Stat3 in Post-Ischemic Myocardial Inflammation

Johns Hopkins University, Baltimore MD

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Abstract

Myocardial reperfusion results in the induction of pro-inflammatory genes through the activation of redoxsensitive[unreadable] nuclear transcription factors. We have found that signal transducer and activator of transcription-3[unreadable] (Stat3) is activated after myocardial ischemia-reperfusion, in a manner dependent on the small GTPase Rac1,[unreadable] and binds to a GAS promoter element in the intercellular adhesion molecule-1 (ICAM-1) gene, a gene which[unreadable] codes for an important endothelial cell adhesion molecule which interacts with leukocytes. After phosphorylation[unreadable] of its serine 727 residue, StatS binds to the transcriptional activator Sp1. We hypothesize that this represents a[unreadable] novel mechanism for enhancing ICAM-1 transcription in endothelial cells (ECs) after ischemia-reperfusion. In[unreadable] support of this idea, inhibition of Stat3/Sp1 activity in cultured ECs significantly reduces the transcription of ICAM-[unreadable] 1 after hypoxia-reoxygenation. In this proposal, we will determine the role of StatS in the regulation of ICAM-1[unreadable] and other pro-inflammatory genes in vascular endothelium after myocardial ischemia-reperfusion. In Aim 1 we[unreadable] will investigate the molecular mechanisms responsible for StatS interaction with Sp1, including the mechanisms[unreadable] involved in binding between the two molecules and the role of phosphorylation of the StatS S727 residue. We[unreadable] will determine whether inhibition of the Stat3-Sp1 interaction affects ICAM-1 gene regulation in ECs, and whether[unreadable] Stat3/Sp1 modifies post-ischemic microvascular inflammation (assessed by videomicroscopy) or myocardial[unreadable] ischemia-reperfusion injury, using in vivo murine models. In Aim 2 we will examine the mechanisms responsible[unreadable] for Rac1-dependent StatS activation after hypoxia-reoxygenation, including how the two molecules bind together,[unreadable] how this binding promotes the phosphorylation of the Y705 and S727 residues of StatS, and which kinases are[unreadable] involved. In Aim 3 we will determine whether activation of StatS in hypoxic-reoxygenated ECs is self-limited by a[unreadable] negative feedback loop involving StatS transcriptional regulation of T-cell lymphoma invasion and metastasis 2[unreadable] (TIAM2), a guanine exchange factor, and RacGAPI, a GTPase-activating protein, both of which in turn[unreadable] downregulate the activation state of Rac1, and thereby of StatS itself.