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      Brain IGF-1 Receptors Control Mammalian Growth and Lifespan through a Neuroendocrine Mechanism

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          There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

          Abstract

          Mutations that decrease insulin-like growth factor (IGF) and growth hormone signaling limit body size and prolong lifespan in mice. In vertebrates, these somatotropic hormones are controlled by the neuroendocrine brain. Hormone-like regulations discovered in nematodes and flies suggest that IGF signals in the nervous system can determine lifespan, but it is unknown whether this applies to higher organisms. Using conditional mutagenesis in the mouse, we show that brain IGF receptors (IGF-1R) efficiently regulate somatotropic development. Partial inactivation of IGF-1R in the embryonic brain selectively inhibited GH and IGF-I pathways after birth. This caused growth retardation, smaller adult size, and metabolic alterations, and led to delayed mortality and longer mean lifespan. Thus, early changes in neuroendocrine development can durably modify the life trajectory in mammals. The underlying mechanism appears to be an adaptive plasticity of somatotropic functions allowing individuals to decelerate growth and preserve resources, and thereby improve fitness in challenging environments. Our results also suggest that tonic somatotropic signaling entails the risk of shortened lifespan.

          Author Summary

          Using a mouse model relevant for humans, we showed that lifespan can be significantly extended by reducing the signaling selectively of a protein called IGF-I in the central nervous system. This effect occurred through changes in specific neuroendocrine pathways. Dissecting the pathophysiological mechanism, we discovered that IGF receptors in the mammalian brain efficiently steered the development of the somatotropic axis, which in turn affected the individual growth trajectory and lifespan. Our work confirms experimentally that continuously low IGF-I and low growth hormone levels favor extended lifespan and postpone age-related mortality. Together with other recent reports, our results further challenge the view that administration of GH can prevent, or even counteract human aging. This knowledge is important since growth hormone is often prescribed to elderly people in an attempt to compensate the unwanted effects of aging. Growth hormone and IGF-I are also substances frequently used for doping in sports.

          Abstract

          Inactivating IGF receptors in the brain decreased growth hormone and IGF-I, and increased lifespan in healthy mice. Such neuroendocrine longevity could be a physiological response to environment.

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          Most cited references 38

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          Disruption of the glucocorticoid receptor gene in the nervous system results in reduced anxiety.

          The glucocorticoid receptor (Gr, encoded by the gene Grl1) controls transcription of target genes both directly by interaction with DNA regulatory elements and indirectly by cross-talk with other transcription factors. In response to various stimuli, including stress, glucocorticoids coordinate metabolic, endocrine, immune and nervous system responses and ensure an adequate profile of transcription. In the brain, Gr has been proposed to modulate emotional behaviour, cognitive functions and addictive states. Previously, these aspects were not studied in the absence of functional Gr because inactivation of Grl1 in mice causes lethality at birth (F.T., C.K. and G.S., unpublished data). Therefore, we generated tissue-specific mutations of this gene using the Cre/loxP -recombination system. This allowed us to generate viable adult mice with loss of Gr function in selected tissues. Loss of Gr function in the nervous system impairs hypothalamus-pituitary-adrenal (HPA)-axis regulation, resulting in increased glucocorticoid (GC) levels that lead to symptoms reminiscent of those observed in Cushing syndrome. Conditional mutagenesis of Gr in the nervous system provides genetic evidence for the importance of Gr signalling in emotional behaviour because mutant animals show an impaired behavioural response to stress and display reduced anxiety.
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            Mice carrying null mutations of the genes encoding insulin-like growth factor I (Igf-1) and type 1 IGF receptor (Igf1r).

            Newborn mice homozygous for a targeted disruption of insulin-like growth factor gene (Igf-1) exhibit a growth deficiency similar in severity to that previously observed in viable Igf-2 null mutants (60% of normal birthweight). Depending on genetic background, some of the Igf-1(-/-) dwarfs die shortly after birth, while others survive and reach adulthood. In contrast, null mutants for the Igf1r gene die invariably at birth of respiratory failure and exhibit a more severe growth deficiency (45% normal size). In addition to generalized organ hypoplasia in Igf1r(-/-) embryos, including the muscles, and developmental delays in ossification, deviations from normalcy were observed in the central nervous system and epidermis. Igf-1(-/-)/Igf1r(-/-) double mutants did not differ in phenotype from Igf1r(-/-) single mutants, while in Igf-2(-)/Igf1r(-/-) and Igf-1(-/-)/Igf-2(-) double mutants, which are phenotypically identical, the dwarfism was further exacerbated (30% normal size). The roles of the IGFs in mouse embryonic development, as revealed from the phenotypic differences between these mutants, are discussed.
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              The plasticity of aging: insights from long-lived mutants.

              Mutations in genes affecting endocrine signaling, stress responses, metabolism, and telomeres can all increase the life spans of model organisms. These mutations have revealed evolutionarily conserved pathways for aging, some of which appear to extend life span in response to sensory cues, caloric restriction, or stress. Many mutations affecting longevity pathways delay age-related disease, and the molecular analysis of these pathways is leading to a mechanistic understanding of how these two processes--aging and disease susceptibility--are linked.
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                Author and article information

                Contributors
                Role: Academic Editor
                Journal
                PLoS Biol
                pbio
                plbi
                plosbiol
                PLoS Biology
                Public Library of Science (San Francisco, USA )
                1544-9173
                1545-7885
                October 2008
                28 October 2008
                : 6
                : 10
                Affiliations
                [1 ] INSERM U893, Hôpital Saint-Antoine, Paris, France
                [2 ] Université Pierre-et-Marie-Curie, Paris, France
                [3 ] INRA, Nouzilly, France
                [4 ] Service d'Anatomopathologie, Hôpital Saint-Antoine, Paris, France
                [5 ] INSERM U549, Centre Paul Broca, Paris, France
                [6 ] Department of Molecular Neurobiology, Max-Planck Institute of Neurobiology, Munich-Martinsried, Germany
                The Salk Institute, United States of America
                Author notes
                * To whom correspondence should be addressed. E-mail: martin.holzenberger@ 123456inserm.fr
                Article
                08-PLBI-RA-1120R3 plbi-06-10-12
                10.1371/journal.pbio.0060254
                2573928
                18959478
                Copyright: © 2008 Kappeler et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
                Page count
                Pages: 10
                Categories
                Research Article
                Developmental Biology
                Diabetes and Endocrinology
                Genetics and Genomics
                Physiology
                Custom metadata
                Kappeler L, De Magalhaes Filho C, Dupont J, Leneuve P, Cervera P, et al. (2008) Brain IGF-1 receptors control mammalian growth and lifespan through a neuroendocrine mechanism. PLoS Biol 6(10): e254. doi: 10.1371/journal.pbio.0060254

                Life sciences

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