Brain-derived erythropoietin protects from focal cerebral ischemia by dual activation of ERK-1/-2 and Akt pathways

FASEB J. 2005 Dec;19(14):2026-8. doi: 10.1096/fj.05-3941fje. Epub 2005 Oct 5.

Abstract

Apart from its hematopoietic function, erythropoietin (Epo) exerts neuroprotective functions in brain hypoxia and ischemia. To examine the mechanisms mediating Epo's neuroprotective activity in vivo, we made use of our transgenic mouse line tg21 that constitutively expresses human Epo in brain without inducing excessive erythrocytosis. We show that human Epo is expressed in tg21 brains and that cortical and striatal neurons carry the Epo receptor. After middle cerebral artery occlusion, human Epo potently protected brains of tg21 mice against ischemic injury, both when severe (90 min) and mild (30 min) ischemia was imposed. Histochemical studies revealed that Epo induced an activation of JAK-2, ERK-1/-2, and Akt pathways in the ischemic brain. This activation was associated with elevated Bcl-XL and decreased NO synthase-1 and -2 levels in neurons. Intracerebroventricular injections of selective inhibitors of ERK-1/-2 (PD98059) or Akt (wortmannin) pathways revealed that both ERK-1/-2 and Akt were required for Epo's neuroprotective function, antagonization of either pathway completely abolishing tissue protection. On the other hand, ERK-1/-2 and Akt blockade did not reverse the neuronal NO synthase-1/-2 inhibition, indicating that Epo down-regulates these NO synthases in an ERK-1/-2 and Akt independent manner. On the basis of our data, the dual activation of ERK-1/-2 and Akt is crucial for Epo's neuroprotective activity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Androstadienes / pharmacology
  • Animals
  • Brain / metabolism
  • Brain Ischemia / metabolism
  • Brain Ischemia / pathology*
  • Enzyme Activation
  • Enzyme Inhibitors / pharmacology
  • Erythropoietin / chemistry*
  • Erythropoietin / metabolism
  • Flavonoids / pharmacology
  • Humans
  • Hypoxia
  • Immunohistochemistry
  • Ischemia
  • Janus Kinase 2
  • Mice
  • Mice, Transgenic
  • Mitogen-Activated Protein Kinase 1 / metabolism*
  • Mitogen-Activated Protein Kinase 3 / metabolism*
  • Models, Biological
  • Neurons / metabolism
  • Nitric Oxide Synthase Type I / metabolism
  • Nitric Oxide Synthase Type II / metabolism
  • Phosphorylation
  • Protein-Tyrosine Kinases / metabolism
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-akt / metabolism*
  • Receptors, Erythropoietin / metabolism
  • Signal Transduction
  • Time Factors
  • Wortmannin
  • bcl-X Protein / metabolism

Substances

  • Androstadienes
  • Enzyme Inhibitors
  • Flavonoids
  • Proto-Oncogene Proteins
  • Receptors, Erythropoietin
  • bcl-X Protein
  • Erythropoietin
  • Nitric Oxide Synthase Type I
  • Nitric Oxide Synthase Type II
  • Nos1 protein, mouse
  • Nos2 protein, mouse
  • Protein-Tyrosine Kinases
  • JAK2 protein, human
  • Jak2 protein, mouse
  • Janus Kinase 2
  • Proto-Oncogene Proteins c-akt
  • Mitogen-Activated Protein Kinase 1
  • Mitogen-Activated Protein Kinase 3
  • 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one
  • Wortmannin