title: Insulin promotes glycogen storage and cell proliferation in primary human astrocytes.
abstract: BACKGROUND
  In the human brain, there are at least as many astrocytes as neurons. Astrocytes are known to modulate neuronal function in several ways. Thus, they may also contribute to cerebral insulin actions. Therefore, we examined whether primary human astrocytes are insulin-responsive and whether their metabolic functions are affected by the hormone.
  
  
  METHODS
  Commercially available Normal Human Astrocytes were grown in the recommended medium. Major players in the insulin signaling pathway were detected by real-time RT-PCR and Western blotting. Phosphorylation events were detected by phospho-specific antibodies. Glucose uptake and glycogen synthesis were assessed using radio-labeled glucose. Glycogen content was assessed by histochemistry. Lactate levels were measured enzymatically. Cell proliferation was assessed by WST-1 assay.
  
  
  RESULTS
  We detected expression of key proteins for insulin signaling, such as insulin receptor β-subunit, insulin receptor substrat-1, Akt/protein kinase B and glycogen synthase kinase 3, in human astrocytes. Akt was phosphorylated and PI-3 kinase activity increased following insulin stimulation in a dose-dependent manner. Neither increased glucose uptake nor lactate secretion after insulin stimulation could be evidenced in this cell type. However, we found increased insulin-dependent glucose incorporation into glycogen. Furthermore, cell numbers increased dose-dependently upon insulin treatment.
  
  
  CONCLUSIONS
  This study demonstrated that human astrocytes are insulin-responsive at the molecular level. We identified glycogen synthesis and cell proliferation as biological responses of insulin signaling in these brain cells. Hence, this cell type may contribute to the effects of insulin in the human brain.
authors: Division of Endocrinology, Diabetology, Angiology, Nephrology and Clinical Chemistry, Department of Internal Medicine, Eberhard Karls University Tübingen, Tübingen, Germany.
authors: Martin
authors: M
authors: Heni
authors: Anita M
authors: AM
authors: Hennige
authors: Andreas
authors: A
authors: Peter
authors: Dorothea
authors: D
authors: Siegel-Axel
authors: Anna-Maria
authors: AM
authors: Ordelheide
authors: Norbert
authors: N
authors: Krebs
authors: Fausto
authors: F
authors: Machicao
authors: Andreas
authors: A
authors: Fritsche
authors: Hans-Ulrich
authors: HU
authors: Häring
authors: Harald
authors: H
authors: Staiger
mesh_terms: D001253:Astrocytes / Q000187:drug effects* / Q000378:metabolism*; D015153:Blotting, Western; D049109:Cell Proliferation / Q000187:drug effects*; D002478:Cells, Cultured; D006003:Glycogen / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000494:pharmacology*
chemical_list: D007328:Insulin; D006003:Glycogen