Thyrotropin receptor (TSHR) Ab’s of the stimulating variety are the cause of hyperthyroid Graves disease. MS-1 is a hamster mAb with TSHR-stimulating activity. To examine the in vivo biological activity of MS-1, mice were treated with purified MS-1 intraperitoneally and the thyroid response evaluated. MS-1 induced a dose-dependent increase in serum thyroxine (T4), with a maximum effect after 10 ∝g of MS-1 was administered. MS-1–secreting hybridoma cells were then transferred into the peritoneum of nude mice to study chronic thyroid stimulation. Serum MS-1 levels detected after 2 weeks were approximately 10–50 ∝g/ml, and the serum TSH was suppressed in all animals. Serum triiodothyronine levels were elevated, but only in animals with low serum MS-1 concentrations. In addition, there was a negative correlation between serum T4 and the serum MS-1 concentrations. These in vivo studies suggested a partial TSHR inactivation induced by excessive stimulation by MS-1. We confirmed this inactivation by demonstrating MS-1 modulation of TSHR function in vitro as evidenced by downregulation and desensitization of the TSHR at concentrations of MS-1 achieved in the in vivo studies. Thus, inactivation of the TSHR by stimulating TSHR autoantibodies (TSHR-Ab’s) in Graves disease patients may provide a functional explanation for the poor correlation between thyroid function and serum TSHR-Ab concentrations.
Takao Ando, Rauf Latif, Terry F. Davies
The transfer of calcium from mother to milk during lactation is poorly understood. In this report, we demonstrate that parathyroid hormone–related protein (PTHrP) production and calcium transport in mammary epithelial cells are regulated by extracellular calcium acting through the calcium-sensing receptor (CaR). The CaR becomes expressed on mammary epithelial cells at the transition from pregnancy to lactation. Increasing concentrations of calcium, neomycin, and a calcimimetic compound suppress PTHrP secretion by mammary epithelial cells in vitro, whereas in vivo, systemic hypocalcemia increases PTHrP production, an effect that can be prevented by treatment with a calcimimetic. Hypocalcemia also reduces overall milk production and calcium content, while increasing milk osmolality and protein concentrations. The changes in milk calcium content, milk osmolality, and milk protein concentration were mitigated by calcimimetic infusions. Finally, in a three-dimensional culture system that recapitulates the lactating alveolus, activation of the basolateral CaR increases transcellular calcium transport independent of its effect on PTHrP. We conclude that the lactating mammary gland can sense calcium and adjusts its secretion of calcium, PTHrP, and perhaps water in response to changes in extracellular calcium concentration. We believe this defines a homeostatic system that helps to match milk production to the availability of calcium.
Joshua VanHouten, Pamela Dann, Grace McGeoch, Edward M. Brown, Karen Krapcho, Margaret Neville, John J. Wysolmerski
Inorganic phosphate is essential for ECM mineralization and also as a constituent of important molecules in cellular metabolism. Investigations of several hypophosphatemic diseases indicated that a hormone-like molecule probably regulates serum phosphate concentration. FGF23 has recently been recognized as playing important pathophysiological roles in several hypophosphatemic diseases. We present here the evidence that FGF23 is a physiological regulator of serum phosphate and 1,25-dihydroxyvitamin D (1,25[OH]2D) by generating FGF23-null mice. Disruption of the Fgf23 gene did not result in embryonic lethality, although homozygous mice showed severe growth retardation with abnormal bone phenotype and markedly short life span. The Fgf23–/– mice displayed significantly high serum phosphate with increased renal phosphate reabsorption. They also showed an elevation in serum 1,25(OH)2D that was due to the enhanced expression of renal 25-hydroxyvitamin D-1α-hydroxylase (1α-OHase) from 10 days of age. These phenotypes could not be explained by currently known regulators of mineral homeostasis, indicating that FGF23 is essential for normal phosphate and vitamin D metabolism.
Takashi Shimada, Makoto Kakitani, Yuji Yamazaki, Hisashi Hasegawa, Yasuhiro Takeuchi, Toshiro Fujita, Seiji Fukumoto, Kazuma Tomizuka, Takeyoshi Yamashita
Joshua N. VanHouten, Pamela Dann, Andrew F. Stewart, Christine J. Watson, Michael Pollak, Andrew C. Karaplis, John J. Wysolmerski
Insulin promotes both metabolism and growth. However, it is unclear whether insulin-dependent growth is merely a result of its metabolic actions. Targeted ablation of insulin receptor (Insr) has not clarified this issue, because of early postnatal lethality. To examine this question, we generated mice with variable cellular mosaicism for null Insr alleles. Insr ablation in approximately 80% of cells caused extreme growth retardation, lipoatrophy, and hypoglycemia, a clinical constellation that resembles the human syndrome of leprechaunism. Insr ablation in 98% of cells, while resulting in similar growth retardation and lipoatrophy, caused diabetes without β-cell hyperplasia. The growth retardation was associated with a greater than 60-fold increase in the expression of hepatic insulin-like growth factor binding protein-1. These findings indicate that insulin regulates growth independently of metabolism and that the number of insulin receptors is an important determinant of the specificity of insulin action.
Tadahiro Kitamura, Yukari Kitamura, Jun Nakae, Antonio Giordano, Saverio Cinti, C. Ronald Kahn, Argiris Efstratiadis, Domenico Accili
The neurohypophyseal peptide [Arg8]-vasopressin (AVP) exerts major physiological actions through three distinct receptor isoforms designated V1a, V1b, and V2. Among these three subtypes, the vasopressin V1b receptor is specifically expressed in pituitary corticotrophs and mediates the stimulatory effect of vasopressin on ACTH release. To investigate the functional roles of V1b receptor subtypes in vivo, gene targeting was used to create a mouse model lacking the V1b receptor gene (V1bR–/–). Under resting conditions, circulating concentrations of ACTH and corticosterone were lower in V1bR–/– mice compared with WT mice (V1bR+/+). The normal increase in circulating ACTH levels in response to exogenous administration of AVP was impaired in V1bR–/– mice, while corticotropin-releasing hormone–stimulated ACTH release in the V1bR–/– mice was not significantly different from that in the V1bR+/+ mice. AVP-induced ACTH release from primary cultured pituitary cells in V1bR–/– mice was also blunted. Furthermore, the increase in ACTH after a forced swim stress was significantly suppressed in V1bR–/– mice. Our results clearly demonstrate that the V1b receptor plays a crucial role in regulating hypothalamic-pituitary-adrenal axis activity. It does this by maintaining ACTH and corticosterone levels, not only under stress but also under basal conditions.
Akito Tanoue, Shuji Ito, Kenji Honda, Sayuri Oshikawa, Yoko Kitagawa, Taka-aki Koshimizu, Toyoki Mori, Gozoh Tsujimoto
Familial neurohypophyseal diabetes insipidus (FNDI) is an autosomal dominant disorder caused by mutations in the arginine vasopressin (AVP) precursor. The pathogenesis of FNDI is proposed to involve mutant protein–induced loss of AVP-producing neurons. We established murine knock-in models of two different naturally occurring human mutations that cause FNDI. A mutation in the AVP signal sequence [A(–1)T] is associated with a relatively mild phenotype or delayed presentation in humans. This mutation caused no apparent phenotype in mice. In contrast, heterozygous mice expressing a mutation that truncates the AVP precursor (C67X) exhibited polyuria and polydipsia by 2 months of age and these features of DI progressively worsened with age. Studies of the paraventricular and supraoptic nuclei revealed induction of the chaperone protein BiP and progressive loss of AVP-producing neurons relative to oxytocin-producing neurons. In addition, Avp gene products were not detected in the neuronal projections, suggesting retention of WT and mutant AVP precursors within the cell bodies. In summary, this murine model of FNDI recapitulates many features of the human disorder and demonstrates that expression of the mutant AVP precursor leads to progressive neuronal cell loss.
Theron A. Russell, Masafumi Ito, Mika Ito, Richard N. Yu, Fred A. Martinson, Jeffrey Weiss, J. Larry Jameson
Large amounts of calcium are transferred to offspring by milk. This demand results in negative calcium balance in lactating mothers and is associated with rapid bone loss. The mechanisms of bone loss during lactation are only partly understood. Several studies have suggested that parathyroid hormone–related protein (PTHrP) might be secreted into the circulation by the lactating mammary gland and regulate bone turnover during lactation. Because mammary development fails in the absence of PTHrP, conventional PTHrP knockout mice cannot be used to address this possibility. To examine this hypothesis, we therefore used mice carrying a β-lactoglobulin promoter-driven Cre transgene, one null PTHrP allele, and one floxed PTHrP allele. Expression of Cre specifically in mammary epithelial cells during late pregnancy and lactation resulted in efficient deletion of the PTHrP gene; mammary gland PTHrP mRNA and milk PTHrP protein were almost completely absent. Removal of PTHrP from the lactating mammary glands resulted in reductions in levels of circulating PTHrP and 1,25-dihydroxy vitamin D and urinary cAMP. In addition, bone turnover was reduced and bone loss during lactation was attenuated. We conclude that during lactation mammary epithelial cells are a source of circulating PTHrP that promotes bone loss by increasing rates of bone resorption.
Joshua N. VanHouten, Pamela Dann, Andrew F. Stewart, Christine J. Watson, Michael Pollak, Andrew C. Karaplis, John J. Wysolmerski
Guanylin and uroguanylin, peptides synthesized in the intestine and kidney, have been postulated to have both paracrine and endocrine functions, forming a potential enteric-renal link to coordinate salt ingestion with natriuresis. To explore the in vivo role of uroguanylin in the regulation of sodium excretion, we created gene-targeted mice in which uroguanylin gene expression had been ablated. Northern and Western analysis confirmed the absence of uroguanylin message and protein in knockout mice, and cGMP levels were decreased in the mucosa of the small intestine. Ussing chamber analysis of jejunum revealed that Na+/H+ exchanger–mediated Na+ absorption and tissue conductance was not altered in the knockout animals, but short-circuit current, an index of electrogenic anion secretion, was reduced. Renal clearance measurements showed that uroguanylin deficiency results in impaired ability to excrete an enteral load of NaCl, primarily due to an inappropriate increase in renal Na+ reabsorption. Finally, telemetric recordings of blood pressure demonstrated increased mean arterial pressure in uroguanylin knockout animals that was independent of the level of dietary salt intake. Together, these findings establish a role for uroguanylin in an enteric-renal communication axis as well as a fundamental principle of this axis in the maintenance of salt homeostasis in vivo.
John N. Lorenz, Michelle Nieman, Jenine Sabo, L. Philip Sanford, Jennifer A. Hawkins, Noeet Elitsur, Lara R. Gawenis, Lane L. Clarke, Mitchell B. Cohen
PKCλ is implicated as a downstream effector of PI3K in insulin action. We show here that mice that lack PKCλ specifically in the liver (L-λKO mice), produced with the use of the Cre-loxP system, exhibit increased insulin sensitivity as well as a decreased triglyceride content and reduced expression of the sterol regulatory element–binding protein-1c (SREBP-1c) gene in the liver. Induction of the hepatic expression of Srebp1c and of its target genes involved in fatty acid/triglyceride synthesis by fasting and refeeding or by hepatic expression of an active form of PI3K was inhibited in L-λKO mice compared with that in control animals. Expression of Srebp1c induced by insulin or by active PI3K in primary cultured rat hepatocytes was inhibited by a dominant-negative form of PKCλ and was mimicked by overexpression of WT PKCλ. Restoration of PKCλ expression in the liver of L-λKO mice with the use of adenovirus-mediated gene transfer corrected the metabolic abnormalities of these animals. Hepatic PKCλ is thus a determinant of hepatic lipid content and whole-body insulin sensitivity.
Michihiro Matsumoto, Wataru Ogawa, Kazunori Akimoto, Hiroshi Inoue, Kazuaki Miyake, Kensuke Furukawa, Yoshitake Hayashi, Haruhisa Iguchi, Yasushi Matsuki, Ryuji Hiramatsu, Hitoshi Shimano, Nobuhiro Yamada, Shigeo Ohno, Masato Kasuga, Tetsuo Noda
Thyroid hormone action is mediated by thyroid hormone receptors (TRs), which are members of the nuclear hormone receptor superfamily. DNA-binding is presumed to be essential for all nuclear actions of thyroid hormone. To test this hypothesis in vivo, the DNA-binding domain of TR-β was mutated within its P-box (GS mutant) using gene targeting techniques. This mutation in vitro completely abolishes TR-β DNA-binding, while preserving ligand (T3) and cofactor interactions with the receptor. Homozygous mutant (TR-βGS/GS) mice displayed abnormal T3 regulation of the hypothalamic-pituitary-thyroid axis and retina identical to abnormalities previously observed in TR-β KO (TR-β–/–) mice. However, TR-βGS/GS mutant mice maintained normal hearing at certain frequencies and did not display significant outer hair cell loss, in contrast to TR-β–/– mice. DNA-binding, therefore, is essential for many functions of the TR, including retinal development and negative feedback regulation by thyroid hormone of the hypothalamic-pituitary-thyroid axis. Inner ear development, although not completely normal, can occur in the absence of TR DNA-binding, suggesting that an alternative and perhaps novel thyroid hormone-signaling pathway may mediate these effects.
Nobuyuki Shibusawa, Koshi Hashimoto, Amisra A. Nikrodhanond, M. Charles Liberman, Meredithe L. Applebury, Xiao Hui Liao, Janet T. Robbins, Samuel Refetoff, Ronald N. Cohen, Fredric E. Wondisford
NO prevents atherogenesis and inflammation in vessel walls by inhibition of cell proliferation and cytokine-induced endothelial expression of adhesion molecules and proinflammatory cytokines. Reduced NO production due to inhibition of either eNOS or iNOS may therefore reinforce atherosclerosis. Patients with end-stage renal failure show markedly increased mortality due to atherosclerosis. In the present study we tested the hypothesis that uremic toxins are responsible for reduced iNOS expression. LPS-induced iNOS expression in mononuclear leukocytes was studied using real-time PCR. The iNOS expression was blocked by addition of plasma from patients with end-stage renal failure, whereas plasma from healthy controls had no effect. Hemofiltrate obtained from patients with end-stage renal failure was fractionated by chromatographic methods. The chromatographic procedures revealed a homogenous fraction that inhibits iNOS expression. Using gas chromatography/mass spectrometry, this inhibitor was identified as phenylacetic acid. Authentic phenylacetic acid inhibited iNOS expression in a dose-dependent manner. In healthy control subjects, plasma concentrations were below the detection level, whereas patients with end-stage renal failure had a phenylacetic acid concentration of 3.49 ± 0.33 mmol/l (n = 41). It is concluded that accumulation of phenylacetic acid in patients with end-stage renal failure inhibits iNOS expression. That mechanism may contribute to increased atherosclerosis and cardiovascular morbidity in patients with end-stage renal failure.
J. Jankowski, M. van der Giet, V. Jankowski, S. Schmidt, M. Hemeier, B. Mahn, G. Giebing, M. Tölle, H. Luftmann, H. Schlüter, W. Zidek, M. Tepel
The type 2 iodothyronine deiodinase (D2) is an integral membrane ER-resident selenoenzyme that activates the pro-hormone thyroxine (T4) and supplies most of the 3,5,3′-triiodothyronine (T3) that is essential for brain development. D2 is inactivated by selective conjugation to ubiquitin, a process accelerated by T4 catalysis and essential for the maintenance of T3 homeostasis. A yeast two-hybrid screen of a human-brain library with D2 as bait identified von Hippel–Lindau protein–interacting deubiquitinating enzyme-1 (VDU1). D2 interaction with VDU1 and VDU2, a closely related deubiquitinase, was confirmed in mammalian cells. Both VDU proteins colocalize with D2 in the ER, and their coexpression prolongs D2 half-life and activity by D2 deubiquitination. VDU1, but not VDU2, is markedly increased in brown adipocytes by norepinephrine or cold exposure, further amplifying the increase in D2 activity that results from catecholamine-stimulated de novo synthesis. Thus, deubiquitination regulates the supply of active thyroid hormone to brown adipocytes and other D2-expressing cells.
Cyntia Curcio-Morelli, Ann Marie Zavacki, Marcelo Christofollete, Balazs Gereben, Beatriz C.G. de Freitas, John W. Harney, Zaibo Li, Guan Wu, Antonio C. Bianco
Obesity is closely associated with the metabolic syndrome, a combination of disorders including insulin resistance, diabetes, dyslipidemia, and hypertension. A role for local glucocorticoid reamplification in obesity and the metabolic syndrome has been suggested. The enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) regenerates active cortisol from inactive 11-keto forms, and aP2-HSD1 mice with relative transgenic overexpression of this enzyme in fat cells develop visceral obesity with insulin resistance and dyslipidemia. Here we report that aP2-HSD1 mice also have high arterial blood pressure (BP). The mice have increased sensitivity to dietary salt and increased plasma levels of angiotensinogen, angiotensin II, and aldosterone. This hypertension is abolished by selective angiotensin II receptor AT-1 antagonist at a low dose that does not affect BP in non-Tg littermates. These findings suggest that activation of the circulating renin-angiotensin system (RAS) develops in aP2-HSD1 mice. The long-term hypertension is further reflected by an appreciable hypertrophy and hyperplasia of the distal tubule epithelium of the nephron, resembling salt-sensitive or angiotensin II–mediated hypertension. Taken together, our findings suggest that overexpression of 11β-HSD1 in fat is sufficient to cause salt-sensitive hypertension mediated by an activated RAS. The potential role of adipose 11β-HSD1 in mediating critical features of the metabolic syndrome extends beyond obesity and metabolic complications to include the most central cardiovascular feature of this disorder.
Hiroaki Masuzaki, Hiroshi Yamamoto, Christopher J. Kenyon, Joel K. Elmquist, Nicholas M. Morton, Janice M. Paterson, Hiroshi Shinyama, Matthew G.F. Sharp, Stewart Fleming, John J. Mullins, Jonathan R. Seckl, Jeffrey S. Flier
It has been found that 4-estren-3α,17β-diol, a synthetic ligand for the estrogen receptor (ER) or androgen receptor (AR), which does not affect classical transcription, reverses bone loss in ovariectomized females or orchidectomized males without affecting the uterus or seminal vesicles, demonstrating that the classical genotropic actions of sex steroid receptors are dispensable for their bone-protective effects, but indispensable for their effects on reproductive organs. We have now investigated the mechanism of action of this compound. We report that, identically to 17β-estradiol or dihydrotestosterone, but differently from raloxifene, estren alters the activity of Elk-1, CCAAT enhancer binding protein–β (C/EBPβ), and cyclic adenosine monophosphate–response element binding protein (CREB), or c-Jun/c-Fos by an extranuclear action of the ER or AR, resulting in activation of the Src/Shc/ERK pathway or downregulation of JNK, respectively. All of these effects are non–sex specific, require only the ligand-binding domain of the receptor, and are indispensable for the antiapoptotic action of these ligands on osteoblastic and HeLa cells. Moreover, administration of 17β-estradiol or 4-estren-3α,17β-diol to ovariectomized mice induces phosphorylation of ERKs, Elk-1, and C/EBPβ, downregulates c-Jun, and upregulates the expression of egr-1, an ERK/SRE target gene. Kinase-initiated regulation of commonly used transcription factors offers a molecular explanation for the profound skeletal effects of sex steroid receptor ligands, including synthetic ones that are devoid of classical transcriptional activity.
Stavroula Kousteni, Li Han, Jin-Ran Chen, Maria Almeida, Lilian I. Plotkin, Teresita Bellido, Stavros C. Manolagas
To elucidate the role of leptin in regulating neuroendocrine and metabolic function during an acute fast, six to eight healthy, lean men were studied under four separate conditions: a baseline fed state and three 72-hour fasting studies with administration of either placebo, low-dose recombinant-methionyl human leptin (r-metHuLeptin), or replacement-dose r-metHuLeptin designed to maintain serum leptin at levels similar to those in the fed state. Replacement-dose r-metHuLeptin administered during fasting prevents the starvation-induced changes in the hypothalamic-pituitary-gonadal axis and, in part, the hypothalamic-pituitary-thyroid axis and IGF-1 binding capacity in serum. Thus, in normal men, the fall in leptin with fasting may be both necessary and sufficient for the physiologic adaptations of these axes, which require leptin levels above a certain threshold for activation. In contrast to findings in mice, fasting-induced changes in the hypothalamic-pituitary-adrenal, renin-aldosterone, and growth hormone–IGF-1 axes as well as fuel utilization may be independent of leptin in humans. The role of leptin in normalizing several starvation-induced neuroendocrine changes may have important implications for the pathophysiology and treatment of eating disorders and obesity.
Jean L. Chan, Kathleen Heist, Alex M. DePaoli, Johannes D. Veldhuis, Christos S. Mantzoros
Rapid oscillations of visceral lipolysis have been reported. To examine the putative role of the CNS in oscillatory lipolysis, we tested the effects of β3-blockade on pulsatile release of FFAs. Arterial blood samples were drawn at 1-minute intervals for 120 minutes from fasted, conscious dogs (n = 7) during the infusion of saline or bupranolol (1.5 μg/kg/min), a high-affinity β3-blocker. FFA and glycerol time series were analyzed and deconvolution analysis was applied to estimate the rate of FFA release. During saline infusion FFAs and glycerol oscillated in phase at about eight pulses/hour. Deconvolution analysis showed bursts of lipolysis (nine pulses/hour) with time-dependent variation in burst frequency. Bupranolol completely removed rapid FFA and glycerol oscillations. Despite removal of lipolytic bursts, plasma FFAs (0.31 mM) and glycerol (0.06 mM) were not totally suppressed and deconvolution analysis revealed persistent non-oscillatory lipolysis (0.064 mM/min). These results show that lipolysis in the fasting state consists of an oscillatory component, which appears to be entirely dependent upon sympathetic innervation of the adipose tissue, and a non-oscillatory, constitutive component, which persists despite β3-blockade. The extinction of lipid fuel bursts by β3-blockade implies a role for the CNS in the maintenance of cyclic provision of lipid fuels.
Katrin Hücking, Marianthe Hamilton-Wessler, Martin Ellmerer, Richard N. Bergman
Shouhong Xuan, Tadahiro Kitamura, Jun Nakae, Katerina Politi, Yoshiaki Kido, Peter E. Fisher, Manrico Morroni, Saverio Cinti, Morris F. White, Pedro L. Herrera, Domenico Accili, Argiris Efstratiadis
Kathrin Maedler, Pavel Sergeev, Frédéric Ris, José Oberholzer, Helen I. Joller-Jemelka, Giatgen A. Spinas, Nurit Kaiser, Philippe A. Halban, Marc Y. Donath
Shoshana Yakar, Clifford J. Rosen, Wesley G. Beamer, Cheryl L. Ackert-Bicknell, Yiping Wu, Jun-Li Liu, Guck T. Ooi, Jennifer Setser, Jan Frystyk, Yves R. Boisclair, Derek LeRoith