Cell type-specific dependency on the PI3K/Akt signaling pathway for the endogenous Epo and VEGF induction by baicalein in neurons versus astrocytes

PLoS One. 2013 Jul 19;8(7):e69019. doi: 10.1371/journal.pone.0069019. Print 2013.

Abstract

The neuroprotective effect of baicalein is generally attributed to inhibition of 12/15-lipoxygenase (12/15-LOX) and suppression of oxidative stress, but recent studies showed that baicalein also activates hypoxia-inducible factor-α (HIF1α) through inhibition of prolyl hydrolase 2 (PHD2) and activation of the phosphatidylinositide-3 kinase (PI3K)/Akt signaling pathway. Yet, the significance and regulation of prosurvival cytokines erythropoietin (Epo) and vascular endothelial growth factor (VEGF), two transcriptional targets of HIF1α, in baicalein-mediated neuroprotection in neurons and astrocytes remains unknown. Here we investigated the causal relationship between the PI3K/Akt signaling pathway and Epo/VEGF expression in baicalein-mediated neuroprotection in primary rat cortical neurons and astrocytes. Our results show that baicalein induced Epo and VEGF expression in a HIF1α- and PI3K/Akt-dependent manner in neurons. Baicalein also protected neurons against excitotoxicity in a PI3K- and Epo/VEGF-dependent manner without affecting neuronal excitability. In contrast, at least a 10-fold higher concentration of baicalein was needed to induce Epo/VEGF production and PI3K/Akt activity in astrocytes for protection of neurons. Moreover, only baicalein-induced astrocytic VEGF, but not Epo expression requires HIF1α, while PI3K/Akt signaling had little role in baicalein-induced astrocytic Epo/VEGF expression. These results suggest distinct mechanisms of baicalein-mediated Epo/VEGF production in neurons and astrocytes for neuroprotection, and provide new insights into the mechanisms and potential of baicalein in treating brain injury in vivo.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Astrocytes / drug effects*
  • Astrocytes / metabolism
  • Cells, Cultured
  • Enzyme Inhibitors / pharmacology
  • Erythropoietin / genetics
  • Erythropoietin / metabolism*
  • Female
  • Flavanones / pharmacology*
  • Hypoxia-Inducible Factor 1, alpha Subunit / metabolism
  • Male
  • Neurons / drug effects*
  • Neurons / metabolism
  • Neuroprotective Agents / pharmacology*
  • Phosphatidylinositol 3-Kinases / metabolism
  • Proto-Oncogene Proteins c-akt / metabolism
  • Rats
  • Rats, Sprague-Dawley
  • Signal Transduction / drug effects
  • Transcriptional Activation / drug effects
  • Vascular Endothelial Growth Factor A / genetics
  • Vascular Endothelial Growth Factor A / metabolism*

Substances

  • Enzyme Inhibitors
  • Flavanones
  • Hif1a protein, rat
  • Hypoxia-Inducible Factor 1, alpha Subunit
  • Neuroprotective Agents
  • Vascular Endothelial Growth Factor A
  • Erythropoietin
  • baicalein
  • Phosphatidylinositol 3-Kinases
  • Proto-Oncogene Proteins c-akt