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
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
Timothy G. Butler, Jeff Schwartz, I. Caroline McMillen
Kathrin Maedler, Pavel Sergeev, Frédéric Ris, José Oberholzer, Helen I. Joller-Jemelka, Giatgen A. Spinas, Nurit Kaiser, Philippe A. Halban, Marc Y. Donath
Lara B. Pupim, Paul J. Flakoll, John R. Brouillette, Deanna K. Levenhagen, Raymond M. Hakim, T. Alp Ikizler
Norma Fox, Greg Priestley, Thalia Papayannopoulou, Kenneth Kaushansky
Obesity is the result of an imbalance between energy intake and energy expenditure. Using high-density DNA microarrays and Northern analyses, we demonstrated that the activation of a nutrient-sensing pathway, the hexosamine biosynthesis pathway (HBP), rapidly decreased the expression of a cluster of nuclear-encoded mitochondrial genes involved in skeletal muscle oxidative phosphorylation. Conversely, the expression of uncoupling protein-1 and of the same mitochondrial genes was increased in brown adipose tissue. Most important, these transcriptional changes were accompanied by a marked decrease in whole-body energy expenditure. Short-term overfeeding replicated this transcriptional pattern, suggesting that this adaptation to nutrient abundance occurs under physiological conditions. Thus, the activation of the HBP by nutrients represents a biochemical link between nutrient availability, mitochondrial proteins, and energy expenditure, and it is likely to play an important role in the regulation of energy balance.
Silvana Obici, Jiali Wang, Rahena Chowdury, Zhaohui Feng, Uma Siddhanta, Kimyata Morgan, Luciano Rossetti