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

• Published in: Journal of cerebral blood flow and metabolism 2020-03, Vol.40 (3), p.513-527
• Main Authors: Ting, Shun-Ming, Zhao, Xiurong, Zheng, Xueping, Aronowski, Jaroslaw
• Format: Article
• Language: English
• Subjects: 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; Neurons - metabolism; Neurons - pathology; NFATC Transcription Factors - metabolism; Original; Rats; Rats, Sprague-Dawley; Tacrolimus - pharmacology; Transcription, Genetic - drug effects; Up-Regulation
• ISSN: 0271-678X; 1559-7016
• DOI: 10.1177/0271678X19838189

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.