Anterior pituitary somatotropes are important metabolic sensors responding to leptin by secreting growth hormone (GH). However, reduced leptin signals caused by fasting have not always correlated with reduced serum GH. Reports show that fasting may stimulate or reduce GH secretion, depending on the species. Mechanisms underlying these distinct somatotrope responses to fasting remain unknown. To define the somatotrope response to decreased leptin signaling we examined markers of somatotrope function over different time periods of fasting. Male and mice were fasted for 24 and 48 h, with female mice fasted for 24 h compared to fed ad libitum controls. Body weight and serum glucose were reduced in both males and females, but, unexpectedly, serum leptin was reduced only in males. Furthermore, in males serum GH levels showed a biphasic response with significant reductions at 24 h followed by a significant rise at 48 h, which coincided with the rise in serum ghrelin levels. In contrast, females showed an increase in serum GH at 24. We then explored mechanisms underlying the differential somatotrope responses seen in males and observed that pituitary levels of Gh mRNA increased, with no distinction between acute and prolonged fasting. By contrast, the Ghrhr mRNA (encoding GH releasing hormone receptor) and the Ghsr mRNA (encoding the ghrelin receptor) were both greatly increased at prolonged fasting times coincident with increased serum GH. These findings show sex differences in the somatotrope and adipocyte responses to fasting and support an adaptive role for somatotropes in males in response to multiple metabolic signals.
Tiffany K. Miles, Ana Rita Silva Moreira, Melody Allensworth-James, Angela Odle, Anessa Haney, Angus MacNicol, Melanie MacNicol, and Gwen V Childs
Weihua Liu, Yuqiang Ji, Haiping Chu, Mo Wang, Bin Yang, and Chunyan Yin
This study investigated the effects of Wnt5a/caveolin/JNK signaling pathway and SFRP5 protein on ox-LDL-induced apoptosis of HUVEC cells. The difference of serological indexes between healthy average weight and obese children and the expression of Wnt 5a and SFRP5 was detected by clinical examination, and the correlation between serum SFRP5, Wnt 5a and the vascular endothelial injury was detected. HUVEC cells were induced by ox-LDL to construct an endothelial injury model, siRNA-transfected cells were used to construct down-regulated SFRP5 and Wnt 5A expression groups, and recombination methods were used to construct up-regulated Wnt5a and SFRP5 expression groups. The expression of Wnt 5a, caveolin-1, JNK and apoptosis-related proteins under different treatments were detected by the Western blot method, and apoptosis was detected by flow cytometry. Serological results showed that the level of Sfrp5 in obese children was significantly lower than that in healthy children, and the level of Wnt5a was significantly higher than that in healthy children. Moreover, Ln Sfrp5 was significantly negatively correlated with Ang-2 in blood circulation, ICAM-1 and E-selectin selectin, but not with VCAM-1. When Wnt5a was up-regulated, the expression of caveolin-1 and JNK increased significantly, Bcl-2 decreased significantly, and the apoptotic rate increased significantly. Nevertheless, when Sfrp5 expression was up-regulated, the result was the opposite. SFRP5 and Wnt5a are involved in the vascular endothelial injury. Wnt5a can promote apoptosis of HUVEC cells through Wnt5a/JNK/Caveolin-1 pathway, while SFRP5 can inhibit apoptosis by interfering with this pathway.
Russell T Turner, Adam J Branscum, Carmen P Wong, Urszula T Iwaniec, and Emily Morey-Holton
The gravitostat is purported to function as a leptin-independent, osteocyte-dependent mechanism for regulation of energy balance. If correct, reduced activation of gravitostat signaling caused by prolonged sitting may contribute to obesity. The gravitostat concept is supported by reduced body mass in rodents following surgical implantation of weighted capsules. However, the procedure induces a confounding injury response. We therefore sought to confirm a gravitostat by decreasing (microgravity and simulated microgravity) or increasing (simulated gravity) weight using less invasive models (spaceflight, hindlimb unloading and centrifugation). We also evaluated changes in weight following non-surgical injury (radiation). Male rats (Wistar, Sprague-Dawley and Fischer-344) ranging in age from 5-12 weeks at launch and flown for 4-19 days in low Earth orbit exhibited slightly lower (4-day flight) or no difference (all other studies) in weight compared to ground controls. Rats subjected to inflight (1.0 G) or ground (1.05 G and 1.56 G) centrifugation during a 19-day mission did not differ in weight. In female rats (Fischer-344), spaceflight (14 days) did not alter ovariectomy-induced weight gain. Finally, hindlimb unloading resulted in weight loss in lean and obese mice. The aforementioned findings are inconsistent with outcomes predicted by a gravitostat; namely, increased mass during weightlessness and decreased mass when subjected to <1 G simulated gravity. Injury (dose-associated graded increases in radiation) mimicked the leptin-independent weight changes attributed to a gravitostat. Taken together, these findings do not support gravitostat regulation of energy balance and suggest injury/stress as an alternative mechanism for weight loss induced by weighted capsules.
Bushra Taqui, Farzad Asadi, Evangelina Capobianco, Daniel Barry Hardy, Alicia Jawerbaum, and Edith Juliana Arany
Maternal diabetes impairs fetal development and increases the risk of metabolic diseases in the offspring. Previously, we demonstrated that maternal dietary supplementation with 6% of olive oil prevents diabetes-induced embryo and fetal defects, in part, through the activation of peroxisome proliferator-activated receptors (PPARs). In this study, we examined the effects of this diet on neonatal and adult pancreatic development in male and female offspring of mothers affected with pre-gestational diabetes. A mild diabetic model was developed by injecting neonatal rats with streptozotocin (90 mg/kg). During pregnancy, these dams were fed a chow diet supplemented or not with 6% olive oil. Offspring pancreata was examined at day 2 and 5 months of age by immunohistochemistry followed by morphometric analysis to determine number of islets, α and β cell clusters and β-cell mass. At 5 months, male offspring of diabetic mothers had reduced β-cell mass that was prevented by maternal supplementation with olive oil. PPARα and PPARγ were localized mainly in α cells and PPARβ/δ in both α and β cells. Although Pparβ/δ and Pparγ RNA expression showed reduction in 5-month-old male offspring of diabetic rats, Pparβ/δ expression returned to control levels after olive-oil supplementation. Interestingly, in vitro exposure to oleic acid (major component of olive oil) and natural PPAR agonists such as LTB4, CPC and 15dPGJ2 also significantly increased expression of all Ppars in αTC1–6 cells. However, only oleic acid and 15dPGJ2 increased insulin and Pdx-1 expression in INS-1E cells suggesting a protective role in β-cells. Olive oil may be considered a dietary supplement to improve islet function in offspring of affected mothers with pre-gestational diabetes.
Chaoyi Zhang, Qianli Zhang, Zhihong Huang, and Quan Jiang
Adropin plays a role in the maintenance of energy homeostasis, insulin resistance prevention, and impaired glucose tolerance. However, the molecular mechanisms by which adropin affects hepatic glucose and lipid metabolism in vitro are not entirely understood. This study intended to examine the roles and underlying mechanisms of adropin in glucose and lipid metabolism in Nile tilapia. In primary cultured tilapia hepatocytes, adropin significantly attenuated oleic acid (OA)-induced glucose output and reduced the activities and mRNA expression of cytosolic phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase), which are involved in gluconeogenesis. In contrast, adropin facilitated glucose uptake activity via glucose transporter 1 (Glut1) upregulation in OA-treated hepatocytes. One-week of adropin treatment reduced the hepatic total lipid accumulation in OA-fed tilapia without changes in body weight. Subsequent studies revealed that adropin suppressed OA-induced intracellular triglyceride accumulation and decreased the expression of genes and proteins involved in lipid metabolisms such as sterol regulatory element-binding protein-1c (SREBP-1c), acetyl-CoA carboxylase α (ACCα) and CD36, but upregulated peroxisome proliferator-activated receptor α (PPARα) levels. In parallel studies, however, adropin had no detectable effects on fatty acid-binding protein 4 (Fabp4) and carnitine palmitoyltransferase 1α (Cpt1α) mRNA expression. Furthermore, adropin treatment dose-dependently increased the phosphorylation level of AMP-activated protein kinase (AMPK). Suppression of AMPK by compound C or AMPKα1 siRNA blocked adropin-induced decreases in the mature form of SREBP-1c expression, glucose output, and intracellular triglyceride content in OA-treated hepatocytes. These findings suggest that teleost adropin could suppress hepatic gluconeogenesis and triglyceride accumulation via a mechanism dependent on AMPK signalling.
Qinglei Yin, Liyun Shen, Yicheng Qi, Dalong Song, Lei Ye, Ying Peng, Yanqiu Wang, Zhou Jin, Guang Ning, Weiqing Wang, Dongping Lin, and Shu Wang
SIRT1, a class III histone/protein deacetylase (HDAC), has been associated with autoimmune diseases. There is a paucity of data about the role of SIRT1 in Graves’ disease. The aim of this study was to investigate the role of SIRT1 in the pathogenesis of GD. Here, we showed that SIRT1 expression and activity were significantly decreased in GD patients compared with healthy controls. The NF-κB pathway was activated in the peripheral blood of GD patients. The reduced SIRT1 levels correlated strongly with clinical parameters. In euthyroid patients, SIRT1 expression was markedly upregulated and NF-κB downstream target gene expression was significantly reduced. SIRT1 inhibited the NF-κB pathway activity by deacetylating P65. These results demonstrate that reduced SIRT1 expression and activity contribute to the activation of the NF-κB pathway and may be involved in the pathogenesis of GD.
Pauline Campos, Jamie J Walker, and Patrice Mollard
In most species, survival relies on the hypothalamic control of endocrine axes that regulate critical functions such as reproduction, growth, and metabolism. For decades, the complexity and inaccessibility of the hypothalamic–pituitary axis has prevented researchers from elucidating the relationship between the activity of endocrine hypothalamic neurons and pituitary hormone secretion. Indeed, the study of central control of endocrine function has been largely dominated by ‘traditional’ techniques that consist of studying in vitro or ex vivo isolated cell types without taking into account the complexity of regulatory mechanisms at the level of the brain, pituitary and periphery. Nowadays, by exploiting modern neuronal transfection and imaging techniques, it is possible to study hypothalamic neuron activity in situ, in real time, and in conscious animals. Deep-brain imaging of calcium activity can be performed through gradient-index lenses that are chronically implanted and offer a ‘window into the brain’ to image multiple neurons at single-cell resolution. With this review, we aim to highlight deep-brain imaging techniques that enable the study of neuroendocrine neurons in awake animals whilst maintaining the integrity of regulatory loops between the brain, pituitary and peripheral glands. Furthermore, to assist researchers in setting up these techniques, we discuss the equipment required and include a practical step-by-step guide to performing these deep-brain imaging studies.
Marianna Minnetti, Valeria Hasenmajer, Riccardo Pofi, Mary Anna Venneri, Krystallenia I Alexandraki, and Andrea M Isidori
The circadian rhythm derives from the integration of many signals that shape the expression of clock-related genes in a 24-h cycle. Biological tasks, including cell proliferation, differentiation, energy storage, and immune regulation, are preferentially confined to specific periods. A gating system, supervised by the central and peripheral clocks, coordinates the endogenous and exogenous signals and prepares for transition to activities confined to periods of light or darkness. The fluctuations of cortisol and its receptor are crucial in modulating these signals. Glucocorticoids and the autonomous nervous system act as a bridge between the suprachiasmatic master clock and almost all peripheral clocks. Additional peripheral synchronizing mechanisms including metabolic fluxes and cytokines stabilize the network. The pacemaker is amplified by peaks and troughs in cortisol and their response to food, activity, and inflammation. However, when the glucocorticoid exposure pattern becomes chronically flattened at high- (as in Cushing’s syndrome) or low (as in adrenal insufficiency) levels, the system fails. While endocrinologists are well aware of cortisol rhythm, too little attention has been given to interventions aimed at restoring physiological cortisol fluctuations in adrenal disorders. However, acting on glucocorticoid levels may not be the only way to restore clock-related activities. First, a counterregulatory mechanism on the glucocorticoid receptor itself controls signal transduction, and second, melatonin and/or metabolically active drugs and nutrients could also be used to modulate the clock. All these aspects are described herein, providing some insights into the emerging role of chronopharmacology, focusing on glucocorticoid excess and deficiency disorders.
Gregory S Y Ong, Timothy J Cole, Gregory H Tesch, James Morgan, Jennifer K Dowling, Ashley Mansell, Peter J Fuller, and Morag J Young
MR activation in macrophages is critical for the development of cardiac inflammation and fibrosis. We previously showed that MR activation modifies macrophage pro-inflammatory signalling, changing the cardiac tissue response to injury via both direct gene transcription and JNK/AP-1 second messenger pathways. In contrast, MR-mediated renal electrolyte homeostasis is critically determined by DNA-binding-dependent processes. Hence, ascertaining the relative contribution of MR actions via DNA binding or alternative pathways on macrophage behaviour and cardiac inflammation may provide therapeutic opportunities which separate the cardioprotective effects of MR antagonists from their undesirable renal potassium-conserving effects. We developed new macrophage cell lines either lacking MR or harbouring a mutant MR incapable of DNA binding. Western blot analysis demonstrated that MR DNA binding is required for lipopolysaccharide (LPS), but not phorbol 12-myristate-13-acetate (PMA), induction of the MAPK/pJNK pathway in macrophages. Quantitative RTPCR for pro-inflammatory and pro-fibrotic targets revealed subsets of LPS- and PMA-induced genes that were either enhanced or repressed by the MR via actions that do not always require direct MR-DNA binding. Analysis of the MR target gene and profibrotic factor MMP12 identified promoter elements that are regulated by combined MR/MAPK/JNK signalling. Evaluation of cardiac tissue responses to an 8-day DOC/salt challenge in mice selectively lacking MR DNA-binding in macrophages demonstrated levels of inflammatory markers equivalent to WT, indicating non-DNA binding-dependent MR signalling in macrophages is sufficient for DOC/salt-induced tissue inflammation. Our data demonstrate that the MR regulates a macrophage pro-inflammatory phenotype and cardiac tissue inflammation, partially via pathways that do not require DNA binding.
Katherine N Makowski, Michael J Kreisman, Richard B McCosh, Ali A Raad, and Kellie M Breen
Peripheral immune/inflammatory challenges rapidly disrupt reproductive neuroendocrine function. This inhibition is considered to be centrally mediated via suppression of gonadotropin-releasing hormone secretion, yet the neural pathway(s) for this effect remains unclear. We tested the hypothesis that interleukin-1β inhibits pulsatile luteinizing hormone secretion in female mice via inhibition of arcuate kisspeptin cell activation, a population of neurons considered to be the gonadotropin-releasing hormone pulse generator. In the first experiment, we determined that the inhibitory effect of peripheral interleukin-1β on luteinizing hormone secretion was enhanced by estradiol. We next utilized serial sampling and showed that interleukin-1β reduced the frequency of luteinizing hormone pulses in ovariectomized female mice treated with estradiol. The interleukin-1β-induced suppression of pulse frequency was associated with reduced kisspeptin cell activation, as determined by c-Fos coexpression, but not as a result of impaired responsiveness to kisspeptin challenge. Together, these data suggest an inhibitory action of interleukin-1β upstream of kisspeptin receptor activation. We next tested the hypothesis that estradiol enhances the activation of brainstem nuclei responding to interleukin-1β. We determined that the expression of interleukin-1 receptor was elevated within the brainstem following estradiol. Interleukin-1β induced c-Fos in the area postrema, ventrolateral medulla, and nucleus of the solitary tract; however, the response was not increased by estradiol. Collectively, these data support a neural mechanism whereby peripheral immune/inflammatory stress impairs reproductive neuroendocrine function via inhibition of kisspeptin cell activation and reduced pulsatile luteinizing hormone secretion. Furthermore, these findings implicate the influence of estradiol on peripherally mediated neural pathways such as those activated by peripheral cytokines.