Inhibition of Signal Transducer and Activator of Transcription 3 (STAT3) reduces neonatal hypoxic‐ischaemic brain damage

Hypoxic-ischaemic encephalopathy is a leading cause of child death, with high mortality and morbidity, including cerebral palsy, epilepsy and cognitive disabilities. Hypoxia-ischaemia (HI) strongly up-regulates Signal Transducer and Activator of Transcription 3 (STAT3) in the immature brain. Our aim was to establish whether STAT3 up-regulation is associated with neonatal HI-brain damage and evaluate the phosphorylated STAT3-contribution from different cell types in eliciting damage. We subjected postnatal day seven mice to unilateral carotid artery ligation followed by 60 min hypoxia. Neuronal STAT3-deletion reduced cell death, tissue loss, microglial and astroglial activation in all brain regions. Astroglia-specific STAT3-deletion also reduced cell death, tissue loss and microglial activation, although not as strongly as the deletion in neurons. Systemic pre-insult STAT3-blockade at tyrosine 705 (Y705) with JAK2-inhibitor WP1066 reduced microglial and astroglial activation to a more moderate degree, but in a pattern similar to the one produced by the cell-specific deletions. Our results suggest that STAT3 is a crucial factor in neonatal HI-brain damage and its removal in neurons or astrocytes, and, to some extent, inhibition of its phosphorylation via JAK2-blockade reduces inflammation and tissue loss. Overall, the protective effects of STAT3 inactivation make it a possible target for a therapeutic strategy in neonatal HI. Current data show that neuronal and astroglial STAT3 molecules are involved in the pathways underlying cell death, tissue loss and gliosis following neonatal hypoxia-ischaemia, but differ with respect to the target of their effect. Y705-phosphorylation contributes to hypoxic-ischaemic histopathology. Protective effects of STAT3 inactivation make it a possible target for a therapeutic strategy in neonatal hypoxia-ischaemia.