role of androgens in regulating PDE5 expression was studied using a previously established rabbit model of hypogonadotropic hypogonadism. In this model, hypogonadism reduced, and testosterone (T) supplementation restored, CC PDE5 gene and protein expression. In addition, T supplementation completely rescued and even enhanced cyclic GMP conversion to metabolites, without changing IC50 for sildenafil (IC50 = 2.16 ± 0.62 nm). In control CC strips, sildenafil dose-dependently increased relaxation induced by electrical field stimulation, with EC50 = 3.42 ± 1.7 nm. Hypogonadism reduced, and T increased, sildenafil effect on...
TL;DR: The findings strongly support the novel concept that high circulating levels of FGF23 are associated with profound disturbances in the regulation of phosphate and vitamin D metabolism as well as calcium homeostasis and that elevated PTH levels likely also contribute to the renal phosphate wasting associated with these disorders.
Abstract: Fibroblast growth factor 23 (FGF23) is a recently characterized protein likely involved in the regulation of serum phosphate homeostasis. Increased circulating levels of FGF23 have been reported in patients with renal phosphate-wasting disorders, but it is unclear whether FGF23 is the direct mediator responsible for the decreased phosphate transport at the proximal renal tubules and the altered vitamin D metabolism associated with these states. To examine this question, we generated transgenic mice expressing and secreting from the liver human FGF23 (R176Q), a mutant form that fails to be degraded by furin proteases. At 1 and 2 months of age, mice carrying the transgene recapitulated the biochemical (decreased urinary phosphate reabsorption, hypophosphatemia, low serum 1,25-dihydroxyvitamin D3) and skeletal (rickets and osteomalacia) alterations associated with these disorders. Unexpectantly, marked changes in parameters of calcium homeostasis were also observed, consistent with secondary hyperparathyroid...
Journal Article•
TL;DR: This review will entertain the possibility that transient sex differences in gene expression in developing brains may cause permanent differences in brain structure but prevent them as well, by compensating for potentially differentiating effects ofsex differences in gonadal hormone levels and sex chromosomal gene expression.
TL;DR: It is proposed that the expression of GPR54 is a "stop signal" for GnRH1, GnRH2, and GnRH3 neuronal migration, leading to suppression of cell growth and modulation of GnRH secretion, which is important for normal sexual development.
Abstract: GPR54 is a novel G protein-coupled receptor speculated to be essential for sexual development. However, its role in the regulation of GnRH types is unknown. To address this issue, we cloned GPR54 from the brain of a cichlid fish (tilapia Oreochromis niloticus) and determined its expression in immature and mature males using our newly developed technique: laser-captured microdissection of single digoxigenin-labeled GnRH neurons coupled with real-time quantitative PCR. The tilapia GPR54 cDNA contains an open reading frame of 1131 bp encoding 377 amino acids and exhibits 56% identity to human GPR54. Absolute copies of GnRH1 and GnRH3, not GnRH2, mRNAs were significantly high in mature compared with immature males. At the single-cell level, only in mature males, GnRH1 mRNA levels were inversely related to GPR54 mRNA (P < 0.002). GPR54 was expressed in a significantly high percentage (45.0–60.0%) of mature GnRH1, GnRH2, and GnRH3 neurons and in immature GnRH3 neurons, which had migrated to the vicinity of thei...
TL;DR: It is implicate that CTs possess a unique property to enhance sFlt-1 production under reduced oxygen, which could consequently antagonize angiogenic activity of VEGF and PlGF.
Abstract: Sufficient cytotrophoblast (CT) invasion into the uterine wall and subsequent remodeling of maternal uterine vasculature is critical to establish uteroplacental circulation. The production of vascular endothelial growth factor (VEGF) family molecules is confirmed in placental cells including CTs, but it is not elucidated how the VEGF system in CTs is controlled by oxygen tension and how it is involved in the development of placental circulation. To address this, we explored the effect of oxygen tension on the expression of VEGF, placenta growth factor (PlGF), and their antagonist, soluble fms-like tyrosine kinase-1 (sFlt-1) using ELISA and real-time PCR in a primary CT cell culture. For comparison, the same was conducted in parallel using other cells comprising placenta, such as human umbilical vein endothelial cells (HUVECs) and villous fibroblasts (VFs). Reduced oxygen resulted in a pronounced increase in sFlt-1 mRNA amount and sFlt-1 release into the culture media in CTs, whereas this was not the case with HUVECs and VFs. Free (not bound to sFlt-1) VEGF was not detected in CT culture media regardless of oxygen concentration, even though VEGF expression was stimulated by reduced oxygen in CTs, which was similar to the stimulation in HUVECs and VFs. Free PlGF was also diminished in CT culture media by reduced oxygen. These results implicate that CTs possess a unique property to enhance sFlt-1 production under reduced oxygen, which could consequently antagonize angiogenic activity of VEGF and PlGF. The presented findings might provide a framework with which to understand the mechanism of uterine vascular remodeling and its perturbations as exemplified in preeclampsia.
TL;DR: GNAS is a complex imprinted gene that uses multiple promoters to generate several gene products, including the G protein alpha-subunit that couples seven-transmembrane receptors to the cAMP-generating enzyme adenylyl cyclase.
Abstract: GNAS is a complex imprinted gene that uses multiple promoters to generate several gene products, including the G protein alpha-subunit (G(s)alpha) that couples seven-transmembrane receptors to the cAMP-generating enzyme adenylyl cyclase. Somatic activating G(s)alpha mutations, which alter key residues required for the GTPase turn-off reaction, are present in various endocrine tumors and fibrous dysplasia of bone, and in a more widespread distribution in patients with McCune- Albright syndrome. Heterozygous inactivating G(s)alpha mutations lead to Albright hereditary osteodystrophy. G(s)alpha is imprinted in a tissue-specific manner, being primarily expressed from the maternal allele in renal proximal tubules, thyroid, pituitary, and ovary. Maternally inherited mutations lead to Albright hereditary osteodystrophy (AHO) plus PTH, TSH, and gonadotropin resistance (pseudohypoparathyroidism type 1A), whereas paternally inherited mutations lead to AHO alone. Pseudohypoparathyroidism type 1B, in which patients develop PTH resistance without AHO, is almost always associated with a GNAS imprinting defect in which both alleles have a paternal-specific imprinting pattern on both parental alleles. Familial forms of the disease are associated with a mutation within a closely linked gene that deletes a region that is presumably required for establishing the maternal imprint, and therefore maternal inheritance of the mutation results in the GNAS imprinting defect. Imprinting of one differentially methylated region within GNAS is virtually always lost in pseudohypoparathyroidism type 1B, and this region is probably responsible for tissue-specific G(s)alpha imprinting. Mouse knockout models show that G(s)alpha and the alternative G(s)alpha isoform XLalphas that is expressed from the paternal GNAS allele may have opposite effects on energy metabolism in mice.