Central insulin signaling is attenuated by long-term insulin exposure via insulin receptor substrate-1 serine phosphorylation, proteasomal degradation, and lysosomal insulin receptor degradation

Endocrinology. 2010 Jan;151(1):75-84. doi: 10.1210/en.2009-0838. Epub 2009 Nov 3.

Abstract

Central insulin signaling is critical for the prevention of insulin resistance. Hyperinsulinemia contributes to insulin resistance, but it is not yet clear whether neurons are subject to cellular insulin resistance. We used an immortalized, hypothalamic, clonal cell line, mHypoE-46, which exemplifies neuronal function and expresses the components of the insulin signaling pathway, to determine how hyperinsulinemia modifies neuronal function. Western blot analysis indicated that prolonged insulin treatment of mHypoE-46 cells attenuated insulin signaling through phospho-Akt. To understand the mechanisms involved, time-course analysis was performed. Insulin exposure for 4 and 8 h phosphorylated Akt and p70-S6 kinase (S6K1), whereas 8 and 24 h treatment decreased insulin receptor (IR) and IR substrate 1 (IRS-1) protein levels. Insulin phosphorylation of S6K1 correlated with IRS-1 ser1101 phosphorylation and the mTOR-S6K1 pathway inhibitor rapamycin prevented IRS-1 serine phosphorylation. The proteasomal inhibitor epoxomicin and the lysosomal pathway inhibitor 3-methyladenine prevented the degradation of IRS-1 and IR by insulin, respectively, and pretreatment with rapamycin, epoxomicin, or 3-methyladenine prevented attenuation of insulin signaling by long-term insulin exposure. Thus, a sustained elevation of insulin levels diminishes neuronal insulin signaling through mTOR-S6K1-mediated IRS-1 serine phosphorylation, proteasomal degradation of IRS-1 and lysosomal degradation of the IR.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cells, Cultured
  • Central Nervous System / drug effects*
  • Central Nervous System / metabolism*
  • Central Nervous System / physiology
  • Down-Regulation / drug effects
  • Insulin / administration & dosage
  • Insulin / metabolism*
  • Insulin / pharmacology*
  • Insulin Receptor Substrate Proteins / metabolism*
  • Intracellular Signaling Peptides and Proteins / metabolism
  • Lysosomes / drug effects
  • Lysosomes / metabolism
  • Metabolic Networks and Pathways / drug effects
  • Metabolic Networks and Pathways / physiology
  • Mice
  • Neurons / drug effects
  • Neurons / metabolism
  • Oncogene Protein v-akt / metabolism
  • Phosphorylation / drug effects
  • Proteasome Endopeptidase Complex / metabolism*
  • Protein Processing, Post-Translational / drug effects
  • Protein-Serine-Threonine Kinases / metabolism
  • Receptor, Insulin / metabolism*
  • Ribosomal Protein S6 Kinases, 90-kDa / metabolism
  • Serine / metabolism
  • TOR Serine-Threonine Kinases
  • Time Factors

Substances

  • Insulin
  • Insulin Receptor Substrate Proteins
  • Intracellular Signaling Peptides and Proteins
  • Irs1 protein, mouse
  • Serine
  • TOR Serine-Threonine Kinases
  • mTOR protein, mouse
  • Receptor, Insulin
  • Oncogene Protein v-akt
  • Protein-Serine-Threonine Kinases
  • Ribosomal Protein S6 Kinases, 90-kDa
  • Rps6ka1 protein, mouse
  • Proteasome Endopeptidase Complex