Deciphering the crosslink between STAT3 and MAPKs during Ischemia/Reperfusion and PostConditioning

Abstract

STAT3 exerts Cardioprotective roles against the ischemia/reperfusion injury (IRI) and during ischemic post-conditioning (IPoC). In cell line models, STAT3 can be phosphorylated on its tyrosine705 and serine727 residues. The involvement of STAT3 in IPoC, its interlink with MAPKS and the specific roles of its Y705 and S727 residues in modifying the transcriptional activity are not clear. We aim to study the kinetics of STAT3 and MAPKs phosphorylation following IRI (with and without IPoC) and investigate their interlink. We also aim to investigate how the variation in the phosphorylated STAT3 residue modifies its transcriptional activity. In vitro H9C2 cells were treated with LIF, STAT3 inhibitor (static) and different MAPKS inhibitors. In vivo C57b male mice were subjected to ischemia followed by different durations of reperfusion, with and without IPoC ( N = 6). The phosphorylation levels of STAT3 and MAPKs were detected at different time points. In addition, in vivo inhibition of STAT3 and ERK was induced, and the effect of these inhibitions on the expression of selected STAT3-regulated genes was assessed by PCR. In vitro Y705 phosphorylation of STAT3 was significantly increased with LIF treatment, but it decreased with static. The MEK/ERK pathway inhibitors inhibited STAT3 phosphorylation at S727 along with a 2-fold increase in the Y705 one. In vivo I/R induced STAT3 and ERK1/2 phosphorylation, while PoC induced a further significant phosphorylation of Y705 STAT3 residue within 15 minutes of reperfusion. No significant effect for I/R and PoC was observed on other MAPKs. IPoC induces STAT3 activation within 15 minutes of phosphorylation, and a cross-link exists between STAT3 and ERK1/2, where the latter induces Ser727 STAT3 phosphorylation. Our results also suggest a competitive phosphorylation between STAT3 S727 and Y705 residues.