Decreased extracellular adenosine levels lead to loss of hypoxia-induced neuroprotection after repeated episodes of exposure to hypoxia

PLoS One. 2013;8(2):e57065. doi: 10.1371/journal.pone.0057065. Epub 2013 Feb 21.

Abstract

Achieving a prolonged neuroprotective state following transient ischemic attacks (TIAs) is likely to effectively reduce the brain damage and neurological dysfunction associated with recurrent stroke. HPC is a phenomenon in which advanced exposure to mild hypoxia reduces the stroke volume produced by a subsequent TIA. However, this neuroprotection is not long-lasting, with the effects reaching a peak after 3 days. Therefore, in this study, we investigated the use of multiple episodes of hypoxic exposure at different time intervals to induce longer-term protection in a mouse stroke model. C57BL/6 mice were subjected to different hypoxic preconditioning protocols: a single episode of HPC or five identical episodes at intervals of 3 days (E3d HPC) or 6 days (E6d HPC). Three days after the last hypoxic exposure, temporary middle cerebral artery occlusion (MCAO) was induced. The effects of these HPC protocols on hypoxia-inducible factor (HIF) regulated gene mRNA expression were measured by quantitative PCR. Changes in extracellular adenosine concentrations, known to exert neuroprotective effects, were also measured using in vivo microdialysis and high pressure liquid chromatography (HPLC). Neuroprotection was provided by E6d HPC but not E3d HPC. HIF-regulated target gene expression increased significantly following all HPC protocols. However, E3d HPC significantly decreased extracellular adenosine and reduced cerebral blood flow in the ischemic region with upregulated expression of the adenosine transporter, equilibrative nucleoside transporter 1 (ENT1). An ENT1 inhibitor, propentofylline increased the cerebral blood flow and re-established neuroprotection in E3d HPC. Adenosine receptor specific antagonists showed that adenosine mainly through A1 receptor mediates HPC induced neuroprotection. Our data indicate that cooperation of HIF-regulated genes and extracellular adenosine is necessary for HPC-induced neuroprotection.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 5'-Nucleotidase / metabolism
  • Adenosine / metabolism*
  • Animals
  • Antigens, CD / metabolism
  • Apyrase / metabolism
  • Cerebrovascular Circulation / drug effects
  • Equilibrative Nucleoside Transport Proteins / genetics
  • Equilibrative Nucleoside Transport Proteins / metabolism
  • Extracellular Space / metabolism*
  • Hypoxia / metabolism*
  • Hypoxia-Inducible Factor 1
  • Ischemic Attack, Transient / genetics
  • Ischemic Attack, Transient / metabolism
  • Ischemic Preconditioning
  • Male
  • Mice
  • Neurons / metabolism*
  • Neuroprotective Agents / pharmacology
  • Receptor, Adenosine A1 / metabolism
  • Regional Blood Flow / drug effects
  • Xanthines / pharmacology

Substances

  • Antigens, CD
  • Equilibrative Nucleoside Transport Proteins
  • Hypoxia-Inducible Factor 1
  • Neuroprotective Agents
  • Receptor, Adenosine A1
  • Xanthines
  • propentofylline
  • 5'-Nucleotidase
  • Apyrase
  • CD39 antigen
  • Adenosine

Grants and funding

This work was supported by National Natural Science Foundation of China 81000487 (to M.C) 81171023 (to Y.Z) and Shanghai Rising-Star Program (11QA1400900) and Shanghai Pujiang Program (12PJ1407200). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.