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      Pseudo-Starvation Driven Energy Expenditure Negatively Affects Ovarian Follicle Development

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          Abstract

          In the present investigation, we examined whether a change in whole body energy fluxes could affect ovarian follicular development, employing mice ectopically expressing uncoupling protein 1 in skeletal muscle (UCP1-TG). Female UCP1-TG and wild-type (WT) mice were dissected at the age of 12 weeks. Energy intake and expenditure, activity, body weight and length, and body composition were measured. Plasma insulin, glucose, leptin, plasma fibroblast growth factor 21 (FGF21) and plasma insulin-like growth factor 1 (IGF1) levels were analyzed and ovarian follicle and corpus luteum numbers were counted. IGF1 signaling was analyzed by immunohistochemical staining for the activation of insulin receptor substrate 1/2 (IRS1/2) and AKT. UCP1-TG female mice had increased energy expenditure, reduced body size, maintained adiposity, and decreased IGF1 concentrations compared to their WT littermates, while preantral and antral follicle numbers were reduced by 40% and 60%, respectively. Corpora lutea were absent in 40% of the ovaries of UCP1-TG mice. Phospho-IRS1, phospho-AKT -Ser473 and -Thr308 immunostaining was present in the granulosa cells of antral follicles in WT ovaries, but faint to absent in the antral follicles of UCP1-TG mice. In conclusion, the reduction in circulating IGF1 levels due to the ectopic expression of UCP1 is associated with reduced immunostaining of the IRS1-PI3/AKT pathway, which may negatively affect ovarian follicle development and ovulation.

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          Most cited references63

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          Caloric restriction.

          Restricting the intake of calories has been practiced as a method for increasing both the length and quality of life for over 500 years. Experimental work confirming the success of this approach in animals has accumulated over the last 100 years. Lifelong caloric restriction (CR) may extend life by up to 50% in rodents, with progressively less impact the later in life it is started. This effect is matched by profound impacts on age related diseases including reduced risk of cancer, neurodegenerative disorders, autoimmune disease, cardiovascular disease and type II diabetes mellitus. The disposable soma theory of ageing suggests that CR evolved as a somatic protection response to enable animals to survive periods of food shortage. The shutdown of reproductive function during CR is consistent with this suggestion, but other features of the phenomenon are less consistent with this theory, and some have suggested that in rodents it may be mostly an artifact of domestication. CR induces profound effects on animals at all levels from the transcriptome to whole animal physiology and behavior. Animals under CR lose weight which is disproportionately contributed to by white adipose tissue. Generally animals on CR change their activity patterns so that they are more active prior to food delivery each day but total activity may be unchanged or reduced. Considerable debate has occurred over the effects of CR on resting metabolic rate (RMR). Total RMR declines, but as body mass and body composition also change it is unclear whether metabolism at the tissue level also declines, is unchanged or even increases. Body temperature universally decreases. Hunger is increased and does not seem to abate even with very long term restriction. Circulating adipokines are reduced reflecting the reduction in white adipose tissue (WAT) mass under restriction and there is a large reduction in circulating insulin and glucose levels. There are profound tissue level changes in metabolism with a generalized shift from carbohydrate to fat metabolism. Four pathways have been implicated in mediating the CR effect. These are the insulin like growth factor (IGF-1)/insulin signaling pathway, the sirtuin pathway, the adenosine monophosphate (AMP) activated protein kinase (AMPK) pathway and the target of rapamycin (TOR) pathway. These different pathways may interact and may all play important roles mediating different aspects of the response. Exactly how they generate the health benefits remains open for debate, however CR results in reduced oxidative stress and enhanced autophagy, both of which could be essential components of the beneficial effects. Most data about the effects of CR in mammals comes from work on rodents. There is limited work on non-human primates that shows promising effects and one randomized controlled trial in humans where physiological markers of the CR response are consistent with the responses in mice and rats. There are also populations of humans voluntarily restricting themselves. Humans on long term restriction report similar negative side effects to those observed in animals - perpetual hunger, reduced body temperature leading to a feeling of being cold, and diminished libido. Considerable effort has been directed in recent years to find drugs that mimic the CR response. Promising candidates are those that intersect with the critical signaling pathways identified above and include biguanides such as metformin that target the insulin signaling pathway, stilbenes (e.g. resveratrol) that affect sirtuin activity and drugs such as rapamycin that interact with mTOR signaling. Whether it will ever be possible to find drugs that capture the health benefits of CR without the negative side-effects remains unclear. Moreover, even if such drugs are developed how the current licensing system for drug use in western societies would cope with them may be a further obstacle to their use. Copyright © 2011 Elsevier Ltd. All rights reserved.
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            Somatotropic signaling: trade-offs between growth, reproductive development, and longevity.

            Growth hormone (GH) is a key determinant of postnatal growth and plays an important role in the control of metabolism and body composition. Surprisingly, deficiency in GH signaling delays aging and remarkably extends longevity in laboratory mice. In GH-deficient and GH-resistant animals, the "healthspan" is also extended with delays in cognitive decline and in the onset of age-related disease. The role of hormones homologous to insulin-like growth factor (IGF, an important mediator of GH actions) in the control of aging and lifespan is evolutionarily conserved from worms to mammals with some homologies extending to unicellular yeast. The combination of reduced GH, IGF-I, and insulin signaling likely contributes to extended longevity in GH or GH receptor-deficient organisms. Diminutive body size and reduced fecundity of GH-deficient and GH-resistant mice can be viewed as trade-offs for extended longevity. Mechanisms responsible for delayed aging of GH-related mutants include enhanced stress resistance and xenobiotic metabolism, reduced inflammation, improved insulin signaling, and various metabolic adjustments. Pathological excess of GH reduces life expectancy in men as well as in mice, and GH resistance or deficiency provides protection from major age-related diseases, including diabetes and cancer, in both species. However, there is yet no evidence of increased longevity in GH-resistant or GH-deficient humans, possibly due to non-age-related deaths. Results obtained in GH-related mutant mice provide striking examples of mutations of a single gene delaying aging, reducing age-related disease, and extending lifespan in a mammal and providing novel experimental systems for the study of mechanisms of aging.
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              Fibroblast growth factor 21 regulates lipolysis in white adipose tissue but is not required for ketogenesis and triglyceride clearance in liver.

              Fibroblast growth factors (Fgfs) are polypeptide growth factors with diverse functions. Fgf21, a unique member of the Fgf family, is expected to function as a metabolic regulator in an endocrine manner. Hepatic Fgf21 expression was increased by fasting. The phenotypes of hepatic Fgf21 transgenic or knockdown mice and high-fat, low-carbohydrate ketogenic diet-fed mice suggests that Fgf21 stimulates lipolysis in the white adipose tissue during normal feeding and is required for ketogenesis and triglyceride clearance in the liver during fasting. However, the physiological roles of Fgf21 remain unclear. To elucidate the physiological roles of Fgf21, we generated Fgf21 knockout (KO) mice by targeted disruption. Fgf21 KO mice were viable, fertile, and seemingly normal. Food intake, oxygen consumption, and energy expenditure were also essentially unchanged in Fgf21 KO mice. However, hypertrophy of adipocytes, decreased lipolysis in adipocytes, and decreased blood nonesterified fatty acid levels were observed when Fgf21 KO mice were fed normally. In contrast, increased lipolysis in adipocytes and increased blood nonesterified fatty acid levels were observed in Fgf21 KO mice by fasting for 24 h, indicating that Fgf21 stimulates lipolysis in the white adipose tissue during feeding but inhibits it during fasting. In contrast, unexpectedly, hepatic triglyceride levels were essentially unchanged in Fgf21 KO mice. In addition, ketogenesis in Fgf21 KO mice was not impaired by fasting for 24 h. The present results indicate that Fgf21 regulates lipolysis in adipocytes in response to the metabolic state but is not required for ketogenesis and triglyceride clearance in the liver.

                Author and article information

                Contributors
                Role: Academic Editor
                Journal
                Int J Mol Sci
                Int J Mol Sci
                ijms
                International Journal of Molecular Sciences
                MDPI
                1422-0067
                30 March 2021
                April 2021
                : 22
                : 7
                : 3557
                Affiliations
                [1 ]National Engineering Research Center for Breeding Swine Industry, College of Animal Science, South China Agricultural University, Guangzhou 510642, China; limeng@ 123456scau.edu.cn
                [2 ]Human and Animal Physiology, Wageningen University, De Elst 1, 6708 WD Wageningen, The Netherlands; shzhaoyu0523@ 123456sina.com (Y.Z.); annelies.bunschoten@ 123456wur.nl (A.B.); jaap.keijer@ 123456wur.nl (J.K.)
                [3 ]German Institute of Human Nutrition in Potsdam-Rehbruecke, Arthur-Scheunert-Allee 114-116, 14558 Nuthetal, Germany; verena.coleman@ 123456dife.de (V.C.); mario.ost@ 123456dife.de (M.O.); anja.voigt@ 123456dife.de (A.V.)
                [4 ]Institute of Nutritional Science, University of Potsdam, 14469 Potsdam, Germany
                Author notes
                [* ]Correspondence: katja.teerds@ 123456wur.nl (K.T.); klaus@ 123456dife.de (S.K.); Tel.: +31-317-485989 (K.T.); +49-33200-88-2326 (S.K.)
                [†]

                These authors contributed equally to this work.

                Author information
                https://orcid.org/0000-0002-9720-7491
                https://orcid.org/0000-0002-0930-1198
                https://orcid.org/0000-0001-8726-185X
                Article
                ijms-22-03557
                10.3390/ijms22073557
                8036485
                33808081
                fa854a56-4bd6-4179-bf5f-1fc77122991e
                © 2021 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 26 February 2021
                : 27 March 2021
                Categories
                Article

                Molecular biology
                ovarian follicular development,igf1,energy metabolism,ucp1,irs1,akt
                Molecular biology
                ovarian follicular development, igf1, energy metabolism, ucp1, irs1, akt

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