title: Reductions in hypothalamic Gfap expression, glial cells and α-tanycytes in lean and hypermetabolic Gnasxl-deficient mice.
abstract: BACKGROUND
  Neuronal and glial differentiation in the murine hypothalamus is not complete at birth, but continues over the first two weeks postnatally. Nutritional status and Leptin deficiency can influence the maturation of neuronal projections and glial patterns, and hypothalamic gliosis occurs in mouse models of obesity. Gnasxl constitutes an alternative transcript of the genomically imprinted Gnas locus and encodes a variant of the signalling protein Gαs, termed XLαs, which is expressed in defined areas of the hypothalamus. Gnasxl-deficient mice show postnatal growth retardation and undernutrition, while surviving adults remain lean and hypermetabolic with increased sympathetic nervous system (SNS) activity. Effects of this knock-out on the hypothalamic neural network have not yet been investigated.
  
  
  RESULTS
  RNAseq analysis for gene expression changes in hypothalami of Gnasxl-deficient mice indicated Glial fibrillary acid protein (Gfap) expression to be significantly down-regulated in adult samples. Histological analysis confirmed a reduction in Gfap-positive glial cell numbers specifically in the hypothalamus. This reduction was observed in adult tissue samples, whereas no difference was found in hypothalami of postnatal stages, indicating an adaptation in adult Gnasxl-deficient mice to their earlier growth phenotype and hypermetabolism. Especially noticeable was a loss of many Gfap-positive α-tanycytes and their processes, which form part of the ependymal layer that lines the medial and dorsal regions of the 3(rd) ventricle, while β-tanycytes along the median eminence (ME) and infundibular recesses appeared unaffected. This was accompanied by local reductions in Vimentin and Nestin expression. Hypothalamic RNA levels of glial solute transporters were unchanged, indicating a potential compensatory up-regulation in the remaining astrocytes and tanycytes.
  
  
  CONCLUSIONS
  Gnasxl deficiency does not directly affect glial development in the hypothalamus, since it is expressed in neurons, and Gfap-positive astrocytes and tanycytes appear normal during early postnatal stages. The loss of Gfap-expressing cells in adult hypothalami appears to be a consequence of the postnatal undernutrition, hypoglycaemia and continued hypermetabolism and leanness of Gnasxl-deficient mice, which contrasts with gliosis observed in obese mouse models. Since α-tanycytes also function as adult neural progenitor cells, these findings might indicate further developmental abnormalities in hypothalamic formations of Gnasxl-deficient mice, potentially including neuronal composition and projections.
authors.affiliation: Integrative Genomics of Ageing Group, Institute of Integrative Biology, University of Liverpool, Crown Str, Liverpool, L69 7ZB, UK.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Holmes
authors.affiliation: Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Crown Str, Liverpool, L69 3BX, UK.
authors.forename: Shi Quan
authors.initials: SQ
authors.lastname: Wong
authors.affiliation: Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Crown Str, Liverpool, L69 3BX, UK.
authors.forename: Michela
authors.initials: M
authors.lastname: Pulix
authors.affiliation: Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Crown Str, Liverpool, L69 3BX, UK.
authors.forename: Kirsty
authors.initials: K
authors.lastname: Johnson
authors.affiliation: Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Crown Str, Liverpool, L69 3BX, UK.
authors.forename: Niamh S
authors.initials: NS
authors.lastname: Horton
authors.affiliation: Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Crown Str, Liverpool, L69 3BX, UK.
authors.forename: Patricia
authors.initials: P
authors.lastname: Thomas
authors.affiliation: Integrative Genomics of Ageing Group, Institute of Integrative Biology, University of Liverpool, Crown Str, Liverpool, L69 7ZB, UK. jp@senescence.info.
authors.forename: João Pedro
authors.initials: JP
authors.lastname: de Magalhães
authors.affiliation: Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Crown Str, Liverpool, L69 3BX, UK. a.plagge@liverpool.ac.uk.
authors.forename: Antonius
authors.initials: A
authors.lastname: Plagge
mesh_terms: D000375:Aging / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000378:metabolism; D002452:Cell Count; D002864:Chromogranins; D063928:Ependymoglial Cells / Q000378:metabolism*; D005260:Female; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000172:deficiency / Q000378:metabolism*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D056426:Genetic Loci; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism*; D007031:Hypothalamus / Q000378:metabolism*; D051379:Mice; D064231:Nestin / Q000378:metabolism; D009457:Neuroglia / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013493:Suprachiasmatic Nucleus / Q000378:metabolism; D013851:Thinness / Q000378:metabolism*
chemical_list: D002864:Chromogranins; D005904:Glial Fibrillary Acidic Protein; D064231:Nestin; D012333:RNA, Messenger; C528900:glial fibrillary astrocytic protein, mouse; C498642:Gnas protein, mouse; D019205:GTP-Binding Protein alpha Subunits, Gs
keywords: Energy homoeostasis; Genomic imprinting; Gfap; Glia; Gnas; Hypothalamus; RNAseq; Tanycyte