Activation of the
Janus Kinase 2/
Signal Transducer and Activator of Transcription 3 (JAK2/STAT3) pathway is known to play a key role in cardiogenesis and to afford cardioprotection against
ischemia-reperfusion in adult. However, involvement of JAK2/STAT3 pathway and its interaction with other signaling pathways in developing heart transiently submitted to
anoxia remains to be explored. Hearts isolated from 4-day-old chick embryos were submitted to
anoxia (30 min) and reoxygenation (80 min) with or without the
antioxidant MPG, the JAK2/STAT3 inhibitor
AG490 or the PhosphoInositide-3-Kinase (PI3K)/Akt inhibitor
LY-294002. Time course of phosphorylation of STAT3α(tyrosine705) and
Reperfusion Injury Salvage
Kinase (RISK)
proteins [PI3K, Akt,
Glycogen Synthase Kinase 3beta (
GSK3beta),
Extracellular signal-Regulated Kinase 2 (ERK2)] was determined in homogenate and in enriched nuclear and cytoplasmic fractions of the ventricle. STAT3
DNA-binding was determined. The chrono-, dromo- and inotropic disturbances were also investigated by electrocardiogram and mechanical recordings. Phosphorylation of STAT3α(tyr705) was increased by reoxygenation, reduced (~50%) by MPG or
AG490 but not affected by
LY-294002. STAT3 and
GSK3beta were detected both in nuclear and cytoplasmic fractions while PI3K, Akt and ERK2 were restricted to cytoplasm. Reoxygenation led to nuclear accumulation of STAT3 but unexpectedly without
DNA-binding.
AG490 decreased the reoxygenation-induced phosphorylation of Akt and ERK2 and phosphorylation/inhibition of
GSK3beta in the nucleus, exclusively. Inhibition of JAK2/STAT3 delayed recovery of atrial rate, worsened variability of cardiac cycle length and prolonged arrhythmias as compared to control hearts. Thus, besides its nuclear translocation without transcriptional activity, oxyradicals-activated STAT3α can rapidly interact with RISK
proteins present in nucleus and cytoplasm, without dual interaction, and reduce the
anoxia-reoxygenation-induced arrhythmias in the embryonic heart.