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      Progesterone Synthesis in the Nervous System: Implications for Myelination and Myelin Repair

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          Abstract

          Progesterone is well known as a female reproductive hormone and in particular for its role in uterine receptivity, implantation, and the maintenance of pregnancy. However, neuroendocrine research over the past decades has established that progesterone has multiple functions beyond reproduction. Within the nervous system, its neuromodulatory and neuroprotective effects are much studied. Although progesterone has been shown to also promote myelin repair, its influence and that of other steroids on myelination and remyelination is relatively neglected. Reasons for this are that hormonal influences are still not considered as a central problem by most myelin biologists, and that neuroendocrinologists are not sufficiently concerned with the importance of myelin in neuron functions and viability. The effects of progesterone in the nervous system involve a variety of signaling mechanisms. The identification of the classical intracellular progesterone receptors as therapeutic targets for myelin repair suggests new health benefits for synthetic progestins, specifically designed for contraceptive use and hormone replacement therapies. There are also major advantages to use natural progesterone in neuroprotective and myelin repair strategies, because progesterone is converted to biologically active metabolites in nervous tissues and interacts with multiple target proteins. The delivery of progesterone however represents a challenge because of its first-pass metabolism in digestive tract and liver. Recently, the intranasal route of progesterone administration has received attention for easy and efficient targeting of the brain. Progesterone in the brain is derived from the steroidogenic endocrine glands or from local synthesis by neural cells. Stimulating the formation of endogenous progesterone is currently explored as an alternative strategy for neuroprotection, axonal regeneration, and myelin repair.

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          Most cited references 223

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          Biology of oligodendrocyte and myelin in the mammalian central nervous system.

          Oligodendrocytes, the myelin-forming cells of the central nervous system (CNS), and astrocytes constitute macroglia. This review deals with the recent progress related to the origin and differentiation of the oligodendrocytes, their relationships to other neural cells, and functional neuroglial interactions under physiological conditions and in demyelinating diseases. One of the problems in studies of the CNS is to find components, i.e., markers, for the identification of the different cells, in intact tissues or cultures. In recent years, specific biochemical, immunological, and molecular markers have been identified. Many components specific to differentiating oligodendrocytes and to myelin are now available to aid their study. Transgenic mice and spontaneous mutants have led to a better understanding of the targets of specific dys- or demyelinating diseases. The best examples are the studies concerning the effects of the mutations affecting the most abundant protein in the central nervous myelin, the proteolipid protein, which lead to dysmyelinating diseases in animals and human (jimpy mutation and Pelizaeus-Merzbacher disease or spastic paraplegia, respectively). Oligodendrocytes, as astrocytes, are able to respond to changes in the cellular and extracellular environment, possibly in relation to a glial network. There is also a remarkable plasticity of the oligodendrocyte lineage, even in the adult with a certain potentiality for myelin repair after experimental demyelination or human diseases.
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            NG2-expressing glial progenitor cells: an abundant and widespread population of cycling cells in the adult rat CNS.

             M. Dawson (2003)
            Glial progenitor cells of the developing CNS committed to the oligodendrocyte lineage (OPCs) express the chondroitin sulfate proteoglycan, NG2. A proportion of OPCs fail to differentiate past the stage at which they express NG2 and the lipid antigen O4 and persist in the adult CNS in a phenotypically immature form. However, the physiological function of NG2(+) cells in the adult CNS is unknown. Using antibodies against NG2 we show that NG2 is expressed by a distinct cell population in the mature CNS with the homogeneous antigenic phenotype of oligodendrocyte progenitors. The morphology of NG2(+) OPCs varies from region to region, reflecting the different structural environments, but they appear to represent a homogeneous population within any one gray or white matter region. A study of nine CNS regions showed that NG2(+) OPCs are numerous throughout the CNS and numbers in the white matter are only 1.5 times that in the gray. Whereas the ratio of OPCs to myelinating oligodendrocytes in the spinal cord gray and white matter approximates 1:4, gray matter regions of the forebrain have a 1:1 ratio, a phenomenon that will have consequences for oligodendrocyte replacement following demyelination. BrdU incorporation experiments showed that NG2(+) cells are the major dividing cell population of the adult rat CNS. Since very little apoptosis was detected and BrdU became increasingly present in oligodendrocytes after a 10-day pulse chase, with a concomitant decrease in NG2(+) BrdU incorporating cells, we suggest that the size of the oligodendrocyte population may actually increase during adult life.
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              Mice lacking progesterone receptor exhibit pleiotropic reproductive abnormalities.

              Although progesterone has been recognized as essential for the establishment and maintenance of pregnancy, this steroid hormone has been recently implicated to have a functional role in a number of other reproductive events. The physiological effects of progesterone are mediated by the progesterone receptor (PR), a member of the nuclear receptor superfamily of transcription factors. In most cases the PR is induced by estrogen, implying that many of the in vivo effects attributed to progesterone could also be the result of concomitantly administered estrogen. Therefore, to clearly define those physiological events that are specifically attributable to progesterone in vivo, we have generated a mouse model carrying a null mutation of the PR gene using embryonic stem cell/gene targeting techniques. Male and female embryos homozygous for the PR mutation developed normally to adulthood. However, the adult female PR mutant displayed significant defects in all reproductive tissues. These included an inability to ovulate, uterine hyperplasia and inflammation, severely limited mammary gland development, and an inability to exhibit sexual behavior. Collectively, these results provide direct support for progesterone's role as a pleiotropic coordinator of diverse reproductive events that together ensure species survival.
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                Author and article information

                Journal
                Front Neurosci
                Front. Neurosci.
                Frontiers in Neuroscience
                Frontiers Research Foundation
                1662-4548
                1662-453X
                05 December 2011
                08 February 2012
                2012
                : 6
                Affiliations
                1UMR 788, INSERM and University Paris-Sud Kremlin-Bicêtre, France
                2M et P Pharma AG Emmetten, Switzerland
                Author notes

                Edited by: Kazuyoshi Tsutsui, Waseda University, Japan

                Reviewed by: Delia Belelli, Ninewells Hospital and Medical School, UK; Nathalie A. Compagnone, Innovative Concept in Drug Development, France

                *Correspondence: Michael Schumacher, INSERM UMR 788, 80, rue du Général Leclerc, 94276 Kremlin-Bicêtre, France. e-mail: michael.schumacher@ 123456inserm.fr

                Present address: Nathalie Gago, Facultad de Medicina, Universidad Central de Venezuela, Caracas, Venezuela

                This article was submitted to Frontiers in Neuroendocrine Science, a specialty of Frontiers in Neuroscience.

                Article
                10.3389/fnins.2012.00010
                3274763
                22347156
                Copyright © 2012 Schumacher, Hussain, Gago, Oudinet, Mattern and Ghoumari.

                This is an open-access article distributed under the terms of the Creative Commons Attribution Non Commercial License, which permits non-commercial use, distribution, and reproduction in other forums, provided the original authors and source are credited.

                Page count
                Figures: 4, Tables: 1, Equations: 0, References: 242, Pages: 22, Words: 20844
                Categories
                Neuroscience
                Review Article

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