Excitatory pathway engaging glutamate, calcineurin, and NFAT upregulates IL-4 in ischemic neurons to polarize microglia

J Cereb Blood Flow Metab. 2020 Mar;40(3):513-527. doi: 10.1177/0271678X19838189. Epub 2019 Mar 19.

Abstract

Excitotoxicity and microglia/macrophage over-activation are the important pathogenic steps in brain damage caused by ischemic stroke. Recent studies from our group suggest that the neurons in ischemic penumbra generate an anti-inflammatory cytokine, interleukin-4 (IL-4). This neuron-produced IL-4 could subsequently convert surrounding microglia/macrophages to a reparative (M2)-phenotype. The present study was designed to establish the mechanisms by which neurons under transient ischemic condition produce/secrete IL-4. We employed primary rat cortical neurons and a validated in vitro ischemic injury model involving transient oxygen-glucose deprivation (OGD). We discovered that only sublethal OGD induces IL-4 production/secretion by neurons. We then showed that excitotoxic stimulus (an integral component of OGD-mediated damage) involving N-methyl-D-aspartate (NMDA), and not kainate receptor, triggers neuronal IL-4 production/release. Of note, oxidative stress or pro-apoptotic stimuli did not induce IL-4 production by neurons. Next, using the calcineurin inhibitor FK506, we implicated this phosphatase in activation of the nuclear factor of activated T-cells (NFAT; a transcription factor activated through calcineurin-mediated dephosphorylation) and propose that this pathway is involved in transcriptional upregulation of the IL-4 synthesis in NMDA-treated neurons. Finally, using a transfer of culture medium from NMDA-conditioned neuron to microglia, we showed that the neuronal IL-4 can polarize microglia toward a restorative, phagocytic phenotype.

Keywords: Calcineurin; NFAT; excitotoxicity; microglia; neuronal interleukin 4.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Calcineurin / metabolism*
  • Calcineurin Inhibitors / pharmacology
  • Cell Hypoxia / drug effects
  • Cerebral Cortex / metabolism*
  • Cerebral Cortex / pathology
  • Glutamic Acid / metabolism*
  • Interleukin-4 / biosynthesis*
  • Microglia / metabolism*
  • Microglia / pathology
  • N-Methylaspartate / pharmacology
  • NFATC Transcription Factors / metabolism*
  • Neurons / metabolism*
  • Neurons / pathology
  • Rats
  • Rats, Sprague-Dawley
  • Tacrolimus / pharmacology
  • Transcription, Genetic / drug effects
  • Up-Regulation*

Substances

  • Calcineurin Inhibitors
  • NFATC Transcription Factors
  • Interleukin-4
  • Glutamic Acid
  • N-Methylaspartate
  • Calcineurin
  • Tacrolimus